JP2009280783A - Pre-expanded particle of polypropylene-based resin, and in-mold expansion molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide pre-expanded particles of a polypropylene-based resin, with which an in-mold expansion molded product is produced with low heating steam pressure, and the in-mold expansion molded product having a small coefficient of contraction and high surface neatness is obtained in molding the pre-expanded particles of a polypropylene-based resin with in-mold expansion. <P>SOLUTION: The pre-expanded particles of a polypropylene-based resin comprise a polypropylene-based resin as a main resin material, which has a melt flow rate of 4 to 20g/10 min, a melting point of 144°C or lower, and a flexural modulus of elasticity of 600 MPa or more wherein the melting point and the flexural modulus of elasticity satisfy equation (1): [flexural modulus of elasticity (MPa)]≥31.19×[melting point (°C)]-3,500. <P>COPYRIGHT: (C)2010,JPO&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 in-mold foam molded articles obtained using the pre-expanded particles. Is.

  The in-mold foam molded article obtained by using the polypropylene resin pre-expanded particles has characteristics such as shape flexibility, light weight, and heat insulation, which are advantages of the in-mold foam molded article. 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 characteristics, in-mold foam molded articles obtained using polypropylene resin pre-expanded particles are used in various applications such as automotive interior members, automotive bumper core materials, heat insulating materials, and cushioning packaging materials. .

  Important properties required for an in-mold foam molded article obtained using polypropylene resin foamed particles include fusion between pre-foamed particles, surface aesthetics, and shrinkage recovery.

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

  The beauty of the surface means that the surface of the in-mold foam molded product is smooth. The decrease in surface aesthetics is considered to be caused by indentations formed in the groove portions between the pre-foamed particles on the surface of the in-mold foam molded body and shrinkage of the in-mold foam molded body, which is considered to be caused by insufficient foaming of the pre-foamed particles. Caused by a streak groove.

  In-mold foam molded articles obtained using polypropylene resin expanded particles usually shrink after being molded and removed from the mold, causing warping and deformation. The shrinkage and deformation of the in-mold foam-molded product can be recovered by a so-called curing process in which the in-mold foam-molded product is held in a heated atmosphere for a certain time. Even after curing, the in-mold foam molding is difficult to recover to the size of the mold, but when the dimensional shrinkage rate of the in-mold foam molding after curing is small compared to the mold, it is said that the shrink recovery property is excellent. ing.

  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. The polypropylene-based resin pre-expanded particles used for in-mold foam molding use a resin having such a characteristic as to be compatible with this, and generally, ethylene-random polypropylene having a melting point of about 140 to 150 ° C. is used. However, due to the recent rise in fuel prices and the like, there is a long-awaited measure for further reducing the molding heating steam pressure.

  As a method of lowering the molding heating vapor 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 in order to achieve high rigidity, the melting point of the resin will be high, so that the molding heating vapor 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 moldings whose appearance is 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 of pre-expanded particles 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 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.

Various techniques have been studied for improving the rigidity of the in-mold foam molded body. In order to obtain high rigidity with a polypropylene resin, it is conceivable to simply use homopolypropylene. For example, Patent Document 1 discloses a DSC obtained by a differential scanning calorimeter with a tensile elastic modulus of 15,000 to 25000 kg / cm ^2. The technique regarding the homopolypropylene-type resin pre-expanded particle | grains whose calorie | heat amount of the high temperature side peak of a curve is 30-60 J / g is disclosed. Further, Patent Document 2 uses a homopolypropylene having a melt flow rate in the range of 20 to 100 g / 10 min or a propylene-α-olefin random copolymer having an α-olefin content of less than 1% by weight, which is relatively low. A technique has been disclosed in which pre-expanded particles capable of obtaining an in-mold expanded molded body at a molding temperature can be produced.

However, in the technique described in Patent Document 1, it is described that the pressure of the heating steam at the time of molding necessary for obtaining a good in-mold foam molded product is 0.4 to 0.6 MPa, as described above. It cannot be molded by a molding machine with a 0.4 MPa pressure resistance specification. Moreover, there is no special description about the surface beauty of a molded object. Further, in the technique described in Patent Document 2, there is no particular description regarding the surface aesthetics and the shrinkage rate, and the minimum molding vapor pressure for achieving fusion of expanded particles of 60% or more is 3.1 kgf / cm ^2. It is hard to say that the molding vapor pressure is low.

Further, for example, Patent Document 3 discloses a resin having a melting point of 155 to 165 ° C., a ratio of Z average molecular weight to weight average molecular weight of 3 to 6, and a melt flow rate of 10 to 150 g / L. Although the technology using particles is disclosed, the main purpose of this document is that foamed particles for in-mold foam molding can be obtained without using the so-called docan method, and the resin melting point is 155 ° C. As can be seen from the above, the heating conditions for obtaining the in-mold foam molded product are extremely high conditions exceeding 4 kgf / cm ² .

  In Patent Document 4, a propylene random copolymer having a melting point of 149 to 157 ° C., an MFR of 1 to 20 g / 10 minutes, and a half-crystal time of a certain value or less is used as the base resin. Technology is disclosed.

  Patent Document 5 discloses a high-temperature-side crystal amount of a melting crystal curve obtained by using differential scanning calorimetry (hereinafter abbreviated as DSC) for the crystalline state of polypropylene resin pre-expanded particles used for in-mold foam molding. A technique for improving the compressive strength of the obtained in-mold foam molded article by setting the relationship between the low-temperature side crystal amount within a certain range is disclosed.

  However, regarding these techniques, the pressure of the heating steam required for in-mold foam molding is as high as 0.4 to 0.5 MPa, and in the same manner as the techniques described in Patent Documents 1 and 2, molding with particularly high pressure resistance is performed. This technology is made possible by using a machine.

  Furthermore, in Patent Document 6, when a polypropylene resin containing 1-butene as a comonomer is used, a resin having a high tensile elastic modulus, that is, a rigidity is obtained with respect to the resin melting point. By using this, a mold having a high rigidity is obtained. A technique is disclosed in which an inner foamed molded product can be obtained.

  However, with regard to this technique, the pressure of the heating steam required for in-mold foam molding is around 0.4 MPa, and although it is a relatively low molding heating steam pressure compared to other techniques, The lowest of these is 0.36 MPa, which is a level just below the specifications of a molding machine with a 0.4 MPa pressure resistance specification that is often used at present. Moreover, there is no special description regarding the surface aesthetics and shrinkage of the molded body.

  Furthermore, Patent Document 7 discloses a polypropylene having high rigidity by using polypropylene resin pre-expanded particles having a propylene / 1-butene random copolymer containing 3 to 12% by weight of 1-butene component as a base resin. A technique for obtaining a resin-based foamed molded article is disclosed. It is described that when this technique is used, molding can be performed even with a molding machine having a pressure resistance of 0.4 MPa, which is often used at present, with the pressure of the molding heating steam being around 0.3 MPa. However, looking at the examples described in the literature, those having a minimum molding pressure of about 0.3 MPa are exemplified, but further low-temperature moldability is desired, and the surface beauty of the in-mold foam molded product There is no special description about the shrinkage rate. In addition, propylene / 1-butene random copolymers that do not contain an ethylene component are hard and brittle compared to polypropylene resin random copolymers that contain an ethylene component, and this property is used as a base resin for in-mold foam molded articles. When used, it leads to the property that the dimensional recoverability after compression and the impact property in a low temperature region are inferior. Polypropylene resin foam molded products are superior to polystyrene resin foam molded products, which are the same in-mold foam molded products, in terms of rigidity, but have superior resistance to repeated impacts and flexibility. Some aspects are used for such purposes. For this reason, the technique described in this technology also has a drawback that it is not suitable for general buffer packaging applications other than applications intended only for rigidity.

  As described above, there is a current situation in which a special molding machine that can withstand a high heating steam pressure is used for an application that requires high rigidity. However, in order to increase the pressure resistance of the molding machine, it is necessary to increase the size of the machine in order to increase the strength of the molding machine, and it is also necessary to increase the thickness of the mold. is there.

  In addition, increasing the pressure of the molding heating steam increases the amount of steam necessary for heating during molding, which increases the utility cost, for example, increasing the amount of cooling water for cooling this. Furthermore, the heating time at the time of molding becomes longer in order to heat to a higher temperature, and more time is required for the process of cooling the heated mold with cooling water, so the production cycle per product becomes longer. Productivity deteriorates. Furthermore, since the mold shape is complicated in in-mold foam molding, depending on the shape, stress may concentrate on a part of the mold during molding heating, and the mold may be damaged, which further increases costs. .

  As described above, the high molding heating steam pressure in the in-mold foam molding has various drawbacks, and it is desirable that molding can be performed with the lowest possible molding heating steam pressure. In the category of existing technology, it is possible to stably produce with a molding machine of 0.4 MPa pressure resistance specification that is widely used at the present time, as well as molding with lower vapor pressure, excellent surface aesthetics and high It is difficult to obtain polypropylene resin pre-expanded particles for in-mold foam molding that have excellent dimensional shrinkage due to rigidity.

Furthermore, Patent Document 8 provides an in-mold foam molded article with excellent surface beauty and rigidity at a relatively low molding vapor pressure by defining the relationship between the resin melting point of the polypropylene resin pre-foamed particles and the heat of crystal melting. Although the method is disclosed, the minimum molding vapor pressure described in the examples is around 0.3 MPa, and further reduction of the vapor pressure is desired. Further, this document does not describe the shrinkage rate of the in-mold foam molded article.
JP-A-8-277340 Japanese Patent Laid-Open No. 10-45938 JP-A-10-306173 Japanese Patent Laid-Open No. 10-316791 JP-A-11-156879 JP 7-258455 A JP-A-1-242638 International Publication No. 2006/075491

  INDUSTRIAL APPLICABILITY The present invention can produce an in-mold foam molded article with a low heating vapor pressure, and the obtained in-mold foam molded article provides a polypropylene resin pre-foamed particle having a small shrinkage ratio and a high surface beauty. There is.

  As a result of diligent research in view of the above problems, by using polypropylene resin pre-expanded particles whose base resin is a polypropylene resin having a certain relationship between flexural modulus and melting point, thermoforming vapor pressure during molding is obtained. The present invention has been completed by finding that an in-mold foam-molded product having a significantly low shrinkage, a low shrinkage rate of the in-mold foam-molded product, and a high surface beauty can be obtained.

That is, according to the first aspect of the present invention, the melt flow rate is 4 g / 10 min or more and 20 g / 10 min or less, the melting point is 145 ° C. or less, the bending elastic modulus is 600 MPa or more, and the melting point and bending elastic modulus satisfy the following formula (1). The present invention relates to pre-expanded polypropylene resin particles characterized by using a polypropylene resin as a base resin.
[Flexural modulus (MPa)] ≧ 31.19 × [melting point (° C.)] − 3500 (1)
As a preferred embodiment,
[1] The polypropylene resin used as the base resin contains 1% by weight or more of 1-butene as a copolymerization component,
[2] The polypropylene resin used as the base resin is an ethylene-propylene-butene random copolymer,
[3] As measured by differential scanning calorimetry, the DSC curve obtained when the temperature is increased from 40 ° C. to 200 ° C. at a rate of 10 ° C./min has two melting peaks. The ratio of the melting peak on the high temperature side (Qh / (Ql + Qh) × 100 calculated from the melting peak calorific value (Ql) on the low temperature side and the melting peak heat value (Qh) on the high temperature side with a peak temperature of 140 ° C. or less. ) Is 10% or more and 50% or less,
[4] The amount of the inorganic dispersant adhering to the surface of the polypropylene resin pre-expanded particles is 1000 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 an 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-foamed particles described above.

  The pre-expanded polypropylene resin particles of the present invention can produce an in-mold expanded molded article having a small dimensional shrinkage and excellent surface aesthetics at a low thermoforming vapor pressure.

  Since the in-mold foam-molded article of the present invention has good dimensional system and surface appearance, it can be suitably used for buffer packaging materials, boxing, automobile members and the like.

The polypropylene resin pre-expanded particles of the present invention have a melt flow rate (hereinafter sometimes referred to as MFR) of 4 g / 10 min or more and 20 g / 10 min or less, a melting point of 145 ° C. or less, and a flexural modulus of 600 MPa or more, A polypropylene resin that has a melting point and a flexural modulus satisfying the following formula (1) is used as a base resin.
[Flexural modulus (MPa)] ≧ 31.19 × [melting point (° C.)] − 3500 (1)

The polypropylene resin of the present invention is a resin mainly composed of propylene as a monomer and may be propylene alone or may contain other copolymerization components. Examples of copolymer components include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1- Α-olefin having 2 or 4 to 12 carbon atoms such as heptene, 3-methyl-1-hexene, 1-octene, 1-decene, cyclopentene, norbornene, tetracyclo [6,2,1 ^1,8 , 1 ^3,6 ] Cyclic olefins such as 4-dodecene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, etc. Diene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyric acid butyl , Methyl methacrylate, maleic anhydride, styrene, methylstyrene vinyltoluene, and vinyl monomers such as divinylbenzene. Among these, it is preferable to use ethylene and 1-butene from the viewpoint of improving cold brittleness resistance and low cost.

  The polypropylene resin used as the base resin of the present invention preferably contains 1% by weight or more of 1-butene as a copolymer component, more preferably 2% by weight or more, and most preferably 3% by weight or more. When 1-butene is contained as a copolymerization component, a polypropylene resin in-mold foam molded article having high crystallinity with respect to the resin melting point and high flexural modulus is easily obtained.

  Furthermore, the polypropylene resin used as the base resin of the present invention is preferably an ethylene-propylene-butene random copolymer. In this case, the ethylene content is preferably 0.5% by weight or more, and 1.0 % By weight or more is more preferable, and 1.5% by weight or more is more preferable. By including ethylene as a comonomer, the melting point of the base resin tends to be lowered at a relatively low cost.

  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 low density polyethylene, polystyrene, polybutene, ionomer, etc. are mixed and used within the range that does not lose the properties of polypropylene resin. Also good.

  The polypropylene resin of the present invention has an MFR of 4 g / 10 min to 20 g / 10 min, preferably 5 g / 10 min to 15 g / 10 min. In the present invention, MFR is measured using an MFR measuring instrument described in JIS K 7210, 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 the value when measured below. When the MFR is in the above range, it is easy to obtain a pre-expanded polypropylene resin particle having a relatively large expansion ratio, and when it is subjected to in-mold foam molding, the mold has excellent surface beauty and small dimensional shrinkage. An inner foamed molded product is obtained.

  The polypropylene resin of the present invention has a melting point of 145 ° C. or lower, preferably 142 ° C. or lower. The melting point here refers to melting a resin particle by heating a sample 5-6 mg from 40 ° C. to 220 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter, and then 10 ° C./min. At a melting peak temperature in the DSC curve obtained at the second temperature increase when the temperature is further increased from 40 ° C. to 220 ° C. at a rate of 10 ° C./min. is there. When the melting point is higher than 145 ° C., molding cannot be performed with a significantly low vapor pressure.

  Further, the flexural modulus of the polypropylene resin of the present invention is 600 MPa or more, preferably 650 MPa or more, and more preferably 700 MPa. When the flexural modulus is less than 600 MPa, the dimensional shrinkage rate of the in-mold foam molded product increases. In the present invention, the flexural modulus is measured according to ASTM D790.

Furthermore, the polypropylene resin of the present invention satisfies the following formula (1) between the flexural modulus and the melting point.
[Flexural modulus (MPa)] ≧ 31.19 × [melting point (° C.)] − 3500 (1)

  When the polypropylene resin is in the range of the above formula (1), the bending elastic modulus is relatively high with respect to the melting point, the rigidity of the obtained in-mold foam molded article is high, and the dimensional shrinkage rate is small, and the melting points are compared. Therefore, molding with a low heating vapor pressure is also possible.

  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. In such a desired particle shape, the resin is molded into polypropylene resin particles having an average particle size of preferably 0.1 to 5 mm, more preferably 0.5 to 3 mm.

  In the present invention, in addition to the polypropylene resin, an antistatic agent, a pigment, a flame retardant improving material, a conductivity improving material and the like may be added as necessary. It is preferable to add to the molten resin.

  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, The mixture in the container is preferably heated to a temperature in the range of -20 ° C to + 10 ° C in the melting point of the polypropylene resin particles and impregnated with the foaming agent, and the temperature and pressure in the container are kept constant. Polypropylene resin pre-expanded particles can be produced by releasing a mixture of polypropylene resin particles and water under pressure under a lower pressure atmosphere than in the container.

  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 alicyclic carbonization such as cyclopentane and cyclobutane. Hydrogen; inorganic gases such as air, nitrogen, carbon dioxide; water, etc. These foaming agents may be used alone or in combination of two or more. Preferably, carbon dioxide, water, or isobutane that enables foaming at a higher magnification.

  The amount used is not limited, and may be appropriately used according to the desired expansion ratio of the polypropylene resin pre-expanded particles. The amount of the foaming agent used is usually 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 dispersant and dispersion aid used varies depending on the type and the type and amount of polypropylene resin used, but usually 0.2 parts by weight to 3 parts by weight of dispersant with respect to 100 parts by weight of water, The dispersion aid is preferably 0.001 part by weight or more and 0.1 part by weight or less. Moreover, in order to make the polypropylene resin particles have good dispersibility in water, it is usually preferable to use 20 to 100 parts by weight with respect to 100 parts by weight of water.

  In order to produce the polypropylene resin pre-expanded particles of the present invention, it is preferable to add a cell nucleating agent to the base resin. When a hydrocarbon foaming agent such as propane, butane, pentane or hexane is used as the cell nucleating agent, an inorganic nucleating agent such as talc, silica or calcium carbonate is added to 100 parts by weight of the polypropylene resin. It is preferable to add 0.005 parts by weight or more and 0.5 parts by weight or less. Moreover, when using inorganic foaming agents, such as air, nitrogen, a carbon dioxide gas, and water, it is preferable to use the said inorganic nucleating agent and / or a water absorbing substance. When water is used as a dispersion medium, water is impregnated into the polypropylene resin, and the impregnated water acts as a foaming agent together with other foaming agents or alone. The water-absorbing substance acts to increase the amount of impregnated water.

  Specific examples of water-absorbing substances include water-soluble inorganic substances such as sodium chloride, calcium chloride, magnesium chloride, borax and zinc borate, water-absorbing organic substances such as melamine, isocyanuric acid, melamine / isocyanuric acid condensate, polyethylene glycol, polyethylene oxide and the like. Polyethers, addition products of polyethers to polypropylene, and alloys thereof, alkali metal salts of ethylene (meth) acrylic acid copolymers, alkali metal salts of butadiene (meth) acrylic acid copolymers, carboxylated nitrile rubber Examples thereof include hydrophilic polymers such as alkali metal salts, alkali metal salts of isobutylene-maleic anhydride copolymer and alkali metal salts of poly (meth) acrylic acid.

  The amount of water-absorbing substance added varies depending on the target foaming ratio, the foaming agent used, and the type of water-absorbing substance used, but when using a water-soluble inorganic substance, 0.01 wt. The amount is preferably not less than 1 part by weight and not more than 1 part by weight. When a hydrophilic polymer is used, it is preferably not less than 0.1 part by weight and not more than 5 parts by weight with respect to 100 parts by weight of the polypropylene resin. Two or more of these water-soluble inorganic substances and hydrophilic polymers may be used in combination. The average cell diameter of the polypropylene resin foamed particles can be adjusted by adjusting the kind and amount of the inorganic nucleating agent and the water-absorbing substance.

  In the polypropylene resin pre-expanded particles of the present invention, the amount of the inorganic dispersant adhering to the surface of the polypropylene resin pre-expanded particles is preferably 1000 ppm or less, more preferably 800 ppm or less, and most preferably 600 ppm or less. If it is in the said range, since the melt | fusion property of polypropylene resin pre-expanded particles is not inhibited in the case of in-mold foam molding, it is preferable.

  When the amount of the inorganic dispersant adhering to the surface of the polypropylene resin pre-expanded particles obtained by the above production method is more than 1000 ppm, the amount of the adhering inorganic dispersant can be reduced by washing the pre-expanded particles. For example, when tricalcium phosphate or tribasic magnesium phosphate is used as the dispersant, a method of washing the pre-foamed particles with a hydrochloric acid aqueous solution, a sodium hexametaphosphate aqueous solution or the like can be mentioned.

  The amount of the adhering inorganic dispersant can be determined from various spectroscopic analyzes or from the amount of ash when the polypropylene resin pre-expanded particles are 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.

  The average cell diameter of the polypropylene resin pre-expanded particles of the present invention is preferably 100 μm or more, and more preferably 120 μm or more. If the average cell diameter is less than 100 μm, the shrinkage rate of the in-mold foam molded product may increase or the surface aesthetics may deteriorate.

  As shown in FIG. 1, the pre-expanded particles of the polypropylene resin of the present invention have two DSC curves obtained when the temperature is raised from 40 ° C. to 200 ° C. at a rate of 10 ° C./min as measured by a differential scanning calorimetry method. It is preferable to have a melting peak, and the peak temperature on the low temperature side of the melting peak is preferably 140 ° C. or lower. More preferably, it is 137 degrees C or less, and 135 degrees C or less is still more preferable. When the peak temperature on the low temperature side is higher than 140 ° C., molding may not be possible at a significantly low vapor pressure.

  Further, the low temperature side peak of the DSC curve, the low temperature side melting peak calorie (Ql), 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 DSC Melting 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 high temperature side peak of the curve and the maximum point between the low temperature side peak and the high temperature side peak The peak ratio (Qh / (Ql + Qh) × 100 (hereinafter abbreviated as DSC ratio)) is preferably 10% or more and 50% or less, and more preferably 15% or more and 40% or less. When the DSC ratio is within the above range, an in-mold foam molded product having a high surface beauty is easily obtained.

  The expansion ratio of the polypropylene resin pre-expanded particles of the present invention is preferably 5 to 50 times, and more preferably 7 to 45 times. Further, a polypropylene resin pre-expanded particle (sometimes referred to as a single-stage expanded particle) of 5 to 35 times is manufactured by the above-described method (sometimes referred to as a single-stage expansion), and the single-stage expanded particle is sealed in a pressure-resistant sealed container. After the pressure in the one-stage expanded particles is made higher than the normal pressure by pressurizing and impregnating with nitrogen, air, etc. at 0.1 to 0.6 MPa, the expanded particles are further heated with steam or the like. By foaming, pre-expanded polypropylene resin particles (hereinafter sometimes referred to as “two-stage expanded particles”) having an expansion ratio equal to or higher than the first-stage expanded particles may be obtained.

Here, the expansion ratio of the 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 / cm ³ ) of the polypropylene resin particles before expansion. From the following equation.
Foaming ratio = d × v / w

  The polypropylene resin pre-expanded particles of the present invention are subjected to in-mold foam molding to obtain an in-mold foam molded body. When used for in-mold foam molding, a) a method for use as it is, b) a method in which an inorganic gas such as air is press-fitted into the pre-foamed particles in advance to impart foaming capability, and c) the pre-foamed particles are gold in a compressed state. A conventionally known method such as a method of filling in a mold and molding can be used.

  As a method for molding an in-mold foam molded body from the polypropylene resin pre-foamed particles of the present invention, for example, the pre-foamed particles are preliminarily air-pressurized in a pressure-resistant container, and air is injected into the particles to give foaming ability. In a mold that can be closed but cannot be sealed, steam or the like is used as a heating medium with a heating steam pressure of about 0.1 to 0.4 MPa (gauge pressure) in a heating time of about 3 to 30 seconds. Molding and pre-expanding the polypropylene resin pre-expanded particles, and then cooling the mold to a level that can prevent deformation of the in-mold foam molding after taking out the in-mold foam molding by water cooling, and then opening the mold And a method for obtaining an in-mold foam molded article.

  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.

The density of the in-mold foam molded body obtained using the above pre-expanded particles 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.

  The propylene resins used in the examples and comparative examples are shown in Table 1 and FIG.

〔融点の測定〕
セイコーインスツルメンツ（株）製のＤＳＣ６２００型示差走査熱量計を用いて、ポリプロピレン系樹脂粒子５〜６ｍｇを１０℃／ｍｉｎの昇温速度で４０℃から２２０℃まで昇温する事により樹脂粒子を融解し、その後１０℃／ｍｉｎで２２０℃から４０℃まで降温することにより結晶化させた後に、さらに１０℃／ｍｉｎで４０℃から２２０℃まで昇温したときに得られるＤＳＣ曲線から、２回目の昇温時の融解ピーク温度を融点として求めた。

[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.

[Flexural modulus of polypropylene resin]
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.

[Expansion ratio of pre-expanded 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

[Fusability evaluation]
The obtained polypropylene resin molded foam-molded product was cut with a cutter knife in the thickness direction of the foam-molded product by about 3 mm, and then the foam-molded product was broken by hand from the cut portion, and the fracture surface was observed. The ratio of the expanded foam particles to the number of the expanded particles constituting the fractured surface was determined, and the following determination was made.
60% or more
Less than 60% ... ×

[Surface property evaluation]
The surface of the obtained polypropylene resin foam molded article 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 judgment.
Less than 100 ... ○
More than 100 ... ×

[Dimensional shrinkage]
The longitudinal dimension of the obtained polypropylene resin foam molded article was measured, and the shrinkage rate with respect to the mold dimension (400 mm) was calculated, and the following determination was made.
Less than 5% ... ○
5% or more ×

[Measurement of amount of adhering dispersant (when the dispersant is magnesium 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 into 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 tribasic magnesium phosphate adhering C (ppm) = 4 using the absorbance coefficient ε (g / L · cm) of tribasic magnesium phosphate at 410 nm measured in advance. 7 × 10 ⁴ · ε · A / W was determined.

Example 1
100 parts by weight of an ethylene-propylene-butene random copolymer (A-1) having a melting point of 140.8 ° C. and a flexural modulus of 953 MPa is used as a polypropylene resin, and polyethylene glycol (PEG manufactured by Lion Corporation) is used as a cell nucleating agent. # 300) After blending 0.5 part by weight and 0.1 part by weight of talc (PKS made by Hayashi Kasei), melt kneading in a 50 mm single screw extruder (20VSE-50-28 type, manufactured by Osaka Seiki Co., Ltd.) did. 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.

  In a pressure-resistant autoclave having a capacity of 10 L, 100 parts by weight of the obtained polypropylene resin particles, 200 parts by weight of water, 1.0 part by weight of tertiary magnesium phosphate as a dispersant, and 0.05 parts by weight of sodium alkylsulfonate as a dispersion aid. Then, 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). Then, after holding for 30 minutes, the valve | bulb of the autoclave lower part was opened, the autoclave content was discharge | released under atmospheric pressure through the 4.0 mm diameter opening orifice, and the 1st stage | paragraph expanded particle was obtained. The resulting single-stage expanded particles had an expansion ratio of 17 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 particles by air impregnation, and heated with 0.11 MPa (gauge pressure) steam to obtain expanded particles with an expansion ratio of about 30 times. The results are shown in Table 2.

  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 pre-expanded particles becomes 0.20 MPa, and 0.20 and 0.25 MPa (gauge pressure) water vapor is used in the thickness direction. A polypropylene resin foamed molded article was obtained by compression molding at 5% and thermoforming. The obtained foamed 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, and the fusion between particles and the mold. The surface state and dimensional shrinkage of the inner foamed molded product were evaluated. The results are shown in Table 2.

（実施例２）
実施例１において、基材樹脂として融点１３８．５℃、曲げ弾性率８７３ＭＰａのエチレン−プロピレン−ブテンランダム共重合体（Ａ−２）とし、表２記載の条件とした以外は、実施例１と同様にして、ポリプロピレン系樹脂予備発泡粒子を得、型内発泡成形体を得た。結果を表２に示す。

(Example 2)
In Example 1, except that the base resin was an ethylene-propylene-butene random copolymer (A-2) having a melting point of 138.5 ° C. and a flexural modulus of 873 MPa, and the conditions described in Table 2 were used, Similarly, a polypropylene resin pre-expanded particle was obtained, and an in-mold expanded molded body was obtained. The results are shown in Table 2.

(Example 3)
In Example 1, except that the base resin is an ethylene-propylene-butene random copolymer (A-3) having a melting point of 143.0 ° C. and a flexural modulus of 1025 MPa, and the conditions described in Table 2 are used, Similarly, a polypropylene resin pre-expanded particle was obtained, and an in-mold expanded molded body was obtained. The results are shown in Table 2.

Example 4
In Example 1, except that the base resin was an ethylene-propylene-butene random copolymer (A-4) having a melting point of 139.7 ° C. and a flexural modulus of 911 MPa, and the conditions described in Table 2 were used, Similarly, a polypropylene resin pre-expanded particle was obtained, and an in-mold expanded molded body was obtained. The results are shown in Table 2.

(Example 5)
In Example 1, except that the base resin was an ethylene-propylene-butene random copolymer (A-5) having a melting point of 141.6 ° C. and a flexural modulus of 987 MPa, and the conditions described in Table 2 were used, Similarly, a polypropylene resin pre-expanded particle was obtained, and an in-mold expanded molded body was obtained. The results are shown in Table 2.

(Example 6)
In Example 1, the base resin was an ethylene-propylene-butene random copolymer (A-6) having a melting point of 132.0 ° C. and a flexural modulus of 684 MPa, and the conditions described in Table 2 were used. Similarly, a polypropylene resin pre-expanded particle was obtained, and an in-mold expanded molded body was obtained. The results are shown in Table 2.

(Comparative Example 1)
In Example 1, as the base resin, an ethylene-propylene-butene random copolymer (A-7) having a melting point of 145.1 ° C. and a flexural modulus of 1128 MPa was used, and the conditions described in Table 2 were used. Similarly, a polypropylene resin pre-expanded particle was obtained, and an in-mold expanded molded body was obtained. The results are shown in Table 3.

（比較例２）
実施例１において、基材樹脂として融点１３６．１℃、曲げ弾性率６７９ＭＰａのエチレン−プロピレンランダム共重合体（Ａ−８）とし、表２記載の条件とした以外は、実施例１と同様にして、ポリプロピレン系樹脂予備発泡粒子を得、型内発泡成形体を得た。結果を表３に示す。

(Comparative Example 2)
In Example 1, except that the base resin was an ethylene-propylene random copolymer (A-8) having a melting point of 136.1 ° C. and a flexural modulus of 679 MPa, and the conditions described in Table 2 were used, the same as in Example 1. As a result, pre-expanded polypropylene resin particles were obtained, and an in-mold foam molded article was obtained. The results are shown in Table 3.

(Comparative Example 3)
In Example 1, an ethylene-propylene random copolymer (A-9) having a melting point of 142.0 ° C. and a flexural modulus of 860 MPa was used as the base resin, and the same conditions as in Table 2 were used except that the conditions shown in Table 2 were used. As a result, pre-expanded polypropylene resin particles were obtained, and an in-mold foam molded article was obtained. The results are shown in Table 3.

  In the examples, moldings having a low molding vapor pressure of 0.20 MPa (gauge pressure) were obtained, and a molded article excellent in fusion property, surface property, and dimensional shrinkage ratio was obtained. In Comparative Examples 1, 2, and 3, the polypropylene resin is out of the scope of the present invention, and molding at 0.25 MPa (gauge pressure) is difficult, and even when molded, the dimensional shrinkage ratio is large. It was.

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. About the Example evaluated and the comparative example, taking a resin melting | fusing point on a horizontal axis | shaft and a bending elastic modulus on the vertical axis | shaft, it graphed. The upper left part surrounded by two straight lines is the range of the melting point and bending elastic modulus of the base resin of the present invention. All examples are within this range. Comparative examples are outside this range.

Claims (6)

The base resin is a polypropylene resin having a melt flow rate of 4 g / 10 min or more and 20 g / 10 min or less, a melting point of 145 ° C. or less, a flexural modulus of 600 MPa or more, and a melting point and flexural modulus satisfying the following formula (1). Polypropylene resin pre-expanded particles characterized in that.
[Flexural modulus (MPa)] ≧ 31.19 × [melting point (° C.)] − 3500 (1)   The polypropylene resin pre-expanded particles according to claim 1, wherein the polypropylene resin used as the base resin contains 1% by weight or more of 1-butene as a copolymer component.   The polypropylene resin pre-expanded particles according to claim 1 or 2, wherein the polypropylene resin used as the base resin is an ethylene-propylene-butene random copolymer.   The DSC curve obtained when the temperature is increased from 40 ° C. to 200 ° C. at a rate of 10 ° C./min, as measured by differential scanning calorimetry, has a peak temperature on the low temperature side of the melting peak. 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 is 10 ° C. or lower. The polypropylene-based resin pre-expanded particles according to any one of claims 1 to 3, wherein the proportion is not less than 50% and not more than 50%.   The polypropylene resin pre-expanded particles according to any one of claims 1 to 4, wherein the amount of the inorganic dispersant adhering to the surface of the polypropylene resin pre-expanded particles is 1000 ppm or less. An 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-foamed particles according to claim 1.

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