JPH11106576A - Polypropylene resin composition, preexpanded particle prepared therefrom, and production of the particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compsn. from which preexpanded particles can be economically prepd. even without using a blowing agent by compounding an ethylene- propylene random copolymer with specified amts. of an ionomer resin and an inorg. filler and/or an org. filler so that the resulting compsn. has a specified water content. SOLUTION: 100 pts.wt. ethylene-propylene random copolymer (A) is compounded with 0.05-20 pts.wt. ionomer resin (B) prepd. by neutralizing an ethylene-(meth)acrylic acid copolymer with an alkali metal and 0-10 pts.wt. inorg. filler and/or org. filler (C) so that the water content of the resulting compsn. (based on the sum of ingredients A and B, under the water vapor pressure at the m.p. of ingredient A) is 1-50 wt.%. Particles made of the compsn. are dispersed in an aq. dispersion medium in a tightly sealed container and heated to a temp. higher than the m.p. of ingredient A but lower than its melting completion temp. to give water-contg. particles. Then, one end of the container is opened to gush out the medium, thus giving preexpanded particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene resin composition having an improved water content, pre-expanded particles comprising the same, and a method for producing the same. More specifically, the present invention relates to, for example, pre-expanded particles from a polypropylene resin composition which can be preferably used as a raw material of an in-mold foam molded article, a method for producing the same, and a highly water-containing polypropylene resin composition used for the same.

[0002]

2. Description of the Related Art Conventionally, polypropylene resin particles containing a foaming agent are dispersed in an aqueous dispersion medium, and the resin is softened while maintaining the pressure in the container at or above the vapor pressure of the foaming agent. There is known a method in which a material is heated to a temperature or higher and then discharged from a pressurized container into a low-pressure atmosphere and foamed (for example, JP-A-52-77174).

[0003] In general, the melting point of a polypropylene resin and the water content under a water vapor pressure at that temperature are as low as less than 1% (wt%, the same applies hereinafter). In the production of pre-expanded particles, a foaming agent such as a volatile organic foaming agent or carbon dioxide has been required.

However, volatile organic foaming agents are not preferred because propane and butane have safety problems such as toxicity and flammability, and chlorofluorocarbons have environmental problems such as destruction of the ozone layer. Further, it is also known that when a volatile foaming agent is used, it is difficult to control the expansion ratio, and the volatile foaming agent itself is expensive, so that there is a disadvantage that the cost is increased.

On the other hand, it is preferable not to use carbon dioxide because it causes global warming. Further, since the pressure must be increased during the production of pre-expanded particles, large equipment is required and the equipment cost is high. There is a disadvantage that.

[0006] As a method of solving the above disadvantages,
A method has been proposed in which polypropylene resin particles containing 30 to 50% of an inorganic filler are foamed using water as a dispersion medium as a foaming agent (Japanese Patent Publication No. 49-2183).

However, in this method, since a large amount of inorganic filler is used, the fusion property between particles during in-mold molding is deteriorated, and the mechanical strength and flexibility of the obtained molded body are impaired. There is.

On the other hand, similarly, a method of obtaining pre-expanded particles of a polypropylene resin by using water as a dispersing medium as a blowing agent is described as a metal salt of a higher fatty acid having 12 to 22 carbon atoms, for example, A
A method using an ethylene-propylene random copolymer having an ethylene content of 4 to 10% containing 0.4 to 10% of a 1 salt or a Zn salt as a base resin (Japanese Patent Application Laid-Open No. 60-18843)
No. 5), a method in which an ethylene-propylene random copolymer having an ethylene content of 2 to 10% is used as a base resin, and the internal pressure of the initial vessel before heating is adjusted to 5 kg / cm ² G with an inorganic gas (Japanese Patent Application Laid-Open No. 60-221440) Publication).

However, in order to obtain pre-expanded particles having a high expansion ratio by these methods, the ethylene content of the ethylene-propylene random copolymer must be 4% or more, and
Heating conditions of 160 ° C. and 10 hours or more are required. When heating is performed at such a high temperature for a long time, fusion of particles in a dispersion medium is likely to occur, and further, productivity is poor and it is not economical.

Accordingly, a method for economically producing pre-expanded polypropylene resin particles having desired physical properties without using a volatile organic foaming agent or a foaming agent such as carbon dioxide, which has been conventionally required in recent years, is not required. The development of is desired.

[0011]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, the present invention relates to a pre-expansion of a polypropylene resin having desired characteristics without using a conventional foaming agent such as a volatile foaming agent or carbon dioxide gas. The present invention has been made to provide a method for economically producing particles, a highly water-containing polypropylene resin composition which can be used in the method, and a pre-expanded particle comprising the composition. 100 parts of a copolymer (parts by weight, hereinafter the same), (B) 0.05 to 20 parts of an ionomer resin obtained by neutralizing an ethylene- (meth) acrylic acid copolymer with an alkali metal ion,
(C) inorganic and / or organic fillers 0-10
And the melting point of the ethylene-propylene random copolymer and the water content under steam pressure at that temperature (ratio to the total amount of the components (A) and (B),
(Hereinafter simply referred to as water content) is 1 to 50%, wherein the ethylene content of the ethylene-propylene random copolymer is 0.05 to 8%. The polypropylene resin composition according to claim 1 (claim 2), wherein the inorganic filler is talc; the polypropylene resin composition according to claim 1 (claim 3); Pre-expanded particles obtained by pre-expanding particles, wherein the expansion ratio is 5 to 50 times, the closed cell ratio is 80 to 100%, and the average cell ratio is 50 to 500 μm. The pre-expanded particles according to claim 4, wherein the DSC curve obtained by differential scanning calorimetry has a peak on a higher temperature side than an intrinsic peak of the ethylene-propylene random copolymer. 5), as well as particles made of claims 1 polypropylene resin composition according, dispersed in an aqueous dispersion medium in a closed vessel, the particles of the ethylene -
After heating to a temperature equal to or higher than the melting point of the propylene random copolymer and lower than the melting end temperature to obtain water-containing particles having a water content of 1 to 50%, one end of the closed container is opened, and the water-containing particles and the aqueous dispersion medium are released. Is released into an atmosphere at a pressure lower than the internal pressure of the closed vessel, and the water-containing particles are foamed (claim 6).

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polypropylene resin composition of the present invention contains an ethylene-propylene random copolymer 10
0 parts, an ionomer resin obtained by neutralizing an ethylene (meth) acrylic acid copolymer with an alkali metal ion 0.05
-20 parts, and 0-10 parts of inorganic and / or organic fillers.

The ethylene-propylene random copolymer has foaming properties, moldability, mechanical strength of the obtained molded article,
Heat resistance, a component used to obtain pre-expanded particles having an excellent balance of flexibility, and the ionomer resin is a component used to increase the water content of the polypropylene-based resin composition. The inorganic filler and / or the organic filler are components used for obtaining pre-expanded particles having higher uniform expansion ratio and having more uniform cells at the time of pre-expansion.

The ethylene content in the ethylene-propylene random copolymer is preferably 0.05 to 8%, more preferably 0.1 to 3.8%. Ethylene content 0.0
If it is less than 5%, the melting point and the degree of crystallinity become too high, so that the foamability of the pre-expanded particles and the fusion property at the time of molding become insufficient, and the flexibility of the obtained molded article tends to be insufficient. is there. If it exceeds 8%, the mechanical strength and heat resistance of the molded article tend to be insufficient.

The ethylene-propylene random copolymer may contain other copolymerizable copolymer components for improving adhesiveness, transparency, impact resistance, gas barrier properties, antistatic properties and moldability. For example, vinyl acetate, methyl methacrylate, vinyl alcohol, methacrylic acid, vinyl chloride and the like may be contained. The copolymerization ratio of the other copolymerization components is preferably 2% or more in order to obtain an effect by using the copolymerization component. The upper limit is 30%.

Although the ethylene-propylene random copolymer varies depending on the ethylene content and the method of preparing the measurement sample, the melt index (MI) is 2%.
0.5-30 g / 10 min at 30 ° C.
20 g / 10 min is preferable, and the flexural modulus (J
5,000k to 20,000k for IS K 7203)
gf / cm ² , and 8000 to 16000 kgf / c
m ² , melting point of 125 to 165 ° C., and further 135
~ 155 ° C is preferred. The MI is 0.5 g / 1
If it is less than 0 minutes, the melt viscosity is too high to obtain pre-expanded particles having a high expansion ratio, and if it exceeds 30 g / 10 minutes, the melt viscosity with respect to the elongation of the resin at the time of foaming is low and the foam is easily broken. , The open cell ratio of the pre-expanded particles tends to increase. If the bending strength is less than 5000 kgf / cm ² , the mechanical strength and heat resistance become insufficient,
If it exceeds 000 kgf / cm ² , the obtained foamed molded article tends to have insufficient flexibility and cushioning properties. Further, when the melting point exceeds 165 ° C, the fusion property at the time of molding,
The buffer characteristics are insufficient, and if the temperature is lower than 125 ° C., the heat resistance tends to be insufficient.

The ethylene-propylene random copolymer may be used in a non-crosslinked state, or may be used after being crosslinked by a peroxide or radiation. These may be used alone or in combination of two or more. By using these ethylene-propylene random copolymers, pre-expanded particles having a high expansion ratio and good moldability can be easily obtained, and the mechanical strength and heat resistance of a molded article manufactured from the obtained pre-expanded particles can be improved. This is preferable because the balance between the properties and the flexibility is improved.

The ionomer resin is obtained by neutralizing an ethylene- (meth) acrylic acid copolymer with an alkali metal ion.

The ethylene- (meth) acrylic acid copolymer serving as the base resin of the ionomer resin has an ethylene content of preferably 25 to 99%, more preferably 50 to 90%. When the ethylene content is less than 25%, ethylene-
Dispersibility in the propylene random copolymer is not sufficient, and particles are likely to fuse together in the container during production of pre-expanded particles. When the ethylene content exceeds 99%,
In order to obtain a predetermined moisture content, a large amount of ionomer resin must be contained, and the mechanical strength of the obtained molded body,
Heat resistance and dimensional stability during water absorption tend to decrease.

The ethylene- (meth) acrylic acid copolymer may contain (meth) acrylic ester as a copolymer component other than ethylene and (meth) acrylic acid to improve flexibility, low-temperature brittleness, and moldability. May be copolymerized. Specific examples of the (meth) acrylate include isobutyl acrylate, methyl methacrylate, ethyl acrylate, 2-ethylhexyl methacrylate, and the like. These may be used alone or in combination of two or more.

In order to obtain the above-mentioned effects, it is preferable to use 5% or more. If it exceeds 20%, a large amount of ionomer resin must be contained in order to obtain a predetermined water content. Strength and heat resistance tend to be insufficient.

The method for producing the ethylene- (meth) acrylic acid copolymer is not particularly limited, and may be a conventional method such as a high-pressure radical polymerization method.

The ionomer resin is produced by partially or completely neutralizing an ethylene- (meth) acrylic acid copolymer with an alkali metal ion.

The alkali metal ions are preferably ions of Li, Na and K belonging to Group Ia of the periodic table. As metal ion sources, hydroxides of alkali metals,
Oxides, carbonates, bicarbonates, acetates and the like may be used.

Various methods are known for converting the ethylene- (meth) acrylic acid copolymer into an ionomer resin. A typical method is melt kneading using an extruder or the like. ) A method of reacting the acrylic acid copolymer with the metal ion source. The degree of neutralization of the carboxyl group contained in the ethylene- (meth) acrylic acid copolymer is preferably from 30 to 90%, more preferably from 40 to 80%. When the degree of neutralization is less than 30%, a large amount of ionomer resin must be contained in order to obtain a predetermined water content, and the obtained molded article has mechanical strength, heat resistance, and dimensional stability upon water absorption. Tends to be insufficient. When the degree of neutralization exceeds 90%, it becomes difficult to produce an ionomer resin.

The amount of the ionomer resin used depends on the (meth) acrylic acid content in the ionomer resin, the type of metal ions, the degree of neutralization, and the like. Usually, a polypropylene resin composition having a predetermined water content is used. In order to obtain, the amount is 0.05 part or more, preferably 0.5 part or more with respect to 100 parts of the ethylene-propylene random copolymer, and has good production stability and foaming characteristics during the production of the pre-expanded particles. In order to impart excellent moldability, mechanical strength, heat resistance and water absorption dimensional stability to the obtained molded body,
It is 20 parts or less, preferably 10 parts or less.

Specific examples of the inorganic filler among the inorganic filler and / or the organic filler include talc, calcium carbonate, calcium hydroxide and the like. These inorganic fillers may be used alone or in combination of two or more. Among these inorganic fillers,
Talc is preferred because pre-expanded particles having uniform cells and a high expansion ratio can be obtained.

The organic filler among the inorganic filler and / or the organic filler is not particularly limited as long as it is solid at a temperature not lower than the melting point of the ethylene-propylene random copolymer. . Specific examples of the organic filler include a fluororesin powder, a silicone resin powder, and a thermoplastic polyester resin powder. These organic fillers may be used alone or in combination of two or more.

The average particle diameter of the filler (including both an inorganic filler and an organic filler) is determined by preparing pre-expanded particles having uniform cells and a high expansion ratio, and from the pre-expanded particles. 0.1 to 50 μm, and more preferably 0.5 to 50 μm, from the viewpoint of obtaining a molded body having excellent mechanical strength and flexibility.
It is preferably from 10 to 10 μm. The average particle diameter is 50
If it exceeds μm, the cell diameter tends to be too large, and if it is less than 0.1 μm, it tends to be less likely to be a foam nucleus point, and the moldability tends to decrease.

The filler is not necessarily used. However, in order to obtain the effect of using the filler, that is, to obtain pre-expanded particles having a high expansion ratio, 100 parts of the ethylene-propylene random copolymer is used. It is preferably at least 0.01 part, more preferably at least 0.1 part, and when forming the pre-expanded particles, develop excellent fusion properties, and obtain mechanical strength, flexibility, etc. from the pre-expanded particles. 10 parts or less, preferably 5 parts
Part or less.

The polypropylene resin composition of the present invention containing the above-mentioned ethylene-propylene random copolymer, ionomer resin, and if necessary, a filler, has a water content under the water vapor pressure at the melting point of the ethylene-propylene random copolymer. Is 1 to 50%, preferably 2 to 20%.

Since the ethylene-propylene random copolymer has a water content of 1 to 50% under the steam pressure at the melting point, desired characteristics can be obtained without using a conventional blowing agent such as a volatile blowing agent or carbon dioxide gas. Thus, pre-expanded particles having a high expansion ratio and having a high expansion ratio are obtained.

When the water content is less than 1%, the apparent expansion ratio is less than 5 times, and when it exceeds 50%, the dispersibility of the particles in the aqueous dispersion medium is reduced, and the closed container is used during the production of the pre-expanded particles. In this case, the particles are aggregated, and it is difficult to obtain uniform pre-expanded particles.

The melting point of the ethylene-propylene random copolymer is determined from the temperature at the top of the melting peak as measured by DSC at a rate of 10 ° C./min. The rate is determined as follows.

That is, 50 g of the polypropylene resin composition particles and 150 g of water were placed in a 300 cc pressure-resistant ampoule.
g, 0.5 g of powdery basic tribasic calcium phosphate as a dispersant, 0.03 of sodium n-paraffin sulfonate
g, and after sealing, heat-treat for 3 hours in an oil bath set to the melting point of the ethylene-propylene random copolymer. Further, after cooling to room temperature, it was taken out, washed sufficiently with water to remove the dispersant, and the weight (X) of the obtained water-containing particles of the polypropylene resin composition obtained by removing the adhering water on the surface was determined. The weight (Y) after drying for 3 hours in an oven set at a temperature 20 ° C. higher than the melting point and cooling to room temperature in a desiccator was determined,
Formula (I):

[0036]

(Equation 1)

Means a value obtained in accordance with However, since the water content is a ratio to the ethylene-propylene random copolymer and the ionomer resin, it is necessary to correct the water content when a filler is used.

The polypropylene resin composition of the present invention containing the ethylene-propylene random copolymer, the ionomer resin, and, if necessary, a filler is usually melt-kneaded using an extruder, kneader, Banbury mixer, roll, or the like. Then, it is preferable to form the particles into a desired particle shape that can be easily used for preliminary foaming, such as a columnar shape, an elliptical columnar shape, a spherical shape, a cubic shape, and a rectangular parallelepiped shape. The particles obtained are usually 0.5
５5 mg / particle.

The particles from the polypropylene resin composition are dispersed in an aqueous dispersion medium in a closed vessel during prefoaming, and heated to a temperature equal to or higher than the softening temperature of the ethylene-propylene random copolymer. It is hydrated.

The water content of the polypropylene resin composition of the present invention under the steam pressure at the melting point of the ethylene-propylene random copolymer is 1 to 50%, preferably 2 to 50%.
Since it is ２０20%, the water content of the particles is also 1 to 50%, preferably 2 to 20%.

The pre-expanded particles from the polypropylene-based resin composition are sealed with particles from the polypropylene-based resin composition containing, for example, the above-mentioned ethylene-propylene random copolymer, ionomer resin, and optionally used filler. The particles are dispersed in an aqueous dispersion medium in a vessel, and the particles are heated to a temperature equal to or higher than the melting point of the ethylene-propylene random copolymer, preferably equal to or higher than the melting point + 5 ° C, and lower than the melting end temperature, preferably lower than the melting end temperature -2 ° C. Then, after a water content of 1 to 50%, preferably 2 to 20% of the particles of the polypropylene resin composition (water-containing particles), one end of the closed container is released, and the water-containing particles and the aqueous dispersion medium are In an atmosphere at a lower pressure than the internal pressure of the closed container, usually,
It is obtained by releasing the particles under atmospheric pressure and foaming the water-containing particles.

The term "melting end temperature" refers to the temperature of the particles 3 to
7 mg was heated to 220 ° C. at a rate of 10 ° C./min by a differential scanning calorimeter, and then to about 40 ° C. at a rate of 10 ° C./min, and then again at a rate of 10 ° C./min. This is the temperature when the temperature rises to 220 ° C. and the end of the endothermic peak of the DSC curve obtained by the second temperature rise returns to the baseline position on the high temperature side.

When dispersing the particles in an aqueous dispersion medium in the closed container, as a dispersant, tribasic calcium phosphate, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, a small amount of a surfactant, for example, Sodium dodecylbenzene sulfonate, sodium n-paraffin sulfonate, sodium α-olefin sulfonate and the like can be used. There are no particular restrictions on the amounts of the dispersant and surfactant used, and any commonly used amounts may be used.

The water-based dispersion medium is, for example, water. The water contains at least one of ethylene glycol, ethyl alcohol, glycerin and the like, if necessary. Is also good.

In the present invention, the water-containing particles and the aqueous dispersion medium are mixed in an atmosphere at a pressure lower than the internal pressure of the closed vessel.
Usually, a means is employed in which the hydrated particles are released under atmospheric pressure to foam the hydrated particles. When releasing the contents, it is preferable to introduce an inorganic gas (excluding carbon dioxide gas) such as nitrogen or air so as to keep the internal pressure of the container within a certain range.

The pre-expanded particles using the polypropylene resin composition thus obtained have an expansion ratio of 5 to 50 times, preferably 7 to 30 times, a closed cell ratio of 80 to 100%, preferably 85 to 100%, and an average Bubble diameter 50-500
μm, preferably 100-300 μm.

When the expansion ratio is less than 5 times, the flexibility and cushioning properties of the obtained molded article become insufficient, and when it exceeds 50 times, the mechanical strength of the obtained molded article decreases.
Heat resistance becomes insufficient. Further, the closed cell rate is 8
If it is less than 0%, the secondary foaming power is insufficient, so that poor fusion occurs at the time of molding, and the mechanical strength of the obtained molded article is reduced. Further, when the average cell diameter is less than 50 μm, there arises a problem that the shape of the obtained molded article is distorted,
If it exceeds 500 μm, the mechanical strength of the obtained molded article will decrease.

The DSC curve obtained by differential scanning calorimetry of the pre-expanded particles of the present invention preferably has a peak at a higher temperature than the intrinsic peak of the ethylene-propylene random copolymer. When there is a peak on the higher temperature side than the intrinsic peak of the ethylene-propylene random copolymer, the obtained polypropylene-based resin pre-expanded particles have good in-mold moldability, and have good mechanical strength and heat resistance. I can get my body.

The DSC curve obtained by differential scanning calorimetry of the pre-expanded particles is 3 to 7 m
g at a heating rate of 10 ° C./min by a differential scanning calorimeter.
This is a DSC curve obtained when the temperature is raised to 20 ° C.

The intrinsic peak of the ethylene-propylene random copolymer is defined as the intrinsic endotherm obtained when a DSC curve of the ethylene-propylene random copolymer as the base resin of the pre-expanded particles is obtained. This is considered to be a peak, which is a so-called peak due to endotherm during melting. On the other hand, the peak on the high temperature side is an endothermic peak appearing on the higher temperature side than the intrinsic peak, and is interpreted as being based on the presence of secondary crystals generated during the production of the pre-expanded particles. In general, a secondary crystal is generated by heating and maintaining the temperature of the ethylene-propylene random copolymer at or above the melting point and below the melting end temperature during the production of the pre-expanded particles. It is desirable that the temperature difference between the intrinsic peak and the peak on the high temperature side is large, and it is preferably 5 ° C or more, more preferably 10 ° C or more. The peak size on the high temperature side is 5 to 60 J /.
g, more preferably 15 to 35 J / g, and the ratio of the size of the peak on the high temperature side to the size of the intrinsic peak is preferably 10 to 50%, more preferably 20 to 40%.

Since the pre-expanded particles from the polypropylene resin composition of the present invention have a closed cell ratio of 80% or more, if necessary, the pre-expanded particles are treated in a pressure vessel under heat and pressure for a certain period of time. Then, after air impregnation, the mixture may be filled in a molding die, and may be foamed by heating, for example, by steam heating, to produce a foamed molded product according to the mold.

The foam molded article thus obtained has a small dimensional shrinkage and a small shape deformation, and therefore has a very high commercial value.

[0053]

EXAMPLES Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to only these examples.

Examples 1 to 7 and Comparative Examples 1 to 5 Ethylene-propylene random copolymer (density 0.90
g / cm ³ , ethylene content 3%, melting point 145 ° C., melting end temperature 160 ° C., MI = 6 g / 10 min) and 100 parts of the ionomer resin and talc (average particle size 9.5 μm) shown in Table 1. The amount shown in Table 1 was added, and the mixture was supplied to a 50 mmφ single screw extruder, melt-kneaded, and then 2.2 mm in diameter.
Of water-cooled polypropylene-based resin composition to obtain particles (pellets) (1.8 mg / particle).

Next, 100 parts of the obtained particles, 1 part of powdery basic calcium triphosphate as a dispersant and 0.05 part of sodium n-paraffinsulfonic acid were added to 300 parts of water.
And the contents of the container were heated to the temperature shown in Table 1 over about 90 minutes.
Hold for 0 minutes. The pressure at this time is about 5.6 kg / c
m ² G.

After that, the pressure in the container was adjusted with compressed air as shown in Table 1.
, And while maintaining this pressure, the valve at the bottom of the closed vessel was opened to release the aqueous dispersion (hydrous particles and aqueous dispersion medium) under atmospheric pressure to perform prefoaming.

Next, the physical properties of the particles and the pre-expanded particles obtained from the polypropylene-based resin composition are as follows: water content, expansion ratio, closed cell ratio, average cell diameter and cell variation, inherent peak temperature of DSC curve, The high temperature side peak temperature was determined according to the following method. Table 1 shows the results.

(Moisture content of the resin composition under the steam pressure at the melting point of the ethylene-propylene random copolymer) was determined by the method described in the above embodiment.

(Expansion ratio) After measuring the weight of the pre-expanded particles, the particles were immersed in ethanol in a 100 cc measuring cylinder, and the volume of the expanded particles was measured from the meniscus before and after the immersion to determine the true density. Was calculated by dividing the density.

(Closed cell ratio) The closed cell volume of the obtained pre-expanded particles was determined using an air comparison specific gravity meter (manufactured by BECKMAN, Model 930), and the closed cell volume was separately measured by a submerged method. The closed cell ratio was calculated by dividing by the obtained apparent volume.

(Average cell diameter) From the obtained pre-expanded particles, 30 pre-expanded particles were arbitrarily taken out, and JIS
The cell diameter was measured according to K6402, and the average cell diameter (d) was calculated.

(Variation of Bubble) The ratio of the average bubble diameter (d) to the standard deviation (σ) representing the variation of the bubble diameter (hereinafter, referred to as “σ”)
U) was calculated by U (%) = (σ / d) × 100.

The smaller U is, the more uniform the bubbles are.

The values of U are classified according to the following criteria:
evaluated.

：: The value of U is less than 35% Δ: The value of U is 35 to 45% ×: The value of U exceeds 45%

(Intrinsic Peak Temperature and Higher Temperature Peak Temperature Based on DSC Curve) 5 mg of the obtained pre-expanded particles were subjected to a differential scanning calorimeter (SSC520 manufactured by Seiko Instruments Inc.).
According to 0), the temperature was raised to 220 ° C. at a rate of 10 ° C./min to obtain a DSC curve. The temperature at the top of the low-temperature endothermic peak (140 to 141 ° C.) of the obtained DSC curve was defined as the intrinsic peak temperature.

On the other hand, the endothermic peak on the high temperature side (160 to
161 ° C.) was taken as the peak temperature on the high temperature side.

[0068]

[Table 1]

From the results shown in Table 1, it can be seen that all of the pre-expanded particles obtained in Examples 1 to 7 are pre-expanded particles having a high expansion ratio, uniform fine cells, and a high closed cell ratio.

On the other hand, it can be seen that the pre-expanded particles obtained in Comparative Examples 1 to 5 have a magnification of less than 5 times and a large cell variation.

In Comparative Example 5, the shrinkage was so remarkable that the closed cell ratio, the average cell diameter and the cell dispersion could not be measured, and no high-temperature peak appeared on the DSC curve.

[0072]

According to the polyolefin resin composition of the present invention, an expansion ratio of 5 can be obtained without using a conventional blowing agent.
Pre-expanded particles having excellent properties of up to 50 times, closed cell ratio of 80 to 100% and average cell diameter of 50 to 500 μm are obtained.

Therefore, when the pre-expanded particles of the present invention are used, the obtained in-mold expanded molded article has a small shrinkage,
Further, since the distortion of the molded product is small, the appearance is excellent, and the production efficiency of the molded product is improved. Therefore, the pre-expanded particles of the present invention can be preferably used for structural members such as shock absorbers for vehicles that require dimensional accuracy, heat-insulating building materials, etc., and are also useful for applications such as cushioning packaging materials. .

Claims (6)

[Claims] 1. An ionomer resin obtained by neutralizing (A) 100 parts by weight of an ethylene-propylene random copolymer and (B) an ethylene- (meth) acrylic acid copolymer with an alkali metal ion. Parts by weight, (C) 0 to 10 parts by weight of an inorganic filler and / or an organic filler,
A polypropylene resin composition, wherein the ethylene-propylene random copolymer has a water content (ratio to the total amount of the components (A) and (B)) at a melting point of 1 to 50% by weight at a melting point. Stuff. 2. The ethylene-propylene random copolymer has an ethylene content of 0.05 to 8% by weight.
The polypropylene-based resin composition as described in the above. 3. The polypropylene resin composition according to claim 1, wherein the inorganic filler is talc. 4. Pre-expanded particles obtained by pre-expanding particles from the polypropylene resin composition according to claim 1, wherein the expansion ratio is 5 to 50 times, the closed cell ratio is 80 to 100%, and the average cell ratio is 50 to 50. Pre-expanded particles having a size of 500 μm. 5. DS obtained by differential scanning calorimetry
The pre-expanded particles according to claim 4, wherein the C curve has a peak on a higher temperature side than an intrinsic peak of the ethylene-propylene random copolymer. 6. The particles comprising the polypropylene resin composition according to claim 1 are dispersed in an aqueous dispersion medium in a closed container, and the particles are at or above the melting point of the ethylene-propylene random copolymer but below the melting end temperature. Heated to the temperature of
After making the water-containing particles have a water content (ratio to the total amount of the components (A) and (B)) of 1 to 50% by weight, one end of the closed container is opened, and the water-containing particles and the aqueous dispersion medium are sealed. A method for producing pre-expanded particles, characterized in that the particles are released into an atmosphere at a pressure lower than the internal pressure of the container and the water-containing particles are expanded.