JP7593760B2 - Acrylic resin film manufacturing method and acrylic resin film manufacturing device - Google Patents

Description

The present invention relates to a method for producing an acrylic resin film and an apparatus for producing an acrylic resin film.

A conventional acrylic resin film manufacturing device is described in JP-A-2-6118. This manufacturing device includes a raw material supplying machine, an extruder to which raw material is supplied from the raw material supplying machine, a gear pump connected downstream of the extruder, a die connected downstream of the gear pump, and a control device that controls the raw material supplying machine and the extruder. The extruder includes a screw and a motor that rotates the screw, and kneads and melts the raw material, and extrudes it as a melt. The control device measures the pressure of the melt between the discharge side of the extruder and the suction side of the gear pump, and controls the amount of raw material supplied to the extruder (Q) and the screw rotation speed (N) so that this pressure remains constant, thereby controlling the amount of melt extruded from the extruder.

Japanese Unexamined Patent Publication No. 2-6118

However, even if Q and N are controlled, the amount of melt extruded from the extruder is not stable, and when the acrylic resin film is produced from the melt through a die, the quality of the acrylic resin film, such as its thickness, may become non-uniform.

Therefore, the present disclosure aims to provide a method and an apparatus for manufacturing an acrylic resin film that can maintain uniformity in the quality of the acrylic resin film.

In order to solve the above problems, a method for producing an acrylic resin film according to one embodiment of the present disclosure includes the steps of:
A supplying step of supplying a raw material for the acrylic resin film from a raw material supplying machine to an extruder;
an extrusion step of melting and kneading the raw materials supplied from the raw material supplying device in the extruder, and extruding a molten material obtained by the melting and kneading to a downstream side of the extruder;
and a pressure increasing step of increasing the pressure of the molten material extruded from the extruder by a gear pump connected to the downstream side of the extruder,
The extruder includes a screw and a motor that rotates the screw.
In the extrusion step,
When the rotation speed of the screw is N and the amount of the raw material fed to the extruder is Q, N is controlled so that the pressure of the melt between the extruder and the gear pump is constant, and the following (i), (ii), and (iii) are satisfied:
(i) Do not control Q; (ii) When the fluctuation range of Q/N from the reference value exceeds a set value, control Q so that the fluctuation range of Q/N becomes equal to or less than the set value, while not controlling Q when the fluctuation range of Q/N is equal to or less than the set value; or (iii) Control Q by reducing the effectiveness of the control of Q so that the pressure of the melt between the extruder and the gear pump becomes constant.

As a result of extensive research, the inventors of the present application have found that, in controlling Q and N, controlling N speeds up the response of the pressure on the discharge side of the extruder, while controlling Q slows down the response of the pressure on the discharge side of the extruder. In this way, because the response of Q control is slow, it is difficult to stably control the pressure on the discharge side of the extruder to be constant, and as a result, when an acrylic resin film is produced from a melt using a die, the quality of the acrylic resin film, such as its thickness, may become non-uniform.
According to the above aspect, N is controlled so that the pressure of the melt between the extruder and the gear pump is constant, and Q is not controlled or is controlled more loosely than N, thereby reducing the effect of controlling Q on the pressure on the discharge side of the extruder. This makes it easy to stably control the pressure on the discharge side of the extruder to a constant value, and makes it possible to maintain uniformity in quality, such as the thickness, of the acrylic resin film when it is produced from the melt downstream of the gear pump.

In one embodiment of the method for producing an acrylic resin film, in (ii) above, the effect of controlling Q is further reduced to control Q.

According to the above embodiment, the control of Q can be loosened, so the pressure on the discharge side of the extruder can be controlled more stably.

In one embodiment of the method for producing an acrylic resin film, in (iii) above, Q is further controlled so that when the fluctuation range of Q/N from the reference value exceeds a set value, the fluctuation range of Q/N is equal to or less than the set value.

According to the above embodiment, the control of Q can be loosened, so the pressure on the discharge side of the extruder can be controlled more stably.

In one embodiment of the method for producing an acrylic resin film, the extruder is preferably a twin-screw extruder.

According to the above embodiment, a twin-screw extruder is more susceptible to pressure fluctuations than a single-screw extruder, but the pressure fluctuations on the discharge side of the twin-screw extruder can be effectively reduced.

In one embodiment of the method for producing an acrylic resin film, the raw material preferably contains multiple types of materials with different shapes.

According to the above embodiment, even if multiple types of materials with different shapes are fed into the extruder, pressure fluctuations at the discharge side of the extruder can be effectively reduced.

In addition, the acrylic resin film manufacturing apparatus according to one embodiment of the present disclosure includes:
a feedstock supplying machine including a feedstock for an acrylic resin film;
an extruder having a screw and a motor for rotating the screw, the extruder melting and kneading the raw material supplied from the raw material supplying device and extruding the raw material as a molten material;
a gear pump connected downstream of the extruder to pressurize and discharge the molten material extruded from the extruder;
When the rotation speed of the screw is N and the amount of the raw material fed to the extruder is Q, N is controlled so that the pressure of the melt between the extruder and the gear pump is constant, and the following (i), (ii), and (iii) are satisfied:
(i) not controlling Q; (ii) controlling Q so that the fluctuation range of Q/N becomes equal to or less than the set value when the fluctuation range of Q/N from the reference value exceeds a set value, while not controlling Q when the fluctuation range of Q/N is equal to or less than the set value; or (iii) controlling Q by reducing the effectiveness of the control of Q so that the pressure of the melt between the extruder and the gear pump becomes constant.

According to the above embodiment, N is controlled so that the pressure of the melt between the extruder and the gear pump (hereinafter also referred to as the pressure on the discharge side of the extruder) is constant, and Q is not controlled or is controlled more loosely than N, so that the effect of controlling Q on the pressure on the discharge side of the extruder can be reduced. This makes it easy to stably control the pressure on the discharge side of the extruder constant, and when an acrylic resin film is produced from the melt downstream of the gear pump, uniformity in quality, such as the thickness of the acrylic resin film, can be maintained.

In one embodiment of the acrylic resin film manufacturing apparatus, in (ii) above, the effectiveness of the control of Q is reduced to control Q.

According to the above embodiment, the control of Q can be loosened while maintaining the fluctuation range of Q/N below a set value, so the pressure on the discharge side of the extruder can be controlled more stably.

In one embodiment of the acrylic resin film manufacturing device, in (iii) above, Q is further controlled so that when the fluctuation range of Q/N from the reference value exceeds a set value, the fluctuation range of Q/N is equal to or less than the set value.

According to the above embodiment, the control of Q can be loosened while maintaining the fluctuation range of Q/N below a set value, so the pressure on the discharge side of the extruder can be controlled more stably.

In one embodiment of the acrylic resin film manufacturing apparatus, the extruder is preferably a twin-screw extruder.

According to the above embodiment, a twin-screw extruder is more susceptible to pressure fluctuations than a single-screw extruder, but the pressure fluctuations on the discharge side of the twin-screw extruder can be effectively reduced.

Acrylic resin film manufacturing method and acrylic resin film manufacturing apparatus according to one aspect of the present disclosure can maintain uniformity in the quality of the acrylic resin film.

FIG. 1 is a schematic diagram showing one embodiment of an acrylic resin film production apparatus. FIG. 2 is a schematic diagram showing a raw material supplying machine of the acrylic resin film manufacturing apparatus. FIG. 2 is a schematic diagram showing each member of the acrylic resin film manufacturing apparatus excluding a raw material supplying device.

The acrylic resin film manufacturing method and acrylic resin film manufacturing apparatus, which are one aspect of the present disclosure, are described in detail below with reference to the illustrated embodiments. Note that some of the drawings are schematic and may not reflect actual dimensions or proportions.

(Embodiment)
<Overview of the Structure>
Fig. 1 is a schematic diagram showing one embodiment of an acrylic resin film production apparatus. As shown in Fig. 1, the acrylic resin film production apparatus 1 includes a raw material supplying machine 2, an extruder 3, a first gear pump 4, a coarse filter 5, a second gear pump 6, a fine filter 7, a die 8, and a control device 9.

The acrylic resin film manufacturing device 1 melts and kneads the raw materials for the acrylic resin film, and forms the acrylic resin film from the melt. In FIG. 1, the direction of the flow of the melt is indicated by an arrow. The raw material feeder 2, extruder 3, first gear pump 4, coarse filter 5, second gear pump 6, high-definition filter 7, and die 8 are arranged in this order from upstream to downstream of the flow of the melt.

The raw material supplying machine 2 contains the raw material for the acrylic resin film. The extruder 3 kneads and melts the raw material supplied from the raw material supplying machine 2, and extrudes the molten material obtained by this melt kneading to the downstream side of the extruder 3. The extruder 3 has a screw and a motor that rotates and drives the screw.

The first gear pump 4 is connected downstream of the extruder 3 and pressurizes and discharges the molten material extruded from the extruder 3. The second gear pump 6 is connected downstream of the first gear pump 4 and pressurizes and discharges the molten material discharged from the first gear pump 4.

The coarse filter 5 is connected between the first gear pump 4 and the second gear pump 6, and filters the molten material discharged from the first gear pump 4. The fine filter 7 is connected downstream of the second gear pump 6, and filters the molten material discharged from the second gear pump 6.

The die 8 is connected downstream of the high-definition filter 7, and forms the molten material discharged from the high-definition filter 7 into a film, which is then transported to a forming roll (not shown). This allows the production of an acrylic resin film.

The control device 9 controls the screw rotation speed N and the supply amount of the raw material to the extruder 3 Q so that the pressure of the melt between the extruder 3 and the first gear pump 4 becomes constant, and also controls the following (i), (ii), and (iii):
(i) Do not control Q. (ii) When the fluctuation range of Q/N from the reference value exceeds a set value, control Q so that the fluctuation range of Q/N becomes equal to or less than the set value, while not controlling Q when the fluctuation range of Q/N is equal to or less than the set value. (iii) Control Q by reducing the effectiveness of the control of Q so that the pressure of the melt between the extruder 3 and the first gear pump 4 becomes constant.

According to the above configuration, N is controlled so that the pressure of the melt between the extruder 3 and the first gear pump 4 (hereinafter also referred to as the pressure on the discharge side of the extruder 3) is constant, and Q is not controlled or is controlled more loosely than N, so that the effect of controlling Q on the pressure on the discharge side of the extruder 3 can be reduced. In short, the inventors of the present application found that the response of Q control is slower than that of N control, and found that due to this delayed response of Q, it is difficult to stably control the pressure on the discharge side of the extruder 3 to a constant value. Based on this knowledge, the inventors of the present application came up with the idea of not controlling Q or controlling Q more loosely than N.

This makes it easy to stably control the pressure on the discharge side of the extruder 3, and maintains uniformity in the quality of the acrylic resin film, such as its thickness, when it is produced from the molten material downstream of the first gear pump 4.

In addition, it is not necessary to control N and Q so that Q/N is constant, and N and Q may be controlled so that Q/N is not constant. In this way, Q does not need to be strictly controlled, and the pressure on the discharge side of the extruder 3 can be controlled more stably.

Here, the supply amount Q of the raw material corresponds to the measured value of the raw material measured by a measuring instrument. If Q is strictly controlled, a time lag occurs in the response of the measured value measured by the measuring instrument, and the response of the pressure on the discharge side of the extruder 3 becomes slower and stable control cannot be performed. In detail, the supply amount instruction value is distributed to each of the multiple measuring instruments at a ratio according to the raw material recipe based on the value of Q. If the value of Q fluctuates up or down, the instruction value to each measuring instrument will also fluctuate, and the raw material will be supplied to the extruder 3 at a ratio that is momentarily different from the raw material recipe due to the difference in the response of each measuring instrument. This causes the bulk density of the raw material to change, making the extruder 3 more susceptible to fluctuations (i.e., pressure fluctuations occur), and the raw material ratio differs from the originally designed ratio, causing a problem of deviation in product performance. In contrast, in the present application, as described above, Q is not strictly controlled, so the pressure on the discharge side of the extruder 3 can be controlled more stably.

<Preferable configuration of each member>
(Acrylic resin film)
Examples of acrylic resins used in acrylic resin films include methacrylic resins (homopolymers of methacrylic acid esters and copolymers containing methacrylic acid esters as the main component). From the viewpoint of imparting impact resistance to the film, it is preferable that the acrylic resin is one in which rubber particles are blended, particularly methacrylic resins in which rubber particles are blended. The methacrylic resin is a homopolymer of methacrylic acid ester or a copolymer containing methacrylic acid esters as the main component. As the methacrylic acid ester, an alkyl ester of methacrylic acid is usually used, and the number of carbon atoms in the alkyl group is about 1 to 4. When a copolymer is used, an acrylic acid ester known to be advantageous as a copolymerization component of a methacrylic resin, or another polymerizable monomer copolymerizable with an alkyl methacrylate ester and/or an acrylic acid ester is used.

The methacrylic resin is preferably obtained by polymerization of monomers consisting of 50 to 100% by weight of a methacrylic acid alkyl ester having an alkyl group with 1 to 4 carbon atoms, 0 to 50% by weight of an acrylic acid ester, and 0 to 49% by weight of at least one other polymerizable monomer that can be copolymerized with these. It is preferably a thermoplastic polymer having a glass transition temperature of 40°C or higher. Here, the acrylic acid ester is more preferably used in the range of 0.1 to 50% by weight, and the more preferable copolymerization ratio of the methacrylic acid alkyl ester is in the range of 50 to 99.9% by weight. The glass transition temperature of this methacrylic resin is more preferably 60°C or higher. In this specification, when the term "monomer" is used simply, it includes not only the case where the monomer is composed of one type of monomer, but also the state where multiple monomers are mixed.

In this thermoplastic polymer, the alkyl methacrylate ester may be an alkyl methacrylate ester having an alkyl group with 1 to 8 carbon atoms. The alkyl group preferably has 1 to 4 carbon atoms. Among these, methyl methacrylate is particularly preferably used from the viewpoint of durability. The alkyl methacrylate ester may be used alone or in combination of two or more kinds.
As the acrylic acid ester, an alkyl acrylate is usually used. As the alkyl acrylate, an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group can be mentioned. The number of carbon atoms in the alkyl group is preferably 1 to 4. Only one type of acrylic acid ester may be used, or two or more types may be used in combination.

Other polymerizable monomers that can be copolymerized with the methacrylic acid alkyl ester and/or the acrylic acid ester include various monomers conventionally known in this field. Examples of such monomers include monofunctional monomers having one polymerizable carbon-carbon double bond in the molecule, and polyfunctional monomers having at least two polymerizable carbon-carbon double bonds in the molecule, with monofunctional monomers being preferred. Specific examples of monofunctional monomers include styrene-based monomers such as styrene, α-methylstyrene, vinyl toluene, halogenated styrene, and hydroxystyrene; vinyl cyanides such as acrylonitrile and methacrylonitrile; unsaturated acids such as acrylic acid, methacrylic acid, maleic anhydride, and itaconic anhydride; maleimides such as N-methylmaleimide, N-cyclohexylmaleimide, and N-phenylmaleimide; unsaturated alcohols such as methallyl alcohol and allyl alcohol; and other monomers such as vinyl acetate, vinyl chloride, ethylene, propylene, 4-methyl-1-pentene, 2-hydroxymethyl-1-butene, methyl vinyl ketone, N-vinylpyrrolidone, and N-vinylcarbazole.

Specific examples of polyfunctional monomers include polyunsaturated carboxylic acid esters of polyhydric alcohols such as ethylene glycol dimethacrylate, butanediol dimethacrylate, and trimethylolpropane triacrylate; alkenyl esters of unsaturated carboxylic acids such as allyl acrylate, allyl methacrylate, and allyl cinnamate; polyalkenyl esters of polybasic acids such as diallyl phthalate, diallyl maleate, triallyl cyanurate, and triallyl isocyanurate; and aromatic polyalkenyl compounds such as divinylbenzene.

Such other polymerizable monomers copolymerizable with alkyl methacrylate esters and/or acrylic esters may be used alone or in combination of two or more.

As mentioned above, the methacrylic resin is preferably a thermoplastic polymer obtained by polymerizing monomers consisting of 50 to 100% by weight, more preferably 50 to 99.9% by weight, of an alkyl methacrylate ester having an alkyl group with 1 to 4 carbon atoms, 0 to 50% by weight, more preferably 0.1 to 50% by weight, of an acrylic ester, and 0 to 49% by weight of at least one other polymerizable monomer that can be copolymerized therewith. Polymers falling within this range can be used alone or as a mixture of two or more polymers.

Methacrylic resin may have a ring structure in the polymer main chain, since this can increase the durability of the film. The ring structure is preferably a heterocyclic structure such as a cyclic acid anhydride structure, a cyclic imide structure, or a lactone ring structure. Specific examples include cyclic acid anhydride structures such as glutaric anhydride structure and succinic anhydride structure; cyclic imide structures such as glutarimide structure and succinimide structure; and lactone ring structures such as butyrolactone and valerolactone. The glass transition temperature of the methacrylic resin can be increased by increasing the ring structure content in the main chain. The cyclic acid anhydride structure or cyclic imide structure can be introduced into the main chain by a method of introducing the cyclic acid anhydride structure by copolymerizing a monomer having a cyclic structure such as maleic anhydride or maleimide, a method of introducing the cyclic acid anhydride structure by a dehydration/demethanolization condensation reaction after polymerization, or a method of introducing the cyclic imide structure by reacting an amino compound.

The polymerization method for the thermoplastic polymer is not particularly limited, but may be a method such as ordinary suspension polymerization, emulsion polymerization, or bulk polymerization. In order to obtain a suitable glass transition temperature or a viscosity that exhibits suitable moldability into a film, it is preferable to use a chain transfer agent during polymerization. The amount of the chain transfer agent may be appropriately determined depending on the type and composition of the monomers.

The methacrylic resin may contain rubber particles in order to impart impact resistance to the film. The rubber particles preferably have an average particle size in the range of 0.05 to 0.4 μm, more preferably 0.06 to 0.3 μm, and particularly preferably 0.1 to 0.25 μm.
The rubber particles are preferably contained in an amount of 3 to 60 parts by weight, more preferably 5 to 50 parts by weight, and even more preferably 10 to 40 parts by weight, per 100 parts by weight of the total of the acrylic resin (e.g., methacrylic resin) and the rubber particles.

The rubber particles are preferably rubber-containing polymers obtained by polymerizing 100 parts by weight of an elastic copolymer having a layer obtained by polymerizing monomers consisting of 50 to 99.9% by weight of an acrylic acid alkyl ester, 0 to 49.9% by weight of at least one other vinyl monomer copolymerizable therewith, and 0.1 to 10% by weight of a copolymerizable crosslinking monomer, in the presence of 100 parts by weight of the elastic copolymer having a layer obtained by polymerizing monomers consisting of 50 to 100% by weight of a methacrylic acid ester, 0 to 50% by weight of an acrylic acid ester, and 0 to 49% by weight of at least one other vinyl monomer copolymerizable therewith, thereby bonding at least one polymerized layer from the latter monomer to the surface of the elastic copolymer. Rubber particles with different average particle sizes can be produced by changing the polymerization conditions.

This rubber-containing polymer can be obtained, for example, by the following method. The above components for the elastic copolymer are polymerized in at least one reaction stage by emulsion polymerization or the like to obtain an elastic copolymer. In the presence of the obtained elastic copolymer, the above-mentioned monomer containing methacrylic acid ester is polymerized in at least one reaction stage by emulsion polymerization or the like. By such multiple-stage polymerization, the monomer containing methacrylic acid ester used in the latter stage is graft-copolymerized to the elastic copolymer, and a crosslinked elastic copolymer having a graft chain is produced. That is, this rubber-containing polymer becomes a graft copolymer having a multi-layer structure containing acrylic acid alkyl ester as the main component of rubber. In addition, when the polymerization of the elastic copolymer is performed in two or more stages, or when the polymerization of the monomer mainly composed of methacrylic acid ester is performed in two or more stages, in either case, it is sufficient that the overall monomer composition is within the above range, not the monomer composition of each stage.

Examples of the alkyl acrylate ester in the rubber-containing polymer include those in which the alkyl group has 1 to 8 carbon atoms. Among these, those in which the alkyl group has 4 to 8 carbon atoms, such as butyl acrylate and 2-ethylhexyl acrylate, are preferred.

Preferred examples of other vinyl monomers that can be copolymerized with alkyl acrylates in rubber-containing polymers include alkyl methacrylates such as methyl methacrylate, butyl methacrylate, and cyclohexyl methacrylate, as well as styrene and acrylonitrile.

In the rubber-containing polymer, the copolymerizable crosslinking monomer used to form the elastic copolymer may have at least two polymerizable carbon-carbon double bonds in one molecule. Examples of such crosslinking monomers include unsaturated carboxylic acid diesters of glycols such as ethylene glycol dimethacrylate and butanediol dimethacrylate; alkenyl esters of unsaturated carboxylic acids such as allyl acrylate, allyl methacrylate, and allyl cinnamate; polyalkenyl esters of polyvalent carboxylic acids such as diallyl phthalate, diallyl maleate, triallyl cyanurate, and triallyl isocyanurate; unsaturated carboxylic acid esters of polyhydric alcohols such as trimethylolpropane triacrylate; and divinylbenzene. Among these, alkenyl esters of unsaturated carboxylic acids and polyalkenyl esters of polyvalent carboxylic acids are preferred. These crosslinking monomers can be used alone or in combination of two or more types as necessary.

The elastic copolymer obtained by polymerization of monomers mainly composed of acrylic acid alkyl esters as described above is grafted with monomers consisting of 50 to 100% by weight of methacrylic acid esters, 0 to 50% by weight of acrylic acid esters, and 0 to 49% by weight of at least one other vinyl monomer copolymerizable therewith. The methacrylic acid esters grafted to the elastic copolymer are preferably methacrylic acid alkyl esters, such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and cyclohexyl methacrylate. Examples of acrylic acid esters that can be copolymerized with these methacrylic acid esters as desired include acrylic acid alkyl esters such as methyl acrylate, butyl acrylate, and cyclohexyl acrylate. Examples of other vinyl monomers that can be copolymerized with methacrylic acid esters and/or acrylic acid esters include styrene and acrylonitrile.

The monomer to be grafted is preferably used in an amount of 10 to 400 parts by weight, more preferably 20 to 200 parts by weight, per 100 parts by weight of the elastic copolymer, and can be polymerized in at least one reaction stage. If the amount of the monomer to be grafted is 10 parts by weight or more, the elastic copolymer is less likely to aggregate, and transparency is improved.

A hard layer mainly composed of methacrylic acid ester can be provided inside the elastic copolymer layer. In this case, the monomers of the hard layer constituting the innermost layer are first polymerized. Then, in the presence of the obtained hard polymer, the monomers constituting the elastic copolymer are polymerized. Furthermore, in the presence of the obtained elastic copolymer, the monomers to be grafted mainly composed of the above-mentioned methacrylic acid ester are polymerized. Here, the hard layer to be the innermost layer is preferably a polymerized monomer composed of 70 to 100% by weight of methacrylic acid ester and 0 to 30% by weight of another vinyl monomer copolymerizable therewith. In this case, it is also effective to use a copolymerizable crosslinkable monomer as one of the other vinyl monomers. As the methacrylic acid ester, an alkyl methacrylate ester, particularly methyl methacrylate, is effective. Such a rubber-containing polymer having a three-layer structure is disclosed, for example, in JP-B-55-27576.

The average particle size of rubber particles can be determined by observation under an electron microscope. For example, each rubber particle is mixed with methacrylic resin to form a film, and the rubber component of the cross section is dyed with ruthenium oxide. After dyeing, the film is observed under an electron microscope, and the average particle size can be determined from the diameter of the dyed outer layer of the particle. Therefore, the particle size referred to here is the number average particle size.

The acrylic resin may contain conventional additives such as ultraviolet absorbers, organic dyes, inorganic dyes, pigments, antioxidants, antistatic agents, surfactants, etc. Among these, ultraviolet absorbers are preferably used because they provide a film with excellent weather resistance for a long period of time.

These ultraviolet absorbents can be used alone or in combination of two or more kinds. The content of the ultraviolet absorbent is appropriately set according to the desired thickness of the acrylic resin extrusion film, and is usually 0.1 parts by weight or more, preferably 0.3 parts by weight or more, and usually 5 parts by weight or less, per 100 parts by weight of the acrylic resin. The transmittance of the acrylic resin extrusion film having the desired thickness at a wavelength of 380 nm can be selected within a range of preferably 25% or less, more preferably 15% or less, and even more preferably 5% or less. For example, in the case of a film having a thickness of 80 μm, in order to exhibit the same ultraviolet absorption ability as the triacetyl cellulose film used as the acrylic resin film, it is preferable to set the amount of the ultraviolet absorbent to about 2.0 parts by weight based on the total of 100 parts by weight of the methacrylic resin and the rubber particles. It is preferable that these additives, including the ultraviolet absorbent, have a melting point of 180° C. or more to prevent the acrylic resin from evaporating as a volatile matter when the acrylic resin is discharged from the die and contaminating the roll, etc.

(Raw material supply machine 2)
Fig. 2 is a schematic diagram showing the raw material supplying machine 2. As shown in Fig. 2, the raw material supplying machine 2 has a first measuring device 21 and a second measuring device 22. All the measuring devices 21, 22 are connected to the extruder 3 via a transport pipe 25. The raw material of the acrylic resin film is fed into each of the measuring devices 21, 22 from a raw material chamber (not shown). The raw material includes a plurality of types of materials having different shapes.

Specifically, acrylic resin (PMMA) pellets are fed as a raw material into the first measuring device 21, and additives are fed as a raw material into the second measuring device 22. The raw material fed into the first measuring device 21 and the raw material fed into the second measuring device 22 have different shapes.

Each weighing device 21, 22 measures the weight of the respective raw material, and sends the amount of raw material determined by the control device 9 to the extruder 3 via the transport pipe 25. In other words, the control device 9 controls the amount of raw material supplied by controlling each weighing device 21, 22 as a single control element in order to control the amount of molten material extruded from the extruder 3.

When multiple types of materials with different shapes are fed from the raw material feeder 2 into the extruder 3 in this way, pressure fluctuations are usually likely to occur on the discharge side of the extruder 3. However, as described above, the presence of the first gear pump 4 and the second gear pump 6 makes it possible to effectively reduce pressure fluctuations on the discharge side of the extruder 3. The raw material may contain multiple types of materials with the same shape. The number of measuring devices may also be increased or decreased.

(Extruder 3)
Fig. 3 is a schematic diagram showing each member of the acrylic resin film production apparatus 1 except for the raw material supplying device 2. As shown in Fig. 3, the extruder 3 is a twin-screw extruder. The extruder 3 has a casing 30, a first screw 31 and a second screw 32 arranged in the casing 30, and a motor 35 that rotates and drives the first screw 31 and the second screw 32.

The casing 30 has an inlet 30a through which the raw material is fed from the raw material feeder 2. In other words, the inlet 30a is connected to the transport pipe 25 of the raw material feeder 2. Note that there may be multiple inlets 30a.

The first screw 31 and the second screw 32 are arranged parallel to each other and rotate in the same direction as shown by the arrows. Note that the first screw 31 and the second screw 32 may rotate in opposite directions.

The raw materials fed from the feed port 30a are mixed and sent downstream by the rotation of the first screw 31 and the second screw 32. At the same time, the raw materials being transported by the first screw 31 and the second screw 32 are melted by a heater (not shown) provided in the casing 30, resulting in the production of a molten material.

The motor 35 is controlled by the control device 9. In other words, the control device 9 controls the motor 35 as one control element to control the amount of molten material extruded from the extruder 3, thereby controlling the rotation speeds of the first screw 31 and the second screw 32.

As described above, since the extruder 3 is a twin-screw extruder, pressure fluctuations at the tip are more likely to occur than in a single-screw extruder. However, as described above, since the extruder 3 has the first gear pump 4 and the second gear pump 6, pressure fluctuations at the tip of the extruder 3 can be effectively reduced.

(First gear pump 4)
As shown in FIG. 3, the first gear pump 4 has a first gear 41, a second gear 42, and a motor 45 that rotates the first gear 41 and the second gear 42. The first gear 41 and the second gear 42 mesh with each other and rotate in opposite directions as shown by the arrows. The melt extruded from the extruder 3 is sent downstream by the rotation of the first gear 41 and the second gear 42. At this time, the melt is pressurized by the first gear pump 4. That is, the value of the second pressure sensor 12 provided between the first gear pump 4 and the coarse filter 5 is larger than the value of the first pressure sensor 11 provided between the extruder 3 and the first gear pump 4. The pressure of the melt is increased by the first gear pump 4 to, for example, 5 MPa, and may be in the range of 3 MPa to 15 MPa.

In this way, the manufacturing apparatus of this embodiment has the first gear pump 4, so even if the amount of melt extruded from the extruder 3 fluctuates and the pressure of the melt fluctuates, the first gear pump 4 can mitigate the pressure fluctuations of the melt downstream of the first gear pump 4, and the melt can be stably molded downstream of the high-definition filter 7.

(Coarse Filter 5)
As shown in FIG. 3, the coarse filter 5 is a filter having an opening size of, for example, 20 μm to 80 μm, preferably 20 μm to 40 μm.

The mesh size of the coarse filter 5 is coarser than that of the high-definition filter 7. This allows the molten material pressurized only by the first gear pump 4 to pass through the coarse filter 5. In other words, the first gear pump 4 only needs to increase the pressure to pass the molten material through the coarse filter 5, so the amount of pressure increase of the molten material by the first gear pump 4 can be reduced.

The pressure of the molten material is reduced by passing through the coarse filter 5. In other words, the reading of the third pressure sensor 13, which is provided between the second gear pump 6 and the coarse filter 5, is smaller than the reading of the second pressure sensor 11. The pressure reduction of the molten material by the coarse filter 5 is, for example, 5 MPa.

In this way, since the coarse filter 5 is provided between the first gear pump 4 and the second gear pump 6, even if the extrusion amount of the melt extruded from the extruder 3 fluctuates and the pressure of the melt fluctuates, the coarse filter 5 in addition to the first gear pump 4 and the second gear pump 6 can mitigate the pressure fluctuation of the melt downstream of each, and the molding of the melt can be more stably performed downstream of the high-definition filter 7. As a result, the uniformity of the quality of the acrylic resin film can be better maintained.

In addition, since a coarse filter 5 is provided between the first gear pump 4 and the second gear pump 6, even if pressure fluctuations occurring between the extruder 3 and the first gear pump 4 propagate downstream, the coarse filter 5 can mitigate these pressure fluctuations.

In addition, the coarse filter 5 is provided upstream of the high-definition filter 7, which improves the durability of the high-definition filter 7.

(Second gear pump 6)
As shown in FIG. 3, the second gear pump 6 has a first gear 61, a second gear 62, and a motor 65 that rotates the first gear 61 and the second gear 62. The first gear 61 and the second gear 62 mesh with each other and rotate in opposite directions as shown by the arrows. The melt filtered by the coarse filter 5 is sent downstream by the rotation of the first gear 61 and the second gear 62. At this time, the melt is pressurized by the second gear pump 6. That is, the value of the fourth pressure sensor 14 provided between the second gear pump 6 and the high-definition filter 7 is larger than the value of the third pressure sensor 13. The pressure of the melt increased by the second gear pump 6 is, for example, 9 MPa, and may be in the range of 1 MPa to 15 MPa.

In this way, since the second gear pump 6 is provided, even if the amount of the molten material extruded from the extruder 3 fluctuates and the pressure of the molten material fluctuates, the second gear pump 6 can mitigate the pressure fluctuations of the molten material downstream of the second gear pump 6, and the molten material can be stably molded downstream of the high-definition filter 7.

In addition, the molten material is pressurized by the first gear pump 4 and the second gear pump 6, so the pressure difference before and after each gear pump can be reduced. This reduces backflow of the molten material in each gear pump.

(High-definition filter 7)
As shown in FIG. 3, the high definition filter 7 is a polymer filter having an aperture size of, for example, 0.5 μm to 30 μm, preferably 1 μm to 10 μm.

The mesh size of the high-definition filter 7 is finer than that of the coarse filter 5. This allows the melt pressurized by the first gear pump 4 and the second gear pump 6 to pass through the fine-mesh high-definition filter 7. In other words, the melt needs to be pressurized highly to pass through the fine-mesh filter 7, but because the melt can be pressurized by both the first gear pump 4 and the second gear pump 6, the pressurization of the melt can be easily increased.

The pressure of the molten material is reduced by passing through the high-definition filter 7. In other words, the numerical value of the discharge pressure from the high-definition filter 7 is smaller than the numerical value of the fourth pressure sensor 14. The numerical value of the discharge pressure from the high-definition filter 7 is the same as the numerical value of the discharge pressure from the die 8. The amount of pressure reduction of the molten material by the high-definition filter 7 can be selected according to the coarseness of the high-definition filter 7, the temperature and flow rate of the molten material, etc., but may be, for example, 7 MPa to 12 MPa.

(Die 8)
3, the die 8 is, for example, a T-die. The melt filtered by the high-definition filter 7 is formed into a sheet by the die 8. The sheet-like melt extruded from the outlet of the die 8 is then conveyed to a forming roll (not shown) located below the outlet of the die 8, where it is cooled and solidified to produce an acrylic resin film.

(Control device 9)
2 and 3, the control device 9 controls the operation of each member. The control device 9 has a first control unit 91, a second control unit 92, and a raw material supplying machine control unit 93.

The first control unit 91 receives a signal from the third pressure sensor 13 and sends a signal to the motor 45 of the first gear pump 4. Specifically, the first control unit 91 controls the motor 45 of the first gear pump 4 so that the resin pressure detected by the third pressure sensor 13 is constant, thereby controlling the rotation speed of the first gear pump 4.

The second control unit 92 receives the signal from the first pressure sensor 11 and sends a signal to the motor 35 of the extruder 3, and further sends a signal of the supply amount Q to the raw material supply machine control unit 93. The raw material supply machine control unit 93 sends a signal of the set value of the supply amount Q based on the received signal of the supply amount Q to each of the measuring devices 21, 22 of the raw material supply machine 2. In other words, the raw material supply machine control unit 93 sends a signal to each of the measuring devices 21, 22 at a predetermined arbitrary ratio in response to the received signal of the supply amount Q.

In this way, the second control unit 92 performs feedback control on the rotation speed N of the first screw 31 and the second screw 32 of the extruder 3 and the supply amount Q of the raw material to the extruder 3. The control of the rotation speed N is performed by controlling the motor 35 of the extruder 3. The control of the supply amount Q is performed by controlling the measuring devices 21 and 22 of the raw material supplying machine 2.

Specifically, the second control unit 92 controls N so that the pressure of the first pressure sensor 11 is constant, and also controls the following (i), (ii), and (iii):
(i) Do not control Q. (ii) When the fluctuation range of Q/N from the reference value exceeds a set value, control Q so that the fluctuation range of Q/N becomes equal to or less than the set value, while not controlling Q when the fluctuation range of Q/N is equal to or less than the set value. (iii) Control Q by reducing the effectiveness of the control of Q so that the pressure of the first pressure sensor 11 becomes constant.

Here, the second control unit 92 may be preset to any one of the above (i), (ii), and (iii). Alternatively, the second control unit 92 may be set to be able to select any one of the above (i), (ii), and (iii).

In the above (i), the second control unit 92 always turns off the control of Q. In other words, the second control unit 92 only controls N.

In (ii) above, the second control unit 92 controls Q when the fluctuation range of Q/N from the reference value exceeds the set value, but turns off the control of Q when the fluctuation range of Q/N is equal to or less than the set value. In other words, Q/N does not have to be a constant reference value. The reference value is a value that is predetermined for each manufacturing device. The fluctuation range refers to the absolute value of the difference from the reference value. For example, Q/N is in the range of 4.5 to 7.5, preferably in the range of 5.5 to 7.0, and more preferably in the range of 6.0 to 6.8. The appropriate range of Q/N varies depending on the size and specifications of the extruder, etc.

In the above (iii), the second control unit 92 controls Q so that the pressure of the first pressure sensor 11 becomes constant, and at the same time controls Q so that the control of Q becomes less effective.
Here, making the control of Q less effective means making the feedback control applied to Q less effective. Specifically, when the feedback control is PID control, "the control is slow" or "the control is loose" means that the gain values set for each control item of proportional control (P), differential control (D), and integral control (I) are such that the fluctuation width of Q/N falls within a predetermined range, and the influence of the control (response to control, etc.) is small. In (iii) above, a gain value is set for Q such that the influence of the feedback control is small (the control is slow). This makes the response to the control of Q, etc. slow.

In this way, the second control unit 92 controls N so that the pressure of the first pressure sensor 11 is constant, and does not control Q or controls Q more loosely than N, thereby reducing the effect of the control of Q on the pressure on the discharge side of the extruder 3. Therefore, it becomes easier to stably control the pressure on the discharge side of the extruder 3 to a constant value, and the uniformity of the quality of the acrylic resin film can be maintained.

Preferably, in (ii) above, Q is controlled by reducing the effectiveness of the control of Q. This allows the control of Q to be relaxed, so that the pressure on the discharge side of the extruder can be controlled more stably.

Preferably, in the above (iii), when the fluctuation range of Q/N from the reference value exceeds a set value, Q is further controlled so that the fluctuation range of Q/N is equal to or less than the set value. This allows the control of Q to be loosened, so that the pressure on the discharge side of the extruder can be controlled more stably.

The manufacturing apparatus of the present disclosure is not limited to the above-described embodiment, and the design can be modified without departing from the spirit of the present disclosure. For example, the design can be modified to increase or decrease the number of gear pumps or the number of filters.

<Production Method>
Next, one embodiment of a method for producing an acrylic resin film will be described with reference to Figs.

First, the raw material for the acrylic resin film is supplied from the raw material supply machine 2 to the extruder 3 (hereinafter referred to as the supply process). The raw material supplied from the raw material supply machine 2 is then melted and kneaded in the extruder 3, and the molten material obtained by melt kneading is extruded downstream of the extruder 3 (hereinafter referred to as the extrusion process). The molten material extruded from the extruder 3 is then pressurized by the first gear pump 4 connected downstream of the extruder 3 (hereinafter referred to as the pressurization process).

In the extrusion process, when the rotation speed of the screws 31 and 32 is N and the supply amount of the raw material to the extruder 3 is Q, N is controlled so that the pressure of the melt between the extruder 3 and the first gear pump 4 is constant, and the following (i), (ii), and (iii) are satisfied:
(i) Do not control Q. (ii) When the fluctuation range of Q/N from the reference value exceeds a set value, control Q so that the fluctuation range of Q/N becomes equal to or less than the set value, while not controlling Q when the fluctuation range of Q/N is equal to or less than the set value. (iii) Control Q by reducing the effectiveness of the control of Q so that the pressure of the melt between the extruder 3 and the first gear pump 4 becomes constant.

By controlling N so that the pressure of the melt between the extruder 3 and the first gear pump 4 is constant, and Q is not controlled or is controlled more loosely than N, the effect of controlling Q on the pressure on the discharge side of the extruder 3 can be reduced. Therefore, it becomes easier to stably control the pressure on the discharge side of the extruder 3 to a constant value, and the uniformity of the quality of the acrylic resin film can be maintained.

Preferably, in (ii) above, Q is controlled by reducing the effectiveness of the control of Q. This allows the control of Q to be relaxed while maintaining the fluctuation range of Q/N below a set value, so that the pressure on the discharge side of the extruder 3 can be controlled more stably. The fluctuation range of Q/N can be set within a range of, for example, 4.5 to 7.5, preferably 5.5 to 7.0, and more preferably 6.0 to 6.8.

Preferably, in the above (iii), when the fluctuation range of Q/N from the reference value exceeds a set value, Q is further controlled so that the fluctuation range of Q/N is equal to or less than the set value. This allows the control of Q to be loosened while maintaining the fluctuation range of Q/N equal to or less than the set value, so that the pressure on the discharge side of the extruder 3 can be controlled more stably.

The manufacturing method of the present disclosure is not limited to the above-described embodiment, and the design can be modified without departing from the spirit of the present disclosure. For example, the manufacturing method of the present disclosure is not limited to being realized by the manufacturing apparatus 1 of FIG. 1, but may be realized by other different apparatuses.

(Example)
Next, an embodiment will be described.

[Example 1]
(1) Preparation of raw resin As the methacrylic resin, pellets of a thermoplastic polymer (glass transition temperature 104°C) which is a copolymer of 97% by weight of methyl methacrylate and 3% by weight of methyl acrylate were used. As the acrylic rubber particles, those produced in the same manner as in Example 3 of the above-mentioned JP-B-55-27576 were used, which have a spherical three-layer structure consisting of an innermost layer of a hard polymer in which methyl methacrylate is copolymerized with a small amount of allyl methacrylate, an intermediate layer of an elastic polymer mainly composed of butyl acrylate and further copolymerized with styrene and a small amount of allyl methacrylate, and an outermost layer of a hard polymer in which methyl methacrylate is copolymerized with a small amount of methyl acrylate, and have an average particle diameter of 0.22 μm.
70 parts of methacrylic resin pellets and 30 parts of acrylic rubber particles were mixed in a super mixer, and then melt-kneaded in a twin-screw extruder to form pellets of a resin composition, which were used as an acrylic resin.

(2) Preparation of acrylic resin film The obtained pellets were melted in another twin-screw extruder (extrusion temperature 230°C to 270°C), passed through a first gear pump, a coarse filter, a second gear pump and a high-definition filter in this order, extruded from a die, and passed through a forming roll (surface temperature 60°C to 100°C) to obtain an acrylic resin film (width 1300mm to 2000mm) by appropriately adjusting the discharge amount and line speed so that the thickness becomes 80 μm. Note that the pellets were pressurized in the first gear pump and the second gear pump under the following conditions.
In the preparation of the acrylic resin film in this Example 1, control of Q and N (QN control) was not carried out in the extruder, that is, control of the raw material supply amount Q shown in the above (i) was not carried out.

[Comparative Example 1]
An acrylic resin film was prepared in the same manner as in Example 1, except that feedback control was performed on the raw material supply amount Q so that Q/N was constant at 6.5 according to the screw rotation speed N.

Next, Table 1 shows the measurement values of the first pressure sensor in Example 1 and Comparative Example 1.

As shown in Table 1, in Example 1, the range between the maximum and minimum values was smaller than in Comparative Example 1, and the standard deviation was also smaller. Thus, it was found that in Example 1, the measurement value of the first pressure sensor was more stable and constant than in Comparative Example 1. Therefore, in Example 1, the pressure on the discharge side of the extruder could be stably controlled to a constant value, so that the uniformity of the quality of the acrylic resin film could be maintained.

REFERENCE SIGNS LIST 1 Acrylic resin film manufacturing device 2 Raw material supply machine 21, 22 First and second measuring devices 3 Extruder 31, 32 First and second screws 35 Motor 4 First gear pump 41, 42 First and second gears 45 Motor 5 Coarse filter 6 Second gear pump 61, 62 First and second gears 65 Motor 7 High-definition filter 8 Die 9 Control device 91, 92 First and second control units 93 Raw material supply machine control unit 11 to 14 First to fourth pressure sensors

Claims (10)

A supplying step of supplying a raw material for the acrylic resin film from a raw material supplying machine to an extruder;
an extrusion step of melting and kneading the raw materials supplied from the raw material supplying device in the extruder, and extruding a molten material obtained by the melting and kneading to a downstream side of the extruder;
and a pressure increasing step of increasing the pressure of the molten material extruded from the extruder by a gear pump connected to the downstream side of the extruder,
The extruder includes a screw and a motor that rotates the screw.
In the extrusion step,
When the rotation speed of the screw is N and the amount of the raw material fed to the extruder is Q, N is controlled so that the pressure of the melt between the extruder and the gear pump is constant, and the following (i), (ii), and (iii) are satisfied:
(i) not controlling Q; (ii) when the fluctuation range of Q/N from the reference value exceeds a set value, controlling Q so that the fluctuation range of Q/N becomes equal to or less than the set value, while not controlling Q when the fluctuation range of Q/N is equal to or less than the set value ; (iii) controlling Q by reducing the effect of controlling Q so that the pressure of the melt between the extruder and the gear pump becomes constant;
The raw material includes a plurality of types of materials having different shapes.
A method for producing acrylic resin film. The method for producing an acrylic resin film according to claim 1, further comprising controlling Q by reducing the effectiveness of the control of Q in (ii). The method for producing an acrylic resin film according to claim 1 or 2, further comprising controlling Q in (iii) so that when the fluctuation range of Q/N from the reference value exceeds a set value, the fluctuation range of Q/N is equal to or less than the set value. The method for producing an acrylic resin film according to any one of claims 1 to 3, wherein the extruder is a twin-screw extruder. 5. The method for producing an acrylic resin film according to claim 1, wherein the gear pump includes a first gear pump and a second gear pump, and a coarse filter is connected between the first gear pump and the second gear pump, and the coarse filter filters the molten material discharged from the first gear pump. a feedstock supplying machine including a feedstock for an acrylic resin film;
an extruder having a screw and a motor for rotating the screw, the extruder melting and kneading the raw material supplied from the raw material supplying device and extruding the raw material as a molten material;
a gear pump connected downstream of the extruder to pressurize and discharge the molten material extruded from the extruder;
When the rotation speed of the screw is N and the amount of the raw material fed to the extruder is Q, N is controlled so that the pressure of the melt between the extruder and the gear pump is constant, and the following (i), (ii), and (iii) are satisfied:
(i) not controlling Q; (ii) when the fluctuation range of Q/N from the reference value exceeds a set value, controlling Q so that the fluctuation range of Q/N becomes equal to or less than the set value, while not controlling Q when the fluctuation range of Q/N is equal to or less than the set value ; or (iii) controlling Q by reducing the effectiveness of the control of Q so that the pressure of the melt between the extruder and the gear pump becomes constant;
The raw material includes a plurality of types of materials having different shapes.
Acrylic resin film manufacturing equipment. The acrylic resin film manufacturing apparatus according to claim 6, wherein in (ii), Q is controlled by reducing the effectiveness of the control of Q. The acrylic resin film manufacturing apparatus according to claim 6 or 7, further comprising, in (iii), controlling Q so that when the fluctuation range of Q/N from the reference value exceeds a set value, the fluctuation range of Q/N is equal to or less than the set value. The acrylic resin film manufacturing apparatus according to any one of claims 6 to 8, wherein the extruder is a twin-screw extruder. 10. The acrylic resin film manufacturing apparatus according to claim 6, wherein the gear pump includes a first gear pump and a second gear pump, and a coarse filter is connected between the first gear pump and the second gear pump, and the coarse filter filters the molten material discharged from the first gear pump.

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