Method for producing resin composition

Abstract

To provide a method for producing a resin composition which exhibits good physical property regardless of a heat history in production while containing polyamide and cellulose nanofiber.SOLUTION: A method for producing a resin composition includes a mixing step of mixing a mixed component containing first polyamide (A1) satisfying a relation of concentration of amino terminal group [NH2]>concentration of carboxyl terminal group [COOH], second polyamide (A2) satisfying a relation of [NH2]<[COOH], and cellulose nanofiber (B), wherein a number average molecular weight (MT) calculated based on a number average molecular weight (MA1) of (A1), mass concentration (CA1) of (A1) in the mixed component, a number average molecular weight (MA2) of (A2), mass concentration (CA2) of (A2) in the mixed component, and total mass concentration (CT) of mass concentrations (CA1) of (A1) and the mass concentration (CA2) of (A2) in the mixed component to a number average molecular weight (M) of the polyamide in the resin composition satisfy a relation of M / MT>1.1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a resin composition containing polyamide and cellulose nanofibers. [Background technology]

[0002] Resin materials are lightweight and have excellent processability, making them widely used in a variety of applications, including automotive components, electrical and electronic components, office equipment housings, and precision components. However, resins alone often lack sufficient mechanical properties and dimensional stability, making composites of resins and various fillers commonly used. In recent years, the use of natural fibers such as cellulose nanofibers (CNFs) as such fillers has been investigated. CNFs have the advantages of being lightweight, reducing the environmental impact of disposal, and significantly improving the physical properties of resin compositions. In particular, various resin compositions have been proposed that combine CNFs with polyamides, which have excellent heat resistance, dimensional stability, and other properties.

[0003] Patent Document 1 describes a polyamide resin composition containing (A) a polyamide in which the amino group terminal concentration [-NH2] and the carboxyl group terminal concentration [-COOH] satisfy the relationship [-NH2]>[-COOH], and (B) cellulose fibers having an average fiber diameter of 500 nm or less.

[0004] Patent Document 2 describes a polyamide resin composition containing (A) a polyamide in which the amino group terminal concentration [-NH2] and the carboxyl group terminal concentration [-COOH] satisfy the relationship [-NH2] < [-COOH], and (B) cellulose fibers having an average fiber diameter of 500 nm or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-7494 [Patent Document 2] Japanese Patent Publication No. 2020-7495 Summary of the Invention [Problem to be solved by the invention]

[0006] The techniques described in Patent Documents 1 and 2 focus on the degradation of cellulose during the production of a resin composition containing polyamide and cellulose fibers. Specifically, the technique described in Patent Document 1 aims to provide a resin composition that enables stable molding by suppressing the generation of gas components due to cellulose decomposition, while the technique described in Patent Document 2 aims to provide a resin composition in which the coloration and odor caused by the release of acid residues from cellulose are reduced. The techniques described in these documents can improve the properties of a resin composition by reducing undesired reactions of cellulose that occur during the production of the resin composition. However, the present inventors' investigations have revealed that in resin compositions containing polyamide and cellulose nanofibers, the polyamide may deteriorate due to the thermal history during production, preventing the resin composition from exhibiting the desired physical properties.

[0007] The present invention aims to solve the above problems and provide a method for producing a resin composition that contains polyamide and cellulose nanofibers and yet exhibits good physical properties regardless of the thermal history during production. [Means for solving the problem]

[0008] The present invention includes the following aspects. [1] A method for producing a resin composition containing polyamide and cellulose nanofibers, comprising: The method includes a mixing step of mixing a first polyamide (A1) having an amino terminal group concentration [NH2]>a carboxyl terminal group concentration [COOH] and a second polyamide (A2) having an amino terminal group concentration [NH2]<a carboxyl terminal group concentration [COOH] with cellulose nanofibers (B) to obtain a resin composition, The number average molecular weight (M A1 ), the mass concentration of the first polyamide (A1) in the mixed component (CA1 ), the number average molecular weight (M A2 ), the mass concentration of the second polyamide (A2) in the mixed component (C A2 ), and the mass concentration of the first polyamide (A1) in the mixed component (C A1 ) and the mass concentration of the second polyamide (A2) (C A2 ) and the total mass concentration (C T ) based on the following formula: M T =(M A1 ×C A1 +M A2 ×C A2 ) / C T The number average molecular weight (M T ) and the number average molecular weight (M) of the polyamide in the resin composition satisfies the following formula (1a): M / M T >1.1 (1a) A method for producing a resin composition that satisfies the above relationship. [2] The amino terminal group concentration [NH2] of the first polyamide (A1) A1 and carboxyl end group concentration [COOH] A1 , the mass concentration (C A1 ), the amino terminal group concentration [NH2] of the second polyamide (A2) A2 and carboxyl end group concentration [COOH] A2 , the mass concentration (C A2 ), and the mass concentration (C A1 ) and the mass concentration of the second polyamide (A2) (C A2 ) and the total mass concentration (C T ) based on the following formulas (1b) to (1d): [NH2] T =([NH2] A1 ×C A1 +[NH2] A2 ×C A2 ) / C T (1b) [COOH] T=([COOH] A1 ×C A1 +[COOH] A2 ×C A2 ) / C T (1c) ([NH2]+[COOH]) T =[NH2] T +[COOH] T (1d) The total concentration ([NH2] + [COOH]) calculated according to T The method according to aspect 1, wherein the amount of the hydroxyl group is 10 μequivalents / g or more and 500 μequivalents / g or less. [3] The above [NH2] T The [COOH] T Ratio to ([NH2] T / [COOH] T 3. The method according to claim 2, wherein the number of sigma-based ... [4] The method according to any one of the above aspects 1 to 3, wherein the total concentration ([NH2] + [COOH]) of the amino terminal group concentration [NH2] and the carboxyl terminal group concentration [COOH] of each of the first polyamide (A1) and the second polyamide (A2) is 10 μequivalents / g or more and 500 μequivalents / g or less. [5] A method for producing a resin composition containing polyamide and cellulose nanofibers, comprising: The method includes a mixing step of obtaining a resin composition by mixing a mixed component containing polyamide (A) and cellulose nanofibers (B), the polyamide (A) having an amino terminal group concentration and a carboxyl terminal group concentration each of which is 20 μequivalents / g or more and at least one of which is 70 μequivalents / g or more, or the polyamide (A) having an amino terminal group concentration and a carboxyl terminal group concentration each of which is 50 μequivalents / g or more and at least one of which is 60 μequivalents / g or more, The number average molecular weight (M) of the polyamide in the resin composition and the number average molecular weight (M) of the polyamide (A) to be mixed A ) is expressed by the following formula (2a): M / M A >1.1 (2a) Fulfilling the relationship, The method for producing a resin composition, wherein the moisture content of the resin composition is higher than the moisture content of the polyamide (A) to be mixed. [6] The method according to aspect 5, wherein the polyamide (A) has a total concentration ([NH2] + [COOH]) of the amino terminal group concentration [NH2] and the carboxyl terminal group concentration [COOH] of 90 μequivalents / g or more and 500 μequivalents / g or less. [7] The method according to any one of the above-mentioned aspects 5 or 6, wherein one of the amino terminal group concentration [NH2] and the carboxyl terminal group concentration [COOH] of the polyamide (A) is 20 μequivalents / g or more and less than 70 μequivalents / g, and the other is 70 μequivalents / g or more and 480 μequivalents / g or less. [8] The method according to any one of Aspects 5 to 7, wherein the resin composition has a moisture content of 100 ppm by mass or more and 5000 ppm by mass or less, and the polyamide (A) to be mixed has a moisture content of 1 ppm by mass or more and 1000 ppm by mass or less. [9] The method according to any one of the above aspects 1 to 8, wherein a part of the resin composition is used as a part of the mixed component.

[10] The method according to any one of the above aspects 1 to 9, wherein the cellulose nanofibers (B) have a number average fiber diameter of 2 nm or more and 1000 nm or less.

[11] The method according to any one of the above aspects 1 to 10, wherein the cellulose nanofibers (B) have an acyl substitution degree (DS) of 0 or more and 1.5 or less.

[12] The method according to any one of the above aspects 1 to 11, wherein the cellulose nanofibers (B) have a crystallinity of 60% or more.

[13] The method according to any one of the above aspects 1 to 12, wherein the average acid-insoluble content of the cellulose nanofibers (B) is 10% by mass or less. [Effects of the Invention]

[0009] According to one aspect of the present invention, a method for producing a resin composition can be provided that can produce a resin composition that contains polyamide and cellulose nanofibers and exhibits good physical properties regardless of the thermal history during production. DETAILED DESCRIPTION OF THE INVENTION

[0010] Exemplary embodiments of the present invention (hereinafter referred to as the present embodiments) will be specifically described below, but the present invention is not limited to these embodiments.

[0011] This embodiment provides a method for producing a resin composition containing polyamide and cellulose nanofibers. The present inventors noticed an unexpected decrease in the molecular weight of polyamides when producing a resin composition by mixing (specifically, by heating and mixing) components containing polyamide and cellulose nanofibers, and conducted various investigations into the cause. As a result, they discovered that the moisture absorption of polyamides, which are inherently hygroscopic, may be more pronounced in the presence of cellulose nanofibers, which are inherently hydrophilic. In other words, heating polyamides in the presence of cellulose nanofibers may accelerate the hydrolysis of the polyamides. After investigating various methods for producing resin compositions with good physical properties despite the hydrolysis of polyamides, they discovered that controlling the structure of the polyamide itself allows the formation of intermolecular amide bonds through the reaction between amino and carboxyl terminal groups during the mixing process, i.e., polymerization, and thereby increases the molecular weight, thereby enabling the production of resin compositions with excellent physical properties.

[0012] Furthermore, after producing a resin composition containing polyamide and cellulose nanofibers and a molded article obtained by molding the same, the resin composition or the molded article may be reused as part of the resin composition. In such cases, the reused resin, due to the inclusion of recycled material, experiences a greater thermal history than a non-recycled resin, resulting in generally inferior physical properties compared to a resin composition composed solely of non-recycled resin. Therefore, in this embodiment, increasing the molecular weight of the polyamide during mixing with cellulose nanofibers is advantageous for reusing such a resin composition or molded article. In other words, in the production of resin compositions and molded articles, the molecular weight of the polyamide in the resin composition and molded article is often lower than the molecular weight of the polyamide used for mixing with cellulose nanofibers due to the thermal history during the mixing process to produce the resin composition and the thermal history during the molding process to produce the molded article from the resin composition. Furthermore, a decrease in molecular weight due to moisture absorption of the polyamide may also occur during storage of the resin composition and molded article. Reusing a resin composition or molded article containing such degraded polyamide as a resin composition material results in a resin composition with inferior physical properties. According to this embodiment, when polyamide containing a portion derived from the resin composition or molded article is mixed with cellulose nanofibers containing a portion derived from the resin composition or molded article in the mixing step, the molecular weight of the polyamide increases. That is, the reduced molecular weight of the polyamide in the resin composition or molded article is restored in the mixing step, thereby producing a resin composition with good physical properties.

[0013] More specifically, this embodiment includes the following first and second aspects.

[0014] The method according to the first aspect includes a mixing step of mixing components including a first polyamide (A1) having an amino terminal group concentration [NH2] > a carboxyl terminal group concentration [COOH] and a second polyamide (A2) having an amino terminal group concentration [NH2] < a carboxyl terminal group concentration [COOH] with cellulose nanofibers (B) to obtain a resin composition. In one embodiment, the number average molecular weight (M A1 ), the mass concentration of the first polyamide (A1) in the mixture (C A1 ), the number average molecular weight (M A2 ), the mass concentration of the second polyamide (A2) in the mixture (C A2 ), and the mass concentration of the first polyamide (A1) in the mixed components (C A1 ) and the mass concentration of the second polyamide (C A2 ) and the total mass concentration (C T ) based on the following formula: M T =(M A1 ×C A1 +M A2 ×C A2 ) / C T The number average molecular weight (M T ) and the number average molecular weight (M) of the polyamide in the resin composition satisfy the following formula (1a): M / M T >1.1 (1a) Satisfy the relationship.

[0015] The method according to the second aspect includes a mixing step of mixing components containing polyamide (A) and cellulose nanofibers (B) to obtain a resin composition, the polyamide (A) having an amino terminal group concentration and a carboxyl terminal group concentration each of which is 20 μequivalents / g or more and at least one of which is 70 μequivalents / g or more, or an amino terminal group concentration and a carboxyl terminal group concentration each of which is 50 μequivalents / g or more and at least one of which is 60 μequivalents / g or more. In one embodiment, the number average molecular weight (M) of the polyamide in the resin composition and the number average molecular weight (M) of the polyamide (A) to be mixed are A ) is expressed by the following formula (2a): M / M A >1.1 (2a) Satisfy the relationship. In one embodiment, the moisture content of the resin composition is higher than the moisture content of the polyamide (A) to be mixed.

[0016] The above formulas (1a) and (2a) are indicators of the degree of increase in the molecular weight of the polyamide in the mixing step of this embodiment. T ratio, and M / M in the above formula (2a) A In one aspect, the ratio M / M is greater than 1.1, preferably 1.15 or greater, 1.2 or greater, 1.25 or greater, 1.3 or greater, or 1.4 or greater, from the viewpoint of significantly increasing the molecular weight of the polyamide in the mixing step to obtain a resin composition with good physical properties, and is preferably 2.5 or less, 2 or less, or 1.5 or less, from the viewpoint of accurately controlling the physical properties of the resin composition. T Ratio and M / M A One way to control the ratio within the range of this embodiment is to control the terminal group concentration of the polyamide to be mixed as exemplified in this embodiment, and then adjust the mixing conditions when adding cellulose nanofibers and mixing at a temperature above the melting temperature of the resin in the mixing process (for example, by setting the mixing time within a predetermined range, for example, 2 minutes or more).

[0017] <Components of Resin Composition> <Polyamide (A1), (A2), (A)> As the polyamides (A1) and (A2) used in the first embodiment and the polyamide (A) used in the second embodiment, various polyamides having an aliphatic structure, an aromatic structure, or a combination thereof can be used. Examples of preferred polyamides are: Polyamides obtained by polycondensation reaction of lactams, such as polyamide 6, polyamide 11, polyamide 12, etc.; Diamines such as 1,6-hexanediamine, 2-methyl-1,5-pentanediamine, 1,7-heptanediamine, 2-methyl-1,6-hexanediamine, 1,8-octanediamine, 2-methyl-1,7-heptanediamine, 1,9-nonanediamine, 2-methyl-1,8-octanediamine, 1,10-decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine, and m-xylylenediamine, as well as butanedioic acid, pentanedioic acid, hexanedioic acid, heptanedioic acid, octanedioic acid, nonanedioic acid, decanedioic acid, and benzyl alcohol. Polyamides obtained as copolymers with dicarboxylic acids such as benzene-1,2-dicarboxylic acid, benzene-1,3-dicarboxylic acid, benzene-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, and cyclohexane-1,4-dicarboxylic acid, for example, polyamide 6,6, polyamide 6,10, polyamide 6,11, polyamide 6,12, polyamide 6,T, polyamide 6,I, polyamide 9,T, polyamide 10,T, polyamide 2M5,T, polyamide MXD,6, polyamide 6,C, polyamide 2M5,C, and the like; and Copolymers obtained by copolymerizing these with each other, such as polyamide 6, T / 6, I, etc., are also included.

[0018] Among these polyamides, aliphatic polyamides such as polyamide 6, polyamide 11, polyamide 12, polyamide 6,6, polyamide 6,10, polyamide 6,11, and polyamide 6,12; and alicyclic polyamides such as polyamide 6,C and polyamide 2M5,C are more preferred.

[0019] The terminal group concentration of the polyamide can be adjusted by any known method, for example, by adding a terminal adjuster that reacts with terminal groups, such as a diamine compound, a monoamine compound, a dicarboxylic acid compound, a monocarboxylic acid compound, an acid anhydride, a monoisocyanate, a monoacid halide, a monoester, or a monoalcohol, to the polymerization solution so that the terminal group concentration is a predetermined value during polymerization of the polyamide.

[0020] Examples of the terminal modifier that reacts with the terminal amino group include: aliphatic monocarboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic acid, pivalic acid, and isobutyric acid; alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid; aromatic monocarboxylic acids such as benzoic acid, toluic acid, α-naphthalenecarboxylic acid, β-naphthalenecarboxylic acid, methylnaphthalenecarboxylic acid, and phenylacetic acid; Dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 5-sodium sulfoisophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, and diglycolic acid; and and mixtures of a plurality of compounds arbitrarily selected from these.

[0021] Among these, from the standpoints of reactivity, stability of the blocked terminals, cost, etc., one or more terminal modifiers selected from the group consisting of acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic acid, benzoic acid, isophthalic acid, terephthalic acid, and adipic acid are preferred.

[0022] Examples of the terminal modifier that reacts with the terminal carboxyl group include: aliphatic monoamines such as methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, decylamine, stearylamine, dimethylamine, diethylamine, dipropylamine, and dibutylamine; Alicyclic monoamines such as cyclohexylamine and dicyclohexylamine; Aromatic monoamines such as aniline, toluidine, diphenylamine, naphthylamine, etc.; Diamines such as tetramethylenediamine, hexamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4- / 2,4,4-trimethylhexamethylenediamine, 5-methylnonamethylenediamine, 2,4-dimethyloctamethylenediamine, metaxylylenediamine, paraxylylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 3,8-bis(aminomethyl)tricyclodecane, bis(4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminopropyl)piperazine, and aminoethylpiperazine; and Any mixture of these may be used.

[0023] Among these, one or more terminal modifiers selected from the group consisting of butylamine, hexylamine, octylamine, decylamine, stearylamine, cyclohexylamine, aniline, and hexamethylenediamine are preferred in terms of reactivity, boiling point, stability of the blocked terminals, cost, and the like.

[0024] The method for adding the terminal modifier to the polyamide and reacting it with the terminal functional group is not particularly limited, but one embodiment is a method in which the terminal modifier is added in any proportion during polymerization and reacted.

[0025] The concentrations of amino end groups and carboxyl end groups are 1 From the viewpoint of accuracy and simplicity, it is preferable to determine the concentration of each end group from the integral value of the characteristic signal corresponding to the end group by H-NMR. As a method for determining the concentration of these end groups, the method described in JP-A-7-228775 is specifically recommended. When using this method, deuterated trifluoroacetic acid is useful as a measurement solvent. 1 The number of 1 H-NMR scans required is at least 300, even when measured with an instrument having sufficient resolution.

[0026] The intrinsic viscosity [η] of each of the polyamides (A1), (A2), and (A), measured in concentrated sulfuric acid at 30°C, is preferably 0.6 dL / g or more, or 0.7 dL / g or more, from the viewpoint of obtaining good physical properties of the resin composition, and is preferably 2.0 dL / g or less, or 1.4 dL / g or less, or 1.2 dL / g or less, or 1.0 dL / g or less, from the viewpoint of ease of production and processing of the resin composition and appearance of the molded product.

[0027] In this disclosure, intrinsic viscosity is synonymous with the viscosity commonly referred to as intrinsic viscosity. A specific method for determining intrinsic viscosity is to measure the ηsp / c of ​​several test solutions with different polymer concentrations in 96% concentrated sulfuric acid at a temperature of 30°C, derive a relationship between each ηsp / c and the concentration (c), and extrapolate the concentration to zero. This value extrapolated to zero is the intrinsic viscosity. Details of how to determine intrinsic viscosity are described, for example, in Polymer Process Engineering (Prentice-Hall, Inc., 1994), pages 291 to 294. From the perspective of accuracy, it is desirable to use at least four test solutions with different polymer concentrations. The recommended polymer concentrations of the viscosity test solutions are preferably 0.05 g / dL, 0.1 g / dL, 0.2 g / dL, and 0.4 g / dL.

[0028] The number average molecular weight of each of the polyamides (A1), (A2), and (A) is preferably 5,000 or more, or 10,000 or more, or 15,000 or more, or 20,000 or more, from the viewpoint of obtaining good physical properties of the resin composition, and is preferably 100,000 or less, or 80,000 or less, or 60,000 or less, or 50,000 or less, from the viewpoint of promoting amide bond formation in the polyamide in the mixing step.

[0029] The weight average molecular weight of each of the polyamides (A1), (A2), and (A) is preferably 5,000 or more, or 10,000 or more, or 15,000 or more, or 20,000 or more, from the viewpoint of obtaining good physical properties of the resin composition, and is preferably 100,000 or less, or 80,000 or less, or 60,000 or less, or 50,000 or less, from the viewpoint of promoting amide bond formation in the polyamide in the mixing step.

[0030] The Mw / Mn of each of the polyamides (A1), (A2), and (A) is preferably 0.2 or more, or 0.5 or more, or 1 or more, from the viewpoint of promoting amide bond formation in the polyamides in the mixing step, and is preferably 5 or less, or 4 or less, or 2 or less, from the viewpoint of accurately controlling the physical properties of the resin composition.

[0031] The number average molecular weight and weight average molecular weight are values ​​determined by gel permeation chromatography in terms of standard polymethyl methacrylate.

[0032] The melting point of each of the polyamides (A1), (A2), and (A) is preferably 220°C or higher, or 230°C or higher, in terms of providing good heat resistance to the resin composition, and is preferably 350°C or lower, or 320°C or lower, or 300°C or lower, in terms of facilitating production and processing of the resin composition. The melting point refers to the peak-top temperature of the endothermic peak that appears when the temperature is increased from 23°C at a rate of 10°C / min using a differential scanning calorimeter (DSC), and when two or more endothermic peaks appear, it refers to the peak-top temperature of the endothermic peak on the highest temperature side.

[0033] The glass transition temperature of each of the polyamides (A1), (A2), and (A) is preferably 0°C or higher, or 10°C or higher, or 30°C or higher, in order to provide a resin composition with good mechanical strength, and is preferably 100°C or lower, or 90°C or lower, or 70°C or lower, in order to provide a resin composition with good toughness and easy production and processing. The glass transition temperature refers to the peak-top temperature at which the storage modulus drops significantly and the loss modulus reaches its maximum when measured using a dynamic viscoelasticity measuring device while increasing the temperature from 23°C at a heating rate of 2°C / min at an applied frequency of 10 Hz. When two or more loss modulus peaks appear, the glass transition temperature refers to the peak-top temperature of the lowest-temperature peak.

[0034] [Polyamide (A1) and Polyamide (A2)] The polyamide (A1) satisfies the relationship of amino terminal group concentration [NH2]>carboxyl terminal group concentration [COOH]. In one aspect, the amino terminal group ratio, which is the ratio of the amino terminal group concentration [NH2] to the carboxyl terminal group concentration [COOH], is greater than 1, preferably 1.01 or more, or 1.05 or more, or 1.10 or more, and preferably 10,000 or less, or 1,000 or less, or 100 or less, or 10 or less.

[0035] The amino end group concentration of the polyamide (A1) is preferably 20 μequivalents / g or more, or 30 μequivalents / g or more, and preferably 150 μequivalents / g or less, or 100 μequivalents / g or less, or 80 μequivalents / g or less.

[0036] The carboxyl end group concentration of the polyamide (A1) is preferably 20 μequivalents / g or more, or 30 μequivalents / g or more, and preferably 150 μequivalents / g or less, or 100 μequivalents / g or less, or 80 μequivalents / g or less.

[0037] The total concentration of the amino terminal group concentration [NH2] and the carboxyl terminal group concentration [COOH] of the polyamide (A1) is preferably 10 μequivalents / g or more, or 50 μequivalents / g or more, or 100 μequivalents / g or more, from the viewpoint of promoting amide bond formation in the polyamide in the mixing step, and is preferably 500 μequivalents / g or less, or 300 μequivalents / g or less, or 135 μequivalents / g or less, from the viewpoint of maintaining good physical properties of the resin composition by preventing the molecular weight of the polyamide from becoming too small.

[0038] The polyamide (A2) satisfies the condition that the amino terminal group concentration [NH2] is less than the carboxyl terminal group concentration [COOH]. In one aspect, the carboxyl terminal group ratio, which is the ratio of the carboxyl terminal group concentration [COOH] to the amino terminal group concentration [NH2], is greater than 1, preferably 1.01 or more, or 1.05 or more, or 1.10 or more, and preferably 10,000 or less, or 1,000 or less, or 100 or less, or 10 or less.

[0039] The amino end group concentration of polyamide (A2) is preferably 20 μequivalents / g or more, or 30 μequivalents / g or more, and preferably 150 μequivalents / g or less, or 100 μequivalents / g or less, or 80 μequivalents / g or less.

[0040] The carboxyl end group concentration of the polyamide (A2) is preferably 20 μequivalents / g or more, or 30 μequivalents / g or more, and preferably 150 μequivalents / g or less, or 100 μequivalents / g or less, or 80 μequivalents / g or less.

[0041] The total concentration of the amino terminal group concentration [NH2] and the carboxyl terminal group concentration [COOH] of the polyamide (A2) is preferably 10 μequivalents / g or more, or 50 μequivalents / g or more, or 100 μequivalents / g or more, from the viewpoint of promoting amide bond formation in the polyamide in the mixing step, and is preferably 500 μequivalents / g or less, or 300 μequivalents / g or less, or 135 μequivalents / g or less, from the viewpoint of maintaining good physical properties of the resin composition by preventing the molecular weight of the polyamide from becoming too small. In a particularly preferred embodiment, the total concentration ([NH2] + [COOH]) of each of the polyamides (A1) and (A2) is within the above-mentioned range.

[0042] In one embodiment, the mass concentration (C A1 ) the mass concentration (C A2 ) to the ratio (C A1 / C A2 ) may be, for example, 10 / 90 or more, or 20 / 80 or more, or 30 / 70 or more, or 40 / 60 or more, from the viewpoint of promoting amide bond formation in the polyamide in the mixing step, and may be, for example, 90 / 10 or less, or 80 / 20 or less, or 70 / 30 or less, or 60 / 40 or less.

[0043] In one embodiment, the amino end group concentration ([NH] A1 ) and carboxyl end group concentration ([COOH] A1 ), the mass concentration of the first polyamide (A1) in the mixture (C A1 ), the amino end group concentration of the second polyamide (A2) ([NH2] A2 ) and carboxyl end group concentration ([COOH] A2 ), the mass concentration of the second polyamide (A2) in the mixture (C A2 ), as well as the mass concentration of the first polyamide (A1) in the mixed components (C A1 ) and the mass concentration of the second polyamide (C A2 ) and the total mass concentration (C T ) based on the following formulas (1b) to (1d): [NH2] T =([NH2] A1 ×C A1 +[NH2] A2 ×C A2 ) / C T (1b) [COOH] T =([COOH] A1 ×C A1 +[COOH] A2 ×C A2 ) / C T (1c) ([NH2]+[COOH]) T =[NH2] T +[COOH] T (1d) The total concentration ([NH2] + [COOH]) calculated according to T is preferably 10 μequivalents / g or more, or 50 μequivalents / g or more, or 100 μequivalents / g or more from the viewpoint of promoting amide bond formation in the polyamide in the mixing step, and is preferably 500 μequivalents / g or less, or 300 μequivalents / g or less, or 200 μequivalents / g or less from the viewpoint of maintaining good physical properties of the resin composition by preventing the molecular weight of the polyamide from becoming too small.

[0044] In one embodiment, the [NH] T The above [COOH] T Ratio to ([NH2] T / [COOH] T ) may be, for example, 1 or more, or 1.5 or more, or 2 or more, and may be, for example, 5 or less, or 4 or less, from the viewpoint of smoothly proceeding with the amide bond-forming reaction of the polyamide in the mixing step.

[0045] [Polyamide A] The polyamide (A) is a polyamide having an amino terminal group concentration and a carboxyl terminal group concentration each of which is 20 μequivalents / g or more and at least one of which is 70 μequivalents / g or more, or an amino terminal group concentration and a carboxyl terminal group concentration each of which is 50 μequivalents / g or more and at least one of which is 60 μequivalents / g or more.

[0046] In one embodiment, the amino terminal group concentration of the polyamide (A) is 20 μequivalents / g or more, or 30 μequivalents / g or more, or 40 μequivalents / g or more, or 50 μequivalents / g or more, from the viewpoint of promoting amide bond formation in the polyamide in the mixing step, and is preferably 150 μequivalents / g or less, or 100 μequivalents / g or less, or 80 μequivalents / g or less, from the viewpoint of maintaining good physical properties of the resin composition by preventing the molecular weight of the polyamide from becoming too small.

[0047] In one embodiment, the carboxyl end group concentration of the polyamide (A) is 20 μequivalents / g or more, or 30 μequivalents / g or more, or 40 μequivalents / g or more, or 50 μequivalents / g or more, from the viewpoint of promoting amide bond formation in the polyamide in the mixing step, and is preferably 150 μequivalents / g or less, or 100 μequivalents / g or less, or 80 μequivalents / g or less, from the viewpoint of maintaining good physical properties of the resin composition by preventing the molecular weight of the polyamide from becoming too small.

[0048] In one embodiment, the polyamide (A) has an amino terminal group concentration or a carboxyl terminal group concentration of 50 μequivalents / g or more, or 60 μequivalents / g or more, or 70 μequivalents / g or more, or 80 μequivalents / g or more, from the viewpoint of promoting amide bond formation in the polyamide in the mixing step. In one embodiment, the polyamide (A) is rich in at least one of amino terminal groups and carboxyl terminal groups, and therefore, the reaction between amino groups and carboxyl groups in the polyamide molecules proceeds smoothly in the mixing step, resulting in a significant increase in molecular weight.

[0049] The total concentration of the amino terminal group concentration [NH2] and the carboxyl terminal group concentration [COOH] of the polyamide (A) is, in one aspect, 90 μequivalents / g or more, preferably 100 μequivalents / g or more, or 110 μequivalents / g or more, from the viewpoint of promoting amide bond formation in the polyamide in the mixing step, and is preferably 500 μequivalents / g or less, or 300 μequivalents / g or less, or 200 μequivalents / g or less, from the viewpoint of maintaining good physical properties of the resin composition by preventing the molecular weight of the polyamide from becoming too small.

[0050] In one embodiment, one of the amino terminal group concentration and the carboxyl terminal group concentration of the polyamide (A) may be 70 μequivalents / g or more, and the other may be less than 70 μequivalents / g. Alternatively, one of the amino terminal group concentration and the carboxyl terminal group concentration may be 60 μequivalents / g or more, and the other may be less than 60 μequivalents / g. In this case, the advantages of increasing the molecular weight in the mixing step are effectively obtained, and the molecular weight of the polyamide in the resin composition does not become too small, resulting in good physical properties of the resin composition. In a preferred embodiment, one of the amino terminal group concentration and the carboxyl terminal group concentration of the polyamide (A) is 20 μequivalents / g or more, or 30 μequivalents / g or more and less than 70 μequivalents / g, or 60 μequivalents / g or less, and the other is 70 μequivalents / g or more, or 100 μequivalents / g or more and 480 μequivalents / g or less, or 300 μequivalents / g or less. In another preferred embodiment, one of the amino terminal group concentration and the carboxyl terminal group concentration of the polyamide (A) is 50 μequivalents / g or more and less than 60 μequivalents / g, and the other is 60 μequivalents / g or more, or 100 μequivalents / g or more and 480 μequivalents / g or less, or 300 μequivalents / g or less.

[0051] The amino terminal group ratio of the polyamide (A), which is the ratio of the amino terminal group concentration [NH2] to the carboxyl terminal group concentration [COOH], is preferably 0.5 or more, or 1 or more, or 1.5 or more, and preferably 10 or less, or 5 or less, or 3 or less.

[0052] In the first embodiment, the molecular weight of the polyamide can be increased in the mixing step by using the polyamide (A1) and the polyamide (A2) in combination, and in the second embodiment, by using the polyamide (A). Without wishing to be bound by theory, it is speculated that the cellulose nanofibers (B) promote amide bonds between the polyamide ends in the mixing step, thereby increasing the molecular weight of the polyamide.

[0053] <Cellulose nanofiber (B)> The raw materials for cellulose nanofibers can be natural cellulose and regenerated cellulose. Examples of natural cellulose include wood pulp obtained from wood species (broadleaf or coniferous trees), non-wood pulp obtained from non-wood species (cotton, bamboo, hemp, bagasse, kenaf, cotton linter, sisal, straw, etc.), and cellulose aggregates produced by animals (e.g., sea squirts), algae, and microorganisms (e.g., acetic acid bacteria). Examples of regenerated cellulose include regenerated cellulose fibers (e.g., viscose, cupra, Tencel), cellulose derivative fibers, and ultrafine threads of regenerated cellulose or cellulose derivatives obtained by electrospinning.

[0054] Cellulose nanofibers refer to fine cellulose fibers obtained by treating pulp or the like with hot water at 100°C or higher to hydrolyze and weaken the hemicellulose, and then defibrating the fibers using a pulverizing method such as a high-pressure homogenizer, microfluidizer, ball mill, disc mill, or mixer (e.g., a homomixer). In one embodiment, the cellulose nanofibers have a number-average fiber diameter of 1 nm or more and 1,000 nm or less. The cellulose nanofibers may be chemically modified as described below.

[0055] The slurry may be prepared by dispersing the cellulose fibers in a liquid medium. Dispersion may be performed using a high-pressure homogenizer, a microfluidizer, a ball mill, a disk mill, a mixer (e.g., a homomixer), or the like. In one embodiment, the liquid medium in the slurry may contain water and, optionally, one or more organic solvents. Examples of organic solvents that can be used include commonly used water-miscible organic solvents, such as alcohols (e.g., methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, t-butanol, etc.) having a boiling point of 50°C to 170°C; ethers (e.g., propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, etc.); carboxylic acids (e.g., formic acid, acetic acid, lactic acid, etc.); esters (e.g., ethyl acetate, vinyl acetate, etc.); ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, etc.); and nitrogen-containing solvents (dimethylformamide, dimethylacetamide, acetonitrile, etc.). In a typical embodiment, the liquid medium in the slurry is substantially water alone.

[0056] Because cellulose raw materials contain alkali-soluble components and sulfuric acid-insoluble components (such as lignin), they may be subjected to a purification process such as delignification by cooking and a bleaching process to reduce the alkali-soluble components and sulfuric acid-insoluble components. However, because purification processes such as delignification by cooking and bleaching processes sever the molecular chains of cellulose, changing the weight-average molecular weight and number-average molecular weight, it is desirable that the purification process and bleaching process of the cellulose raw material be controlled so that the weight-average molecular weight of the cellulose nanofibers and the ratio of the weight-average molecular weight to the number-average molecular weight are within appropriate ranges.

[0057] Furthermore, because refining processes such as delignification by cooking and bleaching processes reduce the molecular weight of cellulose molecules, there are concerns that these processes will result in lower molecular weight cellulose nanofibers and alter the cellulose raw material, increasing the proportion of alkali-soluble matter. Because alkali-soluble matter has poor heat resistance, it is desirable that the refining and bleaching processes of the cellulose raw material be controlled so that the amount of alkali-soluble matter contained in the cellulose raw material is within a certain range or less.

[0058] In one aspect, the number average fiber diameter of the cellulose nanofibers is preferably 2 to 1000 nm, from the viewpoint of obtaining a favorable effect of improving physical properties due to the cellulose nanofibers. The number average fiber diameter of the cellulose nanofibers is more preferably 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more, and more preferably 500 nm or less, or 450 nm or less, or 400 nm or less, or 350 nm or less, or 300 nm or less, or 250 nm or less.

[0059] From the viewpoint of satisfactorily improving the mechanical properties of a resin composition containing cellulose nanofibers with a small amount of cellulose nanofibers, the average fiber length (L) / fiber diameter (D) ratio of the cellulose nanofibers is preferably 30 or more, or 50 or more, or 80 or more, or 100 or more, or 120 or more, or 150 or more. There is no particular upper limit, but from the viewpoint of handleability, it is preferably 5000 or less.

[0060] In this disclosure, the fiber length, fiber diameter, and L / D ratio of cellulose nanofibers are determined by dispersing an aqueous dispersion of cellulose nanofibers using a high-shear homogenizer (e.g., Nippon Seiki Co., Ltd., product name "Excel Auto Homogenizer ED-7") at 15,000 rpm for 5 minutes, diluting the resulting aqueous dispersion with pure water to 0.1 to 0.5 mass %, casting it on mica, and air-drying it to obtain a measurement sample. The measurement sample is then measured using a high-resolution scanning electron microscope (SEM) or atomic force microscope (AFM). Specifically, the length (L) and diameter (D) of 100 randomly selected cellulose nanofibers are measured in an observation field adjusted to a magnification such that at least 100 cellulose nanofibers are observed, and the ratio (L / D) is calculated. The number-average values ​​of the fiber length (L), fiber diameter (D), and ratio (L / D) of the cellulose nanofibers are calculated.

[0061] Alternatively, the fiber length, fiber diameter, and L / D ratio of the cellulose nanofibers in the resin composition can be confirmed by measuring the solid resin composition as a measurement sample using the above-mentioned measurement method.

[0062] Alternatively, the fiber length, fiber diameter, and L / D ratio of the cellulose nanofibers in a resin composition can be confirmed by dissolving the resin components in the resin composition in an organic or inorganic solvent that can dissolve the resin components of the resin composition, separating the cellulose nanofibers, thoroughly washing them with the solvent, and then replacing the solvent with pure water to prepare an aqueous dispersion, diluting the cellulose nanofiber concentration with pure water to 0.1 to 0.5% by mass, casting the dispersion on mica, and air-drying the resulting dispersion as a measurement sample, using the measurement method described above. At this time, the measurement is performed on at least 100 randomly selected cellulose nanofibers.

[0063] The crystallinity of the cellulose nanofibers is preferably 55% or higher. When the crystallinity is within this range, the mechanical properties (strength, dimensional stability) of the cellulose itself are high, and therefore when the cellulose nanofibers are dispersed in a resin, the strength and dimensional stability of the resin composition tend to be high. A more preferred lower limit for the crystallinity is 60%, even more preferably 70%, and most preferably 80%. There is no particular upper limit for the crystallinity of the cellulose nanofibers, and the higher the better, but from a production standpoint, a preferred upper limit is 99%.

[0064] Alkali-soluble polysaccharides such as hemicellulose and acid-insoluble components such as lignin are present between the microfibrils and between the microfibril bundles of plant-derived cellulose nanofibers. Hemicellulose is a polysaccharide composed of sugars such as mannan and xylan, and forms hydrogen bonds with cellulose to bind the microfibrils together. Lignin is a compound with an aromatic ring, and is known to be covalently bonded to hemicellulose in plant cell walls. If a large amount of impurities such as lignin remains in the cellulose nanofiber, discoloration may occur due to heat during processing. Therefore, from the perspective of suppressing discoloration of the resin composition during extrusion and molding, it is desirable to keep the crystallinity of the cellulose nanofiber within the above-mentioned range.

[0065] When the cellulose is cellulose type I crystals (derived from natural cellulose), the degree of crystallinity can be calculated by the Segal method from the diffraction pattern (2θ / deg. 10 to 30) obtained by measuring the sample by wide-angle X-ray diffraction, using the following formula: Crystallinity (%) = ([diffraction intensity due to the (200) plane at 2θ / deg. = 22.5] - [diffraction intensity due to amorphous phase at 2θ / deg. = 18]) / [diffraction intensity due to the (200) plane at 2θ / deg. = 22.5] × 100

[0066] When the cellulose is cellulose type II crystal (derived from regenerated cellulose), the degree of crystallinity can be calculated from the absolute peak intensity h0 at 2θ=12.6° assigned to the (110) plane peak of cellulose type II crystal in wide-angle X-ray diffraction and the peak intensity h1 from the baseline at this interplanar spacing, using the following formula: Crystallinity (%) =h1 / h0 ×100

[0067] Known crystalline forms of cellulose include type I, type II, type III, and type IV, of which types I and II are particularly commonly used, while types III and IV are obtained on a laboratory scale but are not commonly used on an industrial scale. The cellulose nanofibers of the present disclosure are preferably cellulose nanofibers containing cellulose type I crystals or cellulose type II crystals, because they have relatively high structural mobility and, by dispersing the cellulose nanofibers in a resin, a resin composition can be obtained that has a lower linear expansion coefficient and superior strength and elongation during tensile and bending deformation. Cellulose nanofibers containing cellulose type I crystals and having a crystallinity of 55% or more are more preferred.

[0068] Furthermore, from the viewpoint of exhibiting good mechanical properties, the degree of polymerization of the cellulose nanofiber is preferably 100 or more, or 150 or more, or 200 or more, or 300 or more, or 400 or more, or 450 or more, and from the viewpoint of processability, it is preferably 3500 or less, or 3300 or less, or 3200 or less, or 3100 or less, or 3000 or less.

[0069] The degree of polymerization of cellulose nanofibers refers to the average degree of polymerization measured according to the reduced specific viscosity method using a copper ethylenediamine solution described in Verification Test (3) of the "15th Edition Japanese Pharmacopoeia Commentary (published by Hirokawa Shoten)."

[0070] In one embodiment, the weight-average molecular weight (Mw) of the cellulose nanofiber is 100,000 or more, more preferably 200,000 or more. The ratio (Mw / Mn) of the weight-average molecular weight to the number-average molecular weight (Mn) is 6 or less, preferably 5.4 or less. A higher weight-average molecular weight indicates a lower number of terminal groups in the cellulose molecule. Furthermore, since the ratio (Mw / Mn) of the weight-average molecular weight to the number-average molecular weight represents the width of the molecular weight distribution, a lower Mw / Mn indicates a lower number of terminals in the cellulose molecule. Since the terminals of cellulose molecules are the starting points for thermal decomposition, cellulose nanofibers with particularly high heat resistance can be obtained when the cellulose molecules in the cellulose nanofiber have not only a high weight-average molecular weight but also a narrow molecular weight distribution. From the perspective of easy availability of cellulose raw materials, the weight-average molecular weight (Mw) of the cellulose nanofiber may be, for example, 600,000 or less, or 500,000 or less. From the viewpoint of ease of production of cellulose nanofibers, the ratio of weight-average molecular weight to number-average molecular weight (Mn) (Mw / Mn) may be, for example, 1.5 or more, or 2 or more. Mw can be controlled within the above range by selecting a cellulose raw material having an Mw appropriate for the purpose, by subjecting the cellulose raw material to appropriate physical and / or chemical treatments within an appropriate range, or the like. Mw / Mn can also be controlled within the above range by selecting a cellulose raw material having an Mw / Mn appropriate for the purpose, by subjecting the cellulose raw material to appropriate physical and / or chemical treatments within an appropriate range, or the like. In both Mw and Mw / Mn control, examples of the physical treatment include dry or wet grinding using a microfluidizer, ball mill, or disk mill, and physical treatments that apply mechanical forces such as impact, shear, shear, or friction using a crusher, homomixer, high-pressure homogenizer, ultrasonic device, or the like. Examples of the chemical treatment include digestion, bleaching, acid treatment, and conversion to regenerated cellulose.

[0071] The weight-average molecular weight and number-average molecular weight of the cellulose nanofibers referred to here are values ​​determined by dissolving the cellulose nanofibers in N,N-dimethylacetamide containing added lithium chloride and then performing gel permeation chromatography using N,N-dimethylacetamide as a solvent.

[0072] Methods for controlling the degree of polymerization (i.e., average degree of polymerization) or molecular weight of cellulose nanofibers include hydrolysis. Hydrolysis promotes depolymerization of amorphous cellulose inside the cellulose nanofibers, reducing the average degree of polymerization. At the same time, hydrolysis removes impurities such as hemicellulose and lignin in addition to the amorphous cellulose, making the interior of the fiber more porous.

[0073] The hydrolysis method is not particularly limited, and examples include acid hydrolysis, alkaline hydrolysis, hydrothermal decomposition, steam explosion, and microwave decomposition. These methods may be used alone or in combination. In acid hydrolysis, for example, α-cellulose obtained as pulp from fibrous plants is used as the cellulose raw material. This is dispersed in an aqueous medium, and an appropriate amount of a protonic acid, carboxylic acid, Lewis acid, heteropolyacid, or the like is added. The mixture is then heated with stirring, allowing for easy control of the average degree of polymerization. The reaction conditions, such as temperature, pressure, and time, vary depending on the cellulose species, cellulose concentration, acid species, and acid concentration, but are appropriately adjusted to achieve the desired average degree of polymerization. For example, cellulose nanofibers may be treated with a mineral acid aqueous solution of 2% by mass or less at 100°C or higher under pressure for 10 minutes or longer. Under these conditions, the acid or other catalyst component penetrates deep into the cellulose nanofibers, promoting hydrolysis. This reduces the amount of catalyst component required and facilitates subsequent purification.

[0074] Alkali-soluble polysaccharides that cellulose nanofibers may contain include hemicellulose, β-cellulose, and γ-cellulose. Alkali-soluble polysaccharides are understood by those skilled in the art as components obtained as the alkali-soluble portion of holocellulose (i.e., the components remaining after α-cellulose has been removed from holocellulose), which is obtained by solvent extraction and chlorine treatment of plants (e.g., wood). Alkali-soluble polysaccharides are polysaccharides containing hydroxyl groups and have poor heat resistance, which can lead to problems such as decomposition when heated, yellowing during thermal aging, and a decrease in the strength of cellulose nanofibers. Therefore, it is preferable that the alkali-soluble polysaccharide content in cellulose nanofibers is low.

[0075] In one aspect, the average content of alkali-soluble polysaccharides in the cellulose nanofibers is preferably 20% by mass or less, 18% by mass or less, 15% by mass or less, or 12% by mass or less, relative to 100% by mass of the cellulose nanofibers, from the viewpoint of obtaining good dispersibility of the cellulose nanofibers. From the viewpoint of ease of production of the cellulose nanofibers, the content may be 1% by mass or more, 2% by mass or more, or 3% by mass or more.

[0076] The average alkali-soluble polysaccharide content can be determined by the method described in the non-patent document (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000), by subtracting the α-cellulose content from the holocellulose content (Wise method). This method is recognized in the industry as a method for measuring hemicellulose content. The alkali-soluble polysaccharide content is calculated three times for each sample, and the number average of the calculated alkali-soluble polysaccharide contents is taken as the average alkali-soluble polysaccharide content.

[0077] In one aspect, the average content of acid-insoluble components in the cellulose nanofibers is preferably 10% by mass or less, or 5% by mass or less, or 3% by mass or less, relative to 100% by mass of the cellulose nanofibers, from the viewpoint of avoiding a decrease in the heat resistance of the cellulose nanofibers and the resulting discoloration. From the viewpoint of ease of production of the cellulose nanofibers, the content may be 0.1% by mass or more, or 0.2% by mass or more, or 0.3% by mass or more.

[0078] The average acid-insoluble content is determined by quantifying the acid-insoluble content using the Clason method described in the non-patent document (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000). This method is recognized in the art as a method for measuring lignin content. A sample is stirred in a sulfuric acid solution to dissolve cellulose, hemicellulose, and other components, and then filtered through a glass fiber filter. The resulting residue corresponds to the acid-insoluble component. The acid-insoluble component content is calculated from the weight of the acid-insoluble component, and the number average of the acid-insoluble component contents calculated for three samples is used as the average acid-insoluble component content.

[0079] The thermal decomposition temperature (T D ) is 270°C or higher in one aspect, preferably 275°C or higher, more preferably 280°C or higher, and even more preferably 285°C or higher, from the viewpoint of being able to exhibit the heat resistance and mechanical strength desired for in-vehicle applications and the like. The higher the thermal decomposition onset temperature, the better, but from the viewpoint of ease of production of cellulose nanofibers, it may be, for example, 320°C or lower, or 300°C or lower.

[0080] In this disclosure, T D is a value obtained from a graph in thermogravimetry (TG) analysis, where the horizontal axis is temperature and the vertical axis is weight retention %. Starting from the weight of cellulose nanofiber at 150°C (a state where most of the moisture has been removed) (weight loss 0 wt%), the temperature is continued to be increased until the temperature at which 1 wt% weight loss occurs (T 1% ) and the temperature at which 2 wt% weight loss occurs (T 2%The temperature at the point where this line intersects with the horizontal line (baseline) that passes through the starting point of 0 wt% weight loss is T D It is defined as:

[0081] 1% weight loss temperature (T 1% ) is the above T D This is the temperature at which the weight loss reaches 1% by weight, starting from the weight at 150°C, when the temperature is continued to be increased using the method described above.

[0082] Weight loss rate of cellulose nanofiber at 250°C (T 250℃ ) is the weight loss rate when cellulose nanofibers are kept at 250°C under nitrogen flow for 2 hours in TG analysis.

[0083] (chemical modification) The cellulose nanofibers may be chemically modified. The cellulose nanofibers may be chemically modified in advance, for example, at the raw pulp or linter stage, during or after the defibration treatment, or during or after the slurry preparation process, or during or after the drying (granulation) process.

[0084] As a modifying agent for cellulose nanofibers, compounds that react with the hydroxyl groups of cellulose can be used, including esterifying agents, etherifying agents, and silylating agents. In a preferred embodiment, the chemical modification is acylation using an esterifying agent, and acetylation is particularly preferred. As the esterifying agent, acid halides, acid anhydrides, carboxylic acid vinyl esters, and carboxylic acids are preferred.

[0085] The acid halide may be at least one selected from the group consisting of compounds represented by the following formula: R 1 -C(=O)-X (In the formula, R 1 represents an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms, a cycloalkyl group having 3 to 24 carbon atoms, or an aryl group having 6 to 24 carbon atoms, and X is Cl, Br, or I. Specific examples of acid halides include, but are not limited to, acetyl chloride, acetyl bromide, acetyl iodide, propionyl chloride, propionyl bromide, propionyl iodide, butyryl chloride, butyryl bromide, butyryl iodide, benzoyl chloride, benzoyl bromide, and benzoyl iodide. Among these, acid chlorides are preferred in terms of reactivity and ease of handling. In the reaction of the acid halides, one or more alkaline compounds may be added to act as a catalyst and neutralize acidic by-products. Specific examples of alkaline compounds include, but are not limited to, tertiary amine compounds such as triethylamine and trimethylamine; and nitrogen-containing aromatic compounds such as pyridine and dimethylaminopyridine.

[0086] As the acid anhydride, any appropriate acid anhydride can be used. For example, Saturated aliphatic monocarboxylic acid anhydrides such as acetic acid, propionic acid, (iso)butyric acid, and valeric acid; unsaturated aliphatic monocarboxylic acid anhydrides such as (meth)acrylic acid and oleic acid; Alicyclic monocarboxylic acid anhydrides such as cyclohexanecarboxylic acid and tetrahydrobenzoic acid; Aromatic monocarboxylic acid anhydrides such as benzoic acid and 4-methylbenzoic acid; Examples of dibasic carboxylic acid anhydrides include saturated aliphatic dicarboxylic acid anhydrides such as succinic anhydride and adipic acid, unsaturated aliphatic dicarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride, alicyclic dicarboxylic acid anhydrides such as 1-cyclohexene-1,2-dicarboxylic acid anhydride, hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride, and aromatic dicarboxylic acid anhydrides such as phthalic anhydride and naphthalic anhydride; Examples of the tri- or higher basic carboxylic acid anhydrides include polycarboxylic acid (anhydrides) such as trimellitic anhydride and pyromellitic anhydride. In the reaction of an acid anhydride, one or more of the following may be added as a catalyst: an acidic compound such as sulfuric acid, hydrochloric acid, or phosphoric acid; a Lewis acid (for example, a Lewis acid compound represented by MYn, where M represents a semimetallic element such as B, As, or Ge; a base metal element such as Al, Bi, or In; a transition metal element such as Ti, Zn, or Cu; or a lanthanoid element; n is an integer corresponding to the valence of M and represents 2 or 3; and Y represents a halogen atom, OAc, OCOCF3, ClO4, SbF6, PF6, or OSO2CF3(OTf)); or an alkaline compound such as triethylamine or pyridine.

[0087] The vinyl carboxylic acid ester may be selected from the group consisting of vinyl carboxylic acid esters of the following formula: R-COO-CH=CH2 Preferred are vinyl carboxylate esters represented by the formula: {wherein R is any one of an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms, a cycloalkyl group having 3 to 16 carbon atoms, and an aryl group having 6 to 24 carbon atoms.} More preferably, the vinyl carboxylate ester is at least one selected from the group consisting of vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl cyclohexanecarboxylate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl pivalate, vinyl octylate, divinyl adipate, vinyl methacrylate, vinyl crotonate, vinyl pivalate, vinyl octylate, vinyl benzoate, and vinyl cinnamate. In the esterification reaction with a vinyl carboxylate, one or more catalysts selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, alkali metal hydrogencarbonates, primary to tertiary amines, quaternary ammonium salts, imidazole and derivatives thereof, pyridine and derivatives thereof, and alkoxides may be added.

[0088] Examples of alkali metal hydroxides and alkaline earth metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide, etc. Examples of alkali metal carbonates, alkaline earth metal carbonates, and alkali metal hydrogen carbonates include lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, cesium hydrogen carbonate, etc.

[0089] The primary to tertiary amines refer to primary amines, secondary amines, and tertiary amines, and specific examples include ethylenediamine, diethylamine, proline, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-1,3-propanediamine, N,N,N',N'-tetramethyl-1,6-hexanediamine, tris(3-dimethylaminopropyl)amine, N,N-dimethylcyclohexylamine, and triethylamine.

[0090] Examples of imidazole and its derivatives include 1-methylimidazole, 3-aminopropylimidazole, and carbonyldiimidazole.

[0091] Examples of pyridine and its derivatives include N,N-dimethyl-4-aminopyridine and picoline.

[0092] Examples of the alkoxide include sodium methoxide, sodium ethoxide, and potassium t-butoxide.

[0093] The carboxylic acid may be at least one selected from the group consisting of compounds represented by the following formulas: R-COOH (In the formula, R represents an alkyl group having 1 to 16 carbon atoms, an alkenyl group having 2 to 16 carbon atoms, a cycloalkyl group having 3 to 16 carbon atoms, or an aryl group having 6 to 16 carbon atoms.)

[0094] Specific examples of carboxylic acids include at least one selected from the group consisting of acetic acid, propionic acid, butyric acid, caproic acid, cyclohexanecarboxylic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, pivalic acid, methacrylic acid, crotonic acid, pivalic acid, octylic acid, benzoic acid, and cinnamic acid.

[0095] Among these carboxylic acids, at least one selected from the group consisting of acetic acid, propionic acid, and butyric acid, and particularly acetic acid, is preferred from the viewpoint of reaction efficiency. In the reaction of carboxylic acid, one or more of the following may be added as a catalyst: an acidic compound such as sulfuric acid, hydrochloric acid, or phosphoric acid; a Lewis acid (for example, a Lewis acid compound represented by MYn, where M represents a semimetallic element such as B, As, or Ge; a base metal element such as Al, Bi, or In; a transition metal element such as Ti, Zn, or Cu; or a lanthanoid element; n is an integer corresponding to the valence of M and represents 2 or 3; and Y represents a halogen atom, OAc, OCOCF3, ClO4, SbF6, PF6, or OSO2CF3(OTf)); or an alkaline compound such as triethylamine or pyridine.

[0096] Among these esterification reactants, at least one selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, vinyl butyrate, and acetic acid, and among these, acetic anhydride and vinyl acetate are preferred from the viewpoint of reaction efficiency.

[0097] In one embodiment, the chemical modification is acylation. From the viewpoint of affinity with the matrix resin, the degree of acyl substitution (DS) may be 0 or more, or 0.2 or more, or 0.25 or more, or 0.3 or more, or 0.5 or more. Furthermore, since the remaining unmodified cellulose backbone allows for the production of esterified cellulose nanofibers that combine the high tensile strength and dimensional stability inherent to cellulose with the high dispersibility in the matrix resin inherent to the chemical modification, the degree of acyl substitution (DS) is preferably 1.5 or less, or 1.2 or less, or 1.0 or less, or 0.8 or less, or 0.7 or less, or 0.6 or less, or 0.5 or less.

[0098] The degree of acyl substitution (DS) can be calculated from the reflection infrared absorption spectrum of the esterified cellulose nanofiber based on the peak intensity ratio between the peak derived from the acyl group and the peak derived from the cellulose skeleton. The peak of the absorption band of C=O derived from the acyl group is at 1730 cm -1 The absorption band of CO based on the cellulose backbone appears at 1030 cm -1 The DS of esterified cellulose nanofibers was determined by creating a correlation graph between the DS obtained from solid-state NMR measurements of the esterified cellulose nanofibers described below and the modification rate (IR index 1030), which is defined as the ratio of the peak intensity of the absorption band of C=O based on the acyl group to the peak intensity of the absorption band of CO in the cellulose backbone chain, and then calculating the calibration curve from the correlation graph. Degree of substitution DS = 4.13 × IR index (1030) It can be found by using

[0099] The method for calculating the DS of esterified cellulose nanofibers using solid-state NMR is as follows: 13 C solid-state NMR measurements were performed, and the chromaticity can be calculated using the following formula, which is the ratio of the chromatic intensity (Inf) of a signal assigned to one carbon atom derived from the modifying group to the total chromatic intensity (Inp) of signals assigned to carbons C1-C6 derived from the pyranose ring of cellulose, which appear in the range from 50 ppm to 110 ppm. DS=(Inf)×6 / (Inp) For example, when the modifying group is an acetyl group, the signal at 23 ppm assigned to -CH3 can be used. Use 13 The conditions for the C solid-state NMR measurement are, for example, as follows: Equipment:Bruker Biospin Avance500WB Frequency: 125.77MHz Measurement method: DD / MAS method Waiting time: 75 seconds NMR sample tube: 4mmφ Accumulation times: 640 times (approx. 14 hours) MAS: 14,500Hz Chemical shift reference: glycine (external reference: 176.03 ppm)

[0100] The DS heterogeneity ratio (DSs / DSt), defined as the ratio of the degree of modification (DSs) of the fiber surface to the degree of modification (DSt) of the entire fiber (which is synonymous with the above-mentioned degree of acyl substitution (DS)), of the esterified cellulose nanofiber is preferably 1.05 or higher. The higher the DS heterogeneity ratio, the more pronounced the sheath-core-like heterogeneous structure (i.e., a structure in which the fiber surface is highly chemically modified while the fiber center retains a cellulose structure close to the original, unmodified structure). This allows for the high tensile strength and dimensional stability inherent in cellulose, while improving the affinity with resins when composited with resins and the dimensional stability of resin compositions. The DS heterogeneity ratio is more preferably 1.1 or higher, or 1.2 or higher, or 1.3 or higher, or 1.5 or higher, or 2.0 or higher. From the viewpoint of ease of production of chemically modified cellulose nanofibers, it is preferably 30 or lower, or 20 or lower, or 10 or lower, or 6 or lower, or 4 or lower, or 3 or lower. The DSs value varies depending on the degree of modification of the esterified cellulose nanofiber, but as an example, it is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, and even more preferably 0.5 or more, and is preferably 3.0 or less, more preferably 2.5 or less, particularly preferably 2.0 or less, even more preferably 1.5 or less, particularly preferably 1.2 or less, and most preferably 1.0 or less. The preferred range of DSt is as described above for the acyl substituent (DS).

[0101] The smaller the coefficient of variation (CV) of the DS heterogeneity of chemically modified cellulose nanofibers, the smaller the variability in various physical properties of the resin composition, which is preferable. The coefficient of variation is preferably 50% or less, or 40% or less, or 30% or less, or 20% or less. For example, the coefficient of variation can be further reduced in a method in which chemically modified cellulose nanofibers are obtained by defibrating a cellulose raw material and then chemically modifying it (i.e., a sequential method), whereas it can be increased in a method in which defibration and chemical modification of the cellulose raw material are performed simultaneously (i.e., a simultaneous method). While the mechanism of this action is unclear, it is thought that in the simultaneous method, chemical modification is more likely to proceed in the thin fibers produced in the early stages of defibration. Furthermore, when hydrogen bonding between cellulose microfibrils is reduced by chemical modification, defibration proceeds further, resulting in an increase in the coefficient of variation of the DS heterogeneity.

[0102] The coefficient of variation (CV) of the DS heterogeneity ratio is calculated by taking 100 g of an aqueous dispersion of chemically modified cellulose nanofiber (solid content of 10 mass% or more), freeze-pulverizing 10 g portions, and calculating the DS heterogeneity ratio from the DSt and DSs of 10 samples.The coefficient of variation (CV) of the DS heterogeneity ratio can then be calculated using the following formula from the standard deviation (σ) and arithmetic mean (μ) of the DS heterogeneity ratio among the obtained 10 samples. DS heterogeneity ratio = DSs / DSt Coefficient of variation (%) = standard deviation σ / arithmetic mean μ × 100

[0103] The DSs is calculated as follows. Specifically, esterified cellulose nanofibers powdered by freeze-pulverization are placed on a 2.5 mm diameter dish-shaped sample stage, pressed down to flatten the surface, and measured by X-ray photoelectron spectroscopy (XPS). The XPS spectrum reflects the constituent elements and chemical bonding state of only the surface layer of the sample (typically on the order of a few nm). Peak separation is performed on the obtained C1s spectrum, and the DSs can be calculated using the following formula: the integrated intensity (Ixf) of the peak assigned to one carbon atom derived from the modifying group relative to the integrated intensity (Ixp) of the peak assigned to carbons C2-C6 derived from the pyranose ring of cellulose (289 eV, C-C bond). DSs = (Ixf) × 5 / (Ixp) For example, if the modifying group is an acetyl group, after peak separation of the C1s spectrum at 285 eV, 286 eV, 288 eV, and 289 eV, the peak at 289 eV can be used for Ixp and the peak (286 eV) derived from the O-C=O bond of the acetyl group can be used for Ixf. The conditions for the XPS measurement used are, for example, as follows. Equipment used: ULVAC-Phi VersaProbe II Excitation source: mono. AlKα 15kV x 3.33mA Analysis size: approx. 200 μmφ Photoelectron extraction angle: 45° Capture Area Narrow scan: C 1s, O 1s Pass Energy: 23.5 eV

[0104] <Additional Ingredients> The resin composition of this embodiment may further contain additional components as needed to improve its performance. Examples of additional components include dispersants, organic or inorganic fillers other than cellulose, compatibilizers, plasticizers, colorants, fragrances, flow control agents, leveling agents, conductive agents, antioxidants, antistatic agents, UV absorbers, UV dispersants, and deodorizers. The content of any additional components in the resin composition is appropriately selected within a range that does not impair the desired effects of the present invention, and may be, for example, 0.01% by mass to 50% by mass, or 0.1% by mass to 30% by mass.

[0105] The dispersant is preferably a compound capable of reacting with or hydrogen bonding to the hydroxyl groups of cellulose. Suitable examples of the dispersant include one or more selected from the group consisting of cellulose derivatives, polyalkylene oxides, amides, and amines. Cellulose derivatives are cellulose-based substances and therefore have high affinity with cellulose, while they are also thermoplastic resins, and are therefore preferred for their high effect of improving the dispersion stability of cellulose in resin compositions. Dispersants preferably have a boiling point higher than that of water. Note that a boiling point higher than that of water refers to a boiling point higher than the boiling point of water at each pressure on its vapor pressure curve (for example, 100°C at 1 atmosphere).

[0106] Examples of cellulose derivatives include cellulose esters and cellulose ethers, and cellulose esters are preferred from the viewpoint of heat resistance.

[0107] The polyalkylene oxide may be composed of one or more types of oxyalkylene units, and the arrangement of the two or more types of oxyalkylene units may be random or block. A preferred example from the viewpoint of good affinity with cellulose is polyethylene oxide. The number of alkylene oxide repeat units in the polyalkylene oxide may be, for example, 500 to 100,000, 1,000 to 80,000, or 2,000 to 50,000.

[0108] The amide compound is a compound having one or more amide bonds (-C(=O)NH- bonds) in the molecule. The amide compound may be an aliphatic or aromatic amide, or a combination thereof. It is preferable that the amide compound has an amide bond in the molecular skeleton (i.e., a site other than a side chain) in order to improve the dispersibility of cellulose. Examples of the amine compound include primary amines, secondary amines, and tertiary amines, such as amine hexanoic acid.

[0109] Examples of surfactants include copolymers (e.g., block copolymers of propylene oxide and ethylene oxide, block copolymers of tetrahydrofuran and ethylene oxide) obtained by using one or more compounds that provide hydrophilic segments (e.g., polyethylene glycol) and one or more compounds that provide hydrophobic segments (e.g., polypropylene glycol, poly(tetramethylene ether) glycol (PTMEG), polybutadiene diol, etc.), and modified products thereof (e.g., acid-modified products).

[0110] In the resin composition, the amount of dispersant per 100 parts by mass of cellulose nanofibers is preferably 1 part by mass or more, or 5 parts by mass or more, or 10 parts by mass or more, or 20 parts by mass or more, from the viewpoint of good dispersion of cellulose and network formation, and is preferably 500 parts by mass or less, or 300 parts by mass or less, or 200 parts by mass or less, from the viewpoint of reducing variation in the performance of the resin composition.

[0111] <Production of resin composition> The method of this embodiment includes a mixing step of mixing components containing the above-described components to obtain a resin composition. In the mixing step, a mixture containing polyamide (A1), polyamide (A2), and cellulose nanofibers (B) (in a first embodiment) or a mixture containing polyamide (A) and cellulose nanofibers (B) (in a second embodiment) is mixed.

[0112] In one aspect, the amount of cellulose nanofibers per 100 parts by mass of polyamide in each of the mixed components and the resin composition is preferably 0.1 parts by mass or more, or 0.5 parts by mass or more, or 1 part by mass or more, or 2 parts by mass or more, from the viewpoint of obtaining a good effect of improving physical properties, and is preferably 100 parts by mass or less, or 80 parts by mass or less, or 70 parts by mass or less, or 60 parts by mass or less, from the viewpoint of processability.

[0113] In one aspect, the amount of cellulose nanofibers, based on 100% by mass of the total mass of the mixed components and 100% by mass of the total mass of the resin composition, is preferably 0.1% by mass or more, or 0.5% by mass or more, or 1% by mass or more, or 2% by mass or more, or 3% by mass or more, or 5% by mass or more, from the viewpoint of obtaining a good effect of improving physical properties, and is preferably 50% by mass or less, or 40% by mass or less, or 30% by mass or less, or 20% by mass or less, from the viewpoint of processability.

[0114] The mixing is typically melt-kneading. The cellulose nanofibers may be subjected to the mixing step in the form of a dried product or a slurry (e.g., an aqueous dispersion). The heating temperature during melt-kneading of the mixed components may be adjusted depending on the polyamide used, and is preferably a temperature equal to or higher than the melting point of the polyamide but not significantly higher than the melting point. The heating temperature is preferably equal to or higher than the melting point of the polyamide, or equal to or higher than the melting point +20°C, or equal to or higher than the melting point +30°C, or equal to or higher than the melting point +40°C. From the viewpoint of suppressing deterioration of the mixed components, the heating temperature is preferably equal to or lower than the melting point +90°C, or equal to or lower than the melting point +80°C, or equal to or lower than the melting point +70°C. The melting point is the peak-top temperature of the highest endothermic peak that appears when the temperature is increased from 23°C at a rate of 10°C / min using a differential scanning calorimeter (DSC). In embodiments where the mixed components contain multiple polyamides, this refers to the highest melting point.

[0115] The moisture content of the blended components is preferably 5,000 ppm by mass or less, or 2,000 ppm by mass or less, or 1,500 ppm by mass or less, or 1,000 ppm by mass or less, from the viewpoint of suppressing deterioration of the blended components (particularly the polyamide and cellulose nanofibers). On the other hand, from the viewpoint of ease of process control, the moisture content may be, for example, 1 ppm by mass or more, or 100 ppm by mass or more, or 500 ppm by mass or more. In a preferred embodiment, the moisture content of the polyamides to be blended, more specifically, the polyamides (A1) and (A2) or the polyamide (A), is within the above range.

[0116] For melt kneading, an extruder such as a single-screw extruder or a twin-screw extruder can be used, with a twin-screw extruder being preferred for controlling the dispersibility of cellulose. The ratio L / D, obtained by dividing the cylinder length (L) of the extruder by the screw diameter (D), is preferably 40 or more, and particularly preferably 50 or more. Furthermore, the screw rotation speed during kneading is preferably in the range of 100 to 800 rpm, more preferably 150 to 600 rpm. These values ​​vary depending on the screw design. From the viewpoint of suppressing thermal degradation of the resin composition, weak kneading (i.e., kneading under low shear force) is preferred. Weak kneading can be achieved, for example, by providing many conveying zones in the screw configuration of the extruder or by reducing the screw rotation speed.

[0117] Each screw in the cylinder of the extruder is optimized by combining a full-flight screw with an elliptical two-wing screw shape, a kneading element called a kneading disc, and the like.

[0118] In one embodiment, an addition port is provided midway through the cylinder of the extruder, and the raw materials introduced into the addition port are guided to the screw in the cylinder. There are no particular limitations on the location of the addition port, but in one embodiment, the addition port is located downstream of the melt-kneading zone. In normal kneading using an extruder, the initial resin melting zone is the region where the strongest shear is applied, so by adding a filler component to the unmelted resin moving through the conveying zone, the filler is finely dispersed by the shear force generated by the subsequent heating and melting.

[0119] When finely dispersing cellulose nanofibers in polyamide, adding the cellulose nanofibers before the resin melting zone can cause cellulose degradation due to the strong shear force in the resin melting zone, resulting in problems such as loss of the strong crystalline structure inherent to cellulose, reduced mechanical properties as a reinforced resin, and coloration and odor. In particular, when using a high-melting-point resin such as polyamide, the kneading temperature is high, which tends to subject the cellulose nanofibers to a harsh thermal history. From this perspective, adding cellulose nanofibers to pre-melted polyamide is advantageous because the cellulose is dispersed in the polyamide with minimal degradation.

[0120] To reduce the thermal history of the mixed components as they pass through the cylinder, it is preferable to design the cellulose nanofiber addition port downstream of the melt-kneading zone of the extruder. Specifically, it is preferable to design the length (L2) from the cylinder outlet to the addition port to be less than half the total length of the cylinder (L1). Note that the total length of the cylinder also includes parts not involved in kneading (e.g., the conveying zone). Cellulose is introduced through the addition port and mixed into the polyamide melt-kneaded in the extruder.

[0121] When the distance that cellulose nanofibers are transported in the extruder is shorter than that of polyamide, a uniform dispersion can be achieved by devising a screw configuration inside the cylinder after the cellulose nanofibers are mixed in. Specifically, and not limited to this, a high degree of dispersion of cellulose nanofibers can be more reliably achieved by installing one or more counterclockwise screws that create a feed in the opposite direction to the forward direction inside the cylinder downstream of the addition port.

[0122] In the mixing step, it is preferable to reuse a portion of the resin composition and / or molded article as part of the mixed components. Such a resin composition and / or molded article may be the resin composition and / or molded article produced in this embodiment, or may be one produced by another process (for example, a recycled polyamide produced by another process). By returning a resin composition in which the molecular weight of the polyamide has been reduced by the thermal history in the mixing step for producing the resin composition, and / or a molded article in which the molecular weight of the polyamide has been reduced by the thermal history in the mixing step and the thermal history in the molding step for producing a molded article from the resin composition, to the mixing step, the reduced molecular weight of the polyamide can be restored, and a resin composition or molded article with excellent physical properties can be obtained.

[0123] The total ratio of the resin composition-derived components and the molded body-derived components in the mixed components is preferably 1 mass% or more, or 2 mass% or more, or 5 mass% or more, from the viewpoint of obtaining a good effect of recovering the molecular weight reduction as described above, and is preferably 99 mass% or less, or 80 mass% or less, or 50 mass% or less, from the viewpoint of accurately controlling the physical properties of the resin composition.

[0124] <Shape of resin composition> The resin composition of this embodiment can be provided in various shapes. Specific examples include resin pellets, sheets, fibers, plates, rods, etc., with the resin pellet shape being preferred due to ease of post-processing and transportation. Preferred resin pellet shapes include round, oval, and cylindrical shapes, and the shape may vary depending on the cutting method used during extrusion. For example, pellets cut using a cutting method known as underwater cutting are often round, pellets cut using a cutting method known as hot cutting are often round or oval, and pellets cut using a cutting method known as strand cutting are often cylindrical. The preferred pellet diameter for round pellets is 1 mm or more and 3 mm or less. The preferred diameter for cylindrical pellets is 1 mm or more and 3 mm or less, and the preferred length is 2 mm or more and 10 mm or less. The above diameter and length are preferably set to be equal to or greater than the lower limit from the viewpoint of operational stability during extrusion, and are preferably set to be equal to or less than the upper limit from the viewpoint of ease of insertion into a molding machine during post-processing.

[0125] <Characteristics of resin composition> <Moisture percentage> From the viewpoint of the stability over time of the resin composition, the moisture content of the resin composition is preferably 5000 ppm by mass or less, or 2000 ppm by mass or less, or 1500 ppm by mass or less. On the other hand, from the viewpoint of ease of process control, the moisture content may be, in one embodiment, 1 ppm by mass or more, or 100 ppm by mass or more, or 500 ppm by mass or more.

[0126] In one aspect, the moisture content of the resin composition is higher than that of the polyamide to be mixed (more specifically, in the first aspect, that of the mixture of polyamide (A1) and polyamide (A2), and in the second aspect, that of polyamide (A)). In this embodiment, a moisture content of the resin composition higher than that of the polyamide to be mixed is an indicator that water has been generated by the formation of intermolecular amide bonds in the polyamide during the mixing step. According to the method of this embodiment, the polyamide is polymerized through amide bond formation, thereby increasing the molecular weight of the polyamide to a level that satisfies, for example, the above-mentioned formula (1a) or (2a). In one aspect, the ratio of the moisture content of the polyamide in the resin composition to that of the polyamide to be mixed is greater than 1, preferably 1.01 or greater, 1.03 or greater, or 1.05 or greater. The higher the ratio, the more significant the advantages of the method of this embodiment. On the other hand, from the viewpoint of maintaining good physical properties of the resin composition by keeping the moisture content of the polyamide in the resin composition low, the ratio is preferably 1.50 or less, or 1.30 or less, or 1.25 or less.

[0127] <Tensile yield strength> In the resin composition of this embodiment, the cellulose nanofibers contribute to a dramatic improvement in tensile yield strength compared to polyamide alone. The ratio of the tensile yield strength of the resin composition to the tensile yield strength of polyamide alone, taken as 1.0, is preferably 1.1 times or more, more preferably 1.11 times or more, even more preferably 1.12 times or more, and most preferably 1.13 times or more. While there is no particular upper limit to this ratio, from the viewpoint of ease of production, it is preferably 1.5 times, more preferably 1.2 times. The tensile yield strength is a value measured in accordance with JIS K6920-2 using a multipurpose test piece molded in accordance with ISO294-3.

[0128] <Linear expansion coefficient> The resin composition of this embodiment contains cellulose, which allows the resin composition to exhibit low thermal expansion without increasing its specific gravity. Specifically, the thermal expansion coefficient of the resin composition in the temperature range of 20°C to 100°C is preferably 70 ppm / K or less, more preferably 60 ppm / K or less, more preferably 50 ppm / K or less, more preferably 45 ppm / K or less, even more preferably 40 ppm / K or less, and most preferably 35 ppm / K or less. There is no particular lower limit to the thermal expansion coefficient, but from the viewpoint of ease of production, it is preferably, for example, 5 ppm / K, more preferably 10 ppm / K. The thermal expansion coefficient is a value determined by thermomechanical measurement in accordance with ISO11359-2.

[0129] <Tensile breaking strain> The tensile break strain of the resin composition of this embodiment is preferably 10% or more, or 20% or more, or 30% or more, or 40% or more, or 50% or more. Such a resin composition is preferable because it has excellent toughness. Although a higher tensile break strain of the resin composition is preferable, from the viewpoint of ease of production of the resin composition, it may be, for example, 500% or less, or 200% or less, or 100% or less. The tensile break strain is a value obtained as the arithmetic average of five data points of strain at break when a tensile test is performed on an ISO 37 type 3 test piece using a tensile tester at a temperature of 23°C and a relative humidity of 50% at a pulling rate of 5 mm / min.

[0130] <Production of Molded Body> Molded articles of various shapes can be produced from the resin composition of the present embodiment. The mixing step of this embodiment (i.e., a step of mixing components containing polyamide and cellulose nanofibers to obtain a resin composition), a molding step of molding the resin composition; Examples of molding methods include injection molding (e.g., injection compression molding, injection press molding, gas-assisted injection molding, and ultra-high speed injection molding), various extrusion moldings (cold runner method or hot runner method), foam molding (including supercritical fluid injection molding), insert molding, in-mold coating molding, heat-insulating mold molding, rapid heating and cooling mold molding, and various profile extrusion moldings (e.g., two-color molding and sandwich molding). For example, various extrusion moldings are suitable for molding sheets, films, fibers, etc. Inflation methods, calendaring methods, casting methods, etc. can also be used to mold sheets or films. Furthermore, by subjecting the material to a specific stretching operation, it can be molded into heat-shrinkable tubing. It can also be made into hollow molded products by rotational molding, blow molding, etc. In terms of design and cost, injection molding is the preferred molding method.

[0131] The molding temperature can be selected appropriately depending on the composition of the resin composition, etc., but may be, for example, above the melting point of the polyamide used, or above the melting point + 20°C, or above the melting point + 30°C, or below the melting point + 90°C, or below the melting point + 80°C, or below the melting point + 70°C.

[0132] <Uses of resin composition and molded article> The resin composition and molded article of this embodiment are useful as substitutes for steel plates, fiber-reinforced plastics (e.g., carbon fiber-reinforced plastics, glass fiber-reinforced plastics, etc.), resin composites containing inorganic fillers, etc. Suitable applications for the resin composition and molded article include industrial machine parts, general machine parts, automobile, railway, vehicle, ship, and aerospace-related parts, electronic and electrical parts, construction and civil engineering materials, daily necessities, sports and leisure goods, housing components for wind power generation, containers and packaging components, etc. [Example]

[0133] Hereinafter, exemplary embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0134] Evaluation Method <Evaluation of Polyamide and Resin Composition> [Polyamide amino end group concentration [NH2]] The weighed sample was dissolved in a 90% by mass aqueous phenol solution, and the solution was subjected to potentiometric titration with 1 / 50N hydrochloric acid at 25°C to calculate the value.

[0135] [Polyamide carboxyl end group concentration [COOH]] The weighed sample was dissolved in benzyl alcohol at 160°C, and the content was calculated by potentiometric titration at 25°C with 1 / 50N hydrochloric acid as an indicator.

[0136] [Polyamide weight average molecular weight (Mw), number average molecular weight (Mn) and Mw / Mn ratio] The polymer pellets were dissolved in hexafluoroisopropanol, and the content was measured by gel permeation chromatography, and calculated in terms of standard polymethyl methacrylate. The pellet was cut using a microtome (Leica, model number: RM2245) and approximately 5.0 mg was sampled. Hexafluoroisopropyl alcohol containing 0.0848% sodium trifluoroacetate was added at a ratio of 1 mg:1 mL relative to the calculated resin content, and the mixture was left to dissolve for 1 hour. The solution was filtered through a membrane filter with a pore size of 0.22 μm, and the filtrate was used as a sample for gel permeation chromatography. The equipment and measurement conditions used were as follows: Equipment: Tosoh HLC-8320GPC Column: Tosoh SuperHM-M Guard column: Tosoh TSK-GEL Guard Eluent: hexafluoroisopropyl alcohol (sodium trifluoroacetate 0.0848% by mass) Flow rate: 0.3mL / min Detector: RI detector Calibration curve sample: EasiVial™ PM (PMMA) manufactured by AMR (molecular weights: 2,210,000, 1,020,000, 538,500, 260,900, 146,500, 72,800, 30,780, 13,900, 7,290, 1,810, 1,090, 540) Analysis software: EcoSEC-WorkStation

[0137] [Polyamide melting point] The polymer pellets were measured for their endothermic peak top temperatures when heated from 23° C. at a rate of 10° C. / min using a differential scanning calorimeter (DSC8500 manufactured by Perkinelmer). When two or more endothermic peaks appeared, the peak top temperature of the highest temperature peak was taken as the melting point.

[0138] [Glass transition temperature of polyamide] The central part of a plate-shaped multipurpose test piece obtained by molding the polymer in accordance with ISO 294-1 was measured using a dynamic viscoelasticity measuring device (TA Instruments, ARES G2) while raising the temperature from -100°C at a rate of 2°C / min at an applied frequency of 10 Hz. The peak-top temperature at which the storage modulus significantly decreased and the loss modulus reached its maximum was measured. When two or more peaks of the loss modulus appeared, the peak-top temperature of the lowest-temperature peak was taken as the glass transition temperature.

[0139] [Moisture content of polyamide and resin composition] The moisture content (ppm) was measured using a Karl Fischer moisture meter (Coulometric titration trace moisture analyzer CA-200, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) according to a method conforming to ISO 15512.

[0140] <Evaluation of cellulose nanofibers> [Preparation of porous sheet] First, the wet cake was added to tert-butanol, and further dispersed using a mixer or the like until no aggregates were present. The concentration was adjusted to 0.5% by mass per 0.5 g of cellulose solids. 100 g of the resulting tert-butanol dispersion was filtered on filter paper, dried at 150°C, and then the filter paper was peeled off to obtain a sheet. The air resistance of this sheet was 10 g / m2. 2 The porous sheet with a permeability of 100 sec / 100 ml or less was used as the measurement sample. The basis weight W (g / m) of the sample left standing for one day in an environment of 23°C and 50% RH 2 After measuring the air permeability, the air permeability resistance R (sec / 100 ml) was measured using an Oken type air permeability resistance tester (manufactured by Asahi Seiko Co., Ltd., model EG01). At this time, the air permeability resistance R was calculated according to the following formula: 2 The value per unit area was calculated. Weight 10g / m 2 Air resistance per unit (sec / 100ml) = R / W x 10

[0141] [Degree of acyl substitution (DS)] The infrared spectrum of the porous sheet was measured by the ATR-IR method at five points using a Fourier transform infrared spectrophotometer (FT / IR-6200 manufactured by JASCO) under the following conditions. Accumulation times: 64 times, Wavenumber resolution: 4cm -1 , Measurement wavenumber range: 4000 to 600 cm -1 , ATR crystal: diamond, Incident angle: 45° From the obtained IR spectrum, the IR index was calculated using the following formula: IR index = H1730 / H1030 In the formula, H1730 and H1030 are the values ​​at 1730 cm -1 , 1030cm -1 (absorption band of CO stretching vibration of cellulose backbone chain) -1 and 1500cm -1 The line connecting the -1 and 1500cm -1 The line connecting these points is taken as the baseline, and the absorbance is calculated when this baseline is taken as 0. The average degree of substitution at each measurement point was calculated from the IR index according to the following formula, and the average value was taken as DS. DS = 4.13 × IR index

[0142] [Crystallization] The porous sheet was subjected to X-ray diffraction measurement, and the crystallinity was calculated using the following formula. Crystallinity (%)=[I (200) -I (amorphous) ] / I (200) ×100 I (200) : Diffraction peak intensity due to the 200 plane (2θ=22.5°) in cellulose type I crystals I (amorphous) : The halo peak intensity due to amorphous in cellulose type I crystals, which is the peak intensity at an angle 4.5° lower than the diffraction angle of the 200 plane (2θ=18.0°) (X-ray diffraction measurement conditions) Device: MiniFlex (manufactured by Rigaku Corporation) Operation axis 2θ / θ Source CuKα Measurement method: Continuous Voltage 40kV Current 15mA Starting angle 2θ=5° End angle 2θ=30° Sampling width 0.020° Scan speed 2.0° / min Sample: A porous sheet is attached to the sample holder.

[0143] [Average fiber diameter, L / D] The wet cake was diluted to 0.01% by mass with tert-butanol and dispersed using a high-shear homogenizer (IKA, trade name "Ultra Turrax T18") at 25,000 rpm for 5 minutes. The resulting dispersion was cast onto mica and air-dried. The measurement was performed using a high-resolution scanning electron microscope. The magnification was adjusted so that at least 100 cellulose particles were observed. The length (L), major axis (D), and their ratio of 100 randomly selected cellulose particles were measured, and the arithmetic mean of the 100 cellulose particles was calculated.

[0144] [Weight average molecular weight (Mw), number average molecular weight (Mn) and Mw / Mn ratio] 0.88 g of the porous sheet was weighed, chopped into small pieces with scissors, gently stirred, and then 20 mL of pure water was added and left for one day. The water and solids were then separated by centrifugation. 20 mL of acetone was then added, gently stirred, and left for one day. The acetone and solids were then separated by centrifugation. 20 mL of N,N-dimethylacetamide was then added, gently stirred, and left for one day. The N,N-dimethylacetamide and solids were again separated by centrifugation, after which 20 mL of N,N-dimethylacetamide was added, gently stirred, and left for one day. The N,N-dimethylacetamide and solids were then separated by centrifugation. 19.2 g of N,N-dimethylacetamide solution containing 8% lithium chloride by mass was added to the solids, stirred with a stirrer, and visually confirmed to be dissolved. The cellulose-dissolved solution was filtered through a 0.45 μm filter, and the filtrate was used as a sample for gel permeation chromatography. The equipment and measurement conditions used are as follows. Equipment: Tosoh HLC-8120 Column: TSKgel SuperAWM-H (6.0 mm I.D. x 15 cm) x 2 Detector: RI detector Eluent: N,N-dimethylacetamide (lithium chloride 0.2%) Flow rate: 0.6mL / min Calibration curve: pullulan equivalent

[0145] [Average content of alkali-soluble polysaccharides] The alkali-soluble polysaccharide content was determined by subtracting the α-cellulose content from the holocellulose content (Wise method) using the method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000). The alkali-soluble polysaccharide content was calculated three times for each sample, and the number average of the calculated alkali-soluble polysaccharide contents was taken as the average alkali-soluble polysaccharide content of cellulose.

[0146] [Average content of acid-insoluble components] The acid-insoluble components were quantified using the Clason method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000) for cellulose fibers. Bone-dried cellulose fibers were weighed out, placed in a designated container, and 72% by weight of concentrated sulfuric acid was added. The contents were pressed with a glass rod to homogenize the contents, and then autoclaved to dissolve the cellulose and hemicellulose in the acid solution. After cooling, the contents were filtered through glass fiber filter paper, and the acid-insoluble components were isolated as a residue. The acid-insoluble component content was calculated from the weight of the acid-insoluble components, and the number average of the acid-insoluble component contents calculated for the three samples was used as the average acid-insoluble component content.

[0147] ≪Materials used≫ <Polyamide> First polyamide (A1): "UBE Nylon 1013A" (manufactured by Ube Industries, Ltd.) Second polyamide (A2): "UBE Nylon 1013B" (Ube Industries, Ltd.) Recycled Polyamide (R1): It was prepared by the following procedure. Polyamide A1 pellets were mixed in a small mixer (Xplore Instruments, product name "Xplore") at 250°C and 200 rpm for 5 minutes. They were then melted at 250°C in an attached injection molding machine to prepare dumbbell-shaped test specimens conforming to JIS K7127. These specimens were then pulverized in a LabNect Mini Speed ​​Mill MS-05. The resulting powder was subjected to the same melt-mixing, injection molding, and pulverization processes four times to obtain recycled polyamide powder. The resulting resin had a number-average molecular weight (Mn) of 19,363, a weight-average molecular weight (Mw) of 32,647, and an Mw / Mn ratio of 1.69. Recycled Polyamide (R2): It was prepared by the following procedure. Polyamide A1 pellets were mixed in a small mixer (Xplore Instruments, product name "Xplore") at 250°C and 200 rpm for 5 minutes. They were then melted at 250°C in an attached injection molding machine to prepare dumbbell-shaped test specimens conforming to JIS K7127. These specimens were then pulverized in a LabNect Mini Speed ​​Mill MS-05. The resulting powder was subjected to the same melt-mixing, injection molding, and pulverization processes four times to obtain recycled polyamide powder. The resulting resin had a number-average molecular weight (Mn) of 17,431, a weight-average molecular weight (Mw) of 32,668, and an Mw / Mn ratio of 1.87.

[0148] <Cellulose nanofiber> [CNF-1] (unmodified cellulose nanofiber) It was prepared by the following procedure. After cutting the linter pulp, the pulp was subjected to a beating process to shorten and fibrillate the pulp to a high degree in pure water to a solid content of 1.5% by mass, thereby obtaining defibrated cellulose. Here, the beating process was carried out using a disc refiner, with a beating blade having high cutting function (hereinafter referred to as a cutting blade) for 4 hours, followed by another beating for 1.5 hours using a beating blade having high defibration function (hereinafter referred to as a defibration blade) to obtain an unmodified cellulose nanofiber slurry.

[0149] [CNF-2] (acetylated cellulose nanofiber) 1 kg of defibrated cellulose and 19 kg of dimethyl sulfoxide were added to a KAPPA VITA (registered trademark) homomixer (tank size 35 L) and stirred until homogenous. 2.1 kg of vinyl acetate and 0.321 kg of sodium bicarbonate were added, and acetylation was carried out at 60°C for 60 minutes while stirring to obtain an acetylated cellulose nanofiber slurry.

[0150] <Dispersant> Polyethylene glycol-polypropylene glycol copolymer Sannix GL-3000 (degree of polymerization 3000, available from Sanyo Chemical Industries, Ltd.)

[0151] <Production of resin composition> Example 1 To the resulting unmodified cellulose nanofiber slurry, 3 parts by weight of Sannix GL-3000 was added to 7 parts by weight of cellulose nanofiber solids. The mixture was then vacuum-dried at 50°C using a planetary mixer (Hibismix 2P-1, manufactured by Primix Corporation) at 50 rpm. This resulted in dried composite particles C1. 26 parts by weight of UBE Nylon 1013A and 60 parts by weight of UBE Nylon 1013B were added to 14 parts by weight of the resulting dried composite particles. The mixture was then mixed in a small kneader (Xplore Instruments, product name "Xplore") at 250°C and 200 rpm for 5 minutes. The mixture was then melted at 250°C using an attached injection molding machine. Dumbbell-shaped test specimens conforming to JIS K7127 were prepared and used for evaluation. The resulting pellets and dumbbell-shaped test specimens were used for evaluation. In addition, 13 parts by mass of UBE nylon 1013A, 13 parts by mass of recycled polyamide (R1), 30 parts by mass of UBE nylon 1013B, and 30 parts by mass of recycled polyamide (R2) were added to 14 parts by mass of dry composite particles, and the mixture was mixed in a small mixer (manufactured by Xplore instruments, product name "Xplore") at 250°C and 200 rpm for 5 minutes.The mixture was then melted at 250°C in the attached injection molding machine, and dumbbell-shaped test pieces according to JIS K7127 were prepared and evaluated according to the following criteria. ◯: Mn of the composition to which recycled polyamide was added is higher than Mn of the composition to which recycled polyamide was not added. T End ×: Mn of the composition to which recycled polyamide was added is higher than Mn of the composition to which recycled polyamide was not added. T less than

[0152] <Examples 2 to 5, Comparative Examples 1 to 4> Resin compositions were produced and evaluated in the same manner as in Example 1, except that the blending ratios of polyamide and cellulose nanofibers were as shown in Table 4. The results are shown in Table 4.

[0153] [Table 1]

[0154] [Table 2]

[0155] [Table 3]

[0156] [Table 4] [Industrial Applicability]

[0157] The resin composition provided by one aspect of the present invention has excellent physical properties such as heat resistance and dimensional stability, and can be suitably applied to the production of molded articles for a wide range of uses.

Claims

1. A method for producing a resin composition containing polyamide and cellulose nanofibers, Amino end group concentration [NH 2 ]>carboxyl end group concentration [COOH] and the first polyamide (A1) having an amino end group concentration [NH 2 ]<A mixing step of mixing a mixed component containing a second polyamide (A2) having a carboxyl terminal group concentration [COOH] of 100% or more and cellulose nanofibers (B) to obtain a resin composition, The number average molecular weight (M A1 ), the mass concentration (C A1 ), the number average molecular weight (M A2 ), the mass concentration (C A2 ), and the mass concentration (C A1 ) and the mass concentration of the second polyamide (A2) (C A2 ) and the total mass concentration (C T ) based on the following formula: M T =(M A1 ×C A1 +M A2 ×C A2 ) / C T The number average molecular weight (M T ) and the number average molecular weight (M) of the polyamide in the resin composition satisfies the following formula (1a): M / M T >1.1 (1a) Fulfilling the relationship, A method for producing a resin composition, wherein the total concentration ([NH 2 ] + [COOH]) of the amino terminal group concentration [NH 2 ] and the carboxyl terminal group concentration [COOH] of each of the first polyamide (A1) and the second polyamide (A2) is 10 μequivalents / g or more and 500 μequivalents / g or less.

2. The amino terminal group concentration [NH 2 ] A1 and carboxyl end group concentration [COOH] A1 , the mass concentration (C A1 ), the amino terminal group concentration [NH 2 ] A2 and carboxyl end group concentration [COOH] A2 , the mass concentration (C A2 ), and the mass concentration (C A1 ) and the mass concentration of the second polyamide (A2) (C A2 ) and the total mass concentration (C T ) based on the following formulas (1b) and (1c): [NH 2 ] T =([NH 2 ] A1 ×C A1 +[NH 2 ] A2 ×C A2 ) / C T (1b) [COOH] T =([COOH] A1 ×C A1 +[COOH] A2 ×C A2 ) / C T (1c) [NH 2 ] T and [COOH] T calculated according to the above formula, 2 ] T The [COOH] T Ratio to ([NH 2 ] T / [COOH] T 2. The method of claim 1 , wherein n is 1 or more and 5 or less.

3. The method according to claim 1 or 2, wherein the moisture content of the resin composition is higher than the moisture content of the mixture of the first polyamide (A1) and the second polyamide (A2) to be mixed.

4. The method according to any one of claims 1 to 3, wherein the moisture content of the resin composition is 100 ppm by mass or more and 5000 ppm by mass or less, and the moisture content of the first polyamide (A1) and the second polyamide (A2) to be mixed is 1 ppm by mass or more and 1000 ppm by mass or less.

5. The method according to any one of claims 1 to 4, wherein a part of the resin composition is used as part of the mixed components.

6. The method according to any one of claims 1 to 5, wherein the number average fiber diameter of the cellulose nanofibers (B) is 2 nm or more and 1000 nm or less.

7. The method according to any one of claims 1 to 6, wherein the cellulose nanofiber (B) has an acyl substitution degree (DS) of 0 or more and 1.5 or less.

8. The method according to any one of claims 1 to 7, wherein the crystallinity of the cellulose nanofiber (B) is 60% or more.

9. The method according to any one of claims 1 to 8, wherein the average acid-insoluble component content of the cellulose nanofibers (B) is 10 mass% or less.

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