JP2003246864A - Polypropylene resin particles and their preparation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide polypropylene resin particles which are suitable for forming non-crosslinked polypropylene-based expandable resin particles capable of thermofusing by steaming at a low temperature and forming a molding of expanded particles having high rigidity (high compression strength). <P>SOLUTION: The base resin of the polypropylene resin particles is a polypropylene resin having the melting point of at least 158°C. The particles are characterized by having at most 0.95 for the ratio of (ΔH<SB>b</SB>) to (ΔH<SB>a</SB>/ΔH<SB>b</SB>), when the particles are heated (the first heating) from 30°C to 200°C at the heating rate of 10°C/minute, immediately after the first heating, cooled from 200°C to 30°C at the rate of -10°C/minute and successively heated (the second heating) again from 30°C to 200°C, where ΔH<SB>a</SB>and ΔH<SB>b</SB>are the calorific values associated with the endothermic peaks observed in the first and the second heating processes of the DSC (differential scanning calorimetry), respectively. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to polypropylene resin particles suitable for producing expanded polypropylene resin particles and a method for producing the same.

[0002]

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

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 for bumper core materials, door pads, pillars, tool boxes, floor mats, etc., focusing on the excellent properties of EPP molded products, but due to recent environmental and energy problems. There is a demand for weight reduction of vehicles, and at the same time, there is a strong demand for weight reduction of parts constituting the vehicles. Even EPP molded products are no exception, and there has been a demand for even lighter EPP molded products while maintaining the conventional rigidity, cushioning property, and impact energy absorption property. Further, for example, as a box for transporting a fish box or the like, a polystyrene resin in-mold foam molded article (hereinafter referred to as "EPS molded article") is often used because of its high rigidity and low cost. Was there. But EPS
Since the molded product is inferior in impact resistance and heat resistance to the EPP molded product, it is difficult to repeatedly use the molded product. 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. In addition, 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, a method of obtaining a highly rigid EPP molded article by using a propylene-based copolymer resin composed of propylene and a comonomer such as ethylene or butene has also been devised. 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, as in the case of using the high-rigidity EPP particles obtained from the high-rigidity polypropylene resin as described above to obtain a high-rigidity EPP molded body,
In particular, this causes an increase in molding temperature, and often requires steam with a pressure higher than the pressure resistance of the molding machine for producing the EPP molded body, and further a sufficient fusion rate of the expanded particles can be obtained. There is a problem that it is difficult. 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 applicant of the present invention is to disperse polypropylene-based resin particles in a dispersion medium in which an organic peroxide is present, and to disperse the dispersion liquid at a temperature lower than the melting point of the base resin of the polypropylene-based resin particles and the organic peroxide. The expanded particles obtained from the substantially non-crosslinked surface-modified particles formed by decomposing the organic peroxide by maintaining the material at a temperature at which it substantially decomposes, and The inventors have found that an EPP molded body that can achieve fusion bonding and have excellent rigidity is provided, and completed the application first (see Patent Document 4).

[0006]

[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

[0007]

DISCLOSURE OF THE INVENTION The present invention is a non-crosslinked polypropylene system capable of achieving fusion between expanded particles with low temperature steam and giving a highly rigid (high compressive strength) expanded particle molded article. An object of the present invention is to provide a polypropylene resin particle suitable for manufacturing expanded resin particles and a method for manufacturing the same.

[0008]

Means for Solving the Problems
As a result of earnest research to solve the problem, the present invention was completed.
Came to That is, according to the present invention, the following polyp
Production of ropylene resin particles and polypropylene resin particles
A manufacturing method is provided. (1) Based on polypropylene resin with a melting point of 158 ° C or higher
A polypropylene resin particle used as a material resin,
Oil particles were measured with a differential scanning calorimeter at a rate of 10 ° C / min.
Immediately after heating from 30 ° C to 200 ° C (first heating)
Then, cool from 200 ℃ to 30 ℃ at a rate of -10 ℃ / min.
Immediately after that, from 30 ℃ again at a speed of 10 ℃ / min
When heated to 200 ° C (second heating), the first
Of the endothermic curve that appears in the DSC curve during heating
(ΔH_a), And appeared in the DSC curve during the second heating.
Heat quantity of the endothermic curve peak (ΔH_b) Ratio (ΔH_a/ ΔH
_b) Is 0.95 or less
Len resin particles. (2) The melting point is 1 in the dispersion medium containing the organic peroxide.
Polypropylene resin with a temperature of 58 ° C or higher is used as the base resin.
While dispersing the polypropylene resin particles, the dispersion medium
Body than the melting point of the base resin of the polypropylene resin particles
At a low temperature and at a temperature at which the peroxide substantially decomposes
Obtained by holding and decomposing the organic peroxide
A method for producing expanded particles by expanding surface-modified particles
The polypropylene-based tree according to (1)
Oil particles. (3) Based on polypropylene resin with a melting point of 158 ° C or higher
The material resin and the DSC curve by differential scanning calorimetry
Higher than peak of endothermic curve derived from heat of fusion of material resin
The foamed particles having an endothermic curve peak in
Heat of the endothermic curve peak existing on the high temperature side of the surface layer of the particle
Amount (ΔH_s) And the high temperature side of the internal foam layer of the expanded particles
Heat quantity of the endothermic curve peak (ΔH_i) Is ΔH_s
<ΔH_iX 0.86 for the production of expanded particles
It is a polypropylene resin particle, and the differential running of the resin particle
20 to 30 ° C at a rate of 10 ° C / min using a calorimeter
Immediately after heating to 0 ° C (first heating), -10 ° C / min.
Immediately after cooling from 200 ℃ to 30 ℃ at the speed of
Heat again from 30 ° C to 200 ° C at a rate of 10 ° C / min.
(Second heating), DSC at the time of the first heating
Heat quantity of the endothermic curve peak appearing on the curve (ΔH_a) And the
Of the endothermic curve peak that appears in the DSC curve during the second heating
Heat quantity (ΔH_b) Ratio (ΔH_a/ ΔH_b) Is 0.95 or less
Polypropylene resin particles characterized by being (4) Based on polypropylene resin with a melting point of 158 ° C or higher
The material resin and the DSC curve by differential scanning calorimetry
Higher than peak of endothermic curve derived from heat of fusion of material resin
The foamed particles having an endothermic curve peak in
Micro differential thermal analysis on the surface of particles (from 25 ° C to 2
Melting opening based on a temperature rise rate of 10 ° C / sec up to 00 ° C)
Produces expanded particles whose starting temperature is below the melting point of the base resin
For use as a polypropylene-based resin particle
Differential scanning calorimeter at 30 ° C at a rate of 10 ° C / min.
Immediately after heating from 1 to 200 ° C (first heating), -1
Cool from 200 ° C to 30 ° C at a rate of 0 ° C / min,
Immediately after, again at a rate of 10 ° C / min from 30 ° C to 200 ° C
When heating up to (first heating), during the first heating
Of the endothermic curve peak appearing in the DSC curve of_a)
And the endothermic curve that appears in the DSC curve during the second heating
Peak heat quantity (ΔH_b) Ratio (ΔH_a/ ΔH _b) Is 0.
Polypropylene resin characterized by being 95 or less
particle. (5) Based on polypropylene resin with a melting point of 158 ° C or higher
The material resin and the DSC curve by differential scanning calorimetry
Higher than peak of endothermic curve derived from heat of fusion of material resin
The foamed particles having an endothermic curve peak in
Micro differential thermal analysis on the surface of particles (from 25 ° C to 2
Extrapolation based on a heating rate of 10 ° C / sec up to 00 ° C)
Foaming in which the melting start temperature is below the melting point of the base resin + 4 ° C
It is a polypropylene-based resin particle for producing particles.
Then, the resin particles were measured with a differential scanning calorimeter at 10 ° C./min.
Heat from 30 ℃ to 200 ℃ at the speed (first heating)
Immediately after, 200 to 30 ℃ at a rate of -10 ℃ / min
And then immediately again at a rate of 10 ° C / min for 30
When heated from ℃ to 200 ℃ (second heating),
Of the endothermic curve peak that appears in the DSC curve during the first heating
Heat quantity (ΔH_a) And the DSC curve during the second heating
Heat quantity of the endothermic curve peak that appears (ΔH_b) Ratio (ΔH_a/
ΔH_b) Is 0.95 or less
Ropylene-based resin particles. (6) ΔH_a/ ΔH_bIs 0.85 or less
The polypro according to any one of (1) to (5) above
Pyrene-based resin particles. (7) The resin particles have a length (L) and an average diameter (D)
Columnar particles having a ratio (L / D) of 0.5 to 2
The average weight per piece is 0.1-20 mg
The port according to any one of (1) to (6), which is characterized in that
Lipropylene resin particles. (8) Polypro according to any one of (1) to (7) above
A method for producing pyrene-based resin particles having a melting point of 15
Polypropylene resin at 8 ° C or higher was heated and melted
rear, Molten polypropylene resin is
In a cooling medium at least 30 ° C below the crystallization temperature of fat
After cooling with, cut into particles, or Molten polypropylene resin is cut into particles in the molten state.
Immediately after cutting, the crystallization temperature of the polypropylene resin
Also cooled in a cooling medium at least 30 ° C lower, or Molten polypropylene resin is cut into particles in the molten state.
Less than the crystallization temperature of the polypropylene resin while cutting
Characterized by cooling in a cooling medium at least 30 ° C lower
And a method for producing polypropylene-based resin particles.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Base resin for polypropylene resin particles of the present invention (hereinafter sometimes referred to as "present base resin")
The polypropylene resin is a polypropylene homopolymer, or a copolymer of propylene containing 60 mol% or more of a propylene component (preferably containing 80 mol% or more of a propylene component) and another comonomer, Alternatively, it is a mixture of two or more 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 and 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.
Must be 58 ° C or higher, but 158 ° C to 170 ° C
Is preferred. Further, the present base resin has a melt flow rate (MFR) of 0.3 to 100 g in consideration of the heat resistance of the foamed molded product and the foaming efficiency during the production of expanded particles.
/ 10 minutes is preferable, and 1 to 90 g / 10 minutes is particularly preferable. In addition, MFR is JIS K7210 (1
976) and the value measured under test condition 14.

In the present invention, in the polypropylene resin particles, synthetic resin other than the polypropylene resin or / in the polypropylene resin particles is used as long as the intended effect of the present invention is not impaired.
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 effects of the present invention are 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.
Further, these additives were melted in the extruder when the polypropylene resin particles of the present invention (hereinafter sometimes referred to as “present resin particles”) were produced by, for example, cutting the strand extruded by the extruder. It can be contained in the present resin particles by adding and kneading to the present base resin.

The main feature of the polypropylene resin particles of the present invention is that foamed particles capable of achieving fusion between the foamed particles by steam at a low temperature during molding can be easily produced. That is, the polypropylene resin particles of the present invention, in a nitrogen atmosphere, immediately after heating the resin particles from 30 ℃ to 200 ℃ at a rate of 10 ℃ / min (first heating) by a differential scanning calorimeter, 2 at a speed of -10 ° C / min
Cool from 00 ° C to 30 ° C, and immediately afterwards, again at 10 ° C /
Heat from 30 ℃ to 200 ℃ at the speed of minute (second heating)
Of the endothermic curve peak that appears in the DSC curve during the first heating (ΔH _a ) and the amount of the endothermic curve peak that appears in the DSC curve during the second heating (ΔH _b ). The ratio (ΔH _a / ΔH _b ) is 0.95 or less, and preferably ΔH _a / ΔH _b is 0.85 or less. Although the endothermic curve appearing in the DSC curve during the first heating and the endothermic curve appearing in the DSC curve during the second heating are subtly different from each other, they are both shown in FIG. D
The endothermic curve is close to the (SC curve). ΔH _a is the portion enclosed by the straight line connecting the melting end temperature (β in FIG. 2) of the endothermic curve appearing in the DSC curve during the first heating and the 80 ° C. point on the curve, and the portion surrounded by the DSC curve. Corresponding to the area, ΔH _b
Is the area enclosed by the DSC curve and the straight line connecting the melting end temperature (β in FIG. 2) of the endothermic curve appearing in the DSC curve during the second heating and the 80 ° C. point on the curve. Equivalent to. Each of these heat amounts means an endothermic amount (J / g), and the endothermic amount value is expressed as an absolute value. Δ above
The smaller the value of H _a / ΔH _b, the greater the surface modification effect of the resin particles described later. Specifically, ΔH _a / Δ
Expanded particles obtained from resin particles surface-modified with resin particles having a smaller value of H _b can be molded by lower temperature steam or / and are added to the expanded particles prior to molding. It becomes possible to mold with a lower foaming ability. However, the lower limit of the value of ΔH _a / ΔH _b usually does not fall below 0.70. On the contrary, when the value of ΔH _a / ΔH _b exceeds 0.95, the effect is very small.

In order to obtain the resin particles having such a small ΔH _a / ΔH _b value, the polypropylene resin is heated and melted, and then the following (1) or (2) or (3) is applied. All you have to do is perform the operation. (1) The molten polypropylene resin is cooled in a cooling medium at least 30 ° C. lower than the crystallization temperature of the polypropylene resin and then cut into particles. (2) The molten polypropylene resin is cooled in a cooling medium at least 30 ° C. lower than the crystallization temperature of the polypropylene resin immediately after being cut into particles in a molten state. (3) The molten polypropylene resin is cut in a molten state into particles and cooled in a cooling medium at least 30 ° C. lower than the crystallization temperature of the polypropylene resin. Although a gas such as air cannot be used as the cooling medium, a liquid is more efficient and reliable. An aqueous medium is generally used as the cooling medium for such a liquid, and water is preferably used. Not limited to water, there is no particular limitation as long as it does not dissolve the base resin. Examples thereof include ethylene glycol, glycerin, methanol, ethanol, a mixture of water and the alcohol, and the like.

Regarding the cooling in the above (1) to (3), the lower the temperature of the cooling medium (the more rapid the degree of cooling), and the longer the cooling time, the more ΔH _a / Δ.
The present resin particles having a small _Hb value can be obtained. From such a viewpoint, the temperature of the cooling medium needs to be at least 30 ° C. lower than the crystallization temperature of the polypropylene resin, but it is preferably at least 35 ° C. lower than the crystallization temperature of the polypropylene resin, It is more preferably at least 45 ° C. lower than the crystallization temperature of the polypropylene resin, further preferably at least 55 ° C. lower than the crystallization temperature of the polypropylene resin, and at least 6 ° C. lower than the crystallization temperature of the polypropylene resin.
It is particularly preferably 5 ° C. lower, and most preferably at least 80 ° C. lower than the crystallization temperature of the polypropylene resin. However, if the temperature of the cooling medium is too low, the cost for preparing the cooling medium increases more than necessary, so the temperature of the cooling medium is preferably 5 ° C. or higher. Further, the cooling time by the cooling medium is 1
Seconds or more, preferably 5 seconds or more, more preferably 9 seconds or more, 12
Most preferably, it is -20 seconds. The longer the cooling time is, the more effective it is. However, if the cooling is performed for a sufficient time, the above-mentioned effect will be leveled off.

The resin particles having a small ΔH _a / ΔH _b value can be obtained by the above cooling. The ΔH _b value is almost constant when the raw material resin is determined, but ΔH _a tends to show a smaller value as the degree of cooling from the molten state increases. Therefore, the smaller the ΔH _a / ΔH _b value is, the more the index indicates that the degree of cooling is higher. The fact that shows the [Delta] H _a smaller value (i.e. [Delta] H _a / delta
The fact that the H _b value is small) means that the crystallization of the resin particles is suppressed, and the suppression of the crystallization enhances the effect of surface modification on the resin particles described later. Guessed.

The resin particles generally have a length / diameter ratio of 0.
5 to 2.0, preferably 0.8 to 1.3, and average weight per piece (randomly selected 2
(Average value of one piece that weighed 00 pieces at the same time)
Is 0.1 to 20 mg, preferably 0.2
It is adjusted to be ~ 10 mg. If the length / diameter ratio is too small or too large, there is a risk of impeding the filling of the foamed particles obtained therefrom into the mold.
Further, if the average weight per particle becomes too heavy, the cooling efficiency may be deteriorated at the time of the cooling, and conversely if it becomes too light, it becomes difficult to obtain expanded particles.

The method for producing expanded particles (EPP particles) having a low temperature fusion property using the polypropylene resin particles of the present invention (hereinafter also referred to as method A) comprises a surface modification step and an expansion step. In the surface modification step, the present resin particles are dispersed 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 present resin particles and the organic peroxide is The surface of the resin particles is modified by maintaining the temperature at which it is substantially decomposed to decompose the organic peroxide 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. In addition, this expanded particle,
By filling this in a mold and heating it with steam, an EPP molded product with excellent rigidity can be obtained.

The dispersion medium used in the surface modification step in the method A is generally an aqueous medium, preferably water, more preferably ion-exchanged water, but not limited to water, the base material Any solvent or liquid that does not dissolve the resin and can disperse the resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol and the like. The aqueous medium includes a mixed solution of water and an organic solvent such as the alcohol.

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 used by adding 10 to 10 parts by weight, preferably 0.05 to 5 parts by weight in the dispersion medium.

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 usages of (1) to (4) 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 any of the conventional methods of using the organic peroxides described above, in order to obtain EPP particles excellent in heat-sealing property, prior to the production of the EPP particles, a polypropylene-based polypropylene is used in a dispersion medium in which the organic peroxide is present. While dispersing the resin particles, the dispersion medium is maintained 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 remove the organic peroxide. This is different from the use of the present invention in which the surface of the polypropylene resin particles is modified by decomposition to obtain substantially non-crosslinked surface-modified particles.

In the surface modification step, 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 depends on the Vicat softening point (JIS K 6747-1) of the base resin.
981, and 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 decomposes in a state of penetrating deep into the resin particles,
Since the base resin constituting the present resin particles is largely decomposed irrespective of the surface or inside, in some cases,
There is a possibility that only EPP particles that cannot be used for molding may be obtained, and even if molding is possible, the mechanical properties of the finally obtained EPP molded product may be greatly reduced.

In consideration of the above, the organic peroxide used in the above surface modification step has a 1-hour half-life temperature (when the organic oxide is decomposed at a constant temperature, the amount of active oxygen is 1
The temperature at which the initial half of the time) is 20 ° C. or more lower than the Vicat softening point of the present base resin, and 30 ° C. or more lower than the Vicat softening point of the present base resin. Is more preferable. 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 above glass transition temperature is JIS K 71
21-1987, the condition of the test piece was adjusted to "when measuring the glass transition temperature after performing a certain heat treatment".
The glass transition temperature in this case means the midpoint glass transition temperature determined by heat flux DSC. 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. More preferably, it is substantially decomposed at a low temperature as described above, and is 30 or higher than the Vicat softening point of the base resin.
It is more preferable to substantially decompose at a low temperature of ℃ or more.
The organic peroxide has a one-minute half-life temperature of the organic peroxide (the temperature at which the amount of active oxygen becomes half of the initial amount in one minute when the organic oxide is decomposed at a constant temperature) ± 30 ° C
It is particularly preferable to hold in the temperature range of 10 minutes or more to substantially decompose. When attempting to decompose at a temperature lower than [1 minute half-life temperature −30 ° C.], it takes a long time to decompose, resulting in poor efficiency. On the contrary, when trying to decompose at a temperature higher than [1 minute half-life temperature + 30 ° C], the decomposition may be rapid,
There is a risk that the efficiency of surface modification will be reduced. 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.

In order to decompose the organic peroxide, first, the dispersion is adjusted to a temperature at which the organic peroxide is unlikely to be decomposed, and then the dispersion is subjected to the decomposition temperature of the organic peroxide. It can be heated to. At this time, 1-minute half-life temperature ± 3
The temperature rise rate may be selected so that the temperature is maintained in the range of 0 ° C for 10 minutes or longer, but it should be stopped at any temperature within the range of 1 minute half-life temperature ± 30 ° C and held at that temperature for 5 minutes or longer. Is more preferable. 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. "Substantially decomposing" means decomposing until the active oxygen amount of the used peroxide falls to 50% or less of the initial amount, but decomposing until the active oxygen amount falls to 30% or less of the initial amount. Is preferable, and it is more preferable to decompose until the active oxygen amount becomes 20% or less of the initial amount, and it is further preferable to decompose until the active oxygen amount becomes 5% or less of the initial amount. The half-life temperature of the organic peroxide is adjusted to an organic peroxide solution having a concentration of 0.1 mol / L by using a solution relatively inert to radicals (for example, benzene and mineral spirits), It is sealed in a glass tube subjected to nitrogen substitution, immersed in a constant temperature bath set to a predetermined temperature, and thermally decomposed to be measured.

The surface-modified particles are substantially non-crosslinked. In the method A, crosslinking is not substantially progressed because no crosslinking auxiliary agent is used together. The term "substantially non-crosslinked" is defined as follows. That is, regardless of the base resin, the present resin particles, the treated 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). JIS Z 8801 (1966)
The mixture is promptly filtered through a wire mesh having a mesh of 74 μm specified in 1. and the weight of the boiling xylene insoluble matter remaining on the wire mesh 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 the decomposition treatment of the organic peroxide to modify the surface of the present resin particles, and then subjected to the production of expanded particles. The expanded particles are heated while dispersing the surface-modified particles in a dispersion medium in a dispersion medium in the presence of a foaming agent to impregnate the surface-modified particles with the foaming agent, and then when the pressure is released, the expanded particles are obtained. It is preferable to manufacture by a method of releasing the surface-modified particles and the dispersion medium under a low pressure (hereinafter, referred to as “dispersion medium-releasing foaming method”) at a temperature at which is generated. The surface modification step of forming the surface modified particles and the foaming step of obtaining expanded particles from the surface modified particles can be carried out by different devices at different times. When the foaming method is adopted, the organic peroxide having an appropriate decomposition temperature is added to the aqueous medium in a predetermined amount in a predetermined amount, and a usual dispersion medium releasing foaming method is carried out.
It is efficient because the surface modification is completed during the heating and the surface modified particles are automatically obtained.

In the surface-modified resin particles, and in turn, in the EPP particles and EPP moldings obtained from the surface-modified resin particles, the alcohol having a molecular weight of 50 or more produced by the decomposition of the peroxide is in the range of several hundreds to several thousands ppm. May be included. 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. It may be contained in the resin 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 dispersion medium releasing and foaming method, it is preferable to add a dispersant to the dispersion medium so that the surface-modified particles in the container under heating do not fuse with each other. 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.,
At least one of the anion and cation of the compound is a divalent or trivalent inorganic substance. Examples of such inorganic substances include magnesium chloride, magnesium nitrate, magnesium sulfate, aluminum chloride, aluminum nitrate, aluminum sulfate, iron chloride, iron sulfate, 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 foaming agent used in the method for producing expanded polypropylene resin particles include aliphatic hydrocarbons such as propane, butane, hexane, heptane, cycloaliphatic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, Organic physical foaming agents such as halogenated hydrocarbons such as trifluoromethane, 1,2-difluoroethane, 1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride and methylene chloride, nitrogen,
Examples of so-called inorganic physical foaming agents such as oxygen, air, carbon dioxide, and water. It is also possible to use an organic physical foaming agent and an inorganic physical foaming agent in combination. 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. Of these, nitrogen and air are preferable in consideration of the stability of the apparent density of the expanded particles, environmental load, cost, and the like.
As the water used as the foaming agent, water (including ion-exchanged water) used as a dispersion medium for dispersing the surface-modified particles in the closed container may be used as it is.

In the above 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 used, the foaming temperature and the apparent density of the foamed particles to be aimed at. 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 method A, the apparent density is 10 g / L to 500 g by adopting the dispersion medium releasing foaming method.
/ L and produced foamed 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 DSC curve by differential scanning calorimetry of the expanded particles Preferably.
Such expanded particles are expanded particles having a high closed cell rate and suitable for molding. In the case of the present invention, in the obtained expanded particles, the amount of heat at the high temperature peak is 2 J / g to 70 J / g.
Is particularly preferable. Heat quantity of high temperature peak is 2 J / g
If it is less than the above range, the compression strength, energy absorption amount, etc. of the EPP molded product may be reduced. When 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 becomes too high,
This is not preferable because the molding cycle may be lengthened. 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
It is 58 J / g), and is preferably 10 to 60%, more preferably 20 to 50% with respect to the sum of the heat quantity of the high temperature peak and the heat quantity of the intrinsic peak. still,
Sum of heat quantity of high temperature peak and heat quantity of specific peak is 40 J /
It is preferably g to 150 J / g. In the present invention and the present specification, the heat quantity of the high temperature peak and the heat quantity of the intrinsic peak both mean the heat absorption quantity, and the numerical values are expressed as absolute values.

The calorific value of the high temperature peak of the expanded particles is obtained when 2 to 4 mg of expanded particles are heated from room temperature (30 ° C.) to 200 ° C. at 10 ° C./min in a nitrogen atmosphere by a differential scanning calorimeter. Of the endothermic curve peak (high temperature peak) b appearing on the higher temperature side than the temperature at which the intrinsic endothermic curve peak (inherent peak) a derived from the heat of fusion of the base resin observed in the first DSC curve shown in FIG. 1 appears Amount of heat (endotherm)
Which corresponds to the area of the high temperature peak b, and can be specifically obtained as follows. First DS
A straight line (α-β) connecting a point α on the C curve corresponding to 80 ° C. and a point β on the DSC curve corresponding to the melting end temperature T of the expanded particles is drawn. Next, a straight line parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the above-mentioned intrinsic peak a and the high temperature peak b, and σ is the point intersecting with the straight line (α-β). . The area of the high temperature peak b is that of the curve of the high temperature peak b part of the DSC curve, the line segment (σ−β), and the part surrounded by the line segment (γ−σ) (the part shaded in FIG. 1). This is the area, and this corresponds to the amount of heat (endotherm) 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. In addition, the sum of the heat quantity of the high temperature peak and the heat quantity of the specific peak is calculated by the above-mentioned line (α-β)
It corresponds to the area surrounded by the curve.

When the specific peak and 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, if the expanded particles oriented in any direction are cut horizontally from the center in the vertical direction, two cut samples of approximately 9 mg having substantially the same shape are obtained, 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, it is once obtained at 200 ° C. to 10 ° C./min after the first DSC curve is obtained. The temperature is lowered to around 30 ° C, and again 200 ° C at 10 ° C / min.
It is not observed in the second DSC curve obtained when the temperature is raised to 0 ° C., and only the unique peak a corresponding to the endotherm at the time of melting the base resin as shown in FIG. 2 is observed. The temperature at the apex of the peculiar peak a appearing in the first DSC curve of the expanded particles is usually in the range of [Tm-5 ° C] to [Tm + 5 ° C] with reference to the melting point (Tm) of the base resin. Appears (most commonly [Tm-4 ° C] to [Tm + 4 ° C]
Appears in the range of). In addition, the first DSC of expanded particles
The temperature at the apex of the high temperature peak b appearing in the curve is usually [Tm + 5 ° C.] to the melting point (Tm) of the base resin.
Appears in the range [Tm + 15 ° C] (most commonly [Tm
[m + 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, strength physical properties such as compressive strength of the EPP molded product tend to be relatively high, but the minimum fusing temperature is 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 A are those in which the minimum fusing temperature is effectively lowered. 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 by the same method as that for obtaining the DSC curve of the expanded particles as described above by using 2 to 4 mg of the resin particles as a sample. The temperature at the apex of the endothermic curve peak a peculiar to the base resin observed in the obtained second DSC curve (one example of which is shown in FIG. 2), and the melting end temperature (Te) is the peculiar endothermic curve. DSC on the high temperature side of peak a
The intersection (β) between the curve and the high temperature side baseline ( _BL ).

The endothermic curve peak appearing in the second DSC curve for the present resin particles usually appears as one endothermic curve peak on the assumption that it is a peak due to melting of the polypropylene resin. However, when it is composed of a mixture of two or more polypropylene resins,
In rare cases, 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 length from the apex of the peak to the baseline B _L is measured on each straight line, The apex of the peak on the straight line having the longest length is defined as Tm. However, when there are two or more longest straight lines, the peak of the peak on the highest temperature side is set to Tm.

The amount of heat of the above-mentioned high temperature peak in the expanded beads mainly depends on the temperature Ta and the holding time at the temperature and the temperature Tb and the holding time at the temperature and the rising time with respect to the resin particles during the production of the expanded beads. 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 particles 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 ^ThreeMescillin 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 moldable by low temperature steam 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 A show a tendency different from that of the expanded particles obtained by the conventional method. Was divided into inner foam layer without the surface layer portion and surface layer portion of the expanded beads was measured melting point, conventional expanded beads melting point it is an internal foam layer of the melting point (Tm _s) of the surface layer portion of the foamed particles (Tm _i ), the melting point of the surface layer portion (Tm _s ) of the expanded beads obtained by the method A is higher than that of the internal foaming layer (Tm _i ). It was observed to be low. In the expanded particles that can be molded by low-temperature steam, the 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. Further, the melting point (Tm _i ) of the internal foam layer of the expanded particles was cut out from the inside of the expanded particles so as not to include the surface layer portion, and 2 to 4 mg was collected and used 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, when the high temperature peak calorific value was measured by dividing the surface layer portion of the expanded particles and the internal foamed layer not including the surface layer portion, the conventional expanded particles had a high temperature peak calorie (ΔH _s ) at the surface layer portion of the expanded particles. The relationship with the heat quantity (ΔH _i ) of the high temperature peak of the internal foamed layer was such that ΔH _s ≧ ΔH _i × 0.87, whereas in the expanded particles obtained by the method A, ΔH _s < It was observed to be ΔH _i × 0.86. For expanded particles that can be molded with low temperature steam, ΔH _s
<ΔH _i × 0.86, but ΔH _s <ΔH _i
× 0.83 is preferable, and ΔH _s <ΔH _i ×
0.80 is more preferable, and ΔH _s <ΔH _i ×
0.75 is more preferable, and ΔH _s <ΔH _i ×
0.70 is particularly preferable, and ΔH _s <ΔH _i ×
Most preferably, it is 0.60. Also, ΔH _s is
It is preferable that ΔH _s ≧ ΔH _i × 0.25. ΔH
_By satisfying _s <ΔH _i × 0.86, it becomes possible to perform in-mold molding at a lower temperature than that of the foamed particles which are not surface-modified,
The smaller the ΔH _s value, the greater the effect. In addition, ΔH
_s is preferably 1.7 J / g to 60 J / g, more preferably 2 J / g to 50 J / g,
More preferably 3 J / g to 45 J / g, and 4 J
Most preferably, it is / g to 40 J / g.

The high temperature peak calorific value of the surface layer portion 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 the high temperature peak by dividing the above-mentioned expanded particles into the surface layer portion and the inner 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, 200 μm from the surface of the foamed particles toward the center of gravity of the foamed particles. Slices are made from one or more randomly selected locations on the surface of the expanded beads so that no more than 1 is included. 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 The high temperature peak may not be measured accurately. In addition, the surface layer portion obtained from one expanded particle is 2
If the amount is less than 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 which does not include the surface layer portion of the expanded beads is expanded so that the surface of the expanded beads and the portion between the surface of the expanded beads and the center of gravity of the expanded beads of 200 μm are not included. The particles obtained by cutting off the surface layer from the entire surface may be used for the measurement of melting point and high temperature peak. 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.

For each surface of the expanded particles obtained by the method A and the expanded particles obtained by the conventional method, which have not been surface-modified, TA Instruments Japan Co., Ltd. 2 ℃ from 2 ℃ using the "2990 type micro thermal analyzer"
Micro differential thermal analysis (μDTA) was performed under the conditions of a heating rate of 10 ° C./sec. The melting start temperature is the temperature below the melting point of the base resin, whereas the melting start temperature of the surface-modified foamed particles obtained by the conventional method is the melting point of the base resin. It was found that the temperature was 5 ° C. higher than that.
It should be noted that the melting start temperature referred to here is from the baseline (BL) in the μDTA curve based on the μDTA to μD.
It means the temperature at which the TA curve started to change downward (specific heat per hour began to change).

For each of the surface-modified foamed particles obtained by the method A and the surface-modified foamed particles obtained by the conventional method, TA Instruments Japan Co., Ltd. 2 ℃ from 2 ℃ using the "2990 type micro thermal analyzer"
Micro differential thermal analysis (μDTA) was performed under the conditions of a heating rate of 10 ° C./sec. Up to 00 ° C., and an extrapolation melting start temperature of the surface of the surface-modified expanded particles obtained by the method A (claim) The extrapolation melting start temperature referred to in 5) is a temperature of [melting point + 4 ° C.] or lower of the base resin, while the extrapolation of the surface of the expanded particles obtained by the conventional method is not modified. It was found that the melting start temperature is 8 ° C or more higher than the melting point of the base resin. 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 high temperature side of the melting start temperature. Of these, the temperature at the intersection of the tangent line (TL) at which the angle between the tangent line and the straight line extending the base line (BL) to the high temperature side becomes maximum.

The μDTA curve of the expanded particles obtained in Example 1 (surface-modified expanded particles) and the expanded particles obtained in Reference Example 1 (non-surface-modified expanded particles) are shown below. An example is shown in FIG. In FIG. 3, the curve Cm is based on the expanded particles obtained in Example 1, the Pm point on the curve Cm is the melting start temperature thereof, and P
me point is the baseline (BL) and the tangent line (TL)
It is the extrapolation melting start temperature which is the intersection of On the other hand, curve C
nm is based on the expanded particles obtained in Reference Example 1, the Pnm point on the curve Cnm is the melting onset temperature, and the Pnme point is the intersection of the baseline (BL) and the tangent line (TL). It is a certain extrapolation melting onset temperature. Figure 3
Pm, Pme, Pnm and Pnm in are 131 ° C., 135 ° C., 168 ° C. and 171 ° C., respectively. In addition, FIG. 4 is a graph showing the μ relative to the surface-modified EPP expanded particle surface according to another example in which a propylene homopolymer having a melting point of 162 ° C. and an MFR of 18 g / 10 min is used as a base resin.
An example of a DTA curve is shown. In FIG. 4, the curve Cm is μ
It is a DTA curve, the Pm point on the curve Cm is its melting start temperature, and the Pme point is the extrapolation melting start temperature which is the intersection of the said baseline (BL) and the said tangent (TL). Pm and Pme in FIG. 4 are each 140 ° C.
And 142 ° C.

In the above-mentioned micro differential thermal analysis, the expanded particles are fixed to the sample stage of the apparatus (if one expanded particle is too large as it is, it is cut into, for example, half and fixed to an appropriate size. Then, toward the randomly selected location on the surface of the expanded beads, the probe tip (the portion to be brought into contact with the surface of the expanded particles is 0.
(Having a tip of 2 μm) is lowered to contact the surface of the expanded beads. 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. In addition, when only the maximum and minimum values are obtained and the difference between the maximum and minimum values exceeds 10 ° C., 10
It suffices to measure the points, find the arithmetic mean value in the same manner as described above, and adopt it. If the condition is still not met, repeat the same operation.

As for the above-mentioned results by μDTA, the lowering of the melting start temperature on the surface of the expanded particles and / or the lowering of the extrapolation melting temperature on the surface of the expanded particles contributes to the lowering of the minimum fusing temperature required at the time of molding. It is shown that. In the foamed particles that can be molded by low-temperature steam, the melting start temperature of the foamed particle surface based on the above measurement is not higher than the melting point (Tm) of the base resin, but is preferably [Tm-5 ° C] or lower. Tm
It is more preferable that the temperature is −10 ° C. or less, and [Tm-1
5 [deg.] C. or less is more preferable, and [Tm-16
[° C] to [Tm-50 ° C] is particularly preferable,
Most preferably, it is [Tm-17 ° C] to [Tm-35 ° C]. In addition, the foamed particles that can be molded with low-temperature steam have an extrapolation melting start temperature of the surface of the foamed particles based on the above measurement of [Tm + 4 ° C] or lower, but preferably [Tm-1 ° C] or lower. Tm-6 ° C or less is more preferable, [Tm-17 ° C] to [Tm-50 ° C] is further preferable, and [Tm-18 ° C] to [Tm-.
35 [deg.] C.] is most preferable. 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 A was the same as the MFR value of the present resin particles before surface modification, but showed a larger value. Was observed. The MFR value of the expanded beads is preferably 1.2 times or more, more preferably 1.5 times or more, more preferably 1.8 times or more the MFR value of the resin particles before surface modification. Most preferably, it is 3.5 times.
The MFR value of the expanded beads is 0.5 to 1 in consideration of the heat resistance of the EPP molded product and the expansion efficiency during the production of the expanded beads.
50 g / 10 minutes is preferable, and 1 to
It is more preferably 100 g / 10 min, and even more preferably 10-80 g / 10 min.

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 by 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 measure 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.

Furthermore, the expanded beads obtained by the method A are
When an organic peroxide that generates radicals is used, the organic peroxide
Modification table containing a small amount of oxygen due to the addition of oxides
Form a surface. This means that the surface of the expanded particles obtained by the method A is
Surface and the surface of the EPP molding produced from it?
It is clear from Specifically, foaming obtained by method A
The surface of the EPP molded article produced from the particles (that is, expanded particles)
(Substantially the same as the surface of the) and no conventional surface modification
Each of the surfaces of EPP moldings made from expanded foam particles
As a result of comparing these by ATR measurement (total reflection absorption measurement method),
Table of EPP moldings produced from expanded particles obtained by method A
The surface is newly 1033 cm^-1There is a difference in absorption in the vicinity.
It has been confirmed that oxygen alone or an oxygen-containing government
It was confirmed that there were changes such as addition or insertion of functional groups.
It was Specifically, 1166 cm ^-1In the absorption of both
Height (for molded articles from expanded particles obtained by method A)
Absorption peak height and absorption peak height for conventional moldings
From the expanded particles obtained in Method A
1033 cm of the surface of the molded body^-1Height of absorption peak in the vicinity
Is 1033 cm of the surface of the conventional molded body^-1Absorption peak near
It is higher than the height of Ku. Furthermore, the surface view of expanded particles
Based on EDS (energy dispersive analyzer)
As a result of elementary analysis, with regard to the ratio of oxygen and carbon,
In the case of the obtained expanded particles, it was 0.2 (mol / mol).
On the other hand, in the case of conventional expanded particles, 0.09 (mol
/ Mol). From the above, the organic peroxide
Form a modified surface containing a small amount of oxygen by the addition action
It is clear that they are. The formation of such a modified surface
Increases the permeability of steam during molding, and
It is believed to enable molding. From this perspective, low
Foam particles that can be molded with warm steam are
According to the above EDS, the ratio of oxygen to carbon is 0.15.
The above is preferable. Can be formed with low temperature steam
The expanded particles have a modified surface containing oxygen and / or
Reversal of melting point and / or surface layer of expanded particles
Of the high-temperature peak calorific value of
Decrease in melting start temperature and / or extrapolation of the surface of the expanded particles
Due to the lower melting start temperature, the minimum fusing temperature is increased.
It is estimated that it will be 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 obtain 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 / closed and sealed after increasing the internal pressure of bubbles as necessary, and saturated steam is supplied to the EPP molded product. Can be manufactured by employing a batch-type molding method in which the EPP particles are heated to expand each other so as to be fused 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 thereof is 0.41 MPa (G) or 0.45 MPa although it varies slightly depending on the country.
Many are (G). Therefore, the pressure of the saturated steam at the time of expanding and melting the EPP particles is 0.45M.
It is preferably less than or equal to Pa (G), and 0.4
It is more preferably 1 MPa (G) or less or less. In addition, the EPP 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, to obtain a saturated steam supply region (heating region). ), The EPP particles are expanded and fusion-bonded to each other, then passed through a cooling region 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-9-1040
No. 26, JP-A-9-104027, JP-A-10-180888 and the like). In this method, the inside of the passage is the inside of the mold. When increasing the bubble internal pressure of the EPP particles, put the foamed particles in a closed container, and leave the foamed particles in the container for a suitable time to allow the compressed air to permeate the foamed particles. Good. E manufactured by the above method
The apparent density of the PP molded body can be arbitrarily selected depending on the purpose, but is usually in the range of 9 g / L to 600 g / L. E
The apparent density of the PP molded body is JIS K 7222.
It is the apparent overall density (1999). 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. Such laminated composite type in-mold foam molding and its manufacturing method are described in US Pat. No. 5,928,776, US Pat. No. 6,096,417, and US Pat.
U.S. Pat. No. 5,474,841 and European Patent 47.
7476, WO98 / 34770, WO98 / 00
No. 287, Japanese Patent No. 3092227 and the like are described in detail. Further, the insert material can be compositely integrated so that all or part of the insert material is embedded in the molded body. Such an insert composite type in-mold foam molded article and a manufacturing method thereof,
US Pat. No. 6,033,770, US Pat. No. 547484
No. 1, Japanese Unexamined Patent Publication No. 59-1277714, 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.

[0067]

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

Example 1, Reference Example 1 Polypropylene homopolymer (glass transition point: -21 ° C.,
Vicat softening point: 147 ° C., melting point: 162 ° C., crystallization temperature is 123 ° C., MFR: 18 g / 10 minutes) Extruded by adding 0.05 parts by weight of zinc borate powder (cell regulator) per 100 parts by weight. After melt-kneading in the machine, extruded in a strand form from the extruder, 1 second after extrusion, sink the strand in a cooling medium (water adjusted to 18 ° C) in a water tank, take it off while cooling, and cool sufficiently Did (cooling time 13
After that, the strand was pulled up from the cooling medium, and the strand was cut so that the length / diameter ratio was about 1.0 to obtain resin particles having an average weight of 2 mg per particle. The capacity of the cooling medium contained in the water tank was 170 liters. ΔH _a and ΔH _b were measured for the obtained resin particles. The results are shown in Table 1.

Next, in a 400 liter autoclave, 100 parts by weight of the above resin particles and 23 ° C. as a dispersion medium were added.
220 parts by weight of deionized water, sodium dodecylbenzenesulfonate (surfactant) 0.005 parts by weight, kaolin powder (dispersant) 0.3 parts by weight, and aluminum sulfate powder (dispersion strengthening agent) 0.01 parts by weight, Bis (4-t-butylcyclohexyl) peroxydicarbonate as an organic peroxide (1 hour half-life temperature: 58 ° C., 1 minute half-life temperature: 92 ° C.) (in Reference Example 1, no organic peroxide was used). )
And the amount of carbon dioxide gas (foaming agent) shown in Table 1 was charged, and the temperature was 5 than the foaming temperature (165.5 ° C.) while stirring in a sealed state.
The temperature was raised to a temperature lower by 0 ° C. (average heating rate 3 ° C./min), and then the temperature was maintained for 15 minutes. Then, the temperature was raised to the foaming temperature (average temperature rising rate 3 ° C./min) and maintained at the same temperature 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 high pressure 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 foamed particles thus obtained were washed with water and subjected to a centrifuge, and then subjected to 48 ° C. under atmospheric pressure at room temperature of 23 ° C.
After leaving for a long time to cure, the high temperature peak calorific value of the expanded particles,
Each high temperature peak calorific value and each melting point of the surface layer portion and the internal foamed layer, MFR of the foamed particles, apparent density of the foamed particles and the like were measured. The results thereof are shown in Table 1. The expanded particles obtained in Example 1 and Reference Example 1 were substantially non-crosslinked (the boiling xylene insoluble content was 0 in all).

Next, the expanded particles were placed under pressure in a pressure-resistant container to give an increased bubble internal pressure to the expanded particles, and then the bubble internal pressure shown in Table 1 (indicated as the expanded particle internal pressure in the table). At that time, in a mold having a molding space of 250 mm × 200 mm × 50 mm, with a slight gap (about 1 mm) opened without completely closing the mold (when the direction of the molding space 50 mm is 51 mm). ) After filling, the mold is completely clamped, and then the air in the mold is exhausted by steam.
It was molded by the minimum fusion temperature (minimum saturated steam pressure) shown in. After molding, the surface pressure of the molded body in the mold is 0.059
After water cooling to MPa (G), the molded body was taken out of the mold and dried at 60 ° C for 24 hours, and then at room temperature (23 ° C).
Cooled down. Then, after curing in the room for 14 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.
Up to (G), the saturated steam pressure is increased by 0.01 MPa to repeatedly produce a molded body, and the molded body after curing is 250 mm.
25mm with a cutter knife on one side of the 200mm surface
Approximately 10 in the thickness direction of the molded product so as to divide the 0 mm length into two.
After making a notch of mm, the number of foamed particles present in the fracture surface (n) and the number of foamed particles having material fractured (b) were tested by bending and breaking the molded product from the notch.
It means the saturated steam pressure required for the molding when the value of the ratio (b / n) of 1 was 0.50 or more for the first time.

However, in Reference Example 1, the value of (b / n) was 0.30 at the saturated steam pressure of 0.55 MPa (G) which is the pressure resistance of the molding machine used in this test. It 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. The larger the value of (b / n), the better the bending strength and the tensile strength of the molded body, which is preferable.

The compressive strength in Table 1 is 50 mm in length and 50 m in width from the molded body after curing obtained at the minimum fusion temperature.
m, thickness 25 mm, and a test piece obtained by cutting it so that the entire surface of the skin was cut
Z 0234 (1976) Test piece temperature 2 according to method A
A compression test was conducted under conditions of 3 ° C. and a load speed of 10 mm / min until the strain reached 55%. From the stress-strain diagram obtained, 50% was obtained.
The stress at the time of strain was read and used as the compressive strength. Also,
The apparent density (g / L) of the expanded particles in Table 1 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 23
The apparent volume (cm ³ ) of the expanded particles is read from the excluded volume when submerged in water in a graduated cylinder containing 100 cm ³ of water at 0 ° C., and this is converted into a unit of liter. 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-
10.0000 g, and the apparent volume of expanded particles is 50-
90 cm ³ of expanded particles are used. The internal pressure of the expanded particles in Table 1 is expressed by a gauge pressure as described above, and therefore (G) is added after the numerical value. Further, in Example 1 and Reference Example 1, and further in Examples 2 to 4 and Comparative Example 1 described later, the glass transition temperature, the melting point of the base resin, the melting point of the foamed particles and the calorific value of the high temperature peak are Shimadzu Corporation. Shimadzu heat flux differential scanning calorimeter "DSC-5"
It was measured using "0".

The above results show that a dispersion formed by dispersing polypropylene resin particles having ΔH _a / ΔH _b of 0.95 or less in a dispersion medium in which an organic peroxide is present is a polypropylene resin. The surface of the polypropylene-based resin particles is modified by decomposing the organic peroxide by maintaining the temperature at a temperature lower than the melting point of the base resin of the particles and substantially decomposing the organic peroxide. When the step of obtaining substantially non-crosslinked surface-modified particles 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 similar between Example 1 that has undergone the surface modification step and Reference Example 1 that 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 1 and Reference Example 1, both expanded particles have almost the same high-temperature peak calorific value as a whole, but the expanded particle of Example 1 which has undergone the surface modification step has a high-temperature peak calorific value in the surface layer portion, It can be seen that the calorific value at the high temperature of the surface layer portion of the expanded beads of Reference Example 1 which did not undergo the quality step is decreased. The minimum fusing temperature required in Example 1 is 0.36MP
In contrast to a (G), the minimum fusing temperature required in Reference Example 1 exceeded 0.55 MPa (G) even though the internal pressure of the expanded particles was doubled or more than in Example 1. It can be seen that in Example 1, the minimum fusing temperature is lowered by 13 ° C. or more as compared with Reference Example 1. Moreover, the compressive strength of the molded product obtained in Example 1 matches the high temperature peak of the entire expanded particles and the apparent density of the cut sample, and does not particularly decrease. It is considered that the above-mentioned decrease in the high-temperature peak calorific value of the surface layer portion of the expanded particles contributes to the decrease in the minimum fusing temperature required at the time of molding.

Furthermore, regarding the expanded beads obtained in Example 1 and the expanded beads obtained in Reference Example 1, a micro thermal analysis system "2990" manufactured by TA Instruments Japan Co., Ltd. was used for each expanded beads surface. Micro differential thermal analysis (μDT) under the conditions of temperature rising rate of 10 ℃ / sec from 25 ℃ to 200 ℃.
When A) was carried out, the surface of the expanded beads obtained in Example 1 had a melting onset temperature of 131 ° C and an extrapolation melting onset temperature of 135 ° C, whereas the foamed particles obtained in Reference Example 1 The surface of the particles had a melting onset temperature of 168 ° C and an extrapolated melting onset temperature of 171 ° C. It is considered that the decrease in the melting start temperature and / or the decrease in the extrapolation melting temperature on the surface of the expanded beads due to the above μDTA contributes to the decrease in the minimum fusion temperature required at the time of molding.

[0076]

[Table 1]

Examples 2 to 4, Comparative Example 1 Polypropylene homopolymer (glass transition point: -21 ° C,
Vicat softening point: 148 ° C., melting point: 163 ° C., crystallization temperature of 118 ° C., MFR: 8 g / 10 min) Extruded by adding 0.05 part by weight of zinc borate powder (cell regulator) per 100 parts by weight. After melt kneading in the machine, extruded in a strand form from the extruder, and X seconds after extrusion (indicated as X in Table 2)
, The strand is immersed in a cooling medium (water whose temperature is shown in Table 2) in a water tank, and the strand is taken while cooling.
After cooling in the time shown in Table 2 (indicated as cooling time in Table 2), the length / diameter ratio was approximately 1.0 after being pulled out from the cooling medium.
The strand was cut so that the average particle weight of the particles was 2 mg to obtain resin particles. The capacity of the cooling medium contained in the water tank was 170 liters. ΔH _a and ΔH _b were measured for the obtained resin particles. The results are shown in Table 2.

Then, in an autoclave of 400 liters, 100 parts by weight of the above resin particles and 23 ° C. as a dispersion medium.
220 parts by weight of deionized water, sodium dodecylbenzenesulfonate (surfactant) 0.005 parts by weight, kaolin powder (dispersant) 0.3 parts by weight, and aluminum sulfate powder (dispersion strengthening agent) 0.01 parts by weight, Bis (4-t-butylcyclohexyl) peroxydicarbonate (1 hour half-life temperature: 58 ° C., 1 minute half-life temperature: 92 ° C.) as an organic peroxide and the amount of carbon dioxide gas (foaming agent) shown in Table 2 Was charged, and the temperature was raised to 5 ° C lower than the foaming temperature shown in Table 2 with stirring in a closed state (average heating rate 3 ° C /
Min) and held at that temperature for 15 minutes. Next, the temperature is raised to the foaming temperature (average temperature rising rate 3 ° C./min) and the temperature is raised to 15
Hold for 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 high pressure 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 foamed particles were washed with water and subjected to a centrifuge, the obtained foamed particles were washed with water and subjected to a centrifuge, and then allowed to stand for 48 hours under atmospheric pressure at room temperature of 23 ° C., and then, Example 1 The high temperature peak calorie of the entire expanded particles and the apparent density of the expanded particles were measured in the same manner as in. The results are shown in Table 2.

The expanded particles obtained in Examples 2 to 4 and Comparative Example 1 were substantially non-crosslinked (the boiling xylene insoluble content 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, at the bubble internal pressure shown in Table 2 (indicated as the expanded particle internal pressure in the table), 250m
In a mold with a molding space of m × 200 mm × 50 mm,
After the mold was not completely closed and a small gap (about 1 mm) was opened (with the molding space having a direction of 50 mm of 51 mm), the mold was completely clamped, and then exhausted. It was molded in the same manner as in No. 1 at the minimum fusion temperature (minimum saturated steam pressure) shown in Table 2.

[0080]

[Table 2]

The above results indicate that the polypropylene resin particles are dispersed in an aqueous medium in which the organic peroxide is present, and the temperature is lower than the melting point of the base resin of the polypropylene resin particles and the organic peroxide is When the step of modifying the surface of the polypropylene-based resin particles to obtain substantially non-crosslinked surface-modified particles by decomposing the organic peroxide at a temperature at which is substantially decomposed, The obtained expanded particles show that the molding temperature is reduced while maintaining the recyclability of the polypropylene resin.
More specifically, it is as follows.

In Examples 2, 3 and 4 and Comparative Example 1, the apparent densities of the expanded particles were almost the same and the high temperature peak calorific value and the internal pressure of the entire expanded particles were almost the same. Since the apparent densities are the same, it is convenient to compare. From the comparison between Examples 2, 3, and 4 and Comparative Example 1, the minimum fusion temperature in Comparative Example 1 is 0.48 MPa (G), while the minimum fusion temperature in Examples 2, 3, and 4 is 0.41 MPa (G) and 0.43 MPa, respectively
(G) and 0.45 MPa (G). From the above, it can be seen that the minimum fusion temperature of Example 4 is lower than that of Comparative Example 1 by about 2 ° C., and the minimum fusion temperature of Example 3 is about 3.5 as compared to Comparative Example 1. It was found that the minimum fusion temperature was about 5 in Example 2 as compared with Comparative Example 1.
It can be seen that the temperature is lowered by ℃. From the results of Examples 2-4 and Comparative Example 1, if the condition of the surface modification are the same, [Delta] H _a /
It can be seen that the smaller the ratio of ΔH _b, the more the contribution to the reduction of the minimum fusing temperature.

[0083]

INDUSTRIAL APPLICABILITY The present invention is a polypropylene resin particle having a ΔH _a / ΔH _b ratio of 0.95 or less. Can be done. The expanded particles obtained from such surface-modified resin particles (surface-modified particles) are substantially non-crosslinked, and the molding temperature is lower than before, so less energy is required. It can be molded. 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 exceeds the pressure resistance of a general-purpose molding machine, but in the expanded particles obtained from the surface-modified particles, a high-temperature peak calorific value obtained by using a polypropylene resin having a high melting point is high. Even with expanded particles, it is possible to perform molding with steam at a lower temperature than before while maintaining the high rigidity of the obtained EPP molded product, and if surface modification is sufficient, within the pressure resistance of a general-purpose molding machine. Molding is also possible. 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. In addition, surface-modified resin particles,
Since the expanded beads and the molded product are substantially non-crosslinked, they are preferable because they do not impair the environmental suitability and recyclability of the polypropylene resin.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an example of a chart of a second DSC curve of polypropylene 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 1 and Reference Example 1.

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 another example.

Continued front page    (72) Inventor Keiichi Hashimoto             10-3 Satsukicho, Kanuma City, Tochigi Prefecture             KSP Kanuma Research Institute (72) Inventor Taiki Yanagisawa             10-3 Satsukicho, Kanuma City, Tochigi Prefecture             KSP Kanuma Research Institute F-term (reference) 4F070 AA15 DA11 DB01 DC11                 4F074 AA24A AD08 BA32 BA33                       BA34 BA35 BA37 BA40 BA42                       CA24 CA34 CC03X CC04X                       CC04Y CC10X CC32X

Claims (8)

[Claims] 1. A polypropylene resin particle comprising a polypropylene resin having a melting point of 158 ° C. or higher as a base resin, the polypropylene resin particle being measured by a differential scanning calorimeter at a rate of 10 ° C./minute from 30 ° C. to 200 ° C. Immediately after heating to 1 ° C (first heating), 200 ° C to 30 ° C at a rate of -10 ° C / min.
And then immediately again at a rate of 10 ° C / min for 30
When heated from 2 ° C to 200 ° C (second heating), the heat quantity (ΔH _a ) of the endothermic curve peak appearing in the DSC curve during the first heating and the DSC curve during the second heating are shown. The ratio (ΔH _a / to the heat quantity (ΔH _b ) of the peak of the endothermic curve that appears
ΔH _b ) is 0.95 or less, polypropylene-based resin particles. 2. A dispersion medium in which an organic peroxide is present,
While dispersing polypropylene resin particles having a polypropylene resin having a melting point of 158 ° C. or higher as a base resin,
A surface modification obtained by decomposing the organic peroxide by holding the dispersion medium at a temperature lower than the melting point of the base resin of the polypropylene resin particles and at a temperature at which the peroxide is substantially decomposed. The polypropylene-based resin particle according to claim 1, which is used in a method for producing expanded beads by expanding fine particles. 3. A polypropylene system having a melting point of 158 ° C. or higher.
DSC curve by differential scanning calorimetry using resin as base resin
From the endothermic curve peak derived from the heat of fusion of the base resin
Is also an expanded particle having an endothermic curve peak on the high temperature side and
Of the endothermic curve existing on the high temperature side of the surface layer of the expanded particles.
Calorie (ΔH_s) And the high temperature of the internal foam layer of the expanded particles
Heat quantity of the endothermic curve peak existing on the side (ΔH_i) Relationship with
Is ΔH _s<ΔH_iProduces expanded particles that are x 0.86
For use as a polypropylene-based resin particle
Differential scanning calorimeter at 30 ° C at a rate of 10 ° C / min.
Immediately after heating from 1 to 200 ° C (first heating), -1
Cool from 200 ° C to 30 ° C at a rate of 0 ° C / min,
Immediately after, again at a rate of 10 ° C / min from 30 ° C to 200 ° C
When heating up to (first heating), during the first heating
Of the endothermic curve peak appearing in the DSC curve of_a)
And the endothermic curve that appears in the DSC curve during the second heating
Peak heat quantity (ΔH_b) Ratio (ΔH_a/ ΔH_b) Is 0.
Polypropylene resin characterized by being 95 or less
particle. 4. A polypropylene resin having a melting point of 158 ° C. or higher is used as a base resin, and a DSC curve by differential scanning calorimetry shows an endothermic curve peak on the higher temperature side than the endothermic curve peak derived from the heat of fusion of the base resin. Micro-differential thermal analysis of the foamed particles present and on the surface of the foamed particles (25
Polypropylene resin particles for producing expanded particles having a melting start temperature of not higher than the melting point of the base resin based on a temperature rising rate of 10 ° C./sec. Immediately after heating from 30 ° C to 200 ° C at a rate of 10 ° C / min (first heating) with a calorimeter, cooling from 200 ° C to 30 ° C at a rate of -10 ° C / min, and immediately thereafter. When heated again from 30 ° C. to 200 ° C. at a rate of 10 ° C./minute (second heating), the heat quantity (ΔH _a ) of the endothermic curve peak appearing in the DSC curve during the first heating, and The ratio (ΔH _a / ΔH) to the heat quantity (ΔH _b ) of the endothermic curve peak appearing in the DSC curve during the second heating.
_b ) is 0.95 or less, polypropylene-based resin particles. 5. A polypropylene resin having a melting point of 158 ° C. or higher is used as a base resin, and a DSC curve by differential scanning calorimetry shows an endothermic curve peak on the higher temperature side than the endothermic curve peak derived from the heat of fusion of the base resin. Micro-differential thermal analysis of the foamed particles present and on the surface of the foamed particles (25
A polypropylene-based resin particle for producing foamed particles having an extrapolation melting start temperature based on a temperature rising rate of 10 ° C./sec from 200 ° C. to 200 ° C. is not more than [melting point + 4 ° C.] of the base resin, The resin particles were analyzed by a differential scanning calorimeter to give 10
Immediately after heating from 30 ° C. to 200 ° C. at a rate of ° C./min (first heating), cooling from 200 ° C. to 30 ° C. at a rate of −10 ° C./min, and immediately thereafter, again at 10 ° C./min. When heated from 30 ° C. to 200 ° C. at the rate of (second heating), the heat quantity (ΔH _a ) of the endothermic curve peak appearing in the DSC curve during the first heating and the second heating DS of time
A polypropylene resin particle having a ratio (ΔH _a / ΔH _b ) to the heat quantity (ΔH _b ) of an endothermic curve peak appearing on the C curve is 0.95 or less. 6. The polypropylene resin particle according to claim 1, wherein ΔH _a / ΔH _b is 0.85 or less. 7. The resin particles are columnar particles having a ratio (L / D) of the length (L) to the average diameter (D) of 0.5 to 2, and the average weight per particle is 0.1-20 mg
The polypropylene-based resin particles according to any one of claims 1 to 6, wherein 8. A method for producing the polypropylene resin particles according to claim 1, wherein the melting point is 1.
After heating and melting the polypropylene-based resin at 58 ° C. or higher, the molten polypropylene-based resin is cooled in a cooling medium at least 30 ° C. lower than the crystallization temperature of the polypropylene-based resin and then cut into particles, or Alternatively, the molten polypropylene resin is cooled in a cooling medium at least 30 ° C. lower than the crystallization temperature of the polypropylene resin immediately after being cut into particles in the molten state, or the molten polypropylene resin is particles in the molten state. A method for producing polypropylene-based resin particles, which comprises cooling in a cooling medium at least 30 ° C. lower than the crystallization temperature of the polypropylene-based resin while cutting the polypropylene-based resin particles.