JP2007038602A - Resin composition for injection molding, injection-molded article using it and process of injection molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition for an injection molding and a molding process which are best suited for giving a injection-molded article having few flow marks and a good appearance. <P>SOLUTION: The injection molding is conducted under the conditions that the maximum shear speed of the resin composition is ≥10 s<SP>-1</SP>in the injection molding mold and α as determined by formula (1) is larger than 0. The formula (1) is α=3σ<SB>s</SB>/äσ<SB>n</SB>-σ<SB>s</SB>(1-exp(-t/τ))}. In the formula, σ<SB>s</SB>is a shear stress of the resin composition for injection molding under the molding condition; σ<SB>n</SB>is a difference in the first normal stress under the molding condition; τ is a length of time passed after the resin composition for injection molding flows into the mold; and t is a relaxation time of the resin composition for injection molding under the molding condition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an injection molding resin composition and an injection molding method capable of providing an injection molded product having no appearance of a flow mark and having a good appearance.

  Various resin compositions have a good balance between mechanical properties and moldability, and are widely used in various industrial fields. Among resin compositions, polypropylene is widely used particularly in the automotive and electrical component industries because it has a high melting point among general-purpose resins, has excellent heat resistance, has high rigidity, and is lightweight.

  As conventional polypropylene resin compositions, JP-A-57-55952 (Patent Document 1), JP-A-58-1111846 (Patent Document 2), JP-A-59-98157 (Patent Document 3). JP-A-58-17139 (patent document 4), JP-A-57-1777038 (patent document 5), JP-A-57-207630 (patent document 6), JP-A-57-195134. As disclosed in JP-A-57-159841 (Patent Document 8) and JP-A-55-21494 (Patent Document 9), etc., an ethylene / propylene copolymer is used as a polypropylene resin. Attempts have been made to fill inorganic fillers such as polymers and talc. Such a resin composition may have a low surface hardness and poor fluidity. Furthermore, JP-A-60-13838 (Patent Document 10), JP-A-05-59251 (Patent Document 11), JP-A-05-98093 (Patent Document 12) and JP-A-05-98098 ( In Patent Document 13) and the like, surface hardness and molding processability are improved by improving the polypropylene resin and limiting the type of ethylene / α-olefin copolymer.

  In general, it is known that a material having a large die swell is preferable as a resin in which a flow mark hardly appears. Improvements to increase the die swell have been made such as increasing the molecular weight distribution of the resin and increasing the high molecular weight component. Furthermore, as far as the polypropylene resin is concerned, increasing the [η] of the rubber component of the polypropylene block copolymer has been performed. However, even with these, flow marks may be generated, and further improvement has been desired.

  As a polypropylene resin composition with less generation of flow marks, Japanese Patent Application Laid-Open No. 2003-183460 (Patent Document 14) discloses a product of a relaxation time of a resin composition at an injection molding temperature and a shear rate of the resin composition in a mold. It is disclosed that the occurrence of a flow mark is small when the converted shear rate represented by is within a certain numerical range.

JP-A-57-55952 JP 58-1111846 A JP 59-98157 A JP 58-17139 A Japanese Patent Laid-Open No. 57-177038 JP-A-57-207630 JP 57-195134 A Japanese Unexamined Patent Publication No. 57-159841 JP-A-55-21494 JP 60-13838 A Japanese Patent Laid-Open No. 05-59251 JP 05-98093 A JP 05-98098 A JP 2003-183460 A

  An object of the present invention is to provide an optimal injection molding resin composition and an injection molding method in order to solve the above-described problems and to provide an injection molded product having a good appearance and less generation of flow marks. And

In order to achieve the above-mentioned object, the present inventors have investigated through the flow mark generation mechanism that the generation of the flow mark is caused by the unstable flow of the flow front during injection molding, and that the surface curvature of the flow front is It has been found that no flow mark is generated when convex in the traveling direction.
Furthermore, since the surface curvature of the flow front is derived from the first normal stress difference, shear stress, relaxation time and injection molding conditions in the molten state of the resin composition for injection molding, the injection molding conditions satisfying specific conditions. It was found that the flow mark of the injection-molded product was improved by selecting the setting and the resin composition for injection molding, and reached the present invention.

In the present invention, molding is performed under the condition that α defined by the following formula (1) is α> 0 under the molding conditions in which the maximum shear rate of the resin composition in the mold in injection molding is 10 s ⁻¹ or more. The present invention relates to a resin composition for injection molding.

α = 3σ _s / {σ _n −σ _s [1-exp (−t / τ)]} (1)

Where σ _s is the shear stress of the resin composition for injection molding under molding conditions,
σ _n is the first normal stress difference of the resin composition for injection molding under molding conditions,
t is the time from when the resin composition for injection molding flows into the mold,
τ is the relaxation time of the resin composition for injection molding under molding conditions.

The present invention also relates to the above-mentioned injection resin composition comprising an injection molding resin, an elastomer, and an inorganic filler.

The present invention also relates to an injection-molded product using the resin composition for injection molding described above.

The present invention also relates to an injection molding method characterized by using the above-described resin composition for injection molding.

With the resin composition for injection molding and the injection molding method of the present invention, the flow mark of the injection molded product can be improved.

In the injection molding of the present invention, molding is performed under the condition that α defined by the following formula (1) is α> 0 under the molding conditions in which the maximum shear rate of the resin composition in the mold is 10 s ⁻¹ or more. A resin composition for injection molding, characterized by comprising:

α = 3σ _s / {σ _n −σ _s [1-exp (−t / τ)]} (1)

Where σ _s is the shear stress of the resin composition for injection molding under molding conditions,
σ _n is the first normal stress difference of the resin composition for injection molding under molding conditions,
t is the time from when the resin composition for injection molding flows into the mold,
τ is the relaxation time of the resin composition for injection molding under molding conditions.
Here, the first normal stress difference σ _n and the shear stress σ _s of the resin composition for injection molding can be directly evaluated from the steady flow measurement in the molten state. It can also be calculated using storage elastic modulus G ′ and loss elastic modulus G ″ obtained from dynamic viscoelasticity measurement in the molten state.
The relaxation time τ of the resin composition for injection molding in the molten state can be obtained from a stress relaxation measurement after the flow is stopped.

  The injection molding resin is not particularly limited as long as it can be injection-molded. Polyolefin resin such as polyethylene resin and polypropylene resin, polyamide resin such as nylon 6 resin and nylon 66 resin, polyethylene terephthalate resin and polybutylene terephthalate resin, etc. Examples include polyester resins, polyphenylene ether ketone resins such as polyether ketone resins and polyether ether ketone resins, polyphenylene sulfide resins, polyimide resins, polystyrene resins, ABS resins, polyphenyl ether resins, and polycarbonate resins. I can do it. Of these, polypropylene resin is most preferred.

  As a polypropylene resin, a propylene copolymer can be used in addition to a propylene homopolymer. Among these, a propylene block copolymer composed of a crystalline polypropylene component and a random copolymer component is most preferable.

  The propylene block copolymer includes a polypropylene component having a boiling n-heptane insoluble content of 96% by weight or more and a melt flow rate of 5 to 300 g / 10 minutes, preferably 70 to 250 g / 10 minutes, and an intrinsic viscosity [ η] is 2 to 11 dl / g, preferably 2 to 10 dl / g, ethylene having a content of 15 to 50% by weight, preferably 20 to 40% by weight, and a random of α-olefin having 3 or more carbon atoms A propylene block copolymer composed of a copolymer component and a polypropylene resin having a melt flow rate of 1 to 100 g / 10 min is preferable.

  The random copolymer component of ethylene and an α-olefin having 3 or more carbon atoms is, for example, a binary or ternary copolymer of ethylene and propylene and / or another α-olefin. Other α-olefins include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.

  Specific polymers of the binary or ternary copolymer include ethylene-propylene random copolymer, ethylene-1-butene random copolymer, ethylene-1-pentene random copolymer, ethylene-1-hexene random copolymer. Polymer, ethylene-4-methyl-1-pentene random copolymer, ethylene-1-octene random copolymer, ethylene-1 decene random copolymer, ethylene-propylene-1-butene random copolymer, ethylene-propylene-1- Pentene random copolymer, ethylene-propylene-1-hexene random copolymer, ethylene-propylene-4-methyl-1-pentene random copolymer, ethylene-propylene-1-octene random copolymer, ethylene-propylene-1 -Decene random copolymer, etc. It is.

  In the random copolymer component, if the ethylene content is less than 15% by weight, the impact resistance is insufficient, and if it is more than 50% by weight, the rigidity and heat resistance are insufficient, which is not preferable. Further, if the amount of the boiling n-heptane insoluble component indicating the degree of crystallinity of the polypropylene component is less than 96% by weight, the crystallinity is low and the physical properties are inappropriate, which is not preferable. Furthermore, if the melt flow rate is less than 1 g / 10 min, the moldability is lowered, which is not preferable for practical use. On the other hand, when the value is larger than 100 g / 10 min, the physical properties are inferior, and it is not preferable because it cannot be practically used.

  Instead of the so-called unmodified polypropylene as described above, a blended modified polypropylene graft-modified with an unsaturated carboxylic acid and / or a derivative thereof can be used. As the modified polypropylene graft-modified with such an unsaturated carboxylic acid and / or derivative thereof, known ones can be used.

  The propylene block copolymer is a room temperature p-xylene-soluble component, and a random copolymer component composed of ethylene and an α-olefin having 3 or more carbon atoms having the following characteristics: It is preferable to contain 16% by weight.

  The polypropylene resin composition of the present invention contains, as the elastomer component, an olefin-based thermoplastic elastomer or a styrene-based thermoplastic elastomer, or a modified product graft-modified with these unsaturated carboxylic acids and / or derivatives thereof. Can do.

  Olefin-based thermoplastic elastomers include ethylene / propylene rubber (EPR), ethylene / butylene rubber (EBR), ethylene / octene rubber (EOR), ethylene / propylene / butylene rubber (EPBR), and ethylene / propylene / diene rubber (EPDM). Etc. Styrenic thermoplastic elastomers include styrene / butadiene / styrene rubber (SBS), styrene / isoprene / styrene rubber (SIS), SBS hydrogenated styrene / ethylene / butylene / styrene rubber (SEBS), and SIS. Styrene, ethylene, propylene, styrene rubber (SEPS) which is a hydrogenated product of

Of these, EPR, EBR, EOR, SEBS and mixtures thereof are particularly preferably used. As EPR and EBR, the ethylene content is 20 to 90% by weight, particularly 30 to 90% by weight, and the melt flow index (measured at 230 ° C.) is 0.1 to 120 g / 10 minutes, particularly 0.5 It is preferably ˜60 g / 10 minutes.

The polypropylene resin composition of the present invention can contain talc, calcium carbonate, barium carbonate, whiskers, glass fibers, mica and the like as inorganic filler components. Of these, talc is preferable.

The composition ratio of each component of the polypropylene resin composition for injection molding of the present invention is as follows.
The polypropylene resin (A) component is preferably 40 to 100% by weight, particularly preferably 45 to 80% by weight. If it is below the above range, the rigidity is below the practical range, and if it exceeds the above range, the impact resistance is lowered, and the balance between the rigidity and the impact resistance is not preferable.

  The elastomer component is preferably 0 to 50% by weight, particularly preferably 10 to 40% by weight. If it falls below the above range, the impact resistance falls below the practical range, and if it exceeds the above range, the balance between rigidity and impact resistance is not preferred.

  The inorganic filler component is preferably 0 to 30% by weight, particularly preferably 5 to 25% by weight. If it falls below the above range, the rigidity falls below the practical range, and if it exceeds the above range, the balance between rigidity and impact resistance is undesirably impaired.

  The resin composition for injection molding of the present invention is an antioxidant, a heat stabilizer, a nucleating agent, an ultraviolet absorber, a lubricant, an antistatic agent, a flame retardant, a pigment, a dye, and talc as long as the object of the present invention is not impaired. Inorganic fillers, organic fillers and the like may be contained.

  As a method for mixing these components, a kneader such as a biaxial kneader or a Banbury mixer, which is generally used as a kneading method for a resin composition, can be used. The crystalline composition obtained by kneading each composition as described above is usually used after being processed into a pellet form.

Each physical property given in each example and comparative example was based on the following method.
Melt flow rate (MFR): determined in accordance with ASTM D-1238. For example, in the case of a polypropylene resin, it is obtained by measuring the weight of a resin extruded into a strand shape for 10 minutes under a load of 2.16 kg at 230 ° C. using a melt indexer.
The first normal stress difference σ _n and the shear stress σ _s of the resin composition for injection molding in the molten state were calculated by the following method from the storage elastic modulus G ′ and the loss elastic modulus G ″ in the molten state. G ″ is obtained by dynamic viscoelasticity measurement in the molten state. The dynamic viscoelasticity measurement in the molten state was performed using RDS-II or ARES made by Rheometrics equipped with a cone plate having a diameter of 25 mm and a cone angle of 0.1 radians. The measurement frequency range is 400 to 0.01 s ⁻¹ . The measurement temperature is 200 ° C. From G 'and G "obtained by dynamic viscoelasticity measurement in the molten state," Course / Rheology "(edited by the Japan Society of Rheology, Polymer Publications) p.64 and p.71 and Shigeharu Onoki"Chemist's Rheology for "(Chemical Doujin) σ _n and σ _s were calculated by the method described in Chapter 5. σ _n and σ _s are elastic properties at the time of steady flow of the resin composition in the molten state, respectively. G ′ and G ″ represent elastic properties and viscous properties, respectively, when a cyclic strain is applied to the resin composition in the molten state.
The relaxation time τ of the resin composition for injection molding in the molten state is a shear rate at 200 ° C. using RDS-II or ARES manufactured by Rheometrics equipped with a cone plate having a diameter of 50 mm and a cone angle of 0.041 radians. After applying a steady flow at 1 s ^-1 for 3 minutes, measure the stress relaxation after stopping the flow, and obtain it according to the method described in Chapter 2 of "Lecture / Rheology" (edited by the Japan Society of Rheology, Polymer Publishing Society). It was.

Table 1 shows the characteristics of the propylene block copolymers used in Examples and Comparative Examples.
Table 2 shows the characteristics of the elastomers used in the examples and comparative examples.

Examples 1 to 3 (Comparative Example 1)
The components (A) to (C) in the blending ratios shown in Table 3 were mixed using a different direction non-meshing type twin-screw kneading extruder 2UCM manufactured by Ube Industries, Ltd., kneading temperature 200 to 210 ° C., rotor rotation speed It was melt-kneaded at 900 rpm and pelletized.
The flow mark was evaluated by injection molding using UBEMAX D150-10 manufactured by Ube Industries. The mold used is the MVSS mold having a product thickness of 2 mm shown in FIG. 1, and the width and length of the cavity are 142 mm and 365 mm, respectively. The gate is a side one-point gate. The molding conditions are shown in Table 4.
The maximum shear rate of the resin composition in the mold was calculated using a resin flow analysis software MODDFLOW manufactured by Moldflow. When the molding is performed under the mold shown in FIG. 1 and the molding conditions shown in Table 4, the maximum shear rate of the resin composition in the mold is 10 s ⁻¹ or more.
For the evaluation of the flow mark, the flow mark occurrence rate shown in the following equation was used.
Flow mark occurrence rate (%) = {(L ₀ −L ₁ ) / L ₀ } × 100
Here, L ₀ and L ₁ are the length from the gate to the molded product and the distance from the molded product end on the gate side to the flow mark generation point.
The flow mark was evaluated by the following four-step method.
Excellent: Flow mark occurrence rate is less than 25% Good: Flow mark occurrence rate is 25% or more and less than 35% Possible: Flow mark occurrence rate is 35% or more and less than 45% Impossibility: Flow mark occurrence rate is 45% or more

Table 5 shows the parameters in formula (1) and the evaluation results of the flow mark of the injection molded product. The values of σ _n and σ _s are values at shear rates of 100 s ⁻¹ and 10 s ⁻¹ .

FIG. 1 shows an MVSS mold having a product thickness of 2 mm used in the injection molding of the present invention.

Claims (4)

The molding is performed under the condition that α defined by the following formula (1) is α> 0 under the molding conditions in which the maximum shear rate of the resin composition in the mold in the injection molding is 10 s ⁻¹ or more. A resin composition for injection molding.

α = 3σ _s / {σ _n −σ _s [1-exp (−t / τ)]} (1)

Where σ _s is the shear stress of the resin composition for injection molding under molding conditions,
σ _n is the first normal stress difference of the resin composition for injection molding under molding conditions,
t is the time from when the resin composition for injection molding flows into the mold,
τ is the relaxation time of the resin composition for injection molding under molding conditions.
2. The injection resin composition according to claim 1, comprising an injection molding resin, an elastomer, and an inorganic filler. An injection-molded article using the resin composition for injection molding according to claim 1. An injection molding method using the resin composition for injection molding according to claim 1.

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