KR20040072227A - Method for Preparing Polymethyl methacrylate Having Excellent Optical Permeability and Resistance for Discoloration - Google Patents

Abstract

PURPOSE: Provided is a method for preparing polymethyl methacrylate having excellent light transmission and discoloration resistance by inhibiting thermal decomposition of the resin through the addition of two types of radical initiators. CONSTITUTION: The method comprises the steps of: providing a mixture containing 85-99.9 parts by weight of methyl methacrylate, an alkyl acrylate, an A-type radical initiator, a liquid disperse medium, a suspending agent, a buffering salt and a chain transfer agent based on 100 parts by weight of a monomer mixture for polymethyl methacrylate; carrying out suspension polymerization of the resultant mixture at 60-70 deg.C for 30-130 minutes, warming the mixture to 70-120 deg.C for 35 to 55 minutes, and adding a B-type radical initiator thereto to further carry out suspension polymerization, thereby forming polymethyl methacrylate beads; and washing and drying the polymethyl methacrylate beads, simply mixing the beads with an antioxidant and carrying out an extrusion process.

Description

Method for preparing polymethyl methacrylate having excellent optical permeability and resistance for discoloration

The present invention relates to a method for producing polymethyl methacrylate excellent in light transmittance and discoloration resistance. More specifically, in the preparation of polymethyl methacrylate, the suspension polymerization method which is effective for commercial production is applied, but in order to overcome the disadvantage of the suspension polymerization method which reduces light transmittance and discoloration resistance, The present invention relates to a method for producing polymethyl methacrylate having improved light transmittance and discoloration resistance by adding together two radical initiators having different half-life temperatures in the presence of a transition transfer agent.

Polymethyl methacrylate (PMMA) is a polymer of methyl methacrylate (MMA), and refers to a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and acrylate.

Polymethyl methacrylate is not only excellent in transparency and weather resistance, but also excellent in mechanical strength such as tensile strength, elastic modulus, surface gloss, chemical resistance, adhesiveness, and so on, such as decorative articles, signboards, lighting materials, various building materials, It is widely used as an adhesive, a modifier of other plastic materials, and is also widely used as a glass substitute for optical applications due to its excellent transparency.

Such polymethyl methacrylate is prepared by a process such as bulk polymerization, suspension polymerization, or solution polymerization, and mainly by bulk polymerization in the field of display, electronic materials, and optics requiring high optical properties. This is because the polymethyl methacrylate produced by suspension polymerization is lower in permeability and discolored than the polymethyl methacrylate produced by bulk polymerization. In other words, suspension polymerization is a heterogeneous polymerization, which is polymerized in a liquid phase in which monomers, radical initiators, and suspending agents are dispersed. Unnecessary compounds other than monomers are formed by suspensions, suspension stabilizers, etc., which are added for stable dispersion of monomers during the polymerization process. This is because more is introduced into polymethylmethacrylate compared to polymerization.

However, suspension polymerization has a liquid layer that absorbs the heat of reaction compared to the bulk polymerization, and thus, the heat of reaction is easily controlled, and the polymer beads are polymerized in the form of beads of 0.1 to 1 mm after polymerization of the monomer dispersed in the liquid layer. It can be easily separated, so there is an advantage in freely converting varieties in mass production.

Therefore, there is a need for polymethylmethacrylate having improved optical properties and mechanical properties while taking advantage of suspension polymerization.

In order to improve the optical properties and physical properties of polymethyl methacrylate, U.S. Patent No. 5,093,444 regulates the content of sodium sulfate or sodium phosphate, which is used as a suspension stabilizer in methacryl resin compositions for optical discs. The present invention relates to a technique for reducing microbubble formation of a disk molding, and US Pat. No. 5,252,440 adds a fatty acid ester-based releasing agent to improve processability and workability when injection molding an optical disk. It publishes about the methacryl resin composition which carried out suspension polymerization. However, such a conventional technique is limited to the structure of the suspending agent or suspending stabilizer, their composition, the composition of the monomer methyl methacrylate or alkyl acrylate, and the improvement of processability, and fully utilizes the advantages of the suspension polymerization. The optical properties of the rate have not been improved to the extent that they are applied to optical applications.

In general, one of the important factors that lower the optical and mechanical properties of the resin is the thermal decomposition of the resin generated by the thermal history during the heat processing, such as extrusion, injection molding. Brackhaus and Jenckel (Die Makromol Chem 1956, V19, p262) are polymethyl methacrylate radically polymerized with benzoyl peroxide as an initiator. It is known that pyrolysis occurs at the unsaturated end and the saturated end of the main chain in the temperature range. In addition, McNeil (IC McNeil, European Polymer Journal., V4, 21, 1968) reported that polymethyl methacrylate was prepared by radical polymerization and anionic polymerization, followed by thermogravimetric analysis. It is known that the weight of the anionic polymerized resin does not decrease, while the weight decreases. Hirata et al. (Toshimi Hirata et al., Macromolecules, 1985, V18, p1410-1418), showed thermogravimetric analysis of commercially available polymethylmethacrylate in a nitrogen atmosphere and an atmospheric atmosphere. The weight loss is caused by the volatilization of impurities and residual monomers in the region of 160 to 240 ℃ and then by the decomposition of the double bonds at the end of the main chain, irregular cutting of the main chain occurs above 240 ℃, the atmosphere than the nitrogen atmosphere In the atmosphere, the weight loss in the region of 160 to 240 ° C. is less, but the weight loss occurs abruptly in the area of 240 ° C. or higher, which causes oxygen to more stably modify the structure of the main chain terminal or consume alkyl radicals generated by decomposition. Because it plays a role. Furthermore, by measuring the weight loss at isothermal temperature for several temperatures in the temperature range of 276 to 336 ° C, the activation energy for irregular cleavage of the main chain under nitrogen atmosphere is 224 kJ / mol and the frequency factor is 2.9 × 10 ¹⁶ / sec. Known. In addition, Hillary et al., Thermal Degradation of Saturated Poly (methyl methacrylate) Macomolecules, 1988, V21, p528-530, prepared by anionic polymerization of polymethylmethacrylate having no double bond at the backbone end. It is known that the activation energy for thermogravimetric reduction in the temperature range of 315 to 393 ° C. is 260 kJ / mol and the frequency factor is 2 × 10 ¹⁶ / sec. Takashi Kashiwagi, Effects of Weak Linkages on the Thermal and Oxidative Degradation of Poly (methyl methacrylate, Macromolecules, 1986, V19, p2160-2168) is known for thermal decomposition of polymethylmethacrylates produced by radical polymerization. There are three major cases: first, at low temperature, when the double bond at the end of the main chain produced by the disproportionation reaction is thermally unstable, and thermal decomposition starts, and secondly, at the low temperature. In the case where thermal decomposition is started because the tertiary bond between carbon atoms produced by the head-head stop reaction is unstable in heat, thirdly, when the temperature increases, pyrolysis starts with irregular cleavage of the main chain. Tertiary bonds between carbon atoms are most unstable in heat, and the use of chain transfer Of the double bond and the head-to reduce the generation of carbon tracking tertiary binding by the head stop reaction it was known that to improve the heat stability of poly (methyl methacrylate).

Therefore, in order to improve the optical properties and physical properties of polymethyl methacrylate, it is required to improve the defect structure that causes thermal decomposition of polymethyl methacrylate.

In order to solve the above problems, the present invention adds two radical initiators having different half-life temperatures in the presence of a chain transfer transfer agent in the polymerization step of a methyl methacrylate suspension polymer, thereby having excellent light transmittance and discoloration resistance. An object of the present invention is to provide a method for preparing methacrylate and polymethyl methacrylate having excellent light transmittance and discoloration resistance.

The above and other objects of the present invention can be achieved by the present invention described below.

In order to achieve the above object, the present invention provides 85 to 99.9 parts by weight of methyl methacrylate, alkyl acrylate, type A radical initiator, liquid dispersion medium, suspending agent, and buffer salt based on 100 parts by weight of a mixture of monomers of polymethyl methacrylate. And preparing a mixture of chain transfer transfer agents; The prepared mixture was suspended and polymerized at 60 to 70 ° C. for 30 to 130 minutes, and then heated to 70 to 120 ° C. for 35 to 55 minutes, and further suspended and polymerized for 10 to 55 minutes by addition of a type B radical initiator. Producing methacrylate beads; And washing and drying the produced polymethyl methacrylate beads, and then simply mixing the antioxidants and extruding them to prepare a polymethyl methacrylate having excellent light transmittance and discoloration resistance. To provide.

The monomer of the polymethyl methacrylate may be a methyl methacrylate monomer alone or an alkyl acrylate monomer having 1 to 8 carbon atoms of the methyl methacrylate monomer and the alkyl group.

The content of the alkyl acrylate may be 0.1 to 15 parts by weight based on 100 parts by weight of the mixture of monomers.

The type A radical initiator is a 2,2'-azobis 2,4-dimethyl-valeronitrile (2,2'-azobis (2,4-dimethyl-valeronitrile) as a radical initiator having a half-life temperature of 30 hours to 60 ° C for 10 hours. )), 2,2'-azobis 4-methoxy-2,4-dimethyl valeronitrile ((2,2'-azobis (4-methoxy-2,4-dimethyl valeronitrile)), α, α'-bis neodeca Noyl peroxy diisopropyl benzene (α, α'-bis (neodecanoyl peroxy) diisopropyl benzene), isobutyryl peroxide, cumylperoxyneodecanoate, di-normal-propyl peroxy Di-normal-propyl peroxy dicarbonate, diisopropyl peroxy dicarbonate, 1,1,3,3, -tetramethylbutyl peroxy neodecanoate (1,1,3, 3, -tetramethylbuthyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, di-2-ethoxyethyl peroxy dicarbonate peroxy dicarbonate, di-2-ethoxyhexyl dicarbonate, tertiary-hexyl peroxyneode canoate), dimethoxybutyl peroxy dicarbonate, bis 3-methyl-3methoxybutyl peroxy dicarbonate (bis (3-methyl-3-methoxybutyl) peroxy dicarbonate), tertiary-butyl peroxy Neo-tecanoate (tertiary-butyl peroxyneodecanoate), tertiary-hexylperoxypivalate, tertiary-butylperoxypivalate and 3,5,5-trimethylhexanoyl peroxide It can be selected from the group consisting of (3,5,5-trimethylhexanoyl peroxide).

The content of the type A radical initiator may be 0.01 to 5 parts by weight based on 100 parts by weight of the mixture of monomers.

The type B radical initiator is a 2,2'-azobis-isobutyronitrile (2,2'-azobis-isobutyronitrile) and a 2,2'-azobisisobuty as a radical initiator having a half-life temperature of 60 to 80 ° C for 10 hours. Ronitrile (2,2'-azobis (2-methylbutyronitrile)), dimethyl 2,2'-azobis-isobutyrate, Lauroyl peroxide, Stearoyl peroxide, Succinic peroxide, 2,5-dimethyl-2,5-bis 2-ethylhexanoylperoxy hexane (2 , 5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate (1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate) , Tertiary-hexyl peroxy-2-ethylhexanoate, tertiary-butyl peroxy-2-ethylhexanoate, 1 1,1,3,3-tetramethylbutyl peroxy 2-ethylhexanoate, benzoyl peroxide and tert-butyl peroxyiso Butyrate (tertiary-butyl peroxyisobutyrate).

The content of the type B radical initiator may be 0.001 to 1 part by weight based on 100 parts by weight of the mixture of monomers.

The chain transfer transfer agent may be selected from the group consisting of alkyl mercaptans having 1 to 12 carbon atoms in the alkyl group and having one thiol functional group, polythiol mercaptans of the following Chemical Formula 1, and mixtures thereof.

(HS-Y) _n -X

In the formula, HS is a thiol functional group, n is an integer of 2 to 6, X is a central group Glycerol, sorbitol, pentaerythritol, dipentaerythritol, tri-pentaerythritol, tri-methylolethane, trimethylolpropane ( alcohol groups such as tri-methylolpropane, pentahydroxypentane, tri-quinoyl and inositol, and Y is an alkylate having 2 to 5 carbons as a bonding group.

The alkyl mercaptan isopropyl mercaptan, normal butyl mercaptan, tertiary butyl mercaptan, normal-amyl mercaptan, normal-octyl Mercaptan (normal-octyl mercaptan) and normal-dodecyl mercaptan (normal-dodecyl mercaptan) can be selected from the group consisting of the polythiol mercaptan trimethylol ethane tris (3- mercaptopropionate) { trimethylolethane tris (3-mercaptopropionate)}, pentaerythritol tetra (3-mercaptopropionate) {pentaerythritol tetra (3-mercaptopropionate)}, pentaerythritol tetrathioglycolate, trimethylolethane trithioglycol Trimethylolethane trithioglycolate, trimethylolpropane tris {trimethylolpropane tris (3-mercaptopropionate)} and trimeth It may be selected from the group consisting of trimethylpropane trithioglycolate.

The content of the chain transfer transfer agent may be 0.01 to 10 parts by weight.

In addition, the present invention provides a polymethyl methacrylate having excellent light transmittance and discoloration resistance, which is prepared by the above methods.

Hereinafter, the present invention will be described in detail.

In the present invention, in the production of polymethyl acrylate, the chain transition in the polymethyl methacrylate polymerization step in order to prevent a decrease in the light transmittance and discoloration resistance of the suspension polymerization while using a suspension polymerization method that is beneficial for mass production by the polymerization method It is characterized by adding a type A radical initiator and a type B radical initiator in combination in the presence of a transfer agent.

That is, by mixing 85 to 99.9 parts by weight of methyl methacrylate, alkyl acrylate, type A radical initiator, liquid dispersion medium, suspending agent, buffer salt and chain transfer transfer agent with respect to 100 parts by weight of a mixture of monomers of polymethyl methacrylate. The prepared mixture was subjected to suspension polymerization at 60 to 70 ° C. for 30 to 130 minutes, and then heated to 70 to 120 ° C. for 35 to 55 minutes, and further suspension polymerization was carried out for 10 to 55 minutes by adding a type B radical initiator. After washing and drying the methyl methacrylate beads, a simple mixture of antioxidants is prepared by the extrusion process.

In the present invention, the monomer which is a raw material of the polymethyl methacrylate may be a methyl methacrylate monomer alone or a mixture of a methyl methacrylate monomer and an alkyl acrylate monomer having 1 to 8 carbon atoms in the alkyl group. The monomers are methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA) or 2-ethyl hexyl acrylate (2-EHA). Is preferably. In particular, the alkyl acrylate monomers having a methyl methacrylate of 85 to 99.9 parts by weight based on methyl methacrylate alone or 100 parts by weight of the monomer mixture, and the copolymer with the methyl methacrylate monomers based on 100 parts by weight of the monomer mixture It is preferable that it is 0.1-15 weight part, More preferably, it is 1-7 weight part. When the content of the alkyl acrylate monomer that forms the copolymer with the methyl methacrylate monomer is reduced, the thermal stability is lowered, and thus the optical properties are degraded due to the thermal decomposition of the resin generated in the thermoforming process, such as extrusion, injection, This is because an increase in the content of the alkyl acrylate monomer causes a decrease in the mechanical properties and a homogeneity of the polymethyl methacrylate, resulting in a decrease in the light transmittance.

In the present invention, in order to prevent a decrease in light transmittance and discoloration resistance caused by thermal decomposition during suspension polymerization, a type A radical initiator and a type B radical initiator are added together in the polymerization step. The method of addition is the addition of a Type A radical initiator having a half-life temperature of 30 to 60 ° C. to the mixture for the suspension polymer and initial suspension polymerization for 30 to 130 minutes at a low temperature of 60 to 70 ° C. To reduce the defect structure, to produce a polymer having improved optical properties, after the initial suspension polymerization, the temperature is raised to 70 to 120 ℃ for 35 to 55 minutes by adding a type B radical initiator having a half-life temperature of 60 to 80 ℃ Further suspension polymerization for 10 to 55 minutes increases the polymerization conversion to improve productivity and reduce the amount of residual monomers.

In the present invention, the A-type radical initiator is preferably a half-life temperature of 30 to 60 ℃, which is a triple bond of carbon generated by the head-head stop structure by performing the initial polymerization of polymethyl methacrylate at low temperature This is because it reduces the thermal decomposition of the resin, thereby reducing the thermally vulnerable structure. In addition, the type B radical initiator preferably has a half-life temperature of 60 to 80 ° C. After the A-type initiator is exhausted in the initial low temperature reaction, when the reaction temperature is increased, radicals are formed to generate the radicals to cause polymerization. Participation increases the polymerization conversion rate.

As the type A radical initiator, 2,2'-azobis 2,4-dimethyl-valeronitrile (2,2'-azobis (2,4-dimethyl-valeronitrile)), 2,2'-azobis 4-methoxy-2,4-dimethyl valeronitrile ((2,2'-azobis (4-methoxy-2,4-dimethyl valeronitrile)), α, α'-bis neodeca Noyl peroxy diisopropyl benzene (α, α'-bis (neodecanoyl peroxy) diisopropyl benzene), isobutyryl peroxide, cumyl peroxyneodecanoate, di-normal-propyl peroxy Di-normal-propyl peroxy dicarbonate, diisopropyl peroxy dicarbonate, 1,1,3,3, -tetramethylbutyl peroxy neodecanoate (1,1,3 , 3, -tetramethylbuthyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, di-2-ethoxyethyl peroxy dicarbonate (di-2- ethoxyethyl peroxy dicarbonate, di-2-ethoxyhexyl dicarbonate, tertiary-hexyl peroxyneod ecanoate, dimethoxybutyl peroxy dicarbonate, bis 3-methyl-3methoxybutyl peroxy dicarbonate (bis (3-methyl-3-methoxybutyl) peroxy dicarbonate), tertiary-butyl peroxy Neotecanoate (tertiary-butyl peroxyneodecanoate), tertiary-hexylperoxypivalate, tertiary-butylperoxypivalate, 3,5,5-trimethylhexanoyl peroxide (3,5,5-trimethylhexanoyl peroxide) etc. are mentioned.

The content of the type A radical initiator is preferably 0.01 to 5 parts by weight, more preferably 0.1 to 0.2 parts by weight based on 100 parts by weight of the mixture of monomers.

As the type B radical initiator, 2,2'-azobis-isobutyronitrile, 2,2'-azobisisobutyronitrile (2,2'-azobis (2- methylbutyronitrile)), dimethyl 2,2'-azobis-isobutyrate, Lauroyl peroxide, stearoyl peroxide, succinic peroxide, 2,5-dimethyl-2,5-bis 2-ethylhexanoylperoxy hexane (2 , 5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate (1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate) , Tertiary-hexyl peroxy-2-ethylhexanoate, tertiary-butyl peroxy-2-ethylhexanoate, 1 1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, benzoyl peroxide, tert-butyl peroxyisobutyrate (tertiary-butyl peroxyisobutyrate).

The content of the type B radical initiator is preferably 0.001 to 1 parts by weight, more preferably 0.01 to 0.2 parts by weight based on 100 parts by weight of the mixture of monomers.

In addition, the present invention uses a chain transfer agent to control the molecular weight and improve the thermal stability of polymethyl methacrylate, the molecular weight can be controlled by the amount of the initiator, the polymerization reaction by a chain transfer agent When this is stopped, the end of the chain becomes saturated hydrocarbon, and when the chain transfer transfer agent is not used, the bond strength is stronger than the end of the chain having a double bond by disproportionation, so that it has a more stable structure to heat and thus the light of methyl methacrylate resin There is an effect of improving the properties.

Examples of the chain transfer transfer agent include alkyl mercaptans having 1 to 12 carbon atoms in the alkyl group and one thiol functional group, or polythiol mercaptans represented by the following general formula (1).

[Formula 1]

(HS-Y) _n -X

In Formula 1, HS is a thiol functional group, n is an integer of 2 to 6, X is a central group Glycerol, sorbitol, pentaerythritol, dipentaerythritol, tri-pentaerythritol, tri-methylolethane, trimethylolpropane ( alcohol groups such as tri-methylolpropane, pentahydroxypentane, tri-quinoyl and inositol, and Y is an alkylate having 2 to 5 carbons as a bonding group.

As the alkyl mercaptan, isopropyl mercaptan, normal butyl mercaptan, tertiary butyl mercaptan, normal-amyl mercaptan, and normal- Octyl mercaptan (normal-octyl mercaptan), normal-dodecyl mercaptan (normal-dodecyl mercaptan), etc. are mentioned, As a polythiol mercaptan, trimethylol ethane tris (3- mercaptopropionate) {trimethylolethane tris (3-mercaptopropionate)}, pentaerythritol tetra (3-mercaptopropionate), pentaerythritol tetrathioglycolate, trimethylolethane trithioglycolate (3-mercaptopropionate) trimethylolethane trithioglycolate), trimethylolpropane tris (3-mercaptopropionate), trimethylol propane trigly Rate (trithioglycolate trimethylpropane), and the like.

The content of the chain transfer transfer agent is preferably 0.01 to 10 parts by weight.

In addition, in the present invention, in order to improve the optical properties of polymethyl methacrylate, an antioxidant that serves as an antioxidant during thermal processing is added, and as an antioxidant, tris- (nonylphenyl) phosphite (tris- (nonylphenyl) ) phosphite}, tris (2,4-di-tertiary-butylphenyl) phosphite {tris (2,4-di-tertiary-butylphenyl) phosphite}, distearyl pentaerythritol disphosphite, Tris (2-tertiary alkylaryl) phosphates, (1,1'biphenyl) -4,4-diylbisphosphonate tetrakis (2,4-bis (1,1-dimethylethyl) phenyl) ester [(1,1'biphenyl) -4,4-diylbisphosphonous acid tetrakis {2,4-bis (1,1-dimethylethyl) phenyl} ester], aryl di (2- Aryl di (2-alkylaryl) phosphonites), bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite {bis (2,4-di-tertiary-butylphenyl) pentaerythritol-diph osphite},

{Bis (2,6-di-tertiary-butyl-4-methylphenyl) pentaerythio} diphosphite [{bis (2,6-di-tertiary-butyl-4-methylphenyl) pentaerythio} di-phosphite]

Tetrakis (2,4-di-tertary butylphenyl) 4,4'-biphenylylene diphosphonite} and the like are suitable.

In the present invention, the polymerized polymethyl methacrylate is prepared in the form of beads by a suspension polymerization process, and the suspending agent used during the suspension synthesis process is an aqueous solution in which a copolymer of methyl methacrylate-methacrylic acid is saponified with NaOH. 0.6 to 1.5 parts by weight is preferable with respect to 100 parts by weight of the mixture of monomers, and it is preferable to use 0.01 to 0.5 parts by weight of phosphate as a buffer salt to maintain a neutral pH.

The present invention will be described in more detail with reference to the following examples. However, an Example is for illustrating this invention and is not limited only to these.

In addition, the present invention provides a polymethyl methacrylate excellent in light transmittance and discoloration resistance, characterized in that it is produced by the above methods.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to the examples.

Example 1

96 parts by weight of methyl methacrylate, 4 parts by weight of methyl acrylate and 2,2'azobis 2,4-dimethyl-valeronitrile {2,2'azobis (2), which is a type A initiator, based on 100 parts by weight of the monomer mixture. , 4-dimethyl-valeronitrile), 0.1 parts by weight of ADV}, 133 parts by weight of water, 0.82 parts by weight of an aqueous solution in which a copolymer of methyl methacrylate-methacrylic acid as a suspension is saponified with NaOH, and sodium dihydrogen phosphate as a buffer salt. A mixture was prepared by mixing 0.098 parts by weight, 0.053 parts by weight of disodium hydrogen phosphate and 0.33 parts by weight of normal-octylmercaptan (NOM) as a chain transfer transfer agent. The prepared mixture was suspended and polymerized for 120 minutes at an initial reaction temperature of 60 ° C., and then heated up to 105 ° C. for 50 minutes to form 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate as a B-type initiator. 0.03 parts by weight of (1,1,3,3-tetramethylbutyl peroxy 2-ethyl hexanoate, TMPO) was added for 40 minutes to suspension polymerization to produce polymethyl methacrylate beads, which are polymer beads.

The resulting polymer beads were washed with distilled water at 60 ° C. in a centrifuge, then transferred to a drier, and dried by injecting 7.5 m 3 / hr of air at 120 ° C. in which moisture and dust were filtered. The resulting polymer beads had an average particle size of 200 μm and a polymerization conversion of 99.95 wt%. The average particle size was measured by a particle size distribution analyzer, and the polymerization conversion rate was extracted by reprecipitation using chloroform (CHCl ₃ ) and methanol from the polymerized beads and quantitatively analyzed by GC / MSD by internal standard method. .

The number average molecular weight and the weight average molecular weight were made from polymer laboratories (Polymer Laboratories) as polymethyl methacrylate as a standard sample, and tetrahydrofuran (Tetrahydrofuran, THF) as an eluent in gel permeation chromatography (GPC). ) Was measured while flowing at a rate of 1 ml / min, and the results are shown in Table 1.

100 parts by weight of suspension-polymerized polymethylmethacrylate beads and tris (2,4-di-tertiary-butylphenyl) phosphite (TP) 0.2 as an antioxidant After mixing the weight parts by simply mixing into the hopper, after melting the screw at a temperature of 245 ° C in a coaxial fully screwed twin screw extruder with a diameter of 32 mm and a length of 1152 mm, it is stranded from the extruder nozzle and passed through a cooling water tank. It was cut by a cutter and pelletized.

Pelletized polymethacrylate was injection molded into a sheet having a dimension of 150 × 80 × 4 mm at an injection temperature of 230 ° C. and a mold temperature of 60 ° C. by the ASTM D1003 method in the visible light region of 380 to 780 nm in a thickness direction of 150 mm. The light transmittance (% T) was measured and the yellowing index (YI) was measured by the ASTM D1925 method. The light transmittance was averaged by the total number of measured values by combining the transmittances measured at 5 nm intervals in the visible region, and the light transmittance and the yellowing index were performed on five specimens and averaged. The results are shown in Table 2.

[Examples 2 to 9 and Comparative Examples 1 to 8]

The same method as in Example 1 was carried out for the dispersion, suspension, antioxidant and other conditions except that monomers, type A radical initiators, type B radical initiators, chain transfer transfer agents, antioxidants and polymerization conditions were adopted as shown in Table 1 below. After preparing the polymethyl methacrylate, the physical properties are shown in Table 2 below.

division Polymer composition (parts by weight) Polymerization condition Monomer Type A radical initiator Type B radical initiator Chain transfer transfer agent Antioxidant MMA / MA ADV TBPO TMPO LPO BPO NOM TBM ETM TP Example One 96/4 0.1 - 0.03 - - 0.33 - - 0.2 (end) 2 96/4 0.2 - 0.03 - - 0.58 - - 0.2 (end) 3 94/6 - 0.2 - 0.03 - 0.33 - - 0.2 (end) 4 97.5 / 2.5 0.1 - 0.03 - - - 0.12 - 0.2 (end) 5 97.5 / 2.5 0.1 - 0.03 - - - 0.30 - 0.2 (end) 6 97.5 / 2.5 0.1 - 0.03 - - - 0.50 - 0.2 (end) 7 95/5 0.15 - 0.05 - - - - 0.7 0.2 (All) 8 95/5 0.15 - - 0.05 - - - 0.7 0.2 (All) 9 95/5 0.15 - - - 0.05 - - 0.7 0.2 (All) Comparative example One 96/4 - - 0.13 - - 0.33 - - 0.2 (I) 2 96/4 - - - 0.13 - 0.33 - - 0.2 (I) 3 96/4 - - - - 0.13 0.33 - - 0.2 (I) 4 94/6 - 0.2 - 0.13 - 0.33 - - 0.2 (I) 5 97.5 / 2.5 0.1 - 0.03 - - - - - 0.2 (end) 6 95/5 0.2 - - - - - - 0.7 0.2 (All) 7 95/5 0.2 - - - - - - 0.7 0.2 (All) 8 95/5 0.2 - - - - - - 0.7 0.2 (All) MMA / MA: ratio of methyl methacrylate / methyl as a monomer of polymethyl methacrylate ADV: 2,2'-azobis 2,4-dimethyl-valeronitrile {2,2'-azobis (2,4- dimethyl-valeronitrile)} TBPO: tertiary-butyl peroxyneodecanoateTMPO: 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate (1,1,3 , 3-tetramethylbutyl peroxy 2-ethyl hexanoate) LPO: lauroyl peroxide BPO: benzoyl peroxide NOM: normal-octylmercatpan TBM: tert-butyl mercaptan (tertiary-butyl mercaptan) ETM: pentaerythritol tetra (3-mercaptopropionate), a polythiol metcaptan {pentaerythritol tetra (3-mercaptopropionate)} TP: tris (2,4-di-tertiary-butylphenyl Phosphite {tris (2,4-di-tertiary-butylphenyl) phosphite} (A): Polymerized at 60 ° C for 120 minutes, then heated to 105 ° C for 50 minutes, and further polymerized for 40 minutes (B): 82 ° C. After standing polymerization for 60 minutes, the temperature was raised for 50 minutes to 150 ℃ additional polymerization for 40 minutes (c): On the 60 ℃ polymerization for 100 minutes. The temperature was raised to 103 ℃ for 40 minute polymerization for 50 minutes

division Properties Weight average molecular weight (Mw) Number average molecular weight (Mn) Molecular Weight Distribution (Mw / Mn) Light transmittance (% T) Yellowness Index (YI) Example One 94000 54000 1.74 87.5 2.39 2 73000 41000 1.78 87.7 2.40 3 71000 42000 1.69 87.3 2.45 4 165000 93000 1.77 87.1 2.50 5 89000 51000 1.75 87.7 2.45 6 62000 35000 1.77 87.6 2.42 7 88000 51000 1.73 87.7 2.41 8 90000 53000 1.70 87.4 2.45 9 89000 52000 1.71 87.5 2.43 Comparative example One 100000 56000 1.77 85.9 2.83 2 99000 50000 1.78 86.0 2.81 3 119000 67600 1.76 85.7 2.89 4 68000 36000 1.79 85.8 2.75 5 264000 109000 2.42 85.2 2.99 6 92000 52000 1.77 86.4 2.63 7 97000 55000 1.76 86.1 2.66 8 101000 57000 1.77 86.0 2.76

As shown in Tables 1 and 2, Examples 1 to 2 show that the light transmittance and the yellowing index are higher than those of Comparative Examples 1 to 3, in which no A-type radical initiator is added and the initial polymerization temperature is not adjusted to low temperature. Can be.

In addition, Example 3 is more effective than Comparative Example 4 in which the initial polymerization temperature is not controlled to a lower temperature, Examples 4 to 6 are better than Comparative Example 5 in which no chain transfer agent is added, and Examples 7 to 9 are added to the type B radical initiator. It can be seen that the light transmittance and yellowing index are higher than those of Comparative Examples 6 to 8 which are not.

As described above, the method for preparing a polymethyl methacrylate having excellent light transmittance and discoloration resistance according to the present invention is a type A radical initiator and a B radical initiator in the presence of a chain transfer transfer agent in the suspension polymerization step of polymethyl methacrylate. It is a useful invention which improves permeability and discoloration resistance by suppressing thermal decomposition of resin by adding together a type radical initiator.

While the invention has been described in detail above with reference to the described embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope and spirit of the invention, and such modifications and variations fall within the scope of the appended claims. It is also natural.

Claims (11)

A mixture of 85 to 99.9 parts by weight of methyl methacrylate, an alkyl acrylate, a type A radical initiator, a liquid dispersion medium, a suspending agent, a buffer salt, and a chain transfer transfer agent with respect to 100 parts by weight of a mixture of monomers of polymethyl methacrylate is prepared. Preparing; The prepared mixture was suspended and polymerized at 60 to 70 ° C. for 30 to 130 minutes, and then heated to 70 to 120 ° C. for 35 to 55 minutes, and further suspended and polymerized for 10 to 55 minutes by addition of a type B radical initiator. Producing methacrylate beads; And Method for producing a polymethyl methacrylate having excellent light transmittance and discoloration resistance, characterized in that it comprises a step of washing the resulting polymethyl methacrylate beads, drying and simply mixing the antioxidant and extrusion processing. The method of claim 1, The polymethyl methacrylate having excellent light transmittance and discoloration resistance, wherein the polymethyl methacrylate monomer is a methyl methacrylate monomer alone or an alkyl acrylate monomer having 1 to 8 carbon atoms of a methyl methacrylate monomer and an alkyl group. Method for preparing methacrylate. The method of claim 1, The method of producing a polymethyl methacrylate having excellent light transmittance and discoloration resistance, characterized in that the content of the alkyl acrylate is 0.1 to 15 parts by weight based on 100 parts by weight of the mixture of monomers. The method of claim 1, The type A radical initiator has a 2,2'-azobis 2,4-dimethyl-valeronitrile (2,2'-Azobis (2,4-dimethyl-valeronitrile) as a radical initiator having a half-life temperature of 30 hours to 60 ° C for 10 hours. )), 2,2'-azobis 4-methoxy-2,4-dimethyl valeronitrile ((2,2'-azobis (4-methoxy-2,4-dimethyl valeronitrile)), α, α'-bis neodeca Noyl peroxy diisopropyl benzene (α, α'-bis (neodecanoyl peroxy) diisopropyl benzene), isobutyryl peroxide, cumyl peroxyneodecanoate, di-normal-propyl peroxy Di-normal-propyl peroxy dicarbonate, diisopropyl peroxy dicarbonate, 1,1,3,3, -tetramethylbutyl peroxy neodecanoate (1,1,3 , 3, -tetramethylbuthyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, di-2-ethoxyethyl peroxy dicarbonate (di-2- ethoxyethyl peroxy dicarbonate, di-2-ethoxyhexyl dicarbonate, tertiary-hexyl peroxyneod ecanoate), dimethoxybutyl peroxy dicarbonate, bis 3-methyl-3methoxybutyl peroxydicarbonate (bis (3-methyl-3-methoxybutyl) peroxy dicarbonate), tertiary-butyl peroxy neo Tertiary-butyl peroxyneodecanoate, tertiary-hexylperoxypivalate, tertiary-butylperoxypivalate and 3,5,5-trimethylhexanoyl peroxide ( 3,5,5-trimethylhexanoyl peroxide) is a method for producing a polymethyl methacrylate excellent in light transmission and discoloration resistance, characterized in that selected from the group consisting of. The method of claim 1, The content of the type A radical initiator is 0.01 to 5 parts by weight with respect to 100 parts by weight of a mixture of monomers, the method of producing polymethyl methacrylate excellent in light transmittance and discoloration resistance. The method of claim 1, 2,2'-azobis-isobutyronitrile (2,2'-azobis-isobutyronitrile) and 2,2'-azobisisobuty are radical initiators having a type B radical initiator having a half-life temperature of 60 to 80 ° C for 10 hours. Ronitrile (2,2'-azobis (2-methylbutyronitrile)), dimethyl 2,2'-azobis-isobutyrate, Lauroyl peroxide, stearoyl peroxide, succinic peroxide, 2,5-dimethyl-2,5-bis 2-ethylhexanoylperoxy hexane (2 , 5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate (1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate) , Tertiary-hexyl peroxy-2-ethylhexanoate, tertiary-butyl peroxy-2-ethylhexanoate, 1 1,1,3,3-tetramethylbutyl peroxy 2-ethylhexanoate, benzoyl peroxide and tert-butyl peroxyiso Method for producing a polymethyl methacrylate excellent in light transmittance and discoloration resistance, characterized in that selected from the group consisting of butyrate (tertiary-butyl peroxyisobutyrate). The method of claim 1, The content of the type B radical initiator is 0.001 to 1 part by weight based on 100 parts by weight of a mixture of monomers, the method of producing a polymethyl methacrylate excellent in light transmission and discoloration resistance. The method of claim 1, Light-transmitting, characterized in that the chain transfer transfer agent is selected from the group consisting of alkyl mercaptan having 1 to 12 carbon atoms of alkyl group and having one thiol functional group, polythiol mercaptan of Formula 1 below, and mixtures thereof And a method for producing polymethyl methacrylate having excellent discoloration resistance. [Formula 1] (HS-Y) _n -X In the formula, HS is a thiol functional group, n is an integer of 2 to 6, X is a central group Glycerol, sorbitol, pentaerythritol, dipentaerythritol, tri-pentaerythritol, tri-methylolethane, trimethylolpropane ( alcohol groups such as tri-methylolpropane, pentahydroxypentane, tri-quinoyl and inositol, and Y is an alkylate having 2 to 5 carbons as a bonding group. The method of claim 8, The alkyl mercaptan isopropyl mercaptan, normal butyl mercaptan, tertiary butyl mercaptan, normal-amyl mercaptan, normal-octyl Mercaptan (normal-octyl mercaptan) and normal-dodecyl mercaptan (normal-dodecyl mercaptan) selected from the group consisting of, the polythiol mercaptan trimethylol ethane tris (3- mercaptopropionate) {trimethylolethane tris (3-mercaptopropionate)}, pentaerythritol tetra (3-mercaptopropionate) {pentaerythritol tetra (3-mercaptopropionate)}, pentaerythritol tetrathioglycolate, trimethylolethane trithioglycolate ( trimethylolethane trithioglycolate), trimethylolpropane tris {3-methylcappropane tris (3-mercaptopropionate)}} and trimethylol Ropan triglycidyl cholate (trimethylpropane trithioglycolate) method for producing a light-transmitting and polymethyl methacrylate in excellent discoloration resistance, characterized in that the member selected from the group consisting of. The method of claim 1, The method of producing a polymethyl methacrylate having excellent light transmittance and discoloration resistance, characterized in that the content of the chain transfer transfer agent is 0.01 to 10 parts by weight. A polymethyl methacrylate having excellent light transmittance and discoloration resistance, which is prepared by the method of any one of claims 1 to 10.