JP2022021622A - Polypropylene-based resin particles and use thereof - Google Patents

Abstract

To provide novel polypropylene-based resin particles that can afford foamed particles, from which a molded article having an excellent shortened molding cycle (molded article productivity) and surface property can be obtained.SOLUTION: Polypropylene-based resin particles comprise a polypropylene-based resin as a base resin, where a particle weight is in a specified range, a crystal orientation parameter R of the surface is larger than 3.5 and equal to or less than 5, and a L12/D12 shrinkage ratio is 50% or more: L12/D12 shrinkage ratio=100×(1-(average L2/D2 ratio of foamed particles)/(average L1/D1 ratio of resin particles)) (1).SELECTED DRAWING: None

Description

The present invention relates to polypropylene-based resin particles and their use.

The polypropylene-based resin mold in-foam molded product (hereinafter, also simply referred to as “molded product”) includes distribution materials (for example, cushioning packaging materials, return boxes, cushioning materials for truck transportation, etc.), heat insulating materials, civil engineering and building materials, and automobiles. It is widely used in applications such as members (for example, tool boxes, floor core materials, etc.).

The polypropylene-based resin in-mold foam molded product can be obtained by in-mold foam molding of polypropylene-based resin foamed particles (hereinafter, also simply referred to as “foamed particles”). The polypropylene-based resin foamed particles can be obtained by impregnating polypropylene-based resin particles containing a polypropylene-based resin (hereinafter, also simply referred to as “resin particles”) with a foaming agent and then foaming the polypropylene-based resin particles. Can be done.

Conventionally, various polypropylene-based resin mold in-foamed molded bodies, polypropylene-based resin foamed particles, and polypropylene-based resin particles have been developed.

Patent Document 1 discloses polypropylene-based resin prefoamed particles using a polypropylene-based resin composition containing a polypropylene-based resin, a fatty acid amide compound, and a petroleum resin and / or a terpene-based resin as a base resin. There is.

Patent Document 2 describes a polypropylene resin having a melting point of 140 ° C. or higher and 155 ° C. or lower, a melt flow rate of 4.0 g / 10 minutes or more and 10 g / 10 minutes or less, and a melt flow rate of 0.1 g / 10 minutes or more and 2.0 g / 10. Disclosed are polypropylene-based resin foamed particles obtained by foaming polypropylene-based resin particles using a polypropylene-based resin mixture in which a polypropylene-based resin of less than a minute is mixed as a base resin.

Patent Document 3 discloses polypropylene-based resin foam particles composed of polypropylene-based resin particles using a polypropylene-based resin mixture composed of polypropylene-based resin and polypropylene-based wax as a base resin.

Japanese Unexamined Patent Publication No. 2008-274025 Japanese Unexamined Patent Publication No. 2017-179281 WO2017 / 169260 Gazette

However, the above-mentioned conventional technique is not sufficient from the viewpoint of shortening the molding cycle (mold productivity) and providing a molded body having excellent surface properties, and there is room for further improvement.

One embodiment of the present invention has been made in view of the above problems, and an object thereof is a novel polypropylene capable of providing foamed particles capable of shortening a molding cycle and providing a molded product having excellent surface properties. The purpose is to provide based resin particles.

As a result of diligent studies to solve the above problems, the present inventors have obtained the crystal orientation parameter R on the surface of the resin particles, the average L ₁ / D ₁ ratio of the resin particles, and the average L ₂ / D ₂ ratio of the foamed particles. The present invention is completed by finding that it is possible to shorten the molding cycle and provide a molded product having excellent surface properties by using resin particles having a calculated L ₁₂ / D ₁₂ shrinkage ratio within a specific range. It came to.

That is, the polypropylene-based resin particles according to the embodiment of the present invention have the crystal orientation parameter R on the surface of the resin particles exceeding 3.5 and 5 or less, containing the polypropylene-based resin as the base resin, and the weight per grain is 0. .5 mg / grain or more and 5.0 mg / grain or less, and the L ₁₂ / D ₁₂ shrinkage rate calculated by the following formula (1) is 50% or more:
L ₁₂ / D ₁₂ Shrinkage rate = 100 × (1- (average L ₂ / D ₂ ratio of polypropylene-based resin foam particles) / (average L ₁ / D ₁ ratio of polypropylene-based resin particles)) ... 1);
Here, the polypropylene-based resin foamed particles are formed by foaming the polypropylene-based resin particles, and the foaming ratio is 15 times or more.

Further, the method for producing polypropylene-based resin particles according to an embodiment of the present invention is a method for producing polypropylene-based resin particles, and the L ₄₅ / D ₄₅ shrinkage rate obtained by the following formula (2) is 50% or more. The polypropylene-based resin particles include a step of adjusting the crystal orientation parameter R on the surface of the above to be more than 3.5 and 5 or less, and the weight of each polypropylene-based resin particle is 0.5 mg / grain or more and 5.0 mg / grain or less. Is:
L ₄₅ / D ₄₅ Shrinkage rate = 100 × (1- (average L ₅ / D ₅ ratio of polypropylene-based resin foam particles) / (average L ₄ / D ₄ ratio of polypropylene-based resin particles)) ... 2);
Here, the polypropylene-based resin foamed particles are formed by foaming the polypropylene-based resin particles, and the foaming ratio is 15 times or more.

Further, in the method for producing polypropylene-based resin foamed particles according to an embodiment of the present invention, polypropylene-based resin particles having a crystal orientation parameter R of more than 3.5 and 5 or less on the surface of the resin particles in a container, a dispersion medium, and a dispersion medium A dispersion preparation step of mixing a foaming agent to prepare a dispersion, and a release step of discharging the dispersion to a pressure range lower than the internal pressure of the container to obtain polypropylene-based resin foam particles having a foaming ratio of 15 times or more. The L ₆₇ / D ₆₇ shrinkage rate obtained by the following formula (3) is 50% or more:
L ₆₇ / D ₆₇ Shrinkage rate = 100 × (1- (average L ₇ / D ₇ ratio of the polypropylene-based resin foam particles) / (average L ₆ / D ₆ ratio of the polypropylene-based resin particles)) ... (3).

Further, in the method for producing polypropylene-based resin particles according to an embodiment of the present invention, a blend containing polypropylene-based resin is heated in an extruder to be melted and kneaded to prepare a polypropylene-based resin composition. Resin composition preparation process and
An extrusion step of extruding the obtained polypropylene-based resin composition from one or more discharge holes provided in a die provided in the extruder.
A cooling step of solidifying the extruded polypropylene-based resin composition by cooling it using a cooling device provided with a cooling medium.
A pick-up process in which the polypropylene-based resin composition solidified using a pick-up machine is picked up in the gas phase,
Including a shredding step of shredding the polypropylene-based resin composition taken up using a shredding device to obtain polypropylene-based resin particles.
The heating temperature in the resin composition preparation step is Tm ₁ + 40 ° C. to Tm ₁ + 110 ° C., where Tm ₁ is the melting point of the polypropylene-based resin.
The temperature of the cooling medium is Tm _1-150 ° C. or higher and Tm _1-100 ° C. or lower.
The surface temperature of the resin composition in the gas phase in the take _- up step is Tm 1-70 ° C. or lower.
The _average L4 / _D4 ratio of the polypropylene-based resin particles is 2.0 to 5.0.
The stretchability obtained from the following formula (10) is 10 m / min to 100 m / min;
Degree of elongation = take-up speed-resin wire speed ... Equation (10),
Here, the pick-up speed is the pick-up speed per unit time of the polypropylene-based resin composition by the pick-up machine in the pick-up step.
The resin linear velocity is a value obtained from the following equation (11);
Resin linear velocity = discharge amount / (density of the polypropylene-based resin composition x total area of the discharge holes) ... Equation (11),
Here, the discharge amount is the amount of the polypropylene-based resin composition extruded from the extruder per unit time in the extrusion step, and the total area of the discharge holes is the amount provided in the extruder. The sum of the areas of one or more of the discharge holes provided in the die;
The relaxation time obtained from the following equation (12) is greater than 0 seconds and 0.1000 seconds or less;
Relaxation time = distance from the die to the cooling medium / take-up speed ... Equation (12),
Here, the distance from the die to the cooling medium is greater than 0 mm and less than 80 mm.
This is a method for producing polypropylene-based resin particles in which the crystal orientation parameter R on the surface exceeds 3.5 and becomes 5 or less.

According to one embodiment of the present invention, there are effects such as shortening of the molding cycle (mold productivity), being able to provide foamed particles capable of providing a molded body having excellent surface properties, and being able to provide polypropylene-based resin particles. ..

It is a figure which shows an example of the positional relationship between a polypropylene resin particle and incident light at the time of measuring the crystal orientation parameter R of the surface of a resin particle. (A) is a view of the columnar polypropylene-based resin particles according to the embodiment of the present invention as viewed from one direction, and (b) is a substantially spherical polypropylene-based resin particles according to the embodiment of the present invention. Is a view seen from one direction, and (c) is a cross-sectional view taken along the line AA'of (b). (A) is a view of columnar polypropylene resin foamed particles according to an embodiment of the present invention as viewed from one direction, and (b) is a cross-sectional view taken along the line AA'of (a). Yes, (c) is a view of substantially spherical polypropylene-based resin foamed particles according to one embodiment of the present invention as viewed from one direction, and (d) is a cross section taken along the line BB'of (c). It is a figure. Differential Scanning Calorimetry (DSC) is performed on the polypropylene-based resin foamed particles according to the embodiment of the present invention to raise the temperature from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min. It is an example of the DSC curve obtained by. The horizontal axis represents temperature and the vertical axis represents calorific value. It is a figure which shows an example of the enlarged part of the surface of the effervescent molded article in a polypropylene resin mold. It is a figure which shows an example of the boundary line.

An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications can be made within the scope of the claims. The technical scope of the present invention also includes embodiments or examples obtained by appropriately combining the technical means disclosed in different embodiments or examples. Further, by combining the technical means disclosed in each embodiment, new technical features can be formed. In addition, all the academic documents and patent documents described in the present specification are incorporated as references in the present specification.

Further, unless otherwise specified in the present specification, "A to B" representing a numerical range is intended to be "A or more (including A and larger than A) and B or less (including B and smaller than B)".

Further, unless otherwise specified in the present specification, as the structural units, the structural unit derived from the X ₁ monomer, the structural unit derived from the X ₂ monomer, ... And the X _n monomer (n is A copolymer containing (an integer of 2 or more) is also referred to as an X ₁ / X ₂ / ... / X _n copolymer. Unless otherwise specified, the X ₁ / X ₂ / ... / X _n copolymer is not particularly limited in the polymerization mode, and may be a random copolymer or a block copolymer. It may be a graft copolymer or a graft copolymer. Further, unless otherwise specified in the present specification, as the structural units, a structural unit derived from the X ₁ monomer, a structural unit derived from the X ₂ monomer, ... And an X _n monomer (n is Elastomers containing (an integer of 2 or more) are also referred to as X ₁ / X ₂ / ... / X _n rubber.

[1. Technical Idea of One Embodiment of the Present Invention]
In Patent Documents 1 to 3, foaming having excellent surface properties can be provided by using resin particles containing a fatty acid amide compound, an additive such as a petroleum resin and a terpene resin, or a special polypropylene resin. Techniques for providing particles are disclosed. As described above, a conventional person skilled in the art has aimed at providing foamed particles capable of providing a molded product having excellent surface properties, and the point of view of those skilled in the art is the use of a specific additive and a specific resin, that is, the composition of the resin particles ( It was an improvement of the component).

The present inventor has aimed to achieve the above-mentioned problems from a viewpoint different from the conventional viewpoints of those skilled in the art. That is, an object according to an embodiment of the present invention is to provide foamed particles capable of shortening the molding cycle and providing a molded product having excellent surface properties without using a special resin composition of the polypropylene-based resin. It is to provide new polypropylene-based resin particles which can be used.

As a result of diligent studies to solve the above problems, the present inventors have determined that the resin particles have a crystal orientation parameter R on the surface of the resin particles and the L / D shrinkage ratio, which is a physical property, within a specific range. We have found that it is possible to shorten the molding cycle and provide a molded product having excellent surface characteristics, and have completed the present invention.

[2. Polypropylene resin particles]
The polypropylene-based resin particles according to the embodiment of the present invention contain a polypropylene-based resin as a base resin, and the weight per grain is 0.5 mg / grain or more and 5.0 mg / grain or less, and the above formula (1). The L ₁₂ / D ₁₂ shrinkage rate obtained in 1) is 50% or more. In the present specification, "polypropylene resin particles" are also referred to as "resin particles", and "polypropylene resin particles according to an embodiment of the present invention" are also referred to as "the present resin particles".

Since the present resin particles have the above-mentioned structure, it is possible to provide foamed particles capable of providing a molded product having excellent surface properties and a molding cycle without using a special resin composition of the polypropylene-based resin. As used herein, surface property is a property evaluated by surface spread and surface integrity. The molding cycle is the time from the start of molding in the production of the effervescent molded product in a polypropylene resin mold to the end of molding in which the molded product is released. The evaluation method of surface spread, surface consistency and molding cycle will be described in detail in Examples and the like. In one embodiment of the present invention, various polypropylene-based resins can be used, including polypropylene-based resins having a special configuration.

(2-1. Polypropylene resin)
In the present resin particles, the "base resin" is intended to be a resin that accounts for 50% by weight or more of 100% by weight of the resin contained in the resin particles. In the present specification, the "resin contained in the resin particles" is intended to be a polypropylene-based resin contained in the resin particles, and a thermoplastic resin and an elastomer other than the polypropylene-based resin that can be contained in the resin particles. The resin particles contain 50% by weight or more of a polypropylene resin, preferably 60% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight, based on 100% by weight of the resin contained in the resin particles. The above is included, and particularly preferably 90% by weight or more.

Examples of the polypropylene-based resin include polypropylene homopolymers, ethylene / propylene random copolymers, 1-butene / propylene random copolymers, ethylene / 1-butene / propylene random copolymers, and ethylene / propylene block copolymers. , 1-butene / propylene block copolymer, propylene / chlorinated vinyl copolymer, propylene / maleic anhydride copolymer and the like. Only one kind of these may be used, or two or more kinds may be used in combination.

A copolymer such as an ethylene / propylene copolymer has a structural unit derived from an ethylene monomer (also referred to as an ethylene unit) and a structural unit derived from a propylene monomer (also referred to as a propylene unit) as constituent units. The case including and will be described. In this case, a copolymer containing more ethylene units than propylene units is referred to as a polyethylene-based resin, and a copolymer containing more propylene units than ethylene units is referred to as a polypropylene-based resin.

The polypropylene-based resin may contain a thermoplastic resin component other than the polypropylene-based resin and / or an elastomer component as long as the effect of the present invention is not impaired. Examples of the thermoplastic resin other than the polypropylene-based resin include polyolefin-based resins such as polyethylene, other conceivable resins, vinyl acetate-based resins, thermoplastic polyester resins, acrylic acid ester resins, styrene-based resins, and polyamide resins. .. Only one type of these thermoplastic resins may be used, or two or more types may be used in combination. Examples of elastomers other than polypropylene-based resins include ethylene / propylene rubber and ethylene / propylene / butadiene rubber. Only one kind of these elastomers may be used, or two or more kinds thereof may be used in combination. In the present specification, "thermoplastic resin component and / or elastomer component other than polypropylene resin" may be referred to as "other resin".

(2-2. Resin particle additive)
The resin particles may contain various additives in addition to the polypropylene-based resin, if necessary.

In the present specification, an additive contained in polypropylene-based resin particles, in other words, an additive kneaded into polypropylene-based resin particles, is also referred to as a "resin particle additive". The above-mentioned "resin particle additive" can be said to be a component other than the resin (polypropylene resin, thermoplastic resin other than polypropylene resin and elastomer) in the resin particles.

Examples of the resin particle additive contained in the resin particles include hydrophilic compounds, antioxidants, heat stabilizers, ultraviolet absorbers, flame retardants, antistatic agents, metal deactivators, carbon blacks, pigments, and dyes. , Nucleating agent, bubble adjusting agent and the like.

The amount of these resin particle additives is the total amount of all the resin particle additives, preferably 25 parts by weight or less, more preferably 10 parts by weight or less, and 5 parts by weight or less per 100 parts by weight of the resin contained in the resin particles. More preferred. When the total amount of the resin particle additive is 25 parts by weight or less per 100 parts by weight of the resin contained in the resin particles, (a) the polypropylene-based resin in the dispersion liquid in the step of manufacturing the foamed particles using the obtained resin particles. There is no risk of deterioration of the dispersibility of the particles, (b) the average bubble diameter of the obtained foamed particles does not become too fine, and (c) the foamed particles can provide a good molded body in the molding step, and ( d) The obtained molded product has an advantage that the mechanical strength does not decrease.

In order to obtain a molded product having excellent surface properties, the present resin particles include a fatty acid amide compound, a resin particle additive such as a petroleum resin and a terpene resin, as described in Patent Documents 1 to 3, and a resin particle additive. It may further contain a special polyolefin resin. When the resin particles further contain these fatty acid amide compounds, resin particle additives such as petroleum resin and terpene resin, and special polyolefin-based resin, the resin particles provide a molded product having better surface properties. The foamed particles to be obtained can be provided.

(2-3. Weight per grain)
The weight per grain (also referred to as grain weight) of the resin particles is preferably 0.5 mg / grain or more and 5.0 mg / grain or less, and more preferably 0.8 mg / grain or more and 4.0 mg / grain or less. When the weight per grain of the polypropylene-based resin particle is (a) 0.5 mg / grain or more, there is no possibility that the handleability and cutting property of the resin particle are deteriorated, and (b) 5 mg / grain or less. In the in-mold foam molding using the foamed particles obtained from the resin particles, there is no possibility that the filling property of the foamed particles into the mold is lowered. When the foamed particles are excellent in filling property into the mold, the molded product produced by using the foamed particles has an advantage that the drying time after molding is shortened. That is, it can be said that the foamed particles having excellent filling property into the mold can provide a molded product having excellent productivity.

(2-4. Shape of resin particles)
The shape of the resin particles is limited to a columnar column or a polygonal columnar shape. Examples of the shape of the resin particles include a columnar shape (also referred to as a cylindrical shape), a rectangular parallelepiped shape, and a cubic shape. The cross-sectional shape of the columnar particles is not particularly limited, and examples thereof include an ellipse, a substantially circular shape, and a circular shape.

(2-5. Average L ₁ / D ₁ ratio)
The average L ₁ / D ₁ ratio of the present resin particles is preferably 2.0 to 5.0, more preferably 2.3 to 5.0, and 2.5 to 5.0. Is more preferable, 2.7 to 5.0 is more preferable, and 3.0 to 5.0 is further preferable. When the average L ₁ / D ₁ ratio is (a) 2.0 or more, it has an advantage that it can provide foamed particles that can provide a molded product having excellent surface properties, and (b) 5.0 or less. In the case, since the production of the resin particles is easy, there is an advantage that the productivity is excellent.

The average L ₁ / D ₁ ratio is an average value calculated from the L ₁ / D ₁ ratio of 10 randomly selected polypropylene-based resin particles.

L ₁ and D ₁ will be described with reference to FIG. FIG. 2A is a view of columnar polypropylene-based resin particles according to an embodiment of the present invention viewed from one direction, and FIG. 2B is a substantially spherical polypropylene according to an embodiment of the present invention. It is the figure which looked at the system resin particle from one direction, and (c) is the cross-sectional view taken along the line AA' of (b). The _AA'line in FIG. 2B passes through the center in the L1 direction.

As shown in FIGS. 2A and 2B, L1 is the length of the longest portion of the polypropylene _- based resin particles. As shown in FIG. 2A, it can be said that L ₁ is the length of the longest portion of the polypropylene-based resin particles in the longitudinal direction. When the polypropylene-based resin particles are extruded from an extruder or the like to be produced, as will be described later, it can be said that L ₁ is the longest length in the extrusion direction of the polypropylene-based resin particles.

As shown in FIGS. 2 (a) and 2 (c), D ₁ has a maximum diameter D ₁ max and a minimum diameter D ₁ min in a cross section perpendicular to the L ₁ direction of the maximum diameter portion of the polypropylene resin particles. It is an average value and is a value calculated by the following formula (4):
D ₁ = (D ₁ max + D ₁ min) / 2 ... Equation (4).

As shown in FIG. 2A, when the polypropylene-based resin particles are columnar, the maximum diameter portion of the polypropylene-based resin particles may be the end portion of the polypropylene-based resin particles. As shown in FIG. 2 (c), when the polypropylene-based resin particles are substantially spherical, the maximum diameter portion of the polypropylene-based resin particles may be the center of the polypropylene _- based resin particles in the L1 direction.

As shown in FIG. 2 (c), the shape of the cross section of the substantially spherical polypropylene-based resin particles shown in FIGS. 2 (b) and ₂ (c) perpendicular to the L1 direction of the maximum diameter portion is circular. Is. Therefore, in the substantially spherical polypropylene-based resin particles shown in FIGS. 2 (b) and 2 (c), D ₁ max and D ₁ min have the same values.

The average L ₁ / D ₁ ratio can be adjusted by appropriately changing the pick-up speed and shredding speed of the resin particles in the production of the resin particles. For the pick-up speed and shredding speed of resin particles, see the following [3. Method for producing polypropylene-based resin particles] will be described in detail.

In the present resin particles, the cross-sectional shape perpendicular to the L1 direction can be _a closed curve without a recess such as a circle or an ellipse.

(2-6. Crystal orientation parameter R)
The crystal orientation parameter R on the surface of the resin particles is the resin temperature, the area per discharge hole, the discharge amount, the resin linear velocity, the distance from the die to the cooling medium, the temperature of the cooling medium, the cooling time, and the take-up in the production of the resin. It can be adjusted by appropriately changing the speed, the degree of stretching, the relaxation time, the average L1 / D1 ratio, and the like. The following [3. Method for producing polypropylene-based resin particles] will be described in detail.

The crystal orientation parameter R on the surface of the resin particles can be measured by Raman spectroscopy and is a value calculated by the following equation (5). A method for measuring the crystal orientation parameter R on the surface of polypropylene-based resin particles will be described with reference to FIG. 1. FIG. 1 is a diagram showing an example of a state when measuring the crystal orientation parameter R on the surface of polypropylene-based resin particles. The measurement is carried out at an arbitrary point 2 on the side surface of the polypropylene-based resin particles 1 having a randomly selected columnar or polygonal columnar shape. The measurement was performed using an attenuated total reflection method (hereinafter referred to as ATR method) under polarized conditions with the measurement mode as microscopic Raman. First, as shown by the arrow A in FIG. 1, a Raman spectrum is obtained by measuring in a state where the polarization direction of the incident light 3 and the extrusion direction of the resin particles are matched. Next, from the obtained spectrum, the peak intensity (I810) attributed to the combination mode of the expansion and contraction of the main chain of propylene observed near the wavelength of 810 cm ^-1 and the CH3 variable angular vibration, and CH3 observed near the wavelength of 840 cm ^-1 . The crystal orientation parameter R was calculated by taking the ratio of the peak intensity (I840) attributable to the angular vibration of.
Crystal orientation parameter R = (I810) / (I840) ... Equation (5)
The measurement was performed twice in total by changing the position of point 2, and the average value was used. Examples of detailed conditions are shown below, but the device is not limited to the following examples as long as it can perform microscopic measurement by the ATR method.

Laser Raman spectroscopy device: in Vita (RENISHAW)
Measurement mode: Microscopic Raman objective lens: × 20
Beam diameter: 5 μm
Light source: YAG 2nd 532nm
Laser power: 10mW
Diffraction grating: Single 3000gr / mm
Slit: 65 μm
Detector: CCD / RENISHAW 1024 × 256

For the resin particles, the crystal orientation parameter R on the surface of the resin particles obtained by the above formula (5) is preferably more than 3.5, more preferably 4 or more. When the crystal orientation parameter R exceeds 3.5, the obtained resin particles can not only provide a molded product having excellent surface properties, but can also provide foamed particles that shorten the molding cycle.

The upper limit of the crystal orientation parameter R on the surface of the resin particles is preferably 5 or less. When the crystal orientation parameter R is 5 or less, there is an advantage that the productivity of the resin particles is excellent. When resin particles having a crystal orientation parameter R on the surface of the resin particles exceeding 5 are obtained, it becomes necessary to increase the take-up speed of the strands, which may cause production problems such as the strands being cut.

(2-7. L ₁₂ / D ₁₂ shrinkage rate)
The resin particles have an L ₁₂ / D ₁₂ shrinkage ratio of 50% or more, preferably 60% or more, more preferably 70% or more, and 75% or more, which are obtained by the above formula (1). It is more preferably present, and particularly preferably 80% or more. When the L ₁₂ / D ₁₂ shrinkage ratio is 50% or more, the obtained resin particles can provide foamed particles that can shorten the molding cycle and provide a molded product having excellent surface properties.

The upper limit of the L ₁₂ / D ₁₂ shrinkage rate is not particularly limited, but is preferably 100% or less, more preferably 95% or less, still more preferably 90% or less, and 85. % Or less is particularly preferable. When the L ₁₂ / D ₁₂ shrinkage ratio is 100% or less, it has an advantage of excellent productivity.

The polypropylene-based resin foamed particles for specifying the average L ₂ / D ₂ ratio will be described. In the formula (1), the polypropylene-based resin foamed particles for specifying the average L ₂ / D ₂ ratio are formed by foaming the polypropylene-based resin particles in which the average L ₁ / D ₁ ratio is specified in the formula (1). The foaming ratio is 15 times or more. Foaming of polypropylene-based resin particles for which the average L ₁ / D ₁ ratio is specified in the formula (1) for obtaining polypropylene-based resin foamed particles for specifying the average L ₂ / D ₂ ratio in the formula (1). Examples of the method include, but are not limited to, a method having each of the steps (a-1) to (a-3) in order: (a-1) polypropylene-based resin particles and a dispersion medium in a container. And a step of mixing the foaming agent to prepare a dispersion; (a-2) a step of raising the temperature inside the container to a desired foaming temperature and increasing the pressure inside the container to a desired foaming pressure; and (a-3). ) A step of obtaining foamed particles having a foaming ratio of 15 times or more by discharging the dispersion liquid into a pressure range lower than the container internal pressure. The foaming ratio is, for example, 15 times or 20 times. The dispersion medium is, for example, water, and the foaming agent is, for example, carbon dioxide. The foaming temperature is, for example, 153 ° C., and the foaming pressure is, for example, 3 MPa · G. In the present specification, "G" attached to the unit of pressure "Pa · G" indicates that the pressure is represented by a gauge pressure.

Foaming of polypropylene-based resin particles for which the average L ₁ / D ₁ ratio is specified in the formula (1) for obtaining polypropylene-based resin foamed particles for specifying the average L ₂ / D ₂ ratio in the formula (1). As a method, for example, a method having each of the steps (b-1) to (b-5) in order can be mentioned. :: (b-1) 100 polypropylene-based resin particles are placed in an autoclave having a volume of 0.3 m ³ . A step of charging an autoclave (container) by weight of 200 parts by weight, 200 parts by weight of water as a dispersion medium, 1 part by weight of tertiary calcium phosphate as a dispersant, and 0.07 parts by weight of sodium alkylsulfonate as a dispersion aid; (b). -2) Then, 5 parts by weight of carbon dioxide gas as a foaming agent is charged in a container, and the charged raw materials are stirred to prepare a dispersion liquid; (b-3) Next, the temperature inside the container is 153 ° C. ( Step of raising the temperature to 3.0 MPa · G (foaming pressure) in the container by raising the temperature to 3.0 MPa · G (foaming pressure); Step of maintaining pressure; (b-5) Next, one end of the autoclave is opened, and the dispersion liquid in the container is discharged to a non-sealed (under atmospheric pressure) tubular container through an orifice plate of φ3.2 mm. A step of obtaining polypropylene-based resin foamed particles.

The average L ₂ / D ₂ ratio is an average value calculated from the L ₂ / D ₂ ratio of 10 polypropylene-based resin foamed particles randomly selected from the polypropylene-based resin foamed particles obtained as described above. Is.

L ₂ and D ₂ will be described with reference to FIG. FIG. 3A is a view of columnar polypropylene resin foamed particles according to an embodiment of the present invention viewed from one direction, and FIG. 3B is a view taken along the line AA'of FIG. 3A. It is a cross-sectional view. FIG. 3 (c) is a view of substantially spherical polypropylene-based resin foamed particles according to an embodiment of the present invention as viewed from one direction, and FIG. 3 (d) is a view taken along the line BB'of (c). It is a cross-sectional view. The AA'line in FIG. 3A and the BB'line in _FIG . 3C each pass through the center in the L2 direction.

As shown in FIGS. 3 (a) and 3 (c), L ₂ is the length of the longest portion of the polypropylene-based resin foamed particles. As shown in FIG. 3A, it can be said that L ₂ is the length of the longest portion of the polypropylene-based resin foamed particles in the longitudinal direction.

As shown in FIGS. 3A and _3D , D2 has a maximum diameter _D2 max and a minimum diameter _D2 min in a cross section perpendicular to the L2 direction of the maximum diameter portion of the polypropylene _- based resin foamed particles. Is the average value of, and is the value calculated by the following equation (6):
D ₂ = (D ₂ max + D ₂ min) / 2 ... Equation (6).

As shown in FIG. 3A, when the polypropylene-based resin foamed particles are columnar, the maximum diameter portion of the polypropylene-based resin foamed particles may be the end portion of the polypropylene-based resin foamed particles. As shown in FIG. 3D, when the polypropylene-based resin foamed particles are substantially spherical, the maximum diameter portion of the polypropylene-based resin foamed particles may be the center of the polypropylene _- based resin foamed particles in the L2 direction.

As shown in FIG. 3 (d), the shape of the cross section of the substantially spherical polypropylene-based resin foam particles shown in FIGS. 3 (c) and ₃ (d), which is perpendicular to the L2 direction of the maximum diameter portion, is It is circular. Therefore, in the substantially spherical polypropylene-based resin foamed particles shown in FIGS. 3 (c) and 3 (d), D ₂ max and D ₂ min are the same values.

The L ₁₂ / D ₁₂ shrinkage ratio is the resin temperature, the area per discharge hole, the discharge amount, the resin linear velocity, the distance from the die to the cooling medium, the temperature of the cooling medium, the cooling time, and the take-up in the production of the resin particles. It can be adjusted by appropriately changing the speed, the degree of stretching, the relaxation time, the _average L1 / D1 _ratio , and the like. The following [3. Method for producing polypropylene-based resin particles] will be described in detail.

(2-8. Method for manufacturing resin particles)
The production method for obtaining the present resin particles is not particularly limited. The resin particles will be described later [3. It is preferable that the polypropylene-based resin particles are produced by the method for producing polypropylene-based resin particles described in].

[3. Manufacturing method of polypropylene resin particles]
The method for producing polypropylene-based resin particles according to an embodiment of the present invention is a method for producing polypropylene-based resin particles so that the L ₄₅ / D ₄₅ shrinkage rate obtained by the above formula (2) is 50% or more. The polypropylene-based resin particles include a step of adjusting, and the weight per particle is 0.5 mg / grain or more and 5.0 mg / grain or less.

In the present specification, "a method for producing polypropylene-based resin particles according to an embodiment of the present invention" is also referred to as "a method for producing the present resin particles".

Since the method for producing the present resin particles has the above-mentioned structure, it is possible to provide foamed particles capable of shortening the molding cycle and providing a molded product having excellent surface properties without using a special resin composition of the polypropylene-based resin. , Polypropylene resin particles can be obtained.

The method for producing the resin particles is described in [2. Polypropylene-based resin particles] can be suitably used for producing the present resin particles described in the section. The aspects of the polypropylene-based resin particles in the method for producing the present resin particles include preferred embodiments described in the above [2. Polypropylene-based resin particles] may be the same as the embodiment of the polypropylene-based resin particles described in the section.

The method for producing the present resin particles includes, in addition to the known method for producing polypropylene-based resin particles, a step of adjusting the L ₄₅ / D ₄₅ shrinkage ratio obtained by the above formula (2) to be 50% or more. It may be a manufacturing method. In the present specification, the "step of adjusting the L ₄₅ / D ₄₅ shrinkage rate to be 50% or more obtained by the above formula (2)" is also referred to as "L ₄₅ / D ₄₅ shrinkage rate adjusting step".

The method for producing the present resin particles includes, for example, a step of preparing a polypropylene-based resin composition containing (A1) a polypropylene-based resin and, if necessary, another resin and a resin particle additive, and (A2) the polypropylene-based resin. It may further include a step of molding and shredding the resin composition into a desired shape.

The method for producing the present resin particles is, for example, a polypropylene-based resin composition which is a melt-kneaded product by melt-kneading a (B1) polypropylene-based resin and, if necessary, a blend containing another resin and a resin particle additive. A step of preparing the It may further have a step of forming and shredding into a desired shape such as (straw-shaped). By melt-kneading the blend containing the polypropylene-based resin or the like in this way, more uniform polypropylene-based resin particles can be obtained.

In the above (B1), examples of the apparatus for melt-kneading the blended product (melt-kneading apparatus) include an extruder, a kneader, a bambali mixer, and a roll. As the melt-kneading device, an extruder is preferable, and a twin-screw extruder is more preferable, because resin particles can be easily and efficiently produced. The polypropylene-based resin composition, which is a melt-kneaded product, can be extruded, for example, in a strand shape, from one or more discharge holes provided in a die attached to the tip of a melt-kneaded device (for example, an extruder). "Extruding" a polypropylene-based resin composition, which is a melt-kneaded product, from a discharge hole may be referred to as "discharge".

In the above (B2), examples of the device (cooling device) for cooling the melt-kneaded polypropylene-based resin composition include a water tank and a water channel provided with water as a cooling medium. In the above (B2), the cooling of the polypropylene-based resin composition that has been melt-kneaded may be so-called natural cooling only by leaving the polypropylene-based resin composition at room temperature.

In the above (B3), examples of the device (shredding device) for shredding the cooled polypropylene-based resin composition into a desired shape include a pelletizer provided with a cutter blade.

The method for producing the present resin particles is, for example, a step of blending (C1) a polypropylene-based resin and, if necessary, another resin and a resin particle additive to prepare a blend, and (C2) the blend. A step of preparing a polypropylene-based resin composition which is a melt-kneaded product by putting it into an extruder and melt-kneading it, and (C3) a melt-kneaded polypropylene-based resin composition are provided on a die provided in the extruder 1. A step of extruding into a strand shape from one or more discharge holes, a step of passing the extruded polypropylene-based resin composition through a water tank, and a step of solidifying the polypropylene-based resin composition by cooling the extruded polypropylene-based resin composition, and (C5). The step of picking up the polypropylene-based resin composition solidified using a pick-up machine and (C6) the polypropylene-based resin composition picked up using a cutter or the like are columnar, polygonal, tubular (straw-shaped), etc. It may have a step of forming and shredding into a desired shape as described above. In the above (C3), the polypropylene-based resin composition melt-kneaded is extruded directly into the water tank from one or more discharge holes provided in the die provided in the extruder, and the polypropylene-based resin composition is atomized immediately after extrusion. It may be shredded into shapes, cooled, and solidified.

When other resins and / or resin particle additives are used in the above step (C1), these other resins and / or these other resins and / or before blending the polypropylene-based resin with the other resin and / or the resin particle additive. Alternatively, a mixture (resin composition) containing a resin particle additive may be granulated. That is, (i) another resin and / or a resin particle additive is blended in advance to prepare a blend, and (ii) the blend is put into an extruder and melt-kneaded to prepare a resin composition. , (Iii) The resin composition is extruded from one or more ejection holes provided in the die provided in the extruder, and (iv) the extruded resin composition is cooled or cooled and shredded. The resin composition may be formed into a desired particle shape. As the step (C2) above, instead of the blended product, the particles of the other resin and / or the resin particle additive thus granulated and the polypropylene-based resin are put into an extruder, and these are melt-kneaded. It can also be a step of preparing a polypropylene-based resin composition which is a melt-kneaded product. When another resin and / or a resin particle additive is used in the step (C1), the other resin and / or the resin particle additive may be added from the middle of the extruder. That is, as the steps (C1) and (C2) above, after charging only the polypropylene-based resin into the extruder, another resin and / or the resin particle additive is supplied from the middle of the extruder, and they are dispensed in the extruder. A step of mixing and melt-kneading to prepare a polypropylene-based resin composition can be performed, and the subsequent steps (C3) and subsequent steps can also be performed.

The resin particle additive used as needed may be master-batched. That is, a masterbatch resin in which a resin particle additive is contained in another resin at a high concentration may be prepared in advance. In this case, the masterbatch may be added as the resin particle additive. As the resin used when preparing the masterbatch resin, a polypropylene-based resin is preferable, and from the viewpoint of good compatibility, it is possible to make a masterbatch using the same type of polypropylene-based resin as the polypropylene-based resin of the base resin. Most preferred.

The modes of L ₄₅ / D ₄₅ shrinkage, average L ₄ / D ₄ ratio and average L ₅ / D ₅ ratio include preferred embodiments described above [2. Polypropylene resin particles] may be the same as the modes of L ₁₂ / D ₁₂ shrinkage rate, average L ₁ / D ₁ ratio and average L ₂ / D ₂ ratio described in the section. That is, L ₄ , D ₄ , L ₅ and D ₅ can be described by substituting L ₄ for L ₁ , D ₄ for D ₁ , L ₅ for L ₂ , and D ₅ for D ₂ , respectively.

Examples of the L ₄₅ / D ₄₅ shrinkage rate adjusting step include a step of adjusting various conditions in the method for producing resin particles. The various conditions described above include, for example, the resin temperature, the area per discharge hole, the discharge amount, the resin linear speed, the distance from the die to the cooling medium, the temperature of the cooling medium, the cooling time, the take-up speed, the degree of stretching, and relaxation. Examples include time and average L ₄ / D ₄ ratio. The method for producing the resin particles is such that the resin temperature, the area per discharge hole, the discharge amount, the resin linear velocity, so that the L ₄₅ / D ₄₅ shrinkage ratio obtained by the above formula (2) is 50% or more. Manufacture comprising adjusting one or more selected from the group consisting of the distance from the die to the cooling medium, the temperature of the cooling medium, the cooling time, the take-up rate, the stretchability, the relaxation time and the _average L1 / D1 _ratio . It can be said that it is a method. Among these conditions, it is particularly preferable to appropriately adjust the degree of elongation, the distance from the die to the cooling medium, the relaxation time and / or the _average L4 / _D4 ratio. As will be described later, (a) the degree of elongation depends on the discharge amount, the total area of the discharge holes and the take-up speed, (b) the relaxation time depends on the distance from the die to the cooling medium and the take-up speed, and (c) the average. The L ₄ / D ₄ ratio depends on the pick-up speed and the shredding speed. Therefore, it is also a preferred embodiment to appropriately adjust the discharge amount, the total area of the discharge holes, the distance from the die to the cooling medium, the take-up speed and the shredding speed.

The resin temperature is a temperature at which a polypropylene-based resin or a polypropylene-based resin composition containing a polypropylene-based resin is melt-kneaded, and is also referred to as a melt-kneading temperature and a heating temperature. When polypropylene-based resin particles are produced using an extruder, it can be said to be the temperature of the melt-kneaded product (polypropylene-based resin composition) immediately before the melt-kneaded product is extruded from the discharge holes provided in the die.

The resin temperature is not particularly limited, but may be Tm ₁ + 40 ° C. or higher and Tm ₁ + 110 ° C. or lower when the melting point of the polypropylene resin is [Tm ₁ (° C.)]. The melting point of the polypropylene-based resin referred to here is a value obtained as a result of differential scanning calorimetry (DSC) performed using a differential scanning calorimetry. The specific operation procedure is as follows: (1) After heating 4 to 6 mg of polypropylene resin from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min and melting it; (2) 10 After the temperature is lowered from 220 ° C. to 40 ° C. at a temperature lowering rate of ° C./min to crystallize; (3) the temperature is further raised from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min. The temperature of the peak (melting peak) of the DSC curve obtained at the time of the second temperature rise (that is, at the time of (3)) can be obtained as the melting point of the polypropylene resin.

In the polypropylene-based resin foamed particles produced by using the polypropylene-based resin particles containing the polypropylene-based resin, the structure of the polypropylene-based resin particles changes, but the composition of the polypropylene-based resin particles does not change. Further, in the polypropylene-based resin in-mold foam molded body manufactured by using the polypropylene-based resin foamed particles manufactured by using the polypropylene-based resin particles, the structure of the polypropylene-based resin foamed particles changes, but the polypropylene-based resin foamed. The composition of the particles does not change. Therefore, the value of the melting point obtained by analyzing the polypropylene-based resin foamed particles or the foamed molded article in the polypropylene-based resin mold is the value of the melting point of the polypropylene-based resin contained in the polypropylene-based resin particles which are the raw materials thereof. Can be regarded.

In the present specification, the melting point of the polypropylene-based resin foamed particles or the polypropylene-based resin in-mold foam molded product is such that the polypropylene-based resin foamed particles or the polypropylene-based resin in-mold foamed molded product are used instead of the polypropylene-based resin, respectively. , The value obtained by measuring by the same method (DSC) as the melting point of the polypropylene resin.

The area per discharge hole is the area of a cross section per one of one or more discharge holes provided in the die provided in the extruder when polypropylene-based resin particles are produced using an extruder (the area per discharge hole). Cross-sectional area) is intended. In the present specification, the "cross section of the discharge hole" is a cross section obtained when the discharge hole is cut along a plane perpendicular to the direction (extrusion direction) in which the polypropylene-based resin composition (melt-kneaded product) is extruded. Intended. The area per discharge hole can be adjusted by changing the cross-sectional shape of the discharge hole, the cross-sectional diameter of the discharge hole, and the like. The area per discharge hole is not particularly limited, but may be 0.5 mm ² to 8 mm ² .

The discharge amount is intended to be the amount of the polypropylene-based resin composition extruded from the extruder per unit time when the polypropylene-based resin particles are produced using the extruder. The discharge amount is a polypropylene-based resin composition extruded per unit time from one or more discharge holes provided in a die provided in the extruder when polypropylene-based resin particles are produced using the extruder. It can be said that it is the total amount of.

The resin linear velocity is a polyolefin-based resin composition extruded per unit time from one ejection hole provided in a die provided in the extruder when polypropylene-based resin particles are produced using an extruder. Intended for length in extrusion direction. In the present specification, the resin linear velocity is a value obtained by the following formula (7):
Resin linear velocity = discharge amount / (density of polypropylene-based resin composition x total area of discharge holes) ... Equation (7).

Here, the total area of the discharge holes is the sum of the cross-sectional areas of the discharge holes provided in the die provided in the extruder. The "area of the cross section of the discharge hole" may be referred to as the "area of the discharge hole". When the die is provided with a plurality of discharge holes and their cross-sectional areas are the same, the total area of the discharge holes is the area per discharge hole multiplied by the number (total number) of the discharge holes. , Can be asked.

The resin linear velocity is not particularly limited, but may be 3 m / min to 50 m / min, preferably 10 m / min to 50 m / min, more preferably 20 m / min to 40 m / min, and 20 m / min to 30 m / min. Minutes are even more preferred. As described above, the resin linear velocity can be adjusted by changing the discharge amount and the total area of the discharge holes.

The distance from the die to the cooling medium is intended to be the distance from the extrusion-direction end of the ejection hole provided in the die of the extruder to the cooling medium when polypropylene-based resin particles are produced using the extruder. When a water tank provided with water as a cooling medium is used as a cooling device, the distance from the die to the cooling medium can be said to be the distance from the extrusion-direction end of the discharge hole provided in the die to the water surface of the water tank. The distance from the die to the cooling medium is not particularly limited, but may be larger than 0 mm and less than 80 mm, preferably larger than 0 mm and 10 mm or less. As the distance from the die to the cooling medium is closer to 0 mm, it may be difficult to adjust the temperature of the die that affects the resin temperature and the temperature of the cooling medium. When the distance from the die to the cooling medium is 0 mm, the temperature of the die and the temperature of the cooling medium may be particularly difficult to adjust because the die and the cooling medium come into contact with each other.

The temperature of the cooling medium can also be said to be the water temperature when a water tank provided with water as the cooling medium is used as the cooling device. The temperature of the cooling medium is not particularly limited, but may be Tm _1-150 ° C. or higher and Tm _1-80 ° C. or lower, preferably Tm _1-150 ° C. or higher and Tm _1-100 ° C. or lower.

The cooling time is intended to be the time during which the polypropylene-based resin composition is present in the cooling medium provided in the cooling device. When the polypropylene-based resin composition is discharged from the cooling device into the gas phase for take-up and cutting, the cooling time affects the surface temperature of the polypropylene-based resin composition discharged from the cooling device into the gas phase. Can be given. The surface temperature of the polypropylene-based resin composition discharged from the cooling device into the gas phase is not particularly limited, but may be Tm ₁ to 70 ° C. or lower, preferably Tm ₁ to 80 ° C. or lower.

The pick-up speed is intended to be the pick-up speed of the pick-up machine in the case of producing polypropylene-based resin particles using the pick-up machine. The pick-up machine includes, for example, a roller-type pick-up machine that picks up by a roller, and can be used to pick up a polypropylene-based resin composition extruded from one or more discharge holes provided in a die. The take-up speed may be the same as the resin wire speed, or may be faster than the resin wire speed. When the take-up speed is faster than the resin wire speed, it can be said that the polypropylene-based resin composition extruded from one or more discharge holes provided in the die is stretched. That is, in the method for producing the present resin particles, the polypropylene-based resin composition may be stretched.

The stretchability is a value obtained by the following formula (8) in the present specification:
Degree of elongation = take-up speed-resin linear speed ... Equation (8).
The degree of elongation is not particularly limited, but may be 10 m / min to 100 m / min, preferably 10 m / min to 80 m / min, more preferably 10 m / min to 70 m / min, and 10 m / min to 60 m / min. Is more preferable, and 10 m / min to 50 m / min is even more preferable.

The relaxation time means that when polypropylene-based resin particles are produced using an extruder and a take-up machine, the polypropylene-based resin composition is extruded from a discharge hole provided in a die of the extruder and then comes into contact with a cooling medium. Intended for time to. In the present specification, the relaxation time is a value obtained by the following equation (9):
Relaxation time = distance from the die to the cooling medium / take-up speed ... Equation (9).

The relaxation time is not particularly limited, but may be larger than 0 seconds and 0.1000 seconds or less, and more preferably greater than 0 seconds and 0.015 seconds or less. The relaxation time closer to 0 seconds is preferable, but the relaxation time closer to 0 seconds may make it difficult to adjust the temperature of the die and the temperature of the cooling medium, which affect the resin temperature. When the relaxation time is 0 seconds, the temperature of the die and the temperature of the cooling medium may be particularly difficult to adjust because the die and the cooling medium come into contact with each other.

The _average L4 / _D4 ratio can be adjusted by appropriately changing the pick-up speed and the shredding speed. The shredding speed is intended to be the speed at which the polypropylene-based resin composition taken up by a pick-up machine or the like is shredded by a shredding device. When using a shredding device equipped with a blade such as a cutter, the shredding speed can be said to be the rotation speed of the blade. When the take-up speed is high and the shredding speed is slow, large polypropylene _- based resin particles having a large L4, that is, long polypropylene-based resin particles are obtained, and the _average L4 / _D4 ratio becomes large. When the take-up speed is slow and the shredding speed is high, small polypropylene resin particles having a small L4, that is, short polypropylene _- based resin particles are obtained, and the _average L4 / _D4 ratio becomes small.

Preferred embodiments of the method for producing polypropylene-based resin particles according to an embodiment of the present invention include, for example, the following embodiments:
A resin composition preparation step of heating a blend containing a polypropylene-based resin in an extruder to melt it and kneading it to prepare a polypropylene-based resin composition.
An extrusion step of extruding the obtained polypropylene-based resin composition from one or more discharge holes provided in a die provided in the extruder.
A cooling step of solidifying the extruded polypropylene-based resin composition by cooling it using a cooling device provided with a cooling medium.
A pick-up process in which the polypropylene-based resin composition solidified using a pick-up machine is picked up in the gas phase,
Including a shredding step of shredding the polypropylene-based resin composition taken up using a shredding device to obtain polypropylene-based resin particles.
The heating temperature in the resin composition preparation step is Tm ₁ + 40 ° C. to Tm ₁ + 110 ° C., where Tm ₁ is the melting point of the polypropylene-based resin.
The area per one discharge hole in the extrusion step is 0.5 mm ² to 8 mm ² .
The temperature of the cooling medium is Tm _1-150 ° C. or higher and Tm _1-100 ° C. or lower.
The surface temperature of the resin composition in the gas phase in the above-mentioned take _- up step is Tm 1-70 ° C. or lower.
The _average L4 / _D4 ratio of the polypropylene-based resin particles is 2.0 to 5.0.
The stretchability obtained from the following formula (10) is 10 m / min to 100 m / min;
Stretchability = take-up speed-resin wire speed ... Equation (10),
Here, the pick-up speed is the pick-up speed per unit time of the polypropylene-based resin composition by the pick-up machine in the pick-up step.
The resin linear velocity is a value obtained from the following equation (11);
Resin linear velocity = discharge amount / (density of polypropylene-based resin composition x total area of discharge holes) ... Equation (11),
Here, the discharge amount is the amount of the polypropylene-based resin composition extruded from the extruder per unit time in the extrusion step.
The total area of the discharge holes is the sum of the areas of one or more of the discharge holes provided on the die provided in the extruder, and the area per one of the discharge holes is the sum of the areas of the extruder. It is a value obtained by multiplying the total number of the above discharge holes provided by the die;
The relaxation time obtained from the following equation (12) is greater than 0 seconds and 0.1000 seconds or less;
The relaxation time = the distance from the die to the cooling medium / the take-up speed ... Equation (12),
Here, a method for producing polypropylene-based resin particles, wherein the distance from the die to the cooling medium is larger than 0 mm and less than 80 mm.

If it is a preferred embodiment of the present production method as described above, it is possible to provide foamed particles capable of providing a molded product having better surface properties without using a special resin composition of the polypropylene-based resin. Resin particles can be obtained.

(Resin composition preparation process)
In the resin composition preparation step, a polypropylene-based resin, which is a melt-kneaded product, is prepared by preparing a blended product containing a polypropylene-based resin, heating the obtained blended product in an extruder to melt it, and kneading it. This is the step of preparing the composition. The extruder used in the resin composition preparation step is preferably a twin-screw extruder. Regarding the heating temperature (resin temperature) in the resin composition preparation step, the above description is incorporated.

(Extrusion process)
The extrusion step is a step of extruding (discharging) a polypropylene-based resin composition, which is a melt-kneaded product, into, for example, a strand from one or more discharge holes provided in a die provided in the extruder. The above description is incorporated with respect to the aspects relating to the die, the discharge hole, the discharge amount and the resin linear velocity.

(Cooling process)
The extruded polypropylene-based resin composition can be solidified by cooling with a cooling device. The above description is incorporated for aspects of the cooling medium, the cooling device, the distance from the die to the cooling medium and the cooling time.

(Collecting process)
In the pick-up step, the solidified polypropylene-based resin composition is picked up from the cooling medium (cooling device) into the gas phase using a pick-up machine. The above description is incorporated with respect to aspects relating to the take-up machine, take-up speed, stretchability, surface temperature and relaxation time of the polypropylene-based resin composition discharged from the cooling device into the gas phase.

(Shredding process)
In the shredding step, the polypropylene-based resin composition is shredded into a desired shape such as a columnar shape, a polygonal columnar shape, a tubular shape (straw shape), or the like using a shredding device. The above description is incorporated for aspects relating to the shredding device, shredding speed, and _average L4 / _D4 ratio.

[4. Polypropylene resin foam particles]
The polypropylene-based resin foamed particles according to the embodiment of the present invention are described in the above [2. Polypropylene-based resin particles] are preferably foamed particles obtained by foaming the polypropylene-based resin particles described in the section. In the present specification, "polypropylene resin foamed particles according to an embodiment of the present invention" are also referred to as "present foamed particles".

Since the foamed particles have the above-mentioned structure, it is possible to provide a molded product having a shortened molding cycle and excellent surface properties.

The foamed particles are described in the above [3. Method for producing polypropylene-based resin particles], it is preferable that the foamed particles are formed by foaming the resin particles produced by the method for producing the present resin particles described in the section.

Examples of the polypropylene-based resin foamed particles according to the embodiment of the present invention include the following aspects: foamed particles obtained by foaming polypropylene-based resin particles, and (a) the expansion ratio of the expanded particles. (B) (b-1) The polypropylene-based resin particles contain a polypropylene-based resin as a base resin, and (b-2) a weight of 0.5 mg / grain or more per particle 5 .0 mg / grain or less, and (c) L ₈₃ / D ₈₃ shrinkage rate obtained by the following formula (19) is 50% or more. Polypropylene resin foamed particles: L ₈₃ / D ₈₃ shrinkage rate = 100 × (1- (Average L ₃ / D ₃ ratio of the polypropylene-based resin foam particles) / (Average L ₈ / D ₈ ratio of the polypropylene-based resin particles)) ... Formula (19).

(4-1. Average L ₃ / D ₃ ratio)
The _average L3 / _D3 ratio of the foamed particles is preferably 0.80 or more and less than 1.50, more preferably 0.80 to 1.20, and 0.90 to 1.20. It is even more preferably 0.90 to 1.10, and even more preferably 1.00. The closer the average L ₃ / D ₃ ratio is to 1.00, the better the filling property when the foamed particles are filled in the mold.

The description of the L ₃ , D ₃ and average L ₃ / D ₃ ratios in the foam particles is described in the section (2-6. L ₁₂ / D ₁₂ shrinkage rate) above, respectively, for L ₂ , D ₂ and average. The explanation of the L ₂ / D ₂ ratio can be appropriately incorporated.

The embodiments of L ₈₃ / D ₈₃ shrinkage ratio, average L ₈ / D ₈ ratio, L ₈ and D ₈ include preferred embodiments described above [2. Polypropylene resin particles] may be the same as the aspects of L ₁₂ / D ₁₂ shrinkage rate, average L ₁ / D ₁ ratio, L ₁ and D ₁ described in the section. That is, L ₈ , D ₈ , L ₃ and D ₃ can be described by substituting L ₈ for L ₁ , D ₈ for D ₁ , L ₃ for L ₂ , and D ₃ for D ₂ , respectively.

(4-2. Average d ₂ / D ₂ ratio)
The average d ₂ / D ₂ ratio of the foamed particles is preferably 0.80 to 1.20, more preferably 0.90 to 1.10, and 0.95 to 1.05. Is more preferable, and 1 is particularly preferable. The closer the average d ₂ / D ₂ ratio is to 1, the less uneven the foamed particles are, and the better the filling property when the foamed particles are filled in the mold.

The average d ₂ / D ₂ ratio is an average value calculated from the d ₂ / D ₂ ratio of 10 randomly selected polypropylene-based resin foamed particles.

d ₂ will be described with reference to FIG. As shown in FIGS. 3 (b) and 3 (d), d ₂ is the maximum diameter d ₂ max and the minimum diameter d ₂ min in the cross section perpendicular to the L ₂ direction at the center of the L ₂ direction of the polypropylene-based resin foamed particles. It is an average value of and is a value calculated by the following equation (13):
d ₂ = (d ₂ max + d ₂ min) / 2 ... Equation (13).

As shown in FIG. 3D, when the polypropylene-based resin particles are substantially spherical, the center of the polypropylene _- based resin particles in the L2 direction can also be the maximum diameter portion of the polypropylene _- based resin particles. It can be equal to D ₂ . Further, as described above, D ₂ max and D ₂ min have the same value. Therefore, as shown in FIG. _{3D, when the polypropylene-based resin particles are substantially spherical and the shape of the cross section perpendicular to the L2 direction of the maximum diameter portion is circular, D 2 max and D 2 min .} , D ₂ max and d ₂ min all have the same value.

The average d ₂ / D ₂ ratio can be adjusted by appropriately changing the time from the addition of the foaming agent to the release of the dispersion liquid in the production of the foamed particles. The method for producing the foamed particles will be described in detail later.

(4-3. Foaming magnification)
The expansion ratio of the foamed particles is preferably 15 times or more and 25 times or less, more preferably 17 times or more and 22 times or less, further preferably 18 times or more and 21 times or less, and 19 times or more and 20 times. It is particularly preferable that the amount is double or less. When the expansion ratio of the foamed particles is (a) 15 times or more, a lightweight molded body can be provided by using the foamed particles, and (b) when the foaming ratio is 25 times or less, a molded body having strength is obtained. Can be provided.

(4-4. Adhesive components on the surface of foamed particles)
When a dispersant and / or a dispersion aid is used in the production of the present foamed particles, foamed particles to which the dispersant and / or the dispersion aid is attached to the surface can be obtained. A substance adhering to the surface of the foamed particles is also referred to as an adhering component on the surface of the foamed particles. The type and amount of the adhering component of the foamed particles are not particularly limited. Various substances can be adherent components, depending on the substance used in the production of the foamed particles. The foamed particles may be, for example, foamed particles having the dispersant used in the production of the foamed particles adhered to the surface.

(4-5. DSC curve)
A DSC curve can be obtained by performing DSC on polypropylene-based resin foamed particles. Specifically, a DSC curve can be obtained by heating 5 to 6 mg of polypropylene-based resin foam particles from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter. can.

FIG. 4 is an example of a DSC curve obtained by subjecting the polypropylene-based resin foamed particles according to the embodiment of the present invention to DSC in which the temperature is raised from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min. Is. In FIG. 4, the horizontal axis represents temperature and the vertical axis represents heat quantity. The vertical axis indicates heat generation when it goes up, and endothermic when it goes down. The DSC curve shown in FIG. 4 can be said to be the DSC curve at the time of the first temperature rise. There are two peaks in the DSC curve shown in FIG. These two peaks are melting peaks and endothermic peaks.

The polypropylene-based resin foamed particles according to the embodiment of the present invention preferably have two melting peaks as shown in FIG. 4 in the DSC curve obtained as a result of performing DSC on the polypropylene-based resin foamed particles. .. Polypropylene resin foamed particles having such two melting peaks can be produced by a known method.

FIG. 4 will be described in more detail. In FIG. 4, there are two melting peaks. The peak on the low temperature side is referred to as a melting peak on the low temperature side, and the peak temperature of the peak is referred to as the peak temperature on the low temperature side. The peak on the high temperature side is referred to as a melting peak on the high temperature side, and the peak temperature of the peak is referred to as the peak temperature on the high temperature side. Each point in the DSC curve at the time of the first temperature rise of the polypropylene-based resin foamed particles shown in FIG. 4 will be described. Point A represents the amount of heat absorbed at a temperature of 100 ° C. Point B represents the amount of heat absorbed at the temperature at which melting on the high temperature side ends. It can be said that the point B is the intersection of the line from the melting peak on the high temperature side toward the high temperature side and the baseline on the high temperature side (which is also the melting end baseline). Point C represents the point where the amount of heat absorption between the two melting peaks, the low temperature side melting peak and the high temperature side melting peak, is the smallest. The point D represents a point where the straight line and the line segment AB intersect when a straight line parallel to the Y axis is drawn from the point C toward the line segment AB. The amount of heat based on the range surrounded by the low temperature side melting peak, the line segment AD, and the line segment CD is referred to as the low temperature side melting heat amount (Ql). The amount of heat based on the range surrounded by the high temperature side melting peak, the line segment BD, and the line segment CD is referred to as the high temperature side melting heat amount (Qh). The sum of the amount of heat of melting on the low temperature side (Ql) and the amount of heat of melting on the high temperature side (Qh) is the amount of heat of the entire melting peak.

(4-6. DSC ratio)
The ratio of the high temperature side melting heat quantity (Qh) to the total calorific value of the melting peak is referred to as a DSC ratio or a high temperature calorific value ratio. The DSC ratio is expressed by the following formula (14).

DSC ratio (%) = (Qh / (Ql + Qh)) × 100 ... Equation (14).

The polypropylene-based resin foamed particles according to the embodiment of the present invention preferably have a DSC ratio of 10% or more and 50% or less, and more preferably 15% or more and 45% or less. When the DSC ratio is within the range, there is an advantage that a wide range of molding processing conditions can be selected in the in-mold foam molding using polypropylene-based resin foam particles. In the molded product produced by using the polypropylene-based resin foamed particles, the structure of the polypropylene-based resin foamed particles changes, but the composition does not change. Therefore, the value of the DSC ratio of the polypropylene-based resin in-mold foam molded product can be regarded as the same as the DSC ratio of the polypropylene-based resin foamed particles that are the raw materials of the molded product. The DSC ratio of the polypropylene-based resin foamed molded product can be obtained from the DSC curve (specifically, the DSC curve at the time of the first temperature rise) obtained by the same DSC as the polypropylene-based resin foamed particles.

(4-7. Method for producing foamed particles)
The production method for obtaining the present foamed particles is not particularly limited. The foamed particles will be described later [5. It is preferable that the polypropylene-based resin foamed particles are produced by the method for producing polypropylene-based resin foamed particles described in].

[5. Manufacturing method of polypropylene-based resin foam particles]
The method for producing polypropylene-based resin foam particles according to an embodiment of the present invention includes a dispersion liquid preparation step of mixing polypropylene-based resin particles, a dispersion medium and a foaming agent in a container to prepare a dispersion liquid, and the above-mentioned dispersion liquid. Has a release step of releasing polypropylene-based resin foamed particles having a foaming ratio of 15 times or more in a pressure range lower than the internal pressure of the container, and the L ₆₇ / D ₆₇ shrinkage rate obtained by the above formula (3) is obtained. It is 50% or more. In the present specification, "a method for producing polypropylene-based resin foamed particles according to an embodiment of the present invention" is also referred to as "a method for producing the present foamed particles".

Since the method for producing the foamed particles has the above-mentioned structure, the polypropylene-based resin foamed particles can provide a molded product having a shortened molding cycle and excellent surface properties without using a special resin composition of the polypropylene-based resin. Can be obtained.

The method for producing the foamed particles is described in [4. Polypropylene-based resin foamed particles] can be suitably used for producing the present foamed particles described in the section. The aspects of the polypropylene-based resin particles in the method for producing the foamed particles include preferred embodiments described in [2. Polypropylene-based resin particles] may be the same as the embodiment of the polypropylene-based resin particles described in the section. The aspects of the polypropylene-based resin foamed particles in the method for producing the foamed particles include preferred embodiments described in [4. Polypropylene-based resin foamed particles] may be the same as the embodiment of the polypropylene-based resin foamed particles described in the section.

As a method for producing polypropylene-based resin foamed particles according to an embodiment of the present invention, for example, the following aspects may be mentioned:
A resin particle preparation step for preparing polypropylene-based resin particles, a dispersion liquid preparation step for preparing a dispersion liquid by mixing the polypropylene-based resin particles, a dispersion medium, and a foaming agent in a container, and a dispersion liquid in the container. It has a release step of releasing to a pressure range lower than the pressure of the above to obtain polypropylene-based resin foamed particles having a foaming ratio of 15 times or more, and the resin particle preparation step further extrudes a blend containing the polypropylene-based resin. A resin composition preparation step of heating in an in-machine to melt and kneading to prepare a polypropylene-based resin composition, and one or more of the obtained polypropylene-based resin compositions provided on a die provided in an extruder. The extrusion process of extruding from the discharge hole of the above, the cooling step of solidifying the extruded polypropylene-based resin composition by cooling it using a cooling device equipped with a cooling medium, and the polypropylene-based resin solidified using a take-up machine. The resin composition comprises a picking step of taking the composition into the gas phase and a shredding step of shredding the picked-up polypropylene-based resin composition using a shredding device to obtain polypropylene-based resin particles. The heating temperature in the product preparation step is Tm ₁ + 40 ° C to Tm ₁ + 110 ° C when the melting point of the polypropylene resin is Tm ₁ , and the temperature of the cooling medium is Tm _1-150 ° C or higher and Tm _1-100 ° C. The surface temperature of the resin composition in the gas phase in the take-up step is Tm 1-70 ° C. or lower, and the _{average L6} / _D6 ratio of the polypropylene-based resin particles is 2.0 to 5. It is 0.0, and the stretch degree obtained from the following formula (16) is 10 m / min to 100 m / min; the stretchability = take-up speed-resin linear velocity ... Equation (16), where the take-back The speed is the pick-up speed per unit time of the polypropylene-based resin composition by the pick-up machine in the pick-up step, and the resin linear velocity is a value obtained from the following formula (17); the resin linear velocity. = Discharge amount / (Density of the polypropylene-based resin composition × Total area of the discharge holes) ... Equation (17), where the discharge amount is determined per unit time from the extruder in the extrusion step. The amount of the polypropylene-based resin composition to be extruded, and the total area of the discharge holes is the sum of the areas of one or more of the discharge holes provided on the die provided in the extruder; The relaxation time obtained from the equation (18) is greater than 0 seconds and 0.1000 seconds or less; the relaxation time = the distance from the die to the cooling medium / above. Take-up speed ... Equation (18), where the distance from the die to the cooling medium is greater than 0 mm and less than 80 mm, a method for producing polypropylene-based resin foam particles.

The aspect of each step included in the resin particle preparation step includes a preferable aspect, and the above-mentioned [3. Method for producing polypropylene-based resin particles] may be the same as the mode of each step described in the section.

(5-1. L ₆₇ / D ₆₇ shrinkage rate)
The modes of L ₆₇ / D ₆₇ shrinkage, average L ₆ / D ₆ ratio and average L ₇ / D ₇ ratio in the method for producing the foamed particles include preferred embodiments of the above-mentioned L ₁₂ / D ₁₂ shrinkage. It may be the same as the embodiment. That is, L ₆ , D ₆ , L ₇ and D ₇ can be described by substituting L ₆ for L ₁ , D ₆ for D ₁ , L ₇ for L ₂ , and D ₇ for D ₂ , respectively.

(5-2. Container)
The container is not particularly limited. The container is preferably one that can withstand the foaming temperature and the foaming pressure at the time of producing the foamed particles, and more preferably a pressure-resistant container. Examples of the container include an autoclave type pressure-resistant container. The foaming temperature and foaming pressure will be described in detail later.

(5-3. Dispersion medium)
The dispersion medium is not particularly limited. The dispersion medium is preferably an aqueous dispersion medium, and it is preferable to use only water as the dispersion medium. In the method for producing the foamed particles, a dispersion medium obtained by adding methanol, ethanol, ethylene glycol, glycerin or the like to water can also be used as the dispersion medium.

The amount of the dispersion medium used is preferably 100 parts by weight or more, more preferably 130 parts by weight or more, based on 100 parts by weight of the polypropylene-based resin particles. When the amount of the dispersion medium used is 100 parts by weight or more with respect to 100 parts by weight of the polypropylene-based resin particles, the more the amount of the dispersion medium used, the better the dispersibility of the polypropylene-based resin particles in the dispersion liquid. Become.

In the method for producing the foamed particles, when the polypropylene-based resin particles contain a hydrophilic compound and the dispersion medium contains water, the water in the dispersion medium can act as a foaming agent. As a result, the expansion ratio of the obtained foamed particles can be improved.

(5-4. Foaming agent)
Examples of the foaming agent include aliphatic hydrocarbons, halogenated hydrocarbons and inorganic gases. Examples of the aliphatic hydrocarbon include propane, butane, isobutane, pentane, and isopentane. Examples of the halogenated hydrocarbon include monochloromethane, dichloromethane, dichlorodifluoroethane and the like. Examples of the inorganic gas include air, nitrogen, carbon dioxide and the like. For example, water contained in the dispersion medium can be used as a foaming agent. Only one kind of these foaming agents may be used, or two or more kinds may be used in combination. In the method for producing the foamed particles, an inorganic gas and / or water is preferable as the foaming agent because it does not adversely affect the environment. The foaming agent is preferably air and / or carbon dioxide, more preferably carbon dioxide.

The amount of the foaming agent used varies depending on the type of polypropylene resin used, the type of foaming agent, the target foaming ratio, and the like, and cannot be unconditionally specified. The amount of the foaming agent used is preferably, for example, 2 parts by weight or more and 60 parts by weight or less with respect to 100 parts by weight of the polypropylene-based resin particles.

(5-5. Dispersant)
A dispersant may be used in the method for producing the foamed particles. When a dispersant is used in the dispersion liquid preparation step of the method for producing the foamed particles, (a) the polypropylene resin particles can be prevented from coalescing with each other in the dispersion liquid, and / or (b) after the dispersion liquid is released. It is possible to prevent the polypropylene resin particles from coalescing together.

Examples of the dispersant include, but are not limited to, inorganic dispersants such as tricalcium phosphate, magnesium tribasic phosphate, calcium pyrophosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, and silicate. Examples of the silicate include clay minerals such as kaolin, talc and clay. These dispersants may be used alone or in combination of two or more.

The amount of the dispersant used is not particularly limited and may be appropriately changed depending on the type of the dispersant. The amount of the dispersant used is preferably 0.01 parts by weight or more and 3.00 parts by weight or less with respect to 100 parts by weight of the polypropylene-based resin particles. When the amount of the dispersant used is 0.01 parts by weight or more based on (a) 0.01 parts by weight with respect to 100 parts by weight of the polypropylene-based resin particles, the more the amount of the dispersant used increases, the more the polypropylene-based resin is produced in the production of foamed particles. When the possibility of particles coalescing is reduced and (b) 3.00 parts by weight or less, the amount of the dispersant remaining on the surface of the obtained foamed particles decreases as the amount of the dispersant used decreases. As a result, the fusion property of the molded product produced by using the obtained foamed particles tends to be good.

(5-6. Dispersion aid)
In the method for producing the foamed particles, a dispersion aid may be used. When a dispersion aid is used in the dispersion liquid preparation step of the method for producing the foamed particles, (a) the polypropylene resin particles can be prevented from coalescing with each other in the dispersion liquid, and / or (b) after the dispersion liquid is released. , It is possible to prevent the polypropylene resin particles from coalescing together.

The dispersant aid is preferably used with the dispersant. When a dispersant and a dispersion aid are used in the dispersion liquid preparation step of the method for producing the foamed particles, (a) the polypropylene resin particles can be more prevented from coalescing with each other in the dispersion liquid, and / or (b) the dispersion. It is possible to further prevent the polypropylene resin particles from coalescing after the liquid is discharged.

Examples of the dispersion aid include, but are not limited to, anionic surfactants. Examples of the anionic surfactant include (a) carboxylate type, (b) alkyl sulfonate, n-paraffin sulfonate, alkylbenzene sulfonate, alkylnaphthalene sulfonate, sulfosuccinate and other sulfonates. Types, (c) sulfated oils, alkyl sulfates, alkyl ether sulfates, sulfate ester types such as alkylamide sulfates, (c) alkyl phosphates, polyoxyethylene phosphates, alkylallyl ether sulfates, etc. Phosphate-type surfactants can be mentioned. These dispersion aids may be used alone or in combination of two or more.

The amount of the dispersion aid used is not particularly limited and may be appropriately changed depending on the type of the dispersion aid. The amount of the dispersion aid used is, for example, preferably 0.001 part by weight or more and 0.100 part by weight or less, and preferably 0.001 part by weight or more and 0.050 part by weight or less with respect to 100 parts by weight of the polypropylene resin particles. , 0.002 parts by weight or more and 0.040 parts by weight or less is more preferable. When the amount of the dispersion aid used is 0.001 part by weight or more based on (a) 0.001 part by weight with respect to 100 parts by weight of the polypropylene-based resin particles, the more the amount of the dispersion aid used increases, the more polypropylene is used in the production of the foamed particles. When the possibility of coalescence of the resin particles is reduced and (b) 0.100 parts by weight or less, the amount of the dispersant remaining on the surface of the obtained foamed particles increases as the amount of the dispersant aid used decreases. As a result, the fusion property of the molded product produced by using the obtained foamed particles becomes good.

(5-7. Dispersion liquid preparation process)
The dispersion liquid preparation step can be carried out by adding polypropylene-based resin particles, a dispersion medium, a foaming agent, and optionally a dispersant, a dispersion aid, and the like to the container and mixing them. The order in which the polypropylene-based resin particles, the dispersion medium and the foaming agent, and optionally the dispersant and the dispersion aid are added to the container is not particularly limited. The mode of mixing the added raw materials is not particularly limited, and examples thereof include a method of stirring the raw materials using a stirring blade provided in the container or the like.

(5-8. Release step)
As a release step, for example, the pressure inside the container is raised to a pressure higher than the atmospheric pressure in advance, and the dispersion liquid is discharged under the atmospheric pressure to obtain polypropylene-based resin foam particles having a foaming ratio of 15 times or more. It may be carried out. Atmospheric pressure is preferable as the pressure lower than the internal pressure of the container.

(5-9. Heating step and pressurizing step)
The temperature and pressure inside the container when the dispersion is discharged into a pressure range lower than the pressure inside the container are also referred to as foaming temperature and foaming pressure, respectively. The method for producing the foamed particles further includes a heating step of raising (heating) the temperature inside the container to the foaming temperature and / or a pressurizing step of boosting (pressurizing) the pressure inside the container to the foaming pressure. You may be doing it.

(5-10. Foaming temperature)
The foaming temperature varies depending on the type of polypropylene resin used, the type and / or amount of the resin particle additive kneaded (used) in the polypropylene resin, the type and / or amount of the foaming agent, and the like, and cannot be unconditionally specified. .. The foaming temperature is preferably Tm _{2-30 (° C.) or more and Tm 2 +10} (° C.) or less when the melting point of the polypropylene-based resin particles is [Tm ₂ (° C.)].

In the present specification, the melting point Tm ₂ of the polypropylene-based resin particles is measured by the same method (DSC) as the melting point Tm ₁ of the polypropylene-based resin except that the polypropylene-based resin particles are used instead of the polypropylene-based resin. Let it be the obtained value.

In the polypropylene-based resin particles produced using the polypropylene-based resin, the structure of the polypropylene-based resin changes, but the composition of the polypropylene-based resin does not change. Therefore, in one embodiment of the present invention, the melting point Tm ₂ of the polypropylene-based resin particles can be the same as the melting point Tm ₁ of the polypropylene-based resin used for producing the polypropylene-based resin particles.

(5-11. Foaming pressure)
The foaming pressure varies depending on the desired foaming ratio of the polypropylene-based resin foamed particles and cannot be unconditionally defined. The foaming pressure is preferably 0.50 MPa / G or more and 6.0 MPa / G or less, and more preferably 1.0 MPa / G or more and 4.5 MPa / G or less. When the foaming pressure is (a) 0.50 MPa · G or more, there is no possibility that the foaming ratio becomes very low, and when (b) 6.0 MPa · G or less, the average bubbles of the obtained foamed particles are obtained. There is no risk of the diameter becoming finer and there is no risk of deterioration of moldability.

When a dispersion liquid containing polypropylene-based resin particles is discharged from the container to a pressure range lower than the container internal pressure, it is dispersed for the purpose of adjusting the discharge amount (flow rate) and reducing the magnification variation of the obtained foamed particles. The liquid can also be discharged through an open orifice of 2 to 10 mmφ. The "pressure range lower than the internal pressure of the container" is also called a low pressure atmosphere. In the method for producing the effervescent particles, the temperature of the low pressure atmosphere may be adjusted when the dispersion liquid in the container is discharged into the low pressure atmosphere for the purpose of increasing the expansion ratio.

The dispersion prepared in the container may be heated to the foaming temperature under stirring, pressurized to the foaming pressure, and then held at the foaming temperature and the foaming pressure for a certain period of time. The fixed time is usually 5 to 180 minutes, preferably 10 to 60 minutes. The dispersion liquid held for a certain period of time at the foaming temperature and foaming pressure is then released to a low pressure atmosphere (usually under atmospheric pressure) by opening the valve provided at the bottom of the container, whereby polypropylene resin foaming occurs. Can produce particles.

Preferred embodiments of the method for producing the foamed particles include, for example, the following embodiments: (D1) Polypropylene resin particles, a dispersion medium and a foaming agent, and optionally a dispersant in a container provided with a stirring blade. And a dispersion aid and the like are added, and these raw materials are mixed to prepare a dispersion liquid (dispersion liquid preparation step); (D2) A polypropylene-based solution in the dispersion liquid is prepared by stirring the dispersion liquid using a stirring blade. Disperse the resin particles in the container; (D3) After or with stirring, raise the temperature and pressure in the container to the foaming temperature (at least above the softening point temperature of the polypropylene resin particles) and foaming pressure, respectively. Increase the pressure; (D4) Then, if necessary, keep the inside of the container at the foaming temperature and the foaming pressure for a certain period of time; (D5) Then, disperse in the container in a pressure range lower than the internal pressure of the container (for example, under atmospheric pressure). By discharging the liquid and foaming the polypropylene-based resin particles, polypropylene-based resin foamed particles having a foaming ratio of 15 times or more are obtained (release step).

In addition, the following aspects are also preferable embodiments. That is, (E1) polypropylene-based resin particles and a dispersion medium, and optionally a dispersant, a dispersion aid, and the like are charged in a container provided with a stirring blade, and (E2) then a mixture obtained using the stirring blade. It is an embodiment in which any of the following (E3a) to (E3c) is performed as (E3) while stirring the liquid:
(E3a) If necessary, the inside of the container is evacuated, and a foaming agent is introduced at 0.3 MPa · G or more and 2.5 MPa · G or less to prepare a dispersion liquid (dispersion liquid preparation step). After that, the temperature inside the container is raised to a temperature equal to or higher than the softening temperature of the polypropylene-based resin. By raising the temperature, the pressure in the container rises to about 1.0 MPa · G or more and 5.0 MPa · G or less. If necessary, the pressure inside the container is adjusted to the desired foaming pressure by adding a foaming agent in the vicinity of the foaming temperature, and the temperature inside the container is further adjusted to the desired foaming temperature. Polypropylene resin foam particles are obtained by holding the temperature and pressure inside the container at the foaming temperature and foaming pressure for a certain period of time, and then discharging the dispersion liquid into a pressure range lower than the internal pressure of the container (release step). ;
(E3b) If necessary, evacuate the inside of the container, raise the temperature inside the container to near the foaming temperature of the polypropylene resin, and introduce an appropriate foaming agent so that the pressure inside the container becomes the desired foaming pressure. , Prepare the dispersion (dispersion preparation step). After that, the temperature inside the container is maintained near the foaming temperature for a certain period of time, and then the dispersion liquid is discharged to a pressure range lower than the internal pressure of the container to obtain polypropylene-based resin foamed particles (release step); or (E3c). After raising the temperature inside the container to near the foaming temperature, a foaming agent is introduced so that the pressure inside the container becomes a desired foaming pressure, and a dispersion liquid is prepared (dispersion liquid preparation step). After that, the temperature inside the container is maintained near the foaming temperature for a certain period of time, and then the dispersion liquid is discharged to a pressure range lower than the internal pressure of the container to obtain polypropylene-based resin foamed particles (release step).

Before the dispersion liquid is discharged to a pressure range lower than the pressure inside the container, the substance used as a foaming agent is press-fitted into the container to increase the internal pressure inside the container and the pressure at the time of foaming (during release). The opening speed can also be adjusted (controlled). Further, it is also possible to introduce (control) the pressure at the time of foaming (during release) by introducing the substance used as the foaming agent into the container even while the substance is discharged to a lower pressure region than the pressure inside the container. As described above, the foaming ratio can be adjusted by adjusting the pressure at the time of foaming (during release).

As described above, the step of producing polypropylene-based resin foamed particles from polypropylene-based resin particles is called a "one-stage foaming step", and the obtained polypropylene-based resin foamed particles are called "one-stage foamed particles". The method for producing the present foamed particles is to obtain foamed particles having a foaming ratio of at least 15 times or more in the one-step foaming step. That is, in one embodiment of the present invention, the expansion ratio of the one-stage foamed particles is 15 times or more.

In order to obtain polypropylene-based resin foamed particles having a high foaming ratio, there is a method of increasing the amount of the foaming agent used in the one-step foaming step (hereinafter referred to as method 1). Further, as a method other than Method 1, polypropylene-based resin foamed particles (one-stage foamed particles) having a relatively low magnification (foaming ratio of about 15 to 35 times) are obtained in a one-stage foaming step, and then foamed again to obtain a foaming ratio. It is also possible to adopt a method of increasing the value (hereinafter referred to as method 2). In the present specification, the expansion ratio is the density of the polypropylene-based resin (a) before foaming, the weight of the polypropylene-based resin foamed particles, and the volume obtained by submerging the polypropylene-based resin foamed particles in water (or submerged in ethanol). It is a true magnification that can be calculated from.

Examples of the method 2 include methods including the following (i) to (iii). (I) In the one-stage foaming step, one-stage foamed particles having a foaming ratio of 15 to 35 times are produced, and (ii) the one-stage foamed particles are placed in a pressure-resistant container, and 0.1 MPa · G or more with nitrogen, air, carbon dioxide, etc. The pressure inside the one-stage foamed particles (hereinafter, may be referred to as "internal pressure") is made higher than the normal pressure by pressure treatment at 0.6 MPa · G or less, and then (iii) the one-stage foamed particles. Is a method of further foaming by heating with steam or the like. The step of increasing the foaming ratio of the one-stage foamed particles as in Method 2 is called a "two-stage foaming step", and the polypropylene-based resin foamed particles obtained by the method of Method 2 are called "two-stage foamed particles".

[6. Effervescent molded product in polypropylene resin mold]
The polypropylene-based resin in-mold foam molded product according to an embodiment of the present invention is described in the above [4. Polypropylene-based resin foamed particles] is preferably a molded product obtained by in-mold foam molding of the polypropylene-based resin foamed particles. In the present specification, the "polypropylene resin-based in-mold foam molded article according to the embodiment of the present invention" is also referred to as "the present molded article".

Since this molded product has the above-mentioned structure, it has an advantage of being excellent in surface properties.

This molded body is described in the above [3. Method for Producing Polypropylene Resin Foamed Particles], it is preferable that the foamed particles produced by the method for producing the foamed particles described in the above section are foam-molded in a mold.

(6-1. Surface consistency of molded product)
The surface integrity of the molded product can be evaluated by the state between the particles on the surface of the molded product. The state between the particles on the surface of the molded product will be described with reference to FIG. FIG. 5 is a diagram showing an example of an enlarged part of the surface of the polypropylene-based resin mold in-foam molded product. In FIG. 5, there are gaps 5 between 14 polypropylene-based resin foam particles 4 (three particles can be confirmed as a whole) and one particle formed between the three polypropylene-based resin foam particles 4. It is illustrated. The gap 5 between the particles is shown by shading (hatch). In FIG. 5, the line between the polypropylene-based resin foamed particles 4 and the gap 5 between the particles, in other words, the line forming the gap 5 between the particles is referred to as “boundary line 6”. In FIG. 5, for convenience of explanation, the boundary line 6 is shown by a black line, and the other lines (outline lines of the polypropylene-based resin foam particles 4) are shown by gray. As shown in FIG. 5, the gap 5 between the particles formed between the three polypropylene-based resin foamed particles 4 is formed by the three boundary lines 6. Of the three boundary lines 6, two are straight line boundary lines 6a and one is a non-straight line boundary line 6b. In FIG. 5, the non-straight line boundary line 6b is shown by a line thicker than the straight line boundary line 6a. As shown in FIG. 5, the boundary line 6 derived from one polypropylene-based resin foamed particle 4 is referred to as one boundary line 6.

The boundary line 6 will be described more specifically with reference to FIG. FIG. 6 shows an example of the boundary line 3. As shown in FIG. 6, the width of the boundary line 6 is defined as "the width of the boundary line A (width A of the boundary line 6)", and the height of the boundary line 6 is defined as "the height of the boundary line B (height of the boundary line 6)". B) ". The width A of the boundary line 6 is intended to be the length of a line segment connecting one end and the other end of the boundary line 6. The width A of the boundary line 6 can be said to be the shortest distance from one end to the other end of the boundary line 6. The height B of the boundary line 6 is cut off by the line segment connecting one end and the other end of the boundary line 6 and the boundary line 6 when a perpendicular line is drawn for the line segment connecting one end and the other end of the boundary line 6. It can be said that it is the length of the longest perpendicular line among the perpendicular lines. In the present specification, when R obtained by the following formula (15) is less than 1.5, the boundary line 6 is defined as a "straight line boundary line", and when it is 1.5 or more, the boundary line 6 is ". It is a boundary line that is not a straight line. "

A gap between particles may be formed on the surface of the molded product. It is preferable that no gaps between particles are formed on the surface of the molded product. It can be said that a molded product having a surface in which gaps between particles are not formed is extremely excellent in surface consistency. When gaps between particles are formed on the surface of the molded product, the boundary line between the foamed particles and the gaps between the particles is preferably a straight line. When the gaps between the particles are formed on the surface of the molded product, it is preferable that the boundary line between the foamed particles and the gaps between the particles has a small number of non-straight boundaries. When the boundary line between the foamed particles and the gap between the particles is a straight line, it can be said that the molded product has excellent surface consistency. A case where a gap between particles is detected on the surface of the molded product when observing the space between particles per 20 particles on the surface of the molded product will be described. In this case, regarding the boundary line between the foamed particles and the gap between the particles, the number of non-straight boundary lines is preferably 8 or less, more preferably 6 or less, and further preferably 3 or less. preferable.

(6-2. Manufacturing method of molded product)
Examples of the method for producing the present molded product (in-mold foam molding method) include the following methods (A) to (C):
(A) (i) A predetermined internal pressure is applied to the foamed particles by pressurizing the foamed particles with an inorganic gas to impregnate the foamed particles with the inorganic gas. (Ii) After that, the foamed particles are gold. Filling the mold, (iii) Next, the foamed particles are heat-fused together by heating the mold and the foamed particles with steam;
(B) (i) The foamed particles are compressed by gas pressure and filled in the mold. (Ii) Next, the recovery power of the filled foamed particles is utilized, and the mold and the foamed particles are charged using water vapor. A method of heating and fusing foamed particles to each other by heating;
(C) (i) Fill the mold with the foamed particles without any special pretreatment. (Ii) Next, the foamed particles are heat-fused together by heating the mold and the foamed particles with steam. ,Method.

In the method for producing an in-foam foam molded product in a polypropylene resin mold according to an embodiment of the present invention, the molding cycle is short. The molding cycle in the method for producing a polypropylene-based resin in-mold foam molded article according to an embodiment of the present invention is not particularly limited, but is preferably less than 160 seconds, more preferably less than 150 seconds.

The bulk density of the molded product is not particularly limited. The bulk density of the molded product is preferably 15 g / L or more and 350 g / L or less, and more preferably 20 g / L or more and 300 g / L or less.

One embodiment of the present invention may have the following configuration.

[1] Polypropylene-based resin is included as the base resin, the weight per grain is 0.5 mg / grain or more and 5.0 mg / grain or less, and the crystal orientation parameter R on the surface exceeds 3.5 and becomes 5 or less. , L ₁₂ / D ₁₂ shrinkage rate obtained by the following formula (1) is 50% or more, polypropylene-based resin particles: L ₁₂ / D ₁₂ shrinkage rate = 100 × (1- (average L of polypropylene-based resin foamed particles) ₂ / D ₂ ratio) / (Average L ₁ / D ₁ ratio of the polypropylene-based resin particles)) ... Formula (1); Here, the polypropylene-based resin foamed particles foam the polypropylene-based resin particles. The foaming ratio is 15 times or more.

[2] The polypropylene-based resin particles according to [1], wherein the polypropylene-based resin particles have an average L ₁ / D ₁ ratio of 2.0 to 5.0.

[3] Polypropylene resin foamed particles obtained by foaming the polypropylene resin particles according to [1] or [2].

[4] The polypropylene-based resin foamed particles according to [ ₃ ], wherein the polypropylene-based resin foamed particles have an average L3 / _D3 ratio of 0.8 or more and less than 1.5.

[5] The polypropylene-based resin foamed particles according to [3] or [4], wherein the foaming ratio is 15 times or more and 25 times or less.

[6] A polypropylene-based resin in-mold foam molded product obtained by in-mold foam molding of the polypropylene-based resin foamed particles according to any one of [3] to [5].

[7] A method for producing polypropylene-based resin particles, in which the crystal orientation parameter R on the surface exceeds 3.5 and becomes 5 or less, and the L ₄₅ / D ₄₅ shrinkage rate obtained by the following formula (2) is 50% or more. The polypropylene-based resin particles have a weight of 0.5 mg / grain or more and 5.0 mg / grain or less, and the polypropylene-based resin particles are produced so as to be: L ₄₅ / D ₄₅ . Shrinkage rate = 100 × (1- (average L ₅ / D ₅ ratio of polypropylene-based resin foam particles) / (average L ₄ / D ₄ ratio of polypropylene-based resin particles)) ... Equation (2); The polypropylene-based resin foamed particles are obtained by foaming the polypropylene-based resin particles, and the foaming ratio is 15 times or more.

[8] A dispersion preparation step of mixing polypropylene-based resin particles, a dispersion medium, and a foaming agent having a surface crystal orientation parameter R of more than 3.5 and 5 or less in a container to prepare a dispersion, and the above. It has a release step of discharging the dispersion liquid into a pressure range lower than the pressure in the container to obtain polypropylene-based resin foamed particles having a foaming ratio of 15 times or more, and L ₆₇ / obtained by the following formula (3). D ₆₇ A method for producing foamed polypropylene resin particles having a shrinkage rate of 50% or more: L ₆₇ / D ₆₇ shrinkage rate = 100 × (1- ( _{average L7} / D7 ratio of the above polypropylene-based resin foamed particles) / (Average L ₆ / D ₆ ratio of the above polypropylene-based resin particles)) ... Equation (3).

[9] A resin composition preparation step of heating a blend containing a polypropylene-based resin in an extruder to melt it and kneading it to prepare a polypropylene-based resin composition, and a obtained polypropylene-based resin composition. An extrusion step of extruding from one or more ejection holes provided in a die provided in an extruder, and a cooling step of solidifying the extruded polypropylene-based resin composition by cooling it using a cooling device equipped with a cooling medium. Then, the polypropylene-based resin composition solidified by using a take-up machine is taken up in the gas phase, and the polypropylene-based resin composition taken up by using a shredding device is shredded to obtain polypropylene-based resin particles. The heating temperature in the resin composition preparation step including the shredding step of obtaining the above is Tm ₁ + 40 ° C. to Tm ₁ + 110 ° C., where Tm ₁ is the melting point of the polypropylene-based resin, and is the temperature of the cooling medium. Is Tm 1-150 ° C. or higher and Tm _1-100 ° C. or lower, and the surface temperature of the resin composition in the gas phase in the take _- up step is Tm _1-170 ° C. or lower, which is the average of the polypropylene-based resin particles. The L ₄ / D ₄ ratio is 2.0 to 5.0, and the stretch degree obtained from the following formula (10) is 10 m / min to 100 m / min; the stretch degree = take-up speed-resin linear speed. Equation (10), where the take-up speed is the take-up speed per unit time of the polypropylene-based resin composition by the take-up machine in the take-back step, and the resin linear velocity is the following formula (10). It is a value obtained from 11); the resin linear velocity = discharge amount / (density of the polypropylene-based resin composition × total area of the discharge holes) ... Equation (11), where the discharge amount is In the extrusion step, it is the amount of the polypropylene-based resin composition extruded from the extruder per unit time, and the total area of the ejection holes is one provided in the die provided in the extruder. It is the sum of the areas of the above discharge holes; the relaxation time obtained from the following equation (12) is greater than 0 seconds and 0.1000 seconds or less; the relaxation time = the distance from the die to the cooling medium / The take-up speed ... Equation (12), where the distance from the die to the cooling medium is greater than 0 mm and less than 80 mm, and the surface crystal orientation parameter R exceeds 3.5 and becomes 5 or less. A method for producing polypropylene-based resin particles.

Hereinafter, one embodiment of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to such Examples.

The substances used in the examples and comparative examples are as follows.

<Polypropylene resin>
An ethylene-propylene random copolymer (melting point Tm ₁ = 147 ° C., melt flow rate (MFR) = 8 g / L), which is a polypropylene-based resin, was used.

<Resin particle additive>
Polyethylene glycol talc <dispersant>
Tricalcium Phosphate [manufactured by Taihei Kagaku Sangyo Co., Ltd.]
<Dispersion aid>
Sodium alkyl sulfonate (n-soda paraffin sulfonate) [Made by Kao Corporation, Latemul PS]
The evaluation in the examples and comparative examples was performed by the following method.

<Measurement of melting point Tm ₁ of polypropylene resin>
The melting point Tm ₁ of the polypropylene resin is measured by the differential scanning calorimeter DSC [METTTLER.
TOLEDO N. V. DSC822e type manufactured by the same company] was used for the measurement. Specifically: (1) After heating 5 to 6 mg of the sample to be measured from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min and melting it; (2) 10 After the temperature is lowered from 220 ° C. to 40 ° C. at a temperature lowering rate of ° C./min to crystallize; (3) the temperature is further raised from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min. The temperature of the peak (melting peak) of the DSC curve obtained at the time of the second temperature rise (that is, at the time of (3)) was set to the melting point Tm ₁ of the polypropylene resin.

<Measurement of crystal orientation parameter R of polypropylene resin particles>
As will be described later, the Raman spectrum on the surface of the polypropylene-based resin particles obtained by cutting the strands was measured to obtain the crystal orientation parameter R. Specifically, the measurement was carried out at an arbitrary point 2 on the side surface of the randomly selected columnar or polygonal columnar polypropylene resin particles 1. The measurement was performed using an attenuated total reflection method (hereinafter referred to as ATR method) under polarized conditions with the measurement mode as microscopic Raman. First, as shown by the arrow A in FIG. 1, a Raman spectrum was obtained by measuring in a state where the polarization direction of the incident light 3 and the extrusion direction of the resin particles were matched. Next, the peak intensity (I810) attributed to the combination mode of the expansion and contraction of the main chain of propylene observed near the wavelength 810 cm-1 and the CH3 variable angular vibration observed from the obtained spectrum, and CH3 observed near the wavelength 840 cm-1. The crystal orientation parameter R was calculated by taking the ratio of the peak intensity (I840) attributable to the angular vibration of.
Crystal orientation parameter R = (I810) / (I840) ... Equation (5)
The measurement was performed twice in total by changing the position of point 2, and the average value was used. The detailed conditions are shown below.

Laser Raman spectroscopy device: in Vita (RENISHAW)
Measurement mode: Microscopic Raman objective lens: × 20
Beam diameter: 5 μm
Light source: YAG 2nd 532nm
Laser power: 10mW
Diffraction grating: Single 3000gr / mm
Slit: 65 μm
Detector: CCD / RENISHAW 1024 × 256

<Measurement of melting point Tm ₂ of polypropylene resin particles>
The melting point Tm ₂ of the polypropylene-based resin particles was measured by the differential scanning calorimeter DSC [METTTLER TOLEDO N. et al. V. DSC822e type manufactured by the same company] was used for the measurement. Specifically, the DSC is obtained by performing DSC by the same method as described in <Measurement of melting point Tm ₁ of polypropylene resin> described above, except that polypropylene resin particles are used instead of polypropylene resin. The temperature of the peak (melting peak) of the curve was set to the melting point Tm ₂ of the polypropylene-based resin particles.

<Measurement of DSC ratio>
The DSC ratio [= {Qh / (Ql + Qh)} × 100 (%)] was measured by the differential scanning calorimeter [METTTLER TOLEDO N.C. V. DSC822e type manufactured by the same company] was used. Specifically, the DSC curve at the time of the first temperature rise (see FIG. 3) obtained when the temperature of 5 to 6 mg of polypropylene-based resin foam particles is raised from 40 ° C to 220 ° C at a temperature rise rate of 10 ° C / min. The DSC ratio was calculated from the above.

The details of FIG. 3 are as described above. As described above, the low temperature side melting heat amount (Ql) and the high temperature side melting heat amount (Qh) were obtained based on the obtained DSC curve. The DSC ratio was calculated from the obtained Ql and Qh and the above formula (14).

<Measurement of foaming magnification of polypropylene-based resin foamed particles>
First, the density of polypropylene-based resin particles was determined as follows. The obtained polypropylene-based resin particles were weighed in the range of 3 g or more and 10 g or less, and dried at 60 ° C. for 6 hours. Then, the dried polypropylene-based resin particles were allowed to stand in a room at 23 ° C. and 50% humidity for 24 hours or more. Next, the weight w ₁ (g) of the polypropylene-based resin particles was measured. Then, the polypropylene-based resin particles were submerged in ethanol contained in the measuring cylinder, and the volume v ₁ (cm ³ ) of the polypropylene-based resin particles was measured based on the increase in the liquid level position of the measuring cylinder (submersion method). .. Then, the density ρr (= w ₁ / v ₁ ) of the polypropylene-based resin particles was obtained from the weight w ₁ (g) and the volume v ₁ (cm ³ ).

Next, the density of the polypropylene-based resin foamed particles was determined as follows. The obtained polypropylene-based resin foamed particles were weighed in the range of 3 g or more and 10 g or less, and dried at 60 ° C. for 6 hours. Then, the dried polypropylene-based resin foamed particles were allowed to stand in a room at 23 ° C. and 50% humidity for 24 hours or more. Next, the weight w ₂ (g) of the polypropylene-based resin foamed particles was measured. Then, the polypropylene-based resin foamed particles were submerged in ethanol contained in the measuring cylinder, and the volume v ₂ (cm ³ ) of the polypropylene-based resin foamed particles was measured based on the increase in the liquid level position of the measuring cylinder (submerged). Law). Then, the density ρb (= w ₂ / v ₂ ) of the polypropylene-based resin foamed particles was obtained from the weight w ₂ (g) and the volume v ₂ (cm ³ ).

The ratio (ρr / ρb) of the density ρb of the polypropylene-based resin foamed particles to the density ρr of the polypropylene-based resin particles before foaming was defined as the foaming ratio (= ρr / ρb).

<Evaluation method of molding cycle>
The molding cycle in the method for producing an in-foam foam molded product in a polypropylene resin mold was defined as the time from the start of molding to the end of molding in which the molded product was released. Molding starts when the polypropylene-based resin foam particles are filled into the mold, and the molding is heated by sending steam into the mold, then the molded product is water-cooled, and the surface attached to the surface of the plank mold. The mold was opened at the timing when the surface pressure dropped to 0.01 MPa with a pressure gauge, and the time when the mold release was completed was regarded as the end of molding, and the heating pressure of the steam was comparatively evaluated as 0.3 MPa · G. The evaluation criteria are as follows.
◎ (Very excellent): Molding cycle is 140 seconds or more and less than 150 seconds
○ (excellent): molding cycle is 150 seconds or more and less than 160 seconds × (inferior): molding cycle is 160 seconds or more

<Evaluation of surface spread of molded product>
The edge portion of the obtained molded product was visually observed and evaluated on a scale of 1 to 5. The evaluation criteria are as follows. The larger the number, the better the surface quality.
1; 70% or more and 100% or less of the uneven region in the entire area of the edge portion 2; 40% or more and less than 70% of the uneven region in the entire region of the edge portion 3; All of the edge portion The uneven region is 20% or more and less than 40% in the region 4; the uneven region is 10% or more and less than 20% in the entire region of the edge portion 5; the uneven region is present in the entire region of the edge portion The region is 0% or more and less than 10% (Note that 0% of the region having unevenness in the entire region of the edge portion means that there is no region having unevenness in the entire region of the edge portion).

<Evaluation of surface integrity of molded product>
The presence or absence of gaps between the particles was visually detected between the particles per 20 particles on the surface of the obtained in-mold foam molded product. When the gap between the particles was detected, the boundary line between the foamed particles and the gap between the particles was visually detected as a non-straight boundary line, and the number of the boundary line was measured. For the gaps and boundaries between the particles on the surface of the molded product, the description in FIG. 4 and the above section (6-1. Surface consistency of the molded product) can be appropriately referred to. Based on the obtained results, the surface consistency was evaluated according to the following criteria.
◎ (Very excellent): There are no gaps between particles, or there are gaps between particles, and there are 3 or less non-straight borders between the foamed particles and the gaps between the particles. (Excellent): There are gaps between particles, and the boundary line between the foamed particles and the gaps between the particles has 4 or more and 8 or less non-straight boundaries × (Inferior): There are gaps between the particles. And, regarding the boundary line between the foamed particles and the gap between the particles, there are 9 or more non-straight boundaries.

Hereinafter, the methods for producing polypropylene-based resin particles, polypropylene-based resin foamed particles, and polypropylene-based resin in-mold foam molded body in Examples and Comparative Examples will be described.

[Manufacturing method of polypropylene resin particles]
Polypropylene-based resin particles were produced using a twin-screw extruder, a cooling device, a take-up machine, and a cutting device. As the cooling device, a water tank in which the cooling medium is water was used. Specifically, it is as follows. 100 parts by weight of polypropylene resin, 0.5 part by weight of polyethylene glycol and 0.05 part by weight of talc were dry blended. The mixture obtained by dry blending was melt-kneaded at the resin temperature (° C.) shown in Table 1 using a twin-screw extruder to prepare a polypropylene-based resin composition as a melt-kneaded product. Then, the melt-kneaded polypropylene-based resin composition was extruded into a strand shape from a discharge hole provided in a die provided in the twin-screw extruder. Here, the total number (pieces) of the discharge holes and the diameter of the discharge holes (diameter of the cross section of the discharge holes per one discharge hole) provided in the die provided in the twin-screw extruder are as shown in Table 1. .. The amount (kg / hr) of the polypropylene-based resin composition discharged from the extruder was as shown in Table 1. Since the cross-sectional shape of the discharge hole is circular, the area (mm ² ) per discharge hole can be obtained from the discharge hole diameter. Further, the discharge hole diameters of the plurality of discharge holes are the same for each of the twin-screw extruders used in the examples and the comparative examples. Therefore, for each of the twin-screw extruders used in Examples and Comparative Examples, the area of each of the plurality of discharge holes is the same, and therefore, the total area of the discharge holes is one. It can be obtained by multiplying the area per area by the total number (pieces) of discharge holes.

Next, the obtained strand (polypropylene resin composition) was placed in a water tank, cooled with water, and solidified. Here, the distance from the die to the cooling medium and the temperature of the cooling medium are as shown in Table 1.

Next, using a pick-up machine, the solidified strands were picked up from the water tank at the pick-up speed (m / min) shown in Table 1. The surface temperature of the strands taken from the water tank, that is, the surface temperature of the polypropylene-based resin composition discharged into the gas phase from the cooling device was measured with an infrared radiation thermometer, and the results are shown in Table 1.

Next, the taken strands were cut using a cutting device to obtain polypropylene-based resin particles. For the obtained polypropylene-based resin particles, the crystal orientation parameter R, the weight per particle, and the average L ₁ / D ₁ ratio were measured, and the results are shown in Table 1. The average L ₁ / D ₁ ratio can be said to be the average L ₄ / D ₄ ratio, the average L ₆ / D ₆ ratio, and the average L ₈ / D ₈ ratio.

The resin linear velocity, stretchability and relaxation time were calculated based on the above-mentioned equations (11), (10) and (12), and the results are shown in Table 1. The density of the polypropylene-based resin particles was 0.7 to 0.8 g / cm ³ . The melting point Tm ₂ of the polypropylene-based resin particles was 146 ° C.

[Manufacturing method of polypropylene-based resin foam particles]
In a 0.3 m ³ autoclave, 100 parts by weight of polypropylene resin particles, 200 parts by weight of water as a dispersion medium, calcium tertiary phosphate as a dispersant and sodium alkylsulfonate as a dispersion aid were charged, and the container was sealed. Then, 5 parts by weight of carbon dioxide gas was charged into the container as a foaming agent, and the charged raw materials were stirred to prepare a dispersion liquid. Next, the temperature inside the container was raised to 153 ° C. (foaming temperature), and the inside of the container was increased to 3.0 MPa · G (foaming pressure). Then, the temperature and pressure in the container were maintained at the above-mentioned foaming temperature and foaming pressure for 20 minutes. Next, one end of the autoclave is opened, and the dispersion liquid in the container is discharged to a non-sealed (under atmospheric pressure) tubular container through an orifice plate of φ3.2 mm to obtain polypropylene-based resin foam particles. rice field. The DSC ratio, foaming ratio and _average L2 / D2 ratio of the obtained polypropylene _- based resin foamed particles were measured, and the results are shown in Table 1. The L ₁₂ / D ₁₂ shrinkage rate was calculated from the average L ₁ / D ₁ ratio and the average L ₂ / D ₂ ratio, and the results are shown in Table 1. The average L ₂ / D ₂ ratio can be said to be the average L ₃ / D ₃ ratio, the average L ₅ / D ₅ ratio, and the average L ₇ / D ₇ ratio. Further, the L ₁₂ / D ₁₂ shrinkage rate can be said to be the L ₄₅ / D ₄₅ shrinkage rate, the L ₆₇ / D ₆₇ shrinkage rate, and the L ₈₃ / D ₈₃ shrinkage rate.

[Manufacturing method of foam molded product in polypropylene resin mold]
The obtained polypropylene-based resin foamed particles were washed with a hydrochloric acid aqueous solution having a pH of 1 and then with water for 30 seconds each, and dried at 75 ° C. for 20 hours. Then, the polypropylene-based resin foamed particles were cured at room temperature for 1 day or more, and then used for producing a polypropylene-based resin in-mold foam molded product by the method described later.

The polypropylene-based resin foamed particles were put into a pressure-resistant container, and the polypropylene-based resin foamed particles were impregnated with pressurized air to adjust the internal pressure of the foamed particles to 0.10 MPa · G. The foamed particles to which the internal pressure was applied were filled in a mold having a size of 400 mm × 300 mm × 50 mm. Here, the filling rate of the polypropylene-based resin foam particles into the mold was calculated, and the results are shown in Table 1.

Then, the mold and the foamed particles were heated with steam of 0.3 MPa · G to fuse the polypropylene-based resin foamed particles with each other to obtain a polypropylene-based resin foamed molded product. The obtained polypropylene-based resin in-mold foam molded product was released from the mold, dried at 75 ° C. for 20 hours, and further cured at 23 ° C. for 5 hours or more. Then, the surface spread, surface consistency and molding cycle of the obtained polypropylene-based resin in-mold foam molded product were measured. The results are shown in Table 1.

表１から、実施例１～６である、本発明の一実施形態に係るポリプロピレン系樹脂粒子から得られる本発明の一実施形態に係るポリプロピレン系樹脂発泡粒子は、成形サイクルおよび表面性に優れる成形体を提供できることが分かる。比較例１～５である、本発明の範囲外のポリプロピレン系樹脂粒子から得られる本発明の範囲外の発泡粒子は、成形サイクルに劣る成形体を提供することが分かる。

From Table 1, the polypropylene-based resin foamed particles according to the embodiment of the present invention obtained from the polypropylene-based resin particles according to the embodiment of the present invention according to Examples 1 to 6 have excellent molding cycle and surface properties. It turns out that it can provide the body. It can be seen that the foamed particles outside the range of the present invention obtained from the polypropylene-based resin particles outside the range of the present invention, which are Comparative Examples 1 to 5, provide a molded body inferior in the molding cycle.

One embodiment of the present invention can provide polypropylene-based resin particles that can provide foamed particles that can shorten the molding cycle and provide a molded product having excellent surface properties. Various molded products obtained by in-mold foam molding using foamed particles obtained from polypropylene-based resin particles according to an embodiment of the present invention include buffer packaging materials, distribution materials, heat insulating materials, civil engineering and building materials, and automobile members. It can be suitably used for various purposes.

1 Polypropylene-based resin particles 2 Arbitrary points on the side surface of polypropylene-based resin particles 3 One end of incident light emitted from a laser Raman spectroscope 4 Polypropylene-based resin foamed particles 5 Gap between particles 6 Boundary line 6a Straight boundary line 6b Straight line Not a boundary line A Boundary line width B Boundary line height

Claims (9)

Contains polypropylene resin as the base resin,
The crystal orientation parameter R on the surface exceeds 3.5 and becomes 5 or less, the L ₁₂ / D ₁₂ shrinkage rate obtained by the following formula (1) is 50% or more, and the weight per grain is 0.5 mg / grain. Polypropylene resin particles of 5.0 mg / grain or less:
L ₁₂ / D ₁₂ Shrinkage rate = 100 × (1- (average L ₂ / D ₂ ratio of polypropylene-based resin foam particles) / (average L ₁ / D ₁ ratio of polypropylene-based resin particles)) ... 1);
Here, the polypropylene-based resin foamed particles are formed by foaming the polypropylene-based resin particles, and the foaming ratio is 15 times or more. The polypropylene-based resin particles according to claim 1, wherein the polypropylene-based resin particles have an average L ₁ / D ₁ ratio of 2.0 to 5.0. Polypropylene resin foamed particles obtained by foaming the polypropylene resin particles according to claim 1 or 2. The polypropylene-based resin foamed particles according to claim ₃ , wherein the polypropylene-based resin foamed particles have an average L3 / _D3 ratio of 0.8 or more and less than 1.5. The polypropylene-based resin foamed particles according to claim 3 or 4, wherein the foaming ratio is 15 times or more and 25 times or less. A polypropylene-based resin in-mold foam molded product obtained by in-mold foam molding of the polypropylene-based resin foamed particles according to any one of claims 3 to 5. A method for manufacturing polypropylene-based resin particles.
The step of adjusting so that the crystal orientation parameter R on the surface exceeds 3.5 and becomes 5 or less and the L ₄₅ / D ₄₅ shrinkage rate obtained by the following formula (2) becomes 50% or more is included.
The polypropylene-based resin particles have a weight of 0.5 mg / grain or more and 5.0 mg / grain or less per grain.
Manufacturing method of polypropylene resin particles:
L ₄₅ / D ₄₅ Shrinkage rate = 100 × (1- (average L ₅ / D ₅ ratio of polypropylene-based resin foam particles) / (average L ₄ / D ₄ ratio of polypropylene-based resin particles)) ... 2);
Here, the polypropylene-based resin foamed particles are formed by foaming the polypropylene-based resin particles, and the foaming ratio is 15 times or more. A dispersion liquid preparation step of mixing polypropylene-based resin particles, a dispersion medium, and a foaming agent having a surface crystal orientation parameter R of more than 3.5 and 5 or less in a container to prepare a dispersion liquid.
It has a discharge step of discharging the dispersion liquid into a pressure range lower than the pressure in the container to obtain polypropylene-based resin foamed particles having a foaming ratio of 15 times or more.
The L ₆₇ / D ₆₇ shrinkage rate obtained by the following formula (3) is 50% or more.
Manufacturing method of polypropylene-based resin foam particles:
L ₆₇ / D ₆₇ Shrinkage rate = 100 × (1- (average L ₇ / D ₇ ratio of the polypropylene-based resin foam particles) / (average L ₆ / D ₆ ratio of the polypropylene-based resin particles)) ... (3). A resin composition preparation step of heating a blend containing a polypropylene-based resin in an extruder to melt it and kneading it to prepare a polypropylene-based resin composition.
An extrusion step of extruding the obtained polypropylene-based resin composition from one or more discharge holes provided in a die provided in the extruder.
A cooling step of solidifying the extruded polypropylene-based resin composition by cooling it using a cooling device provided with a cooling medium.
A pick-up process in which the polypropylene-based resin composition solidified using a pick-up machine is picked up in the gas phase,
Including a shredding step of shredding the polypropylene-based resin composition taken up using a shredding device to obtain polypropylene-based resin particles.
The heating temperature in the resin composition preparation step is Tm ₁ + 40 ° C. to Tm ₁ + 110 ° C., where Tm ₁ is the melting point of the polypropylene-based resin.
The temperature of the cooling medium is Tm _1-150 ° C. or higher and Tm _1-100 ° C. or lower.
The surface temperature of the resin composition in the gas phase in the above-mentioned take _- up step is Tm 1-70 ° C. or lower.
The _average L4 / _D4 ratio of the polypropylene-based resin particles is 2.0 to 5.0.
The stretchability obtained from the following formula (10) is 10 m / min to 100 m / min;
Degree of elongation = take-up speed-resin linear speed ... Equation (10),
Here, the pick-up speed is the pick-up speed per unit time of the polypropylene-based resin composition by the pick-up machine in the pick-up step.
The resin linear velocity is a value obtained from the following equation (11);
Resin linear velocity = discharge amount / (density of the polypropylene-based resin composition x total area of the discharge holes) ... Equation (11),
Here, the discharge amount is the amount of the polypropylene-based resin composition extruded from the extruder per unit time in the extrusion step, and the total area of the discharge holes is provided in the extruder. The sum of the areas of one or more of the ejection holes provided in the die;
The relaxation time obtained from the following equation (12) is greater than 0 seconds and 0.1000 seconds or less;
Relaxation time = distance from the die to the cooling medium / take-up speed ... Equation (12),
Here, the distance from the die to the cooling medium is greater than 0 mm and less than 80 mm.
A method for producing polypropylene-based resin particles in which the crystal orientation parameter R on the surface exceeds 3.5 and becomes 5 or less.

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