JP2744374B2 - Method for producing coagulated acrylic polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a coagulated acrylic polymer.

[0002]

2. Description of the Related Art Acrylic polymers are produced by methods such as bulk polymerization, suspension polymerization, solution polymerization, and emulsion polymerization.

In a method for producing a polymer using an emulsion polymerization method, a step of removing the polymer from a polymer latex is required. This method includes a method of adding an inorganic salt such as aluminum chloride and magnesium sulfate, and a method of adding sulfuric acid. , An acid drying method, a spray drying method and the like. However, the above-mentioned method has a problem that the obtained polymer is in the form of a fine powder and is difficult to handle, which causes a decrease in productivity and a decrease in molding workability. On the other hand, those molded using these polymers also had problems such as inferior optical properties due to heating and coloring, easy whitening when immersed in hot water, and poor hot water resistance.

As a method of improving coloring, -OSO ₃
M, -COOM, -SO ₃ M (where M is K or Na)
Polymerization using an emulsifier having a group represented by formula (I), and contacting the obtained latex with an aqueous solution of magnesium sulfate to remove the polymer (JP-A-61-108629).
₃ M _2, -PO ₂ M (where M is an alkali metal or alkaline earth metal) Polymerization was conducted by using an emulsifier having a group represented by the obtained latex is contacted with an aqueous solution of magnesium sulfate polymer Removal method (JP-A-63-22)
No. 7606) has been proposed. Although some improvement effect is recognized, it is not satisfactory, and the separated polymer has a disadvantage that it is difficult to handle in a fine powder form, and the hot water resistance is not improved.

[0005]

That is, an object of the present invention is to provide a method for producing an acrylic polymer coagulated product using emulsion polymerization, which comprises the steps of producing an acrylic polymer coagulated product excellent in optical properties, hot water resistance, and handleability. It is an object of the present invention to provide a manufacturing method.

[0006]

Means for Solving the Problems The present inventors have made intensive studies in view of such a situation and found that a method of freezing, thawing, and then dehydrating an acrylic polymer latex obtained by emulsion polymerization was used. The inventors have found that the above problems can be solved by removing the polymer from the latex, and have completed the present invention.

That is, the present invention provides a methacrylic acid ester 50 to 100 wt%, this is copolymerizable with the monomer 0
A process for producing an acrylic polymer coagulate, wherein an acrylic polymer is removed from the latex by emulsion-polymerizing a monomer mixture consisting of 50 to 50% by weight, freezing, thawing and dehydrating the obtained latex. About the method.

The methacrylate used in the present invention includes methyl methacrylate, ethyl methacrylate,
Examples thereof include butyl methacrylate, benzyl methacrylate, and cyclohexyl methacrylate, which are used alone or in combination. Preferred is methyl methacrylate.

Other copolymerizable monomers include acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate and benzyl acrylate, styrene and vinyl. Aromatic vinyl compounds such as toluene and α-methylstyrene, N-cyclohexylmaleimide, N-
N-substituted maleimide compounds such as o-chlorophenylmaleimide and N-tert-butylmaleimide; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; Allyl acid, diallyl maleate, diallyl phthalate, triallyl trimellitate, diallyl fumarate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, divinylbenzene, 1,3-butylene glycol di (meth) acrylate And polyfunctional monomers such as 1,3-butadiene and isoprene, which may be used alone or in combination.

The type and amount of the emulsifier used in the emulsion polymerization of the present invention are selected depending on the stability of the polymerization system, the intended particle size, etc., but anionic surfactants, cationic surfactants, nonionic surfactants Known emulsifiers such as emulsifiers can be used alone or in combination. Particularly, an anionic surfactant is preferably used. Examples of the anionic surfactant include carboxylate salts such as sodium stearate, sodium myristate and sodium N-lauroyl sarcosinate, sulfonates such as sodium dioctylsulfosuccinate and sodium dodecylbenzenesulfonate, and sulfuric acids such as sodium lauryl sulfate. Ester salt, mono-n-
Phosphate salts such as sodium butylphenylpentaoxyethylene phosphate are exemplified.

The polymerization initiator used in the emulsion polymerization is not particularly limited, but includes inorganic peroxides such as potassium persulfate and ammonium persulfate, hydrogen peroxide-ferrous salt system, potassium persulfate-sodium acid sulfite system. Water-soluble redox initiators such as ammonium persulfate-sodium acid sulfite, cumene hydroperoxide-sodium formaldehyde sulfoxylate, tert-butyl hydroperoxide-sodium formaldehyde sulfoxylate, etc. A water-soluble or oil-soluble redox initiator is used.

The chain transfer agent optionally used includes n-dodecyl mercaptan, n-lauryl mercaptan, tert-dodecyl mercaptan, sec-butyl mercaptan and the like.

In the emulsion polymerization, monomers, emulsifiers, initiators, chain transfer agents and the like may be added by any known methods such as a batch addition method, a division addition method and a continuous addition method.

The most characteristic feature of the present invention is that a freezing and thawing method is used as a method for separating an acrylic polymer. However, those separated by a spray drying method or an acid or salt addition method cannot be used in the present invention because handling properties such as drying are deteriorated and stability during extrusion molding is deteriorated.

As the freezing method of the present invention, a known air freezing method, contact freezing method, immersion freezing method, spray freezing method or the like is used. In this case, it is necessary to freeze at a speed of 4 cm / hr or less.
It is important . By adopting these conditions, handleability and extrusion stability in the subsequent steps are further improved. When the temperature of the polymer latex becomes 0 ° C, the freezing starts, when the temperature of the polymer latex reaches -5 ° C, the freezing ends, and the time during that time is defined as the freezing time. The frozen thickness is defined as the freezing speed. Thaw after freezing is 40 ° C ~
It is more preferable to carry out at 100 ° C. and to wash the obtained polymer with water at 0 ° C. to 100 ° C. or warm water.

In the present invention, the freezing and thawing steps for removing the polymer from the latex are thought to proceed by the following mechanism. When the latex is cooled below the freezing point of water, ice crystals are generated in the aqueous phase, and the latex grows while excluding the spherical polymer particles and the water-soluble substance dissolved in the aqueous phase. The spherical polymer particles are trapped between the ice crystals, and the water-soluble substances are also concentrated there and precipitate when the concentration reaches a saturation value.
As the ice crystals grow, the spherical polymer particles are gradually pressed. As the temperature further decreases, the concentrated aqueous solution of the water-soluble substance freezes. As the freezing proceeds, the bare spherical polymer particles are compressed and firmly pressed. When the latex that has undergone this step is melted, the compression of the spherical polymer particles is not destroyed and separates from the aqueous phase as a coagulated product.

It is necessary to add a dye to the ordinary acrylic polymer coagulated product obtained by emulsion polymerization to make the color complementary or to add a stabilizer to suppress yellowing by heating.
According to the invention, the addition of such additives is unnecessary. In addition, handleability and hot water resistance are also improved.

In the production method of the present invention, a lubricant, an ultraviolet absorber, a light stabilizer, a heat stabilizer, an antioxidant, a plasticizer, a dye / pigment, an antistatic agent, a flame retardant may be used as needed at any stage of the process. Etc. can be added.

The acrylic polymer coagulate obtained by the production method of the present invention is used alone or in a blend with another polymer.

[0020]

The present invention will be described in more detail with reference to the following examples. The measurement of various characteristics shown in the examples was performed according to the following methods. (1) Evaluation of fusing and blocking when the coagulated acrylic polymer was dried; drying of the acrylic polymer at 80 ° C. for 10 hours in a hot air dryer of a tray type to cause fusing and blocking. The following table shows the results. X: Fusing and blocking occurred. O: No fusion or blocking occurred. (2) Evaluation of extrusion stability: The extrusion stability when the dried acrylic polymer coagulated material was melt-kneaded and pelletized using a 40φ extruder was examined, and is shown as follows. Stable: Stable extrusion with little surging. Unstable: Surging easily occurred and extrusion could not be performed stably. (3) Total light transmittance; ASTM-D1003 (3 mm plate thickness) (4) Yellow index; ASTM-D1925 (3 mm plate thickness) (5) Evaluation of hot water resistance;
It was immersed in hot water of 2 ° C. for 2 hours, and the haze value was measured by ASTM-D1003 to measure the amount of change in haze value (△ haze).

The abbreviations used in the examples are shown below. Methyl methacrylate (MMA), methyl acrylate (MA), n-octyl mercaptan (n-OM), sodium stearate (SS), sodium lauroyl sarcosinate (LSS).

Parts represent parts by weight and% represents% by weight. (Example 1) Ion-exchanged water 2 was placed in a reaction vessel equipped with a reflux condenser.
50 parts, SS2.5 parts, LSS0.2 parts, MMA47
Parts, 3 parts of MA, and 0.15 part of n-OM. Then, 1.0 part of a 10% aqueous potassium persulfate solution was added,
And kept for 90 minutes.

Then, a 10% aqueous potassium persulfate solution (1.0%) was added.
Parts, MMA 47 parts, MA 3 parts, n-OM
A monomer mixture consisting of 0.15 parts was continuously added over 30 minutes, and after the completion of the addition, the mixture was maintained for 60 minutes to obtain a polymer latex.

The obtained latex was placed in a stainless steel container so as to have a height of 6 cm, and was frozen at −20 ° C. in a freezer. Temperature was measured by placing a thermocouple in latex
Result, 0 ° C. to reach by either et - to pass through the 5 ° C., 6 hours
The required. That is, the freezing speed was 1 cm / hr. After the slowest temperature drop passed -5 ° C, it was cooled for another 2 hours to remove the frozen latex.

After the frozen latex was thawed at 70 ° C., the polymer was separated by filtration. Further, washing and dehydration were repeated three times with hot water at 70 ° C., followed by drying at 80 ° C. for 10 hours. Fusing and blocking did not occur, and a smooth coagulated product was obtained.

The dried coagulated product was melt-kneaded at a cylinder temperature of 250 ° C. using a 40φ extruder to obtain pellets. At this time, surging hardly occurred, and the extrusion was stable. Using these pellets, cylinder temperature 250
Injection molding was performed at 50 ° C. and a mold temperature of 50 ° C. to obtain a 50 × 50 × 3 mm flat plate based on the ASTM standard. Table 1 shows the results of evaluating various characteristics using this test piece. (Examples 2 to 3 ) Table 1 shows the results of the same operations and evaluations as in Example 1 except that the final latex obtained in Example 1 was frozen under different freezing conditions. (Comparative Example 1) The final latex obtained in Example 1 was subjected to salting out coagulation at 70 ° C using twice the amount of a 1% aqueous aluminum chloride solution.
Then, washing and dehydration were repeated three times with 70 ° C warm water and then 80 ° C.
Dried for -10 hours. Since the coagulated material had been fused and blocked, the conditions were changed to 60 ° C. for 15 hours and dried.

The obtained dried coagulated material was melt-kneaded at a cylinder temperature of 250 ° C. using a 40φ extruder to obtain pellets. At this time, surging was apt to occur, and extrusion could not be performed stably. Using these pellets, cylinder temperature 250
Injection molding was performed at 50 ° C. and a mold temperature of 50 ° C. to obtain a 50 × 50 × 3 mm flat plate based on the ASTM standard. Table 1 shows the results of evaluating various characteristics using this test piece. (Comparative Examples 2 to 4) Table 1 shows the results of operations and evaluations performed in the same manner as in Comparative Example 1 except that a 3% aqueous sodium chloride solution, a 2% aqueous magnesium sulfate solution, and a 1% aqueous sulfuric acid solution were used. (Comparative Example 5) The final latex obtained in Example 1 was sprayed into a spray dryer having an inflow hot air temperature of 170 ° C to dry and separate the polymer. The obtained coagulated product was in the form of fine powder.

The obtained dried coagulated material was melt-kneaded at a cylinder temperature of 250 ° C. using a 40φ extruder to obtain pellets. At this time, surging was apt to occur, and extrusion could not be performed stably. Using these pellets, cylinder temperature 250
Injection molding was performed at 50 ° C. and a mold temperature of 50 ° C. to obtain a 50 × 50 × 3 mm flat plate based on the ASTM standard. Table 1 shows the results of evaluating various characteristics using this test piece.

As is clear from Table 1, the acrylic polymer coagulated product obtained by the production method of the present invention has good handleability and extrusion stability, and the molded product obtained therefrom has optical properties and hot water resistance. It can be seen that this is remarkably excellent.

[0030]

[Table 1]

[0031]

According to the method for producing the coagulated acrylic polymer of the present invention, the handleability is remarkably improved in the drying step, and the extrusion stability is also improved. It has the effect. In addition, a molded product having remarkably excellent optical properties such as low thermal coloring and excellent hot water resistance can be obtained, so that the range of use is expanded.

Continuation of front page (56) References JP-A-47-22489 (JP, A) JP-A-4-356502 (JP, A)

Claims (1)

(57) [Claims] 1. A methacrylate unit of 50 to 100.
% By weight, and a monomer mixture composed of 0 to 50% by weight of other monomer units copolymerizable therewith is emulsion-polymerized, and the obtained latex is frozen, melted and dehydrated at a speed of 4 cm / hr or less. A method for producing an acrylic polymer coagulate, comprising removing an acrylic polymer from a latex.