JP7165068B2 - Method for producing foam molded article - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an ester-based elastomer foam molded article.

2. Description of the Related Art Conventionally, a foamed molded product obtained by fusing a plurality of foamed particles made of polystyrene, polypropylene, or the like is widely used as a cushioning material or a packing material. A foamed molded article obtained by fusing a plurality of foamed particles has an advantage that a complicated shape can be formed as compared with a foamed molded article obtained by extrusion foaming. A foam molded article made of polystyrene, polypropylene, or the like has a problem that it is difficult to use it in applications requiring high impact resilience. Therefore, there has been a demand for a foam molded article that can achieve high impact resilience.

Thermoplastic elastomers have excellent impact resilience and high mechanical strength, so they are positioned as engineering elastomers. being considered for use. Molded articles made by foaming thermoplastic elastomers are expected to be lightweight and have high impact resilience inherent in elastomers. A method and the like have been reported (for example, Patent Document 1).

JP 2018-075753 A

Ester-based elastomer expanded particles are difficult to control expansion during in-mold molding compared to expanded particles of general-purpose resins such as polystyrene, and poor adhesion may be one of the causes of the phenomenon of long-term dimensional instability of expanded molded products. In other words, insufficient fusion between particles may occur, and poor appearance may occur due to poor foaming.

In order to solve the above problems, the present inventors have made intensive studies, and found that foamed particles, to which the degree of internal pressure applied is controlled, are placed in a mold while adjusting molding conditions such as steam pressure and cracking rate during molding. The present inventors have found that poor fusion or poor appearance can be suppressed by molding. The present invention is based on such findings, and the representative present invention is as follows.

Section 1.
A cavity formed by a pair of molds comprising a first mold and a second mold provided with a steam inlet is filled with expanded particles containing an ester-based elastomer as a base resin, and the mold is heated with a heating medium. and a method for producing a foamed molded article by heating the foamed particles,
The foamed particles contain 0 to 2% by mass of an inorganic gas in the particles,
The foamed particles are filled with a cracking rate between the first mold and the second mold of 3 to 85%,
The mold and the expanded beads are heated for 5 to 60 seconds with a heating medium having a temperature not lower than the melting point Tm of the expanded beads by 30° C. or more and not more than Tm.
Method.
Section 2.
The foamed particles that fill the cavity are
Expanded beads (A) containing 0.2 to 2% by mass of inorganic gas, or a mixture of the expanded beads (A) and expanded beads (B) containing no inorganic gas,
The mass of the expanded beads (A) is 30 to 100% by mass with respect to the total mass of the expanded beads (A) and (B).
The method of claim 1.
Item 3.
Item 3. The method according to Item 1 or 2, wherein the cracking rate is 10 to 85%.
Section 4.
Item 4. The method according to any one of items 1 to 3, wherein the heating time is 10 seconds to 60 seconds.
Item 5.
Item 5. The method according to any one of Items 1 to 4, wherein the heating temperature is at least 25°C lower than Tm and no higher than 5°C lower than Tm.
Item 6.
Item 6. The method according to any one of Items 1 to 5, wherein the inorganic gas is at least one selected from the group consisting of inert gases and air.
Item 7.
Item 7. The method according to any one of Items 1 to 6, wherein the foam molded article has a porosity of 7% or less.

According to the present invention, it is possible to produce an ester-based elastomer foam-molded article in which poor fusion or poor appearance is suppressed.

It is a block diagram showing an example of a suitable molding apparatus for carrying out the method of the present invention.

A representative manufacturing method of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram showing an example of a molding apparatus suitable for carrying out the manufacturing method of the present invention.

This molding apparatus 1 includes a concave mold 2 as a first mold and a convex mold 3 as a second mold. have. The concave mold 2 comprises a concave main body 5 provided with many steam holes and a frame 6 supporting it, and the convex mold 3 also has a convex main body 7 provided with many steam holes and supporting it. and a frame 8 having a In the mold closing state shown in FIG. 1, a cavity 9 is formed between the concave mold body 5 and the convex mold body 7 to match the outer diameter of the foam molded article to be manufactured. A steam chamber 10 is provided between the concave body 5 and the frame 6 and a steam chamber 11 is also provided between the convex body 7 and the frame 8 . The volume of the steam chamber 10 on the recessed mold 2 side is the volume of the space surrounded by the recessed mold main body 5 and the frame 6 . Also, the volume of the steam chamber 11 on the side of the convex mold 3 is the volume of the space surrounded by the convex main body 7 and the frame 8 .

A steam supply line is connected to the steam chamber 10 on the recessed side 2 via a recessed side pressure regulating steam valve 12, and a drain line is connected to the opposing position via a recessed side drain valve 13. An evacuation pipeline is connected to the pipeline via a vacuum valve 14 . A cooling water supply line is inserted through a cooling water valve 15 into the steam chamber 10 on the recessed mold 2 side, and a pressure gauge 16 is connected at an appropriate location.

Similarly, a steam supply line is connected to the steam chamber 11 on the convex side 3 via a convex side pressure regulating steam valve 17, and a drain line is connected to the opposing position via a convex side drain valve 18. , and an evacuation line is connected to this drain line via a vacuum valve 19 . A cooling water supply pipe is inserted through a cooling water valve 20 into the steam chamber 11 on the side of the convex mold 3, and a pressure gauge 21 is connected at an appropriate place. Although not shown, the molding die 4 is provided with an expanded particle supply port connected to a supply pipeline for filling the cavity 9 with expanded particles.

In order to manufacture an ester-based elastomer foam molded product using the molding apparatus configured as described above, the concave mold 2 and the convex mold 3 are brought close to each other to close the mold 4, and the cavity 9 is filled with foamed particles. Next, the mold 4 is steam-heated to foam and the foamed particles are fused to form an in-mold foam molding, then the mold 4 is cooled, then the mold 4 is opened, and the foam molded body is released. This is done by removing the

The expanded beads used in the production method of the present invention contain an ester-based elastomer as a base resin.
(1) Ester Elastomer The ester elastomer is not particularly limited, but examples thereof include elastomers such as polyethylene terephthalate and polybutylene terephthalate. Ester-based elastomers containing hard segments and soft segments are preferred.

A hard segment is composed of, for example, a dicarboxylic acid component and/or a diol component. It may be composed of two components, a dicarboxylic acid component and a dicarboxylic acid component and a diol component.
Examples of dicarboxylic acid components include components derived from aliphatic dicarboxylic acids such as oxalic acid, malonic acid and succinic acid and their derivatives, and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid and their derivatives.
Diol components include C _2-10 alkylene glycols such as ethylene glycol, propylene glycol, butanediol (eg, 1,4-butanediol), (poly)oxy C _2-10 alkylene glycols, and C _5-12 cycloalkanediols. , bisphenols, or alkylene oxide adducts thereof. The hard segment may have crystallinity.

Soft segments can use polyester type and/or polyether type segments.
Polyester type soft segments include dicarboxylic acids (aliphatic _C4-12 dicarboxylic acids such as adipic acid) and diols ( _C2-10 alkylene glycols such as 1,4-butanediol, ethylene glycol Aliphatic polyesters such as polycondensates with (poly)oxy C _2-10 alkylene glycol), polycondensates of oxycarboxylic acids, and ring-opening polymers of lactones (C _3-12 lactones such as ε-caprolactone) mentioned. The polyester type soft segment may be amorphous. Specific examples of polyesters as soft segments include polyesters of C _2-6 alkylene glycol and C _6-12 alkanedicarboxylic acid such as caprolactone polymer, polyethylene adipate and polybutylene adipate. The number average molecular weight of this polyester may range from 200 to 15,000, may range from 200 to 10,000, or may range from 300 to 8,000.
Polyether-type soft segments include segments derived from aliphatic polyethers such as polyalkylene glycols (eg, polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol). The number average molecular weight of the polyether may range from 200 to 10,000, may range from 200 to 6,000, or may range from 300 to 5,000.

Soft segments include polyesters having polyether units such as copolymers of aliphatic polyesters and polyethers (polyether-polyethers), polyethers such as polyoxyalkylene glycols (e.g., polyoxytetramethylene glycol) It may be a segment derived from a polyester of and an aliphatic dicarboxylic acid.
The mass ratio of the hard segment and the soft segment may be 20:80 to 90:10, 30:70 to 90:10, or 30:70 to 80:20, It may be 40:60 to 80:20, or 40:60 to 75:25.
Further, when the dicarboxylic acid component is a terephthalic acid component and other dicarboxylic acid components, the ester-based elastomer contains 30 to 80% by mass of the hard segment and 5 dicarboxylic acid components other than the terephthalic acid component. It may be contained at a rate of up to 30% by mass. The ratio of the dicarboxylic acid component other than the terephthalic acid component may be 5 to 25% by mass, 5 to 20% by mass, or 10 to 20% by mass. Incidentally, the ratio of the dicarboxylic acid component can be obtained by quantitatively evaluating the NMR spectrum of the resin.
The dicarboxylic acid component other than the terephthalic acid component is preferably an isophthalic acid component. By including the isophthalic acid component, the crystallinity of the elastomer tends to decrease, and the foam moldability is improved, so that a foam molded article with a lower density can be obtained.

As the ester-based elastomer, PELPLENE series and VYLON series manufactured by Toyobo Co., Ltd. can be suitably used. In particular, it is preferable to use the pelprene series.

(2) Physical properties of base resin (ester-based elastomer) The base resin may have a melting point of 100°C to 200°C. When the melting point is 200° C. or lower, softening is facilitated during foaming, and a low-density foam molded product can be easily obtained. When the melting point is 100° C. or higher, shrinkage is less likely to occur after the pre-foaming step, and molding becomes easier. The melting point of the resin may be from 120°C to 200°C, or from 120°C to 190°C.
The base resin may have a heat of crystallization of 0-30 mJ/mg. When the heat of crystallization is 30 mJ/mg or less, the foam moldability is improved, and a low density foam molded product can be easily obtained. The heat of crystallization may be 3-30 mJ/mg, 6-30 mJ/mg, or 9-30 mJ/mg.
The base resin may have a D hardness of 65 or less. When the D hardness is 65 or less, softening during foaming is facilitated, and a low-density foam molded article can be easily obtained. The D hardness may be 20-60, 25-60, or 30-60.
The base resin preferably has a Vicat softening temperature of 60 to 180°C. When the Vicat softening temperature is 60° C. or higher, it is difficult to shrink when exposed to room temperature after foaming. When the Vicat softening temperature is 180°C or less, foaming to a desired expansion ratio is facilitated. More preferably, the Vicat softening temperature is 80°C to 150°C.
The base resin may contain other resins other than the ester-based elastomer as long as the effects of the present invention are not impaired. Other resins may be known thermoplastic resins or thermosetting resins.

The base resin may additionally contain a flame retardant, a coloring agent, an antistatic agent, a spreading agent, a plasticizer, a flame retardant aid, a cross-linking agent, a filler, a lubricant, and the like.
Examples of flame retardants include hexabromocyclododecane, triallyl isocyanurate hexabromide, and the like.
Examples of coloring agents include inorganic pigments such as carbon black, graphite and titanium oxide, organic pigments such as phthalocyanine blue, quinacridone red and isoindolinone yellow, special pigments such as metal powder and pearl, and dyes.
Antistatic agents include polyoxyethylene alkylphenol ether, stearic acid monoglyceride, and the like.
Examples of spreading agents include polybutene, polyethylene glycol, silicone oil, and the like.

(3) Method for producing foamed molded article It is obtained by filling foamed particles contained as a material resin and heating the mold and the foamed particles with a heating medium. For example, a closed mold having a large number of small holes is filled with expanded particles, and the expanded particles are heated and expanded with pressurized steam to fill the gaps between the expanded particles and to fuse and integrate the expanded particles with each other. can be obtained by
When filling the expanded particles, the density of the expanded molded product can be adjusted by, for example, adjusting the cracking rate between the first mold and the second mold to adjust the amount of expanded particles filled. The cracking rate is, for example, 3 to 85%, preferably 5 to 85%, more preferably 10 to 80%. By setting the cracking rate within this range, the beauty of the appearance can be adjusted. Incidentally, the method for specifying the cracking rate is as described in the Examples.

Hot molding is preferably carried out by heating the mold using a heating medium (eg, steam) at a temperature lower than or equal to 30° C. lower than the melting point Tm of the expanded particles and lower than or equal to the melting point Tm. The melting point of the expanded beads refers to the melting point of the expanded beads before the internal pressure is applied to the expanded beads to which the internal pressure is applied by the inorganic gas. More preferably, the temperature of the heating medium is not less than 25° C. lower than Tm and not more than 5° C. lower than Tm. The pressure of the heating medium may be adjusted so that the temperature of the heating medium reaches a desired temperature. The heating time is, for example, 5 seconds to 60 seconds, more preferably 15 seconds to 60 seconds. By setting the temperature, pressure, and heating time of the heating medium within these ranges, it is possible to obtain a foamed molded product with good moldability. The method for specifying the melting point Tm of the expanded beads is as described in Examples.

In the heat molding, the foamed beads may be impregnated with an inorganic gas to improve the foaming power of the foamed beads (internal pressure imparting step). By improving the foaming force, the fusion between the foamed particles is improved during heating and foaming, and the foamed molded product has further excellent mechanical strength and long-term dimensional stability. Inorganic gases are, for example, inert gases or air. Inert gases are, for example, carbon dioxide, nitrogen, helium, argon, and the like. Preferred inorganic gases are air, nitrogen or carbon dioxide.
The amount of the inorganic gas contained in the foamed particles is, for example, 0 to 2% by mass, preferably 0.1 to 1.5% by mass, and 0.2 to 0.2% by mass, based on the mass of the foamed particles containing the inorganic gas. 1.3% by mass is more preferred. When the amount of the inorganic gas is within this range, the fusion rate is high, the appearance is good, and the productivity is improved. The amount of inorganic gas contained in the foamed beads is calculated from the mass W1 (g) of the foamed beads before the internal pressure is applied and the mass W2 (g) of the foamed beads containing the inert gas etc. after the internal pressure is applied, as follows: Calculated by the formula.
Amount of gas contained in expanded beads (% by mass) = ((W2-W1)/W2) x 100

As a method for impregnating the expanded particles with the inorganic gas, for example, there is a method in which the expanded particles are impregnated with the inorganic gas by placing the expanded particles in an inorganic gas atmosphere having a pressure higher than normal pressure. , 0.01 to 2.0 MPa, the foamed particles are allowed to stand in an inorganic gas atmosphere for 1 minute to 24 hours, preferably 5 minutes to 24 hours, and particularly preferably 20 minutes to 18 hours. The expanded particles are preferably impregnated with an inorganic gas before being filled in the mold. good.
When the expanded particles are impregnated with an inorganic gas, the expanded particles may be heated and expanded in the mold as they are. After making expanded particles, they may be filled in a mold and heated to expand. By using such expanded particles with a high expansion ratio, a foamed article with a high expansion ratio can be obtained.

The foam molded article preferably has a density of 0.015 to 0.5 g/cm ³ , more preferably 0.05 to 0.4 g/cm ³ , particularly preferably 0.08 to 0.3 g/cm ³ . Within this range, both compression set and mechanical properties can be well balanced.
Moreover, it is preferable that the foam molded article has a porosity of 7% or less. When the porosity is low, the long-term dimension of the foam molded product is stable. The porosity is a value obtained as follows.
<Porosity (% by volume)>
A part of the molded foam is cut out without the skin, and the external dimensions of the cut piece are measured to determine the apparent volume (H). Next, the cut piece is submerged in ethanol at 23° C., and after removing the air in the cut piece by applying vibration or the like, the true volume (I) of the cut piece is determined from the ethanol liquid level rise. Let the value calculated by the following formula be the porosity (% by volume).
Porosity (volume%) = ((HI) / H) × 100

Foam molded articles can be used, for example, in the industrial field, sporting goods, cushioning materials, seat cushions, automobile members, and the like. In particular, it can be used for applications requiring improvement in compression set.

(4) Method for producing expanded beads The expanded beads to be filled in the mold are produced by a step of impregnating base resin particles with a foaming agent to obtain expandable particles (impregnation step), an expansion step of expanding the expandable particles, and a can be obtained through an internal pressure imparting step in which the foamed particles contain an inorganic gas as necessary.

(4-1) Impregnation Step (a) Resin Particles Resin particles can be obtained using known production methods and production equipment.
For example, resin particles can be produced by granulating a melt-kneaded resin extruded from an extruder by underwater cutting, strand cutting, or the like. The temperature, time, pressure, and the like during melt-kneading can be appropriately set according to the raw materials used and manufacturing equipment.
The melt-kneading temperature in the extruder during melt-kneading is preferably 170 to 250°C, more preferably 200 to 230°C, at which the resin is sufficiently softened. The melt-kneading temperature means the temperature of the melt-kneaded material inside the extruder, which is obtained by measuring the central temperature of the melt-kneaded material flow path near the extruder head with a thermocouple thermometer.

The shape of the resin particles is, for example, spherical, ellipsoidal (egg-shaped), cylindrical, prismatic, pellet-like, or granular.
The resin particles preferably have a L/D ratio of 0.8 to 3, where L is the length and D is the average diameter. When the L/D of the resin particles is within this range, the fillability into the mold is good. In addition, the length L of the resin particles refers to the length in the direction of extrusion, and the average diameter D refers to the diameter of the cross section of the resin particles substantially perpendicular to the direction of the length L.
The average diameter D of the resin particles is preferably 0.5 to 1.5 mm. When the average diameter D is 0.5 mm or more, the retention of the foaming agent is improved, and the expandability of the expandable particles is likely to be improved. When the average diameter D is 1.5 mm or less, the fillability of the foamed particles into the mold is improved, and the thickness of the foamed molded article can be easily increased when producing a plate-shaped foamed molded article.

The resin particles may contain a cell control agent.
Examples of cell control agents include higher fatty acid amides, higher fatty acid bisamides, higher fatty acid salts, inorganic cell nucleating agents, and the like. A plurality of types of these cell control agents may be combined.
Examples of higher fatty acid amides include stearic acid amide and 12-hydroxystearic acid amide.
Examples of higher fatty acid bisamides include ethylenebisstearic acid amide, ethylenebis-12-hydroxystearic acid amide, and methylenebisstearic acid amide.
Higher fatty acid salts include calcium stearate.
Inorganic cell nucleating agents include talc, calcium silicate, synthetic or naturally occurring silicon dioxide, and the like.
The resin particles may also contain flame retardants such as hexabromocyclododecane and triallyl isocyanurate 6-bromide, and colorants such as carbon black, iron oxide and graphite.

(b) Expandable Particles Expandable particles are produced by impregnating resin particles with a foaming agent. As a procedure for impregnating the resin particles with the foaming agent, a known procedure can be used. For example, resin particles, a dispersant, and water are supplied into an autoclave and stirred to disperse the resin particles in water to produce a dispersion. A method of impregnating the foaming agent is mentioned.
The dispersant is not particularly limited, and examples thereof include sparingly water-soluble inorganic substances such as calcium phosphate, magnesium pyrophosphate, sodium pyrophosphate, magnesium oxide and hydroxyapatite, and surfactants such as sodium dodecylbenzenesulfonate.
As the blowing agent, a general-purpose one is used, and examples thereof include air; inert gases such as nitrogen and carbon dioxide (carbon dioxide gas); aliphatic hydrocarbons such as propane, butane and pentane; and halogenated hydrocarbons. Air, inert gases or aliphatic hydrocarbons are preferred. In addition, a foaming agent may be used individually and may use 2 or more types together.

The amount of the foaming agent with which the resin particles are impregnated is preferably 1 to 15 parts by mass with respect to 100 parts by mass of the resin particles. When the content of the foaming agent is 1 part by mass or more, the foaming power does not decrease, and it is easy to foam well even at a high foaming ratio. When the content of the foaming agent is 15 parts by mass or less, breakage of the cell membrane is suppressed, and the plasticizing effect does not become too large, thereby suppressing an excessive decrease in viscosity during foaming and suppressing shrinkage. . A more preferable amount of blowing agent is 2 to 12 parts by weight. Within this range, the foaming power can be sufficiently increased, and even at a high foaming ratio, foaming can be performed more favorably.

The content (impregnation amount) of the foaming agent with which 100 parts by mass of the resin particles are impregnated is measured as follows.
<Blowing agent content (impregnation amount)>
Measure the weight Xg of the resin particles before putting them into the pressure vessel. After the resin particles are impregnated with the foaming agent in the pressure vessel, the weight Yg of the impregnated product is measured after the impregnation is taken out from the pressure vessel. The content (impregnation amount) of the foaming agent with which 100 parts by mass of the resin particles are impregnated is obtained by the following formula.
Foaming agent content (parts by mass) = ((YX)/X) x 100

The temperature at which the resin particles are impregnated with the foaming agent is preferably 10°C to 120°C, more preferably 20°C to 110°C. When the impregnation temperature of the foaming agent is within this range, the time required for impregnating the resin particles with the foaming agent does not become long, and the production efficiency is less likely to decrease. is suppressed. A foaming aid (plasticizer) may be used in combination with the foaming agent. Foaming aids (plasticizers) include diisobutyl adipate, toluene, cyclohexane, ethylbenzene and the like.

The shape of the expandable particles is not particularly limited, and examples thereof include spherical, elliptical (egg-shaped), cylindrical, prismatic, pellet-like, and granular shapes.
The average diameter D of the expandable particles is preferably 0.5 to 1.5 mm. When the average diameter D is 0.5 mm or more, the retention of the foaming agent is improved, and the expandability of the expandable particles is likely to be improved. When the average diameter D is 1.5 mm or less, the fillability of the foamed particles into the mold is improved, and the thickness of the foamed molded article can be easily increased when producing a plate-shaped foamed molded article.

(4-2) Expansion Step (c) Expanded Particles In the expansion step, the expansion temperature and the heating medium are not particularly limited as long as the expandable particles can be expanded to obtain expanded particles.
Before foaming, the surface of the expandable particles may be coated with an anti-coalescence agent such as polyamide powder or a surfactant, or an antistatic agent. Examples of antistatic agents include polyoxyethylene alkylphenol ether, stearic acid monoglyceride, and the like.

The expanded particles preferably have a bulk multiple in the range of 2-70 times. When the bulk multiple is 70 times or less, the resulting foamed molded product is less likely to shrink, has a good appearance, and is less likely to lower in mechanical strength. When the bulk multiple is 2 times or more, the lightweightness of the foamed molded product is less likely to decrease. A more preferable bulk multiple is 5 to 30 times.
The expanded particles preferably have an average cell diameter of 20 to 320 μm. If the average cell diameter is less than 20 μm, the foamed molded article may shrink. When the average cell diameter is within this range, the molded article tends to have good appearance and good fusion. The average cell diameter is more preferably 20-200 μm, and even more preferably 40-150 μm.

The expanded particles preferably have an average particle size of 1.5-5 mm. When the average particle size is 1.5 mm or more, the secondary foamability during molding is less likely to deteriorate. When the average particle size is 5 mm or less, the fillability into a mold is less likely to deteriorate when a foamed molded article is produced by thermal foaming. More preferably, the average particle size is 2 to 5 mm. The method for specifying the average particle size of the expanded beads is as described in Examples.

The expanded particles may contain 0 to 2% by mass of inorganic gas, preferably 0.2 to 2% by mass of inorganic gas. It is more preferable to mix the expanded particles (A) containing 0.2 to 2% by mass of inorganic gas with the expanded particles (B) containing no inorganic gas. The mixing ratio of the foamed particles (A) and (B) is such that the mass of the foamed particles (A) is 30 to 100% by mass with respect to the total mass of the foamed particles (A) and (B) in terms of fusion rate and appearance. Preferably, 40 to 85 mass % is more preferable, and 40 to 80 mass % is even more preferable.
The filler particles are preferably expanded particles containing 0 to 2% by mass of inorganic gas (including a mixture of expanded particles (A) and (B)) from the viewpoint of fusion rate and appearance. A small amount of other expanded particles, such as expanded particles containing more than 2% by mass of an inorganic gas, may also be included. When the filler particles contain other expanded particles, the amount of the other expanded particles is, for example, 10 parts by mass or less, preferably 7 parts by mass or less, or more, based on the total mass of the expanded particles (A) and (B). It is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

EXAMPLES The present invention will be specifically described below with reference to examples, etc., but the present invention is not limited to the embodiments shown in these.

[Inorganic gas content (compressed air content) of foamed particles]
The foamed particles that fill 70% by volume of the volume of the closed container are weighed, charged into the closed container, and after the container is sealed, the container is pressurized with an inorganic gas having a gauge pressure of 0.01 to 2 MPa for an arbitrary period of time. After pressurization, the inorganic gas is purged until the inside of the sealed container reaches atmospheric pressure, and the foamed particles are taken out and weighed. The amount of inorganic gas is calculated by the following formula.
Inorganic gas amount (mass%) = ((ba) / b) × 100
a: Weight (g) of foamed particles before pressurization with inorganic gas
b: Weight (g) of foamed particles after pressurization with inorganic gas

[Cracking rate]
It is calculated by the following formula from the volume in the mold (a) when the pair of molds are completely closed and the volume in the mold (b) after arbitrary cracking is removed.
Cracking rate (%) = ((ba)/a) x 100

[Melting point Tm of expanded particles]
It was measured by the method described in JIS K7121:1987, JIS K7121:2012 "Method for measuring transition temperature of plastic". However, the sampling method and temperature conditions were as follows. After filling 5.5±0.5 mg of the sample into the bottom of the aluminum measurement container without any gap, the container was covered with an aluminum lid. Then, using a differential scanning calorimeter manufactured by Hitachi High-Tech Science Co., Ltd. "DSC7000X, AS-3", under a nitrogen gas flow rate of 20 mL / min, the temperature was lowered from 30 ° C. to -70 ° C. and then held for 10 minutes, from -70 ° C. to 220 DSC when the temperature is raised to ° C. (first temperature rise), the temperature is lowered from 220 ° C. to -70 ° C. after holding for 10 minutes (cooling), and the temperature is raised from -70 ° C. to 220 ° C. after holding for 10 minutes (second temperature rise) got the curve. All temperature rises and falls were performed at a rate of 10° C./min, and alumina was used as a reference material. The melting temperature (melting point) was obtained by reading the top temperature of the largest melting peak observed in the second heating process using analysis software attached to the apparatus.

[Vicat softening temperature]
Vicat softening temperature conforms to ISO306:2004 and is measured by A50 method. A load of 10 N is applied to the test piece, the heat transfer medium is heated at a temperature increase rate of 50° C./hour, and the temperature of the heat transfer medium when the needle-shaped indenter penetrates 1 mm from the surface of the test piece is defined as the Vicat softening temperature.

[Bulk Density and Bulk Multiple of Expanded Particles]
First, Wg was collected as a measurement sample from the foamed particles before the internal pressure was applied, and after allowing this measurement sample to fall naturally into the graduated cylinder, the bottom of the graduated cylinder was struck to make the apparent volume (V) ^cm3 of the sample constant. , its weight and volume are measured, and the bulk density of the expanded beads is calculated based on the following formula. The bulk multiple is the reciprocal of the bulk density.
Bulk density (g/cm ³ )=weight of measurement sample (W)/volume of measurement sample (V)

[Average particle diameter of expanded particles]
About 50 g of the foamed particles were sieved using a low-tap sieve shaker (manufactured by Iida Seisakusho Co., Ltd.) with sieve openings of 26.5 mm, 22.4 mm, 19.0 mm, 16.0 mm, 13.2 mm, 11.20 mm, 9. 50mm, 8.80mm, 6.70mm, 5.66mm, 4.76mm, 4.00mm, 3.35mm, 2.80mm, 2.36mm, 2.00mm, 1.70mm, 1.40mm, 1.18mm, 1.00 mm, 0.85 mm, 0.71 mm, 0.60 mm, 0.50 mm, 0.425 mm, 0.355 mm, 0.300 mm, 0.250 mm, 0.212 mm, 0.180 mm JIS standard sieves for 5 minutes Classify. The weight of the sample on the sieve is measured, and based on the cumulative weight distribution curve obtained from the results, the particle diameter (median diameter) at which the cumulative weight is 50% is defined as the average particle diameter.

[Fusion rate of foam molded product]
On the surface of the foamed molded product (400 mm × 300 mm × thickness 20 mm), a cut line with a depth of about 5 mm was cut with a cutter knife along a straight line connecting the centers of a pair of long sides. The molded body was divided into two parts. An arbitrary range containing 50 or more expanded particles is set for the expanded particles on the fracture surface of the two-divided expanded molded product, and the number (a) of broken expanded particles within the expanded particles within this range; , the number of foamed particles (b) broken at the interface between the foamed particles was counted, and the fusion rate F (%) was calculated by the following formula.
F (%) = (a/(a+b)) x 100

[Appearance evaluation of foam molded product]
On the surface of the foamed molded product, a portion (gap between particles) in which the particles were not filled without any gaps and had depressions was observed. In the range of 100 mm × 100 mm on the surface of the foamed molded product, the number of gaps with a maximum length of 2 mm or more was measured. , and 5 or less, the appearance was judged to be good, and was indicated as "○".
Note that the maximum length of the gap is the longest straight line distance between any two points on the upper surface of the recess.

[Porosity of foamed molded product (% by volume)]
Four rectangular parallelepipeds (85 mm x 25 mm x 12.5 mm) without skin were cut out from the obtained foamed molded article to be used as samples. Accurate dimensions of each sample were measured using vernier calipers or the like and totaled to determine the apparent volume (H).
Each sample was then submerged in ethanol (120 mL; 23° C.) in a graduated glass cylinder (inner volume: 200 mL) using a wire mesh or the like. Air present between the expanded particles was removed by applying light vibration or the like. Taking into account the volume of tools such as wire mesh in ethanol, the volume of the sample was measured from the rise in the ethanol liquid level. The true volume of the four samples was summed to obtain the true volume (I). The porosity (% by volume) was calculated from the apparent volume (H) and the true volume (I) by the following formula.
Porosity (volume%) = ((HI) / H) × 100

<Preparation of expandable particles>
100 parts by mass of an ester-based elastomer ("Pelprene P-75M", a polybutylene terephthalate-based elastomer manufactured by Toyobo Co., Ltd., a Vicat softening temperature of 110 ° C.) serving as a base material for foamed particles, and 0 of ethylene bis-stearic acid amide as a cell modifier .3 parts by mass were put into an extruder, extruded in a molten state from a die with a diameter of 1.0 mm, and immediately after being extruded were cut with a cutter to obtain pellets with an average particle diameter of 1.3 mm.

2,000 g of the obtained pellets, 2,000 g of distilled water, and 3 g of a surfactant (aqueous solution of sodium dodecylbenzenesulfonate: 25% pure content) were placed in an autoclave with an internal volume of 5 L and equipped with a stirrer, and after sealing, foaming was performed while stirring. 450 mL of butane agent (normal butane:isobutane=7:3 (volume ratio)) was injected. Next, the inside of the autoclave was heated to 100°C, heated for 2 hours, and cooled to 25°C. After cooling was completed, the autoclave was depressurized, and the surfactant was immediately washed with distilled water, followed by dehydration to obtain expandable particles. The impregnation amount of the foaming agent in the expandable particles was 7% by mass.

<Preparation of expanded particles>
1.5 kg of the obtained expandable particles are put into a cylindrical pre-expanding machine with an internal volume of 45 L and equipped with a stirrer, heated with steam at 0.11 to 0.15 MPa while being stirred, and expanded (pre-expanded). Foamed particles were obtained. The expanded particles had a bulk density of 0.130 g/cm ³ , a melting point of 152° C., and an average particle diameter of 2.3 mm.

<Applying Internal Pressure to Expanded Beads>
The foamed particles were placed in a closed container, and compressed air was injected as an inorganic gas into the closed container and held at room temperature for 12 hours or more to impregnate the expanded particles with the compressed air (internal pressure was applied). The injection pressure was adjusted in the range of 0.01 to 2.0 MPa so that the compressed air content of the foamed particles was the amount shown in Table 1.
On the other hand, apart from the expanded beads to which the internal pressure was applied in this manner, expanded beads to which the internal pressure was not applied were also obtained in the same manner except for the application of the internal pressure.

<Production of foam molded product>
As a molding apparatus, "DB-7459PP" manufactured by DABO was used.
Filled particles obtained by mixing expanded particles containing compressed air and expanded particles that are not subjected to internal pressure and do not contain compressed air at the ratio shown in Table 1 are molded into a concave mold and a convex mold. A pair of molds (400 mm x 300 mm x 20 mm thick) were filled at the cracking rate shown in Table 1. After the filling was completed, the mold was clamped, heat molding was performed under the heating conditions shown in Table 1, and the mold and the foamed product were sufficiently cooled by standing in a vacuum, and then the mold was opened to take out the foamed product. The foamed molded product taken out was left to stand in an oven at 50 to 70° C. for 4 hours or more to dry it, and the internal moisture and the like were dissipated.
The foamed molded article was taken out from the oven and allowed to stand at room temperature for 3 hours or more, and the fusion rate was measured and the appearance was evaluated. Table 1 shows the results. In addition, as a result of measuring the porosity of the foam molded body of Example 1, it was 6%.
In Table 1, the compressed air content indicates the compressed air content of the expanded beads containing compressed air. The amount of foamed particles containing compressed air and the amount of foamed particles to which internal pressure is not applied indicate the mass ratio (% by mass) of each amount when the total mass of both amounts is 100.

In the comparative example, the cracking rate was 90% or more, that is, a large amount of filler particles were pressed into the mold and heat-molded, and the appearance evaluation was good, but the fusion rate was low. On the other hand, in the examples, by setting the content of the inorganic gas, the cracking rate, etc. of the foamed particles within a predetermined range, a foamed article having a fusion rate of 50% or more and a good appearance was obtained. In particular, when expanded particles containing an inorganic gas and expanded particles not containing an inorganic gas were used in combination (Examples 5 to 7), a foam molded article having a good appearance and a very high fusion rate of 70% or more was obtained. . Moreover, the porosity of the molded article of Example 1 was as low as 6%, and the long-term dimensions were stable.

DESCRIPTION OF SYMBOLS 1... Molding apparatus, 2... Concave mold, 3... Convex mold, 4... Mold, 5... Concave main body, 6... Frame, 7... Convex main body, 8... Frame, 9... Cavity, 10, 11... Steam chamber, 12 ... Concave side pressure regulating steam valve 13 ... Concave side drain valve 14, 19 ... Vacuum valve 15, 20 ... Cooling water valve 16, 21 ... Pressure gauge 17 ... Convex side pressure regulating steam valve 18 ... Convex Mold side drain valve.

Claims (6)

A cavity formed by a pair of molds comprising a first mold and a second mold provided with a steam inlet is filled with expanded particles containing an ester-based elastomer as a base resin, and the mold is heated with a heating medium. and a method for producing a foamed molded article by heating the foamed particles,
The expanded beads are a mixture of expanded beads (A) containing 0.2 to 2% by mass of inorganic gas and expanded beads (B) containing no inorganic gas, wherein the expanded beads (A ) and (B), the mass of the expanded beads (A) is 40 to 85% by mass,
The foamed particles are filled with a cracking rate between the first mold and the second mold of 3 to 85%,
The mold and the expanded beads are heated for 5 to 60 seconds with a heating medium having a temperature not lower than the melting point Tm of the expanded beads by 30° C. or more and not more than Tm.
Method. The method of claim 1, wherein the cracking rate is 10-85%. The method according to claim 1 or 2 , wherein the heating time is 10 seconds to 60 seconds. 4. The method according to any one of claims 1 to 3 , wherein the heating temperature is not less than 25°C lower than Tm and not more than 5°C lower than Tm. 5. The method according to any one of claims 1 to 4 , wherein the inorganic gas is at least one selected from the group consisting of inert gases and air. The method according to any one of claims 1 to 5 , wherein the foamed molded article has a porosity of 7% or less.

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