JP2023117237A - Manufacturing method of extrusion-foaming particles - Google Patents

Abstract

To reduce variation in an expansion ratio and an open cell ratio of extrusion-foaming particles by reducing variation in a die temperature.SOLUTION: A die (10) used in a manufacturing method of the present invention comprises: a plurality of discharge holes (6); a flow path (1) through which a molten resin flows to the discharge holes (6); and heating units (5a and 5b) for heating the molten resin in the flow path (1). The heating units (5a and 5b) are inserted into the die (10), and are rod-shaped heaters which are parallel to the flow path (1).SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for producing extruded foam particles.

Conventionally, in a method for producing extruded foamed particles, it is common to use a flow path called a torpedo flow path in a die of a manufacturing apparatus and to provide a heater on the outer peripheral portion of the die. However, in the case of such a configuration, there has been a tendency for the temperature of the dice to become uneven and uneven.

Further, for example, in Patent Document 1, a plurality of radial channels communicating with a molten resin channel and formed in a radial direction, a circular channel or arc-shaped channel communicating with each of the radial channels, and a circular groove A plurality of nozzles are provided corresponding to the flow paths or arc-shaped groove flow paths and rod-shaped heaters provided in the center of each of the flow paths, and the resin is uniformly heated by uniform heating of the nozzles. Disclosed is a die for resin pellet granulation that is configured to obtain temperature.

JP-A-7-178726

However, the prior art as described above is a technique relating to a method for producing resin pellets, and is not sufficient for application to a method for producing extruded foamed particles, and there is room for further improvement. Specifically, regarding the method for producing extruded foamed particles, if the temperature of the die is uneven or uneven, the obtained extruded foamed particles may have (i) unevenness in the expansion ratio, or (ii) a high open cell rate. Therefore, it was difficult to produce uniform extruded foamed particles. Moreover, if the temperature of the die is locally lowered due to variations in the die temperature, the die holes are clogged with the solidified resin, resulting in a decrease in production efficiency.

Therefore, it has been desired to develop a technique capable of reducing variations in die temperature in a method for producing extruded expanded beads.

One aspect of the present invention has been made in view of the above-mentioned problems, and its object is to reduce the variation in die temperature in a manufacturing apparatus, thereby reducing the variation in expansion ratio and the open cell rate of extruded foam beads obtained. To provide a method for producing extruded foamed particles that can reduce the

That is, one aspect of the present invention includes the following configurations.

[1] A method for producing extruded foam particles of a thermoplastic resin using an extrusion foaming machine having a die, wherein the die has a plurality of ejection holes for ejecting a molten resin, and a plurality of ejection holes for extruding the molten resin to the ejection holes. and a heating section for heating the molten resin in the flow path, the heating section being inserted into the die, and the heating section A method for producing extruded foam particles, which is a bar-shaped heater parallel to the.

[2] The method for producing extruded expanded particles according to [1], wherein the thermoplastic resin is a polypropylene-based resin having a branched structure.

[3] The method for producing extruded expanded beads according to [1] or [2], wherein the flow path has multistage branches in the flow direction of the molten resin.

[4] The method for producing extruded foam particles according to [3], wherein the flow path is branched in at least three stages.

[5] The method for producing extruded expanded particles according to any one of [1] to [4], wherein the method for granulating the extruded expanded particles is a die face cutting method.

[6] An expansion comprising a step of producing extruded expanded beads by the production method according to any one of [1] to [5], and a step of foam-molding the extruded expanded beads obtained by the above steps. A method for producing a molded article.

According to one aspect of the present invention, there is provided a method for producing extruded foamed beads, which can reduce variations in expansion ratio and open cell ratio of the obtained extruded foamed beads by reducing variations in die temperature in a manufacturing apparatus. be able to.

1 is a schematic configuration of an example of a die used in a method for producing extruded foamed beads according to an embodiment of the present invention, and is a view of a channel configuration projected from the back. FIG. FIG. 2 is a diagram in which the channel configuration inside the die is projected from the right side surface of the die shown in FIG. 1, and the channel configuration on the left side of the A-A′ line cross section in FIG. 1 is not shown. FIG. 2 is a schematic configuration of Modified Example 1 of the die used in the method for producing extruded foam beads according to one embodiment of the present invention, and is a diagram in which the channel configuration is projected from the back. FIG. 4 is a cross-sectional view showing Modified Example 2 of the die used in the method for producing extruded expanded beads according to one embodiment of the present invention, and the channel configuration is projected from the cross section. It is a figure which shows the schematic structure of the dice|dies in the conventional manufacturing method. FIG. 6 is a cross-sectional view taken along line B-B' of FIG. 5;

All documents mentioned herein are incorporated herein by reference. In this specification, when "A to B" is described with respect to a numerical range, the description means "A or more and B or less".

[1. Method for producing extruded foamed particles]
An embodiment of the present invention will be described in detail below. Hereinafter, the method for producing extruded expanded beads according to one embodiment of the present invention may be simply referred to as "this production method". A "polypropylene resin having a branched structure" may be referred to as a "branched polypropylene resin".

(1-1. Raw material for extruded expanded particles)
In addition to a crystalline thermoplastic resin and a foaming agent, as raw materials for producing the extruded expanded beads according to one embodiment of the present invention (hereinafter sometimes referred to as "present extruded expanded beads"), Various additives can be added according to the requirements. Examples include flame retardants, heat stabilizers, radical generators, processing aids, weather stabilizers, nucleating agents, foaming aids, antistatic agents, radiation heat transfer inhibitors, and coloring agents. . These additives can be used individually by 1 type or in combination of 2 or more types.

Further, the thermoplastic resin used in the present embodiment is not particularly limited as long as it is a generally known foamable thermoplastic resin. Examples of the thermoplastic resin include polyolefin-based resins, polyester-based resins, polyphenylene ether-based resins, polyamide-based resins, polycarbonate-based resins, and mixtures thereof. The thermoplastic resin is preferably a polyolefin-based resin or a polyester-based resin, and particularly preferably a polypropylene-based resin having a branched structure. In addition, hereinafter, a polypropylene resin having a branched structure may be referred to as a "branched polypropylene resin".

Examples of polyester-based resins include aliphatic polyester resins, aromatic polyester resins, and aliphatic-aromatic polyester resins. Specific examples of polyester resins include polyhydroxyalkanoate, polybutylene succinate (PBS), poly(butylene adipate-co-butylene terephthalate) (PBAT), polyethylene terephthalate (PET), polybutylene terephthalate ( PBT) and the like. In addition, polyhydroxyalkanoates include poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co -3-hydroxybutyrate) (PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly It is at least one selected from the group consisting of (3-hydroxybutyrate-co-3-hydroxyoctadecanoate).

Polyolefin-based resins are not particularly limited, and include polypropylene-based resins. The polypropylene-based resin may be a general-purpose linear polypropylene-based resin, or a branched polypropylene-based resin having a branched structure or a high molecular weight component. As a method for producing a branched polypropylene resin, for example, a linear polypropylene resin (hereinafter, this resin may be referred to as a "raw material polypropylene resin") is irradiated with radiation, or a linear polypropylene resin, a conjugated diene A method such as melt-mixing the compound and the radical polymerization initiator may be used. In the present embodiment, the polypropylene-based resin is particularly preferably a resin having a branched structure, and the production method thereof includes a branched polypropylene system obtained by melt-mixing a linear polypropylene resin, a conjugated diene compound and a radical polymerization initiator. Resins are preferred because they are easy to manufacture and are economically advantageous.

Examples of the linear polypropylene-based resin that can be used in the present embodiment include propylene homopolymers, block copolymers, and random copolymers that are crystalline. As the copolymer of propylene, a polymer containing 75% by weight or more of propylene is preferable because it retains the crystallinity, rigidity, chemical resistance, etc., which are characteristics of polypropylene-based resins. Copolymerizable α-olefins include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene , 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene and other α-olefins having 2 or 4 to 12 carbon atoms; cyclopentene, norbornene, tetracyclo[6,2,11,8,13, 6] Cyclic olefins such as 4-dodecene; 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene Diene such as vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methylstyrene, vinyltoluene, divinylbenzene vinyl monomers such as; Ethylene and 1-butene are particularly preferred in terms of improvement in cold brittleness resistance, low cost, and the like. These may be used alone or in combination of two or more.

Among these, random copolymers are preferred from the viewpoint of moldability in molding of the resulting expanded beads in a mold and physical properties of the resulting molded product. Ethylene random copolymers are preferred.

As the branched polypropylene-based resin that can be used in the present embodiment, a branched polypropylene-based resin obtained by melt-mixing a conjugated diene compound and a radical polymerization initiator with the linear polypropylene-based resin is preferable.

Examples of the conjugated diene compound include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, 2,5-dimethyl-2,4-hexadiene and the like. These may be used alone or in combination of two or more. Among these, butadiene and isoprene are particularly preferable because they are inexpensive, easy to handle, and easy to progress the reaction uniformly.

The amount of the conjugated diene compound added is preferably 0.01 parts by weight or more and 20 parts by weight or less, and 0.05 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the linear polypropylene resin. is more preferable. If the amount of the conjugated diene compound added is less than 0.01 parts by weight, sufficient branching may not be introduced.

Monomers copolymerizable with the conjugated diene compound, e.g., vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, acrylic acid Metal salts, metal methacrylates, acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and stearyl acrylate; methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid 2 - methacrylic acid esters such as ethylhexyl and stearyl methacrylate;

Examples of radical polymerization initiators generally include peroxides, azo compounds, and the like, but initiators having the ability to abstract hydrogen from polypropylene resins and conjugated diene compounds are preferred, and generally ketone peroxides, peroxyketals, hydro Examples include organic peroxides such as peroxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, and peroxyesters. Among these, initiators with particularly high hydrogen abstraction ability are preferred, such as 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane and 1,1-bis(t-butylperoxy)cyclohexane. , n-butyl 4,4-bis(t-butylperoxy)valerate, peroxyketals such as 2,2-bis(t-butylperoxy)butane; dicumyl peroxide, 2,5-dimethyl-2, 5-di(t-butylperoxy)hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, t-butylcumyl peroxide, di-t-butylperoxide, 2,5- dialkyl peroxides such as dimethyl-2,5-di(t-butylperoxy)-3-hexyne; diacyl peroxides such as benzoyl peroxide; t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxy isopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, peroxy esters such as t-butyl peroxyacetate, t-butyl peroxybenzoate, di-t-butyl peroxy isophthalate; and the like. These may be used alone or in combination of two or more.

The amount of the radical polymerization initiator to be added is preferably 0.01 parts by weight or more and 10 parts by weight or less, and 0.05 parts by weight or more and 4 parts by weight or less with respect to 100 parts by weight of the linear polypropylene resin. is more preferable. If the addition amount of the radical polymerization initiator is within the above range, a branched structure can be efficiently introduced. If the amount of the radical polymerization initiator added is less than 0.01 parts by weight, the branched structure may not be sufficiently introduced. Sometimes.

Devices for reacting the linear polypropylene resin, the conjugated diene compound and the radical polymerization initiator include rolls, co-kneaders, Banbury mixers, and Brabender; kneaders such as single-screw extruders and twin-screw extruders; horizontal stirrers such as renewing machines and twin-screw multi-disc devices; vertical stirrers such as double helical ribbon stirrers; and the like. Among these, it is preferable to use a kneader, and in particular, an extruder such as a single-screw extruder or a twin-screw extruder is preferable from the viewpoint of productivity.

There are no particular restrictions on the order and method of mixing and kneading (stirring) the linear polypropylene resin, the conjugated diene compound and the radical polymerization initiator. After mixing the linear polypropylene resin, the conjugated diene compound and the radical polymerization initiator, it may be melt-kneaded (stirred), or after melt-kneading (stirring) the polypropylene resin, the conjugated diene compound or the radical initiator is added. They may be mixed simultaneously or separately, together or separately. It is preferable that the temperature of the kneader (stirrer) is 130° C. or more and 300° C. or less so that the linear polypropylene resin melts and does not thermally decompose. The time for melt-kneading is generally preferably 1 to 60 minutes.

The shape and size of the branched polypropylene resin thus obtained are not limited, and may be in the form of pellets.

The melting point of the branched polypropylene-based resin of the present embodiment is preferably 130° C. or higher and 155° C. or lower, more preferably 135° C. or higher and 153° C. or lower, and 140° C. or higher and 150° C. or lower. is more preferred. If the melting point of the branched polypropylene-based resin is within the above range, the dimensional stability and heat resistance of the in-mold expansion-molded product are improved. In addition, the pressure of the molding heating steam becomes appropriate when the foamed polypropylene resin particles are foam-molded in the mold. If the melting point of the branched polypropylene resin is less than 130°C, the dimensional stability of the in-mold foamed product tends to decrease and the heat resistance of the foamed product tends to be insufficient. There is a tendency for the pressure of the molding heating steam during inner foam molding to increase.

Here, the melting point of the polypropylene-based resin is measured using a differential scanning calorimeter DSC [for example, DSC6200 manufactured by Seiko Instruments Inc.] as follows. That is, 5 to 6 mg of polypropylene resin is heated from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min to melt the resin, and then from 220 ° C. to 40 ° C. at a temperature decrease rate of 10 ° C./min. After crystallization by lowering the temperature, the temperature is again raised from 40°C to 220°C at a heating rate of 10°C/min, and the melting peak temperature in the DSC curve at the time of the second heating is taken as the melting point. .

The branched polypropylene resin of the present embodiment preferably has a melt tension of 3 to 20 cN, more preferably 3 to 15 cN, and more preferably 3 to 10 cN. This configuration has the advantage that the open cell ratio of the expanded beads can be reduced.

The foaming agent used in this embodiment is not particularly limited, but carbon dioxide gas is preferred. Carbon dioxide gas is a preferable foaming agent from the viewpoint of safety during handling and the simplification of required facility specifications. Furthermore, when carbon dioxide gas is used as a foaming agent, a foam having a high expansion ratio can be easily obtained compared to other inorganic foaming agents such as nitrogen and water. The amount of the foaming agent to be added varies depending on the type of thermoplastic resin and the target expansion ratio of the expanded beads, and may be adjusted as appropriate. The following is preferable, and 1 part by weight or more and 10 parts by weight or less is more preferable.

Furthermore, a cell nucleating agent may be added for the purpose of controlling the cell shape of the expanded beads. Examples of cell nucleating agents include sodium bicarbonate-citric acid mixture, monosodium citrate, talc, calcium carbonate, and the like, and these may be used alone or in combination of two or more. The amount of the bubble nucleating agent to be added is not particularly limited, but it is usually preferably 0.01 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the polypropylene resin.

Moreover, other synthetic resins than the branched polypropylene-based resin may be added as the base resin within a range that does not impair the effects of the present invention. Synthetic resins other than branched polypropylene resins include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymer, and ethylene. - ethylene resins such as acrylic acid copolymers and ethylene-methacrylic acid copolymers; styrene resins such as polystyrene, styrene-maleic anhydride copolymers and styrene-ethylene copolymers;

In the present embodiment, stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, ultraviolet stabilizers, fluorescent whitening agents, metallic soaps, and antacid adsorbents are optionally used. Alternatively, additives such as cross-linking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants and antistatic agents may be added. Examples of the antacid adsorbent include magnesium oxide and hydrotalcite.

In this embodiment, there is no limitation on the addition of a coloring agent, and a natural color can be obtained without adding a coloring agent, or a desired color can be obtained by adding a coloring agent such as blue, red, or black. can. Examples of coloring agents include perylene organic pigments, azo organic pigments, quinacridone organic pigments, phthalocyanine organic pigments, threne organic pigments, dioxazine organic pigments, isoindoline organic pigments, and carbon black.

In addition, a method of pressurizing the polypropylene-based resin expanded beads with an inert gas and heating to increase the expansion ratio (for example, the method described in JP-A-10-237212) can also be used.

The weight of the foamed particles in the present embodiment is preferably 3 mg/particle or less, more preferably 2 mg/particle or less, because it is easy to fill and swell to form a compact having a beautiful appearance. Although the lower limit is not particularly limited, it is preferably 0.3 mg/particle or more in consideration of productivity and the like.

In addition, the cell diameter of the expanded beads in the present embodiment is 0.1 to 1 because the expanded beads expand to every corner of the mold in the in-mold foam molding and the shrinkage of the obtained in-mold foam molded product is small. 0 mm, more preferably 0.15 to 0.7 mm.

The in-mold foam molded article of the present embodiment is obtained by filling the foamed particles into a mold which can be closed but not closed, heated with steam, and molded.

In order to form an in-mold foam molded article from the expanded particles of the present embodiment, for example, (i) the expanded particles are pressurized with an inorganic gas to impregnate the particles with the inorganic gas to give a predetermined particle internal pressure. After that, a method of filling a mold and heat-sealing with steam or the like (for example, Japanese Patent Publication No. 51-22951), (ii) Compressing the foamed particles with gas pressure and filling the mold to utilize the resilience of the particles Then, a method of heating and fusing with steam or the like (for example, Japanese Patent Publication No. 53-33996), (iii) After filling a mold with widened gaps with expanded particles, the mold was closed and filled to a predetermined gap. A method such as a method of compressing expanded particles and heat-sealing them with steam or the like can be used.

(1-2. Method for producing extruded expanded particles)
A method for producing the present extruded foamed particles is not particularly limited, and a known extrusion foaming method can be employed. The present method for producing extruded foam particles includes a step of extruding and foaming a thermoplastic resin. A production method using a branched polypropylene-based resin as the thermoplastic resin will be described below as an example. More specifically, the step of extruding and foaming includes, for example, (a) a first step of melt-kneading a branched polypropylene-based resin and a foaming agent in a manufacturing apparatus, and (b) the first step. a second step of discharging the melted resin through a die into a region having a lower pressure than the internal pressure of the manufacturing apparatus.

(1-2-1. First step)
The first step will be specifically described. As a specific example of the first step, in a manufacturing apparatus, after melting a resin composition containing a branched polypropylene resin and optionally an additive such as a bubble nucleating agent, the resin composition is melted. A step of dissolving the foaming agent may be mentioned. The melt-kneading step can also be said to be a step of preparing a molten resin containing a resin composition and a foaming agent.

(foaming agent)
In the manufacturing method, the foaming agent to be used is not particularly limited, but carbon dioxide gas is preferred. By using carbon dioxide gas, the production method has the advantages of low production cost and low environmental load.

In this production method, as the foaming agent, (a) a foaming agent other than carbon dioxide gas may be used, or (b) carbon dioxide gas and a foaming agent other than carbon dioxide gas may be used in combination. Examples of foaming agents other than carbon dioxide gas include (a) physical foaming agents (e.g., (a-1) aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; (a- 2) alicyclic hydrocarbons such as cyclopentane and cyclobutane; (a-3) ethers such as dimethyl ether, diethyl ether and methyl ethyl ether; (a-4) alcohols such as methanol and ethanol; ) inorganic gases such as air and nitrogen; and (a-6) water, etc.), and (b) chemical blowing agents including pyrolytic blowing agents such as sodium bicarbonate, azodicarbonamide, dinitrosopentamethylenetetramine. , and so on.

The amount of the foaming agent to be used is not particularly limited, and may be appropriately adjusted according to the type of the foaming agent and/or the target expansion ratio of the extruded polypropylene-based resin expanded particles. As an example, the amount of the foaming agent used may be 0.5 to 7.0 parts by weight with respect to 100.0 parts by weight of the branched polypropylene resin. .0 parts by weight, may be 0.5 parts by weight to 5.0 parts by weight, may be 0.5 parts by weight to 4.0 parts by weight, and may be 0.5 parts by weight to It may be 3.0 parts by weight.

In the first step, stabilizers (e.g., antioxidants, metal deactivators, phosphorus-based processing stabilizers, UV absorbers, UV stabilizers, optical brighteners, metal soaps, and antacids) are optionally added. adsorbents, etc.) and additives (e.g., cell nucleators, inorganic colorants, organic colorants, crosslinkers, chain transfer agents, lubricants, plasticizers, fillers, reinforcements, pigments, dyes, flame retardants, and charging inhibitors, etc.) may also be used.

Additives such as colorants and/or stabilizers may be formulated (used) as a masterbatch. A masterbatch of additives such as colorants and/or stabilizers contains additives such as colorants and/or stabilizers and any resin (for example, polypropylene resin or branched polypropylene resin) at any ratio. It can be obtained by mixing. The concentration of additives such as colorants and / or stabilizers in the masterbatch is not particularly limited, for example, 5 to 50% by weight of additives such as colorants and / or stabilizers in 100% by weight of the masterbatch. It may be a masterbatch.

In the first step, the resin composition and blowing agent, as well as other optional ingredients, may be mixed before being supplied to the manufacturing equipment or mixed within the manufacturing equipment. In other words, in the first step, the resin composition may be supplied to the manufacturing apparatus, or the resin composition may be prepared (completed) within the manufacturing apparatus. In the first step, (i) the method and order of mixing the resin composition and blowing agent, and optionally other ingredients, or (ii) the resin composition and blowing agent, and optionally The method and order of supplying the other ingredients to the manufacturing equipment are not particularly limited.

Before extruding the molten resin obtained in the first step into the low pressure region, the molten resin may be cooled. A melt cooler or a static mixer can be used as a device for cooling the molten resin.

Here, the temperature maintained from the extruder through the melt cooler to the die (sometimes referred to as "melt cooler-die temperature") is not particularly limited, but when the melting point of the resin composition is T, It is preferably (T-10) ° C. to (T + 30) ° C., more preferably (T-10) ° C. to (T + 25) ° C., and (T - 10) ° C. to (T + 20) ° C. It is more preferably (T-10)°C to (T+15)°C, particularly preferably.

(1-2-2. Second step)
The second step is a step of extruding the molten resin obtained in the first step through a die into a region having a lower pressure than the internal pressure of the manufacturing apparatus, and shredding the extruded molten resin. The second step provides extruded foam particles. Therefore, the second step can also be said to be a granulation step of granulating the extruded polypropylene-based resin expanded particles.

In the second step, the region where the molten resin obtained in the first step is extruded is not particularly limited as long as the pressure is lower than the internal pressure of the manufacturing apparatus. For example, in the second step, the molten resin obtained in the first step may be extruded into a gas phase or into a liquid phase.

In the second step, the molten resin extruded into a region having a lower pressure than the internal pressure of the manufacturing apparatus immediately begins to foam. In the second step, the molten resin being foamed may be shredded, or the molten resin that has finished foaming may be shredded. When shredding the molten resin during foaming, the shredded molten resin may complete foaming in the region to which it is extruded.

The second step (granulation step) can be broadly divided into cold cut method and die face cut method, depending on the region where the molten resin obtained in the first step is extruded and the method of shredding the extruded molten resin. can be separated. Examples of the cold cut method include a method in which a molten resin containing a foaming agent extruded from a die is foamed, and a strand-shaped foam is taken off while cooling in a water tank and then shredded (strand cut method). . The die face cut method is a method in which a molten resin extruded from a hole in a die is cut by a rotating cutter while contacting the surface of the die or ensuring a slight gap.

The die face cutting method is further divided into the following three methods depending on the cooling method. That is, they are an under water cut (hereinafter also referred to as UWC) method, a water ring cut (hereinafter sometimes referred to as WRC) method, and a hot cut (hereinafter sometimes referred to as HC) method. The UWC method is a method in which a chamber attached to the tip of a die is filled with cooling water adjusted to a predetermined pressure so as to be in contact with the resin discharge surface of the die, and the molten resin extruded from the die hole is cut underwater. . In addition, in the WRC method, a cooling drum in which cooling water flows along the inner peripheral surface of the cooling drum connected to the die is arranged downstream from the die, and the molten resin cut by the cutter foams in the air. It is a method of cooling in the cooling water while or after foaming. The HC method is a method in which a molten resin is cut by a cutter in the air, and the cut molten resin is cooled in the air while foaming or after foaming. The HC method also includes a mist cut method further including a step of spraying mixed mist of water and air.

This manufacturing method is characterized by the dies used. The die in this production method is provided at the tip of the extrusion foaming machine, and the molten resin flowing out of the extrusion foaming machine passes through the flow path inside the die at the tip of the extrusion foaming machine and is discharged from the discharge hole. . The die has a plurality of ejection holes for ejecting the molten resin, and the extrusion foaming machine includes a flow path for circulating the molten resin to the ejection holes and a heating section for heating the molten resin in the flow path. and the heating unit is inserted into the die. Also, the heating unit is a rod-shaped heater parallel to the flow path. In this way, since the heating part, which is a rod-shaped heater parallel to the flow path, is inserted into the die, the heating part heats the die from the inside. Therefore, it is possible to reduce temperature variations in the flow path.

In the extrusion foaming method, the molten resin prepared in the extrusion foaming machine is preferably extruded through a die having a plurality of small holes and immediately cut into particles by a rotating cutter. As described above, there are various methods for the region where the molten resin is extruded and the method for shredding the extruded molten resin. can be set as appropriate. For example, when the HC method is used, since a relatively large-sized die is generally used in the HC method, the temperature variation in the flow path of the die is large, and an effect of improving the temperature variation can be expected. In addition to the HC method, the UWC method and WRC method can also be applied to this production method.

The shape of the dice is not particularly limited, but a columnar shape with a square, circular, regular polygonal or the like as the bottom surface is preferable, and a columnar shape with a circular bottom surface is particularly preferable. This configuration has the advantage that variations in flow through the discharge holes are less likely to occur.

Although the diameter of the die is not particularly limited, it is preferably 50 mm to 500 mm, more preferably 50 mm to 470 mm, even more preferably 50 mm to 430 mm, and particularly preferably 50 mm to 400 mm. This configuration has the advantage that the above-described effect of reducing the temperature variation is likely to be exhibited.

Examples of dies used in this manufacturing method are shown below. FIG. 1 is a schematic configuration of an example of a die 10 used in a method for producing extruded expanded beads according to one embodiment of the present invention, and is a view of the channel configuration projected from the back of the die 10. FIG. FIG. 2 is a view of the channel configuration inside the die 10 projected from the right side of the die 10 shown in FIG. In the present specification, the “horizontal direction” and “vertical direction” of the die refer to the horizontal direction (which can be said to be parallel to the ground) and the vertical direction (perpendicular to the ground) of the die attached to the extrusion foaming machine. direction).

As shown in FIGS. 1 and 2, the die 10 includes a flow path 1 through which the molten resin flowing out from the former extrusion foaming machine passes, heating portions 5a and 5b, a discharge hole 6 through which the molten resin is discharged, It has The flow path 1 is composed of a transport member for transporting molten resin from the extruder to the discharge hole 6 . Flow path 1 and discharge hole 6 are in communication. Heating units 5 a and 5 b are provided for heating the molten resin in the flow path 1 .

The heating portions 5a and 5b are inserted and arranged inside the body of the die 10. As shown in FIG. Heating portions 5 a and 5 b are rod-shaped heaters parallel to flow path 1 . In other words, the heating portions 5a and 5b, which are rod-shaped heaters, are inserted into the interior of the die 10 so as to be parallel to the central axis X of the die 10. As shown in FIG. Further, the heating portions 5a and 5b are inserted from the surface of the die 10 opposite to the surface provided with the ejection holes 6 (hereinafter sometimes simply referred to as the back surface). The heating units 5a and 5b are, for example, cartridge heaters inserted from the rear surface of the die 10. FIG.

The flow path 1 branches in three stages in the flow of molten resin. Therefore, the molten resin that has flowed in from the inlet 1a is branched in three steps in the direction of the central axis X before passing through the flow path 1 and being discharged from the discharge hole 6. As shown in FIG. Moreover, as shown in FIGS. 1 and 2, the directions of branching at each stage in the flow path 1 are different from each other.

More specifically, the channel 1 extends from the inlet 1 a along the central axis X and branches horizontally into two at the branching portion A to form the branched channel 2 . In the branched channel 2 , the two channels extending in two directions are branched into two in the vertical direction at the branching portions B<b>1 and B<b>2 to form the branched channel 3 . When viewed from the back side of the die 10, the branching direction of the branched channel 3 at the branching portions B1 and B2 is perpendicular to the branching direction of the branched channel 2 at the branching portion A. In the branched channel 3, the four channels branched at the branching portions B1 and B2 are respectively bent at the bending portions Y1 to Y4 so as to be parallel to the central axis X, and branched in two directions at the branching portions C1 to C4. , and becomes a branch flow path 4 . The branching direction of the branched channel 4 at the branching portions C1 to C4 and the branching direction of the branched channel 3 at the branching portions B1 and B2 are different from each other. In the branch flow path 4, the eight flow paths branched at the branch portions C1 to C4 respectively bend at the bending portions Z1 to Z8 and communicate with the discharge hole 6. FIG. As shown in FIG. 2, the form of branching of the flow path 1 has a shape similar to a drawing showing a match table in a tournament. For this reason, a flow path branched in multiple stages in the X-axis direction like the flow path 1 may be referred to as a "tournament flow path". In addition, in the die used in this embodiment, from the viewpoint that it is possible to design a free flow path that does not interfere with the bar heater as the heating part (the number of bar heaters can also be increased), the flow path is the tournament flow path. is preferably

According to the configuration of the die 10, the heating sections 5a and 5b are arranged inside the tournament shape formed by the channel 1, rather than outside. In other words, the heating sections 5a and 5b are surrounded by channels that constitute tournament channels.

As shown in FIGS. 1 and 2, for example, the heating section 5a is surrounded by a branched channel 2, a branched channel 3, and a branched channel 4. FIG. Moreover, the heating portion 5b is surrounded by the branch flow path 3 and the branch flow path 4. As shown in FIG.

Furthermore, with respect to the arrangement of the heating units 5a and 5b, "arranged inside the tournament shape" or "surrounded by the channels that constitute the tournament channel" can be rephrased as follows. can. That is, in the projected view of the flow path 1 (the flow path 1 shown in FIG. 1) viewed from the back of the die 10, among the straight lines connecting any two points on the surface constituting the tournament flow path, the heating portion 5a or 5b In other words, there is at least one straight line passing through .

In FIG. 1, for example, the heating unit 5a is arranged so that a straight line connecting a point II on the branch channel 4 and a point III on the branch channel 3 passes through. Similarly, the heating part 5b is arranged so that a straight line connecting the points IV and V present in the two branched flow paths 4 facing each other passes through.

As described above, according to the present manufacturing method, in the die 10 used, the heating portions 5a and 5b are arranged inside the tournament shape formed by the flow path 1, so that the temperature variation with respect to the flow path 1 can be reduced. As a result, according to this production method, it is possible to reduce the variation in the expansion ratio and open cell ratio of the extruded foamed particles. In addition, according to this manufacturing method, there is no local temperature drop in the die 10, the possibility that the solidified product of the molten resin clogs the flow path 1 or the discharge hole 6 of the die 10 is reduced, and production stability and production efficiency are improved. improves.

Further, in the die 10, the discharge hole 6 is positioned at the point where the bent portions Z1 to Z8 are bent parallel to the central axis X and extended. Therefore, in the die 10 shown in FIG. 1, the positions of the bent portions Z1 to Z8 correspond to the positions of the discharge holes 6, respectively. As shown in FIG. 1, the heating portions 5a and 5b are arranged so as to be equidistant from adjacent two of the plurality of discharge holes 6. As shown in FIG. As a result, temperature variations in the flow path 1 can be further reduced.

Moreover, the temperature control of the heating portions 5a and 5b may be any temperature control as long as the temperature variation in the flow path 1 can be reduced. Each of the heating portions 5a and 5b may be temperature-controlled separately. Thereby, the temperature of the flow path 1 can be precisely controlled.

Moreover, the heating unit may be arranged on the outer peripheral portion of the channel 1 in addition to the inside of the channel 1 . According to such a configuration, the temperature of the flow path 1 can be precisely controlled by the heating portions 5a and 5b arranged inside the flow passage 1 and the heating portions arranged on the outer peripheral portion of the flow passage 1. FIG.

Further, according to the configuration of the die 10, as shown in FIGS. 1 and 2, the directions of branching at each stage in the flow path 1 are different from each other. That is, in any section parallel to the flow path 1, the flow path 1 penetrating from the inlet 1a to the discharge hole 6 does not appear. Thereby, a space for arranging the heating units 5a and 5b can be secured. In addition, in the sectional view of FIG. 2, the channel configuration of the channel 1 is shown as a projection view.

In this manufacturing method, the channel 1 of the die 10 is not limited to the tournament channel described above. However, from the point of view of being able to design a free flow path that does not interfere with the rod heater, the flow path 1 is preferably a tournament flow path having multiple stages of branching in the flow direction of the resin as described above. Specifically, it is preferable that the flow path 1 is branched in at least three stages.

Moreover, the material used for the die 10 preferably has both hardness and workability, such as chromium-molybdenum steel, aluminum-chromium-molybdenum steel, and the like. This configuration has the advantage of being able to be processed with high dimensional accuracy and having a high pressure resistance against pressure rise of the resin.

Moreover, the arrangement of the heating portions 5a and 5b, which are rod-shaped heaters, is not limited to the inside of the tournament shape formed by the flow path 1, and can be appropriately set according to the structure of the flow path 1. FIG. The heating portions 5a and 5b are inserted into the die 10 and arranged parallel to the flow path 1. As shown in FIG. For example, if the flow path 1 is a tournament flow path that branches into two directions by one stage, even if the heating units 5a and 5b are arranged outside the tournament flow path, the temperature variation in the flow path 1 can be reduced. .

The cross-sectional shape of the flow path 1 is not particularly limited, but is preferably circular, square, regular polygonal, or the like, and particularly preferably circular. This configuration has the advantage that the flow is less likely to stagnate.

Also, one heating unit 5a or 5b may have a plurality of rod-shaped heaters. Since the number of heaters can be increased as the die size increases, there is an advantage that the greater the number of heaters, the smaller the temperature variation in the flow path. For example, one heating unit may have two heaters, preferably three heaters, more preferably four heaters, and still more preferably five heaters. Having a book heater.

A plurality of discharge holes 6 are arranged for one die 10 . Although the size of the discharge hole 6 is not particularly limited, it is preferably 0.1 mm to 10 mm, more preferably 0.1 mm to 6 mm, further preferably 0.2 mm to 4 mm, and 0.2 mm to 4 mm. 3 mm to 2 mm is particularly preferred. This configuration has the advantage that it is possible to obtain foamed particles having a size suitable for molding.

The number of ejection holes 6 in one die 10 is not particularly limited, but is preferably 3 or more, more preferably 5 or more, further preferably 10 or more, further preferably 15. It is particularly preferable that it is above. This configuration has the advantage that the overall cross-sectional area can be increased without increasing the diameter of the discharge hole.

FIG. 3 is a schematic configuration of Modified Example 1 of the die 10 used in the method for producing extruded expanded beads according to one embodiment of the present invention, and is a view of the channel configuration projected from the back.

As shown in FIG. 3, the dice 10A as Modification 1 differs from the configuration shown in FIGS. 1 and 2 in the form of branching in the tournament channel. More specifically, in the die 10A, the channel 1A extends from the inlet 1a along the central axis X, branches off in four directions at the branching portion A, and becomes the branched channel 2A.

In the branched channel 2A branched in four directions, the two channels extending in the vertical direction are respectively bent so as to be parallel to the central axis X, and branched in two directions at the tip branch portions B3 and B5. It becomes the flow path 3A. In the branch flow path 3A, the four flow paths branched at the branch portions B3 and B5 respectively bend at the bending portions Z9, Z10, Z17 and Z18 and communicate with the discharge holes.

Further, in the branched channel 2A branched in the above four directions, the two channels extending in the horizontal direction are each bent so as to be parallel to the central axis X, and branched into three directions at the branch portions B4 and B6 at the tip. and becomes a branch flow path 3A. In the branched channel 3A, the six channels branched at the branching portions B4 and B6 are respectively bent so as to be parallel to the central axis X, and branched in two directions at the tip branching portions C5 to C7 and C8 to C10. It branches and becomes 4 A of branch flow paths. In the branch flow path 4A, 12 flow paths branched at the branching portions C5 to C7 and C8 to C10 respectively bend at the bending portions Z11 to Z16 and Z19 to Z24 and communicate with the discharge holes.

Moreover, the heating portions 5c and 5d are arranged inside the tournament shape formed by the flow path 1A. In other words, the heating portions 5c and 5d are surrounded by the channels that constitute the channel 1A. The heating portion 5c is surrounded by two branched channels 2A, 3A and 4A. Moreover, the heating part 5d is surrounded by the branch flow path 3A and the two branch flow paths 4A.

Even with the configuration shown in FIG. 3, it is possible to further reduce temperature variations in the flow path 1A.

FIG. 4 is a cross-sectional view showing Modified Example 2 of the die 10 used in the method for producing extruded foam beads according to one embodiment of the present invention, and the channel configuration is projected from the cross-section.

As shown in FIG. 4, the die 10B as Modification 2 differs from the configuration shown in FIG. 1 in that the flow path 1B branches in four stages in the flow of the molten resin. In the die 10B, the flow path 1B extends from the inlet 1a along the central axis X and branches horizontally at the branch portion A. Then, the branched flow path branches vertically into two directions at a branching portion B8 to form a branched flow path 3B. The branch flow paths 3B branched in two directions are respectively bent so as to be parallel to the central axis X, and branched in two directions at the branch portions C11 and C12 to form the branch flow paths 4B. Each of the branched channels 4B is bent so as to be parallel to the central axis X, and is branched in two directions at the branching portion D to form the branched channel 7 . Moreover, the heating part 5e is arranged inside the tournament shape formed by the flow path 1B.

Even with the configuration shown in FIG. 4, it is possible to further reduce temperature variations in the flow path 1B.

Here, FIG. 5 shows a schematic configuration of a conventionally used die. FIG. 6 shows a cross-sectional view of the die shown in FIG. 5 taken along line B-B'. The flow path of the conventional die is called a "torpedo flow path", and the die is heated from the outside (periphery) of the die by a band heater or casting heater, which is a heating section. In the torpedo flow path, the larger the die, the greater the temperature difference between the outer side of the die closer to the heater and the center of the die farther from the heater, resulting in variations in die temperature.

In an example of a conventional torpedo flow path, a heating portion 103 is arranged outside (peripheral portion) of a die 100 as shown in FIG. Further, the channel 101 has an inlet 101 a and branches conically inside the die 100 (inner periphery) to form a channel 102 . The shape of the die 100 surrounded by the conically branched flow paths 102 is conical, and the enclosed conical portion is the torpedo 104 . Flow path 102 communicates with discharge hole 105 . In FIG. 5, a plurality of ejection holes 105 can be arranged around the channel 102 .

In the conventional torpedo flow path as shown in FIG. 5, the torpedo 104 was an obstacle, and it was impossible to insert the heater, which is the heating part, from the back side of the die 100 . In contrast, in the tournament channel shown in FIG. 1, the channel 1 can be arranged to avoid the heating portions 5a and 5b, which are rod-shaped heaters. Therefore, the heating portions 5a and 5b, which are rod-shaped heaters, can be inserted from the back side of the die 10. As shown in FIG. This has the advantage of reducing variations in the temperature of the die 10 .

In one embodiment of the present invention, the temperature variation of the die 10 is not particularly limited, but is preferably 9° C. or less, more preferably 8° C. or less, and more preferably 7° C. or less. ° C. or less, more preferably 5 ° C. or less, more preferably 4 ° C. or less, more preferably 3 ° C. or less, even more preferably 2 ° C. or less, 1 °C or less is particularly preferred. This configuration has the advantage of being able to reduce variations in expansion ratio and open cell ratio of the obtained extruded expanded beads. The temperature variation of the die 10 is measured by the method described in Examples.

The heating portion does not extend to the tip of the die as shown in FIGS. For all discharge holes, the shortest distance to the tip of the nearest heating part is obtained, and the average distance is taken as the average distance. The average distance is preferably 20 mm or less, more preferably 10 mm or less, and even more preferably 5 mm or less. This configuration has the advantage of being able to control the temperature of the discharge hole with good responsiveness and accuracy.

When viewed from the surface of the die on the discharge hole side, all the discharge holes are preferably within a range of 40 mm or less, more preferably within a range of 20 mm or less, and within a range of 10 mm or less from the heating part. is more preferred. This configuration has the advantage of reducing variations in the temperature of the discharge holes.

Variation in the expansion ratio of the extruded expanded beads is not particularly limited, but is preferably 7.0% or less, more preferably 6.0% or less, more preferably 5.0% or less, and even more preferably 4.0% or less. , 3.0% or less is particularly preferred. According to this configuration, there is an advantage that there is little variation in the weight of the molded product, which is a product. The variation in the expansion ratio of the extruded expanded beads is measured by the method described in Examples.

The open cell ratio of the extruded expanded beads is not particularly limited, but is preferably 22.0% or less, more preferably 20.0% or less, more preferably 18.0% or less, and more preferably 16.0% or less. 14.0% or less is more preferable, and 12.0% or less is particularly preferable. This configuration has the advantage that a beautiful molded body can be obtained. The open cell ratio of the extruded expanded beads is measured by the method described in Examples.

[Method for producing foam molded product]
The method for producing a foamed molded article according to the present embodiment is a method comprising a step of producing extruded expanded beads by the above-described production method, and a step of foam-molding the extruded expanded beads obtained by the step. In order to produce a foam molded product, the extruded foam particles can be foam-molded by a known method, and there is no particular limitation.

Hereinafter, one embodiment of the present invention will be described in more detail with examples and comparative examples. The invention is not limited to the following examples. In addition, in the examples of one embodiment of the present invention, a branched polypropylene-based resin was used as the thermoplastic resin.

(Test method)
The test methods used for measuring and evaluating various physical properties in Examples and Comparative Examples are as follows.

<Dice temperature variation>
After 10 minutes from the start of production of extruded expanded particles, the granulator was stopped, and the temperature of the surface of the die was measured at 10 points with a contact-type thermometer. I made it with roses.

<Expansion ratio>
The expansion ratio of the extruded polypropylene resin expanded beads was calculated by the following method: (1) the weight w (g) of the extruded expanded beads was measured; , immersed in ethanol contained in a graduated cylinder, and the volume v (cm ³ ) of the extruded expanded particles was measured based on the rise in the liquid level of the graduated cylinder; (3) weight w (g) was converted to volume v ( cm ³ ) to calculate the density ρ ₁ of the extruded foamed beads; (4) Divide the density ρ ₂ of the base resin of the extruded foamed beads by the density ρ ₁ of the extruded foamed beads (ρ ₂ /ρ ₁ ) , and foaming ratio. As the density ρ ₂ of the base resin, the density 0.9 g/cm ³ of a general polypropylene-based resin was adopted.

<Magnification variation>
1 kg of polypropylene-based resin foamed particles are passed through standard sieves (nominal dimensions 1, 1.18, 1.4, 1.7, 2, 2.36, 2.8, 3.35, 11 types of sieves (4, 4.75, 5.6). The weight fraction Wi of the branched polyolefin-based resin expanded particles remaining on each sieve and the expansion ratio Ki were measured, and the average expansion ratio Kav was calculated from the following formula (1).

Kav=Σ(Ki×Wi) Equation (1)
Next, using the weight fraction Wi, the expansion ratio Ki and the average expansion ratio Kav, the formula (2)
σm=[Σ{Wi×(Kav−Ki) ² }] ^1/2 Equation (2)
(i = represents each sieve)
Calculate the standard deviation σm of the foaming ratio from the formula (3)
Magnification variation R (%)=(σm/Kav)×100 Equation (3)
Magnification variation R (%) was obtained from .

<Continuous cell rate>
The open cell ratio of the extruded polypropylene resin expanded particles is measured using an air comparison type hydrometer [manufactured by Tokyo Science Co., Ltd., model 1000] according to the method described in ASTM D2856-87 Procedure C (PROCEDURE C). and asked. More specifically, the open cell ratio of the extruded foamed particles was calculated by performing the following (1) to (3) in order: (1) Using an air comparison type hydrometer, the volume of the extruded foamed particles Vc (cm ³ ) was measured; (2) the total amount of extruded foamed particles after measuring Vc was then submerged in ethanol contained in a graduated cylinder; , the apparent volume Va (cm ³ ) of the extruded foamed beads was obtained; (4) the open cell ratio of the extruded foamed beads was calculated by the following formula:
Open cell ratio (%) = ((Va-Vc) x 100)/Va.

[Example 1]
<Production of branched polypropylene resin composition>
A branched polypropylene resin composition was produced by the following method. A random polypropylene resin, RD265CF (manufactured by Borouge) was supplied to a twin-screw extruder, and then t-butyl peroxyisopropyl monocarbonate (manufactured by NOF Corporation, Perbutyl I) was added as a radical polymerization initiator to 100 parts by weight of RD265CF. .0 parts by weight was fed to a twin screw extruder. Thereafter, 0.4 parts by weight of isoprene per 100 parts by weight of RD265CF was supplied to a twin-screw extruder to prepare a resin mixture in the twin-screw extruder. The feed rate of the resin mixture to the twin-screw extruder was 70 kg/h.

The prepared resin mixture was melt-kneaded in a twin-screw extruder at a cylinder temperature of 180° C. and a screw rotation speed of 230 rpm to obtain a branched polypropylene-based resin composition (melt-kneading step). The obtained branched polypropylene-based resin composition was extruded from a die in the form of a strand at an extruding rate of 70 kg/h (extruding step). The discharged branched polypropylene resin composition (strand) was (a) cooled with water, and then (b) chopped into pellets (cylindrical).

<Production of extruded expanded particles>
A resin mixture was prepared by blending 100 parts by weight of a branched polypropylene-based resin composition and 0.02 parts by weight of talc as a cell nucleating agent. Thereafter, the resin mixture was supplied from the raw material supply section to the twin-screw extruder (melt-kneading section), and melt-kneading of the resin mixture was started at a cylinder temperature of 180° C. and a screw rotation speed of 120 rpm. The feed rate of the resin mixture to the twin-screw extruder was 10 kg/h. During the melt-kneading of the resin mixture, carbon dioxide gas as a blowing agent was forced into the twin-screw extruder from the blowing-agent supply section, and the resulting composition was further melt-kneaded. The amount of foaming agent supplied to the twin-screw extruder was 0.4 kg/h.

The melt-kneaded composition obtained through the melt-kneading step was passed through the die of the granulation unit and discharged at a discharge rate of 10 kg / h into the air phase, which has a lower pressure than the internal pressure of the manufacturing apparatus. Expanded beads were obtained by the WRC method in which the extruded composition was cut in air and the expanded beads were cooled in water. The number of blades used for cutting was two, the number of rotations of the blades was 1200 rpm, and the temperature of water used for WRC was 50°C.

<Dice structure>
As the die, a tournament flow path die was used, which had a structure in which the flow path branched in five steps of 1→2→4→8→16→32. Heating was performed by inserting eight rod-shaped cartridge heaters into the die in parallel with the flow path, and temperature control was provided at four locations (one temperature control was in charge of two cartridge heaters). The temperature variation of the dice with this structure was 0.5°C.

Table 1 shows the structural characteristics of the die and the physical properties of the obtained expanded beads.

[Comparative Example 1]
<Production of extruded expanded particles>
Expanded beads were obtained in the same manner as in Example 1, except that the branched polypropylene-based resin composition produced in the same manner as in Example 1 was used in a die.

<Dice structure>
The die used here has a general structure using a cone called a torpedo, and has a structure in which the flow path spreads radially while maintaining a circular shape along the torpedo. Heating is performed using an aluminum casting heater installed along the outer side of the conical die. The aluminum casting heater is divided into two parts, and the temperature is controlled in each, so the temperature is controlled in two places. be done. The temperature variation of the die with this structure was 9.4°C.

Table 1 shows the structural characteristics of the die and the physical properties of the obtained expanded beads.

Comparing Example 1 and Comparative Example 1, Example 1 was significantly improved in "variation in die temperature", and was also significantly improved in variation in expansion ratio and open cell ratio of the obtained expanded beads.

1, 1A, 1B Channels 2, 2A, 3, 3A, 3B, 4, 4A, 4B Branched channels 5a, 5b, 5c, 5d, 5e Heating part 6 Discharge hole 7 Branched channel 10 Dies A, B1, B3 , B4, B8, C1, C11, C5 branches

Claims (6)

A method for producing extruded foam particles of a thermoplastic resin using an extrusion foaming machine having a die,
The dice are
a plurality of ejection holes for ejecting molten resin;
a flow path for circulating the molten resin to the discharge hole;
a heating unit for heating the molten resin in the flow path,
The heating unit is inserted and arranged inside the die,
The method for producing extruded foam particles, wherein the heating unit is a rod-shaped heater parallel to the flow path. The method for producing extruded expanded particles according to claim 1, wherein the thermoplastic resin is a polypropylene-based resin having a branched structure. The method for producing extruded expanded beads according to claim 1 or 2, wherein the flow path has multistage branches in the flow direction of the molten resin. 4. The method for producing extruded expanded beads according to claim 3, wherein the flow path is branched in at least three stages. The method for producing extruded expanded particles according to any one of claims 1 to 4, wherein the method for granulating the extruded expanded particles is a die face cutting method. A step of producing extruded expanded particles by the production method according to any one of claims 1 to 5;
and a step of foam-molding the extruded foamed particles obtained in the above step.

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