JPH06192462A - Expanded polyolefin resin particle and its production - Google Patents

Abstract

PURPOSE:To provide a resin particle having a large cell diameter and excellent in-mold moldability and to provide a process for its production. CONSTITUTION:The resin particle contains an inorganic gas therein and a blowing aid and a magnesium salt of a higher fatty acid are incorporated in the resin. The process comprises infiltrating an inorganic gas blowing agent into polyolefin resin particles under pressure and releasing the particles into a lower-pressure zone, and polyolefin resin particles impregnated with a blowing aid and a magnesium salt of a higher fatty acid are used as the polyolefin resin particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expanded polyolefin resin particles and a method for producing the same.

[0002]

2. Description of the Related Art A method for producing foamed particles by press-fitting an inorganic gas type foaming agent into a polyolefin resin particle under pressure and releasing it under low pressure is known (Japanese Patent Publication No. 62-61227). Japanese Patent Laid-Open No. 60-22993
6, JP-A-60-245650). In this case, expanded resin particles having a high expansion ratio can be obtained by using polyolefin resin particles containing an inorganic powder or a foaming aid such as a crystal nucleating agent (Japanese Patent Laid-Open Nos. 61-4738 and 6-6).
1-2741). By the way, after press-fitting the inorganic gas type foaming agent into the polyolefin resin containing the foaming aid,
When the foamed particles are obtained by discharging into the low pressure zone, there is a problem that the foamed particles of the obtained foamed particles become too fine and the moldability in the mold is lowered. As for the miniaturization of the cell diameter, the higher the contribution of the foaming aid and the foaming agent to the expansion ratio is,
For example, when an organic phosphorus-based nucleating agent is used as a foaming aid and carbon dioxide is used as a foaming agent, it becomes remarkable.
Then, when the foamed particles having such a fine bubble diameter are molded in the mold, the obtained molded body is liable to shrink, resulting in poor dimensional accuracy.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polyolefin resin expanded particle having a large cell diameter and excellent moldability in a mold, and a method for producing the same.

[0004]

Means for Solving the Problems As a result of earnest studies to solve the above problems, the present inventors have surprisingly found that a polyolefin resin particle containing a magnesium salt of a higher fatty acid together with a foaming aid. The inventors have found that the above problems can be solved by using the above materials, and have completed the present invention. That is, according to the present invention, there is provided a polyolefin resin foamed particle containing an inorganic gas therein, wherein the resin contains a magnesium salt of a higher fatty acid together with a foaming aid in the resin. To be done. Further, according to the present invention, after impregnating an inorganic gas-based foaming agent under pressure into the polyolefin-based resin particles, in the method for producing the polyolefin-based resin foamed particles to be released in the low-pressure zone, the polyolefin-based resin particles, Provided is a method for producing expanded polyolefin resin particles, which comprises using polyolefin resin particles containing a magnesium salt of a higher fatty acid together with a foaming aid.

As the resin for polyolefin resin particles used in the present invention, propylene homopolymer, propylene-
Ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer,
Propylene-based polymers such as propylene-ethylene-butene random copolymers, high-density polyethylene, and linear low-chain copolymers of ethylene and a small amount of α-olefins (C 4, 6, 8, etc.) Examples thereof include ethylene-based copolymers such as density polyethylene. Among these, especially propylene-ethylene random copolymer, propylene-butene random copolymer, propylene-ethylene-
It is preferable to use propylene-based random copolymer resin particles such as butene random copolymer. These polymers may be crosslinked, but non-crosslinked ones are particularly preferable,
The use of non-crosslinked propylene random copolymers is particularly preferred.

The polyolefin resin particles used in the present invention (hereinafter also simply referred to as resin particles) can be obtained by molding a polyolefin resin into particles according to a conventionally known method. In the case of the present invention, , A foaming aid and a magnesium salt of a higher fatty acid are mixed in the resin. In this case, the additives are generally added as powder having a particle size of 0.1 to 150 μm, preferably 1 to 100 μm, but may be added in the form of particles having a larger particle size.
In short, these additives may be added to the resin in any shape. In order to obtain the raw material resin particles used in the present invention, the resin, the foaming aid, and the magnesium salt of the higher fatty acid may be melt-kneaded and then molded into granules, or resin pellets containing a large amount of those additives in advance. Alternatively, resin pellets containing no such additives may be melt-kneaded and then molded.

As the foaming aid used in the present invention, any powder can be used as long as it is a fine powder capable of promoting foaming of the resin particles. As such, for example,
Talc, clay, kaolin, silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, aluminum sulfate, calcium sulfite, magnesium sulfite, calcium oxide, aluminum oxide, Inorganic powders such as synthetic zeolite, and organic aluminum-based, organic phosphorus-based nucleating agents are exemplified,
Among them, an organophosphorus nucleating agent having a high contribution to the improvement of the expansion ratio of the expanded particles, particularly 2,2-methylenebis (4,6-di-tert-butylphenyl) sodium phosphate, bis (4-tert) phosphate. -Butylphenyl) sodium and the like are preferred. The content of the foaming aid in the resin particles is usually in the range of 0.001% by weight to 2% by weight.

In the magnesium salt of higher fatty acid used in the present invention, as the higher fatty acid component, various saturated or unsaturated straight chain or branched chain fatty acids having 8 or more carbon atoms can be used. Further, the higher fatty acid component may be a polyvalent fatty acid. Examples of such higher fatty acid component include palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, sebacic acid and the like. The higher fatty acid magnesium salt is usually contained in the resin particles in an amount of 0.02 to 5% by weight, preferably 0.0
The ratio is 5 to 1% by weight.

The foamed polyolefin resin particles of the present invention are foamed by a foaming agent impregnating step of injecting an inorganic gas foaming agent into the resin particles in a high pressure zone, and the resin particles impregnated with the foaming agent are discharged into a low pressure zone to foam. Consists of steps. In this case, the particle size of the raw material resin is 0.3 to 5 mm, preferably 0.5 to 3 mm.

The step of impregnating the resin particles with the inorganic gas type foaming agent under pressure is carried out by a conventionally known method, for example, by dispersing the resin particles in a dispersion medium in a closed container and applying pressure with the inorganic gas type foaming agent. , By heating for a predetermined time.

Any dispersion medium can be used as long as it does not dissolve the resin particles, and examples of such dispersion media include water, ethylene glycol, glycerin,
Methanol, ethanol and the like can be mentioned, but it is common to use water.

As the inorganic gas type foaming agent, an inorganic gas such as nitrogen, carbon dioxide, argon, air or the like is used, but carbon dioxide is particularly suitable, and these gases are suitable for the pressure inside the container of 60 kg / cm. ^It is common to supply it so that it does not exceed 2.G. There is no particular problem if a volatile organic foaming agent such as propane, butane, pentane, hexane, cyclohexane, dichlorodifluoromethane, trichlorofluoromethane is used in combination up to about 50% by weight. The agent should generally remain below 25% by weight of the total blowing agent, preferably below 20%. The pressure applied by the inorganic gas type foaming agent is at least 15 kg / cm ² · G, preferably 20
It is at least kg / cm ² · G. The time for applying pressure with the foaming agent varies depending on the pressure applied, but it is about several seconds to 1 hour above the melting point of the resin, and usually 5 to 30.
Minutes are enough. The pressurization of the contents of the container with the foaming agent can be performed at any time, and can be performed immediately after the contents of the container are filled, during the temperature rise, or when the foaming temperature is reached. In particular, when carbon dioxide is used as the foaming agent, it can be introduced into the container in the form of dry ice, in which case dry ice is supplied into the container together with resin particles and a dispersion medium, After sealing, the method of heating is adopted. The heating rate of the contents of the container by heating is usually 1 to 10 ° C / min, preferably 2 to 5 ° C.
/ Min.

The temperature at which the resin particles are heated in the dispersion medium under the pressure of the blowing agent gas (foaming temperature) is generally a temperature above the softening point of the resin, but especially near the melting point of the resin particles used. It is suitable. The preferred foaming temperature range depends on the type of resin, and when non-crosslinked polypropylene resin is used, it ranges from 5 ° C lower than the melting point to 15 ° C higher than the melting point, particularly 3 ° C to 10 ° C lower than the melting point.
The optimum range is a high temperature, that is, a temperature of 10 ° C. lower than the melting point to 5 ° C. higher than the melting point of the polyethylene resin. The heating rate when heating to the foaming temperature is
It is 1 to 10 ° C / min, preferably 2 to 5 ° C / min. The melting point of the resin as used herein means about 6 mg of a sample measured by a differential scanning calorimeter at 220 ° C. at a rate of 10 ° C./min.
Up to 50 ° C at 10 ° C / min,
It is the temperature of the peak (specific peak) of the endothermic curve obtained when the temperature is raised again to 220 ° C. at a rate of 10 ° C./minute, and the melting end temperature of the resin is the end temperature of the second endothermic curve. Means

When impregnating the resin particles with the inorganic gas type foaming agent, a resin particle anti-fusion agent may be added to the dispersion medium in order to prevent fusion of the resin particles during heating. This resin particle anti-fusing agent can be used regardless of whether it is organic or inorganic, as long as it is substantially insoluble and non-melting upon heating, but it is generally preferable to use an inorganic one. . Examples of typical anti-fusing agents include aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, tricalcium phosphate, magnesium pyrophosphate and the like. . Such an anti-fusing agent is usually used in the form of fine particles having a particle size of 0.001 to 100 μm, preferably 0.001 to 30 μm. The amount of the anti-fusing agent added is usually about 0.01 to 10 parts by weight with respect to 100 parts by weight of the resin particles. When using the anti-fusion agent, it is desirable to use an emulsifier together in the dispersion medium,
As the emulsifier, anionic surfactants such as sodium dodecylbenzenesulfonate and sodium oleate are suitable. The addition amount of the emulsifier may be about 0.001 to 5.0 parts by weight per 100 parts by weight of the resin particles.

In the present invention, the expandable resin particles obtained by impregnating the resin particles with the foaming agent preferably contain secondary crystals. The expandable resin particles in which the secondary crystals are present give expanded particles having good moldability. When a non-crosslinked polypropylene resin or a non-crosslinked linear polyethylene resin is used as the raw material resin, it is particularly advantageous to allow secondary crystals to be present in the expandable resin particles.

The presence of secondary crystals in the resin particles can be determined by the DSC curve obtained by the differential scanning calorimetry of the resin expanded particles. in this case,
DS obtained by differential scanning calorimetry of expanded resin particles
C curve means 1 to 3 mg of foamed polyolefin resin particles
22 with a differential scanning calorimeter at a temperature rising rate of 10 ° C./min.
It is a DSC curve obtained when the temperature is raised to 0 ° C., for example, the DSC curve obtained when the sample is heated from room temperature to 220 ° C. at a temperature raising rate of 10 ° C./min.
A curve is drawn, and then the temperature is lowered from 220 ° C. to about 40 ° C. at a temperature lowering rate of 10 ° C./min.
The DSC curve obtained when the temperature was raised to 20 ° C. was used as the second DSC curve. From these DSC curves, the specific peak,
A high temperature peak can be obtained. Further, in this case, the unique peak is considered to be due to the so-called heat absorption during melting of the polyolefin resin forming the expanded particles. This peculiar peak is the second one on the first DSC curve.
It appears on the DSC curve for the first time, and the peak temperature is the first
There may be some differences between the 2nd time and the 2nd time, but the difference is 5
<0 ° C, usually <2 ° C. On the other hand, the high temperature peak is an endothermic peak that appears on the higher temperature side than the above-mentioned intrinsic peak in the first DSC curve. The presence of secondary crystals in the resin particles is determined by whether or not this high-temperature peak appears on the DSC curve. If no substantial high-temperature peak appears, the secondary crystals are present in the resin. It is determined that it does not exist. In the case of the present invention, it is desirable that the difference between the temperature of the characteristic peak appearing in the second DSC curve and the temperature of the high temperature peak appearing in the first DSC curve is large, and the second DSC curve. The difference between the temperature of the peak of the specific peak and the temperature of the peak of the high temperature peak is 5 ° C or more, preferably 10 ° C.
That is all.

The DSC curve of the expanded beads obtained by differential scanning calorimetry is shown in the drawing. FIG. 1 relates to expanded particles containing secondary crystals, and FIG. 2 relates to expanded particles not containing secondary crystals. Figure 1
2 and FIG. 2, curves 1 and 2 show DSC curves obtained by measuring expanded particles as a sample (first measurement), and curves 1 ′ and 2 ′ show the first measurement. The DSC curve obtained by measuring the sample after measurement again (2nd measurement) is shown. As can be seen by comparing FIGS. 1 and 2, in the case of expanded particles containing secondary crystals, in the curve 1 showing the first measurement result, in addition to the specific peak B, the high temperature peak A appears, this high temperature peak
The presence of KU A confirms the presence of secondary crystals in the expanded beads. On the other hand, in the case of expanded particles containing no secondary crystals, in curve 2 showing the first measurement result, only the specific peak b appears, but the high temperature peak does not appear,
It is confirmed that the expanded beads do not contain secondary crystals.
The secondary crystal does not exist in the expanded particles of FIG. 2 because the raw material unexpanded resin particles do not undergo the heat treatment at the secondary crystallization promoting temperature (melting point to less than melting end temperature) for a sufficient time, and the temperature is not less than the melting end temperature. Due to foaming at temperature. In the second measurement, the foamed particles shown in FIGS. 1 and 2 do not show the high temperature peaks, but only the specific peaks B'and b '.

In the present invention, in order to obtain expandable resin particles containing secondary crystals, in the case of a non-crosslinked polypropylene resin, the melting point of the resin particles in the pressure vessel is not raised above the melting end temperature thereof. The temperature may be maintained at a temperature about 20 ° C. lower (melting point −20 ° C.) or more and lower than the melting end temperature for a sufficient time, usually 5 to 90 minutes, preferably 15 to 60 minutes. Further, in the case of expanding the secondary crystallized expandable resin particles in this way, the foaming temperature is not less than the melting end temperature of the specific peak, but is the moldability as long as the temperature is at the high temperature peak or less. It is possible to obtain foamed particles of good quality. In the case of non-crosslinked linear low density polyethylene,
Although it is possible to obtain expandable resin particles containing secondary crystals in the same manner as in the case of the non-crosslinked polypropylene resin,
In this case, the heat treatment temperature is not lower than the melting point by about 15 ° C. and lower than the melting end temperature, and the time is from 5 to 5.
90 minutes, preferably 5 to 30 minutes.

The expandable resin particles impregnated with the foaming agent obtained as described above are prepared by removing the foamable resin particles from a pressure vessel,
Usually, it is made into foamed particles by discharging it into a container under normal pressure. The expansion ratio of the expanded beads obtained by the present invention is 3 times or more, preferably 5 to 60 times.

The expanded beads of the present invention obtained as described above have a large cell diameter of 0.05 mm or more,
It is very excellent in moldability. By filling this into a mold and heating it with steam, a molded product having a required shape can be obtained. The molded article obtained by using the expanded beads of the present invention has high dimensional accuracy with its shrinkability significantly suppressed.

[0021]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Examples 1 to 3 500 wtpp of calcium stearate as a neutralizing agent
m-containing non-crosslinked ethylene-propylene random copolymer (2.3% by weight of ethylene component, melting point 146.5 ° C,
Melting end temperature of 165 ° C.) 100 parts by weight of 2,2-methylenebis (4,6-di-te phosphate) as a foaming aid.
rt-butylphenyl) sodium at 500 ppm and higher fatty acid metal salts shown in Table 1 at 2000 to 5000 pp
m, added and melt-kneaded in the extruder, extruded in a strand form from a die at the tip of the extruder, rapidly cooled in water, cut and pelletized into pellets (length: 2.4 mm, cross section diameter: 1.1 mm). ). 100 parts by weight of the pellets, 0.1 parts by weight of fine-particle tricalcium phosphate, 0.2 parts by weight of sodium dodecylbenzenesulfonate, 220 parts by weight of water and 7.5 parts by weight of dry ice (foaming agent). The ingredients were blended and the temperature was raised to 151 ° C. with stirring in a closed container, and the temperature was maintained for 5 minutes. Then, at this temperature, the valve of the closed container was opened and the contents were discharged under atmospheric pressure to foam. At this time, in order to make the pressure inside the container at the time of discharge almost equal to the pressure inside the container just before the start of discharge, while introducing high-pressure carbon dioxide into the container, the pressure inside the container was about 40 kg / cm ^2.
Release was carried out by holding at G. Table 1 shows the average bulk expansion ratio and average cell diameter of the obtained expanded beads.

Next, in order to obtain a plate-shaped molded product having a length and width of 30 cm and a thickness of 5 cm from the foamed particles thus obtained, the foamed particles were filled in a mold and about 4.0 kg / cm.
^It was heated with ² G of steam (temperature: 151.0 ° C.). Then, the quality of the molded product obtained at this time was examined as follows, and the moldability of the expanded beads was evaluated. The results are shown in Table 1.
Shown in.

(Evaluation of Formability of Expanded Particles) O: Shrinkage of the molded product with respect to the mold size is within 3% in both length and width. X: Shrinkage of the molded product with respect to the mold size is more than 3% in at least one of the length and width.

The specific contents of the higher fatty acid metal salt indicated by the symbol in Table 1 are as follows. St-M
g: Magnesium stearate St-Zn: Zinc stearate St-Ba: Barium stearate St-Al: Aluminum stearate

[0026]

[Table 1]

[0027]

EFFECT OF THE INVENTION The expanded polyolefin resin particles of the present invention have a large expansion diameter and a high expansion ratio, are excellent in in-mold moldability, and are filled in a mold and heated and foamed.
A high-quality foamed molded product having excellent dimensional accuracy with significantly suppressed shrinkage.

[Brief description of drawings]

FIG. 1 shows a DSC curve obtained by performing differential scanning calorimetry on expanded particles in which secondary crystals are present, where curve 1 is the first
The first DSC curve is shown, and the curve 1'is the second DSC curve.

FIG. 2 shows a DSC curve obtained by performing differential scanning calorimetry on expanded particles having no secondary crystals, curve 2 shows a first DSC curve, and curve 2 ′ shows a second DSC curve. ing.

[Explanation of symbols]

 A High temperature peak B, B ', b, b' Unique peak

Claims (4)

[Claims] 1. A foamed polyolefin resin particle containing an inorganic gas therein, wherein the resin contains a magnesium salt of a higher fatty acid together with a foaming aid. 2. The polyolefin resin foamed particles according to claim 1, wherein the foaming aid is an organic phosphorus nucleating agent. 3. A method for producing foamed polyolefin resin particles, which comprises impregnating a polyolefin resin particle with an inorganic gas foaming agent under pressure and then releasing the foamed material into a low pressure zone.
A method for producing expanded polyolefin resin particles, wherein polyolefin resin particles containing a magnesium salt of a higher fatty acid together with a foaming aid are used as the polyolefin resin particles. 4. The method according to claim 3, wherein the foaming aid is an organophosphorus nucleating agent.