JP5090213B2 - Method for producing expanded polypropylene resin particles - Google Patents

Description

  The present invention relates to a method for producing polypropylene resin expanded particles used for buffer packaging materials, returnable boxes, automobile bumper core materials, heat insulating materials, and the like. More specifically, the present invention relates to a method for producing expanded polypropylene resin particles in which foaming during the production of expanded polypropylene resin particles is suppressed, production efficiency is improved, and wastewater treatment load in the production process is reduced.

  Conventionally, as a method for producing polypropylene resin foamed particles, polypropylene resin particles, dispersants such as poorly water-soluble inorganic substances, dispersion aids such as surfactants, volatile organic foaming agents, carbon dioxide gas, nitrogen, An inorganic gas foaming agent such as air is dispersed in an aqueous dispersion medium while stirring in a pressure vessel. The dispersion is heated to a constant pressure, and after impregnating the foaming agent into the resin particles at a constant temperature, one end of the pressure vessel Is known, and a dispersion liquid is released under a low-pressure atmosphere to obtain expanded particles. Examples of the dispersion aid include anionic surfactants such as sodium alkanesulfonate and sodium dodecylbenzenesulfonate. (For example, Patent Document 1) using only polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, etc. A method using only nonionic surfactant (e.g., Patent Document 2) are known. However, there is no description about a method in which an anionic surfactant and a nonionic surfactant are always used in combination.

  On the other hand, when an anionic surfactant is used as a dispersion aid, the effect as a dispersion aid is high and a stable dispersion can be obtained. The polypropylene resin particles are separated from the dispersion together with the foam, and as a result, the polypropylene resin particles or the expanded particles remain in the pressure vessel even after one end of the pressure vessel is released and the dispersion is released in a low pressure atmosphere. Or the shape of the obtained expanded polypropylene resin particles is flattened, resulting in a decrease in production efficiency.

  Such a problem may be particularly prominent when foaming polypropylene resin particles containing an antistatic agent in order to impart antistatic properties. This is because when the antistatic agent is contained, the polypropylene resin particles tend to stick (stick) or agglomerate in the pressure vessel, and as a countermeasure, the amount of anionic surfactant as a dispersion aid is increased. It is likely to occur.

Furthermore, when foaming is large, there is also a problem that the wastewater treatment load after foaming becomes large, and a method for producing polypropylene resin expanded particles in which foaming is suppressed as much as possible is desired.
Japanese Patent Laid-Open No. 7-304895 Japanese Patent Laid-Open No. 10-130421

  The present invention suppresses foaming during the production of polypropylene resin foam particles, particularly polypropylene resin foam particles with antistatic performance, improves production efficiency, and reduces wastewater treatment load in the production process. An object of the present invention is to provide a method for producing expanded polypropylene resin particles.

  As a result of diligent research to solve the above problems, the present inventor has produced a polypropylene resin expanded particle by using a nonionic surfactant together with an anionic surfactant as a dispersion aid. As a result, the present inventors have found that the foaming of the water is suppressed, the production efficiency is improved, and the wastewater treatment load in the production process is reduced.

  That is, the first aspect of the present invention is that the polypropylene resin particles, water, inorganic dispersant, anionic surfactant, and foaming agent are accommodated in a pressure-resistant container and dispersed under stirring conditions and the polypropylene resin particles are softened. After raising the temperature above the point temperature, the dispersion in the pressure vessel is discharged into a pressure region lower than the internal pressure of the pressure vessel and foamed to produce polypropylene resin expanded particles. The present invention relates to a method for producing expanded polypropylene resin particles, wherein a surfactant is added.

As a preferred embodiment,
(1) The nonionic surfactant is a modified dimethylpolysiloxane.
(2) The modified dimethylpolysiloxane is at least one selected from polyether-modified dimethylpolysiloxane and polyglycerin-modified dimethylpolysiloxane.
(3) the nonionic surfactant is a higher fatty acid glycerin ester,
(4) It is characterized in that dimethylpolysiloxane and / or silica is further added to the pressure vessel at any time until foaming is completed.
(5) The nonionic surfactant is added to the pressure vessel a plurality of times,
(6) The anionic surfactant is a sulfonate.
(7) The polypropylene resin particles contain 0.1 to 5 parts by weight of an antistatic agent with respect to 100 parts by weight of the polypropylene resin.
(8) The antistatic agent is at least one selected from higher fatty acid glycerin ester and ethanolamine.
(9) Carbon dioxide gas is added to the pressure vessel immediately before foaming,
(10) The water hardness is 0 mg / L or more and 180 mg / L or less,
It is related with the manufacturing method of the polypropylene resin expanded particle of the said description.

  2nd of this invention is related with the polypropylene resin expanded particle obtained by the manufacturing method of the polypropylene resin expanded particle of the above-mentioned description, 3rd of this invention fills the mold with the polypropylene resin expanded particle as described above, The present invention relates to an in-mold foam molded product obtained by heating.

  According to the present invention, the dispersion stability of a dispersion composed of polypropylene resin particles, water, an inorganic dispersant, and a dispersion aid is ensured, and foaming due to stirring and pressure release in the pressure vessel is also suppressed. As a result, there is no problem of sticking the foamed foam particles, the so-called stick phenomenon, or the flattened foam particles, and the amount of polypropylene resin particles or foam particles remaining in the pressure vessel after foaming is reduced. This improves productivity. Furthermore, the waste water treatment load is reduced by reducing foaming, and a method for producing polypropylene resin expanded particles having excellent environmental compatibility can be provided.

  In the present invention, polypropylene resin particles, water, an inorganic dispersant, and an anionic surfactant that acts as a dispersion aid are contained in a pressure vessel, and then the temperature rises above the softening point temperature of the resin particles under stirring conditions. In the method of producing polypropylene-based resin foamed particles, a nonionic surfactant is further added to the pressure vessel. This is a method for producing expanded polypropylene resin particles.

  The polypropylene resin particles used in the present invention are made from a polypropylene resin. There is no restriction | limiting in particular as such a polypropylene resin, A propylene homopolymer, a propylene-alpha-olefin random copolymer, a propylene-alpha-olefin block copolymer, etc. are mentioned. Examples of the α-olefin include α-olefins having 2 to 4 to 15 carbon atoms, and these may be used alone or in combination of two or more. Further, two or more of the aforementioned propylene homopolymer, propylene-α-olefin random copolymer, and propylene-α-olefin block copolymer may be used in combination.

  Among these, in particular, a propylene-ethylene random copolymer, a propylene-ethylene-butene-1 random copolymer, and a propylene-butene-1 random copolymer, and the comonomer content other than propylene is 1 to 5% by weight. In some cases, it exhibits good foaming properties and can be suitably used. Further, the copolymer polymer has a characteristic that it can be easily impregnated with carbon dioxide gas as compared with the homopolymer, and can be suitably used in the present invention.

  Moreover, in order to obtain foamed particles having excellent foamability and moldability, and excellent mechanical strength and heat resistance when formed into an in-mold foam molded product, the melting point of the polypropylene resin is usually 130 to 165 ° C, Is preferably 135 ° C. to 155 ° C. When the melting point is less than 130 ° C., heat resistance and mechanical strength tend to be insufficient. Moreover, when melting | fusing point exceeds 165 degreeC, there exists a tendency for it to become difficult to ensure the melt | fusion at the time of in-mold foam molding.

  Here, the melting point is a temperature of 10 to 10 ° C./min from 40 ° C. to 220 ° C., and then cooled to 40 ° C. at a rate of 10 ° C./min with a differential scanning calorimeter. The peak temperature of the endothermic peak in the DSC curve obtained when the temperature is increased again to 220 ° C. at a rate of 10 ° C./min.

  Furthermore, the melt index of the polypropylene resin is preferably 2 g / 10 min or more and 11 g / 10 min or less, more preferably 3 g / 10 min or more and 10 g / 10 min or less, and most preferably 4 g / 10 min or more and 8 g / min. 10 minutes or less. When the melt index is less than 2 g / 10 minutes, it is difficult to obtain expanded particles with a high expansion ratio, and the bubbles tend to be non-uniform. In addition, when the melt index exceeds 11 g / 10 min, it is easy to foam, and it is easy to obtain expanded particles with a high expansion ratio, but the expanded cells tend to break, and the open cell rate of the expanded particles tends to increase. , Bubbles also tend to be non-uniform. The melt index is a value measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  There is no restriction | limiting in particular as an inorganic type dispersing agent used by this invention, The inorganic type dispersing agent generally used can be used.

  Specifically, aluminosilicates (kaolin, talc, etc.) based on barium sulfate and silica-alumina, aluminum oxide, titanium oxide, calcium phosphate (tricalcium phosphate, etc.), calcium carbonate, magnesium pyrophosphate, magnesium phosphate , Basic magnesium carbonate, basic zinc carbonate and the like.

  Among these, from the viewpoint of having a dispersion effect with a small amount of use and a small wastewater treatment load, any of aluminosilicates mainly composed of barium sulfate, silica-alumina, calcium phosphate (such as tribasic calcium phosphate), and magnesium phosphate Is preferably used.

  The addition amount of such an inorganic dispersant is not particularly limited and can be appropriately adjusted in consideration of the expression of the stabilizing effect of the dispersion and the addition ratio of the anionic surfactant. The amount is preferably 0.01 parts by weight or more and 5 parts by weight or less, more preferably 0.05 parts by weight or more and 4 parts by weight or less, and most preferably 0.1 parts by weight or more with respect to 100 parts by weight of the resin particles. 3 parts by weight or less. If the amount is less than 0.05 parts by weight, the dispersibility of the polypropylene resin particles tends to decrease at a temperature higher than the softening point temperature of the polypropylene resin particles. If the amount exceeds 5 parts by weight, an inorganic dispersant is formed on the surface of the polypropylene resin expanded particles. There is a tendency to adhere a lot.

  In the present invention, an anionic surfactant is added to the pressure vessel. Anionic surfactants act as a dispersion aid. Specific anionic surfactants include alkyl sulfonates, higher alcohol sulfates, alkane sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, sulfosuccinates, α-olefin sulfonates, N -Acyl sulfonate, alkyl sulfate, alkyl ether sulfate, alkyl allyl ether sulfate, alkyl amide sulfate, alkyl phosphate, alkyl ether phosphate, alkyl allyl ether phosphate, alkyl ether carboxylate, N-acylamino acid salts and the like can be mentioned, and one or more of these can be used.

  From the viewpoint of the stability of the dispersion comprising polypropylene resin particles, water, inorganic dispersant, and anionic surfactant, anionic surfactants include alkane sulfonate, alkylbenzene sulfonate, alkyl It must be a sulfonate such as naphthalene sulfonate, sulfosuccinate, α-olefin sulfonate, N-acyl sulfonate, alkyl sulfate, alkyl ether sulfate, alkyl allyl ether sulfate, alkyl amide sulfate. It is most preferable that it is one or more selected from alkane sulfonate, alkylbenzene sulfonate, and α-olefin sulfonate.

  The addition amount of such an anionic surfactant is not particularly limited and may be appropriately adjusted in order to express the stabilizing effect of the dispersion. However, the addition amount is 0 with respect to 100 parts by weight of the polypropylene resin particles. It is preferably 0.001 to 0.5 parts by weight, more preferably 0.003 to 0.3 parts by weight, and most preferably 0.005 to 0.2 parts by weight. It is. If the amount is less than 0.001 part by weight, the dispersion stability of the polypropylene resin particle tends to decrease at a temperature higher than the softening point temperature of the polypropylene resin particle. If the amount exceeds 0.5 part by weight, foaming of the dispersion becomes intense and wastewater treatment is performed. There is a tendency to increase the load of.

  Specific examples of nonionic surfactants used in the present invention include alkyl and alkylallyl polyoxyethylene ethers, alkylallyl formaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropyl alkyl ethers, and polyoxy glycerol esters. Ethylene ether, polyoxyethylene ether of sorbitan ester, polyoxyethylene ether of sorbitol ester, polyethylene glycol fatty acid ester, monoester of higher fatty acid and glycerin, diester of higher fatty acid and glycerin, triester of higher fatty acid and glycerin, glycerin ester, Polyglycerin ester, sorbitan ester, propylene glycol ester, sucrose ester, represented by the following general formulas 1 and 2 Ethanol amine, aliphatic alkanolamide, polyoxyethylene fatty acid amides, polyoxyethylene alkyl amines, amine oxides, and modified dimethylpolysiloxane.

この中でも、分散液の泡立ち抑制効果や分散液の安定性の点から、高級脂肪酸グリセリンエステル、或いは、変性ジメチルポリシロキサンが好ましい。

Among these, higher fatty acid glycerin ester or modified dimethylpolysiloxane is preferable from the viewpoint of suppressing the foaming of the dispersion and the stability of the dispersion.

  Examples of such higher fatty acid glycerol esters include higher fatty acid and glycerol monoesters, higher fatty acid and glycerol diesters, and higher fatty acid and glycerol triesters.

  Further, as the modified dimethylpolysiloxane, polyether-modified dimethylpolysiloxane, dimethicone copolyol and the like are more preferable, and polyoxyalkylene-dimethylpolysiloxane copolymer and polyglycerin-dimethylpolysiloxane copolymer are most preferable. In addition, there is no restriction | limiting in particular in the modification | denaturation group introduction | transduction part in modified | denatured dimethylpolysiloxane, What is necessary is just to use what was introduce | transduced into the side chain of the polysiloxane, the terminal, or both.

  The property of the nonionic surfactant may be liquid or solid. However, in the case of a high viscosity liquid or solid, it is dissolved or dispersed in water in advance and quickly added to the pressure vessel. It is preferable to make it diffuse or dissolve.

  The addition amount of such a nonionic surfactant is not particularly limited and may be appropriately adjusted in order to express the foaming suppression effect of the dispersion, but is 0% relative to 100 parts by weight of the polypropylene resin particles. It is preferably 0.001 part by weight or more and 0.3 part by weight or less, more preferably 0.001 part by weight or more and 0.2 part by weight or less, and most preferably 0.001 part by weight or more and 0.1 part by weight or less. It is. If it is less than 0.0001 part by weight, the foaming suppression effect is low, and even if it exceeds 0.3 part by weight, the foaming suppression effect tends to reach a peak.

  In the present invention, it is more preferable to add dimethylpolysiloxane and / or silica together with the nonionic surfactant. As the nonionic surfactant, it is most preferable to use a modified dimethylpolysiloxane and use dimethylpolysiloxane and / or silica together in terms of foaming suppression effect. In addition, it is preferable to mix such dimethylpolysiloxane and silica with a nonionic surfactant in advance. Furthermore, it is most preferable that dimethylpolysiloxane and silica are uniformly dispersed together with a nonionic surfactant and, if necessary, water.

  In the present invention, an antistatic agent can be contained in the polypropylene resin particles. Specific examples of such an antistatic agent include (a) an antistatic agent mainly composed of a cationic surfactant such as an aliphatic amine salt, a hydroxyalkyl monoethanolamine salt, and an aliphatic quaternary ammonium salt. ,

(B) Alkyl sulfonate, alkane sulfonate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, sulfosuccinate, α-olefin sulfonate, N-acyl sulfonate, alkyl sulfate, alkyl ether sulfate Mainly anionic surfactants such as alkyl allyl ether sulfate, alkyl amide sulfate, alkyl phosphate, alkyl ether phosphate, alkyl allyl ether phosphate, alkyl ether carboxylate, N-acyl amino acid salt Antistatic agent as a component,

(C) Alkyl and alkylallyl polyoxyethylene ether, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropyl alkyl ether, glycerin ester polyoxyethylene ether, sorbitan ester polyoxyethylene ether, sorbitol ester poly Oxyethylene ether, polyethylene glycol fatty acid ester, polyglycerol fatty acid ester, higher fatty acid and glycerol monoester, higher fatty acid and glycerol diester, higher fatty acid and glycerol triester, glycerol ester, polyglycerol ester, sorbitan ester, propylene glycol ester , Sucrose ester, ethanolamine represented by the following general formula 1 and general formula 2, Aliphatic alkanolamide, polyoxyethylene fatty acid amides, polyoxyethylene alkyl amines, nonionic surface active agents antistatic agent as a main component, such as an amine oxide,

(D) Antistatic agents mainly composed of amphoteric surfactants such as carboxybetaine, imidazolinium betaine and aminocarboxylate.

  Among these, from the viewpoint of antistatic performance and moldability of the obtained expanded particles, it is preferable to use at least one of higher fatty acid glycerin ester and ethanolamine represented by general formula 1 or general formula 2.

  From another viewpoint, it is preferable to use an antistatic agent comprising a surfactant having an HLB value of 3 to 11.

  There is no restriction | limiting in particular as a foaming agent used by this invention, The foaming agent generally used can be used. Specific examples include inorganic foaming agents such as carbon dioxide (carbon dioxide), air, oxygen, nitrogen, and water. When water is used, it is preferable to use water in which polypropylene resin particles are dispersed.

  Also, organic foaming agents such as saturated hydrocarbons having 3 to 5 carbon atoms, dimethyl ether, alcohols such as methanol and ethanol whose boiling points are lower than the foamable temperature can be used.

  Among these, from the viewpoint of foamability, small variation in the magnification of the obtained polypropylene resin foamed particles, and uniform cell diameter, carbon dioxide gas or a combination of carbon dioxide gas and water is used as a foaming agent. Is more preferable.

  From the viewpoint of environmental compatibility, water is preferably used as the foaming agent, and more preferably used in combination with carbon dioxide gas.

  In general, when carbon dioxide is used as a foaming agent, a large amount of carbon dioxide dissolves in water. However, when the dispersion is discharged into a low pressure region and foamed, the dissolved carbon dioxide volatilizes, Since the foam of the released dispersion tends to become more intense than when the foaming agent is used, the effects of suppressing foaming and facilitating drainage treatment of the present invention are more prominent.

  On the other hand, from the viewpoint of obtaining expanded particles having a high expansion ratio, it is preferable to use isobutane having a high impregnation property for polypropylene resin as a foaming agent.

  There is no restriction | limiting in particular as addition amount of such a foaming agent, Although it adjusts suitably with foaming magnification etc., it is 0.1 to 50 weight part with respect to 100 weight part of polypropylene resin particles. Preferably, it is 2 to 30 parts by weight, and most preferably 3 to 20 parts by weight. If the amount is less than 0.1 parts by weight, the expansion ratio is difficult to be exhibited. If the amount exceeds 50 parts by weight, the foamed polypropylene resin foam particles tend to break and become open.

  However, when water is used as the foaming agent, 100 parts by weight or more and 500 parts by weight or less of water may be charged in a pressure vessel with respect to 100 parts by weight of the polypropylene resin particles.

  In the present invention, the hardness of water is preferably 0 mg / L or more and 180 mg / L or less. More preferably, the hardness is 0 mg / L or more and 120 mg / L or less, more preferably 0 mg / L or more and 60 mg / L or less, and most preferably more than 0 mg / L and 20 mg / L or less.

Here, the hardness is a so-called American hardness obtained by converting the amount of calcium / magnesium contained in the aqueous medium into the amount of calcium carbonate, which is a commonly used hardness, and is represented by the following formula: be able to.
Hardness (mg / L) = calcium amount (mg / L) × 2.5 + magnesium amount (mg / L) × 4.1

  When the water hardness is 0 mg / L or more and 180 mg / L or less, it is estimated that the deactivation of the anionic surfactant is suppressed. Since the effects of the present invention such as the suppression of foaming and the ease of wastewater treatment appear remarkably, it can be said to be a preferred embodiment.

  In addition, there is no restriction | limiting in particular in the measuring method of the hardness of water, What is necessary is just to measure using a conventionally well-known measuring method and apparatus. For example, measurement by chelate titration method using ethylenediaminetetraacetic acid (EDTA), flame-atomic absorption photometry, ion chromatography, inductively coupled plasma emission spectrometry, inductively coupled plasma mass spectrometry (ICP / MS method), etc. can do.

  In the present invention, when water or carbon dioxide gas is used as the foaming agent, the organic resin and / or inorganic substance (hereinafter referred to as hydrophilicity, water absorption, water solubility, water compatibility, etc.) in the polypropylene resin particles. These are also generally referred to as hydrophilic substances) and are preferably added.

  As such a hydrophilic substance, specifically, (A) a polyalkylene glycol chain such as a copolymer containing a polyalkylene glycol block (for example, Pelestat, trade name of Sanyo Kasei Kogyo Co., Ltd.), polyethylene glycol, polypropylene glycol, etc. (B) hydrophilic polymers such as sodium polyacrylate, cellulose, polyvinyl alcohol, (C) inorganic compounds such as zeolite, bentonite, synthetic hectorite (laponite), and metal borate.

  Further, for example, (a) cationic surfactants such as aliphatic amine salts, hydroxyalkyl monoethanolamine salts, aliphatic quaternary ammonium salts, (b) alkyl sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates. , Sulfosuccinate, α-olefin sulfonate, N-acyl sulfonate, alkyl sulfate, alkyl ether sulfate, alkyl allyl ether sulfate, alkyl amide sulfate, alkyl phosphate, alkyl ether phosphate, Anionic surfactants such as alkyl allyl ether phosphates, alkyl ether carboxylates, N-acyl amino acid salts,

(C) Alkyl and alkylallyl polyoxyethylene ether, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropyl alkyl ether, glycerin ester polyoxyethylene ether, sorbitan ester polyoxyethylene ether, sorbitol ester poly Oxyethylene ether, polyethylene glycol fatty acid ester, glycerin ester, higher fatty acid and glycerin monoester, higher fatty acid and glycerin diester, higher fatty acid and glycerin triester, polyglycerin ester, sorbitan ester, propylene glycol ester, sucrose ester, Ethanolamine, aliphatic alkanolamide, poly represented by the following general formulas 1 and 2 Kishiechiren fatty acid amide, polyoxyethylene alkylamine, nonionic surfactants such as amine oxides, (d) carboxy betaines, imidazolinium betaine, Ya surfactants such as amphoteric surfactants such as amino acid salt

For example, (e) an antistatic agent having the above surfactant as a main component, and (f) at least one selected from an ester bond, an amide bond, an ether bond, a urethane bond, and an imide bond in which a polyolefin block and a hydrophilic polymer block are selected. Antistatic agents having a structure in which they are alternately and alternately bonded through these bonds, for example, the antistatic agents described in the claims of Japanese Patent No. 3488163, can also be mentioned.

  These hydrophilic substances may be used alone or in combination of two or more. Among these, more preferred hydrophilic substances include polyethylene glycol, more preferably an average molecular weight of 200 or more and 9000 or less, and most preferably an average molecular weight of 200 or more and 600 or less.

  Another preferred hydrophilic substance is a block copolymer having a polyolefin block and a polyalkylene glycol block. More specifically, the trade name Perestat manufactured by Sanyo Chemical Industries, Ltd. can be mentioned. Since such a block copolymer has a polyolefin block, it has good compatibility with a polyolefin-based resin, and since it is a solid, handling is good, resulting in poor feeding during extrusion kneading. There is no. As a result, there is no discharge unevenness in extrusion, and polypropylene resin particles having a uniform shape can be produced in the production of polypropylene resin particles by the strand cut method. When such polypropylene resin particles are foamed, there is a tendency to obtain foamed particles having a uniform cell diameter and small variation in magnification. An in-mold foam molded body molded with the foam particles has small intergranular, shrinkage and distortion, is beautiful, has a high fusion rate of the in-mold foam molded body, and has sufficient heat-resistant dimensional stability. Tend.

  The addition amount of the hydrophilic substance used in the present invention is preferably 0.01 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the polypropylene resin. If the amount added is less than 0.01 parts by weight, the foaming ratio cannot be improved by water or carbon dioxide as a foaming agent, and the effect of uniformizing the bubble diameter tends to be small. When the addition amount exceeds 5 parts by weight, shrinkage of the expanded particles tends to occur, or dispersion in the polypropylene resin tends to be insufficient.

  In the present invention, it is also a preferred embodiment to add a foam nucleating agent to the polypropylene resin particles. Foam nucleating agent refers to a substance that promotes the formation of bubble nuclei during foaming, such as talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, titanium oxide, zeolite, Examples include aliphatic metal salts such as calcium stearate and barium stearate, melamine, and boric acid metal salts. These foam nucleating agents may be used alone or in combination of two or more. Among these, talc and calcium carbonate are preferable. In particular, talc is preferable because it has a good dispersibility in a polypropylene resin and a foam having a uniform cell diameter can be easily obtained.

  The addition amount of the foam nucleating agent is appropriately adjusted depending on the type of foam nucleating agent used, the desired expansion ratio, etc., but 0.005 parts by weight or more and 1 part by weight or less with respect to 100 parts by weight of the polypropylene resin. Is preferred. If it is less than 0.005 parts by weight, the expansion ratio may not be increased or the uniformity of the bubble diameter may be reduced. If it exceeds 1 part by weight, the average cell diameter of the foam tends to be too small, and the in-mold foam moldability tends to be poor.

  When talc is used as the foam nucleating agent, a desired average cell diameter tends to be obtained by using 0.02 part by weight or more and 0.5 part by weight or less with respect to 100 parts by weight of the polypropylene resin, and in-mold foam moldability is also achieved. It is preferable because it becomes good.

  In the present invention, additives such as antioxidants, compatibilizers, colorants (carbon black, pigments, dyes, etc.), stabilizers, weathering agents, flame retardants and the like are appropriately added to such an extent that the effects of the present invention are not impaired. In order to improve the dispersibility of these additives, there is a tendency that the polypropylene resin foam particles can be stably produced by adding a higher fatty acid metal salt or the like together with the polypropylene resin particles. .

  What is necessary is just to produce the polypropylene resin particle in this invention using a conventionally well-known method. For example, a polypropylene resin, blended with antistatic agent, hydrophilic substance, foam nucleating agent, etc., added in advance as needed, melt kneaded with an extruder, extruded from a die, cooled, and then with a cutter The method of setting it as the polypropylene-type resin particle resin particle is mentioned.

  In addition, an antistatic agent, a hydrophilic substance, a foam nucleating agent, an antioxidant, a compatibilizer, a colorant, a stabilizer, a weathering agent, a flame retardant, etc. are previously masterbatched with a polyolefin-based resin. A polypropylene resin particle may be blended with a polypropylene resin so that a desired addition amount is obtained, and melt-kneaded in an extruder.

  Next, the manufacturing method of the polypropylene resin expanded particle in this invention is demonstrated.

  In the present invention, polypropylene resin particles, water, an inorganic dispersant, an anionic surfactant, and a foaming agent are accommodated in a pressure-resistant container and dispersed under stirring conditions and above the softening point temperature of the polypropylene resin particles. This is a method for producing polypropylene-based resin foamed particles by discharging the dispersion in the pressure vessel into a pressure range lower than the internal pressure of the pressure vessel and then foaming it. An agent is added to obtain polypropylene resin expanded particles.

  The addition of the nonionic surfactant into the pressure vessel may be performed during the process from when the polypropylene resin particles, water, inorganic dispersant, anionic surfactant, and foaming agent are contained in the pressure vessel to the completion of foaming. It may be performed at the stage or multiple times.

  Specifically, polypropylene resin particles, water, an inorganic dispersant, and an anionic surfactant are charged into a pressure vessel and may be added at the initial stage, or may be added during and after the temperature rise. Further, it may be added during foaming. Further, the nonionic surfactant may be divided and added in a plurality of times at the time point described above. Preferably, it is preferably added at the initial stage, and more preferably at least twice during the initial stage and during foaming. By adding in the initial stage, foaming can be more effectively suppressed, and flattening of the resulting polypropylene resin expanded particles tends to be prevented.

  When discharging the dispersion in the pressure vessel to a pressure range lower than the internal pressure of the pressure vessel, an inorganic substance such as carbon dioxide, nitrogen or air is used immediately before foaming, that is, at any stage before being released to the low pressure region. It is preferable to increase the internal pressure in the sealed container by injecting gas, adjust the pressure release speed during foaming, and adjust the expansion ratio and average bubble diameter.

  When carbon dioxide is added as a foaming agent, solid carbon dioxide (dry ice) is added to the pressure vessel along with polypropylene resin particles, water, inorganic dispersant, anionic surfactant, nonionic surfactant, etc. It may be added, or after charging polypropylene resin particles, water, inorganic dispersant, anionic surfactant, nonionic surfactant, etc. into a pressure vessel, immediately thereafter, during temperature rise or during temperature rise It may be introduced into the pressure vessel as a gas or liquid carbon dioxide gas at any stage before being discharged into the low pressure region, such as later. Or the method which combined these methods is also employable.

  It should be noted that blowing agents such as air other than carbon dioxide, oxygen, nitrogen, saturated hydrocarbons having 3 to 5 carbon atoms, dimethyl ether, methanol, and ethanol may be added in the same manner as carbon dioxide. Further, as described above, when water is used as the foaming agent, it is possible to use water charged in the pressure vessel.

  The average cell diameter of the polypropylene resin expanded particles of the present invention thus produced is preferably 130 μm or more and 500 μm or less, more preferably 160 μm or more and 400 μm or less, and further preferably 210 μm or more and 350 μm or less. If the average cell diameter is less than 130 μm, the resulting foamed molded product tends to have problems such as poor fusion, distortion of the shape, and wrinkles on the surface. There exists a tendency for the buffering characteristic of an inner foaming molding to fall.

  Although there is no restriction | limiting in particular in the expansion ratio of the polypropylene resin expanded particle obtained by this invention, It is preferable that it is 50 times or less. When the expansion ratio exceeds 50 times, bubbles of the obtained expanded particles tend to break, or the dimensional accuracy, mechanical strength, heat resistance and the like of the in-mold expanded molded product tend to be insufficient.

  When trying to obtain a foaming ratio of 20 times or more, it may be 20 times or more at the stage of discharge to the pressure region lower than the internal pressure of the pressure vessel described above (sometimes referred to as single-stage foaming) After producing foamed particles with a foaming ratio of less than 20 times by one-stage foaming, the foamed particles obtained by the first-stage foaming are pressurized with an inorganic gas such as air in a pressure-resistant container to give an internal pressure, and then steam It is more preferable to increase the expansion ratio to 20 times or more by foaming again (sometimes referred to as two-stage foaming) by heating with a heater.

  The polypropylene resin expanded particles of the present invention preferably have two melting peaks in a DSC curve obtained by differential scanning calorimetry as shown in FIG. In the case of a polypropylene resin expanded particle having two melting peaks, an in-mold foam molded article having good in-mold foam moldability and good mechanical strength and heat resistance is obtained.

  Here, the DSC curve obtained by differential scanning calorimetry of polypropylene resin foamed particles refers to 1 to 10 mg of foamed particles heated from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min with a differential scanning calorimeter. It is a DSC curve sometimes obtained.

  As described above, the expanded polypropylene resin particles having two melting peaks can be easily obtained by setting the temperature in the sealed container at the time of foaming to an appropriate value. That is, in the case of the present invention, the temperature in the closed container is usually not less than the softening temperature of the polypropylene resin as the base material, preferably not less than the melting point, more preferably not less than the melting point + 3 ° C., less than the end temperature of melting, more preferably The melting end temperature is −2 ° C. or lower, and in such a case, expanded polypropylene resin particles having two melting peaks tend to be obtained.

  The melting end temperature is a temperature of 10 to 10 ° C./min from 40 ° C. to 220 ° C. and then cooled to 40 ° C. at a rate of 10 ° C./min with a differential scanning calorimeter. The temperature at which the bottom of the melting peak of the DSC curve obtained when the temperature is raised again to 220 ° C. at a rate of 10 ° C./min returns to the baseline position on the high temperature side.

  Of the two melting peaks, the endothermic peak heat quantity on the high temperature side (hereinafter sometimes referred to as Qh) is preferably 5 J / g or more and 40 J / g or less, more preferably 7 J / g or more and 30 J / g or less. It is. If it is less than 5 J / g, the open-cell rate of the polypropylene resin expanded particles tends to be high, and if it exceeds 40 J / g, the fusion property of the in-mold foam molded product tends to be lowered.

  As shown in FIG. 1, the endothermic peak heat quantity Qh on the high temperature side is defined as A where the endothermic quantity is the smallest between the two melting peaks of the DSC curve, and tangent lines are drawn from the point A to the DSC curve. For the portion surrounded by the tangent line and the DSC curve (shaded portion in FIG. 1), the high temperature side is the melting peak heat amount Qh on the high temperature side, and the low temperature side is the melting peak heat amount Ql on the low temperature side.

  The in-mold foam molded article of the present invention is obtained by a molding method in which a polypropylene resin expanded particle obtained as described above is filled in a mold and heated.

  There is no restriction | limiting in particular as a shaping | molding method, A general method can be employ | adopted. For example, a method may be used in which a polypropylene resin foam particle is filled in a mold that can be closed but cannot be sealed, heated with water vapor or the like, and the foam particles are heated and fused together to form the mold. In order to obtain an in-mold foam molded article having good fusing property, mechanical strength, surface appearance, etc., the polypropylene resin foamed particles are kept under pressure of an inorganic gas such as air, nitrogen, carbon dioxide and the like. It is preferable to employ a method in which an internal pressure is applied to the expanded particles, and then the mold is filled and heated to form.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to such examples. The evaluation in the examples and comparative examples was performed by the following method.

(hardness)
The calcium and magnesium concentrations in the aqueous medium were measured by inductively coupled plasma mass spectrometry, and were calculated in terms of the amount of calcium carbonate.

(Dispersion stability)
Regarding the dispersion stability, the polypropylene resin foamed particles and the inside of the pressure-resistant container after foaming were observed and evaluated as follows.
○: There is no stick and no flattened foamed expanded particles. Residual resin is not seen in the pressure vessel after foaming.
(Triangle | delta): The stick which the expanded foamed particles adhered is seen, and there exists a flat expanded particle. Moreover, residual resin exists in the pressure-resistant container after foaming.
X: Resin agglomerates in the pressure vessel before foaming and foamed particles cannot be obtained.

(Foamability)
Open the valve at the bottom of the 10 L pressure-resistant airtight container, discharge the dispersion in the pressure-resistant airtight container to the foaming cylinder under atmospheric pressure to obtain polypropylene-based resin foam particles, receive the liquid discharged from the drain of the foaming cylinder in the container, This was visually observed and evaluated as follows.
○: No bubbling or small bubbling but large bubbles do not grow and immediately disappear. Δ: Bubbling is observed and some growth of bubbles is observed. ×: Bubbling is large and bubbles grow. Is large and does not easily defoam

(Foaming ratio)
After taking 3 to 10 g of expanded particles, drying at 60 ° C. for 6 hours and measuring the weight w, it is put into a graduated cylinder filled with water and submerged, and the volume v is measured from the rise of the water surface, and the true specific gravity of the expanded particles ρb = w / v was determined, and the expansion ratio K = ρr / ρb was determined from the ratio to the density ρr (= 0.9 g / cm ³ ) of the raw material composition.

(Average bubble diameter)
A line corresponding to a length of 1 mm is observed on the cut surface of each sample taken out of the expanded particles and observed with a microscope with respect to the cut surface of each sample cut with great care so as not to destroy the cell membrane. The number of bubbles through which the line segment passes was measured, and thereafter the average bubble diameter was measured according to ASTM D3576.

(Molded product fusion rate)
After a crack having a depth of about 5 mm was made on the surface of the in-mold foam molded body with a knife, the in-mold foam molded body was divided along the crack, the fracture surface was observed, and the number of broken particles relative to the total number of particles observed The ratio was determined as the fusion rate of the compact.

  Next, specific examples and comparative examples are shown. The obtained expanded polypropylene resin particles have two melting peaks in the DSC curve obtained by differential scanning calorimetry in any case. Among the two melting peaks, the endothermic peak heat quantity Qh on the high temperature side was in the range of 8 to 13 J / g.

Example 1
Polypropylene resin composition A (ethylene content in copolymer: 3.0 wt%, MI = 6 g / 10 min, melting point: 144 ° C., calcium stearate: 0.05 wt%), 100 parts by weight of polyethylene glycol ( 0.2 parts by weight of an average molecular weight of 300 (manufactured by Lion) was pre-blended, and then 0.05 parts by weight of talc (manufactured by Hayashi Kasei, Talcan powder PK-S) was added and blended as a foam nucleating agent. This was supplied to a 50 mmφ single screw extruder, melt kneaded at a die tip temperature of 200 ° C., extruded from a cylindrical die having a diameter of 1.8 mm, cooled with water, cut with a cutter, and cylindrical polypropylene resin particles (1. 2 mg / grain) was obtained.

  100 parts by weight of the obtained polypropylene resin particles, 200 parts by weight of water (hardness <0.1 mg / L), 0.7 parts by weight of tribasic calcium phosphate as a dispersing agent, 0.02 parts by weight of sodium alkanesulfonate as a dispersing aid As an initial charge of the nonionic surfactant, 0.005 part by weight of a polyoxyalkylene-dimethylpolysiloxane copolymer was put into a 10 L pressure vessel, deaerated, and 5 parts by weight of carbon dioxide gas was put into the pressure vessel while stirring. And heated to 150 ° C. The pressure container internal pressure at this time was 2.3 MPa (G). Further, carbon dioxide gas was added, and the temperature inside the pressure vessel was adjusted to 2.6 MPa (G) and held for 15 minutes. Then, the valve | bulb of the pressure | voltage resistant container lower part was opened, and the dispersion liquid was discharge | released to the foaming cylinder under atmospheric pressure through the orifice with a diameter of 4 mm, and the polypropylene resin expanded particle was obtained. At this time, during discharge, the pressure was maintained with carbon dioxide gas so that the pressure in the pressure vessel did not decrease.

  The foamed particles obtained here were washed with acid, dried at 60 ° C. for 6 hours, and then pressurized with air in a pressure-resistant container to obtain an air pressure of about 0.2 MPa, filled in a mold and heated. Then, in-mold foam molding was performed to obtain an in-mold foam molded body of 390 mm × 290 mm × 50 mm. Table 1 shows the results of evaluating the obtained polypropylene resin foamed particles and in-mold foam molded article.

（実施例２）
帯電防止剤としてのステアリン酸グリセリンエステル（ＨＬＢ４．３）が２０重量％となるようポリプロピレン系樹脂組成物Ａと混合した。次いでこの混合物を４５ｍｍφ二軸押出機に供給し、ダイス先端温度２００℃で溶融混練した後、押出し、水冷後、カッターで切断し、マスターバッチペレットを得た。

(Example 2)
It mixed with the polypropylene resin composition A so that the glyceryl stearate ester (HLB4.3) as an antistatic agent might be 20 weight%. Next, this mixture was supplied to a 45 mmφ twin screw extruder, melt-kneaded at a die tip temperature of 200 ° C., extruded, cooled with water, and cut with a cutter to obtain master batch pellets.

  The masterbatch pellet and the polypropylene resin composition A are mixed so that the amount of glycerin stearate is 1% by weight, and 100 parts by weight of the mixed resin contains 0 (polyethylene glycol (average molecular weight 300, manufactured by Lion)). Then, 2 parts by weight of the blend was preblended, and then 0.05 parts by weight of talc (manufactured by Hayashi Kasei Co., Ltd., Talcan Powder PK-S) was added and blended. This was supplied to a 50 mmφ single screw extruder, melt kneaded at a die tip temperature of 200 ° C., extruded from a cylindrical die having a diameter of 1.8 mm, cooled with water, cut with a cutter, and cylindrical polypropylene resin particles (1. 2 mg / grain) was obtained.

  100 parts by weight of the obtained polypropylene-based resin particles, 300 parts by weight of water (hardness <0.1 mg / L), 1 part by weight of calcium triphosphate as a dispersant, 0.12 parts by weight of sodium alkanesulfonate as an anionic surfactant In addition, 0.01 part by weight of polyoxyalkylene-dimethylpolysiloxane copolymer / dimethylpolysiloxane / silica mixture (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KS-530) as an initial charge of the nonionic surfactant-containing substance in a 10 L pressure vessel After the charging, it was deaerated, and 5 parts of carbon dioxide gas was put in a pressure vessel while stirring and heated to 150 ° C. The pressure container internal pressure at this time was 2.3 MPa (G). Further, carbon dioxide gas was added, and the temperature inside the pressure vessel was adjusted to 2.6 MPa (G) and held for 15 minutes. Then, the valve | bulb of the pressure | voltage resistant container lower part was opened, and the dispersion liquid was discharge | released to the foaming cylinder under atmospheric pressure through the orifice with a diameter of 4 mm, and the polypropylene resin expanded particle was obtained. Immediately after opening the valve, the same polyoxyalkylene-dimethylpolysiloxane copolymer / dimethyl as previously charged with respect to 100 parts by weight of the polypropylene resin particles was charged as foaming of the nonionic surfactant-containing substance. 0.03 part by weight of a polysiloxane / silica mixture was added from the top of the pressure vessel. Further, during discharge, the pressure in the pressure vessel was maintained with carbon dioxide gas so that the pressure in the pressure vessel did not decrease.

  The obtained foamed particles were washed with acid, dried at 60 ° C. for 6 hours, and then pressurized with air in a pressure-resistant container to obtain an air pressure of about 0.2 MPa, filled in a mold, and heated. In-mold foam molding was performed to obtain an in-mold foam molded body of 390 mm × 290 mm × 50 mm. Table 1 shows the results of evaluating the obtained polypropylene resin foamed particles and in-mold foam molded article.

(Example 3)
Polypropylene resin expanded particles were obtained in the same manner as in Example 2 except that stearic acid glycerin ester (HLB3.8) was used as the nonionic surfactant-containing substance, and in-mold foam molding was performed. Table 1 shows the results of evaluating the obtained polypropylene resin foamed particles and in-mold foam molded article.

Example 4
Polypropylene resin foamed particles were obtained in the same manner as in Example 1 except that kaolin as the dispersant and sodium dodecylbenzenesulfonate as the anionic surfactant were used, and in-mold foam molding was performed. Table 1 shows the results of evaluating the obtained polypropylene resin foamed particles and in-mold foam molded article.

(Example 5)
Polypropylene resin foamed particles were obtained in the same manner as in Example 2 except that hydroxyalkyl monoethanolamine (in the general formula 1, R1 is a mixture of 12 and 14 carbon atoms) was used as the antistatic agent. Molding was performed. Table 1 shows the results of evaluating the obtained polypropylene resin foamed particles and in-mold foam molded article.

(Example 6)
Except that polyethylene glycol was not added, hydroxyalkyl monoethanolamine-added polypropylene resin particles were prepared as described in Example 5. 100 parts by weight of this hydroxyalkyl monoethanolamine-added polypropylene resin particle, 300 parts by weight of water (hardness <0.1 mg / L), 1 part by weight of tribasic calcium phosphate as a dispersant, 0% sodium alkanesulfonate as an anionic surfactant 0.03 part by weight, 0.01 part by weight of a polyoxyalkylene-dimethylpolysiloxane copolymer / dimethylpolysiloxane / silica mixture (trade name: KS-530, manufactured by Shin-Etsu Chemical Co., Ltd.) as an initial charge of the nonionic surfactant-containing substance After putting into a 10 L pressure vessel, it deaerated, and 11 parts by weight of isobutane was put into the pressure vessel while stirring and heated to 140 ° C. The pressure vessel internal pressure at this time was 2.0 MPa (G). After holding for 30 minutes, the valve at the bottom of the pressure vessel was opened, and the dispersion was discharged into a foamed cylinder under atmospheric pressure through an orifice with a diameter of 4 mm to obtain polypropylene-based resin expanded particles. Immediately after opening the valve, the same polyoxyalkylene-dimethylpolysiloxane copolymer / dimethylpolysiloxane / silica mixture as previously charged was charged as the polypropylene-based resin particles 100 as the charging for foaming the nonionic surfactant-containing substance. 0.03 part by weight with respect to parts by weight was added from the top of the pressure vessel. Further, during the discharge, the pressure was maintained with nitrogen gas so that the pressure in the pressure vessel did not decrease.

  The obtained foamed particles were washed with acid, dried at 60 ° C. for 6 hours, and then pressurized with air in a pressure-resistant container to obtain an air pressure of about 0.2 MPa, filled in a mold, and heated. In-mold foam molding was performed to obtain an in-mold foam molded body of 390 mm × 290 mm × 50 mm. Table 1 shows the results of evaluating the obtained polypropylene resin foamed particles and in-mold foam molded article.

(Comparative Example 1)
Except that the nonionic surfactant-containing substance was not used, polypropylene resin expanded particles were obtained in the same manner as in Example 5 and subjected to in-mold foam molding. Table 1 shows the results of evaluating the obtained polypropylene resin foamed particles and in-mold foam molded article.

  It can be seen that Examples 1 to 6 are superior in environmental stability because they are superior in dispersion stability as compared with Comparative Example 1 and have a small foaming of the discharged liquid and a small wastewater treatment load.

It is an example of a DSC curve obtained when the polypropylene resin foamed particles of 1 to 10 mg of the present invention are heated from 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min by a differential scanning calorimeter. A point where the endotherm is the smallest between the two melting peaks of the DSC curve is A, and a tangent line is drawn from the point A to the DSC curve, and among the parts surrounded by the tangent line and the DSC curve, the high temperature side is the high temperature side. The melting peak heat amount Qh, and the low temperature side is the melting peak heat amount Ql on the low temperature side.

Claims (13)

  After the polypropylene resin particles, water, inorganic dispersant, anionic surfactant, and foaming agent are contained in a pressure-resistant container and dispersed under stirring conditions, the temperature is raised above the softening point temperature of the polypropylene resin particles. In the method of producing a polypropylene resin foamed particle by discharging and foaming the dispersion in the pressure vessel in a pressure range lower than the internal pressure of the pressure vessel, adding a nonionic surfactant to the pressure vessel A method for producing expanded polypropylene resin particles.   The method for producing expanded polypropylene resin particles according to claim 1, wherein the nonionic surfactant is a modified dimethylpolysiloxane.   The method for producing expanded polypropylene resin particles according to claim 2, wherein the modified dimethylpolysiloxane is at least one selected from polyether-modified dimethylpolysiloxane and polyglycerin-modified dimethylpolysiloxane.   The method for producing expanded polypropylene resin particles according to claim 1, wherein the nonionic surfactant is a higher fatty acid glycerin ester.   The production of polypropylene-based resin expanded particles according to any one of claims 1 to 4, wherein dimethylpolysiloxane and / or silica is further added to the pressure resistant container at any time until foaming is completed. Method.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 5, wherein the nonionic surfactant is added to the pressure vessel a plurality of times.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 6, wherein the anionic surfactant is a sulfonate.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 7, wherein the polypropylene resin particles contain 0.1 to 5 parts by weight of an antistatic agent with respect to 100 parts by weight of the polypropylene resin.   The method for producing expanded polypropylene resin particles according to claim 8, wherein the antistatic agent is at least one selected from higher fatty acid glycerin ester and ethanolamine.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 9, wherein carbon dioxide gas is added to the pressure vessel immediately before foaming.   The hardness of water is 0 mg / L or more and 180 mg / L or less, The manufacturing method of the polypropylene resin expanded particle as described in any one of Claims 1-10 characterized by the above-mentioned.   The polypropylene resin expanded particle obtained by the manufacturing method of the polypropylene resin expanded particle as described in any one of Claims 1-11.   An in-mold foam-molded article obtained by filling the mold with the polypropylene-based resin expanded particles according to claim 12 and heating.

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