JP5487558B2 - 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, a method for producing polypropylene-based resin expanded particles that can be used as a raw material for an in-mold expanded molded article, is capable of producing stable expanded polypropylene-based resin particles and also reduces the wastewater treatment load in the manufacturing process. About.

  Polypropylene resin is used as a raw material for polypropylene resin particles, and the polypropylene resin particles are made of a dispersant such as a poorly water-soluble inorganic substance, a dispersion aid such as a surfactant, and if necessary, a volatile organic foaming agent or carbon dioxide gas. Disperse in an aqueous medium while stirring with an inorganic gas foaming agent such as nitrogen or air, raise the temperature to constant pressure, constant temperature, impregnate the foaming agent in the resin particles, and then release into a low-pressure atmosphere to make a polypropylene resin Methods for obtaining expanded particles are known (for example, Patent Documents 1 to 3).

  Water is often used as an aqueous medium for obtaining polypropylene resin expanded particles, but adhesion of inorganic dispersants to polypropylene resin expanded particles, which can be seen due to differences in production locations in countries and regions. In order to reduce variation in amount, it has been proposed to use an aqueous medium having an electric conductivity of 0.01 to 20.00 mS / m (Patent Document 4). However, the above proposal describes the relationship between the electrical conductivity of the aqueous medium and the amount of the dispersant attached, but does not mention anything about the surfactant as a dispersion aid.

  In addition, even when the electric conductivity of the aqueous medium is within the above range, the effect of the dispersant is still not stable, and the polypropylene resin foam particles are obtained in a state where they stick together (stick), or the shape is flattened, Furthermore, the polypropylene resin particles may remain in a solidified state in the pressure-resistant container after foaming, and productivity may be reduced.

In addition, as an inorganic dispersant used for producing polypropylene resin expanded particles, a method using calcium phosphate, magnesium pyrophosphate, aluminosilicate, or the like is known, and as a dispersion aid, α- Methods using anionic surfactants such as sodium olefin sulfonate and sodium dodecylbenzene sulfonate and nonionic surfactants such as polyoxyethylene nonylphenyl ether are known (for example, Patent Document 5). The above-described problems of sticking, flattening, and lowering of productivity of the polypropylene resin expanded particles have become apparent when an anionic surfactant is used as a dispersion aid .

  By the way, in such a production method, a suspension containing an inorganic dispersant and a surfactant is released together with the polypropylene resin foam particles during foaming, and the suspension is released from the polypropylene resin foam particles. After being separated, it is either recycled or sent to the wastewater treatment process, where it is discharged into rivers etc. after meeting the wastewater standards. However, it is desired that the amount of the surfactant-derived substance in the suspension is as small as possible from the viewpoint of recycling treatment, wastewater treatment process load, or environmental compatibility. That is, it is desired to reduce the amount of surfactant that is a raw material for production.

  Moreover, when the amount of surfactant used for the production of polypropylene resin expanded particles increases, it is necessary to increase the amount of inorganic dispersant, and as a result, the amount of inorganic dispersant attached to the surface of the resulting polypropylene resin expanded particles Alternatively, the amount of the surfactant (derived substance) is also increased, and there is a problem that the polypropylene-based resin particles need to be washed or the fusion property of the molded product obtained by in-mold molding is lowered.

On the other hand, when carbon dioxide is used as the foaming agent and basic magnesium carbonate or calcium phosphate is used as the inorganic dispersant, it is pointed out that the effect as an inorganic dispersant is reduced because it dissolves under acidic conditions. (For example, Patent Document 6).
Japanese Patent Publication No.56-1344 Japanese Patent Publication No. 4-64332 Japanese Examined Patent Publication No. 4-64334 WO2002 / 100929 JP-A-3-152136 JP-A-6-200071

  The object of the present invention is to provide a method for producing stable foamed polypropylene resin particles in which the problem of lowering productivity such as sticking, flattening, etc. in producing polypropylene resin foamed particles is improved, and in the production process An object of the present invention is to provide a method for producing expanded polypropylene resin particles having excellent environmental compatibility that can be suitably used as a raw material for an in-mold foamed molded article with reduced wastewater treatment load. Furthermore, the present invention provides a method that enables stable production as compared with conventional methods even when carbon dioxide gas is used as a foaming agent and an easily soluble inorganic dispersant such as calcium phosphate is used as an inorganic dispersant. Objective.

  The present inventor worked on solving the problems of sticking, flattening, and productivity reduction when producing polypropylene resin foamed particles, and the specific metal salt contained in the polypropylene resin particles is a dispersion aid. It was presumed that one of the causes of the above problem was that it had a tendency to interact with the surfactant and to deactivate the effect as a dispersion aid.

  In other words, when producing a polypropylene resin, stearic acid is generally used for the purpose of neutralizing (deactivating) the catalyst or catalyst residue (or acid derived from the catalyst residue) used in polymerizing the polypropylene resin. It is known to add a metal salt such as a metal salt or hydrotalcite (hereinafter also simply referred to as a neutralizing agent).

  Such a metal salt as a neutralizing agent is added to a polypropylene resin after polymerization together with an antioxidant and the like, blended, and then melt-molded such as extrusion. Some of the added neutralizing agent remains in the polypropylene resin without reacting, and some of the neutralizing agent is present in the polypropylene resin as another metal salt by neutralization / deactivation reaction. Yes.

  If such a specific metal salt is not added, the resin itself deteriorates due to the catalyst remaining in the polypropylene resin and the acid derived from the catalyst residue, or the corrosion of the molding machine is accelerated. Thus, it is difficult to produce polypropylene-based resin expanded particles having good physical properties and productivity, or molded articles thereof, and it is difficult to add the metal salt without production.

  For this reason, the present inventor conducted intensive research to solve the problem from another viewpoint, and as a result, polypropylene-based resin expanded particles were produced by using an aqueous medium having a hardness of 0 mg / L or more and 180 mg / L or less. The present inventors have found that the problem of sticking, flattening, and productivity reduction at the time can be improved, and polypropylene resin expanded particles having excellent environmental compatibility that can be suitably used as a raw material for an in-mold foam molded article can be produced. Furthermore, the present inventors have found a method that enables more stable production than conventional methods using carbon dioxide as a foaming agent and using an easily soluble inorganic dispersant such as calcium phosphate as an inorganic dispersant.

That is, according to the first aspect of the present invention, polypropylene resin particles containing metal salts, an aqueous medium, an inorganic dispersant, and a dispersion aid are present in a pressure vessel, and the temperature is higher than the softening point temperature of the polypropylene resin particles under stirring conditions. To the pressure range lower than the internal pressure of the pressure vessel, and then expand to obtain polypropylene-based resin expanded particles, wherein the metal salts polymerize the polypropylene resin. A metal salt for neutralizing the catalyst or catalyst residue used in the above, the dispersion aid is an anionic surfactant, carbon dioxide gas is added as a foaming agent in a pressure vessel, and the aqueous medium In the present invention, an aqueous medium having a hardness of 0 mg / L or more and 60 mg / L or less is used in an amount of 150 to 210 parts by weight with respect to 100 parts by weight of polypropylene resin particles. The present invention relates to a method for producing ropylene-based resin expanded particles.

As a preferred embodiment (1) the metal salt is at least one selected from magnesium stearate, calcium stearate, hydrotalcite,
(2) The metal salt contains a metal salt produced by neutralization of the catalyst or catalyst residue used when polymerizing the polypropylene resin,
( 3 ) The hardness of the aqueous medium is more than 0 mg / L and not more than 20 mg / L,
( 4 ) the dispersion aid is a sulfonate,
( 5 ) The inorganic dispersant is an aluminosilicate containing barium sulfate and / or silica-alumina as a main component,
( 6 ) The inorganic dispersant is calcium phosphate and / or magnesium phosphate,
The method for producing the expanded polypropylene resin particles as described above.

   According to the present invention, since the inorganic dispersant and the dispersion aid exhibit a stable effect, there are problems of sticking, flattening, and productivity reduction when producing polypropylene resin expanded particles containing a specific metal salt. It is improved and can produce polypropylene-based resin expanded particles that can be suitably used as a raw material for an in-mold expanded molded article.

  In addition, since the action of the dispersion aid can be stably expressed, and the amount of the dispersion aid can be suppressed, the wastewater treatment load is reduced and the polypropylene system has excellent environmental compatibility. A method for producing resin foam particles can be provided.

  Further, even when carbon dioxide is used as the foaming agent and an inorganic dispersant that is easily dissolved under acidity such as calcium phosphate is used as the inorganic dispersant, stable production can be achieved as compared with the conventional case.

  In the present invention, a polypropylene resin particle containing a metal salt, an aqueous medium, an inorganic dispersant, and a dispersion aid are present in a pressure vessel, and the temperature is raised above the softening point temperature of the polypropylene resin particle under stirring conditions. Next, a method of releasing the contents of the pressure vessel into a pressure range lower than the internal pressure of the pressure vessel to obtain foamed polypropylene resin foamed particles, wherein the metal salt is used for polymerizing the polypropylene resin. Alternatively, the present invention relates to a method for producing expanded polypropylene resin particles, comprising a metal salt that neutralizes a catalyst residue, and using an aqueous medium having a hardness of 0 mg / L or more and 180 mg / L or less as the aqueous medium. .

  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 is preferable because it has a characteristic that it can be easily impregnated with the carbon dioxide gas used in the present invention as compared with the homopolymer.

  In addition, the polypropylene resin is excellent in foamability and moldability, and in order to obtain expanded particles having excellent mechanical strength and heat resistance when used as an in-mold foam molded article, the melting point is usually 130 to 165 ° C. Furthermore, the thing of 135 to 155 degreeC is preferable. 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 to 11 g / 10 minutes, more preferably 3 to 10 g / 10 minutes, and most preferably 4 to 8 g / 10 minutes. When the melt index is less than 2 g / 10 minutes, it becomes difficult to obtain expanded particles having 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.

  In the present invention, the catalyst / co-catalyst used in the production of the polypropylene resin is not particularly limited. However, from the viewpoint that the effect of the present invention is remarkably exhibited, the catalyst / co-catalyst having halogen or catalyst residue is used. When a catalyst / co-catalyst that liberates halogen or acid is used, the effect of the present invention remarkably appears, and examples thereof include a Ziegler-Natta catalyst and a metallocene catalyst.

  The polypropylene resin particles used in the present invention contain metal salts. The metal salts are derived from metal salts that neutralize / deactivate the catalyst or catalyst residue used in polymerizing the polypropylene resin.

  Here, the catalyst or catalyst residue used to polymerize the polypropylene resin is neutralized and deactivated from the metal salt that neutralizes and deactivates the catalyst or catalyst residue used to polymerize the polypropylene resin. Of course, it means that the metal salt itself to be produced includes the metal salt produced by neutralization of the catalyst or catalyst residue used in polymerizing the polypropylene resin.

  Examples of the metal salt as such a neutralizing agent include a metal salt of a higher fatty acid and a metal salt having a layered crystal structure. As a metal salt of higher fatty acid, for example, calcium salt, magnesium salt, zinc salt, strontium salt such as stearic acid, octylic acid, palmitic acid, lauric acid, behenic acid, montanic acid, oleic acid, isostearic acid, ricinoleic acid, Barium salt, and the like. Among these, calcium stearate and magnesium stearate are preferable from the viewpoint of good effect as a neutralizing agent.

  In addition, examples of the metal salt having a layered crystal structure include hydrotalcite, and the use of this hydrotalcite is a preferable embodiment because the effect as a neutralizing agent is good. A plurality of the above metal salts may be selected and used in combination.

  There is no restriction | limiting in particular as addition amount of a metal salt, Although it adjusts suitably so that the effect as a neutralizing agent may act, Generally 0.001-0. 3 parts by weight is preferred, more preferably 0.01 to 0.2 parts by weight, most preferably 0.03 to 0.1 parts by weight.

  When the metal salt is less than 0.001 part by weight, the neutralization effect is hardly exhibited, and when it exceeds 0.3 part by weight, the fusion property when the in-mold foam molded article is obtained from the polypropylene resin foamed particles tends to decrease. It is in.

  Another aspect of the present invention is that the metal salt contains a metal salt produced by neutralization. Here, neutralization in the present invention means neutralizing and capturing the catalyst, catalyst residue, or acid or halogen derived from the catalyst residue used when polymerizing the polypropylene resin as described above. Examples of the metal salt produced by neutralization include various types depending on the type of polypropylene resin polymerization catalyst and the type of neutralizing agent. Examples of the catalyst include chlorides such as titanium trichloride and titanium tetrachloride. When using Ziegler-based catalysts containing products and using calcium stearate, magnesium stearate, hydrotalcite, etc. as neutralizing agents, metal chlorides such as calcium chloride and magnesium chloride are listed as metal salts produced by neutralization. It is done. Such metal chloride tends to be eluted in an aqueous medium in a pressure resistant container when obtaining polypropylene resin expanded particles, and as a result, there is a tendency to deactivate the surfactant as a dispersion aid. In the present invention, an aqueous medium having a hardness of 0 mg / L or more and 180 mg / L or less is used as the aqueous medium, and the amount of magnesium or calcium in the aqueous medium is suppressed in advance. Even if it is dissolved in an aqueous medium, the effect of the surfactant is maintained, and a stable suspension system can be maintained, and the problem of sticking, flattening, and lowering of productivity is solved. Particles can be obtained.

  The lower limit of the hardness of the aqueous medium used in the present invention is 0 mg / L or more, and preferably exceeds 0 mg / L. The upper limit is 180 mg / L or less, preferably 120 mg / L or less, more preferably 60 mg / L or less, and most preferably 20 mg / L or less.

The hardness referred to in the present invention is a so-called American hardness obtained by converting the amount of calcium / magnesium contained in an aqueous medium into the amount of calcium carbonate, which is a commonly used hardness, and generally has the following formula: Can be expressed as
Hardness (mg / L) = calcium amount (mg / L) × 2.5 + magnesium amount (mg / L) × 4.1

  When this hardness exceeds 180 mg / L, it is presumed that calcium or magnesium in the aqueous medium deactivates the effect of the dispersion aid, and as a result, the suspension system in the pressure vessel is not stabilized and obtained. A stick phenomenon in which the expanded polypropylene resin particles are stuck, the expanded particles are flattened, and the amount of the expanded polypropylene resin particles remaining in the pressure vessel after foaming tends to increase, resulting in a tendency to decrease productivity. is there. In addition, when trying to mold flat polypropylene resin foamed particles in a mold, it becomes a cause of poor filling and a decrease in the meltability of the resulting molded foam.

  In order to solve the above problem while using an aqueous medium having a hardness exceeding 180 mg / L, the amount of the dispersion aid and further the inorganic dispersant must be increased, and as a result, the waste water treatment after foaming. This is not preferable from the viewpoint of environmental compatibility. Furthermore, when the amount of the inorganic dispersant is increased, the amount of the inorganic dispersant attached to the surface of the obtained polypropylene resin foamed particles is also increased, which is not preferable because the fusion property of the in-mold foam-formed form is lowered. In order to avoid this, it is not preferable because the amount of the cleaning agent when the foamed particles are cleaned increases.

  In general, the electrical conductivity is said to be proportional to the amount of ions contained in water, but the hardness of the aqueous medium of the present invention is defined as the total amount of calcium and magnesium in the aqueous medium. is there. Therefore, it is not necessarily a value that uniquely corresponds. For example, there is an example in which the hardness of water having an electric conductivity of 25 mS / m is 60 mg / L, and in another example, 120 mg / L.

  The method for measuring the hardness of the aqueous medium is not particularly limited, and may be measured using a conventionally known measurement method or 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.

  Examples of the aqueous medium used in the present invention include water, alcohol, ethylene glycol, and the like, and a mixture thereof. From the viewpoint of the most efficient expression of the dispersant and inorganic dispersion aid used in the present invention and the ease of wastewater treatment, a mixture containing water is more preferred, and water is most preferred.

  In addition, the amount of the aqueous medium used in the present invention is not particularly limited, but from the viewpoint of productivity, 100 to 500 parts by weight is preferable, more preferably 100 parts by weight with respect to 100 parts by weight of the polypropylene resin particles containing a metal salt. 130 to 300 parts by weight, most preferably 150 to 210 parts by weight. If the amount is less than 100 parts by weight, an aqueous suspension system composed of polypropylene resin particles containing a metal salt, an aqueous medium, an inorganic dispersant, and a surfactant may not be stable. If the amount exceeds 500 parts by weight, productivity decreases. .

  In the present invention, when carbon dioxide, which will be described later, is used as a foaming agent, the propylene resin particles are impregnated with carbon dioxide, so that plasticity is imparted to the resin particles, and as a result, the aqueous suspension system tends to become unstable. It becomes. However, the use of an aqueous medium having a hardness of 0 mg / L or more and 180 mg / L or less of the present invention suppresses the reduction of the dispersion aid effect of the surfactant. Can do. In particular, when water is used as the aqueous medium, stable polypropylene-based foamed resin particles can be produced even in such a case with a small use amount of 150 to 210 parts by weight.

  As the dispersion aid used in the present invention, a surfactant can be used. As the surfactant, generally used anionic, nonionic, cationic surfactants, amphoteric surfactants, and the like can be used.

  Specifically, (a) higher alcohol sulfate, alkyl sulfonate, alkane sulfonate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, sulfosuccinate, α-olefin sulfonate, N-acyl sulfone Acid salt, 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-acyl Anionic surfactants such as amino acid salts;

(B) 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 glycerin ester, polyglycerin ester, sorbitan ester, propylene glycol ester, sucrose ester, aliphatic alkanolamide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, amine Nonionic surfactants such as oxides;

(C) Cationic surfactants such as aliphatic amine salts, hydroxyalkyl monoethanolamine salts and aliphatic quaternary ammonium salts; (d) Amphoteric surfactants such as carboxybetaine, imidazolinium betaine and aminocarboxylates. , Etc.

  Dispersibility stabilization effect of aqueous suspension system composed of polypropylene resin particles containing metal salts, aqueous medium, inorganic dispersant, and surfactant, stickiness of polypropylene resin foam particles, flattening, improvement of productivity reduction From the viewpoint of the most prominently appearing, the surfactant is preferably an anionic surfactant, more preferably an alkyl sulfonate, alkane sulfonate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, sulfosuccinic acid. Sulfonates such as salts, α-olefin sulfonates, N-acyl sulfonates, alkyl sulfates, alkyl ether sulfates, alkyl allyl ether sulfates, alkyl amide sulfates, most preferably alkyl sulfonates , Alkane sulfonate, α-olefin sulfonate, alkyl Rubenzenesulfonate.

  The addition amount of the surfactant as such a dispersion aid is not particularly limited and may be appropriately adjusted in order to exhibit the stabilizing effect of the aqueous suspension system. It is preferable that it is 0.001-0.5 weight part with respect to a part, More preferably, it is 0.003-0.3 weight part, Most preferably, it is 0.005-0.2 weight part. If the amount is less than 0.001 part by weight, the dispersibility of the resin particles tends to decrease above the softening point temperature of the resin particle. If the amount exceeds 0.5 part by weight, foaming of the aqueous suspension system becomes severe and the load of wastewater treatment is increased. It tends to grow.

  In addition, since an aqueous medium having a hardness of 0 mg / L or more and 180 mg / L or less is used, a stable amount is always used without variation in the amount of the surfactant used to exhibit a sufficient effect as a dispersion aid. It becomes possible.

  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 based on silica-alumina such as barium sulfate, kaolin, talc, etc., calcium phosphates such as aluminum oxide, titanium oxide and tricalcium phosphate, calcium carbonate, magnesium pyrophosphate, magnesium phosphate, basic Examples thereof include magnesium carbonate and basic zinc carbonate.

  Among these, it is preferable to use an aluminosilicate having barium sulfate and / or silica-alumina as a main component from the viewpoint of a dispersion effect with a small amount of use and a small wastewater treatment load.

  From the standpoint that improvement in stickiness, flattening, and reduction in productivity of the polypropylene resin expanded particles is likely to appear remarkably by using in combination with an aqueous medium having a hardness of 0 mg / L or more and 180 mg / L or less, calcium phosphate and / or Magnesium phosphate is preferred.

  The addition amount of such an inorganic dispersant is not particularly limited and can be appropriately adjusted in consideration of the stabilizing effect of the aqueous suspension system and the addition ratio with the dispersion aid. 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 and 3 parts by weight or less with respect to 100 parts by weight of the particles. It is as follows. If the amount is less than 0.05 parts by weight, the dispersibility of the resin particles tends to decrease at a temperature equal to or higher than the softening point temperature of the resin particles. If the amount exceeds 5 parts by weight, a large amount of the dispersant tends to adhere to the surface of the expanded particles.

  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, water used as an aqueous medium can be used.

  Further, saturated hydrocarbons having 3 to 5 carbon atoms such as propane, n-butane, iso-butane, n-pentane, and iso-pentane, dimethyl ether, alcohols such as methanol and ethanol whose boiling point is lower than the foamable temperature, etc. Organic foaming agents are also included. When methanol or ethanol is used, methanol or ethanol used as an aqueous medium can be used.

  Among these, it is more preferable to use carbon dioxide gas from the viewpoint of foamability and reduction in variation in the magnification of the resulting polypropylene resin foamed particles. From the viewpoint of environmental compatibility, water is preferably used as the foaming agent, and more preferably used in combination with carbon dioxide gas. Furthermore, 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.

  On the other hand, when carbon dioxide is used as a foaming agent and calcium phosphate and / or magnesium phosphate is used in combination as an inorganic dispersant, a polypropylene resin is obtained by using an aqueous medium having a hardness of 0 mg / L or more and 180 mg / L or less. It can be said that it is a more preferable embodiment from the viewpoint that the improvement of sticking, flattening, and productivity reduction of expanded particles is most likely to appear.

  This is because the amount of calcium and / or magnesium in the aqueous medium tends to increase when the aqueous medium is acidified by carbon dioxide gas and a part of calcium phosphate and / or magnesium phosphate is dissolved. It is presumed that it was possible to maintain the effect of the dispersion aid by previously using.

  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 there is. More 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 or the like as an aqueous medium is used as the foaming agent, 100 to 500 parts by weight of water may be used in a pressure resistant container with respect to 100 parts by weight of the polypropylene resin particles.

  When water or carbon dioxide gas is used as the foaming agent, the organic resin and / or inorganic substance having hydrophilicity, water absorption, water solubility, water compatibility, etc. in the polypropylene resin particles (hereinafter referred to as these Are also collectively referred to as hydrophilic substances).

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

  Further, (D) Cationic surfactants such as (D) aliphatic amine salts, hydroxyalkyl monoethanolamine salts, aliphatic quaternary ammonium salts, (b) alkyl sulfonates, alkane sulfonates, alkyl benzene sulfones Acid salt, alkylnaphthalene sulfonate, sulfosuccinate, α-olefin sulfonate, N-acyl sulfonate, alkyl sulfate, alkyl ether sulfate, alkyl allyl ether sulfate, alkyl amide sulfate, alkyl phosphoric acid Anionic surfactants such as salts, alkyl ether phosphates, alkyl allyl ether phosphates, alkyl ether carboxylates, N-acyl amino acid salts, (c) alkyl and alkyl allyl polyoxyethylene ethers, alkyl allyl formaldehyde condensation Polio Ethylene ether, polyoxyethylene polyoxypropyl alkyl ether, glycerin ester polyoxyethylene ether, sorbitan ester polyoxyethylene ether, sorbitol ester polyoxyethylene ether, polyethylene glycol fatty acid ester, glycerin ester, higher fatty acid glycerin ester, poly Nonionic surfactants such as glycerin ester, sorbitan ester, propylene glycol ester, sucrose ester, aliphatic alkanol amide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, amine oxide, (d) carboxybetaine, imidazolinium Surfactants such as amphoteric surfactants such as betaine and aminocarboxylates;

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, such as antistatic agents described in 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 to 9000, and most preferably an average molecular weight of 200 to 600.

  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 occurrence of non-uniform discharge during extrusion, and particles having a uniform shape can be produced in particle production by the strand cut method. When such resin particles are foamed, foamed particles having a uniform cell diameter and small variation in magnification can be obtained. The in-mold foam-formed body molded in the mold using the foamed particles has a small intergranular / shrinkage / distortion, is beautiful, has a high fusion rate of the in-mold foam-formed body, and has sufficient heat-resistant dimensional stability.

  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 addition amount is less than 0.01 parts by weight, the foaming ratio cannot be improved by water or carbon dioxide gas, or the effect of uniformizing the bubble diameter is reduced. 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. 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 foam nucleating agent used or the desired expansion ratio, but it is 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. Preferably there is. When the amount 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 is easily 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, antistatic agents, carbon black, pigments, dyes and other colorants, stabilizers, weathering agents, flame retardants and the like do not impair the effects of the present invention. It can be added as appropriate.

  What is necessary is just to produce the polypropylene resin particle in this invention using a conventionally well-known method. For example, a method in which a polypropylene-based resin, a hydrophilic substance, a foam nucleating agent, or the like previously blended is melt-kneaded with an extruder, extruded from a die, cooled, and then converted into polypropylene-based resin particles with a cutter.

  In addition, hydrophilic substances, foam nucleating agents, antioxidants, compatibilizers, antistatic agents, colorants, stabilizers, weathering agents, flame retardants, etc. are masterbatched with polyolefin resin in advance, and this is finally 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 containing metal salts, an aqueous medium having a hardness of 0 mg / L or more and 180 mg / L or less, an inorganic dispersant, and a dispersion aid are present in a pressure vessel, and polypropylene is stirred under stirring conditions. The temperature is raised above the softening point temperature of the resin-based resin particles, and then the contents of the pressure-resistant container are discharged into a pressure range lower than the internal pressure of the pressure-resistant container and foamed to obtain polypropylene-based resin expanded particles.

  The surfactant as a dispersion aid may be charged in the pressure vessel in advance as described above. However, it is added and melt-kneaded when obtaining polypropylene resin particles, and is not charged directly in the pressure vessel until foaming occurs. It is also possible to act as a dispersion aid by elution from polypropylene resin particles into an aqueous medium.

  When releasing the contents of the pressure vessel into the pressure range lower than the internal pressure of the pressure vessel described above, an inorganic gas such as carbon dioxide, nitrogen or air should be injected at any stage prior to release to the low pressure range. Thus, the internal pressure in the sealed container can be increased, the pressure release speed at the time of foaming can be adjusted, and the foaming ratio and the average cell diameter can be adjusted.

  When carbon dioxide gas, which is a more preferred embodiment of the present invention, is added as a foaming agent, polypropylene resin particles containing metal salts, an aqueous medium having a hardness of 0 mg / L or more and 180 mg / L or less, an inorganic dispersant, and In addition to the presence of a surfactant as a dispersion aid, solid carbon dioxide (dry ice) may be charged into the pressure vessel, polypropylene resin particles containing a metal salt, hardness of 0 mg / L to 180 mg / L Any of the following aqueous medium, inorganic dispersant, and surfactant as a dispersion aid are charged into a pressure-resistant container and immediately after that, before being released into the low-pressure range, such as during temperature rise or after temperature rise. At this stage, gas or liquid carbon dioxide gas may be introduced into the pressure vessel. 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. As described above, when water, alcohol, or the like is used as the foaming agent, it can be used by charging it into a pressure vessel as an aqueous medium.

  The average cell diameter of the polypropylene resin expanded particles of the present invention thus produced is preferably 130 to 500 μm, more preferably 160 to 400 μm, and further preferably 210 to 350 μm. If the average cell diameter is less than 130 μm, the resulting in-mold foam-forming product has problems such as poor fusion, distortion of the shape, and wrinkling on the surface. The cushioning properties of the feature are reduced.

  Although there is no restriction | limiting in particular in the expansion ratio of the polypropylene resin expanded particle obtained by this invention, 50 times or less are preferable. If the expansion ratio exceeds 50 times, the bubbles of the obtained expanded particles tend to break or the dimensional accuracy, mechanical strength, heat resistance, etc. of the in-mold foam-formed product when molded are insufficient. is there.

  In addition, when trying to obtain a foaming ratio of 20 times or more, it may be 20 times or more at the stage of release to a pressure range lower than the internal pressure of the pressure vessel described above (hereinafter sometimes referred to as single-stage foaming). , Producing foamed particles less than 20 times by one-stage foaming, and then pressurizing the foamed particles obtained by the first-stage foaming with an inorganic gas such as air in a pressure-resistant container, and then applying an internal pressure with steam or a heater. It is a more preferable method to increase the magnification to 20 times or more by foaming again by heating (hereinafter sometimes referred to as two-stage foaming).

  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 expanded particles having two melting peaks, an in-mold foam molded article having good in-mold foam moldability and good mechanical strength and heat resistance can be 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 higher than the softening temperature of the polypropylene resin as the base material, preferably higher than the melting point, more preferably higher than the melting point + 5 ° C., lower than the melting end temperature, more preferably melting. By setting the temperature to an end temperature of −2 ° C. or lower, expanded polypropylene resin particles having two melting peaks tend to be obtained.

  The melting end temperature is 1 to 10 mg of polypropylene resin particles increased from 40 ° C. to 220 ° C. at a rate of 10 ° C./min with a differential scanning calorimeter, and then increased to 40 ° C. at a rate of 10 ° C./min. This is the temperature when the bottom of the melting peak of the DSC curve obtained when the temperature is cooled and raised again to 220 ° C. at a rate of 10 ° C./min returns to the baseline position on the high temperature side.

  Moreover, the endothermic peak calorific value on the high temperature side of the two melting peaks (hereinafter sometimes referred to as Qh) is preferably 5 to 40 J / g, and more preferably 7 to 30 J / g. If it is less than 5 J / g, the open-cell ratio of the polypropylene resin expanded particles tends to be high, and if it exceeds 40 J / g, the fusion property when obtaining an 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 polypropylene resin foam molded article of the present invention is a molded article obtained by a molding method in which a mold is filled with polypropylene resin foam particles obtained as described above.

  There is no restriction | limiting in particular as such 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-formed product with good fusing property, mechanical strength, surface appearance, etc., the polypropylene resin foam particles are kept under pressure of an inorganic gas such as air, nitrogen, carbon dioxide. It is preferable to employ a method in which an internal pressure is applied to the expanded particles, and then the mold is filled into a mold and molded.

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. Example 6 is not an example of the present invention but a reference example.

  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.
(Triangle | delta): The stick which the expanded foamed particles adhered is seen, and there exists a flat expanded particle. In addition, there is residual resin in the pressure vessel.
X: Resin agglomerates in the pressure vessel before foaming and foamed particles cannot be obtained.

(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 is made with a knife on the surface of the in-mold foamed product, the in-mold foam-formed product is divided along the crack, the fracture surface is observed, and the fracture particles with respect to the total number of particles observed The ratio of the number was determined and used as the compact fusion rate.

  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
Metal salt-containing polypropylene resin composition A (containing 0.05 parts by weight of calcium stearate as a neutralizing agent with respect to 100 parts by weight of a propylene / ethylene random copolymer, an ethylene content of 3.0% by weight in the copolymer, Polyglycol glycol (average molecular weight 300, manufactured by Lion) is pre-blended to 100 parts by weight of MI = 6 g / 10 min, melting point 144 ° C., and then talc (manufactured by Hayashi Kasei, Talcan as a foam nucleating agent) Powder PK-S) 0.05 parts by weight 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 resin particles were added to 200 parts by weight of pure water (hardness <0.1 mg / L), 0.7 parts by weight of tribasic calcium phosphate as a dispersant, and 0.02 part of sodium alkanesulfonate as a dispersion aid. After putting into a 10 L pressure-resistant airtight container with a weight part, it deaerated, 5 parts of carbon dioxide gas was put in the airtight container, stirring, and it heated at 150 degreeC. The pressure in the sealed container at this time was 2.3 MPa (G). Further, carbon dioxide gas was added, and the temperature inside the sealed container was adjusted to 2.6 MPa (G) and held for 15 minutes. Thereafter, the valve at the bottom of the sealed container was opened, and the aqueous dispersion (resin particles and aqueous dispersion medium) was discharged under atmospheric pressure through an orifice having a diameter of 4 mm to obtain polypropylene-based resin expanded particles. At this time, during discharge, the pressure was maintained with carbon dioxide gas so that the pressure in the container did not decrease.

  The foamed particles obtained here were acid washed, 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, and then subjected to in-mold foam molding, and 390 mm An in-mold foam molded body of × 290 mm × 50 mm was obtained. Table 1 shows the results of the evaluation of the polypropylene resin expanded particles and the in-mold expanded foam.

(Examples 2 to 4)
Polypropylene resin foamed particles were obtained and molded in the same manner as in Example 1 except that the dispersant and dispersion aid listed in Table 1 were used. Table 1 shows the results of the evaluation of the polypropylene resin expanded particles and the in-mold expanded foam.

(Example 5)
Polypropylene resin foamed particles were obtained and molded in the same manner as in Example 1 except that industrial water having a hardness of 30 mg / L was used as the aqueous medium, and the dispersant and dispersion aid shown in Table 1 were used. Table 1 shows the results of the evaluation of the polypropylene resin expanded particles and the in-mold expanded foam.

(Example 6 : Reference example )
Polypropylene resin expanded particles were obtained and molded in the same manner as in Example 1 except that tap water having a hardness of 70 mg / L was used as the aqueous medium, and the dispersant and dispersion aid shown in Table 1 were used. Table 1 shows the results of the evaluation of the polypropylene resin expanded particles and the in-mold expanded foam.

(Example 7)
100 parts by weight of polypropylene-based resin particles obtained in the same manner as in Example 1, 300 parts by weight of pure water (hardness <0.1 mg / L), 0.7 part by weight of tribasic calcium phosphate as a dispersant, and alkane as a dispersion aid After putting into a 10 L pressure-resistant airtight container with 0.02 weight part of sodium sulfonate, it heated at 150 degreeC. The pressure in the sealed container at this time was about 0.5 MPa (G). Next, nitrogen gas was added and the temperature in the sealed container was set to 2.6 MPa (G) and held for 15 minutes. Thereafter, the valve at the bottom of the sealed container was opened, and the aqueous dispersion (resin particles and aqueous dispersion medium) was discharged under atmospheric pressure through an orifice having a diameter of 4 mm to obtain polypropylene-based resin expanded particles. At this time, the pressure was maintained with nitrogen gas so that the pressure in the container did not decrease during the discharge. Further, at the time of discharge, a water vapor blowing port was provided immediately after passing through the orifice so that the water vapor contacts the discharged water dispersion. The blowing temperature at this time was about 98 ° C.

  The foamed particles obtained here were acid washed, 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, and then subjected to in-mold foam molding, and 390 mm An in-mold foam-formed form of × 290 mm × 50 mm was obtained. Table 1 shows the results of the evaluation of the polypropylene resin expanded particles and the in-mold expanded foam.

(Comparative Examples 1-4)
Polypropylene resin foamed particles were obtained and molded in the same manner as in Example 1 except that groundwater (hardness 202 mg / L) was used as the aqueous medium and the dispersant and dispersion aid listed in Table 2 were used. Table 2 shows the results of the evaluation of the polypropylene resin expanded particles and the in-mold expanded foam.

  As shown in the table of results, in Comparative Example 2, the resin agglomerated in the pressure-resistant container before foaming and foamed particles were not obtained.

  Further, in Comparative Example 4, the dispersion stability could be ensured by increasing the amount of the dispersant and the dispersion aid, but the fusion property of the in-mold foam formation was poor and the amount of the dispersant and the dispersion aid was large. There were many suspended solids or dissolved substances in the wastewater, and the wastewater treatment load was greater than in Examples and Comparative Examples 1 to 3.

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. Of the part 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 (7)

Polypropylene resin particles containing metal salts, an aqueous medium, an inorganic dispersant, and a dispersion aid are present in the pressure vessel, and the temperature is raised above the softening point temperature of the polypropylene resin particles under stirring conditions, and then the pressure vessel The pressure-sensitive container contents are discharged into a pressure range lower than the internal pressure of the foamed foam to obtain polypropylene-based resin expanded particles, wherein the metal salt is a catalyst or catalyst residue used when polymerizing the polypropylene-based resin. It contains a metal salt for neutralization, the dispersion aid is an anionic surfactant, carbon dioxide gas is added as a foaming agent in the pressure vessel, and the aqueous medium has a hardness of 0 mg / L or more An aqueous medium of 60 mg / L or less is used in an amount of 150 to 210 parts by weight with respect to 100 parts by weight of the polypropylene resin particles. Production method.   The method for producing expanded polypropylene resin particles according to claim 1, wherein the metal salt is at least one selected from magnesium stearate, calcium stearate, and hydrotalcite.   The method for producing expanded polypropylene resin particles according to claim 1 or 2, wherein the metal salt contains a metal salt produced by neutralizing a catalyst or catalyst residue used in polymerizing the polypropylene resin.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 3, wherein the hardness of the aqueous medium is more than 0 mg / L and 20 mg / L or less. The method for producing expanded polypropylene resin particles according to any one of claims 1 to 4 , wherein the dispersion aid is a sulfonate. The method for producing expanded polypropylene resin particles according to any one of claims 1 to 5 , wherein the inorganic dispersant is an aluminosilicate mainly composed of barium sulfate and / or silica-alumina. . The method for producing expanded polypropylene resin particles according to any one of claims 1 to 5 , wherein the inorganic dispersant is calcium phosphate and / or magnesium phosphate.

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