Modified pulp

Abstract

To provide a modified pulp having superior transparency.SOLUTION: A modified pulp of the present invention comprises cellulose having a carboxyl group content of 1.5 mmol / g or more, and exhibits a total light transmittance of 70% or higher in a dispersion obtained by dispersing the modified pulp in water to achieve a solid concentration of 1 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to modified pulp. [Background technology]

[0002] As a fine cellulose fiber into which an anionic functional group has been introduced, one having excellent transparency and a haze value of 15% or less when dispersed in water at a concentration of 0.2% by mass has been proposed (Patent Document 1). The fine cellulose fiber described in Patent Document 1 is a nanofiber that has been finely divided using a high-pressure homogenizer or the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-25468 Summary of the Invention [Problem to be solved by the invention]

[0004] In contrast, there has been no pulp fiber (for example, fiber length of 100 μm or more, fiber width of 1 μm or more) before being refined that has excellent transparency.

[0005] Therefore, an object of the present invention is to provide a modified pulp having excellent transparency. [Means for solving the problem]

[0006] To achieve the above objective, the modified pulp of the present invention has a cellulose carboxyl group content of 1.5 mmol / g or more, and when dispersed in water to a solids concentration of 1 mass %, the total light transmittance of the dispersion is 70% or more. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide modified pulp having excellent transparency, with the predetermined total light transmittance being 70% or more. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the modified pulp of the present invention, the carboxyl group content of the cellulose is 1.5 mmol / g or more. The carboxyl group content may be, for example, 1.9 mmol / g or more, or 2.2 mmol / g or more. The upper limit of the carboxyl group content is not particularly limited, but is, for example, 3.0 mmol / g or less, or 2.6 mmol / g or less. In the present invention, the carboxyl group may be not only in the acid form (-COOH) but also in the salt form, i.e., in the carboxylate salt form (-COO - X + ) in the carboxylate group. + ) is not particularly limited, and examples thereof include hydrogen ions, metal ions, onium ions, cationic organic compounds, and the like.

[0009] <Method for measuring carboxyl group content> The carboxyl group content can be determined, for example, by preparing 60 mL of a 0.5% to 1% by mass aqueous dispersion from the modified pulp whose dry mass has been precisely weighed, adjusting the pH to about 2.5 with 0.1 M hydrochloric acid, adding 0.05 M aqueous sodium hydroxide dropwise, measuring the electrical conductivity, and continuing until the pH reaches about 11. The volume (V) of the aqueous sodium hydroxide solution consumed in the neutralization stage of the weak acid, in which the change in electrical conductivity is gradual, can be calculated using the following formula. The water may be tap water, but is preferably ion-exchanged water or pure water, and the same applies hereinafter. Carboxyl group content (mmol / g) = V (mL) × (0.05 / dry mass of modified pulp (g))

[0010] The carboxyl group content can also be measured, for example, by the method described later in the Examples below.

[0011] <Total light transmittance> The modified pulp is dispersed in water to a solids concentration of 1% by mass, and the dispersion has a total light transmittance of 70% or more. The total light transmittance may be, for example, 75% or more, 80% or more, 85% or more, or 90% or more. The total light transmittance can be determined, for example, by measuring a dispersion obtained by dispersing the modified pulp in water to a solids concentration of 1% by mass using a spectrophotometer in accordance with JIS K 7361-1.

[0012] <Haze value> The haze value of the dispersion is, for example, 95% or less, 90% or less, 85% or less, or 70% or less when the total light transmittance is within the above range.

[0013] <Method for measuring haze value> The haze value can be determined, for example, by measuring a dispersion obtained by dispersing the modified pulp in water to a solid content concentration of 1% by mass using a spectrophotometer in accordance with JIS K 7105.

[0014] The physical properties of the modified pulp, excluding the carboxyl group content and total light transmittance, are not particularly limited, but may be, for example, as follows.

[0015] <Average fiber length> The average fiber length of the modified pulp is not particularly limited and is, for example, 0.2 mm to 3 mm.

[0016] <Short fiber rate (%)> The modified pulp may also include modified pulp with short fiber length as follows. Examples of modified pulp with short fiber length (hereinafter referred to as "short fiber") include modified pulp with a fiber length distribution of 0.04 mm or more and 0.2 mm or less. The content (%) of short fibers in the modified pulp (i.e., short fiber ratio (%)) is, for example, 10% or more, 15% or more.

[0017] From the viewpoint of transparency and handling, the modified pulp has a short fiber content (%) (i.e., short fiber ratio (%)) of, for example, 10% to 70%, 10% to 60%, 10% to 50%, 10% to 45%, or 15% to 45% in terms of fiber length distribution.

[0018] <Average fiber width> The average fiber width of the modified pulp is not particularly limited, and is, for example, 5 μm to 100 μm, 10 μm to 50 μm, 20 μm to 40 μm, or 20 μm to 30 μm.

[0019] <Method for measuring average fiber length, average fiber width, and fiber distribution> The average fiber length and average fiber width of the modified pulp can be measured, for example, using a fiber tester or fiber length distribution measuring instrument manufactured by Lorentzen & Wettley in accordance with ISO 16065-2: 2007. The fiber length distribution and fiber width distribution of the modified pulp can be measured, for example, using a fiber length distribution measuring instrument in accordance with ISO 16065-2: 2007.

[0020] <Kink> In order to improve transparency, the modified pulp preferably has little bending. Specifically, the modified pulp preferably has a low kink (1 / m) value. For example, the modified pulp has a kink (1 / m) of 1 to 1150, 1 to 900, 1 to 650, 1 to 450, 1 to 300, or 1 to 200.

[0021] <Kink measurement method> The kink of the modified pulp can be measured, for example, using a fiber length distribution measuring instrument in accordance with ISO 16065-2:2007.

[0022] From the viewpoint of reliability, it is desirable that the measurement values ​​of the modified pulp described above be measured on at least 5,000 fibers in accordance with ISO 16065-2:2007.

[0023] <Viscosity> The viscosity of a dispersion (solid content concentration 1% by mass) obtained by dispersing the modified pulp in water is, for example, 1000 mPa·s or more, 5000 mPa·s or more, or 10000 mPa·s or more. In particular, if the average fiber length of the modified pulp is 1 mm or less, the viscosity of the dispersion tends to increase.

[0024] <Viscosity measurement method> The viscosity (mPa·s) of the modified pulp can be measured, for example, using a B-type viscometer at a measurement temperature of 20°C, with measurements being performed at rotation speeds of 6 rpm and 60 rpm, and the thixotropy index (TI) value can also be calculated from each viscosity value. TI value = (viscosity at 6 rpm) / (viscosity at 60 rpm)

[0025] The TI value can be adjusted as appropriate, and when a high TI value is required, the lower limit of the TI value is, for example, 3 or more, 4 or more, or 5 or more. The upper limit of the TI value is, for example, 10 or less, 8 or less, 6 or less, or 5 or less. On the other hand, when a low TI value is preferred, the lower limit is, for example, 1 or more, and the upper limit is, for example, 3 or less, or 2.5 or less.

[0026] Next, a method for producing the modified pulp will be described using an example, but the present invention is not limited to this example. In this example, the modified pulp is produced by oxidizing the pulp in a reaction solution containing an oxidant and a pro-oxidant (co-oxidant) using 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) as a catalyst. In addition to or instead of TEMPO, a TEMPO derivative (e.g., 4-acetamido-TEMPO, 4-carboxyl-TEMPO, 4-phosphonooxy-TEMPO, etc.) may be used as the catalyst.

[0027] In the present invention, the pulp refers to a fibrous material comprising a plurality of cellulose fibers. These cellulose fibers are a collection of a plurality of fine fibers (e.g., microfibrils). These fine fibers are a collection of a plurality of cellulose molecules (hereinafter, sometimes simply referred to as "cellulose"), which are chain-like polymers in which D-glucose is bonded via β(1→4) glucoside bonds. It is also preferable to wash the pulp beforehand. For example, by filtering and dehydrating the pulp using water on a 200-mesh or 235-mesh sieve, it is possible to remove fine fibers and debris that are too small, which is desirable because it improves handleability during production. In other words, pulp is a collection of cellulose fibers of a size that can become residue on a 200-mesh or 235-mesh sieve.

[0028] Examples of the pulp include wood-based pulp (hereinafter simply referred to as "wood pulp"), dissolving pulp, cotton-based pulp such as cotton linter, non-wood-based pulp such as wheat straw, bagasse, paper mulberry, mitsumata, hemp, kenaf, and fruit, and recycled paper pulp prepared from recycled newspapers, magazines, cardboard, etc. One type of pulp may be used alone, or two or more types of pulp may be used in combination. From the viewpoint of ease of availability, wood pulp is easily used as the pulp.

[0029] There are various types of wood pulp, and there are no particular limitations on their use. Examples include paper pulp such as softwood kraft pulp (NBKP), hardwood kraft pulp (LBKP), and thermomechanical pulp (TMP).

[0030] The amount of the catalyst used is not particularly limited, but is, for example, 1 mmol to 5 mmol, or 2 mmol to 5 mmol, per 5 g of the pulp. When the amount of the catalyst used is within the above range, modified pulp having a carboxyl group content of cellulose within a predetermined range and excellent transparency is easily obtained.

[0031] Examples of the oxidizing agent include hypohalous acid, hypohalous acid salts, halous acid, halous acid salts, perhalogen acid, perhalogen acid salts, hydrogen peroxide, and perorganic acids. One type may be used alone, or two or more types may be used in combination. Among these, sodium hypochlorite (NaClO), sodium hypobromite, and the like are preferred because of their low cost. The amount of the oxidizing agent used may be appropriately selected within a range that allows the oxidation treatment to proceed.

[0032] Examples of the pro-oxidant (co-oxidant) include alkali metal bromides and alkali metal iodides, and one type may be used alone or two or more types may be used in combination. Among them, sodium bromide (NaBr) is preferred.

[0033] The amount of the pro-oxidant (co-oxidant) used is not particularly limited, but is preferably set to an amount such that the molar ratio R (amount of pro-oxidant (co-oxidant) used (mmol) / amount of catalyst used (mmol)) with respect to the amount of the catalyst used is R = 1 to 5, R = 1 to 2.5. When the molar ratio R is set within the above range, modified pulp having a carboxyl group content of cellulose within a predetermined range and excellent transparency is easily obtained.

[0034] The dispersion medium for the pulp in the reaction solution is not particularly limited and may be, for example, a protic polar dispersion medium such as water, ethanol, methanol, acetic acid, formic acid, 2-propanol, nitromethane, or aqueous ammonia; an aprotic polar dispersion medium such as acetone, ethyl acetate, tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), dimethyl sulfide (DMS), or dimethylacetamide (DMA); or a nonpolar dispersion medium such as diethyl ether, benzene, toluene, hexane, chloroform, or 1,4-dioxane. One type of dispersion medium may be used alone, or two or more types may be used in combination. Among these, water is preferred from the viewpoint of ease of handling.

[0035] In the oxidation treatment, the conditions such as the reaction temperature, the pH of the reaction solution, the reaction time, and the pressure are not particularly limited and may be selected appropriately. The oxidation treatment proceeds smoothly and efficiently even under mild conditions, so the reaction temperature may be about 15°C to 30°C. In addition, to prevent the oxidation treatment from being hindered by a decrease in the pH of the reaction solution due to the introduction of carboxyl groups into the pulp, an alkaline solution such as an aqueous sodium hydroxide solution may be added to maintain the pH of the reaction solution at about 9 to 12, or 10 to 11. It is desirable to carry out the oxidation treatment until the decrease in pH of the reaction solution is no longer noticeable, but from the viewpoints of preventing fiber shortening and production efficiency, the reaction time is preferably about 2 hours.

[0036] In this manner, the modified pulp can be produced. After the oxidation treatment, the catalyst and other components used may be removed by washing with water or the like.

[0037] The modified pulp can be widely used in various fields, for example, for producing transparent sheets and films. By using the modified pulp, it is possible to produce sheets and films that are excellent in transparency despite being made primarily of pulp. The transparent sheets and films can be widely used, for example, for labels on PET beverage bottles and transparent windows in windowed envelopes, which have previously been made of resin. [Example]

[0038] Example 1 5.0 g of never-dried bleached softwood kraft pulp (NBKP) (hereinafter simply referred to as "pulp") manufactured by Marusumi Paper Co., Ltd. was added to a reaction solution prepared by dissolving 1.0 mmol of TEMPO and 5.0 mmol of NaBr in 500 mL of purified water, and the mixture was stirred for 10 minutes. 34 mL of NaClO solution was then added to the reaction solution, and the pH was maintained at 10.5 by adding 1 M hydrochloric acid and 1 M aqueous sodium hydroxide. The mixture was stirred for 2 hours, and the NaClO solution was treated with ethanol, followed by washing with a large amount of water to obtain modified pulp. The TEMPO used was manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. and had a purity of 98% or more. The NaBr used was manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. and had a special grade model. The NaClO solution used was manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. and had an effective chlorine concentration of 5.0% or more. The 1 M hydrochloric acid and 1 M sodium hydroxide aqueous solutions used were manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. and were for volumetric analysis. The ethanol used was manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. and had a purity of 95.1 to 96.9 vol%.

[0039] (Examples 2 to 5 and Comparative Examples 1 to 4) The modified pulps of Examples 2 to 5 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the amount of TEMPO used was changed as shown in Table 1.

[0040] For the modified pulps of Examples 1 to 5 and Comparative Examples 1 to 4, the carboxyl group content, total light transmittance, haze value, average fiber length, average fiber width, kink and degree of polymerization were measured by the following methods.

[0041] (carboxyl group content) The modified pulp was dispersed in water to a solids concentration of 0.3% by mass, and the dispersion was processed for 1 minute on a strong setting in a household mixer (Panasonic Corporation, Model MX-X701, tumbler type). 70 g of the processed modified pulp was weighed out, 70 g of pure water was added, and the pH was adjusted to approximately 2.5 by adding hydrochloric acid. The mixture was then stirred for 1 hour to obtain a measurement sample. A 1.0 M aqueous solution of sodium hydroxide was added dropwise to the measurement sample, and electrical conductivity measurements were performed until the pH reached approximately 11. The carboxyl group content was calculated using the following formula from the volume (V) of the aqueous sodium hydroxide solution consumed during the neutralization stage of the weak acid, where the change in electrical conductivity was gradual. Carboxyl group content (mmol / g) = V (mL) × (concentration of sodium hydroxide solution (M) / dry mass of modified pulp in measurement sample (g))

[0042] (Total light transmittance) The total light transmittance was measured using a dispersion prepared by dispersing the modified pulp in water to a solids concentration of 1% by mass, and using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., model number: SH 7000) in accordance with JIS K 7361-1.

[0043] (Haze value) The haze value was measured using a dispersion prepared by dispersing the modified pulp in water to a solids concentration of 1% by mass, using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., model number: SH 7000) in accordance with JIS K 7105.

[0044] (Average fiber length, average fiber width and kink) The average fiber length, average fiber width, and kink were measured using a fiber length distribution measuring device (manufactured by Valmet Co., Ltd.) after dispersing the modified pulp in water to a solid content concentration of 0.03 mass% to prepare a dispersion.

[0045] (Degree of polymerization) The degree of polymerization was measured in accordance with JIS P 8215 after adding 20 mL of bis(ethylenediamine)copper(II) hydroxide solution to 0.125 g of modified pulp with pure water to make 20 g (solid content concentration 0.6 mass%), stirring for 1 hour, and then measuring the degree of polymerization according to JIS P 8215. The bis(ethylenediamine)copper(II) hydroxide solution used was a cellulose viscosity measurement solution manufactured by Merck.

[0046] Table 1 shows the amounts of TEMPO used, NaBr used, R (amount of NaBr used / amount of TEMPO used), the carboxyl group content of cellulose in the modified pulp, the total light transmittance, haze value, average fiber length, average fiber width, kink, and degree of polymerization of the modified pulp in Examples 1 to 5 and Comparative Examples 1 to 4 during production.

[0047] [Table 1]

[0048] As shown in Table 1, the modified pulps of Examples 1 to 5, in which the carboxyl group content of the cellulose was 1.5 mmol / g or more, had excellent transparency with a total light transmittance of 70% or more. In particular, the modified pulps of Examples 3 to 5, in which the carboxyl group content of the cellulose was 2.2 mmol / g or more, had even more excellent transparency with a total light transmittance of approximately 89% or more. On the other hand, the modified pulps of Comparative Examples 1 to 4, in which the carboxyl group content of the cellulose was less than 1.5 mmol / g, had poor transparency with a total light transmittance of less than 70%. Note that the degree of polymerization did not differ significantly depending on the carboxyl group content of the cellulose, but the average fiber length, average fiber width, and kink tended to decrease as the carboxyl group content of the cellulose increased.

[0049] Although the present invention has been described above with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Claims

[Claim 1] A modified pulp having a carboxyl group content of cellulose of 1.5 mmol / g or more, and a total light transmittance of a dispersion obtained by dispersing the cellulose in water to a solids concentration of 1% by mass of the cellulose of 1.5 mmol / g or more is 70% or more.

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