JPH0573761B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an acrylic copolymer having excellent solvent resistance, moldability, transparency, and heat deformation resistance, and a method for producing the same. More specifically, the present invention contains a methacrylic acid alkyl ester and an unsaturated nitrile monomer, and has excellent moldability, transparency, and heat deformation resistance like conventional acrylic resins, and also cracks when contacted with solvents. The present invention relates to an acrylic copolymer that does not cause oxidation, and a method for producing the same. (Prior art) Vacuum-formed, heat-processed, or injection-molded acrylic resin molded products have a beautiful appearance and are widely used for decoration. When performing secondary processing such as finishing, gluing, bending, interlocking, perforating, and engraving, there are many opportunities for contact with organic solvents in a gas phase, liquid state, or mist. In such cases, cracks may occur in the molded product depending on the type of solvent used.
This includes the orientation of polymer molecules during the melt molding process, subsequent processing steps, thermal imbalance between the surface and interior of the molded product, mechanical imbalances that occur during mold filling, bending, compression, etc., as well as moisture absorption and solvent Strain energy based on the density imbalance caused by swelling due to penetration is accumulated on the surface and inside of the molded product, and when the solvent penetrates into or near this accumulated location, the strength of the base material and this distortion energy decrease. It is believed that cracks occur because the equilibrium is disrupted. This is a phenomenon called environmental stress cracking. Conventionally, to overcome these drawbacks of acrylic resins, the molecular weight has been increased or the glass transition temperature has been lowered. However, when the molecular weight is increased, solvent resistance is improved, but processability is significantly reduced, making it impossible to use for injection molding and extrusion molding. In addition, methods for lowering the glass transition point include adding plasticizers to lower the apparent glass transition point and reducing residual strain energy, and using acrylic esters with a specific structure as copolymer monomers. There is a method of copolymerization. (Problems to be Solved by the Invention) The former causes undesirable situations such as deterioration of mechanical properties, occurrence of coloring and contamination, and bleeding of additives due to inclusion of impurities other than polymers. Acrylic resin has the fatal disadvantage of spoiling its characteristic visual beauty, and even if the latter does not have the disadvantage of the former, it has poor solvent resistance when in contact with two or more solvents, or There is still a problem in terms of solvent resistance when repeatedly contacted with solvents, and it is not satisfactory. Therefore, there is a need in this technical field for a copolymer that has sufficient solvent resistance to cope with all the conditions that acrylic resin molded products are expected to encounter, and that has other properties equivalent to acrylic resins. It had been. (Means for Solving the Problems) In order to meet this demand, the present inventors have conducted intensive research and have developed a product by blending methacrylic acid alkyl ester and unsaturated nitrile monomer in a specific ratio. The present invention was made based on the discovery that a polymer can provide an acrylic resin molded product that has excellent moldability, transparency, and heat deformation resistance like conventional acrylic resins, and does not crack even when it comes into contact with a solvent. I arrived. The acrylic copolymer of the present invention exhibits excellent solvent resistance against both good solvents such as xylene and methylene chloride, and poor solvents such as water and alcohol, and this is thought to be due to the following reasons. When a methacrylic acid alkyl ester is used and a good solvent enters, there is a region where the energy due to residual strain is smaller than the energy required to break the extruded plate, and no cracks occur in this region. On the other hand, when a poor solvent enters, there is a strong tendency to significantly reduce the mechanical strength of the base material, and the energy required to break the molded product decreases, making it easier for cracks to enter. It is assumed that the intermolecular force due to the CN group is strong and the mechanical strength is strong, and as a result, the occurrence of cracks due to solvents is significantly reduced, and the resistance to poor solvents such as alcohol is particularly strong. It is well known that acrylonitrile and methacrylonitrile are used to improve the alcohol resistance cracks of styrenic resins. However, it has been difficult to copolymerize acrylonitrile and methacrylonitrile with an acrylic resin. The main reason for this is that when copolymerizing acrylonitrile and methyl methacrylate, the effect of improving solvent resistance cannot be achieved unless a large amount of acrylonitrile is used. This impairs colorless transparency, which is one of the characteristics, and the heat deformation resistance temperature decreases significantly. Furthermore, when methacrylonitrile and methyl methacrylate are copolymerized, the polymerization rate becomes extremely slow, resulting in a decrease in industrial productivity. In addition, thermal decomposition properties are poor, a large amount of decomposition gas is generated during high-temperature molding, and the range of molding conditions during injection molding is narrowed, which is a problem. That is, in the present invention, the alkyl group has 1 to 8 carbon atoms.
A copolymer having constitutional units of 80 to 97% by weight of methacrylic acid alkyl ester units, 0.5 to 5% by weight of acrylonitrile units, and 2 to 15% by weight of methacrylonitrile units, and has a weight average molecular weight of 8.0 to 8.0% by weight as measured by GPC. 200,000, a copolymer with a thermal decomposition index α of 13.0 or less, and alkyl methacrylate ester
In a method for polymerizing a monomer mixture consisting of 80 to 97 parts by weight, 0.5 to 5 parts by weight of acrylonitrile, and 2 to 15 parts by weight of methacrylonitrile, azobisiso is added as a polymerization initiator to 100 parts by weight of the monomer mixture. 80-97% by weight of methacrylic acid alkyl ester units characterized by suspension polymerization at 60-95°C using 0.1-0.4 parts by weight of butyronitrile and 0.1-0.5 parts by weight of octyl mercaptan as a chain transfer agent.
A copolymer consisting of 0.5 to 5% by weight of acrylonitrile units and 2 to 15% by weight of methacrylonitrile units, and has a weight average molecular weight of 8 as measured by GPC.
~200,000, and a method for producing a copolymer with a thermal decomposition index α of 13 or less. The methacrylic acid ester unit used in the copolymer of the present invention has an alkyl group having 1 to 8 carbon atoms.
Methyl methacrylate, hexyl methacrylate,
Diethylhexyl methacrylate is preferred. Particularly preferred is methyl methacrylate. The amount of methacrylic acid ester units in the copolymer is required to be 80 to 97% by weight, and particularly preferably 85 to 90% by weight. When it exceeds 97% by weight, it becomes difficult to improve solvent resistance, and when it is less than 80% by weight, colorless transparency and heat deformation resistance are impaired, which is not preferable. The amount of acrylonitrile units used in the copolymer of the present invention is required to be 0.5 to 5% by weight, and particularly preferably 1 to 3% by weight. If it exceeds 5% by weight, the reddish-yellow color of the molded product will become stronger, which is not preferable. If it is less than 0.5% by weight, no improvement in solvent resistance can be expected. The amount of methacrylonitrile units used in the copolymer of the present invention is required to be 2 to 15% by weight, and particularly preferably 3 to 10% by weight. If it exceeds 15% by weight, polymerization productivity will deteriorate and it will be difficult to supply it industrially at a low cost.Moreover, it will undergo severe thermal decomposition during injection molding, increasing the amount of residual monomer in the molded product, lowering HDT, which is undesirable. . If the amount is less than 2% by weight, no improvement in solvent resistance can be expected. It is necessary that the weight average molecular weight of the copolymer is from 80,000 to 200,000; if it is less than 80,000, the mechanical strength will drop significantly and the solvent resistance will be poor. If it exceeds 200,000, the melt viscosity is too high to be used during injection molding. The copolymer must have a thermal decomposition index α of 13 or less; if it exceeds 13, a silvery substance will form during high-temperature injection molding and the copolymer cannot be used. The copolymer of the present invention can be obtained by suspension polymerization, emulsion polymerization, or bulk polymerization. Although continuous bulk polymerization can be carried out using a high temperature polymerization initiator, suspension polymerization is particularly preferred from the viewpoint of economical efficiency. As the polymerization initiator, an azo type initiator is suitable, and in particular, when azoisobutyronitrile is used, a copolymer with excellent polymerization productivity and thermal decomposition property is obtained. When using peroxides such as lauroyl peroxide and t-butyl peroxyhexanoate, the polymerization rate is slow and a large amount of initiator must be used to increase productivity, resulting in thermal decomposition of the resulting copolymer. Sex is also not good. As the chain transfer agent, octyl mercaptan is particularly preferred from the viewpoint of molecular weight control effect and thermal stability of the copolymer. When a thioglycolic acid ester is used, the resulting copolymer has poor thermal decomposition properties. The optimum polymerization temperature for suspension polymerization is 60 to 95°C. Plasticizers, mold release agents, and the like can be used in the copolymer of the present invention as long as they do not impair the purpose of the present invention. An extruded plate formed into a sheet using the copolymer of the present invention can be used for lighting equipment etc. that require solvent resistance. Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples. In addition, each measurement in Examples and Comparative Examples was performed as follows. (Residual monomer of copolymer) Measured by gas chromatography according to a conventional method. (Heat distortion temperature (HDT)) Testing was carried out in accordance with the conditions specified in ASTM-648. (Measurement of Molecular Weight by GPC) Molecular weight measurement by GPC is generally carried out, for example, as described in the literature [Gel Chromatography (Basic), by Takeda et al., published by Kodansha, pp. 97-122]. For example, the molecular weight of the copolymer of the present invention was measured as follows. HSG-20, 50 (manufactured by Shimadzu Corporation) as a column
A calibration curve was created using standard polystyrene manufactured by Pressure Chemical Company. copolymer 75
The elution curve obtained using a sample solution in which 1.0 mg of methanol was dissolved in 30 ml of methyl ketone was divided into equal parts, the height at the division points was measured, and the Mw was calculated using the following formula.

[C] However, Hi is the height of the elution curve at the splitting point,
Mi(p) is the molecular weight of standard polystyrene at division point i, and Qm and Qp are the Q factors of the copolymer and polystyrene, which were set to 40 and 41, respectively. (Measurement of thermal decomposition index α) Using pyrolysis gas chromatography, at 450℃
Decompose the copolymer in an _N2 atmosphere, detect and integrate all decomposed gases decomposed in 60 minutes, and let this be X.
The gases generated in 30 minutes at 270°C are integrated, this is set as Y, and α is calculated as the thermal decomposition index α=Y/X. Solvent resistance tests for molded products are carried out at 23℃ and relative humidity.
The moisture in the molded product is removed by adjusting the conditions in a 50% atmosphere.
The concentration was 0.3 to 0.6% by weight. The specimens were immersed in each solvent at 23°C for a certain period of time, and the occurrence of cracks was observed. Example 1 A monomer solution consisting of 96 parts by weight of methyl methacrylate, 20 parts by weight of methacrylonitrile, 20 parts by weight of acrylonitrile, 0.26 parts by weight of azoisobutyronitrile, and 0.26 parts by weight of octyl mercaptan was placed in a polymerization machine equipped with a jacket. The mixture was suspended in a suspension phase consisting of 250 parts by weight of water and 1 part by weight of potassium polymethacrylate, warm water was passed through the jacket, and polymerization was initiated at a polymerization temperature of 80°C. 250 minutes after the start of polymerization, the polymerization temperature was increased to 95
The temperature was raised to 0.degree. C., and the reaction was continued for an additional 60 minutes to complete the reaction. The obtained polymer was cooled, washed and dried to 0.3
Beads with a diameter of mm were obtained. These beads were extruded using an extruder with a 30mmφ vent at a temperature of 260°C and a vacuum degree of 30°C.
It was pelletized under mmHg conditions. The obtained pellets were molded using an injection molding machine (M-200/
800DM) to injection mold 100×100×3
A plate-like molded product measuring mm square was obtained. The injection molding temperature is
It was 250℃. The copolymer composition in the molded article was analyzed using gas chromatography and found to be 96% by weight of methyl methacrylate units, 20% by weight of methacrylonitrile units, and 2.0% by weight of acrylonitrile units, which were the same as the charged monomer composition. As a result of measuring the residual monomer in the molded product, it was 0.23
It was in weight%. The heat distortion temperature (HDT) was 96°C. The weight average molecular weight Mw was 128,000, and the thermal decomposition index α was 11.0. (Solvent resistance test) The molded product was conditioned in an atmosphere of 23° C. and 50% relative humidity. The moisture content in the molded article was 0.5% by weight.
It was immersed in gasoline, isopropyl alcohol, and xylene at 23°C for 5 hours, 2 hours, and 1 minute each, and the occurrence of cracks was observed. The results are shown in Table 1. Examples 2 to 6, Comparative Examples 1 to 3, 5 Operated under the same conditions as Example 1 except for using the monomer compositions shown in Table 1 Examples 2 to 6, respectively,
The copolymers shown in Table 1 and their moldings were obtained. The evaluation results are shown in Table 1. Comparative Example 4 Methyl methacrylate 88 parts by weight, methacrylonitrile 10 parts by weight, acrylonitrile 2.0 parts by weight, t
A monomer solution consisting of 0.55 parts by weight of butylpaoxydiethylhexanoate and 0.33 parts by weight of octyl mercaptan was suspended in a suspension phase consisting of 250 parts by weight of water and 1 part by weight of potassium polymethacrylate in a polymerization machine equipped with a jacket. , run warm water through the jacket,
Polymerization was started at a polymerization temperature of 80°C. 250 after starting polymerization
The polymerization temperature was raised to 95°C in 1 minute, and the reaction was continued for an additional 60 minutes to complete the reaction. Cooling the obtained polymer,
Beads with a diameter of 0.3 mm were obtained by washing and drying. These beads were extruded using a 30mmφ vented extruder at a temperature of 260°C.
It was pelletized under the condition of a vent vacuum of 30 mmHg. The obtained pellets were injection molded using an injection molding machine (M-200/800DM manufactured by Meiki Seisakusho).
A plate-shaped molded product with a square size of 100 x 100 x 3 mm was obtained. Silver was generated due to thermal decomposition during injection molding. The evaluation results are shown in Table 1. Example 7 A monomer solution consisting of 93 parts by weight of methyl methacrylate, 5.0 parts by weight of methacrylonitrile, 2.0 parts by weight of acrylonitrile, 0.26 parts by weight of azobisisobutyronitrile, and 0.30 parts by weight of octyl mercaptan,
It was suspended in a suspension phase consisting of 250 parts by weight of water and 1 part by weight of potassium polymethacrylate in a polymerization machine equipped with a jacket, heated water was passed through the jacket, and the polymerization temperature was adjusted to 75°C.
Polymerization was started. The polymerization temperature was raised to 95°C 200 minutes after the start of polymerization, and the reaction was continued for an additional 60 minutes to complete the reaction. The obtained polymer is cooled, washed, and dried.
Beads with a diameter of 0.3 mm were obtained. These beads are extruded using a sheet forming machine (SH120 manufactured by Hitachi Zosen, manufactured by Toshiba Machinery).
STU1600H) Size: 1000 x 2000 x 2
mm plate was obtained. The extrusion temperature was 270°C. Analysis of the copolymer composition in the molded product using gas chromatography revealed that methyl methacrylate units
93% by weight, methacrylonitrile units 5.0% by weight,
The acrylonitrile unit content was 2.0% by weight, which was the same as the charged monomer composition. As a result of measuring the residual monomer in the molded product, it was 0.23
It was in weight%. The heat distortion temperature (HDT) was 95°C. The weight average molecular weight Mw was 128,000, and the thermal decomposition index α was 11.0. (Solvent resistance test) The molded product was conditioned in an atmosphere of 23° C. and 50% relative humidity. The moisture content in the molded article was 0.5% by weight.
It was immersed in gasoline, isopropyl alcohol, and xylene at 23°C for 5 hours, 2 hours, and 1 minute each, and the occurrence of cracks was observed. The results are shown in Table 1.

[Table] Example 8 The copolymers shown in Table 2 and their molded articles were obtained by operating under the same conditions as in Example 1 except for using 0.15 parts by weight of octyl mercaptan. The evaluation results are shown in Table 2. All abbreviations and symbols in Table 2 are the same as those in the notes to Table 1.

[Table] (Effects of the Invention) As a result of our earnest efforts to solve these problems, the present inventors used methyl methacrylate, acrylonitrile, and methacrylonitrile in specific proportions, and in the presence of a specific initiator and chain transfer agent. By copolymerizing with acrylic resin, the thermal decomposition properties of the copolymer are greatly improved, resulting in excellent moldability, transparency, and heat deformation resistance similar to conventional acrylic resins, and even when it comes into contact with solvents. The inventors have discovered that a copolymer capable of producing acrylic resin molded articles without cracking can be obtained, and have thus completed the present invention.

Claims (1)

[Scope of Claims] 1 Constituent units are 80 to 97% by weight of methacrylic acid alkyl ester units whose alkyl group has 1 to 8 carbon atoms, 0.5 to 5% by weight of acrylonitrile units, and 2 to 15% by weight of methacrylonitrile units. It is a copolymer with a weight average molecular weight of 8 as measured by GPC.
~200,000, a copolymer with a thermal decomposition index α of 13 or less. 2 80 to 97 parts by weight of a methacrylic acid alkyl ester with an alkyl group having 1 to 8 carbon atoms, 0.5 to 5 parts by weight of acrylonitrile, and methacrylonitrile 2
In a method of polymerizing a monomer mixture consisting of ~15 parts by weight, 0.1~100 parts by weight of azobisisobutyronitrile as a polymerization initiator is added to 100 parts by weight of the monomer mixture.
Suspension polymerization is carried out at 60 to 95°C using 0.4 parts by weight and 0.1 to 0.5 parts by weight of octyl mercaptan as a chain transfer agent.
A copolymer containing 80 to 97% by weight of methacrylic acid alkyl ester units of No. 8, 0.5 to 5% by weight of acrylonitrile units, and 2 to 15% by weight of methacrylonitrile, and has a weight average molecular weight measured by GPC. 80,000 to 200,000, and a method for producing a copolymer having a thermal decomposition index α of 13 or less.