JP2019166644A - Method of producing foamed composite - Google Patents

Abstract

To provide a method of efficiently producing a foamed composite lightweight and excellent in compressive strength and heat insulation.SOLUTION: The method of producing the foamed composite in which a resin powder and a polyolefin-based foamable pellet are simultaneously charged into a mold, and heated and molded while the mold rotated, comprises use of the foamable pellet in a spherical shape coated with a non-foamable resin as much as 5% to 25% of mold volume. The foamable pellet in a spherical shape coated with a non-foamable resin is formed by using two extruders, extruding a foamable resin composition into a rod shape from one extruder and extruding the non-foamable resin from the other one extruder, producing a two-layer rod-shaped resin composition, by a cross head die, in which the foamable resin composition extruded into a rod shape is coated with the non-foamable resin, and sandwiching the two-layer rod-shaped resin composition between two rolls with a hemispherical groove formed and moving at the same time the two rolls in a direction along a rotation axis for forming it into a spherical shape.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing a foam composite used for a heat insulating material, a building material, a cushioning material, an impact absorbing material, a levitation material, and the like.

  As a method for producing a plastic molded body, there are various molding methods such as injection molding, extrusion molding, blow molding, and press molding. However, all of the plastic molded articles molded by these methods are likely to retain distortion at the time of molding, and thus there is a problem in durability. In particular, it is known that in a molded article used outdoors, the life as a plastic molded article is greatly reduced due to the influence of ultraviolet rays, the influence of wind and water damage, the influence of temperature difference, and the like.

  On the other hand, as a molding method for producing a plastic molded article having excellent durability, there is a molding method using a rotational molding apparatus. In the molding method using a rotary molding device, a resin powder is poured into a mold and heated in a biaxial direction while being heated for a certain period of time. To form a molded body. This manufacturing method is characterized in that a plastic molded article having excellent durability can be obtained because there is almost no distortion during molding.

  Further, the molding method using the rotational molding apparatus is characterized by a hollow molded body. In order to improve the compressive strength and heat insulation of the target product, there is a method of filling a hollow part with a foam in a subsequent process. As this foam, foamed urethane and foamed styrene are mainly used. In this case, the number of steps is two, and there are many cases where the problem of working time and the material of the foam material and the skin material to be filled are different from each other, and the adhesion between the foam and the skin often becomes a problem.

  As a method for solving the above problem, there has been proposed a method in which a resin powder serving as a skin material and an olefin-based foamable pellet are simultaneously put into a mold and rotationally molded (see Patent Document 1). According to the present invention, a thermoplastic plastic powder and a polyolefin cross-linked foamable granular material are put in a mold and heated, and a foam composite having high heat insulation and high mechanical strength can be produced. .

  Moreover, in order to improve the intensity | strength of a foamed layer, the method of using a two-layer foamable pellet is also proposed (refer patent document 2). The present invention is a method in which a resin powder as a skin material and foamable pellets are simultaneously put into a mold and rotationally molded. In order to improve the strength of the foamed layer, the entire surface is covered with plastic. Two-layer foam pellets made of cross-linked foamed polyolefin are used.

JP 2000-000908 A Japanese Patent No. 4074319

  In the invention described in Patent Document 2, since the two-layer foamable pellets are formed in a flat shape, the foamable pellets may partially abnormally foam during the molding process. There was a problem that the non-foamed portion constituting the structure was hindered and could not be formed into a uniform skin layer, and the foamed layer was exposed. Therefore, there is a risk that the commercial value is greatly reduced.

  The subject of this invention is related with the method of manufacturing efficiently the plastic molding which was excellent in durability and mechanical strength which consist of a non-foamed layer and a foamed layer.

  The present invention has been found that the above-described conventional problems can be solved by using spherical two-layer foamable pellets.

  For this reason, the method for producing a foam composite according to the present invention is a production method in which resin powder and polyolefin-based foamable pellets are simultaneously placed in a mold and heat-molded while rotating the mold. A spherical foamable pellet coated with a resin is used in an amount of 5% to 25% of the mold volume.

  In the method for producing a foamed composite, the spherical foamable pellet coated with the non-foamable resin uses two extruders, and the foamable resin composition is formed into a rod shape from one extruder. A two-layer rod-shaped resin composition in which a non-foamable resin is extruded from another extruder and the rod-shaped foamable resin composition is coated with the non-foamable resin by a crosshead die. The two-layer rod-shaped resin composition is sandwiched between two rolls formed with hemispherical grooves, and at the same time, these two rolls are moved in the direction along the rotation axis. It is characterized by being formed into a spherical shape.

  Moreover, in the manufacturing method of the said foaming composite, the spherical foamable pellet coat | covered with the said non-foamable resin uses two extruders, and the die | dye for 2 types and 3 layers, from 1 extruder. The foamable resin composition was extruded into a sheet shape and a non-foamable resin was extruded from another extruder, and both surfaces of the sheet-shaped foamable resin composition were sandwiched between the non-foamable resins. A composite sheet having a sandwich structure is prepared, and the composite sheet is formed into a spherical shape by being sandwiched between two rolls having a hemispherical concave pattern formed on the surface thereof.

  ADVANTAGE OF THE INVENTION According to this invention, the foam composite which was excellent in durability and mechanical strength which consist of a non-foamed layer and a foamed layer can be manufactured efficiently.

It is a figure explaining the compounding quantity and visual observation result of a present Example and a comparative example. It is a figure explaining the foam composite_body | complex which concerns on 1st Example. It is a figure explaining the foaming composite_body | complex which concerns on a 1st comparative example.

  Hereinafter, the present invention will be described in detail.

  The present invention uses a manufacturing method in which resin powder and polyolefin-based foamable pellets are simultaneously placed in a mold and heat-molded while rotating the mold, and the spherical shape is coated with a non-foamable resin. The foamable pellets of 5 to 25% of the mold volume are used.

  When the spherical foamable pellets coated with the non-foamable resin are less than 5%, voids are likely to be generated inside the mold, resulting in a problem that the strength of the obtained foamed composite is lowered. In addition, when filling more than 25% of the mold volume, the internal pressure generated at the time of molding is increased, which affects the surface layer of the molded body, causing cracks and foamed layers on the surface, resulting in poor appearance. To do. More preferably, it is preferable to mold within a range of 8% to 20%.

  In the present invention, the resin powder used as the skin material of the foamed composite may be polypropylene, high-density polyethylene, low-density polyethylene, ethylene / α-olefin copolymer, ethylene / vinyl acetate copolymer, or other olefin resin powder. Alternatively, it is possible to use powders such as polyamide resin, polyester resin, and fluororesin. In addition, it is also possible to use a pellet that is pulverized into a powder.

  Spherical foamable pellets coated with a non-foamable resin used in the present invention (hereinafter referred to as “spherical foamable pellets having a two-layer structure with a non-foamed layer” or “spherical foamable structures having a two-layer structure”) As the “pellet”, it is preferably one that can thermally expand twice or more in a range of 150 to 200 ° C. in 5 to 20 minutes to form a foamed layer. More preferably, the non-foamed layer serving as the coating layer is a skin composed of a non-foamable resin so that the foamed layer serving as the core can smoothly follow at the same time as it expands during the molding process. In the case of a resin equivalent to the material or a different resin, any resin can be used as long as adhesion to the skin material can be obtained to some extent.

  The expandable pellet having a two-layer structure used in the present invention needs to be spherical. In pellets with corners or flat pellets, during foam molding, particles in the foaming process are often mixed into the surface layer portion of the non-foamed layer, destroying the skin and exposing the foamed layer to the surface. As a result, not only the strength of the finished molded product is lowered, but also the appearance is deteriorated and the commercial value is remarkably lowered.

  The manufacturing method of the spherical foamable pellet which has a two-layer structure with a non-foamed layer used in this invention is demonstrated in detail.

  The resin used in the non-foamed layer of the spherical foamable pellet having a two-layer structure with a non-foamed layer used in the present invention is preferably a resin selected from polyethylene, polypropylene, polystyrene, and an ethylene-α-olefin copolymer. . More preferably, a polyethylene, an ethylene-α olefin copolymer, or a mixture of two or more of them is preferred. In particular, the non-foamed layer needs to expand following the foaming of the core during the foaming process of the core foaming layer, and the non-foamed layer exhibits a melting behavior similar to that of the resin used for the core foaming layer. preferable.

  Resin used for the foam layer used as the core of the spherical foam pellets having a two-layer structure with a non-foam layer used in the present invention is polyethylene, polypropylene, polystyrene, polyester resin, ethylene-α olefin copolymer, ethylene -Vinyl acetate copolymer etc. can be used. More preferably, one or a mixture of two or more of polyethylene, an ethylene-α olefin copolymer, and an ethylene-vinyl acetate copolymer excellent in cross-linking foaming property is preferable.

  The resin component of the foam layer used as the core of the spherical foam pellets having a two-layer structure with a non-foam layer used in the present invention preferably contains a pyrolytic foaming agent and a crosslinking agent. As this thermally decomposable foaming agent, any one having a decomposition temperature higher than the melting temperature of the resin composition of the above-mentioned foamed layer is preferable, and preferably there is azodicarbonamide, which is equivalent to azodicarbonamide or Hydrazosicarbonamide having higher decomposition temperature, barium azodicarboxylate, dinitrosopentaethylenetetramine, nitrosoguanidine, P, P'-oxybisbenzenesulfonyl semicarbazide, trihydrazine symmetric triazine, bisbenzenesulfonyl hydrazide, Barium azodicarboxylate, azobisisobutyronitrile, toluenesulfonyl hydrazide, etc. are used. These may be used alone or in combination of two or more. The blending amount of the pyrolytic foaming agent is generally about 5 to 20 parts by weight with respect to 100 parts by weight of the resin in the resin composition, and is set according to the desired expansion ratio.

  The resin component of the foam layer used as the core of the spherical foam pellets having a two-layer structure with a non-foam layer used in the present invention contains a crosslinking agent. For this crosslinking agent, organic peroxides such as dicumyl peroxide, 2,5-dimethyl-2,5-bis-tertiary butyl peroxyhexane, 1,3-bis-tertiary peroxyisopropylbenzene, etc. are used. can do. The amount of the crosslinking agent is usually 0.5 to 5 parts by weight with respect to 100 parts by weight of the polyolefin resin. Moreover, in order to perform a crosslinking reaction efficiently, a polyfunctional monomer can be used together as a crosslinking assistant. Examples of the multifunctional monomer include divinylbenzene, trimethylolpropane trimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, and triaryl trimellitic acid. Esters, triallyl isocyanurate, ethyl vinylbenzene, and the like can be used. These polyfunctional monomers may be used alone or in combination of two or more. Usually, the amount used is preferably in the range of 0.1 to 2 parts by weight of the crosslinking agent to 100 parts by weight of the resin.

  The resin component of the outer skin layer used in the present invention can be blended with a flame retardant resin, an inorganic filler, a flame retardant, fiber, and the like to improve the strength of the skin and make it flame retardant. Moreover, carbon black, metal fiber, etc. can be mixed and the electroconductivity and antistatic property can also be provided. Moreover, a weather resistance can also be improved by mixing a ultraviolet absorber and antioxidant.

  The spherical foamable pellets having a two-layer structure with a non-foamed layer used in the present invention can be prepared from two extruders and a spherical molding device. That is, using two extruders, a foamable resin composition as a core is extruded from one extruder into a rod shape, and a non-foamable resin is extruded from the other extruder. A two-layer rod-shaped resin composition in which the rod-shaped foamable resin composition is coated with the non-foamable resin by a die, and the two-layer rod-shaped resin composition is formed into a semicircular groove. Can be formed into a spherical shape by being sandwiched between two rolls formed with, and simultaneously moving these two rolls in the direction along the rotation axis.

  Also, using two extruders and two types and three-layer dies, the foamable resin composition is extruded from one extruder into a sheet, and the other one extruder is a non-foamable resin. To form a composite sheet having a sandwich structure of two types and three layers in which both sides of the sheet-like foamable resin composition are sandwiched between non-foamable resins, and the composite sheet has a hemispherical concave pattern on the surface Can be formed into a spherical shape by being sandwiched between two rolls that have been textured.

  Although the size of the spherical foamable pellet depends on the size of the target molded article, it is usually preferable that the diameter is in the range of 2 mm to 15 mm, more preferably in the range of 3 mm to 10 mm. Is. Small ones having a diameter of 2 mm or less are difficult to be molded into a spherical shape, and the foamed layer is easily mixed with the skin layer of the obtained molded product, which tends to cause a decrease in strength and a decrease in appearance. Moreover, in the foamable pellet exceeding 15 mm, shaping | molding of the thin part of the target molded object becomes unstable, and formation of a uniform foaming layer becomes difficult easily.

  In the present invention, the foam composite can be produced by using a molding method using a rotational molding apparatus. In this case, the metal mold is usually made of a plate or casting made of a metal material such as iron, stainless steel, aluminum, etc. having good thermal conductivity, and is composed of two or more parts or side walls and upper and lower lids. The mold can be heated using hot air, direct fire, or an electric or oil mold. The mold surface temperature is heated to a temperature at which the blowing agent used decomposes. When the mold reaches a temperature at which the foaming agent decomposes, the foaming agent dispersed in the spherical foamable pellets is decomposed and the pellets start to expand inside the mold. Although the temperature which heats a metal mold | die depends on the capacity | capacitance and performance of an installation, the range of 150 to 200 degreeC is preferable. The heating time is preferably in the range of 5 minutes to 20 minutes. If heating temperature is less than 150 degreeC, the undecomposed thing of a foaming agent will remain easily. Further, at 200 ° C. or higher, the foamed pellets are expanded before the skin layer is completely formed, and a phenomenon of damaging the skin layer is likely to occur.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited in any way by the following examples.

  A resin serving as a core obtained by melting and mixing 100 parts by weight of low density polyethylene having a density of 0.920 and MFR 2.0 and 8 parts by weight of azodicarbonamide and 1.0 part by weight of dicumyl peroxide as a blowing agent has a diameter of 40 mm, L / L Extruded into a rod shape with a diameter of 5 mm with an extruder with D = 24, and a non-foamable resin with a crosshead die with another extruder (caliber 40 mm, L / D = 28) Two rods with a diameter of approximately 7 mm, which are uniformly coated with a high density polyethylene of 0.950 and MFR 4.0 to a thickness of 1.0 mm, and the rods are formed with semicircular grooves At the same time as being sandwiched between the two rolls, the two rolls were moved in the direction along the rotation axis and in the opposite directions to form spherical two-layer pellets.

  100 g (10% of the mold volume) of spherical foam pellets of the above two-layer structure and 120 g of high density polyethylene powder with a density of 0.950 and MFR1.0 made of aluminum with an inner method of 100 mm × 100 mm × 100 mm and a wall thickness of 4 mm The mold was put into a mold and heat-molded with a rotary molding machine. The mold temperature was set to 180 ° C., and heat molding was performed for about 15 minutes. Then, after cooling to 80 ° C. or less by natural cooling, the product was taken out from the mold. As a result, as shown in FIG. 1 and FIG. 2, the skin portion 1 was a uniform and beautiful molded body. The inside of the skin portion 1 was filled with a foam layer 2 having a honeycomb structure.

  Resin that forms a core obtained by melt-mixing MFR 2.0, 100 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 15%, and 6 parts by weight of azodicarbonamide and 0.8 parts by weight of dicumyl peroxide as a foaming agent A rod-shaped product having a diameter of about 8 mm, in which an ethylene-α-olefin copolymer having a density of 0.904 and MFR 2.0, which is a non-foamed resin, is uniformly coated to a wall thickness of 1.5 mm. Then, the roll surface was passed between two rolls processed into a hemispherical pattern and continuously cut simultaneously with molding to form a spherical expandable pellet having a two-layer structure.

  180 g of spherical foam pellets of the above two-layer structure (18% of the mold volume) and 120 g of high density polyethylene powder with a density of 0.950 and MFR1.0 are made of aluminum with an internal method of 100 x 100 x 100 mm and a wall thickness of 4 mm The mold was put into a mold and heat-molded with a rotary molding machine. The mold temperature was set to 180 ° C., and heat molding was performed for about 15 minutes. Then, after cooling to 80 ° C. or less by natural cooling, the product was taken out from the mold. As a result, as shown in FIG. 1, the skin portion and the foamed layer were uniform and beautiful molded bodies.

[Comparative Example 1]
Using a crosshead die, a core resin in which 100 parts by weight of low density polyethylene with a density of 0.920 and MFR 2.0 is melt mixed with 8 parts by weight of azodicarbonamide and 1.0 part by weight of dicumyl peroxide as a foaming agent is used. Then, a rod-shaped one provided with a high density polyethylene film having a density of 0.950 and MFR 4.0 as a non-foamable resin on the surface layer portion was compressed and cut to produce a flat two-layer pellet.

  100 g of the above flat two-layer pellets (10% of the mold volume) and 120 g of the same high-density polyethylene powder as in Example 1 were put into an aluminum mold having an inner method of 100 × 100 × 100 mm and a thickness of 4 mm, Heat-molded with a rotary molding machine. The mold temperature was set to 180 ° C., and heat molding was performed for about 15 minutes. Then, after cooling to 80 ° C. or less by natural cooling, the product was taken out from the mold. As a result, as shown in FIG. 1 and FIG. 3, it was observed that a part of the skin portion 1 was in a state in which the foam layer 2 penetrated.

[Comparative Example 2]
Resin that becomes the core by melting and mixing 6 parts by weight of azodicarbonamide as a blowing agent and 1.0 part by weight of dicumyl peroxide as a foaming agent to 100 parts by weight of low density polyethylene having a density of 0.920 and MFR 2.0, The rod-shaped thing provided with the high density polyethylene film of density 0.950 and MFR4.0 used as non-foaming resin in the surface layer part was compression-cut, and the flat two-layer pellet was created. 180 g of this flat two-layer pellet (18% of the mold volume) and 120 g of the same high-density polyethylene powder as in Example 1 were put into an aluminum mold having an inner method of 100 × 100 × 100 mm and a thickness of 4 mm, Heat-molded with a rotary molding machine. The mold temperature was set to 180 ° C., and heat molding was performed for about 15 minutes. Then, after cooling to 80 ° C. or less by natural cooling, the product was taken out from the mold. As a result, as shown in FIG. 1, it was observed that a part of the skin portion was in a state where the foam layer penetrated.

  The manufacturing method of the foam composite which concerns on this invention can be utilized when manufacturing the foam composite used for a heat insulating material, a building material, a cushion material, an impact-absorbing material, a floatation material, etc.

1 Skin part 2 Foam layer

Claims (3)

In the manufacturing method in which resin powder and polyolefin-based foamable pellets are simultaneously put into a mold and heat-molded while rotating the mold.
A method for producing a foamed composite comprising using spherical foamable pellets coated with a non-foamable resin in an amount of 5% to 25% of the mold volume.   The spherical foamable pellets coated with the non-foamable resin use two extruders, extrude the foamable resin composition from one extruder into a rod shape, and another extruder. A non-foaming resin is extruded from the two-layered rod-shaped resin composition in which the rod-shaped foaming resin composition is covered with the non-foaming resin by a crosshead die, and the two-layer rod-shaped resin composition is formed. The resin composition was sandwiched between two rolls in which semicircular grooves were formed, and at the same time, these two rolls were formed into a spherical shape by moving in the direction along the rotation axis. The method for producing a foamed composite according to claim 1, wherein:   The spherical foamable pellets coated with the non-foamable resin use two extruders and two types and three-layer dies, and extrude the foamable resin composition into a sheet form from one extruder. A non-foamable resin is extruded from another extruder, and a composite sheet having a sandwich structure in which both sides of the sheet-like foamable resin composition are sandwiched between non-foamable resins is prepared. 2. The method for producing a foam composite according to claim 1, wherein the sheet is formed into a spherical shape by being sandwiched between two rolls having a hemispherical concave pattern formed on the surface.