JP7296275B2 - Method for producing expanded polypropylene resin-colored expanded particles, polypropylene-based resin-colored expanded particles group, and polypropylene-based resin-colored expanded particles molded article - Google Patents

Description

The present invention provides a method for producing polypropylene-based resin-colored foamed beads colored with a chromatic pigment, polypropylene-based resin-colored foamed beads obtained by the manufacturing method, and polypropylene-based foams obtained by in-mold molding of the foamed beads. It relates to resin-colored expanded particles.

Polypropylene-based resin expanded particle molded products are excellent in shock-absorbing properties, impact resilience, heat-insulating properties, etc., and are lightweight and resistant to chipping. used for

The expanded bead molded product is often used as it is, which is the original white color of the expanded bead. In recent years, however, there has been a demand for vivid and colorful foamed bead moldings as one mode of product sophistication. As a colored expanded bead molded article, for example, Patent Documents 1 and 2 disclose black polypropylene-based resin expanded beads colored using carbon black as a pigment. Further, Patent Document 3 discloses red foamed particles colored with a red organic pigment.

JP-A-7-300537 JP-A-2005-23302 JP 2009-215438 A

However, in the examples of Patent Documents 1 and 2, only the obtaining of black expanded beads using carbon black is studied, and the obtaining of chromatic colored expanded beads molded articles such as red and blue is studied. Not considered. In addition, the colored foamed particles described in Patent Document 3 contained a small amount of pigment and were inferior in vividness of color.

Furthermore, in the prior art, if the amount of pigment added is simply increased in order to obtain a vivid chromatic expanded bead molded article, there is a problem that the obtained expanded bead molded article tends to have color unevenness. . In particular, the expanded bead molded article using chromatic colored expanded particles such as red or blue has a problem that the color unevenness of the molded article is more conspicuous than that of the black expanded bead.

The present invention has been made in view of the above-mentioned problems. The object is to obtain particles.

According to the present invention, there are provided a method for producing polypropylene-based resin-colored expanded beads, a group of polypropylene-based resin-colored expanded beads, and a polypropylene-based resin-colored expanded beads molded product, which are shown below.
[1] A colored masterbatch containing a chromatic pigment, a cell control agent, and a polypropylene resin (A) are melt-kneaded to produce colored resin particles of a polypropylene resin, and the colored resin particles are placed in a sealed container. In addition to dispersing in a dispersion medium, the expandable colored resin particles are impregnated with an inorganic physical blowing agent to form expandable colored resin particles, and the expandable colored resin particles are released together with the dispersion medium into a low-pressure atmosphere from the closed container to expand. A method for producing polypropylene-based resin-colored foamed particles, comprising:
The concentration of the chromatic pigment in the colored masterbatch is 15 to 40% by weight, and the melt flow rate (II) of the colored masterbatch and the melt flow rate (I) of the polypropylene resin (A) ), wherein the ratio [II/I] is more than 1 and 3.5 or less.
[2] Manufacture of the expanded polypropylene-based resin-colored particles according to 1 above, characterized in that the colored masterbatch is blended so that the content in the polypropylene-based resin-colored resin particles is 0.15 to 8% by weight. Method.
[3] The melt flow rate (II) of the colored masterbatch is 10 to 25 g/10 min, and the melt flow rate (II) of the colored masterbatch and the melt flow rate (I) of the polypropylene resin (A) 3. The method for producing the expanded polypropylene-based resin-colored beads according to 1 or 2 above, wherein the ratio [II/I] of the to is 1.5 to 3.5.
[4] The method for producing expanded polypropylene-based resin particles according to any one of [1] to [3] above, wherein the melting point (TmI) of the polypropylene-based resin (A) is 125°C or higher and lower than 155°C.
[5] The above 1, wherein the difference [(TmI) - (TmII)] between the melting point (TmI) of the polypropylene resin and the melting point (TmII) of the colored masterbatch is -10°C to 10°C. 5. The method for producing the polypropylene-based resin-colored foamed beads according to any one of 4.
[6] The cell control agent is one or more metal borate salts selected from zinc borate and magnesium borate, and the number-based arithmetic mean particle size of the metal borate particles is 1 μm. 6. The polypropylene resin according to any one of 1 to 5 above, wherein the polypropylene resin has a particle diameter of 5 μm or less, and the number ratio of particles having a particle diameter of 5 μm or more in the particles of the metal borate is 20% or less. A method for producing colored foamed particles.
[7] The method for producing polypropylene-based resin-colored expanded particles as described in any one of [1] to [6] above, wherein the pigment is a red organic pigment.
[8] A group of expanded beads for in-mold molding comprising polypropylene-based resin-colored expanded beads colored with a chromatic pigment, wherein the apparent density of the expanded beads is 15 to 300 kg/m ³ , and the expanded beads are A group of colored polypropylene-based resin expanded particles, characterized in that the cells located on the outermost surface have an average cell diameter of 50 to 200 μm.
The average cell diameter of the cells located on the outermost surface of the expanded beads is determined after conditioning the expanded beads by allowing the expanded beads to stand in an atmosphere of 23° C., 50% relative humidity, and 1 atm for 2 days. A cross section obtained by randomly extracting one expanded bead, dividing the expanded bead into approximately two parts so as to pass through the center part of the expanded bead, and photographing the cut surface using a scanning electron microscope. In the photograph, the average cell diameter of the cells located on the outermost surface of the expanded bead is obtained by dividing the length C of the circumference of the substantially circular expanded bead by the number n of cells in contact with the circumference of the expanded bead, This operation is performed on 10 randomly selected expanded beads, and the value obtained for each expanded bead is calculated by arithmetic averaging.
[9] The colored polypropylene-based resin expanded beads as described in [8] above, wherein the content of the chromatic pigment in the expanded beads is 0.15 to 8% by weight.
[10] containing one or more metal borate salts selected from zinc borate and magnesium borate;
The number-based arithmetic mean particle size of the metal borate particles is 1 μm or more and 5 μm or less, and the number ratio of particles having a particle size of 5 μm or more in the metal borate particles is 20% or less. 10. The polypropylene-based resin-colored foamed particles according to 8 or 9 above.
[11] A polypropylene-based resin-colored expanded bead molded article obtained by molding the expanded bead group according to any one of [8] to [10] above in a mold.

According to the production method of the present invention, by producing foamed beads using a colored masterbatch in which the chromatic pigment concentration and the melt flow rate are adjusted within specific ranges, vivid colors and uneven colors can be obtained. It is possible to easily obtain chromatic colored polypropylene-based resin-colored foamed particles capable of in-mold molding into a suppressed chromatic colored foamed particle molded product.

The method for producing the expanded polypropylene resin particles of the present invention, the expanded polypropylene resin particles obtained by the production method, and the molded article of the expanded polypropylene resin particles obtained by in-mold molding of the colored expanded particles are described below. A detailed description will be given in this order.

The manufacturing method of the present invention aims to obtain chromatically colored expanded polypropylene resin beads, and the molded article of colored polypropylene resin expanded beads is obtained by performing in-mold molding using the expanded beads. , vivid colors and suppressed color shading.

In the production method, a colored masterbatch containing a chromatic pigment, a cell control agent, and a polypropylene resin (A) are melt-kneaded to produce polypropylene resin-colored resin particles (resin particle production step), The colored resin particles are dispersed in a dispersion medium in an airtight container and impregnated with an inorganic physical blowing agent under heating to form expandable colored resin particles (a step of impregnating the colored resin particles with the dispersion medium). At the same time, the resin is discharged into a low-pressure atmosphere from the sealed container and foamed to produce colored foamed particles of a polypropylene-based resin (foaming step). The resin particle manufacturing process, the foaming agent impregnation process, and the foaming process will be described below in this order.

In the resin particle production step of the method of the present invention, the polypropylene resin (A), a colored masterbatch containing a chromatic pigment, and a cell control agent are supplied to an extruder and melt-kneaded to color the polypropylene resin. Resin particles (hereinafter also simply referred to as “colored resin particles” or “resin particles”) are produced. In the resin particle manufacturing process, a method using a conventionally known extruder can be employed. Specifically, using an extruder, the polypropylene resin (A) as the base resin and the colored masterbatch are supplied to the extruder, melt-kneaded, extruded into strands, cooled, and then cut into appropriate lengths. Alternatively, a method of cooling the strand after or at the same time as cutting the strand into an appropriate length can be used to obtain colored resin particles.

Examples of the polypropylene-based resin (A) include propylene homopolymers and propylene-based copolymers containing 50% by mass or more of structural units derived from propylene. Specific examples of the copolymer include copolymers of propylene and ethylene or α-olefins having 4 or more carbon atoms, such as propylene-ethylene copolymers, propylene-butene copolymers, and propylene-ethylene-butene copolymers. Examples include polymers, propylene-acrylic acid copolymers, propylene-maleic anhydride copolymers, and the like. These copolymers may be block copolymers, random copolymers or graft copolymers. The propylene-based resin-based copolymer preferably contains 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more of structural units derived from propylene.

The flexural modulus of the polypropylene resin (A) is preferably 800 to 1200 MPa, more preferably 850 to 1100 MPa, more preferably 900 to 1000 MPa, from the viewpoint of achieving both moldability of the expanded beads and strength of the molded product. is more preferable.
The flexural modulus can be determined according to JIS K7171 (2008).

A thermoplastic resin other than the polypropylene-based resin can be added to the polypropylene-based resin (A) within a range that does not impair the intended effect of the present invention. The amount of thermoplastic resins other than polypropylene resins added is preferably 35% by weight or less, more preferably 20% by weight or less, and 10% by weight or less in 100% by weight of the mixed resin. is more preferable, it is particularly preferable that it is 5% by weight or less, and it is most preferable that it consists only of the propylene-based resin (A).

Thermoplastic resins other than the polypropylene-based resin (A) include low-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer. Examples include polymers, ethylene-based resins such as ethylene-methacrylic acid copolymers, and styrene-based resins such as polystyrene and styrene-maleic anhydride copolymers.

In the present invention, colored foamed beads are produced by using a colored masterbatch containing a chromatic pigment.
That is, a chromatic pigment and a base resin such as a polypropylene resin are melt-kneaded and granulated to previously produce a colored masterbatch containing the chromatic pigment, and in the colored resin particle production process, the obtained A colored masterbatch, a cell control agent, and a polypropylene-based resin (A) are supplied to an extruder, melt-kneaded, and granulated to form colored resin particles.

By adding a chromatic pigment using a colored masterbatch, the pigment is uniformly dispersed in the base resin. Moreover, from the viewpoint of improving the dispersibility of the pigment in the base resin, the base resin of the colored masterbatch is preferably a polypropylene resin.

In the present specification, the chromatic color refers to a color having the three attributes of hue, lightness, and saturation in the Munsell color system, that is, a color other than black, gray, and white.

As used herein, a chromatic pigment refers to a pigment that colors foamed particles in a chromatic color. The chromatic pigments are exemplified by red pigments, blue pigments, green pigments, yellow pigments, purple pigments, and the like. Moreover, the chromatic pigment may be an inorganic pigment or an organic pigment. Examples of inorganic pigments include chromates such as yellow lead, zinc yellow, and barium yellow; ferrocyanides such as iron blue; sulfides such as cadmium yellow and cadmium red; An acid salt etc. can be mentioned. Examples of organic pigments include azo pigments such as monoazo pigments, disazo pigments, azo lakes, condensed azo pigments, and chelate azo pigments; Examples include polycyclic pigments such as isoindolinone-based and quinophthalone-based pigments. The chromatic pigment may contain titanium oxide, carbon black, or the like for toning. Among the chromatic pigments, organic pigments are preferably used.

Among the above pigments, red organic pigments are preferably used. Red expanded bead molded articles are frequently used for packaging materials, and according to the method of the present invention, colored expanded bead molded articles of bright red color can be molded in molds while suppressing color unevenness. Particles can be obtained easily. From this point of view, it is more preferable to use an azo red organic pigment.

The concentration of the chromatic pigment in the colored masterbatch is 15-40% by weight. When the pigment concentration in the colored masterbatch is within the above range, it is possible to easily obtain expanded particles capable of forming a chromatic molded article with vivid colors and suppressed color unevenness. If the pigment concentration is too low, the obtained expanded bead molded article tends to have color unevenness. If the concentration of the pigment is too high, the pigment aggregates in the masterbatch and the dispersibility is excessively lowered, which may cause uneven color and poor appearance of the expanded bead molded product.

In order to more easily obtain foamed beads capable of forming a brightly colored foamed bead molded product with suppressed color unevenness, the concentration of the chromatic pigment in the colored masterbatch should be 18 to 35% by weight. is more preferred, and 20 to 30% by weight is even more preferred.

As a result of intensive studies by the present inventors, when a chromatic pigment is added using a masterbatch, even if the total amount of the chromatic pigment in the foamed particles is the same, the masterbatch used It was found that color unevenness occurs depending on the pigment concentration.

According to the present invention, by using a colored masterbatch having a pigment concentration within the above range, the obtained expanded bead molded article is vivid in color and has suppressed color unevenness. Although the reason for this is not clear, it is believed that the pigment is dispersed moderately and coarsely in the foamed particles without being too finely dispersed. That is, it is thought that when the pigment concentration in the colored masterbatch is too low, the pigment is too finely dispersed in the foamed particles, which tends to cause color unevenness. Another reason is that by dispersing the pigment moderately and coarsely in the foamed particles without being too finely dispersed, it is possible to suppress the miniaturization of the air bubbles located on the surface and reduce color unevenness. Conceivable.

The melt flow rate (II) of the colored masterbatch is preferably 10-25 g/10 min. A colored masterbatch having a melt flow rate within this range is appropriately dispersed in the polypropylene resin (A), so that the resulting foamed bead molded article obtained by in-mold molding exhibits a vivid chromatic color. At the same time, color unevenness is suppressed. From this point of view, the melt flow rate (II) is more preferably 11 to 20 g/10 min, still more preferably 12 to 18 g/10 min.

In the present invention, the ratio [II/I] of the melt flow rate (II) of the colored masterbatch to the melt flow rate (I) of the polypropylene resin (A) is more than 1 and 3.5 or less. When the ratio [II/I] is within the above range, it is possible to easily produce expanded beads capable of forming a colored expanded bead molded article with reduced color unevenness. This is presumably because the colored masterbatch has a higher melt flow rate than the base resin, so that the colored masterbatch can be well dispersed in the base resin. If the ratio [II/I] is too large, the pigment may be finely dispersed and color unevenness may occur. From this point of view, the ratio [II/I] is preferably 1.3 to 3.0, more preferably 1.5 to 2.5.

Melt flow rate (MFR) is measured according to JIS K7210-1:2014 (temperature 230° C., load 2.16 kg).

In the method of the present invention, it is preferable to mix the colored masterbatch having the above pigment concentration so that the content of the pigment in the colored foamed particles is 0.15 to 8% by weight. By blending the colored masterbatch so that the content of the pigment in the colored foamed particles is within the above range, it is possible to mold a molded product with good color developability and suppressed color unevenness while maintaining the fusion bondability. foamed particles can be obtained. From this point of view, the pigment content in the colored foamed particles is more preferably 0.5 to 5% by weight, still more preferably 1 to 4% by weight.

The melting point (TmI) of the polypropylene-based resin (A) is preferably 125 or more and less than 155°C. When the melting point is within the above range, the expanded beads will be excellent in moldability, heat resistance and the like. From this point of view, the melting point (TmI) is preferably 130°C or higher and lower than 150°C, more preferably 135°C or higher and lower than 145°C.

Furthermore, the difference [(TmI)-(TmII)] between the melting point (TmI) of the polypropylene resin and the melting point (TmII) of the colored masterbatch is preferably -10°C to 10°C.
When the difference between the melting point (TmI) of the polypropylene-based resin and the melting point (TmII) of the colored masterbatch is small, the colored masterbatch is easily dispersed in the polypropylene-based resin (A). It becomes easier to suppress the occurrence of unevenness. From this point of view, the difference [(TmI)-(TmII)] is more preferably -5°C to 5°C, still more preferably -3°C to 3°C.

The melting points of the polypropylene resin and the colored masterbatch are measured as follows.
Based on JIS K7121:2012, condition conditioning (2) of the test piece is subjected to constant heat treatment, and a melting peak is obtained by raising the temperature at 10°C/min. The temperature at the top of the obtained melting peak is taken as the melting point. When two or more melting peaks appear, the temperature at the top of the melting peak with the largest area is taken as the melting point.

In the resin particle manufacturing process of the method of the present invention, a cell control agent is blended. The air bubble control agent serves as a nucleus when air bubbles are generated, and has a function of adjusting the number of air bubbles.
Examples of cell control agents include inorganic powders such as zinc borate, magnesium talc borate, calcium carbonate, borax, and aluminum hydroxide. These cell control agents are preferably used in an amount of 0.001 to 5 parts by weight, more preferably 0.01 to 3 parts by weight, still more preferably 0.05 parts by weight, per 100 parts by weight of the resin particles. ~2 parts by weight.

Among the cell control agents, it is preferable to use one or more metal borate salts selected from zinc borate and magnesium borate. Zinc borate and magnesium borate include salts with various compositions and structures, and it is possible to use one or more of them in combination.

The zinc borate is a general term for metal salts containing boron and zinc that bond with oxygen. Examples of zinc borate include zinc metaborate [Zn(BO ₂ ) ₂ ], basic zinc borate (ZnB ₄ O _7.2ZnO ), etc. Zinc borate includes 2ZnO.3B ₂ O _{3.3.5H 2} O, 3ZnO.2B ₂ O _{3.5H 2} O, and the like can be mentioned, but not limited thereto.

The magnesium borate is a general term for metal salts containing boron and magnesium that bind to oxygen. Examples of magnesium borate include magnesium orthoborate [Mg ₃ (BO ₃ ) ₂ ], magnesium diborate, magnesium pyroborate [(Mg ₂ B ₂ O ₅ ) or (2MgO.B ₂ O ₃ )], metaboron magnesium acid [MgO.B ₂ O ₃ ], trimagnesium tetraborate [(Mg ₃ B ₄ O ₉ ) or (3MgO.2B ₂ O ₃ )], pentamagnesium tetraborate [Mg ₅ B ₄ O ₁₁ ], magnesium hexaborate [MgB ₆ O ₁₀ ], and the like. Examples of magnesium borate include 2MgO.3B ₂ O _{3.nH 2} O (where n is a positive integer), MgO.4B ₂ O _{3.3H 2} O, and MgO.6B ₂ O _{3.18H 2} Examples include, but are not limited to, those represented by chemical formulas such as O.

Among these borate metal salts, zinc borates represented by chemical formulas such as 2ZnO.3B ₂ O _{3.5H 2} O and 3ZnO.2B ₂ O _{3.5H 2 O} are particularly suitable as the _cell control agent. used effectively.

In the present invention, among the zinc borate and magnesium borate, the number-based arithmetic mean particle size of the metal borate particles is 1 μm or more and 5 μm or less, and the particles in the metal borate particles It is preferable that the number ratio of particles having a diameter of 5 μm or more is 20% or less.

When the arithmetic mean particle diameter of the metal borate is within the above range and the particle size distribution is within the above range, the foamed beads have excellent uniformity of cells, which is caused by variations in the cells of the foamed beads. It is possible to obtain an expanded bead molded article in which color unevenness is further suppressed. In addition, the bubble diameter can be expanded appropriately, and color unevenness is further suppressed.

From the viewpoint of suppressing aggregation of the metal borate in the base resin and further increasing the uniformity of the cells of the foamed particles, the average particle size of the metal borate is more preferably 1.5 μm or more and 4 μm or less. , more preferably 2 μm or more and 3 μm or less.

In addition, from the viewpoint of further suppressing the variation of air bubbles in the expanded particles, the number-based proportion of the metal borate particles having a particle diameter of 5 μm or more is more preferably 15% or less, and still more preferably 12% or less. .

The number-based particle size distribution of the metal borate particles is measured as follows.
A number-based particle size distribution can be obtained by converting a volume-based particle size distribution measured by a laser diffraction scattering method into a number-based particle size distribution assuming that the shape of particles is spherical. By arithmetically averaging the particle sizes based on the number-based particle size distribution, the number-based arithmetic mean particle size can be obtained. Also, the number ratio of particles having a particle diameter of 5 μm or more can be obtained from the number-based particle size distribution. The particle size means the diameter of a phantom sphere having the same volume as the particle.

In the method of the present invention, the polypropylene-based resin (A) as the base resin may optionally contain various additives. Examples of such additives include antioxidants, ultraviolet inhibitors, antistatic agents, flame retardants, metal deactivators, lubricants, and the like.

These additives are usually used in the minimum necessary amount. Further, these additives are added to the base resin melted in the extruder and kneaded to produce the resin particles used in the present invention, for example, by cutting the strands extruded by the extruder. It can be contained in the particles.

The colored resin particles obtained in the resin particle manufacturing process are used as expandable colored resin particles in the foaming agent impregnation process, and the expandable colored resin particles are used as colored expanded particles in the expansion process.

In the step of impregnating the foaming agent, the colored resin particles are dispersed in a dispersion medium such as water in a closed container (for example, an autoclave), and the colored resin particles are impregnated with an inorganic physical foaming agent under heating. It is considered as an expandable colored resin particle. In the subsequent foaming step, the expandable colored resin particles are released together with the dispersion medium from the closed vessel into a low-pressure atmosphere and foamed to produce colored foamed beads (hereinafter referred to as foaming agent impregnation and foaming). A continuous foaming method is also referred to as a "dispersion medium releasing foaming method"). The dispersion medium release foaming method is a method capable of efficiently producing colored foamed particles in a short period of time. An autoclave is usually used as the closed container, and water is usually used as the dispersion medium.

When dispersing the resin particles in the dispersion medium in a closed container, a dispersant can be added to the dispersion medium. Dispersants include water-insoluble inorganic substances such as aluminum oxide, tribasic calcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, and mica, and water-soluble polymeric protective colloid agents such as polyvinylpyrrolidone, polyvinyl alcohol, and methylcellulose. is mentioned. These are used singly or in combination of two or more.
Further, when dispersing the resin particles in a dispersion medium in a closed container, a surfactant such as anionic surfactants such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate can be used.

Dispersing aids may also be added to the dispersing medium. Examples of such dispersion strengthening agents include magnesium chloride, magnesium nitrate, magnesium sulfate, aluminum chloride, aluminum nitrate, aluminum sulfate, iron chloride, iron sulfate, and iron nitrate.

Generally, the dispersant is used in an amount of about 0.0001 to 5 parts by weight, and the dispersing aid is used in an amount of about 0.001 to 1 part by weight, per 100 parts by weight of the colored resin particles.

In the dispersion medium release foaming method, the colored resin particles are impregnated with a physical foaming agent in the closed vessel to form expandable colored resin particles.
The addition of the physical blowing agent into the closed container may be performed before the colored resin particles are expanded. For example, when carbon dioxide is used as the physical blowing agent, it is dispersed together with the resin particles in the form of dry ice. It may be added to the medium, or it may be pressurized into the sealed container in a gaseous state.
The impregnation of the resin particles with the physical blowing agent is preferably performed under heat and pressure.

Examples of the inorganic physical foaming agent include carbon dioxide, air, nitrogen, helium, and argon.
These inorganic physical foaming agents may be used alone or in combination of two or more. Among these blowing agents, carbon dioxide, nitrogen, and air are preferably used, and carbon dioxide is more preferable. In addition, an organic physical foaming agent may be included as the physical foaming agent within a range that does not impair the objective effect of the present invention.

The amount of the inorganic physical foaming agent to be added is appropriately selected according to the type of polypropylene resin, the type of foaming agent, the desired apparent density of the foamed particles, and the like. For example, when carbon dioxide is used as the inorganic physical blowing agent, the amount of carbon dioxide added is preferably 0.1 parts by mass to 30 parts by mass, more preferably 0.5 parts by mass with respect to 100 parts by mass of the polypropylene resin particles. It is from 1 part by mass to 15 parts by mass, more preferably from 1 part by mass to 10 parts by mass.

In the dispersion medium releasing and foaming method, the expandable resin particles impregnated with a foaming agent are released from a closed container together with an aqueous dispersion medium into a lower pressure region than in the closed container, thereby expanding the expandable colored resin particles. to obtain colored foamed particles. Here, when the metal borate having an arithmetic mean particle size within a specific range and a particle size distribution within a specific range is used as a cell control agent for the colored resin particles, the uniformity of the cell size can be improved. It is possible to obtain an expanded bead molded article with a high viscoelasticity and in which color unevenness caused by unevenness of cells is further suppressed. The reason for this is that the aqueous dispersion medium absorbed by the metal borate contributes to cell growth, and by equalizing the effect of the aqueous dispersion medium on cell growth, expanded particles with highly uniform cell diameters can be obtained. It is considered to be obtained.

In the dispersion medium release foaming method, before foaming the expandable resin particles, the colored resin particles are held in a dispersion medium within a specific temperature range and heat-treated in a closed vessel to cause crystallization to generate a so-called high temperature peak. It is preferable to provide a step. The heat treatment may be performed before, during, or after impregnation with the foaming agent, or at two or more of these timings. By this heat treatment, it is possible to produce expanded beads having a crystal structure exhibiting a melting peak (intrinsic peak) derived from crystals inherent in the polypropylene-based resin and a melting peak (high-temperature peak) located on the higher temperature side than the peculiar peak. can.

The heat treatment is performed, for example, as follows. A temperature near the melting point of the polypropylene resin that is the base resin of the colored resin particles, more specifically, a temperature (TmI−15° C.) 15° C. lower than the melting point (TmI) or higher, and a melting end temperature (TeI) or less. By holding the resin particles for a sufficient time (preferably about 5 minutes to 60 minutes) at an arbitrary temperature within, some or all of the crystals inherent in the polypropylene resin are melted, and some of the melted crystals are Recrystallize to produce lamellar thick high potential crystals. Thereafter, when the expandable resin particles having the high-potential crystals are expanded at the expansion temperature, crystals (intrinsic crystals) crystallized from the crystals melted by cooling during expansion and high-potential crystals are formed. It is possible to obtain expanded particles with a crystal structure having

Thereafter, expanded particles can be obtained by releasing the expandable resin particles into a low-pressure atmosphere. The temperature of the contents in the closed container when the expandable resin particles are released from the closed container together with the aqueous dispersion medium, that is, the temperature at which the expandable resin particles are expanded (expansion temperature) was determined by taking the melting point of the polypropylene resin as Tm. It is preferably in the range from a temperature 15° C. lower than the melting point (TmI) (TmI-15° C.) to a temperature 10° C. higher than the melting end temperature (TeI+10° C.). Also, the difference between the pressure in the closed container and the pressure in the release atmosphere is preferably 1.0 MPa to 7.0 MPa, more preferably 1.5 MPa to 5.0 MPa.

The melting point (TmI) of the polypropylene resin is determined by the method described above. The melting end temperature (TeI) means an extrapolated melting end temperature measured based on heat flux differential scanning calorimetry described in JIS K7121:2012. "(2) When measuring the melting temperature after performing a constant heat treatment" is adopted as the state adjustment of the test piece, and the heating rate and cooling rate are both 10°C/min.

When the expandable resin particles are discharged from the closed container together with the dispersion medium, the inside of the closed container is pressurized with carbon dioxide, nitrogen, etc., and the pressure in the released closed container is kept constant or gradually increased. Adjusting is preferred.

In particular, when obtaining expanded beads having a low apparent density (high expansion ratio), the expanded beads obtained by the above method are stored in a pressurizable sealed container, and a gas such as air is forced into the container. After performing pressure treatment to increase the internal pressure within the cells of the expanded beads, the expanded beads are taken out from the container and heated with steam or hot air to be expanded again to achieve a low apparent density. Colored foamed particles can be obtained.

Next, the polypropylene-based resin-colored foamed particles of the present invention will be described. The colored expanded beads of the present invention can be obtained, for example, by the method of the present invention.

The colored foamed particles preferably contain 0.15 to 8% by weight of a chromatic pigment. When the content of the pigment in the foamed beads is within the above range, even when foamed beads having a low apparent density are molded, the molded product can be prevented from blurring or uneven in color. be. If the content of the pigment in the foamed particles is too small, there is a risk that the color developability will be deteriorated or color unevenness will occur. If the amount is too large, there is a risk of defective fusion or the like occurring during in-mold molding. From this point of view, the pigment content in the colored foamed particles is preferably 0.5 to 5% by weight, more preferably 1 to 4% by weight.

The colored foamed particles are produced by using the polypropylene-based resin (A) as a base resin and a colored masterbatch containing the chromatic pigment, thereby being colored in a chromatic color such as red or blue. It is what was done. Since it is preferable to use a red organic pigment as the pigment, as described above, the expanded beads are preferably red-colored polypropylene-based resin-colored expanded beads.

The apparent density of the expanded particles is 15-300 kg/m ³ . If the apparent density is too low, the mechanical strength may be lowered and it may become unsuitable for use as a packaging material, cushioning material, or the like. If the apparent density is too high, there is a risk that the lightness and cushioning properties will be impaired. From the above viewpoint, the apparent density of the expanded particles is preferably 18-200 kg/m ³ , more preferably 20-150 kg/m ³ .

The apparent density of expanded beads is measured as follows. First, the expanded beads are left for two days under the conditions of a relative humidity of 50%, a temperature of 23° C. and a temperature of 1 atm to condition the expanded beads. Next, a graduated cylinder filled with water at a temperature of 23° C. is prepared, and an arbitrary amount of foamed particles (mass W1 of foamed particles) is submerged in water in the graduated cylinder using a tool such as a wire mesh. Then, considering the volume of tools such as wire mesh, the volume V1 [L] of the foamed particles read from the water level rise is measured. The apparent density [kg/m ³ ] of the expanded beads can be obtained by dividing the mass W1 [g] of the expanded beads by the volume V1 [L] (W1/V1) and performing unit conversion.

In the colored foamed beads, the average cell diameter of cells located on the outermost surface is 50 to 200 μm. When the average cell diameter is within the above range, the expanded beads are excellent in fusion bondability and can be molded into molded articles with suppressed color unevenness. In particular, if the average cell diameter is too small, the color tends to look whitish, and thus the obtained expanded bead molded article may be likely to have color unevenness. Moreover, there is a possibility that moldability may be impaired. From this point of view, the average cell diameter is preferably 80 μm or more and 180 μm or less, more preferably 100 μm or more and 160 μm or less.

The average cell diameter of cells located on the outermost surface of the expanded beads is obtained as follows. First, the foamed bead is roughly divided into two so as to pass through the central portion of the foamed bead, and a photograph of the cut surface is taken using a scanning electron microscope or the like. In the cross-sectional photograph obtained, the value obtained by dividing the length C of the circumference of a substantially circular foamed bead by the number n of cells in contact with the circumference of the foamed bead is the number of cells located on the outermost surface of one foamed bead. Average bubble diameter. This operation is performed on 10 randomly selected expanded beads, and the value obtained by arithmetically averaging the values obtained for each expanded bead is the average of the cells located on the outermost surface of the expanded beads in this specification. Let it be the bubble diameter.

The average cell diameter (D) of the entire expanded beads of the present invention is preferably 50 μm or more and 200 μm or less, more preferably 55 μm or more and 150 μm or less, and still more preferably 60 μm or more and 120 μm or less. When the average value of the cell diameter (D) of the entire expanded beads is within the above range, the expanded beads are excellent in moldability, mechanical strength and the like.

The average value of cell diameters of expanded beads is determined as follows. The foamed bead is roughly divided into two so as to pass through the central portion of the foamed bead, and a photograph of the cut surface is taken using a scanning electron microscope or the like. In the obtained cross-sectional photograph, four line segments are drawn at equal angles from the outermost surface of the expanded bead through the center to the outermost surface on the opposite side. The number of cells intersecting each line segment is counted, and the total length of the four line segments divided by the total number of cells intersecting the line segment is taken as the average cell diameter of one expanded bead. This operation is performed on 10 randomly selected expanded beads, and the value obtained by arithmetically averaging the values obtained for each of the expanded beads is defined as the average cell diameter of the expanded beads in the present specification.

The average weight of the colored expanded particles is preferably 0.5-10 mg/piece, more preferably 1-5 mg/piece. When the average weight is within the above range, the foamed beads are more excellent in moldability.

The colored foamed particles of the present invention preferably contain a borate metal salt selected from zinc borate and magnesium borate. When the base resin of the colored foamed beads contains a metal borate, the metal borate acts as a cell regulator, and the foam diameter of the obtained colored foamed beads is appropriately enlarged. , the cell diameter becomes more uniform, and a molded article with more suppressed color unevenness can be molded. From the above viewpoint, the metal borate preferably has a number-based arithmetic mean particle size of 1 μm or more and 5 μm or less, and the number ratio of particles having a particle size of 5 μm or more in the particles is 20. % or less. The particle size means the particle size of the primary particles of the metal borate.

The average particle size of the metal borate is more preferably 1.5 μm or more and 4 μm or less, still more preferably 2 μm or more and 3 μm or less, in order to make the bubble diameter of the foamed particles more uniform.
Furthermore, from the same point of view, the number-based proportion of metal borate particles having a particle diameter of 5 μm or more is more preferably 15% or less, and still more preferably 12% or less.

The number-based particle size distribution of the metal borate particles is measured as described above.

The content of the metal borate in the colored expanded beads is preferably 0.001 to 5 parts by weight per 100 parts by weight of the expanded beads. When the content of the metal borate in the expanded beads is within the above range, the expanded beads act more effectively as a cell regulator, and the colored expanded beads have a more uniform cell structure. From the above viewpoint, the content of the metal borate in the colored expanded beads is more preferably 0.01 to 3 parts by weight, more preferably 0.05 to 2 parts by weight per 100 parts by weight of the expanded beads. be.

The colored expanded beads of the present invention preferably have a so-called high temperature peak in the DSC curve.
That is, the expanded beads conform to JIS K7122: 2012, and 1 to 3 mg of expanded beads are used as a measurement sample, and the DSC curve obtained by heating from 23 ° C. to 200 ° C. at a heating rate of 10 ° C./min. It is preferable to have a crystal structure in which a melting peak (specific peak) specific to the resin and a melting peak (high temperature peak) located on the higher temperature side than the specific peak appear.

The heat of fusion at the high temperature peak (high temperature peak heat quantity) of the colored expanded beads is preferably 5 to 40 J/g, more preferably 7 to 30 J/g, from the viewpoint of moldability, mechanical strength, etc. More preferably 10 to 20 J/g.

In addition, the ratio of the high-temperature peak heat quantity to the heat quantity of fusion (total heat quantity of fusion) of the total melting peak of the DSC curve (high-temperature peak heat quantity/total heat quantity of fusion) is preferably 0.05 to 0.3, more preferably 0.3. 1 to 0.25, more preferably 0.15 to 0.2. By setting the ratio of the high-temperature peak heat quantity to the total heat of fusion within such a range, the presence of secondary crystals appearing as high-temperature peaks makes the expanded beads particularly excellent in mechanical strength and excellent in-mold moldability. Become.
The total heat of fusion of the expanded beads is determined by the amount of crystals contained in the polypropylene resin, which is the base resin. and can be controlled by adjusting the retention time.

The total heat of fusion and the high-temperature peak heat in the DSC curve can be obtained by conventionally known methods. Specifically, it can be determined by the method described in the Examples.

The colored foamed bead molded article of the present invention can be obtained by in-mold molding using the colored foamed beads.
That is, by filling the colored foamed particles into a mold and heating with a heating medium such as steam, the colored foamed particles are secondary expanded and fused together to form a desired shape according to the mold. A colored expanded bead molded product can be obtained. The resulting colored foamed bead molded article is colored, and the occurrence of color unevenness is suppressed. The occurrence of color unevenness is particularly noticeable in chromatically colored expanded bead molded articles. Even if it has been processed, the occurrence of color unevenness is effectively suppressed.

Next, the present invention will be described in detail based on examples. However, the present invention is not limited by the examples.

As the polypropylene-based resin (A), the following was used.
Abbreviated name "resin 1": ethylene-propylene random copolymer (ethylene content 3.1% by mass, melting point (TmI) 142°C, melt flow rate (I) 8.0g/10min, flexural modulus 980MPa)

(Melting point (TmI) of polypropylene resin (A))
The melting point of the polypropylene resin was determined according to JIS K7121:1987. Specifically, 2 mg of a pellet-shaped base resin is used as a test piece, and is heated from 30° C. to 200° C. at a heating rate of 10° C./min based on the heat flux differential scanning calorimetry method described in JIS K7121:1987. After raising the temperature to 30 ° C. at a cooling rate of 10 ° C./min, the temperature is again raised from 30 ° C. to 200 ° C. at a rate of 10 ° C./min. The peak temperature was taken as the melting point of the base resin. A heat flux differential scanning calorimeter (manufactured by SII Nanotechnology Co., Ltd., model number: DSC7020) was used as the measurement device.

(Melt flow rate (I) of polypropylene resin)
The melt flow rates of the polypropylene-based resin and the colored masterbatch were measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 190° C. and a load of 2.16 kg.

(Flexural modulus of polypropylene resin)
The flexural modulus of the polypropylene-based resin was determined according to JIS K7171:2008. As the test piece, a 4 mm sheet was prepared by heat-pressing foamed particles at 230° C., and a 80 mm long×10 mm wide×4 mm thick (standard test piece) cut from the sheet was used. The radius R1 of the indenter and the radius R2 of the support base were both 5 mm, the distance between fulcrums was 64 mm, and the test speed was 2 mm/min.

A red pigment masterbatch shown in Table 1 was used as a coloring masterbatch containing a chromatic pigment. The melt flow rate (II) and melting point (TmII) of the colored masterbatch were measured in the same manner as for the polypropylene resin (A).

Zinc borate (ZnB) shown in Table 2 was used as the borate metal salt.

(Particle size distribution of metal borate)
Based on the above method, the particle size distribution of the metal borate was measured using MT3000 manufactured by Microtrac. 1 g of metal borate and 1 g of 1% sodium dodecylbenzenesulfonate aqueous solution were added to 100 g of water, and the mixture was subjected to dispersion treatment for 5 minutes using an ultrasonic shaker, and used as a measurement sample. The refractive index of the sample was set to 1.81.

Carbon dioxide was used as a physical blowing agent.

Examples 1 to 3, and Comparative Examples 1 and 2
(Production of cell control agent masterbatch)
Resin 1 and metal borate salts of the types shown in Table 2 were melt-kneaded by a pressure kneader to produce a cell control agent masterbatch having a metal borate concentration of 10% by mass.

(Production of colored resin particles)
Resin 1 having the compounding amount shown in Table 3, the cell control agent masterbatch having the compounding amount shown in Table 3, and the coloring masterbatch having the compounding amount shown in Table 3 were supplied to an extruder, and melt-kneaded in the extruder. The melted resin was extruded through a die in the form of a strand, cooled in water and then cut with a pelletizer to obtain colored resin particles each having an average mass of 1.3 mg.

(Production of colored foamed particles)
An autoclave having an inner volume of 2 m ³ was charged with 1050 L of water as a dispersion medium, and 500 kg of the resin particles were dispersed in the dispersion medium. Furthermore, 2 kg of kaolin (0.4 parts by mass with respect to 100 parts by mass of resin particles) as a dispersant in a dispersion medium, 30 g (0.006 parts by mass) of sodium dodecylbenzenesulfonate as a surfactant, and 65 g (0.013 parts by weight) of aluminum sulfate were added. While stirring the content in the autoclave and heating it to the foaming temperature shown in Table 4, carbon dioxide as a physical blowing agent was injected into the autoclave until the autoclave internal pressure shown in Table 4 was reached. After holding at that temperature for 10 minutes, while maintaining the autoclave internal pressure shown in Table 4 with pressurized carbon dioxide, one end of the autoclave is opened to release the resin particles together with the dispersion medium to atmospheric pressure. The resin particles were expanded to obtain red expanded particles. The temperature of the content in the autoclave during foaming is shown in Table 4 as the foaming temperature. The resulting colored foamed beads were dehydrated using a centrifuge, and then cured under an atmosphere of atmospheric pressure to recover the pressure inside the cells of the colored foamed beads.

The apparent density of the resulting colored expanded beads, the overall average cell diameter (D) of the expanded beads, the average cell diameter (Ds) of the cells located on the outermost surface, the high-temperature peak heat quantity, and the pre-melting heat quantity were measured. Table 4 shows the results. These measurements were performed after conditioning the expanded beads by placing the expanded beads in an atmosphere of 23° C., 50% relative humidity and 1 atm for 2 days.

(Measurement of apparent density of colored expanded particles)
100 mL of water at 23° C. was placed in a 200 mL graduated cylinder, and after measuring the mass (W1) of foamed particles having a bulk volume of about 50 mL, they were submerged in water in the graduated cylinder using a wire mesh. Considering the volume of the wire mesh, the volume V1 [L] of the foamed particles read from the amount of water level rise was measured. This operation was repeated 5 times for different expanded bead samples, and the apparent density of each expanded bead sample was obtained from each measured value, and the arithmetic average value was taken as the apparent density (kg/m ³ ) of the expanded bead.

(Measurement of average cell diameter (D) of entire colored expanded beads)
The foamed bead was roughly divided into two so as to pass through the central portion of the foamed bead, and a photograph of the cut surface was taken using a scanning electron microscope. In the obtained cross-sectional photograph, four line segments were drawn at equal angles from the outermost surface of the expanded bead through the center to the outermost surface on the opposite side. The number of cells intersecting each line segment was counted, and the total length of the four line segments divided by the total number of cells intersecting the line segment was taken as the average cell diameter of one expanded bead. This operation was performed on 10 randomly selected expanded beads, and the value obtained by arithmetically averaging the values obtained for each of the expanded beads was defined as the average cell diameter of the expanded beads in the present specification.

(Measurement of average cell diameter (Ds) of cells located on the outermost surface of colored expanded beads)
The average cell diameter of cells located on the outermost surface of the expanded beads was obtained as follows. First, the expanded bead was divided into approximately two parts so as to pass through the central portion of the expanded bead, and a photograph of the cut surface was taken using a scanning electron microscope. In the cross-sectional photograph obtained, the value obtained by dividing the length C of the circumference of a substantially circular foamed bead by the number n of cells in contact with the circumference of the foamed bead is the number of cells located on the outermost surface of one foamed bead. It was taken as the average bubble diameter. This operation is performed on 10 randomly selected expanded beads, and the value obtained by arithmetically averaging the values obtained for each expanded bead is the average of the cells located on the outermost surface of the expanded beads in this specification. It was taken as the bubble diameter.

(Measurement of high-temperature peak heat quantity and total heat quantity of fusion of colored foamed particles)
About 3 mg of the expanded particles are sampled, and the temperature is measured from 23° C. to 200° C. at a rate of 10° C./min with a differential thermal scanning calorimeter (DSC.Q1000 manufactured by TA Instruments). Obtain a DSC curve with peaks. In the following description, let A be the resin-specific peak, and let B be the high-temperature peak appearing on the higher temperature side. A straight line (α-β) is drawn connecting the point α corresponding to 80° C. on the DSC curve and the point β on the DSC curve corresponding to the final melting temperature T of the expanded beads. The melting end temperature T refers to the intersection point of the DSC curve on the high temperature side of the high temperature peak B and the high temperature side baseline. Next, a straight line parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the resin-specific peak A and the high-temperature peak B, and the point at which the straight line (α-β) intersects is δ. do. The area of the resin-specific peak A is the area of the portion surrounded by the curve of the resin-specific peak A portion of the DSC curve, the line segment (α-δ), and the line segment (γ-δ). It was taken as the heat of fusion at the peak.
The area of the high temperature peak B is the area of the portion surrounded by the curve of the high temperature peak B portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ). bottom.
The area of the total melting peak is the area of the portion surrounded by the curve of the resin-specific peak A portion of the DSC curve, the curve of the high-temperature peak B portion, and the line segment (α-β), and this was taken as the total heat of fusion. .

(Manufacturing of colored expanded bead molding)
As a mold, a mold having a rectangular parallelepiped molding cavity with inner dimensions of 300 mm in the vertical direction, 250 mm in the horizontal direction, and 25 mm in the thickness direction was used.
With the mold opened 5 mm from the completely closed state, the foamed particles were filled into the molding cavity, and after the filling was completed, the mold was completely closed (cracking amount 5 mm, 20%). After that, steam of 0.20 to 0.38 MPa (G) was supplied into the molding cavity to heat the expanded beads, and the expanded beads were secondary expanded and fused to obtain a colored expanded bead molded product. . The mold was cooled with water until the surface pressure of the colored expanded bead molded article in the mold reached 0.04 MPa (G), the mold was opened, and the colored expanded bead molded article was taken out from the mold. The obtained colored expanded bead molded article was aged for 12 hours in an atmosphere of atmospheric pressure and temperature of 80°C.

(Evaluation of in-mold moldability (moldable range) of colored expanded beads)
In the above-mentioned method (manufacturing of colored expanded bead molded article), the molding steam pressure is changed by 0.02 MPa between 0.20 and 0.38 MPa to mold the expanded bead molded article, and the obtained molded article is fused. In-mold moldability was evaluated for the items of properties, surface appearance (gap = degree of voids), and recoverability (recovery of expansion or contraction after in-mold molding), and those that met the criteria shown below passed. The steam pressure at which all items passed the test was defined as the steam pressure at which molding was possible. The wider the range from the lower limit value to the upper limit value of the steam pressure that can be molded, the wider the moldable range, which is preferable.
The molded bodies shown in Table 4 were evaluated using molded bodies molded at the lowest molding pressure within the moldable range.

(fusion)
The expanded bead molded product is bent and broken, the number of expanded beads present on the fracture surface (C1) and the number of broken expanded beads (C2) are determined, and the ratio of broken expanded beads to the expanded beads (C2/C1 × 100) was calculated as the material destruction rate. The measurement was performed 5 times using different test pieces, and the material destruction rate was determined for each. When the material destruction rate obtained by arithmetically averaging them was 90% or more, it was judged as acceptable.

(Surface appearance)
Draw a square of 100 mm x 100 mm in the center of the expanded bead molding, draw a line diagonally from one corner of the square, and count the number of voids (intervals) of 1 mm x 1 mm or more on the line, When the number of voids was less than 5 and the surface had no unevenness, it was judged as acceptable.

(recoverability)
The thickness near the four corners (10 mm inside from the corners in the center direction) and the center (vertical direction , and a portion that is divided into two equal parts in both the lateral direction) were measured. Next, the ratio (%) of the thickness of the central portion to the thickness of the thickest portion among the four corner portions was calculated, and a ratio of 95% or more was regarded as acceptable.

The shrinkage rate of the molded body was measured by the following method. The shrinkage rate of the expanded bead molded article is determined by measuring the longitudinal dimension of the expanded bead molded article after curing. It was obtained from the ratio of the difference from the longitudinal dimension of

The vividness of the color of the obtained colored expanded bead molded article was evaluated according to the following criteria. Table 4 shows the evaluation results. Color unevenness was visually evaluated on a 5-point scale from the color of the foamed bead molded product to be light and not vivid (1 point) to dark and vivid (5 points). The color unevenness of the foamed bead molded product was evaluated according to the following criteria based on the average values of the evaluations by the examiners.
◎: 4 points or more ○: 3.5 points or more and less than 4 points △: 3 points or more and less than 3.5 points ×: Less than 3 points

The color unevenness of the obtained colored expanded bead molded article was evaluated according to the following criteria. Table 4 shows the evaluation results. The plate surface of the expanded bead molded product was visually evaluated for color unevenness on a 5-point scale from marked color unevenness (1 point) to no color unevenness (5 points), and evaluated by 5 viewers. Based on the average value of , the color unevenness of the expanded bead molding was evaluated according to the following criteria.
◎: 4 points or more ○: 3.5 points or more and less than 4 points △: 3 points or more and less than 3.5 points ×: Less than 3 points

As shown in Table 3, the expanded beads of Examples 1 to 3 were produced using a colored masterbatch (abbreviation: colored MB) having a pigment concentration and a melt flow rate within the above-specified ranges. As shown in No. 4, it was possible to mold a red foamed bead molded article which was vivid in color and suppressed in color unevenness. In particular, as shown in Table 3, the foamed particles of Example 1 were produced using the above-mentioned specific zinc borate as a cell control agent with a number-based average particle size and a number ratio of particles having a particle size of 5 μm or more. The color unevenness of the molded article was further suppressed.

Furthermore, as shown in Table 4, the expanded beads of Examples 1 to 3 have a moldable range shifted to a lower pressure and a wider moldable range than the expanded beads of Comparative Examples 1 and 2. Met. The reason why the expanded beads of the present invention have such excellent moldability is not clear, but it is considered that the average cell diameter of the cells located on the outermost surface of the expanded beads is adjusted within the preferred range.

On the other hand, as shown in Table 3, the expanded beads of Comparative Example 1 were produced using a colored masterbatch with a low pigment concentration, and as shown in Table 4, color unevenness was observed in the molded article. In Comparative Example 2, as shown in Table 3, expanded particles were produced by increasing the blending amount of the pigment masterbatch. This is thought to be caused by the fact that the pigment concentration in the masterbatch was too low, causing the pigment to be too finely dispersed in the expanded beads, and that the diameter of the cells located on the outermost surface of the expanded beads became finer. be done.

Claims (11)

A colored masterbatch containing a chromatic pigment, a cell control agent, and a polypropylene resin (A) are melt-kneaded to produce polypropylene-based resin colored resin particles, and the colored resin particles are placed in a closed container. Dispersed in a dispersion medium, impregnated with an inorganic physical blowing agent to form expandable colored resin particles, and expanded by releasing the expandable colored resin particles together with the dispersion medium from the closed vessel into a low-pressure atmosphere. A method for producing resin-colored foamed particles, comprising:
The concentration of the chromatic pigment in the colored masterbatch is 15 to 40% by weight, and the melt flow rate (II) of the colored masterbatch and the melt flow rate (I) of the polypropylene resin (A) a ratio [II/I] of more than 1 to 3.5 or less.
2. The colored polypropylene resin according to claim 1, wherein the colored masterbatch is blended so that the content of the chromatic pigment in the colored resin particles of the polypropylene resin is 0.15 to 8% by weight. A method for producing expanded particles.
The melt flow rate (II) of the colored masterbatch is 10 to 25 g/10 min, and the ratio of the melt flow rate (II) of the colored masterbatch to the melt flow rate (I) of the polypropylene resin (A) 3. The method for producing polypropylene-based resin-colored expanded beads according to claim 1, wherein [II/I] is from 1.5 to 3.5.
4. The method for producing expanded polypropylene-based resin particles according to any one of claims 1 to 3, wherein the polypropylene-based resin (A) has a melting point (TmI) of 125°C or higher and lower than 155°C.
The difference [(TmI) - (TmII)] between the melting point (TmI) of the polypropylene resin (A) and the melting point (TmII) of the colored masterbatch is -10°C to 10°C. 5. The method for producing the polypropylene-based resin-colored expanded beads according to any one of 1 to 4.
The cell control agent is one or more borate metal salts selected from zinc borate and magnesium borate, and the number-based arithmetic mean particle size of the metal borate particles is 1 μm or more and 5 μm or less. The polypropylene-based resin colored foam according to any one of claims 1 to 5, wherein the number ratio of particles having a particle diameter of 5 µm or more in the particles of the metal borate is 20% or less. Particle production method.
7. The method for producing polypropylene-based resin-colored expanded particles according to any one of claims 1 to 6, wherein the pigment contains a red organic pigment as a main component.
An expanded bead group for in-mold molding comprising polypropylene-based resin-colored expanded beads colored with a chromatic pigment, wherein the apparent density of the expanded beads is 15 to 300 kg/m ³ , and the outermost surface of the expanded beads A group of colored polypropylene-based resin expanded particles, characterized in that the average cell diameter of the cells located therein is from 50 to 200 μm.
The average cell diameter of the cells located on the outermost surface of the expanded beads is determined after conditioning the expanded beads by allowing the expanded beads to stand in an atmosphere of 23° C., 50% relative humidity, and 1 atm for 2 days. A cross section obtained by randomly extracting one expanded bead, dividing the expanded bead into approximately two parts so as to pass through the center part of the expanded bead, and photographing the cut surface using a scanning electron microscope. In the photograph, the average cell diameter of the cells located on the outermost surface of the expanded bead is obtained by dividing the length C of the circumference of the substantially circular expanded bead by the number n of cells in contact with the circumference of the expanded bead, This operation is performed on 10 randomly selected expanded beads, and the value obtained for each expanded bead is calculated by arithmetic averaging.
9. The group of colored polypropylene-based resin expanded particles according to claim 8, wherein the content of the chromatic pigment in the expanded particles is 0.15 to 8% by weight.
containing one or more borate metal salts selected from zinc borate and magnesium borate;
The number-based arithmetic mean particle size of the metal borate particles is 1 μm or more and 5 μm or less, and the number ratio of particles having a particle size of 5 μm or more in the metal borate particles is 20% or less. 10. The group of colored polypropylene-based resin expanded particles according to claim 8 or 9.
A polypropylene-based resin-colored expanded bead molded article obtained by molding the expanded bead group according to any one of claims 8 to 10 in a mold.