JP7129886B2 - Olefin-based thermoplastic elastomer cross-linked expanded particles and olefin-based thermoplastic elastomer cross-linked expanded particles molded article - Google Patents

Description

TECHNICAL FIELD The present invention relates to an olefinic thermoplastic elastomer crosslinked expanded particle and an olefinic thermoplastic elastomer crosslinked expanded particle molded article.

A thermoplastic olefinic elastomer (hereinafter also referred to as “TPO”) is a material that is flexible, has excellent resilience, and has a small compression set. By foaming TPO, weight reduction can be achieved while maintaining these properties. Foamed TPOs are produced by molding methods such as extrusion foaming, press foaming and injection foaming.

The in-mold molding method using expanded particles has a higher degree of freedom in shape than other molding methods, and is a molding method capable of producing a foam molded article having a closed-cell structure. However, conventional TPO foamed beads are inferior in moldability in molds to foamed beads based on general-purpose resins. As a TPO expanded particle having excellent in-mold moldability while maintaining the properties of TPO such as flexibility, for example, Patent Document 1 discloses a multi-block copolymer of a polyethylene block and an ethylene/α-olefin copolymer block. Crosslinked expanded particles obtained by crosslinking and expanding the particles of are disclosed.
When the expanded TPO particles contained a coloring agent, the in-mold moldability tended to deteriorate. In order to improve in-mold moldability, for example, Patent Document 2 discloses TPO expanded particles containing a coloring agent and having a specific average surface layer thickness.

JP 2016-216527 A JP 2018-76464 A

The technique disclosed in Patent Document 2 has made it possible to improve the in-mold moldability of colored TPO foamed particles. However, the in-mold molded product of colored TPO expanded particles was inferior in color uniformity to the in-mold molded product of colored general-purpose expanded particles. In addition, although the in-mold moldability is improved compared to the conventional ones, the moldable range during in-mold molding is narrower than that of foamed beads using general-purpose resin as a base material.

Therefore, the present invention has been made to solve the above-mentioned problems, and it is possible to obtain a crosslinked expanded particle molded product that has excellent in-mold moldability and less color unevenness even with crosslinked expanded particles containing a coloring agent. An object of the present invention is to provide crosslinked expanded particles of an olefinic thermoplastic elastomer.

As a result of earnest research, the present inventors have found that the above problems can be solved by adopting the configuration shown below, and have completed the present invention.
That is, the present invention is as follows.
[1] A crosslinked foamed particle containing a colorant and containing an olefinic thermoplastic elastomer as a base material,
In the DSC curve obtained by heating from 23° C. to 200° C. at a heating rate of 10° C./min, the crosslinked foamed particles have a melting peak (specific peak) specific to the olefinic thermoplastic elastomer and a temperature higher than the specific peak. Crosslinked expanded particles of an olefinic thermoplastic elastomer having a crystal structure in which one or more melting peaks (high-temperature peaks) appear on one side, and wherein the heat of fusion of the high-temperature peaks is 5 J/g or more.
[2] The crosslinked and expanded particles of the olefinic thermoplastic elastomer according to [1], wherein the hot xylene-insoluble matter of the crosslinked and expanded particles is 10 to 70% by weight.
[3] The crosslinked expanded thermoplastic elastomer particles according to [1] or [2], wherein the ratio of the heat of fusion at the high-temperature peak to the total heat of fusion in the DSC curve is 0.1 to 0.6.
[4] The crosslinked and expanded particles of an olefinic thermoplastic elastomer according to any one of [1] to [3], wherein the crosslinked and expanded particles have an apparent density of 30 to 300 kg/m ³ .
[5] The crosslinked and expanded particles of an olefinic thermoplastic elastomer according to any one of [1] to [4], wherein the crosslinked and expanded particles have an average cell diameter of 20 μm or more and less than 50 μm.
[6] The crosslinked and expanded particles of an olefinic thermoplastic elastomer according to any one of [1] to [5], wherein the crosslinked and expanded particles have a coefficient of variation of cell diameter of 30% or less.
[7] The olefinic thermoplastic according to any one of [1] to [6], wherein the content of the colorant is 0.05 parts by weight or more with respect to 100 parts by weight of the olefinic thermoplastic elastomer. Elastomer crosslinked foam particles.
[8] Any one of the above [1] to [7], wherein the olefinic thermoplastic elastomer is a block copolymer having a polyethylene block as a hard segment and an ethylene/α-olefin copolymer block as a soft segment. The olefinic thermoplastic elastomer crosslinked expanded particles according to 1.
[9] A crosslinked expanded thermoplastic elastomer particle molded product obtained by in-mold molding the crosslinked expanded thermoplastic elastomer particles according to any one of [1] to [8] above.
[10] The product (a)×(b) of the tensile strength (a) [MPa] and the tensile elongation (b) [%] of the crosslinked expanded particle molded product is 100 or more, according to the above [9]. A molded article of crosslinked expanded particles of an olefinic thermoplastic elastomer.

According to the present invention, there is provided a crosslinked expanded particle of an olefinic thermoplastic elastomer, which is excellent in moldability in a mold even when the crosslinked expanded particle contains a coloring agent, and which gives a crosslinked expanded particle molded article with little color unevenness. can be done.

4 is a DSC curve of the first heating of the crosslinked expanded particles of the olefinic thermoplastic elastomer in one embodiment of the present invention.

<Crosslinked foamed particles of olefinic thermoplastic elastomer>
The crosslinked and expanded particles of an olefinic thermoplastic elastomer of the present invention are crosslinked and expanded particles containing a thermoplastic olefinic elastomer as a base material and containing a coloring agent. In the DSC curve obtained by heating from to 200 ° C., a melting peak (specific peak) unique to the olefinic thermoplastic elastomer and one or more melting peaks (high temperature peaks) appearing on the higher temperature side than the specific peak Crystal structure and the heat of fusion at the high temperature peak is 5 J/g or more.
According to such crosslinked and expanded particles, even if the crosslinked and expanded particles contain a coloring agent, a molded product having excellent in-mold moldability and less color unevenness can be obtained.

Hereinafter, "crosslinked expanded particles of thermoplastic elastomer" may be referred to as "crosslinked expanded particles", and "molded article of crosslinked expanded thermoplastic elastomer particles" may be referred to as "expanded article" or "molded article".

Although the detailed mechanism of the effects obtained by the present invention is not clear, it is believed that the crosslinked expanded particles of the present invention have a specific crystal structure.

Conventionally, when crosslinked foamed particles with a low proportion of hot xylene insolubles are molded in a mold, it is possible to strongly fuse the crosslinked foamed particles to each other. It was difficult to produce a good molded product because sink marks were likely to occur in the molded product. On the other hand, when crosslinked foamed particles with a high proportion of hot xylene insolubles are molded in a mold, it is difficult to strongly fuse the crosslinked foamed particles to each other. If it was excessively applied, sink marks were formed in the molded article after it was released from the mold.
As described above, the moldable range of the crosslinked expanded particles using TPO as a base material was narrower than that of the expanded particles using a general-purpose resin as a base material. Furthermore, when the crosslinked foamed particles contain a coloring agent, these phenomena become conspicuous, narrowing the moldable range.
The term "sink marks" refers to significant deformation or shrinkage of the molded body that does not restore the shape of the molded body even when the pressure inside the cells of the molded body returns to near atmospheric pressure. When this occurs, it becomes impossible to obtain a molded article having a desired shape.
The crosslinked foamed particles of the present invention have thick lamellar high-potential crystals that appear as a high-temperature peak on the high-temperature side of the characteristic peak of TPO in the DSC curve, so the proportion of hot xylene insolubles is lower than conventional. Even in this case, no sink mark occurs in the molded article after it is released from the mold. Further, even when the proportion of hot xylene-insoluble matter is the same as in the prior art, even if the temperature of the heating medium is increased, the molded body does not suffer from sink marks after the molded body is released from the mold. Therefore, the crosslinked foamed particles of the present invention can provide a good foamed particle molded article with excellent fusion bondability over a wide range of hot xylene-insoluble matter under a wide range of molding heating conditions. That is, the crosslinked foamed particles of the present invention are excellent in moldability in a mold.

Due to its viscoelastic properties, TPO is more difficult to foam than general-purpose resins, and if TPO contains a colorant, it becomes even more difficult to foam TPO uniformly. Therefore, it is considered that the size of the cells in the expanded beads tends to vary, and the expansion ratio between the expanded beads also tends to vary. Therefore, when such foamed beads are molded in a mold, thin portions and thick portions of the bubble film are mixed in the molded product. The portion where the cell membrane is thin has a relatively light color, and the portion where the cell membrane is thick has a relatively dark color, resulting in an expanded bead molded product with large color unevenness.
Since the crosslinked and expanded particles of the present invention have thick lamellar crystals with high potential, even if the TPO contains a coloring agent, the crosslinked and expanded particles have a small variation in cell diameter and a small variation in expansion ratio. It is considered to be Since these high-potential crystals are evenly formed in the polymer crosslinked particles by the crystallization process described later, these crystals act as cell nuclei during foaming, and also moderately in the cell membrane during cell growth. It is believed that the orientation provides crosslinked expanded particles having a good cell structure as described above. By molding the crosslinked foamed particles in a mold, it is possible to obtain a molded article with little color unevenness.
Furthermore, in crosslinked foamed particles containing a colorant, if the cell diameter is reduced, the cell membrane is likely to be broken during foaming or secondary foaming in in-mold molding, resulting in open cells, resulting in reduced in-mold moldability. tended to. In contrast, the crosslinked foamed particles of the present invention have a specific crystal structure exhibiting a high-temperature peak, so that the cell membrane is less likely to break, and a good cell structure is maintained even during in-mold molding. Therefore, it is considered that the air bubbles can be made finer without impairing the in-mold moldability, and as a result, it becomes possible to obtain a molded product with excellent color development and less color unevenness.

Next, the characteristics of the crystal structure of the crosslinked expanded particles containing the colorant of the present invention will be described.
FIG. 1 shows a DSC (Differential Scanning Calorimetry) curve of the first heating of crosslinked foamed particles in one embodiment of the present invention. FIG. 1 is an example of a DSC curve obtained by heating 1 to 3 mg of crosslinked expanded particles from 23° C. to 200° C. at a heating rate of 10° C./min. The vertical axis of the graph shows the difference in the input heat energy per unit time applied to the test piece and the reference substance so that the temperatures of both are equal. The peak is the exothermic peak, the horizontal axis indicates the temperature, the left side is the low temperature side, and the right side is the high temperature side.
In FIG. 1, the DSC curve has a melting peak P a with an apex temperature PT _ma on the low temperature side and _{a melting peak P b with} an apex temperature PT _mb on the high temperature side. In the present invention, the melting peak Pa on the low temperature side is referred to as an intrinsic peak, and the melting peak _Pb on the high temperature side is referred to as _a high temperature peak. Hereinafter, these peaks may be referred to as a unique peak P _a and a high-temperature peak P _b , respectively.
The intrinsic peak P _a is a melting peak derived from the crystal structure originally possessed by TPO constituting the crosslinked expanded particles, and the high-temperature peak _Pb is derived from the crystal structure generated due to the manufacturing process of the crosslinked expanded particles. melting peak.

The heat of fusion of the intrinsic peak _Pa , the heat of fusion of the high temperature peak Pb, and the total heat of fusion in the DSC curve are measured as follows for the DSC curve shown in _FIG .
Let β be the point on the DSC curve corresponding to the melting end temperature. Also, a point on the DSC curve where the tangent line of the baseline of the DSC curve on the higher temperature side than the melting end temperature (β) and the DSC curve on the lower temperature side than the melting end temperature (β) intersects be α. A straight line parallel to the vertical axis of the graph is drawn from the point y on the DSC curve corresponding to the valley between the characteristic peak P _a and the high-temperature peak P _b , and a straight line (α-β) connecting the points α and β Let δ be the point of intersection.

The area (A) of the intrinsic peak P _a is the heat of fusion of the intrinsic peak P _a , and is surrounded by the DSC curve showing the intrinsic peak P _a , the line segment (α-δ), and the line segment (y-δ). It is calculated as the area of the part where
The area ( _B ) of the high-temperature peak _Pb is the heat of fusion of the high-temperature peak Pb, and is surrounded by the DSC curve showing the high-temperature peak _Pb , the line segment (δ-β), and the line segment (y-δ). It is calculated as the area of the part where
The total heat of fusion in the DSC curve is the peak area surrounded by the straight line (α-β) and the DSC curve in the section between points α and β, and the area ( _A ) of the characteristic peak Pa and the high temperature peak _Pb is the sum of the areas (B) of [(A)+(B)].

The crosslinked and expanded particles of the present invention have a crystal structure in which a characteristic peak P _a and a high temperature peak P _b appear in a DSC curve obtained by heating from 23° C. to 200° C. at a heating rate of 10° C./min, and It has a crystal structure in which the heat of fusion ( _B ) of the high temperature peak Pb is 5 J/g or more.
The crosslinked foamed particles of the present invention and the method for producing the same will be described in detail below.

[Polymer particles]
The crosslinked expanded particles of the present invention are obtained by crosslinking TPO contained in polymer particles and expanding the polymer crosslinked particles.

(TPO)
The TPO includes (i) a mixture of a propylene resin as a hard segment and an ethylene rubber as a soft segment, and (ii) a block of a polyethylene block as a hard segment and an ethylene/α-olefin copolymer block as a soft segment. A copolymer etc. are mentioned.

(i) In a mixture having a propylene-based resin as a hard segment and an ethylene-based rubber as a soft segment, the propylene-based resin includes, for example, a propylene homopolymer, a mixture of propylene and ethylene, or an α-olefin having 4 to 8 carbon atoms. A copolymer etc. are mentioned. On the other hand, examples of ethylene rubber include copolymers of ethylene and α-olefins having 3 to 8 carbon atoms, 5-vinyl-2-norbornene, 5-ethylidene-2-norbornene, 5-methylene-2- Examples thereof include copolymers with non-conjugated dienes such as norbornene and dicyclopentadiene.

(ii) A block copolymer having a polyethylene block as a hard segment and an ethylene/α-olefin copolymer block as a soft segment. Copolymers with α-olefins are mentioned. On the other hand, examples of ethylene/α-olefin copolymer blocks include blocks of copolymers of ethylene and α-olefins having 3 to 20 carbon atoms.
Examples of α-olefins having 3 to 20 carbon atoms to be copolymerized with ethylene include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 3-methyl-1-butene, 4-methyl-1-pentene and the like. Among them, propylene, 1-butene, 1-hexene and 1-octene are preferred, and 1-octene is particularly preferred.
The ratio of the ethylene component contained in the polyethylene block is preferably 95% by weight or more, more preferably 98% by weight or more, relative to the weight of the polyethylene block. On the other hand, the ratio of the α-olefin component contained in the ethylene/α-olefin copolymer block is preferably 5% by weight or more, more preferably 10% by weight, based on the weight of the ethylene/α-olefin copolymer block. above, more preferably 15% by weight or more.
Here, the ratio of the ethylene component contained in the polyethylene block and the ratio of the α-olefin component contained in the ethylene/α-olefin copolymer block are obtained from differential scanning calorimetry (DSC) or nuclear magnetic resonance (NMR). Can be calculated based on data.

Commercially available products may be used as the TPO, such as the trade name "Thermoran" (manufactured by Mitsubishi Chemical Co., Ltd.), the trade name "Milastomer" (manufactured by Mitsui Chemicals, Inc.), the trade name "Sumitomo TPE" (manufactured by Sumitomo Chemical Co., Ltd.), Trade name "INFUSE (registered trademark)" (manufactured by Dow Chemical Co.), trade name "Affinity" (manufactured by Dow Chemical Co.), trade name "Prime TPO" (manufactured by Prime Polymer Co.) and the like. .

As the TPO, from the viewpoint of improving recoverability at high temperatures, the above-mentioned (ii) block copolymer having a polyethylene block as a hard segment and an ethylene/α-olefin copolymer block as a soft segment is preferably used. . The hard blocks and soft blocks are preferably arranged linearly.
The block copolymer may have a diblock structure, a triblock structure, or a multiblock structure, but a multiblock structure is particularly preferred.

(ii) As a multi-block copolymer (hereinafter referred to as "multi-block copolymer") having a polyethylene block as a hard segment and an ethylene / α-olefin copolymer block as a soft segment, for example, JP-A-2013- Examples thereof include those described in JP-A-64137. Examples of commercially available multi-block copolymers include "INFUSE (registered trademark)" manufactured by Dow Chemical Company.

<Density>
The density of TPO is preferably 800-1000 g/L, more preferably 850-920 g/L, even more preferably 870-900 g/L.
The density of TPO is a value measured according to ASTM D792-13.

<Type A durometer hardness>
The type A durometer hardness (generally sometimes referred to as "Shore A hardness") of TPO is preferably 65-90, more preferably 75-90, and even more preferably 76-88.
When the type A durometer hardness of the TPO is 65 or more, the dimensional recovery property of the expanded bead molded article obtained by in-mold molding of the crosslinked expanded bead is more difficult to be impaired. When the type A durometer hardness of the TPO is 90 or less, it becomes easier to obtain an expanded bead molded article with excellent flexibility.
Type A durometer hardness of TPO means durometer hardness measured using a Type A durometer according to ASTM D2240-05. When the durometer hardness is measured, the maximum indicated value of the durometer is read within one second after the durometer is pressed against the surface of the sample to be measured.

<Melt flow rate (MFR)>
The melt flow rate (MFR) of TPO is preferably 2 to 10 g/10 minutes, more preferably 3 to 8 g/10 minutes, and still more preferably 4 to 7 g/10 minutes under conditions of 190°C and a load of 2.16 kg. is.
When the melt flow rate of TPO is 2 g/10 minutes or more, the crosslinked foamed particles are more easily fused to each other during in-mold molding. When the melt flow rate of TPO is 10 g/10 minutes or less, the molded article obtained by in-mold molding of the crosslinked expanded particles is excellent in recoverability.
The melt flow rate of TPO is a value measured under conditions of a temperature of 190° C. and a load of 2.16 kg in accordance with JIS K7210-1:2014.

<Flexural modulus>
The flexural modulus of TPO is preferably 10-100 MPa, more preferably 15-50 MPa, still more preferably 20-30 MPa.
The flexural modulus of TPO is a value measured according to JIS K7171:2008.

<Melting point>
The melting point of TPO is preferably 80 to 160°C, more preferably 90 to 150°C, still more preferably 100 to 130°C, particularly preferably 110 to 125°C.
The melting point of TPO is a value measured according to JIS K7121-1987.

(Other polymers)
If necessary, the polymer particles may contain a polymer other than TPO (hereinafter referred to as "other polymer") as long as the object of the present invention is not impaired.
Other polymers include, for example, polyolefin-based resins (e.g., polyethylene-based resins, polypropylene-based resins, polybutene-based resins), thermoplastic resins such as polystyrene-based resins, thermoplastic elastomers other than TPO (e.g., polybutadiene-based elastomers, styrene-butadiene, styrene-isoprene, styrene-butadiene-styrene, styrene-isoprene-styrene block copolymers, and hydrogenated products thereof).
The content of the other polymer is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and still more preferably 5 parts by weight or less based on 100 parts by weight of TPO constituting the polymer particles. Furthermore, it is particularly preferred that the base polymer of the polymer particles consists of only TPO.

(coloring agent)
The TPO constituting the polymer particles contains a coloring agent.
As the colorant, inorganic or organic pigments and dyes can be used.
Examples of organic pigments include monoazo, condensed azo, anthraquinone, isoindolinone, heterocyclic, perinone, quinacridone, perylene, thioindigo, dioxazine, phthalocyanine, nitroso, and phthalocyanine pigments. , organic fluorescent pigments, and the like.
Examples of inorganic pigments include titanium oxide, carbon black, titanium yellow, iron oxide, ultramarine blue, cobalt blue, baked pigments, metallic pigments, mica, pearl pigments, zinc oxide, precipitated silica, cadmium red, and the like. .
Examples of dyes include organic dyes such as anthraquinone-based, heterocyclic-based and perinone-based dyes, basic dyes, acid dyes, and mordant dyes.
In addition, a coloring agent may be used individually by 1 type, and may be used in mixture of 2 or more types.

The colorant can be incorporated into the TPO by supplying it to an extruder and kneading it together with the TPO in the process of obtaining the polymer particles.
From the viewpoint of obtaining a molded article with less color unevenness, the content of the colorant is preferably 0.05 parts by weight or more, more preferably 0.05 part by weight, based on 100 parts by weight of TPO constituting the polymer particles. It is 1 part by weight or more, more preferably 0.2 parts by weight or more. On the other hand, the upper limit is preferably 7 parts by weight, more preferably 5 parts by weight, still more preferably 3 parts by weight.

(Air bubble control agent)
It is preferable that the TPO constituting the polymer particles contain a cell control agent.
Examples of cell control agents include inorganic powders such as talc, mica, zinc borate, calcium carbonate, silica, titanium oxide, gypsum, zeolite, borax, aluminum hydroxide, and carbon. Nucleating agents, phenol-based nucleating agents, amine-based nucleating agents, and organic powders such as polyfluoroethylene resin powders can be used.
In addition, a cell adjustment agent may be used individually by 1 type, and may be used in mixture of 2 or more types.

The cell control agent can be incorporated into the TPO by supplying the cell control agent together with the TPO to an extruder and kneading it in the process of obtaining the polymer particles.
From the viewpoint of obtaining a molded article with better fusion bondability and less color unevenness, the content of the cell control agent is preferably 0.01 to 0.01 parts per 100 parts by weight of TPO constituting the polymer particles. 5 parts by weight, more preferably 0.05 to 3 parts by weight, more preferably 0.05 to 1 part by weight.

(Other additives)
If necessary, other additives may be added to the TPO constituting the polymer particles as long as the objects of the present invention are not impaired.
Other additives include, for example, slip agents, flame retardants, flame retardant aids, cell nucleating agents, plasticizers, antistatic agents, antioxidants, ultraviolet absorbers, light stabilizers, conductive fillers, antibacterial agents, etc. is mentioned.

[Crosslinked expanded particles]
The crosslinked expanded particles of the present invention are obtained by crosslinking the TPO contained in the polymer particles described above and expanding the polymer crosslinked particles.

<Crystal structure>
As described with reference to FIG. 1, the crosslinked expanded particles of the present invention have a melting peak (specific peak P _a ) specific to TPO and one or more melting peaks on the higher temperature side than the specific peak in the DSC curve described above. (high-temperature peak P _b ), and the heat of fusion (B) of the high-temperature peak P _b is 5 J/g or more, preferably 7 J/g or more, more preferably 10 J/g or more. It is a certain crosslinked expanded particle.
If the heat of fusion ( _B ) of the high-temperature peak Pb is less than 5 J/g, even if the crosslinked expanded particles have a crystal structure in which the high-temperature peak appears, the uneven color of the resulting molded product is not improved. Also, it is not possible to widen the moldable range.

The crosslinked expanded particles of the present invention have a total heat of fusion [(A) + (B)] in the DSC curve described above, preferably 40 to 60 J / g, more preferably 45 to 58 J / g, still more preferably 45 to It has a crystal structure of 55 J/g.
When the above-mentioned total heat of fusion [(A) + (B)] is 40 J/g or more, an appropriate amount of hard segments is present in the TPO, so the bubbles are less likely to break during in-mold molding. It is possible to obtain an expanded bead molded article having a
On the other hand, when the above-described total heat of fusion [(A)+(B)] is 60 J/g or less, the crosslinked expanded particles have flexibility.
The difference between the melting peak temperature of the high temperature peak and the melting peak temperature of the characteristic peak is preferably 1 to 10°C, more preferably 3 to 9°C, still more preferably 5 to 8°C.

The crosslinked foamed particles of the present invention have a ratio of the heat of fusion (B) of the high temperature peak to the total heat of fusion [(A) + (B)] in the DSC curve described above [(B) / [(A) + (B) ]] preferably has a crystal structure of 0.1 to 0.6, more preferably 0.2 to 0.5, still more preferably 0.2 to 0.4.
When the above-mentioned ratio [(B)/[(A)+(B)]] is 0.1 or more, it is possible to make it difficult for sink marks to occur in the obtained expanded bead molded article.
On the other hand, when the above ratio [(B)/[(A)+(B)]] is 0.6 or less, the surface property is good and the fusion between the expanded particles is excellent even at a low molding pressure. It is easy to obtain an expanded bead molded product.

The total heat of fusion of the crosslinked expanded particles is determined by the type of thermoplastic olefinic elastomer (TPO) used as a raw material, and the ratio of the heat of fusion at the high-temperature peak to the total heat of fusion [(B)/[(A) + ( B)]] is particularly the condition of step E (crystallization step) among step A (step of obtaining base polymer particles) to step F (foaming step) included in the method for producing crosslinked expanded particles described later. can be controlled by adjusting

<Average particle size>
The crosslinked and expanded particles of the present invention preferably have an average particle size of 1 to 10 mm, more preferably 2 to 8 mm, and still more preferably 3 to 6 mm.
When the average particle size of the crosslinked and expanded particles is within the above range, the crosslinked and expanded particles can be easily produced, and when the crosslinked and expanded particles are molded in the mold, the crosslinked and expanded particles can be easily filled in the mold. .
For example, the average particle size of the cross-linked expanded particles can be controlled by adjusting the particle size of the polymer particles, and the foaming conditions such as the amount of the foaming agent, the foaming temperature and the foaming pressure.

<Apparent density>
The apparent density of the crosslinked expanded particles of the present invention is preferably 30-300 kg/m ³ , more preferably 50-300 kg/m ³ , still more preferably 100-300 kg/m ³ .
By setting the apparent density of the crosslinked expanded particles within the above range, the crosslinked expanded particles can be molded in a mold to obtain an expanded particle molded article having particularly excellent lightness, flexibility and resilience.

The average particle size and apparent density of the crosslinked expanded particles are measured as follows. First, the crosslinked foamed particles are left for two days under the conditions of 50% relative humidity, 23° C. temperature, and 1 atm. Next, a graduated cylinder containing water at a temperature of 23° C. is prepared, and an arbitrary amount of the crosslinked foamed particles (weight W1 of the crosslinked foamed particles) left for two days is placed in the water in the graduated cylinder with a tool such as a wire mesh. Use and submerge. Then, considering the volume of tools such as wire mesh, the volume V1 [L] of the crosslinked foamed particle group read from the water level rise is measured. By dividing this volume V1 by the number (N) of the crosslinked foamed particles in the graduated cylinder (V1/N), the average volume per crosslinked foamed particle is calculated. Then, the diameter of a virtual true sphere having the same volume as the obtained average volume is defined as the average particle diameter [mm] of the crosslinked expanded particles. In addition, the weight W1 (g) of the group of crosslinked foamed particles placed in a measuring cylinder is divided by the volume V1 [L] (W1/V1), and the units are converted to obtain the apparent density [kg/m ³ ] of the crosslinked foamed particles. can be asked for.

<Average value of bubble diameter>
The average cell diameter of the crosslinked expanded particles of the present invention is preferably 20 μm or more and less than 50 μm, more preferably 30 μm or more and less than 50 μm, and still more preferably 35 μm or more and less than 50 μm.
When the average cell diameter of the cross-linked expanded particles is within the above range, the cells are less likely to break during molding in the mold, and the cross-linked expanded particles can be more strongly fused to each other, resulting in favorable expanded particles. A molded article is obtained, and an expanded bead molded article with more excellent color developability and less color unevenness is obtained.
The average value of cell diameters of the crosslinked foamed particles is obtained as follows. The crosslinked and expanded particles are divided into approximately two pieces so as to pass through the central portion of the crosslinked and expanded particles, and a photograph of the cut surface is taken using a scanning electron microscope or the like. In the obtained cross-sectional photograph, 50 or more cells on the cut surface of the crosslinked foamed particles are randomly selected. The cross-sectional area of each bubble is measured using image analysis software or the like, and the diameter of an imaginary perfect circle having the same area as that area is taken as the bubble diameter of each bubble. This operation is performed for at least 10 crosslinked and expanded particles, and the arithmetic average value of the cell diameters of the individual cells is taken as the average value of the cell diameters of the crosslinked and expanded particles (average cell diameter).
For example, the average cell diameter of the crosslinked expanded particles can be controlled by conventionally known methods such as adjusting the amount of foaming agent, foaming conditions, and the blending amount of the cell adjusting agent.

<Variation coefficient of bubble diameter>
The variation coefficient of cell diameter of the crosslinked foamed particles of the present invention is preferably 30% or less.
When the coefficient of variation of the cell diameter of the crosslinked expanded beads is small, such expanded beads are more excellent in moldability in a mold, and an expanded bead molded product with less color unevenness can be obtained.
The variation coefficient of the cell diameter of the crosslinked and expanded particles is obtained by dividing the standard deviation of the cell diameter of each cell of the crosslinked and expanded particles by the average cell diameter of the cells of the crosslinked and expanded particles. The value of standard deviation is the value given by the square root of the unbiased variance.
Since the crosslinked foamed particles have a crystal structure exhibiting a high temperature peak, the variation coefficient of the cell diameter tends to be small. In the crystallization process, high-potential TPO crystals are evenly formed in the polymer particles, and in the foaming process, these high-potential crystals act as cell nuclei, and are oriented appropriately during foaming, resulting in cross-linking and foaming. It is considered that the value of the coefficient of variation of the bubble diameter of the particles becomes smaller.

<Hot xylene-insoluble matter>
The hot xylene-insoluble matter (xylene-insoluble matter obtained by the hot xylene extraction method) of the crosslinked foamed particles of the present invention is preferably 10 to 70% by weight, more preferably 10 to 50% by weight, still more preferably 10 to 40% by weight. .
Incidentally, the "hot xylene-insoluble matter" is one index indicating the crosslinked state of the crosslinked expanded particles, and can be measured by the following method.

About 1 g of a sample of the crosslinked foamed particles is weighed (the weight of the weighed sample is W1b) and heated under reflux in 100 mL of xylene for 6 hours. Then, the residue trapped on the wire mesh is dried in a vacuum dryer at 80° C. for 8 hours.
The dried material (hot xylene-insoluble matter) obtained at this time is weighed [the weight of the dried matter thus weighed is defined as W2b], and the hot xylene-insoluble matter of the crosslinked expanded particles can be obtained by the following formula (1).
Hot xylene insoluble matter (% by weight) = (W2b/W1b) x 100 (1)
The hot xylene-insoluble portion of the crosslinked and expanded particles is determined in the method for producing the crosslinked and expanded particles described later, in addition to the amount of the crosslinking agent added, the stirring conditions and temperature rise when crosslinking the TPO contained in the polymer particles in a closed container. It can also be adjusted according to conditions and the like.

As described above, the crosslinked expanded particles of the present invention have a crystal structure in which the inherent peak P _a and the high temperature peak P _b appear in the DSC curve described above, and the heat of fusion (B) of the high temperature peak P _b is 5 J/g or more. Therefore, it is possible to produce an expanded particle molded product in which the crosslinked expanded particles are strongly fused together without causing sink marks after in-mold molding.

In addition, by attaching an anionic surfactant to the surface of the crosslinked and expanded particles of the present invention, it is possible to improve the fusion between the crosslinked and expanded particles during in-mold molding.
Examples of anionic surfactants include carboxylic acid type, sulfonic acid type, sulfate ester type, phosphate ester type, and polymer type. Among anionic surfactants, alkanesulfonates, polyacrylates, polyacrylic acid sulfonic acid copolymer salts, etc., can be obtained, since crosslinked foamed particles that are particularly effective in improving the adhesion during in-mold molding can be obtained. is preferably attached to the surface of the crosslinked foamed particles. Moreover, anionic surfactant is used individually or in mixture of 2 or more types.

The adhesion amount of the anionic surfactant per unit surface area of the crosslinked foamed particles is preferably 2 mg/m ² or more, more preferably 5 mg/m ² or more, and even more preferably 20 mg/m ² or more. On the other hand, the upper limit of the adhesion amount is approximately 100 mg/m ² or less.
The coating amount of the anionic surfactant on the crosslinked foamed particles is calculated based on the value measured using a TOC (Total Organic Carbon) measuring device. TOC can be measured by the TC-IC method using a total organic carbon meter TOC-V _CSH manufactured by Shimadzu Corporation.

[Method for producing crosslinked expanded particles]
In the method for producing crosslinked and expanded particles of the present invention, the DSC curve obtained by heating the crosslinked and expanded particles from 23° C. to 200° C. at a heating rate of 10° C./min has a characteristic peak _{Pa and a high temperature peak P b .} There is no particular limitation as long as the manufacturing method can be controlled to have a crystal structure that appears and the heat of fusion ( _B ) of the high-temperature peak Pb is 5 J/g or more.
From the viewpoint of easily producing the crosslinked expanded particles having the crystal structure specified in the present invention, the method for producing the crosslinked expanded particles of the present invention preferably includes the following steps A to F.

1. Step A (Step of obtaining polymer particles)
Polymer particles containing TPO are produced by a known granulation method.
A method for obtaining polymer particles is not particularly limited. For example, TPO, a coloring agent, and optionally additives such as a cell control agent are supplied to an extruder to melt the TPO and knead them to obtain a melt-kneaded product. Next, the melt-kneaded product is extruded into strands through small holes of a die attached to an extruder, and after the strands are water-cooled, they are cut into an arbitrary size by a pelletizer to obtain polymer particles. A strand cut method is mentioned.

In addition to the strand cut method, polymer particles can be obtained by a hot cut method in which the melt-kneaded product is extruded into a gas phase and directly cut, or an underwater cut method in which the melt-kneaded product is extruded into water and directly cut. can.

The average weight per polymer particle is preferably 0.1 to 10 mg, more preferably 0.5 to 8 mg, still more preferably 1 to 6 mg.
The "average weight per polymer particle" means a value obtained by dividing the total weight (mg) of 100 randomly selected polymer particles by 100.

2. Process B (dispersion process)
In a closed container, the polymer particles and the cross-linking agent are dispersed in the dispersion medium.
The timing of dispersing the cross-linking agent in the dispersion medium is not particularly limited, and the polymer particles may be dispersed in the dispersion medium before dispersing the cross-linking agent, or after the cross-linking agent is dispersed in the dispersion medium, The polymer particles may be dispersed, or the polymer particles and the cross-linking agent may be dispersed in the dispersion medium at substantially the same timing.

(closed container)
The sealed container is not particularly limited as long as it is a container that can be sealed, but one that can withstand heating and pressure increases is preferably used. Examples of closed containers include autoclaves and the like.

(dispersion medium)
The dispersion medium is not particularly limited as long as it does not dissolve the polymer particles.
Examples of the dispersion medium include water, ethylene glycol, glycerin, methanol, ethanol, etc. Among them, water is preferably used.

(crosslinking agent)
A cross-linking agent is used to cross-link the TPO contained in the polymer particles.
The cross-linking agent is not particularly limited as long as it cross-links TPO. As the cross-linking agent, known organic peroxides can be used. Perbutyl compounds such as 3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, di-tert-butyl peroxide, tert-hexyl peroxybenzoate, etc. Examples include perhexyl compounds and perocta compounds such as 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate.
Among these, permyl-based compounds and perbutyl-based compounds are preferable, percumyl-based compounds are more preferable, and dicumyl peroxide is particularly preferable.
In addition, a crosslinking agent may be used individually by 1 type, and may be used in mixture of 2 or more types.

When TPO having a melting point of Tm is used as a raw material, it is preferable to use a cross-linking agent having a 10-hour half-life temperature in the range of Tm-45°C to Tm+20°C, more preferably in the range of Tm-40°C to Tm+10°C. It is more preferable to use those having
By using the cross-linking agent having the above 10-hour half-life temperature, it becomes easy to adjust the hot xylene-insoluble matter of the cross-linked foamed particles to a desired ratio.

The amount of the cross-linking agent added to the dispersion medium is preferably 0.2 to 5.0 parts by weight, more preferably 0.3 to 3.0 parts by weight, based on 100 parts by weight of the polymer particles, More preferably, it is 0.4 to 0.8 parts by weight. When the amount of the cross-linking agent is within the above range, the efficiency of cross-linking is improved, and cross-linked expanded particles having an appropriate content insoluble in hot xylene (gel fraction) are easily obtained.

(dispersant)
A dispersant may be added to the dispersion medium in order to prevent mutual adhesion of the polymer particles.
Dispersants include, for example, polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose, aluminum oxide, zinc oxide, kaolin, mica, magnesium phosphate, and tricalcium phosphate.

(Surfactant)
A surfactant may be added to the dispersion medium.
Examples of surfactants include sodium oleate, sodium dodecylbenzenesulfonate, sodium alkylbenzenesulfonate, and other anionic surfactants and nonionic surfactants commonly used in suspension polymerization.

(Other additives)
If necessary, other additives may be added to the dispersion medium as long as the object of the present invention is not impaired.
Other additives include, for example, a pH adjuster (for example, carbon dioxide, etc.) that adjusts the pH of the dispersion medium.

3. Step C (crosslinking step)
In the cross-linking step, the TPO is cross-linked by heating to a temperature above the melting point of TPO and to a temperature at which the cross-linking agent is substantially decomposed (hereinafter referred to as "cross-linking temperature").
In the cross-linking step, (i) the polymer particles may be impregnated with a cross-linking agent, and then the cross-linking agent may be decomposed to cross-link the TPO, or (ii) the polymer particles may be impregnated with the cross-linking agent while the cross-linking agent is added. Decomposition may be used to crosslink the TPO.
The "temperature at which the cross-linking agent substantially decomposes" means a temperature equal to or higher than the 1-minute half-life temperature of the cross-linking agent -30°C.

In the case of (i), the polymer particles are impregnated with the cross-linking agent at a temperature at which the polymer particles are softened and at a temperature at which the cross-linking agent is not substantially decomposed (hereinafter referred to as "cross-linking agent impregnation temperature"). is preferred.
Specifically, when the melting point of the raw material TPO is Tm, the impregnation temperature of the cross-linking agent is preferably in the range of Tm-20° C. to the 10-hour half-life temperature of the cross-linking agent. When two or more kinds of cross-linking agents are used, the lowest 10-hour half-life temperature among them is used as a standard.
Here, the holding time at the impregnation temperature is preferably 5 to 90 minutes, more preferably 10 to 60 minutes.

Next, the temperature is raised at a substantially constant heating rate to a temperature above the melting point of TPO contained in the polymer particles and a temperature at which the cross-linking agent is substantially decomposed (cross-linking temperature), and held at the cross-linking temperature for a certain period of time. Therefore, it is preferable to decompose the cross-linking agent to cross-link the TPO.
Specifically, when the melting point of TPO is Tm, the cross-linking temperature is preferably Tm to Tm+80°C, more preferably Tm+10°C to Tm+60°C.
Here, the holding time at the cross-linking temperature is preferably 15 to 60 minutes, more preferably 30 to 45 minutes.

In the case of (ii), the temperature is raised at a substantially constant heating rate to a temperature above the melting point of TPO contained in the polymer particles and to a temperature at which the cross-linking agent is substantially decomposed (cross-linking temperature). It is preferable that the TPO is crosslinked by decomposing the crosslinking agent while impregnating the polymer particles with the crosslinking agent by holding for a certain period of time.
Specifically, the heating rate is preferably 0.3 to 5°C/min, more preferably 0.5 to 3°C/min.
When the heating rate is within the above range, uneven cross-linking is less likely to occur.
When the melting point of the raw material TPO is Tm, the cross-linking temperature is preferably Tm°C to Tm+80°C, more preferably Tm+20°C to Tm+60°C.
Here, the holding time at the cross-linking temperature is preferably 5 to 120 minutes, more preferably 10 to 90 minutes, still more preferably 15 to 70 minutes.

Moreover, the conditions (i) and (ii) may be combined to crosslink the TPO contained in the polymer particles.
Furthermore, at least in step C (crosslinking step), the contents of the container containing the polymer particles in the closed container are stirred while proceeding with the steps, thereby sufficiently advancing the crosslinking of the TPO contained in the polymer particles and It becomes easy to spheroidize the coalesced crosslinked particles.
Stirring of the contents of the container is preferably performed in step B (dispersion step) and step C (crosslinking step), and may also be performed in step D (foaming agent impregnation step) and step E (crystallization step). good.

4. Step D (foaming agent impregnation step)
In the foaming agent impregnation step, the polymer particles or the crosslinked polymer particles are impregnated with the foaming agent.
The timing of performing the foaming agent impregnation step is not particularly limited, and may be performed before step F (foaming step).
Specifically, step D (foaming agent impregnation step) may be performed at any of the following timings, or may be performed at two or more timings.
・During step B (dispersion step) ・After step B (dispersion step) and before step C (crosslinking step) ・During step C (crosslinking step) ・After step C (crosslinking step) and before step E (crystallization step)・During step E (crystallization step) ・After step E (crystallization step) and before step F (foaming step) It is impregnated with coalesced particles. Further, if the TPO contained in the polymer particles is in the process of being crosslinked, the foaming agent is impregnated into the polymer particles in the process of being crosslinked. Further, after the completion of the cross-linking of the TPO contained in the polymer particles, the foaming agent is impregnated into the cross-linked polymer particles.

(foaming agent)
The foaming agent used in the foaming agent impregnation step is not particularly limited as long as it foams the crosslinked polymer particles.
Examples of foaming agents include inorganic physical foaming agents such as air, nitrogen, carbon dioxide, argon, helium, oxygen, and neon; aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and normal hexane; and cyclohexane. , cyclopentane and other alicyclic hydrocarbons, chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride and other halogenated hydrocarbons , dimethyl ether, diethyl ether, organic physical foaming agents such as dialkyl ethers such as methyl ethyl ether.
Among these, inorganic physical blowing agents that do not deplete the ozone layer and are inexpensive are preferred. Among them, nitrogen, air and carbon dioxide are preferred, and carbon dioxide is particularly preferred. These can be used singly or in combination of two or more.
As will be described later, when the foaming agent is added to the closed container, the amount of the foaming agent to be added is determined in consideration of the desired apparent density of the crosslinked foamed particles, the type of TPO, the type of the foaming agent, and the like. Generally, it is preferable to use 5 to 50 parts by weight of the organic physical blowing agent and 0.5 to 30 parts by weight of the inorganic physical blowing agent to 100 parts by weight of the polymer particles or crosslinked polymer particles. .

(Impregnation method)
The method for impregnating the polymer particles or the crosslinked polymer particles with the foaming agent is not particularly limited. to impregnate. It is preferable to proceed with the step of impregnating the foaming agent while stirring the contents in the sealed container.
The temperature at which the foaming agent is impregnated is not particularly limited as long as it is a temperature equal to or higher than the temperature at which the polymer particles or crosslinked polymer particles are softened. It ranges from 20°C to Tm+80°C.

5. Step E (crystallization step)
In the crystallization step, the TPO contained in the crosslinked polymer particles is maintained at a temperature near the melting point for a certain period of time to melt part or all of the TPO crystals and recrystallize part of the melted crystals. to form high-potential crystals.
In the crystallization step, after step C (crosslinking step), (i) the inside of the closed container may be cooled from the cross-linking temperature in step C (crosslinking step) to a temperature near the melting point of TPO, and (ii) the inside of the closed container The contents are cooled, the polymer crosslinked particles are extracted from the closed container, and then the polymer crosslinked particles are dispersed in a dispersion medium in the same or another closed container, and the temperature in the closed container is adjusted to a temperature near the melting point of TPO. The temperature may be raised to

In the case of (i), after step C (crosslinking step), the temperature in the sealed container is lowered from the crosslinking temperature at a substantially constant cooling rate to a temperature near the melting point of TPO (hereinafter referred to as "crystallization treatment temperature"), It is preferable to hold the crystallization treatment temperature for a certain period of time to recrystallize a part of the TPO crystals and generate high potential crystals.
Here, the rate at which the temperature is lowered to a temperature near the melting point of TPO (temperature drop rate) is preferably 0.3 to 5°C/min, more preferably 0.5 to 3°C/min.

In the case of (ii), after step C (crosslinking step), the inside of the closed vessel is cooled to a predetermined temperature, the crosslinked polymer particles are extracted from the closed vessel, and then the crosslinked polymer particles are dispersed in the dispersion medium in the closed vessel. , the temperature is raised to a temperature near the melting point of TPO (crystallization treatment temperature) at a substantially constant heating rate, and the temperature is maintained at the crystallization treatment temperature for a certain period of time to recrystallize a part of the TPO crystals. It is preferred to generate potential crystals.
Here, the rate at which the temperature is raised to a temperature near the melting point of TPO (heating rate) is preferably 0.3 to 5°C/min, more preferably 0.5 to 3°C/min.

Through step E (crystallization step) in the case of (i) or (ii) above, part or all of the melted TPO crystals in the crosslinked polymer particles are melted and melted. Some of the existing crystals are recrystallized, facilitating the formation of lamellar thick high-potential crystals. When the polymer crosslinked particles having such high-potential crystals are expanded in the next step F (expansion step), the crosslinked expanded particles having a crystal structure having high-potential crystals and crystals formed by cooling during expansion is obtained.
Therefore, a unique peak and a high temperature peak in the DSC curve are formed.

The crystallization treatment temperature for generating high-potential crystals is preferably in the range from Tm-15° C. to the final melting temperature, where Tm is the melting point of the raw material TPO.
The crystallization treatment may be performed at a constant temperature, or may be performed by changing the temperature within the above temperature range.
It is preferable to hold for a certain period of time at the crystallization treatment temperature in step E (crystallization step) in the case of (i) or (ii). Here, the holding time at the crystallization treatment temperature is preferably 1 to 60 minutes, more preferably 5 to 45 minutes.
The higher the crystallization treatment temperature, the lower the melting peak temperature of the melting peak (high-temperature peak) that appears on the higher temperature side than the characteristic peak, and the longer the crystallization treatment temperature is held, the larger the heat of fusion of the high-temperature peak tends to be. It is in.
In addition, the smaller the content of the foaming agent in the crosslinked expanded particles in the step D (crystallization step), the larger the heat of fusion at the high temperature peak tends to increase under the same crystallization treatment conditions (crystallization treatment temperature and holding time). .
The melting point Tm and melting end temperature of raw material TPO mean the melting peak temperature and extrapolated melting end temperature, respectively, measured based on heat flux differential scanning calorimetry described in JIS K7121-1987. "(2) Measurement of melting temperature after constant heat treatment" is adopted as the state adjustment of the test piece, and the heating rate and cooling rate are both 10°C/min.

6. Process F (foaming process)
In the foaming step, polymer crosslinked particles containing a foaming agent are foamed.
Specifically, the polymer crosslinked particles (referred to as “expandable crosslinked particles”) impregnated with a foaming agent in step D (foaming agent impregnation step) are expelled from the closed container together with the dispersion medium under pressure in the closed container. It is preferable to produce crosslinked expanded particles by discharging the expandable crosslinked particles in an atmosphere having a lower pressure to expand the expandable crosslinked particles.
In order to obtain crosslinked foamed particles having a crystal structure with a high-temperature peak, the temperature of the contents in the closed container at the time of release should be the same as or about the same temperature as the crystallization treatment temperature in step E (crystallization step). It is preferable to In addition, the pressure inside the closed container is controlled so that the difference between the pressure inside the closed container and the pressure of the release atmosphere is preferably 1.0 to 10 MPa, more preferably 1.5 to 5.0 MPa.

When the expandable crosslinked particles are released from the closed container together with the dispersion medium into an atmosphere having a pressure lower than the pressure inside the closed container, the inside of the container is pressurized with carbon dioxide, air, etc., and the inside of the opened closed container is It is preferable to keep the pressure constant or adjust the pressure so that it increases gradually. Such pressure adjustment can further reduce the variation in the apparent density and cell diameter of the obtained crosslinked expanded particles.

In the DSC curve obtained by heating the crosslinked and expanded particles from 23° C. to 200° C. at a heating rate of 10° C./min, the crosslinked and expanded particles obtained through steps A to F show a melting peak specific to TPO (specific peak) and one or more melting peaks (high temperature peaks) on the higher temperature side than the intrinsic peak. A high temperature peak appears in the DSC curve of the first heating of the crosslinked foamed particles, but after the first heating, it was cooled from 200 ° C. to 23 ° C. at a cooling rate of 10 ° C./min, and again at 10 ° C./min. It does not appear in the DSC curve of the second heating obtained by heating from 23°C to 200°C at a heating rate. In the DSC curve of the second heating, only the endothermic peak derived from the crystals inherent in TPO appears at the same position as the intrinsic peak, so the intrinsic peak and the high-temperature peak can be easily distinguished.

[Expanded bead molding]
An expanded bead molded article can be obtained by in-mold molding of the crosslinked expanded bead of the present invention. The crosslinked and expanded particles of the present invention have a crystal structure in which a characteristic peak P _a and a high temperature peak P _b appear in a DSC curve obtained by heating from 23° C. to 200° C. at a heating rate of 10° C./min, and It has a crystal structure in which the heat of fusion ( _B ) of the high temperature peak Pb is 5 J/g or more. As a result, even if the crosslinked foamed particles contain a coloring agent, it is possible to obtain an expanded bead molded article that has excellent in-mold moldability and little color unevenness.

(in-mold molding)
A molded article of expanded particles can be obtained by a conventionally known method of filling a molding die with crosslinked expanded particles and heat-molding using a heating medium such as steam. Specifically, after the crosslinked and expanded particles are filled in the mold, a heating medium such as steam is introduced into the mold to heat the crosslinked and expanded particles to cause secondary expansion, and at the same time, the crosslinked and expanded particles are separated from each other. It is possible to obtain an expanded bead molded article in which the shape of the molding space is shaped by mutual fusion. Moreover, as a method of filling the mold with the crosslinked foamed particles, a known method can be adopted. A method in which, for example, the crosslinked and expanded particles are pressurized with a pressurized gas to give a predetermined internal pressure to the crosslinked and expanded particles within a range that does not excessively improve the secondary foaming power of the crosslinked and expanded particles, and then filled in the mold. (pressure filling method), a method in which the crosslinked foamed particles are compressed with a pressurized gas and filled in a pressurized mold, and then the pressure in the mold is released (compression filling method), the crosslinked foamed particles are placed in the mold A method of mechanically compressing the cross-linked foamed particles by opening the mold in advance to expand the molding space before filling, and closing the mold after filling (cracking filling method), or a filling method using a combination of these methods is also adopted. You can also

(Mold density)
The apparent density (molded density) of the expanded bead molded article is preferably 40 to 300 kg/m ³ , more preferably 40 to 250 kg/m ³ , still more preferably 45 to 200 kg/m ³ , still more preferably 50 to 180 kg. / ^m3 .
When the molded article density is within the above range, the expanded bead molded article is excellent in lightness, flexibility, resilience, recovery, and tensile properties in a well-balanced manner.
The molded body density (kg/m ³ ) is obtained by dividing the weight W (kg) of the molded body by the volume V (m ³ ) determined from the outer dimensions of the molded body (W/V).

(Tensile properties of compact)
It is preferred that the expanded bead molded article has the following tensile properties when subjected to a tensile test in accordance with JIS K6767:1999.
The tensile strength (a) of the expanded bead molded product is preferably 0.30 to 1.5 MPa, more preferably 0.40 to 1.5 MPa, still more preferably 0.45 to 1.3 MPa, still more preferably 0 .48 to 1.2 MPa.
The tensile elongation (b) of the expanded bead molding is preferably 150 to 400%, more preferably 180 to 350%, even more preferably 200 to 300%, still more preferably 200 to 280%.
The product (a)×(b) of the tensile strength (a) [MPa] and the tensile elongation (b) [%] of the expanded bead molded product is preferably 100 or more, more preferably 100 to 300, and still more preferably 100-250, more preferably 110-230.
When the above tensile strength (a), tensile elongation (b), and (a)×(b) are within the above ranges, the seat cushion material, sports pad material, and shoes have excellent strength and flexibility. It is suitable for applications such as bottom materials.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited by these examples.

Crosslinked expanded particles of Examples 1 to 8 and Comparative Examples 1 to 9 were produced by the method shown below.
[Method for producing crosslinked expanded particles]
<TPO>
As TPO, which is the base polymer, an olefin-based thermoplastic elastomer ("Infuse" manufactured by Dow Chemical Co., Ltd.), which is a multi-block copolymer having polyethylene as a hard block and an ethylene/α-olefin copolymer as a soft block, is used. INFUSE® 9530”) (hereinafter referred to as “TPO(1)”) was used.
The physical properties of TPO (1) are a density of 887 g/L, a type A durometer hardness (Shore A hardness) of 86, and a melt flow rate (MFR) of 5.4 g/10 minutes (at a temperature of 190°C and a load of 2.16 kg). , the flexural modulus was 28 MPa, the melting point was 120°C, and the melting end temperature was 125°C.

<Method for measuring physical properties of TPO>
Density conforms to ASTM D792-13, type A durometer hardness (Shore A hardness) conforms to ASTM D2240-05, melt flow rate (MFR) conforms to JIS K7210-1:2014, and flexural modulus conforms to Each was measured according to JIS K7171:2008.
Further, the melting point was determined according to JIS K7121-1987, and the melting peak temperature and melting end temperature of TPO were obtained. Specifically, about 5 mg of pellet-shaped TPO was used as a test piece, and based on heat flux differential scanning calorimetry, the state of the test piece was adjusted as follows: "(2) When measuring the melting temperature after performing a certain heat treatment. ” was adopted, and the melting peak temperature (melting point) and melting end temperature of TPO were measured under the conditions of a heating rate of 10° C./min, a cooling rate of 10° C./min, and a nitrogen flow rate of 30 mL/min.
A heat flux differential scanning calorimeter (“DSC7020” manufactured by SII Nano Technology Co., Ltd.) was used as a measuring device.

<Colorant>
Table 1 shows the properties of the colorants used in Examples and Comparative Examples.

(Example 1)
1. Step A (Step of obtaining polymer particles)
TPO (1) described above as a base polymer, 0.23 parts by weight of a blue pigment masterbatch shown in Table 1 as a coloring agent and zinc borate as a cell control agent for 100 parts by weight of TPO (1) (ZnB) (“Zinc borate 2335” manufactured by Tomita Pharmaceutical Co., Ltd., average particle size d50: 6 μm) 0.10 parts by weight was supplied to an extruder to melt TPO (1) and knead them. It was made into a molten kneaded product. Next, the melt-kneaded product is extruded into strands through small holes with a hole diameter of 2 mm in a die attached to the extruder, and the strands are water-cooled and then cut into particles having a particle weight of about 5 mg by a pelletizer. Polymer particles were obtained.

2. Process B (dispersion process)
An autoclave having an internal volume of 400 L equipped with a stirrer was charged with 250 L of water as a dispersion medium and 50 kg of the polymer particles obtained above (dried).
Furthermore, 300 g of kaolin as a dispersant (0.6 parts by weight per 100 parts by weight of polymer particles) and 20 g of sodium alkylbenzenesulfonate as a surfactant (0.6 parts by weight per 100 parts by weight of polymer particles) were added to the dispersion medium. 04 parts by weight) and 275 g of dicumyl peroxide (10-hour half-life temperature: 116.4° C., 1-minute half-life temperature: 175.2° C.) as a cross-linking agent (0.55 g per 100 parts by weight of polymer particles). parts by weight) were added, carbon dioxide was injected as a pH adjuster so that the pressure inside the autoclave was 1.0 MPa (G), and the polymer particles were dispersed in the dispersion medium with stirring.

3. Step C (crosslinking step)
Then, the temperature inside the autoclave was raised to 160° C. (crosslinking temperature) at a heating rate of 2.0° C./min while stirring, and the temperature was maintained at 160° C. for 60 minutes to apply the cross-linking agent to the polymer particles. While being impregnated, the TPO (1) contained in the polymer particles was crosslinked.
Then, the temperature in the closed container was lowered to 50° C. (extraction temperature) at a cooling rate of 1.0° C./min, and then the polymer crosslinked particles were taken out from the closed container.

4. Step D (foaming agent impregnation step) and step E (crystallization step)
In an autoclave having an inner volume of 5 L equipped with a stirrer, 3 L of water as a dispersion medium and 1 kg of the crosslinked polymer particles obtained above (dried) were charged, and the polymer was crosslinked in the dispersion medium while stirring. The particles were dispersed.
Furthermore, 3 g of kaolin as a dispersant (0.3 parts by weight per 100 parts by weight of the crosslinked polymer particles) and 0.04 g of sodium alkylbenzenesulfonate as a surfactant (per 100 parts by weight of the crosslinked polymer particles) were added to the dispersion medium. and 40 g of dry ice as a foaming agent (4.0 parts by weight with respect to 100 parts by weight of the crosslinked polymer particles).
Next, while stirring, the temperature inside the autoclave was raised to 119°C (crystallization treatment temperature) at a rate of temperature rise of 2.0°C/min until the pressure inside the autoclave reached 2.5 MPa (G). By injecting carbon dioxide and maintaining at 119° C. for 15 minutes, the polymer crosslinked particles were impregnated with the foaming agent and high potential crystals were formed.

5. Process F (foaming process)
After that, stirring was stopped, and the contents in the autoclave were discharged to atmospheric pressure at 119°C (expansion temperature) to expand the polymer crosslinked particles containing the blowing agent (expandable crosslinked particles). Crosslinked foamed particles were obtained.
The pressure in the autoclave (foaming pressure) immediately before discharging the contents in the autoclave was 2.5 MPa (G).

(Example 2)
The addition amount of the blowing agent was changed to 3.0 parts by weight, the crystallization treatment temperature was changed to 118°C, carbon dioxide was injected so that the pressure inside the autoclave was 2.2 MPa (G), Crosslinked expanded particles of Example 2 were obtained in the same manner as in Example 1, except that the expansion temperature was changed to 118°C.
The foaming pressure was 2.2 MPa (G).

(Example 3)
Example 3 was prepared in the same manner as in Example 1, except that the amount of foaming agent added was changed to 3.0 parts by weight, and carbon dioxide was injected so that the pressure in the autoclave was 2.4 MPa (G). Crosslinked foamed particles were obtained.
The foaming pressure was 2.4 MPa (G).

(Example 4)
Crosslinked expanded particles of Example 4 were obtained in the same manner as in Example 1 except that the amount of the crosslinking agent added was changed to 0.60 parts by weight and the amount of the foaming agent added was changed to 3.0 parts by weight. .
The foaming pressure was 2.4 MPa (G).

(Example 5)
The procedure of Example 1 was repeated except that the colorant was changed to 0.26 parts by weight of the yellow pigment masterbatch shown in Table 1, the crystallization temperature was changed to 118°C, and the foaming temperature was changed to 118°C. to obtain crosslinked foamed particles of Example 5.
The foaming pressure was 2.5 MPa (G).

(Example 6)
The colorant was changed to 0.26 parts by weight of the yellow pigment masterbatch shown in Table 1, the amount of foaming agent added was changed to 3.0 parts by weight, the crystallization treatment temperature was changed to 118 ° C., and the autoclave Crosslinked and expanded particles of Example 6 were obtained in the same manner as in Example 1 except that carbon dioxide was injected so that the internal pressure was 2.2 MPa (G) and the expansion temperature was changed to 118°C.
The foaming pressure was 2.2 MPa (G).

(Example 7)
The colorant was changed to 0.26 parts by weight of the yellow pigment master batch shown in Table 1, the amount of foaming agent added was changed to 3.0 parts by weight, the crystallization treatment temperature was changed to 118 ° C., and the autoclave Crosslinked and expanded particles of Example 7 were obtained in the same manner as in Example 1 except that carbon dioxide was injected so that the pressure was 2.4 MPa (G) and the expansion temperature was changed to 118°C.
The foaming pressure was 2.4 MPa (G).

(Example 8)
The colorant was changed to 2.00 parts by weight of the black pigment masterbatch shown in Table 1, the crystallization treatment temperature was changed to 118°C, and carbon dioxide was injected so that the pressure inside the autoclave was 2.6 MPa (G). Then, crosslinked expanded particles of Example 8 were obtained in the same manner as in Example 1, except that the expansion temperature was changed to 118°C.
The foaming pressure was 2.6 MPa (G).

(Comparative example 1)
1. Step A (Step of obtaining polymer particles)
TPO (1) described above as a base polymer, 0.23 parts by weight of a blue pigment masterbatch shown in Table 1 as a coloring agent and zinc borate as a cell control agent for 100 parts by weight of TPO (1) (ZnB) (“Zinc borate 2335” manufactured by Tomita Pharmaceutical Co., Ltd., average particle size d50: 6 μm) 0.10 parts by weight was supplied to an extruder to melt TPO (1) and knead them. It was made into a molten kneaded product. Next, the melt-kneaded product is extruded into strands through small holes with a hole diameter of 2 mm in a die attached to the extruder, and the strands are water-cooled and then cut into particles having a particle weight of about 5 mg by a pelletizer. Polymer particles were obtained.

2. Process B (dispersion process)
An autoclave having an internal volume of 5 L and equipped with a stirrer was charged with 3 L of water as a dispersion medium and 1 kg of the polymer particles obtained above (dried).
Furthermore, 3 g of kaolin as a dispersant (0.3 parts by weight with respect to 100 parts by weight of polymer particles) and 0.04 g of sodium alkylbenzenesulfonate as a surfactant (per 100 parts by weight of base polymer particles) are added to the dispersion medium. and 8 g of dicumyl peroxide (10-hour half-life temperature: 116.4° C., 1-minute half-life temperature: 175.2° C.) as a cross-linking agent (per 100 parts by weight of polymer particles 0.8 parts by weight) and 40 g of dry ice (4.0 parts by weight with respect to 100 parts by weight of crosslinked polymer particles) as a blowing agent and pH adjuster were added, and the polymer was added to the dispersion medium while stirring. The particles were dispersed.

3. Step C (crosslinking step), Step D (foaming agent impregnation step), Step F (foaming step)
Then, while stirring, the temperature inside the autoclave was raised to 110°C (the impregnation temperature of the cross-linking agent) at a heating rate of 2.0°C/min, and the temperature inside the autoclave was maintained at 110°C for 30 minutes. was heated to 160° C. (crosslinking temperature) at a heating rate of 2.0° C./min and held at 160° C. for 30 minutes. During these steps, carbon dioxide, a blowing agent, was impregnated into the polymer crosslinked particles. After the end of holding, the stirring was stopped, and the contents in the autoclave were discharged to atmospheric pressure to expand the polymer crosslinked particles (expandable crosslinked particles) containing the blowing agent to obtain the crosslinked expanded particles of Comparative Example 1. rice field.
The foaming pressure was 2.5 MPa (G).

(Comparative example 2)
Crosslinked expanded particles of Comparative Example 2 were obtained in the same manner as in Comparative Example 1 except that the amount of dry ice added was changed to 2.5 parts by weight.
The foaming pressure was 1.8 MPa (G).

(Comparative Example 3)
Except for changing the cell regulator to polytetrafluoroethylene (PTFE) (“TFW-1000” manufactured by Seishin Enterprise Co., Ltd., average particle size d50: 10 μm) and changing the amount of dry ice added to 5.0 parts by weight. Crosslinked expanded particles of Comparative Example 3 were obtained in the same manner as in Comparative Example 1.
The foaming pressure was 3.0 MPa (G).

(Comparative Example 4)
Crosslinked expanded particles of Comparative Example 4 were obtained in the same manner as in Comparative Example 1 except that the amount of coloring agent added was changed to 1.15 parts by weight and the amount of dry ice added was changed to 5.0 parts by weight. .
The foaming pressure was 3.0 MPa (G).

(Comparative Example 5)
Crosslinking of Comparative Example 5 was carried out in the same manner as in Comparative Example 1 except that the colorant was changed to 2.80 parts by weight of the black pigment masterbatch shown in Table 1 and the amount of dry ice was changed to 2.0 parts by weight. Foamed particles were obtained.
The foaming pressure was 1.5 MPa (G).

(Comparative Example 6)
Crosslinking of Comparative Example 6 was carried out in the same manner as in Comparative Example 1 except that the colorant was changed to 0.40 parts by weight of the black pigment masterbatch shown in Table 1 and the amount of dry ice added was changed to 3.0 parts by weight. Foamed particles were obtained.
The foaming pressure was 2.0 MPa (G).

(Comparative Example 7)
Crosslinking of Comparative Example 7 was carried out in the same manner as in Comparative Example 1 except that the colorant was changed to 2.8 parts by weight of the black pigment masterbatch shown in Table 1 and the amount of dry ice was changed to 3.0 parts by weight. Foamed particles were obtained.
The foaming pressure was 2.0 MPa (G).

(Comparative Example 8)
Crosslinked expanded particles of Comparative Example 8 were obtained in the same manner as in Comparative Example 1 except that the amount of dry ice added was changed to 3.5 parts by weight.
The foaming pressure was 2.3 MPa (G).

(Comparative Example 9)
The cell regulator was changed to polytetrafluoroethylene (PTFE) (“TFW-1000” manufactured by Seishin Enterprise Co., Ltd., average particle diameter d50: 10 μm), the amount of the cross-linking agent added was changed to 0.60 parts by weight, The addition amount of the blowing agent was changed to 5.0 parts by weight, the crystallization treatment temperature was changed to 121°C, carbon dioxide was injected so that the pressure inside the autoclave was 3.0 MPa (G), Crosslinked expanded particles of Comparative Example 9 were obtained in the same manner as in Example 1 except that the expansion temperature was changed to 121°C.
The foaming pressure was 3.0 MPa (G).

[Evaluation of Physical Properties of Crosslinked Expanded Particles]
The crosslinked expanded particles of Examples 1 to 8 and Comparative Examples 1 to 9 were allowed to stand under conditions of relative humidity of 50%, 23° C., and 1 atm for 2 days to condition the crosslinked expanded particles. Physical properties were evaluated. The evaluation results are shown in Tables 2 and 4.

(apparent density)
Put 100 mL of ethanol at 23° C. in a 200 mL graduated cylinder, weigh the weight Wa (g) in advance, and immerse the crosslinked foamed particles with a bulk volume of about 50 mL in ethanol using a wire mesh, and the volume Va corresponding to the increase in the water level. (cm ³ ) were read. The apparent density (kg/m ³ ) of the crosslinked expanded particles was obtained by calculating Wa/Va and converting the unit into kg/m ³ .
The measurement was performed under atmospheric pressure with a temperature of 23° C. and a relative humidity of 50%.

(Average value of bubble diameter and coefficient of variation of bubble diameter)
10 expanded particles were randomly selected from the group of crosslinked expanded particles. The cross-linked foamed particles were divided into two parts so as to pass through the central part of the cross-linked foamed particles, and an enlarged photograph of the cut surface was taken at a magnification of 50 times. In the enlarged photograph of the obtained cross section, 50 cells on the cut surface of the crosslinked foamed particle are randomly selected, and the area of the cross section of each selected cell is measured using the image processing software NS2K-pro manufactured by Nanosystem Co., Ltd. was measured, and the diameter of an imaginary perfect circle having the same area as that area was taken as the bubble diameter of each bubble. This operation was performed for 10 foamed beads, and the arithmetic average value of the cell diameters of the cells was taken as the average value of the cell diameters of the crosslinked foamed beads (average cell diameter).
The variation coefficient of the cell diameter was obtained by dividing the standard deviation of the cell diameter of the crosslinked and expanded particles by the average cell diameter of the cells of the crosslinked and expanded particles.
The square root of the unbiased variance was used as the standard deviation.

(hot xylene insoluble matter)
About 1 g of a sample of the crosslinked foamed particles was weighed to obtain a sample weight W1b. Put the weighed crosslinked foamed particles in a 150 mL round-bottomed flask, add 100 mL of xylene, heat with a mantle heater and reflux for 6 hours, then filter and separate the undissolved residue with a 100 mesh wire mesh, The residue captured on the wire mesh was dried in a vacuum dryer at 80° C. for 8 hours. The dried material (hot xylene-insoluble matter) obtained at this time was weighed to determine the dried material weight W2b. The weight percentage [(W2b/W1b)×100] (% by weight) of the dry matter weight W2b to the sample weight W1b was taken as the hot xylene-insoluble portion of the crosslinked expanded particles.
In the step of in-mold molding the crosslinked expanded particles, the proportion of the hot xylene insolubles does not change, and the proportion of the hot xylene insolubles in the expanded bead molded product is the same as that of the crosslinked expanded beads.

(Temperature of high-temperature peak Pb, temperature of specific peak Pa, heat of fusion of high-temperature peak Pb ( _B ), total heat of fusion [( _A ) + ( _B )], (B) / [(A) + (B )])
The crosslinked foamed particles were cut into approximately 2 equal parts to obtain a test piece of about 2.5 mg. High temperature peak heat quantity (B) and total heat of fusion [(A) + (B)] are obtained from the DSC curve obtained when heating at a heating rate of 10 ° C./min to 10 ° C. / min. The ratio "(B)/[(A)+(B)]" was calculated.
Also, the melting peak temperature of the intrinsic peak was defined as the intrinsic peak temperature, and the melting peak temperature of the high-temperature peak was defined as the high-temperature peak temperature.
A heat flux differential scanning calorimeter (“DSC7020” manufactured by SII Nano Technology Co., Ltd.) was used as a measuring device. The nitrogen inflow rate was 30 mL/min.

[Method for producing expanded bead molded product]
The crosslinked foamed particles obtained in Examples and Comparative Examples were placed in respective closed containers, and the pressure in the closed container was increased to 0.2 MPa (G) for 12 hours with compressed air, so that the crosslinked foamed particles Internal pressure was applied. The internal pressure of the crosslinked foamed particles taken out from the sealed container was 0.2 MPa (absolute pressure).
Cross-linked foamed particles to which internal pressure is applied are placed in a mold having a flat plate-shaped molding space with a length of 250 mm, a width of 200 mm, and a thickness of 20 mm. direction length 24 mm) and the mold was completely closed after filling was complete (cracking 4 mm, 20%). After that, steam is supplied into the mold to heat the crosslinked and expanded particles so that the pressure in the mold becomes 0.10 MPa (G), and the crosslinked and expanded particles are subjected to secondary expansion, and the crosslinked and expanded particles are mutually interconnected. fused to the The pressure at this time is hereinafter also referred to as "molding pressure". After cooling, the expanded bead molded article was taken out from the mold, and the expanded bead molded article was dried by heating in an oven adjusted to 60° C. for 12 hours to obtain a flat expanded bead molded article.
Expanded bead moldings were produced in the same manner while changing the molding pressure by 0.02 MPa to 0.30 MPa (G).
For the expanded bead molded articles of Examples 1 to 8 and Comparative Examples 1 to 9, from the viewpoint of fusion bondability, appearance (degree of voids), and recoverability (recovery of expansion or contraction after molding), the following The moldability was evaluated according to the criteria of The evaluation results are shown in Tables 3 and 5.

[Moldability evaluation of expanded bead molded product]
(fusion)
The foamed particle molded product is bent and broken, and the number of crosslinked foamed particles (C1) present on the fracture surface and the number of broken crosslinked foamed particles (C2) are determined, and the ratio of the broken crosslinked foamed particles to the above crosslinked foamed particles is determined. (C2/C1×100) was calculated as the material destruction rate. The measurement was performed 5 times using different test pieces, and the material destruction rate was determined for each. evaluated.
A: Material destruction rate of 90% or more B: Material destruction rate of 20% or more and less than 90% C: Material destruction rate of less than 20%

(Appearance (degree of voids))
Draw a rectangle of 100 mm x 100 mm in the center of the plate surface of the expanded bead molding, draw a line diagonally from the corner of the rectangular area, and measure the number of voids (gap) of 1 mm x 1 mm or more on the line. were counted, and the surface appearance of the expanded bead molded product was evaluated according to the following criteria.
A: The number of voids is less than 5 B: The number of voids is 5 or more and less than 10 C: The number of voids is 10 or more

(recoverability)
Measure the thickness of the center and four corners of the expanded bead molded product, calculate the ratio of the thickness of the central part to the thickest part of the four corners, and evaluate the recoverability of the expanded bead molded product according to the following criteria. did.
A: Thickness ratio is 95% or more B: Thickness ratio is 90% or more and less than 95% C: Thickness ratio is less than 90%

(Molding range)
The molding pressure at which all evaluations of fusion bondability, appearance, and recoverability are A is described in the "moldable range" column of the "moldability evaluation" column in Tables 2 and 4 as the moldable range. In addition, "A" when there are 4 or more molding pressures where all evaluations of fusion bondability, appearance, and recoverability are A, "B" when there are 3 points, "C" when there are 2 points, When there was one point, it was evaluated as "D" and shown in the "evaluation" column of the "moldability evaluation" column.
Even when the molding pressure is changed, if a highly evaluated expanded bead molded article can be obtained over a wide range of molding pressure, the crosslinked expanded bead having a wide range of moldable conditions and excellent in-mold moldability can be obtained. can be determined to be
In addition, when molding can be performed at a low molding pressure, the molding cycle is shortened and the productivity is improved. Therefore, it can be said that the crosslinked expanded beads are excellent in the productivity of the expanded bead molded articles.

[Evaluation of physical properties of expanded bead molded product]
The expanded bead molded articles of Examples 1 to 8 and Comparative Examples 1 to 9 obtained at a molding pressure of 0.20 MPa (G) were allowed to stand under conditions of relative humidity of 50%, 23° C., and 1 atm for 2 days. After conditioning, the following physical properties were evaluated. The evaluation results are shown in Tables 2 and 4.
In Comparative Example 9, a good foamed bead molded article was not obtained, so the following physical properties were not evaluated.

(Apparent Density (Compact Density))
Three rectangular parallelepiped specimens of length 50 mm × width 50 mm × thickness 25 mm were cut out from a randomly selected location of the expanded bead molded body so as not to include the skin layer during molding. and external dimensions were measured.
The density W/V (kg/m ³ ) was calculated by dividing the weight W (kg) of the test piece by the volume V (m ³ ) obtained from the outer dimensions of the test piece. The density of each of the three test pieces was calculated, and the arithmetic mean value was taken as the apparent density (molded density) of the expanded bead molded article.

(Tensile strength (a), tensile elongation (b), (a) x (b))
First, according to JIS K6767:1999, a rectangular parallelepiped of 120 mm×25 mm×10 mm was cut out from the foamed bead molded product using a vertical slicer so that all the surfaces were cut surfaces, thereby producing cut pieces. The cut-out piece was cut into a dumbbell-shaped No. 1 shape (measurement portion length: 40 mm, width: 10 mm, thickness: 10 mm) using a jigsaw to obtain a test piece.
This test piece was subjected to a tensile test at a test speed of 500 mm/min according to JIS K6767:1999 to measure the tensile strength (a) and tensile elongation (b) at break of the expanded bead molded product.

(Color unevenness)
The surface of the expanded bead molded article was visually observed, and the state of color tone was evaluated according to the following three-grade criteria.
◯: Almost no shading of color tone was observed on the surface of the expanded bead molded article, and an expanded bead molded article with little color unevenness was obtained.
Δ: Some shading of color tone was observed on the surface of the crosslinked expanded bead molded article, and an expanded bead molded article with some color unevenness was obtained.
x: Many shades of color tone were observed on the surface of the expanded bead molded article, and an expanded bead molded article with much color unevenness was obtained.

(Summary of results)
The crosslinked foamed particles of Comparative Examples 1 to 8 did not have a crystal structure in which a high-temperature peak appeared. In comparison, the in-mold moldability was inferior.
In addition, although the crosslinked expanded beads of Comparative Example 9 had a crystal structure in which a high-temperature peak appeared, the heat of fusion ( _B ) of the high-temperature peak Pb was less than 5 J/g. I didn't get the body.
On the other hand, the crosslinked expanded particles of Examples 1 to 8 had a crystal structure with a high temperature peak, and the heat of fusion ( _B ) of the high temperature peak Pb was 5 J/g or more. As a result, an expanded bead molded article having excellent in-mold moldability and less color unevenness was obtained.

_Pa melting peak (unique peak)
_Pb melting peak (high temperature peak)
PT _ma apex temperature PT _mb apex temperature A Area of characteristic peak B Area of high temperature peak

Claims (9)

A crosslinked foamed particle containing a colorant and containing a thermoplastic olefin elastomer as a base material,
In the DSC curve obtained by heating from 23° C. to 200° C. at a heating rate of 10° C./min, the crosslinked foamed particles have a melting peak (specific peak) specific to the olefinic thermoplastic elastomer and a temperature higher than the specific peak. It has a crystal structure in which one or more melting peaks (high-temperature peaks) appear on the side, the heat of fusion of the high-temperature peak is 5 J/g or more, and the average cell diameter of the crosslinked expanded particles is 20 μm or more and less than 50 μm. A crosslinked foamed particle of an olefinic thermoplastic elastomer. 2. The crosslinked and expanded particles of an olefinic thermoplastic elastomer according to claim 1, wherein the hot xylene-insoluble matter of said crosslinked and expanded particles is 10 to 70% by weight. 3. The crosslinked, expanded thermoplastic elastomer particles according to claim 1, wherein the ratio of the heat of fusion at the high-temperature peak to the total heat of fusion in the DSC curve is 0.1 to 0.6. The crosslinked, expanded thermoplastic elastomer particles according to any one of claims 1 to 3, wherein the crosslinked, expanded particles have an apparent density of 30 to 300 kg/m ³ . The crosslinked and expanded particles of an olefinic thermoplastic elastomer according to any one of claims 1 to 4 , wherein the crosslinked and expanded particles have a coefficient of variation of cell diameter of 30% or less. The crosslinked expanded thermoplastic elastomer particles according to any one of claims 1 to 5 , wherein the content of said colorant is 0.05 parts by weight or more per 100 parts by weight of said thermoplastic olefinic elastomer. The olefinic thermoplastic elastomer according to any one of claims 1 to 6 , wherein the olefinic thermoplastic elastomer is a block copolymer having a polyethylene block as a hard segment and an ethylene/α-olefin copolymer block as a soft segment. Plastic elastomer crosslinked expanded particles. A crosslinked and expanded thermoplastic elastomer particle molded product obtained by molding the crosslinked and expanded thermoplastic elastomer particles according to any one of claims 1 to 7 in a mold. The olefin-based heat according to claim 8 , wherein the product (a) x (b) of the tensile strength (a) [MPa] and the tensile elongation (b) [%] of the crosslinked foamed particle molded product is 100 or more. Plastic elastomer cross-linked expanded particle molding.

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