JP2020165059A - Soluble pulp sheet - Google Patents

Abstract

To provide a soluble pulp sheet useful as raw material for the production of viscose rayon and cellulose derivatives, the soluble pulp sheet particularly excellent in filterability of viscose solution.SOLUTION: A soluble pulp sheet contains an anionic polymer, preferably a water-soluble polymer that contains a carboxy group, a sulfonic acid group, a phosphate group, a hydroxy group or the like and expresses dispersibility by negative charge, at a rate of 0.1 mass% or more and 3 mass% or less to the pulp solid content.SELECTED DRAWING: None

Description

The present invention relates to a dissolving pulp sheet which is a raw material for producing viscose rayon and cellulose derivatives.

Dissolving pulp containing cellulose as a main component is processed into fibers for clothing such as rayon, and is processed into cellulose acetate used for tobacco filter chips, triacetate (TAC) films and the like.

Wood is pulped, and the pulp is molded into a sheet-like form, which is supplied as a raw material for cellulose derivatives and pulp cotton. As an industrial raw material, pulp is formed into a sheet and supplied.

For viscose rayon, a dissolved pulp sheet is made into a slurry in a sodium hydroxide aqueous solution, immersed for a certain period of time to form alkaline cellulose, and then squeezed to remove the sodium hydroxide aqueous solution, and the obtained alkaline cellulose is used. After pulverization, it is reacted with carbon disulfide to obtain cellulose zantate. Cellulose zantate is dissolved in an alkaline solution to prepare a viscose solution (cellulose zantate dissolved in an alkaline solution), which is extruded from the pores and spun to produce. It is important to make a uniform slurry in the first step of making a slurry in a sodium hydroxide aqueous solution. Therefore, if the alkali solubility of the dissolving pulp is good, the rayon can be reacted uniformly in the production of rayon, and the quality of the resulting rayon is good.

Examples of the method for crushing the pulp sheet include (1) wet crushing (Patent Documents 1 and 2), (2) dry crushing (Patent Document 3), and (3) hydrous softening crushing (Patent Document 4). There is a method, but there is no particular method for improving the filterability of the viscose solution.

Further, when viscose rayon is produced by extruding a viscose solution (cellulose zantate dissolved in an alkaline solution) from pores and spinning it, the filterability of the viscose solution is important. Factors that affect the filterability of the viscose solution include the α-cellulose content of the dissolving pulp and foreign substances (resin content, ash content) (Non-Patent Document 1).

Japanese Patent Application Laid-Open No. 2-91101 Japanese Patent Application Laid-Open No. 3-197501 Special Fairness 7-91321 Publication No. JP-A-2-311501

Pulp and Paper Technology Association, "Sulfite Pulp / Dissolving Pulp" (pp. 324-327)

However, even with the method disclosed in the above patent document, it is difficult to completely solve the filterability of the viscose solution of the dissolving pulp sheet, and in particular, the dissolving pulp sheet made of dissolved kraft pulp has the filtering property of the viscose solution. Was inferior.

An object of the present invention is to provide a dissolving pulp sheet having good filterability of a viscose solution.

As a result of diligent studies to solve the above problems, the present inventors have found that a dissolving pulp sheet having specific physical properties is excellent in filterability, and have completed the present invention. The main configuration of the present invention is as follows.
(1) A dissolving pulp sheet containing 0.1% by mass or more and 3% by mass or less of an anionic polymer with respect to the solid pulp content.
(2) The dissolving pulp sheet according to (1), wherein the dissolving pulp is dissolved kraft pulp.
(3) A method for producing a dissolving pulp sheet, which comprises a step of adding 0.1% by mass or more and 3% by mass or less of an anionic polymer with respect to the pulp solid content.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a dissolving pulp sheet having excellent filterability of a viscose solution, and it is possible to provide a dissolving pulp sheet useful as a raw material for producing viscose rayon or a cellulose derivative.

The present invention has found that a dissolving pulp sheet having specific physical properties has good filterability of a viscose solution. Dissolving pulp means chemically purified pulp having high cellulose purity, and in a preferred embodiment, the α-cellulose content is 90% or more. Generally, wood contains the three major components of cellulose, lignin, and hemicellulose, as well as a small amount of resin and ash, but dissolved pulp has high cellulose purity, and is made of synthetic fibers, cellophane, plastics, synthetic glues, and various other cellulose-based materials. It is widely used as a raw material for derivatives.

The filterability of the viscose solution of the dissolving pulp in the present invention can be evaluated by the viscose filterability (Kw). The viscose filterability (Kw) is to evaluate the uniformity of a viscose solution (cellulose zantate dissolved in an alkaline solution) prepared from dissolved pulp by a predetermined method, and is used for impurities and undissolved fibers. When the amount is small, the filterability is good. The viscose filterability can be determined by the following formula according to the reactivity measurement of viscose pulp (FZ / T 50010.13-2011), and the smaller the number, the better the filterability.
Kw (seconds) = (P _2- P ₁ )-(Q _2- Q ₁ )
P1: Time required for filtration when the amount of filtrate reaches 125 mL P2: Time required for filtration when the amount of filtrate reaches 150 mL Q1: Time required for filtration when the amount of filtrate reaches 25 mL Q2: Amount of filtrate Filtration time required when the amount reaches 50 mL In the present invention, it is necessary to contain an anionic polymer in an amount of 0.01% by mass or more and 3% by mass or less per absolute dry weight of the pulp. By containing an anionic polymer, the texture of the dissolving pulp sheet can be improved and the viscose solution can be filtered. The anionic polymer is a water-soluble polymer containing a carboxy group, a sulfonic acid group, a phosphoric acid group, a hydroxy group, etc. and which exhibits dispersibility by a negative charge. For example, carboxymethyl cellulose, TEMPO oxidized cellulose, polycarboxylic acid. , Lignin sulfonic acid, benzene sulfonic acid, alkyl sulfonic acid, polyphosphoric acid, polyvinyl alcohol and the like, which is an anionic polymer containing at least one kind.

The method for incorporating the anionic polymer into the dissolving pulp is not particularly limited. The dissolved pulp sheet may be formed after adding an anionic polymer to the paper material, or may be externally added in the process of forming the dissolved pulp into a sheet shape. An internal addition and an external addition may be used in combination, but the external addition is preferable from the viewpoint of increasing the yield of the anionic polymer.

Examples of the method of externally adding an anionic polymer to a pulp sheet include a bar coater, a blade coater, an air knife coater, a rod coater, a bill blade coater, a bell vapor coater, a gate roll coater, a size press and a calendar size press, and a spray coater. , A known device can be used to apply to at least one side of the pulp sheet. In particular, it is preferable to apply a surfactant to both sides of the pulp sheet by using one or more of these devices, which can suppress curling of the sheet and continuously produce the pulp sheet. It is possible to suppress operational troubles due to curls such as paper jams and poor transportation during finishing. This effect is remarkably exhibited when manufacturing a flat-shaped product.

Further, the external addition of the anionic polymer is preferably performed after the press part by using a spray coater equipped with a one-fluid spray or a two-fluid spray from the viewpoint of further increasing the yield of the surfactant.

Further, the dissolution pulp sheet of the present invention preferably has a density of 0.45 to 0.65 g / cm ³ . When the density exceeds 0.65 g / cm ³ , the strength of the sheet is also improved, and the filterability of the viscose solution is deteriorated. On the other hand, when the density is less than 0.45 g / cm ³ , the smoothing of the sheet is insufficient and the unevenness becomes large, so that the thickness of the pulp sheet becomes uneven and the filterability of the viscose solution deteriorates. To do.

The pulp sheet of the present invention is particularly preferably applied to dissolved kraft pulp produced by the kraft cooking method. The method for producing dissolved kraft pulp will be described below.

The raw material of the present invention is wood chips. In the present invention, it is preferable to include wood chips of softwood, the size and species of the wood chips are not particularly limited, and a single type of wood chips or a mixture of two or more types of wood may be used. In the present invention, high-quality solving pulp can be efficiently produced even for softwood tree species that are relatively difficult to evaporate and bleach. As the chips of softwood used in the present invention, for example, wood chips of the genus Larch or the genus Pine can be preferably used. Regarding the genus Larch, for example, Larix (hereinafter abbreviated as L.) leptolepis (Larch), L. laricina (Larch), L. occidentalis (Save Larch), L. decidua (European Larch), L. gmelinii (Larix) And so on. In addition, as coniferous trees other than larch, for example, Pinus radiata (radiata pine) for pine, Pseudotuga (hereinafter abbreviated as P.) menziesii (daclasfer), P. japonica (togasawara) for Togasawara. ), Etc., Cryptomeria japonica, etc. can be mentioned for the genus Pseudotsuga.

Hydroheat treatment step In the present invention, as a pretreatment before kraft cooking, the chips are hydroheat treated to decompose the hemicellulose content in the wood chips into water-soluble sugars and remove them. Hydrothermal treatment (pre-hydrolysis) as a pretreatment is carried out by treating the wood chips with hot water. The water to be added may be hot water or steam. Since organic acids and the like are generated as the hydrolysis progresses, the pH of the treatment liquid is generally 2 to 5.

The hydrothermal treatment is preferably performed in a temperature range of 150 to 180 ° C. If the temperature is less than 150 ° C., hemicellulose is insufficiently removed, and if it exceeds 180 ° C., hydrolysis becomes excessive and the α-cellulose content also decreases. The treatment time is not particularly limited, but is preferably 15 to 400 minutes, more preferably 20 to 250 minutes, still more preferably 25 to 150 minutes. If the treatment time is too short, the removal of hemicellulose becomes insufficient, and the effect of improving the delignin property 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 decrease, leading to a decrease in pulp yield, and condensation of lignin will lead to deterioration of digestibility in the subsequent kraft cooking step. ..

Further, in the hydrothermal treatment in the present invention, the treatment temperature and the treatment time can be set using the P factor (Pf) as an index. The P factor is a guideline for expressing the total amount of heat given to the reaction system in the pre-hydrolysis treatment. In the present invention, it is expressed by the following formula, and the time is integrated from the time when the chips and water are mixed to the time when the cooking is completed. It is calculated by.

Pf = ∫ln ^-1 (40.48-15106 / T) dt
[In the formula, T represents the absolute temperature at a certain point in time]
The hydrothermal treatment in the present invention is preferably carried out in a range where the P factor (Pf) is 350 to 900, and more preferably 500 to 800. When Pf is less than 350, the removal of hemicellulose is insufficient, and the effect of improving the delignin property due to the removal of hemicellulose is also reduced. Further, when Pf exceeds 900, hydrolysis becomes excessive and α-cellulose content decreases, leading to a decrease in pulp yield, and condensation of lignin causes deterioration of digestibility in the subsequent kraft cooking step. ..

The hydrothermal treatment step can be performed by putting wood chips and water in a pressure-resistant container (pre-hydrolysis kettle), but the shape and size of the container are not particularly limited.

The ratio of wood chips and water supplied to the hydrothermal treatment kettle (pre-hydrolysis kettle) is preferably 1 to 2.3 L / kg. The ratio of wood chips to water supplied to the pre-hydrolyzer is also called the dynamic liquid ratio and is expressed as the amount of water per kg of wood chips. If the dynamic liquid ratio is less than 1.0 L / kg, there is too little water for the wood chips and the hydrolysis is insufficient, and if the liquid ratio exceeds 2.3 L / kg, the top of the pre-hydrolysis kettle It is not preferable because the gas phase portion cannot be sufficiently secured in. The water includes not only the water supplied together with the wood chips, but also the water contained in the wood chips, drain water and the like.

Further, in the pre-hydrolysis kettle, 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 2.0 to. 4.0 L / kg is more preferable. If the liquid ratio is less than 1.0 L / kg, the amount of water is too small for the wood chips, resulting in insufficient hydrolysis, 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 if necessary.

Chip Cleaning / Recovery Step Next, the wood chips after the pre-hydrolysis treatment are recovered by removing the pre-hydrolyzed solution and thoroughly washing the chips with water. Inadequate cleaning can adversely affect subsequent cooking steps.

The hydrolyzed solution can be washed and removed by using a general solid-liquid separator or the like. For example, a container used for pre-hydrolysis may be provided with a solid-liquid separation device such as an extraction screen or a filter cloth, and washing water may be introduced from the lower part of the container to extract from the screen for countercurrent washing.

Craft cooking process The washed chips are put into a cooking pot together with the cooking liquid and used for craft cooking. In addition, it may be used for cooking modified craft methods such as MCC, EMCC, ITC, and Lo-solid. Further, the cooking type 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 is not particularly limited. That is, the step of impregnating the alkaline aqueous solution of the present application and holding the alkaline aqueous solution may be installed separately from the device or site for the purpose of the conventional permeation treatment of the cooking liquid. Preferably, the unbleached pulp that has been digested is washed with a washing device such as a diffusion washer after extracting the cooking liquid. The copper value of the unbleached pulp after washing is preferably 7 to 15, and may be 9 to 13.

The kraft cooking step can be carried out by putting the pre-hydrolyzed wood chips in a pressure-resistant container together with the kraft cooking solution, but the shape and size of the container are not particularly limited. The liquid ratio of the wood chip to 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. ..

Further, in the present invention, an alkaline cooking liquid containing 0.01 to 1.5% by mass of a quinone compound per absolute dry chip is added to the cooking pot. If the amount of the quinone compound added is less than 0.01% by mass, the amount added is too small to reduce the copper value of the pulp after cooking, and the relationship between the copper value and the pulp yield is not improved. Furthermore, the reduction of dregs and the suppression of the decrease in viscosity are also insufficient. Further, even if the amount of the quinone compound added exceeds 1.5% by mass, no further reduction in the copper value of the pulp after cooking and no improvement in the relationship between the copper value and the pulp yield are observed.

The quinone compound used is a quinone compound as a so-called known cooking aid, a hydroquinone compound or a precursor thereof, and at least one compound selected from these can be used. Examples of these compounds include anthraquinone, dihydroanthraquinone (eg, 1,4-dihydroanthraquinone), tetrahydroanthraquinone (eg, 1,4,4a, 9a-tetrahydroanthraquinone, 1,2,3,4-tetrahydroanthraquinone). , Methylanthraquinone (eg 1-methylanthraquinone, 2-methylanthraquinone), methyldihydroanthraquinone (eg 2-methyl-1,4-dihydroanthraquinone), methyltetrahydroanthraquinone (eg 1-methyl-1,4,4a) , 9a-tetrahydroanthraquinone, 2-methyl-1,4,4a, 9a-tetrahydroanthraquinone) and other quinone compounds such as anthraquinone (generally 9,10-dihydroxyanthraquinone) and methylanthrahydroquinone (eg, 2-methyl). Anthraquinone), dihydroanthraquinone (eg, 1,4-dihydro-9,10-dihydroxyanthraquinone) or an alkali metal salt thereof (eg, disodium salt of anthraquinone, 1,4-dihydro-9,10-) It is a hydroquinone compound such as a disodium salt of dihydroxyanthraquinone), and examples thereof include precursors such as anthraquinone, anthraquinone, methylanthronone, and methylanthraquinone. These precursors have the potential to be converted to quinone or hydroquinone compounds under cooking conditions.

When the wood chips are coniferous, the cooking liquor preferably has an active alkali addition rate (AA) of 16 to 22% by mass per weight of the dry wood chips. If the active alkali addition rate is less than 16% by mass, the removal of lignin and hemilulose is insufficient, and if it exceeds 22% by mass, the yield and quality are lowered. Here, the active alkali addition rate is obtained by converting the total addition rate of NaOH and Na ₂ S as the addition rate of Na ₂ O, and multiplys NaOH by 0.775 and Na ₂ S by 0.795. This can be converted into the addition rate of Na ₂ O. The sulfurization degree is preferably in the range of 20 to 35%. In the region where the sulfurization degree is less than 20%, the delignin property is lowered, the pulp viscosity is lowered, and the meal rate is increased.

Kraft cooking is preferably carried out in a temperature range of 120 to 180 ° C, more preferably 140 to 160 ° C. If the temperature is too low, delignin (decrease in copper value) is insufficient, while if the temperature is too high, the degree of polymerization (viscosity) of cellulose decreases. 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 600 minutes or less, and 120 minutes or more and 360 minutes or less. Is even more preferable. If the cooking time is less than 60 minutes, pulping does not proceed, and if it exceeds 600 minutes, the pulp production efficiency deteriorates, which is not preferable.

Further, in the craft cooking in the present invention, the treatment temperature and the treatment time can be set by using the H factor (Hf) as an index. The H factor is a measure of the total amount of heat given to the reaction system during the cooking process, and is expressed by the following formula. The H factor is calculated by integrating the time from the time when the chips and water are mixed to the time when the cooking is completed. It is preferable to carry out craft cooking so that the H factor is 1000 to 2000.

Hf = ∫exp (43.20-16113 / T) dt
[In the formula, T represents the absolute temperature at a certain point in time]
In the present invention, the unbleached (unbleached) pulp obtained after cooking can be subjected to various treatments, if necessary. For example, the unbleached pulp obtained after kraft cooking can be bleached.

In one embodiment, the pulp obtained by kraft cooking can be treated with oxygen delignin. As the oxygen delignin 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 20 to 35% by mass. Sodium hydroxide and potassium hydroxide can be used as the alkali in oxygen delignin, and as oxygen gas, oxygen from the cryogenic separation method, oxygen from PSA (Pressure Swing Adsorption), and VSA (Vacuum Swing Adsorption) can be used. ) Can be used.

The reaction conditions for the oxygen delignin 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 ° C., treatment time is 20 to 180 minutes, and other known conditions can be applied. In the present invention, the oxygen delignin treatment may be performed a plurality of times.

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

The dissolving pulp sheet of the present invention can be used as a raw material for viscose rayon, as a raw material for various cellulose derivatives such as methyl cellulose, ethyl cellulose, acetyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose, and as a raw material for cellulose powder and the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the scope thereof. Unless otherwise specified, parts and% in the example indicate parts by mass and% by mass, respectively. In addition, the filterability and general physical properties specified in the examples are values evaluated by the following methods. The measurement results of the pulp sheets obtained in Examples and Comparative Examples are shown in Table 1.
<Measurement method of physical properties>
Moisture content of pulp sheet: About 10 g of the pulp sheet cut into 3 cm × 3 cm was dried in a blower dryer for 24 hours at 105 ° C. The pulp sheet moisture content was calculated from the weight of the pulp sheet after drying / the weight of the pulp sheet before drying × 100.
-Sheet density: According to JIS P 8118, the density was calculated from the basis weight and the average sheet thickness.
-Sheet texture: Using a flat panel, light was applied from the back surface of the sheet with a fluorescent lamp, and the sensory evaluation was performed visually. The evaluation was made on a scale of 1 to 5, with 1 having a bad texture and 5 having a good texture.
Viscose filterability (Kw): Kw was measured by the following formula in accordance with the reactivity measurement of viscose pulp (FZ / T 50010.13-2011). If the filtrate did not reach 150 mL 10 minutes after the start of filtration, it was evaluated as x (not measurable).
Kw (seconds) = (P _2- P ₁ )-(Q _2- Q ₁ )
P1: Time required for filtration when the amount of filtrate reaches 125 mL P2: Time required for filtration when the amount of filtrate reaches 150 mL Q1: Time required for filtration when the amount of filtrate reaches 25 mL Q2: Amount of filtrate Filtration time when reaches 50 mL

[Comparative Example 1]
A 2-vessel type cooking apparatus consisting of a pre-hydrolyzing pot and a cooking pot was used. Both the pre-hydrolysis kettle and the cooking kettle are gas phase kettles having a top separator at the top. A coniferous tree chip (apparent density: about 430 kg / m ³ ) consisting of larch: radiata pine = 50:50 was pre-hydrolyzed according to the following procedure. First, in a pre-hydrolysis kettle, pre-hydrolysis was performed at a liquid ratio of 3.0 L / kg and a pre-hydrolysis temperature of 170 ° C. for 50 minutes (P factor: about 500).
After the pre-hydrolyzed wood chips were washed and recovered, the recovered wood chips were subsequently subjected to kraft cooking. The craft cooking was carried out in a cooking kettle at a cooking temperature of 158 ° C. for 230 minutes at an H factor (Hf) = 1300. The chemical solution has a composition of active alkali 105 g / L (Na ₂ O conversion value), NaOH 75.6 g / L (Na ₂ O conversion value), Na ₂ S 29.4 g / L (Na ₂ O conversion value), and 28% sulfide degree. The liquid ratio between the wood chips and the cooking chemical solution was 3.2 L / kg.
After the completion of kraft cooking, the obtained unbleached pulp is subjected to oxygen delignin treatment, followed by a sequence of chlorine dioxide treatment (D ₁ ) -alkali extraction / hydrogen peroxide treatment (Ep) -chlorine dioxide treatment (D ₂ ). Bleached and dissolved kraft pulp was obtained. The whiteness of the bleached-dissolved kraft pulp after the bleaching treatment was 90% (ISO whiteness was measured according to JIS P 8148: 2001), and the hemicellulose content was about 4% (measured according to NREL / TP510-42618).
The obtained bleached pulp was sheeted with a double wire machine. At that time, the total linear pressure of the press in the dehydration step consisting of the prepress, the main press, the first high pressure press, and the second high pressure press was set to 350 kg / cm.
The obtained pulp sheet was diluted with water to a slurry concentration of 0.6%, and then the slurry pH was adjusted to 3 with 4N sulfuric acid and allowed to stand for 1 hour. Next, about 8 L of pulp slurry was collected, put into a square hand-plow machine (JIS8222: 2015), left to stand for 10 minutes without stirring, and then pressed with a JIS8222: 2015 compliant press, and dried under 25 cm. A × 25 cm square handmade sheet was obtained. However, the condition of the primary press was a linear pressure of 10 MPa.

[Example 1]
Sheets were formed in the same manner as in Comparative Example 1 except that 0.2% of carboxymethyl cellulose 1 (carboxymethyl cellulose manufactured by Nippon Paper Industries, Ltd., DS = 1.5, 1% viscosity at 25 ° C. of 200 mPa · s) was added to the pulp slurry. did.

[Example 2]
A sheet was formed in the same manner as in Comparative Example 1 except that 0.5% of carboxymethyl cellulose 1 was added to the pulp slurry.

[Example 3]
Aron T-50 (polyacrylic acid manufactured by Toagosei Co., Ltd.) was formed into a sheet in the same manner as in Comparative Example 1 except that 0.2% was added to the pulp slurry.

[Example 4]
Aron T-50 was formed into a sheet in the same manner as in Comparative Example 1 except that 0.5% was added to the pulp slurry.

As shown in Table 1, the dissolving pulp sheets of Examples 1 to 4 containing the anionic polymer had good filterability of the viscose solution.

Claims (3)

A dissolving pulp sheet containing 0.1% by mass or more and 3% by mass or less of an anionic polymer with respect to the solid pulp content. The dissolved pulp sheet according to claim 1, wherein the dissolved pulp is dissolved kraft pulp. A method for producing a dissolving pulp sheet, which comprises a step of adding 0.1% by mass or more and 3% by mass or less of an anionic polymer with respect to the pulp solid content.