Pulping processing method of used paper

Abstract

To provide a pulping processing method of used paper capable of improving a removal ratio of silicon compounds included in the used paper.SOLUTION: A pulping processing method of used paper including the following steps 1 to 3 is provided. Step 1: a step of keeping a raw material slurry including water and used paper having layers containing base materials in at least a part of a substrate assembled under an alkaline condition of pH10 or over and a temperature of 50°C or over and 90°C or under for 30 min. or over and 12 hr. or under. Step 2: a step of kneading the raw material slurry treated in the step 1 under an alkaline condition of pH10 or over and a solid content concentration of 15 mass% or over and 45 mass% or under. Step 3: a step of performing flotation processing on the raw material slurry treated in the step 2.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for pulping waste paper and a method for manufacturing recycled paper from waste paper.

Background Art

[0002] Currently, recycled pulp made from waste paper is used as a raw material for papermaking. However, from the perspective of effective utilization of resources, there is an increasing demand to reuse more waste paper. Examples of waste paper that can be recycled into pulp include newspapers, cardboard, magazines, imitation paper, colored paper (including art paper), high-quality white paper, cards, extra-white paper, medium-white paper, white manila paper, tickets, heavily used waste paper, tea imitation paper (including foreign cardboard), and base paper. Release paper remaining after using labels and seals generally has a release agent such as a compound or a fluorine compound applied to the surface of the paper substrate. Silicone Since the paper substrate of the release paper and the release agent are firmly bonded, it is difficult to separate the pulp from the release agent. Therefore, release paper is often discarded as non-recyclable waste paper.

[0003] Patent Document 1 discloses a pulping method for obtaining recycled pulp from waste pressure-sensitive adhesive paper. In this method, the waste paper is disintegrated in water, and the suspension is treated with a screen having a slit width of 0.5 mm or less in a slit plate to remove substances other than pulp. A surfactant is added to the accept, and while introducing air, the substances other than pulp are separated by foam flotation by stirring. Further, the pulp suspension is mechanically stirred at a concentration of 15% or more. Patent Document 2 also discloses a pulping method for obtaining recycled pulp from waste pressure-sensitive adhesive paper. The method includes a kneading step of treating a raw material slurry having a pH of 6 or less at a solid content concentration of 15 to 30% by weight, a step of treating the pulp treated in this step with a screen having a slit width of 0.2 mm or less, a step of adding caustic soda and a surfactant to the pulp treated in this step, and kneading while applying a compressive force under heating at a solid content concentration of 30 to 40% by weight, and then a flotation step. Patent Document 3 discloses a pulping method for obtaining recycled pulp from pressure-sensitive adhesive waste paper, which is characterized by sequentially carrying out the following steps: a primary flotation process for the raw material slurry; a kneading process at a solids concentration of 20 to 40% by weight; a process for processing with a screen having a slit width of 0.05 to 0.20 mm; and a secondary flotation process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 3-199479 [Patent Document 2] Japanese Patent Application Publication No. 5-163689 [Patent Document 3] Japanese Patent Application Publication No. 5-209383 Summary of the Invention [Problem to be solved by the invention]

[0005] The methods described in Patent Documents 1 to 3 show that recycled paper with high whiteness can be obtained after treatment, but the release agent used Silicone Compounds or fluorine compounds are highly transparent substances, and the remaining amount of these compounds cannot be properly evaluated by whiteness. Furthermore, recycled pulp obtained from conventional release paper has problems such as a decrease in the strength of the recycled paper, a decrease in the uniformity of the coating when the release agent is re-coated on the recycled paper, and air bubbles easily forming when heated and dried after the release agent is coated. Silicone from waste paper containing pulp fibers having a layer containing a compound or a fluorine compound, Silicone It has been difficult to remove compounds or fluorine compounds. Silicone Compounds are mainly used, Silicone Removal of the compounds from the pulp fibers has been a major challenge. The present invention is based on the release agent contained in waste paper. SiliconeProvided are a method for pulping waste paper that improves the removal rate of compounds and a method for manufacturing recycled paper from waste paper.

Means for Solving the Problems

[0006] The present invention relates to a method for pulping waste paper, which comprises the following steps 1 to 3. Step 1: A raw material slurry containing waste paper having a layer containing a compound on at least a part of a base material and water is held at a temperature of 50°C or higher and 90°C or lower under alkaline conditions of pH 10 or higher for 30 minutes or longer and 12 hours or shorter. Silicone Step 2: The raw material slurry treated in Step 1 is kneaded under alkaline conditions of pH 10 or higher at a solid content concentration of 15% by mass or higher and 45% by mass or lower. Step 3: The raw material slurry treated in Step 2 is subjected to a flotation treatment.

[0007] Further, the present invention relates to a method for manufacturing recycled paper from waste paper, which comprises the above steps 1 to 3.

Effects of the Invention

[0008] According to the present invention, there are provided a method for pulping waste paper that improves the removal rate of compounds contained in waste paper and a method for manufacturing recycled paper from waste paper. Further, the present invention provides a method for pulping waste paper and a method for manufacturing recycled paper from waste paper, in which the yield of recycled pulp is good. Silicone

Embodiments for Carrying Out the Invention

[0009] The method for pulping waste paper and the method for manufacturing recycled paper from waste paper of the present invention maintain the yield of recycled pulp while Silicone The mechanism for improving the removal rate of compounds is not clear, but is presumed as follows. In the aging step of Step 1, a sufficient amount of an alkaline agent is permeated into the layer containing a compound such as a release agent layer to Silicone Silicone promote the separation of the compound and pulp fibers and the decomposition of the release agent. In the kneading step of Step 2, SiliconeIt is presumed to promote the detachment of the compound from the pulp fibers and fibrillation. Furthermore, by performing a flotation step (step 3) after step 2, it is presumed that the refined release agent or the like adheres to the bubbles and is discharged and removed out of the system together with the froth. Note that the method for pulping waste paper and the method for manufacturing recycled paper according to the present invention are not limited to the above-described mechanism of action at all.

[0010] <Method for Pulping Waste Paper> The method for pulping waste paper according to the present invention includes the following steps 1 to 3. Step 1: A raw material slurry containing waste paper having a layer containing a compound on at least a part of a base material and water is held at a temperature of 50°C or higher and 90°C or lower under an alkaline condition of pH 10 or higher for 30 minutes or longer and 12 hours or shorter. Silicone Step 2: A step of kneading the raw material slurry treated in step 1 under an alkaline condition of pH 10 or higher at a solid content concentration of 15% by mass or higher and 45% by mass or lower. Step 3: A step of subjecting the raw material slurry treated in step 2 to flotation treatment.

[0011] In the method of the present invention, the waste paper used as a raw material includes waste paper having a layer containing a compound on at least a part of a base material. More specifically, examples include waste paper containing pulp fibers coated with a compound on at least a part of the base material of the waste paper. In the method of the present invention, the base material may be a paper base material, and more preferably a base material containing pulp fibers. Examples of the waste paper used as a raw material include release paper. Note that the waste paper used as a raw material may include waste paper that does not correspond to waste paper having a layer containing a compound on at least a part of a base material. Silicone Silicone Silicone The Silicone compound used in the present invention is Silicone a compound cured on a base material. After this Silicone compound is applied on a paper base material, it is cured by heating or ultraviolet irradiation, and Silicone a resin layer is formed. These Silicone compounds are​​​​Silicone It contains a main agent and a crosslinking agent, and is cured by a catalyst, a photoinitiator, etc. Silicone As the main agent, from the viewpoint of peelability, those containing linear dimethylpolysiloxane in the molecule are Silicone compounds. More specifically, polydimethylsiloxane containing a silanol group at the terminal is Silicone used as the main agent, polymethylhydrogensiloxane is blended as the crosslinking agent, and a thermosetting type that undergoes a condensation reaction by heating in the presence of an organotin catalyst Silicone compound, polydimethylsiloxane containing a vinyl group is Silicone used as the main agent, polymethylhydrogensiloxane is blended as the crosslinking agent, and a thermosetting type that reacts and cures in the presence of a platinum catalyst Silicone compound, Silicone A UV-curing type in which a photoinitiator (photo cationic catalyst) having a maximum absorption in the UV region is blended with a modified silicone in which an alicyclic epoxy group is introduced into the main agent, and cations are generated by UV irradiation to cause reaction and curing Silicone compounds. The waste paper used as the raw material of the present invention may be provided with a blocking layer between the waste paper base material and Silicone the layer containing the compound, and further between the waste paper base material and Silicone the layer formed by curing the compound. Examples of the blocking layer include a blocking layer containing polyvinyl alcohol, polyethylene, or clay. The method for pulping waste paper of the present invention may be a method for pulping waste paper including release paper, and further a method for pulping waste paper including pulp fibers coated with Silicone the compound on at least a part of the base material.

[0012] <Step 1: Aging step> Step 1 is a step of holding a raw material slurry containing waste paper having a layer containing Silicone the compound on at least a part of the base material and water under alkaline conditions of pH 10 or more at a temperature of 50°C or more and 90°C or less for 30 minutes or more and 12 hours or less. Step 1 is a step of having a layer containing SiliconeA step may be included of holding a raw material slurry containing waste paper containing pulp fibers coated with a compound and water at a temperature of 50°C or higher and 90°C or lower under alkaline conditions with a pH of 10 or higher for 30 minutes or longer and 12 hours or shorter. In Step 1, one or more alkaline agents selected from sodium hydroxide, potassium hydroxide, and lithium hydroxide may be mixed into the raw material slurry to bring the raw material slurry to predetermined alkaline conditions.

[0013] The pH of the raw material slurry in Step 1 is 10 or higher, preferably 10.5 or higher, more preferably 11 or higher, from the viewpoints of pulp fiber swelling and chemical agent permeability, and preferably 13.5 or lower, more preferably 13 or lower, still more preferably 12.5 or lower, from the viewpoint of economy. The pH of the raw material slurry is the pH at the temperature during the treatment in Step 1. If the pH of the raw material slurry at 60°C is within the above range, it can be determined that the pH of the raw material slurry during the treatment satisfies the above range. Hereinafter, the same applies to the pH of the raw material slurry in other steps. The pH of the raw material slurry is measured by the following pH measurement method. Hereinafter, the pH of the raw material slurry in other steps is also measured by the same method as the following pH measurement method.

[0014] <pH Measurement Method> Connect a combined pH electrode (glass folding sleeve type manufactured by HORIBA) for pH measurement to a pH meter (pH / Ion Meter F-23 manufactured by HORIBA) and turn on the power. As the internal solution of the pH electrode, a saturated potassium chloride aqueous solution (3.33 mol / L) is used. Next, fill 100 mL beakers with a pH 6.86 standard solution (neutral phosphate standard solution), a pH 9.18 standard solution (borate standard solution), and a pH 12.0 standard solution (saturated calcium hydroxide standard solution), respectively, and immerse them in a thermostatic bath adjusted to the temperature during the treatment for 30 minutes. Immerse the pH measurement electrode in the thermostatically adjusted standard solution for 3 minutes, and perform a calibration operation in the order of pH 6.86 → pH 9.18 → pH 12.0. Adjust the sample (raw material slurry) to be measured to the temperature during the treatment, immerse the electrode of the above pH meter in the sample, and measure the pH after 1 minute.

[0015] From the viewpoints of swelling of pulp fibers and penetrability of chemicals, the treatment temperature of the raw material slurry in Step 1 is 50°C or higher, preferably 55°C or higher, more preferably 60°C or higher, and from the viewpoint of economy, it is 90°C or lower, preferably 80°C or lower, more preferably 70°C or lower.

[0016] In Step 1, the time for holding the raw material slurry at a predetermined temperature is 30 minutes or longer, preferably 60 minutes or longer, more preferably 2 hours or longer, from the viewpoints of swelling of pulp fibers and penetrability of chemicals, and from the viewpoint of economy, it is 12 hours or shorter, preferably 9 hours or shorter, more preferably 6 hours or shorter.

[0017] In the aging step of Step 1, the solid content concentration of the raw material slurry to be subjected to the treatment of Step 1 is preferably 15% by mass or higher, more preferably 20% by mass or higher, still more preferably 25% by mass or higher, from the viewpoint of penetrability of chemicals, and from the viewpoint of economy during dehydration, it is preferably 45% by mass or lower, more preferably 40% by mass or lower, still more preferably 35% by mass or lower. The solid content concentration of the raw material slurry is calculated by the following formula (1) by charging a predetermined amount of the raw material slurry into an empty aluminum cup whose dry mass has been measured, drying it at 105°C for 2 hours or longer with a dryer, measuring the mass of the aluminum cup after moisture removal. Solid content concentration (% by mass) = [((mass of the aluminum cup after drying) - (mass of the empty aluminum cup)) / (mass of the charged raw material slurry)] × 100 (1)

[0018] The aging step of Step 1 can be carried out, for example, by holding the raw material slurry in a tower maintained at a predetermined temperature and keeping the raw material slurry warm. In the aging step of Step 1, the raw material slurry may or may not be heated as long as the raw material slurry can be held at a predetermined temperature. From the viewpoint of holding the raw material slurry at a predetermined temperature, it is preferable to heat the raw material slurry in Step 1. Also, in the aging step of Step 1, the raw material slurry may be stirred.

[0019] In the raw material slurry of Process 1, one or more selected from a bleaching agent, a deinking agent, a scale inhibitor, a pitch control agent, an antifoaming agent, a foaming agent, and a slime control agent may be arbitrarily mixed.

[0020] Examples of the bleaching agent include one or more selected from hydrogen peroxide, hypochlorite, and hyposulfite. Examples of the hypochlorite and hyposulfite include alkali metal salts, and sodium salts are preferred. When using a bleaching agent in Process 1, from the viewpoint of bleaching, the addition amount of the bleaching agent is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, based on the waste paper contained in the raw material slurry, and from the viewpoint of economy, preferably 5% by mass or less, more preferably 4% by mass or less, still more preferably 3% by mass or less. The bleaching agent is added to the raw material slurry accordingly.

[0021] Examples of the deinking agent include one or more selected from alkylene oxide adducts of fats / oils and glycerin, higher fatty acids, alkylene oxide adducts of higher fatty acids, and alkylene oxide adducts of higher alcohols, and are not particularly limited. For example, DI-7020, DI-7250, DI-7300, DI-7460, DI-767 manufactured by Kao Corporation, DIA-Z-100, DIA-Z-5000 manufactured by Nisshin Chemical Research Institute Co., Ltd., Neo Score FW-780, Neo Score FW-790, Neo Score FW-795, FT-467, FT-470, FT-487, FT-511, FT-513, FT-514, FT-515 manufactured by Toho Chemical Co., Ltd., Daihope 940, Daihope 960 manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Lipolite DP-810 manufactured by Nichika Co., Ltd., etc.

[0022] When using a deinking agent in Step 1, from the perspective of the peeling agent, the addition amount of the deinking agent is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, still more preferably 0.05% by mass or more, based on the waste paper contained in the raw material slurry. And from the perspective of operability, the deinking agent is preferably added to the raw material slurry so that it is 0.5% by mass or less, more preferably 0.4% by mass or less, still more preferably 0.3% by mass or less.

[0023] <Step 2: Kneading Step> Step 2 is a step of kneading the raw material slurry treated in Step 1 under alkaline conditions with a pH of 10 or more and a solid content concentration of 15% by mass or more and 45% by mass or less. In Step 2, the kneading treatment is carried out under alkaline conditions with a pH of 10 or more. Since the raw material slurry after being treated in Step 1 is alkaline with a pH of 10 or more, the raw material slurry after being treated in Step 1 may be directly fed to Step 2.

[0024] In the kneading treatment of Step 2, the solid content concentration of the raw material slurry to be subjected to the treatment of Step 2 is Silicone From the perspective of separation and refinement of the compound, it is 15% by mass or more, preferably 20% by mass or more, more preferably 25% by mass or more, and from the perspective of operability, it is 45% by mass or less, preferably 40% by mass or less, more preferably 35% by mass or less. The solid content concentration of the raw material slurry to be subjected to the treatment of Step 2 is calculated by the above formula (1) by the same method as the method for measuring the solid content concentration of the raw material slurry in Step 1.

[0025] The pH of the raw material slurry in Step 2 is Silicone From the perspective of separation and refinement of the compound, it is 10 or more, preferably 10.5 or more, more preferably 11 or more, and from the perspective of operability, it is preferably 13.5 or less, more preferably 13 or less, still more preferably 12.5 or less.

[0026] The treatment temperature of the raw material slurry in Step 2 is SiliconeFrom the viewpoints of separation and refinement of the compound, it is preferably 20 °C or higher, more preferably 25 °C or higher, still more preferably 30 °C or higher, and from the viewpoint of operability, it is preferably 80 °C or lower, more preferably 75 °C or lower, still more preferably 70 °C or lower.

[0027] The kneading step of Step 2 can be carried out using a known kneading device, for example, a kneader, a disperser, or the like. The kneading treatment can be carried out, for example, in a laboratory pulper (PFI mill, manufactured by Kumagai Riki Kogyo Co., Ltd.) that simulates the kneading treatment, with a clearance between the inner wall of the kettle and the gear of 0.1 mm, 10 rotations of the gear counted as 1 count, and under the conditions of 50 counts or more and 500 counts or less. In the kneading step of Step 2, the raw material slurry may or may not be heated as long as the raw material slurry can be maintained at a predetermined temperature.

[0028] One or more selected from a bleaching agent, a deinking agent, a scale inhibitor, a pitch control agent, an antifoaming agent, a foaming agent, and a slime control agent may be optionally mixed into the raw material slurry of Step 2. Preferred embodiments of the bleaching agent and the deinking agent are the same as the preferred embodiments of the bleaching agent and the deinking agent described in Step 1. Also, in Step 2, the preferred addition amounts of the bleaching agent and the deinking agent are the same as the preferred addition amounts of the bleaching agent and the deinking agent described in Step 1.

[0029] <Step 3: Flotation Step> Step 3 is a step of subjecting the raw material slurry treated in Step 2 to a flotation treatment. There is no limitation on the type of flotator in the flotation step of Step 3. Examples include a box-type flotator, an eco-cell flotator, an MT flotator, and the like.

[0030] In the flotation step of Step 3, the solid content concentration of the raw material slurry subjected to the treatment of Step 3 is SiliconeFrom the viewpoint of the removal efficiency of the compound, it is preferably 0.6% by mass or more, more preferably 0.7% by mass or more, still more preferably 0.8% by mass or more, and from the viewpoint of operability, it is preferably 1.5% by mass or less, more preferably 1.4% by mass or less, still more preferably 1.3% by mass or less. The solid content concentration of the raw material slurry to be subjected to the treatment in Step 3 is calculated by the above formula (1) by the same method as the method for measuring the solid content concentration of the raw material slurry in Step 1 above.

[0031] The pH of the raw material slurry in Step 3 is Silicone From the viewpoint of the removal efficiency of the compound, it is preferably 7.5 or more, more preferably 8 or more, still more preferably 8.5 or more, and from the viewpoint of economy, it is preferably 11 or less, more preferably 10.5 or less, still more preferably 10 or less.

[0032] The treatment temperature of the raw material slurry in Step 3 is Silicone From the viewpoint of the removal efficiency of the compound, it is preferably 30°C or more, more preferably 35°C or more, still more preferably 40°C or more, and from the viewpoint of operability, it is preferably 60°C or less, more preferably 55°C or less, still more preferably 50°C or less.

[0033] In Step 3, the treatment time of the raw material slurry is appropriately adjusted according to the number of floaters and the amount of foam, and is not particularly limited. However, Silicone From the viewpoint of the removal efficiency of the compound, it is preferably 3 minutes or more, more preferably 4 minutes or more, still more preferably 5 minutes or more, and from the viewpoint of yield, it is preferably 20 minutes or less, more preferably 15 minutes or less, still more preferably 10 minutes or less.

[0034] <Pretreatment Step> In the method of the present invention, before step 1, one or more steps selected from a disintegration step, a chemical solution addition step, a rough washing step of performing rough washing of the disintegrated waste paper, a dust removal step, a dehydration step (concentration step), and a kneading step can be arbitrarily performed. The kneading step of the pretreatment step may be a kneading step performed under the same conditions as in step 2. In each step, as the alkali agent, deinking agent, and bleaching agent, the alkali agent, deinking agent, and bleaching agent described in step 1 can preferably be used.

[0035] The disintegration step is a step of mixing waste paper and water, and further mixing an alkali chemical or a deinking agent as necessary to obtain a raw material slurry. The chemical solution addition step is a step of adding an alkali chemical, a deinking agent, a bleaching agent, etc. The chemical solution addition step is preferably performed after the dehydration step.

[0036] In the method of the present invention, Silicone From the viewpoint of the removal efficiency of the compound, it is preferable to perform a kneading treatment as a pretreatment step and supply the raw material slurry kneaded in the pretreatment step to step 1. The kneading treatment in the pretreatment step may be a step of kneading the raw material slurry obtained in the disintegration step under alkaline conditions at a solid content concentration of 15% by mass or more and 45% by mass or less.

[0037] In the kneading treatment of the pretreatment step, the solid content concentration of the raw material slurry to be subjected to the treatment is Silicone From the viewpoints of separation and refinement of the compound, it is preferably 15% by mass or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, and from the viewpoint of operability, it is preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less. The solid content concentration of the raw material slurry to be subjected to the kneading treatment in the pretreatment step is calculated by the above formula (1) by the same method as the method for measuring the solid content concentration of the raw material slurry in step 1.

[0038] The pH of the raw material slurry in the kneading treatment of the pretreatment step is SiliconeFrom the viewpoint of the removal efficiency of the compound, it is preferably 10 or more, more preferably 10.5 or more, still more preferably 11 or more, and from the viewpoint of operability, it is preferably 13.5 or less, more preferably 13 or less, still more preferably 12.5 or less.

[0039] In the kneading treatment of the pretreatment step, the treatment temperature of the raw material slurry is Silicone From the viewpoint of the removal efficiency of the compound, it is preferably 20°C or higher, more preferably 25°C or higher, still more preferably 30°C or higher, and from the viewpoint of operability, it is preferably 80°C or lower, more preferably 75°C or lower, still more preferably 70°C or lower.

[0040] <Other steps> Further, in the method of the present invention, between step 2 and step 3, one or more steps selected from a dilution step of mixing the raw material slurry and water to dilute the raw material slurry and a foaming agent addition step of adding a foaming agent to the raw material slurry can be arbitrarily performed.

[0041] <Post-treatment step> Further, in the method of the present invention, after step 3, one or more steps selected from a washing step and a dust removal step can be arbitrarily performed.

[0042] The washing step is, for example, a step of dehydrating and washing fine ink that could not be removed by a flotator, and it is preferably performed after the flotation step. In the washing step, it is preferable to dilute the raw material slurry with a solid content concentration of 0.6 to 1.5% by mass after the flotation with water and then dehydrate and wash the raw material slurry until the solid content concentration is about 10% by mass. As the water for diluting the raw material slurry, clear water, clear white water of a paper machine, etc. can be used.

[0043] In the method of the present invention, each step may be performed a plurality of times as necessary. Also, a step combining a plurality of steps may be repeated.

[0044] <Method for manufacturing recycled paper from waste paper> The present invention provides a method for manufacturing recycled paper from waste paper, which comprises the above-mentioned steps 1 to 3 [hereinafter referred to as the manufacturing method of the present invention]. In the manufacturing method of the present invention, at least a part of the base material Silicone a waste paper having a layer containing a compound, more specifically, a waste paper containing pulp fibers coated with a compound on at least a part of the base material of the waste paper Silicone It may be a method for manufacturing recycled paper from waste paper that manufactures recycled paper from waste paper containing a release paper. In the manufacturing method of the present invention, the preferred embodiments of steps 1, 2, and 3 are the same as the preferred embodiments of steps 1, 2, and 3 described in the method for pulping waste paper of the present invention. In the manufacturing method of the present invention, one or more steps selected from the <pretreatment step>, <other steps>, and <post-treatment step> described in the method for pulping waste paper of the present invention can be arbitrarily performed. The manufacturing method of the present invention may be a method for manufacturing recycled paper by discharging the recycled pulp pulped by performing steps 1 to 3, that is, the recycled pulp pulped by the method for pulping waste paper of the present invention, into a paper machine. An existing paper machine can be used as the paper machine.

Example

[0045] (1) Example 1-1 <Pulping step> In the pulping step, as a release agent on one side of the glassine paper SiliconeUsing the direct-type release paper coated with the compound as a waste paper raw material, a sample was taken so that the absolutely dry solid content was 100 g and charged into a pulper. Water was added to make the total mass 2,000 g, with a solid content concentration of 5% by mass, sodium hydroxide 0.4% by mass (relative to the pulp concentration), a higher alcohol-based deinking agent (manufactured by Kao Corporation, DI-7250) 0.2% by mass (relative to the pulp concentration), and the pulper treatment was carried out at 40 °C for 10 minutes to obtain a raw material slurry containing direct-type release paper and water. The concentrations of sodium hydroxide and the deinking agent are the concentrations relative to the absolutely dry solid content of the direct-type release paper. Also, in the raw material slurry, the charged solid content concentration can be regarded as the solid content concentration calculated in (1) above.

[0046] <Concentration process> In the concentration process, 2,000 g of the raw material slurry was transferred to a centrifuge, and dehydration was carried out using an 80-mesh cloth under the condition of 2,000 rpm until the total mass became 333 g. By the concentration process, the solid content concentration of the raw material slurry was concentrated from 5% by mass to 30% by mass.

[0047] <Chemical solution addition process> In the chemical solution addition process, the following chemicals were added so that the concentration in the raw material slurry became the concentration in Table 1 (% by mass relative to the pulp concentration). The concentration of each chemical in Table 1 is the active ingredient concentration. The raw material slurry obtained by adding the chemicals was subjected to the following Step 1. The concentration of the chemical is the concentration relative to the absolutely dry solid content of the direct-type release paper. (Chemical) · Alkali agent: Aqueous sodium hydroxide solution, concentration 4 mol / L, manufactured by Fujifilm Wako Pure Chemical Corporation · Bleaching agent: Hydrogen peroxide solution, H2O2 concentration 30% by mass, manufactured by Fujifilm Wako Pure Chemical Corporation · Deinking agent: Higher alcohol-based deinking agent (DI-7250, manufactured by Kao Corporation)

[0048] <Step 1: Aging process> Next, 333 g of the slurry with a solid content concentration of 30% was put into a vinyl chloride resin bag so as to keep it at 60 °C, and immersed in a constant temperature bath filled with warm water at 60 °C for 180 minutes to carry out the aging process of the raw material slurry. When the pH of the raw material slurry was measured by the same measurement method as the <pH measurement method>, the pH of the raw material slurry at 60 °C was 12.

[0049] <Step 2: Kneading Step> Next, using a beating machine (PFI mill: manufactured by Kumagai Riki Kogyo Co., Ltd.), the raw material slurry was kneaded under the conditions of 40 °C and 100 counts. The clearance of the beating machine was 0.1 mm. Two counts on the counter attached to the beating machine were approximately 1 second. When the pH of the raw material slurry was measured by the same measurement method as the <pH measurement method>, the pH of the raw material slurry at 60 °C was 12.

[0050] <Dilution Step> A dilution step of diluting the raw material slurry after the kneading step with water was performed. In this dilution step, the solid content concentration of the raw material slurry was changed from 30% by mass to 1% by mass, and the diluted raw material slurry was subjected to the flotation treatment in Step 3.

[0051] <Step 3: Flotation Step> The raw material slurry (4,300 g of pulp slurry with a solid content of 43 g, solid content concentration 1% by mass) was transferred to a flotation machine (manufactured by Kyokuto Shinko Co., Ltd.), and the flotation treatment was performed at 40 °C for 5 minutes. <Washing Step> After the flotation treatment, 300 g of the raw material slurry was sampled, passed through an 80-mesh wire sieve, and the fine particles were dehydrated and filtered to concentrate and wash to 30 g (washing step).

[0052] (2) Example 1-2 Example 1-2 is a method for pulping waste paper in Example 1-1, in which, as a pretreatment step, a kneading step was further performed after the chemical liquid addition step and before Step 1. The additional kneading step was performed under the same conditions as the kneading step (Step 2) in Example 1-1.

[0053] (3) Comparative Example 1-1 Comparative Example 1-1 was subjected to the same treatment as Example 1-1, except that only the deinking agent was added in the chemical liquid addition step. In the aging step of Comparative Example 1-1, the pH of the raw material slurry at 60 °C was 9.4.

[0054] (4) Comparative Example 1-2 Comparative Example 1-2 was subjected to the same treatment as Example 1-2, except that the kneading step in Step 2 was not performed.

[0055] (5) Comparative Examples 1-3, 1-4 Comparative Examples 1-3 and 1-4 were subjected to the same treatment as Example 1-1, except that the aging step in Step 1 was not performed. Note that in Comparative Example 1-3, the kneading step in Step 2 was performed under the condition of 100 counts, and in Comparative Example 1-4, the kneading step in Step 2 was performed under the condition of 200 counts.

[0056] (Measurement method of froth mass) The effluent (froth) in the flotation was collected, and the mass of the collected effluent was measured. The results are shown in Table 1.

[0057] (Measurement method of Si) The content of Si contained in the recycled pulp obtained after the washing step was measured by high-frequency inductively coupled plasma (ICP) optical emission spectrometry (ICP-AES). Specifically, the recycled pulp after the washing step was dried in an electric dryer at 105 °C for 12 hours. 0.1 g of the dry solid of this recycled pulp was weighed into a platinum crucible, a few drops of sulfuric acid were added and allowed to penetrate, and then it was dried to dryness with a heater and then sufficiently ashed in an electric furnace at 550 °C. Then, 1 g of an alkali flux (sodium carbonate: boric acid = 1:0.4 (mass ratio)) was added and melted in an electric furnace at 950 °C. A watch glass was covered, 5 mL of ultrapure water and hydrochloric acid (6N) were added, and it was heated and dissolved on a hot plate at 70 to 80 °C. After cooling, it was made up to 50 mL with ultrapure water to obtain a sample measurement solution. Using a standard solution for atomic absorption analysis (Si: 1,000 mg / L), a solution for calibration curve preparation in the range of 0.2 to 20 mg / L was prepared. An alkali flux and hydrochloric acid were added to each solution to the same extent as in the sample measurement solution. The prepared sample measurement solution was subjected to Si measurement using an ICP emission spectroscopic analyzer under the following conditions. Based on the Si measurement results, the concentration (ppm) of Si in the dry solids of the recycled pulp obtained after the washing process was calculated, and the results are shown in Table 1. The lower the Si content in the dry solids of the recycled pulp, the more Silicone It is a method for pulping waste paper with improved removal rate of compounds from waste paper. Also, when the Si content in the dry solids of the direct release paper (untreated direct release paper) before the treatments of each example and comparative example was measured by the same measurement method, the Si content in the direct release paper was 4,500 ppm.

[0058] (Measurement conditions of ICP emission spectroscopic analyzer) Analyzer: iCAP6500 Duo manufactured by Thermo Fisher Scientific Wavelength: Si 251.611 nm RF power: 1150 W Coolant gas flow rate: 12 L / min Nebulizer flow rate: 0.70 L / min Auxiliary gas: 0.5 L / min Pump flow rate: 50 rpm

[0059] <Measurement method of yield> The total effluent (froth) discharged in the flotation process (Process 3) was poured into an empty aluminum cup whose dry mass had been measured, and dried in a dryer at 105°C until all the water was removed. Next, the mass of the aluminum cup after water removal was measured, and the solid content discharge amount was calculated by the following formula (2). The yield was calculated from the calculated solid content discharge amount by the following formula (3). The results are shown in Table 1. Note that "43" in formula (3) is the solid content mass at the start of flotation (a value calculated from the total slurry amount of 4,300 g and a solid content concentration of 1 mass%). Solid content discharge amount (g) = {(mass of aluminum cup after drying) - (mass of empty aluminum cup)} (2) Yield (%) = {(43 - solid content discharge amount) / 43} × 100 (3)

[0060] As shown in the results of Table 1, from the comparison between Examples 1-1 and 1-2 and Comparative Examples 1-1 to 1-4, the method for pulping waste paper according to the examples (the method for manufacturing recycled paper from waste paper) maintains the yield of recycled pulp while Silicone the removal rate of the compound is improved.

[0061]

Table 1

Claims

1. A method for pulping waste paper, comprising the following steps 1 to 3. Step 1: A raw material slurry containing waste paper having a layer containing a silicon compound on at least a part of a base material and water is held at a temperature of 50°C or higher and 90°C or lower under an alkaline condition of pH 10 or higher for 30 minutes or longer and 12 hours or shorter. Step 2: The raw material slurry treated in Step 1 is kneaded under an alkaline condition of pH 10 or higher at a solid content concentration of 15% by mass or higher and 45% by mass or lower. Step 3: The raw material slurry treated in Step 2 is subjected to a flotation treatment.

2. As a pretreatment step, kneading is performed under the alkaline condition at a solid content concentration of 15% by mass or higher and 45% by mass or lower, and the raw material slurry kneaded in this pretreatment step is supplied to Step 1. The method for pulping waste paper according to Claim 1.

3. In Step 1, the raw material slurry is held at a temperature of 55°C or higher and 70°C or lower for 2 hours or longer and 6 hours or shorter under an alkaline condition of pH 10 or higher. The method for pulping waste paper according to Claim 1 or 2.

4. A method for manufacturing recycled paper from waste paper, comprising the following steps 1 to 3. Step 1: A raw material slurry containing waste paper having a layer containing a silicon compound on at least a part of a base material and water is held at a temperature of 50°C or higher and 90°C or lower under an alkaline condition of pH 10 or higher for 30 minutes or longer and 12 hours or shorter. Step 2: The raw material slurry treated in Step 1 is kneaded under an alkaline condition of pH 10 or higher at a solid content concentration of 15% by mass or higher and 45% by mass or lower. Step 3: The raw material slurry treated in Step 2 is subjected to a flotation treatment.

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