Method for producing expanded polypropylene resin particles, and method for producing in-mold expanded polypropylene resin articles

Abstract

To provide a method for producing polypropylene-based resin foam particles which enables production of polypropylene-based resin foam particles with a high yield, and a method for producing a polypropylene-based resin in-mold foam molded body.SOLUTION: A method for producing polypropylene-based resin foam particles includes the steps of: (i) dispersing polypropylene-based resin particles containing a polypropylene-based resin, carbon black and an NOR type hindered amine-based compound, a peroxide and a foaming agent into an aqueous dispersant in a closed vessel, and obtaining a dispersion liquid; (ii) heating and pressurizing the dispersion liquid; and (iii) discharging the dispersion liquid after heating and pressurization to a pressure region lower than an inner pressure of the closed vessel.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing expanded polypropylene resin beads and a method for producing in-mold foamed polypropylene resin articles. [Background technology]

[0002] The in-mold foamed molded article obtained by filling a mold with polypropylene-based resin foamed particles and heat-molding with water vapor has the advantages of the in-mold foamed article, such as the freedom of shape, light weight, and heat insulation. Due to these characteristics, the in-mold foamed molded article obtained using polypropylene-based resin foamed particles has been used for various applications such as heat insulation materials, cushioning packaging materials, automobile interior parts, and core materials for automobile bumpers. In recent years, further studies have been conducted to improve the quality of the polypropylene-based resin foamed particles used in the polypropylene-based resin in-mold foamed article. For example, in Patent Document 1, a hindered amine-based compound is contained in the polypropylene-based resin foamed particles in order to improve heat resistance and weather resistance. In addition, since black is preferred when used for automobile interior parts, Patent Document 2 proposes that the polypropylene-based resin foamed particles contain carbon black as a colorant and a sterically hindered amine ether-based flame retardant to ensure flame retardancy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-321567 A [Patent Document 2] JP 2018-162370 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a hindered amine flame retardant is contained in the expanded polypropylene resin particles as described in Patent Documents 1 and 2, there is a problem that the yield of the expanded polypropylene resin particles is poor.

[0005] In order to solve the above-mentioned problems in the conventional art, the present invention provides a method for producing expanded polypropylene-based resin beads capable of obtaining expanded polypropylene-based resin beads in a high yield, and a method for in-mold foam molding of polypropylene-based resin. [Means for solving the problem]

[0006] In one or more embodiments of the present invention, the present invention relates to a method for producing expanded polypropylene-based resin beads, the method including: (i) dispersing polypropylene-based resin particles containing a polypropylene-based resin, carbon black, and a NOR-type hindered amine compound, a peroxide, and a blowing agent in an aqueous dispersant in a sealed container to obtain a dispersion; (ii) heating and pressurizing the dispersion; and (iii) releasing the dispersion after the heating and pressurization into a pressure region lower than the internal pressure of the sealed container.

[0007] In one or more embodiments of the present invention, the present invention relates to a method for producing an in-mold foamed polypropylene-based resin article, comprising a step of in-mold foaming the expanded polypropylene-based resin beads obtained by the method for producing expanded polypropylene-based resin beads. Effect of the Invention

[0008] According to the method for producing expanded polypropylene resin beads of the present invention, expanded polypropylene resin beads can be obtained in high yield. In addition, by using the expanded polypropylene resin beads obtained in high yield by the method for producing expanded polypropylene resin beads of the present invention, in-mold expanded polypropylene resin articles can be produced with high productivity. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 shows an example of a differential scanning calorimeter (DSC) curve obtained when polypropylene resin foam particles are heated from 40°C to 220°C at a rate of 10°C / min, showing the calorific value of melting peak Ql on the low temperature side and the calorific value of melting peak Qh on the high temperature side. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The inventors of the present invention have conducted extensive research to solve the above problems. As a result, they have found that polypropylene resin particles, in which carbon black and a NOR-type hindered amine compound have been added to a polypropylene resin, are dispersed in an aqueous dispersant together with a peroxide and a blowing agent, and then heated and pressurized to foam, thereby obtaining polypropylene resin expanded particles with a high yield. Peroxides are known to be used to adjust the physical properties of polypropylene resins, such as the molecular weight and melt flow rate, and to surface-modify polypropylene resins to make them moldable even at low vapor pressures. Surprisingly, the inventors of the present invention have found that the yield of polypropylene resin expanded particles is improved by (a) using a NOR-type hindered amine compound as the hindered amine compound, and (b) dispersing a polypropylene resin containing a NOR-type hindered amine compound and carbon black in an aqueous dispersion medium in which a peroxide is present, and foaming the polypropylene resin.

[0011] (Method of producing expanded polypropylene resin particles) The polypropylene resin particles (hereinafter also simply referred to as "expanded particles") contain a polypropylene resin, a NOR type hindered amine compound, and carbon black.

[0012] The composition of the polypropylene-based resin is not particularly limited, and may be, for example, a propylene homopolymer or a copolymer of propylene and another α-olefin. The copolymer of propylene and another α-olefin may be an olefin-propylene random copolymer or an olefin-propylene block copolymer. Among these, an olefin-propylene random copolymer is preferred. From the viewpoint of dimensional properties and mechanical strength, the polypropylene-based resin preferably contains 50% by weight or more of a propylene (monomer) component, more preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more.

[0013] In the polypropylene-based resin, the other α-olefin copolymerizable with propylene is not particularly limited, and examples thereof include α-olefins having 2 or more carbon atoms. Specific examples include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene. These other α-olefins may be used alone or in combination of two or more. Among these, ethylene and / or 1-butene are preferred from the viewpoints of availability, economy, and foamability during in-mold foaming. The polypropylene-based resins may be used alone or in combination of two or more.

[0014] Although the polypropylene-based resin is not particularly limited, the melting point is preferably 130° C. or more and 165° C. or less, more preferably 135° C. or more and 160° C. or less, and even more preferably 140° C. or more and 155° C. or less. When the melting point of the polypropylene-based resin is within the above-mentioned range, it tends to be easy to obtain an in-mold foamed article having an excellent balance between dimensional stability, mechanical strength, and surface beauty.

[0015] In one or more embodiments of the present invention, the melting point is the peak temperature of an endothermic peak in a DSC curve obtained by using a differential scanning calorimeter (DSC) to heat a resin sample of 1 mg to 10 mg from 20° C. to 220° C. at a heating rate of 10° C. / min, then cooling from 220° C. to 20° C. at a heating rate of 10° C. / min, and again heating from 20° C. to 220° C. at a heating rate of 10° C. / min.

[0016] The melt flow rate (hereinafter sometimes referred to as MFR) of the polypropylene resin is preferably 4.0 g / 10 min or more and 10 g / 10 min or less, more preferably 5.0 g / 10 min or more and 9 g / 10 min or less. When the melt flow rate of the polypropylene resin is within the above-mentioned range, there is a tendency that an in-mold foamed article with little deformation and excellent surface beauty is easily obtained.

[0017] In one or more embodiments of the present invention, the MFR is a value measured using an MFR measuring device specified in JIS K 7210 under the conditions of an orifice of 2.0959±0.005 mmφ, an orifice length of 8.000±0.025 mm, a load of 2160 g, and 230±0.2°C.

[0018] The polypropylene resin particles preferably contain 0.1 to 10 parts by weight of carbon black, more preferably 0.5 to 8 parts by weight, and even more preferably 1 to 5 parts by weight, per 100 parts by weight of the polypropylene resin. When the carbon black content is within this range, the colorability is good, the viscosity of the resin is less likely to decrease, and the yield of the polypropylene resin foam particles is not reduced, making it easier to obtain an in-mold foamed product of good quality.

[0019] The carbon black is not particularly limited, but generally, the primary particle diameter is preferably 10 nm or more and 500 nm or less, more preferably 10 nm or more and 100 nm or less from the viewpoint of the balance between the flame retardancy and mechanical strength of the in-mold foamed article, and even more preferably 10 nm or more and 50 nm or less from the viewpoint of surface beauty. The primary particle diameter of the carbon black can be determined by taking a photograph of the cross section of the cell membrane of the polypropylene resin foamed particle at a magnification of 40,000 times with a transmission electron microscope, measuring the particle diameters of the carbon black primary particles in the X direction and Y direction in the obtained transmission electron microscope photograph, and calculating the average value.

[0020] Specifically, the NOR type hindered amine compound may be a compound represented by the following formula (1). [ka] In the general formula (1), R 1 and R 2 is an s-triazine moiety represented by the following general formula (2), R 3 and R 4 One of the groups is an s-triazine moiety represented by the following general formula (2), R 3 and R 4 The other represents a hydrogen atom.

[0021] [ka] In the general formula (2), R 5 is an alkyl group having 1 to 12 carbon atoms, R 6 represents a methyl group, a cyclohexyl group, or an octyl group.

[0022] In the general formula (2), R 5Specific examples of the alkyl group having 1 to 12 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a 2-ethylbutyl group, an isopentyl group, a 1-methylpentyl group, a 1,3-dimethylbutyl group, a 1-methylhexyl group, an isoheptyl group, a 1,1,3,3-tetramethylpentyl group, a 1-methylundecyl group, and a 1,1,3,3,5,5-hexamethylhexyl group.

[0023] Specific examples of the s-triazine moiety represented by the general formula (2) include, for example, 2,4-bis[(1-methoxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazine, 2,4-bis[(1-cyclohexyloxy-2,2 ,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazine, 2,4-bis[(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazine, and the like.

[0024] Specific examples of the NOR type hindered amine compound represented by the general formula (1) include N,N',N'''-tris{2,4-bis[(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminopropylamine; N,N',N''-tris{2,4-bis[(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminodipropylamine; N,N',N''-tris{2,4-bis[(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminodipropylamine;}-3,3'-ethylenediiminodipropylamine; N,N',N''-tris{2,4-bis[(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6yl}-3,3'-ethylenediiminopropylamine; N,N',N'''-tris{2,4-bis[(1-methoxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6yl}-3,3'-ethylenediiminopropylamine; N,N',N''-tris{2,4-bis[(1-methoxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6yl}-3,3'-ethylenediiminopropylamine. These may be used alone or in combination of two or more.

[0025] The polypropylene resin particles preferably contain 0.01 to 0.50 parts by weight of a NOR type hindered amine compound relative to 100 parts by weight of the polypropylene resin, more preferably 0.02 to 0.40 parts by weight, and even more preferably 0.03 to 0.20 parts by weight. When the content of the NOR type hindered amine compound is within this range, the heat resistance and weather resistance of the polypropylene resin particles tend to be improved, and the yield of the polypropylene resin particles tends to be improved while a good quality in-mold foamed product is easily obtained.

[0026] The polypropylene-based resin particles may contain a non-NOR type hindered amine compound in addition to the NOR type hindered amine compound, if necessary. From the viewpoint of easily improving the yield of the polypropylene-based resin particles, the polypropylene-based resin particles preferably contain 0.50 parts by weight or less of the NOR type hindered amine compound and the non-NOR type hindered amine compound in total, more preferably 0.40 parts by weight or less, and even more preferably 0.30 parts by weight or less, per 100 parts by weight of the polypropylene resin.

[0027] The polypropylene resin particles may contain, as necessary, a cell nucleating agent, a hydrophilic compound, an antioxidant, an antistatic agent, a stabilizer (or a flame retardant) other than the hindered amine compound, and the like.

[0028] Examples of hydrophilic compounds include compounds containing hydrophilic groups such as carboxyl groups, hydroxyl groups, amino groups, sulfo groups, and polyoxyethylene groups in the molecule, and derivatives thereof, including hydrophilic polymers.Preferred examples of the hydrophilic compounds include glycerin, polyethylene glycol, polypropylene glycol, and melamine.There is a tendency to easily obtain in-mold foamed molded products with excellent surface beauty.One type of hydrophilic compound may be used alone, or two or more types may be used in combination.

[0029] The content of the hydrophilic compound in the polypropylene resin particles is preferably 0.01 to 10 parts by weight, more preferably 0.03 to 5 parts by weight, and even more preferably 0.05 to 1 part by weight, relative to 100 parts by weight of the polypropylene resin. When the content of the hydrophilic compound is within the above-mentioned range, it is easy to maintain good surface beauty and mechanical properties of the obtained in-mold foamed article while increasing the expansion ratio.

[0030] As the cell nucleating agent, for example, inorganic nucleating agents such as talc, calcium stearate, calcium carbonate, silica, kaolin, titanium oxide, bentonite, barium sulfate, etc. are generally used. These may be used alone or in combination of two or more. Among these cell nucleating agents, talc is preferred because it can produce uniform cells.

[0031] The content of the cell nucleating agent in the polypropylene resin particles may be appropriately adjusted depending on the desired cell diameter and the type of nucleating agent, and may be 0.001 to 2 parts by weight, or 0.01 to 1 part by weight, per 100 parts by weight of the polypropylene resin. When the content of the cell nucleating agent is within this range, cells that are uniform and have a size suitable for expanded beads are easily obtained.

[0032] The weight of each polypropylene-based resin particle is preferably 0.2 mg or more and 10 mg or less, more preferably 0.5 mg or more and 6.0 mg or less. When the weight of each polypropylene-based resin particle is within the above-mentioned range, it is easy to fill the mold and the shrinkage rate of the obtained in-mold foamed molded product is easy to reduce. The weight of each polypropylene-based resin particle is the average resin particle weight calculated based on the weight of 100 randomly selected polypropylene-based resin particles.

[0033] The polypropylene resin particles can be prepared, for example, as follows. First, polypropylene resin, carbon black, and NOR type hindered amine compound, and other additives as necessary, are mixed by a mixing method such as a dry blend method or a master batch method. Next, the resulting mixture (resin composition) is melt-kneaded using an extruder, kneader, Banbury mixer (registered trademark), roll, etc., and then chopped into particles using a cutter, pelletizer, etc.

[0034] The polypropylene-based resin particles obtained above are dispersed in an aqueous dispersant together with a peroxide and a blowing agent in a sealed container, and the resulting dispersion is heated and pressurized. The heated and pressurized dispersion is then released into a pressure range lower than the internal pressure of the sealed container, thereby obtaining expanded polypropylene-based resin particles.

[0035] Specifically, for example, polypropylene resin particles, peroxide, an aqueous dispersion medium, and if necessary, a dispersant are charged in a sealed container, and then the sealed container is evacuated if necessary, and then a foaming agent is introduced into the sealed container, and then the container is heated to a temperature equal to or higher than the softening temperature of the polypropylene resin. The amount of foaming agent added is adjusted so that the pressure in the sealed container increases by heating to about 1.5 MPa (gauge pressure) or more and 5 MPa or less (gauge pressure). If necessary, after heating, the pressure in the sealed container is adjusted to the desired foaming pressure by further adding foaming agent, and the temperature in the sealed container is held for more than 0 minutes and 120 minutes or less while finely adjusting the temperature to the desired foaming temperature, and then the dispersion liquid (contents in the sealed container) containing polypropylene resin particles impregnated with the foaming agent is released into a pressure range (usually atmospheric pressure) lower than the internal pressure of the sealed container to obtain polypropylene resin expanded particles. The foaming pressure is not particularly limited, but is preferably, for example, 1.5 MPa (gauge pressure) or more and 5 MPa or less (gauge pressure). In one or more embodiments of the present invention, "above the softening temperature of the polypropylene resin" means above the melting point of the polypropylene resin -10° C. In addition, the foaming temperature is not particularly limited as long as it is above the softening temperature of the polypropylene resin, and is preferably, for example, above the melting point of the polypropylene resin -10° C. and above the melting point +10° C., although it is not particularly limited.

[0036] For the purpose of adjusting the expansion ratio, the temperature of the atmosphere for discharging may be adjusted to room temperature to about 110° C. In order to obtain expanded beads with a particularly high expansion ratio, it is desirable to set the temperature of the atmosphere for discharging to about 100° C. using steam or the like.

[0037] The method of introducing the blowing agent may be a method other than the above, for example, polypropylene resin particles, peroxide, aqueous dispersion medium, and if necessary, dispersant, etc. may be charged into a sealed container, and then, if necessary, the sealed container may be evacuated, and then the blowing agent may be introduced while heating to a temperature equal to or higher than the softening temperature of the polypropylene resin. As another method of introducing the blowing agent, polypropylene resin particles, peroxide, aqueous dispersion medium, and if necessary, dispersant, etc. may be charged into a sealed container, and then heated to near the foaming temperature, and the blowing agent may be introduced at this point.

[0038] As a method for adjusting the expansion ratio and average bubble diameter of the polypropylene resin expanded particles, for example, before releasing into a low pressure region, carbon dioxide, nitrogen, air, or a substance used as a blowing agent is injected into a sealed container to increase the internal pressure in the sealed container and adjust the pressure release speed during expansion, and further, carbon dioxide, nitrogen, air, or a substance used as a blowing agent is introduced into the sealed container during release into a low pressure region to control the pressure, thereby adjusting the expansion ratio and average bubble diameter. In addition, the expansion ratio and average bubble diameter can also be adjusted by appropriately changing the temperature inside the sealed container before releasing into a low pressure region (generally the foaming temperature).

[0039] Examples of the blowing agent include saturated hydrocarbons such as propane, butane, and pentane, ethers such as dimethyl ether, alcohols such as methanol and ethanol, inorganic gases such as air, nitrogen, and carbon dioxide, and water. These may be used alone or in combination of two or more.

[0040] Among these, it is preferable that the blowing agent contains an inorganic gas such as carbon dioxide, nitrogen, or air, since this has a particularly small environmental impact and is not flammable, and it is more preferable that the blowing agent contains carbon dioxide, since expanded particles having a relatively high expansion ratio are easily obtained.

[0041] The amount of foaming agent added varies depending on the type of foaming agent and the targeted expansion ratio of the polypropylene-based resin expanded particles, and may be adjusted appropriately. For example, the amount may be 1 part by weight or more and 20 parts by weight or less per 100 parts by weight of the polypropylene-based resin particles.

[0042] Although the reason is not clear, the yield of expanded polypropylene resin particles is improved by dispersing a polypropylene resin containing a NOR type hindered amine compound and carbon black in an aqueous dispersion medium containing a peroxide and foaming it.

[0043] As the peroxide, for example, peroxydicarbonates, peroxyesters, peroxyketals, diacyl peroxides, dialkyl peroxides, and the like can be used.

[0044] The peroxydicarbonates are not particularly limited, but for example, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, bis(4-t-butylcyclohexyl)peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, di(2-ethylhexylperoxy)dicarbonate, dimethoxybutyl peroxydicarbonate, and di(3-methyl-3-methoxybutylperoxy)dicarbonate can be suitably used.

[0045] The peroxy esters are not particularly limited, but examples thereof include cumyl peroxy neodecanoate, t-butyl peroxy neodecanoate, 1-cyclohexyl-1-methylethyl peroxy neodecanoate, 1,1,3,3-tetramethylbutyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, t-hexyl peroxy pivalate, t-butyl peroxy pivalate, t-butyl peroxy-3,5,5-trimethylhexanoate, 1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate, t Preferred examples of the peroxyalkylene oxide that can be used include t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, t-butylperoxylaurate, t-hexylperoxybenzoate, t-butylperoxyisobutyrate, t-hexylperoxyisopropyl monocarbonate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, and t-butylperoxymaleic acid.

[0046] The peroxyketals are not particularly limited, but for example, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-bis(t-butylperoxy)cyclododecane, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and 1,1-di-t-butylperoxy-2-methylcyclohexane can be suitably used.

[0047] The diacyl peroxides are not particularly limited, but for example, isobutyl peroxide, 2,4-dichlorobenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, succinic peroxide, m-toluoylbenzoyl peroxide, and benzoyl peroxide can be suitably used.

[0048] The dialkyl peroxides are not particularly limited, but for example, α,α'-bis(neodecanoylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(m-toluoylperoxy)hexane, and 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane can be suitably used.

[0049] The organic peroxides mentioned above may be used alone or in combination of two or more. Among them, from the viewpoint of further increasing the yield of the expanded polypropylene resin particles, it is preferable to use one or more selected from the group consisting of peroxydicarbonates and peroxyesters, and it is more preferable to use one or more selected from the group consisting of bis(4-t-butylcyclohexyl)peroxydicarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-butylperoxyisopropyl monocarbonate, and t-hexylperoxyisopropyl monocarbonate.

[0050] The sealed container is not particularly limited as long as it can withstand the pressure and temperature inside the container during the production of expanded beads, and an example of the sealed container is an autoclave-type pressure-resistant container.

[0051] As the aqueous dispersion medium, it is preferable to use only water, but it is also possible to use a dispersion medium in which methanol, ethanol, ethylene glycol, glycerin, etc. are added to water. When the polypropylene resin particles contain a hydrophilic compound, the water in the aqueous dispersion medium also acts as a foaming agent, contributing to an improvement in the expansion ratio.

[0052] In order to prevent the polypropylene resin particles from adhering to each other, a dispersant may be added to the aqueous dispersion medium.

[0053] Examples of the dispersant include inorganic dispersants such as tricalcium phosphate, trimagnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, clay, etc. These dispersants may be used alone or in combination of two or more.

[0054] In the method for producing polypropylene-based expanded beads according to one or more embodiments of the present invention, a dispersing aid may be used together with the dispersing agent.

[0055] Examples of the dispersion aid include anionic surfactants such as carboxylates, such as N-acylamino acid salts, alkyl ether carboxylates, and acylated peptides; sulfonate types, such as alkyl sulfonates, n-paraffin sulfonates, alkylbenzene sulfonates, alkyl naphthalene sulfonates, and sulfosuccinates; sulfate ester types, such as sulfated oils, alkyl sulfates, alkyl ether sulfates, alkyl amide sulfates, and alkyl allyl ether sulfates; and phosphate ester types, such as alkyl phosphates and polyoxyethylene phosphates. In addition, polycarboxylate-type polymer surfactants, such as maleic acid copolymer salts and polyacrylates, and polyvalent anionic polymer surfactants, such as polystyrene sulfonates and naphthalsulfonic acid formalin condensate salts, can also be used as the dispersion aid. These dispersion aids may be used alone or in combination of two or more.

[0056] The amount of the dispersant or dispersion aid used can be appropriately determined depending on the type and the type and amount of the polypropylene resin particles used. For example, 0.1 to 3 parts by weight of the dispersant and 0.001 to 0.1 parts by weight of the dispersion aid may be mixed with 100 parts by weight of the aqueous dispersion medium.

[0057] In order to improve dispersibility in the aqueous dispersion medium, the polypropylene-based resin particles may be used in an amount of, for example, 20 parts by weight or more and 100 parts by weight or less per 100 parts by weight of the aqueous dispersion medium.

[0058] In one or more embodiments of the present invention, the yield of polypropylene-based resin expanded particles calculated based on the weight W0 of the polypropylene-based resin particles charged in a sealed container and the weight W1 of the polypropylene-based resin particles remaining in the sealed container after expansion using the following formula (1) is preferably 99.0% or more, and more preferably 99.5% or more. Yield of polypropylene resin foam particles (%) = (W0-W1) / W0 x 100

[0059] The expansion step of obtaining expanded polypropylene resin particles from polypropylene resin particles as described above may be referred to as a "first-stage expansion step", and the expanded polypropylene resin particles thus obtained may be referred to as "first-stage expanded particles".

[0060] If necessary, the first-stage expanded particles can be impregnated with an inorganic gas (e.g., air, nitrogen, carbon dioxide, etc.) to impart internal pressure, and then contacted with water vapor at a specific pressure to obtain polypropylene-based resin expanded particles having an improved expansion ratio compared to the first-stage expanded particles. This expansion process of further expanding the polypropylene-based resin expanded particles to obtain polypropylene-based resin expanded particles having a higher expansion ratio is sometimes called a "second-stage expansion process", and the polypropylene-based resin expanded particles obtained through such a second-stage expansion process are sometimes called "second-stage expanded particles".

[0061] The internal pressure of the inorganic gas impregnated into the first-stage expanded beads is desirably changed appropriately taking into consideration the expansion ratio of the second-stage expanded beads, and may be, for example, 0.12 MPa or more (absolute pressure) to 0.6 MPa or less (absolute pressure).

[0062] The pressure of the water vapor in the second-stage expansion step may be adjusted within a range of 0.02 MPa (gauge pressure) to 0.25 MPa (gauge pressure) or within a range of 0.03 MPa (gauge pressure) to 0.15 MPa (gauge pressure) taking into consideration the expansion ratio of the second-stage expanded particles.

[0063] The expanded polypropylene resin particles may have two melting peaks in a DSC curve obtained by measuring the temperature from 40° C. to 220° C. at a heating rate of 10° C. / min. using a differential scanning calorimeter.

[0064] The polypropylene resin expanded particles preferably have a DSC ratio of 10% to 50%, more preferably 15% to 30%. When the DSC ratio is within this range, a polypropylene resin in-mold foamed article with excellent surface beauty can be easily obtained.

[0065] In one or more embodiments of the present invention, the DSC ratio can be calculated by [Qh / (Ql+Qh)×100], where Ql is the melting peak area on the low temperature side of the DSC curve obtained when heating 5 to 6 mg of polypropylene resin expanded particles from 40° C. to 220° C. at a heating rate of 10° C. / min, and Qh is the melting peak area on the high temperature side of the DSC curve during the first heating. Strictly speaking, as shown in FIG. 1, in the DSC curve, Ql is the melting peak heat quantity on the low temperature side, which is the heat quantity surrounded by the melting peak on the low temperature side and the tangent line from the maximum point between the melting peak on the low temperature side and the melting peak on the high temperature side to the melting start baseline, and Qh is the melting peak heat quantity on the high temperature side, which is the heat quantity surrounded by the melting peak on the high temperature side and the tangent line from the maximum point between the melting peak on the low temperature side and the melting peak on the high temperature side to the melting end baseline.

[0066] Since the DSC ratio varies depending on the temperature and pressure during expansion when producing expanded polypropylene resin beads, expanded beads having a desired DSC ratio can be obtained by appropriately adjusting the expansion temperature and pressure. In general, the DSC ratio tends to decrease when the expansion temperature and pressure are increased, and although it also depends on the type of polypropylene resin, additives, and type of foaming agent, specifically, the DSC ratio decreases by about 5 to 20% when the expansion temperature is increased by 1°C, and decreases by about 0.5 to 5% when the expansion pressure is increased by 0.1 MPa.

[0067] The expansion ratio of the expanded polypropylene resin particles is not particularly limited and may be adjusted as necessary. In one or more embodiments of the present invention, the expansion ratio of the expanded polypropylene resin particles is preferably 3 times or more and 40 times or less, more preferably 3 times or more and 25 times or less.

[0068] In one or more embodiments of the present invention, the expansion ratio of the expanded polypropylene resin particles is determined by measuring the weight w (g) of the expanded polypropylene resin particles, then immersing them in a measuring cylinder containing ethanol, and measuring the volume v (cm) based on the amount of water level rise in the measuring cylinder (submersion method). 3 ) is measured, the true specific gravity ρb=w / v of the expanded polypropylene resin particles is calculated, and the ratio of this to the density ρr of the polypropylene resin particles before expansion (ρr / ρb) is calculated.

[0069] (Method of manufacturing polypropylene resin in-mold foamed article) A polypropylene resin in-mold foamed molded article (hereinafter, simply referred to as "in-mold foamed molded article") can be obtained by in-mold foaming of polypropylene resin expanded particles. Specifically, the polypropylene resin expanded particles are filled into a mold having a predetermined shape, heated with steam or the like, and the expanded particles are heat-fused to each other to form a mold, and then cooled with a refrigerant such as water and then removed to obtain a polypropylene resin in-mold foamed molded article. As the mold, a mold that can be closed but cannot be sealed can be used. By using the polypropylene resin expanded particles having a high yield obtained by the method for producing polypropylene resin expanded particles of the present invention, a polypropylene resin in-mold foamed molded article can be produced with high productivity.

[0070] When polypropylene resin expanded beads are subjected to in-mold foaming after applying a pressure equal to or higher than atmospheric pressure to the inside of the expanded beads, a polypropylene resin in-mold foamed article having no gaps and a beautiful surface and little deformation can be easily obtained. There is no particular limitation on the method for applying a pressure equal to or higher than atmospheric pressure to the inside of the expanded beads, but pressure can be applied to the inside of the expanded beads by, for example, a conventionally known method such as an internal pressure application method or a compression filling method.

[0071] In the internal pressure application method, polypropylene resin foamed beads are held under pressure of inorganic gas in advance to apply an internal pressure equal to or higher than atmospheric pressure to the foamed beads, and the foamed beads to which the internal pressure has been applied are filled into a molding space such as a mold that can be closed but not sealed. The applied internal pressure is preferably 0.12 MPa (absolute pressure) to 0.40 MPa (absolute pressure), and more preferably 0.14 MPa (absolute pressure) to 0.30 MPa (absolute pressure). When the internal pressure of the polypropylene resin foamed beads is within this range, it is easy to obtain an in-mold foamed molded product with a beautiful appearance.

[0072] Examples of inorganic gases used to apply internal pressure include air, nitrogen, helium, neon, argon, and carbon dioxide. These gases may be used alone or in combination of two or more. Among these, air and / or nitrogen, which are highly versatile, are preferred.

[0073] In the compression-filling method, polypropylene resin foamed beads are compressed in a compression tank using pressurized gas to a bulk density of preferably 1.25 to 3 times the bulk density of the foamed beads before filling, more preferably 1.5 to 2.2 times the bulk density of the foamed beads before filling, and the compressed foamed beads are filled into a molding space such as a mold that can be closed but not airtight. When the compression ratio is within this range, it is easy to obtain an in-mold foamed molded product with a beautiful appearance.

[0074] Examples of pressurized gases used for compression include air, nitrogen, helium, neon, argon, and carbon dioxide. These gases may be used alone or in combination of two or more. Among these, air and / or nitrogen, which are highly versatile, are preferred.

[0075] After the polypropylene resin foam particles are filled into a mold or the like, they are heated at a water vapor pressure of about 0.15 MPa (gauge pressure) to 0.4 MPa (gauge pressure) using steam or the like as a heating medium to fuse the polypropylene resin foam particles together. The mold is then cooled with water, opened, and the polypropylene resin in-mold foamed article is removed.

[0076] The polypropylene resin in-mold foamed article can be used for various applications, including, but not limited to, heat insulating materials, shock-absorbing packaging materials, automobile interior parts, and core materials for automobile bumpers. EXAMPLES

[0077] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0078] The substances used in the examples and comparative examples are as follows, but were used without any particular purification. <Polypropylene resin> Polypropylene resin 1: Ethylene-propylene random copolymer [ethylene content 3.1% by weight, MFR = 7.2, melting point 150°C] Polypropylene resin 2: Ethylene-propylene random copolymer [ethylene content 3.5 wt%, MFR = 8.4, melting point 145 °C] <Additive> Carbon black [primary particle size 35 nm] Talc [manufactured by Hayashi Kasei Co., Ltd., Talcan Powder PK-S] Glycerin [manufactured by Lion Corporation, Purified Glycerin D] NOR type hindered amine compound: Hindered amine light stabilizer [manufactured by BASF, Flamestab NOR116FF; chemical formula (3)]

Chem.

Chem.

[0079] The evaluation methods carried out in the following examples and comparative examples will be described below.

[0080] <Measurement of DSC ratio> The DSC ratio was measured using a differential scanning calorimeter [DSC7020, Hitachi High-Tech Science Co., Ltd.]. Specifically, the area of ​​the melting peak on the low-temperature side of the DSC curve obtained when heating 5 to 6 mg of polypropylene resin foamed particles from 40°C to 220°C at a heating rate of 10°C / min during the first heating was taken as Ql, and the area of ​​the melting peak on the high-temperature side was taken as Qh, and the ratio was calculated from [Qh / (Ql+Qh)×100]. Strictly speaking, as shown in FIG. 1, in the DSC curve, the amount of heat surrounded by the melting peak on the low-temperature side and the tangent line from the maximum point between the melting peak on the low-temperature side and the melting peak on the high-temperature side to the melting start baseline was taken as Ql, and the amount of heat surrounded by the melting peak on the high-temperature side and the tangent line from the maximum point between the melting peak on the low-temperature side and the melting peak on the high-temperature side to the melting end baseline was taken as Qh.

[0081] <Measurement of expansion ratio of polypropylene resin expanded beads> Take a polypropylene resin foam particle weighing 3g or more and 10g or less, dry it at 60℃ for 6 hours, and then condition it indoors at 23℃ and 50% humidity. After measuring the weight w1 (g), submerge it in a measuring cylinder containing ethanol, and measure the volume v (cm) by the amount of water level rise in the measuring cylinder (submersion method). 3 ) was measured, and the true specific gravity ρb=w1 / v of the expanded polypropylene resin particles was calculated, and further calculated as the ratio (ρr / ρb) to the density ρr of the polypropylene resin particles before expansion. In the following examples and comparative examples, the density ρr of the polypropylene resin particles before expansion was 0.9 g / cm 3 It was.

[0082] <Yield> After obtaining the polypropylene resin expanded particles in the [Preparation of polypropylene resin expanded particles] described later, the weight W1 of the unexpanded propylene resin particles remaining in the 10 L pressure-resistant autoclave was measured, and the weight of the charged propylene resin particles (1800 g) was taken as W0, and the yield was calculated from [(W0-W1) x 100 / W0]. The yield was evaluated according to the following criteria. Good: Yield is 99.0% or higher Defective: Yield is less than 99.0%

[0083] <Molded object density> The weight of the obtained in-mold foamed polypropylene resin article was divided by the volume and converted into units of g / L.

[0084] Example 1 [Method of manufacturing polypropylene resin particles] The polypropylene resin 1 was 100 parts by weight, carbon black was 3 parts by weight, glycerin was 0.2 parts by weight, talc was 0.05 parts by weight, and NOR-type hindered amine compound was 0.05 parts by weight, and then dry-blended using a blender. The mixture obtained by dry-blending was melt-kneaded at a resin temperature of 220°C using a twin-screw extruder [Toshiba Machine Co., Ltd., TEM26-SX], and the extruded strand was water-cooled in a 2-m-long water tank and then cut to produce polypropylene resin particles (1.2 mg / particle).

[0085] [Preparation of polypropylene resin foam particles] In a 10L pressure-resistant autoclave, 100 parts by weight (1.8 kg) of the polypropylene resin particles obtained above, 300 parts by weight of water, 0.3 parts by weight of kaolin [BASF, ASP170] as a poorly water-soluble inorganic compound, 0.06 parts by weight of sodium dodecylbenzenesulfonate [Kao Corporation, Neopelex G-15] as a surfactant, and 1.0 parts by weight of organic peroxide 1 were charged, and then 5 parts by weight of carbon dioxide was added as a foaming agent under stirring. The contents of the autoclave were heated to a foaming temperature of 156.0°C and held for 10 minutes, and then carbon dioxide was additionally injected to raise the pressure inside the autoclave to a foaming pressure of 2.3 MPa. After holding for 20 minutes at the foaming temperature and foaming pressure, the valve at the bottom of the autoclave was opened, and the contents were released under atmospheric pressure through an opening orifice with a diameter of 3.6 mm to obtain polypropylene resin foamed particles with an expansion ratio of 12 times. During the release, carbon dioxide was injected to maintain the pressure in the container so that the pressure would not decrease.

[0086] [Preparation of polypropylene resin in-mold foamed bodies] The obtained expanded beads were dried at 75°C. The dried expanded beads were placed in a pressure-resistant container, impregnated with pressurized air, and the polypropylene resin expanded beads, which had been adjusted in advance to have an internal pressure of 0.20MPa (absolute pressure), were filled into a mold measuring 370mm long x 320mm wide x 50mm thick. The interior of the mold chamber was then heated with steam at a predetermined pressure to fuse the expanded beads together. After cooling the interior of the mold and the surface of the molded body with water, the molded body was removed to obtain a polypropylene resin in-mold expanded molded body. This operation was carried out by changing the steam pressure from 0.20MPa (gauge pressure) to 0.35MPa in increments of 0.01MPa, and the minimum pressure required for sufficient fusion of the polypropylene resin expanded beads together was determined and used as the lower limit molding pressure. The obtained in-mold expanded molded body was left to stand at 23°C for 2 hours, and then aged at 75°C for 16 hours.

[0087] (Example 2, Comparative Examples 1 to 4) Polypropylene-based resin particles, polypropylene-based resin expanded particles, and polypropylene-based resin in-mold foamed molded articles were produced in the same manner as in Example 1, except that in [Preparation of polypropylene-based resin particles], the type of additives and the resin formulation were changed as shown in Table 1, and in [Preparation of polypropylene-based resin expanded particles], the foaming conditions were changed as shown in Table 1. The evaluation results of the obtained polypropylene-based resin expanded particles and polypropylene-based resin in-mold foamed molded articles are shown in Table 1.

[0088] [Table 1]

[0089] From the above Table 1, it can be seen that the yield of the expanded polypropylene resin particles is good in Examples 1 and 2. In the cases of Comparative Examples 1 and 2, although polypropylene resin particles containing a NOR type hindered amine compound and carbon black are used, the yield of the expanded polypropylene resin particles is poor because no peroxide is present in the aqueous dispersion medium. In addition, in the case of Comparative Example 3, even if the polypropylene resin particles are dispersed in an aqueous dispersion medium containing a peroxide and expanded, the yield of the expanded polypropylene resin particles is poor because the polypropylene resin particles do not contain a NOR type hindered amine compound. In addition, in the case of Comparative Example 4, even if the polypropylene resin particles containing a hindered amine compound are used and expanded in an aqueous dispersion medium containing a peroxide, the yield of the expanded polypropylene resin particles is poor because the polypropylene resin does not contain a NOR type hindered amine compound.

Claims

1. A method for producing expanded polypropylene resin particles, comprising the steps of: (i) a step of dispersing a polypropylene-based resin, carbon black, polypropylene-based resin particles containing a NOR-type hindered amine-based compound, a peroxide, and a blowing agent in an aqueous dispersion medium in a sealed container to obtain a dispersion; (ii) heating and pressurizing the dispersion; and (iii) discharging the dispersion liquid after the heating and pressurization into a pressure region lower than the internal pressure of the sealed container; The polypropylene-based resin particles contain 100 parts by weight of a polypropylene-based resin, 0.1 to 10 parts by weight of carbon black, and 0.01 to 0.50 parts by weight of a NOR-type hindered amine compound.

2. 2. The method for producing expanded polypropylene resin particles according to claim 1, wherein the polypropylene resin particles contain 100 parts by weight of a polypropylene resin, 1 part by weight or more and 5 parts by weight or less of carbon black, and 0.05 parts by weight or more and 0.20 parts by weight or less of a NOR type hindered amine compound.

3. 3. The method for producing expanded polypropylene resin particles according to claim 1, wherein the amount of the peroxide added is 0.01 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the polypropylene resin.

4. The NOR type hindered amine compound is a compound represented by the following general formula (1): 【Chemistry 1】 In the general formula (1), R 1 and R 2 R is an s-triazine moiety represented by the following general formula (2): 3 and R 4 One of the groups is an s-triazine moiety represented by the following general formula (2), R 3 and R 4 The other represents a hydrogen atom, 【Chemistry 2】 In the general formula (2), R 5 is an alkyl group having 1 to 12 carbon atoms, R 6 The method for producing expanded polypropylene resin particles according to any one of claims 1 to 3, wherein represents a methyl group, a cyclohexyl group, or an octyl group.

5. The method for producing expanded polypropylene resin beads according to any one of claims 1 to 4, wherein the peroxide is one or more organic peroxides selected from the group consisting of peroxyesters and peroxydicarbonates.

6. The method for producing expanded polypropylene resin particles according to any one of claims 1 to 5, wherein the foaming agent contains carbon dioxide.

7. The method for producing expanded polypropylene-based resin beads according to any one of claims 1 to 6, wherein a yield of expanded polypropylene-based resin beads calculated by the following formula (1) based on a weight W0 of the polypropylene-based resin particles charged into the sealed container in the step (i) and a weight W1 of the polypropylene-based resin particles remaining in the sealed container after the step (iii) is 99.0% or more. [Formula 1] Yield (%) of polypropylene resin expanded particles = (W0 - W1) / W0 x 100

8. A method for producing an in-mold foamed polypropylene resin article, comprising a step of in-mold foaming the expanded polypropylene resin beads obtained by the method for producing the expanded polypropylene resin beads according to any one of claims 1 to 7.

Images