Method for manufacturing polypropylene resin foam particles
The described method for producing polypropylene resin foam particles using a specific resin blend and pressure release technique addresses the issue of immediate shrinkage in molded products, achieving improved foaming and moldability.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- JSP CORP
- Filing Date
- 2022-10-21
- Publication Date
- 2026-05-15
Smart Images
Figure 0007859762000006 
Figure 0007859762000007 
Figure 0007859762000001
Abstract
Description
[Technical Field]
[0001] This invention relates to a method for producing polypropylene resin foam particles. [Background technology]
[0002] Polypropylene-based foamed particle molded articles are used in a wide range of fields, including electrical and electronics, automobiles, building materials, and general merchandise, because they have superior chemical resistance, impact resistance, and compression strain recovery compared to polystyrene-based foamed particle molded articles. Polypropylene-based foamed particle molded articles are obtained by foaming polypropylene-based resin particles to form polypropylene-based foamed particles, and then molding the resulting polypropylene-based foamed particles in a mold. [Overview of the project] [Problems that the invention aims to solve]
[0003] In recent years, there has been a growing demand for methods of producing polypropylene resin foam particles with excellent foaming properties, from the perspectives of improving productivity during foam particle production and reducing environmental impact.
[0004] However, with conventional methods, when foamed particles obtained by a manufacturing method that improves foaming properties are used for in-molding, the molded product tends to shrink immediately after in-molding, which can reduce the moldability when obtaining a foamed particle molded product from the foamed particles. The object of the present invention is to provide a method for producing foamed particles that is excellent in both foaming properties when obtaining foamed particles from resin particles and moldability when obtaining a foamed particle molded product from the obtained foamed particles. [Means for solving the problem]
[0005] According to the present invention, a method for producing polypropylene resin foam particles as shown below is provided. [1] A method for producing foamed polypropylene resin particles, comprising releasing polypropylene resin particles containing a foaming agent, which are dispersed in a dispersion medium inside a sealed container, from the sealed container to a pressure range lower than the pressure inside the container, thereby foaming the polypropylene resin particles, The aforementioned polypropylene resin particles are obtained by kneading a polypropylene resin (P) as a base resin, which is a polypropylene resin (A) selected from ethylene-propylene random copolymer resin and ethylene-propylene-butene random copolymer resin, and an impact polypropylene resin (B) having a morphology in which polypropylene is the matrix and rubber-like material containing ethylene-propylene rubber is the domain. The mass ratio of the amount of the polypropylene random copolymer resin (A) (a) to the amount of the impact polypropylene resin (B) (b) satisfies a:b = 55:45 to 98:2. The melting point of the polypropylene random copolymer resin (A) is d (°C), and the melting point of the impact polypropylene resin (B) is c (°C), satisfying the following equations (1) and (2), 150 (℃) <c<170(℃) (1) 5°C ≤ cd ≤ 35°C (2) The melt flow rate f (g / 10min) of the polypropylene random copolymer resin (A) measured at 230°C and a load of 2.16 kg, and the melt flow rate e (g / 10min) of the impact polypropylene resin (B) measured at 230°C and a load of 2.16 kg, satisfy the following equations (3), (4), and (5): 3 (g / 10 min) ≤ e (3) 0.3(g / 10min)≦e / f≦8(g / 10min) (4) 3(g / 10min)≦f≦ 10(g / 10min) (5) A method for producing polypropylene resin foam particles characterized by the above. [2] A method for producing polypropylene resin foam particles according to [1], wherein the melt flow rate of the polypropylene resin (P) measured under the conditions of 230°C and a load of 2.16 kg is 5 g / 10 min or more and 20 g / 10 min or less. [3] A method for producing polypropylene resin foam particles according to [1] or [2], wherein the flexural modulus of the impact polypropylene resin (B) is 800 MPa or more and 1200 MPa or less. [4] A method for producing polypropylene resin foam particles according to [1] or [2], wherein the ratio of the flexural modulus of the random copolymer resin (A) to the flexural modulus of the impact polypropylene resin (B) is 0.5 or more and less than 1. [Effects of the Invention]
[0006] According to the present invention, a method for producing foamed particles is provided, which involves kneading a polypropylene-based random copolymer resin (A) and an impact polypropylene resin (B) that satisfy a specific relationship, and then foaming the resulting resin particles using the method described above. This method provides excellent foaming properties when producing foamed particles from resin particles, as well as excellent moldability when using the obtained foamed particles for in-mold molding. [Brief explanation of the drawing]
[0007] [Figure 1] Figure 1 is a diagram showing an example of a micrograph (5000x magnification) of impact polypropylene resin (B). [Figure 2] Figure 2 is a schematic diagram showing an example of the first DSC curve chart for polypropylene resin foam particles with a high-temperature peak. [Modes for carrying out the invention]
[0008] The method for producing polypropylene-based resin foam particles of the present invention will be described in detail below. In the method for producing polypropylene resin foam particles, polypropylene resin particles (hereinafter also referred to as polypropylene resin particles or simply resin particles) are dispersed in a dispersion medium in a sealed container, and impregnated with a physical foaming agent to form foamable resin particles. These foamable resin particles are then released together with the dispersion medium from the sealed container to a pressure lower than the pressure inside the container to cause foaming. This is a so-called dispersion medium release foaming method, thereby producing polypropylene resin foam particles (hereinafter also referred to simply as foam particles).
[0009] In the manufacturing method of the present invention, the polypropylene resin particles use a polypropylene resin (P) as the base resin. The polypropylene resin (P) is obtained by melt-kneading a polypropylene random copolymer resin (A) and an impact polypropylene resin (B). In this invention, a polypropylene resin refers to a resin having 50% by mass or more structural units derived from propylene. Furthermore, "base resin" means that 50% by mass or more of the base resin is a polypropylene resin, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.
[0010] The polypropylene-based random copolymer resin (A) is selected from ethylene-propylene random copolymer resin and ethylene-propylene-butene random copolymer resin. That is, copolymer resin (A) may be either ethylene-propylene random copolymer resin or ethylene-propylene-butene random copolymer resin alone, or it may be a mixture of ethylene-propylene random copolymer resin and ethylene-propylene-butene random copolymer resin.
[0011] As the comonomer component of the ethylene-propylene random copolymer resin, the propylene component is the main component, and it is preferable that the content of the ethylene component in the copolymer resin is 0.5% by mass or more and 6% by mass or less. In addition, the total of the ethylene component and the propylene component in the ethylene-propylene random copolymer resin is 100% by mass. It is more preferable that the content of the ethylene component in the copolymer resin is 0.8% by mass or more and 5.5% by mass or less, and it is even more preferable that it is 1% by mass or more and 5% by mass or less.
[0012] In addition, the content of the comonomer component can be determined by IR spectrum measurement. Here, the ethylene component and the propylene component of the ethylene-propylene copolymer resin respectively mean the structural unit derived from ethylene and the structural unit derived from propylene in the ethylene-propylene copolymer resin. Also, the content of each monomer component in the copolymer resin shall mean the content of the structural unit derived from each monomer in the copolymer resin.
[0013] The ethylene-propylene-butene random copolymer resin has the propylene component as the main component, and examples of the comonomer component include ethylene, 1-butene, cis-2-butene, trans-2-butene, and 2-methylpropene.
[0014] The butene component content of the ethylene-propylene-butene random copolymer resin is preferably 0.2% by mass or more and 15% by mass or less, more preferably 0.3% by mass or more and 12% by mass or less, and even more preferably 1% by mass or more and 10% by mass or less. If the butene component content of the ethylene-propylene-butene random copolymer resin is within the above range, the foamed particles will be excellent in the balance between moldability and rigidity. The butene used for the butene component of the copolymer resin is preferably 1-butene, which is a linear α-olefin.
[0015] Also, the ethylene component content of the ethylene-propylene-butene random copolymer resin is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 5% by mass or less, and even more preferably 0.4% by mass or more and 3% by mass or less.
[0016] In addition, the propylene component content of the ethylene-propylene-butene random copolymer resin is preferably 85% by mass or more and 98% by mass or less, more preferably 86% by mass or more and 95% by mass or less, still more preferably 88% by mass or more and 92% by mass or less.
[0017] The content of the comonomer component can be determined by IR spectrum measurement. Here, the ethylene component, propylene component, and butene component of the ethylene-propylene-butene random copolymer resin respectively mean the structural units derived from ethylene, propylene, and butene in the ethylene-propylene-butene random copolymer resin. Also, the content of each monomer component in the copolymer resin is meant to be the content of the structural units derived from each monomer in the copolymer resin.
[0018] The impact polypropylene resin (B) (hereinafter, the impact polypropylene resin is also referred to as ICP) is a resin having a morphology with polypropylene as a matrix and a rubbery body containing ethylene-propylene rubber as a domain. The rubber refers to something having rubber elasticity and is different from the resin. FIG. 1 shows an example of a micrograph of the impact polypropylene resin (B).
[0019] The morphology of the impact polypropylene resin (B) can be observed by the following method. First, an observation sample is cut from impact polypropylene resin (B). Then, this observation sample is embedded in epoxy resin and stained with ruthenium tetroxide. Sections are then prepared from the sample using an ultramicrotome or similar device. These sections are placed on the grid of a transmission electron microscope (for example, JEOL's "JEM-1040Flash") and observed at a magnification of 10,000x or 5,000x, while cross-sectional images of the impact polypropylene resin (B) (hereinafter sometimes abbreviated as TEM images) are taken. From the cross-sectional images, the morphology of the polypropylene phase and the ethylene propylene rubber phase can be visually observed.
[0020] Furthermore, in impact polypropylene resin (B), the average diameter of the ethylene propylene rubber phase (domain) is preferably 0.5 μm or more and 10 μm or less. The average diameter of the domains composed of ethylene propylene rubber can be calculated using the TEM image. Specifically, the area of 30 randomly selected domains in the TEM image is measured, the measured values are given an arithmetic mean, and then converted to an equivalent circle diameter to calculate the average diameter of the ethylene propylene rubber phase (domain) (average value of the equivalent circle diameter). The average value of the equivalent circle diameter of ethylene propylene rubber is the diameter of a perfect circle having the same area as the average area of the ethylene propylene rubber. Note that the ethylene propylene rubber phase (domain) refers to the ethylene propylene rubber phase alone, and, if ethylene propylene rubber and polyethylene are adjacent, the entire phase of ethylene propylene rubber and polyethylene.
[0021] The content of ethylene propylene rubber (EPR) in impact polypropylene resin (ICP) is more preferably 3% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less.
[0022] The ethylene propylene rubber content in impact polypropylene resin (B) can be measured by the following method: Add 5 g of impact polypropylene resin (B) sample to 500 ml of n-decane at 135°C to completely dissolve the soluble components (soluble polymers). Then, cool to 23°C and leave for 24 hours. Next, centrifuge the solution and decant the separated liquid phase in 1000 ml of acetone to precipitate the polymer (ethylene propylene rubber). Filter off the precipitate, wash it, dry it, and measure its weight. Divide the measured weight by the weight of the sample and express the result as a percentage to determine the ethylene propylene rubber content in impact polypropylene resin (B).
[0023] Impact polypropylene resin (B) is commonly used and commercially available as a polypropylene resin for automobiles and is manufactured through a variety of processes. For example, it can be manufactured in a multi-stage process, where homopolypropylene (homoPP) is polymerized using propylene gas in the first stage, and ethylene propylene rubber (EPR) is polymerized in the second stage using ethylene gas. ICP also includes products supplied as a blend of homoPP and EPR, and also includes what is known as block polypropylene.
[0024] In addition to ethylene propylene rubber, polyethylene can be added to ICP by mixing or by adding ethylene during polymerization. Examples of polyethylene include low-density polyethylene, ultra-low-density polyethylene, linear low-density polyethylene, and high-density polyethylene. These may be used individually or in combination of two or more. The polyethylene content in ICP is preferably 0% to 30% by mass, and more preferably 3% to 27% by mass, based on 100% by mass of the total of polypropylene, ethylene propylene rubber, and polyethylene.
[0025] Furthermore, the ethylene content in the ICP is preferably 10% by mass or more and 40% by mass or less, and more preferably 15% by mass or more and 35% by mass or less. Here, the ethylene content is calculated as the sum of the ethylene content contained in the ethylene propylene rubber and the ethylene content of other added polyethylene. The above content can be determined by a known method determined by IR spectroscopy. Specifically, it can be determined by the method described in the Polymer Analysis Handbook (edited by the Polymer Analysis Research Group of the Japan Society for Analytical Chemistry, published January 1995, published by Kinokuniya Shoten, page numbers and item names: 615-616 "II.2.3 2.3.4 Propylene / Ethylene Copolymer", 618-619 "II.2.3 2.3.5 Propylene / Butene Copolymer"), that is, by a method of quantification based on the relationship between the absorbance of ethylene corrected by a predetermined coefficient and the thickness of a film-like test piece.
[0026] The weight-average molecular weight (Mw) of ICP is preferably between 100,000 and 1,000,000, more preferably between 150,000 and 500,000, and particularly preferably between 110,000 and 400,000. If the weight-average molecular weight of ICP is within the above range, foam particles with better moldability will be obtained. In addition, for ICP, the number-average molecular weight (Mn) is preferably between 20,000 and 50,000, and the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) is preferably between 7 and 10. In this specification, the number-average molecular weight (Mn), weight-average molecular weight (Mw), and Z-average molecular weight (Mz) can be measured by gel permeation chromatography after dissolving 30 mg of the sample in 20 mL of o-dichlorobenzene at 145°C by shaking, and then thermal filtering the solution through a sintered filter with a pore size of 1.0 μm to obtain the analytical sample.
[0027] When impact polypropylene resin (B) is blended with polypropylene random copolymer resin (A), it is possible to improve the moldability of foamed particles during in-mold molding while ensuring foaming properties and a wide molding range during foam particle production. This is thought to be because, when impact polypropylene resin (B) is blended, the foam film strength of the foamed particles is maintained at a high level even when molding is performed at high molding temperatures.
[0028] In the present invention, the ratio of the amount of polypropylene random copolymer resin (A) to the amount of impact polypropylene resin (B) (b) must be within the range of a:b = 55:45 to 98:2 by mass ratio. If the amount of impact polypropylene resin (B) is too high, the bubble film may be prone to bursting, and the foaming improvement effect may not be achieved. On the other hand, if the amount of impact polypropylene resin (B) is too low, shrinkage after foaming will be large, causing the foam particles to shrink, and as a result, the foaming improvement effect may not be achieved. For these reasons, the mass ratio of a to b is preferably in the range of a:b = 60:40 to 97:3, and more preferably a:b = 70:30 to 96:4.
[0029] Furthermore, in the present invention, the melting point of impact polypropylene resin (B) c (°C) and the melting point of polypropylene random copolymer resin (A) d (°C) must satisfy the following equations (1) and (2). 150 (℃) <c<170(℃) (1) 5°C ≤ cd ≤ 35°C (2)
[0030] Because the melting points of impact polypropylene resin (B) and polypropylene random copolymer resin (A) satisfy the relationship in the above equation, even when the temperature inside the sealed container is raised to an appropriate foaming temperature, the presence of crystals in impact polypropylene resin (B) allows the polypropylene resin (P) as a whole to foam easily, and the bubble film is easily stretched, while maintaining an appropriate rigidity as a whole resin (P). Therefore, it is thought that foaming properties can be improved.
[0031] From the above viewpoint, the melting point c (°C) of impact polypropylene resin (B) preferably satisfies the following formula (6), and more preferably satisfies the following formula (7). 155°C <c<168(℃) (6) 158 (℃) <c<165(℃) (7)
[0032] Furthermore, the melting point of impact polypropylene resin (B) c (°C) and the melting point of polypropylene-based random copolymer resin (A) d (°C) preferably satisfy the following formula (7), and more preferably satisfy the following formula (8), from the viewpoint of balancing the imparting of foaming properties and good moldability. 7°C ≤ cd ≤ 30°C (8) 8°C ≤ cd ≤ 25°C (9)
[0033] Furthermore, from the viewpoint of improving moldability, the melting point d (°C) of the polypropylene random copolymer resin (A) preferably satisfies the following formula (10), and more preferably satisfies the following formula (11). 130°C <d<155(℃) (10) 135°C <d<150(℃) (11)
[0034] The melting points of the copolymer resin (A) and the impact polypropylene resin (B) are determined according to JIS K7121:1987. The melting point is defined as the peak temperature of the maximum melting peak that appears on the DSC curve.
[0035] Furthermore, in the present invention, the melt flow rate of impact polypropylene resin (B) e (g / 10min) and the melt flow rate of polypropylene random copolymer resin (A) f (g / 10min) must satisfy the following formulas (3), (4), and (5). 3 (g / 10 min) ≤ e (3) 0.3(g / 10min)≦e / f≦8(g / 10min) (4) 3(g / 10min)≦f≦10(g / 10min) (5)
[0036] If the melt flow rate (hereinafter also referred to as MFR) of impact polypropylene resin (B) is too low, the bubble film portion will not stretch easily during foaming, and the foaming properties will tend to decrease. In addition, residual stress is more likely to remain in the resulting foam particles, which may result in poor moldability. On the other hand, if the MFR of impact polypropylene resin (B) becomes too high compared to the MFR of the copolymer resin, the strength of the bubble film will decrease, making it prone to bursting, which may cause shrinkage of the resulting foamed particles or deterioration of moldability.
[0037] For the reasons stated above, the melt flow rate e (g / 10min) of impact polypropylene resin (B) preferably satisfies the following formula (12), and more preferably satisfies the following formula (13).
[0038] 3.5(g / 10min)≦e(g / 10min)≦80 (12) 4(g / 10min)≦e(g / 10min)≦50 (13)
[0039] Furthermore, the melt flow rate of impact polypropylene resin (B) e (g / 10min) and the melt flow rate of polypropylene random copolymer resin (A) f (g / 10min) preferably satisfy the following formula (11), and more preferably satisfy the following formula (12). 0.5(g / 10min)≦e / f≦7.5(g / 10min) (14) 1(g / 10min)≦e / f≦7(g / 10min) (15)
[0040] Furthermore, the melt flow rate f (g / 10min) of the polypropylene random copolymer resin (A) preferably satisfies the following formula (16), and more preferably satisfies the following formula (17). 4(g / 10min)≦f≦9(g / 10min) (16) 5(g / 10min)≦e / f≦8.5(g / 10min) (17)
[0041] In the present invention, the melt flow rate (MFR) of the polypropylene resin (P) is preferably 5 g / 10 min or more and 20 g / 10 min or less. When the MFR is within this range, a good balance between foaming and moldability is achieved, and foamed particles with low apparent density and excellent in-moldability can be obtained. For this reason, the MFR is more preferably 6 g / 10 min or more and 18 g / 10 min or less, and even more preferably 7 g / 10 min or more and 15 g / 10 min or less.
[0042] In this specification, the melt flow rate (MFR) is measured in accordance with JIS K7210-1:2014, under conditions of a temperature of 230°C and a load of 2.16 kg.
[0043] The copolymer resin (A) and the impact polypropylene resin (B) may contain additives such as bubble regulators, nucleating agents, flame retardants, flame retardant aids, plasticizers, antistatic agents, antioxidants, UV inhibitors, light stabilizers, antibacterial agents, and colorants, to the extent that they do not impair the effects described above. The amount of these additives added is preferably 0.1 to 5 parts by mass per 100 parts by mass of the resin.
[0044] Furthermore, when the impact polypropylene resin (B) is derived from automobile recycled material (ASR), the ash content in the impact polypropylene resin (B) is generally between 0.5% by mass and 20% by mass, and is often between 1% by mass and 10% by mass. In this specification, ASR refers to "automobile shredding residue" as defined in Article 2-5 of the Act on Recycling of End-of-Life Automobiles, Act No. 87 of 2002. More specifically, ASR refers to the material remaining after dismantling an end-of-life automobile, from which recyclable parts such as engines and batteries have been removed, shredding the vehicle, separating metals and other useful materials from the shredded material, and recovering them.
[0045] Furthermore, when automotive recycled material (ASR) is used as impact polypropylene resin (B), impact polypropylene resin (B) often contains carbon black (CB), and the carbon black content is generally between 0.1% by mass and 1% by mass. In addition, the ratio of carbon black (CB) content to ash content (CB amount / ash amount) is generally between 0.005 and 2, and is often between 0.01 and 1.0. When such impact polypropylene resin (B) is used, the MFR satisfies the above formulas (3), (4), and (5), resulting in uniform dispersion of additives in the impact polypropylene resin (B), and obtaining foamed particles with uniform bubble diameter and excellent moldability.
[0046] The ash content and CB content can be measured using a thermogravimetric analyzer.
[0047] The flexural modulus of the impact polypropylene resin (B) is preferably 800 MPa to 1200 MPa, and more preferably 900 MPa to 1100 MPa. If the flexural modulus of polypropylene (B) is within this range, a good balance between foaming and moldability is achieved, and in particular, even with small cell diameters and thin cell films, foamed particles with low apparent density and excellent in-moldability can be obtained.
[0048] Furthermore, the flexural modulus of the polypropylene random copolymer resin (A) is preferably 600 MPa or more and 1200 MPa or less, and more preferably 750 MPa or more and 1000 MPa or less. In addition, the ratio of the flexural modulus of the random copolymer resin (A) to the flexural modulus of the impact polypropylene resin (B) is preferably 0.5 or more and less than 1, and more preferably 0.7 or more and 0.9 or less.
[0049] The flexural modulus of impact polypropylene resin (B) and polypropylene-based random copolymer resin (A) can be determined in accordance with JIS K7171:2008.
[0050] According to the present invention, the apparent density of the resulting foamed particles is preferably 15 kg / m³. 3 More than 400kg / m 3 The following is possible. If the apparent density of the foam particles is too low, the resulting foam particle molded product will shrink significantly, which may make it difficult to manufacture. On the other hand, if the apparent density of the foam particles is too high, the advantages of the foam, such as its light weight and heat insulation properties, may be lost. From this perspective, the apparent density of the foam particles should be 20 kg / m³. 3 More than 300kg / m 3 The following is more preferable, and even more preferably, 24 kg / m 3 More than 240kg / m 3 The following applies:
[0051] If foamed particles with an even lower apparent density are desired, a method can be employed in which foamed particles obtained by a dispersion medium release foaming method (hereinafter referred to as "single-stage foamed particles") are foamed again (hereinafter referred to as the "double-stage foaming method," and foamed particles obtained by the double-stage foaming method are referred to as "double-stage foamed particles"). Double-stage foamed particles can be obtained, for example, by placing single-stage foamed particles in a sealed container and pressurizing them with an inorganic gas or the like to raise the pressure inside the foamed particles to above atmospheric pressure, and then further foaming the foamed particles by heating them with steam or the like.
[0052] The apparent density of foam particles can be determined as follows: The weight W (g) of a group of foamed particles that has been conditioned by leaving them for two days under conditions of 50% relative humidity, 23°C, and 1 atm can be determined by dividing the weight W by the volume V (L) of the foamed particle group (W / V). The volume V (L) of the foamed particle group can be determined by preparing a graduated cylinder containing a liquid such as alcohol (e.g., ethanol) at 23°C, submerging the foamed particle group in the liquid using a wire mesh or similar, and measuring the rise in the liquid level.
[0053] The average bubble diameter of the foamed particles obtained by the present invention is preferably 20 μm to 400 μm, more preferably 40 μm to 300 μm, and even more preferably 50 μm to 200 μm.
[0054] In the manufacturing method of the present invention, when recycled automobile materials are used as the impact polypropylene resin (B), the amount of ash and additives such as carbon black tends to increase, and the average bubble diameter tends to decrease. However, even if the average bubble diameter decreases, by using an impact polypropylene resin (B) having a specific MFR, it is possible to provide a method for producing foamed particles with excellent foaming properties by dispersing the additives well, and furthermore, the resulting foamed particles have good moldability.
[0055] The average bubble diameter of foamed particles is measured as follows: Based on magnified photographs taken under a microscope of the cross-section of a foam particle that has been roughly divided in half, the following can be determined. First, in the magnified photograph of the cross-section of the foam particle, draw four line segments that pass through approximately the center of the bubble cross-section from one surface of the foam particle to the other surface. However, these line segments should be drawn so as to form eight radial lines that extend at equal intervals from approximately the center of the bubble cross-section to the surface of the cut particle. Next, determine the total number N (bubbles) that intersect the four line segments. Determine the sum L (μm) of the lengths of the four line segments, and take the value obtained by dividing the sum L by the sum N (L / N) as the average bubble diameter of one foam particle. Perform this procedure for 10 foam particles, take the arithmetic mean of the average bubble diameters of each foam particle, and take the value obtained by dividing by 0.616 as the average bubble diameter of the foam particle.
[0056] Also, the closed cell ratio of the foamed particles is preferably 75% or more, more preferably 80% or more, still more preferably 85% or more, and particularly preferably 90% or more. If the closed cell ratio is too small, the secondary foaming property of the foamed particles may decrease, and the mechanical properties of the resulting molded body may also decrease.
[0057] The closed cell ratio of the foamed particles is measured as follows. The foamed particles are left to cure for 10 days in a thermostatic chamber under atmospheric pressure, with a relative humidity of 50% and a temperature of 23°C. Next, in the same thermostatic chamber, the apparent volume Va of the cured foamed particles with a bulk volume of about 20 cm 3 is accurately measured by the water immersion method using the cured foamed particles as a measurement sample. After the measurement sample for which the apparent volume Va has been measured is sufficiently dried, the true volume Vx of the measurement sample measured by a Toshiba Beckman air comparison type pycnometer 930 in accordance with Procedure C described in ASTM-D2856-70 is measured. Then, based on these volumes Va and Vx, the closed cell ratio is calculated by the following formula (83), and the average value of N = 5 is taken as the closed cell ratio of the foamed particles.
[0058] Closed cell ratio (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ··· (18) However, Vx: The true volume of the foamed particles measured by the above method, that is, the sum of the volume of the resin constituting the foamed particles and the total volume of the bubbles in the closed cell portion within the foamed particles (cm 3 ) Va: The apparent volume of the foamed particles measured from the rise in the water level when the foamed particles are submerged in a graduated cylinder filled with water (cm 3 ) W: The weight (g) of the measurement sample of the foamed particles ρ: The density (g / cm 3 ) of the resin constituting the foamed particles
[0059] Next, the growth of secondary crystals in the foamed particles obtained by the present invention will be described. Preferably, the foamed particles obtained by the present invention have secondary crystals, and the DSC curve (DSC curve of the first heating) obtained when 2 to 10 mg of the foamed particles are heated from 23°C to 220°C at a heating rate of 10°C / min by differential scanning calorimetry has an endothermic peak a (hereinafter also simply referred to as the "intrinsic peak") intrinsic to the polypropylene resin, and one or more endothermic peaks b (hereinafter also simply referred to as the "high-temperature peak") originating from the secondary crystals on the high-temperature side of the intrinsic peak.
[0060] The heat of fusion (ΔH2) of the high-temperature peak (hereinafter also simply referred to as high-temperature peak heat (ΔH2)) is preferably 5 J / g or more and 30 J / g or less, and more preferably 10 J / g or more and 25 J / g or less. Having the high-temperature peak heat within this range results in foamed particles with excellent fusion properties during molding, as well as a molded article with excellent mechanical strength.
[0061] The DSC curve for the first heating cycle, as well as the intrinsic peak heat quantity and high-temperature peak heat quantity, are measured as follows, in accordance with the measurement method compliant with JIS K7122:1987. First, 2 to 10 mg of foamed particles are collected and their temperature is measured by increasing the temperature from 23°C to 220°C at a rate of 10°C / min using a differential scanning calorimetry (DSC) analyzer. An example of a DSC curve obtained from this measurement is shown in Figure 2. The DSC curve in Figure 2 shows an intrinsic peak a originating from the polypropylene resin constituting the foamed particles, and a high-temperature peak b on the high-temperature side of the intrinsic peak. The heat value of the high-temperature peak b corresponds to its peak area. Specifically, it is determined as follows: First, a straight line (α-β) is drawn connecting point α on the DSC curve corresponding to 80°C and point β on the DSC curve corresponding to the melting end temperature T of the foamed particles. Note that the melting end temperature T is the intersection point of the DSC curve and the high-temperature baseline on the high-temperature side of the high-temperature peak B. Next, a straight line parallel to the vertical axis of the graph is drawn from point γ on the DSC curve, which is in the valley between the intrinsic peak a and the high-temperature peak b, and the point where it intersects with the aforementioned line (α-β) is denoted as δ. The area of the high-temperature peak b is the area enclosed by the curve of the high-temperature peak b portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ) (the shaded area in Figure 2), and this corresponds to the heat quantity of the high-temperature peak. The melting point is measured according to the procedure described above. Furthermore, the high-temperature peak b is observed in the DSC curve from the first heating test, as measured as described above, but not in the DSC curve obtained after the second heating test. In the DSC curve from the second heating test, only the endothermic curve peak characteristic of the PP resin constituting the foamed particles is observed.
[0062] The high-temperature peak heat quantity of foamed particles can be adjusted by well-known methods, and specifically, such adjustment methods are disclosed, for example, in Japanese Patent Application Publication No. 2001-151928.
[0063] Next, the method for producing polypropylene-based resin foam particles of the present invention will be described in more detail. The foamed particles of the present invention are manufactured by a conventionally known foaming method using a dispersion medium. This can be obtained by a method called the dispersion medium release foaming method, in which polypropylene resin particles are dispersed in a dispersion medium such as water in a sealed container such as an autoclave, an inorganic physical foaming agent is injected under pressure, the mixture is heated to a temperature above the softening temperature of the resin particles to impregnate the resin particles with the foaming agent, and while maintaining the pressure inside the sealed container at a pressure above the vapor pressure of the foaming agent, one end of the sealed container below the water surface is opened, and the foamed resin particles are released from the sealed container along with the dispersion medium such as water into a pressure range lower than the pressure inside the container, usually to atmospheric pressure, to cause foaming.
[0064] The resin particles can be produced by mixing the aforementioned polypropylene random copolymer resin (A) and impact polypropylene resin (B) in the aforementioned proportions, adding additives such as foam regulators as needed, supplying the mixture to an extruder for heating and kneading, extruding it from a die as a large number of strands, cooling the strands by passing them through water and then cutting them to appropriate lengths, or by simultaneously extruding a molten resin composition of polypropylene resin (P) from a die into water and cutting and cooling it.
[0065] The polypropylene resin (P) may contain additives such as bubble regulators, nucleating agents, flame retardants, flame retardant aids, plasticizers, antistatic agents, antioxidants, UV inhibitors, light stabilizers, antibacterial agents, and colorants, to the extent that they do not impair the effects described above. The content of these additives is preferably 0.1 to 5 parts by mass per 100 parts by mass of the polypropylene resin (P).
[0066] To adjust the bubble size of the foamed particles, it is preferable to add a bubble regulator. Examples of such bubble regulators include inorganic substances such as talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, and alum. The amount added is preferably 0.001 to 10 parts by weight, and more preferably 0.01 to 5 parts by weight, per 100 parts by weight of polypropylene resin (P). Furthermore, when adding a foam regulator to a polypropylene resin (P), it is possible to blend the foam regulator directly, but it is generally preferable to add it as a foam regulator masterbatch, taking into consideration dispersibility and other factors.
[0067] The weight of the resin particles is preferably 0.02 to 20 mg, and more preferably 0.1 to 6 mg, in order to ensure uniform filling of the foamed particles into the mold.
[0068] When releasing from a high-pressure state where foaming does not occur to a low-pressure state where foaming occurs, the pressure difference between the high-pressure and low-pressure states should be 400 kPa or more, preferably 500 to 15000 kPa.
[0069] The blowing agents used in the dispersion medium release blowing method typically include organic physical blowing agents such as propane, isobutane, butane, isopentane, pentane, cyclopentane, hexane, cyclobutane, cyclohexane, chlorofluoromethane, trifluoromethane, 1,1,1,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, and 1-chloro-1,2,2,2-tetrafluoroethane, as well as inorganic physical blowing agents such as nitrogen, carbon dioxide, argon, and air. Among these, inorganic gas-based blowing agents that do not deplete the ozone layer and are inexpensive are preferred, with nitrogen, air, and carbon dioxide being particularly preferred. Furthermore, a mixture of two or more of these blowing agents can also be used.
[0070] The amount of blowing agent used is appropriately selected depending on the relationship between the apparent density of the foamed particles to be obtained and the foaming temperature. Specifically, in the case of blowing agents other than nitrogen and air, the amount of blowing agent used is usually 2 to 50 parts by weight per 100 parts by weight of resin particles. In the case of nitrogen and air, the pressure inside the sealed container is 10 to 70 kgf / cm². 2 A quantity that falls within the G pressure range is used.
[0071] In a sealed container, water is preferred as the dispersion medium for dispersing resin particles, but any medium that does not dissolve the resin particles can be used. Examples of such dispersion media include ethylene glycol, glycerin, methanol, and ethanol.
[0072] When dispersing resin particles in a dispersion medium in a sealed container and heating it to the foaming temperature, an anti-fusing agent can be used to prevent the resin particles from fusing together. Any anti-fusing agent that does not dissolve in water or other liquids and does not melt when heated can be used, regardless of whether it is inorganic or organic, but inorganic agents are generally preferred.
[0073] Suitable inorganic anti-fusing agents include powders such as kaolin, talc, mica, aluminum oxide, titanium oxide, and aluminum hydroxide. The anti-fusing agent has an average particle size of 0.001 to 100 μm, and is particularly preferably 0.001 to 30 μm. The amount of anti-fusing agent added is usually 0.01 to 10 parts by weight per 100 parts by weight of resin particles.
[0074] Furthermore, anionic surfactants such as sodium dodecylbenzenesulfonate and sodium oleate, as well as aluminum sulfate, are preferably used as dispersing aids. It is generally preferable to add 0.001 to 5 parts by weight of the dispersing aid per 100 parts by weight of resin particles.
[0075] The foamed particles obtained by the present invention are used in the manufacture of polypropylene-based resin foamed particle molded articles (hereinafter also simply referred to as foamed particle molded articles or molded articles). The foamed particle molded body can be obtained by filling the foamed particles into a mold using a conventionally known method as needed, and then heating and molding it with steam. That is, after filling the foamed particles into a mold that can be closed but cannot be sealed, steam is introduced into the mold to heat and foam the foamed particles, causing them to fuse together and resulting in a molded body in which the shape of the molded space is formed. Alternatively, if necessary, a pressurizing operation can be performed to increase the pressure inside the foamed particles, similar to the operation in the two-stage foaming described above, to adjust the internal pressure inside the foamed particles to 0.01 to 0.2 MPa (G) before molding. In this way, a molded body with an even lower apparent density can be obtained.
[0076] The closed-cell ratio of the molded article obtained by in-mold molding is preferably 75% or higher, more preferably 80% or higher, and even more preferably 85% or higher. If the closed-cell ratio is too low, it is difficult to obtain a molded article with low apparent density, and the mechanical properties tend to be inferior.
[0077] The closed-cell ratio of the molded product is measured as follows. The resulting molded body is left to cure for 10 days in a constant temperature room under atmospheric pressure, relative humidity of 50%, and temperature of 23°C. Next, a 25 × 25 × 30 mm sample is cut from the molded body, and the closed-cell ratio of the foamed particles is measured using this sample in the same manner as described above.
[0078] The density of a molded body can be determined by calculating its weight, dividing it by the volume obtained from the external dimensions of the sample, and then converting the units. [Examples]
[0079] Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
[0080] The following raw materials were used in the examples and comparative examples. (Polypropylene-based random copolymer resin (A)) (1) Abbreviation "r-PP1": Random polypropylene manufactured by Prime Polymer Co., Ltd. (ethylene content 2.5% by mass) (2) Abbreviation "r-PP2": Ethylene-propylene-butene random copolymer resin (ethylene content 0.9% by mass, butene content 9.6% by mass) manufactured by Sinopec Shanghai Petrochemical Co., Ltd.
[0081] (Impact polypropylene resin (B)) (1) Abbreviated name "ICP1": Planic polypropylene "PLC-A02", weight-average molecular weight (Mw) 220,000, number-average molecular weight (Mn) 24,000, ethylene component 26% by mass. (2) Abbreviation "ICP2": Block polypropylene "MK112" manufactured by Idemitsu Kosan Co., Ltd. (3) Abbreviation "ICP3": Prime Polymer Co., Ltd. block polypropylene "J762HP" (4) Abbreviation "ICP4": Decomposition raw material for ICP2 (ICP2 is mixed with 0.2 parts by mass of NOF Corporation's Perhexa 25B, melted and kneaded once in an extruder, and then pelletized) (5) Abbreviation "ICP5": Block polypropylene "rPP CPP050RP" manufactured by REEF Technology Co., Ltd., weight-average molecular weight (Mw) 265,000, number-average molecular weight (Mn) 46,000.
[0082] Table 1 shows the various physical properties of these polypropylene resins.
[0083] [Table 1]
[0084] (Bubble regulator) Zinc borate powder (product name: Zinc borate 2335, manufactured by Tomita Pharmaceutical Co., Ltd.)
[0085] (Melting point and heat of fusion of polypropylene resins) In Table 1, the melting point and heat of fusion were measured as follows. The melting point and heat of fusion of polypropylene resin were measured based on the differential scanning calorimetry method described in JIS K7121:1987. First, a test specimen made of polypropylene resin was prepared and allowed to stand for at least one day in an environment of 23°C and 50% RH relative humidity to adjust its condition. After adjusting the condition, the test specimen was heated from 23°C to 200°C at a heating rate of 10°C / min, then cooled down to 23°C at a cooling rate of 10°C / min, and then heated again from 23°C to 200°C at a heating rate of 10°C / min. The peak temperature of the endothermic peak determined by the DSC curve obtained during the second heating was defined as the melting point of the resin. If multiple endothermic peaks appeared in the second DSC curve, the peak temperature of the endothermic peak with the largest area was defined as the melting point. A differential scanning calorimetry device (DSC7020, manufactured by SII Nanotechnology Co., Ltd.) was used to obtain the DSC curve. Furthermore, in the second DSC curve obtained by the method described above, the area of the endothermic peak corresponding to the melting of the polypropylene resin (unit: J) was calculated. The value obtained by dividing this endothermic peak area by the mass of the test specimen (unit: g) was defined as the heat of fusion of the polypropylene resin (unit: J / g).
[0086] Examples 1-4, Comparative Examples 1-6 [Manufacturing of resin particles] First, the polypropylene random copolymer resin (A) and impact polypropylene resin (B) shown in Tables 2 and 3 were supplied to the extruder in the blending ratios shown in Tables 2 and 3. After melt-kneading, zinc borate was added as a foam regulator to a content of 1000 ppm by weight, and the mixture was extruded from the extruder in strand form. After cooling, these strands were cut to obtain colored resin particles weighing approximately 1.0 mg. In Example 4, Comparative Example 1, Comparative Example 2, Comparative Example 5, and Comparative Example 6, colored resin particles were produced by separately adding carbon black masterbatch and talc masterbatch based on r-PP1 to achieve the CB amount and ash content shown in Tables 2 and 3.
[0087] [Table 2]
[0088] [Table 3]
[0089] (Ash content of resin, carbon black content) The ash content of the resin was measured using a Hitachi High-Tech Corporation thermogravimetric analyzer TG / DTA7200, with a platinum sample pan K-Y50-035 PTΦ5×5PAN, as follows. Platinum sample pans 1 and 2, which contained no sample, were placed on a reference balance and a measuring balance, and the zero points were adjusted. Subsequently, 14-16 mg of resin particles or mini-pellets (hereinafter referred to as resin weight) were weighed and placed in platinum sample pan 2, which was then placed on the measuring balance. After that, while continuously recording the weight on the balance, the pan was held at 40°C for 5 minutes under a nitrogen atmosphere, and then the temperature was increased from 40°C to 500°C at a rate of 10°C / min to thermally decompose the organic components contained in the resin particles, leaving inorganic components as a residue. The weight at this stage was referred to as residue weight 1. Next, the temperature was raised from 500°C to 900°C under an air atmosphere to oxidize and remove the CB from the inorganic components. The weight after CB removal was defined as the residue weight 2. Then, the amount of CB was calculated using equation (19) below, and the amount of ash was calculated using equation (20) to determine the amount of CB. CB amount (wt%) = (Residue weight 1 - Residue weight 2) ÷ Resin weight × 100 (19) Ash content (wt%) = residue weight 2 ÷ resin weight × 100 (20)
[0090] [Manufacturing of foamed particles] One kilogram of each of the aforementioned resin particles and three liters of water as a dispersion medium were placed in a five-liter autoclave. Three liters of kaolin were added as a dispersant, and three liters of sodium alkylbenzenesulfonate and one liter of aluminum sulfate were added as dispersion aids to the dispersion medium. Carbon dioxide was injected into a sealed container as a foaming agent, and the mixture was heated and stirred until it reached the foaming temperatures shown in Tables 4 and 5. The mixture was then held at these temperatures for 15 minutes to adjust the high-temperature peak heat. After that, carbon dioxide was continuously injected into the autoclave to maintain the foaming pressure shown in Tables 4 and 5, and the contents of the autoclave were released along with water to atmospheric pressure to obtain colored foamed particles.
[0091] The foaming temperature was determined by fixing the foaming pressure (back pressure inside the autoclave) at 2.1 MPa during the dispersion foaming process, and selecting the temperature at which the apparent density was minimized while maintaining good moldability, to produce the foamed particles. The physical properties of the obtained foamed particles, such as apparent density, were measured and the results are shown in Tables 4 and 5.
[0092] [Table 4]
[0093] [Table 5]
[0094] In Tables 4 and 5, the measurement of high-temperature peak heat quantity (ΔH2), the measurement of apparent density of foamed particles, the measurement of average bubble diameter of foamed particles, and the measurement of closed-cell ratio of foamed particles were performed using the methods described above.
[0095] (High-temperature peak heat energy of foamed particles) Using a Hitachi High-Tech Corporation TG / DTA7200 thermogravimetric analyzer, the DSC curve and high-temperature peak heat quantity for the first heating cycle were measured as follows, in accordance with JIS K7122:1987. First, 2 to 10 mg of foamed particles were collected and measured by raising the temperature from 23°C to 220°C at a rate of 10°C / min using a differential scanning calorimetry (DSC) analyzer. An example of a DSC curve obtained from this measurement is shown in Figure 2. The DSC curve in Figure 2 shows an intrinsic peak a originating from the polypropylene resin constituting the foamed particles, and a high-temperature peak b on the high-temperature side of the intrinsic peak. The heat value of the high-temperature peak b corresponds to its peak area, and was specifically determined as follows. First, a straight line (α-β) was drawn connecting point α on the DSC curve, which corresponds to 80°C, and point β on the DSC curve, which corresponds to the melting termination temperature T of the foamed particles. The melting termination temperature T refers to the intersection point of the DSC curve on the high-temperature side of the high-temperature peak B and the high-temperature baseline. Next, a straight line parallel to the vertical axis of the graph was drawn from point γ on the DSC curve, which corresponds to the trough between the aforementioned intrinsic peak a and the high-temperature peak b, and the point where it intersects with the aforementioned line (α-β) was defined as δ. The area of the high-temperature peak b is the area enclosed by the curve of the high-temperature peak b portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ) (the shaded area in Figure 2), and this corresponds to the heat quantity of the high-temperature peak. The melting point was measured using the above procedure. Furthermore, the high-temperature peak b is observed in the DSC curve from the first heating test, as measured as described above, but not in the DSC curve obtained after the second heating test. In the DSC curve from the second heating test, only the endothermic curve peak characteristic of the PP resin constituting the foamed particles is observed.
[0096] In Tables 4 and 5, the apparent density of the foamed particles, the average bubble diameter of the foamed particles, and the closed-cell ratio of the foamed particles were measured using the methods described above.
[0097] In Tables 4 and 5, the foaming properties were evaluated as follows. Foamed particles are produced by fixing the foaming pressure (back pressure inside a sealed container during foaming) to a constant pressure (specifically 2.1 MPa), resulting in a low apparent density of 80 kg / m³. 3 The following evaluation was based on whether or not it was possible to stably produce foamed particles with a closed-cell ratio of 80% or more.
[0098] More specifically, a smaller ratio expressed as the apparent density of foamed particles / foaming pressure was considered to indicate superior foaming performance.
[0099] [Manufacturing of foamed particle molded products] As a molding die, a mold with a rectangular parallelepiped-shaped molding cavity having internal dimensions of 300 mm in the vertical direction, 250 mm in the horizontal direction, and 50 mm in the thickness direction was used. With the mold completely closed and then opened 5 mm, foam particles were filled into the molding cavity. After filling was complete, the mold was completely closed (cracking amount 5 mm, 10%). Subsequently, steam at 0.20 to 0.44 MPa (G) was supplied into the molding cavity to heat the foam particles, causing secondary foaming and fusion of the particles to obtain a colored foam particle molded body. The mold was water-cooled until the surface pressure of the foam particle molded body inside the mold reached 0.04 MPa (G), then the mold was opened and the colored foam particle molded body was removed from the mold. The obtained foam particle molded body was cured for 12 hours in an atmosphere of atmospheric pressure and a temperature of 80°C.
[0100] In Tables 4 and 5, the moldable range, lower limit fusion pressure, lower limit molding pressure, and moldability were determined as follows.
[0101] (Moldable range of foamed particles (in-moldability)) In the method described above (for manufacturing foamed particle molded articles), foamed particle molded articles were formed by varying the molding steam pressure by 0.01 MPa between 0.20 and 0.44 MPa. The resulting molded articles were evaluated for their fusion properties (degree of fusion between adjacent foamed particles), surface appearance (degree of voids), and recovery properties (degree of shrinkage due to expansion or contraction after in-mold molding). Articles that met the criteria shown below were deemed acceptable, and the steam pressure at which all items of fusion properties, surface appearance, and recovery properties were accepted was defined as the moldable steam pressure. A wider range from the lower limit to the upper limit of the moldable steam pressure indicates a wider moldable range and superior moldability. The upper limit of the moldable range was defined as the upper limit molding pressure, and the lower limit was defined as the lower limit molding pressure. Furthermore, the minimum molding pressure at which a foam particle molded body with acceptable fusion properties (described later) is obtained was defined as the lower limit of the fusion pressure. The evaluation of the molded products shown in the table was performed on molded products molded at the lower limit of the moldable range. Additionally, materials with no moldable range (indicated by "-" in the table) were deemed unmold.
[0102] (Fusibility) The foam particle molded body was bent and fractured, and the number of foam particles present on the fracture surface (C1) and the number of fractured foam particles (C2) were determined. The ratio of fractured foam particles to the number of foam particles present (C2 / C1 × 100) was calculated as the material fracture rate. The above measurement was performed five times using different test pieces, and the material fracture rate for each was determined. A material fracture rate of 90% or higher obtained by arithmetic mean was considered acceptable.
[0103] (Surface appearance) A 100mm x 100mm square was drawn in the center of the foam particle molded body. A line was drawn diagonally from one corner of the square, and the number of voids (gaps) of 1mm x 1mm or larger along this line was counted. The product was deemed acceptable if the number of voids was less than 5 and the surface was free of irregularities.
[0104] (Recoverability) The thickness of a foam particle molded body corresponding to a flat plate-shaped mold with dimensions of 300 mm in length, 250 mm in width, and 50 mm in thickness, was measured near the four corners (10 mm inward from the corners towards the center) and in the center (the part that divides the mold equally in both the lengthwise and widthwise directions). Next, the ratio (%) of the thickness of the center to the thickness of the thickest point near the four corners was calculated, and a ratio of 99% or higher was considered acceptable.
[0105] In Tables 4 and 5, the surface condition at the upper limit molding pressure was evaluated according to the following criteria. The surface condition of the molded body at the upper limit molding pressure was observed, and a condition where the surface appearance of the molded body was good and the absence of wrinkles on the surface could be visually determined was evaluated as good. In addition, a condition where five or more areas with partial wrinkles (groove-like depressions) could be visually determined in the foam particle portion that makes up the surface of the molded body was evaluated as having wrinkles.
[0106] In Tables 4 and 5, the density of the molded body and the closed-cell ratio of the molded body were measured using the method described above.
[0107] In Tables 4 and 5, the shrinkage rate was measured using the following method. The shrinkage rate [%] of the foam particle molded body was calculated by substituting the measured length of the molded body into the formula: (Longest side dimension of the molding die [mm] - Longest side length of the molded body [mm]) / Longest side dimension of the molding die [mm] × 100. The "Longest side length of the molded body [mm]" refers to the length of the longest side of the foam particle molded body obtained in the examples and comparative examples after curing in an 80°C atmosphere for 12 hours, slow cooling, and then curing in a 23°C atmosphere for 6 hours (n=10).
[0108] Comparative Example 1 Comparing Example 1 with Comparative Example 1, the foamed particles of Example 1, because they contain impact polypropylene resin (B), were able to be manufactured at a higher foaming temperature. As a result, the apparent density of the resulting foamed particles, and furthermore the apparent density of the molded article, was lower than that of Comparative Example 1, indicating improved foaming properties. In addition, both the foamed particles of Example 1 and Comparative Example 1 exhibited excellent moldability, but the moldable range of the foamed particles of Example 1 was wider, resulting in even greater moldability.
[0109] Comparative Example 2 is an example in which the resin constituting the foamed particles is the same as in Comparative Example 1, but the foaming temperature is higher. As a result, foaming properties improved and foamed particles with a lower apparent density were obtained, but the moldability of the foamed particles decreased, the shrinkage of the resulting foamed particle molded article increased, and wrinkles appeared on the surface.
[0110] Comparative Example 3 Comparative Example 3 is an example of foaming resin particles consisting solely of impact polypropylene resin (B). In the case of Comparative Example 3, it was possible to increase the foaming temperature. However, the moldability of the resulting foamed particles decreased, and even when the molding pressure was changed, it was not possible to obtain a molded body with the desired shape, so it was determined that molding was not possible. Regarding the physical property measurements, although the resulting foamed particle molded body did not have the desired shape, the measurements were performed using that body. Furthermore, the physical properties such as the apparent density of the foamed particles are those of the foamed particles obtained when this foamed particle molded body was produced.
[0111] Comparative Example 4 Comparative Example 4 is an example in which a large amount of impact polypropylene resin (B) is blended, and the blending ratio of polypropylene random copolymer resin (A) and the blending ratio of impact polypropylene resin (B) are both equal at 50% by mass. The foamed particles of Comparative Example 4 contained a large amount of impact polypropylene resin (B), which improved foaming properties. However, the moldable range narrowed, and moldability decreased.
[0112] Comparative Example 5 Comparative Example 5 is an example in which the blending ratio of impact polypropylene resin (B) is the same as in Example 1, but the MFR is different. Along with a decrease in foaming ability, the moldability of the resulting foamed particles also decreased. This is thought to be due to the influence of residual stress in the resin constituting the foamed particles, which reduced the moldability.
[0113] Comparative Example 6 Comparative Example 6 uses the same blending ratio of impact polypropylene resin (B) as Example 1, but with a different MFR. Although it exhibits excellent foaming properties, the moldability of the resulting foamed particles was reduced. [Explanation of Symbols]
[0114] T Melting end temperature a. Intrinsic peak b. High temperature peak
Claims
1. A method for producing foamed polypropylene resin particles, comprising releasing polypropylene resin particles containing a foaming agent, which are dispersed in a dispersion medium inside a sealed container, from the sealed container to a pressure range lower than the pressure inside the container, thereby foaming the polypropylene resin particles, The polypropylene resin particles are obtained by kneading a polypropylene resin (P) as a base resin, which is a polypropylene resin (A) selected from ethylene-propylene random copolymer resin and ethylene-propylene-butene random copolymer resin, and an impact polypropylene resin (B) having a morphology in which polypropylene is the matrix and rubber-like material containing ethylene-propylene rubber is the domain. The mass ratio of the amount of the polypropylene random copolymer resin (A) (a) to the amount of the impact polypropylene resin (B) (b) satisfies a:b = 55:45 to 98:
2. The melting point of the polypropylene random copolymer resin (A) is d (°C), and the melting point of the impact polypropylene resin (B) is c (°C), satisfying the following equations (1) and (2), 150(℃)<c<170(℃) (1) 5°C ≤ c - d ≤ 35°C (2) The melt flow rate f (g / 10min) of the polypropylene random copolymer resin (A), measured at 230°C and under a load of 2.16 kg, and the melt flow rate e (g / 10min) of the impact polypropylene resin (B), measured at 230°C and under a load of 2.16 kg, satisfy the following equations (3), (4), and (5): 3(g / 10min)≦e (3) 0.3 (g / 10min)≦e / f≦8 (g / 10min) (4) 3 (g / 10min)≦f≦10 (g / 10min) (5) A method for producing polypropylene resin foam particles characterized by the above.
2. A method for producing polypropylene resin foam particles according to claim 1, wherein the melt flow rate of the polypropylene resin (P) measured under the conditions of 230°C and a load of 2.16 kg is 5 g / 10 min or more and 20 g / 10 min or less.
3. A method for producing polypropylene resin foam particles according to claim 1 or 2, wherein the flexural modulus of the impact polypropylene resin (B) is 800 MPa or more and 1200 MPa or less.
4. A method for producing polypropylene resin foam particles according to claim 1 or 2, wherein the ratio of the flexural modulus of the random copolymer resin (A) to the flexural modulus of the impact polypropylene resin (B) is 0.5 or more and less than 1.