JP6357310B2 - Polypropylene resin pre-expanded particles and polypropylene resin in-mold foam-molded product obtained from the polypropylene resin pre-expanded particles - Google Patents

Description

  The present invention relates to a polypropylene resin pre-expanded particle and an in-mold foam molded product obtained from the polypropylene resin pre-expanded particle.

The in-mold foam molded article obtained by using the polypropylene resin pre-expanded particles has characteristics such as shape arbitraryness, buffering property, 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 an in-mold foam molded product obtained using 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. . Recently, in the automobile industry, demand for improving fuel efficiency of automobiles has been increasing for reducing gasoline consumption from the aspect of low environmental impact. There is a demand for weight reduction of the inner foamed molded article.

  Usually, for reducing the weight of the in-mold foamed molded body, a method of maintaining the physical properties of the molded body before weight reduction using a highly rigid polypropylene resin is used. In general, a high-stiffness polypropylene resin is a resin having a low comonomer content and a high melting point. However, as the melting point of the resin increases, the molding heating steam pressure required to obtain a good molded product increases. There is a tendency. For this reason, when a higher rigidity is required, a large amount of heating steam is consumed, resulting in a high utility cost and a high molding processing cost.

  Further, when a high-rigidity resin is used, the heat molding pressure becomes high, so that it is necessary to use a molding machine or a mold having a high pressure resistance specification, which increases the equipment cost in addition to the utility cost. Currently, most of the 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 Up to about 0.36 MPa. Polypropylene resin pre-expanded particles used for in-mold foam molding use a resin with characteristics that can cope with this, and generally a propylene / ethylene random copolymer having a melting point of about 130 to 150 ° C. is used. ing.

On the other hand, various techniques have been studied conventionally for improving the rigidity of the in-mold foam molded article.
In Patent Literature 1, a propylene random copolymer having a melting point of 149 to 157 ° C., a melt flow rate of 1 to 20 g / 10 minutes, and a half-crystal time of a certain value or less is used as the base resin as the base resin. Technology is disclosed. However, this technique requires a molding machine having a high pressure resistance, since the heating steam pressure required for in-mold foam molding is as high as 0.42 MPa.

  Patent Document 2 discloses a polypropylene resin foam molding having high rigidity with a molding heating steam pressure of around 0.3 MPa by using polypropylene resin prefoamed particles containing 1 to butene in an amount of 3 to 12% by weight as a comonomer. A technique for obtaining a body is disclosed. However, a 1-butene homopolypropylene resin random copolymer containing no ethylene component is harder and more brittle than a polypropylene resin containing an ethylene component. When a 1-butene homopolypropylene resin random copolymer is used as a base material resin for a foam, there is a problem that in automobile member applications, buffer characteristics, dimensional recovery after compression, and impact in a low temperature region are inferior. is there.

However, since Patent Documents 1 and 2 are techniques for achieving high rigidity by changing the amount of comonomer at the time of polymerization, they become special varieties as polypropylene resins and have high resin costs.
On the other hand, as a technology for increasing the rigidity of general-purpose polypropylene resins that are generally available on the market, there is a technology that adds an inorganic substance such as a crystal nucleating agent or talc. Molded products tend to deteriorate moldability and reduce rigidity, and almost no technology has been developed.

A technique using a modified polypropylene resin has been reported as a technique for increasing the rigidity of the in-mold foam molded article.
Patent Document 3 discloses a technology in which a highly rigid modified polypropylene resin is added to a polypropylene resin and pre-expanded particles are obtained by an extrusion foaming method. However, in this patent, in order to obtain high rigidity, a high melting point polypropylene homopolymer having high rigidity is used as a starting resin for the modified polypropylene resin, and the amount of addition in the examples is as large as 25%. For this reason, there is room for improvement in the elongation at the time of in-mold foam molding, and there is a problem that it is difficult to obtain a good in-mold foam-molded product.

  Further, Patent Document 4 discloses a technology in which a highly rigid modified polypropylene resin obtained by melt-kneading a polypropylene resin, a radical polymerization initiator, and a conjugated diene compound is used as pre-expanded particles by a decompression foaming method. Has been. However, since all the polypropylene resins of the base resin are modified, the melt viscosity becomes very high, the elongation at the time of in-mold foam molding is deteriorated, and there is a problem that it is difficult to obtain a good in-mold foam molded product. .

  On the other hand, Patent Document 5 discloses a technique of adding a modified polypropylene resin obtained by block copolymerization of a polyether with a polypropylene resin. However, in general, polypropylene resins are not limited to other materials. For example, polypropylene resins having different compositions such as polypropylene homopolymers and propylene / ethylene random copolymers or polypropylene resins having different melt flow rates. The compatibility with is very poor. Therefore, in patent document 5, when a polypropylene-polyether copolymer was added to a polypropylene resin, it was not compatible, and the strength of the in-mold foam molded product was reduced.

JP-A-11-156879 JP-A-1-242638 JP 2008-274024 A JP 2009-256460 A JP 2009-298931 A

  An object of the present invention is to provide a polypropylene resin pre-expanded particle that can provide an in-mold expanded molded article that is excellent in fusion and surface beautification with a molding machine of 0.4 MPa pressure resistance specification and has high rigidity. is there.

  As a result of diligent research in view of the above problems, the present inventor has found that a polypropylene resin having a low resin melting point, that is, a low rigidity, at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement at the time of melting. By adding a small amount of a modified polypropylene resin having a loss tangent tan δ which is a ratio of a storage elastic modulus and a loss elastic modulus of 0.6 or more and 2.0 or less, In order not to impair the compatibility, the present inventors have found that fusion and surface aesthetics are excellent and rigidity is high, and the present invention has been completed.

That is, the first of the present invention is
(A) 95.0 to 99.5% by weight of a polypropylene-based resin, and (B) ratio of storage elastic modulus and loss elastic modulus at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement at 180 ° C. Resin mixture comprising 0.5 to 5.0% by weight of a modified polypropylene resin having a loss tangent tan δ of 0.6 to 2.0 [the total amount of (A) and (B) is 100% by weight] It is related with the polypropylene resin pre-expanded particle obtained by foaming the polypropylene resin particle which uses as a base resin.

As a preferable form,
(1) The polypropylene-based pre-expanded particles as described above, wherein the modified polypropylene-based resin has a melt flow rate of 5 g / 10 min to 80 g / 10 min.
(2) The polypropylene-based resin as described above, wherein the modified polypropylene-based resin is a modified polypropylene-based resin obtained by melt-mixing a linear polypropylene-based resin, a radical polymerization initiator, and a conjugated diene compound. Pre-expanded particles.

  In the second aspect of the present invention, the polypropylene resin particles, water, and a foaming agent are accommodated in a pressure resistant container, dispersed under stirring, and heated to a temperature equal to or higher than the softening point temperature of the polypropylene resin particles. The present invention relates to a method for producing polypropylene resin pre-expanded particles, wherein the dispersion liquid in the pressure resistant container is discharged into a pressure region lower than the internal pressure of the container to foam the polypropylene resin particles.

  A third aspect of the present invention relates to a method for producing a polypropylene resin in-mold foam molded product obtained by filling the polypropylene resin pre-expanded particles in a mold and foam-molding in the mold.

  The polypropylene resin expanded particles of the present invention are excellent in fusion and surface aesthetics during in-mold foam molding on a 0.4 MPa pressure-resistant molding machine, and the obtained foamed molded product may have high rigidity. it can.

In order to determine the melting point of the polypropylene resin of the present invention, in differential scanning calorimetry (DSC), the polypropylene resin particles are heated from 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min, then 10 The temperature is lowered from 220 ° C. to 40 ° C. at a temperature lowering rate of ° C./min, and the second temperature raising operation is performed from 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min. It is an example of a DSC curve. An example of a DSC curve (temperature vs. endothermic amount) obtained from differential scanning calorimetry (DSC) in which the polyolefin resin expanded particles of the present invention are heated from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min. is there. The DSC curve has two melting peaks, and has two melting calorie regions, a low temperature side melting calorie region Ql and a high temperature side melting calorie region Qh.

  The polypropylene resin pre-expanded particles of the present invention include (A) a polypropylene resin and (B) a ratio between a storage elastic modulus and a loss elastic modulus at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement at 180 ° C. These are polypropylene resin pre-expanded particles obtained by foaming polypropylene resin particles using a resin mixture made of a modified polypropylene resin having a loss tangent tan δ of 0.6 or more and 2.0 or less as a base resin.

The (A) polypropylene resin used in the present invention is a polypropylene random copolymer containing 1-butene and / or ethylene as a comonomer.
However, it may contain a comonomer other than 1-butene and ethylene. Examples of such a comonomer include isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, Examples include α-olefins such as 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene. Furthermore, cyclic olefins such as cyclopentene, norbornene, tetracyclo [6,2,1 ^1,8 , 1 ^3,6 ] -4-dodecene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4 -Dienes such as hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene and the like.

  In the present invention, among polypropylene random copolymers, propylene / ethylene / 1-butene random copolymers or propylene / ethylene random copolymers are preferable from the viewpoint of good foamability.

Furthermore, in these propylene / ethylene random copolymers and propylene / ethylene / 1-butene random copolymers, the structural unit consisting of propylene is 90% by weight or more and 99.8% by weight or less in 100% by weight of the polypropylene resin. The structural unit composed of 1-butene and / or ethylene is preferably 0.2% by weight or more and 10% by weight or less, the structural unit composed of propylene is 92% by weight or more and 99% by weight or less, 1-butene and / or ethylene. It is more preferable that the structural unit consisting of 1 to 8% by weight.
When the structural unit composed of propylene exceeds 99.8% by weight and the structural unit composed of 1-butene and / or ethylene is less than 0.2% by weight, the molding heating steam pressure tends to be high during in-mold foam molding. is there. When the structural unit composed of propylene is less than 90% by weight and the structural unit composed of 1-butene and / or ethylene exceeds 10% by weight, the dimensional stability of the in-mold foamed molded product tends to decrease and the compressive strength decreases. Tend.

In the present invention, the structural unit composed of 1-butene is preferably 6% by weight or less, more preferably 3% by weight or more and 5% by weight or less in 100% by weight of the polypropylene resin.
If the structural unit composed of 1-butene exceeds 6% by weight, the rigidity of the polypropylene random copolymer itself tends to be weak, and there is a tendency that practical rigidity such as compressive strength is not satisfied.

In the present invention, the structural unit composed of ethylene is preferably 0.2% by weight or more and 4% by weight or less, more preferably 0.2% by weight or more and 3.5% by weight or less, in 100% by weight of the polypropylene resin.
When the structural unit made of ethylene exceeds 4% by weight, there is a tendency that it cannot endure practical rigidity such as compressive strength.

  The catalyst for polymerizing the polypropylene resin of the present invention is not particularly limited, and a Ziegler-Natta polymerization catalyst, a metallocene polymerization catalyst, or the like can be used.

The melting point of the (A) polypropylene resin used in the present invention is 125 ° C. or higher and 153 ° C. or lower, preferably 130 ° C. or higher and 150 ° C. or lower, and more preferably 135 ° C. or higher and 148 ° C. or lower.
If the melting point of the polypropylene resin is less than 125 ° C., the dimensional stability of the in-mold foam molded product tends to decrease, and if the melting point exceeds 155 ° C., the molding heating steam pressure tends to increase during in-mold foam molding. There is.

  Here, the melting point of the polypropylene resin is measured as follows using a differential scanning calorimeter DSC [for example, DSC6200 type, manufactured by Seiko Instruments Inc.]. That is, 5 to 6 mg of a polypropylene random copolymer resin was heated from 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min to melt the resin, and then from 220 ° C. at a temperature decreasing rate of 10 ° C./min. From the DSC curve obtained when crystallizing by lowering the temperature to 40 ° C. and then increasing again from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min, and giving such a series of temperature history, The melting peak temperature at the second temperature rise is defined as the melting point.

The melt flow rate (hereinafter referred to as “MFR”) of the (A) polypropylene resin used in the present invention is not particularly limited, but is preferably 0.5 g / 10 min to 100 g / 10 min, and preferably 2 g / 10 minutes or more and 50 g / 10 minutes or less is more preferable, and 3 g / 10 minutes or more and 20 g / 10 minutes or less is more preferable.
When the MFR of the polypropylene resin is in the above range, it is easy to obtain polypropylene resin expanded particles having a relatively large expansion ratio, and the surface beauty of the in-mold foam molded product obtained by in-mold foam molding is excellent. A product with a small dimensional shrinkage ratio can be obtained.

  Here, the MFR value of the polypropylene resin was measured using an MFR measuring instrument described in JIS-K7210, with an orifice of 2.0959 ± 0.005 mmφ, an orifice length of 8.000 ± 0.025 mm, a load of 2160 g, and 230 ± 0. It is a value when measured under the condition of 2 ° C.

The (B) modified polypropylene resin in the present invention introduces a long-chain branch by irradiating an electron beam to a linear polypropylene resin (hereinafter, the polypropylene resin is referred to as “raw polypropylene resin”). And a modified polypropylene resin obtained by melt-kneading a raw material polypropylene resin, a radical polymerizable monomer, a radical polymerization initiator, and the like.
In particular, a modified polypropylene resin obtained by melting and kneading a raw material polypropylene resin, a radical polymerizable monomer, and a radical polymerization initiator is preferable because it is easy to produce and economically advantageous. Furthermore, since the modified polyolefin resin and the base resin of the pre-expanded particles are the same polyolefin resin, it can be said that the technical judgment as to whether the rigidity has increased is clear.

Examples of the radical polymerizable monomer used in the production of the (B) modified polypropylene resin of the present invention include conjugated diene monomers such as 1,3-butadiene and isoprene, styrene, α-methylstyrene, and divinylbenzene. Examples thereof include polyfunctional monomers such as aromatic vinyl monomers such as triallyl cyanurate, triallyl isocyanurate, trimethylolpropane triacrylate, and tetramethylolmethane tetraacrylate.
Of these, isoprene is preferred because the base polypropylene-based resin can be modified with a small amount.

  The addition amount of the radical polymerizable monomer in the present invention is preferably 0.1 parts by weight or more and 1 part by weight or less with respect to 100 parts by weight of the polypropylene resin.

The radical polymerization initiator used in the production of the (B) modified polypropylene resin of the present invention is preferably an organic oxide having a high 1-minute half-life temperature and a high hydrogen abstraction property.
As a specific example of the radical polymerization initiator, for example,
1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) Peroxyketals such as oxy) valerate, 2,2-bis (t-butylperoxy) butane;
Hydroperoxides such as permethane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2, 5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, 2,5- Dialkyl peroxides such as dimethyl-2,5-di (t-butylperoxy) hexyne-3;
t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxyisopropyl carbonate, 2,5-dimethyl-2, Examples thereof include peroxyesters such as 5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. These may be used alone or in combination of two or more.
Of these radical polymerization initiators, peroxyesters are preferred because the raw material polypropylene resin can be modified with a small amount.

  The amount of radical polymerization initiator added in the production of the (B) modified polypropylene resin of the present invention is from 0.1 parts by weight to 1.4 parts by weight with respect to 100 parts by weight of the raw material polypropylene resin. preferable.

  The step of producing the (B) modified polypropylene resin in the present invention is preferably performed in an apparatus capable of kneading each raw material in a molten state of the resin. As such a kneading apparatus, an extruder is more preferable because of high productivity, and a twin-screw extruder is particularly preferable because it can react efficiently.

  In the process of producing the (B) modified polypropylene resin in the present invention, there is no particular limitation on the method for supplying each raw material to the extruder. For example, when isoprene is used as the radical polymerizable monomer, the raw material polypropylene Examples thereof include a method in which a resin and a radical polymerization initiator are supplied to a twin screw extruder hopper, and isoprene is press-fitted from the middle of the extruder after the resin is melted.

The MFR at 230 ° C. of the (B) modified polypropylene resin used in the present invention is preferably 5 g / 10 min to 80 g / 10 min, and preferably 8 g / 10 min to 50 g / 10 min. More preferred.
When the MFR of the modified polypropylene resin is less than 5 g / 10 minutes, the viscosity of the modified polypropylene is very high, so the elongation at the time of molding deteriorates, the surface beauty is inferior, and the modified polypropylene resin is added. Since the compatibility with the polypropylene resin is decreased, the rigidity tends to decrease. On the other hand, when the MFR of the modified polypropylene resin exceeds 80 g / 10 min, the degree of modification is low, and thus there is a tendency that the effect of high rigidity is not exhibited.

Loss tangent tan δ (hereinafter simply referred to as “the ratio of the storage elastic modulus and the loss elastic modulus at an angular frequency of 1 rad / s” in the dynamic viscoelasticity measurement at 180 ° C. of the (B) modified polypropylene resin of the present invention. tan δ ”) is preferably 0.6 or more and 2.0 or less, and more preferably 0.8 or more and 1.5 or less.
When the tan δ of the modified polypropylene resin is less than 0.6, the viscosity of the modified polypropylene is very high, so that the elongation at the time of molding deteriorates, the surface beauty is inferior, and the modified polypropylene resin is added. Since the compatibility with the polypropylene resin decreases, the rigidity tends to decrease. When the tan δ of the modified polypropylene resin is more than 2.0, the degree of modification is low, and thus there is a tendency that a high rigidity effect is not exhibited.

As the mixing ratio of (A) polypropylene resin and (B) modified polypropylene resin in the present invention, (A) 95.0 to 99.5 wt% of polypropylene resin and (B) modified polypropylene resin 0. 5 to 5.0% by weight [the total amount of (A) and (B) is preferably 100% by weight], (A) 96.0 to 99.0% by weight of polypropylene resin and (B) modified polypropylene resin 1.0 to 4.0% by weight is more preferable, (A) 97.0 to 99.0% by weight of polypropylene resin and (B) 1.0 to 3.0% by weight of modified polypropylene resin are more preferable.
(B) When the mixing ratio of the modified polypropylene resin is less than 0.5%, there is a tendency that the effect of high rigidity is not exhibited. When the mixing ratio exceeds 5.0% by weight, the melt viscosity of the modified polypropylene resin is low. Since it is high, the elongation at the time of molding deteriorates, the surface beauty is inferior, and the compatibility of the modified polypropylene resin with the polypropylene resin decreases, so that the rigidity tends to decrease.

  The expanded polypropylene resin particles used in the present invention are processed into polypropylene resin particles using a resin mixture comprising (A) polypropylene resin and (B) modified polypropylene resin as a base resin, and then expanded. Can be obtained.

  For example, the polypropylene resin particles used in the present invention are melted by using, for example, a polypropylene resin and a modified polypropylene resin using an extruder, a kneader, a Banbury mixer, a roll, etc., extruded into a strand, and before or after cooling. Then, it is molded into a desired particle shape such as a columnar shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, etc., and becomes a polypropylene resin particle.

In the present invention, in addition to (A) polypropylene-based resin and (B) modified polypropylene-based resin, an antioxidant, a light resistance improver, an antistatic agent, a colorant, and a flame retardant improver are optionally added. Further, an additive such as a conductivity improver may be added to form polypropylene resin particles. These additives are usually preferably added to the molten resin in the production process of polypropylene resin particles.
Moreover, when using carbon dioxide gas, air, or water as a foaming agent described later, it is preferable to add an inorganic nucleating agent and / or a water-absorbing substance that can improve foaming properties.

  The melting point of the polypropylene resin particles used in the present invention can be determined as the melting point of the polypropylene random copolymer of the present invention by measuring the melting point using the differential scanning calorimeter described above. .

The inorganic nucleating agent used in the present invention promotes the formation of bubble nuclei that are the starting point of foaming, contributes to the improvement of the foaming ratio, and also contributes to uniform bubble formation.
Examples of the inorganic nucleating agent include talc, silica, calcium carbonate and the like. These may be used alone or in combination of two or more.

  The content of the inorganic nucleating agent in the present invention is preferably 0.005 wt% or more and 0.5 wt% or less in 100 wt% of the polypropylene resin particles.

  The water-absorbing substance used in the present invention means that when the substance is added to polypropylene resin particles and the polypropylene resin particles are brought into contact with water or impregnated with a foaming agent in an aqueous dispersion, A substance that can contain water.

As a specific example of the water-absorbing substance used in the present invention, for example,
Water-soluble inorganic substances such as sodium chloride, calcium chloride, magnesium chloride, borax, zinc borate;
Special block type polymer with polyethylene glycol and polyether as hydrophilic segments [manufactured by Sanyo Kasei Co., Ltd., trade name: Pelestat];
Alkali metal salt of ethylene- (meth) acrylic acid copolymer, alkali metal salt of butadiene- (meth) acrylic acid copolymer, alkali metal salt of carboxylated nitrile rubber, alkali of isobutylene-maleic anhydride copolymer Hydrophilic polymers such as metal salts and alkali metal salts of poly (meth) acrylic acid;
Polyhydric alcohols such as ethylene glycol, glycerin, pentaerythritol and isocyanuric acid; melamine and the like.
These may be used alone or in combination of two or more.

  The content of the water-absorbing substance in the present invention varies depending on the target foaming ratio, the blowing agent used, and the type of the water-absorbing substance used, and cannot be described in general, but when water-soluble inorganic substances and polyhydric alcohols are used In 100% by weight of polypropylene resin particles, it is preferably 0.01% by weight or more and 2% by weight or less. When a hydrophilic polymer is used, 0.05% by weight or more and 5% by weight in 100% by weight of polypropylene resin particles. It is preferable that it is below wt%.

In the present invention, there is no limitation on the addition of the colorant, and a natural color can be obtained without adding the colorant, or a desired color can be obtained by adding a colorant such as blue, red, or black.
Examples of the colorant include perylene organic pigments, azo organic pigments, quinacridone organic pigments, phthalocyanine organic pigments, selenium organic pigments, dioxazine organic pigments, isoindoline organic pigments, and carbon black.

  The polypropylene resin foamed particles used in the present invention contain a dispersion containing polypropylene resin particles and water in a pressure vessel, and then disperse them under stirring conditions, and in the presence of a foaming agent, The temperature can be raised above the softening point temperature of the resin particles, and then the dispersion in the pressure vessel can be discharged into a pressure range lower than the internal pressure of the pressure vessel to produce polypropylene resin particles by foaming. In addition, this process may be referred to as “one-stage foaming process”, and the polypropylene resin particles obtained in this process may be referred to as “single-stage foam particles”.

More specifically, the following method is mentioned, for example.
(1) After charging polypropylene resin particles and an aqueous dispersion medium, a dispersing agent, etc., if necessary, the inside of the sealed container is evacuated and then 1 MPa (gauge pressure) or more and 2 MPa. The following (gauge pressure) foaming agent is introduced and heated to a temperature equal to or higher than the softening temperature of the polypropylene resin. By heating, the pressure in the sealed container rises to about 2 MPa (gauge pressure) or more and 5 MPa or less (gauge pressure). If necessary, add a foaming agent near the foaming temperature to adjust to the desired foaming pressure, further adjust the temperature, and if necessary, hold the foaming pressure and temperature for a predetermined time, and then By releasing into a pressure range lower than the internal pressure of the sealed container, polypropylene-based resin expanded particles can be obtained.
(2) After charging the pressure-resistant container with polypropylene resin particles, an aqueous dispersion medium, and a dispersant as necessary, the inside of the sealed container is evacuated and then heated to a temperature equal to or higher than the softening temperature of the polypropylene resin. A foaming agent may be introduced while heating.
(3) After charging polypropylene resin particles, aqueous dispersion medium, and dispersing agent if necessary into a pressure vessel, heating to near the foaming temperature, introducing a foaming agent to obtain the foaming temperature, and from the internal pressure of the sealed container Further, it is possible to obtain expanded polypropylene resin particles by releasing into a low pressure range.

  Before releasing into the low-pressure region, carbon dioxide, nitrogen, air or a substance used as a foaming agent is injected to increase the internal pressure in the pressure-resistant container, and the pressure release speed during foaming is adjusted. The foaming ratio can be adjusted by introducing carbon dioxide, nitrogen, air, or a substance used as a foaming agent into the pressure-resistant container and controlling the pressure during the release to the low pressure region.

  Here, the pressure range lower than the internal pressure of the pressure vessel is preferably atmospheric pressure. In this case, the equipment does not become complicated, and no special pressure adjustment in the low pressure region is required.

The temperature in the low pressure range may be room temperature, or may be set to a temperature higher than room temperature. Examples of a method for setting the temperature higher than normal temperature include a method of heating with heated steam.
When a dispersion is discharged into a pressure region heated with heated steam to produce polypropylene resin particles by foaming, the maximum is in the differential curve of the DSC curve of the obtained polypropylene resin foam particles as described later. The value is easy to express and is one of preferred embodiments.
From such a viewpoint, the heating temperature is preferably 60 ° C. or higher and 120 ° C. or lower, and more preferably 70 ° C. or higher and 115 ° C. or lower.

  In order to ensure foamability, it is necessary to raise the temperature to a temperature in the range of the melting point of the polypropylene resin particles −20 ° C. or higher and the melting point of the polypropylene resin particles + 10 ° C. or lower. preferable.

Examples of the blowing agent used in the present invention include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane and hexane; aliphatic cyclized hydrogens such as cyclopentane and cyclobutane; air and nitrogen Inorganic gas such as carbon dioxide, water, etc. These foaming agents may be used alone or in combination of two or more.
Among these, it is preferable to use inorganic gas, and it is particularly preferable to use carbon dioxide gas, air, and water.

  The amount of the foaming agent used in the present invention is not particularly limited, and may be appropriately used depending on the desired expansion ratio of the polypropylene resin expanded particles. The amount of the foaming agent used is preferably 3 to 60 parts by weight with respect to 100 parts by weight of the polypropylene resin particles.

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

In the present invention, it is preferable to use an inorganic dispersant from the viewpoint of enhancing the dispersibility of the dispersion during the production of the polypropylene resin expanded particles and preventing adhesion between the polypropylene resin expanded particles.
Examples of such inorganic dispersants include tricalcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, basic zinc carbonate, aluminum oxide, iron oxide, titanium oxide, aluminosilicate, kaolin, and sulfuric acid. Barium etc. are mentioned.

In the present invention, it is preferable to use a dispersion aid in combination in order to further improve dispersibility. Examples of such a dispersion aid include sodium dodecylbenzene sulfonate, sodium alkane sulfonate, sodium alkyl sulfonate, sodium alkyl diphenyl ether disulfonate, sodium α-olefin sulfonate, and the like.
Among these, as a combination of the inorganic dispersant and the dispersion aid, a combination of tricalcium phosphate and sodium alkylsulfonate is preferable.

  The amount of the inorganic dispersant and dispersion aid used in the present invention varies depending on the type and the type and amount of polypropylene resin used, but usually 0.2 part by weight of the inorganic dispersant with respect to 100 parts by weight of water. The amount is preferably 3 parts by weight or less and more preferably 0.001 part by weight or more and 0.1 parts by weight or less.

  In the present invention, in order to improve the dispersibility in water, it is usually preferable to use polypropylene resin particles in an amount of 20 to 100 parts by weight with respect to 100 parts by weight of water.

The expansion ratio of the expanded polypropylene resin particles of the present invention is not particularly limited, but is preferably 3 to 50 times, more preferably 7 to 45 times.
Here, the expansion ratio of the polypropylene resin expanded particles was determined by measuring the weight w (g) and the ethanol submerged volume v (cm ³ ) of the polypropylene resin expanded particles, and obtaining the true specific gravity ρb = w / v of the expanded particles, The expansion ratio K = ρr / ρb is obtained from the ratio to the density ρr (0.90 g / cm ³ ) of the polypropylene resin particles before foaming.

The bulk density of the expanded polypropylene resin particles of the present invention is not particularly limited, but is preferably 10 g / L or more and 200 g / L or less, and more preferably 12 g / L or more and 150 g / L or less.
Here, the bulk density of the expanded polypropylene resin particles is determined by measuring the weight of the expanded polypropylene resin particles in the container after the polypropylene expanded resin particles are gently put into the container and filling it. Divided by g / L.

  By the way, although the first-stage expanded particles depend on the type of the foaming agent at the time of production, the expansion ratio may not reach 10 times. In such a case, the single-stage foamed particles are impregnated with an inorganic gas (for example, air, nitrogen, carbon dioxide gas, etc.) and given an internal pressure, and then contacted with water vapor at a specific pressure to thereby form the single-stage foam particles. As a result, it is possible to obtain pre-expanded polypropylene resin particles having an improved expansion ratio.

  Thus, the process of further expanding the polypropylene resin pre-expanded particles to obtain a polypropylene resin pre-expanded particle having a higher expansion ratio is referred to as a “two-stage expansion process”. , Sometimes referred to as “two-stage expanded particles”.

In the present invention, the water vapor pressure in the two-stage foaming step is preferably adjusted to 0.04 MPa (gauge pressure) or more and 0.25 MPa (gauge pressure) or less in consideration of the expansion ratio of the two-stage foam particles. More preferably, the pressure is adjusted to 0.05 MPa (gauge pressure) or more and 0.15 MPa (gauge pressure) or less.
If the water vapor pressure in the two-stage foaming step is less than 0.04 MPa (gauge pressure), it may not expand to the required foaming ratio. If it exceeds 0.25 MPa (gauge pressure), the resulting two-stage foam particles melt. It tends to become worn and blocked and cannot be used for subsequent in-mold foam molding.

The internal pressure of the air impregnated in the first-stage expanded particles is preferably changed in consideration of the expansion ratio of the second-stage expanded particles and the water vapor pressure in the second-stage expansion process, but is 0.2 MPa or more (absolute pressure) 0.6 MPa or less (Absolute pressure) is preferred.
If the internal pressure of the air impregnated in the first-stage expanded particles is less than 0.2 MPa (absolute pressure), high-pressure steam is required to improve the expansion ratio, and the second-stage expanded particles tend to block. If the internal pressure of the air impregnated in the first-stage expanded particles exceeds 0.6 MPa (absolute pressure), the resulting second-stage expanded particles are fused and blocked, and cannot be used for subsequent in-mold foam molding. Tend.

  In addition, a single-stage expanded particle having a low expansion ratio may be obtained in a single-stage expansion process, and then a two-stage expanded particle having a desired expansion ratio may be obtained by a two-stage expansion process.

  The bulk density of the two-stage expanded particles in the present invention is preferably 10 g / L or more and 45 g / L or less.

The amount of the inorganic dispersant adhering to the surface of the expanded polypropylene resin particles of the present invention is preferably 2000 ppm or less, more preferably 1300 ppm or less, and even more preferably 800 ppm or less.
When the amount of the inorganic dispersant adhering to the surface of the polypropylene resin foamed particles exceeds 2000 ppm, the fusion property during in-mold foam molding tends to be lowered.

  In the DSC curve obtained by differential scanning calorimetry (DSC) in which the polypropylene resin expanded particles of the present invention are heated from 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min, as shown in FIG. It has at least two melting peaks and has at least two heats of fusion, a low-temperature side heat of fusion (Ql) and a high-temperature side heat of fusion (Qh).

In the present invention, total heat of fusion (Q), low temperature side heat of fusion (Ql), and high temperature side heat of fusion (Qh) are defined as follows.
The total heat of fusion (Q = Ql + Qh), which is the sum of the low-temperature side heat of fusion (Ql) and the high-temperature side heat of heat (Qh), is the endotherm at a temperature of 100 ° C. at which melting starts on the low temperature side in the obtained DSC curve. A line segment AB connecting the endothermic amount (point B) at a temperature at which melting ends on the high temperature side is drawn from (point A), and is a part surrounded by the line segment AB and the DSC curve.
The point at which the endotherm between the two melting calorie regions of the DSC curve, the low-temperature side heat of fusion and the high-temperature side heat of heat, is the smallest, and is point C. A line parallel to the Y-axis is raised from point C toward the line segment AB. The point surrounded by line AD, line CD and DSC curve is the low-temperature melting heat quantity (Ql), and is surrounded by line BD, line CD and DSC curve. The part is the high temperature side heat of fusion (Qh).

In the polyolefin-based resin expanded particles of the present invention, the ratio of the high-temperature side heat of fusion {Qh / (Ql + Qh)} × 100) (%) (hereinafter sometimes referred to as “high-temperature heat quantity ratio”) is 10% to 30%. Or less, more preferably 12% or more and less than 28%.
If the high-temperature calorie ratio of the polypropylene resin foamed particles is less than 10%, the foamed polypropylene resin particles tend to open, and the in-mold foam molded product tends to shrink. When the high-temperature calorie ratio of the polypropylene resin foam particles exceeds 30%, the fusion property is lowered with the deterioration of the foamability of the polypropylene resin foam particles during in-mold foam molding, and the in-mold foam molded body is formed. The gap between the expanded polypropylene resin particles is increased.

The high-temperature heat ratio and the high-temperature side heat of fusion are, for example, the retention time from temperature rise to foaming in the one-stage foaming process (maintenance time from reaching the foaming temperature until foaming), foaming temperature (at the time of foaming) Temperature), foaming pressure (pressure during foaming), and the like.
Generally, by increasing the holding time, lowering the foaming temperature, and lowering the foaming pressure, the high-temperature heat quantity ratio or the high-temperature side heat of fusion tends to increase.

  From the above, it is possible to easily find the conditions for the desired high-temperature calorie ratio and high-temperature side melting peak calorie by experimenting several times with systematically changing the holding time, foaming temperature, and foaming pressure. Can do. The foaming pressure can be adjusted by adjusting the amount of foaming agent.

The average cell diameter of the expanded polypropylene resin particles of the present invention is preferably 0.05 mm or more and 0.4 mm or less, and more preferably 0.1 mm or more and 0.3 mm or less.
If the average cell diameter of the polypropylene resin foamed particles is less than 0.05 mm, the surface beauty of the in-mold foam molded product tends to deteriorate. If the average cell diameter exceeds 0.4 mm, the polypropylene resin foamed particles are liable to open. Thereby, there exists a tendency for an in-mold foaming molding to contract easily.

The particle weight of the expanded polypropylene resin particles of the present invention is preferably 0.5 mg / particle to 4.0 mg / particle, more preferably 0.7 mg / particle to 1.8 mg / particle.
In addition, the polypropylene resin expanded particles having a particle weight of 0.5 mg / particle or more and 4.0 mg / particle or less are obtained by setting the particle weight of the polypropylene resin particles to 0.5 mg / particle or more and 4.0 mg / particle or less. Can be easily obtained.

  As described above, the polypropylene resin particles in the present invention are obtained by extruding a once melted resin into a strand shape, and before cooling or after cooling, a desired particle shape such as a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, etc. However, when the particle weight is less than 0.5 mg / particle, the variation in the particle weight tends to be large and the expanded polypropylene resin particles have a large variation in the expansion ratio. When the grain weight exceeds 4.0 mg / grain, the gap between the foamed particles becomes large during foam molding in the mold, and the surface beauty tends to deteriorate.

In the present invention, the polypropylene resin pre-expanded particles are subjected to in-mold foam molding to form an in-mold foam molded body.
B) Polypropylene resin pre-expanded particles are pressurized with an inorganic gas such as air, nitrogen, carbon dioxide, etc., and the polypropylene resin pre-expanded particles are impregnated with inorganic gas to give a predetermined polypropylene resin pre-expanded particle internal pressure. And then filling the mold and heat-sealing with water vapor,
B) A method of compressing polypropylene resin pre-expanded particles with gas pressure and filling them into a mold, and using the recovery force of the polypropylene resin pre-expanded particles, heat-sealing with water vapor,
C) A method such as a method in which pre-expanded polypropylene resin particles are filled in a mold without heat treatment and heat-sealed with water vapor can be used.

As a specific example of a method of obtaining a polypropylene resin-in-mold foam-molded article using the polypropylene resin pre-expanded particles of the present invention, for example,
Pre-expanded polypropylene resin pre-expanded particles are air-pressed in a pressure-resistant container and air pressure is injected into the polypropylene resin pre-expanded particles to give internal pressure (foaming ability), which is then closed with two molds. Filled into a molding space that can be sealed but cannot be sealed, and molded with a heating time of about 3 seconds to 60 seconds under a steam pressure of about 0.1 MPa to 0.4 MPa (gauge pressure) using water vapor as a heating medium. Then, after pre-expanding the polypropylene resin pre-expanded particles, the mold is cooled to the extent that deformation of the polypropylene resin in-mold foam after taking out the in-mold foam molding by water cooling is suppressed, and then the mold And a method of obtaining a foamed molded product in a polypropylene resin mold.

  The internal pressure of the polypropylene resin pre-expanded particles is, for example, 0.1 MPa or more and 1.0 MPa (1 MPa or more by an inorganic gas such as air or nitrogen) under a temperature condition of 1 hour to 48 hours, room temperature to 80 ° C. in a pressure vessel. It can be adjusted by pressurizing below (gauge pressure).

The density of the in-mold foam molded product obtained using the polypropylene resin pre-expanded particles of the present invention is not particularly limited, but is preferably 10 g / L or more and 200 g / L or less, more preferably 12 g / L or more and 150 g / L or less. preferable.
Here, the density of the in-mold foam molded product is a rectangular parallelepiped test piece cut out from the vicinity of the center of the molded product, the sample volume is calculated from the product of the vertical, horizontal and thickness dimensions, the sample weight is divided by the sample volume, After calculating the density of the sample, it was averaged and expressed in units of g / L.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to such examples.

In the examples and comparative examples, the substances used were as follows, but no particular purification was performed.
● Polypropylene resin ○ Polypropylene resin A: Propylene / ethylene / 1-butene random copolymer [manufactured by TPC, melting point 147 ° C., MFR 6.1 g / 10 min]
○ Polypropylene resin B: Propylene / ethylene random copolymer [manufactured by Prime Polymer, melting point 151 ° C., MFR 9.5 g / 10 min]
○ Polypropylene resin C: Propylene / ethylene random copolymer [manufactured by Prime Polymer Co., Ltd., melting point 136 ° C., MFR 7.3 g / 10 min]

  The evaluation in the examples and comparative examples was performed by the following method.

(Measurement of melting point of polypropylene resin)
The melting point of the polypropylene resin was measured using a differential scanning calorimeter DSC [Seiko Instruments Co., Ltd., DSC6200 type] with 5-6 mg of the obtained polypropylene resin particles at a heating rate of 10 ° C./min. The temperature is raised from 40 ° C. to 220 ° C. to melt the resin particles, and then crystallized by lowering the temperature from 220 ° C. to 40 ° C. at a rate of 10 ° C./min. It is a value calculated | required as a melting peak temperature at the time of the 2nd temperature rise from the DSC curve obtained when it heats up from 40 degreeC to 220 degreeC.

(MFR measurement of polypropylene resin)
For the obtained polypropylene resin particles, using an MFR measuring instrument described in JIS-K7210, orifice 2.0959 ± 0.005 mmφ, orifice length 8.000 ± 0.025 mm, load 2160 g, 230 ± 0.2 It is a value when measured under the condition of ° C.

(Loss tangent of modified polypropylene resin tan δ)
The obtained modified polypropylene resin was hot-pressed at 190 ° C. for 5 minutes using a 1.5 mm-thick spacer to produce a 1.5 mm-thick press plate. The obtained press plate was punched out using a punch having a diameter of 25 mm to obtain a test piece.
As a measuring device, a viscoelasticity measuring device [TA Instruments, ARES] was used, and a parallel plate jig having a diameter of 25 mm was attached. Set up a thermostatic chamber to surround the jig, keep it at 180 ° C, open the thermostat after the jig is preheated, insert a test piece with a diameter of 25 mm between the parallel plates, close the thermostat and preheat for 5 minutes The parallel plate interval was compressed to 1 mm. After compression, the thermostat was opened again, the resin protruding from the parallel plate was scraped off with a brass spatula, the thermostat was closed and the temperature was kept again for 5 minutes, and then dynamic viscoelasticity measurement was started.
The measurement is performed in a range of angular frequency from 0.1 rad / s to 100 rad / s in a nitrogen atmosphere at a strain of 5%, and the storage elastic modulus and loss elastic modulus at each angular frequency are obtained. Loss tangent tan δ calculated loss tangent tan δ = loss elastic modulus / storage elastic modulus Of these results, the value of loss tangent tan δ at an angular frequency of 1 rad / s was adopted.

(Expansion ratio of pre-expanded polypropylene resin particles)
About 3 g or more and 10 g or less of the pre-expanded polypropylene resin particles obtained were weighed and dried at 60 ° C. for 6 hours, then conditioned in a constant temperature and humidity chamber at a temperature of 23 ° C. and a humidity of 50%, and the weight w (g) was determined. After the measurement, the volume v (cm ³ ) is measured by a submerging method to determine the true specific gravity ρb = w / v of the expanded particles, and the expansion ratio K = ρr / from the ratio with the density ρr of the polypropylene resin particles before expansion. ρb was determined.
In the following examples and comparative examples, the density ρr of the polypropylene resin particles before foaming was set to 0.90 g / cm ³ .

(Minimum heating steam pressure)
Using a polypropylene foam molding machine [Daisen Co., Ltd., KD345], adjust the air pressure inside the foam particles to 0.2 MPa (absolute pressure) in advance in a rectangular parallelepiped mold 400 mm long x 300 mm wide x 60 mm thick. The polypropylene resin pre-expanded particles are filled, the air in the mold is first expelled with water vapor of 0.1 MPa (gauge pressure), and then heat-molded for 10 seconds using heating steam of a predetermined pressure, thereby forming polypropylene. -Based resin foam molding was obtained. At this time, the heating steam pressure was increased from 0.20 MPa (gauge pressure) by 0.01 MPa, thereby producing a molded body.
A crack having a depth of about 5 mm was put on the surface of the obtained foamed molded product with a knife, the foamed molded product in the mold was divided along the crack, the fractured surface was observed, and the number of fractured particles relative to the total number of particles on the fractured surface was measured. The ratio was obtained and the molded product fusion rate was evaluated.
The lowest steam pressure at which the fusion rate reached 80% or more was taken as the minimum molding pressure.

(Elongation of molded body surface)
With respect to the in-mold foam molded article obtained at the minimum heating pressure, the surface elongation was evaluated according to the following criteria.
◯: All the contours of the pre-expanded particles are fused with the adjacent pre-expanded particles, and there is no gap between the expanded particles exposed on the surface of the molded body.
X: There is a gap between the expanded particles exposed on the surface of the molded body.

(Foamed molded product density)
A test piece for density measurement having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm was cut out from the center inside of the foamed molded product obtained at the lowest heating pressure using a vertical slicer.
The vertical, horizontal, and thickness dimensions of the obtained density measurement test piece were measured using a caliper to determine the volume V of the test piece, and the weight W was further measured to calculate density = W / V. .

(Compressive strength measurement)
The evaluation method of rigidity was evaluated by static compressive strength.
A test piece of 50 mm in length, 50 mm in width, and 25 mm in thickness for density measurement was conditioned for 24 hours in a constant temperature and humidity chamber with an air temperature of 23 ° C. and a humidity of 50%, and then a tensile and compression tester [Minebea, model: TG-20kN The compression test was performed at a speed of 10 mm / min.
The value calculated at a compression rate of 50% when the test piece was compressed was taken as the compression strength value.

(Comprehensive evaluation)
The criteria for comprehensive evaluation were as follows.
◯: When the surface elongation of the molded body is ◯ and the compressive strength of the modified propylene resin-added product is increased as compared to the product without the modified propylene-based resin.
X: When the molded body surface elongation is x, or when the molded body surface elongation is ◯ and the compression strength of the modified propylene resin-added product is equal to or less than that of the modified propylene-based resin additive-free product.

Example 1
[Production of modified polypropylene resin]
A blend of 100 parts by weight of polypropylene resin A and 0.70 parts by weight of t-butyl peroxy-isopropyl monocarbonate [manufactured by NOF Corporation, Perbutyl I] as a radical polymerization initiator by hand blending. , Is fed to a twin screw extruder [manufactured by Nippon Steel Works, Ltd., TEX44XCT-38] using a measuring feeder, 0.37 parts by weight of isoprene is fed from the middle of the extruder using a liquid addition pump, and a resin temperature of 200 A modified polypropylene resin was obtained by melt-kneading at 0 ° C.
The obtained modified polystyrene resin had a tan δ of 1.2 and an MFR of 11.2 g / 10 min.

[Production of polypropylene resin particles]
To 0.5 parts by weight of the obtained modified polypropylene resin and 99.5 parts by weight of polypropylene resin A, 0.5 parts by weight of polyethylene glycol [manufactured by Lion Corporation, average molecular weight 300] and an inorganic nucleating agent 0.1 part by weight of talc [manufactured by Hayashi Kasei Co., Ltd., Talcan powder PK-S] was added and mixed.
The obtained mixture was melt-kneaded at a resin temperature of 200 ° C. using a twin-screw extruder [manufactured by ONENKI Co., Ltd., TEK45], then extruded into a strand, and the resulting strand was cooled with water and cut. Thus, polypropylene resin particles (1.2 mg / particle) were produced.

[Preparation of expanded polypropylene resin particles]
In a pressure-resistant container having an internal volume of 10 L, 100 parts by weight of the obtained polypropylene-based resin particles, 1 part by weight of powdery basic tribasic calcium phosphate as a dispersing agent, and 0.05% by weight of sodium n-paraffin sulfonate as a dispersing aid 170 parts by weight of an aqueous dispersion medium containing parts, and 6.0 parts by weight of carbon dioxide gas as a foaming agent, and while stirring, the temperature is raised to 150 ° C., which is equal to or higher than the softening point temperature of the polypropylene resin particles. After maintaining for 30 minutes, carbon dioxide gas was additionally injected to adjust the foaming pressure to 2.5 MPa (gauge pressure) and maintained for 30 minutes. Thereafter, while keeping the temperature and pressure inside the pressure vessel constant while injecting carbon dioxide gas, the valve at the bottom of the pressure vessel is opened, and the aqueous dispersion medium is passed through an orifice plate having a hole diameter of 3.6 mmφ to form an unsealed system ( By releasing into a cylindrical container under atmospheric pressure), polypropylene resin pre-expanded particles (single-stage expanded particles) having an expansion ratio of 20 times were obtained. The inside of the cylindrical container was heated to 100 ° C. with steam.

[Preparation of polypropylene resin foam molding]
Using a polypropylene foam molding machine [Daisen Co., Ltd., KD345], adjust the air pressure inside the foam particles to 0.2 MPa (absolute pressure) in advance in a rectangular parallelepiped mold 400 mm long x 300 mm wide x 60 mm thick. The polypropylene resin pre-expanded particles are filled, the air in the mold is first expelled with water vapor of 0.1 MPa (gauge pressure), and then heat-molded for 10 seconds using heating steam of a predetermined pressure, thereby forming polypropylene. -Based resin foam molding was obtained. At this time, the heating steam pressure was increased from 0.20 MPa (gauge pressure) by 0.01 MPa, thereby producing a molded body.
The minimum heating steam pressure at the time of in-mold foam molding and the obtained in-mold foam molded product were evaluated. The results are shown in Table 1.

(Example 2)
In [Preparation of polypropylene resin particles], pre-expanded particles were obtained in the same manner as in Example 1, except that 98 parts by weight of polypropylene resin (A) and 2 parts by weight of modified polypropylene-based resin were obtained. In-mold foaming was obtained using and evaluated.
The results are shown in Table 1.

(Example 3)
In [Preparation of polypropylene resin particles], pre-expanded particles were obtained in the same manner as in Example 1 except that 95 parts by weight of the polypropylene resin (A) and 5 parts by weight of the modified polypropylene resin were obtained. In-mold foaming was obtained using and evaluated. The results are shown in Table 1.

Example 4
In [Preparation of polypropylene resin particles], 98 parts by weight of polypropylene resin (A) and 2 parts by weight of modified polypropylene resin were used. The foaming temperature was 150 ° C. and the foaming pressure was 3.3 MPa in [Preparation of polypropylene resin foam particles]. Except for changing to (gauge pressure) and changing the expansion ratio of the pre-expanded particles to 30 times, pre-expanded particles were obtained in the same manner as in Example 1, and in-mold expansion was obtained using the pre-expanded particles, Evaluation was performed. The results are shown in Table 1.

(Example 5)
In [Preparation of polypropylene resin particles], it was changed to 98 parts by weight of polypropylene resin (A) and 2 parts by weight of modified polypropylene resin, and in [Preparation of expanded polypropylene resin particles], the inside of the cylindrical container was heated. Except not having performed, pre-expanded particles were obtained by the same operation as in Example 1, and in-mold expansion was obtained using the pre-expanded particles, and evaluation was performed. The results are shown in Table 1.

(Example 6)
The polypropylene-based pre-expanded particles (single-stage expanded particles) obtained in Example 5 were dried at 80 ° C. for 6 hours, and then impregnated with pressurized air in a pressure-resistant container, so that the internal pressure was 0.37 MPa ( Absolute pressure), and then contacted with 0.08 MPa (gauge pressure) water vapor to obtain pre-foamed particles by the same operation as in Example 5 except that the two-stage foamed (two-stage foamed particles). In-mold foaming was obtained using the pre-foamed particles and evaluated. The results are shown in Table 1.

( Reference Example 7)
[Preparation of modified polypropylene resin] Pre-expanded particles were obtained in the same manner as in Example 2 except that the radical initiator amount was changed to 0.40 parts by weight and the isoprene amount was changed to 0.45 parts by weight. In-mold foaming was obtained using the pre-foamed particles and evaluated. The results are shown in Table 1.

(Example 8)
In [Production of Modified Polypropylene Resin], pre-expanded particles were obtained in the same manner as in Example 2 except that the amount of radical initiator was 1.30 parts by weight and the amount of isoprene was 0.27 parts by weight. In-mold foaming was obtained using the pre-foamed particles and evaluated. The results are shown in Table 1.

Example 9
In [Production of Modified Polypropylene Resin], the same operation as in Example 2 except that the amount of radical initiator at the time of production of the modified polypropylene resin was 1.30 parts by weight and the amount of isoprene was 0.20 parts by weight. Thus, pre-expanded particles were obtained, in-mold expansion was obtained using the pre-expanded particles, and evaluation was performed. The results are shown in Table 1.

(Example 10)
In [Production of modified polypropylene resin], a modified polyethylene resin was obtained by the same operation as in Example 8, except that the base resin of the modified polypropylene resin was changed to the polypropylene resin (B). Furthermore, pre-expanded particles were obtained by the same operation as in Example 8, and in-mold expansion was obtained using the pre-expanded particles, and evaluation was performed. The results are shown in Table 1.

(Reference Example 1)
In [Preparation of expanded polypropylene resin particles], pre-expanded particles were obtained in the same manner as in Example 5 except that only the polypropylene resin (A) was used. Obtained and evaluated. The results are shown in Table 1.

(Reference Example 2)
[Preparation of expanded polypropylene resin particles] In the same manner as in Example 1 except that only the polypropylene resin (A) was used, pre-expanded particles were obtained, and in-mold expansion was performed using the pre-expanded particles. Obtained and evaluated. The results are shown in Table 1.

(Reference Example 3)
[Preparation of expanded polypropylene resin particles] In the same manner as in Example 4 except that only the polypropylene resin (A) was used, pre-expanded particles were obtained, and in-mold expansion was performed using the pre-expanded particles. Obtained and evaluated. The results are shown in Table 1.
In addition, since Reference Examples 1 to 3 were used as reference values in the compression strength comparison, comprehensive evaluation was not performed.

(Comparative Example 1)
In [Production of polypropylene resin particles], pre-expanded particles were obtained in the same manner as in Example 1 except that 99.8 parts by weight of polypropylene resin (A) and 0.2 parts by weight of modified polypropylene resin were used. In-mold foaming was obtained using the pre-foamed particles and evaluated. The results are shown in Table 1.

(Comparative Example 2)
In [Preparation of polypropylene resin particles], pre-expanded particles were obtained in the same manner as in Example 1 except that 92 parts by weight of polypropylene resin (A) and 8 parts by weight of modified polypropylene-based resin were obtained. In-mold foaming was obtained using and evaluated. The results are shown in Table 1.

(Comparative Example 3)
In [Preparation of polypropylene resin particles], pre-expanded particles were obtained in the same manner as in Example 1 except that 87 parts by weight of polypropylene resin (A) and 13 parts by weight of modified polypropylene resin were used. In-mold foaming was obtained using and evaluated. The results are shown in Table 1.

(Comparative Example 4)
In [Production of Modified Polypropylene Resin], pre-expanded particles were obtained by the same operation as in Example 2 except that the amount of isoprene was changed to 0.62 parts by weight. In-mold foaming was obtained using and evaluated. The results are shown in Table 1.

(Comparative Example 5)
In [Production of Modified Polypropylene Resin], pre-expanded particles were obtained in the same manner as in Example 2, except that the radical initiator amount was changed to 1.5 parts by weight and the isoprene amount was changed to 0.20 parts by weight. In-mold foaming was obtained using the pre-foamed particles and evaluated. The results are shown in Table 1.

(Comparative Example 6)
In [Production of Modified Polypropylene Resin], pre-expanded particles were obtained in the same manner as in Example 2 except that the radical initiator amount was changed to 2.0 parts by weight and the isoprene amount was changed to 0.20 parts by weight. In-mold foaming was obtained using the pre-foamed particles and evaluated. The results are shown in Table 1.

(Example 11)
In [Production of Modified Polypropylene Resin], a modified polypropylene resin was obtained by the same operation as in Example 8, except that the base resin of the modified polypropylene resin was changed to polypropylene resin (B). In [Preparation of polypropylene resin particles], pre-expanded particles were obtained in the same manner as in Example 8, except that the polypropylene resin type was changed to polypropylene resin (B). In-mold foaming was obtained and evaluated. The results are shown in Table 2.

(Reference Example 4)
In [Preparation of expanded polypropylene resin particles], pre-expanded particles were obtained in the same manner as in Example 1 except that only the polypropylene resin (B) was used. Obtained and evaluated. The results are shown in Table 2.
In addition, since Reference Example 4 was used as a reference value in the comparison of compressive strength, comprehensive evaluation was not performed.

(Comparative Example 7)
In [Production of Modified Polypropylene Resin], pre-expanded particles were obtained in the same manner as in Example 11 except that the radical initiator amount was changed to 1.50 parts by weight and the isoprene amount was changed to 0.20 parts by weight. In-mold foaming was obtained using the pre-foamed particles and evaluated. The results are shown in Table 2.

(Example 12)
In [Production of Modified Polypropylene Resin], a modified polypropylene resin was obtained by the same operation as in Example 8, except that the base resin of the modified polypropylene resin was changed to polypropylene resin (C). [Preparation of polypropylene resin particles] In the same manner as in Example 8 except that the polypropylene resin type was changed to polypropylene resin (C), pre-expanded particles were obtained, and the pre-expanded particles were used. In-mold foaming was obtained and evaluated. The results are shown in Table 3.

(Reference Example 5)
In [Preparation of expanded polypropylene resin particles], pre-expanded particles were obtained in the same manner as in Example 1 except that only the polypropylene resin (B) was used. Obtained and evaluated. The results are shown in Table 3.
In addition, since Reference Example 5 was used as a reference value in the compression strength comparison, comprehensive evaluation was not performed.

(Comparative Example 8)
In [Production of Modified Polypropylene Resin], pre-expanded particles were obtained in the same manner as in Example 12 except that the radical initiator amount was changed to 1.50 parts by weight and the isoprene amount was changed to 0.20 parts by weight. In-mold foaming was obtained using the pre-foamed particles and evaluated. The results are shown in Table 3.

As described above, in the polypropylene resin pre-expanded particles, when the technique described in the present invention is used, the high-rigidity is excellent in fusion and surface beauty in a molding machine of 0.4 MPa pressure resistance specification which is often used at present. In-mold foam can be produced. Therefore, it is possible to provide a lightweight foam in the mold.

Claims (5)

(A) 95.0 to 99.5% by weight of a polypropylene-based resin, and (B) ratio of storage elastic modulus and loss elastic modulus at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement at 180 ° C. Resin mixture comprising 0.5 to 5.0% by weight of a modified polypropylene resin having a loss tangent tan δ of 0.6 to 2.0 [the total amount of (A) and (B) is 100% by weight] Is obtained by foaming polypropylene resin particles having a base resin as a base resin ,
A polypropylene resin pre-expanded particle, wherein the melt flow rate of the modified polypropylene resin is 8 g / 10 min or more . The polypropylene resin pre-expanded particles according to claim 1, wherein the melt flow rate of the modified polypropylene resin is 80 g / 10 min or less.   The polypropylene according to claim 1 or 2, wherein the modified polypropylene resin is a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. -Based resin pre-expanded particles. Polypropylene resin particles, water and a foaming agent are accommodated in a pressure vessel and dispersed under stirring conditions, and after raising the temperature above the softening point temperature of the polypropylene resin particles, a pressure range lower than the internal pressure of the pressure vessel The method for producing pre- expanded polypropylene resin particles according to any one of claims 1 to 3, wherein the polypropylene resin particles are expanded by discharging the dispersion in the pressure vessel.   A method for producing a polypropylene resin molded article, which is obtained by filling a polypropylene resin pre-expanded particle according to any one of claims 1 to 3 into a mold and subjecting the resin to foam molding in a mold.