JPH06128327A - High-purity methacrylic resin - Google Patents

Abstract

PURPOSE:To attain high purity and improve transparency and resistances to pyrolysis and discoloration by bulk-polymerizing a specific monomer mixture consisting mainly of methyl methacrylate in an inert-gas atmosphere. CONSTITUTION:A monomer mixture consisting of 80wt.% or more methyl methacrylate and 20wt.% or less other monomer(s) copolymerizable therewith is put in an atmosphere sufficiently purged with nitrogen, and is then kept in an inert gas atmosphere to reduce the dissolved oxygen content thereof to 2ppm or lower and the peroxide content of the methyl methacrylate to 10ppm or lower. To the resulting mixture are added 0.001-0.02wt.% free-radical polymerization initiator and 0.1-0.5wt.% chain transfer agent. The monomers are bulk- polymerized in an inert gas atmosphere at 100-150 deg.C, while the viscosity of the reaction mixture is kept at 5-1,000P. The reaction mixture is then heated to 100-230 deg.C at a reduced pressure to remove most of the volatiles including the residual additives and unreacted monomers. Thus, the title resin is obtained which has a residual mercaptan content of 50ppm or lower and a residual monomer content of 0.5wt.% or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a methacrylic resin having high transparency and containing less foreign matter.

[0002]

2. Description of the Related Art Methacrylic resins are used in many fields such as lighting, signboards, vehicles, etc. due to their excellent transparency and weather resistance.

In recent years, it has been adopted for optical applications such as optical lenses and disk substrates, but especially for optical applications, there is a strong demand from the market for high-purity methacrylic resin containing few foreign substances.

As a method for producing a methacrylic resin, suspension polymerization, bulk polymerization and solution polymerization are known.

[0005]

However, since the polymer produced by the suspension polymerization method uses a suspending / dispersing agent, an auxiliary agent and an aqueous phase, it is unavoidable that foreign matter is mixed in and a large amount of fine foreign matter is present. was there. Further, the thermal decomposition resistance of the polymer is poor and the moldability is poor, and there is an optical problem.

Further, the polymer obtained by the bulk polymerization method has a problem in terms of optical purity because a by-product is generated due to the adoption of high temperature polymerization, molding processability is poor.

Further, the polymer obtained by the solution polymerization method is inferior in optical durability, that is, weather resistance and thermal decomposition resistance due to the residual solvent, so that silver is generated during molding and it is difficult to express an optical function. Had a point.

[0008]

Means for Solving the Problems The inventors of the present invention have made earnest studies in view of the above-mentioned situation, and as a result, methyl methacrylate alone or 80% by weight or more of methyl methacrylate and 20% by weight or less of methacrylic acid was obtained. The amount of dissolved oxygen in a monomer mixture with another monomer copolymerizable with methyl acidate is 2 ppm.
Or less and the amount of peroxide of methyl methacrylate is 10 pp
m or less, in the presence of an inert gas, at a temperature of 100 to 150 ° C., obtained by bulk polymerization while maintaining the viscosity of the system in the range of 5 to 1000 poise, and remaining in the polymer. It was found that a methacrylic resin having a mercaptan content of 50 ppm or less is highly pure and optically excellent,
The present invention has been completed.

The methacrylic resin of the present invention comprises methyl methacrylate alone or a monomer mixture of 80% by weight or more of methyl methacrylate and 20% by weight or less of another monomer copolymerizable with methyl methacrylate. It is a polymer obtained by bulk polymerization. Other monomers copolymerizable with methyl methacrylate include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate,
Butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, acrylic acid 2,
Acrylic esters such as 2,2-trifluoroethyl; ethyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, methacrylic acid 2,2,2-
Methacrylic acid esters such as trifluoroethyl may be mentioned.

The methacrylic resin of the present invention is obtained by bulk-polymerizing methyl methacrylate or a monomer mixture containing methyl methacrylate as a main component, and then reacting an unreacted monomer as a main component from a reaction mixture containing the produced polymer. It can be obtained by separating and removing the volatile matter.

In the polymerization, a monomer mainly containing methyl methacrylate containing a mercaptan and a radical polymerization initiator is supplied to a polymerization reactor.

When the monomer containing methyl methacrylate as the main component is supplied to the polymerization reactor and polymerized, methyl methacrylate or a monomer mixture of methyl methacrylate and another copolymerizable monomer is used. It is necessary to set the dissolved oxygen amount to 2 ppm or less and the methyl methacrylate peroxide amount to 10 ppm or less. By setting the amount of dissolved oxygen in the monomer to 2 ppm or less, the stability of polymerization is improved and the thermal deterioration of the polymer is reduced. If it exceeds 2 ppm, the polymer is colored and the optical properties deteriorate. It is preferably 1 ppm or less.

The methyl methacrylate peroxide is a peroxide of methyl methacrylate produced by contact between methyl methacrylate and oxygen. When it exceeds 10 ppm, the stability of polymerization is poor and a polymer is formed. If you do, it may cause foreign matter. Therefore, the amount of peroxide in the monomer is 5 pp
It is more preferably as small as m or less.

The dissolved oxygen in the monomer can be removed by sufficient nitrogen substitution, and the methyl methacrylate peroxide can be reduced by removing the dissolved oxygen and keeping it in an inert atmosphere.

In the polymerization, mercaptan is used as a chain transfer agent to control the degree of polymerization of the obtained polymer.

The mercaptans to be used include primary, secondary and tertiary mercaptans having an alkyl group or a substituted alkyl group, such as methyl, ethyl and propyl.
Examples thereof include isopropyl, n-butyl, isobutyl, n-octyl, n-dodecyl, sec-butyl, sec-dodecyl and tert-butyl mercaptan. These may be used alone or in combination of two or more. Among these mercaptans, it is preferable to use propyl, n-butyl, tert-butyl and n-octyl mercaptan from the viewpoints of less coloring of the polymer, separation and removal from the reaction mixture, and ease.

The amount of mercaptan used is preferably in the range of 0.1 to 0.5% by weight based on the monomer. Usage is 0.
When it is 1% by weight or less, the degree of polymerization becomes high, and it may be difficult to obtain a polymer having excellent moldability. Further, if it exceeds 0.5% by weight, the degree of polymerization is lowered to lower the mechanical strength of the product, or unreacted mercaptan remains in the polymer to color the product to obtain a high-purity polymer. Becomes difficult.

Examples of the radical polymerization initiator used for the polymerization include 2- (carbamoylazo) -isobutyronitrile, 1,1'-azobis (1-cyclohexanecarbonitrile) and di-tert-butylperoxyase. Rate, tert-butylperoxy-3,3,5-trimethylhexanate, tert-butylperoxyacetate, tert-butylperoxybenzoate, t
ert-butyl peroxyisopropyl carbonate,
1,1-di-tert-butylperoxycyclohexane, methylcyclohexane peroxide, di-ter
Examples include t-butyl peroxide and 2,2 di- (tert-butylperoxy) -butane. These are 1
The seeds may be used alone or in combination of two or more. Of these radical polymerization initiators, tert-
Butyl peroxy-3,3,5-trimethyl hexanate, tert-butyl peroxy isopropyl carbonate and tert-butyl peroxy acetate are preferred.

The amount of the radical polymerization initiator used is preferably in the range of 0.001 to 0.02% by weight based on the monomer.
If it is less than 0.001% by weight, the polymerization does not proceed sufficiently, the viscosity of the system does not increase and the thermal decomposition resistance deteriorates, and if it exceeds 0.02% by weight, the viscosity of the system increases and stable operation cannot be performed.

In the polymerization, the reaction mixture is heated to 100 to 150 in a polymerization reactor pressurized with an inert gas such as nitrogen gas.
Polymerization is carried out by substantially uniformly stirring and mixing at a temperature of C, preferably 120 to 140 C, and maintaining the viscosity of the reaction solution constant at the reaction temperature of the reaction mixture for polymerization.

By setting the polymerization temperature in the range of 100 to 150 ° C., by-products in the polymerization can be reduced. If it is lower than 100 ° C, the polymerization rate becomes slow and the productivity is poor, and if it exceeds 150 ° C, the generation of by-products increases, which remains in the polymer and the optical properties deteriorate. In the reactor, the viscosity of the reaction mixture at the reaction temperature is 5 to 1000 poise, preferably 10 to 500 poise.
Control within the viscosity range of poise. When the viscosity of the reaction mixture is less than 5 poises, the thermal decomposition resistance of the obtained polymer decreases. On the other hand, if the viscosity exceeds 1000 poise, the resulting polymer has excellent thermal decomposition resistance, but it becomes difficult to mix the reaction mixture and remove the heat of polymerization, and it becomes difficult to control stable polymerization.

The production apparatus used in the practice of the present invention is not particularly limited as long as it can obtain the polymer aimed at by the present invention.
The tank reactors described in JP-A-15641 and JP-B-54-38625 are preferable, and those having a function of sufficiently mixing the entire inside of the tank are preferable.

The reaction mixture polymerized to a predetermined viscosity in the polymerization reactor is sent to a devolatilizer to heat the reaction mixture to 100 to 230 ° C. under reduced pressure to remove residual additives such as mercaptan and unreacted monomers. Isolate and remove volatile substances such as. The unreacted monomer content in the final resin is 0.5% by weight or less, preferably 0.2% by weight or less.

The amount of residual mercaptan is 50 ppm or less, preferably 10 ppm or less. If the amount of residual mercaptan exceeds 50 ppm, it will become a foreign substance when the polymer is molded, so it is necessary to reduce the amount.

An apparatus used for separating volatile matter is called a vent extruder or a devolatizer, for example, Japanese Patent Publication No.
The compounds described in JP-B No. 2-17555 and JP-B No. 55-30987 are used. Further, a high-viscosity thin film evaporator such as a vertical inclined blade controller manufactured by Hitachi, Ltd. is used.

The polymer separated from the volatile matter is extruded from a die in a molten state and molded into a desired shape. The methacrylic resin of the present invention can be manufactured batchwise or continuously, but it is preferable to continuously manufacture it in terms of quality stability and productivity.

In the methacrylic resin of the present invention, lubricants such as higher alcohols and higher fatty acid esters can be used. Also, if necessary, a UV absorber,
A heat stabilizer, a colorant, an antistatic agent, etc. can be added.

[0028]

The methacrylic resin of the present invention having the constitution as described above has high transparency, little foreign matter is mixed in the polymer, and is excellent in thermal decomposition resistance and coloration.
It is extremely useful for optical materials such as general molding materials and optical lenses, disk substrates, etc., and can exert industrially excellent effects.

[0029]

EXAMPLES The present invention will be described in more detail with reference to examples below, but these do not limit the present invention. In the examples, "%" means "% by weight" and "part" means "part by weight".

The evaluations in the examples were carried out by the methods shown below.

(1) Measurement of Dissolved Oxygen Amount A fixed amount of a sample is sampled using an analytical instrument sufficiently replaced with nitrogen gas, and titrated with an aqueous ferrous ammonium sulfate solution using methylene blue as an indicator to obtain the amount.

(2) Measurement of Methyl Methacrylate Peroxide A saturated aqueous solution of potassium iodide in isopropanol and acetic acid were added to a sample and heated, and iodine liberated by the peroxide was titrated with 1/10 normal sodium thiosulfate. And calculate from the amount.

(3) Measurement of residual monomer, residual dimer and residual mercaptan The amount was determined by gas chromatography analysis using Shimadzu GC-14A.

Measurement conditions; column: capillary column, carrier gas: nitrogen gas 30 ml / min

[0035]

[Table 1]

(4) Measurement of foreign matter in polymer As for the number of foreign matter of 0.5 μm or more, the number of foreign matter of 0.5 μm or more in 10 cc of a solution prepared by dissolving 1 g of the polymer in 100 cc of methylene chloride was measured by a fine yaikoiko fine particle counter (Hyakuroiko Co. Ltd.). Manufactured).

(5) Thermal decomposition resistance Differential thermal electronic balance (SSC5 manufactured by Seiko Instruments Inc.)
00) is used, and the bending temperature (° C.) when the polymer pellets are heated to 400 ° C. at a heating rate of 5 ° C./min in air is shown.

(6) Coloring property The appearance of a 2 mm thick plate obtained by injection molding polymer pellets under the following conditions was visually determined.

Molding machine: Mitsubishi Heavy Industries, Ltd., 75MS / 1
25 Molding temperature (cylinder) temperature: 225 ° C. Mold volume: 2 mm × 110 mm × 110 mm Mold temperature: 60 ° C. Injection pressure: 900 kg / cm ² Example 1 From 99% by weight of methyl methacrylate and 1% by weight of methyl acrylate To 100 parts by weight of the monomer mixture
Octyl mercaptan 0.25 parts by weight, tert-butyl peroxy 3,5,5 trimethylhexanoate 0.
After mixing with 0035 parts by weight, the pressure was reduced to 50 Torr in a 200 liter polymerization kettle, and then 0.5 kg / cm.
Pressurize while bubbling with nitrogen gas up to ^2, then 5
The pressure was reduced to 0 Torr, and then pressurized to 0.5 kg / cm ^{2 with} nitrogen gas, and the same cycle was performed once again to adjust the dissolved oxygen to 0.5 ppm. The content of methyl methacrylate peroxide in this monomer mixture was 8 ppm.

This monomer mixture was added with nitrogen gas at 5 kg / c.
It was continuously fed at a rate of 15 kg / hr to a 100-liter polymerization kettle equipped with a complete mixing stirrer whose pressure was controlled to m ^2, and the liquid in the kettle was kept at 75 liters to carry out polymerization for 1 month. Polymerization was carried out at a temperature of 135 ° C. to obtain a partial polymer having a polymerization rate of 52% and a viscosity of 20 poise. The viscosity of the partial polymer was measured by a rotary process viscometer attached to a pipe provided in the lower part of the polymerization vessel and continuously feeding the partial polymer to a devolatilization device.

This partial polymer was supplied to a thin film evaporator having a heat transfer area of 0.10 m ² manufactured by Hitachi, Ltd.
0 rpm, jacket temperature 270 ° C, vacuum degree 50 Tor
After the polymer, the unreacted monomer and the by-product were separated by r, they were supplied to the additive kneader. Polymer 10 with stearyl alcohol
0.1 part by weight was kneaded with 0 part by weight, extruded from a die, shaped, and cut into pellets having a diameter of about 3 mm and a length of 3 mm to obtain a methacrylic resin. The residual mercaptan in the obtained polymer was 10 ppm. The residual MMA monomer and the residual MMA dimer each contained 0.12%.
And 0.01% or less.

When the physical properties of this polymer were evaluated, the results shown in Table 2 were obtained. The foreign matter in the molded product in the table is 1
This is an evaluation of a molded product after one month has elapsed when injection molding was continuously performed for one month. As is apparent from this table, it is understood that the polymer of Example 1 was a methacrylic resin having few impurities and no coloration and having good thermal decomposition resistance and high optical purity.

Example 2 92% by weight of methyl methacrylate, 8% by weight of ethyl acrylate, 0.35 parts by weight of n-octyl mercaptan, te
A polymer was obtained from a partial polymer having a polymerization rate of 53% and a viscosity of 5 poises in exactly the same manner as in Example 1 except that 0.0041 parts by weight of rt-butylperoxy 3,5,5 trimethylhexanoate was used. It was The amount of residual mercaptan in the polymer was 5 ppm. The results are shown in Table 2. It can be seen that the same excellent methacrylic resin as in Example 1 was obtained. The residual MMA monomer in the polymer was 0.09%,
The residual MMA dimer was 0.01% or less.

Example 3 A partial polymer having a polymerization rate of 55% and a viscosity of 60 poise was prepared in the same manner as in Example 1 except that methyl methacrylate was 100% by weight and n-octyl mercaptan was 0.022 part. Got united. The amount of residual mercaptan in the polymer was 10 ppm. The results are shown in Table 2. It can be seen that the same excellent methacrylic resin as in Example 1 was obtained. The residual MMA monomer in the polymer was 0.15%, and the residual MMA dimer was 0.01% or less.

Comparative Example 1 Except that the amount of dissolved oxygen in the monomer mixture was 4 ppm,
A polymer was obtained in exactly the same manner as in Example 1. The results are shown in Table 2. From this table, it can be seen that the polymer obtained by polymerizing the monomer mixture having the dissolved oxygen amount of more than 2 ppm is colored.

Comparative Example 2 While bubbling air through methyl methacrylate, 3
A polymer was prepared in the same manner as in Example 1 except that the temperature was kept at 0 ° C. and circulation was continued to adjust the methyl methacrylate peroxide to 20 ppm, and a monomer mixture was obtained using methyl methacrylate. Obtained. The methyl methacrylate peroxide in the monomer mixture was 20 ppm. The evaluation results of the polymer are shown in Table 2. From this table, it can be seen that the molded plate obtained by injection molding a polymer obtained by polymerizing a monomer mixture containing more than 10 ppm of methyl methacrylate peroxide contains many foreign matters.

Comparative Example 3 The polymerization temperature was 160 ° C. and the polymerization initiator was di-tert-.
A polymer was obtained from a partial polymer having a polymerization rate of 60% and a viscosity of 80 poises in the same manner as in Example 1 except that butyl peroxide was changed to 0.0016 parts. Residual MMA in polymer
Monomer and residual MMA dimer are 0.26% and 0.12% or less, respectively, which means that the polymerization temperature is 150 ° C.
It can be seen that the amount of by-products increases when the value exceeds.

Comparative Example 4 The polymerization temperature was 140 ° C. and the polymerization initiator was di-tert-.
A polymer was obtained from a partial polymer having a polymerization rate of 40% and a viscosity of 2 poises in the same manner as in Example 1 except that butyl peroxide was changed to 0.0016 part. The results are shown in Table 2.
From this table, it is understood that when the viscosity of the system is lower than 5 poise, the thermal decomposition resistance of the polymer is poor.

Comparative Example 5 A polymer was obtained in exactly the same manner as in Example 2 except that the jacket temperature of the thin film evaporator was lowered and the degree of vacuum was lowered. The residual mercaptan in the polymer was 70 ppm. The results are shown in Table 2. From this table, the residual mercaptan is 50p
It can be seen that the molded plate obtained by injection molding a polymer having a particle size of more than pm contains many foreign substances.

Comparative Example 6 The procedure of Example 1 was repeated except that 0.0120 parts of tert-butylperoxy 3,5,5 trimethylhexanoate was used, and the viscosity of the partial polymer exceeded 1000 poises. , I couldn't drive stably.

[0051]

[Table 2]

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[Procedure amendment]

[Submission date] January 13, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

The reaction mixture polymerized to a predetermined viscosity in the polymerization reactor is sent to a devolatilizer to heat the reaction mixture at 100 to 240 ° C. under reduced pressure to remove residual additives such as mercaptan and unreacted monomers. Isolate and remove volatile substances such as. The unreacted monomer content in the final resin is 0.5% by weight or less, preferably 0.2% by weight or less.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

(4) Measurement of foreign matter in the polymer For the number of foreign matter of 5 μm or more, 10 g of the polymer was treated with 1 methylene chloride.
The number of foreign matters of 5 μm or more in 1000 cc of the solution dissolved in 000 cc was measured with a Hyakuroiko fine particle counter (manufactured by Hayakuroiko).

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0039

[Correction method] Change

[Correction content]

Molding machine: Mitsubishi Heavy Industries, Ltd., 75MS / 1
25 Molding temperature (cylinder) temperature: 225 to 255 ° C. Mold capacity: 2 mm × 110 mm × 110 mm Mold temperature: 60 ° C. Injection pressure: 900 kg / cm ² Example 1 99% by weight methyl methacrylate, 1% by weight methyl acrylate With respect to 100 parts by weight of the monomer mixture consisting of
Octyl mercaptan 0.25 parts by weight, tert-butyl peroxy 3,5,5 trimethylhexanoate 0.
After mixing with 0035 parts by weight, the pressure was reduced to 50 Torr in a 200 liter polymerization kettle, and then pressurized to 0.5 kg / cm ² while bubbling with nitrogen gas, and further 50 T.
The pressure was reduced to orr, and then pressurized to 0.5 kg / cm ^{2 with} nitrogen gas, and the same cycle was performed again to adjust the dissolved oxygen to 0.5 ppm. The amount of methyl methacrylate peroxide in this monomer mixture was 8 ppm.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0050

[Correction method] Change

[Correction content]

Comparative Example 6 The procedure of Example 1 was repeated except that 0.0220 parts of tert-butylperoxy 3,5,5trimethylhexanoate was used, and the viscosity of the partial polymer exceeded 1000 poises. , I couldn't drive stably.

Claims (1)

[Claims] 1. The amount of dissolved oxygen in a monomer mixture of methyl methacrylate alone or 80% by weight or more of methyl methacrylate and 20% by weight or less of another monomer copolymerizable with methyl methacrylate is 2 ppm. The following was obtained by bulk polymerization while maintaining the viscosity of the system in the range of 5 to 1000 poise at a temperature of 100 to 150 ° C. in the presence of an inert gas, with the amount of peroxide of methyl methacrylate being 10 ppm or less. A high-purity methacrylic resin characterized in that the amount of residual mercaptan in the polymer is 50 ppm or less.