JP7764281B2 - Resin pellet manufacturing method - Google Patents

Description

The present invention relates to a method for producing resin pellets.

Resin pellets made from a resin composition are produced, for example, by a strand-cutting method in which a molten resin composition is extruded into strands, which are then cooled and cut with a strand cutter, or by a center hot-cutting method in which a molten resin composition extruded from a nozzle hole of a die is cut with a rotary blade and the cut pieces are cooled (see, for example, Patent Document 1, etc.).

Japanese Patent Application Laid-Open No. 2000-271928

However, resin pellets formed using only one conventional line can have large variations in pellet size. Furthermore, when resin pellets with such large variations in size are used to form molded articles such as films, the quality of the molded articles can deteriorate due to the non-uniform size of the resin pellets.

The present invention was made in response to the above-mentioned circumstances, and its purpose is to provide a method for producing resin pellets with high size uniformity.

The present invention, which has solved the above problems, has the following configuration.
[1] a polymerization step of polymerizing a monomer to form a thermoplastic resin;
a devolatilization and extrusion step of removing volatile components including unreacted monomers from the polymer obtained in the polymerization step and extruding a resin composition including the thermoplastic resin to form resin pellets, the step being carried out in two or more lines under substantially the same conditions;
A method for producing resin pellets, comprising a mixing step of mixing the resin pellets formed in the two or more lines.
[2] The method according to [1], wherein the thermoplastic resin constituting the resin pellets is a (meth)acrylic resin.
[3] The method according to [2], wherein the (meth)acrylic resin is a resin having a ring structure in the main chain.
[4] The manufacturing method according to [3], further comprising a cyclization step of forming a ring structure in the main chain of the thermoplastic resin formed in the polymerization step by a cyclization condensation reaction, prior to the devolatilization and extrusion steps.

The manufacturing method of the present invention makes it possible to obtain resin pellets with reduced size variation. Furthermore, by using highly uniform resin pellets with reduced size variation, molded products of consistent quality can be obtained.

Investigations into the size variation of resin pellets revealed significant variation in the resin pellets produced through the devolatilization and extrusion processes. During the devolatilization process, the viscosity of the molten resin changes depending on the degree of volatilization. The size of resin pellets produced by extrusion is also affected by viscosity, and changes in viscosity tend to lead to changes in pellet size. It was determined that the combination of the devolatilization and extrusion processes is the cause of the pellet size variation. Furthermore, it was discovered that the manufacturing method of the present invention, which forms resin pellets in two or more series under substantially identical conditions and includes a mixing process in which the resin pellets formed in the two or more series are mixed, narrows the variation rather than widening the variation due to the merging of the variations in each series, thereby producing resin pellets with improved size uniformity. The improved pellet size uniformity can be confirmed, for example, by a reduction in the standard deviation and/or coefficient of variation of the pellet size. Stable resin pellet size can also prevent deterioration in the quality of molded products and a decrease in production efficiency due to pellet size nonuniformity. Furthermore, even for resin pellets containing a (meth)acrylic resin whose melt flow rate is prone to fluctuate, the production method of the present invention, which includes a mixing step of mixing two or more series of resin pellets, can easily reduce the variation in the melt flow rate (specifically, reduce the standard deviation and/or the coefficient of variation. In particular, when a cyclization step of forming a ring structure in the main chain of a thermoplastic resin is included, the variation in the melt flow rate may increase due to the generation of volatile components during the cyclization condensation reaction. However, the production method of the present invention can provide resin pellets with a stable melt flow rate.
In the present invention, forming resin pellets under substantially the same conditions means producing resin pellets using the same recipe in equipment of the same design. The resin pellets produced under the same conditions will be divided into multiple series when the production equipment is cleaned or the equipment used is changed, etc.

(1) Polymerization Step In the polymerization step, a polymerization reaction is carried out to homopolymerize or copolymerize one or more monomers to form a thermoplastic resin.
The polymerization of the monomers may be carried out by any of bulk polymerization, solution polymerization, emulsion polymerization and suspension polymerization, but solution polymerization is preferred from the viewpoint of high safety and low risk of contamination with foreign matter.
The polymerization may be carried out by batch polymerization or continuous polymerization. In the case of continuous batch polymerization, after the polymerization reaction, the contents of the reactor are removed and the reactor is emptied. The raw materials (monomers, etc.) of the next batch may be charged again without cleaning the inside of the reactor, and the next production may be started.

The thermoplastic resin formed in the polymerization process of the present invention is not particularly limited, and examples thereof include (meth)acrylic resins; olefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, and poly(4-methyl-1-pentene); halogen-containing resins such as vinyl chloride and chlorinated vinyl resins; styrene resins such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer (AS resin), and acrylonitrile-butadiene-styrene block copolymer (ABS resin); polyethylene terephthalate, polybutylene terephthalate, etc. Examples of suitable resins include polyesters such as cellulose acetate and polyethylene naphthalate; polyamides such as nylon 6, nylon 66, and nylon 610; cellulose ester resins such as cellulose triacetate, cellulose acetate propionate, and cellulose acetate butyrate; polyacetal; polycarbonate; polyphenylene oxide; polyphenylene sulfide; polyether ether ketone; polysulfone; polyethersulfone; polyoxybenzylene; polyamideimide; and maleimide resins. Of these, (meth)acrylic resins are preferred from the standpoint of heat resistance and transparency.

Monomers used in the polymerization of (meth)acrylic resins include (meth)acrylic acid, (meth)acrylic acid esters, and derivatives thereof (hereinafter, these may be collectively referred to as (meth)acrylic monomers). In this specification, "(meth)acrylic acid" means acrylic acid or methacrylic acid.

Examples of (meth)acrylic acid esters include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; aralkyl (meth)acrylates (preferably _C2-20 aralkyl methacrylates) such as benzyl (meth)acrylate; and esters of (meth)acrylic acid with hydroxycyclic saturated hydrocarbons (preferably hydroxycyclic saturated hydrocarbons having 5 to 20 carbon atoms) such as cyclohexyl (meth)acrylate and dicyclopentanyl (meth)acrylate. The (meth)acrylic acid ester is preferably a methacrylic acid ester, more preferably an alkyl methacrylate, even more preferably a _C1-10 alkyl methacrylate, still more preferably a _C1-7 alkyl methacrylate, and particularly preferably a _C1-4 alkyl methacrylate.

Examples of the (meth)acrylic acid ester derivatives include derivatives into which a hydroxy group has been introduced, for example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, and 2,3,4,5-tetrahydroxypentyl (meth)acrylate; and alkyl α-(1-hydroxyalkyl)acrylates.
The hydroxyalkyl (meth)acrylate is preferably a C _1-20 alkyl hydroxy (meth)acrylate, more preferably a C _1-15 alkyl hydroxy (meth)acrylate, even more preferably a C _1-10 alkyl hydroxy (meth)acrylate, and even more preferably a C _1-5 alkyl hydroxy (meth)acrylate.
The alkyl α-(1-hydroxyalkyl)acrylate is preferably a _C1-20 alkyl α-(1-hydroxy _C1-20 alkyl)acrylate, and examples of the _C1-20 alkyl α-(1-hydroxy C1-20 alkyl)acrylate include _C1-20 alkyl α-(hydroxymethyl)acrylates such as methyl α-(hydroxymethyl)acrylate, ethyl α-(hydroxymethyl)acrylate, isopropyl α-(hydroxymethyl)acrylate, n-butyl α-(hydroxymethyl)acrylate, and t-butyl α-(hydroxymethyl)acrylate; and _C1-20 alkyl α-(1-hydroxy _C2-20 alkyl)acrylates such as methyl α-(1 _{-hydroxyethyl} )acrylate.

In addition, the (meth)acrylic acid ester derivatives also include β-C _1-10 alkyl acrylates (C _1-10 alkyl acrylates) such as methyl crotonate; halogen-introduced derivatives such as chloromethyl (meth)acrylate and 2-chloroethyl (meth)acrylate; and ether bond-introduced derivatives such as dicyclopentanyloxyethyl (meth)acrylate.

The (meth)acrylic acid ester derivative is preferably a derivative into which a hydroxy group has been introduced, more preferably an α-(1-hydroxyalkyl) alkyl acrylate, even more preferably an α-(1-hydroxyC _1-20 alkyl) C _1-20 alkyl acrylate, and still more preferably an α-(hydroxymethyl) C _1-20 alkyl acrylate.

(Meth)acrylic acid derivatives include compounds obtained by hydrolyzing the ester bond of the above-mentioned methacrylic acid ester derivatives, such as crotonic acid, α-(hydroxymethyl)acrylic acid, 2-(1-hydroxyethyl)acrylic acid, and other α-hydroxyalkylacrylic acids.

When the cyclization step described below is included, it is preferable to use a hydroxyl group-introduced derivative of a (meth)acrylic acid ester. The amount of the hydroxyl group-introduced derivative of a (meth)acrylic acid ester used is, based on 100% by mass of the total amount of the monomer components, preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and even more preferably 10% by mass or more, and is, for example, 70% by mass or less, preferably 50% by mass or less, and more preferably 30% by mass or less.

The (meth)acrylic monomer used in the polymerization of the (meth)acrylic resin may be a single monomer or a combination of two or more types. The (meth)acrylic monomer preferably contains (meth)acrylic acid or a (meth)acrylic acid ester as an essential monomer, and more preferably contains a (meth)acrylic acid ester (particularly a methacrylic acid ester) as an essential monomer. The amount of the essential monomer used is, based on 100% by mass of the total amount of the monomer components, preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 65% by mass or more, even more preferably 70% by mass or more, and particularly preferably 75% by mass or more. For example, it is 100% by mass or less, preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

The (meth)acrylic resin may be formed by copolymerizing the (meth)acrylic monomer with another monomer copolymerizable with the (meth)acrylic monomer. Examples of the other monomer include styrene-based monomers such as styrene, vinyl toluene, α-methylstyrene, α-hydroxymethylstyrene, and α-hydroxyethylstyrene; vinyl ester-based monomers such as vinyl acetate, vinyl propionate, vinyl pivalate, vinyl benzoate, and vinyl cinnamate; maleic acid-based monomers such as maleic anhydride, maleic acid, and monoalkyl and dialkyl esters of maleic acid; maleimide-based monomers such as maleimide, methylmaleimide, ethylmaleimide, propylmaleimide, butylmaleimide, hexylmaleimide, octylmaleimide, dodecylmaleimide, stearylmaleimide, phenylmaleimide, and cyclohexylmaleimide; fumaric acid, Examples of suitable other monomers include fumaric acid monomers such as monoalkyl esters and dialkyl esters of the above; nitrogen-containing heterocyclic vinyl compounds such as N-vinylpyrrolidone and N-vinylcarbazole; lactone ring-containing monomers such as α-methylene-γ-butyrolactone, α-methylene-4-methyl-γ-butyrolactone, α-methylene-3-methyl-γ-butyrolactone, α-methylene-4,4-dimethyl-γ-butyrolactone, and α-methylene-δ-valerolactone; vinyl nitriles such as acrylonitrile and methacrylonitrile; vinyl alcohols such as methallyl alcohol and allyl alcohol; olefins such as ethylene, propylene, and 4-methyl-1-pentene; 2-hydroxymethyl-1-butene; and methyl vinyl ketone. Preferred examples of suitable other monomers include styrene-based monomers and nitrogen-containing heterocyclic vinyl compounds, with styrene-based monomers being more preferred. Only one type of the other monomer may be used as a copolymerization component, or two or more types may be used as copolymerization components.

The amount of other monomers (especially styrene-based monomers) used is, for example, 0% by mass or more, preferably 1% by mass or more, and for example, 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on 100% by mass of the total amount of monomer components.

When the cyclization step described below is not included, it is preferable to use a maleic acid-based monomer, a maleimide-based monomer, or a lactone ring-containing monomer as the other monomer. When a maleic acid-based monomer is used as the other monomer, a structure derived from maleic anhydride can be introduced into the main chain of the (meth)acrylic resin. When a maleimide-based monomer is used as the other monomer, a structure derived from N-substituted maleimide can be introduced into the main chain of the (meth)acrylic resin. When a lactone ring-containing monomer is used, a methylene lactone ring structure can be introduced into the main chain of the (meth)acrylic resin. Only one type of maleic acid-based monomer, maleimide-based monomer, and/or lactone ring-containing monomer may be used as a copolymerization component, or two or more types may be used as copolymerization components.
In the polymerization step, when a maleic acid-based monomer, a maleimide-based monomer, and/or a lactone ring-containing monomer is used as another monomer to incorporate a ring structure into the main chain of the (meth)acrylic resin, the amount of the maleic acid-based monomer, the maleimide-based monomer, and/or the lactone ring-containing monomer used is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, relative to 100% by mass of the total amount of the monomer components, and is, for example, 70% by mass or less, preferably 60% by mass or less, and more preferably 50% by mass or less.
In the present invention, the term "having a ring structure in the main chain" refers to an embodiment in which at least one of the carbon atoms forming the ring structure is included in the main chain of the thermoplastic resin.

Preferred examples of the structure derived from maleic anhydride or the structure derived from N-substituted maleimide include the structure represented by the following general formula (1): In the following general formula (1), when X ¹ is an oxygen atom, the structure is derived from maleic anhydride, and when X ¹ is a nitrogen atom, the structure is derived from N-substituted maleimide.

In the general formula (1), ^R1 and ^R2 are each independently a hydrogen atom or a methyl group, and ^X1 is an oxygen atom or a nitrogen atom. When ^X1 is an oxygen atom, ^R3 does not exist. When ^X1 is a nitrogen atom, ^R3 is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms (methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group), cyclopentyl group, cyclohexyl group, benzyl group, or phenyl group.

Preferred examples of the methylene lactone ring structure include the structure shown in general formula (11) below.

In the above general formula (11), R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are each independently a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms; A is a single bond connecting -(CR ¹¹ R ¹² )- and -(CR ¹³ R ¹⁴ )-, or -(CR ¹⁵ R ¹⁶ )-; R ¹⁵ and R ¹⁶ are each independently a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms.
In formula (11), when A is a single bond, the structure represented by formula (11) has a five-membered lactone ring structure, and when A is -(CR ¹⁵ R ¹⁶ )-, the structure represented by formula (11) has a six-membered lactone ring structure.
Examples of the hydrocarbon group in formula (11) include saturated aliphatic hydrocarbon groups (e.g., alkyl groups) having from 1 to 18 carbon atoms, such as a methyl group, an ethyl group, or a propyl group; unsaturated aliphatic hydrocarbon groups (e.g., alkenyl groups) having from 2 to 18 carbon atoms, such as an ethenyl group or a propenyl group; and aromatic hydrocarbon groups (e.g., aryl groups) having from 6 to 18 carbon atoms, such as a phenyl group or a naphthyl group. An alkyl group is preferred, and an alkyl group having from 1 to 10 carbon atoms is more preferred.

Solvents that can be used when polymerizing the monomers by solution polymerization include aromatic hydrocarbon solvents such as toluene, xylene, and ethylbenzene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ether solvents such as tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and anisole; ester solvents such as ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, and 3-methoxybutyl acetate; cellosolve solvents such as methyl cellosolve, ethyl cellosolve, and butyl cellosolve; alcohol solvents such as methanol, ethanol, isopropanol, and n-butanol; nitrile solvents such as acetonitrile, propionitrile, butyronitrile, and benzonitrile; halogenated solvents such as chloroform and dichloromethane; and dimethyl sulfoxide. Preferred polymerization solvents are aromatic hydrocarbon solvents, ketone solvents, and alcohol solvents, with aromatic hydrocarbon solvents and alcohol solvents being more preferred, and aromatic hydrocarbon solvents being even more preferred, with toluene being particularly preferred. These polymerization solvents may be used alone or in combination of two or more.

When the polymerization of the monomers is carried out by solution polymerization, the total concentration of the monomer components in the polymerization reaction solution is, for example, 5% by mass or more, preferably 10% by mass or more, and more preferably 30% by mass or more, and for example, 90% by mass or less, preferably 80% by mass or less, and more preferably 70% by mass or less. The amount of solvent used in the polymerization reaction is not particularly limited, as long as the total concentration of the monomer components in the polymerization reaction solution is within the above range.

A polymerization initiator may be used in the polymerization process, if necessary.

Polymerization initiators that can be used include, for example, azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, dimethyl-2,2'-azobis(2-methylpropionate), and 4,4'-azobis(4-cyanopentanoic acid); persulfates such as potassium persulfate; and organic peroxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexanoate, t-amylperoxyoctoate, t-amylperoxyisononanoate, t-amylperoxyisopropyl carbonate, and t-amylperoxy-2-ethylhexyl carbonate. These may be used alone or in combination of two or more. Among these, it is preferable to use organic peroxides, which have a strong hydrogen abstraction power.

The amount of polymerization initiator used is, for example, 500 ppm or more, preferably 1000 ppm or more, and more preferably 1500 ppm or more, based on the total amount of monomer components, from the viewpoint of increasing the polymerization rate and reducing the amount of remaining unreacted monomer components. Furthermore, the amount of polymerization initiator used is, for example, 2% by mass or less, preferably 1% by mass or less, and more preferably 0.7% by mass or less, based on the total amount of monomer components.

To promote the decomposition of the polymerization initiator, an appropriate amount of a polymerization initiator decomposer, such as a reducing agent such as sodium hydrogen sulfite or a transition metal salt such as ferrous sulfate, may be added to the reaction system.

A chain transfer agent may be used in the polymerization process as needed. Adding a chain transfer agent to the reaction system can lower the molecular weight of the thermoplastic resin. Examples of chain transfer agents include organic thiol compounds; halogen compounds such as carbon tetrachloride, carbon tetrabromide, methylene chloride, bromoform, and bromotrichloroethane; and unsaturated hydrocarbon compounds such as α-methylstyrene dimer, α-terpinene, γ-terpinene, dipentene, and terpinolene. These chain transfer agents may be used alone or in combination with two or more. Among these, organic thiol compounds such as 1-dodecanethiol are preferred because they can prevent a decrease in conversion rate.

The amount of chain transfer agent used is, for example, 200 ppm or more, preferably 400 ppm or more, and more preferably 500 ppm or more, relative to the total amount of monomer components, and is, for example, 5% by mass or less, preferably 1% by mass or less, and more preferably 0.5% by mass or less.

The method of adding the aforementioned monomers, and the optional solvent, polymerization initiator, and chain transfer agent, is not particularly limited. The entire amount may be charged to the reaction vessel at the beginning, or a portion may be charged to the reaction vessel at the beginning, with the remainder being added to the reaction system (reaction vessel) all at once or continuously during the polymerization reaction. The addition may be continuous or intermittent, such as by divided addition, but continuous addition or intermittent addition at intervals of 10 minutes or less is preferred, and continuous addition is more preferred.

The atmosphere in which the monomers are polymerized is not particularly limited, but from the perspective of increasing the efficiency of the polymerization reaction, an inert gas such as nitrogen gas is preferable.

The polymerization temperature when polymerizing the monomers is, for example, 40°C or higher, preferably 60°C or higher, and more preferably 70°C or higher. When a polymerization initiator is used, the polymerization temperature is preferably at least the 10-hour half-life temperature of the polymerization initiator used. The 10-hour half-life temperature refers to the temperature at which the half-life of the polymerization initiator is 10 hours. The polymerization temperature is, for example, 180°C or lower, preferably 150°C or lower, and more preferably 120°C or lower. When a solvent is used, the polymerization temperature is preferably at or below the reflux temperature of the solvent used.

The polymerization time for polymerizing the monomers is not particularly limited and can be set appropriately depending on the progress of the polymerization reaction, but is usually about 2 to 8 hours.

After all the monomers have been added, and optionally the solvent, polymerization initiator, and chain transfer agent, aging may be carried out as needed. Aging further improves the monomer conversion rate. In the aging step, it is preferable to continue stirring at an appropriate temperature, for example, approximately ±30°C of the polymerization temperature (preferably at or above the polymerization temperature). The aging time is, for example, from 0 to 10 hours, preferably from 1 to 5 hours.

The monomer conversion rate at the end of the polymerization reaction is, for example, 80% or more, preferably 85% or more, and more preferably 88% or more.

The weight-average molecular weight (Mw) of the thermoplastic resin in the polymer (preferably the polymerization solution) obtained by the polymerization step is, for example, 50,000 or more, preferably 70,000 or more, more preferably 90,000 or more, and even more preferably 100,000 or more, and is, for example, 300,000 or less, preferably 250,000 or less, and more preferably 200,000 or less. By having the weight-average molecular weight of the thermoplastic resin within this range, it is possible to obtain a resin composition that has good fluidity during molding while maintaining the necessary strength as a resin.

When the thermoplastic resin is a (meth)acrylic resin, the total content of structural units derived from (meth)acrylic monomers (i.e., structural units derived from (meth)acrylic acid, (meth)acrylic acid esters, and derivatives thereof) in all structural units of the (meth)acrylic resin in the polymer (preferably, the polymerization solution) obtained by the polymerization step is, from the viewpoint of transparency, preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and still more preferably 75% by mass or more. There is no particular upper limit, and it may be 100% by mass.
The content ratio of each structural unit in the (meth)acrylic polymer can be determined by dissolving the (meth)acrylic polymer in a heavy solvent, measuring ¹ H-NMR, and calculating the peak area ratio corresponding to each structural unit.

(2) Cyclization Step From the viewpoint of heat resistance, the thermoplastic resin preferably has a ring structure in the main chain.
The ring structure that the thermoplastic resin has in its main chain is preferably at least one selected from the group consisting of a lactone ring structure, a glutarimide structure, a glutaric anhydride structure, a maleic anhydride structure, and an N-substituted maleimide structure.
The thermoplastic resin having a ring structure in the main chain can be formed, for example, by using a maleic acid-based monomer, a maleimide-based monomer, and/or a lactone ring-containing monomer as a monomer in the polymerization step as described above, or by carrying out a cyclization condensation reaction after the polymerization reaction (cyclization step).

Examples of main chain ring structures formed by cyclization condensation reactions include lactone ring structures, glutaric anhydride structures, and glutarimide structures.

When optical components are manufactured using resin pellets formed from a resin composition containing a thermoplastic resin, the main chain ring structure of the thermoplastic resin is preferably a lactone ring structure, a glutaric anhydride structure, or a glutarimide structure, more preferably a lactone ring structure, in order to obtain optical components with excellent optical properties. Furthermore, in terms of moist heat resistance, the main chain ring structure is preferably a lactone ring structure, a glutarimide structure, or a structure derived from an N-substituted maleimide, more preferably a lactone ring structure.

The lactone ring structure is, for example, a 4- to 8-membered ring, preferably a 5- or 6-membered ring due to its superior ring structure stability, and more preferably a 6-membered ring. Examples of 6-membered lactone ring structures include the structure shown in general formula (2) below.

In the general formula (2), R ⁴ , R ⁵ and R ⁶ are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms, and the organic residue may contain an oxygen atom.
Examples of the organic residue in general formula (2) include saturated aliphatic hydrocarbon groups (e.g., alkyl groups) having from 1 to 20 carbon atoms, such as a methyl group, an ethyl group, or a propyl group; unsaturated aliphatic hydrocarbon groups (e.g., alkenyl groups) having from 2 to 20 carbon atoms, such as an ethenyl group or a propenyl group; aromatic hydrocarbon groups (e.g., aryl groups) having from 6 to 20 carbon atoms, such as a phenyl group or a naphthyl group; and groups in which one or more hydrogen atoms in these saturated aliphatic hydrocarbon groups, unsaturated aliphatic hydrocarbon groups, or aromatic hydrocarbon groups have been substituted with at least one group selected from a hydroxy group, a carboxyl group, an ether group, and an ester group, with an alkyl group being preferred.

The lactone ring structure can be formed by dealcoholization or dehydration cyclocondensation (cyclocondensation reaction) between a hydroxy group in a thermoplastic resin and an ester group or carboxyl group. Therefore, when forming a lactone ring structure by a cyclocondensation reaction, it is preferable to homopolymerize a hydroxy group-containing (meth)acrylic monomer such as an α-(1-hydroxyalkyl) alkyl acrylate in the polymerization step, or copolymerize the hydroxy group-containing (meth)acrylic monomer with a (meth)acrylic monomer such as (meth)acrylic acid or a (meth)acrylic acid ester to form a thermoplastic resin in which a hydroxy group and an ester group or a carboxyl group have been introduced into the molecular chain.

When a lactone ring structure is formed in the main chain of a thermoplastic resin by a cyclization condensation reaction, it is preferable to carry out the cyclization condensation reaction so that the content of lactone ring structures in the thermoplastic resin is, for example, 1% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, and for example, 70% by mass or less, preferably 50% by mass or less, more preferably 30% by mass or less.

The content of the lactone ring structure in the thermoplastic resin can be evaluated by known methods, such as nuclear magnetic resonance ( ¹ H-NMR) and/or infrared spectroscopy (IR).

Examples of the glutaric anhydride structure or the glutarimide structure include the structure represented by the following general formula (3): In the following general formula (3), when ^X2 is an oxygen atom, the structure becomes a glutaric anhydride structure, and when ^X2 is a nitrogen atom, the structure becomes a glutarimide structure.

In the general formula (3), ^R7 and ^R8 are each independently a hydrogen atom or a methyl group, and ^X2 is an oxygen atom or a nitrogen atom. When ^X2 is an oxygen atom, ^R9 does not exist, and when ^X2 is a nitrogen atom, ^R9 is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms (methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group), a cyclopentyl group, a cyclohexyl group, or a phenyl group.

A glutaric anhydride structure can be formed by dealcoholization or dehydration cyclocondensation (cyclization condensation reaction) between a carboxyl group in a thermoplastic resin and an ester group or another carboxyl group. Therefore, when forming a glutaric anhydride structure by a cyclocondensation reaction, it is preferable to homopolymerize a (meth)acrylic acid ester or (meth)acrylic acid, or copolymerize a (meth)acrylic acid ester and (meth)acrylic acid, in the polymerization step to form a thermoplastic resin in which a carboxyl group and an ester group or another carboxyl group have been introduced into the molecular chain.

A glutarimide structure can be formed by forming a glutaric anhydride structure through dealcoholization or dehydration cyclocondensation (cyclocondensation reaction) between a carboxyl group in a thermoplastic resin and an ester group or another carboxyl group, followed by imidization with an imidizing agent. Imidization may be carried out immediately following the cyclocondensation reaction, or after the volatilization and extrusion steps described below following the cyclocondensation reaction; however, it is preferably carried out after the volatilization and extrusion steps described below following the cyclocondensation reaction.

The imidizing agent is not particularly limited, but examples include aliphatic hydrocarbon group-containing amines such as methylamine, ethylamine, and n-butylamine; cycloalkylamines having a cycloalkyl group with 3 to 12 carbon atoms such as cyclohexylamine; and arylamines having an aryl group with 6 to 10 carbon atoms such as aniline, benzylamine, toluidine, and trichloroaniline. These imidizing agents may be used alone or in combination of two or more. From the viewpoint of the transparency of the resulting resin pellets, preferred imidizing agents are cyclohexylamine, aniline, and toluidine, with aniline being more preferred. The amount of imidizing agent used may be adjusted appropriately to achieve the desired imidization rate.

Imidization can be carried out by known methods, such as dissolving the thermoplastic resin that has undergone a cyclocondensation reaction in a solvent and adding an imidizing agent to the solution, or melting the thermoplastic resin that has undergone a cyclocondensation reaction in an extruder or the like and adding an imidizing agent to the melt. The reaction temperature during imidization is, for example, 160°C or higher and 400°C or lower.

The solvent used during imidization is preferably a solvent inert to imidization, such as aliphatic alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; aromatic compounds such as benzene, toluene, xylene, chlorobenzene, and chlorotoluene; and ether compounds. These solvents may be used alone or in combination of two or more.

After imidization, it is preferable to remove any unreacted imidizing agent. For example, if imidization is performed using an extruder, the extruder can be equipped with a vent that can reduce the pressure to below atmospheric pressure, allowing the imidizing agent to be removed.

When forming a glutaric anhydride structure or a glutarimide structure in the main chain of a thermoplastic resin, it is preferable to carry out the cyclization condensation reaction and, if necessary, imidization so that the content of the glutaric anhydride structure or glutarimide structure in the thermoplastic resin is, for example, 1% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, and for example, 70% by mass or less, preferably 50% by mass or less, more preferably 30% by mass or less.

The content ratio of glutaric anhydride structures and glutarimide structures in a thermoplastic resin can be determined by known methods, such as the method described in JP 2006-131689 A.

The cyclization condensation reaction may be carried out in the presence of a solvent. Examples of solvents that can be used in the cyclization condensation reaction include the same types of solvents that can be used in the polymerization reaction described above, and preferred embodiments are also the same.
When the polymerization reaction is carried out by solution polymerization, the solvent used in the solution polymerization may be removed once and then a new solvent may be added, or the solvent used in the solution polymerization may be subsequently used as the solvent in the cyclization reaction. However, from the viewpoint of production efficiency, it is preferable to subsequently use the solvent used in the solution polymerization as the solvent in the cyclization reaction.

The concentration of the thermoplastic resin in the cyclization condensation reaction liquid is, for example, 5% by mass or more, preferably 10% by mass or more, and more preferably 30% by mass or more, and for example, 90% by mass or less, preferably 80% by mass or less, and more preferably 70% by mass or less. The amount of solvent used in the cyclization condensation reaction is not particularly limited, as long as the concentration of the thermoplastic resin in the cyclization condensation reaction liquid is within the above range.

The cyclization condensation reaction is preferably carried out in the presence of a catalyst (cyclization catalyst). The cyclization catalyst can be at least one selected from the group consisting of acids, bases, and salts thereof. The acids, bases, and salts thereof may be organic or inorganic, and are not particularly limited. In particular, it is preferable to use an organic phosphorus compound or a compound containing an alkali metal as the cyclization reaction catalyst. Using an organic phosphorus compound or a compound containing an alkali metal as the cyclization catalyst allows the cyclization condensation reaction to be carried out efficiently and reduces discoloration of the resulting thermoplastic resin.

Organophosphorus compounds that can be used as cyclization catalysts include, for example, alkyl (aryl) phosphonous acids and their monoesters or diesters; dialkyl (aryl) phosphinic acids and their esters; alkyl (aryl) phosphonic acids and their monoesters or diesters; alkyl (aryl) phosphinic acids and their esters; phosphite monoesters, diesters, or triesters; methyl phosphate, ethyl phosphate, 2-ethylhexyl phosphate, octyl phosphate, isodecyl phosphate, lauryl phosphate, stearyl phosphate, isostearyl phosphate, phenyl phosphate, dimethyl phosphate, phosphate Examples of suitable phosphate monoesters, diesters, or triesters include diethyl, di-2-ethylhexyl phosphate, diisodecyl phosphate, dilauryl phosphate, distearyl phosphate, diisostearyl phosphate, diphenyl phosphate, trimethyl phosphate, triethyl phosphate, triisodecyl phosphate, trilauryl phosphate, tristearyl phosphate, triisostearyl phosphate, and triphenyl phosphate; mono-, di-, or tri-alkyl(aryl)phosphines; alkyl(aryl)halogen phosphine; mono-, di-, or tri-alkyl(aryl)phosphine oxide; and tetraalkyl(aryl)phosphonium halides. These may be used alone or in combination of two or more. Among these, phosphate monoesters and diesters are particularly preferred due to their high catalytic activity and low coloration.

Examples of compounds containing an alkali metal that can be used as a cyclization catalyst include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; alkali metal alkoxide compounds such as sodium methoxide, sodium ethoxide, sodium phenoxide, potassium methoxide, potassium ethoxide, and potassium phenoxide; and alkali metal salts of organic carboxylic acids such as lithium acetate, sodium acetate, potassium acetate, and sodium stearate. These compounds may be used alone or in combination of two or more. Among these, sodium hydroxide, sodium methoxide, lithium acetate, and sodium acetate are preferred due to their high catalytic activity and low coloration, with sodium methoxide and lithium acetate being more preferred.

The amount of cyclization catalyst used is preferably, for example, 0.001 to 1 part by mass per 100 parts by mass of the thermoplastic resin obtained in the polymerization step.

The reaction temperature for the cyclization step is, for example, 50°C or higher and 300°C or lower, and the reaction time is, for example, 5 minutes to 6 hours. The cyclization step is preferably carried out in the same reactor as the polymerization reaction, and furthermore, the cyclization step is preferably carried out in an autoclave, a shell-and-tube heat exchanger, or the like.

(3) Devolatilization and Extrusion Step Devolatilization refers to a process for removing volatile components such as solvent, residual monomers, etc. from a molten resin. When a cyclization step is included, the devolatilization process also removes alcohol by-produced by the cyclization condensation reaction from the molten resin.
If the devolatilization is insufficient, a large amount of volatile matter remains in the resin composition, which may cause foaming during molding, resulting in molding defects. On the other hand, if the devolatilized resin is extruded in a molten state to form pellets, the pellet size will vary greatly. In the present invention, resin pellets formed in two or more series are mixed, which makes it possible to suppress variation in pellet size.

The equipment used for devolatilization is not particularly limited as long as it is capable of handling molten resin, but examples that can be used include autoclaves, kettle-type reactors, equipment consisting of a heat exchanger and a devolatilization tank, and vented extruders.

When a vented extruder is used for devolatilization, extrusion can be carried out subsequently using the extruder. The extruder preferably has a cylinder and a screw installed within the cylinder, and is equipped with a heating means. The cylinder is preferably equipped with one or more vents, and the vent is more preferably installed at least downstream of the raw material input section in the transport direction within the extruder, and may also be installed upstream of the raw material input section. Devolatilization progresses as the resin composition containing the thermoplastic resin supplied to the extruder is transported from the upstream side to the downstream side of the extruder while being kneaded with the screw.

Devolatilization is preferably carried out at a temperature of 150°C or higher and 350°C or lower, and at a reduced pressure of 13.3 hPa or higher (e.g., 13.3 hPa or higher and 800 hPa or lower). Devolatilization temperatures lower than 150°C can result in insufficient devolatilization and a large amount of residual volatile matter, while devolatilization temperatures higher than 350°C can result in discoloration and decomposition, which is undesirable.

The extrusion is preferably carried out at a temperature of 200°C or higher and 300°C or lower, and a pressure of 10 MPa or higher and 20 MPa or lower.

In the polymerization process, cyclization process, and/or devolatilization and extrusion process, various known additives can be used as needed. Examples of additives include ultraviolet absorbers; phenolic antioxidants (e.g., hydroquinone, 2,6-di-t-butyl-p-cresol, tocopherol, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, etc.); phosphorus-based antioxidants (e.g., triphenyl phosphite, tris(2,4-di-t-butylphenyl)phosphite, etc.); sulfur-based antioxidants (e.g., 2-mercaptobenzimidazole, dilauryl 3,3'-thiodiproline, etc.); Examples of suitable additives include antioxidants such as phenate; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fiber and carbon fiber; near-infrared absorbers; flame retardants such as tris(dibromopropyl)phosphate, triallyl phosphate, and antimony oxide; retardation adjusters such as retardation increasers, retardation decreasers, and retardation stabilizers; antistatic agents including anionic, cationic, and nonionic surfactants; compatibilizers; stabilizers; colorants such as inorganic pigments, organic pigments, and dyes; organic and inorganic fillers; and resin modifiers. These may be used alone or in combination of two or more.

There are no particular restrictions on the amount of additives used, but it is best to adjust the additive content so that it is preferably in the range of 0% to 5% by mass, and more preferably 0% to 2% by mass, based on 100% by mass of the solids content of the resulting resin composition.

The weight-average molecular weight (Mw) of the resin composition containing the thermoplastic resin is, for example, 50,000 or more, preferably 60,000 or more, more preferably 70,000 or more, and even more preferably 80,000 or more, and is, for example, 300,000 or less, preferably 250,000 or less, and more preferably 200,000 or less. By having the weight-average molecular weight of the resin composition within this range, it is possible to obtain a resin composition that has good fluidity during molding while maintaining the necessary strength as a resin.

From the viewpoint of heat resistance, the resin composition containing a thermoplastic resin preferably has a glass transition temperature (Tg) of 100°C or higher. The resin composition may have a plurality of glass transition temperatures of 100°C or higher. The glass transition temperature of the resin composition is more preferably 110°C or higher, and even more preferably 120°C or higher. From the viewpoint of improving processability during molding, the glass transition temperature of the resin composition is preferably less than 300°C, more preferably 200°C or lower, and even more preferably 180°C or lower.
The glass transition temperature of the resin composition can be determined by the starting point method in accordance with the provisions of JIS K7121.

(4) Cutting Step The molten resin composition after the devolatilization and extrusion steps is cut into pellets using a cutter to form resin pellets. The cutting method is not particularly limited, and may be a strand cut method in which the molten resin composition extruded in the form of a strand is cooled and cut using a strand cutter, or a center hot cut method or underwater cut method in which the molten resin composition extruded from a nozzle hole is cut using a rotary blade.

A die is preferably provided downstream of the extruder used in the extrusion step (for example, at the tip of the cylinder), and the molten resin composition can be extruded in a desired shape from the nozzle holes of the die. The shape of the nozzle holes of the die is not particularly limited, and for example, a cylindrical shape is preferable. The number of nozzle holes of the die may be 1 or more, and may be, for example, 100 or more. The hole diameter of the nozzle holes of the die, for example, in the case of a cylindrical shape, can be 1 mm or more and 10 mm or less.
The die is preferably provided with a polymer filter.

The molten resin composition is solidified by cooling. The cooling method may be air cooling or water cooling, but water cooling is preferred.

After cutting, post-processing such as washing, liquid-solid separation, and drying may be performed as needed. Examples of washing methods include water washing, examples of liquid-solid separation methods include centrifugation and vacuum sieving, and examples of drying methods include air drying and vacuum drying.

(5) Mixing Step In the mixing step, two or more series of resin pellets formed according to the same recipe are mixed under substantially the same conditions, that is, in an apparatus of the same design.

In the present invention, "mixing" does not necessarily mean that two or more series of resin pellets are uniformly mixed together, but rather means that two or more series of resin pellets coexist in the same space (in a container such as a hopper or silo).

The mixing method is not particularly limited, and may be, for example, a mixer. A simple and preferred method is to mix two or more series of resin pellets by charging them into the same container, such as a hopper. When two or more series of resin pellets are charged into the same container, the order of charging is not particularly limited. The two or more series of resin pellets may be charged simultaneously. Alternatively, the resin pellets of two series (A and B) (or three or more series) may be divided into multiple groups, such as A1, A2, A3, ..., B1, B2, B3, ..., and then charged in the order A1, B1, A2, B2, ..., alternately (or randomly) by group. Furthermore, the resin pellets of two series (A and B) (or three or more series) may be charged in the order of series, such as first charging all the pellets of series A, and then charging all the pellets of series B. Even when charging in the order of series, mixing occurs at the boundaries between the series, and further mixing progresses due to the uneven flow of pellets when discharging from the container.
Furthermore, the resin pellets introduced into the container (hereinafter referred to as the first container) may be discharged and then introduced again into a container (hereinafter referred to as the second container) to further enhance the degree of mixing. For example, the resin pellets may be divided into a plurality of groups when being dispensed from the first container, and each group may be introduced into the second container in an order different from that in which the groups were dispensed from the first container (preferably in a random order). When re-introducing the resin pellets into the second container, not only may groups of resin pellets dispensed from the same first container be introduced, but groups of resin pellets dispensed from different first containers (provided that these groups are produced under substantially the same conditions) may also be mixed into the same second container.

The more series that are mixed, the more likely it is that resin pellets with higher size uniformity will be obtained.

When mixing two or more series of resin pellets produced under substantially the same conditions, the amount of resin pellets from each of the other series is preferably 0.1 to 100 parts by mass, more preferably 1 to 100 parts by mass, even more preferably 10 to 100 parts by mass, and even more preferably 30 to 100 parts by mass, per 100 parts by mass of resin pellets from the series with the largest proportion (if there are two or more series of resin pellets with the largest proportion, any one of them).

(6) Resin pellets The resin pellets obtained after the mixing step are a mixture of two or more rows of resin pellets produced under substantially the same conditions, and therefore have high pellet size uniformity. More preferably, the resin pellets obtained after the mixing step also have small variations in melt flow rate.

The shape of the resin pellets is not particularly limited, and examples include spherical (including ellipsoidal) and cylindrical (e.g., cylindrical or prismatic) shapes.

The size of the resin pellets is not particularly limited and can be appropriately set depending on the intended use and the like.
The maximum diameter of the cut surface of the resin pellet (the surface formed by the cutter in the cutting step) is, for example, preferably 0.5 mm or more and 15 mm or less, and more preferably 1.0 mm or more and 10 mm or less.
The length of the longest part of the cut surface of the resin pellet in a direction perpendicular to the maximum diameter (perpendicular diameter) is, for example, preferably 0.5 mm or more and 15 mm or less, and more preferably 1.0 mm or more and 10 mm or less.
The length of the resin pellet in the direction perpendicular to the cut surface (pellet length or pellet thickness) is, for example, preferably 0.5 mm or more and 10 mm or less, and more preferably 1.0 mm or more and 8.0 mm or less.

The standard deviation and coefficient of variation of the maximum diameter, orthogonal diameter, and pellet length (or pellet thickness) all indicate the size uniformity of the resin pellets, and it is preferable that the values of one or more (preferably all) are small. Furthermore, it is preferable that the resin pellets after mixing have a reduced standard deviation or coefficient of variation (preferably both) of any (preferably all) of the maximum diameter, orthogonal diameter, and pellet length (or pellet thickness) compared to the resin pellets of all series before mixing.

For example, it is preferable that the resin pellets after mixing have a small standard deviation and/or coefficient of variation of pellet size as follows.
(When maximum diameter is less than or equal to pellet length)
The standard deviations (mm) of the maximum diameter and the perpendicular diameter are each preferably 0.65 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.
The coefficients of variation of the maximum diameter and the perpendicular diameter are each preferably 0.014 or less, and more preferably 0.012 or less.
The standard deviation (mm) of the pellet length is preferably 0.65 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.
The coefficient of variation of the pellet length is preferably 0.022 or less, more preferably 0.020 or less, and even more preferably 0.018 or less.
(When maximum diameter > pellet thickness)
The standard deviations (mm) of the maximum diameter and the perpendicular diameter are each preferably 0.80 or less, more preferably 0.75 or less, and even more preferably 0.70 or less.
The coefficients of variation of the maximum diameter and the perpendicular diameter are each preferably 0.016 or less, and more preferably 0.014 or less.
The standard deviation (mm) of the pellet thickness is preferably 0.80 or less, more preferably 0.70 or less, and even more preferably 0.60 or less.
The coefficient of variation of the pellet thickness is preferably 0.035 or less, more preferably 0.030 or less, and even more preferably 0.025 or less.

The melt flow rate of the resin pellets, measured in accordance with JIS K 7210 (Method B) at a temperature of 240°C and a load of 10 kgf (98 N), is preferably 8 g/10 min or more, more preferably 10 g/10 min or more, and is preferably 50 g/10 min or less, more preferably 40 g/10 min or less, and even more preferably 30 g/10 min or less, from the viewpoint of moldability.
The standard deviation and coefficient of variation of the melt flow rate indicate the stability of the melt flow rate, and it is preferable that these values are small. Furthermore, it is preferable that the standard deviation and/or coefficient of variation of the melt flow rate of the resin pellets after mixing is lower than that of the resin pellets of all series before mixing.
For example, the standard deviation (g/10 min) of the melt flow rate is preferably 0.75 or less, more preferably 0.70 or less, and more preferably 0.60 or less. The coefficient of variation of the melt flow rate is preferably 0.050 or less, more preferably 0.045 or less, and more preferably 0.040 or less.

If the resin pellets contain volatile components such as residual monomers, alcohol by-products of the cyclocondensation reaction, and water, it is preferable that the content of these volatile components be low in order to form molded articles with excellent appearance. Furthermore, it is preferable that the resin pellets after mixing have a reduced standard deviation and/or coefficient of variation in the volatile component content compared to the resin pellets of all series before mixing.

From the viewpoint of molding processability, the amount of residual monomer (particularly methyl methacrylate residuals) in the resin pellets is preferably 3000 ppm or less, more preferably 2500 ppm or less, and even more preferably 2300 ppm or less. The amount of residual monomer in the resin pellets is a value determined by the method described in the Examples below. Unless otherwise specified in the present invention, "ppm" means a value determined in mass terms.
The standard deviation (ppm) of the amount of residual monomer (particularly, methyl methacrylate residual) is, for example, preferably 120 or less, more preferably 110 or less, and more preferably 100 or less. The coefficient of variation of the amount of residual monomer (particularly, methyl methacrylate residual) is, for example, preferably 0.065 or less, more preferably 0.060 or less, and more preferably 0.055 or less.

From the viewpoint of molding processability, the amount of alcohol (particularly methanol) in the resin pellets is preferably 200 ppm or less, more preferably 180 ppm or less, and even more preferably 150 ppm or less. The amount of alcohol in the resin pellets is a value determined by the method described in the examples below.
The standard deviation (ppm) of the alcohol (particularly methanol) amount is, for example, preferably 15 or less, more preferably 10 or less, and more preferably 8 or less. The coefficient of variation of the alcohol (particularly methanol) amount is, for example, preferably 0.120 or less, more preferably 0.110 or less, and more preferably 0.100 or less.

From the viewpoint of molding processability, the moisture content in the resin pellets is preferably 200 ppm or less, more preferably 180 ppm or less, and even more preferably 150 ppm or less. The moisture content in the resin pellets is a value determined by the method described in the examples below.
The standard deviation (ppm) of the water content is, for example, preferably equal to or less than 30, more preferably equal to or less than 25, and more preferably equal to or less than 20. The coefficient of variation of the water content is, for example, preferably equal to or less than 0.320, more preferably equal to or less than 0.300, and more preferably equal to or less than 0.280.

The characteristic values and their standard deviations of resin pellets can be determined, for example, by randomly sampling 10 or more pellets and calculating the arithmetic mean (primary average value) 10 or more times to determine the 10 or more primary average values for each characteristic. The arithmetic mean (secondary average value) of these primary average values is then used as each characteristic value, and the standard deviation of the primary average values is used as the standard deviation of each characteristic value. Furthermore, the coefficient of variation of each characteristic value of resin pellets can be determined from the secondary average value and the standard deviation.

The resin pellets produced using the manufacturing method of the present invention have high size uniformity and preferably little variation in melt flow rate, making it possible to form molded products of consistent quality. Furthermore, by reducing the occurrence of manufacturing problems caused by uneven size of raw resin pellets, it is possible to improve the productivity of molded products.

(7) Molded Articles The resin pellets produced by the production method of the present invention can be molded into various forms and used as various products or parts. Examples of molding methods include injection molding, extrusion molding, blow molding, hollow molding, calendar molding, rotational molding, vacuum molding, and compression molding. The shape of the molded article can be appropriately determined depending on the application, and examples include sheets, films, lenses, tubes, pipes, bags, and containers. In particular, when the thermoplastic resin contained in the resin composition forming the resin pellets is a (meth)acrylic resin, it has an excellent balance of various properties such as optical properties, mechanical strength, moldability, and surface hardness, making it useful as a molded article (optical component) for optical applications. Examples of molded articles for optical applications include films, and specific examples include polarizer protective films, retardation films, viewing angle compensation films, light diffusion films, reflective films, antireflection films, antiglare films, brightness enhancement films, and conductive films for touch panels. The molded articles can also be used in the fields of optical communication systems, optical switching systems, and optical measurement systems, including, for example, solar cells, or sheets or plates such as light guide plates, diffusion plates, front panels, transparent substrates, and transparent conductive substrates such as touch panels in optical products such as head-mounted displays and liquid crystal projectors. Furthermore, examples of molded articles include lenses, lens arrays, lens covers, optical fibers, tail lamps, meter covers, head lamps, lamp covers, light guide rods, and the like, which are used in optical products, in-vehicle products, and household products such as lighting equipment and office automation equipment. The molded articles can also be suitably used as interior and exterior decorations or decorative films for automobiles and various devices.

The molded product may be a molded product consisting solely of resin pellets produced by the manufacturing method of the present invention, or a molded product consisting of a mixture of resin pellets produced by the manufacturing method of the present invention and other pellets.

The molding temperature is not particularly limited, but is preferably in the range of 150°C to 350°C, and more preferably in the range of 200°C to 300°C.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the examples below, and it is of course possible to make appropriate modifications within the scope of the intent described above and below, all of which are within the technical scope of the present invention. In the following, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

First, we will explain the measurement methods used in the following examples.

(1) Weight-average molecular weight The weight-average molecular weight (Mw) of the resin composition was determined in terms of polystyrene using gel permeation chromatography (GPC) using the following apparatus and conditions:
Measurement system: Tosoh GPC system HLC-8220
Measurement column configuration:
Guard column (TSK guard column Super HZ-L, manufactured by Tosoh)
Separation column (TSK Gel Super HZM-M, manufactured by Tosoh), two columns connected in series Reference column configuration:
Reference column (TSK gel Super H-RC, manufactured by Tosoh)
Developing solvent: chloroform (Wako Pure Chemical Industries, special grade)
Flow rate of developing solvent: 0.6 mL/min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit)
Column temperature: 40°C

(2) Glass Transition Temperature The glass transition temperature (Tg) of the resin composition was determined by the starting point method in accordance with the provisions of JIS K7121. Specifically, using a differential scanning calorimeter (Rigaku Corporation, Thermo plus EVO DSC-8230), approximately 10 mg of a sample was heated from room temperature to 200°C (heating rate 20°C/min) under a nitrogen gas flow (100 ml/min), and the temperature was evaluated from the obtained DSC curve. α-Alumina was used as a reference.

(3) Cyclization rate (glutaric anhydride oxidation rate, imidization rate)
The glutaric anhydride oxidation rate or imidization rate in a (meth)acrylic resin was determined from the intensity ratio of the absorption at around 1803 cm ⁻¹ due to carboxylic anhydride groups, the absorption at around 1720 cm ⁻¹ due to ester carbonyl groups, and the absorption at around 1680 cm ⁻¹ due to imide carbonyl groups. Here, the glutaric anhydride oxidation rate or imidization rate is the proportion of carboxylic anhydride groups or imide carbonyl groups in all carbonyl groups.

(4) Size of Resin Pellet The maximum diameter of the cut surface of the resin pellet (the surface formed by the cutting machine in the cutting process), the length of the longest part of the cut surface in a direction perpendicular to the maximum diameter (orthogonal diameter), and the length in the direction perpendicular to the cut surface (pellet length or pellet thickness) were measured.

(5) Melt flow rate (MFR)
The MFR of the resin pellets was measured using a melt indexer (manufactured by Takara Industries Co., Ltd.) in accordance with JIS K 7210 (Method B) at a temperature of 240° C. and a load of 98 N (10 kgf).

(6) Volatile component content (6-1) Methyl methacrylate (MMA)
The amount of volatile MMA remaining in the resin pellets was determined by gas chromatography (Shimadzu Corporation, GC-2014) using a calibration curve prepared using diphenyl carbonate as an internal standard.
(6-2) Methanol (MeOH)
The amount of MeOH in the resin pellets was determined by gas chromatography (Shimadzu Corporation, GC-2014) using a calibration curve prepared using diphenyl carbonate as an internal standard.
(6-3) Moisture The moisture content in the resin pellets was determined by Karl Fischer volumetric titration using a trace moisture analyzer (Mitsubishi Chemical Corporation, CA-100) connected to a moisture vaporizer (Mitsubishi Chemical Corporation, VA-100). Specifically, approximately 1.0 g of pellets was precisely weighed, introduced into the moisture vaporizer maintained at 250°C, and heated for 2 minutes. The total moisture generated here was introduced into the moisture vaporizer using nitrogen gas dried through diphosphorus pentaoxide, and the moisture content was determined by Karl Fischer volumetric titration.

(7) Mean values, standard deviations, and coefficients of variation of various properties of resin pellets (maximum diameter, orthogonal diameter, pellet length (pellet thickness), MFR, volatile component content) The mean values, standard deviations, and coefficients of variation of various properties of each series of resin pellets before mixing and after mixing were measured as follows. First, the properties of 10 randomly selected pellets were examined, and the arithmetic mean (primary average value) was calculated for each property. This procedure was repeated 15 times, and the primary average value of 15 pellets was calculated for each property. The arithmetic mean (secondary average value) and standard deviation of the primary average values of the 15 pellets were calculated, and these were used as the mean values and standard deviations of various properties of each series of resin pellets and after mixing. The coefficient of variation was calculated from the mean values and standard deviations of the various properties.

Example 1
A reaction vessel equipped with a stirrer, a temperature sensor, a cooling condenser, and a nitrogen inlet tube was charged with 83.5 parts of methyl methacrylate, 12 parts of methyl 2-(hydroxymethyl)acrylate, 90.4 parts of toluene, 0.05 parts of tris(2,4-di-tert-butylphenyl)phosphite (manufactured by ADEKA Corporation: Adekastab (registered trademark) 2112), and 0.07 parts of n-dodecyl mercaptan, and the temperature was raised to 105°C while passing nitrogen through. When refluxing began due to the temperature increase, 0.09 parts of tert-amyl peroxy isononanoate (Luperox (registered trademark) 570 manufactured by Arkema Yoshitomi Co., Ltd.) was added as a polymerization initiator, and 0.18 parts of tert-amyl peroxy isononanoate and 4.5 parts of styrene were added dropwise over 2 hours to allow solution polymerization to proceed under reflux at about 105 to 110°C. After completion of the dropwise addition, the mixture was further aged for 4 hours at the same temperature.

Next, 0.075 parts of stearyl phosphate (Phoslex A-18, manufactured by SC Organic Chemical Co., Ltd.) was added as a cyclization catalyst to the polymerization solution in the reaction vessel, and the cyclization condensation reaction to form a lactone ring structure was carried out under reflux at approximately 90-110°C for 2 hours. Next, the polymerization solution was passed through a multi-tube heat exchanger heated to 240°C to complete the cyclization condensation reaction, and then introduced at a processing rate of 100 parts/h (converted to resin amount) into a vent-type twin-screw extruder (L/D=52.5) having a barrel temperature of 250°C, a reduced pressure of 13.3 to 400 hPa (10 to 300 mmHg), one rear vent and four fore vents (referred to as the first, second, third, and fourth vents from the upstream side), a side feeder provided between the third and fourth vents, and a leaf disc-type polymer filter (filtration accuracy: 5 μm) disposed at the tip, for kneading and devolatilization. During this process, separately prepared ion-exchanged water was added at a rate of 1.5 parts/h upstream from the second and fourth vents, and a toluene solution (mixing ratio of 33.74:1:1 by mass) consisting of a zinc octoate toluene solution (Nihon Kagaku Sangyo Co., Ltd., Nikka Octix Zinc 1.8%; cyclization catalyst deactivator), a phenolic antioxidant (ADEKA Corporation, Adeka STAB® AO-60), and a sulfur-based antioxidant (ADEKA Corporation, Adeka STAB® AO-412S) was added at a rate of 0.165 parts/h upstream from the third vent.

After devolatilization was complete, the resin composition remaining in the extruder in a molten state was filtered through a polymer filter and discharged from the tip of the extruder. The extrusion die at the tip of the extruder cylinder had numerous 4mm diameter holes drilled along its circumference and was equipped with a watering cutter. The cooling water used was filtered through a 1μm pore size filter (manufactured by Organo Corporation, product name: Micropore Filter 1EU) and maintained at a temperature within the range of 30±10°C. After cutting and water-cooling solidification, a centrifugal dryer was installed for dehydration, and the resin was transported to a storage silo by gas.

The resulting resin composition containing a (meth)acrylic resin having a lactone ring structure in its main chain had a glass transition temperature of 124°C and a weight-average molecular weight of 132,000.

The above resin pellets were formed in two series (hereinafter referred to as Series A and Series B, respectively). Series A and Series B were produced using the same formulation and equipment of the same design, but the specific equipment used was different. Series A resin pellets and Series B resin pellets were mixed and stirred in a storage silo.

Table 1 shows the primary average value, secondary average value, standard deviation, and coefficient of variation for the size (maximum diameter, orthogonal diameter, pellet thickness) of each resin pellet formed in Series A and Series B, and for the resin pellets after mixing. Table 2 also shows the primary average value, secondary average value, standard deviation, and coefficient of variation for the melt flow rate and volatile component content of each resin pellet formed in Series A and Series B, and for the resin pellets after mixing. In Table 1, the measurement unit for pellet size is "mm."

As shown in Table 1, the manufacturing method of Example 1, which includes a step of mixing resin pellets of Series A and Series B formed under substantially identical conditions, resulted in highly uniform resin pellets with reduced standard deviation and coefficient of variation in pellet size. Furthermore, as shown in Table 2, the manufacturing method of Example 1 also reduced the standard deviation and coefficient of variation in the melt flow rate and volatile component content of the resulting resin pellets.

Example 2
Resin pellets were formed in two series (hereinafter referred to as Series C and Series D, respectively) in the same manner as in Example 1. Series C and Series D were produced using the same recipe using equipment of the same design, but the specific equipment used was different. The resin pellets of Series C were first charged into a storage silo, and then the resin pellets of Series D were charged on top of the resin pellets of Series C. Then, resin pellets consisting of a mixture of the resin pellets of Series C and the resin pellets of Series D were obtained from a discharge outlet installed at the bottom of the storage silo.

Table 3 shows the primary average value, secondary average value, standard deviation, and coefficient of variation for the sizes (maximum diameter, orthogonal diameter, pellet thickness) of the resin pellets formed in Series C and Series D, and the resin pellets after mixing. In Table 3, the measurement unit for pellet size is "mm."

As shown in Table 3, the manufacturing method of Example 2, which includes a step of mixing resin pellets of Series C and Series D formed under substantially identical conditions, made it possible to obtain highly uniform resin pellets with reduced standard deviation and coefficient of variation in pellet size.

Example 3
A reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen gas inlet pipe was charged with 79.4 parts of methyl methacrylate, 20.6 parts of methacrylic acid, a mixed solvent of 90.0 parts of toluene and 22.5 parts of methanol as a polymerization solvent, and 0.05 parts of an antioxidant (manufactured by ADEKA Corporation, trade name: Adekastab 2112), and the temperature was raised to 73°C while nitrogen gas was passed through the reaction vessel. At the time when refluxing due to the temperature increase began, 0.25 parts of dimethyl-2,2'-azobis(2-methylpropionate) (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-601) was added as a polymerization initiator to the reaction vessel, and a solution prepared by dissolving 0.35 parts of dimethyl-2,2'-azobis(2-methylpropionate) (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-601) in a mixed solvent of 7.3 parts of toluene and 1.8 parts of methanol was added dropwise to the reaction vessel over 2 hours, while solution polymerization was carried out under reflux at approximately 71 to 76°C. After the dropwise addition of dimethyl-2,2'-azobis(2-methylpropionate) was completed, the mixture was further aged for 4 hours. The content of repeating units derived from methacrylic acid in the (meth)acrylic resin in the resulting polymerization solution was 20.6%. The weight average molecular weight of the (meth)acrylic resin was 110,000.

Next, 10 parts of a solution of 0.1 parts sodium methoxide dissolved in 9.9 parts methanol as a cyclization catalyst was added dropwise to the polymerization solution in the reactor over a period of 20 minutes at a temperature of approximately 65-70°C to form a homogeneous polymerization solution.

The resulting polymerization solution was introduced into a vent-type twin-screw extruder (hole diameter: 15 mm, L/D: 45) with one rear vent and two fore vents at a barrel temperature of 290°C, a rotation speed of 70 rpm, a vacuum of 13.3 to 400 hPa (10 to 300 mmHg), and at a processing rate of 300 g/h (equivalent to resin). Devolatilization was carried out in the twin-screw extruder, and the extrusion was carried out with an in-screw residence time of approximately 0.9 minutes, yielding transparent resin pellets formed from a resin composition containing a (meth)acrylic resin having a glutaric anhydride structure in its main chain.

The resin composition containing the (meth)acrylic resin having a glutaric anhydride structure in its main chain obtained above had a glass transition temperature of 131°C and a weight-average molecular weight of 100,000. Furthermore, the cyclization rate (glutaric anhydride oxidation rate) of the (meth)acrylic resin having a glutaric anhydride structure in its main chain obtained above was 17.5%.

Resin pellets formed from the resin composition containing a (meth)acrylic resin having a glutaric anhydride structure in its main chain obtained above were introduced from the hopper into a vent-type twin-screw extruder (hole diameter: 15 mm, L/D: 45) with one vent, barrel temperature: 290°C, rotation speed: 300 rpm, vacuum level: 13.3 to 400 hPa (10 to 300 mmHg), at a processing rate of 420 g/h (equivalent to resin amount). Aniline as an imidizing agent was injected from the rear of the hopper using a liquid addition pump at a rate of 101 g/h. The extrusion was carried out with an in-screw residence time of approximately 2.1 minutes, yielding transparent resin pellets formed from a resin composition containing a (meth)acrylic resin having a glutarimide structure in its main chain.

The resin pellets were passed through a die attached to the tip of the extruder and cooled in a water tank filled with cooling water to obtain strands of the resin composition. The cooled strands were then introduced into a cutting machine (pelletizer). The cooling water used was filtered through a 1 μm pore size filter (manufactured by Organo Corporation, product name: Micropore Filter 1EU) and kept at a temperature within the range of 30±10°C. After cutting, the resin pellets were transported to a storage silo.

The resin composition containing the (meth)acrylic resin having a glutarimide structure in its main chain obtained above had a glass transition temperature of 162°C and a weight-average molecular weight of 90,000. Furthermore, the imidization rate of the (meth)acrylic resin having a glutarimide structure in its main chain obtained above was 44.1%.

The above resin pellets were formed in two series (hereinafter referred to as Series E and Series F, respectively). Series E and Series F were produced using the same formulation and equipment of the same design, but the specific equipment used was different. Series E resin pellets and Series F resin pellets were mixed and stirred in a storage silo.

Table 4 shows the primary average value, secondary average value, standard deviation, and coefficient of variation for the sizes (maximum diameter, orthogonal diameter, pellet length) of the resin pellets formed in Series E and Series F, as well as the resin pellets after mixing. In Table 4, the measurement unit for pellet size is "mm."

As shown in Table 4, the manufacturing method of Example 3, which includes a step of mixing resin pellets of Series E and Series F formed under substantially identical conditions, made it possible to obtain highly uniform resin pellets with reduced standard deviation and coefficient of variation in pellet size.

Claims (4)

a polymerization step of polymerizing the monomers to form a thermoplastic resin;
a devolatilization and extrusion step of removing volatile components including unreacted monomers from the polymer obtained in the polymerization step and extruding a resin composition including the thermoplastic resin to form resin pellets, the step being carried out in two or more lines under substantially the same conditions;
A method for producing resin pellets, comprising a mixing step of mixing the resin pellets formed in the two or more lines. The manufacturing method described in claim 1, wherein the thermoplastic resin constituting the resin pellets is a (meth)acrylic resin. The manufacturing method described in claim 2, wherein the (meth)acrylic resin is a resin having a ring structure in the main chain. The manufacturing method described in claim 3 further includes a cyclization step, prior to the devolatilization and extrusion steps, in which a ring structure is formed in the main chain of the thermoplastic resin formed in the polymerization step by a cyclization condensation reaction.