JP5553476B2 - Method for producing expanded polypropylene resin particles and expanded polypropylene resin particles - Google Patents

Description

  The present invention relates to expanded polypropylene resin particles and a method for producing the same. More specifically, for example, the present invention relates to a polypropylene resin foamed particle that can be suitably used as a raw material for an in-mold foam molded product, and a method for producing the same.

  Conventionally, a method in which polypropylene resin particles are dispersed in an aqueous dispersion medium together with a foaming agent, heated to constant pressure and constant temperature, impregnated with the foaming agent in resin particles, and then released into a low-pressure atmosphere to obtain foamed particles. It has been 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, the volatile organic foaming agent is a substance having a global warming potential larger than that of carbon dioxide, and is not environmentally preferable. In addition, 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. On the other hand, since the plasticizing action is large, the expansion ratio and crystalline state of the expanded particles are large. Control is difficult. In addition, since it is a flammable substance, it is necessary to make the equipment explosion-proof, which has the disadvantage of increasing 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 polypropylene-based resin expanded particles that can be suitably used for the production of in-mold foam molded articles, a method using water used as a dispersion medium as a foaming agent has been proposed. ing.

  As a method using water as a foaming agent, crystalline polyolefin polymer particles containing 10 to 70% by weight of an inorganic filler are dispersed in water as a dispersion medium in a sealed container, and a pressure equal to or higher than the saturated vapor pressure of the dispersion and The dispersion is maintained in a high pressure region below the melting point of the crystalline polyolefin polymer particles and under a temperature condition where the crystallization of the polymer particles proceeds, and impregnated with water as a dispersion medium, There has been proposed a method for producing crystalline polyolefin polymer expanded particles by releasing them into a polymer (for example, Patent Document 4). However, since the foamed particles obtained by this method contain a large amount of inorganic filler, the cell diameter tends to be fine and the open cell ratio tends to be high. Mechanical properties such as wear, surface appearance and compressive strength are not sufficient.

  Also, after dispersing the polypropylene resin particles containing a water-soluble inorganic substance or hydrophilic polymer in water in a hermetically sealed container and heating to a temperature higher than the softening temperature of the resin particles to obtain water-containing polypropylene resin particles, There has been proposed a method for producing polypropylene resin expanded particles by discharging them into a low pressure region (for example, Patent Documents 5 to 7). This method describes that polypropylene-based resin 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 expanded particles obtained from the polypropylene-based resin particles containing a water-soluble inorganic substance as described in Patent Document 6, in order to increase the expansion ratio, particularly in order to increase the expansion ratio to 8 times or more, the water-soluble inorganic substance When the amount added is increased, the bubbles tend to be finer in conjunction with each other. As a result, in the in-mold foam molded article using the obtained foamed particles, the fusion property between the foamed particles is lowered. Problems such as these have been observed, leading to a decrease in the product value of molded products and a deterioration in the productivity of molded products. In addition, since the expansion ratio and the bubble diameter change in conjunction with each other, for example, it is difficult to adjust (control) only the expansion ratio while keeping the bubble diameter constant. Limits arise in the production of particles.

  Further, the polypropylene resin foam particles produced by using carbon dioxide gas with the water content of the polypropylene resin particles containing the hydrophilic polymer as described in Patent Document 7 being 8% by weight or more are foamed because of their high water content. There is also a drawback that the expanded particles tend to shrink immediately afterward.

On the other hand, carbon dioxide gas is used as a foaming agent, and polymer particles containing a polypropylene glycol / polyethylene glycol polymer together with an inorganic substance are foamed, and a method for producing foamed particles in which bubbles do not become fine is disclosed (for example, Patent Document 8). In this method, since the compatibility with the polypropylene-based resin is low, it is easy to cause troubles such as strand breakage due to poor dispersion in the process of creating polymer particles, and fluctuation of the molten resin feed in the extruder, Therefore, only a small amount could be added, and since water absorption was low, it was forced to rely on foaming with carbon dioxide gas. In addition, in order to use polypropylene glycol / polyethylene glycol polymer having a large average molecular weight, it is necessary to use a polypropylene resin having a melt index of 10 g / 10 min or more when trying to obtain expanded polypropylene resin particles having a high expansion ratio. was there. Furthermore, there are drawbacks in that the fusion rate between the foamed particles when formed into a molded body tends to decrease, the heat resistance decreases, and the strength decreases.
Japanese Patent Publication No.56-1344 Japanese Patent Publication No. 4-64332 Japanese Examined Patent Publication No. 4-64334 Japanese Patent Publication No.49-2183 JP-A-3-223347 WO 98/25996 Japanese Patent Laid-Open No. 10-152574 Japanese Patent Laid-Open No. 5-163381

  The present invention does not cause the non-uniformity of bubbles and the micronization of bubbles observed in conventional foamed particles, and it is easy to control the bubble diameter and the foaming ratio independently. It is an object of the present invention to provide a method for producing polypropylene resin expanded particles, which can provide a foamed molded article having good adherence and excellent surface properties.

  In order to solve the above-mentioned drawbacks, the present inventors have conducted intensive research to solve the above-mentioned problems. As a result, the polypropylene resin having a melt index of 2 to 9 g / 10 min does not have a predetermined amount of foam nucleation. By impregnating and foaming polypropylene resin particles containing a water-absorbing substance and a foam nucleating agent, the foam of conventional foamed particles is not uneven and the bubbles are not made fine. It has been found that expanded polypropylene resin particles with adjusted can be produced.

  Furthermore, it has been found that by using carbon dioxide gas as a foaming agent in addition to the water, the uniformity of the bubbles becomes better and the expansion ratio is easily increased.

  That is, in the first aspect of the present invention, 0.01 to 5 parts by weight of a water-absorbing substance having no foaming nucleation effect and 0.005 of a foaming nucleating agent are added to 100 parts by weight of a polypropylene resin having a melt index of 2 to 9 g / 10 min. Disperse polypropylene resin particles containing ~ 1 part by weight in an airtight container together with an aqueous dispersion medium, heat to a temperature equal to or higher than the softening temperature of the polypropylene resin particles, and then release to a pressure range lower than the internal pressure of the airtight container And a foaming ratio of 0.1 to 7% by weight, an expansion ratio of 8 to 25 times, an average cell diameter of 130 to 500 μm, and a bubble diameter variation of less than 0.4. .

As a preferred embodiment,
(1) Carbon dioxide gas is further introduced into the sealed container,
(2) With respect to 100 parts by weight of the polypropylene resin particles, 0.5 to 20 parts by weight of carbon dioxide gas is introduced into the sealed container,
(3) The water-absorbing substance having no foam nucleation function is a compound having a polyalkylene glycol chain,
(4) The compound having a polyalkylene glycol chain is polyethylene glycol.
(5) The compound having a polyalkylene glycol chain is a copolymer comprising a polyolefin block and a polyethylene glycol block.
(6) The water-absorbing substance having no foam nucleation function has a melting point lower than 150 ° C.,
(7) The present invention relates to the method for producing expanded polypropylene resin particles as described above, wherein the water-absorbing substance having no foam nucleation function is at least one selected from bentonite, synthetic hectorite, and synthetic zeolite.

  The second of the present invention is a polypropylene system comprising 0.01 to 5 parts by weight of a water-absorbing substance having no foam nucleation function and 0.005 to 1 parts by weight of a foam nucleating agent with respect to 100 parts by weight of a polypropylene resin. A foamed resin particle having a melt index of 2 to 12 g / 10 minutes, a volatile fraction of 0.1 to 7% by weight, an expansion ratio of 8 to 25 times, an average cell diameter of 130 to 500 μm, and a bubble The present invention relates to expanded polypropylene resin-based resin particles having a diameter variation of less than 0.4.

3rd of this invention is the polypropylene resin expanded particle (it calls a polypropylene resin expanded particle (P)) manufactured with the manufacturing method of the said description,
In the production method described above, the polypropylene resin foam particles (referred to as polypropylene resin foam particles (Q)) produced without containing a water-absorbing substance having no foam nucleation function are obtained in terms of volatile fraction and average cell diameter. Further, the present invention relates to a polypropylene resin foamed particle satisfying the following formulas (A) and (B) and having a melt index of 2 to 12 g / 10 minutes of the polypropylene resin foamed particle.
(A) Volatile fraction of polypropylene resin expanded particles (P) ≧ volatile fraction of polypropylene resin expanded particles (Q) × 1.1
(B) Average cell diameter of polypropylene resin expanded particles (P) ≧ average cell diameter of polypropylene resin expanded particles (Q) × 0.7

  According to the present invention, when water is used as a foaming agent, a water-absorbing substance and a foam nucleating agent that do not have a predetermined amount of foaming nucleation action are added to the polypropylene resin, particularly in foaming conditions in which water and carbon dioxide are used as the foaming agent. By using in combination, it is possible to obtain high-magnification polypropylene-based resin expanded particles in which the bubbles of the polypropylene-based resin expanded particles are uniform without being miniaturized and the cell diameter and the expansion ratio can be easily adjusted independently. When the expanded polypropylene resin particles of the present invention are used for in-mold foaming, it is possible to obtain an excellent foamed molded article having a high fusion rate and a small surface area, shrinkage, and distortion.

  In particular, a foamed molded article having good fusion and surface properties can be obtained even when performing in-mold foam molding using the polypropylene resin foamed particles obtained by multiplying the polypropylene resin foamed particles of the present invention by two-stage foaming. It is possible.

  The present invention is based on 100 parts by weight of a polypropylene resin having a melt index of 2 to 9 g / 10 min, 0.01 to 5 parts by weight of a water-absorbing substance having no foam nucleation effect, and 0.005 to 1 part by weight of a foam nucleating agent. The polypropylene resin particles containing the part are dispersed in an airtight 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 released into a pressure range lower than the internal pressure of the airtight container to foam. Polypropylene resin foamed particles having a volatile content of 0.1 to 7% by weight, an expansion ratio of 8 to 25 times, an average cell diameter of 130 to 500 μm, and a cell diameter variation of less than 0.4 are produced.

  In the present invention, the water-absorbing substance having no foaming nucleation function refers to a substance having no foaming nucleation function and a water-absorbing substance.

In the present invention, “having no foam nucleation effect” means that the average cell diameter of the polypropylene resin expanded particles (a) containing 0.5 part by weight of the substance with respect to 100 parts by weight of the polypropylene resin, In the average cell diameter of the expanded polypropylene resin particles (b) obtained by expanding the expanded polypropylene resin particles under exactly the same conditions except that no substance is contained,
(A) average bubble diameter ≧ (b) average bubble diameter × 0.7
A substance when it has a relationship. Here, the average bubble diameter is an average bubble diameter L (av) measured according to a method described later.

  The water-absorbing substance in the present invention generally means a substance having water absorption, hygroscopicity, water solubility or compatibility, and examples of such substances include water-soluble polymers, water-absorbing polymers, hydrophilic polymers. , Water-soluble organic substances, water-absorbing organic substances, hydrophilic organic substances, water-soluble inorganic substances, water-absorbing inorganic substances, hydrophilic inorganic substances, and the like.

  Although there is no restriction | limiting in particular in the water absorption rate of these substances, From a viewpoint of improving the expansion ratio of the polypropylene resin expanded particle obtained, 0.1% or more is preferable, More preferably, it is 0.5% or more. As a measuring method of such a water absorption rate, it can measure, for example based on ASTM D570.

  In the prior art in which a water-soluble inorganic substance is added, it was possible to increase the expansion ratio of the foamed particles by increasing the amount of the water-soluble inorganic substance added. A significant increase in the number of bubbles is observed with the increase, and the average bubble diameter becomes very small. As a result, the thickness of the bubble wall tends to be reduced, and the foamed molded article formed by using such foamed particles has a low fusion rate and increases intergranularity, shrinkage, and strain.

  On the other hand, according to the present invention, since a water-absorbing substance having no foam nucleation function is used, even when the amount of addition is increased to increase the expansion ratio, there is no significant decrease in the average cell diameter. A foamed molded product molded in-mold using foamed particles produced by the production method has a high fusion rate, and is excellent in beauty with small intergranularity, shrinkage, and strain.

  Such a water-absorbing substance having no foaming nucleation function is selected by the method described later, and may include a conventionally known substance. However, the prior art does not mention an independent adjustment method of the expansion ratio and the average cell diameter, and in particular, the present invention is more effective when not only water but also carbon dioxide is used as a foaming agent. To date, no example has been disclosed that discloses a method.

  As described above, the water-absorbing substance having no foaming nucleation action used in the present invention has been described from the point of no foaming nucleation action and water absorption. Examples of such substances are listed below.

  That is, (A) a copolymer having a polyalkylene glycol block (for example, peristat from Sanyo Chemical Industries, Ltd.), a compound having a polyalkylene glycol chain such as polypropylene glycol or polyethylene glycol, (B) sodium polyacrylate, Examples thereof include hydrophilic polymers such as cellulose and polyvinyl alcohol, and inorganic compounds such as (C) zeolite, bentonite, and synthetic hectorite (laponite).

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

(C) Alkyl and alkylallyl polyoxyethylene ether, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropyl alkyl ether, glycerin ester polyoxyethylene ether, sorbitan ester polyoxyethylene ether, sorbitol ester poly Oxyethylene ether, polyethylene glycol fatty acid ester, glycerin ester, higher fatty acid 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,
(D) Surfactants such as amphoteric surfactants such as carboxybetaine, imidazolinium betaine and aminocarboxylate

(E) an antistatic agent comprising the surfactant as a main component, (f) at least one selected from an ester bond, an amide bond, an ether bond, a urethane bond, and an imide bond, wherein the polyolefin block and the hydrophilic polymer block are Examples of the antistatic agent having a structure in which the bonds are alternately and alternately bonded via a bond, such as the antistatic agent described in claims of Japanese Patent No. 3488163, can be given.

  These water-absorbing substances having no foam nucleation function may be used alone or in combination of two or more.

  Among these, a compound having a polyalkylene glycol chain is preferable as a water-absorbing substance having no more preferable foam nucleation function. In particular, polyethylene glycol is preferable. Polyethylene glycol is a substance with extremely low toxicity, and the obtained foamed molded product can be used for applications where it comes into contact with food.

  Further, polyethylene glycol having an average molecular weight of 200 to 9000 is preferable, and polyethylene glycol having an average molecular weight of 200 to 600 is most preferable. In general, glycols have properties that are slightly inferior in compatibility with polypropylene resins, but for polyethylene glycol having a relatively small molecular weight such as an average molecular weight of 200 to 9000, a polypropylene resin and polyethylene glycol are kneaded with an extruder, a strand There are few troubles such as strand breakage due to poor dispersion in the process of producing polypropylene resin particles by the cutting method and unstable feeding of the molten resin, and foamed particles with uniform bubble diameter and small variation in magnification can be obtained. Furthermore, foam molded products molded in-mold using the foamed particles tend to have small intergranular / shrinkage / distortion, beautify, high fusion rate of foam molded products, and sufficient heat-resistant dimensional stability. .

  In addition, by selecting polyethylene glycol having a small average molecular weight, the impregnation property of carbon dioxide gas into polypropylene resin particles becomes high, so when using carbon dioxide as a foaming agent, it is particularly easy to obtain a high expansion ratio, Further, the uniformity of the bubble diameter is further improved, which is further preferable.

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).

  Another suitable compound having a polyalkylene glycol chain is a copolymer containing a polyalkylene glycol block, and in particular, a copolymer comprising a polyalkylene glycol block and a polyolefin block is preferred.

  Specifically, the brand name Perestat manufactured by Sanyo Chemical Industries, Ltd. can be mentioned. Since such a copolymer has a polyolefin block, it has good compatibility with a polypropylene resin, and since it is a solid, handling is good, and poor feeding during extrusion kneading may occur. No. As a result, there is no occurrence of discharge unevenness in extrusion, and resin particles having a uniform shape can be produced in resin 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. Foam molded products molded in-mold using the foamed particles tend to have small intergranularity, shrinkage, and distortion, are beautiful, have high fusion rates, and have sufficient heat-resistant dimensional stability.

  Furthermore, it is preferable that the water-absorbing substance having no foam nucleation action has a melting point lower than 150 ° C. A substance having a melting point lower than 150 ° C. is preferable because it is highly likely to exist as a liquid rather than a solid at the time of foaming, the nucleation action is further reduced, and the bubble diameter and the foaming ratio can be easily controlled. Substances having a melting point of 150 ° C. or higher tend to easily exhibit foaming nucleation, and as a result, surface properties such as fusion, intergranularity, shrinkage, and strain when foamed molded products are reduced. There is a case.

  Specific examples of the substance having a melting point lower than 150 ° C. include a polyethylene glycol (melting point: −13 ° C. in the case of an average molecular weight of 300), a copolymer having a polyolefin block and a polyalkylene glycol block. Perestat (in the case of perestat 303, the melting point is 135 ° C.).

  Further, as another more preferable water-absorbing substance having no foaming nucleus forming action, bentonite, synthetic hectorite, synthetic zeolite and the like can be mentioned. In general, inorganic substances are said to have a foam nucleation effect. However, although these substances are inorganic substances, they have an unexpectedly small foam nucleation action, and therefore can be suitably used.

  The addition amount of the water-absorbing substance having no foam nucleation function of the present invention is 0.01 to 5 parts by weight, preferably 0.03 to 3 parts by weight, with respect to 100 parts by weight of the polypropylene resin. By adjusting the addition amount, it is possible to adjust the volatile fraction and change the expansion ratio. 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 is reduced. The effect of uniforming the bubble diameter is reduced. When the added amount exceeds 5 parts by weight, shrinkage of the polypropylene resin foamed particles tends to occur, and the dispersion of the water-absorbing substance having no foaming nucleus forming action in the polypropylene resin becomes insufficient.

  The foam nucleating agent used in the present invention refers to a substance that promotes the formation of cell nuclei during foaming, such as talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, titanium oxide, Examples thereof include aliphatic metal salts such as zeolite, calcium stearate and barium stearate, melamine, and metal borate. These foam nucleating agents may be used alone or in combination of two or more.

  Among these, talc, metal borate, and calcium carbonate are preferable, and when using talc, which is particularly inexpensive and well-adapted to a water-absorbing substance having no foam nucleation action, a water-absorbing substance polypropylene having no foam nucleation action is used. Dispersibility in a resin is improved, and a foamed molded product having a uniform cell diameter can be easily obtained.

  The addition amount is appropriately adjusted depending on the foaming nucleating agent used or the desired foaming ratio, but 0.005 to 1 part by weight is required with respect to 100 parts by weight of the polypropylene resin, preferably 0. 0.01 to 0.7 parts by weight. When the amount is less than 0.005 parts by weight, the expansion ratio cannot be increased or the uniformity of the bubble diameter is lowered. If it exceeds 1 part by weight, the average cell diameter of the foamed molded product becomes too small, resulting in poor in-mold foam moldability.

  When talc is used as the foam nucleating agent, a desired average cell diameter is easily obtained by using 0.02 to 0.5 parts by weight with respect to 100 parts by weight of the polypropylene resin, and in-mold foam moldability is also improved. Therefore, it is preferable.

  Examples of the polypropylene resin of the present invention include a propylene homopolymer, a propylene-α-olefin random copolymer, and a propylene-α-olefin block copolymer. Examples of the α-olefin include α-olefins having 2 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 has a characteristic that it can be easily impregnated with carbon dioxide gas, which is preferable.

  The melt index of the polypropylene resin used in the present invention is 2 to 9 g / 10 minutes, preferably 3 to 8 g / 10 minutes, and more preferably 4 to 8 g / 10 minutes. When the melt index is less than 2 g / 10 minutes, expanded particles with a high expansion ratio cannot be obtained, and bubbles are not uniform. In addition, when the melt index exceeds 9 g / 10 min, it is easy to foam, and it becomes easy to obtain expanded particles with a high expansion ratio, but the foamed cells break up, the open cell ratio of the expanded particles increases, and the bubbles are also uneven. become.

  The melt index in the present invention is a value measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  The melting point of the polypropylene resin of the present invention is 130 to 165 ° C. because it has excellent foamability and moldability, and it is easy to obtain expanded particles having excellent mechanical strength and heat resistance when formed into an in-mold foam molded product. Are preferred, and those of 135 ° C. to 155 ° C. are more preferred. 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 1 to 10 mg of polypropylene resin is heated from 40 ° C. to 220 ° C. at a rate of 10 ° C./min by a differential scanning calorimeter, and then cooled to 40 ° C. at a rate of 10 ° C./min. The peak temperature of the endothermic peak in the DSC curve obtained when the temperature is raised again to 220 ° C. at a rate of 10 ° C./min.

  In addition to the water-absorbing substance having no foaming nucleation function and foaming nucleating agent added in the present invention, a compatibilizing agent, antistatic agent, coloring agent, stabilizer, weathering agent, flame retardant and the like have the effects of the present invention. It can be added appropriately to such an extent that it is not damaged.

  As described above, the polypropylene resin, the water-absorbing substance having no foaming nucleus forming action and the foaming nucleating agent have been described. In the present invention, these are used as the polypropylene resin particles.

  As a method for making polypropylene resin particles, a conventionally known method may be used. For example, a polypropylene resin, a water-absorbing substance having no foam nucleation function and a foam nucleating agent previously blended are melt-kneaded in an extruder, An example is a method of extruding from a die, cooling, and then forming polypropylene resin particles with a cutter. If a water-absorbing substance having no foaming nucleation action is selected at room temperature or a waxy (semi-liquid) substance such as polyethylene glycol having a molecular weight of 3000 or less, the above-described method may be used. Alternatively, a method may be used in which a fixed amount is supplied in a liquid state to the molten polypropylene resin and kneaded in the charging hopper of the extruder or in the middle of the extruder. When liquid is added, wax-like materials such as polyethylene glycol having a molecular weight of 1000 to 3000 may be added after heating and melting.

  In addition, in the case of a substance that tends to evaporate at the extrusion temperature, such as polyethylene glycol having a molecular weight of 4000 or less, it is desirable to lower the temperature of the cylinder and the die part of the extruder to 250 ° C. or less in order to reduce the evaporation.

  In addition, the water-absorbing substance and the foam nucleating agent having no foam nucleation function are previously masterbatched with a polyolefin resin, and this is blended with a polypropylene resin so that the final addition amount is obtained. It is good also as a polypropylene-type resin particle by melt-kneading.

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

  The expanded polypropylene resin particles in the present invention are prepared by dispersing the polypropylene resin particles prepared 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, Manufacture by discharging into a pressure range lower than the internal pressure. In this case, water as the dispersion medium becomes the foaming agent, and the internal pressure in the sealed container is increased by injecting an inorganic gas such as carbon dioxide, nitrogen or air at any stage before being released into the low pressure region. It is possible to adjust the foaming ratio and the average cell diameter by adjusting the pressure release speed.

  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.

  Thus, when water and carbon dioxide gas are used in combination as a foaming agent, the foaming power can be easily increased, so even when a high foaming ratio is obtained, the amount of foam nucleating agent added can be reduced, resulting in an average cell size. Expanded particles having a large diameter are obtained, and the secondary foamability is also good. In addition, it is presumed that the water-absorbing substance having no foaming nucleation function is likely to hold carbon dioxide together with water, which makes it possible to form a uniform bubble diameter and to further control the bubble diameter and the expansion ratio. To more preferable.

  In the present invention, water is essential as a foaming agent, and it is preferable to use water and carbon dioxide gas in combination, but other physical foaming agents can be used as needed, for example, Saturated hydrocarbons having 3 to 5 carbon atoms, dimethyl ether, alcohols such as methanol and ethanol whose boiling point is lower than the foamable temperature, inorganic foaming agents such as air and nitrogen, and the like can also be used. In addition, the water of a foaming agent utilizes the water of the aqueous dispersion medium accommodated in an airtight container.

  Carbon dioxide gas and other physical foaming agents may be introduced into the sealed container before heating, after the polypolypropylene resin particles are dispersed together with the aqueous dispersion medium in the sealed container, or during heating. 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.

  From the viewpoint of sufficiently impregnating the foaming agent into the polypropylene resin particles and increasing the foaming power, it is preferably introduced before heating. From the viewpoint of suppressing the magnification variation of the obtained polypropylene resin foam particles, foaming is performed. It is also preferable to introduce it into the inside.

  The melt index of the polypropylene resin expanded particles of the present invention thus produced is 2 to 12 g / 10 minutes, preferably 3 to 11 g / 10 minutes, and more preferably 4 to 10 g / 10 minutes. If the melt index is less than 2 g / 10 minutes, the secondary foamability is lowered, and thus the moldability at the time of in-mold molding is lowered. On the other hand, if it exceeds 12 g / 10 minutes, the foaming rate will increase, for example, the bubbles of the foamed particles may break. In addition, the melt index of a polypropylene resin expanded particle can be measured on the same conditions as the melt index of a polypropylene resin.

  According to the method for producing expanded polypropylene resin particles of the present invention, the melt index of the expanded polypropylene resin particles tends to be larger than the melt index of the polypropylene resin as the base resin, but the difference is almost the same. 3 g / 10 min or less. If the melt index of the polypropylene resin is selected in consideration of this point, it is possible to obtain the expanded polypropylene resin particles of the present invention.

  The average cell diameter of the expanded polypropylene resin particles of the present invention is 130 to 500 μm. Preferably it is 160-400 micrometers, More preferably, it is 210-350 micrometers. When the average cell diameter is less than 130 μm, there arises problems such as a decrease in the fusibility of the obtained foamed molded product, distortion of the shape, and generation of wrinkles on the surface. Decreases.

  The bubble diameter variation of the polypropylene resin expanded particles obtained by the present invention is less than 0.4, preferably 0.3 or less, and more preferably 0.2 or less. When the bubble diameter variation is 0.4 or more, the surface properties of the obtained foamed molded article are deteriorated, and the interstices such as wrinkles and dents between the expanded particles and holes are prominent. In order to achieve such bubble size variation, it is possible to use the water-absorbing substance having no foaming nucleation function and foaming nucleating agent used in the present invention, but more preferably, carbon dioxide gas is used in combination as the foaming agent. This makes it easier to achieve. The reason for this is not clear, but it is presumed that the interaction between a water-absorbing substance having no foaming nucleus forming action and carbon dioxide gas has an influence.

  The polypropylene resin foamed particles of the present invention have a melt index of 2 to 12 g / 10 minutes, a volatile fraction of 0.1 to 7% by weight, an expansion ratio of 8 to 25 times, an average cell diameter of 130 to 500 μm, and a variation in cell diameter. Polypropylene resin foamed particles having a particle size of less than 0.4 are preferably produced by a production method using an aqueous dispersion medium as described above, but can also be produced by another method. For example, polypropylene resin particles are contained in a pressure-resistant container, and for example, a foaming agent such as gaseous carbon dioxide gas is injected to impregnate the polypropylene resin particles, and then taken out into the atmosphere to obtain expandable resin particles. Next, it is possible to obtain the expanded polypropylene resin particles of the present invention by storing the expandable resin particles in a foaming apparatus and heating the foamed resin particles for a predetermined time with water vapor or a heater.

  The average bubble diameter L (av) and the bubble diameter variation (S) in the present invention are determined as follows. That is, the center of one randomly selected expanded particle is cut and the cross section that appears is magnified. Here, the X axis and the Y axis perpendicular to each other at the approximate center of the cross section are drawn, the point where the X axis and the Y axis at the approximate center of the cross section intersect with each other is the center O, and the point where the X axis intersects with the end of the cross section. , B and B ′ are points where the Y-axis intersects the end of the cross section.

  Next, the number of bubble walls intersected by the line segment OA is counted, and the value obtained by dividing the length of the line segment OA by the number of bubble walls is further divided by 0.616 to obtain the bubble diameter L (OA). That is, the bubble diameter L (OA) is obtained by the following equation (1).

線分ＯＡ’、線分ＯＢ、線分ＯＢ’についても同様に行い、それぞれＬ（ＯＡ’）、Ｌ（ＯＢ）、Ｌ（ＯＢ’）を求める。なお、気泡壁上に中心Ｏがある場合は、気泡壁として数える。

The same processing is performed for the line segment OA ′, the line segment OB, and the line segment OB ′, and L (OA ′), L (OB), and L (OB ′) are obtained. In addition, when the center O exists on a bubble wall, it counts as a bubble wall.

  Here, four average values L ′ (av) of L (OA), L (OA ′), L (OB), and L (OB ′) are calculated. This operation was carried out on 19 randomly selected polypropylene resin expanded particles, and finally, the average value of L ′ (av) of 20 polypropylene resin expanded particles was further averaged. ).

  On the other hand, the bubble diameter variation (S ′) in one expanded particle is set to a value represented by the following equation (2).

これを前述で選び出した残り１９個の発泡粒子について実施し、最終的に２０個の発泡粒子の気泡径バラツキＳ’を平均した値を気泡径バラツキＳとした。

This was carried out on the remaining 19 expanded particles selected above, and the average value of the bubble diameter variation S ′ of the 20 expanded particles was defined as the bubble diameter variation S.

  The volatile content of the expanded polypropylene resin particles of the present invention is 0.1 to 7% by weight. If the volatile content is less than 0.1% by weight, the desired expansion ratio described later cannot be obtained, and if it exceeds 7% by weight, the resulting polypropylene resin expanded particles shrink and wrinkles are generated on the surface of the expanded particles.

In addition, this volatile matter rate is measured as follows. The weight (W1) of the polypropylene resin expanded particles is measured, and the weight (W2) when the polypropylene resin expanded particles are dried in an oven at 80 ° C. for 12 hours is measured and calculated by the following formula.
Volatiles (%) = (W1-W2) / W2 × 100
In addition, when foamed particles immediately after foaming are used, water adhering to the particle surface may be dehydrated with an air stream and then measured by the method described above.

  Such a volatile component is considered to be mainly composed of water or carbon dioxide contained in the expanded polypropylene resin particles.

  The expansion ratio of the polypropylene resin expanded particles of the present invention is 8 to 25 times, preferably 8 to 20 times, and more preferably 9 to 17 times. If the expansion ratio is 8 times or more, it is possible to satisfactorily adjust the bubble diameter and the expansion ratio by the combined use of a water-absorbing substance having no foam nucleation function and a foam nucleating agent. Also, if the expansion ratio is 25 times or less, the bubbles of the polypropylene resin foamed particles do not break, and the dimensional accuracy, mechanical strength, heat resistance, etc. of the foamed molded product when in-mold foam molding is sufficient. .

  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), Polypropylene resin foam particles of less than 20 times are produced by one-stage foaming, and the obtained polypropylene resin foam particles are pressurized with an inorganic gas such as air in a pressure-resistant container to give an internal pressure, followed by steam heating. Therefore, it is preferable to increase the magnification to 20 times or more by foaming again (sometimes referred to as two-stage foaming). In particular, when the water-absorbing substance having no foam nucleation function of the present invention is included, the water contained in the two-stage foaming can be utilized, and the foaming ratio can be easily increased.

  From the viewpoint of improving the expansion ratio in terms of the volatile content and average cell diameter of the polypropylene resin foam particles obtained by the method for producing polypropylene resin foam particles of the present invention, or from the viewpoint of in-mold moldability, the following are more preferable embodiments. Can be mentioned.

That is, the polypropylene resin foamed particles obtained by the production method of the present invention (hereinafter referred to as polypropylene resin foam particles (P)) and the water-absorbing substance having no foam nucleation function are included, and other conditions are The polypropylene resin expanded particles (hereinafter referred to as polypropylene resin expanded particles (Q)) produced under the same conditions as the polypropylene resin expanded particles (P) are the following (A), in terms of volatile fraction and average cell diameter: It is preferable to satisfy the formula (B).
(A) Volatile fraction of polypropylene resin expanded particles (P) ≧ volatile fraction of polypropylene resin expanded particles (Q) × 1.1
(B) Average cell diameter of polypropylene resin expanded particles (P) ≧ average cell diameter of polypropylene resin expanded particles (Q) × 0.7
When the volatile content of the polypropylene resin expanded particles (P) is less than the volatile content ratio of the polypropylene resin expanded particles (Q) × 1.1, the foaming force at the time of foaming tends to decrease. May not be obtained.

  In addition, when the average cell diameter of the polypropylene resin expanded particles (P) is less than the average cell diameter of the polypropylene resin expanded particles (Q) × 0.7, the average cell diameter is small, so that the melting at the time of in-mold molding is reduced. Wearability may be reduced.

  The polypropylene resin expanded particles of the present invention thus obtained preferably have two melting peaks in the DSC curve obtained by differential scanning calorimetry as shown in FIG.

  In the case of expanded particles having two melting peaks, in-mold foam moldability is good, and there is a tendency to obtain an in-mold foam molded article having good mechanical strength and heat resistance.

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

  As described above, the expanded polypropylene resin particles having two melting peaks can be easily obtained by setting the temperature in the sealed container at the time of foaming to an appropriate value. That is, in the case of the present invention, the temperature in the closed container is usually not lower than the softening temperature of the polypropylene resin as the base material, preferably not lower than the melting point, more preferably not lower than the melting point + 5 ° C., more preferably lower than the melting end temperature. The melting end temperature is −2 ° C. or lower, and in such a case, expanded polypropylene-based resin particles having two melting peaks tend to be obtained.

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

  Further, the endothermic peak calorific value (hereinafter sometimes referred to as Qh) on the high temperature side of the two melting peaks is preferably 5 to 30 J / g, and more preferably 7 to 20 J / g. If it is less than 5 J / g, the open-cell rate of the polypropylene resin expanded particles tends to be high, and if it exceeds 30 J / g, the fusion property when obtaining a foamed 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.

  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)
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.

(Open cell rate)
Using an air comparative hydrometer (manufactured by Tokyo Science Co., Ltd., 1000 type), the closed cell volume of the obtained foamed particles was obtained, and this was obtained by dividing this by the apparent volume obtained separately by the submerged method. The bubble rate (%) was determined by subtracting from 100.

(Volatile content)
The foam particles immediately after foaming are used, and water adhering to the particle surface is blown off with an air stream and dehydrated. Then, the weight (W1) is measured, and the foam particles are further removed in an oven at 80 ° C. The weight (W2) when dried for 12 hours was measured and calculated by the following formula.
Volatiles (%) = (W1-W2) / W2 × 100

(Average bubble diameter L (av))
Cut almost the center of 20 randomly selected foamed particles, and observe the enlarged section. Here, the X axis and the Y axis perpendicular to each other at the approximate center of the cross section are drawn, the point where the X axis and the Y axis at the approximate center of the cross section intersect with each other is the center O, and the point where the X axis intersects with the end of the cross section. The points where the Y axis intersects the end of the cross section are designated as B and B ′.

  Next, the number of bubble walls intersected by the line segment OA is counted, and the value obtained by dividing the length of the line segment OA by the number of bubble walls is further divided by 0.616 to obtain the bubble diameter L (OA). That is, the bubble diameter L (OA) is obtained by the following equation (1).

線分ＯＡ’、線分ＯＢ、線分ＯＢ’についても同様に行い、それぞれＬ（ＯＡ’）、Ｌ（ＯＢ）、Ｌ（ＯＢ’）を求める。なお、気泡壁上に中心Ｏがある場合は、気泡壁として数えた。

The same processing is performed for the line segment OA ′, the line segment OB, and the line segment OB ′, and L (OA ′), L (OB), and L (OB ′) are obtained. In addition, when there was the center O on the bubble wall, it counted as a bubble wall.

  Four average values L ′ (av) of L (OA), L (OA ′), L (OB), and L (OB ′) are calculated, and L ′ (av) of 20 polypropylene-based resin expanded particles is calculated. Furthermore, the averaged value was defined as the average bubble diameter L (av).

(Bubble diameter variation S)
In the measurement of the average cell diameter, the cell diameter variation (S ′) in one expanded particle was calculated from the following equation (2).

２０個の発泡粒子の気泡径バラツキＳ’を平均した値を気泡径バラツキ（Ｓ）とした。

A value obtained by averaging the bubble size variation S ′ of the 20 expanded particles was defined as a bubble size variation (S).

(Expanded particle shrinkage / wrinkles)
○: The surface of the expanded particle is beautiful without wrinkles. ×: The surface of the expanded particle is wrinkled and the expanded particle is contracted.

(Two-stage foaming)
◯: No stick (with a plurality of foam particles attached) △: A small amount of stick occurs.
×: A high vapor pressure is required, and many sticks are generated

(Mold surface properties)
○: Less wrinkles, less intergranularity (dents and holes between foamed particles, etc.), beautiful △: Slight wrinkles, intergranular but good ×: Wrinkles or remarkable intergranularity, sink marks, etc. Yes, poor appearance

(Molded product fusion rate)
After a crack with a depth of about 5 mm is made on the surface of the foamed molded product with a knife, the foamed molded product is divided along the crack, the fracture surface is observed, and the ratio of the number of broken particles to the total number of particles observed is obtained. The molded product fusion rate was used.
The following reference example describes the method for selecting whether or not the water-absorbing substance has no foam nucleation function of the present invention.

(Reference Example 1)
Polypropylene resin A (propylene / ethylene / butene-1 random copolymer: ethylene content 2.6% by weight, butene-1 content 1.4% by weight, melt index 7 g / 10 min, melting point 145 ° C.) 50φ After feeding to a single screw extruder and melt-kneading at 200 ° C., extrusion from a cylindrical die with a diameter of 1.8 mm, water cooling, and cutting with a cutter to obtain cylindrical polypropylene resin particles (1.2 mg / grain) It was.

  100 parts by weight of the obtained polypropylene resin particles were put into a pressure-resistant sealed container together with 300 parts by weight of pure water, 1.0 part by weight of tricalcium phosphate and 0.05 part by weight of sodium dodecylbenzenesulfonate, and then deaerated. While stirring, 14 parts by weight of carbon dioxide gas was placed in a sealed container and heated to 149 ° C. The pressure in the sealed container at this time was 3 MPa (G). Immediately after opening the valve at the bottom of the sealed container, an aqueous dispersion containing polypropylene resin particles and an aqueous dispersion medium was released under atmospheric pressure through an orifice having a diameter of 4 mm to obtain polypropylene resin expanded particles. During discharge, the pressure was maintained with carbon dioxide gas so that the pressure in the container did not decrease.

  The average cell diameter of the polypropylene resin expanded particles not containing the additive thus obtained was 260 μm.

(Reference Example 2)
After blending 0.5 parts by weight of polyethylene glycol (average molecular weight 300, manufactured by Lion) as additive D with 100 parts by weight of polypropylene resin A, this is fed to a 50φ single screw extruder and melt kneaded at 200 ° C. The product was extruded from a cylindrical die having a diameter of 1.8 mm, cooled with water, and cut with a cutter to obtain cylindrical polyethylene glycol-containing polypropylene resin particles (1.2 mg / particle).

  Thereafter, polyethylene glycol-containing polypropylene resin expanded particles were produced in exactly the same manner as in Reference Example 1. Table 1 shows the average cell diameter of the obtained expanded particles. From a comparison with Reference Example 1, it can be seen that polyethylene glycol is a water-absorbing substance having no foam nucleation function of the present invention.

（参考例３）
添加剤Ｄのポリエチレングリコールの代わりに、添加剤Ｅとしてポリオレフィンブロックとポリアルキレングリコールブロックを有するブロック共重合体（ペレスタット３０３、三洋化成製）を用いた以外は参考例２と全く同様にしてポリプロピレン系樹脂発泡粒子を作製した。えられた発泡粒子の平均気泡径を表１に示す。参考例１との比較から、ポリオレフィンブロックとポリアルキレングリコールブロックを有するブロック共重合体は本発明の発泡核形成作用の無い吸水性物質であることがわかる。

(Reference Example 3)
Polypropylene system in exactly the same manner as in Reference Example 2, except that a block copolymer having a polyolefin block and a polyalkylene glycol block (Pelestat 303, manufactured by Sanyo Chemical Co., Ltd.) was used as additive E instead of polyethylene glycol as additive D. Resin foam particles were prepared. Table 1 shows the average cell diameter of the obtained expanded particles. From a comparison with Reference Example 1, it can be seen that the block copolymer having a polyolefin block and a polyalkylene glycol block is a water-absorbing substance having no foam nucleation function of the present invention.

(Reference Examples 4-9)
Polypropylene resin expanded particles were produced in exactly the same manner as in Reference Example 2 except that the following additives F to K were used instead of the additive D polyethylene glycol. Table 1 shows the volatile content and average cell diameter of the obtained foamed particles. It can be seen that any of the additives is a water-absorbing substance having no foam nucleation function of the present invention.

Additive F: Sodium polyacrylate (Aquakeep 10SH-NF, manufactured by Sumitomo Seika)
G: Sodium carboxymethylcellulose (MAC20, manufactured by Nippon Paper Chemicals)
H: Polyvinyl alcohol (PVA205S, manufactured by Kuraray)
I: Bentonite (Wenger Bright 25, manufactured by Hojun)
J: Synthetic hectorite (Laponite RD, manufactured by Toshin Kasei)
K: Synthetic zeolite (NX-100P, manufactured by Nippon Chemical)

(Reference Example 10)
Polypropylene resin expanded particles were prepared in exactly the same manner as in Reference Example 3 except that zinc borate (zinc borate 2335, manufactured by Tomita Pharmaceutical Co., Ltd.) was used as additive L instead of polyethylene glycol as additive D. Table 1 shows the average cell diameter of the expanded particles. It can be seen that this additive is not a water-absorbing substance having no foam nucleation function of the present invention.

  Next, examples of the present invention will be described.

Example 1
Polypropylene resin A (propylene / ethylene / butene-1 random copolymer: ethylene content 2.6 wt%, butene-1 content 1.4 wt%, melt index 7 g / 10 min, melting point 145 ° C.) 100 wt 0.5 parts by weight of additive D (polyethylene glycol having an average molecular weight of 300, manufactured by Lion) is pre-blended with respect to parts, and then 0.03 wt. Of talc (manufactured by Hayashi Kasei, Talcan powder PK-S) as a foam nucleating agent. Part was blended. This was supplied to a 50φ 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 put into a pressure-resistant sealed container together with 300 parts by weight of pure water, 2.0 parts by weight of tricalcium phosphate and 0.05 parts by weight of sodium dodecylbenzenesulfonate, and then deaerated. While stirring, 14 parts by weight of carbon dioxide gas was placed in a sealed container and heated to 149 ° C. The pressure in the sealed container at this time was 2.9 MPa (G). Further, carbon dioxide gas was added, and the temperature inside the sealed container was set to 3.3 MPa (G) and held for 10 minutes. Thereafter, the valve at the bottom of the sealed container was opened, and the aqueous dispersion (resin particles and aqueous dispersion medium) was released under atmospheric pressure through an orifice having a diameter of 4 mm to obtain polypropylene resin expanded particles (single-stage 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 obtained single-stage expanded particles showed two endothermic peaks at about 142 ° C. and about 159 ° C. in differential scanning calorimetry, and as a result of measuring the expansion ratio, the open cell ratio, and the average cell diameter, the expansion ratio was 15 times. The foam ratio was 0.6%, the volatile content ratio was 3.0%, the average bubble diameter was 270 μm, and the bubble diameter variation was 0.07, and the bubble diameter uniformity was excellent.

  The single-stage expanded particles obtained here were washed with an acid, dried at 60 ° C. for 6 hours, impregnated with pressurized air in a pressure-resistant container to bring the internal pressure to about 0.4 MPa, and then about 0.1 MPa. Two-stage foaming was performed by contacting with steam of 07 MPa (G) to obtain two-stage foamed particles having an expansion ratio of 30 times. As a result of observing the surface of the two-stage expanded foam particles with an electron microscope, it was found that the foam diameter of the surface portion was uniform, the surface was not rough, and the thickness of the foam particle surface film was small. . Next, the two-staged foamed particles were again pressurized with air in a pressure-resistant container to achieve an air pressure of about 0.2 MPa, and in-mold foam molding was performed. The surface of the foamed molded product was excellent in smoothness, no wrinkles were generated, the dimensional shrinkage of the foamed molded product was small, the distortion of the foamed molded product was small, the particles were fused well, and it was a beautiful foamed molded product. . The results are shown in Table 2.

（実施例２）
発泡核剤のタルク量を０．３重量部とし、二段発泡条件を表２記載の条件とした以外は実施例１と同様にして一段発泡粒子を得、次いで発泡倍率３０倍の二段発泡粒子とした後、型内成形した。得られた一段発泡粒子は示差走査熱量計測定において、約１４２℃と約１５９℃に２つの吸熱ピークを示し、気泡径の均一性は良好であった。また、二段発泡させた発泡粒子表面を電子顕微鏡にて観察した結果、表面部分の気泡径が均一で、かつ表面の粗れがなく、発泡粒子表面膜の厚みが薄い部分も少ない発泡粒子であった。その二段発泡粒子を使用し、型内発泡成形したところ、発泡成形体の表面は平滑性に優れ、しわの発生も無く、発泡成形体の寸法収縮が小さく、発泡成形体の歪が少なく、粒子どうしの融着に優れ、美麗な発泡成形体であった。結果を表２に示す。

(Example 2)
Single-stage foamed particles were obtained in the same manner as in Example 1 except that the amount of talc of the foam nucleating agent was 0.3 parts by weight and the two-stage foaming conditions were as shown in Table 2, followed by two-stage foaming with a foaming ratio of 30 times After forming particles, molding was performed in a mold. The obtained single-stage expanded particles showed two endothermic peaks at about 142 ° C. and about 159 ° C. in differential scanning calorimetry, and the bubble diameter uniformity was good. In addition, as a result of observing the surface of the expanded foam particles that have been two-stage expanded with an electron microscope, the foam diameter of the surface portion is uniform, the surface is not rough, and the expanded particle surface film has a small thickness. there were. Using the two-stage foamed particles, and foam molding in the mold, the surface of the foam molded body is excellent in smoothness, no wrinkles, dimensional shrinkage of the foam molded body, less distortion of the foam molded body, It was a beautiful foamed molded article with excellent fusion between particles. The results are shown in Table 2.

( Reference Examples 11-14, Examples 7-8 )
Additives F, G, H, J, and K are used in place of polyethylene glycol as additive D, and the amount of these additives and the amount of talc of the foam nucleating agent are those shown in Table 2, and the two-stage foaming conditions are shown. Except for the conditions described in 2, the first-stage expanded particles were obtained in the same manner as in Example 1, and then the second-stage expanded particles having an expansion ratio of 30 times were obtained, followed by in-mold molding. The obtained single-stage expanded particles showed two endothermic peaks at about 142 ° C. and about 159 ° C. in differential scanning calorimetry, and the bubble diameter uniformity was good. In addition, as a result of observing the surface of the expanded foam particles that have been two-stage expanded with an electron microscope, the foam diameter of the surface portion is uniform, the surface is not rough, and the expanded particle surface film has a small thickness. there were. Using the two-stage foamed particles, and foam molding in the mold, the surface of the foam molded body is excellent in smoothness, no wrinkles, dimensional shrinkage of the foam molded body, less distortion of the foam molded body, It was a beautiful foamed molded article with excellent fusion between particles. The results are shown in Table 2.

Example 9
For 100 parts by weight of polypropylene resin B (propylene / ethylene random copolymer: ethylene content 3.2% by weight, MI = 6 g / 10 min, melting point 142 ° C.), additive D (polyethylene glycol having an average molecular weight of 300, (Lion) 0.5 parts by weight was pre-blended, and then 0.05 parts by weight of talc (manufactured by Hayashi Kasei Co., Ltd., Talcan Powder PK-S) was added and blended. This was supplied to a 50φ 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 polyolefin resin particles (1. 2 mg / grain) was obtained.

  100 parts by weight of the obtained polypropylene resin particles were put into a pressure-resistant sealed container together with 200 parts of pure water, 2.0 parts by weight of tricalcium phosphate and 0.05 parts by weight of sodium dodecylbenzenesulfonate, and then deaerated and stirred. Then, 6 parts of carbon dioxide gas was put in a sealed container and heated to 148 ° C. The pressure in the sealed container at this time was 2.8 MPa (G). Further, carbon dioxide gas was added, and the temperature inside the sealed container was set to 3.0 MPa (G) and held for 10 minutes. Thereafter, the valve at the lower part of the sealed container is opened, and the aqueous dispersion containing the polypropylene resin particles and the aqueous dispersion medium is released under atmospheric pressure through an orifice having a diameter of 4 mm to obtain polypropylene resin expanded particles (single-stage expanded particles). Obtained. At this time, during discharge, the pressure was maintained with carbon dioxide gas so that the pressure in the container did not decrease.

  The obtained single-stage expanded particles showed two melting points at about 138 ° C. and about 157 ° C. in differential scanning calorimetry. As a result of measuring the expansion ratio, the open cell ratio, and the average cell diameter, the expansion ratio was 19 times. The ratio was 0.6%, the volatile content ratio was 3.1%, the average bubble diameter was 350 μm, the bubble diameter variation was 0.05, and the bubble diameter uniformity was excellent.

  The single-stage expanded particles obtained here were washed with an acid, dried at 60 ° C. for 6 hours, impregnated with pressurized air in a pressure-resistant container to bring the internal pressure to about 0.4 MPa, and then about 0.1 MPa. Two-stage foaming was performed by contacting with steam of 06 MPa (G) to obtain two-stage foamed particles having an expansion ratio of 30 times. As a result of observing the surface of the two-stage expanded foam particles with an electron microscope, it was found that the foam diameter of the surface portion was uniform, the surface was not rough, and the thickness of the foam particle surface film was small. . Next, the two-staged foamed particles were again pressurized with air in a pressure-resistant container to achieve an air pressure of about 0.2 MPa, and in-mold foam molding was performed. The surface of the foamed molded product was excellent in smoothness, no wrinkles were generated, the dimensional shrinkage of the foamed molded product was small, the distortion of the foamed molded product was small, the particles were fused well, and it was a beautiful foamed molded product. . The results are shown in Table 2.

(Examples 10 to 11)
In place of polyethylene glycol as additive D, additives E and I were used, the amounts of these additives and the amount of talc of the foam nucleating agent were those shown in Table 2, and the two-stage foaming conditions were those shown in Table 2. Except for the above, single-stage expanded particles were obtained in the same manner as in Example 9, and then formed into two-stage expanded particles with an expansion ratio of 30 times, followed by in-mold molding. The obtained single-stage expanded particles had two melting points at about 138 ° C. and about 157 ° C. in differential scanning calorimetry, and the bubble diameter uniformity was good. In addition, as a result of observing the surface of the expanded foam particles that have been two-stage expanded with an electron microscope, the foam diameter of the surface portion is uniform, the surface is not rough, and the expanded particle surface film has a small thickness. there were. Using the two-stage foamed particles, and foam molding in the mold, the surface of the foam molded body is excellent in smoothness, no wrinkles, dimensional shrinkage of the foam molded body, less distortion of the foam molded body, It was a beautiful foamed molded article with excellent fusion between particles. The results are shown in Table 2.

(Comparative Example 1)
Except that additive D was not used, and the two-stage foaming conditions were the same as those described in Table 3, after obtaining single-stage foamed particles in the same manner as in Example 1, and then into two-stage foamed particles with an expansion ratio of 30 times, Molded in-mold. The obtained single-stage expanded particles showed two endothermic peaks at about 142 ° C. and about 159 ° C. in differential scanning calorimetry, but the bubble diameter uniformity was poor and there were large and small variations. In the two-stage foaming, a high vapor pressure is required to increase the foaming ratio to 30 times, and a small amount of sticks to which the foamed particles adhere are observed. When the two-stage foamed particles were used and foam-molded in the mold, the dimensional shrinkage ratio of the foam-molded product was large, wrinkles were observed, and the appearance was poor. The results are shown in Table 3.

（比較例２〜３）
添加剤Ｄの代わりに添加剤Ｈ、Ｌを用い、これらの添加剤量、発泡核剤のタルク量を表３記載の量とし、二段発泡条件を表３記載の条件とした以外は実施例１と同様にして一段発泡粒子を得、次いで発泡倍率３０倍の二段発泡粒子とした後、型内成形した。

(Comparative Examples 2-3)
Examples except that additives H and L were used in place of additive D, the amounts of these additives and the amount of talc of the foam nucleating agent were those shown in Table 3, and the two-stage foaming conditions were those shown in Table 3. In the same manner as in No. 1, single-stage expanded particles were obtained, and then double-stage expanded particles having an expansion ratio of 30 times were obtained, followed by molding in a mold.

  When additive H was used and talc was not added, the obtained single-stage expanded particles showed two endothermic peaks at about 142 ° C. and about 159 ° C. in the differential scanning calorimetry measurement. It was bad and there were large and small variations. Further, in order to increase the expansion ratio to 30 times by two-stage foaming, a high vapor pressure is required, and many sticks to which the expanded particles adhere are observed. When these two-stage expanded particles were used and subjected to in-mold foam molding, the dimensional shrinkage ratio of the foam molded article was large, wrinkles were observed, and the appearance was inferior.

  When additive L was used and talc was not added, the uniformity of the bubble diameter of the single-stage expanded particles was good, but the bubble diameter was small, wrinkles were observed, and the expanded particles were contracted. In addition, when foam molding was performed in the mold, wrinkles were observed, and the fusing property was poor. The above results are shown in Table 3.

(Comparative Example 4)
Except that additive D was not used, and the two-stage foaming conditions were the same as those described in Table 3, after obtaining single-stage foamed particles in the same manner as in Example 9, and then into two-stage foamed particles with an expansion ratio of 30 times, Molded in-mold. The obtained single-stage expanded particles showed two melting points at about 138 ° C. and about 157 ° C. in differential scanning calorimetry, but the bubble diameters were slightly different. In the two-stage foaming, a high vapor pressure is required to increase the expansion ratio to 30 times, and many sticks to which the foamed particles adhere are observed. When the two-stage foamed particles were used and foam-molded in the mold, the dimensional shrinkage ratio of the foam-molded product was large, wrinkles were observed, and the appearance was poor. The results are shown in Table 3.

(Example 12)
Foaming was performed in the same manner as in Example 1 except that the addition amount of polyethylene glycol as additive D was 0.1 part by weight, and two endothermic peaks were observed at about 142 ° C. and about 159 ° C. in differential scanning calorimetry. Single-stage expanded particles were obtained. The expansion ratio was 9 times, and the average cell diameter was 250 μm. The relationship between the expansion ratio and the average cell diameter including the results of Example 1 is shown in FIG. The single-stage expanded particles obtained as described above and the single-stage expanded particles obtained in Example 1 were each pressurized with air in a pressure-resistant container to an air pressure of about 0.2 MPa, and subjected to in-mold foam molding to achieve a fusion rate. Evaluation was performed. The results are shown in Table 4.

本実施例においては発泡倍率が変化しても平均気泡径の変化が小さく、平均気泡径が変化することによる影響を受けずに、発泡倍率のコントロールが行えることがわかる。また、発泡倍率を増加させても発泡成形体の融着率が低下しないことがわかる。

In this example, it can be seen that even if the expansion ratio changes, the change in the average cell diameter is small and the expansion ratio can be controlled without being affected by the change in the average cell diameter. It can also be seen that the fusion rate of the foamed molded product does not decrease even when the expansion ratio is increased.

(Comparative Example 5)
Foaming was carried out in the same manner as in Comparative Example 3 except that the additive amount of zinc borate as additive L was changed to 0.01 part by weight or 0.1 part by weight. Single-stage expanded particles having two endothermic peaks at 0 ° C. were obtained. When the addition amount was 0.01 parts by weight, the expansion ratio was 8 times and the average cell diameter was 260 μm. When the addition amount was 0.1 parts by weight, the expansion ratio was 15 times and the average cell diameter was 190 μm. The relationship between the expansion ratio and the average cell diameter is shown in FIG. In addition, each single-stage expanded particle was pressurized with air in a pressure-resistant vessel to an air pressure of about 0.2 MPa, and in-mold foam molding was performed to evaluate the fusion rate. The results are shown in Table 4.

  In this comparative example, it can be seen that the average cell diameter changes greatly with an increase in the expansion ratio, and it is difficult to control the expansion ratio without significantly changing the average cell diameter. It can also be seen that when the expansion ratio is increased, the fusion rate of the foamed molded product decreases.

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. It is a graph which shows an expansion ratio and an average bubble diameter when changing the amount of additives and obtaining polypropylene resin expanded particles having different expansion ratios.

Claims (12)

It comprises 0.01 to 5 parts by weight of a water-absorbing substance having no foam nucleation effect and 0.005 to 1 part by weight of a foam nucleating agent with respect to 100 parts by weight of a polypropylene resin having a melt index of 2 to 9 g / 10 min. Polypropylene resin particles are dispersed in an airtight 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 released into a pressure region lower than the internal pressure of the airtight container to be foamed, and the volatile content rate 0.1 to 7% by weight, expansion ratio 8 to 25 times, average bubble diameter 130 to 500 μm, bubble diameter variation is less than 0.4,
A method for producing polypropylene resin expanded particles, comprising obtaining polypropylene resin expanded particles in which the water-absorbing substance having no foam nucleation function has a melting point lower than 150 ° C. It comprises 0.01 to 5 parts by weight of a water-absorbing substance having no foam nucleation effect and 0.005 to 1 part by weight of a foam nucleating agent with respect to 100 parts by weight of a polypropylene resin having a melt index of 2 to 9 g / 10 min. Polypropylene resin particles are dispersed in an airtight 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 released into a pressure region lower than the internal pressure of the airtight container to be foamed, and the volatile content rate 0.1 to 7% by weight, expansion ratio 8 to 25 times, average bubble diameter 130 to 500 μm, bubble diameter variation is less than 0.4,
A method for producing a polypropylene resin foamed particle, wherein the water-absorbing substance having no foaming nucleation action is at least one selected from bentonite, synthetic hectorite, and synthetic zeolite. Method for producing a foamed polypropylene resin particles according to claim 1, characterized in that introduced into the further closed container carbon dioxide. Method for producing a foamed polypropylene resin particles according to claim 2, characterized in that introduced into the further closed container a carbonated gas.   The method for producing expanded polypropylene resin particles according to claim 3, wherein 0.5 to 20 parts by weight of carbon dioxide gas is introduced into the sealed container with respect to 100 parts by weight of the polypropylene resin particles. The method for producing expanded polypropylene resin particles according to claim 4, wherein 0.5 to 20 parts by weight of carbon dioxide gas is introduced into the sealed container with respect to 100 parts by weight of the polypropylene resin particles. The method for producing expanded polypropylene resin particles according to any one of claims 1, 3, and 5 , wherein the water-absorbing substance having no foaming nucleus forming action is a compound having a polyalkylene glycol chain. The method for producing expanded polypropylene resin particles according to claim 7 , wherein the compound having a polyalkylene glycol chain is polyethylene glycol. The method for producing expanded polypropylene resin particles according to claim 7 , wherein the compound having a polyalkylene glycol chain is a copolymer comprising a polyolefin block and a polyethylene glycol block. A polypropylene resin foamed particle comprising 0.01 to 5 parts by weight of a water-absorbing substance having no foam nucleation function and 0.005 to 1 part by weight of a foam nucleating agent with respect to 100 parts by weight of a polypropylene resin, Melt index of the polypropylene resin expanded particles is 2 to 12 g / 10 minutes, volatile content is 0.1 to 7% by weight, expansion ratio is 8 to 25 times, average bubble diameter is 130 to 500 μm, and bubble diameter variation is less than 0.4 And
The polypropylene-based resin-based resin expanded particles, wherein the water-absorbing substance having no function of forming foam nuclei has a melting point lower than 150 ° C. A polypropylene resin foamed particle comprising 0.01 to 5 parts by weight of a water-absorbing substance having no foam nucleation function and 0.005 to 1 part by weight of a foam nucleating agent with respect to 100 parts by weight of a polypropylene resin, Melt index of the polypropylene resin expanded particles is 2 to 12 g / 10 minutes, volatile content is 0.1 to 7% by weight, expansion ratio is 8 to 25 times, average bubble diameter is 130 to 500 μm, and bubble diameter variation is less than 0.4 And
The polypropylene-based resin-based resin foamed particles, wherein the water-absorbing substance having no foam nucleation function is at least one selected from bentonite, synthetic hectorite, and synthetic zeolite. A polypropylene resin expanded particle (referred to as polypropylene resin expanded particle (P)) manufactured by the manufacturing method according to claim 1 or 2,
3. The production method according to claim 1, wherein the polypropylene resin foam particles (referred to as polypropylene resin foam particles (Q)) produced without containing a water-absorbing substance having no foam nucleation function are volatile fractions. In addition, in the average cell diameter, the polypropylene resin foamed particles satisfy the following formulas (A) and (B) and have a melt index of 2 to 12 g / 10 min of the polypropylene resin foamed particles (P). .
(A) Volatile fraction of polypropylene resin expanded particles (P) ≧ volatile fraction of polypropylene resin expanded particles (Q) × 1.1
(B) Average cell diameter of polypropylene resin expanded particles (P) ≧ average cell diameter of polypropylene resin expanded particles (Q) × 0.7

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