JP2022096231A - Polypropylene-based resin foam particle, and foam particle molding - Google Patents

Abstract

To provide polypropylene-based resin foam particles which enable production of a foam particle molding having good appearance and excellent mechanical physical properties such as compression strength in a wide molding heating temperature range; and polypropylene-based resin foam particles which enable production of a foam particle molding having a desired shape and good appearance even by omitting a cure step.SOLUTION: There is provided a foam particle molding in which cylindrical polypropylene-based resin foam particles having a through hole and foam particles are mutually fused to each other. An average pore diameter d of the foam particles is within a specific range, and a ratio d/D of the average pore diameter d to an average outer diameter D is within a specific range. A polypropylene-based resin constituting the foam particles is an ethylene-propylene-butene copolymer, a butene component content and an ethylene component content are specific amounts, and bending elastic modulus of the polypropylene-based resin is within a specific range.SELECTED DRAWING: None

Description

The present invention relates to polypropylene-based resin foamed particles containing an ethylene-propylene-butene copolymer as a base resin and a polypropylene-based resin foamed particle molded body.

Polypropylene-based resin foamed particle molded products are used for various purposes because they are lightweight and have excellent cushioning properties, rigidity, and the like. In the polypropylene-based resin foamed particle molded product, for example, polypropylene-based resin foamed particles are filled in a molding mold and heated with steam to cause secondary foaming of the foamed particles and melt the surfaces thereof to fuse them to each other. It is obtained by an in-mold molding method of molding into a desired shape. The foamed particle molded product after molding is cooled with water, air, or the like in the molding mold and then released from the molding mold.

Conventionally, in order to improve the in-mold moldability of the foamed particles and the physical properties of the foamed particle molded body, a copolymer obtained by copolymerizing propylene with another monomer may be used as the polypropylene-based resin. Among the copolymers, attempts have been made to use a ternary copolymer obtained by copolymerizing propylene, 1-butene and ethylene. For example, Patent Document 1 discloses polypropylene-based resin prefoamed particles using an ethylene-propylene-1-butene random copolymer having a specific melting point and melt index as a base resin. Further, Patent Document 2 discloses polypropylene-based resin foamed particles containing a polypropylene-based resin containing a structural unit composed of 1-butene and a polypropylene-based resin having a high melting point.

When the foamed particle molded body after in-mold molding is stored at room temperature, the steam that has flowed into the bubbles of the foamed particle molded body during in-mold molding condenses in the bubbles, and the inside of the bubbles becomes negative pressure, resulting in the foamed particle molded body. Volume shrinkage may occur and the molded body may be significantly deformed. Therefore, after the foamed particle molded body is released, a curing step is usually required to restore the shape of the foamed particle molded body by allowing it to stand for a predetermined time in a high temperature atmosphere adjusted to a temperature of, for example, about 60 ° C. to 80 ° C. Is.

In the production of polypropylene-based resin foamed particle molded products, attempts have been made to omit the curing step. For example, Patent Document 3 discloses a technique for fusing foamed particles composed of a foam core layer and a coating layer while maintaining voids between the particles, and according to Patent Document 3, the curing step can be omitted. It is supposed to be. Further, Patent Document 4 discloses a technique for in-mold molding of foamed particles using a polypropylene-based resin having a specific melting point, melt flow index, Z average molecular weight, and the like. According to Patent Document 4, curing is performed. It is said that the time can be shortened.

Japanese Unexamined Patent Publication No. 10-316791 WO2016 / 60162 Japanese Patent Application Laid-Open No. 2003-39565 Japanese Unexamined Patent Publication No. 2000-129028

Polypropylene resin foam particles are required to be moldable in a wide temperature range. In particular, from the viewpoint of reducing the burden on the device and reducing the energy used, it is required to be able to mold at a lower temperature. Further, the foamed particle molded body is required to have sufficient rigidity and an excellent appearance. Further, there is a demand for the development of polypropylene-based resin foamed particles capable of producing a foamed particle molded product having good rigidity and appearance even when the curing step is omitted.

In the techniques described in Patent Documents 1 and 2, the heating temperature range that can be molded is narrow, and if the curing step is omitted, the foamed particle molded product is significantly shrunk and deformed, and the foamed particle molded product has a good appearance. Was difficult to manufacture.
In the technique described in Patent Document 3, although the curing step can be omitted, the appearance of the molded product is deteriorated because voids are formed between the foamed particles of the molded product. Further, when the foamed particle molded product of Patent Document 3 is used as, for example, an energy absorbing material, the rigidity and strength are insufficient. According to the technique of Patent Document 4, although the curing process can be shortened, the curing process is required, and if the curing process is omitted, the foamed particle molded body shrinks and deforms, and the appearance is good. It was difficult to obtain a foamed particle molded product.

The present invention has been made in view of the above background, and is a polypropylene-based resin foam capable of producing a foamed particle molded body having a good appearance and excellent mechanical properties such as compressive strength in a wide molding heating temperature range. It is intended to provide particles. Further, it is an object of the present invention to provide polypropylene-based resin foamed particles capable of producing a foamed particle molded product having a desired shape and having a good appearance even if the curing step is omitted.

One aspect of the present invention is a tubular polypropylene-based resin foamed particle having a through hole.
The average pore diameter d of the through holes of the foamed particles is less than 1 mm, and the ratio d / D of the average pore diameter d to the average outer diameter D of the foamed particles is 0.4 or less.
The polypropylene-based resin constituting the foamed particles is an ethylene-propylene-butene copolymer.
The total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer is 2% by mass or more and 15% by mass or less, and the butene component is contained with respect to the ethylene component content [mass%]. The ratio of amount [mass%] is 2 or more,
The polypropylene-based resin foamed particles have a flexural modulus of 800 MPa or more.

Another aspect of the present invention is a foamed particle molded body in which polypropylene-based resin foamed particles are fused to each other and has open spaces in which they communicate with each other.

According to the polypropylene-based resin foamed particles, a foamed particle molded body having a good appearance and excellent mechanical properties such as compression strength can be produced in a wide range of molding heating temperatures. Further, even if the curing step is omitted, it is possible to produce a foamed particle molded product having a good appearance and excellent mechanical properties.

In addition, the foamed particle molded product has a good appearance and is excellent in mechanical properties such as compressive strength.

FIG. 1 is an explanatory diagram showing a method of calculating the area of a high temperature peak.

In the present specification, when a numerical value or a physical property value is inserted before and after using "-", it is used as including the values before and after that. Further, when expressing a numerical value or a physical property value as a lower limit, it means that it is equal to or more than the numerical value or the physical property value, and when expressing a numerical value or a physical property value as an upper limit, it means that it is equal to or less than the numerical value or the physical property value. Further, "% by weight" and "% by mass", and "parts by weight" and "parts by mass" are substantially synonymous with each other. Further, in the following description, the polypropylene-based resin foamed particles are appropriately referred to as “foamed particles”, and the foamed particle molded body is appropriately referred to as “molded body”.

The foamed particles have a tubular shape having through holes, the average pore diameter d is less than 1 mm, and the ratio [d / D] of the average pore diameter d to the average outer diameter D is 0.4 or less. Further, the bending elastic modulus of the polypropylene-based resin constituting the foamed particles is 800 MPa or more, and the polypropylene-based resin contains an ethylene-propylene-butene copolymer. The total amount of the butene component content and the ethylene component content of the ethylene-propylene-butene copolymer is 2 to 15% by mass. The ratio of the butene component content C _bu to the ethylene component content C _et in the ethylene-propylene-butene copolymer (specifically, C _bu / C _et ) is 2 or more. When the foamed particles have the above-mentioned structure, it is possible to produce a molded product having a good appearance and excellent strength at the time of compression under a wide range of molding heating temperature conditions. Further, even if the curing step is omitted, it is possible to produce a molded product having a desired shape and having a good appearance.

(Ethylene-propylene-butene copolymer)
The total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer (hereinafter, also simply referred to as “copolymer”) which is the base resin of the foamed particles is 2% by mass or more 15 It is mass% or less, and the mass ratio (butene component content / ethylene component content) between the butene component content and the ethylene component content is 2 or more. The total of the butene component content, the ethylene component content, and the propylene component content in the copolymer is 100% by mass.

If the total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer is too small, it may not be possible to obtain a molded product having a good appearance at a low molding heating temperature. From this point of view, the total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer is 2% by mass or more as described above. From the viewpoint of enabling molding at a lower molding heating temperature, the total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer is preferably 5% by mass or more. It is more preferably more than 6% by mass, and even more preferably 8% by mass or more. On the other hand, if the total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer is too large, if the curing step is omitted, the molded product shrinks and deforms after the mold release. It becomes difficult to suppress it, and there is a possibility that a molded product having a desired shape and having a good appearance cannot be obtained. From this point of view, the total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer is 15% by mass or less as described above. The total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer is 14% by mass or less from the viewpoint of making it easier to suppress the remarkable shrinkage and deformation of the molded product after the mold release. It is preferably present, and more preferably 12% by mass or less.

The ratio C _bu / C _et of the butene component content C _bu to the ethylene component content C _et in the ethylene-propylene-butene copolymer is 2 or more. If the ratio C _bu / C _et is too small, it may not be possible to in-mold the foamed particles under a wide range of molding heating temperature conditions. Further, when the curing step is omitted, the molded product tends to shrink and deform after the mold is released. The ratio C _bu / C _et is preferably 3 or more, more preferably 5 or more, still more preferably 6 or more, from the viewpoint that the molding heating temperature becomes wider and the shrinkage and deformation of the molded product can be more easily suppressed. , Even more preferably 7 or more, particularly preferably 9 or more, and most preferably 13 or more. On the other hand, the upper limit of the ratio C _bu / C _et is not particularly limited from the above viewpoint, but is preferably 50, more preferably 30, and even more preferably 20.

From the viewpoint that the melting point can be lowered while maintaining the rigidity of the resin, the butene component content of the ethylene-propylene-butene copolymer is preferably 2% by mass or more, more preferably 5% by mass or more. It is more preferably 6% by mass or more, further preferably 7% by mass or more, particularly preferably more than 7% by mass, and most preferably 8% by mass or more. On the other hand, the butene component content of the ethylene-propylene-butene copolymer is less than 15% by mass, preferably 14% by mass or less, and more preferably 12% by mass or less. When the butene component content of the ethylene-propylene-butene copolymer is within the above range, the foamed particles are excellent in the balance between moldability and rigidity. The butene used as the butene component of the copolymer is preferably 1-butene, which is a linear α-olefin. Further, the ethylene-propylene-butene copolymer is preferably a random copolymer.

From the viewpoint of improving formability, the ethylene component content of the ethylene-propylene-butene copolymer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.4% by mass or more. Is. Further, from the viewpoint of improving the moldability when the curing step is omitted and shortening the water cooling time during in-mold molding, the ethylene component content of the ethylene-propylene-butene copolymer is preferably 5% by mass. % Or less, more preferably 4% by mass or less, still more preferably 3% by mass or less, particularly preferably 2% by mass or less, and most preferably 1.2% by mass or less.
The propylene component content of the ethylene-propylene-butene copolymer is preferably 85% by mass or more, more preferably 86% by mass or more, and further preferably 88% by mass. The propylene component content of the ethylene-propylene-butene copolymer is preferably 98% by mass or less, more preferably 95% by mass or less, and further preferably 92% by mass or less.

In the ethylene-propylene-butene copolymer, the total amount of the butene component content C _bu and the ethylene component content C _et is more than 6% by mass and 15% by mass or less, and the above-mentioned butene component content C _bu is 6. It is particularly preferable that it is by mass or more and less than 15% by mass, and it is most preferable that the ratio C _bu / C _et is 6 or more. In this case, the balance between moldability and rigidity is excellent, and the moldability when the curing step is omitted is better. Further, the water cooling time at the time of in-mold molding is shortened.

The ethylene-propylene-butene copolymer may contain a monomer component other than the ethylene component, the propylene component, and the butene component, but it is preferably composed of these three types of monomer components, and these three types are preferable. It is more preferable that it consists of only a monomer component.
The content of these monomer components can be determined by IR spectrum measurement.

The ethylene component, propylene component, and butene component of the ethylene-propylene-butene copolymer mean a constituent unit derived from ethylene, a constituent unit derived from propylene, and a constituent unit derived from butene in the ethylene-propylene-butene copolymer, respectively. The monomer component other than the ethylene component, the propylene component and the butene component means a constituent unit derived from ethylene, a constituent unit derived from propylene and a constituent unit derived from a monomer other than the constituent unit derived from butene.
Further, the content of each monomer component in the copolymer means the content of the constituent unit derived from each monomer in the copolymer.

The polypropylene-based resin constituting the foamed particles may contain a polymer other than the ethylene-propylene-butene copolymer as long as the object effect of the present invention is not impaired. Examples of other polymers include other polypropylene-based resins such as ethylene-propylene random copolymer, propylene-butene random copolymer, and propylene homopolymer, and polypropylene-based resins such as polyethylene-based resin and polystyrene-based resin. Examples of thermoplastic resins other than the above. The content of the other polymer in the polypropylene-based resin constituting the foamed particles is preferably 20% by mass or less, more preferably 10% by mass or less, and further preferably 5% by mass or less. , 0, that is, it is particularly preferable that the polypropylene-based resin constituting the foamed particles contains only the ethylene-propylene-butene copolymer as the polymer.

From the viewpoint of achieving both in-mold moldability and heat resistance, the melting point of the polypropylene resin is preferably 135 ° C. or higher, more preferably 136 ° C. or higher, still more preferably 137 ° C. or higher, and particularly preferably 138 ° C. or higher. From the viewpoint of improving in-mold moldability, the melting point of the polypropylene resin is preferably 145 ° C. or lower, more preferably 142 ° C. or lower, and further preferably 140 ° C. or lower.

The melting point of the polypropylene resin is determined based on JIS K7121: 1987. Specifically, "(2) When measuring the melting temperature after performing a certain heat treatment" is adopted as the state adjustment, and the state-adjusted test piece is heated from 30 ° C. at a heating rate of 10 ° C./min. The DSC curve is obtained by raising the temperature to 200 ° C., and the peak temperature of the melting peak is taken as the melting point. When a plurality of melting peaks appear on the DSC curve, the peak temperature of the melting peak having the largest area is used as the melting point.

From the viewpoint of foamability, the melt flow rate (MFR) of the polypropylene-based resin is preferably 2 to 10 g / 10 minutes, more preferably 5 to 9 g / 10 minutes. The MFR of the polypropylene-based resin is a value measured based on JIS K7210-1: 2014 under the conditions of a test temperature of 230 ° C. and a load of 2.16 kg.

The foamed particles have an endothermic peak due to melting (that is, a resin-specific peak) peculiar to polypropylene-based resin and 1 on the high temperature side thereof in the DSC curve obtained when heating from 23 ° C. to 200 ° C. at a heating rate of 10 ° C./min. It is preferable to have a crystal structure in which the above melting peaks (that is, high temperature peaks) appear. The DSC curve is obtained by differential scanning calorimetry (DSC) according to JIS K7121: 1987 using 1 to 3 mg of foamed particles as a test sample.
The resin-specific peak is an endothermic peak due to melting inherent in the polypropylene-based resin constituting the foamed particles, and is considered to be due to the endothermic heat at the time of melting the crystal originally possessed by the polypropylene-based resin. On the other hand, the endothermic peak on the high temperature side of the resin-specific peak (that is, the high-temperature peak) is an endothermic peak that appears on the high-temperature side of the resin-specific peak on the DSC curve. When this high temperature peak appears, it is presumed that secondary crystals are present in the resin. After heating from 23 ° C to 200 ° C at a heating rate of 10 ° C / min (that is, the first heating) as described above, the temperature is 200 ° C to 23 ° C at a cooling rate of 10 ° C / min. In the DSC curve obtained when the mixture was cooled to 30 ° C. and then heated again from 23 ° C. to 200 ° C. at a heating rate of 10 ° C./min (that is, the second heating), the polypropylene constituting the foamed particles was obtained. Since only the endothermic peak due to melting, which is peculiar to the based resin, can be seen, it is possible to distinguish between the resin peculiar peak and the high temperature peak. The temperature of the apex of this resin-specific peak may be slightly different between the first heating and the second heating, but the difference is usually within 5 ° C.

The heat of fusion of the high temperature peak of the foamed particles is preferably 5 to 40 J / g, more preferably 7 to 30 J / g, and further preferably 10 to 20 J / g.
The ratio of the heat of melting of the high temperature peak to the heat of melting of the total melting peak of the DSC curve (heat of melting of the high temperature peak / heat of melting of the total melting peak) is preferably 0.05 to 0.3, more preferably. It is 0.1 to 0.25, more preferably 0.15 to 0.2.
By setting the ratio of the heat of fusion of the high temperature peak to the heat of fusion of the total melting peak in such a range, the foamed particles are particularly excellent in mechanical strength due to the presence of secondary crystals appearing as the high temperature peak, and are formed in the mold. It is thought that it will be excellent in sex.
Here, the heat of fusion of the total melting peak means the total amount of heat of melting obtained from the areas of all the melting peaks of the DSC curve.

If the flexural modulus of the polypropylene-based resin constituting the foamed particles is too low, the molded body may be significantly shrunk and deformed to obtain a molded body having a desired shape if the curing step is omitted. From this point of view, the flexural modulus of the polypropylene resin is 800 MPa or more as described above. From the viewpoint of making it easier to suppress significant shrinkage and deformation of the molded product when the curing step is omitted, the flexural modulus is preferably 850 MPa or more, more preferably 880 MPa or more, and more preferably 900 MPa or more. Is particularly preferable. From the viewpoint of improving moldability, the flexural modulus is preferably 1200 MPa or less, more preferably 1100 MPa or less, and further preferably 1000 MPa or less.
The flexural modulus of the polypropylene resin can be determined based on JIS K7171: 2008.

The foamed particles have a tubular shape having through holes, the average pore diameter d is less than 1 mm, and the ratio d / D of the average pore diameter d to the average outer diameter D is 0.4 or less. By using a polypropylene-based resin containing the specific ethylene-propylene-butene copolymer as the base resin as the foamed particles and having the specific through holes, the appearance is good under wide molding heating temperature conditions. , It is possible to manufacture a molded product having excellent strength at the time of compression. Further, even if the curing step is omitted, a good molded product can be produced. The reason why the foamed particles have through holes to improve the moldability is that the heating medium such as steam supplied in the molding process passes through the through holes and spreads to the inside of the foamed particles group, so that the mold is filled. It is considered that the entire foamed particles are sufficiently heated to improve the secondary foaming property and the fusion property of the foamed particles.

The tubular foam particles having through holes preferably have at least one tubular hole penetrating the axial direction of the columnar foam particles such as a cylinder and a prism. It is more preferable that the foamed particles are columnar and have a tubular hole penetrating the axial direction thereof.
Further, from the viewpoint of improving the fusion property, a coating layer covering the surface of the foamed particles may be formed on the foamed particles. The coating layer is preferably composed of, for example, a polyolefin-based resin having a melting point lower than that of the polypropylene-based resin constituting the foamed particles.

If the foamed particles do not have through holes, it may be difficult to mold the molded product at a low molding heating temperature. Further, when the curing step is omitted, it may be difficult to produce a good molded product. On the other hand, even when the foamed particles have through holes, if the average pore diameter d is too large, the appearance of the molded product may be deteriorated and the strength at the time of compression may be deteriorated. .. In addition, the secondary foamability of the foamed particles during in-mold molding may decrease. From this point of view, the average pore size d of the foamed particles is less than 1 mm as described above. The average pore size d of the foamed particles is 0.9 mm or less from the viewpoint of further improving the appearance of the molded body, further improving the compressive strength, and further improving the secondary foamability of the foamed particles. Is more preferable, 0.85 mm or less is more preferable, and 0.8 mm or less is further preferable. From the viewpoint of ease of manufacture, the lower limit of the average pore size d of the foamed particles is approximately 0.2 mm or more.

The average pore diameter d of the through holes of the foamed particles is obtained as follows. Fifty or more foamed particles randomly selected from the foamed particle group are cut at a position where the area of the cut surface is maximum, perpendicular to the penetrating direction of the through hole. A photograph of the cut surface of each foamed particle is taken, the cross-sectional area (specifically, the opening area) of the through hole portion is obtained, the diameter of a virtual perfect circle having the same area as the area is calculated, and these are arithmetically performed. The average value is taken as the average pore diameter d of the through holes of the foamed particles.

The average outer diameter D of the foamed particles is preferably 2 mm or more, more preferably 2.5 mm or more, still more preferably 3 mm or more, from the viewpoint of increasing the filling property of the foamed particles into the mold and increasing the rigidity of the molded product. Yes, and preferably 5 mm or less, more preferably 4.5 mm or less, still more preferably 4.3 mm or less.

If the ratio d / D of the average pore diameter d to the average outer diameter D of the foamed particles is too large, the appearance of the molded body may be deteriorated and the strength at the time of compression may be deteriorated. Further, in this case, the secondary foamability of the foamed particles at the time of in-mold molding may decrease. From this point of view, the ratio d / D is 0.4 or less as described above. From the viewpoint of improving the appearance of the molded product, improving the compressive strength, and further improving the secondary foamability, the d / D is preferably 0.35 or less, and 0. It is more preferably 3 or less, further preferably 0.25 or less, and particularly preferably less than 0.2. The ratio d / D is preferably 0.1 or more from the viewpoint of ease of manufacture.

The average outer diameter D of the foamed particles is determined as follows. Fifty or more foamed particles randomly selected from the foamed particle group are cut at a position where the area of the cut surface is maximum, perpendicular to the penetrating direction of the through hole. A photograph of the cut surface of each foamed particle is taken, the cross-sectional area of the foamed particle (specifically, the cross-sectional area including the opening of the through hole) is obtained, and the diameter of a virtual perfect circle having the same area as the area is calculated. Then, the calculated average value is taken as the average outer diameter D of the foamed particles.

The average value of the wall thickness t of the foamed particles is preferably 1.2 mm or more and 2 mm or less. When the average value of the wall thickness t is within this range, the wall thickness of the foamed particles is sufficiently thick, so that the secondary foamability at the time of in-mold molding is further improved. Further, from the viewpoint that the foamed particles are less likely to be crushed by an external force and the compressive stress of the molded body is further improved, the average wall thickness t of the foamed particles is more preferably 1.3 mm or more, still more preferably 1.5 mm. That is all.

The wall thickness t of the foamed particles is the distance from the surface of the foamed particles (that is, the outer surface) to the outer edge of the through hole (that is, the inner surface of the foamed particles), and is a value obtained by the following formula (1).
t = (Dd) / 2 ... (1)
d: Average hole diameter (mm) of through holes
D: Average outer diameter (mm) of foamed particles

Further, the ratio t / D of the average wall thickness t to the average outer diameter D of the foamed particles is preferably 0.35 or more and 0.5 or less. When t / D is within the above range, the filling property of the foamed particles is good and the secondary foaming property can be further improved in the in-mold molding of the foamed particles. Therefore, a molded product having excellent rigidity can be manufactured at a lower molding heating temperature.

From the viewpoint of the balance between the lightness and rigidity of the molded body, the apparent density of the foamed particles is preferably 10 kg / m ³ or more and 150 kg / m ³ or less, and more preferably 15 kg / m ³ or more and 100 kg / m ³ or less. More preferably, it is 20 kg / m ³ or more and 80 kg / m ³ or less. Conventionally, particularly in the case of producing a molded product having a low apparent density, the molded product is remarkably easily deformed after mold release, and it is difficult to omit the curing step. On the other hand, in the foamed particles in the present disclosure, even when the apparent density is small, the curing step can be omitted, and a better molded product can be produced in the non-curing form. The non-curing form means a molding method in which curing is not performed after in-mold molding.

The apparent density of the foamed particles is such that the foamed particles are left in a measuring cylinder containing alcohol (for example, ethanol) at 23 ° C. at a relative humidity of 50%, 23 ° C., and 1 atm for one day (weight W of the foamed particles). (G)) is submerged using a wire net or the like, the volume V (L) of the foamed particle group is obtained from the rising water level, and the weight of the foamed particle group is divided by the volume of the foamed particle group (W / V). It can be obtained by converting the unit into [kg / m ³ ].

The ratio of the apparent density of the foamed particles to the bulk density of the foamed particles (that is, the apparent density / bulk density) is preferably 1.7 or more from the viewpoint of further increasing the rigidity of the molded body and improving the appearance. And, preferably 2.3 or less, more preferably 2.1 or less, still more preferably 1.9 or less.

The bulk density of the foamed particles is determined as follows. Foamed particles were randomly taken out from the foamed particle group and placed in a measuring cylinder having a volume of 1 L, and a large number of foamed particles were accommodated up to a scale of 1 L so as to be in a naturally deposited state. Is divided by the accommodating volume V2 (1L]) (W2 / V2) and the unit is converted to [kg / m ³ ] to obtain the bulk density of the foamed particles.

The foamed particles have excellent in-mold moldability, and a good molded product can be produced at a wide range of molding heating temperatures. Further, even if the curing step is omitted, a good molded product can be manufactured without the molded product being significantly shrunk or deformed. The reason why the foamed particles can produce a good molded product even if the curing step is omitted is not clear, but it is considered as follows.

The foamed particles are made of a polypropylene-based resin having a bending elastic modulus of a specific value or higher as a base resin. Therefore, it is considered that it is easy to suppress the shrinkage of the molded body after the mold release, and the dimensional change is suppressed. Further, the foamed particles are composed of an ethylene-propylene-butene copolymer having a copolymer composition in a specific range and have through holes having a predetermined shape, so that the foamed particles can be molded at a lower molding pressure. Is. Therefore, it is considered that the amount of heat received by the foamed particles by the heating medium such as steam in the in-mold molding can be suppressed to a low level, and the dimensional change due to the heat shrinkage of the molded body can be suppressed. Further, when the molded body has small air gaps derived from the through holes of the foamed particles, air immediately flows into the bubbles inside the molded body after the mold is released, and as a result, the internal pressure of the entire molded body is increased, and as a result, the molded body is formed. It is thought that the dimensions of the above can be easily stabilized at an early stage.
For the above reasons, it is considered that the foamed particles can produce a good molded product with stable dimensions even if the curing step is omitted.

[Manufacturing method of foamed particles]
The foamed particles include, for example, polypropylene-based resin particles using the ethylene-propylene-butene copolymer as a base resin in a dispersion medium (for example, a liquid), the resin particles are impregnated with a foaming agent, and the foaming agent is contained. It can be produced by a method of discharging resin particles under low pressure (that is, a method of foaming by releasing a dispersion medium). Specifically, polypropylene-based resin particles using an ethylene-propylene-butene copolymer as a base resin are dispersed in a dispersion medium in a closed container, and after heating, a foaming agent is press-fitted to apply a foaming agent to the resin particles. It is preferably impregnated. Then, after undergoing a holding step of growing secondary crystals at a constant temperature, it is preferable to foam the resin particles containing a foaming agent by releasing the contents in the closed container under low pressure to obtain foamed particles.

(Manufacturing of polypropylene resin particles)
The resin particles used for producing the foamed particles are produced, for example, as follows. First, the base resin is supplied into the extruder, heated and kneaded to obtain a resin melt. The base resin is an ethylene-propylene-butene copolymer, and for example, an additive such as a bubble nucleating agent is blended in the extruder as needed. After that, the resin melt can be obtained by extruding the resin melt into a tubular strand shape having through holes from the small holes of the die attached to the tip of the extruder, cooling the mixture, and cutting the resin particles. The cutting method can be selected from a strand cutting method, a hot cutting method, an underwater cutting method and the like. In this way, tubular non-foamed polypropylene-based resin particles having through holes can be obtained.

The particle size of the resin particles is preferably 0.1 to 3.0 mm, more preferably 0.3 to 1.5 mm. The length / diameter (specifically, outer diameter) ratio of the resin particles is preferably 0.5 to 5.0, and more preferably 1.0 to 3.0. The average mass per particle (determined from the mass of 200 randomly selected particles) is preferably adjusted to be 0.1 to 20 mg, more preferably 0.2 to 10 mg. It is more preferably 0.3 to 5 mg, and particularly preferably 0.4 to 2 mg.

In the strand cut method, the particle diameter, length / diameter ratio, and average mass of the resin particles are prepared by appropriately changing the extrusion speed, take-up speed, cutter speed, etc. when extruding the resin melt. Can be done by.

(Manufacturing of foamed particles)
An aqueous dispersion medium is used as a dispersion medium (specifically, a liquid) for dispersing the resin particles obtained as described above in a closed container. The aqueous dispersion medium is a dispersion medium containing water as a main component. The proportion of water in the aqueous dispersion medium is preferably 60% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more. Examples of the dispersion medium other than water in the aqueous dispersion medium include ethylene glycol, glycerin, methanol, ethanol and the like.

Resin particles include bubble preparation agents, crystal nucleating agents, colorants, flame retardants, flame retardants, plasticizers, antistatic agents, antioxidants, UV inhibitors, light stabilizers, and conductive materials, as required. Additives such as fillers and antibacterial agents can be added. Inorganic powders such as talc, mica, zinc borate, calcium carbonate, silica, titanium oxide, gypsum, zeolite, boric acid, aluminum hydroxide, and carbon; phosphoric acid-based nucleating agents and phenol-based nucleating agents. , Amine-based nucleating agent, organic powder such as polyfluoroethylene-based resin powder, and the like. When the bubble adjusting agent is added, the content of the bubble adjusting agent in the resin particles is preferably 0.01 to 1 part by mass with respect to 100 parts by mass of the polypropylene-based resin.

In the dispersion medium release foaming method, it is preferable to add a dispersant to the dispersion medium so that the polypropylene-based resin particles heated in the container do not fuse with each other in the container. The dispersant may be any one that prevents the polypropylene-based resin particles from fusing in the container, and can be used regardless of whether it is an organic-based or an inorganic-based dispersant, but a fine-grained inorganic substance is preferable because of its ease of handling. Examples of the dispersant include clay minerals such as amsunite, kaolin, mica, and clay. Clay minerals may be natural or synthetic. Examples of the dispersant include aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide and the like. One or more dispersants are used. Among these, it is preferable to use clay mineral as the dispersant. The dispersant is preferably added in an amount of about 0.001 to 5 parts by mass per 100 parts by mass of the resin particles.

When a dispersant is used, it is preferable to use an anionic surfactant such as sodium dodecylbenzene sulfonate, sodium alkylbenzene sulfonate, sodium lauryl sulfate, and sodium oleate as a dispersion aid. The amount of the dispersion aid added is preferably 0.001 to 1 part by mass per 100 parts by mass of the resin particles.

As a foaming agent for foaming polypropylene-based resin particles, it is preferable to use a physical foaming agent. Examples of the physical foaming agent include an inorganic physical foaming agent and an organic physical foaming agent, and examples of the inorganic physical foaming agent include carbon dioxide, air, nitrogen, helium, and argon. Examples of the organic physical foaming agent include aliphatic hydrocarbons such as propane, butane and hexane, cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane, chlorofluoromethane, trifluoromethane, 1,1-difluoromethane and 1 -Halogenated hydrocarbons such as chloro-1,1-dichloroethane, 1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride and the like can be mentioned. The physical foaming agent may be used alone or in combination of two or more. Further, an inorganic physical foaming agent and an organic physical foaming agent can be mixed and used. From the viewpoint of environmental load and handleability, an inorganic physical foaming agent is preferably used, and carbon dioxide is more preferable. When an organic physical foaming agent is used, it is preferable to use n-butane, i-butane, n-pentane, and i-pentane from the viewpoint of solubility in polypropylene resin and foamability.

The amount of the foaming agent added to 100 parts by mass of the polypropylene-based resin particles is preferably 0.1 to 30 parts by mass, and more preferably 0.5 to 15 parts by mass.

In the process of manufacturing foamed particles, as a method of impregnating the resin particles with a foaming agent, the resin particles are dispersed in an aqueous dispersion medium in a closed container, the foaming agent is press-fitted while heating, and the foaming agent is applied to the resin particles. The impregnation method is preferably used.

The internal pressure of the closed container at the time of foaming is preferably 0.5 MPa (G: gauge pressure) or more. On the other hand, the internal pressure of the closed container is preferably 4.0 MPa (G) or less. Within the above range, foamed particles can be safely produced without fear of damage or explosion of the closed container.

By raising the temperature of the aqueous dispersion medium in the foamed particle manufacturing step at 1 to 5 ° C./min, the temperature at the time of foaming can be set in an appropriate range.

Foamed particles having a crystal structure in which a resin-specific melting peak (resin-specific peak) and one or more melting peaks (high-temperature peak) appear on the high-temperature side of the DSC curve by differential scanning calorimetry (DSC) are, for example, as follows. It is obtained as follows.

A one-stage holding step of holding at a temperature equal to or higher than (melting point of polypropylene resin -20 ° C) and lower than (melting end temperature of polypropylene resin) for a sufficient time, preferably about 10 to 60 minutes, during heating in the foamed particle manufacturing step. conduct. Then, the temperature is adjusted from (melting point of polypropylene resin −15 ° C.) to (melting end temperature of polypropylene resin + 10 ° C.). Then, if necessary, a two-stage holding step of holding at that temperature for a further sufficient time, preferably about 10 to 60 minutes is performed. Next, the effervescent resin particles containing the effervescent agent are discharged from the closed container under low pressure to be foamed, whereby the effervescent particles having the above-mentioned crystal structure can be obtained. Foaming is preferably carried out in a closed container at (melting point of polypropylene resin −10 ° C.) or higher, and more preferably at (melting point of polypropylene resin) or higher (melting point of polypropylene resin + 20 ° C.) or lower. ..

The foamed particles obtained as described above are pressurized with air or the like to increase the internal pressure of the bubbles, and then heated with steam or the like to foam (two-stage foaming), and the foamed particles have a lower apparent density. It can also be.

(Manufacturing of molded product)
The molded product can be obtained by in-mold molding (that is, in-mold molding method) of the foamed particles. The in-mold molding method is performed by filling the foam particles in the molding mold and heat-molding using a heating medium such as steam. Specifically, after the foamed particles are filled in the molding mold, a heating medium such as steam is introduced into the molding mold to heat the foamed particles to cause secondary foaming, and the foamed particles are fused to each other for molding. It is possible to obtain a molded product in which the shape of the space is shaped. Further, it is preferable to mold the foamed particles by a pressure molding method (see, for example, Japanese Patent Publication No. 51-22951). In the pressure molding method, first, the foamed particles are pressure-treated in advance with a pressurized gas such as air to increase the pressure inside the bubbles of the foamed particles, and the pressure inside the foamed particles is 0.01 to 0 to 0, which is higher than the atmospheric pressure. .3 MPa Adjust to a higher pressure. Next, the foamed particles are filled in the molding mold under atmospheric pressure or reduced pressure, and then a heating medium such as steam is supplied into the mold to heat-fuse the foamed particles. In addition, foamed particles can also be molded by a compression filling molding method (see Japanese Patent Publication No. 4-46217). In the compression filling molding method, first, foamed particles pressurized to a pressure higher than the atmospheric pressure are filled in a molding mold pressurized to an atmospheric pressure or higher by a compressed gas. Next, a heating medium such as steam is supplied into the cavity to heat the foamed particles, and the foamed particles are heated and fused. In addition, foamed particles can also be molded by a normal pressure filling molding method (see Japanese Patent Publication No. 6-49795). In the normal pressure filling molding method, first, foamed particles having a high secondary foaming force obtained under special conditions are filled into the cavity of the molding mold under atmospheric pressure or reduced pressure. Next, a heating medium such as steam is supplied into the cavity to heat the foamed particles, and the foamed particles are heated and fused. Further, the foamed particles can also be molded by a method in which the above molding methods are combined (see Japanese Patent Publication No. 6-22919).

(Molded body)
The molded body is, for example, formed by in-mold molding of foamed particles, and is composed of a large number of foamed particles fused to each other. The molded body has a communication void. The communicating voids of the molded body include voids formed by communicating through holes of a plurality of foamed particles with each other, and voids formed by communicating the through holes of the foamed particles with the voids formed between the foamed particles. , Voids formed by communicating voids between foamed particles are formed by connecting them in a complicated manner.

The porosity of the molded product is 4% or more and 12% or less from the viewpoint of achieving a good balance between appearance and mechanical properties, and from the viewpoint of making it easier to suppress significant shrinkage and deformation of the molded product when the curing step is omitted. It is preferably 5% or more and 10% or less.

The porosity of the molded product can be determined as follows. First, a rectangular parallelepiped shape (length 20 mm x width 100 mm x height 20 mm test piece is cut out from the central part of the molded body. Then, this test piece is submerged in a measuring cylinder containing ethanol and the rise in the ethanol liquid level is observed. The true volume Vc [L] of the test piece is obtained. Further, the apparent volume Vd [L] is obtained from the external dimensions of the test piece. From the obtained true volume Vc and the apparent volume Vd, the following formula (2) is used. The void ratio of the molded product can be obtained.
Porosity (%) = [(Vd-Vc) / Vd] × 100 ... (2)

From the viewpoint of the balance between lightness and rigidity, the density of the molded body is preferably 10 kg / m ³ or more and 100 kg / m ³ or less, more preferably 15 kg / m ³ or more and 80 kg / m ³ or less, and more preferably 20 kg / m. It is more preferably ³ or more and 50 kg / m ³ or less. When the apparent density of the conventional molded product is small, it tends to shrink and deform significantly after mold release, so it is necessary to restore the dimensions of the molded product by providing a curing step. The molded product in the present disclosure has stable dimensions without a curing step even when the apparent density is small.

Since the foamed particles are excellent in moldability at a low molding heating temperature, the moldable temperature range in which a good molded product can be obtained during the production of the molded product is widened. Further, even when the curing step is omitted, a molded product having a good appearance and excellent mechanical strength can be obtained, so that the productivity is also excellent.

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

The following measurements and evaluations were carried out on the resins, foamed particles and molded products used in Examples and Comparative Examples. The evaluation of the foamed particles or the molded product was performed after the foamed particles or the molded product were allowed to stand for 24 hours under the conditions of a relative humidity of 50%, 23 ° C. and 1 atm to adjust the state.

<Polypropylene resin>
Table 1 shows the properties of the polypropylene-based resin used. The ethylene-propylene-butene copolymer used in this example is a random copolymer.

(Monomer component content of polypropylene resin)
The monomer component content of the polypropylene-based resin (specifically, ethylene-propylene-butene copolymer) was determined by a known method determined by an IR spectrum. Specifically, the Polymer Analysis Handbook (edited by the Japan Society for Analytical Chemistry, Polymer Analysis Research Council, publication date: January 1995, publisher: Kii Kuniya Bookstore, page numbers and item names: 615-616 "II. 2.3 2.3.4 Propene / Ethylene Copolymer ”, 618-619“ II.2.3 2.3.5 Propene / Butene Copolymer ”), that is, ethylene and butene. The absorbance was determined by a method of quantifying from the relationship between the value corrected by a predetermined coefficient and the thickness of the film-shaped test piece. More specifically, first, a polypropylene-based resin was hot-pressed in an environment of 180 ° C. to form a film, and a plurality of test pieces having different thicknesses were prepared. Then, by measuring the IR spectrum of each test piece, the absorbance at 722 cm ^-1 and 733 cm ^-1 derived from ethylene (A ₇₂₂ , A ₇₃₃ ) and the absorbance at 766 cm ^-1 derived from butene (A ₇₆₆ ) were read. rice field. Next, for each test piece, the ethylene component content in the polypropylene-based resin was calculated using the following formulas (3) to (5). The value obtained by arithmetically averaging the ethylene component contents obtained for each test piece was taken as the ethylene component content (unit: wt%) in the polypropylene resin.
( _K'733 ) _c = 1 / 0.96 {( _K'733 ) _a -0.268 (K' ₇₂₂ ) _a } ... (3)
( _K'722 ) _c = 1 / 0.96 {( _K'722 ) _a -0.268 (K' ₇₂₂ ) _a } ... (4)
Ethylene component content (%) = 0.575 {( _K'722 ) _c + ( _K'733 ) _c } ... (5)
However, in the formulas (3) to (5), _K'a : apparent extinction coefficient at each wave number ( _K'a = A / ρt), _K'c : corrected extinction coefficient, A: absorbance, ρ: resin. Density (unit: g / cm ³ ), t: thickness of film-shaped test piece (unit: cm). The above formulas (3) to (5) can be applied to a random copolymer.
Further, for each test piece, the butene component content in the polypropylene-based resin was calculated using the following formula (6). The value obtained by arithmetically averaging the butene component contents obtained for each test piece was taken as the ethylene component content (%) in the polypropylene resin.
Butene component content (%) = 12.3 (A ₇₆₆ / L) ... (6)
However, in the formula (6), A: absorbance and L: the thickness (mm) of the film-shaped test piece.

(Melting point of polypropylene resin)
The melting point of the polypropylene resin was determined based on JIS K7121: 1987. Specifically, "(2) When measuring the melting temperature after performing a certain heat treatment" is adopted as the state adjustment, and the state-adjusted test piece is heated from 30 ° C to 200 at a heating rate of 10 ° C / min. The DSC curve was obtained by raising the temperature to ° C., and the peak temperature of the melting peak was taken as the melting point. As the measuring device, a heat flux differential scanning calorimetry device (manufactured by SII Nanotechnology Co., Ltd., model number: DSC7020) was used.

(Polypropylene resin melt flow rate)
The melt flow rate (that is, MFR) of the polypropylene-based resin was measured in accordance with JIS K7210-1: 2014 under the conditions of a temperature of 230 ° C. and a load of 2.16 kg.

(Bending elastic modulus of polypropylene resin)
A polypropylene resin was heat-pressed at 230 ° C. to prepare a 4 mm sheet, and a test piece having a length of 80 mm × a width of 10 mm × a thickness of 4 mm was cut out from this sheet. The flexural modulus of this test piece was determined in accordance with JIS K7171: 2008. The radius R1 of the indenter and the radius R2 of the support stand are both 5 mm, the distance between the fulcrums is 64 mm, and the test speed is 2 mm / min.

<Effervescent particles>
Table 2 shows the properties of the foamed particles.

(Average hole diameter d of through holes)
The average pore diameter of the through holes of the foamed particles was determined as follows. 100 foamed particles randomly selected from the state-adjusted foamed particle group were cut perpendicular to the penetrating direction of the through hole at the position where the area of the cut surface was maximized. The cut surface of each foamed particle was photographed, and the cross-sectional area (opening area) of the through-hole portion in the cross-sectional photograph was obtained. The diameter of a virtual perfect circle having the same area as the cross-sectional area was calculated, and the value obtained by arithmetically averaging these was taken as the average pore diameter (d) of the through holes of the foamed particles.

(Average outer diameter D)
The average outer diameter of the foamed particles was determined as follows. 100 foamed particles randomly selected from the state-adjusted foamed particle group were cut perpendicular to the penetrating direction of the through hole at the position where the area of the cut surface was maximized. The cut surface of each foamed particle was photographed to determine the cross-sectional area of the foamed particle (including the opening of the through hole). The diameter of a virtual perfect circle having the same area as the cross-sectional area was calculated, and the value obtained by arithmetically averaging these was taken as the average outer diameter (D) of the foamed particles.

(Average wall thickness t)
The average wall thickness of the foamed particles was calculated by the following formula (7).
Average wall thickness t = (average outer diameter D-average hole diameter d) / 2 ... (7)

(Aspect ratio L / D)
Before measuring the average outer diameter D of the foamed particles and the average pore diameter d of the through holes, the maximum length of 100 foamed particles in the penetration direction of the through holes was measured with a nogis, and these were arithmetically averaged to obtain the foamed particles. The average length L of the foamed particles was obtained, and the average aspect ratio L / D of the foamed particles was obtained by dividing the average length L by the average outer diameter D.

(Apparent density)
The apparent density of the foamed particles was determined as follows. First, prepare a graduated cylinder containing ethanol at a temperature of 23 ° C, and use a wire mesh in the ethanol in the graduated cylinder to put an arbitrary amount of foamed particles (mass W1 [g] of the foamed particles) after adjusting the state. And sank. Then, in consideration of the volume of the wire mesh, the volume V1 [L] of the foamed particle group read from the water level rise was measured. The apparent density of the foamed particles is calculated by dividing the mass W1 [g] of the foamed particles placed in the graduated cylinder by the volume V1 [L] (W1 / V1) and converting the unit to [kg / m ³ ]. I asked.

(The bulk density)
The bulk density of the foamed particles was determined as follows. Foamed particles are randomly taken out from the state-adjusted foamed particle group and placed in a measuring cylinder having a volume of 1 L. The bulk density of the foamed particles was determined by dividing W2 [g] by the accommodating volume V2 (1 [L]) (W2 / V2) and converting the unit into [kg / m ³ ].

(The amount of heat of fusion of each peak of the DSC curve of the foamed particles)
One foamed particle was collected from the foamed particle group after the state adjustment. Using these foamed particles as a test piece, the test piece is heated from 23 ° C to 200 ° C at a heating rate of 10 ° C / min by a differential thermal scanning calorimeter (specifically, DSC.Q1000 manufactured by TA Instruments). The DSC curve when the temperature was raised was obtained. FIG. 1 shows an example of a DSC curve. As illustrated in FIG. 1, a resin-specific peak ΔH1 and a high-temperature peak ΔH2 having an apex on the high-temperature side of the apex of the resin-specific peak ΔH1 appear on the DSC curve.
Next, a straight line L1 was obtained by connecting the point α on the DSC curve at a temperature of 80 ° C. and the point β at the melting end temperature T of the foamed particles. Next, a straight line L2 parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the resin-specific peak ΔH1 and the high-temperature peak ΔH2, and the point where the straight line L1 and the straight line L2 intersect is δ. And said. The point γ can also be said to be a maximum point existing between the resin-specific peak ΔH1 and the high-temperature peak ΔH2.
The area of the resin-specific peak ΔH1 is the area of the curve of the resin-specific peak ΔH1 portion of the DSC curve and the portion surrounded by the line segment α-δ and the line segment γ-δ, which is the heat of fusion of the resin-specific peak. And said.
The area of the high temperature peak ΔH2 is the area of the curve of the high temperature peak ΔH2 portion of the DSC curve and the portion surrounded by the line segment δ-β and the line segment γ-δ, and this is taken as the heat of fusion of the high temperature peak.
The area of the total melting peak is the area of the portion surrounded by the curve of the resin-specific peak ΔH1 portion of the DSC curve, the curve of the high temperature peak ΔH2 portion, and the line segment α-β (that is, the straight line L1). The amount of heat of melting of the melting peak was used.
The above measurements were performed on 5 foamed particles, and the arithmetic mean values are shown in Table 2.

<Molded body>
Table 3 shows the properties of the molded product.

(Evaluation of in-mold formability)
In-mold moldability is evaluated by examining the moldable range. Specifically, first, the molded product was molded by changing the molding steam pressure between 0.20 and 0.28 MPa (G) by 0.02 MPa by the method of <Manufacturing the molded product> described later. The molded product after mold release was allowed to stand in an oven at 80 ° C. for 12 hours. The curing process is 12 hours of standing in the oven. After the curing step, the state of the molded product was adjusted by allowing the molded product to stand at a relative humidity of 50%, 23 ° C., and 1 atm for 24 hours. Next, the fusion property and recoverability of the molded product (specifically, the recovery property of expansion or contraction after in-mold molding) were evaluated. As a result, those that met the following criteria were regarded as acceptable, and the steam pressure that passed all the items (that is, the steam pressure that the accepted product could be obtained) was defined as the steam pressure that can be molded. The wider the range from the lower limit value to the upper limit value of the moldable steam pressure, the wider the moldable molding heating temperature range.

(Fusionability)
The molded body was bent and broken, the number C1 of the foamed particles present in the fracture surface and the number C2 of the broken foamed particles were obtained, and the ratio of the broken foamed particles to the foamed particles (that is, the material fracture rate) was calculated. .. The material fracture rate is calculated from the formula C2 / C1 × 100. The above measurements were performed 5 times using different test pieces to determine the material fracture rate. When the arithmetic mean value of the material destruction rate was 80% or more, it was regarded as passing.

(Recoverability)
The thickness of the vicinity of the four corners (specifically, 10 mm inside from the corner in the center direction) and the center (vertically, The thickness of each of the portions (parts divided into two equal parts in the horizontal direction) was measured. Next, the ratio (unit:%) of the thickness of the thinnest part to the thickness of the thickest part in the vicinity of the four corners was calculated, and the case where the ratio was 95% or more was regarded as acceptable.

(Evaluation of in-mold formability in non-cultivated form)
The meltability and recoverability were evaluated in the same manner as in the above-mentioned evaluation of in-mold moldability, except that the molded product after mold release was allowed to stand at 23 ° C. for 12 hours without performing a curing step. Based on the evaluation results, the judgment was made according to the following criteria.
◯: A passing product could be obtained at any of the molding steam pressures.
X: No accepted product could be obtained at any of the molding steam pressures.

In <Manufacturing of a molded product> described later, a molded product obtained at a molding pressure of 0.24 MPa (G) is allowed to stand for 24 hours at a relative humidity of 50%, 23 ° C., and 1 atm to adjust the state. , The void ratio of the molded body, the density of the molded body, the measurement of 50% compressive stress, and the surface property evaluation were performed. In Comparative Example 3, a molded product obtained at a molding pressure of 0.20 MPa (G) whose state was adjusted was used for each measurement and evaluation.

(Porosity of molded product)
The porosity of the molded product was determined as follows. A rectangular parallelepiped shape (length 20 mm x width 100 mm x height 20 mm) cut out from the center of the molded body is submerged in a measuring cylinder containing ethanol, and the true volume of the test piece is Vc [ L] was obtained. Further, the apparent volume Vd [L] was obtained from the external dimensions of the test piece. From the obtained true volume Vc and the apparent volume Vd, the void ratio of the molded body was obtained by the following formula (8). Asked.
Porosity (%) = [(Vd-Vc) / Vd] × 100 ... (8)

(Molded body density)
The molded body density (kg / m ³ ) is calculated by dividing the weight (g) of the molded body by the volume (L) obtained from the external dimensions of the molded body and converting the unit.

(Compressive stress at 50% strain)
A test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm was cut out from the center of the molded body so that the skin layer on the surface of the molded body was not included in the test piece. Based on JIS K6767: 1999, a compression test was performed at a compression rate of 10 mm / min to determine a 50% compressive stress of the molded product.

(Surface evaluation)
Evaluation was made based on the following criteria.
A: Shows a good surface condition with few particle gaps on the surface of the foamed particle molded body and inconspicuous unevenness due to through holes, etc. B: Due to particle gaps and / or through holes, etc. on the surface of the foamed particle molded body. Some unevenness is observed C: Unevenness due to particle gaps and / or through holes is significantly observed on the surface of the foamed particle molded body.

(Evaluation of water cooling time)
In the <manufacturing of the molded body> described later, after the heating is completed, the pressure is released and the time required for water cooling until the value of the surface pressure gauge attached to the inner surface of the molding mold drops to 0.04 MPa (G) (that is, water cooling). Time) was measured and evaluated according to the following criteria based on the measured water cooling time. The water cooling time was evaluated by the water cooling time in molding at a molding pressure of 0.26 MPa (G). The reason why the condition of the molding pressure of 0.26 MPa (G) is adopted for the evaluation of the water cooling time is that the higher the molding pressure, the longer the water cooling time tends to be.
A: Water cooling time is 70 seconds or less B: Water cooling time is over 70 seconds and 120 seconds or less C: Water cooling time is over 120 seconds

Hereinafter, the method for producing the foamed particles and the method for producing the molded product in Examples 1 to 3 and Comparative Examples 1 to 4 will be described.
(Example 1)
<Manufacturing of polypropylene-based foam particles>
Polypropylene resin 1 (abbreviated as PP1) was melt-kneaded in an extruder at a maximum set temperature of 230 ° C. to obtain a resin melt. PP1 is an ethylene-propylene-butene copolymer having a butene component content of 9.0% by mass and an ethylene component content of 1.0% by mass. The characteristics of PP1 are shown in Table 1. Next, the resin melt is extruded into a strand shape having a tubular shape having a through hole from a small hole of a die attached to the tip of the extruder, and after cooling with water while taking the strand shape, the mass is about 1. It was cut to 5 mg. In this way, cylindrical polypropylene-based resin particles having through holes were obtained. The aspect ratio of the polypropylene-based resin particles is 2.5. In the production of the resin particles, zinc borate as a bubble adjusting agent was supplied to the extruder, and 500 mass ppm of zinc borate was contained in the polypropylene-based resin.

1 kg of polypropylene-based resin particles are charged in a closed container of 5 L together with 3 L of water as a dispersion medium, and 0.3 parts by mass of kaolin as a dispersant and a surfactant (sodium alkylbenzene sulfonate) are further charged with respect to 100 parts by mass of the resin particles. 0.004 parts by mass was added into the closed container. After adding 70 g of dry ice as a foaming agent into the closed container, the closed container was sealed and heated to a foaming temperature of 143.2 ° C. while stirring the inside of the closed container. The pressure inside the container (impregnation pressure) at this time was 3.1 MPa (G). After holding at the same temperature (that is, 143.2 ° C.) for 15 minutes, the contents of the container were released under atmospheric pressure to obtain foamed particles. The foamed particles were dried at 23 ° C. for 24 hours.

Next, the foamed particles were put into the pressure-resistant container, and air was press-fitted into the pressure-resistant container to increase the pressure inside the container, and the air was impregnated into the bubbles to increase the internal pressure of the foamed particles in the bubbles. Next, steam was supplied to the foamed particles (one-stage foamed particles) taken out from the pressure-resistant container so that the pressure in the pressure-resistant container became the pressure shown in Table 2, and the particles were heated under atmospheric pressure. The pressure inside the bubbles (however, the gauge pressure) in the one-stage foamed particles taken out from the pressure-resistant container was the value shown in Table 2. As a result, the apparent density of the one-stage foamed particles was reduced to obtain foamed particles (two-stage foamed particles).

<Manufacturing of molded products>
For the production of the molded product, the foamed particles obtained by the above two-stage foaming were dried at 23 ° C. for 24 hours. The effervescent particles after drying were pressurized with pressurized air, and the internal pressure in the effervescent particles was set to 0.10 MPa (G). Next, an exhaust process in which a flat plate molding die having a cracking amount adjusted to 6 mm, length 300 mm × width 250 mm × thickness 60 mm is filled with foamed particles, molded, and steam is supplied from both sides of the die for 5 seconds for preheating. Was done. Then, steam was supplied from one side of the mold until the pressure reached 0.08 MPa (G) lower than the predetermined molding pressure, and heating was performed on the other side. Next, steam is supplied from the other surface side of the mold until the pressure reaches 0.04 MPa (G) lower than the molding pressure, and then heating is performed on one side, and then heating is performed until the predetermined molding pressure is reached (that is, main heating). Was done. After the heating was completed, the pressure was released, and after water cooling until the surface pressure due to the foaming force of the molded product became 0.04 MPa (G), the mold was opened and the molded product was taken out. Next, a curing step was performed in which the molded product was allowed to stand in an oven at 80 ° C. for 12 hours. The molded product was manufactured in this way.

(Example 2)
Foamed particles were obtained in the same manner as in Example 1 except that the polypropylene-based resin 1 was changed to the polypropylene-based resin 2 (abbreviated as PP2) and the foaming temperature was changed to the values shown in Table 2. Further, a molded product was obtained in the same manner as in Example 1. PP2 is an ethylene-propylene-butene copolymer, and its monomer component content and the like are shown in Table 1.

(Example 3)
Foamed particles were obtained in the same manner as in Example 1 except that the polypropylene-based resin 1 was changed to the polypropylene-based resin 3 (abbreviated as PP3) and the impregnation pressure and the foaming temperature were changed to the values shown in Table 2. Further, a molded product was obtained in the same manner as in Example 1. PP3 is an ethylene-propylene-butene copolymer, and its monomer component content and the like are shown in Table 1.

(Comparative Example 1)
Effervescent particles were obtained in the same manner as in Example 1 except that the resin particles having no through holes were produced during the production of the polypropylene-based resin particles. The foamed particles of this example were substantially spherical foamed particles having no through holes. Further, a molded product was obtained in the same manner as in Example 1.

(Comparative Example 2)
In the production of polypropylene-based resin particles, foaming was carried out in the same manner as in Example 1 except that the pore diameters of the small holes of the die for forming the through holes were changed and the carbon dioxide pressure and the foaming temperature were changed to the values shown in Table 2. Obtained particles. Further, a molded product was obtained in the same manner as in Example 1.

(Comparative Example 3)
Foamed particles were obtained in the same manner as in Example 1 except that the polypropylene-based resin 1 was changed to the polypropylene-based resin 4 (abbreviated as PP4) and the impregnation pressure and the foaming temperature were changed to the values shown in Table 2. Further, a molded product was obtained in the same manner as in Example 1. PP4 is an ethylene-propylene-butene copolymer, and its monomer component content and the like are shown in Table 1.

(Comparative Example 4)
Foamed particles were obtained in the same manner as in Example 1 except that the polypropylene-based resin 1 was changed to the polypropylene-based resin 5 (abbreviated as PP5) and the impregnation pressure and the foaming temperature were changed to the values shown in Table 2. Further, a molded product was obtained in the same manner as in Example 1. PP5 is an ethylene-propylene copolymer, and its monomer component content and the like are shown in Table 1.

As can be understood from Tables 2 to 3, according to the foamed particles of Examples 1 to 3, it is possible to produce a molded product having a good appearance and excellent strength at the time of compression under a wide range of molding pressures. Further, even if the curing step is omitted, a molded body having a good appearance and excellent mechanical strength can be produced.

Claims (10)

Cylindrical polypropylene-based resin foam particles with through holes.
The average pore diameter d of the through holes of the foamed particles is less than 1 mm, and the ratio d / D of the average pore diameter d to the average outer diameter D of the foamed particles is 0.4 or less.
The polypropylene-based resin constituting the foamed particles is an ethylene-propylene-butene copolymer.
The total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer is 2% by mass or more and 15% by mass or less, and the butene component is contained with respect to the ethylene component content [mass%]. The ratio of amount [mass%] is 2 or more,
Polypropylene-based resin foamed particles having a flexural modulus of the polypropylene-based resin of 800 MPa or more. The total amount of the butene component content and the ethylene component content in the ethylene-propylene-butene copolymer is more than 6% by mass and 15% by mass or less, and the butene component content is 6% by mass or more and 15%. The polypropylene-based resin foamed particles according to claim 1, which are less than mass%. The polypropylene-based resin foamed particles according to claim 1 or 2, wherein the ratio of the butene component content [mass%] to the ethylene component content [mass%] is 6 or more. The polypropylene-based resin foamed particles according to any one of claims 1 to 3, wherein the ethylene component content in the ethylene-propylene-butene copolymer is 0.05% by mass or more and 3% by mass or less. The polypropylene-based resin foamed particles according to any one of claims 1 to 4, wherein the polypropylene-based resin has a melting point of 135 ° C. or higher and 145 ° C. or lower. The polypropylene-based resin foamed particles according to any one of claims 1 to 5, wherein the average outer diameter D is 2 mm or more and 5 mm or less. The polypropylene-based resin foamed particles according to any one of claims 1 to 6, wherein the polypropylene-based resin foamed particles have an average wall thickness t of 1.2 mm or more and 2 mm or less. The polypropylene-based resin foamed particles according to any one of claims 1 to 7, wherein the ratio d / D is 0.25 or less. The polypropylene-based resin foamed particles according to any one of claims 1 to 8, wherein the apparent density of the foamed particles is 10 kg / m ³ or more and 100 kg / m ³ or less. A foamed particle molded body in which the polypropylene-based resin foamed particles according to any one of claims 1 to 9 are fused to each other and have communicating voids.

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