JP2009161668A - Method for producing polyolefinic resin pre-expanded particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing polyolefinic resin pre-expanded particles so that the particles are stably dispersed in a dispersion medium, mutual fusion between the particles is not inhibited during molding, and a dispersing agent sticking on the surfaces of the particles does not contaminate or corrode a molding die. <P>SOLUTION: The method for producing the polyolefinic resin pre-expanded particles comprises processes of: charging a dispersion liquid containing polyolefinic resin particles, water, and the dispersing agent, and a foaming agent into a pressure-resistant container; heating the pressure-resistant container to a prescribed temperature under pressure; and releasing the dispersion liquid into an atmosphere having pressure lower than that in the pressure-resistant container. In this method, the dispersing agent is an inorganic sulfate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides a method for producing polyolefin resin pre-expanded particles that can be used for the production of a polyolefin resin foam molded article used for buffer packaging materials, boxing, heat insulating materials, automobile bumper core materials, and the like, and the method described above. The present invention relates to a polyolefin resin pre-expanded particle and a foam-molded product thereof.

  Polyolefin resin foam moldings are used in buffer packaging materials, automobile bumpers, etc., and such foam moldings can be obtained by filling pre-manufactured polyolefin resin pre-expanded particles into a mold and molding them. It is manufactured. The polyolefin resin pre-expanded particles used here are dispersed in a dispersion medium such as water in a closed container together with the foaming agent, and heated to impregnate the polyolefin resin particles with the foaming agent. Generally, the polyolefin resin particles are produced by discharging them from a container under a low pressure atmosphere.

  In the production method, when the polyolefin resin particles are dispersed in the dispersion medium, an inorganic substance such as calcium carbonate, tricalcium phosphate, basic magnesium carbonate is used to stabilize the dispersion state of the resin particles in the dispersion medium. Or a dispersing agent such as an aqueous polymer protective colloid such as N-polyvinylpyrrolidone or polyvinyl alcohol, if necessary, in combination with a dispersing aid such as a surfactant. These dispersants / dispersing aids have an action of covering the surface of the resin particles to give the resin particles affinity for water and preventing adhesion between the particles. For this reason, a stable dispersion of resin particles can be obtained.

  By the way, the dispersant remaining on the surface of the obtained pre-expanded particles inhibits the fusibility between the pre-expanded particles when forming the pre-expanded particles, and a foamed molded article having excellent strength cannot be obtained. There is.

  In addition, the dispersant remaining on the surface of the pre-expanded particles is peeled off at the time of molding, and the peeled dispersant acts on the metal forming the mold together with the resin fragments generated in the manufacturing process of the pre-foamed particles. The problem of contaminating can also arise.

  On the other hand, as a foaming agent used for producing foamed particles, volatile organic compounds such as butane, inorganic gases such as carbon dioxide and nitrogen, and water are known. In recent years, cheap and safe foaming agents such as carbon dioxide and water have been frequently used from the viewpoint of safety and cost.

  When carbon dioxide is used as a foaming agent, a dispersion medium such as water is acidified. Therefore, it is known that when carbon dioxide is used as the foaming agent, it is preferable to use a dispersant different from the dispersant used when a volatile organic compound, nitrogen or water is used as the foaming agent. Patent Document 1 discloses the use of finely divided aluminum oxide. Patent Document 2 discloses the use of finely divided basic magnesium carbonate. Patent Document 3 discloses the use of a particulate silicate mineral.

  However, even when these dispersants are used, the dispersion state is unstable, and the polyolefin resin particles aggregate in the dispersion medium, so that pre-foamed particles cannot be obtained or stirring of the dispersion becomes difficult. There is. In particular, when a low melting point resin is used or when the temperature of the dispersion is high, the dispersion state tends to become unstable. Further, even if the pre-expanded particles can be produced, the strength of the foamed molded product obtained by insufficient fusion between the pre-expanded particles at the time of molding may be insufficient. Furthermore, when pre-expanded particles are molded, there is a possibility that the dispersant adhering to the surface of the pre-expanded particles adheres to the mold and contaminates / corrodes the mold.

Patent Documents 4 to 6 describe a process for producing polyolefin foam particles, and disclose carbon dioxide as a foaming agent together with other foaming agents. Furthermore, barium sulfate which is an inorganic sulfate is disclosed as a dispersant together with other dispersants. However, it does not disclose a production method using carbon dioxide as a foaming agent and barium sulfate as a dispersant. Furthermore, Patent Documents 4 to 6 do not describe or suggest the effects of the present invention.
Japanese Examined Patent Publication No. 62-61227 Japanese Patent Laid-Open No. 60-32835 JP-A-6-200071 Japanese Patent Laid-Open No. 7-11042 JP-A-7-165972 JP-A-8-281682

  An object of the present invention is to provide a production method capable of stably producing polyolefin resin foamed pre-expanded particles without aggregation between particles in a dispersion medium when carbon dioxide is used as a foaming agent. Another object of the present invention is to provide a process for producing a polyolefin resin foamed pre-foamed particle which gives a foamed molded article having excellent strength by sufficiently fusing the pre-foamed particles during molding. Still another object of the present invention is to provide a method for producing polyolefin resin foamed pre-expanded particles that does not contaminate or corrode the mold during molding.

  The present inventor has found that the object of the present invention is achieved when an inorganic sulfate is used as a dispersant. The present invention relates to the following method for producing pre-expanded particles, resin pre-expanded particles and a foam-molded product.

(1) A dispersion containing polyolefin resin particles, water, a dispersant and a foaming agent containing carbon dioxide are placed in a pressure-resistant container, and the pressure-resistant container is heated to a predetermined temperature under pressure. In a method for producing polyolefin resin pre-expanded particles, wherein the dispersant is an inorganic sulfate, the method further comprises:
(2) The method for producing polyolefin resin pre-expanded particles according to (1), wherein the inorganic sulfate is a sulfate that is hardly soluble in water.
(3) The method for producing polyolefin resin pre-expanded particles according to (2), wherein the water-insoluble inorganic sulfate is barium sulfate.
(4) The method for producing polyolefin resin pre-expanded particles according to any one of (1) to (3), wherein the inorganic sulfate has an average particle diameter of 0.01 to 20 μm.
(5) The process for producing polyolefin resin pre-expanded particles according to (1), wherein a dispersion aid is used together with the inorganic sulfate.
(6) Polyolefin resin pre-expanded particles obtained by the method for producing polyolefin resin pre-expanded particles according to any one of (1) to (5).
(7) A polyolefin resin foamed molded article obtained by filling the mold with the polyolefin resin pre-expanded particles according to (6) and heating.

  According to the production method of the present invention, even when carbon dioxide is used as the foaming agent, the dispersion stability of the resin particles is good, so that the polyolefin resin pre-foamed particles can be produced stably. Further, there is no fusion between the produced pre-expanded particles. Further, the used dispersant can be easily removed by washing with water. In the in-mold molding using the polyolefin resin pre-expanded particles after washing, the fusion of the polyolefin resin pre-expanded particles proceeds sufficiently. Furthermore, the dispersant used in the present invention has a property that it is difficult to adhere to aluminum that is often used in an in-mold molding die. Therefore, the dispersant used in the present invention is difficult to adhere to the mold even during molding, and can be easily removed even when it adheres to the mold. For this reason, when the pre-expanded particles of the present invention are used, the molding efficiency can be improved without contaminating the mold.

  Polyolefin resins used in the present invention include polyethylene resins such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ethylene-vinyl acetate copolymer, propylene homopolymer, and ethylene-propylene random copolymer. , Ethylene-propylene block copolymer, propylene-butene random copolymer, ethylene-propylene-butene random copolymer, maleic anhydride-propylene random copolymer, maleic anhydride-propylene block copolymer, propylene-anhydrous Examples thereof include polypropylene resins such as maleic acid graft copolymers, and styrene-modified polyolefins. These polyolefin-based resins are preferably non-crosslinked, but crosslinked resins can also be used. Among these, non-crosslinked ethylene-propylene random copolymer, propylene-butene random copolymer, and ethylene-propylene-butene random copolymer are preferable.

  The polyolefin resin is formed into the shape of polyolefin resin particles using a known method. For example, it is melted by using an extruder, a kneader, a Banbury mixer (trademark), a roll or the like, and processed into a polyolefin resin particle in which the weight of one grain is preferably 0.2 to 10 mg, more preferably 0.5 to 6 mg. Is done. Generally, it is preferable to melt by using an extruder and to manufacture by a strand cut method. For example, a polyolefin resin extruded in a strand form from a circular die is cooled and solidified with water, air or the like to cut a polyolefin resin particle having a desired shape.

  When using styrene-modified polyolefin, the resin particles are prepared, for example, in the same manner as described above, and while the polyolefin resin particles are dispersed in a dispersion medium, a vinyl monomer such as styrene is used. Can be produced by impregnating polymerization.

  Moreover, it is preferable to add a cell nucleating agent during the production of the polyolefin resin particles because the cell diameter when the polyolefin resin pre-expanded particles can be adjusted to a desired value. As the cell nucleating agent, nucleating agents such as talc, calcium carbonate, silica, kaolin, titanium oxide, bentonite and barium sulfate are generally used. The amount of the cell nucleating agent added varies depending on the type of polyolefin resin to be used and the type of cell nucleating agent, and cannot be specified unconditionally. It is preferable that it is below weight part.

Furthermore, during the production of polyolefin resin particles, various additives can be added as necessary within a range that does not impair the properties of the polyolefin resin. Examples of additives include colorants such as carbon black and organic pigments; antistatic agents such as alkyldiethanolamides, alkyldiethanolamines, hydroxyalkylethanolamines, fatty acid monoglycerides, and fatty acid diglycerides;
IRGANOX (registered trademark) 1010 (Ciba Specialty Chemicals), IRGANOX (registered trademark) 1076 (Ciba Specialty Chemicals), IRGANOX (registered trademark) 1330 (Ciba Specialty Chemicals), IRGANOX (registered trademark) 1425 WL (Ciba Specialty Chemicals), IRGANOX ( Hindered phenolic antioxidants such as (registered trademark) 3114 (registered trademark) (Ciba Specialty Chemicals);

Phosphorus processing stabilizers such as IRGAFOS (registered trademark) 168 (Ciba Specialty Chemicals), IRGAFOS (registered trademark) P-EPQ (Ciba Specialty Chemicals), IRGAFOS 126; lactone processing stabilizers; hydroxylamine processing stabilizers, IRGANOX (Registered trademark) MD1024 (Ciba Specialty Chemicals) and other metal deactivators; TINUVIN (registered trademark) 326 (Ciba Specialty Chemicals), benzotriazole ultraviolet absorbers such as TINUVIN (registered trademark) 327; TINUVIN (registered trademark) 120 Benzoate light stabilizers such as: CHIMASSORB119 (Ciba Specialty Chemicals), CHIMASSORB (registered trademark) 944 (Ciba Specialty Chemicals), INUVIN (R) 622 (Ciba Specialty Chemicals), TINUVIN (R) hindered amine light stabilizers such as 770;

Non-halogen flame retardants such as halogen flame retardants and antimony trioxide flame retardants; FLAMESTTAB (registered trademark) NOR116 (Ciba Specialty Chemicals), MELAPUR (registered trademark) MC25 (Ciba Specialty Chemicals); hydrotalcite, Examples include acid neutralizers such as calcium stearate; crystal nucleating agents such as IRGASTAB (registered trademark) NA11 (Ciba Specialty Chemicals); amide-based additives such as erucic acid amide and ethylenebisstearic acid amide.

  The polyolefin resin pre-expanded particles in the present invention include, for example, a dispersion liquid containing polyolefin resin particles, a dispersion medium, a dispersant, and a dispersion aid used as necessary, and carbon dioxide in a pressure vessel. A foaming agent is charged in a pressure vessel, heated to a predetermined temperature equal to or higher than the softening temperature of the polyolefin resin, and under pressure, the dispersion is kept at a lower pressure than in the pressure vessel while keeping the temperature and pressure constant. It is obtained by releasing in the atmosphere.

  The pressure vessel to be used is not particularly limited as long as it can withstand the pressure in the vessel and the temperature in the vessel at the time of producing the pre-foamed particles, and examples thereof include an autoclave type pressure vessel.

  Examples of the blowing agent containing carbon dioxide include carbon dioxide or a mixed blowing agent containing carbon dioxide as a main component. The carbon dioxide content in the mixed foaming agent is 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more. Examples of blowing agents that can be used in combination with carbon dioxide include aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane, dichlorodi Examples thereof include volatile organic compounds such as halogenated hydrocarbons such as fluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride, inorganic gases such as nitrogen, and water.

  The amount of foaming agent containing carbon dioxide varies depending on the type of polyolefin resin used, the type of foaming agent, the target foaming ratio, etc., and cannot be specified unconditionally. The amount is preferably 2 parts by weight or more and 60 parts by weight or less.

  The amount of water constituting the dispersion is 100 parts by weight or more and 500 parts by weight of water with respect to 100 parts by weight of the polyolefin resin particles in order to improve the dispersibility of the polyolefin resin particles in the dispersion medium. The following is preferable.

In the present invention, an inorganic sulfate is used as a dispersant. Examples of inorganic sulfates include magnesium sulfate (MgSO ₄ ), potassium sulfate (K ₂ SO ₄ ), silver sulfate (Ag ₂ SO ₄ ), calcium sulfate (CaSO ₄ ), barium sulfate (BaSO ₄ ), lead sulfate (PbSO ₄ ). ), Strontium sulfate (SrSO ₄ ) and the like, and these can be used alone or in combination. Among them, it is preferable to use an inorganic sulfate that is insoluble in water because good dispersion stability can be obtained even in a relatively small amount. Examples of inorganic sulfates that are insoluble in water include calcium sulfate (CaSO ₄ ), barium sulfate (BaSO ₄ ), lead sulfate (PbSO ₄ ), and strontium sulfate (SrSO ₄ ). Of these, barium sulfate is more preferred because of its good dispersibility. Here, the term “insoluble in water” means that the solubility in 100 ml of water at 100 ° C. is 1 g or less.

  The inorganic sulfate used in the present invention is preferably in the form of fine powder, more preferably an average particle size of 0.01 to 20 μm, still more preferably 0.01 to 10 μm. The average particle size of the inorganic sulfate was obtained by calculating the particle size distribution using a laser light diffraction / scattering type particle size distribution analyzer, and calculating the cumulative curve with the total volume of the powder group from which the particle size distribution was determined as 100%. This refers to the particle diameter (Median diameter) at the point where the cumulative curve is 50%.

  The amount of the dispersant used varies depending on the type and amount of the polyolefin resin particles, the foaming agent, etc., and cannot be generally specified, but is 0.2 to 5.0 parts by weight with respect to 100 parts by weight of the polyolefin resin particles. Or less, and more preferably 0.5 parts by weight or more and 3.0 parts by weight or less.

  In the present invention, a dispersion aid may be used together with the dispersant. As the dispersion aid, an anionic surfactant having a linear carbon chain having 10 to 18 carbon atoms as a hydrophobic group is preferable. Examples of the anionic surfactant having a linear carbon chain having 10 to 18 carbon atoms as a hydrophobic group include an alkyl sulfate having 10 to 18 carbon atoms, an alkyl sulfonate having 10 to 18 carbon atoms, and 10 to 10 carbon atoms. 18 fatty acid salt C10-18 alkyl phosphate and the like. Among these, alkyl sulfonates having 10 to 18 carbon atoms are preferable from the viewpoints of dispersion stability, fusion properties of molded articles, prevention of mold contamination / corrosion and cost, and wastewater treatment. Use of an alkyl sulfonate is more preferable because the effect can be maximized. Examples of the linear alkyl sulfonate having 12 carbon atoms include sodium lauryl sulfonate.

  The amount of dispersing aid used varies depending on the type, type and amount of polyolefin resin used, type of foaming agent, etc., and cannot be specified unconditionally, but is preferably 1.5 to 10% by weight of the dispersing agent. Preferably it is 4.5 to 7.5 weight%. It is preferable for the amount of the dispersion aid to be in the above-mentioned range because better dispersion stability tends to be obtained.

  Further, in the present invention, a dispersion reinforcing agent may be used together with the dispersing agent. Examples of the dispersion strengthening agent include magnesium chloride, magnesium nitrate, aluminum chloride, aluminum nitrate, iron chloride, iron nitrate and the like. The amount of the dispersion strengthening agent varies depending on the type, the type and amount of the polyolefin resin to be used, the type of foaming agent, etc., and cannot be specified unconditionally, but is preferably 1 to 30% by weight of the dispersing agent.

  A foaming agent containing carbon dioxide is added to a dispersion liquid containing polyolefin resin particles, water, a dispersing agent, and a dispersing aid used as necessary in a pressure vessel in this manner, and stirred. Then, the pressure is increased to a predetermined pressure, the temperature is increased to a predetermined temperature, and the pressure is maintained for a predetermined time, usually 5 to 180 minutes, preferably 10 to 60 minutes. Thereafter, the polyolefin-based resin pre-expanded particles can be produced by releasing the pressurized dispersion liquid in a low-pressure atmosphere (usually atmospheric pressure) by opening a valve provided in the lower part of the pressure-resistant container. .

  When the dispersion containing polyolefin resin particles is discharged into a low-pressure atmosphere, it can also be discharged through an opening orifice having a diameter of 2 to 10 mm for the purpose of adjusting the flow rate and reducing variation in magnification. In some cases, the low-pressure atmosphere is heated with steam for the purpose of increasing the expansion ratio.

  The temperature at which the contents of the pressure vessel are heated (hereinafter sometimes referred to as the foaming temperature) varies depending on the melting point [Tm (° C.)] of the polyolefin resin used, the type of foaming agent, etc. It is determined from the range of Tm−30 (° C.) to Tm + 10 (° C.). In addition, the pressure in the pressure vessel (hereinafter sometimes referred to as foaming pressure) varies depending on the type of polyolefin resin used, the type of foaming agent, and the desired expansion ratio of the pre-expanded particles, and cannot be specified unconditionally. It is determined from a range of approximately 1 to 8 MPa (gauge pressure).

  The melting point of the polyolefin-based resin here refers to the polyolefin-based resin particles by heating the sample 5-6 mg from 40 ° C. to 220 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter. From the DSC curve obtained by melting and then crystallizing by lowering the temperature from 220 ° C. to 40 ° C. at 10 ° C./min, and then increasing the temperature from 40 ° C. to 220 ° C. at 10 ° C./min. It is a value calculated | required as a melting peak temperature at the time of temperature rising.

  The polyolefin-based resin pre-expanded particles obtained as described above can be made into a polyolefin-based resin expanded molded body by a conventionally known molding method. For example, a) Pre-expanded particles are pressurized with an inorganic gas, such as air or nitrogen, impregnated with the inorganic gas in the pre-expanded particles to give a predetermined internal pressure of the pre-expanded particles, filled in a mold, B) a method in which the pre-expanded particles are compressed by gas pressure and filled in a mold, and a heat-fusing with steam using the recovery force of the pre-expanded particles, c) a pre-treatment. A method such as a method in which pre-expanded particles are filled in a mold without being heated and heat-sealed with water vapor can be used.

  The in-mold foam-molded product obtained by using the foamed particles by the production method of the present invention can be used for applications such as a heat insulating material, a buffer packaging material, an automobile interior member, and a core material for an automobile bumper.

  Next, the manufacturing method of the polyolefin resin pre-expanded particles of the present invention will be described in detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples. Evaluation was performed as follows.

<Dispersion stability>
The dispersion stability was evaluated according to the following criteria.
X: When polyolefin resin particles dispersed in an aqueous dispersion medium in a pressure vessel are heated to a temperature equal to or higher than the softening temperature of the polyolefin resin particles, the pressure vessel cannot be stirred and cannot be pre-foamed. The resulting foamed particles can be fused together after drying, and the size and shape of the foamed particles are irregular. ○: Pre-foaming is possible, and the obtained foamed particles are dried. Good spherical foam particles with no mutual fusion

<Fusibility in molded product>
The fusing property in the molded body was evaluated according to the following criteria.
○: After cutting the obtained polyolefin-based resin foam molded article with a cutter knife in the thickness direction of the foam molded article by about 10 mm, the foam molded article is broken by hand from the cut portion. The fracture surface is observed, and there is no breakage at the boundary of the pre-foamed particle, and the material of the pre-foamed particle is broken. Δ: The material breakage of the pre-foamed particle and the break at the boundary of the pre-foamed particle are mixed. Destruction at the particle boundary occurs

<Expansion ratio of pre-expanded particles>
The true magnification of the pre-expanded particles was measured. Pre-expanded particles whose weight was measured in advance were submerged in ethanol with a known volume, the density of the pre-expanded particles was determined from the increased ethanol volume, and the density of the pre-expanded particles was calculated from the resin density before foaming. .

(Examples 1-5)
First, ethylene-propylene random copolymer (resin density: 0.90 g / cm ³ , melt flow index: 7 g / 10 min, melting point: 142 ° C.) 100 parts by weight and melamine (manufactured by BASF) 0.1 part by weight and talc 0 .03 parts by weight of the mixture is dry blended into a mixture, the mixture is melt-kneaded in an extruder, extruded into a strand from a circular die, cooled with water, cut with a cutter, and the weight of one grain is 1.2 mg / grain Resin particles were obtained.

  100 parts by weight (1.55 kg) of the obtained resin particles were placed in a pressure vessel having an internal volume of 10 liters equipped with a stirrer. 300 parts by weight of water and a dispersant (precipitation barium sulfate, average particle size 0.7 μm, manufactured by Sakai Chemical Industry Co., Ltd.) and a dispersion aid (sodium lauryl sulfonate, hereinafter referred to as Ra) in the amounts shown in Table 1 In some cases, a dispersion of resin particles was obtained. While stirring the dispersion, 14 parts by weight of liquid carbon dioxide gas was added, and the dispersion was heated to 147.2 ° C. At this time, gaseous carbon dioxide was added to adjust the internal pressure of the pressure vessel to 3.2 MPa.

  Next, a mixture of resin particles and water is discharged into the atmosphere through a circular orifice having a diameter of 3.6 mm while maintaining the internal pressure in the pressure resistant vessel at 3.0 to 3.2 MPa (gauge pressure) with gaseous carbon dioxide. Thus, polypropylene resin pre-expanded particles (hereinafter sometimes referred to as pre-expanded particles) were obtained. The obtained polypropylene resin pre-foamed particles were washed with water and dried, and then the presence or absence of fusion between the particles and the foaming ratio were measured. The results are shown in Table 1.

The pre-expanded particles washed with water and dried were allowed to stand at room temperature and normal pressure for 6 hours, and then pressurized with air at 20 ° C. and 3 kg / cm ² for 24 hours. Next, the pre-expanded particles were filled in a 400 mm × 300 mm × 60 mm mold and heated with 0.3 to 0.24 MPa (gauge pressure) steam to form. Table 1 shows the results obtained by drying the obtained molded body for 15 hours in an oven at 75 ° C., and then measuring the fused state between the expanded particles in the molded body.

（比較例１〜８）
分散剤として表１に示す量の第三リン酸カルシウム（平均粒径：４．５μｍ、太平化学産業（株）製）、水酸化アルミニウム（平均粒径：１．２μｍ、日本軽金属（株）製）、酸化アルミニウム（平均粒径：１．０μｍ、日本軽金属（株）製）、水酸化マグネシウム（平均粒径：０．８μｍ、堺化学工業（株）製）、カオリン（平均粒径：０．４μｍ、Ｅｎｇｅｌｈａｌｄ社製）、分散助剤として表１に示す量のラウリルスルホン酸ナトリウム（Ｒａ）又は、ドデシルベンゼンスルホン酸ナトリウム（ＤＢＳ）を用いた以外は実施例１〜５と同様の評価を行った。

(Comparative Examples 1-8)
Tricalcium phosphate in an amount shown in Table 1 as a dispersant (average particle size: 4.5 μm, manufactured by Taihei Chemical Industry Co., Ltd.), aluminum hydroxide (average particle size: 1.2 μm, manufactured by Nippon Light Metal Co., Ltd.), Aluminum oxide (average particle size: 1.0 μm, manufactured by Nippon Light Metal Co., Ltd.), magnesium hydroxide (average particle size: 0.8 μm, manufactured by Sakai Chemical Industry Co., Ltd.), kaolin (average particle size: 0.4 μm, The same evaluation as in Examples 1 to 5 was performed except that sodium lauryl sulfonate (Ra) or sodium dodecylbenzene sulfonate (DBS) in the amount shown in Table 1 was used as a dispersion aid.

  From the results shown in Table 1, it can be seen that the pre-expanded particles obtained even with a small amount of dispersant in the production method of the present invention have no fusion between the particles, so that sufficient dispersion stability is maintained. Moreover, it turns out that the fusion inhibitory effect in shaping | molding of the dispersing agent adhering to the pre-expanded particle surface is small.

  In Comparative Examples 1 to 8, it can be seen that the dispersion of the production method of the present invention is stable in the pressure resistant container when compared with the fine inorganic salt having a particle size substantially equal to that of barium sulfate used in the examples. Even with tricalcium phosphate and aluminum hydroxide, the expanded particles can be obtained without fusing the particles. However, compared to the examples, a large amount of the dispersant is used and the fusion-inhibiting property of the expanded molded product tends to be large.

  In addition, when compared with aluminum oxide used in Examples of Patent Document 1 and kaolin used in Examples of Patent Document 3, barium sulfate has excellent dispersion stability and fusion property in a molded body. It is clear.

(Example 6, Comparative Examples 9, 10)
In order to compare the reactivity between metals and various dispersants, precipitated aluminum barium sulfate (average particle size 0.7 μm, Sakai Chemical Industry ( Co., Ltd.), tricalcium phosphate (average particle size 4.5 μm, manufactured by Taihei Chemical Industry Co., Ltd.), kaolin (average particle size 0.4 μm, manufactured by Engelhard) and sodium dodecylbenzenesulfonate (DBS) or lauryl sulfone 10 ml of a solution dispersed in 100 parts of water in the presence of sodium acid (Ra) was poured and dried in an oven at 140 ° C. for 3 hours.

After drying, it was taken out from the oven, and the attached solid matter was removed by the following three methods.
(1) Vibration: Give vibration to the aluminum cup and wipe off the dry solids (2) Washing water: Gently pour pure water on the aluminum cup and wash away the dry solids (3) Wiping: With Kimwipe (registered trademark) Wipe and wipe dry matter The ease with which the attached dry matter was removed was evaluated according to the following criteria. The results are shown in Table 2.
◎: Dry solids can be completely removed, and the metallic luster is restored. ○: Dry solids can be completely removed, but discoloration is observed in the metal. Δ: Dry solids can be removed. X remains partially: dried solids cannot be removed

表２に示したとおり、本発明における分散剤の乾固物は水洗等によって容易に除去することができ、洗浄後のアルミカップの表面には金属光沢が復活していることから金属との反応性が小さいということが分かる。

As shown in Table 2, the dried solid product of the dispersant in the present invention can be easily removed by washing with water, etc., and since the metallic luster has been restored on the surface of the aluminum cup after washing, the reaction with the metal It turns out that the nature is small.

  On the other hand, the dried solid product of the dispersant shown in the comparative example is difficult to remove by washing, and the surface of the aluminum cup after washing is discolored. This indicates that the dispersant of the comparative example is reactive with metal.

Claims (7)

  A dispersion containing polyolefin resin particles, water, a dispersing agent and a blowing agent containing carbon dioxide are placed in a pressure vessel, and the pressure vessel is heated to a predetermined temperature under pressure. A method for producing polyolefin resin pre-expanded particles, wherein the dispersant is an inorganic sulfate, wherein the polyolefin resin pre-expanded particles are discharged under a lower pressure atmosphere than the inside.   2. The method for producing polyolefin resin pre-expanded particles according to claim 1, wherein the inorganic sulfate is a sulfate that is hardly soluble in water.   The method for producing polyolefin resin pre-expanded particles according to claim 2, wherein the water-insoluble inorganic sulfate is barium sulfate.   The average particle diameter of the said inorganic sulfate is 0.01-20 micrometers, The manufacturing method of the polyolefin-type resin pre-expanded particle as described in any one of Claims 1-3.   The method for producing pre-expanded polyolefin resin particles according to claim 1, wherein a dispersion aid is used together with the inorganic sulfate.   Polyolefin resin pre-expanded particles obtained by the method for producing polyolefin resin pre-expanded particles according to any one of claims 1 to 5.   A polyolefin resin foam-molded article obtained by filling the mold with the polyolefin resin pre-expanded particles according to claim 6 and heating.