JP3013951B2 - Acrylic resin manufacturing method - 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 an acrylic resin useful as a plastic material having excellent transparency.

[0002]

2. Description of the Related Art Acrylic resin is a plastic excellent in transparency, light resistance, mechanical strength, moldability and workability, and is used for signboards, lighting equipment, vehicle parts and various decorative articles. Have been. In recent years, lenses, optical disks,
Applications in the optical field such as optical fibers are expanding, and there is a need for a method for producing a high-quality acrylic resin having a narrow molecular weight distribution and excellent optical properties.

Conventionally, suspension polymerization, bulk polymerization, solution polymerization, and the like have been known as methods for industrially producing an acrylic resin used for a molding material. The suspension polymerization method can produce an acrylic resin having a relatively narrow molecular weight distribution because the polymerization reaction is easily controlled, but the dispersant or dispersion stabilizer used in the production remains in the resin. However, there are drawbacks such as a decrease in optical properties, a batch production is mainly performed, the production process is complicated, productivity is low, and a large amount of wastewater treatment is required.

[0004] The bulk polymerization method is advantageous over the suspension polymerization method in that it does not use a dispersant or a dispersion stabilizer, does not require a large amount of wastewater treatment, and has relatively easy continuity with good productivity. There is a point. However, when the monomer conversion rate (hereinafter, referred to as the conversion rate) increases, the phenomenon of acceleration of the polymerization rate, which is generally known as the gel effect, occurs, and the viscosity and the temperature rise rapidly during the polymerization reaction, so that the heat of polymerization is removed. It is difficult to control the polymerization reaction on an industrial scale, it is difficult to increase the conversion rate, the molecular weight distribution of the acrylic resin produced is wide, and impurities such as oligomers and gelled products are produced as by-products. Disadvantages, such as poor optical properties.

In order to improve these disadvantages of the bulk polymerization method, Japanese Patent Application Laid-Open No. 49-37993 discloses a conversion rate of 50%.
After reaching ~ 80%, a method has been proposed in which a viscosity reducing agent such as toluene and a radical polymerization initiator are additionally added to increase the conversion to 85% or more. However, it is usually very difficult to control the polymerization reaction until the conversion reaches 50 to 80% by the bulk polymerization method, and the amount of the radical polymerization initiator and the polymerization temperature are limited to specific ranges. The range of manufacturable conditions is very narrow and it is extremely difficult to implement on an industrial scale. In addition, the addition of a viscosity reducing agent or the addition of a radical polymerization initiator changes the polymerization conditions such as the polymerization temperature, and has a disadvantage that the molecular weight distribution of the obtained acrylic resin is widened and the optical properties are lowered.

JP-A-63-77909 discloses that a monomer mixture comprising methyl methacrylate, vinyl aromatic, maleic anhydride and alkyl acrylate is polymerized to a conversion of 60% in the presence or absence of a solvent. After that, about 15 to 33% by weight of a solvent is added and the conversion is 80%.
% Has been proposed. However, it is usually difficult to control the polymerization reaction up to a conversion of 60% by suppressing the gel effect in the absence of a solvent. On the other hand, if the conversion is 60% or more, the viscosity of the polymerization reaction solution is extremely high, it is difficult to mix the solvent with the solvent uniformly, the polymerization temperature becomes uneven, and the molecular weight distribution of the obtained acrylic resin becomes wide. There is.

In the solution polymerization method, gelation occurs when the amount of the solvent used is small, and the molecular weight distribution of the obtained acrylic resin is widened. However, when the solvent is used in an amount equal to or more than the monomer, the temperature during the polymerization reaction is increased. Adjustment and molecular weight adjustment are relatively easy, and since no dispersant or the like is used, optical properties are good and a resin having a narrow molecular weight distribution can be produced. However, as is well known, the use of a large amount of a solvent has a disadvantage in that the polymerization rate, particularly the polymerization rate in the early stage of the polymerization, is low, so that productivity is deteriorated and it is difficult to obtain a polymer having a high molecular weight. There is.

[0008]

DISCLOSURE OF THE INVENTION The present invention eliminates the drawbacks of the prior art relating to the polymerization of acrylic resins, makes it easy to control the polymerization reaction, has a narrow molecular weight distribution, and has excellent optical properties. It is an object of the present invention to provide a method for producing a.

According to the present invention, a monomer comprising 70% by weight to 95% by weight of methyl methacrylate and another copolymerizable vinyl compound is converted into a radical polymerization initiator by using two or more polymerization reactors. In producing acrylic resin by polymerization by the action, (1) monomer is added to the first polymerization reactor.
And the resulting polymer-containing mixture is transferred to a subsequent polymerization reactor including a final polymerization reactor, and (2) a subsequent polymerization reaction Mixing the solvent and the polymer-containing mixture transferred from the first polymerization reactor at a ratio of 30 to 90/70 to 10 in a reactor, and (3) a conversion ratio of the monomer in the latter polymerization reactor. (4) equalizing the polymerization temperature in the first and second polymerization reactors and maintaining the temperature change within a range of ± 10 ° C., and (5) final polymerization. The present invention relates to a method for producing an acrylic resin, comprising removing a solvent, an unreacted monomer and a low-molecular-weight polymer from a polymer mixture obtained in a reactor.

Other vinyl compounds copolymerizable with methyl methacrylate include alkyl acrylates such as methyl acrylate, ethyl acrylate and butyl acrylate, alkyl methacrylates such as ethyl methacrylate, butyl methacrylate and lauryl methacrylate, acrylonitrile and methacrylonitrile. And unsaturated nitriles such as α-chloroacrylonitrile, styrene compounds such as styrene and α-methylstyrene, acrylamide, methacrylamide, acrylic acid, methacrylic acid, vinyl chloride, vinylidene chloride and the like. These may be used alone or in combination of two or more.

Methyl methacrylate is JIS K671
A product having the product quality described in No. 6 and removing dissolved oxygen to an amount that does not affect the polymerization reaction, usually to 100 ppm or less can be used. The other copolymerizable vinyl compound may be of a quality equivalent to methyl methacrylate.
If the amount of methyl methacrylate is less than 70% by weight, the transparency, mechanical strength and the like are lowered, and the inherent properties of the acrylic resin are lost, which is not preferable.

As the radical polymerization initiator, an organic peroxide or an azo compound can be used. Examples of the organic peroxide include diacyl peroxides such as lauroyl peroxide and benzoyl peroxide;
1-bis (t-butylperoxy) cyclohexane,
Peroxyketals such as 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, peroxydicarbonates such as diisopropylperoxydicarbonate and di-2-ethylhexylperoxydicarbonate; Examples include peroxyesters such as t-butylperoxy-2-ethylhexanoate and t-butylperoxyisobutyrate. Examples of the azo compound include azobisisobutyronitrile and 1,1-azo Biscyclohexane-t-carbonitrile and the like can be mentioned. These may be used alone or in combination of two or more. The radical polymerization initiator is monomer 1
It is used in a ratio of 0.0005 to 0.5 parts by weight per 00 parts by weight.

The solvent has a solubility in the monomer and the acrylic resin to be formed and does not substantially inhibit the polymerization reaction, and has a boiling point of about 40 to 225 ° C., preferably 60 to 225 ° C.
What is in the range of about 150 ° C. can be used. Specific examples include tetrahydrofuran, methyl ethyl ketone, hexane, heptane, octane, benzene, methyl isobutyrate, toluene, xylene, cyclohexane, cyclododecane, isooctane, decalin, dimethyl sulfoxide, ethylene carbonate, and normal butanol. These may be used alone or in combination of two or more. These solvents are used after the dissolved oxygen is removed to an amount that does not affect the polymerization reaction.

The solvent and the polymer-containing mixture formed in the first polymerization reactor have a weight ratio of (polymer-containing mixture / solvent) of 30 to 90/70 to 10, preferably 40 to 80/70.
In the range of 60 to 20, the mixture is supplied to the subsequent reactor and uniformly mixed. If the amount of the solvent is less than the above lower limit, the viscosity of the polymerization reaction solution becomes high due to the gel effect, and it becomes difficult to control the polymerization reaction, which is not preferable. Conversely, if the solvent is more than the upper limit, there is no difference in the ease of controlling the polymerization reaction,
It takes a long time to remove the solvent, unreacted monomer, low molecular weight polymer, and the like from the produced polymerization mixture, which is not preferable because productivity is deteriorated.

In the present invention, the conversion to a polymer is made 10 to 35%, preferably about 15 to 30% in the first polymerization reactor, and a solvent is added in the latter polymerization reactor to polymerize to a high conversion. Therefore, unlike the conventional solution polymerization method, the polymerization rate in the first polymerization reactor is high, and the viscosity of the polymerization reaction solution is increased by the action of the solvent in the high conversion region of the subsequent polymerization reactor where the gel effect is easily generated. Since it can be maintained at a low level and the temperature change due to polymerization heat is small, the control of the polymerization reaction is easy, the molecular weight distribution of the obtained acrylic resin is narrow, and the generation of impurities such as low molecular weight polymers is reduced. Further, since the conversion in the first polymerization reactor is 35% or less, the viscosity of the polymerization reaction solution is low, and the mixing with the solvent in the subsequent polymerization reactor is easy and has little effect on the polymerization conditions. Furthermore, since the viscosity of the polymerization reaction solution is low, expensive special equipment is not required for the polymerization reactor.

If the conversion in the first polymerization reactor exceeds 35%, a gel effect is liable to occur, and it becomes difficult to control the polymerization reaction. If the conversion in the subsequent polymerization reactor is less than 80%, the amount of unreacted monomer increases, and the recovery device and operation become complicated, which is not preferable. Therefore, it is preferable to increase the conversion in the latter polymerization reactor as much as possible. The polymerization temperature was 60 to 180 ° C. in both the first and second polymerization reactors.
Preferably, the range of 80 to 150 ° C is suitable. At this time, the polymerization temperature in each polymerization reactor is set to be the same, and the polymerization is performed while maintaining the temperature fluctuation within a range of ± 10 ° C., preferably within a range of ± 5 ° C. If the polymerization temperature is lower than 60 ° C., the polymerization rate is low and a large amount of radical polymerization initiator is required, which is not economical. On the other hand, if the temperature exceeds 180 ° C., the amount of impurities such as a low molecular weight polymer increases, which is not preferable. or,
If the temperature change exceeds ± 10 ° C., it is not preferable because it becomes difficult to control the polymerization rate and the molecular weight distribution becomes wide.

In the present invention, various mercaptans such as n-butyl mercaptan, isobutyl mercaptan, n-octyl mercaptan and lauryl mercaptan, or octyl thioglycolate are used for the purpose of controlling the molecular weight of the acrylic resin to be formed and improving the thermal stability. And other chain transfer agents such as thioglycolic acid esters. The use amount of the chain transfer agent is preferably in the range of 0.05 to 0.8 parts by weight per 100 parts by weight of the mixture. Furthermore, the raw material mixed solution used in the present invention is an additive that does not inhibit the polymerization reaction at the start of the reaction or during the reaction, for example, a plasticizer such as dioctyl phthalate, a lubricant such as stearyl alcohol, and an anthraquinone red. Dyes, pigments such as phthalocyanine blue and titanium dioxide, antioxidants such as hindered phenol or resorcinol compounds, and ultraviolet inhibitors such as benzotriazine and benzotriazole can also be added.

The acrylic resin of the present invention can be produced in two or more stirred tank polymerization reactors. One example of the method for producing the acrylic resin of the present invention will be described in detail below with reference to FIG. 1 using two polymerization reactors. In the raw material adjusting tank 1, a mixture of a monomer mixture composed of a predetermined methyl methacrylate or another vinyl compound copolymerizable with methyl methacrylate, a radical polymerization initiator and, if necessary, a chain transfer agent and various additives is mixed at about 20 ° C. Mix uniformly at a temperature of.
The mixture is withdrawn by a first metering pump 2, dust having a diameter of 0.2 μm or more is removed by a filter 3, and the temperature of the resulting polymerization reaction solution is adjusted to 60 to 18 by a first heater 4.
The temperature is raised to 0 ° C., preferably 80 to 150 ° C., and supplied to the first polymerization reactor 5 which has been adjusted to the same temperature. First
The conversion rate in the polymerization reactor 5 is 10 to 35%, preferably 15 to 35%.
Polymerize to 30%. The change in the conversion can be known by measuring the temperature change and / or the viscosity change of the polymerization reaction solution during the polymerization reaction.

After the completion of the polymerization reaction in the first polymerization reactor 5, the produced polymer-containing mixture and a predetermined amount of the solvent heated to a temperature slightly lower than the boiling point are supplied to a second metering pump 7 and a solvent metering pump 8, respectively. To the second polymerization reactor 10. If necessary, an additional copolymerizable vinyl compound or chain transfer agent is supplied to the reactor from the additional raw material line 11. The temperature of the polymer-containing mixture and the solvent supplied to the second polymerization reactor 10 are adjusted by the second heater 9. The polymerization temperature in the second polymerization reactor 10 is the same as in the first polymerization reactor. The polymer-containing mixture and the solvent may be supplied to the second polymerization reactor 10 while mixing using a static mixer or the like. Polymerization is performed until the addition ratio in the second polymerization reactor 10 becomes 80% or more, preferably 95% or more, and substantially the entire amount of the radical polymerization initiator is consumed. The temperature of the polymerization reaction solution is
The evaporated solvent is condensed in the second condenser 12 and controlled by the reflux to the second polymerization reactor 10 and the temperature control by the jacket of the polymerization reactor, within ± 10 ° C, preferably ± 5 ° C. Will be maintained. The reaction pressure in both the first and second polymerization reactors is preferably higher than the saturated vapor pressure of methyl methacrylate.

After the completion of the polymerization reaction in the second polymerization reactor 10, the resulting polymer-containing mixture is supplied to a third metering pump 13
Is sent to the third heater 14, which raises the temperature to about 220 to 260 ° C. in as short a time as possible.
The pressure at this time is set higher than the saturated vapor pressure of the solvent to prevent a decrease in the heating function. The heated polymer-containing mixture is flushed by a deaerator 16 through a needle valve at the lower part of the liquid transfer line 15, and the solvent, unreacted monomer is removed from the polymer-containing mixture at a temperature of 220 to 260 ° C and a pressure of 10 to 150 mmHg. , Low molecular weight polymers and the like are removed.
If the temperature is 220 ° C. or lower, the temperature of the acrylic resin after flashing decreases, and the removal of the solvent, the low molecular weight polymer and the like becomes insufficient, which is not preferable. On the other hand, if the temperature is 270 ° C. or higher, a gelled substance or the like is generated, and the acrylic resin is deteriorated by thermal decomposition, which is not preferable. The removed solvent, low molecular weight polymer and the like are sent to a recycling line via a solvent etc. removal line 17. By this deaeration, the content of the solvent, the low molecular weight polymer and the like in the acrylic resin is reduced to 1% by weight or less, preferably 0.1% by weight or less. It is withdrawn by the metering pump 18 and pelletized by the pelletizer 19.

Here, the raw material adjusting tank 1 and the first polymerization reactor 3
May be the same. A solvent from the polymer-containing mixture,
The removal of the low molecular weight polymer or the like can be performed by a thin film evaporator for high viscosity (for example, trade name “EXEV”) besides the flash type device described above.
A ″, manufactured by Shinko Pantech Co., Ltd.) or an extruder with a vent may be used, and it is more preferable to use them together with the deaerator of the present invention. Acrylic resin can be supplied to a single-screw or multi-screw extruder.The raw material adjustment tank, polymerization reactor, line and metering pump of this device are all temperature-controlled by passing a heating medium or refrigerant through the jacket. In addition, the line for transferring the acrylic resin mixture is designed to be as short as possible so that no sediment is generated.The raw material adjusting tank and the polymerization reactor are sufficiently replaced with an inert gas. As described above, the example using two polymerization reactors has been described.
In the present invention, three or more reactors can be used,
It is also possible to operate continuously. When three or more polymerization reactors are used, the operation is carried out by setting the attained conversion in each polymerization reactor after the second polymerization reactor to be sequentially higher.

[0022]

The present invention will be described in more detail with reference to the following examples and comparative examples. The following methods were used to measure the monomer conversion, total light transmittance, molecular weight, and molecular weight distribution of the acrylic resin in the examples. (1) Monomer conversion ratio The polymer-containing mixture 5 from the first and second polymerization reactors was used.
10 g is taken as a sample in a test tube and cooled with liquid oxygen. After measuring the weight of the sample, the sample is completely dissolved in chloroform, and the solution is poured into methanol of about 20 times the weight of the sample with stirring to precipitate the acrylic resin.
The acrylic resin is separated by filtration, dried under reduced pressure at about 60 ° C. for 16 hours, and the weight of the obtained acrylic resin is measured. The conversion was determined from the ratio of the weight of the acrylic resin after drying to the weight of the sample. The solvent content in the polymer-containing mixture in the latter polymerization reactor was determined by gas chromatogram and calculated. (2) Total light transmittance Injection molding of the produced acrylic resin (resin temperature 230
° C, injection pressure 750 Kgf / cm ² )
The measurement is performed according to ASTM D1003 using a sample molded into a plate having a size of 100 mm x 3 mm (thickness). (3) Molecular weight, molecular weight distribution GPC apparatus (Tosoh HLC-8020 type, column is S
(Hodex KF-80M), a sample prepared by dissolving 0.3 g of the produced acrylic resin in 100 ml of tetrahydrofuran was measured, and the number average molecular weight, weight average molecular weight and molecular weight distribution were determined based on a calibration curve prepared with standard polymethyl methacrylate. Ask.

Example 1 In a raw material adjusting tank 1, 4750 g of methyl methacrylate and 250 g of methyl acrylate were mixed at 20 ° C., and nitrogen gas was blown into the mixture at a flow rate of 150 ml / min for about 10 minutes to remove dissolved oxygen. The dissolved oxygen in this mixture is DO
Meter (UC-12-SOL type, manufactured by Central Science)
Was less than 5 ppm. After adding 5 g of lauroyl peroxide and 15 g of lauroyl mercaptan to this mixed solution and mixing them uniformly, the first metering pump 2 was used.
, And dust and the like having a diameter of 0.2 μm or more are removed by the filter 3, and the temperature is increased to 120 ° C. by the first heater,
The solution was transferred to the first polymerization reactor 5 whose temperature was adjusted to 120 ° C., the temperature was 120 ° C., the pressure was kg / cm ² , and the rotation speed of the stirring blade was 150 r.
Polymerized at pm for 1 hour. At this time, the conversion was 29%. The temperature change during this period was within ± 2 ° C. This polymer-containing mixture was withdrawn by a second metering pump 7 and 1
The solution was transferred to the second polymerization reactor 10 whose temperature was adjusted to 20 ° C.
Then, 4500 g of xylene heated to 120 ° C. by the solvent metering pump 8 was supplied to the second polymerization reactor 10,
The mixture was mixed and polymerized at the same temperature for 3 hours while stirring at a rotation speed of 150 rpm. At this time, the conversion was 89%. The temperature change during this period was within ± 3.5 ° C.

The polymer-containing mixture is pumped to a third metering pump 13
And heated to 245 ° C., and then flushed to a deaerator 16 at a temperature of 240 ° C. and a reduced pressure of 50 mmHg or less to remove solvents, low molecular weight polymers and the like. The acrylic resin was taken out from the nozzle of the fourth metering pump 18 below the deaerator 16 with a strand, cooled in a water tank of the pelletizer 19, and cut with a cutter to form pellets. The total light transmittance of the produced acrylic resin was as good as 93%, the number average molecular weight measured by GPC was 40500, the weight average molecular weight was 78570, and the molecular weight distribution was 1.94.

Comparative Example 1 4500 g of xylene was added to a mixture of 4750 g of methyl methacrylate and 250 g of methyl acrylate in the raw material adjusting tank 1.
Polymerization was carried out in the same manner as in Example 1 except that was added. The addition ratio after polymerization for 1 hour was 8%, and the polymerization rate was 31% even after the polymerization was continued for 3 hours. The polymerization rate was lower than that in Example 1 and was not practical. Comparative Example 2 Example 1 except that xylene was not added in the second polymerization reactor.
Was polymerized in the same manner as described above. However, in the second polymerization reactor, about 2
The temperature of the polymer-containing mixture began to rise from the time when the polymerization was carried out for 5 minutes, and the temperature could not be controlled. The temperature of the mixture is 1
When the temperature reached 70 ° C., 5000 g of xylene at about 10 ° C. was added and mixed uniformly. Immediately after cooling, the mixture was withdrawn from the second polymerization reactor into a stainless steel container, and the temperature was reduced to 40 ° C.
Cooled down to: The addition rate at this time was 62%. The number average molecular weight of the acrylic resin obtained by this method is 3
The weight average molecular weight was 9,700, the molecular weight distribution was 2.74, the molecular weight distribution was wide, and the total light transmittance was 90%.

[0026]

In producing an acrylic resin containing methyl methacrylate as a main component, multi-stage polymerization is carried out, the addition ratio of the first stage is suppressed to 10 to 35%, and a specific amount of a solvent is added in the latter stage, and the conversion is carried out. After the conversion is 80% or more, the solvent, low molecular weight components and the like are removed. (1) Even at a high conversion of 80% or more, the change in viscosity is small and the polymerization reaction is easily controlled. (2) A high-quality acrylic resin having a high total light transmittance and a narrow molecular weight distribution can be obtained. (3) Since the viscosity of the polymerization reaction solution is low, an inexpensive polymerization reactor can be used. And so on.

[0027]

[Brief description of the drawings]

FIG. 1 is a flow sheet according to a method for producing an acrylic resin of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw material adjustment tank 2 1st metering pump 3 Filter 4 1st heating machine 5 1st polymerization reactor 6 1st condenser 7 2nd metering pump 8 Solvent metering pump 9 2nd heating machine 10 2nd polymerization Reactor 11 Line for additional raw material 12 Second condenser 13 Third pump 14 Third heater 15 Liquid transfer line 16 Degassing device 17 Removal line for solvent etc. 18 Fourth constant pump 19 Pelletizer

Claims (1)

(57) [Claims] 1. The method of claim 1 wherein two or more polymerization reactors are used.
In producing an acrylic resin by polymerizing a monomer composed of methyl methacrylate by weight to 95% by weight and another vinyl compound copolymerizable by the action of a radical polymerization initiator, (1) a first polymerization reaction Only the monomer
And the resulting polymer-containing mixture is transferred to a subsequent polymerization reactor including a final polymerization reactor. (2) The latter polymerization reactor
Mixing the polymer-containing mixture and the solvent transferred from the first polymerization reactor at a weight ratio of 30 to 90/70 to 10; (3) the conversion rate of the monomer in the subsequent polymerization reactor is (4) The polymerization temperature in the first and second polymerization reactors is the same, and the temperature change is ±
(5) removing the solvent, unreacted monomer and low-molecular-weight polymer from the polymer mixture obtained in the final polymerization reactor, and maintaining the temperature within a range of 10 ° C. .