JP2003313353A - Expanded polypropylene resin particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide expanded polypropylene resin particles which can achieve fusion among expanded particles by treatment with low-temperature steam to give an expanded particle molding having high rigidity (high compressive strength) and/or high heat resistance. <P>SOLUTION: The expanded polypropylene resin particles are ones using as the base resin a polypropylene resin having a melting point of 155°C or higher, a tensile yield strength of 31 MPa or higher, a tensile elongation at break of 20% or higher, and a molecular weight distribution (Mw/Mn) or 4.4 or larger, wherein the particles give an endotherm peak on the side higher than the endotherm peak ascribable to the heat of fusion of the base resin in a DSC curve as determined by differential scanning calorimetry, and the heat of fusion of the endotherm peak on the high-temperature side is 10-60 J/g. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expanded polypropylene resin particles, and more particularly, to expanded polypropylene resin particles in which the fusion temperature during in-mold molding is effectively reduced.

[0002]

2. Description of the Related Art In recent years, there has been a movement to integrate plastic materials. Among them, polypropylene resins are particularly excellent in balance of mechanical strength, heat resistance, workability, price, easy incineration, easy recycling and the like. Because of its excellent properties, the field of application is expanding. As one of application fields of polypropylene-based resin, in-mold foamed molded article of polypropylene-based resin expanded particles (hereinafter sometimes referred to as “EPP molded article” or “expanded particle molded article” or simply “molded article”) The polypropylene resin is widely used as a packaging material, a building material, a heat insulating material, and the like because properties such as a buffering property and a heat insulating property can be added without losing the excellent properties of the polypropylene resin.

[0003] Expanded particles using a polypropylene resin having a melting point of 155 ° C or higher as a base resin can produce an EPP molded article having high heat resistance and / or obtain an EPP molded article having a large compressive strength. This is preferable because it can be performed. An expanded particle using a polypropylene resin having a melting point of 155 ° C. or more as a base resin is described in, for example, [Patent Document 1]. However, with the foamed particles described therein, the fusion rate between the foamed particles cannot be increased unless steam at an extremely high temperature is used during in-mold molding. The use of steam at an extremely high temperature leads to an increase in cost, and the load on the molding machine is large, so it is necessary to increase the durability of the molding machine, and there is a problem that the molding machine becomes expensive or large. At the same time, it leads to an increase in the weight of the mold and an increase in the cost of producing the mold. Therefore, there has been a demand for foamed particles that can be molded with lower-temperature steam while being foamed particles using a high melting point polypropylene-based resin as a base resin.

[0004]

[Patent Document 1] International Publication No. 96/31558 pamphlet

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide foamed particles which can be molded with a lower temperature steam while being foamed particles using a high melting point polypropylene resin as a base resin. I do.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by selecting a specific base resin, the fusion between the foamed particles with a lower temperature steam is performed. Have been found to provide an EPP molded body having high heat resistance and / or high compressive strength, and completed the present invention. That is, according to the present invention, there are provided the expanded polypropylene resin particles according to the following [1] to [6]. [1] Melting point is 155 ° C or higher, tensile yield strength is 31 MPa
As described above, the tensile elongation at break is 20% or more, and the molecular weight distribution (M
(w / Mn) is a foamed particle comprising a polypropylene resin having a base resin of 4.4 or more, and the foamed particle has an endothermic curve derived from a heat of fusion of the substrate resin in a DSC curve by differential scanning calorimetry. An endothermic curve peak exists on the higher temperature side than the peak, and the heat of fusion of the higher endothermic curve peak is 1
Foamed polypropylene resin particles having a weight of 0 to 60 J / g. [2] The base resin has a melt flow rate (MFR) of 1
The base resin has a melt flow rate (MFR) of 1 to 60 g / 10 minutes.
The expanded polypropylene resin particles according to [1] above, wherein [3] Relationship between the calorific value (ΔH _s ) of the endothermic curve peak existing on the high temperature side of the surface layer portion of the foamed particles and the caloric value (ΔH _i ) of the endothermic curve peak existing on the high temperature side of the internal foamed layer of the foamed particles. Is ΔH _s <ΔH _i × 0.86. The expanded polypropylene resin particles according to the above [1] or [2], wherein [4] Micro-differential thermal analysis on the surface of the foamed particles (from 25 ° C. to 200 ° C. at a heating rate of 10 ° C./sec)
The foamed polypropylene resin particles according to any of [1] to [3], wherein the melting start temperature based on the melting point is equal to or lower than the melting point of the base resin. [5] Micro-differential thermal analysis on the surface of the expanded particles (conditions of temperature increase rate from 25 ° C to 200 ° C at a rate of 10 ° C / sec)
Of extrapolation melting based on the temperature of the base resin [melting point + 4 ° C]
The expanded polypropylene resin particles according to any one of the above [1] to [3], wherein: [6] The expanded polypropylene resin particles according to any one of [1] to [5], wherein the polypropylene resin particles are dispersed in a dispersion medium in which an organic peroxide is present, and the dispersion medium is the polypropylene. A substantially non-crosslinked surface modification by decomposing the organic peroxide at a temperature lower than the melting point of the base resin of the base resin particles and at a temperature at which the organic peroxide is substantially decomposed. A polypropylene-based material produced by a method comprising: a surface modification step of obtaining particles; and a foaming step of foaming the surface-modified particles using a foaming agent to obtain substantially non-crosslinked foamed particles. Resin foam particles.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As the base resin of the polypropylene resin particles used in the present invention (hereinafter sometimes referred to as “base resin”), a polypropylene homopolymer or a propylene component Is a copolymer of propylene and another comonomer containing 70 mol% or more (preferably containing a propylene component of 80 mol% or more), or a mixture of two or more kinds selected from these resins. .

Examples of copolymers of propylene containing at least 70 mol% of a propylene component with other comonomers include ethylene-propylene random copolymer, ethylene-propylene block copolymer, propylene-butene random copolymer, ethylene-propylene-butene Examples include random copolymers.

The melting point of the base resin is 155 ° C. or higher in order to increase the heat resistance of the final EPP molded article and / or to increase the compressive strength.
C. or higher, more preferably 158.degree. C. or higher, and most preferably 160.degree. C. or higher. The upper limit of the melting point is usually about 170 ° C.

In order to increase the compressive strength of the final EPP molded article, the present base resin has a tensile yield strength of 31M.
It is at least Pa, but preferably at least 32 MPa. Although the upper limit of the tensile yield strength is not particularly specified, it is usually at most 45 MPa. In addition, the present base resin is used to prevent bubbles from breaking during the formation of bubbles during the production of foamed particles, and further to prevent bubbles from breaking during the heating during molding in a mold. The tensile elongation at break is 20% or more, preferably 100% or more, more preferably 200 to 1000%. The above tensile yield strength and tensile elongation at break are both JIS
K 6758 (1981).

Further, the present base resin has a molecular weight distribution (Mw / Mn) of 4 in order to lower the molding steam temperature during in-mold molding, even if the expanded particles are made of a high-melting base resin. It is 4 or more, but preferably 4.5 to 10. The molecular weight distribution was determined by the GPC method using a weight average molecular weight M in terms of polystyrene measured using the following apparatus and conditions.
It is a value calculated from w and the number average molecular weight Mn. <GPC measuring device> Apparatus: WATERS 150C Column: TOSO GMHHR-H (S) HT Detector: RI detector for liquid chromatogram <Measurement conditions> Solvent: 1,2,4-trichlorobenzene Measurement temperature: 145 ° C Flow rate: 1.0 ml / min Sample concentration: 2.2 mg / ml Injection volume: 160 microliter Calibration curve: Universal Calibration Analysis program: HT-GPC (Ver. 1.0)

The base resin is a melt flow rate (JIS K6758 (1981)) abbreviated as MFR.
Year)) is preferably from 1 g / 10 min to 60 g / 10 min. If the MFR is less than 1 g / 10 minutes, the effect of lowering the molding steam temperature during in-mold molding may be insufficient. The MFR is 60 g /
If the time exceeds 10 minutes, the obtained in-mold molded article may be fragile. From such a viewpoint, the MF of the base resin is
R is more preferably from 10 g / 10 min to 50 g / 10 min.

The base resin having the above-mentioned properties of the present invention is one of those sold as a polypropylene resin, and thus can be easily obtained on the market. The base resin having the above-mentioned properties of the present invention can be produced by various methods, and in particular, employs a slurry polymerization process or a bulk polymerization process, or a multi-stage polymerization including a slurry polymerization process or a bulk polymerization process. A process (for example, a multi-stage polymerization process of gas-phase polymerization and bulk polymerization) is adopted, and the isotactic index (the ratio of insoluble components after extraction of boiling normal heptane) is 85% by weight or more, and ¹³ C-NMR.
The mmmm pentad% by analysis is 85 to 97.5%,
The weight average molecular weight is 200,000 or more (preferably 200
000 to 550,000), and can be easily obtained by production (including post-treatment such as removal of atactic component) so that the number average molecular weight is 20,000 or more (preferably 20,000 to 53000). In this case, the obtained polypropylene resin If the (co) polymerization conditions are selected so that the content ratio of the propylene component in the solution becomes 99% by weight, the production can be more easily performed. Further, the polypropylene-based resin obtained through a slurry polymerization process or a bulk polymerization process, or a multi-stage polymerization process including a slurry polymerization process or a bulk polymerization process, is more apt than the polypropylene-based resin obtained through another polymerization process. It is suitable as the base resin of the invention. The numerical value of the molecular weight distribution can be easily increased by selecting a polymerization catalyst or blending two or more polypropylene resins having different average molecular weights. Examples of the polymerization catalyst that can be used include a homogeneous catalyst such as a metallocene catalyst or a heterogeneous catalyst such as a Ziegler-Natta type catalyst, and include a slurry polymerization process or a bulk polymerization process, or a slurry polymerization process or a bulk polymerization process. In the multi-stage polymerization process including
Ziegler-Natta type catalysts are preferred.

In the present invention, a synthetic resin and / or an elastomer other than the polypropylene resin can be added to the base resin within a range that does not impair the intended effect of the present invention. The amount of the synthetic resin and / or elastomer other than the polypropylene resin is preferably at most 35 parts by weight, more preferably at most 20 parts by weight, per 100 parts by weight of the polypropylene resin. It is particularly preferred that it is at most 10 parts by weight, most preferably at most 5 parts by weight.

Other synthetic resins other than the above-mentioned polypropylene resins include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene,
Ethylene resins such as linear ultra low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, or polystyrene, styrene-maleic anhydride copolymer, etc. Styrene resins and the like are exemplified.

The elastomer may be ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1-butene rubber, styrene-butadiene rubber or its hydrogenated product, isoprene rubber, neoprene rubber, nitrile rubber, or styrene-butadiene block. Elastomers such as copolymer elastomers and hydrogenated products thereof are exemplified.

The base resin may contain various additives as long as the desired effects of the present invention are not impaired. Such additives include, for example, antioxidants, UV inhibitors, antistatic agents, flame retardants,
Examples thereof include a metal deactivator, a pigment, a dye, a nucleating agent, and a bubble regulator. Examples of the cell regulator include inorganic powders such as zinc borate, talc, calcium carbonate, borax, and aluminum hydroxide. These additives are preferably used in a total amount of 20 parts by weight or less, more preferably 5 parts by weight or less per 100 parts by weight of the base resin. These additives are usually used in the minimum necessary amount. In addition, these additives are used, for example, when cutting the strands extruded by an extruder to produce the polypropylene resin particles used in the present invention (hereinafter sometimes referred to as “the present resin particles”). Can be contained in the present resin particles by adding and kneading to the present base resin that has been melted.

The resin particles of the present invention were obtained by melting the base resin in an extruder, cutting the extruded strands, and quenching the strands immediately after extrusion when manufacturing the resin particles. Are preferred. Such quenched resin particles can efficiently perform surface modification described below. The quenching of the strand immediately after the extrusion is carried out immediately after the strand is extruded, preferably by 50%.
It can be carried out by placing in water adjusted to not more than 40 ° C., more preferably in water adjusted to not more than 40 ° C., most preferably in water adjusted to not more than 30 ° C. The strand that has been sufficiently cooled is pulled out of the water and cut into appropriate lengths to form the present resin particles of a desired size. The resin particles are usually adjusted to have a length / diameter ratio of 0.5 to 2.0, preferably 0.8 to 1.3, and have an average weight per piece (chosen at random). The average value per 200 pieces measured simultaneously is adjusted to be 0.1 to 20 mg, preferably 0.2 to 10 mg.

The foamed particles of the present invention are produced by impregnating the present resin particles with a foaming agent and then foaming the resin particles. The foamed particles of the present invention obtained in this way have the same melting point of the foamed particles of the present invention and the base resin, and the same heat dissipation and apparent density of the high-temperature endothermic curve peak of the foamed particles described below, As compared with foamed particles obtained by using a polypropylene resin different from the base resin used in the present invention, an in-mold molded article can be obtained even when steam at a lower temperature is used.

Further, it is preferable that the expanded particles of the present invention have been subjected to surface modification described below. The foamed particles on which the surface modification has been performed are preferable because the in-mold molding can be performed at a lower temperature than the foamed particles on which the surface modification has not been performed. In particular, when the present resin particles are used, the surface modification effect is excellent.

The surface-modified foamed particles are obtained by dispersing the present resin particles in a dispersion medium in which an organic peroxide is present, and dispersing the obtained dispersion (hereinafter, also referred to as a dispersion) in the present resin. A surface in which the surface of the resin particles is modified by decomposing the organic peroxide while maintaining a temperature lower than the melting point of the base resin of the particles and at which the organic peroxide is substantially decomposed. It can be produced by obtaining modified particles (hereinafter sometimes referred to as “surface-modified particles”) and then foaming the surface-modified particles into particles. The foamed particles thus obtained are excellent in heat-fusibility, and can be fused between the foamed particles with low-temperature steam. The expanded particles are filled in a mold and heated with steam to obtain an EPP molded body having excellent heat resistance and / or rigidity.

The dispersion medium used for producing the surface-modified particles is generally an aqueous medium, preferably water, and more preferably ion-exchanged water. Any solvent or liquid that does not dissolve and can disperse the present resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol, and the like. The aqueous medium includes a mixture of water and an organic solvent such as the alcohol.

As the organic peroxide, various kinds of conventionally known organic peroxides, for example, isobutyl peroxide [50 ° C. /
85 ° C], cumyl peroxy neodecanoate [55 ° C
/ 94 ° C], α, α'-bis (neodecanoylperoxy) diisopropylbenzene [54 ° C / 82 ° C], di-
n-propyl peroxydicarbonate [58 ° C / 94
° C], diisopropyl peroxydicarbonate [56
C / 88C], 1-cyclohexyl-1-methylethyl peroxyneodecanoate [59C / 94C], 1,
1,3,3-tetramethylbutyl peroxy neodecanoate [58 ° C / 92 ° C], bis (4-t-butylcyclohexyl) peroxydicarbonate [58 ° C / 92 °
° C], di-2-ethoxyethyl peroxydicarbonate [59 ° C / 92 ° C], di (2-ethylhexylperoxy) dicarbonate [59 ° C / 91 ° C], t-hexylperoxy neodecanoate [63 ° C / 101 ° C],
Dimethoxybutyl peroxydicarbonate [64 ° C /
102 ° C.], di (3-methyl-3-methoxybutylperoxy) dicarbonate [65 ° C./103° C.], t-butyl peroxy neodecanoate [65 ° C./104
° C], 2,4-dichlorobenzoyl peroxide [74
° C / 119 ° C], t-hexylperoxypivalate [71 ° C / 109 ° C], t-butylperoxypivalate [73 ° C / 110 ° C], 3,5,5-trimethylhexanoyl peroxide [77 ° C / 113 ° C], octanoyl peroxide [80 ° C / 117 ° C], lauroyl peroxide [80 ° C / 116 ° C], stearoyl peroxide [80 ° C / 117 ° C], 1,1,3,3-tetramethylbutyl Peroxy 2-ethylhexanoate [8
4 ° C / 124 ° C], succinic peroxide [87 ° C
/ 132 ° C], 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane [83 ° C / 11
9 ° C], 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate [90 ° C / 138
° C], t-hexylperoxy-2-ethylhexanoate [90 ° C / 133 ° C], t-butylperoxy-2
-Ethylhexanoate [92 ° C / 134 ° C], m-toluoylbenzoyl peroxide [92 ° C / 131
° C], benzoyl peroxide [92 ° C / 130 ° C],
t-butyl peroxyisobutyrate [96 ° C./136
° C], 1,1-bis (t-butylperoxy) -2-methylcyclohexane [102 ° C / 142 ° C], 1,1-
Bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane [106 ° C / 147 ° C], 1,1-
Bis (t-hexylperoxy) cyclohexane [10
7 ° C / 149 ° C], 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane [109
° C / 149 ° C], 1,1-bis (t-butylperoxy) cyclohexane [111 ° C / 154 ° C], 2,2-
Bis (4,4-dibutylperoxycyclohexyl) propane [114 ° C / 154 ° C], 1,1-bis (t-butylperoxy) cyclododecane [114 ° C / 153
° C], t-hexylperoxyisopropyl monocarbonate [115 ° C / 155 ° C], t-butylperoxymaleic acid [119 ° C / 168 ° C], t-butylperoxy-3,5,5-trimethylhexanoate [119
° C / 166 ° C], t-butyl peroxylaurate [1
18 ° C / 159 ° C], 2,5-dimethyl-2,5-di (m-toluoylperoxy) hexane [117 ° C / 1
56 ° C.], t-butyl peroxyisopropyl monocarbonate [118 ° C./159° C.], t-butyl peroxy-2-ethylhexyl monocarbonate [119 ° C. /
161 ° C.], t-hexylperoxybenzoate [1
19 ° C./160° C.], 2,5-dimethyl-2,5-di (benzoylperoxy) hexane [119 ° C./158
° C]. The temperature on the left side in [] immediately after each of the above organic peroxides is a one-hour half-life temperature described later, and the temperature on the right side is a one-minute half-life temperature described later. The organic peroxides may be used alone or in combination of two or more, usually in an amount of 0.01 to 100 parts by weight of the present resin particles.
It is necessary to add 10 to 10 parts by weight, preferably 0.05 to 5 parts by weight, more preferably 0.1 to 3 parts by weight in the dispersion medium.

In the dispersion comprising the above-mentioned organic peroxide, the present resin particles and the dispersion medium, if the weight ratio of the present resin particles / dispersion medium is too large, uniform surface modification of the present resin particles may not be performed. There is. In that case, some of the surface-modified particles that have undergone excessive reforming are mixed, which causes a large number of modified resin particles to fuse together in a closed container during the next foaming step. Then, there is a possibility that it becomes a large lump and cannot be discharged out of the closed container. From such a viewpoint, the weight ratio of the present resin particles / dispersion medium is preferably 1.3 or less.
2 or less are more preferable, 1.1 or less are still more preferable,
Most preferably, it is 1.0 or less. However, if the weight ratio is too small, effective low-temperature moldability may not be imparted to the obtained foamed particles unless the amount of the organic peroxide used in the present resin particles is increased. An increase in the amount of the organic peroxide leads to an increase in cost. In order to further reduce the use amount of the organic peroxide, the weight ratio of the present resin particles / dispersion medium is preferably 0.6 or more,
More preferably, it is 0.7 or more.

In general, radicals generated by an organic peroxide have three types of chain transfer functions of hydrogen abstraction, addition, and β decay. In the present invention, among these three functions, those having a particularly large addition effect, that is, those generating oxygen radicals during decomposition are particularly preferable, and among them, peroxide having a carbonate structure is most preferable. When the organic peroxide is used, a chain transfer agent or the like can be used in combination as needed (previously contained in the present resin particles or / and added in a dispersion medium). It is.
The oxygen radical is a radical of oxygen alone,
It means an oxygen radical to which an organic group generated by decomposition of an organic peroxide is bonded.

Heretofore, the following methods of using organic peroxides for polypropylene have been known. The organic particles are uniformly impregnated with the organic peroxide and the crosslinking aid, and the organic peroxide is decomposed at a temperature exceeding the melting point of the polypropylene to crosslink the polypropylene. A composition containing polypropylene and an organic peroxide is uniformly melt-kneaded in an extruder at a temperature exceeding the melting point of polypropylene to uniformly decompose the organic peroxide, thereby obtaining a polypropylene having a narrow molecular weight distribution. (JP-A-3-152136). Polypropylene particles are uniformly impregnated with an organic peroxide and a cross-linking aid, and the organic peroxide is decomposed at a temperature lower than the melting point of the polypropylene to introduce a long-chain branched or cross-linked structure into the polypropylene, thereby increasing the melt tension of the polypropylene. (JP-A-11-80262). The polypropylene having the increased melt tension is then melt-kneaded with a foaming agent in an extruder and used for extrusion foaming. The composition containing the polypropylene, the organic peroxide and the maleic anhydride is uniformly melt-kneaded in an extruder at a temperature exceeding the melting point of the polypropylene and graft-polymerized. Conventional methods of using organic peroxides are as follows.In order to obtain expanded particles having excellent heat-fusibility, prior to the production of the expanded particles, a polypropylene-based resin is dispersed in a dispersion medium containing an organic peroxide. While dispersing the particles, the dispersion is decomposed by maintaining the dispersion at a temperature lower than the melting point of the base resin of the polypropylene resin particles and at a temperature at which the organic peroxide is substantially decomposed. This is different from the method of the present invention in which the surface of the polypropylene resin particles is modified to obtain substantially non-crosslinked surface-modified particles.

In the present invention, the organic peroxide is substantially decomposed at a temperature lower than the melting point of the base resin. Therefore, the one-hour half-life temperature of the organic peroxide (the constant temperature at which the amount of active oxygen is reduced to half the initial amount in one hour when the organic oxide is decomposed at a certain temperature) is determined by the present base material. It is preferred that the resin has a Vicat softening point (JIS K 6747-1981, the same applies hereinafter) or less. If the one-hour half-life temperature of the organic peroxide used exceeds the Vicat softening point of the base resin, a high temperature higher than the melting point of the base resin is required to rapidly decompose the peroxide. And, in some cases, it is not preferable because it cannot be substantially decomposed at a temperature lower than the melting point of the base resin. When the peroxide is substantially decomposed at a high temperature equal to or higher than the melting point of the base resin, the peroxide is decomposed while penetrating deep into the resin particles. Since the material resin is largely decomposed as a whole regardless of the surface or inside, depending on the case, there is a possibility that only foamed particles that cannot be used for molding can be obtained,
Further, even if molding can be performed, the mechanical properties of the finally obtained EPP molded article may be greatly reduced.

In consideration of the above, it is preferable that the organic peroxide used in the method of the present invention has a one-hour half-life temperature that is at least 20 ° C. lower than the Vicat softening point of the base resin. 30 ° C below the Vicat softening point of the base resin
More preferably, the temperature is low. The one-hour half-life temperature is preferably equal to or higher than the glass transition temperature of the present base resin.
C., more preferably 50 to 90C. The above glass transition temperature is JIS K
According to 7121-1987, the condition adjustment of the test piece is “when a glass transition temperature is measured after performing a certain heat treatment”, and means the midpoint glass transition temperature obtained by heat flux DSC. Further, it is preferable that the peroxide is substantially decomposed in the dispersion medium in which the present resin particles are present at a temperature lower than the Vicat softening point of the present base resin, and is 20 ° C. higher than the Vicat softening point of the present base resin. It is more preferable to substantially decompose at a low temperature or more, and it is further preferable to substantially decompose at a temperature of 30 ° C. or more lower than the Vicat softening point of the base resin. In the present invention, the organic peroxide is a one-minute half-life temperature of the organic peroxide (when the amount of active oxygen is reduced to half the original amount in one minute when the organic peroxide is decomposed at a constant temperature). It is particularly preferable to maintain the temperature in a temperature range of ± 30 ° C. for 10 minutes or more to substantially decompose. If the decomposition is to be performed at a temperature lower than [1 minute half-life temperature -30 ° C.], it takes a long time to decompose, so that the efficiency is deteriorated. Conversely, [1 minute half-life temperature +30
[° C.], the decomposition may be rapid and the efficiency of the surface modification may be reduced. In addition, 1 minute half-life temperature ± 30 ° C
Holding for 0 minutes or more facilitates substantial decomposition of the organic peroxide. The longer the retention time in the range of a half-life temperature of ± 30 ° C. for one minute, the more reliably the organic peroxide can be decomposed, but longer than a certain time is no longer necessary. Longer times than necessary will lead to lower production efficiency.
The holding time in the above temperature range should normally be no more than 60 minutes. To decompose the organic peroxide, first prepare the dispersion adjusted to a temperature at which the organic peroxide is not easily decomposed, and then heat the dispersion to the decomposition temperature of the organic peroxide. Good. At this time, the heating rate may be selected so that the temperature is maintained within a range of a half-life temperature of ± 30 ° C. for 1 minute or more, but stopped at an arbitrary temperature within a range of a half-life temperature of ± 30 ° C. for 1 minute. More preferably, the temperature is maintained for 5 minutes or more. As the optional temperature at that time, a temperature within a half-life temperature of 1 minute ± 5 ° C. is most preferable.

The term "substantially decompose" means that the organic peroxide used is decomposed until the active oxygen content becomes 50% or less of the initial value, but the active oxygen content is 30% or less of the initial value. The active oxygen content is preferably decomposed to 20% or less of the initial amount, more preferably the active oxygen amount is reduced to 5% or less. The above-mentioned half-life temperature of the organic peroxide is adjusted by using a solution relatively inert to radicals (for example, benzene or mineral spirit) to prepare a 0.1 mol / L organic peroxide solution. Then, it is sealed in a glass tube replaced with nitrogen, immersed in a thermostat set at a predetermined temperature, and thermally decomposed to be measured.

In the present invention, the resin particles, the surface-modified particles, the foamed particles and the EPP molded product obtained therefrom are preferably substantially non-crosslinked. In producing the above-mentioned surface-modified particles, the crosslinking does not substantially proceed because no crosslinking aid or the like is used in combination. In addition, being substantially non-crosslinked is defined as follows. That is, regardless of the base resin, the present resin particles, the surface-modified particles, the foamed particles, and the EPP molded product, each was used as a sample (1 g of the sample was used per 100 g of xylene), and immersed in boiling xylene for 8 hours. JIS Z 880 that specifies network screens
1 (1966), the mixture is quickly filtered through a wire mesh having a mesh of 74 μm, and the weight of the boiling xylene-insoluble matter remaining on the wire mesh is measured. When the proportion of the insoluble content is 10% by weight or less of the sample, it is referred to as substantially non-crosslinked, but the proportion of the insoluble content is preferably 5% by weight or less of the sample,
It is more preferably at most 3% by weight, most preferably at most 1% by weight. The smaller the proportion of the insoluble matter, the easier it is to reuse. The insoluble content P (%) is represented by the following equation. P (%) = (M ÷ L) × 100 where M is the weight (g) of the insoluble matter, and L is the weight (g) of the sample.

The present resin particles are prepared by dispersing the present resin particles or surface-modified particles in a dispersing medium in a closed container in the presence of a foaming agent, and heating the resin particles or surface-modified particles to the present resin particles or surface-modified particles under heating conditions. After the step of impregnating the resin particles (foaming agent impregnating step), the resin particles or the surface-modified particles and the dispersion medium are discharged into the low-pressure zone at a temperature at which the expanded particles are generated when the pressure is released. Step of obtaining (resin particle foaming step)
(Hereinafter referred to as “dispersion medium releasing foaming method”).

In the present invention, a surface modifying step for forming the above-mentioned surface-modified particles, and a foaming step of obtaining foamed particles from the surface-modified particles (foaming agent impregnating step + resin particle foaming step)
It is possible to carry out the above-mentioned surface modification step by adding a predetermined amount of the above-mentioned organic peroxide having an appropriate decomposition temperature to a dispersion medium in a closed container, although it is possible to carry out the above-mentioned step in a different apparatus. Then, the surface-modified particles are impregnated with a foaming agent in the same container and then subjected to a foaming step by a usual dispersion medium release foaming method to obtain foamed particles from the surface-modified particles. In the foaming step, the weight ratio of the resin particles / dispersion medium is 0.5 or less, preferably 0.5 to 0. 0, from the viewpoint of preventing fusion of the surface-modified particles in the closed container.
It is preferably set to 1. The weight ratio of the resin particles / dispersion medium in the surface modification step is 0.6 to 1.3.
When the surface modification step and the foaming step are performed in the same container, the weight ratio of the resin particles / the dispersion medium in the foaming step is set to 0.5 or less. The dispersion medium may be added to the container after the quality process.

In the above-mentioned surface-modified particles, and finally the foamed particles and EPP molded articles obtained therefrom, alcohol having a molecular weight of 50 or more produced by the decomposition of the peroxide contains about several hundred ppm to several thousand ppm. May be included. When bis (4-t-butylcyclohexyl) peroxydicarbonate shown in Examples described later is used as such an alcohol, Pt-butylcyclohexanol is the surface modification of the present invention. May be contained in the porous particles. Other alcohols can be included if other peroxides are used. Examples of such alcohols include isopropanol, S-butanol, 3-methoxybutanol, 2-ethylhexylbutanol, and t-butanol.

In the dispersion medium releasing foaming method, it is preferable to add a dispersant to the dispersion medium so that the heated resin particles or surface-modified particles in the container do not fuse with each other in the container. As such a dispersing agent, any dispersing agent may be used as long as it prevents fusion of the present resin particles or surface-modified particles in a container, and can be used regardless of whether it is organic or inorganic. Therefore, a finely divided inorganic substance is preferable. For example, natural or synthetic clay minerals such as amsunite, kaolin, mica, and clay, aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate,
Iron oxide or the like can be used alone or in combination of several kinds.

Further, in the dispersion medium releasing foaming method, the dispersing power of the dispersant is enhanced (even if the amount of the dispersant added is reduced, the present resin particles or the surface-modified particles can be fused in a container. It is preferred to add a dispersion enhancer (to prevent) to the dispersion medium. Such a dispersion enhancer is an inorganic compound that can be dissolved in at least 1 mg or more in 100 cc of water at 40 ° C., wherein at least one of an anion and a cation of the compound is divalent or trivalent. is there. Such inorganic substances include, for example, magnesium chloride, magnesium nitrate, magnesium sulfate, aluminum chloride, aluminum nitrate, aluminum sulfate,
Examples thereof include iron chloride, iron sulfate, and iron nitrate.

Usually, the resin particles or surface-modified particles 100
The dispersant is used at about 0.001 to 5 parts by weight, and the dispersion enhancer is used at about 0.0001 to 1 part by weight per part by weight.

The foaming agent used in producing the foamed particles of the present invention includes aliphatic hydrocarbons such as propane, butane, hexane and heptane; cycloaliphatic hydrocarbons such as cyclobutane and cyclohexane; and chlorofluoromethane. , Trifluoromethane, 1,2-difluoroethane, 1,2,2,
Organic physical foaming agents such as halogenated hydrocarbons such as 2-tetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride, and so-called inorganic physical foaming agents such as nitrogen, oxygen, air, carbon dioxide, and water are exemplified. . An organic physical foaming agent and an inorganic physical foaming agent can be used in combination. In the present invention, those mainly containing one or more inorganic physical blowing agents selected from the group consisting of nitrogen, oxygen, air, carbon dioxide and water are particularly preferably used. Among them, nitrogen and air are preferable in consideration of the stability of the apparent density of the expanded particles, the environmental load, the cost, and the like.
As the water used as the foaming agent, water (including ion-exchanged water) used as a dispersion medium for dispersing the surface-modified particles in the closed container may be used as it is.

In the above-mentioned dispersion medium release foaming method, the filling amount of the physical foaming agent into the container is appropriately selected according to the type of the foaming agent to be used, the foaming temperature and the apparent density of the intended foamed particles. For example, in the case where nitrogen is used as a foaming agent and water is used as a dispersion medium, for example, the pressure in a closed container in a stable state immediately before the start of foaming, that is, the pressure (gauge pressure) in the space inside the closed container. But 0.6-6MP
It is preferable to select so as to be a. In general, it is desirable that the smaller the apparent density of the target expanded particles, the higher the pressure in the space in the container, and the higher the apparent density of the target expanded particles, the lower the pressure in the space is. There is a tendency.

In the present invention, the above-mentioned dispersion medium release foaming method is employed, and the apparent density is from 10 g / L to 500 g / L and the DSC by differential scanning calorimetry (heat flux differential scanning calorimetry, hereinafter the same) of the foamed particles is used. It is preferable to produce expanded particles in which the peak of the endothermic curve peak (high-temperature peak) exists on the higher temperature side than the peak of the endothermic curve peak (intrinsic peak) derived from the heat of fusion of the base resin in the curve. Such expanded particles are high in closed cells and suitable for molding. In the case of the present invention, the calorie at the high temperature peak of the obtained expanded particles is 10 J / g to 60 J / g.
When the calorific value of the high-temperature peak is less than 10 J / g, the obtained E
The compression strength of the PP molded product tends to be insufficient. Also 60
When it exceeds J / g, the effect of reducing the molding temperature is low. In the present invention, the heat quantity of the high temperature peak is particularly 12 J /
g to 58 J / g are preferred. Further, the calorie of the high-temperature peak is preferably 10 to 60% with respect to the sum of the calorie of the high-temperature peak and the calorie of the specific peak, and 20 to 50%.
Is more preferable. Further, it is preferable that the sum of the heat quantity of the high-temperature peak and the heat quantity of the specific peak is 40 J / g to 150 J / g. In this specification, the calorific value of the high-temperature peak and the calorific value of the specific peak both mean an endothermic amount, and the numerical value is expressed as an absolute value.

The calorie at the high temperature peak of the foamed particles was determined by measuring 2 to 10 mg of the foamed particles at room temperature (10 to 10 mg) using a differential scanning calorimeter.
(A 40 ° C.) to 220 ° C. at a rate of 10 ° C./min, a unique endothermic curve peak (specific peak) a derived from the heat of fusion of the base resin observed in the first DSC curve shown in FIG. Calorie (endothermic amount) of endothermic curve peak (high-temperature peak) b where a vertex appears higher than the temperature at which the vertex appears
And corresponds to the area of the high-temperature peak b, and can be specifically determined as follows. First, DS
A straight line (α-β) connecting a point α on the C curve corresponding to 80 ° C. and a point β on the DSC curve corresponding to the melting end temperature T of the foamed particles is drawn. Next, a straight line parallel to the vertical axis of the graph is drawn from a point γ on the DSC curve corresponding to a valley between the above-mentioned specific peak a and the high-temperature peak b, and a point intersecting the straight line (α-β) is defined as σ. . The area of the high-temperature peak b is the area of the curve surrounded by the high-temperature peak b portion of the DSC curve, the line segment (σ-β), and the line segment (γ-σ) (the hatched portion in FIG. 1). Area, which corresponds to the calorific value of the hot peak. The melting end temperature T refers to the intersection of the DSC curve on the high temperature side of the high temperature peak b and the high temperature side baseline. Further, the sum of the heat quantity of the high-temperature peak and the heat quantity of the specific peak corresponds to the area of a portion surrounded by the straight line (α-β) and the DSC curve. When measuring the intrinsic peak and the high-temperature peak of the expanded particles by the differential scanning calorimeter as described above, the weight per expanded particle was 2 mg.
If the weight is less than 2 mg to 10 mg, a plurality of foamed particles having a total weight of 2 mg to 10 mg may be used as they are for measurement, and if the weight per foamed particle is 2 mg to 10 mg, one foamed particle may be used. It may be used for measurement as it is, and when the weight per foamed particle exceeds 10 mg, the weight obtained by cutting one foamed particle into a plurality of pieces is 2%.
One cut sample of 10 mg to 10 mg may be used for the measurement. However, this cut sample is obtained by cutting one foamed particle using a cutter or the like, but upon cutting, the surface of the foamed particle originally possessed is not cut off, and each cut sample is cut. It is preferable that the cut particles are cut so as to have the same shape as much as possible, and in each cut sample, the surface area of the expanded particles remaining without being cut off has the same area as much as possible. For example, when the weight per foamed particle is 18 mg, if the foamed particles directed in any direction are cut horizontally from the center in the vertical direction, two cut samples of about 9 mg having almost the same shape are obtained, In each of the cut samples, the surface of the foamed particles having the powder from the beginning is left as it is, and the surface area is almost the same in each cut sample. One of the two cut samples thus obtained may be used for the measurement of the unique peak and the high-temperature peak as described above. In this specification, when simply referred to as "high-temperature peak of expanded particles" without any notice, it refers to the calorific value of the high-temperature peak obtained by the above measurement, which is the surface layer of expanded particles described later. The calorie of the hot peak for the portion and the calorie of the hot peak for the inner foam layer are different.

The high-temperature peak b is observed in the first DSC curve measured as described above. Cool down to around (40-50 ° C), then 10 ° C again
Second D obtained when the temperature is raised to 220 ° C./min.
It is not observed in the SC curve, but only an intrinsic peak a corresponding to an endotherm during melting of the base resin as shown in FIG. 2 is observed. In addition, the temperature of the peak of the intrinsic peak a appearing in the first DSC curve of the expanded particles is usually [Tm-5 ° C] to [Tm + 5 ° C] based on the melting point (Tm) of the base resin.
(Most commonly [Tm-4 ° C.] to [Tm
m + 4 ° C.]. Further, the temperature at the top of the high-temperature peak b appearing in the first DSC curve of the expanded particles is:
When the melting point (Tm) of the base resin is used as a reference, usually, [Tm
+ 5 ° C] to [Tm + 15 ° C] (most commonly appears in the range of [Tm + 6 ° C] to [Tm + 14 ° C]). Also, the temperature at the apex of the intrinsic peak a observed in the second DSC curve of the expanded particles (the temperature corresponding to the melting point of the base resin) is usually represented by [ Tm−2 ° C.] to [Tm + 2 ° C.].

As described above, the expanded particles of the present invention are obtained by DSC
In the measurement, those having a crystal structure in which a high-temperature peak appears on the first DSC curve are preferable, but the calorific value of this high-temperature peak is strongly affected by the difference between the melting point of the resin and the foaming temperature. The high-temperature peak calorific value of the foamed particles acts as a factor that determines the minimum fusion temperature, particularly with respect to the fusion between the foamed particles. As used herein, the term "minimum fusing temperature" means the temperature at which the minimum saturated steam pressure necessary for the foamed particles to fuse in the mold is given. The high-temperature peak calorific value is closely related to this minimum fusion temperature. It tends to be lower. The value of the high-temperature peak calorific value is strongly influenced by the level of the foaming temperature applied to the resin at the stage of producing the foamed particles,
When the same base resin is used, the high-temperature peak calorific value tends to be smaller when the foaming temperature is higher than when the foaming temperature is lower.

However, when an EPP molded article is obtained by using expanded particles having a small high-temperature peak calorific value, the minimum fusion temperature tends to be relatively low, but the strength and physical properties such as the compressive strength (rigidity) of the EPP molded article. Tends to decrease relatively. On the other hand, when an EPP molded body is obtained by using expanded particles having a large high-temperature peak calorie, the strength physical properties such as the compressive strength of the EPP molded body tend to be relatively high, but the minimum fusion temperature becomes relatively high. However, as described above, there is a problem that steam at a high pressure is required when producing an EPP molded body. In other words, the most preferred expanded particles are those having the opposite properties such as a low minimum fusion temperature and relatively high strength properties such as the compressive strength of the EPP molded article. The expanded particles of the present invention are those in which the minimum fusion temperature is effectively lowered even when the high-temperature peak calorific value is large. In particular, the expanded particles obtained from the surface-modified particles have a greater effect of lowering the minimum fusion temperature. When an EPP molded article is produced using the expanded particles of the present invention, an EPP molded article having excellent mechanical properties such as heat resistance and / or compressive strength can be obtained.

The expanded particles having a high-temperature peak in the DSC curve are heated to a temperature higher than the melting end temperature (Te) of the base resin when the present resin particles or surface-modified particles are dispersed in a dispersion medium in a closed container and heated. Without stopping at an arbitrary temperature (Ta) within a range of not less than 20 ° C. lower than the melting point (Tm) of the base resin and less than the melting end temperature (Te), and the temperature (Ta) is sufficient. For about 10 to 60 minutes, and then adjust the temperature from 15 ° C. lower than the melting point (Tm) to an arbitrary temperature (Tb) in the range of melting end temperature (Te) + 10 ° C., and stop at that temperature If necessary at the temperature for a further sufficient time, preferably about 10 to 60 minutes,
After the holding, the resin particles or the surface-modified particles can be obtained by a method in which the resin particles or the surface-modified particles are released from the closed container under a low pressure and foamed. The melting point (Tm) is defined as the resin particles 2 to 4
mg as a sample, a differential scanning calorimetry was performed on the resin particles in the same manner as in obtaining the DSC curve of the expanded particles as described above, and the second DSC
The melting end temperature (Te) is the temperature at the apex of the endothermic curve peak a peculiar to the base resin observed in the curve (one example of which is shown in FIG. 2). The point of intersection (β) between the curve and the high-temperature side baseline (B _L ). The endothermic curve peak that appears in the second DSC curve for the present resin particles usually appears as one endothermic peak, assuming that it is a peak based on the melting of the polypropylene resin. However, 2
In the case of a mixture of the above-mentioned polypropylene resins, two or more endothermic peaks may be rarely observed. In that case, (perpendicular to the horizontal axis) vertical axis parallel to the graph along with passing an apex of each peak draw straight lines, the baseline B _L from the top of the peak in each linear
The length of the peak on the straight line having the longest length is defined as Tm. However, if two or more straight lines of the same length exist and the longest straight line cannot be specified,
The peak of the highest temperature peak is defined as Tm.

The magnitude of the amount of heat at the high temperature peak in the expanded particles mainly depends on the temperature Ta, the holding time at the temperature, the temperature Tb, the holding time at the temperature, and the rising time of the resin particles when producing the expanded particles. Depends on temperature rate. The calorific value of the high-temperature peak of the expanded particles tends to increase as the temperature Ta or Tb falls within the above-mentioned temperature range and as the holding time increases. Normal,
The heating rate during heating (average heating rate from the start of heating to the start of temperature holding) is 0.5 to 5 ° C./min. By repeating the preliminary experiment in consideration of these points, it is possible to easily know the production conditions of the expanded particles having the desired high-temperature peak calorific value.

The temperature range described above is an appropriate temperature range when an inorganic physical foaming agent is used as a foaming agent. When an organic physical foaming agent is used in combination, the appropriate temperature range shifts to a lower temperature side than the above-mentioned temperature range depending on the type and amount used.

The apparent density (g / L) of the expanded particles is as follows:
The weight (g) of the expanded particles is represented by the apparent volume (L) of the expanded particles.
It is calculated by dividing. The apparent volume of the expanded particles is
Approximately foamed particles left at 23 ° C under atmospheric pressure for 48 hours or more
5 g in 100 cm of water at 23 ° C ^ThreeMessilin housed
From the volume excluded when submerged in water in the
Apparent volume (cm^Three) And read this one liter
It can be obtained by converting to a place. For this measurement, expandable particles
Weight of 0.5000 to 10.0000 g and expanded particles
Apparent volume is 50-90cm^ThreeMultiple shots
Foam particles are used.

It should be noted that the surface-modified particles obtained above
The measurement results show that the foamed particles that can be molded with low-temperature steam (hereinafter, referred to as “surface-modified foamed particles”) have the following structural specificity.

As a result of DSC measurement of the foamed particles, the surface-modified foamed particles show a different tendency from the foamed particles obtained by the conventional method. Was divided into inner foam layer without the surface layer portion and surface layer portion of the expanded beads was measured melting point, conventional expanded beads melting point it is an internal foam layer of the melting point (Tm _s) of the surface layer portion of the foamed particles (Tm whereas there is a property of always higher compared to _i), surface modified blowing particles become towards the surface layer portion melting point (Tm _s) is lower than the melting point of the inner foam layer (Tm _i) Was observed. Therefore, the surface modified foam particles, Tm _s is preferably less 0.05 ° C. or higher than Tm _i, more preferably 0.1 ° C. or more lower, still more preferably 0.3 ° C. or more lower.

The melting point of the surface layer portion of the foamed particles (Tm _s) is
The surface layer portion of the foamed particles was cut out, 2 to 4 mg were collected, and the same operation as in the measurement of the high-temperature peak calorie of the foamed particles was performed except that this was used as a sample. Means temperature. The melting point (Tm _i ) of the internal foamed layer of the foamed particles was calculated from the above-mentioned high-temperature peak calorie of the foamed particles except that 2 to 4 mg were cut out from the inside of the foamed particles so as not to include the surface layer portion and collected as a sample. It means the temperature at the top of the intrinsic peak a of the second DSC curve obtained by performing the same operation as the measurement.

When the high-temperature peak calorie was measured separately for the surface layer portion of the foamed particles and the internal foamed layer not including the surface layer portion, the conventional foamed particles showed a high-temperature peak calorie (ΔH _s ) of the surface layer portion of the foamed particles. While the relationship with the calorific value (ΔH _i ) of the high-temperature peak of the internal foamed layer was such that ΔH _s ≧ ΔH _i × 0.87, the surface-modified foamed particles had ΔH _s ≧ ΔH _i × 0.87.
It was observed that _s <ΔH _i × 0.86. Therefore,
The surface-modified foamed particles preferably have ΔH _s <ΔH _i × 0.86, more preferably ΔH _s <ΔH _i × 0.80, and ΔH _s <ΔH _i × 0.75. It is more preferable that ΔH _s <ΔH _i × 0.70, and it is most preferable that ΔH _s <ΔH _i × 0.60. ΔH _s is ΔH _s ≧ ΔH _i × 0.25
It is preferable that The surface-modified expanded particles have ΔH _s <
ΔH _i × 0.86 makes it possible to perform in-mold molding at a lower temperature than foamed particles that have not been surface-modified, and ΔH _s
The effect becomes larger as the value becomes smaller. Note that ΔH _s is
1.7 J / g to 60 J / g, preferably 2 J / g
/ G to 50 J / g, more preferably 3 J / g.
４５45 J / g, more preferably 4 J / g〜4
Most preferably, it is 0 J / g.

The high-temperature peak calorie of the surface layer portion of the expanded particles is as follows:
The surface layer portion of the foamed particles is cut out, 2 to 4 mg are collected, and this is used as a sample. Also,
The high-temperature peak calorie of the internal foamed layer of the foamed particles was cut out from the inside of the foamed particles so as not to include the surface layer portion, and was 2 to 4 m.
g can be determined by performing the same operation as in the measurement of the high-temperature peak calorie of the expanded particles described above, except that this is used as a sample.

The method of preparing a sample when measuring the melting point and the high-temperature peak calorie by dividing the foamed particles into a surface layer portion and an internal foamed layer not containing the surface layer portion is described below. The surface layer portion of the foamed particles may be subjected to measurement by slicing the surface layer portion using a cutter knife, a microtome or the like and collecting the surface layer portion. However, the surface of the foamed particles always exists on the entire surface of the surface layer portion of the sliced foamed particles,
On the back side of the surface layer part of the sliced expanded particles,
200 μm from the surface of the expanded particles to the center of gravity of the expanded particles
Is sliced from one or more randomly selected locations on the surface of the foamed particles so as not to include a portion exceeding. On the back surface of the surface layer portion of the sliced foamed particles, when a portion exceeding 200 μm is included from the surface of the foamed particles toward the center of gravity of the foamed particles, the inner foamed layer is contained in a large amount, and the melting point of the surface layer portion and There is a possibility that the high-temperature peak calorie cannot be measured accurately. When the surface layer portion obtained from one foamed particle is less than 2 to 4 mg, the above operation may be repeated using a plurality of foamed particles to collect a required amount of the surface layer portion. On the other hand, the inner foaming layer that does not include the surface layer portion of the foamed particles has an entire surface of the foamed particles such that a portion between the surface of the foamed particles and 200 μm from the surface of the foamed particles toward the center of gravity of the foamed particles is not included. What is necessary is just to provide the measurement of a melting point and a high-temperature peak calorific value using what cut | disconnected the surface layer part from. However, when the size of the foamed particles is too small and the 200 μm portion is cut off from the above surface to remove the internal foamed layer, the surface of the foamed particles and the surface of the foamed particles are directed toward the center of gravity of the foamed particles. 1
When the surface layer portion is cut off from the entire surface of the foamed particles so as not to include the portion between 00 μm and the surface portion of the foamed particles is used as the internal foamed layer, and the internal foamed layer still disappears, An inner foam layer is obtained by cutting off the surface layer from the entire surface of the foam particles so as not to include a portion between 50 μm from the surface of the foam particles toward the center of gravity of the foam particles. When the amount of the inner foam layer obtained from one foam particle is less than 2 to 4 mg, the above operation may be repeated using a plurality of foam particles to collect a necessary amount of the inner foam layer.

The micro-thermal analysis system “2990” manufactured by TIA Instruments Japan, Inc. was applied to the surfaces of the foamed particles of the surface-modified foamed particles and the non-surface-modified foamed particles obtained by the conventional method. Differential thermal analysis (μDT) from 25 ° C. to 200 ° C. at a rate of 10 ° C./sec.
When A) was performed, the melting onset temperature of the surface of the surface-modified foamed particles (the melting onset temperature in claim 4) was lower than the melting point of the base resin, whereas the conventional method was used. It was found that the melting start temperature of the surface of the obtained non-surface-modified foamed particles was 5 ° C. higher than the melting point of the base resin. The melting start temperature mentioned here is the above-mentioned μD
Baseline (B) in μDTA curve based on TA
L) means the temperature at which the μDTA curve began to change downward (specific heat per hour began to change).

The micro-thermal analysis system “2990” manufactured by TIA Instruments Japan was applied to the surfaces of the foamed particles of the surface-modified foamed particles and the non-surface-modified foamed particles obtained by the conventional method. Differential thermal analysis (μDT) from 25 ° C to 200 ° C at a rate of 10 ° C / sec.
When A) was performed, the extrapolation / melting start temperature (the extrapolation / melting start temperature in claim 5) of the surface of the surface-modified expanded particles is a temperature not higher than the [melting point + 4 ° C.] of the base resin. On the other hand, it was found that the extrapolated melting start temperature of the surface of the unmodified surface expanded particles obtained by the conventional method was higher than the melting point of the base resin by 8 ° C. or more. The extrapolation melting start temperature here means a straight line obtained by extending the base line (BL) of the μDTA curve to a higher temperature side and a tangent drawn from each point on the μDTA curve higher than the melting start temperature. The temperature at the intersection of the tangent line (TL) at which the angle between the tangent line and the straight line obtained by extending the base line (BL) to the high temperature side is the maximum.

In the in-mold molding of the foamed particles, since the fusion of the foamed particles is performed between the surfaces of the foamed particles, it is significant that only the surface of the foamed particles is thermally analyzed. It seems impossible to determine the tendency of only the surface of the expanded particles to start melting by the DSC method. ΜDTA makes it possible.
In addition, the heating rate in μDTA is set to 10 ° C. per second, which is close to the heating rate when heating the foamed particles during actual in-mold molding (such a fast heating rate). Is difficult with the DSC method). Therefore, it is significant to perform the analysis at a temperature rising rate similar to the actual in-mold forming. For this reason, the present invention employs micro-differential thermal analysis (μDTA) on the surface of the expanded particles. Although the melting start temperature based on this measurement may not indicate the melting start temperature in a strict sense, the tendency of the temperature of the melting start temperature and the tendency of the molding temperature are well matched. ing. In the present invention, the extrapolation melting start temperature is defined separately from the above-mentioned melting start temperature. Both observe almost the same tendency except that the extrapolated melting onset temperature is a slightly higher value due to the difference in the calculation method. However, since the extrapolated melting start temperature has less error, the reproducibility is more excellent.

FIGS. 3 and 4 show the relationship between μ and the surface of the expanded particles.
FIG. 4 shows an example of a DTA curve, and a method for obtaining a melting start temperature and an extrapolation melting start temperature of the surface of the expanded particles will be described with reference to these drawings. FIG. 3 shows a melting point of 161 ° C. and MFR1.
1 shows an example of a μDTA curve for each of a surface of a surface-modified expanded particle and a surface of a non-surface-modified expanded particle using a propylene homopolymer of 8 g / 10 min as a base resin. In FIG. 3, a curve Cm is an example of a μDTA curve with respect to the surface of the surface-modified foamed particles.
The point m is the melting start temperature, and the point Pme is the extrapolation melting start temperature at the intersection of the baseline (BL) and the tangent (TL). On the other hand, the curve Cnm is an example of a μDTA curve for the foamed particles that are not surface-modified,
The Pnm point on the curve Cnm is the melting onset temperature,
The nme point is defined by the baseline (BL) and the tangent (T
Extrapolation melting start temperature at the intersection with L). Pm, Pme, Pnm and Pnm in FIG.
31 ° C, 135 ° C, 168 ° C and 171 ° C. FIG. 4 is a surface-modified foamed particle having a base resin of a propylene homopolymer having a melting point of 161 ° C. and an MFR of 18 g / 10 minutes (the surface modification is slightly smaller than that of FIG. 3).
3 shows an example of a μDTA curve for the surface of FIG. In FIG. 4, the curve Cm is a μDTA curve, and Pm on the curve Cm
The point is the melting onset temperature, and the Pme point is the extrapolation melting onset point at the intersection of the baseline (BL) and the tangent (TL). Pm and Pme in FIG. 4 are 140 ° C. and 142 ° C., respectively.

In the micro-differential thermal analysis, the foamed particles are fixed to the sample stage of the apparatus (if one foamed particle is too large as it is, for example, cut into half and fixed to an appropriate size). Then, the probe tip center (the part to be brought into contact with the foamed particle surface has a tip of 0.2 μm each in the vertical and horizontal directions) descends toward a randomly selected portion on the surface of the foamed particle and makes contact with the foamed particle surface It is performed in a state where it is made to be. As the melting onset temperature and extrapolation onset temperature of the expanded particle surface by the micro-differential thermal analysis, arithmetic mean values of eight points excluding the maximum value and the minimum value from the measurement results at ten different measurement points are adopted. When there are a plurality of maximum values and a plurality of minimum values, arithmetic mean values of several points other than those are adopted. In addition, when the measured values at the average of 10 points are all the same, or when only the maximum value and the minimum value are obtained and the difference between the maximum value and the minimum value is within 10 ° C., The average value is used. When only the maximum value and the minimum value are obtained and the difference between the maximum value and the minimum value exceeds 10 ° C., the measurement is further performed on 10 points on different surfaces, and the same procedure as described above is performed. Then, the arithmetic mean value is obtained, and the obtained value may be used. If the condition is still not met, the same operation is repeated. ΜDTA above
The results indicate that the reduction in the onset of melting temperature on the surface of the expanded particles and / or the reduction in the onset of extrapolation on the surface of the expanded particles contributes to the reduction in the minimum fusion temperature required during molding. For the foamed particles that can be molded with low-temperature steam, the melting start temperature of the foamed particle surface based on the above measurement is equal to or lower than the melting point (Tm) of the base resin, but is preferably equal to or lower than [Tm-5 ° C], [Tm-10 ° C] or lower, more preferably [Tm-15 ° C] or lower, particularly preferably [Tm-16 ° C] to [Tm-50 ° C], and [Tm- 17 ° C] to [Tm-35
° C]. Further, the foamed particles that can be molded with low-temperature steam have an extrapolated melting start temperature of [Tm + 4 ° C.] or less based on the above measurement,
[Tm-1 ° C.] or lower, preferably [Tm-6]
° C] or lower, and [Tm-17 ° C]
~ [Tm-50 ° C], more preferably [Tm
-18 ° C] to [Tm-35 ° C]. In addition, such a decrease in the minimum fusing temperature is caused by the fact that the melting point of the base resin is 158 ° C. or higher and E
This is particularly effective in the case of PP particles. The lower the melting start temperature of the foamed particle surface, the greater the contribution to the lowering of the minimum fusion temperature required during molding, but if the melting start temperature is too low, the compressive strength of the resulting molded article, etc. There is a possibility that the mechanical properties and the like may be reduced.

When MFR was measured, it was observed that the value of MFR of the surface-modified foamed particles was equal to or larger than the value of MFR of the present resin particles before surface modification. . The MFR value of the surface-modified expanded particles is preferably 1.2 times or more, more preferably 1.5 times or more, the MFR value of the present resin particles before surface modification. Most preferably, it is 8-3.5 times.
The value of the MFR of the surface-modified foamed particles is determined in consideration of the heat resistance of the EPP molded article and the foaming efficiency at the time of producing the foamed particles.
It is preferably set to 0.5 to 150 g / 10 min, more preferably to 1 to 60 g / 10 min, and even more preferably to 10 to 80 g / 10 min.

The MFR of the expanded particles refers to the expanded particles of 2
A press sheet having a thickness of 0.2 mm to 1 mm is prepared on a heating press machine adjusted to a temperature of 00 ° C., and a sample is cut out from the sheet into a pellet or a rod. This is a value measured by the same method as the measurement. In measuring the MFR of the foamed particles, it is necessary to avoid the inclusion of bubbles and the like in the sample in order to obtain an accurate measurement value. If the inclusion of bubbles is inevitable, the same sample can be repeatedly prepared up to three times to prepare a press sheet for defoaming with a heating press board.

Further, the surface-modified foamed particles are subjected to a surface modification step.
In particular, an oxygen radical is used as the above-mentioned organic peroxide.
When using the generated organic peroxide,
A modified surface containing some oxygen is formed by the addition
It is. This depends on the surface of the
Analysis of the surface of the EPP molded body manufactured by
ing. Specifically, manufactured from surface-modified expanded particles
Surface of the EPP molded body (ie, the surface of the surface-modified foamed particles)
(Substantially the same) and conventional unmodified foam particles
Each of the surfaces of the EPP molded body manufactured from the
As a result of comparison by R measurement (total reflection absorption measurement method), surface modification
The surface of the EPP molded body made from expanded particles has a new
1033cm^-1Make sure there is a difference in absorption around
Addition of oxygen alone or addition of oxygen-containing functional groups
Or it was recognized that there was a change such as insertion. concrete
Has 1166cm^-1Peak heights for absorption of
Absorption peak height for molded articles from surface-modified expanded particles
The same absorption peak height)
Of the surface of the molded article obtained from the surface-modified expanded particles
33cm ^-1The height of the absorption peak near
1033cm of the surface^-1Higher than the height of the nearby absorption peak
Has become. In addition, EDS (E)
Elemental analysis using an energy dispersive analyzer)
As a result, regarding the ratio of oxygen to carbon, in the case of surface-modified foamed particles,
0.2 (mol / mol) compared to the conventional
In the case of foam particles, it was 0.09 (mol / mol).
From the above, the amount of organic peroxide slightly
It is obvious that a modified surface containing oxygen is formed.
You. The formation of such a modified surface is due to the steam permeability during molding.
It is believed that transients are advantageous. From this perspective, the table
The surface-modified foamed particles meet the above-mentioned EDS on the surface of the foamed particles.
The ratio of oxygen to carbon is preferably 0.15 or more.
Good.

In addition to the surface-modified expanded particles, the surface-modified expanded particles are made of the base resin, and the high-temperature peak calorific value of the surface layer of the expanded particles is reduced and / or the melting start temperature of the expanded particles surface or / and the surface of the expanded particles is increased. It is presumed that the lowering of the extrapolation melting start temperature effectively reduces the minimum fusion temperature.

After aging under the atmospheric pressure, the foamed particles of the present invention may be made to have a higher expansion ratio by increasing the internal pressure of the cells as necessary, and then heating using steam or hot air. Is possible.

The EPP molded body is filled with foamed particles in a mold which can be heated and cooled and which can be opened / closed and sealed, after increasing the internal pressure of the cell if necessary, and supplying saturated steam to the inside of the mold. The foamed particles can be manufactured by employing a batch-type molding method in which the foamed particles are heated, expanded, fused to each other, and then cooled and taken out of the mold. As a molding machine used in the batch molding method, there are already a large number of molding machines in the world, and although they vary slightly depending on the country, the pressure resistance is 0.41 MPa (G) or 0.45 MPa (G). There are many things. Therefore, the pressure of the saturated steam when expanding and fusing the expanded particles is preferably 0.45 MPa (G) or less, more preferably 0.41 MPa (G) or less. . In addition, the EPP molded body increases the internal pressure of the bubbles as necessary, and then continuously supplies the foamed particles between belts that move continuously up and down in the passage, thereby forming a saturated steam supply region (heating region). ), The expanded particles are expanded and fused together, then cooled by passing through a cooling area, and then the obtained molded body is taken out from the passage and cut into appropriate lengths sequentially (continuous molding method ( For example, Japanese Patent Application Laid-Open Nos. 9-104026 and 9-10
No. 4027 and a molding method described in JP-A-10-180888). In this method, the inside of the passage is inside the mold. In addition, when increasing the internal pressure of the foamed particles, put the foamed particles in a closed container,
What is necessary is just to let the pressurized air permeate the foamed particles by leaving the pressurized air in the container for an appropriate period of time. The gas supplied under pressure can be used without any problem as long as it is an inorganic gas that does not liquefy or solidify under the required pressure, but can be used without any problem. In addition, nitrogen, oxygen, air, carbon dioxide, and argon are selected. Alternatively, those containing two or more inorganic gases as main components are particularly preferably used, and among them, nitrogen and air are preferable in consideration of environmental load and cost.

The internal pressure P (MP
a) is measured by the following operation. Here, an example is shown in which the internal pressure of the EPP particles is increased using air. First, the foamed particles used for molding are placed in a closed container, and pressurized air is introduced into the container (usually so that the air pressure in the container maintains a range of 0.98 to 9.8 MPa in gauge pressure). ) In the state of supply, the inside pressure of the foamed particles is increased by allowing the air to penetrate into the foamed particles by leaving the foamed particles to stand for an appropriate time. The foamed particles having a sufficiently increased internal pressure are supplied into a mold of a molding machine. The internal pressure of the foamed particles is determined by using a part of the foamed particles immediately before molding in the mold (hereinafter, referred to as a foamed particle group),
It is determined by performing the following operations.

Within 60 seconds after the group of expanded particles immediately before the in-mold molding with the increased internal pressure is taken out of the pressurized tank, a large number of needle holes having a size not allowing the expanded particles to pass but allowing air to freely pass are formed. 23 ° C, relative humidity 50
Move to constant temperature room at atmospheric pressure of 5%. Subsequently, the weight is read on a balance in the constant temperature room. The weight was measured by taking out the above-mentioned expanded particle group from the pressurized tank and measuring
Seconds later. The weight at this time is defined as Q (g). Subsequently, the bag is left in the constant temperature room for 48 hours. The pressurized air in the foamed particles permeates through the cell membrane with time and escapes to the outside, so that the weight of the foamed particles decreases accordingly, and 48
After time, the weight has substantially stabilized since equilibrium has been reached. After the above 48 hours, the weight of the bag is measured again,
The weight at this time is defined as U (g). Then, immediately, all of the foamed particle group is taken out of the bag in the same constant temperature chamber, and the weight of only the bag is read. Let the weight be Z (g). Any of the above weights shall be read up to 0.0001 g.
The difference between Q (g) and U (g) is defined as an increased air amount W (g), and the internal pressure P (MPa) of the expanded particles is calculated from the following equation. still,
This internal pressure P corresponds to a gauge pressure.

P = (W ÷ M) × R × T ÷ V In the above equation, M is the molecular weight of air.
Adopt a constant of 8.8 (g / mol). R is a gas constant, and is 0.0083 (MPa · L / (K · mo) here.
l) The constant of (1) is adopted. T means absolute temperature, 23
Because the atmosphere of ° C is adopted, here, 296
(K) is a constant. V means a volume (L) obtained by subtracting the volume of the base resin occupied in the expanded particle group from the apparent volume of the expanded particle group.

The apparent volume (L) of the expanded particle group is 4
Eight hours later, the entire amount of the foamed particles taken out of the bag was immediately immersed in water in a graduated cylinder containing 100 cm ³ of water at 23 ° C. in the same temperature-controlled room.
The volume Y (cm ³ ) of the expanded particle group is calculated, and the volume Y (cm ³ ) is obtained by converting the volume into liter (L) units. The apparent expansion ratio of the expanded particle group is determined by the density of the base resin (g / c).
m ³ ) by dividing the apparent density (g / cm ³ ) of the expanded particle group. In addition, the apparent density (g
/ Cm ³ ) is the above-mentioned expanded particle group weight (U (g) and Z
(Difference from (g)) by the volume Y (cm ³ ). In the above measurement, the foamed particle group weight (difference between U (g) and Z (g)) was 0.5000 to 1
A plurality of foamed particle groups having an amount of 0.0000 g and a volume Y of 50 to 90 cm ³ are used.

The internal pressure in the cells of the expanded particles is 0.00
The pressure is preferably 5 to 0.98 MPa, more preferably 0.1 to 0.98 MPa.
01 to 0.69 MPa, most preferably 0.029 to
0.49 MPa. If the internal pressure of the cells becomes too small, the secondary foaming power at the time of molding becomes insufficient. To compensate for this, the saturated steam pressure introduced into the mold at the time of molding must be set higher. On the other hand, if the internal pressure of the cells becomes too high, the secondary foaming force during molding becomes excessive, impeding the penetration of saturated steam into the molded body, and as a result, the temperature of the central part of the molded body becomes insufficient, and the mutual expansion of the foamed particles occurs. Fusing tends to be poor. Furthermore, the foamed particles of the present invention have a small decrease in the apparent volume of the foamed particles under a pressurized atmosphere, and can increase the pressure difference between the foamed particle bubbles and the external atmosphere. As a result, it is necessary to apply an internal pressure. Time can be shortened.

The apparent density of the EPP molded article produced by the above method can be arbitrarily selected depending on the purpose, but is usually 9 g.
/ L to 600 g / L. Incidentally, the apparent density of the EPP molded body is defined by JIS K7222 (1999).
Means the apparent overall density. However, the volume of the compact used for the calculation of the apparent overall density is the volume calculated from the outer dimensions, but if the shape is complicated and the calculation from the outer dimensions is difficult, then the Exclusion volume at that time is adopted.

A surface decoration material can be laminated and integrated on at least a part of the surface of the EPP molded body. A method for producing such a laminated composite type in-mold foam molded article is disclosed in US Pat. No. 5,928,776, US Pat. No. 6,096,417, US Pat.
No. 6, WO98 / 34770, WO98 / 00278
And Japanese Patent No. 3092227. Further, the insert material can be compositely integrated so that all or a part of the insert material is embedded in the EPP molded body of the present invention. A method for producing such an insert composite type in-mold foam molded article is disclosed in US Pat. No. 6,033,770 and US Pat.
No. 841, JP-A-59-127714, JP-A-3092227 and the like.

The EPP molded body produced as described above preferably has an open cell ratio of 40% or less, more preferably 30% or less, and preferably 25% or less based on Procedure C of ASTM-D2856-70. % Is most preferred. A molded article having a smaller open cell ratio has better mechanical strength.

[0073]

The present invention will be described below with reference to examples and comparative examples.

Example 1, Comparative Examples 1 and 2 Polypropylene homopolymer resin 10 selected from Table 1
0 parts by weight, zinc borate powder (cell regulator) 0.05
After adding the parts by weight and melt-kneading in the extruder, the mixture is extruded into a strand form from the extruder, and the strand is immediately
C. in water adjusted to 10 ° C., taking off while quenching, cooling sufficiently, pulling out of water, cutting strands so that length / diameter ratio becomes approximately 1.0, and averaging weight per particle Obtained 2 mg of resin particles. Then, in a 400 liter autoclave, 100 kg of the resin particles,
220 kg of ion-exchanged water at 18 ° C. (resin particle / dispersion medium weight ratio of 0.45) as dispersion medium, 0.005 kg of sodium dodecylbenzenesulfonate (surfactant), 0.3 kg of kaolin powder (dispersant) and aluminum sulfate powder (Dispersion enhancer) After 0.01 kg was charged and sealed, carbon dioxide gas was injected under pressure until the pressure in the autoclave reached 490 KPa (G). Next, the temperature was raised to a temperature lower by 5 ° C. than the foaming temperature shown in Table 2 while stirring in the closed state (average temperature raising rate: 4 ° C./min), and then the temperature was increased to 15 ° C.
Hold for minutes. Next, the temperature was raised to the foaming temperature (average temperature raising rate: 3 ° C./min) and maintained at the same temperature for 15 minutes. Immediately after the foaming temperature was reached, high-pressure carbon dioxide (foaming agent) was continuously injected into the autoclave so that the pressure in the autoclave immediately before foaming reached the pressure shown in Table 2. Next, one end of the autoclave was opened, and the contents of the autoclave were released under atmospheric pressure to obtain expanded particles. Incidentally, the pressure inside the autoclave during discharging the resin particles from the autoclave,
The release was performed while supplying carbon dioxide gas into the autoclave so as to maintain the pressure in the autoclave immediately before the release. After the obtained foamed particles are washed with water and centrifuged, they are left for 48 hours under the atmospheric pressure of a room temperature of 23 ° C. to be cured, and then the high-temperature peak calorie of the entire foamed particle, the apparent density of the foamed particle, and the like are measured. It was measured. The results are shown in Table 2.
In addition, the foamed particles obtained in Example 1 and Comparative Examples 1 and 2 are:
All were substantially non-crosslinked (boiling insolubles in xylene were all 0).

Next, the foamed particles are placed under pressurized air in a pressure vessel to apply an increased bubble internal pressure to the foamed particles. In a mold having a molding space of 250 mm × 200 mm × 50 mm, a small gap (about 1 mm) is opened without completely closing the mold (the direction of the molding space 50 mm is 5 mm).
After filling (in a state of 1 mm) and then completely closing the mold, the air in the mold was evacuated with steam and then molded at a predetermined saturated steam pressure. After molding, after water cooling until the surface pressure of the molded body in the mold becomes 59 kPa (G),
The molded body was taken out of the mold, dried at 60 ° C. for 24 hours, and cooled to room temperature (23 ° C.). Subsequently, the molded body was cured in the room for 14 days. Incidentally, the predetermined saturated steam pressure is defined as the minimum fusion temperature (minimum saturated steam pressure) shown in Table 2 by repeatedly manufacturing a molded article while changing the saturated steam pressure from 150 kPa (G) to 550 kPa (G) in steps of 10 kPa. It was measured.

The minimum fusing temperature in Table 2 is 250 m
An about 10 mm cut in the thickness direction of the molded body was cut into one side of a 250 mm x 200 mm surface of the cured molded body molded with a m x 200 mm x 50 mm mold using a cutter knife so as to divide the length by 250 mm. After the insertion, a test was conducted in which the molded body was bent from the cut portion and fractured, and the value (b / n) of the ratio (b / n) of the number (b) of the foamed particles present in the fractured surface to the number (b) of the foamed particles whose material was broken was determined. 0.50 for the first time
It means the saturated steam pressure required for molding when the above is reached. The number (n) of the foamed particles is the sum of the number of the foamed particles peeled between the foamed particles and the number (b) of the foamed particles whose material is broken in the foamed particles. In addition, (b /
The larger the value of n), the greater the bending strength and tensile strength of the molded body, which is preferable.

Further, the compressive strength of the cured body obtained at the lowest fusing temperature was measured. Table 2 shows the results. The compressive strength in Table 2 refers to a test piece obtained by cutting a molded body so as to have a length of 50 mm, a width of 50 mm, and a thickness of 25 mm (the skin of the entire surface is cut).
According to JIS Z 0234 (1976) Method A, the strain is 55 under the condition of a specimen temperature of 23 ° C. and a load speed of 10 mm / min.
%, The stress at 50% strain was read from the obtained stress-strain diagram, and this was taken as the compressive strength.

Example 1 and Comparative Examples 1 and 2 show examples in which no surface modification with an organic peroxide was performed. Example 1 is a foamed particle using a high melting point polypropylene resin having a melting point of 161 ° C. exceeding 158 ° C. as a base resin, but the molecular weight distribution of the base resin is 4.4 or more.
Since it was 1, it was possible to make the value of (b / n) 0.50 or more by molding with a small (low temperature) saturated steam pressure. Further, the tensile elongation at break of the base resin is 20
% Or more of 560%, the foamed particles obtained have excellent closed cell properties, and the tensile yield strength of the base resin is 31M.
The compressive strength of the EPP molded product obtained from the fact that it was 34 MPa or more of Pa was also relatively high in strength corresponding to the apparent density of the molded product and the high-temperature peak calorific value of the foamed particles. In Example 1, the melting point of the base resin was as high as 161 ° C., the MFR of the base resin was relatively small at 18 g / 10 min, the high-temperature peak calorie of the expanded particles was relatively large at 26 J / g, and the internal pressure was high. Is small at 197 kPa (G), and is molded at a small saturated steam pressure of 400 kPa and the value of (b / n) is 0.50 or more, even though surface modification with an organic peroxide is not performed. It can be said that the obtained molded article is a truly surprising result.

On the other hand, in Comparative Example 1 with respect to Example 1, as in Example 1, a polypropylene resin having a high melting point exceeding 158 ° C. was used as the base resin, and the tensile elongation at break, tensile yield strength and expanded particles of the base resin were increased. Was substantially the same as Example 1, but the compressive strength of the EPP molded article was slightly inferior to Example 1. Further, in Comparative Example 1, since the molecular weight distribution of the base resin was 4.1, which was less than 4.4, the molding was not performed using a much higher (high temperature) saturated steam pressure than that in Example 1 (( b / n) could not be increased to 0.50 or more. In Comparative Example 2 with respect to Example 1, as in Example 1, a high melting point polypropylene resin having a melting point exceeding 158 ° C. was used as the base resin, and the tensile elongation at break of the base resin, the tensile yield strength, and the high-temperature peak of the expanded particles. The calorific value and the minimum fusion temperature were substantially the same as in Example 1, but the molecular weight distribution of the base resin was less than 4.4.
6, and the MFR was considerably large at 63 g / 10 min, so that the compressive strength of the EPP molded article was significantly inferior to that of Example 1. The above results indicate that even if the expanded particles have a large high-temperature peak of 10 J / g or more using a polypropylene resin having a high melting point of 161 ° C. as a base resin, the molecular weight distribution of the base resin is 4.4 or more. When compared with other foamed particles having a molecular weight distribution of the base resin of less than 4.4 and having the same performance, a molded article excellent in fusion between the foamed particles with low-temperature saturated steam can be obtained. Or EPP molded articles having higher compressive strength as compared with expanded particles having the same minimum fusing temperature.

Example 2, Comparative Examples 3 to 6 Polypropylene homopolymer resin 10 selected from Table 1
0 parts by weight, zinc borate powder (cell regulator) 0.05
After adding the parts by weight and melt-kneading in the extruder, the mixture is extruded into a strand form from the extruder, and the strand is immediately
C. in water adjusted to 10 ° C., taking off while quenching, cooling sufficiently, pulling out of water, cutting strands so that length / diameter ratio becomes approximately 1.0, and averaging weight per particle Obtained 2 mg of resin particles. Then, in a 400 liter autoclave, 100 kg of the resin particles,
As a dispersion medium, 220 kg of ion-exchanged water at 18 ° C. (resin particle / dispersion medium weight ratio of 0.45), 0.005 kg of sodium dodecylbenzenesulfonate (surfactant), 0.3 kg of kaolin (dispersant), and aluminum sulfate powder ( 0.01 kg of dispersion enhancer, bis (4-t-butylcyclohexyl) peroxydicarbonate as an organic peroxide (1 hour half-life temperature 58 ° C., 1 minute half-life temperature 9)
2 ° C.), and after sealing, carbon dioxide gas was injected under pressure until the pressure in the autoclave reached 490 KPa (G).
Then, the temperature was raised to a temperature lower by 5 ° C. than the foaming temperature shown in Table 3 while stirring in the closed state (average temperature rising rate:
° C / min) and held at that temperature for 15 minutes. At the time of this temperature rise, the half-life of the used organic peroxide for 1 minute ± 30 ° C.
Was 15 minutes. Then
The temperature was raised to the foaming temperature (average heating rate: 3 ° C./min) and maintained at the same temperature for 15 minutes. Immediately after reaching the foaming temperature,
High-pressure carbon dioxide gas (foaming agent) was continuously injected into the autoclave so that the pressure in the autoclave immediately before foaming became the pressure shown in Table 3. Next, one end of the autoclave was opened, and the contents of the autoclave were released under atmospheric pressure to obtain expanded particles. The release was performed while supplying nitrogen gas into the autoclave so that the pressure in the autoclave during the release of the resin particles from the autoclave was maintained at the pressure in the autoclave immediately before the release. After the obtained foamed particles are washed with water and centrifuged, they are left to cure at room temperature of 23 ° C. under the atmospheric pressure for 48 hours, and then cured at high temperature. The high-temperature peak calorie of each layer, the melting start temperature and extrapolation melting start temperature of the foamed particle surface by μDTA described above, and the apparent density of the foamed particles were measured. Table 3 shows the results. In addition, the expanded particles obtained in Example 2 and Comparative Examples 3 to 6 were substantially non-crosslinked (boiling xylene insolubles were all 0).

Next, the foamed particles are placed under pressurized air in a pressure-resistant container to give the foamed particles an increased internal bubble pressure. In a mold having a molding space of 250 mm × 200 mm × 50 mm, a small gap (about 1 mm) is opened without completely closing the mold (the direction of the molding space 50 mm is 5 mm).
After filling and then completely closing the mold, the air in the mold was evacuated with steam, and then molded repeatedly with saturated steam in the same manner as in Example 1, Comparative Examples 1 and 2. Fusing temperature (minimum saturated steam pressure)
Was measured. Further, compressive strength of the cured compact obtained at the lowest fusion temperature was measured in the same manner as in Example 1 and Comparative Examples 1 and 2. These results are also shown in Table 3.

Example 2 and Comparative Examples 3 to 6 show examples in which surface modification with an organic peroxide was performed. Therefore, in any of the examples, a compact having a value of (b / n) of 0.50 or more was obtained by molding at a small saturated steam pressure. In particular, in Example 2, the melting point of the base resin was 161
° C, the base resin has a relatively low MFR of 18 g / 10 min, and the high-temperature peak calorie of the expanded particles is as large as 40 J / g. / N) is 0.5
The fact that zero or more compacts were obtained is a truly surprising result. This result indicates that despite the same surface modification as in Comparative Examples 3 to 6, the expanded particles of Example 1 had a smaller high-temperature peak calorie at the surface layer of the expanded particles,
Due to the fact that the melting start temperature and extrapolated melting start temperature of the foamed particle surface due to TA are reduced, the fact that the molecular weight distribution of the base resin was 4.4 or more enhanced its surface modifying effect,
It is presumed that molding became possible with lower temperature saturated steam. On the other hand, in Comparative Example 3 with respect to Example 2, the tensile yield strength of the base resin was 30 MPa, which was less than 31 MPa, even though the apparent density of the expanded particles, the high-temperature peak calorie of the expanded particles, and the internal pressure were equivalent. Thus, the compression strength of the obtained compact was lower than that of Example 2. Further, the molecular weight distribution of the base resin is less than 4.3, which is 4.3.
Therefore, the reforming effect is inferior to that of Example 1, and the value of (b / n) is set to 0.50 or more unless molded using a higher (higher) saturated steam pressure than that of Example 2. I couldn't. Further, Comparative Example 4 with respect to Example 2 shows that although the tensile yield strength and the tensile elongation at break of the base resin, the apparent density of the expanded particles, the high-temperature peak calorie of the expanded particles, and the internal pressure are equal, the base resin has 3. Molecular weight distribution is 4.
The value of (b / n) could not be increased to 0.50 or more without molding using a higher (higher temperature) saturated steam pressure than that of Example 2 because it was 4.0, which was less than 4. .

Further, Comparative Example 5 with respect to Example 2 shows that the tensile strength of the base resin, the apparent density of the expanded particles, the high-temperature peak of the expanded particles, and the internal pressure were the same, but the tensile strength of the base resin was Since the elongation at break was less than 20% and 18%, the obtained expanded particles were inferior in closed cell properties, and the compression strength of the resulting molded article was lower than that of Example 2. Furthermore, since the molecular weight distribution of the base resin is 4.0, which is less than 4.4, it is larger than that of Example 2 (high temperature).
If molding is not performed using a saturated steam pressure, the above (b /
The value of n) could not be increased to 0.50 or more. Comparative Example 6 with respect to Example 2 shows that the base resin had the same tensile yield strength and tensile elongation at break, the apparent density of the foamed particles, the high-temperature peak of the foamed particles, and the internal pressure, which were equivalent to those in Example 2. Since the molecular weight distribution of the material resin was 3.6, which is less than 4.4, and the MFR of the base resin showed a considerably large value of 63 g / 10 minutes, the minimum fusion temperature was slightly higher than that of Example 2. Although it was only high, the compressive strength of the obtained molded article was much lower than that of Example 2. The above results indicate that the surface modification with organic peroxide
Even when the expanded particles have a large high-temperature peak of 10 J / g or more using a polypropylene resin having a high melting point of 161 ° C. or more as a base resin, the molecular weight distribution is 4.
Compared with a base resin having a molecular weight distribution of less than 4.4, the base resin having a molecular weight distribution of 4 or more is superior in fusion between expanded particles with a lower temperature of saturated steam and has a higher compressive strength. This shows that a large compact can be obtained. Also, it can be seen that the lower the fusion temperature, the lower the MFR of the base resin tends to be, but the lower the compressive strength of the molded article obtained. If the tensile elongation at break of the base resin is less than 20% or the tensile yield strength of the base resin is 31M
If it is less than Pa, it can be seen that the compression strength of the obtained molded body is inferior.

[0084]

[Table 1]

[0085]

[Table 2]

[0086]

[Table 3]

[0087]

The expanded particles of the present invention have a melting point of at least 155 ° C., a tensile yield strength of at least 31 MPa, and a tensile elongation at break of 20.
% Or more and a molecular weight distribution (Mw / Mn) of 4.4 or more is a foamed particle using a polypropylene resin as a base resin, and the foamed particle is a DSC by differential scanning calorimetry.
An endothermic curve peak exists on a higher temperature side than an endothermic curve peak derived from the heat of fusion of the base resin in the curve, and the heat of fusion of the higher-temperature endothermic curve peak is 10 to 60 J / g. In addition to a high fusion rate, a molded article having excellent heat resistance and / or compressive strength can be obtained by using low-temperature saturated steam as compared with conventional foamed particles of the same type. In particular, foamed particles obtained from polypropylene-based resin particles that have undergone a step of surface treatment with an organic peroxide, together with the surface treatment effect, have a high fusion rate between the foamed particles, and have high heat resistance and / or compressive strength. An excellent effect can be obtained in that a molded article excellent in the above-mentioned properties can be obtained by using saturated steam at an extremely low temperature as compared with conventional equivalent foamed particles. Therefore, by using the expanded particles of the present invention, it is possible to provide an EPP molded article having high physical properties (high rigidity) and / or high heat resistance and / or light weight at lower cost than before.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a first DSC curve chart of expanded polypropylene resin particles having a high-temperature peak.

FIG. 2 is a diagram showing an example of a chart of a second DSC curve of polypropylene-based resin particles.

FIG. 3 is a view showing a polypropylene-based resin foamed particle obtained through a surface modification step using a polypropylene homopolymer resin having a melting point of 161 ° C. as a base resin, and obtained without a surface modification step. FIG. 4 is a diagram showing an example of a μDTA curve based on micro thermomechanical analysis for the expanded particle surface of each of the expanded polypropylene resin expanded particles.

FIG. 4 is a diagram based on micro-thermomechanical analysis of a foamed particle surface of a polypropylene-based resin foamed particle obtained through a surface modification step using a polypropylene homopolymer resin having a melting point of 161 ° C. as a base resin. It is a figure showing another example of a μDTA curve.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Keiichi Hashimoto             10-3 Satsuki-cho, Kanuma-shi, Tochigi             JSP Kanuma Research Institute F term (reference) 4F074 AA24 AB01 AB02 AB03 AB05                       BA32 BB02 BC12 CA34 CA42                       CA49 DA08 DA33

Claims (6)

[Claims] 1. A melting point of 155 ° C. or more and a tensile yield strength of 3
Expanded particles comprising a polypropylene resin having a base resin of 1 MPa or more, a tensile elongation at break of 20% or more, and a molecular weight distribution (Mw / Mn) of 4.4 or more, wherein the expanded particles are measured by differential scanning calorimetry. In the DSC curve, an endothermic curve peak exists on a higher temperature side than an endothermic curve peak derived from the heat of fusion of the base resin, and the amount of heat of fusion of the higher endothermic curve peak is 10 to 60 J / g. Polypropylene resin foam particles. 2. A melt flow rate (MF) of the base resin.
2. The expanded polypropylene resin particles according to claim 1, wherein R) is 1 to 60 g / 10 min. 3. 3. The calorific value (ΔH _s ) of the endothermic curve peak existing on the high temperature side of the surface layer portion of the expanded particles and the calorie (ΔHs) of the endothermic curve peak existing on the high temperature side of the internal foamed layer of the expanded particles.
3. The expanded polypropylene resin particles according to claim 1, wherein the relationship with _i ) is ΔH _s <ΔH _i × 0.86. 4. 4. A melting onset temperature based on micro differential thermal analysis (from 25 ° C. to 200 ° C. at a heating rate of 10 ° C./sec) at the surface of the foamed particles is not more than the melting point of the base resin. The expanded polypropylene resin particles according to any one of claims 1 to 3. 5. An extrapolation melting start temperature based on micro differential thermal analysis (a condition of a heating rate of 10 ° C./sec from 25 ° C. to 200 ° C.) on the surface of the expanded particles is [the melting point +
4 [deg.] C.] or lower, and the expanded polypropylene resin particles according to any one of claims 1 to 3. 6. The polypropylene resin foam particles according to claim 1, wherein the polypropylene resin particles are dispersed in a dispersion medium in which an organic peroxide is present, and the dispersion medium is dispersed in the polypropylene resin particles. Substantially non-crosslinked surface-modified particles having a temperature lower than the melting point of the base resin of the resin particles and being maintained at a temperature at which the organic peroxide is substantially decomposed to decompose the organic peroxide. And a foaming step of foaming the surface-modified particles using a foaming agent to obtain substantially non-crosslinked foamed particles. Expanded particles.