JP2009235357A - Method of drying wet cake - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of drying a wet cake without forming lumps in drying the wet cake containing water, an organic solvent and a thermoplastic resin. <P>SOLUTION: The drying method comprises a feeding step of feeding a part of the wet cake containing water, the organic solvent and the thermoplastic resin into a dryer, heating under reduced pressure, adjusting the inside of the dryer to normal pressure and cooling, and then feeding the residue or a part of the residue of the wet cake into the dryer, and heating under reduced pressure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for drying a wet cake, and more particularly to a drying method for preventing generation of a lump when a wet cake containing water, an organic solvent, and a thermoplastic resin is dried.

  In general, when polymethyl methacrylate or (meth) acrylic acid ester monomer copolymer, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-styrene-butadiene resin, etc. are industrially produced, Part is produced by bulk polymerization, suspension polymerization, emulsion polymerization, and only a part is produced by solution polymerization.

  Patent Document 1 discloses a method in which a copolymer containing a carboxyl group-containing acrylic monomer having excellent handling properties and heat stability is solution-polymerized, washed and solid-liquid separated. In this manufacturing method, the volatile matter content remaining in the wet cake containing water, organic solvent, and thermoplastic resin is large, so the odor is strong and the volatile matter in the subsequent molding process is increased. Further improvements are required.

On the other hand, as a method for drying the wet cake, there is known a method of collectively supplying to a dryer and drying under reduced pressure as described in Patent Document 2, but water and an organic solvent as described in Patent Document 1, When a wet cake containing a thermoplastic resin is dried, a lump is generated in the initial stage of drying, which makes it difficult to pull out from the dryer, and the wet cake yield after drying is poor. there were.
JP 2006-265543 A JP 2005-40738 A

  The objective of this invention is providing the drying method of the wet cake which prevents a lump from producing | generating at the time of drying the wet cake containing water, an organic solvent, and a thermoplastic resin.

The method for drying a wet cake of the present invention that achieves the above object is as follows.
(1) A part of a wet cake containing water, an organic solvent, and a thermoplastic resin is put into the dryer and heated under reduced pressure. After the interior of the dryer is cooled to normal pressure, the remaining or remaining 1 of the wet cake is cooled. A method for drying a wet cake, characterized in that it has a supply step in which a part is additionally charged into the dryer and heated under reduced pressure,
(2) The drying method of the wet cake according to (1), wherein cooling in the dryer in the supplying step is performed at a temperature lower by 0.1 to 20 ° C. than the time of the reduced pressure heating,
(3) The drying method of the wet cake according to (1) or (2), wherein the temperature inside the dryer in the supplying step is 30 to 100 ° C., and the pressure is reduced to 80 to 99 kPa from the normal pressure state,
(4) The drying method of a wet cake according to (1), (2) or (3), wherein the dryer is a vibration type or a fluid type,
(5) The thermoplastic resin is a carboxyl group-containing acrylic copolymer composed of a copolymer containing an unsaturated carboxylic acid alkyl ester unit and an unsaturated carboxylic acid unit (1), (2 ), (3) or (4) wet cake drying method,
(6) The method for drying a wet cake according to (1), (2), (3), (4) or (5), wherein the thermoplastic resin has an average particle size of 10 to 5000 μm,
(7) (1), (2), (3), (4), (5) or (1), wherein the wet cake is a cake obtained by solid-liquid separation of the slurry with a centrifuge (6) The wet cake drying method.

  According to the present invention, in the method for drying a wet cake containing water, an organic solvent, and a thermoplastic resin, when the wet cake is charged into the dryer, a supply step of repeating sequential charging and heating under reduced pressure is provided. By making the temperature at which the wet cake is charged lower than that at the time of heating under reduced pressure, it is possible to suppress the formation of lumps at the initial stage of drying. Thereby, improvement effects, such as the improvement of handling property, such as extraction from a dryer, suppression of drying unevenness, and the improvement of a yield, are acquired.

  Hereinafter, a method for drying a wet cake containing water, an organic solvent, and a thermoplastic resin of the present invention will be specifically described.

  The wet cake to be dried in the present invention contains water, an organic solvent, and a thermoplastic resin. The wet cake is not particularly limited.For example, a wet cake obtained by polymerization of a thermoplastic resin, a wet cake obtained by polymerization, washing, solid-liquid separation, or the like, or pre-drying these wet cakes. The wet cake obtained in this way can be illustrated. The polymerization method may be any of bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization. Water and the organic solvent may be added at any stage of polymerization or washing.

  In the drying method of the present invention, it has a supply step of sequentially putting the wet cake and the reduced pressure heating into the dryer repeatedly, and the temperature in the dryer when the wet cake is charged is lower than the temperature at the reduced pressure heating. To do. In the supplying step, first, a part of the wet cake is put into a dryer and heated under reduced pressure. Next, after the inside of the dryer is cooled to normal pressure, the remaining portion of the wet cake or the remaining portion is additionally charged and heated under reduced pressure. By repeating such a supply operation, a wet cake having a capacity suitable for the dryer performance is supplied. After the supply of a predetermined amount of wet cake is completed, the temperature of the reduced pressure heating may be increased stepwise to dry.

  In this way, by sequentially supplying the wet cake while repeating its charging and heating under reduced pressure, the amount of agglomerates generated in the initial stage of drying is reduced, and the average particle size of the thermoplastic resin after drying is reduced. be able to. In addition, by lowering the temperature at which the wet cake is introduced below the temperature of the reduced pressure heating, the amount of mass produced can be further reduced, and the average particle size of the thermoplastic resin after drying can be further reduced. .

  In the present invention, the number of times the wet cake is sequentially added is 2 times or more, preferably 5 times or more, more preferably 7 times or more. The number of times of charging can be changed depending on the properties of the wet cake and the performance of the dryer. The upper limit of the number of inputs is not particularly limited, but is preferably about 9 from the viewpoint of productivity.

  The pressure at the time of reduced pressure heating in the supplying step may be reduced by 80 kPa or more from normal pressure, preferably 80 to 99 kPa from normal pressure, more preferably 90 to 99 kPa. If the pressure at the time of reduced pressure heating is not at least 80 kPa lower than the normal pressure, the drying efficiency of the wet cake is insufficient and the productivity is deteriorated.

  The temperature in the dryer at the time of heating under reduced pressure in the wet cake supplying step is preferably 30 to 100 ° C, more preferably 40 to 80 ° C, and even more preferably 50 to 70 ° C. When the temperature at the time of reduced pressure heating in the supply step is less than 30 ° C., the drying efficiency of the wet cake is insufficient, and the time required for the supply operation becomes long. Moreover, when the temperature at the time of reduced-pressure heating in a supply process exceeds 100 degreeC, it will become easy to produce | generate a lump.

  After the wet cake supply operation is completed and the last wet cake is in a predetermined dry state, the temperature of the reduced pressure heating may be increased stepwise to further remove water and the organic solvent. The temperature at the final stage of heating under reduced pressure is preferably 70 to 150 ° C, more preferably 120 to 140 ° C.

  The interval from when a part of the wet cake is introduced and the reduced pressure heating is started to when the inside of the dryer is returned to the normal pressure state in order to add a part of the next wet cake is preferably 20 minutes or less, more preferably. Is 15 minutes or less, more preferably 10 minutes or less, and the lower limit may be about 5 minutes. If the interval at which the wet cake is sequentially added exceeds 20 minutes, the time required for the wet cake supply operation becomes long, and the productivity is lowered.

  In the drying method of the present invention, the degree of the cooling temperature that lowers the temperature in the dryer below the temperature during reduced pressure heating when the wet cake is charged is preferably 0.1 to 20 ° C., more preferably 1 to 10%. The temperature may be lowered, and more preferably 3 to 7 ° C. When the cooling temperature is less than 0.1 ° C., the effect of suppressing the formation of a lump is not sufficiently obtained. On the other hand, if the cooling temperature is higher than 20 ° C., the time required for the wet cake supply operation becomes longer, and the productivity is lowered. In addition, the temperature at which the wet cake is charged may be the temperature of the temperature adjusting means such as the jacket temperature, instead of the temperature in the dryer.

  As the dryer used in the present invention, a vibratory or fluid dryer is preferable. When using a vibration dryer, the amplitude of the vibration dryer is preferably 10 mm or less, more preferably 7 mm or less, and even more preferably 5 mm or less. The vibration period is preferably 10 Hz or more, more preferably 30 Hz or more, and even more preferably 50 Hz or more. The vibration dryer may be vertical or horizontal, and has a mechanism capable of passing cooling water, steam-controlled hot water, and steam through a jacket as temperature control means. As this temperature control means, an electric heater may be wound around the dryer, or a steam serpentine may be provided inside.

  In the case of using a fluid dryer, the fluid dryer is preferably one that allows the material to be dried to flow with hot air or cold air, and the gas flow rate is preferably 5 to 50 m / min, more preferably 15 to 30 m / min. . Moreover, a batch type or a continuous type may be sufficient.

  If the wet cake before drying has a solid content of 1% by weight or more, preferably 20% by weight or more, more preferably 40% by weight or more, the drying method of the present invention can be applied. When the solid content of the wet cake before drying is less than 1% by weight, the drying efficiency is poor. Therefore, the solid content may be increased by solid-liquid separation or preliminary drying. The wet cake used in the drying method of the present invention is preferably obtained by solid-liquid separation using a centrifuge.

  The solid content of the wet cake after drying is preferably 90% by weight or more, more preferably 95% by weight, and still more preferably 99% by weight or more.

The average particle diameter of the thermoplastic resin obtained by the drying method of the present invention is preferably 10 to 5000 μm, more preferably 100 to 1000 μm, still more preferably 300 to 700 μm. When the average particle size of the thermoplastic resin is smaller than 10 μm, handling properties such as entrainment of droplets when reduced in pressure and generation of dust are worsened. Moreover, when the average particle diameter of a thermoplastic resin is larger than 5000 micrometers, productivity will fall, such as the time concerning drying becoming long. The average particle size here is 3350 μm, 2000 μm, 1000 μm, 710 μm, 500 μm, 250 μm, 100 μm in order of the sieve opening after passing through the wet cake and measuring the weight of the wet cake remaining on each sieve. As the weighted average value of the sieve openings based on the weight fraction for each sieve opening, the particle diameter calculated from the following formula is evaluated as the average particle diameter. In addition, after supplying a wet cake to a sieve as conditions of a sieve, after applying a vibration and sieving for 15 minutes, the residual wet cake weight on a sieve is measured.
Average particle size (μm)
= [Sieving aperture x (weight of wet cake remaining on sieve / total amount of wet cake used for measurement)] For each sieve that passed 100 µm, the sieve opening is 50 µm.

  Although it does not restrict | limit especially as a thermoplastic resin contained in the wet cake dried by this invention, For example, the acrylic resin manufactured by solution polymerization, a styrene resin, an olefin resin, etc. are mentioned. Among them, an acrylic resin is preferable, and a carboxyl group-containing acrylic copolymer (A) composed of a copolymer containing an unsaturated carboxylic acid alkyl ester unit and an unsaturated carboxylic acid unit is particularly preferable. The carboxyl group-containing acrylic copolymer (A) is a polymerization step (I) for producing an organic solvent slurry containing the copolymer, and the slurry is subjected to solid-liquid separation, washed in water at a specific temperature, and again subjected to solid-liquid separation. It can be produced by washing step (II) to obtain particles of copolymer (A).

  The carboxyl group-containing acrylic copolymer (A) is not particularly limited as long as it is obtained by copolymerizing a carboxyl group-containing acrylic monomer. Any carboxyl group-containing acrylic monomer that can be copolymerized with the monomer can be used. Preferable carboxyl group-containing acrylic monomers include compounds represented by the following general formula (1), hydrolysates of maleic acid and maleic anhydride, and the like. In particular, acrylic acid and methacrylic acid are preferable from the viewpoint of excellent thermal stability, and methacrylic acid is more preferable. These can be used alone or in combination.

(However, R represents any one selected from hydrogen and an alkyl group having 1 to 5 carbon atoms)

  Examples of other acrylic monomers copolymerizable with the carboxyl group-containing acrylic monomers used include methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, dodecyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, benzyl methacrylate, lauryl methacrylate, dodecyl methacrylate, trifluoroethyl methacrylate And acrylic acid esters or methacrylic acid esters or their (fluoro) alkyl ester monomers. Among these, from the viewpoint of excellent optical characteristics and thermal stability, alkyl methacrylates and alkyl acrylates are preferable, methyl methacrylate and ethyl methacrylate are more preferable, and methyl methacrylate is particularly preferable. These may be used alone or as a mixture of two or more.

  If necessary, in addition to the acrylic monomer, other vinyl monomers that can be copolymerized, such as vinyl acetate, vinyl benzoate, styrene, α-methylstyrene, and acrylonitrile may be used. . Other unsaturated monomers may be used alone or as a mixture of two or more.

  The carboxyl group-containing acrylic copolymer (A) improves the pigment dispersibility of ordinary acrylic polymers, improves compatibility with polymers such as nylon and polycarbonate, and makes it possible to realize a functional polymer alloy. Furthermore, it functions as an effective functional group for imparting photosensitivity and developability to the acrylic polymer by a polymer reaction utilizing a carboxyl group. Further, the heat resistance can be improved and the refractive index can be adjusted by utilizing the intramolecular reaction of the acrylic polymer.

  The carboxyl group-containing acrylic monomer is copolymerized in such an amount that the acid value of the carboxyl group-containing acrylic copolymer (A) is preferably 5 to 300 mgKOH, more preferably 5 to 250 mgKOH. desirable.

  The polymerization step (I) in the method for producing a carboxyl group-containing acrylic copolymer (A) is an organic solvent that does not contain an aromatic group, and is a raw material of an unsaturated carboxylic acid alkyl ester monomer and an unsaturated carboxylic acid. A monomer mixture containing an acid monomer is dissolved, and the monomer mixture is copolymerized in an organic solvent (B) in which the solubility of the copolymer (A) is 1 g / 100 g or less. A slurry is obtained. Copolymerization can be carried out in the presence or absence of a polymerization initiator. In the polymerization step, the monomer mixture containing the carboxyl group-containing acrylic monomer as a raw material is dissolved, and the solubility of the carboxyl group-containing acrylic copolymer (A) is 1 g / 100 g or less in the organic solvent (B). Is carried out by a so-called “precipitation polymerization method” in which the carboxyl group-containing acrylic copolymer (A) is precipitated. In this case, the carboxyl group-containing acrylic copolymer (A) can be isolated by filtering and drying the slurry solution after polymerization. Here, the “solubility of the carboxyl group-containing acrylic copolymer (A)” means that after stirring for 24 hours at 23 ° C. with respect to 100 g of the organic solvent (B) of the carboxyl group-containing acrylic copolymer (A). This means the amount of dissolution.

  As the organic solvent (B) used in the polymerization step (I), it is necessary to enable the above-described precipitation polymerization method and not to contain an aromatic. Specific examples include one or more selected from aliphatic hydrocarbons, carboxylic acid esters, ketones, ethers, and alcohols. Among these, one or more selected from aliphatic hydrocarbons, carboxylic acid esters, and ketones are preferable. In particular, one or more selected from aliphatic hydrocarbons and carboxylic acid esters are preferred.

  Examples of the aliphatic hydrocarbon used as the organic solvent (B) include linear hydrocarbons having 5 to 10 carbon atoms, aliphatic hydrocarbons having side chains, and alicyclic hydrocarbons. Specific examples include n-pentane, n-hexane, cyclohexane, n-heptane, n-octane, n-nonane, n-decane and various isomers thereof.

  Examples of the carboxylic acid ester used as the organic solvent (B) include an ester composed of a saturated aliphatic carboxylic acid and a saturated alcohol. Specific examples of the saturated carboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, and the like. In addition, examples of the saturated alcohol include linear and branched alcohols having 1 to 10 carbon atoms. Preferred carboxylic acid esters include formic acid-n-propyl, isopropyl formate, formic acid-n-butyl, formic acid isobutyl, formic acid-n-pentyl, formic acid-n-hexyl, acetic acid-n-propyl, isopropyl acetate, acetic acid-n- Butyl, isobutyl acetate, acetic acid-n-pentyl, acetic acid-n-hexyl, acetic acid-n-heptyl, acetic acid-n-octyl, acetic acid-n-nonyl, methyl propionate, ethyl propionate, propionate-n-propyl, Isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, n-hexyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, n-butyl butyrate, Various different types such as isobutyl butyrate, n-pentyl butyrate, n-hexyl butyrate Mention may be made of the body.

  The ketone used as the organic solvent (B) is a ketone having 1 to 10 carbon atoms and comprising a linear and branched saturated aliphatic group. Specific examples thereof include methyl-n-butyl ketone and methyl isobutyl ketone. And ethyl isobutyl ketone.

  As the organic solvent (B), a mixture of aliphatic hydrocarbon and carboxylic acid ester is particularly preferable. In this case, the preferred mixing ratio of the aliphatic hydrocarbon and the carboxylic acid ester is not particularly limited, but is preferably in the range of 5/95 to 70/30 by weight, and more preferably in the range of 10/90 to 50/50. In particular, the range of 20/80 to 40/60 is preferable. When the mixing ratio is less than 5/95, the copolymer formed during the polymerization tends to stick to the reaction vessel. Moreover, when the mixing ratio is greater than 70/30, it tends to be difficult to precisely control the copolymer composition.

  In addition, when precipitation polymerization is performed in the polymerization step (I), if water is used in the polymerization reaction system, it may be difficult to precisely control the copolymer composition, and water should be kept within the controllable range of the copolymer composition. Most preferably, water is not positively added unless the component used in the polymerization reaction system such as an organic solvent contains a very small amount of water as an impurity.

  The polymerization temperature can be arbitrarily set, but is preferably a temperature not higher than the boiling point of the organic solvent to be used. Especially, it is preferable to superpose | polymerize at the polymerization temperature of 100 degrees C or less, and it is more preferable to superpose | polymerize at the polymerization temperature of 90 degrees C or less. The lower limit of the polymerization temperature is not particularly limited as long as the polymerization proceeds, but is usually 50 ° C. or higher, preferably 60 ° C. or higher from the viewpoint of productivity considering the polymerization rate. The polymerization time is not particularly limited as long as it is a time sufficient to obtain a necessary polymerization rate, but is preferably in the range of 60 to 360 minutes, and particularly preferably in the range of 90 to 240 minutes from the viewpoint of production efficiency.

  Moreover, it is preferable to control the dissolved oxygen concentration in the polymerization liquid to 5 ppm or less from the viewpoint of improving the thermal stability of the carboxyl group-containing acrylic copolymer (A). A more preferable range of dissolved oxygen concentration is 0.01 to 3 ppm, and further preferably 0.01 to 1 ppm. Here, the dissolved oxygen concentration in the present invention is a value obtained by measuring dissolved oxygen in the polymerization solution using a dissolved oxygen meter (for example, DO meter B-505 manufactured by Iijima Electronics Co., Ltd., which is a galvanic oxygen sensor). is there. For the method of reducing the dissolved oxygen concentration to 5 ppm or less, a method of passing an inert gas such as nitrogen, argon or helium into the polymerization vessel, a method of bubbling an inert gas directly into the polymerization solution, or an inert gas before starting the polymerization A method of performing pressure relief once or twice after filling the polymerization vessel, a method of degassing the closed polymerization vessel before charging the monomer mixture, and then filling with an inert gas, A method of passing an inert gas through the polymerization vessel can be exemplified.

  A preferred ratio of the monomer mixture used in the production of the carboxyl group-containing acrylic copolymer (A) is such that the monomer mixture is 100% by weight and the carboxyl group-containing acrylic monomer is 15 to 50% by weight. %, More preferably 20 to 45% by weight. When the copolymerization amount of the carboxyl group-containing acrylic monomer is less than 15% by weight, modification by copolymerization and development to a polymer reaction or the like may be difficult. When the copolymerization amount of the carboxyl group-containing acrylic monomer exceeds 50% by weight, the control of the copolymer composition and the control of the molecular weight distribution tend to deviate from those desired. In addition, when a polymer reaction is performed and it is considered to be used as a photosensitive resin, the affinity or hydrogen bonding property with the pigment becomes too strong, and pigment seeding (aggregation) may occur easily. is there. In addition, the sensitivity difference between the exposed and unexposed areas with respect to the developer tends to be small, and a fine and clear development pattern tends to be difficult to form.

  In addition, these monomer mixtures may be charged in an organic solvent in a batch and copolymerized, or may be copolymerized while being added in portions or sequentially. More preferably, for the purpose of reducing the composition distribution of the monomer units constituting the carboxyl group-containing acrylic copolymer (A) to be formed, the weight composition ratio in the monomer mixture is arbitrarily set, and divided additions are made. Or the method of adding sequentially is mentioned.

  Copolymerization can be carried out in the presence or absence of a polymerization initiator, but is preferably carried out in the presence of a polymerization initiator. As the polymerization initiator, it is preferable to use a radical polymerization initiator, and as the radical polymerization initiator, any commonly used initiator can be used, among which 2,2′-azobisisobutyronitrile, Azo such as 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis-2-methylbutyronitrile Compounds, lauroyl peroxide, benzoyl peroxide, t-butylperoxyneodecanate, t-butylperoxypivalate, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, dicumyl An organic peroxide such as peroxide can be preferably used.

  The amount of the polymerization initiator used is preferably 0.001 to 2.0 parts by weight, particularly 0.01 to 1.0 part by weight, based on 100 parts by weight of the monomer mixture used for copolymerization. .

  In the present invention, a chain transfer agent such as alkyl mercaptan, carbon tetrachloride, carbon tetrabromide, dimethylacetamide, dimethylformamide, and triethylamine can be added for the purpose of controlling the molecular weight.

  In this production method, since the carboxyl group-containing acrylic copolymer (A) is easily precipitated and precipitated, it is necessary to consider the balance of solubility in the carboxyl group-containing acrylic copolymer (A) and the organic solvent (B). is there. From this point of view, it is preferable to design polymerization conditions such as copolymer species, copolymer composition, and reaction solvent in consideration of solubility parameters of each component.

  The solubility parameter δp of the carboxyl group-containing acrylic copolymer (A) is preferably in the range of 7.0 to 12.0, and more preferably 7.5 to 10.5. When δp is less than 7.0, the gasoline resistance and oil resistance are inferior, and there are cases where many practical limitations are imposed. When δp exceeds 12.0, the cohesive force of the polymer becomes too strong, and when processed into a molded product or dissolved and used, the viscosity becomes too high and the handleability tends to deteriorate.

  In the present invention, it is necessary to consider the balance of solubility in the carboxyl group-containing acrylic copolymer (A) and the organic solvent (B) in order to easily precipitate and deposit the carboxyl group-containing acrylic copolymer (A). . From this point of view, it is preferable to design polymerization conditions such as copolymer species, copolymer composition, and reaction solvent in consideration of solubility parameters of each component.

In the present invention, the solubility parameter δ (MPa ^1/2 ) is defined as “POLYMER HANDBOOK FOURTH EDITION”; BRANDRUP, E.I. H. IMMERGUT, and E.I. A. By GRULKE, p. Data described in TABLE VII of VII / 675-714, WILEY INTERSCIENCE (1999) were employed. In addition, about the organic solvent which is not described in TABLE7, the value computed by the method of Small described in the said literature was employ | adopted. The Small method is described in p. Adopting the cohesive energy constant F (MPa ^1/2 · cm ³ · / mol) of specific atoms and atomic groups according to the Small method given in TABLE 2 of VII / 675-714, the density is s (g / cm ³ ) The basic molecular weight is M (g / mol), and the solubility parameter δ (MPa ^1/2 ) is calculated by δ = (sΣF) / M. It should be noted that 1 (MPa ^1/2 ) = 2.046 (cal / cm ³ ) ^1/2 .

Further, the solubility parameter δ in the case of a mixture composed of two or more kinds of organic solvents is calculated by the following formula from the molar fraction Xi (%) of each solvent component in the mixed organic solvent and the solubility parameter δi of each solvent component. did.
δ = Σ (δi × Xi / 100)

Further, the solubility parameter δ ((cal / cm ³ ) ^1/2 ) of the copolymer is the same as that described in p. It calculated from the value of TABLE3 of VII / 675-714.

  In the present invention, when copolymerizing the carboxyl group-containing acrylic monomer, the absolute value of the difference between the solubility parameter of the carboxyl group-containing acrylic copolymer (A) and the solubility parameter of the organic solvent (B) (ΔSP ) Is preferably selected so that the copolymer composition and solvent type are 1.0 or more. The polymerization is more preferably 1.1 or more, and in particular, the polymerization is carried out under the condition of 1.2 or more so that there is no adhesion to the wall of the polymerization tank during the polymerization, and the produced copolymer can be easily taken out as a powder. Is preferable. In addition, by designing the polymerization conditions so that the above ΔSP is in the range of 1.0 to 3.0, more preferably in the range of 1.5 to 2.9, the charged monomer mixture composition and generation before the polymerization start It is more desirable in terms of precise control that does not cause a large shift in the copolymer composition of the copolymer to be produced, and molecular weight control with a narrow molecular weight distribution and high uniformity.

  In this production method, an organic solvent slurry (hereinafter referred to as copolymer (A) slurry) containing a carboxyl group-containing acrylic copolymer (A) polymerized with a specific polymerization solvent obtained in the polymerization step (I). Must be purified in the following washing step (II). That is, after solid-liquid separation of the copolymer (A) slurry obtained in the polymerization step (I) (hereinafter referred to as first filtration), water is added to the obtained copolymer (A), In this washing step, washing is performed at a temperature of 50 to 120 ° C., and solid-liquid separation (hereinafter referred to as second filtration) is performed again from the washing solution at 50 to 120 ° C. to obtain a copolymer (A). By passing through such washing step (II), particles of copolymer (A) having few volatile components and excellent handling properties can be obtained, and further, copolymer (A) obtained through second filtration ) Exhibits the effect of greatly improving the thermal stability and colorless transparency.

  The method for solid-liquid separation of the copolymer (A) slurry in the first filtration is not particularly limited, and a common centrifuge, pressure filter, suction filter, belt filter, or the like is preferably used. A polymer cake can be obtained. The volatile content in the cake of the copolymer (A) after solid-liquid separation is not particularly limited, and is usually 50 to 90% by weight.

  Next, water is added to the cake of the copolymer (A) obtained by separation and fractionation by the first filtration, and the copolymer (A) is washed by heating with stirring. Aggregate. The amount of water added at the time of washing is 200 to 2,000 parts by weight, preferably 200 to 1,000 parts by weight, most preferably 200 to 600 parts with respect to 100 parts by weight of the cake obtained by the first filtration. Parts by weight. When the amount of water added is 200 parts by weight or less, not only a sufficient cleaning effect cannot be obtained, but also the agglomeration of particles becomes insufficient, and the handling property is lowered, which is not preferable. If the amount of water added exceeds 2,000 parts by weight, the wastewater treatment load increases, which is not preferable.

By setting the ratio of the copolymer cake and water obtained by the first filtration within the above range, the concentration of the copolymer (A) in the cleaning liquid is 0.1 to 50% by weight, preferably 1 to 30% by weight. More preferably, it can be 1 to 20% by weight. Here, the concentration of the copolymer (A) in the cleaning liquid is calculated as follows.
Concentration (% by weight) of copolymer (A) in the cleaning liquid
= 100 × (1-α / 100) × (copolymer cake amount (parts by weight)) / (copolymer cake amount (parts by weight) + water addition amount (parts by weight))
In the above formula, α represents the volatile content (% by weight) of the copolymer cake.

The volatile content (% by weight) in the copolymer cake is the weight loss rate (weight) calculated by the following formula from the weight change when the cake is heated at 80 ° C. for 12 hours in a vacuum dryer. %).
Volatile content (% by weight) in copolymer cake
= Weight reduction rate (wt%)
= [(Weight before heat treatment−weight after heat treatment) / weight before heat treatment] × 100

  Moreover, in the washing | cleaning process (II), you may add the solvent which does not melt | dissolve a copolymer (A) in the range which the density | concentration of a copolymer (A) satisfy | fills the above at the time of washing | cleaning.

  In the washing step (II), the washing temperature and the subsequent second filtration temperature are 50 to 120 ° C., preferably 60 to 100 ° C., more preferably 60 to 90 ° C. When the washing temperature and the second filtration temperature are less than 50 ° C., the washing effect is not sufficient, and the thermal stability of the resulting copolymer (A) tends to decrease, which is not preferable. Moreover, since aggregation of particle | grains is inadequate, the copolymer (A) obtained becomes a fine powder form and tends to be inferior to handling property. Moreover, when exceeding 120 degreeC, since copolymer particle | grains will coalesce and it will become a block shape, it will become difficult to take out as particle | grains.

  The apparatus for performing the above washing operation is not particularly limited as long as the washing temperature can be controlled within the above range, and an autoclave or the like equipped with a normal stirrer can be used. It is also possible to preheat the copolymer (A) slurry and / or the water added thereto during washing.

  The method of solid-liquid separation (second filtration) of the water slurry obtained by the above washing operation is not particularly limited as long as it can be filtered at the above temperature, and is a normal centrifuge, pressure filtration. A filter, a suction filter, a belt filter, or the like can be preferably used. By carrying out the washing method of the present invention, the volatile content of the copolymer after the second filtration can be made 10 to 80% by weight, preferably 20 to 50% by weight, and the load of the subsequent drying step Can be reduced.

  The carboxyl group-containing acrylic copolymer (A) obtained by this production method has a weight average molecular weight (hereinafter also referred to as Mw) in the range of 2,000 to 1,000,000 in the production method of the preferred embodiment. In a more preferred embodiment, it is possible to obtain a product in the range of 5,000 to 500,000. When Mw is less than 2,000, the carboxyl group-containing acrylic copolymer (A) may not be precipitated or precipitated as a dispersoid in the organic solvent (B) and may not meet the purpose of the present invention. . In addition, the polymer is brittle and the mechanical properties tend to be poor. When Mw exceeds 1,000,000, high-molecular weight substances that are not sufficiently melted or dissolved in melt-molded or solution-coated products tend to remain as foreign matters, and fisheye and repellency defects are likely to occur. Tend to be.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Each measurement and evaluation was performed by the following method.

(1) Solid content in wet cake The weight change before and after the heat treatment was measured for each wet cake before and after drying with a ket moisture meter, and the solid content was evaluated from the weight reduction rate calculated from the following equation.
Solid content in wet cake (wt%)
= 100-weight reduction rate (wt%)
= 100 − [(weight before heat treatment−weight after heat treatment) / weight before heat treatment] × 100

(2) Average particle diameter of wet cake after drying 3350 μm, 2000 μm, 1000 μm, 710 μm, 500 μm, 250 μm, 100 μm Opening the wet cake through the sieve in the order of opening, and measuring the weight of the wet cake remaining on each sieve The particle diameter calculated from the following formula was evaluated as the average particle diameter. In addition, as a condition of the sieve, the wet cake was put into the sieve, and the weight of the wet cake remaining on the sieve was measured after being shaken for 15 minutes.
Average particle size (μm)
= (The total of each sieve of sieve opening x (weight of wet cake remaining on the sieve / total amount of wet cake used for measurement))
However, a particle diameter of 50 μm is used for those having passed 100 μm.

(3) Mass of mass (wt%)
After drying, the weight of the wet cake that did not pass through the sieve was measured through a vibrating sieve having a mesh opening size of 7 mm, and the weight% calculated from the following formula was evaluated as the mass.
Mass (wt%)
= (Weight of wet cake that did not pass through sieve / total amount of wet cake after drying) x 100

The production of the wet cake used in the examples was carried out by the following method.
In a stainless steel autoclave having a capacity of 20000 liters and equipped with a baffle and a fiddle-type stirring blade, methacrylic acid; 25 parts by weight, methyl methacrylate; 75 parts by weight, n-heptane; 900 parts by weight, laurolyl peroxide; A mixed substance containing 8 parts by weight was supplied, and the system was bubbled with nitrogen gas of 10 L / min for 15 minutes while stirring at 250 rpm. Next, nitrogen gas was flowed at a flow rate of 5 L / min, and the reaction system was heated to 80 ° C. while stirring. When the internal temperature reaches 80 ° C., the polymerization is started. The internal temperature is maintained at 80 ° C. for 90 minutes, and after the temperature is raised to 95 ° C., the polymerization is terminated for 90 minutes, and the copolymer slurry (a-1 )

  The polymerization was a heterogeneous system in which the copolymer was dispersed as a dispersoid in the form of a slurry from the initial stage of polymerization, and the polymerization proceeded well without any adhesion to the wall of the polymerization tank. The polymerization rate was 75%.

  In order to analyze the properties of the copolymer, a small amount of the resulting slurry was added to the qualitative filter paper No. The solution was suction filtered using No. 1 and dried at 80 ° C. for 12 hours to obtain a powdery copolymer (a′-1). The obtained copolymer (a′-1) was observed at a magnification of 10,000 using a scanning electron microscope (hereinafter also referred to as “SEM”), and the primary particle diameter was analyzed (image analysis software used: Scion Corporation, image analysis). As a result of calculation by the software “Scion Image”, the number average particle size was 2.0 μm. Moreover, Mw by GPC measurement was 150,000, and molecular weight distribution (Mw / Mn) was 4.49. The copolymer composition of the copolymer (a′-1) was methyl methacrylate unit (MMA) / methacrylic acid unit (MAA) (weight ratio) = 72/28. The absolute value ΔSP of the difference in solubility parameter between the copolymer (a′-1) (δp = 10.25) and the organic solvent n-heptane was 2.85.

  In order to analyze the properties of the copolymer, the copolymer slurry (a-1) was subjected to solid-liquid separation at 25 ° C. with a pressure filter (manufactured by Mitsubishi Chemical Corporation) to obtain a copolymer cake. The obtained cake was dried at 80 ° C. for 12 hours in a vacuum dryer, and the volatile content was determined to be 78% by weight. Subsequently, the obtained cake was supplied to a stainless steel washing tank equipped with a baffle and a foudra-type stirring blade, 400 parts of ion exchange water was added to 100 parts of the cake, and 25 ° C. and a rotation speed of 250 rpm. Agitation was started. While continuously stirring this mixture at 250 rpm, the temperature was raised to 80 ° C. over 60 minutes, and a washing operation was performed for 60 minutes from the time when the internal temperature reached 80 ° C. Subsequently, while maintaining the obtained slurry at 80 ° C., it was transferred to a pressure filter, subjected to solid-liquid separation at 80 ° C. (second filtration), and further dried at 80 ° C. for 12 hours. A copolymer (A-1) was obtained.

  The obtained copolymer (A-1) had a volatile content of 23% by weight, and was observed with a SEM at 150 times, and the number average particle size calculated by image analysis of the primary particle size was 520 μm. Met. Moreover, Mw by GPC measurement was 120,000, and molecular weight distribution (Mw / Mn) was 3.14. The copolymer composition of the copolymer (A-1) was MMA / MAA (weight ratio) = 72/28, which was the same as that before washing.

  The above-mentioned copolymer slurry (a-1) was subjected to solid-liquid separation (first filtration) at 25 ° C. with a pressure filter (manufactured by Mitsubishi Chemical Corporation) to obtain a copolymer cake. This copolymer cake was used as a wet cake before drying. When the weight change of this wet cake was measured with a kett moisture meter, the solid content was 62 wt%.

Example 1
200 kg of wet cake is supplied to a horizontal vibratory dryer equipped with a baffle with a capacity of 5000 liters while vibrating, the inside of the system is reduced from normal pressure to 99 kPa, hot water is passed through the jacket, and the jacket temperature is kept at 50 ° C. for 20 minutes. It was. Next, the warm water of the jacket was stopped, the inside of the system was returned to normal pressure, and when the jacket temperature was cooled to 5 ° C. with respect to the heating temperature of 50 ° C., an additional 200 kg of wet cake was supplied. After the supply, the system was again depressurized from normal pressure to 99 kPa, warm water was passed through the jacket, and the jacket temperature was maintained at 50 ° C. for 20 minutes. After the above operation was repeated nine times, the temperature was raised stepwise from normal pressure to 99 kPa in a stepwise manner to 120 ° C. When the effluent became 1 kg / hour or less, the drying was completed, and a wet cake was obtained after drying. It was.

  The obtained wet cake after drying was passed through a vibration sieve having a mesh opening size of 7 mm, and the mass was calculated to be 1 wt%. When the change in weight of the wet cake was measured with a kett moisture meter after drying, the solid content was 99 wt%. In addition, after drying, the wet cake was passed through sieves in the order of 3350 μm, 2000 μm, 1000 μm, 710 μm, 500 μm, 250 μm, and 100 μm openings, and the weight of the wet cake remaining on each sieve was measured. It was.

(Example 2)
When the wet cake was additionally charged, a wet cake after drying was obtained by the same drying method as in Example 1 except that the cooling temperature of the jacket temperature was changed to 1 ° C.

  The obtained wet cake after drying was passed through a vibration sieve having a mesh opening size of 7 mm, and the mass was calculated to be 3 wt%. When the weight change of the wet cake was measured with a kett moisture meter after drying, the solid content was 98 wt%. After drying, the wet cake was passed through a sieve in the order of 3350 μm, 2000 μm, 1000 μm, 710 μm, 500 μm, 250 μm, and 100 μm, and the weight of the wet cake remaining on each sieve was measured. The average particle size was 960 μm.

(Example 3)
A wet cake after drying was obtained by the same drying method as in Example 1 except that the pressure after the additional supply of the wet cake was changed from normal pressure to 70 kPa.

  The obtained wet cake after drying was passed through a vibration sieve having a mesh opening size of 7 mm, and the mass was calculated to be 5 wt%. When the weight change of the wet cake was measured with a kett moisture meter after drying, the solid content was 96 wt%. 3350 μm, 2000 μm, 1000 μm, 710 μm, 500 μm, 250 μm, 100 μm After drying, the wet cake was passed through a sieve and the weight of the wet cake remaining on each sieve was measured. The average particle size was 750 μm.

(Comparative Example 1)
When the pressure was returned to normal pressure, a wet cake was obtained after drying by the same drying method as in Example 1 except that the warm water in the jacket was kept flowing.

  The obtained wet cake after drying was passed through a vibration sieve having a mesh opening size of 7 mm, and the mass was calculated to be 10 wt%. When the weight change of the wet cake was measured with a kett moisture meter after drying, the solid content was 97 wt%. After drying, the wet cake was passed through a sieve in the order of 3350 μm, 2000 μm, 1000 μm, 710 μm, 500 μm, 250 μm, and 100 μm, and the weight of the wet cake remaining on each sieve was measured. The average particle size was 1200 μm.

(Comparative Example 2)
A wet cake was obtained after drying by the same drying method as in Example 1 except that the number of times of wet cake charging was set to 1 and the reduced pressure heating temperature was set to 120 ° C.

  The obtained wet cake after drying was passed through a vibrating sieve having a mesh opening size of 7 mm, and the mass was calculated to be 15 wt%. When the change in weight of the wet cake was measured with a kett moisture meter after drying, the solid content was 99 wt%. 3350 μm, 2000 μm, 1000 μm, 710 μm, 500 μm, 250 μm, 100 μm After drying, the wet cake was passed through a sieve and the weight of the wet cake remaining on each sieve was measured. The average particle size was 1560 μm.

  The results of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1.

Claims (7)

  Part of a wet cake containing water, organic solvent, and thermoplastic resin is placed inside the dryer and heated under reduced pressure. After the inside of the dryer is cooled to normal pressure, the rest or the remaining part of the wet cake is dried. A method for drying a wet cake, comprising a supply step of additionally charging the inside of the machine and heating under reduced pressure.   The method for drying a wet cake according to claim 1, wherein cooling in the dryer in the supplying step is performed at a temperature lower by 0.1 to 20 ° C than during the heating under reduced pressure.   The method for drying a wet cake according to claim 1 or 2, wherein the temperature inside the dryer in the supplying step is reduced to 30 to 100 ° C and the pressure is reduced to 80 to 99 kPa from a normal pressure state.   4. The method for drying a wet cake according to claim 1, wherein the dryer is a vibration type or a fluid type.   5. The thermoplastic resin is a carboxyl group-containing acrylic copolymer composed of a copolymer containing an unsaturated carboxylic acid alkyl ester unit and an unsaturated carboxylic acid unit. The drying method of the described wet cake.   6. The method for drying a wet cake according to claim 1, wherein the thermoplastic resin has an average particle size of 10 to 5000 [mu] m.   The method for drying a wet cake according to claim 1, 2, 3, 4, 5 or 6, wherein the wet cake is a cake obtained by solid-liquid separation of a slurry with a centrifuge.