JP5561762B2 - Polyolefin resin expanded particles, polyolefin resin expanded particles molded body, and method for producing polyolefin resin expanded particles - Google Patents

Description

  The present invention relates to a polyolefin resin expanded particle, a polyolefin resin expanded particle molded body, and a method for producing a polyolefin resin expanded particle.

The polyolefin resin expanded particles can be molded into various shapes according to the application. The polyolefin resin foamed particle molded body obtained from the foamed particles by in-mold molding is used in a wide range of applications such as various packaging cushioning materials and automobile impact absorbing materials. However, it is lighter in weight as a foamed particle molded body used for applications such as precision packaging materials that require flexibility, and seat cushion materials that require tactile sensation and shape recovery after compression. Therefore, there is a demand for a flexible molded body, and further a molded body having a small compression set and excellent recoverability.
For example, Patent Literature 1 describes foam beads for in-mold foam molding made of a resin composition of a polyolefin resin and an amorphous rubber polymer. Patent Document 2 describes polyolefin resin expanded particles in which a base resin is a composition comprising a polyolefin resin and a polyolefin rubber.

JP 2003-147116 A Japanese Patent Laid-Open No. 5-140362

  Conventionally, as a means for obtaining a foamed particle molded body excellent in flexibility and lightness, a polyolefin resin is made to contain a large amount of an elastomer component. However, with this method, a foamed particle molded body having sufficient flexibility and recoverability could not be obtained.

Patent Document 1 only describes that foamed particles having a foaming ratio of 4 times were obtained, which was insufficient as flexibility and left a problem in lightness.
In addition, the foamed particle molded body obtained by in-mold molding of the foamed particles obtained in Patent Document 2 has a compressive strength of about 2 kg / cm ² , leaving a problem in flexibility.

On the other hand, adding a plasticizer to a polyolefin resin is known to improve the flexibility of the resin. However, when adding a large amount of plasticizer to the base resin that forms expanded particles in order to improve flexibility, the base resin is melted and kneaded with an extruder and extruded into a strand, and then with a pelletizer, etc. When producing resin particles by cutting, the resin particles could not be stably obtained because the base resin was too plasticized.
Further, when foaming resin particles, if the resin particles containing a foaming agent are released into the atmospheric pressure together with the dispersion medium from a sealed container under pressure, the foamed particles are fused together to block. It was difficult to stably obtain expanded particles. Furthermore, when molding in-mold, there is a problem that the filling property of the foamed particles is reduced, and in the method using a plasticizer, due to the specific problems that occur when producing foamed particles and foamed particle molded bodies, It was difficult to obtain a foamed particle molded body excellent in flexibility, light weight and recoverability.

  In view of the above-mentioned problems, the present invention provides a polyolefin resin foamed particle capable of obtaining a foamed particle molded article having excellent flexibility and recoverability and having a low apparent density (high foaming ratio), and a method for producing the foamed particle Another object of the present invention is to provide a polyolefin-based resin foam particle molded body that is obtained from the foamed particles by in-mold molding and has excellent flexibility and recoverability.

According to the present invention, the following polyolefin resin expanded particles, polyolefin resin expanded particle molded bodies, and methods for producing polyolefin resin expanded particles are provided.
[1] A resin composition comprising 80 to 30% by weight of a polyolefin resin and 20 to 70% by weight of a thermoplastic elastomer (however, the total of the polyolefin resin and the thermoplastic elastomer is 100% by weight);
Comprising 15 to 95 parts by weight of mineral oil with respect to 100 parts by weight of the resin composition,
The weight ratio of the blending amount of the mineral oil to the blending amount of the thermoplastic elastomer is 0.4 to 3,
Polyolefin resin foamed particles having an apparent density of 15 to 150 g / L.
[2] A molded body obtained by in-mold molding of the polyolefin-based resin expanded particles according to 1 above, wherein the molded body has an apparent density of 10 to 100 g / L, and has a compression set (JIS K6767). A polyolefin-based resin foamed particle molded body characterized by being 6% or less.
[3] 80-30% by weight of a polyolefin resin, 20-70% by weight of a thermoplastic elastomer (the total of the polyolefin resin and the thermoplastic elastomer is 100% by weight), 0-70 parts by weight (the polyolefin system) A blended mineral oil) and a melt-kneaded product obtained by melt-kneading to form resin particles,
Using the resin particles, the foaming agent, and mineral oil of 0 to 70 parts by weight (parts by weight relative to 100 parts by weight of the total amount of the polyolefin resin and the thermoplastic elastomer) as a dispersion medium in a closed container Disperse, impregnate the resin particles with a foaming agent and the mineral oil,
Subsequently, the resin particles containing the foaming agent and the mineral oil are foamed, and 15 to 95 parts by weight (which is a part by weight based on 100 parts by weight of the total amount of the polyolefin resin and the thermoplastic elastomer). A process for producing foamed polyolefin-based resin particles, comprising foamed particles containing oil and having a weight ratio of the blended amount of the mineral oil to the blended amount of the thermoplastic elastomer of 0.4 to 3 .

The polyolefin resin expanded particles of the present invention (hereinafter also simply referred to as expanded particles) are composed of a resin composition comprising a specific amount of a polyolefin resin and a thermoplastic elastomer, and a specific amount of mineral oil. Despite the addition of mineral oil, it is a foam particle with excellent in-moldability that has no stickiness and has no problems such as filling of the foam particles during molding and insufficient fusion between the foam particles. is there.
Further, according to the method for producing foamed particles of the present invention, in the resin particle production process for producing resin particles that are precursors of the foamed particles of the present invention, the thermoplastic elastomer is excellent in compatibility with mineral oil. Therefore, problems such as a decrease in production stability in the pelletizing process at the time of producing resin particles and a deterioration in the cut property of the strand are prevented. In addition, in the impregnation step of impregnating the foaming agent and mineral oil in a closed container, the thermoplastic elastomer is excellent in compatibility with the mineral oil, so the mineral oil added in the impregnation step is effective. It is possible to impregnate the resin particles. Furthermore, in the foaming process in which the resin particles containing the foaming agent and mineral oil are foamed, fusion between the foamed particles is prevented.
Furthermore, by combining the blending of mineral oil in the resin particle manufacturing process and the blending of mineral oil in the impregnation process, the amount of mineral oil can be adjusted and the degree of flexibility can be widely adjusted. . In addition, by blending the mineral oil in two steps, a resin particle manufacturing process and an impregnation process, a larger amount of mineral oil can be contained in the expanded particles. Further, even when the blending amount of the mineral oil is the same, the impregnation time in the impregnation step is maintained while maintaining the production stability during the production of the resin particles, rather than blending the entire amount of the mineral oil in one step. It can be shortened.
The polyolefin resin expanded particle molded body of the present invention (hereinafter also referred to as expanded particle molded body or molded body) is a molded body having a low apparent density obtained by molding the expanded particles in a mold. Therefore, since it is a compact with a small compression set, excellent recoverability, light weight, and excellent flexibility, it has high precision packaging materials for packaging, tactile sensation and recoverability that require flexibility. It can be suitably used for required uses such as a seat cushion material.

Hereinafter, the polyolefin resin expanded particles of the present invention, the production method thereof, and the polyolefin resin expanded particles molded body obtained from the expanded particles will be described in detail.
The polyolefin resin expanded particles of the present invention contain a resin composition comprising a polyolefin resin and a thermoplastic elastomer. When the resin composition contains a thermoplastic elastomer, the resin particles that are precursors for obtaining the foamed particles can contain a large amount of mineral oil described later.

  The polyolefin resin used in the present invention is not particularly limited in its composition and synthesis method as long as the monomer for polymerization contains olefin, but preferably contains 50% by weight or more of olefin component. It is preferable to contain 70% by weight or more. Examples of the polyolefin resin include polypropylene resins such as propylene homopolymer, propylene random copolymer, propylene block copolymer, propylene graft copolymer, high density polyethylene, medium density polyethylene, low density polyethylene, Polyethylene resins such as chain ultra-low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, polybutene, and mixtures thereof can be used. Of these, polypropylene resins are preferred.

  The melt flow rate (MFR) of the polyolefin resin is preferably 0.1 to 20 g / 10 minutes. When the MFR is within the above range, the load on the extruder during the resin particle production process is not excessive, the mixed state of the resin is not deteriorated, and the tension of the melt-kneaded product is continuously reduced. Better foamed particles can be obtained without bubbles. From this viewpoint, the lower limit of MFR is preferably 0.5 g / 10 minutes, and more preferably 1.0 g / 10 minutes. On the other hand, the upper limit is preferably 15 g / 10 min, and more preferably 10 g / 10 min.

Melt flow rate (MFR) is measured based on test conditions M (temperature 230 ° C., load 2.16 kg) of JIS K7210 (1999) for polypropylene resins, and JIS K7210 (1999) for polyethylene resins. ) And the test condition D (temperature 190 ° C., load 2.16 kg).

Examples of the thermoplastic elastomer used in the present invention include polybutadiene, polyisoprene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, styrene-butadiene copolymer, styrene-butadiene, styrene-isoprene, and styrene-butadiene. -Styrene, Styrene-Isoprene-Styrene Block Copolymer, and Hydrogenated Polymers Styrene-Ethylene-Ethylene-Propylene Block Copolymer (SEP), Styrene-Ethylene-Butylene-Styrene Block Copolymer (HEBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), hydrogenated styrene butadiene rubber (HSBR), styrene-ethylene Len - ethylene - propylene - like block copolymer of styrene (SEEPS). Also, so-called dynamically crosslinked elastomers such as ethylene-propylene rubber (EPM) and ethylene-propylene-diene terpolymer (EPDM) can be used. Among these, from the viewpoint of excellent compatibility with the polyolefin-based resin, hydrogenated products, SEEPS, and dynamically cross-linked elastomers are preferable, and HSBR is particularly preferable.

The expanded particles of the present invention contain a resin composition composed of the polyolefin resin and the thermoplastic elastomer. The blending ratio of the resin composition is such that the blending ratio of the polyolefin resin is 80 to 30% by weight and the blending ratio of the thermoplastic elastomer is 20 to 70% by weight (however, the blending ratio of the polyolefin resin and the thermoplastic elastomer is The total is 100% by weight).
When the amount of the thermoplastic elastomer is too small (the amount of the polyolefin resin is too large), the flexibility of the foamed particles and the foamed particle molded body obtained from the foamed particles may be lowered. In addition, since the blending amount of mineral oil is relatively large with respect to the thermoplastic elastomer, pelletization in the resin particle manufacturing process may become unstable, and dispersion may occur during the impregnation process, causing the resin particles to melt. There is a risk that foamed particles may not be obtained. In addition, the foamed particles may be fused together, making it impossible to perform in-mold molding. Furthermore, the mineral oil that cannot fully impregnate the expanded particles bleeds out or covers the expanded particle surface, the expanded particles become sticky, and it becomes difficult to fill the expanded particles with the mold, and the moldability decreases. There is a possibility that a foamed particle molded body cannot be obtained. From this viewpoint, the blending ratio of the thermoplastic elastomer is preferably 25% by weight or more.
On the other hand, when the blending amount of the thermoplastic elastomer is too large (the blending amount of the polyolefin resin is too small), there is a possibility that the foamed particles are likely to become open cells. In addition, the resin composition may be too soft and it may be difficult to obtain moldable foam particles. From this viewpoint, the blending ratio of the thermoplastic elastomer is preferably 65% by weight or less, more preferably 60% by weight or less.

  Various additives can be added to the resin composition as desired. Examples of such additives include antioxidants, ultraviolet light inhibitors, antistatic agents, flame retardants, metal deactivators, nucleating agents, and bubble regulators. Examples of the air conditioner include inorganic powders such as zinc borate, talc, calcium carbonate, borax, and aluminum hydroxide. These additives are preferably used in a total amount of 20 parts by weight or less per 100 parts by weight of the resin composition, and more preferably 5 parts by weight or less. These additives are usually used in the minimum necessary amount. Moreover, these additives can be contained in the resin particles by, for example, adding and kneading the resin composition to a melt-kneaded material melted in an extruder in the resin particle manufacturing process.

  The mineral oil used in the present invention is one that is separated, distilled and refined from crude oil or petroleum, and is a mixture containing aromatic rings, naphthene rings, paraffin chains and the like. In particular, those having a pour point of 0 ° C. or less such as aroma mineral oil, naphthenic mineral oil, paraffin mineral oil and the like are preferable, and paraffin mineral oil is particularly preferable among these. In the present invention, since the compatibility between the mineral oil and the thermoplastic elastomer is good, the polyolefin resin can contain a large amount of mineral oil.

Content of mineral oil is 15-95 weight part with respect to 100 weight part of resin compositions which consist of the said polyolefin resin and the said thermoplastic elastomer. The lower limit is preferably 20 parts by weight, more preferably 22 parts by weight. On the other hand, the upper limit is preferably 90 parts by weight, more preferably 80 parts by weight, and still more preferably 70 parts by weight.
If the content of mineral oil is too small, the foamed particles obtained, and the foamed particle molded body, may have insufficient flexibility and recoverability. On the other hand, when the content is too large, dispersion of the resin particles during the impregnation step may be deteriorated to cause condensation between the resin particles. In addition, when the dispersibility at the time of an impregnation process deteriorates and a resin particle produces condensation, condensation will be seen also in the foamed particle after foaming. In the foaming process, the foamed particles may condense. When the mold is filled, the foamed particles may be solidified to make it impossible to fill the foamed particles in the mold, or a secondary foaming failure may occur during in-mold molding. In the foamed particle molded body, the shrinkage of the foamed particle molded body after molding is excessive, the heat resistance of the foamed particle molded body is reduced, or mineral oil bleeds out, causing contamination due to stickiness and dust adsorption There is a possibility that problems such as being likely to occur occur.

  When an excessive amount of mineral oil is blended, the excessive amount of mineral oil appears as stickiness on the surface of the resin particles and / or the expanded particles. Therefore, if the resin particles and / or the expanded particles are not sticky, it is considered that the total amount of the blended mineral oil is impregnated in the resin particles and / or the expanded particles. Therefore, when resin particles and / or expanded particles without stickiness are obtained, the blending amount of mineral oil added to the resin particles and / or expanded particles in the resin particle production process and the impregnation process, Furthermore, the content of the mineral oil in the foamed particle molded body does not change greatly.

Weight ratio of the amount of the mineral oil to the amount of the thermoplastic elastomer, Ru 0.4 to 3 der. Within the above range, the thermoplastic elastomer and the mineral oil have good compatibility, and a large amount of mineral oil can be contained in the polyolefin-based resin. Good foamed particles can be obtained, and the foamed particles can be obtained as a foamed particle molded body having excellent flexibility and recoverability. The weight ratio, good Mashiku is 0.5-2.

  The apparent density of the expanded particles of the present invention is 15 to 150 g / L. If the apparent density of the expanded particles is too small, the mechanical strength such as the compressive strength and tensile strength of the finally obtained expanded particle molded product is reduced, or the expanded expanded particle molded product after in-mold molding is increased, There is a risk that it is difficult to maintain the target shape. From this viewpoint, the lower limit of the apparent density is preferably 20 g / L, more preferably 25 g / L, and still more preferably 30 g / L. On the other hand, when the apparent density is too large, the flexibility and lightness of the foamed particle molded body obtained by molding the foamed particles in a mold may be reduced. From this viewpoint, the upper limit is preferably 120 g / L, more preferably 100 g / L, and still more preferably 90 g / L.

  The apparent density of the expanded particles was measured by preparing a graduated cylinder containing water at 23 ° C., and leaving the graduated cylinder for about 50 ml of expanded particles (relative humidity 50%, 23 ° C., 1 atm for 2 days). The weight W) of the expanded particle group is sunk using a wire mesh or the like, and the volume V (L) of the expanded particle group is read from the rise in water level. It can be determined by dividing (W / V) from the volume V (L) and the weight W (g) of the expanded particles in the graduated cylinder.

Next, the manufacturing method of the polyolefin-type resin expanded particle of this invention is demonstrated.
The expanded particles are manufactured through a manufacturing process including at least a resin particle manufacturing process, an impregnation process, and a foaming process.
In the resin particle production process, the polyolefin resin 80 to 30% by weight and the thermoplastic elastomer 20 to 70% by weight (however, the total of the polyolefin resin and the thermoplastic elastomer is 100% by weight). And 0 to 70 parts by weight of the mineral oil (parts by weight relative to 100 parts by weight of the total amount of the polyolefin resin and the thermoplastic elastomer), supplied to an extruder and melt-kneaded to obtain a melt-kneaded product, Resin particles are produced by a known granulation method such as a method of extruding the melt-kneaded material from an extruder into a strand shape and cutting the strand into a size suitable for forming expanded particles.

  In the above-described method, the strand cutting method can be adopted when the strand is cooled by water cooling and then cut into a predetermined length. In addition, resin particles can be obtained by an underwater cut method in which the strands are cooled to a predetermined length or simultaneously with the cutting to obtain resin particles. In particular, the strand cutting method is preferable because the apparatus is inexpensive and can be easily implemented.

As described above, when the resin particles used in the present invention contain mineral oil, by containing a specific amount of the thermoplastic elastomer, surging due to poor biting (subtle variations in ejection during extrusion) And inconveniences such as strand cutting becomes difficult due to the strand-shaped extrudate becoming too flexible, and the resin particle production process can be performed stably.

  In the resin particle production process, the polyolefin resin and the thermoplastic elastomer can be charged with separate feeders, or they can be preliminarily mixed with a tumbler or the like and then charged into the hopper at once. . A part of the mineral oil can be added after being premixed together with the polyolefin resin and thermoplastic elastomer by the tumbler or the like, or can be directly injected into the extruder by a pump or the like. There is no restriction | limiting in particular in an injection | throwing-in order, The said polyolefin resin, a thermoplastic elastomer, and mineral oil should just be melt-kneaded, it may become a melt-kneaded material, it granulates, and a resin particle may be formed.

  The blending amount of the mineral oil blended in the resin particle manufacturing process is 0 to 70 parts by weight (0 parts by weight, ie, resin particle manufacturing) with respect to 100 parts by weight of the total blending amount of the polyolefin resin and the thermoplastic elastomer. Including the case where no mineral oil is added in the process). The lower limit is preferably 5 parts by weight, more preferably 10 parts by weight. On the other hand, the upper limit is preferably 50 parts by weight, more preferably 40 parts by weight. When the blending amount is within the above range, the occurrence of surging due to poor biting at the time of extrusion, and strand cutting does not become difficult due to being too flexible, and it is possible to obtain resin particles more stably. it can.

  The average weight per resin particle is usually preferably 0.01 to 10.0 mg, more preferably 0.1 to 5.0 mg. The average weight of the resin particles is a value obtained by dividing the weight (mg) of 200 randomly selected resin particles by 200.

  In the impregnation step, the resin particles and the foaming agent obtained as described above are dispersed in a dispersion medium such as water in a sealed container, and heated under stirring to soften the resin particles, and then the foaming agent. Is impregnated into the resin particles. Furthermore, when mineral oil is added, the mineral oil is also impregnated into the resin particles.

  As the foaming agent, an organic physical foaming agent, an inorganic physical foaming agent, or a mixture thereof can be used. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, butane, hexane, pentane and heptane, alicyclic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, halogenated hydrocarbons such as methyl chloride, ethyl chloride, and methylene chloride, and dialkyl ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, and the like. It can be used by mixing. Examples of the inorganic physical foaming agent include nitrogen, carbon dioxide, argon, air, water, and the like, and two or more of these can be used in combination. When an organic physical foaming agent and an inorganic physical foaming agent are mixed and used, those arbitrarily selected from the above-mentioned organic physical foaming agent and inorganic physical foaming agent can be used in combination. In addition, when using together an inorganic type physical foaming agent and an organic type physical foaming agent, it is preferable that an inorganic type physical foaming agent contains at least 30 weight% or more.

Among the foaming agents, an inorganic physical foaming agent is particularly preferable from the viewpoint of environmental friendliness, and nitrogen, air, carbon dioxide, and water are particularly preferable. In addition, when water is used as a dispersion medium in the impregnation step, water as a dispersion medium can be used as a foaming agent by using a mixture of the resin particles with a water absorbent resin.
The amount of the foaming agent used is determined in consideration of the apparent density of the target foamed particles, the type of the resin composition, or the type of the foaming agent. Usually, the organic physical foaming per 100 parts by weight of the resin particles. It is preferable to use 5 to 50 parts by weight of the agent and 0.5 to 30 parts by weight of the inorganic physical foaming agent.

  The dispersion medium for dispersing the resin particles in the impregnation step is not limited to the above-described water, and any solvent that does not dissolve the resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol and the like, but usually water is used.

  In the above method, in the dispersion medium, a poorly water-soluble inorganic substance such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin or the like is provided in the dispersion medium as necessary so that the resin particles are uniformly dispersed in the dispersion medium. It is preferable to disperse a dispersing aid such as a dispersing agent such as a substance and an anionic surfactant such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate. The amount of the dispersant added to the dispersion medium in the impregnation step is a ratio of the weight of the resin particles to the weight of the dispersant (the weight of the resin particles / the weight of the dispersant) based on the weight of the resin particles. 2000, more preferably 30 to 1000. The ratio of the weight of the dispersant to the weight of the dispersion aid (as the amount of active ingredient) (the weight of the dispersant / the weight of the dispersion aid) is preferably 0.1 to 500, and more preferably 1 to 100.

  In the impregnation step, mineral oil can be impregnated with the foaming agent. The blending amount is 0 to 70 parts by weight with respect to the total blending amount of the polyolefin resin and the thermoplastic elastomer (0 part by weight, that is, including the case where no mineral oil is added in the impregnation step). It is. The lower limit is preferably 10 parts by weight, more preferably 20 parts by weight. On the other hand, the upper limit is preferably 60 parts by weight, more preferably 50 parts by weight.

The total amount of the mineral oil blended in the resin particle manufacturing step and the mineral oil blended in the impregnation step is 15 parts by weight with respect to a total of 100 parts by weight of the polyolefin resin and the thermoplastic elastomer. -95 parts by weight.
As described above, when the blending amount of the mineral oil is small, the mineral oil can be blended only in either the resin particle manufacturing process or the impregnation process. However, the production stability during granulation of resin particles is improved by blending the mineral oil in two stages, the resin particle production process and the impregnation process, rather than blending the entire amount of mineral oil in one process. In addition, the impregnation time in the impregnation step can be shortened. Furthermore, by blending the mineral oil in two stages of the resin particle manufacturing process and the impregnation process, a larger amount of the mineral oil can be contained in the expanded particles.
The lower limit of the amount is preferably 20 parts by weight, more preferably 22 parts by weight. On the other hand, the upper limit is preferably 90 parts by weight, more preferably 80 parts by weight, and still more preferably 70 parts by weight. Further, in the resin particle production step and the impregnation step, it is preferable to add a larger amount of the impregnation step because stability during production of the resin particles is improved.

  In the foaming step, foaming is performed by releasing resin particles containing the foaming agent and mineral oil from the inside of the sealed container at a temperature equal to or higher than the softening temperature of the resin particles under a low pressure (usually atmospheric pressure). . In this case, when the contents in the sealed container are discharged from the sealed container to the low pressure region, back pressure is applied to the sealed container with the used foaming agent or an inorganic gas such as nitrogen, air, etc. It is preferable to release the contents in such a manner that the content does not drop rapidly. By such an operation, the apparent density of the obtained expanded particles becomes more uniform. The obtained expanded particles contain 15 to 95 parts by weight of mineral oil.

  The impregnation step and the foaming step are preferably performed continuously in the same sealed container from the viewpoint of improving production efficiency. For the impregnation step and the foaming step, known foaming methods described in JP-B-49-2183, JP-B-56-1344, JP-B-62-61227 and the like can be employed.

Next, the polyolefin resin foamed particle molded body of the present invention will be described.
The foamed particle molded body of the present invention is produced by an in-mold molding method using the foamed particles. As the in-mold forming method, a known method can be employed.
For example, using a pair of male and female molding dies used in conventional molding of foamed particles, the foamed particles are filled into the mold cavity under atmospheric pressure or reduced pressure, and the mold is closed to increase the mold cavity volume. A method using a reduced pressure molding method (for example, Japanese Examined Patent Publication No. 46-38359) in which compression is performed so as to decrease by 5 to 70%, and then a heating medium such as steam is supplied into the mold and heating is performed, and the expanded particles are heated and fused ). In addition, the foamed particles are pre-pressurized with a pressurized gas to increase the pressure in the foamed particles, thereby increasing the secondary foamability of the foamed particles and maintaining the secondary foamability under atmospheric pressure or reduced pressure. Filled with foam particles in the mold cavity and closed, and then heated by supplying a heat medium such as steam into the mold and heated to melt the foam particles (for example, Shokosho) No. 51-2951) and the like. In addition, after filling the cavities pressurized above the atmospheric pressure with compressed gas with foamed particles pressurized above the pressure, a heating medium such as steam is supplied into the cavities and heated to produce the foamed particles. It is also possible to mold by a compression filling molding method (Japanese Patent Publication No. 4-46217). In addition, after filling foam particles with high secondary foaming power obtained under special conditions into a cavity of a pair of male and female molds under atmospheric pressure or reduced pressure, a heating medium such as steam is then supplied. It can also be molded by an atmospheric pressure filling molding method (Japanese Patent Publication No. 6-49795) or a method combining the above methods (Japanese Patent Publication No. 6-22919) or the like. it can.

  The apparent density of the foamed particle molded body of the present invention thus obtained is 10 to 100 g / L. Since the foamed particle molded body is a molded body having a higher expansion ratio than before, it has excellent flexibility, recoverability, light weight, and cushioning characteristics. It can be suitably used as a material.

  If the apparent density of the foamed particle molded body is too low, the mechanical strength such as compressive strength and tensile strength will be low, and when used as a packaging material or cushioning material for precise packaging, it cannot withstand the load. There is a risk of bottoming out. From this viewpoint, the lower limit of the apparent density of the foamed particle molded body is preferably 15 g / L, and more preferably 20 g / L. On the other hand, when the apparent density is too high, flexibility and lightness may be lowered. From this viewpoint, the upper limit is preferably 90 g / L, more preferably 85 g / L, and still more preferably 70 g / L.

  The apparent density d (g / L) of the foamed particle molded body is measured as it is if it is a rectangular parallelepiped molded body, and cut into a rectangular parallelepiped if it is an irregular shaped molded body. This is obtained by measuring the vertical, horizontal, and height dimensions of the test piece, multiplying it to calculate the volume V (L), and dividing the weight W (g) of the test piece.

  Since the foamed particle molded body of the present invention contains the polyolefin-based resin, the thermoplastic elastomer, and the mineral oil, the flexibility, particularly the recoverability after compression is dramatically improved. . In particular, the foamed particle molded body of the present invention is a foamed particle molded body excellent not only in flexibility but also in recoverability after compression.

The foamed particle molded body of the present invention has a compression set measured by JIS K 6767 of 6% or less, exhibits excellent recoverability of the shape after compression, and is a packaging material or cushion material for a precise packaged article. It is a suitable foamed particle molded body. When used in the above applications, the compression set is preferably as low as possible, preferably 5% or less, more preferably 4% or less.

The measurement of the compressive stress at the time of 50% strain of the foamed particle molded body of the present invention is a value determined according to JIS K6767. The lower the compressive stress at the time of 50% strain, the better the flexibility, and the molded article suitable as a packaging material or cushioning material for a precise packaged object. When used in the above applications, the foamed particle molded body is preferably 180 kPa or less, more preferably 150 kPa or less, and still more preferably 120 kPa or less.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
Table 1 below shows the types and physical properties of the thermoplastic elastomers used in the examples and comparative examples.

Example 1
(Resin particle manufacturing process)
As the polyolefin resin, ethylene content 2.7 wt%, MFR 5 g / 10 min, melting point 143 ° C. ethylene propylene random copolymer (hereinafter also referred to as PP1) 50 wt%, and thermoplastic elastomer (E1) 50 shown in Table 1 % By weight and 25 parts by weight of mineral oil (paraffinic process oil, Idemitsu Kosan Dyna Oil PW90; parts by weight with the total amount of the polyolefin resin and the thermoplastic elastomer as 100 parts by weight) in a tumbler After premixing, these were put into an extruder, melt-kneaded and extruded into strands, and cut and granulated with a pelletizer to obtain a particle weight of about 2 mg to obtain resin particles.

(Impregnation process)
1 kg of the obtained resin particles and 300 g of mineral oil (paraffinic process oil, Idemitsu Kosan Dyna Oil PW90; 30 parts by weight with respect to a total of 100 parts by weight of the polyolefin resin and the thermoplastic elastomer), Along with 3 liters (L) of water as a dispersion medium, the mixture is charged into a 5 L sealed container equipped with a stirrer, and further 3 g of kaolin as a dispersant and 0.04 g of sodium alkylbenzene sulfonate as a dispersion aid in the dispersion medium, And 0.1 g of aluminum sulfate was added, and 80 g of CO ₂ (8 parts by weight with respect to 100 parts by weight of the resin particles) was injected as a foaming agent into the sealed container.
(Foaming process)
Thereafter, the temperature was raised to the foaming temperature under stirring and maintained at that temperature for 15 minutes, and then the contents were released under atmospheric pressure to obtain foamed particles.

  The obtained expanded particles are put into a pressurized tank, pressurized for 12 hours at a pressure of 0.3 MPa (G) to give an internal pressure, and after taking out, a gold plate is obtained that is 250 mm long × 250 mm wide × 100 mm thick. The foamed particles were filled into the mold, molded in the mold by heating with steam, and the foamed particle molded body was cured in an oven at 80 ° C. for 12 hours to obtain a foamed particle molded body. Table 2 shows the physical properties and the like of the obtained expanded particles and the expanded molded article.

Example 2
In the resin particle production process, resin particles were obtained in the same manner as in Example 1. Next, the amount of the mineral oil (PW90) in the impregnation step was the same as in Example 1 except that the amount was 65 parts by weight with respect to a total of 100 parts by weight of the polyolefin resin and the thermoplastic elastomer. Foamed particles were obtained by the operation. Further, in-mold molding was performed in the same manner as in Example 1 to obtain a foamed particle molded body. Table 2 shows the physical properties and the like of the obtained expanded particles and the expanded molded article.

Example 3
In the resin particle production process, resin particles were obtained in the same manner as in Example 1 except that the amount of the thermoplastic elastomer was 29% by weight (PP1 was 71% by weight) and no mineral oil was added. Next, the same operation as in Example 1 was carried out except that 40 parts by weight of mineral oil (PW90) in the impregnation step was added (parts by weight relative to 100 parts by weight of the total amount of the polyolefin resin and the thermoplastic elastomer). Expanded particles were obtained. Further, in-mold molding was performed in the same manner as in Example 1 to obtain a foamed particle molded body. Table 2 shows the physical properties and the like of the obtained expanded particles and the expanded molded article.

Examples 4-6
Resin particles and foamed particles were produced in the same manner as in Example 3 except that the type of thermoplastic elastomer was changed, and a foamed particle molded body was obtained.
Table 2 shows the physical properties and the like of the obtained expanded particles and the expanded molded article.

Example 7
In the resin particle production process, resin particles were obtained in the same manner as in Example 1. Next, in the impregnation step, expanded particles were obtained in the same manner as in Example 1 except that mineral oil was not added. Further, in-mold molding was performed in the same manner as in Example 1 to obtain a foamed particle molded body. Table 2 shows the physical properties and the like of the obtained expanded particles and the expanded molded article.

Example 8
In the resin particle production process, resin particles were obtained in the same manner as in Example 1 except that the thermoplastic elastomer E2 shown in Table 1 was used and no mineral oil was added. Next, expanded particles were obtained in the same manner as in Example 1 except that mineral oil (PW90) was added in the impregnation step in the amount shown in Table 2. Further, a foamed particle molded body was obtained in the same manner as in Example 1. Table 2 shows the physical properties and the like of the obtained expanded particles and the expanded molded article.

Example 9
Resin particles were obtained in the same manner as in Example 1 except that mineral oil was not added in the resin particle production process. Next, expanded particles were obtained in the same manner as in Example 1 except that the mineral oil (PW90) in the amount shown in Table 2 was added only in the impregnation step. Further, in-mold molding was performed in the same manner as in Example 1 to obtain a foamed particle molded body. Table 2 shows the physical properties and the like of the obtained expanded particles and the expanded molded article.

Comparative Example 1
Expanded particles were obtained in the same manner as in Example 3 except that the resin particles of Example 3 were used and no mineral oil was added in the impregnation step. Further, in-mold molding was performed in the same manner as in Example 1 to obtain a foamed particle molded body. Since it does not contain mineral oil, it has excellent dispersibility in the impregnation step and in-mold moldability, but the obtained foamed particle molded body lacks flexibility and recoverability.

Comparative Example 2
Resin particles and expanded particles were obtained in the same manner as in Comparative Example 1 except that the type of thermoplastic elastomer was changed. Further, in-mold molding was performed in the same manner as in Example 1 to obtain a foamed particle molded body. Although there was no problem in dispersibility and in-mold moldability in the impregnation step, the obtained foamed particle molded body was insufficient in recoverability.

Comparative Example 3
Resin particles in the same manner as in Example 3 except that the blending amount of the mineral oil in the resin particle manufacturing process was 100 parts by weight (parts by weight relative to 100 parts by weight of the total blending amount of the polyolefin resin and the thermoplastic elastomer). Manufactured. However, since the strand became too flexible, granulation could not be performed and resin particles could not be obtained. In addition, surging due to poor biting during extrusion also occurred.

Comparative Example 4
Except for using the resin particles obtained in Example 3, the blending amount of the mineral oil in the impregnation step was 120 parts by weight (parts by weight relative to 100 parts by weight of the total amount of the polyolefin resin and the thermoplastic elastomer). In the same manner as in Example 3, foamed particles were produced. The dispersibility in the impregnation step was lowered, the resin particles were agglomerated, and the foamed particles were agglomerated, and it was not possible to obtain foamed particles that could be used for in-mold molding.

Comparative Example 5
Resin particles and foamed particles were obtained in the same manner as in Example 3 except that the polyolefin resin was blended in the ratio shown in Table 2. Since the blended amount of the thermoplastic elastomer was small, the foamed particles were sticky, and the foamed particles could not be filled in the molding die, and a foamed particle molded body could not be obtained.

Comparative Example 6
Resin particles and foamed particles were obtained in the same manner as in Example 3 except that the thermoplastic elastomer was blended in the ratio shown in Table 2. Since the blended amount of the thermoplastic elastomer was too large, the foamed particles became open-celled, and secondary foaming did not occur during in-mold molding, and a foamed particle molded body could not be obtained.

Evaluation of dispersion stability ○: After foaming in the foaming step, no condensation occurred between the foamed particles.
X: Condensation between the foamed particles occurred after foaming in the foaming process.

Evaluation of in-mold moldability A: The surface of the foamed particle molded body is not sticky, and the shrinkage ratio of the foamed particle molded body is 10% or less.
○: Although the surface of the foamed particle molded body is somewhat sticky, a foamed particle molded body can be obtained.
X: The surface of the foamed particles is sticky, the foamed particles cannot be filled into the molding die, and the foamed particle molded body cannot be obtained.

Claims (3)

A resin composition comprising 80 to 30% by weight of a polyolefin resin and 20 to 70% by weight of a thermoplastic elastomer (however, the total of the polyolefin resin and the thermoplastic elastomer is 100% by weight);
Comprising 15 to 95 parts by weight of mineral oil with respect to 100 parts by weight of the resin composition,
The weight ratio of the blending amount of the mineral oil to the blending amount of the thermoplastic elastomer is 0.4 to 3,
Polyolefin resin foamed particles having an apparent density of 15 to 150 g / L.
A molded product obtained by in-mold molding of the polyolefin resin expanded particles according to claim 1, wherein the molded product has an apparent density of 10 to 100 g / L and a compression set (JIS K 6767) of 6 % Molded polyolefin resin foam particles, characterized by being less than or equal to%.
80 to 30% by weight of a polyolefin resin, 20 to 70% by weight of a thermoplastic elastomer (the total of the polyolefin resin and the thermoplastic elastomer is 100% by weight), 0 to 70 parts by weight (the polyolefin resin and heat The blended amount of the plastic elastomer is 100 parts by weight with respect to a total of 100 parts by weight of mineral oil), and the melt-kneaded product obtained by melt-kneading is granulated into resin particles,
Using the resin particles, the foaming agent, and mineral oil of 0 to 70 parts by weight (parts by weight relative to 100 parts by weight of the total amount of the polyolefin resin and the thermoplastic elastomer) as a dispersion medium in a closed container Disperse, impregnate the resin particles with a foaming agent and the mineral oil,
Next, 15 to 95 parts by weight of a mineral oil containing foaming agent and mineral oil is foamed (the amount is 100 parts by weight with respect to the total amount of the polyolefin resin and the thermoplastic elastomer). And a foamed particle having a weight ratio of the blended amount of the mineral oil to the blended amount of the thermoplastic elastomer of 0.4 to 3 is obtained.