JP7744172B2 - Antibacterial paper and its manufacturing method - Google Patents

Description

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

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

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

Generally, a binder such as starch is applied to the surface of paper to improve its sizing ability, printing properties, surface strength, and other characteristics. The inventors investigated the external application of an antibacterial agent to paper to impart antibacterial properties to the paper, and found that when an antibacterial agent is incorporated into a coating solution containing additives such as a sizing agent, thickening and aggregation can occur depending on the combination of the antibacterial agent and the sizing agent contained in the coating solution, making it difficult to produce antibacterial paper using external application.

In light of this situation, the objective of the present invention is to provide a technology for producing excellent antibacterial paper by coating it with an antibacterial agent.

The present invention includes, but is not limited to, the following inventions.
[1] A method for producing antibacterial paper, comprising applying a clear coating liquid containing a cationic antibacterial agent and starch to base paper.
[2] The method according to [1], wherein the starch contains oxidized starch.
[3] The method according to [1] or [2], wherein the antibacterial agent contains a surfactant.
[4] Antibacterial paper having a clear coating layer containing a cationic antibacterial agent and starch on a base paper.
[5] The antibacterial paper according to [4], which is a wood-free paper that does not have a pigment coating layer.
[6] The antibacterial paper according to [4] or [5], wherein the starch contains oxidized starch.
[7] The antibacterial paper according to any one of [4] to [6], wherein the antibacterial agent contains a surfactant.

The present invention provides excellent antibacterial paper and a method for producing the same.

The present invention relates to antibacterial paper having an antibacterial layer formed on base paper. The antibacterial paper of the present invention has a clear coating layer containing a cationic antibacterial agent and starch on the base paper, and is obtained by applying a surface treatment liquid (coating liquid) to the base paper.

The antibacterial paper of the present invention has antibacterial properties, with an antibacterial activity value of approximately 3.0 or higher as measured based on the antibacterial test method of JIS L1902. However, since the antibacterial test measures the extent to which bacterial growth can be inhibited, if the sample originally has bacteriostatic (bactericidal) properties, the inoculated bacteria may not grow and the antibacterial activity value may be low. Therefore, in the present invention, antibacterial properties are considered to be present even if the number of viable bacteria immediately after inoculation in the antibacterial test is less than 20.

In the present invention, a layer containing an antibacterial agent and starch is provided on the base paper, and the amount applied can be adjusted, for example, by adjusting the viscosity of the surface treatment solution or the application speed. That is, by lowering the viscosity using a surfactant or the like, it is possible to make it easier for the application solution to penetrate into the paper, or by applying it at high speed, it is possible to make the application solution remain on the paper surface. Furthermore, in one embodiment of the present invention, by applying a polysaccharide such as starch to the surface of the paper, not only the surface strength of the paper but also its stiffness is improved, and the polysaccharide can also penetrate appropriately into the paper layers, thereby improving interlayer strength.

The antibacterial paper obtained by the present invention can be used as a product without any restrictions for a variety of applications, such as printing paper, writing paper, book paper, newsprint, packaging paper, tissue paper, base paper for pigment-coated paper, various information recording paper such as inkjet recording, thermal recording, and carbonless copying, and the base paper for these applications. Considering its use as printing paper, the post-printing gloss of the antibacterial paper of the present 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 more is good, and 7 or more is particularly good. Furthermore, from the perspective of suppressing printing problems, the interlaminar 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/m ² , 35 to 300 g/m ² , or 40 to 250 g/m 2. In other embodiments, the basis weight of the antibacterial paper may be, for example, 45 to 100 g/m ² , 50 to 90 g/m ² , or 55 to 80 g/m ² .

The antibacterial paper of the present invention preferably has a relative air permeability of 1.4 or more, more preferably 3.0 or more or 5.0 or more. Furthermore, the antibacterial paper of the present invention preferably has a CD breaking length of 3.0 km or more, more preferably 4.0 km or more or 4.5 km or more. If the relative air permeability or breaking length is too low, there is a risk of paper tearing during the production of the antibacterial paper.

The ash content of the antibacterial paper of the present invention can be set as appropriate, but can be, for example, between 0.1% and 40% by weight, and preferably between 5% and 30% by weight. If the ash content is higher than 30% by weight, the filler in the paper may inhibit the bonding between fibers, resulting in a lack of stiffness and strength of the paper. The ash content in paper is measured in accordance with JIS-P8252.

In one embodiment, the antibacterial paper according to the present invention is uncoated paper that does not have a pigment coating layer, and may be uncoated wood-free paper.
Base paper
The base paper used in the present invention comprises a pulp raw material. There are no particular limitations on the pulp raw material used, and 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 polyolefin, polyamide, and polyester can be used. Specifically, materials commonly used as raw materials for papermaking, such as mechanical pulp (MP), deinked pulp (DIP, also known as recycled paper pulp), hardwood kraft pulp (LKP), and softwood kraft pulp (NKP), can be suitably used, and one or more of these can be used in combination as appropriate. These pulps can be unbleached pulp, which is not bleached, or bleached pulp, which has been bleached by one or several methods. Examples of mechanical pulp include groundwood pulp (GP), refined groundwood pulp (RGP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), chemi-ground pulp (CGP), and semi-chemical pulp (SCP). Deinked pulp is not particularly limited, and may be made from sorted waste paper such as fine paper, medium-grade paper, low-grade paper, newspaper, flyers, and magazines, or unsorted waste paper containing these, or office waste paper including copy paper, thermal paper, and carbonless paper, confidential waste paper, and paper cups. Cellulose nanofibers, cellulose nanofibrils, microfibril cellulose, microcrystalline cellulose, and cellulose powder may also be used. The base paper used in the present invention is not particularly limited, and examples include copy paper, newsprint, medium-grade paper, liner, and medium-strength paper. In one embodiment, the base paper used in 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 impair the effects of this invention. Internal additives include, but are not limited to, inorganic chemicals such as aluminum sulfate (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, and various modified starches, styrene-butadiene copolymers, latex, and vinyl acetate adhesives; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; internal paper strength enhancers such as urea-formalin resin and melamine-formalin resin; internal sizing agents such as rosin sizing agents, AKD sizing agents, ASA sizing agents, petroleum sizing agents, and neutral rosin sizing agents; aluminum sulfate, retention aids, retention aids, UV inhibitors, anti-fading agents, drainage aids, coagulants, bulking agents, pH adjusters, slime control agents, colorants (dyes, pigments), and fluorescent dyes. Various cellulose nanofibers and microfiber cellulose may also be used as internal additives.

The base paper used in the present invention can be filled with commonly used fillers, such as one or more inorganic or organic fillers. 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, and inorganic particles recycled from papermaking sludge and deinking froth. Examples of organic fillers include urea-formalin resin, vinyl chloride resin, polystyrene resin, urea/formalin resin, melamine resin, styrene/butadiene copolymer resin, phenolic resin, and hollow plastic particles.

The base paper of the present invention can be made by known methods. For example, a stock mixture of the above-mentioned raw materials is appropriately diluted, and after removing foreign matter with a screen or cleaner as necessary, the mixture is sprayed from the headbox of a papermaking machine onto a papermaking wire to form a wet paper. The base paper of the present invention can be produced using various papermaking machines, such as Fourdrinier, cylinder, multi-cylinder, short-wire, and twin-wire papermaking machines. Examples of twin-wire papermaking machines include gap formers and on-top formers. Base paper may also be produced using crescent former and Yankee dryer papermaking machines. The conditions for the pressing and drying processes after papermaking can be adjusted as appropriate.

The conditions for making the base paper may be either neutral or acidic. Specifically, in the present invention, the pH of the stock during papermaking is preferably 3.0 to 9.0, and more preferably 4.0 to 8.0.

Clear Coating Layer In the present invention, a clear coating layer (antibacterial layer) containing at least a cationic antibacterial agent and starch is provided on the base paper to impart antibacterial properties. The coating amount (coating weight) of the antibacterial layer in the present invention is not particularly limited, but can be, for example, in the range of 0.1 to 10 g/ ^m² on both sides, preferably 0.5 to 5.5 g/ ^m² , and more preferably 1.0 to 3.0 g/ ^m² . If the coating weight is too high, the absolute amount of moisture increases, which increases the drying load and may make drying more likely to occur.

(Antibacterial agent)
In the present invention, an antibacterial agent is applied to the base paper, and a cationic antibacterial agent is used as the antibacterial agent. The cationic antibacterial agent may be used alone or in combination of two or more antibacterial agents. In the present invention, the antibacterial agent refers to an agent that can impart antibacterial properties, and commercially available antibacterial agents, bactericides, disinfectants, etc. can be used. For example, an agent that has not only antibacterial properties but also antiviral properties can be used as the antibacterial agent.

Examples of cationic antibacterial agents include ethoxysilanes, alkyl quaternary ammonium salts, alkyldimethylbenzylammonium chloride, benzalkonium chloride, and benzethonium chloride, with alkyl quaternary ammonium salts, alkyldimethylbenzylammonium chloride, and benzalkonium chloride being preferred. Commercially available products include Sanizol B-50, Lipocard CB-50, and Corkinstar D-125.

In the present invention, organic or inorganic antibacterial agents can be used, as long as the effects of the present invention are not impaired, and hybrid antibacterial agents consisting of organic and inorganic antibacterial agents can also be used.

Examples of organic antibacterial agents include ethylene oxide, glutaraldehyde, ortho-phthalaldehyde, cresol, chitosan, hinokitiol, mustard extract, iodine-based agents such as povidone-iodine, biguanides such as chlorhexidine, dye-based agents such as acrinol, polyphenol-based, benzimidazole-based, phthalimide-based, isothisolone-based, pyridine-based, and nitrile-based antibacterial agents.

Inorganic antibacterial agents include, for example, silver-based antibacterial agents, copper-based antibacterial agents, and zinc-based antibacterial agents, with silver-based antibacterial agents being preferred from the standpoint of safety. Silver-based antibacterial agents are not particularly limited as long as they are inorganic compounds that support silver ions. Specific 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. Copper-based antibacterial agents are not particularly limited as long as they are inorganic compounds that support copper ions. Specific 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. Zinc-based antibacterial agents are not particularly limited as long as they are inorganic compounds that support zinc ions. Specific 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 a zeolite-based antibacterial agent, it is preferable to use an antibacterial zeolite obtained by replacing some of the ion-exchangeable metals in zeolite with at least one metal selected from silver, copper, and zinc.

Commercially available inorganic antibacterial agents include, for example, Silver Bread, Cozy Pack Air, AG Alpha (registered trademark) CF-01, AG Alpha (registered trademark) CF-04, Novalon, Kesmon, Allerimub, MP-102SVC13, Silver Ace, Zeomic, Lock-3, and Ion Pure.

(starch)
In the present invention, the above antibacterial agent and starch are used in combination. In the present invention, starch is applied to base paper as a surface strength agent together with the cationic antibacterial agent, which can impart surface strength, water resistance, printability, etc. to the paper.

When applying an antibacterial agent and starch together, the solids weight ratio of the antibacterial agent to the starch can be, for example, 2:1 to 1:200, preferably 1:1 to 1:150, or alternatively 1:2 to 1:100 or 1:3 to 1:50.

In addition, starch modified by various known methods may be used in the present invention. Modification methods include, for example, enzyme modification using α-amylase, esterification, cationization, acetylation, aldehyde conversion, and hydroxyethylation. Esterification includes acetate esterification and phosphate esterification, while etherification includes carboxy etherification and hydroxy etherification. To maximize the retrogradation stability-improving effect of the present invention, it is preferable to use self-modified starch that has been modified in a paper mill using acetylated tapioca starch or other raw materials to reduce its viscosity. In particular, APS-modified starch that has been thermochemically modified by adding ammonium persulfate (APS) as an oxidizing agent, or enzyme-modified starch that has been hydrolyzed using α-amylase is preferred. Self-modified starch that has been modified in a paper mill allows for easy viscosity adjustment at the manufacturing site and is also cost-effective.

In addition to starch, adhesives used in surface treatment may include, for example, cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, and cellulose nanofibers, microfiber cellulose, guar gum, xanthan gum, gum arabic, dextrin, alginic acid, hyaluronic acid, xylan, glucomannan, carrageenan, polyacrylamide, polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, and modified alcohols such as acetoacetylated polyvinyl alcohol, latex, styrene-butadiene copolymers, polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, polyvinyl chloride, polyvinylidene chloride, and polyacrylic esters. These may be used alone or in combination of two or more. In the present invention, polysaccharides such as starch preferably account for 50% or more of the adhesive in the antibacterial layer, more preferably 80% or more. If the proportion is less than 50%, the viscosity of the surface treatment solution may decrease, resulting in adverse effects such as reduced strength and stiffness, and increased costs.

In the present invention, various sizing agents can be used in the clear coating layer. For example, surface sizing agents such as styrene-based sizing agents, olefin-based sizing agents, acrylate-based sizing agents, styrene-acrylic sizing agents, cationic sizing agents, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA) may be used. When a surface sizing agent is used, the solids concentration in the surface treatment solution is preferably 0.05 to 5% by weight, and more preferably 1 to 3% by weight.

The weight ratio of the antibacterial agent to the surface sizing agent can be, for example, 99:1 to 1:99, preferably 90:10 to 10:90, or 80:20 to 20:80 or 70:30 to 30:70.

Furthermore, the surface treatment liquid (coating liquid) of the present invention may contain various auxiliary agents, such as dispersants, thickeners, water-retaining agents, antifoaming agents, water-resistant agents, colorants, and conductive agents, as needed.
The device (coater) for applying the surface treatment liquid is not particularly limited, and known devices can be used. Examples of coaters that can be used include pond-type size presses, film-transfer type gate roll coaters and lot metering size presses, as well as blade coaters, spray coaters, and curtain coaters. Also, so-called calendar sizing can be performed, in which application is performed using an applicator or spray in a calendar or super calendar. Furthermore, the coating liquid can be sprayed and applied in front of the Yankee dryer.

In the present invention, other layers may be provided in addition to the clear coating layer, i.e., for example, a pigment coating layer may be provided in addition to the layer containing the polysaccharide and the antibacterial agent.
After the clear coating layer is provided on the base paper, the paper may be passed through a known finishing device, such as a super calender, gloss calender, soft calender, or high-temperature soft nip calender, to finish the product, or it may be left untreated or bypassed.

The present invention will be illustrated below with specific examples, but it is not intended that the present invention be limited to these examples. In each example and comparative example, unless otherwise specified, "parts" and "%" are by weight, and numerical ranges are stated as including their endpoints.

Experiment 1. Preparation and Evaluation of Clear Coating Solution: A coating solution was prepared by adding an antibacterial agent to a starch solution in a 500 mL container. Specifically, the antibacterial agent shown in the table below was added to a mixture of 300 g of starch solution (Nihon Shokuhin Kako Co., Ltd., Nisshoku MS3800, solids content: 4.0%) and 1.2 g of antifoaming agent (Kurita Water Industries, Ltd., Kuresu 480, concentration: 1%), and the mixture was stirred with a spatula for 3 minutes to prepare the coating solution.

The foamability of the prepared coating liquid was evaluated. Specifically, 200 mL of the coating liquid was gently poured into a 2 L measuring cylinder, and then 0.1 kg/ ^m2 of air was passed through a Kinoshita Glass Bowl Filter G2 (Kinoshita Rika Kogyo Co., Ltd.), and the tip was submerged under the sample liquid surface for 10 seconds. After 10 seconds, the bowl filter was removed and the foam height (the measuring cylinder scale (ml) at the top of the foam, based on a static liquid surface of 200 ml) was recorded, and the time until the foam returned to the original liquid surface was measured.

When cationic and zwitterionic antibacterial agents were added to a clear coating solution containing starch, not many bubbles were generated, and any bubbles that did occur disappeared within a short period of time. On the other hand, when anionic or nonionic antibacterial agents were added to a clear coating solution, bubbles were more likely to occur, and the bubbles that did occur were more difficult to dissipate (amount of foam after 10 minutes for Samples 1-4: 100 ml).

Experiment 2. Production and evaluation of antibacterial paper 2-1. Production of antibacterial paper A coating solution was prepared by mixing the raw materials in the following proportions. Specifically, in a 1 L container, the raw materials were mixed with water (ion-exchanged water) at a liquid temperature of 40°C, and the mixture was stirred with a spatula for 3 minutes to prepare the coating solution.

Next, each coating liquid was applied to both sides of a base paper for fine paper (basis weight: approximately 60 g/m ² ) that had neither pigment nor clear coating using a Hishira copier (One Step Processor S-III type, Daitosha), and then the paper was air-dried for 24 hours to produce fine paper.

2-2. Evaluation of antibacterial paper The produced fine paper was evaluated as follows: When evaluating, the paper was left to stand overnight in a constant temperature and humidity room (25°C, relative humidity: 50%) to condition the humidity.
(1) Basis Weight and Coating Amount The basis weight was measured before and after coating, and the coating amount (g/m ² ) was calculated from these basis weights.
(2) Interlaminar Strength A 20 cm x 1.5 cm 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.).
(3) Smoothness, Air Permeability, and Relative Air Permeability The smoothness and air permeability (air resistance) of the produced fine paper were measured using an Oken-type air permeability/smoothness tester (manufactured by Asahi Seiko Co., Ltd.) in accordance with JAPAN TAPPI No. 5. The air permeability value was also divided by the basis weight of each sample to determine the relative air permeability.
(4) Breaking Length A 20 cm x 1.5 cm sample was prepared using a punching machine (manufactured by Kumagaya Riki Kogyo Co., Ltd.), and the tensile strength was measured using a tensile strength tester (Horizontal Tensile Tester, manufactured by Kumagaya Riki Kogyo Co., Ltd.) based on JIS P-8113. The breaking length was calculated by dividing the tensile strength value by the basis weight of each sample.
(5) Antibacterial activity
Based on the antibacterial test method of JIS L1902, 2.8cm x 2.8cm wood-free paper samples were used as test specimens. 0.2mL of a test solution containing Staphylococcus aureus (test bacteria concentration: ^1.0x105 to ^3.0x105 CFU/mL) was inoculated onto the surface of the test specimen, which was then cultured at 37°C for 18 to 24 hours. Immediately after inoculation and after culture, 20mL of washout solution was added to wash out the test bacteria from the test specimen, the viable bacteria count in the washout solution was measured, and the antibacterial activity value (A) was calculated using the following formula. Washed cotton cloth (Cotton No. 3-1) was used as a control sample (JIS L0803).

When a coating liquid containing a cationic antibacterial agent and starch was used based on the present invention, there was no problem of foaming in the coating liquid, and the coating liquid could be applied smoothly.
Furthermore, when a cationic antibacterial agent and starch are used in combination according to the present invention, the interlaminar strength of fine paper is greatly improved, and according to the present invention, antibacterial paper with excellent strength can be obtained.

Claims (7)

A method for producing antibacterial paper of fine paper without a pigment coating, comprising:
The method includes applying a clear coating solution containing a cationic antimicrobial agent and oxidized starch to the base paper. The method of claim 1, wherein the oxidized starch is oxidized using ammonium persulfate as an oxidizing agent. The method of claim 1 or 2, wherein the antibacterial agent comprises a surfactant. This antibacterial paper is made of fine paper that does not have a pigment coating layer, and has a clear coating layer containing a cationic antibacterial agent and oxidized starch on the base paper. The antibacterial paper according to claim 4 , wherein the clear coating layer contains a sizing agent. The antibacterial paper according to claim 4 or 5 , wherein the antibacterial agent comprises a surfactant. The antibacterial paper according to any one of claims 4 to 6 , having a basis weight of 45 to 100 g/ ^m2 and a relative air permeability of 1.4 or more.