JP5399126B2 - Method for producing polyolefin resin expanded particles and polyolefin resin expanded particles - Google Patents

Description

  The present invention relates to a method for producing polyolefin resin expanded particles used for in-mold molding and the like and polyolefin resin expanded particles.

  Polyolefin resins have a good balance of mechanical strength, heat resistance, chemical resistance, processability, price, etc., and are excellent in incineration and recyclability. A foamed particle molded body obtained by in-mold molding of foamed particles made of such a polyolefin resin has excellent properties of the polyolefin resin as described above, and is excellent in toughness, compression strain recovery, and the like. Therefore, it is widely used for packaging materials, building materials, vehicle shock absorbing materials, and the like.

  When producing low-density polyolefin-based resin expanded particles by increasing the expansion ratio, there is a problem that the obtained expanded particles tend to shrink. In particular, when an inorganic physical foaming agent is used as a foaming agent, an improvement in foaming ratio cannot be expected as compared with an organic physical foaming agent. Therefore, for the purpose of improving the foaming ratio, water-soluble inorganic substances, water-soluble resins, water absorption In some cases, water commonly used as a dispersion medium for resin particles also acts as a foaming agent. Shrinkage easily occurs, especially with foamed particles having a low density, and the shrinkage tends to be significant. Further, the cell structure is difficult to be uniform, and the density variation among the foamed particles tends to occur.

  If the expanded particles shrink, it becomes difficult to manage the density of the expanded particles. Furthermore, when foamed particles that have been shrunk are molded in a mold, it is difficult to obtain a desired low-density foamed particle compact. Moreover, in order to improve the secondary foamability of the foamed particles at the time of in-mold molding, a process of applying an internal pressure to the foamed particles may be performed, but there is a problem that the efficiency of the internal pressure applying process is lowered.

  Conventionally, in order to obtain low-density polyolefin resin expanded particles, low-density expanded particles once contracted are produced, and the contracted expanded particles are recovered under heating conditions or pressurized in a pressure vessel. Perform a shrinkage recovery process to recover or expand to a density that does not shrink, pressurize the foamed particles in a pressure vessel, and heat-foam the pressurized foamed particles again to obtain the desired low-density foamed particles In addition to the foaming process, it was necessary to perform a secondary process such as performing two-stage foaming to obtain

  For the purpose of solving the shrinkage problem, Patent Document 1 discloses resin particles obtained by blending a metal borate such as zinc borate as a foam regulator when producing polyolefin resin foam particles. It is disclosed to use. According to this method, it is possible to produce expanded polyolefin resin particles having a high expansion ratio and uniform cell diameter, and the expanded molded product molded in-mold using such expanded polyolefin resin particles is shrunk. It is said that the ratio is small and the dimensional stability is improved.

Japanese Patent No. 3638960

However, it has become possible to produce polyolefin-based foamed resin particles with an apparent density of 85 kg / m ³ (bulk density 53 kg / m ³ ) in one step by blending the boric acid metal salt. When low-density foam particles are produced, the resulting foam particles tend to shrink, so a shrinkage recovery step is necessary. Further, when the blending amount of the boric acid metal salt is increased in order to improve the foaming efficiency, the foamed particles are greatly shrunk, and there is room for improvement in that respect.

  When foamed particles having a small cell diameter are molded in-mold to produce a molded body, the resulting foamed particle molded body has excellent appearance. However, in the conventional polyolefin resin foamed particles, if the bubble diameter is too small, the bubble film thickness becomes thin, so that the closed cell ratio tends to decrease due to heating during in-mold molding. However, the surface of the obtained foamed particle molded body was not smooth and was not easily smoothened. On the other hand, even when the closed cell structure can be maintained, the foamed particle surface is easily melted excessively by heating at the time of molding in the mold, and voids are generated on the surface of the resulting foamed particle molded body, or the molded body contracts greatly. As a result, it was difficult to maintain the shape of the mold, leaving room for improvement.

  The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to reduce the steps such as shrinkage recovery treatment and two-stage foaming treatment, and to produce low-density foamed particles. The object is to provide a method for producing polyolefin resin foamed particles, which is capable of producing foamed particles having a uniform cell structure over a density range and small density variation from particle to particle, and is excellent in moldability. Another object of the present invention is to provide expanded polyolefin resin particles.

As a result of intensive studies in view of the above problems, the present inventors have used polyolefin resin particles containing a specific amount of one or more resins selected from aromatic polycarbonate resins and polyethylene terephthalate in resin particles. Thus, it has been found that the above problems can be solved by producing polyolefin resin expanded particles, and the present invention has been completed.

That is, the gist of the present invention is the invention described in the following (1) to (11).
(1) In the method for producing foamed particles by releasing foamable resin particles obtained by impregnating a polyolefin-based resin particle with a foaming agent, together with a dispersion medium, from the inside of the sealed container under a pressure lower than the pressure in the sealed container, The polyolefin resin particles contain at least one resin (A) selected from an aromatic polycarbonate resin and polyethylene terephthalate, and the total content of the resin (A) constitutes the resin particles. A method for producing polyolefin resin expanded particles (hereinafter, sometimes referred to as a first embodiment), which is 15 parts by weight or less (excluding 0) with respect to 100 parts by weight.
(2) The total content of the resin (A) in the polyolefin resin particles is 0.01 to 12 parts by weight with respect to 100 parts by weight of the polyolefin resin constituting the resin particles. The manufacturing method of the polyolefin resin expanded particle as described in said (1).
(3) The method for producing polyolefin resin expanded particles according to (1) or (2), wherein the resin (A) is an aromatic polycarbonate resin.
(4) The method for producing expanded polyolefin-based resin particles according to (3), wherein the polycarbonate-based resin has a melt mass flow rate of 5 to 80 g / 10 minutes at 300 ° C. and a load of 1.2 kgf.
(5) The method for producing expanded polyolefin resin particles according to any one of (1) to (4), wherein the polyolefin resin is a polypropylene resin.
(6) The method for producing expanded polyolefin resin particles according to any one of (1) to (5), wherein the foaming agent is an inorganic physical foaming agent.
(7) The method for producing expanded polyolefin resin particles according to (6), wherein the foaming agent is carbon dioxide.
(8) The method for producing polyolefin resin expanded particles according to any one of (1) to (7), wherein the dispersion medium is an aqueous dispersion medium.
(9) Polyolefin resin foamed particles containing one or more resins (A) selected from aromatic polycarbonate resins and polyethylene terephthalate, wherein the total content of the resin (A) constitutes the resin particles Polyolefin resin expanded particles (hereinafter sometimes referred to as a second embodiment), characterized in that it is 15 parts by weight or less (excluding 0) with respect to 100 parts by weight of the polyolefin resin.
(10) The polyolefin resin expanded particles according to (9) above, wherein the apparent density is 15 to 200 kg / m ³ and the average cell diameter is 10 to 300 μm.
(11) The apparent density (X) after pressurizing the expanded particles with compressed air under the conditions of 30 ° C. and 0.2 MPa (G) for 24 hours and then leaving them under normal pressure of 23 ° C. for 24 hours; The polyolefin resin foam as described in (9) or (10) above, wherein the ratio (X / Y) to the apparent density (Y) of the expanded foam particles before compression is 0.9 to 1.0 particle.

According to the method for producing expanded polyolefin resin particles of the present invention, polyolefin resin particles containing a specific amount of one type of resin (A) selected from aromatic polycarbonate resin and polyethylene terephthalate in producing expanded particles. By using, even if the bubbles are fine, it becomes possible to produce low density foamed particles with little shrinkage after foaming. Since the obtained foamed particles hardly shrink immediately after foaming, a secondary process such as a recovery process such as pressurization or heating of the particles becomes unnecessary or reduced. Furthermore, the polyolefin resin expanded particles obtained by the production method of the present invention have a fine cell diameter and little variation in a wide density range, and the density distribution of the expanded particles is also narrow.
In addition, since the polyolefin resin expanded particles of the present invention contain a specific amount of the resin (A) in the expanded particles, not only when the bubbles are coarse, but also when the bubbles are fine, closed cells are formed during in-mold molding. Since the structure can be maintained, the secondary foamability is excellent and the fusing property is excellent, so that the in-mold foam-molded product obtained from the foamed particles has excellent dimensional stability and good appearance. Furthermore, since the polyolefin-based resin expanded particles of the present invention can maintain a closed cell structure even during the two-stage expansion process, expanded particles having a lower apparent density than conventional ones can be obtained by two-stage expansion.

The “method for producing polyolefin resin expanded particles” according to the first aspect of the present invention and the “polyolefin resin expanded particles” according to the second aspect will be described below.
[1] “Method for producing polyolefin resin expanded particles” according to the first aspect “Method for producing polyolefin resin expanded particles (hereinafter sometimes simply referred to as expanded particles)” according to the first aspect of the present invention Release foaming resin particles obtained by impregnating a polyolefin resin particle (hereinafter sometimes simply referred to as resin particles) with a foaming agent, together with a dispersion medium, from the inside of the sealed container to a pressure lower than the pressure in the sealed container. In the method for producing foamed particles, the polyolefin resin particles contain at least one resin (A) selected from an aromatic polycarbonate resin and polyethylene terephthalate , and the total amount of the resin (A) A tree having a content of 15 parts by weight or less (excluding 0) with respect to 100 parts by weight of polyolefin resin constituting the resin particles. Characterized by using particles.
The polyolefin resin particles used in the method for producing polyolefin resin foam particles, the impregnation of the foaming agent into the resin particles, and the foaming of the resin particles are described below.

(1) Polyolefin resin particles The polyolefin resin particles used in the method for producing polyolefin resin foamed particles contain a specific amount of one or more resins (A) selected from aromatic polycarbonate resins and polyethylene terephthalate. ing.
(1-1) Polyolefin-based resin In the present invention, the polyolefin-based resin constituting the polyolefin-based resin particle is a polyolefin-based resin having an olefin component unit as a main component, specifically, a polypropylene-based resin or a polyethylene-based resin. Furthermore, the mixture of 2 or more types of those etc. is mentioned. The above-mentioned “main component” means that the olefin component unit is contained in the polyolefin resin in an amount of 50% by weight or more, and the content thereof is preferably 75% by weight or more, more preferably 85% by weight. % Or more, more preferably 90% by weight or more.
Examples of the polypropylene resin include a propylene homopolymer or a copolymer of propylene and another olefin copolymerizable with propylene. Examples of other olefins copolymerizable with propylene include ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1 Examples thereof include α-olefins having 4 to 10 carbon atoms such as heptene and 3-methyl-1-hexene. The copolymer may be a random copolymer or a block copolymer, and may be not only a binary copolymer but also a ternary copolymer. The other olefin copolymerizable with propylene in the copolymer is preferably contained in a proportion of 25% by weight or less, particularly 15% by weight or less, and the lower limit is 0.3% by weight. Preferably there is. These polypropylene resins can be used alone or in combination of two or more.
On the other hand, examples of the polyethylene resin include resins having an ethylene component unit of 50% by weight or more, such as high density polyethylene, low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene. Copolymer, ethylene-propylene-butene-1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 Copolymers and the like, and a mixture of two or more thereof are also included.
Among the polyolefin resins described above, a polypropylene resin is preferable because it is particularly excellent in the balance between mechanical strength and heat resistance.

(1-2) Resin (A)
In the present invention, the polyolefin resin particles contain one or more resins (A) selected from an aromatic polycarbonate resin and polyethylene terephthalate , and the total content of the resin (A) is a polyolefin resin. It is 15 parts by weight or less (however, 0 is not included) with respect to 100 parts by weight.
By producing polyolefin resin foamed particles using polyolefin resin particles containing a specific amount of resin (A) in the resin particles, even if the foamed resin particles are low-density foamed particles, The effect of suppressing shrinkage (shrinkage suppression effect) is exhibited, and further, the effect of improving the foaming ratio (foaming ratio improving effect) can be expected together with the effect of improving the uniformity of the bubble diameter (bubble uniforming effect).

  In the present invention, the aromatic polycarbonate-based resin refers to a polymer represented by the following general chemical formula (1) that contains 50 mol% or more, preferably 70 mol% or more of a basic structural unit having a carbonic acid bond.

上記一般化学式（１）において、Ｒはビスフェノール類の芳香族炭化水素である。
また、芳香族ポリエステル系樹脂とは、芳香族ジカルボン酸成分とジオール成分とを含むポリエステルであり、例えば、ポリエチレンテレフタレート、ポリプロピレンテレフタレート、ポリブチレンテレフタレート、ポリシクロヘキサンジメチレンテレフタレート、ポリエチレンナフタレート、ポリブチレンナフタレートなどが挙げられる。
前記樹脂（Ａ）の中でも、上記効果をより有効に発揮させるためには、芳香族ポリカーボネート系樹脂が好ましい。

In the above general chemical formula (1), R is a bisphenol aromatic hydrocarbon.
The aromatic polyester resin is a polyester containing an aromatic dicarboxylic acid component and a diol component. For example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexanedimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate. A phthalate etc. are mentioned.
Among the resins (A), an aromatic polycarbonate resin is preferable in order to exhibit the above effects more effectively.

  The total content of the resin (A) in the resin particles is 15 parts by weight or less (however, 0 is not included) with respect to 100 parts by weight of the polyolefin resin constituting the resin particles. When the content of the resin (A) in the resin particles is within the above range, it is possible to obtain foamed particles with uniform air bubbles without impairing the excellent characteristics of the polyolefin resin as described above, and A high shrinkage prevention effect is obtained, and the foaming magnification improvement effect is also excellent. That is, if the content of the resin (A) is too small, the desired effect of addition is not sufficiently exhibited. On the other hand, if the content is too large, the rigidity of the base resin of the resin particles is increased, so that the original properties of the polyolefin resin are expressed. There is a possibility that the expansion ratio of the resin at the time of foaming is reduced and the effect of improving the expansion ratio is not obtained. From such a viewpoint, the upper limit of the total content of the resin (A) in the resin particles is preferably 12 parts by weight, more preferably 10 parts by weight with respect to 100 parts by weight of the polyolefin resin constituting the resin particles. More preferably 7 parts by weight, particularly preferably 5 parts by weight, and most preferably 3 parts by weight. On the other hand, the lower limit is preferably 0.01 parts by weight, more preferably 0.05 parts by weight, and still more preferably 0.1 parts by weight with respect to 100 parts by weight of the polyolefin resin constituting the resin particles. is there.

(1-3) Method for Producing Polyolefin Resin Particles Containing Resin (A) As a method for granulating resin particles, polyolefin is used so that the resin (A) is dispersed in the continuous phase of the polyolefin resin. The resin and resin (A) are sufficiently melt-kneaded with an extruder or the like, the melt-kneaded product is extruded into a strand or sheet, and the resin particles are cut or crushed into a desired size. A conventionally known method of manufacturing can be employed.
As specific melt kneading conditions, (a) a polyolefin resin and a resin (A) are sufficiently mixed at a melting temperature when the resin (A) is generally extruded by an extruder, for example, at a temperature of about 280 ° C. Method of melt-kneading, (b) Add the resin (A) to the polyolefin resin so that the concentration of the resin (A) in the masterbatch is 3 to 50% by weight, and both at a temperature of about 280 ° C. A method for preparing a master batch of the resin (A) by sufficiently melting and mixing, adding the master batch to the polyolefin resin, and melt-kneading the polyolefin resin and the master batch at a temperature of about 220 ° C. (C) A method of adding a powdery resin (A) to a polyolefin resin and melt-kneading at a temperature of about 220 ° C.
The presence of finely dispersed resin (A) in the continuous phase of the polyolefin resin can be confirmed by observing the cross section of the polyolefin resin particles with a transmission electron microscope.

  The dispersion diameter of the resin (A) in the polyolefin resin particles is preferably 5 μm or less, although it depends on the target expansion ratio (apparent density). When the dispersion diameter of the resin (A) is within the above range, it is possible to produce foamed particles that are particularly uniform in bubbles and small in shrinkage, and the effect of improving the foaming ratio is high. From this viewpoint, the dispersion diameter of the resin (A) is preferably 1 μm or less, more preferably 0.5 μm or less. The lower limit of the dispersion diameter of the resin (A) is not particularly limited from the above viewpoint, but if the dispersion diameter is too small, the bubbles of the foamed particles obtained may become finer and the closed cell ratio of the foamed particles may decrease. Therefore, the lower limit of the dispersion diameter is preferably about 0.01 μm.

The melt mass flow rate of the aromatic polycarbonate resin is preferably 5 to 80 g / 10 minutes, more preferably 5 to 75 g / 10 minutes. The melt mass flow rate of polyethylene terephthalate is preferably 5 to 80 g / 10 minutes, more preferably 10 to 70 g / 10 minutes. When the melt flow rate is in the above range, it becomes easy to finely disperse the resin (A) in the continuous phase of the polyolefin resin.
The melt mass flow rate is a value measured under conditions of 300 ° C. and a load of 1.2 kgf in the case of an aromatic polycarbonate-based resin based on ISO 1133: 1997, and 280 ° C. in the case of polyethylene terephthalate . It is a value measured under the condition of a load of 2.16 kgf.

(2) Impregnation of foaming agent into polyolefin resin particles (2-1) Foaming agent As a foaming agent for foaming resin particles, an inorganic physical foaming agent or an organic physical foaming agent can be used. Examples of the inorganic physical foaming agent include carbon dioxide, air, nitrogen, helium, and argon. Examples of organic physical foaming agents include aliphatic hydrocarbons such as propane, butane and hexane, cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane, chlorofluoromethane, trifluoromethane, and 1,1-difluoroethane. Halogen such as 1-chloro-1,1-difluoroethane, 1,2,2,2-tetrafluoroethane, 1-chloro-1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride Hydrocarbons and the like.
The said foaming agent may be used independently, or may mix and use 2 or more types. In addition, an inorganic physical foaming agent and an organic physical foaming agent may be mixed and used. However, many of the compounds used as organic physical foaming agents are flammable or cause problems of ozone layer destruction, and those that do not easily cause these problems are expensive and impractical. In view of these, it is preferable to use an inorganic physical foaming agent, and it is more preferable to use carbon dioxide among inorganic physical foaming agents.

The amount of foaming agent to be added is appropriately determined depending on the desired foaming ratio. In order to obtain foamed particles having a density of 20 to 200 kg / m ³ in one step without going through a two-stage foaming step, When using a physical foaming agent in a gaseous state, it is preferable to add it so that the equilibrium vapor pressure in the sealed container immediately before the start of foaming is 0.5 to 6.0 MPa (G). When a foaming agent such as dry ice is used, it is preferably added in an amount of 5 to 30 parts by weight with respect to 100 parts by weight of the resin particles.

  In the present invention, the polyolefin resin particles are impregnated with the foaming agent in advance, such as a method of impregnating the resin particles with the foaming agent while being previously pressurized in the gas phase in the sealed container, or a dispersion medium in the sealed container. There is a method in which the resin particles are impregnated with a foaming agent while being dispersed, pressurized and heated, but the latter method is preferred from the viewpoint of impregnation and productivity of the foaming agent. In addition, as a dispersion medium, the same thing as the following can be used.

(2-2) Dispersion medium It is preferable to use an aqueous dispersion medium as the dispersion medium for dispersing the expandable resin particles. In the present invention, the aqueous dispersion medium is a dispersant mainly composed of water. The proportion of water in the aqueous dispersion medium is preferably 60% by weight or more, more preferably 70% by weight or more, and still more preferably 80% by weight. Examples of the dispersion medium other than water in the aqueous dispersion medium include alcohols, glycols, glycerin and the like that do not dissolve the resin particles, but water is usually used.
In addition, in the case where resin particles are impregnated with a foaming agent in a gas phase in a closed container to obtain expandable resin particles, after the impregnation of the foaming agent, a dispersion medium is added to the sealed container as it is and the expandable resin particles Alternatively, the foamable resin particles may be dispersed in a dispersion medium of another sealed container by taking out the foamable resin particles from the sealed container.

When dispersing resin particles and expandable resin particles in a dispersion medium, an anti-fusing agent is added to the dispersion medium in order to prevent the resin particles from fusing together by heating during dispersion or heating in the subsequent foaming step. Can be added. As the anti-fusing agent, any organic or inorganic type can be used as long as it does not dissolve in the dispersion medium and does not melt by heating. Generally, an inorganic anti-fusing agent is used. The As the inorganic anti-fusing agent, powders such as mica, kaolin, aluminum oxide, titanium oxide, and aluminum hydroxide are suitable. As the anti-fusing agent, those having an average particle diameter of 0.01 to 100 μm are used, and those having an average particle diameter of 0.1 to 30 μm are particularly preferable.
When an anti-fusing agent is used, it is preferable to use an anionic surfactant such as sodium dodecylbenzene sulfonate, sodium alkyl sulfonate, or sodium oleate as a dispersion aid. The anti-fusing agent is preferably added in an amount of about 0.01 to 2 parts by weight per 100 parts by weight of the resin particles, and the dispersion aid is preferably added in an amount of about 0.001 to 1 part by weight per 100 parts by weight of the resin particles.

(3) Foaming of polyolefin resin particles impregnated with a foaming agent The foamable resin particles containing a foaming agent dispersed in a dispersion medium in a sealed container are opened together with the dispersion medium by opening one end of the sealed container. The foamed resin particles can be expanded to obtain expanded particles by releasing them under an atmosphere at a lower pressure than the inside, usually at atmospheric pressure. Usually, the pressure in the container at this time is preferably at least 0.5 MPa (G) or more, and the temperature in the container is set to a temperature of the melting point of the polyolefin resin constituting the polyolefin resin foamed particles −10 ° C. or more. It is preferable that the melting point of the polyolefin resin is not lower than the melting point and not higher than 20 ° C.
Melting | fusing point of the said polyolefin resin is calculated | required as follows based on JISK7121-1999. That is, about 6 mg of a sample (resin particles) was heated to 220 ° C. at a rate of temperature increase of 10 ° C./min by a differential scanning calorimeter, then cooled to about 50 ° C. at a rate of temperature decrease of 10 ° C./min. The temperature at the top of the endothermic peak (inherent peak) derived from the melting of the polyolefin resin crystals in the DSC curve obtained when heated to 220 ° C. at a rate of minutes is determined as the melting point of the polyolefin resin. When two or more endothermic peaks derived from the polyolefin resin are observed, the temperature at the top of the largest endothermic peak is defined as the melting point of the polyolefin resin.

According to the method for producing foamed polyolefin resin particles of the present invention, foaming is fine over a wide density range, with little variation in bubble diameter, a narrow density distribution of foamed particles, and hardly shrinking after foaming. Particles can be produced. In particular, in the conventional foamed particles, when the apparent density is low, large shrinkage was observed after the production regardless of the size of the bubble diameter. However, according to the production method of the present invention, even in the range of the apparent density of 80 kg / m ³ or less, It is possible to produce expanded particles which are fine and uniform and hardly shrink after foaming. The production method of the present invention is particularly suitable for producing expanded particles having an apparent density of 70 kg / m ³ or less, and further 60 kg / m ³ or less.
Since the obtained foamed particles hardly shrink immediately after foaming, a secondary process such as a recovery process such as pressurization or heating of the particles becomes unnecessary or reduced.
Incidentally, the polyolefin resin expanded particles obtained by the method of the present invention as described above can be aged under atmospheric pressure and then subjected to pressure treatment under pressurized air to give an internal pressure. By the two-stage foaming step of heating using water vapor or hot air, it is possible to obtain foam particles having a lower apparent density.

[2] About “Polyolefin Resin Foamed Particles” According to Second Embodiment “Polyolefin resin foamed particles” according to the second embodiment of the present invention are one or more selected from aromatic polycarbonate resins and polyethylene terephthalate. Polypropylene resin foamed particles containing the resin (A), and the total content of the resin (A) is 15 parts by weight or less (where 0 is It is not included.)
The polyolefin resin expanded particles of the present invention are polyolefin resin expanded particles containing a specific amount of one or more kinds of resins (A) selected from aromatic polycarbonate resins and polyethylene terephthalate. Since the closed cell structure can be maintained during heating in the mold, the secondary foamability is excellent and the fusion property is excellent, so that a foamed particle molded body having an excellent appearance can be produced.

(1) Polyolefin-based resin expanded particles The polyolefin-based resin particles used for manufacturing the “polyolefin-based resin expanded particles” according to the second aspect of the present invention are the “manufactured polyolefin-based resin expanded particles according to the first aspect”. This is the same as the polyolefin resin particles described in “Method”.
The “polyolefin resin foamed particles” according to the second aspect obtained by foaming the polyolefin resin particles is the method described in “Method for producing polyolefin resin foamed particles” described in the first aspect. Can be manufactured more.

(2) Average cell diameter The polyolefin-based resin expanded particles of the present invention preferably have an average cell diameter of 10 to 300 µm.
When the bubble diameter is within the above range, secondary foaming is sufficiently performed at the time of heat molding, and the fusion property between the particles becomes good. Therefore, a foamed particle molded body having better appearance and mechanical properties is obtained. Can be obtained. From this viewpoint, the average cell diameter of the expanded particles is more preferably 20 to 250 μm, and further preferably 25 to 200 μm. In particular, since the foamed particles of the present invention contain a specific amount of the resin (A), even if the average cell diameter is 150 μm or less, and even 100 μm or less, the secondary foaming ability is excellent and the fusion property is excellent, and the appearance is good. Can be obtained.

  In this specification, the average cell diameter of the expanded particles is a value measured by the following method. First, the foamed particles are cut into approximately two equal parts to obtain a foamed particle cross section, and the cross section is enlarged and projected with a microscope. In this enlarged projection view, four straight lines passing from the surface of the foamed particle to the other surface and passing through the center of the bubble cross section are drawn at substantially equal angular intervals. Subsequently, the total number of bubbles intersecting the four straight lines: N [number] is obtained. Then, a value obtained by dividing the total length of each of the four straight lines: L [μm] by the total number of bubbles: N [number] (L / N) is an average bubble diameter of the expanded particles. [Μm].

(3) Apparent density The apparent density of the expanded polyolefin resin particles of the present invention is preferably 15 to 200 kg / m ³ .
When the apparent density is within the above range, the obtained foamed particle molded body has excellent mechanical strength. From this point of view, more preferably 20~150kg / ^{m 3,} more preferably from 25~100kg / ^{m 3.}

  The average cell diameter and apparent density correlate with the content of the resin (A), the type of foaming agent, the amount of foaming agent added, the foaming temperature, the retention time during foaming, etc., and adjust these factors as appropriate. By doing so, the target average cell diameter and apparent density can be adjusted.

The apparent density in the present invention refers to the volume of the expanded particle group obtained by submerging the expanded particle group whose weight has been measured in advance in a graduated cylinder using a wire mesh or the like, and the volume of the expanded particle group obtained from the rise in the water level. It is a value obtained by dividing by the unit conversion to kg / m ³ .

  The expanded polyolefin resin particles of the present invention contain the resin (A) in the expanded particles, so that even if the bubbles are fine, the expanded particles can maintain the closed cell structure during in-mold molding. It is. Such foamed particles are characterized in that the apparent density of the foamed particles after pressure treatment does not change significantly compared to the apparent density of the foamed particles before pressure treatment. Specifically, the appearance of the expanded resin particles after pressurizing the polyolefin resin expanded particles with compressed air under the conditions of 30 ° C. and 0.2 MPa (G) for 24 hours and then leaving them under normal pressure of 23 ° C. for 24 hours. The ratio (X / Y, hereinafter referred to as shrinkage ratio) between the density (X) and the apparent density (Y) of the expanded particles before pressurization is preferably 0.9 to 1.0. When the shrinkage ratio is in the above range, a foamed particle molded body that is particularly excellent in secondary foamability at the time of in-mold molding and has a better surface appearance can be obtained. From this viewpoint, the shrinkage rate is more preferably 0.92 to 1.0, and still more preferably 0.95 to 1.0.

  In addition, since the polyolefin-based resin expanded particles of the present invention maintain a closed cell structure at the time of two-stage expansion, they can be made into expanded particles having a lower apparent density than before by a two-stage expansion process.

[3] In-mold molding using polyolefin resin expanded particles Polyolefin resin expanded particles of the present invention (polyolefin resin expanded particles obtained by the production method of the first aspect of the present invention, second aspect of the present invention The foamed particles are fused with each other by filling the foamed polyolefin resin particles) into a mold and heating with water vapor to cause secondary foaming and fusion of the foamed particles. A molded body formed into a desired shape can be obtained.
Further, the polyolefin resin expanded particles obtained by the production method of the present invention have less shrinkage of the expanded particles, less variation in the bubble diameter of each particle, and the density distribution of the particle group becomes narrower. Since the polyolefin-based resin foamed particles are excellent in secondary foaming ability during in-mold molding, the resulting in-mold foam-molded product has excellent dimensional stability and good appearance.

Next, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.
The raw materials and evaluation methods used in the examples and comparative examples are described below.
(1) Raw materials used in this example and comparative example (a) Polyolefin resin As polyolefin resin, ethylene-propylene random copolymer (ethylene component content: 2.8 wt%, melting point: 143 ° C, melt mass flow) Late: 5 g / 10 min (ISO 1133-1997: 230 ° C., load 2.16 kgf or less, referred to as polyolefin (a)) was used.
(B) Resin (A), etc. Resins (A) used in Examples 1 to 11 and Comparative Example 10 and resins used in Comparative Examples 5 to 9 (hereinafter referred to as resin (B)) are shown in Table 1. Shown in In Comparative Examples 2 to 4, zinc borate (manufactured by Tomita Pharmaceutical Co., Ltd., zinc borate 2335) was used instead of the resin (A).

(C) Preparation of master batch Twin screw extruder having an inner diameter of 30 mm with 95 parts by weight of polyolefin (a) and 5 parts by weight of resin (A), resin (B) or bubble regulator (zinc borate) shown in Table 1 , Melt-kneaded, extruded into a strand, and this strand was cooled with water and cut with a pelletizer to prepare a master batch. In the case of producing a master batch of the resin (A) (A-1, 2, 3, 4, 5), the extruder temperature is set to 280 ° C. and both are melt-kneaded. Extruded into strands at ℃. In the case of producing another master batch, the extruder temperature was set to 220 ° C., both were melt-kneaded, and the melt-kneaded product was extruded into a strand at 220 ° C.

(D) Production of polyolefin resin particles Polyolefin resin particles were produced by the method described in the following methods 1 to 3. In Examples 1 to 11, after the resin particles were prepared, the dispersion particle diameter of the resin (A) was measured by the method described later. The results are shown in Table 2.
(D-1) Method 1
The masterbatch is blended with the polyolefin (a) shown in Table 1 so that the resin (A), resin (B) or zinc borate is in the amount shown in the table, and fed to a single-screw extruder with an inner diameter of 40 mm for extrusion. After melt-kneading at a machine setting temperature of 220 ° C. and extruding into a strand, the strand was cooled with water and then cut with a pelletizer so that the particle weight was about 1.0 mg to produce resin particles.
(D-2) Method 2
The polyolefin (a) shown in Table 1 is blended with the pellet-shaped resin (A) in the amount shown in the table, supplied to a single-screw extruder with an inner diameter of 40 mm, and melt-kneaded at an extruder set temperature of 280 ° C. The resin was extruded into a strand at a resin temperature of 220 ° C., the strand was cooled with water, and then cut with a pelletizer so that the particle weight was about 1.0 mg to produce resin particles.
(D-3) Method 3
The polyolefin A shown in Table 1 is blended with the powdery resin (A) in the amount shown in the table, supplied to a single-screw extruder with an inner diameter of 40 mm, melt-kneaded at an extruder set temperature of 220 ° C., and strands Then, the strand was cooled with water, and then cut with a pelletizer so that the particle weight was about 1.0 mg to produce resin particles.

(2) Evaluation method (b) Measurement of dispersed particle size of resin (A) in resin composition After embedding resin particles with epoxy resin and staining with ruthenium tetroxide, an ultrathin section was cut out at room temperature, Observation was performed at a magnification of 6000 with a transmission electron microscope (JEM1010 manufactured by JEOL Ltd.). Of the dispersed resin (A) present in the 150 × 150 μm range of the obtained image, arbitrarily measure the major axis of 10 locations and perform arithmetic average, and the average value is the dispersed particles of resin (A). The diameter was [μm]. In addition, resin (A) and resin (A) whose dispersion diameter is remarkably larger than other dispersed resins (A) were excluded from the measurement of the long diameter.
(B) Apparent density of expanded particles The obtained expanded particles were dried in an oven at 40 ° C for 12 hours. After drying, the foamed particle group was pressurized with air in a 0.2 MPa (G) pressure vessel for 12 hours. Submerged foam particles after pressurization whose weight was measured in advance were submerged in water in a graduated cylinder using a wire mesh, and the volume of the foam particles was determined from the rise in water level, and divided by the weight of the foam particles to kg / m By converting the unit to ³ , the apparent density [kg / m ³ ] of the expanded particles was obtained.

(C) Average cell diameter of expanded particles Arbitrarily select 10 expanded particles from the obtained expanded particle group, obtain the average cell diameter for each of the expanded particles according to the above method, and arithmetically average these values. Thus, the average cell diameter [μm] of the expanded particles was determined.

(D) Shrinkage of expanded particles The shrinkage of expanded particles was evaluated according to the following criteria.
○: No shrinkage is observed in the particles left at room temperature for 1 hour after foaming.
Δ: After foaming, the particles left at room temperature for 1 hour have shrinkage, but no further shrinkage is observed in the particles after drying in an oven at 60 ° C. for 12 hours.
X: The particles after drying in an oven at 60 ° C. for 12 hours have shrinkage.
(E) Shrinkage ratio The apparent density (Y) [kg / m ³ ] of the expanded particles before pressurization was determined by the method (b) above. Thereafter, the expanded particles are accommodated in a pressure vessel, and compressed air is injected into the pressure vessel so that the internal pressure of the vessel becomes 0.2 MPa as a gauge pressure, and the pressure is released after being held at 30 ° C. for 24 hours. The foamed particles were taken out from the container. The taken-out expanded particles were left in a constant temperature and humidity chamber under normal pressure at 23 ° C. and 50% relative humidity for 24 hours, and the apparent density (X) [kg / m ³ ] of the expanded particles after pressurization was determined. The ratio (X / Y) of the apparent density Y of the expanded particles after pressurization to the apparent density X of the expanded particles before pressurization was determined as the shrinkage ratio.
(F) Uniformity of density of foamed particles The uniformity of density of foamed particles (uniformity of bubbles) was evaluated according to the following criteria. Note that the degree of variation in the density of the expanded particles correlates with the uniformity of the bubbles in the expanded particles. If the bubbles are not uniform, the degree of variation in density increases.
About 200 mm in diameter and 50 mm in height at the top (3.35 mm) of JIS sieve (mesh opening 1.18, 1.40, 1.70, 2.00, 2.36, 2.80, 3.35 mm) 200 milliliters (ml) of foamed particles were added, and after shaking for 10 minutes with a low-tap shaker, the weight of the foamed particles remaining in each stage was measured, and the standard deviation of the particle diameter was calculated. A standard deviation of 0.4 mm or more was evaluated as “particle uniformity: x”, and a standard deviation of less than 0.4 mm was evaluated as “particle uniformity: ◯”.

(G) Shrinkage of foamed particle molded body The shrinkage of the foamed particle molded body was evaluated according to the following criteria.
○: After the foamed particle molded body was dried in an oven at 60 ° C. for 12 hours, the thickness of the central portion of the molded body was 95% or more of the thickness of the peripheral portion.
(Triangle | delta): After drying an expanded particle molded object for 12 hours in 60 degreeC oven, the thickness of the center part of a molded object is less than 95% of the thickness of a peripheral part, and is 90% or less.
X: After the foamed particle molded body was dried in an oven at 60 ° C. for 12 hours, the thickness of the central portion of the molded body was less than 90% of the thickness of the peripheral portion.
(H) External appearance of molded body The external appearance of the molded body was evaluated according to the following criteria.
○: No voids between particles due to poor secondary foaming of foamed particles on the surface of the molded body.
X: There are interparticle voids due to secondary foaming failure of the foamed particles on the surface of the molded body.

(L) Mechanical strength of the foamed particle molded body The 50% compression stress of the foamed particle molded body was measured to evaluate the mechanical strength of the molded body. From the central part of the molded body, cut out a test piece so as to be a rectangular parallelepiped shape except for the skin layer at the time of molding, 50 mm long × 50 mm wide × 25 mm thick, and with respect to this test piece, the compression speed is 10 mm / min. Based on JIS K 6767-1999, the load at the time of 50% strain was calculated | required, this was divided | segmented by the pressure-receiving area of the test piece, and 50% compressive stress [kPa] was calculated | required.

[Examples 1 to 11]
In Examples 1 to 11, foamed particles were produced by the method described below, and then the obtained foamed particles were molded in a mold to obtain a foamed particle molded body. The above-mentioned evaluation was performed on these foamed particles and the foamed particle molded body.
(1) Production of expanded particles 1000 g of polyolefin resin particles obtained by the method described in any one of methods 1 to 3, 3000 ml of water as a dispersion medium, 3 g of kaolin as a dispersant, and dodecylbenzenesulfone as a dispersion aid. Carbon dioxide (dry ice) was charged in an autoclave having an internal volume of 5 liters (L) equipped with a stirrer so that the amount of sodium acid 0.04 g and the amount shown in Table 2 as a foaming agent was shown in Table 2 under stirring. After raising the temperature to the foaming temperature and holding at that temperature for 15 minutes, the contents in the autoclave were released under atmospheric pressure to obtain polypropylene resin foamed particles. In Example 9, air (Air) was used as a foaming agent, and after raising the temperature to the foaming temperature shown in Table 2, compressed air was injected until the pressure in the autoclave reached the pressure shown in Table 2, and foaming was performed. Compressed air was appropriately injected and adjusted so as to maintain the pressure for 15 minutes until immediately before. The pressure shown in Table 2 means a gauge pressure.
The obtained expanded polypropylene resin particles were evaluated for apparent density, average cell diameter, shrinkage, shrinkage rate, and uniformity. The results are summarized in Table 2.

(2) Production of Foamed Particle Molded Body The foamed particles obtained in (1) above are filled into a 250 × 200 × 50 mm flat plate mold and heated with steam at the pressure shown in Table 2 to obtain the foamed particles. After secondary foaming, fusing and cooling, the molded product was obtained by removing from the mold. In addition, the steam pressure at the time of shaping | molding was made into the pressure which shows the maximum fusion rate, without a molded object shrink | contracting greatly.
The molded body was evaluated for apparent density, appearance, and recoverability. The results are summarized in Table 2.

[Comparative Examples 1 to 10]
Comparative Example 1 is an example in which the resin (A) is not used, and foamed particles and a foamed particle molded body were produced in the same manner as in Example 1 except that the resin (A) was not used.
Comparative Examples 2 to 4 are examples in which zinc borate was used instead of resin (A), and foamed particles and foamed particle molding were performed in the same manner as in Examples 1, 2, and 9 except that zinc borate was used. The body was manufactured.
Comparative Examples 5 to 9 are examples in which a resin (resin (B)) other than the resin (A) was used instead of the resin (A), and in the same manner as in Example 2 except that the resin (B) was used. Foamed particles and foamed particle molded bodies were produced.
Comparative Example 10 is an example in which the resin (A) in the resin particles is used in an amount exceeding the total content defined in the present invention, and the total content of the resin (A) in the resin particles is 17.5 parts by weight. Foamed particles and a foamed particle molded body were produced in the same manner as in Example 4 except that certain resin particles were used. The expanded particles and the expanded particle molded body obtained in the comparative example were evaluated in the same manner as in Examples, except that the dispersion particle diameter of the resin (A) was not measured.
The results are summarized in Table 3.

Claims (11)

In a method for producing foamed particles by releasing foamable resin particles obtained by impregnating a polyolefin-based resin particle with a foaming agent together with a dispersion medium from the inside of the sealed container under a pressure lower than the pressure in the sealed container,
The polyolefin resin particles contain at least one resin (A) selected from an aromatic polycarbonate resin and polyethylene terephthalate, and the total content of the resin (A) constitutes the resin particles. A method for producing expanded polyolefin-based resin particles, which is 15 parts by weight or less (excluding 0) with respect to 100 parts by weight of the resin. The total content of the resin (A) in the polyolefin resin particles is 0.01 to 12 parts by weight with respect to 100 parts by weight of the polyolefin resin constituting the resin particles. The manufacturing method of the polyolefin-type resin expanded particle as described in any one of. The method for producing expanded polyolefin resin particles according to claim 1 or 2, wherein the resin (A) is an aromatic polycarbonate resin. The method for producing expanded polyolefin resin particles according to claim 3, wherein the polycarbonate resin has a melt mass flow rate of 5 to 80 g / 10 min at 300 ° C and a load of 1.2 kgf. The method for producing expanded polyolefin resin particles according to any one of claims 1 to 4, wherein the polyolefin resin is a polypropylene resin. The method for producing expanded polyolefin resin particles according to any one of claims 1 to 5, wherein the foaming agent is an inorganic physical foaming agent. The method for producing expanded polyolefin resin particles according to claim 6, wherein the foaming agent is carbon dioxide. The method for producing expanded polyolefin resin particles according to any one of claims 1 to 7, wherein the dispersion medium is an aqueous dispersion medium. A polyolefin-based resin foamed particle containing at least one resin (A) selected from an aromatic polycarbonate-based resin and polyethylene terephthalate, wherein the total content of the resin (A) constitutes the resin particle Polyolefin-based resin expanded particles, which are 15 parts by weight or less (excluding 0) with respect to 100 parts by weight. The polyolefin resin expanded particles according to claim 9, wherein an apparent density is 15 to 200 kg / m ³ and an average cell diameter is 10 to 300 μm. The expanded particles were pressurized with compressed air under conditions of 30 ° C. and 0.2 MPa (G) for 24 hours, and then allowed to stand under normal pressure of 23 ° C. for 24 hours. The polyolefin resin foamed particles according to claim 9 or 10, wherein the ratio (X / Y) of the foamed particles to the apparent density (Y) is 0.9 to 1.0.