JP2000226466A - Propylene based resin prefoamed particle and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide propylene based resin prefoamed particles high in expansion ratio and good in molding fusion characteristics without using a volatile blowing agent or increasing foaming pressure. SOLUTION: In the process for producing propylene based resin prefoamed particles comprising dispersing resin particles from a polypropylene based resin composition containing (A) 100 pts.wt. ethylene/propylene random copolymer having an ethylene content of 1.5-4.5 wt.% and (B) 0.001-10 pts.wt. alkali metal salt of an ethylene/(meth) acrylic acid copolymer in an aqueous medium in a closed vessel to form a mixture, then heating the mixture up to the foaming temperature which is not lower than the softening temperature of the resin particles, introducing an inorganic gas therein, and subsequently releasing the resulting resin particles into a pressure zone whose pressure is lower than the inner pressure of the closed vessel, the temperature of the mixture is retained in the temperature range of from not higher than the foaming temperature to the temperature of the foaming temperature minus 1 deg.C for not shorter than 30 minutes, and then foaming is effected to obtain prefoamed particles showing two melting points in the DSC curve by differential scanning calorimetry with a temperature difference ΔT between the two melting points of >=20.0 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pre-expanded propylene resin particle and a method for producing the same. More specifically, the present invention relates to, for example, a pre-expanded propylene-based resin particle which can be suitably used as a raw material of an in-mold foam molded article, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, propylene-based resin particles are dispersed in an aqueous dispersion medium in a closed container, heated and pressurized, and then discharged into a low-pressure region to form propylene-based resin pre-expanded particles. In order to impart good in-mold moldability to the thus-produced propylene-based resin pre-expanded particles, a DSC curve measured by a differential scanning calorimeter has a crystal structure showing two melting points. This is well known (for example, JP-A-59-176336).

A method for producing propylene-based resin pre-expanded particles using an inorganic gas such as carbon dioxide, nitrogen or air as a blowing agent is already known (for example, Japanese Patent Application Laid-Open No. Sho 60-2).
No. 21440, JP-A-60-229936,
JP-A-8-259724 and the like).

However, when pre-expanded particles are to be produced from a propylene-based resin such as an ethylene-propylene random copolymer by using the above-mentioned inorganic gas as a foaming agent, the resin of the inorganic gas used as a foaming agent is used. The reason is that the expansion force of the foaming agent is insufficient due to insufficient solubility in the foaming agent, or the expansion force of the foaming agent cannot be effectively expressed as the expansion ratio of the pre-expanded particles during foaming due to high permeability. Therefore, it is difficult to increase the expansion ratio of the pre-expanded particles.

Therefore, the present inventors disperse resin particles containing the propylene resin and the hydrophilic polymer as base resins in an aqueous dispersion medium, and heat the resin particles to a temperature higher than the softening temperature of the propylene resin to reduce the water content. After 1 to 50% of the hydrated resin particles are released into a low-pressure atmosphere and the hydrated resin particles are foamed, a dispersion medium can be used without using a volatile foaming agent and / or an inorganic gas-based foaming agent. Using a certain water as a foaming agent, to develop an epoch-making method of producing propylene-based resin pre-expanded particles having desired physical properties,
It has been previously filed (Japanese Patent Application No. 8-84124).
This technology uses water as the foaming agent, so it is safe without flammability.In addition, the foaming agent is inexpensive, more environmentally friendly, and uses an inorganic gas-based foaming agent such as air or nitrogen. This is an excellent technology that makes it easier to increase the foaming ratio, but it has a higher boiling point and higher latent heat of vaporization than conventional foaming agents, so the difference between the pressure inside the sealed container and the pressure outside the sealed container is high. Unless (= foaming pressure) is relatively large, there is a disadvantage that it is difficult to increase the foaming ratio.

[0006] The above disadvantages are described in, for example, Japanese Patent Application Laid-Open No. Hei 8-2597.
As in the case of using water as the blowing agent, similar to the findings disclosed in Japanese Patent Application Publication No. 24, in which an inorganic gas-based blowing agent such as carbon dioxide is used, as shown in FIG. There is a close relationship between the heat absorption amount ΔH of the high-temperature side peak and the expansion ratio of the pre-expanded particles, and when the heat absorption amount of the high-temperature side peak increases, the phenomenon that the expansion ratio of the pre-expanded particles decreases linearly occurs. Due to being.

On the other hand, the endothermic amount at the high temperature side peak is closely related to the in-mold moldability, and in order to maintain good in-mold moldability, the endothermic amount must be within a certain range. It has been reported that it needs to be maintained (for example, JP-A-8-20662).

Therefore, it is necessary to increase the foaming pressure in order to improve the expansion ratio while maintaining the endothermic amount of the high-temperature side peak within a range where the in-mold moldability can be favorably maintained.

In the method of producing pre-expanded propylene-based resin particles using an inorganic gas-based blowing agent, a DSC curve shows two melting points by keeping the temperature in a temperature range near the foaming temperature for a certain time. A method for stably producing pre-expanded particles having a crystal structure is also known. For example, according to JP-A-5-17615 and JP-A-3-223347, in the case of a non-crosslinked polypropylene resin, it is usually kept in a temperature range near the foaming temperature for 5 to 90 minutes, preferably 15 to 60 minutes. It is described that an intended product can be obtained by performing the method. However, the holding is performed in two stages, and the process management is complicated. In addition, using the method of maintaining the temperature in two stages as described above, for example, as described in the embodiment of JP-A-5-17615, the difference between the first stage holding temperature and the second stage holding temperature is determined. The present inventors have found that, when the holding time is set to 15 minutes at 5 ° C., the first stage and the second stage, the effect of improving the expansion ratio is not sufficient in the present invention.

On the other hand, the propylene-based resin pre-expanded particles
It has been reported that, by increasing the temperature difference ΔT between two melting points in a DSC curve measured by a differential scanning calorimeter, moldability in a mold is improved, for example, in JP-A-59-17633.
No. 6 suggests that a temperature difference corresponding to ΔT is preferably 5 ° C. or more. However, this publication does not specifically describe pre-expanded particles having a temperature difference corresponding to ΔT of more than 13 ° C., and also does not describe a method for producing pre-expanded particles having ΔT of more than 13 ° C.

[0011]

Means for Solving the Problems Accordingly, the present inventors have:
Without raising the foaming pressure, the temperature was relatively close to the foaming temperature, and by holding it in a temperature range below the foaming temperature for a longer period of time, we thought that it would be possible to increase the foaming ratio, and conducted intensive research. As a result, when foaming is performed after maintaining the temperature for a long time of 30 minutes or more in the temperature range of the foaming temperature or lower and the foaming temperature of -1 ° C. or higher, the temperature of the high-temperature side peak increases and the temperature of the low-temperature side peak increases. As a result, the temperature difference ΔT between the two melting points becomes 2
It was found that the temperature increased to 0.0 ° C. or more. For the obtained pre-expanded particles having ΔT of 20.0 ° C. or more,
Obviously, the relationship between the heat absorption ΔH of the peak on the high temperature side and the expansion ratio has changed from that where ΔT is less than 20 ° C., and the expansion ratio at the same ΔH has been improved. And 2
Considering the relationship between the temperature difference ΔT between the two melting points and the improvement ratio described later, surprisingly, as ΔT increases, the improvement ratio increases almost linearly, and the effect of improving the expansion ratio increases accordingly. I found that.

Further, when an in-mold molding experiment was conducted on the propylene-based resin pre-expanded particles having a ΔT of 20.0 ° C. or more, the heat vapor pressure during molding can be reduced because of good molding fusing property. In addition, the inventors have found that the range of heating conditions for obtaining a molded article having good quality is wide.

The present invention has been made based on the above-mentioned findings, and (A) 100 parts by weight (hereinafter referred to as "parts") of an ethylene-propylene random copolymer having an ethylene content of 1.5 to 4.5% by weight; (B) Pre-expanded particles from a propylene-based resin composition containing 0.001 to 10 parts of an alkali metal salt of an ethylene- (meth) acrylic acid copolymer, wherein the pre-expanded particles are measured by a differential scanning calorimeter. D
The propylene-based resin pre-expanded particles exhibit two melting points in the SC curve and have a temperature difference ΔT between the two melting points of 20.0 ° C. or more (Claim 1). 5 to 4.5% by weight of 100 parts of an ethylene-propylene random copolymer and (B) an alkali metal salt of ethylene- (meth) acrylic acid copolymer 0.001 to 0.001
After dispersing resin particles from a propylene-based resin composition containing 10 parts in an aqueous medium in a closed container to form a mixture, the mixture is heated to a foaming temperature not lower than the softening temperature of the resin particles, and inorganic gas is used. A method for producing pre-expanded particles by releasing the mixture into a pressure region lower than the internal pressure of the closed vessel, wherein the temperature of the mixture is not higher than the expansion temperature and not lower than -1 ° C. A method for producing propylene-based resin pre-expanded particles characterized by foaming after being kept in a temperature range for 30 minutes or more (claim 2), and the inorganic gas is a nitrogen-containing inorganic gas. The present invention relates to a method for producing pre-expanded propylene resin particles according to claim 2 (claim 3).

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A propylene-based resin composition (hereinafter also referred to as a PP resin composition) for obtaining propylene-based resin pre-expanded particles (hereinafter also referred to as PP pre-expanded particles) of the present invention comprises (A) ) Component having an ethylene content of 1.5 to
4.5% by weight, preferably 1.5 to 4.0% by weight of an ethylene-propylene random copolymer (hereinafter also referred to as EP random copolymer (A)) is used. When the ethylene content is less than 1.5% by weight, the melting point of the PP resin composition increases, and the heat resistance, mechanical strength, and the like of a molded product obtained by molding the PP pre-expanded particles in a mold are improved. ,
DSC of PP pre-expanded particles by differential scanning calorimetry
The temperature difference ΔT between the two melting points in the curve (hereinafter simply referred to as ΔT
When the amount exceeds 4.5% by weight, ΔT tends to increase, but the melting point decreases, and the heat resistance and mechanical strength of the molded body decrease. In addition, since the foaming temperature in the production of PP pre-expanded particles is lowered, the expansion ratio is undesirably lowered.

The MI (melt index) of the EP random copolymer (A) is 230 ° C., 2.16 kg / cm ^2.
0.5 to 40 g / 10 min, and further 3 to 30 g / 10
Minutes are preferred. When the MI is less than 0.5 g / 10 min, the melt viscosity is too high to obtain pre-expanded particles having a high expansion ratio. The viscosity tends to be low and the foam tends to be broken, so that it is difficult to obtain pre-expanded particles having a high expansion ratio.

Although the melting point of the EP random copolymer (A) varies depending on not only the ethylene content but also the MI, etc., in the present invention, the ethylene content is 1.5 to 4.5% by weight.
Is used, the temperature is usually about 130 to 165 ° C, preferably 135 to 160 ° C. The melting point is 130 ° C
If it is less than, the ethylene content increases, so that ΔT tends to increase, but the heat resistance and mechanical strength of the molded article tend to decrease, and if it exceeds 165 ° C, the heat resistance and mechanical strength of the molded article are reduced. Although improving, ΔT tends to be hard to increase.

In the PP resin composition, as the component (B), an alkali metal salt of an ethylene- (meth) acrylic acid copolymer (hereinafter, also referred to as an ethylene ionomer (B))
Is used. Ethylene ionomer (B) is PP
It is included in order to increase the sorption amount of the foaming agent into the resin particles (hereinafter also referred to as PP resin particles) from the resin composition.

The ethylene ionomer (B) is used in an amount of 70 to 97% by weight of ethylene, more preferably 8 to 80% by weight, from the viewpoint of ensuring sufficient compatibility with the propylene resin and a sufficient amount of sorbed water.
0 to 95% by weight and 3 to 30% by weight of (meth) acrylic acid,
Further, a carboxyl group of 5 to 20% by weight of the copolymer is converted into a salt with an alkali metal ion such as a sodium ion or a potassium ion, and the ionic cross-linking between the molecules is preferable, and the ionization degree is 40 to 100%. 50-1
Those having 00% are preferred.

The degree of ionization is determined by the mol% of the introduced metal ions with respect to 100 mol% of the carboxyl groups in the ethylene- (meth) acrylic acid copolymer.

Specific examples of the ethylene-based ionomer (B) include, for example, "Himilan" (trade name) manufactured by DuPont-Mitsui Polychemicals Co., Ltd.

The amount of the ethylene ionomer (B) to be used is 0.1 to 100 parts of the EP random copolymer (A).
001 to 10 parts, preferably 0.01 to 10 parts, more preferably 0.01 to 5 parts. The usage amount is 0.0
If the amount is less than 01 parts, the amount of water sorbed to the PP resin particles in the closed container decreases, and the effect of improving the expansion ratio becomes smaller than in the case where the ethylene ionomer (B) is not added. When the content exceeds 10 parts, the amount of water sorbed to the PP resin particles increases, but the production stability at the time of production of the pre-expanded particles and the molded article obtained by in-mold molding from the pre-expanded particles. It is not preferable because qualities such as mechanical strength, heat resistance, and dimensional characteristics at the time of water absorption are deteriorated.

The PP resin composition has uniform air bubbles.
In order to obtain independent and high expansion ratio pre-expanded particles, a filler can be contained.

The average particle diameter of the filler is such that pre-expanded particles having uniform cells and high expansion ratio can be obtained, and a molded article having excellent mechanical strength and flexibility can be obtained from the pre-expanded particles. From the point that it can be obtained, 50 μm or less,
Further, the thickness is preferably 20 μm or less, from the viewpoint of preventing poor dispersion due to secondary aggregation and handling workability.
It is preferably 1 μm or more, more preferably 0.5 μm or more.

The filler includes an inorganic filler and an organic filler. Specific examples of the inorganic filler include, for example, talc, calcium carbonate, calcium hydroxide, silica,
Mica, kaolin, diatomaceous earth, rock wool, wollastonite and the like can be mentioned. Among them, talc is preferable because pre-expanded particles having uniform cells and high expansion ratio can be obtained. The organic filler is not particularly limited as long as it is solid at a temperature equal to or higher than the softening temperature of the EP random copolymer (A), and specific examples thereof include a fluororesin powder such as polytetrafluoroethylene; Silicone resin powder, thermoplastic polyester resin powder and the like can be mentioned. The filler may be used alone or in combination of two or more.

In order to obtain pre-expanded particles having a high expansion ratio, the amount of the filler used is preferably selected from EP random copolymer (A).
0.003 parts or more to 100 parts, further 0.00
5 parts or more, and when molding the pre-expanded particles, in order to obtain excellent fusion properties and obtain a molded article having excellent mechanical strength and flexibility from the pre-expanded particles. And 3 parts or less, more preferably 2 parts or less.

The PP resin composition may further contain, if necessary, organic pigments such as azo, phthalocyanine, quinacridone, and perylene, carbon black, ketjen black, titanium oxide, cobalt violet, cobalt blue, and ultramarine blue. In addition to such inorganic pigments, dyes, stabilizers such as antistatic agents and antioxidants, and the like can be contained.

The PP pre-expanded particles of the present invention contain an EP random copolymer (A), an ethylene ionomer (B) and, if necessary, fillers, pigments, dyes, antistatic agents, stabilizers, and the like. Pre-expanded particles from the PP resin composition, wherein the pre-expanded particles show two melting points in a DSC curve measured by a differential scanning calorimeter, and the temperature difference ΔT between the two melting points is 20.0 ° C. or more. Pre-expanded particles. Since ΔT is 20.0 ° C. or more, the effect of good moldability in the mold can be obtained.

The DSC curve obtained by the differential scanning calorimeter measurement is obtained when 1 to 10 mg of PP pre-expanded particles are heated from 40 ° C. to 220 ° C. at a rate of 10 ° C./min by a differential scanning calorimeter. It is a DSC curve.

For example, in the case of the DSC curve of the pre-expanded particles obtained by the production method of the present invention described later, two endothermic peaks appear as shown in FIG. The ΔT is defined as the temperature at the top of the peak on the low temperature side of the two peaks, the melting point on the low temperature side,
When the temperature at the peak of the high-temperature side peak is taken as the high-temperature side melting point
It refers to the temperature difference between these two melting points.

Next, an example of a method for producing PP pre-expanded particles will be described.

The PP pre-expanded particles are usually, for example,
The PP resin composition is melt-kneaded using an extruder, a kneader, a Banbury mixer, a roll, or the like, and then 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. It is manufactured by producing PP resin particles by molding and prefoaming.

The conditions for producing PP resin particles are as follows:
Although there is no particular limitation on the size of the PP resin particles, for example, it is common to melt and knead them in an extruder to produce particles of about 0.3 to 5 mg / particle.

In the production method of the present invention, the PP resin particles produced as described above are dispersed in an aqueous medium in a closed vessel to form a mixture. The PP resin particles are
Usually, it is dispersed in an aqueous medium at room temperature to about 90 ° C.

The aqueous medium may be any solvent that does not dissolve the PP resin particles. Usually, water or a mixture of water and one or more of ethylene glycol, glycerin, methanol, ethanol and the like is used. Water is preferred from the viewpoints of environment, economy and the like.

Usually, about 0.1 to 1 part and about 0.001 to 0.01 part of a surfactant which is a dispersant and a dispersing aid are added to the aqueous medium with respect to 100 parts of the aqueous medium. You.

Specific examples of the dispersant include, for example, tribasic calcium phosphate, basic magnesium carbonate, basic zinc carbonate, calcium carbonate and the like.

Further, specific examples of the surfactant include:
For example, sodium dodecylbenzene sulfonate, sodium n-paraffin sulfonate, sodium α-olefin sulfonate and the like can be mentioned.

The amount of the PP resin particles dispersed in the aqueous medium is 3 to 100 parts per 100 parts of the aqueous medium.
Further, 10 to 80 parts is preferable. If the amount of the PP resin particles is less than 3 parts, the productivity tends to decrease, the production cost increases, and the economy tends to be reduced. Meanwhile, 1
When the amount is more than 00 parts, the PP resin particles tend to thermally fuse in the closed container during heating.

Next, the mixture is heated to a foaming temperature equal to or higher than the softening temperature of the PP resin particles, and an inorganic gas is introduced. Thereafter, the mixture is discharged into a pressure region lower than the internal pressure of the closed container to perform PP prefoaming. Particles are produced. At this time, the mixture is kept in a temperature range of the foaming temperature or lower and the foaming temperature of -1 ° C. or higher for 30 minutes or more before foaming.

As the foaming temperature equal to or higher than the softening temperature of the PP resin particles, a temperature of from the melting point of the PP resin composition to -10 ° C. to + 30 ° C. is usually employed.
Is preferable, and a melting point + 5 ° C to a melting point + 15 ° C is more preferable. If the foaming temperature is lower than the melting point of −10 ° C., it tends to be difficult to foam. If the foaming temperature is higher than the melting point of + 30 ° C., all the secondary crystals of the PP resin particles in the closed container are melted because the foaming temperature is too high. The melting point of the pre-expanded particles is reduced to one, and the resin particles tend to fuse together in the container. For example, when using a PP resin composition having a melting point of 145 ° C., the foaming temperature is usually 135 to 17
5 ° C, preferably 145 to 165 ° C, more preferably 150 to 160 ° C.

The softening temperature in the present invention is defined as AST
MD-648 is a value measured under a load of 4.6 kg / cm ² , and the melting point is the temperature at the top of the melting peak as measured by DSC at 10 ° C./min.

The term “holding in a temperature range of not higher than the foaming temperature and not lower than the foaming temperature −1 ° C. for 30 minutes or more” means that after the temperature is raised toward the foaming temperature, a predetermined foaming process is performed during the temperature rise. Holding the temperature of the mixture in the closed vessel in the temperature range during the counting of the holding time of 30 minutes or more from the time when the temperature becomes -1 ° C., as described in the example of JP-A-5-17615. As described, the difference in holding temperature between the first stage and the second stage was 5 ° C.,
Setting the holding time to 15 minutes for both stages is a different concept in that heat treatment is performed efficiently and pre-expanded particles having a large ΔT are obtained. During the counting of the holding time, the temperature of the mixture in the closed vessel is controlled to 1 ° C. between the foaming temperature −1 ° C. and the foaming temperature, which is very difficult regardless of the volume and shape of the closed vessel. Not temperature control. For example, it can be performed by feedback-controlling the temperature control system of a closed container typified by steam, heat medium oil, an electric heater or the like according to the temperature in the container.

The holding time is 30 minutes or longer, and the longer the holding time, the more the effect of the present invention tends to increase. Is considered to be performed sufficiently. However, considering the productivity of the pre-expanded particles,
It is preferable to keep the time to about 5 hours or less.

The timing of the introduction of the inorganic gas into the closed container is not particularly limited. However, from the viewpoint of reducing the load on the container and the stability of the foaming pressure, it is usually used during the holding time, especially during the holding time. It takes place in the second half of the hour. At this time, the pressure increase rate is about 1 to 6 kg / cm ² / min. The equipment load is small and safe, and the thermodynamic equilibrium state in the closed vessel is not unnecessarily disturbed and the productivity is not reduced. It is preferable from the viewpoint of.

As the inorganic gas, carbon dioxide gas, nitrogen, a nitrogen-containing inorganic gas such as air, helium, argon and the like are used. These gases used in the present invention are not foaming agents, but are merely introduced into a closed container in order to increase the foaming pressure during the production of pre-expanded particles and to increase the depressurization rate, It is sufficient that the desired foaming pressure can be achieved, but nitrogen-containing inorganic gases such as nitrogen and air are most preferably used in consideration of the impact on the global environment and costs.

In the case where the PP resin particles in the closed container are prefoamed by being discharged from the closed container, the container being discharged is preferably in order to facilitate the release of the PP resin particles from the closed container into a low-pressure atmosphere. It is preferable to maintain the internal pressure to maintain the foaming pressure. Specifically, it is preferable to supply the inorganic gas into the closed container and release the gas while keeping the pressure in the closed container constant.

The foaming pressure is the difference between the internal pressure of the closed container and the pressure in a low pressure range at the time of foaming. Usually, the low pressure range to be released is atmospheric pressure. In that case, the foaming pressure will be equal to the gauge pressure of the closed container.

The foaming pressure varies depending on the desired foaming ratio. In order to obtain pre-expanded particles having a foaming ratio of about 3 to 50, the foaming pressure is usually about 8 to 60 kg / cm ² G, preferably about 8 to 60 kg / cm ² G. 45 kg / cm ² G, more preferably 8 to 30
kg / cm ² G. If foaming pressure is less than 8 kg / cm ² G, after which the average expansion ratio is reduced, in some cases tend to unexpanded resin particles become intermixed with the product, 60 kg / cm ² G
In addition to this, the facility load is increased, the cell diameter of the obtained pre-expanded particles is reduced, the thickness of the cell membrane forming the cells is reduced, the cells are liable to break during expansion, and the pre-expanded particles are , The closed cell ratio of the molded article decreases, and as a result, the quality such as the mechanical strength of the molded article tends to decrease. Therefore, as described above, it is preferable to increase the expansion ratio without increasing the expansion pressure as much as possible.

When the pre-expanded particles are produced by the above-described method, two melting points are shown in a DSC curve by differential scanning calorimetry, and the temperature difference ΔT between the two melting points is 2
PP pre-expanded particles having a temperature of 0.0 ° C. or higher are obtained.

[0050]

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

The evaluation in Examples and Comparative Examples was performed by the following method.

(Expansion ratio) About 1 to 1
After accurately weighing 3 g, the sample was completely immersed in an ethanol aqueous solution about half filled in a 100 ml measuring cylinder, and from the meniscus reading of the ethanol aqueous solution before and after immersion,
The true density of the pre-expanded particles was calculated by determining the volume of the pre-expanded particles and dividing the weight by the volume.

Next, the density of the pellets (resin particles) of the propylene-based resin composition used to obtain the pre-expanded particles was divided by the true density of the pre-expanded particles, and the obtained value was used as the expansion ratio. .

(Improvement Ratio) First, when the holding for a long time as in the present invention is not performed, there is a substantially linear negative correlation between the high-temperature peak endothermic amount ΔH and the expansion ratio. In order to show that, for Comparative Examples 1 to 4, the relationship between the high-temperature peak endothermic amount ΔH and the expansion ratio was plotted as shown in FIG. From FIG. 2, it can be seen that the relationship between ΔH and the expansion ratio is almost linear in the results of the four levels in which the holding was not performed for a long time. This is a graph similar to FIG. 6 of JP-A-8-259724.

Next, the same graph was plotted on the same graph for Examples 1 to 4 in which the holding was performed for a long time.
The difference from the expected value of the expansion ratio on the regression line in H was determined, and the difference was defined as the improvement ratio.

Here, the calorific value ΔH of the high-temperature side peak is a point at which the slope becomes zero again between two endothermic peaks in the DSC curve of the pre-expanded particles, as shown in FIG. From the high temperature side, draw a tangent to the DSC curve,
It represents the amount of endotherm determined from the area of a substantially triangular region formed by the tangent line and the peak on the high temperature side of the DSC curve.

Example 1 An ethylene-methacrylic acid copolymer (methacrylic acid unit content: 15% by weight) was added to 100 parts of an ethylene-propylene random copolymer (ethylene content: 3.9% by weight, MI = 10 g / 10 minutes). Ionomer obtained by cross-linking between molecules by converting the carboxyl group of sodium into a sodium salt (ionization degree: 59%)
2 parts, and filler (talc, average particle size 9.5 μm)
0.3 parts was supplied to an extruder and melt-mixed to produce propylene-based resin particles (1.8 mg / particle, melting point: 146.5 ° C.).

Next, the obtained propylene resin particles 1
00 parts, 1 part of powdery basic tribasic calcium phosphate as a dispersing agent, and 0.02 part of sodium n-paraffin sulfonate as a dispersing aid were charged together with 300 parts of water in an airtight container (200 liter internal volume). . Next, the content in the closed container is heated to 154.2 ° C. over about 90 minutes, and then the steam pressure in the jacket is controlled by a control valve so that the temperature is in a temperature range of 154.2 ° C. or more and 155.2 ° C. or less. After the temperature is controlled and maintained for 87 minutes, the foaming temperature 15
By foaming at 5.2 ° C., pre-expanded propylene resin particles were obtained. In the latter half of the temperature holding period, air was introduced into the closed container, the internal pressure of the closed container was adjusted to 30 kg / cm ² G, and then released to the atmosphere via a circular orifice. During the discharge, air was quantitatively introduced into the closed container so that the foaming pressure could be kept constant.

FIG. 1 shows a DSC curve of the obtained pre-expanded particles.
Shown in When the temperature difference (peak temperature difference) ΔT between the two melting points (peak temperature) ΔT was determined from the endothermic amount ΔH of the high temperature side peak and the two melting points (peak temperatures), ΔH = 11.8 mJ respectively.
/ Mg, ΔT = 21.1 ° C. The expansion ratio is 2
It was 2.0 times. From ΔH = 11.8 mJ / mg, the expected value of the expansion ratio when no holding was performed for a long time was as follows:
2, the expansion ratio of the actually obtained pre-expanded particles is 25.4 times.
Since it was 0, the improvement ratio was 6.6 times from the difference.

Example 2 The holding temperature was 153.9-154.9 ° C. (foaming temperature 15
4.9 ° C.), and propylene-based resin pre-expanded particles were obtained in the same manner as in Example 1 except that the holding time was 83 minutes. ΔH of the obtained pre-expanded particles = 14.8 mJ / m
g, ΔT = 21.0 ° C., the expansion ratio was 16.5 times,
The improvement ratio was 5.2 times.

Example 3 The holding temperature was 152.5 to 153.5 ° C. (foaming temperature 15
3.5 ° C.), and propylene-based resin pre-expanded particles were obtained in the same manner as in Example 1 except that the holding time was 40 minutes. ΔH of the obtained pre-expanded particles = 15.0 mJ / m
g, ΔT = 20.4 ° C., the expansion ratio was 14.0 times,
The improvement ratio was 3.0 times.

Example 4 Pre-expanded propylene resin particles were obtained in the same manner as in Example 3 except that the holding time was changed to 86 minutes. ΔH of the obtained pre-expanded particles = 16.2 mJ / mg, ΔT = 21.2 ° C.
The expansion ratio was 14.8 times and the improvement ratio was 5.5 times.

Comparative Example 1 Pre-expanded propylene resin particles were obtained in the same manner as in Example 1 except that the holding time was changed to 17 minutes. ΔH = 9.7 mJ / mg, ΔT = 19.5 ° C., and the expansion ratio of the obtained pre-expanded particles were 18.3 times.

Comparative Example 2 Pre-expanded propylene resin particles were obtained in the same manner as in Example 2 except that the holding time was changed to 15 minutes. ΔH = 12.9 mJ / mg, ΔT = 19.6 ° C. of the obtained pre-expanded particles
And the expansion ratio was 13.9 times.

These physical properties are almost the same as those in the case of the above-mentioned prior art in which the holding temperature in the second stage is 5 ° C. higher than that in the first stage, and each holding time is 15 minutes. That is, in the method of dividing into two stages, since the temperature is not maintained for a long time as in the manufacturing method of the present invention, it is considered that the secondary crystal does not grow sufficiently during the temperature maintenance. This also proves the effectiveness of the present invention.

Comparative Example 3 Pre-expanded propylene resin particles were obtained in the same manner as in Example 2 except that the holding time was changed to 28 minutes. ΔH of the obtained pre-expanded particles = 14.1 mJ / mg, ΔT = 19.8 ° C.
And the expansion ratio was 12.6 times.

Comparative Example 4 Pre-expanded propylene resin particles were obtained in the same manner as in Example 3 except that the holding time was changed to 13 minutes. ΔH of the obtained pre-expanded particles = 14.6 mJ / mg, ΔT = 19.7 ° C.
The expansion ratio was 11.6 times.

Hereinafter, the effects of the present invention will be summarized.

As shown in FIG. 2, in the production of the pre-expanded particles, when the holding time is shorter than 30 minutes, the relationship between ΔH and the expansion ratio has a negative linear correlation. On the other hand, when the holding time is 30 minutes or more as in the production method of the present invention, the expansion ratio departs from the negative linear correlation and the expansion ratio is specifically improved.

From FIG. 3 showing the relationship between the temperature difference ΔT between the two melting points and the improvement ratio, the relationship between ΔT and the improvement ratio is as follows.
There is a positive linear correlation, and it can be seen that as ΔT increases, the expansion ratio increases.

Furthermore, when each of the pre-expanded particles obtained in each of the above examples was subjected to in-mold molding, the molding and fusing properties were all lower than when using each of the pre-expanded particles obtained in the comparative example. Was good, and the obtained molded article was a good molded article excellent in all of heat resistance, mechanical strength, and dimensional characteristics when absorbing water.

[0072]

According to the production method of the present invention, the expansion ratio can be improved without increasing the expansion pressure.

Further, the PP pre-expanded particles of the present invention have good molding and fusing properties, and by using this,
A good molded body having excellent heat resistance, mechanical strength, and dimensional characteristics when absorbing water can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing a DSC curve of pre-expanded particles obtained in Example 1. The DSC curve is used to describe the temperature difference ΔT between the two melting points and the high-temperature peak endotherm ΔH.

FIG. 2 is a regression line that derives an expected value of the expansion ratio from the high-temperature peak endothermic amount ΔH and the expansion ratio of the pre-expanded particles of Comparative Examples 1 to 4 in which the holding was not performed for a long time at the expansion temperature to the expansion temperature-1 ° C. 9 is a graph for explaining how to determine the improvement magnification by holding for a long time.

FIG. 3 is a graph showing a relationship between a temperature difference ΔT between two melting points and an improvement ratio.

[Explanation of symbols]

 1 regression line

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naruhiko Akamatsu 5-1-1 Torikai Nishi, Settsu-shi, Osaka Kaneka Chemical Industry Co., Ltd. F-term (reference) 4F074 AA25A AA31 BA32 BA33 BA67 CA24 CA34 CA38 CC32X CC32Y CC34Y 4J002 BB151 BB232 FD010 FD070 FD090 FD100

Claims (3)

[Claims] 1. An alkali metal salt of (A) 100 parts by weight of an ethylene-propylene random copolymer having an ethylene content of 1.5 to 4.5% by weight and (B) an ethylene- (meth) acrylic acid copolymer Pre-expanded particles from a propylene-based resin composition containing 0.001 to 10 parts by weight, the pre-expanded particles exhibit two melting points in a DSC curve measured by a differential scanning calorimeter, and a temperature difference ΔT between the two melting points. Is 20.0 ° C. or higher. 2. (A) 100 parts by weight of an ethylene-propylene random copolymer having an ethylene content of 1.5 to 4.5% by weight and (B) an alkali metal salt of an ethylene- (meth) acrylic acid copolymer 0 After dispersing resin particles from a propylene-based resin composition containing 0.001 to 10 parts by weight in an aqueous medium in a closed container to form a mixture, the mixture is heated to a foaming temperature not lower than the softening temperature of the resin particles. And introducing an inorganic gas, and then releasing the inorganic gas into a pressure range lower than the internal pressure of the closed container to produce pre-expanded particles, wherein the temperature of the mixture is equal to or lower than the expansion temperature, the expansion temperature − A method for producing propylene-based resin pre-expanded particles, characterized in that foaming is carried out after being kept in a temperature region of 1 ° C. or more for 30 minutes or more. 3. The method for producing pre-expanded propylene resin particles according to claim 2, wherein the inorganic gas is a nitrogen-containing inorganic gas.