JP7149480B2 - Method for producing acrylic resin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an acrylic resin film by a melt extrusion method.

Since acrylic resin films are excellent in transparency and weather resistance, they are mainly used as building materials as surface protective materials for polycarbonate, vinyl chloride, and the like.
As a method for producing such an acrylic resin film with good thickness accuracy by a melt extrusion method, for example, Patent Document 1 describes (1) the opening degree of the exit (die slip) from which the melt is discharged / the average film thickness of the film is 10 to 1.2, extruding the melt through a die slip, (2) while the glass transition temperature of the multilayer acrylic resin is higher than or equal to (3) from the die slip to the contact roll or metal belt This document describes a method for producing an acrylic resin film characterized in that the distance is 100 mm or less, and (4) both sides are brought into contact with a roll or a metal belt to form the film.

JP-A-2003-25412

According to the production method described in Patent Document 1, an acrylic resin film can be produced with high thickness accuracy. There is a problem that the flow of the molten resin becomes unstable between them, and the thickness accuracy is lowered.

An object of the present invention is to solve the above conventional problems, and in a method for producing an acrylic resin film by a melt extrusion method, an acrylic resin film that is excellent in thickness accuracy even when the film formation speed is increased. An object of the present invention is to provide a method for producing a manufacturable acrylic resin film.

As a result of repeated studies to solve the above-mentioned problems, the present inventors found that the extrusion rate adjusted by the amount of resin composition discharged from the die, the die lip clearance, and the die lip width, that is, the raw material resin composition By establishing a specific relationship between the speed at which the melt is extruded from the die and the take-up speed of the roll that takes up the melt discharged from the die, excellent thickness accuracy is achieved even when the film forming speed is increased. The present inventors have found that it is possible to obtain an acrylic resin film having a high degree of stability, and have completed the present invention through further studies based on this finding.

That is, the gist of the present invention is the following [1] to [7].
[1] A method for producing an acrylic resin film by a melt extrusion method,
The speed (V ₁ ) at which the melt of the resin composition containing the acrylic polymer having a multilayer structure is extruded from the die and the take-up speed (V ₂ ) of the film made of the resin composition are expressed by the following formula (1 ) is satisfied, a method for producing an acrylic resin film.
V ₂ /V ₁ ≦15 Formula (1)

[2] The method for producing an acrylic resin film according to [1], wherein V ₁ is 0.5 to 3.0 m/min.
[3] The method for producing an acrylic resin film according to [1] or [2], wherein the die lip clearance is 0.1 to 1.8 mm.
[4] The method for producing an acrylic resin film according to any one of [1] to [3], wherein the resin composition has a solvent-soluble content of 30 to 70% by mass.
[5] The method for producing an acrylic resin film according to any one of [1] to [4], wherein the acrylic resin film has a thickness of 20 to 200 μm.
[6] The method for producing an acrylic resin film according to any one of [1] to [5], wherein the acrylic resin film has a thickness accuracy of 15% or less.

[7] The acrylic polymer having a multilayer structure has a core-shell multilayer structure consisting of three layers of a core, an inner shell, and an outer shell,
The polymer (a) constituting the core contains 40 to 98.99% by mass of structural units derived from methyl methacrylate and 1 to 59% by mass of structural units derived from an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms. , a polymer containing 0.01 to 1% by mass of structural units derived from a grafting agent and 0 to 0.5% by mass of structural units derived from a crosslinking agent,
The polymer (b) constituting the inner shell contains 70 to 99.5% by mass of structural units derived from alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and 0 to 29 mass% of structural units derived from methyl methacrylate. %, 0.5 to 5% by mass of structural units derived from a grafting agent, and 0 to 5% by mass of structural units derived from a cross-linking agent, and constituting the outer shell (c) is a polymer having a glass transition temperature of 80° C. or higher, containing 80 to 99% by mass of structural units derived from methyl methacrylate and 1 to 19% by mass of structural units derived from alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. The method for producing an acrylic resin film according to any one of [1] to [6].

According to the present invention, in a method for producing an acrylic resin film by a melt extrusion method, it is possible to produce an acrylic resin film having excellent thickness accuracy even when the film forming speed is increased. can provide

<Method for producing acrylic resin film>
The method for producing an acrylic resin film of the present invention is a method for producing an acrylic resin film by a melt extrusion method,
The speed (V ₁ ) at which the melt of the resin composition containing the acrylic polymer having a multilayer structure is extruded from the die and the take-up speed (V ₂ ) of the film made of the resin composition are expressed by the following formula (1 ) is a method for producing an acrylic resin film characterized by satisfying
V ₂ /V ₁ ≦15 Formula (1)

According to the present invention, it is possible to obtain an acrylic resin film having excellent thickness accuracy even when the film forming speed is increased.

In the present invention, it is important that V ₂ /V ₁ is 15 or less. V ₂ /V ₁ is preferably 4 or more, more preferably 5 or more, and even more preferably 6 or more, from the viewpoint of improving thickness accuracy and film appearance. When V ₂ /V ₁ is less than 4, there are cases where appearance defects such as die lines tend to occur. On the other hand, V ₂ /V ₁ is preferably 14 or less, more preferably 13 or less, and even more preferably 12 or less from the viewpoint of obtaining an acrylic resin film with high thickness accuracy.

V1 and V2 in the _formula ( ₁ ) are defined as follows.
V1 (m _/ min) = Q / 60 / D / (L x W) x 1000 Formula (2)
In formula (2), Q (kg/hour) is the amount discharged from the die, D is the density of the resin composition (g/cm ³ ), L (mm) is the die lip clearance, and W (mm) is the die lip width. .

V ₂ (m/min): Film take-up speed The film take-up speed can be calculated from the diameter and number of revolutions of the metal roll that initially takes up the melt discharged from the die.

Said V ₁ is preferably 0.5 to 3.0 m/min, more preferably 0.7 to 2.9 m/min, still more preferably 0.8 to 2.8 m/min, especially Preferably 1.0-2.7 m/min, most preferably 1.2-2.5 m/min.
Also, the V2 is preferably ₁ to 45 m/min, more preferably 5 to 40 m/min, even more preferably 10 to 30 m/min. When V ₁ and V ₂ are within the above ranges, it is possible to obtain an acrylic resin film having excellent thickness accuracy even when the film forming speed is increased.

The discharge rate Q is preferably 10 to 60 kg/hour, more preferably 15 to 55 kg/hour, still more preferably 20 to 50 kg/hour, although it depends on the die size.

The die lip clearance L is preferably 0.1 to 1.8 mm, more preferably 0.3 to 1.5 mm, and still more preferably, from the viewpoint of increasing the film thickness accuracy and making it easier to obtain a film with less die lines. is 0.6 to 1.0 mm.
From the same viewpoint as the die lip clearance L, the die lip width W is preferably 300 to 700 mm, more preferably 350 to 600 mm, still more preferably 400 to 550 mm.

The melt extrusion temperature in the production method of the present invention is preferably 200 to 300°C, more preferably 220 to 280°C, still more preferably 240 to 270°C. When the melt-extrusion temperature is within the above range, the thermal decomposition of the raw material resin composition is less likely to proceed, and the occurrence of coloring and foreign matter can be suppressed. The melt extrusion temperature in the manufacturing method of the present invention is the set barrel temperature of the extruder.
In the present invention, the residence time of the resin composition in the film-forming apparatus including the extruder is preferably 10 minutes or less, more preferably 7 minutes or less. When the residence time is within the above range, thermal decomposition and coloration of the resin composition can be suppressed.

Examples of the production method of the present invention include a method in which a resin composition containing an acrylic polymer having a multilayer structure is melted with an extruder and produced by a T-die method, an inflation method, a calendar method, or the like. From the viewpoint of obtaining a good film, the T-die method is particularly preferred.

As an extruder used in the production method of the present invention, it is preferable to use an extruder having a single or twin screw. Moreover, from the viewpoint of suppressing coloration, it is preferable to use an extruder having a vent and perform melt-kneading under reduced pressure or under a nitrogen stream.
In addition, in the production method of the present invention, it is preferable to install a polymer filter from the viewpoint of removing foreign matter, and furthermore, it is preferable to install a gear pump in order to further increase the thickness accuracy.

In the production method of the present invention, from the viewpoint of improving the surface smoothness and thickness accuracy of the acrylic resin film, the extruded melt is preferably taken up using a metal mirror roll or mirror belt and pressed. is preferred. Examples of the mirror surface roll made of metal include an elastic metal roll and a rigid metal roll. From the viewpoint of improving the surface smoothness of the acrylic resin film, it is preferable to use a combination of an elastic metal roll and a rigid metal roll.
When a mirror roll or mirror belt is used, the pressing pressure is preferably 0.5 MPa or more, more preferably 1.0 MPa or more, from the viewpoint of improving the surface smoothness of the acrylic resin film.
When a mirror roll or mirror belt is used, the surface temperature thereof is preferably 50 to 130° C., more preferably 60 to 90° C., from the viewpoint of improving the surface smoothness, haze, appearance, etc. of the acrylic resin film. °C.

According to the present invention, for example, an acrylic resin film having a thickness of 20 to 200 μm can be obtained with high thickness accuracy. Furthermore, the thickness of the acrylic resin film is preferably 25 to 180 μm, more preferably 30 to 150 μm, from the viewpoints of improving the handleability of the acrylic resin film and keeping the cost low. When the thickness is equal to or more than the lower limit, the rigidity is increased, and the handleability of the acrylic resin film is improved. Moreover, when the film thickness is equal to or less than the upper limit, the balance between the strength of the acrylic resin film and the manufacturing cost is improved.

The thickness accuracy of the acrylic resin film obtained by the present invention is preferably 15% or less, more preferably 10% or less, still more preferably 7% or less, particularly preferably 5% or less, and most preferably 5% or less. Preferably, it is 3% or less.
The thickness accuracy of the film can be determined by the method described in Examples.

<Resin composition used as raw material>
In the production method of the present invention, a resin composition containing an acrylic polymer having a multilayer structure is used as a raw material. The resin composition as a raw material will be described in detail below.

<<Acrylic polymer having a multilayer structure>>
The acrylic polymer having a multilayer structure used in the present invention is not particularly limited as long as it has a multilayer structure, and examples thereof include acrylic polymers having a core-shell multilayer structure. Moreover, the number of layers constituting the multilayer structure is not particularly limited, and may be two layers or three layers or more.
Among these, from the viewpoint of improving the impact resistance of the acrylic resin film, an acrylic polymer having a core-shell multilayer structure is preferable. An acrylic polymer having a core-shell multilayer structure consisting of three layers of shells (outer layers) is preferred. In the present invention, the acrylic polymer having a core-shell multilayer structure consisting of three layers means that the core and the inner shell, and the inner shell and the outer shell are respectively composed of different polymers.
In addition, when the resin composition containing the acrylic polymer having a core-shell multilayer structure consisting of three layers is melt-kneaded, all or part of the outer shell is fused to form a matrix, The matrix contains core-shell particles consisting of two layers, a core and an inner shell.

The acrylic polymer having a core-shell multilayer structure composed of three layers, a core (inner layer), an inner shell (intermediate layer), and an outer shell (outer layer), will be described below in detail. The polymer constituting the core is referred to as "polymer (a)", the polymer constituting the inner shell as "polymer (b)", and the polymer constituting the outer shell as "polymer (c)". explain.

[Polymer (a): polymer constituting the core]
The polymer (a) is a polymer containing a structural unit derived from methyl methacrylate, a structural unit derived from an alkyl acrylate, a structural unit derived from a grafting agent, and optionally a structural unit derived from a cross-linking agent. is preferred.

Although the alkyl acrylate used in the polymer (a) is not particularly limited, the alkyl group preferably has 1 to 8 carbon atoms, more preferably 2 to 6 carbon atoms. When the carbon number of the alkyl group in the alkyl acrylate is within the above range, the thermal decomposition resistance of the acrylic polymer having a multilayer structure is improved, and the hot water whitening resistance and boiling water whitening resistance of the acrylic resin film are improved. do. Specific alkyl acrylates include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, t-butyl acrylate, n-butylmethyl acrylate, n-heptyl acrylate, 2-ethylhexyl acrylate, Examples include n-octyl acrylate and the like. These can be used individually by 1 type or in combination of 2 or more types.
Among these, n-butyl acrylate is particularly preferable from the above viewpoint.

The polymer (a) is used for the purpose of chemically bonding the polymer (a) and the polymer (b), and for the purpose of assisting the formation of the crosslinked structure of the polymer (a). It preferably contains a structural unit derived from the grafting agent.
The grafting agent used for the polymer (a) is not particularly limited as long as it is a monomer having two or more different polymerizable groups. Examples include allyl methacrylate, allyl acrylate, mono- or di-allyl maleate, Mono- or di-allyl fumarate, crotyl acrylate, crotyl methacrylate and the like can be mentioned. These grafting agents can be used singly or in combination of two or more.
Among these, allyl methacrylate is preferable from the viewpoint of improving the bonding ability between the polymer (a) and the polymer (b) and improving the stress whitening resistance and transparency of the acrylic resin film.

The polymer (a) is used for the purpose of forming a crosslinked structure in the polymer (a) and for the purpose of forming a crosslinked structure between the polymer (a) and the polymer (b). , may contain a structural unit derived from a cross-linking agent.
The cross-linking agent used in the polymer (a) is not particularly limited as long as it is a monomer having two or more of the same kind of polymerizable groups (excluding the grafting agent). compounds, diallyl compounds, divinyl compounds, diene compounds, trivinyl compounds and the like. More specifically, ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, divinylbenzene, trivinylbenzene, ethylene glycol diallyl ether, Propylene glycol diallyl ether, butadiene and the like can be mentioned. These cross-linking agents can be used singly or in combination of two or more.

The amount of structural units derived from methyl methacrylate in the polymer (a) is preferably 40 to 98.99% by mass, more preferably 45 to 96.9% by mass, based on the total structural units of the polymer (a). %. When the amount of structural units derived from methyl methacrylate is at least the above lower limit, the acrylic resin film has improved weather resistance, and when it is at most the above upper limit, the impact resistance of the acrylic resin film improves.

The amount of structural units derived from alkyl acrylate in the polymer (a) is preferably 1 to 59% by mass, more preferably 3 to 55% by mass, based on the total structural units of the polymer (a). When the amount of the structural unit derived from the alkyl acrylate is at least the lower limit, the thermal decomposition resistance of the acrylic polymer having a multilayer structure is improved. and boiling water whitening resistance are improved.

The amount of structural units derived from the grafting agent in the polymer (a) is preferably 0.01 to 1% by mass, more preferably 0.1 to 0, based on the total structural units of the polymer (a). 0.5 mass %. When the amount of structural units derived from the grafting agent is at least the above lower limit, the bonding strength between the polymer (a) and the polymer (b) is improved, and when it is at most the above upper limit, acrylic The impact resistance of the resin film is improved.

The amount of the structural unit derived from the cross-linking agent in the polymer (a) is preferably 0 to 0.5% by mass, more preferably 0 to 0.2% by mass, based on the total structural units of the polymer (a). %. When the amount of structural units derived from the cross-linking agent is within the above range, the impact resistance of the acrylic resin film is improved.

Polymer (a) and polymer (b), which will be described later, are preferably insoluble in solvents such as acetone, that is, grafted. When the polymer (a) and the polymer (b) are grafted, the polymer (a) and the polymer (b) form particles having a two-layer structure in the matrix of the polymer (c) described later. It is preferable because it becomes present and improves the impact resistance of the acrylic resin film.

[Polymer (b): Polymer Constituting Inner Shell]
The polymer (b) is a polymer containing a structural unit derived from an alkyl acrylate, a structural unit derived from a grafting agent, and optionally a structural unit derived from methyl methacrylate and a structural unit derived from a cross-linking agent. is preferred.

Examples of the alkyl acrylate used for the polymer (b) include the alkyl acrylates exemplified for the polymer (a), which improve the thermal decomposition resistance of the acrylic polymer having a multi-layer structure and improve the acrylic resin film. From the viewpoint of improving hot water whitening resistance and boiling water whitening resistance, n-butyl acrylate is particularly preferred.

Examples of the grafting agent used for the polymer (b) include the grafting agents exemplified for the polymer (a). Allyl methacrylate is preferable from the viewpoint of improving the resistance to stress whitening and improving the transparency of the acrylic resin film.

Examples of the cross-linking agent used for the polymer (b) include the cross-linking agents exemplified for the polymer (a), from the viewpoint of forming a cross-linked structure in the polymer (b), and from the viewpoint of the polymer (a). From the viewpoint of forming a crosslinked structure with the polymer (b), diacryl compounds, dimethacryl compounds, diallyl compounds, divinyl compounds and the like are preferred.

The amount of structural units derived from alkyl acrylate in the polymer (b) is preferably 70 to 99.5% by mass, more preferably 80 to 99% by mass, based on the total structural units of the polymer (b). be. When the structural unit derived from alkyl acrylate is at least the above lower limit, the impact resistance of the acrylic resin film is improved, and when it is at most the above upper limit, the stress whitening resistance and transparency of the acrylic resin film are improved. do.

The amount of structural units derived from methyl methacrylate in the polymer (b) is preferably 0 to 29% by mass, more preferably 0 to 20% by mass, based on the total structural units of the polymer (b). When the amount of the structural unit derived from methyl methacrylate is within the above range, the impact resistance of the acrylic resin film is improved.

The amount of structural units derived from the grafting agent in the polymer (b) is preferably 0.5 to 5% by mass, more preferably 1 to 4% by mass, based on the total structural units of the polymer (b). is. When the amount of the structural unit derived from the grafting agent is at least the above lower limit, the stress whitening resistance of the acrylic resin film is improved. On the other hand, when it is equal to or less than the above upper limit, the impact resistance of the acrylic resin film is improved.

The amount of the structural units derived from the cross-linking agent in the polymer (b) is preferably 0 to 5% by mass, more preferably 0 to 2% by mass, based on the total structural units of the polymer (b). When the amount of structural units derived from the cross-linking agent is within the above range, the impact resistance of the acrylic resin film is improved.

In the present invention, polymer (b) is preferably softer than polymer (a) and polymer (c). The polymer (b) is softer than the polymer (a) and the polymer (c), thereby improving the impact resistance.

[Polymer (c): Polymer Constituting Outer Shell]
Polymer (c) is preferably a polymer containing a structural unit derived from methyl methacrylate and a structural unit derived from alkyl acrylate.
Examples of the alkyl acrylate used for the polymer (c) include the alkyl acrylates exemplified for the polymer (a), which improve the thermal decomposition resistance of the acrylic polymer having a multi-layer structure and improve the acrylic resin film. Methyl acrylate and n-butyl acrylate are particularly preferred from the viewpoint of improving hot water whitening resistance and boiling water whitening resistance.

The amount of structural units derived from methyl methacrylate in the polymer (c) is preferably 80 to 99% by mass, more preferably 85 to 98% by mass, based on the total structural units of the polymer (c). When the amount of the structural unit derived from methyl methacrylate is at least the above lower limit, the stress whitening resistance of the acrylic resin film is improved. On the other hand, when it is equal to or less than the above upper limit, the thermal decomposition resistance of the acrylic resin film is improved.

The amount of structural units derived from alkyl acrylate in the polymer (c) is preferably 1 to 19% by mass, more preferably 2 to 15% by mass, based on the total structural units of the polymer (c). When the amount of the structural unit derived from the alkyl acrylate is at least the lower limit, the thermal decomposition resistance of the acrylic polymer having a multilayer structure is improved, and when it is at least the lower limit, the stress whitening resistance of the acrylic resin film is improved. improve sexuality.

The glass transition temperature of the polymer (c) is preferably 80°C or higher, more preferably 90°C or higher, still more preferably 100°C or higher. The higher the glass transition temperature of the polymer (c), the more improved the hot water whitening resistance and boiling water whitening resistance of the acrylic resin film. The glass transition temperature can be adjusted by changing the type and amount of the monomer to be copolymerized with methyl methacrylate, or by controlling the stereoregularity by the polymerization temperature or the like. The glass transition temperature of polymer (c) is usually 130° C. or lower.

The glass transition temperature of polymer (c) can be measured according to JIS K7121:2012. That is, without containing the polymer (a) and the polymer (b), only the polymer (c) is separately synthesized, the obtained polymer (c) is heated once to 250° C., and then heated to 30° C. The DSC curve was measured by differential scanning calorimetry under the conditions of cooling to ° C. or less and then raising the temperature from 30 ° C. to 230 ° C. at 20 ° C./min. The desired midpoint glass transition temperature can be the glass transition temperature of the polymer (c).

Polymer (c) is preferably soluble in solvents such as acetone, ie, not crosslinked. When the polymer (c) is not crosslinked, the polymer (c) is forms a matrix in which particles composed of the polymer (a) and the polymer (b) are present, improving the ease of production of the acrylic resin film.

[Mass ratio of polymer (a), polymer (b) and polymer (c)]
The amount of the polymer (a) in the acrylic polymer having a multilayer structure is preferably 1 to 30% by mass, more preferably 3 to 20% by mass, and still more preferably 4 to 15% by mass. . When the amount of the polymer (a) is at least the lower limit, the thermal stability and productivity of the acrylic resin film are improved. On the other hand, when the amount of the polymer (a) is equal to or less than the upper limit, the impact resistance and flexibility of the acrylic resin film are improved.

The amount of the polymer (b) in the acrylic polymer having a multilayer structure is preferably 20 to 45% by mass, more preferably 25 to 40% by mass, still more preferably 28 to 35% by mass. . When the amount of the polymer (b) is at least the lower limit, the thermal stability and productivity of the acrylic resin film are improved. On the other hand, when the amount of the polymer (b) is equal to or less than the upper limit, the impact resistance and flexibility of the acrylic resin film are improved.

The amount of the polymer (c) in the acrylic polymer having a multilayer structure is preferably 50 to 75% by mass, more preferably 55 to 70% by mass, still more preferably 58 to 68% by mass. . When the amount of the polymer (c) is at least the above lower limit, the fluidity of the acrylic polymer having a multilayer structure and the moldability of the acrylic resin film are improved. When the amount of the polymer (c) is equal to or less than the upper limit, the impact resistance and stress whitening resistance of the acrylic resin film are improved.

[Melt Flow Rate (MFR) of Acrylic Polymer Having Multilayer Structure]
The acrylic polymer having a multilayer structure has a melt flow rate of preferably 0.5 to 20 g/10 min, more preferably 0.8 to 10 g/10 min at 230° C. under a load of 3.8 kg. be. When the melt flow rate of the acrylic polymer having a multilayer structure is at least the above lower limit, the fluidity of the acrylic polymer having a multilayer structure and the moldability of the acrylic resin film are improved. On the other hand, when the melt flow rate is equal to or less than the upper limit, the mechanical properties of the acrylic resin film are improved.
The melt flow rate in the present invention can be measured at 230° C. under a load of 3.8 kg according to JIS K7210-1:2014.

[Method for Producing Acrylic Polymer Having Multilayer Structure]
The method for producing the acrylic polymer having a multilayer structure used in the present invention is not particularly limited. It can be obtained by forming by
More specifically, 40 to 98.99% by mass, more preferably 45 to 96.9% by mass of methyl methacrylate, and 1 to 59% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group in the presence of an emulsifier %, more preferably 3-55% by weight, grafting agent 0.01-1% by weight, more preferably 0.1-0.5% by weight and cross-linking agent 0-0.5% by weight, more preferably 0- A latex (I) containing the polymer (a) is obtained by polymerizing 0.2% by mass (primary polymerization).
Then, in the presence of latex (I), 70 to 99.5% by mass, more preferably 80 to 99% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, 0 to 29% by mass of methyl methacrylate, more preferably 0 to 20% by weight, 0.5 to 5% by weight of grafting agent, more preferably 1 to 4% by weight and 0 to 5% by weight, more preferably 0 to 2% by weight of crosslinker, in the latex (I) is used as a seed for polymerization (secondary polymerization) to obtain latex (II) containing polymer (a) and polymer (b).
Then, in the presence of latex (II), 80 to 99% by weight, more preferably 85 to 98% by weight, methyl methacrylate and 1 to 19% by weight, more preferably 1 to 19% by weight, alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. 2 to 15% by mass of the latex (II) as a seed is polymerized (tertiary polymerization) to obtain the polymer (a) as the core, the polymer (b) as the inner shell, and the polymer (c) as the outer shell. A latex (III) containing an acrylic polymer having a multi-layered structure is obtained. Next, after the latex (III) is coagulated to obtain a slurry, the slurry is washed and dewatered, and the dewatered slurry is dried to obtain the polymer (a) as the core and the polymer (b) as the inner shell. ), an acrylic polymer having a multilayer structure containing the polymer (c) as an outer shell can be obtained.

[Polymerization initiator]
There are no particular restrictions on the polymerization initiator used in the production of acrylic polymers having a multilayer structure, but water-soluble inorganic initiators such as potassium persulfate and ammonium persulfate; inorganic initiators such as sulfites and thiosulfates redox initiators using salts, etc.; redox initiators using organic peroxides with ferrous salts, sodium sulfoxylates, or the like.
The polymerization initiator may be added to the reaction system all at once at the start of the polymerization, or may be added to the reaction system at the start of the polymerization and during the polymerization in consideration of the reaction rate and the like. The amount of the polymerization initiator used can be appropriately set, for example, so that the average particle size of the acrylic polymer having a multilayer structure falls within the range described below.

〔emulsifier〕
Emulsifiers used in the production of acrylic polymers having a multilayer structure are not particularly limited, but examples include anionic emulsifiers such as long-chain alkylsulfonates, alkyl sulfosuccinates, and alkylbenzenesulfonates; polyoxyethylene alkyl ethers. , nonionic emulsifiers such as polyoxyethylene nonylphenyl ether; polyoxyethylene nonylphenyl ether sulfates such as sodium polyoxyethylene nonylphenyl ether sulfate; polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene alkyl ether sulfate; Examples include nonionic/anionic emulsifiers such as alkyl ether carboxylates such as sodium oxyethylene tridecyl ether acetate. The amount of the emulsifier used can be appropriately set, for example, so that the average particle size of the acrylic polymer having a multilayer structure falls within the range described below.

[Chain transfer agent]
In the present invention, a chain transfer agent can be used in each polymerization for the purpose of adjusting the molecular weight of the acrylic polymer having a multilayer structure. Particularly in the tertiary polymerization, the melt flow rate of the acrylic polymer having a multilayer structure can be adjusted to the above range by adding a chain transfer agent to the reaction system to adjust the molecular weight of the polymer (c). can.
Chain transfer agents used for producing acrylic polymers having a multilayer structure are not particularly limited, but examples include alkyl mercaptans such as n-octylmercaptan, n-dodecylmercaptan, t-dodecylmercaptan and n-hexadecylmercaptan; xanthogen disulfides such as dimethylxanthogen disulfide and diethylxanthogen disulfide; thiuram disulfides such as tetrathiuram disulfide; and halogenated hydrocarbons such as carbon tetrachloride and ethylene bromide.

The amount of the chain transfer agent to be used can be appropriately set within a range that allows the polymer to have a predetermined molecular weight in each polymerization. The amount of the chain transfer agent used in the tertiary polymerization varies depending on the amount of the polymerization initiator used in the tertiary polymerization, etc., but the monomers used in the tertiary polymerization, specifically methyl methacrylate and It is preferably 0.05 to 2 parts by mass, more preferably 0.08 to 1 part by mass, relative to 100 parts by mass of the total amount of alkyl acrylate.

[Ultraviolet absorber]
In the method for producing an acrylic polymer having a multilayer structure, a reactive ultraviolet absorber may be used as necessary in any one or more of the primary polymerization, secondary polymerization and tertiary polymerization. good. As the reactive ultraviolet absorber, for example, 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-1,2,3-benzotriazole can be used. When a reactive UV absorber is used, the reactive UV absorber is introduced into the molecular chain of the acrylic polymer having a multilayer structure, thereby improving the UV resistance of the acrylic polymer having a multilayer structure. The amount of the reactive ultraviolet absorber to be added is preferably 0.05 to 5 parts by mass with respect to 100 parts by mass of the total amount of monomers used for polymerization of the acrylic polymer having a multilayer structure.

In the production method, the primary polymerization, the secondary polymerization and the tertiary polymerization may be carried out sequentially in one polymerization tank, or the primary polymerization, the secondary polymerization and the tertiary polymerization may be carried out Although the polymerization may be carried out sequentially by changing the polymerization tank, it is preferable to carry out each polymerization sequentially in one polymerization tank. The temperature of the reaction system during polymerization is preferably 30-120°C, more preferably 50-100°C.

Each of the above polymerizations can be carried out by mixing the above monomers, specifically methyl methacrylate, alkyl acrylate, grafting agent and cross-linking agent in the above proportions and supplying the mixture to the reaction system. The rate at which the monomer is supplied to the reaction system is not particularly limited, but it is preferably 0.05 to 3% by mass/minute, more preferably 0.05 to 3% by mass, based on the total amount of monomers used in each polymerization. is 0.1 to 1% by mass/minute, more preferably 0.2 to 0.8% by mass/minute. By supplying at the above rate, it is possible to prevent the formation of undesirable polymer aggregates and the adhesion of polymer scales to the reaction tank, and fish eyes, etc., which may occur due to contamination of polymer aggregates and polymer scales. can be prevented from causing poor appearance.

Coagulation of the latex obtained by the above method can be carried out by a known method. As the solidification method, a freezing solidification method, a salting out solidification method, an acid precipitation solidification method, and the like can be mentioned. Among these methods, the freeze-coagulation method is preferable because it does not require the addition of a coagulant, which is an impurity for the acrylic polymer having a multilayer structure.

It is preferable to thoroughly wash and dehydrate the slurry obtained by coagulation. Washing and dewatering the slurry can remove water-soluble components such as emulsifiers and catalysts from the slurry. Washing and dehydration of the slurry can be performed using, for example, a filter press, a belt press, a Guina centrifuge, a screw decanter centrifuge, or the like. From the viewpoint of productivity and washing efficiency, it is preferable to use a screw decanter centrifuge. It is preferable to wash and dewater the slurry at least twice. As the number of times of washing and dehydration increases, the remaining amount of water-soluble components decreases. From the viewpoint of productivity, the number of times of washing and dehydration is preferably 3 or less.

Furthermore, it is preferable to dry the obtained slurry. Drying of the slurry is carried out so that the moisture content of the acrylic polymer having a multilayer structure obtained by the above method is preferably less than 0.2% by mass, more preferably less than 0.1% by mass. preferable. The higher the moisture content, the more the ester hydrolysis reaction occurs in the multi-layered acrylic polymer during melt extrusion molding, which tends to generate carboxyl groups in the molecular chains, resulting in streaks in the acrylic resin film. easy to invite

The obtained acrylic polymer having a multilayer structure is preferably pelletized in order to facilitate transportation, storage, molding, and the like. An extruder used for pelletizing an acrylic polymer having a multilayer structure preferably has a vent. Preferably the vent is a vacuum vent or an open vent. At least one vent is preferably provided downstream of the resin melting start portion. The pressure in the vacuum vent is preferably 30 Torr or less, more preferably 15 Torr or less, still more preferably 9 Torr or less, and most preferably 6 Torr or less. When the pressure in the vacuum vent is within the above range, the devolatilization efficiency is good, and residual moisture and residual monomers can be reduced.

The cylinder heating temperature of the extruder used for pelletizing the acrylic polymer having a multilayer structure is preferably 210 to 270°C, more preferably 220 to 260°C, still more preferably 230 to 250°C. is. The residence time in the extruder is preferably 7 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less. The higher the cylinder heating temperature or the longer the residence time, the greater the shearing energy given to the acrylic polymer having a multilayer structure, etc., and the more likely the thermal decomposition of the polymer proceeds, so the hot water whitening resistance of the film decreases.

The average particle size of the acrylic polymer having a multilayer structure is preferably 0.01 µm or more, more preferably 0.04 µm or more, still more preferably 0.05 µm or more, and particularly preferably 0.07 µm or more. is preferably 0.35 μm or less, more preferably 0.3 μm or less, still more preferably 0.2 μm or less, and particularly preferably 0.15 μm or less. If the average particle size is too large, the stress whitening resistance of the acrylic resin film tends to decrease. The average particle size is obtained by the method described in Examples based on the light scattering method.

≪Acrylic resin≫
The resin composition used in the present invention may contain an acrylic resin in addition to the acrylic polymer having a multilayer structure. When the resin composition contains an acrylic resin, the obtained acrylic resin film has improved mechanical strength and thickness accuracy.
From the viewpoint of improving the mechanical strength and workability of the acrylic resin film, the preferable content of the acrylic resin is preferably 4 to 50 parts by mass with respect to 100 parts by mass of the acrylic polymer having a multilayer structure. , more preferably 6 to 30 parts by mass, more preferably 8 to 20 parts by mass.

The acrylic resin preferably contains a structural unit derived from methyl methacrylate and, if necessary, a structural unit derived from acrylic acid ester. Acrylic acid esters that can be used in acrylic resins include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, s-butyl acrylate, t-butyl acrylate, amyl acrylate, and isoamyl. acrylates, n-hexyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, cyclohexyl acrylate, norbornenyl acrylate, isobornyl acrylate, benzyl acrylate, phenoxyethyl acrylate, 2-hydroxyethyl acrylate, 2 - ethoxyethyl acrylate, glycidyl acrylate, allyl acrylate, phenyl acrylate, and the like. Among these, alkyl acrylates in which the alkyl group has 1 to 6 carbon atoms are preferred.

The amount of the structural unit derived from methyl methacrylate in the acrylic resin is preferably 85 to 100% by mass, more preferably 90 to 100% by mass, from the viewpoint of improving the mechanical strength of the acrylic resin film.
Further, when the acrylic resin contains a structural unit derived from an acrylic acid ester, the amount thereof is preferably 0 to 15% by mass in the acrylic resin from the viewpoint of improving the thickness accuracy of the acrylic resin film. Yes, more preferably 0 to 10% by mass.

The glass transition temperature of the acrylic resin used in the present invention is preferably 95°C or higher, more preferably 100°C or higher, and even more preferably 105°C or higher. When the glass transition temperature is within the above range, the thickness accuracy of the acrylic resin film is improved. The glass transition temperature of the acrylic resin used in the present invention is usually 130°C or lower.
The glass transition temperature of the acrylic resin can be measured by the same method as for the polymer (c) of the acrylic polymer having a multilayer structure.

The melt flow rate of the acrylic resin used in the present invention at 230° C. under a load of 3.8 kg is preferably 0.5 to 20 g/10 minutes, more preferably 0.8 to 10 g/10 minutes. When the melt flow rate is within the above range, the ease of production of the acrylic resin film is improved.
The melt flow rate in the present invention can be measured at 230° C. under a load of 3.8 kg according to JIS K7210-1:2014.

The method for producing the acrylic resin is not particularly limited, and for example, it can be produced by a known polymerization method such as a radical polymerization method or an anion polymerization method. The production conditions are not particularly limited, and a desired acrylic resin can be obtained by appropriately adjusting the polymerization temperature, polymerization time, type and amount of chain transfer agent, type and amount of polymerization initiator, and the like.

In order to facilitate transportation, storage, molding, etc., the acrylic resin used in the present invention is preferably pelletized in the same manner as the acrylic polymer having a multilayer structure. Pelletization of the acrylic polymer can be carried out under the same conditions as for pelletization of the acrylic polymer having a multilayer structure.

It is preferable to dry the acrylic resin to reduce the moisture content before extruding. The moisture content of the acrylic resin before being subjected to extrusion molding is preferably less than 0.2% by mass, more preferably less than 0.1% by mass. The higher the moisture content, the easier it is for the occurrence of streaks in the film.

According to the production method of the present invention, an acrylic resin film can be produced with high thickness accuracy even when a resin composition as a raw material contains a relatively large amount of an acrylic polymer having a multilayer structure. . The solvent-soluble content in the resin composition is preferably 30 to 70% by mass, more preferably 40 to 70% by mass, even more preferably 45 to 70% by mass. When the soluble matter in the resin composition is within the above range, the effects of the present invention are likely to be effectively exhibited.
The solvent-soluble content herein can be measured by the method described in Examples.

<<Optional component>>
The resin composition used in the present invention contains known additives such as ultraviolet absorbers, antioxidants, light stabilizers, plasticizers, polymer processing aids, lubricants, dyes, and pigments as necessary. good too.
When the resin composition contains additives, the content thereof is preferably 20% by mass or less in the resin composition.
The additive may be added, for example, to the resin composition that is molten in the film forming machine, may be dry blended to the resin composition that has been pelletized, or may be added to the acrylic polymer having a multilayer structure and / Or it may be added when the acrylic resin is pelletized (masterbatch method).

The resin composition used in the present invention preferably contains an ultraviolet absorber. Examples of UV absorbers include 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol]. The content of the ultraviolet absorber is preferably 0.05 to 5 parts by mass with respect to 100 parts by mass of the total amount of the resin composition.

<Usage mode of acrylic resin film>
The acrylic resin film obtained by the present invention may be used as a single layer, or as a laminate with one or more other resin layers. Other resin layers include, but are not limited to, carbonate-based polymers, vinyl chloride-based polymers, vinylidene fluoride-based polymers, vinyl acetate-based polymers, maleic acid-based copolymers, methacrylic resins, ABS resins, and AES. Resins and AS resins are preferably used because they have good adhesion to the acrylic resin film obtained by the present invention.

The present invention will be described in more detail based on examples below, but the present invention is not limited to these examples. In the examples, "parts" means "mass parts" unless otherwise specified.
Incidentally, the measuring method and the like in the present example are as follows.

[Measuring method]
<Thickness accuracy>
The thickness of the film was measured with a micrometer at intervals of 5 mm in a range of 1000 mm in the machine direction (MD direction) of the film obtained in Examples and Comparative Examples.
From the obtained average value and standard deviation of the thickness, the coefficient of variation was calculated from the following formula (3) and used as an index of thickness accuracy. A smaller coefficient of variation indicates better thickness accuracy.
Variation coefficient (%) = standard deviation of thickness / average value of thickness × 100 Equation (3)
The pass/fail criteria for thickness accuracy were as follows.
Variation coefficient is less than 15%: ○ (pass)
Variation coefficient of 15% or more: × (failed)

<die line>
In a dark room, the film was irradiated with an HID light source (Polarion Light NP-1 (output: 35 W), manufactured by Polarion), and the parallel streaks generated in the film flow direction obtained in Examples and Comparative Examples were removed. It was counted visually and evaluated by the following indices.
The number of streaks in the film flow direction is 5 or less: ◎ (Pass)
The number of streaks in the machine direction of the film is 6 or more and 10 or less: ○ (practically no problem level)
The number of streaks in the film flow direction is 11 or more: △ (failed)
In addition, in the present examples and comparative examples, there was no case corresponding to Δ (failed).

<Measurement of Solvent-Soluble Content in Resin Composition>
2 g of the resin composition used in Examples and Comparative Examples was added to 50 mL of acetone and stirred at room temperature for 24 hours. The entire amount of the resulting liquid was centrifuged at 20000 rpm and 0° C. for 180 minutes using a centrifuge (CR20G III, manufactured by Hitachi Koki Co., Ltd.). The supernatant liquid and the precipitate are separated, the supernatant liquid is dried under vacuum at 50 ° C. for 8 hours, the weight of the obtained sample (solvent soluble matter) is measured, and the solvent soluble matter is calculated from the formula (4) was calculated.
Solvent-soluble content (% by mass) = weight of solvent-soluble matter ÷ weight of sample × 100 Formula (4)

<Average particle size>
The latex containing the sample particles was diluted 200 times with water, and the average particle size was determined by light scattering using a laser diffraction/scattering particle size distribution analyzer (LA-960, manufactured by Horiba, Ltd.). .

<Melt flow rate>
According to JIS K7210-1:2014, the melt flow rate was measured at 230° C. under a load of 3.8 kg.

<Glass transition temperature>
According to JIS K7121:2012, using a differential scanning calorimeter (manufactured by Shimadzu Corporation, DSC-50), the temperature was once raised to 250° C. and then cooled to room temperature. Thereafter, the DSC curve was measured by differential scanning calorimetry under the condition that the temperature was raised from room temperature to 230°C at a rate of 20°C/min. The temperature was taken as the glass transition temperature.

[Manufacturing example]
Production examples of an acrylic polymer having a multilayer structure and an acrylic resin will be described below. Methyl methacrylate is abbreviated as "MMA", n-butyl acrylate as "nBA", methyl acrylate as "MA", allyl methacrylate as "ALMA", and n-octyl mercaptan (chain transfer agent) as "nOM".

<Production of acrylic polymer having multilayer structure>
[Production Example 1: Production of acrylic polymer (A1) having a multilayer structure]
150 parts of ion-exchanged water, 1.3 parts of sodium dodecylbenzenesulfonate and 0.05 parts of sodium carbonate were placed in a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet, monomer inlet tube and reflux condenser. After charging, the inside of the container was sufficiently purged with nitrogen gas to create a state in which there was substantially no influence of oxygen.
Next, after the temperature inside the reaction vessel was adjusted to 80° C., 0.015 part of potassium persulfate was put into the reaction vessel and stirred for 5 minutes. Then, a monomer mixture consisting of 2.5 parts of MMA, 2.5 parts of nBA and 0.015 parts of ALMA was continuously added dropwise over 20 minutes to carry out emulsion polymerization. After the dropwise addition was completed, the mixture was stirred for an additional 30 minutes, and emulsion polymerization was carried out so that the conversion rate was 98% or more to obtain a latex containing the polymer (a-1).

0.030 parts of potassium persulfate was charged into the reactor containing the latex containing the polymer (a-1) and stirred for 5 minutes. Then, a monomer mixture consisting of 2 parts of MMA, 28 parts of nBA and 0.9 parts of ALMA was continuously added dropwise over 40 minutes to carry out seed emulsion polymerization using the polymer (a-1) as a seed. After the dropwise addition was completed, the mixture was further stirred for 30 minutes, and seed emulsion polymerization was carried out so that the conversion rate was 98% or more to obtain a latex containing polymer (a-1) and polymer (b-1). .

0.055 parts of potassium persulfate was charged into the reactor containing the latex containing the polymer (a-1) and the polymer (b-1) and stirred for 5 minutes. Thereafter, a monomer mixture consisting of 62 parts of MMA, 3 parts of nBA and 0.25 parts of nOM was continuously added dropwise over 100 minutes to carry out seed emulsion polymerization. After the completion of the dropwise addition, the mixture was further stirred for 60 minutes, and seed emulsion polymerization was performed using the polymer (a-1) and the polymer (b-1) as seeds so that the conversion rate was 98% or more, thereby obtaining the polymer (a -1), a latex containing polymer (b-1) and polymer (c-1) was obtained.
Table 1 shows the monomer unit composition ratio of the polymer (a-1), the polymer (b-1) and the polymer (c-1) and the average particle size of the acrylic polymer (A1) having a multilayer structure. show.

The latex was placed in an atmosphere of -20°C for 4 hours to freeze. The resulting frozen product was put into 3 times the amount of water at 80° C. and melted to obtain a slurry. The slurry was washed and dewatered with a centrifugal force of 2100 G using a screw decanter centrifuge. Subsequently, ion-exchanged water was added so that the slurry concentration became 10%, and washing and dehydration were performed again using the screw decanter centrifuge.

Thereafter, the dehydrated slurry is dried in a continuous fluidized bed dryer set at 80° C. to obtain an acrylic polymer having a core-shell multilayer structure (hereinafter referred to as an acrylic polymer having a multilayer structure (A1). do.) The obtained acrylic polymer (A1) having a three-layer structure had an average particle diameter of 0.09 μm, and a mass ratio of each layer (inner layer:intermediate layer:outer layer) was 5:31:64. The glass transition temperature of polymer (c-1) was 110°C.
The acrylic polymer (A1) having a multilayer structure was supplied to a vented single-screw extruder and pelletized under conditions of a vent vacuum pressure of 5 Torr and a melt extrusion temperature of 245°C.

[Production Example 2: Production of acrylic polymer (A2) having a multilayer structure]
Polymer (a-1), polymer (b-1) and polymer (c-1) by the same method as in Production Example 1 except that the monomer unit composition ratio was changed as shown in Table 1. Pellets of an acrylic polymer (A2) having a multilayer structure were obtained. The average particle size of the acrylic polymer (A2) having a three-layer structure was 0.09 μm, and the mass ratio of each layer (inner layer:intermediate layer:outer layer) was 5:30:65. The glass transition temperature of polymer (c-2) was 96°C.

<Production of acrylic resin>
[Production Example 3: Production of acrylic resin (B1)]
A monomer mixture was prepared by adding 92 parts of purified MMA and 8 parts of MA to an autoclave equipped with a stirrer and a sampling tube. A polymerization initiator [2,2′-azobis(2-methylpropionitrile), hydrogen abstraction capacity: 1%, 1-hour half-life temperature: 83° C.] 0.006 parts and nOM 0.15 parts were added to the monomer mixture. It was added and dissolved to obtain a raw material liquid. Then, nitrogen gas was used to expel the oxygen gas in the manufacturing apparatus.

The raw material liquid is supplied from an autoclave to a continuous flow tank reactor controlled at a temperature of 140° C. at a constant flow rate so as to have an average residence time of 120 minutes, and bulk polymerization is performed at a polymerization conversion rate of 57%. A system resin (B1) was obtained.

The liquid discharged from the tank reactor is heated to 240 ° C., supplied at a constant flow rate to a twin-screw extruder equipped with an open vent and a vacuum vent controlled at 250 ° C., and insulated at the extruder feed port. Volatilized components (monomers, dimers, trimers, etc.) were discharged through an open vent by flash evaporation. In addition, components (monomers, etc.) volatilized during melt-kneading by the twin screw were discharged from a vacuum vent evacuated to 6 Torr provided downstream of the feed port of the extruder.
The resin component from which most of the volatile components were removed was extruded with a twin screw to obtain a strand, and then the strand was cut with a pelletizer to pelletize the acrylic resin (B1).
The obtained acrylic resin (B1) had a glass transition temperature of 110° C. and an MFR of 2 g/10 minutes.

[Examples 1 to 6 and Comparative Examples 1 to 3]
The pellets of the acrylic polymers (A1) and (A2) having a multilayer structure and the acrylic resin (B1) are dry blended at the ratio shown in Table 2, and a single screw extruder with a diameter of 65 mm, a gear pump, and a die lip width of 500 mm is used. It was supplied to a film forming apparatus equipped with a T-die, two metal mirror surface rolls, and a take-up machine. A film with a width of 400 mm was produced under the conditions shown in Table 2 with the barrel temperature of the extruder set at 260°C, the adapter and gear pump temperatures at 255°C, and the die temperature at 260°C. A length of 1000 mm was sampled from the central portion of 300 mm in the width direction of the obtained acrylic resin film, and each of the above evaluations was performed.
The molten resin extruded from the die was sandwiched between an elastic metal roll and a rigid metal roll with an air gap of 80 mm and a temperature of 70° C. at a roll pressing pressure of 1.4 MPa to form a film.

In Examples 1 to 6, the speed (V ₁ ) at which the melt of the resin composition is extruded from the die and the take-up speed (V ₂ ) of the film made of the resin composition satisfy the relationship of formula (1). The thickness accuracy of the resulting film was excellent. In Example 5, the die line was likely to occur, but it was at a practical level. On the other hand, in Comparative Examples 1 to 3, the speed (V ₁ ) at which the melt of the resin composition is extruded from the die and the take-up speed (V ₂ ) of the film made of the resin composition satisfy the relationship of formula (1). was not satisfied, and the thickness accuracy of the obtained film was inferior.

The acrylic resin film obtained by the present invention can be suitably used for building materials, automobiles, and the like.

Claims (3)

A method for producing an acrylic resin film by a melt extrusion method, comprising:
The speed (V₁) and the take-up speed (V₂) satisfies the following formula (1)and the V ₁ is 1.39 m/min or less, the V ₂ is 5 to 40 m / min,
The die has a die lip clearance of 0.1 to 1.8 mm,
The solvent-soluble content of the resin composition is 30 to 70% by mass,
The acrylic resin film has a thickness of 20 to 200 μm, A method for producing an acrylic resin film, characterized by:
V.₂/V₁≦15 Formula (1) 2. The method for producing an acrylic resin film according to claim 1 , wherein the acrylic resin film has a thickness accuracy of 15% or less. The acrylic polymer having a multilayer structure has a core-shell multilayer structure consisting of three layers of a core, an inner shell, and an outer shell,
The polymer (a) constituting the core contains 40 to 98.99% by mass of structural units derived from methyl methacrylate and 1 to 59% by mass of structural units derived from an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms. , a polymer containing 0.01 to 1% by mass of structural units derived from a grafting agent and 0 to 0.5% by mass of structural units derived from a crosslinking agent,
The polymer (b) constituting the inner shell contains 70 to 99.5% by mass of structural units derived from alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and 0 to 29 mass% of structural units derived from methyl methacrylate. %, 0.5 to 5% by mass of structural units derived from a grafting agent, and 0 to 5% by mass of structural units derived from a cross-linking agent, and constituting the outer shell (c) is a polymer having a glass transition temperature of 80° C. or higher, containing 80 to 99% by mass of structural units derived from methyl methacrylate and 1 to 19% by mass of structural units derived from alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. The method for producing an acrylic resin film according to claim 1 or 2 , wherein