JPS6339004B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a saponified ethylene-vinyl acetate copolymer that has a lower melt index and excellent mechanical properties, environmental stress cracking, etc. by subjecting a specific ethylene-vinyl acetate copolymer to a specific heat treatment. The present invention relates to a method for manufacturing. In general, saponified ethylene-vinyl acetate copolymers have lower melting points, hardness, expansion strength, bending strength, and
High bending rigidity, solvent resistance, abrasion resistance,
Excellent gas permeability. Furthermore, it has excellent adhesion to various inorganic and organic substrates including metals, and is widely used as coating materials for powder coatings, adhesives for textile interlining, and various lamination adhesives. Ethylene-vinyl acetate copolymers are produced by digital polymerization such as high-pressure polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. By the way, when saponified ethylene-vinyl acetate copolymer is used in powder coatings, it is necessary to apply surface light to improve the adhesion of the powder coating to metal, to suppress the occurrence of environmental stress cracks, and to increase surface hardness. In order to improve the quality of the powder coating material, it is preferable to use an ethylene-vinyl acetate copolymer having a relatively high vinyl acetate content as a raw material. Therefore, when trying to produce an ethylene-vinyl acetate copolymer with a high vinyl acetate content by radical copolymerization, the vinyl acetate unit has high free radical chain transferability, so ethylene has a low melt index that satisfies the physical properties of powder coatings. -Vinyl acetate copolymers cannot be easily produced. For this reason,
A method of adding a polyisocyanate compound to a saponified ethylene-vinyl acetate copolymer for the purpose of improving physical properties for powder coatings (Japanese Patent Application Laid-Open No. 51-5353,
50−116525) has been proposed. However, these methods have problems in food hygiene, processing stability, and insufficient physical properties such as environmental stress cracking. Therefore, the present inventors conducted intensive studies to solve these problems, and found that by subjecting a saponified ethylene-vinyl acetate copolymer having a relatively high vinyl acetate unit to a specific heat treatment, ,
The present inventors have discovered a method for producing a saponified ethylene-vinyl acetate copolymer that has a lower melt index and is superior in mechanical properties, environmental stress cracking, and other qualities, resulting in the present invention. That is, the present invention uses an ethylene-vinyl acetate copolymer containing 10 to 60% by weight of vinyl acetate units.
Ethylene with a reduced melt index characterized by saponifying ~99% by weight and then heat-treating at a temperature of 60 to 250°C in the presence of an alkali catalyst of 100 to 2000 ppm in terms of alkali metal per saponified product. This is a method for producing saponified vinyl acetate copolymer. The reason why the melt index decreases when saponified ethylene-vinyl acetate copolymer is heated in the presence of an alkali catalyst is because a partial crosslinking reaction occurs due to the reaction between the hydroxyl group of the vinyl alcohol unit and the acetoxy group of the vinyl acetate unit. It seems to be for waking up.
The present invention will be explained in detail below. The ethylene-vinyl acetate copolymer used in the present invention is produced by known radical polymerization methods such as high-pressure polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In addition to ethylene and vinyl acetate, a copolymer of about 10% by weight or less of unsaturated hydrocarbons such as propylene, butene-1, and styrene can also be used. The content of vinyl acetate units in the ethylene-vinyl acetate copolymer used in the present invention is 10 to 60% by weight. If it is less than 10% by weight, ethylene-
A vinyl acetate copolymer can be produced, and a saponified ethylene-vinyl acetate copolymer having a sufficiently smaller melt index can be produced. If it is more than 60% by weight, the water resistance of the saponified ethylene-vinyl acetate produced therefrom will decrease and the quality as a powder coating will deteriorate, which is not preferable. Saponification of the ethylene-vinyl acetate copolymer can be carried out by known methods. For example, a homogeneous system in a good solvent of hydrocarbons such as toluene or xylene, or a mixed solvent system in which an alcohol such as methanol is added to this, or a non-solvent in which an alcohol such as methanol or ethanol and water is added as necessary. In the heterogeneous system inside, alkali metal compounds such as sodium and potassium hydroxides and alkoxides are used as saponification reaction catalysts for saponification. A saponification rate of 50 to 99% is suitable. If the saponification rate is less than 50% by weight, the hardness decreases and the quality for powder coatings etc. deteriorates, which is not preferable. Furthermore, if the saponification rate is 99% by weight or more, the melt index will not decrease much even if the method of the present invention is applied, which is not preferable. The saponified ethylene-vinyl acetate copolymer before heat treatment preferably has a melt index of 20 to 60. The alkali catalysts used in the present invention include hydroxides, oxides, and alkoxides of lithium, sodium, and potassium, including alkoxides of ethylene-vinyl alcohol copolymers. As mentioned above, alkali metal compounds such as sodium hydroxide are used to saponify the ethylene-vinyl acetate copolymer, but since these catalysts are present in the ethylene-vinyl acetate saponified product, this residual Alkali metal compounds can be used as alkali catalysts in the present invention. The amount of the alkali catalyst used in the present invention is preferably 100 to 2000 ppm based on the saponified ethylene-vinyl acetate in terms of alkali metal.
If the amount of the catalyst is too small, the heat treatment time will be long, and if the amount of the catalyst is too large, the product will become easily colored, which is not preferable. In the heat treatment in the present invention, it is necessary to reduce the volatile content in the saponified ethylene-vinyl acetate copolymer to be treated. The presence of volatiles inhibits the crosslinking reaction. Therefore, it is desirable to keep the volatile content at 1% by weight or less. The heat treatment temperature is 60
℃~250℃. If the temperature is below 60℃, the reaction rate will be slow and the heat treatment will take a long time; if the temperature exceeds 250℃,
This is not preferred because the saponified ethylene-vinyl acetate copolymer is colored. Any heat treatment method may be used as long as it can accommodate and raise the temperature of the saponified ethylene-vinyl acetate copolymer, but the alkali catalyst of the present invention is deactivated when it absorbs carbon dioxide gas in the air. Therefore, it is not desirable to be in the atmosphere.
A reduced pressure heater, a reduced pressure dryer, a heater in an inert gas atmosphere not containing carbon dioxide gas, a dryer, etc. are used. Also, melt kneading is one method, and an extruder, Banbury mixer, roll, etc. can be used. The heat treatment time depends on the saponification rate of the saponified ethylene-vinyl acetate copolymer, the amount of alkali catalyst, the heating temperature, the heat treatment method, and the target melt index of the saponified ethylene-vinyl acetate copolymer after treatment. Change depending on. One method is to check changes over time. Through these heat treatments, it is preferable to reduce the melt index value to about 1/5 to 2/3 of the value before the treatment. The saponified ethylene-vinyl acetate copolymer whose melt index is lowered by the method of the present invention has excellent mechanical properties and environmental stress cracking resistance, and has good quality as a powder coating. . In addition, each measurement value shown in this invention was measured by the following method, respectively. (1) Vinyl acetate content and its saponification rate JISK
-6730-1977. (2) Melt index (MI) Washed with a methanol solution of phosphoric acid, neutralized the alkaline component in the saponified ethylene-vinyl acetate copolymer, and dried, JISK-
6760-1971 at 190°C under a load of 2.16 kg. The unit of measurement value is g/10 minutes. (3) Alkaline component content It was determined by extracting the alkaline component from the saponified ethylene-vinyl acetate copolymer with hot water and titrating it with hydrochloric acid using phenolphthalene as an indicator. (4) Constant strain environmental stress cracking test (ESCR test) This test was carried out in accordance with JISK-6760 using a 10% by weight aqueous solution of Igepearl with a thickness of 3 mm and a notch depth of 0.5 mm. (5) Tensile test Tensile test was conducted on a 1 mm thick press sheet in accordance with JISK-6760. (6) Volatile content (%) Weight loss was measured under drying conditions of 105°C, 5 Torr, and 3 hours, and the value was calculated by dividing the weight loss by the weight of the original sample. Example 1 Ethylene-vinyl acetate copolymer (vinyl acetate unit content: 43% by weight, MI = 60) obtained by high-pressure polymerization was saponified in a heterogeneous system using sodium hydroxide in a methanol solvent, and the ethylene-vinyl acetate copolymer was Methanol washing was performed to remove excess alkali components in the saponified polymer. Alkaline component content (Na equivalent) 510ppm, saponification rate 97.5% by weight,
A saponified ethylene-vinyl acetate copolymer having a melt index of 36 was obtained. Drying and heat treatment
It was carried out using a rotary dryer under the conditions of 90°C and 50 Torr, and changes over time were confirmed by melt index, volatile content, and ESCR test. The results are shown in Table 1. The tensile test results are also shown in Table 2.

[Table] Comparative Example 1 The saponified product obtained by saponification and washing with methanol in the same manner as in Example 1 was washed with a methanol solution of phosphoric acid to neutralize the alkaline components in the saponified product. Drying and heat treatment were performed using a rotary dryer at 90°C and 50 Torr, and melt index, tensile test, and ESCR test were performed. The results are shown in Table 2. Comparative Example 2 Saponification and methanol washing were performed in the same manner as in Example 1, and the alkaline component content (Na equivalent) was 950 ppm.
A saponified ethylene-vinyl acetate copolymer having a saponification rate of 99.5% by weight and a melt index of 39 was obtained. Drying and heat treatment were carried out using a rotary dryer at 90° C. and 50 Torr, and the physical properties were measured in the same manner as in Example 1. The results are shown in Table 2. Example 2 An ethylene-vinyl acetate copolymer (vinyl acetate unit content: 43% by weight, MI = 60) produced by high-pressure polymerization was saponified in a heterogeneous system using sodium hydroxide in a methanol solvent to form an ethylene-vinyl acetate copolymer. Methanol washing was performed to remove excess alkaline components in the saponified polymer. A saponified ethylene-vinyl acetate copolymer having an alkali component content (Na equivalent) of 320 ppm, a saponification rate of 97.0% by weight, and a melt index of 33 was obtained. The mixture was extruded and granulated using a vented 30 mmφ extruder at 190° C. for a residence time of 3 minutes while evaporating methanol. The results of measuring the physical properties in the same manner as in Example 1 are shown in the second example.
Shown in the table. Example 3 Ethylene-vinyl acetate copolymer produced by high-pressure polymerization (vinyl acetate unit content 43% by weight, MI = 60) was heterogeneously saponified using sodium hydroxide in a methanol solvent to produce ethylene-vinyl acetate copolymer. Methanol washing was performed to remove excess alkaline components in the combined saponified product. Alkaline component content (Na equivalent) 290ppm, saponification rate 79.5% by weight,
A saponified ethylene-vinyl acetate copolymer having a melt index of 40 was obtained. Drying and heat treatment
Conducted in a rotary dryer at 90℃ and 50Torr, melt index, tensile test, ESCR
A test was conducted. The results are shown in Table 2. Example 4 An ethylene-vinyl acetate copolymer (vinyl acetate unit content: 32% by weight, MI = 60) obtained by high-pressure polymerization was subjected to heterogeneous saponification using sodium hydroxide in a methanol solvent to produce an ethylene-vinyl acetate copolymer. Methanol washing was performed to remove excess alkaline components in the saponified product. A saponified ethylene-vinyl acetate copolymer having an alkali component content (Na equivalent) of 250 ppm, a saponification rate of 80% by weight, and a melt index of 46 was obtained. 50% drying and heat treatment
The melt index, tensile test, and ESCR test were conducted using a rotary dryer at 5 Torr and ℃. The results are shown in Table 2.

【table】

Claims (1)

[Scope of Claims] 1. After saponifying 50 to 99% by weight of an ethylene-vinyl acetate copolymer containing 10 to 60% by weight of vinyl acetate units, 100% by weight of the saponified product in terms of alkali metal.
60-250 in the presence of ~2000ppm alkaline catalyst
1. A method for producing a saponified ethylene-vinyl acetate copolymer having a reduced melt index, the method comprising heating at a temperature of .degree. 2. The production method according to claim 1, wherein the alkali catalyst is an alkali metal compound. 3. The manufacturing method according to claim 1, wherein the volatile content in the saponified ethylene-vinyl acetate copolymer before heat treatment is 1% by weight or less. 4. The manufacturing method according to claim 1, wherein the heat treatment is carried out under reduced pressure or in a gas atmosphere not containing carbon dioxide gas. 5. The manufacturing method according to claim 1, wherein the heat treatment is performed by melt-kneading using an extruder.