JP5295557B2 - Method for producing polyolefin resin pre-expanded particles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing preliminarily foamed particles of a polyolefin-based resin, which are stably dispersed in a dispersion medium and characterized in that a dispersing agent sticking on the surface of each particle does not inhibit mutual fusion during molding and does not contaminate or corrode a mold. <P>SOLUTION: The method for producing the preliminarily foamed particles of a polyolefin-based resin, comprises charging a dispersion containing polyolefin-based resin particles, water, a dispersing agent and a dispersing aid, and a foaming agent into a pressure-resistant container, then heating the inside of the pressure-resistant container to a prescribed temperature under pressure, and releasing the dispersion into an atmosphere having a pressure lower than that in the pressure-resistant container while keeping the temperature and pressure constant, wherein the dispersing agent is magnesium phosphate and the pH of the dispersion in the pressure-resistant container is &lt;9. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a method for producing polyolefin resin pre-expanded particles that can be suitably used for producing a polyolefin resin-in-mold foam-molded article used for buffer packaging materials, boxing, heat insulating materials, automobile bumper core materials, and the like, The present invention relates to polyolefin resin pre-expanded particles obtained by a production method and a polyolefin resin in-mold foam-molded product obtained from the polyolefin resin pre-expanded particles.

  Polyolefin resin in-mold foam moldings are used in various fields such as cushioning packaging materials and automobile bumpers, and such in-mold foam moldings are filled with pre-manufactured polyolefin resin pre-expanded particles in a mold. It is manufactured by molding. 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 dispersing the polyolefin resin particles in the dispersion medium, it is known to use a dispersant to stabilize the dispersion state of the resin particles in the dispersion medium. For example, calcium carbonate Dispersing agents such as inorganic substances such as tricalcium phosphate and basic magnesium carbonate, and aqueous polymer protective colloids such as N-polyvinylpyrrolidone and polyvinyl alcohol, and dispersing aids such as surfactants as necessary. Use in combination. These dispersing agents / dispersing aids contribute to stabilization of the dispersion state because the surface of the resin particles is coated to make the resin particles easy to conform to water or to prevent adhesion between the resin particles. .

  It is also known that a dispersant remains on the surface of the pre-expanded particles thus obtained. Depending on the amount of the remaining dispersant and the kind and characteristics of the dispersant, the pre-expanded particles may be formed. In addition, the melt-bonding properties of the pre-foamed particles may be hindered, and an in-mold foam-molded product having good meltability may not be obtained. 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 with the metal forming the mold together with the resin fragments generated in the pre-expanded particle manufacturing process. The problem of contaminating the mold can also arise. Therefore, various methods for removing the dispersant adhering to the pre-expanded particles have been studied.

  As a method for removing the dispersant on the surface of the pre-foamed particles, there are known a method in which pre-foamed particles are submerged and washed (Patent Document 1), a method in which a large amount of water is sprayed from a nozzle and washed (Patent Document 2), and the like. It has been. However, these methods have problems such as that a large amount of water is required for cleaning, and the cleaning cost is high and the removal efficiency is poor.

Patent Document 3 discloses the use of tribasic calcium phosphate and magnesium pyrophosphate, which are inorganic weak acid salts of alkaline earth metals, as suspending agents, but the surface suspending agent remains without washing. The amount is 0.4 to 0.65 part / 100 parts of the foamed particles, and without washing, the suspending agent attached to the surface of the foamed particles is not reduced.
JP 60-56514 A JP-A-4-57838 JP-A-8-225675

  An object of the present invention is dispersion-stable in a dispersion medium, and there is little dispersant adhering to the surface of the pre-expanded particles without special operations such as washing, and the pre-expanded particles do not inhibit fusion during molding. It is an object of the present invention to provide a method for producing pre-expanded polyolefin resin foam particles in which the dispersant adhering to the surface does not contaminate or corrode the mold.

As a result of intensive research to solve the above problems, we put a dispersion liquid containing a polyolefin resin particle in a pressure-resistant container with a dispersion medium, a dispersing agent, and a dispersion aid. After heating to a predetermined temperature, while maintaining the temperature and pressure constant, the dispersion is discharged as a dispersant in the production of polyolefin resin pre-expanded particles by releasing the dispersion into a low-pressure atmosphere than in the pressure-resistant container . By using a simple substance of magnesium diphosphate and tribasic magnesium phosphate and a hydrate thereof , or a mixture thereof , the dispersion of the polyolefin-based resin particles in the pressure vessel becomes stable. When the pH of the dispersion is less than 9, an in-mold foam molded article having good fusion properties can be obtained without performing special operations such as washing on the prefoamed particles. Dispersing agent adhered to the surface contamination of the mold, polyolefin-based resin foam pre-expanded particles without the corrosion and have completed the present invention found that the resulting.

That is, according to the first aspect of the present invention, a dispersion liquid and a foaming agent containing polyolefin resin particles, a dispersion medium, a dispersant, and a dispersion aid are placed in a pressure vessel, and the pressure vessel is pressurized to a predetermined temperature. In the method for producing polyolefin resin pre-expanded particles, after heating, releasing the dispersion into a low-pressure atmosphere than in the pressure vessel while keeping the temperature and pressure constant,
Production of polyolefin resin pre-expanded particles in which the dispersant is a simple substance of dibasic magnesium phosphate and tribasic magnesium phosphate and hydrates thereof , or a mixture thereof , and the pH of the dispersion in the pressure vessel is less than 9. Regarding the method.

As a preferred embodiment,
(1) The method for producing polyolefin resin pre-expanded particles according to claim 1, wherein the dispersant is tribasic magnesium phosphate.
(2) The dispersion aid is an anionic surfactant having a linear carbon chain having 10 to 18 carbon atoms as a hydrophobic group.
(3) The dispersion aid is a linear alkyl sulfonate having 12 carbon atoms,
(4) The foaming agent comprises carbon dioxide,
The present invention relates to a method for producing the polyolefin resin pre-expanded particles described above.

  A second aspect of the present invention relates to a polyolefin resin pre-expanded particle obtained by the method for producing a polyolefin resin pre-expanded particle described above, and a third aspect of the present invention uses the polyolefin resin pre-expanded particle as a mold. The present invention relates to a polyolefin resin in-mold foam molded article obtained by filling and heating.

  According to the production method of the present invention, the pre-expanded particles obtained have a small amount of the adhering dispersant obtained without washing. In addition, when carbon dioxide is used as the foaming agent, the pH of the dispersion in the pressure vessel can be adjusted to less than 9 without using an additive such as a pH adjuster, and the dispersion stability is further improved. It becomes good.

  Furthermore, it has been found that the dispersant used in the present invention has a property that it is difficult to adhere to aluminum. Therefore, even if a dispersant is attached to the surface of the polyolefin resin pre-expanded particles, it is difficult for the dispersant to adhere to the mold during molding, and it can be easily dropped even if attached to the mold. The molding efficiency can be improved without contaminating.

The method for producing pre-expanded polyolefin resin particles according to the present invention comprises placing a dispersion liquid comprising a polyolefin resin particle, a dispersion medium, a dispersant, a dispersion aid and a foaming agent in a pressure vessel, In the method for producing polyolefin-based resin pre-expanded particles, in which the dispersion is discharged under a low-pressure atmosphere from inside the pressure-resistant container while keeping the temperature and pressure constant after heating to a predetermined temperature . A simple substance of magnesium phosphate and tribasic magnesium phosphate, a hydrate thereof, and a mixture thereof are used, and the pH of the dispersion in the pressure vessel is made to be less than 9.

  As the polyolefin resin constituting the polyolefin resin particles used in the present invention, 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 Examples thereof include polypropylene resins such as copolymers, propylene-maleic anhydride graft copolymers, and styrene-modified polyolefins. These polyolefin-based resins are preferably non-crosslinked, but crosslinked resins can also be used.

  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.

  In addition, as a method for producing resin particles of styrene-modified polyolefin, for example, polyolefin resin particles are produced 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. There is a method of forming resin particles by impregnating and polymerizing the body.

  In the production of the polyolefin resin particles, it is preferable to add a cell nucleating agent 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, but is generally 0.001 part by weight or more with respect to 100 parts by weight of the polyolefin resin. It is preferable that it is below the weight part.

  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, 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;

Metal deactivators such as hydroxylamine-based processing stabilizers, IRGANOX® MD 1024 (Ciba Specialty Chemicals);
Benzotriazole ultraviolet absorbers such as TINUVIN (registered trademark) 326 (Ciba Specialty Chemicals), TINUVIN (registered trademark) 327;
Benzoate light stabilizers such as TINUVIN® 120;

Hindered amine light stabilizers such as CHIMASSORB 119 (Ciba Specialty Chemicals), CHIMASSORB (registered trademark) 944 (Ciba Specialty Chemicals), TINUVIN (registered trademark) 622 (Ciba Specialty Chemicals), TINUVIN (registered trademark) 770;
Flame retardant aids such as halogen flame retardants and antimony trioxide;
Non-halogen flame retardants such as FLAMESTAB (registered trademark) NOR116 (Ciba Specialty Chemicals), MELAPUR (registered trademark) MC25 (Ciba Specialty Chemicals);

Acid neutralizers such as hydrotalcite and calcium stearate;
Crystal nucleating agents such as IRGASTAB (registered trademark) NA11 (Ciba Specialty Chemicals);
Examples include amide type additives such as erucic acid amide and ethylene bis stearic acid amide.

  In the pressure-resistant container, the polyolefin resin pre-expanded particles in the present invention are charged with a dispersion liquid and a foaming agent containing polyolefin resin particles, a dispersion medium, a dispersing agent, and a dispersion aid in a pressure container, up to a predetermined temperature. It is obtained by heating and releasing the dispersion into an atmosphere at a lower pressure than in the pressure vessel while keeping the temperature and pressure constant under pressure.

  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 include aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, dichlorotetra Examples include volatile organic compounds such as halogenated hydrocarbons such as fluoroethane, methyl chloride, ethyl chloride, and methylene chloride, inorganic gases such as carbon dioxide and nitrogen, and water. These can be used alone or in combination. Among them, the foaming agent contains carbon dioxide, so that the pH of the dispersion in the pressure vessel can be made less than 9 without using a pH adjuster, and the dispersion stability is better, and foaming is performed. It is preferable from the viewpoint of strength, safety, and cost, and the foaming agent is more preferably made of carbon dioxide.

  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.

  In the present invention, the dispersion medium is not particularly limited as long as it does not dissolve the polyolefin resin particles, and examples thereof include water, methanol, ethanol, glycerin, ethylene glycol, and the like, but it is preferable to use water.

  The amount of the dispersion medium used is 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 in order to improve the dispersibility of the polyolefin resin particles in the dispersion medium. It is preferable.

  In the present invention, magnesium phosphate is used as a dispersant. The magnesium phosphate referred to in the present invention comprises a simple substance of dibasic magnesium phosphate and tertiary magnesium phosphate and hydrates thereof, and a mixture thereof may be used. In addition, other magnesium phosphate salts may be included. Of these, tribasic magnesium phosphate is more preferred because of its good dispersibility.

  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.

  Dispersing aids include anionic surfactants such as alkylbenzene sulfonates, n-paraffin sulfonates and α-olefin sulfonates, and nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene sorbitan fatty acid esters. Agents, amphoteric surfactants such as alkylbetaines and alkylamine oxides, anionic polymer surfactants such as polyacrylates, polystyrene sulfonates, maleic acid α-olefin copolymer salts, and nonionics such as polyvinyl alcohol Surfactants such as polymer surfactants can be mentioned, and these can be used alone or in combination of two or more.

  Among them, it is preferable to use an anionic surfactant, and it is more preferable to use an anionic surfactant having a linear carbon chain having 10 to 18 carbon atoms as a hydrophobic group. Examples of the anionic surfactant having a linear carbon chain having 10 to 18 carbon atoms as a hydrophobic group include alkyl sulfates having 10 to 18 carbon atoms, alkyl sulfonates 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 more preferable from the viewpoints of dispersion stability, fusion property of in-mold foam moldings, prevention of mold contamination / corrosion and cost, and wastewater treatment. It is preferable to use a linear alkyl sulfonate 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.

  There is no particular limitation on the method of adjusting the dispersion containing the polyolefin resin particles, dispersion medium, dispersant, and dispersion aid adjusted in the pressure vessel to less than pH 9, for example, acid and / or as a pH adjuster. Examples thereof include the use of a weak acid salt and a method of using a foaming agent that exhibits acidity when dissolved in a dispersion medium, such as carbon dioxide. Here, when a foaming agent containing carbon dioxide is used, it is preferable because the amount of carbon dioxide dissolved in the dispersion medium can be reduced to a pH of less than 9 by adding the amount necessary for foaming, which is preferable. .

  In the present invention, the pH of the dispersion may be measured by measuring the pH of the dispersion containing polyolefin resin particles, a dispersion medium, a dispersant, and a dispersion aid in a pressure resistant container, or dispersed by adding a foaming agent. When the pH of the liquid changes, after adding a foaming agent and heating the inside of the pressure vessel to a predetermined temperature under pressure, the dispersion is put under a lower pressure atmosphere than inside the pressure vessel while keeping the temperature and pressure constant. What measured the dispersion liquid extract | collected immediately after discharge | release may be used.

  When adjusting the pH of the dispersion in the pressure vessel to less than 9 with a pH adjuster, it is preferable to adjust the pH of the dispersion before pressurization to less than 9.

  The pH of the dispersion in the pressure vessel is less than 9, preferably 8 or less, more preferably 7 or less.

  If the pH of the dispersion is 9 or more, the amount of dispersant adhering to the obtained polyolefin resin pre-expanded particles is large, and good fusion properties cannot be obtained when the polyolefin resin pre-expanded particles are molded.

  In this way, the dispersion containing polyolefin-based resin particles, dispersion medium, dispersant, and dispersion aid adjusted in the pressure vessel is added with a foaming agent and pressurized to a predetermined pressure with stirring. After the temperature is raised to a predetermined temperature and held for a fixed time, usually 5 to 180 minutes, preferably 10 to 60 minutes, the pressurized dispersion is opened in a low pressure atmosphere by opening a valve provided at the lower part of the pressure vessel. The polyolefin resin pre-expanded particles can be produced by releasing them under (normally atmospheric pressure).

  In addition, when using the water which comprises a dispersion medium as a foaming agent, it is preferable to pressurize inside a pressure-resistant container with inorganic gas, such as nitrogen, air, and a carbon dioxide.

  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 filled with saturated steam for the purpose of increasing the expansion ratio.

  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.)] of the polyolefin resin to be used, the type of foaming agent, etc., and cannot generally be specified. It is determined from the range of −30 (° C.) to Tm + 10 (° C.). In addition, the pressure for pressurizing the inside of 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. 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 resin pre-expanded particles obtained as described above can be made into a polyolefin resin in-mold foam-molded product 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 pre-expanded particles are compressed by gas pressure and filled in a mold, and a heat-fusing method is carried out with steam using the recovery force of the pre-expanded particles. 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 polyolefin resin-in-mold foam-molded article thus obtained exhibits good fusion properties.

  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.

<Evaluation of dispersion stability>
The evaluation of dispersion stability was evaluated by the following index. That is, when the polyolefin resin particles dispersed in the aqueous dispersion medium in the 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. In the case of pre-foaming, the obtained foamed particles are observed after drying, and the particles that are good sphere foam particles without fusing each other are fused, and the foam particles are fused with each other. Those having an irregular size and shape were marked with Δ.

<Measurement of surface adhering dispersant amount of pre-expanded particles>
An aqueous solution (colorimetric solution) containing 50.0 mL of W (g) and an aqueous solution (colorimetric liquid) containing 0.022% ammonium metavanadate (% by weight, the same applies hereinafter), 0.54% ammonium molybdate and 3% nitric acid. Pre-expanded particles were collected in a conical beaker, stirred for 1 minute, and allowed to stand for 10 minutes. The obtained liquid phase was put in a quartz cell having an optical path length of 1.0 cm, and the absorbance A (−) at 410 nm was measured with a spectrophotometer.

For the same colorimetric solution, the amount of adhering dispersant C (ppm) = 4 using the absorbance coefficient ε (g / L · cm) at 410 nm of tricalcium phosphate and tribasic magnesium phosphate measured in advance. 0.0 × 10 ⁴ · ε · A / W (tricalcium phosphate), C (ppm) = 4.7 × 10 ⁴ · ε · A / W (tribasic magnesium phosphate).

<Evaluation of fusing property in in-mold foam molding>
The obtained polyolefin resin in-mold foam-molded product is cut by about 10 mm in the thickness direction of the in-mold foam-molded product with a cutter knife, and then the in-mold foam-molded product is broken by hand from the cut portion. Observe the fractured surface, ○ that does not break at the boundary of the pre-foamed particles and causes the material destruction of the pre-foamed particles, △ that the material destruction of the pre-foamed particles and the fracture at the boundary of the pre-foamed particles are mixed, △, The case where the breakage at the boundary of the pre-expanded particles completely occurred was marked as x.

<Expansion ratio of pre-expanded particles>
The expansion ratio of the pre-expanded particles is a so-called true magnification. The pre-expanded particles whose weight has been measured in advance are submerged in ethanol whose volume is known in advance, and the density of the pre-expanded particles is obtained from the increased ethanol volume, and the resin before expansion The density was obtained by dividing the density of the pre-expanded particles from the density.

(Examples 1-3)
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 (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.

  The obtained resin particles are put into a 10-liter pressure vessel having a stirrer, and 100 parts by weight (1.55 kg) of the resin particles are used as a dispersing agent, magnesium triphosphate (manufactured by Taihei Chemical Industrial Co., Ltd.). ) And sodium lauryl sulfonate (hereinafter sometimes referred to as Ra) as a dispersion aid were dispersed in 300 parts by weight of water to obtain a dispersion. 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 / absence of fusion between the particles, the foaming ratio, and the amount of the surface adhering dispersant were measured. The results are shown in Table 1.

Washed and dried pre-expanded particles are allowed to stand at room temperature and normal pressure for 6 hours and then subjected to pressure treatment with air at 20 ° C. and 3 kg / cm ² for 24 hours, and then the pre-expanded particles are molded into a 400 mm × 300 mm × 60 mm mold. And heated with water vapor of 0.3 to 0.24 MPa (gauge pressure). The obtained in-mold foam molded article was dried in an oven at 75 ° C. for 15 hours, and the results of measuring the fused state between the foamed particles in the in-mold foam molded article are shown in Table 1.

Example 4
First, 100 parts by weight of ethylene-propylene random copolymer (resin density: 0.90 g / cm ³ , melt flow index: 7 g / 10 min, melting point: 142 ° C.) and 0.03 part by weight of talc are dry blended to form a mixture, The 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 1.8 mg / grain.

  100 parts by weight (1 kg) of the obtained polypropylene resin particles, 200 parts by weight of water, the amount of tribasic magnesium phosphate (produced by Taihei Chemical Sangyo Co., Ltd.) shown in Table 1 as a dispersant, and Table 1 as a dispersion aid. The indicated amount of sodium lauryl sulfonate (Ra) was charged into a 10 liter pressure-resistant autoclave, the pH of the dispersion was adjusted to 8.9 with 1N hydrochloric acid, and 18 parts by weight of isobutane was added as a blowing agent with stirring. . The autoclave contents were heated to a foaming temperature of 137 ° C. Thereafter, isobutane was additionally injected to increase the pressure inside the autoclave to a foaming pressure of 1.8 MPa. After maintaining the foaming temperature and the foaming pressure for 30 minutes, the valve at the bottom of the autoclave was opened, and through an opening orifice having a diameter of 4.0 mm, The contents of the autoclave were released under atmospheric pressure to obtain polypropylene resin pre-expanded particles. Other than that evaluated similarly to Examples 1-3.

(Comparative Examples 1-6)
The amount of tribasic magnesium phosphate (Comparative Examples 1 and 2), tribasic calcium phosphate (Comparative Examples 3 to 5), calcium pyrophosphate (Comparative Example 6), magnesium pyrophosphate (Comparative Example 7) shown in Table 1 as the dispersant. Potassium metaphosphate (Comparative Example 8) (all manufactured by Taihei Chemical Industrial Co., Ltd.) Pre-foaming as in Examples 1 to 3 except that sodium lauryl sulfonate (Ra) in the amount shown in Table 1 was used as a dispersion aid. Particles were obtained and evaluated.

(Comparative Example 9)
The same evaluation as in Example 4 was performed except that the pH of the dispersion was not adjusted.

  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 3 to 8, it can be seen that the dispersion of the production method of the present invention is stable in the pressure vessel when compared with various general dispersants. Even with tribasic calcium phosphate, expanded particles can be obtained without fusing the particles. Compared to the examples, in addition to using a large amount of dispersant, the amount of adhesion tends to be large and the inhibition of fusion in the in-mold foam molded product tends to be large. is there. In addition, the dispersion is stable in the region where the pH is 9 or less, and it is only the tertiary magnesium phosphate that has no fusion inhibition in the in-mold foam molded product. As described above, when the pH of the dispersion is 9 or more, although the dispersion is performed, the fusion-inhibiting property in the in-mold foam-molded product is increased.

(Example 5, Comparative Example 10)
In order to compare the reactivity of metals with various dispersants, commercially available aluminum cups were used as dispersion models in the amounts of tribasic magnesium phosphate and tribasic calcium phosphate shown in Table 2 (both Taihei Chemical Industry ( 10 ml of a dispersion of 100 parts of water in the presence of sodium lauryl sulfonate (Ra) was added and dried in an oven at 140 ° C. for 3 hours. After drying, take it out of the oven and attach the dried solids. (1) Give vibration to the aluminum cup and wipe off the dried solids. (2) Gently pour pure water into the aluminum cup and wash away the dried solids ( 3) Wipe with Kimwipe (Registered Trademark) and wipe dry matter. Evaluate by the above three methods, and it can be completely removed by that method. Evaluation was made with ◯ indicating that the metal could be discolored but having discoloration, △ indicating that the metal could be removed by the method, but △ indicating that the metal remained, and x indicating that the metal could not be removed. The results are shown in Table 2.

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, it is reactive with metal. It can be seen that is small.

  On the other hand, it was found that the dried solid product of the dispersant shown in the comparative example is difficult to wash and the surface of the aluminum cup after washing is discolored, so that it has reactivity with the metal.

Claims (7)

A dispersion liquid and a foaming agent containing polyolefin resin particles, a dispersion medium, a dispersant, and a dispersion aid are placed in a pressure vessel, and the pressure vessel is heated to a predetermined temperature under pressure, and then the temperature and pressure are kept constant. In the method for producing polyolefin resin pre-expanded particles, in which the dispersion is released in a low-pressure atmosphere than in the pressure-resistant container,
The polyolefin resin pre-expanded particles, wherein the dispersant is a simple substance of dibasic magnesium phosphate and tribasic magnesium phosphate and a hydrate thereof, or a mixture thereof, and the pH of the dispersion in the pressure vessel is less than 9. Production method.   The method for producing pre-expanded polyolefin-based resin particles according to claim 1, wherein the dispersant is magnesium triphosphate.   The method for producing polyolefin resin pre-expanded particles according to claim 1 or 2, wherein the dispersion aid is an anionic surfactant having a linear carbon chain having 10 to 18 carbon atoms as a hydrophobic group. The method for producing pre-expanded polyolefin resin particles according to claim 3 , wherein the dispersion aid is a linear alkyl sulfonate having 12 carbon atoms.   The method for producing polyolefin resin pre-expanded particles according to any one of claims 1 to 4, wherein the foaming agent comprises carbon dioxide.   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-in-mold foam-molded product obtained by filling the polyolefin resin pre-expanded particles according to claim 6 in a mold and heating.