JPH0520444B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an ethylene-acrylic acid copolymer or an ethylene-ethyl acrylate-acrylic acid copolymer with good hue.

Processes for producing relatively low molecular weight polyolefins by thermally degrading high molecular weight polyolefins such as polypropylene, polybutene, high pressure, medium pressure and low pressure polyethylene are known.
This thermal degradation method is a reaction that involves scission of polymer chains, and is generally thermally decomposed at a high temperature of about 300 to 450°C in an inert gas such as nitrogen. The molecular weight polymer has a wax-like appearance. The problem with this degradation method is that although it is carried out in an inert atmosphere, the degraded product is colored yellow to reddish brown and has poor heat resistance.

In order to improve these shortcomings, the Special Publication No. 43-9368
The publication discloses a method of thermally degrading a high molecular weight polyolefin in an atmosphere of steam or an inert gas containing steam. Although this method shows an improvement in hue compared to the method carried out in the absence of water vapor, it is still insufficient, especially when the degraded product is subsequently subjected to a modification treatment, as the hue deteriorates even further. The reality is that the problem of poor heat resistance has not been fully resolved.

Furthermore, Japanese Patent Application Laid-Open No. 53-65389 discloses ethylene-ethyl acrylate with improved hue and solubility.
A method for making an acrylic acid terpolymer is disclosed. In this method, a relatively high molecular weight ethylene-ethyl acrylate copolymer is thermally degraded in the presence of water or steam and simultaneously hydrolyzed to produce an ethylene-ethyl acrylate-acrylic acid ternary copolymer. The method relates to a method for preventing significant coloration of products that occurs when the ethylene-ethyl acrylate copolymer is kept in a solid state in an extruder by reducing the pressure in the zone where the ethylene-ethyl acrylate copolymer remains in a solid state;
After the ethyl acrylate copolymer is heated and sufficiently melted, water or steam is injected and reacted to produce an ethylene-ethyl acrylate-acrylic acid ternary copolymer with an improved hue and an arbitrarily reduced molecular weight. This is the way to obtain union.

However, the hue in this case is 2 in terms of Cardner color number.
However, it cannot be said that it has been sufficiently improved.

The present inventor has solved the problem of coloring of the product associated with a method of heating an ethylene-ethyl acrylate copolymer in the presence of water to obtain a low molecular weight ethylene-acrylic acid copolymer with a relatively reduced molecular weight. The present invention was completed for the purpose of solving the problem.

The cause of the above coloring is not yet clear, but unsaturated chains are inevitably generated due to polymer chain scission and decomposition reactions due to degradation, and free carboxylic acid groups generated from the ethyl acrylate moiety are It is thought that excessive decomposition such as decarboxylation may also be a cause. Therefore, this coloring problem depends on the extent to which it is necessary to degrade the raw material ethylene-acrylate copolymer with a relatively high molecular weight, that is, the severity of the degradation reaction. In addition, it also depends on the degree of saponification, i.e., to what extent the ethyl acrylate moiety in the raw material ethylene-ethyl acrylate copolymer molecule is hydrolyzed.

The melt index of the degraded product exemplified in the above-mentioned Japanese Patent Application Laid-Open No. 53-65389 is 580 to 680,
From this, low molecular weight ethylene-acrylic acid copolymers or ethylene-ethyl acrylate-acrylic acid copolymers are required for various uses, and relatively high molecular weight ethylene-ethyl acrylate copolymers are required. If one attempts to obtain it by degrading or hydrolyzing the coalesce, one encounters a problem of coloration of the degraded product, which is greater than what has been experienced in the past.

The present inventor has proposed a method for solving this coloring problem, and
The present invention was arrived at as a result of continuing searches to find a simple and reliable method to solve the problem of poor heat resistance of colored degraded products.

That is, one of the main objects of the present invention is to provide a low molecular weight ethylene-acrylic acid copolymer suitable as a raw material for producing a copolymer having ionic crosslinks, preferably having a viscosity average molecular weight of about 30,000 or less, and An ethylene-acrylic acid binary copolymer that does not substantially contain an ethyl acrylate moiety in its molecular chain,
The object of the present invention is to provide a method for improving the hue of a product produced by a decomposition reaction of a relatively high molecular weight ethylene-acrylic acid ester copolymer.

Another object of the present invention is to produce a degraded ethylene-ethyl acrylate-acrylic acid copolymer useful as a raw material for elmagillon adhesives, hot melt adhesives, water-based paints, etc. with a relatively high molecular weight. An object of the present invention is to provide a method for improving the hue of a product produced by a decomposition reaction of an ethylene-ethyl acrylate copolymer.

The Gardner color number of the present invention is significantly superior to 1 or less compared to the conventionally disclosed reduced products of 2 to 8, and the hue does not deteriorate even when exposed to various subsequent severe resin modification steps. The object of the present invention is to obtain an ethylene-acrylic acid copolymer having good heat resistance without producing a deterioration odor etc. by decomposing a relatively high molecular weight ethylene-acrylic acid ester copolymer.

The present invention provides a new and simple method that can achieve these objectives.

That is, according to the present invention, an ethylene-ethyl acrylate copolymer and water are placed in a reactor, and an inert gas is bubbled from the bottom of the reactor to reduce the oxygen concentration in the reaction system to 5 ppm or less, and the temperature is lowered. 200~500℃,
By performing thermal decomposition at a pressure in the range of 5 to 500 kg/cm ² , an ethylene-acrylic acid copolymer or an ethylene-ethyl acrylate-acrylic acid copolymer with good color can be produced.

The ethylene-ethyl acrylate copolymer referred to in the present invention refers to a commercially available ethylene-ethyl acrylate copolymer having a relatively high molecular weight that can be easily obtained by, for example, a high-pressure copolymerization method known in the industry using a free radical catalyst. It is a polymer, its melt index is approximately 300g/10min or less, the content of ethyl acrylate in the molecular chain is approximately 1 to 40% by weight,
Preferably it is 5 to 30% by weight. In addition, the method of creating an inert atmosphere in the present invention is not particularly limited, but for example, a method of completely eliminating air by passing an inert gas such as nitrogen, carbon dioxide, argon, or helium through the reaction system is possible. It is preferred to use nitrogen.

The oxygen concentration in the reaction system is 5 ppm or less, preferably 3 ppm or less, as measured by the usual Brady method.
Particularly preferably, it is 1 ppm or less.

The following method can be used to reduce the oxygen concentration in the reaction system to 5 ppm or less. First, in order to eliminate oxygen dissolved in the water in the reaction system, inert gas is bubbled from the bottom of the reaction vessel to completely eliminate dissolved oxygen, and the air inside the reactor is heated with inert gas. This is achieved by repeating pressure and pressure release purge operations.

The effects of the present invention can be obtained, for example, from a relatively high molecular weight raw material ethylene-ethyl acrylate copolymer with an average molecular weight of tens to hundreds of thousands to a low molecular weight ethylene-ethyl acrylate copolymer with an average molecular weight of several thousand that does not substantially contain ethyl acrylate. This effect is most noticeable when the degree of molecular weight reduction is very large, such as in the production of acrylic acid copolymers.

Furthermore, the present invention can be applied to a method for producing a copolymer whose molecular weight is arbitrarily reduced, and the ethyl acrylate content is about 3 mol% or less based on the ethyl acrylate of the ethylene-ethyl acrylate copolymer. From copolymers that do not substantially contain ethyl acrylate moieties to copolymers that contain about 50 mol% or more of ethyl acrylate,
It can be advantageously applied to either.

For example, for the purpose of obtaining an ionic polymer by further crosslinking the copolymer obtained by the present invention with metal ions, it is desirable that the content of ethyl acrylate moieties in the copolymer be as small as possible, and The content of ethyl acrylate in the copolymer that is processed into salt or ammonium salt and used as a suspension in water-based paints or adhesives varies depending on the purpose of use. can be used.

The amount of water to be present when carrying out the present invention is not particularly limited, but for example, as described above, water containing about 3 mol% or less of ethyl acrylate based on the ethylene-ethyl acrylate copolymer may be used. When producing a copolymer that does not contain an ethyl acrylate moiety, approximately
It is desirable to use large amounts of water, greater than 400 moles, preferably in the range from 400 to 1500 moles.

Furthermore, the reaction temperature and reaction pressure when carrying out the present invention depend on the properties of the raw materials used, namely ethylene-
Although it is controlled by factors such as the average molecular weight of the ethyl acrylate copolymer, the content of ethyl acrylate, the degree of molecular weight reduction, and the amount of coexisting water, the temperature is usually 200 to 500°C and the pressure is 5 to 500 kg. / ^cm2 ,
The reaction time is 1 to 10 hours, preferably 2 to 6 hours.

Note that water in the present invention includes liquid, water vapor, and a mixture thereof.

Ethylene with good hue obtained by the present invention
Acrylic acid copolymer or ethylene-ethyl acrylate-acrylic acid copolymer is excellent as a product as it is, but on the other hand, metal ions, amines,
The present invention provides modified copolymers such as metal ionic crosslinked copolymers that are advantageous as raw materials that are modified with ammonium salts and have extremely good hue.

For example, as a method for modifying an ethylene-acrylic acid copolymer or an ethylene-ethyl acrylate-acrylic acid copolymer having a good hue obtained by the present invention, the reaction vessel is continuously utilized.
(1) A method of denaturation under an inert gas atmosphere with an oxygen concentration of 5 ppm or less, (2) A method of denaturation simply under an inert gas atmosphere, (3) A method of denaturation in an open system, or a method of denaturation according to the present invention. The obtained product having a good color is taken out from the reaction vessel and is modified using other equipment such as an extruder or roll mill (4) Method of modification under an inert gas atmosphere (5) Method of modification in an open system, etc. Various methods can be used, but when the purpose is to produce a modified product, the modification method (1) not only allows continuous production of the modified product, but also produces a modified product with a significantly better hue. This is advantageous because it allows you to

Any known metal ion or metal compound suitable for the neutralization reaction for metal ionic crosslinking of the ethylene-acrylic acid copolymer or ethylene-ethyl acrylate-acrylic acid copolymer according to the present invention may be suitably used. However, the first ion group includes Na ⁺ , K ⁺ , Li ⁺ , Mg ⁺⁺ ,
Ca ⁺⁺ , Ba ⁺⁺ , Zn ⁺⁺ , Sb ⁺⁺ , Cu ⁺⁺ , Fe ⁺⁺ , Al ⁺⁺⁺ , Fe ⁺⁺⁺
Those selected from the others and mixtures thereof are included, and among these, alkali metal ions are particularly preferred, and among the metal compounds forming the source of the second ion group, sodium hydroxide as a so-called basic metal compound, Magnesium hydroxide, potassium hydroxide, zinc hydroxide, magnesium oxide, sodium methoxide, sodium ethoxide, magnesium oxide, nickel acetate, sodium carbonate, magnesium acetate, zinc acetate and the like are included.

Hereinafter, the present invention will be explained in more detail with reference to Examples, but it is clear that widely different embodiments can be constructed without departing from the spirit and scope of the invention, and therefore the present invention is limited in the accompanying claims. Other than these limitations, the embodiments are not limited to these limitations.

Example 1 Ethylene-ethyl acrylate polymer (ethyl acrylate content 14% by weight, melt index 9
g/10min) 200g along with 2kg of water into a pressurized container with a capacity of 3.8 and equipped with a magnetic stirrer.
After bubbling nitrogen gas from the bottom of the container for one hour to completely eliminate the oxygen dissolved in the water, the air inside the pressurized container is pressurized with nitrogen gas (50 kg/
cm ² ) and depressurization (1 Kg/cm ² ) was repeated five times, and the oxygen concentration in the system was measured and found to be 1 ppm or less. (The above measurement was based on the Brady method). The container was then heated to 350 °C in a nitrogen atmosphere.
The decomposition reaction was carried out for 4 hours at 200 Kg/cm ² at a temperature of 200 Kg/cm 2 , followed by air cooling.

The product has a viscosity average molecular weight of 6,000, and the infrared absorption curve shows that this compound is composed of 5 mol% ethyl acrylate and 95 mol% acrylic acid, based on the ethyl acrylate of the ethylene-ethyl acrylate copolymer. The hue was 1 or less in terms of the number of Cardner colors.

The above-mentioned viscosity average molecular weight in this example, the following examples, and comparative examples was determined from the limiting viscosity [η] measured in a 135° C. decalin solution using the following formula.

[η]=KM〓 K=14.3×10 ^-5 [dl/g] α=0.82 Example 2 Ethylene-ethyl acrylate copolymer (ethyl acrylate content 14% by weight, melt index 9g/10min) 200g and 2 kg of water in a pressurized container with a capacity of 3.8 cm equipped with a magnetic stirrer.
After bubbling nitrogen gas from the bottom of the container for one hour to completely eliminate the oxygen dissolved in the water, the air inside the pressurized container was pressurized with nitrogen gas (50Kg/cm ² ).
The pressure release (1Kg/cm ² ) operation was repeated 5 times and the oxygen concentration in the system was measured (Brady method).
It was less than 1 ppm. Next, the container was heated and reacted in a nitrogen atmosphere for 4 hours at 350°C and 200Kg/cm ² , and then cooled to 200°C. An aqueous solution of 11 g of sodium hydroxide dissolved in water was injected into the reactor, and reacted with stirring at 200° C. and 50 Kg/cm ² for 2 hours, followed by air cooling.

The product has a viscosity average molecular weight of 4000, and from the infrared absorption curve, this compound has a
It contained 2 mol% ethyl acrylate, 8 mol% acrylic acid, and 90 mol% sodium acrylate. Its hue was 1 or less on the Gardner color number.

Comparative Example 1 200 g of ethylene-ethyl acrylate copolymer (ethyl acrylate content 14% by weight, melt index 9 g/10 min) was charged together with 2 kg of water into a pressurized container with a capacity of 3.8 and equipped with a magnetic stirrer. Without removing the oxygen contained in 2 kg of water, the internal air was pressurized with nitrogen (50 kg/cm ² ).
After repeating the pressure relief (1 Kg/cm ² ) operation five times, the oxygen concentration in the system was measured (Brady method) and found to be 10 ppm. Next, the container was heated, and decomposition and reaction were carried out under the conditions of 200 kg/cm ² and 350° C. for 4 hours in a nitrogen atmosphere, and then air-cooled.

The product has a viscosity average molecular weight of 6000, and the infrared absorption curve shows that this compound consists of 5 mol% ethyl acrylate and 95 mol% acrylic acid, based on ethyl acrylate in the ethylene-ethyl acrylate copolymer. The hue was 3 in terms of the number of Cardner colors.

Comparative Example 2 200 g of ethylene-ethyl acrylate copolymer (ethyl acrylate content 14% by weight, melt index 9 g/10 min) was charged together with 2 kg of water into a pressurized container with a capacity of 3.8 and equipped with a magnetic stirrer. The air inside the container is filled with nitrogen gas at atmospheric pressure.
After removing it for a while, the oxygen concentration in the system was measured and found to be 50 ppm. Then heat the container,
The decomposition reaction was carried out under the conditions of 350° C. and 200 Kg/cm ² for 4 hours in a nitrogen atmosphere, and then air-cooled.

The product has a viscosity average molecular weight of 6000, and the infrared absorption curve shows that this compound consists of 5 mol% ethyl acrylate and 95 mol% acrylic acid, based on ethyl acrylate in the ethylene-ethyl acrylate copolymer. The hue was 8 in terms of the number of Cardner colors.

Claims (1)

[Claims] 1. Put the ethylene-ethyl acrylate copolymer and water in a reactor, bubble inert gas from the bottom of the reactor to reduce the oxygen concentration in the reaction system to 5 ppm or less, and raise the temperature to 200 A method for producing an ethylene-acrylic acid copolymer or an ethylene-ethyl acrylate-acrylic acid copolymer having a good hue, characterized by thermally decomposing the copolymer at a temperature of ~500°C and a pressure of 5-500 Kg/ ^cm2 . 2. The ethylene-acrylic acid copolymer or ethylene-acrylic acid copolymer with good hue according to claim 1, wherein the reaction product has a viscosity average molecular weight of 30,000 or less.
A method for producing an ethyl acrylate-acrylic acid copolymer.