JP2018070835A - Polyester resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin composition that contains a polyester resin and cellulose nanofibers, but allows the cellulose nanofibers to exhibit excellent dispersibility, wherein, a molding of the composition ensures high transparency and heat resistance and also has high mechanical strength.SOLUTION: A polyester resin composition contains a water-soluble polyester resin, and cellulose nanofibers.SELECTED DRAWING: None

Description

  The present invention relates to a polyester resin composition.

  Polyester resin, which is a polymer of polyvalent carboxylic acid and polyol, has excellent transparency, mechanical strength, weather resistance, and flexibility. Functions are added and performance is improved.

  In recent years, cellulose fiber, which is a naturally occurring component, has attracted attention as a green reinforcing fiber material for reducing environmental impact.

  For example, Patent Document 1 discloses that a resin composition is compounded by blending a polyester-based synthetic resin emulsion and cellulose fibers having an average fiber diameter of 200 nm or less, and the compounded resin composition. It is disclosed that a dry film having high strength can be formed.

JP 2009-197122 A

  However, even when trying to combine such a resin emulsion and cellulose nanofiber, it is difficult to mix them uniformly, and the resin composition tends to be in a non-uniform state, so the transparency of the molded product is low. It is easily damaged. In addition, the molded article has a problem that it cannot secure a mechanical strength as high as expected.

  The object of the present invention is excellent in dispersibility of cellulose nanofibers despite the fact that it contains a polyester resin and cellulose nanofibers, and the molded product can ensure high transparency and heat resistance, as well as high mechanical strength. It is providing the polyester resin composition which can have.

  The polyester resin composition according to the present invention contains a water-soluble polyester resin and cellulose nanofibers.

  In the polyester resin composition according to the present invention, the water-soluble polyester resin preferably has a glass transition temperature in the range of −60 to 110 ° C.

  In the polyester resin composition according to the present invention, the water-soluble polyester resin has a residue of a polyvalent carboxylic acid, and the residue of the polyvalent carboxylic acid has a residue of a metal sulfonate group-containing polyvalent carboxylic acid. Is preferred.

  In the polyester resin composition according to the present invention, the amount of the metal sulfonate group-containing polyvalent carboxylic acid residue relative to the entire polycarboxylic acid residue is preferably in the range of 1 to 30 mol%.

  In the polyester resin composition according to the present invention, the cellulose nanofiber preferably has a carboxyl group at a ratio in the range of 0.5 to 2.0 mmol / g.

  In the polyester resin composition according to the present invention, the amount of cellulose nanofibers relative to the water-soluble polyester resin is preferably in the range of 0.1 to 50% by mass.

  According to the present invention, despite containing a polyester resin and cellulose nanofibers, the cellulose nanofibers are excellent in dispersibility, the molded product can ensure high transparency and heat resistance, and have high mechanical strength. The polyester resin composition which can have is obtained.

  Hereinafter, an embodiment of the present invention will be described.

  The polyester resin composition according to this embodiment contains a water-soluble polyester resin (A) and cellulose nanofibers (B). For this reason, it is excellent in the dispersibility of the cellulose nanofiber (B) in a polyester resin composition, Therefore The molded article produced from a polyester resin composition has the outstanding transparency and heat resistance, and high mechanical strength. Can do.

  First, the water-soluble polyester resin (A) will be specifically described.

[Water-soluble polyester resin (A)]
The water-soluble polyester resin (A) has a polycarboxylic acid residue and a polyol residue. The water-soluble polyester resin (A) is a polymerization product of a monomer component including, for example, a polyvalent carboxylic acid component (a) and a polyol component (b).

  In addition, it is judged based on technical common sense that water-soluble polyester resin (A) has water solubility. The water-soluble polyester resin (A) preferably satisfies at least one of the following (1) to (5). (1) When water at room temperature is sprayed at a spray pressure of 0.005 MPa for 20 minutes on the entire surface of a thin film having a thickness of 20 μm formed only from the water-soluble polyester resin (A), this thin film is completely dissolved in water. (2) When water at 50 ° C. is sprayed for 10 minutes at a spraying pressure of 0.005 MPa over the entire surface of a thin film having a thickness of 20 μm formed from the water-soluble polyester resin (A), the entire thin film is dissolved in water. (3) The water-soluble polyester resin (A) and water at room temperature are mixed at a mass ratio of 1: 5, and when the obtained liquid is irradiated with ultrasonic waves for 20 minutes, the water-soluble polyester resin (A) is completely dissolved in water. To do. (4) When the water-soluble polyester resin (A) and water at 50 ° C. are mixed at a mass ratio of 1: 5, and the obtained liquid is irradiated with ultrasonic waves for 10 minutes, the water-soluble polyester resin (A) is completely dissolved in water. Dissolve. (5) When the water-soluble polyester resin (A) and the aqueous solvent are mixed at a mass ratio of 1: 5 and the obtained liquid is stirred at 90 ° C. for 1 hour, the water-soluble polyester resin (A) is completely dissolved in the solvent. . The aqueous solvent is water or a mixed solvent of water and a hydrophilic solvent. The hydrophilic solvent may be a known solvent that is mixed with water.

  In order for the water-soluble polyester resin (A) to have water solubility, the water-soluble polyester resin (A) preferably has a water-solubilizing group. The water solubility-imparting group is a group having an ionic polar group. The polar group may be neutralized. The water-solubilizing group is contained in at least one of, for example, a polycarboxylic acid residue and a polyol residue.

  The component which comprises water-soluble polyester resin (A) is demonstrated concretely.

(Residue of polyvalent carboxylic acid)
The residue of the polyvalent carboxylic acid is derived from the polyvalent carboxylic acid component (a). The polyvalent carboxylic acid component (a) contains at least one of a polyvalent carboxylic acid and an ester-forming derivative of the polyvalent carboxylic acid. The ester-forming derivative of a polyvalent carboxylic acid is a compound derived from a polyvalent carboxylic acid and has an ester-forming derivative group derived from a carboxyl group. An ester-forming derivative derived from a carboxyl group is a group that can react with a hydroxyl group to form an ester. For example, a group obtained by dehydrating a carboxyl group, a group obtained by esterifying a carboxyl group, and a group obtained by halogenating a carboxyl group At least one group selected from the group consisting of:

  The polyvalent carboxylic acid component (a) preferably has no reactive functional group other than the carboxyl group. In particular, the polyvalent carboxylic acid preferably has no ethylenically unsaturated bond, amino group, imino group, hydrazino group, nitro group, carbonyl group, epoxy group, or cyano group. In addition, the ionic polar group which a water solubility provision group has is remove | excluded from the reactive functional group here.

  The polyvalent carboxylic acid includes, for example, at least one of an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid. Aromatic dicarboxylic acids include, for example, terephthalic acid, isophthalic acid, phthalic acid, diphenic acid, naphthalic acid, 1,2-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid and 2,6- It contains at least one component selected from the group consisting of naphthalenedicarboxylic acid. The aliphatic dicarboxylic acid may be any of linear, branched and alicyclic. Aliphatic dicarboxylic acids include, for example, oxalic acid, malonic acid, succinic acid, maleic acid, itaconic acid, glutaric acid, adipic acid, pimelic acid, 2,2-dimethylglutaric acid, suberic acid, azelaic acid, sebacic acid, dodecane. It contains at least one component selected from the group consisting of diacid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, diglycolic acid, and thiodipropionic acid.

  The polyvalent carboxylic acid preferably contains a metal sulfonate group-containing polyvalent carboxylic acid. That is, it is preferable that the residue of polyvalent carboxylic acid includes the residue of metal sulfonate group-containing polyvalent carboxylic acid. The residue of the metal sulfonate group-containing polyvalent carboxylic acid is a water-solubilizing group and has a metal sulfonate group as a polar group. In this case, excellent water solubility can be imparted to the water-soluble polyester resin (A).

  The metal sulfonate group-containing polyvalent carboxylic acid includes an alkali metal salt of 5-sulfoisophthalic acid, an alkali metal salt of 2-sulfoisophthalic acid, an alkali metal salt of 4-sulfoisophthalic acid, an alkali metal salt of sulfoterephthalic acid, and 4 -It is preferable to contain at least one compound selected from the group consisting of alkali metal salts of sulfonaphthalene-2,6-dicarboxylic acid. In this case, particularly excellent water solubility can be imparted to the water-soluble polyester resin (A), and a product made from the polyester resin composition containing the water-soluble polyester resin (A) achieves higher transparency. it can. The metal in the metal sulfonate group-containing polyvalent carboxylic acid is more preferably sodium, potassium, or lithium.

  The amount of the residue of the metal sulfonate group-containing polyvalent carboxylic acid relative to the entire residue of the polyvalent carboxylic acid is preferably in the range of 1 to 30 mol%. When the amount of the residue of the metal sulfonate group-containing polyvalent carboxylic acid is within this range, high heat resistance and higher mechanical strength can be imparted to a product made from the polyester resin composition. The amount of the metal sulfonate group-containing polyvalent carboxylic acid residue relative to the polyvalent carboxylic acid residue is more preferably in the range of 5 to 20 mol%.

  The polyvalent carboxylic acid may contain a trivalent or higher polyvalent carboxylic acid. That is, the polycarboxylic acid residue may have a trivalent or higher polyvalent carboxylic acid residue. The residue of a trivalent or higher polyvalent carboxylic acid is a water-solubilizing group and has an unreacted carboxyl group as a polar group. In this case, the water-soluble polyester resin (A) can have high water solubility. Trivalent or higher polyvalent carboxylic acids include, for example, hemimellitic acid, trimellitic acid, trimedic acid, merophanic acid, pyromellitic acid, benzenepentacarboxylic acid, meritic acid, cyclopropane-1,2,3-tricarboxylic acid, cyclohexane It contains at least one compound selected from the group consisting of pentane-1,2,3,4-tetracarboxylic acid and ethanetetracarboxylic acid.

(Polyol residue)
The polyol residue is derived from the polyol component (b). The polyol component (b) contains at least one of a polyol and an ester-forming derivative of the polyol. An ester-forming derivative of a polyol is a compound derived from a polyol and has an ester-forming derivative group derived from a hydroxyl group. The ester-forming derivative group derived from a hydroxyl group is a group that can react with a carboxyl group to form an ester, and includes, for example, a group obtained by acetate-forming a hydroxyl group.

  The polyol component (b) preferably does not have a reactive functional group other than the hydroxyl group. In particular, it is preferable that the above polyvalent carboxylic acid and polyol do not have a reactive functional group. In these cases, the amount of the reactive functional group of the water-soluble polyester resin (A) is reduced, or the water-soluble polyester resin (A) is no longer reactive. If it does so, the reactivity of water-soluble polyester resin (A) will reduce, Therefore, even if water-soluble polyester resin (A) is heated, the water-solubility of water-soluble polyester resin (A) becomes difficult to fall. In addition, the ionic polar group which a water solubility provision group has is not contained in a reactive functional group. In particular, the polyol preferably has no ethylenically unsaturated bond, amino group, imino group, hydrazino group, nitro group, carbonyl group, epoxy group, or cyano group.

  Examples of the polyol include ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. 2,2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 2,2,4- Trimethyl-1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol 4,4'-dihydroxybiphenol, 4,4'-methylenedipheno Le, including 1,5-dihydroxynaphthalene, 2,5-dihydroxynaphthalene, 2,2-bis (4-hydroxyphenyl) propane (bisphenol A), and at least one component selected from the group consisting of bisphenol S. The polyethylene glycol contains at least one component selected from the group consisting of, for example, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene glycol, heptaethylene glycol, and octaethylene glycol. Polypropylene glycol includes at least one component selected from the group consisting of dipropylene glycol, tripropylene glycol, and tetrapropylene glycol, for example.

  The polyol component (b) is in particular ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, propylene glycol, 2,2-dimethyl-1,3-propanediol, and 1,4-cyclohexanedi. It is preferable to include at least one component selected from the group consisting of methanol.

  The ratio of the polyvalent carboxylic acid component (a) to the polyol component (b) includes the total number of carboxyl groups and ester-forming derivative groups contained in the polyvalent carboxylic acid component (a) and the polyol component (b). It is preferable that the hydroxyl group and the total number of ester-forming derivative groups thereof are adjusted so that the molar ratio is in the range of 1: 1 to 1: 2.5. In this case, the ratio of trivalent or higher polyvalent carboxylic acids, which are water-solubilizing components, is calculated as a dicarboxylic acid.

  In synthesizing the water-soluble polyester resin (A), the monomer component may contain a reactive phosphorus-containing compound (c). That is, the water-soluble polyester resin (A) may have a residue of the reactive phosphorus-containing compound (c). In this case, the water-soluble polyester resin (A) can have excellent flame retardancy.

  The reactive phosphorus-containing compound (c) can be condensed or polycondensed by reacting with at least one of the polyvalent carboxylic acid component (a) and the polyol component (b). Specifically, the reactive phosphorus-containing compound (c) preferably has an ester-forming functional group in the molecule. The ester-forming functional group is at least one group selected from the group consisting of a carboxyl group, an ester-forming derivative group of a carboxyl group, a hydroxyl group, and an ester-forming derivative group of a hydroxyl group. The reactive phosphorus compound (c) contains, for example, a compound represented by the following formula (e).

  The glass transition temperature (Tg) of the water-soluble polyester resin (A) is preferably in the range of −60 to 110 ° C. In this case, a molded product formed from the polyester resin composition can have high flexibility. The glass transition temperature of the water-soluble polyester resin (A) is more preferably in the range of −40 to 80 ° C., and further preferably in the range of −20 to 40 ° C.

  The number average molecular weight of the water-soluble polyester resin (A) is preferably in the range of 3000 to 50000. Within this range, the water-soluble polyester resin (A) has high mechanical strength, has sufficiently high water solubility, and can maintain excellent solution stability. The solution stability means that the change of the solution with time is small, and the water-soluble polyester resin (A) does not precipitate and can be stably stored for a long time. The number average molecular weight of the water-soluble polyester resin (A) is more preferably in the range of 5000 to 30000. In addition, the number average molecular weight of water-soluble polyester resin (A) is derived | led-out from the measurement result by gel permeation chromatography (polystyrene conversion).

  The degree of water solubility of the water-soluble polyester resin (A) is a balance between the number-average molecular weight of the water-soluble polyester resin (A) and the proportion of the water-soluble component used to produce the water-soluble polyester resin (A). It is adjusted by setting it well. That is, it is preferable that the number average molecular weight of the water-soluble polyester resin (A) and the ratio of the water-solubilizing component used for producing the water-soluble polyester resin (A) are appropriately set.

[Method for producing water-soluble polyester resin]
The water-soluble polyester resin (A) is produced by polymerizing a monomer component containing a polyvalent carboxylic acid component (a) and a polyol component (b) by a known polyester production method.

  For example, when the polyvalent carboxylic acid component (a) is a polyvalent carboxylic acid and the polyol component (b) is a polyol, a direct ester for reacting the polyvalent carboxylic acid and the polyol in a single step reaction. The reaction is adopted.

  For example, when the polyvalent carboxylic acid component (a) is an ester-forming derivative of a polyvalent carboxylic acid and the polyol component (b) is a polyol, an ester-forming derivative of a polyvalent carboxylic acid and a polyol The water-soluble polyester resin (A) may be produced through a first-stage reaction that is a transesterification reaction of the above and a second-stage reaction in which the reaction product of the first-stage reaction is polycondensed.

  The method for producing the water-soluble polyester resin (A) through the first stage reaction and the second stage reaction will be described more specifically. In the transesterification reaction which is the first stage reaction, all raw materials used for the production of the water-soluble polyester resin (A) may be contained in the reaction system from the beginning. For example, transesterification is carried out by gradually heating to 150 to 260 ° C. under normal pressure conditions in an inert gas atmosphere such as nitrogen gas while the dicarboxylic acid diester and polyol are held in a reaction vessel. The reaction proceeds.

  The polycondensation reaction that is the second stage reaction proceeds within a temperature range of 160 to 280 ° C. under a reduced pressure of 6.7 hPa (5 mmHg) or less, for example.

  In the first-stage reaction and second-stage reaction, even when a conventionally known titanium, antimony, lead, zinc, magnesium, calcium, manganese, alkali metal compound, or the like is added as a catalyst in the reaction system at an arbitrary time. Good.

  Further, when a trivalent or higher polyvalent carboxylic acid is used as the water-solubilizing component, the water-soluble polyester resin obtained as described above can be neutralized with a basic compound such as an alkali metal compound. preferable.

[Cellulose nanofiber (B)]
Next, the cellulose nanofiber (B) will be specifically described.

  In the following, nanofiber means a fibrous substance having a diameter in the range of 1 nm to 1000 nm (1 μm). In particular, the number average fiber diameter of the cellulose nanofiber (B) according to this embodiment is preferably in the range of 2 to 150 nm, and more preferably in the range of 2 to 100 nm. The maximum fiber diameter of the cellulose nanofiber (B) is preferably 1000 nm or less, and more preferably 500 nm or less. The number average fiber diameter and the maximum fiber diameter of the cellulose nanofiber (B) can be measured, for example, as follows. A cellulose nanofiber (B) dispersion having a solid content of 0.05 to 0.10% by mass is prepared, and the dispersion is cast on a carbon film-coated grid that has been subjected to a hydrophilization treatment. A sample for observation with a microscope (TEM) is used. In addition, when a fiber with a large fiber diameter is included, a scanning electron microscope (SEM) image of the glass-cast surface may be observed. Then, observation with an electron microscope image is performed at a magnification of 5000 times, 10000 times, or 50000 times depending on the size of the constituent fibers. At that time, assuming an axis of an arbitrary image width in the obtained image, the sample and observation conditions (magnification, etc.) are adjusted so that 20 or more fibers intersect the axis. Then, after obtaining an observation image that satisfies this condition, two random axes, vertical and horizontal, per image are drawn on this image, and the fiber diameter of the fibers crossing the axis is visually read. In this way, images of at least three non-overlapping surface portions are taken with an electron microscope, and the value of the fiber diameter of the fibers intersecting with each of the two axes is read (thus, at least 20 × 2 × 3 = 120). Information on the fiber diameter of the fiber). From the result of the fiber diameter thus obtained, the number average fiber diameter and the maximum fiber diameter can be calculated.

  The cellulose nanofiber (B) can be obtained by mechanically defibrating natural cellulose. It can also be obtained by subjecting natural cellulose to chemical treatment and chemical defibration. Natural cellulose includes cellulose isolated from cellulose biosynthetic systems such as plants, animals, and bacteria-producing gels. Examples of natural cellulose include softwood pulp, hardwood pulp, cotton pulp, bacterial cellulose, cellulose isolated from sea squirts, cellulose isolated from seaweed, and the like.

  In order to produce cellulose nanofiber (B) from natural cellulose by mechanical defibration, a known method can be adopted. Specifically, for example, cellulose nanofiber (B) can be obtained by subjecting natural cellulose to a homomixer treatment, a high-pressure homogenizer treatment, an ultra-high pressure homogenizer treatment, or the like under high-speed rotation.

  The cellulose nanofiber (B) according to this embodiment is preferably a cellulose nanofiber that has been defibrated by chemical treatment.

  In order to produce the cellulose nanofiber (B) from natural cellulose by chemical defibration, a known method can be adopted. The chemical defibration method includes, for example, an oxidation reaction step (I) and a dispersion step (III). The chemical defibrating method may further include a purification step (II). In the oxidation reaction step (I), the hydroxyl group at the C6 position of each glucose unit in the natural cellulose molecule is oxidized and modified by allowing the N-oxyl compound and a co-oxidant to act on the raw natural cellulose added to water. Then, a reactant cellulose (also referred to as oxidized cellulose) having a carboxyl group or the like is obtained. In the purification step (II), impurities and the like generated in the oxidation reaction step (I) are removed from the oxidized cellulose to obtain oxidized cellulose impregnated with water. In the dispersion step (III), the oxidized cellulose impregnated with water is further dispersed in an aqueous solvent or the like. Thereby, the dispersion of the cellulose nanofiber (B) in which the cellulose nanofiber (B) is dispersed in the aqueous solvent can be obtained. Hereinafter, each step will be described.

(I) Oxidation reaction step First, a dispersion is prepared by dispersing natural cellulose in a solvent and sufficiently swelling the natural cellulose with the solvent. The solvent is preferably water. The natural cellulose concentration in the dispersion is arbitrary as long as the natural cellulose can be sufficiently diffused. In addition, after natural cellulose is sufficiently swollen with a solvent in the dispersion, for example, hydrochloric acid or the like is used to remove metal ions contained in the dispersion and metal ions adhering to and inside the fibers of the natural cellulose. It is also preferable to carry out acid cleaning by the above.

  Next, an N-oxyl compound is added to the dispersion as an oxidation catalyst. Examples of the N-oxyl compound include compounds having a nitroxy radical that is generally used as an oxidation catalyst. The N-oxyl compound is preferably a water-soluble compound, and piperidine nitroxyoxy radical is particularly preferable. N-oxyl compounds include 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO) or 4-acetamido-2,2,6,6-tetramethylpiperidinooxy radical (4-acetamido- TEMPO) is preferred. A catalytic amount is sufficient for the addition amount of the N-oxyl compound, but it is preferably in the range of 0.1 to 4 mmol / l, more preferably 0.2 to 2 mmol / l.

  Subsequently, the reaction can be initiated by adding a co-oxidant to the dispersion. The co-oxidant contains, for example, at least one component selected from the group consisting of hypohalous acid, salts thereof, halous acid, salts thereof, perhalogen acids, salts thereof, hydrogen peroxide, and perorganic acids. . The co-oxidant preferably contains an alkali metal hypohalite. Examples of alkali metal hypohalites include sodium hypochlorite and sodium hypobromite. The co-oxidant is not a substance that directly oxidizes the hydroxyl group of cellulose, but a substance that oxidizes an N-oxyl compound used as an oxidation catalyst.

  Further, when sodium hypochlorite is used as the co-oxidant, it is preferably used in the presence of an alkali metal bromide such as sodium bromide. In this case, since the reaction rate in the oxidation reaction of natural cellulose is improved, the reaction efficiency can be improved. The addition amount of the alkali metal bromide is preferably about 1 to 40 times mole amount, more preferably about 10 to 20 times mole amount relative to the N-oxyl compound.

  It is preferable to maintain the pH of the dispersion within the range of about 8 to 11 after the addition of the co-oxidant, that is, after the start of the reaction. In addition, after the reaction starts, the pH of the dispersion decreases as the oxidation reaction proceeds. Therefore, it is preferable to maintain the pH of the dispersion at about 10 to 11 by dropping an alkali metal aqueous solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution to neutralize the dispersion. The temperature of the dispersion is arbitrary at about 4 to 40 ° C., but is not particularly limited to these ranges.

  The end point of the oxidation reaction is taken when the pH of the dispersion no longer changes. As a result, the hydroxyl group at the C6 position of each glucose unit in the natural cellulose molecule is selectively oxidized and modified to produce a reactant cellulose having a carboxyl group and the like. That is, a liquid mixture containing oxidized cellulose is thereby obtained. In addition, the obtained oxidized cellulose has the structure of the alkali metal salt in which the carboxyl group on the cellulose was converted to the alkali metal in the corresponding aqueous alkali metal solution by the neutralization treatment with the aqueous alkali metal solution already described. That is, the oxidized cellulose obtained by the above neutralization treatment is an alkali metal neutralized oxidized cellulose. For example, when the carboxyl group is neutralized with an aqueous sodium hydroxide solution, the oxidized cellulose is a sodium-neutralized oxidized cellulose.

  In addition, the quantity of a carboxyl group required in order to obtain the cellulose nanofiber (B) which concerns on this embodiment changes with kinds of natural cellulose. Moreover, the greater the amount of carboxyl groups, the smaller the maximum fiber diameter and number average fiber diameter of cellulose nanofibers. For this reason, depending on the type of natural cellulose, the degree of oxidation is controlled by the addition amount of the co-oxidant and the reaction time, and the cellulose nanofiber (B ) Can be obtained. In general, the addition amount of the co-oxidant is preferably in the range of about 5 to 10 mmol with respect to 1 g of natural cellulose, and the reaction is completed in the range of about 5 to 120 minutes and at most within 240 minutes. preferable.

(I ′) Additional reduction step (I) In the oxidation reaction step, in addition to oxidation of some hydroxyl groups at the C6 position of glucose units in natural cellulose molecules to carboxyl groups, some hydroxyl groups in cellulose molecules Since groups may be oxidatively modified to aldehyde groups and ketone groups, a small amount of aldehyde groups and ketone groups are formed on the oxidized cellulose. Therefore, the method of this embodiment is an additional process for reducing aldehyde groups and ketone groups by further treating oxidized cellulose with a reducing agent after (I) oxidation reaction step and before (II) purification step described later. It is preferable to include a reduction step. Thereby, an aldehyde group and a ketone group can be reduced and converted into a hydroxyl group.

  Specifically, for example, a mixed solution is prepared by dispersing oxidized cellulose in water, and after adjusting the pH of the mixed solution to about 10, a reducing agent is added to the mixed solution at room temperature for 10 minutes to 10 hours. React to a certain extent. Thereby, an aldehyde group and a ketone group can be reduced and converted into a hydroxyl group.

Examples of reducing agents include hydride reducing agents such as lithium borohydride (LiBH ₄ ), sodium borohydride (NaBH ₄ ), sodium cyanoborohydride (NaBH ₃ CN), and the like.

  The amount of the reducing agent relative to the oxidized cellulose is preferably in the range of 0.1 to 4% by mass, and more preferably in the range of 1 to 3% by mass. Thereby, the liquid mixture containing the oxidized cellulose additionally reduced is obtained. The mixed liquid may be washed with, for example, distilled water to remove impurities, and the solid content obtained may be further dispersed in distilled water to obtain a mixed liquid containing oxidized cellulose.

  Distilled water is added to the obtained oxidized cellulose after further reduction to obtain a mixed solution containing oxidized cellulose, and 1N hydrochloric acid is further added to adjust the pH of the solution to about 2, and then, for example, 10 to 30 ° C. Then, it can be converted to COOH (carboxylic acid) type oxidized cellulose by stirring for 1 to 3 hours. In addition, a known neutralizing base (neutralizing agent) is added to the mixed solution containing oxidized cellulose converted to COOH type, and neutralized, so that COOH type oxidized cellulose is converted to, for example, an alkali metal neutralized type. It may be converted into oxidized cellulose or amine neutralized oxidized cellulose. As the neutralizing base (neutralizing agent), for example, lithium hydroxide, triethylamine, aqueous ammonia and the like can be used. Thereby, the liquid mixture containing the oxidized cellulose in which the counter cation is converted from the alkali metal neutralized oxidized cellulose to other alkali metal or amine is obtained. The counter cation is at least one selected from the group consisting of, for example, a lithium cation, a triethylammonium cation, and an ammonium cation.

(II) Purification Step (I) After the oxidation reaction step or (I ′) additional reduction step, a mixed solution containing oxidized cellulose or a cake-like product containing oxidized cellulose may be purified. In the purification step, unreacted raw materials, by-products and the like can be removed from the oxidized cellulose to purify the oxidized cellulose. At this time, for example, washing with water and filtration are repeated for a mixed solution containing oxidized cellulose. Thereby, an aqueous dispersion in which oxidized cellulose of high purity (99% by mass or more) is dispersed in water is obtained. In the purification, an appropriate apparatus such as a continuous decanter may be used. The aqueous dispersion containing oxidized cellulose thus obtained preferably has a solid content concentration of oxidized cellulose in the range of about 10 to 50% by mass. If it is in this range, it can suppress that the energy required for dispersion | distribution becomes excessive in the below-mentioned dispersion | distribution process (III).

(III) Dispersion Step A mixed liquid containing oxidized cellulose obtained in each of the steps as described above, a cake-like product containing oxidized cellulose, or an aqueous dispersion containing oxidized cellulose is further added to an aqueous dispersion medium. A dispersion of cellulose nanofibers (B) can be obtained by performing a dispersion treatment for dispersion.

  Dispersers used in the dispersion process include powerful mixers such as homomixers, high-pressure homogenizers, ultra-high-pressure homogenizers, ultrasonic dispersion processing, beaters, disk-type refiners, conical-type refiners, double-disk-type refiners, and grinders. One device is mentioned. As the disperser, for example, a screw mixer, a paddle mixer, a disper mixer, a turbine mixer, or the like may be used.

  In addition, the dried body of a cellulose nanofiber (B) can also be obtained by drying the dispersion of a cellulose nanofiber (B). As a drying method of the dispersion of the cellulose nanofiber (B), a known method can be adopted. For example, when the dispersion medium is water, spray drying, freeze-drying method, and the like can be mentioned. In the case of a mixed solvent with a solvent, a drying method using a drum dryer and a spray drying method using a spray dryer may be mentioned.

It is preferable that a cellulose nanofiber (B) contains a carboxyl group in the ratio in the range of 0.5-2.0 mmol / g. In this case, cellulose nanofibers can be finely dispersed in an aqueous solvent, and a highly transparent dry film can be easily obtained when compounded with a polyester resin. It is more preferable that the cellulose nanofiber (B) contains a carboxyl group at a ratio in the range of 1.0 to 2.0 mmol / g. In addition, the quantity of the carboxyl group of a cellulose nanofiber (B) is computable as follows. For example, 60 mL of a slurry sample solution containing 0.5 to 1% by weight of cellulose nanofibers precisely weighed in terms of dry weight is prepared, and 0.1 M hydrochloric acid aqueous solution is added to adjust the pH of the sample solution to about 2.5. And Subsequently, electric conductivity is measured while dropping 0.05 M aqueous sodium hydroxide solution into the sample solution. The measurement is performed until the pH of the sample solution reaches about 11, and the value of the amount of sodium hydroxide (V) consumed in the neutralization step of the weak acid whose electric conductivity changes slowly is obtained. From the value of this amount of sodium hydroxide (V), the amount of carboxyl groups can be calculated based on the following formula (1).
Amount of carboxyl groups (mmol / g) = V (ml) × [0.05 / weight of cellulose] (1)

[Polyester resin composition]
The polyester resin composition contains the above-described water-soluble polyester resin (A) and cellulose nanofiber (B). Since the water-soluble polyester resin (A) has water solubility, excellent dispersibility of the cellulose nanofiber (B) can be ensured. For this reason, although it contains a polyester resin and cellulose nanofibers, a molded product formed from this polyester resin composition can ensure high transparency and heat resistance and have high mechanical strength. Can do.

  It is preferable that the quantity of the cellulose nanofiber (B) with respect to water-soluble polyester resin (A) exists in the range of 0.1-50 mass%. In this case, the molded product formed from the polyester resin composition can ensure high transparency and heat resistance, and can have higher mechanical strength. The amount of the cellulose nanofiber (B) relative to the water-soluble polyester resin (A) is more preferably in the range of 1 to 10% by mass.

  The polyester resin composition may contain various additives as necessary as long as the effects of the present invention are not impaired. Examples of the additive include an antifoaming agent, a leveling agent, a flame retardant, a crosslinking agent, an antistatic agent, an antifungal agent, and an antibacterial agent.

  The polyester resin composition can be produced, for example, as follows.

  First, an aqueous solution of the water-soluble polyester resin (A) is prepared by adding an aqueous solvent to the water-soluble polyester resin (A) described above. The aqueous solvent is water or a mixed solvent of water and a hydrophilic solvent. The hydrophilic solvent may be a known solvent that is mixed with water. Examples of hydrophilic solvents include alcohols such as methanol, ethanol, 2-propanol, propylene glycol; glycol ethers such as propylene glycol monomethyl ether, ethyl cellosolve, butyl cellosolve; and cyclohexanone.

  Moreover, the aqueous dispersion of the above-mentioned cellulose nanofiber (B) is prepared. The dispersion of cellulose nanofibers (B) may be a dispersion of cellulose nanofibers (B) obtained in the (III) dispersion step in the method for producing cellulose nanofibers (B) described above. In addition, (III) a dried body of cellulose nanofiber (B) obtained by drying after the dispersion step is placed in a container, and an aqueous solvent is added thereto, followed by dispersion treatment using, for example, a homomixer or a homogenizer. May be dispersed in an aqueous solvent to prepare a dispersion of cellulose nanofibers (B).

  A polyester resin composition is prepared by mixing an aqueous solution of the water-soluble polyester resin (A), a dispersion of the cellulose nanofibers (B), and additives as necessary to prepare a mixture, and kneading the mixture. A thing is obtained. A known method can be employed for kneading the mixed solution, and for example, kneading can be performed using an apparatus such as a mixer, a homomixer, a homogenizer, an ultrasonic homogenizer, a three-roll mill, or a kneader.

  By applying the polyester resin composition onto, for example, a base material and molding it into a sheet, a molded product having excellent mechanical properties and high transparency can be obtained. For this reason, a polyester resin composition can be used suitably for an optical film for displays, for example. The polyester resin composition can also be suitably used as a binder for spun yarn, a backing material for fibers such as carpets and carpets, and a sizing agent for fiber-reinforced plastics (FRP).

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

(1) Synthesis of polyester resin (PES-1 to PES-12) (1-1) Synthesis of water-soluble polyester resin (PES-1 to PES-11) Stirrer, nitrogen gas inlet, thermometer, rectifying tower, The titanium tetrabutoxide as a catalyst and the components shown in the columns “Polyvalent carboxylic acid component” and “Polyol component” in Table 1 are placed in a 1000 ml reaction vessel equipped with a cooler. Prepared. The molar ratio of polycarboxylic acid component: polyol component is 1: 2. The mixture was heated to 200 ° C. with stirring and mixing in a nitrogen atmosphere under normal pressure, and then gradually heated to 250 ° C. over 4 hours to proceed the transesterification reaction.

  Next, while stirring this mixed solution in a reaction vessel, the pressure is gradually reduced from normal pressure to 0.67 hPa (0.5 mmHg) at a temperature of 250 ° C., and then stirred for 2 hours in this state. The polycondensation reaction was allowed to proceed. Thereby, a water-soluble polyester resin was obtained.

  By mixing 100 parts by mass of the obtained water-soluble polyester resin, 40 parts by mass of butyl cellosolve, and 260 parts by mass of water and stirring them at a temperature of 80 to 90 ° C. for 2 hours while stirring them, the concentration is 25 masses. % Aqueous solution of water-soluble polyester resin was obtained.

(1-2) Synthesis of water-insoluble polyester resin (PES-12) In a 1000 ml reaction vessel equipped with a stirrer, a nitrogen gas inlet, a thermometer, a rectifying tower, and a cooler, a titanium tetra catalyst as a catalyst A mixed solution was prepared by adding butoxide and the components shown in the columns of “polyvalent carboxylic acid component” and “polyol component” in Table 1, followed by transesterification under the same conditions as in (1-1). By causing the polymerization reaction to proceed, a water-insoluble polyester resin was obtained.

  By mixing 100 parts by mass of the obtained water-insoluble polyester resin and 300 parts by mass of toluene and stirring them for 2 hours at a temperature of 80 to 90 ° C. while stirring them, water-insoluble with a concentration of 25% by mass is obtained. A solution of a polyester resin was obtained.

In addition, the components described in Table 1 are as follows.
-PEG1000: Polyethylene glycol Sanyo Chemical Industries, Ltd. (number average molecular weight of about 1000).

(2) Preparation of Cellulose Nanofiber Dispersion (2-1) Preparation of Aqueous Dispersion of Cellulose Nanofibers (TOC-1 to TOC-8) After sufficiently swelling softwood bleached kraft pulp with water, acid Metal ions were removed by washing.

  1 g (solid content) of softwood bleached kraft pulp after washing, 0.1 g of sodium bromide, 0.0156 g of 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO), and 100 g of ion-exchanged water in a beaker After putting, TEMPO was dissolved by stirring at room temperature for 30 minutes to prepare a solution.

  Subsequently, sodium hypochlorite was added to the solution. Immediately after adding sodium hypochlorite, using an automatic titrator ("GT-100" manufactured by Mitsubishi Chemical Corporation), a 0.5N aqueous sodium hydroxide solution is added dropwise to bring the pH of the solution to about 10. Retained. The end point of the oxidation reaction was determined when no decrease in pH of the solution was observed.

  Subsequently, after adding 0.1 g of ethanol to the solution, 0.1 g of sodium borohydride was added, and the solution was stirred at room temperature for 3 hours to perform additional reduction of oxidized cellulose.

  Subsequently, the obtained mixed solution was sufficiently washed with a glass filter to remove impurities, thereby obtaining additional reduced oxidized cellulose.

In the synthesis of TOC-2 to 4 and 7, distilled water is added to the obtained oxidized cellulose after further reduction to obtain a mixed solution of oxidized cellulose, and further 1N hydrochloric acid is added to adjust the pH of the solution to 2. did. Subsequently, this mixed liquid was converted into COOH-type oxidized cellulose by stirring for 2 hours, and then neutralized using a neutralizing base (neutralizing agent) corresponding to the “neutralizing agent” in Tables 2 to 5. As a result, a mixed liquid containing alkali metal neutralized and amine neutralized oxidized cellulose was obtained. In Tables 2 to 5, when Li is written in the column of “neutralizing agent”, lithium hydroxide, when K is written, potassium hydroxide, when NH ₃ is written, Ammonia water was used as a neutralizing base.

  Subsequently, an aqueous dispersion containing oxidized cellulose at a ratio of 0.1% by mass was prepared by adding distilled water to the mixed solution containing oxidized cellulose. An aqueous dispersion of transparent cellulose nanofibers was prepared by further dispersing the prepared aqueous dispersion using a homomixer (Homomixer MARKII manufactured by PRIMIX).

  In order to confirm the dispersion state of the aqueous dispersion, the transmittance at a wavelength of 600 nm of a 0.1 mass% aqueous dispersion was measured using a spectrophotometer (UV-1800, manufactured by Shimadzu Corporation), and the result When the transmittance was 80% or more, it was judged that the cellulose nanofibers were sufficiently dispersed. In addition, it was confirmed that cellulose nanofibers were sufficiently dispersed by light scattering when the aqueous dispersion was shaken between two orthogonal polarizing plates.

  A dry body of cellulose nanofiber is prepared by completely drying a part of each cellulose nanofiber, and 0.1M hydrochloric acid aqueous solution is added to 60 mL of a sample solution of a slurry of 0.5% by mass of the dry body of cellulose nanofiber. By adding, the pH of the sample solution was adjusted to about 2.5. Subsequently, 0.05 M sodium hydroxide was added dropwise to this sample solution to measure the electrical conductivity, and the amounts of carboxyl groups calculated from the amount of the dropped sodium hydroxide solution were listed in Tables 2 to 5. .

  Moreover, it described similarly in Tables 2-5 about the number average fiber diameter computed from the TEM image of each cellulose nanofiber, and the SEM image, and the largest fiber diameter.

(2-2) Preparation of aqueous dispersion of Leocrista C-2SP By adding distilled water to cellulose single nanofiber (Daiichi Kogyo Seiyaku Co., Ltd., product name Leocrista C-2SP), cellulose oxide (carboxyl amount 1) (.64 mmol / g, number average fiber diameter 3 nm, maximum fiber diameter less than 50 nm) was prepared in an amount of 0.1% by mass. The prepared aqueous dispersion was further dispersed using a homomixer (Homomixer MARKII manufactured by PRIMIX). Thereby, an aqueous dispersion of Leocrystala C-2SP was prepared.

(3) Preparation of polyester resin composition [Examples 1-36]
The water-soluble polyester resin solution having a concentration of 25% by mass obtained in (1-1) and the aqueous dispersion of cellulose nanofibers obtained in (2) are shown in Table 2 in terms of the amount (% by mass) of cellulose nanofibers relative to the polyester resin. The mixture was mixed so as to have the ratio described in ˜5, and was mixed uniformly using a homomixer (hommixer MARKII manufactured by PRIMIX) and a high shear type homomixer (CLEAMIX CLM-1.5S manufactured by M Technique Co., Ltd.). . This prepared the polyester resin composition of Examples 1-36, respectively. The types of polyester resin and the types of cellulose nanofibers in each example are as shown in Tables 2 to 5.

[Comparative Examples 1 to 11]
The water-soluble polyester resin solution having a resin concentration (resin solid content) of 25% by mass obtained in (1-1) was directly used as a polyester resin composition. The kind of polyester resin in each comparative example is as shown in Tables 5-6.

[Comparative Example 12]
A water-soluble polyester resin (PES-1) solution having a concentration of 25% by mass obtained in (1-1) and methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., product name Metrolz SM15, methoxy group substitution degree 1.8) are mixed with polyester. Blended so that the amount of methylcellulose with respect to the resin was 10% by mass, these were used using a homomixer (Homomixer MARKII manufactured by PRIMIX) and a high shear type homomixer (Cleamix CLM-1.5S manufactured by M Technique Co., Ltd.). And mixed. Thereby, a polyester resin composition was prepared.

[Comparative Example 13]
The water-insoluble polyester resin (PES-12) solution having a concentration of 25% by mass obtained in (1-2) and the aqueous dispersion of cellulose nanofibers obtained in (2) are used in an amount of cellulose nanofibers of 10 to the polyester resin. %, And the mixture was mixed using a homomixer (Homomixer MARKII manufactured by PRIMIX) and a high shear type homomixer (Cleamix CLM-1.5S manufactured by M Technique Co., Ltd.). Therefore, it was difficult to mix uniformly. Accordingly, Comparative Example 13 is not subjected to the following evaluation test (4).

(4) Evaluation test The following evaluation test was done with respect to the polyester resin composition. The evaluation results are shown in Tables 2 to 6 below.

(4-1) Tensile strength After putting the polyester resin composition into a petri dish made of polypropylene and drying it at a temperature of 40 ° C overnight, it is further heated at a temperature of 90 ° C, so that it is completely dried (absolutely dry state) ) Having a film thickness of 200 μm was prepared. The film was cut to produce a strip-shaped test piece having a size of 50 mm × 5 mm, and the test piece was left in a thermostatic oven at a temperature of 25 ° C. and a humidity of 60% for more than half a day. Subsequently, a tensile test of the test piece was performed using a tensile tester (A & D Co., Ltd. Tensilon Universal Material Tester) at a tensile speed of 100 mm / min. The tensile strength (MPa) was calculated by dividing the maximum load during the tensile test by the cross-sectional area before the test of the test piece.

(4-2) Elongation A tensile test of the test piece was performed in the same manner as in (4-1). The elongation (%) was calculated by dividing the amount of elongation of the test piece immediately before breaking by the length of the test piece before the test.

(4-3) Heat resistance After putting the polyester resin composition into a petri dish made of polypropylene and drying it at a temperature of 40 ° C overnight, it is further heated at a temperature of 90 ° C, so that it is completely dried (an absolutely dry state) ) Having a film thickness of 50 μm. The film was cut to produce a strip-shaped test piece having a size of 20 mm × 5 mm. The test piece was heated from room temperature to 200 ° C. at a heating rate of 5 ° C./min while applying a load of 9.8 mN to the test piece using TMA manufactured by Rigaku Corporation. As a result of measuring the elongation, it was evaluated as follows.

A: Less than 1% shape change rate at 200 ° C. B: Not satisfying A, less than 5% shape change rate at 150 ° C. C: Not satisfying A and B, less than 5% shape change rate at 100 ° C. D: A and B are not satisfied and the shape change rate at 100 ° C. is 5% or more. (4-4) Flexibility A polyester resin composition is applied onto a PET film (product name: Lumirror T-60, film thickness: 100 μm, manufactured by Toray Industries, Inc.). -It dried and produced the film | membrane with a film thickness of 15 micrometers or 3 micrometers. This film was completely bent along the mandrel outer shape using a cylindrical mandrel bending tester having a diameter of 2 mm, and the appearance of the film was observed and evaluated as follows.

A: No crack was found in the film with a film thickness of 15 μm B: No crack was found in the film with a film thickness of 15 μm, but no crack was found in the film with a film thickness of 3 μm (4-5) Transparent (Total light transmittance)
A polyester resin composition was applied and dried on a PET film (manufactured by Toray Industries, Inc., product name Lumirror T-60, film thickness 100 μm) to prepare a film having a film thickness of 3 μm. The total light transmittance (%) of this film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model number NDH2000).

(4-6) Adhesiveness A polyester resin composition was applied and dried on a PET film (product name: Lumirror T-60, manufactured by Toray Industries, Inc., film thickness: 100 μm) to prepare a film having a film thickness of 3 μm. The presence or absence of peeling of the film when it was peeled off vigorously after a Nichiban cello tape (registered trademark) was applied to this film was evaluated and evaluated as follows.

A: No film peeling B: Film peeling

Claims (6)

  A polyester resin composition containing a water-soluble polyester resin and cellulose nanofibers. The glass transition temperature of the water-soluble polyester resin is in the range of −60 to 110 ° C.,
The polyester resin composition according to claim 1. The water-soluble polyester resin has a residue of a polyvalent carboxylic acid,
The polycarboxylic acid residue includes a metal sulfonate group-containing polyvalent carboxylic acid residue,
The polyester resin composition according to claim 1 or 2. The amount of the residue of the metal sulfonate group-containing polyvalent carboxylic acid relative to the entire residue of the polyvalent carboxylic acid is in the range of 1 to 30 mol%.
The polyester resin composition according to claim 3. The cellulose nanofiber has a carboxyl group at a ratio in the range of 0.5 to 2.0 mmol / g.
The polyester resin composition as described in any one of Claims 1-4. The amount of the cellulose nanofibers relative to the water-soluble polyester resin is in the range of 0.1 to 50% by mass.
The polyester resin composition as described in any one of Claims 1-5.