JP2012072279A - Resin pellet for foam molding, method for manufacturing the same and method for manufacturing foamed resin molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide resin pellets for foam molding which can reduce the variability of expansion ratios, a method for manufacturing the same, and a method for manufacturing a foamed resin molded article.SOLUTION: The resin pellets for foam molding are obtained by bonding the powder of a resin to be foamed (a polyamide resin) and the powder of a chemical blowing agent (ADCA) with a binder to produce a powder mixture and subjecting the powder mixture to extrusion molding. According to this manufacturing method, since the chemical blowing agent is mixed with the resin to be foamed, which are relatively small powders before being pelletized, the dispersion of the chemical blowing agent and the resin to be foamed can be more increased than conventionally. Further, since the water content of the resin pellets for foam molding is set at less than 5 wt.%, the error of the expansion ratio due to the vaporization of water can be rendered small. By so doing, the variation of expansion ratios can be reduced.

Description

  The present invention relates to a resin pellet for foam molding that is a raw material of a foamed resin molded product, a method for producing the pellet, and a method for producing a foamed resin molded product.

  As a method for producing a foamed resin molded product, a production method is known in which a powder of a chemical foaming agent is blended into pellets of a base resin, which is the main component of the foamed resin molded product, and then charged into an injection molding machine (for example, Patent Document 1).

JP 2003-2998 A (paragraph [0002])

  However, since the particle diameter of the pellet (1 mm or more. Generally, the average particle diameter is often 1 to 5 mm) is too large with respect to the chemical foaming agent which is a fine granular material. Therefore, it was difficult to improve the dispersibility between the base resin and the chemical foaming agent. For this reason, there existed a problem that the dispersion | variation in foaming magnification generate | occur | produced.

  This invention is made | formed in view of the said situation, and aims at provision of the resin pellet for foam molding which can reduce the dispersion | variation in foaming ratio, its manufacturing method, and the manufacturing method of a foamed resin molded product.

  In order to achieve the above object, the resin pellet for foam molding according to the invention of claim 1 comprises a powder of a chemical foaming agent and a powder of a foamed resin to be foamed with the chemical foaming agent. It is characterized by being bonded with a water-containing binder and having a moisture content of less than 5% by weight.

  The invention of claim 2 is characterized in that in the resin pellet for foam molding of claim 1, the melting start temperature typified by the melting point of the resin to be foamed is higher than the foaming start temperature of the chemical foaming agent.

  The invention of claim 3 is characterized in that, in the resin pellet for foam molding of claim 1 or 2, the binder is composed of water and a polyvinyl alcohol resin.

  According to a fourth aspect of the present invention, there is provided the foamable resin pellet according to any one of the first to third aspects, wherein the foamed resin powder has an average particle size of 250 to 400 μm and a chemical foaming agent. It has the characteristics in the average particle diameter of 5-30 micrometers.

  The method for producing a foamed resin molded product according to the invention of claim 5 is characterized in that the resin pellet for foam molding according to any one of claims 1 to 4 is used.

  According to a sixth aspect of the present invention, there is provided a method for producing a resin pellet for foam molding, comprising a powder containing a chemical foaming agent and a foamed resin powder to be foamed with the chemical foaming agent, in a binder containing water. It is characterized by extruding the combined powder and granule mixture and drying the resulting extrudate until the moisture content is less than 5% by weight.

[Foamed resin]
Examples of the “foamed resin” according to the present invention include polyolefin resin, polyamide resin, polyester resin, polycarbonate resin, and ABS resin.

  Examples of the polyolefin resin include homopolymers such as polyethylene and polypropylene, copolymer polymers, and blend polymers. Examples of polyamide resins include 6-nylon, 11-nylon, 12-nylon, 46-nylon, 6,6-nylon, 6,10-nylon, 6,12-nylon, and other homopolymers, copolymer polymers or blend polymers. Can be mentioned. The polyester resin is preferably an aromatic polyester, for example, a homopolymer such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), a copolymer or a blend polymer. The polycarbonate resin may be either an aliphatic polycarbonate or an aromatic polycarbonate. Specific examples include homopolymers such as bisphenol A-polycarbonate (BisA-PC) and isosorbide-polycarbonate, copolymer polymers, and blend polymers. The ABS resin is not particularly limited to the copolymerization ratio, and may be flame retardant ABS with a reduced butadiene ratio.

[Chemical foaming agent]
The “chemical foaming agent” according to the present invention may be a reactive type or a thermal decomposition type, but is preferably a thermal decomposition type. Moreover, as long as the effect of this invention is not inhibited, these may be individual or may use 2 or more types together. The reactive type includes an inorganic chemical foaming agent such as a mixture of sodium hydrogen carbonate and an acid, and an organic chemical foaming agent such as an isocyanate compound. In the thermal decomposition type, inorganic chemical foaming agents such as sodium hydrogen carbonate (bicarbonate), ammonium hydrogen carbonate, ammonium carbonate, zinc carbonate, sodium nitrate, sodium citrate, azo compounds, nitroso compounds, sulfonyl hydrazide compounds, sulfonyl semicarbazide compounds And organic chemical foaming agents such as triazole compounds. Specific examples of the organic chemical foaming agent include azodicarbonamide (ADCA), N, N′-dinitrosopentamethylenetetramine (DPT), azobisisobutyronitrile (AIBN), and the like.

[Binder]
The “binder” according to the present invention is composed of water and an organic binder. Specific examples of the organic binder include starch and polyvinyl alcohol resin. Examples of starch include rice starch, potato starch and corn starch. The polyvinyl alcohol resin may be either fully saponified polyvinyl alcohol or partially saponified polyvinyl alcohol, but the partially saponified type is preferred.

[Melting start temperature typified by melting point]
The “melting start temperature typified by the melting point” according to the present invention refers to the melting point of a resin having a melting point and the melting point of a resin having no melting point to the extent that the resin can be extruded after the glass transition. Temperature

[Foamed resin molded products]
Examples of the “foamed resin molded product” according to the present invention include automotive parts, cooking utensils, medical utensils and the like. Examples of automobile parts include an engine cover, a battery tray, an oil pan, a radiator top, a fuse case, and a cylinder head cover.

[Method for producing foamed resin molded product]
The molding method of the foamed resin molded product may be a core back type foam molding method, or may be a molding method in which the foamed resin is simply filled into the cavity of the molding die without performing the core back. . In addition, an apparatus for melting foam molding resin pellets during foam molding is not particularly limited as long as it is a known technique. For example, a melt kneader such as a single-screw extruder, a twin-screw extruder, or a Banbury mixer is often used.

  In addition to the chemical foaming agent, the “foam molding resin pellet” according to the present invention can contain a foam nucleating agent and a reinforcing agent. Examples of the foam nucleating agent include talc, clay, silica, calcium carbonate, calcium silicate and the like. Examples of the reinforcing agent include glass fiber, carbon black, graphite, calcium carbonate, talc, mica and the like.

  The “foam molding resin pellet” according to the present invention further includes various stabilizers such as an antioxidant, an antistatic agent, an ultraviolet ray inhibitor, a light stabilizer, a colorant, a lubricant, and a flame retardant as necessary. Etc. can be contained.

  In the present invention, a resin pellet for foam molding can be produced by extruding a powder mixture obtained by mixing a powdered resin powder and a chemical foaming agent powder. As described above, according to the present invention, since the chemical foaming agent is mixed with the foamed resin that is a relatively small powder before the resin pellets, the dispersibility between the chemical foaming agent and the foamed resin is conventionally improved. Can be increased. Here, since the binder according to the present invention contains water, if the extruded product obtained by extruding the powder mixture is directly used as the resin pellet for foam molding, the water contained in the binder in the molding die is removed. Will cause an error in the expansion ratio. However, in the present invention, since the extrudate is dried and the water content is less than 5% by weight is used as the resin pellet for foam molding, the error of the foaming ratio due to water vaporization can be reduced. As described above, in the present invention, the dispersibility between the chemical foaming agent and the resin to be foamed can be increased, and the error in the foaming ratio due to the vaporization of water can be reduced, thereby reducing the variation in the foaming ratio. be able to.

  In addition, the resin pellet for foam molding may be used as a main pellet which is a main raw material of the foam molded resin product, or may be used as a so-called foaming agent master batch pellet used by being mixed with the main pellet.

  In the resin to be foamed according to the present invention, the melting start temperature represented by the melting point may be lower than the foaming start temperature of the chemical foaming agent, or higher than the foaming start temperature of the chemical foaming agent as in the invention of claim 2. Also good. In addition, according to the structure of invention of Claim 2, even if it is a case where it cannot mix with a chemical foaming agent by the method of knead | mixing with a chemical foaming agent by making a to-be-foamed resin into a molten state (compound), a resin pellet is used. Can be manufactured.

  The binder according to the present invention may be composed of water and starch as described above, or may be composed of water and a polyvinyl alcohol-based resin as in the third aspect of the invention. According to invention of Claim 3, compared with the case where a starch-type resin is used, the coupling | bonding of the granular material of resin to be foamed and the granular material of a chemical foaming agent can be performed favorably. This is presumably because the polyvinyl alcohol-based resin suppresses excessive moisture absorption like starch and reduces the difference in moisture content before and after drying.

  Moreover, it is possible to use a commercially available product in general by setting the average particle size of the foamed resin powder particles to 250 to 400 μm and the average particle size of the chemical foaming agent powder particles to 5 to 30 μm. (Invention of claim 4)

  The resin pellet for foam molding according to the present invention has an average particle size of 1 to 3 mm, which is almost the same as the average particle size (1 to 5 mm) of the conventional resin pellet. The resin pellet for foam molding is composed of a polyamide resin powder, a chemical foaming agent, and a talc powder combined as a “foamed resin” with a binder containing water, The water content is 0.2% by weight. The binder is composed of a polyvinyl alcohol resin (hereinafter referred to as PVA) and water. The remaining 99.8% by weight excluding moisture is blended in a weight ratio of polyamide resin: chemical foaming agent: talc: PVA = 72.18 / 0.27 / 17.55 / 10. In addition, the partial saponification type | mold is used for PVA.

  As the chemical foaming agent, azodicarbonamide (hereinafter referred to as ADCA) is used, and the foaming start temperature is 180 to 210 ° C., which is lower than the melting point of the polyamide resin, 220 ° C.

  The resin pellet for foam molding is manufactured as follows. First, polyamide resin granules having an average particle diameter of 250 to 400 μm, ADCA granules having an average particle diameter of 5 to 30 μm, and talc having an average particle diameter of 5.5 μm The granular material is taken at a weight ratio of 72.18 / 0.27 / 17.55, and these granular materials are kneaded with a binder containing water to obtain a viscous granular material mixture. The binder is adjusted so that the weight of PVA and water is 10/35 when the total weight of polyamide resin, ADCA and talc is 90.

  Next, the powder mixture is, for example, pressed from one side of a plate having a large number of circular holes, extruded into a linear shape, and cut into a length of 1 to 3 mm. And the moisture content of a molded object is reduced to 0.2 weight% by drying the obtained molded object at 80 degreeC for 4 hours, and the resin pellet for foam molding is obtained.

  Next, a method for manufacturing an engine cover as a “foamed resin molded product” according to the present invention using the above-described foamed resin pellets will be described. For this purpose, first, foam molding resin pellets are put into a cylinder of a core back type injection foam molding machine. At this time, the foamed resin pellets are dried in advance if necessary. Next, the polyamide resin is heated to a melting point (220 ° C.) or higher in the cylinder to be in a molten state, and talc and a chemical foaming agent (ADCA) are kneaded and dispersed in the molten polyamide resin. At this time, the chemical foaming agent is heated to the foaming start temperature (180 to 210 ° C.) or higher and foaming starts.

  Next, the molten polyamide resin in the cylinder is filled into the molding die. Then, the movable mold of the molding die is core-backed to foam-mold the molten polyamide resin. Next, the polyamide resin in the molding die is cooled, and the movable die is opened to remove the engine cover.

  In the present embodiment, a resin pellet for foam molding is manufactured by extrusion molding a powder mixture obtained by mixing a powder of resin to be foamed (polyamide resin) and a powder of chemical foaming agent (ADCA). Can do. Thus, according to this embodiment, since the chemical foaming agent is mixed with the foamed resin that is a relatively small powder before the resin pellets, the dispersibility of the chemical foaming agent and the foamed resin is improved. It can be increased than before. Here, since the binder contains water, if the extruded product obtained by extruding the powder mixture is subjected to foam molding as it is, water is vaporized in the molding die during foam molding, resulting in an error in the expansion ratio. It will occur. However, in this embodiment, since the extrudate was dried and the moisture content was less than 5% by weight was used as the foam molding resin pellet, the influence of water on the foaming ratio can be suppressed. As described above, in this embodiment, the dispersibility between the chemical foaming agent and the resin to be foamed can be increased, and the error in the foaming ratio due to the vaporization of water can be reduced, thereby reducing the variation in the foaming ratio. can do.

[Other Embodiments]
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various other than the following can be made without departing from the scope of the invention. It can be changed and implemented.

  (1) The resin pellet for foam molding in the above embodiment has a configuration in which a foamed resin (polyamide resin), a chemical foaming agent (ADCA), and talc are combined with a binder, but only the foamed resin and the chemical foaming agent are used. In addition to the resin to be foamed, the chemical foaming agent, and the talc, a configuration in which glass fibers and pigments are bonded with a binder may be used.

  (2) In the above-described embodiment, only the foam molding resin pellets are charged into the injection molding machine. However, in addition to the foam molding resin pellets, additives (for example, reinforcing agents, antioxidants, plasticizers, etc.) Or a batch of a master batch of the additive or a pellet of a thermoplastic resin may be added.

  (3) The weight of the binder relative to the total weight of the resin to be foamed, the chemical foaming agent, and talc is not limited to the above embodiment, but the binder is increased to increase the amount of the resin to be foamed, the chemical foaming agent, and the particles of talc. The bondability of may be improved.

  (4) Also, the weight ratio of polyvinyl alcohol (PVA) and water in the binder is not limited to the above embodiment, and the binder binding ability may be improved by increasing the proportion of PVA.

  Although not belonging to the technical scope of the present invention, using the technology of the present invention, an antioxidant, an antistatic agent, an anti-ultraviolet agent, a light stabilizer, etc. can be used instead of the chemical foaming agent granular material. You may manufacture the composite resin pellet which combined the granular material of various stabilizers, or the granular material of the coloring agent with the granular material of resin.

Claims (6)

The chemical foaming agent powder and the foamed resin powder to be foamed with the chemical foaming agent are combined with a binder containing water,
A resin pellet for foam molding characterized by having a water content of less than 5% by weight.   The resin pellet for foam molding according to claim 1, wherein a melting start temperature represented by a melting point of the resin to be foamed is higher than a foaming start temperature of the chemical foaming agent.   The resin pellet for foam molding according to claim 1 or 2, wherein the binder comprises the water and a polyvinyl alcohol resin.   The average particle diameter of the granular material of the foamed resin is 250 to 400 μm, and the average particle diameter of the granular material of the chemical foaming agent is 5 to 30 μm. The resin pellet for foam molding according to claim 1.   A method for producing a foamed resin molded product, wherein the foamed resin pellet according to any one of claims 1 to 4 is used.   Obtained by extruding a powder mixture obtained by bonding a powder of a chemical foaming agent and a powder of a foamed resin foamed with the chemical foaming agent with a binder containing water. A method for producing foamed resin pellets, comprising drying an extruded product until the water content is less than 5% by weight.