JP5132883B2 - Molded product with snap fit - Google Patents

Description

  The present invention relates to a molded article having a snap fit portion formed from a resin composition in which a polytetrafluoroethylene-based resin having a fibril-forming ability is blended with a polybutylene terephthalate resin.

  Polybutylene terephthalate resin (hereinafter sometimes referred to as PBT resin), which is a crystalline thermoplastic polyester resin, has excellent mechanical properties, electrical properties, other physical and chemical properties, and good processability. Therefore, it is used as an engineering plastic for a wide range of applications such as automobiles, electric / electronic parts, etc., and can be suitably used for a molded product having a snap-fit portion in combination with its excellent repeated fatigue characteristics. PBT resin alone is used for molded products with snap-fit parts, but it has improved mechanical properties such as strength and rigidity while maintaining good fluidity in response to recent demands for smaller and thinner walls. Is required. As a method for improving mechanical properties, various reinforcing materials and additives are known, and when high mechanical strength and rigidity are required, inorganic fibrous reinforcement typified by glass fiber etc. A material is used. However, when inorganic fibrous reinforcement is added, strength, rigidity, and heat resistance are improved, but fluidity, appearance, and toughness are greatly reduced, and the resulting material becomes brittle. The springiness of the sheet is weak, and problems such as breakage due to repeated characteristics often occur, and improvement has been demanded.

  Also, it is widely known that a crystal nucleating agent is added to PBT resin to improve mechanical properties, and although a certain mechanical property improvement effect can be obtained, the effect is low compared with inorganic fibrous reinforcement, The effect of improving strength and rigidity cannot be obtained. Accordingly, it has been desired to develop a PBT resin composition suitable for a molded article having a snap fit portion that maintains toughness while maintaining fluidity during molding and has improved strength and rigidity.

  In response to the above requirements, Patent Document 1 maintains high fluidity by blending a high molecular weight PBT resin with a low molecular weight PBT to such an extent that the heat resistance and mechanical strength characteristics are not lost. Although a PBT resin composition having a hinge property has been proposed, the flowability at the time of molding is improved by this method, but the effect of improving strength and rigidity cannot be obtained.

In Patent Document 2, a resin composition excellent in rigidity and toughness is proposed by blending glass fiber or the like with a specific copolymer polyester resin, but a decrease in fluidity is recognized by the addition of glass fiber. It is not suitable for a molded product having a thin-walled portion.
JP-A-5-179114 JP-A-8-217965

  An object of the present invention is to provide a resin material suitable for a molded article that maintains toughness and has excellent fluidity, strength, and appearance and has a snap-fit portion.

  As a result of intensive studies to achieve the above object, the present inventors can obtain a resin material suitable for a molded article having a snap-fit portion by selectively blending a specific polytetrafluoroethylene-based resin with a PBT resin. As a result, the present invention has been completed.

  That is, the present invention is formed by injection molding a resin composition in which 0.1 to 5 parts by weight of a polytetrafluoroethylene resin having (B) fibril-forming ability is added to 100 parts by weight of (A) polybutylene terephthalate resin. And a molded product having a snap-fit portion in a part thereof.

  In this invention, the resin material which mix | blended the polytetrafluoroethylene-type resin which has a fibril formation ability is used for PBT resin, This maintains toughness and has the outstanding fluidity | liquidity, intensity | strength, and external appearance. Therefore, it is suitably used for a molded product having a snap fit portion.

  Hereinafter, the constituent components of the resin material of the present invention will be described in detail. First, (A) PBT resin, which is the basic material of the resin material of the present invention, is terephthalic acid or its ester-forming derivative and C4 alkylene glycol (1,4-butanediol) or its ester-forming derivative. It is a thermoplastic resin obtained by polycondensation, and may be a copolymer containing 70% by weight or more of butylene terephthalate repeating units.

  Dibasic acid components other than terephthalic acid or its ester-forming derivatives (lower alcohol esters, etc.) include aliphatic, aromatic poly, such as isophthalic acid, naphthalenedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, and succinic acid. The basic acid or its ester-forming derivative is raised. Examples of glycol components other than 1,4-butanediol include ordinary alkylene glycols such as ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, hexamethylene glycol, neopentyl glycol, cyclohexane dimethanol, and the like. Alkylene oxide adduct alcohols such as lower alkylene glycols such as octanediol, aromatic alcohols such as bisphenol A, 4,4'-dihydroxybiphenyl, ethylene oxide 2 mol adducts of bisphenol A, propylene oxide 3 mol adducts of bisphenol A And polyhydroxy compounds such as glycerin and pentaerythritol or ester-forming derivatives thereof. In the present invention, any PBT resin obtained by polycondensation using the above compound as a monomer component can be used as the component (A) of the present invention, and is used alone or in admixture of two or more.

  The intrinsic viscosity of the PBT resin (A) used in the present invention is not particularly limited, but it is preferably 1.0 g / dl or less as a measured value at a concentration of 0.5% by weight and 25 ° C. using O-chlorophenol as a solvent. This is to improve the adhesion with the mold during molding, improve the friction characteristics, and improve the flow characteristics.

  Next, in the present invention, (B) a polytetrafluoroethylene resin having a fibril forming ability is used. The object of the present invention cannot be achieved without the ability to form fibrils.

  Moreover, the compounding quantity is 0.1-5 weight part with respect to 100 weight part of (A) PBT resin, Preferably it is 0.2-3 weight part. If the blending amount is too small, sufficient strength / rigidity improvement effect cannot be obtained. If the blending amount is too large, the original mechanical properties and appearance of the PBT resin may be impaired, and the moldability may be problematic. It becomes difficult.

  The polytetrafluoroethylene-based resin in the present invention is a single or copolymer of a fluorine-containing monomer such as tetrafluoroethylene, chlorotrifluoroethylene, vinylidene fluoride, hexafluoropropylene, perfluoroalkyl vinyl ether, or the fluorine-containing monomer. And a copolymer of a copolymerizable monomer such as ethylene, propylene, and (meth) acrylate.

  Examples of such polytetrafluoroethylene resins include homopolymers such as polytetrafluoroethylene, polychlorotrifluoroethylene, and polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymers, and tetrafluoroethylene. -Copolymers such as a perfluoroalkyl vinyl ether copolymer, an ethylene-tetrafluoroethylene copolymer, and an ethylene-chlorotrifluoroethylene copolymer are exemplified. These polytetrafluoroethylene resins can be used alone or in combination. Further, these polytetrafluoroethylene resins can be used in a dispersed form.

  In the present invention, “fibril forming ability” refers to dispersion (fibrillation) when subjected to plasticizing shear stress in extrusion or injection molding, and as such a polytetrafluoroethylene-based resin, Those not subjected to baking or radiation treatment are preferred. Polytetrafluoroethylene resins having such fibril-forming ability are widely commercially available, such as Teflon 800J manufactured by Mitsui / DuPont Fluorochemical, Fullon CD-076 manufactured by Asahi Glass, and Metabrene A3800 manufactured by Mitsubishi Rayon.

  In the present invention, a crystal nucleating agent is preferably used as the component (C).

As the crystal nucleating agent, both organic and inorganic substances can be used. Organic substances include calcium oxalate, sodium oxalate, calcium benzoate, calcium phthalate, calcium tartrate, magnesium stearate, polyacrylate, and other polymers, polyester, polyethylene, polypropylene and other polymers, and polymer cross-linking A thing etc. can be used individually or in mixture of 2 or more types. As the inorganic substance, Zn powder, Al powder, graphite, or alone such as carbon _{black, ZnO, MgO, Al 2 O} 3, TiO 2, MnO 2, SiO 2, Fe 3 O metal oxide such as _4, nitride Nitride such as aluminum, silicon nitride, titanium nitride, boron nitride, inorganic salts such as Na ₂ CO ₃ , CaCO ₃ , MgCO ₃ , CaSO ₄ , CaSiO ₃ , BaSO ₄ , Ca ₃ (PO ₄ ) ₃ , talc, Clays such as kaolin, clay and clay can be used alone or in combination of two or more. Particularly preferred are boron nitride, and clays such as talc, kaolin, clay, clay, and more preferred are boron nitride and talc. Particularly preferred is talc having an average particle diameter of 1 to 8 μm.

  (C) The compounding quantity of a crystal nucleating agent is 0.1-20 weight part with respect to 100 weight part of (A) PBT resin, Preferably it is 0.2-10 weight part. When the amount is too small, the effect of increasing the crystallization rate is not sufficient. When the amount is excessively added, the formability is inferior and the toughness is decreased.

  In the present invention, a polycarbonate resin is preferably used as the component (D). (D) The polycarbonate resin can be obtained by a reaction between a dihydroxy compound and a carbonate such as phosgene or diphenyl carbonate. The dihydroxy compound may be an alicyclic compound or the like, but is preferably an aromatic compound (particularly a bisphenol compound).

Bisphenol compounds include bisphenols [eg, bis (hydroxyaryl) C _1-6 alkane; bis (hydroxyaryl) C _4-10 cycloalkane; 4,4′-dihydroxydiphenyl ether; 4,4′-dihydroxydiphenylsulfone; 4,4′-dihydroxydiphenyl sulfide; 4,4′-dihydroxydiphenyl ketone and the like]. Preferred polycarbonate resins include bisphenol F, bisphenol AD, bisphenol A, polycarbonates based on 1,1-bis (hydroxyphenyl) C _5-6 cycloalkane, especially bisphenol A type polycarbonates.

  The (D) polycarbonate resin is usually added in an amount of 5 to 50 parts by weight, preferably 5 to 30 parts by weight, per 100 parts by weight of the (A) PBT resin. By adding a polycarbonate resin, the appearance of the molded product is improved. When it is added excessively, a decrease in fluidity is observed and the moldability is poor.

Furthermore, the resin composition of the present invention can be blended with known substances that are generally added to thermoplastic resins and the like in order to impart desired properties according to the purpose. For example, antioxidants, UV absorbers, stabilizers such as light stabilizers, flame retardants, flame retardant aids, antistatic agents (excluding ionic surfactants and conductive carbon black) , lubricants, release agents Molding agents, coloring agents such as dyes and pigments, plasticizers and the like can be blended. In particular, the addition of an antioxidant for improving the heat resistance is effective.

  The PBT resin composition of the present invention is easily prepared by equipment and methods generally used as conventional resin composition preparation methods. For example, a predetermined amount of the components constituting the composition of the present invention can be mixed at once and melt-kneaded with a single or twin screw extruder to obtain pellets of the desired composition. Further, it is an effective technique for improving the dispersion of the polytetrafluoroethylene polymer in the PBT resin to previously pulverize the PBT resin into a powder and add the polytetrafluoroethylene polymer powder thereto.

  The molding method of the resin composition of the present invention is not particularly limited, such as injection molding, extrusion molding, blow molding and the like, but is preferably injection molding.

  The PBT resin composition of the present invention exhibits high flow characteristics at the time of molding, is excellent in strength, rigidity, mechanical properties, and snap fit, and combined with the heat resistance of PBT resin, electric / electronic equipment, automobile parts, It is particularly suitable for a coupling part having a snap fit portion such as a casing, a chassis, a housing, a tray, and a switch constituting an OA device. The mating material for snap-fit fitting is made of resin, metal, ceramic, etc., but the present invention is not limited to this and can be used.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.
Examples 1-5, Comparative Examples 1-5
As shown in Table 1, each component was dry blended at a ratio shown in Table 1 with respect to 100 parts by weight of polybutylene terephthalate resin, and then melt-kneaded at 260 ° C. and pelletized using a 30 mmφ twin screw extruder. Each test piece was molded from this pellet and various physical properties were measured. The results are shown in Table 1.

Moreover, the detail of the used component and the measuring method of physical property evaluation are as follows.
(A) Polybutylene terephthalate resin (PBT)
500FP made by Wintech Polymer
(B) Polytetrafluoroethylene resin (PTFE)
(B-1) Teflon 800J made by Mitsui / Dupont Fluorochemical;
(B'-1) Asahi ICI fluoropolymer full-on L169J; no fibril forming ability
(C) Crystal Nucleating Agent Talc; Hayashi Kasei Micron White 5000A
(D) Polycarbonate resin (PC)
Iupilon H-3000 made by Mitsubishi Engineering Plastics
[Bending strength, flexural modulus]
The obtained pellets were dried at 140 ° C. for 3 hours, then injection molded at a molding temperature of 260 ° C. and a mold temperature of 80 ° C. to prepare bending test pieces, which were evaluated according to the evaluation criteria defined in ISO178.
[Melt viscosity]
The obtained pellets were dried at 140 ° C. for 3 hours and then measured with a capillograph manufactured by Toyo Seiki in accordance with the evaluation criteria defined in ISO 1143.
[Snap fit insertion test]
A snap-fit insertion test was performed using a snap-fit evaluation molded piece as shown in FIG. The snap fit insertion force was measured by measuring the insertion force Fa by the method shown in FIG. 2 using the molded piece of FIG. Moreover, destruction at the time of insertion was also judged by whether snap fit was broken. The test was performed at n = 5, the snap fit insertion force showed an average value, and the breaking at the time of insertion was evaluated as “◯”, and the case where even one was broken as “X”.
[Snap fit extraction test]
Using a snap fit evaluation molded piece as shown in FIG. 1, a snap fit removal test was performed. The snap-fit removal force was measured by using the molded piece of FIG. 1 and pulling it by the method shown in FIG. For those broken at less than 300 N, the removal force Fb was shown. The test was performed with n = 5, the snap-fit removal force showed an average value, and even when one piece was broken at the time of removal, the broken state was shown.

It is a figure which shows the molded piece for snap fit evaluation. It is a schematic diagram which shows the state of a snap fit insertion test. It is a schematic diagram which shows the state of a snap fit extraction test.

Claims (4)

(A) Has an ability to form (B) fibrils with respect to 100 parts by weight of polybutylene terephthalate resin having an intrinsic viscosity (measured at 0.5% by weight, 25 ° C. using O-chlorophenol as a solvent at a concentration of 0.5% by weight) of 1.0 g / dl or less. Molded with 0.1-5 parts by weight of polytetrafluoroethylene resin, formed by injection molding a resin composition that does not contain ionic surfactant and conductive carbon black, and part of which has a snap-fit part Goods.   The molded article according to claim 1, wherein the resin composition further comprises (C) a crystal nucleating agent in an amount of 0.1 to 20 parts by weight per 100 parts by weight of the polybutylene terephthalate resin.   The molded article according to claim 2, wherein (C) the crystal nucleating agent is talc having an average particle diameter of 1 to 8 µm.   The molded article according to any one of claims 1 to 3, wherein the resin composition further comprises (D) 5 to 50 parts by weight of a polycarbonate-based resin with respect to 100 parts by weight of the polybutylene terephthalate resin.

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