JP7518347B2 - Manufacturing method of molded body - Google Patents

Description

The present invention relates to a method for producing a molded body.

Patent Document 1 discloses a technology in which a raw resin composition is melt-kneaded, the resulting molten resin composition is injected from a head to form a parison, and the parison is then blow-molded to produce a molded article.

JP 2020-55942 A

The raw resin composition may contain a masterbatch of additives such as antioxidants. The masterbatch is usually produced by melt-kneading the additives and binder resin in an extruder, extruding the mixture into a rod-like shape from the extruder to form a string, and then cutting the string into pellets of about 3 to 5 mm.

When a masterbatch is produced in this manner, the heat applied during melt-kneading can cause the additives to deteriorate (by oxidation or decomposition, etc.).

The present invention was made in consideration of these circumstances, and provides a method for producing a molded body that can suppress the deterioration of additives contained in the master batch.

According to the present invention, there is provided a method for producing a molded body, which includes an extrusion step and a molding step, in which a raw resin composition is melt-kneaded to form a molten resin composition by extruding the molten resin composition from a head in the extrusion step, and a molded body is formed by molding the parison using first and second molds that can be opened and closed in the molding step, the raw resin composition includes a base resin and an additive master batch, and the additive master batch is a granulated product of an additive and a binder resin.

The present invention is characterized by the use of an additive masterbatch, which is a granulated product of additives and binder resin. The granulated product can be produced without melt-kneading, so it is possible to suppress the deterioration of the additives due to the heat applied during melt-kneading.

Various embodiments of the present invention will be described below. The embodiments described below can be combined with each other.
Preferably, in the above-described method, a coating is formed on the surface of the granules by melting and solidifying the binder resin.
Preferably, in the method described above, the binder resin comprises a polyethylene-based elastomer.
Preferably, in the above-described method, the difference in melt flow rate between the base resin and the binder resin is 10 g/10 min or less, and the melt flow rate is a value obtained by measuring in accordance with JIS K-7210 at a test temperature of 190° C. and a test load of 2.16 kg.
Preferably, the method according to the above, wherein the proportion of the additive in the additive masterbatch is 50 to 99% by weight.

An example of a molding machine 1 that can be used in the method for producing a molded body according to one embodiment of the present invention is shown. FIG. 2 is a partially cutaway perspective view of a coating 11b1 of a granulated product of the additive master batch 11b.

The following describes the embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. In addition, each feature can be an invention independently.

1 and 2, a molding machine 1 that can be used to implement a manufacturing method for a molded body according to one embodiment of the present invention will be described. The molding machine 1 includes a resin supplying device 2, an extrusion head 18, and first and second split molds 21, 22. The resin supplying device 2 includes a hopper 12, an extruder 13, an injector 16, and an accumulator 17. The extruder 13 and the accumulator 17 are connected via a connecting pipe 25. The accumulator 17 and the extrusion head 18 are connected via a connecting pipe 27.
Each component will be described in detail below.

<Hopper 12, Extruder 13, Raw Material Resin Composition 11>
The hopper 12 is used to feed the raw resin composition 11 into the cylinder 13a of the extruder 13. After being fed from the hopper 12 into the cylinder 13a, the raw resin composition 11 is heated in the cylinder 13a to melt and become a molten resin composition 11m. The raw resin composition 11 is also transported toward the tip of the cylinder 13a by the rotation of a screw disposed in the cylinder 13a. The screw is disposed in the cylinder 13a, and transports the molten resin composition 11m while kneading it by its rotation.

The raw resin composition 11 contains a base resin 11a and an additive master batch 11b.

The base resin 11a is a thermoplastic resin such as polyolefin or polyester, and examples thereof include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene-based elastomers, and mixtures thereof. The form of the base resin 11a is not particularly limited, but is usually in the form of pellets.

The additive master batch 11b is a granulated product of additives and binder resin. Examples of additives include antioxidants, pigments, and fillers. Examples of antioxidants include phosphorus-based antioxidants and phenol-based antioxidants. The binder resin is any thermoplastic resin capable of retaining the shape of the granulated product. Examples of binder resins include the resins mentioned above as the base resin. The proportion of the additive master batch in the raw resin composition 11 is, for example, 0.1 to 20 mass%, and preferably 0.5 to 5 mass%. Specifically, this proportion is, for example, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 mass%, and may be within a range between any two of the numerical values exemplified here.

The granulated material is preferably columnar, and more preferably cylindrical. The longitudinal length of the granulated material (height if the granulated material is columnar) and the equivalent circle diameter of the end face are each, for example, 1 to 10 mm, preferably 2 to 5 mm, and specifically, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 mm, and may be within a range between any two of the numerical values exemplified here.

The granulated product of the additive master batch 11b can be produced by mixing powdered binder resin and additives and granulating them with a granulator. Binder resin is usually sold in the form of pellets, but in that case, the powdered binder resin can be obtained by crushing the pellets (e.g., freeze-crushing). The average particle size of the binder resin is, for example, 20 to 300 μm, and preferably 40 to 120 μm. Specifically, this average particle size may be, for example, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 150, 200, 250, or 300 μm, and may be within a range between any two of the numerical values exemplified here. The value of [average particle size of binder resin/average particle size of additives] is, for example, 0.1 to 10, and preferably 0.2 to 5. Specifically, this value may be, for example, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, and may be within a range between any two of the numerical values exemplified here. In this specification, "average particle size" refers to the particle size at an integrated value of 50% in the particle size distribution determined by a laser diffraction/scattering method.

In one example, granulation can be performed by compressing the mixed powder obtained by mixing the binder resin and the additives. Granulation can be wet granulation in which a volatile liquid (e.g., water, ethanol) is added to the mixed powder, or dry granulation in which a volatile liquid is not added to the mixed powder. For example, in extrusion granulation, the mixed powder can be granulated by applying pressure to it and extruding it from an opening in a die. Pressure can be applied to the mixed powder using a screw, plunger, roller, or the like. According to this method, heat is less likely to be applied to the additives than when a master batch is produced by melt kneading, so deterioration of the additives due to excessive heat is suppressed.

The granulated material obtained by such a method may break apart when subjected to impact, making it difficult to handle. Therefore, by heat-treating the surface of the granulated material after the granulation, a coating 11b1 in which the binder resin is melted and solidified can be formed as shown in FIG. 2. This improves the mechanical strength of the granulated material and improves its handleability. The coating 11b1 may be formed on the entire surface of the granulated material, or on a part of the surface of the granulated material. In other words, the surface of the granulated material may have a portion on which the coating 11b1 is not formed. In addition, since the inside 11b2 of the coating 11b1 of the granulated material is in a compressed state of the binder resin and additive powder, when the coating is destroyed by the screw of the extruder 13, the binder resin and additive powder are released. The heat treatment can be performed, for example, by blowing hot air onto the surface of the granulated material, or by preparing a mold with an appropriate shape and instantaneously heating only the surface.

The heat treatment can be performed by heating the surface of the granulated material to a temperature equal to or higher than the melting point of the binder resin. In this case, in order to prevent deterioration of the additives due to heat, it is preferable that the heating temperature is low, and in order to lower the heating temperature, it is preferable that the melting point of the binder resin is low. The melting point of the binder resin is preferably 100°C or lower, and more preferably 80°C or lower. This melting point is preferably 40°C or higher. If the melting point is too low, it may melt at room temperature and become difficult to handle. This melting point is, for example, 40 to 100°C, specifically, for example, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100°C, and may be within a range between any two of the numerical values exemplified here. In this specification, "melting point" means the melting peak temperature Tpm measured according to JIS K 7121:2012.

The binder resin preferably contains a polyethylene-based elastomer (hereinafter, "PE-based elastomer"). PE-based elastomers are elastomers that have polyethylene as hard segments and a specific rubber component as soft segments. Examples include C-4 PE-based elastomers that contain butene as a comonomer for ethylene, C-6 PE-based elastomers that contain hexene, and C-8 PE-based elastomers that contain octene.

PE-based elastomers generally have a low melting point, so by including a PE-based elastomer in the binder resin, the melting point of the binder resin can be lowered. Furthermore, by including a PE-based elastomer in the binder resin, the impact resistance at low temperatures of the molded body produced can be improved. The proportion of the PE-based elastomer in the binder resin is, for example, 20 to 100% by mass, and preferably 50 to 100% by mass. Specifically, this proportion can be, for example, 20, 30, 40, 50, 60, 70, 80, 90, or 100% by mass, and may be within a range between any two of the numerical values exemplified here.

The proportion of additives in the additive master batch 11b is not particularly limited, and is, for example, 10 to 99% by mass. When producing a master batch by melt kneading, powdered additives and pelleted binder resin are usually mixed, so the difference in particle size between the additives and the binder resin is large, and it is difficult for the two to mix uniformly. For this reason, the proportion of additives in a conventional master batch was usually about 30% by mass. On the other hand, the additive master batch 11b of this embodiment is produced by mixing a powdered binder resin and an additive and granulating the mixed powder obtained by mixing the powdered binder resin and the additive with a granulator, so that the difference in particle size between the additives and the binder resin is small, and the two are easily mixed uniformly, and the proportion of additives in the additive master batch 11b is easy to increase. This proportion is preferably 50% by mass or more, and more preferably 60, 70, or 80% by mass or more. Specifically, this ratio may be, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, or 99% by mass, and may be within a range between any two of the values exemplified here.

It is preferable that the difference in melt flow rate (hereinafter, "MFR") between the base resin 11a and the binder resin is 10 g/10 min or less. If this difference is large, it is difficult to mix uniformly when melt-kneaded in the extruder 13. This difference is, for example, 0 to 10 g/10 min, specifically, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 g/10 min, and may be within a range between any two of the numerical values exemplified here. The MFR of the base resin and the binder resin is, for example, 0 to 10, specifically, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 g/10 min, and may be within a range between any two of the numerical values exemplified here. In one example, the MFR of the base resin is 0.5 to 3 g/10 min (preferably 1 to 2 g/10 min), and the MFR of the binder resin is 0.1 to 1 g/10 min. In this specification, "MFR" refers to the value obtained by measuring in accordance with JIS K-7210 at a test temperature of 190°C and a test load of 2.16 kg.

<Injector 16>
The cylinder 13a is provided with an injector 16 for injecting a foaming agent into the cylinder 13a. When the raw resin composition 11 is not foamed, the injector 16 can be omitted. The foaming agent injected from the injector 16 can be a physical foaming agent, a chemical foaming agent, or a mixture thereof, with the physical foaming agent being preferred. Examples of the physical foaming agent include carbon dioxide gas and nitrogen gas. Examples of the chemical foaming agent include those that generate carbon dioxide gas by a chemical reaction between an acid (e.g., citric acid or a salt thereof) and a base (e.g., baking soda). The chemical foaming agent may be introduced from the hopper 12 instead of being injected from the injector 16.

<Accumulator 17, Extrusion Head 18>
The molten resin composition 11m, to which a foaming agent is or is not added, is extruded from the resin extrusion port of the cylinder 13a and injected into the accumulator 17 through the connecting pipe 25. The accumulator 17 includes a cylinder 17a and a piston 17b that can slide inside the cylinder 17a, and the molten resin composition 11m can be stored in the cylinder 17a. Then, by moving the piston 17b after a predetermined amount of the molten resin composition 11m is stored in the cylinder 17a, the molten resin composition 11m is extruded through the connecting pipe 27 from a ring slit provided in the extrusion head 18 and drooped down to form a parison 23. The parison 23 may be cylindrical or sheet-shaped. The parison 23 may also be single-layered or multi-layered.

<Molds 21, 22>
The parison 23 is introduced between the open molds 21 and 22. The parison 23 is molded using the openable and closable molds 21 and 22 to obtain a molded body.

The molds 21 and 22 have cavity surfaces 21a and 22a. When the molds 21 and 22 are closed, the cavity surfaces 21a and 22a combine to form a cavity corresponding to the desired molded body.

2. Method for Producing Molded Article The method for producing a molded article according to one embodiment of the present invention is so-called direct blow molding or vacuum molding, and includes an extrusion step and a molding step.

<Extrusion process>
As shown in Fig. 1, in the extrusion process, the raw resin composition 11 is melt-kneaded in the extruder 13, and the molten resin obtained is extruded from the head to form a parison 23, which is then placed between the open dies 21 and 22. The granules of the additive master batch 11b are broken down into powder by the shearing force of the screw of the extruder 13, and are easily mixed uniformly with the base resin 11a. Even if a coating 11b1 of the binder resin is formed on the granules, the coating 11b1 is broken down by the shearing force of the screw, causing the granules to break apart.

<Molding process>
In the molding step, before the molten parison 23 solidifies, the dies 21 and 22 are closed to mold the parison 23 to form a molded body. The molding method using the dies 21 and 22 is not particularly limited, and may be blow molding in which air is blown into the cavity of the dies 21 and 22 to mold the parison 23, or vacuum molding in which the cavity is depressurized from the inner surface of the cavity of the dies 21 and 22 to mold the parison 23, or a combination thereof. The molded body is preferably hollow. When the molten resin contains a foaming agent, the parison 23 becomes a foamed parison, and the molded body becomes a foamed molded body.

<Post-processing>
In a post-process, the green bodies with burrs are taken out of the molds 21 and 22 and the burrs are removed from the green bodies, thereby obtaining the desired green body.

Applications of the molded bodies are not particularly limited, but examples include ducts, containers, etc.

1: Molding machine 2: Resin supply device 11: Raw resin composition 11a: Base resin 11b: Additive master batch 11b1: Film 11b2: Inside 11m: Molten resin composition 12: Hopper 13: Extruder 13a: Cylinder 16: Injector 17: Accumulator 17a: Cylinder 17b: Piston 18: Extrusion head 21: First split mold 21a: Cavity surface 22: Second split mold 22a: Cavity surface 23: Parison 25: Connecting pipe 27: Connecting pipe 29: Pinch section

Claims (4)

A method for producing a molded body, comprising an extrusion step and a molding step,
In the extrusion step, a molten resin composition obtained by melt-kneading a raw material resin composition is extruded from a head to form a parison,
In the molding step, the parison is molded using first and second molds that can be opened and closed to form a molded body;
The raw material resin composition includes a base resin and an additive masterbatch,
The additive masterbatch is a granulated product of an additive and a binder resin,
The granulated material is produced by mixing the powdered binder resin and the additive and granulating the mixture with a granulator,
The granulation is carried out by compressing a mixed powder obtained by mixing the binder resin and the additives,
a coating formed on the surface of the granules by melting and solidifying the binder resin;
The proportion of the additive in the additive masterbatch is 50 to 99% by weight. 2. The method of claim 1 ,
The difference in melt flow rate between the base resin and the binder resin is 10 g/10 min or less,
The melt flow rate is a value obtained by measuring in accordance with JIS K-7210 at a test temperature of 190° C. and a test load of 2.16 kg. A method for producing a molded body, comprising an extrusion step and a molding step,
In the extrusion step, a molten resin composition obtained by melt-kneading a raw material resin composition is extruded from a head to form a parison,
In the molding step, the parison is molded using first and second molds that can be opened and closed to form a molded body;
The raw material resin composition includes a base resin and an additive masterbatch,
The additive masterbatch is a granulated product of an additive and a binder resin,
The granulated material is produced by mixing the powdered binder resin and the additive and granulating the mixture with a granulator,
The granulation is carried out by compressing a mixed powder obtained by mixing the binder resin and the additives,
a coating formed on the surface of the granules by melting and solidifying the binder resin;
The difference in melt flow rate between the base resin and the binder resin is 10 g/10 min or less,
The melt flow rate is a value obtained by measuring in accordance with JIS K-7210 at a test temperature of 190° C. and a test load of 2.16 kg. The method according to any one of claims 1 to 3,
The method according to claim 1, wherein the binder resin comprises a polyethylene-based elastomer.