JP2007145882A - Multistage-polymerized methacrylic resin polymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multistage-polymerized methacrylic resin polymer that retains external appearances of a molded article and exhibits enhanced flow properties on injection molding and enhanced moldability in fabrication such as extrusion molding, blow molding, vacuum forming, pressure forming or stretch molding while suffering from no reduction in mechanical strength. <P>SOLUTION: The multistage-polymerized methacrylic resin polymer is a copolymer comprised of 70-99.5 wt.% of a methyl methacrylate monomer and 0.5-30 wt.% of a monomer composed of at least one other vinyl monomer copolymerizable with methyl methacrylate that is obtained by polymerizing a copolymer (A) having a weight-average molecular weight of 5,000-180,000 as measured by the gel permeation chromatography and subsequently polymerizing a copolymer (B) having a weight-average molecular weight of 80,000-800,000 in the presence of the copolymer (A) and has an average particle size of 0.1-0.5 mm. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention maintains the appearance of a molded product, improves flow characteristics in injection molding, and improves moldability in secondary processing such as extrusion molding, blow molding, vacuum, pressure molding, and stretch molding. It is related with the methacrylic resin polymer of multistage polymerization which does not reduce mechanical strength.

  Methacrylic resin is characterized by its higher light transmittance, weather resistance, and higher rigidity than other plastic transparent resins as a transparent resin, and is used for vehicle parts, lighting equipment, building materials, signboards, paintings, and windows for display devices. It is used in a wide range of applications such as nameplates.

  In recent years, for those molded products, those having extremely difficult moldability and workability have increased.For example, in the case of injection molding, when the fluidity is poor based on the enlargement and thinning, the injection pressure becomes high, There arises a problem that molding cannot be performed or molding distortion increases. For this reason, a high fluidity resin capable of lowering the injection pressure is desired. On the other hand, it is desired that the appearance, mechanical strength such as solvent resistance, and heat resistance do not decrease.

  Conventionally, as a known method for improving the mechanical strength and processability of methacrylic resins, fluidity is imparted with a low molecular weight methacrylic resin, and mechanical strength is imparted with a high molecular weight or a micro-crosslinked structure. Techniques have been reported in which high molecular weight or low molecular weight methacrylic resins that impart processability in a mixed state are melt-mixed or molecular weight distribution is expanded using a branched structure (for example, see Patent Documents 1 and 2). .

  However, with this method, methacrylic resins having different molecular weights cannot be uniformly melt-mixed in an extruder or injection molding machine because of their different viscosities, and methacrylic resins having a high molecular weight are partially dispersed. There is a defect in which defects exist and the surface appearance deteriorates. Further, in the method using micro-crosslinking using a polyfunctional monomer, it is very difficult to control the polyfunctional monomer, and when it is too much, the mixing uniformity is lowered and the appearance of the molded product is lowered. Too little will have no effect.

  In order to improve such a problem, there is a technique for obtaining methacrylic resins having different molecular weights by multistage polymerization.

  However, when the inner layer has a higher molecular weight than the outer layer, the high molecular weight of the inner layer cannot be dispersed when processed (see Patent Documents 3 and 4). Moreover, even if the inner layer has a lower molecular weight than the outer layer, if the ratio of methyl methacrylate is low, heat resistance and permeability are reduced (see Patent Document 5).

Japanese Patent Publication No. 1-2865 Japanese Patent Laid-Open No. 9-207196 JP-A-6-41387 JP-A-7-196882 JP-A-3-37255

  As described above, the present invention maintains the appearance of the molded product, improves flow characteristics in injection molding, and improves moldability in secondary processing such as extrusion molding, blow molding, vacuum, pressure molding, and stretch molding. On the other hand, the present invention relates to a methacrylic resin polymer of multi-stage polymerization that does not reduce mechanical strength.

  As a result of earnest research to solve these problems, the molecular weight and molecular weight difference between the first and second stages are within a certain range, and the weight ratio of the first and second stages is optimized according to the molecular weight difference. By using a multi-stage polymerization methacrylic resin polymer, the flow characteristics in injection molding are improved while maintaining the appearance of the molded product, and extrusion, blow molding, secondary processing such as vacuum and pressure molding, etc. It has been found that the mechanical strength is improved while improving the formability of the steel.

That is, the invention according to claim 1 is a monomer comprising 0.1 to 99.5 wt% of methyl methacrylate monomer and at least one other vinyl monomer copolymerizable with methyl methacrylate. After copolymerizing a copolymer (A) having a weight average molecular weight of 50,000 to 180,000 as measured by gel permeation chromatography, ) And a methacrylic resin polymer obtained by polymerizing the copolymer (B) having a weight average molecular weight of 80,000 to 800,000, and having an average particle diameter of 0.1 mm to 0.5 mm, and A methacrylic resin polymer of multistage polymerization satisfying the following (1) to (3).
(Weight average molecular weight of copolymer (B)) − (Weight average molecular weight of copolymer (A)) ≧ 10,000 (1)
(Weight average molecular weight of copolymer (B)) − (weight average molecular weight of copolymer (A)) ≦ 200,000 (weight ratio of copolymer (A)): (copolymer (B) Weight ratio) = 5: 95 to 50:50 (2)
(Weight average molecular weight of copolymer (B))-(weight average molecular weight of copolymer (A))> 200,000 (weight ratio of copolymer (A)): (copolymer (B) Weight ratio) = 20: 80 to 80:20 (3)

  The invention according to claim 2 is the methacrylic resin polymer of multistage polymerization according to claim 1, which is obtained by two-stage polymerization by suspension polymerization or emulsion polymerization.

  In the multistage polymerization methacrylic resin polymer of the present invention, the appearance of the molded product can be maintained, the flow characteristics in injection molding can be improved, and extrusion molding, blow molding, vacuum, pressure molding, While improving the formability in secondary processing such as stretch molding, it does not reduce the mechanical strength.

  Hereinafter, the present invention will be described in more detail. The composition of the copolymer (A) and the copolymer (B) in the present invention includes 70 to 99.5 wt% of methyl methacrylate monomer. If it is less than 70 wt%, heat resistance and optical performance are insufficient, and if it is 99.5 wt% or more, thermal stability is insufficient. Especially preferably, it is 85-99 wt%.

  Further, the weight percentage of the amount of methyl methacrylate alone constituting the copolymer (A) when the copolymer (A) is 100 wt% and the copolymer when the copolymer (B) is 100 wt% ( The difference in weight percentage of the methyl methacrylate monomer constituting B) is preferably within 15 wt%. By making it within 15 wt%, the refractive index of the copolymer (A) and the copolymer (B) becomes close, and the optical properties of the obtained methacrylic resin polymer can be maintained, which is preferable. More preferably, it is within 10 wt%.

  Examples of the other vinyl monomer copolymerizable with methyl methacrylate used in the copolymer (A) and the copolymer (B) in the present invention include alkyl methacrylates having 2 to 18 alkyl groups and alkyl groups. In addition to alkyl acrylates having 2 to 18 carbon atoms, α, β-unsaturated acids such as acrylic acid and methacrylic acid, unsaturated group-containing divalent carboxylic acids such as maleic acid, fumaric acid and itaconic acid, and alkyls thereof. Aromatic vinyl compounds such as esters, styrene, α-methylstyrene, and nucleus-substituted styrene, vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, etc., and ethylene glycol di (meth ) Acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate Rate, ethylene glycol such as tetraethylene glycol di (meth) acrylate, or the oligomers of both end hydroxyl groups esterified with acrylic acid or methacrylic acid: two such as neopentyl glycol di (meth) acrylate and hexanediol dimethacrylate Ester of hydroxyl group of acrylic acid with acrylic acid or methacrylic acid: ester of polyhydric alcohol derivative such as trimethylolpropane or pentaerythritol with acrylic acid or methacrylic acid: polyfunctional monomer such as divinylbenzene These can be used alone or in combination of two or more. Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferably used from the viewpoints of light resistance, heat stability, heat resistance, and fluidity. , Methyl acrylate, ethyl acrylate, and n-butyl acrylate are particularly preferable.

  The average particle diameter of the multistage polymerization methacrylic resin polymer obtained in the present invention is 0.1 mm to 0.5 mm. If it is smaller than 0.1 mm, it will be in a powder state and will float in the air. If it is larger than 0.5 mm, the dispersibility of the second-stage high-molecular-weight copolymer (B) is lowered, which is not preferable. The average particle diameter can be obtained by classification using a sieve based on JIS-Z8801 and calculating particles having a weight of 50 wt%. The shape is not particularly limited, but a substantially spherical shape is preferable because of good handling and uniformity.

The weight average molecular weight of the copolymer (A) in the present invention is preferably from 50,000 to 180,000, and the weight average molecular weight of the copolymer (B) is preferably from 80,000 to 800,000. In addition, the copolymer (A) is the first stage, the copolymer (B) is the second stage,
(Weight average molecular weight of copolymer (B)) − (Weight average molecular weight of copolymer (A)) ≧ 10,000 (1)
It is. It is very important in the present invention that the copolymerization (A) has a lower molecular weight than the copolymerization (B). If the copolymerization (A) has a high molecular weight, the homogeneity at the time of melt-mixing will soon be increased. It will fall and a defective appearance of the molded product will occur. The copolymer (A) is a part resulting from fluidity, the copolymer (B) is a part resulting from mechanical strength, and the mixed state of the copolymer (A) and the copolymer (B) is Due to workability. When the difference in polymerization average molecular weight between the copolymer (A) and the copolymer (B) is 10,000 or less, there is no effect. The polymerization average molecular weight difference is preferably 50,000 or more, and more preferably the polymerization average molecular weight difference is 70,000 or more. Further, the copolymer (A) having a weight average molecular weight of less than 50,000 is not preferable because it cannot be stably polymerized. On the other hand, if it is larger than 180,000, the fluidity is greatly lowered, which is not preferable. More preferably, it is 10,000-150,000, More preferably, it is 20,000-120,000. On the other hand, if the weight average molecular weight of the copolymer (B) is less than 80,000, the mechanical strength is not good. On the other hand, if it exceeds 800,000, melt dispersibility cannot be obtained, and it is not good because it is difficult to obtain stability during polymerization. More preferably, it is 90,000-500,000, More preferably, it is 100,000-400,000.

  The weight average molecular weight measured in the present invention is measured by gel permeation chromatography. Using a standard methacrylic resin that has a narrow molecular weight distribution and a known molecular weight and is available as a reagent in advance, a calibration curve can be created from the elution time and molecular weight, and the molecular weight of each sample can be measured from the calibration curve.

  Copolymer (A) monomer composition and weight average molecular weight range and copolymer (B) monomer composition and weight average molecular weight range are one copolymer each, May be plural. In the case of a plurality of, for example, when there are two or more copolymers in the composition and weight average molecular weight range of the copolymer (A), the average monomer composition is the composition of the copolymer (A). Yes, the average weight average molecular weight is the weight average molecular weight of the copolymer (A). The same applies to the copolymer (B).

  In the present invention, the weight ratio of the copolymer (A) and the copolymer (B) is determined by the weight average molecular weight difference.

(Weight average molecular weight of copolymer (B)) − (Weight average molecular weight of copolymer (A)) ≦ 200,000 (weight ratio of copolymer (A)): (copolymer (B) (Weight ratio) = 5: 95-50: 50 (2)
(Weight average molecular weight of copolymer (B))-(Weight average molecular weight of copolymer (A))> 200,000 (weight ratio of copolymer (A)): (copolymer (B) (Weight ratio) = 20: 80 to 80:20 (3)

  When the difference in weight average molecular weight between the copolymer (B) and the copolymer (A) is 200,000 or less, the weight ratio of the copolymer (A) is 5 wt% to 50 wt%, and the copolymer (B) Is 95 wt% to 50 wt%. If the copolymer (A) is less than 5 wt%, the mixing ratio is small, so there is no effect. When the copolymer (B) is less than 50 wt%, the mechanical strength is lowered, which is not good. More preferably, (weight ratio of copolymer (A)) :( weight ratio of copolymer (B)) is 10:90 to 50:50, more preferably 10:90 to 40:60. .

  On the other hand, when the weight average molecular weight difference between the copolymer (B) and the copolymer (A) in the present invention is larger than 200,000, the viscosity difference increases, and the uniform dispersibility varies depending on the weight ratio. . The weight ratio of the copolymer (A) is 20 wt% to 80 wt%, and the copolymer (B) is 80 wt% to 20 wt%. If the copolymer (A) or the copolymer (B) is less than 20 wt%, the dispersibility of the copolymer (B) is lowered in both cases, and the appearance defect is not good in the molded product. Preferably, (weight ratio of copolymer (A)) :( weight ratio of copolymer (B)) is 10:90 to 90:10. More preferably, it is 30: 70-70: 30.

  The method for producing a methacrylic resin polymer for multistage polymerization in the present invention is not particularly limited, and specifically,

1. Copolymer (A) is polymerized in advance, and the specified amount of copolymer (A) already obtained is added to and mixed with the specified amount of monomer for polymerizing the remaining copolymer (B). Then, by carrying out a polymerization reaction, the ratio and molecular weight of each are controlled to produce.

2. A method for producing by copolymerizing the copolymer (A) in advance and then adding the raw material composition mixture of the copolymer (B) at once or sequentially.
Is mentioned.

  Particularly preferably, This method is preferable because the respective compositions of the copolymer (A) and the copolymer (B) can be easily controlled, and a multilayer structure can be stably obtained. As a polymerization method therefor, a suspension polymerization method or an emulsion polymerization method can be used. Either is preferred.

  As a polymerization initiator for producing the copolymer (A) and the copolymer (B) in the present invention, when using free radical polymerization, di-t-butyl peroxide, dilauroyl peroxide, t- Peroxides such as butyl peroxy 2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane And general azo-based radical polymerization initiators such as azobisisobutyronitrile, azobisisovaleronitrile, 1,1-azobis (1-cyclohexanecarbonitrile) can be used, either alone or Two or more types may be used in combination. A combination of these radical initiators and an appropriate reducing agent may be used as a redox initiator. These initiators are generally used in the range of 0.001 to 1 wt% with respect to the monomer mixture.

  In order to adjust the molecular weight of the copolymer (A) and the copolymer (B) in the present invention, a chain transfer agent that is generally used can be used in the case of producing by radical polymerization. Examples of the chain transfer agent include n-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris (thioglycolate), pentaerythritol tetrakis (thioglycolate). Etc.) are preferably used. Generally, it is generally used in the range of 0.001 to 1 wt% with respect to the monomer mixture.

  In order to obtain a methacrylic resin polymer of multistage polymerization in the present invention, a dye, pigment, heat stabilizer such as hindered phenol or phosphate, benzotriazole, 2-hydroxybenzophenone, phenyl salicylate as necessary UV absorbers such as ester, plasticizers such as phthalate ester, fatty acid ester, trimellitic acid ester, phosphate ester, and polyester, higher fatty acid, higher fatty acid ester, higher fatty acid mono, di, or Release agents such as triglycerides, lubricants such as higher fatty acid esters and polyolefins, antistatic agents such as polyethers, polyetheresters, polyetheresteramides, alkylsulfonates, alkylbenzenesulfonates, phosphorus Flame retardants such as phosphorus / chlorine and phosphorus / bromine In order to prevent glare of reflected light, organic light diffusing agents such as methyl methacrylate / styrene copolymer beads, inorganic light diffusing agents such as barium sulfate, titanium oxide, calcium carbonate, talc, etc. An acrylic rubber or the like obtained by polymerization may be used. When these additives are blended, it can be carried out by a known method. For example, a method in which an additive is dissolved in a monomer mixture in advance and polymerized is used.

  The multistage polymerization methacrylic resin polymer in the present invention may be used alone or in combination with another resin. In the case of mixing, the mixture may be blended and heated and melted and mixed with an extruder, an injection molding machine or the like, or the pellets heated and mixed with an extruder may be used. The additives mentioned above may be blended and mixed at this time.

  The methacrylic resin polymer obtained in the present invention may be used as it is for molding processing such as injection molding or extrusion molding, or may be used after being transformed into a shape such as pellets. Further, a plurality of methacrylic resin polymers of the present invention having different compositions may be combined, or may be combined with an existing methacrylic resin. As a combination method, they may be used after blending or may be compounded once by an extruder and pelletized.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The unit displayed in parts represents parts by weight.

1. Measurement of weight average molecular weight of methacrylic resin Tosoh Corporation gel permeation chromatography (HLC-8120 + 8020) column and Tosoh TSK Super HH-M (2) + Super H2500 (1) are arranged in series. Performed by RI, 0.02 g of methacrylic resin was dissolved in 20 cc of a THF solvent, and the elution time and strength were measured at an injection amount of 10 ml and a development flow rate of 0.3 ml / min. The weight average molecular weight was determined based on a calibration curve using a methacrylic resin having a known monodispersed weight average molecular weight made by GL Science as a standard sample. The weight average molecular weight of the mixture was determined by subtracting the weight average molecular weight of any single substance from the weight average molecular weight of the mixture to obtain the weight average molecular weight and the ratio of the remaining simple substance of the mixture.

2. Measurement of average particle diameter JTS-200-45-33 (aperture 500 μm), 34 (aperture 425 μm), 35 (aperture 355 μm), 36 (aperture 300 μm), 37, based on JIS-Z8801 (Apertures 250 μm), 38 (apertures 150 μm) 61 (catch pan) is old and the average particle size measured when sieving with vibration force MAX for 10 minutes using tester TSK B-1 The particle diameter of 50 wt% was measured to determine the average particle diameter.

3. Measurement of Melt Flow Rate Using a Toyo Seiki melt indexer F-B01, the melt flow rate was measured under conditions of 230 ° C. and a load of 3.8 kg according to the conditions of ISO 1133 cond 13.

4). Evaluation of injection pressure during injection molding A dumbbell test piece was prepared at a mold temperature of 55 ° C using a ASTM-1 dumbbell test mold at a barrel temperature of 230 ° C using a Dynamelter M-70 molding machine manufactured by Meiki Seisakusho. The pressure was increased at a speed of 30 cc / sec until the short shot point could be filled, and a molded product was prepared by holding pressure at the injection pressure +20 MPa for 10 sec, and the maximum injection pressure at the short shot point was measured.

5. 3. Evaluation of appearance of molded product In the dumbbell test piece obtained in the above, the appearance was inspected to determine whether the shape reflected by the fluorescent lamp was deformed or irregularly reflected, and the number of problems was recorded.

6). 3. Evaluation of stretch processability Using the dumbbell test piece obtained in Step 1, the test piece surface temperature was heated to 150 ° C. in an environment of 150 ° C., and then the dumbbell was uniaxially stretched at a speed of 100 mm / sec, and the stretchable magnification was measured.

7). Evaluation of solvent resistance test It evaluated by the cantilever method. The cantilever method is the aforementioned 4. The test piece 2 was cut out from the dumbbell test piece obtained in Step 1, and the test piece 2 having a length of 127 mm × 12.7 mm width × 3.2 mm thickness was cut out, and the test piece 2 was set using the fixing jig 1 under the conditions shown in FIG. Then, a load was applied using a 2 kg weight 3 using a 2 mm diameter thread 5 and the time when the test piece 2 broke at the fulcrum portion of the filter paper 4 soaked with ethanol was measured as shown in FIG. .

[Reference Example 1] (Acrylic resin polymerization of copolymer (A) only)
In a 60 L reactor, 100 parts of these in a ratio of 98 wt% methyl methacrylate and 2 wt% methyl acrylate, 0.25 parts lauryl peroxide, 0.17 parts n-octyl mercaptan, 200 parts deionized water, 0.5 parts of calcium triphosphate, 0.3 part of calcium carbonate and 0.003 part of sodium lauryl sulfate are added and mixed by stirring. Suspension polymerization is carried out at a reaction temperature of 80 ° C. for 150 minutes, followed by 60 at 92 ° C. After completion of the polymerization reaction, the polymerization reaction was substantially completed, and then cooled to 50 ° C., a mineral acid was added, washed, dehydrated and dried to obtain a bead-like methacrylic resin. The bead polymer was measured by gel permeation chromatography to obtain the resin of Reference Example 1 shown in Table 1.

[Example 1]
As a first stage in a 60 L reactor, a total of 70 parts, methyl acrylate 6 wt%, and a total of 70 parts, lauryl peroxide 0.175 parts, n-octyl mercaptan 0.193 parts Polymer (A) raw material), 200 parts of deionized water, 0.5 part of calcium triphosphate, 0.3 part of calcium carbonate and 0.003 part of sodium lauryl sulfate are added and mixed with stirring. The reaction temperature of the reactor is 80. Suspension polymerization was carried out at 150 ° C. for 150 minutes, and a small amount of the polymer was taken out. It was measured by gel permeation chromatography and confirmed to be a copolymer (A) having a weight average molecular weight of 100,000. 60 minutes after that, 30 parts of these were in a ratio of 94 wt% of methyl methacrylate and 6 wt% of methyl acrylate, which are raw materials for the second stage copolymer (B), 0.006 parts of lauryl peroxide, n -0.012 part of octyl mercaptan is charged into the reactor, followed by suspension polymerization at 80 ° C for 90 minutes, followed by aging at 92 ° C for 60 minutes to complete the polymerization reaction, and then cooling to 50 ° C. Mineral acid was added, washed and dehydrated and dried to obtain a bead-like methacrylic resin. This bead-like polymer was measured by gel permeation chromatography, and as shown in Table 1, calculated using the results of the weight average molecular weight of the previous copolymer (A), the weight average molecular weight was 100,000 and the ratio was It was confirmed that the copolymer (A) was 72 wt% and the copolymer (B) had a weight average molecular weight of 460,000 and a ratio of 28 wt%.

[Examples 2 and 3]
In Example 2, in the composition ratio of the monomers shown in Table 1, in Example 2, the monomer of the copolymer (A) was 82 parts, the amount of the raw material n-octyl mercaptan was 0.29 parts, and the copolymer (B ) Monomer and the amount of raw material n-octyl mercaptan is 0.009 parts, and in Example 3, the copolymer (A) monomer is 22 parts, and the amount of n-octyl mercaptan is Example 2 in Table 1 in the same manner as in Example 1, except that 0.176 part, the copolymer (B) monomer was 78 parts, and the amount of n-octyl mercaptan was 0.105 part. 3 methacrylic resin polymer was obtained.

[Comparative Example 1]
With the composition ratio of the monomers in Table 1, in Example 1, the order of introduction of the copolymer (A) and the copolymer (B) was reversed, so that the methacrylic group in Comparative Example 1 in Table 1 was used. A resin polymer was obtained.

[Comparative Example 2]
In the composition ratio of the monomers shown in Table 1, 17 parts of the monomer of the copolymer (A) and 0.193 parts of the raw material n-octyl mercaptan, the monomer of the copolymer (B) And a methacrylic resin polymer of Comparative Example 2 in Table 1 was obtained in the same manner as in Example 1, except that the amount of Nn-octyl mercaptan as a raw material was 0.012 part.

[Comparative Example 3]
In the same manner as in Example 1 except that the composition ratio of the monomers shown in Table 1 is 0.25 part of calcium triphosphate, 0.15 part of calcium carbonate, and 0.0015 part of sodium lauryl sulfate in Example 1. A methacrylic resin polymer of Comparative Example 3 in Table 1 was obtained.

[Comparative Example 4]
A copolymer having a weight average molecular weight of 100,000 (A) in the same manner as in Reference Example 1 except that the amount of n-octyl mercaptan in Reference Example 1 is 0.275 parts with the composition ratio of the monomers in Table 1. A methacrylic resin polymer was obtained. Next, in a 60 L reactor, a total of 100 parts in a ratio of 94 wt% methyl methacrylate and 6 wt% methyl acrylate, 0.25 parts lauryl peroxide, 0.04 parts n-octyl mercaptan, 200 deionized water 200 Part, 0.5 part of calcium triphosphate, 0.3 part of calcium carbonate and 0.003 part of sodium lauryl sulfate were added and mixed by stirring, followed by suspension polymerization at a reaction temperature of 80 ° C. for 150 minutes, followed by 92 ° C. The mixture was aged for 60 minutes to substantially complete the polymerization reaction, then cooled to 50 ° C., charged with mineral acid, washed and dehydrated and dried to obtain a bead-like methacrylic resin. This bead-shaped polymer was measured by gel permeation chromatography to obtain a methacrylic resin polymer as a copolymer (B) having a weight average molecular weight of 460,000 shown in Table 1. These were mixed by a tumbler at a ratio of 28 wt% of the copolymer (A) and 72 wt% of the copolymer (B) to obtain a methacrylic resin composition of Comparative Example 4 shown in Table 1.

[Example 4]
In the composition ratio of the monomers shown in Table 1, 10 parts of the copolymer (A) monomer and 0.53 parts of the raw material n-octyl mercaptan in Example 1 were prepared. The methacrylic resin polymer of Example 4 shown in Table 1 was obtained in the same manner as in Example 1 except that 90 parts of the monomer and the amount of raw material n-octyl mercaptan were 0.113 parts.

[Comparative Example 5]
Resin of Comparative Example 5 in Table 1 in the same manner as in Reference Example 1 except that the composition ratio of the monomers in Table 1 and the amount of n-octyl mercaptan as a raw material in Reference Example 1 is 0.45 parts. Got.

  The average particle diameter of the methacrylic resin obtained in Reference Example 1, Examples 1 to 3, Comparative Examples 1 to 4, Example 4, and Comparative Example 5 was determined. The results are shown in Table 2.

  Thereafter, each methacrylic resin polymer was extruded with a 30 mmφ single-screw extruder at 250 ° C., pelletized, and pellets for injection molding were produced. These pellets were used for injection molding to produce dumbbell test pieces, and the injection pressure, appearance of the molded product, stretch workability, and solvent resistance were evaluated. The results are shown in Table 2.

  Whether the methacrylic resins of Examples 1 to 3 and Comparative Examples 1 to 4 having different weight average molecular weights with respect to the acrylic resin of Reference Example 1 have the same or lower melt flow rate but the same injection pressure. Alternatively, molding can be performed even when the thickness is lowered, and no distortion remains during molding. Further, in the stretch processability, in Reference Example 1, it was possible to stretch only up to 320%, and it broke at more than that, but none of them broke even when stretched at 500% or more.

  In addition, regarding the solvent resistance, the test piece in Reference Example 1 was broken in 80 seconds, whereas both the Examples and Comparative Examples had equivalent or higher durability. However, in Examples 1 to 3, there was no defect in the appearance of the molded product, whereas in Comparative Example 1, the molecular weight of the copolymer (A) was larger than the molecular weight of the copolymer (B). A large amount of small lumps were generated on the surface of the molded product, and the appearance of the molded product was all problematic.

  In Comparative Example 2, the weight average molecular weight difference between the copolymer (A) and the copolymer (B) is 300,000, while the ratio of the copolymer (A) and the copolymer (B) is 15:85. As a result, a large amount of small lumps not melt-dispersed occurred on the surface of the molded product, and there was a problem in the overall appearance of the molded product.

  In Comparative Example 3, since the average particle diameter is as large as 0.7 mm, the obtained bead-like methacrylic resin polymer cannot be sufficiently melted, and a large amount of small lumps not melted and dispersed in the molded product are generated on the surface of the molded product. The appearance of the molded products was all problematic.

  In Comparative Example 4, the copolymer (A) and the copolymer (B) were blended and mixed. However, the copolymer (A) and the copolymer (B) could not be sufficiently uniformly melted, and also melted. There was a problem with all the appearance of the molded product because a large amount of undispersed lumps were generated on the surface of the molded product.

  Further, Example 4 and Comparative Example 5 both have the same melt flow rate, but Example 4 using copolymer (A) and copolymer (B) having different average molecular weights is molded at a lower injection pressure. I was able to.

  By using the multi-stage polymerization methacrylic resin polymer of the present invention, appearance quality is very important, display (device) windows for mobile phones, liquid crystal monitors, liquid crystal televisions, etc., light guide plates used in liquid crystal displays, displays Forehead of equipment, paintings, forehead, windows for taking in external light, display signs, exteriors of carport roofs, sheets of display shelves, covers for lighting fixtures, gloves, etc. Molded products that have secondary processing such as blow molding, and molded products that improve moldability while maintaining the appearance quality in taillights, headlamps, and other optical components for vehicles, while not reducing mechanical strength Can be provided.

It is the schematic of the cantilever method used by the present Example, the comparative example, and the reference example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixed jig 2 Test piece 3 Weight of 2 kg 4 Filter paper soaked with ethanol 5 Thread

Claims (2)

A copolymer composed of 70 to 99.5 wt% of methyl methacrylate monomer and 0.5 to 30 wt% of monomer composed of at least one other vinyl monomer copolymerizable with methyl methacrylate. Then, after polymerizing the copolymer (A) having a weight average molecular weight of 50,000 to 180,000 measured by gel permeation chromatography, the weight average molecular weight is 8 in the presence of the copolymer (A). It is a methacrylic resin polymer obtained by polymerizing a copolymer (B) of 10,000 to 800,000, the average particle diameter is 0.1 mm to 0.5 mm, and the following (1) to (3) A methacrylic resin polymer of multistage polymerization characterized by being satisfied.
(Weight average molecular weight of copolymer (B)) − (Weight average molecular weight of copolymer (A)) ≧ 10,000 (1)
(Weight average molecular weight of copolymer (B)) − (Weight average molecular weight of copolymer (A)) ≦ 200,000 (weight ratio of copolymer (A)): (copolymer (B) (Weight ratio) = 5: 95-50: 50 (2)
(Weight average molecular weight of copolymer (B))-(Weight average molecular weight of copolymer (A))> 200,000 (weight ratio of copolymer (A)): (copolymer (B) (Weight ratio) = 20: 80 to 80:20 (3)   The methacrylic resin polymer for multistage polymerization according to claim 1, which is obtained by two-stage polymerization by suspension polymerization or emulsion polymerization.

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