[DESCRIPTION]

[Invention Title]

Copolyester resin composition for profile extrusion molding and molded articles made from the same [Technical Field]

The present invention relates to a copolyester resin composition for profile extrusion molding and molded articles made from the same. More particularly, the present invention relates to a copolyester resin composition for profile extrusion molding, which shows improved melt flowability and thus increased melt processability during the production of profile extrusion products, such that the products can have increased transparency and, at the same time, excellent dimensional stability, as well as molded articles made from the resin composition. [Background Art]

Although the melt viscosity of polyester resins, which are generally used, is a level suitable for sheet molding by use of an injection process and calender rolls, it is relatively low for use in profile extrusion molding of products which have a constant cross-sectional area without the need of the calender rolls.

Particularly, when a polyester resin copolymerized with 1,4- cyclohexanedimethanol is used, it is very difficult to obtain products having the desired dimensions, because the cooling rate of the resin is very low. Also, in the case of polyester resins, which are used for the production of sheets and bottles and are obtained by copolymerizing ethylene glycol and terephthalic acid with other various glycols or dicarboxylic acids, there is a problem in that it is difficult to use these resins in

applications requiring transparency, because these resins exhibit a whitening phenomenon caused by crystallization, when the efficiency of cooling the resins is reduced.

For these reasons, various techniques for improving extrusion properties have been developed, but these have only comprised efforts to modify resins through polymerization. Regarding this, US Patent No. 5,399,595 discloses the use of a copolyester having a high intrinsic viscosity (IV). Said patent discloses adding 0.5-5.0 mol% of a dicarboxylic acid sulfomonomer, such that the copolyester has a high IV of 0.70-1.20 dl/g. In this case, extrusion of the copolyester is possible, but it is difficult to prevent the whitening phenomenon caused by crystallization. US Patent No. 4,983,711 discloses a method of increasing melt viscosity by adding a trifunctional monomer upon extrusion blow molding. Said method comprises adding 0.10-0.25 mol% of trimellitic acid or trimellitic anhydride to a copolyester resin containing diacid residues consisting essentially of terephthalic acid and diol residues consisting essentially of 25-75 mol% of ethylene glycol and 25-75 mol% of 1,4- cyclohexanedimethanol. In this case, the molecular weight of the copolyester resin is increased due to branching, thus increasing the melt viscosity thereof, but there is a problem in that the shear stress of the resin is increased due to the high melt viscosity, thus increasing the pressure in a molding machine during the processing of the resin. Also, because an irregular melt fracture is formed around an extrusion die, the dimensional stability of a product made of the resin is deteriorated, thus adversely affecting the transparency of the product.

Meanwhile, US Patent No. 6,100,320 discloses a method of reducing the resistance of a product to an extrusion die by adding a zinc-based lubricant in a profile extrusion process.

According to said patent, the zinc-based lubricant is added to a copolyester resin, comprising a diacid acid component of terephthalic acid and either a diol component of 50-85 mol% ethylene glycol and 15-50 mol% neopentyl glycol or a diol component of 5- 97 mol% ethylene glycol and 3-95 mol% 1,4-cyclohexanedimethanol, during the processing of the resin. In this case, the zinc-based lubricant acts as an external lubricant to reduce the resistance of the polymer to the extruder die, so that the irregular melt fracture does not occur. However, there are problems in that the dispersion of the zinc- based lubricant during the processing of the resin is not smoothly accomplished due to the high melting point thereof, and the lubricant particles are agglomerated like fisheyes during the production of a product from the resin, thus resulting in unmelted portions. [Disclosure] [Technical Problem]

Accordingly, the present inventors have conducted studies to solve the above- described problems and to produce products having better properties than those of profile extrusion products made from the prior copolyester resins and, as a result, found that, when a mono- or distearyl acid phosphate was added to a polyester resin copolymerized with 1,4-cyclohexanedimethanol, the problem of the irregular melt fracture of a melted resin during profile extrusion was solved, and it was possible to produce a product having better transparency resulting from improved dispersibility of the resin, compared to those of the resins disclosed in the prior patents. On the basis of this finding, the present invention has been completed.

Thus, it is an object of the present invention to provide a copolyester resin composition for profile extrusion molding, which has improved processability and

transparency and thus excellent dimensional stability, as well as molded articles made from the resin composition. [Technical Solution]

To achieve the above object, the present invention provides a copolyester resin composition for profile extrusion molding, comprising:

(a) a copolyester resin obtained by the esterification and polycondensation of (i) a dicarboxylic acid component comprising terephthalic acid, (ii) a diol component comprising 20-80 mol% 1,4-cyclohexanedimethanol and 20-80 mol% ethylene glycol, and (iii) 0.05-0.5 mol% multifunctional monomer based on the dicarboxylic acid; and (b) 50-5000 ppm, based on the copolyester resin, of a mono- or distearyl acid phosphate. [Description of Drawings]

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. 1 schematically shows a profile extruder, which is used for the extrusion of molded articles according to the present invention. * description of signs marked in Drawing * 10 : cutter 20 : take-off unit 30 : former 40 : forming die

50 : extrusion die 60 : extruder [Best Mode]

Hereinafter, the present invention will be described in further detail.

As described above, in the present invention, the mono- or disteary acid phosphate is added to a polyester resin copolymerized with 1,4-cyclohexanedimethanol. This resin composition shows improved processability, such as flowability, in the use thereof for the production of profile extrusion products having a constant cross-sectional area, such as pipes or tubes. Thus, the present invention provides the copolyester resin composition for profile extrusion molding, which can be produced into products, which have a clean product surface, excellent transparency and improved dimensional stability, as well as molded products made from the resin composition.

The copolyester resin, which is used in the present invention, is prepared through a first step of esterification and a second step of polycondensation.

The first step of esterification can be conducted in a batch or continuous process. Although each of the raw materials for use in the esterification can be separately added, it is most preferable to add the raw materials in the form of a slurry of the dicarboxylic acid component in the diol component. More specifically, the polyfunctional monomer, and optionally polyethylene glycol bisphenol-A, are added and allowed to react with the copolyester resin, prepared by allowing the dicarboxylic acid component, comprising terephthalic acid, to react with the diol component comprising ethylene glycol and 1,4-cyclohexanedimethanol.

In this regard, it is preferable to add the diol component to the dicarboxylic acid component in a content ratio of 1.2-3.0 (diol component): 1 (dicarboxylic acid component) and subject these components to esterification under conditions of temperature of 230-

260 ^° C and pressure of 1.0-3.0 kg/cm ² , but the present invention is not limited thereto.

More preferably, the esterification is carried out at a temperature of 240-260 ^° C and still

more preferably 245-255 °C . Also, the esterification is carried out for a time period of 100-300 minutes, which can be suitably adjusted depending on the esterification temperature and pressure and the molar ratio of glycol to dicarboxylic acid, which are used in the present invention. Examples of the dicarboxylic acid, which is used to improve the physical properties of the copolyester resin in the present invention, include, in addition to terephthalic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 1,3- cyclohexanedicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid and 2,6-naphthalenedicarboxylic acid, but are not limited thereto. Preferably, isophthalic acid is used in an amount of 1-40 mol% based on the terephthalic acid.

Meanwhile, as the diol component, which is used in the present invention, each of ethylene glycol and 1,4-cyclohexanedimethanol is used in an amount of 20-80 mol%.

Particularly, the 1,4-cyclohexanedimethanol is used to improve the moldability and other physical properties of a homopolymer composed of only terephthalic acid and ethylene glycol and can be used in the form of a cis-isomer, a trans-isomer or a mixture thereof. It is used in an amount similar to the mol% required in a final polymer. To prevent inferior moldability resulting from crystallization, 20-80 mol% of 1,4- cyclohexanedimethanol is used, based on the total amount of the glycol component. In addition to the above diol component, other glycol components, which can be used in the present invention, include 1,2-propanediol, 1,3 -propanediol, 1 ,4-butanediol, 2,2-dimethyl- 1,3 -propanediol, 1,6-hexanediol, 1 ,2-cyclohexanediol, 1 ,4-cyclohexanediol, 1 ,2-cyclohexanedimethanol and 1,3-cyclohexanedimethanol.

The multifunctional monomer, which is used in the present invention, serves as a cross-linking agent to improve profile extrusion properties, and examples thereof includes trimellitic acid, trimellitic anhydride, hemimellitic acid, hemimellitic anhydride, trimesic acid, tricarballyic acid, trimethylolpropane, trimethylolethane, glycerin and pentaerythritol, but are not limited thereto.

The multifunctional monomer is used in an amount of 0.05-0.5 mol% based on the dicarboxylic acid component. If it is used in an amount of less than 0.05 mol%, the composition will not reach melt strength useful for profile extrusion molding, and if it is used in an amount of more than 0.5 mol%, it will reduce transparency due to active crosslinking action, making it impossible to obtain a desired molded article.

Meanwhile, polyethyleneglycol bisphenol-A, which can be additionally used in the present invention, functions to increase the moldability of the copolyester resin and is represented by Formula 1 below:

[Formula 1]

wherein m+n is an integer ranging from 2 to 12.

The polyethyleneglycol bisphenol-A is preferably used in an amount of 0.1-20 mol% based on the dicarboxylic acid component. If it is used in an amount of less than 0.1 mol%, it will be difficult to realize the effect of improving properties by adding the polyethyleneglycol bisphenol-A, and if it exceeds 20 mol%, it will reduce reactivity.

A catalyst is not required in the esterification, but can be optionally added to

shorten the reaction time.

After completion of the first step esterification, the second step polycondensation is carried out. Before initiating the polycondensation, components that are conventionally used in polycondensation, for example, a polycondensation catalyst, a stabilizer and a coloring agent, can be selectively used, if necessary.

Polycondensation catalysts usable in the present invention include titanium compounds, germanium compounds and antimony compounds, but are not limited thereto.

The titanium-based catalyst acts as a catalyst for the polycondensation of the polyester resin copolymerized with 15 wt% or more, based on the weight of terephthalic acid, of 1,4-cyclohexanedimethanol. Such a titanium-based catalyst can perform the reaction, even when it is used in smaller amounts than antimony-based catalysts. Also, it is more inexpensive, compared to germanium-based catalysts.

Examples of the titanium-based catalyst, which can be used in the present invention, include tetraethyltitanate, acethyltripropyltitanate, tetrapropyltitanate, tetrabutyltitanate, tetrabutyltitanate, polybutyltitanate, 2-ethylhexyltitanate, octyleneglycoltitanate, lactatetitanate, triethanolaminetitanate, acetylacetonatetitanate, ethylacetoaceticestertitanate, isostearyltitanate, titanium dioxide, coprecipitates of titanium dioxide and silicon dioxide, and coprecipitates of titanium dioxide and zirconium dioxide.

Moreover, the amount of the polycondensation catalyst to be used affects the color of the final polymer, and thus may be varied depending on the desired color and the stabilizer and coloring agent used. Preferably, the polycondensation catalyst is used in an amount of 1-100 ppm as a titanium element based on the weight of the final polymer, and more preferably, in an amount of 1-50 ppm as a titanium element, and is used in an

amount of 10 ppm or less as silicon element. If the amount of the titanium element is less than 1 ppm, the desired polymerization degree cannot be achieved, and if it exceeds 100 ppm, the color of the final polymer can be yellowed, making it impossible to obtain a desired color. In addition, other additives such as a stabilizer and a coloring agent can also be used in the present invention.

Examples of the stabilizer, which can be used in the present invention, generally include phosphoric acid, trimethylphosphate, triethylphosphate, triethyl phosphonoacetate, etc., and it is preferably added in an amount of 10-100 ppm as a phosphorus element based on the weight of the final polymer. If the stabilizer is added in an amount of less than 10 ppm, it will be difficult to obtain a desired light color, and if it exceeds 100 ppm, it will be impossible to reach a high polymerization degree.

Also, examples of the coloring agent, which can be used to improve the color of the polymer in the present invention, include conventional coloring agents such as cobalt acetate and cobalt propionate, and the coloring agent is preferably added in an amount of 0-100 ppm based on the weight of the final polymer.

In addition to the above-mentioned coloring agent, an organic compound known in the art may also be used as the coloring agent in the present invention.

Meanwhile, the second step polycondensation, which is conducted after adding the above-described components, is preferably carried out at 260-290 ^° C under a reduced pressure of 400-0.1 mmHg, but is not limited thereto.

The polycondensation step is conducted for the period of time required to reach a desired intrinsic viscosity. At this time, the reaction temperature is generally in the range

of 260-290 ^° C, preferably 260-280 °C , and more preferably 265-275 "C .

Also, the polycondensation is conducted under a reduced pressure of 400-0.1 mmHg in order to remove glycol as a byproduct, thus obtaining a polyester resin copolymerized with 1,4-cyclohexanedimethanol. According to the present invention, the mono- or distearyl acid phosphate is added to the polyester resin copolymerized as described above in order to impart excellent processability, such as flowability, to the resin in the extrusion of the resin.

Examples of the lubricant, which is used in the present invention, include organic acids such as mono- or distearyl acid phosphates, but are not limited thereto. The mono or distearyl phosphate-based lubricant is represented by Formula 2 below: [Formula 2]

O

Il ( HO^- P-f OC ₁₈ H ₃₇ ) ₃ - _n

wherein n is an integar of 1 or 2. The mono- or distearyl acid phosphate-based lubricant is preferably used in an amount of 50-5000 ppm (parts per million) based on the weight of final polymer. If the mono- or distearyl acid phosphate-based lubricant is used in an amount less than 50 ppm, it cannot perform smooth dispersion action due to the insufficient use thereof, and thus cannot suppress an irregular melt fracture phenomenon, which occurs when the resin is released from an extruder die. On the other hand, if the amount of the mono- or distearyl acid phosphate-based lubricant added exceeds 5000 ppm, it will be difficult to rotate screws due to the excessive use thereof, and the transfer of heat into products will not be

accomplished due to the excessive powder chips, so that the transparency of unmelted products will be reduced, making it impossible to obtain desired molded articles. The inventive copolyester composition for profile extrusion molding as described above can be extruded according to a conventional profile extrusion method, thus obtaining profile extrusion products having constant cross-sectional area, such as pipes and tubes, which are improved with respect to irregular shapes on the surface thereof, and with respect to the color and dimensional stability thereof. [Mode for Invention]

Hereinafter, the present invention will be described in further detail with examples and comparative examples. It is to be understood, however, that these examples are for illustrative purposes only and are not to be construed to limit the scope of the present invention.

Physical properties shown in Examples and Comparative Examples below were measured in the following manner. Profile extruder

As shown in FIG. 1, a profile extruder was used, which comprises a cutter 10, a take-off unit 20, a former 30, a forming die 40, an extrusion die 50 and an extruder 60.

The former 30 and the take-off unit 20, which were used in profile extrusion, were those generally used in the art. The single-screw extruder had an L/D ratio of 30, and had a general structure capable of extruding polyolefin and polyvinyl chloride.

The temperature of the extruder cylinder was 240 ^° C , the temperature of the die was 220 °C, and the RPM of the former was 30. Products were square-shaped tubes having a thickness of 0.5 mm.

Transparency (%) and haze

Measurements were performed using a haze-meter manufactured by Nippon Denshoku, Japan.

Surface defects Products made using the extruder as shown in FIG. 1 were observed over an area of 300 mm in the extrusion direction and 15 mm in a direction perpendicular to the extrusion direction. The surface defects were expressed as a numerical value of the number of patterns caused by irregular melt fractures in the production of the products, i.e., the number of lines generated in a direction perpendicular to the extrusion direction. Fisheyes

Products made using the extruder as shown in FIG. 1 were observed over an area of 300 mm in the extrusion direction and 15 mm in a direction perpendicular to the extrusion direction. The number of fisheyes occurring on the surface of the products was expressed as a numerical value. Melt pressure

Measurements were made using an extrusion blow molding machine manufactured by Bekum, Germany. 20 min after about 20 kg of a sample was introduced into the molding machine, an average value was determined when the difference between the set internal temperature and the actual internal temperature of the molding machine was less than ± 1 "C and the deviation of the melt pressure was less than 4 bar.

Melt viscosity

Measurements were made in a region of shear rate (l/s)=l using a parallel plate- type Physica Rheometer manufactured by Physica, USA.

Melt strength

Measurements were made using an extrusion blow molding machine manufactured by Bekum, Germany. That is, while an extruding process was conducted under conditions of 20 RPM, cycle time of 17 sec, a die diameter of 30 mm, and an extruder temperature and die temperature of 195-220 ^° C and 190-205 ^° C , respectively, the diameter of a portion of material extruded from the extrusion blow molding machine, which was located downwards at a distance of 100 mm from a die of the molding machine, was determined.

The melt strength (%) was calculated according to the following equation:

{(X-D)} over {D } times 100 wherein, X is the diameter of a portion of material, which is distant from a die by 10 cm, and D is the die diameter. Thus, if X is smaller than D, the melt strength (%) has a negative value. Meanwhile, when X is larger than D, the melt strength (%) has a positive value.

Example 1 In a 3-L reactor equipped with a stirrer and a discharge condenser, 2.0 g of trimellitic anhydride, based on 6 mol of terephthalic acid, was added to a copolyester resin comprising 294 g of 1,4-cyclohexanedimethanol and 469 g of ethyleneglycol. Then, 1O g of polyethyleneglycol bisphenol-A, having m+n=2 in Formula 1, was added thereto and the contents of the reactor were mixed with each other while the temperature in the reactor was slowly increased to 255 "C .

At this time, generated water was discharged out of the system to perform esterification of the contents of the reactor. After completion of the generation and discharge of water, the esterification product was transferred into a polycondensation

reactor equipped with a stirrer, a cooling condenser and a vacuum system.

Then, 0.5 g of tetrabutyltitanate, 0.4 g of triethylphosphate and 0.5 g of cobalt acetate were added to the esterification product. While the inner temperature of the reactor was raised from 240 ^° C to 275 ^° C , ethylene glycol was discharged over 40 minutes during low vacuum reaction in which the pressure was reduced from atmospheric pressure to 50 mmHg. Then, while the pressure of the reactor was slowly reduced to 0.1 mmHg, the polycondensation reaction was further carried out until the product reached a desired inherent viscosity. The resulting polymer was discharged out of the reactor and cut in the form of chips. The resin produced through the above reaction procedures was dried in a dehumidifying dryer at 65 ^° C for 6 hours in order to prevent the IV of the resin from being reduced. The dried resin was pre-mixed with 0.66 g of mono- or distearyl acid phosphate in a mixer (tumbler). Then, the resin was manufactured into a profile product using a general profile extruder as shown in FIG. 1. The above reaction conditions together with the results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure are shown in Table 1 below.

Example 2

A profile product was manufactured in the same manner as in Example 1, except that 0.66 g of a mono- or distearyl acid phosphate monomer was added. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Example 3

A profile product was manufactured in the same manner as in Example 1, except

that the mono- or distearyl acid phosphate as an additive were made into a master batch using a twin screw extruder without conducting pre-mixing in the mixer, and then the master batch was added in an amount of 0.66 g based on the total weight of the polymer. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Example 4

A profile product was manufactured in the same manner as in Example 1, except that 31 mol% isophthalic acid, based on the amount of terephthalic acid, was added to prepare a copolymer. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Example 5

A profile product was manufactured in the same manner as in Example 1, except that the polyethyleneglycol bisphenol A monomer was not added in the reaction step. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Example 6 A profile product was prepared in the same manner as in Example 1, except that

190 g of the polyethyleneglycol bisphenol A monomer was added. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Comparative Example 1

A profile product was manufactured in the same manner as in Example 1 , except that the mono- or distearyl acid phosphate compound was not added. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Comparative Example 2

A profile product was manufactured in the same manner as in Example 1, except that the polyethyleneglycol bisphenol-A in the polymerization step and the mono- or distearyl acid phosphate compound in the profile extrusion step were not added. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Comparative Example 3

A profile product was manufactured in the same manner as in Example 1, except that a zinc-based lubricant was used in place of the mono- or distearyl acid phosphate.

The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Comparative Example 4 A profile product was manufactured in the same manner as in Comparative

Example 3, except that a phosphorus-based stabilizer was additionally used. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Comparative Example 5

A profile product was manufactured in the same manner as in Comparative

Example 3, except that 31 mol% isophthalic acid based on terephthalic acid was used to prepare a copolymer. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

Comparative Example 6

The manufacturing of a profile product was conducted in the same manner as in Example 1, except that trimellitic acid and polyethyleneglycol bisphenol-A were not added in the polymerization step, and no other material was added in the profile extrusion of the polymer. However, in this case, the profile product was not manufactured due to low melt viscosity and strength. The results of measurement of surface defects, fisheyes, transparency, melt viscosity, melt strength and melt pressure, together with the reaction conditions, are shown in Table 1 below.

[Table 1]

[Industrial Applicability]

As can be seen Examples and Comparative Examples, according to the present

invention, the mono- or distearyl acid phosphate-based lubricant is added to the polyester resin copolymerized with 1,4-cyclohexanedimethanol. The use of the copolyester resin comprising this lubricant makes it possible to obtain profile extrusion products having excellent color and dimensional stability and a clean product surface, compared to the use of copolyester resins according to the prior methods.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the present invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they fall within the scope of the appended claims and their equivalents.