JP7162051B2 - Method for producing expanded polypropylene resin particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing expanded polypropylene resin particles and its use.

Polypropylene resin in-mold foam molded products (hereinafter also referred to as “in-mold foam molded products”, “foam molded products” or “molded products”) are used as cushioning packaging materials, distribution materials (e.g. returnable boxes, truck transportation cushioning materials, etc.), heat insulating materials, civil engineering and construction materials, automobile parts (for example, tool boxes, floor core materials, etc.). Polypropylene-based resin in-mold expansion molded products can also provide characteristics such as water permeability, air permeability, and sound absorption to the molded product by providing voids, and are also used for applications such as sound absorbing materials. .

As a method for producing a polypropylene resin foam molded product having continuous voids formed by molding expanded polypropylene resin particles (hereinafter also referred to as "expanded particles"), foamed polypropylene resin particles having a specific shape are heat-molded. Methods have been disclosed (US Pat. The techniques disclosed in these documents are characterized by the use of foamed polypropylene resin particles having a hollow cylinder, a hollow irregular shape, or cross-sectional irregularities such as a cross.

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

As a method for obtaining expanded beads, (1) thermoplastic resin particles are dispersed in an aqueous dispersion medium together with a foaming agent in a vessel to prepare a dispersion liquid, and (2) the inside of the vessel is heated to heat the inside of the vessel. A known method is to impregnate thermoplastic resin particles with a foaming agent under a constant pressure and a constant temperature, and then (3) discharge the dispersion into a low-pressure atmosphere to obtain foamed particles. Examples of foaming agents 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). disclosed.

Also, a method is known in which water used as a dispersion medium is used as a foaming agent (Patent Documents 8 and 9).

JP-A-7-138399 JP-A-7-138400 International publication WO2006/016478 JP 2007-217597 A Japanese Patent Publication No. 56-1344 Japanese Patent Publication No. 4-64332 Japanese Patent Publication No. 62-61227 JP 2003-171516 A JP-A-2004-67768

However, in the above-described prior art, when an inorganic foaming agent is used as a foaming agent, there is no foaming of a polypropylene resin that can provide a polypropylene resin in-mold foam molded article having a high porosity and a high magnification. From the viewpoint of obtaining particles, there is room for further improvement.

One embodiment of the present invention has been made in view of the above problems, and its object is (i) a method for producing expanded polypropylene resin beads using an inorganic foaming agent, which has a high porosity and Novel foamed polypropylene resin particles capable of providing a polypropylene resin-based in-mold expansion-molded article with a high magnification, and (ii) a novel polypropylene-based resin foamed in-mold having a high porosity and a high magnification. The object is to provide a molded article.

The present inventors have completed the present invention as a result of intensive studies to solve the above problems.

That is, the method for producing expanded polypropylene resin particles according to one embodiment of the present invention includes a step of dispersing polypropylene resin particles in an aqueous dispersion medium together with a blowing agent in a pressure vessel, and a step of heating the inside of the pressure vessel to a temperature and pressurizing the inside of the pressure vessel; a step of releasing expanded polypropylene resin particles into a region, wherein the polypropylene resin particles are added to the polypropylene resin (a) and 100 parts by weight of the polypropylene resin (a) with a hydrophilic substance ( b) 1.0 parts by weight or more and 10 parts by weight or less, and 1.0 parts by weight or more and 10 parts by weight or less of the nucleating agent for foaming (c), and the hydrophilic substance (b) and the nucleating agent for foaming (c) total amount of 2.5 parts by weight or more and 20 parts by weight or less, and containing 1.0 parts by weight or more and 5.0 parts by weight or less of higher fatty acid amide (d). The foamed resin beads 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 a differential scanning calorimetry (DSC) measurement of the foamed beads of 40° C. to 220° C. The foaming agent has a DSC ratio calculated from a DSC curve obtained when the temperature is raised to ° C. at a rate of 10 ° C./min. is an inorganic blowing agent containing carbon dioxide.

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

(a) is an external view of _a polypropylene-based resin expanded bead according to _{one embodiment of the present invention, showing L 1 ,} D ₁ max, It is a diagram explaining each value of D ₁ min, (b) is an external view of a polypropylene resin particle according to one embodiment of the present invention, and the L ₂ / D ₂ ratio of the polypropylene resin particle is calculated. FIG. 10 is a diagram explaining each value of L ₂ , D ₂ max, and D ₂ min used for It is an example of a DSC curve at the time of the first temperature rise of expanded polypropylene resin particles.

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

Unless otherwise specified herein, "A to B" representing a numerical range intends "A or more (including A and greater than A) and B or less (including B and less than B)".

Unless otherwise specified in this specification, structural units include structural units derived from the X1 monomer, structural units derived from the X2 monomer, ... and _Xn monomers (where _n is ₂ or more (integers of) are also referred to as "X ₁ -X ₂ -...-X _n copolymers". The X ₁ -X ₂ -...-X _n copolymer is not particularly limited in its polymerization mode unless otherwise specified, and may be a random copolymer or a block copolymer. may be a graft copolymer.

[1. Technical idea of one embodiment of the present invention]
As a result of intensive studies by the present inventors, the inventors have found that the above-described Patent Documents 1 to 3 have room for improvement or problems as shown below.

Patent Literatures 1 and 2 disclose a technique of using foamed polypropylene resin particles having a specific shape, that is, an irregular shape. In order to produce these irregular shaped polypropylene resin foamed particles, it is necessary to produce resin particles corresponding to the shape. The productivity of the generally used resin particles having a particle size of 1 to 10 mg per particle is low, which is economically disadvantageous.

Examples of Patent Documents 3 and 4 only disclose cases in which a volatile organic foaming agent is used as a foaming agent for obtaining a high foaming ratio. These techniques using volatile organic blowing agents have room for improvement in terms of environmental aspects and facility costs. Volatile organic blowing agents have the effect of plasticizing thermoplastic resins, making it easy to obtain high expansion ratios. , which the inventor has independently found. Specifically, as a result of intensive studies, when only the foaming agent is changed to an inorganic foaming agent from the formulations of Examples of Patent Documents 3 and 4, a mold having a high porosity and a high magnification ratio is used. The present inventor independently found that it is difficult to obtain an inner foam molded article.

When inorganic blowing agents such as nitrogen and air are used, the global warming potential is smaller than that of volatile organic blowing agents, and there is no need to make the equipment explosion-proof. Advantageous. Therefore, an object of an embodiment of the present invention is to provide a polypropylene resin-based in-mold expansion-molded article having a high porosity and a high magnification in a production method using an inorganic foaming agent as the foaming agent. It is to obtain expanded polypropylene-based resin particles.

The present inventor believes that when an inorganic foaming agent is used, the performance of impregnating the thermoplastic resin with the inorganic foaming agent is very low, and therefore a sufficient amount of impregnation for high foaming cannot be obtained even at high pressure. Found the problem on my own. In order to solve this problem, the present inventors have conducted extensive studies. As a result, polypropylene-based resin particles made of a polypropylene-based resin composition containing specific amounts of a polypropylene-based resin (a), a hydrophilic substance (b), a foam nucleating agent (c), and a higher fatty acid amide (d) were obtained. The present inventors have found that the above problems can be solved by making expanded polypropylene resin beads having a specific cell diameter, DSC ratio, and average L ₁ /D ₁ ratio, which are produced using an inorganic foaming agent. The invention has been completed.

[2. Method for Producing Expanded Polypropylene Resin Particles]
A method for producing expanded polypropylene resin particles according to one embodiment of the present invention includes the steps of: dispersing polypropylene resin particles in an aqueous dispersion medium together with a foaming agent in a pressure vessel; The step of heating the inside of the pressure vessel and pressurizing the inside of the pressure vessel, and the aqueous dispersion medium in which the polypropylene resin particles and the foaming agent are dispersed in a pressure range lower than the internal pressure of the pressure vessel. a step of releasing and obtaining foamed polypropylene resin particles, wherein the polypropylene resin particles are composed of the polypropylene resin (a) and the hydrophilic substance (b) with respect to 100 parts by weight of the polypropylene resin (a) 1.0 parts by weight or more and 10 parts by weight or less, and 1.0 parts by weight or more and 10 parts by weight or less of the foam nucleating agent (c), and the sum of the hydrophilic substance (b) and the foam nucleating agent (c) 2.5 parts by weight or more and 20 parts by weight or less and containing 1.0 parts by weight or more and 5.0 parts by weight or less of higher fatty acid amide (d). The particles have an average L ₁ /D ₁ ratio of 1.3 to 3.5, a cell diameter of 30 μm to 100 μm, and a differential scanning calorimetry (DSC) of the expanded particles from 40° C. to 220° C. 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 expansion ratio is 15 times or more and 35 times or less, and the foaming agent is dioxide 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 expanded polypropylene resin beads, and L ₁ is a polypropylene resin. D 1 is the length of the longest part of the expanded beads, 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 expanded polypropylene resin beads. is the value calculated by equation (1):
D1=( _D1max + _D1min )/2 Expression ( ₁ ).

Since the method for producing expanded polypropylene resin beads 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 expanded particles that can provide a polypropylene-based resin in-mold expansion-molded product. Furthermore, in one embodiment of the present invention, expanded polypropylene resin particles and polypropylene resin in-mold expansion-molded articles with reduced fricative noise can be obtained.

In the present specification, the "method for manufacturing expanded polypropylene resin particles" may be referred to as "method for manufacturing". In this specification, "polypropylene-based resin particles" may be referred to as "resin particles".

(2-1. Polypropylene resin particles)
(Polypropylene resin (a))
The polypropylene resin (a) used in one embodiment of the present invention is a polymer containing 50% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more of propylene monomer units. The polypropylene-based resin (a) used in one embodiment of the present invention is preferably a highly stereoregular one polymerized with a metallocene catalyst or a Ziegler-type titanium chloride-based catalyst. Specific examples of the polypropylene resin (a) include propylene homopolymer, ethylene-propylene random copolymer (also referred to as "ethylene-propylene random copolymer"), propylene-butene random copolymer, Ethylene-propylene-butene random copolymer (also referred to as "butene-ethylene-propylene random copolymer"), ethylene-propylene block copolymer, maleic anhydride-propylene random copolymer, maleic anhydride-propylene Block copolymers, maleic anhydride-g-propylene graft copolymers, etc., may be mentioned, and each of these may be 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. Although these polypropylene resins (a) are preferably non-crosslinked, crosslinked ones can also be used. As used herein, "butene" is intended to mean "1-butene". By "maleic anhydride-g-propylene graft copolymer" is intended maleic anhydride grafted onto a propylene polymer backbone.

The polypropylene resin (a) used in one embodiment of the present invention preferably has a melt index (hereinafter referred to as MI) of 1 g/10 min or more and 30 g/10 min or less, and 2 g/10 min or more and 20 g/10 min. Minutes or less is more preferable.

If the MI of the polypropylene-based resin (a) is less than 1 g/10 minutes, the foaming force in producing expanded beads tends to be low, making it difficult to obtain expanded beads with a high expansion ratio. As a result, it tends to be difficult to ensure the fusion strength between the expanded particles when the obtained expanded particles are formed into an expanded molded article. When the MI of the polypropylene resin (a) exceeds 30 g/10 minutes, the foamed polypropylene resin particles tend to break (easily break) and the open cell ratio of the expanded polypropylene resin particles tends to increase.

The MI value of the polypropylene resin (a) is a value measured at a temperature of 230°C and a load of 2.16 kg according to 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 foam molded article having excellent mechanical strength and heat resistance. °C, particularly preferably 135 to 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, 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) using a differential scanning calorimeter. The specific operating procedure is as follows: (1) After melting 1 to 10 mg of polypropylene resin from 40° C. to 220° C. at a rate of 10° C./min; (2) from 220° C. After cooling to 40° C. at a rate of 10° C./min for crystallization; (3) heating again from 40° C. to 220° C. at a rate of 10° C./min. Let the peak temperature of the endothermic peak in the DSC curve obtained during the second heating (that is, at the time of (3)) be the melting point.

In the method for producing expanded polypropylene resin beads according to one embodiment of the present invention, polypropylene made of a polypropylene resin composition obtained by adding a hydrophilic substance (b) and an expansion nucleating agent (c) to a polypropylene resin (a) system resin particles are used. As a result, the water used as the aqueous dispersion medium can be used as the foaming agent, the water used as the foaming agent can be easily incorporated into the resin, and the cell diameter can be easily made finer. As a result, according to the method for producing expanded polypropylene resin beads according to one embodiment of the present invention, expanded polypropylene resin beads with high expansion ratio can provide a polypropylene resin in-mold expansion-molded product with high expansion ratio and high porosity. can be obtained. A "cell" may also be referred to as a "bubble".

(Hydrophilic substance (b))
The hydrophilic substance (b) used in one embodiment of the present invention includes (i) boric acid metal salts such as borax and zinc borate, and (ii) water-soluble inorganic substances such as sodium chloride, calcium chloride, and magnesium chloride. , (iii) ammeline, melamine, isocyanuric acid, water-absorbing organic substances having a triazine skeleton such as melamine-isocyanuric acid condensates, (iv) polyethers such as polyethylene glycol and polyethylene oxide, and (v) glycerin, diglycerin, etc. polyols. These hydrophilic substances (b) may be used singly or in combination of two or more.

In the method for producing expanded polypropylene resin beads according to one embodiment of the present invention, the hydrophilic substance (b) includes (i) an organic substance having a triazine skeleton and having a molecular weight of 300 or less per unit triazine skeleton, and (ii) It preferably contains at least one selected from the group consisting of metal borate salts. In other words, among the hydrophilic substances (b) described above, those having a triazine skeleton such as melamine are easy to add when producing polypropylene-based resin particles and easy to increase the expansion ratio of expanded beads. However, a hydrophilic substance (b) containing at least one organic substance having a molecular weight of 300 or less per triazine skeleton or a metal borate is preferred.

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

The method for producing expanded polypropylene resin particles according to one embodiment of the present invention may be in an aspect in which the following substances are not substantially used: (i) ethylene-acrylic acid-maleic anhydride terpolymer. , 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, copolymer Polyamides such as nylon, and (iii) thermoplastic polyester elastomers such as block copolymers of polybutylene terephthalate and polytetramethylene glycol. Here, "substantially not using the following substances" can also be said to mean that the above substances contained in the expanded polypropylene resin beads to be obtained are 10 ppm or less based on the expanded polypropylene resin beads.

The amount of the hydrophilic substance (b) added in the production method according to one embodiment of the present invention is preferably 1.0 parts 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. Here, the added amount of the hydrophilic substance (b) refers to the weight of the hydrophilic substance (b) in a non-absorbed state. In this 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 parts by weight per 100 parts by weight of the polypropylene resin (a), there is a tendency that the expansion ratio of the expanded polypropylene resin particles cannot be improved. If 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 article becomes long, and the shrinkage rate of the molded article deteriorates. That is, there is a tendency that the shrinkage ratio increases and the voids in the molded body are easily filled.

(Expansion nucleating agent (c))
The foam nucleating agent (c) used in one embodiment of the present invention is a substance that promotes the formation of cell nuclei during foaming of resin particles. Examples of the foam nucleating agent (c) include inorganic substances such as talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide and titanium oxide. These foam nucleating agents (c) may be used alone or in combination of two or more. Among these, talc is preferable as the foaming nucleating agent (c) because it facilitates obtaining expanded particles having good dispersibility in the polypropylene-based resin (a) and having uniform cells.

The addition amount of the foam nucleating agent (c) in the production method according to one embodiment of the present invention is preferably 1.0 parts 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. The addition amount of the foaming nucleating agent (c) can also be said to be the content of the foaming nucleating agent (c) in the polypropylene-based resin composition.

If the amount of the foam nucleating agent (c) added is less than 1.0 parts by weight with respect to 100 parts by weight of the polypropylene resin (a), there is a tendency that the porosity of the expanded polypropylene resin particles cannot be improved. . If the amount of the foaming nucleating agent (c) added is more than 10 parts by weight per 100 parts by weight of the polypropylene resin (a), the cell diameter of the expanded beads becomes too small, and the expanded beads during in-mold foam molding are not formed. The secondary foaming force is deteriorated, the fusion bondability of the in-mold foam molded product is deteriorated, 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 one embodiment of the present invention is 2.5 parts by weight or more and 20 parts by weight or less. 3.0 parts by weight or more and 18.0 parts by weight or less is more preferable, and 4.0 parts by weight or more and 8.0 parts by weight or less is even more preferable. If the total amount of hydrophilic substance (b) and foam nucleating agent (c) added is less than 2.5 parts by weight, the foamability and porosity tend to decrease, and the total amount added is less than 20 parts by weight. If it exceeds, the foamed particles tend to shrink extremely, and there is a tendency that good products 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. A higher fatty acid amide formed from a higher fatty acid having less than 10 carbon atoms as a raw material does not exhibit a sufficient effect of suppressing fricative noise, and a higher fatty acid having more than 25 carbon atoms is difficult to obtain and impractical. Higher fatty acid amides (d) include saturated fatty acid amides, unsaturated fatty acid amides and bis fatty acid amides. Specifically, saturated fatty acid amides include lauric acid amide, palmitic acid amide, stearic acid amide, and behemic acid amide, and unsaturated fatty acid amides include erucic acid amide, oleic acid amide, brassic acid amide, and elaidic acid amide. Bis-fatty acid amides include methylenebisstearic acid amide, methylenebislauric acid amide, ethylenebisstearic acid amide, ethylenebislauric acid amide, methylenebisoleic acid amide, methylenebiserucic acid amide, ethylenebisoleic acid amide, ethylenebiseruka and acid amides. 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 one embodiment of the present invention is 1.0 parts by weight or more and 5.0 parts by weight or less with respect to 100 parts by weight of the polypropylene resin (a). and more preferably 1.5 parts by weight or more and 4.5 parts by weight or less. The added amount of the higher fatty acid amide (d) can also be said to be the content of the higher fatty acid amide (d) in the polypropylene-based resin composition.

If the amount of the higher fatty acid amide (d) added is less than 1.0 parts by weight per 100 parts by weight of the polypropylene resin (a), the effect of suppressing fricative noise is not exhibited. If the amount of the higher fatty acid amide (d) added is more than 5.0 parts by weight per 100 parts by weight of the polypropylene resin (a), the dispersant tends to adhere to the surface of the obtained expanded polypropylene resin particles. As a result, when the expanded beads are used for in-mold foam molding, there is a tendency for poor adhesion between the expanded beads to occur.

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

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

When adding various additives 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. Various additives may be added to the molten polypropylene resin (a) in the production of the polypropylene resin particles.

(Method for producing polypropylene resin particles)
The polypropylene-based resin (a) in the production method according to one embodiment of the present invention is usually melt-kneaded using an extruder, a kneader, a Banbury mixer, rolls, etc. to produce expanded beads, and is formed into a cylindrical or elliptical shape. It can be processed into a resin particle shape such as a shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, or the like.

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 expanded polypropylene-based resin beads according to one embodiment of the present invention may further include a granulation step.

As a method for producing polypropylene resin particles, for example, (1) an extruder, a kneader, a Banbury mixer, a roll, or the like is used to melt-knead a polypropylene resin composition 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 cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, a cylindrical shape (straw shape), etc. and a method for obtaining polypropylene resin particles.

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

Each of the various additives used as necessary may be masterbatched. In other words, a masterbatch resin may be prepared in advance by adding a high concentration of additives to other resins. In this case, the masterbatch can be added as an additive. As the resin used when preparing the masterbatch resin, a polypropylene resin is preferable, and from the viewpoint of good compatibility, it is possible to masterbatch using the same type of polypropylene resin as the polypropylene resin of the base resin. Most preferred.

(Particle weight of polypropylene resin particles)
Regarding the size of the polypropylene resin particles in the production method according to one embodiment of the present invention, the weight per particle (also referred to as particle weight) is preferably 0.1 mg or more and 30 mg or less, and 0.3 mg or more and 10 mg. The following are more preferred. Here, the weight per grain of 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 one embodiment of the present invention, the average L ₂ /D ₂ ratio of the polypropylene-based resin particles is preferably 2.5 or more and 7.0 or less.

Here, the average L ₂ /D ₂ ratio of 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. 1(b) is an external view of polypropylene resin particles according to one embodiment of the present invention, and L ₂ and D ₂ max used for calculating the L ₂ /D ₂ ratio of the polypropylene resin particles. , and D ₂ min. As shown in FIG. 1( _b ), L2 is the length of the longest part of the polypropylene resin particles. As shown in (b) of _FIG . 1, D2 is the average value of the maximum diameter _D2max and the minimum diameter _D2min in the cross section perpendicular to the L2 direction of the polypropylene resin particles, and the following formula ( ₂ ) It is a value calculated by
D2=(D2max ₊ D2min)/ ₂ Expression ( ₂ )
As shown in FIG. 1( _b ), L2 can also be said to be the length of the longest part in the longitudinal direction of the polypropylene resin particles. As will be described later, when the polypropylene-based resin particles are produced by being extruded from an extruder or the like, it can be said that L2 is the length of the longest part of the polypropylene _- based resin particles in the extrusion direction. D ₂ is the 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 hourglass-shaped such that the diameter at the center in the longitudinal direction is smaller than the diameter at the ends in the longitudinal direction, the maximum diameter portion of the polypropylene-based resin particles is the end of the polypropylene-based resin particles. obtain. When the polypropylene-based resin particles are substantially spherical, the maximum diameter portion of the polypropylene-based resin particles may be the center of the polypropylene _- based resin particles in the L2 direction.

When the polypropylene _- based resin particles are cylindrical as shown in _FIG . D ₂ min can take a substantially constant value along the L ₂ direction.

In the method for producing expanded polypropylene-based resin beads according to an embodiment of the present invention, the polypropylene-based resin particles more preferably have an average L ₂ /D ₂ ratio of less than 4.0. Polypropylene-based resin particles having an average L ₂ /D ₂ ratio of less than 4.0 are easier to produce than polypropylene-based resin particles having an average L ₂ /D ₂ ratio of 4.0 or more. Therefore, according to the above configuration, the method for producing expanded polypropylene resin particles has excellent productivity. In the method for producing expanded polypropylene-based resin beads according to one 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 one embodiment of the present invention, (1) the polypropylene resin particles are dispersed in an aqueous dispersion medium together with a foaming agent in a pressure vessel, and (2) the temperature is equal to or higher than the softening temperature of the polypropylene resin particles. After heating the inside of the pressure vessel to and pressurizing the inside of the pressure vessel, (3) the aqueous dispersion medium in which the polypropylene resin particles and the foaming agent are dispersed is released to a pressure region lower than the internal pressure of the pressure vessel. By doing so, expanded polypropylene resin particles can be obtained. "Aqueous dispersion medium in which polypropylene-based resin particles and a foaming agent are dispersed" may be referred to as "dispersion".

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

According to the method for producing expanded polypropylene resin beads according to one embodiment of the present invention, by using an inorganic foaming agent, a high porosity and a high magnification can be obtained without using a volatile organic foaming agent. It is possible to obtain expanded polypropylene resin particles capable of providing a polypropylene resin in-mold expansion molded product. Volatile organic blowing agents such as propane and butane (i) have a greater global warming potential than carbon dioxide, and (ii) act to plasticize thermoplastic resins, making it easy to obtain a high expansion ratio. On the other hand, due to its plasticizing action, it becomes difficult to control the expansion ratio and crystalline state of the expanded particles, and (iii) since it is a combustible substance, it is necessary to make the equipment explosion-proof, resulting in high equipment costs. It has drawbacks such as

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

The amount of the inorganic foaming agent to be used in the manufacturing method according to one embodiment of the present invention varies depending on the type of polypropylene resin (a) used, the desired foaming ratio, etc., and cannot be defined unconditionally. 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 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 internal pressure and internal temperature of the container during production of the expanded beads. As the pressure-resistant container, for example, an autoclave-type pressure-resistant container can be used.

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

(Dispersant and Dispersing Aid)
In the production method according to one embodiment of the present invention, it is preferable to add a dispersant to the aqueous dispersion medium in order to prevent coalescence of the polypropylene resin particles. Examples of dispersants include inorganic dispersants such as tricalcium phosphate, trimagnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay. These may be used individually by 1 type, and may use 2 or more types together.

Further, it is preferable to add a dispersing aid together with the dispersant to the aqueous dispersion medium. Examples of dispersing aids include sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium alkylsulfonate, sodium alkyldiphenyletherdisulfonate, and sodium α-olefinsulfonate. These may be used individually by 1 type, and may use 2 or more types together.

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

In the production method according to one embodiment of the present invention, in order to improve the dispersibility in the aqueous dispersion medium, the polypropylene resin particles are usually 20 parts by weight with respect to 100 parts by weight of the aqueous dispersion medium. It is preferable to use from 100 parts by weight to 100 parts by weight.

A specific example of the method for producing expanded polypropylene resin beads according to one embodiment of the present invention is as follows.

That is, (B1) with respect to 100 parts by weight of polypropylene resin (a), 1.0 parts by weight or more and 10 parts by weight or less of hydrophilic substance (b) and 1.0 parts by weight or more and 10 parts by weight of foam nucleating agent (c) parts or less and 1.0 to 5.0 parts by weight of the higher fatty acid amide (d) is dispersed in an aqueous dispersion medium in a pressure vessel, and after charging a dispersant or the like. , (B2) introducing carbon dioxide of about 1 to 2 MPa (gauge pressure) as a foaming agent into a pressure vessel, and (B3) softening temperature of polypropylene resin (a) or higher (preferably melting point of polypropylene resin particles −25° C. or more and the melting point of the polypropylene resin particles +25° C. or less, more preferably, the melting point of the polypropylene resin particles −15° C. or more and the melting point of the polypropylene resin particles +15° C. or less. Heat the inside of the pressure vessel. (B4) By heating, the pressure in the pressure vessel rises to approximately 1.5 MPa (gauge pressure) to 3 MPa (gauge pressure). (B5) Add carbon dioxide into the pressure vessel near the foaming temperature to adjust the foaming pressure to a desired level, and bring the temperature to a temperature suitable for foaming (hereinafter sometimes referred to as "foaming temperature"). After adjusting the temperature, (B6) the material is discharged into a pressure range lower than the internal pressure of the pressure vessel to obtain foamed polypropylene resin particles.

As a time to introduce carbon dioxide as a blowing agent, or after charging a pressure vessel with polypropylene resin particles, an aqueous dispersion medium, and, if necessary, a dispersant, etc., the polypropylene resin (a) is softened in the pressure vessel. Carbon dioxide may be introduced into the pressure vessel while heating to a temperature equal to or higher than the temperature.

The above steps (B1) to (B6) for producing expanded beads from resin particles are collectively referred to as a "single-stage expansion process", and the obtained expanded polypropylene resin particles are also referred to as "single-stage expanded particles". call.

In this specification, the melting point of the polypropylene-based resin particles is obtained by measuring in the same manner as the melting point of the polypropylene-based resin (a) (DSC), except that the polypropylene-based resin particles are used instead of the polypropylene-based resin. value. 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 expanded polypropylene resin particles obtained by the manufacturing method according to one embodiment of the present invention is such that when the expanded particles are filled into the mold during in-mold expansion molding, a suitable contact area between the expanded particles is maintained. A columnar shape with an average L ₁ /D ₁ ratio of 1.3 or more and 3.5 or less is preferable because it is possible to form high voids.

(Average L ₁ /D ₁ ratio of foamed polypropylene resin particles)
Here, the average L ₁ /D ₁ is an average value calculated from the L ₁ /D ₁ ratio of 10 randomly selected expanded polypropylene-based resin beads. L ₁ and D ₁ will be described with reference to FIG. 1(a). FIG. 1(a) is an external view of expanded polypropylene resin beads according to one embodiment of the present invention, and L ₁ and D used for calculating the L ₁ /D ₁ ratio of the expanded polypropylene resin beads. It is a figure explaining _each value of 1max and _D1min . As shown in FIG. ₁ (a), L1 is the length of the longest part of the expanded polypropylene resin particles. As shown in (a) of FIG. 1, 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 expanded polypropylene resin beads. is the value calculated by equation (1):
D1=( _D1max + _D1min )/2 ( ₁ ).

As shown in FIG. ₁ (a), L1 can also be said to be the length of the longest part in the longitudinal direction of the expanded polypropylene resin beads. 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 foamed polypropylene resin beads, and is calculated by the above formula (1). It can be said that it is a value that When the polypropylene-based resin expanded beads are hourglass-shaped such that the diameter of the center in the longitudinal direction is smaller than the diameter of the ends in the longitudinal direction, the maximum diameter portion of the expanded polypropylene-based resin beads is the end of the expanded polypropylene-based resin beads. can be part. When the polypropylene-based resin expanded beads are substantially spherical, the maximum diameter portion of the polypropylene-based resin expanded beads may be the center of the polypropylene _- based resin expanded beads in the L1 direction.

Specific examples of the expanded particles having a columnar shape include a columnar shape and an elliptical columnar shape. When the expanded polypropylene resin particles have _a columnar shape (cylindrical shape) as shown in FIG. D ₁ max and D ₁ min can take approximately constant values along the L ₁ direction.

When the average L ₁ /D ₁ ratio of the expanded particles is less than 1.3, it becomes difficult to obtain a foamed article having a sufficient porosity when the expanded particles are filled into a mold and subjected to in-mold expansion molding. Tend. When the average L ₁ /D ₁ ratio of the expanded beads exceeds 3.5, clogging of the expanded beads tends to occur at the filling port when the expanded beads are filled into the mold, which causes poor filling of the expanded beads. In addition, the resulting foamed molded product tends to vary in porosity among local areas.

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

The cell diameter of the polypropylene-based resin foamed beads obtained by the production method according to one embodiment of the present invention provides an appropriate balance between the secondary foaming power of the foamed beads, and as a result, when the foamed beads are filled into a mold, The thickness is preferably 30 μm or more and 100 μm or less because it facilitates strong fusion between the expanded particles while maintaining the generated voids.

If the cell diameter of the expanded particles is less than 30 µm, the secondary foaming force during in-mold foam molding tends to be too low, and the fusion bondability of the molded product tends to deteriorate. When the cell diameter exceeds 100 μm, the secondary foaming force during in-mold foam molding is too high, and the porosity of the foam molded product 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 expanded polypropylene resin particles can be adjusted by adjusting the expansion pressure and the amount of the foam nucleating agent (c) used.

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

When the DSC ratio of the expanded beads is less than 40%, it tends to be difficult to increase the porosity of the expanded molded article. This is presumably because the secondary foaming power of the expanded particles is increased, which reduces the porosity during in-mold foam molding. When the DSC ratio of the expanded particles exceeds 70%, it tends to be difficult to fuse the expanded particles during in-mold foam molding. In the case of in-mold foam molding, if the temperature of the steam used for molding is increased in order to promote the fusion between the foamed particles, the porosity of the resulting foamed molded product will decrease. It tends to be difficult to achieve both.

The DSC ratio of the expanded polypropylene resin particles can be adjusted by adjusting the expansion temperature.

Here, the DSC ratio of the polypropylene-based resin expanded beads can be obtained from the DSC curve at the time of the first heating obtained by differential scanning calorimetry of the expanded beads. The DSC curve for the first heating of the expanded beads is the DSC curve obtained when 1 to 10 mg of the expanded beads are heated from 40° C. to 220° C. at a rate of 10° C./min using a differential scanning calorimeter. It's about.

The heat of fusion α and the heat of fusion β will be described with reference to FIG. FIG. 2 is an example of a DSC curve during the first heating of polypropylene-based resin expanded beads. 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 at which the endothermic amount between the two melting peaks, the low-temperature peak and the high-temperature peak, is the smallest. Point A can also be said to be a maximum point. Let B be the point of contact between the 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 line passing through the maximum point A and the high temperature side. From the area surrounded by the line segment AB and the DSC curve, the heat of fusion α (J/g) of the low-temperature side peak is calculated, and from the area surrounded by the line segment AC and the DSC curve, the heat of fusion β (J/ g) are calculated respectively.

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

Further, a two-stage expansion process is known as a method for adjusting single-stage expanded beads to a high expansion ratio, and the following methods can be exemplified.

For example, the expanded polypropylene resin particles obtained by performing the one-stage expansion step are placed in a pressure-resistant sealed container, and then nitrogen, air, carbon dioxide, etc. are added to 0.1 MPa (gauge pressure) or more, ) Pressurized impregnation (pressurization treatment) is carried out in the following range to increase the pressure inside the expanded polypropylene resin beads higher than normal pressure (1 atm). After that, the expanded polypropylene resin particles are heated with water vapor or the like at a pressure of 0.01 MPa (gauge pressure) or more and 0.60 MPa (gauge pressure) or less to further expand them. This makes it possible to obtain expanded polypropylene resin beads having an expansion ratio higher than that of the first-stage expanded beads.

The step of adjusting the single-stage expanded beads to a high expansion ratio is called a "two-stage expanded process", and the obtained polypropylene-based resin expanded beads are called "two-stage expanded beads". A method for producing expanded polypropylene-based resin beads according to an embodiment of the present invention may include a first-stage expansion process and a two-stage expansion process.

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

In expanded polypropylene resin particles produced using polypropylene resin particles, the structure of the polypropylene resin particles changes, but the composition of the polypropylene resin particles does not change. In addition, in a polypropylene resin in-mold expansion molded article manufactured using expanded polypropylene resin particles manufactured using polypropylene resin particles, the structure of the expanded polypropylene resin particles changes, but the expanded polypropylene resin particles The composition of the particles does not change. therefore,
(i) The melting point or MI value obtained by analyzing the expanded polypropylene resin particles or the polypropylene resin in-mold expansion molded product is the polypropylene resin contained in the raw polypropylene resin particles ( a) can be regarded as the melting point, or MI value,
(ii) The DSC ratio obtained by analyzing the polypropylene resin-based in-mold expansion-molded product can be regarded as the DSC ratio of the expanded polypropylene-based resin particles as the raw material.

In this specification, the melting point of the expanded polypropylene resin particles or the polypropylene resin in-mold expansion-molded product is the melting point of the expanded polypropylene resin particles or the polypropylene resin in-mold expansion-molded product, except that the polypropylene resin is used instead of the expanded polypropylene resin particles or the polypropylene resin in-mold expansion molded product. , 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 expanded polypropylene resin particles can be measured as follows: (C1) Expanded polypropylene resin particles are placed in an oven capable of reducing pressure so that the expanded polypropylene resin particles do not contact each other. (C2) Next, under a pressure of −0.05 to −0.10 MPa (gauge pressure), and at a temperature of +20 to 35° C. of the melting point of the expanded polypropylene resin particles, treat for 30 minutes. (C3) Then, the polypropylene resin is removed from the oven, and the polypropylene resin is sufficiently cooled. (C4) Then, the MI of the polypropylene-based resin is measured by the same method as for the polypropylene-based resin (a).

In the present specification, the MI of the polypropylene resin-based in-mold expansion-molded product can be measured as follows: (D1) pulverizing the polypropylene resin-based in-mold expansion-molded product using a mixer or the like; (D2) Next, the same treatment ((C1) and (C2)) as for the expanded polypropylene resin particles described above is performed except that a pulverized in-mold polypropylene resin expansion molded product is used instead of the expanded polypropylene resin particles, and the polypropylene resin is obtained. (D3) Then, remove the polypropylene resin from the oven and cool the polypropylene resin sufficiently; (D4) Then, the same as the polypropylene resin (a) The MI of the polypropylene-based resin is measured according to the method.

In the present specification, the DSC ratio of the polypropylene resin-based in-mold expansion-molded product is determined in the same manner as for the polypropylene-based resin expanded particles, except that the polypropylene-based resin in-mold expansion-molded product is used instead of the polypropylene-based resin expanded particles. Based on the DSC curve at the time of the first heating obtained in (DSC), the value obtained by the same method as for the expanded polypropylene resin particles.

[3. Expanded polypropylene resin particles]
The expanded polypropylene-based resin particles according to one embodiment of the present invention are prepared according to the above [2. Method for Producing Expanded Polypropylene Resin Beads]. Since the expanded polypropylene resin particles according to one embodiment of the present invention have the above structure, it is possible to provide a polypropylene resin in-mold expansion molded article having a high porosity and a high magnification. Furthermore, since the expanded polypropylene resin particles according to one embodiment of the present invention have the above-described structure, they have the advantage of reducing frictional noise, and provide a polypropylene resin-based in-mold expansion-molded article in which frictional noise is suppressed. be able to.

[4. Polypropylene resin in-mold expansion molding]
The polypropylene resin-based in-mold expansion-molded product according to one embodiment of the present invention is prepared according to the above [2. Method for Producing Expanded Polypropylene-Based Resin Beads]. Since the polypropylene resin-based in-mold expansion-molded product according to one embodiment of the present invention has the above structure, it has a high porosity and a high magnification. Furthermore, the polypropylene resin-based in-mold expansion-molded product according to one embodiment of the present invention has the above-described structure, and thus has the advantage of low frictional noise.

The above [2. Method for Producing Expanded Polypropylene Resin Beads], and expanded polypropylene resin beads produced by the method for producing expanded polypropylene resin beads described in the section [3. Polypropylene Resin Expanded Particles] The polypropylene resin expanded particles described in the section above are formed into a polypropylene resin in-mold expansion-molded article by general in-mold expansion molding. A known method can be adopted for the in-mold foam molding method. The porosity of the in-mold foam molded product is strongly related to the sound absorption properties. The porosity of the in-mold expansion molded product obtained using the expanded beads obtained by the manufacturing method according to one embodiment of the present invention is preferably 5% or more and 50% or less, more preferably 10% or more and 45% or less. When the porosity of the in-mold foam molded product is less than 5%, the sound absorption coefficient at the peak frequency is lowered, and sufficient sound absorption characteristics cannot be obtained. If the porosity of the in-mold foam-molded product exceeds 50%, the contact area between the foamed particles decreases, and not only does the in-mold foam-molded product crack easily, but also the mechanical strength of the in-mold foam-molded product decreases, making practical use difficult. I can't stand

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

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

[2] The hydrophilic substance (b) is at least one selected from the group consisting of (i) an organic substance having a triazine skeleton and a molecular weight per unit triazine skeleton of 300 or less, and (ii) a metal borate. The method for producing expanded polypropylene resin particles according to [1], which contains seeds.

[3] The method for producing expanded polypropylene resin particles according to [1] or [2], wherein the polypropylene resin particles have an average L ₂ /D ₂ ratio of less than 4.0.

[4] Expanded polypropylene resin beads obtained by the method for producing expanded polypropylene resin beads according to any one of [1] to [3].

[5] An in-mold expansion molded product using the expanded polypropylene resin particles according to [4], characterized in that the in-mold expansion molded product has a porosity of 5% or more and 50% or less. Polypropylene resin in-mold expansion 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.

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 min butene-ethylene-propylene random Copolymer/polypropylene resin B: Ethylene-propylene 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 an MI of 7.0 g/10 min (2) Hydrophilic substance (b)
・Melamine [product name: melamine, manufactured by Nissan Science Industries 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) foam nucleating agent (c)
・ Talc [product name: talcan powder PK-S, manufactured by Hayashi Kasei Co., Ltd.]
(4) Higher fatty acid amide (d)
・ Ethylene bis stearamide [product name: ALFLOW H50F, manufactured by NOF Corporation]
・Erucamide [product name: ALFLOW 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: Himilan SD100, manufactured by DuPont Mitsui Polychemicals Co., Ltd.: Ethylene ionomer resin in which the intermolecular crosslinks of ethylene-methacrylic acid copolymer are crosslinked with metal ions]
(6) Blowing agent/carbon dioxide [manufactured by Air Water Inc.]
- Isobutane [manufactured by Mitsui Chemicals, Inc.].

Evaluations in Examples and Comparative Examples were carried out by the following methods.

<DSC ratio of foamed polypropylene resin particles>
The DSC ratio [= {β / (α + β)} × 100 (%)] is measured using a differential scanning calorimeter [manufactured by Seiko Instruments Inc., DSC6200], and 10 It was calculated from the DSC curve (see FIG. 2) at the first temperature increase obtained when the temperature was increased from 40° C. to 220° C. at a temperature increase rate of ° C./min.

<Average L ₂ /D ₂ Ratio of Polypropylene Resin Particles, Average L ₁ /D ₁ Ratio of Expanded Polypropylene Resin Particles>
Regarding the polypropylene resin particles, L ₂ (length of the longest part), D ₂ max (maximum diameter in the cross section perpendicular to the L ₂ direction), D ₂ min (L ₂ direction and The minimum diameter in cross section) was measured using vernier calipers, and the L ₂ /D ₂ ratio was calculated. D2 was calculated according to the following formula ( ₂ ). Then, the average L ₂ /D ₂ ratio was calculated from the average value of the L ₂ /D ₂ ratios of 10 polypropylene-based resin particles.
D2=(D2max ₊ D2min)/ ₂ ( ₂ ).

Regarding the expanded polypropylene resin beads, L ₁ (length of the longest part), D ₁ max (maximum diameter in the cross section perpendicular to the L ₁ direction), D ₁ min (perpendicular to the L ₁ direction) shown in FIG. (minimum diameter in a rough cross section) was measured using a vernier caliper to calculate the L ₁ /D ₁ ratio. 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 ratios of 10 foamed polypropylene resin beads.
D1=( _D1max + _D1min )/2 ( ₁ ).

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

<Expansion Ratio of Expanded Polypropylene Resin Beads (Single-stage Expanded Beads and Two-stage Expanded Beads)>
The weight (g) (referred to as w) of expanded polypropylene resin particles having a bulk volume of about 50 cm ³ was determined. The expanded polypropylene resin particles were submerged in ethanol contained in a graduated cylinder, and the volume of the expanded polypropylene resin particles (also referred to as ethanol submersion volume) (cm ³ ) (assumed to be v) was measured. The expansion ratio was obtained from the weight w, the volume v, and the density (g/cm ³ ) (referred to as d) of the polypropylene-based resin (a) according to the following formula (3). The density d of the polypropylene-based resin composition was 0.9 g/cm ³ .
Expansion ratio of expanded polypropylene resin particles=d×v/w (3).

<Apparent Density of Expanded Polypropylene Resin Beads (Single-stage Expanded Beads and Two-stage Expanded Beads)>
After the expanded polypropylene resin particles were gently put into a wide-mouthed 10-liter container until it overflowed, the mouth of the 10-liter container was scraped off so that the volume of the expanded polypropylene resin particles added was 10 liters. After measuring the weight of the foamed polypropylene resin particles in a 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 polypropylene resin in-mold expansion molded product>
The weight (g) (referred to as W) of the obtained polypropylene resin-based in-mold expansion molded product (length 400 mm x width 300 mm x thickness 40 mm) was measured, and the length, width and thickness dimensions of the molded product were measured with a vernier caliper. The volume (cm ³ ) (assumed to be V) was calculated. The molded body density was obtained by W/V. However, the unit was converted to g/L.

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

<Friction noise of polypropylene resin in-mold expansion molded product>
The planar part of the obtained polypropylene resin in-mold expansion molded product (length 400 mm x width 300 mm × thickness 40 mm) was brought into contact with the corner of another separately prepared polypropylene resin expansion molded product (same size). By reciprocating the corner portion in this state, the polypropylene-based resin foam molded articles were rubbed against each other, and the presence or absence of frictional noise was evaluated. Evaluation criteria are as follows.
◯: Almost no fricative sound is generated, but it is slightly generated when moved several times.
x: A large fricative sound is generated when moved.

<Peak sound absorption coefficient of polypropylene resin in-mold expansion molded product>
Based on JIS A1405, normal incident sound absorption coefficient was measured at 500 to 6400 Hz with a sample thickness of 40.0 mm. A polypropylene resin in-mold expansion molded product (length 400 mm×width 300 mm×thickness 40 mm) was cut into a diameter of 29 mm and a thickness of 40.0 mm so that the surface having the surface skin layer was the sound wave incident surface. The normal incidence sound absorption coefficient was measured under the condition that the sound wave-reflecting rigid wall and the sample were in close contact, that is, there was no background air. For the measurement of the normal incidence sound absorption coefficient, a normal incidence sound absorption coefficient measuring device SR-4100 manufactured by Ono Sokki Co., Ltd. was used.

From the obtained frequency-normal incidence sound absorption coefficient curve, the normal incidence sound absorption coefficient (peak sound absorption coefficient) at the frequency at which the normal incidence sound absorption coefficient becomes maximum was read.

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

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

[Preparation of Polypropylene Resin Expanded Particles (Two-Stage Expanded Particles)]
The single-stage expanded particles obtained in Examples 1 to 11, 13 to 18 and Comparative Examples 1 to 13, 15 to 18, and 20 were each placed in a 1 m ³ pressure-resistant container and air-pressurized to form the single-stage expanded particles at a rate of 0.30. An internal pressure of ~0.40 MPa (absolute pressure) was applied. Next, after transferring the first-stage expanded beads to a two-stage expansion machine, the first-stage expanded beads are heated with steam at 0.040 to 0.120 MPa (gauge pressure) to further expand the first-stage expanded beads, and the polypropylene resin expanded beads ( Two-stage expanded particles) were obtained. The DSC ratio, cell system, expansion ratio, and apparent density of the obtained two-stage expanded beads were measured, and the results are shown in Tables 1-6.

[Preparation of polypropylene resin in-mold expansion molded product]
The two-stage expanded beads obtained in Examples 1-11, 13-18, Comparative Examples 1-13, 15-18, and 20, and the one-stage expanded particles obtained in Example 12, Comparative Examples 14, 19, 21, and 22 Without applying internal pressure to the expanded beads, the two-stage expanded beads or the single-stage expanded beads were filled into a mold having a length of 400 mm, a width of 300 mm, and a thickness of 40 mm. Here, the cracking amount was set to 6 mm. After that, the mold and the foamed particles were heated with steam of 0.30 MPa (gauge pressure) to fuse the foamed particles to obtain an in-mold foamed product. The density, porosity and sound absorption coefficient of the obtained in-mold foam molded article were measured, and the frictional noise was evaluated. Tables 1 to 6 show the results.

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 resin (a) within the scope of the present invention, the hydrophilic substance (b), the foam nucleating agent (c), and the higher fatty acid amide (d) are mixed in a predetermined manner. It can be seen that the expanded particles can provide an in-mold foam-molded article having a high expansion ratio, a high porosity and a high sound absorption rate, and excellent frictional noise suppression performance.

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

In Comparative Example 2, since the amount of the foam nucleating agent (c) was insufficient, the cell diameter became coarse and the secondary foaming force during in-mold foam molding increased. It turns out that the rate is insufficient.

In Comparative Example 3, it can be seen that an excessive amount of the hydrophilic substance (b) causes the in-mold foam-molded product to shrink and fill the voids, resulting in an insufficient sound absorption coefficient.

In Comparative Example 4, the amount of the foam nucleating agent (c) was excessive, resulting in a fine cell diameter and an excessively low secondary foaming force during in-mold foam molding. was deteriorated, cracking occurred, 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), the in-mold foam produced fricative noise, indicating that the performance was insufficient (evaluation of the fricative noise was x).

In Comparative Example 6, the excessive amount of the higher fatty acid amide (d) increased the amount of the dispersant adhering to the surface of the expanded polypropylene resin beads when the expanded polypropylene resin beads were produced. However, the fusion bonding of the mold deteriorated and cracks occurred, making it impossible to obtain a good in-mold foam molded product.

In Comparative Examples 7 to 9, as a result of blending within the range of the example of Patent Document 3 (International Publication WO2006/016478), the foamability was inferior, the expansion ratio was low, and the in-mold foam molded product produced frictional noise. It turns out to be insufficient. In addition, it can be seen that the cell diameter becomes coarse and the secondary foaming force during in-mold foam molding increases, and as a result, the voids of the in-mold foam molded body are filled and the sound absorption coefficient becomes insufficient.

In Comparative Examples 10 and 11, as a result of not adding the foam nucleating agent (c), the cell diameter became coarse, and as a result, the secondary foaming force during in-mold foam molding increased, and as a result, the voids in the in-mold foam molded product were filled, resulting in a sound absorption coefficient. is found to be insufficient. Moreover, as a result of not adding the higher fatty acid amide (d), the in-mold foam-molded product generates fricative noise, indicating that the performance is insufficient (evaluation of fricative noise is x).

In Comparative Examples 12 and 13, as a result of blending within the range of Examples of Patent Document 8 (Japanese Patent Application Laid-Open No. 2003-171516), it can be seen that the voids in the in-mold foam molded product are filled and the sound absorption coefficient is insufficient. Moreover, as a result of not adding the higher fatty acid amide (d), the in-mold foam-molded product generates fricative noise, indicating that the performance is insufficient (evaluation of fricative noise is x).

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 in the in-mold foam molded product were filled and the sound absorption was insufficient.

In Comparative Example 15, as a result of the DSC ratio exceeding the range of the present application, the secondary foaming power at the time of in-mold foam molding was increased, resulting in poor foamability and insufficient performance (expansion ratio). Furthermore, the fusion-bonding of the in-mold foam-molded product deteriorated, cracking occurred, and a good in-mold foam-molded product could not be obtained.

In Comparative Example 16, the L ₁ /D ₁ of the expanded particles was below the range of the present application, and as a result, the filling property of the expanded particles during in-mold foam molding became very good (excessive), and the voids of the in-mold foam molded product were filled, resulting in sound absorption. It turns out that the rate is insufficient.

In Comparative Example 17, the L ₁ /D ₁ of the expanded particles exceeded the range of the present application, and as a result, the fillability of the expanded particles during in-mold expansion molding became very poor, and a good in-mold expansion molded article could not be obtained. .

In Comparative Example 18, the total addition amount of the hydrophilic substance (b) and the foam nucleating agent (c) was below the range of the present application, resulting in poor foamability and sound absorbing performance.

In Comparative Example 19, the total added amount of the hydrophilic substance (b) and the foam nucleating agent (c) exceeded the range of the present application, resulting in over-expansion and severe shrinkage of the expanded beads, and good expanded beads could not be obtained. I didn't.

In Comparative Example 20, a formulation corresponding to Example 13 of Patent Document 9 (Japanese Unexamined Patent Application Publication No. 2004-67768) was used. , it is found that the performance is insufficient.

In Comparative Examples 21 and 22, the formulations were the same as in Examples 1 and 5 of the present application, respectively, but the foaming agent used was changed from carbon dioxide to isobutane. As a result, overexpansion occurred, and the shrinkage of the expanded beads became severe, and satisfactory expanded beads could not be obtained.

According to one embodiment of the present invention, it is possible to obtain polypropylene-based resin expanded beads that can provide a polypropylene-based resin in-mold expansion-molded article having a high porosity and a high magnification. Therefore, one embodiment of the present invention can be suitably used in various fields such as the field of packaging materials, the field of cushioning materials, the field of heat insulating materials, and the field of building materials.

Claims (4)

A step of dispersing polypropylene-based resin particles in an aqueous dispersion medium together with a foaming agent in a pressure vessel;
heating the interior of the pressure vessel to a temperature equal to or higher than the softening temperature of the polypropylene resin particles and pressurizing the interior of the pressure vessel; and the aqueous dispersion medium in which the polypropylene resin particles and the blowing agent are dispersed. to a pressure region lower than the internal pressure of the pressure vessel to obtain expanded polypropylene resin particles,
The polypropylene-based resin particles are
With respect to polypropylene resin (a) and 100 parts by weight of polypropylene resin (a),
Hydrophilic substance (b) 1.0 parts by weight or more and 10 parts by weight or less,
and 1.0 parts by weight or more and 10 parts by weight or less of the foam nucleating agent (c),
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 a polypropylene resin composition containing 1.0 parts by weight or more and 5.0 parts by weight or less of a higher fatty acid amide (d),
The expanded polypropylene resin 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,
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 in differential scanning calorimetry (DSC) of the expanded beads is 40% or more and 70% or less,
and an expansion ratio of 15 times or more and 35 times or less,
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 per unit triazine skeleton of 300 or less, and (ii) a metal borate. ,
The blowing agent is an inorganic blowing agent containing carbon dioxide,
A method for producing expanded polypropylene resin particles, characterized by: The method for producing expanded polypropylene resin beads according to claim 1, wherein the polypropylene resin particles have an _average L2/D2 ratio of less _than 4.0. Expanded polypropylene resin particles obtained by expanding polypropylene resin particles using a blowing agent,
The polypropylene-based resin particles are
polypropylene resin (a), and
Per 100 parts by weight of polypropylene resin (a),
Hydrophilic substance (b) 1.0 parts by weight or more and 10 parts by weight or less,
and 1.0 parts by weight or more and 10 parts by weight or less of the foam nucleating agent (c),
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 a polypropylene resin composition containing 1.0 parts by weight or more and 5.0 parts by weight or less of a higher fatty acid amide (d),
The expanded polypropylene resin 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,
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 in differential scanning calorimetry (DSC) of the expanded beads is 40% or more and 70% or less,
and an expansion ratio of 15 times or more and 35 times or less,
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 per unit triazine skeleton of 300 or less, and (ii) a metal borate. ,
The expanded polypropylene resin particles, wherein the foaming agent is an inorganic foaming agent containing carbon dioxide . An in-mold expansion molded product using the expanded polypropylene resin particles according to claim 3 ,
The in-mold foam molded product has a porosity of 5% or more and 50% or less.
A polypropylene resin-based in-mold expansion molded product characterized by:

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