JP3198469B2 - Expanded polyolefin resin particles and method for producing the same - Google Patents

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 of producing expanded particles by injecting an inorganic gas-based blowing agent under pressure into polyolefin-based resin particles and releasing the same under a low pressure is known (Japanese Patent Publication No. 62-12727, JP-A-60-22993
No. 6, JP-A-60-245650). In this case, expanded particles having a high expansion ratio can be obtained by using polyolefin-based resin particles containing a foaming aid such as an inorganic powder and a crystal nucleating agent (Japanese Patent Application Laid-Open Nos.
1-2741). By the way, after injecting an inorganic gas-based foaming agent into a polyolefin-based resin containing a foaming aid,
When the foamed particles are obtained by discharging the foamed particles into a low-pressure zone, there is a problem that the foamed particles obtained have a too small cell diameter, and the in-mold moldability is reduced. The finer the bubble diameter, the more the foaming aid and the foaming agent that contribute to the expansion ratio are used,
For example, when an organic phosphorus-based nucleating agent is used as a foaming aid and carbon dioxide is used as a foaming agent, this becomes remarkable.
When the foamed particles having such a fine cell diameter are molded in a mold, the resulting molded body is liable to shrink, resulting in poor dimensional accuracy.

[0003]

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

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, surprisingly, the polyolefin resin particles contain a magnesium salt of a higher fatty acid together with a foaming aid together with a foaming aid. It has been found that the above-mentioned problems can be solved by using the above, and the present invention has been completed. That is, according to the present invention, there is provided expanded polyolefin-based resin particles, wherein the expanded polyolefin-based resin particles containing an inorganic gas therein contain a magnesium salt of a higher fatty acid together with a foaming aid in the resin. Is done. Further, according to the present invention, after impregnating the polyolefin-based resin particles with an inorganic gas-based blowing agent under pressure, in the method for producing expanded polyolefin-based resin particles to be released to a low pressure zone, as the polyolefin-based resin particles, A method for producing expanded polyolefin-based resin particles, comprising using polyolefin-based resin particles containing a magnesium salt of a higher fatty acid together with a foaming aid.

The resin for the polyolefin resin particles used in the present invention includes propylene homopolymer, propylene-
Ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer,
A propylene-based polymer such as a propylene-ethylene-butene random copolymer, or a high-density polyethylene, or a linear low-molecular-weight copolymer that is a copolymer of ethylene and a small amount of an α-olefin (carbon number of 4, 6, 8, etc.) Examples include ethylene copolymers such as high density polyethylene. Among these, propylene-ethylene random copolymer, propylene-butene random copolymer, propylene-ethylene-
The use of propylene-based random copolymer resin particles such as butene random copolymer is preferred. These polymers may be crosslinked, but non-crosslinked ones are particularly good.
The use of a non-crosslinked propylene random copolymer is particularly preferred.

[0006] 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. A foaming aid and a magnesium salt of a higher fatty acid are mixed into the resin. In this case, these additives are generally added as a 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 an arbitrary 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 a higher fatty acid may be melt-kneaded and then formed into granules, or a resin pellet containing a large amount of those additives in advance. Alternatively, resin pellets not containing these additives may be melt-kneaded before molding.

As the foaming aid used in the present invention, any fine powder can be used as long as it can promote the foaming of the resin particles. Such things include, 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 zeolites, and organic aluminum-based, organic phosphorus-based nucleating agents such as, for example,
Among them, organophosphorus-based nucleating agents having a high contribution to the improvement of the expansion ratio of the expanded particles, in particular, sodium 2,2-methylenebis (4,6-di-tert-butylphenyl) phosphate and 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.

[0008] In the magnesium salt of higher fatty acid used in the present invention, as the higher fatty acid component, various saturated or unsaturated linear or branched fatty acids having 8 or more carbon atoms can be used. The higher fatty acid component may be a polyhydric fatty acid. Such higher fatty acid components include, for example, 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 0.02% by weight.
It is a ratio of 5 to 1% by weight.

The foamed polyolefin resin particles of the present invention are obtained by foaming the resin particles impregnated with an inorganic gas-based blowing agent into the resin particles in a high pressure zone, and foaming the resin particles impregnated with the foaming agent into a low pressure zone by foaming. Process. 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-based blowing agent under pressure may be carried out by a conventionally known method, for example, by dispersing the resin particles in a dispersion medium in a closed container and pressing the inorganic gas-based blowing agent under pressure. This is performed by heating for a predetermined time.

As the dispersion medium, any one may be used as long as it does not dissolve the resin particles. Examples of such a dispersion medium include water, ethylene glycol, glycerin, and the like.
Methanol, ethanol and the like can be mentioned, but water is generally used.

As the inorganic gas-based foaming agent, an inorganic gas such as nitrogen, carbon dioxide, argon, or air or a gas containing the same is used. Particularly, carbon dioxide is preferable, and the gas is preferably 60 kg / cm. ^It is common to supply so as to be ² · G or less. There is no particular problem even if volatile organic blowing agents such as propane, butane, pentane, hexane, cyclohexane, dichlorodifluoromethane, and trichlorofluoromethane are used up to about 50% by weight. The agent should generally not exceed 25%, preferably 20%, by weight of the total blowing agent. The pressure applied by the inorganic gas-based foaming agent is at least 15 kg / cm ² · G, preferably 20 kg / cm ² · G.
kg / cm ² · G or more. The time for pressurizing with a foaming agent varies depending on the pressure for pressurizing, but is several seconds to about 1 hour above the melting point of the resin, and usually 5 to 30 hours.
A minute is 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 filling the contents of the container, during the temperature rise, or at the time when the foaming temperature is reached. In particular, when carbon dioxide is used as a blowing agent, it can be introduced into the container in the form of dry ice. In this case, dry ice is supplied into the container together with the resin particles and the dispersion medium, and After sealing, a 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 under pressure of the blowing agent gas in the dispersion medium (foaming temperature) is generally equal to or higher than the softening point of the resin. It is suitable. The preferred foaming temperature range varies depending on the type of the resin. When a non-crosslinked polypropylene resin is used, the temperature ranges from 5 ° C. lower than the melting point to 15 ° C. higher than the melting point, particularly from 3 ° C. lower than the melting point to 10 ° C.
The optimum range is a high temperature range, and a range from 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,
The temperature is 1 to 10C / min, preferably 2 to 5C / min. The melting point of the resin referred to in the present specification means that about 6 mg of a sample is measured at a rate of 10 ° C./min at 220 ° C. by a differential scanning calorimeter.
Up to about 50 ° C at 10 ° C / min.
The temperature of the endothermic curve peak (intrinsic peak) obtained when the temperature is raised again to 220 ° C. at a rate of 10 ° C./min. The melting end temperature of the resin is the end temperature of the second endothermic curve. Means

When impregnating the resin particles with an inorganic gas-based blowing agent, a resin particle anti-fusing agent can be added to the dispersion medium in order to prevent the resin particles from fusing 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 at the time of heating, but generally, inorganic is preferable. . Examples of typical anti-fusing agents include, for example, aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, tricalcium phosphate, magnesium pyrophosphate and the like. . Such an anti-fusion 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 is usually about 0.01 to 10 parts by weight based on 100 parts by weight of the resin particles. When using an anti-fusing agent, it is desirable to use an emulsifier in the dispersion medium,
As an emulsifier, an anionic surfactant such as sodium dodecylbenzenesulfonate or sodium oleate is suitable. The amount of the emulsifier added 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 a 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-based resin or a non-crosslinked linear polyethylene-based resin is used as a raw material resin, it is particularly advantageous that secondary crystals are present in the expandable resin particles.

The presence of secondary crystals in the resin particles can be determined by a DSC curve obtained by differential scanning calorimetry of the expanded resin particles. in this case,
DS obtained by differential scanning calorimetry of resin expanded particles
The C curve refers to expanded polyolefin resin particles 1 to 3 mg.
Was measured at a heating rate of 10 ° C./min by a differential scanning calorimeter.
The DSC curve obtained when the temperature was raised to 0 ° C., for example, the DSC curve obtained when the sample was heated from room temperature to 220 ° C. at a temperature rising rate of 10 ° C./min is the first DSC
Then, the temperature was lowered from 220 ° C. to a temperature of about 40 ° C. at a rate of 10 ° C./min, and again at a rate of 10 ° C./min.
The DSC curve obtained when the temperature was raised to 20 ° C. was used as the second DSC curve, and a unique peak,
High temperature peaks can be determined. In this case, the intrinsic peak is considered to be due to the so-called endothermic during melting of the polyolefin-based resin constituting the expanded particles. This unique peak is also used in the first DSC curve for the second time.
In the second DSC curve, the peak apex temperature is 1st.
There may be a slight difference between the second and the second round, but the difference is 5
Less than 2 ° C, usually less than 2 ° C. On the other hand, a 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 intrinsic 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 at the top of the intrinsic peak and the temperature at the top of the high temperature peak is 5 ° C. or more, preferably 10 ° C.
That is all.

Next, the DSC curve of the expanded particles 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 containing no secondary crystals. FIG.
In FIG. 2 and FIG. 2, curves 1 and 2 show the DSC curves obtained by measuring the 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 the measurement again (the second measurement) is shown. As can be seen by comparing FIGS. 1 and 2, in the case of expanded particles containing secondary crystals, curve 1 showing the first measurement results shows that in addition to intrinsic peak B, high-temperature peak A appears and this high-temperature peak
It is confirmed that secondary crystals are present in the foamed particles by the presence of kuA. On the other hand, in the case of the expanded particles containing no secondary crystal, the curve 2 showing the first measurement result shows only the intrinsic peak b but no high-temperature peak.
It is confirmed that the expanded particles do not contain secondary crystals.
The reason why secondary particles are not present in the expanded particles in FIG. 2 is that the raw material unexpanded resin particles are not subjected to heat treatment for a sufficient time at the secondary crystallization accelerating temperature (from the melting point to a temperature lower than the melting end temperature). Due to foaming at temperature. In the second measurement, high-temperature peaks do not appear in the expanded particles shown in FIGS. 1 and 2, but only intrinsic peaks B 'and b' appear.

In the present invention, in order to obtain expandable resin particles containing secondary crystals, in the case of a non-crosslinked polypropylene resin, the resin particles are heated to a melting point in a pressure vessel without being heated to the melting end temperature or higher. The temperature may be maintained at a temperature about 20 ° C. lower than the melting point (−20 ° C.) or higher and lower than the melting end temperature for a sufficient time, usually 5 to 90 minutes, preferably about 15 to 60 minutes. When the secondary crystallized foamable resin particles are foamed in this way, the foaming temperature is not less than the melting end temperature of the intrinsic peak, but is not higher than the high temperature peak. Can be obtained. In the case of non-crosslinked linear low density polyethylene,
Foamable resin particles containing secondary crystals can be obtained in the same manner as in the case of the non-crosslinked polypropylene resin,
The heat treatment temperature in this case is a temperature not less than about 15 ° C. lower than the melting point and less than the melting end temperature, and the time is 5 to 5.
90 minutes, preferably 5 to 30 minutes.

The foaming resin particles impregnated with the foaming agent obtained as described above are mixed with the foaming resin particles from a pressurized container in a low pressure zone,
Normally, foamed particles are formed by discharging into a container under normal pressure. The expansion ratio of the expanded particles obtained by the present invention is 3 times or more, preferably 5 to 60 times.

The expanded particles of the present invention obtained as described above have a large cell diameter of 0.05 mm or more,
Very good in moldability. This is filled in a mold and heated with steam to obtain a molded article having a required shape. The molded article obtained by using the expanded particles of the present invention has high dimensional accuracy, in which the shrinkage is significantly suppressed.

[0021]

Next, the present invention will be described in more detail with reference to 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,
2,2-methylenebis (4,6-di-te-phosphate) as a foaming aid per 100 parts by weight of melting end temperature (165 ° C.)
rt-butylphenyl) sodium at 500 ppm and higher fatty acid metal salts shown in Table 1 at 2000-5000 pp.
m, melt-kneaded in an extruder, extruded into a strand from a die at the tip of the extruder, quenched in water, cut and granulated into pellets (length 2.4 mm, cross-sectional diameter 1.1 mm) ). 100 parts by weight of these pellets, 0.1 part by weight of finely divided 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) After mixing, the mixture was heated to 151 ° C. while stirring in a closed container, and kept at this temperature for 5 minutes. Then, at this temperature, the valve of the closed container was opened and the contents were released under atmospheric pressure to foam. At this time, in order to make the pressure in the container at the time of discharge substantially equal to the pressure in the container immediately before the start of discharge, the pressure in the container was reduced to about 40 kg / cm ² while introducing high-pressure carbon dioxide into the container.
Release was performed while holding at G. Table 1 shows the average bulk expansion ratio and average cell diameter of the obtained expanded particles.

Next, in order to obtain a plate-like molded body having a size of 30 cm in length and width and a thickness of 5 cm from the foamed particles thus obtained, the foamed particles are filled in a mold, and about 4.0 kg / cm.
Heated with ² G steam (temperature: 151.0 ° C.). Next, the quality of the molded article obtained at this time was examined as follows, and the moldability of the expanded particles was evaluated. Table 1 shows the results.
Shown in

(Evaluation of Moldability of Expanded Particles) ：: Shrinkage rate of molded article with respect to mold size is within 3% in both length and width ×: Shrinkage rate of molded article with respect to mold dimension is at least any of more than 3%

The specific contents of the metal salts of higher fatty acids indicated by symbols 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]

The foamed polyolefin resin particles of the present invention have a high foaming ratio with a large cell diameter, excellent moldability in a mold, and are filled in a mold and foamed by heating.
A high-quality foam molded article with excellent dimensional accuracy, in which shrinkage is significantly suppressed.

[Brief description of the drawings]

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

FIG. 2 shows a DSC curve obtained by differential scanning calorimetry of 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' Specific peak

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-86737 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/18

Claims (4)

(57) [Claims] 1. A foamed polyolefin-based resin particle containing an inorganic gas therein, wherein the foamed polyolefin-based resin particle contains a magnesium salt of a higher fatty acid together with a foaming aid in the resin. 2. The polyolefin resin foam particles according to claim 1, wherein the foaming aid is an organic phosphorus nucleating agent. 3. A method for producing expanded polyolefin resin particles, which comprises impregnating a polyolefin resin particle with an inorganic gas blowing agent under pressure and releasing the polyolefin resin particle 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 organic phosphorus nucleating agent.