JP2013100554A - Pre-expanded particle of polyolefin resin, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide two-step expanded particles of polyolefin resin, which are reduced in impairment of productivity and restriction on facilities, and also reduced in magnification variations between expanded particles and bubble variations, and can provide, when used for in-mold expansion molding, an in-mold expansion molded product excellent in fusion bonding between two-step expanded particles, surface properties and dimensional accuracy.SOLUTION: The two-step expanded particles of polyolefin resin are obtained by expanding polyolefin resin particles composed of (a) a polyolefin resin containing, relative to 100 pts.wt. thereof, 0.2 pts.wt. or more and 5 pts.wt. or less of (b) a polyolefin-polyether block copolymer and 0.005 pts.wt. or more and 2 pts.wt. or less of (c) a foaming core agent to obtain first-step expanded particles; and further expanding the first-step expanded particles by pressuring them with an inorganic gas such as air in a pressure tight container to give an internal pressure thereto followed by vapor-heating.

Description

  The present invention relates to polyolefin resin pre-expanded particles (two-stage expanded particles) and a method for producing the same. More specifically, for example, the present invention relates to a polyolefin resin pre-expanded particle (two-stage expanded particle) that can be suitably used as a raw material for an in-mold expanded molded article, and a method for producing the same.

  In-mold foam molded products obtained by filling polyolefin resin pre-expanded particles in a mold and heat-molding with water vapor, etc., are the advantages of in-mold foam molded products, lightness, heat insulation, etc. With the characteristics of. This in-mold foam molded article is superior in chemical resistance, heat resistance, and strain recovery rate after compression, compared to an in-mold foam molded article obtained using polystyrene resin foam particles. It is suitably used for various applications such as a heat insulating material, a cushioning packaging material, an automobile interior member, and a core material for an automobile bumper.

  Conventionally, polyolefin resin particles are dispersed in a water-based 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. There are known depressurization foaming methods to obtain. 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 blowing agents are substances that have a greater global warming potential than carbon dioxide, and volatile organic blowing agents such as propane and butane are poorly soluble in water, so they are dispersed in water. It is difficult to uniformly impregnate the polyolefin-based resin particles, and it is difficult to control the expansion ratio and crystal state of the pre-expanded particles. 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 thermoplastic 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 economically producing polyolefin resin pre-foamed particles that can be used suitably for the production of in-mold foam molded products, a method that uses water used as a dispersion medium as a foaming agent is proposed. Has been.

For example, Patent Documents 4 and 5 use, as a raw material resin, a polypropylene resin to which a hydrophilic polymer is added in order to increase the amount of water impregnated in the resin when pre-expanded particles are produced using water as a foaming agent. A method is disclosed. It is disclosed that ionomer resins, cross-linked polyvinyl alcohol, cross-linked polyethylene oxide polymers and the like can be used as hydrophilic substances, and that ionomer resins are particularly preferably used. However, since the hydrophilic polymer is generally poorly dispersible in the polyolefin resin, when a polyolefin resin particle containing an ionomer resin is produced using a full flight screw in a general single screw extruder, the dispersion is not achieved. Because of the poorness, there was a tendency that the variation in the magnification between the pre-expanded particles was large, and the bubble variation was also large. For this reason, when obtaining the in-mold foam-molded product, there are problems that weight variation occurs and color unevenness is severe. By producing resin particles using a dalmage screw having high kneadability, the dispersion is improved to some extent, but it is not perfect, and there is also a problem that the maximum discharge amount is lowered and the productivity is greatly deteriorated. In addition, since the water content of the ionomer resin is low, it is necessary to add a large amount when trying to obtain a high magnification, and there is a reduction in strength of the in-mold foam molded body and surface wrinkles of the in-mold foam molded body, resulting in dimensional shrinkage, There was a problem of high cost.
Japanese Patent Publication No.56-1344 Japanese Patent Publication No. 4-64332 Japanese Examined Patent Publication No. 4-64334 International Publication No. WO 97/38048 Japanese Patent Laid-Open No. 10-152574

  The subject of the present invention relates to polyolefin resin pre-expanded particles (two-stage expanded particles), which impairs productivity and has few restrictions on facilities, and has small magnification variation between the pre-expanded particles (single-stage expanded particles) and small bubble variation. Polyolefin-based resin pre-foaming that can be used for in-mold foam molding to obtain in-mold foam molded products with excellent fusion, surface properties and dimensional accuracy between pre-foamed particles (two-stage foam particles) It is to provide particles (two-stage expanded particles).

  As a result of diligent research, the present inventors have determined from a polyolefin resin composition containing 0.2 to 5 parts by weight of a polyolefin / polyether block copolymer and a foam nucleating agent for 100 parts by weight of a polyolefin resin. It has been found that the above-mentioned problems can be solved by using the polyolefin resin particles, and the present invention has been completed.

  That is, the first of the present invention is that the polyolefin-polyether block copolymer (b) is 0.2 parts by weight or more and less than 5 parts by weight with respect to 100 parts by weight of the polyolefin resin (a), and the foam nucleating agent (c) 0 Polyolefin resin particles composed of a polyolefin resin containing 0.005 parts by weight or more and 2 parts by weight or less are expanded to obtain single-stage expanded particles, and the single-stage expanded particles are added with an inorganic gas such as air in a pressure-resistant container. The present invention relates to a polyolefin resin two-stage expanded particle that is further foamed by applying pressure and applying an internal pressure, followed by steam heating.

As a preferred embodiment,
(1) The polyolefin resin (a) is a polypropylene resin.
(2) The polyether part of the polyolefin / polyether block copolymer (b) is made of polyethylene glycol,
(3) The expansion ratio is 6 to 50 times, and the average cell diameter is 50 to 800 μm.
(4) The polyolefin resin comprises a hydrophilic substance (d) other than the polyolefin / polyether block copolymer,
(5) The hydrophilic substance (d) other than the polyolefin / polyether block copolymer is at least one selected from the group consisting of melamine, glycerols, and zinc borate, in an amount of 1 part by weight or less.
It relates to the polyolefin resin two-stage expanded particles described above.

  The second aspect of the present invention is that the polyolefin-polyether block copolymer (b) is 0.2 parts by weight or more and less than 5 parts by weight with respect to 100 parts by weight of the polyolefin resin (a), and the foaming nucleating agent (c) 0. Polyolefin resin particles comprising polyolefin resin containing 005 parts by weight or more and 2 parts by weight or less are dispersed in an airtight dispersion medium together with a foaming agent in a hermetic container, and heated to a temperature equal to or higher than the softening temperature of the polyolefin resin particles. After the pressure is released, the pressure is released to a pressure range lower than the internal pressure of the sealed container, the polyolefin resin particles are expanded to obtain single-stage expanded particles, and the single-stage expanded particles are added with an inorganic gas such as air in the pressure-resistant container. The method for producing a polyolefin resin two-stage foamed particle as described above, wherein the foam is further foamed by steam heating after applying pressure and applying an internal pressure. The have aspect, a method for producing a polyolefin resin bunk expanded particles of the described the use of carbon dioxide as a blowing agent.

  The polyolefin resin pre-expanded particles (single-stage expanded particles) of the present invention have small magnification variation and bubble variation between polyolefin pre-expanded particles (single-stage expanded particles). Further, when the polyolefin resin pre-expanded particles (two-stage expanded particles) of the present invention are used for in-mold foam molding, the mold is excellent in fusion between the foam particles of the in-mold foam molded article, surface property, and dimensional accuracy. An inner foamed molded product is obtained.

  The method for producing polyolefin resin pre-expanded particles (two-stage expanded particles) according to the present invention can reduce the environmental burden without impairing productivity and suppressing elution of organic substances into the aqueous dispersion medium.

The polyolefin resin pre-expanded particles (one-stage expanded particles) of the present invention have a polyolefin-polyether block copolymer (b) of 0.2 parts by weight or more and less than 5 parts by weight with respect to 100 parts by weight of the polyolefin resin (a). The foaming nucleating agent (c) is made by foaming polyolefin resin particles comprising a polyolefin resin containing 0.005 part by weight or more and 2 parts by weight or less .

  The polyolefin / polyether block copolymer (b) used in the present invention is a block copolymer in which a polyether portion composed of polyethylene glycol or polypropylene glycol and a polyolefin portion composed of polyethylene or polypropylene are alternately bonded, Can be appropriately selected and used.

  Polyolefin / polyether block copolymers that are generally available include the constitutional unit structure and polymerization molecular weight of the polyolefin part, the constitutional unit structure and polymerization molecular weight of the polyether part, and the repetition number of alternating bonds between the polyolefin part and the polyether part. Different versions of each element are provided. There are no particular limitations on the elements that characterize these polyolefin / polyether block copolymers, but the pre-expanded particles (single-stage expanded particles) that the polyether portion of the polyolefin / polyether block copolymer (b) is made of polyethylene glycol. ) Is reduced, and the resulting pre-expanded particles (two-stage expanded particles) are preferable because they do not cause poor fusion when used for in-mold molding.

  The melting point of the polyolefin / polyether block copolymer is preferably not less than the melting point of the polyolefin resin used as the base of the polyolefin resin particles −50 ° C. or higher and the melting point of the polyolefin resin + 40 ° C. or lower, more preferably the polyolefin resin. The melting point is preferably in the range of −40 ° C. to the melting point of the polyolefin resin + 20 ° C., more preferably the melting point of the polyolefin resin −30 ° C. to the melting point of the polyolefin resin + 10 ° C. If the melting point is not within the above range, the dispersibility of the polyolefin / polyether block copolymer in the base polyolefin resin is poor, and the effect of reducing the pre-expanded particle (single-stage expanded particle) variation in magnification and the effect of reducing bubble variation Tends to be lost.

  The number average molecular weight (Mn) of the polyolefin / polyether block copolymer is preferably 2000 or more and 60000 or less, more preferably 4000 or more and 40000 or less, and further preferably 5000 or more and 30000 or less. Within the said range, there exists a tendency for the heat resistance of the in-mold foaming molding obtained to become favorable.

  Further, as the polyolefin / polyether block copolymer, a substance containing a metal salt in the polyolefin / polyether block copolymer can also be used. Such materials generally have antistatic properties and are commercially available as polyolefin / polyether block copolymer antistatic agents.

  Examples of such a polyolefin / polyether block copolymer include “Pelestat 330”, “Pelestat 300”, and “Pelestat 230” manufactured by Sanyo Chemical Industries, Ltd.

  The amount of the polyolefin-polyether block copolymer used is 0.2 to 5 parts by weight, preferably 0.3 to 2 parts by weight, based on 100 parts by weight of the polyolefin resin. If the amount of polyolefin / polyether block copolymer used is less than 0.2 parts by weight, only polyolefin resin pre-expanded particles (single-stage expanded particles) with a low expansion ratio can be obtained. When trying to obtain pre-expanded particles (single-stage expanded particles) at a magnification, the amount of other hydrophilic substances used cannot be reduced. If the amount of the polyolefin / polyether block copolymer used exceeds 5 parts by weight, the whiteness of the resulting polyolefin-based pre-expanded particles (single-stage expanded particles) will decrease, and the strength will decrease. Shrinkage tends to occur immediately after the foamed particles (first-stage foamed particles) are foamed, and the strength of the in-mold foam molded product tends to decrease, and the cost increases.

In the present invention, a hydrophilic substance (d) other than the polyolefin / polyether block copolymer may be used in combination. The hydrophilic substance is a substance that increases the amount of impregnated moisture in the resin when producing expanded particles. As a specific example of the hydrophilic substance (d) other than the polyolefin / polyether block copolymer, sodium chloride is used. Water-soluble inorganic substances such as calcium chloride, magnesium chloride, borax, calcium borate, zinc borate; water-absorbing organic substances such as melamine, isocyanuric acid, melamine / isocyanuric acid condensate; And hydrophilic polymers such as C _{12 to} C ₁₈ fatty alcohols such as pentaerythritol, cetyl alcohol and stearyl alcohol. Furthermore, hydrophilic substances described in International Publication No. WO97 / 38048 and JP-A-10-152574 can also be used. Two or more of these hydrophilic substances such as water-soluble inorganic substances, water-absorbing organic substances and hydrophilic polymers may be used in combination.

  Among them, the use of melamine, glycerols, and zinc borate makes it easy to obtain a high expansion ratio even when added in small amounts. It is preferable without impairing moldability.

  The addition amount of the hydrophilic substance (d) other than the polyolefin / polyether block copolymer is desirably 1 part by weight or less of the polyolefin-based resin, preferably 0.7 part by weight or less, and more preferably 0.5 part by weight. Or less. When the amount of the hydrophilic substance (d) other than the polyolefin / polyether block copolymer exceeds 1 part by weight, the resulting pre-expanded polyolefin resin particles (one-stage or two-stage foam) have non-uniform cells. And in-mold foam moldability may be poor.

  More preferably, 1 part by weight or less of at least one selected from the group consisting of melamine, glycerols and zinc borate is added to 100 parts by weight of the polyolefin resin.

  The foam nucleating agent (c) used in the present invention refers to a substance that promotes the formation of bubble nuclei during foaming. For example, talc, calcium carbonate, silica, kaolin, barium sulfate, magnesium hydroxide, calcium hydroxide, water Examples thereof include inorganic substances such as aluminum oxide, aluminum oxide, titanium oxide and zeolite, and fatty acid metal salts such as calcium stearate and barium stearate. These foam nucleating agents may be used alone or in combination of two or more. Among these, talc, calcium carbonate, and calcium stearate are preferable because uniform bubbles can be easily obtained when used in combination with the polyolefin / polyether block copolymer.

  The amount of the foam nucleating agent (c) varies depending on the foam nucleating agent to be used and cannot be generally determined, but is 0.005 to 2 parts by weight with respect to 100 parts by weight of the polyolefin resin. The content is preferably 0.01 parts by weight or more and 1 part by weight or less. For example, when talc is used as the foam nucleating agent, the amount is preferably 0.005 parts by weight or more and 1 part by weight or less, more preferably 0.01 parts by weight or more and 0.001 part by weight or less with respect to 100 parts by weight of the polyolefin resin. 5 parts by weight or less, more preferably 0.02 parts by weight or more and 0.2 parts by weight or less.

  When the addition amount of the foam nucleating agent is less than 0.005 parts by weight, there is a problem that the expansion ratio of the polyolefin resin pre-expanded particles (single-stage expanded particles) cannot be increased and the uniformity of the bubbles is lowered. When the amount of the foam nucleating agent added is more than 2 parts by weight, the average cell diameter of the polyolefin resin pre-expanded particles (single-stage expanded particles) becomes too small, and the secondary foam of the pre-expanded particles (single-stage expanded particles or two-stage expanded particles) Foamability is lowered and in-mold foam moldability becomes poor.

  Various additives such as a compatibilizer, an antistatic agent, a colorant, a stabilizer, a weathering agent, and a flame retardant can be appropriately added to such an extent that the effects of the present invention are not impaired.

  The polyolefin resin used in the present invention may be a polyolefin resin conventionally used, and examples thereof include a polypropylene resin and a polyethylene resin.

  Examples of the polypropylene resin 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.

  The melting point of the polypropylene resin that can be used in the present invention is preferably 130 to 160 ° C, more preferably 135 to 150 ° C. When the melting point is less than 130 ° C., heat resistance and mechanical strength tend to be insufficient. Moreover, when melting | fusing point exceeds 160 degreeC, there exists a tendency for it to become difficult to ensure the fusion | fusion at the time of in-mold foam molding. In addition, the low-melting point resin can be used together to increase the fusion of pre-expanded particles (two-stage expanded particles) during in-mold molding, and the high melting point resin can be used together to maintain the shape immediately after in-mold molding. It can also be made easier.

  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.

  The melt index (hereinafter referred to as MI value) of the polypropylene resin is preferably 0.5 to 30 g / 10 minutes, and more preferably 2 to 20 g / 10 minutes.

  When the MI value is less than 0.5 g / 10 minutes, it is difficult to obtain high-expanding polyolefin resin pre-expanded particles (single-stage expanded particles or double-stage expanded particles). Bubbles of the expanded particles (one-stage expanded particles or two-stage expanded particles) tend to break, and the open-cell ratio of the polyolefin resin pre-expanded particles (first-stage expanded particles or two-stage expanded particles) tends to increase.

  In the present invention, the MI value is a value measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  In addition to polypropylene resins, other thermoplastic resins such as low density polyethylene, linear density polyethylene, polystyrene, polybutene, and ionomer may be mixed and used as long as the properties of the polypropylene resin are not lost. good.

  Examples of polyethylene resins include high density polyethylene resins, low density polyethylene resins, linear low density polyethylene resins, ethylene homopolymers, ethylene-α-olefin random copolymers, ethylene-α-olefins. Examples thereof include block copolymers. Examples of the α-olefin include α-olefins having 3 to 15 carbon atoms, and these may be used alone or in combination of two or more. Further, two or more of the aforementioned ethylene homopolymer, ethylene-α-olefin random copolymer, and ethylene-α-olefin block copolymer may be used in combination.

  Among these, in particular, an ethylene-propylene random copolymer, an ethylene-octene-1 random copolymer, and an ethylene-4-methyl-1-pentene random copolymer exhibit good foaming properties and can be suitably used. Further, the copolymer polymer is preferable because it has a characteristic that it can be easily impregnated with the carbon dioxide gas used in the present invention as compared with the homopolymer.

  The polyolefin resin is usually melted using an extruder, kneader, Banbury mixer, roll, etc. so that pre-expanded particles (single-stage expanded particles) can be easily produced. It is preferably processed into a resin particle shape such as a shape. As for the size of the resin particles, the weight of one particle is preferably 0.1 mg to 30 mg, and more preferably 0.3 mg to 10 mg. The weight of one resin particle is an average resin particle weight obtained from 100 resin particles randomly, and is expressed in mg / particle.

  In the present invention, water is used as the foaming agent. In the present invention, “use water as a foaming agent” can be determined, for example, by measuring the water content. As another method, it is also possible to measure pre-expanded particles (single-stage expanded particles) immediately after expansion with a polymer moisture meter or a Karl Fischer moisture meter.

  In the present invention, water may be used as a foaming agent, and other physical foaming agents may be used in combination. Other physical blowing agents include saturated hydrocarbons such as propane, butane and pentane, ethers such as dimethyl ether, alcohols such as methanol and ethanol whose boiling point is lower than the foamable temperature, air, nitrogen, carbon dioxide, etc. An inorganic gas is mentioned. Among them, it is desirable to use carbon dioxide gas because it has a particularly low environmental load and no danger of combustion.

  By using water and carbon dioxide in combination, it is easy to increase the foaming power, so even when obtaining a high expansion ratio, the amount of foam nucleating agent added can be reduced, resulting in preliminary foaming with a large average cell diameter. Particles (single-stage foam particles or double-stage foam particles) are obtained, and the secondary foamability tends to be good.

  The polyolefin resin pre-expanded particles (one-stage expanded particles) of the present invention are, for example, 0.2 parts by weight or more and 5 parts by weight of a polyolefin / polyether block copolymer (b) with respect to 100 parts by weight of the polyolefin resin (a). Less than, foaming nucleating agent (c) 0.005 parts by weight or more and 2 parts by weight or less, and polyolefin resin particles containing a hydrophilic substance (d) other than the polyolefin / polyether block copolymer as necessary, Disperse together with a foaming agent in an aqueous dispersion medium in a sealed container, heat and pressurize to a temperature higher than the softening temperature of the polyolefin resin, and then release it to a pressure range lower than the internal pressure of the sealed container to foam the polyolefin resin particles. Although it is obtained by this, the water which is a dispersion medium acts as a foaming agent. In addition, nitrogen or air is injected before releasing into the low pressure region, thereby increasing the internal pressure in the sealed container, adjusting the pressure release speed during foaming, and adjusting the foaming ratio and the average cell diameter. When a gaseous physical foaming agent such as carbon dioxide gas is used at room temperature, the polyolefin resin particles and water are introduced into a sealed container, and then a physical foaming agent such as carbon dioxide gas is introduced into the container.

  Specifically, for example, the following procedure can be used.

  Carbon dioxide gas in which the internal pressure of the sealed container becomes about 1 to 3 MPa after the polyolefin container is charged with polyolefin resin particles, an aqueous dispersion medium, and a dispersant as necessary, and then the inside of the sealed container is evacuated as necessary. And heated to a temperature equal to or higher than the softening temperature of the polyolefin resin. By heating, the pressure in the sealed container rises to about 1.5 MPa to 4 MPa. Carbon dioxide is added near the foaming temperature to adjust the foaming pressure to the desired level, and after adjusting the temperature, it is discharged into a pressure range lower than the internal pressure of the sealed container to give polyolefin resin pre-expanded particles (single-stage expanded particles) )

  Alternatively, after preparing polyolefin resin particles, aqueous dispersion medium, and dispersing agent if necessary in an airtight container, the inside of the airtight container is evacuated and then heated to a temperature equal to or higher than the softening temperature of the polyolefin resin. Carbon dioxide gas may be introduced while being introduced.

  In addition, after preparing polyolefin resin particles, aqueous dispersion medium, and dispersing agent if necessary in a closed container, heating to near the foaming temperature, introducing air or nitrogen, etc., and setting the foaming temperature, the sealed container The polyolefin resin pre-expanded particles (single-stage expanded particles) are obtained by discharging into a pressure range lower than the internal pressure.

  The expansion ratio of the polyolefin resin pre-expanded particles (single-stage expanded particles) obtained by the production method of the present invention is preferably 6 to 50 times, more preferably 10 to 25 times, and more preferably. It is 10 times or more and 20 times or less.

  If the expansion ratio is less than 6 times, the advantage of weight reduction cannot be obtained, and the flexibility and buffering properties of the obtained in-mold foam molded product tend to be insufficient. There is a tendency that the dimensional accuracy, mechanical strength, heat resistance and the like of the in-mold foam-molded product are insufficient.

  In the present invention, the polyolefin resin pre-expanded particles (single-stage expanded particles) obtained by the above-mentioned method are pressurized with an inorganic gas such as air in a pressure-resistant container, and after applying internal pressure, steam heating is performed. Further foaming may be used to further increase the magnification.

  In the present invention, the polyolefin resin particles are dispersed in an aqueous dispersion medium in a sealed container, impregnated with a foaming agent at high temperature and high pressure, and released into a pressure region lower than the internal pressure of the sealed container for foaming. This is called “single-stage foaming”, and the polyolefin resin pre-foamed particles obtained by single-stage foaming may be called “single-stage foamed particles”.

  Furthermore, pressurizing the single-stage expanded particles with an inorganic gas such as air in a pressure vessel, for example, applying internal pressure, and further foaming by steam heating is referred to as “two-stage expansion”. The polyolefin resin pre-expanded particles obtained by foaming may be referred to as “two-stage expanded particles”.

  In the present invention, when the polyolefin resin pre-expanded particles having an expansion ratio of 20 times or more are to be obtained, the first-stage expanded particles obtained by the first-stage expansion can be further two-stage expanded.

In the present invention, the expansion ratio of the polyolefin resin pre-expanded particles (one-stage expanded particles or two-stage expanded particles) is the weight w (g) of the polyolefin resin pre-expanded particles (single-stage expanded particles or two-stage expanded particles). After the measurement, the volume v (cm ³ ) is measured by a submerging method to determine the true specific gravity ρb = w / v of the polyolefin resin foamed particles, which is a ratio with the density ρr of the polyolefin resin particles before foaming.

  The average cell diameter of the polyolefin resin pre-expanded particles (one-stage expanded particles or two-stage expanded particles) of the present invention is preferably 50 μm or more and 800 μm or less, more preferably 100 μm or more and 600 μm or less, and further preferably 200 μm or more and 500 μm or less. is there. When the average cell diameter is less than 50 μm, there are cases where the shape of the obtained in-mold foam molded product is distorted and the surface is wrinkled. When the average cell diameter exceeds 800 μm, the buffer properties of the in-mold foam molded product to be obtained May decrease.

  The open cell ratio of the polyolefin resin pre-expanded particles (one-stage expanded particles or two-stage expanded particles) of the present invention is preferably 0 to 12%, more preferably 0 to 8%, still more preferably 0 to 5%. is there. When the open cell ratio exceeds 12%, when used for in-mold molding, the foamed particles are inferior in foamability during steam heating in the mold, and the obtained in-mold foam molded product tends to shrink. is there.

  The polyolefin resin pre-expanded particles (one-stage expanded particles or two-stage expanded particles) of the present invention preferably have two or more melting peaks in a DSC curve obtained by differential scanning calorimetry. In the case of polyolefin-based resin foamed particles having two or more melting peaks, in-mold foam moldability is good, and an in-mold foam molded article having good mechanical strength and heat resistance tends to be obtained.

  Here, the DSC curve obtained by differential scanning calorimetry of polyolefin-based resin pre-expanded particles (single-stage expanded particles or double-stage expanded particles) is 1-10 mg of polyolefin-based resin expanded particles measured at 10 ° C./min with a differential scanning calorimeter. DSC curve obtained when the temperature is raised from 40 ° C. to 220 ° C.

  As described above, the polyolefin resin pre-expanded particles (one-stage expanded particles or two-stage expanded particles) having two melting peaks can be easily obtained by setting the temperature in the sealed container at the time of the first stage expansion to an appropriate value. When the polyolefin resin is a polyolefin resin, the softening temperature of the polyolefin resin particles impregnated with the foaming agent is usually not less than the melting point of the polyolefin resin serving as the base material, preferably not less than the melting point + 3 ° C., preferably less than the melting end temperature. Is selected from a melting end temperature of −2 ° C. or lower.

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

  When the polyolefin resin pre-expanded particles (two-stage expanded particles) obtained in the present invention are used for in-mold foam molding, the following conventionally known methods can be used. B) A method for use as it is, b) A method for injecting an inorganic gas such as air into the two-stage foamed particles in advance to give foaming ability, and c) A method for filling the two-stage foamed particles into a mold in a compressed state and molding. .

Among these, the method (b) in which an inorganic gas such as air is press-fitted into pre-expanded particles (two-stage expanded particles) in advance to impart foaming ability is preferable. Specifically, an in-mold foam molded product can be obtained by the following in-mold foam molding method.
1) The polyolefin resin pre-expanded particles (two-stage expanded particles) are pressurized with air in a pressure-resistant container, and the foaming ability is imparted by press-fitting air into the polyolefin-based resin pre-expanded particles (two-stage expanded particles).
2) The obtained polyolefin resin pre-expanded particles (two-stage expanded particles) are filled into a molding space consisting of two molds that can be closed but cannot be sealed.
3) Molding with a water vapor pressure of about 0.2 to 0.4 MPa (G) and a heating time of about 3 to 30 seconds using water vapor or the like as a heating medium to melt the polyolefin resin pre-expanded particles (two-stage expanded particles). Put on.
4) Cool the mold with water.
5) Open the mold and take out the in-mold foam molding.

  The in-mold expanded molded article using the polypropylene resin pre-expanded particles (two-stage expanded particles) obtained in the present invention can be used for applications such as a heat insulating material, a buffer packaging material, an automobile interior member, and a core material for an automobile bumper. it can. It is particularly desirable to use a foam using the pre-expanded particles (two-stage expanded particles) obtained in the present invention for a shock-absorbing packaging material in which an in-mold expanded molded body with a high expansion ratio is often used. It is.

  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 pre-expanded particles (single-stage expanded particles or double-stage expanded particles), dry at 60 ° C. for 6 hours, measure the weight w (g), and then measure the volume v (cm ³ ) by the submersion method. The true specific gravity ρb = w / v of the pre-expanded particles was determined, and the expansion ratio K = ρr / ρb was determined from the ratio to the density ρr of the polyolefin resin particles before foaming.

(Magnification variation R)
1 kg of the polyolefin-based resin expanded particles was added to a standard sieve (nominal dimensions 1, 1.18, 1.4, 1.7, 2, 2.36, 2.8, 3.35, JIS Z8801 (1994) attached table 2. 11 sieves (4, 4.75, 5.6). The weight fraction Wi and the expansion ratio Ki of the polyolefin resin pre-expanded particles remaining on each sieve are measured, and the average expansion ratio Kav is calculated from the following formula (1).

Next, using the weight fraction Wi, the expansion ratio Ki, and the average expansion ratio Kav, the formula (2)

Calculate the standard deviation σm of the foaming ratio from the equation (3)

From this, the magnification variation R (%) was determined.

The expansion ratio Ki of the polyolefin-based resin pre-expanded particles (one-stage expanded particles or two-stage expanded particles) remaining on each sieve was determined as follows. The weight Gi of polyolefin resin foam particles remaining on each sieve is accurately weighed to 0.001 g (rounded off to the fourth decimal place), and then the weighed polyolefin resin pre-foamed particles of known weight are added to 100 ml of water at 23 ° C. The volume yi (cm ³ ) of the polyolefin resin foamed particles is read from the scale that rises when submerged in the water in the graduated cylinder in which the polyolefin resin is contained, and the weight Gi (g) of the polyolefin resin foamed particles is calculated as the polyolefin resin. The apparent density di of the polyolefin resin pre-expanded particles of each sieve is obtained by dividing by the volume yi (cm ³ ) of the expanded particles and converting this to g / L units. Finally, the expansion ratio Ki = ds / di was determined from the ratio with the density ds (= 900 g / L) of the base resin.
A: R value is less than 5% B: R value is 5% or more and less than 8% Δ: R value is 8% or more and less than 10% X: R value is 10% or more and less than 15% XX: R Value is over 15%

(Bubble uniformity, average bubble diameter)
Carefully pay attention not to break the bubble film, cut the expanded particles almost at the center, expand the cut surface with a microscope, and remove the pre-expanded particles from the surface of the pre-expanded particles (single-stage expanded particles or double-stage expanded particles). The following measurement was performed on the portion (A) excluding the surface layer portion having a thickness corresponding to 5% of the diameter. When an arbitrary direction is an x direction and a direction orthogonal to the x direction is a y direction, the ferret diameters dx and dy of a cell are measured in the x and y directions. Ask for.
di = (dx + dy) / (2 × 0.785)

The di is measured for 40 or more consecutively adjacent bubbles so that there is no deviation in the radial direction in the portion (A). The average bubble diameter d and the variation coefficient u of the bubble diameter of one pre-expanded particle (one-stage expanded particle or two-stage expanded particle) are calculated by the following equations. Here, n is the number of bubbles measured for di, and σ is the standard deviation of the bubble diameter.
d = Σ (di) / n
u = σ / d × 100
U is determined for three or more pre-expanded particles (single-stage expanded particles or double-stage expanded particles), and the average is U. Bubble uniformity was evaluated according to the following criteria.
◎: U is 30 or less ○: U exceeds 30 and 35 or less ×: U is more than 35

(Formability)
In the molding evaluation, a mold having an in-mold foam molded body design outer dimension of 400 mm × 300 mm × 20 mm was used.

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

(Surface properties of molded products)
After molding, the mixture was allowed to stand at 23 ° C. for 2 hours, then cured at 65 ° C. for 6 hours, and then allowed to stand in a room at 23 ° C. for 4 hours. .
◎: Wrinkles, less intergranular, beautiful ○: Slight wrinkles, intergranular but good x: Wrinkles, sink marks and poor appearance

(Dimension shrinkage of molded product)
After molding, it is allowed to stand at 23 ° C. for 2 hours, then cured at 65 ° C. for 6 hours, and then measured for the longitudinal dimension of the in-mold foam molded product obtained by leaving it in a room at 23 ° C. for 4 hours. The ratio of the difference between the mold dimension and the dimension of the in-mold foam molded body with respect to the mold dimension was defined as the mold dimension shrinkage rate, and was evaluated according to the following criteria.
◎: Dimensional shrinkage ratio against mold is 4% or less ○: Dimensional shrinkage ratio against mold exceeds 4% and 7% or less ×: Dimensional shrinkage ratio against mold is larger than 7%

Example 1
Polypropylene-polyethylene glycol block copolymer (Sanyo Kasei Co., Ltd.) with respect to 100 parts by weight of polypropylene resin (propylene-ethylene random copolymer: ethylene content 3.0%, MI = 6 g / 10 min, melting point 143 ° C.) ), Pelestat 303, melting point 135 ° C.) and 0.5 parts by weight of talc (manufactured by Hayashi Kasei Co., Ltd., Talcan powder PK-S) were added and dry blended. After feeding to a single screw extruder equipped with a 50 mm full flight screw, melt kneading, extruding from a cylindrical die having a diameter of 1.8 mm, water cooling, cutting with a cutter, and cylindrical polyolefin resin particles (1.2 mg / Grain) was obtained.

  100 parts by weight of the obtained polyolefin resin particles were put into a pressure-resistant sealed container together with 200 parts by weight of pure water, 0.5 part by weight of tricalcium phosphate and 0.03 part by weight of sodium dodecylbenzenesulfonate, and then deaerated. While stirring, 6 parts by weight of carbon dioxide gas was placed in a sealed container and heated to 148 ° C. The pressure at this time was 3 MPa. Immediately after opening the valve at the bottom of the sealed container, the aqueous dispersion (resin particles and aqueous dispersion medium) was discharged under atmospheric pressure through an orifice having a diameter of 4 mm to obtain pre-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 first-stage expanded particles showed two melting points at 136 ° C. and 156 ° C. in differential scanning calorimetry, and the expansion ratio was 9 times, which was higher than in the case of Comparative Examples 1, 2 and 6. . The uniformity of the bubbles was excellent, the average bubble diameter was 194 μm, and the magnification variation R was 7. The single-stage expanded particles obtained here were dried at 60 ° C. for 6 hours, then impregnated with pressurized air in a pressure-resistant container to set the internal pressure to about 0.4 MPa, and about 0.09 MPa of steam and Two-stage foaming was carried out by contacting to obtain two-stage foamed particles having an expansion ratio of 30 times. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, and had an average bubble diameter of 289 μm and excellent bubble uniformity. As a result of observing the surface of the two-stage expanded pre-expanded particles with an electron microscope, it was a two-stage expanded particle having a uniform cell diameter and no surface roughness. Next, the pre-expanded particles that had been two-stage expanded were again pressurized with air in a pressure resistant container to an air pressure of about 0.19 MPa, and in-mold foam molding was performed. The surface of the molded in-mold foamed product has excellent smoothness, no wrinkles, small dimensional shrinkage of the molded product, little distortion of the molded product, excellent fusion between particles, and beautiful in-mold foaming It was a molded body.

(Example 2)
Foaming, two-stage foaming, and in-mold molding were performed in the same manner as in Example 1 except that 0.75 parts by weight of the polypropylene / polyethylene glycol block copolymer as an additive and 0.1 parts by weight of talc were used. The first-stage expanded particles had two melting points, an expansion ratio of 11 times, excellent bubble uniformity, an average cell diameter of 234 μm, and a ratio variation R of 4 was excellent. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, had an average cell diameter of 327 μm and excellent cell uniformity. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the molded body is small, distortion of the molded body is small, and the particles are fused. It was an excellent and beautiful in-mold foam molding.

(Example 3)
Foaming, two-stage foaming, and in-mold molding were performed in the same manner as in Example 1 except that 1 part by weight of the polypropylene / polyethylene glycol block copolymer as an additive was used. The single-stage expanded particles obtained by the single-stage expansion exhibited two melting points, the expansion ratio was 12 times, the bubble uniformity was excellent, and the average bubble diameter was 246 μm. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, had excellent bubble uniformity, an average bubble diameter of 333 μm, and a magnification variation R of 4. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the molded body is small, distortion of the molded body is small, and particles are fused. It was an excellent and beautiful in-mold foam molding.

Example 4
Foaming, two-stage foaming, and in-mold molding were performed in the same manner as in Example 1 except that the additive polypropylene / polyethylene glycol block copolymer was 4.5 parts by weight. The single-stage expanded particles obtained by the single-stage expansion showed two melting points, the expansion ratio was 19 times, and the average cell diameter was 288 μm. The uniformity of the bubbles was almost uniform, although somewhat inferior to Examples 1-3. The magnification variation R was 2 and excellent. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, had an average cell diameter of 335 μm, and had excellent cell uniformity. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the molded body is small, distortion of the molded body is small, and the particles are fused. It was an excellent and beautiful in-mold foam molding.

(Example 5)
0.5 parts by weight of polypropylene / polyethylene glycol block copolymer as an additive, 0.2 parts by weight of melamine (manufactured by Nissan Chemical Industries, Ltd.) and 0.03 parts by weight of talc as other hydrophilic additives Was foamed, two-stage foamed and molded in-mold as in Example 1. The first-stage expanded particles obtained by the first-stage expansion exhibited two melting points, the expansion ratio was 9 times, and the average cell diameter was 380 μm. The uniformity of the bubbles was almost uniform, although somewhat inferior to Examples 1-3. The magnification variation R was as excellent as 7. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, and had an average bubble diameter of 567 μm and excellent bubble uniformity. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the molded body is small, distortion of the molded body is small, and the particles are fused. It was an excellent and beautiful in-mold foam molding.

(Example 6)
0.5 parts by weight of polypropylene / polyethylene glycol block copolymer as additive, 0.2 parts by weight of melamine (manufactured by Nissan Chemical Industries, Ltd.) and 0.2 part by weight of talc as other hydrophilic additives In the same manner as in Example 1, foaming, two-stage foaming, and in-mold molding were performed. The first-stage expanded particles obtained by the first-stage expansion showed two melting points, the expansion ratio was 16 times, and the average cell diameter was 252 μm. The uniformity of the bubbles was almost uniform, although somewhat inferior to Examples 1-3. The magnification variation R was as excellent as 3. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles exhibited two melting points in the differential scanning calorimeter measurement, and had an average cell diameter of 311 μm and excellent bubble uniformity. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the molded body is small, distortion of the molded body is small, and the particles are fused. It was an excellent and beautiful in-mold foam molding.

(Example 7)
0.5 parts by weight of an additive polypropylene / polyethylene glycol block copolymer, 0.2 parts by weight of polyethylene glycol (manufactured by Lion Corporation, # 300) as a hydrophilic additive, 0.1 part by weight of talc In the same manner as in Example 1, foaming, two-stage foaming, and in-mold molding were performed. Single-stage expanded particles obtained by single-stage expansion showed two melting points, an expansion ratio of 17 times, and an average cell diameter of 301 μm. Excellent uniformity of bubbles. The magnification variation R was excellent at 1. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, and had an average cell diameter of 364 μm and excellent bubble uniformity. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the molded body is small, distortion of the molded body is small, and the particles are fused. It was an excellent and beautiful in-mold foam molding.

(Example 8)
1 part by weight of a polypropylene / polyethylene glycol block copolymer as an additive, 0.5 parts by weight of polyethylene glycol (manufactured by Lion Corporation, polyethylene glycol # 300) as a hydrophilic additive, 0.1 part by weight of talc In the same manner as in Example 1, foaming, two-stage foaming, and in-mold molding were performed. The single-stage expanded particles obtained by the single-stage expansion showed two melting points, the expansion ratio was 19 times, and the average cell diameter was 309 μm. Excellent uniformity of bubbles. The magnification variation R was excellent at 1. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, and had excellent bubble uniformity with an average bubble diameter of 359 μm. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the molded body is small, distortion of the molded body is small, and the particles are fused. It was an excellent and beautiful in-mold foam molding.

Example 9
0.5 parts by weight of the additive polypropylene / polyethylene glycol block copolymer, 0.1 parts by weight of zinc borate (Zinc Borate 2335, manufactured by Tomita Pharmaceutical Co., Ltd.) as other hydrophilic additives, no talc added Otherwise, foaming, two-stage foaming, and in-mold molding were performed in the same manner as in Example 1. The first-stage expanded particles obtained by the first-stage expansion showed two melting points, the expansion ratio was 15 times, and the average cell diameter was 189 μm. The uniformity of the bubbles was almost uniform, although somewhat inferior to Examples 1-3. The magnification variation R was as excellent as 3. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, and had an average cell diameter of 238 μm and excellent bubble uniformity. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the molded body is small, distortion of the molded body is small, and the particles are fused. It was an excellent and beautiful in-mold foam molding.

(Example 10)
1 part by weight of polypropylene / polyethylene glycol block copolymer as an additive and 0.1 part by weight of talc were used. Carbon dioxide gas as a blowing agent was not used, nitrogen gas was introduced into the container and heated to 151 ° C. Others were evaluated in the same manner as in Example 1, one-stage foaming, two-stage foaming, and in-mold molding. The first-stage expanded particles obtained by the first-stage expansion showed two melting points, the expansion ratio was 10 times, and the average cell diameter was 144 μm. The uniformity of the bubbles was almost uniform, although somewhat inferior to Examples 1-3. The magnification variation R was as excellent as 7. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, and had an average bubble diameter of 208 μm and excellent bubble uniformity. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded body is excellent in smoothness, little wrinkles are generated, small dimensional shrinkage of the molded body, excellent fusion of particles, and beautiful mold It was an inner foamed molded product.

(Example 11)
Other than changing the additive polypropylene-polyethylene glycol block copolymer (b-2) (manufactured by Sanyo Kasei Co., Ltd., Pelestat 300, melting point 135 ° C.) to 1 part by weight to make 0.1 parts by weight of talc In the same manner as in Example 1, foaming, two-stage foaming, and in-mold molding were performed. The first-stage expanded particles obtained by the first-stage expansion showed two melting points, the expansion ratio was 12 times, and the average cell diameter was 241 μm. The uniformity of the bubbles was excellent. The magnification variation R was as excellent as 4. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, had an average cell diameter of 327 μm and excellent cell uniformity. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded body is excellent in smoothness, little wrinkles are generated, small dimensional shrinkage of the molded body, excellent fusion of particles, and beautiful mold It was an inner foamed molded product.

(Example 12)
Other than changing the additive polypropylene-polyethylene glycol block copolymer (b-3) (manufactured by Sanyo Kasei Co., Ltd., Pelestat 230, melting point 163 ° C.) to 1 part by weight to make 0.1 part by weight of talc In the same manner as in Example 1, foaming, two-stage foaming, and in-mold molding were performed. The single-stage expanded particles obtained by single-stage expansion exhibited two melting points, an expansion ratio of 11 times, and an average cell diameter of 195 μm. The uniformity of the bubbles was excellent. The magnification variation R was as excellent as 4. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, and had excellent bubble uniformity with an average bubble diameter of 272 μm. As a result of in-mold molding evaluation, the surface of the obtained in-mold foam molded body is excellent in smoothness, little wrinkles are generated, small dimensional shrinkage of the molded body, excellent fusion of particles, and beautiful mold It was an inner foamed molded product.

(Comparative Example 1)
Foaming was performed in the same manner as in Example 1 except that the additive polypropylene / polyethylene glycol block copolymer was not used and only 0.1 part by weight of talc was used. Only a low expansion ratio of 7 times was obtained, and the average bubble diameter was as small as 135 μm. In the two-stage foaming, a high vapor pressure is required to increase the expansion ratio to 30 times, and many sticks to which pre-foamed particles (two-stage foamed particles) are adhered were observed. When the two-stage foamed particles were used and subjected to in-mold foam molding, the resulting in-mold foam molded article had a large dimensional shrinkage, wrinkles were observed, and the appearance was poor.

(Comparative Example 2)
Foaming was carried out in the same manner as in Example 1 except that the additive polypropylene / polyethylene glycol block copolymer was 0.1 parts by weight and talc was 0.1 parts by weight. Only a low expansion ratio of 8 times was obtained, the average bubble diameter was 153 μm, and the magnification variation R was as large as 11. In the two-stage foaming, a high vapor pressure is required to increase the expansion ratio to 30 times, and many sticks to which pre-foamed particles (two-stage foamed particles) are adhered were observed. When the two-stage foamed particles were used and subjected to in-mold foam molding, the resulting in-mold foam molded article had a large dimensional shrinkage, wrinkles were observed, and the appearance was poor.

(Comparative Example 3)
0.1 parts by weight of an additive polypropylene / polyethylene glycol block copolymer, 0.2 parts by weight of melamine (manufactured by Nissan Chemical Industries, Ltd.) as another hydrophilic substance, and 0.1 parts by weight of talc as a foam nucleating agent Except that, foaming was performed in the same manner as in Example 1. The expansion ratio was 13 times, the average bubble diameter was 189 μm, and large and small bubbles were mixed, resulting in poor uniformity. The magnification variation R was as large as 9. There was no problem in expanding the expansion ratio to 30 times by the two-stage foaming, but the dimensional shrinkage ratio of the in-mold foam molding obtained by using the two-stage foamed particles and performing the foam molding in the mold was large. Occurrence was seen and the appearance was inferior.

(Comparative Example 4)
Foaming was carried out in the same manner as in Example 1 except that 30 parts by weight of the polypropylene / polyethylene glycol block copolymer as an additive and 0.1 parts by weight of talc as a foam nucleating agent were used. The expansion ratio was 16 times, the average cell diameter was 245 μm, the center side of the pre-expanded particles (single-stage expanded particles) was a small bubble, and the surface layer side was a non-uniform one that became a large bubble. The variation in magnification was as large as 8 and the expansion ratio was 16 times. Although there was no problem in increasing the expansion ratio to 30 times by two-stage foaming, the dimensional shrinkage ratio of the in-mold foam molding obtained by using the two-stage foamed particles and foam-molding in the mold was a little large, and wrinkles And surface irregularities were observed, and the appearance was poor.

(Comparative Example 5)
Polyethylene / polyethylene glycol block copolymer as additive is not used, ethylene ionomer resin (Mitsui DuPont Polychemical, Himiran 1707, melting point 89 ° C.) obtained by sodium ion crosslinking of ethylene- (meth) acrylic acid copolymer Was foamed in the same manner as in Example 1 except that 0.1 part by weight of talc was used as the foam nucleating agent. The expansion ratio was 11 times, and the average bubble diameter was 180 μm. The magnification variation R was as large as 16, and the variation in bubbles was also large. Although there was no particular problem in the two-stage foaming, when the two-stage foamed particles were used and foamed in-mold, the dimensional shrinkage ratio of the molded body was large, wrinkles were observed, and the appearance was inferior. Polyolefin resin particles containing an ionomer resin were prepared by an extruder having low kneadability, and it was considered that poor dispersion of the ionomer resin occurred. In addition, wrinkles were generated on the surface of the in-mold foam molded product, and the dimensional shrinkage was small, which caused defects because the ionomer resin was a resin with a large increase in viscosity due to a temperature drop during foaming. It can be seen that there is no problem when a polypropylene / polyethylene glycol block copolymer is used.

(Comparative Example 6)
Polypropylene ester amide (b′-1) (manufactured by Ciba Specialty Chemicals, IRGASTAT P18, melting point 180 ° C.) is used in an amount of 1 part by weight. Foaming was performed in the same manner as in Example 1 except that 0.1 part by weight of talc was used as the foam nucleating agent. The expansion ratio was as low as 10 times, and the average bubble diameter was as small as 126 μm. The magnification variation R was as large as 12, and the bubble variation was large, and it was considered that the polyether ester amide dispersion was poor. In the two-stage foaming, a high vapor pressure is required to increase the expansion ratio to 30 times, and generation of sticks to which the pre-expanded particles (two-stage expanded particles) are adhered was observed. When the two-stage expanded particles were used and subjected to in-mold foam molding, the compact had a large dimensional shrinkage, wrinkles were observed, and the appearance was poor.

(Comparative Example 7)
No additive polypropylene / polyethylene glycol block copolymer is used, 1 part by weight of maleic acid-modified polypropylene (manufactured by Toyo Kasei Kogyo Co., Ltd., Toyotack, melting point 150 ° C.), 0.1% by weight of talc as a foam nucleating agent It was made to foam like Example 1 except having set it as the part. The expansion ratio was as low as 8 times, and the average bubble diameter was as small as 130 μm. The magnification variation R was as large as 11. In the two-stage foaming, a high vapor pressure is required to increase the expansion ratio to 30 times, and many sticks to which pre-foamed particles (two-stage foamed particles) are adhered were observed. When the two-stage expanded particles were used and subjected to in-mold foam molding, the compact had a large dimensional shrinkage, wrinkles were observed, and the appearance was poor. Moreover, it was inferior to melt | fusion.

(Comparative Example 8)
No additive polypropylene / polyethylene glycol block copolymer is used, and 1 part by weight of a crosslinked polyalkylene oxide (Sumitomo Seika Co., Ltd., Aqua Coke TWB-P, melting point 60 ° C.) is used as a hydrophilic polymer. Foaming was performed in the same manner as in Example 1 except that 0.1 part by weight of talc was used. The expansion ratio was 11 times, and the average bubble diameter was 320 μm. The magnification variation R was as large as 13, the dimensional shrinkage ratio of the molded body was large, and the fusion was poor.

Comparison between Comparative Examples 5 to 8 and Examples shows the result of inferior surface magnification, dimensional accuracy, and fusion of the foamed molded article in the mold depending on the type of hydrophilic polymer and the variation in magnification of foamed particles and bubbles. It can be seen that the use of the polypropylene / polyethylene glycol block copolymer has improved them and the expansion ratio can be improved.

Claims (8)

  Polyolefin-polyether block copolymer (b) 0.2 part by weight or more and less than 5 parts by weight and foaming nucleating agent (c) 0.005 part by weight or more and 2 parts by weight with respect to 100 parts by weight of polyolefin resin (a) Polyolefin resin particles made of polyolefin resin containing the following were expanded to obtain single-stage expanded particles, and the single-stage expanded particles were pressurized with an inorganic gas such as air in a pressure-resistant container to give an internal pressure. Later, polyolefin resin two-stage expanded particles that are further foamed by steam heating.   The polyolefin resin two-stage expanded particles according to claim 1, wherein the polyolefin resin (a) is a polypropylene resin.   The polyolefin resin two-stage expanded particles according to claim 1 or 2, wherein the polyether part of the polyolefin-polyether block copolymer (b) is made of polyethylene glycol.   The polyolefin resin two-stage expanded particles according to any one of claims 1 to 3, which have an expansion ratio of 6 to 50 times and an average cell diameter of 50 to 800 µm.   The polyolefin resin two-stage expanded particles according to any one of claims 1 to 4, wherein the polyolefin resin comprises a hydrophilic substance (d) other than the polyolefin / polyether block copolymer.   The polyolefin resin according to claim 5, wherein the hydrophilic substance (d) other than the polyolefin / polyether block copolymer is at least one part by weight selected from the group consisting of melamine, glycerols and zinc borate. Two-stage expanded particles.   Polyolefin-polyether block copolymer (b) 0.2 part by weight or more and less than 5 parts by weight and foaming nucleating agent (c) 0.005 part by weight or more and 2 parts by weight with respect to 100 parts by weight of polyolefin resin (a) Polyolefin resin particles comprising a polyolefin resin containing the following are dispersed in an airtight dispersion medium together with a foaming agent in an aqueous dispersion medium, heated and pressurized to a temperature equal to or higher than the softening temperature of the polyolefin resin particles, Released into a pressure range lower than the internal pressure to obtain single-stage expanded particles that foam the polyolefin resin particles, and further, the single-stage expanded particles were pressurized with an inorganic gas such as air in a pressure-resistant container to give an internal pressure. The method for producing the polyolefin resin two-stage expanded particles according to any one of claims 1 to 6, which is further foamed by steam heating. The method for producing polyolefin resin two-stage expanded particles according to claim 7, wherein carbon dioxide gas is used as a foaming agent.