Styrene monomer composition, method for producing same, and method for producing recycled styrene-based resin

Abstract

A significant reduction in conversion rate has been observed with a recycled styrene-based resin composition obtained by polymerizing a recycled styrene monomer produced by a conventional method compared with a styrene-based resin composition obtained by polymerizing a petroleum-derived styrene monomer. The purpose of the present invention is to provide a styrene monomer composition comprising (A) a recycled styrene monomer derived from a pyrolysis product of a styrene-based resin product containing a cellulose-based compound, and (B) a pyrolysis compound derived from a pyrolysis product of the styrene-based resin product other than the recycled styrene monomer (A), wherein the pyrolysis compound (B) is contained in an amount of 5 × 10-2 parts by mass or less with respect to 100 parts by mass of the recycled styrene monomer (A).

Description

Styrene monomer composition, its production method, and production method for recycled styrene resin

[0001] The present invention relates to a styrene monomer composition, a method for producing the same, and a method for producing a recycled styrene-based resin.

[0002] The environmental impact of plastic waste has increased in recent years, and recycling plastic waste is important for reducing waste and improving sustainability.

[0003] Styrene is widely used as a raw material for important plastic products such as polystyrene (PS), which is produced primarily by copolymerization of styrene alone or with other monomers.

[0004] Styrene is a chemically stable molecule, and obtaining high-quality recycled styrene requires removing impurities from discarded styrene-based resin compositions and optimizing reaction conditions, making effective recycling technically difficult.

[0005] Patent Document 1 discloses a method for recycling waste polystyrene products, which is characterized by including a step of subjecting the waste polystyrene products to thermal decomposition treatment to obtain recycled styrene monomer from the waste polystyrene.

[0006] WO2021 / 230312

[0007] However, when used waste polystyrene products are collected, some amount of other resins such as paper, cellophane tape, etc. are mixed in. In such a case, when recycled styrene monomer produced according to the method disclosed in Patent Document 1 is used, the polymerized recycled styrene-based resin composition may have a significantly lower conversion rate than a styrene-based resin composition polymerized from a petroleum-derived styrene monomer.

[0008] The present inventors investigated the decrease in the conversion rate of recycled styrene-based resin compositions and found that thermal decomposition compounds derived from waste resin products, including cellulose-derived papers used in resin products such as food containers, decrease the conversion rate of recycled styrene-based resin compositions.

[0009] Cellulose-based compounds such as paper and cellophane used in styrene-based resin products such as food containers are used as paper sheets bearing product information, wrapping paper to protect products, or cellophane tape for temporary fastening, and are difficult to completely remove in the recycling process of styrene-based resin products. On the other hand, although the amount of cellulose-based compounds such as paper and cellophane used in styrene-based resin products is small, they have been causing adverse effects on the recycling of styrene-based resin compositions.

[0010] As a result of extensive research, the present inventors have succeeded in suppressing the decrease in the conversion rate of recycled styrene-based resin compositions by appropriately controlling the concentration of pyrolysis compounds derived from waste resin products containing cellulose-based compounds, such as paper and cellophane, and have completed the present invention.

[0011] [1] An object of the present invention is to provide a styrene monomer composition, comprising: a recycled styrene monomer (A) derived from a thermal decomposition product of a styrene-based resin product containing a cellulose compound; and a thermal decomposition compound (B) derived from the thermal decomposition product of the styrene-based resin product and being a compound other than the recycled styrene monomer (A), wherein the thermal decomposition compound (B) is in an amount of 5×10 relative to 100 parts by mass of the recycled styrene monomer (A). －２ The present invention provides a styrene monomer composition comprising:

[0012] By using the present styrene monomer composition, the recycled styrene-based resin, which is a polymer thereof, can suppress a decrease in conversion rate compared to conventional recycled styrene-based resins.

[0013] [2] In the styrene monomer composition according to [1], the thermally decomposable compound (B) may be furfural.

[0014] [3] Another object of the present invention is to provide a recycled styrene-based resin, which is a polymer of the styrene monomer composition according to [1] or [2].

[0015] The recycled styrene-based resin, which is a polymer of the present styrene monomer composition, can suppress the decrease in conversion rate compared to conventional recycled styrene-based resins.

[0016] [4] Another object of the present invention is to provide a laminate comprising: a base layer containing the recycled styrene-based resin according to [3]; and an adhesive layer provided on one side of the base layer.

[0017] A laminate using a recycled styrene-based resin, which is a polymer of the present styrene monomer composition, can provide a laminate in which the decrease in conversion rate is suppressed compared to laminates using conventional recycled styrene-based resins.

[0018] [5] The laminate according to [4] may be an adhesive sticker or an adhesive tape.

[0019] [6] Another object of the present invention is to provide a method for producing a recycled styrene-based resin, comprising a polymerization step of polymerizing the styrene monomer composition according to [1] or [2].

[0020] By using this method, it is possible to produce a recycled styrene-based resin in which the decrease in conversion rate is suppressed compared to conventional recycled styrene-based resins.

[0021] DEFINITIONS For convenience, certain terms used in this application are collected here. Unless defined otherwise, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[0022] Although the numerical ranges and parameters set forth in the present invention are approximate, the numerical values ​​set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in each test measurement. Also, as used herein, the term "about" generally means within 10%, 5%, 1%, or 0.5% of a given value or range. Alternatively, the term "about" means within an acceptable standard error as considered by one of ordinary skill in the art.

[0023] Hereinafter, embodiments of the present invention will be described. The following embodiments are merely examples, and the scope of the present invention is not limited to the following embodiments. Note that similar content will not be described again to avoid repetition.

[0024] <Styrene Monomer Composition> The styrene monomer composition contains a recycled styrene monomer (A) derived from the thermal decomposition product of a styrene-based resin product containing a cellulose compound, and a thermal decomposition compound (B) derived from the thermal decomposition product of the styrene-based resin product and being a compound other than the recycled styrene monomer (A). The styrene monomer composition can be used in bulk polymerization or solution polymerization, which are conventional methods for producing styrene-based resins, and can be used as a raw material for producing recycled styrene-based resins. The styrene monomer composition may further contain petroleum-derived styrene monomer (fresh styrene monomer).

[0025] Resin products refer to resin products that are no longer needed, regardless of whether they are usable or not, and may be in the shape they were in at the time of disposal or may be crushed pieces of such products. Resin products containing styrene resins and cellulose compounds are waste resin products including paper and cellophane, which are cellulose compounds, manufactured using or partially using styrene resins. Resin products include the adjusted waste resin products described below.

[0026] <Paper and cellophane made from cellulose compounds> Paper and cellophane made from cellulose compounds are paper and cellophane made from cellulose in part or in part, and examples thereof include, but are not limited to, paper sheets bearing product information, wrapping paper for protecting products, and cellophane tape for temporary fastening.

[0027] <Recycled Styrene Monomer (A)> The recycled styrene monomer (A) is a styrene monomer (pyrolyzed styrene monomer) recovered from a pyrolysis product obtained by pyrolyzing a styrene-based resin product containing a cellulose-based compound, and may be recovered via distillation or may be a mixture with petroleum-derived styrene monomer (fresh styrene monomer).

[0028] <Thermal Decomposition Compound (B)> The thermal decomposition compound (B) is an impurity other than thermally decomposed styrene monomer, which is recovered from a thermal decomposition product obtained by thermally decomposing a styrene-based resin product containing a cellulose-based compound. The thermal decomposition compound (B) may be recovered via distillation. In an embodiment, the thermal decomposition compound (B) is furfural.

[0029] The thermal decomposition compound (B) is 5 × 10 －２ (0.05) parts by mass or less (for example, 4 × 10 －２ Parts by mass, 3 x 10 －２ Parts by mass, 5 x 10 －３ Parts by mass or less, 1×10 －３ Parts by mass or less, 5 x 10 －４ Parts by mass or less and 1×10 －４ (parts by mass or less).

[0030] When mixing a pyrolyzed styrene monomer derived from a pyrolysis product of a styrene-based resin product containing a cellulose compound with fresh styrene monomer, the pyrolyzed compound (B) is mixed in an amount of 5 × 10 with respect to 100 parts by mass of recycled styrene monomer (A). －２ It is preferable to mix the styrene monomer composition in an amount of 100 parts by mass or less, since this can prevent a decrease in the conversion rate of the recycled styrene-based resin obtained by polymerizing the styrene monomer composition.

[0031] The styrene-based resin product containing a cellulose-based compound may further contain a thermoplastic resin other than the styrene-based resin and the cellulose-based compound, and / or additives such as a paraffin-based hydrocarbon, an antioxidant, an antistatic agent, a lubricant, a release agent, and a hydrophilic additive.

[0032] <Method for producing styrene monomer composition> In the method for producing a styrene monomer composition of the present embodiment, the thermally decomposed compound (B) is mixed with 5×10 －２ The method includes a mixing step of mixing fresh styrene monomer with a mixture containing recycled styrene monomer (A) and a thermally decomposed compound (B) so that the amount of the recycled styrene monomer (A) and the thermally decomposed compound (B) is 100 parts by mass or less.

[0033] In one embodiment, the method for producing a styrene monomer composition further comprises a pyrolysis step of pyrolyzing the resin product to obtain a pyrolysis product. In one embodiment, the method for producing a styrene monomer composition further comprises a distillation purification step of distilling and purifying the pyrolysis product. In one embodiment, the pyrolysis product is oily (also referred to as pyrolysis oil).

[0034] Furthermore, if necessary, alkaline earth oxides and / or hydroxides, iron oxides, and / or aluminum oxides, etc. may be added to the resin product or the prepared resin product in the thermal decomposition step, thereby obtaining a thermal decomposition product with low chlorine, nitrogen, and sulfur contents.

[0035] In the pyrolysis step in which the resin product is pyrolyzed to obtain a pyrolysis product, the prepared resin product is preferably supplied to a pyrolysis furnace and heated to a temperature of 400 to 800°C in a non-oxidizing atmosphere. The non-oxidizing atmosphere is preferably an inert gas atmosphere such as nitrogen, water vapor, carbon dioxide, or argon, or a negative pressure atmosphere. The pyrolysis gas generated in this step is sent to a condenser and condensed to become pyrolysis oil (pyrolysis product), which is then sent to a distillation purification step in which the pyrolysis oil is purified by distillation.

[0036] Distillation purification step In the distillation purification step of distilling and purifying the pyrolysis product, for example, it is preferable to use two distillation columns, and separate compounds having a boiling point lower than that of styrene in the first distillation column and compounds having a boiling point higher than that of styrene in the second distillation column.

[0037] <Recycled styrene-based resin> The recycled styrene-based resin is a polymer having styrene-based monomer units obtained by polymerizing a styrene monomer composition. The recycled styrene-based resin preferably has more than 15% by mass and 100% by mass or less of styrene-based monomer units in 100% by mass of the polymer having styrene-based monomer units. In one aspect, the recycled styrene-based resin may be a polymer of a styrene-based monomer (styrene-based polymer). In one aspect, the recycled styrene-based resin may be a copolymer having styrene-based monomer units and (meth)acrylic monomer units (styrene-(meth)acrylic copolymer).

[0038] The styrene-based polymer may be a styrene-based monomer homopolymer obtained by polymerizing only one type of styrene-based monomer, or a copolymer obtained by polymerizing only two or more types of styrene-based monomer. Furthermore, the styrene-based polymer preferably contains 95% by mass or more of styrene-based monomer units, more preferably (substantially) 100% by mass, of the styrene-based polymer. The content of the styrene-based monomer units in 100% by mass of the styrene-based polymer is, for example, 95, 96, 97, 98, 99, 99.5, or 100% by mass, and may be within a range between any two of the values ​​exemplified here. Note that when two or more types of styrene-based monomer units are used, the content refers to the total mass. From the viewpoint of minimizing dimensional change, the styrene-based polymer is preferably a styrene homopolymer.

[0039] The (meth)acrylic monomer unit is a (meth)acrylic acid monomer unit or a (meth)acrylic acid ester monomer unit. The styrene-(meth)acrylic copolymer is a styrene-(meth)acrylic acid copolymer or a styrene-(meth)acrylic acid ester copolymer.

[0040] <Method for Producing Recycled Styrenic Resin> The method for producing a recycled styrene-based resin according to this embodiment includes a polymerization step of polymerizing the styrene monomer composition.

[0041] Polymerization methods for producing recycled styrene-based resins include known styrene polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. From the standpoints of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferred. Examples of solvents that can be used include alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

[0042] During polymerization of the styrene monomer composition, polymerization aids such as a polymerization initiator, a chain transfer agent, a crosslinking agent, and other polymerization aids may be used as necessary. The polymerization initiator is preferably a radical polymerization initiator, and examples of the polymerization initiator include peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-t-butylperoxycyclohexyl)propane, and 1,1-di(t-amylperoxy)cyclohexane, hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide, alkyl peroxides such as t-amylperoxyisononanoate, and dialkyl peroxides such as t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, and di-t-hexyl peroxide. Examples of the peroxides include peroxyesters such as t-butylperoxyacetate, t-butylperoxybenzoate, and t-butylperoxyisopropyl monocarbonate; peroxycarbonates such as t-butylperoxyisopropyl carbonate and polyether tetrakis(t-butylperoxycarbonate); N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), and N,N'-azobis[2-(hydroxymethyl)propionitrile]; and these may be used alone or in combination of two or more. Examples of chain transfer agents include aliphatic mercaptans such as n-dodecyl mercaptan and tert-dodecyl mercaptan, aromatic mercaptans, thiocarboxylic acids such as thioglycolic acid and mercaptopropionic acid, polyfunctional mercaptans in which the hydroxyl group of a polyhydric alcohol such as ethylene glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, or sorbitol is esterified with thioglycolic acid or mercaptopropionic acid, pentaphenylethane, α-methylstyrene dimer, and terpinolene. Among these, aliphatic mercaptans, aromatic mercaptans, thiocarboxylic acids, and polyfunctional mercaptans are preferred from the viewpoint of ease of molecular weight adjustment.

[0043] In the case of continuous polymerization, recycled styrene-based resins can be produced by a method including a polymerization step, a devolatilization step, and a granulation step.

[0044] First, in the polymerization step, a known complete mixing tank type agitation tank or tower type reactor is used, and the polymerization reaction is controlled by adjusting the polymerization temperature etc. so as to achieve the target molecular weight, molecular weight distribution and reaction conversion rate.

[0045] The polymer solution containing the polymer that has left the polymerization process is transferred to the devolatilization process, where unreacted monomers and polymerization solvent are removed. The devolatilization process is composed of a vacuum devolatilization tank equipped with a heater or a devolatilization extruder equipped with a vent. The molten polymer that has left the devolatilization process is transferred to the granulation process. In the granulation process, the molten resin is extruded in the form of strands through a multi-hole die and processed into pellets using the cold cut method, the in-air hot cut method, or the underwater hot cut method.

[0046] <Laminate> A laminate according to this embodiment includes an adhesive layer and a base layer provided on one side of the adhesive layer, and the base layer contains the recycled styrene-based resin. In one embodiment, the laminate is an adhesive sticker or an adhesive tape. In another embodiment, the other side of the adhesive layer includes a release layer.

[0047] The adhesive layer may be formed from an adhesive containing an acrylic adhesive and a natural rubber adhesive.

[0048] The adhesive layer may be made of any material, as long as it adheres to the release layer and to a plastic substrate or other substrate, such as a rubber-based adhesive material or an acrylic resin-based adhesive material, and the release layer can be easily peeled off from the adhesive layer. Examples of the material include polyester film and paper (release paper) coated with a release agent.

[0049] The present invention will be described in more detail below with reference to examples, but these examples are merely illustrative and are not intended to limit the scope of the present invention.

[0050] Examples 1 to 5 and Comparative Examples 1 to 3 Styrene Monomer Composition Resin products containing various ratios of styrene resin and cellulose compound were prepared by tumble blending. The resulting resin was thermally decomposed at approximately 550°C under a nitrogen atmosphere in accordance with the thermal decomposition apparatus described in JP 2021-134281 A, and a pyrolysis oil (pyrolysis product) was recovered. The resulting pyrolysis product was subjected to a distillation process, and the styrene monomer was separated and purified in a first distillation column and a second distillation column, resulting in a styrene monomer composition. Various styrene monomer compositions with different concentrations of pyrolysis compound (B) and fresh styrene monomer were mixed to achieve the composition ratios shown in Table 1. Recycled styrene resins were prepared under the conditions shown in Table 1. A polymerization process was performed by connecting the first and second reactors, which were complete mixing agitation tanks, and the third reactor, a plug-flow reactor equipped with a static mixer, in series. A styrene resin was produced under the conditions shown in Table 1. The volumes of the first reactor, second reactor, and third reactor were 39 liters, 39 liters, and 16 liters, respectively. A raw material solution was prepared using the raw material composition shown in Table 1, and the raw material solution was continuously supplied to the first reactor at the flow rate shown in Table 1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor to achieve the addition concentration (concentration by mass relative to the total amount of raw material monomer (styrene)) shown in Table 1, and the mixture was mixed uniformly.

[0051] The polymerization initiators listed in Table 1 are as follows: Polymerization initiator: 2,2-di(4,4-t-butylperoxycyclohexyl)propane [Pertetra A manufactured by NOF Corporation]

[0052] In the third reactor, a temperature gradient was applied along the direction of flow, and the temperatures at the intermediate portion and outlet portion were adjusted to be those shown in Table 1. Subsequently, the polymer-containing solution continuously removed from the third reactor was introduced into a vacuum devolatilizer tank equipped with a preheater, which was configured of two stages in series, and the temperature of the preheater was adjusted to give a resin temperature shown in Table 1, and the pressure was adjusted to be that shown in Table 1, thereby separating unreacted styrene and ethylbenzene. The polymer was then extruded into strands through a multi-hole die, and the strands were cooled and cut by a cold-cut method to be pelletized.

[0053] <Conversion Rate> The conversion rate of styrene was calculated as follows. The conversion rate of the recycled styrene-based resin was calculated by weighing the polymerization liquid obtained at the outlet of the third reactor (weight before heating (X)), heating it in an oven at 160°C for 24 hours, and weighing the solid matter obtained by volatilizing the styrene monomer (weight after heating (Y)), using the following formula: Conversion rate (%) = weight after heating (Y) / weight before heating (X) × 100

[0054] <Decrease in Conversion Rate Compared to Example 1> The ratio (%) of the conversion rate compared to Example 1 was calculated based on [conversion rate (%) in each recycled styrene-based resin / conversion rate (%) of Example 1], and the decrease in conversion rate (%) compared to Example 1 was calculated based on [100 - ratio (%) of the conversion rate compared to Example 1].

[0055]

[0056] The thermal decomposition compound (B) is 5×10 －２ When the amount of the thermally decomposed compound (B) was 5×10 parts by mass or less relative to 100 parts by mass of the recycled styrene monomer (A) (Examples 2 to 5), the attenuation rate of the conversion rate relative to Example 1 was at most 4.0%, and the decrease in the conversion rate of the recycled styrene resin was suppressed. －２ When the amount exceeded parts by mass (Comparative Examples 1 to 3), the conversion rate decreased by at least 6.9% relative to Example 1, so the conversion rate of the recycled styrene-based resin was significantly reduced.

Claims

1. A styrene monomer composition comprising: a recycled styrene monomer (A) derived from a thermal decomposition product of a styrene-based resin product containing a cellulose compound; and a thermal decomposition compound (B) derived from the thermal decomposition product of the styrene-based resin product and being a compound other than the recycled styrene monomer (A), wherein the thermal decomposition compound (B) is in a proportion of 5 x 10 with respect to 100 parts by mass of the recycled styrene monomer (A). －２ parts by weight or less of a styrene monomer composition.

2. The styrene monomer composition according to claim 1, wherein the thermally decomposing compound (B) is furfural.

3. A recycled styrene-based resin which is a polymer of the styrene monomer composition according to claim 1.

4. A laminate comprising a substrate layer containing the recycled styrene-based resin according to claim 3, and an adhesive layer provided on one side of the substrate layer.

5. The laminate according to claim 4, which is an adhesive sticker or an adhesive tape.

6. A method for producing a recycled styrene-based resin, comprising a polymerization step of polymerizing the styrene monomer composition according to claim 1.

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