JP7062334B2 - Binder for ceramics - Google Patents

Description

The present invention relates to a binder used for ceramic molding.

In recent years, a precise molded body made of ceramic or glass has been obtained by molding a paste in which an inorganic powder such as ceramic powder or glass powder is dispersed in a binder resin composition and then firing the paste. Further, in a substrate on which a semiconductor element is mounted, for example, alumina, silicon nitride, glass ceramic and the like are being used as ceramic materials having excellent insulating properties and high thermal conductivity. Among them, glass ceramic is becoming more useful because Ag, Cu, and Au, which have low conduction resistance of the wiring material that is fired at the same time as the substrate, can be used.

The pre-baking sheet (ceramic green sheet) for performing wiring printing is usually manufactured through a series of steps of laminating, debindering, and firing. As the required characteristics for the ceramic green sheet in this application, it is required that the binder has a debinder property, that is, the thermal decomposition temperature of the binder is low and the residual coal residue (organic residue) after firing is small.

As the binder resin used for ceramic molding, PVB (polyvinyl butyral), PVA (polyvinyl alcohol), PEG (polyethylene glycol), PEO (polyethylene oxide) and the like have been conventionally used. Among them, PVB has been widely used because it can impart strength and appropriate flexibility to the obtained ceramic green sheet. PVA, PEG and PEO are mainly used for press molding of ceramic powders due to their economic advantages. Further, an acrylic binder resin has been proposed as a binder resin that thermally decomposes at a relatively low temperature when performing ceramic molding (Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 9-142941 Japanese Unexamined Patent Publication No. 10-291834

However, since ceramic binder resins such as PVA, PEG, and PEO have a high thermal decomposition temperature, when used for firing low melting point glass, which is often used in plasma display panels, for example, the decomposition residue of the binder resin is added to the sintered body. There was a problem that may remain. Further, although the acrylic binder resin is thermally decomposed at a relatively low temperature, there has been a demand for a binder that thermally decomposes at a lower temperature.

An object of the present invention is to provide a binder for ceramics having a lower thermal decomposition temperature than the conventional one.

As a result of diligent studies to achieve such an object, the present inventor has found that it is extremely effective to blend cellulose nanofibers (CNF) into a binder for ceramics, and completed the present invention.

The present invention provides:
(1) A binder for ceramics containing cellulose nanofibers and a dispersion medium.

According to the present invention, it is possible to provide a binder for ceramics having a low thermal decomposition temperature.

Hereinafter, the present invention will be described in detail. In the present invention, "-" includes a fractional value. That is, "X to Y" includes the values X and Y at both ends thereof.

The binder for ceramics of the present invention is characterized by containing cellulose nanofibers and a dispersion medium.

<Cellulose nanofiber>
In the present invention, the cellulose nanofiber (CNF) is a fine fiber in which pulp or the like, which is a raw material for cellulose, is miniaturized to the nanometer level, and the fiber diameter is about 3 to 500 nm. The average fiber diameter and average fiber length of the cellulose nanofibers are randomly selected using an atomic force microscope (AFM) when the diameter is 20 nm or less and a field emission scanning electron microscope (FE-SEM) when the diameter is 20 nm or more. The 200 selected fibers were analyzed. Cellulose nanofibers are obtained by applying mechanical force to pulp to make them finer, or carboxylated cellulose (also called oxidized cellulose), carboxymethylated cellulose, and cellulose into which a phosphate ester group is introduced. It can be obtained by defibrating modified cellulose obtained by chemical modification such as cationized cellulose. The average fiber length and average fiber diameter of the fine fibers can be adjusted by oxidation treatment and defibration treatment.

The average aspect ratio of the cellulose nanofibers used in the present invention is usually 50 or more. The upper limit is not particularly limited, but is usually 1000 or less. The average aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length / average fiber diameter

<Cellulose raw material>
The origin of the cellulose raw material, which is the raw material of the cellulose nanofibers, is not particularly limited, but for example, plants (for example, wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (coniferous unbleached kraft pulp (NUKP)). , Conifer bleached kraft pulp (NBKP), broadleaf unbleached kraft pulp (LUKP), broadleaf bleached kraft pulp (LBKP), bleached kraft pulp (BKP), conifer unbleached sulphite pulp (NUSP), conifer bleached sulphite pulp (NBSP) ), Hardwood sulphite pulp (LSP), thermomechanical pulp (TMP), recycled pulp, used paper, etc.), animals (eg, squirrels), algae, microorganisms (eg, acetic acid bacteria (acetobacter)), microbial products, etc. The cellulose raw material may be any one of these or a combination of two or more of them, but is preferably a cellulose raw material derived from a plant or a microorganism (for example, cellulose fiber), and more preferably. It is a plant-derived cellulose raw material (for example, cellulose fiber).

The number average fiber diameter of the cellulose raw material is not particularly limited, but is about 30 to 60 μm in the case of softwood kraft pulp, which is a general pulp, and about 10 to 30 μm in the case of hardwood kraft pulp. In the case of other pulps, the one that has undergone general purification is about 50 μm. For example, when a chip or the like having a size of several cm is purified, it is preferable to perform mechanical treatment with a dissociator such as a refiner or a beater to adjust the size to about 50 μm.

<Chemical denaturation>
[Carboxymethylation]
In the present invention, when carboxymethylated cellulose is used as the modified cellulose, the carboxymethylated cellulose may be obtained by carboxymethylating the above-mentioned cellulose raw material by a known method, or by using a commercially available product. May be good. In either case, the degree of carboxymethyl group substitution per anhydrous glucose unit of cellulose is preferably 0.01 to 0.50. The following method can be mentioned as an example of a method for producing such carboxymethylated cellulose. Using cellulose as a starting material, 3 to 20 times by mass of water and / or lower alcohol as a solvent, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary Use a single medium such as butanol or a mixed medium of two or more kinds. When the lower alcohol is mixed, the mixing ratio of the lower alcohol is 60 to 95% by mass. As the mercerizing agent, 0.5 to 20 times mol of alkali metal hydroxide per anhydrous glucose residue of the bottoming material, specifically sodium hydroxide and potassium hydroxide is used. The bottoming material, the solvent, and the mercerizing agent are mixed, and the reaction temperature is 0 to 70 ° C., preferably 10 to 60 ° C., and the reaction time is 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Then, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times per glucose residue, the reaction temperature is 30 to 90 ° C., preferably 40 to 80 ° C., and the reaction time is 30 minutes to 10 hours, preferably 1 hour. The etherification reaction is carried out for about 4 hours.

In the present specification, "carboxymethylated cellulose", which is a kind of modified cellulose used for preparing cellulose nanofibers, is one in which at least a part of the fibrous shape is maintained even when dispersed in water. say. Therefore, it is distinguished from carboxymethyl cellulose, which is a kind of water-soluble polymer. When the aqueous dispersion of "carboxymethylated cellulose" is observed with an electron microscope, a fibrous substance can be observed. On the other hand, even when the aqueous dispersion of carboxymethyl cellulose, which is a kind of water-soluble polymer, is observed, no fibrous substance is observed. In addition, the peak of cellulose I-type crystals can be observed when "carboxymethylated cellulose" is measured by X-ray diffraction, but cellulose I-type crystals are not observed in the water-soluble polymer carboxymethyl cellulose.

[Carboxylation]
In the present invention, when carboxylated (oxidized) cellulose is used as the modified cellulose, carboxylated cellulose (also referred to as oxidized cellulose) can be obtained by carboxylating (oxidizing) the above-mentioned cellulose raw material by a known method. .. Although not particularly limited, in the case of carboxylation, the amount of carboxyl groups should be adjusted to 0.6 to 2.0 mmol / g with respect to the absolute dry mass of the anion-modified cellulose nanofibers. Is preferable, and it is more preferable to adjust the temperature to 1.0 mmol / g to 2.0 mmol / g.

As an example of the carboxylation (oxidation) method, a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide or a mixture thereof. The method can be mentioned. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of the cellulose is selectively oxidized, and the cellulose fiber having an aldehyde group and a carboxyl group (-COOH) or a carboxylate group (-COO-) on the surface. Can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

The N-oxyl compound is a compound capable of generating a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it is a compound that promotes the desired oxidation reaction. For example, 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivative (for example, 4-hydroxy TEMPO) can be mentioned.

The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing cellulose as a raw material. For example, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.05 to 0.5 mmol is further preferable, with respect to 1 g of cellulose that is completely dried. Further, it is preferably about 0.1 to 4 mmol / L with respect to the reaction system.

The bromide is a compound containing bromine, and examples thereof include alkali metals bromide that can be dissociated and ionized in water. Further, the iodide is a compound containing iodine, and an example thereof includes an alkali metal iodide. The amount of bromide or iodide used can be selected within the range in which the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, still more preferably 0.5 to 5 mmol with respect to 1 g of dry cellulose.

As the oxidizing agent, known ones can be used, and for example, halogens, hypohalogenic acids, subhalogen acids, perhalonic acids or salts thereof, halogen oxides, peroxides and the like can be used. Of these, sodium hypochlorite, which is inexpensive and has a low environmental impact, is preferable. As the amount of the oxidizing agent used, for example, 0.5 to 500 mmol is preferable, 0.5 to 50 mmol is more preferable, and 1 to 25 mmol is more preferable, and 3 to 10 mmol is most preferable with respect to 1 g of cellulose which is absolutely dry. Further, for example, 1 to 40 mol is preferable with respect to 1 mol of the N-oxyl compound.

Oxidation of cellulose allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40 ° C, and may be room temperature of about 15 to 30 ° C. As the reaction progresses, a carboxyl group is generated in the cellulose, so that the pH of the reaction solution is lowered. In order to efficiently proceed the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8 to 12, preferably about 10 to 11. Water is preferable as the reaction medium because it is easy to handle and side reactions are unlikely to occur.

The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually about 0.5 to 6 hours, for example, about 0.5 to 4 hours.

Further, the oxidation reaction may be carried out in two stages. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency is not affected by the reaction inhibition by the salt produced as a by-product in the first-stage reaction. Can be oxidized well.

As another example of the carboxylation (oxidation) method, there is a method of oxidizing by contacting a gas containing ozone with a cellulose raw material. By this oxidation reaction, the hydroxyl groups at at least the 2-position and the 6-position of the glucopyranose ring are oxidized, and the cellulose chain is decomposed. The ozone concentration in the gas containing ozone is preferably 50 to 250 g / m ³ , and more preferably 50 to 220 g / m ³ . The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, more preferably 5 to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. The ozone treatment temperature is preferably 0 to 50 ° C, more preferably 20 to 50 ° C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, preferably about 30 to 360 minutes. When the ozone treatment conditions are within these ranges, it is possible to prevent the cellulose from being excessively oxidized and decomposed, and the yield of the oxidized cellulose becomes good. After the ozone treatment, the additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, the additional oxidation treatment can be performed by dissolving these oxidizing agents in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the solution.

The amount of the carboxyl group of the oxidized cellulose can be adjusted by controlling the reaction conditions such as the amount of the oxidizing agent added and the reaction time described above.

[Cationation]
As the chemically modified cellulose, cellulose obtained by further cationizing the carboxylated cellulose can be used. The cation-modified cellulose is prepared by adding a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrite or a halohydrin type thereof to the carboxylated cellulose raw material, and an alkali hydroxide as a catalyst. It can be obtained by reacting a metal (sodium hydroxide, potassium hydroxide, etc.) in the presence of water or an alcohol having 1 to 4 carbon atoms.

The degree of cation substitution per glucose unit is preferably 0.02 to 0.50. By introducing a cationic substituent into the cellulose, the celluloses electrically repel each other. Therefore, the cellulose into which a cation substituent is introduced can be easily nano-deflated. If the degree of cation substitution per glucose unit is less than 0.02, nano-deflation cannot be sufficiently performed. On the other hand, if the degree of cation substitution per glucose unit is larger than 0.50, it may not be obtained as nanofibers because it swells or dissolves. In order to efficiently perform defibration, it is preferable that the cationically modified cellulose raw material obtained above is washed. The degree of cation substitution can be adjusted by the amount of the cationizing agent to be reacted and the composition ratio of water or an alcohol having 1 to 4 carbon atoms.

[Esterification]
Esterified cellulose can be used as the chemically modified cellulose. The cellulose can be obtained by a method of mixing a powder or an aqueous solution of a phosphoric acid compound A with the above-mentioned cellulose raw material, or a method of adding an aqueous solution of a phosphoric acid compound A to a slurry of a cellulose raw material.

Examples of the phosphoric acid-based compound A include phosphoric acid, polyphosphoric acid, phosphite, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among these, a compound having a phosphoric acid group is preferable because it is low in cost, easy to handle, and the phosphoric acid group can be introduced into the cellulose of the pulp fiber to improve the defibration efficiency. Compounds having a phosphoric acid group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and phosphorus. Examples thereof include tripotassium acid, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate and the like. These can be used alone or in combination of two or more. Of these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, and phosphoric acid from the viewpoint of high efficiency of introduction of phosphoric acid group, easy defibration in the following defibration step, and easy industrial application. Ammonium salt is more preferred. In particular, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. Further, the phosphoric acid-based compound A is preferably used as an aqueous solution because the uniformity of the reaction is enhanced and the efficiency of introducing the phosphoric acid group is increased. The pH of the aqueous solution of the phosphoric acid-based compound A is preferably 7 or less because the efficiency of introducing the phosphoric acid group is high, but pH 3 to 7 is preferable from the viewpoint of suppressing the hydrolysis of the pulp fiber.

The following method can be mentioned as an example of the method for producing phosphoric acid esterified cellulose. A phosphoric acid-based compound A is added to a dispersion of a cellulose raw material having a solid content concentration of 0.1 to 10% by mass with stirring to introduce a phosphoric acid group into the cellulose. When the cellulose raw material is 100 parts by mass, the amount of the phosphoric acid compound A added is preferably 0.2 to 500 parts by mass and more preferably 1 to 400 parts by mass as the amount of the phosphorus element. When the ratio of the phosphoric acid-based compound A is at least the above lower limit value, the yield of the fine fibrous cellulose can be further improved. However, if the upper limit is exceeded, the effect of improving the yield will reach a plateau, which is not preferable from the viewpoint of cost.

At this time, in addition to the cellulose raw material and the phosphoric acid-based compound A, powders or aqueous solutions of other compounds B may be mixed. The compound B is not particularly limited, but a nitrogen-containing compound showing basicity is preferable. "Basic" here is defined as the aqueous solution exhibiting a pink to red color in the presence of a phenolphthalein indicator, or the pH of the aqueous solution being greater than 7. The basic nitrogen-containing compound used in the present invention is not particularly limited as long as the effect of the present invention is exhibited, but a compound having an amino group is preferable. Examples thereof include, but are not limited to, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like. Of these, urea, which is low in cost and easy to handle, is preferable. The amount of compound B added is preferably 2 to 1000 parts by mass, more preferably 100 to 700 parts by mass, based on 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95 ° C, more preferably 30 to 90 ° C. The reaction time is not particularly limited, but is about 1 to 600 minutes, more preferably 30 to 480 minutes. When the conditions of the esterification reaction are within these ranges, it is possible to prevent the cellulose from being excessively esterified and easily dissolved, and the yield of the phosphate esterified cellulose becomes good. After dehydrating the obtained phosphoric acid esterified cellulose suspension, it is preferable to heat-treat it at 100 to 170 ° C. from the viewpoint of suppressing hydrolysis of cellulose. Further, it is preferable to heat at 130 ° C. or lower, preferably 110 ° C. or lower while water is contained in the heat treatment, remove water, and then heat-treat at 100 to 170 ° C.

The degree of phosphate group substitution per glucose unit of the phosphoric acid esterified cellulose is preferably 0.001 to 0.40. By introducing a phosphate group substituent into cellulose, the celluloses electrically repel each other. Therefore, cellulose having a phosphate group introduced can be easily nano-deflated. If the degree of phosphate substitution per glucose unit is less than 0.001, nano-defibration cannot be sufficiently performed. On the other hand, if the degree of phosphate substitution per glucose unit is larger than 0.40, it may not be obtained as nanofibers because it swells or dissolves. In order to efficiently perform defibration, it is preferable that the phosphoric acid esterified cellulose raw material obtained above is washed by boiling and then washing with cold water.

<Dissolution>
In the present invention, the device for defibrating is not particularly limited, but a strong shearing force is applied to the aqueous dispersion by using a device such as a high-speed rotary type, a colloid mill type, a high pressure type, a roll mill type, and an ultrasonic type. Is preferable. In particular, in order to efficiently deflate, it is preferable to use a wet high-pressure or ultra-high pressure homogenizer capable of applying a pressure of 50 MPa or more to the aqueous dispersion and applying a strong shearing force. The pressure is more preferably 100 MPa or more, still more preferably 140 MPa or more. In addition, prior to the defibration / dispersion treatment with a high-pressure homogenizer, it is also possible to pre-treat the above CNF using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer, if necessary. Is. The number of treatments (passes) in the defibrating device may be once, twice or more, and preferably twice or more.

In the dispersion treatment, modified cellulose is usually dispersed in a solvent. The solvent is not particularly limited as long as it can disperse the modified cellulose, and examples thereof include water, an organic solvent (for example, a hydrophilic organic solvent such as methanol), and a mixed solvent thereof.

The solid content concentration of the modified cellulose in the dispersion is usually 0.1% by mass or more, preferably 0.2% by mass or more, and more preferably 0.3% by mass or more. As a result, the amount of the liquid becomes appropriate with respect to the amount of the cellulose fiber raw material, which is efficient. The upper limit is usually 10% by mass or less, preferably 6% by mass or less. This makes it possible to maintain liquidity.

Prior to the defibration treatment or the dispersion treatment, a preliminary treatment may be performed as necessary. Pretreatment may be performed using a mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer.

The cellulose nanofibers used in the present invention may be, in particular, in oxidized cellulose nanofibers and carboxymethylated cellulose nanofibers, the carboxyl group, carboxyalkyl group and the like may be in the form of a metal salt such as a sodium salt, or may be in the acid type. It may be cellulose nanofibers. Further, hydrophobicity may be imparted and used by a method using a cationic additive.

<Acid-type cellulose nanofiber>
Examples of the method for producing the acid-type cellulose nanofibers include a method of desalting the cellulose nanofiber salt with a cation exchange resin and a method of acid-treating the cellulose nanofiber salt with hydrochloric acid or the like to replace the metal salt with a proton.

<Dispersion medium>
The binder for ceramics of the present invention contains water or an organic solvent as a dispersion medium. As the dispersion medium, a mixed solvent of water and an organic solvent may be used. Examples of the organic solvent include ethyl alcohol, isopropyl alcohol, butyl alcohol, toluene, xylene, methyl ethyl ketone, ethyl acetate, methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane and N-methyl. -2-pyrrolidone, tetrahydrofuran, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, acetonitrile, and combinations thereof.

The amount of the organic solvent in the mixed solvent is preferably 5% by mass or more, more preferably 10% by mass or more. The upper limit of the amount is not limited, but is preferably 95% by mass or less, and more preferably 90% by mass or less.

<Other binder components>
The binder for ceramics of the present invention may contain other binder components in addition to the above-mentioned essential components of cellulose nanofibers and dispersion medium. Examples of other binder components include polyvinyl acetal and acrylic resins.

Examples of the polyvinyl acetal that can be used in the present invention include polyvinyl butyral, polyvinyl etylal, polyvinyl propyral, polyvinyl octylal, polyvinyl phenylal, and the like, or derivatives thereof. One type of these may be used, or two or more types may be used in combination.

Examples of the acrylic resin that can be used in the present invention include (i) a methacrylate alkyl ester monomer, (ii) an unsaturated carboxylic acid monomer, an amino group-containing (meth) acrylic acid alkyl ester monomer, and a hydroxyl group. At least one selected from the group of contained (meth) acrylic acid alkyl ester monomers, (iii) polyfunctional (meth) acrylic acid alkyl ester monomers, and (iv) other copolymerizable monomers. Examples thereof include a copolymer obtained by copolymerizing a monomer mixture containing. The methacrylic acid alkyl ester monomer is preferably contained in at least two kinds and 90 to 99% by mass in the monomer mixture. As the methacrylic acid alkyl ester monomer, methacrylic acid esters having 1 to 8 carbon atoms are preferable in terms of heat decomposition, and specific examples thereof include methyl methacrylate, ethyl methacrylate, and normal butyl methacrylate. , Isobutyl methacrylate, 2-ethylhexyl methacrylate and the like, and isobutyl methacrylate and 2-ethylhexyl methacrylate are more preferable.

At least one monomer selected from the group of unsaturated carboxylic acid monomer, amino group-containing (meth) acrylic acid alkyl ester monomer, and hydroxyl group-containing (meth) acrylic acid alkyl ester monomer is a single amount. It is preferably contained in the body mixture in an amount of 0.1 to 5% by mass, more preferably 0.1 to 2% by mass. The monomer is appropriately selected depending on the type of ceramic material. Specific examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and the like, and the amino group-containing (meth) acrylic acid alkyl ester monomer is (meth). ) Dimethylaminoethyl acrylate, diethylaminoethyl (meth) acrylate and the like are examples of hydroxyl group-containing (meth) acrylic acid alkyl ester monomers: 2-hydroxyethyl (meth) acrylic acid, (meth) acrylic acid 2 -Hydroxypropyl, 2-hydroxybutyl (meth) acrylate and the like can be mentioned.

The polyfunctional (meth) acrylic acid alkyl ester monomer is preferably contained in the monomer mixture in an amount of 0.001 to 0.1% by mass. Specific examples include trimethylolpropane tri (meth) acrylate, butylene glycol dimethacrylate, 1,6 hexanediol dimethacrylate, 1,3 butylene glycol dimethacrylate, triethylene glycol dimethacrylate, ethylene glycol dimethacrylate, and Nippon Kayaku. Examples thereof include Yakusha-made, trade name Kayarad DPHA, etc., and one type or a mixture of two or more types can be used.

Other monomers copolymerizable with the above-mentioned monomers can be blended so that the total amount of the monomer mixture does not exceed 100% by mass. It is approximately 10% by mass or less. Specific examples include styrene, acrylonitrile, acrylamide, allyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, benzyl methacrylate, vinyl acetate and the like. One type or a mixture of two or more types can be used.

As the polymerization initiator used for the above-mentioned copolymerization, it is preferable to use an aliphatic peroxide (however, the number of carbon atoms is 4 to 18) or an azo-based polymerization initiator. Specific examples of the aliphatic peroxide include di-n-propylperoxydicarbonate, diisopropylperoxydicarbonate, isobutyl peroxide, di-t-butyl peroxide, t-butylperoxy2-ethylhexanoate, and t. -Butyl peroxylaurate, octanonyl peroxide, lauryl peroxide, stearyl peroxide and the like can be mentioned. Specific examples of the azo-based polymerization initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-methylbutyronitrile), and 2,2'-azobis (2). , 4-Dimethylvaleronitrile), 1,1'-azobis (cyclohexane-1-carbonitrile), dimethyl 2,2'azobis (2-methylpropionate) and the like. The amount of the polymerization initiator added is preferably 0.1 to 3% by mass with respect to 100 parts by mass of the monomer mixture.

The acrylic resin is preferably a copolymer whose molecular weight is adjusted only by the polymerization initiator without containing a chain transfer agent. Examples of the copolymerization method include well-known methods such as a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method.

In addition to the above-mentioned other binder components, the binder for ceramics of the present invention may contain other components such as a plasticizer and a dispersant according to the purpose. When other components are blended in the binder for ceramics of the present invention, they can be mixed by a conventional device or means, and the temperature conditions and the like are not particularly limited.

In the binder for ceramics of the present invention, the blending ratio of each component is not particularly limited, but the cellulose nanofibers in the binder are preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass in terms of solid content. Particularly preferably, it is contained in the range of 1.0 to 10% by mass. By using the cellulose nanofibers in such a range, it is possible to impart excellent dispersibility and affinity to the ceramic material of the binder, and there is an excellent effect of improving moldability and processability.

When the binder for ceramics of the present invention contains other binder components, it is preferably contained in the range of 0 to 100% by mass, more preferably 0 to 50% by mass, based on the solid content of the cellulose nanofibers.

When the ceramic binder of the present invention is used for ceramic molding, the ceramic material that can be used is not limited to the following, but for example, borosilicate glass powder, ceramics such as alumina and silicon nitride, and glass transition. Examples thereof include glass powder used in a plasma display (PDP) having a temperature (Tg) of 350 to 500 ° C. and a heat softening temperature of 400 to 550 ° C., and fine titanium oxide powder having photocatalytic activity.

Since the binder for ceramics of the present invention contains cellulose nanofibers, the thermal decomposition temperature is low. Therefore, when ceramic molding is performed using this ceramic binder, the obtained ceramic molded body (sintered body) has a low residual coal ratio.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[Measuring method of carboxyl group amount]
Prepare 60 mL of a 0.5 mass% slurry (aqueous dispersion) of carboxylated cellulose, add a 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then add a 0.05 N sodium hydroxide aqueous solution to drop the pH to 11. The electric conductivity was measured until the pH became, and the amount of sodium hydroxide consumed in the neutralization step of the weak acid in which the change in the electric conductivity was gradual was calculated by using the following formula:
Amount of carboxyl group [mmol / g carboxylated cellulose] = a [mL] × 0.05 / mass of carboxylated cellulose [g].

[Measurement method of carboxymethyl substitution per glucose unit]
Approximately 2.0 g of carboxymethylated cellulose fiber (absolutely dried) was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution prepared by adding 10 mL of special grade concentrated nitric acid to 90 mL of methanol was added, and the mixture was shaken for 3 hours to change the carboxymethylated cellulose salt (CM-modified cellulose) into hydrogen-type CM-modified cellulose. 1.5 to 2.0 g of hydrogen-type CM-formed cellulose (absolutely dried) was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. Hydrogenated CM-ized cellulose was moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH was added, and the mixture was shaken at room temperature for 3 hours. Excess NaOH was back titrated with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator. The degree of carboxymethyl substitution (DS) was calculated by the following equation:
A = [(100 x F'-(0.1 N H ₂ SO ₄ ) (mL) x F) x 0.1] / (absolute dry mass (g) of hydrogen-type CM-formed cellulose)
DS = 0.162 x A / (1-0.058 x A)
A: 1N NaOH amount (mL) required to neutralize 1 g of hydrogen-type CM-formed cellulose
F: 0.1N H ₂ SO ₄ factor F': 0.1N NaOH factor

[Measurement of pyrolysis temperature]
The thermal decomposition temperature of the ceramic binder obtained in each example was measured by using a thermal analyzer DTA (manufactured by Rigaku Co., Ltd.) at a heating rate of 10 ° C./min and under a nitrogen atmosphere with the temperature and mass of the ceramic binder. Changes were measured. The temperature reduced by 50% from the initial mass was defined as the 50% decomposition temperature (T ₅₀ ). The results are shown in Table 1.

<Example 1>
5.00 g (absolutely dry) of bleached unbeaten kraft pulp (whiteness 85%) derived from coniferous trees is TEMPO (Sigma Aldrich) 39 mg (0.05 mmol per 1 g of absolute dry cellulose) and 514 mg of sodium bromide (absolutely dry). It was added to 500 mL of an aqueous solution in which 1.0 mmol) was dissolved in 1 g of cellulose, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite content was 6.0 mmol / g, and the oxidation reaction was started. Although the pH in the system decreased during the reaction, 3M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system did not change. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g. This was adjusted to pH 8 and 1.0% (w / v) with water and sodium hydroxide, and treated three times with an ultra-high pressure homogenizer (20 ° C., 150 MPa) to obtain a carboxylated cellulose nanofiber salt as a binder for ceramics. A (COONa type) aqueous dispersion was obtained. The average fiber diameter was 3 nm and the aspect ratio was 250.

<Example 2>
A cation exchange resin (“Amberjet 1024” manufactured by Organo Corporation) was added to the aqueous dispersion of the carboxylated cellulose nanofiber salt obtained in Example 1, and the mixture was stirred and contacted at 20 ° C. for 0.3 hours. .. Then, the cation exchange resin and the aqueous dispersion were separated by a metal mesh (opening 100 mesh) to obtain an aqueous dispersion of carboxylated cellulose nanofibers (COOH type) as a binder for ceramics in a yield of 95%. rice field. The average fiber diameter was 3 nm and the aspect ratio was 240.

<Example 3>
To a stirrer that can mix pulp, add 200 g of pulp (LSP (hardwood sulphite pulp), manufactured by Nippon Paper Industries Co., Ltd.) by dry mass and 111 g of sodium hydroxide by dry mass to reduce the solid content of pulp to 20% by mass. Water was added so that it would be. Then, after stirring at 30 ° C. for 30 minutes, 216 g (in terms of active ingredient) of sodium monochloroacetate was added. After stirring for 30 minutes, the temperature was raised to 70 ° C. and the mixture was stirred for 1 hour. Then, the reaction product was taken out and neutralized, and then washed to obtain a carboxylmethylated pulp having a carboxymethyl substitution degree of 0.25 per glucose unit. Then, the carboxymethylated pulp was adjusted to pH 8 and solid content 1% with water and sodium hydroxide, and defibrated by treating with a high-pressure homogenizer at a pressure of 20 ° C. and 150 MPa five times, and carboxy as a binder for ceramics. An aqueous dispersion of methylated cellulose nanofiber salt was obtained. The obtained carboxymethylated cellulose nanofibers had an average fiber diameter of 5 nm and an aspect ratio of 500.

<Example 4>
A cation exchange resin (“Amberjet 1024” manufactured by Organo Corporation) was added to the aqueous dispersion of the carboxymethylated cellulose nanofiber salt obtained in Example 3, and the mixture was stirred and contacted at 20 ° C. for 0.3 hours. rice field. After that, the cation exchange resin and the aqueous dispersion are separated by a metal mesh (opening 100 mesh), and 95% of the aqueous dispersion of carboxymethylated cellulose nanofibers (CH ₂ COOH type) as a binder for ceramics is collected. Obtained at a rate. The average fiber diameter was 5 nm and the aspect ratio was 500.

The results in Table 1 suggest that the binder for ceramics of the present invention containing cellulose nanofibers and a dispersion medium has a low thermal decomposition temperature.

Claims (1)

A binder for ceramics
Contains cellulose nanofibers and dispersion medium,
The cellulose nanofiber is a binder for ceramics which is a carboxymethylated cellulose nanofiber having a degree of carboxymethyl substitution of 0.01 to 0.50 .