JP2023173941A - Porous particle and method for producing the same - Google Patents

Abstract

To efficiently obtain porous particles which have good dispersibility to resin and use an environment-friendly base material by a simple method at low cost.SOLUTION: A production method includes the steps of: mixing a fine cellulose fiber slurry and a water-soluble porosifying agent; and obtaining porous particles from the mixture by a spraying and drying device. Porous particles contain a fine cellulose fiber as a main component, and has a BET specific surface area of 20-100 m2/g, a bulk density of less than 200 g/L, and an average fiber diameter of the fiber cellulose fiber of 10-1,000 nm.SELECTED DRAWING: Figure 1

Description

The present invention relates to porous particles containing fine cellulose fibers as a main component, and a method for producing the same. The present invention also relates to a resin composition in which porous particles and a resin are composited, and a molded article of the resin composition.

Fine cellulose fibers called microfibrillated cellulose and cellulose nanofibers (CNF) are lightweight, yet have high modulus of elasticity and high strength, and have been actively developed for use in composite materials. There are two methods for producing fine cellulose fibers: chemical treatments such as TEMPO oxidation treatment, acid treatment, and enzyme treatment, and mechanical treatments such as high-pressure homogenizers and millers. Fine cellulose fibers are obtained in the form of an aqueous dispersion. This aqueous dispersion is a slurry with a significantly low solids concentration due to its high viscosity. Therefore, methods for making composite materials with resin include methods of kneading dry pulp together with resin, methods of kneading until the water evaporates, and methods of removing water by freeze drying or spray drying and adding it to resin. Proposed.

As a method for obtaining CNF from which water has been removed, for example, Patent Document 1 proposes a method in which fine cellulose fibers obtained by TEMPO oxidation treatment are powdered using a spray drying device. However, with this method, when dried, cohesive force acts between the fine cellulose fibers, making it impossible to disperse them into single fibers in the resin, making it impossible for the fine cellulose fibers to exhibit their original performance.

Patent Document 2 proposes a method of producing CNF with a large specific surface area by adding an organic solvent such as t-butanol, benzene, or 1,4-dioxane to CNF, freeze-drying it, and then pulverizing it. Since both solvents freeze at below freezing temperatures, freeze-drying inhibits the cohesive force acting between the fibers, making it possible to obtain dry CNF with a large specific surface area, which can also be made into powder in a subsequent process. . However, freeze-drying is inefficient because it requires a long takt time and requires a pulverization step to obtain CNF in powder form. In addition, in drying methods other than freeze-drying, all organic solvents have low boiling points, so unless the solvent is replaced with another high-boiling point organic solvent, the organic solvent will volatilize before the water, and then the water will volatilize. Therefore, cohesive force acts between the fibers, making it impossible to obtain a high specific surface area. In addition, solvent replacement increases costs because a large amount of organic solvent is used, and is also unfavorable from the viewpoint of production efficiency, carbon neutrality, and SDGs.

In Patent Document 3, a hydrophilic liquid such as glycerin or a surfactant and a hydrophilic solid such as a water-soluble polysaccharide are added to bacterial cellulose or microfibrous cellulose to suppress the cohesive force acting between the fibers, A method of making it porous has been proposed. If it is porous, the penetration of the solvent will be good, and it is expected that the properties of fine cellulose fibers will be exhibited by improving redispersibility and anchoring the resin in the pores. However, the proposed hydrophilic liquid has extremely high hydrophilicity, so the effect of making it porous is low, and it has a good affinity with cellulose, so it is difficult to remove by drying. Similarly, surfactants cannot be removed by drying. Remaining impurities may cause problems; for example, when using a resin composition after kneading, impurities, especially surfactants, may bleed out, causing problems in adhesion and adhesion with other parts. Therefore, it is necessary to remove the surfactant by washing, which is inefficient. On the other hand, water-soluble polysaccharides do not have the effect of inhibiting hydrogen bonds between fibers, so they do not contribute to porosity in the first place.

Patent Document 4 discloses a method of obtaining a redispersible fine cellulose fiber dispersion by adding an organic solvent having a boiling point higher than that of the dispersion solvent to an aqueous dispersion of fine cellulose fibers to inhibit the cohesive force that acts during drying. is proposed. However, simply having a high boiling point does not effectively or uniformly inhibit the cohesive force, and it is not possible to uniformly disperse single fibers in the resin. Furthermore, if a solvent with a high boiling point or high hydrophilicity is used, there is a risk that it will remain in the fine cellulose fibers.

Patent Document 5 proposes a method that enables redispersion by adding hydrophobic inorganic fine particles to fine fibrous cellulose, but since inorganic fine particles have a low effect of preventing agglomeration between cellulose, porous Furthermore, since the inorganic fine particles remain in the raw material, it is not suitable for use in electronic/electrical parts such as printed circuit boards, where the contamination of impurities is likely to directly affect performance.

Furthermore, in recent years, there has been a growing movement to move away from plastics due to carbon neutrality and the social problem of ocean pollution caused by microplastics, and there are also many attempts to replace plastic particles with natural, environmentally friendly materials. .

Patent Document 6 proposes a method of replacing microbeads with cellulose particles. This method is the same as Patent Document 1, and since an aqueous dispersion of fine cellulose fibers is spray-dried, even if the surface is wrinkled, they are aggregated, and there is a risk that it may not be possible to uniformly disperse single fibers in the resin. There is.

International Publication No. 2011/071156 JP2020-158737A Japanese Patent Application Publication No. 9-132601 Special table 2018-521168 publication International Publication No. 2017/047631 International Publication 2019/151486

The present invention was made in view of the above-mentioned situation, and an object of the present invention is to obtain porous particles that have good dispersibility in resins and can be efficiently composited with resins. Another object of the present invention is to provide a manufacturing method that allows such porous particles to be obtained efficiently and at low cost using a simple method. Furthermore, we aim to create porous particles made from environmentally friendly materials.

As a result of intensive studies to solve the above problems, the inventors of the present invention found that porous particles with specific physical properties have excellent dispersibility in resins, and can be expected to improve the physical properties of resin compositions when composited with resins. The present invention has been completed.

That is, the present invention provides porous particles mainly composed of fine cellulose fibers, which have a BET specific surface area of 20 to 100 m ² /g, a bulk density of less than 200 g/L, and an average fiber diameter of the fine cellulose fibers of 10 to 1000 nm. The present invention relates to porous particles characterized by the following.

Preferably, the porous particles contain a water-soluble polymer.

The present invention also relates to porous particles obtained from a slurry containing a water-soluble porosity-forming agent together with the fine cellulose fibers.

It is preferable that the water-soluble porosity-forming agent has a boiling point of 180°C or higher and a water-octanol partition coefficient of -1.2 to 0.8.

The present invention also relates to a resin composition containing the porous particles and resin.

Furthermore, the present invention relates to a molded article containing the resin composition.

Furthermore, the present invention relates to a method for producing porous particles, which comprises the steps of mixing a fine cellulose fiber slurry and a water-soluble porosity-forming agent, and obtaining porous particles from the mixture using a spray drying device. It is preferable that the water-soluble porosity-forming agent has a boiling point of 180°C or higher and a water-octanol distribution coefficient of -1.2 to 0.8. Moreover, it is preferable that the water-soluble porosity-forming agent is a glycol ether or a carbonate.

In the present invention, the porous particles are mainly composed of fine cellulose fibers and have a large specific surface area, so when composited with a resin, the porous particles easily disintegrate into fibers and generate less coarse particles. , the physical properties of the resin composition can be improved. Furthermore, since the bulk density is less than 200 g/L, the torque during compounding can be lowered, and the moldability and production efficiency of the resin composition are excellent.

Electron microscope image of cellulose particles 1 according to Example 1 of the present invention Electron microscope image of cellulose particles 2 according to Example 2 of the present invention Electron microscope image of cellulose particles 3 according to Example 3 of the present invention Electron microscope image of cellulose particles 4 according to Example 4 of the present invention Electron microscope image of cellulose particles A according to Comparative Example 1 of the present invention Electron microscope image of cellulose particles B according to Comparative Example 2 of the present invention Electron microscope image of cellulose particles C according to Comparative Example 3 of the present invention Electron microscope image of cellulose particles D according to Comparative Example 4 of the present invention Electron microscope image of cellulose particles E according to Comparative Example 5 of the present invention

[Porous particles]
A first aspect of the present invention is a porous particle mainly composed of fine cellulose fibers, which has a BET specific surface area of 20 to 100 m ² /g, a bulk density of less than 200 g/L, and an average fiber diameter of the fine cellulose fibers. These porous particles are characterized by having a diameter of 10 to 1000 nm. The "main component" refers to the component with the highest content among the components constituting the porous particles, and the content is preferably 50% by weight or more, more preferably 70% by weight or more.

The BET specific surface area of the porous particles is 20 to 100 m ² /g. The BET method is used to measure the specific surface area. If the BET specific surface area is less than 20 m ² /g, the specific surface area is small, and when composited with a resin, it cannot be dispersed in a fibrous form, and the strength physical properties such as tensile strength, elastic modulus, and toughness expected for a resin composition are There is a possibility that the effects of improving heat stability such as improvement in heat resistance and low coefficient of linear thermal expansion may become insufficient. When the BET specific surface area of the porous particles exceeds 100 m ² /g, the viscosity when compounded with a resin increases significantly, and, for example, the torque applied to the rotor of a kneader increases. When this kneading torque becomes high, excessive energy and time are required to obtain a good dispersion state, resulting in poor production efficiency and increased cost.

The porous particles have a bulk density of less than 200 g/L. The bulk density can be measured using a known bulk density measuring device. When the bulk density is 200 g/L or more, for example, when compounding resin and porous particles using a kneading machine, there is an advantage that the kneading torque is small, but the small torque means that the specific surface area is small. This means that the porous particles are small, and there is a problem that the reinforcing effect of the resin by the porous particles becomes small.

Porous particles may be chemically modified. "Chemical modification" here means any treatment that replaces all or part of the hydroxyl groups of the fine cellulose fibers with functional groups different from the hydroxyl groups. Since there are functional groups suitable for modification depending on the resin used during compounding with a resin such as kneading, it is preferable to design the functional group to be substituted arbitrarily. For example, polypropylene and polyethylene, which are typical general-purpose resins, are preferably chemically modified with a functional group that imparts hydrophobicity, such as an alkyl group, a silyl group, or a phenyl group, by acylation or esterification with a hydroxyl group. Acylation and esterification of cellulose with hydroxyl groups are well known and commonly used in the technical field, and the chemical modification methods that can be applied to each state of fine cellulose fibers, such as powder, water dispersion, and organic solvent dispersion, differ; The chemically modified material to be used is not particularly limited. In particular, as chemical modification, it is preferable to use a hydrophobizing agent to replace the hydroxyl groups of cellulose with hydrophobic groups. Examples of such hydrophobic treatment include any hydrophobic treatment such as acylation, esterification, alkylation, etherification, tosylation, and epoxidation.

[Fine cellulose fiber]
The average fiber diameter of the fine cellulose fibers in the present invention is 10 nm to 1000 nm. When the fiber diameter is within this range, the dispersibility when composited with a resin is improved, and various effects expected from fine cellulose fibers, as described below, are exhibited. The average fiber diameter of the fine cellulose fibers is preferably 10 nm to 500 nm, more preferably 10 nm to 300 nm, even more preferably 20 nm to 200 nm. The average fiber diameter is measured using the following procedure. First, the obtained (porous) particles are placed on a sample stage and observed with a high-resolution electron microscope (FE-SEM) at a magnification of 20,000 times, and lines are drawn in the horizontal and vertical directions of the obtained SEM image. Next, the fiber diameters of at least 20 or more fibers that intersect with the two lines are actually measured from the enlarged image, and the number average fiber diameter is calculated from the measurement results. Furthermore, the number average fiber diameters are similarly calculated for at least two locations on the surface of the powder placed on the sample stage, and the average value of all the number average fiber diameters is taken as the average fiber diameter.

Such fine cellulose fibers are obtained by micronizing cellulose fibers. The equipment for micronizing cellulose fibers is not particularly limited, but includes, for example, high-pressure homogenizer treatment (high-pressure dispersion treatment using a Manton-Gorlin type disperser), Lanier type pressure homogenizer, ultra-high pressure homogenizer treatment (UltamizerTM), etc. (manufactured by Sugino Machine Co., Ltd.), a dispersion device such as a bead mill or a meteor mill, and a homogenizer such as a mass colloider (manufactured by Masuko Sangyo Co., Ltd.). Since the production efficiency of the above-mentioned micronization processing apparatus is generally low, it is preferable to perform pretreatment in advance with a crusher because the production efficiency will be increased. Although the degree of beating of cellulose fibers is not particularly limited, it is also possible to use a beating machine used for paper manufacturing, such as a double disc refiner or a beater, for pretreatment before the finer treatment. In particular, in the case of a micronization processing device such as a high-pressure homogenizer that passes through an orifice, if beating is not performed in the pretreatment, there is a risk that the raw material will become clogged, making stable micronization processing impossible.

There are no particular limitations on the cellulose fibers that can be used in the micronization process, and known ones can be used, such as softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), softwood bleached sulfite pulp (NBSP), etc. Mechanical pulps such as wood bleaching chemical pulp, ground wood pulp (GP), thermomechanical pulp (TMP), chemical thermomechanical pulp (BCTMP); non-wood pulps such as hemp, bamboo, straw, kenaf, mitsumata, mulberry, cotton; Waste paper pulp can be used. One type of these cellulose fibers can be used alone or two or more types can be used in combination. In the present invention, the type of cellulose such as cellulose type I and cellulose type II is not particularly limited, but cellulose type I natural fibers such as cotton, cotton linters, and wood pulp are preferred. More preferred is NBKP, which is a bleached wood pulp derived from coniferous trees in which fibrillation progresses more easily than cutting during fibrillation of fibers. Cellulose type II fibers, represented by regenerated cellulose, have a lower degree of crystallinity than cellulose type I fibers, so they tend to become short fibers during fibrillation treatment, and are less effective in improving strength when composited with resin. This is not preferable as there is a risk of this happening.

The cellulose fibers are mainly used, but if necessary, modified pulps such as cationized pulp and mercerized pulp, synthetic fibers and chemical fibers such as rayon, vinylon, nylon, acrylic, polyester, polyolefin, carbon, and aramid, Alternatively, microfibrillated pulp can be used alone or in combination. The proportion of cellulose fibers is 50% by weight or more, preferably 60% by weight or more, and more preferably 70% by weight or more, based on all the fibers constituting the porous particles of the present invention.

Cellulose fibers can be uniformly dispersed in water due to the hydroxyl groups of cellulose molecules, but the viscosity of the slurry depends on the fiber length and surface area of the cellulose fibers. For example, even if cellulose fibers of the same weight exist, if the fiber diameter of the cellulose fibers is small, the number of fibers will inevitably increase, and the surface area of cellulose will increase accordingly, which will inevitably increase the viscosity of the slurry. It turns out. Fine cellulose fibers obtained by chemical treatments such as TEMPO oxidation treatment can be obtained with fiber diameters on the order of single nanometers, but for the above-mentioned reasons, their viscosity is extremely high, making it impossible to use highly concentrated slurry. In the present invention, in which porous particles mainly composed of fine cellulose fibers are obtained, the concentration is not preferred because it is greatly influenced by cost.

On the other hand, fine cellulose fibers obtained by chemical treatments such as TEMPO oxidation treatment have an average fiber diameter of less than 10 nm, on the order of single nanometers, and the cohesive force acting between the fibers is strong, so there is a risk that they cannot be obtained as porous particles in the present invention. It is also difficult to measure the average fiber diameter in the particle state. Therefore, CNF subjected to TEMPO oxidation treatment with a carboxyl group content of 0.1 mmol/g or more, at least 1.2 mmol/g or more is not preferable for the present invention. Therefore, the carboxy group content of the fine cellulose fibers of the present invention is preferably less than 1.2 mmol/g, more preferably less than 0.1 mmol/g. If it is difficult to measure the average fiber diameter, use a transmission electron microscope. A dispersion of fine cellulose fibers with a concentration of 0.05% is prepared, and this dispersion is applied onto a hydrophilic carbon-coated grid to serve as an observation sample. Observation is performed at a magnification that allows the thinnest fibers to be seen, and lines are drawn in the horizontal and vertical directions of the obtained TEM image. Next, the fiber diameters of at least 20 or more fibers that intersect with the two lines are actually measured from the enlarged image, and the number average fiber diameter is calculated from the measurement results. Furthermore, the number average fiber diameters are similarly calculated for at least two locations on the surface of the observation sample, and the average value of all the number average fiber diameters is taken as the average fiber diameter. Further, when measuring the average fiber diameter of a slurry of mechanically treated CNF, the same method can be used, but the observation is performed at a magnification of 20,000 times.

The method for measuring the carboxy group content is as follows. Take cellulose fibers with a dry weight of 0.5 g in a 100 mL beaker, add ion-exchanged water to make a total of 55 mL, add 5 mL of 0.01 M sodium chloride aqueous solution to prepare a dispersion liquid, and stir until the cellulose fibers are sufficiently dispersed. The dispersion is stirred. The pH was adjusted to 2.5 to 3 by adding 0.1M hydrochloric acid to this dispersion, and using an automatic titrator (AUT-50, manufactured by DKK Toa Co., Ltd.), a 0.05M aqueous sodium hydroxide solution was added to the solution for a waiting time. It is added dropwise to the dispersion for 60 seconds, and the conductivity and pH values are measured every minute. Measurements are continued until the pH reaches about 11 to obtain a conductivity curve. From this conductivity curve, the titer of sodium hydroxide is determined, and the carboxyl group content of the cellulose fibers is calculated using the following formula.

Carboxy group content (mmol/g) = sodium hydroxide titration x sodium hydroxide aqueous solution concentration (0.05M)/weight of cellulose fiber (0.5g)

Due to its hydroxyl groups, cellulose fibers have the property of forming hydrogen bonds between fibers during the dehydration process. In the case of sheets such as paper, for example, strength is developed in the process of forming hydrogen bonds, while shrinkage occurs in the drying process due to interaction between fibers. In particular, as the fiber diameter decreases, the stiffness of the fibers decreases and the cohesive force acting between the fibers increases, so this shrinkage is noticeable. Furthermore, it is known that sheets made using extremely fibrillated fibers have complete adhesion between the fibers, so that the films made become transparent. In other words, it is difficult to obtain particles in the form of fine cellulose fibers using normal dehydration and drying methods. Therefore, it is necessary to suppress shrinkage during drying or to inhibit hydrogen bonding between fibers. The specific method that has been proposed so far is to replace fine cellulose fibers with a hydrophilic solvent such as acetone, then replace them with a more hydrophobic solvent such as a mixed solvent of toluene and acetone, and then dry them. Other methods have been proposed. However, this method has two problems. The first step is to replace the dispersion solvent, water, with acetone. Cellulose fibers have a higher water retention capacity as the fiber diameter becomes smaller, so replacing water with a solvent is a very time-consuming process and is a factor that reduces productivity in actual production. In addition, since the substitution is made with a highly hydrophobic solvent, hydrogen bonds are inhibited, and the surface tension of the solvent is also low, so although the cohesive force is smaller than that of water, shrinkage occurs, so that fine cellulose fibers are A decrease in the large specific surface area that it had was inevitable.

Therefore, the porous particles of the present invention are preferably obtained from a slurry containing fine cellulose fibers and a water-soluble porosity-forming agent. Specifically, as a method to remove water without shrinking or agglomerating fine cellulose fibers after micronization treatment, production efficiency is greatly improved by drying a slurry containing a water-soluble porosity-forming agent. be able to. This water-soluble porosity-forming agent preferably has a boiling point of 180°C or higher. Furthermore, in the present invention, the specific surface area of the porous particles can be controlled by adjusting the amount of the water-soluble porous agent added. For example, in the present invention, the water-soluble porosity-forming agent can be used preferably in a proportion of 50 to 1000 parts by weight per 100 parts by weight (mass) of fine cellulose fibers.

Although the water-soluble porosity-forming agent used in the present invention is not particularly limited, it is preferable that the boiling point of the water-soluble porosity-forming agent is 180°C or higher. It is known that hydrogen bonds between fibers are formed when the dry moisture content is between 10 and 20% by weight. When this hydrogen bond is formed, a water-soluble porosity-forming agent is present in the particles and inhibits the hydrogen bond and cohesive force acting between the fibers, making it possible to make the particles porous. If a water-soluble porosity-forming agent with a boiling point of less than 180° C. is used, even if the amount added is increased, it will volatilize during the drying process, and it will not be possible to achieve sufficient porosity. Therefore, a water-soluble porosity-forming agent having a boiling point of 180°C or higher is preferable, and more preferably 200°C or higher. For example, primary alcohols with a molecular weight lower than hexanol are materials that are both water-soluble and hydrophobic, but they are more volatile than water during the drying process and cannot sufficiently inhibit hydrogen bonding and cohesive force. It cannot be used in the present invention. However, drying methods different from normal drying conditions were used, such as drying using air filled with the vapor of a water-soluble porosity-forming agent, or using multi-stage drying using a solvent with a lower vapor pressure than water. In this case, the boiling point does not necessarily need to be 180°C or higher.

The water-soluble porosity-forming agent preferably has a solubility in water of 10% by weight or more, more preferably 20% by weight or more. When using a porosity-enhancing agent with a solubility in water of less than 10% by weight, the amount of porosity-enhancing agent added is limited, so the desired BET specific surface area can be controlled only by the amount of porosity-enhancing agent added. It can be difficult to do so. Further, as the drying progresses, the amount of solvent decreases and the porosity-forming agent that cannot be dissolved is separated, which may make it difficult to uniformly form pores. Note that such a hydrophobic porosity-forming agent can be emulsified with an emulsifier or the like to make the pores uniform to some extent, but the uniformity is inferior to that of a water-soluble porosity-forming agent. On the other hand, when a porosity-enhancing agent with a solubility in water of 10% by weight or more is used, it can be uniformly dispersed in the slurry, and since it has a high solubility in water, it does not separate during the drying process. By uniformly inhibiting hydrogen bonds during the process, uniform pores can be created.

The water-soluble porosity-forming agent preferably has a water-octanol partition coefficient of -1.2 to 0.8, more preferably -1.0 to 0.6, and more preferably -0.5 to 0.5. It is more preferably 0 to 0.4, and even more preferably 0 to 0.4. The water-octanol partition coefficient is an evaluation value of hydrophilicity and hydrophobicity. After adding a water-soluble porosity-forming agent to a flask containing n-octanol and water, it is shaken to form a water-soluble porosity in each phase. It is calculated from the concentration of the curing agent using the following formula.

"Water-octanol partition coefficient" = Log10 (concentration in octanol phase/concentration in water phase)

If the value of this water-octanol partition coefficient is too low, there is a risk of causing aggregation between cellulose fibers due to high hydrophilicity. In addition, if the value is too high, the water-soluble porosity-forming agent has high hydrophobicity and the amount that can be added to the slurry is limited, so there is a risk that the desired performance may not be obtained.

Specifically, the water-soluble porosity-forming agent that can be used in the present invention includes the following. For example, higher alcohols such as 1,5-pentanediol and 1-methylamino-2,3-propanediol, lactones such as iprosin caprolactone and α-acetyl-γ-butyllactone, diethylene glycol, and 1,3-butylene glycol. , glycols such as propylene glycol, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, diethylene glycol monobutyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether, triethylene glycol monobutyl ether , glycol ethers such as tetraethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monoisobutyl ether, tripropylene glycol monomethyl ether, diethylene glycol diethyl ether, propylene carbonate, ethylene carbonate, etc. Other examples include, but are not limited to, glycerin, N-methylpyrrolidone, and the like. Among these, glycol ethers and carbonates have high boiling points and many have low water/octanol partition coefficients even if they have high solubility in water, and are therefore most suitable for the present invention.

In addition to the fine cellulose fibers and the water-soluble porosity-forming agent, the slurry used in the present invention contains 3 to 80 parts by weight of a water-soluble polymer as a binder for connecting the fibers, preferably 3 to 80 parts by weight per 100 parts by weight of the cellulose fibers. It is preferable that the amount is 5 to 50 parts by weight, more preferably 10 to 30 parts by weight. In addition to its function as an adhesive, the water-soluble polymer can also function to improve the dispersibility of cellulose. In order to obtain uniform pores, it is necessary for the fibers to be uniformly dispersed in the slurry, but water-soluble polymers fix on the surface of cellulose fibers and play a role similar to a protective colloid, resulting in poor dispersibility. improves. If the amount of water-soluble polymer added is less than 3 parts by weight, the dispersibility of fine cellulose fibers will deteriorate, making it difficult to obtain uniform pores. On the other hand, if the amount is more than 80 parts by weight, the water-soluble polymer will fill the pores and cannot be dispersed when compounded with the resin, which is not preferable.

The water-soluble polymers include cellulose derivatives such as methylcellulose, carboxymethylcellulose (CMC), hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and hydroxyalkylcellulose, and polysaccharides such as phosphoesterified starch, cationized starch, and cornstarch. Preference is given to using derivatives of. In particular, cellulose derivatives are particularly preferred because they have good compatibility with cellulose fibers and can improve dispersibility in the slurry.

In addition, the slurry containing fine cellulose fibers and a water-soluble porosity-forming agent may contain fillers in addition to the water-soluble polymer. For example, inorganic fillers such as silica particles and alumina particles, organic fillers such as silicone powder, etc. can be used. These particles can be added to the extent that they do not affect the pores or specific surface area of the porous particles, but it is preferable to use particles with an average particle diameter of less than 2 μm as much as possible. If the average particle diameter is 2 μm or more, pores with large pore diameters will open due to gaps between particles, resulting in an excessively high bulk, which is not preferable. In addition, since these fillers have the effect of lowering the viscosity of the slurry, it is possible to increase the slurry concentration, which is suitable for increasing production efficiency. On the other hand, if the amount added is too large, the specific surface area may decrease or increase significantly depending on the particles added, and impurities may increase, which is not preferable.

Basically, it is necessary to use water as the solvent for the slurry used in the present invention, but for the purpose of improving drying efficiency, alcohols such as methanol, ethanol, t-butyl alcohol, ketones such as acetone, methyl ethyl ketone, etc. It is possible to add up to 50% by weight of the total amount of solvents, such as ethers such as diethyl ether and ethyl methyl ether, which have a higher vapor pressure than water. Addition of 50% by weight or more of these solvents is not preferable because the dispersibility of fine cellulose fibers deteriorates and pores become non-uniform.

In the present invention, the method for drying the slurry containing fine cellulose fibers and a water-soluble porosity-forming agent into particles is not particularly limited, but spray drying can be suitably used.

For spray drying, a known spray drying device can be used. Examples of atomizers include disk-type atomizers and pressurized nozzles, and pressurized nozzles include two-fluid nozzles and three-fluid nozzles. The atomizer to be used can be appropriately selected depending on the particle size and properties of the slurry, but in the case of the nozzle method in the present invention, there is a risk of clogging due to poor dispersion of fine cellulose fibers, so a disk-type atomizer is preferable. .

The spray drying device used in the present invention is not limited to the specifications described above, but commonly available spray drying devices such as CL-8i manufactured by Okawara Kakoki Co., Ltd. can be used.

Since the sprayer is generally installed in a drying oven, the resulting particles are collected in a dry state, but other drying equipment may be used to volatilize the residual solvent.

The solid content of the porous particles is preferably 80% by weight or more, more preferably 85% by weight or more, and even more preferably 90% by weight or more.

[Resin composition]
A second aspect of the present invention is a resin composition containing the porous particles and resin described above.

Thermoplastic resins, thermosetting resins, and rubbers can be used in the resin composition of the present invention. There are no particular restrictions on the type of resin that can be used, but examples of thermoplastic resins include polyethylene resin, polypropylene resin, polylactic acid resin, polyvinyl alcohol resin, polyamide resin, acrylonitrile-butadiene-styrene resin, acrylonitrile-styrene resin, and polystyrene resin. Examples include methyl methacrylate resin, polyvinylidene chloride resin, ethylene vinyl alcohol resin, polyacrylonitrile resin, polyacetal resin, polyketone resin, and cyclic polyolefin resin. Examples of thermosetting resins include epoxy resins, phenol resins, melamine resins, urea resins, and unsaturated polyester resins. Examples of rubber include natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, butyl rubber, nitrile rubber, chloroprene rubber, acrylic rubber, fluororubber, ethylene propylene rubber, chlorosulfonated polyethylene, urethane rubber, and silicone. Examples include rubber. In addition, the resin composition may include antifoaming agents, preservatives, fillers, colorants, plasticizers, leveling agents, conductive agents, antistatic agents, ultraviolet absorbers, and deodorants to the extent that the performance of the present invention is not impaired. , auxiliary agents such as heat-resistant materials, and fiber materials such as reinforcing fibers, conductive fibers, and heat-resistant fibers can be mixed as appropriate.

The resin composition of the present invention can be obtained as a molded article by various molding methods. Appropriate molding methods need to be used depending on the type of resin and the desired shape of the molded product; examples include extrusion molding, injection molding, hot press molding, melt extrusion molding, blow molding, vacuum molding, and heat molding. .

Regarding the porous particles, the above explanation regarding the first aspect of the present invention also applies to the second aspect.

There are no particular limitations on the method of compounding the porous particles and the resin, and known methods such as melt kneading and dry mixing may be used, but melt kneading is preferred. During kneading, the fine cellulose fibers are porous and particulate, so that they can be uniformly dispersed in the resin. Further, chemical modification depending on the type of resin can be applied. For kneading, a known kneader such as an extruder, mixing roller, kneader, or mixer can be used.

[Molded object]
A third aspect of the present invention is a molded article containing a resin composition.

Regarding the resin composition, the above explanation regarding the second aspect of the present invention also applies to the third aspect.

The molded article refers to any form such as a film, a sheet, or a structure, and is produced using a resin composition. The method for producing the molded body is not particularly limited and any known method may be used, such as injection molding, extrusion molding, blow molding, press molding, etc.

The form and manufacturing method of the molded body can be selected depending on the purpose of use. It can be used in place of parts used in electronic devices, home appliances, various containers, building materials, furniture, stationery, automobiles, and household goods. For example, it can be used for the housings and exterior parts of electronic devices and home appliances, various storage cases, tableware, interior parts of building materials, interior materials of automobiles, and other daily life items.

[Method for manufacturing porous particles]
A fourth aspect of the present invention is a method for producing porous particles, comprising the steps of mixing a fine cellulose fiber slurry and a water-soluble porosity-forming agent, and obtaining porous particles from the mixture using a spray drying device. Regarding the fine cellulose fibers, slurry, water-soluble porosity-forming agent, and porous particles, the explanations in other aspects of the present invention also apply to the fourth aspect. Moreover, the porous particles according to the first aspect of the present invention can be efficiently manufactured by the manufacturing method according to the fourth aspect of the present invention.

The porous particles of the present invention can be obtained by a manufacturing method that includes at least a step of mixing a fine cellulose fiber slurry and a water-soluble porosity-forming agent, and a step of obtaining porous particles from the mixture using a spray drying device. A water-soluble polymer may be further mixed in the step of mixing the fine cellulose fiber slurry and the water-soluble porosity-forming agent. Regarding the water-soluble polymer, the explanation in other aspects of the present invention also applies here.

Hereinafter, the present invention will be explained in more detail using Examples and Comparative Examples, but the scope of the present invention is not limited to the Examples.
(Measurement items and test methods in Examples)

[Measurement of solid content of cellulose particles]
5 g of cellulose particles are collected, placed in a weighing bottle, weighed before drying, dried in an oven at 105° C. until a constant weight is reached, and weighed after drying. It was calculated using the following formula from the weight of the cellulose particles before and after drying after subtracting the weight of the weighing bottle.

Solid content (%) = Weight after drying (g) / Weight before drying (g) × 100

[Measurement of BET specific surface area]
A specific surface area measuring device (Belsorp max, manufactured by Microtrac Bell Co., Ltd.) was used for the measurement. Measurement was performed under the conditions of adsorption gas: nitrogen, sample amount: 0.1 g, pretreatment: 120°C for 3 hours, and BET Plot was calculated from the measurement data in the relative pressure range of 0.05 to 0.30 (P/P0). The BET specific surface area was calculated.

[Particle size measurement]
A laser diffraction particle size distribution analyzer (model: LA-950, manufactured by Horiba, Ltd.) was used for the measurement. A small amount of cellulose particles are added to 10 mL of acetone, stirred with a magnetic stirrer, and then dispersed for 10 seconds with an ultrasonic cleaner (manufactured by Branson). The dispersion is added to a measurement cell that has been filled with acetone in advance until it reaches the measurement area, and then the measurement is performed. The refractive index was set to 1.47 for cellulose particles and 1.3591 for acetone, and the particle size distribution was obtained. The average particle diameter was defined as the median diameter (d50).

[Bulk density measurement]
The measurement was carried out using a bulk density measuring device (model: KAM-1, manufactured by As One Corporation). Cellulose particles are loaded into the chute of the measuring device, opened, and dropped into a 100 mL container placed below. After removing the excess cellulose particles by scraping them off, the weight of the cellulose particles in the container was measured and calculated from the following formula.

Bulk density (g/mL) = particle weight (g) / particle volume (mL)

[Combined test]
For the compounding test, a kneader (trade name: Laboplasto Mill, model: 4C-150, manufactured by Toyo Seiki Co., Ltd.) and a mixer (model: R60, manufactured by Toyo Seiki Co., Ltd.) were used. 41 g of polypropylene resin (model number: J105G, manufactured by Prime Polymer Co., Ltd.) was weighed, put into a mixer heated to 220° C., and pre-kneaded at 10 rpm. Thereafter, the rotation speed was changed to 30 rpm, and 1 g of fine cellulose fiber powder was weighed and added. After the addition was completed, the rotation speed was changed to 50 rpm, and kneaded for 10 minutes. Then, the torque value at the end of kneading was read.
Further, the torque value of only the polypropylene resin was measured in advance, and a value of △ or higher was considered to be a pass based on the following criteria.

○: 1.2 times or more and less than 1.5 times the torque value of resin only △: 1.5 times or more and less than 2.0 times, or 1.1 times or more and less than 1.2 times the torque value of resin only ×: 2.0 times or more of the torque value of resin only, or 1.0 times or more and less than 1.1 times

[Dispersibility evaluation]
Weigh 30 mg of the composite resin, place it on a slide glass, and heat it with a hot stirrer (trade name: REXIM, model: RSH-6DN, manufactured by As One Corporation) at 240°C. Once the resin has melted, cover it with another glass slide, press it, and cool it to obtain a sample for dispersion evaluation.
A biological microscope (trade name: Eclipse, model: Ni-U, manufactured by Nikon Corporation) equipped with a differential interference device and a phase contrast device was used for dispersibility evaluation. 10 visual fields were randomly observed at a magnification of 200 times, coarse objects of 10 μm or more were counted, and based on the total number of 10 visual fields, △ or higher was considered to be a pass based on the following criteria.
〇: Less than 10 large objects △: 10 or more to less than 100 large objects ×: 100 or more large objects

[Measurement of average fiber diameter]
When porous particles are obtained using fine cellulose fibers 1 and 2, the particle surface is observed using a high-resolution electron microscope (Model: SU-8020, manufactured by Hitachi High-Technology), and the horizontal SEM image obtained at 20,000 times Draw a line in the direction and vertically. Next, the fiber diameters of at least 20 or more fibers intersecting the two lines are actually measured from the enlarged image, and the number average fiber diameter is calculated from the measurement results. Furthermore, the number average fiber diameter was calculated in the same way for two locations on the surface of the fiber sheet, and the average value of the number average fiber diameters was taken as the average fiber diameter. A dispersion of fine cellulose fibers with a concentration of 0.05% was prepared, and this dispersion was applied onto a hydrophilized carbon-coated grid as an observation sample using a transmission electron microscope (Model: JSM-2100, Japan). (manufactured by Denshisha). Lines are drawn in the horizontal and vertical directions of the TEM image obtained at a magnification of 20,000 times for mechanically treated CNF and at a magnification that allows the thinnest fibers to be seen for TEMPO oxidized CNF. Next, the fiber diameters of at least 20 or more fibers that intersect with the two lines are actually measured from the enlarged image, and the number average fiber diameter is calculated from the measurement results. Furthermore, the number average fiber diameters are similarly calculated for at least two locations on the surface of the observation sample, and the average value of all the number average fiber diameters is taken as the average fiber diameter.

(Example 1)
[Preparation process 1 of fine cellulose fiber]
Bleached softwood kraft pulp was dispersed in ion-exchanged water to a concentration of 2% by weight, beaten using a double-disc refiner as a pretreatment, and further heated to a pressure of 750 bar using a high-pressure homogenizer (model: LAB1000, manufactured by SMT). Fine cellulose fiber slurry 1 was obtained by adjusting the temperature and performing the treatment 10 times.

[Mixing process]
In the fine cellulose fiber slurry 1 obtained in the above preparation step, carboxymethyl cellulose (product name: Sunrose, model number: MAC) was dissolved in ion-exchanged water to a concentration of 1% by weight based on 100 parts by weight of solid content of fine cellulose fibers. -200HC, manufactured by Nippon Paper Industries Co., Ltd.), 500 parts by weight of propylene carbonate as a water-soluble porosity-forming agent, and ion-exchanged water was added so that the final solid content concentration was 0.7% by weight. The slurry was dispersed using a homomixer (model: CM-100, manufactured by As One Corporation) until it was uniformly mixed, to obtain a fine cellulose fiber-containing material 1.

[Spray drying process]
The fine cellulose fiber-containing material 1 obtained in the above preparation step was spray-dried using a spray dryer equipped with a disc atomizer MC-50 (model: CL-8i, manufactured by Okawara Kakoki Co., Ltd.) to obtain cellulose particles 1. . Spray drying was carried out under the following conditions: flow rate: 35 mL/min, atomizer rotation speed: 35,000 rpm, inlet temperature: 180°C, outlet temperature: 100°C, and cyclone differential pressure: 0.60 kPa.

(Example 2)
Cellulose particles 2 were obtained in the same manner as in Example 1 except that no carboxymethyl cellulose was added in the above preparation step.

(Example 3)
Cellulose particles 3 were obtained in the same manner as in Example 1, except that propylene carbonate was changed to diethylene glycol monobutyl ether in the above preparation step, and the number of parts added was 350 parts by weight.

(Example 4)
[Preparation process 2 of fine cellulose fiber]
The fine cellulose fiber slurry 1 obtained in the above fine cellulose fiber preparation step 1 was diluted to 0.3% by weight, and the time was adjusted so that the concentration of the supernatant was 0.04 to 0.06% at 1500G. Centrifugation was performed and the supernatant liquid was collected. The supernatant is poured into a glass filter equipped with a polyethersulfone MF membrane with a pore size of 0.05 μm, and the supernatant is concentrated while stirring with a tabletop stirrer until the concentration is 1% by weight, resulting in a fine cellulose fiber slurry. I got 2.

[Blending process]
Cellulose particles 4 were obtained in exactly the same manner as in Example 1 except that the fine cellulose fiber slurry 1 was changed to this fine cellulose fiber slurry 2.

(Comparative example 1)
Cellulose particles A were obtained in the same manner as in Example 1 except that propylene carbonate was not added in the above preparation step.

(Comparative example 2)
[Preparation process 3 of fine cellulose fiber]
Bleached softwood kraft pulp was used, TEMPO (manufactured by Aldrich) was used as an oxidation catalyst, sodium hypochlorite (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., Cl: 5%) was used as an oxidizing agent, and bromide was used as a co-oxidizing agent. Sodium (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was used. Bleached softwood kraft pulp was dispersed in ion-exchanged water to a concentration of 1% by weight, TEMPO was added to the pulp at 1.25% by weight, sodium bromide was added to the pulp at 12.5% by weight, and sodium hypochlorite was added to the pulp at 28% by weight. 0.4% by weight of each was added in order, and the pH was maintained at 10.5 by dropwise addition of 0.5M sodium hydroxide to carry out the oxidation reaction. Dripping of sodium hydroxide was stopped after an oxidation time of 120 minutes to obtain oxidized pulp. This oxidized pulp was thoroughly washed with ion-exchanged water, diluted again to 1% by weight, and defibrated using a homomixer (model: CM-100, manufactured by As One Corporation) to obtain fine cellulose fiber slurry 3. .

[Blending process]
Cellulose particles B were obtained in exactly the same manner as in Example 2, except that the fine cellulose fiber slurry 1 was changed to the fine cellulose fiber slurry 3.

(Comparative example 3)
Cellulose particles C were obtained in the same manner as in Comparative Example 1, except that carboxymethylcellulose was not added in the preparation step and 10 parts by weight of titanium oxide (model number: TTO-51(C), manufactured by Ishihara Sangyo Co., Ltd.) was added.

(Comparative example 4)
Cellulose particles D were obtained in the same manner as in Example 1, except that propylene carbonate was replaced with triethylene glycol monomethyl ether in the blending step, and the number of parts added was 350 parts by weight.

(Comparative example 5)
Cellulose particles E were obtained in the same manner as in Example 1, except that propylene carbonate was replaced with dipropylene glycol dimethyl ether in the preparation step, and the number of parts added was 350 parts by weight.

1 to 4 are electron microscope images of the particles obtained in Examples 1 to 4, and it can be seen from these images that the particles obtained are porous. Furthermore, from the results of Examples 1 to 4 shown in Table 3, it was confirmed that when the porous particles of the present invention mainly composed of fine cellulose were combined with resin, the kneading torque increased due to the addition of resin during kneading. It can be seen that the performance of the resin can be expected to improve because it has good dispersibility and good dispersibility.

In Comparative Example 1, since no water-soluble porosity-forming agent was added, there were no pores as shown in the electron microscope image of FIG. 5, and the BET specific surface area shown in Table 3 was small. As a result, the dispersibility during kneading was poor and coarse particles were noticeable, and the torque was equivalent to that of the resin alone, so it can be seen that no improvement in the performance of the resin can be expected. Since Comparative Example 1 is non-porous, the fiber diameter is measured by TEM observation when the fine cellulose fibers 1 are in a dispersion state.

In Comparative Example 2, TEMPO oxidized CNF with an average fiber diameter of less than 10 nm is used for the fine cellulose fibers, so the cohesive force between the fibers is strong, and a wrinkled appearance is seen in the electron microscope image in Figure 6. However, no pores are formed and the BET specific surface area is small. This shows that the dispersibility during kneading was poor and coarse particles were noticeable, and the torque was equivalent to that of the resin alone, so it can be seen that no improvement in the performance of the resin can be expected.

In Comparative Example 3, a water-soluble porosity-forming agent was not added and titanium oxide was added instead, but it was not possible to prevent agglomeration between cellulose fibers, and no pores were formed as shown in Figure 7. , BET specific surface area is small. As a result, the dispersibility during kneading was poor and coarse particles were noticeable, and the torque was equivalent to that of the resin alone, so it can be seen that no improvement in the performance of the resin can be expected. Since Comparative Example 3 is non-porous, the fiber diameter is measured by TEM observation when the fine cellulose fibers 1 are in a dispersion state.

In Comparative Example 4, when the type of water-soluble porosity-forming agent was changed to triethylene glycol monomethyl ether, which has a large negative water/octanol partition coefficient value and is highly hydrophilic, it was found that aggregation between cellulose fibers could be prevented. As shown in FIG. 8, since no pores are formed, the BET specific surface area is small. As a result, the dispersibility during kneading was poor and coarse particles were noticeable, and the torque was equivalent to that of the resin alone, so it can be seen that no improvement in the performance of the resin can be expected. Furthermore, since it is highly hydrophilic, it has a high affinity with cellulose, and a large amount remains in particles, which may have an adverse effect when made into a composite material with a resin. Since Comparative Example 4 was non-porous, the fiber diameter was measured by TEM observation when the fine cellulose fibers 1 were in a dispersion state.

In Comparative Example 5, when the type of water-soluble porosity-forming agent was changed to triethylene glycol monomethyl ether, which has a boiling point of less than 180°C, the ethylene glycol monomethyl ether volatilized before the water when drying the slurry. Since aggregation between cellulose fibers cannot be prevented and pores are not generated as shown in FIG. 9, the BET specific surface area is small. As a result, the dispersibility during kneading was poor and coarse particles were noticeable, and the torque was equivalent to that of the resin alone, so it can be seen that no improvement in the performance of the resin can be expected. Since Comparative Example 5 is non-porous, the fiber diameter is measured by TEM observation when the fine cellulose fibers 1 are in a dispersion state.

Claims (13)

Porous particles mainly composed of fine cellulose fibers, characterized by having a BET specific surface area of 20 to 100 m ² /g, a bulk density of less than 200 g/L, and an average fiber diameter of the fine cellulose fibers of 10 to 1000 nm. porous particles. The porous particle according to claim 1, further comprising a water-soluble polymer. Porous particles according to claim 1 or 2, obtained from a slurry containing a water-soluble porosity-forming agent together with the fine cellulose fibers. The porous particles according to claim 3, wherein the water-soluble porosity-forming agent has a boiling point of 180°C or higher and a water-octanol partition coefficient of -1.2 to 0.8. A resin composition comprising the porous particles according to claim 1 or 2 and a resin. A resin composition comprising the porous particles according to claim 3 and a resin. A resin composition comprising the porous particles according to claim 4 and a resin. A molded article containing the resin composition according to claim 5. A molded article containing the resin composition according to claim 6. A molded article containing the resin composition according to claim 7. A method for producing porous particles, comprising the steps of mixing a fine cellulose fiber slurry and a water-soluble porosity-forming agent, and obtaining porous particles from the mixture using a spray drying device. The method for producing porous particles according to claim 11, wherein the water-soluble porosity-forming agent has a boiling point of 180° C. or higher and a water-octanol partition coefficient of -1.2 to 0.8. The method for producing porous particles according to claim 11 or 12, wherein the water-soluble porosity-forming agent is a glycol ether or a carbonate.

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