JP7837766B2 - Additives for recycled polyamide resins and recycled polyamide resin compositions - Google Patents

Description

This invention relates to an additive for recycled polyamide resins and a recycled polyamide resin composition containing the additive.

Polyamide resins such as nylon-6, nylon-6, and nylon-12 possess excellent physical properties such as heat resistance and abrasion resistance, and also exhibit superior resistance to hydrocarbon solvents such as gasoline and oil. Therefore, they are used in a variety of molding applications, including machine parts, automotive parts, and electrical and electronic components.

However, polyamide resins exhibit a significant decrease in melt viscosity and melt tension at temperatures above their melting point. Therefore, when applied to melting processes performed at temperatures above the melting point, such as blow molding, extrusion molding, and foam molding, problems can arise that make molding difficult. Specifically, in blow molding and extrusion molding, problems such as uneven wall thickness due to drawdown can occur, and in foam molding, problems such as uneven cell structure can occur.

Patent Document 1 describes adding a thickening agent (B) to a polyamide resin to increase its melt viscosity. This thickening agent is provided by coating the polyamide resin with 100 parts by weight of reactive polymer particles (B-1) having a glass transition temperature of 60°C or higher and a volume-average particle diameter in the range of 50 to 500 μm, and 0.5 to 30 parts by weight of polymer particles (B-2) having a volume-average particle diameter of 0.01 to 0.5 μm. In the examples, a monomer (glycidyl methacrete) having epoxy groups is used in the production of polymer particles (B-1), and therefore, polymer particles (B-1) have epoxy groups. Furthermore, their weight-average molecular weight is disclosed as 52,000 to 67,000.

Patent Document 2 does not describe melt viscosity, but it describes the use of 80 to 99 parts by weight of a core-shell polymer and 1 to 20 parts by weight of a copolymer of alkyl (meth)acrylate and an unsaturated carboxylic acid as an impact resistance modifier for polyamide resins. The molecular weight of the copolymer is not disclosed.

Meanwhile, with growing concern for resource reuse and environmental protection, recycling is being demanded in various fields. Regarding polyamide resins, efforts to collect used waste and reuse it as recycled polyamide resin are attracting attention.

Japanese Patent Publication No. 2007-31607 Japanese Unexamined Patent Publication No. 63-61013

As mentioned above, polyamide resins require improved moldability during melt processing. Simultaneously, there is also a need to improve the tensile properties of the resulting molded articles.
However, the technologies described in Patent Document 1 or 2 were insufficient to improve the formability during melt processing and to further improve the tensile properties of the molded article.

In view of the above situation, the present invention aims to provide an additive for recycled polyamide resins and a recycled polyamide resin composition containing the additive, which can improve the moldability of recycled polyamide resins during melt processing and improve the tensile properties of molded articles containing recycled polyamide resins.

The inventors of this invention discovered that by incorporating a copolymer containing specific constituent monomers and having an average molecular weight within a specific range into a recycled polyamide resin, the moldability of the recycled polyamide resin during melt processing is improved, and furthermore, the tensile properties of the resulting molded article are improved, leading to the present invention.

In other words, the present invention is an additive for recycled polyamide resin comprising a first polymer, wherein the first polymer comprises (i) a carboxyl group-containing vinyl monomer, and
(ii) (meth)acrylic acid monomers and/or aromatic vinyl monomers,
The present invention relates to an additive for recycled polyamide resins, comprising a copolymer in which the first polymer has a number average molecular weight of 2,000 to 25,000.
Preferably, the carboxyl group-containing vinyl monomer accounts for 15% to 50% by weight of 100% by weight of the first polymer.
Preferably, the first polymer is a copolymer comprising (i) a carboxyl group-containing vinyl monomer and (ii) a (meth)acrylic acid ester monomer as constituent monomers.
Preferably, the additive for the recycled polyamide resin has a weight-average molecular weight of 30,000 or more.
Preferably, the first polymer constitutes particles, and at least a portion of the second copolymer is located on the outside of the particles.
Preferably, the second polymer is a polymer containing a methacrylate monomer and/or an aromatic vinyl monomer as constituent monomers.
Preferably, the sum of the methacrylic acid ester monomer and the aromatic vinyl monomer accounts for 50% to 100% by weight of the second polymer (100% by weight).
Preferably, the first polymer and/or the second polymer is a non-rubber polymer.
Preferably, the first polymer and the second polymer are both non-rubber polymers, the first polymer constitutes particles, and at least a portion of the second polymer is located on the outside of the particles.
The present invention also relates to a modifier for recycled polyamide resins, comprising the aforementioned additive and an impact strength modifier. Preferably, the impact strength modifier is a core-shell type impact strength modifier. Preferably, the impact strength modifier is a polyolefin-based elastomer.
Furthermore, the present invention relates to a recycled polyamide resin composition containing a recycled polyamide resin and an additive for the recycled polyamide resin, wherein the proportion of the additive to the total of the recycled polyamide resin and the additive is 0.1 to 10% by weight, and also to a recycled polyamide resin composition containing a recycled polyamide resin and a modifier for the recycled polyamide resin, wherein the proportion of the modifier to the total of the recycled polyamide resin and the modifier is 1 to 40% by weight.
Preferably, the recycled polyamide resin composition further contains a reinforcing material, wherein the proportion of the reinforcing material is 10 to 60% by weight relative to 100% by weight of the total of the recycled polyamide resin and the reinforcing material.
Furthermore, the present invention also relates to pellets or molded articles made of the recycled polyamide resin composition.

According to the present invention, it is possible to provide an additive for recycled polyamide resins and a recycled polyamide resin composition containing the additive, which can improve the moldability of recycled polyamide resins during melt processing and improve the tensile properties of molded articles containing recycled polyamide resins. According to a preferred embodiment of the present invention, the additive for recycled polyamide resins can reduce the fluidity of the recycled polyamide resin during melting, and further increase the melt viscosity or melt tension of the recycled polyamide resin. Furthermore, the additive for recycled polyamide resins can be blended with an impact strength modifier to the recycled polyamide resin, thereby further enhancing the impact resistance improvement effect of the impact strength modifier in addition to the effects described above.

The embodiments of the present invention will be described in detail below.

(Additive for recycled polyamide resins)
The additive for recycled polyamide resin of this embodiment contains at least a first polymer. The additive for recycled polyamide resin according to a preferred embodiment preferably contains a second polymer in addition to the first polymer, as it exhibits excellent granulation properties during the manufacture of the additive. The additive for recycled polyamide resin is used by being blended with recycled polyamide resin and may be a molecular chain elongator for the recycled polyamide resin, an agent that improves the moldability of the recycled polyamide resin during melt processing, or an agent that improves the tensile properties of a molded article containing recycled polyamide resin.

(first polymer)
The first polymer is a copolymer comprising a carboxyl group-containing vinyl monomer and a (meth)acrylic acid ester monomer and/or an aromatic vinyl monomer as constituent monomers.

The first polymer has carboxyl groups derived from the carboxyl group-containing vinyl monomer. When the recycled polyamide resin and the first polymer are mixed by melt kneading or other means, the carboxyl groups of the first polymer can react with the terminal amino groups of the recycled polyamide resin. This reaction elongates the molecular chains of the recycled polyamide resin, and in addition, a branched structure may be introduced into the recycled polyamide resin. It is presumed that this mechanism improves the moldability of the recycled polyamide resin during melt processing and further improves the tensile properties of the resulting molded article. On the other hand, when a polymer having epoxy groups instead of carboxyl groups was blended with the recycled polyamide resin, the effect of improving the moldability of the recycled polyamide resin during melt processing was not sufficient.

The carboxyl group-containing vinyl monomer is not particularly limited, but examples include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid. One of these may be used, or two or more may be used in combination. Of these, acrylic acid and/or methacrylic acid are preferred, and methacrylic acid is more preferred.

The content of the carboxyl group-containing vinyl monomer can be appropriately set from the viewpoint of improving moldability during melt processing, improving the tensile properties of the molded article, and productivity. The content may be, for example, 10% by weight or more of 100% by weight of the first polymer, but it is preferably 15% by weight or more, and more preferably 20% by weight or more. Within this range, the effect of improving moldability during melt processing is particularly excellent. However, if the content of the carboxyl group-containing vinyl monomer is too high, the water content of the first polymer increases, making post-processing during production complicated. Therefore, the content is preferably 50% by weight or less, and more preferably 45% by weight or less.

From the viewpoint of productivity, the first polymer contains, as a constituent monomer, either or both of the following: a carboxyl group-containing vinyl monomer, a (meth)acrylic acid ester monomer, and an aromatic vinyl monomer. It is preferable that the first polymer contains a (meth)acrylic acid ester monomer because it exhibits excellent effects in improving the moldability of recycled polyamide resins during melt processing and improving the tensile properties of molded articles.

The (meth)acrylate monomer is not particularly limited, but examples include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate. Among these, alkyl (meth)acrylate monomers are preferred, alkyl (meth)acrylate monomers with 1 to 4 carbon atoms in the alkyl group are more preferred, and methyl methacrylate is particularly preferred.

The aromatic vinyl monomer is not particularly limited, but examples include styrene, α-methylstyrene, and p-methylstyrene. Among these, styrene is preferred.

The higher the molecular weight of the first polymer, the more preferable it is from the viewpoint of improving moldability during melt processing and improving the tensile properties of the molded article. Specifically, the number-average molecular weight of the first polymer is preferably in the range of 2,000 to 25,000, measured by gel permeation chromatography (GPC) in terms of polystyrene-equivalent molecular weight. If the number-average molecular weight is less than 2,000, the thermal stability of the polymer may be insufficient. If the number-average molecular weight exceeds 25,000, the stability of the latex may decrease during polymer production, making efficient production difficult. Polymers with a number-average molecular weight of 25,000 or less can be suitably produced using a chain transfer agent during polymerization.

The first polymer is preferably a non-rubber polymer. A non-rubber polymer is a polymer that does not have cross-linking structures between its molecular chains. By using a non-rubber polymer, the reaction between the carboxyl groups of the first polymer and the terminal amino groups of the recycled polyamide resin proceeds more efficiently, making it easier to achieve improved moldability during melt processing and improved tensile properties of the molded article.

(Second double combination)
The aforementioned second polymer is an optional component that can improve granulation during manufacturing. Because the first polymer has a small molecular weight, when it is powdered alone, it becomes a fine powder, which can be difficult to handle. Therefore, in order to obtain the first polymer as a powder with an appropriate particle size that is easy to handle, it is desirable to manufacture the first polymer together with the second polymer, which has a larger molecular weight, and then isolate the first polymer together with the second polymer. Furthermore, the presence of the second polymer improves the dispersibility of the first polymer in the recycled polyamide resin, allowing the reaction between the recycled polyamide resin and the first polymer to proceed efficiently, thereby further improving the moldability of the recycled polyamide resin during melt processing.

From the viewpoint of improving granulation properties, the weight-average molecular weight of the second polymer is preferably 100,000 or more, measured as polystyrene-equivalent molecular weight by GPC. More preferably, it is 150,000 or more, and even more preferably 180,000 or more. While there is no particular upper limit, it is preferably 1,000,000 or less, more preferably 700,000 or less, and even more preferably 500,000 or less.

The monomers constituting the second polymer are not particularly limited, but it is preferable that they include a methacrylic acid ester monomer and/or an aromatic vinyl monomer. From the viewpoint of improving moldability during melt processing and improving the tensile properties of the molded article, it is more preferable to include an aromatic vinyl monomer. Furthermore, from the viewpoint of polymerization conversion rate and granulation properties, it is even more preferable to include a methacrylic acid ester monomer.

The methacrylate monomer is not particularly limited, but examples include alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate; and hydroxyalkyl methacrylates such as 2-hydroxyethyl methacrylate. Among these, alkyl methacrylate monomers are preferred, alkyl methacrylate monomers with 1 to 4 carbon atoms in the alkyl group are more preferred, and methyl methacrylate is particularly preferred.

The aromatic vinyl monomer is not particularly limited, but examples include styrene, α-methylstyrene, and p-methylstyrene. Among these, styrene is preferred.

The total content of the methacrylic acid ester monomer and aromatic vinyl monomer is preferably 50% to 100% by weight of the second polymer, more preferably 55% to 95% by weight, and even more preferably 60% to 90% by weight.

From the viewpoint of improving granulation properties, the second polymer preferably contains an acrylic acid ester monomer in addition to the methacrylic acid ester monomer and/or aromatic vinyl monomer.

The acrylic acid ester monomer is not particularly limited, but examples include alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; and hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate. Among these, alkyl acrylate monomers are preferred, alkyl acrylate monomers with 1 to 4 carbon atoms in the alkyl group are more preferred, and butyl acrylate is particularly preferred.

From the viewpoint of improving granulation properties, the content of the acrylic acid ester monomer is preferably 0% to 50% by weight, more preferably 5% to 45% by weight, and even more preferably 10% to 40% by weight, of 100% by weight of the second polymer.

The second polymer is preferably a non-rubber polymer. The non-rubber polymer allows the reaction between the carboxyl groups of the first polymer and the terminal amino groups of the recycled polyamide resin to proceed more efficiently, making it easier to achieve improved moldability during melt processing and improved tensile properties of the molded article.

A preferred embodiment of the additive for recycled polyamide resin may contain the first polymer and the second polymer, and the relationship between the two polymers is not particularly limited. However, from the viewpoint of improving granulation, it is preferable that the first polymer constitutes the particles and at least a portion of the second polymer is located on the outside of the particles. At least a portion of the second polymer may coat the outer surface of the particles. Alternatively, a portion of the second polymer may be located on the outside of the particles, and the remainder may be impregnated into the interior of the particles.

Furthermore, it is preferable that the first and second polymers are not chemically bonded together. In this case, by kneading the additive with the recycled polyamide resin, it is considered that the first and second polymers exist separately from each other within the recycled polyamide resin matrix.

In the additive for recycled polyamide resin, the proportion of the first polymer to the total of the first and second polymers can be set as appropriate, but for example, it may be 10 to 100% by weight, preferably 20 to 90% by weight, and more preferably 30 to 80% by weight.

The weight-average molecular weight of the entire additive for the recycled polyamide resin is preferably 30,000 or more, measured by GPC in terms of polystyrene-equivalent molecular weight. More preferably, it is 40,000 or more, and even more preferably 50,000 or more. While there is no particular upper limit, it is preferably 1,000,000 or less, more preferably 500,000 or less, and even more preferably 300,000 or less.

The additive for recycled polyamide resin according to this embodiment is used by being blended with recycled polyamide resin and can improve the moldability of the recycled polyamide resin during melt processing and improve the tensile properties of the molded article containing the recycled polyamide resin. The amount of the additive blended with the recycled polyamide resin can be appropriately set, but it is preferable that the ratio of the additive to the total of the recycled polyamide resin and the additive is 0.1% by weight or more and 10% by weight or less. When the ratio of the additive is within this range, the effects of improving moldability during melt processing and improving the tensile properties of the molded article can be suitably achieved while maintaining the unique physical properties of the recycled polyamide resin. The ratio is more preferably 0.2 to 8% by weight, and even more preferably 0.3 to 5% by weight. Furthermore, since the effect of improving the tensile properties of the molded article is significant, it is particularly preferable that the ratio be 1.5% by weight or more.

(Method for manufacturing additives for recycled polyamide resins)
The method for producing the additive for recycled polyamide resin can be a conventional polymerization method and is not particularly limited. For example, bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc., can be used, but emulsion polymerization is preferred. When producing the first polymer, it is preferable to carry out polymerization in the presence of a chain transfer agent in order to control the molecular weight. Furthermore, when producing the first polymer and the second polymer in succession, first, the latex of the first polymer is produced by emulsion polymerization, and then monomer components for the second polymer and polymerization initiators are added to the latex to polymerize the monomer components.

The chain transfer agents that can be used in the production of the first polymer are not particularly limited, but include primary mercaptan chain transfer agents such as n-butyl mercaptan, n-octyl mercaptan, n-hexadecyl mercaptan, n-dodecyl mercaptan, and n-tetradecyl mercaptan; secondary mercaptan chain transfer agents such as sec-butyl mercaptan and sec-dodecyl mercaptan; tertiary mercaptan chain transfer agents such as t-dodecyl mercaptan; and mercaptan compounds, 2-ethyl mercaptans, etc. Examples include thioglycolic acid esters such as hexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris (thioglycolate), and pentaerythritol tetrakiss (thioglycolate), as well as thiophenol, tetraethyl thiuram disulfide, pentanephenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, ethylene bromide, styrene oligomers such as α-methylstyrene dimer, and terpinolenes. These may be used individually or in combination of two or more. The amount of chain transfer agent used should be appropriately set according to the desired number-average molecular weight of the first polymer.

The emulsifier (dispersant) that can be used in emulsion polymerization is not particularly limited, and anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, etc. may be used. In addition, dispersants such as polyvinyl alcohol, alkyl-substituted cellulose, polyvinylpyrrolidone, and polyacrylic acid derivatives may be used.
The anionic surfactants among the emulsifiers mentioned above are not particularly limited, but examples include the following compounds: fatty acid soaps such as potassium laurate, potassium coconut fatty acid, potassium myristate, potassium oleate, potassium oleate diethanolamine salt, sodium oleate, potassium palmitate, potassium stearate, sodium stearate, mixed fatty acid sodium soap, semi-hardened beef tallow fatty acid sodium soap, castor oil potassium soap; and sodium dodecyl sulfate, higher alcohol sodium sulfate, dodecyl sulfate triethanolamine, dodecyl sulfate ammonium, polyoxyethylene alkyl ether sulfate sodium, polyoxyethylene alkyl ether sulfate triethanolamine, polyoxyethylene alkylphenyl ether sulfate sodium, 2-ethylhexyl sulfate sodium. Sodium methyl sulfate; sodium alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate; sodium dialkyl sulfosuccinates such as sodium di-2-ethylhexyl sulfosuccinate; sodium alkylnaphthalene sulfonate; sodium alkyldiphenyl ether disulfonate; potassium alkyl phosphate; phosphate ester salts such as sodium polyoxyethylene lauryl ether phosphate; sodium salts of naphthalene sulfonic acid formalin condensate; polycarboxylic acid type polymer anions; sodium acyl (beef tallow) methyl taurate; sodium acyl (coconut) methyl taurate; sodium cocoyl isethionate; sodium α-sulfo fatty acid esters; sodium amide ether sulfonate; oleyl sarcosine; sodium lauroyl sarcosinate; rosinic acid soap, etc.

Furthermore, while the nonionic surfactants among the emulsifiers mentioned above are not particularly limited, examples include the following compounds: polyoxyethylene alkyl allyl ethers or polyoxyethylene alkyl ethers such as polyoxyethylene nonylphenyl ether, polyoxyethylene oleyl ether, and polyoxyethylene lauryl ether; polyoxyethylene sorbitan esters such as polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan monostearate; polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate, polyethylene glycol monostearate, and polyethylene glycol monooleate; and oxyethylene/oxypropylene block copolymers.

Furthermore, while the cationic surfactants among the emulsifiers mentioned above are not particularly limited, examples include the following compounds: alkylamine salts such as coconutamine acetate, stearylamine acetate, octadecylamine acetate, and tetradecylamine acetate; and quaternary ammonium salts such as lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, distearyldimethylammonium chloride, alkylbenzyldimethylammonium chloride, hexadecyltrimethylammonium chloride, and behenyltrimethylammonium chloride.

Furthermore, while the amphoteric surfactants among the emulsifiers mentioned above are not particularly limited, examples include the following compounds: alkyl betaines such as lauryl betaine, stearyl betaine, and dimethyl lauryl betaine; sodium lauryl diaminoethylglycine; amide betaine; imidazoline; lauryl carboxymethyl hydroxyethyl imidazolinium betaine, etc.

These emulsifiers (dispersants) may be used individually or in combination of two or more.

When employing emulsion polymerization, known polymerization initiators, such as 2,2'-azobisisobutyronitrile, hydrogen peroxide, potassium persulfate, and ammonium persulfate, can be used as thermal decomposition initiators.

Furthermore, redox-type initiators can also be used, which combine peroxides such as organic peroxides (e.g., t-butyl peroxyisopropyl carbonate, paramenthane hydroperoxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-hexyl peroxide) and inorganic peroxides (e.g., hydrogen peroxide, potassium persulfate, ammonium persulfate) with, if necessary, reducing agents such as sodium formaldehyde sulfoxylate and glucose, transition metal salts such as iron(II) sulfate, chelating agents such as disodium ethylenediaminetetraacetate, and phosphorus-containing compounds such as sodium pyrophosphate.

When a redox-type initiator is used, polymerization can be carried out even at low temperatures where the peroxide does not substantially decompose thermally, allowing the polymerization temperature to be set over a wide range, which is preferable. Among these, it is preferable to use organic peroxides such as cumene hydroperoxide, dicumyl peroxide, and t-butyl hydroperoxide as redox-type initiators. The amount of the initiator used, and when a redox-type initiator is used, the amounts of the reducing agent, transition metal salt, chelating agent, etc., can be used within known ranges. Furthermore, when polymerizing monomers having two or more radically polymerizable double bonds, known chain transfer agents can be used within known ranges. Additionally, surfactants can be used, but this is also within known ranges.

The solvent used during emulsion polymerization can be any solvent that allows the emulsion polymerization to proceed stably; for example, water can be suitably used.

The temperature during emulsion polymerization is not particularly limited, as long as the emulsifier is uniformly dissolved in the solvent. For example, it is 40 to 75°C, preferably 45 to 73°C, and more preferably 49 to 71°C.

When the additive for recycled polyamide resin is manufactured by emulsion polymerization, for example, the latex of the additive can be solidified by mixing it with an acid such as hydrochloric acid or a divalent or higher metal salt such as calcium chloride, magnesium chloride, magnesium sulfate, aluminum chloride, or calcium acetate. Then, the additive can be separated from the aqueous medium by heat treatment, dehydration, washing, and drying according to known methods. The obtained additive is preferably washed with water and/or an organic solvent.

Alternatively, the additive can be isolated by adding an alcohol such as methanol, ethanol, or propanol, or a water-soluble organic solvent such as acetone, to the latex of the additive to precipitate it. After separating the additive from the solvent by centrifugation or filtration, it can be dried. Another method involves adding a slightly water-soluble organic solvent, such as methyl ethyl ketone, to the latex of the additive to extract the additive from the latex into the organic solvent layer. After separating the organic solvent layer, the additive can be precipitated by mixing it with water or other solvents.

Furthermore, the latex additive can be directly powdered by spray drying. The resulting powder is preferably washed with water and/or an organic solvent. Alternatively, calcium chloride, magnesium chloride, magnesium sulfate, aluminum chloride, etc., can be added to the resulting powder, preferably as a solution such as an aqueous solution, and re-dried as necessary to achieve the same effect as the washing described above.

(Modifier for recycled polyamide resins)
The modifier for recycled polyamide resin in this embodiment includes the above-mentioned additive for recycled polyamide resin and an impact strength modifier. The impact strength modifier is not particularly limited and may be one of conventionally known types. Specifically, it is desirable to select one or more from the group consisting of core-shell type impact strength modifiers, polyolefin-based elastomers, polyester elastomers, and polyamide elastomers. Among these, core-shell type impact strength modifiers or polyolefin-based elastomers are preferred.

The aforementioned core-shell type impact strength modifier is composed of polymer particles that are graft copolymers. These polymer particles consist of a shell layer and one or more core layers. The shell layer refers to the polymer layer located on the surface side of the polymer particles and is also called the graft layer. The core layer refers to the polymer layer located inside the polymer particles beyond the shell layer and is composed of a rubbery polymer. The core layer may be a single layer or may consist of two or more layers with different monomer compositions. The shell layer covers the surface of the core layer, but is not limited to covering the entire surface of the core layer; it is sufficient to cover at least a portion of the core layer's surface.

(Core layer)
The core layer is composed of a rubbery polymer. The rubbery polymer preferably contains one or more selected from the group consisting of natural rubber, diene rubber, acrylate rubber, and polyorganosiloxane rubber, and more preferably contains one or more selected from the group consisting of diene rubber, acrylate rubber, and polyorganosiloxane rubber.

(Diene-based rubber)
Diene rubber is an elastic body that contains constituent units derived from diene monomers as its constituent units. The core layer is more preferably made of diene rubber, and particularly preferably made of diene rubber, because it can lower the glass transition temperature of the resulting elastic body, significantly improve the impact resistance of the resulting recycled polyamide resin composition to the molded article, and has low raw material costs.

Examples of diene monomers include 1,3-butadiene, isoprene(2-methyl-1,3-butadiene), and 2-chloro-1,3-butadiene. These diene monomers may be used individually or in combination of two or more.

Diene rubber may further contain, as constituent units, constituent units derived from vinyl monomers other than diene monomers that are copolymerizable with diene monomers.

Examples of vinyl monomers other than diene monomers that can copolymerize with diene monomers (hereinafter also referred to as vinyl monomer A) include: (a) aromatic vinyl monomers such as styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene; (b) vinyl carboxylic acids such as acrylic acid and methacrylic acid; (c) alkyl (meth)acrylates such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate; (d) methacrylate Examples include hydroxyl group-containing vinyl monomers such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; (e) glycidyl group-containing vinyl monomers such as glycidyl methacrylate and 4-hydroxybutyl acrylate glycidyl ether; (f) unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile; (g) vinyl halides such as vinyl chloride, vinyl bromide, and chloroprene; (h) vinyl acetate; and (i) alkenes such as ethylene, propylene, butylene, and isobutylene. The vinyl monomer A described above may be used alone or in combination of two or more types.

The content of constituent units derived from vinyl monomer A in the diene rubber is not particularly limited. Preferably, the diene rubber contains 50 to 100% by weight of constituent units derived from the diene monomer and 0 to 50% by weight of constituent units derived from vinyl monomer A, based on 100% by weight of constituent units.

The diene rubber may further contain constituent units derived from polyfunctional monomers such as diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, allyl methacrylate, ethylene glycol dimethacrylate, and 1,3-butylene dimethacrylate. That is, these polyfunctional monomers may be used in the polymerization of the diene rubber.

Suitable examples of diene-based rubbers include butadiene rubber (polybutadiene rubber), styrene/butadiene copolymer rubber (poly(styrene/butadiene) rubber), poly(acrylonitrile/butadiene) rubber, and butadiene/acrylic acid ester copolymer. Butadiene rubber is an elastic material containing 50 to 100% by weight of 1,3-butadiene-derived constituent units out of 100% by weight of its constituent units.

The diene rubber is preferably a butadiene rubber containing 50 to 100% by weight of structural units derived from 1,3-butadiene and 0 to 50% by weight of structural units derived from vinyl monomer A, and more preferably a 1,3-butadiene homopolymer containing 100% by weight of structural units derived from 1,3-butadiene.

Because the resulting elastic material has a low glass transition temperature, the resulting recycled polyamide resin composition exhibits a significant improvement in impact resistance to molded articles, and the raw material costs are low, the core layer is more preferably made of butadiene rubber, and particularly preferably of butadiene rubber.

(Acrylate-based rubber)
Acrylate-based rubber is an elastic material that contains constituent units derived from (meth)acrylate monomers.

Examples of (meth)acrylate monomers include (a) alkyl (meth)acrylate esters having an alkyl group with 1 to 22 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate; (b) aromatic ring-containing (meth)acrylate esters such as phenoxyethyl (meth)acrylate and benzyl (meth)acrylate; (c) hydroxyalkyl (meth)acrylate esters such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; (d) glycidyl group-containing (meth)acrylate esters such as glycidyl (meth)acrylate and glycidyl alkyl (meth)acrylate; and (e) alkoxyalkyl (meth)acrylate esters. These (meth)acrylate monomers may be used individually or in combination of two or more.

Acrylate-based rubber may further contain, as constituent units, constituent units derived from vinyl monomers other than (meth)acrylate monomers that are copolymerizable with (meth)acrylate monomers. Examples of vinyl monomers other than (meth)acrylate monomers that are copolymerizable with (meth)acrylate monomers include (a) the diene monomers described above, and (b) monomers other than (meth)acrylate monomers among vinyl monomer A.

The aforementioned acrylic rubber has a crosslinked structure. To introduce a crosslinked structure, for example, a crosslinking agent and/or a graft crossing agent can be used when polymerizing monomer components to synthesize the polymer of the core layer. Examples of crosslinking agents and graft crossing agents include: (a) allylalkyl (meth)acrylates such as allyl (meth)acrylate and allylalkyl (meth)acrylate; (b) polyfunctional (meth)acrylates such as monoethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate; and (c) polyfunctional monomers such as diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, and divinylbenzene. These crosslinking agents and graft crossing agents may be used individually or in combination of two or more.

Suitable acrylate-based rubbers include butyl polyacrylate rubber and butyl acrylate/2-ethylhexyl acrylate copolymer rubber. Butyl polyacrylate rubber is an elastic material containing 50 to 100% by weight of butyl acrylate components out of 100% by weight of its constituent units.

Suitable examples of polyorganosiloxane-based rubbers include silicone rubber and silicone/acrylate-based rubbers.

Examples of silicone rubbers include polymethyl silicone rubber and polymethylphenyl silicone rubber. Examples of silicone/acrylate-based rubbers include polyorganosiloxane/butyl acrylate copolymers.

In one embodiment, the core layer preferably contains one or more materials selected from the group consisting of butadiene rubber, styrene/butadiene copolymer rubber, acrylate-based rubber, and silicone rubber.

(Shell layer)
The shell layer is preferably formed from a polymer containing constituent units derived from vinyl monomers. Examples of vinyl monomers include aromatic vinyl compounds, vinyl cyanide compounds, unsaturated carboxylic acid esters, acrylamide monomers, and maleimide monomers.

Suitable examples of the aromatic vinyl compound include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, t-butylstyrene, α-methylvinyltoluene, dimethylstyrene, chlorostyrene, dichlorostyrene, bromostyrene, and dibromostyrene.

Suitable examples of the aforementioned vinyl cyanide compound include acrylonitrile, methacrylonitrile, and ethacrylonitrile.

The unsaturated carboxylic acid esters mentioned above are preferably (a) alkyl acrylates having an alkyl group with 1 to 22 carbon atoms, such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, dodecyl acrylate, stearyl acrylate, and behenyl acrylate; (b) alkyl methacrylates having an alkyl group with 1 to 22 carbon atoms, such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, dodecyl methacrylate, stearyl methacrylate, and behenyl methacrylate; and (c) alkoxyalkyl methacrylates having an alkyl group with 1 to 22 carbon atoms and an alkoxyl group, such as methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxymethyl (meth)acrylate, and ethoxyethyl (meth)acrylate.

Suitable examples of the acrylamide monomer include acrylamide, methacrylamide, and N-methylacrylamide.

Suitable maleimide monomers include N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-hexylmaleimide, N-octylmaleimide, N-dodecylmaleimide, N-cyclohexylmaleimide, and N-phenylmaleimide.

The polymer constituting the shell layer preferably contains one or more monomers selected from alkyl acrylates and alkyl methacrylates. These monomers may be used individually or in combination of two or more.

Furthermore, the polymer constituting the shell layer preferably further contains at least one reactive vinyl monomer selected from the group consisting of carboxyl group-containing vinyl monomers, hydroxyl group-containing vinyl monomers, and glycidyl group-containing vinyl monomers as constituent monomers. By including the reactive vinyl monomer as a constituent monomer in the shell layer, reactivity with the recycled polyamide resin can be imparted to the core-shell type impact strength modifier. As a result, the dispersibility of the core-shell type impact strength modifier in the recycled polyamide resin is improved, and the impact strength improvement effect can be enhanced. Simultaneously, the dispersibility of the additive in the recycled polyamide resin can also be improved. Among the reactive vinyl monomers, carboxyl group-containing vinyl monomers are preferred because they exhibit particularly good reactivity with the recycled polyamide resin. The reactive vinyl monomer may be used alone or in combination of two or more types.

Suitable examples of the carboxyl group-containing vinyl monomer include acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, fumaric acid, isocrotonic acid, vinyloxyacetic acid, alyloxyacetic acid, 2-(meth)acryloylpropanoic acid, 3-(meth)acryloylbutanoic acid, 4-vinylbenzoic acid, 2-methacryloyloxyethyl succinic acid, 2-methacryloyloxyethyl maleic acid, 2-methacryloyloxyethyl phthalic acid, and 2-methacryloyloxyethyl hexahydrophthalic acid. Among these, acrylic acid and/or methacrylic acid are preferred, and methacrylic acid is more preferred.

Suitable examples of the hydroxyl group-containing vinyl monomer include hydroxyalkyl esters of (meth)acrylates, such as hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, which have an alkyl group with 1 to 22 carbon atoms and a hydroxyl group.

Suitable examples of the glycidyl group-containing vinyl monomer include glycidyl (meth)acrylate.

The amount of the reactive vinyl monomer used can be appropriately set according to the desired effect and is not particularly limited. However, when the reactive vinyl monomer is a carboxyl group-containing vinyl monomer, the proportion of the carboxyl group-containing vinyl monomer in the total polymer particles of the core-shell type impact strength modifier is preferably 0.05 to 1.4% by weight. When this proportion is within this range, the effect of improving the impact strength of the recycled polyamide resin by incorporating the core-shell type impact strength modifier can be enhanced. The lower limit of the proportion is preferably 0.1% by weight, more preferably 0.2% by weight. The upper limit of the proportion is preferably 1.2% by weight, more preferably 1.0% by weight, even more preferably 0.9% by weight, even more preferably 0.7% by weight, particularly preferably 0.6% by weight, and most preferably 0.5% by weight.

The weight ratio of the shell layer to the total polymer particles of the core-shell type impact strength modifier is preferably 1 to 50% by weight, more preferably 5 to 40% by weight, and even more preferably 10 to 30% by weight, from the viewpoint of compatibility between the core-shell type impact strength modifier and the recycled polyamide resin, and from the viewpoint of the effect of improving impact strength.

(Particle size of core-shell type impact strength modifier)
The particle size of the polymer particles, which are core-shell type impact strength modifiers, can be set as appropriate, but the volume-average particle size of the polymer particles is usually 100 nm or more. Since impact strength tends to improve as the particle size increases, especially at low temperatures, the volume-average particle size is preferably 130 nm or more, preferably 150 nm or more, more preferably 160 nm or more, and even more preferably 170 nm or more. On the other hand, since the polymerization reaction takes longer and productivity tends to decrease as the particle size of the polymer particles increases, the volume-average particle size is preferably 400 nm or less, more preferably 350 nm or less, even more preferably 300 nm or less, and even more preferably 250 nm or less. The volume-average particle size of the polymer particles is a value measured using a particle size measuring device in the latex state of the polymer particles, as shown in the Examples section. The volume-average particle size of the polymer particles can also be calculated from a transmission electron microscope (TEM) image of the recycled polyamide resin composition. The particle size of polymer particles can be controlled by the type and amount of polymerization initiators, chain transfer agents, redox agents, emulsifiers, etc., as well as the polymerization temperature and polymerization time.

(Method for producing polymer particles that are core-shell type impact strength modifiers)
The method for producing polymer particles that are core-shell type impact strength modifiers can be conventional and is not particularly limited. For example, bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization can be employed, but emulsion polymerization, i.e., emulsion graft polymerization, is preferred. Specifically in emulsion graft polymerization, first, latex for the core layer particles is produced by emulsion polymerization, and then monomer components for the shell layer and polymerization initiators are added to the latex to polymerize the monomer components.

(Polyolefin-based elastomer)
Examples of the aforementioned polyolefin-based elastomers include polyolefin-based elastomers and hydrogenated styrene-based thermoplastic elastomers. Specific examples include ethylene/propylene copolymer, ethylene/butene-1 copolymer, ethylene/hexene-1 copolymer, ethylene/propylene/dicyclopentadiene copolymer, ethylene/propylene/5-ethylidene-2-norbornene copolymer, unhydrogenated or hydrogenated styrene/isoprene/styrene triblock copolymer, unhydrogenated or hydrogenated styrene/butadiene/styrene triblock copolymer, ethylene/methacrylic acid copolymer, or copolymers in which some or all of the carboxylic acid portion is a salt with sodium, lithium, potassium, zinc, or calcium; ethylene/methyl acrylate copolymer, Ethylene/ethyl acrylate copolymer, ethylene/methyl methacrylate copolymer, ethylene/ethyl methacrylate copolymer, ethylene/ethyl acrylate-g-maleic anhydride copolymer (where "g" represents a graft, the same applies hereafter), ethylene/methyl methacrylate-g-maleic anhydride copolymer, ethylene/ethyl acrylate-g-maleimide copolymer, ethylene/ethyl acrylate-g-N-phenylmaleimide copolymer, or partially saponified copolymers thereof; ethylene/glycidyl methacrylate copolymer, ethylene/vinyl acetate/glycidyl methacrylate copolymer, ethylene/methyl methacrylate /glycidyl methacrylate copolymer, ethylene/glycidyl acrylate copolymer, ethylene/vinyl acetate/glycidyl acrylate copolymer, ethylene/glycidyl ether copolymer, ethylene/propylene-g-maleic anhydride copolymer, ethylene/butene-1-g-maleic anhydride copolymer, ethylene/propylene/1,4-hexadiene-g-maleic anhydride copolymer, ethylene/propylene/dicyclopentadiene-g-maleic anhydride copolymer, ethylene/propylene/2,5-norbornadiene-g-maleic anhydride copolymer, ethylene/propylene-g-N-phenylmaleimide copolymer Examples include ethylene/butene-1-g-N-phenylmaleimide copolymer, hydrogenated styrene/butadiene/styrene-g-maleic anhydride copolymer, hydrogenated styrene/isoprene/styrene-g-maleic anhydride copolymer, ethylene/propylene-g-glycidyl methacrylate copolymer, ethylene/butene-1-g-glycidyl methacrylate copolymer, ethylene/propylene/1,4-hexadiene-g-glycidyl methacrylate copolymer, ethylene/propylene/dicyclopentadiene-g-glycidyl methacrylate copolymer, hydrogenated styrene/butadiene/styrene-g-glycidyl methacrylate copolymer, and the like. Examples of elastomers that can be used industrially include Toughmer MH7020, MH7010, and MA8510 from Mitsui Chemicals, Hymiran 1706 from Mitsui DuPont, SEBS ToughTec M1943 from Asahi Kasei, and PA-bond959, PA-bond969, and PA-bond979 from Polymer Asia.

The modifier for recycled polyamide resin of this embodiment includes the additive of this embodiment and an impact strength improver. The proportion of the additive included in the modifier can be appropriately determined by those skilled in the art. However, from the viewpoint of balancing the effects achieved by the additive and the effects achieved by the impact strength improver, the ratio of the amount of the additive to the total amount of the additive and impact strength improver is preferably 0.1% by weight or more and 25% by weight or less, more preferably 0.5% by weight or more and 15% by weight or less, and even more preferably 1% by weight or more and 10% by weight or less.

The modifier for recycled polyamide resin according to this embodiment can be manufactured by mixing the additive of this embodiment with an impact strength improver. While the additive and impact strength improver may be mixed in powder form, it is preferable to mix them in latex form, then dry them to obtain a powder. In particular, when the impact strength improver is a core-shell type impact strength improver, the latex mixing method dramatically improves the melt tension of the recycled polyamide resin composition in addition to improving impact strength, which is effective for improving parison retention during blow molding. This is thought to be because, during latex blending, the additive can better mix with the shell portion of the core-shell type impact strength improver, and as a result, when the modifier is kneaded with the recycled polyamide resin, the additive is uniformly dispersed in the recycled polyamide resin along with the dispersion of the core-shell type impact strength improver.

(Amount of modifier added)
The modifier for recycled polyamide resin of this embodiment is used by being blended with recycled polyamide resin and can provide effects such as improving moldability during melt processing, improving the tensile properties of the molded article, and improving the impact strength of the recycled polyamide resin. The amount of the modifier blended with the recycled polyamide resin can be set as appropriate, but it is preferable that the ratio of the modifier to the total of the recycled polyamide resin and the modifier is 1% by weight or more and 40% by weight or less. When the ratio of the modifier is within the above range, it is possible to suitably provide the effects of improving moldability during melt processing, improving the tensile properties of the molded article, and improving the impact strength of the recycled polyamide resin while maintaining the physical properties unique to recycled polyamide resin. The above ratio is more preferably 3 to 30% by weight, and even more preferably 5 to 25% by weight.

(Recycled polyamide resin)
Recycled polyamide resin refers to polyamide resin that is made by reusing polyamide resin that has been used and discarded as a product, or waste polyamide resin discharged during the manufacturing process of polyamide resin or polyamide resin molded products. Furthermore, the term recycled polyamide resin as used in this application also includes mixtures obtained by mixing recycled polyamide resin with unused, fresh polyamide resin.

The polyamide resin is not limited to polymers having an acid amide bond (-CONH-), but examples include polymers obtained by polycondensation of diamines and dibasic acids, polymers obtained by polycondensation of diamine derivatives such as diformyl and dibasic acids, polymers obtained by polycondensation of dibasic acid derivatives such as dimethyl esters and diamines, polymers obtained by reaction of dinitrile or diamide with formaldehyde, polymers obtained by polyaddition of diisocyanate and dibasic acid, polymers obtained by self-condensation of amino acids or their derivatives, and polymers obtained by ring-opening polymerization of lactams. Furthermore, the polyamide resin may contain a polyether block. The polyamide resin may be used alone or in mixtures of two or more types.

Specific examples of polyamide resins include aliphatic polyamides such as nylon 4, nylon 6, nylon 6,6, nylon 7, nylon 9, nylon 11, nylon 12, nylon 46, nylon 56, nylon 410, nylon 412, nylon 610, and nylon 612; semi-aromatic polyamides such as nylon 6T, nylon 6I, nylon 9T, nylon 10T, nylon M5T, and nylon MXD6; and copolymer polyamides such as nylon 6/66, nylon 6/12, nylon 6/66/12, nylon 6/6T, nylon 66/6T, nylon 6/6I, nylon 6T/6I, nylon 6T/12, and nylon 66/6T/6I. Among these, nylon 6, nylon 6,6, nylon 11, and nylon 12 are preferred from the viewpoint of versatility.

(Other resins)
The recycled polyamide resin composition of this embodiment may or may not contain thermoplastic resins other than recycled polyamide resin. When a thermoplastic resin other than recycled polyamide resin is included, the thermoplastic resin is not particularly limited, but examples include polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl acetate, polyurethane, polytetrafluoroethylene, ABS resin, AS resin, acrylic resin, polyacetal, polycarbonate, modified polyphenylene ether, polyethylene terephthalate, polybutylene terephthalate, cyclic polyolefin, etc. The amount of other thermoplastic resins is not particularly limited, but for example, it is 0 to 100 parts by weight, preferably 0 to 50 parts by weight, more preferably 0 to 30 parts by weight, and even more preferably 0 to 10 parts by weight per 100 parts by weight of recycled polyamide resin.

(Other additives)
The recycled polyamide resin composition of this embodiment may appropriately contain additives that can be incorporated into general thermoplastic resin compositions. Such additives are not particularly limited, but examples include flame retardants, flame retardant enhancers, anti-dripping agents, reinforcing agents, fillers, antioxidants, pigments, dyes, conductivity imparters, hydrolysis inhibitors, thickeners, plasticizers, lubricants, ultraviolet absorbers, antistatic agents, flow improvers, mold release agents, compatibilizers, and heat stabilizers.

From the viewpoint of improving impact strength, the recycled polyamide resin composition of this embodiment preferably contains a reinforcing material. Examples of reinforcing materials include glass fibers, carbon fibers, boron fibers, asbestos fibers, polyvinyl alcohol fibers, polyester fibers, acrylic fibers, fully aromatic polyamide fibers, polybenzoxazole fibers, polytetrafluoroethylene fibers, kenaf fibers, bamboo fibers, hemp fibers, bagasse fibers, high-strength polyethylene fibers, alumina fibers, silicon carbide fibers, potassium titanate fibers, brass fibers, stainless steel fibers, steel fibers, ceramic fibers, and basalt fibers. Among these, glass fibers, carbon fibers, and metal fibers are preferred, with glass fibers being more preferred, due to their high impact strength improvement effect. The reinforcing material may be used alone or in combination of two or more types.

The amount of reinforcing material can be set as appropriate, but it is preferable that the reinforcing material accounts for 10 to 60% by weight of the total amount of recycled polyamide resin and the reinforcing material (100% by weight), more preferably 15 to 50% by weight, and even more preferably 20 to 40% by weight.

(Method of manufacturing the composition)
The method for producing the recycled polyamide resin composition of this embodiment is not particularly limited, and general methods for producing thermoplastic resin compositions can be applied. For example, the recycled polyamide resin composition can be obtained by mixing the raw materials using a Henschel mixer or a tumbler mixer, and then performing melt kneading. For this melt kneading, a kneader such as a single-screw or twin-screw extruder, a Banbury mixer, a pressure kneader, or a mixing roll can be used. Pellets made from the recycled polyamide resin composition can be produced by such melt kneading.

The recycled polyamide resin composition of this embodiment can be molded into a predetermined shape to form a molded article. The molding method is not particularly limited; for example, injection molding, extrusion molding, blow molding, foam molding, calendering, inflation molding, rotational molding, press molding, etc., can be used.

(Application)
The recycled polyamide resin composition and molded articles of this embodiment are used in automotive applications such as cylinder head covers, engine covers, intake manifolds, radiator tanks, oil pans, accelerator pedals, canisters, fuel tubes, air brake tubes, exhaust gas tubes, hydrogen injectors, ducts, industrial fasteners, and door mirror stays; in electrical and electronic applications such as coil bobbins, connectors, gears, sockets, switches, electric blanket coated wires, fiber optic cable coatings, power tools, and wire bundling materials; and in hydraulic and pneumatic applications such as connectors and tubes, bearings, covers, and housings. Examples of applications include mechanical applications such as bearings, pressure-resistant hoses, and cable ties; building materials such as curtain rail components, aluminum sash corners, door rollers, handrails, curtain rollers, and door handles; sports and leisure applications such as sports shoe soles, ski and snowboard equipment, reels, and diving snorkels; packaging materials and containers such as shrink wrap film, food packaging film, alcoholic beverage bottles, and pesticide bottles; daily necessities such as toothbrushes, chair legs and armrests, combs, knives and forks; and medical applications such as medical catheters and pipes, medical packs, and sutures, but are not particularly limited.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Number-average molecular weight or weight-average molecular weight)
The number-average molecular weight or weight-average molecular weight was determined by dissolving the sample in tetrahydrofuran (THF), filtering the soluble portion through a 0.2 μm filter, and then using a high-speed GPC instrument (Tosoh Corporation, HLC-8220) (sample solution: 20 mg sample/10 mL THF; columns: one TSKguardcolumn SuperHZ-H and two TSKgel SuperHZM-H columns, Tosoh Corporation; column temperature: 40°C; detector: differential refractometer; flow rate: 0.35 mL/min; injection volume: 10 μL; calibration curve: standard polystyrene).

(Volume-average particle diameter of polymer particles)
The volume-average particle size of polymer particles was measured in the polymer particle latex state. A NanoTrac Wave manufactured by Nikkiso Co., Ltd. was used as the measuring device.

(Polymerization conversion rate)
A portion of the obtained latex was sampled and accurately weighed, then dried in a hot air dryer at 120°C for 1 hour. The weight after drying was accurately weighed as the solid content. Next, the ratio of the weighing results before and after drying was determined as the solid component ratio in the latex. Finally, the polymerization conversion rate was calculated using this solid component ratio according to the following formula.
Formula: Polymerization conversion rate = (Total weight of raw materials × Solid component ratio - Total weight of raw materials other than monomer) / Weight of monomer × 100 (%)

(Example 1)
<Manufacturing of additive latex>
In a glass reactor equipped with a thermometer, stirrer, reflux condenser, nitrogen inlet, and monomer and emulsifier addition device, 100 parts by weight of deionized water, 0.147 parts by weight of sodium hydroxide, and 1.353 parts by weight of polyoxyethylene lauryl ether phosphate were charged, and the mixture was heated to 70°C while stirring in a nitrogen atmosphere.
To this, 0.0025 parts by weight of disodium ethylenediaminetetraacetate, 0.0015 parts by weight of ferrous sulfate heptahydrate, 0.3 parts by weight of sodium formaldehyde sulfoxylate, and 0.01 parts by weight of t-butyl hydroperoxide were added and stirred.
A mixture consisting of 11.05 parts by weight of methacrylic acid (hereinafter referred to as MAA), 38.95 parts by weight of methyl methacrylate (hereinafter referred to as MMA), 0.9 parts by weight of t-dodecyl mercaptan (chain transfer agent), 0.9 parts by weight of n-octyl mercaptan (chain transfer agent), and 0.451 parts by weight of polyoxyethylene lauryl ether phosphate was added over 150 minutes. During the addition, aqueous sodium hydroxide solution was added as needed to maintain the pH at 6.5 to 7.0, and t-butyl hydroperoxide was added as needed to promote polymerization. After the addition of the mixture was completed, the mixture was stirred for 30 minutes while cooling the temperature from 70°C to 50°C, and t-butyl hydroperoxide was added as needed during stirring to promote polymerization. As a result, a primary polymer (number average molecular weight: 5,500) was formed with a polymerization conversion rate of 97%.
Subsequently, a mixture of 43.28 parts by weight of MMA, 6.72 parts by weight of butyl acrylate (hereinafter referred to as BA), 0.451 parts by weight of polyoxyethylene lauryl ether phosphate, and 0.08 parts by weight of t-butyl hydroperoxide was added over 150 minutes. During the addition, aqueous sodium hydroxide solution was added as needed to maintain the pH at 6.5 to 7.0. After the addition was complete, 0.01 parts by weight of t-butyl hydroperoxide was added three times at 10-minute intervals, and the mixture was stirred for 30 minutes to form a second polymer with a polymerization conversion rate of 98%. As a result, a latex additive (weight-average molecular weight: 194,600) containing the first and second polymers was obtained.
<Obtaining the white resin powder additive>
650 parts by weight of deionized water and 3.5 parts by weight of a 25% by weight aqueous solution of calcium chloride were heated to 70°C while stirring, and the additive latex was added to obtain a slurry containing coagulated latex particles. Subsequently, the coagulated latex particle slurry was heated to 95°C, dehydrated, and dried to obtain particulate additives containing the first polymer and the second polymer as the white resin powder of Example 1.

(Example 2)
<Manufacturing of additive latex>
In a glass reactor equipped with a thermometer, stirrer, reflux condenser, nitrogen inlet, and monomer and emulsifier addition device, 100 parts by weight of deionized water, 0.147 parts by weight of sodium hydroxide, and 1.353 parts by weight of polyoxyethylene lauryl ether phosphate were charged, and the mixture was heated to 70°C while stirring in a nitrogen atmosphere.
To this, 0.0025 parts by weight of disodium ethylenediaminetetraacetate, 0.0015 parts by weight of ferrous sulfate heptahydrate, 0.3 parts by weight of sodium formaldehyde sulfoxylate, and 0.01 parts by weight of t-butyl hydroperoxide were added and stirred.
A mixture of 14.37 parts by weight of MAA, 50.63 parts by weight of MMA, 0.9 parts by weight of t-dodecyl mercaptan (chain transfer agent), 0.9 parts by weight of n-octyl mercaptan (chain transfer agent), and 0.451 parts by weight of polyoxyethylene lauryl ether phosphate was added over 150 minutes. During the addition, aqueous sodium hydroxide solution was added as needed to maintain the pH at 6.5 to 7.0, and t-butyl hydroperoxide was added as needed to promote polymerization. After the addition of the mixture was complete, the mixture was stirred for 30 minutes while cooling the temperature from 70°C to 50°C, and t-butyl hydroperoxide was added as needed during stirring to promote polymerization. As a result, a primary polymer (number average molecular weight: 7,200) was formed with a polymerization conversion rate of 97%.
Subsequently, a mixture of 24.5 parts by weight of MMA, 10.5 parts by weight of BA, 0.451 parts by weight of polyoxyethylene lauryl ether phosphate, and 0.08 parts by weight of t-butyl hydroperoxide was added over 150 minutes. During the addition, aqueous sodium hydroxide solution was added as needed to maintain the pH at 6.5 to 7.0. After the addition was complete, 0.01 parts by weight of t-butyl hydroperoxide was added three times at 10-minute intervals, and the mixture was stirred for 30 minutes to form a second polymer with a polymerization conversion rate of 98%. Thus, a latex additive (weight-average molecular weight: 55,000) containing the first and second polymers was obtained.
<Obtaining the white resin powder additive>
650 parts by weight of deionized water and 3.5 parts by weight of a 25% by weight aqueous solution of calcium chloride were heated to 70°C while stirring, and the additive latex was added to obtain a slurry containing coagulated latex particles. Subsequently, the coagulated latex particle slurry was heated to 95°C, dehydrated, and dried to obtain particulate additives containing the first polymer and the second polymer as the white resin powder of Example 2.

(Examples 3-4 and Comparative Example 1) Production of Recycled Polyamide Resin Compositions Pellets and test pieces were prepared from a composition containing recycled polyamide resin and the white resin powder of the additive, according to the following description, and the MFR, tensile properties, and Izod impact strength were measured. However, in Comparative Example 1, the evaluation was performed without using the white resin powder of the additive. MFR was used as an index to indicate the moldability during melt processing. A smaller MFR value indicates lower fluidity during melting and better moldability during melt processing.

(Pellet and test specimen preparation conditions)
(a) Recycled polyamide 6 resin (RA6G00, manufactured by Refineverse) Addition amounts as shown in the table below (b) White resin powder of the additive obtained in Example 1 1 part by weight or 2 parts by weight (c) Hindered phenol antioxidant (Irganox 1010, manufactured by BASF) 0.21 parts by weight (d) Phosphorus-based processing stabilizer (Irgafos 168, manufactured by BASF) 0.09 parts by weight

The mixtures described in (a) to (d) above were kneaded and extruded in a twin-screw extruder (TEX44SS manufactured by Japan Steel Works Ltd.) heated to a barrel temperature of 230 to 260°C at a screw rotation speed of 100 rpm to obtain pellets.
These pellets were dried in a dryer at 80°C for 12 hours to sufficiently reduce their moisture content. Then, test specimens were prepared using an injection molding machine (FANUC FAS100B) under the conditions of a molding temperature of 270-290°C and a mold temperature of 80°C.

(MFR)
The pellets prepared under the aforementioned conditions were dried in a hot air dryer at 120°C for 12 hours. The MFR value was then measured according to JIS K7210 Method A, under conditions of a measurement temperature of 280°C and a load of 5 kg.

(Tensile properties)
For the 3.2 mm thick ASTM D638-1 type test specimens prepared using the method described above, the tensile properties (tensile fracture strain) were measured at 23°C in a completely dry state, at a test speed of 50 mm/min, in accordance with the ASTM D638 standard.

(Izod impact strength)
For the test specimens prepared using the method described above, measuring 63.5 mm in length, 12.7 mm in width, and 3.2 mm in thickness, with a v-notch, the Izod impact strength was measured at -30°C and 23°C in a completely dry state, according to the ASTM D256 standard.
The results of the above measurements are shown in Table 1.

Table 1 shows that, compared to Comparative Example 1, Examples 3 and 4 have lower MFR values, meaning they exhibit better moldability during melt processing and also have better tensile properties in the molded articles.

(Examples 5-7 and Comparative Example 2) Preparation of Recycled Polyamide Resin Compositions Pellets and test pieces consisting of compositions containing recycled polyamide resin and the white resin powder of the additive were prepared according to the above method, except that the extrusion temperature was changed to 230-280°C, according to the formulations shown in Table 2. MFR, tensile properties, and Izod impact strength were measured according to the above method. However, in Comparative Example 2, the evaluation was performed without using the white resin powder of the additive. The results obtained are shown in Table 2.
Furthermore, recycled polyamide 66 resin (RA7N00, manufactured by Refineverse Co., Ltd.) was used as the recycled polyamide resin.

Table 2 shows that Examples 5-7 have lower MFR values compared to Comparative Example 2, indicating better moldability during melt processing and better tensile properties of the molded articles.

(Examples 8-9, Comparative Example 3, and Reference Example 1) Preparation of Recycled Polyamide Resin Compositions Pellets and test pieces were prepared according to the following description, consisting of a composition containing recycled polyamide resin and the white resin powder of the additive, according to the formulations shown in Table 3. MFR, tensile properties, and Izod impact strength were measured according to the method described above. However, in Comparative Example 3 and Reference Example 1, the evaluation was performed without using the white resin powder of the additive. Also, in Reference Example 1, unused polyamide resin was used for the evaluation instead of recycled polyamide resin. The results obtained are shown in Table 3.

(Pellet and test specimen preparation conditions)
(a) Recycled polyamide 6 resin (manufactured by Yueh Chemical Co., Ltd. (YH800)) or unused polyamide 6 resin (manufactured by UBE Corporation, 1030B) parts by weight as listed in Table 3 (b) White resin powder of the additive obtained in Example 2 Parts by weight as listed in Table 3 (c) Hindered phenol antioxidant (manufactured by BASF, Irganox 1010) 0.21 parts by weight (d) Phosphorus-based processing stabilizer (manufactured by BASF, Irgafos 168) 0.09 parts by weight

From the mixtures described in (a) to (d) above, pellets were obtained using the method described above, and then test specimens were prepared.

Table 3 shows that Examples 8 and 9 have lower MFR values compared to Comparative Example 3, meaning they exhibit better moldability during melt processing and also have better tensile properties. Furthermore, Examples 8 and 9 also exhibit better tensile properties compared to Reference Example 1.

Claims (10)

An additive for recycled polyamide resins comprising a first polymer and a second polymer ,
The first polymer comprises (i) a carboxyl group-containing vinyl monomer, and
(ii) (meth)acrylic acid monomers and/or aromatic vinyl monomers,
It is a copolymer containing,
The first polymer has a number-average molecular weight of 2,000 to 25,000.
An additive for recycled polyamide resin, wherein the first polymer and the second polymer are each non-rubber polymers, the first polymer constitutes particles, and at least a portion of the second polymer is located outside the particles . The additive for recycled polyamide resin according to claim 1, wherein the carboxyl group-containing vinyl monomer accounts for 15% to 50% by weight of 100% by weight of the first polymer. The additive for recycled polyamide resin according to claim 1 or 2, wherein the first polymer is a copolymer comprising (i) a carboxyl group-containing vinyl monomer and (ii) a (meth)acrylic acid ester monomer as constituent monomers. The additive for recycled polyamide resin according to any one of claims 1 to 3, wherein the weight-average molecular weight of the additive for recycled polyamide resin is 30,000 or more. The additive for recycled polyamide resin according to any one of claims 1 to 4 , wherein the second polymer is a polymer containing a methacrylic acid ester monomer and/or an aromatic vinyl monomer as constituent monomers. The additive for recycled polyamide resin according to claim 5 , wherein the sum of the methacrylic acid ester monomer and the aromatic vinyl monomer accounts for 50% by weight or more and 100% by weight or less of the second polymer by 100% by weight. The product contains recycled polyamide resin and an additive for recycled polyamide resin according to any one of claims 1 to 6 .
A recycled polyamide resin composition in which the proportion of the additive is 0.1 to 10% by weight relative to 100% by weight of the total amount of the recycled polyamide resin and the additive. The recycled polyamide resin composition according to claim 7 , further containing a reinforcing material, wherein the proportion of the reinforcing material to the total weight of the recycled polyamide resin and the reinforcing material is 10 to 60% by weight. Pellets comprising the recycled polyamide resin composition according to claim 7 or 8 . A molded article comprising the recycled polyamide resin composition according to any one of claims 7 to 9 .