JPH0551609B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a nitrile resin composition having excellent impact resistance. [Prior Art] Nitrile resin is a thermoplastic polymer with excellent gas and vapor barrier properties and solvent resistance, and in recent years its practical value has increased as a packaging material in the fields of food, agricultural medicines, cosmetics, etc. is recognized. In the production of nitrile resins, a method is generally known in which a monomer mixture containing unsaturated nitrile as a main component is graft-polymerized in the presence of rubber for the purpose of imparting impact resistance. technology is shown. For example, a method of graft polymerizing an unsaturated nitrile and an acrylic acid alkyl ester to a conjugated diene rubber (Japanese Patent Publication No. 46-25005) or a method of graft polymerizing an unsaturated nitrile and an aromatic vinyl compound to a conjugated diene rubber ( Japanese Patent Publication 1973-
75294) etc. are shown. Important points in the production of such nitrile resin compositions are control of the grafting ratio between the rubber phase, which provides impact resistance, and the surrounding matrix phase, and control of the molecular weight of the matrix phase, which influences processability. The practicality of the resulting resin is determined by how well-balanced both physical properties are imparted to the polymer. In order to improve impact resistance, a method of pre-swelling the rubber with a part of the monomer before the start of polymerization (Japanese Unexamined Patent Publication No. 1973-
However, in order to improve processability, molecular weight regulators such as mercaptans are used, and in order to further enhance the effect of molecular weight regulators,
A method using a PH regulator is known (JP-A-Sho).
54-71839). [Problem to be solved by the invention] However, the influence of mercaptan on the polymerization reaction mechanism not only affects the molecular weight adjustment but also the grafting ratio, which also affects the impact resistance, making it difficult to maintain a proper balance between both physical properties. It is difficult to obtain a resin, and for example, increasing the amount of a molecular weight regulator improves processability, but the impact resistance decreases to an extent that it cannot be used for practical purposes. In addition, the above polymerization method has unstable die swelling of the polymer, and conventional molding methods used for known thermoplastic resin materials, such as extrusion molding, injection molding, blow molding, and inflation film formation, Problems such as deterioration of shape and surface condition occurred. In view of these problems, the present inventors have determined that the conversion rate of the polymer is 5 to 5.
Although a method has been disclosed in which the pH of the polymerization system is adjusted to 5 or less while the polymerization concentration is 90 wt%, and a molecular weight regulator is also added continuously or in portions, it is still insufficient. An object of the present invention is to provide a method for producing a nitrile resin that has a good balance between impact resistance and processability. [Means for Solving the Problems] The present inventors have finally arrived at the present invention as a result of further intensive studies. That is, in the present invention, the conjugated diene monomer is
Polymerization of 100 parts by weight of a mixture of unsaturated nitrile and other monomers copolymerizable with it in an aqueous medium together with a molecular weight modifier in the presence of 1 to 40 parts by weight of a diene-based rubbery polymer containing % by weight or more. A method for producing an impact-resistant nitrile resin composition, which comprises continuously adding an acid from immediately after the start of polymerization or 30 minutes after the start of polymerization until the peak of polymerization to bring the pH of the polymerization system to 5 or less. It is. The diene-based rubbery polymer used in the present invention refers to at least one monomer selected from a conjugated diene-based monomer and an unsaturated nitrile copolymerizable with the same, an aromatic vinyl compound, an unsaturated carboxylic acid ester, etc. It is a copolymer with the body. Conjugated diene monomers include 1-3 butadiene, 2.3-dimethyl-1.3-
Butadiene, 2,3-diethyl-1,3-butadiene,
Examples include isoprene and chloroprene, with 1-3 butadiene being preferred. Examples of unsaturated nitriles include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, etc.
Acrylonitrile is preferred. Examples of the aromatic vinyl compound include styrene, α-methylstyrene, vinyltoluene, and vinylxylene, with styrene being preferred. Examples of unsaturated carboxylic acid esters include esters of acrylic acid or methacrylic acid such as methyl, ethyl, propyl, and butyl. Methyl acrylate and methyl methacrylate are preferred. This diene-based rubbery polymer can be produced by various known methods, but emulsion polymerization is preferred. Other monomers copolymerizable with unsaturated nitriles include unsaturated carboxylic acid esters, aromatic vinyl compounds, α-olefins, vinyl ethers, and vinyl esters, among which unsaturated nitriles,
As for the unsaturated carboxylic acid ester and the aromatic vinyl compound, those exemplified above can be used. α-olefins include isobutene, 2-methyl-1-butene, 2-methyl-1-pentene,
Examples include 2-methyl-1-hexene, 2-methyl-1-heptene, 2-ethyl-1-butene, 2-propyl-1-butene, and isobutene is preferred. Examples of the vinyl ether include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ethers, butyl vinyl ethers, isopropyl vinyl ether, and the like, with methyl vinyl ether being preferred. Examples of vinyl esters include vinyl acetate, vinyl propionate, and vinyl butyrate, with vinyl acetate being preferred. The amount of the diene rubbery polymer added is 1 to 40 parts by weight, preferably 5 to 30 parts by weight. The amount added
If it exceeds 40 parts by weight, processability will deteriorate, and if it is less than 1 part by weight, impact resistance will deteriorate. The molecular weight regulator used in the present invention is an alkyl mercaptan, such as n-dodecyl mercaptan, tert-dodecyl mercaptan, n-dodecylthiol acetate, pentaerythritol tetrakis (β-
mercaptopropionate), limonene dimercaptan, etc. Preferably, organic mercapto compounds containing two or more mercapto groups in the molecule, such as pentaerythritol tetrakis (β- mercaptopropionate) and limonene dimercaptan. The amount of the molecular weight regulator to be added is determined by the required molecular weight, but if added in a large amount, the heat resistance and mechanical properties will deteriorate, so 0.1 to 3% by weight based on the monomers to be polymerized is suitable. be. In the present invention, the polymerization peak time is the time point during the polymerization reaction when the reaction rate per unit time becomes the highest, or in other words, the time point when the monomer consumption rate per unit time in the system becomes the highest. The timing at which the polymerization peak occurs can be controlled by adjusting the amount of catalyst, the amount of chain transfer agent, etc., but it is preferable that the peak occurs by 4 hours after the start of the polymerization reaction. If the time until the polymerization peak exceeds 4 hours, the reaction will take an abnormally long time, and the amount of phosphoric acid consumed will increase, resulting in high costs. Furthermore, if the polymerization peak occurs earlier than 3 hours, heat generation occurs due to rapid reaction, making it difficult to remove the heat. Preferably from the 3rd hour to the 4th hour. In the present invention, the pH within the polymerization system from immediately after the start of polymerization to the peak of polymerization is set to 5 or less, and the pH regulator used for this purpose may be either an inorganic acid or an organic acid. Examples of organic acids include acetic acid, propionic acid, citric acid, 3-mercaptopropionic acid, ascorbic acid, and phosphoric acid ester. Preferred acids are acetic acid, citric acid, phosphoric acid, 3
-Mercaptopropionic acid. In the present invention, the pH is generally adjusted from PH=9 to
When carrying out graft polymerization using a rubbery polymer latex with a pH of 10, this is different from the conventional purpose of initiating polymerization by adjusting the pH to a neutral pH of 6 to 8. By keeping the temperature in the almost completely acidic range of 5 or less, mercaptan as a molecular weight regulator does not affect the grafting reaction,
It works effectively only for its original purpose of controlling molecular weight regulators. This pH is preferably in the range of 2.5 to 4 due to problems with the materials of the polymerization reactor and the like. The timing of pH adjustment is that it is not very effective to adjust the pH only at the start of polymerization or for a long time from the start to the end of polymerization. A desired polymer can be obtained by continuing the process. Polymerization initiators used in the present invention include peracid catalysts such as persulfuric acid, peracetic acid, and perphthalic acid, persalt catalysts such as potassium persulfate, hydrogen peroxide, benzoyl peroxide, chlorobenzoyl peroxide, and There are peroxidation catalysts such as acetyl oxide, lauryl peroxide, and dicumyl peroxide, and these can be used alone or in combination of two or more. Suitable emulsifiers in the present invention include sodium or potassium salts of myristic acid, palmitic acid, stearic acid, lauric acid, oleic acid, cetyl sulfate,
sodium, potassium or ammonium salts such as lauryl sulfate, oleinsulfonic acid and stearylsulfonic acid; higher amine salts such as laurylamine hydrochloride and stearylamine hydrobromide;
Examples include polymeric substances such as polyvinylpyrrolidone, sodium polyacrylate, and methylcellulose. The polymerization method suitable for the present invention is emulsion polymerization.
Polymerization is carried out at any temperature between ~100°C and in the presence of a radical polymerization initiator, and the polymerized product is obtained as a latex. This latex is solidified by a conventional method,
Wash with water and dry to obtain a polymer. The obtained polymer is a thermoplastic resin, and it can be processed and molded by extrusion molding, injection molding, calendar molding, blow molding, etc. by adding ordinary compounding ingredients such as antioxidants, stabilizers, colorants, and lubricants. It is possible. The resin obtained by the method of the present invention has higher impact resistance and easier processability than rubber-reinforced nitrile polymers produced by conventional techniques, and also has solvent resistance and vapor and gas barrier properties. Therefore, it is useful as a molding material for bottles, films, sheets, etc. for foods, agricultural medicines, cosmetics, etc. [Example] The present invention will be explained below with reference to Examples. Note that "parts" and "%" below are based on weight. Example 1 (A) Production of diene rubber latex A mixture consisting of the following components was stirred in a stainless steel polymerization reactor in a nitrogen atmosphere and heated at 45°C for 20 minutes.
Polymerization was carried out for a period of time, and the polymerization was completed at a conversion rate of 90%. After the polymerization was completed, excess monomer was removed by stripping to obtain a synthetic rubber latex with a solid content of 30%. Acrylonitrile 40 parts 1-3 butadiene 60 parts Fatty acid soap 2.4 parts Azobisisobutyronitrile 0.3 parts Tertiary dodecyl mercaptan 0.5 parts Water 200 parts After drying the latex, the solid content was collected and elemental analysis revealed the acrylonitrile in the rubber. When the content was determined, it was 38wt%. (B) Production of graft polymer Raw materials having the following composition were charged into a polymerization reactor, and polymerization was started at 58° C. with stirring under a nitrogen atmosphere. The pH at the start of polymerization was 7.4. Water 200 parts Acrylonitrile 75 parts Methyl acrylate 25 parts Rubber latex of (A) above 33 parts (solid content 10 parts) Sodium dioctyl sulfosuccinate 1.31 parts Polyvinylpyrrolidone 0.47 parts Potassium persulfate 0.06 parts Tertiary dodecyl mercaptan 2.0 parts Polymerization starts 30 minutes after polymerization starts Phosphoric acid was continuously added to the system to maintain pH=3 until the peak of polymerization, and polymerization was further carried out at 58° C. for 5 hours. Note that the reaction peak occurred 3 hours after the start of polymerization. The obtained latex was coagulated by adding a dilute aluminum sulfate aqueous solution (concentration 45%), washed with water, and dried to obtain a powdery polymer. This polymer was pressure molded at 170° C. and 140 kg/cm ² to obtain a transparent, pale yellow sheet. Izot impact strength of test pieces made from this sheet (23℃ AS
Table 1 shows the results of measuring the melt index (according to TM D256) and the melt index (ASTM D1238) of the obtained polymer. Comparative Example 1 Polymerization was carried out in the same manner as in Example 1, except that the pH of the polymerization system was not adjusted. The Izo impact strength and melt index values of the produced polymers are shown in Table 1. Comparative Example 2 Polymerization was carried out in the same manner as in Example 1, except that the pH of the polymerization system was adjusted to 3 at the start of polymerization, and then no further pH adjustment was performed. The change in pH of the reaction system over time was as follows. After 1 hour: 3.8, after 2 hours: 5.3, after 3 hours:
6.2, 4 hours later: 6.5, 6 hours later: 6.7, 8 hours later:
6.8 The Izot impact strength and melt index values of the polymers produced are shown in Table 1. Comparative Example 3 In Example 1, after adjusting the pH of the polymerization system to 3 at the start of polymerization, phosphoric acid was continuously added to maintain the pH of the polymerization system at 3 until the end of polymerization. The Izo impact strength and melt index values of the produced polymers are shown in Table 1. Example 2 Polymerization was carried out in the same manner as in Example 1, except that the pH of the polymerization system was adjusted to 4 from the start of polymerization to the peak of polymerization in Example 1. The Izo impact strength and melt index values of the produced polymers are shown in Table 1.

〔Effect of the invention〕

The nitrile resin composition obtained by the present invention has excellent impact resistance compared to resins made by conventional techniques, and is of great industrial value.

Claims (1)

[Claims] 1. In the presence of 1 to 40 parts by weight of a diene rubber-like polymer containing 50% by weight or more of a conjugated diene monomer, 100 parts by weight of a mixture of unsaturated nitrile and other monomers copolymerizable with it. When polymerizing with a molecular weight regulator in an aqueous medium, the pH of the polymerization system is adjusted to 5 or less by continuously adding an acid from immediately after the start of the polymerization or 30 minutes after the start of the polymerization until the peak of the polymerization. A method for producing an impact nitrile resin composition.