JP5410080B2 - Method for reducing poorly water-soluble inorganic compounds adhering to the surface of polyolefin resin foam particles - Google Patents

Description

  The present invention relates to a poorly water-soluble inorganic material attached to the surface of a polyolefin resin foam particle that can be suitably used for the production of a polyolefin resin foam molded article used for buffer packaging materials, boxing, heat insulating materials, automobile bumper core materials, etc. It relates to a method for reducing compounds.

  Polyolefin-based resin foam moldings are widely used for automobile parts such as buffer packaging materials and bumper core materials. These polyolefin resin foam moldings are produced from polyolefin resin foam particles.

  Usually, polyolefin resin foam particles are produced by impregnating a resin particle dispersed with an inorganic dispersant in an aqueous medium in a pressure-resistant container such as an autoclave, and then impregnating the resin particles impregnated with the foaming agent into resin particles. A method of releasing and foaming in a low-pressure atmosphere from the inside of the container at a temperature equal to or higher than the softening temperature is employed.

  At this time, in order to stabilize the dispersion state of the resin particles in the aqueous medium, the surface of the resin particles is coated to make the resin particles easy to conform to water, and has an action of preventing adhesion between the particles, aluminum oxide, Dispersants such as inorganic substance dispersants such as titanium oxide, tricalcium phosphate, magnesium triphosphate and kaolin, and aqueous polymer protective colloids such as N-polyvinylpyrrolidone and polyvinyl alcohol are used.

  However, these dispersants remain on the surface of the obtained polyolefin resin expanded particles, and particularly in the case of inorganic dispersants, the amount of the dispersant used is large, so the amount of dispersant remaining on the surface of the expanded particles is also large. Tend to be. Polyolefin resin foamed particles with a large amount of adhering dispersant remove the dispersant adhering to the foamed particles, because even if the foamed particles are heated in the molding process of the in-mold foamed molded product, the particles are difficult to fuse together It was hoped to do.

As a method for removing the dispersant on the surface of the expanded particles, there are a method in which the expanded particles are submerged and washed (Patent Document 1), a method in which the foamed particles are sprayed with a specific mineral acid aqueous solution and cleaned (Patent Document 2), and the like. Are known. However, these methods have a problem in that a large amount of water, an acid aqueous solution, and acid-resistant equipment are required for cleaning, and a cleaning cost and a processing cost of cleaning waste liquid are required.
Japanese Patent Laid-Open No. 9-124832 JP-A-8-225675

  An object of the present invention is to provide polyolefin resin expanded particles in which the amount of the hardly water-soluble inorganic compound adhering to the surface of the polyolefin resin expanded particles is reduced.

As a result of intensive studies to solve the above-mentioned problems, the present inventors put the polyolefin resin foam into a separate pressure-resistant container without applying internal pressure to the polyolefin resin foam particles, and treated with steam. The inventors have found that the amount of the hardly water-soluble inorganic compound adhering to the particle surface can be reduced, and have completed the present invention.

That is, the present invention is a method for producing polyolefin resin expanded particles that reduces the hardly water-soluble inorganic compound adhering to the surface, and includes the polyolefin resin particles, the hardly water-soluble inorganic compound, and the surfactant in the pressure vessel. After introducing an aqueous dispersion and a foaming agent, the polyolefin resin particles were impregnated with a foaming agent at a constant pressure and a constant temperature, and then released into a low-pressure atmosphere to obtain polyolefin resin foamed particles . The present invention relates to a method for producing foamed polyolefin resin particles, wherein the foamed polyolefin resin particles are put in another pressure vessel without being subjected to internal pressure, and treated with steam. As a preferred embodiment , the present invention relates to the above-mentioned method for producing polyolefin resin expanded particles , wherein the poorly water-soluble inorganic compound is an alkaline earth metal salt.

  According to the method of the present invention, the hardly water-soluble inorganic compound adhering to the surface of the polyolefin resin foamed particles can be easily reduced. In addition, the polyolefin resin expanded particles treated by the method of the present invention have a less water-soluble inorganic compound adhering to the surface compared to the original polyolefin resin expanded particles, and therefore melt when melt-molded in the mold. An in-mold foam molded article with good adhesion can be obtained.

The method for producing a polyolefin resin foamed particle for reducing the hardly water-soluble inorganic compound adhering to the surface of the present invention includes an aqueous dispersion containing a polyolefin resin particle, a hardly water-soluble inorganic compound, a surfactant in a pressure-resistant container, and foaming. A polyolefin resin particle is impregnated with a foaming agent at a constant pressure and a constant temperature after charging, and then released into a low-pressure atmosphere to obtain a polyolefin resin foam particle , and then the polyolefin resin foam Without applying internal pressure to the particles, the particles are put into another pressure vessel and treated with steam.

  In order to treat the polyolefin resin expanded particles with steam, the polyolefin resin expanded particles can be put in a pressure vessel or the like. 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 foamed particles. If the amount of foamed particles to be used is small, steam may be directly blown.

  The temperature of the steam is preferably 100 ° C. or higher and 150 ° C. or lower, and more preferably 100 ° C. or higher and 135 ° C. or lower. The treatment time with steam is preferably 1 second to 60 seconds, more preferably 5 seconds to 30 seconds.

  When the treatment with steam is performed, the polyolefin resin foamed particles may be impregnated with an inorganic gas or the like and then treated with steam to obtain polyolefin resin foam particles whose apparent density is adjusted to be small. The inorganic gas used at this time includes air, nitrogen, carbon dioxide, etc., but air is preferable from the viewpoint of cost and environment.

  Polyolefin resins constituting the polyolefin resin particles of the present invention include high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer and other polyethylene resins, propylene homopolymer, 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 Examples thereof include polypropylene resins such as polymers and propylene-maleic anhydride graft copolymers. These polypropylene resins are preferably non-crosslinked, but crosslinked resins can also be used.

  The polypropylene resin has a melt flow index (hereinafter sometimes referred to as MI) of preferably 0.5 g / 10 min to 30 g / 10 min, preferably 3 g / 10 min to 10 g / 10 min. Further preferred.

  If the MI is less than 0.5 g / 10 minutes, the melt viscosity may be too high and it may be difficult to obtain expanded particles with a high expansion ratio. If the MI exceeds 30 g / 10 minutes, The melt viscosity is low and the foam tends to break, and it tends to be difficult to obtain expanded particles having a high expansion ratio.

  The polyolefin resin is formed into the shape of polyolefin resin particles using a known method. For example, it is melted using an extruder, a kneader, a Banbury mixer (trademark), a roll or the like, and processed into polyolefin resin particles having a weight of 0.2 to 10 mg, preferably 0.5 to 6 mg. 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.

  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 foamed particles can be adjusted to a desired value. As the cell nucleating agent, inorganic nucleating agents such as talc, calcium stearate, calcium carbonate, silica, kaolin, titanium oxide, bentonite and barium sulfate are generally used. Among them, it is preferable to use talc because a uniform cell can be obtained.

  The amount of cell nucleating agent added varies depending on the type of polyolefin resin used and the type of cell nucleating agent, and cannot be specified unconditionally, but is 0.001 part by weight or more and 2 parts by weight with respect to 100 parts by weight of polyolefin resin. Part or less.

  Furthermore, when manufacturing the polyolefin resin particles, various additives can be added as necessary within the range not impairing 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; polyethylene glycol, glycerin, melamine, polyether- Water-absorbing compounds such as polyolefin resin block copolymers; IRGANOX (registered trademark) 1010 (Ciba), IRGANOX (registered trademark) 1076 (Ciba), IRGANOX (registered trademark) 1330 (Ciba), IRGANOX (registered trademark) 1425WL ( Hindered phenolic antioxidants such as Ciba), IRGANOX (registered trademark) 3114 (registered trademark) (Ciba); IRGAFOS (registered trademark) 168 (Ciba), IRGAFOS (registered) Standard) Phosphorus processing stabilizers such as P-EPQ (Ciba) and IRGAFOS 126; Lactone processing stabilizers; Hydroxylamine processing stabilizers, metal deactivators such as IRGANOX (registered trademark) MD1024 (Ciba); TINUVIN ( Benzotriazole type ultraviolet absorbers such as registered trademark) 326 (Ciba) and TINUVIN (registered trademark) 327; benzoate type light stabilizers such as TINUVIN (registered trademark) 120; CHIMASSORB119 (Ciba), CHIMASSORB (registered trademark) 944 (Ciba) ), Hindered amine light stabilizers such as TINUVIN (registered trademark) 622 (Ciba), TINUVIN (registered trademark) 770; flame retardant aids such as halogen flame retardants and antimony trioxide; FLAMESTAB (registered trademark) NOR116 (Ciba) , MELAPU Non-halogen flame retardants such as (registered trademark) MC25 (Ciba); acid neutralizers such as hydrotalcite and calcium stearate; crystal nucleating agents such as IRGASTAB (registered trademark) NA11 (Ciba); erucic acid amide, ethylenebis Examples include amide-based additives such as stearic acid amide.

  The polyolefin resin expanded particles used in the present invention are produced as follows. The polyolefin resin particles, poorly water-soluble inorganic compound and surfactant obtained by the above method are dispersed in water in a pressure vessel to form an aqueous dispersion, and a foaming agent is introduced into the pressure vessel, and the temperature is raised and constant. The pressure and constant temperature can be obtained by impregnating a polyolefin resin particle with a foaming agent and then releasing it into a lower pressure atmosphere than in the pressure vessel.

  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 expanded particles, and examples thereof include an autoclave type pressure vessel.

  In order to improve the dispersibility of the polyolefin resin particles in the aqueous dispersion, it is preferable to use 100 parts by weight or more and 500 parts by weight or less of water with respect to 100 parts by weight of the polyolefin resin particles.

  The poorly water-soluble inorganic compound used in the present invention refers to an inorganic compound having a solubility in water at 25 ° C. of less than 1% by weight. Specifically, alkaline earth metal salts such as calcium carbonate, barium carbonate, tricalcium phosphate, dicalcium phosphate, tribasic magnesium phosphate, tertiary barium phosphate, barium sulfate and calcium pyrophosphate, alumino such as kaolin and clay Examples include silicates. Among these, when the poorly water-soluble inorganic compound is an alkaline earth metal salt, the effect of reducing the poorly water-soluble inorganic compound attached to the surface of the polyolefin resin foamed particles of the present invention is remarkable.

  The amount of the hardly water-soluble inorganic compound varies depending on the type and the type and amount of the polyolefin-based resin particles used, and cannot be generally specified. The amount is preferably not more than parts by weight, more preferably not less than 0.2 parts by weight and not more than 3.0 parts by weight.

  Surfactants used as binders for attaching poorly water-soluble inorganic compounds to polyolefin resin particles include anionic surfactants, nonionic surfactants, amphoteric surfactants, anionic polymer surfactants, Surfactants such as nonionic polymer surfactants can be used. Examples of the anionic surfactant include sodium dodecylbenzene sulfonate, sodium n-paraffin sulfonate, sodium α-olefin sulfonate, sodium alkyldiphenyl ether sulfonate, and the like. Nonionic surfactants include polyoxyethylene alkyl ether, poly Examples of amphoteric surfactants such as oxyethylene sorbitan fatty acid esters include alkylbetaines and alkylamine oxides, and examples of anionic polymer surfactants include polyacrylates, polystyrene sulfonates, and maleic acid α-olefin copolymers. Examples of nonionic polymer surfactants such as salts include polyvinyl alcohol. These can be used alone or in combination of two or more.

  The preferred surfactant varies depending on the kind of the poorly water-soluble inorganic compound to be used, and thus cannot be defined unconditionally. For example, when tribasic magnesium phosphate or tribasic calcium phosphate is used as the poorly water-soluble inorganic compound, an anionic interface is used. It is preferable to use an activator because the dispersion state becomes stable.

  The amount of the surfactant used varies depending on the type and the type and amount of the polyolefin resin to be used, and cannot be generally defined. It is preferable that it is below the weight part.

  As the foaming agent used in the present invention, a readily volatile organic foaming agent such as butane or pentane, an inorganic gas such as nitrogen, carbon dioxide, or air, or water is used.

  The amount of foaming agent used varies depending on the type of polyolefin resin used, the type of foaming agent, the target foaming ratio, etc., and cannot be specified unconditionally, but is 2 parts by weight with respect to 100 parts by weight of polyolefin resin particles. The amount is preferably 60 parts by weight or less.

  The aqueous dispersion containing polyolefin resin particles, poorly water-soluble inorganic compound, and surfactant prepared in the pressure vessel as described above is pressurized to a predetermined pressure with stirring by adding a foaming agent. The temperature is raised to a predetermined temperature and held for a certain period of time, usually 5 to 180 minutes, preferably 10 to 60 minutes, and then the pressurized dispersion is lowered by opening a valve provided at the lower part of the pressure vessel. Polyolefin resin foamed particles can be produced by releasing them under an atmosphere (usually under atmospheric pressure).

  The temperature at which the inside of the pressure vessel is heated (hereinafter sometimes referred to as the foaming temperature) varies depending on the melting point [Tm (° C.)], type, etc. of the polyolefin resin to be used and cannot be generally specified. In the case of a product, it is preferable to heat to a softening temperature or higher, more preferably to Tm−30 (° C.) or higher and Tm + 10 (° C.) or lower.

  In addition, melting | fusing point of the polyolefin-type resin composition here is using the differential scanning calorimeter by heating up 4-6 mg of polyolefin-type resin particles from 40 degreeC to 220 degreeC with the temperature increase rate of 10 degreeC / min. DSC obtained when the polyolefin resin particles are melted and then crystallized by decreasing the temperature from 220 ° C. to 40 ° C. at 10 ° C./min, and then further increasing the temperature from 40 ° C. to 220 ° C. at 10 ° C./min. It is a value obtained from the curve as the melting peak temperature at the second temperature increase.

  The pressure in the pressure vessel varies depending on the desired expansion ratio of the polyolefin resin foamed particles, and cannot be generally specified, but is preferably 0.50 MPa · G or more and 6.0 MPa · G or less, more preferably 1.0 MPa · G or more. It is preferably 4.5 MPa · G or less.

  The polyolefin resin foamed particles obtained as described above have a large amount of the hardly water-soluble inorganic compound adhering to the surface. When the foamed particles are used for in-mold foam molding, the hardly water-soluble inorganic compound is obtained. In some cases, the fusion between the polyolefin resin expanded particles is hindered, and good fusion properties may not be obtained.

  However, the amount of the poorly water-soluble inorganic compound adhering to the surface can be reduced preferably by 100 ppm or more, more preferably by 300 ppm or more by treating such polyolefin resin expanded particles with steam. Since the amount of the hardly water-soluble inorganic compound adhering to the surface of the polyolefin resin expanded particles before treatment is different, it is difficult to uniformly define, but it is difficult to adhere to the surface of the expanded polyolefin resin particles after being treated with steam. The amount of the water-soluble inorganic compound is more preferably 650 ppm or less.

  In the present invention, the amount of the hardly water-soluble inorganic compound adhering to the surface of the polyolefin resin foam particles is measured by washing the polyolefin resin foam particles with water, drying in an oven at 60 ° C. for 24 hours, and then removing the polyolefin resin from the oven. The resin foam particles are immediately left in a room set at a temperature of 23 ° C. and a relative humidity of 50% for 72 hours. Next, in a room set to the same conditions, 100 g of polyolefin resin foamed particles were accurately weighed to the third decimal place and rounded to the third decimal place). Weight of polyolefin resin expanded particles: F (g). Next, the entire amount of the foamed particles used for the above weight measurement is immersed in 5 L of 1N aqueous hydrochloric acid and washed, then immersed in 5 L of ion exchange water to wash out the hydrochloric acid solution, and then into 5 L of 1 N aqueous sodium hydroxide. After immersing and washing, sodium hydroxide is washed by immersing in 5 L of ion exchange water. After repeating this operation twice, the entire amount of the expanded particles is dried in an oven at 60 ° C. for 24 hours, then taken out of the oven and immediately left in a room set at 23 ° C. and 50% relative humidity for 72 hours. Subsequently, the weight: S (g) of the polyolefin-based resin expanded particles is obtained in a room set to the same conditions in the same manner as described above. The difference between the weight: F and the weight: S is the amount of the poorly water-soluble inorganic compound adhering to the surface of the polyolefin resin expanded particles.

  Since the polyolefin resin expanded particles with reduced water-insoluble inorganic compound adhering to the surface of the present invention have a small amount of hardly adhering water-soluble inorganic compound, the in-mold foam molded product obtained from the polyolefin resin expanded particles is fused. Wearability is good. Therefore, it can be suitably used for applications requiring strength and weight reduction, for example, automobile members such as buffer packaging materials and bumper core materials.

  Next, the manufacturing method of the polyolefin-type resin expanded particle of this invention is demonstrated in detail, giving an Example and a comparative example. The present invention is not limited to the following examples.

<Measurement of melt flow index>
The melt flow index (MI) was measured using an MI measuring instrument described in JIS K7210, with an orifice of 2.0959 ± 0.005 mmφ, an orifice length of 8.000 ± 0.025 mm, a load of 2160 g, and 230 ± 0.2 ° C. It is a value when measured under conditions.

<Measurement of flexural modulus>
The flexural modulus was measured according to JIS K7106. <Measurement of apparent density>
The polyolefin resin expanded particles are put in a 10 L container, and the weight (g) of the expanded particles in the container is measured. The obtained weight was divided by the container capacity (L) to obtain an apparent density (g / L).

<Measurement of amount of poorly water-soluble inorganic compound adhering to the surface of polyolefin resin foam particles>
The foamed polyolefin resin particles are washed with water, dried in an oven at 60 ° C. for 24 hours, and then the polyolefin resin foam particles taken out from the oven are immediately left in a room set at a temperature of 23 ° C. and a relative humidity of 50% for 72 hours. Next, in a room set to the same conditions, 100 g of polyolefin resin foamed particles were accurately weighed to the third decimal place and rounded to the third decimal place). Weight of polyolefin resin expanded particles: F (g). Next, the entire amount of the foamed particles used for the above weight measurement is immersed in 5 L of 1N aqueous hydrochloric acid and washed, then immersed in 5 L of ion exchange water to wash out the hydrochloric acid solution, and then into 5 L of 1 N aqueous sodium hydroxide. After immersing and washing, sodium hydroxide is washed by immersing in 5 L of ion exchange water. After repeating this operation twice, the entire amount of the expanded particles is dried in an oven at 60 ° C. for 24 hours, then taken out of the oven and immediately left in a room set at 23 ° C. and 50% relative humidity for 72 hours. Subsequently, the weight: S (g) of the polyolefin-based resin expanded particles is obtained in a room set to the same conditions in the same manner as described above. The difference between weight: F and weight: S was the amount of the poorly water-soluble inorganic compound adhering to the surface of the polyolefin resin foamed particles.

<Measurement of internal pressure>
A suitable amount of the foam particles impregnated with air is taken from a pressurized tank into a polyethylene bag of about 70 mm × 100 mm having a large number of fine holes through which the foam particles cannot pass but air can freely pass through. The weight is measured in a constant temperature room with an atmospheric pressure of 50% relative humidity. Let this weight be Q (g). The weight after standing for 48 hours in the same temperature chamber is measured, and this weight is defined as U (g). The difference between Q (g) and U (g) is defined as the amount of impregnation air W (g), and the internal pressure P (MPa · G) of the expanded particles is calculated by the following formula. Note that the weight of the bag containing the expanded particles is Z (g).

  P = (W ÷ M) × R × T ÷ V

  M in the above formula is the molecular weight of air, R is a gas constant, T is an absolute temperature (K), V is a volume (L) obtained by subtracting the volume of the base resin occupying in the foamed particles from the apparent volume of the foamed particles, Here, M = 28.8 (g / mol) and R = 0.0083 (MPa · L / (K · mol)) are employed. The apparent volume (L) of the expanded particles was such that the entire amount of the expanded particles taken out of the bag after 48 hours was immediately submerged in ethanol in a graduated cylinder containing 0.2 L of ethanol at 23 ° C. in the same temperature chamber. It is calculated | required by calculating the volume Y (L) of a foaming particle group from the time scale. The apparent expansion ratio of the expanded particles is determined by dividing the density (g / L) of the base resin by the apparent density (g / L) of the expanded particles. The apparent density (g / L) of the expanded particles is obtained by dividing the expanded particle weight (difference between U (g) and Z (g)) by the volume Y (L).

  In the above measurement, a plurality of expanded particle groups in an amount such that the volume Y is 0.050 to 0.15 L are used.

Example 1
The base resin is MI = 7/10 minutes, the melting point is 143 ° C., the flexural modulus is 800 MPa, the ethylene-propylene random copolymer containing 3.6 wt% of ethylene as a comonomer, polyethylene glycol ( The ethylene-propylene random copolymer, polyethylene glycol, and talc were blended using 0.5 parts by weight of PEG300 (manufactured by Lion Corporation) and 0.1 parts by weight of talc as a cell nucleating agent. The blended mixture was melt-kneaded in an extruder, extruded into a strand from a circular die, cooled with water, and cut with a cutter to obtain polypropylene resin particles having a weight of 1.2 mg / grain.

100 parts by weight of the obtained polypropylene-based resin particles, 200 parts by weight of water, 1.0 part by weight of magnesium triphosphate (manufactured by Taihei Chemical Industrial Co., Ltd.) as a poorly water-soluble inorganic compound, and sodium alkyl sulfonate as a surfactant in an amount of 0. 035 parts by weight was charged in a pressure-resistant autoclave having a capacity of 2.0 m ³ , and 4.8 parts by weight of carbon dioxide gas was added as a foaming agent with stirring. The autoclave contents were heated to a foaming temperature of 147 ° C. Thereafter, carbon dioxide gas was additionally injected to increase the pressure in the autoclave to a foaming pressure of 2.8 MPa · G, and after maintaining for 30 minutes at the foaming temperature and the foaming pressure, the valve at the bottom of the autoclave was opened and 3.6 mmφ × 5 holes The contents of the autoclave were discharged under atmospheric pressure through the opening orifice of to obtain polypropylene-based resin expanded particles. The amount of the hardly water-soluble inorganic compound adhering to the surface of the obtained polypropylene resin foamed particles was 960 ppm.

  The obtained expanded polypropylene resin particles were placed in a pressure-resistant container and treated with 0.02 MPa · G steam for 30 seconds to obtain expanded polypropylene resin particles. The amount of the poorly water-soluble inorganic compound adhering to the surface of the obtained polypropylene resin expanded particles was 180 ppm.

(Example 2)
The polypropylene resin expanded particles used in Example 1 were impregnated with air by air pressure treatment to give an internal pressure of 0.28 MPa · G, then placed in a pressure-resistant container, and 30 MPa with 0.05 MPa · G steam. For 2 seconds to obtain expanded polypropylene resin particles. The amount of the hardly water-soluble inorganic compound adhering to the surface of the obtained polypropylene resin foamed particles was 510 ppm.

(Example 3)
As a base resin, MI = 6/10 minutes, melting point 136 ° C., flexural modulus 700 MPa, ethylene glycol as a comonomer, 100 wt parts of ethylene-propylene random copolymer containing ethylene, The ethylene-propylene random copolymer, polyethylene glycol, and talc were blended using 0.5 parts by weight of PEG300 (manufactured by Lion Corporation) and 0.1 parts by weight of talc as a cell nucleating agent. The blended mixture was melt-kneaded in an extruder, extruded into a strand from a circular die, cooled with water, and cut with a cutter to obtain polypropylene resin particles having a weight of 1.2 mg / grain.

100 parts by weight of the obtained polypropylene-based resin particles, 200 parts by weight of water, 0.6 parts by weight of calcium triphosphate (manufactured by Taihei Chemical Industrial Co., Ltd.) as a poorly water-soluble inorganic compound, and 0.03 parts by weight of sodium alkyl sulfonate as a surfactant Were charged in a pressure-resistant autoclave having a capacity of 2.0 m ³ , and 6.0 parts by weight of carbon dioxide gas was added as a foaming agent with stirring. The autoclave contents were heated to a foaming temperature of 147 ° C. Thereafter, carbon dioxide gas was additionally injected to increase the pressure in the autoclave to a foaming pressure of 2.8 MPa · G, and after maintaining for 30 minutes at the foaming temperature and the foaming pressure, the valve at the bottom of the autoclave was opened and 3.6 mmφ × 5 holes The contents of the autoclave were discharged under atmospheric pressure through the opening orifice of to obtain polypropylene-based resin expanded particles. The amount of the hardly water-soluble inorganic compound adhering to the surface of the obtained polypropylene resin expanded particles was 840 ppm.

  The obtained expanded polypropylene resin particles were placed in a pressure-resistant container and treated with 0.02 MPa · G steam for 30 seconds to obtain expanded polypropylene resin particles. The amount of the hardly water-soluble inorganic compound adhered to the obtained polypropylene-based resin expanded particles was 370 ppm.

Example 4
The polypropylene resin expanded particles used in Example 3 were impregnated with air by air pressure treatment to give an internal pressure of 0.28 MPa · G, and then placed in a pressure-resistant container, and 30% with 0.06 MPa · G steam. For 2 seconds to obtain expanded polypropylene resin particles. The amount of the poorly water-soluble inorganic compound adhering to the surface of the obtained polypropylene resin expanded particles was 150 ppm.

(Example 5)
As a base resin, MI = 2/10 min, melting point 123 ° C., 100 parts by weight of linear low density polyethylene containing 8.2 wt% of 4-methylpentene as a comonomer, polyethylene glycol (trade name: trade name: The linear low density polyethylene and talc were dry blended using 0.5 parts by weight of PEG300 (manufactured by Lion) and 0.1 parts by weight of talc as a cell nucleating agent. The dry blended mixture was melt-kneaded in an extruder, extruded into a strand from a circular die, cooled with water, and cut with a cutter to obtain polyethylene resin particles having a weight of 1.2 mg / grain.

100 parts by weight (2.0 kg) of the obtained polyethylene resin particles, 200 parts by weight of water, 0.5 part by weight of tricalcium phosphate (manufactured by Taihei Chemical Industrial Co., Ltd.) as a poorly water-soluble inorganic compound, and alkylsulfonic acid as a surfactant 0.05 parts by weight of sodium was charged into a pressure-resistant autoclave having a capacity of 0.01 m ³ , and 8 parts by weight of carbon dioxide gas was added as a blowing agent with stirring. The autoclave contents were heated to a foaming temperature of 123 ° C. Thereafter, carbon dioxide gas is additionally injected to increase the pressure in the autoclave to a foaming pressure of 4.5 MPa · G, and after maintaining for 30 minutes at the foaming temperature and the foaming pressure, the valve at the bottom of the autoclave is opened and 3.6 mmφ × 1 hole The contents of the autoclave were discharged into a steam atmosphere through the opening orifices of the polyethylene resin to obtain polyethylene-based resin expanded particles. The amount of the hardly water-soluble inorganic compound adhering to the surface of the obtained polyethylene resin expanded particles was 760 ppm.

  The obtained foamed particles were impregnated with air by air pressure treatment to give an internal pressure of 0.28 MPa · G, and then treated with 0.03 MPa · G of steam for 30 seconds to obtain polyethylene-based resin foamed particles. The amount of the hardly adhering water-soluble inorganic compound of the obtained polypropylene resin expanded particles was 390 ppm.

(Comparative Example 1)
The polypropylene resin foam particles used in Example 3 are collected in a suitable amount in a polyethylene bag of about 100 cm × 100 cm having a large number of fine holes through which the foam particles cannot pass but air can freely pass, and air (room temperature, air The resultant was treated at an original pressure of 6.5 MPa · G) for 60 seconds to obtain expanded polypropylene resin particles. The amount of the hardly water-soluble inorganic compound adhering to the surface of the obtained polypropylene resin expanded particles was 790 ppm.

(Comparative Example 2)
The polypropylene resin expanded particles used in Example 3 were washed with water for 60 seconds to obtain polypropylene resin expanded particles. The amount of the hardly water-soluble inorganic compound adhering to the surface of the obtained polypropylene resin foamed particles was 680 ppm.

Claims (2)

A method for producing polyolefin resin expanded particles that reduces poorly water-soluble inorganic compounds adhering to the surface,
Introducing polyolefin resin particles, poorly water-soluble inorganic compound, aqueous dispersion containing surfactant and foaming agent into the pressure-resistant container, and impregnating the polyolefin resin particles with foaming agent at a constant pressure and constant temperature. After that, after obtaining polyolefin resin expanded particles by releasing in a low-pressure atmosphere ,
A method for producing polyolefin resin foamed particles, wherein the foamed polyolefin resin particles are put in a separate pressure vessel and treated with steam without applying an internal pressure to the polyolefin resin foam particles . The method for producing expanded polyolefin resin particles according to claim 1 , wherein the hardly water-soluble inorganic compound is an alkaline earth metal salt.