Method for manufacturing recycled pulp from used sanitary products

Abstract

A recycled pulp that is reusable sanitary products is efficiently manufactured by recovering pulp fiber from used sanitary products containing the pulp fiber and a polymer absorbent. The method of the present invention comprises: a step applying a mechanical force to the used sanitary products in an aqueous solution containing a polyvalent metal ion or an acidic aqueous solution with a pH of 2.5 or lower and thus degrading the used sanitary products into the pulp fiber and other materials; a step separating the pulp fiber from the mixture of the pulp fiber and other materials that has been formed in the degradation step; and a step treating the pulp fiber thus separated with an ozone-containing aqueous solution with a pH of 2.5 or lower.

Claims

1. A recycled pulp having an ash content of 0.11% by weight or less, wherein the recycled pulp is recovered from a used sanitary product comprising pulp fibers containing organic waste and superabsorbent polymer, wherein the recycled pulp has a water absorption performance ranging from 17.2 g/g to 18.1 g/g.

2. The recycled pulp of claim 1, wherein the ash content ranges from 0.05% by weight to 0.11% by weight.

3. The recycled pulp of claim 1, wherein the recycled pulp includes fluff pulp fibers.

4. The recycled pulp of claim 1, wherein the recycled pulp includes chemical pulp fibers.

5. The recycled pulp of claim 1, wherein the recycled pulp has a water retention performance of 7.92 g/g to 8.3 g/g.

6. The recycled pulp of claim 1, wherein the ash content is 0.06% by weight or less.

7. A sanitary product comprising: recycled pulp fibers having an ash content of about 0.11% by weight or less, wherein the recycled pulp is recovered from a used sanitary product comprising pulp fibers containing organic waste and superabsorbent polymer, wherein the recycled pulp has a water absorption performance ranging from 17.2 g/g to 18.1 g/g; and a superabsorbent polymer (SAP).

8. The sanitary product of claim 7, wherein the ash content ranges from about 0.05% by weight to about 0.11% by weight.

9. The sanitary product of claim 7, wherein the sanitary product is selected from the group consisting of a disposable diaper, an incontinence pad, a urine collection pad, a sanitary napkin and a panty liner.

10. The sanitary product of claim 7, wherein the recycled pulp fibers include fluff pulp fibers.

11. The sanitary product of claim 7, wherein the recycled pulp fibers include chemical pulp fibers.

12. The sanitary product of claim 7, wherein the SAP comprises a starch-based particulate, an acrylic acid-based particulate or an amino acid-based particulate.

13. The sanitary product of claim 7, wherein the SAP comprises a starch-based fibrous polymer, an acrylic acid-based fibrous polymer or an amino acid-based fibrous polymer.

14. A disposable diaper comprising: recycled pulp fibers having an ash content of about 0.11% by weight or less, wherein the recycled pulp is recovered from a used sanitary product comprising pulp fibers containing organic waste and superabsorbent polymer, wherein the recycled pulp has a water absorption performance ranging from 17.2 g/g to 18.1 g/g; and a superabsorbent polymer (SAP).

15. The disposable diaper of claim 14, wherein the ash content ranges from about 0.05% by weight to about 0.11% by weight.

16. The disposable diaper of claim 14, wherein the recycled pulp fibers include fluff pulp fibers.

17. The disposable diaper of claim 14, wherein the recycled pulp fibers include chemical pulp fibers.

18. The disposable diaper of claim 14, wherein the SAP comprises a starch-based particulate, an acrylic acid-based particulate or an amino acid-based particulate.

19. The disposable diaper of claim 14, wherein the SAP comprises a starch-based fibrous polymer, an acrylic acid-based fibrous polymer or an amino acid-based fibrous polymer.

Description

EXAMPLES

(1) The ozone water generator, artificial organic waste and physiological saline indicated below were used in the following examples and comparative examples.

(2) [Ozone Water Generator]

(3) Manufacturer: Mitsubishi Electric Corp.

(4) Name: Ozone generator

(5) Model: OS-25V

(6) Ozone water variable concentration range: 1 mg/m.sup.3 to 80 mg/m.sup.3

(7) Ozone water exposure tank volume: 30 L

(8) [Artificial Organic Waste]

(9) 1:1:1 (weight ratio) mixture of equine serum, bovine intestinal mucin and glycerin

(10) [Physiological Saline]

(11) Saline having concentration of 0.9%

Example 1

(12) After immersing a commercially available disposable diaper (Moony Size M, Unicharm Corp.) in 3 L of physiological saline containing 1% artificial organic waste for 10 minutes to adsorb the artificial organic waste thereto, the diaper was immersed for 3 minutes in aqueous calcium chloride solution (pH 10.5) having a concentration of 5% to allow SAP in the diaper to be dehydrated by the crosslinking action of Ca. The diaper was then removed from the aqueous calcium chloride solution, placed in a mesh pouch (measuring 30 cm on all sides, N-No. 250HD manufactured by NBC Meshtec Inc.) and dehydrated for 5 minutes in a dehydration tank to remove excess moisture retained by the pulp, followed by placing in 10 L of an aqueous citric acid solution (pH 2.2) having a concentration of 1% and subjecting to ozone treatment by blowing in ozone gas at 80 mg/m.sup.3 (containing 80 mg of ozone in 1 m.sup.3, with the remainder consisting of oxygen) for 30 minutes. The amount of dissolved ozone in the treatment water 30 minutes later was 30 ppm and the pH was 2.4. As a result of straining the treated water through a mesh filter having an opening size of 2 mm×2 mm, only pulp was able to be recovered without any SAP present.

(13) When the ash content of the recovered pulp was analyzed according to “5. Ash Content Testing Method” of “2. General Testing Methods” of the Japanese Specifications of Sanitary Napkin Materials, it was determined to have decreased to 0.10% by weight. Furthermore, the ash content of the pulp initially contained in the commercially available disposable diapers used in the examples and comparative examples (to also be referred to as “unused pulp”) was 0.18% by weight. As a result of this treatment, it was possible to remove fine residual contaminants inherently contained in the unused pulp and obtain recycled pulp having an ash content lower than that of unused pulp.

Example 2

(14) After immersing a commercially available disposable diaper (Moony Size M, Unicharm Corp.) in 3 L of physiological saline containing 1% artificial organic waste for 10 minutes to adsorb the artificial organic waste thereto, the diaper was immersed for 3 minutes in aqueous citric acid solution (pH 1.6) having a concentration of 10% to allow SAP in the diaper to be dehydrated by the action of the acid. The diaper was then removed from the aqueous citric acid solution, placed in a mesh pouch (measuring 30 cm on all sides, N-No. 250HD manufactured by NBC Meshtec Inc.), and dehydrated for 5 minutes in a dehydration tank to remove excess moisture retained by the pulp, followed by placing in 10 L of an aqueous citric acid solution (pH 2.2) having a concentration of 1% and subjecting to ozone treatment by blowing in ozone gas at 80 mg/m.sup.3 for 30 minutes. The amount of dissolved ozone in the treatment water 30 minutes later was 32 ppm and the pH was 2.0. As a result of straining the treated water through a mesh filter having an opening size of 2 mm×2 mm, only pulp was able to be recovered without any SAP present.

(15) When the ash content of the recovered pulp was analyzed in the same manner as Example 1, it was determined to have decreased to 0.06% by weight. As a result of this treatment, it was possible to obtain recycled pulp having an ash content lower than that of unused pulp.

Comparative Example 1

(16) After allowing commercially available disposable diapers (Moony Size M, Unicharm Corp.) to absorb 200 mL of physiological saline, 8 diapers were placed in the washing tub of a twin tub compact washing machine (Seisei AST-01 manufactured by Alumis Co., Ltd.) followed by adding 80 g of calcium oxide (CaO, Wako Pure Chemical Industries, Ltd.) and then adding 6.5 L of aqueous sodium hypochlorite solution having a concentration of 250 ppm (obtained by diluting sodium hypochlorite manufactured by Wako Pure Chemical Industries, Ltd. with tap water). After washing for 15 minutes, the liquid in the washing tub was drained followed by the further addition of 6.5 L of aqueous sodium hypochlorite solution having a concentration of 250 ppm (obtained by diluting sodium hypochlorite manufactured by Wako Pure Chemical Industries, Ltd. with tap water). After washing for 15 minutes, the pulp floating in the liquid in the washing tub was skimmed off and placed in a mesh pouch (measuring 25 cm on all sides, N-No. 250HD manufactured by NBC Meshtec Inc.), and dehydrated for 5 minutes in a dehydration tank. The recovered pulp was rinsed for 15 minutes with tap water while still in the mesh pouch and again dehydrated for 5 minutes in a dehydration tank. The recovered pulp was then dried for 24 hours in a hot air dryer at 105° C. When the ash content of the recovered pulp was analyzed in the same manner as Example 1, it was determined to be extremely high at 8.51% by weight and was incompatible with sanitary material standards.

Comparative Example 2

(17) After immersing a commercially available disposable diaper (Moony Size M, Unicharm Corp.) in 3 L of physiological saline containing 1% artificial organic waste for 10 minutes to adsorb the artificial organic waste thereto, the diaper was immersed in 10 L of aqueous citric acid solution (pH 2.2) having a concentration of 1% followed by subjecting to ozone treatment by blowing in ozone gas at 80 mg/m.sup.3 for 30 minutes. The amount of dissolved ozone in the treatment water 30 minutes later was 1 ppm and the pH was 3.0. In this comparative example, since the ozone was consumed by degradation of the artificial organic waste, the amount of dissolved ozone in the treatment water 30 minutes later was lower in comparison with Example 1 and Example 2. As a result of straining the treatment water with a mesh filter having an opening size of 2 mm×2 mm, a large amount of jelly-like SAP remained and it was not possible to recover only recover pulp. When the ash content of the recovered pulp was analyzed in the same manner as Example 1, it was determined to be high at 0.55% by weight. If the CT value of ozone treatment is high, degradation of SAP does not proceed and low-quality pulp ends up being obtained under these conditions. The effects of ozone treatment were determined to be poor unless organic waste is separated and removed prior to ozone treatment.

(18) The results of measuring the ash content, water absorption performance and water retention performance of the recovered pulp in the examples and comparative examples are collectively shown in Table 1.

(19) Furthermore, the methods used to measure water absorption performance and water retention performance are as indicated below.

(20) Incidentally, the ash content of pulp initially contained in the commercially available disposable diapers used in the examples and comparative examples, their water absorption performance and their water retention performance were 0.18% by weight, 16.4 g/g and 7.60 g/g, respectively.

(21) [Ash Content]

(22) Ash content refers to the amount of inorganic or non-combustible residue remaining following asking of organic matter. Ash content is measured in accordance with “5. Ash Content Testing Method” of “2. General Testing Methods” of the Japanese Specifications of Sanitary Napkin Materials. Namely, ash content is measured in the manner indicated below.

(23) After preliminarily intensely heating a platinum, quartz or porcelain crucible to 500° C. to 550° C. for 1 hour and then allowing to cool, the crucible is weighed precisely. 2 g to 4 g of sample are collected and placed in the crucible followed by again precisely weighing the crucible containing the sample, initially subjecting to mild heating after having removed or shifted the position of the cover of the crucible as necessary, and then gradually raising the temperature to intensely heat for 4 hours or more at 500° C. to 550° C. and ash the sample until carbides no longer remained. After allowing to cool, the crucible is weighed precisely. The residue is again asked until it reaches a constant weight and allowed to cool followed by precisely measuring the weight thereof as the amount of ash (%).

(24) [Water Absorption Performance]

(25) Water absorption performance refers to the weight of water absorbed by pulp fibers per unit weight, and is measured in the manner indicated below.

(26) (1) A Nylon net (250 mesh Nylon net manufactured by NBC Meshtec Inc., 200 mm×200 mm) is prepared followed by precisely determining the weight of the net N.sub.0 (g).

(27) (2) Approximately 5 g of measurement sample are placed in the Nylon net followed by precisely determining the weight of the sample including the Nylon net pouch A.sub.0 (g).

(28) (3) One liter of physiological saline having a concentration of 0.9% is placed in a beaker and the prepared Nylon net pouch containing the sample is immersed therein and allowed to stand for 3 minutes.

(29) (4) The pouch is lifted out of the beaker and allowed to stand undisturbed for 3 minutes on a drainage net to drain off the physiological saline.

(30) (5) The weight A (g) of the Nylon net pouch containing the sample after draining off the physiological saline is measured.

(31) (6) Another Nylon net cut to the same size is prepared, steps (3) and (4) are carried out in the same manner with the exception of not adding a sample, and the weight N (g) of the Nylon net pouch only is measured after draining off the physiological saline.

(32) (7) Water absorption performance (g/g) is then calculated using the equation indicated below.

(33) Water absorption performance=(A-N-(A.sub.0-N.sub.0))/(A.sub.0-N.sub.0) (8) Measurements are carried out 10 times followed by determining the average of the 10 measured values.

(34) [Water Retention Performance]

(35) Water retention performance is measured in the manner indicated below.

(36) The weight B (g) of the sample obtained after measuring water absorption performance is measured after having dehydrated the sample for 90 seconds at 150 G with a centrifugal separator (Model H130 Centrifuge manufactured by Kokusan Co., Ltd., rotating speed of 850 rpm=150 G).

(37) Water retention performance=(B—N-(A.sub.0-N.sub.0))/(A.sub.0-N.sub.0)

(38) Measurements are carried out 10 times followed by determining the average of the 10 measured values.

(39) TABLE-US-00001 TABLE 1 Ash Water Absorption Water Retention Content (%) Performance (g/g) Performance (g/g) Unused pulp 0.18 16.4 7.60 Example 1 0.10 17.2 7.92 Example 2 0.06 18.1 8.30 Comp. Ex. 1 8.51 8.0 2.84 Comp. Ex. 2 0.55 14.4 6.30

(40) [Verification of Superabsorbent Polymer Dehydrating Effects of Citric Acid and Calcium Chloride]

(41) After a commercially available disposable diaper (Moony Size M, Unicharm Corp.) was immersed for 10 minutes in 3 L of physiological saline, the diaper was lifted out of the physiological saline followed by immediately weighing the disposable diaper that had absorbed water for use as the post-absorption weight. Next, after having immersed the disposable diaper that had absorbed water for 3 minutes in 3 L of various concentrations (wt %) of aqueous citric acid solution or aqueous calcium chloride solution, the diaper was lifted out of each solution followed immediately by weighing for use as the post-dehydration weight. The value obtained from the equation post-dehydration weight/post-absorption weight×100 (to also be referred to as the “weight ratio”) was then calculated. The average values of the results of measuring N=3 times for each concentration are shown in Table 2. Furthermore, Table 2 also indicates the pH values of each concentration of the aqueous citric acid solution or aqueous calcium chloride solution.

(42) TABLE-US-00002 TABLE 2 Citric Acid Calcium Chloride Solution Concentration pH Weight Ratio pH Weight Ratio 1% 2.2 90% 9.5 88% 3% 2.0 86% 10.8 82% 5% 1.8 80% 10.8 77% 7% 1.5 75% 11.0 77% 10%  1.3 72% 11.0 76%

(43) When SAP that has absorbed excrement additionally absorbs water and swells in a treatment tank, since the volume thereof becomes excessively large making treatment difficult, it is important that the weight ratio at least be greater than 100%, and since treatment becomes easier as volume decreases, treatment efficiency increases. Accordingly, the weight ratio is preferably 100% or less, more preferably 90% or less and even more preferably 80% or less.

(44) [Verification of Change in Ozone Treatment Efficiency attributable to Artificial Organic Waste]

(45) 29 g of superabsorbent polymer and 100 g of artificial organic waste were added to 10 L of treatment water (1% aqueous citric acid solution) followed by treating by blowing in ozone gas at 80 mg/m.sup.3 for 30 minutes. The amount of dissolved ozone in the treatment water 30 minutes later was 1.2 ppm and the superabsorbent polymer degradation rate was 36%.

(46) When treatment was carried out in the same manner without adding artificial organic waste, the amount of dissolved ozone in the treatment water 30 minutes later was 25 ppm and the superabsorbent polymer degradation rate was 99%.

(47) In the case of having added artificial organic waste as a model of human waste to treatment water, in addition to the dissolved ozone concentration in the treatment solution decreasing in comparison with the absence of organic waste, degradation of superabsorbent polymer was also confirmed to decrease. This is because, since a large amount of ozone is consumed by degradation of the organic waste, degradation of the superabsorbent polymer proceeds with difficulty.

(48) In the present invention, treatment is able to be carried out efficiently by washing and degrading used sanitary products in a solution in which a superabsorbent polymer does not absorb water or swell resulting in a mixture mainly composed of pulp and residual superabsorbent polymer, followed by treating the mixture with ozone.

INDUSTRIAL APPLICABILITY

(49) Recycled pulp manufactured according to the method of the present invention is able to be preferably reused in the manufacturing of sanitary products.