WO2023063081A1 - ポリプロピレン系樹脂発泡粒子及び発泡粒子成形体の製造方法 - Google Patents
ポリプロピレン系樹脂発泡粒子及び発泡粒子成形体の製造方法 Download PDFInfo
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- WO2023063081A1 WO2023063081A1 PCT/JP2022/036167 JP2022036167W WO2023063081A1 WO 2023063081 A1 WO2023063081 A1 WO 2023063081A1 JP 2022036167 W JP2022036167 W JP 2022036167W WO 2023063081 A1 WO2023063081 A1 WO 2023063081A1
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- expanded
- particles
- stage
- polypropylene resin
- resin particles
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Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B1/00—Layered products having a non-planar shape
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B1/00—Layered products having a non-planar shape
- B32B1/08—Tubular products
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/16—Making expandable particles
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/16—Making expandable particles
- C08J9/18—Making expandable particles by impregnating polymer particles with the blowing agent
Definitions
- the present disclosure relates to a method for producing black polypropylene-based resin expanded particles and a method for producing an expanded particle molding using the expanded particles.
- Polypropylene-based resin expanded particle moldings are lightweight and have excellent cushioning properties, rigidity, etc., and are used in a variety of applications.
- Polypropylene-based resin foamed beads are produced by, for example, filling a mold with polypropylene-based resin foamed beads and heating with steam to cause secondary foaming of the foamed beads and melt the surfaces of the foamed beads to fuse them together. It is manufactured by an in-mold molding method in which the material is molded into a desired shape. Since the molded article immediately after molding tends to swell due to secondary foaming, in order to obtain an expanded bead molded article having a desired shape, the expanded bead molded article is cooled with water, air, or the like in the mold and then released from the mold.
- the expanded polypropylene resin particles used in the production of the expanded bead molded article as described above are produced by dispersing the polypropylene resin particles in a dispersion medium in a closed container, and then dispersing the resin particles in the dispersion medium. is impregnated with an inorganic physical blowing agent, and the resin particles impregnated with the blowing agent are released together with the dispersion medium from a closed container into a low-pressure environment.
- a foaming method is hereinafter referred to as a direct foaming method.
- a black foamed particle molding is in demand.
- a black foamed bead molded article is obtained by in-mold molding polypropylene-based resin foamed beads containing carbon black as a coloring agent (see Patent Document 1).
- the present invention has been made in view of such a background, and provides expanded polypropylene resin particles capable of producing an expanded particle molded article having a high degree of blackness and less conspicuous color unevenness at a low molding heating temperature with good productivity. It is an object of the present invention to provide a method and a method for producing an expanded bead molded article using the expanded polypropylene resin particles.
- One aspect of the present invention is a method for producing cylindrical expanded polypropylene resin particles having through holes,
- polypropylene resin particles dispersed in a dispersion medium are impregnated with an inorganic physical blowing agent, and the resin particles are released together with the dispersion medium from the closed container under a pressure lower than in the closed container, thereby increasing the bulk.
- a single-stage expansion step for obtaining single-stage expanded particles with a magnification M of 1 ; After increasing the pressure in the cells of the first-stage expanded particles, the first-stage expanded particles are heated to further expand the first-stage expanded particles to obtain the expanded polypropylene resin particles having a bulk ratio M of 2 .
- the resin particles have a cylindrical shape with through holes, the resin particles contain carbon black, and the content of carbon black in the resin particles is 0.1% by weight or more and 5% by weight or less,
- the bulk ratio M1 of the single-stage expanded particles is 5 times or more and 25 times or less,
- polypropylene resin foamed beads are molded by filling a molding die with the polypropylene resin foamed beads obtained by the above manufacturing method, and supplying a heating medium to fuse the foamed beads to each other. It's in the way the body is made.
- black expanded polypropylene resin particles having a cylindrical shape with through-holes are obtained by performing the first-stage expansion process and the two-stage expansion process. According to the polypropylene-based resin foamed particles obtained in this manner, an expanded particle molded article having a high degree of blackness and inconspicuous color unevenness can be molded with high productivity at a low molding heating temperature.
- FIG. 1 is a schematic diagram of the appearance of expanded beads.
- FIG. 2 is a schematic cross-sectional view of an expanded bead having no coating layer in a direction parallel to the penetration direction of the through holes.
- FIG. 3 is a schematic cross-sectional view of an expanded bead having no coating layer in a direction perpendicular to the penetration direction of the through holes.
- FIG. 4 is a schematic cross-sectional view of an expanded bead having a coating layer in a direction parallel to the penetrating direction of the through holes.
- FIG. 5 is a schematic cross-sectional view of an expanded bead having a coating layer in a direction perpendicular to the penetrating direction of the through holes.
- FIG. 6(a) is a photograph showing the external appearance of the expanded bead molded article of Comparative Example 1
- FIG. 6(b) is a photograph showing the external appearance of the expanded bead molded article of Example 1.
- FIG. 7 is an explanatory diagram showing a method of calculating the area of the high temperature peak.
- expanded polypropylene resin beads are referred to as “two-step expanded beads” or “expanded beads” as appropriate, and expanded bead moldings are referred to as “molded articles” as appropriate. Further, the expanded beads obtained by the one-step expansion process are appropriately referred to as “one-step expanded beads”. Expanded beads having a foamed layer made of polypropylene resin are generally called polypropylene resin expanded beads.
- cylindrical expanded particles containing through-holes and containing carbon black are obtained.
- the expanded particles are black and are used to produce black moldings.
- a molded article is obtained by filling a mold with foamed particles, supplying a heating medium to the mold, and fusing the foamed particles to each other. Since the molded article immediately after molding tends to swell due to secondary foaming, in order to obtain an expanded bead molded article having a desired shape, the expanded bead molded article is cooled with water, air, or the like in the mold and then released from the mold.
- Such a molding method is appropriately called "in-mold molding".
- cylindrical resin particles having through-holes containing carbon black in the range of 0.1% by weight or more and 5% by weight or less are used. Furthermore, the bulk ratio M1 of the single-stage expanded particles obtained in the first-stage expansion process is adjusted to a range of 5 to 25 times, and this bulk ratio M1 and the expanded polypropylene resin particles obtained in the two-stage expansion process (that is, two The ratio M 2 /M 1 to the bulk ratio M 2 of the stepped expanded particles) is adjusted to 1.2 or more and 3.0 or less.
- an expanded particle molded article having a high degree of blackness and less conspicuous color unevenness can be molded with high productivity at a low molding heating temperature (specifically, a low molding pressure). can do.
- expanded beads having a high closed cell ratio can be obtained.
- the two-step foaming process it is possible to suppress a phenomenon in which the first-step expanded particles are fused to each other to form lumps (a phenomenon called blocking).
- the bulk ratio M1 of the first-stage expanded beads is less than 5 times, it may be difficult to sufficiently increase the closed cell ratio of the expanded beads obtained in the second-stage expansion step, or blocking may easily occur.
- the bulk ratio M1 of the single-stage expanded particles is preferably 8 times or more, more preferably 10 times or more, and even more preferably 12 times or more.
- the bulk ratio M1 of the single-stage expanded beads exceeds 25 times, the blackness of the finally obtained expanded bead molded product may be insufficient, and color unevenness may become more noticeable.
- the bulk magnification M1 of the single-stage expanded particles is preferably 20 times or less, more preferably 18 times or less.
- the bulk ratio M1 of the single-stage expanded beads is preferably 8 times or more and 20 times or less. It is preferably 10 times or more and 18 times or less.
- the bulk magnification ratio M 2 /M 1 is preferably 1.4 or more, more preferably 1.8 or more, and even more preferably 2.0 or more.
- M 2 /M 1 exceeds 3.0, it may become difficult to sufficiently increase the closed cell ratio of the obtained expanded beads in the two-step expansion process, or blocking may easily occur.
- the bulk magnification ratio M 2 /M 1 is preferably 2.8 or less, more preferably 2.5 or less.
- the bulk magnification ratio M 2 /M 1 is 1.4 or more and 2.8 or less. preferably 1.8 or more and 2.5 or less.
- the bulk ratio M1 of the single-stage expanded beads is a value obtained as follows. First, the bulk density [kg/m 3 ] of the single-stage expanded particles is measured by the method described later. Next, by dividing the density [kg/m 3 ] of the polypropylene resin constituting the foamed layer of the first-stage expanded particles by the bulk density [kg/m 3 ] of the first-stage expanded particles, the bulk ratio M of the first-stage expanded particles is obtained. 1 [times] is required.
- the bulk ratio M2 of the two-stage expanded particles is a value obtained as follows. First, the bulk density [kg/m 3 ] of the two-stage expanded particles is measured by the method described later.
- a two-stage foaming process that is, a two-stage foaming process
- a two-stage foaming process namely a one-stage foaming process and a two-stage foaming process
- the bulk density of the foamed particles obtained in each foaming process is adjusted within the predetermined range and relationship.
- two-stage expanded beads are manufactured.
- the two-stage expanded particles obtained by performing such two-stage expansion enable the production of a molded article having a high degree of blackness and less color unevenness. The reason for this is considered as follows.
- an expanded bead molded article produced using expanded polypropylene resin particles produced by the above direct expansion method tends to have a lower degree of blackness and more conspicuous color unevenness. This tendency was particularly remarkable when it was attempted to expand to a desired bulk ratio in a single expansion.
- One of the reasons for this is considered to be that while a large number of cells are formed during foaming, the cells near the surface of the expanded bead are strongly affected by cooling, resulting in an excessive increase in the number of cells near the surface.
- the bulk magnification M1 of the first-stage expanded particles in the process is reduced, and a two-stage expansion process is provided to increase the bulk ratio M 2 can be increased to a desired magnification within a range in which the relationship with the bulk magnification M1 is within a predetermined range.
- a two-stage expansion process is provided to increase the bulk ratio M 2 can be increased to a desired magnification within a range in which the relationship with the bulk magnification M1 is within a predetermined range.
- the bulk ratio M1 is made smaller in the first-stage expansion step, It is preferable to increase the bulk magnification ratio M 2 /M 1 in the foaming step.
- the single-stage expanded particles preferably have a bulk ratio M 1 of 5 times or more and 20 times or less and a bulk ratio ratio M 2 /M 1 of 1.4 or more and 3.0 or less. More preferably, the particles have a bulk ratio M 1 of 10 times or more and 18 times or less, and a bulk ratio M 2 /M 1 of 1.8 or more and 2.5 or less.
- the bulk ratio M2 of polypropylene resin expanded beads is 10 times or more and 75 times or less. More preferably 20 times or more and 75 times or less, more preferably more than 30 times and 75 times or less, and particularly preferably 35 times or more and 50 times or less.
- expanded particles with a high bulk ratio tend to have lower blackness and uneven color. According to the production method of the present disclosure, it is possible to suppress a decrease in blackness and occurrence of color unevenness even with expanded beads having a high bulk ratio, such as, for example, a bulk ratio exceeding 30 times.
- resin particles containing carbon black in the range of 0.1% by weight or more and 5% by weight or less are used as the black colorant. If the carbon black content is less than 0.1% by weight, the blackness of the expanded bead molded article may be insufficient, or the expanded bead molded article may have conspicuous color unevenness. From this point of view, the content of carbon black in the resin particles is preferably 0.5% by weight or more, more preferably 1.0% by weight or more, and preferably 2.0% by weight or more. More preferred. On the other hand, if the carbon black content exceeds 5% by weight, it may become difficult to mold the foamed particles at a low molding heating temperature. Also, the water cooling time may become longer.
- the content of carbon black in the resin particles is preferably 4.5% by weight or less, more preferably 4.0% by weight or less, and 3.5% by weight or less. More preferred. From the viewpoint of obtaining a molded article having a higher degree of blackness and less conspicuous color unevenness with higher productivity, the content of carbon black in the resin particles should be 0.5% by weight or more and 4.5% by weight or less. is preferred, more preferably 1.0% by weight or more and 4.0% by weight or less, and even more preferably 2.0% by weight or more and 3.5% by weight or less.
- carbon black for example, channel black, roller black, furnace black, thermal black, acetylene black, ketjen black, etc. can be used.
- Furnace black is preferable as the carbon black from the viewpoint of excellent balance between dispersibility in polypropylene resin and material cost.
- cylindrical resin particles having through-holes are used, and the expanded beads have through-holes. Therefore, even if the amount of carbon black is large in the range of 0.1% to 5% by weight, in-mold molding exhibits good moldability at a low molding heating temperature and shortens the molding cycle. can do.
- the reason why the moldability of the expanded beads is good is that the heating medium such as steam supplied in the molding process spreads to the inside of the expanded beads group through the through-holes, so that the entire expanded beads filled in the mold is sufficiently heated, and the secondary foamability and fusion bondability of the expanded beads are improved.
- the reason why the molding cycle is shortened is that the secondary foaming force can be moderately suppressed compared to the expanded beads having no through-holes, and the cooling time in the molding process can be shortened.
- Cooling in the molding process is performed, for example, by water cooling.
- expanded particles having through holes have been suitably used for producing molded articles that have high porosity due to the through holes and are excellent in sound absorption and lightness (for example, JP-A-2015-143046 Gazette).
- the expanded beads produced through the two-stage expansion process tend to have smaller through-holes than the expanded beads produced directly through the first-stage expansion process and have a similar apparent density. For this reason, the production of expanded beads having through-holes by a two-step expansion process has rarely been carried out.
- the circularity of the through holes is preferably 0.90 or more.
- the through-holes are less likely to be crushed in the two-step foaming process, so that the effect of improving the moldability of the expanded beads and the effect of shortening the water-cooling time during molding are more likely to be exhibited.
- the circularity of the through-holes is more preferably 0.92 or more, and even more preferably 0.95 or more.
- the circularity of the through-holes is determined, for example, by changing the shape of the die for forming the through-holes in the resin particle granulation process, or by changing the water temperature when cooling the strands, which is usually performed at a water temperature of about 25 ° C. By adjusting the temperature to a low temperature (for example, 15° C. or less), the temperature can be adjusted within the above range.
- the upper limit of circularity of the through-hole is one.
- the through-holes are formed during the two-stage expansion. It is preferable to set the circularity of the through-holes of the single-stage expanded particles within the above range because the particles are more likely to be crushed.
- the circularity of the through-holes of the single-stage expanded beads is measured and calculated as follows. 50 or more single-stage expanded beads randomly selected from a group of single-stage expanded beads are cut perpendicularly to the penetration direction of the through-hole at the position where the area of the cut surface is maximized. A photograph of the cut surface of each single-stage expanded bead is taken, and the cross-sectional area S (specifically, the opening area) and the peripheral length C (that is, the circumference of the opening) of the through-hole portion are obtained.
- ⁇ means the circumference ratio.
- the degree of circularity of the through-hole of each single-stage expanded bead is such that the area of the cut surface of the single-stage expanded bead is the maximum as described above. is determined by the circularity of the through hole at the position where
- the expanded bead 1 is cylindrical and has a through hole 11.
- the foamed bead 1 has a foamed layer 2 made of polypropylene resin.
- the foamed beads 1 may be composed of a polypropylene resin in a foamed state as shown in FIGS. 2 and 3, but are composed of a polypropylene resin in a foamed state as shown in FIGS. It is preferable to have a foam layer 2 and a covering layer 3 covering this.
- 1 to 5 are examples of forms of foamed beads, and the present invention is not limited to these drawings.
- both the foamed layer 2 and the coating layer 3 preferably contain carbon black, and the content thereof is 0 in each layer. It is preferably 1 wt% or more and 5 wt% or less, more preferably 0.5 wt% or more and 4.5 wt% or less, and 1.0 wt% or more and 4.0 wt% or less. More preferably, it is particularly preferably 2.0% by weight or more and 3.5% by weight or less. In this case, the color unevenness of the molded article can be made less conspicuous. From the same point of view, it is preferable that the foam layer 2 and the coating layer 3 have approximately the same carbon black content.
- the expanded bead 1 is cylindrical, rectangular, or the like, and preferably has at least one cylindrical hole (that is, through hole 11) penetrating in the axial direction. It is more preferable that the expanded bead 1 is cylindrical and has a cylindrical hole passing through in the axial direction.
- the average hole diameter d of the through-holes 11 of the expanded particles can be, for example, 5 mm or less, preferably 4 mm or less, more preferably 3 mm or less. Also, the ratio d/D of the average hole diameter d of the through-holes 11 to the average outer diameter D of the expanded beads 1 can be set to 1 or less, for example.
- the average pore diameter d of the through-holes 11 of the expanded beads is less than 1 mm, and the ratio d/D of the average pore diameter d to the average outer diameter D of the expanded beads is 0.4 or less.
- the average hole diameter d of the through holes is preferably 0.95 mm or less, more preferably 0.90 mm or less, and even more preferably 0.85 mm or less.
- the ratio d/D is preferably 0.35 or less, more preferably 0.3 or less, and even more preferably 0.25 or less.
- the average pore diameter d of the expanded beads is preferably 0.2 mm or more, more preferably 0.4 mm or more.
- the ratio d/D is preferably 0.05 or more.
- pretreatment pressurization may be performed to apply internal pressure in advance to the foamed particles before being filled in the molding die, or pretreatment pressurization may not be performed. It is possible to produce an expanded bead molded article having a high degree of blackness, less conspicuous color unevenness, a desired shape, excellent surface properties and rigidity, while omitting a curing step without performing pretreatment pressurization. can.
- the average pore diameter d of the through-holes of the expanded beads is less than 1 mm, and the ratio d/D of the average pore diameter d to the average outer diameter D of the expanded beads is 0.4 or less.
- the foamed particles do not have through-holes and the curing step is omitted, significant shrinkage and deformation of the molded article cannot be suppressed.
- the thickness of the cylindrical expanded beads is sufficiently ensured. The secondary foamability of the expanded particles is enhanced, and the molded article has excellent surface properties and rigidity.
- the average pore diameter d of the expanded beads can be adjusted by adjusting the pore diameter dr of through holes in the resin particles, which will be described later. In addition, it can be adjusted by adjusting the apparent density of the foamed particles or the amount of heat of fusion at the high temperature peak. Further, in the two-stage foaming step, the average pore diameter d can be more easily adjusted to a small value by adjusting the bulk magnification ratio M 2 /M 1 higher within the above range. Also, the average outer diameter D of the expanded beads can be adjusted by adjusting the average outer diameter Dr of the resin particles, which will be described later.
- the average pore diameter d of the through-holes of the expanded particles is obtained as follows. 50 or more foamed beads randomly selected from the group of foamed beads are cut perpendicularly to the penetration direction of the through-hole at the position where the area of the cut surface is maximized. A photograph of the cut surface of each foamed particle is taken, the cross-sectional area of the through-hole portion (specifically, the opening area) is determined, the diameter of a virtual perfect circle having the same area as that area is calculated, and the arithmetic mean is calculated. The obtained value is defined as the average pore diameter d of the through-holes of the foamed particles.
- the through-hole diameter of each expanded bead is the diameter at the position where the cross-sectional area of the expanded bead is maximized as described above. determined by
- the average outer diameter D of the expanded beads is preferably 2 mm or more, more preferably 2 mm or more, from the viewpoint that the thickness of the cylindrical expanded beads increases to improve the secondary foamability of the expanded beads and the rigidity of the molded article. 5 mm or more, more preferably 3 mm or more. On the other hand, it is preferably 5 mm or less, more preferably 4.5 mm or less, and even more preferably 4.3 mm or less, from the viewpoint of improving filling properties into the mold during molding.
- the average outer diameter D of the expanded beads is obtained as follows. 50 or more foamed beads randomly selected from the group of foamed beads are cut perpendicularly to the penetration direction of the through-hole at the position where the area of the cut surface is maximized. Take a picture of the cut surface of each foamed bead, find the cross-sectional area of the foamed bead (specifically, the cross-sectional area including the opening of the through hole), and calculate the diameter of an imaginary perfect circle having the same area as that area. and the average outer diameter D of the expanded beads is obtained by arithmetically averaging these values.
- the outer diameter of each expanded bead should be such that the area of the cut surface of the expanded bead in the direction perpendicular to the penetration direction is the maximum as described above. is determined by the outer diameter at the position where
- the average thickness t of the cylindrical foamed particles is preferably 1.2 mm or more and 2 mm or less. If the average value of the thickness t is within this range, the thickness of the expanded beads is sufficiently thick, so that the secondary foamability during in-mold molding is further improved. In addition, the foamed particles are less likely to be crushed by an external force, and the rigidity of the molded article is further improved. From this point of view, the average thickness t of the expanded beads is more preferably 1.3 mm or more and 2 mm or less, and still more preferably 1.5 mm or more and 2 mm or less.
- the ratio t/D of the average wall thickness t to the average outer diameter D of the expanded beads is preferably 0.35 or more and 0.5 or less.
- t/D is within the above range, the filling property of the expanded beads is good and the secondary foamability is further improved in the in-mold molding of the expanded beads. Therefore, a molded article having excellent surface properties and rigidity can be produced at a lower molding heating temperature.
- the foam layer is composed of polypropylene resin.
- a polypropylene-based resin refers to a homopolymer of a propylene monomer and a propylene-based copolymer containing 50% by mass or more of structural units derived from propylene.
- the polypropylene-based resin is preferably a propylene-based copolymer obtained by copolymerizing propylene and other monomers.
- Propylene-based copolymers include propylene and ⁇ -olefins having 4 to 10 carbon atoms, such as ethylene-propylene copolymers, butene-propylene copolymers, hexene-propylene copolymers, and ethylene-propylene-butene copolymers.
- a copolymer with is preferably exemplified. These copolymers are, for example, random copolymers, block copolymers, etc., and are preferably random copolymers.
- the polypropylene-based resin may contain a plurality of types of polypropylene-based resins.
- the polypropylene-based resin that constitutes the foam layer may contain a polymer other than the polypropylene-based resin within a range that does not impair the object and effect of the present disclosure.
- examples of other polymers include thermoplastic resins other than polypropylene-based resins, such as polyethylene-based resins and polystyrene-based resins, and elastomers.
- the content of the other polymer in the polypropylene-based resin constituting the foam layer is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. , 0, that is, it is particularly preferable that the foamed layer contains substantially only a polypropylene-based resin as a polymer.
- the polypropylene resin constituting the foam layer is an ethylene-propylene random copolymer, and the content of the ethylene component in the copolymer is 0.5% by mass or more and 5.0% by mass or less. is preferably The total amount of ethylene component and propylene component in the ethylene-propylene random copolymer is 100% by mass.
- the content of the ethylene component in the copolymer is The amount is more preferably 3.5% by mass or less, even more preferably 2.8% by mass or less, and particularly preferably 2.0% by mass or less. From the same point of view, the content of the ethylene component in the copolymer is preferably 0.5% by mass or more.
- the copolymer From the viewpoint of being able to mold a molded article having excellent surface properties and rigidity at a lower molding heating temperature (that is, a low molding pressure), and from the viewpoint of obtaining an expanded particle molded article having excellent energy absorption, the copolymer 2.
- the content of the ethylene component therein is more preferably 1.0% by mass or more, still more preferably 1.2% by mass or more, and even more preferably 1.5% by mass or more. More than 0% by weight is particularly preferred. From the same point of view, the content of the ethylene component in the copolymer is preferably 5.0% by mass or less.
- the content of the monomer component in the copolymer can be determined by IR spectrum measurement.
- the ethylene component and the propylene component of the ethylene-propylene copolymer mean the structural units derived from ethylene and the structural units derived from propylene in the ethylene-propylene copolymer, respectively.
- the content of each monomer component in the copolymer means the content of structural units derived from each monomer in the copolymer.
- the melting point Tmc of the polypropylene-based resin forming the foam layer is preferably 158°C or less.
- a molded article having excellent surface properties and rigidity can be molded at a lower molding heating temperature (that is, a lower molding pressure).
- the melting point Tmc of the polypropylene-based resin forming the foam layer is preferably 155° C. or lower, more preferably 150° C. or lower.
- the melting point Tmc of the polypropylene resin constituting the foam layer is preferably 135° C. or higher, more preferably 138° C. or higher.
- the temperature is 140° C. or higher.
- the melting point Tmc of the polypropylene-based resin constituting the foamed layer is preferably 135° C. or higher and 158° C. or lower. It is more preferably 138° C. or higher and 155° C. or lower, and even more preferably 140° C. or higher and 150° C. or lower.
- the melting point of polypropylene-based resin is determined based on JIS K7121:1987. Specifically, as the conditioning, "(2) When measuring the melting temperature after performing a constant heat treatment" is adopted, and the conditioned test piece is heated from 30 ° C. at a heating rate of 10 ° C./min. A DSC curve is obtained by raising the temperature to 200° C., and the apex temperature of the melting peak is taken as the melting point. When a plurality of melting peaks appear in the DSC curve, the apex temperature of the melting peak with the largest area is taken as the melting point.
- the melt mass flow rate (that is, MFR) of the polypropylene-based resin constituting the foam layer is preferably 5 g/10 minutes or more, more preferably 6 g/10 minutes or more. Preferably, it is more preferably 7 g/10 minutes or more.
- the MFR is preferably 12 g/10 minutes or less, more preferably 10 g/10 minutes or less, from the viewpoint of further increasing the rigidity of the molded article.
- the MFR of a polypropylene resin is a value measured under conditions of a test temperature of 230°C and a load of 2.16 kg based on JIS K7210-1:2014.
- the bending elastic modulus of the polypropylene-based resin forming the foam layer is preferably 800 MPa or more and 1600 MPa or less.
- the flexural modulus of the polypropylene-based resin constituting the foam layer should be 850 MPa or more and 1600 MPa or less.
- the flexural modulus of the constituting polypropylene-based resin is preferably 800 MPa or more and 1550 MPa or less, more preferably 800 MPa or more and 1500 MPa or less, and even more preferably 800 MPa or more and less than 1200 MPa.
- the flexural modulus of polypropylene resin can be determined according to JIS K7171:2008.
- the closed cell ratio of the expanded beads should be 88% or more from the viewpoint of ensuring good in-mold moldability of the expanded beads and from the viewpoint of obtaining good surface properties and rigidity of the obtained expanded beads molded product. is preferred, 90% or more is preferred, and 95% or more is more preferred.
- the closed cell content of the expanded beads can be measured using an air comparison hydrometer based on ASTM-D2856-70 Procedure C. Specifically, it is measured as follows. The foamed particles having a bulk volume of about 20 cm 3 after conditioning were used as a measurement sample, and the apparent volume Va was accurately measured by the ethanol soaking method as described below. After sufficiently drying the measurement sample whose apparent volume Va was measured, according to the procedure C described in ASTM-D2856-70, the true volume of the measurement sample measured by Accupic II 1340 manufactured by Shimadzu Corporation Measure the value of Vx.
- Vx The true volume of the expanded bead measured by the above method, that is, the sum of the volume of the resin constituting the expanded bead and the total volume of the closed cells in the expanded bead (unit: cm 3 )
- Va Apparent volume of expanded beads measured from the increase in water level when the expanded beads are submerged in a graduated cylinder containing ethanol (unit: cm 3 )
- W Weight of sample for measurement of foamed particles (unit: g)
- ⁇ Density of resin constituting expanded beads (unit: g/cm 3 )
- the foamed beads are preferably foamed beads with a multilayer structure having a foam layer and a coating layer covering the foam layer.
- the coating layer is made of, for example, a polyolefin resin.
- Polyolefin-based resins include, for example, polyethylene-based resins, polypropylene-based resins, polybutene-based resins, and the like.
- the polyethylene-based resin refers to homopolymers of ethylene monomers and ethylene-based copolymers containing more than 50% by mass of structural units derived from ethylene.
- the polyolefin resin is preferably a polyethylene resin or a polypropylene resin, more preferably a polypropylene resin.
- polypropylene-based resins include ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-propylene-butene copolymers, and propylene homopolymers. Among them, ethylene-propylene copolymers or ethylene-propylene- Butene copolymers are preferred.
- the melting point Tms of the polyolefin resin forming the coating layer is preferably lower than the melting point Tmc of the polypropylene resin forming the foam layer. That is, it is preferable that Tms ⁇ Tmc. In this case, the meltability of the foamed particles is improved, and molding at a lower temperature becomes possible. Furthermore, in this case, it becomes easier to suppress significant shrinkage/deformation when the curing step is omitted. The reason for this is not clear, but by molding at a low molding heating temperature, the amount of heat received by the foamed particles from a heating medium such as steam during molding in the mold can be suppressed to a lower level, and the dimensional change due to thermal shrinkage of the molded product can be reduced.
- Tmc-Tms ⁇ 5 is preferable, Tmc-Tms ⁇ 6 is more preferable, and Tmc-Tms ⁇ 8. It is even more preferable to have From the viewpoint of suppressing peeling between the foam layer and the coating layer and mutual adhesion between foam particles, Tmc ⁇ Tms ⁇ 35 is preferable, Tmc ⁇ Tms ⁇ 20 is more preferable, and Tmc ⁇ Tms It is more preferred that ⁇ 15.
- the melting point Tms of the polyolefin resin constituting the coating layer is preferably 120° C. or higher and 145° C. or lower, and more preferably 125° C. or higher and 140° C. or lower. is more preferred.
- the melting point of the polyolefin resin that constitutes the coating layer is obtained based on JIS K7121:1987. Specifically, it is determined by the same conditions and method as those for the polypropylene-based resin that constitutes the foamed layer. However, when a plurality of melting peaks appear in the DSC curve, the apex temperature of the lowest melting peak is taken as the melting point.
- the MFR of the polyolefin resin that constitutes the coating layer is preferably about the same as the MFR of the polypropylene resin that constitutes the foam layer. is preferably 2 to 15 g/10 minutes, more preferably 3 to 12 g/10 minutes, and even more preferably 4 to 10 g/10 minutes.
- the polyolefin resin is a polypropylene resin
- its MFR is a value measured under conditions of a test temperature of 230°C and a load of 2.16 kg based on JIS K7210-1:2014.
- When is a polyethylene resin its MFR is a value measured under conditions of a test temperature of 190°C and a load of 2.16 kg based on JIS K7210-1:2014.
- the foamed layer is composed of a foamed polypropylene resin, and the coating layer may be in a foamed state or non-foamed state. It is made of foamed polyolefin resin.
- the covering layer is substantially non-foamed.
- substantially non-foamed includes a state in which cells disappear after foaming, and means that there is almost no cell structure.
- the thickness of the coating layer is, for example, 0.5 to 100 ⁇ m. Further, an intermediate layer may be further provided between the foam layer and the covering layer.
- the mass ratio (mass% ratio) of the resin that makes up the foam layer and the resin that makes up the coating layer is determined from the viewpoint of improving moldability while maintaining the rigidity of the molded product, and preventing significant shrinkage and shrinkage when the curing step is omitted. From the viewpoint of more easily suppressing deformation, the ratio is preferably 99.5:0.5 to 80:20, more preferably 99:1 to 85:15, still more preferably 97:3 to 90:10.
- the mass ratio is represented by the ratio of the resin forming the foam layer to the resin forming the coating layer.
- the foamed beads have a melting peak (that is, a unique peak) specific to the polypropylene resin and one or more on the high temperature side in the DSC curve obtained when heated from 23 ° C. to 200 ° C. at a heating rate of 10 ° C./min. It is preferable to have a crystal structure that exhibits a melting peak (that is, a high temperature peak).
- a DSC curve is obtained by differential scanning calorimetry (DSC) according to JIS K7121:1987 using 1 to 3 mg of foamed particles as a test sample.
- the peculiar peak is an endothermic peak peculiar to the polypropylene-based resin constituting the expanded beads, and is considered to be due to the endothermic peak at the time of melting of the crystals originally possessed by the polypropylene-based resin.
- the high temperature peak is an endothermic peak appearing on the high temperature side of the characteristic peak in the DSC curve. When this high temperature peak appears, it is presumed that secondary crystals are present in the resin.
- the temperature is cooled from 200 ° C. to 23 ° C. at a cooling rate of 10 ° C./min.
- the amount of heat of fusion at the high-temperature peak of the expanded beads is preferably 5 to 40 J/g, more preferably 7 to 30 J/g, from the viewpoints of further improving the moldability of the expanded beads and obtaining a molded article having excellent rigidity. More preferably 10 to 20 J/g.
- the ratio of the heat of fusion of the high-temperature peak to the heat of fusion of all the melting peaks of the DSC curve is preferably 0.05 to 0.3, more preferably 0.1 to 0.25, more preferably 0.15 to 0.2.
- the amount of heat of fusion of all melting peaks means the total amount of heat of fusion determined from the areas of all the melting peaks of the DSC curve.
- the amount of heat of fusion at each peak of the DSC curve of the expanded beads is a value obtained as follows. First, one expanded bead is sampled from the expanded bead group after condition adjustment.
- a DSC curve is obtained when the test piece is heated from 23° C. to 200° C. at a heating rate of 10° C./min with a differential thermal scanning calorimeter.
- An example of a DSC curve is shown in FIG. As exemplified in FIG. 7, the DSC curve has a unique peak ⁇ H1 and a high temperature peak ⁇ H2 having an apex on the high temperature side of the apex of the unique peak ⁇ H1.
- a straight line L1 is obtained by connecting the point ⁇ on the DSC curve at a temperature of 80° C. and the point ⁇ at the melting end temperature T of the expanded beads.
- a straight line L2 parallel to the vertical axis of the graph is drawn from the point ⁇ on the DSC curve corresponding to the valley between the above-mentioned characteristic peak ⁇ H1 and the high-temperature peak ⁇ H2, and the intersection of the straight lines L1 and L2 is ⁇ . do.
- the point ⁇ can also be said to be a maximum point existing between the characteristic peak ⁇ H1 and the high-temperature peak ⁇ H2.
- the area of the peculiar peak ⁇ H1 is the area of the portion surrounded by the curve of the peculiar peak ⁇ H1 portion of the DSC curve, the line segment ⁇ - ⁇ , and the line segment ⁇ - ⁇ , and this is defined as the heat of fusion of the peculiar peak.
- the area of the high temperature peak ⁇ H2 is the area of the portion surrounded by the curve of the high temperature peak ⁇ H2 portion of the DSC curve, the line segment ⁇ - ⁇ , and the line segment ⁇ - ⁇ , and this is the heat of fusion of the high temperature peak.
- the area of the total melting peak is the area of the portion surrounded by the curve of the characteristic peak ⁇ H1 portion of the DSC curve, the curve of the high temperature peak ⁇ H2 portion, and the line segment ⁇ - ⁇ (that is, the straight line L1). This is the heat of fusion at the peak.
- the apparent density of the expanded particles is preferably 10 kg/m 3 or more and 150 kg/m 3 or less, more preferably 15 kg/m 3 or more and 100 kg/m 3 or less. , more preferably 20 kg/m 3 or more and 80 kg/m 3 or less, and particularly preferably 25 kg/m 3 or more and 45 kg/m 3 or less.
- the apparent density of the expanded particles is determined by leaving the expanded particles in a graduated cylinder filled with alcohol (e.g., ethanol) at 23°C under the conditions of 50% relative humidity, 23°C, and 1 atm for one day (the weight of the expanded particles W (g)) is submerged using a wire mesh or the like, the volume V (L) of the expanded bead group is obtained from the rise in the water level, and the weight of the expanded bead group is divided by the volume of the expanded bead group (W/V), It can be obtained by converting the unit to [kg/m 3 ].
- alcohol e.g., ethanol
- the apparent density ratio of the particles is preferably 1.7 or greater.
- the apparent density/bulk density is preferably 1.7 or more and 2.3 or less, more preferably 1.7 or more and 2.5. 1 or less, more preferably 1.7 or more and 1.9 or less.
- the bulk density of expanded particles is determined as follows. Expanded particles are randomly taken out from the group of expanded particles and placed in a graduated cylinder with a volume of 1 L. A large number of expanded particles are accommodated up to the scale of 1 L so as to be in a state of natural accumulation, and the mass of the accommodated expanded particles is W2 [g]. is divided by the storage volume V2 (1 L) (W2/V2), and the unit is converted to [kg/m 3 ] to obtain the bulk density of the expanded particles.
- the polypropylene-based resin particles are appropriately referred to as "resin particles".
- resin particles having a multilayer structure having a core layer and a coating layer covering the core layer (hereinafter, appropriately referred to as multilayer resin particles) ) is used.
- resin particles are manufactured as follows. First, a polypropylene resin as a base resin, carbon black, and additives such as cell nucleating agents, which are supplied as necessary, are fed into an extruder, heated and kneaded to obtain a resin melt-kneaded product. Carbon black is added so that the content of carbon black in the resin particles is 0.1% by weight or more and 5% by weight or less. Thereafter, the resin particles are obtained by extruding the resin melt-kneaded material into a cylindrical strand having through holes through a small hole of a die attached to the tip of the extruder, cooling it, and cutting it. The extrudate is cut, for example with a pelletizer.
- a cutting method can be selected from a strand cutting method, a hot cutting method, an underwater cutting method, and the like. In this manner, cylindrical resin particles having through holes can be obtained.
- a core layer forming extruder and a coating layer forming extruder are used to obtain a resin melt-kneaded product of each raw material, and the melt-kneaded products are combined in a die and mixed.
- a shell-and-core type composite composed of a non-foamed cylindrical core layer and a non-foamed coating layer covering the outer surface of the cylindrical core layer is formed, and attached to the tip of the extruder.
- Multilayered resin particles can be obtained by cooling and cutting the composite while extruding it in the form of a strand through the pores of the spinneret.
- the particle diameter Lr (in other words, maximum length) of the resin particles is preferably 0.1 to 3.0 mm, more preferably 0.3 to 1.5 mm.
- the ratio (Lr/Dr) of the maximum length Lr to the outer diameter Dr of the resin particles is preferably 0.5 to 5.0, more preferably 1.0 to 3.0.
- the average mass per particle is preferably adjusted to 0.1 to 20 mg, more preferably 0.2 to 10 mg, More preferably 0.3 to 5 mg, particularly preferably 0.4 to 2 mg.
- the mass ratio of the core layer to the coating layer in the case of multilayer resin particles is preferably from 99.5:0.5 to 80:20, more preferably from 99:1 to 85:15, still more preferably from 97:3 to It is 90:10.
- the mass ratio is represented by core layer:coating layer.
- the average hole diameter d of the through-holes in the expanded beads can be adjusted within the desired range.
- the hole diameter dr of the through holes in the core layer of the resin particles can be adjusted, for example, by adjusting the hole diameter of the small holes of the die for forming the through holes (that is, the inner diameter of the die). Further, by adjusting the hole diameter dr of the through-holes of the resin particles, the particle diameter, and the average mass, the average outer diameter and average thickness of the expanded particles can be adjusted within the above desired range.
- the through-holes of the resin particles are improved.
- the average pore diameter dr is preferably less than 0.25 mm, more preferably less than 0.24 mm, even more preferably 0.22 mm or less.
- the average hole diameter dr of the through holes of the resin particles is preferably 0.1 mm or more.
- the ratio dr/Dr of the average pore diameter dr to the average outer diameter Dr of the resin particles is preferably 0.4 or less, more preferably 0.3 or less, and 0.25 or less. It is more preferably 0.2 or less, particularly preferably 0.2 or less. From the viewpoint of production stability of resin particles having through holes, the ratio dr/Dr of the average pore diameter dr to the average outer diameter Dr of the resin particles is preferably 0.1 or more.
- the average pore diameter dr of the through-holes of the resin particles is obtained as follows. 50 or more resin particles randomly selected from the resin particle group are cut perpendicularly to the penetrating direction of the through hole at the position where the area of the cut surface is maximized. A photograph of the cut surface of each resin particle is taken, the cross-sectional area of the through-hole portion (specifically, the opening area) is determined, the diameter of a virtual perfect circle having the same area as that area is calculated, and the arithmetic mean is calculated. The obtained value is taken as the average pore diameter dr of the through holes of the resin particles. Even when the size of the through-hole of each resin particle is not uniform in the direction of penetration, the diameter of the through-hole of each resin particle is maximized by the area of the cross section of the resin particle as described above. Defined by the pore size at the location.
- the average outer diameter Dr of the resin particles is obtained as follows. 50 or more resin particles randomly selected from the resin particle group are cut perpendicularly to the penetrating direction of the through hole at the position where the area of the cut surface is maximized. Take a photograph of the cross section of each resin particle, determine the cross-sectional area of the resin particle (specifically, the cross-sectional area including the opening of the through hole), and calculate the diameter of a virtual perfect circle having the same area as that area. The arithmetic mean value of these is taken as the average outer diameter Dr of the resin particles.
- the outer diameter of each resin particle is such that the area of the cross section of the resin particle in the direction perpendicular to the penetration direction is the maximum as described above. is determined by the outer diameter at the position where
- the particle diameter, length/outer diameter ratio and average mass of the resin particles are adjusted by appropriately changing the extrusion speed, take-up speed, cutter speed, etc. when extruding the resin melt-kneaded product. It can be done by
- An aqueous dispersion medium is used as a dispersion medium (specifically, a liquid) for dispersing the resin particles obtained as described above in a closed container.
- the aqueous dispersion medium is a dispersion medium (specifically liquid) containing water as a main component.
- the proportion of water in the aqueous dispersion medium is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.
- Examples of the dispersion medium other than water in the aqueous dispersion medium include ethylene glycol, glycerin, methanol, and ethanol.
- the core layer of the resin particles may contain a cell control agent, a crystal nucleating agent, a coloring agent, a flame retardant, a flame retardant aid, a plasticizer, an antistatic agent, an antioxidant, an ultraviolet inhibitor, and a light stabilizer.
- a cell control agent such as talc, mica, zinc borate, calcium carbonate, silica, titanium oxide, gypsum, zeolite, borax, aluminum hydroxide, carbon, etc.; , an amine-based nucleating agent, and an organic powder such as a polyfluoroethylene-based resin powder.
- the content of the cell control agent is preferably 0.01 to 1 part by mass with respect to 100 parts by mass of the polypropylene resin.
- dispersant When dispersing the resin particles in the dispersion medium, it is preferable to add a dispersant to the dispersion medium so that the resin particles heated in the container do not fuse with each other.
- a dispersant any agent that prevents fusion of the resin particles in the container can be used, and it can be used regardless of whether it is organic or inorganic. However, fine inorganic particles are preferable because of ease of handling.
- examples of dispersants include clay minerals such as amsnite, kaolin, mica and clay. Clay minerals may be natural or synthetic. Dispersants include aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide and the like. One or two or more dispersants are used. Among these, it is preferable to use a clay mineral as a dispersant. It is preferable to add about 0.001 to 5 parts by mass of the dispersant per 100 parts by mass of the resin particles.
- an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylbenzenesulfonate, sodium laurylsulfate, and sodium oleate together as a dispersing aid.
- the amount of the dispersing aid added is preferably 0.001 to 1 part by mass per 100 parts by mass of the resin particles.
- the resin particles in the dispersion medium are impregnated with the inorganic physical foaming agent in a closed vessel.
- the resin particles are discharged from the closed container under a lower pressure than inside the closed container.
- single-stage expanded particles having a bulk ratio M of 1 are obtained.
- Examples of inorganic physical foaming agents for foaming resin particles include carbon dioxide, air, nitrogen, helium, and argon. Carbon dioxide is preferably used from the viewpoint of environmental load and handling.
- the amount of foaming agent added to 100 parts by mass of resin particles is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 15 parts by mass.
- a method for impregnating the resin particles with the blowing agent includes dispersing the resin particles in an aqueous dispersion medium in a closed vessel, and pressurizing the blowing agent into the resin particles while heating.
- a method of impregnation is preferably used.
- the internal pressure of the closed container during foaming is preferably 0.5 MPa (G: gauge pressure) or more.
- the internal pressure of the closed container is preferably 4.0 MPa (G) or less.
- the temperature during foaming can be kept within an appropriate range.
- a one-stage holding step is performed in which the temperature is maintained at (the melting point of the polypropylene resin ⁇ 20° C.) or higher and below the (melting end temperature of the polypropylene resin) for a sufficient time, preferably about 10 to 60 minutes. . After that, the temperature is adjusted from (melting point of polypropylene resin ⁇ 15° C.) to below (melting end temperature of polypropylene resin +10° C.). Then, if necessary, a two-stage holding step is performed in which the temperature is maintained for a sufficient time, preferably about 10 to 60 minutes.
- Foaming is preferably carried out in a sealed container at (melting point of polypropylene resin ⁇ 10° C.) or higher, more preferably at (melting point of polypropylene resin) or higher (melting point of polypropylene resin +20° C.) or lower. .
- the resin particles are released from the closed container into a low-pressure atmosphere (usually under atmospheric pressure)
- the resin particles are cooled by being exposed to the open air while forming a cell structure.
- the cell structure is stabilized, and single-stage expanded particles are obtained.
- the temperature of the atmosphere in which the resin particles are emitted is preferably less than 80°C.
- the obtained single-stage expanded particles can be dried by standing still for 12 hours or more in an atmosphere of 23° C. and 50%, for example.
- the temperature Tu of the atmosphere in which the resin particles are released is preferably 40° C. or higher, more preferably 60° C. or higher.
- the melting point Tmc of the polypropylene resin constituting the resin particles and the temperature of the atmosphere in which the resin particles are released is preferably 65° C. or more and 85° C. or less.
- the first-step expanded beads are heated by applying internal pressure to the first-step expanded beads.
- the single-stage expanded beads are further expanded to obtain polypropylene-based resin expanded beads having a bulk ratio M of 2 (that is, double-stage expanded beads).
- the two-step foaming process is performed, for example, as follows. First, the single-stage expanded particles are placed in a pressure container. An internal pressure is applied to the first-stage expanded beads in a pressure vessel to raise the pressure inside the cells of the first-stage expanded beads to the atmospheric pressure or higher. Next, the first-stage expanded beads are taken out from the pressure vessel and further expanded by heating the first-stage expanded beads under a pressure lower than the pressure inside the cells of the first-step expanded beads.
- two-stage expanded beads are obtained.
- Examples of the method for applying internal pressure to the single-stage expanded particles include impregnation with an inorganic gas. Air, carbon dioxide, or the like is used as the inorganic gas. A heating medium such as steam or heated air is used for heating.
- the internal pressure applied to the first-step expanded beads is preferably atmospheric pressure or higher, and is preferably 0.1 MPa (G) or higher, from the viewpoint of easily obtaining the two-step expanded beads having a predetermined bulk ratio M2 . is preferred, 0.2 MPa (G) or more is more preferred, and 0.3 MPa (G) or more is even more preferred.
- the upper limit of the internal pressure applied to the single-stage expanded beads is approximately 1 MPa (G).
- the heating time of the first-stage expanded particles is from 3 seconds to 60 seconds, from the viewpoint of suppressing blocking between the first-stage expanded particles and easily obtaining the two-stage expanded particles having a predetermined bulk ratio M2 .
- a molded body can be obtained by in-mold molding the expanded beads (two-stage expanded beads) obtained as described above (that is, in-mold molding method).
- the in-mold molding method is carried out by filling a mold with expanded particles and heating and molding using a heating medium such as steam. Specifically, after the foamed particles are filled in the mold, a heating medium such as steam is introduced into the mold to heat the foamed particles for secondary foaming, and the foamed particles are mutually fused and molded.
- a molded body in which the shape of the space is shaped can be obtained.
- the method for producing expanded beads according to the present disclosure may include at least a one-step expansion step and a two-step expansion step as expansion steps, and a three-step or more expansion step is performed in order to obtain expanded beads with a high bulk ratio.
- the porosity of the molded body is preferably 4% or more, more preferably 4.5% or more, and more preferably 5%. It is more preferable that it is above. On the other hand, from the viewpoint of further improving rigidity and surface properties, the porosity of the molded body is preferably 15% or less, more preferably 12% or less.
- the density of the compact is preferably 10 kg/m 3 or more and 100 kg/m 3 or less. In this case, it is possible to improve the lightness and rigidity of the molded body in a well-balanced manner. From the viewpoint of further improving the rigidity of the molded article, the density of the molded article is more preferably 20 kg/m 3 or more, further preferably 25 kg/m 3 or more. From the viewpoint of further improving the lightness of the molded article, the density of the molded article is more preferably 80 kg/m 3 or less, and even more preferably 50 kg/m 3 or less.
- the density of the molded body is calculated by dividing the weight (g) of the molded body by the volume (L) obtained from the outer dimensions of the molded body and converting the result into units. For example, when the molded body has at least a partially complicated shape and it is difficult to determine the volume from the external dimensions of the molded body, the volume of the molded body can be determined by the submersion method.
- Molded bodies are also used as sound absorbing materials, shock absorbing materials, cushioning materials, etc. in various fields such as the field of vehicles such as automobiles and the field of construction.
- the following physical properties were measured and evaluated for the resins, expanded particles, and molded bodies used in Examples and Comparative Examples.
- the measurement and evaluation of the physical properties of the expanded beads were carried out after the expanded beads were allowed to stand for 24 hours under the conditions of 50% relative humidity, 23° C., and 1 atm.
- the physical properties of the molded body are measured and evaluated using the molded body that has been conditioned by allowing the molded body after the curing process to stand for 24 hours under the conditions of 50% relative humidity, 23 ° C., and 1 atm. gone.
- Table 1 shows the properties and the like of the polypropylene-based resin used for producing the expanded beads.
- Both the ethylene-propylene copolymer and the ethylene-propylene-butene copolymer used in this example are random copolymers. These copolymers are polypropylene resins containing a propylene component as a main component. The densities of the polypropylene resins of PP1 and PP2 are 900 kg/m 3 .
- the melting point of the polypropylene resin was obtained based on JIS K7121:1987. Specifically, "(2) When measuring the melting temperature after performing a constant heat treatment" is adopted as the condition adjustment, and the condition-adjusted test piece is heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. A DSC curve was obtained by heating up to °C, and the apex temperature of the melting peak was defined as the melting point. A heat flux differential scanning calorimeter (manufactured by SII Nanotechnology Co., Ltd., model number: DSC7020) was used as the measurement device.
- melt flow rate of polypropylene resin The melt flow rate (that is, MFR) of the polypropylene resin was measured according to JIS K7210-1:2014 under the conditions of a temperature of 230° C. and a load of 2.16 kg.
- Tables 2 and 3 show the properties of the multilayered resin particles and foamed particles.
- carbon black is described as "CB" in the table.
- the maximum length of the multilayer resin particles was determined as follows. The maximum length of 100 multilayer resin particles randomly selected from the multilayer resin particle group was measured with a vernier caliper, and the value obtained by arithmetically averaging these values was taken as the maximum length of the multilayer resin particles.
- the average pore diameter of the through-holes of the multilayer resin particles was determined as follows. 100 multilayer resin particles randomly selected from the multilayer resin particle group were cut perpendicularly to the penetrating direction of the through-hole at a position where the area of the cut surface was approximately maximum. A photograph of the cut surface of each multilayer resin particle was taken, and the cross-sectional area (opening area) of the through-hole portion in the cross-sectional photograph was determined. The diameter of a virtual perfect circle having the same area as the cross-sectional area was calculated, and the value obtained by arithmetically averaging these values was taken as the average pore diameter (dr) of the through-holes of the multilayer resin particles.
- the average outer diameter of the multilayer resin particles was determined as follows. 100 multilayer resin particles randomly selected from the multilayer resin particle group were cut perpendicularly to the penetrating direction of the through-hole at a position where the area of the cut surface was approximately maximum. A photograph of the cut surface of each multilayer resin particle was taken, and the cross-sectional area (including the opening of the through-hole) of the multilayer resin particle was obtained. The diameter of a virtual perfect circle having the same area as the cross-sectional area was calculated, and the value obtained by arithmetically averaging these values was taken as the average outer diameter (Dr) of the multilayer resin particles.
- the average pore size of the through-holes of the expanded beads was determined as follows. 100 expanded beads randomly selected from the group of expanded beads after conditioning were cut perpendicularly to the penetration direction of the through-hole at the position where the area of the cut surface was approximately maximum. A photograph of the cut surface of each expanded bead was taken, and the cross-sectional area (opening area) of the through-hole portion in the cross-sectional photograph was determined. The diameter of an imaginary perfect circle having the same area as the cross-sectional area was calculated, and the value obtained by arithmetically averaging these values was taken as the average pore diameter (d) of the through-holes of the expanded beads.
- the average outer diameter of the expanded beads was determined as follows. 100 expanded beads randomly selected from the group of expanded beads after conditioning were cut perpendicularly to the penetration direction of the through-hole at the position where the area of the cut surface was approximately maximum. A photograph of the cut surface of each expanded bead was taken to determine the cross-sectional area of the expanded bead (including the opening of the through-hole). The diameter of an imaginary perfect circle having the same area as the cross-sectional area was calculated, and the value obtained by arithmetically averaging these values was taken as the average outer diameter (D) of the expanded beads.
- Average wall thickness t (average outer diameter D - average pore diameter d) / 2 (IV)
- the bulk density of the expanded beads was determined as follows. Expanded particles are randomly taken out from the group of expanded particles after conditioning, placed in a graduated cylinder with a capacity of 1 L, and a large number of expanded particles are accommodated up to the 1 L scale so as to be in a state of natural accumulation. The bulk density of the expanded beads was obtained by dividing W2 [g] by the storage volume V2 (1 [L]) (W2/V2) and converting the unit into [kg/m 3 ].
- the bulk ratio M1 of the single-stage expanded particles was measured and calculated as follows. First, using the single-stage expanded beads after condition adjustment, the bulk density of the single-stage expanded beads was calculated by the above method. Next, by dividing the density [kg/m 3 ] of the polypropylene resin constituting the foamed layer of the first-stage expanded particles by the bulk density [kg/m 3 ] of the first-stage expanded particles, the bulk ratio M of the first-stage expanded particles is obtained. 1 [times] was obtained. The bulk ratio M2 of the two-stage expanded particles was also measured and calculated in the same manner as described above, except that the two-stage expanded particles were used instead of the one-stage expanded particles.
- the apparent density of the expanded beads was determined as follows. First, a graduated cylinder containing ethanol at a temperature of 23°C was prepared, and an arbitrary amount of expanded particles (mass of expanded particles W1 [g]) after conditioning was placed in the ethanol in the graduated cylinder using a wire mesh. and sank. Then, considering the volume of the wire mesh, the volume V1 [L] of the foamed particles read from the water level rise was measured. The apparent density of the expanded particles was obtained by dividing the mass W1 [g] of the group of expanded particles placed in the graduated cylinder by the volume V1 [L] (W1/V1) and converting the unit to [kg/m 3 ]. asked.
- the closed cell content of the foamed beads was measured according to ASTM-D2856-70 procedure C using an air-comparative hydrometer. Specifically, it was obtained as follows. The foamed particles having a bulk volume of about 20 cm 3 after conditioning were used as a measurement sample, and the apparent volume Va was accurately measured by the ethanol soaking method as described below. After sufficiently drying the measurement sample whose apparent volume Va was measured, according to the procedure C described in ASTM-D2856-70, the true volume of the measurement sample measured by Accupic II 1340 manufactured by Shimadzu Corporation was measured.
- Vx The true volume of the expanded bead measured by the above method, that is, the sum of the volume of the resin constituting the expanded bead and the total volume of the closed cells in the expanded bead (unit: cm 3 )
- Va Apparent volume of expanded beads measured from the increase in water level when the expanded beads are submerged in a graduated cylinder containing ethanol (unit: cm 3 )
- W Weight of sample for measurement of foamed particles (unit: g)
- ⁇ Density of resin constituting expanded beads (unit: g/cm 3 )
- the fusion bondability and recoverability (specifically, recoverability of expansion or shrinkage after in-mold molding) of the molded body were evaluated.
- the steam pressure that passed all the items in the evaluation criteria described later that is, the steam pressure at which a passing product could be obtained
- the molded body is molded in the same manner except that the curing step of leaving the molded body to stand for 12 hours in a high-temperature atmosphere adjusted to a temperature of 80 ° C. is not performed.
- a molded article was produced and evaluated for fusion bondability and recoverability. As a result, if a passing product was obtained at any molding steam pressure, it was evaluated as " ⁇ ", and if a passing product could not be obtained at any molding steam pressure, it was evaluated as " ⁇ ". bottom.
- the molded body is bent and broken, and the number C1 of expanded particles present on the fracture surface and the number C2 of broken expanded particles are determined, and the ratio of the number of broken expanded particles to the number of expanded particles present on the broken surface ( That is, the material destruction rate) was calculated.
- the material destruction rate is calculated from the formula C2/C1 ⁇ 100. The above measurement was performed 5 times using different test pieces, and the material destruction rate was determined for each. When the arithmetic mean value of the material destruction rate was 90% or more, it was judged as acceptable.
- Tables 4 and 5 show the properties of the molded bodies of Examples and Comparative Examples.
- Pretreatment pressurization step Pretreatment pressurization was carried out by placing the expanded beads in a sealed container, pressurizing the expanded beads with compressed air, and applying an internal pressure of 0.1 MPa (G) to the expanded beads.
- M is the molecular weight of air
- R is the gas constant
- T is the absolute temperature
- V is the volume (L) obtained by subtracting the volume of the base resin occupying the expanded bead group from the apparent volume of the expanded bead group.
- M 28.8 (g/mol)
- R 0.0083 (MPa ⁇ L/(K ⁇ mol))
- T 296 (K).
- the molded body density (kg/m 3 ) was calculated by dividing the weight (g) of the molded body by the volume (L) determined from the outer dimensions of the molded body and converting the unit.
- a test piece of 50 mm long ⁇ 50 mm wide ⁇ 25 mm thick was cut out from the central part of the molded body so that the skin layer on the surface of the molded body was not included in the test piece. Based on JIS K6767:1999, a compression test was performed at a compression rate of 10 mm/min to determine the 50% compressive stress of the compact.
- the surface of the molded article was observed, and the surface property was evaluated based on the following criteria.
- the color depth of the molded article was evaluated from the L* value of the molded article according to the following criteria.
- the L* value is an index of brightness, and the lower the value, the higher the degree of blackness and the darker the black.
- Color unevenness Visually, the surface of the molded body has no color unevenness and exhibits a uniform black color (5 points). Color unevenness was evaluated, and based on the average value of the evaluations by 5 viewers, the color unevenness of the expanded bead molded article was evaluated according to the following criteria. A: 4 points or more B: 3 points or more and less than 4 points C: Less than 3 points
- Example 1 ⁇ Production of expanded polypropylene particles> PP1 and carbon black shown in Table 1 were melt-kneaded in a core layer-forming extruder at a maximum set temperature of 245° C. to obtain a resin melt-kneaded product. Further, PP3 and carbon black shown in Table 1 were melt-kneaded in an extruder for coating layer formation at a maximum set temperature of 245° C. to obtain a resin melt-kneaded product. Then, each resin melt-kneaded product was extruded from the extruder for forming the core layer and the extruder for forming the coating layer from the tip of a coextrusion die provided with a small hole for forming a through hole.
- the melted and kneaded resins are combined in the die to form a sheath core composed of a non-foamed cylindrical core layer and a non-foamed coating layer covering the outer surface of the cylindrical core layer.
- a complex of molds was formed.
- the composite is extruded into a cylindrical strand having a through hole through the pores of the mouthpiece attached to the tip of the extruder. It was cut so that the mass was approximately 1.5 mg.
- a multilayer resin particle comprising a cylindrical core layer having through holes and a coating layer covering the core layer was obtained.
- the maximum length Lr of the multilayer resin particles was 2 mm, the average pore diameter dr of the through holes was 0.21 mm, and the average outer diameter Dr was 1.15 mm.
- zinc borate as a cell regulator was supplied to the extruder for forming the core layer, and 500 ppm by mass of zinc borate was contained in the polypropylene resin.
- the ratios shown in Table 2 were used for the blending amounts of carbon black in the core layer and the coating layer.
- the contents of the container were discharged into an atmospheric pressure atmosphere at a temperature of 75° C. to obtain single-stage expanded beads.
- the single-stage expanded particles were dried at 23° C. and 50% for 24 hours. Thus, expanded beads having a bulk ratio of 15.0 were obtained.
- the temperature Tu of the atmosphere for releasing the resin particles was adjusted by introducing air for cooling into the space immediately below the closed container.
- the first-stage expanded beads are placed in a pressure container (specifically, a pressurized tank) for applying internal pressure to the expanded beads, and air is forced into the pressure container to increase the pressure in the container. was impregnated into the cells to increase the internal pressure within the cells of the single-stage expanded particles.
- a pressure container specifically, a pressurized tank
- Table 2 The values shown in Table 2 were the pressures inside the cells (that is, the internal pressure) in the single-stage expanded beads taken out of the pressure-resistant container.
- the first-stage expanded particles taken out from the pressure vessel are placed in another pressure vessel (specifically, a metal drum) for heating the expanded particles, and the pressure inside the pressure vessel is Steam was supplied so that the pressure of (that is, the drum pressure) was the pressure shown in Table 2, and the mixture was heated under atmospheric pressure.
- the apparent density of the single-stage expanded beads was lowered to obtain black expanded beads (two-stage expanded beads) having a bulk ratio of 35.6 times.
- the predetermined molding pressure was set as the lowest pressure among the molding pressures at which acceptable products can be obtained in the above-described evaluation of the fusion bondability of the green mold.
- FIG. 6(b) shows a photograph of the appearance of the molded article obtained in this example.
- Example 2 This example is an example in which the bulk magnification ratio M 2 /M 1 is changed.
- single-stage expanded beads were obtained in the same manner as in Example 1 except that the conditions of the single-stage expansion process were changed as shown in Table 2 and the bulk ratio M1 of the single-stage expanded beads was changed to 24.5.
- the two-step expansion process was carried out in the same manner as in Example 1, except that the single-step expanded particles were used, the conditions of the two-step expansion process were changed as shown in Table 2, and the bulk ratio M2 of the two-step expanded particles was set to 36.0. Foamed beads were produced.
- a molded article was obtained in the same manner as in Example 1 using the two-stage expanded particles.
- Example 3 This example is an example in which the resin forming the foam layer is changed. Specifically, first, multilayer resin particles were produced in the same manner as in Example 1, except that PP2 in Table 1 was used as the resin for forming the core layer. Next, using the multi-layered resin particles, the single-step expanded beads were obtained in the same manner as in Example 1, except that the conditions of the first-step expansion step were changed as shown in Table 2, and the bulk ratio M1 of the single-step expanded beads was changed to 15.2 times. got The two-step expansion process was carried out in the same manner as in Example 1, except that the single-step expansion particles were used, the conditions of the two-step expansion process were changed as shown in Table 2, and the bulk ratio M2 of the two-step expansion particles was 36.1 times. Foamed beads were produced. A molded article was obtained in the same manner as in Example 1 using the two-stage expanded particles.
- Example 4 This example is an example of manufacturing a compact having a large density. Specifically, the conditions of the first-stage expansion process and the two-stage expansion process were changed as shown in Table 2, the bulk ratio M2 of the two-stage expanded particles was set to 20.0 times, and carbon black in the core layer and the coating layer Two-stage expanded beads were produced in the same manner as in Example 1, except that the blending amount of was set to the ratio shown in Table 2. A molded article was obtained in the same manner as in Example 1 using the two-stage expanded particles.
- Example 5 This example is an example in which the blending amount of carbon black is increased. Specifically, except that the conditions of the first-stage foaming process and the two-stage foaming process were changed as shown in Table 2, and that the blending amount of carbon black in the core layer and the coating layer was set to the ratio shown in Table 2, Example Two-stage expanded beads were produced in the same manner as in 1. A molded article was obtained in the same manner as in Example 1 using the two-stage expanded particles.
- Example 6 This example is an example of manufacturing a compact having a low density. Specifically, the conditions of the one-stage expansion process and the two-stage expansion process were changed as shown in Table 2, and the bulk ratio M2 of the two-stage expanded particles was set to 44.6 times. to produce two-stage expanded beads. A molded article was obtained in the same manner as in Example 1 using the two-stage expanded particles.
- This example is an example in which a molded article is produced using single-stage expanded particles. Specifically, in the one-stage expansion step, the expansion conditions were changed as shown in Table 3, and expanded beads (that is, , single-stage expanded particles) were produced. A two-stage foaming process was not performed. A molded article was obtained in the same manner as in Example 1 using the single-stage expanded particles. In addition, the external appearance photograph of the molded object obtained in this example is shown in Fig.6 (a).
- Example 2 This example is an example in which the bulk ratio M1 is too large and the bulk ratio ratio M2 / M1 is too small.
- single-stage expanded beads were obtained in the same manner as in Example 1 except that the conditions of the single-stage expansion step were changed as shown in Table 3 and the bulk ratio M1 of the single-stage expanded beads was changed to 29.9.
- the two-step expansion process was carried out in the same manner as in Example 1, except that the single-step expansion particles were used, the conditions of the two-step expansion process were changed as shown in Table 3, and the bulk ratio M2 of the two-step expansion particles was 35.6 times. Foamed beads were produced.
- a molded article was obtained in the same manner as in Example 1 using the two-stage expanded particles.
- This example is an example in which the resin forming the foam layer is changed and the molded article is produced using single-stage expanded particles. Specifically, first, multilayer resin particles were produced in the same manner as in Example 1, except that PP2 in Table 1 was used as the resin for forming the core layer. Next, using this multi-layered resin bead, in the one-stage expansion step, the expansion conditions were changed as shown in Table 3, and expanded beads having a bulk ratio of 36.0 were produced in the same manner as in Example 1. Expanded beads (ie, single-stage expanded beads) were produced. A two-stage foaming process was not performed. A molded article was obtained in the same manner as in Example 1 using the single-stage expanded particles.
- Example 4 This example is an example in which the blending amount of carbon black is excessively increased and a molded article is produced using single-stage expanded particles.
- the multi-layered resin particles were prepared in the same manner as in Example 1 except that the amount of carbon black blended in the core layer forming extruder and the coating layer forming extruder was changed as shown in Table 3. manufactured.
- Expanded beads were produced in the same manner as in Example 1, except that expanded beads having a bulk ratio of 35.9 were produced by changing the expansion conditions as shown in Table 3 in the one-step expansion step using the multilayered resin beads. (that is, single-stage expanded beads) were produced. A two-stage foaming process was not performed.
- a molded article was obtained in the same manner as in Example 1 using the single-stage expanded particles.
- Example 5 This example is an example in which a compact having a large density was produced using single-stage expanded particles. Specifically, first, the multi-layered resin particles were prepared in the same manner as in Example 1 except that the amount of carbon black blended in the core layer forming extruder and the coating layer forming extruder was changed as shown in Table 3. manufactured. Multi-layer resin in the same manner as in Example 1, except that the conditions of the first-stage foaming step were changed as shown in Table 3, and the blending amount of carbon black in the core layer and the coating layer was set to the ratio shown in Table 3. Particles were produced.
- Expanded beads were produced in the same manner as in Example 1, except that expanded beads having a bulk ratio of 20.0 were produced by changing the expansion conditions as shown in Table 3 in the one-step expansion step using the multilayered resin beads. (that is, single-stage expanded beads) were produced. A two-stage foaming process was not performed. A molded article was obtained in the same manner as in Example 1 using the single-stage expanded particles.
- Example 6 This example is an example in which the bulk magnification ratio M 2 /M 1 is too large.
- single-stage expanded beads were obtained in the same manner as in Example 1 except that the conditions of the single-stage expansion step were changed as shown in Table 3 and the bulk ratio M1 of the single-stage expanded beads was changed to 10.1.
- the two-step expansion process was carried out in the same manner as in Example 1, except that the single-step expansion particles were used, the conditions of the two-step expansion process were changed as shown in Table 3, and the bulk ratio M2 of the two-step expansion particles was 36.0 times. Foamed beads were produced. In the two-step foaming process, the foamed particles were fused (blocked) to each other, so the molding process was not performed.
- This example is an example using foamed particles that do not have through-holes. Specifically, first, the blending amount of carbon black blended in the core layer forming extruder and the coating layer forming extruder was changed as shown in Table 3, and the multi-layer resin particles without through holes were used. A multilayer resin particle was produced in the same manner as in Example 1, except for the above. Using this multi-layer resin bead, two-stage expanded beads were produced in the same manner as in Example 1, except that the conditions of the first-stage expansion step were changed as shown in Table 3. A molded article was obtained in the same manner as in Example 1 using the two-stage expanded particles.
- Example 8 This example is an example of producing a compact having a low density.
- a multilayer resin particle was produced in the same manner as in Example 1, except that the conditions of the first-stage expansion step and the second-stage expansion step were changed as shown in Table 3.
- Expanded beads were produced in the same manner as in Example 1, except that expanded beads having a bulk ratio of 44.8 were produced by changing the expansion conditions in the one-step expansion step as shown in Table 3 using these multi-layered resin beads. (that is, single-stage expanded beads) were produced. A two-stage foaming process was not performed.
- a molded article was obtained in the same manner as in Example 1 using the single-stage expanded particles.
- the expanded beads obtained in Examples 1 to 6 can give molded articles having deep black color and inconspicuous color unevenness.
- such molded articles can be produced with good productivity over a wide range from low molding heating temperatures to high molding heating temperatures. Furthermore, the time required for water cooling during molding is short, and the molding cycle is shortened.
- the black molded article of Example 1 has a deep color and inconspicuous color unevenness. In other examples, the color depth was comparable to that of Example 1, and color unevenness was not conspicuous.
- expanded beads having a high closed cell ratio can be obtained. In Examples 1 to 6, blocking did not occur in the two-stage foaming process.
- Example 1 By comparing Example 1 and Example 2, when the ratio M 2 /M 1 of the bulk ratio M 2 of the two-stage expanded particles to the bulk ratio M 1 of the first-stage expanded particles is 1.8 or more, the black color becomes more black. It was possible to produce a molded body with a high
- the bulk ratio M1 of the single-stage expanded beads was small, and the ratio M2 / M1 of the bulk ratio M2 of the two-stage expanded beads to the bulk ratio M1 of the single-stage expanded beads was too small. Also in , the obtained molded article had a slightly low degree of blackness and slightly conspicuous color unevenness.
- Comparative Example 4 Although the two-step foaming process was not performed, it was possible to produce a molded article with a high degree of blackness and inconspicuous color unevenness due to the high blending ratio of carbon black. However, since the blending ratio of carbon black is too high, moldability is deteriorated, and the range of molding heating temperature capable of molding a molded article with high blackness and inconspicuous color unevenness is narrow. Also, the water cooling time was long.
- Comparative Example 7 it was possible to produce a molded article with high blackness and inconspicuous color unevenness. However, since it does not have through-holes, the moldability is remarkably deteriorated, and the range of molding heating temperature capable of molding a molded article with high blackness and inconspicuous color unevenness is narrow. Also, the water cooling time was long. Moreover, when the curing step was omitted, a good compact could not be produced.
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Abstract
Description
密閉容器内において、分散媒に分散させたポリプロピレン系樹脂粒子に無機物理発泡剤を含浸させ、上記樹脂粒子を分散媒と共に上記密閉容器から上記密閉容器内よりも低圧下に放出することにより、嵩倍率M1倍の一段発泡粒子を得る一段発泡工程と、
上記一段発泡粒子の気泡内の圧力を上昇させた後、上記一段発泡粒子を加熱することにより、上記一段発泡粒子をさらに発泡させて嵩倍率M2倍の上記ポリプロピレン系樹脂発泡粒子を得る二段発泡工程と、を有し、
上記樹脂粒子が貫通孔を有する筒形状であり、上記樹脂粒子はカーボンブラックを含み、上記樹脂粒子中のカーボンブラックの含有量が0.1重量%以上5重量%以下であり、
上記一段発泡粒子の嵩倍率M1が5倍以上25倍以下であり、
上記一段発泡粒子の嵩倍率M1に対する上記ポリプロピレン系樹脂発泡粒子の嵩倍率M2の比M2/M1が、1.2以上3.0以下である、ポリプロピレン系樹脂発泡粒子の製造方法にある。
一方、一段発泡粒子の嵩倍率M1が25倍を超える場合には、最終的に得られる発泡粒子成形体の黒色度が不十分になったり、色むらが目立ちやすくなるおそれがある。かかる観点から、一段発泡粒子の嵩倍率M1は、20倍以下であることが好ましく、18倍以下であることがより好ましい。
発泡粒子の独立気泡率をより高めるとともに、黒色度がより高く、色むらがより目立ちにくい成形体を得る観点からは、一段発泡粒子の嵩倍率M1は8倍以上20倍以下であることが好ましく、10倍以上18倍以下であることがより好ましい。
一方、M2/M1が3.0を超える場合には、二段発泡工程において、得られる発泡粒子の独立気泡率を十分に高くすることが困難になったり、ブロッキングが発生し易くなるおそれがある。かかる観点から、嵩倍率の比M2/M1は2.8以下であることが好ましく、2.5以下であることがより好ましい。
発泡粒子の独立気泡率をより高めるとともに、黒色度がより高く、色むらがより目立ちにくい成形体を得る観点からは、嵩倍率の比M2/M1は1.4以上2.8以下であることが好ましく、1.8以上2.5以下であることがより好ましい。
二段発泡粒子の嵩倍率M2は、次のようにして求められる値である。まず、二段発泡粒子の嵩密度[kg/m3]を後述する方法により測定する。次に、二段発泡粒子の発泡層を構成するポリプロピレン系樹脂の密度[kg/m3]を上記二段発泡粒子の嵩密度[kg/m3]で除すことにより、二段発泡粒子の嵩倍率M1[倍]が求められる。
従来、嵩倍率の高い発泡粒子においては、黒色度の低下や、色むらの発生がより生じやすいものであった。本開示の製造方法によれば、たとえば嵩倍率30倍を超えるような嵩倍率の高い発泡粒子であっても、黒色度の低下や、色むらの発生を抑制することが可能である。
一方、カーボンブラックの含有量が5重量%を超えると、発泡粒子を低い成形加熱温度で成形することが困難になるおそれがある。また、水冷時間が長くなるおそれがある。かかる観点から、樹脂粒子中のカーボンブラックの含有量は、4.5重量%以下であることが好ましく、4.0重量%以下であることがより好ましく、3.5重量%以下であることがさらに好ましい。
黒色度がより高く、色むらがより目立ちにくい成形体をより生産性良く得る観点からは、樹脂粒子中のカーボンブラックの含有量は、0.5重量%以上4.5質量%以下であることが好ましく、1.0重量%以上4.0質量%以下であることがより好ましく、2.0重量%以上3.5質量%以下であることがさらに好ましい。
従来、貫通孔を有する発泡粒子は、その貫通孔に起因して、空隙率が高く、吸音性や軽量性に優れる成形体の製造に好適に使用されてきた(たとえば、特開2015-143046号公報)。一方、二段発泡工程を経て製造された発泡粒子は、一段発泡により直接製造された、同程度の見掛け密度の発泡粒子と比較して貫通孔が潰れて小さくなる傾向があり、その特徴を活かし難くなるため、貫通孔を有する発泡粒子を二段発泡工程で製造することはほとんど行われていなかった。
貫通孔の円形度は、たとえば樹脂粒子の造粒工程において、貫通孔を形成するためのダイの形状を変更したり、通常25℃程度の水温で行われていたストランドを冷却する際の水温を低温(例えば15℃以下)に調整したりすることにより、上記範囲に調節することができる。貫通孔の円形度の上限は、1である。また、たとえば後述する発泡粒子(つまり、二段発泡粒子)の貫通孔の平均孔径dが1mm未満といった、平均孔径dの小さな発泡粒子を得ようとした場合には、二段発泡時に貫通孔がより潰れやすいため、一段発泡粒子の貫通孔の円形度を上記範囲内とすることが好ましい。
円形度=4πS/(C×C)・・・(α)
ここで、πは円周率を意味する。
なお、各一段発泡粒子の貫通孔の孔径が貫通方向に一様でない場合であっても、各一段発泡粒子の貫通孔の円形度は、上記のように一段発泡粒子の切断面の面積が最大となる位置での貫通孔の円形度によって定められる。
図1~図5に例示されるように、発泡粒子1は、筒形状であり、貫通孔11を有している。図2~図5に示すように、発泡粒子1は、ポリプロピレン系樹脂から構成された発泡層2を有する。発泡粒子1は、図2及び図3に示すように、発泡状態のポリプロピレン系樹脂から構成されていてもよいが、図4及び図5に示すように、発泡状態のポリプロピレン系樹脂から構成される発泡層2と、これを被覆する被覆層3とを有することが好ましい。なお、図1~図5は、発泡粒子の形態の例示であり、本発明はこれらの図面に限定されるものではない。
なお、養生工程とは、ポリプロピレン系樹脂発泡粒子の型内成形後に通常行われる工程であり、具体的には、離型後の成形体を60℃から80℃程度の温度に調整された高温雰囲気下で所定時間静置させることにより、成形時の加熱による成形体の体積収縮を回復させる工程である。ただし、養生工程を行うことも可能である。また、成形時には、成形型内に充填する前の発泡粒子に予め内圧を付与する前処理加圧を行ってもよいし、前処理加圧を行わなくてもよい。前処理加圧を行わなくても、養生工程を省略しつつ、黒色度が高く、色むらが目立ちにくく、所望の形状を有する、表面性及び剛性に優れた発泡粒子成形体を製造することができる。
t=(D-d)/2 ・・・(I)
d:貫通孔の平均孔径(mm)
D:発泡粒子の平均外径(mm)
成形体の剛性を更に高めるという観点、養生工程を省略した場合の寸法変化をより確実に抑制するという観点から、共重合体中のエチレン成分の含有量は、共重合体中のエチレン成分の含有量は、3.5質量%以下であることがより好ましく、2.8質量%以下であることがさらに好ましく、2.0質量%以下であることが特に好ましい。同様の観点から、共重合体中のエチレン成分の含有量は0.5質量%以上であることが好ましい。
一方、より一層低い成形加熱温度(つまり、低い成形圧)で表面性や剛性に優れる成形体を成形することができるという観点、エネルギー吸収性により優れる発泡粒子成形体を得る観点から、共重合体中のエチレン成分の含有量は1.0質量%以上であることがより好ましく、1.2質量%以上であることがさらに好ましく、1.5質量%以上であることがよりさらに好ましく、2.0質量%を超えることが特に好ましい。同様の観点から、共重合体中のエチレン成分の含有量は5.0質量%以下であることが好ましい。
なお、IRスペクトル測定により共重合体中のモノマー成分の含有量を求めることができる。エチレン-プロピレン共重合体のエチレン成分、プロピレン成分は、エチレン-プロピレン共重合体におけるエチレン由来の構成単位、プロピレン由来の構成単位をそれぞれ意味する。また、共重合体中の各モノマー成分の含有量は、共重合体中の各モノマー由来の構成単位の含有量を意味するものとする。
成形体の剛性を更に高めるという観点、養生工程を省略した場合の寸法変化をより確実に抑制するという観点から、発泡層を構成するポリプロピレン系樹脂の曲げ弾性率は、850MPa以上1600MPa以下であることが好ましく、900MPa以上1600MPa以下であることがより好ましく、950MPa以上1600MPa以下であることがさらに好ましく、1200MPa以上1600MPa以下であることが特に好ましい。
一方、より一層低い成形加熱温度(つまり、低い成形圧)で表面性や剛性に優れる成形体を成形することができるという観点、エネルギー吸収性により優れる発泡粒子成形体を得る観点から、発泡層を構成するポリプロピレン系樹脂の曲げ弾性率は、800MPa以上1550MPa以下であることが好ましく、800MPa以上1500MPa以下であることがより好ましく、800MPa以上1200MPa未満であることがさらに好ましい。
なお、ポリプロピレン系樹脂の曲げ弾性率は、JIS K7171:2008に基づき、求めることができる。
独立気泡率(%)=(Vx-W/ρ)×100/(Va-W/ρ)・・・(II)
ただし、
Vx:上記方法で測定される発泡粒子の真の体積、即ち、発泡粒子を構成する樹脂の容積と、発泡粒子内の独立気泡部分の気泡全容積との和(単位:cm3)
Va:発泡粒子を、エタノールの入ったメスシリンダーに沈めた際の水位上昇分から測定される発泡粒子の見掛けの体積(単位:cm3)
W:発泡粒子測定用サンプルの重量(単位:g)
ρ:発泡粒子を構成する樹脂の密度(単位:g/cm3)
固有ピークとは、発泡粒子を構成するポリプロピレン系樹脂に固有の吸熱ピークであり、ポリプロピレン系樹脂が本来有する結晶の融解時の吸熱によるものであると考えられる。一方、高温ピークとは、DSC曲線で上記固有ピークよりも高温側に現れる吸熱ピークである。この高温ピークが現れる場合、樹脂中に二次結晶が存在するものと推定される。なお、上記のように10℃/分の加熱速度で23℃から200℃までの加熱(つまり、第1回目の加熱)を行った後、10℃/分の冷却速度で200℃から23℃まで冷却し、その後再び10℃/分の加熱速度で23℃から200℃までの加熱(つまり、第2回目の加熱)を行ったときに得られるDSC曲線においては、固有ピークのみが見られるため、固有ピークと高温ピークとを見分けることができる。この固有ピークの頂点の温度は、第1回目の加熱と第2回目の加熱とで多少異なる場合があるが、通常、その差は5℃以内である。
また、上記高温ピークの融解熱量と、DSC曲線の全融解ピークの融解熱量の比(高温ピークの融解熱量/全融解ピークの融解熱量)は、好ましくは0.05~0.3、より好ましくは0.1~0.25、更に好ましくは0.15~0.2である。
高温ピークの融解熱量及び全融解ピークの融解熱量との比をこのような範囲にすることで、高温ピークとして表れる二次結晶の存在により、発泡粒子は特に機械的強度に優れると共に、型内成形性に優れるものになると考えられる。
ここで、全融解ピークの融解熱量とは、DSC曲線の全ての融解ピークの面積から求められる融解熱量の合計をいう。
上記発泡粒子のDSC曲線の各ピークの融解熱量は、次のようにして求められる値である。まず、状態調節を行った後の発泡粒子群から1個の発泡粒子を採取する。この発泡粒子を試験片として用い、試験片を示差熱走査熱量計によって23℃から200℃まで加熱速度10℃/分で昇温させたときのDSC曲線を得る。図7にDSC曲線の一例を示す。図7に例示されるように、DSC曲線には、固有ピークΔH1と、固有ピークΔH1の頂点よりも高温側に頂点を有する高温ピークΔH2とが現れる。
次いで、DSC曲線上における温度80℃での点αと、発泡粒子の融解終了温度Tでの点βとを結び直線L1を得る。次に、上記の固有ピークΔH1と高温ピークΔH2との間の谷部に当たるDSC曲線上の点γからグラフの縦軸と平行な直線L2を引き、直線L1と直線L2との交わる点をδとする。なお、点γは、固有ピークΔH1と高温ピークΔH2との間に存在する極大点ということもできる。
固有ピークΔH1の面積は、DSC曲線の固有ピークΔH1部分の曲線と、線分α-δと、線分γ-δとによって囲まれる部分の面積であり、これを固有ピークの融解熱量とする。
高温ピークΔH2の面積は、DSC曲線の高温ピークΔH2部分の曲線と、線分δ-βと、線分γ-δとによって囲まれる部分の面積であり、これを高温ピークの融解熱量とする。
全融解ピークの面積は、DSC曲線の固有ピークΔH1部分の曲線と高温ピークΔH2部分の曲線と、線分α-β(つまり、直線L1)とによって囲まれる部分の面積であり、これを全融解ピークの融解熱量とする。
貫通孔の平均孔径dが1mm未満であるとともに、平均外径Dに対する平均孔径dの比d/Dが0.4以下である発泡粒子をより確実に製造する観点から、樹脂粒子の貫通孔の平均孔径drが0.25mm未満であることが好ましく、0.24mm未満であることがより好ましく、0.22mm以下であることが更に好ましい。貫通孔を有する樹脂粒子の製造安定性の観点からは、樹脂粒子の貫通孔の平均孔径drは0.1mm以上であることが好ましい。
また、同様の観点から、樹脂粒子の平均外径Drに対する平均孔径drの比dr/Drは0.4以下であることが好ましく、0.3以下であることがより好ましく、0.25以下であることが更に好ましく、0.2以下であることが特に好ましい。貫通孔を有する樹脂粒子の製造安定性の観点からは、樹脂粒子の平均外径Drに対する平均孔径drの比dr/Drは0.1以上であることが好ましい。
空隙率(%)=[(Vd-Vc)/Vd]×100・・・(III)
表1に、発泡粒子の製造に使用したポリプロピレン系樹脂の性状等を示す。なお、本例において使用したエチレン-プロピレン共重合体、エチレン-プロピレン-ブテン共重合体は、いずれもランダム共重合体である。これらの共重合体は、プロピレン成分を主成分とするポリプロピレン系樹脂である。PP1及びPP2のポリプロピレン系樹脂の密度は、900kg/m3である。
ポリプロピレン系樹脂を230℃でヒートプレスして4mmのシートを作製し、このシートから長さ80mm×幅10mm×厚さ4mmの試験片を切り出した。この試験片の曲げ弾性率を、JIS K7171:2008に準拠して求めた。なお、圧子の半径R1及び支持台の半径R2は共に5mmであり、支点間距離は64mmであり、試験速度は2mm/minである。
ポリプロピレン系樹脂の融点は、JIS K7121:1987に基づき求めた。具体的には、状態調節として「(2)一定の熱処理を行なった後、融解温度を測定する場合」を採用し、状態調節された試験片を10℃/minの加熱速度で30℃から200℃まで昇温することによりDSC曲線を取得し、該融解ピークの頂点温度を融点とした。なお、測定装置は、熱流束示差走査熱量測定装置(エスアイアイ・ナノテクノロジー(株)社製、型番:DSC7020)を用いた。
ポリプロピレン系樹脂のメルトフローレイト(つまり、MFR)は、JIS K7210-1:2014に準拠し、温度230℃、荷重2.16kgの条件で測定した。
多層樹脂粒子の最大長さは、以下のように求めた。多層樹脂粒子群から無作為に選択した100個の多層樹脂粒子について、その最大長さをノギスで測定し、これらを算術平均した値を多層樹脂粒子の最大長さとした。
多層樹脂粒子の貫通孔の平均孔径は、以下のように求めた。多層樹脂粒子群から無作為に選択した100個の多層樹脂粒子について、切断面の面積が概ね最大となる位置で、貫通孔の貫通方向に対して垂直に切断した。各多層樹脂粒子の切断面の写真を撮影し、断面写真における貫通孔部分の断面積(開口面積)を求めた。断面積と同じ面積を有する仮想真円の直径を算出し、これらを算術平均した値を、多層樹脂粒子の貫通孔の平均孔径(dr)とした。
多層樹脂粒子の平均外径は、以下のように求めた。多層樹脂粒子群から無作為に選択した100個の多層樹脂粒子について、切断面の面積が概ね最大となる位置で、貫通孔の貫通方向に対して垂直に切断した。各多層樹脂粒子の切断面の写真を撮影し、多層樹脂粒子の断面積(貫通孔の開口部も含む)を求めた。断面積と同じ面積を有する仮想真円の直径を算出し、これらを算術平均した値を、多層樹脂粒子の平均外径(Dr)とした。
一段発泡粒子の貫通孔の円形度は、以下のように求めた。一段発泡粒子の発泡粒子群から無作為に選択した50個の一段発泡粒子を、切断面の面積が概ね最大となる位置で、貫通孔の貫通方向に対して垂直に切断した。各一段発泡粒子の切断面の写真を撮影し、貫通孔部分の断面積S(具体的には、開口面積)及び周囲長C(つまり、開口部の円周)を求めた。円形度は、以下の式(α)により求めた。
円形度=4πS/(C×C)・・・(α)
ここで、πは円周率を意味する。
発泡粒子の貫通孔の平均孔径は、以下のように求めた。状態調節後の発泡粒子群から無作為に選択した100個の発泡粒子について、切断面の面積が概ね最大となる位置で、貫通孔の貫通方向に対して垂直に切断した。各発泡粒子の切断面の写真を撮影し、断面写真における貫通孔部分の断面積(開口面積)を求めた。断面積と同じ面積を有する仮想真円の直径を算出し、これらを算術平均した値を、発泡粒子の貫通孔の平均孔径(d)とした。
発泡粒子の平均外径は、以下のように求めた。状態調節後の発泡粒子群から無作為に選択した100個の発泡粒子について、切断面の面積が概ね最大となる位置で、貫通孔の貫通方向に対して垂直に切断した。各発泡粒子の切断面の写真を撮影し、発泡粒子の断面積(貫通孔の開口部も含む)を求めた。断面積と同じ面積を有する仮想真円の直径を算出し、これらを算術平均した値を、発泡粒子の平均外径(D)とした。
発泡粒子の平均肉厚は、下記式(IV)により求めた。
平均肉厚t=(平均外径D-平均孔径d)/2・・・(IV)
発泡粒子の嵩密度は、以下のように求めた。状態調節後の発泡粒子群から発泡粒子を無作為に取り出して容積1Lのメスシリンダーに入れ、自然堆積状態となるように多数の発泡粒子を1Lの目盛まで収容し、収容された発泡粒子の質量W2[g]を収容体積V2(1[L])で除して(W2/V2)、単位を[kg/m3]に換算することにより、発泡粒子の嵩密度を求めた。
一段発泡粒子の嵩倍率M1は、次のようにして測定、算出した。まず、状態調節後の一段発泡粒子を用い、一段発泡粒子の嵩密度を上記の方法により算出した。次に、一段発泡粒子の発泡層を構成するポリプロピレン系樹脂の密度[kg/m3]を上記一段発泡粒子の嵩密度[kg/m3]で除すことにより、一段発泡粒子の嵩倍率M1[倍]を求めた。なお、二段発泡粒子の嵩倍率M2についても、一段発泡粒子の代わりに二段発泡粒子を用いた点を除いて、上記の方法と同様にして測定、算出した。
発泡粒子の見掛け密度は、以下のように求めた。まず、温度23℃のエタノールが入ったメスシリンダーを用意し、状態調節後の任意の量の発泡粒子群(発泡粒子群の質量W1[g])をメスシリンダー内のエタノール中に金網を使用して沈めた。そして、金網の体積を考慮し、水位上昇分より読みとられる発泡粒子群の容積V1[L]を測定した。メスシリンダーに入れた発泡粒子群の質量W1[g]を容積V1[L]で除して(W1/V1)、単位を[kg/m3]に換算することにより、発泡粒子の見掛け密度を求めた。
発泡粒子の独立気泡率は、ASTM-D2856-70手順Cに基づき空気比較式比重計を用いて測定した。具体的には、次のようにして求めた。状態調節後の嵩体積約20cm3の発泡粒子を測定用サンプルとし、下記の通りエタノール没法により正確に見掛けの体積Vaを測定した。見掛けの体積Vaを測定した測定用サンプルを十分に乾燥させた後、ASTM-D2856-70に記載されている手順Cに準じ、島津製作所社製アキュピックII1340により測定される測定用サンプルの真の体積の値Vxを測定した。そして、これらの体積値Va及びVxを基に、下記の式(V)により独立気泡率を計算し、サンプル5個(N=5)の平均値を発泡粒子の独立気泡率とした。
独立気泡率(%)=(Vx-W/ρ)×100/(Va-W/ρ)・・・(V)
ただし、
Vx:上記方法で測定される発泡粒子の真の体積、即ち、発泡粒子を構成する樹脂の容積と、発泡粒子内の独立気泡部分の気泡全容積との和(単位:cm3)
Va:発泡粒子を、エタノールの入ったメスシリンダーに沈めた際の水位上昇分から測定される発泡粒子の見掛けの体積(単位:cm3)
W:発泡粒子測定用サンプルの重量(単位:g)
ρ:発泡粒子を構成する樹脂の密度(単位:g/cm3)
状態調節を行った後の発泡粒子群から1個の発泡粒子を採取した。この発泡粒子を試験片として用い、試験片を示差熱走査熱量計(具体的には、ティー・エイ・インスツルメント社製DSC.Q1000)によって23℃から200℃まで加熱速度10℃/分で昇温させたときのDSC曲線を得た。DSC曲線において、高温ピークの面積を求め、これを高温ピークの融解熱量とした。
上記測定を5個の発泡粒子について行い、算術平均した値を表2、表3に示した。
まず、後述の<成形体の製造>の方法で、成形スチーム圧を0.20~0.38MPa(G)の間で0.02MPaずつ変化させて成形体を製造した。なお、成形前に、発泡粒子に0.1MPa(G)の内圧を付与する前処理加圧を行い、クラッキング量を10%(つまり、6mm)に設定して成形を行った。離型後、成形体を80℃のオーブン中で12時間静置した。80℃のオーブン中での12時間の静置が養生工程である。養生工程後、成形体を相対湿度50%、23℃、1atmの条件にて24時間静置することにより、成形体の状態調節を行った。次いで、成形体の融着性、回復性(具体的には、型内成形後の膨張または収縮の回復性)を評価した。その結果、後述する評価基準でいずれの項目でも合格となったスチーム圧(つまり、合格品が取得可能であったスチーム圧)を養生成形可能なスチーム圧とした。なお、養生成形可能なスチーム圧が低く、その範囲が広い程、成形性が優れることを意味する。
上記(養生成形可能範囲)の評価において得られた状態調節後の成形体について、色の濃さ、色むらを評価した。その結果、後述する評価基準でいずれの項目でも「A」評価となったスチーム圧を、色の濃さ及び色むらが良好な成形体を成形可能なスチーム圧とした。
上記(養生成形可能範囲)において、成形体を離型した後に、80℃の温度に調整された高温雰囲気下で12時間静置させるという養生工程を行わないこと以外は同様の方法により成形体を製造し、成形体の融着性、回復性の評価を行った。その結果、いずれかの成形スチーム圧において、合格品を取得することができた場合を「○」と評価し、いずれの成形スチーム圧においても合格品を取得できなかった場合を「×」と評価した。
成形体を折り曲げて破断させ、破断面に存在する発泡粒子の数C1と破壊した発泡粒子の数C2とを求め、上記破断面に存在する発泡粒子の数に対する破壊した発泡粒子の数の比率(つまり、材料破壊率)を算出した。材料破壊率は、C2/C1×100という式から算出される。異なる試験片を用いて上記測定を5回行い、材料破壊率をそれぞれ求めた。材料破壊率の算術平均値が90%以上であるときを合格とした。
縦300mm、横250mm、厚み60mmの平板形状の金型を用いて得られた成形体における四隅部付近(具体的には、角より中心方向に10mm内側)の厚みと、中心部(縦方向、横方向とも2等分する部分)の厚みをそれぞれ計測した。次いで、計測した箇所のうち最も厚みの厚い箇所の厚みに対する最も厚みの薄い箇所の厚みの比(単位:%)を算出し、比が95%以上であるときを合格とした。
表4、表5に、実施例、比較例の成形体の性状等を示す。
前処理加圧は、発泡粒子を密閉容器内に入れ、圧縮空気により発泡粒子を加圧し、発泡粒子に0.1MPa(G)の内圧を付与することにより行った。なお、発泡粒子の内圧は、以下のようにして測定した値である。成形型内に充填する直前の、内圧が高められた状態の発泡粒子群の重量をQ(g)とし、48時間経過後の発泡粒子群の重量をU(g)として、該重量Q(g)とU(g)の差を増加空気量W(g)とし、式P=(W÷M)×R×T÷Vにより発泡粒子の内圧P(MPa(G))を計算した。ただし、式中、Mは空気の分子量、Rは気体定数、Tは絶対温度、Vは発泡粒子群の見掛け体積から発泡粒子群中に占める基材樹脂の体積を差し引いた体積(L)を意味し、本例では、M=28.8(g/mol)、R=0.0083(MPa・L/(K・mol))、T=296(K)である。
成形体密度(kg/m3)は、成形体の重量(g)を成形体の外形寸法から求められる体積(L)で除し、単位換算することにより算出した。
成形体の表面にあるスキン層が試験片に含まれないように、成形体の中心部から縦50mm×横50mm×厚み25mmの試験片を切り出した。JIS K6767:1999に基づき、圧縮速度10mm/分にて圧縮試験を行い成形体の50%圧縮応力を求めた。
成形体の空隙率は、以下のように求めた。成形体の中心部から直方体形状(縦20mm×横100mm×高さ20mmの試験片を切り出した。この試験片を、エタノールを入れたメスシリンダー中に沈めてエタノールの液面の上昇分から試験片の真の体積Vc[L]を求めた。また、試験片の外形寸法から見掛けの体積Vd[L]を求めた。求められた真の体積Vcと見掛けの体積Vdから下記式(VI)により成形体の空隙率を求めた。
空隙率(%)=[(Vd-Vc)/Vd]×100・・・(VI)
成形体の表面を観察し、表面性を下記基準に基づいて評価した。
A:成形体の表面に粒子間隙が少なく、かつ貫通孔等に起因する凹凸が目立たない良好な表面状態を示す。
B:成形体の表面に粒子間隙および/または貫通孔等に起因する凹凸がやや認められる。
C:成形体の表面に粒子間隙および/または貫通孔等に起因する凹凸が著しく認められる。
成形体の表面から無作為に5か所の部位を選択し、分光色差計(日本電色工業社製「SE2000」)を用いてL*値を測定し、それらの算術平均値を成形体のL*値とした。なお、測定範囲は30mmΦとし、測定方法は反射法とした。
成形体の色の濃さを、成形体のL*値から以下の基準により色の濃さを評価した。なお、L*値は明るさの指標であり、その値が低いほど黒色度が高く、黒色が濃いことを意味している。
A:L*値が24未満
B:L*値が24以上28未満
C:L*値が28以上
目視にて、成形体の表面に色むらがなく、均一な黒色を呈している(5点)から、著しい色むらがあり、灰色の部分が散見される(1点)までの5段階評価で色むらの評価を行い、5人の観者の評価の平均値をもとに以下の基準で発泡粒子成形体の色むらを評価した。
A:4点以上
B:3点以上4点未満
C:3点未満
<ポリプロピレン系発泡粒子の製造>
表1に示すPP1及びカーボンブラックを芯層形成用押出機内で最高設定温度245℃にて溶融混練して樹脂溶融混練物を得た。また、表1に示すPP3及びカーボンブラックを被覆層形成用押出機内で最高設定温度245℃にて溶融混練して樹脂溶融混練物を得た。次いで、芯層形成用押出機及び被覆層形成用押出機から各樹脂溶融混練物を、貫通孔を形成するための小孔を備えた共押出ダイの先端から押出した。このとき、ダイ内で各樹脂溶融混練物を合流させて、非発泡状態の筒状の芯層と、該筒状の芯層の外側表面を被覆する非発泡状態の被覆層とからなる鞘芯型の複合体を形成させた。押出機先端に付設された口金の細孔から複合体を、貫通孔を有する筒形状を有するストランド状に押し出し、ストランド状物を引取ながら水温を10℃に調整した冷水で水冷した後、ペレタイザーで質量が約1.5mgとなるように切断した。このようにして、貫通孔を有する円筒状の芯層と該芯層を被覆する被覆層とからなる多層樹脂粒子を得た。多層樹脂粒子の最大長さLrは2mmであり、貫通孔の平均孔径drは0.21mm、平均外径Drは1.15mmであった。多層樹脂粒子における、芯層と被覆層との質量比は、芯層:被覆層=95:5(つまり、被覆層の質量比が5%)とした。なお、多層樹脂粒子の製造に際し、芯層形成用押出機に気泡調整剤としてのホウ酸亜鉛を供給し、ポリプロピレン系樹脂中にホウ酸亜鉛500質量ppmを含有させた。また、芯層及び被覆層におけるカーボンブラックの配合量は、表2に示す割合とした。
多層樹脂粒子1kgを、分散媒としての水3Lともに内容積5Lの密閉容器内に仕込み、更に多層樹脂粒子100質量部に対し、分散剤としてカオリン0.3質量部、界面活性剤(アルキルベンゼンスルホン酸ナトリウム)0.004質量部を密閉容器内に添加した。発泡剤として二酸化炭素を密閉容器内に添加した後、密閉容器を密閉し、密閉容器内を攪拌しながら発泡温度150.1℃まで加熱した。このときの容器内圧力(つまり、含浸圧力、二酸化炭素圧力)は2.2MPa(G)であった。同温度(つまり、159.1℃)で15分保持した後、容器内容物を温度75℃の大気圧雰囲気下に放出して一段発泡粒子を得た。この一段発泡粒子を23℃、50%で24時間乾燥させた。このようにして、嵩倍率15.0倍の発泡粒子を得た。なお、樹脂粒子を放出する雰囲気の温度Tuは、密閉容器直下の空間に冷却のための空気を導入することにより調整した。
次いで、発泡粒子に内圧を付与するための耐圧容器(具体的には、加圧タンク)内に一段発泡粒子を入れ、耐圧容器内に空気を圧入することにより、容器内の圧力を高め、空気を気泡内に含浸させて一段発泡粒子の気泡内の内圧を高めた。耐圧容器から取り出した一段発泡粒子における気泡内の圧力(つまり、内圧)は表2に示す値であった。次いで、耐圧容器から取り出した一段発泡粒子(内圧が付与された一段発泡粒子)を、発泡粒子を加熱するための別の耐圧容器(具体的には、金属製のドラム)に入れ、耐圧容器内の圧力(つまり、ドラム圧力)が表2に示す圧力となるようスチームを供給し、大気圧下で加熱した。以上により、一段発泡粒子の見掛け密度を低下させ、嵩倍率35.6倍の黒色の発泡粒子(二段発泡粒子)を得た。
成形体の製造には、二段発泡粒子を23℃で24時間乾燥させたものを用いた。また、予め前処理加圧により二段発泡粒子に0.1MPaの内圧を付与した。次いで、クラッキング量を10%(つまり、6mm)に調節した、縦300mm×横250mm×厚さ60mmの平板成形型に発泡粒子を充填し、型締めして金型両面からスチームを5秒供給して予備加熱する排気工程を行った。その後、所定の成形圧より0.08MPa(G)低い圧力に達するまで、金型の一方の面側からスチームを供給して一方加熱を行った。次いで、成形圧より0.04MPa(G)低い圧力に達するまで金型の他方の面側よりスチームを供給して一方加熱を行った後、所定の成形圧に達するまで加熱(つまり、本加熱)を行った。加熱終了後、放圧し、成形体の発泡力による表面圧力が0.04MPa(G)になるまで水冷した後、型から離型した。離型後、成形体を80℃のオーブン中で12時間静置して養生した。養生工程後、成形体を相対湿度50%、23℃、1atmの条件にて24時間静置することにより、成形体の状態調節を行った。なお、所定の成形圧は、上述の養生成形における融着性の評価において合格品を取得可能な成形圧のうち、最も低い圧力となる値として設定した。本例において、得られた成形体の外観写真を図6(b)に示す。
本例は、嵩倍率の比M2/M1を変更した例である。具体的には、一段発泡工程の条件を表2に示すよう変更し、一段発泡粒子の嵩倍率M1を24.5倍とした以外は実施例1と同様にして一段発泡粒子を得た。この一段発泡粒子を用い、二段発泡工程の条件を表2に示すよう変更し、二段発泡粒子の嵩倍率M2を36.0倍とした以外は、実施例1と同様にして二段発泡粒子を製造した。また、この二段発泡粒子を用いて実施例1と同様にして成形体を得た。
本例は、発泡層を形成する樹脂を変更した例である。具体的には、まず、芯層を形成するための樹脂として、表1のPP2を用いた以外は、実施例1と同様にして多層樹脂粒子を作製した。次いで、この多層樹脂粒子を用い、一段発泡工程の条件を表2に示すよう変更し、一段発泡粒子の嵩倍率M1を15.2倍とした以外は実施例1と同様にして一段発泡粒子を得た。この一段発泡粒子を用い、二段発泡工程の条件を表2に示すよう変更し、二段発泡粒子の嵩倍率M2を36.1倍とした以外は、実施例1と同様にして二段発泡粒子を製造した。また、この二段発泡粒子を用いて実施例1と同様にして成形体を得た。
本例は、密度の大きな成形体を製造した例である。具体的には、一段発泡工程及び二段発泡工程の条件を表2に示すよう変更し、二段発泡粒子の嵩倍率M2を20.0倍としたこと、芯層及び被覆層におけるカーボンブラックの配合量を表2に示す割合としたこと以外は、実施例1と同様にして二段発泡粒子を製造した。また、この二段発泡粒子を用いて実施例1と同様にして成形体を得た。
本例は、カーボンブラックの配合量を増加させた例である。具体的には、一段発泡工程及び二段発泡工程の条件を表2に示すよう変更したこと、芯層及び被覆層におけるカーボンブラックの配合量を表2に示す割合としたこと以外は、実施例1と同様にして二段発泡粒子を製造した。また、この二段発泡粒子を用いて実施例1と同様にして成形体を得た。
本例は、密度の小さな成形体を製造した例である。具体的には、一段発泡工程及び二段発泡工程の条件を表2に示すよう変更し、二段発泡粒子の嵩倍率M2を44.6倍としたこと以外は、実施例1と同様にして二段発泡粒子を製造した。また、この二段発泡粒子を用いて実施例1と同様にして成形体を得た。
本例は、一段発泡粒子を用いて成形体を作製した例である。具体的には、一段発泡工程において、発泡条件を表3に示すように変更し、嵩倍率35.7倍の発泡粒子を製造した点を除いて、実施例1と同様にして発泡粒子(つまり、一段発泡粒子)を製造した。二段発泡工程は行っていない。また、この一段発泡粒子を用いて、実施例1と同様にして成形体を得た。なお、本例において得られた成形体の外観写真を図6(a)に示す。
本例は、嵩倍率M1が大きすぎるとともに、嵩倍率の比M2/M1が小さすぎる例である。具体的には、一段発泡工程の条件を表3に示すよう変更し、一段発泡粒子の嵩倍率M1を29.9倍とした以外は実施例1と同様にして一段発泡粒子を得た。この一段発泡粒子を用い、二段発泡工程の条件を表3に示すよう変更し、二段発泡粒子の嵩倍率M2を35.6倍とした以外は、実施例1と同様にして二段発泡粒子を製造した。また、この二段発泡粒子を用いて実施例1と同様にして成形体を得た。
本例は、発泡層を形成する樹脂を変更すると共に、一段発泡粒子を用いて成形体を作製した例である。具体的には、まず、芯層を形成するための樹脂として、表1のPP2を用いた以外は、実施例1と同様にして多層樹脂粒子を作製した。次いで、この多層樹脂粒子を用い、一段発泡工程において、発泡条件を表3に示すように変更し、嵩倍率36.0倍の発泡粒子を製造した点を除いて、実施例1と同様にして発泡粒子(つまり、一段発泡粒子)を製造した。二段発泡工程は行っていない。また、この一段発泡粒子を用いて、実施例1と同様にして成形体を得た。
本例は、カーボンブラックの配合量を過剰に増やすと共に、一段発泡粒子を用いて成形体を作製した例である。具体的には、まず、芯層形成用押出機、被覆層形成用押出機に配合するカーボンブラックの配合量を表3に示すように変更した以外は、実施例1と同様にして多層樹脂粒子を製造した。この多層樹脂粒子を用い、一段発泡工程において、発泡条件を表3に示すように変更し、嵩倍率35.9倍の発泡粒子を製造した点を除いて、実施例1と同様にして発泡粒子(つまり、一段発泡粒子)を製造した。二段発泡工程は行っていない。また、この一段発泡粒子を用いて、実施例1と同様にして成形体を得た。
本例は、一段発泡粒子を用いて密度の大きな成形体を作製した例である。具体的には、まず、芯層形成用押出機、被覆層形成用押出機に配合するカーボンブラックの配合量を表3に示すように変更した以外は、実施例1と同様にして多層樹脂粒子を製造した。一段発泡工程の条件を表3に示すよう変更したこと、芯層及び被覆層におけるカーボンブラックの配合量を表3に示す割合としたこと以外は、以外は、実施例1と同様にして多層樹脂粒子を作製した。この多層樹脂粒子を用い、一段発泡工程において、発泡条件を表3に示すように変更し、嵩倍率20.0倍の発泡粒子を製造した点を除いて、実施例1と同様にして発泡粒子(つまり、一段発泡粒子)を製造した。二段発泡工程は行っていない。また、この一段発泡粒子を用いて、実施例1と同様にして成形体を得た。
本例は、嵩倍率の比M2/M1が大きすぎる例である。具体的には、一段発泡工程の条件を表3に示すよう変更し、一段発泡粒子の嵩倍率M1を10.1倍とした以外は実施例1と同様にして一段発泡粒子を得た。この一段発泡粒子を用い、二段発泡工程の条件を表3に示すよう変更し、二段発泡粒子の嵩倍率M2を36.0倍とした以外は、実施例1と同様にして二段発泡粒子を製造した。二段発泡工程において、発泡粒子同士が互いに融着(ブロッキング)したため、成形工程は行わなかった。
本例は、貫通孔を有さない発泡粒子を用いた例である。具体的には、まず、芯層形成用押出機、被覆層形成用押出機に配合するカーボンブラックの配合量を表3に示すように変更したこと、貫通孔を有さない多層樹脂粒子としたこと以外は、実施例1と同様にして多層樹脂粒子を製造した。この多層樹脂粒子を用い、一段発泡工程の条件を表3に示すよう変更したこと以外は、実施例1と同様にして二段発泡粒子を製造した。また、この二段発泡粒子を用いて実施例1と同様にして成形体を得た。
本例は、密度の小さな成形体を作製した例である。一段発泡工程及び二段発泡工程の条件を表3に示すよう変更したこと以外は、実施例1と同様にして多層樹脂粒子を作製した。この多層樹脂粒子を用い、一段発泡工程において、発泡条件を表3に示すように変更し、嵩倍率44.8倍の発泡粒子を製造した点を除いて、実施例1と同様にして発泡粒子(つまり、一段発泡粒子)を製造した。二段発泡工程は行っていない。また、この一段発泡粒子を用いて、実施例1と同様にして成形体を得た。
図6(b)に示すように、実施例1の黒色の成形体は、色が濃く、色むらも目立たないことがわかる。他の実施例でも、実施例1と遜色ない程度の色の濃さであり、色むらも目立たなかった。また、実施例1~6によれば、独立気泡率の高い発泡粒子が得られる。なお、実施例1~6では、二段発泡工程におけるブロッキングも生じなかった。実施例1と実施例2との対比により、一段発泡粒子の嵩倍率M1に対する二段発泡粒子の嵩倍率M2の比M2/M1が1.8以上である場合には、より黒色の濃い成形体を製造可能であった。
Claims (10)
- 貫通孔を有する筒形状のポリプロピレン系樹脂発泡粒子を製造する方法であって、
密閉容器内において、分散媒に分散させたポリプロピレン系樹脂粒子に無機物理発泡剤を含浸させ、上記樹脂粒子を分散媒と共に上記密閉容器から上記密閉容器内よりも低圧下に放出することにより、嵩倍率M1倍の一段発泡粒子を得る一段発泡工程と、
上記一段発泡粒子の気泡内の圧力を上昇させた後、上記一段発泡粒子を加熱することにより、上記一段発泡粒子をさらに発泡させて嵩倍率M2倍の上記ポリプロピレン系樹脂発泡粒子を得る二段発泡工程と、を有し、
上記樹脂粒子が貫通孔を有する筒形状であり、上記樹脂粒子はカーボンブラックを含み、上記樹脂粒子中のカーボンブラックの含有量が0.1重量%以上5重量%以下であり、
上記一段発泡粒子の嵩倍率M1が5倍以上25倍以下であり、
上記一段発泡粒子の嵩倍率M1に対する上記ポリプロピレン系樹脂発泡粒子の嵩倍率M2の比M2/M1が、1.2以上3.0以下である、ポリプロピレン系樹脂発泡粒子の製造方法。 - 上記ポリプロピレン系樹脂発泡粒子の嵩倍率M2が10倍以上75倍以下である、請求項1に記載のポリプロピレン系樹脂発泡粒子の製造方法。
- 上記一段発泡粒子の嵩倍率M1に対する上記ポリプロピレン系樹脂発泡粒子の嵩倍率M2の比M2/M1が1.8以上2.5以下である、請求項1又は2に記載のポリプロピレン系樹脂発泡粒子の製造方法。
- 上記一段発泡粒子の貫通孔の貫通方向に対する垂直断面において、貫通孔の円形度が0.90以上である、請求項1~3のいずれか1項に記載のポリプロピレン系樹脂発泡粒子の製造方法。
- 上記一段発泡工程において、上記ポリプロピレン系樹脂粒子を放出する雰囲気の温度Tuが80℃未満である、請求項1~4のいずれか1項に記載のポリプロピレン系樹脂発泡粒子の製造方法。
- 上記ポリプロピレン系樹脂発泡粒子は、上記ポリプロピレン系樹脂発泡粒子を構成するポリプロピレン系樹脂の融点Tmcよりも低い融点Tmsを示すポリオレフィン系樹脂から構成された被覆層を有する多層構造の発泡粒子である、請求項1~5のいずれか1項に記載のポリプロピレン系樹脂発泡粒子の製造方法。
- 上記ポリプロピレン系樹脂発泡粒子の上記貫通孔の平均孔径dが1mm未満であるとともに、上記ポリプロピレン系樹脂発泡粒子の平均外径Dに対する上記平均孔径dの比d/Dが0.4以下である、請求項1~6のいずれか1項に記載のポリプロピレン系樹脂発泡粒子の製造方法。
- 上記ポリプロピレン系樹脂発泡粒子の平均外径Dが2mm以上5mm以下であるとともに、平均肉厚tが1.2mm以上2mm以下である、請求項1~7のいずれか1項に記載のポリプロピレン系樹脂発泡粒子の製造方法。
- 上記ポリプロピレン系樹脂発泡粒子の嵩倍率M2が30倍を超え75倍以下である、請求項1~8のいずれか1項に記載のポリプロピレン系樹脂発泡粒子の製造方法。
- 請求項1~9のいずれか1項に記載の製造方法により得られる上記ポリプロピレン系樹脂発泡粒子を成形型内に充填し、加熱媒体を供給して上記ポリプロピレン系樹脂発泡粒子を相互に融着させる、発泡粒子成形体の製造方法。
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JP2015143046A (ja) | 2014-01-31 | 2015-08-06 | 株式会社ジェイエスピー | 自動車用物品収納部材 |
WO2016027892A1 (ja) * | 2014-08-21 | 2016-02-25 | 株式会社カネカ | 防汚染性および成形性に優れる導電性ポリプロピレン系樹脂発泡粒子およびポリプロピレン系樹脂発泡粒子の製造方法およびポリプロピレン系樹脂発泡成形体 |
WO2016060162A1 (ja) * | 2014-10-15 | 2016-04-21 | 株式会社カネカ | ポリプロピレン系樹脂発泡粒子、ポリプロピレン系樹脂型内発泡成形体およびその製造方法 |
JP2018162369A (ja) * | 2017-03-24 | 2018-10-18 | 株式会社カネカ | ポリプロピレン系樹脂黒色発泡粒子の製造方法 |
WO2021157369A1 (ja) * | 2020-02-04 | 2021-08-12 | 株式会社ジェイエスピー | ポリプロピレン系樹脂発泡粒子、及びポリプロピレン系樹脂発泡粒子成形体 |
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