HK1244498B - Polyamide resin composition - Google Patents

Description

Polyamide resin composition

Technical Field

The present invention relates to a polyamide resin composition comprising cellulose fibers and a polyamide resin and having a good color tone despite high viscosity, in other words, high polymerization degree and high strength.

Background Art

Resin compositions made by reinforcing polyamide resins with inorganic fillers such as glass fiber, carbon fiber, talc, and clay are widely known. However, the use of reinforcing materials composed of these inorganic fillers presents problems such as poor mechanical properties and heat resistance unless a large amount is added, and the resulting resin composition becomes heavier due to its high specific gravity.

In recent years, research has focused on using cellulose as a reinforcement for resin materials. Cellulose includes cellulose obtained from trees; cellulose obtained from non-wood resources such as rice, cotton, kenaf, bagasse, abaca, and hemp; and bacterial cellulose produced by microorganisms. These are abundant on Earth. Cellulose has excellent mechanical properties, and incorporating cellulose into resins is expected to improve the properties of the resin composition. Furthermore, cellulose has a lower specific gravity than inorganic fillers, so incorporating cellulose into the resin does not increase the weight of the resulting resin composition.

A common method for incorporating cellulose into thermoplastic resins is to melt-mix the resin and cellulose. However, this method directly mixes the cellulose into the resin in an aggregated state, making it impossible to obtain a resin composition in which the cellulose is uniformly dispersed. Consequently, the properties of the resin composition cannot be fully improved.

As a technique for improving the dispersibility of cellulose in a resin, for example, WO2011/126038 discloses mixing an aqueous dispersion of cellulose fibers having an average fiber diameter of 10 μm or less with monomers constituting a polyamide resin, followed by melt polymerization, to produce a polyamide resin composition in which the cellulose is uniformly dispersed. JP2013-79334A discloses obtaining a polyamide resin composition with a good color tone by polymerization without the use of an acid catalyst.

Summary of the Invention

However, the method described in WO2011/126038 has the problem of cellulose decomposition and coloration due to the long melt polymerization time. The method described in JP2013-79334A requires maintaining the polymer in a molten state for a long time to further increase the degree of polymerization, which may result in coloration. Furthermore, the resulting high melt viscosity makes extraction difficult.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a cellulose-containing polyamide resin composition having a good color tone and good removability despite high viscosity, in other words, high degree of polymerization and high strength.

The present inventors have conducted intensive studies to solve such problems and have found that the above-mentioned object can be achieved by increasing the molecular weight of a polyamide resin composition having a specific relative viscosity by solid-phase polymerization, thereby completing the present invention.

The gist of the present invention is as follows.

(1) A polyamide resin composition comprising 0.01 to 50 parts by mass of cellulose fiber relative to 100 parts by mass of a polyamide resin, having a relative viscosity of 2.3 or greater, an L value of 20 or greater, an a value of 10 or less, and a b value of 20 or less in a Lab color space.

(2) The polyamide resin composition according to (1) above, further comprising phosphorous acid or sodium hypophosphite.

(3) The polyamide resin composition according to (1) or (2) above, wherein the polyamide resin is polyamide 6.

(4) The polyamide resin composition according to any one of (1) to (3) above, wherein the average fiber diameter of the cellulose fibers is 500 nm or less.

(5) A method for producing the polyamide resin composition according to any one of (1) to (4) above, comprising subjecting a polyamide resin composition having a relative viscosity of 2.2 or less to solid phase polymerization.

According to the present invention, it is possible to provide a polyamide resin composition in which cellulose is uniformly dispersed and which has a good color tone and good removability despite high viscosity, in other words, high strength.

DETAILED DESCRIPTION

The polyamide resin in the present invention is a polymer having an amide bond formed from aminocarboxylic acid, lactam or diamine and dicarboxylic acid.

Examples of the aminocarboxylic acid include 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and p-aminomethylbenzoic acid.

Examples of the lactam include ε-caprolactam and ω-laurolactam.

Examples of the diamine include butanediamine, hexamethylenediamine, nonanediamine, decanediamine, undecanediamine, dodecanediamine, 2,2,4-/2,4,4-trimethylhexamethylenediamine, 5-methylnonanediamine, 2,4-dimethyloctanediamine, m-xylylenediamine, p-xylylenediamine, 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.

Examples of the dicarboxylic acid include adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 5-sodium sulfoisophthalate, hexahydroterephthalic acid, hexahydroisophthalic acid, and diglycolic acid.

More specifically, the polyamide resin in the present invention includes polycaprolactam (polyamide 6), polybutylene adipamide (polyamide 46), polyhexamethylene adipamide (polyamide 66), polyhexamethylene sebacamide (polyamide 610), polyhexamethylene dodecane diamide (polyamide 612), polyundecamethylene adipamide (polyamide 116), polyundecamethylene (polyamide 11), polydodecamethylene (polyamide 12), polytrimethylhexamethylene terephthalamide (polyamide TMHT), polyhexamethylene terephthalamide (polyamide 6T), and polyhexamethylene isophthalamide (polyamide 6I). , polyhexamethylene terephthalamide/polyhexamethylene isophthalamide (polyamide 6T/6I), polybis(4-aminocyclohexyl)methane dodecamide (polyamide PACM12), polybis(3-methyl-4-aminocyclohexyl)methane dodecamide (polyamide dimethyl PACM12), polymethylene adipamide (polyamide MXD6), polynonane terephthalamide (polyamide 9T), polydecane terephthalamide (polyamide 10T), polyundecanediamine terephthalamide (polyamide 11T), and polyundecanediamine hexahydroterephthalamide (polyamide 11T(H)). These may be copolymers or mixtures. Among them, polyamide 6, polyamide 66, polyamide 11, polyamide 12, and copolymers and mixtures thereof are preferred.

Examples of the cellulose fibers used in the present invention include those derived from wood, rice, cotton, kenaf, bagasse, abaca, and hemp. Examples include biologically derived cellulose such as bacterial cellulose, valonia cellulose, and ascidian cellulose. Furthermore, examples include regenerated cellulose and cellulose derivatives.

The polyamide resin composition of the present invention can improve mechanical strength due to the inclusion of cellulose fibers. To fully enhance mechanical strength, it is preferable to uniformly disperse the cellulose fibers in the resin without causing them to aggregate. Cellulose fibers are more easily dispersed when they have more hydroxyl groups on their surfaces that come into contact with the polyamide resin. Therefore, a larger overall surface area is preferred. Therefore, it is preferable to miniaturize the cellulose fibers as much as possible.

The cellulose fibers used to obtain the resin composition of the present invention preferably have an average fiber diameter of 10 μm or less, more preferably 500 nm or less. When the average fiber diameter is greater than 10 μm, the surface area of the cellulose fibers may decrease, thereby reducing the dispersibility of the cellulose. On the other hand, considering the productivity of the cellulose fibers, the lower limit of the average fiber diameter is preferably 4 nm. The average fiber diameter of the cellulose fibers after melt polymerization or after the resin composition is formed into a molded body tends to be smaller than the average fiber diameter of the cellulose fibers used. This is because the cellulose fibers are fragmented due to shear forces caused by melt polymerization and molding.

Cellulose fibers having an average fiber diameter of 10 μm or less can be obtained by tearing cellulose fibers and then microfibrillating them. Examples of microfibrillation methods include various pulverization devices such as ball mills, mortar grinders, high-pressure homogenizers, and mixers. Commercially available aqueous dispersions of microfibrillated cellulose fibers include, for example, "CELISH" manufactured by Daicel FineChem.

As cellulose fibers having an average fiber diameter of 10 μm or less, bacterial cellulose produced by bacteria can also be cited. As bacterial cellulose, for example, cellulose produced by acetic acid bacteria of the genus Acetobacter can be cited as the producing bacteria. Plant cellulose is formed by bundling (bundling) cellulose molecular chains, and very fine microfibers are formed in bundles. In contrast, the cellulose produced by acetic acid bacteria is originally in the form of ribbons with a width of 20 to 50 nm, forming an extremely fine network compared to plant cellulose. Since bacterial cellulose produces acetic acid together with the above-mentioned cellulose, it sometimes coexists with acetic acid. In this case, it is preferable to replace the solvent with water.

Examples of cellulose fibers with an average fiber diameter of 10 μm or less include micronized cellulose. Micronized cellulose can be produced, for example, by oxidizing cellulose fibers in an aqueous solution containing an N-oxyl radical compound, an auxiliary oxidant, and alkali metal bromide, followed by washing and defibration. Examples of N-oxyl radical compounds include 2,2,6,6-tetramethylpiperidinyl-1-oxyl radicals. Examples of auxiliary oxidants include sodium hypochlorite and sodium chlorite.

The oxidation reaction of cellulose fibers is carried out by adding an alkaline compound such as sodium hydroxide aqueous solution to a pH of approximately 10 until no change in pH is observed. The reaction temperature is preferably room temperature. Residual N-oxyl radical compounds, auxiliary oxidants, and alkali metal bromide in the system are preferably removed after the reaction. Examples of water washing methods include filtration and centrifugation. Examples of defibration methods include methods using the various pulverization devices exemplified above for microfibrillation.

The aspect ratio (average fiber length/average fiber diameter) of the cellulose fibers is preferably 10 or greater, more preferably 50 or greater, and even more preferably 100 or greater. When the aspect ratio is 10 or greater, the mechanical strength of the polyamide resin composition is further improved.

The content of the cellulose fiber in the polyamide resin composition needs to be 0.01 to 50 parts by mass relative to 100 parts by mass of the polyamide resin, preferably 0.05 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, and even more preferably 0.1 to 10 parts by mass. When the content of the cellulose fiber is less than 0.01 parts by mass relative to 100 parts by mass of the polyamide resin, there is no effect of improving mechanical strength. On the other hand, when the content of the cellulose fiber is greater than 50 parts by mass relative to 100 parts by mass of the polyamide resin, it is sometimes difficult to include the cellulose fiber in the resin composition, or the resulting resin composition may be colored.

The polyamide resin composition of the present invention can be produced by subjecting a polyamide resin composition having a relative viscosity of 2.2 or less to solid phase polymerization.

The method for producing the polyamide resin composition to be subjected to solid phase polymerization is not particularly limited, and an example thereof includes a method in which monomers constituting the polyamide resin and an aqueous dispersion of cellulose fibers are mixed, and a catalyst is added as needed to carry out melt polymerization.

The aqueous dispersion of cellulose fibers to be subjected to melt polymerization can be obtained by stirring purified water and cellulose fibers with a mixer, etc. The solid content is preferably 0.01 to 50% by mass.

The mixed solution of the monomer constituting the polyamide resin and the aqueous dispersion of the cellulose fibers is preferably a uniform dispersion stirred with a mixer or the like. Melt polymerization can be carried out by heating the mixed solution to a temperature of 150 to 270°C and stirring. At this time, the water in the aqueous dispersion of the cellulose fibers can be discharged by slowly discharging the water vapor. The melt polymerization needs to be terminated when the relative viscosity is 2.2 or less. When the relative viscosity after melt polymerization is greater than 2.2, the risk of coloration is high. On the other hand, the lower limit of the relative viscosity after melt polymerization is preferably 1.3. When the relative viscosity after melt polymerization is less than 1.3, sometimes the operation after melt polymerization becomes difficult, or the time until the practically required degree of polymerization is reached becomes longer, thereby causing cellulose decomposition and failing to increase the viscosity of the resulting resin composition.

The polyamide resin composition obtained by melt polymerization is preferably cut into pellets after removal. From the perspective of handling and efficiency during refining described below, the pellets are preferably 2 to 5 mm in diameter and 3 to 6 mm in length, more preferably 3 to 4 mm in diameter and 4 to 5 mm in length.

In order to remove unreacted monomers and oligomers, the melt-polymerized polymer is preferably immersed in water at 90 to 100° C. for purification.

Solid-phase polymerization is preferably performed by heating the melt-polymerized polymer, or the optionally refined polymer, under an inert gas flow or reduced pressure at a temperature below the melting point of the polyamide resin composition for at least 30 minutes, more preferably at least 1 hour. Heating temperatures below (melting point of the polyamide resin composition - 75°C) may slow the solid-phase polymerization reaction rate. On the other hand, heating temperatures near the melting point of the polyamide resin composition may cause the polymer to fuse or discolor.

During polymerization, a polymerization catalyst may be used to improve polymerization efficiency. The polymerization catalyst may be added before melt polymerization, during melt polymerization, before refining, during refining, before solid-phase polymerization, or in any of the steps of solid-phase polymerization. It is preferably added before melt polymerization. The polymerization catalyst is not particularly limited as long as it is a catalyst commonly used in melt polymerization of polyamides. Preferably, a phosphorus compound is used, and more preferably, phosphorous acid or sodium hypophosphite is used. By using phosphorous acid or sodium hypophosphite, the polymerization efficiency during solid-phase polymerization is significantly improved. Therefore, compared to the case where no polymerization catalyst is used, the degree of polymerization can be increased in a short time.

In the above-mentioned production method, since the cellulose fibers are directly subjected to melt polymerization in the form of an aqueous dispersion, the cellulose fibers do not coagulate with each other. As a result, a polyamide resin composition in which the cellulose fibers are well dispersed can be obtained. In addition, since the solid-phase polymerization is carried out at a low temperature below the melting point of the resin composition, the decrease in workability and the occurrence of coloration associated with the increase in viscosity during melt polymerization can be suppressed.

By above-mentioned manufacture method, the relative viscosity of the polyamide resin composition of gained can be set to more than 2.3, preferably can be set to more than 2.5.In addition, for the color of the polyamide resin composition of gained, the L value in Lab color space can be set to more than 20, a value is set to less than 10, b value is set to less than 20, preferably the L value can be made to more than 30, a value is set to less than 7, b value is set to less than 20, more preferably the L value can be set to more than 40, a value is set to less than 5, b value is set to less than 20.If the L value is lower than 20, then become almost black tone, if the a value is greater than 10, then become reddish tone, if the b value is greater than 20, then become yellowish tone.

The average fiber diameter of the cellulose fibre in the polyamide resin composition is preferably below 500nm, more preferably below 100nm, further preferably below 50nm.The average fiber diameter of the cellulose fibre in the polyamide resin composition is that below 500nm means that cellulose fibre does not condense and disperses evenly in the resin composition.Thus, obtain the resin composition of mechanical properties excellence such as flexural strength, flexural modulus.In addition, even if the content of cellulose fibre is less amount, also can obtain the polyamide resin composition that mechanical properties improve.So evenly dispersed with the polyamide resin composition of cellulose fibre can obtain by melt polymerization as mentioned above by the monomer that constitutes polyamide resin and the uniform mixed dispersion liquid of the aqueous dispersion of cellulose fibre.

The polyamide resin composition may contain pigments, heat stabilizers, antioxidants, weathering agents, plasticizers, lubricants, mold release agents, antistatic agents, impact resistance agents, flame retardants, compatibilizers, and the like, as long as the effects of the present invention are not impaired.

The polyamide resin composition may contain other polymers other than the polyamide resin as long as the effects of the present invention are not impaired. Examples of other polymers include polyolefins, polyesters, polycarbonates, polystyrenes, polymethyl (meth)acrylates, poly(acrylonitrile-butadiene-styrene) copolymers, liquid crystal polymers, and polyacetals.

The polyamide resin composition of the present invention can be made into a molded body by injection molding. The injection molding machine used in injection molding is not particularly limited, and for example, a screw in-line type injection molding machine and a plunger type injection molding machine can be cited. In the barrel of the injection molding machine, the heated and molten polyamide resin composition is measured per injection, injected in a molten state in the mold, cooled and solidified in a prescribed shape, and then taken out from the mold as a molded body. The resin temperature during injection molding is preferably above the melting point of the polyamide resin composition, preferably less than (melting point + 100°C). The polyamide resin composition for injection molding is preferably fully dried. A polyamide resin composition with a high moisture content sometimes foams in the barrel of the injection molding machine, making it difficult to obtain an optimal molded body. Therefore, the moisture content of the polyamide resin composition for injection molding is preferably less than 0.3% by mass, more preferably less than 0.1% by mass.

The polyamide resin composition of the present invention has a good color tone and high viscosity, thereby having excellent mechanical strength. Therefore, the polyamide resin composition of the present invention can be well provided for automotive applications, electrical and electronic equipment applications, agricultural and aquatic products applications, medical equipment applications, sundry goods, etc.

Examples of automotive applications include body parts such as bumpers, instrument panels, glove boxes, decorative parts, door trims, ceilings, floors, lamp reflectors, brush holders, fuel pump module parts, switchboards, seat reed valves, wiper motor gears, speedometer frames, electromagnetic ignition coils, alternators, switches, sensor parts, tie rod ball stabilizers, ECU cables, exhaust control valves, connectors, exhaust brake solenoid valves, engine valves, radiator fans, starters, injectors, panels around the engine, hoods, and motor covers.

Examples of electrical and electronic equipment applications include computers, mobile phones, music players, car navigation systems, SMT connectors, IC card connectors, optical fiber connectors, micro switches, capacitors, chip carriers, coil packages, transistor packages, IC sockets, switches, relay components, capacitor cases, thermistors, various coil bobbins, FDD mainframes, and tape coder heads. Mounts), stepping motors, bearings, razor bases, LCD projection TV lamp housings, microwave oven parts, induction cooker coil bases, dryer nozzles, steam dryer parts, steam iron parts, DVD pickup bases, commutator bases, circuit boards, ICs, LCD fixtures, food cutters, DAT cylinder bases, copier gears, printer fuser unit parts, LCD panel light guides, communications equipment (antennas), semiconductor sealing materials, power modules, fuse boxes, water pump impellers, pipes for semiconductor manufacturing equipment, game console connectors, air conditioner drain pans, garbage disposal containers, vacuum cleaner motor fan guides, microwave oven roller races (electronic lens rings), capstan motor bearings, street lights, submersible pumps, motor insulators, motor brush holders, circuit breaker parts, computer housings, mobile phone housings, office automation equipment housing parts, and gas meters.

Examples of agricultural and aquatic uses include containers, cultivation containers, and floats.

Examples of medical device applications include syringes and intravenous drip containers.

Examples of the miscellaneous goods include plates, cups, spoons, flower pots, refrigerators, fans, toys, ballpoint pens, rulers, clips, drainage materials, fences, storage boxes, construction switchboards, hot water supply equipment pump casings, impellers, joints, valves, and faucet equipment.

The polyamide resin composition of the present invention can be formed into a film or sheet by known film-forming methods such as T-die extrusion and inflation molding. Films and sheets formed from the polyamide resin composition of the present invention can be used, for example, as film capacitors, release films for FPDs, and insulating films for automotive motors.

The polyamide resin composition of the present invention can be molded into a foam by using a chemical foaming agent, a supercritical gas, or an inert gas. The foam molded from the polyamide resin composition of the present invention can be used in the fields of electrical and electronic equipment and automobiles.

The polyamide resin composition of the present invention can be formed into various fibers and nonwoven fabrics by known spinning methods such as melt spinning, flash spinning, electrospinning, and melt blowing. Fibers and nonwoven fabrics formed from the polyamide resin composition of the present invention can be used as bag filters for electrostatic dust collection, baling yarn for electric motors, core materials for clothing, dry nonwoven fabrics, and felts.

Example

The physical properties of the polyamide resin composition were measured by the following methods.

(1) Relative viscosity

The polyamide resin composition was dissolved in 96% sulfuric acid so that the concentration of polyamide after cellulose removal was 1 g/dL, and the viscosity was measured at 25° C. using an Ubbelohde viscometer.

(2) Removal of molten polymer

The molten polymer was extruded at a nitrogen pressure of 0.7 MPa. A yield of 80% or more of the theoretical yield calculated from the charged monomers was judged as "good", and a yield of less than 80% was judged as "poor".

(3) Hue (L value, a value, b value)

The pellets of the polyamide resin composition were filled in a particle measurement cuvette (35 mm in diameter x 15 mm in height), which is an accessory of a spectrocolorimeter SE-6000 manufactured by Nippon Denshoku Co., Ltd., and the reflectance was measured using the spectrocolorimeter SE-6000. The light source was a C-2 light source.

(4) Flexural strength and flexural modulus

After the polyamide resin composition is fully dried, it is molded using an injection molding machine (manufactured by Toshiba Machine Co., Ltd., Model IS-80G) using a mold for a 1/8-inch 3-point bending test piece according to the ASTM standard to produce a test piece of 127 mm in length × 12.7 mm in width × 3.2 mm in thickness (1/8 inch).

The obtained test pieces were used to measure flexural strength and flexural modulus according to ASTM D790. The ambient temperature was set to 23° C. and the deformation rate was set to 1 mm/min.

(5) Average fiber diameter of cellulose fibers

The cellulose fibers subjected to melt polymerization were freeze-dried as needed and observed using a field emission scanning electron microscope (S-4000 manufactured by Hitachi, Ltd.).

The cellulose fibers in the polyamide resin composition were sliced into sections having a thickness of 100 nm using a freezing ultramicrotome, stained with OsO 4 (osmium tetroxide), and observed using a transmission electron microscope (JEM-1230 manufactured by JEOL Ltd.).

The length in the direction perpendicular to the longitudinal direction was measured from the obtained electron microscope image, and the largest value was taken as the fiber diameter. Similarly, the fiber diameters of 10 cellulose fibers (single fibers) were measured, and the average value of the 10 fibers was calculated as the average fiber diameter.

For cellulose fibers having a large fiber diameter, the cellulose fibers themselves or the polyamide resin composition pellets sliced with a thickness of 10 μm were observed using a stereomicroscope (OLYMPUS SZ-40), and the average fiber diameter was determined in the same manner as when using electron microscope images.

Example 1

[Preparation of Aqueous Dispersion of Cellulose Fibers]

CELISH KY110N (aqueous dispersion containing 15% by mass of cellulose fibers having an average fiber diameter of 125 nm manufactured by Daicel FineChem) was used as the aqueous dispersion of cellulose fibers. Purified water was added to this aqueous dispersion and stirred with a mixer to prepare an aqueous dispersion containing 3% by mass of cellulose fibers.

[Melt polymerization]

70 parts by mass of the resulting aqueous dispersion of cellulose fibers and 100 parts by mass of ε-caprolactam were further stirred and mixed in a mixer until a uniform dispersion was formed. While stirring the mixed dispersion and maintaining the pressure at 0.7 MPa, the pressure was increased to 240°C over 4 hours. The pressure was then released to atmospheric pressure, and melt polymerization was carried out at 240°C for 0.5 hours.

After the melt polymerization is completed, the polyamide resin composition is taken out and cut into pellets.

[Refining, solid phase polymerization]

The obtained pellets were refined by treating them in hot water at 95°C for 12 hours, and then dried at 100°C for 12 hours.

The dried particles were solid-phase polymerized at 170°C for 15 hours under a nitrogen stream.

Examples 2 to 8, Comparative Example 2

[Melt polymerization]

Compared with Example 1, melt polymerization was carried out in the same manner as in Example 1 except that the cellulose fiber content, the presence or absence of a polymerization catalyst, its type and content when used, and the reaction time were changed as shown in Table 1.

After the melt polymerization is completed, the polyamide resin composition is taken out and cut into pellets.

[Refining, solid phase polymerization]

Using the obtained pellets, purification and solid phase polymerization were carried out in the same manner as in Example 1.

Example 9

[Preparation of Aqueous Dispersion of Cellulose Fibers]

50 mL of a culture medium composed of 0.5% glucose, 0.5% polypeptone, 0.5% yeast extract, and 0.1% magnesium sulfate heptahydrate was injected into each 200 mL Erlenmeyer flask and sterilized by steam autoclaving at 120°C for 20 minutes. One microliter of Gluconacetobacter xylinus (NBRC 16670) grown on a test tube slant agar medium was inoculated and statically cultured at 30°C for 7 days. After 7 days, a white gel-like film of bacterial cellulose formed on the upper layer of the culture medium.

The obtained bacterial cellulose was crushed with a mixer, and then repeatedly immersed in water and washed to replace the water, thereby preparing an aqueous dispersion having a cellulose fiber content of 4.1% by mass. The average fiber diameter of the cellulose fibers was 60 nm.

[Melt polymerization]

The melt polymerization was carried out in the same manner as in Example 1 except that 24.4 parts by mass of the obtained aqueous dispersion of cellulose fibers and 100 parts by mass of ε-caprolactam were used to prepare pellets.

[Refining, solid phase polymerization]

Using the obtained pellets, purification and solid phase polymerization were carried out in the same manner as in Example 1.

Example 10

[Preparation of Aqueous Dispersion of Cellulose Fibers]

2 g of cellulose (qualitative filter paper No. 1) was dispersed in 100 mL of water in which 0.025 g of 2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl radical and 0.25 g of sodium bromide were dissolved. Subsequently, a 13% by mass aqueous solution of sodium hypochlorite was added as an auxiliary oxidant in an amount of 4.3 mmol per 1 g of pulp. A sodium hydroxide aqueous solution was added at a pH of 10.5 using a pH stat, and the reaction was stopped when the pH no longer changed. The contents were washed with water four times by centrifugation, and defibrated using a household mixer for 30 minutes to prepare an aqueous dispersion having a cellulose fiber content of 1.6% by mass. The average fiber diameter of the resulting cellulose fibers was 10 nm.

[Melt polymerization]

95 parts by mass of the resulting aqueous dispersion of cellulose fibers and 150 parts by mass of ε-caprolactam were stirred and mixed in a mixer until a uniform dispersion was formed. While stirring the mixed dispersion and maintaining the pressure at 0.7 MPa, the pressure was raised to 240°C over 6 hours. The pressure was then released to atmospheric pressure, and melt polymerization was carried out at 240°C for 0.5 hours. The equivalent amounts of each component, calculated as 100 parts by mass of the ε-caprolactam (150 parts by mass), are shown in Table 1.

After the melt polymerization is completed, the polyamide resin composition is taken out and cut into pellets.

[Refining, solid phase polymerization]

Using the obtained pellets, purification and solid phase polymerization were carried out in the same manner as in Example 1.

Comparative Example 1

[Melt polymerization]

The cellulose fiber content in the mixed dispersion used for melt polymerization was adjusted to 60 parts by mass relative to 100 parts by mass of ε-caprolactam. Using this mixed dispersion, melt polymerization was carried out in the same manner as in Example 1, except that the reaction time was changed to 1.5 hours. However, the cellulose fiber content exceeded the range specified in the present invention, resulting in cellulose separation and failure to obtain a cellulose-containing polymer.

Comparative Examples 3 to 6

[Melt polymerization]

Compared with Example 1, melt polymerization was carried out in the same manner as in Example 1 except that the cellulose fiber content, the presence or absence of a polymerization catalyst, its type and content when used, and the reaction time were changed as shown in Table 1.

After the melt polymerization is completed, the polyamide resin composition is taken out and cut into pellets.

[Refined]

The obtained pellets were refined in the same manner as in Example 1.

Comparative Example 7

[Preparation of Aqueous Dispersion of Cellulose Fibers]

2 g of cellulose (qualitative filter paper No. 1) was dispersed in 100 mL of water in which 0.025 g of 2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl radical and 0.25 g of sodium bromide were dissolved. Subsequently, a 13% by mass sodium hypochlorite aqueous solution was added as an auxiliary oxidant in an amount of 4.3 mmol per 1 g of pulp. A sodium hydroxide aqueous solution was added at a pH of 10.5 using a pH stat, and the reaction was stopped when the pH no longer changed. The contents were washed four times with water by centrifugation, and defibrated using a household mixer for 30 minutes to prepare an aqueous dispersion having a cellulose fiber content of 1.6% by mass. The average fiber diameter of the resulting cellulose fibers was 10 nm.

[Melt polymerization]

95 parts by mass of the resulting aqueous dispersion of cellulose fibers and 150 parts by mass of ε-caprolactam were stirred and mixed in a mixer until a uniform dispersion was achieved. 0.3 parts by mass of phosphorous acid was further added as a polymerization catalyst. The mixed dispersion was then heated to 240°C over 6 hours while stirring and maintaining the pressure at 0.7 MPa. The pressure was then released to atmospheric pressure, and melt polymerization was carried out at 240°C for 1 hour. The equivalent amounts of each component, calculated as 100 parts by mass of the ε-caprolactam added (150 parts by mass), are shown in Table 1.

After the melt polymerization is completed, the polyamide resin composition is taken out and cut into pellets.

[Refined]

The obtained pellets were treated in hot water at 95°C for 12 hours, refined, and dried.

Table 1 shows the melt polymerization conditions, property values of the molten polymer, takeout properties of the molten polymer, solid phase polymerization conditions, and property values of the solid phase polymer of Examples 1 to 10 and Comparative Examples 1 to 7.

The polyamide resin compositions of Examples 1 to 10 all have a relative viscosity of 2.3 or greater, an L value of 20 or greater, an a value of 10 or less, and a b value of 20 or less.

Comparison between Example 1 and Examples 5 and 6 shows that the relative viscosity after solid-phase polymerization increases when phosphorous acid or sodium hypophosphite is used as the polymerization catalyst during solid-phase polymerization for the same time.

The polyamide resin composition of Comparative Example 2 has a value of more than 10 and a value of more than 20 because the relative viscosity of the polyamide resin composition used in the solid-phase polymerization is higher than the preferred range specified in the present invention.

Since the polyamide resin composition of Comparative Example 3 did not use cellulose fibers, it had low flexural strength.

The polyamide resin compositions of Comparative Examples 4 to 7 all had poor removability because their polymerization degrees were increased solely through melt polymerization. Furthermore, their b-values exceeded 20. Among them, the polyamide resin composition of Comparative Example 6 reached the upper limit of viscosity for melt polymerization. Even if the polymerization time was extended beyond this limit, cellulose decomposed and the viscosity did not increase.

Claims (5)

1. A polyamide resin composition, characterized in that it contains 0.01 to 50 parts by weight of cellulose fibers relative to 100 parts by weight of the polyamide resin, wherein the relative viscosity of the polyamide resin in the polyamide resin composition is 2.3 or higher, and the polyamide resin composition has an L value of 20 or higher, an a value of 10 or lower, and a b value of 20 or lower in the Lab color space. The polyamide resin composition is obtained by solid-state polymerization of a polyamide resin composition with a relative viscosity of 2.2 or less. 2. The polyamide resin composition according to claim 1, characterized in that it further contains sodium phosphorous acid or sodium hypophosphite. 3. The polyamide resin composition according to claim 1 or 2, wherein the polyamide resin is polyamide 6. 4. The polyamide resin composition according to claim 1 or 2, characterized in that the average fiber diameter of the cellulose fibers is less than 500 nm. 5. A method for manufacturing a polyamide resin composition, characterized in that, in manufacturing the polyamide resin composition according to any one of claims 1 to 4, a composition of a polyamide resin with a relative viscosity of 2.2 or less is subjected to solid-state polymerization.