JP5239514B2 - Thermoplastic resin molded body and method for producing the same - Google Patents

Description

  The present invention relates to a thermoplastic resin molded body and a method for producing the thermoplastic resin molded body. More specifically, the present invention relates to a thermoplastic resin molded article having excellent rigidity and impact strength, and a method for producing the thermoplastic resin molded article.

Conventionally, a thermoplastic resin molded body, in particular, a propylene-based resin molded body, has been used in many fields as an industrial material such as an automobile part or a household appliance part.
For example, Patent Document 1 discloses a molded product obtained by molding a composition containing a polypropylene resin and a nucleating agent as a polypropylene resin molded product having mechanical properties, temperature characteristics, and hardness. A polypropylene resin molded body produced by heat treatment in the range of ° C. is described.

  Patent Document 2 discloses that a propylene copolymer having mechanical properties, temperature characteristics, and hardness has an α-olefin unit content of 0.5 mass% to 10 mass% and a melt flow rate of 0. A propylene copolymer produced by a method of heat-treating a propylene copolymer having a temperature of -10 ° C to + 5 ° C centering on its melting point is described. .

Patent Document 3 describes a method of heating the polymer composition at 75 ° C. to 150 ° C. for 1 hour to 100 hours as a method for improving the rigidity and toughness of the ethylene-propylene polymer composition.
JP-A-62-256837 JP-A-62-283111 International Publication No. 01/81074 Pamphlet

However, the rigidity and impact strength of the thermoplastic resin molded articles described in Patent Documents 1 to 3 are not sufficient, and further improvements are required.
Under such circumstances, an object of the present invention is to provide a thermoplastic resin molded article excellent in rigidity and impact strength and a method for producing the same.

  As a result of intensive studies, the present inventors have been able to improve the rigidity and impact strength of the obtained thermoplastic resin molded body by performing pressure holding treatment of the molded body in multiple stages in the production process. As a result, the present invention has been completed. Specifically, the invention is as follows.

  The first aspect of the present invention includes a filling step of filling a thermoplastic resin with a mold cavity of an injection molding machine having a maximum injection pressure of P, and substantially stopping and holding the filling of the thermoplastic resin. A first pressure-holding step, and a second pressure-holding step of pressing and holding the thermoplastic resin that has undergone the first pressure-holding step.

Moreover, the 2nd aspect of this invention is a thermoplastic resin molded object manufactured by the said manufacturing method, Comprising: The thermoplastic resin molded object which satisfies the following requirements (1) to requirements (4). .
Requirement (1) Lc / La ≦ 1.50
Requirement (2) Lc ≧ 10.0
Requirement (3) F ₁ ≧ 0.07
Requirement (4) F ₂ ≧ 0.06
[In the above requirements (1) to (4), La uses the long-period interval calculated from the small-angle X-ray scattering profile and the crystallinity calculated using the heat of fusion measured by differential scanning calorimetry. Lc represents the crystal lamella thickness (unit: nm) calculated from the distance between the crystal lamellae and the long-period interval, and F ₁ represents a wave number of 997 cm ^{−. The} degree of orientation calculated from the infrared dichroic ratio measured at ¹ is shown, and F ₂ denotes the degree of orientation calculated from the infrared dichroic ratio measured at a wave number of 973 cm ⁻¹ . ]

The third aspect of the present invention is a thermoplastic resin molded body manufactured by the above-described manufacturing method and satisfies the following requirements (2) to (5). .
Requirement (2) Lc ≧ 10.0
Requirement (3) F ₁ ≧ 0.07
Requirement (4) F ₂ ≧ 0.06
Requirement (5) La ≧ 8.0
[In the above requirements (2) to (5), La uses the long-period interval calculated from the small-angle X-ray scattering profile and the crystallinity calculated using the heat of fusion measured by differential scanning calorimetry. Lc represents the crystal lamella thickness (unit: nm) calculated from the distance between the crystal lamellae and the long-period interval, and F ₁ represents a wave number of 997 cm ^{−. The} degree of orientation calculated from the infrared dichroic ratio measured at ¹ is shown, and F ₂ denotes the degree of orientation calculated from the infrared dichroic ratio measured at a wave number of 973 cm ⁻¹ . ]

Here, the “maximum injection pressure” in the present invention refers to the maximum value of the injection pressure that can be reached by the molding machine to be used in the filling process, and is a value specific to the injection molding machine to be used. The specific numerical value varies depending on the capacity of the molding machine, but in the present invention, this maximum injection pressure is P. The maximum injection pressure P is preferably, for example, 1000 kgf / cm ^{2 to} 2500 kgf / cm ² , but is not limited to this range.
The “molded body precursor” refers to a molded body formed through the second pressure holding step, that is, a molded body before the heat treatment step.
The “crystal lamella” refers to a crystal formed by folding a molecular chain of a polymer forming a resin in a thermoplastic resin molded body.
The “long period interval” refers to the distance between the centers of gravity of the individual crystal lamellae in the laminated structure of crystal lamella, amorphous region and crystal lamella. The “distance between crystal lamellae (La)” refers to the distance between crystal lamellae in the laminated structure, that is, the thickness of an amorphous region. The “crystal lamella thickness (Lc)” refers to the thickness of each crystal lamella.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the thermoplastic resin molding which has higher rigidity and high impact strength compared with the past.

[Method for producing resin molded article]
The method for producing a thermoplastic resin molded body (hereinafter also simply referred to as a molded body) according to the present invention includes a filling step, a first pressure-holding step, and a second pressure-holding step.
Here, the “filling step” refers to a step of filling a mold with a thermoplastic resin (hereinafter also simply referred to as a resin).
The form of the resin in the filling step is substantially in a molten state from the viewpoint that the degree of molecular chain orientation (F ₁ and F ₂ ) of the polymer can be made higher when it is formed into a molded body. Is preferred. Here, the “substantially molten state” means a state in which the resin has fluidity as a whole. That is, it does not mean that all the molecular chains of the polymer forming the resin are in intense thermal motion.

  In addition, in order to make the external appearance shape of the obtained molded object favorable, you may heat a metal mold | die beforehand at the time of filling. The heating temperature is preferably 10 ° C to 70 ° C, and preferably 20 ° C to 60 ° C.

  For filling the resin, a filling method using an injection molding machine is used. As described above, the resin is substantially in a molten state, and is filled in the space (mold cavity) inside the mold with a predetermined injection pressure.

Further, the “first pressure holding step” refers to a step of substantially stopping the filling of the thermoplastic resin and holding it for a predetermined time. By providing this first pressure-holding step, the resin is cooled. As a result, the melt viscosity increases, and the molecular chains can be efficiently oriented in the subsequent second pressure-holding step.
Here, “substantially stop filling” means that almost no pressure is applied to the nozzle for filling the resin, and no resin is injected from the tip of the nozzle, or the mold cavity is already filled. The state where it is injected slightly to the extent that it does not affect the applied resin.

The pressure and holding time (holding time) in the first holding pressure step are not particularly limited as long as the molten resin is cooled and, as a result, the melt viscosity is increased. Such conditions are preferable.
The pressure at the time of holding pressure varies depending on the size of the mold cavity, but is preferably 5% or less of the maximum injection pressure P in the filling step, preferably 2% or less, and preferably 0%. More preferred. The pressure holding time (holding time) is preferably 2 seconds or longer and 30 seconds or shorter, and more preferably 3 seconds or longer and 20 seconds or shorter.

  The “second pressure-holding step” refers to a step in which the resin filled in the mold cavity that has undergone the first pressure-holding step is further pressurized and held at a predetermined pressure. By providing this second pressure holding step, it is possible to further increase the degree of orientation of the molecular chains of the polymer when it is formed into a molded body. This makes it possible to improve the rigidity and impact resistance of the resulting molded body.

The pressure in the second pressure holding step varies depending on the size of the mold cavity, but is preferably 15% or more, more preferably 20% or more, and more preferably 30% or more of the maximum injection pressure P in the filling step. Most preferably.
The pressure holding time (holding time) is preferably 0.5 second to 60 seconds, and more preferably 1 second to 50 seconds. Moreover, it is preferable that the temperature of the metal mold | die at the time of holding pressure is 10 to 70 degreeC, and it is preferable that it is 20 to 60 degreeC.

  The method for measuring the pressure at the time of holding pressure varies depending on the type of the desired molded body, but in general, the pressure is measured using a pressure gauge provided in the molding machine.

The “heat treatment step” refers to a step of heat-treating the molded body precursor obtained in the second pressure holding step under predetermined conditions. By performing the heat treatment step, it is possible to further increase the degree of orientation of the molecular chains when formed into a molded body. This makes it possible to improve the rigidity and impact resistance of the resulting molded body in a shorter time.
This heat treatment step is preferably performed at a temperature not lower than the crystallization temperature of the resin and not higher than the melting point. Specifically, for example, when a molded body is obtained using a propylene-based resin, the heat treatment temperature is higher than the crystallization temperature of about 120 ° C. and lower than the melting point of about 170 ° C. The temperature is preferably 165 ° C, more preferably 135 ° C to 160 ° C, and still more preferably 150 ° C to 160 ° C. By performing heat treatment at such a temperature, it is possible to improve mechanical properties, particularly rigidity.

  In addition, from the viewpoint of mechanical properties of the obtained molded article, particularly impact strength, it may be composed of a plurality of steps such as a first heat treatment step and a second heat treatment step. The first heat treatment step is a heat treatment at a temperature not lower than the crystallization temperature of the resin and not higher than the melting point, and the second heat treatment step is a step of heat treatment at a temperature not lower than the glass transition point of the resin and not higher than the melting point. The heat treatment temperature in the first heat treatment step is preferably higher than the heat treatment temperature in the second heat treatment step.

  Specifically, for example, when a molded body is obtained using a propylene-based resin, the first heat treatment temperature is higher than the crystallization temperature of about 120 ° C. and lower than the melting point of about 170 ° C., as described above. It is temperature, it is preferable that it is 125 to 165 degreeC, it is more preferable that it is 135 to 160 degreeC, and it is still more preferable that it is 150 to 160 degreeC. The heat treatment temperature of the second heat treatment step is higher than about 0 ° C. which is a glass transition point and lower than about 170 ° C. which is a melting point, preferably 80 ° C. to 135 ° C., preferably 90 ° C. to More preferably, it is 130 degreeC, and it is still more preferable that it is 100 to 125 degreeC.

The melting point, crystallization temperature, and glass transition temperature are calculated using known methods. For example:
Using a differential scanning calorimeter, a predetermined amount of the Izod test piece of the molded body precursor is sealed in an aluminum pan, and then the temperature is changed as shown in steps A to C below. The melting point is determined as the endothermic peak of the heat flow curve observed during stage B, and the crystallization temperature is determined as the exothermic peak of the heat flow curve observed during stage C. Further, the glass transition point is calculated from the extrapolated glass transition start temperature and extrapolated glass transition end temperature from the step-like change portion in stage B. In addition, the temperature raising / lowering speed at this time is 10 degree-C / min.
Step A: Room temperature to -90 ° C
Stage B: -90 ° C to 200 ° C
Stage C: 200 ° C to 40 ° C

  The heat treatment time is 10 minutes to 400 hours, preferably 10 minutes to 300 hours, and more preferably 10 minutes to 200 hours. Even when heat treatment is performed in multiple stages, the heat treatment time of each step is preferably within the above range. By making the heating time longer than 10 minutes, it is possible to improve mechanical properties, particularly impact strength. Further, by making the heating time shorter than 400 hours, it becomes possible to prevent the decomposition of the propylene resin and to impart sufficient mechanical properties.

  For other thermoplastic resins, the heat treatment temperature is preferably (melting point−30 ° C.) or more and not more than the melting point of the thermoplastic resin, and (melting point−30 ° C.) or more and (melting point−5 ° C.) or less. Is more preferable. In addition, when performing the heat treatment in multiple stages, the heat treatment temperature in the first treatment step is preferably (melting point−30 ° C.) or more and not more than the melting point of the thermoplastic resin, (melting point−30 ° C.) or more, The melting point is more preferably −5 ° C. or less. The heat treatment temperature in the second treatment step is preferably (melting point− (melting point−glass transition temperature) × 0.5) or more and (melting point−30 ° C.) or less of the thermoplastic resin.

  As the heat treatment method, for example, (1) a method in which the mold is directly heated to 150 ° C. to 170 ° C. without taking out the molded body precursor from the mold, and (2) the molded body precursor is heated to 150 ° C. to 170 ° C. (3) a method of placing a molded body precursor in an oven filled with nitrogen, argon, air, etc. at 150 ° C to 170 ° C, and (4) 150 ° C to 170 ° C. Examples thereof include a method of immersing the molded body precursor in a bath filled with an inert liquid such as silicon oil at 0 ° C. or water. Among them, (3) a method of placing a molded body precursor in an oven filled with nitrogen, argon, air, etc. at 150 ° C. to 170 ° C., (4) an inert liquid such as silicon oil, water at 150 ° C.-170 ° C. It is preferable to use a method of immersing the molded body precursor in a bath filled with the slag.

Examples of resins used in the present invention include olefin resins such as ethylene resins and propylene resins, butylene ester resins such as butylene terephthalate resins and ethylene terephthalate resins, other styrene resins, carbonate resins, amide resins, Examples include acetal resins. Of these, olefin resins, ester resins, amide resins, acetal resins and the like, which are resins having crystallinity, are preferably used, olefin resins and ester resins are more preferably used, and olefin resins are used. Most preferred. Preferable olefin resin includes propylene resin.
These resins may be not only homopolymers but also copolymers with other compounds as described below. Examples of other compounds include ethylene and α-olefins having 4 or more carbon atoms.

  These resins generally have a lower melt flow than the resin used for the molded product because the resin molded product according to the present invention satisfies the requirements (1) to (4) or (2) to (5). It is preferable to have a rate. In the case of a propylene-based resin, the melt flow rate measured at a temperature of 230 ° C. in accordance with ASTM D1238 is 15 g / 10 minutes or less, more preferably 12 g / 10 minutes or less, and 0.0001 g / 10 minutes to 10 g. More preferably, it is / 10 minutes. When the melt flow rate exceeds 15 g / 10 min, it tends to be difficult to improve the rigidity and impact strength of the resulting molded article.

  As the propylene-based resin, it is preferable to use a propylene homopolymer or a copolymer of propylene and at least one olefin selected from the group consisting of ethylene and an α-olefin having 4 or more carbon atoms (provided that The propylene homopolymer may contain 1.0% by mass or less of ethylene or an α-olefin having 4 or more carbon atoms (the total amount of the propylene homopolymer is 100% by mass).

  Here, the copolymer of propylene and at least one olefin selected from the group consisting of ethylene and an α-olefin having 4 or more carbon atoms is at least selected from the group consisting of ethylene and an α-olefin having 4 or more carbon atoms. Examples thereof include a propylene random copolymer composed of a kind of olefin and propylene, or a propylene block copolymer containing a propylene homopolymer portion and a propylene-ethylene random copolymer portion. (However, the propylene homopolymer portion may contain 1.0% by mass or less of ethylene or an α-olefin having 4 or more carbon atoms. The total amount of the propylene homopolymer is 100% by mass. .)

  The propylene resin preferably used in the present invention is a propylene homopolymer or a propylene random copolymer, and more preferably a propylene homopolymer.

From the viewpoint of increasing rigidity, heat resistance, or hardness, isopropylene, measured by ¹³ C-NMR of the propylene homopolymer, propylene random copolymer, and homopolymer portion of the propylene block polymer The pentad fraction is preferably 0.94 or more.

The isotactic pentad fraction is defined as A.I. Isotactic linkage (in other words, propylene monomer) in pentad units in a polypropylene molecular chain measured by the method described by Zambelli et al. In Macromolecules, 6, 925 (1973) (ie, using ¹³ C-NMR) Is the fraction of propylene monomer units at the center of a chain of 5 consecutive meso-bonded units (provided that the NMR absorption peak assignment is then based on published Macromolecules, 8, 687 (1975)). Do).

Specifically, the isotactic pentad fraction is measured as the area fraction of the mmmm peak in the total absorption peak in the methyl carbon region of the ¹³ C-NMR spectrum. By this method, NPL standard material CRM No. of NATIONAL PHYSICAL LABORATORY, UK It was 0.944 when the isotactic pentad fraction of M19-14 Polypropylene PP / MWD / 2 was measured.

  The intrinsic viscosity ([η], unit: dl / g) of the propylene-based resin is preferably 1.2 dl / g or more from the viewpoint of improving mechanical properties, in particular, from the viewpoint of improving impact strength. Preferably it is 1.3 dl / g or more, More preferably, it is 1.4 dl / g or more.

  Moreover, as molecular weight distribution (ratio of weight average molecular weight (Mw) and number average molecular weight (Mn) (Mw / Mn)) measured by gel permeation chromatography (GPC) of propylene-based resin, preferably 3 7, more preferably 3-5.

As a manufacturing method of propylene-type resin, the method of manufacturing with a well-known polymerization method using a well-known polymerization catalyst is mentioned.
Examples of the polymerization catalyst include a catalyst system comprising (a) a solid catalyst component containing magnesium, titanium, halogen, and an electron donor as essential components, (b) an organoaluminum compound, and (c) an electron donor component. Is mentioned. As this catalyst system, for example, as described in JP-A-1-319508, JP-A-7-216017, JP-A-10-212319, etc., If necessary, in the presence of an ester compound, the general formula Ti (OR ₁ ) _a X _4-a (R ₁ is a hydrocarbon group having 1 to 20 carbon atoms, X is a halogen atom, and a is 0 <a ≦ 4. The trivalent titanium obtained by treating the solid product obtained by reducing the titanium compound represented by the formula with an organic magnesium compound in the presence of titanium tetrachloride and, if necessary, an ester compound. An α-olefin polymerization catalyst system containing a compound-containing solid catalyst component, an organoaluminum compound, and an electron donating compound can be mentioned.

  Examples of the polymerization method of the propylene-based resin include a bulk polymerization method, a solution polymerization method, a slurry polymerization method, and a gas phase polymerization method. These polymerization methods may be either batch type or continuous type, and these polymerization methods may be arbitrarily combined.

  The amount of (a) the solid catalyst component, (b) the organoaluminum compound, and (c) the electron donor component used in the above polymerization method, and the method for supplying each catalyst component to the polymerization tank are determined by the known method for using the catalyst. It may be determined as appropriate.

  The polymerization temperature is usually −30 ° C. to 300 ° C., preferably 20 ° C. to 180 ° C. The polymerization pressure is usually atmospheric pressure to 10 MPa, preferably 0.2 MPa to 5 MPa. As the molecular weight regulator, for example, hydrogen can be used.

  In the method for producing a propylene-based resin, preliminary polymerization may be performed before polymerization (main polymerization) is performed. Examples of the prepolymerization method include a method in which a small amount of propylene is supplied in the presence of (a) a solid catalyst component and (b) an organoaluminum compound and is carried out in a slurry state using a solvent.

In addition, you may add resin other than said resin and various additives as needed.
Examples of resins other than the above resins include elastomers. Examples of the additive include an antioxidant, an ultraviolet absorber, a nucleating agent, an inorganic filler, and an organic filler.

[Resin molding]
As described above, the present invention also provides a resin molded body that satisfies at least one of the following requirements (1) to (4) or requirements (2) to (5) (hereinafter also simply referred to as a molded body). It is.
Requirement (1) Lc / La ≦ 1.50
Requirement (2) Lc ≧ 10.0
Requirement (3) F ₁ ≧ 0.07
Requirement (4) F ₂ ≧ 0.06
Requirement (5) La ≧ 8.0
[In the above requirements (1) to (5), La uses the long-period interval calculated from the small-angle X-ray scattering profile and the crystallinity calculated using the heat of fusion measured by differential scanning calorimetry. Lc represents the crystal lamella thickness (unit: nm) calculated from the distance between the crystal lamellae and the long-period interval, and F ₁ represents a wave number of 997 cm ^{−. The} degree of orientation calculated from the infrared dichroic ratio measured at ¹ is shown, and F ₂ denotes the degree of orientation calculated from the infrared dichroic ratio measured at a wave number of 973 cm ⁻¹ . ]

In the said requirement (1), the impact strength of the molded object obtained can be made sufficient by Lc / La being 1.50 or less. Lc / La is preferably 0.5 to 1.50, more preferably 0.55 to 1.45, and still more preferably 0.6 to 1.40.
Moreover, in the said requirement (2), the bending elastic modulus of the molded object obtained can be made sufficient by the thickness (Lc) of a crystal lamella being 10.0 nm or more. The crystal lamella thickness (Lc) is preferably 10.0 nm to 25.0 nm, more preferably 10.5 nm to 24.5 nm, and still more preferably 11.0 nm to 24.0 nm.

In the above requirement (3), by the degree of orientation (F ₁₎ 0.07 or more, the impact strength of the obtained molded body may be sufficient. The degree of orientation (F ₁ ) is preferably 0.07 to 0.50, more preferably 0.08 to 0.50, and still more preferably 0.08 to 0.40.
In the above requirement (4), by the degree of orientation (F ₂₎ of less than 0.06, the impact strength of the obtained molded body may be sufficient. The degree of orientation (F ₂ ) is preferably 0.06 to 0.50, more preferably 0.07 to 0.50, and still more preferably 0.07 to 0.40.

  Moreover, in the said requirement (5), the impact strength of the molded object obtained can be made sufficient by making distance between crystal lamellae (La) into 8.0 nm or more. The distance between crystal lamellae (La) is preferably 8.2 nm to 15.5 nm, more preferably 8.5 nm to 15.3 nm, and still more preferably 8.9 nm to 15.1 nm.

In the requirements (1) to (5), the long period interval, the distance between the crystal lamellae, the thickness of the crystal lamella, and the degree of orientation are calculated using a known method. Specifically, it is as follows.
The long period interval is calculated by measuring a small-angle X-ray scattering profile and using the scattering angle corresponding to the obtained peak and the following Bragg equation.
Lp (nm) = λ / 2 sin θ
[Wherein, λ represents a wavelength (0.154 (nm) is used in the present invention), and θ represents a scattering angle. ]
The distance between the crystal lamellae is determined using the long-period interval (Lp) calculated by the above method and the crystallinity (χ) calculated using the heat of fusion measured by differential scanning calorimetry.
La (nm) = Lp (1-0.01 × χ)
Since Lc corresponds to the difference between Lp and La, Lc is obtained from Lp and La calculated by the above method.

The degree of crystallinity (χ) is determined using the heat of fusion (ΔHm) measured by differential scanning calorimetry and the following equation.
χ (%) = ΔHm / ΔH ⁰ m × 100
[Amount of heat of fusion (ΔH ⁰ m) at a crystallinity of 100% R. The value (208 J / g) described by Krigbaum et al. In Journal Polymer Science, 3,767 (1965) is used. ]

The degree of orientation (F ₁ and F ₂ ) is calculated from the infrared dichroic ratio (D) measured by a micro infrared spectrophotometer and the following equation.
F = (D-1) / (D + 2)
The infrared dichroic ratio (D) is calculated as a ratio of maximum transmittance and minimum transmittance (maximum transmittance / minimum transmittance) by rotating the polarizer. For 997 In the present invention (cm ^-1) and 973 (cm ^-1), respectively infrared dichroic ratio (D) was measured, 997 measured at (cm ^-1), the calculated degree of orientation F _1, 973 measured at (cm ^-1), the calculated degree of orientation and F _2.

The resin forming the resin molded body that satisfies such requirements is not particularly limited as long as it has a lower melt flow rate than the resin generally used for the molded body. Specifically, the melt flow rate of the resin measured according to ASTM D1238 is 15 g / 10 min or less, more preferably 12 g / 10 min or less, and 0.0001 g / 10 min to 10 g / 10 min. Is more preferable. By setting the melt flow rate to 15 g / 10 min or less, the rigidity and impact strength of the obtained molded body can be improved.
In addition, it is preferable that the resin molding which concerns on this invention is an injection molding.

The physical properties of the test pieces used in Examples and Comparative Examples were measured according to the following methods.
(1) Melt flow rate (MFR, unit: g / 10 minutes)
Measured according to ASTM D1238. Measurement was performed under the conditions of a measurement temperature of 230 ° C. and a load of 21 N.

(2) Flexural modulus (unit: MPa)
The bending elastic modulus at 23 ° C. was measured using a 3.2 mm-thick test piece molded by injection molding in accordance with ASTM D790.

(3) Izod impact strength (unit: kJ / m ² )
In accordance with JIS-K-7110, an Izod impact strength at 23 ° C. was measured using a 3.2 mm thick test piece molded by injection molding and notched after molding.

(4) Intrinsic viscosity ([η], unit: dl / g)
Using a Ubbelohde viscometer, reduced viscosities were measured at three points of concentrations of 0.1 g / dl, 0.2 g / dl and 0.5 g / dl. Intrinsic viscosity is calculated according to the calculation method described in “Polymer Solution, Polymer Experiments 11” (published by Kyoritsu Shuppan Co., Ltd.), page 491. That is, the reduced viscosity is plotted against the concentration, and the concentration is extrapolated to zero. Obtained by extrapolation. Polypropylene was evaluated at a temperature of 135 ° C. using tetralin as a solvent.

(5) Crystallinity (χ, unit:%)
The degree of crystallinity (χ) was calculated from the following formula [1].
χ (%) = ΔHm / ΔH ⁰ m × 100 Formula [1]
(In the formula, the heat of fusion (ΔH ⁰ m) at a degree of crystallinity of 100% was the value (208 J / g) described by WR Krigbaum et al. In Journal Polymer Science, 3,767 (1965). ΔHm is obtained by sealing about 6 mg of a sliced piece prepared by slicing the center of a molded Izod specimen with a cutter using mDSC (Q100) manufactured by TA Instruments Japan, Inc. in an aluminum pan. The temperature was raised from room temperature to 200 ° C. at 10 ° C./min, and was calculated from the area of the melting peak of the heat flow curve observed between 100 and 180 ° C. at the time of temperature rise.

(6) Long period interval (Lp, unit: nm)
The long cycle interval is calculated by the following formula [2] according to Bragg's equation by measuring a small-angle X-ray scattering pattern by measuring Through-View using a Rigaku NANO-Viewer (MicroMax-007). did.
Lp (nm) = λ / 2 sin θ Formula [2]
(In the formula, λ represents a wavelength (0.154 (nm)), and θ represents a scattering angle.)

(7) Crystal lamella thickness (Lc, unit: nm), distance between crystal lamellae (La, unit: nm)
The crystal lamella thickness (Lc) and the distance between crystal lamellae (La) were calculated by the following formulas [3-1] and [3-2] from the crystallinity (χ) and the long period interval (Lp).
Lc (nm) = Lp × 0.01 × χ Formula [3-1]
La (nm) = Lp (1-0.01 × χ) Formula [3-2]

(8) Degree of orientation (F, unit:-)
The degree of orientation (F) was determined by the following procedure.

(8-1)
Using a microtome, 1 mm in the MD (flow) direction, 3 mm in the ND (thickness) direction, and 6 μm in the MD (width) direction were formed.
(8-2)
Using a microscopic IR (IMV-400 manufactured by JASCO Corporation), an infrared two-color ratio (D) at a position of 500 μm is obtained from the surface layer (end surface in the MD direction) of the thin piece prepared in (8-1). It was. The infrared dichroic ratio (D) was calculated as the ratio of maximum transmittance to minimum transmittance (maximum transmittance / minimum transmittance) by rotating the polarizer. The infrared dichroic ratio (D) was measured for 997 (cm ⁻¹ ) and 973 (cm ⁻¹ ), respectively.
(8-3)
The degree of orientation (F ₁ and F ₂ ) was calculated from the infrared two-color ratio (D) by the following formula [4].
F (−) = (D−1) / (D + 2) Formula [4]

(9) Heat treatment Heat treatment is performed by placing the test piece in a stainless steel container 20 cm wide, 20 cm wide, 2 cm high in a gear oven, 22 cm long, 22 cm wide, and 0.5 cm thick. This was carried out after covering with a plate. Table 1 shows the heat treatment temperature and time.

  As the propylene-based resin, the following propylene-based resin (propylene homopolymer) produced using the catalyst described in JP-A-10-212319 was used.

PP-1 (propylene resin)
A propylene homopolymer having an intrinsic viscosity of 2.0 dl / g, an MFR of 3 g / 10 min, and an isotactic pentad fraction of 0.975.

PP-2 (propylene resin)
A propylene homopolymer having an intrinsic viscosity of 1.5 dl / g, an MFR of 8 g / 10 min, and an isotactic pentad fraction of 0.980.

[Example 1]
Using PP-1 as the propylene resin, using an injection molding machine (Toshiba Machine IS100EN), setting the cylinder temperature to 220 ° C., the injection time of 25 seconds, and the cooling time of 25 seconds. did. After filling (firing speed 35%) and holding at pressure 0 for 10 seconds (first pressure holding step), pressure holding (pressure 50%) was performed (second pressure holding step). The test piece was heat-treated in a gear oven under the conditions shown in Table 1. Using the test piece after heat treatment, the flexural modulus and Izod impact strength were measured. The results are shown in Table 2.

[Examples 2 to 4]
The test piece was formed in the same manner as in Example 1 except that the test piece was molded and heat-treated as described in Table 1. The results are shown in Table 2.

[Comparative Examples 1 to 10]
The test pieces were formed in the same manner as in Example 1 except that the test pieces were molded and heat-treated as described in Tables 3 and 5. The results are shown in Tables 4 and 6.

  From the above results, it was shown that according to the method for producing a resin molded body according to the present invention, it is possible to provide a resin molded body having high rigidity and excellent Izod impact strength.

Claims (3)

A filling step of filling thermoplastic resin into a mold cavity of an injection molding machine having a maximum injection pressure of P;
A first pressure holding step of substantially stopping and holding the filling of the thermoplastic resin;
A second pressure holding step of pressing and holding the thermoplastic resin that has undergone the first pressure holding step, and a method for producing a thermoplastic resin molded body,
The pressure in the first holding pressure step is 5% or less of the maximum injection pressure P,
The pressure in the second holding pressure step is 15% or more of the maximum injection pressure P,
The thermoplastic resin is a propylene resin, and the melt flow rate of the propylene resin is 15 g / 10 min or less under the measurement conditions of ASTM D1238.
A method for producing a thermoplastic resin molded article. The method for producing a thermoplastic resin molded body according to claim 1 , wherein the pressure holding time in the first pressure holding step is 2 seconds or more. Method for producing a thermoplastic resin molded article according to claim 1 or 2 further comprising a heat treatment step of heat-treating the molded precursor formed by the second pressure holding step.