JP2005023302A - Method for producing polypropylene-based resin-foamed particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing foamed particles capable of being heat-formed by a low temperature steam even if they are colored foamed particles. <P>SOLUTION: This method for producing the polypropylene-based resin-foamed particles comprises a resin particle-producing process of melting/mixing/kneading a base resin consisting of a polypropylene-based resin having ≥1,200 MPa tensile elastic modulus with a colored mixture consisting of a thermoplastic polymer with a coloring agent to granulate a foaming resin composition particles in which the coloring agent exists as covered by the thermoplastic resin in the base resin, a surface-modifying process of modifying the surface of the foaming resin composition particles with an organic peroxide in a dispersion medium, a foaming agent-impregnating process of impregnating a foaming agent into the foaming resin composition particles and a foaming process of foaming the surface-modified foaming resin composition particles impregnated with the foaming agent. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  Polypropylene-based resin expanded particle molded body (hereinafter also referred to as “EPP molded body”) is a buffering material that does not impair the excellent mechanical strength, heat resistance, chemical resistance, and easy recyclability of propylene. In addition, since the foam-specific properties such as heat insulation can be added, it is used in a wide range of industrial fields such as packaging materials and building materials.

  In particular, the so-called bead-type in-mold foam molded article, in which pre-foamed particles are prepared from a polypropylene resin, filled in a mold that can be opened and closed, and heat-sealed with steam, has a superior buffering property and an improved molding property. Due to its formality, it is used in the automotive field such as automotive bumper cores and door pads. In recent years, a lighter and more rigid EPP molded body has been demanded in the automobile field from the viewpoint of stricter collision safety standards and improved fuel efficiency.

  However, in general, the rigidity of the polypropylene resin increases and the melting point also increases, and the steam pressure during molding increases, so a special molding machine that can handle high steam pressure is required, and the amount of steam consumed Is known to increase. Accordingly, it has been expected to develop expanded polypropylene resin particles that can be molded with low-temperature steam even if the polypropylene resin has high rigidity.

  In response to this expectation, the present applicant can propose foamed particles that can be fused with low-temperature steam, a method for producing the same, and a foamed particle molded body, and can provide foamed particles that can be fused with low-temperature steam. (See Patent Document 1).

  On the other hand, in recent years, it has been required to differentiate from polystyrene resin foam particle molded bodies, and it has been required to give a high-class feeling to automobile bumper core materials, door pads, and the like. Therefore, it is necessary to color the EPP compact.

  Regarding the coloring of the EPP molded body, an invention is disclosed in which an EPP molded body is manufactured by mixing a base resin with a mixture (so-called masterbatch) in which carbon black, which is a colorant, is melted and kneaded in advance with a base resin. (See Patent Document 2).

  Based on these findings, the present inventors tried to produce surface-modified expanded particles described in Patent Document 1 using a master batch of carbon black as a colorant. However, the obtained expanded particles could not be heat-molded with low temperature steam.

JP 2002-167460 A JP-A-7-300537

  This invention makes it a subject to provide the manufacturing method of the foaming particle which can be heat-molded with low temperature steam even if it is a colored foaming particle.

As a result of intensive studies to solve the above problems, the present inventors have found that the base resin of the masterbatch is the same as the base resin of the expanded particles, and because carbon black was used as the colorant, the surface of the carbon black It was found that the reforming was hindered, and as a result, it was impossible to heat form with low temperature steam. For this reason, the inventors of the present invention used a base resin of the master batch different from the base resin of the foamed particles, more specifically, a specific thermoplastic polymer to heat carbon black, which is a colorant dispersed in the master batch. It has been found that carbon black as a colorant does not inhibit surface modification if dispersed in a state of being wrapped in a plastic polymer, and the present invention has been completed.
That is, according to this invention, the manufacturing method of the polypropylene resin expanded particle shown below is provided.
[1] A base resin composed of a polypropylene resin having a tensile modulus of 1200 MPa or more and a colored mixture composed of a thermoplastic polymer and a colorant are melt-kneaded so that the colorant is contained in the base resin. A resin particle manufacturing step of granulating the foaming resin composition particles that are covered with coalescence, and a surface modification step of modifying the surface of the foaming resin composition particles with an organic peroxide in a dispersion medium; A foaming agent impregnation step of impregnating the foaming resin composition particles with a foaming agent; and a foaming step of foaming the surface-modified foaming resin composition particles impregnated with the foaming agent. A method for producing expanded polypropylene resin particles.
[2] Resin particles for granulating foaming resin composition particles by melt-kneading a base resin made of a polypropylene resin having a tensile modulus of 1200 MPa or more and a colored mixture containing an ethylene polymer and a colorant A production step, a surface modification step of modifying the surface of the foaming resin composition particles with an organic peroxide in a dispersion medium, a foaming agent impregnation step of impregnating the foaming resin composition particles with a foaming agent, And a foaming step of foaming the surface-modified foaming resin composition particles impregnated with a foaming agent.
[3] The method for producing expanded polypropylene resin particles according to [2], wherein the ethylene polymer is ethylene-propylene rubber.
[4] Resin particles for granulating foaming resin composition particles by melt-kneading a base resin made of a polypropylene resin having a tensile modulus of 1200 MPa or more, and a colored mixture containing a thermoplastic elastomer and a colorant A production step, a surface modification step of modifying the surface of the foaming resin composition particles with an organic peroxide in a dispersion medium, a foaming agent impregnation step of impregnating the foaming resin composition particles with a foaming agent, And a foaming step of foaming the surface-modified foaming resin composition particles impregnated with a foaming agent.
[5] Melting and kneading a base resin composed of a propylene homopolymer having a tensile modulus of 1200 MPa or more, a colored mixture containing a copolymer of propylene and an α-olefin other than propylene and a colorant, and foaming A resin particle production process for granulating resin composition particles, a surface modification process for modifying the surface of the foam resin composition particles with an organic peroxide in a dispersion medium, and a foam resin composition particle A foaming agent impregnating step for impregnating a foaming agent, and a foaming step for foaming the surface-modified foaming resin composition particles impregnated with the foaming agent. .
[6] The method for producing expanded polypropylene resin particles according to any one of [1] to [5], wherein the colorant is carbon black.
[7] The method for producing expanded polypropylene resin particles according to [6] above, wherein the carbon black has an average particle diameter of 5 nm to 100 nm.
[8] The above [6] or [7], wherein the carbon black content is 0.1 wt% or more and less than 5.0 wt% with respect to the resin composition constituting the foaming resin composition particles ] The manufacturing method of the polypropylene resin expanded particle of description.

  The method for producing expanded polypropylene resin particles of the present invention granulates the foamed resin composition particles in which the colorant is covered with the thermoplastic polymer in the base resin in the resin particle production process. In the surface modification step of modifying the surface of the resin composition particles for use with the organic peroxide in the dispersion medium, the surface modification with the organic oxide is not hindered. Accordingly, colored polypropylene resin expanded particles that can be molded with low-temperature steam are obtained.

  In addition, since the colorant is carbon black in particular, the production method of the present invention is easy to be incorporated into a masterbatch base resin, thereby covering the surface of the carbon black, and surface modification during the surface modification in the subsequent step. It is difficult to disturb. Thereby, the obtained expanded particles are suitable for producing a black or gray EPP compact.

In addition, since the average particle diameter of the carbon black is 5 nm to 100 nm, the production method of the present invention can obtain uniformly colored expanded particles, and when expanded, the carbon black aggregates when expanded. Since the bubble wall is not destroyed and it is less likely to form a continuous bubble, secondary foaming of the expanded particles is not reduced. Therefore, if the expanded particles obtained by the method of the present invention are used, a good EPP molded product can be produced.

  Further, in the production method of the present invention, when carbon black of 0.1 wt% or more and less than 5.0 wt% is used with respect to the resin composition constituting the foaming resin composition particles, good color development is obtained. The foamed particles obtained are excellent in secondary foaming. When such expanded particles are used, a good black or gray EPP molded product can be produced.

  The method for producing polypropylene-based resin expanded particles (hereinafter also simply referred to as “present expanded particles”) of the present invention is intended to obtain colored expanded particles, and comprises a polypropylene-based resin having a tensile elastic modulus of 1200 MPa or more. A base resin (hereinafter also simply referred to as “the base resin”) and a colored mixture containing a specific thermoplastic polymer and a colorant (hereinafter also simply referred to as “masterbatch”) are melt-kneaded and foamed. Resin particle production process for granulating resin composition particles (hereinafter also simply referred to as “the present resin particles”), and a surface modification process for modifying the surface of the present resin particles with an organic peroxide in a dispersion medium And a foaming agent impregnation step of impregnating the resin particles with a foaming agent, and a foaming step of foaming the surface-modified resin particles impregnated with the foaming agent.

  The base resin used in the resin particle production process of the method of the present invention is made of a polypropylene resin having a tensile elastic modulus of 1200 MPa or more. As the polypropylene resin, either a propylene homopolymer or a copolymer of propylene and other comonomers containing 70 mol% or more of propylene component (preferably containing 80 mol% or more of propylene component), or A mixture of two or more selected from these resins is used.

  Examples of the copolymer of propylene containing 70 mol% or more of the propylene component and other comonomers include, for example, propylene-ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer, propylene-ethylene-butene random copolymer. Etc. are exemplified.

  The polypropylene resin constituting the base resin has a tensile modulus of 1200 MPa or more. This base resin satisfies the high rigidity required in the automobile field. From this viewpoint, the tensile modulus of the polypropylene resin constituting the base resin is preferably 1250 MPa or more, more preferably 1300 MPa or more, and further preferably 1360 MPa to 2500 MPa.

  As a high-rigidity polypropylene resin having a tensile modulus of 1200 MPa or more, most of the propylene homopolymer exhibits such high rigidity, and even if it is a copolymer of propylene and another comonomer, the comonomer component is contained. Those having an extremely small proportion tend to exhibit such high rigidity.

In addition, the tensile elasticity modulus in this specification is the value calculated | required on the following conditions according to JISK7161 (1994).
Test piece Test piece 1A type described in JIS K 7162 (1994) (Direct molding by injection molding)
Tensile speed 1mm / min

  In addition, the polypropylene resin constituting the base resin preferably has a tensile yield strength of 31 MPa or more in order to increase the compressive strength of the final EPP molded product, but is 32 MPa or more. Is more preferable. The upper limit of the tensile yield strength is not particularly limited, but is usually 45 MPa.

  In addition, the polypropylene-based resin prevents bubble breakage during formation of bubbles during the production of foamed particles, and further prevents bubble breakage of foamed particles during heating during in-mold molding. The tensile elongation at break is preferably 20% or more, more preferably 100% or more, and further preferably 200 to 1000%.

  The tensile yield strength and tensile elongation at break are both based on the measurement method described in JIS K 6758 (1981).

  The melting point of the polypropylene resin is preferably 145 ° C. or higher, more preferably 155 ° C. or higher, in order to increase the heat resistance of the final EPP molded body, and is preferably 158 ° C. or higher. More preferably, it is most preferably 160 ° C. or higher. The upper limit of the melting point is usually about 170 ° C.

  The polypropylene resin preferably has a melt flow rate abbreviated as MFR of 3 g / 10 min or more and 100 g / 10 min or less. If the MFR is less than 3 g / 10 min, the effect of lowering the molding steam temperature during in-mold molding may be insufficient. Moreover, when the MFR exceeds 100 g / 10 min, the obtained EPP molded product may be brittle. From such a viewpoint, the MFR of the base resin is more preferably 10 g / 10 min or more and 70 g / 10 min or less.

  In addition, the MFR measurement method referred to in this specification adopts the values obtained under JIS K7210 (1976) test condition 14 except for the MFR of the master batch.

  In the resin particle production process of the method of the present invention, a synthetic resin other than the polypropylene resin can be added to the base resin within a range that does not impair the intended effect of the present invention. The amount of the synthetic resin other than the polypropylene resin added is preferably at most 35 parts by weight, more preferably at most 20 parts by weight per 100 parts by weight of the polypropylene resin. Even more preferably 10 parts by weight or less, and particularly preferably 5 parts by weight or less.

  Examples of synthetic resins other than the polypropylene resin include high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, and other ethylene resins, or polystyrene, styrene. -Styrenic resins such as maleic anhydride copolymer are exemplified.

In addition, this base resin can contain various additives as desired. Examples of such additives include antioxidants, ultraviolet light inhibitors, antistatic agents, flame retardants, metal deactivators, nucleating agents, and bubble regulators.
Examples of the air conditioner include inorganic powders such as zinc borate, talc, calcium carbonate, borax, and aluminum hydroxide. These additives are preferably used in a total amount of 20 parts by weight or less, more preferably 5 parts by weight or less per 100 parts by weight of the base resin. These additives are usually used in the minimum necessary amount. These additives may be added and kneaded to the base resin melted in the extruder, for example, when the resin particles used in the present invention are produced by cutting the strands extruded by the extruder. Can be contained in the resin particles.

  In addition, in the case of a mixed resin composition in which the base resin contains a synthetic resin other than the above-described polypropylene resin, various additives, etc., the mixed resin composition depends on the type and amount of the additive. There is a possibility that the tensile elastic modulus of the object is lowered. In the present invention, in order not to impair the initial effects of the present invention, the tensile elastic modulus of the mixed resin composition (the same measurement method as the tensile elastic modulus of the base resin) does not fall below 1200 MPa. Preferably, the additive is added such that it does not fall below 1250 MPa, and most preferably does not fall below 1300 MPa.

  The specific thermoplastic polymer constituting the masterbatch according to the present invention (hereinafter also simply referred to as “masterbatch base resin”) is different from the base resin constituting the expanded particles, Examples thereof include those in which a colorant is covered with a thermoplastic polymer, specifically, an ethylene polymer, a thermoplastic elastomer, a copolymer of propylene and an α-olefin other than propylene (however, Only when the polypropylene resin of the base resin is a propylene homopolymer). If the masterbatch base resin described above is used, the surface modification is hindered because the colorant is covered with the thermoplastic polymer and dispersed in the polypropylene resin as the base resin during the surface modification process of the resin particles. Therefore, it is considered that the obtained expanded particles can be molded with low temperature steam. In addition, when the master batch is melt-kneaded with the base resin using an extruder, extruded into a strand shape, cooled and cut to an appropriate length to produce foaming resin particles, the colorant is exposed on the cut surface. The surface modification may be hindered. Even in such a case, if the surface other than the cut surface is surface-modified, the obtained expanded particles can be molded with low-temperature steam.

  In the present specification, the presence of the colorant covered with the thermoplastic polymer in the base resin means that the base resin is in a sea state and the colorant covered in the thermoplastic polymer is in an island shape. It is a state of being dispersed. In this case, it is preferable that the particle diameter or length of the thermoplastic polymer and the colorant dispersed in an island shape is 200 μm or less. When the resin particles having such a configuration are used, the size of the bubbles does not vary when foaming, so that the strength of the obtained EPP molded body does not decrease. From this point of view, the island-shaped particle size or length is more preferably 150 μm or less, and even more preferably 100 μm or less. On the other hand, the lower limit of the particle size or length is preferably 0.05 μm or more because the colorant can be covered with the thermoplastic polymer and does not hinder surface modification, and more preferably 0.08 μm or more. Preferably, 0.1 μm or more is more preferable. In addition, it is not necessary that all the colorants are covered with the thermoplastic polymer in the base resin, and any base material can be used as long as it becomes foamed particles that can be heat-molded with low-temperature steam that is the object of the present invention The resin may include a resin in which the colorant is partially covered with the thermoplastic polymer and does not exist.

  The particle size or length described above is placed in liquid nitrogen using resin composition particles for foaming, and the resin particles are sliced by a microtome on a plane perpendicular to the extrusion direction, and the sliced surface is subjected to a transmission electron microscope. From the photograph taken in step 1, the maximum particle size or maximum length of the island-shaped material in which the colorant in the vicinity of the peripheral surface of the resin particle is covered with the thermoplastic polymer is randomly selected at one location for one resin particle. Measure and adopt an average value of 100 resin particles. At that time, either the base resin or the thermoplastic polymer can be colored so that the particle size or length can be understood as necessary.

  In the present invention, in the surface modification step, the surfaces of the resin particles are modified with an organic peroxide in a dispersion medium. As a result, the foamed particles can be heat-molded with low-temperature steam. That is, surface modification is not hindered if the colorant in the vicinity of the surface of the resin particles (however, when the resin particles are cut into a strand or the like) is covered with at least a thermoplastic polymer. Therefore, when this surface or peripheral surface portion is photographed with a transmission electron microscope, the base resin becomes sea-like, and the colorant covered with the thermoplastic polymer is island-like and dispersed. If this can be confirmed, the surface has been modified.

  In the method of the present invention, as a method for selecting a masterbatch base resin in which the base resin described above is in a sea state and the colorant is covered with a thermoplastic polymer and is dispersed in an island shape, for example, The master batch base resin and the colorant are melt-kneaded using a conventionally known extruder to produce a master batch, and then the base resin and master batch are melt-kneaded using a conventionally known extruder. What is necessary is just to manufacture a resin particle. The obtained resin particles are photographed in the same manner as the method for measuring the particle diameter or length of the dispersed particles in the form of islands, and as a result, the base resin becomes sea-like and the colorant is heated. Any masterbatch base resin that is covered with a plastic polymer and is dispersed in an island shape can be suitably used in the present invention.

  Examples of the method for adjusting the base resin to be in a sea state and adjusting the colorant to be dispersed in the form of islands covered with a thermoplastic polymer include, for example, the viscosity of a masterbatch containing a colorant. May be larger than the viscosity of the polypropylene resin as the base resin. As a method of adjusting the viscosity, there is usually a method of adjusting with MFR. On the contrary, when the viscosity of the master batch is smaller than the viscosity of the polypropylene resin that is the base resin, there is a method in which the addition amount of the master batch is 30 parts by weight or less with respect to 100 parts by weight of the polypropylene resin.

In the present invention, the MFR of the master batch is 0.1 g / 10 min or more and 50 g / 10 min or less, and the base resin is in a sea state, and the colorant is covered with the thermoplastic polymer inside the base resin. This is preferable because the islands are present and dispersed. When the MFR is less than 0.1 g / 10 min, when producing the resin particles, the load on the extruder is increased, the discharge amount is decreased, and the productivity may be decreased. From the above viewpoint, 0.2 g / 10 min or more is more preferable, and 0.3 g / 10 min or more is further preferable. On the other hand, if the MFR exceeds 50 g / 10 min, it may be difficult to obtain a state in which the colorant is dispersed in an island shape covered with a thermoplastic polymer inside the sea-like base resin. is there. From such a viewpoint, the MFR of the base resin is more preferably 30 g / 10 min or less, and further preferably 10 g / 10 min or less.
The MFR measurement method for the master batch described above employs a value measured at a temperature of 230 ° C. and a load of 68.64 N in accordance with JIS K7210 (1976).

  In the method of the present invention, an ethylene polymer is used as the masterbatch base resin. Examples of the ethylene polymer include linear ethylene homopolymer, branched ethylene homopolymer, copolymer of ethylene and α-olefin other than ethylene, ethylene-vinyl acetate copolymer, ethylene -What an ethylene component unit exceeds 50 mol%, such as an acrylic acid copolymer and an ethylene-methacrylic acid copolymer, is mentioned.

  Among the ethylene polymers, an ethylene polymer having a density of less than 930 g / L is preferable from the viewpoint of obtaining foamed particles having excellent surface smoothness such as the resulting resin particles for foaming having less irregularities on the surface. Usually, the lower limit of the density is about 850 g / L.

  Examples of the ethylene polymer having a density of less than 930 g / L include linear ethylene homopolymers, branched ethylene homopolymers, and ethylene-propylene rubbers.

  Examples of the linear ethylene homopolymer include linear low density polyethylene and low density polyethylene, and examples of the branched ethylene homopolymer include low density polyethylene. Is about 910 g / L.

  Further, when the above-mentioned ethylene-propylene rubber is molded, the foamed particles are excellent in secondary foaming properties, foamable particles that can be molded with steam at a lower temperature, and foamed particles having excellent impact resistance in an EPP molded product. It is preferable because it can be obtained. Examples of the ethylene-propylene rubber include binary systems such as ethylene-propylene rubber and ternary systems of ethylene-propylene-diene rubber. Among these, when ethylene-propylene rubber binary is used as a masterbatch base resin, the base resin is in a sea state, and the colorant is easily dispersed in an island form in the state of being present in the thermoplastic polymer. The master batch is preferable because it is excellent in balance with being able to be manufactured at a low cost.

  Among the above-described ethylene-propylene rubbers, those having an ethylene component of 70 to 95 mol% are preferred because they have more dispersibility. Such an ethylene-propylene rubber is excellent in elasticity, and tends to be present in an island shape covering the colorant in the base resin made of polypropylene resin. Therefore, since the obtained expanded particles are prevented from mixing the colorant with the base resin, they can be uniformly colored and heat-molded with low-temperature steam, and have excellent secondary foamability.

  The MFR of the above-described ethylene polymer is preferably 2 to 30 g / 10 minutes from the viewpoint of dispersibility. When the MFR is less than 2 g / 10 min, when producing the resin particles, the load on the extruder becomes high, the discharge amount is reduced, and the productivity may be reduced. From this viewpoint, 3 g / 10 min or more is preferable, and 4 g / 10 min or more is more preferable. On the other hand, if the MFR exceeds 30 g / 10 minutes, the resulting EPP molded product may have reduced rigidity such as compression strength. From such a viewpoint, the MFR of the mixture is preferably 25 g / 10 min or less, and more preferably 20 g / 10 min or less.

  In the method of the present invention, a thermoplastic elastomer is used as the masterbatch base resin. Examples of the thermoplastic elastomer include styrene-butadiene copolymer elastomers, styrene-isoprene copolymer elastomers and hydrogenated styrene-butadiene-butylene-styrene block copolymer elastomers (also referred to as SBBS), and styrene. -Styrene polymer elastomers such as ethylene-butylene-styrene block copolymer elastomers (also referred to as SEBS), olefin polymer elastomers such as ethylene-octene polymer elastomers, ethylene-butylene polymer elastomers, chlorinated polyethylene, chlorine And polypropylene.

The MFR of the thermoplastic elastomer is preferably 1 to 15 g / 10 minutes from the viewpoint of dispersibility.
When the MFR is less than 1 g / 10 min, when producing the resin particles, the load on the extruder is increased, the discharge amount is decreased, and the productivity may be decreased. From this viewpoint, 1.5 g / 10 min or more is preferable, and 2 g / 10 min or more is more preferable. On the other hand, if the MFR exceeds 15 g / 10 minutes, the resulting EPP molded article may have a reduced rigidity such as compressive strength. From such a viewpoint, the MFR of the mixture is preferably 10 g / 10 min or less, and more preferably 8 g / 10 min or less.

  In addition to the above, the master batch base resin used in the method of the present invention includes a copolymer of propylene and an α-olefin other than propylene. However, this is limited to the case where the polypropylene resin of the base resin is a propylene homopolymer. In such a configuration, since the colorant is covered with the thermoplastic polymer inside the base resin and becomes the present resin particles, the surface modification step is not hindered during the surface modification step. Can be molded with steam.

  Examples of the copolymer of propylene and an α-olefin other than propylene include propylene component units such as propylene-ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer, propylene-ethylene-butene random copolymer, and the like. Containing 70 mol% or more.

Moreover, it is preferable from a dispersible point that MFR of the copolymer of propylene and alpha-olefins other than propylene is 1-20 g / 10min.
When the MFR is less than 1 g / 10 min, when producing the resin particles, the load on the extruder is increased, the discharge amount is decreased, and the productivity may be decreased. From this viewpoint, 1.5 g / 10 min or more is preferable, and 2 g / 10 min or more is more preferable. On the other hand, if the MFR exceeds 20 g / 10 min, the resulting EPP molded article may have a reduced rigidity such as compressive strength. From such a viewpoint, the MFR of the mixture is preferably 15 g / 10 min or less, and more preferably 10 g / 10 min or less.

The colorant used in the present invention may be an inorganic pigment or an organic pigment. Examples of the inorganic pigment include chromates such as chrome yellow, zinc yellow, and barium yellow. And ferrocyanides such as bitumen, sulfides such as cadmium yellow and cadmium red, oxides such as iron black and brown, silicates such as ultramarine, titanium oxide, and carbon black. Examples of organic pigments include monoazo pigments, disazo pigments, azo lakes, condensed azo pigments, chelate azo pigments, and other azo pigments, or phthalocyanines, anthraquinones, perylenes, perinones, thioindigos, quinacridones, dioxazines, Examples thereof include polycyclic pigments such as isoindolinone and quinophthalone.
Among the above colorants, those having a functional group on the surface are preferable because the surface of the colorant can be easily covered with the thermoplastic polymer.
Examples of the functional group include a hydroxyl group, a carboxyl group, a carbonyl group, an aldehyde group, an ether group, a quinone group, a carboxylic anhydride group, and a lactone structure.

  Among the above colorants, black is preferable from the viewpoint of easy color adjustment when recycled, and among blacks, carbon black is preferable because a dark color is produced in a small amount. Furthermore, carbon black is preferable because it is easily incorporated into the masterbatch base resin and the surface thereof is easily coated, so that the surface modification becomes difficult to be inhibited during the surface modification in the subsequent step.

  Examples of the carbon black include gas furnace black, oil furnace black, acetylene black, channel black, roller black, thermal black, and ketjen black.

  Among these carbon blacks, those having a functional group on the surface are preferable because the surface is easily coated with a masterbatch base resin.

  The average particle diameter of the carbon black can obtain uniformly colored foamed particles, and when foaming, the cell walls of the foamed particles are destroyed by agglomeration of the carbon black to form continuous foams. The average particle size is preferably 5 to 100 nm because there is no risk of lowering secondary foaming. Furthermore, 10 nm or more is more preferable, and 15 nm or more is more preferable from the viewpoint of easy aggregation without aggregation. On the other hand, 80 nm or less is more preferable, and 60 nm or less is more preferable from the viewpoint of color developability such that the color becomes dark with a small amount.

The average particle size of the carbon black is measured with an electron microscope.
Specifically, take a photograph containing hundreds of particles in the field of view, measure 1000 randomly with a fixed diameter (Green diameter) as the representative diameter, and calculate the number-based cumulative distribution curve from the obtained values. The 50% diameter of the cumulative distribution based on the number is adopted as the average particle diameter.

  In the method of the present invention, the content of carbon black is preferably 0.1% by weight or more with respect to the resin composition constituting the resin particles from the viewpoint of excellent color development, and 0.2% by weight or more is preferable. More preferred is 0.3% by weight or more. On the other hand, in order to prevent the foamed particles obtained from becoming continuous cells and causing a decrease in secondary foaming, it is preferably less than 5.0% by weight, more preferably 4.5% by weight or less, and 4.0% by weight or less. Further preferred.

In the master batch used in the present invention, the mixing weight ratio (% by weight) of the master batch base resin and carbon black is preferably 40:60 to 90:10.
If the mixing weight ratio of the carbon black exceeds 60% by weight, the surface coating of the carbon black with the masterbatch base resin is lowered, and the amount of carbon black mixed into the base resin side increases, so that the organic peroxide described later There is a possibility that the surface modification by hinders. On the other hand, if the mixing weight ratio is less than 10% by weight, a large amount of the master batch is used, so that the blending ratio of the master batch base resin is relatively high and physical properties such as compression strength may be lowered.

  The addition amount of the master batch in the method of the present invention is 30 parts by weight with respect to 100 parts by weight of the base resin, although it depends on the mixing weight ratio of the master batch base resin and carbon black and the final carbon black content. Or less, more preferably 20 parts by weight or less, still more preferably 10 parts by weight or less. The lower limit is usually 0.5 parts by weight. If the amount exceeds 30 parts by weight, the tensile modulus may decrease and the rigidity may be lowered, and depending on the type of the masterbatch base resin, the processability such as difficulty in kneading becomes large in the resin particle manufacturing process described later. There is a risk of damage.

  The resin composition in the present resin particles obtained by melt-kneading the base resin and the master batch does not impair the initial effects of the present invention. (The same measurement method as the tensile modulus of the base resin) is not less than 1200 MPa, preferably not less than 1250 MPa, and most preferably not less than 1300 MPa. It is preferable that a synthetic resin, an additive, and a master batch are contained.

  In the resin particle production process of the method of the present invention, the present resin particles are produced by melt-kneading the base resin, the master batch, and, if necessary, additives. As a method for producing the resin particles, a method using a conventionally known extruder can be employed. Specifically, a master batch is melt-kneaded with the base resin using a twin screw extruder, extruded into a strand shape, cooled, and cut to an appropriate length, or after a strand is cut to an appropriate length Or the method of obtaining the resin particle for foaming by the method of cooling simultaneously with a cutting | disconnection, etc. is mentioned.

  Examples of the additive include an antioxidant, an ultraviolet ray inhibitor, an antistatic agent, a flame retardant, a metal deactivator, a nucleating agent, and a bubble adjusting agent. Examples of the air conditioner include inorganic powders such as zinc borate, talc, calcium carbonate, borax, and aluminum hydroxide. The total content of these additives is preferably 20 parts by weight or less, more preferably 5 parts by weight or less per 100 parts by weight of the base resin. The lower limit content of these additives is approximately 0.01 parts by weight. These additives are added and kneaded to the base resin melted in the extruder when, for example, the resin particles used in the method of the present invention are produced by cutting the strands extruded by the extruder. This can be contained in the resin particles.

  In addition, as this resin particle, what was obtained by quenching the strand immediately after extrusion when manufacturing this resin particle by cut | disconnecting the strand which this base-material resin melt-kneaded in the extruder, and was extruded. preferable. When the resin particles are so cooled, the surface modification described later can be performed efficiently. The quenching of the strand immediately after the extrusion is adjusted immediately after extruding the strand, preferably in water adjusted to 50 ° C. or lower, more preferably in water adjusted to 40 ° C. or lower, most preferably 30 ° C. or lower. This can be done by placing it in water. By such rapid cooling, the surface modification of the resin particles is effectively performed in the surface modification step described later. Then, the sufficiently cooled strand is pulled up from the water and cut into an appropriate length to form the resin particles having a desired size. The resin particles are usually adjusted to have a length / diameter ratio of 0.5 to 2.0, preferably 0.8 to 1.3, and the average weight per particle (chosen at random). The average value of 200 weights measured simultaneously is adjusted to be 0.1 to 20 mg, preferably 0.2 to 10 mg.

The method of the present invention includes a surface modification step of modifying the surface of the resin particles produced in the resin particle production step described above with an organic peroxide in a dispersion medium.
In the surface modification step, the surface of the foamed particles subjected to the surface modification is modified by modifying the surface of the resin particles with an organic peroxide in a dispersion medium. In-mold molding is possible with lower temperature steam as compared with no expanded particles.
In addition, it is preferable that the surface modification in this specification does not proceed to the center of the expanded particles. As for what progressed to the center of the foamed particles, a large number of the modified resin particles are fused into a large lump in the sealed container and may not be released outside the sealed container. When molding, there is a possibility that the foamed particles are formed into open cells that are not secondary foamed.

In the surface modification step in the present invention, for example, the present resin particles are dispersed in a dispersion medium in which an organic peroxide is present, and the obtained dispersion is more than the melting point of the base resin constituting the present resin particles. The surface modified particles (hereinafter referred to as “surface modified particles”) whose surface is modified by maintaining the temperature at a low temperature and at a temperature at which the organic peroxide is substantially decomposed to decompose the organic peroxide. May be referred to as “fine particles”).
The surface-modified foam particles obtained in this way are excellent in heat-fusibility, and even between low-temperature steam, the foam particles can be fused.

  The dispersion medium used in the production of the surface-modified particles is generally an aqueous medium, preferably water, and more preferably ion-exchanged water, but is not limited to water. In addition, any solvent or liquid that can disperse the resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol, and the like. The aqueous medium includes a mixed solution of water and an organic solvent such as the alcohol.

  Examples of the organic peroxide used for the surface modification of the resin particles include various conventionally known ones such as isobutyl peroxide, cumylperoxyneodecanoate, α, α′-bis (neodecanoylperperoxide). Oxy) diisopropylbenzene, di-n-propylperoxydicarbonate, diisopropylperoxydicarbonate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneo Decanoate, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, di (2-ethylhexylperoxy) dicarbonate, t-hexylperoxyneodecanoate, Dimethoxybutyl peroxydicarbonate, di (3 -Methyl-3-methoxybutylperoxy) dicarbonate, t-butylperoxyneodecanoate, 2,4-dichlorobenzoyl peroxide, t-hexylperoxypivalate, t-butylperoxypivalate, 3, 5,5-trimethylhexanoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, succinic peroxide, 2, 5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate T-butylperoxy-2-ethylhexanoate, -Toluoyl benzoyl peroxide, benzoyl peroxide, t-butylperoxyisobutyrate, di-t-butylperoxy-2-methylcyclohexane, 1,1-bis (t-hexylperoxy) -3,3 5-trimethylcyclohexane, 1,1-bis (t-hexylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butyl) Peroxy) cyclohexane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-bis (t-butylperoxy) cyclododecane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxymaleic acid, t-butylperoxy-3,5,5-trimethylhexene Noate, t-butylperoxylaurate, 2,5-dimethyl-2,5-di (m-toluoylperoxy) hexane, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl mono Examples include carbonate, t-hexyl peroxybenzoate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, and the like. The organic peroxide is preferably added in an amount of usually 0.01 to 10 parts by weight per 100 parts by weight of the resin particles alone or in combination of two or more. If the amount is less than 0.01 parts by weight, the surface may not be sufficiently modified. On the other hand, when the amount exceeds 10 parts by weight, the polypropylene resin as the base resin is decomposed, and there is a possibility that the secondary foaming at the time of forming into an open cell is lowered. From this viewpoint, it is necessary to add 0.05 to 5 parts by weight, more preferably 0.1 to 3 parts by weight, in the dispersion medium.

  In the dispersion composed of the organic peroxide, the present resin particles, and the dispersion medium, if the weight ratio of the present resin particles / dispersion medium is too large, uniform surface modification may not be performed on the present resin particles. If so, the surface modified particles are mixed with the ones whose modification has progressed excessively, and in the next foaming process, a large number of the modified resin particles are fused together in a sealed container, resulting in a large size. There is a possibility that it becomes a lump and cannot be discharged outside the sealed container. From such a viewpoint, in the surface modification step, the weight ratio of the resin particles / dispersion medium is preferably 1.3 or less, more preferably 1.2 or less, still more preferably 1.1 or less, 0.0 or less is most preferable. However, if this weight ratio is too small, there is a possibility that effective low-temperature formability cannot be imparted to the resulting foamed particles unless the amount of organic peroxide used in the resin particles is increased. When the amount of the organic peroxide used is increased, the polypropylene resin constituting the base resin is decomposed, and the resulting foamed particles may become open-celled, resulting in a decrease in secondary foaming. In order to reduce the amount of the organic peroxide used, the weight ratio of the resin particles / dispersion medium is preferably 0.6 or more, and more preferably 0.7 or more.

The organic peroxide is substantially decomposed at a temperature lower than the melting point of the base resin. Accordingly, the one-hour half-life temperature of the organic peroxide (the constant temperature when the amount of active oxygen becomes half of the initial value in one hour when the organic oxide is decomposed at a constant temperature) It is preferable that it is below Vicat softening point (JIS K 6747-1981, the same shall apply hereinafter) of the resin. When the 1-hour half-life temperature of the organic peroxide used exceeds the Vicat softening point of the base resin, a high temperature higher than the melting point of the base resin is required to rapidly decompose the peroxide. Therefore, it is not preferable. In some cases, it cannot be substantially decomposed at a temperature lower than the melting point of the base resin, which is not preferable. When the peroxide is substantially decomposed at a temperature higher than the melting point of the base resin, the peroxide is decomposed in a state where it penetrates deep into the resin particles. Since the resin material is greatly decomposed as a whole regardless of the surface or inside, in some cases, there is a possibility that only foamed particles that cannot be used for molding may be obtained, and even if molding can be obtained, it is finally obtained. There exists a possibility that the mechanical physical property of an EPP molded object may fall large.

  Considering the above, the organic peroxide used preferably has a one-hour half-life temperature of 20 ° C. or more lower than the Vicat softening point of the base resin, and the Vicat softening point of the base resin. It is more preferable that the temperature is 30 ° C. or higher. The one-hour half-life temperature is preferably equal to or higher than the glass transition temperature of the base resin, more preferably 40 to 100 ° C., and 50 to 90 ° C. in view of handling properties. Is more preferable.

  The glass transition temperature means an intermediate-point glass transition temperature obtained by heat flux DSC according to JIS K 7121-1987. (Regarding the state adjustment of the test piece in this test method, “after performing a certain heat treatment, Adopt “when measuring temperature”).

The peroxide is preferably substantially decomposed below the Vicat softening point of the base resin in the dispersion medium in which the resin particles are present, and is 20 ° C. higher than the Vicat softening point of the base resin. It is more preferable to substantially decompose at a low temperature as described above, and it is further preferable to substantially decompose at a temperature of 30 ° C. or more higher than the Vicat softening point of the base resin. The organic peroxide has a one-minute half-life temperature of the organic peroxide (the temperature at which the amount of active oxygen is half of the original in one minute when the organic oxide is decomposed at a constant temperature) ± It is particularly preferable to keep the temperature in the temperature range of 30 ° C. for 10 minutes or more and substantially decompose. If it is attempted to decompose at a temperature lower than [one minute half-life temperature −30 ° C.], it takes a long time to decompose, resulting in poor efficiency. On the other hand, when the decomposition is attempted at a temperature higher than [one minute half-life temperature + 30 ° C.], the decomposition may be abrupt and the surface modification efficiency may be deteriorated. Moreover, if it maintains for 10 minutes or more in the range of half-life temperature +/- 30 degreeC for 1 minute, it will become easy to decompose organic peroxide substantially. The longer the holding time in the range of 1 minute half-life temperature ± 30 ° C., the more reliably the organic peroxide can be decomposed, but a longer time is no longer necessary. Longer times than necessary will lead to a decrease in production efficiency. The holding time in the above temperature range should normally be at most 60 minutes. To decompose the organic peroxide, first prepare the dispersion adjusted to a temperature at which the organic peroxide is difficult to decompose, and then heat the dispersion to the decomposition temperature of the organic peroxide. Good. At this time, the rate of temperature rise may be selected so that the temperature is maintained in the range of 1 minute half-life temperature ± 30 ° C. for 10 minutes or more. It is more preferable to hold the temperature for 5 minutes or more. As the arbitrary temperature at that time, the temperature within 1 minute half-life temperature ± 5 ° C. is most preferable. In addition, substantially decomposing means decomposing until the active oxygen content of the used peroxide is 50% or less of the original, but decomposing until the active oxygen content is 30% or less of the initial. It is preferable to decompose until the amount of active oxygen becomes 20% or less of the initial amount, and further preferable to decompose until the amount of active oxygen becomes 5% or less of the initial amount.

  The above-mentioned half-life temperature of the organic peroxide is adjusted to a 0.1 mol / L concentration organic peroxide solution using a solution that is relatively inert to radicals (for example, benzene, mineral spirit, etc.) It is sealed in a glass tube subjected to nitrogen substitution, immersed in a thermostat set at a predetermined temperature, pyrolyzed and measured.

  The surface modification in the present invention, as described above, decomposes the peroxide in the dispersion medium in which the present resin particles are present in a relatively narrow temperature range above room temperature and below the Vicat softening point of the base resin. It is done by letting. However, since there is a temperature within the temperature range at which the crystal structure of the base resin changes from a smectic structure (low melting point crystal) to an α crystal, the change to the α crystal is suppressed, and the smectica on the surface of the resin particles is suppressed. Unless the proportion of the structure (low melting point crystal) is maintained, the obtained expanded particles cannot be molded with low temperature steam.

  In addition, as described above, an object of the present invention is to provide a method for producing foamed particles that prevents the colorant from inhibiting surface modification and can be heat-molded with low-temperature steam. The mechanism by which the colorant inhibits the surface modification is thought to be due to the catalytic action of the colorant when the dispersion medium is heated during the surface modification. That is, since the colorant such as carbon black and a color pigment composed of a transition metal has a catalytic action of decomposing peroxide at a lower temperature, the colorant is exposed on the surface of the resin particles. As a result of the catalytic action of the colorant, the peroxide decomposes at a low temperature, and most of the peroxide decomposes before the temperature range where the decomposition is expected (surface modification temperature). It is thought that it cannot be modified.

  In the method of the present invention, it is preferable that the present resin particles, surface modified particles, expanded particles having a modified surface that can be molded at low temperature, and EPP molded products obtained therefrom are substantially non-crosslinked. In the production of the surface modified particles, the crosslinking does not proceed substantially because a crosslinking aid or the like is not used in combination. The term “substantially non-crosslinked” is defined as follows. That is, regardless of the base resin, the present resin particles, the surface modified particles, the present expanded particles, and the EPP molded body, each was used as a sample (use 1 g of sample per 100 g of xylene), and this was immersed in boiling xylene for 8 hours. Filter quickly with a wire mesh of 74 μm mesh specified in JIS Z 8801 (1966), which defines a standard mesh screen, and measure the weight of the boiling xylene-insoluble matter remaining on the wire mesh. A case where the insoluble content is 10% by weight or less of the sample is called substantially non-crosslinked, but the insoluble content is preferably 5% by weight or less and preferably 3% by weight or less. More preferably, it is most preferably 1% by weight or less. The smaller the insoluble content, the easier it is to reuse. The content P (%) of the insoluble matter is represented by the following formula (1).

P (%) = (M ÷ L) × 100 (1)
However, M is the weight (g) of insoluble matter, and L is the weight (g) of the sample.

  The expanded particles having a modified surface that can be molded at low temperature (hereinafter referred to as “surface modified expanded particles”) obtained from the surface modified particles described above have the following structural specificity. This is clear from the measurement results.

As a result of DSC measurement of the expanded particles, the surface-modified expanded particles tend to be different from the expanded particles obtained by the conventional method. When the melting point was measured by dividing the surface layer portion of the expanded particle and the internal expanded layer not including the surface layer portion, the conventional expanded particle had a melting point (Tm _s ) of the surface layer portion of the expanded particle (Tm _s ). _In contrast to _i ), the surface-modified foamed particles have a property of necessarily higher than that of _i ), whereas the melting point (Tm _s ) of the surface layer portion is lower than the melting point (Tm _i ) of the inner foamed layer. It was observed that Therefore, the surface modified foam particles, Tm _s is preferably less 0.05 ° C. or higher than Tm _i, more preferably 0.1 ° C. or more lower, still more preferably 0.3 ° C. or more lower.

The melting point (Tm _s ) of the surface layer portion of the expanded particle was obtained by performing the same operation as the measurement of the high temperature peak heat quantity of the expanded particle described above except that the surface layer portion of the expanded particle was cut out and 2 to 4 mg was collected and used as a sample. It means the temperature of the peak of the intrinsic peak a of the second DSC curve. In addition, the melting point (Tm _i ) of the internal foam layer of the foam particles is cut from the inside of the foam particles so as not to include the surface layer portion, and 2 to 4 mg is collected, and this is used as a sample. It means the temperature of the apex of the intrinsic peak a of the second DSC curve obtained by performing the same operation as the measurement.

In addition, when the high temperature peak calorific value was measured by dividing into a surface layer portion of the expanded particle and an internal expanded layer not including the surface layer portion, the conventional expanded particle had a high temperature peak heat (ΔH _s ) of the surface layer portion of the expanded particle and the internal expanded layer. In contrast to the high temperature peak heat quantity (ΔH _i ), there was a property that ΔH _s ≧ ΔH _i × 0.87, whereas in the surface-modified foamed particles, ΔH _s <ΔH _i × 0.86 It was observed that Therefore, as the surface-modified foamed particles, ΔH _s <ΔH _i × 0.86 is preferable, ΔH _s <ΔH _i × 0.83 is more preferable, and ΔH _s <ΔH _i × 0.78. Is more preferable, ΔH _s <ΔH _i × 0.75 is particularly preferable, and ΔH _s <ΔH _i × 0.73 is most preferable. In addition, ΔH _s is preferably ΔH _s ≧ ΔH _i × 0.25. Since the surface-modified foamed particles satisfy ΔH _s <ΔH _i × 0.86, in-mold molding can be performed at a lower temperature than foamed particles that are not surface-modified, and the effect becomes greater as the ΔH _s value becomes smaller. Thereby, in-mold molding can be performed with low-temperature steam without reducing the rigidity of the portion of the unit molded body made of the surface-modified foam particles. ΔH _s is preferably 1.7 J / g to 60 J / g, more preferably 2 J / g to 50 J / g, still more preferably 3 J / g to 45 J / g, and 4 J / G to 40 J / g is most preferable.

  The high temperature peak calorific value of the surface layer portion of the expanded particle can be determined by performing the same operation as the measurement of the high temperature peak heat amount of the expanded particle described later except that the surface layer portion of the expanded particle is cut out and 2 to 4 mg is collected and used as a sample. . In addition, the high temperature peak calorific value of the internal foamed layer of the foamed particles is cut out from the inside of the foamed particles so as not to include the surface layer portion, and 2 to 4 mg are collected and used as a sample to measure the high temperature peak calorific value of the foamed particles described later. The same operation can be performed.

A method of measuring the melting point and the high temperature peak calorie by dividing the foamed particle into a surface layer portion and an internal foam layer not including the surface layer portion is as follows.
The surface layer portion of the expanded particle may be sliced using a cutter knife, a microtome, etc., and the surface layer portion may be collected and used for measurement. However, the surface of the foamed particle always exists on the entire surface of the surface layer portion of the sliced foamed particle, but on the back surface of the surface layer portion of the sliced foamed particle, the surface of the foamed particle faces the center of gravity of the foamed particle. In other words, the surface of the expanded particle is sliced from one or a plurality of points selected at random so that a part exceeding 200 μm is not included. When a portion exceeding 200 μm from the surface of the foamed particle toward the center of gravity of the foamed particle is included on the back surface of the surface layer part of the sliced foamed particle, the internal foamed layer is contained in a large amount, and the melting point of the surface layer part and There is a possibility that the high temperature peak calorie cannot be measured accurately. In addition, when the surface layer part obtained from one expanded particle is less than 2-4 mg, what is necessary is just to collect the required amount surface layer part by repeating the said operation using several expanded particle.
On the other hand, the internal foam layer that does not include the surface layer portion of the foam particle is the entire surface of the foam particle so that the surface of the foam particle and the portion between the surface of the foam particle and 200 μm from the surface of the foam particle toward the center of gravity of the foam particle are not included. What is necessary is just to use for the melting | fusing point and high temperature peak calorie | heat amount measurement using what cut | disconnected the surface layer part from. However, if the size of the expanded particles is too small and the internal foam layer disappears when the 200 μm portion is cut off from the above surface, the surface of the expanded particles and the surface of the expanded particles are directed toward the center of gravity of the expanded particles. If the surface of the foamed particle is cut out from the entire surface of the foamed particle so that the portion between 100 μm is not included, and the inner foamed layer still disappears, the surface of the foamed particle The surface of the foamed particle is cut off from the entire surface of the foamed particle so as not to include a part between the surface of the foamed particle and the center of gravity of the foamed particle. When the internal foamed layer obtained from one foamed particle is less than 2 to 4 mg, the above operation is repeated using a plurality of foamed particles to collect the required amount of the internal foamed layer.

  The method of the present invention comprises a step of producing the resin particles, a surface modification step of modifying the surface of the resin particles with an organic peroxide in a dispersion medium, and a foaming agent impregnation step of impregnating the resin particles with a foaming agent. And a foaming step of foaming the surface-modified resin particles impregnated with the foaming agent.

The foaming method of the surface modified particles in the foaming step can be roughly divided into two methods.
One is to impregnate the resin particles with a foaming agent under high temperature and high pressure, and after reducing the temperature to room temperature, the pressure is removed and taken out as foamable resin particles, and the foamable resin particles are removed using a heating medium such as steam or hot air. This is a foaming method. The other is a method of obtaining foamed particles by discharging the surface-modified particles and the dispersion medium into a low-pressure zone at a temperature at which the surface-modified particles can be foamed (hereinafter referred to as “dispersion medium release foaming method”). The step of foaming the surface-modified particles by a method is referred to as “dispersion medium releasing foaming step”). In the method of the present invention, it is preferable to employ a dispersion medium releasing foaming method that is excellent in productivity. According to this method, foamed particles can be produced efficiently in a short time.

  When the dispersion medium releasing foaming method is employed in the foaming step, the surface modification step and the foaming step including the dispersion medium releasing foaming step can be performed at different times with different apparatuses. It is preferable to obtain foamed particles by continuously performing a foaming process including a surface modification process and a dispersion medium releasing foaming process in the same container because foamed particles can be produced efficiently in a short time.

  In the foaming process including the dispersion medium releasing foaming process, in order to prevent the surface-modified particles in the sealed container from fusing, the weight ratio of the surface-modified particles / the dispersion medium is 0.5 or less, Preferably it is 0.5 to 0.1. In addition, when the weight ratio of the present resin particles / the dispersion medium in the surface modification step is 0.6 to 1.3, and the surface modification step and the foaming step are performed in the same container In order to make the weight ratio of the surface modified particles / the dispersion medium in the foaming process 0.5 or less, the dispersion medium may be added to the container after the surface modification process.

  In the surface modified particles, the expanded particles having a modified surface that can be molded at low temperature, and the EPP molded body thereof, there are several alcohols having a molecular weight of 50 or more that are generated along with the decomposition of the organic peroxide. About 100 ppm to several thousand ppm can be contained. As such an alcohol, when bis (4-t-butylcyclohexyl) peroxydicarbonate shown in Examples described later is used, Pt-butylcyclohexanol is contained in the surface-modified particles. It can be contained in. Other alcohols can be included if other peroxides are used. Examples of such alcohol include isopropanol, S-butanol, 3-methoxybutanol, 2-ethylhexylbutanol, and t-butanol.

  In the dispersion medium releasing foaming method, it is preferable to add a dispersant to the dispersion medium so that the surface-modified particles under heating in the container do not fuse with each other in the container. Such a dispersant is not limited as long as it prevents fusion of the surface-modified particles in the container, and can be used regardless of whether it is organic or inorganic. Inorganic substances are preferred. For example, natural or synthetic clay minerals such as amusnite, kaolin, mica, clay, aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide and the like in one kind or a combination of several kinds Can be used.

  Furthermore, in the above dispersion medium releasing foaming method, a dispersion strengthening agent that strengthens the dispersing power of the dispersing agent (prevents fusion of surface-modified particles within the container even if the amount of the dispersing agent added is small) is dispersed. You may add in a medium. Such a dispersion strengthening agent is an inorganic compound that can be dissolved in at least 1 mg or more in 100 cc of water at 40 ° C., and at least one of the anion or cation of the compound is a divalent or trivalent inorganic substance. . Examples of such inorganic substances include magnesium chloride, magnesium nitrate, magnesium sulfate, aluminum chloride, aluminum nitrate, aluminum sulfate, iron chloride, iron sulfate, and iron nitrate.

  Usually, the dispersant is used in an amount of about 0.001 to 5 parts by weight and the dispersion strengthener is used in an amount of about 0.0001 to 1 part by weight per 100 parts by weight of the surface-modified particles.

  Examples of the foaming agent used in producing the expanded particles include aliphatic hydrocarbons such as propane, butane, hexane, and heptane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, trifluoromethane, Organic physical foaming agents such as halogenated hydrocarbons such as 1,2-difluoroethane, 1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, nitrogen, oxygen, air, carbon dioxide, A so-called inorganic physical foaming agent such as water is exemplified. An organic physical foaming agent and an inorganic physical foaming agent can be used in combination. In the method of the present invention, those having as a main component one or more inorganic physical foaming agents selected from the group of nitrogen, oxygen, air, carbon dioxide and water are particularly preferably used. Among these, nitrogen and air are preferable in view of the stability of the apparent density of the expanded particles, environmental load, cost, and the like. When water is used as the foaming agent, water (including ion-exchanged water) used as a dispersion medium in order to disperse the surface modified particles in the sealed container may be used as it is.

  In the dispersion medium releasing foaming method, the filling amount of the physical foaming agent into the container is appropriately selected according to the type of foaming agent used, the foaming temperature, and the apparent density of the intended foamed particles. For example, when nitrogen is used as the foaming agent and water is used as the dispersion medium, the pressure in the sealed container in a stable state immediately before the start of foaming, that is, the pressure in the space in the sealed container (gauge pressure) However, it is preferable to select so that it may become 0.6-6 MPa. Usually, it is desirable that the pressure in the space in the container is increased as the apparent density of the target foamed particles is small, and the pressure in the space is decreased as the apparent density of the target foamed particles is increased. Is desirable.

  In the dispersion medium releasing foaming method, the physical foaming agent may be filled in the container at the same time as the temperature rise, filled in the middle of the temperature rise, or filled in a stable state immediately before the start of foaming. Any foaming agent may be impregnated.

  The expanded particles obtained by the method of the present invention and having a modified low-temperature moldable surface preferably have an apparent density of 10 g / L to 500 g / L. When the apparent density is less than 10 g / L, the mechanical strength of the finally obtained EPP molded product may be weakened. When the apparent density exceeds 500 g / L, the EPP molded product loses the lightness specific to the foam. There is a fear.

  The present expanded particles have an endotherm derived from the heat of fusion of the base resin in a DSC curve obtained by heat flux differential scanning calorimetry (hereinafter also simply referred to as “differential scanning calorimetry”). It is preferable that the end of the endothermic curve peak (high temperature peak) exists on the higher temperature side than the top of the curve peak (inherent peak). Such expanded particles have a high closed cell ratio and are suitable for thermoforming.

  The amount of heat at the high temperature peak is preferably 15 J / g or more, more preferably 20 J / g or more, and even more preferably 25 J / g or more from the viewpoint of increasing the compression strength of the obtained EPP molded article. On the other hand, it is preferably 60 J / g or less, more preferably 55 J / g or more, and even more preferably 50 J / g or more from the viewpoint of reducing the reduction effect of the molding temperature. Moreover, it is preferable that the heat quantity of the said high temperature peak is 15 to 60% with respect to the sum total of the heat quantity of a high temperature peak, and the calorie | heat amount of an intrinsic peak. As a result, when the heat quantity of the high temperature peak is less than 15% with respect to the total heat quantity of all the endothermic curve peaks, it can be molded with low temperature steam when molding, but the compression strength and energy of the resulting EPP molded product There is a possibility that the amount of absorption may decrease. If it exceeds 60%, the air pressure that must be applied to the foamed particles prior to molding the foamed particles may become too high, or the molding cycle may be prolonged. From this viewpoint, it is more preferably 20 to 50%. Moreover, it is preferable that the sum total of the calorific value of the high temperature peak and the calorific value of the intrinsic peak is 40 J / g to 150 J / g. In addition, the heat quantity of the high temperature peak and the heat quantity of the intrinsic peak referred to in this specification both mean the endothermic quantity, and the numerical value is expressed as an absolute value.

The amount of heat at the high temperature peak of the expanded particles is as shown in FIG. 1 obtained when 2-4 mg of expanded particles are heated from room temperature (10-40 ° C.) to 220 ° C. at 10 ° C./min by a differential scanning calorimeter. The amount of heat of the endothermic curve peak (high temperature peak) b appearing on the higher temperature side than the temperature at which the intrinsic endothermic curve peak (intrinsic peak) a derived from the heat of fusion of the base resin found in the DSC curve of Specifically, it can be obtained as follows.
First, a straight line (α−β) connecting a point α corresponding to 80 ° C. on the DSC curve and a point β on the DSC curve corresponding to the melting end temperature T of the expanded particles is drawn. 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 intrinsic peak a and the high temperature peak b, and the point intersecting with the straight line (α−β) is defined as σ. . The area of the high temperature peak b is that of the portion surrounded by the curve of the high temperature peak b portion of the DSC curve, the line segment (α-β), and the line segment (γ-σ) (the hatched portion in FIG. 1). This is the area, which corresponds to the amount of heat at the high temperature peak. The melting end temperature T is the intersection of the DSC curve on the high temperature side of the high temperature peak b and the high temperature side baseline.
Moreover, the sum total of the heat amount of the high temperature peak and the heat amount of the intrinsic peak corresponds to the area of the portion surrounded by the straight line (α-β) and the DSC curve.

  When the intrinsic peak and the high temperature peak of the expanded particles are measured by the differential scanning calorimeter as described above, when the weight per expanded particle is less than 2 mg, a plurality of expanded foams having a total weight of 2 mg to 10 mg. The particles may be used for the measurement as they are, and when the weight per foamed particle is 2 mg to 10 mg, the foamed particles may be used for the measurement as it is, and the weight per foamed particle. Is more than 10 mg, one cut sample having a weight of 2 to 10 mg obtained by cutting one expanded particle into a plurality of particles may be used for the measurement. However, this cut sample is obtained by cutting one foamed particle using a cutter or the like, but at the time of cutting, the surface of the foamed particle that is originally provided is left without being cut, and each cut sample It is preferable that the foamed particles are cut so as to have the same shape as much as possible, and in each cut sample, the area of the surface of the expanded particles remaining without being cut is as much as possible. For example, when the weight per expanded particle is 18 mg, if the expanded particle oriented in an arbitrary direction is cut horizontally from the middle of the vertical direction, two approximately 9 mg cut samples having substantially the same shape are obtained. In each cut sample, the surface of the expanded particles from the beginning is left as it is, and the area of the surface is almost the same in each cut sample. One of the two cut samples thus obtained may be used for the measurement of the intrinsic peak and the high temperature peak as described above. In the present specification, when simply expressed as “the high temperature peak of the expanded particle” without any notice, it means the heat quantity of the high temperature peak obtained by the above measurement, and this is the surface layer of the expanded particle described above. The amount of heat at the high temperature peak for the part and the amount of heat at the high temperature peak for the internal foam layer are different.

  This high temperature peak b is observed in the first DSC curve measured as described above, but after obtaining the first DSC curve, it is once around 40 ° C. at 220 ° C. to 10 ° C./min. When the base resin is melted as shown in FIG. 2, it is not observed in the second DSC curve obtained when the temperature is lowered to (40 to 50 ° C.) and again raised to 220 ° C. at 10 ° C./min. Only the intrinsic peak a corresponding to the endotherm of is observed.

  The temperature at the peak of the intrinsic peak a appearing in the first DSC curve of the expanded particles is usually in the range of [Tm−5 ° C.] to [Tm + 5 ° C.] based on the melting point (Tm) of the base resin. (Most commonly appears in the range of [Tm−4 ° C.] to [Tm + 4 ° C.]). Further, the temperature at the apex of the high temperature peak b appearing in the first DSC curve of the expanded particles usually appears in the range of [Tm + 5 ° C.] to [Tm + 15 ° C.] based on the melting point (Tm) of the base resin. (Most commonly appears in the range of [Tm + 6 ° C.] to [Tm + 14 ° C.]). In addition, the temperature at the top of the intrinsic peak a observed in the second DSC curve of the expanded particles (temperature corresponding to the melting point of the base resin) is usually determined based on the melting point (Tm) of the base resin. Tm-2 ° C.] to [Tm + 2 ° C.].

  As described above, the expanded particles obtained by the method of the present invention have a crystal structure in which a high temperature peak appears in the first DSC curve in the DSC measurement. It is strongly influenced by the difference between the melting point and the foaming temperature.

  In general, the high-temperature peak heat quantity of the expanded particles acts as a factor for determining the minimum fusion temperature particularly with respect to the fusion between the expanded particles. The high temperature peak calorific value is closely related to this minimum fusing temperature. When the same base resin is used, the minimum fusing temperature is lower when the high temperature peak calorific value is larger than when the high temperature peak calorific value is larger. Tend to be lower. The value of the high temperature peak heat quantity is strongly influenced by the foaming temperature at which the resin particles are foamed in the production stage of the foamed particles. When the same base resin is used, the higher the foaming temperature, the higher the temperature. The peak calorific value tends to be small.

  The minimum fusing temperature means a temperature at which the foam particles are fused in the mold to give the lowest saturated steam pressure necessary to obtain a practical state as an EPP molded body.

  However, in general, when obtaining an EPP molded article using expanded particles having a small high-temperature peak heat quantity, the minimum fusing temperature tends to be relatively low, but the strength physical properties such as compression strength (rigidity) of the EPP molded article, etc. Tends to decrease relatively. On the other hand, when obtaining an EPP molded product using expanded particles having a high high temperature peak heat quantity, the minimum fusion temperature is relatively high although strength properties such as compressive strength of the EPP molded product tend to be relatively high. As described above, there is a problem that high pressure steam may be required when manufacturing an EPP compact. That is, the most preferred foamed particles are foamed particles that have the contradictory properties of generally having a lowest minimum fusing temperature and relatively high strength properties such as compression strength of the EPP molded article. These points also apply to the present expanded particles obtained by the method of the present invention.

  The expanded particles obtained by the method of the present invention have a modified surface, and the minimum fusion temperature is effectively reduced. Therefore, when an EPP molded body is produced using the present expanded particles obtained by the method of the present invention, an EPP molded body having excellent mechanical properties such as compressive strength can be obtained even when molded with low-temperature steam. it can.

  The foamed particles having a high temperature peak in the DSC curve are not heated above the melting end temperature (Te) of the base resin when the surface-modified particles are dispersed in a dispersion medium and heated in a closed container. , Stopped at an arbitrary temperature (Ta) within a range of 20 ° C. lower than the melting point (Tm) of the base resin and lower than the melting end temperature (Te), and a sufficient time at the temperature (Ta), preferably 10 Hold for about ~ 60 minutes, and then adjust the temperature to 15 ° C lower than the melting point (Tm) to an arbitrary temperature (Tb) in the range of melting end temperature (Te) + 10 ° C, stop at that temperature, and if necessary, at that temperature Furthermore, after maintaining for a sufficient time, preferably about 10 to 60 minutes, the surface-modified particles can be obtained by releasing and foaming from the inside of the sealed container under a low pressure.

The melting point (Tm) is a differential scanning calorimetry of the resin particles in the same manner as the DSC curve of the expanded particles as described above using 2 to 4 mg of the resin particles as a sample. This is the temperature at the apex of the endothermic curve peak a unique to the base resin found in the second DSC curve (an example of which is shown in FIG. 2), and the melting end temperature (Te) is the inherent temperature. This is the intersection (β) between the DSC curve on the high temperature side of the endothermic curve peak a and the high temperature side baseline (B _L ). The endothermic curve peak appearing in the second DSC curve for the resin particles usually appears as one endothermic curve peak on the premise that it is a peak based on melting of the polypropylene resin. However, when it consists of a mixture of two or more polypropylene resins, there are rarely two or more endothermic peaks. In that case, a straight line that passes through the vertex of each peak and is parallel to the vertical axis of the graph (orthogonal to the horizontal axis) is drawn, and the length from the peak vertex to the baseline _{BL on} each straight line is measured. The peak apex on the straight line having the longest length is defined as Tm. However, when two or more longest straight lines exist, the peak apex on the highest temperature side is defined as Tm.

  The amount of heat at the high temperature peak in the expanded particles mainly depends on the temperature Ta, the holding time at the temperature, the temperature Tb, and the temperature for the resin particles (surface modified particles) when the expanded particles are produced. Depends on the holding time and the heating rate. The amount of heat at the high temperature peak of the expanded particles tends to increase as the temperature Ta or Tb is lower in the temperature range or as the holding time is longer. Usually, 0.5 to 5 ° C./min is employed as the rate of temperature rise during heating (average rate of temperature rise from the start of heating to the start of temperature holding). By repeating the preliminary experiment in consideration of these points, it is possible to easily know the production conditions of the present expanded particles exhibiting a desired high temperature peak heat quantity.

  The temperature Ta or Tb range described above is an appropriate temperature range when an inorganic physical foaming agent is used as the foaming agent. When an organic physical foaming agent is used in combination, the appropriate temperature range tends to shift to a lower temperature side than the above temperature range depending on the type and amount of use.

The apparent density (g / L) of the foamed particles is calculated by dividing the weight (g) of the foamed particles by the apparent volume (L) of the foamed particles. The apparent volume of the expanded particles is an excluded volume when about 5 g of the expanded particles left at 23 ° C. and atmospheric pressure for 48 hours or more are submerged in water in a measuring cylinder containing 100 cm ³ of water at 23 ° C. From this, the apparent volume (cm ³ ) of the present expanded particles is read and converted into liters. For this measurement, a plurality of the foamed particles are used in such an amount that the weight of the foamed particles is 0.5000 to 10.0000 g and the apparent volume of the foamed particles is 50 to 90 cm ³ .

  The present expanded particles obtained by the method of the present invention are aging under atmospheric pressure, and after increasing the internal pressure of the bubbles as necessary, by heating with steam or hot air, the expanded particles with higher expansion ratio and Is possible.

  The EPP molded body molded using the present foamed particles obtained by the method of the present invention can be heated and cooled, and can be opened, closed, and sealed after increasing the bubble internal pressure as necessary. Manufacture using a batch molding method that fills the mold, supplies saturated steam, heats the expanded particles in the mold, expands them, fuses them together, and then cools them to remove them from the mold Can do. As a molding machine used in the batch molding method, a number of molding machines already exist all over the world, and the pressure resistance is 0.41 MPa (G) or 0.45 MPa (G) although it varies slightly depending on the country. There are many things. Therefore, the pressure of the saturated steam when the expanded particles are expanded and fused is preferably 0.45 MPa (G) or less, and more preferably 0.41 MPa (G) or less.

  Further, the EPP molded body can be manufactured by employing a continuous molding method (for example, molding methods described in JP-A-9-104026, JP-A-9-104027, JP-A-10-180888, etc.). . In the continuous molding method, the foamed particles whose internal pressure is increased as necessary are continuously supplied between belts that move continuously along the top and bottom of the passage, and a saturated steam supply region (heating The foamed particles are expanded and fused when passing through the region), and then cooled by passing through the cooling region, and then the obtained molded product is taken out from the passage and sequentially cut to an appropriate length. Thus, an EPP molded body is manufactured.

  In order to increase the bubble internal pressure of the foamed particles, the foamed particles are put in a sealed container and left for an appropriate time in a state where pressurized air is supplied into the container. It only has to penetrate. The gas supplied under pressure can be used without any problem as long as the main component is an inorganic gas that does not liquefy or solidify under the required pressure, but is further selected from the group consisting of nitrogen, oxygen, air, carbon dioxide, and argon. Alternatively, those mainly composed of two or more inorganic gases are particularly preferably used, and among them, nitrogen and air are preferable in consideration of environmental load and cost.

The internal pressure P (MPa) of the expanded foam particles whose internal pressure is increased is measured by the following operation. In this example, air is used to increase the internal pressure of the expanded particles.
First, the present expanded particles used for molding are placed in a closed container, and pressurized air is supplied into the container (usually, the air pressure in the container is maintained within a range of 0.98 to 9.8 MPa as a gauge pressure). (Ii) The internal pressure of the foamed particles can be increased by allowing the foamed particles to stand for an appropriate time in the supplied state to allow air to permeate the foamed particles. The expanded particles whose internal pressure is sufficiently increased are supplied into a mold of a molding machine.

  The internal pressure of the expanded particles can be obtained by performing the following operation using a part of the expanded particles immediately before in-mold molding (hereinafter referred to as the expanded particle group).

  Within 60 seconds after taking out the present expanded particle group immediately before in-mold molding whose internal pressure has been increased from the pressurized tank, a number of needle holes of a size that allows the expanded foam to pass therethrough but allows air to pass freely are provided. It is housed in a polyethylene bag of about 70 mm × 100 mm and moved to a temperature-controlled room under atmospheric pressure with an air temperature of 23 ° C. and a relative humidity of 50%. Subsequently, the weight is read on a balance in the temperature-controlled room. The weight is measured 120 seconds after the above expanded particle group is taken out from the pressurized tank. The weight at this time is defined as Q (g). The bag is then left in the same greenhouse for 48 hours. Since the pressurized air in the expanded particles permeates the bubble film and escapes to the outside as time passes, the weight of the expanded particles decreases accordingly, and after 48 hours, the weight has reached equilibrium. The weight is stable. After 48 hours, the weight of the bag is measured again, and the weight at this time is defined as U (g). Then, immediately, take out all the foam particles from the bag in the same temperature chamber and read the weight of the bag alone. Let the weight be Z (g). Any of the above weights shall be read up to 0.0001 g. The difference between Q (g) and U (g) is the increased air amount W (g), and the internal pressure P (MPa) of the expanded particles is calculated from the following equation (2). The internal pressure P corresponds to a gauge pressure.

P = (W ÷ M) × R × T ÷ V (2)
However, in the formula (2), M is the molecular weight of air, and here, a constant of 28.8 (g / mol) is adopted. R is a gas constant, and here, a constant of 0.0083 (MPa · L / (K · mol)) is adopted. T means an absolute temperature, and since an atmosphere of 23 ° C. is adopted, it is a constant of 296 (K) here. V means a volume (L) obtained by subtracting the volume of the base resin in the expanded particle group from the apparent volume of the expanded particle group.

The apparent volume (L) of the present expanded particle group is the water in the graduated cylinder containing 100 cm ^{3 of} 23 ° C. water immediately after the entire amount of the present expanded particle group taken out of the bag 48 hours later was stored in the same constant temperature chamber. The volume Y (cm ³ ) of the expanded particle group is calculated from the scale when submerged in water, and is calculated by converting the volume into units of liters (L). The apparent density (g / cm ³ ) of the expanded particle group can be obtained by dividing the weight of the expanded particle group (difference between U (g) and Z (g)) by the volume Y (cm ³ ).
In the above measurement, the foamed particle group weight (difference between U (g) and Z (g)) is 0.5000 to 10.0000 g and the volume Y is 50 to 90 cm ^3. A group of expanded particles is used.

As described above, in the method of the present invention, by specifying the master batch base resin in the master batch, the polypropylene resin of the base resin is sea-like, and the colorant is covered with the thermoplastic polymer inside the base resin. Therefore, it is considered that the colorant does not hinder the surface modification of the resin particles by the organic peroxide in the subsequent step.
Thereby, in the method of this invention, it can heat-mold with low temperature steam, and can obtain the foaming particle excellent in color development.

  In addition, a surface decoration material can be laminated and integrated on at least a part of the surface of the EPP molded body using the expanded particles obtained by the method of the present invention. US Pat. No. 5,928,776, US Pat. No. 6,096,417, US Pat. No. 6,033,770, US Pat. No. 5,474,841, European Patent No. 477476, WO 98/34770 , WO98 / 00287, Japanese Patent No. 3092227 and the like.

  Further, in the present expanded particle EPP molded body obtained by the method of the present invention, the insert material can be combined and integrated such that all or part of the insert material is embedded. Such insert composite type in-mold foam moldings are described in detail in US Pat. No. 6,033,770, US Pat. No. 5,474,841, Japanese Patent Publication No. 59-127714, Japanese Patent No. 3092227, etc. Are listed.

  The use of the EPP molded body using the present expanded particles obtained by the method of the present invention includes automobile materials such as packaging materials, building materials, heat insulating materials, bumper core materials, door pads, pillars, tool boxes, floor I-mats, etc. Is mentioned. Among these, it is preferable to use as an impact absorbing material such as a bumper core material for automobiles and a helmet core material.

  Hereinafter, the present invention will be described in detail with reference to examples and comparative examples.

Table 1 shows the type of polypropylene resin used as the base resin in Examples and Comparative Examples, glass transition temperature, Vicat softening temperature, melting point, tensile modulus, and melt flow rate (shown as “MFR” in the table). It was.
Table 2 shows abbreviations, compositions, and average particle diameters of colorants used in Examples and Comparative Examples.
Table 3 shows the abbreviations of the base resins (indicated in the table as “masterbatch base resin”), the types of masterbatch base resins, and the MFRs of the masterbatch base resins used in the examples and comparative examples.

Examples 1-8, Comparative Examples 1-3
A master batch having the composition shown in Tables 4 to 6 was prepared in advance by a twin screw extruder, and the master batch was formulated so as to have the colorant content in the resin composition shown in Tables 4 to 6, and the resin composition After adding 0.05 parts by weight of zinc borate powder (bubble regulator) to 100 parts by weight of the product and melt-kneading in a twin-screw extruder, it is extruded into a strand form from the extruder, and the strand is immediately brought to 25 ° C. Taken into the adjusted water while rapidly cooling, after sufficiently cooled, withdrawn from the water, cut the strand so that the length / diameter ratio is about 1.0, the average weight per particle is 2mg Resin composition particles for foaming were obtained.

About the obtained foaming resin composition particle | grains, the particle size or length of the island-shaped part which consists of a thermoplastic polymer and a coloring agent was measured as follows.
First, the foaming resin composition particles were placed in liquid nitrogen, the foaming resin composition particles were sliced with a microtome on a plane perpendicular to the extrusion direction, and the sliced surface was photographed with a transmission electron microscope. From the obtained photograph, the maximum particle diameter or the maximum length of the portion where the colorant in the vicinity of the peripheral surface of the foaming resin composition particles is covered with the thermoplastic polymer is not present for one foaming resin composition particle. One place was measured for the purpose, and the average value of 100 foaming resin composition particles was defined as the particle size or length of the island-shaped portion. At that time, the master batch base resin was colored so that the particle size or length of the island-shaped portion could be understood.

  When the sliced surface of the foaming resin composition particles obtained in the examples was observed, the colorant was covered with the thermoplastic polymer, the base resin became sea-like, and the colorant became the thermoplastic polymer. What was covered was dispersed as islands. The length was 0.05 μm or more and 200 μm or less.

  Tables 4 to 6 show the base resin used in the resin composition in the present resin particles, the composition of the master batch, the melt flow rate of the master batch (referred to as MFR in the table), and the content of the colorant in the resin composition. showed that.

  Subsequently, 100 parts by weight of the foaming resin composition particles, 300 parts by weight of ion-exchange water, 0.01 parts by weight of sodium dodecylbenzenesulfonate (surfactant) and 0.3 parts by weight of kaolin (dispersing agent) are added to a 5-liter autoclave. Parts, 0.01 parts by weight of powdered aluminum sulfate (dispersing aid), and then 1.0 part by weight of organic peroxide (bis (4-t-butylcyclohexyl) peroxydicarbonate) and dry ice (Table 4) After adding the amount of foaming agent shown in -6, the temperature was raised at a rate of 2 ° C / min to 5 ° C lower than the foaming temperature in Tables 4-6 while stirring, and held at that temperature for 15 minutes Then, the temperature was increased at a rate of temperature increase of 2 ° C./min and held at the foaming temperature shown in Tables 4 to 15 for 15 minutes, and then the pressure in the autoclave (P: MPa (G)) was (P + 0.49 MPa ( G)) Uni nitrogen was pressed, then to obtain a foamed particles released by opening the one end of the autoclave The autoclave contents into a space under atmospheric pressure. The release was performed while supplying nitrogen into the autoclave so that the pressure in the autoclave during the release of the resin particles from the autoclave was maintained at the pressure in the autoclave immediately before the release.

Reference example 1
The same procedure as in Example 1 was conducted except that no colorant was added. The formulation and results are shown in Table 4.

After the foamed particles obtained in Examples 1 to 8, Comparative Examples 1 to 3 and Reference Example 1 were washed with water and allowed to stand at atmospheric pressure for 24 hours and then cured, The apparent density, the high temperature peak heat amount of the surface layer portion, and the high temperature peak heat amount of the internal foam layer were measured.
The high temperature peak heat quantity and apparent density of the expanded particles, the high temperature peak heat quantity of the surface layer portion, and the high temperature peak heat quantity of the internal foam layer were measured according to the method described above. The measurement results are shown in Tables 4-6.

  Using the obtained expanded particles, an EPP molded body was molded as shown below.

  Using a molding machine capable of withstanding a saturated steam pressure of 0.45 MPa (G), a slight gap is formed in the mold having a molding space of length 400 mm × width 200 mm × thickness 50 mm without completely closing the mold. (Approx. 10 mm) is filled in an open state (60 mm in the direction of thickness 50 mm), and then the mold is completely clamped after exhausting the air in the mold with steam, and the steam with the molding pressure shown in Tables 4 to 6 is used. Heat molding was carried out by feeding into a mold.

  After heat molding, after water cooling until the surface pressure of the EPP molded body in the mold becomes 0.059 MPa (G), the EPP molded body is taken out from the mold, cured at 60 ° C. for 24 hours, and then cooled to room temperature. Thus, an EPP molded body was obtained.

  The base resin, the present resin particle, the surface modified particle, the present expanded particle and the EPP molded product obtained in Examples and Comparative Examples are all substantially non-crosslinked, and the boiling xylene insolubles are all present. 0.

  The molding pressure at the time of heat molding in Tables 4 to 6 in this example was changed repeatedly by changing the molding pressure by 0.01 MPa (G) from 0.15 MPa (G) to 0.45 MPa (G). The lowest molding pressure with a deposition rate of 0.6 was adopted.

The specific measurement of the fusion rate described above was performed as follows.
First, the obtained EPP molded body was cut with a cutter knife in the thickness direction of the molded body by about 10 mm, and then the molded body was broken from the cut portion by hand. Next, the number of expanded particles (n) present on the fracture surface and the number of expanded particles (b) with material destruction were measured, and the ratio (b / n) of (n) and (b) was fused. Rate.

  The apparent density and 50% compressive strength of the obtained EPP molded product were measured, and the secondary foamability, the L value, and the hue were evaluated. The results are shown in Tables 4-6.

  The apparent density of the EPP compacts in Tables 4-6 was measured according to the method described above.

Measurement of 50% compressive strength of the EPP compacts in Tables 4 to 6 was performed as follows.
First, from the obtained EPP molded body, a test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm was cut out (the entire skin was cut). Next, the test piece was subjected to a compression test according to JIS Z 0234-1976 A method at a test piece temperature of 23 ° C. and a load speed of 10 mm / min until the strain reached 55%, and the obtained stress-strain diagram Further, the stress at the time of 50% strain was read, and this was taken as the compressive strength.

The secondary foaming properties shown in Tables 4 to 6 were evaluated by the following methods.
<Evaluation of secondary foamability>
A: There is no gap between the expanded particles on the surface of the EPP molded body, and the corner shape is the same as the mold shape.
○: There are few gaps between the expanded particles on the surface of the EPP molded body, and the corner shape is slightly rounder than the mold shape.
Δ: There are many gaps between the foamed particles on the surface of the EPP molded body, and the corner shape is rounder than the mold shape.

The L values in Tables 4 to 6 were measured by the following method. The L value was measured by setting the measurement mode to Lab using a trade name “X-Rite 948 Spectrocolorimeter” manufactured by X-Rite.
<Evaluation of hue>
From the result of the L value, the hue was evaluated as follows.
A: L value is 0 or more and 20 or less.
○ ... L value is more than 20 and 60 or less.
Δ: The L value exceeds 60 and is 80 or less.
X ... L value exceeds 80 and is 100 or less.

  As shown in Table 4, the molding pressure of Comparative Example 1 is 0.44 MPa (G), whereas the molding pressures of Examples 1 to 3 are 0.41 MPa (G) as in Reference Example 1. Molding was possible with low temperature steam. This is due to the difference in the master batch base resin. In addition, the foamed particles obtained in Examples 2 and 3 are excellent in surface smoothness such as less irregularities on the surface, and in particular, the foamed particles in Example 3 are excellent in secondary foamability and have the same secondary foamability. Then, it was likely that the molding pressure could be made lower than the foamed particles of Examples 1 and 2.

  When Example 3 and Example 4 are compared in Table 4, the molding pressure of Example 3 is 0.41 MPa (G), whereas the molding pressure of Example 4 is 0.43 MPa (G). Yes. This is because 30 nm carbon black was used in Example 3, while 120 nm carbon black was used in Example 4.

  When Example 5 and Comparative Example 2 are compared in Table 5, the molding pressure of Comparative Example 2 is 0.45 MPa (G), whereas the molding pressure of Example 5 is 0.43 MPa (G). In Example 5, molding was possible with low temperature steam. This is due to the difference in the master batch base resin.

In Table 6, when Examples 6-8 are compared with Comparative Example 3, the molding pressure of Comparative Example 3 is 0.43 MPa (G), whereas the molding pressure of Examples 6-8 is 0.41 MPa (G In Examples 6-8, molding was possible with low temperature steam. This is due to the difference in the master batch base resin.
In addition, the foamed particles obtained in Examples 6 and 8 are excellent in surface smoothness such as less irregularities on the surface, and in particular, the foamed particles in Example 8 are excellent in secondary foamability and have the same secondary foamability. If so, the molding pressure was likely to be lower than that of the foamed particles of Examples 6 and 7.

FIG. 1 is a diagram illustrating an example of a first DSC curve chart of the base resin. FIG. 2 is a diagram illustrating an example of a second DSC curve chart of the base resin.

Claims (8)

  A base resin made of a polypropylene resin having a tensile modulus of 1200 MPa or more and a colored mixture made of a thermoplastic polymer and a colorant are melt-kneaded so that the colorant covers the thermoplastic polymer inside the base resin. A resin particle production process for granulating the existing resin composition particles for foaming, a surface modification process for modifying the surface of the resin composition particles for foaming with an organic peroxide in a dispersion medium, and A polypropylene resin comprising: a foaming agent impregnation step for impregnating a resin composition particle with a foaming agent; and a foaming step for foaming the surface-modified foaming resin composition particle impregnated with the foaming agent. A method for producing expanded particles.   A resin particle manufacturing step of granulating foaming resin composition particles by melt-kneading a base resin composed of a polypropylene resin having a tensile modulus of 1200 MPa or more and a colored mixture containing an ethylene polymer and a colorant; A surface modification step of modifying the surface of the foaming resin composition particles with an organic peroxide in a dispersion medium, a foaming agent impregnation step of impregnating the foaming resin composition particles with a foaming agent, and a foaming agent. And a foaming step of foaming the impregnated surface-modified foaming resin composition particles. A method for producing polypropylene-based resin foamed particles.   The method for producing expanded polypropylene resin particles according to claim 2, wherein the ethylene polymer is ethylene-propylene rubber.   A resin particle manufacturing step of granulating foaming resin composition particles by melt-kneading a base resin composed of a polypropylene resin having a tensile modulus of 1200 MPa or more and a colored mixture containing a thermoplastic elastomer and a colorant; A surface modification step of modifying the surface of the foaming resin composition particles with an organic peroxide in a dispersion medium, a foaming agent impregnation step of impregnating the foaming resin composition particles with a foaming agent, and a foaming agent. And a foaming step of foaming the impregnated surface-modified foaming resin composition particles. A method for producing polypropylene-based resin foamed particles.   Resin composition for foaming by melt-kneading a base resin composed of a propylene homopolymer having a tensile modulus of 1200 MPa or more, a colored mixture containing a copolymer of propylene and an α-olefin other than propylene and a colorant A resin particle manufacturing process for granulating product particles, a surface modification process for modifying the surface of the foaming resin composition particles with an organic peroxide in a dispersion medium, and a foaming agent on the foaming resin composition particles A method for producing expanded polypropylene resin particles, comprising: a foaming agent impregnation step for impregnating; and a foaming step for foaming the surface-modified foaming resin composition particles impregnated with the foaming agent.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 5, wherein the colorant is carbon black.   The average particle diameter of carbon black is 5 nm-100 nm, The manufacturing method of the polypropylene resin expanded particle of Claim 6 characterized by the above-mentioned.   The polypropylene system according to claim 6 or 7, wherein the content of carbon black is 0.1 wt% or more and less than 5.0 wt% with respect to the resin composition constituting the foaming resin composition particles. A method for producing resin foam particles.

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