JPWO2019189462A1 - Manufacturing method of polypropylene-based resin foam particles - Google Patents

Abstract

An object of the present invention is to provide polypropylene-based resin foamed particles having a high porosity and capable of providing a polypropylene-based resin foamed molded article having a high magnification by using an inorganic foaming agent. Manufactured using a polypropylene resin composition containing a specific amount of a polypropylene resin, a hydrophilic substance, a foam nucleating agent, and a higher fatty acid amide, and an inorganic foaming agent, a specific cell diameter, DSC ratio, average L ₁ /. Let it be a polypropylene-based resin foamed particle having a D _{1 ratio.}

Description

The present invention relates to a method for producing polypropylene-based resin foam particles and its use.

The polypropylene-based resin in-mold foam molded product (hereinafter, also referred to as “in-mold foam molded product”, “foam molded product” or “molded product”) is a buffer packaging material, a distribution material (for example, a return box, for truck transportation). It is widely used in applications such as cushioning materials), heat insulating materials, civil engineering and building materials, and automobile parts (for example, tool boxes, floor core materials, etc.). The polypropylene-based resin mold in-foam molded product can also be provided with characteristics such as water permeability, breathability, and sound absorption by providing voids, and is also used as a sound absorbing material. ..

Polypropylene-based resin foamed particles (hereinafter, also referred to as “foamed particles”) are molded, and polypropylene-based resin foamed particles having a specific shape are heat-molded as a method for producing a polypropylene-based resin foamed molded article having communicating voids. The method is disclosed (Patent Document 1 and Patent Document 2). The techniques disclosed in these documents are characterized by using polypropylene-based resin foam particles having a hollow cylinder or a hollow irregular shape, or a cross-shaped unevenness such as a cross shape.

Patent Document 3 and Patent Document 4 disclose a method for obtaining a polypropylene-based resin foam molded article having a high porosity. According to these methods, since the resin particles are not hollow and have a complicated shape, it is possible to easily and economically provide a polypropylene-based resin foam molded product having a high void ratio without reducing the productivity of the resin particles. ..

As a method for obtaining foamed particles, (1) in the container, the thermoplastic resin particles are dispersed together with the foaming agent in an aqueous dispersion medium to prepare a dispersion liquid, and (2) the inside of the container is heated to raise the temperature inside the container. A method is known in which a thermoplastic resin particle is impregnated with a foaming agent at a constant pressure and a constant temperature, and then (3) the dispersion liquid is discharged under a low pressure atmosphere to obtain foamed particles. Examples of the foaming agent include a method using a volatile organic foaming agent such as propane and butane (Patent Document 5) and a method using an inorganic foaming agent such as carbon dioxide, nitrogen and air (Patent Documents 6 and 7). It is disclosed.

Further, a method of using water used as a dispersion medium as a foaming agent is known (Patent Document 8 and Patent Document 9).

Japanese Unexamined Patent Publication No. 7-138399 Japanese Unexamined Patent Publication No. 7-138400 International release WO2006 / 016478 Japanese Unexamined Patent Publication No. 2007-217579 Special Publication No. 56-1344 Tokuho 4-6433 Special Publication No. 62-61227 Japanese Unexamined Patent Publication No. 2003-171516 Japanese Unexamined Patent Publication No. 2004-67768

However, in the above-mentioned prior art, when an inorganic foaming agent is used as the foaming agent, polypropylene-based resin foaming can provide a polypropylene-based resin in-mold foam molded product having a high porosity and a high magnification. From the point of view of obtaining particles, there was room for further improvement.

One embodiment of the present invention has been made in view of the above problems, and an object of the present invention is (i) a method for producing polypropylene-based resin foamed particles using an inorganic foaming agent, which has a high void ratio and has a high void ratio. New polypropylene-based resin foamed particles capable of providing a high-magnification polypropylene-based resin in-mold foam molded article, and (ii) new polypropylene-based resin in-mold foam having a high void ratio and high magnification. To provide a molded body.

As a result of diligent studies to solve the above problems, the present inventors have completed the present invention.

That is, the method for producing the polypropylene-based resin foamed particles according to the embodiment of the present invention is a step of dispersing the polypropylene-based resin particles in an aqueous dispersion medium together with a foaming agent in a pressure-resistant container, which is equal to or higher than the softening temperature of the polypropylene-based resin particles. The step of heating the inside of the pressure-resistant container to a temperature and pressurizing the inside of the pressure-resistant container, and the pressure of the aqueous dispersion medium in which the polypropylene-based resin particles and the foaming agent are dispersed are lower than the internal pressure of the pressure-resistant container. It has a step of releasing it into a region to obtain polypropylene-based resin foam particles, and the polypropylene-based resin particles are hydrophilic substances (a) with respect to 100 parts by weight of the polypropylene-based resin (a) and the polypropylene-based resin (a). b) 1.0 part by weight or more and 10 parts by weight or less, and 1.0 part by weight or more and 10 parts by weight or less of the foam nucleating agent (c), and the hydrophilic substance (b) and the foaming nucleating agent (c) The polypropylene-based resin composition comprises a total amount of 2.5 parts by weight or more and 20 parts by weight or less and 1.0 part by weight or more and 5.0 parts by weight or less of the higher fatty acid amide (d). The resin foam particles have an average L ₁ / D ₁ ratio of 1.3 or more and 3.5 or less, a cell diameter of 30 μm or more and 100 μm or less, and are 40 ° C. to 220 ° C. by differential scanning calorimetry (DSC) of the foamed particles. The DSC ratio calculated from the DSC curve obtained when the temperature is raised to 10 ° C./min is 40% or more and 70% or less, and the foaming ratio is 15 times or more and 35 times or less. Is an inorganic foaming agent containing carbon dioxide.

In one embodiment of the present invention, a polypropylene-based resin capable of providing a polypropylene-based resin in-mold foam molded article having a high porosity and a high magnification in a production method using an inorganic foaming agent as a foaming agent. Foamed particles can be obtained.

(A) is an external view of polypropylene-based resin foamed particles according to an embodiment of the present invention, and _{L 1} , D ₁ max, used for calculating _{the L 1} / D _{1 ratio of the polypropylene-based resin foamed particles.} is a diagram that describes the values of D 1 _min, (b) is an external view of a polypropylene resin particles according to an embodiment of the present invention, it calculates the L _{2 /} D ₂ ratio of the polypropylene resin particles It is a figure explaining each value of L ₂ , D ₂ max, and D _{2 min used for this.} This is an example of the DSC curve at the time of the first temperature rise of the polypropylene-based resin foamed particles.

An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications can be made within the scope of the claims. The technical scope of the present invention also includes embodiments or examples obtained by appropriately combining the technical means disclosed in the different embodiments or examples. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. In addition, all the academic documents and patent documents described in the present specification are incorporated as references in the present specification.

Unless otherwise specified in the present specification, "A to B" representing a numerical range is intended to be "A or more (including A and larger than A) and B or less (including B and smaller than B)".

Unless otherwise specified in the present specification, the structural units include _{a structural unit derived from an X 1} monomer, a structural unit derived from an X ₂ monomer, ..., And an X _n monomer (n is 2 or more). A copolymer containing (an integer of) is also referred _{to as "X 1-} X ₂ -...- X _{n copolymer".} Unless otherwise specified, the X ₁ −X ₂ − ··· −X _n copolymer is not particularly limited in the polymerization mode, and may be a random copolymer or a block copolymer. It may be a graft copolymer or a graft copolymer.

[1. Technical Thought of One Embodiment of the Present Invention]
As a result of diligent studies by the present inventor, it has been found that the above-mentioned Patent Documents 1 to 3 have room for improvement or problems as shown below.

Patent Documents 1 and 2 disclose techniques for using polypropylene-based resin foam particles having a specific shape, that is, a variant shape. In order to produce these irregularly shaped polypropylene-based resin foam particles, it is necessary to produce resin particles corresponding to the shape. However, since the production of the resin particles is complicated, in-mold foam molding of polypropylene-based resin foam particles is performed. The productivity of the resin particles having a particle size of 1 to 10 mg, which is generally used, is low, which is economically disadvantageous.

In the examples of Patent Documents 3 and 4, only the case where a volatile organic foaming agent is used as the foaming agent for obtaining a high foaming ratio is disclosed. These technologies using volatile organic foaming agents have room for improvement in terms of environment and equipment cost. In addition, the volatile organic foaming agent has the effect of plasticizing the thermoplastic resin, and while it is easy to obtain a high foaming ratio, the plasticizing effect makes it difficult to control the foaming ratio and the crystal state of the foamed particles. , The present inventor has found it independently. Specifically, as a result of diligent studies, when the compounding of the examples of Patent Documents 3 and 4 is carried out by changing only the foaming agent to an inorganic foaming agent, the mold has a high porosity and a high magnification. The present inventor has independently found that it is difficult to obtain an internally foamed molded product.

When using inorganic foaming agents such as nitrogen and air, the global warming potential is smaller than that of volatile organic foaming agents, and equipment does not need to be explosion-proof. It is advantageous. Therefore, an object according to an embodiment of the present invention is to provide a polypropylene-based resin in-mold foam molded article having a high porosity and a high magnification in a production method using an inorganic foaming agent as a foaming agent. It is to obtain polypropylene-based resin foamed particles.

According to the present inventor, when an inorganic foaming agent is used, the impregnation performance of the inorganic foaming agent into the thermoplastic resin is very low, and therefore a sufficient impregnation amount for high foaming cannot be obtained even at a high pressure. I found the problem on my own. In order to solve this problem, the present inventor has studied diligently. As a result, polypropylene-based resin particles composed of a polypropylene-based resin composition containing a specific amount of each of the polypropylene-based resin (a), the hydrophilic substance (b), the foam nucleating agent (c), and the higher fatty acid amide (d). used, is manufactured in inorganic foaming agent, a particular cell size, by a foamed polypropylene resin particles having a DSC ratio, and average L _{1 /} D ₁ ratio, found that the above problems can be solved, the The invention was completed.

[2. Manufacturing method of polypropylene-based resin foam particles]
The method for producing polypropylene-based resin foam particles according to an embodiment of the present invention is a step of dispersing the polypropylene-based resin particles in an aqueous dispersion medium together with a foaming agent in a pressure-resistant container, up to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles. The step of heating the inside of the pressure-resistant container and pressurizing the inside of the pressure-resistant container, and the aqueous dispersion medium in which the polypropylene-based resin particles and the foaming agent are dispersed are placed in a pressure range lower than the internal pressure of the pressure-resistant container. It has a step of releasing to obtain polypropylene-based resin foam particles, and the polypropylene-based resin particles are hydrophilic substances (b) with respect to 100 parts by weight of the polypropylene-based resin (a) and the polypropylene-based resin (a). 1.0 part by weight or more and 10 parts by weight or less, and 1.0 part by weight or more and 10 parts by weight or less of the foam nucleating agent (c), and the total of the hydrophilic substance (b) and the foaming nucleating agent (c). The polypropylene-based resin composition comprises a polypropylene-based resin composition having an amount of 2.5 parts by weight or more and 20 parts by weight or less and 1.0 part by weight or more and 5.0 parts by weight or less of the higher fatty acid amide (d). The particles have an average L ₁ / D ₁ ratio of 1.3 or more and 3.5 or less, a cell diameter of 30 μm or more and 100 μm or less, and are from 40 ° C. to 220 ° C. by differential scanning calorimetry (DSC) of foamed particles. The DSC ratio calculated from the DSC curve obtained when the temperature is raised at a rate of 10 ° C./min is 40% or more and 70% or less, and the foaming ratio is 15 times or more and 35 times or less. It is an inorganic foaming agent containing carbon.

Here, the average L ₁ / D ₁ ratio is an average value calculated from _{the L 1} / D ₁ ratio of 10 randomly selected polypropylene-based resin foamed particles _{, and L 1} is a polypropylene-based resin. _{D 1} is the length of the longest part of the foamed particles, and D 1 is the average value of the maximum diameter D ₁ max and the minimum diameter D _{1 min in the cross section perpendicular to the L 1} direction of the polypropylene resin foam particles, and is described below. It is a value calculated by the formula (1):
D ₁ = (D ₁ max + D ₁ min) / 2 ... Equation (1).

Since the method for producing polypropylene-based resin foam particles according to one embodiment of the present invention has the above configuration, it has a high porosity and a high magnification in the production method using an inorganic foaming agent as a foaming agent. It is possible to provide polypropylene-based resin foamed particles, which can provide a polypropylene-based resin in-mold foam molded product. Further, in one embodiment of the present invention, polypropylene-based resin foamed particles and polypropylene-based resin foamed molded article in which friction noise is suppressed can be obtained.

In the present specification, the "method for producing polypropylene-based resin foam particles" may be referred to as a "production method". In the present specification, "polypropylene resin particles" may be referred to as "resin particles".

(2-1. Polypropylene resin particles)
(Polypropylene resin (a))
The polypropylene-based resin (a) used in one embodiment of the present invention is a polymer in which the propylene monomer unit is 50% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more. The polypropylene-based resin (a) used in one embodiment of the present invention is preferably one that is polymerized with a metallocene catalyst or a Ziegler-type titanium chloride-based catalyst and has high stereoregularity. Specific examples of the polypropylene-based resin (a) include a propylene homopolymer, an ethylene-propylene random copolymer (also referred to as "ethylene-propylene-based random copolymer"), a propylene-butene random copolymer, and the like. Ethylene-propylene-butene random copolymer (also referred to as "butene-ethylene-propylene-based random copolymer"), ethylene-propylene block copolymer, maleic anhydride-propylene random copolymer, maleic anhydride-propylene Examples thereof include a block copolymer, a maleic anhydride-g-propylene graft copolymer, and the like, and each of them is used alone or in combination of two or more. In particular, ethylene-propylene random copolymers, propylene-butene random copolymers, and ethylene-propylene-butene random copolymers can be preferably used. Further, these polypropylene-based resins (a) are preferably non-crosslinked, but crosslinked ones can also be used. As used herein, "butene" is intended as "1-butene". The "maleic anhydride-g-propylene graft copolymer" is intended to have maleic anhydride grafted onto the main chain of the propylene polymer.

The polypropylene-based resin (a) used in one embodiment of the present invention preferably has a melt index (hereinafter, MI) of 1 g / 10 minutes or more and 30 g / 10 minutes or less, and 2 g / 10 minutes or more and 20 g / 10. More preferably, it is less than a minute.

If the MI of the polypropylene-based resin (a) is less than 1 g / 10 minutes, the foaming power at the time of producing the foamed particles is low, and it tends to be difficult to obtain the foamed particles having a high foaming ratio. As a result, it tends to be difficult to secure the fusion strength between the foamed particles when the obtained foamed particles are used as a foamed molded product. When the MI of the polypropylene-based resin (a) exceeds 30 g / 10 minutes, the bubbles of the polypropylene-based resin foamed particles tend to break easily (easily break), and the continuous foaming rate of the polypropylene-based resin foamed particles tends to increase.

The MI value of the polypropylene-based resin (a) is a value measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

The polypropylene-based resin (a) used in one embodiment of the present invention has a melting point of preferably 130 to 168 ° C., more preferably 133 to 160 ° C. in order to obtain a foamed molded product having excellent mechanical strength and heat resistance. ° C., particularly preferably 135-155 ° C. When the melting point of the polypropylene-based resin (a) is 135 to 155 ° C., there is a strong tendency to easily balance moldability with mechanical strength and heat resistance.

Here, the melting point of the polypropylene-based resin (a) is a value obtained as a result of differential scanning calorimetry (DSC) performed using a differential scanning calorimetry. The specific operation procedure is as follows: (1) After heating 1 to 10 mg of polypropylene resin from 40 ° C. to 220 ° C. at a rate of 10 ° C./min to melt; (2) from 220 ° C. After cooling to 40 ° C. at a rate of 10 ° C./min for crystallization; (3) the temperature is raised again from 40 ° C. to 220 ° C. at a rate of 10 ° C./min. The peak temperature of the endothermic peak in the DSC curve obtained at the time of the second temperature rise (that is, at the time of (3)) is defined as the melting point.

In the method for producing polypropylene-based resin foamed particles according to an embodiment of the present invention, polypropylene composed of a polypropylene-based resin composition obtained by adding a hydrophilic substance (b) and a foaming nucleating agent (c) to a polypropylene-based resin (a). Uses based resin particles. As a result, water used as an aqueous dispersion medium can be used as a foaming agent, and water used as a foaming agent can be easily taken into the resin and the cell diameter can be easily miniaturized. As a result, according to the method for producing polypropylene-based resin foamed particles according to an embodiment of the present invention, the polypropylene-based resin foamed particles having a high magnification and a high void ratio can be provided. Can be obtained. The "cell" may also be referred to as a "bubble".

(Hydrophilic substance (b))
The hydrophilic substance (b) used in one embodiment of the present invention is (i) metal borate salts such as borosand and zinc borate, and (ii) water-soluble inorganic substances such as sodium chloride, calcium chloride and magnesium chloride. , (Iii) water-absorbent organic substances having a triazine skeleton such as ammeline, melamine, isocyanuric acid, melamine / isocyanuric acid condensate, (iv) polyethylene glycol, polyether such as polyethylene oxide, and (v) glycerin, diglycerin and the like. It can be selected from the group consisting of polyols. These hydrophilic substances (b) may be used alone or in combination of two or more.

In the method for producing polypropylene-based resin foam particles according to an embodiment of the present invention, the hydrophilic substance (b) is (i) an organic substance having a triazine skeleton and having a molecular weight of 300 or less per unit triazine skeleton, and (ii). It is preferable to contain at least one selected from the group consisting of metal borate salts. In other words, among the above-mentioned hydrophilic substances (b), a triazine skeleton such as melamine is present because it is easy to add when producing polypropylene-based resin particles and it is easy to increase the expansion ratio of the expanded particles. A hydrophilic substance (b) containing at least one organic substance having a molecular weight of 300 or less per unit triazine skeleton or a metal borate salt is preferable.

Here, in the present specification, the following substances shall not be regarded as hydrophilic substances (b): (i) ethylene-acrylic acid-maleic anhydride ternary copolymer, ethylene- (meth) acrylic acid. Copolymers, carboxyl group-containing polymers such as ionomer resins obtained by cross-linking ethylene- (meth) acrylic acid copolymers with metal ions, polyamides such as (ii) nylon 6, nylon 6,6, and copolymerized nylon, and (iii). ) Thermoplastic polyester-based elastomers such as polybutylene terephthalate and block copolymers of polytetramethylene glycol. The above-mentioned carboxyl group-containing polymers, polyamides and thermoplastic polyester-based elastomers are sometimes referred to as "hydrophilic polymers".

The method for producing polypropylene-based resin foam particles according to an embodiment of the present invention may be an embodiment in which the following substances are substantially not used: (i) Ethylene-acrylic acid-maleic anhydride ternary copolymer. , Ethylene- (meth) acrylic acid copolymer, carboxyl group-containing polymer such as ionomer resin obtained by cross-linking ethylene- (meth) acrylic acid copolymer with metal ions, (ii) nylon 6, nylon 6,6, copolymerization Polypolymers such as nylon, and thermoplastic polyester elastomers such as (iii) polybutylene terephthalate and block copolymers of polytetramethylene glycol. Here, "substantially not using the following substances" can be said to mean that the substance contained in the obtained polypropylene-based resin foamed particles is 10 ppm or less based on the polypropylene-based resin foamed particles.

The amount of the hydrophilic substance (b) added in the production method according to the embodiment of the present invention is preferably 1.0 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the polypropylene resin (a). , 1.5 parts by weight or more and 9.5 parts by weight or less is more preferable. Here, the amount of the hydrophilic substance (b) added refers to the weight of the hydrophilic substance (b) in a state where it does not absorb water. In the present specification, the "addition amount" can also be said to be the "usage amount". The amount of the hydrophilic substance (b) added can also be said to be the content of the hydrophilic substance (b) in the polypropylene-based resin composition.

If the amount of the hydrophilic substance (b) added is less than 1.0 part by weight with respect to 100 parts by weight of the polypropylene resin (a), the expansion ratio of the polypropylene resin foamed particles tends to be unable to be improved. When the amount of the hydrophilic substance (b) added exceeds 10 parts by weight with respect to 100 parts by weight of the polypropylene resin (a), the drying time of the molded product becomes long and the shrinkage rate of the molded product deteriorates. That is, the shrinkage rate tends to increase and the voids in the molded product tend to be easily filled.

(Effervescent nucleating agent (c))
The foaming nucleating agent (c) used in one embodiment of the present invention is a substance that promotes the formation of bubble nuclei when the resin particles are foamed. Examples of the effervescent nucleating agent (c) include inorganic substances such as talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, and titanium oxide. As these effervescent nucleating agents (c), one type may be used alone, or two or more types may be used in combination. Among these, talc is preferable as the effervescent nucleating agent (c) because talc has good dispersibility in the polypropylene resin (a) and makes it easy to obtain effervescent particles having uniform bubbles.

The amount of the foam nucleating agent (c) added in the production method according to the embodiment of the present invention is preferably 1.0 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the polypropylene resin (a). , 1.5 parts by weight or more and 9.5 parts by weight or less is more preferable. The amount of the foaming nucleating agent (c) added can also be said to be the content of the foaming nucleating agent (c) in the polypropylene-based resin composition.

When the amount of the foam nucleating agent (c) added is less than 1.0 part by weight with respect to 100 parts by weight of the polypropylene resin (a), the porosity of the polypropylene resin foam particles tends to be unable to be improved. .. When the amount of the foam nucleating agent (c) added is more than 10 parts by weight with respect to 100 parts by weight of the polypropylene resin (a), the cell diameter of the foamed particles becomes too fine, and the foamed particles during in-mold foam molding The secondary foaming force deteriorates, the meltability of the foamed molded product in the mold deteriorates, and cracks tend to occur easily.

The total amount of the hydrophilic substance (b) and the foam nucleating agent (c) contained in the polypropylene-based resin composition in the production method according to the embodiment of the present invention is 2.5 parts by weight or more and 20 parts by weight or less. It is preferable, more preferably 3.0 parts by weight or more and 18.0 parts by weight or less, and further preferably 4.0 parts by weight or more and 8.0 parts by weight or less. When the total addition amount of the hydrophilic substance (b) and the foam nucleating agent (c) is less than 2.5 parts by weight, the foamability and porosity tend to decrease, and the total addition amount is 20 parts by weight. If it exceeds the limit, the foamed particles tend to shrink extremely easily, and a good product cannot be obtained.

(Higher fatty acid amide (d))
The higher fatty acid amide used in one embodiment of the present invention is preferably formed from a higher fatty acid having 10 to 25 carbon atoms as a raw material. Higher fatty acid amides formed from higher fatty acids having less than 10 carbon atoms are not sufficiently effective in suppressing friction noise, and higher fatty acids having more than 25 carbon atoms are difficult to obtain and are not practical. Examples of the higher fatty acid amide (d) include saturated fatty acid amides, unsaturated fatty acid amides and bis fatty acid amides. Specifically, the saturated fatty acid amide includes lauric acid amide, palmitate amide, stearic acid amide, behemic acid amide and the like, and the unsaturated fatty acid amide includes erucic acid amide, oleic acid amide, brassic acid amide, ellagic acid amide and the like. Examples of bis fatty acid amides include methylene bisstearic acid amide, methylene bislauric acid amide, ethylene bisstearic acid amide, ethylene bislauric acid amide, methylene bisoleic acid amide, methylene biserucic acid amide, ethylene bisoleic acid amide, and ethylene bisuelka. Acid amide and the like can be mentioned. These higher fatty acid amides (d) may be used alone or in combination of two or more.

The amount of the higher fatty acid amide (d) added in the production method according to the embodiment of the present invention is 1.0 part by weight or more and 5.0 parts by weight or less with respect to 100 parts by weight of the polypropylene resin (a). Is preferable, and more preferably 1.5 parts by weight or more and 4.5 parts by weight or less. The amount of the higher fatty acid amide (d) added can also be said to be the content of the higher fatty acid amide (d) in the polypropylene-based resin composition.

When the amount of the higher fatty acid amide (d) added is less than 1.0 part by weight with respect to 100 parts by weight of the polypropylene resin (a), the effect of suppressing friction noise is not exhibited. When the amount of the higher fatty acid amide (d) added is more than 5.0 parts by weight with respect to 100 parts by weight of the polypropylene resin (a), the dispersant easily adheres to the surface of the obtained polypropylene-based resin foamed particles. As a result, when in-mold foam molding is performed using the foamed particles, poor fusion between the foamed particles tends to occur.

(Additive)
In the production method according to the embodiment of the present invention, when the polypropylene-based resin particles are produced, if necessary, a colorant, an antistatic agent, an antioxidant, a phosphorus-based processing stabilizer, and a lactone-based processing stabilizer are used. Agents, lubricants, metal deactivators, benzotriazole UV absorbers, benzoate light stabilizers, hindered amine light stabilizers, flame retardants, flame retardants, acid neutralizers, crystal nucleating agents, amide additives, etc. Various additives can be added to the polypropylene-based resin (a) within a range that does not impair the characteristics of the polypropylene-based resin (a). Examples of the colorant include carbon black.

In the method for producing polypropylene-based resin foamed particles according to an embodiment of the present invention, the above-mentioned carboxyl group-containing polymer, polyamide, thermoplastic polyester-based elastomer, etc., which are not regarded as the hydrophilic compound (b), are used in the polypropylene-based resin ( It can also be added to a).

When various additives are added to the polypropylene-based resin (a), it is preferable to mix the various additives with the polypropylene-based resin (a) using a blender or the like before producing the polypropylene-based resin particles. Further, in the production of polypropylene-based resin particles, various additives may be added to the molten polypropylene-based resin (a).

(Manufacturing method of polypropylene resin particles)
The polypropylene-based resin (a) in the production method according to the embodiment of the present invention is usually melt-kneaded using an extruder, a kneader, a Banbury mixer, a roll, or the like to produce foamed particles, and is cylindrical or elliptical. It can be processed into a resin particle shape such as a shape, a sphere, a cube shape, or a rectangular parallelepiped shape.

The step of processing the polypropylene-based resin (a) into the shape of resin particles, in other words, the step of producing polypropylene-based resin particles is also referred to as a granulation step. The method for producing polypropylene-based resin foamed particles according to an embodiment of the present invention may further include a granulating step.

As a method for producing polypropylene-based resin particles, for example, (1) the polypropylene-based resin composition is melt-kneaded using an extruder, a kneader, a Bambari mixer, a roll, or the like to prepare a melt-kneaded product, and then (2). By cooling the melt-kneaded product and (3) forming the melt-kneaded product into a desired shape such as a columnar shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular shape, a tubular shape (straw shape), or the like. , A method of obtaining polypropylene-based resin particles can be mentioned.

Hereinafter, a method for producing polypropylene-based resin particles will be specifically described by taking the case of using an extruder as an example. For example, polypropylene-based resin particles can be produced by the following methods (A1) to (A5): (A1) polypropylene-based resin (a), hydrophilic substance (b), foam nucleating agent (c) and The higher fatty acid amide (d) and, if necessary, various additives are blended to prepare a blend, and (A2) the blend is put into an extruder and melt-kneaded to prepare a polypropylene resin composition. Then, (A3) the polypropylene-based resin composition was extruded from a die provided in the extruder, and (A4) the extruded polypropylene-based resin composition was solidified by being cooled by passing it through water or the like, and then (A5) solidified. The polypropylene-based resin composition is shredded into a desired shape such as a columnar shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular shape, or the like with a cutter. Alternatively, in the above (A3), the polypropylene-based resin composition melt-kneaded may be extruded directly into water from a die provided in the extruder, and immediately after that, it may be shredded into particle shapes, cooled, and solidified. By melt-kneading the blended product in this way, more uniform polypropylene-based resin particles can be obtained.

Each of the various additives used as needed may be masterbatched. That is, a masterbatch resin in which an additive is contained in a high concentration in another resin may be prepared in advance. In this case, the masterbatch can be added as an additive. As the resin used when preparing the masterbatch resin, a polypropylene-based resin is preferable, and from the viewpoint of good compatibility, a masterbatch can be made using the same type of polypropylene-based resin as the polypropylene-based resin of the base resin. Most preferred.

(Grain weight of polypropylene resin particles)
The size of the polypropylene-based resin particles in the production method according to the embodiment of the present invention is preferably such that the weight per grain (also referred to as grain weight) is 0.1 mg or more and 30 mg or less, and 0.3 mg or more and 10 mg. The following is more preferable. Here, the weight per grain of the polypropylene-based resin particles is the average resin particle weight obtained from 100 randomly selected polypropylene-based resin particles, and is hereinafter expressed in mg / grain.

(Average L ₂ / D ₂ ratio of polypropylene resin particles)
As for the shape of the polypropylene-based resin particles in the production method according to the embodiment of the present invention, _{it is preferable that the average L 2} / D ₂ ratio of the polypropylene-based resin particles is 2.5 or more and 7.0 or less.

Here, the average L ₂ / D ₂ ratio of the polypropylene-based resin particles is an average value calculated from _{the L 2} / D _{2 ratio of 10 randomly selected polypropylene-based resin particles.} L ₂ and D ₂ will be described with reference to FIG. 1 (b). FIG. 1B is an external view of the polypropylene-based resin particles according to the embodiment of the present invention, and _{L 2} , D ₂ max used for calculating _{the L 2} / D _{2 ratio of the polypropylene-based resin particles.} , D ₂ min is the figure explaining each value. As shown in FIG. 1 (b), L ₂ is the length of the longest portion of the polypropylene-based resin particles. As shown in FIG. 1 (b), D ₂ is an average value of the maximum diameter D ₂ max and the minimum diameter D _{2 min in the cross section perpendicular to the L 2} direction of the polypropylene resin particles, and is the following equation (2). It is a value calculated in.
D ₂ = (D ₂ max + D ₂ min) / 2 ・ ・ ・ ・ ・ Equation (2)
As shown in FIG. 1 (b), it can be said that L ₂ is the length of the longest portion of the polypropylene-based resin particles in the longitudinal direction. When the polypropylene-based resin particles are produced by being extruded from an extruder or the like, as will be described later, L ₂ can be said to be the longest length in the extrusion direction of the polypropylene-based resin particles. D _{2 is an average value of the maximum diameter D 2} max and the minimum diameter D ₂ min in the cross section perpendicular to _{the L 2} direction of the maximum diameter portion of the polypropylene resin particles, and is calculated by the above formula (2). It can be said that it is a value. When the polypropylene-based resin particles are drum-shaped such that the central diameter in the longitudinal direction is smaller than the diameter of the end portion in the longitudinal direction, the maximum diameter portion of the polypropylene-based resin particles is the end portion of the polypropylene-based resin particles. obtain. When the polypropylene resin particles are substantially spherical, the maximum diameter portion of the polypropylene resin particles may be L ₂ direction of the center of the polypropylene resin particles.

When the polypropylene resin particles is cylindrical as shown in (b) of FIG. 1, the cross-sectional shape perpendicular to the L ₂ direction, the circle may be a free closed curve of the concave portion such as an ellipse, D 2 _max and D ₂ min can take a substantially constant value along the _{L 2 direction.}

In the method for producing polypropylene-based resin foam particles according to an embodiment of the present invention, _{it is more preferable that the polypropylene-based resin particles have an average L 2} / D ₂ ratio of less than 4.0. Polypropylene resin particles having an average _L 2 / _{D 2} ratio is less than 4.0, compared with the average _L 2 / _{D 2} ratio is 4.0 or more polypropylene resin particles, manufacture is easier. Therefore, according to the above configuration, the method for producing polypropylene-based resin foam particles is excellent in productivity. In the method for producing polypropylene-based resin foam particles according to an embodiment of the present invention, _{it is more preferable that the polypropylene-based resin particles have an average L 2} / D ₂ ratio of 2.5 or more and less than 4.0.

In the production method according to the embodiment of the present invention, (1) the polypropylene-based resin particles are dispersed in an aqueous dispersion medium together with a foaming agent in a pressure-resistant container, and (2) a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles. After heating the inside of the pressure-resistant container and pressurizing the inside of the pressure-resistant container, (3) the aqueous dispersion medium in which polypropylene-based resin particles and foaming agent are dispersed is released to a pressure range lower than the internal pressure of the pressure-resistant container. By doing so, polypropylene-based resin foamed particles can be obtained. An "aqueous dispersion medium in which polypropylene-based resin particles and a foaming agent are dispersed" may be referred to as a "dispersion liquid".

(Foaming agent)
The foaming agent used in the production method according to the embodiment of the present invention is an inorganic foaming agent containing carbon dioxide, preferably carbon dioxide alone. Examples of the inorganic foaming agent that can be used in combination with carbon dioxide include water, nitrogen, and air (mixture of oxygen, nitrogen, and carbon dioxide).

According to the method for producing polypropylene-based resin foamed particles according to an embodiment of the present invention, by using an inorganic foaming agent, it has a high porosity and a high magnification without using a volatile organic foaming agent. It is possible to obtain polypropylene-based resin foamed particles that can provide a polypropylene-based resin in-mold foam molded product. Volatile organic foaming agents such as propane and butane have (i) a substance having a global warming coefficient higher than that of carbon dioxide, and (ii) have the effect of plasticizing a thermoplastic resin, making it easy to obtain a high foaming ratio. On the other hand, due to its plasticizing action, it is difficult to control the expansion ratio and crystal state of the foamed particles, and since it is a (iii) flammable substance, it is necessary to make the equipment explosive, resulting in high equipment cost. It has drawbacks such as becoming.

By adopting the configuration according to one embodiment of the present invention, it becomes easy to increase the foaming force even when an inorganic foaming agent containing carbon dioxide is used, and foam molding in a polypropylene resin mold having a high magnification and a high porosity. It is possible to obtain high-magnification polypropylene-based resin foam particles that can provide a body. In addition, since it is not necessary to make the equipment explosion-proof, it is advantageous in terms of equipment cost.

The amount of the inorganic foaming agent used in the production method according to the embodiment of the present invention varies depending on the type of polypropylene resin (a) used, the target foaming ratio, and the like, and cannot be unconditionally specified. The amount of the inorganic foaming agent used is generally in the range of 2 to 60 parts by weight with respect to 100 parts by weight of the polypropylene resin (a).

(Pressure-resistant container)
The pressure-resistant container in which the polypropylene-based resin particles are dispersed is not particularly limited as long as it can withstand the pressure inside the container and the temperature inside the container during the production of foamed particles. Examples of the pressure-resistant container include an autoclave type pressure-resistant container.

(Aqueous dispersion medium)
Water is preferable as the aqueous dispersion medium. A dispersion medium in which methanol, ethanol, ethylene glycol, glycerin or the like is added to water can also be used.

(Dispersant and dispersion aid)
In the production method according to the embodiment of the present invention, it is preferable to add a dispersant to the aqueous dispersion medium in order to prevent the polypropylene-based resin particles from coalescing with each other. Examples of the dispersant include inorganic dispersants such as calcium tertiary phosphate, magnesium tertiary phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay. These may be used alone or in combination of two or more.

Further, it is preferable to add a dispersion aid together with the dispersant in the aqueous dispersion medium. Examples of the dispersion aid include sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium alkylsulfonate, sodium alkyldiphenyl ether disulfonate, sodium α-olefin sulfonate and the like. These may be used alone or in combination of two or more.

The amount of the dispersant and the dispersion aid added varies depending on the type thereof and the type and amount of the polypropylene-based resin (a) used, and can be appropriately set. The amount of the dispersant and the dispersion aid added is usually preferably 0.1 part by weight or more and 3 parts by weight or less of the dispersant with respect to 100 parts by weight of the aqueous dispersion medium, and 0.001 part by weight or more of the dispersion aid. It is preferably 0.200 parts by weight or less.

In the production method according to the embodiment of the present invention, in order to improve the dispersibility in the aqueous dispersion medium, polypropylene-based resin particles are usually 20% by weight based on 100 parts by weight of the aqueous dispersion medium. It is preferable to use more than 100 parts by weight.

Specific examples of the method for producing polypropylene-based resin foam particles according to an embodiment of the present invention are as follows.

That is, with respect to 100 parts by weight of the (B1) polypropylene resin (a), 1.0 part by weight or more and 10 parts by weight or less of the hydrophilic substance (b) and 1.0 part by weight or more and 10 parts by weight of the foam nucleating agent (c). After the polypropylene-based resin particles containing 1.0 part by weight or more and 5.0 parts by weight or less of the higher fatty acid amide (d) are dispersed in an aqueous dispersion medium in a pressure-resistant container and charged with a dispersant or the like. , (B2) Carbon dioxide of about 1 to 2 MPa (gauge pressure) is introduced as a foaming agent into the pressure-resistant container, and (B3) the softening temperature or higher of the polypropylene-based resin (a) (preferably the melting point of the polypropylene-based resin particles). Temperature range of -25 ° C or higher and the melting point of polypropylene resin particles + 25 ° C or lower, more preferably the melting point of polypropylene resin particles -15 ° C or higher and melting point of polypropylene resin particles + 15 ° C or lower) Heat the inside of the pressure-resistant container. (B4) By heating, the pressure inside the pressure-resistant container rises to about 1.5 MPa (gauge pressure) to about 3 MPa (gauge pressure). (B5) In the vicinity of the foaming temperature, carbon dioxide is further added to the pressure-resistant container to adjust the foaming pressure to a desired level, and the temperature is adjusted to a temperature suitable for foaming (hereinafter, may be referred to as “foaming temperature”). After adjusting the temperature, it is released into a pressure range lower than the internal pressure of the (B6) pressure-resistant container to obtain polypropylene-based resin foam particles.

When carbon dioxide is introduced as a foaming agent, or after charging polypropylene-based resin particles, an aqueous dispersion medium, a dispersant, etc., in a pressure-resistant container, the inside of the pressure-resistant container is softened. Carbon dioxide may be introduced into the pressure-resistant container while heating to a temperature higher than the temperature.

The steps (B1) to (B6) for producing the foamed particles from the resin particles are collectively referred to as a "one-step foaming step", and the obtained polypropylene-based resin foamed particles are also referred to as "one-step foamed particles". Call.

In the present specification, the melting point of the polypropylene-based resin particles is obtained by measuring by the same method (DSC) as the melting point of the polypropylene-based resin (a) except that polypropylene-based resin particles are used instead of the polypropylene-based resin. The value is set. In one embodiment of the present invention, the melting point of the polypropylene-based resin (a) can also be regarded as the melting point of the polypropylene-based resin particles.

The shape of the polypropylene-based resin foamed particles obtained by the production method according to the embodiment of the present invention maintains an appropriate contact area between the foamed particles when the foamed particles are filled into the mold during in-mold foam molding. Since it is possible to form high voids, _{it is preferable that the columnar shape has an average L 1} / D ₁ ratio of 1.3 or more and 3.5 or less.

_{(Average L 1} / D ₁ ratio of polypropylene-based resin foam particles)
Here, the average L ₁ / D ₁ is an average value calculated from _{the L 1} / D ₁ ratio of 10 randomly selected polypropylene-based resin foam particles. L ₁ and D ₁ will be described with reference to FIG. 1 (a). FIG. 1A is an external view of the polypropylene-based resin foamed particles according to the embodiment of the present invention, and _{L 1} , D used to calculate _{the L 1} / D _{1 ratio of the polypropylene-based resin foamed particles.} It is a figure explaining each value of ₁ max and D _{1 min.} As shown in FIG. 1 (a), L ₁ is the length of the longest portion of the polypropylene-based resin foamed particles. As shown in FIG. 1 (a), D ₁ is an average value of the maximum diameter D ₁ max and the minimum diameter D _{1 min in the cross section perpendicular to the L 1} direction of the polypropylene resin foamed particles, and is as follows. It is a value calculated by the formula (1):
D ₁ = (D ₁ max + D ₁ min) / 2 ... (1).

As shown in FIG. 1 (a), it can be said that L ₁ is the length of the longest portion of the polypropylene-based resin foam particles in the longitudinal direction. D _{1 is the average value of the maximum diameter D 1} max and the minimum diameter D ₁ min in the cross section perpendicular to _{the L 1} direction of the maximum diameter portion of the polypropylene resin foamed particles, and is calculated by the above formula (1). It can be said that it is a value. When the polypropylene-based resin foam particles are drum-shaped such that the central diameter in the longitudinal direction is smaller than the diameter of the end portion in the longitudinal direction, the maximum diameter portion of the polypropylene-based resin foam particles is the edge of the polypropylene-based resin foam particles. Can be a department. When PP beads are substantially spherical, the maximum diameter portion of the foamed polypropylene resin particles may be L ₁ direction of the center of the PP beads.

Specific examples of the columnar foam particles include a columnar shape and an elliptical columnar shape. If the polypropylene resin expanded particles have a columnar shape (cylindrical shape) as shown in (a) of FIG. 1, L ₁ direction perpendicular cross-sectional shape, a circle, can become a recess without closed curve such as an ellipse, D ₁ max and D ₁ min can take substantially constant values along the _{L 1 direction.}

If the average L ₁ / D ₁ ratio of the foamed particles is less than 1.3, it becomes difficult to obtain a foamed molded product having a sufficient porosity when the foamed particles are filled in a mold and foamed in the mold. Tend. If the average L ₁ / D ₁ ratio of the foamed particles exceeds 3.5, the foamed particles are likely to be clogged at the filling port when the foamed particles are filled in the mold, which causes poor filling of the foamed particles. Not only that, the porosity of the obtained foamed molded product between the regions tends to vary.

By adjusting L ₂ / D ₂ of the polypropylene-based resin particles, the average L ₁ / D ₁ of the polypropylene-based resin foamed particles can be adjusted.

The cell diameter of the polypropylene-based resin foamed particles obtained by the production method according to the embodiment of the present invention has an appropriate balance of the secondary foaming force of the foamed particles, and as a result, when the foamed particles are filled in the mold. It is preferably 30 μm or more and 100 μm or less because the generated voids are retained and the foamed particles are easily fused firmly.

When the cell diameter of the foamed particles is less than 30 μm, the secondary foaming force during in-mold foam molding tends to be too low, and the meltability of the molded product tends to deteriorate. If the cell diameter exceeds 100 μm, the secondary foaming force during in-mold foam molding tends to be too high, and the porosity when the foamed molded product is formed tends to be low. In particular, the porosity tends to decrease in the surface layer in contact with the mold surface.

The cell diameter of the polypropylene-based resin foamed particles can be adjusted by adjusting the foaming pressure and the amount of the foaming nucleating agent (c) used.

(DSC ratio of polypropylene-based resin foam particles)
The polypropylene-based resin foam particles obtained by the production method according to the embodiment of the present invention have two melting peaks on the DSC curve obtained by differential scanning calorimetry (DSC), and the heat of fusion α (calorific value α of the low temperature side peak). J / g), the value obtained by multiplying β / (α + β) when the heat of fusion β (J / g) of the high temperature side peak is 100 (hereinafter, may be referred to as “DSC ratio”, and the unit is%. There is) is preferably 40% or more and 70% or less, and more preferably 45% or more and 60% or less.

When the DSC ratio of the foamed particles is less than 40%, it tends to be difficult to increase the porosity of the foamed molded product. It is considered that this is because the secondary foaming force of the foamed particles is increased and the porosity is reduced during in-mold foam molding. If the DSC ratio of the foamed particles exceeds 70%, fusion between the foamed particles tends to be difficult during in-mold foam molding. In in-mold foam molding, if the temperature of the steam used for molding is raised to promote fusion between the foamed particles, the porosity of the obtained foamed molded product decreases, so that the porosity can be secured and fused. It tends to be difficult to achieve both.

The DSC ratio of the polypropylene-based resin foamed particles can be adjusted by adjusting the foaming temperature.

Here, the DSC ratio of the polypropylene-based resin foamed particles can be obtained from the DSC curve at the time of the first temperature rise obtained by the differential scanning calorimetry of the foamed particles. The DSC curve at the time of the first temperature rise of the foamed particles is a DSC curve obtained when 1 to 10 mg of the foamed particles are heated from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min by a differential scanning calorimeter. That is.

The heat of fusion α and the heat of fusion β will be described with reference to FIG. FIG. 2 is an example of the DSC curve at the time of the first temperature rise of the polypropylene-based resin foamed particles. Each point in the DSC curve at the time of the first temperature rise shown in FIG. 2 will be described. Let A be the point where the amount of heat absorption between the two melting peaks, the low temperature side peak and the high temperature side peak, is the smallest. Point A can also be said to be a maximum point. Let B be the point of contact between the straight line passing through the maximum point A and the DSC curve on the low temperature side, and let C be the point of contact between the straight line passing through the maximum point A and the high temperature side. The heat of fusion α (J / g) of the peak on the low temperature side from the area surrounded by the line segments AB and the DSC curve, and the heat of fusion β (J / g) of the peak on the high temperature side from the area surrounded by the line segments AC and the DSC curve. g) is calculated respectively.

The one-step expansion ratio of the polypropylene-based resin foam particles can be adjusted by adjusting the foaming temperature, the foaming pressure, the amount of the hydrophilic substance (b) used, and the amount of the foaming nucleating agent (c) used. ..

Further, a two-stage foaming step is known as a method for adjusting the one-stage foamed particles to a high magnification, and the methods shown below can be exemplified.

For example, polypropylene-based resin foam particles obtained by performing a one-step foaming step are placed in a pressure-resistant airtight container and then charged with nitrogen, air, carbon dioxide, etc. at 0.1 MPa (gauge pressure) or more, 0.6 MPa (gauge pressure). ) Pressure impregnation (pressure treatment) is performed in the following range to make the pressure in the polypropylene-based resin foam particles higher than the normal pressure (1 atm). Then, the polypropylene-based resin foamed particles are further foamed by heating with steam or the like having a pressure in the range of 0.01 MPa (gauge pressure) or more and 0.60 MPa (gauge pressure) or less. As a result, polypropylene-based resin foamed particles having a foaming ratio higher than that of the one-stage foamed particles can be obtained.

The process of adjusting the one-stage foamed particles to a high magnification is called a "two-stage foaming process", and the obtained polypropylene-based resin foamed particles are called "two-stage foamed particles". The method for producing polypropylene-based resin foamed particles according to an embodiment of the present invention may include a one-step foaming step and a two-step foaming step.

The foaming ratio of the polypropylene-based resin foamed particles (one-stage foaming and / or two-stage foaming) obtained by the production method according to the embodiment of the present invention is 15 times or more and 35 times or less. If the foaming ratio of the foamed particles is (i) less than 15 times, the merit of weight reduction cannot be obtained, and if (ii) exceeds 35 times, the dimensional accuracy, mechanical strength, etc. of the foamed molded product in the mold can be obtained. Tends to be inadequate.

In the polypropylene-based resin foamed particles produced using the polypropylene-based resin particles, the structure of the polypropylene-based resin particles changes, but the composition of the polypropylene-based resin particles does not change. Further, in the polypropylene-based resin in-mold foam molded body produced by using the polypropylene-based resin foamed particles produced by using the polypropylene-based resin particles, the structure of the polypropylene-based resin foamed particles changes, but the polypropylene-based resin foamed. The composition of the particles does not change. Therefore,
(I) The value of the melting point or MI obtained by analyzing the polypropylene-based resin foamed particles or the polypropylene-based resin in-mold foam molded product is the polypropylene-based resin contained in the polypropylene-based resin particles as raw materials thereof (i). It can be regarded as the melting point of a) or the value of MI,
(Ii) The DSC ratio obtained by analyzing the polypropylene-based resin foamed molded article can be regarded as the DSC ratio of the polypropylene-based resin foamed particles as the raw material thereof.

In the present specification, the melting point of the polypropylene-based resin foamed particles or the polypropylene-based resin in-mold foam molded product is different from the polypropylene-based resin, except that the polypropylene-based resin foamed particles or the polypropylene-based resin in-mold foamed molded product are used, respectively. , The value obtained by measuring by the same method (DSC) as the melting point of the polypropylene resin (a).

In the present specification, the MI of the polypropylene-based resin foam particles can be measured as follows: (C1) The polypropylene-based resin foam particles are placed in a decompressable oven so that the polypropylene-based resin foam particles do not come into contact with each other. (C2) Next, the polypropylene-based resin foamed particles are treated at a pressure of -0.05 to -0.10 MPa (gauge pressure) and at a temperature of + 20 to 35 ° C. for 30 minutes. Thereby, the polypropylene-based resin foamed particles are returned to the polypropylene-based resin while removing the air inside the polypropylene-based resin foamed particles; (C3) Then, the polypropylene-based resin is taken out from the oven and the polypropylene-based resin is sufficiently cooled. (C4) Then, the MI of the polypropylene-based resin is measured by the same method as that of the polypropylene-based resin (a).

In the present specification, the MI of the polypropylene-based resin in-mold foam molded product can be measured as follows: (D1) The polypropylene-based resin in-mold foam molded product is pulverized using a mixer or the like; (D2). Next, the same treatments ((C1) and (C2)) as those for the polypropylene-based resin foamed particles described above were performed except that the crushed polypropylene-based resin foamed molded product was used instead of the polypropylene-based resin foamed particles, and polypropylene was used. The foamed molded product in the based resin mold is returned to the polypropylene-based resin; (D3), and the polypropylene-based resin is taken out from the oven to sufficiently cool the polypropylene-based resin; (D4), and then the same as the polypropylene-based resin (a). The MI of the polypropylene-based resin is measured by the method.

In the present specification, the DSC ratio of the polypropylene-based resin foamed molded product is the same as that of the polypropylene-based resin foamed particles except that the polypropylene-based resin foamed molded product is used instead of the polypropylene-based resin foamed particles. Based on the DSC curve at the time of the first temperature rise obtained in (DSC), the value is set to the value obtained by the same method as the polypropylene-based resin foamed particles.

[3. Polypropylene resin foam particles]
The polypropylene-based resin foamed particles according to the embodiment of the present invention are described in the above [2. Method for producing polypropylene-based resin foam particles]], the polypropylene-based resin foam particles are produced by the method for producing polypropylene-based resin foam particles. Since the polypropylene-based resin foamed particles according to the embodiment of the present invention have the above-mentioned structure, it is possible to provide a polypropylene-based resin in-mold foam molded product having a high porosity and a high magnification. Further, since the polypropylene-based resin foamed particles according to the embodiment of the present invention have the above-mentioned structure, they have an advantage that the frictional noise is small, and provide a polypropylene-based resin in-mold foam molded product in which the frictional noise is suppressed. be able to.

[4. Polypropylene resin mold in-foam molding]
The polypropylene-based resin in-mold foam molded product according to an embodiment of the present invention is described in the above [2. It is obtained by in-mold foam molding of polypropylene-based resin foamed particles produced by the method for producing polypropylene-based resin foamed particles described in the section [Method for producing polypropylene-based resin foamed particles]. Since the polypropylene-based resin in-mold foam molded product according to the embodiment of the present invention has the above-mentioned structure, it has a high porosity and a high magnification. Further, since the polypropylene-based resin in-mold foam molded product according to the embodiment of the present invention has the above-mentioned structure, it has an advantage that the friction noise is small.

Above [2. Method for producing polypropylene-based resin foamed particles] The polypropylene-based resin foamed particles produced by the method for producing polypropylene-based resin foamed particles described in the section described above, and the above [3. The polypropylene-based resin foamed particles described in the section of [Polypropylene-based resin foamed particles] become a polypropylene-based resin foamed molded product by general in-mold foam molding. As the in-mold foam molding method, a known method can be adopted. The porosity of the foamed molded product in the mold is strongly related to the sound absorption characteristics. The porosity of the foamed molded product in the mold obtained by using the foamed particles obtained by the production method according to the embodiment of the present invention is preferably 5% or more and 50% or less, and more preferably 10% or more and 45% or less. If the porosity of the foamed molded product in the mold is less than 5%, the sound absorption coefficient at the peak frequency decreases, and sufficient sound absorption characteristics cannot be obtained. When the porosity of the foamed molded product in the mold exceeds 50%, not only the contact area between the foamed particles is reduced and the foamed molded product in the mold is likely to be cracked, but also the mechanical strength is lowered for practical use. Can't stand.

One embodiment of the present invention may have the following configuration.

[1] A step of dispersing polypropylene-based resin particles in an aqueous dispersion medium together with a foaming agent in the pressure-resistant container, heating the inside of the pressure-resistant container to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles, and the inside of the pressure-resistant container. It includes a step of pressurizing and a step of releasing the aqueous dispersion medium in which the polypropylene-based resin particles and the foaming agent are dispersed into a pressure range lower than the internal pressure of the pressure-resistant container to obtain polypropylene-based resin foamed particles. The polypropylene-based resin particles are 1.0 part by weight or more and 10 parts by weight or less of the hydrophilic substance (b) and foam nuclei with respect to 100 parts by weight of the polypropylene-based resin (a) and the polypropylene-based resin (a). Agent (c) 1.0 parts by weight or more and 10 parts by weight or less, and the total amount of the hydrophilic substance (b) and the foam nucleating agent (c) is 2.5 parts by weight or more and 20 parts by weight or less, and It is composed of a polypropylene-based resin composition containing 1.0 part by weight or more and 5.0 parts by weight or less of the higher fatty acid amide (d), and the polypropylene-based resin foamed particles have an average L ₁ / D ₁ ratio of 1.3 or more. DSC curve obtained when the temperature is 3.5 or less, the cell diameter is 30 μm or more and 100 μm or less, and the temperature is raised from 40 ° C. to 220 ° C. at a rate of 10 ° C./min by differential scanning calorimetry (DSC) of foamed particles. The DSC ratio calculated from the above is 40% or more and 70% or less, the foaming ratio is 15 times or more and 35 times or less, and the foaming agent is an inorganic foaming agent containing carbon dioxide. , A method for producing polypropylene-based resin foam particles.

[2] At least one selected from the group consisting of (i) an organic substance having a triazine skeleton and a molecular weight of 300 or less per unit triazine skeleton, and (ii) a metal borate salt. The method for producing polypropylene-based resin foam particles according to [1], which comprises seeds.

[3] the polypropylene-based resin particles have an average L _{2 /} D ₂ ratio is less than 4.0, the production method of the polypropylene resin foamed beads according to [1] or [2].

[4] Polypropylene resin foamed particles obtained by the method for producing polypropylene resin foamed particles according to any one of [1] to [3].

[5] An in-mold foam molded product using the polypropylene-based resin foamed particles according to [4], wherein the void ratio of the in-mold foam molded product is 5% or more and 50% or less. Polypropylene resin mold in-foam molding.

Next, one embodiment of the present invention will be described based on Examples and Comparative Examples, but the present invention is not limited to these Examples.

The polypropylene-based resins and additives used in Examples and Comparative Examples are as follows.

(1) Polypropylene resin (a)
-Polypropylene resin A: melting point 149 ° C., density 0.90 g / cm ³ , 1-butene content 3.8% by weight and ethylene content 0.5% by weight, MI 10.0 g / 10 minutes butene-ethylene-propylene random Copolymer / Polypropylene resin B: Ethylene-propylene-based random copolymer having a melting point of 144 ° C., a density of 0.90 g / cm ³ , an ethylene content of 3.5% by weight, and a MI of 7.0 g / 10 minutes (2) Hydrophilic substance (B)
・ Melamine [Product name: Melamine, manufactured by Nissan Kagaku Kogyo Co., Ltd.]
・ Ammeline [Product name: Ammeline, manufactured by Tokyo Chemical Industry Co., Ltd.]
・ Zinc borate [Product name: HA-1, manufactured by Sakai Chemical Industry Co., Ltd.]
(3) Effervescent nucleating agent (c)
・ Talc [Product name: Talcan powder PK-S, manufactured by Hayashi Kasei Co., Ltd.]
(4) Higher fatty acid amide (d)
-Ethylene bisstearic acid amide [Product name: Alflo H50F, manufactured by NOF CORPORATION]
・ Erucic acid amide [Product name: Alflo P-10, manufactured by NOF CORPORATION]
(5) Other additives-Carbon black [Product name: MCF88, manufactured by Mitsubishi Chemical Corporation]
-Hydrophilic polymer (carboxyl group-containing polymer) [Product name: Hymilan SD100, manufactured by Mitsui DuPont Polychemical Co., Ltd .: Ethylene ionomer resin in which the molecules of an ethylene-methacrylic acid copolymer are crosslinked with metal ions]
(6) Foaming agent / carbon dioxide [manufactured by Air Water Inc.]
-Isobutane [manufactured by Mitsui Chemicals, Inc.].

The evaluation in Examples and Comparative Examples was carried out by the following method.

<DSC ratio of polypropylene-based resin foam particles>
To measure the DSC ratio [= {β / (α + β)} × 100 (%)], use a differential scanning calorimeter [manufactured by Seiko Instruments Co., Ltd., DSC6200 type] to measure 5 to 6 mg of polypropylene-based resin foam particles. It was calculated from the DSC curve (see FIG. 2) at the time of the first temperature rise obtained when the temperature was raised from 40 ° C. to 220 ° C. at a temperature rising rate of ° C./min.

<Average L ₂ / D ₂ ratio of polypropylene resin particles, average L ₁ / D ₁ ratio of polypropylene resin foam particles>
_{Regarding polypropylene-based resin particles, L 2} (length of the longest part), D ₂ max (maximum diameter in the cross section perpendicular to the _{L 2 direction), and D 2} min (vertical to the _{L 2} direction) shown in FIG. 1 (b). the minimum diameter) was measured using a caliper in the cross section was calculated L 2 _/ D ₂ ratio. D ₂ was calculated according to the following equation (2). _{Then, the average L 2} / D ₂ ratio was calculated from the average value _{of the L 2} / D ₂ ratio of 10 polypropylene-based resin particles.
D ₂ = (D ₂ max + D ₂ min) / 2 ... (2).

For polypropylene-based resin foamed particles, (the length of the longest _{portion) L 1} shown in FIGS. 1 (a), (maximum diameter in the _{L 1} direction perpendicular cross _{section) D 1 max, D 1 min} (L 1 and vertical The minimum diameter in a cross section) was measured using a caliper, and the L ₁ / D ₁ ratio was calculated. D ₁ was calculated according to the following formula (1). _{Then, the average L 1} / D ₁ ratio was calculated from the average value _{of the L 1} / D ₁ ratio of 10 polypropylene-based resin foam particles.
D ₁ = (D ₁ max + D ₁ min) / 2 ... (1).

<Cell diameter of polypropylene-based resin foam particles>
Arbitrarily 10 polypropylene-based resin foam particles were taken out and cut. The cut surface of each foamed particle was observed with a magnifying glass equipped with a gauge of 2 mm and a magnifying glass of 60 times, and the number of cells hung on the gauge was counted. The cell diameter was calculated by the following formula (2), where N (pieces) was taken as the average value of the measured number of cells of the 10 polypropylene-based resin foam particles.
Cell diameter (μm) = 2000 / N (pieces) ... (2).

<Expansion ratio of polypropylene resin foam particles (one-stage foam particles and two-stage foam particles)>
The weights (g) (w) of the polypropylene-based resin foam particles having a bulk volume of about 50 cm ^{3 were determined.} The polypropylene-based resin foamed particles are submerged in ethanol contained in the measuring cylinder, and the volume of the polypropylene-based resin foamed particles (also referred to as ethanol submerged volume) (cm ^{3) based on the increase in the liquid level position of the measuring cylinder.} ) (Let's be v) was measured. The foaming ratio was determined by the following formula (3) from the weight w, the volume v, and the density (g / cm ^{3) (d) of the polypropylene resin (a).} The density d of the polypropylene-based resin composition was 0.9 g / cm ³ .
Foaming magnification of polypropylene-based resin foamed particles = d × v / w (3).

<Apparent density of polypropylene-based resin foam particles (one-stage foam particles and two-stage foam particles)>
The polypropylene-based resin foam particles were gently charged into a wide-mouthed 10-liter container until it overflowed, and then the mouth of the 10 L container was scraped off so that the volume of the charged polypropylene-based resin foam particles became 10 L. After measuring the weight of the polypropylene-based resin foam particles contained in the 10 L container, the weight was divided by the volume of 10 L, and the apparent density was expressed in units of g / L.

<Density of foam molded product in polypropylene resin mold>
The weight (g) (W) of the obtained polypropylene-based resin mold in-foam molded product (length 400 mm × width 300 mm × thickness 40 mm) was measured, and the length, width and thickness of the molded product were measured with a caliper. The volume (cm ³ ) (referred to as V) was calculated. The molded body density was determined by W / V. However, it was converted so that the unit was g / L.

<Porosity of foam molded product in polypropylene resin mold>
From the obtained polypropylene-based resin mold in-foam molded product (length 400 mm × width 300 mm × thickness 40 mm), a rectangular parallelepiped sample having a size of 20 × 20 × 40 mm was cut out so as to include a surface skin layer. ^{The apparent volume (cm 3} ) (referred to as V1) of the rectangular parallelepiped sample was determined from the external dimensions. ^{Furthermore, the rectangular parallelepiped sample is immersed in a certain amount of ethanol contained in the graduated cylinder, and the volume (cm 3} ) (V2) of the rectangular parallelepiped sample is increased based on the amount of increase in the liquid level position of the graduated cylinder at that time. It was measured. The porosity was calculated by the following formula (4).
Porosity (%) = {(V1-V2) / V1} x 100 ... (4).

<Fricative sound of foamed molded product in polypropylene resin mold>
The flat portion of the obtained polypropylene-based resin foam molded article (length 400 mm × width 300 mm × thickness 40 mm) was brought into contact with the corner portion of another polypropylene-based resin foam molded article (same size) prepared separately. By reciprocating the corners in this state, the polypropylene-based resin foam molded products were rubbed against each other, and the presence or absence of friction noise was evaluated. The evaluation criteria are as follows.
◯: Almost no friction noise is generated, but it is slightly generated after moving several times.
X: A loud fricative is generated when the vehicle is moved.

<Peak sound absorption coefficient of foam molded product in polypropylene resin mold>
According to JIS A1405, the vertical incident sound absorption coefficient at a sample thickness of 40.0 mm and 500 to 6400 Hz was measured. It was cut out from a polypropylene-based resin mold in-foam molded product (length 400 mm × width 300 mm × thickness 40 mm) with a diameter of 29 mm and a thickness of 40.0 mm so that the surface having the surface skin layer became the sound wave incident surface. The vertical incident sound absorption coefficient was measured in a state where the rigid wall reflecting sound waves and the sample were in close contact with each other, that is, in a state where there was no back air. A vertical incident sound absorption coefficient measuring device SR-4100 manufactured by Ono Sokki Co., Ltd. was used for measuring the vertical incident sound absorption coefficient.

From the obtained frequency-vertical incident sound absorption curve, the vertical incident sound absorption coefficient (peak sound absorption coefficient) at the frequency at which the vertical incident sound absorption coefficient was maximized was read.

<Examples 1 to 18, Comparative Examples 1 to 22>
[Preparation of polypropylene resin particles]
The polypropylene resin (a), the hydrophilic substance (b), the effervescent nucleating agent (c), the higher fatty acid amide (d) and other additives shown in Tables 1 to 6 are mixed, if necessary. A mixture (blend) was prepared. The mixture was melt-kneaded (resin temperature 210 ° C.) with a 26 mmφ twin-screw extruder to prepare a polypropylene-based resin composition. Polypropylene-based resin composition is extruded into a strand shape from the tip of an extruder, and then granulated by cutting the extruded polypropylene-based resin composition, and polypropylene having the resin particles L / D shown in Tables 1 to 6. A based resin particle (1.2 mg / grain) was produced.

[Preparation of polypropylene-based resin foamed particles (single-stage foamed particles)]
In a 10 L pressure resistant container, 100 parts by weight of the obtained polypropylene-based resin particles, 200 parts by weight of water as an aqueous dispersion medium, 0.4 parts by weight of tertiary calcium phosphate as a dispersant, and 0.07 parts by weight of sodium alkanesulfonate as a dispersion aid. , And 6 parts by weight of carbon dioxide (Examples 1 to 18, Comparative Examples 1 to 20) or 15 parts by weight of isobutane (Comparative Examples 21 to 22) were charged as a foaming agent. The charged raw materials were stirred, and polypropylene-based resin particles were dispersed in an aqueous dispersion medium together with a foaming agent in a pressure-resistant container. The inside of the pressure-resistant container was heated under stirring to bring the foaming temperature (temperature inside the pressure-resistant container) to the temperature shown in Tables 1 to 6. After that, carbon dioxide (Examples 1 to 18, Comparative Examples 1 to 21) or isobutane (Comparative Examples 21 to 22) is added to the pressure-resistant container to pressurize the inside of the pressure-resistant container, and the pressure inside the pressure-resistant container is shown in the table. The pressure was adjusted to the pressure (foaming pressure) described in 1 to 6. The inside of the pressure-resistant container was held at the foaming temperature and foaming pressure shown in Tables 1 to 6 for 30 minutes. Then, while maintaining the foaming pressure in the container with carbon dioxide (Examples 1 to 18 and Comparative Examples 1 to 20) or isobutane (Comparative Examples 21 to 22), the mixture is dispersed through a 3.6 mmφ orifice provided at the bottom of the pressure-resistant container. The liquid (an aqueous dispersion medium in which polypropylene-based resin particles and a foaming agent are dispersed) was released under atmospheric pressure to obtain polypropylene-based resin foamed particles (one-stage foamed particles). Then, the one-stage foamed particles were dried at 75 ° C. for 24 hours. The foaming temperature is equal to or higher than the softening temperature of the polypropylene-based resin particles used. The DSC ratio, cell system, foaming ratio, and apparent density of the obtained one-stage foamed particles were measured, and the results are shown in Tables 1 to 6.

[Preparation of polypropylene-based resin foam particles (two-stage foam particles)]
The one-stage foamed particles obtained in Examples 1 to 11 and 13 to 18 and Comparative Examples 1 to 13, 15 to 18 and 20 ^{were placed in a pressure-resistant container of 1 m 3} and air-pressurized to 0.30 into the one-stage foamed particles. An internal pressure of ~ 0.40 MPa (absolute pressure) was applied. Next, after transferring the one-stage foamed particles to the two-stage foaming machine, the one-stage foamed particles are heated with steam of 0.040 to 0.120 MPa (gauge pressure) to further foam the one-stage foamed particles, and the polypropylene-based resin foamed particles (polypropylene resin foamed particles). Two-stage foamed particles) were obtained. The DSC ratio, cell system, foaming ratio, and apparent density of the obtained two-stage foamed particles were measured, and the results are shown in Tables 1 to 6.

[Preparation of foamed molded article in polypropylene resin mold]
Two-stage foamed particles obtained in Examples 1-11, 13-18, Comparative Examples 1-13, 15-18, 20, and one-stage particles obtained in Example 12, Comparative Examples 14, 19, 21, 22. The two-stage foamed particles or the one-stage foamed particles were filled in a mold having a length of 400 mm, a width of 300 mm, and a thickness of 40 mm without applying internal pressure to the foamed particles. Here, the cracking amount was set to 6 mm. Then, the mold and the foamed particles were heated with steam of 0.30 MPa (gauge pressure), and the foamed particles were fused to each other to obtain an in-mold foamed molded product. With respect to the obtained in-mold foam molded product, the molded product density, porosity and sound absorption coefficient were measured, the frictional sound was evaluated, and the results are shown in Tables 1 to 6.

実施例１〜１８では、本発明の範囲内のポリプロピレン系樹脂（ａ）と、親水性物質（ｂ）と、発泡核剤（ｃ）と、高級脂肪酸アミド（ｄ）とを所定の配合としてなる発泡粒子は、高発泡倍率であり、且つ空隙率および吸音率が高く、且つ摩擦音抑制性能が良好な型内発泡成形体を提供できることが分かる。

In Examples 1 to 18, the polypropylene-based resin (a) within the scope of the present invention, the hydrophilic substance (b), the effervescent nucleating agent (c), and the higher fatty acid amide (d) are blended in a predetermined manner. It can be seen that the foamed particles can provide an in-mold foamed molded product having a high foaming ratio, high porosity and sound absorption coefficient, and good friction noise suppression performance.

In Comparative Example 1, it can be seen that the foamability is inferior and the performance (foaming ratio) is insufficient due to the insufficient amount of the hydrophilic substance (b).

In Comparative Example 2, the cell diameter became coarse due to the insufficient amount of the foam nucleating agent (c), and the secondary foaming force during the foam molding in the mold became high. As a result, the voids of the foam molded product in the mold were filled and sound absorption was performed. It turns out that the rate is insufficient.

In Comparative Example 3, it can be seen that when the amount of the hydrophilic substance (b) becomes excessive, the foamed molded product in the mold shrinks, the voids are filled, and the sound absorption coefficient becomes insufficient.

In Comparative Example 4, the cell diameter became finer due to the excessive amount of the foam nucleating agent (c), and the secondary foaming force during in-mold foam molding became too low. As a result, the in-mold foam molded product was fused. Was deteriorated and cracks were generated, and a good in-mold foam molded product could not be obtained.

In Comparative Example 5, as a result of not adding the higher fatty acid amide (d), a fricative sound of the foamed molded product in the mold was generated, and it was found that the performance was insufficient (the friction sound evaluation was ×).

In Comparative Example 6, the amount of the higher fatty acid amide (d) was excessive, and as a result, the amount of the dispersant adhering to the surface of the foamed particles when the polypropylene-based resin foamed particles were produced increased. The fusion of the molds deteriorated and cracks occurred, and a good in-mold foam molded product could not be obtained.

In Comparative Examples 7 to 9, as a result of blending within the range of Examples of Patent Document 3 (International Publication WO 2006/016478), the foamability is inferior, the foaming ratio is low, and the fricative noise of the foamed molded product in the mold is generated and the performance is performed. It turns out to be inadequate. Further, it can be seen that the cell diameter becomes coarse and the secondary foaming force at the time of foam molding in the mold becomes high, and as a result, the voids of the foamed molded product in the mold are filled and the sound absorption coefficient becomes insufficient.

In Comparative Examples 10 to 11, as a result of not adding the foam nucleating agent (c), the cell diameter became coarse and the secondary foaming force at the time of foam molding in the mold increased, and as a result, the voids of the foam molded product in the mold were filled and the sound absorption coefficient. It turns out that is insufficient. Further, it can be seen that as a result of not adding the higher fatty acid amide (d), a fricative noise of the foamed molded product in the mold is generated, and the performance is insufficient (the friction noise evaluation is ×).

It can be seen that in Comparative Examples 12 to 13, as a result of blending within the range of Examples of Patent Document 8 (Japanese Unexamined Patent Publication No. 2003-171516), the voids of the foamed molded product in the mold are filled and the sound absorption coefficient becomes insufficient. Further, it can be seen that as a result of not adding the higher fatty acid amide (d), a fricative noise of the foamed molded product in the mold is generated, and the performance is insufficient (the friction noise evaluation is ×).

In Comparative Example 14, as a result of the DSC ratio falling below the range of the present application, the secondary foaming force during in-mold foam molding increased, and as a result, the voids of the in-mold foam molded product were filled and the sound absorption coefficient became insufficient.

In Comparative Example 15, as a result of the DSC ratio exceeding the range of the present application, it can be seen that the secondary foaming force at the time of in-mold foam molding is high, the foamability is inferior, and the performance (foaming ratio) is insufficient. Further, the fusion of the in-mold foam molded product deteriorated and cracks occurred, so that a good in-mold foam molded product could not be obtained.

In Comparative Example 16, as _{a result of the L 1} / D ₁ of the foamed particles falling below the range of the present application, the filling property of the foamed particles became very good (excessive) during the foaming molding in the mold, and the voids of the foamed molded product in the mold were filled to absorb sound. It turns out that the rate is insufficient.

In Comparative Example 17, as _{a result of the L 1} / D ₁ of the foamed particles exceeding the range of the present application, the filling property of the foamed particles became very poor during the foamed molding in the mold, and a good foamed molded product in the mold could not be obtained. ..

In Comparative Example 18, as a result of the total addition amount of the hydrophilic substance (b) and the foaming nucleating agent (c) being less than the range of the present application, it can be seen that the foaming property and the sound absorbing performance are inferior.

In Comparative Example 19, as a result of the total addition amount of the hydrophilic substance (b) and the effervescent nucleating agent (c) exceeding the range of the present application, hyperfoaming occurs and the shrinkage of the effervescent particles becomes severe, and good effervescent particles can be obtained. There wasn't.

In Comparative Example 20, as a result of the formulation corresponding to Example 13 of Patent Document 9 (Japanese Unexamined Patent Publication No. 2004-67768), the foamability was inferior, the foaming ratio was low, and the fricative noise of the foamed molded product in the mold was generated. , It turns out that the performance is insufficient.

In Comparative Examples 21 to 22, the foaming agent used was changed from carbon dioxide to isobutane in the same formulation as in Examples 1 and 5, respectively. As a result, hyperfoaming occurred and the shrinkage of the foamed particles became severe, and good foamed particles could not be obtained.

According to one embodiment of the present invention, polypropylene-based resin foamed particles that have a high porosity and can provide a polypropylene-based resin in-mold foam molded article having a high magnification can be obtained. Therefore, one embodiment of the present invention can be suitably used in various fields such as a packaging material field, a cushioning material field, a heat insulating material field, and a building member field.

Claims (5)

A process of dispersing polypropylene-based resin particles in an aqueous dispersion medium together with a foaming agent in a pressure-resistant container.
The step of heating the inside of the pressure-resistant container to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles and pressurizing the inside of the pressure-resistant container, and the aqueous dispersion medium in which the polypropylene-based resin particles and the foaming agent are dispersed. Is released into a pressure range lower than the internal pressure of the pressure-resistant container to obtain polypropylene-based resin foamed particles.
The polypropylene-based resin particles are
With respect to 100 parts by weight of polypropylene-based resin (a) and polypropylene-based resin (a)
Hydrophilic substance (b) 1.0 part by weight or more and 10 parts by weight or less,
And 1.0 part by weight or more and 10 parts by weight or less of the foam nucleating agent (c),
Moreover, the total amount of the hydrophilic substance (b) and the effervescent nucleating agent (c) is 2.5 parts by weight or more and 20 parts by weight or less.
It is composed of a polypropylene-based resin composition containing 1.0 part by weight or more and 5.0 parts by weight or less of the higher fatty acid amide (d).
The polypropylene-based resin foam particles are
The average L ₁ / D ₁ ratio is 1.3 or more and 3.5 or less.
The cell diameter is 30 μm or more and 100 μm or less.
In differential scanning calorimetry (DSC) of foamed particles, the DSC ratio calculated from the DSC curve obtained when the temperature is raised from 40 ° C. to 220 ° C. at a rate of 10 ° C./min is 40% or more and 70% or less.
Moreover, the foaming ratio is 15 times or more and 35 times or less.
The foaming agent is an inorganic foaming agent containing carbon dioxide.
A method for producing polypropylene-based resin foam particles, which is characterized by the above. The hydrophilic substance (b) contains at least one selected from the group consisting of (i) an organic substance having a triazine skeleton and a molecular weight of 300 or less per unit triazine skeleton, and (ii) a metal borate salt. The method for producing polypropylene-based resin foam particles according to claim 1. The polypropylene-based resin particles have an average L _{2 /} D ₂ ratio is less than 4.0, the manufacturing method of the foamed polypropylene resin particles according to claim 1 or 2. Polypropylene resin foamed particles obtained by the method for producing polypropylene resin foamed particles according to any one of claims 1 to 3. An in-mold foam molded product using the polypropylene-based resin foamed particles according to claim 4.
The porosity of the foamed molded product in the mold is 5% or more and 50% or less.
A polypropylene-based resin mold in-foam molded product.

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