JP2023123237A - Antibacterial water-absorbing sheet - Google Patents

Abstract

To provide an antibacterial water-absorbing sheet containing pulp, which is biodegradable and environmentally friendly, while suppressing the proliferation of various germs inside the sheet.SOLUTION: An antibacterial water-absorbing sheet contains pulp and plant-derived antibacterial fiber, but is free of oil-derived synthetic fiber.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to an antibacterial water absorbent sheet containing pulp.

Due to global warming, the number of hot summer days has increased, and conversely, heavy rains have caused large changes in soil moisture content, making it difficult to grow plants such as vegetables and seedlings outdoors in a stable manner. It has become to. In the cultivation of vegetables and seedlings, too much water in the soil causes root rot. Conversely, if there is not enough water, it will dry out. If germs contained in water are absorbed by the roots, vegetables and cuttings may become susceptible to disease, grow unattractively, and yield will be reduced. Cuttings are a method of growing seedlings by inserting a part of young branches into the soil to encourage rooting.In recent years, it has been used to produce bonsai seedlings, which are traded at high prices, and high-quality cedar seedlings with low pollen. It is a method that is used.

The irrigation sheet is a type of water absorption sheet, and is a sheet that supplies water to plants. It absorbs water from the bottom water supply tray and supplies water to the soil from the bottom of the pot. In addition, various water absorbent sheets have been proposed (see Patent Documents 1 to 7, etc.).

These days, consumers are highly conscious of the quality of vegetables and bonsai, and tend to shy away from poor-looking things, and higher quality is required in the production of vegetables and cuttings. In addition, it is required to increase the yield by reducing root rot and withering by keeping the moisture content of the soil to an appropriate amount. In addition, the outflow of plastics from rivers to the sea has been highlighted, and global value is placed on eliminating plastics, biodegradable, and reproducible (sustainable) products that do not increase CO2 in the atmosphere. is awaited.

A method of using a polyester water-absorbing sheet has been proposed in order to improve the quality of cuttings and the efficiency of seedling production (see Patent Document 4). Patent Document 4 does not mention antibacterial properties or biodegradability. Also, polyester is a petroleum-derived material and is not biodegradable.

It has also been proposed to use a nonporous hydrophilic film to block germs and supply only water and nutrients to vegetables (see Patent Document 5). However, Patent Document 5 does not mention the antibacterial properties of the film itself.

There has also been proposed a composite sheet for a water vaporization board comprising polyvinyl alcohol-based fibers and binder fibers (see, for example, Patent Document 6). However, both the polyvinyl alcohol-based fiber and the binder fiber are petroleum-derived materials and are not biodegradable.

A low-density antibacterial water-absorbing sheet using petroleum-derived synthetic fibers has also been proposed as a water-absorbing material for humidifiers (see Patent Document 7). However, these synthetic fibers, including vinylon fibers, silver-impregnated acrylic antibacterial fibers, and polyester binder fibers, are all petroleum-derived materials and are not biodegradable.

JP 2016-198012 A International Publication No. 2015/186830 JP 2020-191852 A JP 2019-24396 A Japanese Patent No. 4142725 JP-A-11-140756 JP-A-10-8398

The irrigation sheets for horticulture and agriculture have been described above, but there are various other types of water-absorbing sheets such as transpiration sheets for humidifiers, drip-absorbing sheets for sashimi and meat, toilet sheets for pets, and the like.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a biodegradable, environmentally friendly antibacterial water absorbent sheet while suppressing the growth of bacteria inside the sheet.

The antibacterial water-absorbing sheet that solves the above purpose,
It is characterized by containing pulp and plant-derived antibacterial fibers and not containing petroleum-derived synthetic fibers.

According to this antibacterial water absorbent sheet, the antibacterial fiber suppresses the growth of bacteria inside the sheet. In addition, since it does not contain petroleum-derived synthetic fibers, it is a biodegradable, environmentally friendly antibacterial water absorbent sheet.

The pulp may be wood pulp or cotton pulp. Plant-derived antibacterial fibers include fibers containing 95% by weight or more of rayon, fibers containing 95% by weight or more of cupra, fibers containing 95% by weight or more of lyocell, polylactic acid fibers (PLA), and antibacterial agents may be kneaded and spun, or may be provided with an antibacterial agent in post-processing after spinning. It is important that it does not contain petroleum-derived synthetic fibers and may contain petroleum-derived additives.

Also,
The compounding ratio of the pulp and the antibacterial fiber is 50% by mass or more and 80% or less by mass, and the antibacterial fiber is 20% by mass or more and 50% by mass, when the total of the pulp and the antibacterial fiber is 100% by mass. It is characterized by the following.

If the compounding ratio of the antibacterial fiber is less than 20% by mass, sufficient antibacterial properties cannot be obtained when the sheet is formed. On the other hand, if it is more than 50% by mass, the wet strength of the sheet when wet with water may be low, and biodegradation when buried in soil may be slow, and the cost is high, which is not economical. .

Also,
The antibacterial fiber is characterized in that the antibacterial agent is kneaded into fiber raw materials and spun, or the antibacterial agent is vapor-deposited on the surface of the fiber.

By doing so, it is possible to prevent the antibacterial agent from flowing out together with the water when the antibacterial water absorbent sheet is used.

Also,
The antibacterial fiber is characterized by containing 95% by mass or more of rayon.

An antibacterial fiber containing 95% by mass or more of rayon is plant-derived and inexpensive.

Also,
It may be characterized by a Klemm water absorbency of 80 mm/10 min or more and 140 mm/10 min or less.

The value of the Klemm water absorbency is a value obtained by measuring the water absorbency in the MD direction according to the method described in JIS P8141.

moreover,
The pulp may be characterized by having a freeness of 500 mlCSF or more and 700 mlCSF or less.

The value of freeness is a value measured by the method of JIS P8121-2.

Also,
With respect to 100% by mass of the pulp and the antibacterial fiber combined, 1.0% by mass or more and 3.0% by mass or less of a dry paper strength agent and 1.5% by mass or more of a wet paper strength agent are included 4 It may be characterized by containing .0% by mass or less.

That is, 1.0% by mass or more and 3.0% by mass or less of a dry paper strength agent is added to a total of 100% by mass of the pulp and the antibacterial fiber, and 1.5% by mass of a wet paper strength agent. More than 4.0% by mass or less may be added.

According to the present invention, it is possible to provide a biodegradable, environmentally friendly antibacterial water absorbent sheet while suppressing the growth of germs inside the sheet.

An embodiment of the antibacterial water absorbent sheet of the present invention will be described in detail below. The antibacterial water absorbent sheet of the present embodiment is a watering sheet obtained by wet papermaking using raw materials consisting of pulp, antibacterial fiber, dry paper strength agent, and wet paper strength agent. In addition, the antibacterial water-absorbent sheet of the present embodiment can be suitably used as a bottom water-watering mat or the like that supplies water to the roots moderately and uniformly during the production of bonsai cuttings and vegetables. Furthermore, it can also be used as a transpiration plate for a humidifier, a drip absorbent sheet for sashimi or meat, a pet toilet sheet, and the like.

Pulp is generally a natural fiber extracted from wood by chemically treating wood, and the one derived from coniferous trees is called NBKP, and the one derived from broad-leaved trees is called LBKP. Non-wood plant-derived pulps include cotton pulp and the like. Any plant-derived pulp can be used for the antibacterial water absorbent sheet of the present embodiment. NBKP and LBKP are preferable from the point of cost.

The freeness of the pulp is preferably in the range of 500 ml CSF or more and 700 ml CSF or less when measured by the method of JIS P8121-2. If it is less than 500 ml CSF, the water absorbency of the sheet will be low, and sufficient water cannot be supplied to plants when used as a watering sheet. If it is higher than 700 ml CSF, sufficient sheet strength cannot be obtained. In addition, the degree of water absorption increases, and when used as an irrigation sheet, too much water is supplied, which may cause root rot.

Antibacterial fibers are those that are spun by kneading inorganic antibacterial agents such as quaternary ammonium salts of antibacterial agents, silver, copper, and titanium oxide into the raw materials of fibers, and those that are antibacterial by post-processing after spinning. It may be one to which an agent is applied. However, since water flows inside the irrigation sheet, there is a concern that the antibacterial agent may flow out together with the water if the sheet is impregnated with an antibacterial agent, and the antibacterial effect will not last. Therefore, if the antibacterial agent is kneaded into the raw material of the fiber and spun, or if the antibacterial agent is vapor-deposited on the fiber surface in a post-processing after spinning, there is little risk that the antibacterial agent will flow out together with the water. preferable. Further, since some inorganic antibacterial agents are inferior in light resistance and water resistance, quaternary ammonium salt antibacterial agents are preferable. Specifically, a rayon-based antibacterial fiber obtained by kneading a quaternary ammonium salt into a viscose liquid, which is the raw material of the fiber, is preferable. The rayon base contains 95% by mass or more of rayon when the entire rayon base is 100% by mass. Viscose is a kind of rayon material, is a reproducible material made from wood pulp, and is biodegradable because it consists of cellulose. Note that polylactic acid fiber (PLA) derived from corn or potato may be used instead of rayon (viscose liquid). Alternatively, it may be cupra-based or lyocell-based. The shape of the fiber is preferably a size that allows wet papermaking. Examples include a fiber diameter of 1.7 dtex (thickness) and a fiber length of 5 mm (length), length) and the fiber length is 5 mm (length). If the fiber length is longer than 5 mm, it becomes difficult to disperse in water, and the texture of the sheet deteriorates. On the other hand, if the fiber diameter is thicker than 2.5 dtex, the sheet itself becomes stiff and inconvenient to use. On the other hand, if the fiber diameter is smaller than 1.5 dtex, the fabric lacks stiffness and is difficult to work with.

The compounding ratio of the antibacterial fiber is preferably in the range of 20% by mass or more and 50% by mass or less when the total of the pulp and the antibacterial fiber is 100% by mass, and if it is lower than 20% by mass, the sheet has sufficient antibacterial properties. is not obtained. On the other hand, if it is more than 50% by mass, the wet strength of the sheet when wet with water may be low, and biodegradation when buried in soil may be slow, and the cost is high, which is not economical. . Pulp makes up the rest of the blending ratio.

The fibers of the antibacterial water-absorbing sheet can be loosened by boiling it with an aqueous solution of sodium hydroxide, hydrochloric acid, or an organic solvent. The loosened fibers are colored with a dyeing solution, and the difference in color is observed under a microscope. When the Herzberg staining solution described in JIS P8120 is used, wood pulp is dyed blue, and viscose is dyed dark bluish violet. It is possible to identify the compounding ratio by observing more than one fiber. It is also possible to measure the freeness of the fibers loosened as described above and obtain the freeness of the pulp from the compounding ratio.

The dry paper strength agent is exemplified by polyacrylic resin, and the addition amount is preferably in the range of 1.0% by mass or more and 3.0% by mass or less with respect to 100% by mass of pulp and antibacterial fiber. If it is less than 1.0% by mass, sufficient dry paper strength cannot be obtained. If it is more than 3.0% by mass, the formation of the sheet is deteriorated, and the production line such as the dryer is easily soiled.

The wet paper strength agent is exemplified by a polyamide epoxy resin, and is preferably added in an amount of 1.5% by mass or more and 4.0% by mass or less with respect to 100% by mass of pulp and antibacterial fiber. If it is less than 1.5% by mass, sufficient wet paper strength cannot be obtained. If the amount is more than 4.0% by mass, the biodegradability is deteriorated, the texture of the sheet is deteriorated, and the production line such as the dryer is easily soiled.

The antibacterial water-absorbing sheet of the present embodiment is a paper machine such as a cylinder paper machine, a fourdrinier paper machine, a short wire paper machine, an inclined paper machine, or a combination paper machine made by combining the same or different paper machines among these. It can be produced by a method of making paper using a machine or the like. In addition to the essential components, a drainage agent, a dispersant, and a thickening agent can be appropriately selected and added to the raw material slurry. The raw material slurry is adjusted to have a solid content concentration of 0.1% by mass or more and 5% by mass or less. It is also possible to appropriately add internal additives such as pH adjusters, antifoaming agents, pitch control agents, and slime control agents, depending on the purpose.

This raw material slurry is further diluted to a predetermined concentration and made into paper. Next, the paper-made web is dried after removing excess moisture by a method such as suction or wet pressing. A drying device such as a Yankee dryer, a cylinder dryer, an air dryer, an infrared dryer, or a suction dryer can be used for drying.

The Klemm water absorbency of the antibacterial water absorbent sheet of the present embodiment is desirably 80 mm/10 min or more and 140 mm/10 min or less when the water absorbency in the MD direction is measured according to the method described in JIS P8141. If it is less than 80 mm/10 min, it will not be possible to supply sufficient water to the soil and plants when using it as an irrigation sheet. If it is higher than 140 mm/10 min, the water content of the soil becomes too high when it is used as a watering sheet, which may cause root rot.

The antibacterial water-absorbing sheet of this embodiment can be used not only as a watering sheet for gardening and agriculture, but also as a transpiration plate for a humidifier. Since the sheet itself has antibacterial properties, it is not necessary to impregnate polyester nonwoven fabric, which is generally used for transpiration sheets, with an antibacterial agent, and it can be used as a material for the transpiration plate as it is. Moreover, since it is kneaded into the fiber itself, the antibacterial agent does not elute. Therefore, cleaning of the humidifier is reduced due to its long-lasting antibacterial properties. Other uses include water-absorbing mats for planters, water-absorbing sheets for drips from sashimi and meat, toilet sheets for pets, and the like.

The antibacterial water absorbent sheet of the present embodiment described above contains pulp and plant-derived antibacterial fibers, and does not contain petroleum-derived synthetic fibers. It is a biodegradable, eco-friendly antibacterial water absorbent sheet that does not contain any synthetic fibers derived from it.

(preferred embodiment)
Preferred examples are given below to more specifically describe the compounding ratio, the amount added, and the physical properties, but the present invention is not limited to the examples described here. Methods for measuring physical properties described in Examples and Comparative Examples are shown below.

1) Freeness of pulp Measured according to JIS P8121-2. Units are mlCSF.

2) Basis weight It was measured by the method described in JIS P8124. The unit is g/ ^m2 .

3) Tensile strength Tensile strength was measured according to the method described in JIS P8113. Specifically, the tensile strength of a strip sample having a width of 15 mm and a length of 220 mm was measured. The unit is kN/m.

4) Wet Tensile Strength Wet tensile strength was measured according to the method described in JIS P8135. A strip sample having a width of 15 mm and a length of 220 mm is immersed in pure water at 25° C. for 3 minutes. The wet tensile strength of the 4 strip samples subjected to the immersion treatment was collectively measured, and the value per piece was calculated from the measured data of the 4 strip samples collectively. The unit is kN/m.

5) Water absorption (Klemm method)
The water absorption in the MD direction was measured according to the method described in JIS P8141. The test piece was cut into a width of 15 mm and a length of 220 mm, and vertically immersed in water up to 15 mm from the lower end. The higher the value, the better the water absorption.

6) Antibacterial test (bacterial liquid absorption method)
According to the method described in JIS L 1902, the antibacterial activity value was measured by the bacterial liquid absorption method. A test piece was cut to 65 mm x 65 mm. Staphylococcus aureus was used as the test bacteria, and the amount of bacteria was measured immediately after and 18 hours after the sheet was inoculated with the bacteria, and the antibacterial activity value was measured. An antibacterial activity value of 3.0 or more according to the JIS criterion was defined as ◯. Less than 3.0 was antibacterial: ×.

7) Biodegradability test A test piece was cut into a size of 50 mm x 50 mm, and the weight mass (A) g was measured. The cut sample was buried in a pot containing commercially available leaf mulch. After 3 months, it was dug out, washed with water to remove excess soil, dried, and weighed (B) g. Weight loss rate (biodegradation rate) = {(AB)/A} x 100. Judgment was made biodegradability: ◯ for 85% or more, and biodegradability: x for less than 85%.

(Example 1)
70 mass % of wood pulp NBKP and 30 mass % of LBKP were beaten with a double disc refiner (DDR) to obtain wood pulp with a freeness of 570 ml CSF.

75% by mass of the obtained wood pulp and 25% by mass of antibacterial fiber 2.2 dtex×5 mm (rayon base) were dispersed with a tappy disintegrator. The compounding ratio referred to here is the compounding ratio when the pulp and the antibacterial fiber are combined to 100% by mass (the same applies hereinafter). Furthermore, 1.7% by mass of a dry paper strength agent and 2.5% by mass of a wet paper strength agent were added to obtain a raw material. The amount of the paper strength agent added is the amount added to 100% by mass when the sum of the pulp and the antibacterial fiber is 100% by mass (the same applies hereinafter).

Using the obtained raw material, a sheet was produced by a hand making machine and dried by a cylinder dryer to obtain an antibacterial water absorbent sheet with a basis weight of 102 g/m ² .

(Example 2)
70 mass % of wood pulp NBKP and 30 mass % of LBKP were beaten with a double disc refiner (DDR) to obtain wood pulp with a freeness of 570 ml CSF.

50% by mass of the obtained wood pulp and 50% by mass of antibacterial fiber 2.2 dtex × 5 mm (rayon base) were dispersed with a tappy type disintegrator, and further 2.4% by mass of dry paper strength agent and 3.5% of wet paper strength agent. % by mass was added to obtain a raw material.

A sheet was produced in the same manner as in Example 1 to obtain an antibacterial water absorbent sheet with a basis weight of 106 g/m ² .

(Example 3)
100% by mass of wood pulp NBKP was beaten with DDR to obtain wood pulp with a freeness of 700 ml CSF.

75% by mass of the obtained wood pulp and 25% by mass of antibacterial fiber 1.7 dtex × 5 mm (rayon base) were dispersed with a tappy type disintegrator, and further 1.7% by mass of dry paper strength agent and 2.5% of wet paper strength agent. % by mass was added to obtain a raw material.

Using the obtained raw material, a sheet was produced by a manual machine and dried by a cylinder dryer to obtain an antibacterial water absorbent sheet with a basis weight of 97 g/m ² .

(Example 4)
80% by mass of wood pulp NBKP and 20% by mass of wood pulp LBKP were beaten by DDR to obtain wood pulp with a freeness of 698 ml CSF.

75% by mass of the obtained wood pulp, 18% by mass of antibacterial fiber 2.2 dtex × 5 mm (rayon base) and 7% by weight of antibacterial fiber 1.7 dtex × 5 mm (rayon base) were dispersed with a tappy disintegrator, and further dried paper A raw material was obtained by adding 1.4% by mass of a strength agent and 2.0% by mass of a wet paper strength agent.

Using this obtained raw material, paper was made with an inclined short mesh paper machine to obtain an antibacterial water absorbent sheet with a basis weight of 103 g/m ² .

(Example 5)
Using the raw material of Example 4, papermaking was carried out by reducing the speed of an inclined short wire paper machine to obtain an antibacterial water absorbent sheet with a basis weight of 130 g/m ² .

(Example 6)
100% by mass of wood pulp NBKP was disintegrated with a Tappi disintegrator to obtain wood pulp with a freeness of 730 ml CSF.

75% by mass of the obtained wood pulp and 25% by mass of antibacterial fiber 2.2 dtex × 5 mm (rayon base) were dispersed with a tappy type disintegrator, and further 1.7% by mass of dry paper strength agent and 2.5% of wet paper strength agent. % by mass was added to obtain a raw material.

Using the obtained raw material, a sheet was produced with a handsheet machine and dried with a cylinder dryer to obtain an antibacterial water absorbent sheet with a basis weight of 105 g/m ² .

(Example 7)
90% by mass of wood pulp NBKP and 10% by mass of wood pulp LBKP were beaten with a double disc refiner (DDR) to obtain wood pulp with a freeness of 643 ml CSF.

80% by mass of the obtained wood pulp and 20% by mass of antibacterial fiber 1.7 dtex × 5 mm (rayon base) were dispersed with a tappy type disintegrator, and further 1.0% by mass of dry paper strength agent and 1.5% of wet paper strength agent. % by mass was added to obtain a raw material.

Using the obtained raw material, a sheet was produced by a manual machine and dried by a cylinder dryer to obtain an antibacterial water absorbent sheet with a basis weight of 100 g/m ² .

(Example 8)
90% by mass of wood pulp NBKP and 10% by mass of wood pulp LBKP were beaten with a double disc refiner (DDR) to obtain wood pulp with a freeness of 544 ml CSF.

50% by mass of the obtained wood pulp and 50% by mass of antibacterial fiber 2.2 dtex × 5 mm (rayon base) are dispersed with a tappy type disintegrator, and further 3.0% by mass of dry paper strength agent and 4.0% of wet paper strength agent. % by mass was added to obtain a raw material.

Using the obtained raw material, a sheet was produced by a hand making machine and dried by a cylinder dryer to obtain an antibacterial water absorbent sheet with a basis weight of 102 g/m ² .

(Comparative example 1)
70% by mass of wood pulp NBKP and 30% by mass of LBKP were beaten by DDR to obtain wood pulp with a freeness of 570 ml CSF.

100% by mass of the obtained wood pulp was dispersed with a tappy type disintegrator, and 0.6% by mass of a dry paper strength agent and 1.0% by mass of a wet paper strength agent were added to obtain a raw material. In this Comparative Example 1, no antibacterial fiber was used.

Using the raw material thus obtained, a sheet was produced by a hand making machine and dried by a cylinder dryer to obtain a water absorbent sheet with a basis weight of 104 g/m ² .

(Comparative example 2)
Disperse 100% by mass of antibacterial fiber 2.2 dtex x 5 mm (rayon base) with a tapping machine, and add 3.4% by mass of dry paper strength agent and 4.5% by weight of wet paper strength agent to prepare the raw material. Obtained. In this Comparative Example 2, no pulp was used.

Using this obtained raw material, a sheet was produced by a hand making machine and dried by a cylinder dryer to obtain an antibacterial water absorbent sheet with a basis weight of 110 g/m ² .

(Comparative example 3)
100% by mass of wood pulp NBKP was beaten with DDR to obtain wood pulp with a freeness of 450 ml CSF.

25% by mass of the obtained wood pulp and 75% by mass of antibacterial fiber 2.2 dtex × 5 mm (rayon base) were dispersed with a tappy type disintegrator, and further 2.4% by mass of dry paper strength agent and 3.5% of wet paper strength agent. % by mass was added to obtain a raw material. In Comparative Example 3, a large amount of antibacterial fiber was used.

Using the obtained raw material, a sheet was produced by a manual machine and dried by a cylinder dryer to obtain an antibacterial water absorbent sheet with a basis weight of 100 g/m ² .

(Comparative example 4)
100% by mass of wood pulp NBKP was beaten with DDR to obtain wood pulp with a freeness of 450 ml CSF.

85% by mass of the obtained wood pulp and 15% by mass of antibacterial fiber 2.2 dtex × 5 mm (rayon base) were dispersed with a tappy type disintegrator, and further 1.7% by mass of dry paper strength agent and 2.5% by weight of wet paper strength agent. % by mass was added to obtain a raw material. In Comparative Example 4, a large amount of wood pulp was used.

Using the raw material thus obtained, a sheet was produced using a handsheet machine and dried using a cylinder drier to obtain a water absorbent sheet with a basis weight of 114 g/m ² .

(Comparative example 5)
Petroleum-derived PET (polyester fiber) fiber 1.7 dtex × 5 mm 70% by mass and petroleum-derived binder fiber (amorphous polyester fiber, melting point 110 ° C.) 2.2 dtex × 5 mm 30% by mass are dispersed with a tappy disintegrator, and the raw material got

Using this obtained raw material, a sheet was produced with a hand-sheeting machine and dried with a cylinder drier to obtain a water absorbent sheet with a basis weight of 101 g/m ² .

Table 1 shows the mixing ratios, measured values and test results of the raw materials of Examples 1-8, and Table 2 shows the mixing ratios, measured values and test results of the raw materials of Comparative Examples 1-5.

In Comparative Example 4 containing 15% by mass of the antibacterial fiber, the result of the antibacterial test (antibacterial property) was x. This is thought to be due to the lack of antibacterial fibers. On the other hand, in Example 7 containing 20% by mass of the antibacterial fiber, the result of the antibacterial test (antibacterial property) is ◯.

Moreover, in Comparative Example 3 containing 75% by mass of the antibacterial fiber, the result of the biodegradability test (biodegradability) is x. I think this is because there was too much antibacterial fiber. On the other hand, in Examples 2 and 8 containing 50% by mass of the antibacterial fiber, the result of the biodegradability test (biodegradability) is ◯.

From the above, it is preferable that the compounding ratio of pulp and antibacterial fiber is 20% by mass or more and 50% or less by mass when the total of pulp and antibacterial fiber is 100% by mass, and the remainder is pulp.

In Comparative Example 3, the biodegradability was rated as x, but the weight mass reduction rate (biodegradation rate) was 52%, exceeding 50%. In Comparative Example 4, the antibacterial property was rated as x, but according to the JIS criteria, if the antibacterial activity value is 2.0 or more, the antibacterial effect is recognized. It exceeded 2.0.

In addition, in Comparative Example 5 using petroleum-derived synthetic fibers, the result of the biodegradability test (biodegradability) is x. More specifically, the weight loss rate (biodegradability) is 0%. From the above, it is necessary not to contain petroleum-derived synthetic fibers.

Furthermore, in Comparative Example 4 in which the freeness of the pulp is 450 ml CSF, the water absorbency of the sheet is as low as 66 mm/10 min. On the other hand, in Examples 1 and 2 in which the freeness of the pulp is 570 ml CSF, the water absorbency of the sheet exceeds 100 mm/10 min, which is sufficient. Therefore, the lower limit of freeness of pulp is preferably 500 ml CSF.

In Example 3, in which the freeness of the pulp is 700 ml CSF, the sheet has a water absorbency of 117 mm/10 min and a wet tensile strength of 0.65 kN/m. On the other hand, in Example 6 in which the freeness of the pulp is 730 ml CSF, although the water absorption of the sheet is 130 mm/10 min, the wet tensile strength is slightly below 0.5 kN/m, so the freeness of the pulp is is preferably 700 ml CSF or less.

The water absorbency of the sheet must be in a range in which water can be supplied sufficiently but not too much, and as a result of numerous studies, it is preferably in the range of 80 mm/10 min or more and 140 mm/10 min or less.

In Comparative Example 2, instead of containing no wood pulp, a large amount of 3.4% by mass of dry paper strength agent and 4.5% by mass of wet paper strength agent was added, but the tensile strength and wet tensile strength of the sheet remains low, indicating that the addition of strength agents alone is not sufficient. On the other hand, as in Comparative Example 1, when the wood pulp is 100% by mass, the tensile strength and wet tensile strength are relatively high even if the amount of the dry paper strength agent and the wet strength agent added is small. I understand. Based on these facts, the tensile strength and wet tensile strength of the sheet can be improved by increasing the blending ratio of wood pulp, but in order to suppress the growth of various bacteria inside the sheet, it is necessary to add antimicrobial fibers. be. Also, when comparing Example 1 and Example 6, in which the amounts of the dry paper strength agent and the wet paper strength agent added are the same, the higher the freeness of the pulp, the lower the tensile strength and wet tensile strength. I understand. By adding antibacterial fiber, the blending ratio of wood pulp is reduced, and the tensile strength and wet tensile strength are reduced, and the tensile strength and wet tensile strength are reduced by increasing the freeness of the pulp. It can be seen from the results of each example that addition of a dry paper strength agent and a wet paper strength agent can compensate for this. Whether it is a dry paper strength agent or a wet paper strength agent, if the amount added is large, the formation of the sheet will deteriorate and the production line such as the dryer will become dirty easily, so it is necessary to keep it below a certain level. In addition, since it is a petroleum-derived additive, the greater the amount added, the worse the biodegradability. In Example 8, 3.0% by mass of dry paper strength agent and 4.0% by mass of wet paper strength agent are added, but the result of biodegradability test (biodegradability) is ○ . For these reasons, it is preferable to set the upper limit of the dry strength agent to 3.0% by mass and the upper limit of the wet strength agent to 4.0% by mass. On the other hand, the lower limit is also related to the blending ratio of pulp. In Example 7 in which the pulp compounding ratio was set to the preferred upper limit of 80% by mass, only 1.0% by mass of the dry paper strength agent and 1.5% by mass of the wet paper strength agent were added, Since the tensile strength is 4.41 kN/m and the wet tensile strength is 0.83 kN/m, the lower limit of the dry paper strength agent is 1.0% by mass, and the upper limit of the wet strength agent is 1.0% by mass. It is preferably 5% by mass.

In addition, it can be seen from Examples 4 and 5 that even if the basis weight is changed, the water absorbency is little affected. On the other hand, from Examples 1 and 8, it can be seen that the lower the density, the better the water absorption.

Claims (5)

An antibacterial water absorbent sheet containing pulp and plant-derived antibacterial fibers and not containing petroleum-derived synthetic fibers. The compounding ratio of the pulp and the antibacterial fiber is 50% by mass or more and 80% or less by mass, and the antibacterial fiber is 20% by mass or more and 50% by mass, when the total of the pulp and the antibacterial fiber is 100% by mass. The antibacterial water absorbent sheet according to claim 1, characterized by: 3. The antibacterial water absorbent sheet according to claim 1, wherein said antibacterial fiber is obtained by kneading an antibacterial agent into fiber raw material and spinning it, or by vapor-depositing an antibacterial agent on the surface of the fiber. 4. The antibacterial water absorbent sheet according to any one of claims 1 to 3, wherein the antibacterial fiber contains 95% by mass or more of rayon. 5. The antibacterial water absorbent sheet according to any one of claims 1 to 4, wherein the Kremm water absorbency is 80 mm/10 min or more and 140 mm/10 min or less.