JP7385671B2 - Resin composition, resin molded article containing the same, and method for producing resin molded article - Google Patents

Description

The present invention relates to a resin composition, a resin molded article containing the same, and a method for producing a resin molded article.

In an injection molded article, a weld line, also called a weld line, may be formed at a position corresponding to a portion where molten resin joins within the mold. This weld line may cause a poor appearance in the injection molded article and may result in a structural defect. As a means for preventing the formation of weld lines, a heat and cool method is known in which injection molding is carried out by heating the mold temperature to a temperature higher than the glass transition temperature of the resin that is the raw material for the injection molded article.

On the other hand, the resin composition used in the production of the above injection molded product includes aluminum pigments for the purpose of imparting a high-class feel to the injection molded product and differentiating it from other injection molded products. It is known to use a resin composition containing the following. However, when an injection molded article is obtained by performing injection molding using the above heat and cool method using the above resin composition as a raw material, although the formation of weld lines is prevented, the above aluminum pigment does not form inside the mold. It is known that the molten resin is unevenly distributed on the surface of the molten resin and adheres to the mold, thereby contaminating the mold. On the other hand, JP 2016-010957 A (Patent Document 1) and JP 2014-185328 A (Patent Document 2) disclose the above-mentioned metallization by coating aluminum flake particles constituting an aluminum pigment with a resin. It is proposed to suppress type contamination.

Japanese Patent Application Publication No. 2016-010957 Japanese Patent Application Publication No. 2014-185328

However, there is a need for further improvements to the techniques disclosed in Patent Document 1 and Patent Document 2 to suppress mold contamination. This is because in the techniques disclosed in Patent Document 1 and Patent Document 2, there is a possibility that the resin coating the aluminum flake particles will melt in the high-temperature mold, and the resin will melt around the aluminum flake particles. This is because it is presumed that by mixing the aluminum flakes with the molten resin, it becomes insufficient to prevent the aluminum flake particles from being unevenly distributed on the surface of the molten resin. Therefore, in injection molding that prevents the formation of weld lines by using the heat and cool method, technology to suppress mold contamination when using a resin composition containing aluminum pigment as a raw material has not yet been realized. However, there is a strong need for its development.

In view of the above circumstances, an object of the present invention is to provide a resin composition that can suppress mold contamination, a resin molded article containing the same, and a method for producing a resin molded article.

The present inventors have made extensive studies to solve the above problems and have completed the present invention. Specifically, although the detailed mechanism is unknown, coupling agents are among the countless additives that are incorporated into this type of resin composition, and it has been shown that coupling agents have an effective effect on suppressing mold contamination. I found out. Based on this knowledge, when injection molding using the heat and cool method is performed using a resin composition containing a thermoplastic resin and aluminum flake particles having a coupling agent attached to at least a portion of the surface, The present invention was developed based on the idea that mold contamination could be suppressed.

That is, the present invention has the following features.
The resin composition according to the present invention is a resin composition used for manufacturing an injection molded article, and the resin composition contains a thermoplastic resin and aluminum flake particles, and the aluminum flake particles are A coupling agent is attached to at least a portion of the surface.

The coupling agent is preferably a silane coupling agent.
More preferably, the coupling agent is an amino-based silane coupling agent.

The coupling agent is preferably contained in an amount of 0.1 parts by mass or more and 10 parts by mass or less based on 100 parts by mass of the aluminum flake particles.

It is preferable that the aluminum flake particles are contained in an amount of 0.5 parts by mass or more and 230 parts by mass or less based on 100 parts by mass of the thermoplastic resin, with the coupling agent attached to the surface thereof.

The thermoplastic resin is preferably one or more resins selected from the group consisting of acrylonitrile-butadiene-styrene resin, styrene-acrylonitrile copolymer, polystyrene, and polyethylene.

The resin molded article according to the present invention contains the above resin composition.
The method for producing a resin molded article according to the present invention includes the step of preparing the resin composition, and maintaining the inner wall surface of the resin composition at a temperature higher than the glass transition temperature of the thermoplastic resin by at least 70°C. and a step of obtaining a resin molded body by cooling the resin composition in the mold.

According to the present invention, it is possible to provide a resin composition that can suppress mold contamination, a resin molded article containing the same, and a method for producing a resin molded article.

Hereinafter, an embodiment (hereinafter also referred to as "this embodiment") according to the present invention will be described in more detail. In this specification, the notation in the format "A to B" means the upper and lower limits of the range (i.e., from A to B), and when there is no unit described in A and only in B, The units of and the units of B are the same.

[Resin composition]
The resin composition according to this embodiment is a resin composition used for manufacturing an injection molded article. The resin composition contains a thermoplastic resin and aluminum flake particles. A coupling agent is attached to at least a portion of the surface of the aluminum flake particles. A resin composition having such characteristics can suppress mold contamination when injection molding is performed using a heat and cool method. Each feature of the resin composition according to this embodiment will be described below.

The above-mentioned resin composition is a resin composition used for manufacturing an injection molded article as described above. The term "injection molded article" refers to a molded article obtained by applying a conventionally known injection molding method to a resin composition containing a thermoplastic resin. Specifically, it refers to a molded article obtained by heating and fluidizing the above resin composition in a cylinder equipped in a conventionally known injection molding machine, injecting it into a mold, and cooling it in the mold. . Further, in this specification, the term "resin molded article" refers to an injection molded article obtained by applying an injection molding method to the resin composition according to the present embodiment.

<Thermoplastic resin>
The resin composition according to this embodiment contains a thermoplastic resin and aluminum flake particles as described above. As used herein, the term "thermoplastic resin" refers to a resin that can be softened by heating and used in the injection molding method described above. Therefore, as long as the resin is softened by heating and can be used in the above-mentioned injection molding method, it is treated as a "thermoplastic resin" in this specification even if it is generally included in the concept of "thermosetting resin". shall be taken as a thing.

Examples of the thermoplastic resin contained in the resin composition include acrylonitrile-butadiene-styrene resin (ABS resin), acrylonitrile-styrene-acrylate resin (ASA resin), and acrylonitrile-ethylene-propylene-diene-styrene resin (AES resin). Rubber reinforced resins such as polystyrene (PS resin), styrene-acrylonitrile copolymer (AS resin), styrene-maleic anhydride copolymer, (meth)acrylic acid ester-styrene copolymer, etc. Polymers; Olefin resins such as polyethylene (PE resin) and polypropylene; cyclic polyolefin resins; polyester resins; polyamide resins; polycarbonate resins; polyarylate resins; polyacetal resins; polyvinyl chloride, ethylene-vinyl chloride polymers, poly Vinyl chloride resins such as vinylidene chloride; (meth)acrylic resins such as (co)polymers using one or more (meth)acrylic acid esters such as polymethyl methacrylate (PMMA); polyphenylene ether; polyphenylene sulfide; Fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride; Liquid crystal polymers; Imide resins such as polyimide, polyamideimide, and polyetherimide; Ketone resins such as polyetherketone and polyetheretherketone; Polysulfone, polyethersulfone, etc. Sulfone resins; urethane resins; polyvinyl acetate; polyethylene oxide; polyvinyl alcohol; polyvinyl ether; polyvinyl butyral; phenoxy resins; photosensitive resins; biodegradable plastics.

The various thermoplastic resins described above may be contained alone in the resin composition, or may be contained in a mixture of two or more. Here, in this specification, the term "(meth)acrylic" means at least one of acrylic and methacryl. The term "(meth)acrylo" also means at least one of acrylo and methacrylo.

The thermoplastic resin is preferably one or more resins selected from the group consisting of ABS resin, AS resin, PS resin, and PE resin. Thereby, a resin molded article having a desired shape can be molded from the resin composition with a high yield, and thus the resin molded article can be applied to various uses.

The weight average molecular weight (Mw) of the thermoplastic resin is preferably 2,000 to 7,000,000, more preferably 2,000 to 1,000,000. Further, as the thermoplastic resin, it is preferable to use a thermoplastic resin having a glass transition temperature of 280° C. or lower, and it is more preferable to use a thermoplastic resin having a glass transition temperature of 150° C. or lower. Even when the thermoplastic resin has at least one of the above-mentioned weight average molecular weight and glass transition temperature, a resin molded article having a desired shape can be molded from the resin composition with a high yield, thereby making it possible to mold the resin molded article with a high yield. It can be applied to various uses.

<Aluminum flake particles>
The resin composition according to this embodiment contains a thermoplastic resin and aluminum flake particles as described above. A coupling agent is attached to at least a portion of the surface of the aluminum flake particles. As used herein, "aluminum flake particles" refer to particles containing aluminum and having a flat flake shape. That is, the aluminum flake particles may be flaky particles made of aluminum or aluminum alloy, and may be made of metal (such as copper, nickel, iron, tin, or an alloy thereof). The particles may be flaky particles obtained by vapor-depositing aluminum onto a base material of metal or non-metal (ceramic particles such as alumina, titania, glass, mica, etc.). These aluminum flake particles can be obtained by conventionally known methods. The surface of the aluminum flake particles is preferably smooth from the viewpoint of exhibiting desired surface gloss, whiteness, and brightness in the resin composition.

In the resin composition, the aluminum flake particles are preferably included in an amount of 0.5 parts by mass or more and 230 parts by mass or less based on 100 parts by mass of the thermoplastic resin, with a coupling agent to be described later attached to the surface thereof. . When the above-mentioned resin composition contains aluminum flake particles in a content within the above-mentioned range based on 100 parts by mass of the thermoplastic resin, mold contamination can be more fully suppressed. Here, when the resin composition is not prepared in the form of a masterbatch as described below, in the resin composition, the aluminum flake particles are attached to the surface of the thermoplastic resin 100 with the coupling agent described below attached to the surface of the aluminum flake particles. It is preferable that the content is 0.5 parts by mass or more and 50 parts by mass or less based on parts by mass.

When the resin composition is not prepared in the form of a masterbatch as described below, and the content of aluminum flake particles is less than 0.5 parts by mass, the resin composition cannot achieve the desired surface gloss. Tend. In addition, when the content of aluminum flake particles exceeds 50 parts by mass, the dispersibility of the aluminum flake particles in the thermoplastic resin deteriorates, making it impossible to obtain sufficient strength in the resin molded article obtained from the resin composition. Tend. From the viewpoint of achieving the effects of the present invention more fully, when the resin composition is not prepared in the form of a masterbatch as described below, the aluminum flake particles are coated with the thermoplastic resin with the coupling agent attached to the surface. It is more preferable that the amount is 0.5 parts by mass or more and 25 parts by mass or less based on 100 parts by mass of the resin.

On the other hand, the resin composition may be prepared in the form of a masterbatch as described below. In this case, the content of the aluminum flake particles is preferably 5 parts by mass or more and 230 parts by mass or less based on 100 parts by mass of the thermoplastic resin, with a coupling agent to be described later attached to the surface thereof.

The average particle diameter (D50) of the aluminum flake particles is preferably 2 to 150 μm, more preferably 5 to 50 μm. The average thickness (t) of the aluminum flake particles is preferably 0.01 to 10 μm, more preferably 0.08 to 1.6 μm. Furthermore, the average aspect ratio of the aluminum flake particles is preferably 5 to 2,500, more preferably 10 to 150.

Here, the "average aspect ratio" means the ratio of the average particle diameter (D50) and the average thickness (t) of the aluminum flake particles, and specifically, the average particle diameter (D50) of the aluminum flake particles (unit: can be determined from the formula: (μm)/average thickness (t) of aluminum flake particles (unit: μm).

The average particle diameter (D50) and average thickness (t) of aluminum flake particles are determined when a resin composition is the object to be measured, and when a resin molded article is obtained by applying an injection molding method to the resin composition. can be determined by the following measurement methods.

The average particle diameter (D50) and average thickness (t) of aluminum flake particles can be determined by the following method when a resin composition is the object to be measured. That is, by observing pellets of the resin composition using a scanning electron microscope (SEM), the particle size of 50 or more aluminum flake particles is measured, and based on the particle size of the 50 or more particles, the size of the aluminum flake particles is determined. Calculate the average particle size. If it is difficult to observe the particle size of aluminum flake particles using pellets, the surface of the pellets may be polished to form a flat surface, or the pellets may be made into a film using a heat press machine, and these may be subjected to SEM. The average particle size of the aluminum flake particles can be calculated by: The average thickness of the aluminum flake particles can also be calculated by measuring 50 or more aluminum flake particles using a SEM in the same way as the measurement of the average particle size. Even if it is difficult to observe the thickness of the aluminum flake particles using pellets, the surface of the pellets can be polished or made into a film in the same manner as the measurement of the average particle size, and the average thickness of the aluminum flake particles can be measured using SEM using the pellets. can be calculated.

The average particle diameter (D50) and average thickness (t) of aluminum flake particles are calculated by calculating the average particle diameter and average thickness of aluminum flake particles using a resin composition as an object to be measured, when a resin molded object is the object to be measured. The method can be the same. If it is difficult to measure the resin molded product as it is, the above average particle size and average thickness can be determined by cutting the surface of the resin molding to form a flat cross section and observing this cross section using SEM. Can be done.

(coupling agent)
A coupling agent is attached to at least a portion of the surface of the aluminum flake particles. A coupling agent has a reactive group that chemically bonds with an inorganic compound and a reactive group that chemically bonds with an organic compound in one molecule, and has the effect of bonding the inorganic compound and the organic compound through itself. refers to a compound that has This can improve the adhesion between the aluminum flake particles and the thermoplastic resin, and when the above resin composition is used for injection molding, the aluminum flake particles are unevenly distributed on the surface of the molten thermoplastic resin in the mold. can be restrained from doing so.

Here, when the coupling agent is "attached" to the surface of the aluminum flake particles, it means that the coupling agent is bonded to the surface of the aluminum flake particles through a chemical bond due to the reactive group of the coupling agent that chemically bonds with the above-mentioned inorganic compound. It means to do.

The coupling agent is preferably a silane coupling agent. For example, as a silane coupling agent, R _A -Si(OR _B ) ₃ or R _A -SiR _B (OR _B ) ₂ (R _A : alkyl group, aryl group, or alkenyl group having 2 to 18 carbon atoms, R _B : An alkyl group having 1 to 3 carbon atoms) It is preferable to use a silane coupling agent represented by the chemical formula: Furthermore, it is preferable that R _A has a functional group. Examples of the functional group that R _A has include an amino group, a ureido group, an epoxy group, a sulfide group, a vinyl group, a (meth)acryloxy group, a mercapto group, a ketimino group, a glycidyl group, a phenyl group, an imidazole group, an isocyanate group, etc. can do. More preferably, the coupling agent is an amino-based silane coupling agent.

Specific examples of silane coupling agents include γ-methacryloxypropyltrimethoxysilane, vinyltrichlorosilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyl-tris(β-methoxyethoxy)silane, and vinylmethoxysilane. , vinyltrimethoxysilane, vinylethoxysilane, vinyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxy Silane, 3-mercaptopropyltrimethoxysilane, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, N,N'-bis[3-(trimethoxysilyl)propyl ] Ethylenediamine, tetraisocyanatesilane, monomethyltriisocyanatesilane, etc. can be mentioned.

Furthermore, as the above-mentioned coupling agent, it is also possible to use a titanium (titanate) type coupling agent, a zirconia type coupling agent, an aluminum type coupling agent, etc. Specific titanate coupling agents include, for example, isopropyl isostearoyl diacryl titanate, isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, and tetra(2,2-diallyloxymethyl-1-butyl)bis(di- (tridecyl) phosphite titanate and the like. Specific examples of the zirconia coupling agent include tetranormal propoxyzirconium, tetranormal butoxyzirconium, zirconium tetraacetylacetonate, zirconium tributoxyacetylacetonate, zirconium tributoxystearate, and zirconyl acetate. Specific examples of aluminum-based coupling agents include acetalkoxyaluminum diisopropylate, zircoaluminate, alkyl acetoacetate aluminum diisopropylate, acetalkoxyaluminum diisopropylate, and the like.

The coupling agent is preferably contained in an amount of 0.1 parts by mass or more and 10 parts by mass or less based on 100 parts by mass of the aluminum flake particles. The coupling agent is preferably contained in an amount of 0.15 to 3 parts by weight, and even more preferably 0.2 to 2 parts by weight, based on 100 parts by weight of the aluminum flake particles. When the content of the coupling agent is within the above range, the adhesion between the aluminum flake particles and the thermoplastic resin can be further improved.

When the content of the coupling agent is less than 0.1 part by mass based on 100 parts by mass of the aluminum flake particles, the adhesion between the aluminum flake particles and the thermoplastic resin tends to be insufficient. When the content of the coupling agent exceeds 10 parts by mass based on 100 parts by mass of the aluminum flake particles, the aluminum flake particles tend to aggregate easily.

The method for attaching the coupling agent to the surface of the aluminum flake particles is not particularly limited, and any conventionally known method can be used as long as it does not adversely affect the effects of the present invention. For example, the coupling agent can be attached to the surface of the aluminum flake particles by kneading the coupling agent and the aluminum flake particles using a conventionally known kneader, mixer, or stirrer. In this case, an organic solvent can also be added as appropriate. As the organic solvent, for example, one selected from the group consisting of ethanol, isopropyl alcohol, toluene, xylene, MEK, methanol, hexane, butanol, acetone, ethylene glycol, methyl cellosolve, and butyl cellosolve can be used alone. It is also possible to use a mixed solvent obtained by mixing two or more types selected from the group consisting of the above-mentioned organic solvents.

Furthermore, when kneading the coupling agent and aluminum flake particles using a conventionally known kneader or the like, it is preferable to add deionized water as necessary. This makes it easier to attach the coupling agent to the surface of the aluminum flake particles. The amount of deionized water added can be 0.03 to 3 parts by mass per 100 parts by mass of aluminum flake particles. In order to promote the adhesion reaction of the coupling agent to the surface of the aluminum flakes, the temperature inside the cylinder of the kneader containing the coupling agent and the aluminum flake particles is heated to 20 to 80°C, and the kneading The temperature of the kneaded product containing the coupling agent and aluminum flake particles obtained by using a machine can be heated to 20 to 80°C.

(Organic compounds such as fatty acids)
The aluminum flake particles have one or more organic compounds selected from the group consisting of fatty acids such as oleic acid and stearic acid, aliphatic amines, aliphatic amides, aliphatic alcohols, and ester compounds attached to the surface of the aluminum flake particles. Good too. These organic compounds can improve surface gloss by suppressing unnecessary oxidation on the surface of aluminum flake particles. The above organic compound may be added as a grinding aid when aluminum flake particles are obtained by grinding aluminum powder. The content of the organic compound is preferably less than 2 parts by mass per 100 parts by mass of the aluminum flake particles.

When the organic compound such as the fatty acid is attached to the surface of the aluminum flake particles, the coupling agent and the organic compound mix on the surface of the aluminum flake particle due to chemical equilibrium. Or, it is estimated that they exist as coexisting layers.

(Other additives)
The resin composition according to the present embodiment may further contain the following additives depending on the purpose, as long as they do not adversely affect the effects of the present invention. Examples of additives include coloring agents such as mica, colored pigments, phosphorescent pigments, colored dyes, and fluorescent dyes, fillers, antioxidants, anti-aging agents, heat stabilizers, weathering stabilizers, ultraviolet absorbers, and infrared absorbers. agents, photochromic agents, antifouling agents, antistatic agents, plasticizers, lubricants, flame retardants, optical brighteners, light diffusing agents, crystal nucleating agents, flow modifiers, impact modifiers, pigment dispersants, etc. be able to.

[Method for manufacturing resin composition]
The resin composition according to this embodiment can be manufactured by a conventionally known method. For example, the above resin composition can be obtained by the following manufacturing method. That is, first, as described above, by kneading a coupling agent and aluminum flake particles using a kneader or the like, aluminum flakes particles having the coupling agent attached to their surfaces (hereinafter referred to as "coupling agent-attached aluminum flake particles") are formed. ”). Next, the coupling agent-attached aluminum flakes particles and the thermoplastic resin are mixed into a Banbury mixer, a single-screw vented extruder, a twin-screw vented extruder, a kneader, a roll, and a feeder router. The above resin composition can be obtained by melt-kneading using the above melt-kneading machine. The temperature during melt-kneading may be appropriately selected based on the glass transition temperature of the resin used as the thermoplastic resin, and can be, for example, 100 to 300°C.

Here, the resin composition obtained by the above-mentioned manufacturing method is a master batch in which a predetermined amount of aluminum flake particles are filled into a thermoplastic resin in order to obtain better dispersibility of aluminum flake particles in a resin molded article to be described later. It can be prepared in the form of In this case, the content of the aluminum flake particles in the resin composition, with the coupling agent attached to the surface thereof, may be 5 parts by mass or more and 230 parts by mass or less based on 100 parts by mass of the thermoplastic resin. preferable.

[Resin molded body]
The resin molded article according to this embodiment contains the resin composition described above. This makes it possible to provide glittering resin molded bodies in various shapes without contaminating the mold. In the resin molded article, the formation of weld lines is also suppressed. The above-mentioned resin molded body can be used as a glittering resin molded body for housings of electronic devices such as notebook computers and mobile phones, household electric appliances such as vacuum cleaners, electric fans, telephones, and printers, and housings of office equipment. It is suitable for applications such as interior and exterior parts of automobiles, miscellaneous goods, and residential equipment. The resin molded article described above can be used not only as a final product but also as a component in a product. Therefore, the present invention is not limited to the above-mentioned applications, but can be applied to a wide variety of applications.

[Method for manufacturing resin molded body]
The method for producing a resin molded article according to the present embodiment includes a step of preparing the resin composition (first step), and heating the resin composition at a temperature higher than the glass transition temperature of the thermoplastic resin by at least 70°C. The method includes a step of injecting into a mold with an inner wall surface maintained (second step), and a step of obtaining a resin molded body by cooling the resin composition in the mold (third step). By using the method for manufacturing resin molded bodies having these characteristics, it is possible to obtain resin molded bodies of various shapes that have glitter and suppress the formation of weld lines without contaminating the mold. Become. Each of the first to third steps will be explained below.

<First step>
The first step is a step of preparing a resin composition. In this step, the resin composition can be prepared by specifically carrying out the method for producing a resin composition described above.

<Second process>
The second step is a step of injecting the resin composition into a mold whose inner wall surface is maintained at a temperature at least 70° C. higher than the glass transition temperature of the thermoplastic resin. Specifically, in this step, a mold for injection molding is first prepared according to the conventionally known heat and cool method, and the temperature of the inner wall surface of the mold is adjusted using a conventionally known mold temperature control means. The thermoplastic resin is heated to a temperature that is at least 70° C. higher than the glass transition temperature of the thermoplastic resin. Next, the thermoplastic resin contained in the resin composition is melted by heating within the cylinder of a conventionally known injection molding machine. Finally, a resin composition containing a molten thermoplastic resin is injected into a mold whose inner wall surface is maintained at the above temperature.

Thereby, it is possible to prevent the formation of weld lines in the resin molded article obtained by the present manufacturing method. Furthermore, since the adhesion between the aluminum flake particles and the thermoplastic resin is improved by the coupling agent, uneven distribution of the aluminum flake particles on the surface of the molten thermoplastic resin in the mold is also suppressed.

Here, the temperature of the inner wall surface of the mold is preferably a temperature higher than the glass transition temperature of the thermoplastic resin by 70°C or more as described above, and is higher than the glass transition temperature of the thermoplastic resin by more than 80°C. More preferably, the temperature is higher, for example by 90°C or more. The upper limit of the temperature of the inner wall surface of the mold may be set equal to the molding temperature of the thermoplastic resin. The glass transition temperature of a thermoplastic resin can be measured by using differential thermal analysis (DTA).

<3rd process>
The third step is a step of obtaining a resin molded body by cooling the resin composition in the mold. Specifically, in this step, the resin composition injected into the mold is cooled according to a conventionally known heat and cool method. Thereafter, a resin molded body can be obtained by dividing the mold. Since the resin molded article is manufactured using a heat and cool method, it is possible to prevent the formation of weld lines. Furthermore, since the adhesion between the aluminum flake particles and the thermoplastic resin is improved by the coupling agent, the uneven distribution of the aluminum flake particles on the surface of the molten thermoplastic resin in the mold is suppressed, and the split metal Contamination of the mold by aluminum flake particles can be suppressed. Since the resin molded body prevents the aluminum flake particles from being unevenly distributed on the surface of the molten resin, high smoothness can also be obtained on the surface of the resin molded body.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

[Manufacture of resin composition (masterbatch)]
The resin compositions of Examples 1 to 3 and Comparative Examples 1 to 2 were produced by using the following method.

<Example 1>
Aluminum paste prepared in paste form (product name (product number): "5422NS", manufactured by Toyo Aluminum Co., Ltd.) containing aluminum flake particles with an average particle size (d50) of 21 μm and an average thickness (t) of 0.5 μm , solid content 500 g) was dispersed in 2 L of mineral spirit to obtain a dispersion. Aluminum flake particles were obtained by filtering and washing this dispersion. Next, the above aluminum flake particles, 3 g of deionized water, and 3 g of γ-aminopropyltriethoxysilane (trade name (product number): "KBE-903", manufactured by Shin-Etsu Chemical Co., Ltd.) were dissolved in 60 g of isopropyl alcohol. The treated solution was put into a commercially available kneader mixer. Further, these were kneaded for 1 hour in the above-mentioned kneader mixer to obtain a coupling agent-adhered aluminum flake particle dispersion having a solid content of 55% by mass.

730 g of the above coupling agent-attached aluminum flake particle dispersion (solid content 400 g) and 1600 g of acrylonitrile-butadiene-styrene resin (ABS resin, product name (product number): "GA-501", manufactured by Japan A & L Co., Ltd., glass transition (temperature: 90°C) using a mixer to obtain a mixture. This mixture was kneaded and granulated using an extruder (trade name: "ZSK type twin-screw extruder", manufactured by Coperion Co., Ltd.) at a temperature in the cylinder of 190°C to 220°C, and the resin composition was molded into pellets. A masterbatch was manufactured. In this resin composition, the content of aluminum flake particles was 25 parts by mass based on 100 parts by mass of the thermoplastic resin in a state where the coupling agent was attached to the surface.

<Example 2>
The resin composition (masterbatch ) was manufactured.

<Example 3>
The resin composition (masterbatch ) was manufactured.

<Comparative example 1>
A treatment solution containing the above-mentioned coupling agent is applied to the aluminum flake particles contained in a dispersion of the above aluminum paste (product name (product number): "5422NS", manufactured by Toyo Aluminum Co., Ltd., solid content: 500 g) in mineral spirit. An aluminum flake particle dispersion having a solid content of 55% by mass was prepared from the above dispersion without kneading using. Next, a mixture was obtained by mixing the above aluminum flake particle dispersion (solid content: 400 g) and the same ABS resin as in Example 1, and the above mixture was mixed using the same extruder as in Example 1, and the same as in Example 1. By kneading and granulating under the following conditions, a resin composition (masterbatch) molded into pellets was manufactured.

<Comparative example 2>
Resin-coated aluminum paste (product name (product number)) containing aluminum flake particles with an average particle diameter (d50) of 21 μm and an average thickness (t) of 0.5 μm, and the surface of the aluminum flake particles is coated with an acrylic resin. : "FZ5422" manufactured by Toyo Aluminum Co., Ltd.) was prepared. Next, a mixture was obtained by mixing this resin-coated aluminum paste (solid content 400 g) and the same ABS resin as in Example 1, and the mixture was heated using the same extruder as in Example 1 and under the same conditions as in Example 1. A resin composition (masterbatch) molded into pellets was produced by kneading and granulating the resin composition.

[Manufacture of resin molded bodies]
Next, by performing the following steps, the resin compositions of Examples 1 to 3 and Comparative Examples 1 to 2 are prepared from the corresponding Examples 1 to 3 and Comparative Examples 1 to 2. Resin molded bodies of Comparative Example 2 were manufactured.

First, 42 g of the resin composition (masterbatch) and 800 g of the ABS resin were put into a vented twin-screw extruder with a diameter of 20 mm (trade name: "ZSK type twin-screw extruder", manufactured by Coperion Co., Ltd.). A molding resin composition having an aluminum flake particle content of 1% by mass was prepared by melt-mixing and extruding at a temperature of 220° C. in a cylinder (first step). Next, using an injection molding machine (product name: "FNX220III", manufactured by Nissei Jushi Kogyo Co., Ltd.), the above molding resin composition was molded into a rectangular shape with a width of 120 mm, a length of 150 mm, and a thickness of 5 mm with a plurality of through holes. (second step).

In the second step, the temperature inside the cylinder of the injection molding machine was set at 240°C. On the other hand, plate molding molds with inner wall surface temperatures heated to 80°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C and 200°C were prepared, and injection molding was performed. The above molding resin composition was injected from the molding machine into each plate mold.

Furthermore, using a commercially available low-temperature oil temperature controller and water-cooled temperature controller, the temperature of the inner wall surface of each plate molding mold was set to 30°C to cool the molding resin composition in the mold, and then A resin molded body was manufactured by dividing each plate into molds (third step). That is, by performing the third step, the inner wall surface temperature was heated to 80°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C for plate forming. Each resin molded body (10 pieces in total) was manufactured using a mold.

Here, since the plate molding die has a plurality of through holes, a portion where the molten resin joins occurs within the die. For this reason, when injection molding is performed without using the heat and cool method and without heating the inner wall temperature of the mold to at least 70°C higher than the glass transition temperature of ABS resin, the molten resin in the mold of the resin molded product is A weld line may be formed at a location corresponding to the merging portion.

[Evaluation of resin molded body]
<Visual confirmation of weld line formation>
It was visually observed whether weld lines were formed on the surfaces of the resin molded bodies of Examples 1 to 3 and Comparative Examples 1 to 2. As a result, Examples 1 to 3 and comparative examples were obtained using a plate molding die in which the inner wall surface temperature was heated to 160°C or higher, which is at least 70°C higher than the glass transition temperature of ABS resin. No weld lines were observed on the surfaces of the resin molded bodies of Comparative Examples 1 to 2. On the other hand, on the surfaces of the resin molded bodies of Examples 1 to 3 and Comparative Examples 1 to 2, which were obtained using a plate molding die whose inner wall surface temperature was heated to 150°C or less, Weld lines were observed in both cases.

<Confirmation of mold contamination>
A transparent adhesive tape (product name: "Cello Tape (registered trademark)", manufactured by Nichiban Co., Ltd.) with a length of 80 mm and a width of 24 mm was applied to the surface of each resin molded body of Examples 1 to 3 and Comparative Examples 1 to 2. ) and rubbed the tape with a fingertip to bring the transparent adhesive tape into close contact with the surface of each resin molded product of Examples 1 to 3 and Comparative Examples 1 to 2, and then The transparent adhesive tape was peeled off at 180 degrees. Next, the transparent adhesive tape that had been peeled off from the surface of the resin molded body was attached to a black mount, and the tape was peeled off at a magnification of 500 times using a digital microscope (product name: "VHX-6000", manufactured by Keyence Corporation). The number of aluminum flake particles adhering to the transparent adhesive tape was determined. The evaluation was performed in one field of view (400 μm x 600 μm) and ranked based on the following criteria. The results are shown in Table 1. Here, the number of aluminum flake particles attached to the above transparent adhesive tape shows a positive correlation with the number of aluminum flake particles that are unevenly distributed on the surface of the molten resin in the mold and cause mold contamination. It is estimated that Therefore, by determining the number of aluminum flake particles attached to the transparent adhesive tape and ranking them based on the following criteria, each resin of Examples 1 to 3 and Comparative Examples 1 to 2 was evaluated. It becomes possible to evaluate whether the composition can suppress mold contamination when injection molding using the heat and cool method is performed.

A: The number of aluminum flake particles is 3 or less, and it is estimated that mold contamination can be suppressed more fully.
B: The number of aluminum flake particles is 4 to 10, and it is estimated that mold contamination can be suppressed.
C: The number of aluminum flake particles is 11 or more, and it is estimated that mold contamination is insufficiently suppressed.

[Consideration]
From the above, the resin compositions of Examples 1 to 3 and the resin molded articles containing the same were injection molded using a mold heated to at least 70°C higher than the glass transition temperature of the thermoplastic resin. In this case, the formation of weld lines can be prevented to the same extent as in the conventional resin molded bodies (Comparative Examples 1 and 2). Further, according to Table 1, the resin compositions of Examples 1 to 3 and resin molded articles containing the same were injected using a mold heated to at least 70°C higher than the glass transition temperature of the thermoplastic resin. It is understood that when molding is performed, uneven distribution of aluminum flake particles on the surface of the molten resin can be suppressed compared to Comparative Examples 1 and 2, thereby suppressing mold contamination.

Although the embodiments and examples of the present invention have been described above, it is planned from the beginning to combine the configurations of the above-described embodiments and examples as appropriate.

The embodiments and examples disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and it is intended that all changes within the meaning and range equivalent to the claims are included.

Claims (8)

A resin composition used for manufacturing an injection molded article,
The resin composition contains a thermoplastic resin and aluminum flake particles,
The aluminum flake particles have an average particle size of 2 μm or more and 150 μm or less, and an average thickness of 0.01 μm or more and 10 μm or less ,
A resin composition, wherein a coupling agent is attached to at least a portion of the surface of the aluminum flake particles, and the coupling agent increases the adhesion between the thermoplastic resin and the aluminum flake particles. The resin composition according to claim 1, wherein the coupling agent is a silane coupling agent. The resin composition according to claim 1 or 2, wherein the coupling agent is an amino-based silane coupling agent. The resin composition according to any one of claims 1 to 3, wherein the coupling agent is contained in an amount of 0.1 parts by mass or more and 10 parts by mass or less based on 100 parts by mass of the aluminum flake particles. The aluminum flake particles are contained in an amount of 0.5 parts by mass or more and 230 parts by mass or less based on 100 parts by mass of the thermoplastic resin with the coupling agent attached to the surface thereof. The resin composition according to any one of the items. According to any one of claims 1 to 5, the thermoplastic resin is one or more resins selected from the group consisting of acrylonitrile-butadiene-styrene resin, styrene-acrylonitrile copolymer, polystyrene, and polyethylene. The resin composition described. A resin molded article comprising the resin composition according to any one of claims 1 to 6. A step of preparing the resin composition according to any one of claims 1 to 6;
Injecting the resin composition into a mold whose inner wall surface is maintained at a temperature higher than the glass transition temperature of the thermoplastic resin by at least 70°C;
A method for producing a resin molded body, the method comprising: obtaining a resin molded body by cooling the resin composition in the mold.