JP5103265B2 - Method for producing multistage polymer and method for producing methacrylic resin composition - Google Patents

Description

  The present invention relates to a method for producing a multistage polymer capable of imparting excellent impact resistance, and a method for producing a methacrylic resin composition using the multistage polymer obtained by the method.

  Conventionally, methacrylic resins are widely used in various molded products because they are excellent in transparency and weather resistance and are easy to melt-mold. However, a molded product made of methacrylic resin is insufficient in impact resistance, and there is a problem that cracks, chips and the like are likely to occur when subjected to stress such as dropping, collision and vibration.

  Therefore, as a means for improving the impact resistance of thermoplastic resins including methacrylic resins, polymer particles including an elastic polymer layer and a hard polymer layer are obtained by multi-stage emulsion polymerization, and the multi-stage polymer particles are used as the thermoplastic resin. Various methods of blending in are proposed (Patent Documents 1 to 7).

  However, when the multistage polymer particles are blended in the thermoplastic resin as described above, although the impact resistance is improved, there is a problem that an appearance defect called unevenness called fish eye occurs on the surface of a molded product obtained therefrom. It was. Some of Patent Documents 1 to 7 aim to reduce this fish eye, but in any case, it is still impossible to reduce the fish eye to a sufficiently satisfactory level. .

JP-A-11-71437 JP 2001-247621 A JP-A-10-324787 JP-A-9-263614 JP 2002-348312 A JP 2003-128735 A Japanese Patent Laid-Open No. 2003-211446

  Accordingly, the present invention provides a method for producing a multistage polymer capable of imparting excellent impact resistance to a methacrylic resin composition while suppressing the occurrence of defects called fish eyes, and the multistage polymer obtained by the method. It aims at providing the manufacturing method of the methacrylic resin composition using this.

  The present inventor has intensively studied to solve the above problems. As a result, in the polymerization step when producing multistage polymer particles having an elastic layer and a hard layer, the formed polymer particles tend to fuse together to form aggregates, and the presence of the aggregates is I found out that it was the cause. And based on this knowledge, if the latex obtained in the polymerization step is filtered using a specific filter medium, it becomes possible to remove the agglomerates satisfactorily, and the multistage polymer obtained through this filtration treatment is obtained. When used, it has been found that the generation of fish eyes is suppressed, and the present invention has been completed.

That is, in the method for producing a multistage polymer of the present invention, at least one elastic polymer layer obtained by polymerizing a monomer mainly composed of alkyl acrylate and a monomer mainly composed of alkyl methacrylate are polymerized. A latex comprising at least one hard polymer layer, the latex comprising the multi-stage polymer is prepared by an emulsion polymerization method, and the latex is upstream of a plurality of regions having different densities. A filter is obtained by passing through a filter medium having a filtration accuracy of 50 μm or less, and a multistage polymer is recovered from the filtrate. .
The method for producing a methacrylic resin composition of the present invention comprises a polymer formed by polymerizing a multistage polymer (A) obtained by the method for producing a multistage polymer of the present invention and a monomer mainly composed of alkyl methacrylate. The combination (B) is melt-kneaded.

  ADVANTAGE OF THE INVENTION According to this invention, the multistage polymer which can provide the impact resistance excellent in the methacryl resin composition, suppressing generation | occurrence | production of the defect called a fish eye can be provided. Thereby, while having the outstanding impact resistance, the effect that the methacryl resin composition with few fish eyes can be obtained is acquired.

  The method for producing a multistage polymer of the present invention is obtained by polymerizing at least one elastic polymer layer obtained by polymerizing a monomer mainly composed of alkyl acrylate and a monomer mainly composed of alkyl methacrylate. This is a method for obtaining a multistage polymer comprising at least one hard polymer layer.

  The multistage polymer to be obtained in the present invention includes at least one elastic polymer layer and at least one hard polymer layer. The layer structure is not particularly limited. For example, it has a two-layer structure consisting of an inner layer (elastic polymer layer) / outer layer (hard polymer layer), and an inner layer (hard polymer layer) / outer layer (elastic polymer layer). Two-layer structure, three-layer structure consisting of inner layer (hard polymer layer) / intermediate layer (elastic polymer layer) / outer layer (hard polymer layer), inner layer (elastic polymer layer) / intermediate layer (hard polymer layer) / 3 layer structure consisting of outer layer (elastic polymer layer), inner layer (elastic polymer layer) / inner layer side intermediate layer (hard polymer layer) / outer layer side intermediate layer (elastic polymer layer) / outer layer (hard polymer layer) For example). Among these layer structures, a layer structure in which the outermost layer (outer layer) is a hard polymer layer is preferable in terms of excellent miscibility with a methacrylic resin. For example, the inner layer (hard polymer layer) / intermediate layer (elastic weight) A three-layer structure consisting of a combined layer) / outer layer (hard polymer layer) is preferred.

  Hereinafter, as an example of a preferable multistage polymer, a constituent material of a multistage polymer having a three-layer structure including an inner layer (hard polymer layer) / intermediate layer (elastic polymer layer) / outer layer (hard polymer layer) will be described. In addition, it cannot be overemphasized that these description can be suitably applied to the multistage polymer of another layer structure by changing according to a polymerization order etc., for example.

  The elastic polymer layer constituting the intermediate layer is obtained by polymerizing a monomer mainly composed of alkyl acrylate. For example, 50 to 99.9% by weight of alkyl acrylate can be copolymerized therewith. It is formed of an elastic copolymer obtained by polymerizing a monomer composed of 0 to 49.9% by weight of another vinyl monomer and 0.1 to 10% by weight of a copolymerizable crosslinkable monomer. Is preferred. As the alkyl acrylate, the other vinyl monomer, and the crosslinkable monomer, two or more of them may be used as long as the composition falls within the above range.

  Examples of the alkyl acrylate used as a raw material for the elastic polymer layer include those having an alkyl group having 1 to 8 carbon atoms. In particular, an alkyl group having 4 to 8 carbon atoms such as butyl acrylate and 2-ethylhexyl acrylate is preferable.

  The other vinyl monomer used as a raw material for the elastic polymer layer may be a compound that can be copolymerized with the alkyl acrylate. It is a monofunctional compound having one heavy bond. For example, methacrylic acid esters such as methyl methacrylate, butyl methacrylate and cyclohexyl methacrylate; aromatic vinyl compounds such as styrene; vinylcyan compounds such as acrylonitrile;

  The copolymerizable cross-linkable monomer used as a raw material for the elastic polymer layer may be any one having at least two polymerizable carbon-carbon double bonds in one molecule. Unsaturated carboxylic acid diesters of glycols such as methacrylate, butanediol dimethacrylate; Alkenyl esters of unsaturated carboxylic acids such as allyl acrylate, allyl methacrylate, allyl cinnamate; diallyl phthalate, diallyl maleate, tri Polyalkenyl esters of polybasic acids such as allyl cyanurate and triallyl isocyanurate; unsaturated carboxylic acid esters of polyhydric alcohols such as trimethylolpropane triacrylate; divinylbenzene; and the like. Alkenyl esters of acids and polybasic acids Polyalkenyl ester, and the like preferably.

  The hard polymer layer constituting the outer layer is formed by polymerizing a monomer mainly composed of alkyl methacrylate, for example, 50 to 100% by weight of alkyl methacrylate and 0 to 50% by weight of acrylic ester. And a hard polymer obtained by polymerizing a monomer composed of 0 to 49% by weight of another vinyl monomer copolymerizable therewith. As the alkyl methacrylate, acrylic acid ester and other vinyl monomers, two or more of those which fall within the respective definitions may be used as long as the composition falls within the above range.

  As said alkyl methacrylate used as a raw material of the said outer-layer hard polymer layer, the ester which has a C1-C8 alkyl group is preferable, for example, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid Examples include 2-ethylhexyl and cyclohexyl methacrylate.

  Examples of the acrylic ester used as a raw material for the outer hard polymer layer include alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, and cyclohexyl acrylate. It is done.

  The other vinyl monomer used as necessary as a raw material for the outer hard polymer layer may be a compound copolymerizable with the alkyl methacrylate and / or acrylate ester. Aromatic vinyl compounds such as these; vinylcyan compounds such as acrylonitrile; and the like.

  The hard polymer layer constituting the inner layer is formed by polymerizing a monomer mainly composed of alkyl methacrylate, for example, 70 to 100% by weight of alkyl methacrylate, and other copolymerizable with this. It is preferably formed of a hard polymer obtained by polymerizing a monomer composed of 0 to 30% by weight of a vinyl monomer. As long as the composition of the alkyl methacrylate and the other vinyl monomer falls within the above-mentioned range, two or more of those that fall within the respective definitions may be used.

  As said alkyl methacrylate used as a raw material of the said inner-layer hard polymer layer, the ester which has a C1-C4 alkyl group is mentioned preferably, for example, Methyl methacrylate is especially preferable.

  The other vinyl monomer used as necessary as a raw material for the inner hard polymer layer may be a compound copolymerizable with the alkyl methacrylate, for example, methyl acrylate, ethyl acrylate, And acrylic acid esters such as butyl acrylate and cyclohexyl acrylate; aromatic vinyl compounds such as styrene; vinylcyan compounds such as acrylonitrile; and the like. Further, as the other vinyl monomer, the above-described crosslinkable monomer can be used as an arbitrary raw material for the elastic copolymer layer.

In the method for producing a multistage polymer of the present invention, first, the raw materials as described above are polymerized by an emulsion polymerization method to prepare a latex containing the multistage polymer.
In conducting the emulsion polymerization, a known emulsion polymerization method may be employed, and there is no particular limitation. For example, in order to obtain the above-mentioned multi-layer polymer having a three-layer structure, first, the inner hard polymer layer is formed in a medium containing an initiator such as an emulsifier and a polymerization initiator under an inert gas atmosphere such as nitrogen. A monomer as a raw material is polymerized. At this time, the monomer is preferably polymerized in two stages. That is, a predetermined amount of the monomer is polymerized to obtain seed particles, and the remaining monomers are polymerized in the presence of the seed particles to form polymer particles as an inner layer. Is preferred. Thus, by polymerizing in two steps, the particle diameter and the number of particles of the finally obtained three-layered polymer can be adjusted to desired values. Next, after polymerizing the monomer used as the raw material of the elastic polymer layer in the presence of the obtained polymer particles as the inner layer, subsequently, the outer layer hard in the presence of the obtained polymer particles. A monomer used as a raw material for the polymer layer is polymerized. Thereby, a multistage polymer having a three-layer structure consisting of an inner layer / intermediate layer / outer layer can be obtained in a latex state.

  Examples of the medium used for polymerization in forming the multistage polymer include water-based media such as water and a mixed solvent of water and a water-miscible solvent. This aqueous medium is preferably added in a lump, divided or continuously so as to have a ratio of about 50 to 150 parts by weight with respect to 100 parts by weight of the total amount of monomers constituting the inner layer, intermediate layer and outer layer. .

  The emulsifier used for the polymerization when forming the multistage polymer is not particularly limited, and examples thereof include an anionic emulsifier such as a linear or branched sodium alkylbenzene sulfonate such as sodium dodecylbenzene sulfonate. . The emulsifier is preferably added all at once, divided or continuously so as to be a ratio of about 0.01 to 1 part by weight with respect to 100 parts by weight of the total amount of monomers constituting the inner layer, intermediate layer and outer layer. .

Examples of the polymerization initiator used for polymerization when forming the multistage polymer include persulfuric acid compounds such as potassium persulfate and ammonium persulfate. The polymerization initiator is added all at once, divided or continuously so as to be a ratio of about 0.01 to 1 part by weight with respect to 100 parts by weight of the total amount of monomers constituting the inner layer, intermediate layer and outer layer. Is preferred.
In the polymerization for forming the multistage polymer, a pH adjuster such as sodium carbonate may be used as necessary. Moreover, the polymerization temperature at the time of the said polymerization is about 60-90 degreeC normally.

  When the multistage polymer is a polymer having a three-layer structure as described above, the weight ratio of inner layer / intermediate layer / outer layer is set to inner layer / intermediate layer / outer layer = 30 to 40/40 to 50/10 to 30. preferable. When the ratio of the inner layer is smaller than the above range, the surface hardness is likely to be lowered. On the other hand, when it is larger than the above range, the impact resistance may be lowered. If the proportion of the intermediate layer is smaller than the above range, the impact resistance tends to be insufficient, whereas if it is larger than the above range, the surface hardness may be lowered. Even if the ratio of the outer layer is smaller or larger than the above range, the dispersibility of the resulting polymer particles tends to decrease.

  The particle diameter of the multistage polymer is not particularly limited. For example, when the multistage polymer is the above-described three-layer polymer, the particle diameter of the polymer particles is 0.05 to 0 on a weight average basis. A range of .40 μm is preferable in terms of impact resistance. If the particle diameter of the multistage polymer particles is too large, the impact resistance is maintained, but whitening defects are likely to occur on the material surface by heating, whereas if the particle diameter is too small, the impact resistance is insufficient. Tend. In addition, the particle diameter of a multistage polymer can be adjusted with the addition amount of the emulsifier at the time of superposition | polymerization, the preparation amount of a monomer, etc.

In this way, a latex containing a multistage polymer is obtained by emulsion polymerization.
In the method for producing a multistage polymer of the present invention, the latex is then filtered by passing a plurality of regions having different densities through a filter medium having a higher density on the downstream side than on the upstream side. To do. Thereby, the aggregate of the polymer particles formed in the polymerization process is efficiently removed, and it becomes possible to suppress the generation of fish eyes. Further, according to such filtration, the latex subjected to filtration first passes through a filter medium having a low density (in other words, a large opening), and then has a high density (in other words, the opening is small). Since it passes through the (small) filter medium, the filtration speed is high and the life until the filter medium is blocked is also long.

  In order to provide the filter medium with a plurality of regions having different densities so that the downstream side has a higher density than the upstream side, for example, a method of laminating a plurality of filter media with different filtration accuracy or a continuous filtration in the thickness method For example, a method using a material manufactured so that the accuracy may be changed. Examples of commercially available filtration devices equipped with such a filter medium include “Duoflow (registered trademark)” manufactured by Cuno Co., Ltd. and “Profile II” manufactured by Nippon Pole Co., Ltd.

  The filter medium is not particularly limited as long as it has a plurality of regions having different densities so that the downstream side has a higher density than the upstream side. For example, a filter cloth, a metal mesh, various plastics ( One or more of polyethylene, polypropylene, polyester, polytetrafluoroethylene, polyvinylidene fluoride, etc.) may be used. Among these, plastic filter media such as polyethylene, polypropylene, and polyester are particularly suitable because they are less likely to be mixed with latex (filtrate) and economical.

In the present invention, the filtration accuracy of the filter medium is preferably 50 μm or less. More preferably, it is 20 micrometers or less, More preferably, it is 5 micrometers or less. When the filtration accuracy exceeds 50 μm, aggregates in the latex cannot be sufficiently collected, and the number of fish eyes generated tends to increase due to the aggregates that have passed through the filter medium.
In addition, the filtration accuracy of the filter medium in the present invention means a particle diameter (μm) when the collection efficiency required in a predetermined filtration test is 50%. Here, the filtration test and the collection efficiency are obtained as follows. That is, the filtration test is performed by using ACFTD (Arizona sand, median diameter 7 μm) as a test powder and passing a dispersion obtained by dispersing the test powder in a liquid medium through a filter medium. Then, the number of particles in the dispersion before the filtration test and the number of particles in the filtrate after the filtration test are measured for each particle diameter with a particle counter, and the collection efficiency calculated according to the following formula is 50%. The particle diameter (μm) at the time is defined as the filtration accuracy.
Collection efficiency (%) = [(nA−nB) / nA] × 100
However, nA represents the number of particles when measured for particles having a predetermined particle size present in the dispersion before the filtration test, and nB represents the filtration test among the particles present in the filtrate after the filtration test. This represents the number of particles having the same particle size as that measured in the previous dispersion.

  In the method for producing a multistage polymer of the present invention, the multistage polymer is recovered from the filtrate obtained by the filtration.

  The multistage polymer can be isolated and recovered from the latex by a known method such as a salting out method, an acid precipitation method, a spraying method, or a freezing method. For example, the salting-out method is preferable because it is the simplest and excellent in operability. Hereinafter, the isolation method by the salting out method will be described as an example of the isolation method of the multistage polymer.

The filtrate (latex) obtained by the filtration is salted out by continuously adding it to a salting-out agent-containing aqueous solution heated to a predetermined temperature under stirring conditions, and includes a salt containing a multistage polymer aggregate. It becomes a depositing slurry. Incidentally, the agglomerates formed by salting out here are electrically bonded in an aqueous solution, and are well dispersed during subsequent melt-kneading, and therefore do not participate in the generation of fish eyes.
Examples of the salting-out agent used for salting-out include magnesium sulfate, aluminum sulfate, and aluminum chloride. Among these, magnesium sulfate is particularly preferable. The temperature of the salting-out agent-containing aqueous solution (that is, the salting-out temperature) may be appropriately set depending on the type of polymer and stirring conditions, but is generally 50 ° C. or higher and lower than 100 ° C., preferably 60 ° C. or higher, more preferably It is good that it is 70 degreeC or more. The stirring speed at the time of salting out may be a speed that can uniformly stir the latex added to the salting-out agent-containing aqueous solution and the obtained salting-out slurry. Moreover, the dripping speed | rate of latex should just be a speed | strength of the grade which a multistage polymer can fully aggregate.

The multistage polymer is obtained as a dry powder by dehydrating and drying the salting-out slurry. Dehydration can be performed by, for example, a bucket-type or decanter-type centrifuge. Moreover, drying can be performed by a fluid dryer, a vibration dryer, a hot air dryer, etc., for example. The salting-out slurry is preferably washed with water in advance for the purpose of removing water-soluble impurities (such as a salting-out agent) before dehydration.
The dry powder of the multistage polymer thus obtained preferably has a bulk specific gravity measured according to JIS-K-6721 of 0.28 g / cm ³ or more from the viewpoint of excellent handleability.

  The method for producing a methacrylic resin composition of the present invention comprises a multi-stage polymer obtained by the above-described method for producing a multi-stage polymer of the present invention (hereinafter sometimes referred to as “multi-stage polymer (A)”), and methacrylic acid. A polymer obtained by polymerizing an alkyl-based monomer (hereinafter also referred to as “polymer (B)”) is melt-kneaded.

  In the present invention, the polymer (B) to be used for melt kneading is obtained by polymerizing a monomer mainly composed of alkyl methacrylate, for example, 50 to 100% by weight of alkyl methacrylate and copolymerized therewith. A polymer obtained by polymerizing a monomer composed of 0 to 50% by weight of another possible vinyl monomer is preferable. As long as the composition of the alkyl methacrylate and the other vinyl monomer falls within the above-mentioned range, two or more of those that fall within the respective definitions may be used.

As said alkyl methacrylate used as a raw material of a polymer (B), the ester which has a C1-C4 alkyl group is mentioned preferably, for example, and methyl methacrylate is especially preferable.
The other vinyl monomer used as a raw material for the polymer (B) may be any compound that can be copolymerized with the alkyl methacrylate, such as methyl acrylate, ethyl acrylate, acrylic. Examples thereof include acrylic acid esters such as butyl acid and cyclohexyl acrylate; aromatic vinyl compounds such as styrene; vinylcyan compounds such as acrylonitrile; and the like.
About the polymerization method at the time of forming the said multistage polymer (B), a well-known method, conditions, etc. should just be employ | adopted suitably, and it does not restrict | limit in particular.

  In the present invention, in the melt-kneading, the multistage polymer (A) and the polymer (B) are multistage polymer (A): polymer (B) = 5: 95 to 70:30 (weight ratio). ) Is preferably supplied to the twin-screw kneading extruder. If the multi-stage polymer (A) is less than the above range, the impact resistance tends to be lowered. On the other hand, if it is more than the above range, the melt viscosity is increased and the moldability may be impaired. Preferably, multistage polymer (A): polymer (B) = 10: 90-60: 40 (weight ratio), more preferably multistage polymer (A): polymer (B) = 15: 85-50 : 50 (weight ratio) is preferable. In order to supply the multistage polymer (A) and the polymer (B) to the extruder at the predetermined ratio, for example, two quantitative supply feeders are provided in the extruder, and each feed amount is set to a predetermined ratio. Alternatively, the multistage polymer (A) and the polymer (B) may be mixed in advance at a predetermined ratio, and the mixture may be charged into an extruder.

In the present invention, the melt kneading is carried out by the following formula (I)
E = P / W (I)
(In formula (I), E is the specific energy (kW · h / kg), P is the motor power consumption (kW) of the extruder, and W is the extrusion per unit time of the resin composition extruded from the extruder. (Amount (kg / h) is indicated.)
It is preferable to carry out so that the specific energy calculated | required by 0.10-0.60kW / h / kg. Here, the specific energy calculated | required by the said formula (I) is the resin composition extruded from an extruder at the time of melt kneading with a multistage polymer (A) and a polymer (B) from an extruder per unit weight. This is the amount of energy applied, and the larger the value, the higher the kneading effect. When the specific energy is less than 0.10, the dispersibility of the multistage polymer (A) becomes insufficient, and a large amount of fish eyes tend to be generated. On the other hand, when the specific energy exceeds 0.60, Deterioration becomes large, and there is a risk of strength reduction and coloring. Preferably, the specific energy is 0.15 to 0.30 kW · h / kg.

  The power consumption of the motor in the above formula (I) can be obtained by a known method. For example, if the motor of the extruder is a DC motor, the motor power consumption (kW) is calculated by the product of the current (A) and the voltage (V), so an ammeter and a voltmeter are connected to the extruder. Power consumption (kW) can be obtained by mounting and measuring current (A) and voltage (V).

The specific energy is, for example, the screw shape of the extruder, the ratio (L / D) of the screw length (L) to the screw diameter (D), the cylinder temperature, the screw rotation speed, the extrusion amount, and the like. It can be easily controlled by changing the conditions.
The screw shape of the extruder can be arbitrarily changed by rearranging the elements constituting the screw. For example, a reverse philite element having a groove shape that changes the direction in which the molten resin is sent out to the reverse direction is screwed. When added to the element configuration, the specific energy increases. Therefore, the specific energy can be increased or decreased depending on whether or not the reverse philite element is installed or the number of the inverted phirite elements.
The ratio (L / D) between the screw length (L) and the screw diameter (D) of the extruder can be adjusted by changing the number of cylinder blocks. When L / D is increased, the specific energy increases because the time that the resin stays in the extruder becomes longer. On the other hand, when L / D is reduced, the specific energy is reduced because the time during which the resin stays in the extruder is shortened.

  The specific energy can be controlled by changing the conditions at the time of extrusion, for example, by changing the cylinder temperature of the extruder and the screw rotation speed. That is, if the cylinder temperature is set high, the viscosity of the molten resin decreases, so that the specific energy can be reduced. Conversely, if the cylinder temperature is set low, the viscosity of the molten resin increases, so the specific energy. Can be increased. Also, if the screw extrusion rate is increased when the resin extrusion amount is made constant, the extrusion amount per rotation decreases, so the motor power consumption can be reduced and the specific energy can be reduced. When the number of revolutions is lowered, the amount of extrusion per one time increases, so that the motor power consumption increases and the specific energy can be increased.

The twin-screw kneading extruder used in the present invention is not particularly limited as long as it is a twin-screw kneading extruder capable of melt-kneading while applying the specific energy as described above.
The rotation type of the twin-screw kneading extruder includes a non-meshing type same direction rotation, a meshing type same direction rotation, a non-meshing type different direction rotation, and a meshing type different direction rotation. In terms of having a structure and being able to increase the rotational speed because the load is smaller than that in the different direction rotation, the meshing type same direction rotation type is preferable. As a screw used in that case, for example, a screw having a triple thread type or a double thread type can be used, but a double thread type that can increase the hold-up amount of the apparatus is more preferable. The screw diameter of the extruder can be appropriately selected according to the production amount, and is usually about 30 to 200 mm.
In the twin-screw extruder used in the present invention, for example, a foreign material in the molten resin can be removed by mounting a known filter medium on the breaker plate portion or the extrusion tip portion of the extruder. Although there is no restriction | limiting in particular as this filter medium, For example, a sintered wire mesh, a sintered nonwoven fabric, a sintered metal powder, a wire mesh etc. are mentioned. The mesh of the filter medium is preferably 200 mesh or less, more preferably 300 mesh or less, in order to reliably remove foreign matter.

  Various conditions for performing the melt kneading, for example, the kneading temperature (cylinder setting temperature) and the vent degassing pressure may be appropriately set according to the melt viscosity of the resin used so that the specific energy falls within the above range. Good. For example, the kneading temperature is usually 200 to 300 ° C., preferably 220 ° C. to 280 ° C., and the pressure for vent degassing is usually 1 to 700 Torr.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not restrict | limited to these. In the following Examples and Comparative Examples, “part” means “part by weight” and “%” means “% by weight”.

Example 1
<Preparation of latex>
Into a 5 L glass reaction vessel, together with the total amount of the aqueous solution consisting of the following medium raw material (a), the mixture consisting of the following inner layer hard polymer raw material (b) is charged in an amount corresponding to 15%, and stirring is performed in a nitrogen atmosphere Polymerization was carried out at 80 ° C. for 60 minutes. Thereafter, the entire amount of the aqueous solution consisting of the following additional initiator raw material (c) was added and stirred, and the remaining 85% of the mixture consisting of the inner layer hard polymer raw material (b) was continuously added at 85 ° C. for 80 minutes, The mixture was aged at the same temperature for 30 minutes with stirring to obtain a latex containing a hard polymer. Subsequently, the whole amount of the aqueous solution consisting of the following additional initiator raw material (d) is added to this latex and stirred, and then the total amount of the mixture consisting of the following intermediate layer elastic polymer raw material (e) is continuously continued at 85 ° C. for 90 minutes. Then, the mixture was aged for 90 minutes at the same temperature while stirring, to obtain a latex containing a polymer having a structure having an elastic polymer layer (rubber elastic layer) outside the hard polymer layer as an inner layer. Subsequently, the whole amount of the aqueous solution consisting of the following additional initiator raw material (f) was added to this latex and stirred, and then the total amount of the mixture consisting of the following outer layer hard polymer raw material (g) was continuously added at 85 ° C. for 60 minutes. And then aged for 30 minutes at the same temperature with stirring.

[Medium raw material (a)]
Ion-exchanged water 151 parts Sodium carbonate 0.07 parts

[Inner layer hard polymer raw material (b)]
Methyl methacrylate 65.8 parts Methyl acrylate 4.1 parts Allyl methacrylate 0.14 parts Ion-exchanged water 15.5 parts Sodium dodecylbenzenesulfonate 0.37 parts Potassium persulfate 0.008 parts

[Additional initiator raw material (c)]
Deionized water 7.4 parts Potassium persulfate 0.04 parts [Additional initiator raw material (d)]
Sodium dodecylbenzenesulfonate 0.48 parts Deionized water 16.4 parts Potassium persulfate 0.08 parts

[Interlayer elastic polymer raw material (e)]
Butyl acrylate 73.4 parts Styrene 14.9 parts Allyl methacrylate 1.8 parts [Additional initiator raw material (f)]
Ion exchange water 8 parts Potassium persulfate 0.04 part [Outer layer hard polymer raw material (g)]
Methyl methacrylate 37.8 parts Methyl acrylate 2.2 parts

  Thus, the inner layer is methyl methacrylate / methyl acrylate / allyl methacrylate rigid cross-linked polymer, the intermediate layer is butyl acrylate / styrene / allyl methacrylate soft elastic copolymer, and the outer layer is methyl methacrylate / methyl acrylate. A latex containing a multistage polymer having a spherical three-layer structure consisting of a hard polymer and having a weight ratio of each layer of 35/45/20 was obtained. The average particle size of the polymer particles in the latex was measured by a dynamic light scattering method using a light scattering photometer (“DLS-7000” manufactured by Otsuka Electronics Co., Ltd.) and found to be 0.28 μm. Moreover, the solid content concentration in the latex determined by the dry weight method was 50%.

<Recovery of filtration and multistage polymer>
Next, a filter made of polyester and equipped with a filter medium (filter element) having a nominal filtration accuracy of 1 μm provided with a plurality of regions having different densities in the thickness direction so that the downstream side has a higher density than the upstream side. The latex obtained above was filtered at 80 ° C. using an apparatus (“Duoflow (registered trademark) filter system” manufactured by Cuno Co., Ltd.).
Next, 100 parts of the filtered latex (filtrate) was continuously added with stirring to 150 parts of a 0.7% strength magnesium sulfate aqueous solution that had been heated to 80 ° C. in advance, whereby the polymer was salted. The salting out slurry was obtained. The obtained slurry was washed with 10 times the amount of pure water with respect to the polymer weight in a centrifuge and dehydrated, and then dried in a vacuum dryer at 80 ° C. to dry the multistage polymer. I got a powder.

<Production of methacrylic resin composition>
A methacrylic resin pellet (glass transition temperature 103 ° C.) obtained by a bulk polymerization method using a monomer component having a composition of 97.8% methyl methacrylate and 2.2% methyl acrylate was prepared. When 0.1 g of this methacrylic resin was dissolved in 10 mL of chloroform and the reduced viscosity at 25 ° C. was measured with a Canon-Fenske viscosity tube, it was 0.068 L / g.
After mixing 20 parts of the dry powder of the multistage polymer obtained above and 80 parts of the methacrylic resin pellets with a super mixer, the resulting mixture was mixed with a twin-screw extruder (“TEX-30” manufactured by Nippon Steel Works, Ltd.). ": Mesh type same direction rotation type, screw diameter 30mm, L / D = 42, screw element configuration with reverse philite elements with groove shape in reverse direction at 3 locations, 300 mesh stainless steel wire mesh on breaker plate part 1) was used, and the mixture was melt-kneaded at a set temperature of the cylinder of 230 ° C. and a screw speed of 250 rpm to obtain a pellet-shaped methacrylic resin composition having a diameter of about 3 mm and a length of about 3 mm. At this time, the extrusion rate of the resin composition extruded from the extruder is 15 kg / h, the motor power consumption of the extruder is 3.60 kW, and the specific energy obtained by the above formula (I) is 0.24 kW · h / kg.

<Evaluation>
Fish eyes were evaluated by the following method using the obtained pellet-shaped methacrylic resin composition. The results are shown in Table 1.
[Fish Eye Detection Method]
Fish eyes generated when the obtained methacrylic resin composition was formed into a film were detected using a fish eye counter system manufactured by Optical Control Systems GmbH (OCS). That is, after the pellets of the obtained methacrylic resin composition were dried in a hot air circulating oven at 80 ° C. for 12 hours, the pellets were uniaxial extruder (manufactured by OCS Co., Ltd.) with a cylinder diameter set to 255 ° C. "ME-20") is supplied from a hopper, discharged from a T-die (lip opening 0.5 mm, width 150 mm) under the condition of a screw speed of 40 rpm, and subsequently rotated at a take-up speed of 4 m / min at 70 ° C. The film was cooled with a mirror-surface metal roll set to about 80 μm thick. This film is inspected with a CCD camera system ("FSA-100" manufactured by OCS Co., Ltd .: minimum resolution 14 μm or more), and the portion where the light transmittance is 50% or less is defined as a fish eye, and the fish eye of 25 to 350 μmΦ exceeds 350 μmΦ. Each fisheye was counted.

(Example 2)
The same operation as in Example 1 was carried out except that the filter medium (filter element) used in the filtration in Example 1 was changed to a filter element having a nominal filtration accuracy of 10 μm to obtain a multistage polymer dry powder.
Next, using the obtained multistage polymer, the same operation as in Example 1 was performed to obtain a pellet-shaped methacrylic resin composition having a diameter of about 3 mm and a length of about 3 mm. At this time, the extrusion rate of the resin composition extruded from the extruder is 15 kg / h, the motor power consumption of the extruder is 3.60 kW, and the specific energy obtained by the above formula (I) is 0.24 kW · h / kg.
Fish eyes were evaluated using the obtained pellet-like methacrylic resin composition. The results are shown in Table 1.

(Example 3)
The filter medium (filter element) used in the filtration in Example 1 was subjected to the same operation as in Example 1 except that the filtration accuracy was changed to a filter element made of polypropylene with a nominal filtration accuracy of 50 μm, and the multistage polymer was dried. I got a powder.
Next, using the obtained multistage polymer, the same operation as in Example 1 was performed to obtain a pellet-shaped methacrylic resin composition having a diameter of about 3 mm and a length of about 3 mm. At this time, the extrusion rate of the resin composition extruded from the extruder is 15 kg / h, the motor power consumption of the extruder is 3.60 kW, and the specific energy obtained by the above formula (I) is 0.24 kW · h / kg.
Fish eyes were evaluated using the obtained pellet-like methacrylic resin composition. The results are shown in Table 1.

(Comparative Example 1)
A multi-stage polymer dry powder was obtained by performing the same operation as in Example 1 except that the filtration in Example 1 was performed using a single-piece stainless steel wire mesh having a 330 mesh (aperture 45 μm). . In addition, when filtering using the above stainless steel wire mesh, the mesh was immediately closed after filtration of latex was started and filtration became impossible. By repeating the operation of resuming filtration a plurality of times, a predetermined amount of latex could be filtered.
Next, using the obtained multistage polymer, the same operation as in Example 1 was performed to obtain a pellet-shaped methacrylic resin composition having a diameter of about 3 mm and a length of about 3 mm. At this time, the extrusion rate of the resin composition extruded from the extruder is 15 kg / h, the motor power consumption of the extruder is 3.60 kW, and the specific energy obtained by the above formula (I) is 0.24 kW · h / kg.
Fish eyes were evaluated using the obtained pellet-like methacrylic resin composition. The results are shown in Table 1.

(Comparative Example 2)
Except that the filtration in Example 1 was performed using a 140-mesh (mesh opening 106 μm) single-piece stainless steel wire mesh, the same operation as in Example 1 was performed to obtain a dry powder of a multistage polymer. .
Next, using the obtained multistage polymer, the same operation as in Example 1 was performed to obtain a pellet-shaped methacrylic resin composition having a diameter of about 3 mm and a length of about 3 mm. At this time, the extrusion rate of the resin composition extruded from the extruder is 15 kg / h, the motor power consumption of the extruder is 3.60 kW, and the specific energy obtained by the above formula (I) is 0.24 kW · h / kg.
Fish eyes were evaluated using the obtained pellet-like methacrylic resin composition. The results are shown in Table 1.

(Comparative Example 3)
Except that no filtration was performed in Example 1, the same operation as in Example 1 was performed to obtain a multistage polymer dry powder.
Next, using the obtained multistage polymer, the same operation as in Example 1 was performed to obtain a pellet-shaped methacrylic resin composition having a diameter of about 3 mm and a length of about 3 mm. At this time, the extrusion rate of the resin composition extruded from the extruder is 15 kg / h, the motor power consumption of the extruder is 3.60 kW, and the specific energy obtained by the above formula (I) is 0.24 kW · h / kg.
Fish eyes were evaluated using the obtained pellet-like methacrylic resin composition. The results are shown in Table 1.

Claims (5)

Including at least one elastic polymer layer formed by polymerizing a monomer mainly composed of alkyl acrylate and at least one hard polymer layer formed by polymerizing a monomer mainly composed of alkyl methacrylate. A method for obtaining a multistage polymer comprising:
Prepare a latex containing the multistage polymer by emulsion polymerization,
The latex is filtered by passing through a filter medium having a plurality of regions having different densities so that the downstream side has a higher density than the upstream side and the filtration accuracy is 50 μm or less, and the filtrate is obtained. A method for producing a multistage polymer, wherein the multistage polymer is recovered from the process. The filter medium manufacturing method of the multistage polymer of claim 1 Symbol mounting is made of plastic.   Melting and kneading a multistage polymer (A) obtained by the method for producing a multistage polymer according to claim 1 and a polymer (B) obtained by polymerizing a monomer mainly composed of alkyl methacrylate. A method for producing a methacrylic resin composition. In the melt-kneading, the multistage polymer (A) and the polymer (B) are mixed at a ratio of multistage polymer (A): polymer (B) = 5: 95 to 70:30 (weight ratio). The method for producing a methacrylic resin composition according to claim 3, wherein the method is performed by supplying to a shaft kneading extruder. The melt kneading is represented by the following formula (I)
E = P / W (I)
(In formula (I), E is the specific energy (kW · h / kg), P is the motor power consumption (kW) of the extruder, and W is the extrusion per unit time of the resin composition extruded from the extruder. (Amount (kg / h) is indicated.)
5. The method for producing a methacrylic resin composition according to claim 3, wherein the specific energy obtained in step 1 is 0.10 to 0.60 (kW · h / kg).