WO2022191316A1 - ポリプロピレン系樹脂発泡粒子の製造方法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の製造方法及び発泡粒子成形体の製造方法 Download PDFInfo
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- WO2022191316A1 WO2022191316A1 PCT/JP2022/010913 JP2022010913W WO2022191316A1 WO 2022191316 A1 WO2022191316 A1 WO 2022191316A1 JP 2022010913 W JP2022010913 W JP 2022010913W WO 2022191316 A1 WO2022191316 A1 WO 2022191316A1
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- polypropylene
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Definitions
- the present invention relates to a method for producing expanded polypropylene resin particles and a method for producing an expanded particle molded product.
- Expanded particle molded articles made of expanded polypropylene resin particles are lightweight and have excellent cushioning properties, rigidity, etc., and are used in various applications.
- the expanded bead molded product is produced by, for example, a method called an in-mold molding method, in which polypropylene-based resin expanded beads are filled into a mold and then heated by supplying a heating medium such as steam into the mold.
- a heating medium such as steam into the mold.
- the foamed particles undergo secondary foaming and their surfaces melt.
- the foamed particles in the mold are fused together, and a molded article having a shape corresponding to the shape of the cavity of the mold can be obtained. Since the molded article immediately after molding tends to swell due to secondary foaming, it is released from the molding die after being cooled with water, air, or the like in the molding die.
- the expanded polypropylene resin particles used for the production of expanded bead molded products are obtained by impregnating polypropylene resin particles dispersed in a dispersion medium in a closed container with an inorganic physical blowing agent, and then placing the resin particles together with the dispersion medium in a closed container. It is often manufactured by a method of releasing to a lower pressure environment than a closed container. Such a foaming method is sometimes called a direct foaming method.
- Patent Document 1 polypropylene resin colored particles to which a coloring pigment is added are expanded by a direct expansion method to produce expanded beads, and then the expanded beads are molded in a mold to form polypropylene resin colored expanded particles.
- a method of making a body is described. Carbon black is sometimes used as a coloring pigment to be added to the polypropylene-based resin colored particles from the viewpoint of imparting a high-class feeling to the molded article.
- the present invention has been made in view of such a background, and manufactures polypropylene-based resin expanded beads capable of forming good expanded bead molded articles with excellent filling properties of expanded beads, high degree of blackness, and inconspicuous color unevenness. 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 core layer in which a polypropylene-based resin is used as a base resin, and 0.1 parts by mass or more and less than 5 parts by mass of carbon black is blended with respect to 100 parts by mass of the polypropylene-based resin, and a polyolefin-based resin is used as a base resin, and 0.1 parts by mass or more and less than 5 parts by mass of carbon black is blended with respect to 100 parts by mass of the polyolefin resin, and a coating layer that covers the core layer
- Polypropylene resin particles comprising A dispersion step of dispersing in a dispersion medium; After impregnating the polypropylene-based resin particles in the dispersion medium with the inorganic physical blowing agent in a closed container, the polypropylene-based resin particles are transferred from the closed container together with the dispersion medium into an atmosphere having a pressure lower than that in the closed container.
- a heating medium is supplied into the mold to The present invention relates to a method for producing an expanded bead molded article in which the expanded bead molded article is produced by performing inner molding.
- a method for producing expanded polypropylene resin particles capable of forming a favorable expanded bead molded article having excellent filling properties of expanded particles, a high degree of blackness, and inconspicuous color unevenness, and the polypropylene resin. It is possible to provide a method for producing an expanded bead molding using expanded beads.
- FIG. 1 is an explanatory diagram showing a method of calculating a high-temperature peak heat quantity.
- the method for producing the expanded polypropylene resin particles comprises adding the specific polypropylene resin particles (hereinafter referred to as “resin particles”) to the dispersion medium, as described above. ), a one -stage expansion step of expanding the core layer of the resin particles so that the bulk ratio M1 is 5 times or more and 25 times or less to obtain single-stage expanded beads, and
- the two-stage expanded particles are obtained by expanding such that 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 1.2 or more and 3.0 or less.
- molded article a lightweight foamed bead molded article having excellent surface properties, high blackness, and inconspicuous color unevenness.
- a core layer having a polypropylene-based resin as a base resin and a coating layer covering the core layer are provided, and the core layer and the coating layer are mixed with a predetermined amount of carbon black as a black colorant. Particles are used. If the resin particles do not have a coating layer, it may be difficult to mold the expanded beads at a low molding temperature. Moreover, in this case, the filling property of the expanded beads may be lowered, and depending on the molding conditions, the surface properties of the expanded bead molded article may be lowered.
- the amount of carbon black compounded in the core layer is 0.1 parts by mass or more and less than 5 parts by mass with respect to 100 parts by mass of the polypropylene resin. Moreover, the amount of carbon black compounded in the coating layer is 0.1 parts by mass or more and less than 5 parts by mass with respect to 100 parts by mass of the polyolefin resin.
- the content of carbon black in the core layer is 0.1 parts by mass or more, preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and still more preferably 2.0 parts by mass or more based on 100 parts by mass of the polypropylene resin.
- the content of carbon black in the core layer is less than 5.0 parts by mass, preferably 4.5 parts by mass or less, more preferably 4.0 parts by mass or less, and still more preferably 3.0 parts by mass or less per 100 parts by mass of the polypropylene resin.
- the amount of carbon black to be blended in the coating layer is 0.1 parts by mass or more, preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and still more preferably 2.5 parts by mass or more based on 100 parts by mass of the polyolefin resin.
- the amount of carbon black blended into the coating layer is less than 5.0 parts by mass, preferably 4.5 parts by mass or less, more preferably 4.0 parts by mass or less, and still more preferably 3.0 parts by mass or less per 100 parts by mass of the polyolefin resin.
- carbon black is a resin component that constitutes the coating layer. It is preferred that they are evenly dispersed throughout.
- the amount of carbon black blended into the coating layer and the amount of carbon black blended into the core layer be approximately the same. More specifically, the mass ratio of the amount of carbon black blended in the coating layer to the amount of carbon black blended in the core layer is preferably 0.8 or more and 1.2 or less, more preferably 0.9 or more and 1.2. It is preferably 1 or less, and most preferably 1, that is, the amount of carbon black blended in the core layer is equal to the amount of carbon black blended in the coating layer.
- the carbon black blended in the core layer and the coating layer of the foamed particles is a black coloring agent, and as described above, the effect can be exhibited with a relatively small blending amount. It is a material different from the others. Furthermore, by setting the amount of carbon black in the coating layer to 0.1 parts by mass or more and less than 5 parts by mass with respect to 100 parts by mass of the polyolefin resin, the foamed particles can be filled while maintaining good moldability. You can get the boost effect.
- 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.
- the dibutyl phthalate (that is, DBP) oil absorption of the carbon black is preferably less than 150 mL/100 g, more preferably 140 mL/100 g or less, even more preferably 130 mL/100 g or less, and 120 mL/100 g. It is particularly preferably 110 mL/100 g or less, most preferably 110 mL/100 g or less.
- DBP oil absorption is a value measured according to ASTM D2414-79.
- the BET specific surface area of the carbon black is preferably 200 m 2 /g or less, more preferably 150 m 2 /g or less, and even more preferably 100 m 2 /g or less. By using such carbon black, it is possible to more easily obtain expanded beads having a desired degree of blackness and excellent filling properties.
- the BET specific surface area of carbon black is a value measured by the BET method according to ASTM D-3037.
- the core layer of the resin particles is expanded such that the bulk ratio M1 of the first -stage expanded particles is 5 times or more and 25 times or less.
- the core layer of the resin particles is mainly expanded to form a foam layer, thereby improving the filling property of the expanded particles and the blackness of the finally obtained expanded particle molded product, thereby reducing variations in color tone. be able to.
- the coating layer is in a foamed state, there is a possibility that the effects described above may be impaired. Therefore, it is preferred that the coating layer is not substantially foamed in the one-step foaming step.
- the single-stage expanded beads obtained by the single-stage expansion process consist of a foamed layer containing a polypropylene-based resin as a base resin, a foamed layer containing the specific amount of carbon black, and a non-foamed layer covering the foamed layer.
- a base resin of the coating layer is a polyolefin-based resin, and the specific amount of carbon black is added to the coating layer.
- the above-mentioned "non-foaming state" includes a state in which the coating layer is not foamed and contains no bubbles, and a state in which the bubbles disappear after foaming, and means that there is almost no cell structure in the coating layer. do.
- the bulk magnification ratio M 2 /M 1 is too low, it becomes difficult to obtain the effect of foaming the resin particles in two stages. As a result, the degree of blackness of the expanded beads may be lowered and the variation in color tone may be increased.
- These problems can be easily avoided by setting the bulk magnification ratio M 2 /M 1 to 1.2 or more, preferably 1.4 or more, more preferably 1.8 or more, and further preferably 2.0 or more. be able to.
- the bulk ratio M 1 of the first-stage expanded particles is the density (unit: kg/m 3 ) of the polypropylene-based resin forming the expanded layer of the first-stage expanded particles, that is, the layer formed by expanding the core layer of the resin particles. It is a value divided by the bulk density (unit: kg/m 3 ).
- the bulk ratio M 2 of the expanded beads is the density (unit: kg/m 3 ) of the polypropylene-based resin constituting the expanded layer of the expanded beads, that is, the layer corresponding to the core layer of the resin particles. It is a value divided by (unit: kg/m 3 ). A method for measuring the bulk density of the single-stage expanded beads and the expanded beads will be 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 ratio of the expanded beads obtained in each foaming process is adjusted within the above-mentioned predetermined range.
- expanded beads are produced.
- the 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.
- expanded bead molded articles produced using expanded polypropylene resin particles produced by a direct expansion method tended to have a lower degree of blackness and tended to have more conspicuous color unevenness. This tendency was particularly remarkable when foaming to a desired bulk ratio in a single foaming.
- One of the reasons for this is considered to be that while a large number of bubbles are formed during foaming, the number of bubbles near the surface of the expanded bead is strongly affected by cooling, resulting in an excessive increase in the number of bubbles near the surface.
- the bulk ratio 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 of the expanded particles.
- M2 can be increased to a desired magnification within a range in which the relationship with the bulk magnification M1 satisfies the above specific relationship.
- the above manufacturing method can produce expanded beads with a high degree of blackness and a small variation in color tone.
- the bulk ratio M 1 is made smaller, and the bulk ratio ratio M 2 /M 1 is made larger in the two-stage 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 ratio M 2 /M 1 of 1.8 or more and 3.0 or less.
- the obtained volume can be compared with the case where the expanded beads are expanded to a desired bulk ratio by one expansion, for example.
- the filling properties of the foamed particles are enhanced.
- the reason why such an effect is obtained is not clear at the present time, for example, the non-foamed coating layer containing the specific amount of carbon black improves the fluidity of the expanded particles, or the above two-step A possible reason for this is that the irregularities of the foamed particles change during the foaming step.
- the polypropylene-based resin particles are dispersed in a dispersion medium.
- the core layer of the resin particles is composed of polypropylene resin.
- the polypropylene-based resin mentioned above 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, propylene-butene 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 core layer may contain a plurality of types of polypropylene-based resins.
- the polypropylene-based resin constituting the core layer is any one of ethylene-propylene random copolymer, ethylene-propylene-butene random copolymer, and propylene-butene copolymer. is preferably
- the core layer may contain a polymer other than the polypropylene-based resin within a range that does not impair the effects described above.
- 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 core layer is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and 0% by mass, that is, It is particularly preferred that the core layer contains substantially only a polypropylene-based resin as a polymer.
- the polypropylene resin constituting the core layer is an ethylene-propylene random copolymer, and the content of the ethylene component in the copolymer is preferably 0.5% by mass or more and 5.0% by mass or less.
- Such expanded particles obtained by expanding resin particles can increase the rigidity of a molded article and form a molded article having good surface properties at a lower molding temperature.
- 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 more preferably 4.5% by mass or less, further preferably 4.0% by mass or less. 0.5% by mass or less is particularly preferred.
- the content of the ethylene component in the copolymer is preferably 0.5% by mass or more from the viewpoint of suppressing an excessive increase in the molding pressure of the expanded beads.
- the content of the ethylene component in the copolymer should be 1.0% by mass or more. is more preferably 1.2% by mass or more, even more preferably 1.5% by mass or more, and particularly preferably more than 2.0% by mass.
- the polypropylene resin that is the base resin of the core layer is ethylene-propylene-butene. It is a polymer or a propylene-butene copolymer, and the butene component content in these copolymers is more preferably 2% by mass or more and 15% by mass or less, and more preferably 5% by mass or more and 12% by mass or less. is more preferred.
- the polypropylene resin that is the base resin of the core layer is an ethylene-propylene-butene copolymer, and the total amount of the butene component content and the ethylene component content in the copolymer is 2. It is preferably not less than 15% by mass and the mass ratio of the butene component content to the ethylene component content (butene component content/ethylene component content) is preferably 0.5 or more.
- the mass ratio of the butene component content to the ethylene component content (butene component content/ethylene component content) is preferably 2 or more, more preferably 5 or more, and still more preferably 10 or more.
- the upper limit is preferably 30, more preferably 20.
- the total of the butene component content, ethylene component content, and propylene component content in the copolymer is defined as 100% by mass.
- the content of the monomer component in the copolymer can be determined by IR spectrum measurement.
- the ethylene component, propylene component and butene component in the copolymer mean ethylene-derived structural units, propylene-derived structural units and butene-derived structural units in the copolymer, respectively.
- the content of each monomer component in the copolymer means the content of structural units derived from each monomer in the copolymer.
- 0.1 parts by mass or more and less than 5 parts by mass of carbon black is added to the polypropylene resin forming the core layer based on 100 parts by mass of the polypropylene resin.
- Polypropylene resins contain cell modifiers, crystal nucleating agents, flame retardants, flame retardant aids, plasticizers, antistatic agents, antioxidants, UV inhibitors, light stabilizers, as long as they do not impair the effects described above. Additives such as agents and antibacterial agents may also be included.
- the content of the additive in the core layer is preferably, for example, 0.01 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the polypropylene resin.
- one or more metal borate salts selected from zinc borate and magnesium borate are contained as a cell control agent in the polypropylene-based resin that constitutes the core layer.
- the above-mentioned zinc borate is a general term for metal salts containing boron and zinc that bond with oxygen.
- Examples of zinc borate include zinc metaborate [Zn(BO 2 ) 2 ] and basic zinc borate [ZnB 4 O 7.2ZnO ].
- Examples of zinc borate include those represented by chemical formulas such as 2ZnO.3B 2 O 3.3.5H 2 O and 3ZnO.2B 2 O 3.5H 2 O, but are limited to these. not.
- Magnesium borate is a general term for metal salts containing boron and magnesium that bind to oxygen.
- Examples of magnesium borate include magnesium orthoborate [Mg 3 (BO 3 ) 2 ], magnesium diborate, magnesium pyroborate [(Mg 2 B 2 O 5 ) or (2MgO.B 2 O 3 )], metaboron magnesium acid [MgO.B 2 O 3 ], trimagnesium tetraborate [(Mg 3 B 4 O 9 ) or (3MgO.2B 2 O 3 )], pentamagnesium tetraborate [Mg 5 B 4 O 11 ], magnesium hexaborate [MgB 6 O 10 ], and the like.
- magnesium borate examples include 2MgO.3B 2 O 3.nH 2 O (where n is a positive integer), MgO.4B 2 O 3.3H 2 O, and MgO.6B 2 O 3.18H 2 Examples include, but are not limited to, those represented by chemical formulas such as O.
- zinc borate represented by a chemical formula such as 2ZnO.3B 2 O 3.3.5H 2 O and 3ZnO.2B 2 O 3.5H 2 O is particularly preferred.
- the number-based arithmetic mean particle size of the metal borate (hereinafter also simply referred to as the average particle size) is 1 ⁇ m or more, and the number ratio of particles with a particle size of 5 ⁇ m or more in the metal borate is 20% or less.
- the number-based arithmetic mean particle diameter of the metal borate is within the above range and the particle size distribution is within the above range, the foamed particles have more excellent cell uniformity and less color unevenness. It is possible to obtain an expanded bead molded article with a good appearance.
- the average particle size of the metal borate is preferably 1 ⁇ m or more and 5 ⁇ m or less, and more preferably 1.5 ⁇ m or more, because it is possible to suppress the aggregation of the metal borate and improve the uniformity of the foamed particles. It is more preferably 4 ⁇ m or less, and further preferably 2 ⁇ m or more and 3 ⁇ m or less.
- the number-based proportion of the metal borate particles having a particle diameter of 5 ⁇ m or more is more preferably 15% or less, and still more preferably 12% or less, because it is possible to further suppress the variation in air bubbles of the expanded particles. is.
- the number-based particle size distribution can be obtained by assuming that the shape of the particles is spherical and converting to the number-based particle size distribution. By arithmetically averaging the particle sizes based on the number-based particle size distribution, the number-based arithmetic mean particle size can be obtained. Also, the number ratio of particles having a particle diameter of 5 ⁇ m or more can be obtained from the number-based particle size distribution.
- the particle size means the diameter of a phantom sphere having the same volume as the particle.
- the content of the metal borate is preferably 0.001% by mass or more and 3% by mass or less with respect to 100 parts by mass of the polypropylene-based resin constituting the core layer.
- the content of the borate metal salt in the resin particles is 0.001% by mass or more, the resin particles act more effectively as a cell regulator, and the expanded particles have a more uniform cell structure.
- the content of the metal borate in the resin particles is 3% by mass or less, it is possible to suppress excessive fineness of the cells of the expanded particles.
- the content of the metal borate in the resin particles is 0.01% by mass or more and 1% by mass or less with respect to 100 parts by mass of the polypropylene resin constituting the core layer. It is preferably 0.03% by mass or more and 0.5% by mass or less, more preferably.
- the melting point Tmc of the polypropylene-based resin forming the core layer is preferably 158°C or less.
- the melting point Tmc of the polypropylene-based resin constituting the core layer is preferably 155° C. or lower, more preferably 150° C. or lower.
- the melting point Tmc of the polypropylene resin constituting the core layer is preferably 135° C. or higher, more preferably 138° C. or higher. More preferably, the temperature is 140° C. or higher.
- the melting point of polypropylene-based resin is determined based on JIS K7121:1987. Specifically, first, a test piece made of polypropylene resin is prepared, and the test piece is adjusted according to "(2) When measuring the melting temperature after performing a certain heat treatment" in JIS K7121: 1987. I do. Both the heating rate and the cooling rate in conditioning are 10° C./min. A DSC curve is obtained by heating the conditioned test piece from 30° C. to 200° C. at a heating rate of 10° C./min. 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 Tmc.
- the melt mass flow rate (that is, MFR) of the polypropylene resin constituting the core layer is preferably 5 g/10 minutes or more, more preferably 6 g/10 minutes or more, and 7 g/10 minutes or more. More preferred. In this case, the expandability and moldability of the expanded beads can be further enhanced.
- 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 core layer is preferably 800 MPa or more and 1600 MPa or less.
- the bending elastic modulus of the polypropylene-based resin constituting the core layer is preferably 850 MPa or more, more preferably 900 MPa or more, and even more preferably 950 MPa or more.
- the bending elastic modulus of the polypropylene-based resin forming the core layer is preferably 1600 MPa or less.
- the bending elastic modulus of the polypropylene-based resin constituting the core layer is 1550 MPa or less. It is preferably 1500 MPa or less, more preferably less than 1200 MPa.
- the flexural modulus of polypropylene resin can be obtained based on JIS K7171:2008.
- the core layer of the resin particles is covered with a coating layer.
- the coating layer may cover the entire surface of the core layer, or may cover a portion of the surface of the core layer. From the viewpoint of obtaining the above effects more reliably, the coating layer preferably covers 50% or more, more preferably 60% or more, of the surface area of 100% of the resin particles. , more preferably 70% or more.
- the resin particles may have a multi-layered structure including a columnar core layer and a coating layer covering the side peripheral surface of the core layer.
- the mass ratio of the coating layer to the total mass of the core layer and the coating layer is preferably 0.5% or more and 20% or less, and 1% or more and 15% or less. more preferably 3% or more and 10% or less. In this case, it is possible to more easily obtain expanded beads having a high degree of blackness, a small variation in color tone, and excellent filling properties.
- polyolefin-based resins that make up the coating layer include polyethylene-based resins, polypropylene-based resins, and polybutene-based resins.
- the polyolefin-based resin constituting the coating layer is preferably a polyethylene-based resin or a polypropylene-based resin, and more preferably a polypropylene-based resin.
- polypropylene-based resins include ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-propylene-butene copolymers, and propylene homopolymers.
- the content of the polypropylene-based resin in the coating layer is preferably 95% by mass or more, more preferably 97% by mass or more, from the viewpoint that the carbon black is easily dispersed well without being unevenly distributed in the coating layer. It is more preferably 99% by mass or more, particularly preferably more than 99.5% by mass, and most preferably 100% by mass, that is, the polyolefin-based resin constituting the coating layer consists only of polypropylene-based resin.
- the coating layer may contain a polymer other than the polyolefin resin as long as it does not impair the effects described above.
- examples of other polymers include thermoplastic resins other than polyolefin resins such as polystyrene resins, elastomers, and the like.
- the content of the other polymer in the coating layer is preferably 20% by mass or less, more preferably 10% by mass or less, from the viewpoint that carbon black is easily dispersed well without being unevenly distributed in the coating layer. It is preferably 5% by mass or less, particularly preferably less than 0.5% by mass, and 0% by mass, that is, the coating layer may contain substantially only the polyolefin resin as the polymer. Most preferred.
- 0.1 parts by mass or more and less than 5 parts by mass of carbon black is added to 100 parts by mass of the polyolefin resin in the polyolefin resin constituting the coating layer.
- the polyolefin resin contains crystal nucleating agents, flame retardants, flame retardant aids, plasticizers, antistatic agents, antioxidants, UV inhibitors, light stabilizers, and antibacterial agents, as long as they do not impair the effects described above. Additives such as may be included.
- the content of the additive in the coating layer is preferably, for example, 0.01 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the polyolefin resin.
- the polyolefin resin particles constituting the coating layer contain silica particles and higher fatty acid amide, and the total content of the silica particles and the higher fatty acid amide in the coating layer is 0. It is preferable that it is 05 mass % or more and 3 mass % or less. In this case, it is possible to prevent deposits derived from the expanded particles from accumulating in the mold during in-mold molding, and to obtain an expanded bead molded article with superior surface properties. From the viewpoint of further enhancing this effect, the total content of the silica particles and the higher fatty acid amide content in the coating layer is more preferably 0.1% by mass or more and 2% by mass or less, and more preferably 0.2% by mass. More preferably, the content is 1% by mass or less.
- the mass ratio of the silica particles and the higher fatty acid amide in the polyolefin resin particles constituting the coating layer is preferably 1:0.2 to 1:8, preferably 1:0. .8 to 1:6 is more preferred, and 1:1 to 1:5 is even more preferred.
- higher fatty acid amide means a fatty acid amide having a hydrocarbon group with 12 or more carbon atoms.
- Specific examples of higher fatty acid amides include saturated fatty acid amides such as lauric acid amide, palmitic acid amide, stearic acid amide and behenic acid amide; and unsaturated fatty acid amides such as oleic acid amide, erucic acid amide and nervonic acid amide. mentioned.
- the melting point Tms of the polyolefin resin forming the coating layer is preferably 120°C or higher and 145°C or lower, more preferably 125°C or higher and 140°C or lower.
- the melting point Tms of the polyolefin-based resin forming the coating layer is preferably lower than the melting point Tmc of the polypropylene-based resin forming the core layer.
- the difference Tmc ⁇ Tms between the melting point Tmc of the polypropylene resin and the melting point Tms of the polyolefin resin is preferably 5° C. or more, more preferably 6° C. or more, and 8° C. It is more preferable that it is above.
- the difference Tmc ⁇ Tms between the melting point Tmc of the polypropylene resin and the melting point Tms of the polyolefin resin is 35. °C or less, more preferably 20°C or less, and even more preferably 15°C or less.
- the method for measuring the melting point of the polyolefin resin constituting the coating layer is the same as that of the polypropylene resin constituting the foam layer described above, except that the test piece made of polyolefin resin is used instead of the test piece made of polypropylene resin. It is the same as the method for measuring the melting point. However, when a plurality of melting peaks appear in the DSC curve, the apex temperature of the melting peak on the lowest temperature side is taken as the melting point Tms.
- the MFR of the polyolefin resin constituting the coating layer is preferably about the same as the MFR of the polypropylene resin constituting the core layer, specifically, preferably 2 g/10 min or more and 15 g/10 min or less. , 3 g/10 min or more and 12 g/10 min or less, and more preferably 4 g/10 min or more and 10 g/10 min or less. According to the foamed particles obtained by foaming such resin particles, it is possible to reliably suppress separation between the foamed layer and the coating layer.
- 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.
- resin particles for example, a coextrusion device equipped with a core layer forming extruder, a coating layer forming extruder, and a coextrusion die connected to these two extruders may be used.
- Resin particles can be produced, for example, by a strand cut method.
- a polypropylene resin for forming the core layer, carbon black, and optional additives are melt-kneaded to form a melt-kneaded product for forming the core layer. to make.
- the polyolefin resin for forming the coating layer, carbon black, and optional additives are melt-kneaded to prepare a melt-kneaded product for forming the coating layer.
- These melt-kneaded materials are co-extruded and combined in a die to form a multi-layer composite composed of a non-foamed columnar core layer and a non-foamed coating layer covering the outer surface of the core layer.
- the extrudate is cooled by passing it through a water bath. Resin particles can then be obtained by cutting the extrudate to a desired length.
- the method for producing the resin particles is not limited to the method described above, and a hot cutting method, an underwater cutting method, or the like may be employed.
- the resin particles are dispersed in the dispersion medium by stirring after putting the resin particles into the dispersion medium.
- the dispersing step may be performed in a closed container used in the one-step foaming step to be performed later, or may be performed in a container different from the closed container used in the one-step foaming step. From the viewpoint of simplification of the manufacturing process, it is preferable to carry out the dispersing process in a closed container used in the one-stage foaming process.
- an aqueous dispersion medium containing water as a main component is used as the dispersion medium.
- the aqueous dispersion medium may contain hydrophilic organic solvents such as ethylene glycol, glycerin, methanol and ethanol.
- 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.
- a dispersant to the dispersion medium.
- a dispersant By adding a dispersant to the dispersion medium, it is possible to suppress the fusion between the resin particles heated in the container in the one-stage expansion step.
- the amount of the dispersant added is preferably 0.001 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the resin particles.
- the dispersing agent an organic dispersing agent or an inorganic dispersing agent can be used, but it is preferable to use a fine particulate inorganic material as the dispersing agent because of ease of handling.
- the dispersant includes, for example, clay minerals such as amsnite, kaolin, mica, and clay, aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide, and the like. can be used. These dispersants may be used alone, or two or more dispersants may be used in combination. Among these, it is preferable to use a clay mineral as a dispersant. Clay minerals may be natural or synthetic.
- an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylbenzenesulfonate, sodium laurylsulfate, and sodium oleate together as a dispersing aid.
- the amount of the dispersion aid added is preferably 0.001 parts by mass or more and 1 part by mass or less 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 container.
- Carbon dioxide, air, nitrogen, helium, argon and the like can be used as the inorganic physical foaming agent for foaming the resin particles.
- Carbon dioxide is preferably used from the viewpoint of environmental load and handling.
- the amount of the foaming agent to be added is preferably 0.1 parts by mass or more and 30 parts by mass or less, and preferably 0.5 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the resin particles.
- the foaming agent is supplied into a closed vessel, and the pressure inside the closed vessel is increased to impregnate the resin particles in the dispersion medium with the foaming agent.
- the pressure inside the closed vessel is increased to impregnate the resin particles in the dispersion medium with the foaming agent.
- the impregnation of the foaming agent into the resin particles can be further promoted.
- the pressure inside the sealed container during foaming is preferably 0.5 MPa (G) or more in terms of gauge pressure.
- the pressure in the sealed container is preferably 4.0 MPa (G) or less in gauge pressure.
- the temperature during foaming can be kept within an appropriate range.
- the temperature Tu of the atmosphere in which the resin particles are released can be adjusted to a low temperature.
- the temperature Tu of the atmosphere in which the resin particles are emitted is preferably less than 80°C, more preferably 75°C or less.
- the temperature Tu of the atmosphere in which the resin particles are released is low, the blackness of the obtained expanded particles tends to be low, making it difficult to obtain a lightweight molded article with a high degree of blackness.
- the manufacturing method even when the temperature Tu of the atmosphere in which the resin particles are emitted is adjusted to a low temperature of, for example, less than 80° C., the blackness of the finally obtained molded body is increased. be able to.
- 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 core layer of the resin particles and the resin particles are released.
- the difference [Tmc ⁇ Tu] from the temperature Tu of the atmosphere is preferably 65° C. or more and 85° C. or less.
- the resin particles are heated when the foaming agent is impregnated, it is preferable to heat and foam in the following manner. That is, first, (melting point of polypropylene resin ⁇ 20° C.) or higher and below (melting end temperature of polypropylene resin) is performed for a sufficient time, preferably about 10 to 60 minutes, for a one-stage holding step. 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.
- the temperature inside the closed container is set to (the melting point of the polypropylene-based resin -10°C) or higher to expand the resin particles. It is more preferable that the temperature in the sealed container during foaming is from (the melting point of the polypropylene resin) to (the melting point of the polypropylene resin +20° C.) or less.
- the reason why the mechanical strength and moldability of the expanded beads can be improved by heating and foaming under the above-mentioned conditions is thought to be the formation of secondary crystals in the polypropylene resin that constitutes the core layer. Whether or not secondary crystals are formed in the polypropylene resin can be judged by the presence or absence of a high temperature peak in the DSC curve. A method for determining whether or not there is a high temperature peak will be described later.
- 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 bulk ratio M1 of the first -stage expanded particles is, for example, the type of base resin of the core layer, the amount of foaming agent added in the first-stage expansion process, the temperature at the time of foaming, the temperature of the atmosphere in which the contents are released from the closed container, and the temperature of the closed container. It can be adjusted by the pressure difference between the internal pressure and the pressure of the environment where the contents are released from the sealed container.
- the bulk ratio M1 of the first -stage expanded particles is a value obtained by dividing the density (unit: kg/m 3 ) of the polypropylene-based resin constituting the core layer of the resin particles by the bulk density (unit: kg/m 3 ) of the first-stage expanded particles. is.
- a method for calculating the bulk density of the single-stage expanded particles is as follows. First, the single-stage expanded beads are allowed to stand in an environment of 50% relative humidity, 23° C. temperature, and 1 atm pressure for 24 hours or longer to adjust the state of the single-stage expanded beads.
- the single-stage expanded particles after the condition adjustment are filled into a graduated cylinder so that they naturally accumulate, and the bulk volume (unit: L) of the single-stage expanded particles is read from the scale of the graduated cylinder. Then, the bulk density (unit: kg/m 3 ) of the single-stage expanded particles is obtained by converting the value obtained by dividing the mass (unit: g) of the group of the single-stage expanded particles in the graduated cylinder by the bulk volume described above. can be done.
- ⁇ Two-stage foaming process> In the two-step expansion process, first, internal pressure is applied to the first-step expanded beads. More specifically, after putting the single-stage expanded particles into a pressure container, the inside of the pressure-resistant container is pressurized with an inorganic gas such as air or carbon dioxide to impregnate the single-stage expanded particles with the inorganic gas. As a result, the pressure inside the cells of the single-stage expanded particles is made equal to or higher than the atmospheric pressure. After that, the single-stage expanded beads taken out from the pressure vessel are heated using a heating medium such as steam or heated air under an environment with a pressure lower than the pressure inside the cells, so that the single-stage expanded beads can be further expanded. As a result, it is possible to obtain expanded beads (two-stage expanded beads) having a bulk ratio of M2 and a bulk ratio M2 of 1.2 to 3.0 times as large as M1.
- an inorganic gas such as air or carbon dioxide
- the bulk ratio M2 of the expanded beads is, for example, the type of the base resin of the expanded layer of the first-step expanded beads, and the pressure difference between the pressure inside the cells in the first-step expanded beads to which internal pressure is applied and the pressure of the environment where the heating is performed. , heating temperature, heating time, and the like. A method for measuring the bulk ratio M2 of the expanded beads will be described later.
- the production method of the present invention by having a predetermined two-stage foaming process, while achieving an improvement in productivity in the one-stage foaming process, the filling property is excellent, and the blackness is high and the color unevenness is less noticeable. It is possible to obtain expanded particles capable of in-mold molding into particle compacts.
- the internal pressure applied to the first-step expanded beads is preferably atmospheric pressure or higher from the viewpoint of easily obtaining expanded beads having a desired bulk ratio M2 , and is 0.1 MPa (G ) or higher, more preferably 0.2 MPa (G) or higher, and even more preferably 0.3 MPa (G) or higher.
- the upper limit of the internal pressure applied to the single-stage expanded beads is approximately 1 MPa (G), preferably 0.8 MPa (G) or less.
- the heating time of the first-stage expanded particles in the two-stage expansion process is set to a range of 3 seconds or more and 60 seconds or less from the viewpoint of easily obtaining expanded particles having a desired bulk ratio M2 while suppressing blocking between the first-stage expanded particles. is preferred.
- the temperature of the heating medium is preferably in the range of 80°C or higher and 120°C or lower.
- the polypropylene-based resin expanded beads obtained as described above have a foamed layer having a polypropylene-based resin as a base material and a coating layer having a polyolefin-based resin as a base resin and covering the foamed layer.
- the foam layer contains 0.1 parts by mass or more and less than 5 parts by mass of carbon black with respect to 100 parts by mass of the polypropylene resin
- the coating layer contains 0.1 parts by mass or more and less than 5 parts by mass of carbon black.
- the expanded beads preferably do not have through-holes from the viewpoint of enhancing the appearance and rigidity of the resulting molded article.
- the polypropylene resin forming the foamed layer of the foamed particles is the same as the polypropylene resin forming the core layer of the resin particles, so the above description of the polypropylene resin can be appropriately referred to.
- the polyolefin resin forming the coating layer of the expanded particles is the same as the polyolefin resin forming the coating layer of the resin particles.
- the closed cell ratio of the expanded beads is preferably 88% or more, preferably 90% or more, and more preferably 95% or more. In this case, high in-mold moldability can be obtained more stably. Further, with such expanded beads, it is possible to easily obtain an expanded bead molded article having good surface properties and excellent rigidity.
- 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. First, the expanded beads are allowed to stand in an environment of 50% relative humidity, 23° C. temperature, and 1 atm pressure for 24 hours or longer to adjust the state of the expanded beads. After collecting a measurement sample so that the bulk volume of the foamed particles after conditioning, that is, the value of the marked line when naturally deposited in a graduated cylinder is about 20 cm 3 , the apparent volume of the measurement sample is measured. Measure. The apparent volume of the measurement sample is specifically the volume corresponding to the amount of rise in the liquid level when the measurement sample is submerged in a graduated cylinder containing ethanol at a temperature of 23°C.
- the true volume of the measurement sample measured by Accupic II 1340 manufactured by Shimadzu Corporation. measure the value. Then, using these volume values, the closed cell ratio of the measurement sample is calculated based on the following formula (1). The above operation is performed five times using different measurement samples, and the arithmetic average value of the closed cell ratios obtained by these five measurements is taken as the closed cell ratio of the expanded beads.
- Vx (unit: cm 3 ) in the above formula (1) is the true volume of the expanded bead (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).
- Va (unit: cm 3 ) is the apparent volume of the foamed bead (that is, the volume measured from the rise in liquid level when the foamed bead is submerged in a measuring cylinder containing ethanol)
- W (unit: : g) is the mass of the measurement sample
- ⁇ (unit: g/cm 3 ) is the density of the polypropylene resin forming the foam layer.
- the first DSC curve obtained when heated from 23 ° C. to 200 ° C. at a heating rate of 10 ° C./min shows an endothermic peak due to melting specific to the polypropylene resin constituting the foam layer, and an endothermic peak from this endothermic peak. It preferably has a crystal structure in which one or more melting peaks located on the high temperature side appear. Expanded beads having such a crystal structure are excellent in mechanical strength and moldability.
- the endothermic peak due to melting specific to the polypropylene resin appearing in the DSC curve is referred to as "resin specific peak”
- the melting peak appearing on the higher temperature side than the resin specific peak is referred to as "high temperature peak”.
- the resin-specific peak is generated by heat absorption when crystals inherent in the polypropylene-based resin forming the foam layer melt.
- the high-temperature peak is caused by the melting of secondary crystals formed in the polypropylene-based resin forming the foam layer during the manufacturing process of the expanded beads. That is, when a high-temperature peak appears in the DSC curve, it is presumed that secondary crystals are formed in the polypropylene-based resin.
- Whether or not the expanded beads have the above-described crystal structure can be determined based on the DSC curve obtained by performing differential scanning calorimetry (DSC) under the above-described conditions in accordance with JIS K7121:1987.
- DSC differential scanning calorimetry
- 1 to 3 mg of foamed particles may be used as a sample.
- the temperature is cooled from 200 ° C. to 23 ° C. at a cooling rate of 10 ° C./min.
- the polypropylene resin constituting the foam layer Since only the endothermic peak due to the melting specific to .sup.2 is seen, the resin specific peak and the high temperature peak can be distinguished.
- the temperature at the top of this resin-specific peak may slightly differ between the first heating and the second heating, but the difference is usually within 5°C.
- the amount of heat of fusion at the high-temperature peak of the expanded beads is preferably 5 J/g or more and 40 J/g or less, and 7 J/g, from the viewpoint of further improving the moldability of the expanded beads and obtaining a molded article having excellent rigidity. It is more preferably 30 J/g or more, and further preferably 10 J/g or more and 20 J/g or less.
- the heat of fusion at the high-temperature peak mentioned above is a value obtained as follows. First, using 1 to 3 mg of expanded beads after conditioning as a sample, differential scanning calorimetry is performed under the conditions described above to obtain a DSC curve. An example of a DSC curve is shown in FIG. When the foamed beads have a high temperature peak, the DSC curve has a resin-specific peak ⁇ H1 and a high-temperature peak ⁇ H2 having a peak on the high temperature side of the peak of the resin-specific peak ⁇ H1, as shown in FIG.
- the melting end temperature T is the end point on the high temperature side of the high temperature peak ⁇ H2, that is, the intersection of the high temperature peak ⁇ H2 and the baseline on the higher temperature side than the high temperature peak ⁇ H2 in the DSC curve.
- a straight line L2 parallel to the vertical axis of the graph is drawn through the maximum point ⁇ existing between the resin-specific peak ⁇ H1 and the high-temperature peak ⁇ H2.
- the straight line L2 divides the resin-specific peak ⁇ H1 and the high-temperature peak ⁇ H2.
- the heat of fusion of the high-temperature peak ⁇ H2 can be calculated based on the area of the portion surrounded by the portion forming the high-temperature peak ⁇ H2 in the DSC curve, the straight lines L1, and the straight lines L2.
- the bulk ratio M2 of the expanded beads is preferably 10 times or more and 75 times or less, more preferably 20 times or more and 75 times or less, further preferably 30 times or more and 75 times or less, and 35 times or more. 60 times or less is particularly preferable.
- the bulk ratio M2 of the expanded beads is preferably 10 times or more and 75 times or less, more preferably 20 times or more and 75 times or less, further preferably 30 times or more and 75 times or less, and 35 times or more. 60 times or less is particularly preferable.
- the bulk ratio M2 of the expanded beads is a value obtained by dividing the density (unit: kg/m 3 ) of the polypropylene-based resin constituting the core layer of the resin beads by the bulk density (unit: kg/m 3 ) of the expanded beads.
- a method for measuring the bulk density of the expanded particles is as follows. First, the expanded beads are left in an environment of 23° C., 50% RH, and 1 atm for 24 hours or more to adjust the state of the expanded beads. After conditioning, the foamed particles are filled in a graduated cylinder so that they naturally accumulate, and the bulk volume (unit: L) of the foamed particles is read from the scale of the graduated cylinder. Then, the bulk density of the expanded particles (unit: kg/m 3 ) can be obtained by converting the value obtained by dividing the mass (unit: g) of the group of expanded particles in the graduated cylinder by the bulk volume described above. .
- An expanded bead molded article can be obtained by in-mold molding the expanded bead.
- 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, further preferably 50 kg/m 3 or less, and 35 kg/m 3 or less. is particularly preferred.
- the density of the molded article is calculated by dividing the mass (unit: g) of the molded article by the volume (unit: L) determined from the outer dimensions of the molded article and converting the unit. If it is not easy to determine the volume from the outer dimensions of the molded body, the volume of the molded body can be determined by the submersion method.
- the manufacturing method of the expanded particle molding is, for example, as follows. First, foamed particles to be used for producing a molded article are prepared. The expanded beads obtained by the above-described manufacturing method may be used as they are for the production of the molded article. Further, the foamed particles can be impregnated with an inorganic gas such as air in a pressure container to apply an internal pressure to increase the pressure inside the cells of the foamed particles and perform in-mold molding.
- an inorganic gas such as air in a pressure container to apply an internal pressure to increase the pressure inside the cells of the foamed particles and perform in-mold molding.
- a molding die having a cavity corresponding to the shape of the desired molding is filled with foamed particles.
- a heating medium is supplied into the mold to heat the expanded particles. Steam, for example, can be used as the heating medium.
- the foamed particles in the mold are heated by the heating medium and are fused together while undergoing secondary foaming. As a result, the expanded particles in the mold can be integrated to form a molded product.
- the molded body in the mold is cooled to stabilize its shape.
- the in-mold molding is completed by removing the molded body from the molding die.
- the compact may be cured by standing in an atmosphere of about 60 to 80° C. for 12 hours or longer, if necessary.
- the expanded particles have excellent filling properties, have a high degree of blackness, and can be molded into good expanded particle molded articles with inconspicuous color unevenness. In particular, even with expanded particles having a high bulk ratio, it is possible to suppress a decrease in blackness and a deterioration in fillability.
- the expanded bead molded article obtained by in-mold molding of the expanded polypropylene resin particles contains, for example, 0.1 parts by mass or more and less than 5 parts by weight of carbon with respect to 100 parts by weight of the resin constituting the expanded bead molded article.
- the expanded bead molded article contains black, has a molded body density of 10 kg/m 3 or more and 35 kg/m 3 or less, and has an L* value of less than 24. Furthermore, a 100 mm ⁇ 100 mm square is drawn in the center of the surface of the expanded bead molded product, and a diagonal line is drawn from one corner of the square. ) is 3 or less.
- the L* value of the expanded bead molded product is preferably 23 or less, more preferably 21 or less.
- the L* value of the expanded bead molded product can be obtained by the following method. Five measurement positions are selected at random from the surface of the molded article, and the L* value is measured using a spectral color difference meter (for example, "SE2000" manufactured by Nippon Denshoku Industries Co., Ltd.). Then, the arithmetic average value of the L* values obtained at these five measurement positions is taken as the L* value of the compact.
- the measurement range shall be 30 mm ⁇ , and the measurement method shall be the reflection method.
- Table 1 shows the polypropylene-based resins and polyolefin-based resins used in this example. Both the ethylene-propylene copolymer and the ethylene-propylene-butene copolymer used in this example are random copolymers.
- the density of the polypropylene resins (PP1, PP2 and PP3) shown in Table 1 is 900 kg/m 3 .
- Comonomer component content of polypropylene resin Monomer component content of polypropylene resin (specifically, ethylene-propylene copolymer and ethylene-propylene-butene copolymer) is determined by a known method determined by IR spectrum. asked. Specifically, Polymer Analysis Handbook (Edited by Japan Society for Analytical Chemistry Polymer Analysis Research Round-table Conference, publication date: January 1995, publisher: Kinokuniya Bookstore, page numbers and item names: 615-616 "II. 2.3 2.3.4 Propylene/Ethylene Copolymers”, 618-619 “II.2.3 2.3.5 Propylene/Butene Copolymers”), i.e.
- ethylene and butene It was obtained by a method of quantifying from the relationship between the absorbance corrected by a predetermined coefficient and the thickness of the film-like test piece. More specifically, first, a polypropylene resin was hot-pressed in an environment of 180° C. to form a film, and a plurality of test pieces having different thicknesses were prepared. Next, by measuring the IR spectrum of each test piece, the absorbance at 722 cm -1 and 733 cm -1 derived from ethylene (A 722 , A 733 ) and the absorbance at 766 cm -1 derived from butene (A 766 ) were read. rice field. Next, for each test piece, the ethylene component content in the polypropylene resin was calculated using the following formulas (2) to (4).
- the content of the butene component in the polypropylene resin was calculated using the following formula (5).
- the value obtained by arithmetically averaging the butene component contents obtained for each test piece was defined as the butene component content (unit: mass %) in the polypropylene resin.
- Butene component content 12.3 (A 766 /L) (5)
- A means the absorbance
- L means the thickness (unit: mm) of the film-like test piece.
- Flexural Modulus A 4 mm sheet was prepared by heat-pressing the resin shown in Table 1 at 230° C., and a test piece of 80 mm length ⁇ 10 mm width ⁇ 4 mm thickness was cut out from this sheet.
- the flexural modulus of this test piece was determined according to JIS K7171:2008.
- the radius R1 of the indenter and the radius R2 of the support are both 5 mm, the distance between fulcrums is 64 mm, and the test speed is 2 mm/min.
- the melting points of the resins shown in Table 1 were obtained based on JIS K7121:1987. Specifically, first, the state of a test piece made of resin was adjusted based on "(2) In the case of measuring the melting temperature after performing a certain heat treatment" described in JIS K7121:1987. A DSC curve was obtained by heating the conditioned specimen from 30°C to 200°C at a heating rate of 10°C/min. The apex temperature of the melting peak appearing on the DSC curve was taken as the melting point. A heat flux differential scanning calorimeter (manufactured by SII Nanotechnology Co., Ltd., model number: DSC7020) was used as a measuring device.
- melt flow rate (that is, MFR) of the resin shown in Table 1 was measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 230°C and a load of 2.16 kg.
- Example 1 In producing the expanded beads of Example 1, first, a coextrusion device comprising a core layer forming extruder, a coating layer forming extruder, and a coextrusion die connected to these two extruders was prepared. The extrudate extruded from the co-extrusion apparatus was cut by a strand cut method to prepare multilayer resin particles. Specifically, PP1 shown in Table 1, carbon black in the ratio shown in Table 2 with respect to PP1, and a cell control agent are supplied to a core layer forming extruder, and melt-kneaded in the extruder to form a core layer. A melt-kneaded material for forming was obtained.
- Furnace black (DBP oil absorption of 100 mL/mg, BET specific surface area of 80 m 2 /g, average particle size of 20 nm) was used as the carbon black, zinc borate was used as the cell control agent, and zinc borate was added. The amount was set to 500 mass ppm with respect to the polypropylene resin.
- the number-based arithmetic mean particle size of this zinc borate was 2.8 ⁇ m, and the number ratio of particles having a particle size of 5 ⁇ m or more was 10%.
- Microtrac MT3000 was used to measure the particle size distribution of zinc borate, and the number-based particle size distribution of zinc borate was measured according to the method described above. 1 g of zinc borate and 1 g of a 1% aqueous solution of sodium dodecylbenzenesulfonate were added to 100 g of water, and the mixture was dispersed for 5 minutes using an ultrasonic shaker, and used as a sample for measurement. The sample refractive index was 1.81 and the sample shape was aspherical.
- melt-kneaded materials are co-extruded and combined in a die to form a composite consisting of a non-foamed columnar core layer and a non-foamed coating layer covering the side peripheral surface of the core layer.
- the extrudate is cooled in water while being taken up, and cut into an appropriate length using a pelletizer to form a core layer and a coating layer covering the side peripheral surface of the core layer.
- Multilayered resin particles consisting of were obtained. Note that the multilayer resin particles do not have through-holes.
- the single-stage expanded particles were dried for 24 hours in an atmosphere with a temperature of 23° C. and a relative humidity of 50%. As described above, a single-stage expanded bead having a foamed layer formed by foaming the core layer and a non-foamed coating layer covering the foamed layer was 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.
- Example 2 Example 3
- the pressure in the sealed container in the first-stage expansion process that is, foaming agent pressure
- the steam pressure in the two-stage expansion process that is, drum pressure
- Table 2 The manufacturing method of the expanded beads of Example 1 is the same as that of Example 1, except that the values are changed to those shown.
- Example 4 The method for producing expanded beads in Example 4 is the same as the method for producing expanded beads in Example 1, except that the resin constituting the coating layer is changed from PO1 to PO2.
- Example 5 The method for producing expanded beads in Example 5 was the same as the method for producing expanded beads in Example 1, except that the resin constituting the core layer of the resin beads (that is, the expanded layer of the expanded beads) was changed from PP1 to PP2. is.
- Example 6 In the method for producing expanded beads of Example 6, the pressure in the sealed container in the first-stage expansion process (that is, the foaming agent pressure), the expansion temperature, and the steam pressure in the second-stage expansion process (that is, the drum pressure) are shown in Table 2.
- the method for producing expanded beads in Example 5 is the same as that of Example 5, except that the values were changed to those shown.
- Example 7 In the method for producing expanded beads of Example 7, the resin constituting the core layer of the resin beads (that is, the expanded layer of the expanded beads) was changed from PP1 to PP3, and the pressure in the closed container in the one-stage expansion step (that is, expanded).
- the method for producing expanded beads was the same as in Example 1, except that the pressure of the agent), the expansion temperature, and the steam pressure (that is, the drum pressure) in the two-stage expansion process were changed to the values shown in Table 2.
- Comparative example 2 The method for producing the expanded beads of Comparative Example 2 was the same as the method for producing the expanded beads of Comparative Example 1, except that the amount of carbon black blended in the core layer and the coating layer was changed to the values shown in Table 3.
- Comparative Example 5 The method for producing the expanded beads of Comparative Example 5 is the same as the method for producing the expanded beads of Example 3, except that the coating layer does not contain carbon black.
- ⁇ Bulk magnification M 1 of single-stage expanded particles The single-stage expanded beads were allowed to stand for 24 hours or more in an environment of a relative humidity of 50%, a temperature of 23° C. and an atmospheric pressure of 1 atm to adjust the state of the single-stage expanded beads.
- the single-stage expanded particles after conditioning were filled in a graduated cylinder so as to naturally accumulate, and the bulk volume (unit: L) of the single-stage expanded particles was read from the scale of the graduated cylinder. Thereafter, the mass (unit: g) of the group of single-stage expanded particles in the graduated cylinder was divided by the bulk volume described above, and the unit was further converted to calculate the bulk density (unit: kg/m 3 ) of the single-stage expanded particles. .
- the bulk ratio M1 of the first -stage expanded particles was calculated by dividing the density of the polypropylene-based resin constituting the foamed layer by the bulk density of the first-stage expanded particles.
- Tables 2 and 3 show the bulk ratio M1 of the single-stage expanded beads of Examples, Comparative Examples, and Reference Examples.
- ⁇ Bulk magnification M 2 of expanded particles The bulk density (unit: kg/m 3 ) of the expanded beads was measured in the same manner as the method for measuring the bulk density of the first-step expanded beads, except that the expanded beads were used instead of the first-stage expanded beads. Then, the bulk ratio M2 of the expanded particles was calculated by dividing the density of the polypropylene-based resin forming the expanded layer by the bulk density of the expanded particles. Tables 2 and 3 show the bulk magnification M2 and bulk density of the expanded beads of Examples, Comparative Examples and Reference Examples.
- 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 Mass of sample for measurement of expanded beads (unit: g)
- ⁇ Density of resin constituting expanded beads (unit: g/cm 3 )
- Tables 2 and 3 show the closed cell ratios of the expanded beads of Examples, Comparative Examples, and Reference Examples.
- High-temperature peak calorie A DSC curve was obtained by performing differential scanning calorimetry in accordance with JIS K7121:1987 using 1 to 3 mg of expanded beads after conditioning.
- the measurement start temperature was 23° C.
- the measurement end temperature was 200° C.
- the heating rate was 10° C./min.
- "DSC.Q1000" manufactured by TA Instruments was used as a measuring device.
- the area of the high-temperature peak in the DSC curve obtained by the method described above was calculated, and this value is shown in Tables 2 and 3 as the high-temperature peak heat quantity.
- the method for measuring the angle of repose is as follows.
- an angle of repose measuring device "Fluid Surface Angle Measuring Instrument FSA-100S” manufactured by Tsutsui Rigakuki Co., Ltd. was used, and the angle of repose was measured by the cylindrical rotation method. Specifically, first, expanded particles with a bulk volume of 200 mL were placed in a cylindrical container with a volume of 500 mL. Next, the container was rotated for 3 minutes at a rotating speed of 26 seconds per revolution to adjust the deposition state of the foamed particles.
- the container After conditioning the expanded beads, the container continued to rotate. Then, the rotation of the container was stopped immediately before the upper portion of the deposit of foamed particles in the container collapsed.
- a goniometer was set in accordance with the upper and lower ends of the slopes in the deposit of foamed particles formed by this operation, and the angles of the slopes were measured. The angle of the slope thus obtained was taken as the angle of repose of the foamed particles.
- the symbol “A” is used when the angle of repose is less than 27°, and the symbol “B” when the angle of repose is 27° or more and less than 30°. , 30° or more and less than 33°, the symbol “C”, and 33° or more, the symbol “D”.
- the angle of repose is a value related to the ease of flow of the expanded particles, and the smaller the angle of repose, the easier the expanded particles flow and the higher the filling property.
- the method for evaluating the filling property when the foamed particles are filled into the mold is as follows. Specifically, a molded article was produced in the same manner as described for evaluation of minimum molding pressure, except that the amount of cracking in evaluation of minimum molding pressure described later was set to 0% and filled with expanded particles. A square of 100 mm ⁇ 100 mm was drawn in the center of the obtained molded body, and a diagonal line was drawn from one corner of the square. The number of voids (gap) having a size of 1 mm ⁇ 1 mm or more existing on this diagonal line was counted.
- 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. Then, when the arithmetic mean value of these material destruction rates was 90% or more, it was determined to be acceptable.
- ⁇ Surface properties> A 100 mm ⁇ 100 mm square was drawn in the center of the molded body, and a diagonal line was drawn from one corner of the square. The number of voids (gap) having a size of 1 mm ⁇ 1 mm or more existing on this diagonal line was counted, and when the number of voids was less than 3, it was judged as acceptable.
- ⁇ Recoverability> In a plan view of the molded body in the thickness direction, the thickness of the molded body at four positions located 10 mm inward from each vertex toward the center and the thickness of the molded body at the central portion were measured. Next, the ratio (unit: %) of the thickness of the thinnest portion to the thickness of the thickest portion among the measured portions was calculated, and when the thickness ratio was 95% or more, it was judged to be acceptable.
- the color tone was evaluated based on the determination of the color depth of the molded article based on the L* value in the CIE 1976 L*a*b* color system and the degree of color unevenness of the molded article.
- the method for measuring the L* value is as follows. First, five sites were randomly selected from the skin surface of the molded body, that is, the surface that was in contact with the mold during in-mold molding. was used to measure the L* value. The measurement range was 30 mm ⁇ , and the measurement method was the reflection method. Then, the arithmetic average value of the L* values at these five measurement positions was taken as the L* value of the compact.
- the L* values of the molded articles composed of the expanded beads of Examples and Comparative Examples were as shown in the "L* value” column of the "color tone” column in Tables 2 and 3.
- the symbol “A” is given when the L* value of the molded product is less than 24, and the L* value is 24 or more.
- the symbol “B” is described, and when the L* value is 28 or more, the symbol “C” is described.
- the L* value is an index of brightness, and the lower the value, the higher the degree of blackness and the darker the black.
- the degree of unevenness in color tone of the molded body was evaluated. Specifically, visually, the surface of the molded body has no color unevenness and exhibits a uniform black color (5 points) to marked color unevenness and gray areas can be seen here and there (1 point). The color unevenness was evaluated according to the 5-grade evaluation, and the average value (evaluation score) of the evaluation scores of the 5 viewers was calculated.
- the symbol "A" is given when the evaluation score is 4 points or more, and when the evaluation score is 3 points or more and less than 4 points.
- a symbol "B” is indicated, and a symbol “C” is indicated when the evaluation score is less than 3 points. Since carbon black was not blended in the foamed particles of Reference Example, color tone was not evaluated in Reference Example. Therefore, the symbol "-" is entered in the color tone column in Reference Examples.
- the expanded beads obtained by the production methods of Examples 1 to 7 are excellent in fillability. In addition, by in-mold molding these expanded beads, it is possible to obtain a good expanded bead molded article having a high degree of blackness and inconspicuous color unevenness.
- the expanded beads obtained by the production methods of Examples had good filling properties even when the bulk ratio was high, had a high degree of blackness, and had a small variation in color tone. According to a comparison between Example 1 and Example 3, when the ratio M 2 /M 1 of the bulk ratio M 2 of the two-step expanded beads to the bulk ratio M 1 of the first-step expanded beads is 1.8 or more, It can be understood that it is possible to produce a darker black molded body.
- the expanded beads of Examples 5 to 7 had a particularly short water cooling time.
- the foamed beads obtained by the production method of Comparative Example 3 do not have a non-foamed coating layer, and therefore are inferior to the foamed beads of Examples in fillability.
- the expanded beads obtained by the production method of Comparative Example 4 have too high a bulk ratio M1 of the single-stage expanded beads, the resulting molded article has a low blackness and tends to have a large variation in color tone. Moreover, the expanded beads obtained by the manufacturing method of Comparative Example 4 do not have a non-foamed coating layer, and therefore are inferior to the expanded beads of Examples in fillability. From the comparison between Comparative Examples 3 and 4, it can be understood that the expanded beads of Comparative Example 4, which have a higher bulk ratio M2 than that of Comparative Example 3, have a lower filling property than that of Comparative Example 3. Further, since the foamed particles of Comparative Example 4 have a lower filling property than that of Reference Example 2, which will be described later, it can be seen that the foam layer containing carbon black deteriorates the filling property.
- Reference Examples 1 and 2 are examples in which neither the foam layer nor the coating layer contains carbon black.
- the expanded beads of Reference Examples 1 and 2 had a white color tone. Comparing Reference Example 1 and Reference Example 2, the filling property of the expanded beads obtained in Reference Example 1 was slightly improved compared to the filling property of the expanded beads obtained in Reference Example 2. On the other hand, when comparing Example 1 and Comparative Example 3, which have the same configuration except for the presence or absence of a coating layer, in the examples in which carbon black is blended, the filling properties of the foamed particles obtained in Example 1 are superior to those of the comparative example. It can be understood that the filling properties of the expanded particles obtained in 3 are greatly improved. Furthermore, when comparing Example 1 with Comparative Example 5 in which carbon black was not blended in the coating layer, the filling properties of the expanded beads obtained in Example 1 were similar to those obtained in Comparative Example 5. It can be understood that the packing property of the particles is improved.
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Abstract
Description
密閉容器内において前記分散媒中の前記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た後、前記ポリプロピレン系樹脂粒子を前記分散媒とともに前記密閉容器から前記密閉容器内よりも低圧の雰囲気中に放出することにより、前記ポリプロピレン系樹脂粒子の前記芯層を発泡させて嵩倍率5倍以上25倍以下の一段発泡粒子を得る一段発泡工程と、
前記一段発泡粒子の気泡内の圧力を上昇させた後、前記一段発泡粒子を加熱することにより前記一段発泡粒子をさらに発泡させてポリプロピレン系樹脂発泡粒子を得る二段発泡工程と、を含み、
前記一段発泡粒子の嵩倍率M1に対する前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。
前記ポリプロピレン系樹脂発泡粒子(以下、「発泡粒子」または「二段発泡粒子」という。)の製造方法は、前述したように、分散媒に前記特定のポリプロピレン系樹脂粒子(以下、「樹脂粒子」という。)を分散させる分散工程と、前記樹脂粒子の芯層を嵩倍率M1が5倍以上25倍以下となるように発泡させて一段発泡粒子を得る一段発泡工程と、前記一段発泡粒子を、前記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1.2以上3.0以下となるように発泡させて前記二段発泡粒子を得る二段発泡工程と、を有している。このように、前記特定のポリプロピレン系樹脂粒子を二段階で発泡させることにより、高い黒色度を有し、色調のばらつきが小さく、充填性に優れた発泡粒子を容易に得ることができる。さらに、このようにして得られた発泡粒子によれば、軽量で、表面性に優れるとともに、黒色度が高く、色むらの目立たない発泡粒子成形体(以下、「成形体」という。)を容易に得ることができる。
なお、一段発泡粒子及び発泡粒子の嵩密度の測定方法については後述する。
分散工程では、前記ポリプロピレン系樹脂粒子を分散媒中に分散させる。
分散工程においては、前記樹脂粒子を分散媒中に投入した後、攪拌することにより樹脂粒子を分散媒中に分散させる。分散工程は、後に行う一段発泡工程において用いる密閉容器内で行ってもよいし、一段発泡工程において用いる密閉容器とは別の容器内で行ってもよい。製造工程の簡素化の観点からは、分散工程を、一段発泡工程において用いる密閉容器内で行うことが好ましい。
一段発泡工程においては、まず、密閉容器内において分散媒中の樹脂粒子に無機物理発泡剤を含浸させる。樹脂粒子を発泡させるための無機物理発泡剤としては、二酸化炭素、空気、窒素、ヘリウム、アルゴン等を使用することができる。環境に対する負荷や取扱い性の観点から、好ましくは二酸化炭素が用いられる。発泡剤の添加量は、樹脂粒子100質量部に対して0.1質量部以上30質量部以下であることが好ましく、0.5質量部以上15質量部以下であることが好ましい。
二段発泡工程においては、まず、一段発泡粒子に内圧を付与する。より具体的には、一段発泡粒子を耐圧容器内に入れた後、耐圧容器内を空気や二酸化炭素等の無機ガスで加圧して一段発泡粒子に無機ガスを含浸させる。これにより、一段発泡粒子の気泡内の圧力を大気圧以上とする。その後、耐圧容器から取り出した一段発泡粒子を、気泡内の圧力よりも低圧の環境下でスチームや加熱空気などの加熱媒体を用いて加熱することにより、一段発泡粒子をさらに発泡させることができる。以上の結果、嵩倍率がM2であり、嵩倍率M2が嵩倍率M1の1.2倍以上3.0倍以下である発泡粒子(二段発泡粒子)を得ることができる。
以上により得られたポリプロピレン系樹脂発泡粒子は、ポリプロピレン系樹脂を基材とする発泡層と、ポリオレフィン系樹脂を基材樹脂とし、発泡層を被覆する被覆層とを有している。また、発泡層中には、ポリプロピレン系樹脂100質量部に対して0.1質量部以上5質量部未満のカーボンブラックが含まれており、被覆層中には、ポリオレフィン系樹脂100質量部に対して0.1質量部以上5質量部未満のカーボンブラックが含まれている。発泡粒子は、得られる成形体の外観及び剛性をより高める観点から、貫通孔を有さないことが好ましい。
ただし、上記式(1)におけるVx(単位:cm3)は発泡粒子の真の体積(つまり、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)であり、Va(単位:cm3)は発泡粒子の見掛けの体積(つまり、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液面の上昇分から測定される体積)であり、W(単位:g)は測定用サンプルの質量であり、ρ(単位:g/cm3)は発泡層を構成するポリプロピレン系樹脂の密度である。
前記発泡粒子を型内成形することにより、発泡粒子成形体を得ることができる。成形体の密度は10kg/m3以上100kg/m3以下であることが好ましい。この場合には、成形体の軽量性と剛性とをバランスよく向上させることができる。成形体の剛性がより向上するという観点から、成形体の密度は20kg/m3以上であることがより好ましく、25kg/m3以上であることがさらに好ましい。成形体の軽量性がより向上するという観点から、成形体の密度は80kg/m3以下であることがより好ましく、50kg/m3以下であることがさらに好ましく、35kg/m3以下であることが特に好ましい。成形体の密度は、成形体の質量(単位:g)を成形体の外形寸法から求められる体積(単位:L)で除し、単位換算することにより算出される。成形体の外形寸法から体積を求めることが容易でない場合には、水没法により成形体の体積を求めることができる。
ポリプロピレン系樹脂(具体的には、エチレン-プロピレン共重合体及びエチレン-プロピレン-ブテン共重合体)のモノマー成分含有量は、IRスペクトルにより決定する公知の方法により求めた。具体的には、高分子分析ハンドブック(日本分析化学会高分子分析研究懇談会編、出版年月:1995年1月、出版社:紀伊国屋書店、ページ番号と項目名:615~616「II.2.3 2.3.4 プロピレン/エチレン共重合体」、618~619「II.2.3 2.3.5 プロピレン/ブテン共重合体」)に記載されている方法、つまり、エチレン及びブテンの吸光度を所定の係数で補正した値とフィルム状の試験片の厚み等との関係から定量する方法により求めた。より具体的には、まず、ポリプロピレン系樹脂を180℃環境下でホットプレスしてフィルム状に成形し、厚みの異なる複数の試験片を作製した。次いで、各試験片のIRスペクトルを測定することにより、エチレン由来の722cm-1及び733cm-1における吸光度(A722、A733)と、ブテン由来の766cm-1における吸光度(A766)とを読み取った。次いで、各試験片について、以下の式(2)~(4)を用いてポリプロピレン系樹脂中のエチレン成分含有量を算出した。各試験片について得られたエチレン成分含有量を算術平均した値をポリプロピレン系樹脂中のエチレン成分含有量(単位:質量%)とした。
(K´733)c=1/0.96{(K´733)a-0.268(K´722)a}・・・(2)
(K´722)c=1/0.96{(K´722)a-0.268(K´722)a}・・・(3)
エチレン成分含有量=0.575{(K´722)c+(K´733)c}・・・(4)
ただし、式(2)~(4)において、K´aは各波数における見かけの吸光係数(K´a=A/ρt)、K´cは補正後の吸光係数、Aは吸光度、ρは樹脂の密度(単位:g/cm3)、tはフィルム状の試験片の厚み(単位:cm)を意味する。なお、上記式(2)~(4)はランダム共重合体に適用することができる。
ブテン成分含有量=12.3(A766/L)・・・(5)
ただし、式(5)において、Aは吸光度、Lはフィルム状の試験片の厚み(単位:mm)を意味する。
表1に示す樹脂を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/分である。
表1に示す樹脂の融点は、JIS K7121:1987に基づき求めた。具体的には、まず、JIS K7121:1987に記載の「(2)一定の熱処理を行なった後、融解温度を測定する場合」に基づいて樹脂からなる試験片の状態を調節した。状態調節後の試験片を10℃/分の加熱速度で30℃から200℃まで昇温することによりDSC曲線を取得した。そして、DSC曲線に現れた融解ピークの頂点温度を融点とした。なお、測定装置としては、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。
表1に示す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。
実施例1の発泡粒子の作製に当たっては、まず、芯層形成用押出機と、被覆層形成用押出機と、これら2台の押出機に接続された共押出ダイとを備えた共押出装置を用い、共押出装置から押し出された押出物をストランドカット方式により切断して多層樹脂粒子を作製した。具体的には、表1に示すPP1と、PP1に対して表2に示す割合のカーボンブラックと、気泡調整剤とを芯層形成用押出機に供給し、押出機内で溶融混練して芯層形成用溶融混練物を得た。なお、カーボンブラックとしてはファーネスブラック(DBP吸油量100mL/mg、BET比表面積80m2/g、平均粒径20nm)を使用し、気泡調整剤としてはホウ酸亜鉛を使用し、ホウ酸亜鉛の添加量はポリプロピレン系樹脂に対して500質量ppmとした。
このようにして得られた多層樹脂粒子100kgを、分散媒としての220Lの水とともに内容積400Lの密閉容器内に投入した。次いで、密閉容器内に、多層樹脂粒子100質量部に対して0.3質量部の分散剤と、分散助剤として0.004質量部のアルキルベンゼンスルホン酸ナトリウムと0.01質量部の硫酸アルミニウムとを添加し、多層樹脂粒子を分散媒中に分散させた。分散剤としてはカオリンを使用した。
その後、密閉容器内を攪拌しながら密閉容器内に無機物理発泡剤としての二酸化炭素を供給し、容器内の温度を表2に示す発泡温度まで上昇させた。表2の「発泡剤圧力」欄に、このときの容器内圧力(つまり、含浸圧力、二酸化炭素圧力)を示す。容器内の温度が表2に示す発泡温度に到達した後、この温度を15分保持することにより、多層樹脂粒子に発泡剤を含浸させた。発泡剤の含浸が完了した後、密閉容器を開放し、内容物を温度75℃の大気圧雰囲気下に放出することにより多層樹脂粒子の芯層を発泡させた。一段発泡粒子の互着はなく、また、収縮している様子は観察されなかった。この一段発泡粒子を温度23℃、相対湿度50%の雰囲気中で24時間乾燥させた。以上により、芯層が発泡してなる発泡層と、発泡層を被覆する非発泡状態の被覆層とを備えた一段発泡粒子を得た。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。
次に、一段発泡粒子を耐圧容器としての加圧タンク内に入れ、加圧タンクを密閉した。この状態で加圧タンク内を無機ガスとしての空気で加圧し、一段発泡粒子の気泡内の圧力が表2の「内圧」欄に示す値となるように、気泡内に空気を含浸させた。一段発泡粒子への内圧の付与が完了した後、一段発泡粒子を加圧タンクから取り出し、金属製のドラムに入れた。その後、一段発泡粒子に表2の「ドラム圧力」欄に示す圧力を有するスチームを供給し、大気圧下で加熱した。以上により、一段発泡粒子をさらに発泡させて発泡粒子(二段発泡粒子)を得た。このようにして得られた発泡粒子の諸特性は、表2に示す通りであった。
実施例2及び実施例3の発泡粒子の製造方法は、一段発泡工程における密閉容器内の圧力(つまり、発泡剤圧力)及び二段発泡工程におけるスチームの圧力(つまり、ドラム圧力)を表2に示す値に変更した以外は、実施例1の発泡粒子の製造方法と同様である。
実施例4の発泡粒子の製造方法は、被覆層を構成する樹脂をPO1からPO2に変更した以外は、実施例1の発泡粒子の製造方法と同様である。
実施例5の発泡粒子の製造方法は、樹脂粒子の芯層(つまり、発泡粒子の発泡層)を構成する樹脂をPP1からPP2に変更した以外は、実施例1の発泡粒子の製造方法と同様である。
実施例6の発泡粒子の製造方法は、一段発泡工程における密閉容器内の圧力(つまり、発泡剤圧力)、発泡温度、及び二段発泡工程におけるスチームの圧力(つまり、ドラム圧力)を表2に示す値に変更した以外は、実施例5の発泡粒子の製造方法と同様である。
実施例7の発泡粒子の製造方法は、樹脂粒子の芯層(つまり、発泡粒子の発泡層)を構成する樹脂をPP1からPP3に変更し、一段発泡工程における密閉容器内の圧力(つまり、発泡剤圧力)、発泡温度、及び二段発泡工程におけるスチームの圧力(つまり、ドラム圧力)を表2に示す値に変更した以外は、実施例1の発泡粒子の製造方法と同様である。
比較例1の発泡粒子の製造方法においては、まず、実施例1と同様の方法により多層樹脂粒子を作製した。そして、この樹脂粒子を一段発泡工程のみで嵩倍率35倍まで発泡させることにより発泡粒子を作製した。比較例1の発泡粒子の製造方法においては、二段発泡工程は実施していない。比較例1における一段発泡工程の発泡温度及び発泡剤圧力は表3に示した通りであった。
比較例2の発泡粒子の製造方法は、芯層及び被覆層に配合するカーボンブラックの量を表3に示す値に変更した以外は、比較例1の発泡粒子の製造方法と同様である。
比較例3及び比較例4の発泡粒子の製造方法においては、まず、芯層のみからなる単層の樹脂粒子を作製した。具体的には、表1に示すPP1と、PP1に対して表3に示す割合のカーボンブラックと、気泡調整剤とを押出機に供給し、押出機内で溶融混練して溶融混練物を得た。そして、押出機から溶融混練物を押出することにより、非発泡状態の円柱状の芯層からなる押出物を形成させた。押出物を引き取りながら水中で冷却し、ペレタイザーを用いて適当な長さに切断することにより、芯層のみからなる樹脂粒子を得た。その後、表3に示す条件で一段発泡工程及び二段発泡工程を行うことにより、樹脂粒子を発泡させて発泡粒子を得た。
比較例5の発泡粒子の製造方法は、被覆層中にカーボンブラックを配合しない以外は、実施例3の発泡粒子の製造方法と同様である。
参考例1の発泡粒子の製造方法においては、まず、芯層及び被覆層にカーボンブラックを配合しない以外は、実施例1と同様の方法により樹脂粒子を作製した。その後、表3に示す条件で一段発泡工程及び二段発泡工程を行うことにより、樹脂粒子を発泡させて発泡粒子を得た。
参考例2の発泡粒子の製造方法においては、まず、芯層中にカーボンブラックを配合しない以外は、比較例3及び比較例4と同様の方法により樹脂粒子を作製した。その後、表3に示す条件で一段発泡工程及び二段発泡工程を行うことにより、樹脂粒子を発泡させて発泡粒子を得た。
一段発泡粒子を相対湿度50%、温度23℃、気圧1atmの環境下で24時間以上静置し、一段発泡粒子の状態を調節した。状態調節後の一段発泡粒子をメスシリンダー内に自然に堆積するようにして充填し、メスシリンダーの目盛から一段発泡粒子群の嵩体積(単位:L)を読み取った。その後、メスシリンダー内の一段発泡粒子群の質量(単位:g)を前述した嵩体積で除し、さらに単位換算することにより、一段発泡粒子の嵩密度(単位:kg/m3)を算出した。そして、発泡層を構成するポリプロピレン系樹脂の密度を一段発泡粒子の嵩密度で除することにより、一段発泡粒子の嵩倍率M1を算出した。表2及び表3に、実施例、比較例及び参考例の一段発泡粒子の嵩倍率M1を示す。
一段発泡粒子に替えて発泡粒子を用い、前述した一段発泡粒子の嵩密度の測定方法と同様にして発泡粒子の嵩密度(単位:kg/m3)を測定した。そして、発泡層を構成するポリプロピレン系樹脂の密度を発泡粒子の嵩密度で除することにより、発泡粒子の嵩倍率M2を算出した。表2及び表3に、実施例、比較例及び参考例の発泡粒子の嵩倍率M2及び嵩密度を示す。
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、これらの体積の値Va及びVxを用い、下記の式(6)に基づいて測定用サンプルの独立気泡率を計算した。以上の操作を測定用サンプルを変更して5回行い、5つの測定用サンプルにおける独立気泡率の算術平均値(N=5)を発泡粒子の独立気泡率とした。
ただし、上記式(6)における記号の意味は以下の通りである。
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質量(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1~3mgを用い、JIS K7121:1987に準拠して示差走査熱量測定を行うことによりDSC曲線を取得した。なお、DSCにおける測定開始温度は23℃、測定終了温度は200℃、加熱速度は10℃/分とした。また、測定装置としてはティー・エイ・インスツルメント社製「DSC.Q1000」を使用した。前述した方法により得られたDSC曲線における高温ピークの面積を算出し、この値を高温ピーク熱量として表2及び表3に示した。
安息角及び評価用成形型に充填した際の充填性に基づいて、発泡粒子の充填性の評価を行った。安息角の測定方法は以下の通りである。発泡粒子の安息角の測定には、筒井理学機器株式会社製の安息角測定装置「流動表面角測定器FSA-100S」を用い、円筒回転法により安息角の測定を行った。具体的には、まず、嵩体積200mLの発泡粒子を容積500mLの円筒型容器内に入れた。次に、回転速度を1周26秒とし、容器を3分間回転させて発泡粒子の堆積状態を調整した。発泡粒子の状態調整が終わった後、更に容器の回転を継続した。そして、容器内の発泡粒子の堆積物の上部が崩れる直前に容器の回転を停止させた。この操作により形成された発泡粒子の堆積物における、斜面の上端と下端とに合わせて角度計を設定し、斜面の角度を測定した。このようにして得られた斜面の角度を発泡粒子の安息角とした。
縦300mm×横250mm×厚さ60mmの内寸法を有するキャビティを備えた成形型内に発泡粒子を充填した後、成形型内に加熱媒体としてのスチームを供給して型内成形を行った。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。型内成形は、より詳細には、以下の手順により行った。まず、成形型を閉鎖した後、成形型の厚み方向における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、後述する本加熱における成形圧より0.08MPa(G)低い圧力に達するまで、成形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、本加熱における成形圧より0.04MPa(G)低い圧力に達するまで成形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。その後、成形型の両面からスチームを供給して本加熱を行った。本加熱が完了した後、成形型内の圧力を解放し、成形体の発泡力による表面圧力が0.04MPa(G)になるまで成形型内において成形体を冷却した。その後、成形型から成形体を取り出した。離型後の成形体を80℃のオーブン中で12時間静置して養生工程を行った。以上により、縦300mm×横250mm×厚さ60mmの成形体を得た。
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。そして、これらの材料破壊率の算術平均値が90%以上であるときを合格と判定した。
成形体の中央部に100mm×100mmの正方形を描き、該正方形の一の角から対角線を引いた。この対角線上に存在する1mm×1mmの大きさ以上のボイド(間隙)の数を数え、ボイドの数が3個未満であるときを合格と判定した。
成形体を厚み方向から見た平面視において、各頂点より中心方向に10mm内側となる4か所の位置における成形体の厚みと、中央部における成形体の厚みと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、厚みの比が95%以上であるときを合格と判定した。
前述した最低成形圧での型内成形を行った際に、本加熱が完了した時点から、成形体の発泡力による表面圧力が0.04MPa(G)に到達した時点までの時間を計測し、この時間を水冷時間とした。
前述した最低成形圧での型内成形により得られた成形体の質量(単位:g)を成形体の外形寸法から求められる体積(単位:L)で除した後、単位換算することにより成形体の密度(単位:kg/m3)を算出した。
色調の評価は、CIE 1976 L*a*b*表色系におけるL*値に基づく成形体の色の濃さの判定及び成形体の色ムラの程度の判定に基づいて行った。L*値の測定方法は以下の通りである。まず、成形体のスキン面、つまり、型内成形時に成形型と接触していた面から無作為に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*値を測定した。なお、測定範囲は30mmΦとし、測定方法は反射法とした。そして、これら5か所の測定位置におけるL*値の算術平均値を成形体のL*値とした。実施例及び比較例の発泡粒子からなる成形体のL*値は表2及び表3の「色調」欄のうち「L*値」欄に示す通りであった。また、表2及び表3の「色調」欄のうち「色の濃さ」の欄には、成形体のL*値が24未満である場合には記号「A」、L*値が24以上28未満である場合には記号「B」、L*値が28以上である場合には記号「C」を記載した。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。
Claims (8)
- ポリプロピレン系樹脂を基材樹脂とし、前記ポリプロピレン系樹脂100質量部に対して0.1質量部以上5質量部未満のカーボンブラックが配合された芯層と、ポリオレフィン系樹脂を基材樹脂とし、前記ポリオレフィン系樹脂100質量部に対して0.1質量部以上5質量部未満のカーボンブラックが配合され、前記芯層を被覆する被覆層と、を備えたポリプロピレン系樹脂粒子を分散媒に分散させる分散工程と、
密閉容器内において前記分散媒中の前記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た後、前記ポリプロピレン系樹脂粒子を前記分散媒とともに前記密閉容器から前記密閉容器内よりも低圧の雰囲気中に放出することにより、前記ポリプロピレン系樹脂粒子の前記芯層を発泡させて嵩倍率5倍以上25倍以下の一段発泡粒子を得る一段発泡工程と、
前記一段発泡粒子の気泡内の圧力を上昇させた後、前記一段発泡粒子を加熱することにより前記一段発泡粒子をさらに発泡させてポリプロピレン系樹脂発泡粒子を得る二段発泡工程と、を含み、
前記一段発泡粒子の嵩倍率M1に対する前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。 - 前記一段発泡粒子の嵩倍率M1に対する前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3.0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。
- 前記一段発泡工程において、前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40℃以上80℃未満である、請求項1または2に記載のポリプロピレン系樹脂発泡粒子の製造方法。
- 前記被覆層の基材樹脂である前記ポリオレフィン系樹脂の融点Tmsが前記芯層の基材樹脂である前記ポリプロピレン系樹脂の融点Tmcよりも低い、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。
- 前記ポリプロピレン系樹脂発泡粒子の嵩倍率M2が30倍以上75倍以下である、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。
- 前記カーボンブラックが、ジブチルフタレート吸油量が150mL/100g未満の着色用カーボンブラックである、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。
- 前記芯層の基材樹脂であるポリプロピレン系樹脂がエチレン-プロピレン-ブテン共重合体またはプロピレン-ブテン共重合体であるとともに、これらの共重合体におけるブテン成分含有量が2質量%以上15質量%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。
- 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により得られたポリプロピレン系樹脂発泡粒子を成形型内に充填した後、前記成形型内に加熱媒体を供給して型内成形を行うことにより発泡粒子成形体を作製する、発泡粒子成形体の製造方法。
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