JP7843167B2 - Antibacterial paper and method for manufacturing the same - Google Patents

Description

This invention relates to antibacterial paper and a method for producing the same.

Antibacterial paper with added antibacterial properties is known. For example, Patent Document 1 describes paper with an inorganic antibacterial agent such as antibacterial zeolite added externally, and Patent Document 2 describes paper with an antibacterial agent added internally. Furthermore, Patent Document 3 proposes the production of antibacterial paper using an aqueous solution of chlorhexidine gluconate.

Japanese Patent Application Publication No. 09-003799 Japanese Patent Application Publication No. 09-003800 Japanese Patent Publication No. 2009-242299

The object of this invention is to provide an excellent antibacterial paper and a method for producing the same.

The present invention is not limited to the following inventions.
[1] A method for producing antibacterial paper, comprising coating an antibacterial agent and a polysaccharide onto a base paper.
[2] The method according to [1], wherein a coating solution containing an antibacterial agent and a polysaccharide is applied to the base paper.
[3] The method according to [1] or [2], wherein the polysaccharide contains starch and the antibacterial agent contains a surfactant.
[4] The method according to any one of [1] to [3], wherein the coating solution is applied by a pounding method or a film transfer method.
[5] Antibacterial paper having a layer on the base paper containing an antibacterial agent and polysaccharides.
[6] The antibacterial paper described in [5], wherein the weight ratio of the antibacterial agent to the polysaccharide is 2:1 to 1:200.
[7] The antibacterial paper according to [5] or [6], wherein the polysaccharide contains starch and the antibacterial agent contains a surfactant.
[8] The antibacterial paper according to any one of [5] to [7], which is a fine paper that does not have a pigment coating layer.
[9] Antimicrobial paper possessing antiviral activity, as described in any of [5] to [8].

According to the present invention, excellent antibacterial paper and a method for producing the same are provided.

This invention relates to antibacterial paper having an antibacterial layer provided on a base paper. The antibacterial paper according to this invention has a transparent antibacterial layer containing an antibacterial agent and polysaccharides on the base paper, and is obtained by applying a surface treatment liquid (coating liquid) to the base paper.

The antibacterial paper according to the present invention possesses antibacterial properties, and its antibacterial activity value, measured according to the antibacterial test method of JIS L1902, is approximately 3.0 or higher. However, since antibacterial testing measures the extent to which bacterial growth can be suppressed, if the sample itself has antibacterial (bactericidal) properties, the inoculated bacteria may not grow, resulting in a low antibacterial activity value. Therefore, in this invention, antibacterial properties are considered to exist even if the number of viable bacteria immediately after inoculation in the antibacterial test is less than 20.

In a preferred embodiment, the antibacterial paper according to the present invention possesses not only antibacterial properties but also antiviral activity. Preferably, the antibacterial paper according to the present invention has an antiviral activity value (Mv) of approximately 2.0 or higher, as measured according to JIS L1922, and may have an antiviral activity value of 2.5 or higher, 3.0 or higher, or 3.5 or higher.

In this invention, a layer containing an antibacterial agent and polysaccharides is provided on the base paper. The amount of coating can be adjusted, for example, by adjusting the viscosity of the surface treatment solution or the coating speed. Specifically, by lowering the viscosity using a surfactant, the coating solution can penetrate more easily into the paper, or by applying it at high speed, the coating solution can remain on the paper surface. Furthermore, in one embodiment of this invention, by coating the paper surface with polysaccharides such as starch, not only the surface strength but also the stiffness of the paper can be improved. Additionally, the interlayer strength can be improved by the appropriate penetration of the polysaccharides into the paper layers.

The antibacterial paper obtained in this invention can be used as a product without limitation for various applications. For example, it can be used as printing paper, writing paper, book paper, newsprint, packaging paper, tissue paper, base paper for pigment-coated paper, various information recording papers such as inkjet recording, thermal recording, and carbonless copying, and their base papers. Considering its use as printing paper, the post-print gloss of the antibacterial paper according to this invention is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. On a 10-point scale, 4 or higher is considered good, and 7 or higher is considered particularly good. Furthermore, from the viewpoint of suppressing problems during printing, the interlayer strength in the MD direction is preferably 90 gf/15 mm or more, more preferably 100 gf/15 mm or more, and even more preferably 110 gf/15 mm or more.

The basis weight of the antibacterial paper according to the present invention is not particularly limited, but can be, for example, 25 to 500 g/ ^m² , 35 to 300 g/ ^m² , or 40 to 250 g/m². In other embodiments, the basis weight of the antibacterial paper may be, for example, 45 to 100 g/ ^m² , 50 to 90 g/ ^m² , or 55 to 80 g/ ^m² .

The antibacterial paper according to the present invention preferably has a specific air permeability of 1.4 or higher, and more preferably 3.0 or higher or 5.0 or higher. Furthermore, the antibacterial paper according to the present invention preferably has a tear length in the CD direction of 3.0 km or higher, and more preferably 4.0 km or higher or 4.5 km or higher. If the specific air permeability or tear length is too low, paper tearing or other problems may occur during the manufacturing of the antibacterial paper.

The ash content in the antibacterial paper according to the present invention can be set as appropriate, but for example, it can be 0.1% by weight or more and 40% by weight or less, and preferably 5% by weight or more and 30% by weight or less. If the ash content is higher than 30% by weight, the bonding between fibers may be inhibited by the paper filler, which may result in insufficient stiffness and strength of the paper. The ash content is measured in accordance with JIS-P8252.

In one embodiment, the antibacterial paper according to the present invention is an uncoated paper that does not have a pigment coating layer, and may be an uncoated fine paper.
Base paper
The base paper used in the present invention comprises pulp raw materials. There are no particular restrictions on the pulp raw materials used; in addition to wood pulp, non-wood pulps such as bamboo pulp, linter pulp, hemp, bagasse, kenaf, esparto grass, and straw, semi-synthetic fibers such as rayon and acetate, and synthetic fibers such as polyolefins, polyamides, and polyesters can be used. Specifically, mechanical pulp (MP), deinked pulp (DIP, also called recycled paper pulp), hardwood kraft pulp (LKP), and softwood kraft pulp (NKP), which are commonly used as papermaking raw materials, can be suitably used, and one or more of these may be blended as appropriate. These pulps may be unbleached pulp or bleached pulp that has been bleached by one or more means. Examples of mechanical pulps include wood pulp (GP), refined wood pulp (RGP), thermomechanical pulp (TMP), chemothermetic pulp (CTMP), chemigland pulp (CGP), and semi-chemical pulp (SCP). Deinking pulp can be made from sorted waste paper such as fine paper, medium-grade paper, lower-grade paper, newspapers, flyers, and magazines, or unsorted waste paper containing a mixture of these, or from office waste paper including copy paper, thermal paper, and carbonless paper, as well as confidential waste paper and paper cups; there are no particular limitations. Cellulose nanofibers, cellulose nanofibrils, microfibril cellulose, microcrystalline cellulose, and cellulose powder can also be used. There are no particular limitations on the base paper used in this invention; for example, copy paper, newspaper, medium-grade paper, liners, and core paper can be used. In one embodiment, the base paper according to the present invention is fine paper, and only chemical pulp is used as the pulp for the base paper.

Various internal additives may be added to the base paper used in this invention, as long as they do not hinder the effects of the invention. While not limited to the above, internal additives may include: inorganic chemicals such as aluminum sulfate, polyaluminum chloride, sulfuric acid, hydrochloric acid, sodium hydroxide, and sodium bicarbonate; organic chemicals such as polyacrylamide polymers, polyvinyl alcohol polymers, oxidized starch, esterified starch, cationized starch, various other modified starches, styrene-butadiene copolymers, latex, and vinyl acetate adhesives; cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose; internal paper strength enhancers such as urea-formaldehyde resin and melamine-formaldehyde resin; internal sizing agents such as rosin-based sizing agents, AKD-based sizing agents, ASA-based sizing agents, petroleum-based sizing agents, and neutral rosin-based sizing agents; aluminum sulfate, yield enhancers, yield boosters, UV inhibitors, fade inhibitors, water drainage enhancers, coagulants, bulking agents, pH adjusters, slime control agents, colorants (dyes, pigments), and fluorescent dyes. Furthermore, various cellulose nanofibers and fine cellulose fibers may be used as internal additives.

The base paper used in this invention can be filled with commonly used fillers, for example, one or more inorganic or organic fillers can be used. Examples of inorganic fillers include heavy calcium carbonate, light calcium carbonate, calcium sulfite, gypsum, talc, kaolin, engineered kaolin, calcined kaolin, white carbon, amorphous silica, delaminated kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, recycled inorganic particles from papermaking sludge and deinking floss, etc. Examples of organic fillers include urea-formaldehyde resin, polyvinyl chloride resin, polystyrene resin, urea/formaldehyde resin, melamine resin, styrene/butadiene copolymer resin, phenolic resin, and hollow plastic particles.

The base paper of this invention can be manufactured by known methods. For example, the pulp, prepared by mixing the above raw materials, is appropriately diluted, and after removing foreign matter with a screen or cleaner as needed, it is sprayed from the headbox of the paper machine onto the papermaking wire to form wet paper. The base paper of this invention can be manufactured using various paper machines, such as long-screen, cylinder-screen, multi-cylinder cylinder-screen, short-screen, and twin-wire paper machines. Examples of twin-wire paper machines include gap formers and on-top formers. In addition, the base paper may be manufactured using crescent formers or Yankee dryer type paper machines. The conditions in the pressing and drying processes after papermaking can be adjusted as appropriate.

Furthermore, the papermaking conditions for the base paper can be either neutral or acidic. Specifically, in this invention, the pH of the paper pulp during papermaking is preferably 3.0 to 9.0, and more preferably 4.0 to 8.0.

Coating (coating process)
In this invention, in order to impart antibacterial properties, a layer (antibacterial layer) containing at least an antibacterial agent and a polysaccharide is provided on the base paper. In this invention, the amount of antibacterial layer applied (coating amount) is determined appropriately according to the surface strength required of the paper, etc., and is not particularly limited, but for example, it can be in the range of 0.1 to 10 g/m² on ^both sides, preferably 0.5 to 5.0 g/ ^m² , and more preferably 1.0 to 3.0 g/ ^m² . If the coating amount is excessive, the absolute amount of moisture increases, which increases the drying load and may lead to drying failure.

The weight ratio of the antibacterial agent to the polysaccharide can be, for example, 2:1 to 1:200, preferably 1:1 to 1:150, and may also be 1:2 to 1:100 or 1:3 to 1:50.
(Antibacterial agent)
In this invention, an antibacterial agent is applied to the base paper, but there are no restrictions on the antibacterial agent used; one antibacterial agent may be used alone, or two or more antibacterial agents may be used in combination. In this invention, an antibacterial agent means a drug that can impart antibacterial properties, and commercially available antibacterial agents, disinfectants, etc., can be used. For example, a drug that has not only antibacterial properties but also antiviral properties can be used as an antibacterial agent.

Preferred antimicrobial agents include surfactant-based antimicrobial agents, such as nonionic surfactants, cationic surfactants, and anionic surfactants, which can be used without limitation. Examples of nonionic surfactant antimicrobial agents include glycerin fatty acid esters and polyoxyethylene alkyl ethers; examples of cationic surfactant antimicrobial agents include ethoxysilane-based and alkyl quaternary ammonium salts, alkyldimethylbenzylammonium chloride, benzalkonium chloride, and benzethonium chloride; examples of anionic surfactant antimicrobial agents include linear alkylbenzene sulfonate sodium; and examples of amphoteric surfactant antimicrobial agents include alkyldiaminoethylglycine chloride and alkylpolyaminoethylglycine. Examples of commercially available surfactant-based antibacterial agents include Kokinstar D-125, Poem DL-100, Lipocard CB-50, Sanizol B-50, Emulgen 106, Amhitol 20N, Neoperex G-15, Amolden GR-150, Amolden V-500HP, Poem M-200, Nikkanon RB, Nikkanon RB-40 (quaternary ammonium salt), QB-2500, QC-2500, Lipocard 210-80E, Botanicle (registered trademark), REZOMA, Air Heal, Karaseed, Keisanit (registered trademark), Best Clean Mind, Mydol 10, Mydol 12, Kotamin 24P, Kotamin 86W, NS Soap, OS Soap, and HYP-KK171.

In this invention, non-surfactant organic antibacterial agents and inorganic antibacterial agents can be used, and hybrid antibacterial agents combining organic and inorganic antibacterial agents can also be used.

Examples of organic antimicrobial agents include ethylene oxide, glutaraldehyde, orthophthalaldehyde, cresol, chitosan, hinokitiol, mustard extract, iodine-based agents such as povidone-iodine, biguanide-based agents such as chlorhexidine, dye-based agents such as acrinol, polyphenol-based, benzimidazole-based, phthalimide-based, isotisolone-based, pyridine-based, and nitrile-based antimicrobial agents.

As inorganic antibacterial agents, for example, silver-based antibacterial agents, copper-based antibacterial agents, or zinc-based antibacterial agents can be used, and silver-based antibacterial agents are preferred from the viewpoint of safety. There are no particular restrictions on silver-based antibacterial agents as long as they are inorganic compounds supporting silver ions, but specifically, examples include inorganic adsorbents such as activated carbon, activated alumina, and silica gel, and inorganic ion exchangers such as zeolite, hydroxyapatite, zirconium phosphate, titanium phosphate, and potassium titanate. As copper-based antibacterial agents, there are no particular restrictions on inorganic compounds supporting copper ions, but specifically, examples include inorganic adsorbents such as activated carbon, activated alumina, and silica gel, and inorganic ion exchangers such as zeolite, hydroxyapatite, zirconium phosphate, titanium phosphate, and potassium titanate. As zinc-based antibacterial agents, there are no particular restrictions on inorganic compounds supporting zinc ions, but specifically, examples include inorganic adsorbents such as activated carbon, activated alumina, and silica gel, and inorganic ion exchangers such as zeolite, hydroxyapatite, zirconium phosphate, titanium phosphate, and potassium titanate. When using zeolite-based antibacterial agents, antibacterial zeolites obtained by substituting some of the ion-exchangeable metals in the zeolite with at least one metal selected from silver, copper, and zinc are preferably used.

Examples of commercially available inorganic antibacterial agents include Silver Bullet, Cozy Pack Air, AG Alpha® CF-01, AG Alpha® CF-04, Novalon, Kesmon, Allerimove, MP-102SVC13, Silver Ace, Zeomic, Lock-3, and Ion Pure.

(polysaccharide)
In this invention, a surface coating solution containing polysaccharides such as starch as an adhesive (binder) is applied to the base paper, thereby providing surface strength, water resistance, printability, and other properties.

Regarding polysaccharides, there are no particular limitations as long as they can be used as an adhesive, and examples include starch, cellulose, chitin, glycogen, agarose, and pectin. For starch, for example, corn starch, tapioca starch, potato starch, wheat starch, and rice starch can be suitably used.

Furthermore, in this invention, starch that has been modified in various ways by known methods may be used. Modification methods include, for example, enzymatic denaturation using α-amylase, esterification, cationization, acetylation, aldehyde formation, and hydroxyethylation. Esterification methods include acetic acid esterification and phosphate esterification, while etherification methods include carboxyether formation and hydroxyether formation. To fully exhibit the aging stability improvement effect of this invention, it is preferable to use self-modified starch, which is made from acetylated tapioca starch or similar raw materials and modified to reduce viscosity within the paper mill. In particular, it is preferable to use APS-modified starch, which is thermochemically modified by adding ammonium persulfate (APS) as an oxidizing agent, or enzymatically modified starch hydrolyzed using α-amylase. Self-modified starch, which is modified within the paper mill, allows for easy viscosity adjustment at the manufacturing site and is also cost-effective.

The adhesive used for surface treatment is not particularly limited as long as it contains at least polysaccharides. Besides starch, other adhesives may be used, either alone or in combination of two or more. For example, cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, and cellulose nanofibers, fine cellulose fibers, guar gum, xanthan gum, gum arabic, dextrin, alginic acid, hyaluronic acid, xylan, glucomannan, carrageenan, polyacrylamide, polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, latex, styrene-butadiene copolymers, polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, polyvinyl chloride, polyvinylidene chloride, and polyacrylic acid esters may be used. In this invention, it is preferable that the proportion of polysaccharides such as starch in the adhesive within the antibacterial layer is 50% or more. More preferably, it is 80% or more. If it is less than 50%, the viscosity of the surface treatment liquid will decrease, potentially leading to adverse effects such as deterioration of strength and hardness, and the cost will also increase.

In this invention, a sizing agent may be incorporated into the antibacterial layer to enhance sizing properties. When using a sizing agent, various types can be used; for example, surface sizing agents such as styrene-based sizing agents, olefin-based sizing agents, acrylate-based sizing agents, styrene-acrylic sizing agents, and cationic sizing agents may be used. When using a surface sizing agent, the solid content concentration in the surface treatment solution is preferably 0.05 to 5% by weight, and more preferably 1 to 3% by weight.

Furthermore, the surface treatment liquid (coating liquid) of the present invention may contain various auxiliary agents as needed, such as dispersants, thickeners, water-retaining agents, defoaming agents, water-resistant agents, colorants, and conductive agents.
The device (coater) used to apply the surface treatment solution is not particularly limited, and any known device can be used. Suitable coaters include pound-type size presses, film transfer type gate roll coaters and lot metering size presses, as well as blade coaters, spray coaters, and curtain coaters. Furthermore, so-called calender sizing can be performed using an applicator or spray in a calender or supercalender. Additionally, the coating solution can be sprayed in front of a Yankee dryer.

In this invention, another layer may be provided in addition to the layer containing polysaccharides and antibacterial agents. For example, a layer containing polysaccharides and antibacterial agents may be provided after a clear coating layer or a pigment coating layer has been applied.

After applying the clear coating layer to the base paper, the paper may be fed through a publicly known finishing device, such as a supercalender, gloss calender, soft calender, or high-temperature soft nip calender, for product finishing, or it may be left untreated or bypassed.

The present invention will be illustrated below with specific examples, but the present invention is not limited to these examples. In this specification, unless otherwise specified, "parts" refers to "parts by weight," and "%" refers to "weight percent," with numerical ranges including their endpoints.

Manufacturing of antibacterial paper (1) Samples 1-14
600 g of coating solution was prepared by mixing the raw materials in the following proportions. Specifically, the raw materials were mixed with water (ion-exchanged water) at a liquid temperature of 40°C in a 1 L container, and the mixture was stirred with a spatula for 3 minutes to prepare the coating solution.

Next, both sides of a base paper for high-quality paper (basis weight: approximately 60 g/ ^m² , neutral paper) that had not been coated with either pigment or clear coating were coated with each coating solution using a Hishira copier (One-Step Processor S-III, Daito Co., Ltd.), and then air-dried overnight to produce high-quality paper.
(2) Samples 15-17
Coating solutions 13 to 15 were prepared by adding an antibacterial agent and a surface sizing agent to 2000 kg of a 4% starch solution in the following proportions.

Next, both sides of a base paper for high-quality paper (basis weight: 65.1 g/ ^m² , neutral paper) that had not been coated with pigment or clear coating were coated with each coating solution using a gate roll coater to produce high-quality paper.

The following evaluations were conducted on the high-quality paper produced for antibacterial purposes . For the evaluation, the paper was left to stand overnight in a constant temperature and humidity chamber (25°C, 50% humidity) to regulate its humidity before being used.
(1) Application amount The basis weight was measured before and after application, and the application amount (g/ ^m² ) was calculated from these basis weights.
(2) Post-print gloss The prepared high-quality paper was printed using an RI printing press (manufactured by Akira Seisakusho) with an ink volume of 1.5 cc (Beni TV20, manufactured by DIC Corporation) and a printing speed of 100 rpm. After drying overnight in a forced-air dryer, the ink density of the printed area was measured using a Macbeth densitometer (RD918, KOLLMORGEN) and a 75° gloss meter (GM-26PRO/TOUCH, Murakami Color Technology Laboratory) to evaluate the post-print gloss. 30% or higher is considered good, and 65% or higher is considered particularly good.
(3) Interlaminar strength A 20cm x 1.5cm sample was prepared using a punching machine (manufactured by Kumagai Riki Kogyo Co., Ltd.), and the interlaminar strength was measured using a universal testing machine (RTG-1210, Orientec Co., Ltd.). An interlaminar strength of 90 gf/15 mm or higher in the MD direction is considered good, and 100 gf/15 mm or higher is considered particularly good.
(4) Relative Air Permeability The air permeability (air resistance) of the prepared high-quality paper was measured using the Ogakuen-type air permeability and smoothness tester (manufactured by Asahi Seiko Co., Ltd.) in accordance with JAPAN TAPPI No. 5. The relative air permeability was calculated by dividing the value of air permeability by the basis weight of each sample. A relative air permeability of 1.4 or higher is considered good, and 3.0 or higher is considered particularly good.
(5) Fracture Length A 20cm x 1.5cm sample was prepared using a punching machine (manufactured by Kumagai Riki Kogyo Co., Ltd.), and the tensile strength was measured using a tensile strength tester (horizontal tensile tester, manufactured by Kumagai Riki Kogyo Co., Ltd.) in accordance with JIS P-8113. The fracture length was determined by dividing the tensile strength value by the basis weight of each sample. A fracture length of 4.0km or more in the CD direction is considered good, and 4.5km or more is considered particularly good.
(6) Antibacterial activity
Based on the antimicrobial testing method of JIS L1902, a 2.8 cm × 2.8 cm sample of high-quality paper was used as the test piece. 0.2 mL of a test solution containing Staphylococcus aureus (test bacterial concentration: 1.0 × ^10⁵ to 3.0 × ^10⁵ CFU/mL) was inoculated onto the surface of the test piece and incubated at 37°C for 18 to 24 hours. Immediately after inoculation and after incubation, 20 mL of wash solution was added to wash the test bacteria from the test piece, and the number of viable bacteria in the wash solution was measured. The antimicrobial activity value (A) was calculated using the following formula. As a control sample, washed cotton cloth (cotton 3-1) was used (JIS L0803).

(7) Antiviral activity For samples 1, 3, 4, 7, 16, and 17, the antiviral activity value (Mv) was measured in accordance with JIS L1922:2016. The weight of the sheet used in the test was 0.4 g, and influenza virus (H3N2, ATCC VR-1679) was used as the test virus.

As is clear from the table, simply coating a paper substrate with starch did not impart antibacterial properties (Sample 1), and simply coating it with an antibacterial agent resulted in low paper strength and poor gloss (printability) after printing (Sample 2).

On the other hand, by using an antibacterial agent and starch in combination based on the present invention, paper with sufficient strength while possessing antibacterial properties was obtained. Furthermore, the printability of certain antibacterial agents was improved when combined with starch (Samples 3-7, 12, 14).

Furthermore, samples 3, 4, 7, 16, and 17 were confirmed to possess excellent antiviral activity.

Claims (9)

A method for producing antibacterial paper , comprising applying an antibacterial agent and a polysaccharide to a base paper, wherein the base paper is high-quality paper . The method according to claim 1, wherein a coating solution containing an antibacterial agent and a polysaccharide is applied to a base paper. The method according to claim 1 or 2, wherein the polysaccharide contains starch and the antibacterial agent contains a surfactant. The method according to any one of claims 1 to 3, wherein the coating solution is applied by a pounding method or a film transfer method. Antibacterial paper having a layer containing an antibacterial agent and polysaccharides on the base paper, and the base paper being high-quality paper . The antibacterial paper according to claim 5, wherein the weight ratio of the antibacterial agent to the polysaccharide is 2:1 to 1:200. The antibacterial paper according to claim 5 or 6, wherein the polysaccharide contains starch and the antibacterial agent contains a surfactant. The antibacterial paper according to any one of claims 5 to 7, which is a high-quality paper without a pigment coating layer. An antibacterial paper according to any one of claims 5 to 8, possessing antiviral activity.