JP2020045374A - Method for producing resin composition - Google Patents

Abstract

To provide a method for producing a composition which is excellent in production efficiency and contains a fine cellulose fiber excellent in rigidity and heat resistance and a biodegradable resin.SOLUTION: In a method for producing a resin composition that melt-kneads a fine cellulose fiber and a biodegradable resin, the fine cellulose fiber has an average fiber width of 2-15,000 nm and an average fiber length of 0.1-2.0 mm, the fine cellulose fiber is powdery object, the powdery object contains moisture, a ratio of the moisture of the powdery object is 10-90 mass%, and melt-kneading is performed on such temperature and pressure conditions that water contained in the powdery object of the fiber cellulose fiber is in a subcritical state.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a resin composition, and more particularly, to a method for producing a resin composition containing fine cellulose fibers and a biodegradable resin.

  BACKGROUND ART Conventionally, for the purpose of improving the mechanical properties of a molded article made of a thermoplastic resin, a resin composition obtained by kneading cellulose resin with the thermoplastic resin has been used as a molding material. For example, Patent Literature 1 discloses a method in which cellulose fibers are dispersed in water and kneaded with a heated and melted thermoplastic resin by utilizing the high hydrophilicity of the cellulose fibers. Patent Document 2 discloses that after melt-kneading a first thermoplastic resin in which cellulose fibers are directly melted, pelletizing, dry-blending with pellets of a second thermoplastic resin, and melt-kneading again. A method involving at least a two-stage melt-kneading process is disclosed.

  On the other hand, in the field of plastics, biodegradable resins and seawater-decomposable resins have attracted attention in recent years from the viewpoint of environmental impact. However, biodegradable resins and the like have disadvantages such as low strength characteristics and heat resistance, and a long molding cycle time.

There is a technique in which a cellulosic material and a biodegradable resin are combined to compensate for the above-mentioned drawbacks of the biodegradable resin. Patent Literature 3 discloses a polylactic acid resin composition containing a polylactic acid resin, vegetable fiber, and powdered cellulose. Patent Document 4 discloses a biodegradable resin composition containing a biodegradable resin and cellulose having a crystallinity of less than 50%. Patent Document 5 discloses a method for producing a composition containing a polylactic acid resin and a cellulose having a crystallinity of less than 50% using a specific melt-kneading apparatus. Patent Document 6 discloses a composition containing 75% by weight or more of polylactic acid and 0.05 to 10% by weight of cellulose nanofibers. Patent Document 7 discloses a method for producing a fine cellulose fiber-containing resin composition, in which the proportion of water is 10 to 60% by mass and melt-kneading is performed under temperature and pressure conditions at which water is in a subcritical state. ing. Patent Document 8 discloses a composition containing a resin obtained by pulverizing a specific cellulose fiber-containing sheet and a resin.
However, none of these technologies has produced a cellulose-containing biodegradable resin composition having high productivity and sufficient rigidity and heat resistance.

Japanese Patent No. 5211571 Japanese Patent No. 5169188 JP 2007-138106 A JP 2011-006712 A JP 2011-152787 A Republished 2007/136086 JP 2017-128717 A JP 2018-131700 A

  In the field of biodegradable resins such as polylactic acid, there has been a demand for development of resin composites having excellent rigidity and heat resistance without impairing biodegradability.

  In order to solve the problems of the related art, the present inventors have developed a composition containing fine cellulose fiber and biodegradable resin having excellent production efficiency when performing compounding and having excellent rigidity and heat resistance. The study was conducted for the purpose of providing a method of manufacturing a product.

As a result of diligent studies to solve the above problems, the present inventors, in the state of containing a powdery material and biodegradable resin obtained by pulverizing a sheet containing a specific fine cellulose fiber, and, It has been found that, by melt-kneading at a temperature and a pressure in a subcritical state, a resin composition capable of molding a resin composite having excellent production efficiency and excellent rigidity and heat resistance can be obtained.
Specifically, the present invention has the following configuration.

[1] In the method for producing a resin composition by melt-kneading a fine cellulose fiber and a biodegradable resin, the fine cellulose fiber has an average fiber width of 2 to 15000 nm and an average fiber length of 0.1 to 2. 0 mm, the fine cellulose fiber is a powdery material, the powdery material contains water, the water content of the powdery material is 10 to 90% by mass, and the melt-kneading is performed using the fine cellulose fiber. A method for producing a resin composition, comprising: performing melt-kneading under conditions of temperature and pressure at which water contained in a powdery substance is in a subcritical state.
[2] The method for producing a resin composition according to [1], wherein the powdery material of fine cellulose fibers is obtained by shredding a sheet-like material of cellulose.
[3] The method for producing a resin composition according to [1] or [2], wherein the powdery material of the fine cellulose fibers is obtained by slicing a sheet of fibrillated cellulose fibers.
[4] The method for producing a resin composition according to any one of [1] to [3], wherein the biodegradable resin is pelletized in advance.
[5] The method for producing a resin composition according to any one of [1] to [4], wherein the biodegradable resin is polylactic acid.
[6] a pulverizing step of pulverizing pulp containing cellulose fibers;
A sheet forming step of forming the cellulose fibers subjected to the micronization treatment into a sheet,
Powdering step of powdering the sheet-like fine cellulose fibers,
The water content of the fine cellulosic fiber powder, water adjustment step of adjusting if necessary,
A method for producing a resin composition, comprising: a step of melt-kneading a powder of the fine cellulose fiber and a resin in a subcritical state.

  ADVANTAGE OF THE INVENTION According to the manufacturing method of this invention, the dispersibility of the fine cellulose fiber in resin can be made very high, and the molded object of machine parts etc. which have excellent rigidity and heat resistance can be provided.

  Hereinafter, the present invention will be described in detail. The description of the components described below may be made based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit and an upper limit.

<Fine cellulose fiber>
(Physical properties of fine cellulose fibers)
The fine cellulose fiber used for melt kneading is a fine cellulose fiber having an average fiber width of 2 to 15,000 nm and an average fiber length of 0.1 to 2.0 mm, and the fine cellulose fiber is a powder. It contains water, and the proportion of water in the powder is 10 to 90% by mass.

  The fine cellulose fiber is a fine cellulose fiber having an average fiber width of 2 to 15000 nm measured by the method described below. The fine cellulose fiber is preferably an aggregate of cellulose molecules having a type I (parallel chain) crystal structure. The average fiber width of the fine cellulose fibers is preferably 4 to 12000 nm, more preferably 20 to 10000 nm, and further preferably 50 to 8000 nm. When the average fiber width is 2 nm or more, the dissolution in water as cellulose molecules can be suppressed, so that physical properties (strength, rigidity, and dimensional stability) as fine fibers can be easily exhibited. In particular, when the average fiber width is 10,000 nm or less, the width becomes significantly narrower than the fiber width of the fibers contained in the ordinary papermaking pulp, and exhibits characteristics different from ordinary papermaking pulp. When the average fiber width of the fine cellulose fibers is within the above range, not all the fine cellulose fibers need to be within the range of the fiber width, and some of the fine cellulose fibers may have a fiber width exceeding the upper limit. , May be less than the lower limit. That is, thick fibers and thin fibers may be mixed.

The average fiber width is measured by the following method. An aqueous suspension of fine cellulose fibers having a solid content of 0.05 to 0.1% by mass is prepared, and the suspension is cast on a carbon membrane-coated grid subjected to hydrophilization to prepare a sample for electron microscope observation. . Observation with an electron microscope image is performed at a magnification according to the width of the fine cellulose fibers constituting the fibers. Here, the “width” is a shorter distance between ends of the fine cellulose fiber. However, the sample, observation conditions and magnification are adjusted so as to satisfy the following conditions (1) and (2).
(1) One straight line X is drawn at an arbitrary position in the observation image, and 20 or more fine cellulose fibers intersect the straight line X.
(2) In the same image, a straight line Y perpendicular to the straight line is drawn, and 20 or more fine cellulose fibers intersect the straight line Y.
The width of the fine cellulose fibers intersecting with the straight line X and the straight line Y is visually read from the observation image satisfying the above conditions. Thus, at least three sets of images of the non-overlapping surface portion and three or more different observation images are observed, and the width of the fine cellulose fiber intersecting with the straight lines X and Y is read for each image. In this way, a fiber width of at least 20 × 2 × 3 = 120 fibers is read. The fiber width in the present invention is an average value of the fiber widths thus read.

  The average fiber length of the fine cellulose fibers measured by the method described below is 0.1 mm to 2.0 mm. The average fiber length is preferably from 0.1 mm to 1.0 mm, more preferably from 0.3 mm to 0.6 mm. When the average fiber length of the fine cellulose fibers is equal to or more than the lower limit, the strength of the fine cellulose fiber-containing resin composition is more easily improved by the reinforcing effect of the fibers. When the content is equal to or less than the upper limit, the dispersibility of the fine cellulose fiber becomes good in the subsequent melt-kneading step. Further, the strength of the fine cellulose fiber-containing resin composition can be further improved.

  The measurement of the average fiber length is obtained by measuring the length-weighted average fiber length. For example, it can be measured using a Kayani fiber length measuring instrument (model FS-200) manufactured by Kayani Automation. In addition, the measurement of the average fiber length is not limited to the above-described device, and can be measured using an equivalent product. The fiber length of at least 120 fine cellulose fibers is measured, and the average value is defined as the average fiber length.

  The axis ratio (major axis / minor axis) of the fine cellulose fibers is preferably in the range of 20 to 10,000. When the axial ratio is 20 or more, it is easy to form a molded product, and when the axial ratio is 10000 or less, it is possible to prevent the viscosity of the fiber slurry from becoming excessively high. When the axial ratio is in the range of 20 to 10000, high drainage can be maintained in the step of making a mixed dispersion described below. The axial ratio in the present embodiment is a value obtained from an average fiber length measurement value obtained by using a Kajaani fiber length measuring device (model FS-200) manufactured by Kayani Automation and an average fiber width obtained by observation with an electron microscope. is there. Here, “long axis” means the average fiber length, and “short axis” means the average fiber width.

(Miniaturization process)
Examples of a method for refining the cellulose fibers include a method using a known pulverizer or a paper-making beating machine. For example, a method of pulverizing cellulose fibers by wet pulverization or dry pulverization and dissociating the cellulose fibers from each other can be used. The detailed miniaturization treatment is described in, for example, paragraphs 0032 to 0035 of WO2013 / 137449, and can be performed with reference to the description. In the present invention, a paper refining machine, particularly a refurbner or a beater, is preferred, and it is particularly preferred to dilute and swell cellulose with water and beat it.

It is preferable to beat the cellulose fiber so that the freeness is 100 to 500 ml as measured by the following measurement method (a).
The measurement method (a) is a method called “0.3 g method” or “irregular freeness measurement method” so that the content of the fine cellulose fibers contained in the aqueous dispersion is 0.3 g in absolute dry mass. The freeness of the water dispersion is measured in accordance with JIS P 8121-2 (2012) except that the adjustment is made and an 80 mesh sieve made of stainless steel wire is used as the sieve attached to the Canadian Standard Freeness Tester. .

  The freeness of the aqueous dispersion measured by the measurement method (a) may be 100 to 500 ml, preferably 150 to 450 ml, and more preferably 200 to 400 ml. By setting the freeness of the aqueous dispersion as measured by the measurement method (a) within the above range, it becomes easy to uniformly mix the resin component with the resin component. Furthermore, by setting the freeness of the aqueous dispersion as measured by the measurement method (a) to be within the above range, the rigidity and heat resistance of the resin composite (molded product) are increased, and the resin composite (molded product) is improved. ) Can have a good appearance.

  Before or after the cellulose fiber refining treatment, chemical modification treatment such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation treatment, phosphorus oxoacid treatment, ozone treatment, kraft treatment , Sulfite treatment, bleaching treatment, and enzyme treatment.

As a cellulose fiber raw material for obtaining fine cellulose fibers, it is preferable to use pulp (cellulose fiber-containing material). Pulp includes wood pulp, non-wood pulp, and deinked pulp. Examples of the wood pulp include hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolved pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen bleached kraft. Chemical pulp such as pulp (OKP) is exemplified. Also, semi-chemical pulp such as semi-chemical pulp (SCP) and chemical ground wood pulp (CGP), and mechanical pulp such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of the non-wood pulp include cotton pulp such as cotton linter and cotton lint, non-wood pulp such as hemp, straw and bagasse, cellulose isolated from sea squirt and seaweed, and the like. Examples of the deinked pulp include deinked pulp made from waste paper.
Among them, the cellulose fiber raw material is preferably virgin pulp. Here, the virgin pulp means pulp having no history of papermaking.

(Sheet forming process)
It is preferable that the above-mentioned fine cellulose fiber is once processed into a sheet shape to obtain a fine cellulose fiber-containing sheet. The method of forming the sheet is not particularly limited, but for example, a paper containing a fine cellulose fiber is used and the paper is formed by an ordinary paper making method. In this case, the solid content concentration of the slurry is preferably 0.1 to 10.0% by mass, more preferably 0.5 to 5.0% by mass. If the solid content concentration of the slurry containing fine cellulose fibers is equal to or more than the above lower limit, a powdery material sufficiently containing fine cellulose fibers can be easily produced in the powdering step described later. When the content is equal to or less than the upper limit, it is possible to prevent the slurry containing the fine cellulose fibers from forming an aggregate. The slurry of the fine cellulose fibers may contain a known papermaking chemical such as a sizing agent or a paper strength agent, if necessary.

  The moisture content of the fine cellulose fiber-containing sheet may be 10 to 90% by mass, preferably 12 to 80% by mass, and more preferably 15 to 70% by mass. By setting the moisture content of the fine cellulose fiber-containing sheet to 10% by mass or more, formation of strong hydrogen bonds between the cellulose fibers can be suppressed, and as a result, mixing with the resin is facilitated. Can be. Further, by setting the moisture content of the fine cellulose fiber-containing sheet to 90% by mass or less, it is possible to prevent the sheet from being broken during papermaking, and to facilitate mixing with the resin component. If the water content is excessive, the productivity at the time of kneading with the resin tends to decrease.

The moisture content of the fine cellulose fiber-containing sheet can be calculated by measuring the weight of the fine cellulose fiber-containing sheet cut into a predetermined size before and after drying. Specifically, the weight of the cut fine cellulose fiber-containing sheet before drying is measured, and then the cut fine cellulose fiber-containing sheet is dried at 110 ° C. for 3 hours, and the weight after drying is measured. The water content is calculated by the following equation.
Water content (%) = (weight before drying−weight after drying) / weight before drying × 100

The density of fine cellulose fiber-containing sheet is preferably 0.55~1.05g / cm ^3, more preferably 0.65~1.00g / cm ^3, 0.70~0.95g / cm ³ is more preferable. By setting the density of the fine cellulose fiber-containing sheet within the above range, pulverization can be easily performed, and uniform mixing with the resin component can be easily performed. In addition, by setting the density of the fine cellulose fiber-containing sheet within the above range, it is possible to suppress the sheet from being broken when the roll is wound up.

Conventionally, when producing a powder from an aqueous dispersion of fine cellulose fibers, it has been necessary to provide a step of removing water from the aqueous dispersion containing a large amount of water. Further, when producing a resin composite using an aqueous dispersion of fine cellulose fibers, it is difficult to knead with a resin component, or fine cellulose fibers may be aggregated in the step of concentrating the aqueous dispersion. In addition, there is a problem that the fine cellulose fibers are not uniformly dispersed in the resin component. By forming the fine cellulose fiber-containing sheet having a water content of 10 to 90% by mass once, the water content of the conventional water dispersion of fine cellulose fibers (usually 90 to 99.9%) is compared with that of the conventional water dispersion. Significantly less. For this reason, the energy required when pulverizing from the fine cellulose fiber-containing sheet can be reduced, and the production efficiency of the powder can be significantly increased. In addition, by pulverizing the fine cellulose fiber-containing sheet and kneading and melting it with the resin, it becomes easy to uniformly disperse the fine cellulose fibers in the resin component. As described above, the formation of the fine cellulose fiber-containing sheet is preferable because powdering and compounding can be efficiently performed.
The basis weight of the fine cellulose fiber-containing sheet is preferably 1.0~1000g / ^{m 2,} more preferably 5.0~500g / ^{m 2,} more preferably 10.0~100g / ^{m 2.} If the basis weight of the fine cellulose fiber sheet is equal to or more than the lower limit, sufficient sheet strength can be ensured and continuous production is facilitated.If the basis weight is equal to or less than the upper limit, the fine cellulose fiber-containing sheet is powdered in the subsequent stage. It becomes easier to do.

  The fine cellulose fiber-containing sheet may be in the form of a roll (winding) formed by continuously winding the sheet, or may be in the form of a single sheet (plain). For this reason, the sheet containing fine cellulose fibers has an advantage that it is excellent in handling properties and easy to transport. Further, when producing a sheet containing fine cellulose fibers, a conventional paper product or a conveying device for producing a sheet can be used as it is, so that costs for capital investment and the like can be suppressed. The obtained sheet containing fine cellulose fibers can be packaged with a film or wrapping paper. By packaging, it is possible not only to prevent water evaporation until the next powdering step, but also to prevent foreign matter from being mixed. The inclusion of foreign matter may cause a deterioration or abnormality in the quality of the obtained resin composition or a molded article using the resin composition.

(Powderizing step)
The fine cellulose fibers used in the present invention can be more easily and uniformly dispersed with the biodegradable resin by being powdery when melt-kneaded. As a result, the rigidity and heat resistance of the obtained resin composition can be further improved. The term "powder" does not necessarily mean that all of the fine cellulose fibers are powder.
It is preferable that the particle diameter (major axis) of the powdery material is 10 mm or less, and 0.1 mm or more is included in 50% or more. It is more preferably 7 mm or less, 0.3 mm or more, particularly preferably 5 mm or less, 0.5 mm or more. If the particle size of the powder exceeds 10 mm, the dispersibility in the resin is poor and the powder tends to be lump. When the particle size of the powdery material is 0.1 mm or less, the productivity of the powdery material is reduced, or the moisture is evaporated by the pulverizing energy, the fine cellulose fibers are easily aggregated, and the dispersibility in the resin is reduced. become worse.

  The method for obtaining the powdery material of the fine cellulose fibers is not particularly limited, but a method of slicing the fine cellulose fiber-containing sheet is preferable. For example, a method of cutting and pulverizing a sheet containing fine cellulose fibers can be used. The cutting or pulverization can be performed using a known pulverizer or shredder such as an atomizer, a cutter mill, a bead mill, a ball mill, and a jet mill.

The average particle diameter of the powdery substance can be measured by analyzing an image taken with an optical microscope or the like. Also, it can be measured by Cam Kaiser P4 manufactured by Verder Scientific Co., Ltd. or PITA-04 manufactured by Seishin Enterprise Co., Ltd.
When the obtained fine cellulose fiber powder is stored, it may be stored in a container or the like in order to prevent contamination of impurities and evaporation of water.

<Biodegradable resin>
The term “biodegradable” in the present invention refers to a property that can be decomposed into low molecular compounds by microorganisms in nature, and specifically, JISK6953 (ISO14855) “aerobic under controlled aerobic composting conditions”. And the ultimate biodegradability and disintegration test.
The biodegradable resin is not particularly limited as long as it is a resin having biodegradability, but a polyester resin excellent in affinity with fine cellulose fibers is preferable. It is considered that the polyester-based resin has an appropriate polarity and hydrophilicity and thus has an excellent affinity for fine cellulose fibers.

  Examples of the biodegradable polyester resin include polyhydroxybutyrate, polycaprolactone, polybutylene succinate, polybutylene succinate / adipate, polyethylene succinate, polylactic acid resin, polymalic acid, polyglycolic acid, polydioxanone, poly (2 -Oxetanone); aliphatic aromatic copolyester resins such as polybutylene succinate / terephthalate, polybutylene adipate / terephthalate, polytetramethylene adipate / terephthalate; starch, cellulose, chitin, chitosan, gluten, gelatin And a mixture of natural polymers such as zein, soy protein, collagen, and keratin with the above-mentioned aliphatic polyester resin or aliphatic aromatic copolyester resin. Among these, aliphatic polyester resins are preferred from the viewpoint of processability, economy, availability in large quantities, and the like, and polylactic acid resins are more preferred from the viewpoint of physical properties.

  Polylactic acid resin is a polylactic acid obtained by condensation polymerization of only a lactic acid component as a raw material monomer, and / or a polylactic acid obtained by condensation polymerization of a lactic acid component and a hydroxycarboxylic acid component as raw material monomers. contains.

  Lactic acid has optical isomers of L-lactic acid (L-form) and D-lactic acid (D-form). In the present invention, as the lactic acid component, any one of the optical isomers or both may be contained, but from the viewpoint of moldability, lactic acid having high optical purity containing any of the optical isomers as a main component is used. Is preferred.

  The content of the L-form or the D-form, that is, the content of the larger one of the isomers is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, and 98 to 100 mol% in the lactic acid component. % Is more preferred. In addition, since the total content of the L-form and the D-form in the lactic acid component is preferably substantially 100 mol%, the content of the smaller of the isomers is 0 to 0% in the lactic acid component. 20 mol% is preferable, and 0 to 10 mol% is more preferable.

  When only the lactic acid component is subjected to polycondensation, the content of the L-form or the D-form in the lactic acid component, that is, the content of the larger of the isomers is preferably 80 to 100 mol%, and 90 to 100 mol%. Is more preferable, and 98 to 100 mol% is further preferable. Since the total content of the L-form and the D-form in the lactic acid component is substantially 100 mol%, the content of the smaller of the isomers is 0 to 20 mol% in the lactic acid component. Is preferably 0 to 10 mol%, more preferably 0 to 2 mol%.

  When the lactic acid component and the hydroxycarboxylic acid component are polycondensed, the content of the L-form or D-form in the lactic acid component, that is, the content of the larger one of the isomers is preferably 85 to 100 mol%, 90-100 mol% is more preferable. Since the total content of the L-form and the D-form in the lactic acid component is substantially 100 mol%, the content of the smaller of the isomers is 0 to 15 mol% in the lactic acid component. Is preferable, and 0 to 10 mol% is more preferable.

  On the other hand, examples of the hydroxycarboxylic acid component include hydroxycarboxylic acid compounds such as glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid, and hydroxyheptanoic acid, and are used alone or in combination of two or more. can do. Among these, glycolic acid and hydroxycaproic acid are preferable from the viewpoints of compatibility of strength and flexibility, heat resistance, and transparency of the biodegradable resin composition.

  In the present invention, the dimer of the lactic acid and the hydroxycarboxylic acid compound may be contained in each component. The dimer of lactic acid is exemplified by lactide which is a cyclic dimer of lactic acid, and the dimer of hydroxycarboxylic acid compound is exemplified by glycolide which is a cyclic dimer of glycolic acid. The lactide is L-lactide which is a cyclic dimer of L-lactic acid, D-lactide which is a cyclic dimer of D-lactic acid, meso-lactide in which D-lactic acid and L-lactic acid are cyclically dimerized, And DL-lactide, which is a racemic mixture of D-lactide and L-lactide, and any of the lactides can be used in the present invention. However, both the strength and flexibility of the biodegradable resin composition, heat resistance From the viewpoints of transparency and transparency, D-lactide and L-lactide are preferred. The dimer of lactic acid may be contained in any lactic acid component when only the lactic acid component is polycondensed or when the lactic acid component and the hydroxycarboxylic acid component are polycondensed.

  The content of the lactic acid dimer is preferably from 80 to 100 mol%, more preferably from 90 to 100 mol%, in the lactic acid component from the viewpoint of achieving both the strength and flexibility of the biodegradable resin composition.

  The content of the dimer of the hydroxycarboxylic acid compound is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, in the hydroxycarboxylic acid component, from the viewpoint of achieving both the strength and flexibility of the biodegradable resin composition. Is more preferred.

  The polycondensation reaction of only the lactic acid component and the polycondensation reaction of the lactic acid component and the hydroxycarboxylic acid component are not particularly limited, and can be performed using a known method.

  Thus, by selecting the starting monomers, for example, polylactic acid comprising 85% by mole or more and less than 100% by mole of either L-lactic acid or D-lactic acid and more than 0% by mole and 15% by mole or less of the hydroxycarboxylic acid component can be obtained. Among them, lactide, which is a cyclic dimer of lactic acid, glycolide, which is a cyclic dimer of glycolic acid, and polylactic acid obtained by using caprolactone as a raw material monomer are preferable.

  Further, in the present invention, two types of polylactic acid obtained using lactic acid components having different isomers as main components are used as polylactic acid from the viewpoint of compatibility between strength and flexibility of the biodegradable resin composition and heat resistance. Stereocomplex polylactic acid composed of polylactic acid may be used.

  One polylactic acid constituting the stereocomplex polylactic acid [hereinafter referred to as polylactic acid (A)] contains 90 to 100 mol% of L-form and 0 to 10 mol% of other components including D-form. The other polylactic acid (hereinafter referred to as polylactic acid (B)) contains 90 to 100 mol% of D-form and 0 to 10 mol% of other components including L-form. Other components other than the L-form and the D-form include dicarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, lactones, and the like having a functional group capable of forming two or more ester bonds. And polyesters, polyethers, polycarbonates and the like having two or more of the above functional groups in the molecule.

  The weight ratio of polylactic acid (A) to polylactic acid (B) [polylactic acid (A) / polylactic acid (B)] in the stereocomplex polylactic acid is preferably from 10/90 to 90/10, and from 20/80 to 80/80. / 20 is more preferred, and 40/60 to 60/40 is even more preferred.

  The content of polylactic acid in the polylactic acid resin is preferably 80% by weight or more, more preferably 90% by weight or more, and further preferably substantially 100% by weight.

  The polylactic acid resin can be synthesized by the above-mentioned method, and commercially available products include, for example, “Laissia series” such as Laissia H-100, H-280, H-400, H-440 (Mitsui Chemicals, Inc.). "Nature Works" (manufactured by NatureWorks) such as 3001D, 3051D, 4032D, 4042D, 6201D, 6251D, 7000D, 7032D, and Ecoplastic U'z S-09, S-12, S-17, etc. "Ecoplastic U'z series" (manufactured by Toyota Motor Corporation) and Terramac TE-2000 (manufactured by Unitika). Among these, from the viewpoints of compatibility between the strength and flexibility of the biodegradable resin composition, and the heat resistance, Laissia H-100, H-280, H-400, H-440 (manufactured by Mitsui Chemicals, Inc.) 3001D, 3051D, 4032D, 4042D, 6201D, 6251D, 7000D, 7032D (manufactured by Nature Works), Ecoplastic U'z S-09, S-12, S-17 (manufactured by Toyota Motor Corporation), Terramac TE-2000 ( Unitika) is preferred.

<Melting and kneading process>
In the melt-kneading step, the above-described powdered material of the fine cellulose fiber having a predetermined moisture content and the biodegradable resin are subjected to temperature and pressure conditions at which water contained in the powdered material of the fine cellulose fiber becomes a subcritical state. This is the step of melt-kneading.

  As a specific method, for example, the powdered material of the fine cellulose fiber and the biodegradable resin are each weighed and mixed at a predetermined ratio, and put into a heat-resistant pressure chamber capable of forming subcritical water. A method of melt-kneading may be used.

  The water content (the ratio of water to the total of fine cellulose fibers and water) of the fine cellulose fiber powder to be melt-kneaded is 10 to 90% by mass, preferably 12 to 80% by mass, and more preferably 15 to 70% by mass. More preferred. When the ratio is equal to or more than the lower limit, the efficiency of dispersing the fine cellulose fiber into the biodegradable resin by the subcritical water is further enhanced. When the amount is equal to or less than the above upper limit, the amount of heat generated during melt-kneading can be prevented from becoming excessive, and the decomposition of fine cellulose fibers can be suppressed. Further, the time and effort for removing the water that has played a role of dispersing the fine cellulose fibers into the biodegradable resin from the fine cellulose-containing resin composition is reduced, and the production efficiency is improved.

  The water content of the fine cellulose fiber powder to be melt-kneaded is the water content of the fine cellulose fiber powder immediately before melt-kneading. In order to adjust the water content to the above-mentioned preferable value, a process for controlling the moisture content such as drying and humidification of the fine cellulose fiber powder before melt-kneading may be provided. For example, before the melt-kneading, a predetermined amount of water may be added to the fine cellulose fiber powder, and the water content may be adjusted by stirring for a certain time with a stirrer such as a blender.

The mixing ratio of the fine cellulose fiber powder (in terms of solid content) and the biodegradable resin is appropriately set according to the desired physical properties and the physical properties of the biodegradable resin. For example, the blending amount (solid equivalent) of the fine cellulose powder is preferably 1 to 100 parts by mass (solid content), and more preferably 5 to 90 parts by mass based on 100 parts by mass (solid content) of the biodegradable resin. Is more preferable, and 10 to 80 parts by mass is further preferable.
If the compounding amount of the fine cellulose fiber powder is not less than the lower limit, the biodegradable resin can be sufficiently reinforced, and if not more than the upper limit, the obtained fine cellulose fiber-containing resin composition The toughness can be sufficiently maintained.

  In mixing the fine cellulose fiber powder and the biodegradable resin, for example, a tumbler mixer, a Henschel mixer, or the like can be used. At this time, various additives may be mixed at the same time. Examples of the additive include an antioxidant, an ultraviolet absorber, a filler, a pigment, a dye, an antistatic agent, a lubricant, and a plasticizer.

  As a device for melt-kneading the mixed materials, the water contained in the powdery material of the fine cellulose fiber is brought into a subcritical state, and a heat pressure capable of melting and kneading the fine cellulose fiber and the biodegradable resin is used. Devices with a chamber are preferred. As such an apparatus, for example, a known apparatus that employs a pressurized heating furnace of a type in which pressure and heat are applied from the outside as a chamber and performs melting and kneading while stirring in the chamber is applicable. Above all, an apparatus having a mechanism for vaporizing and removing moisture in the chamber at an arbitrary timing is more preferable.

  The temperature in the chamber during the melt-kneading is preferably higher than 100 ° C and 300 ° C or lower, more preferably 150 ° C or higher and 250 ° C or lower. The pressure in the chamber during melt-kneading is not higher than the saturated steam pressure at the melt-kneading temperature, and is preferably 0.5 MPa to 25 MPa, more preferably 1 MPa to 20 MPa. When the temperature range and the pressure range are equal to or more than the lower limit of the pressure range, it is easy to bring the water contained in the powdery material of the fine cellulose fiber into a subcritical state, and the dispersibility of the fine cellulose fiber in the biodegradable resin is improved Can be improved. When the temperature and pressure are not more than the upper limits of the temperature range and the pressure range, the fine cellulose fiber or the biodegradable resin is decomposed, and the fiber strength or resin strength necessary for improving the strength of the target resin composition is lost. Can be sufficiently suppressed. In addition, the subcritical state of water suitable in the present invention is more than 100 ° C and 300 ° C or lower and 0.5 to 25 MPa, and the more preferable subcritical state of water is 150 ° C or higher and 250 ° C or lower and 1 MPa to 20 MPa. is there.

  The time for melt-kneading is preferably 1 to 60 minutes, more preferably 2 to 30 minutes, even more preferably 3 to 15 minutes. When it is at least the lower limit, fine cellulose fibers can be sufficiently uniformly dispersed in the biodegradable resin. When it is not more than the above upper limit, the decomposition of the biodegradable resin and the fine cellulose fiber can be sufficiently suppressed.

  As one of the indexes for judging the completion of the melt-kneading, the torque required for stirring during the melt-kneading is measured, and the torque decreases after the torque reaches a maximum value.

  After the fine cellulose fibers and the biodegradable resin are uniformly mixed by melt-kneading, it is preferable to remove the water in the chamber. By lowering the temperature and pressure of the chamber sufficiently from the critical point of water and vaporizing the water, moisture can be removed from the inside of the chamber.

  After the completion of the melt kneading, the target fine cellulose fiber molten resin composition is taken out of the chamber. The temperature at the time of removal is not particularly limited, but is preferably a temperature equal to or higher than the melting point of the biodegradable resin in order to prevent the biodegradable resin from attaching and remaining in the chamber. It is preferable that the removed fine cellulose fiber-containing resin composition is supplied to an extruder, discharged into a rod shape from a die of the extruder, cooled, cut, and formed into a pellet shape.

<Action mechanism>
The details of the mechanism of the melt-kneading in the melt-kneading process are not yet elucidated, but are presumed as follows. The subcritical water in the chamber is activated, its relative dielectric constant is reduced, and its ionic product is increased. The water activated in this way defibrate the fine cellulose fibers that have aggregated together to form monofilaments and prevent their re-aggregation. Further, the activated water disperses the biodegradable resin into a state close to a single polymer molecular chain. As a result, it is presumed that the dispersed polymer molecules and the monofilaments of the fine cellulose fibers are stirred in the chamber and mixed efficiently, thereby obtaining a resin composition containing fine cellulose fibers which is uniformly dispersed and mixed. Is done.
According to the production method of the present invention, a resin composition containing fine cellulose fibers having excellent rigidity and heat resistance and a biodegradable resin can be obtained. The reason for this is that by appropriately controlling the water content of the fine cellulose fiber powder at the time of melt-kneading, it is possible to suppress the degradation and decomposition of the fine cellulose fiber, and to disperse the fine cellulose with extremely high dispersibility in the biodegradable resin. It is possible that the fibers can be kneaded.
During the melt-kneading, if the water content of the fine cellulose fiber powder is low, the amount of activated water contributing to the kneading of the fine cellulose fiber and the biodegradable resin is reduced, and the dispersibility is considered to be poor. Conversely, when the water content is too high, the amount of heat generated and the amount of activated water are excessive, and it is considered that the fine cellulose fibers and the biodegradable resin are decomposed or deteriorated. When the dispersibility decreases or the fine cellulose fibers or the biodegradable resin decomposes or deteriorates, it is difficult to increase the mechanical strength of the fine cellulose fiber-containing resin composition.

It is considered that Patent Documents 1 and 2 mentioned above have the following problems.
In the method of Document 1 (Japanese Patent No. 5211571), a large amount of water is kneaded with a thermoplastic resin together with cellulose fibers and vaporized during kneading, so that the amount of generated heat increases, and the cellulose fibers deteriorate. It is thought that it is.
In the method of Document 2 (Japanese Patent No. 5169188), after melt-kneading a cellulose fiber with a first thermoplastic resin, the resulting mixture is pelletized, dry-blended with a pellet of a second thermoplastic resin, and re-blended. It is considered that the cellulose fibers are deteriorated because they undergo at least two stages of melt kneading, ie, melt kneading. Further, since the cellulose fibers are melt-kneaded without being dispersed in water, it is considered that the dispersibility of the cellulose fibers in the resin is inferior.

  In the method disclosed in Japanese Patent No. 4950939, pulp in a state in which cellulose fibers are dehydrated and bonded is treated with subcritical water to decompose the cellulose fibers and knead them with a thermoplastic resin. As is clear from the description of this document, when cellulose fibers are mixed with water in a subcritical state, the cellulose fibers are usually decomposed. However, in the production method of the present invention, since the water content of the fine cellulose fiber powder is adjusted as described above, while suppressing the decomposition of the fine cellulose fiber, the fine cellulose fiber is increased in the biodegradable resin. Melting and kneading can be performed according to the degree of dispersion.

<Fine cellulose fiber-containing resin composition>
In the manufacturing method described above, the mixture containing the fine cellulose fiber powder, water, and the biodegradable resin is melt-kneaded under the temperature and pressure conditions at which the water becomes a subcritical state, whereby the resin To obtain a resin composition in which fine cellulose fibers are dispersed.

<Production process of fine cellulose fiber-containing resin composition>
As described above, as a production process of the fine cellulose fiber-containing resin composition,
A refining step of refining pulp containing cellulose fibers,
A sheet forming step of forming the cellulose fibers subjected to the micronization treatment into a sheet,
Powdering step of powdering the sheet-like fine cellulose fibers,
The water content of the fine cellulosic fiber powder, water adjustment step of adjusting if necessary,
The method includes at least a step of melt-kneading the powdery material of the fine cellulose fiber and the resin in a subcritical state.

<Molded body>
The fine cellulose fiber-containing resin composition of the present invention can be used as a material for a molded article.
The method for producing a molded article using the fine cellulose fiber-containing resin composition is not particularly limited, and for example, injection molding, extrusion molding, blow molding, press molding, and the like can be applied.

  Hereinafter, examples of the present invention will be described. In the following examples, “%” means “% by mass”, and “parts” means “parts by mass”.

[Example 1]
・ Production of powdery material of fine cellulose fiber-containing sheet Water is added to softwood bleached kraft pulp (manufactured by Oji Paper Co., Ltd., water content: 50% by mass), and dispersed so that the solid concentration becomes 4.0% by mass. did. Thereafter, continuous circulation beating was performed with a double disc refiner to refine the cellulose fibers. The freeness (0.3 g method) of the obtained aqueous dispersion of fine cellulose fibers was 230 ml (fiber length and fiber width are described in Table 1).
The obtained aqueous dispersion of fine cellulose fibers was paper-made with a fourdrinier paper machine, and was then dewatered and dried to obtain a sheet having the moisture and basis weight shown in Table 1. The fine cellulose fiber-containing sheet was pulverized by a vertical pulverizer “VM42K” manufactured by Orient Pulverizer Co., Ltd. to obtain a pulverized product (powder) containing fine cellulose fibers. In addition, since the water content was reduced during the pulverization due to evaporation of the water content, the water content of the powdery material was measured, and the water content was adjusted by adding water so as to obtain the water content shown in Table 1.

・ Production of resin composition containing fine cellulose fiber and biodegradable resin 8 kg of pulverized product (powder) of the obtained fine cellulose fiber sheet and polylactic acid pellet (PLA: manufactured by Unitika, Terramac TE-2000, MFR 12 g) / 10 min) were dry-blended. Thereafter, the mixture was put into a mixing chamber of a melt mixing apparatus (manufactured by M & F Technology Co., Ltd., model number: MF-1000), and the water in the mixing chamber was brought into a subcritical state at 200 ° C. and 5 MPa, and was melt-kneaded for 2 minutes. Thereafter, the rod-shaped fine cellulose fiber-containing resin composition was extruded from the resin discharge port, placed on a stainless steel tray, cooled at room temperature, and solidified. The solidified fine cellulose fiber-containing resin composition was cut into pellets (master batch pellets). The content of the fine cellulose fibers in the masterbatch pellet was 40% by mass.

  The obtained masterbatch pellets are dry-blended and diluted with polylactic acid pellets (Terramac TE-2000) so that the content of fine cellulose fibers becomes 20% by mass, and then injection molding machine (manufactured by Nissei Plastic Co., Ltd.) : “NPX7-1F”) to obtain a rectangular molded body (length: 80 mm, width: 10 mm, thickness: 4.0 mm). At this time, the temperature of the heating cylinder (cylinder) was set to 200 ° C., and the mold temperature was set to 40 ° C.

[Examples 2 to 5]
The procedure was performed in the same manner as in Example 1 except that the freeness of the aqueous dispersion of fine cellulose fibers, the moisture of the fine cellulose fiber sheet, and the moisture of the powdery material were changed as shown in Table 1. The freeness of Example 5 was also measured by the 3 g method, and the value was 450 mlcsf.
[Examples 6 to 8]
The procedure was performed in the same manner as in Example 1 except that the amount of the cellulose fiber was changed as shown in Table 2.

[Comparative Example 1]
The same as in Example 1 except that the mixture was charged into a twin-screw kneader (KZW15 manufactured by Technovel, screw diameter 15 mm) and melted and kneaded (rotation speed 300 / min, processing speed 300 g / h, kneading temperature 190 ° C). Carried out.

[Comparative Example 2]
It carried out like Example 1 except having made sheet moisture into 5 mass%, and powder moisture into 3%.

(Measuring method)
(1) Average fiber length of fine cellulose fiber "JAPAN TAPPI Paper pulp test method No. 52: 2000 Pulp and paper-Fiber length test method-Optical automatic measurement method" manufactured by Kayani Co., Ltd .: Fiber length measuring device "FiberLab" Was used to measure the length-load average fiber length of the fine cellulose fibers, which was taken as the average fiber length of the fine cellulose fibers.

(2) Average Fiber Width of Fine Cellulose Fiber The surface of the fine cellulose fiber-containing sheet was observed with a scanning electron microscope. At this time, when an axis having an arbitrary image width in the vertical and horizontal directions was assumed in the obtained image, a sample and observation conditions (magnification and the like) were set such that at least 20 fibers intersected the axis with respect to at least the axis. With respect to the observation image satisfying the conditions, a random axis of two lengths and two widths per image was drawn, and the fiber width of the fiber intersecting the axis was visually read. In this way, images of at least three non-overlapping surface portions are observed with an electron microscope, and the value of the fiber width of each intersecting fiber of two axes is read (minimum 20 × 2 × 3 = 120 fiber widths). Values were calculated. This was defined as the average fiber width of the fine cellulose fibers.

(3) Moisture Content of Fine Cellulose Fiber-Containing Sheet Immediately after the production (within 30 minutes), 16 fine cellulose fiber-containing sheets cut into a size of 25 cm wide × 25 cm long were prepared and weighed. (Weight before drying). Thereafter, the sampled sheet containing fine cellulose fibers was dried at 110 ° C. for 3 hours, and the weight after drying was measured to determine the water content.
Water content (%) = (weight before drying−weight after drying) / weight before drying × 100

(4) Freeness (0.3g method)
Freeness was measured by the irregular freeness measurement method (0.3 g method). The irregular freeness measurement method is a measurement method based on JIS P 8121-2 (2012) "Pulp-Freeness test method-Part 2: Canadian standard freeness method". The sieve plate with a hole attached to a Canadian standard freeness tester is a measuring method using a stainless steel 80 mesh sieve plate.
Specifically, the disintegrated pulp was diluted with water so as to have a solid concentration of 0.030% by mass. The sample temperature was adjusted to 20 ° C., and 1000 mL of the sample was transferred to a measuring cylinder. The opening of the measuring cylinder was closed by hand, the measuring cylinder was inverted, the sample was mixed, and the sample was poured into a drainage cylinder. The lower lid was opened, and after 5 seconds had elapsed, the air cock was opened and the sample flowed down. The drainage from the side orifice was collected, the amount was read and the read amount was defined as the freeness. In addition, only in Example 5, the freeness was measured by the ordinary 3 g method.

(5) Basis Weight of Fine Cellulose Fiber-Containing Sheet The basis weight of the fine cellulose fiber-containing sheet was determined by measuring the weight of 16 sheets having a width of 25 cm and a length of 25 cm. However, do not adjust the humidity, and adjust the grammage within 30 minutes after making the sheet.

(6) Average particle size of powder The average particle size of the obtained pulverized product (granule) was as shown in Tables 1 and 2. The average particle diameter of the pulverized product (granule) was calculated by performing an image analysis process after observing with an optical microscope.
(7) Water content adjustment of powder The water content of the pulverized material (granules) was dried at 110 ° C. for 3 hours and measured. Water was added to the powder so as to obtain the water content shown in Tables 1 and 2, and the container was sealed. For 1 hour.

(8) Flexural Properties of Molded Product The flexural strength and flexural modulus of the molded article (resin composite) were measured according to JIS K7171 “Plastics—How to determine flexural properties”. Tensilon (model: RTG-1250) manufactured by A & D Corporation was used as a tensile tester. The tensile speed at the time of measuring the tensile strength was 2.0 mm / min.
(9) Thermal Deformation Temperature of Molded Body Load Deflection Temperature Measured by the flatwise method (load: 0.45 MPa) in accordance with JIS K 7191 "Plastic-Determining Load Deflection Temperature". The span was fixed at 64 mm, and the measurement was performed at the center of the test piece using a test piece (80 mm × 10 mm, thickness 4 mm) made of an injection molded body.
(10) Appearance The appearance was visually determined and evaluated according to the following criteria.
：: When observing the surface of the molded article, the number of large cellulose fiber lumps that can be visually observed is 10 or less. △: When the surface of the molded article is observed, 11 or more large cellulose fiber lumps that can be visually observed. ×: When observing the surface of the molded body, there are 31 or more large lumps of large cellulose fibers that can be visually observed.

<Discussion>
The molded article made of the fine cellulose-containing resin composition of the example had excellent mechanical properties. It is considered that the reason for this is that the water in the subcritical state at the time of melt-kneading enhanced the dispersibility of the fine cellulose fibers in the biodegradable resin.
On the other hand, the molded article of Comparative Example 1 had poor mechanical properties. It is considered that the reason for this is that the fine cellulose fibers tended to agglomerate due to low water content during melt-kneading, resulting in poor dispersibility. Also, the molded article of Comparative Example 2 was inferior in mechanical properties. It is considered that the reason for this is that the amount of heat generated is large and the fine cellulose fibers are deteriorated due to too much water at the time of melt-kneading.
From the above, according to the method for producing a fine cellulose fiber-containing resin composition of the present invention, it is possible to obtain extremely high dispersibility by kneading the fine cellulose fibers in the resin while suppressing the degradation and decomposition of the fine cellulose fibers. Understood. Furthermore, it is clear that molded articles such as mechanical parts having excellent mechanical properties can be produced by using the fine cellulose fiber-containing resin composition of the present invention.

Claims (6)

  In a method for producing a resin composition by melt-kneading a fine cellulose fiber and a biodegradable resin, the fine cellulose fiber has an average fiber width of 2 to 15000 nm and an average fiber length of 0.1 to 2.0 mm. The fine cellulose fiber is a powdery material, the powdery material contains water, the water content of the powdery material is 10 to 90% by mass, and the melt-kneading is performed using the powdery material of the fine cellulose fiber. Melt kneading under conditions of temperature and pressure at which water contained in the mixture becomes a subcritical state. The method for producing a resin composition according to claim 1, wherein the powdery material of the fine cellulose fibers is obtained by shredding a sheet-like material of cellulose. The method for producing a resin composition according to claim 1, wherein the powdery material of the fine cellulose fibers is obtained by slicing a sheet-like material of fine cellulose fibers.   The method for producing a resin composition according to any one of claims 1 to 3, wherein the biodegradable resin is pelletized in advance.     The method for producing a resin composition according to any one of claims 1 to 4, wherein the biodegradable resin is polylactic acid. A refining step of refining pulp containing cellulose fibers,
A sheet forming step of forming the cellulose fibers subjected to the micronization treatment into a sheet,
Powdering step of powdering the sheet-like fine cellulose fibers,
The water content of the fine cellulosic fiber powder, water adjustment step of adjusting if necessary,
A method for producing a resin composition, comprising: a step of melt-kneading a powder of the fine cellulose fiber and a resin in a subcritical state.