JP2000080589A - Modification of cellulose fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a modification method in which interfiber bonding area increases, interlayer strength is improved and other sheet strength also increases. SOLUTION: The method of this invention is to give mechanical force to slurry where cellulose fiber is dispersed in an aqueous solution including 72.2-98.6 wt.% amine-N-oxide having >=4.5 D dipole moment. The amine-N-oxide is pref. N-methylmorpholine-N-oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cellulose fiber used in the pulp and paper industry, and more particularly, to a method for modifying a cellulose fiber so as to improve the adhesive force between the cellulose fibers and impart excellent strength to the paper. About.

[0002]

2. Description of the Related Art A method for producing paper by making cellulose fiber such as wood pulp into a sheet by wet papermaking has been widely practiced. As a method of improving the strength of the obtained paper, there is a beating method in which a mechanical force is applied to cellulose fibers in a water slurry. By beating, cellulose fibers are modified by causing fibrillation and increasing entanglement between fibers and bonding area between fibers, and beating is widely and generally performed. By this beating, the strength of pull, rupture, interlayer, etc. is remarkably improved.

[0003] However, when beating is performed on the cellulose fiber by this method, the fiber is gradually cut and miniaturized, so that the drainage water is reduced and the tear strength is also reduced. In an extreme case, problems such as a decrease in productivity of the papermaking process occur. Further, when the degree of beating of the cellulose fiber is advanced, the fibrillation of the fiber and the cutting of the fiber are advanced, and the bond between the fibers is increased, so that the propagation of the fracture is facilitated and the tear strength is reduced. However, the degree of beating must be limited. Therefore, the improvement of the paper strength by beating may be unsatisfactory depending on the use of the paper.

Another method for improving the sheet strength is to add an organic polymer-based paper-strength enhancer such as starch or polyacrylamide to cellulose fibers during papermaking.
It is also widely known to increase sheet strength by increasing the bond strength between fibers. However, in this method, although the additives and the addition method have been variously improved, the formation of the sheet is deteriorated, the yield of the paper strength enhancer itself is low, and the material is easily affected by changes in raw materials. There are some problems such as difficult condition control and high cost. After all, improving the strength of paper with a paper-strength enhancer is not satisfactory for some applications.

[0005] On the other hand, natural cellulose fibers such as wood pulp and linter generally comprise a crystalline portion and an amorphous portion, although the composition varies depending on their origin. As an attempt to improve the strength of paper by an amorphous method in which the proportion of the amorphous region of cellulose is increased, Tappi Vol. 48 (No. 2) 7
2 (1965), there is a method of treating a sheet with liquid ammonia. However, this method has an effect of improving strength in the treatment of paper obtained after papermaking, but the strength is rather reduced when the treatment is performed on a cellulose fiber state before papermaking.

[0006] Further, as an amorphization method using an organic solvent for cellulose, JP-A-44-2592 and Polymer C
A method using a dimethylsulfoxide-sulfur dioxide-amine-based solvent as described in hemistry Vol. 29 113 (1991) and the like is known. However, the amorphization method using these solvents is suitable for completely amorphizing cellulose in these solvents that do not completely contain water, but is not suitable when hydrous pulp is used as it is. Absent.

On the other hand, highly polar amine-N-oxides are also known as organic solvents which can completely amorphize and dissolve cellulose fibers and can be spun as regenerated cellulose fibers. SENNI-GAKKAISHI vol.51. 9) It is described in 422 (1995) and the like. Even if the amine-N-oxides contain water, they have the characteristic that they can be made amorphous by heating the cellulose fibers, so that it is not necessary to keep the cellulose in a completely dry state in advance.

Means for improving the physical properties of paper after wet papermaking by treating cellulose fibers with their morphology using amine-N-oxides include 55% to 72% by weight of N-methylmorpholine. -N-oxide (NMM
O) It is known that the tensile strength of paper obtained by wet-making cellulose fibers treated in an aqueous solution is improved (WO95 /
07386).

[0009]

As described above, as described above,
Various means have been attempted to improve the strength of paper as described above, but none of these means has been necessarily satisfactory depending on the use of paper. A method for improving the strength sufficiently in terms of the interlayer strength of paper has not been found, and the present inventor has increased the inter-fiber bonding area, improved the interlayer strength, and also improved other sheet strengths. The task is to propose a method.

[0010]

In order to solve the above problems, the present invention employs the following constitution. That is, the present invention
“Amine-N- having a dipole moment of 4.5 Debye or more
A method of modifying cellulose fibers, comprising applying mechanical force to a slurry in which cellulose fibers are dispersed in an aqueous solution containing 72.2% by weight to 98.6% by weight of oxides.

In the above invention, N-methylmorpholine-N-oxide is recommended as the amine-N-oxide.

The present inventors have disclosed the above-mentioned WO 95/073.
Although the technique described in JP-A-86-86 was examined, sufficient interlayer strength was not obtained. As a result of further research, the NMMO concentration range in the above-mentioned document was lower than 72.2% by weight of NMMO (equivalent to hemihydrate), which is the lower limit of the concentration at which the cellulose was amorphized. -It has been found that oxides do not take advantage of the characteristics of cellulose as an amorphous solvent, and the present invention has been achieved.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Cellulose fibers used in the present invention are paper pulp, dissolving chemical pulp, cotton fiber, etc. obtained from wood fibers, linters, bast fibers, etc., and may be bleached or non-bleached. Bleaching can be used alone or in combination. Alternatively, pulp that has been beaten in advance can be used.

The concentration of cellulose fibers in the slurry at the time of performing the treatment of the present invention is from 1% by weight to 10% by weight.
Is preferred. If the cellulose concentration is too low, the processing efficiency is reduced and the cost is increased, which is not preferable. On the other hand, when the cellulose concentration is too high, the amine-N-
It is not preferable because it is impossible to uniformly impregnate the cellulose fiber with the aqueous oxide solution.

The amine-N-oxides having a dipole moment of 4.5 Debye or more include N-methylmorpholine-N-oxide (NMMO), dimethylethanolamine-N-oxide (DMEAO), and dimethylcyclohexylamine. N-oxide (DMCAO),
Dimethylbenzylamine-N-oxide (DMBA
O), dimethyl homopiperidine-N-oxide (PM
HPO) can be used. Among these, processability,
From the viewpoint of cost and safety, N-methylmorpholine-N-oxide (NMMO) is particularly preferred.

It is believed that the interaction between the N—O dipole of the amine-N-oxides and the OH group in the cellulose breaks hydrogen bonds within and between the molecules of the cellulose, resulting in non-crystallization. The concentration of the amine-N-oxide aqueous solution varies depending on the amine-N-oxide used, but in any case, it needs to be 72.2% by weight to 98.6% by weight, and 72.2% by weight to 82% by weight. % By weight is particularly preferred.

When the concentration of the amine-N-oxide aqueous solution is 7
When the content is less than 2.2% by weight, the cellulose is hardly amorphized. Further, when the concentration of the amine-N-oxide aqueous solution is higher than 98.6% by weight, the melting point of the amine-N-oxide aqueous solution is high and the workability is poor. This is not preferable because the portion gels unevenly and binds the cellulose fibers.
Also, a small amount of water is needed to activate the cellulose.

The temperature of the amine-N-oxide aqueous solution is 3
The temperature is preferably from 0 ° C to 70 ° C. If the temperature of the aqueous solution is too low, the aqueous solution solidifies or the impregnation into the cellulose fibers becomes non-uniform, and if the temperature of the aqueous solution is too high, the reaction proceeds rapidly, and the amorphous portion gels unevenly. It is not preferable because cellulose fibers are bound.

The device used to apply mechanical force to the cellulose fibers as impregnated in the solvent may be any device that meets the purpose, such as a single-disc refiner or a double-disc refiner used for beating in the paper industry. Refiner, niagara beater, ball mill,
It is possible to use a PFI mill. As the strength of the mechanical force, the degree of crystallinity of the fiber as defined below is 3 to 10.
%. When the decrease in crystallinity is less than 3%, the strength of the paper is not sufficiently improved. When the decrease in crystallinity exceeds 10%, the tear strength of the paper starts to decrease.

Hereinafter, the present invention will be described in more detail with reference to Examples, but it is needless to say that the present invention is not limited thereto. The evaluation method used in this example is as follows.

(1) Preparation of cellulose fiber sheet: JIS
According to P8209, a round hand-made sheet was produced so that the absolute basis weight was 60 g / m ² . However, the density of the paper was 0.55 g / cm ³ in Example 1, Comparative Example 1 and Comparative Example 2,
In Example 2, Comparative Example 3 and Comparative Example 4, 0.6
Pressing was performed while adjusting the pressure so as to be 5 g / cm ³ . (2) Freeness (Canadian standard type): JIS P812
1 (3) Crystallinity: measured according to the Segal method. The intensity value of the X-ray diffraction pattern was read and determined by the following equation. Crystallinity = {(I ₀₀₂ −I _am ) / I ₀₀₂ } × 100 (%) where I ₀₀₂ is the diffraction angle 2θ of the X-ray diffraction diagram = 22.5
The diffraction intensity in degrees, I _am, is also the diffraction angle 2θ = 18.5.
(4) Sheet density: JIS P8118 (5) Delamination strength: JAPAN TAPPI Paper pulp test method No. 54 (internal bond strength of paper and paperboard). Two double-sided tapes were stuck on both sides of the sheet, and the force required to peel the inside of the sheet through the tape was defined as the delamination strength. (6) Tensile strength: JIS P8113

[0022]

<Example 1> Commercially available softwood bleached kraft pulp (NBK) having a water content of 56% by weight so as to have the compounding amount shown in Table 1
P) (crystallinity 81%) flaked into NM
MO · Monohydrate (manufactured by Nippon Emulsifier Co., Ltd.) was diluted and uniformly impregnated with an aqueous NMMO solution at 60 ° C. to obtain a NMMO concentration of 75% by weight, and kept at 60 ° C. for 10 minutes. Under the conditions shown in 1, a mechanical force was applied by a PFI mill (manufactured by Kumagaya Rikoki Kogyo Co., Ltd.). After beating, 1
After diluting in 0 liter of water and stirring, filtration with a filter cloth was repeated twice to obtain a modified cellulose fiber from which NMMO had been removed. Table 2 shows the evaluation results of the obtained sheets.

<Comparative Example 1> As shown in Table 1, the number of revolutions of the PFI mill was set so that the freeness was almost the same as that of Example 1, NBKP was impregnated with a 60% by weight NMMO aqueous solution, and treated with the PFI mill. Was done. By performing the same filtration treatment as in Example 1, a treated cellulose fiber (Comparative Example 1) was obtained. Evaluation was performed by forming a sheet in the same manner as in Example 1, and the results are shown in Table 2.

<Comparative Example 2> As shown in Table 1, the cellulose fiber concentration, the clearance, and the like were obtained in an aqueous medium without using NMMO so that the freeness was almost the same as in Example 1.
The number of revolutions was set, and beating was performed with a PFI mill. After beating, a process of diluting in 10 liters of water and filtering through a filter cloth was repeated twice to obtain a treated cellulose fiber (Comparative Example 2). Evaluation was performed by forming a sheet in the same manner as in Example 1, and the results are shown in Table 2.

<Example 2> Commercially hardwood bleached kraft pulp having a water content of 62% by weight under the blending amounts and processing conditions shown in Table 1
(LBKP) (crystallinity: 77%) was made into a flake form, and was uniformly impregnated with an NMMO aqueous solution obtained by diluting NMMO monohydrate to prepare a NMMO concentration of 75% by weight. After keeping the temperature at 60 ° C., mechanical force was applied by a PFI mill. By performing the same filtration treatment as in Example 1, a modified cellulose fiber (Example 2) was obtained. Evaluation was performed by forming a sheet in the same manner as in Example 1, and the results are shown in Table 2.

<Comparative Example 3> As shown in Table 1, the number of revolutions was set so that the freeness was almost the same as in Example 2,
LBKP was impregnated with a 60 wt% NMMO aqueous solution and treated with a PFI mill. By performing the same filtration treatment as in Example 1, a treated cellulose fiber (Comparative Example 3) was obtained. Evaluation was performed by forming a sheet in the same manner as in Example 1, and the results are shown in Table 2.

<Comparative Example 4> As shown in Table 1, the cellulose fiber concentration, the clearance, and the number of revolutions were set in an aqueous medium without using NMMO so that the freeness was almost the same as in Example 2, and the PFI was measured. Beating was performed in a mill. After beating, 1
The process of diluting in 0 liter of water and filtering through a filter cloth was repeated twice to obtain a treated cellulose fiber (Comparative Example 4). Evaluation was performed by forming a sheet in the same manner as in Example 1, and the results are shown in Table 2.

As shown in Table 2, under the conditions of the PFI mill treatment, the cellulose fibers were treated (Examples 1 and 2) in a 75 wt% NMMO aqueous solution capable of amorphizing the cellulose fibers. The degree of crystallinity is 4 compared to treatment in a 60% by weight NMMO aqueous solution that cannot amorphize the fiber (Comparative Examples 1 and 3) or beating treatment in water (Comparative Examples 2 and 4). -6%. In this case, the delamination strength is 75% by weight NMM.
The treatment (Example 1 and Example 2) in an O aqueous solution improved the beating treatment (Comparative Example 2 and Comparative Example 4) to about twice as much. Also, the tensile strength (break length) is 75% by weight.
Beating treatment (Comparative Example 2 and Comparative Example 4) by performing beating treatment (Example 1 and Example 2) in an NMMO aqueous solution
Was improved by about 1 km. These strength-improving effects were improved by about 0.5 km as compared with those subjected to the 60% by weight NMMO concentration treatment (Comparative Example 1 and Comparative Example 3) in which amorphization did not proceed.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

As explained in detail above, the present invention provides:
It is very useful to treat cellulose fibers with amine-N-oxides in a specific concentration range, since the effect of imparting excellent strength properties to the sheet when wet-making the cellulose fibers is provided.

Claims (2)

[Claims] 1. An amine-N-oxide having a dipole moment of 4.5 Debye or more from 72.2% by weight to 98.6% by weight.
A method for modifying a cellulose fiber, comprising applying mechanical force to a slurry in which the cellulose fiber is dispersed in an aqueous solution containing weight%. 2. The method according to claim 1, wherein the amine-N-oxide is N-methylmorpholine-N-oxide.