JP2019163426A - Process for producing polypropylene-based resin expanded particle - Google Patents

Abstract

To provide a process for producing polypropylene-based resin expanded particle that reduces the load on wastewater treatment by reducing the used amount of water-absorptive substance added to obtain a high expansion ratio in a single expansion step using inorganic gas as the expanding agent as well as that hardly makes the cell size finely divided.SOLUTION: Provided is a process for producing polypropylene-based resin expanded particle in which polypropylene-based resin particles containing 3 pts.wt. to 15 pts.wt. of spherical hollow glass composition for 100 pts.wt. of polypropylene-based resin are dispersed in an aqueous dispersion medium in a closed vessel, impregnated with an inorganic gas as an expanding agent by pressurization, and heated to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles, and thus obtained polypropylene-based resin particles are released into a region having a pressure lower than the inner pressure of the closed vessel, to produce polypropylene-based resin expanded particles.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing expanded polypropylene resin particles.

  In-mold foam moldings obtained by filling polypropylene resin foam particles in molds and heat-molding with water vapor are the advantages of in-mold foam moldings, such as shape flexibility, lightness, and heat insulation. have. In addition, compared with in-mold foam moldings using similar synthetic resin foam particles, compared with in-mold foam moldings obtained using polystyrene resin foam particles, chemical resistance, heat resistance, strain recovery after compression The dimensional accuracy, heat resistance, and compressive strength are excellent as compared with an in-mold foam molded article using polyethylene resin expanded particles. Due to these characteristics, in-mold foam molded articles obtained using polypropylene resin foam particles are used in various applications such as heat insulating materials, shock-absorbing packaging materials, automobile interior members, and automobile bumper core materials. Depending on the application, colored in-mold foam molded products are preferred, but when the cells in the expanded particles are fine, the color tends to look whitish, and it is necessary to increase the colorant in order to obtain the desired color. It was.

  Conventionally, as a foaming agent used in this field, a volatile organic foaming agent has been used since foamed particles with a high expansion ratio can be obtained. However, due to increasing interest in environmental problems, in recent years, inorganic gases such as air, nitrogen, oxygen, carbon dioxide (carbon dioxide) have been used as blowing agents. When inorganic gas is used as a foaming agent, it is difficult to obtain a high magnification in a single foaming process because of its low solubility in polypropylene resin, and the foaming ratio is increased by adding a cell nucleating agent such as talc. However, since the cell diameter can be easily reduced, a water-absorbing substance such as polyethylene glycol or glycerin may be added in order to use an inorganic gas as a foaming agent as in Patent Document 1. However, when resin particles are dispersed in an aqueous dispersion medium in the production stage of expanded particles, since polyethylene glycol and glycerin are water-soluble substances, they may elute into the dispersion medium and cause a load on wastewater treatment. It was.

  Patent Documents 2 and 3 exemplify the use of spherical hollow glass compositions such as shirasu balloons as fillers and fillers for polypropylene resin foams. However, in these documents, the spherical hollow glass composition is only exemplified as one of many fillers and fillers in order to impart rigidity and the like to the polypropylene-based foam molded article.

  Patent Document 4 discloses a manufacturing method in which polypropylene, scallop shell powder, shirasu balloon, and foaming agent pellets are melted and mixed to obtain a closed cell foam material (beads). Patent Document 5 discloses a production method in which a polyolefin resin containing 0.3 to 1.5% by weight of a microporous granular material such as a shirasu balloon is foamed. However, Patent Documents 4 and 5 relate to extrusion foaming.

International Publication No. 2016/13675 JP-A-5-70621 International Publication No. 2012/09082 JP 2007-29938 A JP 2010-37367 A

  The object of the present invention is to reduce the amount of a water-absorbing substance added in order to obtain a high magnification in a single foaming process using an inorganic gas as a foaming agent in the production of polypropylene resin expanded particles, or An object of the present invention is to provide a method for producing polypropylene resin foamed particles, in which the cell diameter is difficult to be miniaturized while eliminating the load on wastewater treatment.

  As a result of intensive studies to solve the above problems, the inventor of the present invention uses polypropylene resin particles containing 3 parts by weight or more and 15 parts by weight or less of a spherical hollow glass composition with respect to 100 parts by weight of polypropylene resin. In the case of producing foamed particles using an inorganic gas as a foaming agent, the amount of the water-absorbing substance used is reduced or eliminated, and the polypropylene resin foamed particles having a desired magnification can be obtained while suppressing cell miniaturization. A manufacturing method that can be manufactured was found and the present invention was completed.

That is, this invention consists of the following structures.
(1) A method for producing polypropylene resin expanded particles, wherein polypropylene resin particles containing 3 to 15 parts by weight of a spherical hollow glass composition with respect to 100 parts by weight of polypropylene resin are contained in a sealed container. Dispersed in an aqueous dispersion medium, impregnated with inorganic gas as a foaming agent under pressure, and released polypropylene resin particles heated to a temperature above the softening temperature of the polypropylene resin particles to a pressure range lower than the internal pressure of the sealed container A method for producing expanded polypropylene resin particles, comprising obtaining expanded polypropylene resin particles.
(2) A method for producing expanded polypropylene resin particles, comprising 3 parts by weight or more and 15 parts by weight or less of a spherical hollow glass composition, and 0.1 to 10 parts by weight of a colorant with respect to 100 parts by weight of polypropylene resin. The method for producing expanded polypropylene resin particles according to (1), comprising using polypropylene resin particles including:
(3) The method for producing expanded polypropylene resin particles according to (2), wherein the colorant is carbon black.
(4) The method for producing expanded polypropylene resin particles according to any one of (1) to (3), wherein the spherical hollow glass composition is a shirasu balloon.
(5) The method for producing expanded polypropylene resin particles according to any one of (1) to (4), wherein the inorganic gas as the foaming agent is carbon dioxide.
(6) A polypropylene resin foamed particle obtained by the method for producing a polypropylene resin foamed particle according to any one of (1) to (5), which has the following features (11) to (22): Polypropylene resin foam particles.
(11) The average cell diameter of the polypropylene resin expanded particles is 100 μm or more.
(22) The expansion ratio of the polypropylene resin expanded particles is 15 times or more.
(7) In the molding space in which the foamed particles obtained by the method for producing polypropylene-based resin foamed particles according to any one of (1) to (5) can be closed by two molds but cannot be sealed. A method for producing a foamed molded product in a polypropylene resin mold, wherein the foamed particles are heated by water vapor through water vapor holes arranged in a mold.

  Even when producing foamed particles using inorganic gas as a foaming agent by the production method of the present invention, the use of a water-absorbing substance that increases the load of wastewater treatment is reduced or eliminated, and the cell is made finer. While suppressing, it is possible to produce polypropylene resin expanded particles having a desired magnification.

It is an example of the DSC curve obtained when the polypropylene resin expanded particles obtained by the production method of the present invention are heated at a rate of 10 ° C./min from 40 ° C. to 220 ° C. with a differential scanning calorimeter (DSC). . Here, the melting peak calorific value on the low temperature side, which is the amount of heat surrounded by the tangent to the melting start baseline from the maximum point between the melting peak on the low temperature side and the low temperature side peak and the high temperature side peak, is Ql, the high temperature side of the DSC curve Qh is the high-temperature side melting peak calorie, which is the amount of heat surrounded by the tangent line from the maximum point between the melting peak, low-temperature side peak, and high-temperature side peak to the melting end baseline.

  In the present invention, polypropylene resin particles containing 3 parts by weight or more and 15 parts by weight or less of the spherical hollow glass composition with respect to 100 parts by weight of the polypropylene resin are used in producing the polypropylene resin foamed particles.

  The polypropylene resin used as the base resin in the present invention is not particularly limited as long as it contains 50% by weight or more of propylene as the main component of the monomer. For example, propylene homopolymer, olefin-propylene random A copolymer, an olefin-propylene block copolymer, etc. are mentioned. These may be used alone or in combination of two or more.

  The copolymerizable olefin in the polypropylene resin used in the present invention is not particularly limited, and examples thereof include olefins having 2 or 4 carbon atoms. Specifically, ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1- Examples include α-olefins such as heptene, 3-methyl-1-hexene, 1-octene, and 1-decene, and cyclopentene, norbornene, and tetracyclo [6,2,11,8,13,6] -4- Cyclic olefins such as dodecene, dienes such as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, etc. Can be mentioned. In addition, these olefins having 2 or 4 or more carbon atoms may be used alone or in combination of two or more.

  Among these, ethylene or α-olefin is preferable and ethylene and 1-butene are most preferable from the viewpoint of availability, economy, and mechanical properties.

  The copolymerizable olefin content in the polypropylene resin used in the present invention is preferably 0 to 10% by weight, more preferably 1 to 7% by weight, more preferably 1.5 to 6% by weight. % Or less is more preferable, and 1.5% by weight or more and 5% by weight or less is particularly preferable. When the copolymerizable olefin content in the polypropylene resin is within this range, the resulting polypropylene resin in-mold foam-molded product tends to have good mechanical strength and high dimensional stability at high temperatures.

  In the polypropylene resin used in the present invention, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate are further included in the range not impairing the object of the present invention. , Vinyl monomers such as methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and divinyl benzene may be copolymerized.

 Among the above polypropylene resins, ethylene-propylene random copolymer and 1-butene-propylene random copolymer containing ethylene and 1-butene from the viewpoints of good foamability, improved cold brittleness resistance, and low cost. An ethylene-1-butene-propylene random copolymer can be suitably used.

  The melting point of the polypropylene resin used in the present invention is not particularly limited, but is preferably 130 ° C. or higher and 155 ° C. or lower, more preferably 140 ° C. or higher and 151 ° C. or lower. When the melting point of the polypropylene resin is in the above-described range, an in-mold foam molded article having an excellent balance of dimensional properties, mechanical strength, and surface aesthetics can be obtained when the obtained foamed particles are molded by in-mold foam molding. It tends to be easy.

  The melting point in the present invention refers to a polypropylene resin or polypropylene resin particles 1 mg to 10 mg heated from 40 ° C. to 220 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter DSC, and then The peak temperature of the endothermic peak in the DSC curve obtained when cooling from 220 ° C. to 40 ° C. at a rate of temperature decrease of 10 ° C./min and increasing the temperature from 40 ° C. to 220 ° C. at a rate of 10 ° C./min. is there.

  The melt flow rate (hereinafter sometimes referred to as MFR) of the polypropylene resin used in the present invention is preferably 3.0 g / 10 min or more and 12 g / 10 min or less, more preferably 5.0 g / 10. Min. To 9.0 g / 10 min. When the melt flow rate of the polypropylene resin is in the above-mentioned range, when the obtained foamed particles are subjected to in-mold foam molding, there is a tendency that an in-mold foam molded body with little deformation and excellent surface beauty is easily obtained. is there.

  The measurement of MFR in the present invention uses an MFR measuring instrument described in JIS K7210, under conditions of orifice 2.0959 ± 0.005 mmφ, orifice length 8.000 ± 0.025 mm, load 2160 g, 230 ± 0.2 ° C. It is a value when measured by.

  The polypropylene resin used in the present invention can be obtained using a catalyst such as a Ziegler catalyst, a metallocene catalyst, a post metallocene catalyst. When a Ziegler catalyst is used, a polymer having a large Mw / Mn tends to be obtained.

  The polypropylene resin used in the present invention can be adjusted in characteristics such as molecular weight and melt flow rate by oxidative decomposition using an organic peroxide. In order to oxidatively decompose the polypropylene resin, for example, a polypropylene resin added with an organic peroxide can be heated and melted in an extruder.

  The spherical hollow glass composition used in the present invention preferably contains 40 to 80% by mass of SiO2, 10 to 40% by mass of Al2O3, and 1 to 18% by mass of Fe2O3 in the glass composition. Spherical hollow glass compositions having this composition include shirasu balloons made by firing and foaming shirasu, which is a volcanic product, and pearlite, obsidian, or similar stones by firing and foaming glassy volcanic rocks. Perlite obtained by firing and foaming rocks, fly ash obtained by classifying ash collected by a dust collector from coal ash generated when pulverized coal is burned at a coal-fired power plant, and glass material, A processed product in which a glass waste material or the like is artificially formed into a hollow shape is exemplified. Among these, a shirasu balloon can be particularly preferably used.

The spherical hollow glass composition used in the present invention can be of any type, but the spherical hollow glass composition preferably has an average particle size of 2 μm to 180 μm and an average particle size of 20 μm to 90 μm. Are particularly preferred. The bulk specific gravity of preferably 0.1g / cm ³ ~1.0g / cm ³ spherical hollow glass composition, and more preferably ^{0.1g / cm 3 ~0.7g / cm 3} .

  The content of the spherical hollow glass composition in the resin particles in the present invention is 3 parts by weight or more and 15 parts by weight or less, preferably 4 parts by weight or more with respect to 100 parts by weight of the polypropylene resin. 12 parts by weight or less. When the amount is less than 3 parts by weight, the effect of improving the magnification ratio of the expanded particles tends to be small. When the amount exceeds 15 parts by weight, the ratio of the polypropylene resin is low, and the properties derived from the polypropylene resin are low. There is a risk of damage.

  In the production of the polypropylene resin expanded particles of the present invention, expanded particles with a desired magnification can be obtained even if the amount of water-absorbing substance added to the resin particles is reduced or eliminated. As the water-absorbing substance, for example, a water-absorbing substance described in WO2016 / 136875 is incorporated, and preferably a substance such as melamine, glycerin, polyethylene glycol, zinc borate and the like is used.

  The polypropylene resin particles may contain a cell nucleating agent, an antioxidant, an antistatic agent, a colorant, a flame retardant, and the like, if necessary, in addition to the polypropylene resin mixture as the base resin. Such an additive may be preliminarily added to another resin in a high concentration to form a master batch, and this master batch resin may be added to the polypropylene resin mixture. As a resin used for such a master batch resin, a polyolefin resin is preferable, and a polypropylene resin is more preferable.

  As the cell nucleating agent used in the present invention, inorganic nucleating agents such as talc, calcium stearate, calcium carbonate, silica, kaolin, titanium oxide, bentonite and barium sulfate are generally used. These may be used alone or in combination of two or more. Among these cell nucleating agents, a cell having uniform talc can be obtained, which is preferable. The content of the cell nucleating agent in the polypropylene resin particles may be appropriately adjusted depending on the intended cell diameter and the type of the nucleating agent. The amount is preferably 001 parts by weight or more and 0.5 parts by weight or less, more preferably 0.01 parts by weight or more and 0.2 parts by weight or less. When the content of the cell nucleating agent is within the range, cells having a uniform size suitable for expanded particles can be easily obtained.

  As the colorant, carbon black, ultramarine, cyanine pigment, azo pigment, quinacridone pigment cadmium yellow, chromium oxide, iron oxide, perylene pigment, anthraquinone pigment, and the like can be used. The content of the colorant in the polypropylene resin particles is not limited, and may be adjusted according to the coloring power of the colorant and the desired color. The colorant is 0.01 part by weight with respect to 100 parts by weight of the polypropylene resin. It is preferably 15 parts by weight or less and more preferably 0.1 parts by weight or more and 10 parts by weight or less. When the content is within the above range, a good color can be easily obtained without impairing the in-mold foam moldability of the foamed particles.

  As the colorant, carbon black, which is a fine powder of carbon obtained by incomplete combustion of natural gas or petroleum, or thermal decomposition, may be used as a black pigment when emphasizing the appearance in terms of color and colorability. Many are preferred forms.

  The content of carbon black in the polypropylene resin particles is preferably 0.1 parts by weight or more and 10 parts by weight or less, preferably 1 part by weight or more and 8 parts by weight or less with respect to 100 parts by weight of the polypropylene resin. It is more preferable that When the content is in this range, the colorability is good, the viscosity of the resin is hardly lowered, and when the obtained foamed particles are molded in-mold, an in-mold foam-molded article with good quality is obtained. It is a tendency to be easily done.

  The carbon black in the present invention preferably has a primary particle size of more than 0 nm and 100 nm or less. Preferably they are 10 nm or more and 50 nm or less. When the primary particle size is in this range, the colorability is excellent, and uniform black expanded particles tend to be obtained. The primary particle size of carbon black in the present invention was obtained by taking a photograph of a cross section of the cell membrane of the obtained polyolefin-based resin expanded particles magnified 40,000 times with a transmission electron microscope, and the obtained transmission electron micrograph. The particle diameters (Ferre diameter) in the X direction and the Y direction of 50 carbon black primary particles are measured arbitrarily, and the average value is calculated. Examples of such carbon black include channel black, roller black, disk, gas furnace black, oil furnace black, thermal black, acetylene black, and the like, and one or more of these can be used.

  In the method for producing polypropylene resin expanded particles of the present invention, first, polypropylene resin particles are produced.

  Examples of the method for producing the polypropylene resin particles in the present invention include the following methods.

  First, a polypropylene resin and a spherical hollow glass composition, and, if necessary, a mixture of other additives are mixed by a mixing method such as a dry blend method or a master batch method.

  Next, the resulting mixture is melt-kneaded using an extruder, kneader, Banbury mixer (registered trademark), roll, etc., and then chopped using a cutter, pelletizer, etc., to obtain a particle shape, thereby producing a polypropylene system Resin particles are obtained.

  The weight per one polypropylene resin particle in the present invention is preferably 0.2 mg or more and 10 mg or less, and more preferably 0.5 mg or more and 6.0 mg or less. When the weight per one polypropylene resin particle is within the above range, the size and filling properties are likely to be good when the obtained foamed particles are subjected to in-mold foam molding.

  Here, the weight per one polypropylene resin particle is the average resin particle weight obtained from 100 particles of randomly selected polypropylene resin particles.

  Usually, the composition and particle weight of the polypropylene resin particles are hardly changed even after the foaming process and the in-mold foam molding process, and the same properties are exhibited even when the foam particles and the in-mold foam molding are remelted.

  In the present invention, the polypropylene resin particles obtained in this way are dispersed in an aqueous dispersion medium in a closed container, impregnated with an inorganic gas as a foaming agent under pressure, and above the softening temperature of the polypropylene resin particles. Polypropylene resin foam particles are produced by releasing the polypropylene resin particles heated to the above temperature (foaming temperature) into a pressure range lower than the internal pressure of the sealed container.

  In one embodiment of the present invention, “more than the softening temperature of polypropylene resin particles” means that the melting point of the polypropylene resin used is −10 ° C. or more. The foaming temperature is not particularly limited, and may be any temperature as long as it is equal to or higher than the softening temperature of the polypropylene resin particles, and is not particularly limited. For example, the melting point of the polypropylene resin used is -10 ° C or higher and melting point + 10 ° C or lower. Is preferred.

  For the purpose of adjusting the expansion ratio, the temperature of the released atmosphere may be adjusted to about room temperature to about 110 ° C. In particular, in order to obtain expanded particles with a high expansion ratio, it is desirable to set the temperature of the atmosphere to be released to about 100 ° C. with steam or the like.

  The pressure (foaming pressure) for impregnating the foaming agent in the closed container in the present invention is preferably about 1.5 MPa (gauge pressure) or more and 5.0 MPa or less (gauge pressure), and about 2.5 MPa (gauge pressure). ) To 3.5 MPa (gauge pressure). When the foaming pressure is within the range, foamed particles having an excellent balance between the cell diameter and the foaming ratio are easily obtained.

  As the foaming agent in the present invention, an inorganic gas such as carbon dioxide, nitrogen, air or the like is used because it has a small environmental load and has no risk of combustion. Among these foaming agents, carbon dioxide is preferable because expanded particles having a relatively high expansion ratio can be easily obtained. These may be used alone or in combination of two or more.

  Specific examples of the method for producing expanded polypropylene resin particles in the present invention include the following methods.

  (1) After charging polypropylene-based resin particles, an aqueous dispersion medium, and a dispersant as necessary into a sealed container, the inside of the sealed container is evacuated as necessary, and then into the sealed container, an inorganic gas as a foaming agent And then heated to a temperature higher than the softening temperature of the polypropylene resin. The amount of inorganic gas added as a foaming agent is adjusted so that the pressure in the sealed container rises to about 1.5 MPa (gauge pressure) or more and 5 MPa or less (gauge pressure) by heating. If necessary, after heating, add inorganic gas as a foaming agent to adjust to the desired foaming pressure, and further hold the temperature for more than 0 minutes and 120 minutes or less while finely adjusting the foaming temperature. Then, it is discharged into a pressure region (usually atmospheric pressure) lower than the internal pressure of the sealed container adjusted to 80 ° C. or higher and 110 ° C. or lower with water vapor or the like to obtain polypropylene resin expanded particles.

  Examples of the method of introducing a foaming agent different from the above in the present invention include the following methods.

  (2) A method in which a foaming agent is introduced by charging solid carbon dioxide in the form of dry ice at the same time as charging polypropylene resin particles, an aqueous dispersion medium, and a dispersant as required.

  (3) After charging polypropylene resin particles, aqueous dispersion medium, and dispersing agent, if necessary, in a sealed container, the inside of the sealed container is evacuated and then the softening temperature of the polypropylene resin or higher. A method of introducing a foaming agent while heating to a temperature of.

  (4) In a closed container, polypropylene resin particles, an aqueous dispersion medium, and a dispersant as required are charged, and then, if necessary, the inside of the closed container is evacuated and heated to near the foaming temperature. A method of introducing a blowing agent at this point.

  Examples of the method for increasing the expansion ratio of the expanded polypropylene resin particles include a method for increasing the internal pressure in the sealed container, a method for increasing the pressure release speed, and a method for increasing the temperature in the sealed container before discharge.

  The sealed container used in the present invention is not particularly limited, and may be any container that can withstand the pressure in the container and the temperature in the container at the time of producing the expanded particles, and examples thereof include an autoclave type pressure resistant container.

  In the method for producing polypropylene resin expanded particles in the present invention, it is preferable to use a dispersant in the aqueous dispersion medium in order to prevent coalescence of the polypropylene resin particles.

  Examples of the dispersant used in the present invention include inorganic dispersants such as tricalcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay.

  These dispersants may be used alone or in combination of two or more.

  In the method for producing expanded polypropylene resin particles in the present invention, it is preferable to use a dispersion aid together with the dispersant.

As an example of the dispersion aid used in the present invention, for example,
Carboxylate types such as N-acyl amino acid salts, alkyl ether carboxylates, acylated peptides;
Sulfonate types such as alkyl sulfonates, n-paraffin sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, sulfosuccinates;
Sulfate ester types such as sulfated oil, alkyl sulfate, alkyl ether sulfate, alkyl amide sulfate, alkyl allyl ether sulfate;
Anionic surfactants such as phosphate ester types such as alkyl phosphates and polyoxyethylene phosphates can be mentioned.

  In addition, as dispersion aids, polyanionic polymer surfactants such as maleic acid copolymer salts and polyacrylates, polystyrene anion salts such as polystyrene sulfonates and naphthalsulfonic acid formalin condensate salts are used. Molecular surfactants can also be used.

  These dispersing aids may be used alone or in combination of two or more.

  Among these, at least one selected from the group consisting of tricalcium phosphate, magnesium triphosphate, barium sulfate or kaolin as a dispersing agent, and n-paraffin sulfonic acid soda and alkylbenzene sulfonic acid as a dispersing aid. It is preferable to use at least one selected in combination.

  The amount of the dispersant and the dispersion aid used in the present invention varies depending on the type and the type and amount of the polypropylene resin particles to be used. Usually, the dispersant is 0.1 weight with respect to 100 parts by weight of the aqueous dispersion medium. It is preferable to add from 3 parts by weight to 3 parts by weight, and it is preferable to add from 0.001 parts by weight to 0.1 parts by weight of the dispersion aid.

  In order to improve the dispersibility in the aqueous dispersion medium, the polypropylene resin particles are usually preferably used in an amount of 20 to 100 parts by weight with respect to 100 parts by weight of the aqueous dispersion medium.

  In one embodiment of the present invention, as described above, a foaming step for obtaining polypropylene resin foamed particles from polypropylene resin particles may be referred to as a “single-stage foaming step”. The particles are sometimes referred to as “single-stage expanded particles”.

  The expanded polypropylene resin particles of the present invention are obtained when 5-6 mg of expanded polypropylene resin particles are heated from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min in measurement by differential scanning calorimetry. It is preferable to have two melting peaks in the DSC curve.

  The expanded polypropylene resin particles of the present invention 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 foam-molded product having a high surface beauty is easily obtained.

  Here, as shown in FIG. 1, the DSC ratio is the amount of heat surrounded by a tangent line from the melting point on the low temperature side and the maximum point between the low temperature side peak and the high temperature side peak to the melting start baseline. The melting peak calorific value is Ql, and the high temperature side melting peak calorific value is Qh, which is the amount of heat surrounded by the tangent line from the maximum point between the melting peak on the high temperature side of the DSC curve and the low temperature side peak to the high temperature side peak. The ratio of the melting peak on the high temperature side [Qh / (Ql + Qh) × 100] calculated from these.

  Since the DSC ratio changes depending on the temperature and pressure at the time of foaming when producing the polypropylene resin foamed particles, the foamed particles having the desired DSC ratio can be obtained by appropriately adjusting the foaming temperature and the foaming pressure. Obtainable. In general, the DSC ratio tends to decrease as the foaming temperature and foaming pressure increase, and it depends on the type of polypropylene resin, additive, and type of foaming agent. When the temperature is increased by 1 ° C., the DSC ratio decreases by about 5 to 20%, and when the foaming pressure is increased by 0.1 MPa, the DSC ratio decreases by about 0.5 to 5%.

  In the present invention, the expansion ratio of the polypropylene resin expanded particles is not particularly limited, and may be adjusted as necessary. By using the production method of the present invention, it can also be suitably used when producing expanded particles having an expansion ratio of 15 times or more.

The expansion ratio of the expanded polypropylene resin particles is determined by measuring the weight w (g) of expanded polypropylene resin particles, submerging them in a graduated cylinder containing ethanol, and then increasing the volume of the graduated cylinder by water level (submerged method). The value calculated by measuring v (cm ³ ), calculating the true specific gravity ρb = w / v of the polypropylene resin expanded particles, and further calculating the ratio (ρr / ρb) with the density ρr of the polypropylene resin particles before expansion. It is.

  The average cell diameter of the expanded polypropylene resin particles of the present invention is preferably 100 μm or more and 500 μm or less, and more preferably 150 μm or more and 400 μm or less. When the average cell diameter of the polypropylene resin foamed particles is in the above range, the color tone and appearance of the obtained polypropylene resin in-mold foam molded product are likely to be good.

  Here, the average bubble diameter is a value measured as follows.

  In an image obtained by microscopic observation of the cut surface of the foamed particle, a straight line passing through substantially the center of the foamed particle is drawn, and the foamed particle is determined from the number of bubbles n passing through the straight line and the intersection of the straight line and the surface of the foamed particle The diameter L (μm) is read and obtained by the equation (1).

  Average bubble diameter (μm) = L / n (1)

  By using the foamed particles of the present invention, a polypropylene resin in-mold foam-molded product can be obtained. A method for producing a polypropylene resin-in-mold foam-molded product is that a polypropylene-based resin foam particle is filled into a mold space that can be closed but cannot be sealed, and water vapor holes arranged in the mold. In this method, the foamed particles are heated with water vapor, and the foamed particles are heated and fused with each other to be molded according to the mold, taken out after being cooled with a coolant such as water, and the like. It is preferable that the polypropylene-based resin expanded particles apply a pressure equal to or higher than the atmospheric pressure inside the expanded particles before in-mold foam molding. In-mold foam molding using foam particles to which pressure equal to or higher than the atmospheric pressure is applied to the inside of the foam particles makes it easy to obtain a polypropylene resin in-mold foam molded article having no intergranularity and a beautiful surface and little deformation. Although there is no restriction | limiting in particular in the method of providing the pressure more than atmospheric pressure inside a foamed particle, For example, a pressure can be provided inside a foamed particle by methods, such as the conventionally known internal pressure provision method and the compression filling method.

  In the internal pressure application method, a polypropylene resin expanded particle is previously held under pressure of an inorganic gas to apply an internal pressure of atmospheric pressure or higher to the expanded particle, and the expanded particle to which the internal pressure is applied can be closed but is not sealed. Fill the molding space such as a mold.

  The internal pressure is preferably from 0.12 MPa (absolute pressure) to 0.40 MPa (absolute pressure), more preferably from 0.14 MPa (absolute pressure) to 0.30 MPa (absolute pressure). When the internal pressure of the polypropylene resin expanded particles is within the above range, it tends to be easy to obtain an in-mold expanded molded article having a beautiful appearance. As the inorganic gas used for applying the internal pressure, air, nitrogen, helium, neon, argon, carbon dioxide or the like can be used. These gases may be used alone or in combination of two or more. Among these, highly versatile air and nitrogen are preferable.

  In the compression filling method, polypropylene resin foam particles are compressed in a compression tank using a pressurized gas, preferably to a bulk density of 1.25 to 3 times the bulk density of the foam particles before filling, more preferably before filling. The foamed particles are compressed to a bulk density of 1.5 to 2.2 times the bulk density, and the compressed foamed particles are filled in a molding space such as a mold that can be closed but not sealed.

  When the compression ratio is within the above range, it tends to be easy to obtain an in-mold foam molded article having a beautiful appearance.

  As the pressurized gas used for the compression, air, nitrogen, helium, neon, argon, carbon dioxide or the like can be used. These gases may be used alone or in combination of two or more. Among these, highly versatile air and nitrogen are preferable.

  After filling polypropylene resin expanded particles into a mold or the like by the above method, heating is performed for about 3 to 50 seconds at a heating water vapor pressure of about 0.15 to 0.4 MPa (G) using water vapor or the like as a heating medium. After molding with time and fusing the polypropylene resin foamed particles, the mold is cooled by water cooling, and then the mold is opened to obtain a foam in a polypropylene resin mold.

  In addition, when heating using water vapor | steam, it is preferable to raise pressure over the time for about 5 to 30 seconds until it sets it as the target heating water vapor pressure.

  Next, although the polypropylene resin expanded particle of this invention and its manufacturing method are demonstrated in detail, giving an Example and a comparative example, it is not limited to these.

In the examples and comparative examples, the substances used were as follows, but were used without any particular purification.
○ Polypropylene resin (commercially available or resin manufacturer's sample)
Polypropylene resin A: ethylene-propylene random copolymer [MFR = 7.5 g / 10 min, melting point 146.1 ° C.]
Polypropylene resin B: ethylene-1-butene-propylene random copolymer [MFR = 6.7 g / 10 min, melting point 143.0 ° C.]
○ Carbon black Carbon black was used as a carbon black masterbatch containing 40% by weight in a polypropylene resin (MFR = 7.5 g / 10 min, melting point 146.1 ° C.). Table 1 also shows the average particle size of carbon black in the obtained expanded particles.
○ Other additives Shirasu Balloon [Marunaka Shirato Co., Ltd., Marlite 735C]
・ Glycerin [manufactured by Lion Corporation, purified glycerin D]
-Polyethylene glycol [Lion Corporation, average molecular weight 300]
・ Talc [Made by Hayashi Kasei Co., Ltd., Talcan Powder PK-S]

The evaluation methods implemented in the examples and comparative examples will be described.
<Particle size of carbon black>
The photograph which expanded the cross section of the cell membrane of the obtained polyolefin resin expanded particle 40,000 times with the transmission electron microscope was image | photographed. In the obtained transmission electron micrograph, arbitrarily measure the particle diameter (Ferre diameter) in the X direction and Y direction for 50 carbon black primary particles, respectively, calculate the average value, did.
<Measurement of expansion ratio>
The obtained expanded polypropylene resin particles were dried at 60 ° C. for 2 hours and allowed to stand in a room at a temperature of 23 ° C. and a humidity of 50% for 1 hour, and then the weight w (g) was measured. The volume v (cm3) was measured, and the true specific gravity ρb = w ÷ v of the expanded particles was calculated.
Then, the expansion ratio = ρr ÷ ρb was calculated from the ratio with the density ρr of the polyethylene resin particles before foaming.
<DSC ratio of expanded particles>
Obtained when 5-6 mg of polypropylene resin expanded particles are heated from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min using a differential scanning calorimeter [DSC6200 type, manufactured by Seiko Instruments Inc.] The DSC curve (illustrated in FIG. 1) has two peaks, and was calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side of the melting peak by the following equation.
DSC ratio = Qh / (Ql + Qh) × 100
<Measurement of average cell diameter of expanded particles>
The obtained polypropylene resin foam particles were cut at the center of the foam particles using a double-edged razor [manufactured by Feather, high stainless steel double-edged].
In the image obtained by observing the cut surface with an optical microscope [manufactured by Keyence Corporation, VHX-100] at a magnification of 50 times, a straight line passing through almost the center of the expanded particle is drawn, and the straight line penetrates. The number of bubbles n and the foamed particle diameter L (μm) determined from the intersection between the straight line and the foamed particle surface were read and calculated from the following equation.
Average bubble diameter (μm) = L / n
The average cell diameter was calculated for 10 foamed particles, and the average value was obtained.

(Example 1)
[Production of polypropylene resin particles]
The polypropylene resin A was used as the polypropylene resin, and the Shirasu balloon was weighed to 10 parts by weight with respect to 100 parts by weight of the polypropylene resin, and dry blended. The dry blended mixture was melt-kneaded at a resin temperature of 220 ° C. using a twin-screw extruder [manufactured by Toshiba Machine Co., Ltd., TEM26-SX], and the extruded strand was water-cooled in a 2 m long water tank. Cut to produce polypropylene resin particles (1.2 mg / grain).
[Preparation of expanded polypropylene resin particles]
In a pressure-resistant autoclave having a capacity of 10 L, 100 parts by weight (2.4 kg) of the obtained polypropylene resin particles, 200 parts by weight of water, and tribasic calcium phosphate as a poorly water-soluble inorganic compound [manufactured by Taihei Chemical Industry Co., Ltd.] 5 parts by weight, sodium alkyl sulfonate (sodium n-paraffin sulfonate) as a surfactant (0.03 parts by weight, manufactured by Kao Corporation, Latemuru PS), and carbon dioxide as a foaming agent under stirring 5 parts by weight were added.

  The autoclave contents were heated to a foaming temperature of 148.5 ° C. as shown in Table 1. Thereafter, carbon dioxide as a foaming agent was additionally injected, and the internal pressure of the autoclave was increased to the foaming pressure of 3.3 MPa described in Table 1. After maintaining at the foaming temperature and foaming pressure for 30 minutes, the valve at the bottom of the autoclave is opened, and the autoclave contents are discharged into an atmosphere adjusted to 95 ° C. with water vapor through an opening orifice (1 hole) having a diameter of 3.6 mm. Thus, expanded polypropylene resin particles were obtained.

  About the obtained polypropylene resin foamed particles, the expansion ratio, DSC ratio, and average cell diameter were measured. The results are shown in Table 1.

(Examples 2-6, Comparative Examples 1-2, Reference Examples 1-2)
In [Preparation of Polypropylene Resin Particles], the types and mixing amounts of the polypropylene resin and additives are changed as shown in Table 1, and in [Preparation of Polypropylene Resin Expanded Particles], the foaming temperature is as shown in Table 1. Except for changing to, polypropylene resin particles and polypropylene resin foamed particles were produced in the same manner as in Example 1.

  Table 1 shows the evaluation results of the obtained polypropylene resin expanded particles.

  As can be seen from Example 1 and Comparative Examples 1 and 2, when the production method of the present invention is used, although the foaming ratio is equal to or higher than when only a nucleating agent such as talc is used. Therefore, expanded particles having a large cell diameter can be obtained. In addition, as can be seen from Examples 1 to 6 and Reference Examples 1 and 2, by using the production method of the present invention, a water-absorbing substance is not used, or the addition amount is 1/3 of Reference Example 1. In Example 2, the foaming ratio is the same as that in the case of using a water-absorbing substance as in Reference Examples 1 and 2, and foamed particles of relatively coarse cells having a cell diameter of 150 μm or more are obtained.

Claims (7)

A method for producing polypropylene resin expanded particles,
Polypropylene resin particles containing 3 parts by weight or more and 15 parts by weight or less of a spherical hollow glass composition are dispersed in an aqueous dispersion medium in an airtight container with respect to 100 parts by weight of the polypropylene resin, and an inorganic gas is used as a foaming agent under pressure The polypropylene resin foam particles are obtained by releasing the polypropylene resin particles impregnated and heated to a temperature equal to or higher than the softening temperature of the polypropylene resin particles into a pressure range lower than the internal pressure of the sealed container. A method for producing expanded polypropylene resin particles.   A method for producing polypropylene resin expanded particles, comprising 3 parts by weight to 15 parts by weight of a spherical hollow glass composition and 0.1 parts by weight to 10 parts by weight of a colorant with respect to 100 parts by weight of the polypropylene resin. 2. The method for producing expanded polypropylene resin particles according to claim 1, wherein polypropylene resin particles are used.   The method for producing expanded polypropylene resin particles according to claim 2, wherein the colorant is carbon black.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 3, wherein the spherical hollow glass composition is a shirasu balloon.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 4, wherein the inorganic gas as the foaming agent is carbon dioxide. It is a polypropylene resin expanded particle obtained by the manufacturing method of the polypropylene resin expanded particle of any one of Claims 1-5, Comprising: The polypropylene resin expanded particle which has the characteristics of the following (1)-(2) .
(1) The average cell diameter of the polypropylene resin expanded particles is 100 μm or more.
(2) The expansion ratio of the polypropylene resin expanded particles is 15 times or more.   The foamed particles obtained by the method for producing polypropylene resin foamed particles according to any one of claims 1 to 5 are filled in a molding space that can be closed but cannot be sealed by two molds. A method for producing a foamed molded article in a polypropylene resin mold, wherein the foamed particles are heated with water vapor through water vapor holes arranged in the mold.

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