JP2010265424A - Method of production of polypropylene-based resin preliminary foaming particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide polypropylene-based resin particles capable of producing polypropylene-based resin preliminary foaming particles having a high foaming magnification and no fluctuation of cell. <P>SOLUTION: This method of producing polypropylene-based resin preliminary foaming particles uses as a base material resin, a polypropylene-based resin composition containing: 100 pts.wt. of a polypropylene-based resin comprising 80 wt.% or more and 99 wt.% or less of a polypropylene-based resin having a comonomer content of less than 4.0 wt.%, and 1 wt.% or more and 20 wt.% or less of a polypropylene-based resin having a comonomer content of 4.0 wt.% or more; and 0.01 pt.wt. or more and 10 pts.wt. or less of a hydrophilic compound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing polypropylene-based resin pre-expanded particles used as a raw material for buffer packaging materials, boxes, heat insulating materials, automobile bumper core materials, and the like.

  Polypropylene-based resin-molded foam-molded bodies are widely used for cushioning packaging materials, automobile members such as bumper core materials, and the like. These polypropylene resin-in-mold foam-molded articles are produced from polypropylene resin pre-expanded particles.

  Usually, in order to produce polypropylene resin pre-expanded particles, polypropylene resin particles dispersed in an aqueous medium together with an inorganic dispersant in a pressure vessel such as an autoclave are impregnated with a foaming agent, and then resin particles impregnated with the foaming agent. A method is employed in which foam is released and foamed at a temperature equal to or higher than the resin particle softening temperature in a low-pressure atmosphere from inside the container.

  As the foaming agent, a method using a volatile organic foaming agent such as propane and butane (Patent Document 1) and a method using an inorganic gas such as carbon dioxide, nitrogen and air (Patent Document 2) are disclosed.

  In recent years, inorganic gas is often used for environmental considerations. However, when inorganic gas is used as a foaming agent, there is a problem that the expansion ratio is inferior to that of a volatile organic foaming agent. Therefore, a method of using an additive such as a water-soluble inorganic compound for improving foamability is disclosed (Patent Document 3). Although this method improves the expansion ratio, the cells of the polypropylene resin pre-expanded particles become non-uniform, and the in-mold foam molded product obtained using such pre-expanded particles has a large shrinkage ratio and dimensional stability. There was a problem of being inferior. Moreover, the method (patent document 4) of adding a metal borate as another additive is disclosed. In this method, in order to improve the expansion ratio, it is necessary to increase the amount of addition, the cell diameter of the obtained pre-expanded particles becomes small, and the mold obtained by using such pre-expanded particles The foamed molded article has a problem that the shrinkage rate is increased.

  Further, as a method not using an additive, as disclosed in Patent Document 5, a polypropylene resin having a specific crystallinity, a polyethylene resin in which an α-olefin having 4 or more carbon atoms is copolymerized, and a crystal purity is A foamed sheet obtained by foaming a polyolefin resin composition comprising 95% or more homopolypropylene resin with a chemical foaming agent is disclosed, and the resin composition is intended to improve the stress characteristics of the foam. It is said.

  On the other hand, as a technique for mixing two or more kinds of resins, the melting point temperature difference is 15 ° C. or higher and 30 ° C. or lower for the purpose of obtaining an in-mold foam molded article having good surface properties and dimensional properties under a wide range of molding processing conditions. Polypropylene resin pre-expanded particles using a polypropylene resin having a melt index of 3 g / 10 min or more and 20 g / 10 min or less as a base resin is disclosed (Patent Document 6).

  Further, in Patent Document 7, in-mold molding of a complicated shape, it is possible to eliminate the internal collapse by drying in a short time, and good surface beauty is obtained, and furthermore, the beauty of the thin-walled portion is excellent. For the purpose of obtaining an in-mold molded product, a polypropylene resin having an MFR containing 1-butene and ethylene as a comonomer of 10 g / 10 min to 30 g / 10 min and an ethylene as a comonomer of 0.1 g / 10 min. Polypropylene resin pre-expanded particles using a polypropylene resin composition containing a polypropylene resin of 3 g / 10 min or less and a petroleum resin and / or a terpene resin as a base resin are disclosed.

JP 52-77174 A JP-A-60-245650 JP-A-3-223347 WO 98/25996 Japanese Patent Laid-Open No. 10-45975 JP 2006-96805 A JP 2008-106150 A

  An object of the present invention is to provide a method for producing polypropylene resin pre-expanded particles having a high expansion ratio and no cell variation.

  As a result of intensive studies to solve the above problems, the present inventors use a polypropylene resin obtained by mixing a polypropylene resin having a small comonomer amount as a main component and a polypropylene resin having a large comonomer amount. As a result, it was found that the obtained polypropylene resin pre-expanded particles had little variation in cell diameter and the expansion ratio was improved, and the present invention was completed.

That is, the present invention has the following configuration.
[1] 80% by weight or more and 99% by weight or less of a polypropylene resin having a comonomer amount of less than 4.0% by weight, and 1% by weight or more and 20% by weight or less of a polypropylene resin having a comonomer amount of 4.0% by weight or more A polypropylene resin pre-expanded particle comprising a polypropylene resin composition containing 0.01 to 10 parts by weight of a hydrophilic compound with respect to 100 parts by weight of a polypropylene resin as a base resin Production method.
[2] The method for producing pre-expanded polypropylene resin particles according to [1], wherein the polypropylene resin having a comonomer amount of 4.0% by weight or more is powdery.
[3] A polypropylene resin having a comonomer amount of less than 4.0% by weight, a polypropylene resin having a comonomer amount of 4.0% by weight or more, and a hydrophilic compound are preblended and then introduced into an extruder and melt-kneaded. The polypropylene resin particles thus obtained are introduced into a pressure vessel together with water, a foaming agent and a dispersing agent, and the pressure vessel is maintained at a predetermined temperature and pressure, and then the polypropylene resin particles are lower than the pressure inside the pressure vessel. The method for producing pre-expanded polypropylene resin particles according to [1] or [2], which is obtained by releasing in an atmosphere.

  According to the method of the present invention, it is possible to obtain polypropylene resin pre-expanded particles having a small cell diameter variation and a high expansion ratio, regardless of additives such as a nucleating agent.

  The method for producing pre-expanded polypropylene resin particles of the present invention comprises a polypropylene resin having a comonomer amount of less than 4.0% by weight of 80% by weight to 99% by weight and a comonomer amount of 4.0% by weight or more. A base material resin is a polypropylene resin composition containing 0.01 to 10 parts by weight of a hydrophilic compound with respect to 100 parts by weight of a polypropylene resin containing 1 to 20% by weight of the resin. It is characterized by.

  The polypropylene resin in the present invention refers to a resin having a main component of propylene as a monomer. Copolymerizable comonomers include, for example, ethylene, butene-1, isobutene, pentene-1, 3-methyl-butene-1, hexene-1, 4-methyl-pentene-1, 3,4-dimethyl-butene- 1, α-olefins having 2 or 4 to 12 carbon atoms such as 1, heptene-1, 3-methyl-hexene-1, octene-1, and decene-1. Examples of resins using these include propylene homopolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, propylene-butene random copolymer, ethylene-propylene-butene random copolymer, anhydrous Examples thereof include a maleic acid-propylene random copolymer, a maleic anhydride-propylene block copolymer, and a propylene-maleic anhydride graft copolymer. These polypropylene resins are preferably non-crosslinked, but crosslinked resins can also be used.

  The polypropylene resin used in the present invention is 80% by weight or more and 99% by weight or less of a polypropylene resin having a comonomer amount of less than 4.0% by weight, and 1% by weight of a polypropylene resin having a comonomer amount of 4.0% by weight or more. More than 20% by weight, preferably 90% by weight to 99% by weight of a polypropylene resin having a comonomer amount of less than 4.0% by weight, and a polypropylene resin having a comonomer amount of 4.0% by weight or more. 1 to 10% by weight is included. If it is the said range, a foaming ratio is high and the polypropylene resin pre-expanded particle with a uniform cell diameter is obtained.

  A polypropylene resin having a comonomer amount of less than 4.0% by weight and a polypropylene resin having a comonomer amount of 4.0% by weight or more have a similar melting point and melt flow index (hereinafter sometimes referred to as MI). Resins are preferred. If the melting point and the MI are greatly different, the foaming stability may be lacking and the cell may be likely to vary. The melting point difference between resins is preferably within 20 ° C, more preferably within 10 ° C.

  The melt flow index of a polypropylene resin having a comonomer amount of less than 4.0% by weight and a polypropylene resin having a comonomer amount of 4.0% by weight or more is 0.5 g / 10 min or more and 30 g / 10 min or less. Preferably 3 g / 10 min or more and 15 g / 10 min or less is more preferable. When MI is less than 0.5 g / 10 minutes, the melt viscosity is too high to obtain polypropylene foam pre-expanded particles with a high expansion ratio, and when it exceeds 30 g / 10 minutes, melting with respect to the elongation of the resin at the time of foaming is achieved. The viscosity tends to be low and the foam tends to break, and it tends to be difficult to obtain pre-expanded polypropylene resin particles having a high expansion ratio.

  The melting point of the polypropylene resin having a comonomer amount of less than 4.0% by weight and the polypropylene resin having a comonomer amount of 4.0% by weight or more is preferably 125 ° C. or more and 165 ° C. or less, and 130 ° C. or more and 150 ° C. The following are more preferable.

  A polypropylene resin having a comonomer amount of 4.0% by weight or more is preferably powdery because the expansion ratio tends to be improved. The term “powder” as used herein refers to those having an average particle diameter of 3 mm or less, preferably 1 mm or less.

  The polypropylene resin composition of the present invention comprises a polypropylene resin having a comonomer amount of less than 4.0% by weight of 80% to 99% by weight and a comonomer amount of 4.0% by weight or more of 1% by weight. It contains 0.01 part by weight or more and 10 parts by weight or less of the hydrophilic compound with respect to 100 parts by weight of the polypropylene resin containing 20% by weight or less.

  Examples of the hydrophilic compound include a hydrophilic inorganic compound and a hydrophilic organic compound. The hydrophilic inorganic compound refers to a compound that dissolves in water or has hygroscopicity, and specific examples include magnesium sulfate, sodium chloride, magnesium chloride, zinc borate, and borax.

  The hydrophilic organic compound used in the present invention is a compound containing a hydrophilic group such as a carboxyl group, a hydroxyl group, an amino group, an amide group, an ester group, a sulfo group, or a polyoxyethylene group in the molecule. Including. Other hydrophilic organic compounds include organic compounds having a triazine ring such as melamine (chemical name: 1,3,5-triazine-2,4,6-triamine), isocyanuric acid, and isocyanuric acid condensate.

  The hydrophilic polymer is a polymer having a water absorption rate of 0.5% by weight or more measured in accordance with ASTM D570, and is a so-called hygroscopic polymer, several times to several hundred times its own weight without dissolving in water. Water-absorbing polymers that are water-absorbing polymers that are difficult to dehydrate even under pressure, and water-soluble polymers that are soluble in water at room temperature to high temperature. Specifically, transition of carboxylic acid groups of ethylene-acrylic acid-maleic anhydride terpolymer and ethylene- (meth) acrylic acid copolymer such as alkali metal ions such as sodium ion and potassium ion and zinc ion Ionomer resins neutralized with metal ions and crosslinked between molecules, carboxyl group-containing polymers such as ethylene- (meth) acrylic acid copolymers, polyamides such as nylon-6, nylon-6,6, and copolymerized nylon , Polyether-polyolefin resin block copolymers represented by nonionic water-absorbing polymers such as polyethylene glycol and polypropylene glycol, Pelestat (trade name, manufactured by Sanyo Kasei Co., Ltd.), Aqua Coke (trade name, Sumitomo Seika Co., Ltd.) And the like, and the like. These may be used alone or in combination of two or more. Among the hydrophilic polymers, a hydrophilic monomer, a nonionic water-absorbing polymer, and a polyether-polyolefin resin block copolymer have relatively good dispersion stability in a pressure vessel, and This is preferable because it exhibits water absorption in a small amount.

  Among these hydrophilic substances, a hydrophilic organic compound is preferable, and among the hydrophilic organic compounds, a hydrophilic organic compound that is liquid at room temperature is particularly preferable because the effect of the present invention is large. Examples of the hydrophilic organic compound that is liquid at room temperature include liquid polyhydric alcohols such as polyethylene glycol and glycerin.

  A polypropylene resin composition is made into the shape of a polypropylene resin particle using a known method. For example, it is melt-kneaded using an extruder, kneader, Banbury mixer (trademark), roll or the like, and processed into polypropylene resin particles having a weight of 0.2 to 10 mg, preferably 0.5 to 6 mg. . When melt-kneading in an extruder, a polypropylene resin having a comonomer amount of less than 4.0% by weight, a polypropylene resin having a comonomer amount of 4.0% by weight or more, a hydrophilic compound, and other additives as necessary The additive to be added is a method in which a pre-blended mixture is charged into an extruder, and each material is charged into an extruder with a quantitative feeder or the like. A polypropylene-based resin having a comonomer amount of less than 4.0% by weight, A polypropylene resin pre-expanded particle having a higher expansion ratio tends to be obtained by pre-blending a polypropylene resin having a comonomer amount of 4.0% by weight or more and a hydrophilic compound, and then adding the mixture to an extruder and melt-kneading. This is preferable.

  The raw material charged into the extruder is preferably melt kneaded and manufactured by a strand cut method. For example, polypropylene resin particles having a desired shape can be obtained by cutting a polypropylene resin composition extruded in a strand form from a circular die by cooling with water, air or the like and solidifying it.

  A cell nucleating agent can be illustrated as an additive added as needed. By adding a cell nucleating agent, there is a tendency that the cell diameter when the polypropylene resin pre-expanded particles are made 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 polypropylene resin used and the type of cell nucleating agent, and cannot be specified unconditionally, but 0.001 part by weight or more and 2 parts by weight with respect to 100 parts by weight of polypropylene resin. Part or less.

  Furthermore, as other additives, for example, colorants such as carbon black and organic pigments; antistatic agents such as alkyldiethanolamides, alkyldiethanolamines, hydroxyalkylethanolamines, fatty acid monoglycerides, fatty acid diglycerides; hindered phenolic antioxidants Agents; phosphorus processing stabilizers; lactone processing stabilizers; hydroxylamine processing stabilizers, metal deactivators; benzotriazole UV absorbers; benzoate light stabilizers; hindered amine light stabilizers; halogen flame retardants and Examples include flame retardant aids such as antimony trioxide; non-halogen flame retardants; acid neutralizers; crystal nucleating agents; amide additives such as erucic acid amide and ethylene bis stearic acid amide.

  In the present invention, the polypropylene resin pre-expanded particles are produced, for example, as follows. The polypropylene resin particles obtained by the above method are introduced into a pressure vessel together with water, a foaming agent and a dispersant, and the pressure vessel is maintained at a predetermined temperature and pressure, and then the polypropylene resin particles are placed in the pressure vessel. It can be produced by discharging into a lower pressure 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 polypropylene resin pre-expanded particles, and examples thereof include an autoclave type pressure vessel.

  In order to improve the dispersibility of the polypropylene resin particles in water, 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 polypropylene resin particles.

  As the dispersant, it is preferable to use a hardly water-soluble inorganic compound. Here, the poorly water-soluble inorganic compound 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, calcium pyrophosphate, kaolin, clay, etc. And aluminosilicate.

  The amount of the dispersant used varies depending on the type and the type and amount of the polypropylene resin particles to be used, and cannot be generally specified, but is 0.2 to 5 parts by weight with respect to 100 parts by weight of the polypropylene resin particles. Preferably, it is 0.2 parts by weight or more and 3.0 parts by weight or less.

  A dispersing aid may be used in combination with the dispersing agent. As the dispersion aid, it is preferable to use a surfactant, such as an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, an anionic polymer surfactant, a nonionic polymer surfactant, etc. Surfactant etc. are mentioned. 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. A preferred dispersing aid varies depending on the type of dispersing agent used, and thus cannot be defined unconditionally. For example, when using tribasic magnesium phosphate and tribasic calcium phosphate as the dispersing agent, it is possible to use an anionic surfactant. This is preferable because the dispersion state becomes stable.

  The amount of the dispersing aid varies depending on the type and the type and amount of the polypropylene-based resin to be used, and cannot be specified unconditionally. Usually, the dispersing aid is 0.001 part by weight or more and 0.2 to 100 parts by weight of water. It is preferable that it is below the weight part.

  As the foaming agent used in the present invention, inorganic gases such as nitrogen, carbon dioxide, and air, and water can be used.

  The amount of foaming agent used varies depending on the type of polypropylene 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 polypropylene resin particles. The amount is preferably 60 parts by weight or less.

  The aqueous dispersion containing the polypropylene resin particles adjusted in the pressure vessel as described above is pressurized to a predetermined pressure with stirring, heated to a predetermined temperature, and is usually 5 hours. After holding for ~ 180 minutes, preferably 10-60 minutes, the pressurized water dispersion comprising polypropylene resin particles is opened in a low pressure atmosphere (usually by opening the valve provided at the bottom of the pressure vessel Polypropylene resin pre-expanded particles can be produced by releasing them under atmospheric pressure).

  The predetermined temperature for heating the inside of the pressure vessel (hereinafter sometimes referred to as the foaming temperature) varies depending on the melting point [Tm (° C)], type, etc. of the polypropylene resin to be used, and cannot be generally specified, but the polypropylene resin composition It is preferable to heat above the softening temperature of a thing, More preferably, it is preferable to heat to Tm-30 (degreeC) or more and Tm + 10 (degreeC) or less.

  The melting point of the polypropylene resin here refers to a polypropylene resin by heating 4 to 6 mg of polypropylene resin particles from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min using a differential scanning calorimeter. From the DSC curve obtained when the resin particles are melted and then crystallized by lowering the temperature from 220 ° C. to 40 ° C. at 10 ° C./min and then further increasing from 40 ° C. to 220 ° C. at 10 ° C./min. This is a value obtained as the melting peak temperature at the second temperature increase.

  The polypropylene resin pre-expanded particles obtained as described above preferably have an average cell diameter of 100 μm or more and 400 μm or less, and tend to be uniform.

  Next, the manufacturing method of the polypropylene 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.

<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. Measured under conditions.

<Measurement of flexural modulus>
The flexural modulus was measured according to JIS K7106.

<Measurement of average particle diameter>
The average particle size of the polypropylene resin was determined as follows. The average value of the longest linear distance among the resin particles and the distance between the straight lines perpendicular to the straight line is defined as the particle diameter of one resin particle, and the average particle diameter is determined by measuring the particle diameter of 50 randomly extracted resin particles. The average value was measured as the average particle size.

<Measurement of expansion ratio>
The expansion ratio Xp is obtained as follows. The weight of the pre-expanded particles to be measured is W _1, and ethanol is put in a graduated cylinder to determine the volume V ₁ . All the pre-expanded particles whose weight has been measured are put into a graduated cylinder, the volume V ₂ after all the pre-expanded particles are immersed in ethanol with a push rod or the like is determined, and the expansion ratio is determined by the following equation.
Xp = (V ₂ −V ₁ ) × 0.9 / W ₁

<Evaluation of average cell diameter and cell uniformity>
Cut the vicinity of the center of the polypropylene resin pre-expanded particles with a cutter, etc., count the number of cells existing at a distance of 2.0 mm near the center of the cut surface, and pre-expand the value obtained by dividing 2.0 mm by the number of cells obtained The average cell diameter was determined as the average value of 20 pre-expanded particles.

  Cell uniformity was observed in the vicinity of the center of the cut surface of the pre-foamed particles by 2.0 mm × 2.0 mm, and the cell diameter of the pre-foamed particles obtained by the above method was 0.5 times or less and 1.5 times. The determination was made to the extent that there was a cell having the above cell diameter (hereinafter referred to as a detached cell). The circles in Table 1 indicate that 20 pre-expanded particles are observed and the detached cells present in the observation region are 10% or less.

Example 1
MI = 7 g / 10 minutes, melting point 136 ° C., flexural modulus 700 MPa, ethylene-propylene random copolymer 97.5% by weight containing 3.6% by weight of ethylene as a comonomer, MI = 8 g / 10 minutes, melting point 139 ° C. Bending elastic modulus of 800 MPa, ethylene as a comonomer, 2.0% by weight, 2.5% by weight of a powdered ethylene-propylene-butene random copolymer having an average particle size of 0.8 mm containing 2.0% by weight of a butene, and a resin 100 parts by weight of the ethylene-propylene random copolymer using 0.5 parts by weight of polyethylene glycol (trade name: PEG300, manufactured by Lion Corporation) as a hydrophilic polymer and 0.1 parts by weight of talc as a cell nucleating agent And powdered ethylene-propylene-butene random copolymer and talc, respectively, with polyethylene feeder A metering pump Lumpur, charged into the extruder, melt-kneaded extruded into strands from a circular die, cooled with water and cut with a cutter, the weight of the grain was obtained polypropylene resin particles of 1.2 mg / particle.

100 parts by weight of the obtained polypropylene resin particles, 200 parts by weight of water, 0.5 part by weight of magnesium triphosphate (manufactured by Taihei Chemical Industrial Co., Ltd.) as a dispersing agent, 0.03 part by weight of sodium alkyl sulfonate as a dispersing aid Was put in a pressure-resistant autoclave having a capacity of 0.01 m ³ , and 6 parts by weight of carbon dioxide gas was added as a blowing agent under stirring. The autoclave contents were heated and heated to a foaming temperature of 142.5 ° C. Thereafter, carbon dioxide gas is additionally injected to increase the pressure in the autoclave to a foaming pressure of 3.0 MPa · G. After maintaining the foaming temperature and the foaming pressure for 30 minutes, the valve at the bottom of the autoclave is opened and 3.6 mmφ × 1 hole The autoclave contents were discharged under atmospheric pressure through the opening orifice of the polypropylene resin to obtain polypropylene resin pre-expanded particles. The expansion ratio of the obtained polypropylene resin pre-expanded particles was 14.9 times.

(Example 2)
MI = 7 g / 10 min, melting point 136 ° C., flexural modulus 700 MPa, 97.5 parts by weight of ethylene-propylene random copolymer containing 3.6% by weight of ethylene as a comonomer, MI = 8 g / 10 min, melting point 139 ° C. With respect to 2.5 parts by weight of a powdery ethylene-propylene-butene random copolymer containing 2.0% by weight of ethylene as a comonomer and 2.0% by weight of butene as a comonomer, polyethylene glycol ( (Product name: PEG300, manufactured by Lion) 0.5 parts by weight, 0.1 part by weight of talc as a cell nucleating agent, the ethylene-propylene random copolymer, the ethylene-propylene-butene random copolymer, polyethylene glycol , Pre-blended with talc. 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 resin particles, 200 parts by weight of water, 0.5 part by weight of magnesium triphosphate (manufactured by Taihei Chemical Industrial Co., Ltd.) as a dispersing agent, 0.03 part by weight of sodium alkyl sulfonate as a dispersing aid Was put in a pressure-resistant autoclave having a capacity of 0.01 m ³ , and 6 parts by weight of carbon dioxide gas was added as a blowing agent under stirring. The autoclave contents were heated and heated to a foaming temperature of 142.5 ° C. Thereafter, carbon dioxide gas is additionally injected to increase the pressure in the autoclave to a foaming pressure of 3.0 MPa · G. After maintaining the foaming temperature and the foaming pressure for 30 minutes, the valve at the bottom of the autoclave is opened and 3.6 mmφ × 1 hole The autoclave contents were discharged under atmospheric pressure through the opening orifice of the polypropylene resin to obtain polypropylene resin pre-expanded particles. The expansion ratio of the obtained polypropylene resin pre-expanded particles was 15.5 times.

(Example 3)
MI = 7 g / 10 min, melting point 136 ° C., flexural modulus 700 MPa, ethylene-propylene random copolymer 95% by weight containing 3.6% by weight of ethylene as a comonomer, MI = 9 g / 10 min, melting point 137 ° C., flexural elasticity The rate is 800 MPa, ethylene as a comonomer is 3.0% by weight, butene is 1.5% by weight, and an average particle diameter of 0.7 mm of a powdered ethylene-propylene-butene random copolymer is 5% by weight. On the other hand, 0.3 parts by weight of glycerin (manufactured by Lion) as the hydrophilic polymer and 0.05 parts by weight of talc as the cell nucleating agent were used, and the ethylene-propylene random copolymer and the ethylene-propylene-butene random copolymer were used. , Polyethylene glycol and talc were pre-blended. 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 resin particles, 200 parts by weight of water, 0.5 part by weight of magnesium triphosphate (manufactured by Taihei Chemical Industrial Co., Ltd.) as a dispersing agent, 0.03 part by weight of sodium alkyl sulfonate as a dispersing aid Was put in a pressure-resistant autoclave having a capacity of 0.01 m ³ , and 6 parts by weight of carbon dioxide gas was added as a blowing agent under stirring. The autoclave contents were heated and heated to a foaming temperature of 142.5 ° 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 × 1 hole The autoclave contents were discharged under atmospheric pressure through the opening orifice of the polypropylene resin to obtain polypropylene resin pre-expanded particles. The expansion ratio of the obtained polypropylene resin pre-expanded particles was 14.4 times.

(Comparative Example 1)
As a base resin, MI = 7 g / 10 min used in Example 1, melting point 136 ° C., flexural modulus 700 MPa, 100 parts by weight of ethylene-propylene random copolymer containing 3.6% by weight of ethylene as a comonomer, Polyethylene glycol (trade name: PEG300, manufactured by Lion Corporation) 0.5 parts by weight as a hydrophilic polymer, 0.1 parts by weight of talc as a cell nucleating agent, and the ethylene-propylene random copolymer and talc with a quantitative feeder. Polyethylene glycol was charged into the extruder with a metering pump, melt kneaded, 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.

  The obtained polypropylene resin particles were expanded under the same conditions as in Example 1 to obtain polypropylene resin pre-expanded particles. The expansion ratio of the obtained polypropylene resin pre-expanded particles was 14.0 times.

(Comparative Example 2)
As the base resin, MI = 7 g / 10 min used in Example 3, melting point 136 ° C., flexural modulus 700 MPa, ethylene-propylene random copolymer containing 3.6% by weight of ethylene as a comonomer, The ethylene-propylene random copolymer, polyethylene glycol, and talc were preblended using 0.3 part by weight of glycerin (manufactured by Lion) as the hydrophilic polymer and 0.05 part by weight of talc as the 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.

  The obtained polypropylene resin particles were expanded under the same conditions as in Example 3 to obtain polypropylene resin pre-expanded particles. The expansion ratio of the obtained polypropylene resin pre-expanded particles was 12.9 times.

Claims (3)

  Polypropylene comprising 80% to 99% by weight of a polypropylene resin having a comonomer amount of less than 4.0% by weight, and 1% to 20% by weight of a polypropylene resin having a comonomer amount of 4.0% by weight or more. A polypropylene resin composition containing a hydrophilic compound in an amount of 0.01 to 10 parts by weight with respect to 100 parts by weight of a resin as a base resin.   2. The method for producing pre-expanded polypropylene resin particles according to claim 1, wherein the polypropylene resin having a comonomer amount of 4.0% by weight or more is powdery.   Obtained by pre-blending a polypropylene resin having a comonomer amount of less than 4.0% by weight, a polypropylene resin having a comonomer amount of 4.0% by weight or more, and a hydrophilic compound, and then adding the mixture to an extruder for melt kneading. The obtained polypropylene resin particles are introduced into a pressure vessel together with water, a foaming agent and a dispersant, and the pressure vessel is maintained at a predetermined temperature and pressure, and then the polypropylene resin particles are placed in an atmosphere lower than the pressure inside the pressure vessel. The manufacturing method of the polypropylene resin pre-expanded particle of Claim 1 or 2 obtained by discharge | release.