Patent Description:
Acrylonitrile butadiene styrene (ABS), which is now in mass production, is dried in a fluidized bed dryer through processes such as synthesis and dehydration and products having various moisture contents and residual monomers are produced by controlling a hot-air temperature and a hot-air velocity.

Depending on various drying conditions, final product properties such as moisture contents and residual monomer concentrations are determined, where the longer the residence time and the higher the hot-air temperature, the final product tends to show a lower residual monomer content.

However, in the process of setting drying conditions for producing a polymer having a desired level of residual monomer content, the residual monomer content is changed depending on dryer factors such as bed sizes, feed rates of polymers and superficial velocities, polymer particle characteristics and process characteristics, in addition to residence times and hit-air temperatures, whereby there is no definite quantitative index for predicting the residual monomer.

Therefore, indicators for making products having a desired level of residual monomer are required by developing drying condition factors for control of the residual monomer in the ABS particles.

<CIT> describes producing a water absorbent resin by drying a particulate hydrogel. An unsaturated monomer is polymerized. A particulate hydrogel crosslinked polymer is dried, which is obtained by micronization of a hydrogel polymer during or after the polymerization at a solid content concentration of <NUM>% by weight or more. An amount of a peroxide in the particulate hydrogel crosslinked polymer is <NUM> to <NUM> ppm relative to the weight of the solid content of the particulate hydrogel crosslinked polymer. A drying temperature of the particulate hydrogel crosslinked polymer is <NUM> or more.

<CIT> describes manufacturing a polyacrylic acid (salt)-based water-absorbing resin. A predetermined monomer preparing step, polymerization step, drying step, and surface crosslinking step are sequentially carried out. An acetic acid concentration in acrylic acid or the like supplied in the monomer preparing step is in a range of <NUM> ppm to <NUM> ppm on the acrylic acid basis, and an acetic acid concentration lowering rate defined by a predetermined formula is <NUM>% or higher.

<CIT> describes removing residual monomer from granular vinyl chloride paste resin. A granular vinyl chloride paste resin obtained by drying a polymer latex produced from a monomer mixture based on a vinyl chloride monomer is brought into contact with an air stream at <NUM>-<NUM>. The mean article diameter of the granular vinyl chloride paste resin is <NUM>-<NUM>. The time of contact with the air stream is about <NUM> to <NUM>.

<CIT> describes molding of an ABS-based resin having rubber particles located at a depth of <NUM>-<NUM> from a surface of the molding. The particles morphologically comprise particles having an a/b ratio not greater than <NUM> and not smaller than <NUM>, wherein a and b represent a major axis and a minor axis, respectively. When a section taken by a microtome in parallel with a surface of the molding is observed in an electron micrograph, and assuming that the total area of the rubber particles as observed in the electron micrograph is <NUM>%, the total area of the A particles accounts for at least <NUM>% and that of the B particles is in a range of <NUM>-<NUM>%.

The present application is intended to provide an indicator for making a product having a desired level of residual monomer by developing a drying condition factor for residual monomer control.

The problems known from the prior art are solved by the subject matter according to claim <NUM>. Particular embodiments are given by the features of the dependent claims. The present application relates to a residual monomer content controlling method of a polymer.

The method is a method for controlling a residual monomer content in a polymer according to a drying process using a dryer,.

which provides a residual monomer content controlling method of the polymer using a hot-air mass ratio factor represented by Equation <NUM> below.

In Equation <NUM> above, A is a mass (Kg) of hot-air flowing into the dryer, and B is a mass (Kg) of the polymer flowing into the dryer.

The present application relates to a method for controlling a residual monomer content in a polymer, and in the case where a hot-air temperature and a hot-air velocity are maintained, the controlling method can predict the content of the residual monomer without influence of other external factors by adjusting a hot-air mass ratio.

The present application relates to a residual monomer content controlling method of a polymer.

In a method for preparing a polymer, the residual monomer was controlled by drying a product in a fluidized bed dryer following processes such as synthesis and dehydration.

Typically, the fluidized bed dryer is a drying machine that removes moisture while supplying hot-air to polymer particles containing moisture to move the polymer particles.

Conventionally, in order to remove the residual monomer of the polymer by using this fluidized bed dryer, the retention time was increased and the hot-air temperature was raised to lower the residual monomer content in the final product.

However, the process of controlling the residual monomer through the process of removing moisture using the fluidized bed dryer has been affected by various factors other than the hot-air temperature and the residence time. For example, factors of dryer factors such as bed sizes, polymer feed rates, hot-air flow rates and superficial velocities, polymer particle characteristics and process characteristics, and the like have affected the residual monomer content.

Hereinafter, the meanings of the factors will be described.

The retention time means a time that polymer particles containing moisture are retained while moving from an inlet of a fluidized bed dryer to an outlet thereof.

The hot-air temperature means a temperature of air flowing into a fluidized bed dryer to remove moisture from polymer particles containing moisture.

The bed size means a volume of a space capable of hot-air drying polymer particles containing moisture in a fluidized bed dryer.

The polymer feed rate means an inflow rate of polymer particles containing moisture.

The hot-air flow rate means a flow rate of air flowing into a fluidized bed dryer in order to remove moisture from polymer particles containing moisture.

The superficial velocity means an apparent velocity in which an inflow rate of polymer particles containing moisture is divided by a bed section area.

As described above, conventionally, when the residual monomer was removed through the drying process of the polymer, it was affected by various factors, and thus there were difficulties in controlling the residual monomer in the final product to a desired level.

In this regard, the present invention is intended to provide an indicator for making a product having a desired level of residual monomer by developing a drying condition factor for residual monomer control.

As one example, the present application is a method for controlling a residual monomer content in a polymer according to a drying process using a dryer,.

which may provide a residual monomer content controlling method of the polymer using a hot-air mass ratio factor represented by Equation <NUM> below.

Thus, by controlling the hot-air mass ratio represented by Equation <NUM> through the method for controlling the residual monomer content in the polymer according to the present application, it is possible to control the residual monomer content in the polymer regardless of one or more external factors selected from the group consisting of bed sizes, superficial velocities, hot-air flow rates, retention times and polymer types.

Specifically, the hot-air mass ratio factor represented by Equation <NUM> means the mass (Kg) of the hot-air flowing into the dryer relative to the mass (Kg) of the polymer flowing into the dryer.

As the hot-air mass ratio represented by Equation <NUM> increases, the content of the residual monomer may be decreased linearly or non-linearly.

Specifically, the increase of the hot-air mass ratio represented by Equation <NUM> means that the mass of the hot-air flowing into the dryer is larger than the mass of the polymer flowing into the dryer. Therefore, since a large amount of hot-air is supplied to dry a small amount of moisture-containing polymer, the content of the residual monomer in the final product is reduced.

The content of the residual monomer is controlled by further comprising a hot-air temperature factor.

For example, as the hot-air temperature increases under a condition that the hot-air mass ratio represented by Equation <NUM> is constant, it shows a tendency to decrease the content of the residual monomer.

At this time, the residual monomer content of the polymer is controlled to <NUM> ppm or less within a range of the hot-air temperature of <NUM> to <NUM> and the hot-air mass ratio of <NUM> to <NUM>.

Also, the residual monomer content of the polymer can be controlled to <NUM> ppm or less within the range of the hot-air temperature of <NUM> to <NUM> and the hot-air mass ratio of <NUM> to <NUM>.

Furthermore, the residual monomer content of the polymer can be controlled to <NUM> ppm or less within the range of the hot-air temperature of <NUM> to <NUM> and the hot-air mass ratio of <NUM> to <NUM>.

From this, it can be seen that the residual monomer content can be predicted depending on the hot-air mass ratio under a specific temperature condition.

The content of the residual monomer may be controlled by further comprising a hot-air velocity factor.

For example, as the hot-air velocity increases under a condition that the hot-air mass ratio represented by Equation <NUM> and the hot-air temperature are constant, it shows a tendency to decrease the content of the residual monomer.

The hot-air velocity means a velocity of air flowing into the fluidized bed dryer in order to remove moisture from polymer particles containing moisture.

At this time, when the hot-air temperature is maintained at <NUM>, the residual monomer content of the polymer can be controlled to <NUM> ppm or less within a range of the hot-air velocity of <NUM> to <NUM>/s.

Also, when the hot-air temperature is maintained at <NUM> and the hot-air mass ratio is <NUM> to <NUM> within the range of the hot-air velocity of <NUM> to <NUM>/s, the residual monomer content of the polymer can be controlled to <NUM> ppm or less.

Furthermore, when the hot-air temperature is maintained at <NUM> and the hot-air mass ratio is <NUM> to <NUM> within the range of the hot-air velocity of <NUM> to <NUM>/s, the residual monomer content of the polymer can be controlled to <NUM> ppm or less.

In addition, when the hot-air temperature is maintained at <NUM> and the hot-air mass ratio is <NUM> to <NUM> within the range of the hot-air velocity of <NUM> to <NUM>/s, the residual monomer content of the polymer can be controlled to <NUM> ppm or less.

Thus, when the hot-air temperature and the hot-air velocity are maintained, the residual monomer content can be predicted depending on the hot-air mass ratio.

The polymer capable of controlling the residual monomer content by the method according to the present invention is not particularly limited, but may be, for example, an acrylonitrile butadiene styrene (ABS) copolymer.

Hereinafter, the present application will be described in more detail by way of examples according to the present application and comparative examples that do not comply with the present application.

In a fluidized bed dryer having a bed section area of <NUM> x <NUM> and a bed height of <NUM>, while the hot-air temperature was changed to <NUM>, <NUM> and <NUM>, respectively, the contents of the residual monomer were measured according to hot-air mass ratios including the current mass-production dryer standard.

The results were shown in <FIG> below. Referring to <FIG>, it can be confirmed that as the hot-air mass ratio increases, the content of the residual monomer decreases.

In the same fluidized bed dryer as that of Example <NUM>, while the hot-air temperature was kept constant at <NUM> and the hot-air velocity was changed to <NUM>/s and <NUM>/s, respectively, the contents of the residual monomer were measured according to hot-air mass ratios.

In a fluidized-bed dryer, while the residence time and the hot-air temperature were changed to <NUM>/<NUM> and <NUM>/<NUM>, respectively, under a superficial velocity condition of <NUM>/s on the bed having a section area of <NUM>×<NUM> and a height of <NUM>, the contents of the residual monomer were measured. The results were shown in Table <NUM> below.

However, the results in Table <NUM> were results shown only under the very high superficial velocity condition on the bed having a section area of <NUM>×<NUM> and a height of <NUM>, and it was confirmed that these results were not shown under other conditions.

Such results are because the residence time and the superficial velocity, and the like change depending on the polymer inflow rate, the bed size and the physical property difference of the polymer.

That is, it means that regardless of the residence time and the hot-air temperature, when the hot-air is supplied at a very high velocity, a polymer having the very low residual monomer content can be produced.

Thus, it can be seen that such a method makes it difficult to predict the residual monomer content.

Claim 1:
A method for controlling a residual monomer content in a polymer according to a drying process using a dryer,
wherein the residual monomer content controlling method of the polymer uses a hot-air mass ratio factor represented by Equation <NUM> below:<MAT>
wherein A is a mass (Kg) of hot-air flowing into the dryer, and B is a mass (Kg) of the polymer flowing into the dryer,
wherein the residual monomer content in the polymer is controlled regardless of one or more external factors selected from the group consisting of bed sizes, superficial velocities, hot-air flow rates, retention times and polymer types,
wherein the content of the residual monomer is controlled by further comprising a hot-air temperature factor, wherein the residual monomer content in the polymer is controlled to <NUM> ppm or less within a range of a hot-air temperature of <NUM> to <NUM> and a hot-air mass ratio of <NUM> to <NUM>.