JP2014070314A - Method of manufacturing dissolving pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dissolving pulp suitable for manufacturing a semi-synthetic fiber.SOLUTION: A dissolving pulp suitable for manufacturing a semi-synthetic fiber such as rayon can be obtained by treating the dissolving pulp with a slit screen having a specific slit width.

Description

  The present invention relates to a dissolving pulp, particularly a dissolving pulp (dissolving kraft pulp) produced by a kraft method. The dissolving pulp of the present invention is particularly useful for viscose rayon applications.

  Dissolving pulp used in the production of rayon generally has a high α-cellulose content of 88-98%. α-cellulose is a portion that does not dissolve when pulp is treated with 17.5% sodium hydroxide, and cellulose is the main component. In order to obtain dissolved pulp of this degree of purity, hemicellulose must be removed from the pulp, for example by steam prehydrolysis (prehydrolysis) before cooking of kraft pulp or by cold caustic extraction in the bleaching process. It is known to remove hemicellulose from pulp.

  In general, dissolving pulp containing a high percentage of pentosan and other hemicelluloses is not preferred for rayon applications. This is because there are problems in filtration, spinning and fiber properties, and the morphological structure of the pulp has not changed sufficiently to obtain the desired reactivity.

  Viscose rayon is produced by extruding and spinning a viscose solution (cellulose xanthate dissolved in an alkali solution) through pores. Therefore, when dissolving pulp is used for viscose rayon, the filterability of the viscose solution prepared from the dissolving pulp is important. Factors affecting the filterability include α-cellulose content, foreign matters (resin content, ash content) and the like (Non-patent Document 1).

  Japanese Unexamined Patent Application Publication No. 2010-202793 (Patent Document 1) discloses a cellulose ester using dissolved pulp having a dichloromethane extract amount of 0.1 ppm to 30 ppm as a raw material.

JP 2010-202793 A

Paper Pulp Technology Association, “Sulphite and Dissolved Pulp” (pages 324-327)

  An object of the present invention is to provide a dissolving pulp suitable for the production of semi-synthetic fibers including rayon, and to provide a dissolving kraft pulp that is particularly useful for viscose rayon applications.

  As a result of intensive studies on the above problems, it was found that the filterability of the viscose solution obtained from the dissolving pulp can be greatly improved by treating the dissolving pulp using a slit screen having a specific slit width, and the present invention is completed. It came to.

That is, the present invention includes the following inventions.
(1) A method for improving the filterability of a viscose solution prepared from dissolved pulp, comprising treating the dissolved pulp with a slit screen having a slit width of 0.15 to 0.3 mm.
(2) A method for producing a dissolving pulp, comprising treating the dissolving pulp with a slit screen having a slit width of 0.15 to 0.3 mm.
(3) The method as described in (2) for manufacturing the dissolving pulp for semisynthetic fiber manufacture.
(4) The method according to (2) or (3), wherein the dissolving pulp is dissolving kraft pulp and / or dissolving sulfite pulp.

  The dissolved kraft pulp of the present invention has a low viscosity and excellent filterability when used as a viscose solution, so that viscose rayon can be efficiently produced from the dissolved pulp of the present invention.

  The dissolving pulp in the present invention means a chemically purified pulp having a high cellulose purity. In a preferred embodiment, the α-cellulose content (content) is 90% or more, and a higher α-cellulose content. (For example, 93% or more, 96% or more, 98% or more). Here, the α-cellulose content of the pulp is a portion that does not dissolve when the pulp is treated with 17.5% sodium hydroxide. Generally, wood contains three major components of cellulose, lignin, and hemicellulose, and a small amount of resin and ash, but dissolved pulp has high cellulose purity, chemical fiber, cellophane, plastic, synthetic glue, and various other celluloses. Widely used as a raw material for derivatives.

  The dissolving pulp of the present invention is dissolved sulfite (sulfite) pulp and / or dissolved kraft pulp. What is dissolved sulfite pulp (DSP)? What is dissolved pulp and dissolved kraft pulp (DKP) produced by the sulfite method? It is a dissolving pulp produced by the kraft cooking method (KP method).

  In the present invention, the filterability of the viscose solution obtained from the dissolved pulp can be greatly improved by treating the dissolved pulp with a slit screen having a slit width of 0.15 to 0.3 mm. Although details of this reason are not completely clear, undissolved fibers, bundling fibers, wrinkles, etc. are of a size that is removed (rejected) when processed with a slit screen having a slit width of 0.15 to 0.3 mm. Since there are many organic substances other than pulp fibers, it is assumed that the filterability is greatly improved by removing such foreign matters. That is, organic matter other than pulp fibers such as uncooked fibers, bundling fibers, and straws increases the viscosity of the viscose solution and lowers the filterability when converted into a viscose solution.

  In the present invention, the filterability (Kr) of a viscose solution prepared from dissolved pulp is in accordance with RP JIS revised round-table conference “Dissolved Pulp Test Method (draft)” (issued in January 1957, Appendix 2, p1-10). Can be measured. Specifically, for a viscose solution prepared from dissolved pulp according to the “dissolved pulp test method (draft)”, the viscosity is measured by the method described later in the examples, and from the viscosity, the following formula can be obtained. it can. Filterability is so good that a number is small.

Kr = 10 ⁵ × k × filtration area / (viscosity) ^0.4
Here, k is a clogging coefficient and can be obtained by the following equation.
t / v = k / 2 × t + 1 / S ₀
[Wherein, t: filtration time, v: filtration amount, S ₀ : initial filtration rate]
If the screen used by this invention is a slit type, a shape etc. will not be ask | required in particular. A slit screen is a screen in which slit-like holes are provided in a base material, and foreign matters having a specific size or more can be removed by adjusting the width of the slit. In the present invention, a slit screen having a specific slit width is used as a screen, but the slit screen can efficiently process a slurry of dissolving pulp as compared with a screen having round or square holes. And clogging of the screen is less likely to occur. Further, it is possible to efficiently separate and remove foreign substances such as adhesive substances that are difficult to remove with a screen having round or square holes. Moreover, you may use the pressure-type slit screen which processes by applying a pressure.

  As described above, in order to remove foreign substances and improve the filterability of the viscose solution, the slit width needs to be 0.3 mm or less. On the other hand, if the slit width is too narrow, the load in the screen processing step increases, so the slit width is in the range of 0.15 to 0.3 mm. Moreover, you may combine a round hole screen, a cleaner, etc. in addition to the slit screen of this invention as needed.

  The raw material of the present invention is wood chips. The wood chip of the present invention is not particularly limited in size and tree species as long as it contains either softwood or hardwood wood chips, and a single wood chip or a mixture of two or more kinds of wood chips. But you can. In the present invention, a high-quality dissolving pulp can be efficiently produced even for tree species that are relatively difficult to digest and bleach, such as conifers. As a softwood chip used in the present invention, for example, a larch genus or a pine genus wood chip can be suitably used. As for the genus Larix, for example, Larix (hereinafter abbreviated as L.) leptolepis (Larix), L. laricina (Tamarack), L. occidentalis (Larix larch), L. decidua (European larch), L. gmeliniii (Guimatsu) and the like. Examples of conifers other than the genus Larix include Pinus radiata (Pinus radiata) for Pinus genus and Pseudotsuga (hereinafter abbreviated as P.) menziesii (Dacrasfer), P. Regarding Cryptomeria japonica, such as japonica (Togasawara).

Production of dissolved kraft pulp As described above, in a preferred embodiment, the dissolved pulp of the present invention is a dissolved kraft pulp produced by a kraft cooking method (KP method). Although not limited to this, manufacture of the melt | dissolution kraft pulp of this invention is demonstrated below.

(1) Prehydrolysis step In the present invention, as a pretreatment before kraft cooking, the chip is hydrolyzed to decompose and remove the hemicellulose content in the wood chips into water-soluble sugars. Can do. The hydrolysis treatment (prehydrolysis) as a pretreatment is carried out by treating wood chips with high-temperature water. The water to be added may be hot water or steam. Since an organic acid or the like is generated by the progress of hydrolysis, the pH of the treatment liquid is generally 2 to 5.

  The prehydrolysis treatment is preferably performed in a temperature range of 150 to 180 ° C. If temperature is less than 150 degreeC, removal of hemicellulose will become inadequate, and when it exceeds 180 degreeC, hydrolysis will become excess and alpha-cellulose content will also fall. The treatment time is not particularly limited, but is preferably 30 to 400 minutes, more preferably 35 to 250 minutes, and further preferably 40 to 150 minutes. When the treatment time is too short, the removal of hemicellulose becomes insufficient, and the delignification improving effect due to the removal of hemicellulose is also reduced. On the other hand, if the treatment time is too long, hydrolysis will be excessive and the α-cellulose content will be reduced, resulting in a decrease in pulp yield, and condensing of lignin will lead to deterioration in digestibility in the subsequent kraft cooking process. .

  In the prehydrolysis treatment in the present invention, the treatment temperature and treatment time can be set using the P factor (Pf) as an index. The P-factor is a standard indicating the total amount of heat given to the reaction system in the prehydrolysis treatment, and is expressed by the following formula in the present invention, and time integration is performed from the time when chips and water are mixed until the end of cooking. To calculate.

Pf = ∫ln ⁻¹ (40.48-15106 / T) dt
[Wherein T represents an absolute temperature at a certain point]
The prehydrolysis treatment in the present invention is preferably performed in a range where the P factor (Pf) is 350 to 800. If Pf is less than 350, the removal of hemicellulose is insufficient, and the effect of improving delignification due to the removal of hemicellulose is also reduced. On the other hand, when Pf exceeds 800, hydrolysis becomes excessive and the α-cellulose content is reduced, resulting in a decrease in pulp yield, and condensing of lignin leads to deterioration in digestibility in the subsequent kraft cooking process. .

The prehydrolysis step can be performed by putting wood chips and water in a pressure resistant container (prehydrolysis kettle), but the shape and size of the container are not particularly limited.
The ratio when supplying wood chips and water to the prehydrolysis kettle is preferably 1 to 2.3 L / kg. The ratio of wood chips to water supplied to the prehydrolysis kettle is also called the dynamic liquid ratio and is shown as the amount of water per kg of wood chips. If the dynamic liquid ratio is less than 1.0 L / kg, the amount of water is too small relative to the wood chips, resulting in insufficient hydrolysis. If the liquid ratio exceeds 2.3 L / kg, the top of the prehydrolysis tank In this case, it is not preferable because the gas phase portion cannot be sufficiently secured. The water includes not only water supplied with the wood chip but also water contained in the wood chip, drain water, and the like.

  In the prehydrolysis step, the liquid ratio of wood chips to water can be, for example, 1.0 to 5.0 L / kg, preferably 1.5 to 4.5 L / kg, and 2.0 to 4 0.0 L / kg is more preferable. If the liquid ratio is less than 1.0 L / kg, hydrolysis is insufficient because the amount of water is too small relative to the wood chips, and if the liquid ratio exceeds 5.0 L / kg, the size of the container becomes excessive. Therefore, it is not preferable. Moreover, you may add a small amount of mineral acid as needed.

(2) Chip Cleaning / Recovery Step Next, the wood chip after the pre-hydrolysis treatment can be recovered by removing the pre-hydrolysis solution and sufficiently washing the chip with water. Insufficient cleaning can cause adverse effects in subsequent cooking steps.

  Washing and removal of the hydrolyzed liquid can be performed by using a general solid-liquid separator. For example, an extraction screen can be provided in a container used for prehydrolysis, and washing water can be introduced from the bottom of the container and extracted from the screen for countercurrent cleaning.

(3) Kraft cooking step The washed chips are put into a digester together with the cooking liquor and can be used for kraft cooking under general conditions. As the digester, either a continuous digester or a batch-type digester can be used, but a continuous digester is preferable because it is more energy efficient. Moreover, you may use for cooking of correction craft methods, such as MCC, EMCC, ITC, and Lo-solid. Also, there are no particular limitations on cooking types such as 1 vessel liquid phase type, 1 vessel gas phase / liquid phase type, 2 vessel liquid phase / gas phase type, and 2 vessel liquid phase type. That is, the step of impregnating and holding the alkaline aqueous solution of the present application may be installed separately from the conventional apparatus or part for the permeation treatment of the cooking liquid. Preferably, the unbleached pulp that has been cooked is washed with a washing device such as a diffusion washer after extracting the cooking liquor. In the case of softwood, the kappa number of unbleached pulp after washing is preferably 10-22, and may be 12-20. In the case of hardwood, it is preferably 5-20, and may be 6-16.

  The kraft cooking process can be performed by putting the pre-hydrolyzed wood chips together with the kraft cooking liquid in a pressure resistant container, but the shape and size of the container are not particularly limited. The liquid ratio between the wood chip and the chemical solution can be, for example, 1.0 to 5.0 L / kg, preferably 1.5 to 4.5 L / kg, and more preferably 2.0 to 4.0 L / kg. .

  Kraft cooking is preferably performed in a temperature range of 120 to 220 ° C, more preferably 150 to 180 ° C. If the temperature is too low, delignification (decrease in the kappa number) is insufficient, while if the temperature is too high, the degree of polymerization (viscosity) of cellulose decreases. In addition, the cooking time in the present invention is the time from when the cooking temperature reaches the maximum temperature until the temperature starts to decrease, but the cooking time is preferably 60 minutes or more and 10 hours, and preferably 120 minutes or more and 240 minutes or less. preferable. If the cooking time is less than 60 minutes, pulping does not proceed, and if it exceeds 10 hours, the pulp production efficiency deteriorates, which is not preferable.

  Moreover, the kraft cooking in this invention can set process temperature and process time by setting H factor (Hf) as a parameter | index. The H factor is a standard representing the total amount of heat given to the reaction system during the cooking process, and is represented by the following equation. The H factor is calculated by time integration from the time when chips and water are mixed until the end of cooking.

Hf = ∫exp (43.20-16113 / T) dt
[Wherein T represents an absolute temperature at a certain point]
In the present invention, the unbleached pulp obtained after cooking can be subjected to various treatments as necessary.

  In one embodiment, oxygen delignification treatment can be performed on pulp obtained by kraft cooking. As the oxygen delignification used in the present invention, a known medium concentration method or high concentration method can be applied as it is. In the case of the medium concentration method, the pulp concentration is preferably 8 to 15% by mass, and in the case of the high concentration method, it is preferably performed at 20 to 35% by mass. As the alkali in oxygen delignification, sodium hydroxide and potassium hydroxide can be used. As oxygen gas, oxygen from a cryogenic separation method, oxygen from PSA (Pressure Swing Adsorption), VSA (Vacuum Swing Adsorption) Oxygen etc. from) can be used.

The reaction conditions for the oxygen delignification treatment are not particularly limited, but the oxygen pressure is 3 to 9 kg / cm ² , more preferably 4 to 7 kg / cm ² , the alkali addition rate is 0.5 to 4% by mass, and the temperature is 80%. -140 degreeC and processing time can be made into 20-180 minutes, and other things can apply well-known conditions. In the present invention, the oxygen delignification treatment may be performed a plurality of times.

  The pulp that has been subjected to the oxygen delignification treatment is then sent to a washing step, and after washing, it is sent to a multistage bleaching step to perform a multistage bleaching treatment. The multi-stage bleaching treatment of the present invention is not particularly limited, but acid (A), chlorine dioxide (D), alkali (E), oxygen (O), hydrogen peroxide (P), ozone (Z), It is preferable to combine a known bleaching agent such as peracid and a bleaching aid. For example, the first stage of the multistage bleaching process uses a chlorine dioxide bleaching stage (D) or an ozone bleaching stage (Z), the second stage is an alkali extraction stage (E), the hydrogen peroxide stage (P), the third stage or later. A bleaching sequence using chlorine dioxide or hydrogen peroxide is preferably used. The number of stages after the third stage is not particularly limited, but considering energy efficiency, productivity, etc., it is preferable to finish in three or four stages in total. Further, a chelating agent treatment stage with ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) or the like may be inserted during the multistage bleaching treatment.

  Since the dissolved kraft pulp (DKP) produced by the present invention is free of hemicellulose and various phenols, high-quality dissolved kraft pulp can be easily produced by ordinary oxygen delignification treatment or bleaching treatment. .

  EXAMPLES Next, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example. Unless otherwise specified, in the present invention,% and the like are based on weight, and the numerical range includes the end points.

Example 1
Bleached and dissolved kraft pulp (α-cellulose content: 94.7%) was treated with a slit screen (slit width: 0.2 mm). The treatment conditions were 8 L / min water volume, about 10 g of pulp was processed every 6 minutes, the screen size was 260 mm × 310 mm, the slits were 70 mm long, 95 mm 0.2 mm wide, 3 intervals at 4 mm intervals. The ones in line were used.

  A viscose solution was prepared from the resulting bleach-dissolved kraft pulp, and the amount of foreign matter, viscosity, and filterability (Kr) of the viscose solution were measured. The viscose solution was prepared in accordance with the RP JIS revised round-table conference “Dissolved Pulp Test Method (Draft)” (issued in January 1957, Appendix 2, pages 1 to 10).

The amount of foreign matter, viscosity, and filterability (Kr) of the viscose solution were measured by the following methods.
Foreign matter amount: The amount of foreign matter was counted under the condition of resolution 800 dpi by capturing images with a dirt analyzer (EPSON GT-X770) and performing image analysis. The color of the base filter was set to 0, black was set to 100, the color density was digitized, and those having a color density of 65% or more were counted as foreign matters (threshold value 65%). Specifically, a viscose solution obtained by converting 4 g of pulp into a viscose solution was used to measure all foreign matters on the filter using an ADVANTEC PF040 filter, and the number of foreign matters of 50 μm or more was measured.
・ Viscosity: Put the viscose solution in a graduated transparent tube and place it in a water bath at 20 ± 0.1 ℃. After leaving for 15-30, drop 1/8 inch ball bearing steel ball (0.1300 ± 0.003g) onto the center of the tube with tweezers and measure the number of seconds required to fall between 20cm on the tube scale.
Filterability (Kr): RP JIS revision round-table conference, dissolving pulp test method (draft) (published in January 1957, Appendix 2, p1-10).

Comparative Example 1
For the commercially available bleach-dissolved kraft pulp used in Example 1, the amount of foreign matter, viscosity, and filterability (Kr) of the viscose solution used for dissolving the pulp was not the same as in Example 1, except that the foreign matter was not removed by the slit screen. Measured.

  As shown in Table 1, the filterability (Kr: 371) of the viscose solution prepared from the dissolved kraft pulp from which the foreign matter was removed by the slit screen (0.2 mm) Compared with filterability (Kr: 657), it was remarkably improved.

Claims (4)

  A method for producing a dissolving pulp, comprising treating the dissolving pulp with a slit screen having a slit width of 0.15 to 0.3 mm.   The process according to claim 1 for producing dissolving pulp for the production of semi-synthetic fibers.   A method for improving the filterability of a viscose solution prepared from dissolved pulp, comprising treating the dissolved pulp with a slit screen having a slit width of 0.15 to 0.3 mm.   The method according to claim 1 or 2, wherein the dissolving pulp is dissolving kraft pulp and / or dissolving sulfite pulp.