JP2007031484A - Polyamide resin composition for engine cover and the engine cover produced by using the composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyamide resin composition excellent in moldability and capable of being molded into an engine cover reduced in weight, hanving high rigidity and high heat resistance, and having impact resistance as well, especially having excellent impact resistance at a low temperature, and to provide the engine cover produced by using the composition. <P>SOLUTION: This polyamide resin composition for the engine cover contains at least two kinds of polyamide resins having relative viscosities different from each other and a swelling lamellar silicate salt, wherein a mixture of the polyamide resins contained therein has a relative viscosity of ≥2.6. The engine cover is produced by using the polyamide resin composition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polyamide resin composition for an engine cover and an engine cover manufactured using the composition.

  In recent years, automobiles frequently use injection-molded products made of resin materials in order to achieve both weight reduction and productivity for realizing excellent fuel efficiency. Conventionally, the plasticization of parts made of metal materials has extended to parts in engine rooms that are exposed to harsh environments in terms of temperature and other conditions. Today, various parts are produced with resin materials. Yes. Among these, the engine cover is most prominently made of resin, and is a component for the purpose of preventing engine noise and vibration and improving design.

  As engine cover resin materials, polyamide resin compositions such as polyamide 6 resin and polyamide 66 resin reinforced with glass fiber have been used so far. This is because it is a material that meets a wide range of required performance such as impact resistance and recyclability in addition to high heat resistance because it is a component installed directly above the cylinder head. However, in order to meet the demand for further weight reduction, there has been a limit in the conventional reinforcing material made of glass fiber or inorganic filler. On the other hand, reduction of production cost from a viewpoint different from performance is also a potentially great demand, and materials that meet this demand have a simple material composition and excellent productivity (injection moldability, recyclability, etc.). Need to be. Of course, it goes without saying that material properties essential for an engine cover are developed.

  Under such a background, an engine cover using a polyamide composite material in which a silicate layer of a swellable layered silicate is dispersed in a polyamide resin at a molecular level has been proposed (see Patent Documents 1 and 2). However, these polyamide composite materials still have room for improvement in impact resistance, and the development of impact resistance particularly at low temperatures has been a major issue.

Various attempts to improve the impact resistance of such polyamide composite materials have been proposed. For example, according to a mixture with an impact resistance improving material made of an olefin copolymer (see Patent Document 3), the polyamide composite material The impact resistance can be greatly improved. However, in this method, contrary to the improvement in impact resistance, the excellent heat resistance and rigidity inherent in the polyamide composite material tend to decrease, which is not preferable in terms of material properties. On the other hand, the present inventors have attempted to improve impact resistance mainly by modifying the polyamide composite material itself, for example, increasing the molecular weight of the matrix resin during the production of the polyamide composite material (see Patent Document 4) or swelling property. Optimization of the cation exchange capacity and initial particle size of the layered silicate has been proposed (see Patent Document 5). Although these polyamide composite materials were effective in improving impact resistance as a result, there was still room for further improvement in terms of injection moldability or the balance between impact resistance and heat resistance / rigidity.
JP-A-2-240160 JP-A-11-303678 Japanese Patent No. 2528163 JP-A-11-172100 International Publication WO02 / 50187

  The present invention provides a polyamide resin composition for an engine cover that can form a molded article having excellent moldability, light weight, high rigidity, and high heat resistance, as well as excellent impact resistance, particularly impact resistance at low temperatures. And providing an engine cover manufactured using the composition.

  The present invention is an engine cover characterized in that it contains at least two kinds of polyamide resins having different relative viscosities and a swellable layered silicate, and the relative viscosity of the contained polyamide resin mixture is 2.6 or more. The present invention relates to a polyamide resin composition and an engine cover manufactured using the polyamide resin composition.

  According to the polyamide resin composition for an engine cover of the present invention, an engine cover having excellent moldability, light weight, high rigidity, and high heat resistance, as well as excellent impact resistance, particularly low temperature impact resistance. Obtainable.

  The polyamide resin composition for engine covers of the present invention comprises at least two types of polyamide resins having different relative viscosities and a swellable layered silicate, and the relative viscosity of the contained polyamide resin mixture is 2.6 or more, particularly 2.6 to 3.5, preferably 2.7 to 3.4. If the relative viscosity of the polyamide resin mixture (hereinafter simply referred to as the mixed polyamide resin) is less than 2.6, the impact resistance of the molded article made of the polyamide resin composition tends to be inferior. It is not preferable as a resin composition.

  The relative viscosity of the mixed polyamide resin is the relative viscosity of the mixture of all the polyamide resins contained in the polyamide resin composition, and can be calculated as a weighted average value of the relative viscosities of the individual polyamide resins. For example, the relative viscosity (weighted average value) of a mixed polyamide resin comprising 30% by weight of a polyamide resin having a relative viscosity of 2.8 and 70% by weight of a polyamide resin having a relative viscosity of 3.1 is 3.01.

  In this specification, the relative viscosity of the polyamide resin is a value measured under the conditions of a temperature of 25 ° C. and a concentration of 1 g / dl using 96 mass% concentrated sulfuric acid as a solvent.

  The individual relative viscosities of at least two types of polyamide resins contained in the polyamide resin composition may be different from each other as long as the relative viscosities of the mixed polyamide resins are within the above range. From the viewpoint of achieving both impact resistance, rigidity and heat resistance, polyamide resin A having a relative viscosity of 2.0 or more and less than 3.0 and polyamide resin B having a relative viscosity of 3.0 or more and 4.0 or less should be used. Is preferred. By using at least two types of polyamide resins having different relative viscosities, it is possible to more effectively achieve both excellent impact resistance, particularly low temperature impact resistance, high rigidity and heat resistance in the obtained molded product.

From the viewpoint of achieving both impact resistance, rigidity and heat resistance, it is particularly preferable that the polyamide resins A and B have a relative viscosity below.
Polyamide resin A; relative viscosity 2.3 to less than 3.0, preferably 2.5 to 2.9, more preferably 2.7 to 2.9;
Polyamide resin B; relative viscosity of 3.0 or more and 3.8 or less, preferably 3.1 or more and 3.8 or less, more preferably 3.1 or more and 3.4 or less.

  The blending ratio of the polyamide resin A and the polyamide resin B is not particularly limited as long as the relative viscosity of the mixed polyamide resin is within the above range, and is usually 20:80 to 95: 5, particularly 30 by weight ratio (A: B). : It is preferable that it is 70-80: 20.

The polyamide resins A and B may each independently be a polyamide resin as shown below.
The polyamide resin is a polymer having an amide bond in the main chain, the main raw material of which is aminocarboxylic acid, lactam or diamine and dicarboxylic acid (including a pair of salts thereof). Specific examples of the raw materials include aminocarboxylic acids such as 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and paraaminomethylbenzoic acid. Examples of the lactam include ε-caprolactam, ω-undecanolactam, and ω-laurolactam. Examples of the diamine include tetramethylene diamine, hexamethylene diamine, undecamethylene diamine, dodecamethylene diamine, 2,2,4- / 2,4,4-trimethylhexamethylene diamine, 5-methylnonamethylene diamine, 2,4- Dimethyloctamethylenediamine, metaxylylenediamine, paraxylylenediamine, 1,3-bis (aminomethyl) cyclohexane, bis (4-aminocyclohexyl) methane, bis (3-methyl-4-aminocyclohexyl) methane, 2, There are 2-bis (4-aminocyclohexyl) propane, bis (aminopropyl) piperazine, aminoethylpiperazine and the like. Examples of the dicarboxylic acid include adipic acid, speric acid, azelaic acid, sebacic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, and 5-sodium sulfone. Examples include isophthalic acid, hexahydroterephthalic acid, and hexahydroisophthalic acid. These diamines and dicarboxylic acids can also be used as a pair of salts.

  Preferred examples of such polyamide resin include polycaproamide (nylon 6), polytetramethylene adipamide (nylon 46), polyhexamethylene adipamide (nylon 66), polycaproamide / polyhexamethylene adipamide copolymer (Nylon 6/66), polyundecamide (nylon 11), polycaproamide / polyundecamide copolymer (nylon 6/11), polydodecamide (nylon 12), polycaproamide / polydodecamide copolymer (nylon 6/12), Polyhexamethylene sebacamide (nylon 610), polyhexamethylene dodecamide (nylon 612), polyundecamethylene adipamide (nylon 116), polyhexamethylene isophthalamide (nylon 6I), polyhexamethylene terephthalate Mido (nylon 6T), polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer (nylon 6T / 6I), polycaproamide / polyhexamethylene terephthalamide copolymer (nylon 6 / 6T), polycaproamide / polyhexamethylene isophthalate Amide copolymer (nylon 6 / 6I), polyhexamethylene adipamide / polyhexamethylene terephthalamide copolymer (nylon 66 / 6T), polyhexamethylene adipamide / polyhexamethylene isophthalamide copolymer (nylon 66 / 6I), poly Trimethylhexamethylene terephthalamide (nylon TMDT), polybis (4-aminocyclohexyl) methane dodecamide (nylon PACM12), polybis (3-methyl-4-amino) Cyclohexyl) methane dodecamide (nylon dimethyl PACM12), poly-m-xylylene terephthalamide (nylon MXD6), polyundecamethylene terephthalamide (nylon 11T), and mixtures thereof or copolymers thereof. Of these, nylon 6 and nylon 66 are particularly preferable.

  The swellable lamellar silicate has a structure composed of a negatively charged crystal layer mainly composed of silicate and a cation having ion exchange ability interposed between the layers. By including the swellable layered silicate, an effect of improving rigidity and heat resistance can be obtained, and as a result, it is possible to effectively achieve both impact resistance, rigidity and heat resistance. The swellable layered silicate desirably has a cation exchange capacity determined by the method described later of 50 meq / 100 g or more. When the cation exchange capacity is less than 50 meq / 100 g, the swelling ability is low, and therefore, the molding performance using the polyamide resin composition of the present invention remains substantially in an uncleavage state, and an improvement in performance is recognized. I can't. In the present invention, the upper limit of the value of the cation exchange capacity is not particularly limited, and an appropriate one may be selected from swellable layered silicates that can be actually prepared.

  Such swellable layered silicates may be naturally occurring, artificially synthesized or modified, for example, smectites (montmorillonite, beidellite, hectorite, soconite, etc.), vermiculites (vermiculite, etc.), mica Family (fluorine mica, muscovite, paragonite, phlogopite, lepidrite, etc.), brittle mica family (margarite, clintonite, anandite, etc.), chlorite (donbasite, sudoite, kukeite, clinochlore, chamonite, nimite, etc.) In the present invention, Na-type or Li-type swellable fluorine mica and montmorillonite are particularly preferably used.

The swellable fluoromica preferably used in the present invention generally has a structural formula represented by the following formula;
M _α (Mg _X Li _β ) Si ₄ O _Y F _Z
(In the formula, M represents an ion-exchangeable cation, specifically sodium or lithium. Α, β, X, Y, and Z each represents a coefficient, and 0 ≦ α ≦ 0.5. 0 ≦ β ≦ 0.5, 2.5 ≦ X ≦ 3, 10 ≦ Y ≦ 11, and 1.0 ≦ Z ≦ 2.0.

  As a method for producing such a swellable fluorine mica, for example, silicon oxide, magnesium oxide and various fluorides are mixed, and the mixture is completely melted in a temperature range of 1400 to 1500 ° C. in an electric furnace or a gas furnace. A melting method in which a crystal of swellable fluorinated mica grows in the reaction vessel during the cooling process.

On the other hand, there is also a method of using talc [Mg ₃ Si ₄ O ₁₀ (OH) ₂ ] as a starting material and intercalating alkali metal ions to impart swellability to obtain a swellable fluorine mica (Japanese Patent Laid-Open No. Hei. No. 2-149415). In this method, swellable fluoromica can be obtained by heat-treating talc and alkali silicofluoride mixed at a predetermined blending ratio in a magnetic crucible at a temperature of 700 to 1200 ° C. for a short time.

  At this time, the amount of alkali silicofluoride mixed with talc is preferably in the range of 10 to 35% by mass of the entire mixture. If it is out of this range, the yield of swellable fluorinated mica tends to decrease.

The montmorillonite used in the present invention is represented by the following formula, and can be obtained by refining a naturally produced product using a water treatment or the like;
M _a Si (Al _2-a Mg) O ₁₀ (OH) ₂ .nH ₂ O
(In the formula, M represents a cation such as sodium, and 0.25 ≦ a ≦ 0.6. Further, the number of water molecules bonded to the ion-exchangeable cation between layers depends on conditions such as cation species and humidity. In the formula, it is expressed as nH ₂ O).

  In addition, montmorillonite is known to have isomorphic ion substitution products such as magnesia montmorillonite, iron montmorillonite, iron magnesia montmorillonite, and these may be used.

  The initial particle size of the swellable layered silicate is not particularly limited. Here, the initial particle diameter is the particle diameter of the swellable layered silicate as a raw material used in producing the polyamide resin composition of the present invention, and the silicate in the molded article formed using the polyamide resin composition. It is different from the size of the layer. However, this particle size also has a considerable influence on the physical properties of the obtained molded product, in particular the rigidity and heat resistance. Therefore, it is desirable to take this point into consideration when selecting the mixing ratio of the swellable layered silicate described later, and it is preferable to control the particle size by pulverizing with a jet mill or the like as necessary. Here, when the swellable fluoromica mineral is synthesized by the intercalation method, the initial particle size can be changed by appropriately selecting the particle size of talc as a raw material. This is a preferable method in that the initial particle diameter can be adjusted in a wider range by using in combination with pulverization.

  The blending ratio of the swellable layered silicate is not particularly limited as long as the object of the present invention is achieved, and it is usually preferably 0.5 to 20% by mass with respect to the total amount of the polyamide resin composition of the present invention. It is more preferable to set it as 0.5-10 mass%. When the blending ratio is less than 0.5% by mass, the effect of adding the swellable layered silicate such as improvement in rigidity and heat resistance is poor. On the other hand, when the blending ratio exceeds 20% by mass, it is not preferable because it is difficult to dispense from the autoclave and the impact resistance is deteriorated.

  The mixing ratio of the swellable layered silicate with respect to the total composition can be measured as an inorganic ash content when the composition contains no inorganic component other than the swellable layered silicate.

  The polyamide resin composition of the present invention has any mixed form as long as it contains at least two types of polyamide resins having different relative viscosities (particularly polyamide resins A and B) and a swellable layered silicate. Good. For example, (1) a mixture form of composite particles obtained by melt-kneading and pulverizing all components, and (2) polyamide resin A composite particles and polyamide resin B in which a swellable layered silicate is contained and dispersed in polyamide resin A Examples include a mixture form in which particles are mixed, and (3) a mixture form in which polyamide resin B composite particles in which a swellable layered silicate is contained and dispersed in polyamide resin B and polyamide resin A particles are mixed. . Here, the dimension of the resin particles is not particularly limited, and for example, the maximum dimension of the particle cross section may be about 0.01 to 5 mm. The resin particles are used in a concept including so-called pellets. The mixing means in particular when obtaining a polyamide resin composition is not restrict | limited, For example, what is necessary is just to mix using a tumbler etc. There are no particular restrictions on the equipment or operating conditions.

  In the present invention, the polyamide resin composition preferably has the mixed form of (2) above from the viewpoint of more effectively improving the rigidity and heat resistance / impact resistance of the molded product.

  Among the mixed forms of (2) above, in consideration of production cost, the polyamide resin composition comprises polyamide resin A pellets and polyamide resin B containing a swellable layered silicate contained and dispersed in polyamide resin A. It is preferable that pellets are mixed. A polyamide resin composition capable of forming a molded product having desired rigidity, heat resistance and impact resistance by merely forming the reaction product into a pellet shape after synthesis of the polyamide resins A and B without undergoing melt kneading. This is because a product is obtained.

  The polyamide resin A composite particles are more preferably those in which a silicate layer of a swellable layered silicate is dispersed at a molecular level in a polyamide resin A matrix. Here, the silicate layer is a basic unit constituting the swellable layered silicate, and is a plate-like inorganic crystal obtained by breaking the layer structure of the swellable layered silicate (hereinafter referred to as “cleavage”). . The silicate layer in the present invention means each silicate layer or a state in which a polyamide molecular chain is inserted between the layers but the laminated structure is not completely broken. It does not have to be peeled to the sheet. In addition, when dispersed in the polyamide resin matrix, the swellable layered silicate silicate layer has an average distance of 1 nm or more, and does not form a lump with each other. The state that is. Here, the lump refers to a state in which the raw swellable layered silicate is not cleaved at all. The interlayer distance is the distance between the centers of gravity of the silicate layers. Such a state can be confirmed, for example, by observation with a transmission electron microscope for the test piece of the polyamide resin composition or the polyamide resin A composite particles.

  A method for producing polyamide resin A composite particles in which the swellable layered silicate is dispersed in the polyamide resin A at the molecular level will be described. Basically, a predetermined monomer is charged into an autoclave in the presence of an appropriately selected swellable layered silicate, and then an initiator such as water is used, at a temperature of 240 to 300 ° C., a pressure of 0.2 to 3 MPa, 1 to The melt polycondensation method may be used within a range of 15 hours. When the polyamide resin A is nylon 6, it is preferable to perform polymerization at a temperature of 250 to 280 ° C., a pressure of 0.5 to 2 MPa, and a range of 3 to 5 hours. After completion of the polymerization, the reaction product is usually discharged in a strand form, cooled and solidified, and then cut to obtain pellets. In order to remove the polyamide monomer remaining in the polyamide resin after polymerization, it is preferable to scour the polyamide resin A composite particles with hot water. In this case, the treatment is preferably performed in hot water at 90 to 100 ° C. for 8 hours or more.

  The compounding amount of the swellable layered silicate is not particularly limited as long as the object of the present invention is achieved, but from the viewpoint of improving the rigidity and heat resistance and the yield of the polyamide resin A, the polyamide resin A It is preferable to set it as 0.5-20 mass% with respect to the monomer which forms, and it is more preferable to set it as 0.5-10 mass%.

  Further, it is desirable to provide a step of mixing the above-described swellable layered silicate and a part of the polyamide monomer required for the polymerization of the polyamide resin A in a dispersion medium such as water, methanol, ethanol, ethylene glycol or the like. In general, the temperature condition in this step is preferably room temperature or, if necessary, room temperature or higher and below the boiling point of the dispersion medium, and it is desirable to use a homomixer, an ultrasonic dispersing machine, a high-pressure dispersing machine, or the like.

  In producing the polyamide resin A composite particles, an acid may be added. Generally speaking, it is preferable to add an acid because the cleavage of the swellable layered silicate is promoted and the dispersion of the silicate layer in the polyamide resin matrix further proceeds.

  The acid may be an organic acid or an inorganic acid if pKa (25 ° C., value in water) is 0 to 6 or a negative acid. Specifically, benzoic acid, sebacic acid, formic acid, acetic acid, chloro Examples include acetic acid, trichloroacetic acid, trifluoroacetic acid, nitrous acid, phosphoric acid, phosphorous acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, sulfuric acid, perchloric acid and the like.

  The amount of acid added is about 1.0 to 5.0 moles relative to the total cation exchange capacity of the swellable layered silicate used, and the cleavage of the swellable layered silicate and the polymerization in the polyamide resin matrix It is preferable from the point of action as a catalyst.

  The polyamide resin B particles may be obtained by an ordinary melt polymerization method regardless of batch type or continuous type. In the production method, after a predetermined monomer is charged into an autoclave, an initiator such as water is used, and melt polycondensation may be performed within a range of a temperature of 240 to 300 ° C., a pressure of 0.2 to 3 MPa, and a pressure of 1 to 15 hours. . When nylon 6 is used as the resin matrix, it is preferable to polymerize at a temperature of 250 to 280 ° C., a pressure of 0.5 to 2 MPa, and a range of 3 to 5 hours. In order to remove the polyamide monomer remaining in the polyamide resin after polymerization, it is preferable to scour the pellets of the polyamide resin with hot water. In this case, hot water at 90 to 100 ° C. Among them, the process for 8 hours or more may be performed.

  The polyamide resin composition of the present invention includes a heat stabilizer, an antioxidant, a reinforcing material, a pigment, an anti-coloring agent, a weathering agent, a flame retardant, a plasticizer, a crystal nucleating agent, a release agent, as long as the properties are not significantly impaired. Additives such as molds and other thermoplastic resins may be added.

  Examples of the heat stabilizer and the antioxidant include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, alkali metal halides, and mixtures thereof.

  Examples of reinforcing materials include clay, talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon, carbon black, zeolite, hydro Examples include talcite, metal fiber, metal whisker, ceramic whisker, potassium titanate whisker, boron nitride, graphite, glass fiber, and carbon fiber.

  Examples of the thermoplastic resin include polybutadiene, butadiene / styrene copolymer, acrylic rubber, ethylene / propylene copolymer, ethylene / propylene / diene copolymer, natural rubber, chlorinated butyl rubber, elastomer such as chlorinated polyethylene, and the like. Modified with maleic anhydride, styrene / maleic anhydride copolymer, styrene / phenylmaleimide copolymer, polyethylene, polypropylene, butadiene / acrylonitrile copolymer, polyvinyl chloride, polyethylene terephthalate, polyacetal, polyvinylidene fluoride, Polysulfone, polyphenylene sulfide, polyether sulfone, phenoxy resin, polyphenylene ether, polymethyl methacrylate, polyether ketone, polycarbonate, polytetrafur Roechiren, polyarylate, and the like.

  The mixed form of the additive is not particularly limited, and particularly when the polyamide resin composition has the mixed form of (2), the additive may be contained in the polyamide resin A composite particles, It may be contained in the polyamide resin B particles, or may be mixed with the polyamide resin A composite particles and the polyamide resin B particles as single component particles of the additive.

  When the engine cover is manufactured using the polyamide resin composition of the present invention, known molding such as injection molding, extrusion molding, compression molding or the like may be performed, but injection molding is performed from the viewpoint of manufacturing cost reduction. It is preferable. There are no particular restrictions on the resin temperature, mold temperature, injection pressure and injection speed. However, from the viewpoint of impact resistance of the engine cover, the influence of the mold temperature is large, and it is preferable to keep the mold temperature low within a range that does not impair the releasability and surface appearance. Specifically, the mold temperature is 100 ° C. or lower, preferably 80 ° C. or lower.

Hereinafter, the present invention will be described more specifically with reference to examples.
The measurement methods of the raw materials and physical property tests used in Examples and Comparative Examples are as follows.

1. Raw Material (1) Swellable Fluorine Mica (M-1)
To talc pulverized so as to have an average particle diameter of 4.0 μm by a ball mill, sodium silicofluoride having an average particle diameter of 10 μm was mixed so as to be 15% by mass of the total amount. This was put into a magnetic crucible and reacted at 850 ° C. for 1 hour in an electric furnace to obtain a swellable fluorine mica (M-1) having an average particle size of 4.0 μm. The composition of this swellable fluorinated mica was Na _0.60 Mg _2.63 Si ₄ O ₁₀ F _1.77 , and the cation exchange capacity obtained by the measurement method described later was 110 meq / 100 g.
(2) Polyamide resin (P-3)
“A1030BRF” manufactured by Unitika Ltd. was used. The relative viscosity measured by the viscosity measurement described later was 3.1. The product was in the form of pellets.
(3) Polyamide resin (P-4)
“A1030BRT” manufactured by Unitika Co., Ltd. was used. The relative viscosity by viscosity measurement described below was 3.4. The product was in the form of pellets.

2. Measuring method (1) Cation exchange capacity It calculated | required based on the cation exchange capacity | capacitance measuring method (JBAS-106-77) of bentonite (powder) by the Japan Bentonite Industry Association standard test method.
That is, using a device in which a leachate container, a leach tube, and a receiver are connected in a vertical direction, first, all of the ion-exchangeable cations between the layers are made with a 1N ammonium acetate aqueous solution in which the layered silicate is adjusted to pH = 7. Is replaced with NH ₄ ⁺ . Then, after thoroughly washing with water and ethyl alcohol, the above NH ₄ ⁺ type layered silicate is immersed in a 10% by mass potassium chloride aqueous solution, and NH ₄ ⁺ in the sample is exchanged for K ⁺ . To do. Subsequently, the NH ₄ ⁺ leached with the above-described ion exchange reaction was neutralized and titrated with a 0.1N aqueous sodium hydroxide solution to obtain a cation exchange capacity (milli equivalent / capacity of the swellable layered silicate as a raw material). 100 g).

(2) Inorganic ash content of polyamide resin composition The dry pellets of the polyamide resin composition are precisely weighed in a magnetic crucible, and the residue after incineration for 15 hours in an electric furnace maintained at 500 ° C is used as the inorganic ash, according to the following formula: The inorganic ash content was determined.
Inorganic ash content (mass%) = {inorganic ash mass (g)} / {total mass of sample before incineration (g)} × 100

(3) Relative viscosity (molecular weight) of polyamide resin
The polyamide resin dried pellets were dissolved in 96% by mass concentrated sulfuric acid so as to have a concentration of 1 g / dl, and the inorganic components were separated by filtration with a G-3 glass filter, followed by measurement. The measurement was performed at 25 ° C. using an Ubbelohde viscometer.

(4) Melt fluidity (flow length) of polyamide resin composition
Molding was performed under the conditions of a resin temperature of 240 ° C., a mold temperature of 80 ° C., and an injection pressure of 55 MPa using a dedicated mold with one-point gate on one side from which a spiral molded product having a thickness of 2 mm and a width of 20 mm can be collected. The length (mm) in the flow direction of the obtained molded product represents the melt fluidity of the test material under the molding conditions, and the relative fluidity was evaluated by comparing the materials. In addition, it represents that the fluidity | liquidity of material is so good that the flow length is large.
The flow length is 280 mm or more within a range where there is no practical problem, and preferably 300 mm or more.

(5) Rigidity (flexural modulus)
Measured based on ASTM D-790.
The bending elastic modulus is 3.0 GPa or more within a range where there is no practical problem, and preferably 3.3 GPa or more.

(6) Heat resistance (deflection temperature under load)
Based on ASTM D-648, the load was measured at 0.45 MPa.
The deflection temperature under load is 120 ° C. or higher within a range where there is no practical problem, and preferably 130 ° C. or higher.

(7) Impact resistance (surface impact strength)
The impact strength was evaluated by dropping a weight from a predetermined height onto a molded product as shown in FIG. 1 using a DuPont impact tester. At this time, the portion directly giving an impact force to the molded product was a disk having a diameter of 30 mm and a thickness of 5 mm, and surface impact was applied. The impact resistance was quantified by calculating the maximum applied energy (J) at which the molded product did not break under an atmosphere of −30 ° C. under a condition consisting of a combination of a predetermined height and a weight load.
G = (maximum height at which the specimen does not break) x (gravity acceleration) x (weight load)
The surface impact strength is within a range where there is no practical problem of 5.0 J or more, and preferably 5.4 J or more.

[Synthesis Example 1] Polyamide resin (P-1)
Add 400 g of swellable fluorinated mica M-1 (total cation exchange capacity is equivalent to 0.44 mol) to a solution obtained by mixing 1 kg of ε-caprolactam and 1 kg of water, and use a homomixer at room temperature. Stir for 1.5 hours. An autoclave with an internal volume of 30 liters was prepared by previously charging 9 kg of ε-caprolactam and 50.7 g (0.44 mol) of 85 mass% phosphoric acid aqueous solution and melting them at 95 ° C. The mixture was heated to 260 ° C. with stirring, and the pressure was increased to 0.7 MPa. Thereafter, while gradually releasing water vapor, the temperature of 260 ° C. and the pressure of 0.7 MPa were maintained for 1 hour, and the pressure was released to normal pressure over 1 hour, followed by polymerization for 10 minutes.
When the polymerization was completed, the reaction product was discharged into a strand, cooled and solidified, and then cut to obtain a pellet made of polyamide resin. Next, the pellets were refined with hot water at 95 ° C. for 8 hours and then dried.
Content of the silicate layer in P-1 by ash measurement was 4.2 mass%. The relative viscosity was 2.3.

[Synthesis Example 2] Polyamide resin (P-2)
Add 400 g of swellable fluorinated mica M-1 (total cation exchange capacity is equivalent to 0.44 mol) to a solution obtained by mixing 1 kg of ε-caprolactam and 1 kg of water, and use a homomixer at room temperature. Stir for 1.5 hours. An autoclave having an internal volume of 30 liters was prepared by previously charging 9 kg of ε-caprolactam and 50.7 g (0.44 mol) of 85 mass% phosphoric acid aqueous solution and melting them at 95 ° C. The mixture was heated to 260 ° C. with stirring, and the pressure was increased to 0.7 MPa. Thereafter, while gradually releasing water vapor, the temperature of 260 ° C. and the pressure of 0.7 MPa were maintained for 1 hour, and the pressure was released to normal pressure over 1 hour, followed by polymerization for 30 minutes while allowing nitrogen to flow. Thereafter, P-2 pellets were obtained in the same manner as in Synthesis Example 1, followed by scouring and drying.
Content of the silicate layer in P-2 by ash content measurement was 4.2 mass%. The relative viscosity was 2.8.

Examples 1-7 and Comparative Examples 1-5
A polyamide resin composition comprising a pellet mixture having the composition shown in Table 1 or Table 2 was subjected to injection molding of various test pieces using an IS-100 molding machine manufactured by Toshiba Machine Co., Ltd., and each was subjected to a test.

  In Example 1, good impact resistance is exhibited and fluidity is good, so that productivity is excellent, but rigidity and heat resistance tend to be slightly low. In Examples 2 to 4, the balance of impact resistance, rigidity, and heat resistance was excellent, and good fluidity was exhibited. In Example 5, the rigidity and heat resistance were particularly excellent and the impact resistance was relatively low.

  Comparative Examples 1 to 4 show cases in which the polyamide resin is used alone, but in any case, the impact resistance and the rigidity or the heat resistance tend to conflict with each other, and are not suitable as an engine cover material. Also in Comparative Example 5, the balance between impact resistance and rigidity or heat resistance is not desirable.

The shape of the test piece used for the impact resistance evaluation test is shown.

Claims (5)

  A polyamide resin composition for an engine cover comprising at least two kinds of polyamide resins having different relative viscosities and a swellable layered silicate, wherein the relative viscosity of the contained polyamide resin mixture is 2.6 or more. .   The at least two types of polyamide resins having different relative viscosities are polyamide resin A having a relative viscosity of 2.0 or more and less than 3.0 and polyamide resin B having a relative viscosity of 3.0 or more and 4.0 or less. The polyamide resin composition for engine covers described in 1.   The polyamide resin composition for an engine cover according to claim 2, wherein polyamide resin A composite particles containing polyamide resin A containing and dispersing swellable layered silicate and polyamide resin B particles are mixed. .   3. The polyamide resin composition for an engine cover according to claim 2, wherein a polyamide resin A pellet containing polyamide resin A containing and dispersing a swellable layered silicate and a polyamide resin B pellet are mixed. object. The engine cover manufactured using the polyamide resin composition for engine covers in any one of Claims 1-4.

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