JP2003253003A - Method for producing surface-modified particles and method for producing expanded polypropylene resin particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-crosslinked polypropylene resin expanded particle capable of achieving fusion between expanded particles by low-temperature steam and providing a high-rigidity (high compressive strength) expanded particle molded article. And a method for industrially advantageously producing expanded non-crosslinked polypropylene resin particles from the surface-modified particles. SOLUTION: A dispersion formed by dispersing polypropylene resin particles in a dispersion medium in which an organic peroxide is present has a temperature lower than the melting point of the base resin of the resin particles and the organic peroxide is A method for obtaining substantially non-crosslinked surface-modified particles by decomposing the organic peroxide while maintaining the temperature at which the resin particles substantially decompose, wherein the resin particles /
A method for producing surface-modified particles, wherein the weight ratio of the dispersion medium is 1.3 or less.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing surface-modified particles and a method for producing expanded polypropylene resin particles.

[0002]

2. Description of the Related Art In recent years, due to the trend of integration of plastic materials, polypropylene resins are particularly excellent in mechanical strength, heat resistance, processability, price balance, and easy incineration and easy recyclability. Due to its unique characteristics, it is expanding its fields of application. Similarly, in-mold foam molding of non-crosslinked polypropylene resin foamed particles (hereinafter referred to as "EPP
A "molded product" or "foamed particle molded product" or simply "molded product" may be added with properties such as cushioning property and heat insulating property without losing the excellent properties of the polypropylene resin. Therefore, it is widely used as a packaging material, a building material, a heat insulating material, and the like.

However, in recent years, there are more and more opportunities for higher performance than ever before. For example, for automobile applications, there has been a history of being widely used in bumper core materials, door pads, pillars, tool boxes, floor-mats, etc., focusing on the excellent properties of EPP molded products. Therefore, the weight reduction of the vehicle has been demanded, and at the same time, the weight reduction of the parts constituting the vehicle has been strongly demanded. Even an EPP molded product is no exception, and there has been a demand for an even lighter EPP molded product while maintaining the rigidity, cushioning property and impact energy absorption property up to now. Further, for example, generally, as a carrying box for transporting a fish box or the like, since it has high rigidity and is inexpensive, an in-mold foam molded article of polystyrene-based resin foam particles (hereinafter referred to as “E”) is used.
The "PS molded body" was often used. However, the EPS molded body has higher impact resistance than the EPP molded body,
Due to poor heat resistance, repeated use was difficult.
In recent years, due to increasing public awareness of environmental issues and the like, many requests have been made to use EPP molded products that have excellent environmental compatibility and that can be repeatedly used. It has been desired.

By the way, in order to obtain a highly rigid EPP molded product, some improvements have been made so far, for example, the use of a highly rigid polypropylene resin as a raw material. As the high-rigidity polypropylene-based resin, generally, a propylene-based copolymer or a propylene homopolymer having a small composition ratio of comonomer such as ethylene and butene, which are copolymerization components, is known. It was possible to obtain a highly rigid EPP molded body. A technique related to this is described in, for example, [Patent Document 1]. However, in general, a high-rigidity polypropylene resin has a high melting point as well as a high rigidity, and when these high-rigidity raw materials are used, an increase in processing temperature for obtaining an EPP molded product, particularly a molding temperature It caused a rise. Conventionally, a molding machine for manufacturing an EPP molded body has a structure that can withstand a high molding temperature, that is, a structure that can withstand high-pressure steam. Rigid non-crosslinked polypropylene resin expanded particles (hereinafter referred to as "EPP particles"
Or to simply obtain "high-rigidity EPP molded article" by using "expanded particles"), when steam with a pressure higher than the pressure of the molding machine for producing the EPP molded article is required. However, there is a problem in that it is difficult to obtain a sufficient value for the fusion rate of the expanded particles. In reality, EPP moldings capable of maintaining a sufficient fusion rate can be obtained, and the number of molding machines that can handle the production is limited. Therefore, EPP particles that can be molded by steam at a lower temperature (low pressure) are obtained. A method was desired.

Conventionally, there has also been devised a method of obtaining a highly rigid EPP molded product by using a polypropylene copolymer resin composed of polypropylene and a comonomer such as ethylene or butene. In this method, the endothermic curve peak (hereinafter referred to as "high temperature" in the DSC curve by differential scanning calorimetry of foamed particles) is higher than the endothermic curve peak derived from the heat of fusion of the base resin (hereinafter sometimes referred to as "inherent peak"). It may be referred to as a “peak”), and the amount of heat of the high temperature peak is increased to a value larger than that conventionally controlled. The technology relating to this is described in, for example, [Patent Document 2] and [Patent Document 3]. When the expanded particles obtained by these methods are used, a highly rigid EPP obtained from the above highly rigid polypropylene resin is used.
As in the case of trying to obtain a highly rigid EPP molded product by using particles, in particular, the molding temperature rises.
In many cases, steam having a pressure exceeding the pressure resistance of a molding machine for manufacturing a molded body is required, and there is a problem that it is difficult to obtain a sufficient value for the fusion rate of the expanded particles.
In reality, there is a limited number of molding machines that can produce EPP compacts that maintain a sufficient fusion rate and can be used for production. Therefore, a method for obtaining EPP particles that can be compacted with lower temperature steam is desired. It had been.

The present inventors disperse the polypropylene resin particles in a dispersion medium in which an organic peroxide is present, and the dispersion medium is at a temperature lower than the melting point of the base resin of the polypropylene resin particles, and The expanded particles obtained from the substantially non-crosslinked surface-modified particles formed by decomposing the organic peroxide by holding it at a temperature at which the organic peroxide substantially decomposes, and It has been found that an EPP molded body which can achieve fusion between the foamed particles and has excellent rigidity is provided ([Patent Document 4]).

[0007]

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

[Patent Document 2] Japanese Patent No. 2886248

[Patent Document 3] Japanese Patent Laid-Open No. 11-156879

[Patent Document 4] Japanese Patent Laid-Open No. 2002-167460

[0008]

DISCLOSURE OF THE INVENTION The present invention is a non-crosslinked polypropylene which can achieve mutual fusion of expanded particles with low temperature steam and can provide a highly rigid (high compressive strength) expanded particle molded article. It is an object of the present invention to provide a method for producing surface-modified particles capable of stably producing expanded resin resin particles and a method for industrially advantageously producing non-crosslinked polypropylene resin expanded particles from the surface-modified particles.

[0009]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, the following method for producing surface-modified particles and method for producing polypropylene-based resin expanded particles is provided. (1) A dispersion formed by dispersing polypropylene resin particles in a dispersion medium in which an organic peroxide is present is at a temperature lower than the melting point of the base resin of the resin particles, and the organic peroxide is substantially A method for obtaining substantially non-crosslinked surface-modified particles by keeping the organic peroxide at a temperature at which the resin particles / dispersing medium weight ratio is 1.3 or less. And a method for producing surface-modified particles. (2) The method for producing surface-modified particles according to claim 1, wherein the resin particle / dispersion medium weight ratio is 0.6 to 1.3. (3) The organic peroxide is decomposed by maintaining the dispersion in a temperature range of 1 minute half-life temperature ± 30 ° C. of the organic peroxide for 10 minutes or more to decompose the organic peroxide. The method for producing surface-modified particles according to 2). (4) The above-mentioned (1) to (3), wherein the organic peroxide mainly generates oxygen radicals when decomposed.
A method for producing surface-modified particles according to any one of 1. (5) The one-hour half-life temperature of the organic peroxide is not less than the glass transition point of the polypropylene resin that is the base resin of the resin particles and not more than the Vicat softening point (1) ~ The method for producing surface-modified particles according to any one of (4). (6) The method for producing surface-modified particles according to any of (1) to (5), wherein the organic peroxide is a peroxide having a carbonate structure. (7) The surface-modified particles produced by the method according to any one of (2) to (6) above are foamed with a foaming agent to obtain substantially non-crosslinked expanded particles. Method for producing expanded polypropylene resin particles. (8) A dispersion formed by dispersing polypropylene resin particles in a dispersion medium containing an organic peroxide at a resin particle / dispersion medium weight ratio of 0.6 to 1.3. Substantially non-crosslinked surface-modified particles by decomposing the organic peroxide by keeping the organic peroxide at a temperature lower than the base resin melting point of the resin particles and substantially decomposing the organic peroxide. And a foaming agent under pressure and heating conditions under a condition that the weight ratio of the resin particles / the dispersion medium is 0.5 or less with respect to the surface-modified particles in the dispersion medium. And a foaming agent impregnating step of impregnating with the foaming agent and a foaming step of resin particles in which the surface-modified particles impregnated with the foaming agent are discharged together with the dispersion medium into a low pressure zone to foam. Method for producing particles.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The polypropylene resin which is the base resin of the polypropylene resin particles used in the present invention (hereinafter sometimes referred to as "the base resin") is a polypropylene homopolymer or a propylene component. Is a copolymer of propylene containing 60 mol% or more (preferably containing 80 mol% or more of propylene component) and another comonomer, or a mixture of two or more kinds selected from these resins. .

Examples of copolymers of propylene containing 60 mol% or more of propylene component with other comonomers include ethylene-propylene random copolymers, ethylene-propylene block copolymers, propylene-butene random copolymers, ethylene-propylene-butene. Examples thereof include random copolymers.

The melting point of the base resin is 1 in order to improve mechanical properties such as compressive strength of the final EPP molded product.
The temperature is preferably 30 ° C. or higher, more preferably 135 ° C. or higher, even more preferably 145 ° C. or higher, and most preferably 158 ° C. or higher.
The upper limit of the melting point is usually about 170 ° C. Furthermore,
Considering the heat resistance of the foamed molded product and the foaming efficiency at the time of manufacturing the foamed particles, the present base resin resin has a melt flow rate (MF).
R) is preferably 0.3 to 100 g / 10 minutes, and particularly preferably 1 to 90 g / 10 minutes. The MFR is a value measured under test condition 14 of JIS K7210 (1976).

In the present invention, in the polypropylene resin particles, synthetic resin other than polypropylene resin or /
And elastomers can be added. The amount of addition of synthetic resin other than polypropylene resin or / and elastomer is 100 parts by weight of polypropylene resin,
It is preferably at most 35 parts by weight, and at most 2
It is more preferably 5 parts by weight, even more preferably at most 15 parts by weight, most preferably at most 10 parts by weight.

As synthetic resins other than polypropylene resins, high density polyethylene, medium density polyethylene,
Ethylene resin such as low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, or polystyrene. Examples thereof include styrene-based resins such as styrene-maleic anhydride copolymer.

The above-mentioned elastomers include ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1-butene rubber, styrene-butadiene rubber and hydrogenated products thereof, isoprene rubber, neoprene rubber, nitrile rubber, or styrene-butadiene block. Examples of the elastomer include copolymer elastomers and hydrogenated products thereof.

The base resin of the present invention may contain various additives as long as the intended effect of the present invention is not impaired. Such additives include, for example, antioxidants, UV inhibitors, antistatic agents, flame retardants,
Examples thereof include metal deactivators, pigments, dyes, nucleating agents, and bubble control agents. 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, particularly 5 parts by weight or less, per 100 parts by weight of the base resin.
In addition, these additives are used, for example, in the extruder when the polypropylene resin particles used in the present invention (hereinafter sometimes referred to as “the present resin particles”) are produced by cutting strands extruded by the extruder. It can be contained in the present resin particles by adding and kneading to the present base resin melted in step 1.

As the present resin particles for obtaining the surface-modified particles, the present base resin is melted in an extruder and the extruded strands are cut to produce the present resin particles. Those obtained by quenching are preferred. With the resin particles thus rapidly cooled,
The surface modification can be efficiently performed. Quenching of the strands immediately after extrusion is controlled immediately after extrusion of the strands, preferably in water adjusted to 50 ° C or lower, more preferably in water adjusted to 40 ° C or lower, most preferably 30 ° C or lower. It can be done by putting it in the water. Then, the sufficiently cooled strand is pulled out from water and cut into an appropriate length to obtain the 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 an average weight per one (randomly selected. The average value of 200 pieces simultaneously measured) is adjusted to 0.1 to 20 mg, preferably 0.2 to 10 mg.

The method for producing expanded beads according to the present invention comprises a surface modification step and an expansion step (expanding agent impregnating step + expanding resin particles). In the surface modification step, while dispersing the resin particles in the dispersion medium in which the organic peroxide is present,
The obtained dispersion (hereinafter, also referred to as a dispersion) is maintained at a temperature lower than the melting point of the base resin of the resin particles and at a temperature at which the organic peroxide is substantially decomposed, The surface of the resin particles is modified by decomposing to obtain substantially non-crosslinked surface-modified particles. The surface-modified particles thus obtained are foamed with a foaming agent in the subsequent foaming step to be converted into substantially non-crosslinked expanded particles. The expanded beads obtained in this way have excellent heat-sealing properties, and the steam-bonding at low temperature allows the expanded beads to be fused. The foamed particles can be filled in a molding die and heated with steam to obtain an EPP molded body having excellent rigidity.

The dispersion medium used in the surface modification step is generally an aqueous medium, preferably water, more preferably ion-exchanged water, but it is not limited to water and can dissolve the base resin. Any solvent or liquid that can disperse the present resin particles without being used can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol and the like. The aqueous medium includes a mixed solution of water and an organic solvent such as the alcohol.

As the organic peroxide, various conventionally known organic peroxides such as 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 / 88 ° C], 1-cyclohexyl-1-methylethylperoxy neodecanoate [59 ° C / 94 ° C], 1,
1,3,3-Tetramethylbutylperoxy 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.
-Ethyl hexanoate [92 ° C / 134 ° C], m-toluoyl benzoyl 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
[Deg.] C / 166 [deg.] C], t-butyl peroxylaurate [1
18 ° C./159° C.], 2,5-dimethyl-2,5-di (m-toluoylperoxy) hexane [117 ° C./1
56 ° C], t-butylperoxyisopropyl monocarbonate [118 ° C / 159 ° C], t-butylperoxy-2-ethylhexyl monocarbonate [119 ° C /
161 ° C.], t-hexyl peroxybenzoate [1
19 ° C / 160 ° C], 2,5-dimethyl-2,5-di (benzoylperoxy) hexane [119 ° C / 158
° C] etc. are illustrated. The temperature on the left side in [] immediately behind each of the organic peroxides is the 1-hour half-life temperature described later, and the temperature on the right side is the 1-minute half-life temperature described later. The organic peroxide may be used alone or in combination of two or more, and is generally 0.01 per 100 parts by weight of the 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 composed of the organic peroxide, the resin particles and the dispersion medium, if the weight ratio of the resin particles / dispersion medium becomes too large, uniform surface modification cannot be performed on the resin particles. There is. In that case, the surface-modified particles include particles that have undergone excessive modification, which causes a large number of the modified resin particles to fuse together in the closed container during the subsequent foaming process. As a result, it may become a large lump, and it may not be possible to discharge it outside the closed container. From such a viewpoint, in the present invention, the weight ratio of the present resin particles / dispersion medium is 1.3 or less, preferably 1.2 or less, more preferably 1.1 or less, and further preferably 1.0. It is considered as follows. However, if this weight ratio is too small, there is a possibility that sufficient low-temperature moldability cannot be imparted to the obtained expanded particles unless the amount of the organic peroxide used in the resin particles is increased. An increase in the amount of organic peroxide used leads to an increase in cost. In order to reduce the amount of the organic peroxide used, the weight ratio of the resin particles / dispersion medium is preferably 0.6 or more,
It is more preferably 7 or more.

In general, the radicals generated by the organic peroxide have three types of chain transfer actions of hydrogen abstraction, addition and β decay. In the present invention, those having a particularly large addition effect among the three effects, that is, those generating an oxygen radical upon decomposition are particularly preferable, and among them, peroxide having a carbonate structure is most preferable. When using the organic peroxide, it is possible to use a chain transfer agent or the like in combination (preliminarily contained in the resin particles or / and added to the dispersion medium and used in combination), if necessary. Is.
The oxygen radicals include radicals of simple oxygen,
It means an oxygen radical to which an organic group produced by decomposition of an organic peroxide is bonded.

Conventionally, the following utilization methods are known as the use of the organic peroxide for polypropylene. The polypropylene particles are homogeneously 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 melt-kneaded uniformly in an extruder at a temperature exceeding the melting point of polypropylene to uniformly decompose the organic peroxide, thereby obtaining polypropylene having a narrow molecular weight distribution. (JP-A-3-152136). Melt tension of polypropylene by introducing long chain branching or cross-linking structure into polypropylene by decomposing the organic peroxide at a temperature lower than the melting point of polypropylene by uniformly impregnating polypropylene particles with organic peroxide and a crosslinking aid (Japanese Patent Laid-Open No. 11-80262). This polypropylene having an increased melt tension is then melt-kneaded with a foaming agent in an extruder and used for extrusion foaming. A composition containing polypropylene, an organic peroxide and maleic anhydride is uniformly melt-kneaded in an extruder at a temperature above the melting point of polypropylene to carry out graft polymerization. In the conventional methods of using organic peroxides, in order to obtain EPP particles having excellent heat-sealing property, polypropylene resins are used in a dispersion medium in which the organic peroxide is present prior to the production of the EPP particles. While the particles are dispersed, the dispersion liquid is kept 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 to decompose the organic peroxide. By doing so, the surface of the polypropylene resin particles is modified to obtain substantially non-crosslinked surface-modified particles, which is different from the method of the present invention.

In the present invention, the organic peroxide is substantially decomposed at a temperature lower than the melting point of the base resin. Therefore, the 1-hour half-life temperature of the organic peroxide (the constant temperature when the amount of active oxygen becomes half the initial amount in 1 hour when the organic oxide is decomposed at the constant temperature) is It is preferably below the Vicat softening point of the resin (JIS K 6747-1981, the same applies hereinafter). When the 1-hour half-life temperature of the organic peroxide used exceeds the Vicat softening point of the base resin, a temperature higher than the melting point of the base resin is required to quickly decompose the peroxide. Is not preferable, and in some cases, it is not possible to substantially decompose at a temperature lower than the melting point of the present base resin, which is not preferable. When the peroxide is substantially decomposed at a temperature higher than the melting point of the base resin, the peroxide is decomposed in a state of penetrating deep into the resin particles, and thus the base group constituting the resin particles is formed. Since the material resin is largely decomposed entirely on the surface and inside, there is a possibility that only EPP particles that cannot be used for molding can be obtained in some cases, and even if molding is possible, it is finally obtained. There is a possibility that the mechanical properties of the EPP molded body may be significantly reduced. Considering the above, the organic peroxide used in the method of the present invention preferably has a 1-hour half-life temperature of 20 ° C. or more lower than the Vicat softening point of the base resin. It is more preferable that the temperature is 30 ° C. or more lower than the Vicat softening point of the resin. The 1-hour half-life temperature is preferably equal to or higher than the glass transition temperature of the base resin, more preferably 40 to 100 ° C., and 50 to 90 ° C. in consideration of handleability and the like. Is more preferable. The glass transition temperature is JIS K 7121-1.
According to 987, the condition of the test piece is measured in "when measuring the glass transition temperature after performing a certain heat treatment", and the glass transition temperature in this case is the midpoint glass transition temperature determined by the heat flux DSC. Means
Further, it is preferable that the peroxide is substantially decomposed at a temperature below the Vicat softening point of the present base resin in a dispersion medium in which the present resin particles are present, and is 20 ° C. higher than the Vicat softening point of the present base resin. It is more preferable that the resin is substantially decomposed at a low temperature as described above, and it is further preferable that the resin is substantially decomposed 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 1-minute half-life temperature of the organic peroxide (when the organic oxide is decomposed at a constant temperature,
It is particularly preferable to maintain the temperature in the range of ± 30 ° C. when the amount of active oxygen becomes half of the initial amount in 1 minute) for 10 minutes or more to substantially decompose it. [1 minute half-life temperature-
When attempting to decompose at a temperature lower than 30 ° C.], it takes a long time to decompose, and thus the efficiency becomes poor. On the contrary, if the decomposition is attempted at a temperature higher than [1 minute half-life temperature + 30 ° C.], the decomposition may be rapid and the efficiency of surface modification may be deteriorated. Further, when the half-life temperature of 1 minute ± 30 ° C. is maintained for 10 minutes or more, it becomes easy to substantially decompose the organic peroxide. The holding time in the range of the one-minute half-life temperature ± 30 ° C. allows the organic peroxide to be more reliably decomposed as the holding time becomes longer, but it is no longer necessary for a certain time or longer. A longer time than necessary will lead to a decrease in production efficiency. The holding time in the above temperature range should normally be no longer than 60 minutes. To decompose the organic peroxide, first prepare the dispersion adjusted to a temperature at which the organic peroxide is difficult to decompose, and then heat the dispersion to the decomposition temperature of the organic peroxide. Good. At this time, the heating rate may be selected so that the temperature is maintained within the range of 1-minute half-life temperature ± 30 ° C for 10 minutes or more. However, the temperature may be stopped at any temperature within the range of 1-minute half-life temperature ± 30 ° C. It is more preferable to maintain the temperature for 5 minutes or more. As the arbitrary temperature at that time, a temperature within 1 minute half-life temperature ± 5 ° C. is most preferable. The peroxide is preferably substantially decomposed at the glass transition temperature of the present base resin or higher. Considering the handling property of the peroxide, the peroxide is substantially decomposed in the range of 40 to 100 ° C. It is more preferable to cause it to decompose, and it is even more preferable to substantially decompose it in the range of 50 to 90 ° C. Also, “substantially decomposing” means decomposing until the active oxygen amount of the used peroxide becomes 50% or less of the initial amount, but decomposing until the active oxygen amount becomes 30% or less of the initial amount. It is preferable that the decomposition is performed until the amount of active oxygen becomes 20% or less of the initial amount, and it is further preferable that the amount of active oxygen is decomposed to 5% or less of the initial amount.
The half-life temperature of the organic peroxide is adjusted with a 0.1 mol / L concentration of an organic peroxide solution by using a solution relatively inactive to radicals (such as benzene and mineral spirits). Then, it is sealed in a glass tube that has been purged with nitrogen, immersed in a constant temperature bath set to a predetermined temperature, and thermally decomposed for measurement.

In the present invention, the treated particles are substantially non-crosslinked. In the present invention, since a crosslinking aid is not used in combination, crosslinking does not substantially proceed. The term "substantially non-crosslinked" is defined as follows. That is, regardless of the base resin, the present resin particles, the surface-modified particles, the EPP particles, and the EPP molded body, each of them was used as a sample (1 g of sample was used per 100 g of xylene), and after dipping in boiling xylene for 8 hours, the standard JIS Z 8801 (19) that defines the mesh screen
66), and the mixture is rapidly filtered through a wire net having a mesh of 74 μm, and the weight of the boiling xylene insoluble matter remaining on the wire net is measured. The case where the proportion of the insoluble matter is 10% by weight or less of the sample is referred to as substantially non-crosslinking, but the proportion of the insoluble matter is preferably 5% by weight or less of the sample, and is preferably 3% by weight or less. More preferably, it is most preferably 1% by weight or less. The smaller the proportion of the insoluble matter, the easier it is to reuse. The insoluble content P (%) is expressed by the following formula. P (%) = (M ÷ L) × 100 where M is the weight (g) of the insoluble matter and L is the weight (g) of the sample.

As described above, the present resin particles are subjected to decomposition of the organic peroxide to modify the surface of the present resin particles, and then are used for the production of expanded particles. The foamed particles are obtained by impregnating the surface-modified particles thus obtained with the foaming agent under heating and heating conditions while dispersing the surface-modified particles thus obtained in a dispersion medium in a closed container in the presence of the foaming agent ( (Foaming agent impregnation step), and then, the foamed particles are obtained by releasing the surface-modified resin particles and the dispersion medium into the low-pressure zone at a temperature at which foamed particles are formed when the pressure is released (resin expanded particle step) ( Hereinafter, it is preferably produced by the "dispersion medium releasing foaming method". In the present invention, the surface modification step of forming the surface modified particles and the foaming step of obtaining expanded particles from the surface modified particles (foaming agent impregnation step + resin particle foaming step) are performed by separate devices. Although it can be carried out at another time, the above-mentioned organic peroxide having an appropriate decomposition temperature is added in a predetermined amount to the dispersion medium in the closed container to carry out the above-mentioned surface modification step, and then in the same container. It is also possible to obtain expanded particles from the surface-modified particles by impregnating the surface-modified particles with a foaming agent and performing a foaming step by a usual dispersion medium releasing foaming method. In the foaming step, the weight ratio of the resin particles / the dispersion medium is 0.5 or less, preferably 0.5 to 0.1, from the viewpoint of preventing fusion of the surface-modified particles in a closed container. It is preferable. When the weight ratio of the resin particles / dispersion medium in the surface modification step is 0.6 to 1.3 and the surface modification step and the foaming step are performed in the same container, , The above resin particles in the foaming process /
In order to reduce the weight ratio of the dispersion medium to 0.5 or less, the dispersion medium may be added in the container after the surface modification step.

In the surface-modified particles of the present invention, and further in the EPP particles and EPP moldings obtained therefrom, the alcohol having a molecular weight of 50 or more produced by the decomposition of the peroxide is from several hundred ppm to several thousand. It may be contained in the order of ppm. When bis (4-t-butylcyclohexyl) peroxydicarbonate shown in the examples described later is used as such alcohol, Pt-butylcyclohexanol is used as the surface modification of the present invention. May be contained in the fine particles. Other alcohols may be included if other peroxides are used. As such alcohol,
For example, isopropanol, S-butanol, 3-methoxybutanol, 2-ethylhexylbutanol, t-
An example is butanol.

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

Further, in the above dispersion medium releasing foaming method, the dispersive power of the dispersant is strengthened (the fusion of the surface-modified particles is prevented in the container even if the amount of the dispersant added is reduced).
It is preferable to add a dispersion strengthener to the dispersion medium. Such a dispersion enhancer is an inorganic compound which can dissolve at least 1 mg or more in 100 cc of water at 40 ° C.,
An inorganic substance in which at least one of an anion and a cation of the compound is divalent or trivalent. Examples of such inorganic substances include magnesium chloride, magnesium nitrate, magnesium sulfate, aluminum chloride, aluminum nitrate, aluminum sulfate, iron chloride, iron sulfate, iron nitrate and the like.

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

Examples of the blowing agent used in the method for producing expanded polypropylene resin particles of the present invention include aliphatic hydrocarbons such as propane, butane, hexane and heptane, cycloaliphatic hydrocarbons such as cyclobutane and cyclohexane,
Organic physical blowing agents such as chlorofluoromethane, trifluoromethane, 1,2-difluoroethane, 1,2,2,2-tetrafluoroethane, halogenated hydrocarbons such as methyl chloride, ethyl chloride and methylene chloride,
So-called inorganic physical foaming agents such as nitrogen, oxygen, air, carbon dioxide, and water are exemplified. It is also possible to use an organic physical foaming agent and an inorganic physical foaming agent in combination. In the present invention, those containing, as a main component, one or more inorganic physical foaming agents selected from the group of nitrogen, oxygen, air, carbon dioxide and water are particularly preferably used. Among them, considering the stability of apparent density of expanded particles, environmental load and cost,
Nitrogen and air are preferred. 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 dispersion medium releasing foaming method, the filling amount of the physical foaming agent into the container is appropriately selected according to the kind of the foaming agent to be used, the foaming temperature and the apparent density of the foamed particles intended. For example, when nitrogen is used as the foaming agent and water is used as the dispersion medium, the pressure in the closed container in a stable state immediately before the start of foaming, that is, the pressure in the space inside the closed container (gauge pressure) But 0.6-6MP
It is preferable to select so as to be a. Usually, it is desirable that the smaller the apparent density of the target foamed particles, the higher the pressure in the space within the container, and the lower the apparent density of the target foamed particles, the lower the pressure in the space. There is a tendency.

In the present invention, the dispersion medium releasing foaming method is adopted, and the DSC is obtained by the differential scanning calorimetry of the expanded particles (heat flux differential scanning calorimetry, the same applies hereinafter) having an apparent density of 10 g / L to 500 g / L. It is preferable to produce expanded particles having an endothermic curve peak (high temperature peak) on the higher temperature side than the endothermic curve peak (inherent peak) derived from the heat of fusion of the base resin in the curve. Such expanded particles are
It is an expanded particle suitable for molding that has a high closed cell rate. In the case of the present invention, it is particularly preferable that the heat quantity of the high temperature peak in the obtained expanded particles is 2 J / g to 70 J / g. If the amount of heat at the high temperature peak is less than 2 J / g, the compression strength, energy absorption amount, etc. of the EPP molded product may be reduced. If it exceeds 70 J / g, the air pressure required in the step of increasing the air pressure in the expanded particles before molding the expanded particles may be too high or the molding cycle may be lengthened, which is not preferable. In the present invention, the amount of heat of the high temperature peak is particularly 3 J / g to 65 J /
g (more preferably 12 J / g to 58 J / g), and preferably 10 to 60% with respect to the sum of the heat amount of the high temperature peak and the heat amount of the intrinsic peak, and preferably 20 to 50.
% Is more preferable. Further, 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.
Is preferred. In addition, the heat quantity of the high temperature peak and the heat quantity of the specific peak in the present specification both mean the heat absorption quantity, and the numerical value is expressed as an absolute value.

The calorific value of the high temperature peak of the expanded beads is 10 ° C. from room temperature (10 to 40 ° C.) to 220 ° C. with 2 to 4 mg of expanded beads in a nitrogen atmosphere by a differential scanning calorimeter.
The first DS shown in Fig. 1 obtained when the temperature was raised at 1 / min.
The heat quantity (endothermic amount) of the endothermic curve peak (high temperature peak) b appearing on the higher temperature side than the temperature at which the unique endothermic curve peak (inherent peak) a derived from the heat of fusion of the base resin recognized in the C curve appears. This corresponds to the area of the high temperature peak b, and can be specifically determined as follows. First, a straight line (α-β) connecting a point α on the DSC curve corresponding to 80 ° C. and a point β on the DSC curve corresponding to the melting end temperature T of the expanded particles is drawn. Next, the above-mentioned unique peak a
A straight line parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the high temperature peak b and the high temperature peak b, and the straight line (α
Let σ be the point that intersects −β). The area of the high temperature peak b is
The curve of the high temperature peak b part of the DSC curve and the line segment (σ−
(β) and a line segment (γ-σ) (see FIG. 1)
The shaded area in Fig. 2) corresponds to the amount of heat at the high temperature peak. The melting end temperature T is the intersection of the DSC curve on the high temperature side of the high temperature peak b and the high temperature side baseline. Further, the sum of the heat quantity of the high temperature peak and the heat quantity of the specific peak is expressed by the straight line (α-β) and D
It corresponds to the area surrounded by the SC curve.

When the specific peak and the high temperature peak of the expanded particles are measured by the differential scanning calorimeter as described above, when the weight per expanded particle is less than 2 mg,
A plurality of expanded particles having a total weight of 2 mg to 10 mg may be used as they are for measurement, and when the weight per expanded particle is 2 mg to 10 mg, one expanded particle may be used as it is for measurement. If the weight per expanded particle is more than 10 mg, one cut sample obtained by cutting one expanded particle into a plurality of pieces and having a weight of 2 to 10 mg is used for the measurement. do it. However, this cut sample was obtained by cutting one foamed particle using a cutter or the like, but at the time of cutting, the surface of the foamed particle originally held was not cut and left as it was, and each cut sample was cut. It is preferable to cut evenly so that the shape is as uniform as possible and in each cut sample so that the area of the surface of the expanded particles left without being cut out is the same as much as possible. For example, when the weight per expanded particle is 18 mg, two expanded samples of approximately 9 mg having substantially the same shape can be obtained by cutting expanded particles oriented in any direction horizontally from the center in the vertical direction. In each cut sample, the surface of the expanded particles that it originally has is left as it is, and the surface area of each cut sample is almost the same. One of the two cut samples thus obtained may be used for measuring the intrinsic peak and the high temperature peak as described above. In the present specification, when simply expressed as "high temperature peak of expanded particles", it means the heat quantity of the high temperature peak obtained by the above measurement, which is the surface layer of expanded particles described later. The heat quantity of the high-temperature peak regarding the part and the heat quantity of the high-temperature peak regarding the inner foam layer are different.

Although this high-temperature peak b is recognized in the first DSC curve measured as described above, once the first DSC curve was obtained, the temperature was once increased from 220 ° C to 10 ° C / min. The temperature is lowered to around 40 ° C (40 to 50 ° C), and 1 again.
Not observed in the second DSC curve obtained when the temperature was raised to 220 ° C. at 0 ° C./min, and only the specific peak a corresponding to the endotherm at the time of melting of the base resin as shown in FIG. 2 was observed. To be The temperature at the apex of the unique peak a appearing in the first DSC curve of the expanded particles is the melting point (T
m) as a reference, usually, [Tm-5 ° C] to [Tm +
5 ° C] (most commonly [Tm-4 ° C])
Appears in the range of [Tm + 4 ° C]). Further, the temperature at the apex of the high temperature peak b appearing in the first DSC curve of the foamed particles is usually based on the melting point (Tm) of the base resin,
It appears in the range of [Tm + 5 ° C] to [Tm + 15 ° C] (most commonly, it appears in the range of [Tm + 6 ° C] to [Tm + 14 ° C]). In addition, the temperature at the apex of the unique peak a (temperature corresponding to the melting point of the base resin) observed in the second DSC curve of the expanded particles is usually [based on the melting point (Tm) of the base resin] It appears in the range of Tm-2 ° C] to [Tm + 2 ° C].

As described above, it is preferable that the EPP particles have a crystal structure in which a high temperature peak appears in the first DSC curve in the DSC measurement. Strongly influenced. EP
The high-temperature peak calorific value of P particles acts as a factor that determines the minimum fusing temperature, particularly with respect to fusing of EPP particles to each other. The minimum fusion temperature as used herein means a temperature at which the minimum saturated steam pressure required for fusion of EPP particles with each other in the mold is given. The high-temperature peak calorific value is closely related to this minimum fusion temperature, and when the same base resin is used,
A smaller high temperature peak calorific value tends to result in a lower minimum fusing temperature than a large high temperature peak calorific value. The value of this high temperature peak calorific value is strongly influenced by the high and low foaming temperatures given to the resin at the production stage of the EPP particles, and when the same base resin is used, the high temperature peak calorific value is higher than that when the foaming temperature is low. Values tend to be small.

However, EPP having a small amount of high temperature peak heat
When an EPP molded product is obtained by using particles, the minimum fusion temperature tends to be relatively low, but strength physical properties such as the compression strength (rigidity) of the EPP molded product tend to be relatively lowered. On the other hand, when an EPP molded product is obtained by using expanded particles having a large amount of high-temperature peak heat, the strength properties such as the compression strength of the EPP molded product tend to be relatively high, but the minimum fusion temperature becomes relatively high. As described above, there arises a problem that steam of high pressure may be required when manufacturing the EPP molded body. That is, the most preferable expanded particles are expanded particles having contradictory properties such that the minimum fusion temperature is low and the strength properties such as compressive strength of the EPP molded product are relatively high. The expanded beads obtained by the method of the present invention have the minimum fusion temperature effectively reduced. When a foamed particle molded product is produced using the expanded beads, a molded product having practical strength in mechanical properties such as compressive strength can be obtained.

The expanded particles having a high temperature peak in the DSC curve have a melting end temperature (Te) of the base resin constituting the surface-modified particles when the surface-modified particles are dispersed in a dispersion medium and heated in a closed container. ) Without raising the temperature above, stop at any temperature (Ta) within a range of 20 ° C. lower than the melting point (Tm) of the base resin and less than the melting end temperature (Te) and stop at that temperature (Ta). Sufficient time, preferably 10-6
Hold for about 0 minutes, then adjust to a temperature (Tb) in the range of 15 ° C lower than the melting point (Tm) to the end temperature of melting (Te) + 10 ° C, stop at that temperature, and further at that temperature if necessary. It can be obtained by a method in which the surface-modified particles are discharged for a sufficient period of time, preferably about 10 to 60 minutes, and then discharged from the closed container under a low pressure to foam.
The melting point (Tm) means the differential scanning calorimetry of the resin particles in the same manner as the DSC curve of the expanded particles as described above using 2 to 4 mg of the resin particles as a sample. This is the temperature at the apex of the endothermic curve peak a peculiar to the base resin observed in the second DSC curve (one example of which is shown in FIG. 2) obtained by this, and the melting end temperature (T
e) refers to the intersection (β) of the DSC curve on the high temperature side of the specific endothermic curve peak a and the high temperature side baseline ( _BL ). The endothermic curve peak that appears in the second DSC curve for the present resin particles usually appears as one endothermic curve peak, assuming that it is a peak based on the melting of the polypropylene resin. However, in the case of being composed of a mixture of two or more polypropylene resins, rarely two or more endothermic peaks may be observed. In that case, a straight line that passes through the apex of each peak and is parallel to the vertical axis of the graph (orthogonal to the horizontal axis) is drawn, and the apex of the peak is measured from each peak to the baseline _BL
Is measured, and the apex of the peak on the straight line having the longest length is defined as Tm. However, the longest straight line is 2
When there is more than one, the peak of the peak on the highest temperature side is set to Tm.

Further, the magnitude of the amount of heat of the above-mentioned high-temperature peak in the expanded beads is mainly due to the temperature Ta and the holding time at the temperature and the temperature Tb and the holding time at the temperature and the rise with respect to the resin particles when the expanded beads are produced. Depends on temperature rate. The calorific value of the high temperature peak of the expanded beads tends to increase as the temperature Ta or Tb falls within the above 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 maintenance) 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 beads exhibiting 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 the foaming agent. When the organic physical foaming agent is used in combination, the appropriate temperature range shifts to the lower temperature side than the above temperature range depending on the type and the amount used.

The apparent density (g / L) of the expanded beads is
The weight (g) of the expanded particles is expressed by the apparent volume (L) of the expanded particles.
It is calculated by dividing. The apparent volume of expanded particles is
Foamed particles left at 23 ° C and atmospheric pressure for more than 48 hours
5 g of water at 23 ° C 100 cm ³Mescillin containing
From the excluded volume when submerged in the water in the dar, the expanded particles
Apparent volume of (cm³) And read this
It can be obtained by converting to rank. Foamed particles for this measurement
0.5000 to 10.0000 g, and expanded particles
Apparent volume of 50-90 cm³The amount of
Foam particles are used.

As described above, the EPP particles which can be formed by low temperature steam and which are obtained from the surface-modified particles obtained by decomposing the organic peroxide to modify the surface of the resin particles have the following structure. It has been found from the measurement results that it has specificity.

As a result of the DSC measurement of the expanded particles, the expanded particles obtained by the method of the present invention show a tendency different from that of the expanded particles obtained by the conventional method. When the melting point was measured by dividing the surface layer portion of the expanded particles and the internal foam layer not including the surface layer portion, the conventional expanded particles had a melting point (Tm
_s ) had the property of always being higher than the melting point (Tm _i ) of the internal foam layer, whereas the expanded particles obtained by the method of the present invention had a melting point (Tm _s ) of the surface layer portion. It was observed that the melting point was lower than the melting point (Tm _i ) of the inner foam layer. As the expanded particles that can be molded by low-temperature steam, Tm _s is preferably lower than Tm _i by 0.05 ° C. or more, more preferably 0.1 ° C. or more, and 0.3 ° C.
More preferably, it is lower than the above.

The melting point (Tm _s ) of the surface layer of the expanded beads is
The surface layer portion of the expanded beads was cut out, 2 to 4 mg were collected, and this was used as a sample. Means temperature. The melting point (Tm _i ) of the internal foam layer of the expanded particles was measured by cutting out from the inside of the expanded particles so that the surface layer portion was not included, collecting 2 to 4 mg, and using this as a sample. Means the temperature at the apex of the unique peak a of the second DSC curve obtained by performing the same operation as.

Further, the surface layer portion of the expanded particles and the surface layer portion are included.
The high temperature peak calorific value was measured by dividing the inner foam layer.
However, the conventional expanded particles have a high temperature pit at the surface layer of the expanded particles.
Calorie (ΔH_s) And the amount of heat at the high temperature peak of the internal foam layer
(ΔH_i) Is ΔH_s≧ ΔH_iX 0.87
Foams obtained by the method of the present invention, while having properties
For particles, ΔH_s<ΔH_iObserved to be x 0.86
It was For expanded particles that can be molded with low temperature steam, ΔH
_s<ΔH_i× 0.86 is preferable, ΔH _s<Δ
H_iX0.80 is more preferable, and ΔH_s<ΔH
_i× 0.75 is more preferable, ΔH_s<ΔH_i
X 0.70 is particularly preferred, and ΔH _s<ΔH_i×
Most preferably, it is 0.60. Also, ΔH_sIs
ΔH_s≧ ΔH_iIt is preferably × 0.25. ΔH_s
<ΔH_iX 0.86, so the surface is modified
In-mold molding becomes possible at a lower temperature than that of non-foamed particles. ΔH
_sThe smaller the value, the greater the effect. In addition, ΔH_sIs
It is preferably 1.7 J / g to 60 J / g, and 2 J
/ G to 50 J / g is more preferable, and 3 J / g
To 45 J / g is more preferable, and 4 J / g to 4
Most preferably, it is 0 J / g.

The high temperature peak calorific value of the surface layer of the expanded beads is
It can be determined by performing the same operation as in the measurement of the high-temperature peak calorific value of the expanded particles, except that the surface layer portion of the expanded particles is cut out and 2 to 4 mg are collected and used as a sample. Also,
The high-temperature peak calorific value of the internal foam layer of the expanded particles is 2 to 4 m when cut out from the inside of the expanded particles so as not to include the surface layer portion.
It can be determined by performing the same operation as the above-mentioned measurement of the high temperature peak calorific value of the expanded particles except that g is collected and used as a sample.

The method for measuring the melting point and high temperature peak calorie by dividing the above-mentioned expanded particles into the surface layer portion and the inner foam layer not containing the surface layer portion is as follows. As for the surface layer portion of the expanded beads, the surface layer portion may be sliced with a cutter knife, a microtome or the like, and the surface layer portion may be collected and used for the measurement.
However, the surface of the foamed particles is always present on the entire surface of the surface layer portion of the sliced foamed particles, but on the back surface of the surface layer portion of the sliced foamed particles, the surface of the foamed particles faces from the center of gravity of the foamed particles. Randomly selected on the surface of the expanded particles so that the area exceeding 200 μm is not included 1
Sliced from one or more locations. When the back surface of the surface layer portion of the sliced foamed particles includes a portion exceeding 200 μm from the surface of the foamed particle toward the center of gravity of the foamed particle, a large amount of the internal foamed layer is contained, and the melting point of the surface layer portion and There is a possibility that the high temperature peak heat quantity cannot be accurately measured. When the surface layer portion obtained from one expanded particle is less than 2 to 4 mg, the above operation may be repeated using a plurality of expanded particles to collect a required amount of the surface layer portion. On the other hand, the inner foam layer that does not include the surface layer portion of the foamed particles has the entire surface of the foamed particles so that the surface of the foamed particles and the portion between the surface of the foamed particles and 200 μm toward the center of gravity of the foamed particles are not included. The one obtained by cutting off the surface layer may be used for the measurement of the melting point and the high-temperature peak calorific value. However, when the size of the foamed particles is too small and the internal foamed layer disappears when the portion of 200 μm from the above surface is cut off, the surface of the foamed particles and the surface of the foamed particles go to the center of gravity of the foamed particles. When the surface layer is cut off from the entire surface of the expanded particles so that the area between 100 μm and 100 μm is not used as the internal expanded layer, and when the internal expanded layer is still lost, the surface of the expanded particles is The surface layer part cut off from the entire surface of the expanded particle is used as the internal expanded layer so that the part between the surface of the expanded particle and the center of gravity of the expanded particle does not include 50 μm. When the internal foam layer obtained from one expanded particle is less than 2 to 4 mg, the above operation may be repeated using a plurality of expanded particles to collect a required amount of the internal foam layer.

Further, with respect to the surface of each of the expanded particles obtained by the method of the present invention and the expanded particles obtained by the conventional method and the expanded particles not obtained by the conventional method, TA Instruments Japan Micro Thermal Analysis System "299
Type 0 micro thermal analyzer ", 25 ℃
Micro-differential thermal analysis (μDTA) was performed at a temperature rising rate of 10 ° C./sec from 100 to 200 ° C., and the melting start temperature of the surface of the expanded beads obtained by the method of the present invention after the surface modification While the temperature is lower than the melting point of the base resin, the melting start temperature of the surface of the expanded beads obtained by the conventional method without the surface modification step is 5 ° C. higher than the melting point of the base resin. It turned out to be. The melting start temperature here means the temperature at which the μDTA curve starts to change downward from the baseline (BL) in the μDTA curve based on the μDTA (the specific heat per hour has started to change).

Further, with respect to each surface of the expanded particles obtained by the method of the present invention and the expanded particles obtained by the conventional method and the expanded particles not obtained by the conventional method, TA Instruments Japan Micro Thermal Analysis System "299
Type 0 micro thermal analyzer ", 25 ℃
Micro-differential thermal analysis (μDTA) was performed at a temperature rising rate of 10 ° C./sec from 1 to 200 ° C., and the extrapolated melting start temperature of the surface of the surface-modified expanded particles obtained by the method of the present invention Is a temperature not higher than the melting point of the base resin + 4 ° C, whereas the extrapolation melting start temperature of the surface of the expanded particles that have not been surface-modified by the conventional method is higher than the melting point of the base resin. It was also found that the temperature was 8 ° C or higher. The extrapolation melting start temperature here is a straight line obtained by extending the baseline (BL) of the μDTA curve to the high temperature side and a tangent line drawn from each point on the μDTA curve on the higher temperature side than the melting start temperature. Of the tangent and the baseline (B
L) is the temperature at the intersection with the tangent line (TL) at which the angle between it and the straight line extending to the high temperature side is maximum.

The above μDTA for each of the expanded particles obtained in Example 5 and the expanded particles obtained in Comparative Example 3 described later.
An example of the curve is shown in FIG. In FIG. 3, the curve Cm is based on the expanded particles obtained in Example 5, and the curve C
The Pm point on m is the melting start temperature, and the Pme point is the extrapolation melting start temperature which is the intersection of the baseline (BL) and the tangent line (TL). On the other hand, the curve Cnm is based on the expanded particles obtained in Comparative Example 3, and the curve Cn
The Pnm point on m is the melting start temperature, and the Pnme point is the extrapolation melting start temperature which is the intersection of the baseline (BL) and the tangent line (TL). Pm in FIG.
Pme, Pnm and Pnme are 131 ° C. and
135 ° C, 168 ° C and 171 ° C. Also, in FIG.
An example of the μDTA curve for the surface-modified EPP expanded particle surface based on Example 7 described below is shown. In FIG. 4, the curve Cm is a μDTA curve, and Pm on the curve Cm
The point is the melting start temperature, and the Pme point is the extrapolation melting start temperature which is the intersection of the baseline (BL) and the tangent line (TL). Pm and Pme in FIG. 4 are 140 ° C. and 142 ° C., respectively.

In the micro-differential thermal analysis, the expanded particles are fixed to the sample stage of the device (if one expanded particle is too large as it is, it is cut in half, for example, and fixed to an appropriate size. Then, the probe tip (the part to be brought into contact with the surface of the foamed particle has a tip of 0.2 μm in each length and width) is lowered toward the randomly selected location on the surface of the foamed particle, Conducted in contact. As the melting start temperature and the extrapolation melting start temperature of the surface of the expanded beads by the micro differential thermal analysis, an arithmetic mean value of 8 points excluding the maximum value and the minimum value is adopted from the measurement results of 10 different measurement points. When there are a plurality of maximum values and a plurality of minimum values, the arithmetic mean value of several points excluding them is adopted. In addition, when all the measured values at the average of 10 points are the same, or when only the maximum and minimum values are obtained and the difference between the maximum and minimum values is within 10 ° C, the phase of 10 points The average value is adopted. If only the maximum and minimum values are obtained and the difference between the maximum and minimum values exceeds 10 ° C, 10 points on different surfaces are measured and the same procedure as above is applied. The arithmetic mean value may be calculated and used. If the condition is still not met, repeat the same operation.

The results obtained by the above μDTA show that the decrease in the melting start temperature on the surface of the expanded particles contributes to the decrease in the minimum fusing temperature required at the time of molding. From this, in 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 equal to or lower than [Tm-5 ° C]. Is preferred, it is more preferably [Tm-10 ° C] or lower, even more preferably [Tm-15 ° C] or lower, and particularly preferably [Tm-16 ° C] to [Tm-50 ° C]. , [Tm-17 ° C] to [Tm-35 ° C] are most preferable. Further, in the foamed particles that can be molded by low-temperature steam, the extrapolation melting start temperature of the surface of the foamed particles based on the above measurement is [Tm + 4 ° C.] or less
-1 ° C] or lower, more preferably [Tm-6 ° C] or lower, and [Tm-17 ° C] to [Tm].
m-50 ° C.] is more preferable, and [Tm-18
Most preferably, it is [° C]-[Tm-35 ° C]. In addition, such a decrease in the minimum fusing temperature is particularly effective in the case of EPP particles in which the melting point of the base resin is 158 ° C. or higher and which has a high temperature peak. The lower the melting start temperature of the foamed particle surface, the greater the contribution to the reduction of the minimum fusion temperature required at the time of molding, but if the melting start temperature is too low, the compression strength of the resulting molded article, etc. There is a possibility that mechanical properties and the like may deteriorate.

When the MFR was measured, the MFR value of the expanded beads obtained by the method of the present invention was the same as the MFR value of the resin particles before surface modification, but a larger value. It was observed. In the present invention, the M of the expanded particles is
The FR value is preferably 1.2 times or more, more preferably 1.5 times or more, and more preferably 1.8 to 3.5 times the MFR value of the resin particles before surface modification. Is most preferable. The MFR value of the expanded particles is
Considering the heat resistance of the molded product and the foaming efficiency during the production of expanded particles, it is preferably 0.5 to 150 g / 10 minutes, more preferably 1 to 100 g / 10 minutes, It is more preferable that the amount is 10 to 80 g / 10 minutes.

The MFR of the expanded particles is 2 times the expanded particles.
A press sheet having a thickness of 0.2 mm to 1 mm was prepared with a heating press machine whose temperature was adjusted to 00 ° C., and a sample was cut into pellets or rods from the sheet, and the sample was used to prepare the MFR It is a value measured by the same method as the measurement. Incidentally, in measuring the MFR of the expanded particles, it is necessary to avoid inclusion of bubbles or the like in the sample in order to obtain an accurate measurement value. When air bubbles are unavoidable, the same sample can be repeated up to three times to prepare a press sheet for defoaming with a heating press machine.

Further, the expanded beads obtained by the method of the present invention are
When using an organic peroxide that generates oxygen radicals,
Contains some oxygen due to the addition of organic peroxide
Form a modified surface. This was obtained by the method of the invention
Of the surface of the expanded particles and the EPP molded product produced from it
It is clear from the surface analysis. Specifically,
Of an EPP molded product produced from expanded particles obtained by the method
The surface (ie, substantially the same as the surface of the expanded particles)
EPP composition made from expanded particles without surface modification
ATR measurement (total reflection absorption measurement) of each surface
Method), from the expanded particles obtained by the method of the present invention
On the surface of the manufactured EPP molded body, 1033c is newly added.
m^-1It has been confirmed that there is a difference in absorption around the
Addition or insertion of functional groups containing body or oxygen
It was recognized that there was a change in. Specifically, 116
6 cm^-1Both peak heights in absorption of (by the method of the present invention
The height of the absorption peak from the obtained expanded particles and the
When the absorption peak height for conventional molded products is the same
In addition, 1 of the surface of the molded product from the expanded particles obtained by the method of the present invention
033 cm^-1The height of the absorption peak in the vicinity is the same as that of conventional molded products.
Surface 1033cm ^-1Higher than the height of absorption peaks in the vicinity
Is getting worse. Furthermore, as an observation of the surface of expanded particles, EDS
Elemental analysis was performed by (energy dispersive analyzer)
As a result, regarding the ratio of oxygen and carbon, the foam obtained by the method of the present invention
In the case of particles, it was 0.2 (mol / mol)
However, in the case of conventional expanded particles, 0.09 (mol / mo
l). From the above, the addition of organic peroxide
Forming a modified surface containing some oxygen by use
It is obvious that The formation of such a modified surface is
It is thought that the permeability of steam is advantageous. Like this
From this perspective, foamed particles that can be molded with low-temperature steam are
Oxygen and carbon by the above EDS on the surface of expanded particles
The ratio is preferably 0.15 or more. For the present invention
The EPP particles obtained by the method contain the above oxygen.
Modified surface or / and reversal of melting point or / and above
Decrease in the high-temperature peak calorific value of the surface layer of the expanded particles and / or
And / or lowering the melting start temperature on the surface of the expanded particles
Due to the decrease of the extrapolation melting start temperature on the surface of the expanded particles,
It is estimated that the minimum fusing temperature is reduced.

The EPP particles obtained by the above-mentioned method are aged under atmospheric pressure, and if necessary, the internal pressure of the bubbles is increased, and then heated with steam or hot air to produce a foam having a higher expansion ratio. It can be a particle.

The EPP compact is filled with EPP particles in a mold that can be heated and cooled and can be opened and closed and sealed after the pressure inside the bubbles is increased as necessary, and saturated steam is supplied to the mold. Can be manufactured by adopting a batch-type molding method in which the EPP particles are heated to be expanded and fused to each other, and then cooled and taken out from the mold. As a molding machine used in the batch type molding method, a large number of molding machines already exist all over the world, and the pressure resistance of the molding machine is 0.41 MPa (G) or 0.45 MPa (G) although it varies slightly depending on the country. There are many things. Therefore, the pressure of saturated steam when expanding and fusing the EPP particles is 0.45 MPa (G)
It is preferably below or below, 0.41 MPa
It is more preferable that it is less than or equal to (G). Also, E
The PP molded body continuously supplies the EPP particles between the belts that continuously move along the upper and lower sides of the passage after increasing the internal pressure of the bubbles, if necessary, so that the saturated steam supply area (heating area) is generated. When passing, the EPP particles are expanded and fused,
After that, it is passed through a cooling area to be cooled, and then the obtained molded body is taken out from the passage and sequentially cut into an appropriate length (for example, JP-A-9-104026 and JP-A-9-104027). It can also be produced by a molding method described in JP-A-10-180888. In this method, the inside of the passage is the inside of the mold. still,
In order to increase the bubble internal pressure of the EPP particles, the foamed particles may be put in a closed container, and the compressed air may be allowed to permeate the foamed particles by leaving the foamed particles in the container for a suitable time. . The gas supplied under pressure can be used without any problem as long as the main component is an inorganic gas that does not liquefy or solidify under the required pressure, but is further selected from the group consisting of nitrogen, oxygen, air, carbon dioxide, and argon. Alternatively, those 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 in which air is used to increase the internal pressure of the EPP particles is shown. First, the EPP particles used for molding are placed in a closed container, and pressurized air is supplied into the container (usually, the air pressure in the container is maintained within a range of 0.98 to 9.8 MPa in gauge pressure). ) The internal pressure of the EPP particles is increased by allowing the air to permeate the EPP particles by leaving the supplied state for an appropriate time. The EPP particles whose internal pressure has been sufficiently increased are supplied into the mold of the molding machine. The internal pressure of the EPP particles is obtained by performing the following operation using a part of the EPP particles immediately before in-mold molding (hereinafter, referred to as a foamed particle group).

Within 60 seconds after taking out the expanded particle group immediately before in-mold molding with the increased internal pressure from the pressure tank, a large number of needle holes of a size that does not allow the expanded particles to pass but allows air to freely pass are formed. Stored in a polyethylene bag of about 70 mm x 100 mm, the temperature is 23 ° C and the relative humidity is 50.
Move to a temperature-controlled room under the atmospheric pressure of. Then, it is placed on a scale in the temperature-controlled room and the weight is read. The weight is measured after the foamed particle group is taken out of the pressure tank by 120.
Seconds later. The weight at this time is defined as Q (g). Then, the bag is left in the same temperature-controlled room for 48 hours. Since the pressurized air in the expanded particles permeates the bubble film and escapes to the outside with the passage of time, the weight of the expanded particle group decreases accordingly.
After the time, the equilibrium is reached and the weight is substantially stable. After 48 hours, weigh the bag again,
The weight at this time is U (g). Immediately thereafter, all the foamed particle groups are 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.
Using the difference between Q (g) and U (g) as the increased air amount W (g), 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

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

The apparent volume (L) of the expanded particle group is 4
From the scale when the total amount of the expanded particle group taken out from the bag after 8 hours was immediately submerged in the water in the graduated cylinder containing 100 cm ³ of water at 23 ° C. in the constant temperature chamber,
It is determined by calculating the volume Y (cm ³ ) of the expanded particle group and converting this to the unit of liter (L). The apparent expansion ratio of the expanded particle group is the density of the base resin (g / c
It is determined by dividing m ³ ) by the apparent density (g / cm ³ ) of the expanded particle group. Also, the apparent density of the expanded particles (g
/ Cm ³ ) is the weight of the expanded particle group (U (g) and Z
It is obtained by dividing (difference from (g)) by the volume Y (cm ³ ). In the above measurement, the expanded particle group weight (difference between U (g) and Z (g)) was 0.5000 to 1.
A plurality of expanded particle groups are used in an amount of 0.0000 g and a volume Y of 50 to 90 cm ³ .

The internal pressure in the bubbles of the EPP particles is 0.0
05 to 0.98 MPa is preferable, more preferably 0.01 to 0.69 MPa, most preferably 0.029 MPa.
Is about 0.49 MPa. If the cell internal pressure becomes too small, the secondary foaming force at the time of molding becomes insufficient, and in order to compensate for this, the saturated steam pressure introduced into the mold at the time of molding must be set high. On the other hand, if the internal pressure of the bubbles becomes too high, the secondary foaming force at the time of molding becomes excessive, which hinders the saturated steam from penetrating into the inside of the molded body, resulting in a shortage of the temperature at the center of the molded body, resulting in mutual interference of EPP particles. Fusing tends to be defective. Furthermore, the EPP foamed particles obtained by the method of the present invention have a small decrease in the apparent volume of the EPP particles under a pressurized atmosphere, and it is possible to increase the pressure difference between the EPP particle bubbles and the external atmosphere. As a result, the time required to apply the internal pressure can be shortened. The apparent density of the EPP molded product produced by the above method can be arbitrarily selected depending on the purpose, but is usually in the range of 9 g / L to 600 g / L. The apparent density of an EPP molded product is JIS K 72
22 (1999) is the apparent overall density. However, the volume of the molded body used to calculate the apparent overall density is the volume calculated from the outer dimensions, but if the shape is complicated and calculation from the outer dimensions is difficult, submerge the molded body in water. The excluded volume is used.

A surface decoration material can be laminated and integrated on at least a part of the surface of the EPP molded product. A method for producing such a laminated composite type in-mold foam molded article is described in US Pat. No. 5,928,776, US Pat. No. 6,096,417, US Pat. No. 6,033,770, US Pat. No. 5,474,841, and European Patent 47747.
6, WO98 / 34770, WO98 / 00287
And Japanese Patent No. 3092227. Further, in the EPP molded product of the present invention, the insert material can be compositely integrated by embedding all or part of the insert material. A method for manufacturing such an insert composite type in-mold foam molded article is described in US Pat. No. 6,033,770 and US Pat. No. 5,474.
841, JP-A-59-127714, Japanese Patent No. 3092227, and the like.

The EPP molded article produced as described above preferably has an open cell rate of 40% or less, more preferably 30% or less, based on the procedure C of ASTM-D2856-70. Most preferably, it is at most%. The smaller the open cell ratio, the better the mechanical strength.

[0066]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples.

Examples 1 to 5, Comparative Examples 1 to 3 0.05 parts by weight of zinc borate powder (cell regulator) was added to 100 parts by weight of the polypropylene resin selected from Table 1 and melted in the extruder. After kneading, the mixture was extruded in a strand form from an extruder, immediately put in water adjusted to 18 ° C., and taken out while being rapidly cooled. After being sufficiently cooled, the strand was taken out of water and the length / diameter ratio was about 1. The strand was cut so as to be 0 to obtain resin particles having an average weight of 2 mg per particle. Next, in a 400 liter autoclave, 100 parts by weight of the above resin particles, 220 parts by weight of ion exchanged water at 18 ° C. as a dispersion medium (resin particle / dispersion medium weight ratio 0.45), sodium dodecylbenzene sulfonate (surfactant) 0 0.005 parts by weight, kaolin powder (dispersing agent) 0.3 parts by weight, aluminum sulfate powder (dispersion strengthening agent) 0.01 parts by weight, and organic peroxides shown in Table 2 (not used in Comparative Examples) are listed. The amount shown in Table 3 and the amount shown in Tables 3 and 4 were added to carbon dioxide gas (foaming agent), and the mixture was stirred in a closed state and heated to a temperature 5 ° C lower than the foaming temperature shown in Tables 3 and 4. (Average heating rate 4 ° C / min)
It was held at that temperature for 15 minutes. Table 3 shows the time during which the organic peroxide used was kept within the range of one-minute half-life ± 30 ° C during this temperature increase. Then, the temperature is raised to the foaming temperature (average heating rate 3 ° C./min) and the temperature is increased to 1
Hold for 5 minutes. Then, one end of the autoclave was opened to release the contents of the autoclave under atmospheric pressure to obtain expanded particles. Note that carbon dioxide gas was supplied into the autoclave so that the internal pressure of the autoclave during the release of the resin particles from the autoclave was maintained at the internal pressure of the autoclave immediately before the release. The obtained expanded particles were washed with water, subjected to a centrifuge, and then allowed to stand at room temperature under atmospheric pressure of 23 ° C. for 48 hours for curing. Also, each melting point, MFR of expanded particles, apparent density of expanded particles, and the like were measured. The results are shown in Tables 3 and 4. In addition, Example 1
5 and Comparative Examples 1 to 3 were substantially non-crosslinked (boiling xylene insoluble matter was 0). Next, after placing the expanded particles in a pressure vessel under pressurized air to apply the increased bubble internal pressure to the expanded particles, the bubble internal pressures shown in Tables 3 and 4 (indicated as the internal pressure of the expanded particles in the table). ), 250mm × 200m
In a mold having a molding space of m × 50 mm, the mold is not completely closed and a small gap (about 1 mm) is opened (filling space of 50 mm in a direction of 51 mm) and then filled. After the mold was completely clamped, the air in the mold was exhausted by steam, and then the molding was performed at the minimum fusion temperature (minimum saturated steam pressure) shown in Tables 3 and 4. After molding, the molded body in the mold was water-cooled until the surface pressure reached 0.059 MPa (G), the molded body was taken out of the mold, dried at 60 ° C. for 24 hours, and then cooled to room temperature (23 ° C.). . Continued 1
After curing in the room for 4 days, the apparent density, compressive strength and b / n ratio were measured for the molded body. The minimum fusion temperature (minimum saturated steam pressure) is 0.15 MPa.
(G) to 0.55 MPa (G), the saturated steam pressure is increased by 0.01 MPa to repeatedly produce a molded body, and a 250 mm x 200 mm surface of the cured molded body is 250 mm long with a cutter knife on one surface of the surface. After making a cut of about 10 mm in the thickness direction of the molded body so as to divide into two,
According to a test of bending and breaking the molded body from the cut portion, the value (b / n) of the number (n) of the expanded particles existing on the fracture surface and the number (b) of the expanded particles present in the material fracture is 0.50 for the first time. It means the saturated steam pressure required for molding when the above is reached.

However, Comparative Example 1, Comparative Example 2 and Comparative Example 3
Then, the pressure resistance of the molding machine used in this test is 0.5
At a saturated steam pressure of 5 MPa (G), the values of (b / n) were 0, 0.12 and 0.30, respectively, and did not reach 0.50. In order to obtain a value of (b / n) of 0.50 or more, a higher saturated steam pressure is required. The number (n) of the expanded particles is the sum of the number of the expanded particles separated between the expanded particles and the number (b) of the expanded particles whose material is destroyed in the expanded particles. Incidentally, the larger the value of (b / n), the larger the bending strength and the tensile strength of the molded body, which is preferable.

Further, the compressive strength of the molded body after curing obtained at the lowest fusion temperature was measured. The results are shown in Tables 3 and 4. The compressive strength in Tables 3 and 4 is a test piece obtained by cutting the molded body to a length of 50 mm, a width of 50 mm, and a thickness of 25 mm (the surface of which is cut on the entire surface). JIS Z 0234 (1976)
According to method A, a compression test is conducted until the strain reaches 55% under the conditions of a test piece temperature of 23 ° C. and a load speed of 10 mm / min, the stress at 50% strain is read from the obtained stress-strain diagram, and this is compressed. It was considered as strength. Moreover, the apparent density (g / L) of the expanded particles in Tables 3 and 4 is calculated by dividing the weight of the expanded particles by the apparent volume of the expanded particles. Specifically, after curing, the weight (g) of a plurality of randomly selected expanded particles was measured, and then 100 cm ³ of water at 23 ° C was measured.
The apparent volume (cm ³ ) of the expanded particles is read from the excluded volume when submerged in water in the graduated cylinder in which is stored, and this is converted to a liter unit. The apparent density (g / L) of the expanded particles is calculated from this measured value. For this measurement, the expanded particle weight is 0.5000 to 10.0000 g,
In addition, expanded particles having an apparent volume of expanded particles of 50 to 90 cm ³ are used. The internal pressure of the expanded particles in Tables 3 and 4 is
Since it is expressed by gauge pressure as described above, (G) is added after the numerical value. Further, in Examples 1 to 5 and Comparative Examples 1 to 3, and further in Examples 6 to 7 and Comparative Example 4 described later, the glass transition temperature, the melting point of the base resin,
The melting point and the calorific value of the high temperature peak of the expanded beads were measured using a Shimadzu heat flux differential scanning calorimeter “DSC-50” manufactured by Shimadzu Corporation.

The above results show that a dispersion formed by dispersing polypropylene resin particles in a dispersion medium in which an organic peroxide is present has a temperature lower than the melting point of the base resin of the polypropylene resin particles and The surface of the polypropylene-based resin particles is modified by maintaining the temperature at which the organic peroxide is substantially decomposed to decompose the organic peroxide to obtain substantially non-crosslinked surface-modified particles. When the process is adopted, the expanded particles obtained therefrom show that the molding temperature is reduced while maintaining the recyclability of the polypropylene resin. More specifically, it is as follows. The apparent density of the expanded particles is the same in Example 2 which has undergone the surface modification step and Comparative Example 1 which has not undergone the surface modification step,
The high temperature peak calorie of the whole expanded particles is almost the same, and the apparent density of the obtained molded product and the apparent density of the cut sample of the sample for measuring the compressive strength are the same, which is convenient for comparison. From the comparison between Example 2 and Comparative Example 1, the minimum fusion temperature in Comparative Example 1 exceeds 0.55 MPa (G), while the minimum fusion temperature in Example 2 is 0.4.
It is 4 MPa (G), and it can be seen that the minimum fusing temperature of Example 2 is lower than that of Comparative Example 1 by 7 ° C. or more. Moreover, the compressive strength of the molded body obtained in Example 2 is commensurate with the high-temperature peak calorific value of the whole expanded particles,
There is no particular decline.

In Example 4 which has undergone the surface modification step and Comparative Example 2 which has not undergone the surface modification step, the apparent density of the expanded particles is almost the same, and the high temperature peak calorie of the whole expanded particles is almost the same, Since the apparent density of the obtained molded body and the apparent density of the cut sample of the sample for measuring the compressive strength are almost the same, it is convenient to compare. From the comparison between Example 4 and Comparative Example 2, the minimum fusing temperature in Comparative Example 2 is 0.55M.
While it exceeds Pa (G), the minimum fusing temperature in Example 4 is 0.38 MPa (G).
It can be seen that in comparison with Comparative Example 2, the minimum fusing temperature is lowered by 12 ° C. or more. Moreover, the compressive strength of the molded product obtained in Example 4 is commensurate with the high-temperature peak calorific value of the expanded particles as a whole, and is not particularly lowered.

In Example 1 which has undergone the surface modification step and Example 3 which has undergone the surface modification step, the apparent densities of the expanded particles are almost the same, and the high temperature peak calorific value of the entire expanded particles is almost the same. It is convenient to compare the apparent density of the molded body and the apparent density of the cut sample of the sample for measuring the compressive strength, which are almost the same. From the comparison between Example 1 and Example 3, the minimum fusing temperature in Example 1 is 0.48MP.
a (G), the minimum fusing temperature in Example 3 is 0.35 MPa (G), and the minimum fusing temperature in Example 3 is about 9 ° C. lower than in Example 1. You can see that it is done. In Example 3, the organic peroxide used in Example 1 is different, and the other conditions can be said to be almost the same. Therefore, the result is that the organic peroxide having a carbonate structure is used. Indicates that the effect of reducing the minimum fusion temperature is excellent.

The apparent density of the expanded particles is similar between Example 5 which has undergone the surface modification step and Comparative Example 3 which has not undergone the surface modification step.
Although the high-temperature peak calorie of the whole expanded particles is almost the same, the apparent density of the obtained molded product and the apparent density of the cut sample of the sample for measuring the compressive strength are slightly different, but can be compared. From the comparison between Example 5 and Comparative Example 3, the minimum fusing temperature required in Example 5 is 0.36 MPa (G), whereas the minimum fusing temperature required in Comparative Example 3 is 0.55 MPa.
It can be seen that, beyond (G), the minimum fusing temperature of Example 5 is lower than that of Comparative Example 3 by 13 ° C. or more. Moreover, the compressive strength of the molded body obtained in Example 5 corresponds to the high-temperature peak calorific value of the entire expanded particles and the apparent density of the cut sample, and does not particularly decrease.

Further, regarding the expanded particles obtained in Example 5 and the expanded particles obtained in Comparative Example 3, a micro thermal analysis system "2990" manufactured by TA Instruments Japan Co., Ltd. was used for each expanded particle surface. Micro differential thermal analysis (μDT)
When A) was carried out, the surface of the expanded beads obtained in Example 5 had a melting onset temperature of 131 ° C and an extrapolation melting onset temperature of 135 ° C, whereas the foamed particles obtained in Comparative Example 3 The surface of the particles had a melting onset temperature of 168 ° C and an extrapolated melting onset temperature of 171 ° C. The above-mentioned results by μDTA indicate that the decrease in the melting start temperature and / or the decrease in the extrapolation melting start temperature on the surface of the expanded particles contributes to the decrease in the minimum fusing temperature required at the time of molding. Although the unit column is omitted in Table 4, the unit is the same as in Table 3.

Example 6 0.05 part by weight of zinc borate powder (cell adjuster) was added to 100 parts by weight of polypropylene resin selected from Table 1, melt-kneaded in the extruder, and then strands were formed from the extruder. Extruded into a shape, immediately put the strand in water adjusted to 18 ° C, take it off while cooling rapidly, and after sufficiently cooling, pull up from the water and cut the strand so that the length / diameter ratio is about 1.0. Thus, resin particles having an average weight of 2 mg were obtained. Then, in a 400 liter autoclave, with respect to 100 parts by weight of the resin particles,
120 parts by weight of ion-exchanged water at 18 ° C. (resin particle / dispersion medium weight ratio 0.83) and the amount of the organic peroxide shown in Table 2 were charged, and the organic peroxide was halved for 1 minute while stirring. The mixture was heated to the target temperature (average temperature rising rate: 3 ° C./min) and kept at that temperature for 5 minutes to complete the decomposition of the organic peroxide (1% of the organic peroxide used during this heating). The time kept within the range of the half-life of ± 30 ° C. for minutes was as shown in Table 5.). Immediately after that, 100 parts by weight of ion-exchanged water at 18 ° C. was added to the resin particle / dispersion medium weight ratio of 0.45, and sodium dodecylbenzenesulfonate (surfactant) 0.005 was further added to the autoclave. Parts by weight and kaolin powder (dispersant) 0.3
Parts by weight, aluminum sulfate powder (dispersion strengthening agent) 0.01
Parts by weight, and the amount shown in Table 5 (these addition amounts are all based on 100 parts by weight of the resin particles) carbon dioxide gas (foaming agent) is charged, and the temperature is 5 or more than the foaming temperature shown in Table 5 while stirring in a sealed state. The temperature was raised to a temperature lower by 0 ° C. (average heating rate 4 ° C./min), and then the temperature was maintained for 15 minutes. Then
The temperature was raised to the foaming temperature (average heating rate 3 ° C./min) and the temperature was maintained for 15 minutes. Then, one end of the autoclave was opened to release the contents of the autoclave under atmospheric pressure to obtain expanded particles. Note that carbon dioxide gas was supplied into the autoclave so that the internal pressure of the autoclave during the release of the resin particles from the autoclave was maintained at the internal pressure of the autoclave immediately before the release. The obtained expanded particles were washed with water and subjected to a centrifuge, then allowed to stand at room temperature under atmospheric pressure of 23 ° C. for 48 hours for curing, and then the high temperature peak calorie of the expanded particles was measured in the same manner as in Examples 1-5. did. The results are shown in Table 5. The expanded particles obtained in Example 6 were
It was substantially non-crosslinked (the boiling xylene insoluble content was 0
Met).

Then, the expanded particles were placed under pressure in a pressure-resistant container to give the expanded particles an increased bubble internal pressure, and then the bubble internal pressure shown in Table 5 (indicated as the internal pressure of the expanded particles in the table). ), A slight gap (about 1 mm) is opened in the mold having a molding space of 250 mm × 200 mm × 50 mm without completely closing the mold (molding space 50 mm
(With a direction of 51 mm), and then completely clamping the mold, and then exhausting the air in the mold with steam,
Molding was performed in the same manner as in Examples 1 to 5 at the lowest fusion temperature (minimum saturated steam pressure). After molding, the molded body was water-cooled until the surface pressure of the molded body became 0.059 MPa (G), taken out of the mold, dried at 60 ° C. for 24 hours, and then cooled to room temperature (23 ° C.). Then, after curing in the room for 14 days, the apparent density, compressive strength and b / n ratio were measured for the molded body. Further, the compression strength of the molded body obtained after curing at the lowest fusion temperature was measured in the same manner as above. The results are shown in Table 5. The results of Example 6 compared with Example 2 show that the resin particle / dispersion medium weight ratio is 0.
In the case where the surface modification step was performed at 6 or more (Example 6), a smaller amount of the organic peroxide was obtained as compared with the case where the surface modification step was performed in which the resin particle / dispersion medium weight ratio was 0.45. It is shown that the same level of surface modification is achieved by the use of oxides. Specifically, it is as follows. The apparent density of the expanded particles is shown in Example 6 which has undergone the surface modification step with a resin particle / dispersion medium weight ratio of 0.83 and Example 2 which has undergone the surface modification step with a resin particle / dispersion medium weight ratio of 0.45. However, the high temperature peak calorific value of the whole expanded particles and the internal pressure of the expanded particles are almost the same, and the apparent density of the obtained molded body and the apparent density of the cut sample of the sample for measuring the compression strength are the same. It is convenient for The results of comparison between Example 6 and Example 2 show that the amount of organic peroxide required in Example 2 was 1 part by weight in order to obtain the same level of minimum fusing temperature, whereas Example 6 showed that It shows that the amount of organic peroxide required is only 0.32 parts by weight, that is, the amount of organic peroxide used can be reduced.

Comparative Example 4 Surface modification was carried out by using 66 parts by weight of ion-exchanged water to 100 parts by weight of resin particles (resin particle / dispersion medium weight ratio 1.5), and the foaming temperature was changed to 166.5 ° C. The operation of Example 6 was repeated except for the above. However, since the resin particle / dispersion medium weight ratio was 1.5, the modified resin particles were fused to each other in the closed container to form a large lump, which could not be discharged to the outside of the closed container. Could not be manufactured. This result indicates that when the resin particle / dispersion medium weight ratio exceeds 1.3 in the surface modification step, it is difficult to sufficiently disperse the polypropylene resin particles, and as a result, in the foaming step, the surface-modified resin particles are kept in a closed container. Indicates that it becomes easy to fuse and form a large lump, that is, it becomes difficult to produce expanded particles.

Example 7 0.05 part by weight of zinc borate powder (cell adjuster) was added to 100 parts by weight of polypropylene resin selected from Table 1 and melt-kneaded in the extruder. Extruded into a shape, immediately put the strand in water adjusted to 18 ° C, take it out while cooling rapidly, and after sufficiently cooling, pull out from the water and cut the strand so that the length / diameter ratio is about 1.0. Thus, resin particles having an average weight of 2 mg were obtained. Then, in a 400 liter autoclave, with respect to 100 parts by weight of the resin particles,
120 parts by weight of ion-exchanged water at 18 ° C. (resin particles / dispersion medium weight ratio 0.83), sodium dodecylbenzenesulfonate (surfactant) 0.005 parts by weight and kaolin powder (dispersant) 0.3 parts by weight, Aluminum sulfate powder 0.0
13 parts by weight and the amount of the organic peroxide shown in Table 2 were charged, the temperature was raised to 90 ° C. of the organic peroxide with stirring (average heating rate 5 ° C./min), and the temperature was adjusted to 10 The decomposition of the organic peroxide was completed by holding it for a minute (in this heating, the time during which the organic peroxide used was kept within a range of 1 minute half-life ± 30 ° C as shown in Table 5). there were.). Immediately after that, add 1 ° C of ion-exchanged water at 18 ° C into the autoclave.
The resin particle / dispersion medium weight ratio was 0.45 by adding 100 parts by weight. Then, while stirring, carbon dioxide gas (foaming agent) was added to the autoclave at an equilibrium pressure of 0.49 MPa.
After press-fitting so as to give (G), the temperature was raised by 1 ° C. lower than the foaming temperature shown in Table 5 at an average heating rate of 0.16 ° C./min. Immediately thereafter, while the carbon dioxide gas (foaming agent) was being pressed in, the pressure inside the autoclave was maintained at 1.18 MPa (G) so as to be stable, and the average heating rate was 0.0 until the foaming temperature.
The temperature was raised at 29 ° C / min. Then, one end of the autoclave was opened to release the contents of the autoclave under atmospheric pressure to obtain expanded particles. Note that carbon dioxide gas was supplied into the autoclave so that the internal pressure of the autoclave during the release of the resin particles from the autoclave was maintained at the internal pressure of the autoclave immediately before the release. The obtained expanded particles were washed with water and subjected to a centrifuge, then allowed to stand at room temperature under atmospheric pressure of 23 ° C. for 48 hours for curing, and then the high temperature peak calorie of the expanded particles was measured in the same manner as in Examples 1-5. did. The results are shown in Table 5. The expanded beads obtained in Example 7 were substantially non-crosslinked (the boiling xylene insoluble content was 0).

Then, the expanded particles were placed under pressure in a pressure vessel to give an increased bubble internal pressure to the expanded particles. ), The mold having a molding space of 250 mm × 200 mm × 50 mm is opened (a molding space of 50 mm with a small gap (about 1 mm) without completely closing the mold).
(With a direction of 51 mm), and then completely clamping the mold, and then exhausting the air in the mold with steam,
Molding was carried out in the same manner as in Examples 1 to 5 at the minimum fusion temperature (minimum saturated steam pressure). After molding, the molded body was water-cooled until the surface pressure of the molded body became 0.059 MPa (G), taken out of the mold, dried at 60 ° C. for 24 hours, and then cooled to room temperature (23 ° C.). Then, after curing in the room for 14 days, the apparent density, compressive strength and b / n ratio were measured for the molded body. Further, the compression strength of the molded product obtained at the lowest fusion temperature was measured in the same manner as above. The results are shown in Table 5. The results of Example 7 are
As in Example 6, the resin particle / dispersion medium weight ratio was 0.6.
As described above, after passing through the surface modification step, foaming was started from the state of the resin particle / dispersion medium weight ratio of 0.45 (the autoclave contents were started to be released under atmospheric pressure), and the results were also carried out. Similar to Example 6, it is shown that a high level of surface modification is achieved using a small amount of organic peroxide. Regarding the expanded beads after curing obtained in Example 7, the surface of the expanded beads was analyzed by a micro thermal analysis system “299 of TA Instruments Japan KK”.
Type 0 micro thermal analyzer ", 25 ℃
Micro-differential thermal analysis (μDTA) was performed at a temperature rising rate of 10 ° C./sec from 1 to 200 ° C., and the surface of the expanded beads obtained in Example 7 had a melting start temperature of 140 ° C.
And the extrapolation melting start temperature was 142 ° C.

[0080]

[Table 1]

[0081]

[Table 2]

[0082]

[Table 3]

[0083]

[Table 4]

[0084]

[Table 5]

[0085]

According to the method of the present invention, the surface modification is performed on the resin particles in the condition that the weight ratio of polypropylene resin particles / dispersion medium is 1.3 or less, so that the variation of the modification of each particle becomes small. Surface modification can be performed efficiently, and as a result, the production of expanded particles becomes easy. Further, when the surface modification is performed on the resin particles in a state where the polypropylene resin particle / dispersion medium weight ratio is 0.6 or more, the amount of the organic peroxide used can be reduced. Reduction of the amount of organic peroxide used contributes to cost reduction and reduction of load on drainage. Further, when an organic peroxide having a carbonate bond is used as the organic peroxide, a high surface modification effect can be obtained. By using the surface-modified particles obtained by the method of the present invention, it is possible to provide expanded particles in which the molding temperature is lowered while maintaining the environmental suitability and recyclability of the polypropylene resin. This reduction in molding temperature greatly contributes to energy saving. In particular, the polypropylene resin particle / dispersion medium weight ratio is 0.6 to 1.3.
When the surface modification is performed on the resin particles in the state of, and then the resin particles / dispersion medium weight ratio is changed to 0.5 or less in the foaming step to produce the foamed particles, the amount of the organic peroxide used is reduced. Thus, it is possible to efficiently produce expanded beads whose molding temperature is lowered. Conventionally, in order to improve the physical properties such as high rigidity of EPP molded products, it is necessary to use expanded particles having a high high-temperature peak calorific value, which are obtained by using a polypropylene resin having a high melting point. There was a problem that the temperature exceeded the pressure resistance of a general-purpose molding machine,
In the expanded particles obtained by the method of the present invention, even the expanded particles having a high high-temperature peak calorie obtained by using a polypropylene resin having a high melting point, while maintaining the high rigidity of the obtained EPP molded product, Molding can be performed with steam at a lower temperature than before, and molding can be performed within the pressure resistance of a general-purpose molding machine if surface modification is sufficient. Therefore, by using the expanded particles obtained by the method of the present invention, it becomes possible to provide an EPP molded article having higher physical properties (high rigidity) and / or lighter weight than ever before.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a first DSC curve chart of expanded polypropylene-based resin particles for molding.

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

FIG. 3 is a diagram showing an example of a μDTA curve based on a micro thermomechanical analysis for the surface of expanded particles obtained in each example based on Example 5 and Comparative Example 3.

FIG. 4 is a diagram showing an example of a μDTA curve based on micro thermomechanical analysis for the surface of expanded beads obtained in Example 7.

Continued front page    (72) Inventor Hidehiro Sasaki             10-3 Satsukicho, Kanuma City, Tochigi Prefecture             KSP Kanuma Research Institute F-term (reference) 4F070 AA15 AB09 AC56 AE30 BA08                       BB02                 4F074 AA24 BA01 BA31 BC04 BC11                       CA35 CC03X CC04X CC04Y                       CC05Z

Claims (8)

[Claims] 1. A dispersion formed by dispersing polypropylene resin particles in a dispersion medium in which an organic peroxide is present, wherein the dispersion has a temperature lower than the melting point of the base resin of the resin particles and the organic peroxide. A method for obtaining substantially non-crosslinked surface-modified particles by maintaining the temperature at which is substantially decomposed to decompose the organic peroxide,
The method for producing surface-modified particles, wherein the weight ratio of the dispersion medium is 1.3 or less. 2. The resin particle / dispersion medium weight ratio is from 0.6 to
The method for producing surface-modified particles according to claim 1, wherein the ratio is 1.3. 3. The organic peroxide is decomposed by keeping the dispersion in a temperature range of 1 minute half-life temperature ± 30 ° C. of the organic peroxide for 10 minutes or more to decompose the organic peroxide. Two
The method for producing surface-modified particles according to 1. 4. The organic peroxide is one which mainly generates oxygen radicals when decomposed.
4. The method for producing surface-modified particles according to any one of 3 above. 5. The one-hour half-life temperature of the organic peroxide is not less than the glass transition point of the polypropylene resin as the base resin of the resin particles and not more than the Vicat softening point. 5. The method for producing surface-modified particles according to any one of 1 to 4. 6. The organic peroxide is a peroxide having a carbonate structure, wherein the organic peroxide is a peroxide.
A method for producing surface-modified particles according to any one of 1. 7. A polypropylene characterized in that the surface-modified particles produced by the method according to any one of claims 2 to 6 are expanded with a foaming agent to obtain substantially non-crosslinked expanded particles. Method for producing expanded resin particles. 8. A dispersion formed by dispersing polypropylene resin particles in a dispersion medium in which an organic peroxide is present at a resin particle / dispersion medium weight ratio of 0.6 to 1.3. Is maintained at a temperature lower than the melting point of the base resin of the resin particles and at a temperature at which the organic peroxide is substantially decomposed to decompose the organic peroxide, and thereby the substantially non-crosslinked surface modification is performed. Surface modification step for obtaining fine particles, and a blowing agent under pressure and heating under a condition that the weight ratio of the resin particles / the dispersion medium is 0.5 or less with respect to the surface modified particles in the dispersion medium. A polypropylene system characterized by including a foaming agent impregnation step of impregnating under the conditions, and a resin particle foaming step of releasing the surface-modified particles impregnated with the foaming agent together with the dispersion medium into a low-pressure zone for foaming. A method for producing expanded resin particles.