JP5281333B2 - Process for producing polypropylene resin pre-expanded particles and polypropylene resin pre-expanded particles - Google Patents

Description

  The present invention relates to a method for producing polypropylene resin pre-expanded particles and polypropylene resin pre-expanded particles.

  Conventionally, polypropylene resin particles are dispersed in an aqueous dispersion medium together with a foaming agent, and the temperature is raised and the resin particles are impregnated with the foaming agent at a constant pressure and constant temperature, and then released into a low-pressure atmosphere to obtain pre-foamed particles. The method is known. Examples of the blowing agent include a method using a volatile organic blowing agent such as propane and butane (for example, Patent Document 1) and a method using an inorganic gas such as carbon dioxide, nitrogen, and air (for example, Patent Documents 2 and 3). It is disclosed.

  However, volatile organic foaming agents such as propane and butane have the effect of plasticizing polypropylene-based resins, and it is easy to obtain a high expansion ratio. However, since the plasticizing action is large, the expansion ratio and crystal state of pre-expanded particles are large. Is difficult to control. Moreover, since it is a flammable substance, it is necessary to make the equipment explosion-proof, which tends to increase the equipment cost.

  On the other hand, when an inorganic gas such as nitrogen or air is used, the impregnation ability into the polypropylene resin is very low, and there is a problem that a sufficient impregnation amount for high foaming cannot be obtained even at high pressure.

  As a method for solving these drawbacks and economically producing pre-expanded polypropylene resin particles that can be suitably used for the production of in-mold foam molded products, a method using water used as a dispersion medium as a foaming agent is proposed. Has been.

  As a method of using water as a foaming agent, polypropylene resin particles containing a water-soluble inorganic substance or hydrophilic polymer are dispersed in water in a sealed container and heated to a temperature higher than the softening temperature of the resin particles to obtain water-containing polypropylene resin particles. Then, a method for producing the polypropylene resin pre-expanded particles by releasing the dispersion into a low pressure region has been proposed (for example, Patent Documents 4 to 6). This method describes that polypropylene resin pre-expanded particles having a high expansion ratio can be obtained with a low internal pressure of the container while using environmentally friendly water, carbon dioxide gas, nitrogen and the like as a foaming agent.

  However, in the production method for obtaining pre-expanded particles from polypropylene resin particles containing a water-soluble inorganic substance as described in Patent Document 4 and a metal borate as described in Patent Document 5, in order to increase the expansion ratio, It is necessary to increase the amount of water-soluble inorganic materials, metal borate salts, etc. Especially when the amount of water-soluble inorganic materials or metal borate salts is increased in order to increase the expansion ratio to 8 times or more, these additives are added to the dispersion medium water. Since it eluted in large quantities, there existed a problem that the wastewater treatment cost increased.

In addition, the polypropylene resin pre-expanded particles produced using carbon dioxide gas with a water content of 8 wt% or more containing a hydrophilic polymer as described in Patent Document 6 have a high water content. There is also a tendency for the pre-expanded particles to shrink immediately after expansion.
Japanese Patent Publication No.56-1344 Japanese Patent Publication No. 4-64332 Japanese Examined Patent Publication No. 4-64334 JP-A-3-223347 WO 98/25996 Japanese Patent Laid-Open No. 10-152574

  The present invention achieves a desired expansion ratio even when the amount of the water-absorbing substance is reduced when obtaining polypropylene resin pre-expanded particles using an inorganic foaming agent having a low environmental impact such as carbon dioxide gas or water. It is an object of the present invention to provide a manufacturing method that can be used.

As a result of diligent research to solve the above problems, the present inventors have added a water-absorbing substance to a polypropylene resin, and when producing polypropylene resin pre-expanded particles using water or carbon dioxide gas, A polypropylene resin having a melting point of 150 ° C. or less and a polypropylene resin having a melting point of 160 ° C. or more are blended in a predetermined amount as a polypropylene resin, and a desired foaming ratio is obtained by using polyethylene glycol as a water-absorbing substance. It has been found that the water-absorbing substance required for this can be reduced.

That is, the first of the present invention is
After dispersing the polypropylene resin particles containing a water-absorbing substance together with an aqueous dispersion medium in a sealed container, using inorganic gas as a foaming agent and heating to a temperature equal to or higher than the softening temperature of the polypropylene resin particles, the internal pressure of the sealed container In a method for producing polypropylene resin pre-expanded particles having a foaming ratio of 8 times or more and 25 times or less, which is released into a lower pressure range and foamed,
Polypropylene resin constituting the polypropylene resin particles is a polypropylene resin (A) having a resin melting point of 150 ° C. or less (A) 80 wt% or more and 99 wt% or less, and a polypropylene resin (B) 1 having a resin melting point of 160 ° C. or more comprises a wt% to 20 wt%, water-absorbing material, characterized in that a polyethylene glycol, a method for producing a pre-expanded polypropylene resin particles.

As a preferred embodiment,
(1) The melt flow rate of the polypropylene resin (B) is larger than that of the polypropylene resin (A),
(2) Carbon dioxide gas is further introduced into the sealed container,
(3) The polypropylene resin (B) having a resin melting point of 160 ° C. or higher contains 99% by weight or more of propylene,
The present invention relates to a method for producing the pre-expanded polypropylene resin particles described above.

  A second aspect of the present invention is a DSC curve obtained when the temperature is increased from 40 ° C. to 210 ° C. at a rate of 10 ° C./min by the differential scanning calorimetry of the polypropylene resin pre-expanded particles. The ratio of the high temperature side melting peak calorie to the total melting peak calorie is 15% or more and 40% or less, and relates to the polypropylene resin pre-expanded particles obtained by the production method described above.

  According to the present invention, a polypropylene resin obtained by blending a predetermined amount of a polypropylene resin (B) having a resin melting point of 160 ° C. or higher with a polypropylene resin (A) having a resin melting point of 150 ° C. or lower is used as a blowing agent. By using and foaming, the water-absorbing substance added to obtain a desired foaming ratio can be reduced. Therefore, it is excellent in economic efficiency, and it is possible to reduce the elution of the water-absorbing substance into the process waste water.

  In the present invention, polypropylene resin particles containing a water-absorbing substance are dispersed in a sealed container together with an aqueous dispersion medium, heated to a temperature equal to or higher than the softening temperature of the polypropylene resin particles, and then a pressure lower than the internal pressure of the sealed container. In the method for producing pre-expanded polypropylene resin particles having an expansion ratio of 8 times or more and 25 times or less, the polypropylene resin has a resin melting point of 150 ° C. or less and 80% by weight of the polypropylene resin (A). This is a method for producing polypropylene resin pre-expanded particles, comprising 1 wt% or more and 20 wt% or less of a polypropylene resin (B) having a resin melting point of 99 wt% or less and 160 ° C. or more.

  In preparing polypropylene resin pre-expanded particles using a polypropylene resin (A) having a resin melting point of 150 ° C. or lower and a predetermined amount of polypropylene resin (B) blended as a polypropylene resin, It is possible to reduce the amount of the water-absorbing substance used for obtaining the foaming ratio. In other words, when the polypropylene resin pre-expanded particles are produced with the same amount of water-absorbing substance, the expansion ratio becomes high.

  The reason why the above effect can be obtained by blending the polypropylene resin (B) is not clear, but is considered as follows. In order to produce polypropylene resin pre-expanded particles, a predetermined amount of crystals that are newly formed above the resin melting point is grown by heating and holding above the softening temperature of the polypropylene resin particles. Is desired. The higher temperature side crystal has a higher melting point as the temperature for heating and holding (hereinafter sometimes referred to as annealing temperature) is higher, but the amount of crystal tends to decrease. For this reason, when the polypropylene resin (B) having a high resin melting point is blended, the annealing temperature is higher than when only the polypropylene resin (A) is used, and the resin viscosity at the time of foaming is lowered. On the other hand, it is considered that the film is greatly deformed, that is, the foaming ratio is increased.

  Note that if the annealing temperature is increased without blending the polypropylene resin (B), the expansion ratio may increase, but the high temperature side crystals do not grow sufficiently. It tends to occur.

  The resin melting point of the polypropylene resin (A) used in the present invention is 150 ° C. or lower, preferably 140 ° C. or lower. When the resin melting point exceeds 150 ° C., the melt-bonding property between the polypropylene resin pre-expanded particles during in-mold molding is deteriorated. Examples of such polypropylene resins include ethylene-propylene random copolymers, propylene-butene random copolymers containing 80% by weight or more of propylene, more preferably 85% by weight or more, and still more preferably 90% by weight or more, Examples thereof include an ethylene-propylene block copolymer and an ethylene-propylene-butene terpolymer.

  The polypropylene resin (A) is 80% by weight or more and 99% by weight or less, and more preferably 85% by weight or more and 97% by weight or less in the polypropylene resin constituting the polypropylene resin particles. When the content is less than 80% by weight, the annealing temperature becomes too high, and when the foam is released from the closed container and foams, fusion easily occurs between the polypropylene resin pre-expanded particles. Is not sufficiently high, the effect of the present invention to achieve a predetermined foaming ratio with a small amount of water-absorbing substance is insufficient.

  The resin melting point of the polypropylene resin (B) in the present invention is 160 ° C. or higher, and preferably 161 ° C. or higher. When the resin melting point is less than 160 ° C., the annealing temperature is not sufficiently high, so that a predetermined foaming ratio cannot be achieved with a small amount of water-absorbing substance. As such a polypropylene resin, for example, a propylene homopolymer, an ethylene-propylene random copolymer, preferably containing 95% by weight or more, more preferably 97% by weight or more, and still more preferably 99% by weight or more, A propylene-butene random copolymer, an ethylene-propylene block copolymer, an ethylene-propylene-butene terpolymer, and the like are exemplified, and a propylene homopolymer is preferable.

  Here, the resin melting point of the polypropylene-based resins (A) and (B) is as follows. In differential scanning calorimetry (DSC), the sample 1 to 10 mg is heated from 40 ° C. to 210 ° C. at a rate of 10 ° C./min. After holding at temperature for 5 minutes, then the temperature is lowered from 210 ° C. to 40 ° C. at a rate of 10 ° C./minute, held at that temperature for 5 minutes, and then heated again from 40 ° C. to 210 ° C. at a rate of 10 ° C./minute. The melting peak temperature of

  Further, the melt flow rate (may be referred to as MFR) of the polypropylene resin (A) in the present invention is preferably 2 g / 10 min or more and 9 g / 10 min or less, and preferably 4 g / 10 min or more and 8 g / 10 min or less. It is more preferable. When the MFR is less than 2 g / 10 min, high-expanding ratio polypropylene-based resin pre-expanded particles cannot be obtained. When the MFR exceeds 9 g / 10 min, there is a tendency that sinks are likely to occur in the in-mold foam molding. .

  On the other hand, when the MFR of the polypropylene resin (B) in the present invention is larger than that of the polypropylene resin (A), the expansion ratio of the polypropylene resin pre-expanded particles tends to be higher, and as a result, the amount of the water-absorbing substance added is increased. Can be reduced. The MFR of the polypropylene resin (B) is preferably 4 g / 10 min to 100 g / 10 min, and more preferably 5 g / 10 min to 50 g / 10 min.

  Here, the MFR measurement of the polypropylene resins (A) and (B) was performed using an MFR measuring apparatus described in JIS-K7210, with an orifice of 2.0959 ± 0.005 mmφ, an orifice length of 8.000 ± 0.025 mm, It is a value when measured under conditions of a load of 2160 g and 230 ± 0.2 ° C.

  The MFR may be adjusted, for example, by using an organic peroxide. Examples of the organic peroxide that can be used include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide; 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1- Peroxyketals such as bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, 2,2-bis (t-butylperoxy) butane; Hydroperoxides such as peroxide, 1,1,3,3-tetramethylbutyl hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2,5-di (T-Butylperoxy) hexane α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxide) Dialkyl peroxides such as oxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; peroxys such as di (3-methyl-3-methoxybutyl) peroxydicarbonate and di-2-methoxybutylperoxydicarbonate Dicarbonate: t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxy Isopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylpa Oxy) hexane, t- butyl peroxy acetate, t- butyl peroxybenzoate, etc. peroxy esters such as di -t- butyl peroxy isophthalate and the like.

  The water-absorbing substance in the present invention generally means water-absorbing, hygroscopic, water-soluble or compatible substances, such as water-absorbing polymer, water-absorbing organic substance, water-absorbing inorganic substance, etc. Can be mentioned. Among these water-absorbing substances, those having no foaming nucleation function are preferable because there is no significant decrease in average cell diameter even when the amount of addition is increased to increase the expansion ratio.

  Specific examples of the water-absorbing polymer include sodium polyacrylate, cellulose, polyvinyl alcohol, a copolymer containing a polyalkylene glycol block (for example, trade name Perestat from Sanyo Chemical Industries, Ltd.), and the like.

  Specific examples of water-absorbing organic substances include compounds having a polyalkylene glycol chain such as polypropylene glycol and polyethylene glycol; melamine (chemical name 1,3,5-triazine-2,4,6-triamine), ammelin ( 1,3,5-triazine-2-hydroxy-4,6-diamine), ammelide (1,3,5-triazine-2,4-hydroxy-6-amine), cyanuric acid (1,3,5) 5-triazine-2,4,6-triol), isocyanuric acid (1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione), acetoguanamine (1,3,5) -Triazine-2,4-diamine-6-methyl), benzoguanamine (1,3,5-triazine-2,4-diamine-6-phenyl), tris (methyl) Compounds having a triazine skeleton such as sosocyanurate, tris (ethyl) isocyanurate, tris (butyl) isocyanurate, tris (2-hydroxyethyl) isocyanurate, melamine / isocyanuric acid condensate; aliphatic amine salt, hydroxyalkylmonoethanolamine Cationic surfactants such as salts and aliphatic quaternary ammonium salts; alkyl sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, sulfosuccinates, α-olefin sulfonates, N-acyl sulfonates, 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-A Anionic surfactants such as sil amino acid salts; alkyl and alkylallyl polyoxyethylene ether, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropyl alkyl ether, glycerin ester polyoxyethylene ether, sorbitan ester poly Oxyethylene ether, polyoxyethylene ether of sorbitol ester, 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 alkylamines, amine oxides and other nonionic surface actives Agent; carboxy betaine, imidazolinium betaine, an amphoteric surfactant such as amino acid salt; and the like.

  Specific examples of the water-absorbing inorganic material include zeolite, bentonite, and synthetic hectorite (laponite). These water-absorbing substances may be used alone or in combination of two or more.

  Among these, preferable water-absorbing substances include compounds having a polyalkylene glycol chain, and polyethylene glycol is particularly preferable.

  Furthermore, polyethylene glycol having an average molecular weight of 200 or more and 9000 or less is preferable, and polyethylene glycol having an average molecular weight of 200 or more and 600 or less is most preferable. In general, glycols have properties that are slightly inferior in compatibility with polypropylene resins, but for polyethylene glycol having a relatively low molecular weight such as an average molecular weight of 200 or more and 9000 or less, the polypropylene resin and polyethylene glycol are kneaded in an extruder, There is a tendency that troubles such as strand breakage due to poor dispersion in the process of producing polypropylene resin particles by the strand cut method and unstable feeding of the molten resin are less likely to occur. It is also possible to use a mixture of polyethylene glycols having different molecular weights.

  The average molecular weight of polyethylene glycol can be measured using a liquid chromatograph mass spectrometer (for example, LCQ Advantage manufactured by Thermo Fisher Scientific).

  The addition amount of the water-absorbing substance of the present invention is preferably 0.01 to 5 parts by weight, more preferably 0.03 to 3 parts by weight, with respect to 100 parts by weight of the polypropylene resin. It is. It is possible to change the expansion ratio by adjusting the addition amount. When the addition amount is less than 0.01 parts by weight, the effect of improving the expansion ratio by water or carbon dioxide gas tends to be small. On the other hand, when the addition amount exceeds 5 parts by weight, shrinkage of the polypropylene resin pre-expanded particles tends to occur and the dispersion of the water-absorbing substance in the polypropylene resin tends to be insufficient.

  In the present invention, for the purpose of adjusting the bubble diameter, a foam nucleating agent that promotes the formation of bubble nuclei during foaming may be added as necessary. Examples of the foam nucleating agent include aliphatic metals such as talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, titanium oxide, zeolite, calcium stearate, and barium stearate. Examples include salts, melamine, and metal borate salts. These foam nucleating agents may be used alone or in combination of two or more.

  Of these, talc, metal borate, or calcium carbonate is preferred.

  The amount of the foam nucleating agent is appropriately adjusted depending on the foam nucleating agent used or the desired expansion ratio, but is preferably 0.005 parts by weight or more and 1 part by weight with respect to 100 parts by weight of the polypropylene resin. Part or less, more preferably 0.01 part by weight or more and 0.7 part by weight or less. If the amount is less than 0.005 parts by weight, the expansion ratio tends to be difficult to increase. If the amount exceeds 1 part by weight, the in-mold foam moldability tends to be poor.

  In addition to the water-absorbing substance and foaming nucleating agent added in the present invention, a compatibilizer, an antistatic agent, a colorant, a stabilizer, a weathering agent, a flame retardant, and the like are appropriately added to such an extent that the effects of the present invention are not impaired. Is possible.

  Moreover, you may add synthetic resins other than a polypropylene resin in the range which does not impair the effect of this invention. Synthetic resins other than polypropylene resins include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, ethylene-vinyl acetate copolymer ethylene-acrylic acid. Examples thereof include ethylene resins such as copolymers and ethylene-methacrylic acid copolymers, and styrene resins such as polystyrene and styrene-maleic anhydride copolymers.

  Although the polypropylene resin and the water-absorbing substance have been described above, these are used as the polypropylene resin particles in the present invention.

  As a method for preparing polypropylene resin particles, a conventionally known method may be used. For example, together with the polypropylene resin (A), the polypropylene resin (B), a water-absorbing substance, and the additive added as necessary, in advance. Examples include a method of melting and kneading with an extruder, extruding from a die, cooling, and cutting with a cutter into a desired particle shape such as a cylindrical shape, an elliptical column shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, or the like. The grain weight is preferably 0.2 to 10 mg, more preferably 0.5 to 6 mg.

  The water-absorbing substance is previously masterbatched with a polyolefin-based resin, blended with a polypropylene-based resin so that a final addition amount is obtained, and melt-kneaded with an extruder to obtain a polypropylene-based resin particle. It is also good.

  Next, the manufacturing method of the polypropylene resin pre-expanded particles in the present invention will be described.

  The polypropylene resin pre-expanded particles in the present invention are prepared by dispersing the polypropylene resin particles produced as described above together with an aqueous dispersion medium in a sealed container, heating to a temperature equal to or higher than the softening temperature of the polypropylene resin particles, and then sealed container. It is produced by discharging into a pressure range lower than the internal pressure.

  The aqueous dispersion medium referred to in the present invention includes water, and water, ethanol, methanol, isopropanol and the like can be used.

  In the present invention, water, which is an aqueous dispersion medium, becomes a foaming agent and increases the internal pressure in the sealed container by injecting an inorganic gas such as carbon dioxide, nitrogen, or air at any stage before being released into the low pressure region. The pressure release rate during foaming can be adjusted to adjust the foaming ratio and the average cell diameter.

  Moreover, it is preferable to use water and a carbon dioxide gas together as a foaming agent. Furthermore, other physical foaming agents can be used as needed, for example, saturated hydrocarbons having 3 to 5 carbon atoms, dimethyl ether, or methanol or ethanol whose boiling point is lower than the foamable temperature. Inorganic foaming agents such as alcohols, air, and nitrogen can also be used.

  Carbon dioxide gas and other physical foaming agents may be introduced into the sealed container before heating after dispersing the polypropylene resin particles together with the aqueous dispersion medium in the sealed container, or during heating. Alternatively, it may be introduced after heating, or may be introduced immediately before foaming. Moreover, you may foam, introducing, so that the pressure in an airtight container may not fall during foaming. Further, it may be introduced in several times.

  When carbon dioxide gas, which is a more preferred embodiment of the present invention, is further added as a foaming agent, polypropylene resin particles, water and solid carbon dioxide gas (dry ice) may be charged into a sealed container, or polypropylene resin. Gas or liquid carbon dioxide gas may be introduced into the container at any stage after the particles and water are charged into the sealed container and before being released into the low pressure region. Or the method which combined these methods is also employable.

  As described above, when water and carbon dioxide are used together as the foaming agent, the foaming power can be easily increased. Therefore, even when a high foaming ratio is obtained, the amount of the water-absorbing substance added can be reduced.

  The expansion ratio of the polypropylene resin pre-expanded particles of the present invention is 8 to 25 times, preferably 9 to 20 times. If the expansion ratio is less than 8 times, the lightweight property of the in-mold foam molded product is low when the in-mold foam molding is performed, and if the expansion ratio exceeds 25 times, the amount of water-absorbing substance added increases, so shrinkage after foaming. Becomes larger.

  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 region lower than the internal pressure of the above-mentioned closed container (sometimes referred to as single-stage foaming), After producing polypropylene resin pre-expanded particles of less than 20 times by one-stage foaming, pressurizing the obtained polypropylene-based resin pre-expanded particles with an inorganic gas such as air in a sealed container, and applying internal pressure, steam It is preferable to increase the magnification by 20 times or more by foaming again by heating (sometimes referred to as two-stage foaming).

  When the polypropylene resin pre-expanded particles of the present invention thus obtained were heated at a rate of 10 ° C./min from 40 ° C. to 210 ° C., 1-10 mg of the polypropylene resin pre-expanded particles were measured by differential scanning calorimetry. In the DSC curve obtained in the above, it has two melting peaks.

  Moreover, in the measurement by the differential scanning calorimetry of the polypropylene resin pre-expanded particles of the present invention, the melting peak calorie (Ql (J / g)) based on the low-temperature side melting peak and the high-temperature side melting peak among the two melting peaks. Based on the melting peak calorie (Qh (J / g)), the ratio of the melting peak calorie based on the high temperature side melting peak to the total melting peak calorie (Qh / (Ql + Qh)) (hereinafter sometimes referred to as DSC peak ratio) However, it is preferably 15% or more and 40% or less, and more preferably 20% or more and 30% or less. When the DSC peak ratio is less than 15%, there is a tendency to cause sink marks in the in-mold foam molding during in-mold foam molding. When the DSC peak ratio exceeds 40%, melting between the polypropylene resin pre-expanded particles during in-mold foam molding is likely to occur. Wearability tends to decrease.

  Here, the melting peak calorie (Ql) based on the low temperature side melting peak and the melting peak calorie (Qh) based on the high temperature side melting peak will be described with reference to FIG. Is the heat quantity surrounded by the tangent line from the local maximum point between the low temperature side melting peak and the high temperature side melting peak to the melting start baseline, and the melting peak calorie (Qh) based on the high temperature side melting peak is the low temperature side melting peak. The amount of heat enclosed by the tangent line from the maximum point between the high-temperature side melting peaks to the end-of-melting baseline.

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

  In addition, evaluation in Examples and Comparative Examples was performed by the following method.

(Foaming ratio)
Take 3 to 10 g of polypropylene resin pre-expanded particles, dry at 60 ° C. for 6 hours, measure the weight w, put in a graduated cylinder containing water, submerge it, measure the volume v from the rise of the water surface, The true specific gravity ρb = w / v of the system resin pre-expanded particles 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.

  Next, examples of the present invention will be described.

Example 1
Propylene homopolymer (MFR: 5.8 g / 10 min, resin melting point) to 95 parts by weight of polypropylene-based resin (A) of ethylene-propylene random copolymer (MFR: 6.0 g / 10 min, resin melting point: 137.4 ° C.) : 161.4 ° C.) 5 parts by weight of polypropylene resin (B), 0.5 part by weight of polyethylene glycol (average molecular weight: 300) and 0.035 part by weight of powdery talc are blended, and the blend is biaxially extruded. Extruded with a machine to obtain 1.2 mg of polypropylene resin particles. In a sealed container, 100 parts by weight of the resin particles, 265 parts by weight of water, 1.5 parts by weight of tertiary calcium phosphate as a dispersant and 0.075 parts by weight of normal paraffin sulfonic acid soda were added, and the aqueous dispersion was stirred. 6 parts by weight of carbon dioxide was added as a foaming agent, and the temperature was raised to the annealing temperature shown in Table 1. At this time, after adding gaseous carbon dioxide to adjust the internal pressure of the container to 3.0 MPa and maintaining the temperature for 30 minutes, a circular orifice having a diameter of 4 mm attached to a small hole nozzle provided at the bottom of the sealed container The aqueous dispersion was discharged under atmospheric pressure to obtain polypropylene resin pre-expanded particles having an expansion ratio of 14.8 times and a DSC peak ratio of 22.9%. Note that no fusion between the polypropylene resin pre-expanded particles was observed.

  In contrast to Comparative Example 1 in which the polypropylene resin (B) is not blended, it can be seen that in the examples, the more the polypropylene resin (B) is blended, the smaller the amount of polyethylene glycol can be set to the same expansion ratio. It can also be seen that the amount of polyethylene glycol can be further reduced by increasing the melt flow rate of the polypropylene resin (B). In addition, when the amount of polyethylene glycol is constant, it can be seen that the greater the amount of polypropylene resin (B) blended, and the higher the melt flow rate, the higher the expansion ratio. However, in Comparative Example 2 where 30% by weight of the polypropylene resin (B) is blended, the expansion ratio of the polypropylene resin pre-expanded particles is reduced due to shrinkage, and many fusions between the polypropylene resin pre-expanded particles are generated. As a result.

( Reference Example 1 )
Propylene homopolymer (MFR: 5.8 g / 10 min, resin melting point) to 95 parts by weight of a polypropylene resin (A) of an ethylene-propylene random copolymer (MFR: 7.2 g / 10 min, resin melting point: 142.5 ° C.) : 161.4 ° C.) 5 parts by weight of polypropylene resin (B), 0.3 part by weight of melamine and 0.05 part by weight of powdered talc are blended, and the blend is extruded with a twin screw extruder. 2 mg of polypropylene resin particles were used. In a sealed container, 100 parts by weight of the resin particles, 265 parts by weight of water, 1.5 parts by weight of tertiary calcium phosphate as a dispersant and 0.075 parts by weight of normal paraffin sulfonic acid soda were added, and the aqueous dispersion was stirred. While keeping the inside of the sealed container at 3.0 MPa with nitrogen, the temperature was raised to the annealing temperature shown in Table 1. Then, after maintaining the temperature for 30 minutes, the aqueous dispersion was discharged under atmospheric pressure through a circular orifice with a diameter of 4 mm attached to a small hole nozzle provided at the bottom of the sealed container, and the foaming ratio was 15.2 times, DSC peak. Polypropylene resin pre-expanded particles having a ratio of 23.0% were obtained. Note that no fusion between the polypropylene resin pre-expanded particles was observed.

( Reference Example 3)
Polypropylene resin pre-expanded particles were obtained in the same manner as in Example 1 except that the composition and annealing temperature shown in Table 1 were used. The evaluation results are shown in Table 1.

( Reference Example 2 )
Extrusion was carried out in the same manner as in Example 6 except that the amount of melamine was changed to 0.25 parts by weight to obtain polypropylene resin particles. Carbon dioxide gas was supplied in the same manner as in Example 1 and foamed at the annealing temperature shown in Table 1 to obtain polypropylene resin pre-expanded particles. The evaluation results are shown in Table 1.

Even when carbon dioxide gas is not used, it can be seen that even in the case of Reference Example 1 where the amount of melamine is smaller than that of Reference Example 3 in which the polypropylene resin (B) is not blended, the same expansion ratio can be obtained. Moreover, it turns out that the direction of the reference example 2 which uses a carbon dioxide gas can further reduce a melamine amount further than Example 6 which does not use a carbon dioxide gas.

It is a DSC curve obtained when the polypropylene resin pre-expanded particles of Example 1 are heated from 40 ° C. to 210 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter. The horizontal axis is the temperature, and the vertical axis is the amount of change in heat per unit time. The shaded portion on the low temperature side is Ql, and the shaded portion on the high temperature side is Qh.

Claims (5)

After dispersing the polypropylene resin particles containing a water-absorbing substance together with an aqueous dispersion medium in a sealed container, using inorganic gas as a foaming agent and heating to a temperature equal to or higher than the softening temperature of the polypropylene resin particles, the internal pressure of the sealed container In a method for producing polypropylene resin pre-expanded particles having a foaming ratio of 8 times or more and 25 times or less, which is released into a lower pressure range and foamed,
Polypropylene resin constituting the polypropylene resin particles is a polypropylene resin (A) having a resin melting point of 150 ° C. or less (A) 80 wt% or more and 99 wt% or less, and a polypropylene resin (B) 1 having a resin melting point of 160 ° C. or more comprises a wt% to 20 wt%, water-absorbing material, characterized in that a polyethylene glycol method for producing a pre-expanded polypropylene resin particles.   The method for producing pre-expanded polypropylene resin particles according to claim 1, wherein the melt flow rate of the polypropylene resin (B) is larger than that of the polypropylene resin (A).   Carbon dioxide gas is further introduce | transduced in an airtight container, The manufacturing method of the polypropylene resin pre-expanded particle of Claim 1 or 2 characterized by the above-mentioned.   The method for producing pre-expanded polypropylene resin particles according to any one of claims 1 to 3, wherein the polypropylene resin (B) having a resin melting point of 160 ° C or higher contains 99% by weight or more of propylene. . The DSC curve obtained when the temperature is raised from 40 ° C. to 210 ° C. at a rate of 10 ° C./min by differential scanning calorimetry of polypropylene resin pre-expanded particles has two melting peaks and is melted on the high temperature side. 5. The polypropylene resin pre-expanded particles obtained by the production method according to claim 1, wherein a ratio of a peak heat amount to a total melting peak heat amount is 15% or more and 40% or less.

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