JP2010070580A - Polyamide resin composition and molded article obtained by molding the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a molded article of polyamide being light weight, and having not only high rigidity and high heat resistance, but also excellent impact resistance, especially the impact resistance at low temperature, and dimensional stability, and the molded article of the polyamide, especially an engine cover produced by the method. <P>SOLUTION: A polyamide resin composition is obtained by blending 0.2-40 pts.mass of talc based on 100 pts.mass of a polyamide resin. The talc includes (a) untreated talc and (b) treated talc, and a blending ratio (mass ratio) of (a) and (b) is 0.02≤(b)/(a)≤50. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polyamide resin composition and an engine cover obtained by molding the same.

  Polyamide resins are widely used in the fields of civil engineering and architecture including automobile parts and electric / electronic parts because of their excellent physical and chemical properties. In the automotive field, in order to achieve both weight reduction and productivity to achieve low fuel consumption, resin-molded injection molded products are being used. Of these, polyamide resin is often used as a material for various mechanical parts. in use. In recent years, plasticization is also progressing in parts in engine rooms that are exposed to harsh environments in terms of temperature and other conditions. In particular, the plasticization is remarkable in covers such as engine covers and timing belt covers.

  As a resin material for a cover, a polyamide resin composition such as a polyamide 6 resin or a polyamide 66 resin reinforced with glass fiber or an inorganic filler has been used so far. This is because the material satisfies a wide range of required performance such as impact resistance and recyclability in addition to high heat resistance. However, in order to meet the demand for weight reduction while maintaining the necessary mechanical properties, there has been a limit in conventional reinforcing materials made of glass fiber or inorganic filler. On the other hand, reduction of production cost from a viewpoint different from performance is also a big demand, and materials that meet this need to have a simple material composition and excellent productivity (injection moldability, recyclability, etc.). .

  Under such a background, an engine cover using a polyamide resin 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 Document 1). However, although these polyamide resins are excellent in moldability and recyclability, they have insufficient impact resistance, and it has been a big problem to develop impact resistance particularly at low temperatures.

  Various methods for improving the impact resistance of such a polyamide resin have been proposed. For example, a swellability used as a raw material as a mixture with an impact resistance improving material composed of an olefin copolymer or as a modification of the polyamide resin itself. Although optimization of the cation exchange capacity of the layered silicate and its initial particle size has been proposed, it was effective in improving impact resistance, but in terms of the balance between impact resistance, heat resistance and rigidity, The problem remained.

Therefore, the inventors of the present invention proposed a polyamide resin composition (Patent Document 2) in which the relative viscosity and the compounding amount of the swellable layered silicate are in a specific ratio, and the balance between impact resistance, heat resistance, and rigidity is balanced. Although it was obtained, there was a new problem that the dimensional stability was lowered. In other words, in recent years, automobile engine covers have been designed to completely cover the engine because of the emphasis on designability, and therefore a large molded body is required, and it is necessary to further increase rigidity and dimensional stability. In the technique, warpage occurred in the obtained molded body, and a problem occurred in dimensional accuracy. In particular, the warpage of the engine cover for a large engine with a displacement of more than 2.5 liters increased remarkably, and the problem of dimensional stability was serious.
JP-A-2-240160 JP 2006-131831

  The present invention provides a method for producing a polyamide molded article having excellent impact resistance (particularly, impact resistance at low temperature) and dimensional stability in addition to being lightweight, having high rigidity and high heat resistance, and the method It is an object of the present invention to provide a polyamide molded product manufactured by the above, particularly an engine cover.

  As a result of intensive studies to solve such problems, the present inventors have found that the above object can be achieved by blending specific talc in a polyamide resin composition in which talc is blended with polyamide resin. The headline, the present invention has been reached.

  That is, the gist of the present invention is as follows.

(1) A polyamide resin composition in which 0.2 to 40 parts by mass of talc is blended with respect to 100 parts by mass of polyamide resin, and the talc is composed of (a) untreated talc and (b) treated talc, A polyamide resin composition, wherein a blending ratio (mass ratio) of (a) and (b) is 0.02 ≦ (b) / (a) ≦ 50.
(2) Specific gravity is 1.25 or less, The polyamide resin composition of (1) characterized by the above-mentioned.
(3) (b) The treated talc is treated at a heating temperature of 700 to 1200 ° C. after mixing talc and alkali silicofluoride, and the blend (mass ratio) of the talc / silica fluorosilicate is 90/10. It is -65/35, The polyamide resin composition of (1) or (2) characterized by the above-mentioned.
(4) A molded product obtained by molding the polyamide resin composition of (1) to (3).
(5) The molded product according to (4), wherein the molded product is an engine cover having an average thickness of a flat portion of 3 mm or less and a projected area of 1500 cm ² or more.

According to the present invention, there is provided a polyamide resin composition excellent in impact resistance, in particular, impact resistance at low temperature and dimensional stability in addition to being lightweight and having high rigidity and high heat resistance, and a molded product comprising the same. Since the fluidity and moldability of the polyamide resin composition can be improved,
It is possible to provide a molded product that is thin and has a side of 500 mm or more.

  The polyamide resin of the present invention may be 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 material include aminocarboxylic acids such as: 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, paraaminomethylbenzoic acid, and the like. Examples of the lactam include ε-caprolactam, ω-undecanolactam, and ω-laurolactam. Examples of the diamine include, for example, tetramethylene diamine, hexamethylene diamine, undecamethylene diamine, dodecamemethylene diamine, 2,2,4 / 1 / 2,4,4trimethylhexamethylenediamine, 5-methylnonnamethylenediamine, 2, 4-Dimethyloctamethylenediamine, metaxylylenediamine, paragylylenediamine, 1,3-dibis (aminomethyl) cyclohexane, bis (4-aminocyclohexyl) methane, bis (3-methyl-4-monoaminocyclohexyl) methane-2 2 bis (4 1 aminocyclohexyl) propane, bis (aminopropyl) piperazine, aminoethylpiperazine, and the like. Examples of dicarboxylic acids include: Adipic acid, peric acid, azelaic acid, sebacic acid, dodecanoic acid, terephthalic acid, isophthalic acid, 2-monochloroterephthalic acid, 2-monomethylterephthalic acid, 5-monomethylisophthalic acid, monosodium Examples include sulfoisophthalic acid, hexahydroterephthalic acid, and hexahydroisophthalic acid. These diamines and dicarboxylic acids can also be used as a pair of salts.

  Preferable specific examples of the polyamide resin include, for example, polycaproamide (nylon 6), polytetramethylene adipamide (nylon 46), polyhexamethylene adipamide (nylon 66), polycaproamide / polyhexamethylene adipa 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 61), polyhexamethylene terephthalamide (Nylon 6T), polyhexamethylene terephthalamide / polyhexamethylene Sophthalamide copolymer (nylon 6T / 61), polycaproamide / polyhexamethylene terephthalamide copolymer (nylon 6 / 6T), polycaproamide / polyhexamethylene isophthalamide copolymer (nylon 6/61), polyhexamethylene adipa Polyamide / polyhexamethylene terephthalamide copolymer (nylon 66 / 6T), polyhexamethylene adipamide / polyhexamethylene isophthalamide copolymer (nylon 66/61), polytrimethylhexamethylene terephthalamide (nylon TMDT), polybis ( 4 monoaminocyclohexyl) methane dodecamide (nylon PACM12), polybis (3 1 methyl-4 1 aminocyclohexyl) methane dodecamide (nylon dimethyl PACM12), polymetaxylylene adipamide (nylon MXD6), polyundecamethylene terephthalamide ( Nylon 11T) and these Mixture or copolymers thereof. Of these, nylon 6 and nylon 66 are particularly preferred.

  In the present invention, the relative viscosity of the polyamide resin composition (measured under the conditions of 96 mass% concentrated sulfuric acid as a solvent, temperature 25 ° C., concentration 1 g / dl) is not particularly limited, but is preferably 2.5 or more and 4.0 or less, more preferably It is 2.8 or more and 3.5 or less. If the relative viscosity is too low, the impact resistance becomes small, and if it is too high, the fluidity deteriorates.

  In the present invention, as the talc to be blended with the polyamide resin, it is necessary to use a mixture of (a) untreated talc and (b) treated talc.

Here, untreated talc refers to a powder obtained by pulverizing talc calculated in nature, which is hydrous magnesium silicate composed of magnesium hydroxide and silicate, and has the composition formula Mg ₃ Si ₄ O ₁₀ (OH) ₂ It is a clay mineral indicated by. As shown in the following formula (1), serpentine (Mg ₃ Si ₂ O ₅ (OH) ₄ ) is hydrothermally altered, or obtained by catalytic modification of dolomite (CaMg (CO ₃ ) ₂ ). is there.

2Mg ₃ Si ₂ O ₅ (OH) ₄ + 3CO ₂ → Mg ₃ Si ₄ O ₁₀ (OH) ₂ + ₃ MgCO ₃ + 3H ₂ O
3CaMg (CO ₃ ) ₂ + 4SiO ₂ + H ₂ O → Mg ₃ Si ₄ O ₁₀ (OH) ₂ + 3CaCO ₃ + 3CO ₂ (1)

  The untreated talc used in the present invention preferably has a particle size of 1 to 50 μm. Naturally produced untreated talc is not uniform in particle size, so when they are used as a polyamide resin composition and molded products are molded, not only the appearance of the molded product is impaired, but also the dimensions Also inferior in stability. It is preferable to classify, etc., to make the particle size uniform, or to perform pulverization and fine powdering by jet milling. Here, the particle diameter is an average particle diameter defined as a particle diameter value when the weight accumulation is 50% when the particle diameter distribution is measured using a particle size distribution measuring device such as a laser scattering particle size distribution meter. Point to. From the viewpoint of improving dimensional stability, an aspect ratio of 25 or more is preferable. When the aspect ratio is less than 25, warpage and torsional deformation occur in the molded product after molding, so that dimensional stability decreases. Since warpage and torsional deformation tend to appear remarkably in large molded products, dimensional stability is required for large molded products such as engine covers.

  The aspect ratio indicates the ratio between the major axis and the minor axis of the filler, but in the case of a plate-like filler, it indicates the ratio of the average diameter and thickness of the flat plate.

  In the present invention, the treated talc means an artificially modified surface treatment or composition of untreated talc. Examples of the surface treatment method include surface modification with a treatment agent such as alkali silicofluoride, a silane coupling agent, a titanate coupling agent, and a fatty acid. As a treatment method, untreated talc is mixed and stirred according to a predetermined formulation with the treatment agent, or after spraying the treatment agent on the untreated talc, heating and drying are performed within a range that does not impair the activity of the treatment agent. By doing so, processing talc is obtained. Examples of the artificially modified composition of untreated talc include layered silicates. Among them, the swellable fluoromica obtained by heat-treating untreated talc and alkali fluorosilicate is the present invention. As the processing talc used in, it can be suitably used.

  In the swellable fluoromica used in the present invention, the silicate layer can be uniformly dispersed at the molecular level in the polyamide resin matrix. Here, the silicate layer is a basic unit constituting the swellable fluorine mica, and is a plate-like inorganic crystal obtained by breaking the layer structure of the swellable fluorine mica (hereinafter referred to as “cleavage”). In the present invention, when swellable fluoromica is used as the treatment talc, the silicate layer is a single silicate layer or a polyamide molecular chain inserted between the layers. It means a state that is not completely collapsed, and it is not always necessary to cleave them one by one. Also, being uniformly dispersed at the molecular level means that when the swellable fluoric mica silicate layer is dispersed in the polyamide resin matrix, each layer maintains an average interlayer distance of 1 nm or more and does not form a lump. The state which is doing. Here, the lump refers to a state in which the swellable fluorine mica that is a raw material 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 by performing observation with a transmission electron microscope, for example, on the pellet (polyamide composite material test piece).

  In the present invention, the swellable fluorinated mica that is suitably used as the treated talc is obtained by heat-treating a mixed powder of alkali silicofluoride and talc represented by the general formula (2). The particle size of talc and alkali silicofluoride used as raw materials is preferably 2 μm or less.

M _α (Mg _γ Li _β ) Si ₄ O _δ F _ε (2)
(In the formula, M represents an ion-exchangeable cation, specifically sodium or lithium. A, b, γ, δ, and ε each represent a coefficient, and 0 ≦ α ≦ 0.5, 0 ≦ β ≦ 0.5, 2.5 ≦ γ ≦ 3, 10 ≦ δ ≦ 11, 1.0 ≦ ε ≦ 2.0)

  As an alkali silicofluoride, sodium silicofluoride, lithium silicofluoride, and potassium silicofluoride are preferably used, and the blending amount with talc needs to be 10 to 35% by mass. Preferably they are 15 mass%-30 mass%. When it is less than 10 mass% or exceeds 35 mass%, the production rate of the swellable fluorinated mica is lowered.

  The heating temperature when sodium silicofluoride or lithium silicofluoride is used as the raw material is preferably 700 to 900 ° C, more preferably 780 to 900 ° C. When the temperature is lower than 700 ° C. or higher than 900 ° C., the generation rate of the swellable fluorine mica is lowered. When the temperature is higher than 900 ° C., the swellable fluorine mica is sintered, and then a pulverization process is required. . The heating time is preferably 30 minutes to 2 hours. When potassium silicofluoride is used as a raw material, the heating temperature is preferably 700 to 1200 ° C. When the temperature is less than 700 ° C. or exceeds 900 ° C., the generation rate of swellable fluorinated mica is lowered, and 1200 ° C. is reduced. If it exceeds, the swellable fluorine mica will sinter and then a pulverization step will be required. In the present invention, it is most preferable to hold at 900 ° C. or higher for 1 hour.

  In the present invention, when swellable fluorine mica is used as the treatment talc, it has a structure comprising a negatively charged crystal layer mainly composed of silicate and a cation having ion exchange ability interposed between the layers. It is desirable that the cation exchange capacity determined by the method described later is 50 meq / 100 g or more. When the composite material is produced, it remains substantially in an uncleavable state and is not uniformly dispersed, so that no performance improvement is observed. The upper limit of the value of the cation exchange capacity is not particularly limited, and an appropriate one may be selected from swellable fluorine mica that can be actually prepared.

  In the present invention, there is no particular limitation on the initial particle size of the swellable fluorine mica. Here, the initial particle diameter is the particle diameter of the swellable fluoromica as a raw material used in producing the polyamide resin used in the present invention, and is different from the size of the silicate layer in the pellet. However, this particle size also has a considerable influence on the physical properties of the molded product, in particular the rigidity and heat resistance, so it is desirable to consider this point when selecting the mixing ratio of the above-mentioned swellable fluoromica. Accordingly, it is preferable to control the particle size by pulverizing with a jet mill or the like. This means that the laminated structure is not completely collapsed, and it is not always necessary to cleave them one by one. Also, being uniformly dispersed at the molecular level means that when the swellable fluoric mica silicate layer is dispersed in the polyamide resin matrix, each layer maintains an average interlayer distance of 1 nm or more and does not form a lump. The state which is doing. Here, the lump refers to a state in which the swellable fluorine mica that is a raw material 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 by performing observation with a transmission electron microscope, for example, on a test piece of a pellet or a polyamide composite material.

  The swellable fluoromica used in the present invention 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, and is obtained by a method described later. It is desirable that the cation exchange capacity is 50 meq / 100 g or more, and those having a cation exchange capacity of less than 50 meq / 100 g have a low swellability, so that they are substantially not produced during the production of pellets or polyamide composites. Therefore, it remains in an uncleavable state and does not disperse uniformly, so that no improvement in performance is observed. 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 fluorine mica that can be actually prepared.

  In the present invention, the total amount of talc to be blended with the polyamide resin is 0.2 to 40 parts by weight with respect to 100 parts by weight of the polyamide resin, and the specific blending amount is with respect to 100 parts by weight of the polyamide resin. It is preferable to blend (a) 0.1 to 10 parts by mass of untreated talc and (b) 0.1 to 10 parts by mass of treated talc, (a) 0.1 to 8 parts by mass of untreated talc and (b) treated talc. More preferably, 0.1 to 5 parts by mass are blended. When the total amount of talc added to the polyamide resin is less than 0.2 parts by mass, the dimensional stability and mechanical properties are not sufficient, and the total amount of talc added to the polyamide resin exceeds 40 parts by mass. , Impact resistance and fluidity are reduced.

  The blending ratio (mass ratio) of (a) untreated talc and (b) treated talc needs to be blended at 0.02 ≦ (b) / (a) ≦ 50, preferably 0.1 ≦ (b ) / (A) ≦ 10, more preferably 0.2 ≦ (b) / (a) ≦ 5. When (b) / (a) <0.02, the effect of improving the dimensional stability when the resulting polyamide resin composition is molded is poor. Further, when (b) / (a)> 50, the impact resistance and fluidity of a molded product obtained by molding the polyamide resin composition are lowered.

  When only untreated talc is added, it is effective in improving dimensional stability while maintaining impact resistance, but results in poor improvement in mechanical strength. On the contrary, when only treated talc is added, it is effective for improving the mechanical strength, but the dimensional stability in a large molded product is poor, and the impact resistance is remarkably lowered. In the case of molded products that require impact resistance and strength to withstand usage environments such as automobile engine covers and timing belt covers, such as use in cold regions, mechanical strength, dimensional stability, and impact resistance It is necessary to satisfy all of the properties, and it can be achieved that the untreated talc and the treated talc are mixed in a certain ratio.

   By using the (a) untreated talc and (b) the particle size of the treated talc, it is possible to obtain a polyamide resin composition described in the present application. (a) Untreated talc and (b) It is important that the treated talc is uniformly dispersed in the polyamide resin. There is no particular limitation on the production method to uniformly disperse each other, but (a) untreated talc and (b) a melt polymerization method in which treated talc is added when polymerizing polyamide, and (a) untreated talc is added to the polyamide resin. (b) There is a melt kneading method in which the treated talc is melt kneaded. In particular, (a) untreated talc and (b) treated talc are most preferable for the polymerization method in order to uniformly disperse each other in the polyamide resin. Furthermore, it is preferable that the aspect ratio is close. When the particle diameters of (a) untreated talc and (b) treated talc do not match, the polyamide resin composition at the time of molding has spots in the flow of the plasticized resin, particularly in the thickness direction of the molded product ( Anisotropy occurs in the distribution of a) untreated talc or (b) treated talc, the surface impact strength of the obtained molded product tends to decrease, and the amount of warpage tends to increase. Further, in a molded product in which designability is important, for example, an engine cover or the like, unevenness occurs in the glossiness of the surface of the molded product, which is not preferable.

  A method for producing the polyamide resin of the present invention will be described. First, in the presence of a predetermined range amount of untreated talc and treated talc, a predetermined amount of monomer is charged into an autoclave, and then an initiator such as water is used, temperature 240 to 300 ° C., pressure 0.2 to 3 MPa, 1 to 15 hours The melt polymerization method may be carried out within the range. When nylon 6 is used as the resin matrix, 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. As an example of the polymerization conditions, after completion of the preparation of a predetermined raw material, the mixture is heated to 260 ° C. over 1.5 hours while stirring and the pressure is increased to 1.5 MPa. Thereafter, while gradually releasing water vapor, the temperature of 260 ° C. and the pressure of 1.5 MPa are maintained for 1 hour, and the pressure is released to normal pressure over an additional hour. When the pressure in the autoclave is reduced to normal pressure, stirring is performed for 10 to 30 minutes while circulating nitrogen. At that time, the degree of polymerization of the polyamide resin increases according to the stirring time at normal pressure, and the degree of polymerization varies depending on various conditions. However, it is generally about 10 minutes at normal pressure and about 110 at a normal pressure and 30 minutes at normal pressure. The degree of polymerization is about 200.

  As a measure of the degree of polymerization, it can be shown by relative viscosity (measured at 25 ° C.) using concentrated sulfuric acid, the relative viscosity at a polymerization degree of 110 is 2.3, and the relative viscosity at a polymerization degree of 200 is 3.0. It is.

In the polyamide resin composition of the present invention, a preferable range of the relative viscosity is 2.0 to 3.5, and 2.3 to 3.2 is more preferable. When the relative viscosity of the polyamide resin composition is less than 2.0, the degree of polymerization becomes too low and sufficient impact resistance cannot be obtained. Further, when the relative viscosity of the polyamide resin composition exceeds 3.5, the degree of polymerization becomes high and sufficient impact resistance can be obtained. However, when the polyamide resin molded body is molded, the molten resin has sufficient fluidity. In particular, when injection molding a large molded product with a thin thickness such that the average thickness of the flat part of the molded product is 3 mm or less and the projected area is 1500 cm ² or more, the molten resin flows to the end of the mold. Therefore, it is not preferable because it becomes a short shot. In order to eliminate short shots, if the resin temperature is increased or the injection pressure is increased, for example, by increasing the resin temperature, flow can be secured, but for large molded products, the resin required for one shot Since the amount is large and the time required for one molding cycle is long, the polyamide resin stays at a high temperature for a long time in the molding machine, which leads to deterioration of the resin and mechanical properties, particularly impact resistance. Absent. Increasing the injection pressure is not preferable because it causes distortion of the molded product and increases warpage and the like, and is not preferable because gas or the like is generated at the flow front and the molded product is easily burnt. Furthermore, in order to obtain a molded product having a good appearance and good mold transfer, it is preferable to mold the injection pressure in a decreasing direction.

  When the polymerization of the polyamide resin is completed, the molten polyamide resin is then discharged (extruded) into a strand shape, cooled and solidified, and then cut to obtain pellets. Thereafter, in order to remove the polyamide monomer remaining in the polyamide resin, the pellets are preferably scoured with hot water. In this case, the treatment is preferably performed in hot water at 90 to 100 ° C. for 8 hours or more.

  When melt polymerization is performed by adding untreated talc and treated talc as described above, silicate and a part of the polyamide monomer required for the polymerization of the polyamide resin are dispersed in a dispersion medium such as water, methanol, ethanol, ethylene glycol or the like. It is desirable to provide a mixing step. 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 disperser, a high-pressure disperser, or the like.

  An acid may be added when melt polymerization is performed by adding untreated talc or treated talc. In general, the addition of an acid promotes the dispersion of untreated talc and treated talc in the polyamide resin matrix.

  The acid may be pKa (25 ° C., value in water) of 0 to 6, or an organic acid or an inorganic acid as long as it is a negative acid, specifically benzoic acid, sebacic acid, formic acid, acetic acid. Chloroacetic 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 preferably about 0.01 to 0.5 times the weight of the treated talc from the viewpoint of dispersion of the treated talc and the action as a polymerization catalyst in the polyamide resin matrix.

  The polyamide resin pellets obtained by the above-described melt polymerization can be made into a higher molecular weight reinforced polyamide resin by further using solid phase polymerization. In solid phase polymerization, a reinforced polyamide resin obtained by melt polymerization is usually inactivated after being formed into pellets having a diameter of 2 to 5 mm and a length of 3 to 6 mm, preferably a diameter of 3 to 4 mm and a length of 4 to 5 mm. It is preferable to carry out the reaction at a temperature below the melting point of the polyamide for 5 hours or more, preferably for 10 hours or more under the flow of gas or under reduced pressure. At this time, the temperature of the solid phase polymerization is more preferably 10 ° C. or more lower than the melting point and 150 ° C. or more. If the temperature is less than 150 ° C., the polymerization rate is slow, whereas if the temperature is near the melting point, the pellet may be fused, which is not preferable.

  In the case of solid phase polymerization, phosphoric acid and sulfuric acid may be added to the reaction system in an appropriate amount by using these sodium salts as catalysts for the purpose of increasing the polymerization rate, or at a temperature lower than the temperature at which solid phase polymerization is performed. Pre-crystallization of the pellet may be performed in advance.

  Moreover, a melt mixed line method is mentioned as a method of making a polyamide resin contain an untreated talc and a treated talc. The melt kneading may be performed at 240 to 300 ° C. and pelletized. When nylon 6 is used as the resin matrix, it is preferable to melt and blend at 250 to 280 ° C.

  The polyamide resin may contain a thermoplastic resin. Examples of the thermoplastic resin include polybutadiene, butadiene / styrene copolymer, acrylic rubber, ethylene / propylene copolymer, ethylene / propylene / butadiene copolymer, natural Elastomers such as rubber, chlorinated butyl rubber and chlorinated polyethylene, or modified products thereof with maleic anhydride, styrene / maleic anhydride copolymer, styrene / phenylmaleimide copolymer, polyethylene, polypropylene, butadiene / acrylonitrile copolymer , Polyvinyl chloride, Polyethylene terephthalate, Polyacetal, Polyvinylidene chloride, Polysulfone, Polyphenylene sulfide, Polyethersulfone, Benoxy resin, Polyphenylene ether, Polymethyl methacrylate, Polyether Examples include ketones, polycarbonates, polytetrafluoroethylene, polyarylate, and polyamide resins other than the polyamide resins (A) and (B) described above.

  The blending amount of the thermoplastic resin is not particularly limited as long as the object of the present invention is achieved, and it is usually preferably 10% by mass or less based on the pellet.

  When molding the polyamide resin of the present invention, as long as the object can be achieved, heat stabilizer, antioxidant, reinforcing material, pigment, anti-coloring agent, weathering agent, light resistance agent, flame retardant, plasticizer, crystal nucleating agent An additive such as a release agent may be added. These additives may be added when preparing the polyamide resin.

  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, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon, carbon black, zeolite, metal fiber, Metal whisker, ceramic whisker, potassium titanate whisker, boron nitride, graphite, glass fiber, carbon fiber and the like can be mentioned.

  There are no particular restrictions on the mold temperature, injection pressure, and injection speed during injection molding; the impact of the mold temperature is significant in terms of impact resistance of the molded product, especially the engine cover, and does not impair mold release or surface appearance. It is desirable to keep the mold temperature low within the range, and it is preferable that the mold temperature is 100 ° C. or less, preferably 80 ° C. or less.

  The polyamide molded product produced by the method of the present invention shown above satisfies a surface impact strength of 4.5 J or more at -30 ° C., a heat resistance temperature of 140 ° C. or more, and a flexural modulus of 5.0 GPa or more, It has excellent toughness, rigidity, impact resistance and heat resistance. Furthermore, the specific gravity is desirably 1.25 or less for weight reduction.

  In particular, a disk with a thickness of 1.6 mmt and a diameter of 100 mm was formed by the method of the present invention, and the amount of warpage La when it was placed on a horizontal plate was 0.5 mm or less, and the warp after dry heat treatment at 120 ° C. for 2 hours The amount of increase ΔL indicated by ΔL = Lb-La when the amount is Lb is 2 mm or less, and it is possible to manufacture a molded article having excellent dimensional stability.

  Thus, the method of the present invention is useful in the manufacture of engine covers used in special environments. According to the method of the present invention, it is possible to produce a molded article having high rigidity, heat resistance and dimensional stability, and also having impact resistance in a low temperature atmosphere sufficient as a practical material. This is useful for manufacturing engine covers for large engines with a thickness of 3 mm or less and a projected area of 2500 cm2 or more.

  Further, the present invention can be used for automobile engine covers, timing belt covers, ship engine covers, outboard motors, cultivators, and covers that cover engines of various internal combustion engines. Moreover, it can be used not only around the engine, but also on the outer panel of automobiles, large home appliances, large machine casings, and the like.

  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.Measurement method

(1) Cation exchange capacity The cation exchange capacity was determined based on the cation exchange capacity measurement method (JBAS-106-77) of bentonite (powder) by the standard test method of Japan Bentonite Industry Association. That is, using an apparatus in which a leachate container, a leach tube, and a receiver are connected in the vertical direction, first, all of the ion-exchangeable cations between the layers are firstly washed with a 1N ammonium acetate aqueous solution prepared by adjusting the swellable fluorine mica to pH 7. Change to NH4 +. Then, after sufficiently washing with water and ethyl alcohol, the NH4 + type swellable fluorine mica is immersed in a 10% by mass aqueous potassium chloride solution to replace NH4 + in the sample with K +. Subsequently, the cation exchange capacity (milli equivalent / 100 g) of the swellable fluorinated mica as a raw material was obtained by neutralizing titrating NH4 + leached with the above-described ion exchange reaction using a 0.1N sodium hydroxide aqueous solution. It was.

(2) Ash content About 5 g of pellets are placed in a crucible, weighed, incinerated at 400 ° C x 2 h, and further at 600 ° C x 3 h, and cooled sufficiently to room temperature while suppressing moisture absorption in a desiccator. The inside residue was calculated as the inorganic ash (mass%) by the following formula.
Inorganic ash (mass%) = {Inorganic ash mass (g)} / {Total mass of sample before incineration (g)} x 100

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

(4) Specific gravity
Measurement was performed based on JISK7112. 1.4 or less was accepted.

(5) Rigidity (flexural modulus)
Based on ASTMD-790, the measurement was performed under conditions of 23 ° C. × 50% RH. Passed 3GPa or higher. The test piece was molded using an injection molding machine EC-100 type (screw diameter 3.2 cm) manufactured by Toshiba Machine Co., Ltd. at a cylinder temperature of 260 ° C., a mold temperature of 80 ° C., and a clamping force of 100 t.

(6) Heat resistance (deflection temperature under load)
Based on ASTMD-648, the load was measured at 1.8 MPa. 100 ° C or higher was accepted. The test piece was molded using an injection molding machine EC-100 type (screw diameter 3.2 cm) manufactured by Toshiba Machine Co., Ltd. at a cylinder temperature of 260 ° C., a mold temperature of 80 ° C., and a clamping force of 100 t.

(7) Impact resistance (surface impact strength)
Using an EC-100 type injection molding machine manufactured by TOSHIBA MACHINE CO., LTD. (Screw diameter: 3.2 cm), the vertical direction as shown in Fig. 1 under the conditions of a cylinder temperature of 260 ° C, a mold temperature of 80 ° C, and a clamping force of 100t A box-shaped product of L) 67 mm, width (W) 90 mm, height (H) 40 mm, and wall thickness (T) 2 mmt was molded. With respect to this molded product, the impact strength was evaluated by dropping a weight from a predetermined height using a DuPont impact tester. At this time, the part that directly applied the 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 the condition of a combination of a predetermined height and weight load. The molded product was placed in an atmosphere of −30 ° C. until immediately before the evaluation.
G = (maximum height at which the specimen does not break) x (gravity acceleration) x (weight load)
3.9J or higher was accepted.

(8) Dimensional stability (measurement of warpage)
Using Toshiba Machine's injection molding machine EC-100 type (screw diameter 3.2 cm), a cylinder temperature of 260 ° C, mold temperature of 80 ° C, mold clamping force of 100t, a 1.6mmt thick circle with a diameter of 100mm The plate was formed with a side gate. After leaving at 23 ° C. in an absolutely dry state for 24 hours, the disc was allowed to stand on a horizontal plate, the four points in FIG. 2 were measured, and the amount of warpage La was measured. The reference points are a and b, which are in contact with the horizontal board, whereas c and d are points with a large warpage in the height direction. The amount of warpage [mm] was obtained by the following equation.
Warpage amount = (c + d) / 2- (a + b) / 2
Further, the amount of warpage Lb after standing at 120 ° C. for 2 hours was measured by the above method, and the difference ΔL = Lb−La was calculated as the amount of deformation.
The absolute dry time was 0.2 mm or less, and the heat treatment was 2 mm or less.

(9) Fluidity (Bar flow type)
Using Toshiba Machine's injection molding machine EC-100 type (screw diameter 3.2cm), cylinder temperature 260 ° C, mold temperature 80 ° C, clamping force 100t, injection pressure 100MPa, speed 150mm / s, injection time 5 Molding was performed using a dedicated die for one-point gates on one side under the second condition (fixed condition). The dedicated mold has a shape in which a spiral shaped product having a thickness of 2 mm and a width of 20 mm can be collected, has a gate at the center of the spiral, and has a maximum flow length of 800 mm. Since the molding conditions are all fixed and injection molding is performed, the flow length varies depending on the fluidity of the molten resin. The longer the flow length, the better the fluidity.
More than 500mm was accepted.

2.Raw material (A) Untreated talc Micro ace K1 manufactured by Nippon Talc Co., Ltd. Weight average particle size 7μm, aspect ratio 30
(B) Treated talc-swelling fluorinated mica To talc pulverized with a ball mill to an average particle size of 4.0 μm, sodium silicofluoride having an average particle size of 10 μm was mixed so that the total amount was 15% by mass. This was put in a magnetic crucible and reacted at 850 ° C. for 1 hour in an electric furnace to obtain swellable 7-mica (M-1) having an average particle size of 4.0 μm. The composition of this swellable fluoromica was Nao.60Mg2.63Si4010F1.77, and the cation exchange capacity was 110 meq / 100 g.

Example 1
10 g of talc and 10 g of swellable fluoromica were added to a solution obtained by mixing 1 kg of ε-caprolactam and 500 g of water, and stirred at room temperature for 1.5 hours using a homomixer. The total amount of this dispersion was charged with 9 kg of ε-caprolactam in advance and charged in an autoclave with an internal volume of 30 liters that had been melted at 95 ° C. The mixture was heated to 260 ° C over 1.5 hours with stirring, and a pressure of 1.5 MPa The pressure was increased to. After that, while gradually releasing water vapor, maintain the temperature at 260 ° C and the pressure of 1.5 MPa for 1 hour, release the pressure to normal pressure over 1 hour, and stir at normal pressure for 30 minutes while circulating nitrogen to increase the degree of polymerization. It was. The time required for the series of polymerization steps was 4 hours. When the polymerization was completed, the reaction product was discharged into a strand shape, cooled, solidified, and then cut to obtain a pellet made of a polyamide resin composition. The pellets were then refined with hot water at 95 ° C. for 8 hours and then dried. The ash content was 0.2% and the relative viscosity was 3.0. Various types of molded products can be manufactured by using injection molding machine EC-100 type (screw diameter 3.2cm) manufactured by Toshiba Machine Co., Ltd. with cylinder temperature 260 ° C, mold temperature 80 ° C, injection time 10 seconds, cooling time 10 seconds. Obtained and subjected to various evaluations. The results are shown in Table 1.

Examples 2-15
Polymerization was carried out in the same manner as in Example 1 except that the composition of talc and swellable fluoromica and the stirring time at normal pressure during polyamide polymerization were changed as shown in Tables 1 and 2. After scouring and drying, injection molding was performed to obtain various molded products, and various evaluations were performed. The results are shown in Table 2.

Comparative Examples 1-13
Polymerization was carried out in the same manner as in Example 1 except that the composition of talc and swellable fluoromica and the stirring time at normal pressure during polyamide polymerization were changed as shown in Tables 3 and 4. After scouring and drying, injection molding was performed to obtain various molded products, and various evaluations were performed. The results are shown in Tables 3 and 4. In Comparative Example 13, both the untreated talc and the treated talc were blended more than a predetermined amount, so that no strands could be drawn during melt-kneading, and a resin pellet of the polyamide resin composition could not be obtained.

  In Examples 1 to 15, as compared with Comparative Examples, the balance of rigidity, heat resistance, impact resistance and fluidity was good and high dimensional stability was exhibited, and all of them exhibited practically excellent performance.

In Comparative Examples 1 to 3, since the treatment talc was not added, the flexural modulus was low. In Comparative Example 4, the treated talc was not added, but since the untreated talc was mixed in a large amount, the flexural modulus was improved, but the surface impact strength was remarkably reduced. In Comparative Examples 5 to 8, since the untreated talc was not added, the amount of warpage was large. In Comparative Examples 9 to 10, since the blending ratio of the treated talc and the untreated talc is different from the range of the present invention, Comparative Example 9 has a shorter flow length, and Comparative Example 10 has a lower surface impact strength. . Since Comparative Examples 11-12 had more talc amounts than the range of this invention, the surface impact strength fell and the flow length became short.

It is the schematic which shows the shape of the test piece used for the impact resistance evaluation test of this invention. It is the schematic which shows the disk figure and measurement point which were used for the curvature amount measurement of this invention.

       (A) is a top view of a disk, (B) is sectional drawing.

Claims (5)

A polyamide resin composition in which 0.2 to 40 parts by mass of talc is blended with respect to 100 parts by mass of polyamide resin, wherein the talc comprises (a) untreated talc and (b) treated talc, (a) And a blending ratio (mass ratio) of (b) is 0.02 ≦ (b) / (a) ≦ 50. 2. The polyamide resin composition according to claim 1, wherein the specific gravity is 1.25 or less. (B) The treated talc is mixed at a heating temperature of 700 to 1200 ° C. after mixing talc and alkali silicate fluoride, and the blending (mass ratio) of the talc / alkali silicate fluoride is 90/10 to 65 / The polyamide resin composition according to claim 1, wherein the polyamide resin composition is 35. The molded article formed by shape | molding the polyamide resin composition in any one of Claims 1-3. The molded article according to claim 4, wherein the molded article is an engine cover having an average thickness of a flat portion of 3 mm or less and a projected area of 1500 cm ² or more.