JP2011224477A - Method for dispersing flocculated powder of biopolymer nanoparticles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide not only a method for efficiently and perfectly dispersing biopolymer nanoparticle powder being a form of flocculated matter of biopolymer nanoparticles but also printing coated paper suitable as a paper coating biolatex binder and having excellent printability by the coating with a dispersion.SOLUTION: A water dispersion of the biopolymer nanoparticles is prepared by stirring biopolymer nanoparticle flocculated powder in water with a temperature of 60°C or below by a mechanical mixer until the average particle size measured by a dynamic light scattering method of the biopolymer nanoparticle flocculated powder becomes 400-1,000 nm and further continuing stirring for 3 min or above to obtain a dispersion wherein the average particle size measured by the dynamic light scattering method is 50-400 nm. The printing coated paper coated with a coating solution based on pigment compounded with the biopolymer nanoparticle dispersion prepared by this method is provided.

Description

  The present invention is a method for efficiently and completely dispersing agglomerated powder of biopolymer nanoparticles in water using a mechanical mixer, and a coating liquid containing a pigment containing the dispersion as a main component. It relates to coated paper for printing.

  In recent years, not only petroleum-based synthetic materials but biomaterials with excellent biodegradability have attracted attention due to increasing environmental awareness. Among them, polymers made from starch-based materials are attracting attention as adhesives.

  Patent Document 1 describes a method of preparing biopolymer nanoparticles by an extrusion process. In this case, the biopolymer, such as starch or starch derivative or a mixture thereof, is treated under high shear in the presence of a crosslinking agent. Patent Document 1 describes starch nanoparticles, an aqueous dispersion of the nanoparticles, and an extrudate prepared by the above process that swells in an aqueous medium and becomes a low viscosity dispersion after immersion. Yes. The starch particles thus obtained have a narrow particle size distribution and are described as having a particle size of less than 400 nm nanometers, in particular less than 200 nm nanometers, and are further specified by their viscosity. Patent Document 1 mentions various uses of starch nanoparticles including adhesives, but these uses have not been demonstrated and there is no specific disclosure.

  Moreover, the following uses are proposed about the biopolymer nanoparticle as described in patent document 1. FIG. That is, use as a wet end additive or paper surface sizing agent in papermaking slurry (Patent Document 2), use as a binder in pigment coated paper (Patent Document 3), use as an environmentally friendly adhesive (Patent Document 3) Patent Document 4), application as a corrugated board manufacturing adhesive (Patent Document 5).

International Publication WO00 / 69916 US Pat. No. 7,160,420 US Pat. No. 6,825,252 US Pat. No. 6,921,430 US Patent Publication 2004/0241382

  An object of the present invention is to provide a method for efficiently and completely dispersing a biopolymer nanoparticle powder in the form of an aggregate of biopolymer nanoparticles in water with a standard mixing device. Is suitable as a biolatex binder for paper coating. Moreover, the subject of this invention is providing the coating paper for printing provided with the outstanding printability by coating the said dispersion liquid.

  The agglomerated powder of biopolymer nanoparticles as described in Patent Document 1 is difficult to disperse in water completely and efficiently, and the development of technology has been desired.

  As a result of intensive studies on the above problems, the present inventor has found that the agglomerated powder of bio-nanoparticles can be well dispersed in water by a specific method, and has completed the present invention. That is, according to the present invention, a method for preparing an aqueous dispersion of biopolymer nanoparticles, the biopolymer nanoparticle aggregated powder in water at 60 ° C. or less with a mechanical mixer, the average particle diameter measured by the dynamic light scattering method Stirring until further reaching 400 to 1000 nm, further stirring for 3 minutes or more to obtain a dispersion having an average particle size measured by the dynamic light scattering method of biopolymer nanoparticles of 50 to 400 nm, Including the above method is provided.

  Furthermore, when the present inventors blended the biopolymer nanoparticle dispersion prepared by the above method as a binder in the pigment coating liquid, pigment coated paper having excellent surface strength, bending stiffness, and blister resistance at the time of off-wheel printing can be obtained. It was found that it can be obtained. That is, according to the present invention, there is provided a coated paper for printing coated with a pigment coating liquid containing the biopolymer nanoparticle dispersion prepared by the above method.

That is, the present invention includes, but is not limited to, the following inventions.
(1) A method for preparing an aqueous dispersion of biopolymer nanoparticles, in which biopolymer nanoparticle aggregates were measured by a dynamic light scattering method using a mechanical mixer in water at 60 ° C. or less to which an alkaline substance was added. Stirring until the average particle size reaches 400 to 1000 nm, and further continuing stirring for 3 minutes or more to obtain a dispersion having an average particle size of 50 to 400 nm as measured by the dynamic light scattering method of biopolymer nanoparticles. Comprising the above method.
(2) The method according to (1), wherein the mixer is a turbine mixer.
(3) The method according to (1), wherein when the agglomerated powder of biopolymer nanoparticles is mixed with water, the alkaline substance is added to adjust the dispersion to have a pH of 7.5 to 11. .
(4) When the agglomerated powder of biopolymer nanoparticles is mixed with water, 0.1 to 5% by weight of caustic soda or 0.2 to 10% by weight with respect to the dry weight of the agglomerated powder of biopolymer nanoparticles Sodium bicarbonate or 0.1 to 5% by weight sodium carbonate or 0.2 to 10% by weight ammonium hydroxide is added as the alkaline substance so that the pH of the dispersion becomes 7.5 to 11. The method according to (3), wherein the adjustment is performed.
(5) A living body produced by plasticizing a polymer mixture containing starch or a starch derivative or at least 50% by weight starch by applying a shear force in the presence of a crosslinking agent to an aggregated powder of biopolymer nanoparticles The method according to any one of (1) to (4), which is a polymer.
(6) A pigment-based coating liquid containing the biopolymer nanoparticle dispersion prepared by any of the methods (1) to (5) is applied to a base paper mainly composed of wood fibers. Coated paper.

  According to the present invention, the agglomerated powder of biopolymer nanoparticles can be efficiently and completely dispersed in water. Further, according to the present invention, a coated paper having excellent surface strength, bending stiffness, and blister resistance during off-wheel printing can be obtained.

  The inventor surprisingly prepared an aqueous dispersion efficiently by dispersing agglomerated powder of biopolymer nanoparticles (for example, starch nanoparticles described in International Publication WO 00/69916) by a specific method. Further, the present inventors have found that this dispersion of biopolymer nanoparticles is extremely suitable as an adhesive (binder) used for a pigment coating layer of coated paper.

  In general, in the manufacture of coated paper, a pigment coating layer is provided by coating a pigment coating solution on a base paper mainly composed of wood fibers. At this time, a pigment and an adhesive are blended in the pigment coating solution. The adhesive used for the coating layer of the coated paper is required to have a certain level of strength and flexibility, and to have liquid characteristics suitable for coating when blended in a coating solution. As such an adhesive, a latex obtained by synthesizing a petroleum-based raw material is widely used as a pigment coating adhesive for coated paper.

Biopolymer Nanoparticle The biopolymer used in the present invention is made from a vegetable polymer such as starch, and is obtained by applying a shearing force (share) in the presence of a crosslinking agent, as will be described later. It is. Such biopolymers have a nano-level particle size (biopolymer nanoparticles), which depend on their particle size distribution, dispersion properties, thin film formation properties, and drying behavior, but depending on the coated paper It has latex characteristics suitable as a pigment coating adhesive.

  Various biopolymers are attracting attention for various reasons. These biopolymers can be used immediately and have long-term stability. In addition, biopolymers are environmentally advantageous because they use renewable resources as raw materials instead of petroleum-based raw materials. Furthermore, the biopolymer has a low viscosity, is easy to handle and has excellent workability in the field as compared with a normal starch adhesive. Therefore, using biopolymer nanoparticles as a binder for coated paper can also contribute to energy saving. Biopolymers can then be considered as bio-type substitutes that can be used in place of petroleum-based synthetic latex used in many adhesive applications.

  Such a biopolymer is a nano-sized particle, but as a product, it may be distributed in the form of a powder in which nanoparticles are aggregated. Biopolymer nanoparticles are typically in the nanometer size range, but can also be in the micrometer size range. Biopolymer dispersions can be prepared with high solids content due to their relatively low viscosity, dispersions are stable, quick to dry, and use no solvent, an environmentally friendly medium (water) It is attracting attention because it is prepared using

  In general, natural polymers such as starch have been limited in use because of their very poor storage stability. There are two reasons for the short storage stability of aqueous biopolymer dispersions. (1) starch adhesive solutions and pastes have a strong tendency to gel or degrade and are only stable for hours or days; and (2) starch adhesives in water are resistant to fungi and bacteria It becomes a good growth medium. Therefore, as a paste (school adhesive) used in school work or the like, a white polyvinyl acetate latex that is quickly dried and has a storage stability of more than 6 months is commonly used.

  The present inventor found that biopolymer nanoparticles (for example, biopolymer latex as prepared by the method described in Patent Document 1 and International Publication WO00 / 40617) were superior to synthetic adhesives made from petroleum resources. It has been found to have adhesive properties. However, if the above two problems are not specifically solved, the stability of these biopolymers is still limited to a few days or weeks, and its application range is limited. However, for example, as shown in Patent Document 1, when nanoparticles are formed by performing a crosslinking treatment using high amylopectin-type starch (over 95% amylopectin, less than 5% amylose) as a raw material, it is stable over a long period of time. Biopolymers can be obtained. In addition, the type of starch is preferably corn starch (corn starch). It is also effective to add a suitable non-toxic biocide formulation to prevent fungal or bacterial growth.

  The combination of high amylopectin-type starch and a suitable biocide that is non-toxic (to humans) was able to achieve a 100% biodegradable adhesive with storage stability over 6 months. In order to provide a safe and 100% biodegradable adhesive (ie without gelation or degradation or microbial growth) with storage stability of more than 6 months, suitable for high amylopectin starch nanoparticles, Combination with non-toxic biocides is preferred. Furthermore, it has been found that the paper binding properties of adhesives based on starch nanoparticles are superior compared to polyvinyl acetate latex. That is, when the biopolymer nanoparticle dispersion of the present invention is used as an adhesive for pigment coating, pigment coated paper having excellent surface strength, bending stiffness, and blister resistance during off-ring printing can be obtained.

  The agglomerated powder of the biopolymer nanoparticles of the present invention can be produced as described in Patent Document 1. For example, biopolymers such as starch and other polysaccharides (such as cellulose, hemicellulose and gum) and proteins (eg, gelatin, whey protein) are subjected to shear forces (shares) in the presence of a crosslinker to By processing, nanoparticles can be obtained. Such biopolymers may be pre-modified by acylation, phosphorylation, hydroxyalkylation, oxidation, etc. with, for example, cationic groups, carboxymethyl groups. Starch, a mixture of starch and other (bio) polymers (containing at least 50% starch) are preferred. Particularly preferred are high amylopectin starches (ie low amylose starches), ie starches having an amylopectin content of 75% or more, especially 90% or more, such as waxy starch. The biopolymer preferably has a dry substance content of 50% by weight or more, in particular 60% by weight or more at the start of the treatment.

  The treatment by shearing force means a mechanical treatment in this specification. Specifically, an extrusion process performed under high shear conditions at a high temperature (40 ° C. or higher, particularly 60 ° C. or higher, lower than the decomposition point of the polymer, for example, 200 ° C. or lower, particularly 140 ° C. or lower). It is. Shearing can be performed by applying at least 100 joules of specific mechanical energy (SME) per gram of biopolymer. Depending on the processing equipment used, the minimum energy may be greater. Further, when using a material that has not been gelatinized in advance, the minimum SME may be larger, for example, 250 J / g or more, particularly 500 J / g or more. The mechanical treatment is preferably performed at a high temperature. When starch is the raw material, the processing temperature can be lowered by using an alkaline medium or by using pregelatinized starch. During mechanical processing, the biopolymer is present in an aqueous solvent such as water or a water / alcohol mixture at a high concentration, preferably greater than 50% by weight. For example, a pressure of 5 to 150 bar can be applied to facilitate processing at high concentrations. Plasticizers can be present in addition to water or water / alcohol mixtures, for example plastics such as polyols (ethylene glycol, propylene glycol, polyglycols, glycerol, sugar alcohols, urea, citrate esters, etc.) The agent can be present in an amount of 5-40% by weight of the biopolymer. However, water can already act as a plasticizer. The total amount of plasticizer (ie water and other plasticizers such as glycerol) is preferably 15-50%. Lubricants such as lecithin or other phospholipids or monoglycerides can also be present, for example, in amounts of 0.5-2.5% by weight. Acids, preferably solid or semi-solid organic acids (maleic acid, citric acid, oxalic acid, lactic acid, gluconic acid, etc.) or carbohydrate degrading enzymes such as amylase in an amount of 0.01-5% by weight of the biopolymer. Can exist. These acids or enzymes aid in mild depolymerization that may be advantageous in the process of producing specific size nanoparticles.

  An important step in the process of producing biopolymer latex is cross-linking during mechanical processing. Crosslinking is preferably reversible. That is, some or all of the cross-linking is cut after the mechanical processing step. Suitable reversible crosslinkers include crosslinkers that form chemical bonds at low moisture concentrations and dissociate or hydrolyze in the presence of higher moisture concentrations. This type of cross-linking results in a temporary high viscosity during processing, but the viscosity decreases after processing. Examples of reversible crosslinkers include dialdehydes and polyaldehydes, and acid and mixed anhydrides that reversibly form hemiacetals. Suitable dialdehydes and polyaldehydes include glutaraldehyde, glyoxal, periodic acid oxidized carbohydrates and the like. Glyoxal is a particularly preferred cross-linking agent for producing latex particles. Such crosslinkers can be used alone or as a mixture of reversible crosslinkers or as a mixture of reversible and irreversible crosslinkers. Thus, conventional crosslinkers such as epichlorohydrin and other epoxides, triphosphates, divinylsulfone can be used as irreversible crosslinkers for polysaccharide biopolymers, whereas dialdehydes Thiol reagents and the like can be used for proteinaceous biopolymers. The cross-linking reaction can be catalyzed with acid or base. The amount of cross-linking agent is conveniently from 0.1 to 10% by weight with respect to the biopolymer. The cross-linking agent may already be present at the start of mechanical processing, but in the case of biopolymers that have not been pre-gelatinized such as granular starch, the cross-linking agent is added later, i.e. during mechanical processing. It is preferable.

  The mechanically treated crosslinked biopolymer is then subsequently concentrated in a suitable solvent, usually in water and / or another aqueous solvent (such as an alcohol) at a concentration of 4-50% by weight, in particular a concentration of 10-40% by weight. It is made into a latex by dispersing in Prior to dispersion, a cryogenic pulverization step can be performed, but stirring with mild heating may be performed. By such treatment, a gel that spontaneously becomes latex or a gel that becomes latex by adsorption of water is obtained. Such viscosity behavior improves the properties of the mixture and can be exploited for further uses of biopolymer particles. If necessary, the dispersed biopolymer may be further cross-linked by the cross-linking agent described above or other cross-linking agents.

Dispersion method The present invention relates to a method for preparing an aqueous dispersion of biopolymer nanoparticles. Specifically, in this invention, the average particle diameter which measured the biopolymer nanoparticle aggregate by the dynamic light-scattering method with the mechanical mixer in the water of 60 degrees C or less which added the alkaline substance becomes 400-1000 nm. The mixture is further stirred for 3 minutes or longer to obtain a dispersion having an average particle diameter of 50 to 400 nm as measured by the dynamic light scattering method of biopolymer nanoparticles. By doing in this way, the aggregation powder of the biopolymer nanoparticle which is hard to disperse | distribute can be efficiently disperse | distributed in water.

  In the present invention, an alkaline substance is a substance that exhibits alkalinity when dissolved in water. Examples include alkali metal hydroxides (eg, lithium hydroxide, sodium hydroxide, potassium hydroxide), alkaline earth metal hydroxides (eg, magnesium hydroxide, calcium hydroxide), etc. More specifically, alkali metal aluminates such as sodium aluminate, potassium aluminate, and lithium aluminate, alkali metal carbonates such as lithium carbonate, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate, Alkali hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide, alkali metal silicates such as lithium silicate, sodium silicate, and potassium silicate, and monoethanolamine, diethanolamine , Triethanolamine, monoisopropanolamine Diisopropanolamine, and it can be exemplified alkanolamines such as triisopropanolamine and the like. Most preferably, 0.1 to 5% by weight of caustic soda (sodium hydroxide) or 0.2 to 10% by weight of sodium bicarbonate or 0.1 to 0.1% by dry weight of the agglomerated powder of biopolymer nanoparticles. 5% by weight sodium carbonate or 0.2-10% by weight ammonium hydroxide can be used as the alkaline substance.

  In the present invention, the addition timing of the alkaline substance is not particularly limited. For example, the alkaline substance may be added to water or the biopolymer in advance, but the alkaline substance is added when the agglomerated powder of the biopolymer nanoparticles is mixed with water. Is preferred. The addition amount of the alkaline substance may be adjusted according to the system, but it is preferably added so that the pH of the dispersion is in the alkaline range, and the pH of the dispersion is 7.5 to 11, more preferably pH 8. It is more preferable to add so that it may become 0-11. In the acidic region, the dispersibility of the biopolymer is remarkably inferior, and it takes time until complete dispersion.

The liquid in which the biopolymer nanoparticles are dispersed is preferably at a temperature of 60 ° C. or lower. This is because the strength expression level may decrease when the temperature exceeds 60 ° C.
In the present invention, biopolymer nanoparticles are dispersed in water using a mechanical mixer. A mechanical mixer having a high shearing force can disperse quickly, but in the present invention, a method has been found that can efficiently disperse even a mixer having a low shearing force. In addition, the mechanical mixer is not particularly limited. In addition to a type in which a propeller-like stirrer is mounted in a container and stirring is performed by rotating the stirrer, a type in which stirring is performed by rotating the container itself is also possible. Good. In the present invention, a turbine mixer or a coreless mixer that is a type in which a propeller-like stirrer is mounted in a container and stirring is performed by rotating the stirrer is preferable. In the case of a mixer that performs stirring by rotating the stirring bar, the shape of the stirring bar and the number of stirring blades are not particularly limited. For example, an impeller stirrer having three blades in two upper and lower stages can be used. The rotation speed of the stirrer can be about 10 to 2000 rotations per minute at 50 Hz.

  Furthermore, in this invention, it stirs until the average particle diameter measured by the dynamic light-scattering method becomes 400-1000 nm, and also continues stirring for 3 minutes or more, extracts a dispersion liquid, and measures biopolymer nanoparticle A dispersion is prepared so that the average particle diameter measured by the dynamic light scattering method is 50 to 400 nm. In the present invention, the average particle size may be monitored while stirring.

  Stirring after reaching 400 to 1000 nm is not particularly limited as long as it is 3 minutes or longer and the average particle diameter finally becomes 50 to 400 nm. For example, with an impeller type stirrer, a rotation speed of 200 rpm is more preferably 10 minutes or more.

  In the present invention, the average particle size is finally set to 50 to 400 nm by stirring after 400 to 1000 nm. However, when the average particle size is less than 200 nm, surface strength, blister resistance, bending stiffness, etc. Since various performances improve, it is more preferable.

Coated paper The aqueous dispersion of biopolymer nanoparticles obtained as described above is extremely suitable as an adhesive compounded in the pigment coating liquid of coated paper. That is, the above aqueous dispersion of biopolymer nanoparticles is easy to handle as a paint because it has a low viscosity even at a relatively high concentration. Further, by blending the above aqueous dispersion of biopolymer nanoparticles into the pigment coating layer, the surface strength, bending stiffness, and blister resistance during off-wheel printing of the resulting pigment coated paper are improved. Such effects are surprising and not predictable by those skilled in the art from the prior art.

  In the present invention, the base paper is not particularly limited as long as it is mainly composed of wood fibers, and various base papers can be used. Further, the type and amount of the pigment to be blended in the coating liquid are not particularly limited. Various additives can be freely added, and an adhesive other than biopolymer nanoparticles can be used in combination. In addition, a coating method, a coating amount, a drying method, and the like are not particularly limited, and a known method can be applied to the present invention.

  The following examples illustrate the invention, but the examples in no way limit the invention. Unless indicated otherwise, parts indicate dry parts per 100 weight, and% indicates% by weight. The average particle diameter of the biopolymer nanoparticle dispersion and the obtained coated paper for printing were tested by the following evaluation method.

<Evaluation methods>
(1) Average particle diameter of biopolymer nanoparticles: The volume particle size distribution of the particles was measured using a dynamic light scattering apparatus (Zeta Sizer Nano Zeta Sizer 3000HSA manufactured by Malvern). The measurement was performed using a nanoparticle dispersion (0.5 solid content%). The particle size was defined as the average particle size when the volume cumulative distribution was 50% by volume.
(2) Blister resistance: Using an offset rotary printing press B2T600 manufactured by Toshiba Corporation, the dryer drying temperature was raised during printing until the blister was generated, and the paper surface temperature when the blister was generated was defined as the blister generation temperature. In addition, the appearance of the surface state of the obtained printed matter was inspected according to the following criteria. ◎: Extremely good, ○: Good, △: Average, ×: Inferior (3) ISO bending stiffness: L / W bending tester (manufactured by Lorentzen & Wettre) was used to calculate the bending stiffness from the bending resistance value of 15 ° based on ISO 2493. did.
(4) Surface strength: A printing speed of 8000 sheets / hour with an A3 size plate using a flatland printing ink (Hi-Unity Neo M manufactured by Toyo Ink Manufacturing Co., Ltd.) on a Roland offset flat-screen printing machine (two colors) Printed on coated paper for printing. The picking strength of the surface of the printed material obtained based on the following criteria was evaluated from the appearance. A: Very good, B: Good, B: Slightly inferior, X: Inferior
Example 1
Biopolymer (BP) nanoparticle agglomerated powder (ECOSPHERE (registered trademark) 92202, manufactured by ECOSYNTHETIX) was dissolved in 50 ° C. water in which 0.5% by weight (based on the weight of biopolymer nanoparticles) of sodium hydroxide was dissolved. The mixture was added to a concentration of 30%, and the mixture was stirred at 220 rpm for 30 minutes using a turbine mixer (an impeller stirrer having 3 blades in two upper and lower stages, stirring layer: 3 m ³ ). After stirring for 30 minutes, no dust or the like could be visually confirmed, and the average particle size measured by the dynamic light scattering method was 400 nm. From this state, stirring was further continued at 220 rpm for 15 minutes. The average particle diameter measured by the dynamic light scattering method after stirring was 250 nm. The pH of the resulting dispersion of biopolymer nanoparticles was 8.5.

  A coating solution was prepared by blending the dispersion of biopolymer nanoparticles thus obtained. This coating solution is composed of 70 parts of heavy calcium carbonate (FMT-97 manufactured by Pfematec Co., Ltd.), 30 parts of fine clay (Hydra gloss manufactured by KaMin Co., Ltd.), biopolymer nanoparticle dispersion 11 for all pigments as an adhesive. Part and further 4 parts of phosphoric esterified starch (MS-4600 manufactured by Nippon Shokuhin Kako Co., Ltd.) and the solid content concentration was 64%.

The thus-prepared coating solution was coated on a high-quality base paper having a basis weight of 45 g / m ^{2 with} a blade coater at a coating speed of 1200 m / min so that the coating amount was 12 g / m ² per side. Further, a surface treatment was performed with a super calender under the conditions of a treatment temperature of 65 ° C., a treatment linear pressure of 200 kN / m, and a 4-nip to obtain a coated paper for printing.

Example 2
In the dispersion step of the biopolymer nanoparticle aggregated powder, the mixture was stirred for 30 minutes at 220 rpm with a stirrer, and further stirred for 3 minutes (the average particle diameter of the biopolymer nanoparticles in the dispersion measured by the dynamic light scattering method was 340 nm). ) Was carried out in the same manner as in Example 1 to obtain a coated paper for printing.

Example 3
In the dispersion step of the biopolymer nanoparticle aggregated powder, the mixture was stirred with a stirrer at 220 rpm for 30 minutes, and further stirred for 1 hour (the average particle diameter of the biopolymer nanoparticles in the dispersion measured by the dynamic light scattering method was 200 nm). ) Was carried out in the same manner as in Example 1 to obtain a coated paper for printing.

Example 4
In the dispersion process of the biopolymer nanoparticle agglomerated powder, water added with 1.0% sodium bicarbonate by weight with respect to the biopolymer nanoparticles was used instead of 0.5% caustic soda with respect to the biopolymer nanoparticles. The coated paper for printing was obtained in the same manner as in Example 1 except that the average particle size of the biopolymer nanoparticles in the dispersion measured by the dynamic light scattering method was 255 nm. The pH of the resulting dispersion of biopolymer nanoparticles was 7.

Example 5
Instead of blending 11 parts of the biopolymer nanoparticle dispersion, 5.5 parts of biopolymer nanoparticles as an adhesive and 5 parts of styrene-butadiene copolymer latex (NPSR, manufactured by JSR Co., Ltd.) having an average particle diameter of 100 nm are used. A coating paper for printing was obtained in the same manner as in Example 1 except that the coating liquid containing 5 parts was used.

Example 6
In the step of dispersing the biopolymer nanoparticle aggregated powder, the mixture was stirred for 30 minutes at 220 rpm with a stirrer, and further stirred for 20 minutes (the average particle diameter of the biopolymer nanoparticles in the dispersion measured by the dynamic light scattering method was 190 nm). ) Was carried out in the same manner as in Example 1 to obtain a coated paper for printing.

Example 7
In the step of dispersing the biopolymer nanoparticle aggregated powder, the mixture was stirred for 30 minutes at 220 rpm with a stirrer, and further stirred for 30 minutes (the average particle diameter of the biopolymer nanoparticles in the dispersion measured by the dynamic light scattering method is 130 nm). ) Was carried out in the same manner as in Example 1 to obtain a coated paper for printing.

Example 8
A coated paper for printing was obtained in the same manner as in Example 1 except that 0.1% by weight (based on the weight of biopolymer nanoparticles) of sodium hydroxide was added. The pH of the obtained dispersion of biopolymer nanoparticles was 7, and the average particle diameter of the biopolymer nanoparticles in the dispersion measured by dynamic light scattering was 320 nm.

Example 9
A coated paper for printing was obtained in the same manner as in Example 7 except that 0.1% by weight (based on the weight of biopolymer nanoparticles) of sodium hydroxide was added. The pH of the dispersion of the obtained biopolymer nanoparticles was 7, and the average particle diameter of the biopolymer nanoparticles of the dispersion measured by the dynamic light scattering method was 250 nm.

Comparative Example 1
In the dispersion process of the agglomerated powder of biopolymer nanoparticles, only stirring was performed at 1500 rpm for 30 minutes with a stirrer (the average particle diameter of the biopolymer nanoparticles in the dispersion measured by the dynamic light scattering method was 400 nm). In the same manner as in Example 1, a coated paper for printing was obtained.

Comparative Example 2
In the dispersion step of the biopolymer nanoparticle aggregated powder, Example 1 was used except that water without adding an alkaline substance was used (the average particle diameter of the biopolymer nanoparticles in the dispersion measured by the dynamic light scattering method was 500 nm). In the same manner, a coated paper for printing was obtained.

Comparative Example 3
In the step of dispersing the biopolymer nanoparticle aggregated powder, the temperature of water was set to 95 ° C. (the average particle size of the biopolymer nanoparticles in the dispersion measured by the dynamic light scattering method was 410 nm). The coated paper for printing was obtained.

Comparative Example 4
Example 1 except that instead of the biopolymer nanoparticle dispersion, a coating liquid containing 11 parts of styrene-butadiene copolymer latex (NPSR, manufactured by JSR Corporation) having an average particle diameter of 100 nm was used as an adhesive. In the same manner as above, a coated paper for printing was obtained.

Comparative Example 5
For printing, except that a coating solution containing 11 parts of hydroxyethyl etherified starch (HES: Ethylex2005, manufactured by Tate & Lyle) as an adhesive was used instead of the biopolymer nanoparticle dispersion. Coated paper was obtained.

  The above results are shown in Table 1.

Claims (6)

A method for preparing an aqueous dispersion of biopolymer nanoparticles,
Stirring the biopolymer nanoparticle aggregates in water at 60 ° C. or less to which an alkaline substance has been added until the average particle size measured by a dynamic light scattering method becomes 400 to 1000 nm by a mechanical mixer;
Further, stirring is continued for 3 minutes or more to obtain a dispersion having an average particle size of 50 to 400 nm measured by a dynamic light scattering method of biopolymer nanoparticles,
Including the above method.   The method of claim 1, wherein the mixer is a turbine mixer.   The method according to claim 1, wherein when the agglomerated powder of biopolymer nanoparticles is mixed with water, the alkaline substance is added to adjust the pH of the dispersion to 7.5 to 11.   When the agglomerated powder of biopolymer nanoparticles is mixed with water, 0.1 to 5% by weight of caustic soda or 0.2 to 10% by weight of hydrogen carbonate based on the dry weight of the agglomerated powder of biopolymer nanoparticles. Sodium or 0.1 to 5 wt% sodium carbonate or 0.2 to 10 wt% ammonium hydroxide is added as the alkaline substance to adjust the pH of the dispersion to 7.5 to 11. The method of claim 3.   An agglomerated powder of biopolymer nanoparticles is a biopolymer made by plasticizing a starch or starch derivative or a polymer mixture containing at least 50 wt% starch by applying shear in the presence of a cross-linking agent. The method according to any one of claims 1 to 4, wherein:   The coating which coated the coating liquid which has a biopolymer nanoparticle dispersion liquid prepared by the method in any one of Claims 1-5 mainly on a wood fiber as a main component paper.