JP2009221259A - Method for producing expanded polypropylene resin particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing expanded polypropylene resin particles which can give an in-mold expanded molding of a low shrinkage, and in particular to provide a method for producing expanded polypropylene resin particles which can give a low-shrinkage in-mold expanded molding even at an expansion ratio as high as above 30 times. <P>SOLUTION: Provided is a method for producing expanded polypropylene resin particles comprising further expanding expanded polypropylene resin particles obtained from a polypropylene resin having a weight-average molecular weight (Mw) of 100,000 or higher in terms of polystyrene and a melt flow rate (MFR) of 1 g/10 min or higher and satisfying the following formula (1): MFR (g/10 min)≤16-2.5×10<SP>-5</SP>Mw (wherein Mw is the weight-average molecular weight of the polypropylene resin in terms of polystyrene). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing expanded polypropylene resin particles. In detail, it is related with the manufacturing method of the polypropylene-type resin expanded particle which can be used as a raw material of an in-mold foaming molding.

  An in-mold foam molded product obtained by filling polypropylene resin foam particles in a mold and heat-molding with water vapor or the like is an advantage of the in-mold foam molded product, such as arbitrary shape, lightness, heat insulation, etc. Has characteristics. This in-mold foam molded article is superior in chemical resistance, heat resistance, and strain recovery rate after compression, compared to the in-mold foam molded article obtained using polystyrene resin foam particles. In addition, the dimensional accuracy, heat resistance, and compressive strength are superior to the in-mold foam molded article using polyethylene resin expanded particles. Due to these characteristics, in-mold foam molded articles obtained using polypropylene resin foam particles are used in various applications such as heat insulating materials, shock-absorbing packaging materials, automobile interior members, and automobile bumper core materials.

  Polypropylene resin foamed particles are obtained by dispersing polypropylene resin particles in water in a pressure-resistant container, adding a foaming agent, and maintaining the temperature at a constant temperature near the melting point of the polypropylene resin under high pressure and impregnating the foaming agent. It can be produced by a method of releasing in a low pressure atmosphere. This method is called a decompression foaming method or an autoclave method.

  However, particularly when carbon dioxide having high safety is used as a foaming agent, a high carbon dioxide pressure is required to produce polypropylene resin expanded particles having a high expansion ratio of 20 times or more by the decompression foaming method. To do. In addition, the foamed particles obtained have a small cell diameter and closed cell ratio, which causes the properties of the molded product to deteriorate. For this reason, there has been proposed a method (two-stage foaming method) in which expanded particles having a low expansion ratio are once manufactured, and the expanded particles are heated to produce expanded particles having a high expansion ratio (Patent Document 1). .

  On the other hand, in-mold foam molded articles obtained using polypropylene resin foam particles usually shrink after being molded and removed from the mold. The contracted molded body recovers in size over time, but does not recover to the mold size. In particular, a molded article having a high expansion ratio causes a large shrinkage because the cell membrane is thin. Therefore, a so-called curing process is required in which the molded body is held in a warm atmosphere for a certain period of time. Therefore, in order to shorten the curing time, there is a demand for expanded particles that can produce an in-mold expanded molded article having a small shrinkage rate.

In Patent Document 1, when producing expanded particles having a high expansion ratio by the two-stage expansion method, when the expansion ratio is E and the number of bubbles per 1 mm ² is n, 2 <E ^1/3 × n ^1/2 <45 It is described that when the expanded particles having the above relationship are used as raw material expanded particles (first-stage expanded particles), it is possible to produce two-stage expanded particles that give a molded article having a small shrinkage rate.

In Patent Document 2, the melt flow rate is 0.5 to 6 g / 10 min, the Z average molecular weight (Mz) is 1,200,000 or more, and the endothermic energy resulting from the secondary crystal obtained by differential scanning calorimetry is 1 to 20 J / It is disclosed that a foamed particle obtained by two-stage foaming using a polypropylene resin characterized by g can be obtained, and using this foamed particle, a molded article having a small shrinkage rate can be obtained. Yes.
JP 59-133233 A JP 2000-198872 A

  The subject of the present invention is a technique different from Patent Documents 1 and 2 that can produce an in-mold foam molded article having a small shrinkage rate even if the polypropylene resin foamed particles are obtained by multistage foaming such as two-stage foaming. The present invention provides a novel method for producing expanded polypropylene resin particles.

The inventor has a specific polystyrene-equivalent weight average molecular weight (hereinafter sometimes referred to as Mw) and melt flow rate (hereinafter sometimes referred to as MFR, the unit is g / 10 minutes) as a raw material of the expanded particles. It has been found that the above-mentioned problems can be solved by using a polypropylene-based resin having the following. That is, the present invention is a method for producing the following expanded polypropylene resin particles and an in-mold expanded molded article using the expanded particles obtained.
(1) Polypropylene obtained from a polypropylene resin having a polystyrene-equivalent weight average molecular weight (Mw) of 100,000 or more, a melt flow rate (MFR) of 1 g / 10 min or more and satisfying the following formula (1) A foamed polypropylene resin expanded particle is further produced by foaming the expanded polypropylene resin particle.
MFR (g / 10 min) ≦ 16−2.5 × 10 ⁻⁵ Mw (1)
In the formula, MFR represents the melt flow rate of the polypropylene resin, and Mw represents the polystyrene equivalent weight average molecular weight of the polypropylene resin.
(2) The method for producing expanded polypropylene resin particles according to (1), wherein the melt flow rate (MFR) of the polypropylene resin further satisfies the following formula (2).
MFR (g / 10 min) ≧ 9.5-2.5 × 10 ⁻⁵ Mw (2)
(3) The polypropylene resin foam according to any one of (1) to (2), wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polypropylene resin is 4.5 or less. Particle manufacturing method.
(4) The method for producing expanded polypropylene resin particles according to (3), wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polypropylene resin is 4 or less.
(5) The method for producing expanded polypropylene resin particles according to any one of (1) to (4), wherein the Z-average molecular weight (Mz) of the polypropylene resin is 1.1 million or less.
(6) The method for producing expanded polypropylene resin particles according to any one of (1) to (5), wherein the polypropylene resin is a resin containing a copolymer component based on ethylene.
(7) The method for producing expanded polypropylene resin particles according to (6), wherein the polypropylene resin is a resin containing 1 to 10% by weight of a copolymer component based on ethylene.
(8) The method for producing expanded polypropylene resin particles according to any one of (1) to (7), wherein the polypropylene resin is a resin containing 3.5 to 6% by weight of ethylene as a copolymer component.
(9) The method for producing expanded polypropylene resin particles according to any one of (1) to (8), wherein the polypropylene resin is a resin subjected to degradation treatment with an organic peroxide.
(10) An in-mold foam molded article having an expansion ratio of 30 to 60 times, obtained by molding the polypropylene resin expanded particles obtained by the production method according to any one of (1) to (9).
(11) The in-mold foam molded product according to (10), wherein the expansion ratio is 35 to 50 times.

  When the polypropylene resin expanded particles obtained by the production method of the present invention are used, an in-mold expanded molded article having a high expansion ratio and a small shrinkage can be obtained.

The polypropylene resin used in the present invention preferably contains ethylene as a copolymerization component. When ethylene is contained, expanded particles and in-mold expanded molded articles can be easily obtained. Preferred ethylene content is 1 to 10% by weight, further 1 to 7% by weight, further 2 to 7% by weight, further 3 to 7% by weight, further 3.5 to 6% by weight, especially 3.5 to 5% by weight. In addition, content of the copolymerization component based on ethylene in a polypropylene resin can be measured using ¹³ C-NMR.

  The polypropylene resin used in the present invention preferably contains 80% by weight or more of propylene as a monomer, and may contain a copolymer component other than ethylene. Other copolymer components include 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-butene, Α-olefins having 4 to 12 carbon atoms such as heptene, 3-methyl-1-hexene, 1-octene, 1-decene; cyclopentene, norbornene, tetracyclo [6,2,11,8,13,6] -4- Cyclic olefins such as dodecene; dienes such as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene; Vinyl, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, meta Methyl acrylic acid, maleic anhydride, styrene, methyl styrene, vinyl toluene, and vinyl monomers such as divinylbenzene and the like, may be used these one or two or more.

  The polypropylene resin used in the present invention can be either a random copolymer or a block copolymer. In particular, it is preferable to use an ethylene-propylene random copolymer or an ethylene-propylene-butene random terpolymer having high versatility. An ethylene-propylene random copolymer having an ethylene content of 1 to 7% by weight, more preferably 3 to 7% by weight, further 3.5 to 6% by weight, in particular 3.5 to 5% by weight, or ethylene-propylene -Butene random terpolymers are preferred.

FIG. 1 shows a range of Mw and MFR of the polypropylene resin used in the present invention by a thick triangle. As shown in FIG. 1, the polypropylene resin used in the present invention has an MFR that satisfies the following formula (1).
MFR ≦ 16−2.5 × 10 ⁻⁵ Mw (1)
In the formula, MFR represents the melt flow rate (unit: g / 10 minutes) of the polypropylene resin, and Mw represents the polystyrene equivalent weight average molecular weight of the polypropylene resin.

  Conventional polypropylene-based resins used for foamed particles for in-mold molding often have Mw and MFR that do not satisfy the above formula (1) (the region on the right side of the range showing the present invention in FIG. 1).

  For example, a comparison between a polypropylene resin disclosed in Japanese Patent Application Laid-Open No. 2000-198872 (Patent Document 2) and the resin according to the present invention is as follows. The above publication discloses foamed particles using a propylene-based copolymer as a base resin, and physical properties such as Z average molecular weight and MFI required from the foamed particles are disclosed in Examples and Comparative Examples. When the Mw is plotted on the horizontal axis and the MFR is plotted on the vertical axis for the polypropylene-based resin used in Fig. 1, it becomes the points indicated by Resin 1 to Resin 7 in FIG. 1, and any resin is included in the region of the present invention. I understand that there is no.

  Thus, compared with the case where the polypropylene resin having Mw and MFR exemplified in the above publication is used, the range defined in the present invention, and when using the same Mw polypropylene resin, the shrinkage occurs. It is possible to obtain foamed particles that give an in-mold foam-molded product that is small and has low distortion. The reason for this is that, as a result of detailed studies by the inventors, if the resin has the same Mw, a resin with a low MFR is used. This is because it has been estimated that an in-mold foam-molded article having a small shrinkage rate can be provided.

  This point is also apparent from examples and comparative examples of the present invention described later. However, when the above publication is used as an example, resin 1 and resin 7 have substantially the same ethylene content, as shown in FIG. According to the above publication, the in-mold foam molded body using the resin 1 has a small shrinkage ratio, and the in-mold foam molded body using the resin 7 has a large shrinkage ratio. It is supported by having it.

Furthermore, the polypropylene resin used in the present invention preferably has an MFR that satisfies the following formula (2). It is more preferable to have an MFR that satisfies the following formula (3) or (4), and it is particularly preferable to have an MFR that satisfies the following formula (5) or (6).
MFR ≦ 15.5−2.5 × 10 ⁻⁵ Mw (2)
9.5-2.5 × 10 ⁻⁵ Mw ≦ MFR ≦ 16-2.5 × 10 ⁻⁵ Mw (3)
9.5-2.5 × 10 ⁻⁵ Mw ≦ MFR ≦ 15.5-2.5 × 10 ⁻⁵ Mw (4)
13-2.5 × 10 ⁻⁵ Mw ≦ MFR ≦ 16-2.5 × 10 ⁻⁵ Mw (5)
13-2.5 × 10 ⁻⁵ Mw ≦ MFR ≦ 15.5-2.5 × 10 ⁻⁵ Mw (6)
The polypropylene resin used in the present invention has a Mw of 100,000 or more as shown in FIG. If the Mw is less than 100,000, the MFR increases and it becomes difficult to obtain expanded polypropylene resin particles having a foaming ability. The Mw of the polypropylene resin is preferably 200,000 or more, more preferably 300,000 or more.

  As shown in FIG. 1, the MFR of the polypropylene resin used in the present invention is 1 g / 10 minutes or more, preferably 2 g / 10 minutes or more. When the MFR is less than 1 g / 10 minutes, it is difficult to obtain polypropylene resin expanded particles. The upper limit of MFR of the polypropylene resin used in the present invention is preferably less than 7 g / 10 minutes. Furthermore, the MFR of the polypropylene resin used in the present invention is preferably 2 to 6 g / 10 minutes, particularly 3 to 6 g / 10 minutes.

  The polypropylene resin used in the present invention may have a Z average molecular weight (hereinafter sometimes referred to as Mz) of 1.1 million or less, particularly 1 million or less. Further, the ratio (Mw / Mn) of Mw and number average molecular weight (hereinafter sometimes referred to as Mn) of the polypropylene resin used in the present invention is preferably 4.5 or less, and more preferably 4.0. In particular, 1.5 to 4.0 is particularly preferable. When Mw / Mn exceeds 4.5, the shrinkage rate of the in-mold foam molded product tends to increase.

  MFR is measured using an MFR measuring instrument described in JIS-K7210 under the conditions of orifice 2.0959 ± 0.005 mmφ, orifice length 8.000 ± 0.025 mm, load 2160 g, 230 ± 0.2 ° C.

Further, Mn, Mw and Mz of the present invention are measured under the following conditions.
measuring equipment:
Waters Alliance GPC 2000 Type Gel Permeation Chromatography (GPC)
column:
2 TSKgel GMH6-HT,
Two TSKgel GMH6-HTL (each inner diameter 7.5mm x length 300mm, manufactured by Tosoh Corporation)
Mobile phase: o-dichlorobenzene (containing 0.025% BHT)
Column temperature: 140 ° C
Flow rate: 1.0 mL / min
Sample concentration: 0.15% (W / V) -o-dichlorobenzene Injection amount: 500 μL
Molecular weight calibration: Polystyrene conversion (calibration with standard polystyrene)

  The polypropylene resin used in the present invention can be produced, for example, by subjecting a polypropylene resin to degradation treatment (oxidative decomposition) with an organic peroxide. A polypropylene resin having desired Mw and MFR can be obtained by adjusting the kind of the original polypropylene resin, the kind and amount of the organic peroxide, the treatment temperature and the time. When a polypropylene resin is subjected to degradation treatment, the molecular weight usually decreases and the MFR tends to increase. Therefore, a polypropylene resin used in the present invention can be obtained by degrading a polypropylene resin having a large molecular weight such as Mw and a small MFR.

  It is preferable that the usage-amount of an organic peroxide is 0.001-0.1 weight part with respect to 100 weight part of polypropylene resins. In order to degrade the polypropylene resin, a polypropylene resin added with an organic peroxide can be heated and melted in an extruder.

  Examples of the organic peroxide that can be used include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, t-butylperoxylaurate, 2,5-dimethyl2,5-di ( Benzoylperoxy) hexane, t-butylperoxybenzoate, dicumyl peroxide, 1,3-bis (t-butylperoxyisopropyl) benzene, t-butylperoxyisopropyl monocarbonate and the like.

  The polypropylene resin used in the present invention can also be obtained by adjusting the polymerization conditions using a catalyst such as a metallocene catalyst or a post metallocene catalyst. It is preferable to use a method in which a general-purpose polypropylene resin is decomposed with an organic peroxide because a polypropylene resin having a desired MFR, Mw, or the like can be easily obtained. It is also possible to use a method in which a polypropylene resin obtained by using a catalyst such as a metallocene catalyst or a post metallocene catalyst is further subjected to degradation treatment with an organic peroxide.

  The polypropylene resin used in the present invention is preferably in an uncrosslinked state, but may be crosslinked by treatment with an organic peroxide or radiation. Two or more polypropylene resins may be mixed.

  In addition to polypropylene resins, other thermoplastic resins such as low density polyethylene, linear density polyethylene, polystyrene, polybutene, and ionomer may be mixed and used as long as the properties of the polypropylene resin are not lost. good.

  The melting point of the polypropylene resin used in the present invention is preferably 130 ° C. or higher and 150 ° C. or lower, more preferably 132 ° C. or higher and 145 ° C. or lower. When the melting point is within this range, a good in-mold foam molded product tends to be obtained even with a frequently used 0.4 MPa pressure-resistant molding machine.

  The method for measuring the melting point is as follows. Using a differential scanning calorimeter (DSC), 5-6 mg of polypropylene resin particle sample is heated from 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min to melt the resin. Next, crystallization is performed by lowering the temperature from 220 ° C. to 40 ° C. at 10 ° C./min. After crystallization, the temperature is further increased from 40 ° C. to 220 ° C. at 10 ° C./min. In the DSC curve obtained at the second temperature increase, the melting peak temperature is defined as the melting point.

  The polypropylene resin is usually melted using an extruder, kneader, Banbury mixer, roll, etc., so that it is easy to produce foamed particles, and the resin particle shape such as cylindrical, elliptical, spherical, cubic, rectangular parallelepiped It is preferable to process it. As for the size of the resin particles, the weight of one particle is preferably 0.1 mg to 30 mg, and more preferably 0.3 mg to 10 mg. The weight of one resin particle is an average resin particle weight obtained from 100 resin particles randomly, and is expressed in mg / particle.

  When adding an additive to resin, it is preferable to mix with raw material resin using a blender etc. before manufacture of the said polypropylene resin particle. Moreover, you may add an additive in molten resin. An example of the additive is a cell nucleating agent. When using a hydrocarbon-based blowing agent such as propane, butane, pentane, hexane, etc., an inorganic nucleating agent such as talc, silica, calcium carbonate is added in an amount of 0.005-0.5 with respect to 100 parts by weight of the polypropylene-based resin. It is preferable to add parts by weight. 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.

  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 blowing agent used, and the type of water-absorbing substance used, but when a water-soluble inorganic substance is used, 0.01 to 100 parts by weight with respect to 100 parts by weight of the polypropylene resin. It is preferably 1 part by weight, and when using a water-absorbing organic substance, it is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the polypropylene resin, and when using a hydrophilic polymer, the polypropylene resin It is preferable that it is 0.1-5 weight part with respect to 100 weight part. Two or more of these water-soluble inorganic substances, water-absorbing organic substances and hydrophilic polymers may be used in combination.

  Furthermore, when producing polypropylene resin particles, if necessary, colorant, antistatic agent, antioxidant, phosphorus processing stabilizer, lactone processing stabilizer, metal deactivator, benzotriazole UV absorber, benzoate Add additives such as light stabilizers, hindered amine light stabilizers, flame retardants, flame retardant aids, acid neutralizers, crystal nucleating agents, amide additives, etc. within a range that does not impair the properties of the polypropylene resin. be able to.

  The said polypropylene resin particle can be made into a polypropylene resin expanded particle using the method known conventionally. For example, the following method can be mentioned. Polypropylene resin particles are dispersed in a dispersion medium in a pressure vessel and a foaming agent is added. Next, at a temperature higher than the temperature at which the polypropylene resin particles soften, preferably at a melting point of polypropylene resin particles of −25 ° C. or higher, a melting point of the polypropylene resin particles of + 25 ° C. or lower, more preferably at a melting point of polypropylene resin particles of −15 ° C. or higher. The melting point of the resin resin particles is heated to a temperature in the range of 15 ° C. or lower, and the pressure is applied to impregnate the polypropylene resin particles with the foaming agent. Thereafter, one end of the pressure vessel is opened, and the polypropylene resin particles are produced by releasing the polypropylene resin particles into a lower pressure atmosphere than in the pressure vessel.

  There is no particular limitation on the pressure-resistant container in which the polypropylene resin particles are dispersed, and any pressure-resistant container that can withstand the pressure in the container and the temperature in the container at the time of producing the foamed particles may be used.

  As the dispersion medium, methanol, ethanol, ethylene glycol, glycerin, water, and the like can be used, and it is preferable to use water among them.

  In order to prevent coalescence of polypropylene resin particles in the dispersion medium, it is preferable to use a dispersant. Examples of the dispersant include inorganic dispersants such as tricalcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay.

  Further, it is preferable to use a dispersion aid together with the dispersant. Examples of dispersing aids include N-acyl amino acid salts, alkyl ether carboxylates, carboxylate types such as acylated peptides, alkyl sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, sulfosuccinates, etc. Sulfate type, sulfate oil, alkyl sulfate, alkyl ether sulfate, sulfate ester type such as alkylamide sulfate, phosphoric acid such as alkyl phosphate, polyoxyethylene phosphate, alkyl allyl ether sulfate An anionic surfactant such as an ester type can be exemplified. Also, polycarboxylic acid type polymer surfactants such as maleic acid copolymer salts and polyacrylates, polyvalent anionic polymer surfactants such as polystyrene sulfonates and naphthalsulfonic acid formalin condensate salts, etc. Can be used.

  As the dispersion aid, it is preferable to use a sulfonate type anionic surfactant, and it is also preferable to use one or a mixture of two or more selected from alkyl sulfonates and alkylbenzene sulfonates. Preferably, an alkyl sulfonate is more preferably used, and using an alkyl sulfonate having a linear carbon chain having 10 to 18 carbon atoms as a hydrophobic group reduces the dispersant adhering to the expanded particles. This is particularly preferable because it can be performed.

  Among these, it is preferable to use one or more selected from tricalcium phosphate, tribasic magnesium phosphate, barium sulfate or kaolin as a dispersant, and n-paraffin sulfonic acid soda as a dispersion aid.

  The amount of the dispersant or dispersion aid used varies depending on the type and the type and amount of polypropylene resin used, but usually 0.2 to 3 parts by weight of the dispersant is blended with 100 parts by weight of the dispersion medium. It is preferable to add 0.001 to 0.1 parts by weight of a dispersion aid. Moreover, in order to make the polypropylene resin particles have good dispersibility in the dispersion medium, it is usually preferable to use 20 to 100 parts by weight with respect to 100 parts by weight of the dispersion medium.

  There are no particular restrictions on the type of foaming agent used in the production of polypropylene resin expanded particles. For example, aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane; inorganic gases such as air, nitrogen, and carbon dioxide Water and the like and mixtures thereof can be used. Among these, inorganic gas, particularly carbon dioxide is preferable from the viewpoints of safety and the like, and the point that the effects of the present invention can be greatly utilized. When water is used as the blowing agent, water used as a dispersion medium can be used.

  In the present invention, the polypropylene resin foam particles once produced are impregnated with an inert gas such as air to give foaming power, and then further foamed by heating to produce higher magnification polypropylene resin foam particles. Adopt a two-stage foaming method. By this method, expanded particles having a high expansion ratio can be obtained. In addition, the two-stage foamed particles may be further foamed. In the present invention, the original polypropylene-based resin expanded particles may be referred to as “one-stage expanded particles”, and the resulting higher-magnification polypropylene-based resin expanded particles may be referred to as “two-stage expanded particles”.

  The expansion ratio of the expanded polypropylene resin particles produced in the present invention is not particularly limited, but is 2 to 60 times, preferably 3 to 40 times. In particular, a range of 20 to 40 times, further 25 to 35 times, further 25 to 33 times, and further 26 to 33 times is preferable.

  In the DSC curve obtained by the differential scanning calorimeter (DSC) measurement (sample 3 to 6 mg, temperature range 40 ° C. to 220 ° C., heating rate 10 ° C./min), the polypropylene resin expanded particles obtained in the present invention are: It is preferable to have two melting peaks on the low temperature side and the high temperature side. When the polypropylene resin expanded particles have two melting peaks, the range of molding conditions such as a heating temperature range is widened when performing in-mold foam molding.

Ratio of heat of fusion on the high temperature side (Q _H / (Q _H + Q _L ) × 100) that can be calculated from the low temperature side heat of fusion Q _L and the high temperature side heat of fusion Q _H corresponding to the two melting peaks of the DSC curve (below) , DSC ratio) is preferably in the range of 10 to 40%. Here, the low-temperature side melting heat Q _L corresponds to a region surrounded by a tangent drawn from the local maximum point between the low-temperature side melting peak and the high-temperature side melting peak to the baseline near the melting start temperature and the low-temperature side melting peak. The amount of heat. Further, the high temperature side melting peak heat quantity Q _H is a heat quantity corresponding to a region surrounded by a tangent drawn from the maximum point to the base line near the melting end temperature and the high temperature side melting peak.

  When the DSC ratio is less than 10%, the closed cell ratio of the polypropylene resin foamed particles is low, and the shrinkage ratio of the in-mold foam molded product tends to increase. When the DSC ratio exceeds 40%, there may be a case where the secondary foaming force at the time of in-mold foam molding of the polypropylene resin foamed particles cannot be sufficiently obtained, and an in-mold foam molded product having inferior fusion between particles can be obtained. There is a case.

  When the polypropylene resin expanded particles obtained in the present invention are used for in-mold foam molding, the following conventionally known methods can be used. B) A method for use as it is, b) A method for injecting an inorganic gas such as air into foamed particles in advance to impart foaming ability, and c) A method for filling foamed particles in a mold in a compressed state.

Among these, the method (b) in which an inorganic gas such as air is press-fitted into the foamed particles in advance to impart foamability is preferable. Specifically, an in-mold foam molded product can be obtained by the following in-mold foam molding method.
1) The foaming ability is imparted by pressurizing the polypropylene resin foamed particles with air in a pressure resistant container and pressing the air into the polypropylene resin foamed particles.
2) The obtained polypropylene resin expanded particles are filled into a molding space composed of two molds, which can be closed but cannot be sealed.
3) Molding is performed using steam or the like as a heating medium at a steam pressure of about 0.2 to 0.4 MPa (G) and a heating time of about 3 to 30 seconds to fuse the polypropylene-based resin expanded particles.
4) Cool the mold with water 5) Open the mold and take out the in-mold foam molded body.

  The expansion ratio of the obtained in-mold foam molded product is not particularly limited, but is 3 to 90 times, preferably 4 to 60 times. When a conventional polypropylene foam molded article has a high expansion ratio of 30 to 60 times, shrinkage of the in-mold foam molded article tends to occur. Therefore, the in-mold foam molded product obtained from the polypropylene resin foam particles used in the present invention is useful when it has a foaming ratio of 30 to 60 times, further 35 to 55 times, further 35 to 50 times, and further 40 to 50 times. It is.

  The in-mold foam-molded article using the polypropylene resin foam particles obtained in the present invention can be used for applications such as a heat insulating material, a buffer packaging material, an automobile interior member, and a core material for an automobile bumper. It is a particularly desirable usage method to use a foamed body using the foamed particles obtained in the present invention for a buffer packaging material in which an in-mold foamed molded body having a high expansion ratio is often used.

  Next, the present invention will be described based on examples and comparative examples. Unless otherwise indicated, “part” and “%” are based on weight. In addition, the evaluation method of an expanded particle and an in-mold expansion molding is as follows.

(Expansion ratio of polypropylene resin expanded particles)
About ³ to 10 g of the expanded particles are taken and dried at 60 ° C. for 6 hours, and then the weight W (g) and the submerged volume V (cm ³ ) are measured. The expansion ratio is calculated from the resin density of the polypropylene resin of 0.9 (g / cm ³ ) according to the following formula.
Foaming ratio = V / (W / 0.9)

(Average bubble diameter)
Ten pieces are arbitrarily taken out from the foamed particles, and the foamed particles are cut with great care so that the bubble film is not broken. In a magnified photomicrograph (× 100 magnification) of the cut surface, a line segment corresponding to a length of 2 mm is drawn on the portion excluding the surface layer portion, and the number of bubbles passing through the line segment is counted. Similarly, for the other nine expanded particles, the number of bubbles is counted, and the average of the number of bubbles of 10 expanded particles is defined as the average number of bubbles. The average cell diameter of the expanded particles is calculated by dividing 2 mm by the average number of cells.

(Foaming ratio of in-mold foam molding)
The dry weight W (g) of the in-mold foam molded product, the submerged volume V (cm ³ ), and the resin density 0.9 (g / cm ³ ) of the polypropylene resin are calculated by the following equation.
Foaming ratio of in-mold foam molding = V / (W / 0.9)

(Shrinkage ratio of in-mold foam molding)
The shrinkage rate was evaluated using an in-mold foam molded body obtained from a flat plate mold having an outer dimension of 400 mm × 300 mm × 20 mm. After molding, the mixture was allowed to stand at room temperature for 1 hour, and then cured at 75 ° C. for 3 hours. Furthermore, it left still at room temperature for 1 hour, and measured the length of the longitudinal direction of the in-mold foaming molding. Further, curing at 75 ° C. and standing at room temperature were repeated until the in-mold foam molded product had a certain size, the length in the longitudinal direction was measured, and the ratio to the mold length was defined as the shrinkage rate.

(Fusion rate of in-mold foam molding)
A crack having a depth of about 5 mm was made with a knife in the width direction on the surface of the in-mold foam molded body cured at 75 ° C. for 3 hours and allowed to stand at room temperature for 1 hour. The in-mold foam molded body was divided along the cracks, and the fracture surface was observed. The ratio of the number of broken particles to the total number of particles on the fracture surface was taken as the fusion rate of the in-mold foam molded product.

(Surface property of in-mold foam molding)
The surface of the above-mentioned in-mold foam-molded product was observed after curing at 75 ° C. for 3 hours and then allowed to stand at room temperature for 1 hour. The surface property was evaluated according to the following criteria.
◎: Wrinkles, less intergranular, beautiful ○: Slight wrinkles, intergranular but good x: Wrinkles, sink marks and poor appearance

The polypropylene resins used in the examples and comparative examples are as follows.
Polypropylene resin A: ethylene-propylene random copolymer degraded by organic peroxide, ethylene content: 4.0% by weight, MFR: 5.2 g / 10 min, Mn: 100,000, Mw: 370,000, Mz: 940,000, Mw / Mn: 3.7, melting point: 137 ° C.
Polypropylene resin B: ethylene-propylene random copolymer, ethylene content: 3.4% by weight, MFR: 6.1 g / 10 min, Mn: 91,000, Mw: 430,000, Mz: 1.3 million, Mw / Mn : 4.7, melting point: 141 ° C,

(Example)
100 parts of polypropylene resin A, 0.05 part of talc and 0.5 part of polyethylene glycol having an average molecular weight of 300 were mixed. The mixture was supplied to a 50 mmφ single screw extruder, melted and kneaded, and then extruded from a cylindrical die having a diameter of 1.8 mmφ. The extruded strand was cooled with water and then cut with a cutter to obtain cylindrical polypropylene resin particles (1.2 mg / particle).

  100 parts of the obtained polypropylene resin particles were put into a pressure-tight sealed container together with 200 parts of pure water, 1.0 part of tricalcium phosphate and 0.05 part of sodium dodecylbenzenesulfonate, and deaerated. Next, while stirring the contents, 6 parts of carbon dioxide gas was placed in a sealed container and heated to 143 ° C. The pressure at this time was 3 MPa. Next, the valve at the bottom of the sealed container was opened, and the contents (resin particles and aqueous dispersion medium) were released under atmospheric pressure through an orifice having a diameter of 4 mmφ to obtain expanded particles (single-stage expanded particles). During discharge, the pressure in the container was maintained with carbon dioxide gas so that the pressure in the container did not decrease.

  The obtained single-stage expanded particles showed two melting points at 131 ° C. and 151 ° C. in differential scanning calorimetry, and the expansion ratio and average cell diameter were 15 times and 137 μm, respectively.

  The obtained expanded particles (single-stage expanded particles) are dried at 60 ° C. for 6 hours, then impregnated with pressurized air in a pressure resistant container to bring the internal pressure to about 0.4 MPa, and then about 0.08 MPa. By making it contact with the vapor of (G), two-stage foaming was performed to obtain two-stage foamed particles having an expansion ratio of 30 times and a DSC ratio of 23.5%.

  The two-stage foamed particles were again pressurized with air in a pressure resistant container to give an internal pressure of about 0.17 MPa. The obtained foamed particles were filled into a flat plate mold (400 mm × 300 mm × 20 mm) and molded with 0.26 MPa (G) steam to obtain an in-mold foam molded product with a foaming ratio of 44 times. Table 1 shows the shrinkage rate, fusion rate, and surface property of the obtained in-mold foam molded article.

(Comparative example)
Single-stage expanded particles were obtained in the same manner as in Example 1 except that the polypropylene resin B was used and the heating temperature of the polypropylene resin particles in a pressure-resistant sealed container was 147 ° C. The obtained single-stage expanded particles showed two melting points at 138 ° C. and 156 ° C. in differential scanning calorimetry, and the expansion ratio and average cell diameter were 16 times and 193 μm, respectively. Two-stage foaming was performed under the same conditions as in Example 1 to obtain two-stage foamed particles having an expansion ratio of 31 times and a DSC ratio of 25.0%. Using the obtained two-stage expanded particles, an in-mold expanded molded article having an expansion ratio of 44 times was obtained under the same conditions as in Example 1. Table 1 shows the shrinkage rate, fusion rate, and surface property of the obtained in-mold foam molded article.

As is clear from Table 1, the polypropylene resin expanded particles obtained by the present invention can give an in-mold expanded molded article having a small shrinkage rate.

It is a graph which shows the range of the styrene conversion weight average molecular weight (Mw) and melt flow rate (MFR) of the polypropylene resin used for this invention.

Claims (11)

Polypropylene resin foam obtained from a polypropylene resin having a polystyrene-reduced weight average molecular weight (Mw) of 100,000 or more, a melt flow rate (MFR) of 1 g / 10 min or more and satisfying the following formula (1) A method for producing expanded polypropylene resin particles, wherein the particles are further expanded.
MFR (g / 10 min) ≦ 16−2.5 × 10 ⁻⁵ Mw (1)
In the formula, MFR represents the melt flow rate of the polypropylene resin, and Mw represents the polystyrene equivalent weight average molecular weight of the polypropylene resin. The method for producing expanded polypropylene resin particles according to claim 1, wherein the melt flow rate (MFR) of the polypropylene resin further satisfies the following formula (2).
MFR (g / 10 min) ≧ 9.5-2.5 × 10 ⁻⁵ Mw (2)   The ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polypropylene resin is 4.5 or less. Production of expanded polypropylene resin particles according to any one of claims 1 to 2. Method.   The method for producing expanded polypropylene resin particles according to claim 3, wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polypropylene resin is 4 or less.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 4, wherein the polypropylene resin has a Z-average molecular weight (Mz) of 1.1 million or less.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 5, wherein the polypropylene resin is a resin containing a copolymer component based on ethylene.   The method for producing expanded polypropylene resin particles according to claim 6, wherein the polypropylene resin is a resin containing 1 to 10% by weight of a copolymer component based on ethylene.   The method for producing expanded polypropylene resin particles according to claim 7, wherein the polypropylene resin is a resin containing 3.5 to 6% by weight of ethylene as a copolymer component.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 8, wherein the polypropylene resin is a resin subjected to degradation treatment with an organic peroxide.   An in-mold foam-molded article having an expansion ratio of 30 to 60 times, obtained by in-mold molding of the polypropylene resin foamed particles obtained by the production method according to claim 1.   The in-mold foam molded article according to claim 10, wherein the expansion ratio is 35 to 50 times.