JP7692255B2 - Method for producing resin solution - Google Patents

Description

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

The development of recycling technology for waste plastics has become an important issue in light of the recent increase in waste and the effective use of limited resources. Methods for recycling waste plastics can be broadly divided into three categories: material recycling, which reuses waste plastic as is; chemical recycling, which chemically breaks down waste plastics to recover basic chemical raw materials such as monomers; and thermal recycling, which recovers thermal energy from waste plastics.

Of these, material recycling and chemical recycling are desirable from the perspective of reducing the environmental impact, as they allow waste plastics to be reused by converting them into raw materials for products, thereby reducing the consumption of limited natural resources and the amount of waste sent to landfill sites through the circular use of resources.

In material recycling, waste plastic is turned into raw materials such as flakes or pellets, which are then melted and molded, and reused as resin material for the same product or a different plastic product. In order to meet quality standards for resin materials, foreign matter and dirt must be removed and the plastic must basically be made into the same type of plastic. In material recycling, if different types of waste plastic are mixed into the collected waste plastic, the properties of the recycled plastic will deteriorate, so technology is needed to separate the collected waste plastic with high precision.

In chemical recycling, waste plastics are converted into other chemical substances and reused, for example by pyrolyzing them at high temperatures to produce chemical raw materials such as synthetic gas or decomposed oil, or by chemically decomposing them to produce monomers. Compared to material recycling, it is often possible to recycle plastics even if they contain different types of plastics or contain foreign matter or dirt. On the other hand, if different types of plastics are mixed, this can sometimes cause problems in the process.

Therefore, waste plastics that are not suitable for material recycling or chemical recycling are currently processed through thermal recycling, and there is a strong demand for separation technology to obtain waste plastics suitable for material recycling and chemical recycling.

As a waste plastic separation technique, Patent Document 1 discloses a waste plastic sorting method for separating recycled plastics from waste plastics containing multiple types of materials, which includes a material sorting process for sorting the recycled plastics based on differences in wavelength absorbance due to the materials, and a centrifugation process for increasing the purity of the recycled plastics based on differences in specific gravity due to the materials, and which separates at least one type of the recycled plastics as recycled plastic by type through the material sorting process and the centrifugation process.

JP 2017-170653 A

However, the method described in Patent Document 1 requires two steps, a material selection step and a centrifugation step, and is not efficient.

The present invention has been made in consideration of the above circumstances, and aims to provide a method for dissolving resin from waste plastics, which is a mixture containing multiple resins, and a method for producing a resin solution that can dissolve resins other than the specific resin without dissolving the specific resin. In other words, the present invention aims to provide a method for efficiently separating a specific resin as a solid and resins other than the specific resin as a resin solution from waste plastics, which is a mixture containing multiple resins.

In order to solve the above problems, the present invention has the following aspects.
[1] A method for dissolving a resin from a mixture containing multiple types of resins, which does not dissolve a specific resin but dissolves resins other than the specific resin, comprising: selecting a solvent having a relative energy difference based on the Hansen solubility parameter for the specific resin of greater than 1 and a relative energy difference based on the Hansen solubility parameter for resins other than the specific resin of less than 1; and contacting the mixture with the solvent to dissolve the resins other than the specific resin.
[2] The method for dissolving a resin according to [1], wherein the specific resin contains a chlorine element.
[3] The method for dissolving a resin according to [1] or [2], wherein the mixture contains at least one resin selected from the group consisting of polyethylene, polypropylene, polystyrene, and polyvinyl chloride.
[4] The method for dissolving a resin according to any one of [1] to [3], wherein the solvent contains two or more types of solvents.
[5] A method for producing a resin solution, comprising the method for dissolving a resin according to any one of [1] to [4] as a resin dissolving step.

According to the present invention, it is possible to provide a method for dissolving resins from waste plastics, which is a mixture containing a plurality of resins, which does not dissolve a specific resin but can dissolve resins other than the specific resin.
Further, it is possible to provide a method for producing a resin solution, the method including the resin dissolving method as a resin dissolving step.

FIG. 1 is a schematic diagram showing how to determine the Hansen solubility parameter value and the interaction radius. 1 is a schematic diagram showing the distance between the solubility parameter values of two substances, substance 1 and substance 2. FIG. FIG. 2 is a schematic diagram showing a case where the relative energy difference between substance 1 and substance 2 based on the Hansen solubility parameters is within 1. FIG. 2 is a schematic diagram showing a case where the relative energy difference between substance 1 and substance 2 based on the Hansen solubility parameters is greater than 1. 1 is a _schematic diagram showing the relationship between the Hansen solubility parameter of a solvent L, the Hansen spheres S(P _A1 ) and S(P _A2 ) of resins P _A1 and P _A2 , and the Hansen spheres S(P _B1 ) and S(P _B2 ) of resins _P B1 and P B2.

The following describes in detail the embodiments of the present invention. However, the following description is merely an example of the embodiments of the present invention, and the present invention is not limited to these contents, and can be modified and implemented within the scope of the gist of the invention.

The method for dissolving a resin according to the present embodiment is a method for dissolving a resin from a mixture containing a plurality of types of resins, which does not dissolve a specific resin but dissolves resins other than the specific resin. Specifically, the method for dissolving a resin includes selecting a solvent having a relative energy difference based on the Hansen solubility parameter of more than 1 for the specific resin and a relative energy difference based on the Hansen solubility parameter of 1 or less for resins other than the specific resin, and contacting the mixture with the solvent to dissolve the resins other than the specific resin.
Hereinafter, the Hansen solubility parameter and the method for determining the relative energy difference will be described.

<Hansen Solubility Parameter>
Hansen solubility parameters (hereinafter simply referred to as "HSP") are based on the idea that two substances with similar intermolecular interactions are likely to dissolve in each other. HSP is composed of energy (δd) derived from intermolecular dispersion forces, energy (δp) derived from intermolecular dipole interactions, and energy (δh) derived from intermolecular hydrogen bonds. These three parameters can be regarded as coordinates in a three-dimensional space (Hansen space).

The HSP value of an evaluation sample having an unknown HSP value can be calculated by the following method.
In the Hansen solubility parameter space specified by plotting the HSP values (δd _m , δp _m , δh _m ) in a three-dimensional space, a number of pure substances (substances consisting of one type of compound) having known HPS values are plotted, and the Hansen sphere is specified based on the presence or absence of the solubility of the evaluation sample in the pure substances, and the HSP value of the evaluation sample is calculated by determining the central value of the Hansen sphere (Hansen sphere method).
The HSP value of the evaluation sample can also be calculated from information on the average molecular structure by using the atomic group contribution method.
In both the Hansen Solubility Parameters in Practice (HSPiP) and the group contribution method, the HSP value of the evaluation sample can be calculated using, for example, computer software Hansen Solubility Parameters in Practice (HSPiP).
In the case of the Hansen ball method, the evaluation sample may be a pure substance or a mixture.

A method for determining the central values of the Hansen sphere, that is, the HSP values (δd _m , δp _m , δh _m ), will be described with reference to FIG.
First, the HSP values of about 15 to 30 pure substances having known HSP values are plotted in the three-dimensional space (coordinate axes being the dispersion force term δd, the dipole-dipole force term δp, and the hydrogen bond force term δh) illustrated in FIG.
At this time, for example, pure substances that show solubility in the evaluation sample are indicated by a circle, and pure substances that do not show solubility in the evaluation sample are indicated by a cross, as shown in Figure 1. Next, based on the plotted solubilities of the evaluation samples, the phantom sphere that includes the pure substances that show solubility (indicated by a circle in Figure 1) and does not include the pure substances that do not show solubility (indicated by a cross in Figure 1) and has the smallest radius is determined as the Hansen sphere S (shown as a sphere in Figure 1).
The radius of the Hansen sphere S (the minimum radius) is the interaction radius _R0 that dissolves the pure substance shown by the circle in the figure and indicates compatibility, and the central values (δd _m , δp _m , δh _m ) of the obtained Hansen sphere S are the HSP values of the evaluation sample.
The HSP values of the above pure substances used to determine the Hansen sphere are, for example, a dispersion term δd of about 10 to 25 MPa ^1/2 , a dipole-dipole term δp of about 0 to 20 MPa ^1/2 , and a hydrogen bond term δh of about 0 to 20 MPa ^1/2 .
In addition, since solubility depends on temperature, when determining the Hansen ball, it is preferable to carry out the solubility test at a temperature at which the resin actually dissolves.

Next, Figure 2 is a schematic diagram showing the distance between the solubility parameters of two substances, substance 1 and substance 2. First, the Hansen spheres of substance 1 and substance 2 are determined by the above-mentioned method. When the HSP value of substance 1 is ( _δd1 , _δp1 , _δh1 ) and the HSP value of substance 2 is ( _δd2 , _δp2 , _δh2 ), the distance between the HSP values of the two substances (hereinafter also simply referred to as "Ra") can be calculated by the following formula 1.
Ra={4×(δd ₁ - δd ₂ ) ² + (δp ₁ - δp ₂ ) ² + (δh ₁ - δh ₂ ) ² } ^0.5 Equation 1

The relative energy difference (hereinafter, also simply referred to as "RED") of substance 1 to substance 2 based on the Hansen solubility parameters can be calculated by the following formula 2, where the interaction radius of substance 2 is _R0 .
RED=Ra/R ₀ formula 2

3 is a schematic diagram showing a case where the RED based on the Hansen solubility parameters of substance 1 for substance 2 is within 1. In this case, as shown in FIG. 3, the HSP values (δd ₁ , δp ₁ , δh ₁ ) of substance 1 are located inside the Hansen sphere S2 of substance 2 (including the surface of the sphere).

4 is a schematic diagram showing a case where RED based on the Hansen solubility parameters of substance 1 for substance 2 is greater than 1. In this case, as shown in FIG 4, the HSP values ( _δd1 , _δp1 , _δh1 ) of substance 1 are located outside S2 of the Hansen sphere of substance 2 (not including the surface of the sphere).

The method for dissolving a resin according to the present embodiment is a method for dissolving a resin other than a specific resin from a mixture containing a plurality of types of resins. Specifically, the method for dissolving a resin includes selecting a solvent having a relative energy difference based on the Hansen solubility parameter for the specific resin of more than 1 and a relative energy difference based on the Hansen solubility parameter for the resin other than the specific resin of not more than 1, and contacting the mixture with the solvent to dissolve the resin other than the specific resin.
The specific resin may be one type or more than one type. The resin other than the specific resin may be one type or more than one type.
Hereinafter, the specific resin will be referred to as “resin A,” and any resin other than the specific resin will be referred to as “resin B.” In this embodiment, from a mixture containing resin A and resin B, only resin B is dissolved.

<How to select a solvent>
Resin A is made up of resins P _A1 to P _Ax , and resin B is made up of resins P _B1 to P _By . x represents the number of types of resins constituting resin A and is an integer of 1 or more. y represents the number of types of resins constituting resin B and is an integer of 1 or more.
The value of x is not particularly limited, but from the viewpoint of facilitating the selection of the solvent, it is preferably 1 to 3, and more preferably 1 to 2. The value of y is not particularly limited, but from the viewpoint of facilitating the selection of the solvent, it is preferably 1 to 5, and more preferably 1 to 3. The value of x+y is not particularly limited, but from the viewpoint of facilitating the selection of the solvent, it is preferably 2 to 8, and more preferably 2 to 5.

The Hansen spheres S(P _A1 ) to S(P _Ax ) of the resins P _A1 to P _Ax are determined by the above-mentioned method. Then, from the obtained Hansen spheres S(P _A1 ) to S(P _Ax ), the HSP values [δd(P _A1 ), δp(P _A1 ), δh(P _A1 )] to [δd(P _Ax ), δp(P _Ax ), δh(P _Ax )] and the interaction radii R ₀ ( _{P A1} ) to R ₀ (P _Ax ) of _the resins P A1 to P Ax are determined.
Similarly, the Hansen spheres S(P _B1 ) to S(P _By ) of P _B1 to P _By are determined, respectively. Then, from the obtained Hansen spheres S(P _B1 ) to S(P _{By )} , the HSP values [δd(P _B1 ), δp(P _B1 ), δh(P _B1 )] to [δd(P _By ), δp(P _By ), δh(P _By )] and the interaction radii R ₀ (P _B1 ) to R ₀ (P _By ) of the resins P B1 to P _By are determined, respectively.

The HSP values of the selected solvent L are assumed to be tentative values [δd(L), δp(L), δh(L)].
The HSP values [δd(P _A1 ), δp(P _A1 ), δh(P _A1 )] to [δd(P _Ax ), δp(P _Ax ), δh(P _Ax )] of resins P _A1 to P _Ax are substituted into (δd ₂ , δp ₂ , δh ₂ ) of the above formula 1, and the HSP values [δd(L), δp(L), δh(L)] of solvent L are substituted into (δd ₁ , δp ₁ , δh ₁ ) of the above formula 1 to obtain Ra(P _A1 ) to Ra(P _Ax ). The obtained Ra(P _A1 ) to Ra(P _Ax ) are functions of δd(L), δp(L), and δh(L). Then, RED(P _A1 ) to RED(P _{Ax )} are obtained by substituting the interaction radii R ₀ (P _A1 ) to R ₀ (P _Ax ) of P _A1 to P Ax and the obtained Ra(P _A1 ) to Ra(P _Ax ) into the _above formula 2. The obtained RED(P _A1 ) to RED(P _Ax ) are functions of δd(L), δp(L), and δh(L).

Similarly, the HSP values [δd(P _B1 ), δp(P _B1 ), δh(P _B1 )] to [δd(P _By ), δp(P _By ), δh(P _By )] of resins P _B1 to _P By are substituted into (δd ₂ , δp ₂ , δh ₂ ) of the above formula 1, and the HSP values [δd(L), δp(L), δh(L)] of solvent L are substituted into (δd ₁ , δp ₁ , δh ₁ ) of the above formula 1 to obtain Ra(P _B1 ) to Ra(P _By ). The obtained Ra(P _B1 ) to Ra(P _By ) are functions of δd(L), δp(L), and δh(L). Then, the interaction radii _R0 (P _B1 ) to _R0 (P _{By ) of P B1 to} P _By and the obtained Ra(P _B1 ) to Ra(P _By ) are respectively substituted into the above formula 2 to obtain RED(P _B1 ) to RED(P _By ). The obtained RED(P _B1 ) to RED(P _By ) are functions of δd(L), δp(L), and δh(L).

In this embodiment, a solvent L is selected that has HSP values [δd(L), δp( _{L), δh(L)] such that all of RED(P A1 )} to RED(P _Ax ) are greater than 1 and all of RED(P B1 ) to RED(P _By ) are less than or equal to 1.
Figure 5 shows the relationship between the HSP value of solvent L when x is ₂ and y is 2, the Hansen spheres S(P _A1 ), S(P _A2 ) of resins P _A1 and P _A2 , and the Hansen spheres S( _{P B1} ), S(P _B2 ) of resins P B1 and P B2. As shown in Figure 5, the HSP value [δd(L), δp(L), δh(L)] of solvent L is located outside the Hansen spheres S(P _A1 ), S(P _A2 ) of resins P _A1 and P _A2 (not including the surface of the sphere), and inside the Hansen spheres S(P _B1 ), S(P _B2 ) of resins P _B1 and P _B2 (including the surface of the sphere).

In this embodiment, all of RED(P _A1 ) to RED(P _Ax ) are greater than 1, preferably greater than 2.5, and more preferably greater than 3. When all of RED(P _A1 ) to RED(P _Ax ) are greater than (equal to) the lower limit, dissolution of the resins P _A1 to P _Ax constituting the resin A by the solvent L is suppressed. The upper limit of RED(P _A1 ) to RED(P _Ax ) is not particularly limited, but is, for example, 10 or less.

In this embodiment, all of RED(P _B1 ) to RED(P _By ) are 1 or less, preferably 0.9 or less, and more preferably 0.8 or less. When all of RED(P _B1 ) to RED(P _By ) are equal to or less than the upper limit values, dissolution of the resins P _B1 to P By constituting the resin B _by the solvent L is promoted. The lower limit values of RED(P _B1 ) to RED(P _By ) are not particularly limited, but are, for example, 0.1 or more.

The distances Ra(P _A1 ) to Ra(P _Ax ) between the HSP value of the solvent L and the HSP values of the resins P _A1 to P _Ax are not particularly limited as long as all of RED(P _A1 ) to RED(P _Ax ) are greater than 1, but are preferably, for example, 5 MPa ^1/2 or more, and more preferably 10 MPa ^1/2 or more.

The distance Ra(P _B1 ) to Ra(P _By ) between the HSP value of the solvent L and the HSP values of the resins P _B1 to P _By is not particularly limited as long as all of RED(P _B1 ) to RED(P _By ) are 1 or less, but is preferably, for example, 8 MPa ^1/2 or less, and more preferably 5 MPa ^1/2 or less.

To select a solvent L having HSP values [δd(L), δp(L), δh(L)] such that all of RED(P _B1 ) to RED(P _By ) are 1 or less, this means that when y is 2 or more, all of the Hansen spheres S(P _B1 ) to S(P _By ) of the resins P _B1 to P _By have overlapping portions.
That is, when resins P _Bc and P _Bd where y = c and y = d are randomly selected from resin B, the relationship between Ra(P _{Bc -P} Bd ), obtained by substituting the HSP value of P _Bc [δd(P _Bc ), δp(P _Bc ), δh(P _Bc )] and the HSP value of P _Bd [δd(P _Bd ), δp(P _Bd ), δh(P _Bd )] into (δd ₁ , δp ₁ , δh ₁ ) and (δd ₂ , δp ₂ , _{δh 2} ) in the above formula 1, the interaction radius R ₀ (P _Bc ) of P _Bc , and the interaction radius R ₀ (P _Bd ) of P _Bd satisfy the following formula 3.
{R ₀ (P _Bc )+R ₀ (P _Bd )}≧Ra (P _Bc −P _Bd ) Equation 3

When there is a combination of resins P _B1 to P _By that does not satisfy formula 3, the resins of resin B may be appropriately reselected. That is, an arbitrary resin is removed from P _B1 to _P By constituting resin B so as to satisfy formula 3. In this case, the removed resin constitutes resin A.

<Resin>
The type of resin contained in the mixture of the present embodiment is not particularly limited, and examples thereof include polyolefin resins such as polyethylene, polypropylene, polybutadiene, and polymethylpentene; vinyl resins such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer; polystyrene resins such as polystyrene, acrylonitrile-styrene resin, and acrylonitrile-butadiene-styrene resin; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polytrimethylene terephthalate; and polystyrene-based resins such as triacetate. Examples of suitable resins include: cellulose; polycarbonate; urethane resins such as polyurethane and acrylic-modified polyurethane; polymethylpentene; polysulfone resins such as polyethersulfone, polyphenylsulfone, and polysulfone; polyetheretherketones such as polyetherketone, polyetheretherketone, and polyetherketoneketone; polyphenylene sulfide; polyimide-based resins such as polyetherimide and polyimide; polyamide-based resins such as polyamide 6, polyamide 66, and polyamide 11; acrylic resins; fluorine-based resins; phenolic resins; epoxy resins; melamine resins; urea resins; unsaturated polyester resins; alkyd resins.
The mass average molecular weight of the resin contained in the mixture of the present embodiment is not particularly limited as long as the effects of the present invention can be obtained, but may be, for example, 10,000 to 100,000, or 100,000 to 1,000,000.

The resin of this embodiment is solid at 30° C. or less. The form of the resin is not particularly limited as long as the effects of the present invention can be obtained, but examples of the form include a molded product molded into a package such as a PET bottle, a pellet form, a flake form, etc. The size of the resin is not particularly limited as long as the effects of the present invention can be obtained, but the major axis of the resin is about 1 to 100 mm.
From these resins, resin A and resin B can be arbitrarily selected according to the application described below.

<Solvent>
The solvent of the present embodiment is not particularly limited as long as it has an HSP value in which all of RED(P _A1 ) to RED(P _Ax ) are greater than 1 and all of RED(P _B1 ) to RED(P _By ) are equal to or less than 1. Examples of the solvent include esters such as methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, pentyl acetate, benzyl acetate, benzyl benzoate, ethyl benzoate, and butyl benzoate, ketones such as acetone, diisobutyl ketone, ethyl methyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone, γ-butyrolactone, and N-methyl-2-pyrrolidone, diethyl ether, methyl-tert-butyl ether, diisopropyl ether, dimethoxymethane, and dimethoxyethane. ethers such as 1,4-dioxane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, methyltetrahydrofuran, anisole, phenetole, and 2-methoxytetrahydropyran; methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-methyl-2-butanol, methoxypropanol, diacetone alcohol, cyclohexanol, 2-fluoroethanol, and 2,2,2-trifluoroethane; Examples of the organic solvent include alcohols such as ethanol and 2,2,3,3-tetrafluoro-1-propanol; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, and triethylene glycol dimethyl ether; organic solvents having an amide group such as N,N-dimethylformamide, acetamide, and N,N-dimethylacetamide; organic solvents having a nitrile group such as acetonitrile, isobutyronitrile, propionitrile, and methoxyacetonitrile; organic solvents having a carbonate group such as ethylene carbonate, propylene carbonate, and 1,2-glycerol carbonate; halogenated hydrocarbons such as methylene chloride, chloroform, tetrachloroethane, and chlorobenzene; and hydrocarbons such as n-pentane, cyclohexane, n-hexane, 1-octadecene, benzene, toluene, xylene, 2,2,4-trimethylpentane, cyclohexene, ethylbenzene, d-limonene, and 1-limonene.

One type of solvent may be used alone, or two or more types may be used in combination. That is, the solvent of this embodiment may be a mixture of two or more types of solvents (hereinafter, also referred to as a "mixed solvent"). Examples of the mixed solvent include a mixture of two or more types of the solvents listed above.

Other mixed solvents include petroleum fractions obtained in the refining process of crude oil, such as atmospheric residual oil, vacuum diesel, vacuum residual oil, desulfurized atmospheric residual oil, desulfurized vacuum diesel, light cracked diesel, and heavy cracked diesel; vegetable oils, such as soybean oil, rapeseed oil, sunflower oil, corn oil, cottonseed oil, peanut oil, olive oil, palm oil, sesame oil, rice oil, and orange oil, and waste oils thereof. In addition, the above-mentioned solvents may be further mixed into these mixed solvents.

When a mixed solvent is used as the solvent in this embodiment, the HSP value of the mixed solvent may be determined by the method described above, or may be determined as a weighted average of the HSP values of the solvents constituting the mixed solvent as described below.
The mixed solvent L is composed of solvents _L1 to _Lz , and the content ratios of the solvents _L1 to _Lz to the total volume of all the solvents before mixing are V( _L1 ) to V(Lz ₎ , respectively. If the HSP values of the solvents _L1 to _Lz are [δd( _L1 ), δp( _L1 ), δh( _L1 )] to [δd( _Lz ), δp( _Lz ), δh( _Lz )], respectively, the HSP values of the mixed solvent, [δd(L), δp(L), δh(L)], can be calculated by the following formulas 4 to 6.

In this embodiment, the HSP value of the mixed solvent is preferably calculated using the above formulas 4 to 6.

The boiling point of the solvent in this embodiment is not particularly limited as long as the effects of the present invention can be obtained, but may be, for example, 80 to 700°C, 150 to 500°C, or 200 to 400°C.
The density of the solvent in this embodiment is not particularly limited as long as the effects of the present invention can be obtained, but may be, for example, 0.70 to 1.5 g/cm ³ , 0.80 to 1.2 g/cm ³ , or 0.85 to 1.2 g/cm ³ .

<Combination of Resin A, Resin B and Solvent L>
In this embodiment, it is preferable that resin A contains a chlorine element. Also, in this embodiment, it is preferable that resin B and solvent L do not contain a chlorine element. When the solution obtained by the resin dissolving method and the resin solution manufacturing method of this embodiment is used as a raw material for chemical recycling described below, if the resin solution contains a chlorine element, hydrogen chloride is generated during the chemical recycling process, which may corrode the equipment used in the chemical recycling. Since resin A contains a chlorine element and resin B and solvent L do not contain a chlorine element, the resulting solution does not contain a chlorine element, making it possible to prevent corrosion of the equipment.
The resin contained in the mixture of the present embodiment is preferably at least one resin selected from the group consisting of polyethylene, polypropylene, polystyrene, and polyvinyl chloride.

When the resins constituting resin A are polystyrene and polyvinyl chloride, and the resins constituting resin B are polyethylene and polypropylene, examples of solvents that have a relative energy difference based on the Hansen solubility parameters with respect to resin A of more than 1 and a relative energy difference based on the Hansen solubility parameters with respect to resin B of 1 or less include benzene, cyclohexane, and ethylbenzene.

When the resins constituting resin A are polypropylene and polyvinyl chloride, and the resins constituting resin B are polyethylene and polystyrene, examples of solvents that have a relative energy difference based on the Hansen solubility parameters with resin A of more than 1 and a relative energy difference based on the Hansen solubility parameters with resin B of 1 or less include butyl benzoate, benzyl acetate, and orange oil.

When the resins constituting resin A are polyethylene and polyvinyl chloride, and the resins constituting resin B are polypropylene and polystyrene, examples of solvents that have a relative energy difference based on the Hansen solubility parameters with respect to resin A of more than 1 and a relative energy difference based on the Hansen solubility parameters with respect to resin B of 1 or less include chlorobenzene.

When the resins constituting resin A are polyethylene and polypropylene, and the resins constituting resin B are polystyrene and polyvinyl chloride, examples of solvents that have a relative energy difference based on the Hansen solubility parameters with respect to resin A of more than 1 and a relative energy difference based on the Hansen solubility parameters with respect to resin B of 1 or less include N-methylpyrrolidone and N,N-dimethylacetamide.

When the resin constituting resin A is polypropylene and the resin constituting resin B is polyethylene, polystyrene, or polyvinyl chloride, examples of solvents that have a relative energy difference based on the Hansen solubility parameters of more than 1 with respect to resin A and a relative energy difference based on the Hansen solubility parameters of 1 or less with respect to resin B include ethyl benzoate, 2-methoxytetrahydropyran, a mixed solvent of 81% by mass of d-limonene and 19% by mass of 1,2-glycerol carbonate, a mixed solvent of 64% by mass of d-limonene and 36% by mass of dimethylformamide, a mixed solvent of 58% by mass of tetrahydrofuran and 42% by mass of cyclohexanone, a mixed solvent of 62% by mass of ethyl acetate and 38% by mass of benzyl benzoate, and a mixed solvent of 58% by mass of methyl ethyl ketone and 42% by mass of benzyl benzoate.

When the resin that constitutes resin A is polyvinyl chloride and the resin that constitutes resin B is polyethylene, polypropylene, or polystyrene, examples of solvents that have a relative energy difference based on the Hansen solubility parameters with respect to resin A of more than 1 and a relative energy difference based on the Hansen solubility parameters with respect to resin B of 1 or less include 1,1,1,2-tetrachloroethane, d-limonene, o-xylene, and toluene.

(Conditions for dissolving resin)
In the method for dissolving a resin according to the present embodiment, the ratio of the mixture to the total mass of the solvent is not particularly limited as long as it is capable of dissolving resin B, but may be, for example, 1 to 50% by mass, 1 to 40% by mass, or 1 to 30% by mass.
In the method for dissolving a resin according to the present embodiment, the ratio of resin B to the total mass of the solvent is not particularly limited as long as resin B can be dissolved in the solvent, but may be, for example, 1 to 20% by mass, 1 to 18% by mass, or 1 to 15% by mass.
The temperature at which resin B is dissolved is not particularly limited as long as resin B can be dissolved; however, as long as resin A does not soften or melt at the temperature, it may be 15 to 100°C, 20 to 90°C, or 30 to 80°C.
When dissolving the resin B, it is preferable to carry out stirring, ultrasonic treatment, or the like.

In the method for dissolving a resin according to the present embodiment, it is preferable that all of the resin B is dissolved, but 80 to 100 mass % or 90 to 100 mass % of the total mass of the resin B may be dissolved.
In the method for dissolving a resin according to the present embodiment, it is preferable that resin A is not dissolved, but resin A may be dissolved in an amount of 0 mass % or more and less than 1 mass % relative to the total mass of resin A, or 0 to 0.5 mass % may be dissolved.

For example, if the resin contains heteroatoms such as halogen elements, the amount of dissolved resin can be confirmed by measuring the content of heteroatoms in the solution. The amount of dissolved resin that does not contain heteroatoms can be measured by a conventionally known analytical method, such as infrared spectroscopy, gas chromatography mass spectrometry, and gel filtration permeation chromatography.

<Method of producing resin solution>
The method for producing a resin solution according to the present embodiment includes the above-described resin dissolving method as a resin dissolving step, and can obtain a resin solution in which resin A is not dissolved and only resin B is dissolved.

<Uses of the resin dissolving method and the resin dissolving solution manufacturing method>
The applications of the method for dissolving a resin and the method for producing a resin solution according to this embodiment are roughly divided into two types: a method using resin A and a method using resin B.

(Method using resin A)
An example of a method for utilizing the resin A remaining after the resin dissolving method of the present embodiment is material recycling.
In this specification, "material recycling" refers to a recycling method in which waste plastics consisting of one type of resin are regenerated into plastic products as plastic raw materials.

When resin A is recycled as materials, first, the resin solution obtained by the resin dissolving method of the present embodiment is subjected to solid-liquid separation to separate resin A. The obtained resin A is washed and dried to obtain resin A as a solid. The obtained resin A can be treated by a material recycling method known in the art.
In material recycling, it is preferable to use one type of resin A. Resin A used in material recycling is preferably polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene resin, acrylic resin, or the like.

(Method using resin B)
An example of a method for utilizing the resin B dissolved by the method for dissolving a resin according to the present embodiment is chemical recycling.
In this specification, "chemical recycling" refers to a recycling method in which waste plastics, which are mixtures containing multiple types of resins, are regenerated into chemical raw materials by chemically converting (decomposing, etc.). Examples of chemical recycling include raw material/monomerization in which waste plastics are chemically decomposed and returned to plastics or monomers, blast furnace feedstock in which waste plastics are used as a reducing agent in steelworks, coke oven chemical feedstock in which hydrocarbon oils, coke, and coke oven gas are obtained by decomposing waste plastics in a coke oven, gasification in which waste plastics are thermally decomposed to obtain synthetic gas, and gasification in which waste plastics are thermally decomposed to obtain synthetic gas.

When chemically recycling resin B, first, the resin solution containing solid resin A obtained by the resin dissolving method of this embodiment is subjected to solid-liquid separation to separate resin A and obtain a solution in which resin B is dissolved in solvent L. Then, it is preferable to use the obtained solution as a raw material for chemical recycling.

In this embodiment, the dissolving solution is preferably used in the raw material/monomerization reaction in which waste plastics are chemically decomposed and returned to plastics and monomers in chemical recycling. When the raw material/monomerization reaction is performed, it is preferable to use resins consisting of polyethylene, polypropylene, polystyrene, and polyvinyl chloride as the mixture containing multiple types of resins in this embodiment, and it is preferable to select polyvinyl chloride as resin A and polyethylene, polypropylene, and polystyrene as resin B.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. Example 3 is a reference example.

<Resin>
The following resins were used as the resins to be dissolved.
Polyvinyl chloride (product name: KVC 933J-N, manufactured by Showa Kasei Kogyo Co., Ltd., density: 1.325 g/cm ³ )
Polystyrene (product name: Toyo Styrol GP G201C, manufactured by Toyo Styrene Co., Ltd., density: 1.040 g/cm ³ )
Low-density polyethylene (product name: Novatec LD LJ802, manufactured by Japan Polyethylene Co., Ltd., density: 0.918 g/cm ³ )
Hereinafter, polyvinyl chloride will be abbreviated as PVC, polystyrene as PS, and low-density polyethylene as LDPE (the same applies in Tables 1 and 3). Since PVC, PS, and LDPE differ in shape and color, it is possible to visually determine which resin has dissolved in the examples described later.

<Solvent>
The following solvents were used to dissolve the resin.
Light cracked diesel oil/orange oil (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 177°C, density: 0.845g/ ^cm3 )
Light aromatic solvent (product name: Swazol 1000, manufactured by Maruzen Petrochemical Co., Ltd., boiling point range: 160 to 180°C, density: 0.875 g/cm ³ )
Light cracked gas oil is a light fraction of the gas oil fraction obtained by fluid catalytic cracking reaction (boiling point range: 175 to 365° C.). Hereinafter, light cracked gas oil will be abbreviated as LCO (the same applies in Tables 2 and 3).

<Calculation of HPS value, _R0, etc.>
For the above resins, the Hansen ball was determined by the Hansen ball method using HSPiP, and the HSP value and _R0 were obtained. The HSP value and _R0 of the resins are shown in Table 1. Similarly, for the above solvents, the Hansen ball was determined by the Hansen ball method using HSPiP, and the HSP value was obtained. The HSP value of the solvent is shown in Table 2. The solubility when determining the Hansen ball was judged based on 25°C.

<Measurement of chlorine content>
The chlorine concentrations in the solutions obtained in Examples 1 to 4 and Comparative Examples 1 and 2 described below were measured using a trace chlorine/sulfur analyzer (TCL-2100V, manufactured by Mitsubishi Chemical Analytical Co., Ltd.).

[Example 1]
PVC was selected as resin A1, PS was selected as resin B1, and LCO was selected as the solvent. The HSP value of PVC and the HSP value of LCO were respectively substituted into ( _δd2 , _δp2 , _δh2 ) and ( _δd1 , _δp1 , _δh1 ) in the above formula 1 to obtain the HSP value distance (Ra(A1)) between PVC and LCO. Furthermore, RED(A1), which is the relative energy difference based on the Hansen solubility parameters of LCO with respect to PVC, was obtained from _R0 and Ra(A1) of PVC. Similarly, the HSP values of PS and LCO were substituted into ( _δd2 , _δp2 , _δh2 ) and ( _δd1 , _δp1 , _δh1 ) in the above formula 1, respectively, to determine the HSP value distance (Ra(B1)) between PS and LCO. Furthermore, RED(B1), which is the relative energy difference of LCO with respect to PS based on the Hansen solubility parameters, was determined from _R0 and Ra(B1) of PS. Ra(A1), RED(A1), Ra(B1), and RED(B1) are shown in Table 3.
90 g of LCO was added to a mixture of 5 g of PVC and 5 g of PS, and the mixture was stirred at 25° C. for 60 minutes. When the state of dissolution was visually observed, it was confirmed that PS was completely dissolved and solid PVC was observed. The amount of chlorine in the solution is shown in Table 3.

[Example 2]
PVC was selected as resin A1, PS was selected as resin B1, and orange oil was selected as the solvent. The HSP value of PVC and the HSP value of orange oil were substituted into (δd ₂ , δp ₂ , δh ₂ ) and (δd ₁ , δp ₁ , δh ₁ ) of the above formula 1, respectively, to obtain the HSP value distance (Ra(A1)) between PVC and orange oil. Furthermore, RED(A1), which is the relative energy difference based on the Hansen solubility parameters of orange oil to PVC, was obtained from R ₀ and Ra(A1) of PVC. Similarly, the HSP values of PS and orange oil were substituted into ( _δd2 , _δp2 , _δh2 ) and ( _δd1 , _δp1 , _δh1 ) in the above formula 1, respectively, to determine the HSP value distance (Ra(B1)) between PS and orange oil. Furthermore, RED(B1), which is the relative energy difference of orange oil to PS based on the Hansen solubility parameters, was calculated from _R0 and Ra(B1) of PS. Ra(A1), RED(A1), Ra(B1), and RED(B1) are shown in Table 3.
90 g of orange oil was added to a mixture of 5 g of PVC and 5 g of PS, and the mixture was stirred at 25° C. for 60 minutes. When the state of dissolution was visually observed, it was confirmed that PS was completely dissolved in the orange oil and that PVC was solid. The amount of chlorine in the solution is shown in Table 3.

[Example 3]
PVC was selected as resin A1, LDPE as resin B2, and orange oil as the solvent. The HSP value of PVC and the HSP value of orange oil were respectively substituted into (δd ₂ , δp ₂ , δh ₂ ) and (δd ₁ , δp ₁ , δh ₁ ) of the above formula 1 to obtain the HSP value distance (Ra(A1)) between PVC and orange oil. Furthermore, RED(A1), which is the relative energy difference based on the Hansen solubility parameters of orange oil for PVC, was obtained from R ₀ and Ra(A1) of PVC. Similarly, the HSP value of LDPE and the HSP value of orange oil were substituted into ( _δd2 , _δp2 , _δh2 ) and ( _δd1 , _δp1 , _δh1 ) in the above formula 1, respectively, to obtain the HSP value distance (Ra(B2)) between LDPE and orange oil. Furthermore, RED(B2), which is the relative energy difference based on the Hansen solubility parameters of orange oil in LDPE, was obtained from _R0 and Ra(B2) of LDPE. Ra(A1), RED(A1), Ra(B2), and RED(B2) are shown in Table 3.
90 g of orange oil was added to a mixture of 5 g of PVC and 5 g of LDPE, and the mixture was stirred at 25° C. for 60 minutes. When the state of dissolution was visually observed, the LDPE was completely dissolved, and the solid PVC was confirmed. The amount of chlorine in the solution is shown in Table 3.

[Example 4]
PVC was selected as resin A1, PS as resin B1, LDPE as resin B2, and orange oil as the solvent. The HSP value of PVC and the HSP value of orange oil were respectively substituted into (δd ₂ , δp ₂ , δh ₂ ) and (δd ₁ , δp ₁ , δh ₁ ) of the above formula 1 to obtain the HSP value distance (Ra(A1)) between PVC and orange oil. Furthermore, RED(A1), which is the relative energy difference based on the Hansen solubility parameters of orange oil for PVC, was obtained from R ₀ and Ra(A1) of PVC. Similarly, the HSP value of PS and the HSP value of orange oil were substituted into (δd ₂ , δp ₂ , δh ₂ ) and (δd ₁ , δp ₁ , δh ₁ ) of the above formula 1, respectively, to obtain the HSP value distance (Ra(B1)) between PS and orange oil. Furthermore, the relative energy difference RED(B1) based on the Hansen solubility parameter of orange oil for PS was obtained from R ₀ and Ra(B1) of PS. Furthermore, the HSP value of LDPE and the HSP value of orange oil were substituted into (δd ₂ , δp ₂ , δh ₂ ) and (δd ₁ , δp ₁ , δh ₁ ) of the above formula 1, respectively, to obtain the HSP value distance (Ra(B2)) between LDPE and orange oil. Furthermore, the relative energy difference RED(B2) based on the Hansen solubility parameters of orange oil for PS was calculated from _R0 and Ra(B2) of LDPE. Ra(A1), RED(A1), Ra(B1), RED(B1), Ra(B2), and RED(B2) are shown in Table 3.
85 g of orange oil was added to a mixture of 5 g of PVC, 5 g of PS, and 5 g of LDPE, and the mixture was stirred at 25° C. for 60 minutes. When the state of dissolution was visually observed, it was found that PS and LDPE were completely dissolved, and solid PVC was confirmed. The amount of chlorine in the solution is shown in Table 3.

[Comparative Example 1]
PVC was selected as resin A1, LDPE was selected as resin B2, and LCO was selected as the solvent. The HSP value of PVC and the HSP value of LCO were respectively substituted into ( _δd2 , _δp2 , _δh2 ) and ( _δd1 , _δp1 , _δh1 ) in the above formula 1 to obtain the HSP value distance (Ra(A1)) between PVC and LCO. Furthermore, RED(A1), which is the relative energy difference based on the Hansen solubility parameters of LCO for PVC, was obtained from _R0 and Ra(A1) of PVC. Similarly, the HSP value of LDPE and the HSP value of LCO were substituted into ( _δd2 , _δp2 , _δh2 ) and ( _δd1 , _δp1 , _δh1 ) in the above formula 1, respectively, to obtain the HSP value distance (Ra(B2)) between LDPE and LCO. Furthermore, RED(B2), which is the relative energy difference based on the Hansen solubility parameters of LCO in LDPE, was obtained from _R0 and Ra(B2) of LDPE. Ra(A1), RED(A1), Ra(B2), and RED(B2) are shown in Table 3.
90 g of LCO was added to a mixture of 5 g of PVC and 5 g of LDPE, and the mixture was stirred at 25° C. for 60 minutes. The dissolved state was visually observed, and solid PVC and LDPE were confirmed. The amount of chlorine in the solution is shown in Table 3.

[Comparative Example 2]
PVC was selected as resin A1, LDPE was selected as resin B2, and Swazol 1000 was selected as the solvent. The HSP value of PVC and the HSP value of Swazol 1000 were substituted into (δd ₂ , δp ₂ , δh ₂ ) and (δd ₁ , δp ₁ , δh ₁ ) of the above formula 1, respectively, to obtain the HSP value distance (Ra(A1)) between PVC and Swazol 1000. Furthermore, RED(A1), which is the relative energy difference based on the Hansen solubility parameters of Swazol 1000 with respect to PVC, was obtained from R ₀ and Ra(A1) of PVC. Similarly, the HSP value of LDPE and the HSP value of Swazol 1000 were substituted into ( _δd2 , _δp2 , _δh2 ) and ( _δd1 , _δp1 , _δh1 ) in the above formula 1, respectively, to obtain the HSP value distance (Ra(B2)) between LDPE and Swazol 1000. Furthermore, RED(B2), which is the relative energy difference based on the Hansen solubility parameters of Swazol 1000 with respect to LDPE, was obtained from _R0 and Ra(B2) of LDPE. Ra(A1), RED(A1), Ra(B2), and RED(B2) are shown in Table 3.
To a mixture of 5 g of PVC and 5 g of LDPE, 90 g of Swazol 1000 was added and stirred at 25° C. for 60 minutes. When the state of dissolution was visually observed, solid PVC and LDPE were confirmed. The amount of chlorine in the solution is shown in Table 3.

In Examples 1 to 4, in which a solvent having a RED based on the Hansen solubility parameters of more than 1 for resin A1 and a RED based on the Hansen solubility parameters of 1 or less for resin B1 and/or resin B2 was selected, resin A1 was not dissolved, and only resin B1 and/or resin B2 could be dissolved.
On the other hand, in Comparative Examples 1 and 2 in which a solvent having a RED based on the Hansen solubility parameters of greater than 1 for resin A1 and a RED based on the Hansen solubility parameters of greater than 1 for resin B2 was selected, resin A1 did not dissolve, but resin B2 could not be dissolved either.

Claims (2)

A method for dissolving a resin from a mixture containing multiple types of resins, which does not dissolve a specific resin but dissolves resins other than the specific resin, comprising selecting a solvent (excluding a solvent consisting only of xylene) having a relative energy difference based on the Hansen solubility parameter for the specific resin of greater than 1 and a relative energy difference based on the Hansen solubility parameter for resins other than the specific resin of less than 1, and contacting the mixture with the solvent to dissolve the resins other than the specific resin, wherein the solvent comprises two or more types of solvents, and the resins other than the specific resin comprise polypropylene or polystyrene . The method for producing a resin solution according to claim 1, wherein the specific resin contains a chlorine element.

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