Method for producing regenerated acrylic resin, and acrylic resin film

Abstract

The invention relates to a method for producing a regenerated acrylic resin and an acrylic resin film. Provided is a method for producing a regenerated acrylic resin by removing a highly adhesive layer from an acrylic resin substrate to which the highly adhesive layer has been adhered, the manufacturing method comprises a step of immersing the acrylic resin base material to which the easily adhesive layer is adhered in an aqueous alkali solution and performing alkali treatment, and the syndiotacticity represented by triad of the acrylic resin contained in the acrylic resin base material is 54% or more. The temperature of the aqueous alkali is 30-90 DEG C inclusive, and a treatment parameter, which is represented by the product of the temperature of the aqueous alkali and the time for immersion in the aqueous alkali, is 2000-10000 DEG C * min inclusive.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a recycled acrylic resin and an acrylic resin film. Background Art

[0002] A liquid crystal display device usually has two polarizers disposed on both sides of a liquid crystal cell. To protect the surfaces of the polarizers, a polarizer protection film is provided on the polarizers. As the polarizer protection film, an acrylic film is sometimes used (see Patent Documents 1 and 2). In addition, in order to improve the adhesion between the acrylic film and the polarizer, an easy-bonding layer is sometimes formed on one side of the acrylic film (see Patent Document 3). In this case, an adhesive is applied to the easy-bonding layer, whereby the polarizer protection film is adhered to the polarizer.

[0003] In recent years, from the viewpoint of effective utilization of materials, efforts have been made to recycle resins using part of the scraps of films as raw materials. For an acrylic film having an easy-bonding layer, when manufacturing a resin for an optical film using part of the scraps as raw materials, in order to prevent defects in the optical film caused by the easy-bonding layer remaining as foreign matter, it is necessary to remove the easy-bonding layer.

[0004] Here, as a method for removing a layer (heterogeneous layer) formed of a resin different from the base material and laminated on the base material formed of a resin, for example, Patent Document 4 discloses the following method: A heterogeneous layer provided on a base material made of a synthetic resin or a cellulose organic acid ester is removed in an alkaline aqueous solution at 105°C or higher, and then the alkaline aqueous solution is removed from the base material.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Publication No. 2023 / 238885

[0008] Patent Document 2: International Publication No. 2023 / 238886

[0009] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2010-55062

[0010] Patent Document 4: Japanese Unexamined Patent Application Publication No. 2001-310970 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] In the regeneration of an acrylic film having an easy-to-bond layer, the method described in Patent Document 4 can also be applied. However, when the syndiotactic regularity represented by the triad of the acrylic resin constituting the acrylic film is high, if the temperature of the aqueous alkali solution is increased or the treatment time is extended, the removal rate of the easy-to-bond layer becomes high, but sometimes the hydrolysis rate of the regenerated acrylic resin becomes high.

[0013] An object of the present invention is to provide a method for producing a regenerated acrylic resin that can increase the removal rate of the easy-to-bond layer and suppress hydrolysis.

[0014] Means for Solving the Problem

[0015] (1) A method for producing a regenerated acrylic resin, which is a method for removing the easy-to-bond layer from an acrylic resin substrate having an easy-to-bond layer attached thereto to produce a regenerated acrylic resin. The production method includes a step of performing alkali treatment by immersing the acrylic resin substrate having the easy-to-bond layer attached thereto in an aqueous alkali solution. The syndiotactic regularity represented by the triad of the acrylic resin contained in the acrylic resin substrate is 54% or more, the temperature of the aqueous alkali solution is 30°C or more and 90°C or less, and the treatment parameter represented by the product of the temperature of the aqueous alkali solution and the immersion time in the aqueous alkali solution is 2000°C·min or more and 10000°C·min or less.

[0016] (2) The method for producing a regenerated acrylic resin according to (1), wherein the syndiotactic regularity represented by the triad of the acrylic resin is 55% or more.

[0017] (3) The method for producing a regenerated acrylic resin according to (1) or (2), wherein the content ratio of the structural unit derived from methyl methacrylate in the acrylic resin is 98% by weight or more.

[0018] (4) The method for producing a regenerated acrylic resin according to any one of (1) to (3), wherein the glass transition temperature of the acrylic resin is 120°C or more.

[0019] (5) The method for producing a regenerated acrylic resin according to any one of (1) to (4), wherein the syndiotactic regularity represented by the triad of the acrylic resin is 80% or less.

[0020] (6) The method for producing a regenerated acrylic resin according to any one of (1) to (5), wherein the main chain of the acrylic resin does not contain a ring structure.

[0021] (7) The method for producing a regenerated acrylic resin according to any one of (1) to (6), wherein the easy-to-bond layer contains a urethane resin.

[0022] (8) An acrylic resin film having a glass transition temperature of 120 °C or higher and a contact angle with water at 25 °C of 65.0 ° or higher and 71.0 ° or lower.

[0023] (9) An acrylic resin film having an isotacticity represented by a triad of 54% or higher and a contact angle with water at 25 °C of 65.0 ° or higher and 71.0 ° or lower.

[0024] (10) The acrylic resin film according to (9), which is an acrylic resin having a content rate of a structural unit derived from methyl methacrylate of 98% by weight or higher.

[0025] (11) The acrylic resin film according to (9) or (10), having a glass transition temperature of 120 °C or higher.

[0026] Effect of the Invention

[0027] According to the present invention, there can be provided a method for producing a recycled acrylic resin that can increase the removal rate of the easy-bonding layer and suppress hydrolysis. Detailed Description of the Invention

[0028] Hereinafter, embodiments of the present invention will be described.

[0029] [Method for Producing Recycled Acrylic Resin]

[0030] The manufacturing method of the recycled acrylic resin according to this embodiment is a method of manufacturing a recycled acrylic resin by removing an easily adhesive layer from an acrylic resin substrate having the easily adhesive layer attached thereto. Specifically, the manufacturing method of the recycled acrylic resin according to this embodiment includes a step of subjecting the acrylic resin substrate having the easily adhesive layer attached thereto to an alkali treatment by immersing it in an aqueous alkali solution. Here, the syndiotacticity represented by the triad of the acrylic resin contained in the acrylic resin substrate is 54% or more. In addition, the temperature of the aqueous alkali solution is 30°C or higher and 90°C or lower. When the temperature of the aqueous alkali solution is lower than 30°C, the removal rate of the easily adhesive layer becomes low, and when it exceeds 90°C, the hydrolysis rate of the recycled acrylic resin becomes high. Further, the treatment parameter represented by the product of the temperature of the aqueous alkali solution and the immersion time in the aqueous alkali solution is 2000°C·min or higher and 10000°C·min or lower. When the treatment parameter is lower than 2000°C·min, the removal rate of the easily adhesive layer becomes low, and when it exceeds 10000°C·min, the hydrolysis rate of the recycled acrylic resin becomes high. It should be noted that if the hydrolysis rate of the recycled acrylic resin becomes high, there is a concern that the thermal decomposition resistance of the recycled acrylic resin decreases, or that when the recycled acrylic resin film is re-molded, the recycled acrylic resin reacts to generate gels or the like, resulting in granular defects, which is not preferable. It should be noted that the hydrolysis rate of the recycled acrylic resin is evaluated by measuring the contact angle of the recycled acrylic resin film with water.

[0031] In this specification and claims, the acrylic resin refers to a polymer of a monomer having an acryloyl group and / or a monomer having a methacryloyl group. At this time, the acrylic resin can be either a homopolymer or a copolymer. When the acrylic resin is a copolymer, the acrylic resin can be a copolymer of a monomer not having an acryloyl group or a methacryloyl group.

[0032] The temperature of the aqueous alkali solution is 30°C or higher and 90°C or lower, preferably 45°C or higher and 85°C or lower, more preferably 60°C or higher and 80°C or lower. In addition, the treatment parameter is 2000°C·min or higher and 10000°C·min or lower, preferably 3300°C·min or higher and 8000°C·min or lower, more preferably 3600°C·min or higher and 7200°C·min or lower.

[0033] The immersion time in the aqueous alkali solution is not particularly limited, and is, for example, 60 min or longer and 180 min or shorter.

[0034] The alkali contained in the aqueous alkali solution is not particularly limited, and examples thereof include sodium hydroxide, lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, etc., and two or more thereof can be used in combination. Among these, lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferred, and sodium hydroxide and potassium hydroxide are particularly preferred.

[0035] The pH of the aqueous alkali solution is not particularly limited, and is, for example, 10 or more and 14 or less.

[0036] It should be noted that the aqueous alkali solution may contain a surfactant or may not contain a surfactant.

[0037] In the present embodiment, as the acrylic resin substrate with an easy-to-bond layer attached thereto, for example, those obtained by crushing the scraps generated when manufacturing a polarizer protection film having an easy-to-bond layer formed on one side of an acrylic film can be used. At this time, after crushing the scraps, they can be sized.

[0038] The thickness of the acrylic film is not particularly limited, and is, for example, 10 μm or more and 100 μm or less. In addition, the thickness of the easy-to-bond layer is not particularly limited, and is, for example, 0.2 μm or more and 0.4 μm or less.

[0039] It should be noted that the acrylic film is obtained, for example, by stretching a blank film having an easy-to-bond layer formed on one side. In addition, the acrylic film is obtained, for example, by forming an easy-to-bond layer on one side after stretching the blank film.

[0040] The method for manufacturing the recycled acrylic resin of the present embodiment may further include: a step of filtering the aqueous alkali solution impregnated with the acrylic resin substrate with an easy-to-bond layer attached thereto, a step of washing the filtrate with water, and a step of drying the washed filtrate. At this time, the acrylic resin substrate with an easy-to-bond layer attached thereto can be sized while being immersed in the aqueous alkali solution, or the dried filtrate can be sized.

[0041] The recycled acrylic resin manufactured by the method for manufacturing the recycled acrylic resin of the present embodiment is mixed and used with an unused acrylic resin as needed.

[0042] The recycled acrylic resin is not particularly limited and can be applied to electronic materials and the like. For example, a film containing the recycled acrylic resin can be used as a substrate for an antenna, a substrate for a display, a substrate for a touch panel, etc. As a substrate for a display, a film for a liquid crystal display, a surface protection film, a polarizer protection film, etc. can be cited. The film containing the recycled acrylic resin can utilize optical properties and is particularly suitable for use in known optical applications such as around a liquid crystal display device such as an optically isotropic film, a polarizer protection film, and a transparent conductive film. In addition, the film containing the recycled acrylic resin can be adhered to a polarizer and used as a polarizing plate. That is, the film containing the recycled acrylic resin can be used as a polarizer protection film of the polarizing plate.

[0043] In addition, the recycled acrylic resin produced by the method for producing a recycled acrylic resin of the present embodiment is also suitable for chemical recycling (for example, a method of forming decomposition products by thermal decomposition, recovering decomposition oil, and reusing it as a chemical raw material or fuel). Generally, in order to improve the heat resistance and thermal stability of an acrylic resin, a ring structure is introduced into the main chain of the acrylic resin, or a monomer having a rigid structure is copolymerized. However, these structures become impurities when the acrylic resin is subjected to chemical recycling, which is not preferable. In this regard, since the recycled acrylic resin produced by the method for producing a recycled acrylic resin of the present embodiment has a high content rate of structural units derived from methyl methacrylate, it is expected that the yield of monomers recovered as decomposition oil will be high, and good chemical recyclability can be expected.

[0044] [Acrylic resin]

[0045] The syndiotacticity represented by the triad of the acrylic resin contained in the acrylic resin substrate is 54% or more, preferably 55% or more, more preferably 56% or more, and still more preferably 57% or more. When the syndiotacticity represented by the triad of the acrylic resin contained in the acrylic resin substrate is 54% or more, the glass transition temperature of the acrylic resin tends to increase and the heat resistance improves. In addition, the syndiotacticity represented by the triad of the acrylic resin contained in the acrylic resin substrate is preferably 80% or less, and from the viewpoints of the molding processing temperature of the recycled acrylic resin, the toughness of the molded body, and the secondary processability, it is more preferably 67% or less, still more preferably 65% or less, and even more preferably 63% or less.

[0046] The syndiotacticity represented by the triad of the acrylic resin is the ratio of the chain of three structural units (triad) being rr. It should be noted that in the chain of two structural units (dyad), those with the same configuration are called meso (m), and those with the opposite configuration are called racemic (r).

[0047] The glass transition temperature of the acrylic resin is preferably 120°C or higher, more preferably exceeding 120°C, still more preferably 121°C or higher, and particularly preferably 122°C or higher. The glass transition temperature of the acrylic resin is preferably 135°C or lower, more preferably 130°C or lower, from the viewpoints of the molding processing temperature of the recycled acrylic resin and the secondary processability of the molded body.

[0048] The content rate of the structural units derived from methyl methacrylate in the acrylic resin is preferably 98% by weight or more, more preferably 99% by weight or more, and still more preferably 100% by weight.

[0049] The monomers other than methyl methacrylate that constitute the acrylic resin are not particularly limited. For example, acrylic alkyl esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc.; acrylic aryl esters such as phenyl acrylate; acrylic cycloalkyl esters such as cyclohexyl acrylate, norbornenyl acrylate, etc.; alkyl methacrylates other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, butyl methacrylate, etc.; methacrylic aryl esters such as phenyl methacrylate; methacrylic cycloalkyl esters such as cyclohexyl methacrylate, norbornenyl methacrylate, etc.; aromatic vinyl compounds such as styrene, α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; methacrylonitrile.

[0050] The weight-average molecular weight of the acrylic resin is preferably 50,000 or more and 200,000 or less, more preferably 70,000 or more and 180,000 or less, still more preferably 80,000 or more and 160,000 or less, and even more preferably 90,000 or more and 150,000 or less. If the weight-average molecular weight of the acrylic resin is 50,000 or more, the mechanical properties of the molded article of the recycled acrylic resin tend to be improved. If it is 200,000 or less, the moldability of the recycled acrylic resin tends to be improved.

[0051] The weight-average molecular weight of the acrylic resin can be 400,000 or more. If the weight-average molecular weight of the acrylic resin is 400,000 or more, the mechanical properties of the molded article of the recycled acrylic resin tend to be further improved. For example, a resin film with excellent bending resistance can be obtained. In this case, the weight-average molecular weight of the acrylic resin is preferably 600,000 or more, more preferably 700,000 or more, still more preferably 800,000 or more. The upper limit of the weight-average molecular weight (Mw) is not particularly limited. From the viewpoint of moldability, it is preferably 4,000,000 or less, more preferably 3,500,000 or less, still more preferably 3,000,000 or less, particularly preferably 2,000,000 or less, and extremely preferably 1,500,000 or less.

[0052] The ratio (dispersion) of the weight-average molecular weight to the number-average molecular weight of the acrylic resin is preferably 1.6 or more and 2.5 or less, more preferably 1.7 or more and 2.2 or less. If the dispersion of the acrylic resin is 1.6 or more, the fluidity of the recycled acrylic resin tends to increase and it is easy to mold. If it is 2.5 or less, the mechanical properties such as impact resistance, toughness, and bending resistance of the molded article of the recycled acrylic resin tend to be improved.

[0053] It should be noted that the number-average molecular weight and weight-average molecular weight of the acrylic resin are values converted to standard polystyrene measured by gel permeation chromatography (GPC). In addition, the number-average molecular weight and weight-average molecular weight of the acrylic resin can be controlled by the types and amounts of polymerization initiators and chain transfer agents used in the synthesis of the acrylic resin.

[0054] The synthesis method of the acrylic resin is not particularly limited. For example, anionic polymerization method and radical polymerization method can be cited. Among these, the radical polymerization method is preferred (for example, refer to Patent Documents 1 and 2). It should be noted that in the anionic polymerization method, an organometallic compound is used as a polymerization initiator and an organic solvent is used as a medium. Therefore, it is not preferred in terms of the residual impurities and the environment. Here, the syndiotacticity of the acrylic resin can be controlled by the polymerization temperature of the acrylic resin. For example, by lowering the polymerization temperature of the acrylic resin, the syndiotacticity of the acrylic resin becomes larger.

[0055] [Easy adhesion layer]

[0056] The easy adhesion layer contains a resin and may also contain a crosslinking agent. The easy adhesion layer is formed, for example, by coating an easy adhesive containing a resin and then drying it. Here, the resin can be a thermosetting resin or a thermoplastic resin. In addition, the easy adhesion layer may have thermosetting properties alone or may not have thermosetting properties.

[0057] The resin is not particularly limited. For example, urethane resin, epoxy resin, etc. can be cited. Among these, urethane resin is preferred.

[0058] The urethane resin is not particularly limited, and known materials can be used (for example, refer to Patent Document 2). The urethane resin preferably has a carboxyl group. As the urethane resin having a carboxyl group, for example, a polyester urethane resin having a carboxyl group can be cited. As a commercially available product of the polyester urethane resin having a carboxyl group, for example, SUPERFLEX 210 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) can be cited.

[0059] The crosslinking agent is not particularly limited as long as it is a material that can crosslink with the resin, and known materials can be used (for example, refer to Patent Document 2). As a material that can crosslink with the urethane resin having a carboxyl group, for example, compounds and polymers having an epoxy group, a carbodiimide group, an oxazoline group, etc. can be cited. As a commercially available product of the polymer having an oxazoline group, for example, EPOCROS WS700 (manufactured by Nippon Shokubai Co., Ltd.) can be cited.

[0060] [Acrylic resin film]

[0061] The contact angle of the acrylic resin film of the present embodiment with respect to water at 25 °C is 65.0° or more and 71.5° or less, preferably 65.4° or more and 70.8° or less, more preferably 67.0° or more and 70.0° or less. The acrylic resin film of the present embodiment is formed, for example, using a recycled acrylic resin manufactured by the manufacturing method of the recycled acrylic resin of the present embodiment and a known forming method.

[0062] The glass transition temperature of the acrylic resin film of the present embodiment can be 120 °C or higher. In this case, the glass transition temperature of the acrylic resin film of the present embodiment is preferably more than 120 °C, more preferably 121 °C or higher, and still more preferably 122 °C or higher. From the viewpoint of secondary processability, the glass transition temperature of the acrylic resin film of the present embodiment is preferably 135 °C or lower, more preferably 130 °C or lower.

[0063] The syndiotactic regularity represented by the triad of the acrylic resin film of the present embodiment can be 54% or more. In this case, the syndiotactic regularity represented by the triad of the acrylic resin film of the present embodiment is preferably 55% or more, more preferably 56% or more, and still more preferably 57% or more. In addition, the acrylic resin film of the present embodiment preferably contains an acrylic resin having a content of a structural unit derived from methyl methacrylate of 98% by weight or more. Further, the acrylic resin film of the present embodiment preferably has a glass transition temperature of 120 °C or higher.

[0064] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and the above embodiments can be appropriately changed within the scope of the gist of the present invention.

[0065] [Examples]

[0066] Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples. The Examples of the present invention will be described, but the present invention is not limited to the Examples. It should be noted that the measurement methods of various physical properties are as follows.

[0067] (Conversion rate)

[0068] By the gravimetric method, from the ratio of the weight of the solid component of the acrylic resin after drying in an oven heated to 150 °C for 30 min to the weight of the monomer charged, that is, the formula

[0069] (Weight of solid component of acrylic resin / Weight of monomer charged) × 100

[0070] The conversion rate is determined.

[0071] (Syndiotactic regularity represented by triad)

[0072] Using a 400 MHz nuclear magnetic resonance apparatus AVANCEIII (manufactured by Bruker), the acrylic resin was measured in deuterated chloroform solution at 22 °C and with 16 cumulative scans. 11H-NMR spectrum. Next, measure the area (X) of the region from 0.60 to 0.95 ppm and the area (Y) of the region from 0.60 to 1.25 ppm with tetramethylsilane (TMS) set to 0 ppm, and then calculate the syndiotacticity represented by triads using the following formula.

[0073] (X / Y)×100

[0074] (Glass transition temperature)

[0075] Using a simultaneous differential thermal - thermogravimetric analyzer STA7200 (manufactured by Hitachi High - Tech Science Corporation), heat - treat the acrylic resin to remove residual monomers and decomposition products of polymerization initiators. Specifically, under a nitrogen gas flow rate of 200 mL / min, heat from 40 °C to 190 °C at a heating rate of 10 °C / min, and then hold at 190 °C for 2.0 to 2.5 minutes to heat - treat the acrylic resin.

[0076] Using a high - sensitivity differential scanning calorimeter DSC7000X (manufactured by Hitachi High - Tech Science Corporation), measure the glass transition temperature of the heat - treated acrylic resin. Specifically, first, under a nitrogen gas flow rate of 40 mL / min, heat from 40 °C to 160 °C at a heating rate of 10 °C / min, cool to 40 °C, and then heat from 40 °C to 160 °C at a heating rate of 10 °C / min. Then, read the mid - point glass transition temperature from the DSC curve measured during the second heating.

[0077] (Weight - average molecular weight, number - average molecular weight, and dispersity)

[0078] Using a high - performance GPC device HLC - 8220GPC (manufactured by Tosoh), calculate the weight - average molecular weight (Mw), number - average molecular weight (Mn), and dispersity (Mw / Mn) of the acrylic resin. At this time, use a sample solution prepared by dissolving 20 mg of the acrylic resin in 10 mL of tetrahydrofuran, and perform the analysis under the following conditions.

[0079] Detector: RI detector

[0080] Solvent: Tetrahydrofuran

[0081] Guard column: TSKgel guardcolumn SuperHZ - H (manufactured by Tosoh)

[0082] Analysis column: TSKgel SuperHZM - H × 2 columns (manufactured by Tosoh)

[0083] Measurement temperature: 40 °C

[0084] Standard substance: Standard polystyrene (manufactured by Tosoh Corporation)

[0085] (Contact angle with water)

[0086] Using a contact angle meter DMο-501 (manufactured by Kyowa Interface Science Co., Ltd.), the contact angle with water at 25 °C of the regenerated acrylic resin film was measured by the droplet method.

[0087] (Production of acrylic resin A1)

[0088] In a 4 L glass reactor equipped with a stirrer having an H-type stirring blade, 150 parts by weight of deionized water, 0.20 parts by weight of tricalcium phosphate as a dispersant, 0.0075 parts by weight of sodium α-olefin sulfonate, and 0.30 parts by weight of sodium chloride were charged. Then, under a nitrogen atmosphere, while stirring at 250 rpm, 100 parts by weight of methyl methacrylate (MMA), 0.289 parts by weight of n-octyl mercaptan as a chain transfer agent, and 0.065 parts by weight of 2,2'-azobis(isobutyric acid) dimethyl ester V-601 (manufactured by Fujifilm Wako Pure Chemical Corporation) as a polymerization initiator were added to the reactor. Then, the liquid temperature in the reactor was raised to 70 °C to start polymerization, and 0.10 parts by weight of tricalcium phosphate was added to the reactor 2 hours after the start of polymerization. At this time, an exothermic peak accompanied by a gel effect was observed 4 hours and 20 minutes after the start of polymerization. Then, heating was started 7 hours after the start of polymerization, and the liquid temperature in the reactor was raised to 95 °C. It should be noted that the conversion rate 7 hours after the start of polymerization was 93%. Then, 2 hours after the liquid temperature in the reactor reached 95 °C, the liquid temperature in the reactor was cooled to room temperature to end the polymerization, and an acrylic resin dispersion was obtained. It should be noted that the conversion rate at the end of polymerization was 99%. Relative to the weight of the monomers charged, the acrylic resin dispersion was acid-washed with 1N hydrochloric acid in a weight ratio of 0.1 times, and then washed with water to remove the dispersant. Then, the washed acrylic resin dispersion was dehydrated and dried to obtain bead-shaped acrylic resin A1.

[0089] (Production of acrylic resin A3)

[0090] Acrylic resin A3 was produced by the same method as in Production Example 1 of Japanese Patent No. 6827272.

[0091] (Physical properties of acrylic resin A1)

[0092] The syndiotacticity represented by the triad of acrylic resin A1 was 57%, the glass transition temperature was 120 °C, the content of the structural unit derived from methyl methacrylate was 100% by weight, Mw was 83,000, and Mw / Mn was 1.81.

[0093] (Physical properties of acrylic resin A3)

[0094] The syndiotacticity represented by the triad of acrylic resin A3 is 75%, the glass transition temperature is 128 °C, the content of the structural unit derived from methyl methacrylate is 100% by weight, Mw is 67,000, and Mw / Mn is 1.07.

[0095] (Production of acrylic resin pellets)

[0096] Using a co-rotating, intermeshing twin-screw extruder KZW15TWIN-45MG (manufactured by TECHNOVEL CORPORATION) with a die diameter of 15 mm and L / D = 45 at the outlet, acrylic resin A1 or A3 was extruded at a resin temperature of 255 °C. At this time, the strand-like molten resin extruded from the die was cooled in a water bath and then pelletized with a pelletizer to obtain acrylic resin pellets.

[0097] (Acrylic resin A2)

[0098] As acrylic resin A2 (acrylic resin pellets) with a syndiotacticity of 51% represented by the triad, PARAPET HR-S (manufactured by Kuraray) was used. The glass transition temperature of acrylic resin A2 is 116 °C, Mw is 91,000, and Mw / Mn is 1.68.

[0099] (Production of blank film)

[0100] After drying the acrylic resin pellets at 90 °C for 4 hours, using a co-rotating, intermeshing twin-screw extruder KZW15TWIN-45MG (manufactured by TECHNOVEL CORPORATION) with a T-die diameter of 15 mm and L / D = 45 at the outlet, the acrylic resin pellets were extruded at a resin temperature of 240 °C. At this time, the sheet-like molten resin extruded from the T-die was cooled with a cooling roll to obtain a blank film with a width of 130 mm and a thickness of 160 μm.

[0101] (Production of easy-bonding agent)

[0102] To 100 g of a carboxyl group-containing polyester urethane resin SUPERFLEX 210 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) with a solid content of 33% by weight, 20 g of an oxazoline group-containing resin EPOCROS WS700 (manufactured by Nippon Shokubai Co., Ltd.) with a solid content of 25% by weight was added, and then stirred for 3 minutes to obtain an easy-bonding agent.

[0103] (Production of blank film with easy-bonding layer)

[0104] After subjecting one side of the blank film to corona discharge treatment, an easy-bonding agent is coated using a rod coater (line number #6). Subsequently, the blank film coated with the easy-bonding agent is put into a hot air dryer and dried at 80 °C for about 1 minute to form an easy-bonding layer, obtaining a blank film with an easy-bonding layer.

[0105] (Manufacture of stretched film with easy-bonding layer)

[0106] Using a simultaneous twin-screw stretching machine IMC-1905 (manufactured by Iwamoto Seisakusho), the blank film with an easy-bonding layer is stretched at 135 °C with a stretching ratio of 2 times in both the MD and TD directions, obtaining a stretched film with an easy-bonding layer. The thickness of the stretched film with an easy-bonding layer is 40 μm, and the thickness of the easy-bonding layer is 0.35 μm.

[0107] (Examples 1 - 8, Comparative Examples 1 - 10)

[0108] The stretched film with an easy-bonding layer is cut with a shredder to obtain chips of about 5 mm × 15 mm. The obtained chips of the stretched film with an easy-bonding layer are acrylic resin substrates with an easy-bonding layer attached.

[0109] In a flask equipped with a stirring device, under specified conditions (refer to Table 1), 100 g of the chips of the stretched film with an easy-bonding layer are immersed in 1000 ml of a 4 wt% NaOH aqueous solution for alkali treatment. Subsequently, filtration is carried out using a 200-mesh stainless steel filter, and the filtrate is washed with water and then dried to obtain regenerated acrylic resin.

[0110] It should be noted that in Comparative Examples 7, 9, and 10, alkali treatment is not performed, and purified water is used instead of the 4 wt% NaOH aqueous solution for treatment.

[0111] (Manufacture of regenerated acrylic resin pellets)

[0112] Instead of acrylic resin A1 or A3, regenerated acrylic resin is used, and otherwise, the same operations as in (Manufacture of acrylic resin pellets) are carried out to obtain regenerated acrylic resin pellets.

[0113] (Manufacture of regenerated acrylic resin film)

[0114] Instead of acrylic resin pellets, regenerated acrylic resin pellets are used, and otherwise, the same operations as in (Manufacture of blank film) are carried out to obtain a regenerated acrylic resin film.

[0115] (Removal rate of easy-bonding layer)

[0116] Put 0.1 g of the regenerated acrylic resin and 9 g of a 4 wt% NaOH aqueous solution into a test tube, and then heat at 90 °C for 3 hours to dissolve the components of the easily adherent layer remaining in the regenerated acrylic resin, obtaining a solution. After putting the obtained solution into a glass cuvette (cell) with an optical path length of 1 cm, measure the absorbance Ab1 at a wavelength of 250 nm using an ultraviolet-visible spectrophotometer V-550 (manufactured by JASCO Corporation, Japan).

[0117] Instead of the regenerated acrylic resin, use a thin piece of a stretched film with an easily adherent layer, and perform the same operations as above to measure the absorbance Ab2 at a wavelength of 250 nm.

[0118] Calculate the removal rate of the easily adherent layer using the following formula.

[0119] (1 - Ab1 / Ab2) × 100

[0120] It should be noted that it is speculated that the light absorption at a wavelength of 250 nm mainly comes from the aromatic ring of the polyester of the urethane resin contained in the easily adherent layer.

[0121] (Comprehensive evaluation)

[0122] Based on the removal rate of the easily adherent layer and the contact angle of the regenerated acrylic resin film with water, conduct a comprehensive evaluation. The criteria for the comprehensive evaluation when using acrylic resins A1, A2, or A3 are as follows.

[0123] A: When the removal rate of the easily adherent layer is 80% or more and the contact angle with water is 65.0° or more

[0124] B: When the removal rate of the easily adherent layer is 60% or more and less than 80% and the contact angle with water is 60° or more, or when the removal rate of the easily adherent layer is 80% or more and the contact angle with water is 60° or more and less than 65°

[0125] C: When the removal rate of the easily adherent layer is less than 60%, or when the removal rate of the easily adherent layer is 60% or more and the contact angle with water is less than 60°

[0126] Table 1 and Table 2 show the removal rate of the easily adherent layer, the contact angle of the regenerated acrylic resin film with water, and the evaluation results of the comprehensive evaluation.

[0127] [Table 1]

[0128]

[0129] [Table 2]

[0130]

[0131] As can be seen from Table 1, in Examples 1 to 8, the hydrolysis rate of the recycled acrylic resin is low and the removal rate of the easy-to-bond layer is high. Therefore, the defects of the recycled acrylic resin film are few.

[0132] In contrast, in Comparative Examples 1 to 4, the treatment parameters are 750 to 1800 °C·min, so the removal rate of the easy-to-bond layer is low. The treatment parameter of Comparative Example 5 is 14400 °C·min, so the hydrolysis rate of the recycled acrylic resin is high. The temperature of the alkaline aqueous solution in Comparative Example 6 is 120 °C, so the hydrolysis rate of the recycled acrylic resin is high. In Comparative Examples 7, 9, and 10, since no alkali treatment is performed, the easy-to-bond layer is not removed. In Comparative Example 8, the syndiotactic regularity represented by the triad of acrylic resin A2 is 51%, so even if the treatment parameter is 7200 °C·min, the hydrolysis rate of the recycled acrylic resin is high.

Claims

1. A method for manufacturing a recycled acrylic resin, which is a method for manufacturing a recycled acrylic resin by removing an easily adhesive layer from an acrylic resin substrate having the easily adhesive layer attached thereto. The manufacturing method includes a step of subjecting the acrylic resin substrate having the easily adhesive layer attached thereto to an alkali treatment by immersing it in an aqueous alkali solution. The syndiotactic regularity represented by the triad of the acrylic resin contained in the acrylic resin substrate is 54% or more. The temperature of the aqueous alkali solution is 30°C or more and 90°C or less. The treatment parameter represented by the product of the temperature of the aqueous alkali solution and the immersion time in the aqueous alkali solution is 2000°C·min or more and 10000°C·min or less.

2. The method for manufacturing a regenerated acrylic resin according to claim 1, wherein, The syndiotactic regularity represented by the triad of the acrylic resin is 55% or more.

3. The method for manufacturing a regenerated acrylic resin according to claim 1 or 2, wherein, The content rate of the structural unit derived from methyl methacrylate in the acrylic resin is 98% by weight or more.

4. The method for manufacturing a recycled acrylic resin according to claim 1 or 2, wherein, The glass transition temperature of the acrylic resin is 120°C or more.

5. The method for manufacturing a regenerated acrylic resin according to claim 1 or 2, wherein, The syndiotactic regularity represented by the triad of the acrylic resin is 80% or less.

6. The method for manufacturing a regenerated acrylic resin according to claim 1 or 2, wherein, The main chain of the acrylic resin does not contain a ring structure.

7. The method for manufacturing a regenerated acrylic resin according to claim 1 or 2, wherein, The easily adhesive layer contains a urethane resin.

8. An acrylic resin film having a glass transition temperature of 120°C or more. The contact angle with water at 25°C is 65.0° or more and 71.5° or less.

9. An acrylic resin film having a syndiotactic regularity represented by the triad of 54% or more. The contact angle with water at 25°C is 65.0° or more and 71.5° or less.

10. The acrylic resin film according to claim 9, which contains an acrylic resin having a content rate of the structural unit derived from methyl methacrylate of 98% by weight or more.

11. The acrylic resin film according to claim 9, which has a glass transition temperature of 120°C or more.

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