JP2010013606A - Polypropylene-based resin pre-expanded particle, and polypropylene-based resin in-mold expansion molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide polypropylene-based resin pre-expanded particles producible under a low heating vapor pressure, having a small dimensional shrinkage percentage, and affording an in-mold expansion molded product having high surface beautifulness in in-mold expansion molding of the polypropylene-based resin pre-expanded particles. <P>SOLUTION: The polypropylene-based resin pre-expanded particles comprise a polypropylene-based resin polymerized with a metallocene-based polymerization catalyst as a substrate resin, wherein the polypropylene-based resin has the following requirements (a) to (c): (a) 90-100 mol% of a propylene structural unit, and 0-10 mol% of an ethylene and/or a &ge;4C &alpha;-olefin structural units being present; (b) the total amount of regioirregular units based on 2,1-insertion and 1,3-insertion of propylene monomer units of the total polypylene insertions measured by<SP>13</SP>C-NMR being &lt;0.5 mol%; and (c) the melt flow rate being &ge;0.5 to &le;100 g/10 min. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to polypropylene resin pre-expanded particles used for automobile interior members, automobile bumper cores, heat insulating materials, cushioning packaging materials, pass boxes, and the like, and polypropylene resin in-mold foam molding obtained using the pre-expanded particles It is about the body.

  The polypropylene resin in-mold foam-molded product obtained by using the polypropylene-based resin pre-expanded particles has characteristics such as shape flexibility, light weight, and heat insulation, which are advantages of the in-mold foam-molded product. Compared to similar in-mold foam moldings, it is superior in chemical resistance, heat resistance and strain recovery after compression compared to in-mold foam moldings obtained using polystyrene resin pre-expanded particles. In addition, the dimensional accuracy, heat resistance, and compressive strength are excellent as compared with the in-mold foam molded body obtained using the polyethylene resin pre-expanded particles. Due to these features, the polypropylene resin-molded in-mold molded products obtained using polypropylene resin pre-expanded particles are used in various applications such as automotive interior parts, automotive bumper core materials, heat insulation materials, and cushioning packaging materials. It has been.

  Important properties required for polypropylene resin in-mold foam molded products obtained using polypropylene resin pre-expanded particles include fusion between polypropylene resin pre-expanded particles, surface aesthetics, and shrinkage recovery. It is done.

  The fusion property between the polypropylene resin pre-expanded particles is the degree of fusion between the polypropylene resin pre-expanded particles in the polypropylene resin in-mold foam, and if the fusion is insufficient, The mechanical strength of the foam molded article becomes insufficient. In particular, in many cases, the melt-bonding property is insufficient inside the in-mold foamed molded product.

  The surface is beautiful to the extent that the surface of the foamed molded product in the polypropylene resin mold is smooth. The decrease in surface aesthetics may be due to insufficient foaming of the polypropylene resin pre-expanded particles. Indentations and polypropylene resin formed in the grooves between the polypropylene resin pre-expanded particles on the surface of the polypropylene resin in-mold molded product It is caused by streak-like grooves that are thought to be caused by the shrinkage of the in-mold foam molding.

  The polypropylene resin in-mold foam-molded product obtained by using the polypropylene resin pre-expanded particles usually shrinks when being taken out from the mold after molding, causing warping and deformation. The shrinkage and deformation of the polypropylene resin-in-mold foam-molded product can be recovered by a so-called curing process in which the polypropylene-based resin mold-in-mold foam-molded product is held in a heated atmosphere for a certain time. Even after curing, the polypropylene resin in-mold foam molded article does not recover to the size of the mold, but when the dimensional shrinkage of the cured polypropylene resin mold in the mold after curing is small, Excellent shrinkage recovery.

  Most molding machines for in-mold foam molding of polypropylene resin pre-expanded particles occupy a specification with a pressure resistance of 0.4 MPa, and the molding heating steam pressure normally produced using the molding machine is approximately 0. It is up to about 36 MPa. Polypropylene-based resin pre-expanded particles used for in-mold foam molding use a resin having such a characteristic that can cope with this, and generally, ethylene-random polypropylene having a melting point of about 140 to 150 ° C. is used. However, due to the recent increase in fuel prices and the like, further measures for reducing the pressure of the formed heating steam are awaited.

  As a method for lowering the molding heating steam pressure, there is a method using a material having a lower melting point of the base resin, that is, a method using random polypropylene in the range of 130 ° C. Generally, the melting point of the propylene resin and the rigidity of the resin are When a resin having a positive correlation and a low melting point is used, the rigidity is low, and the shrinkage and deformation of the in-mold foam molded product tend to increase.

  On the other hand, if a resin having a low comonomer content and a high melting point is used to achieve high rigidity, the melting point of the resin will be high, and the molding heating steam pressure required to obtain a good in-mold foam molded product will be high There is a tendency. For this reason, when higher rigidity is required, it is necessary to use a molding machine or a die having a high pressure resistance specification, which increases the equipment cost and increases the utility cost, thereby increasing the molding processing cost.

  In recent years, the number of in-mold foam molded products whose appearance is regarded as important is increasing. This is often used for automobile interior parts and returnable boxes used in places where users can see. In addition to the physical properties such as rigidity, light weight, and heat insulation that are usually required for in-mold foam molded products, it is good. Appearance is required. In-mold foam moldings show gaps between pre-expanded particles and turtle shell patterns due to the manufacturing method, but many products that emphasize the appearance dislike them. In order to make the gaps between the pre-expanded particles inconspicuous, generally, a method of increasing the molding heating steam pressure at the time of in-mold foam molding and promoting the fusion of the pre-expanded particles is adopted. That is, in order to obtain an in-mold foam molded article having a high surface beauty, it is necessary to make the molding heating steam pressure at the time of in-mold foam molding higher than the pressure required for fusion between the pre-expanded particles.

  As described above, there is a need for a technology that can stably produce a foam-in-molded polypropylene resin mold with high rigidity and high surface beauty at a lower molding processing temperature without using a special molding machine. It has been.

With respect to the technique for improving the rigidity of the polypropylene resin-molded in-mold foam, various techniques have been studied for the base resin used for the polypropylene resin pre-expanded particles. Most of them relate to polypropylene resins polymerized using so-called Ziegler-Natta catalysts made of titanium chloride and alkylaluminum, which are currently commercially available. On the other hand, in recent years, polymerization catalyst technology for polypropylene resins has been extensively studied, and various improvements in the performance of polypropylene resins are being studied. Among them, by using a so-called metallocene polymerization catalyst, a stereoregularity is controlled, and a resin having a high melting point rigidity compared to a polypropylene resin obtained using a conventional Ziegler polymerization catalyst is obtained. (For example, Patent Document 1).
JP 2006-57010 A

  Polypropylene resin that can be produced with low molding heating steam pressure, and has a small dimensional shrinkage and high surface aesthetics. There is a need for the development of pre-expanded particles.

  As a result of diligent research in view of the above problems, the present invention uses a propylene resin having a specific structure polymerized using a metallocene polymerization catalyst as a base resin, so that the molding heating steam pressure during in-mold foam molding is extremely low. Further, the present invention has been completed by finding out that the obtained polypropylene-based resin-molded foam-molded product has a low dimensional shrinkage and high surface aesthetics.

That is, the first aspect of the present invention is a polypropylene resin pre-expanded particle characterized in that a polypropylene resin polymerized with a metallocene polymerization catalyst is used as a base resin, and the polypropylene resin has the following requirements ( It relates to polypropylene resin pre-expanded particles having a) to (c).
(A) The structural unit consisting of propylene is 90 to 100 mol%, and the structural unit consisting of ethylene and / or an α-olefin having 4 or more carbon atoms is present in an amount of 0 to 10 mol%.
(B) The total amount of position irregular units based on 2,1-insertion and 1,3-insertion of propylene monomer units in all polypropylene insertions, as measured by ¹³ C-NMR, is less than 0.5 mol%. .
(C) The melt flow rate is 0.5 g / 10 min or more and 100 g / 10 min or less.

As a preferred embodiment,
(1) The ratio of the melting peak on the high temperature side, Qh / (Ql + Qh, having two melting peaks in the differential scanning calorimetry method, calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side ) × 100 is 10% or more and 50% or less,
(2) The amount of the inorganic dispersant adhering to the surface is 2000 ppm or less,
The above-mentioned polypropylene resin pre-expanded particles are characterized by the following.

A second aspect of the present invention relates to a polypropylene resin-in-mold foam-molded article having a density of 10 kg / m ³ or more and 300 kg / m ³ or less, obtained by using the polypropylene resin pre-expanded particles described above.

  According to the present invention, it is possible to produce a polypropylene resin in-mold foam-molded product having a small dimensional shrinkage ratio and high surface beauty at a low molding heating steam pressure.

The polypropylene resin pre-expanded particles of the present invention comprise a propylene polymer polymerized with a metallocene polymerization catalyst having the following requirements (a) to (c) as a base resin. Expanded particles.
(A) The structural unit consisting of propylene is 90 to 100 mol%, and the structural unit consisting of ethylene and / or an α-olefin having 4 or more carbon atoms is present in an amount of 0 to 10 mol%.
(B) The total amount of position irregular units based on 2,1-insertion and 1,3-insertion of propylene monomer units in all polypropylene insertions, as measured by ¹³ C-NMR, is less than 0.5 mol%. .
(C) The melt flow rate is 0.5 g / 10 min or more and 100 g / 10 min or less.

  In the polypropylene resin of the present invention, the structural unit composed of propylene is 90 to 100 mol%, and the structural unit composed of ethylene and / or an α-olefin having 4 or more carbon atoms is 0 to 10 mol%.

Examples of the structural unit composed of ethylene and / or an α-olefin having 4 or more carbon atoms include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1- Alpha-olefins having 2 or 4 to 12 carbon atoms such as pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene, cyclopentene, norbornene, tetracyclo Cyclic olefins such as [6,2,1 ^1,8 , 1 ^3,6 ] -4-dodecene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1, Examples include dienes such as 4-hexadiene and 7-methyl-1,6-octadiene. Among these, the use of ethylene and 1-butene tends to be resistant to cold brittleness. , Preferable in terms of low cost and the like.

  The polypropylene resin of the present invention further includes vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl. Vinyl monomers such as toluene and divinylbenzene may be copolymerized.

The polypropylene resin of the present invention has a total amount of position irregular units based on 2,1-insertion and 1,3-insertion of propylene monomer units in all polypropylene insertions as measured by ¹³ C-NMR. %.

  The polypropylene resin having the above-mentioned position irregular unit amount can be obtained by polymerization with a metallocene catalyst containing a metallocene compound represented by the following general formula [I] as an essential component.

（上記一般式［Ｉ］において、Ｒ１、Ｒ２、Ｒ３、Ｒ４、Ｒ５、Ｒ６、Ｒ７、Ｒ８、Ｒ９、Ｒ１０、Ｒ１１、Ｒ１２、Ｒ１３、Ｒ１４は水素、炭化水素基、ケイ素含有基から選ばれ、それぞれ同一でも異なっていてもよい。Ｍは第４族遷移金属であり、Ｙは炭素原子またはケイ素原子であり、Ｑはハロゲン、炭化水素基、アニオン配位子または孤立電子対で配位可能な中性配位子から同一または異なる組合せで選んでもよく、ｊは1〜４の整数である。）
なお、本発明のポリプロピレン系樹脂の全ポリピレン挿入中のプロピレンモノマー単位の２，１−挿入及び１，３−挿入に基づく位置不規則単位量は、Ｐｏｌｙｍｅｒ， ３０， １３５０（１９８９）や特開平７−１４５２１２号公報に開示された情報を参考に容易に算出することができる。

(In the above general formula [I], R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14 are selected from hydrogen, hydrocarbon group, silicon-containing group, Each may be the same or different, M is a Group 4 transition metal, Y is a carbon atom or a silicon atom, and Q can be coordinated by a halogen, a hydrocarbon group, an anionic ligand or a lone pair of electrons. The neutral ligands may be selected in the same or different combinations, and j is an integer of 1 to 4.)
The amount of position irregular units based on 2,1-insertion and 1,3-insertion of propylene monomer units during the insertion of all polypropylene in the polypropylene resin of the present invention is described in Polymer, 30, 1350 (1989) and It can be easily calculated with reference to the information disclosed in JP-A-145212.

  The polypropylene resin of the present invention has a melt flow rate (MFR) of 0.5 g / 10 min to 100 g / 10 min, preferably 2 g / 10 min to 50 g / 10 min. The MFR measurement according to the present invention is performed using an MFR 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. When the MFR is in the above range, it is easy to obtain polypropylene resin pre-expanded particles having a relatively large expansion ratio, and the surface beauty of the polypropylene resin in-mold foam molding obtained by in-mold foam molding is excellent. A product having a small dimensional shrinkage rate is obtained.

  These polypropylene resins are preferably in a non-crosslinked state, but may be crosslinked by peroxide or radiation. Also, other thermoplastic resins that can be mixed with polypropylene resin, such as low density polyethylene, linear density polyethylene, polystyrene, polybutene, ionomer, etc., may be mixed and used as long as the properties of the polypropylene resin are not lost. good.

  The above polypropylene resin is usually melted in advance using an extruder, kneader, Banbury mixer, roll, etc. so as to be easily used for pre-foaming, and has a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, etc. Molded into a desired particle shape to form polypropylene resin particles.

  In the present invention, in addition to the polypropylene resin, an antistatic agent, a pigment, a flame retardant improver, a conductivity improver and the like may be added as necessary to form polypropylene resin particles. It is preferable to add to the molten resin in the production process of the resin particles.

  The polypropylene resin pre-expanded particles of the present invention are prepared by placing a dispersion containing polypropylene resin particles, a foaming agent, water, a dispersant and a dispersion aid in a pressure vessel, heating to a predetermined temperature, And the mixture in the container is preferably heated to a temperature in the range of the melting point of the polypropylene resin −20 ° C. or higher and the polypropylene resin + 10 ° C. or lower and impregnated with the foaming agent to keep the temperature and pressure in the container constant. It can be produced by releasing the mixture in the container under a lower pressure atmosphere than in the container under pressure.

  Examples of the foaming agent impregnated into the polypropylene resin particles used in the present invention include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; and aliphatic cyclization such as cyclopentane and cyclobutane. Hydrogen; inorganic gases such as air, nitrogen and carbon dioxide; water and the like. These foaming agents may be used alone or in combination of two or more. Among these, it is preferable to use carbon dioxide gas, water, or isobutane that enables foaming at a higher magnification.

  Further, the amount of the foaming agent is not limited, and may be appropriately used according to the desired expansion ratio of the polypropylene resin pre-expanded particles. The amount used is 3 parts by weight with respect to 100 parts by weight of the polypropylene resin particles. The amount is preferably 60 parts by weight or less.

  There is no particular limitation on the pressure vessel used when producing the polypropylene resin pre-expanded particles, and any pressure-resistant vessel that can withstand the pressure and temperature in the vessel at the time of producing the polypropylene resin pre-expanded particles may be used. For example, an autoclave-type pressure vessel Can be given.

  Examples of the dispersant that can be used in the present invention include tribasic calcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, basic zinc carbonate, aluminum oxide, iron oxide, titanium oxide, and aluminosilicate. And inorganic dispersants such as barium sulfate.

  Examples of the dispersion aid that can be used in the present invention include sodium dodecylbenzene sulfonate, sodium n-paraffin sulfonate, and sodium α-olefin sulfonate. Among these, as a combination of a dispersant and a dispersion aid, a combination of tricalcium phosphate and sodium dodecylbenzenesulfonate is preferable.

  The amount of the dispersant and the dispersion aid varies depending on the type and the type and amount of the polypropylene-based resin used, but it is usually 0.2 to 3 parts by weight of the dispersant with respect to 100 parts by weight of water. Preferably, the dispersion aid is 0.001 to 0.1 part by weight. Moreover, in order to make a polypropylene resin particle favorable in the dispersibility in water, it is preferable to use normally 20-100 weight part with respect to 100 weight part of water.

  The expansion ratio of the polypropylene resin pre-expanded particles obtained by the above production method is preferably 5 to 50 times, and more preferably 7 to 45 times. Further, a dispersion liquid containing polypropylene resin particles, foaming agent, water, dispersant, and dispersion aid is put in a pressure vessel, heated to a predetermined temperature, and under pressure, the mixture in the vessel is preferably Melting point of polypropylene resin −20 ° C. or higher and polypropylene resin + 10 ° C. or lower and impregnating with foaming agent, keeping the temperature and pressure in the container constant, and maintaining the mixture in the container under pressure Manufactures pre-expanded particles (hereinafter sometimes referred to as single-stage pre-expanded particles) that are 5 to 35 times in the first stage of foaming, such as being released in a low-pressure atmosphere from the inside of the container. After the particles are put in a pressure-resistant airtight container and the pressure in the one-stage expanded pre-expanded particles is made higher than the normal pressure by pressure treatment in which nitrogen, air or the like is impregnated with 0.1 to 0.6 MPa, the one-stage expanded preliminary Foam particles By further heating and foaming with a team or the like, a polypropylene resin pre-expanded particle (hereinafter, sometimes referred to as a two-stage expanded pre-expanded particle) having a higher expansion ratio than the expansion ratio of the first-stage expanded pre-expanded particle is obtained. Also good.

Here, the expansion ratio of the polypropylene resin pre-expanded particles is obtained by determining the weight w (g) and the ethanol submerged volume v (cm ³ ) of the polypropylene resin pre-expanded particles, and the density d (g / g cm ³ ) is obtained from the following equation.
Foaming ratio = d × v / w

  As shown in FIG. 1, the polypropylene resin pre-expanded particles of the present invention are obtained when the polypropylene resin pre-expanded particles are heated from 40 ° C. to 200 ° C. at a rate of 10 ° C./min in the differential scanning calorimetry method. The DSC curve has two melting peaks, and the melting peak calorie Ql on the low temperature side, which is the amount of heat surrounded by the tangent to the melting start baseline from the maximum point between the low temperature side peak and the high temperature side peak, The ratio Qh of the melting peak on the high temperature side calculated from the high temperature side melting peak calorie Qh, which is the amount of heat surrounded by the tangent to the melting end baseline from the maximum point between the high temperature side peak and the low temperature side peak and the high temperature side peak / (Ql + Qh) × 100 (hereinafter abbreviated as DSC ratio) is preferably 10% to 50%, more preferably 15% to 40%. . When the DSC ratio is within this range, a polypropylene resin-in-mold foam-molded product having a high surface beauty is easily obtained.

  The polypropylene resin pre-expanded particles of the present invention preferably have an amount of inorganic dispersant adhering to the surface of 2000 ppm or less. If it is the said range, it exists in the tendency for a polypropylene resin in-mold foam-molding body with favorable melt | fusion property to be obtained when in-mold foam-molding is performed.

  In addition, about the amount of adhesion part inorganic powder of this invention, it can quantify from various spectroscopic analyzes or the amount of ash when a polypropylene resin pre-expanded particle is burned. For example, when phosphate is used as a dispersant, the dried pre-foamed particles are an aqueous solution (colorimetric solution) containing 0.022 wt% ammonium metavanadate, 0.54 wt% ammonium molybdate and 3 wt% nitric acid. 50.0 mL and W (g) of pre-expanded particles were placed in a conical beaker, stirred for 1 minute, and allowed to stand for 10 minutes. The obtained liquid phase is put in a quartz cell having an optical path length of 1.0 cm, and the absorbance A (−) at 410 nm is measured with a spectrophotometer, and can be obtained from the absorbance of a standard phosphate solution.

  In order to make the polypropylene resin pre-expanded particles of the present invention into a polypropylene resin in-mold foam molded product, a) a method of performing in-mold foam molding as it is, b) an inorganic gas such as air in advance in the polypropylene resin pre-foamed particles Injecting mold and applying internal pressure (foaming ability), then performing in-mold foam molding, c) Filling polypropylene resin pre-expanded particles in a mold in a compressed state, and performing in-mold foam molding, etc. Conventionally known methods can be used.

  As a specific example of a method for obtaining a polypropylene resin pre-expanded molded article using the polypropylene resin pre-expanded particles of the present invention, for example, the polypropylene resin pre-expanded particles are preliminarily air-pressurized in a pressure-resistant container, An internal pressure (foaming ability) is imparted by pressurizing air into the foamed particles, and this is filled in a mold that can be closed but cannot be sealed, and 0.1 to 0.4 MPa ( Molded with a steam pressure of about 3 to 30 seconds with a heating steam pressure of about gauge pressure), and the polypropylene-based resin pre-foamed particles are fused together, and then the molding mold is taken out of the in-mold foam-molded product by water cooling. After cooling to a level that can prevent deformation of the foam molded product in the resin mold, the mold is opened, and a method of obtaining a foam molded product in the polypropylene resin mold is listed. It is.

  In addition, the internal pressure of the polypropylene resin pre-expanded particles is 0.1 to 1.0 MPa (gauge pressure) by an inorganic gas such as air and nitrogen under a temperature condition of room temperature to 80 ° C. for 1 to 48 hours, for example. ) Can be adjusted by applying pressure.

Thus, the density of the polypropylene resin in-mold foam molded product obtained by using the polypropylene resin pre-expanded particles of the present invention is preferably 10 kg / m ³ or more and 300 kg / m ³ or less, more preferably 15 kg. / m ³ or more and 250 kg / m ³ or less.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

[Measurement of melting point]
Using a DSC6200 differential scanning calorimeter manufactured by Seiko Instruments Inc., 5-6 mg of polypropylene resin particles are heated from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min to melt the resin particles. Then, after crystallizing by lowering the temperature from 220 ° C. to 40 ° C. at 10 ° C./min, the second rise from the DSC curve obtained when the temperature is further raised from 40 ° C. to 220 ° C. at 10 ° C./min. The melting peak temperature when warm was determined as the melting point.

(Measurement of flexural modulus)
After drying the polypropylene resin at 80 ° C for 6 hours, a 35t injection molding machine is used to produce a 6.4mm bar (width 12mm, length 127mm) at a cylinder temperature of 200 ° C and a mold temperature of 30 ° C. Then, a bending test was performed according to ASTM D790 within one week to obtain a bending elastic modulus.

[Measurement of DSC ratio]
In the DSC curve obtained by raising the temperature of polypropylene resin pre-expanded particles 5-6 mg from 40 ° C. to 200 ° C. at a rate of 10 ° C./min using a DSC 6200 type differential scanning calorimeter manufactured by Seiko Instruments Inc. For the two melting peaks, the melting peak calorie Ql on the low temperature side, which is the amount of heat surrounded by the tangent to the melting start baseline from the maximum point between the low temperature side peak and the high temperature side peak, and the high temperature side peak of the DSC curve The high temperature side melting peak heat quantity Qh, which is the amount of heat surrounded by the tangent to the melting end baseline from the maximum point between the low temperature side peak and the high temperature side peak, and the ratio of the high temperature side melting peak (Qh / (Ql + Qh) × 100) was calculated.

[Expansion ratio of pre-expanded polypropylene resin particles]
Obtains the bulk volume of about 50 cm ³ of polypropylene by weight of the resin pre-expanded particles w (g) and ethanol submerged volume v (cm ^3), was determined by the following formula from the density d of before foaming of the resin particles (g / cm ³⁾ .
Foaming ratio = d × v / w

[Measurement of amount of adhered inorganic dispersant (when inorganic dispersant is calcium phosphate)]
The dried pre-expanded particles were prepared by adding 50.0 mL of an aqueous solution (colorimetric solution) containing 0.022 wt% ammonium metavanadate, 0.54 wt% ammonium molybdate and 3 wt% nitric acid and W (g). The sample was placed 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.

Using the absorbance coefficient ε (g / L · cm) of 410 mg of tribasic magnesium phosphate measured in advance for the same colorimetric solution, the amount of tribasic magnesium phosphate C (ppm) = 5 0.0 × 10 ⁴ · ε · A / W was determined.

[Fusion rate evaluation]
The obtained polypropylene resin mold in-mold foam was cut with a cutter knife in the direction of the thickness of the polypropylene resin mold in-mold about 3 mm, and then manually in the polypropylene resin mold in-mold foam mold. The fracture surface was observed and the ratio of the destroyed polypropylene resin pre-expanded particles to the number of polypropylene resin pre-expanded particles constituting the fracture surface was determined.

[Surface property evaluation]
The surface of the obtained foamed molded product in the polypropylene resin mold was observed, and the average number of depressions and gaps of 1 mm ² or more between particles per 10 cm ² was determined as the following determination.
Less than 100 ... ○
More than 100 ... ×

[Dimensional shrinkage]
The longitudinal dimension of the obtained foamed polypropylene resin mold was measured, and the dimensional shrinkage ratio with respect to the mold dimension (400 mm) was calculated to make the following determination.
Less than 0.1% ... ○
0.1% or more ×

Example 1
As a polypropylene resin, 100 parts by weight of a propylene polymer polymerized with a metallocene polymerization catalyst and having a melting point of 149 ° C., an MFR of 5.0, and a flexural modulus of 1325 MPa is used as a cell nucleating agent, and polyethylene glycol (PEG # 300 manufactured by Lion Corporation). ) After blending 0.5 part by weight and 0.1 part by weight of talc (PKS manufactured by Hayashi Kasei), it was melt-kneaded in a 50 mm single-screw extruder (20VSE-50-28 type, manufactured by Osaka Seiki Co., Ltd.) The obtained melt-kneaded resin was extruded into a strand from a circular die, cooled with water, and cut with a pelletizer 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, 1.0 part by weight of tertiary calcium phosphate as a dispersing agent, and 0.05 part by weight of sodium alkyl sulfonate as a dispersing aid were charged into a pressure-resistant autoclave having a capacity of 10 L. Under stirring, 6.25 parts by weight of carbon dioxide gas was added as a foaming agent. The temperature of the autoclave was raised and heated to a foaming temperature of 146.4 ° C., and then carbon dioxide was added to make the autoclave internal pressure 3.0 MPa (gauge pressure). Thereafter, after holding for 30 minutes, the valve at the lower part of the autoclave was opened, and the autoclave contents were discharged under atmospheric pressure through an opening orifice of 4.0 mmφ to obtain single-stage expanded pre-expanded particles. The resulting single-stage expanded pre-expanded particles had an expansion ratio of 15 times and a DSC ratio of the melting point peak of 20%. An internal pressure of 0.32 MPa was applied to the obtained one-stage expanded pre-expanded particles by air impregnation and heated with 0.11 MPa (gauge pressure) steam to obtain expanded particles having an expansion ratio of about 30 times. The results are shown in Table 1.

The obtained polypropylene resin pre-expanded particles were washed with an aqueous hydrochloric acid solution having a pH of 1, and then dried at 75 ° C., and using a polyolefin foam molding machine KD-345 manufactured by Daisen Corporation, the length was 300 mm × width 400 mm × thickness 21 mm. Is filled with polypropylene resin pre-expanded particles adjusted in advance so that the air pressure inside the polypropylene resin pre-expanded particles is 0.20 MPa, and compressed by 5% in the thickness direction and heat-molded, A polypropylene resin molded in-mold foam was obtained. The obtained foamed polypropylene resin mold was subjected to a fusion rate evaluation, and a molding heating vapor pressure at which the fusion rate reached 60% or more was determined. Further, the obtained polypropylene resin-in-mold foam-molded product was allowed to stand at room temperature for 1 hour, then cured and dried in a thermostatic chamber at 75 ° C. for 3 hours, taken out again to room temperature, and then allowed to stand at room temperature for 1 hour. The surface state and the dimensional shrinkage rate of the in-mold foam molded product were evaluated. The results are shown in Table 1.

(Example 2)
In Example 1, an ethylene-propylene random copolymer having a melting point of 137 ° C., an MFR of 16.1, and a flexural modulus of 1053 MPa obtained by polymerizing a polypropylene resin with a metallocene polymerization catalyst was used except that the conditions described in Table 1 were used. In the same manner as in No. 1, a polypropylene resin pre-expanded particle and a polypropylene resin in-mold expanded molding were obtained. The results are shown in Table 1.

(Example 3)
In Example 1, an ethylene-propylene random copolymer having a melting point of 133 ° C., an MFR of 18.0, and a flexural modulus of 950 MPa obtained by polymerizing a polypropylene resin with a metallocene polymerization catalyst was used except that the conditions described in Table 1 were used. In the same manner as in No. 1, a polypropylene resin pre-expanded particle and a polypropylene resin in-mold expanded molding were obtained. The results are shown in Table 1.

(Comparative Example 1)
In Example 1, an ethylene-propylene random copolymer having a melting point of 153 ° C., an MFR of 6.0, and a flexural modulus of 1350 MPa obtained by polymerizing a polypropylene resin with a Ziegler polymerization catalyst was used, except that the conditions described in Table 1 were used. In the same manner as in No. 1, a polypropylene resin pre-expanded particle and a polypropylene resin in-mold expanded molding were obtained. The results are shown in Table 1.

(Comparative Example 2)
In Example 1, an ethylene-propylene-butene random copolymer having a melting point of 145 ° C., an MFR of 6.0, and a flexural modulus of 1050 MPa obtained by polymerizing a polypropylene resin with a Ziegler polymerization catalyst, except for the conditions shown in Table 1, In the same manner as in Example 1, polypropylene resin pre-expanded particles and a polypropylene resin in-mold foam molded article were obtained. The results are shown in Table 1.

(Comparative Example 3)
In Example 1, an ethylene-propylene random copolymer having a melting point of 142 ° C., an MFR of 6.2, and a flexural modulus of 860 MPa obtained by polymerizing a polypropylene resin with a Ziegler polymerization catalyst was used, except that the conditions described in Table 1 were used. In the same manner as in No. 1, a polypropylene resin pre-expanded particle and a polypropylene resin in-mold expanded molding were obtained. The results are shown in Table 1.

  In the examples, polypropylene resins that can be molded at a lower molding heating steam pressure and superior in surface properties and dimensional shrinkage compared to the case of using the resins having the same flexural modulus shown in the comparative examples. An in-mold foam molded product was obtained.

It is an example of a DSC curve obtained when a differential scanning calorimeter is used to measure polypropylene resin pre-expanded particles according to the present invention. The horizontal axis is the temperature, and the vertical axis is the endothermic amount. The peak on the low temperature side is Ql, and the peak on the high temperature side is Qh.

Claims (4)

A polypropylene resin pre-expanded particle comprising a polypropylene resin polymerized with a metallocene polymerization catalyst as a base resin, wherein the polypropylene resin has the following requirements (a) to (c): -Based resin pre-expanded particles.
(A) The structural unit consisting of propylene is 90 to 100 mol%, and the structural unit consisting of ethylene and / or an α-olefin having 4 or more carbon atoms is present in an amount of 0 to 10 mol%.
(B) The total amount of position irregular units based on 2,1-insertion and 1,3-insertion of propylene monomer units in all polypropylene insertions, as measured by ¹³ C-NMR, is less than 0.5 mol%. .
(C) The melt flow rate is 0.5 g / 10 min or more and 100 g / 10 min or less.   In the measurement by the differential scanning calorimetry method, it has two melting peaks, the ratio Qh / (Ql + Qh) × 100 of the melting peak on the high temperature side calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side. The polypropylene resin pre-expanded particles according to claim 1, wherein the ratio is 10% or more and 50% or less.   3. The polypropylene resin pre-expanded particles according to claim 1, wherein the amount of the inorganic dispersant adhering to the surface is 2000 ppm or less. A polypropylene resin in-mold foam-molded article having a density of 10 kg / m ³ or more and 300 kg / m ³ or less, obtained using the polypropylene resin pre-expanded particles according to claim 1.

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