JP6482203B2 - Manufacturing method of injection molded body - Google Patents

Description

  The present invention is an injection-molded article obtained by molding a resin composition containing a polyamide resin, having a beautiful, heavy, high-quality piano black appearance, high hardness, excellent scratch resistance, and heat resistance. It is about.

  Conventionally, a molded body having a piano black-like appearance has a high glossiness in addition to a black surface, and thus has a high-class feeling and is preferred by many users. For this reason, molded bodies with a piano black-like appearance can be used in the interiors of automobiles such as the casings of many electrical appliances such as televisions, printers, and telephones, and around the instrument panels and handles of automobiles, shift covers, and window switches. Is also actively used.

Polycarbonate resin is a thermoplastic resin excellent in impact resistance, heat resistance, thermal stability and the like, and its molded body is widely used in fields such as electrical and electronic parts, machines, and automotive parts. Patent Document 1 proposes a casing for a personal computer made of polycarbonate resin having an appearance of piano black like from the viewpoint of design and design while taking advantage of these excellent performances.
However, the polycarbonate resin molded article has insufficient scratch resistance, and it has been difficult to maintain a piano black-like appearance for a long period of time due to stress applied during use.

  Patent Document 2 discloses a molded body having a piano black-like appearance in which a clear coat film containing a fluorine additive is formed on the surface of a black molded body to improve scratch resistance. Since this molded body requires a clear coat film forming step after molding, there is a problem that the process becomes complicated and the cost is high, and since the clear coat film is formed by coating, There was a problem that peeling and scraping occurred due to impact, and durability was poor.

On the other hand, Patent Document 3 discloses a resin composition comprising a polyamide resin containing carbon black, a reinforcing material, and a weathering agent and having high rigidity and excellent surface smoothness, surface glossiness, and weather discoloration. ing. This polyamide resin composition can be suitably used for vehicle body support parts for vehicles such as automobile door mirrors and room mirrors by taking advantage of the characteristics.
Since the resin composition contains carbon black as described above, the resin composition is black and a molded article having a surface gloss is obtained. Also, since inorganic particles and inorganic fibers are used as the reinforcing material, the resin composition has rigidity and The bending strength was high. However, since the resin composition described in the cited document 3 contains a reinforcing material, the resulting molded product is floated on the surface. That is, the resin composition is a beautiful, heavy and high-quality piano. A molded product having a black-like appearance could not be obtained.

JP 2012-126777 A JP 2012-236175 A International Publication No. 2000/32693

  The present invention solves the above-mentioned problems, is composed of a resin composition using a polyamide resin, has a beautiful, heavy, high-quality piano black-like appearance, high hardness, scratch resistance, heat resistance It is an object of the present invention to provide an injection molded article that is excellent in performance and can be suitably used as a casing for various electric appliances and an interior material for automobiles.

The inventors of the present invention have arrived at the present invention as a result of intensive studies to solve the above problems.
That is, the gist of the present invention is as follows.
(1) A molded body formed by injection molding a polyamide resin composition containing 0.1 to 10 parts by mass of cellulose fibers with respect to 100 parts by mass of a polyamide resin,
The average fiber diameter of the cellulose fibers in the molded body is 10 μm or less,
The thermal deformation temperature at a load of 1.8 MPa, measured according to ASTM D648 of the molded body, is 60 ° C. or higher,
The 20-degree specular gloss value of the molded body surface is 70 or more,
The pencil hardness measured according to JIS-K-5600-5-4 on the surface of the molded body is 2B or more,
L * value of the molding surface, after following abrasion test, a method for producing a molded article out morphism Ru der 4 or less,
A method for producing an injection-molded article, wherein the injection molding of the polyamide resin composition is performed using a mold whose surface is polished with an abrasive having a particle size of 1000 mesh or more .
Abrasion test: Taber abrasion test performed on the surface of the molded body using a CSBER wear wheel manufactured by TABER under the condition of 200 rotations under a load of 250 g.

  The injection-molded article of the present invention is composed of a polyamide resin composition containing an appropriate amount of cellulose fibers having a small average fiber diameter, and thus has excellent surface smoothness, high hardness, scratch resistance, and heat resistance. Are better. Furthermore, the cellulose fiber which is an organic fiber is easily dyed into a black pigment, and thus has a beautiful, heavy and high-quality piano black-like appearance. Therefore, such an injection molded article of the present invention can be suitably used as a casing for various electrical appliances and an interior material for automobiles.

FIG. 1 is a surface image of an injection-molded body of Comparative Example 6 that is damaged by contact with a metal piece. FIG. 2 is an image of a metal piece in contact with the surface of the injection molded body of Comparative Example 6 and scratched. FIG. 3 is a surface image of the injection-molded body of Example 1 after the pencil hardness test. FIG. 4 is a surface image of the injection-molded body of Comparative Example 6 after the pencil hardness test.

Hereinafter, the present invention will be described in detail.
The injection-molded article of the present invention is a molded article obtained by injection-molding a polyamide resin composition containing 0.1 to 10 parts by mass of cellulose fibers with respect to 100 parts by mass of polyamide resin.
The polyamide resin used in the present invention refers to a polymer having an amide bond formed from an amino acid, lactam or diamine and a dicarboxylic acid.

Examples of monomers that form such a polyamide resin include 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, paraaminomethylbenzoic acid, and the like.
Examples of the lactam include ε-caprolactam and ω-laurolactam.

Examples of diamines include tetramethylene diamine, hexamethylene diamine, nonamethylene diamine, decamethylene diamine, undecamethylene diamine, dodecamethylene diamine, 2,2,4- / 2,4,4-trimethylhexamethylene diamine, and 5-methyl. Nonamethylenediamine, 2,4-dimethyloctamethylenediamine, metaxylylenediamine, paraxylylenediamine, 1,3-bis (aminomethyl) cyclohexane, 1-amino-3-aminomethyl-3,5,5-trimethyl Cyclohexane, 3,8-bis (aminomethyl) tricyclodecane, bis (4-aminocyclohexyl) methane, bis (3-methyl-4-aminocyclohexyl) methane, 2,2-bis (4-aminocyclohexyl) propane, Bis (aminopropyl) pipette Jin, and an amino ethyl piperazine.
Dicarboxylic acids include 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- Examples include sodium sulfoisophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, and diglycolic acid.

  More specifically, the polyamide resin used in the present invention includes polycaproamide (nylon 6), polytetramethylene adipamide (nylon 46), polyhexamethylene adipamide (nylon 66), polyhexamethylene sebaca. Mido (nylon 610), polyhexamethylene dodecane (nylon 612), polyundecane methylene adipamide (nylon 116), polyundecanamide (nylon 11), polydodecanamide (nylon 12), polytrimethylhexamethylene terephthalamide (Nylon TMHT), polyhexamethylene terephthalamide (nylon 6T), polyhexamethylene isophthalamide (nylon 6I), polyhexamethylene terephthalamide / isophthalamide (nylon 6T / 6I), polybis (4-aminocyclohexane) Syl) methane dodecamide (nylon PACM12), polybis (3-methyl-4-aminocyclohexyl) methane dodecamide (nylon dimethyl PACM12), polymetaxylylene adipamide (nylon MXD6), polynonamethylene terephthalamide (nylon 9T) , Polydecamethylene terephthalamide (nylon 10T), polyundecamethylene terephthalamide (nylon 11T), polyundecamethylene hexahydroterephthalamide (nylon 11T (H)), and these copolymers and mixtures. May be. Among them, particularly preferred polyamide resins are nylon 6, nylon 66, nylon 11, nylon 12, and copolymers and mixtures thereof.

  The polyamide resin is produced by a polymerization method described later, or by further using a solid phase polymerization method.

  The relative viscosity of the polyamide resin used in the present invention is preferably 1.5 to 5.0 at a temperature of 25 ° C. and a concentration of 1 g / 100 ml, using 96% sulfuric acid as a solvent, and preferably 1.7 to 4. More preferably 0. If the relative viscosity of the polyamide resin is less than 1.5, the mechanical properties are liable to deteriorate. On the other hand, when the relative viscosity exceeds 5.0, the flowability of the polyamide resin composition is lowered, and the injection moldability is likely to be lowered.

  Next, the cellulose fibers used in the present invention include those derived from wood, rice, cotton, hemp, kenaf and the like, as well as those derived from organisms such as bacterial cellulose, valonia cellulose and squirt cellulose. Also included are regenerated cellulose, cellulose derivatives and the like.

  In the present invention, an injection-molded article having a beautiful, heavy, and high-quality piano black-like appearance, high hardness, scratch resistance, and heat resistance can be obtained in a resin without agglomerating cellulose fibers. It is necessary to disperse uniformly. For that purpose, the dispersibility of the cellulose fiber to the polyamide resin and the affinity between the polyamide resin and the cellulose fiber are important. Further, in order to make the cellulose fiber have properties such as hydroxyl groups as much as possible, it is important to increase the surface area of the cellulose fiber. For this reason, it is necessary to use as fine a cellulose fiber as possible.

Therefore, in the present invention, the cellulose fibers contained in the molded body are required to have an average fiber diameter of 10 μm or less, among which the average fiber diameter is preferably 500 nm or less, and more preferably 300 nm or less. It is preferable that it is 100 nm or less especially.
Cellulose fibers having an average fiber diameter exceeding 10 μm cannot increase the surface area of the cellulose fibers, and it becomes difficult to improve the dispersibility and affinity for the polyamide resin and the monomers forming the polyamide resin. Accordingly, when the average fiber diameter of the cellulose fibers exceeds 10 μm, a molded article having poor surface smoothness, hardness, scratch resistance, and heat resistance is obtained.
The lower limit of the average fiber diameter is not particularly limited, but is preferably 4 nm or more in consideration of the productivity of cellulose fibers.

  In order to make the average fiber diameter of the cellulose fibers contained in the molded product 10 μm or less, it is preferable to use those having an average fiber diameter of 10 μm or less as the cellulose fibers added to the polyamide resin. As such cellulose fibers having an average fiber diameter of 10 μm or less (hereinafter sometimes referred to as cellulose fibers (A)), those obtained by microfibrillation by tearing cellulose fibers are preferable. Various pulverizing devices such as a ball mill, a stone mill, a high-pressure homogenizer, a high-pressure pulverizer, and a mixer can be used as means for microfibrillation. As the cellulose fiber (A), for example, “Serisch” manufactured by Daicel Finechem Co., Ltd. can be used as a commercially available product.

  Moreover, the aggregate of the cellulose fiber taken out as a waste thread can also be used in the manufacturing process of the textiles using a cellulose fiber as a cellulose fiber (A). The production process of the textile product includes spinning, woven fabric, nonwoven fabric production, and other textile product processing. Since these cellulose fiber aggregates are scrap fibers after the cellulose fibers have undergone these steps, the cellulose fibers are refined.

  Further, as the cellulose fiber (A), bacterial cellulose produced by bacteria can be used. For example, those produced using an Acetobacter group acetic acid bacterium as a producing bacterium can be used. Plant cellulose is the one in which molecular chains of cellulose converge and is formed by bundling very thin microfibrils, whereas cellulose produced from acetic acid bacteria originally has a width of 20 to 50 nm. It is in the form of a ribbon, and forms an extremely fine network compared to plant cellulose.

Moreover, even if it uses the refined cellulose fiber obtained by passing through a water washing and a physical defibrating process after oxidizing a cellulose fiber in presence of an N-oxyl compound as a cellulose fiber (A). Good.
There are various types of N-oxyl compounds, such as 2,2,6,6-tetramethylpiperidine-1-oxyl radical (hereinafter referred to as TEMPO) as described in Cellulose (1998) 5,153-164. preferable. Such a compound is added to the reaction aqueous solution in a catalytic amount range.
To this aqueous solution, sodium hypochlorite or sodium chlorite is added as a co-oxidant, and the reaction is allowed to proceed by adding an alkali metal bromide. An alkaline compound such as an aqueous sodium hydroxide solution is added to maintain the pH at around 10, and the reaction is continued until no change in pH is observed. The reaction temperature may be room temperature. After the reaction, it is preferable to remove the N-oxyl compound remaining in the system. Various methods such as filtration and centrifugation can be employed for washing.
Then, the cellulose fiber (A) refined | miniaturized can be obtained by passing through a physical defibration process using the above various grinders.

  The cellulose fibers in the molded body preferably have an aspect ratio (average fiber length / average fiber diameter) which is a ratio of the average fiber diameter to the average fiber length of 10 or more, and more preferably 50 or more, and more preferably 100 or more. It is preferable. When the aspect ratio is 10 or more, the mechanical properties of the obtained injection-molded product are easily improved.

And content of the cellulose fiber contained in the molded object of this invention needs to be 0.1-10 mass parts with respect to 100 mass parts of polyamide resins, and 0.5-10 mass in particular among them. Parts, and more preferably 0.5 to 5 parts by mass.
When the content of the cellulose fiber is less than 0.1 parts by mass with respect to 100 parts by mass of the polyamide resin, the obtained injection-molded product has low hardness and is inferior in heat resistance and mechanical properties.
On the other hand, when the content of the cellulose fiber exceeds 10 parts by mass with respect to 100 parts by mass of the polyamide resin, it becomes difficult to uniformly disperse the cellulose fiber in the resin composition, The surface smoothness is inferior, the specular gloss value is low, and it is difficult to obtain a high-quality piano black.

  In particular, the injection molded product of the present invention is obtained by obtaining the polyamide resin composition of the present invention by a production method as described later, so that even if the cellulose fiber content is small, it can be uniformly distributed in the polyamide resin. Since it is dispersed, it is possible to achieve high hardness, excellent heat resistance and mechanical properties.

Cellulose fibers have a very high affinity with water, and the smaller the average fiber diameter, the better the dispersion state with respect to water. Further, when water is lost, cellulose fibers are strongly aggregated by hydrogen bonding, and once aggregated, it becomes difficult to achieve a dispersion state similar to that before aggregation. In particular, this tendency becomes more prominent as the average fiber diameter of the cellulose fibers decreases.
Therefore, the cellulose fiber is preferably combined with the polyamide resin in a state containing water. Therefore, in the present invention, a polyamide resin composition containing cellulose fibers is obtained by performing a polymerization reaction of monomers constituting the polyamide resin in the presence of cellulose fibers containing water during the polymerization of the polyamide resin. It is preferable to take the method of obtaining. Such a production method makes it possible to uniformly disperse the cellulose fibers in the polyamide resin without aggregating them. Details of this manufacturing method will be described later.

  The injection-molded article of the present invention is obtained by injection-molding the above polyamide resin composition. As described above, the injection-molded article of the present invention is excellent in surface smoothness. And since a cellulose fiber is an organic fiber and it is easy to be dye | stained with the black pigment | dye added, the injection molded object of this invention will have a beautiful, heavy, and high quality piano black-like external appearance. In addition, as described above, by containing an appropriate amount of cellulose fibers having a small average fiber diameter, the injection-molded product has high hardness and excellent scratch resistance and heat resistance.

Next, the surface appearance of the injection molded product of the present invention will be described in detail.
First, the injection molded product of the present invention has a 20-degree specular gloss value of 70 or more on the surface of the molded product, and preferably 75 or more. When this value is less than 70, the injection-molded product is inferior in glossiness, and it becomes difficult to exhibit a piano black-like appearance.
The 20-degree specular gloss value is an average value obtained by measuring the 20-degree specular gloss value at any five points on the surface of the injection-molded product with Nippon Denshoku Industries Co., Ltd. Gloss Meter VG7000.

Furthermore, the injection-molded article of the present invention has high surface hardness, and the pencil hardness of the molded article surface measured according to JIS-K-5600-5-4 is 2B or more, preferably B or more. When the pencil hardness is less than 2B, the surface of the injection-molded product is easily damaged, and the piano black-like appearance is easily impaired.
Pencil hardness measured the pencil hardness of arbitrary 5 points | pieces of the surface of an injection molded body according to JIS-K-5600-5-4.
When the surface of the injection-molded body has a low pencil hardness, when the surface is scratched with a writing pressure of writing a piece of metal on the surface, it is scratched as shown in FIG. The appearance will be impaired. In FIG. 1, the surface of the molded body obtained in Comparative Example 6 to be described later is scratched with a writing pressure sufficient to write characters using the metal piece shown in FIG. 2 instead of the pencil of the pencil hardness test. The photograph was taken using a SU8020 field emission scanning electron microscope manufactured by Hitachi High-Technologies Corporation.

The injection-molded article of the present invention has excellent surface scratch resistance, and the L * value of the molded article surface after the wear test is 4 or less, preferably 3 or less. When the L * value on the surface of the molded body after the abrasion test exceeds 4, the surface of the molded body is worn, becomes whitish, and cannot have a beautiful, heavy and high-quality piano black appearance.
The abrasion test is a Taber abrasion test conducted on the surface of the molded body using a TABER CS-5 abrasion wheel under a load of 250 g under the condition of 200 revolutions. The L * value of the molded body surface after the abrasion test. Is measured using a color difference meter SE-6000 (light source: C-2) manufactured by Nippon Denshoku Co., Ltd. for any three points on the surface portion where the abrasion test was performed, and is expressed as an average value thereof. In addition, when measuring the L * value, standard alignment was performed using a white glass plate made of ceramic glass.

Furthermore, in the injection molded article of the present invention, the 20-degree specular gloss value of the surface of the molded article after the abrasion test is preferably 70 or more, and more preferably 75 or more. That is, since the injection-molded article of the present invention is excellent in scratch resistance, it has a high glossiness even after being subjected to a wear test. If the 20-degree specular gloss value after the abrasion test is less than 70, the glossiness is inferior, it becomes difficult to exhibit a piano black-like appearance, and the scratch resistance is inferior.
The 20-degree specular gloss value was measured with a Gloss Meter VG7000 manufactured by Nippon Denshoku Industries Co., Ltd., as described above. It is expressed as an average value.

  As described above, since the injection-molded article of the present invention satisfies the above-mentioned conditions, it can maintain a beautiful, heavy and high-quality piano black appearance for a long period of time.

  Furthermore, the injection-molded article of the present invention is excellent in heat resistance by containing an appropriate amount of cellulose fiber, and has a heat distortion temperature of 60 ° C. or higher at a load of 1.8 MPa, measured according to ASTM D648 of the molded article. Among them, the temperature is preferably 65 ° C. or higher. When the heat distortion temperature is less than 60 ° C., the heat resistance is inferior, and it is difficult to use in applications that are exposed to high temperatures such as automotive interior materials.

The injection-molded article of the present invention is further excellent in mechanical properties by containing an appropriate amount of cellulose fibers having a small average fiber diameter.
In the injection molded article of the present invention, the bending strength is preferably 65 MPa or more. In particular, when nylon 6 or nylon 66 is used as the polyamide resin, the bending strength is preferably 120 MPa or more, more preferably 130 MPa or more, and further preferably 140 MPa or more.
When bending strength is smaller than said value, it does not have sufficient intensity | strength and it becomes difficult to use it for various uses.

In the injection-molded article of the present invention, the flexural modulus is preferably 1.8 GPa or more. In particular, when nylon 6 or nylon 66 is used as the polyamide resin, the flexural modulus is preferably 2.5 GPa or more, more preferably 3.0 GPa or more, and more preferably 3.3 GPa or more. preferable.
When the flexural modulus is smaller than the above value, the rigidity is poor and the film becomes too soft. Therefore, even if the bending strength is within the above range, the versatility is poor, which is not practically preferable.

The injection-molded article of the present invention exhibits a piano black-like appearance as described above. For this purpose, it is preferable that the polyamide resin composition forming the injection-molded article contains a black pigment.
Examples of the black pigment in the present invention include black pigments and black dyes. Specific examples include carbon black, nigrosine, titanium-iron composite oxide, and aniline black. Two or more types of black pigments may be mixed and used.
The content of the black pigment in the injection-molded product is preferably 0.1 to 5 parts by mass and more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the polyamide resin. When the content of the black pigment is less than 0.1 parts by mass, it is difficult to make the appearance be piano black. On the other hand, when the content exceeds 5 parts by mass, the surface smoothness is inferior and the molded article is inferior in quality.
The black pigment is preferably mixed in a mixture composed of a polyamide resin and a cellulose fiber obtained by the method for preparing a polyamide resin composition in the present invention to be described later. Examples thereof include mixing by addition during polymerization.
Moreover, the method of melt-kneading the same kind polyamide resin and black pigment | dye mixture as the polyamide resin composition in this invention, and producing a master chip previously can also be used. If this method is used, the black pigment mixture can be added at a high concentration, and can also be added by dry blending during molding.

  Further, the polyamide resin composition in the present invention may contain other polymers as long as the characteristics are not significantly impaired. Examples of such other polymers include polybutadiene, butadiene-styrene copolymer, acrylic rubber, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, natural rubber, chlorinated butyl rubber, and chlorinated polyethylene. Elastomers, and acid-modified products thereof such as maleic anhydride, styrene-maleic anhydride copolymer, styrene-phenylmaleimide copolymer, polyvinyl chloride, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyvinylidene fluoride, polysulfone, Polyphenylene sulfide, polyether sulfone, phenoxy resin, polyphenylene ether, polymethyl methacrylate, polyether ketone, polyarylate, polycarbonate, polytetrafluoroethylene And the like.

  Furthermore, in the polyamide resin composition of the present invention, layered silicates such as swellable mica, non-swellable mica, and synthetic smectite, glass fiber, carbon fiber, talc, clay, mica, A reinforcing material such as wollastonite, calcium carbonate, and barium sulfate, a heat stabilizer, an antioxidant, a weathering agent, a flame retardant, a plasticizer, a crystal nucleating agent, a mold release stabilizer, and the like may be contained.

Next, the manufacturing method of the polyamide resin composition in this invention is demonstrated.
In producing the polyamide resin composition in the present invention, it is preferable to prepare a polyamide resin and cellulose fibers in advance by the following method. That is, it is possible to obtain a polyamide resin and a cellulose fiber by conducting a polymerization reaction of a monomer constituting the polyamide resin in the presence of cellulose fiber having an average fiber diameter of 10 μm or less and containing water. preferable. For example, it is preferable to perform a polymerization reaction by mixing a monomer constituting the polyamide resin and an aqueous dispersion of cellulose fibers having an average fiber diameter of 10 μm or less.

  The aqueous dispersion of cellulose fibers in this preparation method is obtained by dispersing cellulose fibers having an average fiber diameter of 10 μm or less in water, and the content of cellulose fibers in the aqueous dispersion is 0.01 to 50% by mass. It is preferable to do. The aqueous dispersion of cellulose fibers can be obtained by stirring purified water and cellulose fibers with a mixer or the like.

  And the aqueous dispersion of a cellulose fiber and the monomer which comprises a polyamide resin are mixed, and it is set as a uniform dispersion by stirring with a mixer etc. Thereafter, the dispersion is heated, and the temperature is raised to 150 to 270 ° C., followed by a polymerization reaction by stirring. At this time, water in the aqueous dispersion of cellulose fibers can be discharged by gradually discharging water vapor when the dispersion is heated. In the polyamide polymerization, a catalyst such as phosphoric acid or phosphorous acid may be added as necessary. Further, a black pigment may be added during the polyamide polymerization. And after completion | finish of a polymerization reaction, after paying out the obtained resin composition, it is preferable to cut | disconnect and pelletize.

  Further, when bacterial cellulose is used as the cellulose fiber, a cellulose fiber aqueous dispersion obtained by immersing bacterial cellulose in purified water and replacing the solvent may be used. When using a solvent-substituted bacterial cellulose, it is preferable to adjust the solvent concentration to a predetermined concentration and then mix with the monomer constituting the polyamide resin and proceed the polymerization reaction in the same manner as described above.

  In such a preparation method, cellulose fibers having an average fiber diameter of 10 μm or less are used, and the cellulose fibers are subjected to a polymerization reaction in an aqueous dispersion, thereby being subjected to a polymerization reaction with good dispersibility. Become. Furthermore, the cellulose fibers subjected to the polymerization reaction are improved in dispersibility by agitation with the monomer and water during the polymerization reaction and by stirring at the above temperature conditions, and the fibers aggregate. It is possible to obtain a mixture in which cellulose fibers having a small average fiber diameter are well dispersed. Thus, according to this preparation method, since the dispersibility of the cellulose fibers is improved, it is contained in the mixture after the completion of the polymerization reaction, rather than the average fiber diameter and fiber length of the cellulose fibers added before the polymerization reaction. Cellulosic fibers may have a smaller average fiber diameter and fiber length.

  Moreover, in this preparation method, the process of drying a cellulose fiber becomes unnecessary, and since it can manufacture without passing through the process which the scattering of a fine cellulose fiber produces, it becomes possible to obtain a mixture with sufficient operativity. Moreover, since it is not necessary to replace water with an organic solvent for the purpose of uniformly dispersing the monomer and cellulose, the handling is excellent and the discharge of chemical substances can be suppressed during the production process.

Next, the manufacturing method of the injection molded body of the present invention will be described.
The injection-molded article of the present invention is obtained by injection-molding the above-mentioned polyamide resin composition. As the injection molding conditions, the cylinder temperature is preferably 180 to 280 ° C, and more preferably 220 to 270 ° C, The temperature is preferably 20 to 140 ° C, and more preferably 60 to 120 ° C.
And in this invention, it is preferable that the metal mold | die used in injection molding is what the surface was grind | polished. When the mold surface is polished with an abrasive, the abrasive particle size is preferably 1000 mesh or more, more preferably 3000 mesh or more, and even more preferably 5000 mesh or more. When injection molding is performed using a mold whose surface is polished with an abrasive having a particle size of less than 1000 mesh, the appearance of the resulting injection molded article may not be like piano black.
In addition, when the resin composition containing inorganic fiber like glass fiber is injection-molded, the mold surface may be damaged. However, since the polyamide resin composition in the present invention contains cellulose fibers that are soft organic fibers as a fiber component, even if it is injection molded using a mold that is mirror-finished by surface polishing as described above, A molded body having a piano black-like appearance can be obtained with good operability without damaging the mold.

  The injection-molded article of the present invention has a piano black-like appearance, high hardness, and excellent scratch resistance and heat resistance. Therefore, the injection-molded article should be suitably used as a housing for various electrical appliances and an interior material for automobiles. Can do.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.
The measurement methods and evaluation methods for various characteristic values in the examples of the present invention are as follows.
(1) Average fiber diameter of cellulose fiber (1.1) Average fiber diameter of cellulose fiber before polymerization reaction Cellulose fibers freeze-dried as necessary were subjected to a field emission scanning electron microscope (S-4000 manufactured by Hitachi, Ltd.). ). The length in the direction perpendicular to the longitudinal direction of the cellulose fiber (single fiber) was measured from an electron microscope (SEM) image. At this time, the maximum of the lengths in the vertical direction was taken as the fiber diameter. Similarly, the fiber diameter of 10 cellulose fibers (single fibers) was measured, and the average value of 10 fibers was calculated as the average fiber diameter.
(1.2) Average fiber diameter of cellulose fibers in injection-molded body A 100 nm-thick section was collected from the injection-molded body using a frozen ultramicrotome, stained with OsO ₄ (osmium tetroxide), and permeated. Observation was performed using a scanning electron microscope (JEM-1230 manufactured by JEOL Ltd.). The length in the direction perpendicular to the longitudinal direction of the cellulose fiber (single fiber) was measured from the electron microscope image. At this time, the maximum of the lengths in the vertical direction was taken as the fiber diameter. Similarly, the fiber diameter of 10 cellulose fibers (single fibers) was measured, and the average value of 10 fibers was calculated as the average fiber diameter.
In addition, about the thing with a large fiber diameter of a cellulose fiber, it observes using a stereomicroscope (OLYMPUS SZ-40) in the state which cut out the 10 micrometers section | slice with the microtome, or an injection-molded body as it is, and obtained. The fiber diameter was measured in the same manner as described above from the obtained image, and the average fiber diameter was determined.

(2) L * value of the surface of the injection-molded product after the wear test After the following wear test was performed on the obtained injection-molded product, the L * value of the surface portion on which the wear test was performed was determined by the above method. It was measured.
(Abrasion test)
Taber abrasion test performed on the surface of an injection molded body using a TABER CS-5 abrasion wheel under a load of 250 g and 200 revolutions.

(3) 20 degree specular gloss value of the surface of the molded body It was measured by the method described above.
Further, the 20-degree specular gloss value of the surface of the molded article after the wear test was measured by the above method for the surface portion on which the wear test was performed after the wear test described in (2) above.

(4) Pencil hardness on the surface of the injection-molded product was measured by the method described above.

(5) Thermal deformation temperature of injection molded body Test piece of the obtained injection molded body (length x width x thickness = 127 mm (5 inches) x 12.7 mm (1/2 inch) x 3.2 mm (1 / 8 inch)) and measured by the above method.

(6) Bending strength and flexural modulus of injection molded body Test piece of the obtained injection molded body (length x width x thickness = 127 mm (5 inches) x 12.7 mm (1/2 inch) x 3.2 mm (1/8 inch)), and the bending strength and the flexural modulus were measured at 23 ° C. according to ASTM D790.

Example 1
As an aqueous dispersion of cellulose fibers, serisch KY110N (manufactured by Daicel Finechem Co., Ltd .: containing 15% by mass of cellulose fibers having an average fiber diameter of 150 nm) was added to this, and purified water was added thereto, followed by stirring with a mixer. An aqueous dispersion having a fiber content of 3% by mass was prepared.
40 parts by mass of the aqueous dispersion of cellulose fibers and 120 parts by mass of ε-caprolactam were further stirred and mixed with a mixer until a uniform dispersion was obtained. Subsequently, the mixed dispersion was heated to 240 ° C. with stirring, and the pressure was increased from 0 MPa to 0.7 MPa while gradually releasing water vapor. Thereafter, the pressure was released to atmospheric pressure, and a polymerization reaction was carried out at 240 ° C. for 1 hour. When the polymerization was completed, it was discharged and cut to obtain a pellet containing polyamide resin and cellulose fiber. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Dry blending of the obtained pellets and a black pigment mixture (total 0.5 parts by mass) composed of carbon black having a quantity of 0.15 parts by mass and nigrosine being 0.35 parts by mass with respect to 100 parts by mass of the polyamide resin A resin composition was produced. At this time, a polyamide chip and a black pigment mixture previously formed into a master chip by melt kneading were used.
The resin composition is put into an injection molding machine (FANUC S-2000i), and the surface is polished with an abrasive having a particle size of 1000 mesh under the conditions of a cylinder temperature of 260 ° C and a mold temperature of 80 ° C. The molded product was obtained by injection molding using a mold. Using the obtained injection-molded product, L * value, specular gloss value, and pencil hardness were measured. Further, FIG. 3 shows the surface of the molded article after measuring the pencil hardness (taken using a SU8020 field emission scanning electron microscope manufactured by Hitachi High-Technologies Corporation). .

Example 2
In the same manner as in Example 1, except that Celish KY110N was used, an aqueous dispersion having a cellulose fiber content of 6% by mass was prepared, and this aqueous dispersion of cellulose fiber was used. Polymerization was performed to obtain pellets containing polyamide resin and cellulose fibers. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Example 3
In the same manner as in Example 1, serisch KY110N was used to prepare an aqueous dispersion having a cellulose fiber content of 10% by mass. An aqueous dispersion of this cellulose fiber was 60 parts by mass, and ε-caprolactam was 120 parts by mass. Except that was used, polymerization was performed in the same manner as in Example 1 to obtain pellets containing polyamide resin and cellulose fibers. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Production Example 1: Production of bacterial cellulose 50 ml of a medium composed of 0.5 mass% glucose, 0.5 mass% polypeptone, 0.5 mass% yeast extract and 0.1 mass% magnesium sulfate heptahydrate was added to 200 ml. The solution was dispensed into a conical flask and steam sterilized at 120 ° C. for 20 minutes in an autoclave. One platinum ear of Gluconacetobacter xylinus (NBRC 16670) grown on a test tube slant agar medium was inoculated, and left to stand at 30 ° C. for 7 days. Seven days later, a white gel film-like bacterial cellulose was formed in the upper layer of the culture solution.

Example 4
The bacterial cellulose obtained in Production Example 1 was used as the cellulose fiber. Bacterial cellulose was crushed with a mixer, and then water substitution was performed by repeating immersion and washing with water. Using 4 parts by mass of an aqueous dispersion of bacterial cellulose after water replacement (containing 6.5% by mass of bacterial cellulose having an average fiber diameter of 60 nm), 130 parts by mass of ε-caprolactam and 35 parts by mass of purified water Then, polymerization was carried out in the same manner as in Example 1 to obtain pellets containing polyamide resin and cellulose fibers. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Example 5
In the same manner as in Example 4, an aqueous dispersion of bacterial cellulose after water replacement was prepared, and 10 parts by mass of this aqueous dispersion, 130 parts by mass of ε-caprolactam, and 30 parts by mass of purified water were uniformly dispersed. The mixture was stirred and mixed with a mixer until it became liquid, and polymerization was performed in the same manner as in Example 1 to obtain pellets containing polyamide resin and cellulose fibers. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Example 6
In the same manner as in Example 4, an aqueous dispersion of bacterial cellulose after water replacement was prepared, and 20 parts by mass of this aqueous dispersion, 130 parts by mass of ε-caprolactam, and 30 parts by mass of purified water were uniformly dispersed. The mixture was stirred and mixed with a mixer until it became liquid, and polymerization was performed in the same manner as in Example 1 to obtain pellets containing polyamide resin and cellulose fibers. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Example 7
Purified water was added to the aggregate of cellulose fibers produced as waste yarn in the nonwoven fabric manufacturing process, and the mixture was stirred with a mixer to prepare an aqueous dispersion containing 3% by mass of cellulose fibers having an average fiber diameter of 120 nm.
170 parts by mass of this aqueous dispersion of cellulose fibers, 255 parts by mass of ε-caprolactam, and 30 parts by mass of purified water were stirred and mixed with a mixer until a uniform dispersion was obtained, and polymerization was conducted in the same manner as in Example 1. And a pellet containing polyamide resin and cellulose fiber was obtained. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.

Example 8
Purified water was added to an aggregate of cellulose fibers extracted as waste yarn in the nonwoven fabric manufacturing process, and the mixture was stirred with a mixer to prepare an aqueous dispersion containing 6% by mass of cellulose fibers having an average fiber diameter of 3240 nm.
425 parts by mass of this aqueous dispersion of cellulose fiber, 510 parts by mass of ε-caprolactam, and 30 parts by mass of purified water were stirred and mixed with a mixer until a uniform dispersion was obtained, and polymerization was conducted in the same manner as in Example 1. And a pellet containing polyamide resin and cellulose fiber was obtained. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Example 9
In the same manner as in Example 8, purified water was added to the aggregate of cellulose fibers produced as waste yarn in the nonwoven fabric production process, and the mixture was stirred with a mixer, and 10 mass% of cellulose fibers having an average fiber diameter of 3240 nm were contained. An aqueous dispersion was prepared.
204 parts by mass of this aqueous dispersion of cellulose fiber, 255 parts by mass of ε-caprolactam, and 30 parts by mass of purified water were stirred and mixed with a mixer until a uniform dispersion was obtained, and polymerization was conducted in the same manner as in Example 1. And a pellet containing polyamide resin and cellulose fiber was obtained. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Example 10
Polymerization was carried out in the same manner as in Example 3 to obtain pellets containing polyamide resin and cellulose fibers. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for dry blending a black pigment mixture (1.0 parts by mass in total) consisting of carbon black having a mass of 0.3 parts by mass and nigrosine being 0.7 parts by mass with respect to 100 parts by mass of the polyamide resin, Example 3 and A resin composition was produced in the same manner, and then injection molded under the same conditions as in Example 3 to obtain a molded body.

Example 11
Using the resin composition obtained by dry blending the pellets and the black pigment mixture obtained in Example 1, using a mold whose surface is polished with an abrasive having a particle size of 8000 mesh and finished with a mirror finish, injection molding is performed. Except that, injection molding was performed under the same conditions as in Example 1 to obtain a molded body.

Comparative Example 1
Polymerization was carried out in the same manner as in Example 1 except that an aqueous dispersion of cellulose fibers was not added to obtain polyamide resin pellets. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Comparative Example 2
As an aqueous dispersion of cellulose fibers, serisch KY100S (manufactured by Daicel Finechem Co., Ltd .: containing 25% by mass of cellulose fibers having an average fiber diameter of 180 nm) was added to this, and purified water was added thereto, followed by stirring with a mixer. An aqueous dispersion having a fiber content of 15% by mass was prepared.
The cellulose fiber aqueous dispersion 208 parts by mass, ε-caprolactam 260 parts by mass and purified water 30 parts by mass were stirred and mixed with a mixer until a uniform dispersion was obtained, and polymerization was carried out in the same manner as in Example 1. A pellet containing polyamide resin and cellulose fiber was obtained. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Comparative Example 3
Using the pellets obtained in Comparative Example 2 treated with hot water, scoured, and dried, the amount of carbon black relative to 100 parts by mass of the polyamide resin is 0.3 parts by mass and 0.7 parts by mass. A resin composition was produced in the same manner as in Comparative Example 2, except that a black pigment mixture composed of nigrosine (1.0 parts by mass in total) was dry blended, and then injection-molded under the same conditions as in Comparative Example 2, A molded body was obtained.

Comparative Example 4
As the cellulose fiber, serisch KY110N (manufactured by Daicel Finechem Co., Ltd .: cellulose fiber having an average fiber diameter of 150 nm containing 15% by mass) was freeze-dried and then pulverized to prepare a powder.
A twin screw extruder having a screw diameter of 30 mm and an average groove depth of 2.5 mm is blended with 100 parts by mass of nylon 6 (BRL number average molecular weight 17000 manufactured by Unitika Ltd.) and 2 parts by mass of the obtained powdery cellulose. (PCM-30 manufactured by Ikegai Co., Ltd.) and melt kneaded at a barrel temperature of 240 ° C., a screw rotation speed of 120 rpm, and a residence time of 2.7 minutes. The melt-kneaded product was discharged, cut into pellets, and the resulting pellets were dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Comparative Example 5
Cotton short fibers (average fiber diameter: 16 μm) were used as cellulose fibers, purified water was added, and the mixture was stirred with a mixer to prepare an aqueous dispersion having a cellulose fiber content of 10 mass%.
52 parts by mass of this aqueous dispersion of cellulose fibers, 260 parts by mass of ε-caprolactam, and 30 parts by mass of purified water were stirred and mixed with a mixer until a uniform dispersion was obtained, and polymerization was carried out in the same manner as in Example 1. A pellet containing polyamide resin and cellulose fiber was obtained. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.

Comparative Example 6
254 parts by mass of ε-caprolactam, 25.4 parts by mass of water, 12.7 parts by mass of layered silicate (swelling fluorine mica, Somasif ME-100 manufactured by Corp Chemical Co.), and 0.25 parts by mass of phosphorous acid ( While stirring at 80 ° C., the mixture was stirred and mixed with a homogenizer until a uniform solution was obtained. Subsequently, the mixed solution was heated to 240 ° C. with stirring, and the pressure was increased from 0 MPa to 0.7 MPa while gradually releasing water vapor. Thereafter, the pressure was released to atmospheric pressure, and a polymerization reaction was carried out at 240 ° C. for 1 hour. When the polymerization was completed, it was discharged and cut to obtain pellets containing polyamide resin and layered silicate. The obtained pellets were treated with hot water at 95 ° C., scoured and dried.
Except for using the obtained pellets, a black pigment mixture was dry blended to produce a resin composition in the same manner as in Example 1, and then injection molding was performed under the same conditions as in Example 1. Got.
The surface of the molded product after measuring the pencil hardness of the obtained molded product (photographed using a SU8020 field emission scanning electron microscope manufactured by Hitachi High-Technologies Corp.) Is shown in FIG.

Comparative Example 7
Nylon 6 (Unitika BRL number average molecular weight 17000) 100 parts by mass is blended with 5 parts by mass of glass fiber T-262H (fiber diameter 10.5 μm, length 3 mm) manufactured by Nippon Electric Glass Co., Ltd. The mixture was supplied to a twin-screw extruder (PCM-30 manufactured by Ikegai Co., Ltd.) having an average groove depth of 30 mm and melted and kneaded at a barrel temperature of 270 ° C., a screw rotation speed of 120 rpm, and a residence time of 2.7 minutes. The melt-kneaded product was discharged, cut into pellets, and the resulting pellets were dried.
A resin composition was produced in the same manner as in Example 1 except that the obtained pellets were used, and then injection molding was performed under the same conditions as in Example 1 to obtain a molded body.

  Table 1 shows the results of measuring the characteristic values of the injection molded articles obtained in Examples 1 to 11 and Comparative Examples 1 to 7.

Since the molded bodies obtained in Examples 1 to 11 were obtained by using a composition in which fine cellulose fibers were uniformly dispersed in a polyamide resin without agglomeration, cellulose fibers having an average fiber diameter of 10 μm or less And the characteristic values specified in the present invention were satisfied. In other words, it had a beautiful, heavy, high-quality piano black appearance, high hardness, scratch resistance, and heat resistance.
Since the molded product of Example 3 has a high cellulose fiber content, the L * value of the molded product surface increased to nearly 4 after the abrasion test. By increasing, the L * value on the surface of the molded body could be lowered, and the 20-degree specular gloss value on the surface of the molded body could be improved.
In Example 11, when injection molding was performed using a mold whose surface was polished with an abrasive having a particle size of 8000 mesh and finished with a mirror finish, the L * value was lower than that in Example 1, and the specular gloss was low. A molded product having a high value was obtained.

On the other hand, since the molded body obtained in Comparative Example 1 did not contain cellulose fibers, it was inferior in heat resistance.
In the molded product obtained in Comparative Example 2, since the resin composition contained excessive cellulose fibers, the molded product surface was floated, the surface appearance was poor, and the molded product was both before and after the wear test. The surface was inferior to the 20-degree specular gloss value.
The molded body obtained in Comparative Example 3 was obtained by increasing the black pigment content as compared with Comparative Example 2, but no improvement in the 20-degree specular gloss value on the surface of the molded body was observed.
Since the molded body obtained in Comparative Example 4 used a resin composition obtained by melt-kneading polyamide resin and cellulose fiber, aggregation of cellulose fibers occurred, and cellulose fibers having an average fiber diameter exceeding 10 μm were contained. It became. For this reason, the 20-degree specular gloss value of the molded body surface was inferior, and the heat resistance was also inferior.
Since the molded body obtained in Comparative Example 5 contained cellulose fibers having an average fiber diameter of more than 10 μm, the obtained molded body had an inferior 20 ° specular gloss value on the surface of the molded body, and was heat resistant. The property was also inferior.
Since the molded body obtained in Comparative Example 6 did not contain cellulose fibers, but instead contained layered silicate, it was inferior in scratch resistance as apparent from FIG. The L * value and 20-degree specular gloss value of the molded body surface were inferior, and the pencil hardness was also inferior.
Since the molded body obtained in Comparative Example 7 did not contain cellulose fibers but instead contained glass fibers, the surface appearance was inferior, and the 20-degree specular gloss value of the molded body surface was inferior. . In addition, when the glass fiber-containing resin composition is injection-molded on a mold whose surface is polished with an abrasive of 1000 mesh or more, the mold surface is scratched, and then the molded product obtained by injection molding is scratched on the surface. Was transcribed.

Claims (1)

A molded body formed by injection molding a polyamide resin composition containing 0.1 to 10 parts by mass of cellulose fibers with respect to 100 parts by mass of a polyamide resin,
The average fiber diameter of the cellulose fibers in the molded body is 10 μm or less,
The thermal deformation temperature at a load of 1.8 MPa, measured according to ASTM D648 of the molded body, is 60 ° C. or higher,
The 20-degree specular gloss value of the molded body surface is 70 or more,
The pencil hardness measured according to JIS-K-5600-5-4 on the surface of the molded body is 2B or more,
L * value of the molding surface, after following abrasion test, a method for producing a molded article out morphism Ru der 4 or less,
A method for producing an injection-molded article, wherein the injection molding of the polyamide resin composition is performed using a mold whose surface is polished with an abrasive having a particle size of 1000 mesh or more .
Abrasion test: Taber abrasion test performed on the surface of the molded body using a CSBER wear wheel manufactured by TABER under the condition of 200 rotations under a load of 250 g.