JP6434584B2 - Polyolefin resin expanded particles - Google Patents

Description

  The present invention relates to a polyolefin resin expanded particle containing an inorganic filler.

  For the purpose of improving mechanical strength and imparting functionality such as flame retardancy, a technique for blending an inorganic filler into polyolefin resin expanded particles has been developed. A polyolefin-based resin expanded particle molded body containing an inorganic filler (sometimes referred to as an inorganic filler-containing molded body) is effectively used, for example, as a dielectric as described in Patent Document 1.

Special table 2008-512502 gazette

  However, when the polyolefin resin expanded particles contain a large amount of inorganic filler, there is a problem in molding the inorganic filler-containing expanded particles. That is, polyolefin resin foamed particles containing an inorganic filler have a problem that they tend to be open-celled during molding, and the fusibility tends to be insufficient. If the meltability of the polyolefin resin expanded particles is insufficient, the inorganic filler-containing molded product becomes extremely brittle, and particularly in a thick molded product, the meltability of the polyolefin resin expanded particles tends to be insufficient.

  Therefore, in order to realize sufficient fusion property of the polyolefin resin expanded particles, the molding pressure is increased when the in-mold molding of the polyolefin resin expanded particles is performed. However, if the molding pressure is increased, the polyolefin resin foamed particles may become open-celled, or the foamed particles near the surface of the molded body containing the inorganic filler may be crushed, so that the vicinity of the surface of the molded body and the inside of the molded body There is a possibility that the density difference between the surface and the inside of the molded body becomes large and the inorganic filler existing per unit volume of the molded body tends to be dispersed unevenly. If the inorganic filler is dispersed non-uniformly, the functionality of the molded body imparted by the inorganic filler may be non-uniform or insufficient.

  An object of the present invention is to provide a polyolefin-based foamed particle containing an inorganic filler, which contains an inorganic filler and is excellent in moldability such as fusibility.

The present invention provides (1) a foamed polyolefin resin particle containing an inorganic filler, comprising a foamed core layer formed from a polyolefin resin and a coating layer formed from a polyolefin resin, The weight ratio of the layer to the core layer is 1:99 to 20:80, the core layer contains an inorganic filler in the range of 5 wt% to 90 wt%, and the inorganic filling contained in the coating layer The blending amount of the agent is smaller than the blending amount of the inorganic filler contained in the core layer (however, 0 is included), and the polyolefin resin forming the core layer includes a carboxylic acid-modified polyolefin resin. And the polyolefin resin foamed particles, wherein the content of the carboxylic acid component in the polyolefin resin forming the core layer is 0.15 to 10% by weight,
(2) The core layer includes the polyolefin-based resin expanded particles according to the above (1), which contains an inorganic filler in a range of 30 wt% to 90 wt%.

  ADVANTAGE OF THE INVENTION According to this invention, what was excellent in in-mold moldability, such as a meltability, can be provided as an inorganic filler containing polyolefin-type expanded particle, while containing an inorganic filler.

FIG. 1A is a schematic side view schematically showing an example of polyolefin resin foamed particles in the present invention. FIG. 1B is a schematic cross-sectional schematic diagram schematically showing a schematic state of a cross section taken along line AA of FIG. 1A. FIG. 2 is a graph showing a preferable range of the content of the carboxylic acid component with respect to the added amount of the inorganic filler.

[Polyolefin resin foamed particles 1]
The polyolefin-based resin expanded particles 1 in the present invention contain an inorganic filler, and include a core layer 2 in a foamed state and a coating layer 3 that covers the core layer 2 as shown in FIGS. 1A and 1B. Configured.

(Inorganic filler)
The inorganic filler contained in the polyolefin resin expanded particles 1 is not particularly limited, but a finer particle size is preferable because it is more easily dispersed uniformly in the polyolefin resin. Moreover, what can disperse | distribute an inorganic filler more uniformly as the polyolefin resin foamed particle 1 can be prepared as an inorganic filler can be uniformly disperse | distributed in a thermoplastic resin.

  Examples of the inorganic filler used in the present invention include carbons such as carbon black and graphite, fibers such as glass fibers, metal fibers, and carbon fibers, and inorganic water such as aluminum hydroxide, calcium hydroxide, and magnesium hydroxide. Inorganic carbonates such as oxides, calcium carbonate, magnesium carbonate and barium carbonate, inorganic sulfites such as calcium sulfite and magnesium sulfite, inorganic sulfates such as calcium sulfate, magnesium sulfate and aluminum sulfate, iron oxide, aluminum oxide and zinc oxide , Inorganic oxides such as silicon oxide, lead oxide, magnesium oxide, cobalt oxide, titanium oxide, calcium oxide, borates such as zinc borate, calcium borate, magnesium borate, aluminum borate, other talc, clay, Examples include clays or natural minerals such as kaolin and zeolite. That.

  As the inorganic filler, the above-mentioned inorganic oxides are preferable, and among them, metal oxides can be preferably used in terms of excellent uniformity, abrasion resistance, scratch resistance, and the like. Examples thereof include aluminum oxide, zinc oxide, silicon oxide, lead oxide, magnesium oxide, cobalt oxide, and titanium oxide.

  As the inorganic filler, titanium oxide can be suitably selected from the viewpoint of excellent wear resistance among metal oxides.

  Here, the compound belonging to the above-mentioned titanium oxide includes not only a compound containing only titanium as a metal species, but also a compound containing a metal species other than titanium in addition to titanium.

  As the inorganic filler, one kind selected from the above-mentioned compounds may be used, or two or more kinds selected from various compounds may be used in combination. is there.

(Core layer 2)
The core layer 2 is made of a foamed state. The foam structure that forms the core layer 2 is a structure formed by foaming a polyolefin resin. The core layer 2 is formed by adding a foaming agent as described later to a polyolefin resin and foaming the foamable resin composition using a predetermined apparatus and predetermined conditions.

(Foaming agent)
Examples of the foaming agent include organic physical foaming agents and inorganic physical foaming agents. Examples of the organic physical blowing agent include aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane, and alicyclic hydrocarbons such as cyclobutane and cyclohexane. Examples of the inorganic physical foaming agent include air, nitrogen, carbon dioxide, oxygen, argon, water and the like.

(Polyolefin resin)
The polyolefin resin in the present invention refers to an olefin homopolymer, an olefin alone or a copolymer containing an olefin, or a mixture of two or more thereof. An olefin-only copolymer is a copolymer of two or more olefins, and an olefin-containing copolymer is a copolymer of an olefin and another monomer component, and the olefin component ratio is 50 wt. % Of copolymer shall be indicated. The polyolefin-based resin may be a resin composition containing other thermoplastic resin and / or elastomer in addition to the homopolymer and / or copolymer. In this case, the resin composition whose olefin component ratio in a composition is 50 weight% or more shall be shown.

  Examples of the olefin homopolymer include polypropylene, polyethylene, polybutene, and polypentene. As the copolymer containing only olefin or olefin, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, An ethylene copolymer having an ethylene component ratio of 50% by weight or more, such as an ethylene-maleic anhydride copolymer, an ethylene ionomer in which molecules of the ethylene-methacrylic acid copolymer are crosslinked with metal ions, and a propylene-ethylene copolymer A propylene component having a propylene component ratio of 50% by weight or more such as a polymer, propylene-butene copolymer, propylene-ethylene-butene terpolymer, propylene-acrylic acid copolymer, propylene-maleic anhydride copolymer, etc. A copolymer is mentioned. These copolymers may be any of block copolymers, random copolymers, and graft copolymers.

  The polyolefin resin that forms the base resin contained in the foamable resin composition is preferably a polypropylene resin because it is excellent in rigidity, wear resistance and processability, is inexpensive and is versatile. The polypropylene resin is a propylene copolymer having a propylene component ratio of 50% by weight or more such as polypropylene, propylene-ethylene random copolymer, propylene-butene random copolymer, propylene-ethylene-butene terpolymer. Or a mixture of two or more of these.

  A polyolefin resin that has been crosslinked by peroxide or radiation may be used, but a non-crosslinked one should be used because it is easy to form a uniformly mixed state of inorganic fillers to be described later. Is preferred.

  The polyolefin resin forming the core layer of the foamed particles of the present invention has a polar group-containing polymer as an acid anhydride such as acetic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, methacrylic acid, maleic acid, acrylic acid. Those obtained by blending a carboxylic acid-modified olefin polymer obtained by copolymerizing one or more selected from the above are preferred, and those comprising maleic anhydride-modified polypropylene are particularly preferred. It is preferable that the carboxylic acid-modified polymer is blended so that the carboxylic acid component is contained in a proportion of 0.15 to 10% by weight in the polyolefin resin forming the core layer. The content of the carboxylic acid component is more preferably 0.2 to 8% by weight, still more preferably 0.3 to 6% by weight.

  The carboxylic acid component in the polyolefin resin forming the core layer is derived from the carboxylic acid-modified olefin polymer, and the content of the carboxylic acid component in the polyolefin resin forming the core layer is the polyolefin resin. It depends on two factors: the amount of the carboxylic acid-modified olefin polymer blended therein and the modification rate of the carboxylic acid or its derivative in the polymer.

  In the carboxylic acid-modified olefin polymer, the modification rate of the carboxylic acid or its derivative is 0.5 to 15% by weight, more preferably 1 to 8% by weight from the viewpoint of the affinity between the polyolefin resin and the inorganic filler. Is preferred.

  Although depending on the proportion of the inorganic filler, the carboxylic acid-modified olefin polymer is preferably blended in the core layer in a proportion of 3 to 30% by weight together with the inorganic filler and the polyolefin resin. It is more preferable that it is mix | blended in the ratio of 5-25 weight%, and it is still more preferable that it is mix | blended in the ratio of 6-20 weight%. When the carboxylic acid-modified olefin polymer is blended with the polyolefin resin forming the core layer of the expanded particles, the affinity between the inorganic filler and the polyolefin resin is excellent, and the apparent density of the expanded particles varies. It becomes even smaller. In addition, as a method of blending the carboxylic acid-modified olefin polymer in the core layer, when preparing resin particles for obtaining expanded particles, together with the polyolefin resin and the inorganic filler, the carboxylic acid-modified olefin polymer is mixed. Examples thereof include a method of kneading a coalescence or carboxylic acid-modified olefin polymer master batch, or a method of kneading an inorganic filler surface-treated with a carboxylic acid-modified olefin polymer and a polyolefin resin. By using the resin particles having the core layer in which the carboxylic acid-modified olefin polymer is blended as described above, the expanded particles are produced by a known method, whereby the carboxylic acid is contained in the base resin constituting the expanded particles. A product obtained by blending a modified olefin polymer can be obtained.

  In the polyolefin resin particles, as the blending amount of the inorganic filler increases, the inorganic filler becomes a break point, and there is a risk that bubbles are easily broken during foaming or secondary foaming during molding. Therefore, it is preferable to adjust the compounding quantity of a carboxylic acid modified olefin polymer with the increase in the compounding quantity of an inorganic filler. The content (y) (% by weight) of the carboxylic acid component in the core layer and the blending amount (x) (% by weight) of the inorganic filler preferably satisfy the following formula (1), and are within this range. This is preferable because the risk of the foamed bubbles becoming open or broken is reduced during foaming.

(Inorganic filler in the core layer 2)
In the polyolefin resin expanded particles 1, the inorganic filler is present at least in the core layer 2.

(Content of inorganic filler in core layer 2)
The core layer 2 contains an inorganic filler in a range of 5% by weight to 90% by weight with respect to the core layer 2, but imparts high functionality to the foamed particles, and the inorganic filler is uniformly dispersed. From the viewpoint of more effectively obtaining the polyolefin resin expanded particles 1 having excellent properties, the inorganic filler is preferably blended in the range of 30% by weight to 85% by weight, preferably 40% by weight to 80% by weight. It is more preferable that it is mix | blended in the range of 50 weight% or more and 80 weight% or less.

(Additive)
In addition to the base resin as described above, additives may be appropriately added to the foamable resin composition as long as the effects of the present invention are not impaired. Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a pigment, a dye, a nucleating agent, and a bubble adjusting agent.

(Coating layer 3)
The coating layer 3 is a layer composed of a resin composition, and covers the periphery of the core layer 2 as shown in FIGS. 1A and 1B.

  The coating layer 3 is formed of a polyolefin resin. As polyolefin resin used as base resin, resin which can be selected as polyolefin resin which makes base resin which comprises the above core layers 2 can be mentioned.

(Presence or absence of an inorganic filler in the coating layer 3)
In the polyolefin resin expanded particles 1, the inorganic filler may be present in the coating layer 3. Therefore, the coating layer 3 may be a layer containing no inorganic filler.

  More specifically, the coating layer 3 includes an inorganic filler so that the blending ratio of the inorganic filler blended in the coating layer 3 is smaller than the blending ratio of the inorganic filler blended in the core layer 2. It is a layer or a layer containing no inorganic filler.

  Even if the coating layer 3 is a layer that does not contain an inorganic filler or a layer that contains an inorganic filler, the blending ratio of the inorganic filler blended in the coating layer is determined by the core layer. The coating layer 3 of the polyolefin-based resin foamed particles 1 is more fusible than the core layer 2 because it is smaller than the blending ratio of the inorganic filler blended in the foamable resin composition constituting Excellent. Therefore, in molding the polyolefin resin foamed particle molded body in a mold as will be described later, the adjacent polyolefin resin foamed particles 1 are more than the foamed particles constituted only by the structure corresponding to the core layer 2. The effect that it becomes easy to make it fuse | melt reliably is acquired. Therefore, when molding the expanded particles to improve the fusing property, it is possible to obtain a good molded article without requiring an operation such as increasing the molding pressure or pressurizing the expanded particles in advance. Moreover, the density difference between the surface layer and the inner layer of the obtained molded body can be reduced.

  The coating layer 3 preferably has a lower expansion ratio than the core layer 2 from the viewpoint of excellent fusion between the expanded particles when the polyolefin-based resin expanded particles are molded in-mold, and is not expanded or substantially It is more preferable that it is in a non-foamed state.

(Weight ratio of coating layer 3 and core layer 2)
In the polyolefin resin foamed particles 1, the weight ratio of the coating layer 3 to the core layer 2 is 1:99 to 20:80. With such a weight ratio, the core layer with a large amount of the inorganic filler is surely covered with the coating layer, so that the foamed particles have an excellent amount of the inorganic filler and have excellent fusion properties during molding. Can be obtained. From this viewpoint, the weight ratio of the coating layer 3 to the core layer 2 is more preferably 1:99 to 15:85, and further preferably 1:99 to 10:90.

  The coating layer 3 preferably contains a polyolefin resin having a melting point lower than that of the polyolefin resin forming the core layer 2 or substantially not showing the melting point. When a polyolefin resin having a low melting point or no melting point is included, the polyolefin resin foamed particles can obtain a desired in-mold molded product even if molded in a mold with a lower heating water vapor pressure.

(Melting point difference between coating layer 3 and core layer 2)
The coating layer 3 and the core layer 2 preferably have a melting point difference between the melting point of the polyolefin resin forming the coating layer 3 and the melting point of the polyolefin resin forming the core layer 2 in the range of 0 to 50 ° C. More than 45 ° C., more preferably 5 ° C. or more and 40 ° C. or less. When the polyolefin resin forming the coating layer is an amorphous polyolefin resin having no melting point, the Vicat softening temperature of the amorphous polyolefin resin is higher than the melting point of the polyolefin resin forming the core layer 2. Is preferably low and more preferably 5 ° C. or more. The upper limit of the difference between the melting point and the softening point is about 100 ° C.

  In the polyolefin resin foamed particles 1, the polyolefin resin forming the coating layer 3 and the polyolefin resin forming the core layer 2 are configured so as to satisfy the above range, whereby the foamed particles are molded in-mold. At this time, it is not necessary to increase the heating water vapor pressure in order to fuse the foamed particles, and the foamed particles can be fused to each other even at a relatively low temperature, thereby obtaining a desired in-mold molded product. Can do.

  In the expanded particles of the present invention, a DSC curve (first 1C) obtained when 2 to 10 mg of the expanded particles are heated from 23 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min by a heat flux differential scanning calorimetry method. The DSC curve of the repetitive heating has an endothermic peak A inherent to the polyolefin resin (hereinafter also simply referred to as “inherent peak”) and one or more endothermic peaks B (hereinafter simply referred to as “high temperature”) on the higher temperature side of the inherent peak. It is also preferable to have a peak. The ratio of the heat of fusion of the high temperature peak (hereinafter also simply referred to as the high temperature peak heat) to the total heat of fusion (total of the heat of fusion of the intrinsic peak and the heat of fusion of the high temperature peak) in the DSC curve is 0.1 or more. Is preferable, more preferably 0.15 or more, and still more preferably 0.2 or more. The upper limit of the ratio of heat of fusion is about 0.4, more preferably 0.3. Within the above range, the foamed particles can be fused together while controlling the secondary foaming force of the foamed particles, which is preferable because a foamed particle molded body having a uniform density can be obtained.

  The above-described DSC curve of the first heating, the intrinsic peak calorific value, and the high temperature peak calorific value are measured by a measuring method based on JIS K7122 (1987). The high temperature peak of the expanded particles can be adjusted by a well-known method, and specifically, the adjusting method is disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-151928.

  The average particle diameter of the polyolefin-based resin expanded particles 1 is preferably 0.5 to 10 mm, more preferably 0.8 to 5 mm. More preferably, it is 1-3 mm. The average particle diameter is the maximum dimension (mm) for each of 200 or more polyolefin resin foam particles arbitrarily taken from the polyolefin resin foam particles left for 2 days under the conditions of 50% relative humidity, 23 ° C. and 1 atm. ) Is measured with calipers, and is determined from the arithmetic average value of the maximum dimension.

The bulk density of the polyolefin resin expanded particles 1 is preferably 0.03~1.5g / cm ^3, more preferably 0.05~1.2g / cm ^3. More preferably, it is 0.05-0.8 g / cm < ³ >.

[Function of polyolefin resin expanded particle 1]
The polyolefin resin expanded particles 1 contain an inorganic filler in the core layer 2 at a blending ratio with respect to the core layer 2 in the range of 5 wt% to 90 wt%. The polyolefin-based resin expanded particles 1 include the core layer 2 as a layer in which more inorganic fillers are distributed, and the coating layer 3 as a layer with a small or no inorganic filler distribution. Even if the expanded particles 1 as a whole contain a large amount of an inorganic filler, the fusing property of the surface of the expanded polyolefin resin particles 1 is maintained. For this reason, even when molding a polyolefin resin foamed particle molded body using a polyolefin resin foamed particle 1 containing a large amount of an inorganic filler, a molding pressure is applied during preparation of the polyolefin resin foamed particle molded body. It is possible to reduce the demand to increase Furthermore, as the polyolefin-based resin expanded particle molded body, an inorganic filler having excellent uniform dispersibility can be formed. Moreover, also about the polyolefin resin expanded particle molded object formed using the polyolefin resin expanded particle 1, what contains an inorganic filler in various quantity can be prepared.

[Preparation Method of Polyolefin Resin Expanded Particle 1]
The polyolefin resin expanded particles 1 can be prepared, for example, as follows.

  Prepare two extruders, knead the resin composition for forming the core layer 2 with one extruder, knead the resin composition constituting the coating layer 3 with the other extruder, By performing co-extrusion from this die, a sheath-core type string-like composite comprising a core layer and a coating layer covering the core layer is obtained. Next, the string-like composite is cut with a predetermined weight or size with a cutting machine equipped with a take-up machine to obtain columnar pellet-shaped resin particles composed of a non-foamed core layer and a coating layer.

  Further, the resin particles and the foaming agent are accommodated in a pressure vessel that can be sealed and opened, and the resin particles are impregnated with the foaming agent. Then, the inside of a pressure vessel is heated more than the softening temperature of base resin which comprises a core layer, and an expandable resin particle is prepared. Then, by opening the sealed pressure vessel, the expandable resin particles in the pressure vessel are released from the sealed vessel into a low-pressure atmosphere. At this time, the core layer 2 is foamed to form the core layer 2. Further, along with the formation of the core layer 2, the coating layer forms a coating layer 3 that covers the core layer 2. In this way, the polyolefin resin expanded particles 1 are formed.

[Polyolefin resin foamed body]
The polyolefin-based resin expanded particle molded body in the present invention is formed by in-mold molding of expanded particles including the polyolefin-based resin expanded particles 1 including the core layer 2 and the coating layer 3 as described above. In addition, the polyolefin-based resin expanded particle molded body may include a product formed by in-mold molding using only the polyolefin-based resin expanded particle 1 including the core layer 2 and the coating layer 3 as described above as the expanded particle. An example in which the polyolefin resin foamed particle molded body is plate-shaped is shown, but the shape of the polyolefin resin foamed particle molded body is not limited to this and can be set as appropriate.

(Apparent density)
Although the apparent density of the polyolefin resin expanded particle molded body is not particularly limited, the apparent density is preferably 0.05 to 0.8 g / cm ³ . The apparent density of the foamed particle molded body can be determined by dividing the weight of the molded body by the volume of the molded body. The volume of the molded body can be determined from the outer dimensions of the molded body.

(Fusion rate)
The polyolefin-based resin expanded particle molded body is not particularly limited in terms of the fusion rate of the polyolefin-based resin expanded particles 1 as long as the integrity can be maintained. However, in consideration of obtaining a molded body having excellent mechanical strength. For example, the fusion rate of the polyolefin resin expanded particles 1 constituting the polyolefin resin expanded particle molded body is preferably 60% or more, more preferably 70% or more, and particularly preferably 80% or more.

(Measurement of fusion rate)
In the molded article of polyolefin resin foamed particles, the fusion rate of the polyolefin resin foamed particles 4 can be evaluated by the material fracture rate at the fracture surface by a bending test. That is, the bending fracture surface (fracture surface in which 100 or more foamed particles exist) of the foamed particle molded body is observed, and the number of foam particles broken at the interface and the number of foam particles peeled off at the interface are counted. Then, the percentage of the number of broken foam particles relative to the total number of foam particles broken and the number of foam particles peeled at the interface is defined as the fusion rate.

[Formation method of foamed polyolefin resin particles]
The polyolefin resin expanded particle molded body can be prepared using, for example, an in-mold molding method. That is, first, a mold designed in a desired shape is prepared according to the polyolefin resin expanded particle molded body to be obtained. Next, the polyolefin resin foamed particles 1 are filled in a mold. Steam is supplied into the mold to heat the mold. At this time, the coating layers 3 of the adjacent polyolefin resin expanded particles 1 are fused together, and the polyolefin resin expanded particles 1 are secondarily expanded to fill the gaps between the expanded particles, and are filled in the mold. The polyolefin resin expanded particles 1 are integrated. Thereafter, the mold is cooled, the contents are taken out from the mold, and a polyolefin resin expanded particle molded body is obtained.

  In the present invention, a polyolefin resin foamed particle molded body having various functions can be obtained by appropriately changing the type and blending amount of the inorganic filler. The obtained polyolefin resin expanded particle molded body can be used in various applications.

  In this invention, what has various functions can be prepared as a polyolefin-type resin expanded particle molded object by changing suitably the kind and compounding quantity of an inorganic filler. Further, when preparing the polyolefin resin expanded resin molded body by an in-mold molding method or the like, the coating layer 3 of the polyolefin resin expanded resin particle 1 is softened so that the polyolefin resin expanded resin particles 1 can be efficiently fused smoothly. Therefore, the molding pressure at the time of carrying out the in-mold molding method can be kept lower than before.

Examples 1-5
[Preparation of inorganic-containing masterbatch]
A biaxial shaft having an inner diameter of 30 mm with the ratio of the polyolefin resin, inorganic filler, and carboxylic acid-modified polyolefin polymer (carboxylic acid modification rate 5%) shown in Table 1 constituting the resin composition constituting the core layer as shown in Table 2. Supplied to an extruder, melt-kneaded at 200-220 ° C. and extruded into a strand to obtain an extrudate, and the strand-shaped extrudate was cooled and cut to obtain an inorganic-containing master batch for the core layer . In Table 2, “MPP” as the type of resin indicates carboxylic acid-modified polyolefin, and maleic anhydride-modified polypropylene (H3000P (carboxylic acid modification rate: 5 wt%) manufactured by Toyobo Co., Ltd.) was used.

  In Table 2, the content of the carboxylic acid component indicates the content of the carboxylic acid component contained in the polyolefin resin having the core layer composition. The resin melting point difference between the core layer and the coating layer indicates a difference between the melting point of the polyolefin resin constituting the core layer and the melting point of the polyolefin resin constituting the coating layer. The weight ratio of the core layer / coating layer indicates the weight ratio (%) of each of the core layer and the coating layer in the total weight of the particles.

[Production of resin particles]
Using an extruder having a 65 mm inner diameter core layer forming extruder and an outer layer forming extruder having an inner diameter of 30 mm provided with a multilayer strand forming die on the outlet side, the core layer forming inorganic material prepared as described above The master batch and the polyolefin resin for forming the coating layer are respectively supplied to the core layer extruder and the coating layer extruder in the proportions shown in Table 2, and melt-kneaded to obtain a melt-kneaded product. Extruded as a strand with a coating layer on the core layer through a small hole in the die that was introduced into the forming die, joined in the die, and attached to the tip of the die, and the extruded strand was cooled with water, cut with a pelletizer and dried. Thus, cylindrical resin particles were obtained. In Examples 1 to 5, multilayer resin particles are obtained.

[Production of expanded particles]
800 g of the resin particles obtained above and 3 L of water as a dispersion medium are charged in a 5 L sealed container, and 0.3 parts by weight of kaolin as a dispersant and a surfactant are added to 100 parts by weight of the resin particles in the dispersion medium. (Product name: Neogen, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., sodium alkylbenzene sulfonate) 0.4 parts by weight (as an active ingredient) and 0.01 parts by weight of aluminum sulfate are added as foaming agents in a sealed container. Carbon dioxide was injected in the amount shown in Table 3, heated to a temperature 5 ° C. lower than the foaming temperature shown in Table 3 with stirring, and maintained for 15 minutes to adjust the high temperature peak heat amount, and the foaming temperature shown in Table 3 Then, the container contents were released together with water under atmospheric pressure to obtain expanded particles having an apparent density shown in Table 3. At this time, in Examples 1 to 5, multilayer expanded particles are obtained. Further, the physical properties of the obtained multilayer foamed particles are as shown in Table 3. And the expanded particle obtained at this time becomes the polyolefin resin expanded particle of the present invention.

[Foamed particle compact]
The polyolefin-based resin expanded particles obtained above are subjected to a pressurizing process for increasing the internal pressure in the expanded particles with a pressurized gas (air) under the conditions shown in Table 4 as necessary, and then 300 mm long × 200 mm wide × Cracking filling was performed on a flat plate mold having a thickness of 60 mm, and in-mold molding was performed by steam heating to obtain a plate-like foamed particle molded body. The heating method was such that steam was supplied for 5 seconds with the double-sided drain valves opened and preheating (exhaust process) was performed, and then a pressure lower than the molding vapor pressure shown in Table 4 by 0.08 MPa (G). Then, one heating was performed in the opposite direction at a pressure lower than the molding vapor pressure shown in Table 4 by 0.04 MPa (G), and then the main heating was performed from both sides with the molding vapor pressure shown in Table 4. . After the heating was completed, the pressure was released, and after air cooling for 30 seconds, the mold was opened and the molded product in the mold was taken out from the mold. The obtained foamed particle molded body was cured in an oven at 80 ° C. for 12 hours to obtain a polyolefin resin foamed particle molded body. Table 4 shows the physical properties of the obtained molded body.

Comparative Example 1
In Comparative Example 1, expanded particles were produced in the same manner as in Example 1 except that 40% by weight of the polyolefin resin was used for the core layer, 60% by weight of titanium oxide was used as the inorganic filler, and no coating layer was provided. . A foamed particle molded body was prepared in the same manner as in Example 1 using the foamed particles. Under the same conditions as in Example 1, the foamed particles were not fused and the foamed particle molded body could not be obtained. When the molding steam pressure was increased in order to fuse the foamed particles, the foamed particles became open cells, and a foamed particle molded body could not be obtained.

  For Comparative Example 1, an attempt was also made to prepare a foamed particle molded body by performing in-mold molding after applying an internal pressure to the foamed particles. In this case, although it was possible to obtain a foamed particle molded body, it was inferior in fusion property. With the expanded particles of Comparative Example 1, even if an attempt was made to form a thick expanded particle molded body as in this example, a satisfactory expanded particle molded body could not be obtained.

  The physical property evaluation methods of the expanded particles and the expanded molded particles were as follows.

[Bulk density of expanded particles]
The bulk density of the expanded particles was determined as follows. First, a 1 L graduated cylinder was prepared, and a group of expanded particles was filled up to a 1 L marked line in the graduated cylinder. The bulk density (g / cm ³ ) of the foamed particles was determined by measuring the weight (g / L) of the filled foam particles per liter and converting the unit.

[Apparent density of molded foam particles]
The apparent density of the foamed particle compact was determined by dividing the weight (g) of the compact by the volume (cm ³ ) determined from the external dimensions of the compact.

[Fusibility]
For the foamed molded product, the fusing property was measured and evaluated by the following method. The foamed molded body is bent and broken, and the number of foamed resin particles (C1) and the number of broken foamed resin particles (C2) present on the fractured surface are obtained, and the ratio of the destroyed foamed resin particles to the foamed resin particles ( C2 / C1 × 100) was calculated as the material fracture rate. The above measurement was performed 5 times using different test pieces, the respective material destruction rates were obtained, and the arithmetic average value thereof was defined as the fusion rate (%). Based on the fusion rate determined by the above measuring method, the evaluation was made into the following criteria: ◎, ○, ×. In addition, (double-circle) and (circle) show that it is excellent in fusibility, and x shows that it is inferior to fusibility.

A: The fusion rate is 80% or more.
A: The fusion rate is 60% or more and less than 80%.
X: The fusion rate is less than 60%.

[High temperature peak heat]
The high temperature peak heat quantity (J / g) was obtained by sampling 10 foam particles randomly from the obtained foam particle group, and measuring the intrinsic peak heat quantity and high temperature peak heat quantity of each foamed particle by the method described above. Then, the ratio of the high temperature peak heat quantity to the total heat of fusion was determined, and the value obtained by arithmetically averaging the measured values was defined as the ratio of the high temperature peak heat quantity to the total heat of fusion of the expanded particles.

1 Polyolefin resin foamed particles 2 Core layer 3 Coating layer

Claims (2)

In polyolefin resin expanded particles containing inorganic filler,
It consists of a foamed core layer formed from a polyolefin resin and a coating layer formed from a polyolefin resin,
The weight ratio of the coating layer to the core layer is 1:99 to 20:80,
The core layer contains an inorganic filler in the range of 5 wt% to 90 wt%,
The proportion of the inorganic filler contained in the coating layer is less than the amount of the inorganic filler contained in the core layer (however, including 0),
The polyolefin resin forming the core layer includes a carboxylic acid-modified polyolefin resin, and the content of the carboxylic acid component in the polyolefin resin forming the core layer is 0.15 to 10% by weight. Polyolefin resin foam particles.   The polyolefin resin expanded particles according to claim 1, wherein the core layer contains an inorganic filler in a range of 30 wt% to 90 wt%.

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