JP2003041494A - Method of producing high-whiteness pulp having excellent discoloration-resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an economical method for producing high-whiteness pulp of excellent discoloration-resistance giving a high-quality pulp suitable as a raw material for sensitive paper. SOLUTION: Timbers are Kraft-cooked and the resultant unbleached pulp with a Kappa number of <=23 is subjected to the oxygen bleaching at a level of >=40% delignification. Further, the oxygen bleached pulp is subjected to the ozone bleaching in >=25% pulp concentration to lower the PN value down to >=2.8, and allowed to undergo multi-stage bleaching including the hydrogen peroxide bleaching and the chlorine dioxide bleaching whereby the high- whiteness pulp for the sensitive paper having excellent discoloration-resistance is produced economically.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-whiteness pulp for a light-sensitive material having excellent fading properties, and more specifically, it is an economical and high-whiteness base paper for a high-whiteness photosensitive material. The present invention relates to a method for producing a high-whiteness pulp for a sensitive material, which is excellent in discoloration and is capable of obtaining a high-quality pulp suitable as a raw material.

[0002]

2. Description of the Related Art Generally, quality characteristics required for a pulp for a sensitive material include that the characteristics of the sensitive material are not adversely affected, that the whiteness is high, and that the color fading is low. In particular, whiteness is the most important factor as a characteristic for obtaining the sharpness of an image as a light-sensitive material, and it is required that the color fading is small in order to maintain the whiteness.

However, in conventional pulp bleaching, a method of bleaching stepwise using oxygen, chlorine, hypochlorite, hydrogen peroxide, chlorine dioxide, etc. has been adopted.
Generally, pulp containing a large amount of chlorine and hypochlorite has high whiteness, but tends to change to yellow and has a problem of poor discoloration.

Conventionally, as a bleaching method for pulp having excellent fading properties, for example, Japanese Patent Application Laid-Open No. 8-311789 discloses a bleaching method which uses a lot of hydrogen peroxide. However, it reaches a satisfactory level. Not not. In particular, for base papers for light-sensitive materials and the like, pulp having high whiteness and excellent color fading properties is preferable.

Recently, due to restrictions on the use of chlorine-based chemicals due to regulations on AOX and chloroform, it is noted that ozone, which has a stronger bleaching power than chlorine-based bleaching agents and produces no harmful substances, is used for bleaching pulp. Has been done. When ozone is used, the fading property is improved compared to the conventional pulp containing a large amount of chlorine and hypochlorite, but the whiteness improvement per amount used is not so effective, and the higher whiteness is achieved by ozone. In addition to the high unit price, there was the problem that the cost would increase considerably.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above problems in pulp production and to provide a high quality, high quality white paper which is economical and has excellent fading properties and which is suitable as a raw material for a base paper for a sensitive material. It is an object of the present invention to provide a method for producing a high-whiteness pulp for a sensitive material, which is capable of obtaining a pulp and has excellent discoloration properties.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the inventors of the present invention bleached ozone with a high-concentration pulp to a PN value after ozone bleaching to a certain level or less. It has been found that a high-whiteness pulp having excellent discoloration can be obtained more economically.

That is, according to the method for producing a high-whiteness pulp for a sensitive material having excellent fading properties of the present invention, unbleached pulp having a Kappa number of 23 or less obtained by kraft cooking wood with a delignification degree of 40% or more. Oxygen bleaching, then pulp concentration 25% by weight
After bleaching with ozone as described above, the PN value is set to 2.8 or less, and multi-stage bleaching including bleaching with hydrogen peroxide and bleaching with chlorine dioxide is performed.

In the present invention, the PN value after ozone bleaching is preferably 2.1 or less, more preferably 1.4 or less.

In the present invention, the Kappa number of the unbleached pulp is preferably 19 or less.

In the present invention, ozone bleaching is preferably carried out at a pulp concentration of 30% by mass or more.

Further, the present invention is characterized in that an acid treatment of pH 4 or less is carried out before ozone bleaching.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a high-whiteness pulp for a light-sensitive material having excellent discoloration of the present invention will be described in detail below.

Generally, the PN value after ozone bleaching is about 2.8, and the pulp concentration is 1 to 5% by mass of low concentration pulp or 30 to 40% by mass of high concentration pulp.
In the present invention, high-whiteness pulp can be obtained by bleaching with ozone at a pulp concentration of 25% by mass or more and bleaching in multiple stages with a PN value of 2.8 or less.

The unbleached pulp which has been subjected to the usual kraft digestion is kept at a kappa number of 23 or less, preferably 19 or less, and is subjected to oxygen bleaching with a delignification degree of 40% or more. PN value of 2.8 or less, preferably 2.1 or less, more preferably 1.4 or less. The pulp concentration at that time is 25 mass% or more, preferably 30 mass% or more. If any of these conditions are below the desired effect,
Higher bleaching chemical requirements increase costs.

In the wood cooking method, if it is a kraft method, the cooking liquor is divided and added, or sodium polysulfide is used, or two-stage oxygen bleaching with oxygen is performed, and further multistage after ozone bleaching is performed. It does not matter whether ozone bleaching is carried out during bleaching or the final bleaching stage is terminated with a hydrogen peroxide bleaching stage.

The unbleached Kappa number after cooking is 23 or less,
It is necessary to stabilize the kappa number by facilitating the separation and removal of undigested wood chips. If the unbleached Kappa number is higher than this, the undigested wood chips will increase rapidly, making it difficult to separate the undigested wood chips, resulting in unstable operation and unstable Kappa number. Further, in this case, the washing efficiency of unbleached pulp is also deteriorated, and the delignification degree in the subsequent oxygen bleaching is reduced. Therefore, the unbleached Kappa number should be kept at 23 or less, preferably 19 or less for oxygen bleaching. Is an essential condition.

The degree of delignification of oxygen bleaching varies depending on the unbleached Kappa number, but it is usually 30% to 6%.
It is in the range of about 0% delignification. Further, in this case, since the delignification degree is limited depending on the oxygen bleaching method, the delignification degree of 4 or less is obtained when the unbleached Kappa number is 23 or less.
If it is 0% or more, ozone bleaching has the effect of reducing the amount of ozone used, which has a high unit price. Further, by setting the delignification degree of oxygen bleaching to 40% or more, a predetermined PN value of 2.8 or less after ozone bleaching can be obtained, and it is high in subsequent multi-stage bleaching by hydrogen peroxide bleaching and chlorine dioxide bleaching. Whiteness is obtained.

When the PN value is high, it is difficult to obtain a high whiteness as well as a large amount of lignin and a large amount of bleaching chemicals are used. When the PN value is 2.8 or higher, hydrogen peroxide bleaching and the use of chlorine dioxide after that are used. Even if the amount is increased, such an effect is not obtained and it is difficult to obtain high whiteness. However, when the PN value after ozone bleaching is 2.8 or less, the amount of lignin becomes small, and high whiteness can be obtained by multi-stage bleaching without using much hydrogen peroxide bleaching and chlorine dioxide bleaching thereafter.

To facilitate understanding of the following description, "P
The meaning and definition of "N number" will be explained in advance. In the present invention, the Kappa number based on JIS-P-8211, which is generally measured as an index of the amount of lignin in unbleached pulp after cooking, is displayed. It was indicated by "PN number" based on TAPPI-T-214 as an index of the amount of lignin after that, because the Kappa number measurement adjusts the amount of pulp to bring the amount of potassium permanganate consumption into a predetermined range. However, since the amount of lignin after ozone bleaching is small and the amount of pulp needs to be increased, the measurement becomes complicated and difficult.
In addition, it is easy to measure under a fixed amount of conditions and has excellent reproducibility.

In the present invention, the pH is adjusted before ozone bleaching.
It is preferable to perform an acid treatment of 4 or less. That is, before adding ozone, the treatment conditions are pH 4 or less, preferably pH 2 to 4, temperature 80 to 100 ° C., reaction time 60 to 120 minutes, and pulp concentration 5 to 15 mass%. Examples of chemicals for adjusting pH include sulfuric acid, and in addition,
In the next step, white ozone water or chlorine dioxide white water can also be used.

Here, in the combination of high temperature acidic reaction before ozone bleaching and ozone bleaching, a reaction such as oxidation of a color-forming group such as a carbonyl group in cellulose involved in fading to a carboxyl group not involved in fading is included. Therefore, it is considered that it stabilizes efficiently and selectively. In addition, the PN value is lower than that in the sequence of ozone bleaching only, and high whiteness is obtained by subsequent multi-stage bleaching of hydrogen peroxide and chlorine dioxide.

The reaction temperature of ozone bleaching is 25 ° C. or higher, and the reaction time depends on the apparatus for mixing and stirring unbleached pulp and ozone, but it is usually about 5 seconds to about 1 minute, and depending on the processing conditions up to about 1 hour, the processing pH. Is preferably in the range of about 1 to 4 under acidic conditions, and the amount of ozone added is preferably 0.5% by mass (versus dry pulp) or more.

In the ozone stage, the ozone used in the present invention has an ozone concentration of 2 to 25% by mass, and the ozone supply method is as follows.
Either an ozone supply method using an oxygen ozonizer or an ozone supply method provided with a device for concentrating ozone may be used.
The ozone may be added by a general method, and ozone gas is introduced to bleach the pulp.

Regarding the action of the present invention, ozone has a strong oxidizing power, is highly reactive with aromatic rings and double bonds, and quickly decomposes residual lignin in pulp, but the higher the concentration of pulp, the higher the concentration. It is considered that ozone is consumed rapidly and this reaction remarkably progresses so that it can be reacted to a low PN value. Therefore, in a high-concentration pulp having a pulp concentration of 25% by mass or more, a high whiteness can be obtained because the ozone addition rate can be increased to a low PN value. Further, when the ozone addition rate is the same, the PN number is lower than that of the low-concentration pulp, and the ozone addition rate can be reduced by the reduced amount, which is more economical.

Further, it is considered that ozone efficiently and selectively stabilizes a color-forming group such as a carbonyl group in pulp involved in fading, including a reaction such as oxidation to a carboxyl group not involved in fading. To be

[0027]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. In addition, the examples described below are based on an experiment in which a situation of an actual process is simulated in a laboratory. Further, hereinafter, the acid treatment stage before ozone bleaching is abbreviated as A, the ozone stage as Z, the chlorine dioxide stage as D, the hydrogen peroxide stage as P, the chlorine stage as C, and the hypo (hypochlorite) stage as H. To do.

Further, acid treatment (A) stage before ozone bleaching,
Bleaching except for the ozone (Z) stage is carried out by an ordinary polyethylene bag method, and the reaction conditions are as follows. Chlorine (C) stage: pulp concentration 3.5% by mass, 50 ° C, 30 minutes Hypo (H) stage: pulp concentration 11% by mass, 54 ° C, 90 minutes Chlorine dioxide (D) stage: pulp concentration 11% by mass, 72 ℃, 100 minutes Hydrogen peroxide (P) stage: Pulp concentration 11 mass%, 72 ℃, 100 minutes

Example 1 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> Domestic hardwood was kraft cooked (kappa number 18.1), oxygen bleached, and delignification degree 41.0% ( Kappa number 10.
The pulp of 7) is thoroughly washed with a Buchner funnel and dehydrated. This pulp is transferred to a polyethylene bag and the pulp concentration is 11% by mass.
Was adjusted to pH 2.0, sulfuric acid was added, and the mixture was stirred well, adjusted to pH 2.0, and then dehydrated by a centrifuge to make the pulp concentration 35% by mass.

Next, ion-exchanged water was added to make the pulp concentration 3
Ozone gas having an ozone concentration of 2% by mass was adjusted to 0% by mass, and treated for 6 minutes under the conditions of an ozone addition rate of 0.5% by mass (versus dry pulp) and a reaction temperature of 25 ° C. After completion of the reaction, the pulp was transferred to a Buchner funnel and dehydrated and washed, and the PN value was measured. The measurement results are shown in Table 1.

Thereafter, hydrogen peroxide was added to 0.
Add 7% by mass (vs. dry pulp) to bleach hydrogen peroxide (P
₁ ), chlorine dioxide is added in an amount of 0.5% by mass (vs. dry pulp), chlorine dioxide is bleached (D ₁ ), and hydrogen peroxide is added in an amount of 0.3% by mass (vs. dry pulp). Hydrogen peroxide bleaching (P ₂ ) is carried out, and chlorine dioxide is added to 0.4% by mass.
A chlorine dioxide bleaching (D ₂ ) was carried out by adding (against dry pulp). After each bleaching, the pulp was transferred to a Buchner funnel and dewatered and washed. The finally obtained pulp was also thoroughly washed with a Buchner funnel and dehydrated, and then the whiteness and fading property were measured. The measurement results are shown in Table 1.

Example 2 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In Example 1, the ozone addition rate in ozone bleaching was 0.75.
The same procedure as in Example 1 was carried out except that the mass% (vs. dry pulp) was used. The measurement results are shown in Table 1.

Example 3 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In Example 1, the ozone addition rate in ozone bleaching was set to 1.0% by mass (vs. dry pulp). Except for this, the same procedure as in Example 1 was performed. The measurement results are shown in Table 1.

Example 4 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In Example 1, domestic hardwood was kraft cooked (kappa number 23.0), oxygen bleached, and delignification degree. 53.4%
(Kappa number 10.8) pulp, ozone bleaching pulp concentration was adjusted to 25 mass%, ozone addition rate 1.0 mass%
The same procedure as in Example 1 was carried out except that the (external dry pulp) was used. The measurement results are shown in Table 1.

Example 5 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In the same manner as in Example 4 except that the pulp concentration in ozone bleaching was adjusted to 30% by mass. Carried out. The measurement results are shown in Table 1.

Example 6 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In Example 1, domestic hardwood was kraft cooked (kappa number 19.0), oxygen bleached, and delignification degree. 45.0%
(Kappa number 10.4) pulp, ozone bleaching pulp concentration was adjusted to 35 mass%, ozone addition rate 1.2 mass%
The same procedure as in Example 1 was carried out, except that the pulp was treated with (extra dry pulp) at a reaction temperature of 25 ° C. for 10 minutes. The measurement results are shown in Table 1.

[0037] <bleaching with _{A-Z-P 1 -D 1} -P 2 -D 2 Sequence> Example 7
In Example 1, before ozone bleaching, the pulp concentration was 11% by mass, the reaction temperature was 90 ° C., and the reaction time was 90 minutes.
Was carried out in the same manner as in Example 1 except that the ozone addition rate was 0.4% by mass (vs. dry pulp). The measurement results are shown in Table 1.

[0038] <bleaching with _{A-Z-P 1 -D 1} -P 2 -D 2 Sequence> Example 8
Example 7 was carried out in the same manner as Example 8 except that the ozone addition rate was 0.5% by mass (vs. dry pulp). The measurement results are shown in Table 1.

[0039] <bleaching with _{A-Z-P 1 -D 1} -P 2 -D 2 Sequence> Example 9
Example 7 was carried out in the same manner as Example 8 except that the ozone addition rate was 0.75% by mass (vs. dry pulp).
The measurement results are shown in Table 1.

Example 10 <Bleaching by AZP ₁ -D ₁ -P ₂ -D ₂ sequence>
Example 7 was carried out in the same manner as in Example 8 except that the ozone addition rate was 1.0% by mass (vs. absolute dry pulp). The measurement results are shown in Table 1.

Comparative Example 1 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In Example 1, the ozone addition rate in ozone bleaching was 0.4% by mass (vs. dry pulp). Except for this, the same procedure as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 2 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In Comparative Example 1, the pulp concentration in ozone bleaching was 3% by mass,
The same procedure as in Comparative Example 1 was performed except that the treatment was performed for 40 minutes.
The measurement results are shown in Table 1.

Comparative Example 3 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In Comparative Example 2, the ozone addition rate in ozone bleaching was 0.5% by mass (vs. dry pulp). Except for this, the same procedure as in Comparative Example 2 was performed. The measurement results are shown in Table 1.

Comparative Example 4 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In Example 1, domestic hardwood was kraft cooked (kappa number 28.0), oxygen bleached, and delignification degree. 55.4%
Example 1 was carried out in the same manner as in Example 1 except that (kappa number 12.5) pulp and ozone bleached pulp had a pulp concentration of 3.0 mass% and a treatment time of 40 minutes. The measurement results are shown in Table 1.

Comparative Example 5 <Bleaching by Z-P ₁ -D ₁ -P ₂ -D ₂ sequence> In Example 1, domestic hardwood was bleached with oxygen after kraft cooking, and the degree of delignification was 37.0% (Kappa number: 11). .4), and the same procedure as in Example 1 was performed. The measurement results are shown in Table 1.

[0046] <bleaching with _{C-P 1 -H-D 1} -P 2 -D 2 Sequence> Comparative Example 6
In Example 1, ozone bleaching was not performed and chlorine was 2.0
Mass% (against dry pulp) and chlorine bleaching, adding 0.7 mass% of hydrogen peroxide (against dry pulp) and hydrogen peroxide bleaching (P ₁ ), 0.3% of hypo % (Vs. absolute dry pulp) is added to perform hypo bleaching (H), 0.36 mass% of chlorine dioxide (vs. absolute dry pulp) is added to perform chlorine dioxide exposure (D ₁ ), and hydrogen peroxide is added. Hydrogen peroxide bleaching (P ₂ ) is performed by adding 0.2% by mass (to absolute dry pulp), and chlorine dioxide bleaching (D ₂ ) is further performed by adding 0.3% by mass of chlorine dioxide (to absolute dry pulp). Example 1 was repeated except that The measurement results are shown in Table 1.

The above Examples 1 to 10 and Comparative Examples 1 to 6
The high-whiteness pulp for light-sensitive material produced according to the above was measured by the following test method, and the results are shown in Table 1 below.

Each test method is as follows. <Whiteness> The whiteness was measured according to the Hunter whiteness method according to JIS P8123.

<Kappa number> The Kappa number is JIS P
It was measured according to 8211.

<PN value> The PN value is TAPPI T21.
It measured according to 4.

<PC Value> The PC value was measured as an index of the color fading property. The PC value was measured by treating the hand-made pulp sheet after the whiteness measurement for 18 hours at 85 ° C. and a humidity of 95%.
The whiteness after fading was measured and calculated from the following formula 1.

[0052]

[Equation 1]

[0053]

[Table 1]

Evaluation: From the results shown in Table 1, it is clear that the production method of the present invention can give pulp having high whiteness and excellent fading properties. Further, from Examples 1 to 3 and Comparative Examples 1 to 3, the PN value in ozone bleaching according to the present invention is 2.8.
The following is preferred, 2.1 or less is more preferred, and 1.4
The following are particularly preferable, and from the comparison of Example 1 and Comparative Example 5, it is preferable that the degree of delignification after oxygen bleaching is 40% or more because the ozone requirement for obtaining the same result is small. 3 to 5 and Comparative Example 4 show that even if the degree of delignification of oxygen bleaching is 40% or more, the Kappa number after cooking is preferably 23 or less. From Examples 3 to 5, Example 1 and Comparative Example 3, ozone bleached pulp is obtained. It is preferable that the concentration is 25% or more. From the comparison between Example 6 and Examples 3 to 4, the ozone amount in ozone bleaching is 1.0% by mass, the pulp concentration is 25 to 30%, and the treatment time is 6.0 minutes. In Example 1 to Example 8 and Example 8 to Example 8, it is found that the effect is almost saturated, and even if a combination of a higher ozone amount, a higher pulp concentration and a longer processing time is not obtained, the effect is not so great.
From 11 it can be seen that acid treatment prior to ozone bleaching is preferred. In addition, from the comparison between Example 2 and Comparative Example 6, almost the same P
It can be seen that even with N value, ozone bleaching has a better PC value.

[0055]

Industrial Applicability As described above, the method for producing a high-whiteness pulp for a sensitive material having excellent fading properties according to the present invention removes unbleached pulp having a Kappa number of 23 or less obtained by kraft cooking wood. Oxygen bleaching at a lignin degree of 40% or more, then ozone bleaching at a pulp concentration of 25% by mass or more, a PN value of 2.8 or less, and multi-stage bleaching including hydrogen peroxide bleaching and chlorine dioxide bleaching, High-quality pulp that is economical and excellent in fading can be produced, and its quality is superior to conventional bleaching methods, so it is especially suitable as a raw material for base paper for sensitive materials. Can be obtained.

Claims (6)

[Claims] 1. An unbleached pulp having a Kappa number of 23 or less obtained by kraft cooking wood is bleached with oxygen at a delignification degree of 40% or more, and then ozone bleached at a pulp concentration of 25% by mass or more, and then a PN value is obtained. Is 2.8 or less, and multi-stage bleaching including hydrogen peroxide bleaching and chlorine dioxide bleaching is performed, and a method for producing a high-whiteness pulp for a sensitive material having excellent fading properties. 2. The method for producing a high-whiteness pulp for a sensitive material having excellent discoloration properties according to claim 1, wherein the PN value after ozone bleaching is 2.1 or less. 3. The method for producing a high-whiteness pulp for a sensitive material having excellent fading properties according to claim 2, wherein the PN value after ozone bleaching is 1.4 or less. 4. The method for producing a high-whiteness pulp for a sensitive material having excellent fading properties according to claim 1, wherein the unbleached pulp has a Kappa number of 19 or less. 5. The method for producing a high-whiteness pulp for a sensitive material having excellent color fading properties according to claim 1, 2, 3 or 4, wherein ozone bleaching is carried out at a pulp concentration of 30% by mass or more. 6. The method for producing a high-whiteness pulp for a sensitive material having excellent fading properties according to claim 1, 2, 3, 4 or 5, wherein an acid treatment at a pH of 4 or less is performed before ozone bleaching. .