TITLE OF INVENTION

A METHOD TO PRODUCE A WELL-DISPERSED MgO NANOPARTICLE-BASED ZIEGLER-NATTA CATALYST, AND USAGE IN PRODUCING ULTRA HIGH MOLECULAR

WEIGHT POLYETHYLENE

TECHNICAL FIELD

The present invention relates to a method for producing an olefin polymerization catalyst, particularly a Ziegler-Natta catalyst, using well-dispersed MgO nanoparticles as its carrier, and a method for producing ultra high molecular weight polyethylene micro-fine powder, which comprises a step of polymerizing ethylene in the presence of the catalyst. The present invention also relates to the ultra high molecular weight polyethylene micro-fine powder produced in the method above, and a molding product made from a material containing this one.

BACKGROUND

Ultra high molecular weight polyethylene (UHMWPE) has excellent impact toughness, self- lubricating ability, and high abrasion resistance, and has been used for gears, bearings, guide rails, slide parts, artificial hip joints, and machine parts, etc. Because UHMWPE has poor flowability in melting process, the special molding method using the polymer powder is required, thereby the defect resulting from a particle surface may causes a problem. Therefore, various researches have been conducted for improving particle morphology of the UHMWPE powder. Ziegler-Natta catalyst is the most publicly available catalyst as catalyst upon polymerizing olefin such as ethylene. In general, in ethylene polymerization using solid polymerization catalyst, the particle diameter of produced polyethylene powder is generally determined by the particle diameter and the activity of the catalyst. When the growth of polyethylene particle while being polymerized is surpressed by lowly activating the catalyzer, the cost of the catalyst per amount of production of the polyethylene goes up, therefore there is a problem that the whole producing cost goes up. Furthermore, in this regard, catalyst residual amount contained in the produced polyethylene increases, thus it is not desirable for the quality of the polyethylene.

Then, the improvement of the catalysts for obtaining UHMWPE having the smaller particle diameter is proposed (Patent Literatures 1 and 2). Patent Literature 1 discloses UHMWPE powder having the particle diameter in the range of ca. 8-15 pm. Patent Literature 2 discloses the UHMWPE powder below with the particle diameter of 40 pm or less. However, as these examples, a method for micronizing the UHMWPE powder via the particle diameter requires complicated catalyst preparation, and futhermore there was a limitation in the micronization of the catalysts. Thus, in these methods, UHMWPE powder having the particle diameter of less than 5 pm cannot be selectively produced at low cost.

A method for producing UHMWPE micro-fine powder, in which UHMWPE slurry just after polymerization is sheared at high-speed, is also proposed (Patent Literature 3). However, the particle diameter of the UHMWPE powder according to this method is still in a range of 20-30 pm, it is still impossible to produce the UHMWPE powder with the particle diameter less than 5 pm. Furthermore, such process for the UHMWPE slurry requires an additional equipment.

On the other hand, the following method of obtaining UHMWPE powder with a smaller particle diameter has been proposed. In the method UHMWPE powder is dissolved in a solvent, the obtained UHMWPE solution is cooled down, and UHMWPE is precipitated (Non-patent Literatures 1 and 2). Non-patent Literature 1 discloses a method of precipitating UHMWPE micro-fine powder that is spharical or aproximately spherical with a 0.1 -1.0 pm particle diameter by rapidly cooling down UHMWPE decaline or decane solution. Non-patent Literature 2 discloses that a 1-2 pm particle diameter UHMWPE micro-fine powder, obtained by precipitating after cooling and centrifugating UHMWPE biphenyl ether solution, is separated. However, these methods using a solvent are not suitable for mass production of UHMWPE micro-fine powder, thus there may be a practical problem. Another method of obtaining small particle diameter UHMWPE powder by crushing commercial product of UHMWPE powder with various medium is proposed (Non-patent Literature 3). Nonpatent Literature 3 discloses that more than 50% of the processed UHMWPE particles had the particle diameter of less than 4 μιη. However, the particle form of the UHMWPE powder obtained through the method was irregular, hence, it was still impossible to selectively produce UHMWPE powder having the uniform and a less than a 5 μιτι particle diameter.

As mentioned above, any method has not been established yet for directly and selectively producing the UHMWPE, which has the so-called nanosize (less than 5μηι or typically approximately 1 μηη particle diameter). At present, only a few commercial products are available as micro-fine-type UHMWPE, for example, GUR® by Ticona, SUNFINE®AQ by Asahi Kasei, and Miperon ^® by Mitsui Chemical are publicly known. These products are UHMWPE having the particle diameter of approximately several tens μηη, and they are used for rubber or cosmetic materials as modifiers or additives.

PRIOR ART [Patent Literature 1] US patent publication 2010/0196711 A1 [Patent Literature 2] US patent US 7,601 ,423 B2 [Patent Literature 3] US patent US 4,972,035

[Non-patent Literature 1] "Submicron-Size Particles of Ultrahigh Molecular Weight Polyethylene Produced via Nonsolvent and Temperature-Induced Crystallization" Yaravoy et al., Journal of Biomedical Material Research (2000), 53, p. 152-160.

[Non-patent Literature 2] "Preparation and Characterization of Spherical and Irregularly Shaped Micron and Submicron-sized UHMWPE Particles" Wunder et al., 48th Annual Meeting of the Orthopedic Research Society, 2002 [Non-patent Literature 3] "Research and Development Report: Production of Fine Particulate Ultra High Molecular Weight Poly (ethylene) for Biological Response Studies" Leigh et al., Journal of applied Biomaterials (1992), 3, p. 77-80.

[Non-patent Literature 4] " MgO/MgCI ₂ /TiCI4 Core-Shell Catalyst for Establishing Structure- Performance Relationship in Ziegler-Natta Olefin Polymerization", Patchanee Chammingkwan, Vu Quoc Thang, Minoru Terano, Toshiaki Taniike, Topics in Catalysis, 2014, 57, 91-97.

SUMMARY OF INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

Inventors according to the present invention challenged to product UHMWPE micro-fine powder using the Ziegler-Natta catalyst at low cost although it used to be impossible. The aim according to the present invention is to produce a novel Ziegler-Natta catalyst with uniform and extremely minimized particle diameter in simple steps, and to obtain UHMWPE micro-fine powder with the particle diameter less than 5 μιη from a polymerization vessel, using the novel Ziegler-Natta catalyst.

In the present invention, magnesium oxide (MgO) nanoparticles are transformed into well- dispersed MgO nanoparticles by processing MgO particles as a carrier of the Ziegler-Natta catalyst in simple steps. Subsequently, the nano-sized Ziegler-Natta catalyst (MgO/MgC /TiCU) is successfully prepared in simple steps by chlorinating and titanating only a surface of the MgO nanoparticles above with TiCU. In the present invention, the UHMWPE micro-fine powder whose particle diameter is one-digit-order lower than previous particle diameter values, that is, several micrometers or typically approximately 1 μιη is successfully synthesized using the nano-sized Ziegler- Natta catalyst.

That is, the present invention is as follows;

(1): A method for producing a well-dispersed MgO nanoparticle-based olefin polymerization catalyst, which comprises a step of producing well-dispersed MgO nanoparticles by mixing MgO particles, a hydrocarbon solvent, and a surfactant, and a step of contacting the well-dispersed MgO nanoparticles with titanium tetrachloride (TiCU).

(2) : A method for producing the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst according to the method (1 ), wherein the step of preparing the well-dispersed MgO nanoparticles includes the steps of refluxing a mixture of the MgO particles, the hydrocarbon solvent, and a polyoxyethylene alkyl amine for half an hour to several hours at a temperature equal to or more than a boiling point of the hydrocarbon solvent using the polyoxyethylene alkyl amine as a surfactant; and washing the processed MgO particles by heptane; wherein the step of contacting the well-dispersed MgO nanoparticles with the titanium tetrachloride (TiCI ₄ ) includes the steps of adding TiCU to a dispersion liquid in which the well-dispersed MgO nanoparticles are distributed in heptane; catalyzing a surface part of the well-dispersed MgO nanoparticles by heating the obtained mixture in a reflux condition of a temperature from 100°C to 180°C for 1 hour to 5 hours; and afterwards washing an obtained catalyst particle.

(3) : The method according to the method (1) or (2), wherein the olefin polymerization catalyst is a Ziegler-Natta catalyst.

(4) : A well-dispersed MgO nanoparticle-based ofefin polymerization catalyst obtained in the method according to the method (1 ) or (2). (5): A well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst obtained in the method according to the method (3).

(6): A method for producing ultra high molecular weight polyethylene micro-fine powder, which comprises a step of ethylene polymerization in the presence of the well-dispersed MgO nanoparticle- based Ziegler-Natta catalyst of (5).

(7): Ultra high molecular weight polyethylene micro-fine powder, obtained in the method according to the method (6), and whose median diameter (D50) in particle diameter distribution is less than 5 μηι. (8): A molding product, made from a material including the ultra high molecular weight polyethylene micro-fine powder according to (7).

ADVANTAGEOUS EFFECT OF INVENTION

In the method for producing polymerization catalyst according to the present invention is what a MgO carrier particle used in the previous metnod is modified. Surprisingly, according to the present invention, it is succeeded in producing the so-called nano-sized Ziegler Natta catalyst, which used to be impossible, in such a simple way. The method of producing the polymerization catalyst according to the present invention is a method to produce catalyst for producing UHMWPE having excellent properties at extremely low cost.

The catalyst according to the present invention comprises MgO as a major component, and Chlorine atoms bringing its catalyst activity exist only on an surface layer of the MgO. This fact is supported by the result of the experiment in which only the surface of the MgO nanoparticle-based Ziegler-Natta catalyst without dispersing process is chlorinated (see Non-patent Literature 4). Thus, the amount of the chlorine residue in the UHMWPE produced using the catalyst according to the present invention is remarkably low. It is expected that yellow-coloring in storage or use of the UHMWPE does not easily occur on the UHMWPE obtained using the catalyst according to the present invention.

Compared with the previous UHMWPE micro-fine particles, the UHMWPE micro-fine particles according to the present invention have a one-digit lower particle diameter, therefore its dispersibility regarding its processibility and other materials are surprisingly improved. The UHMWPE micro-fine particles according to the present invention is useful not only for usage of the same modifier or additive as those of the existing micro-fine particles, but also for compression-molding or coating.

BRIEF DESCRIPTION OF FIGURES

Fig.1 shows particle diameter distribution curves of E-Cat50 (Example 2-1 ) and E-Cat200 (Example 2-2) according to an example of the catalyst according to the present inventioin, and Cat-50 (Comparative Example 2-1) and Ind-Cat (Comparative Example 2-2) as comparative examples.

Fig.2 shows particle diameter distribution curves of E-Cat20(Example 5-1 ) and E-Cat50(Example 5- 2) according to an example of the catalyst according to the present inventioin, and E-Cat100(Example 5-3) and E-Cat200(Example 5-4) as comparative examples. Fig.3 shows appearance of sheets made from E-PE50 as an example according to the present invention (upper), and sheets made from Ind-PE as a comparative example (lower), when compression-molding at 120 °C, 130 °C, 135 °C, and 140 °C in order from the left.

Fig.4 shows an outer surface of a coating layer made from E-PE50 as an example of the UHMWPE according to the present invention. Fig.5 shows an outer surface of a coating layer made of Ind-PE as a comparative example.

Fig.6 shows appearance in which the surface of the coating layer of E-PE50 as the example of UHMWPE according to the present invention is scratched with tweezers.

Fig.7 shows appearance in which the surface of the coating layer of Ind-PE as the example of UHMWPE as the comparative example is scratched with tweezers.

Fig.8 shows appearance in which a surface of HDPE sheet is scratched. DETAILED DESCRIPTION

[1] Production of well-dispersed MgO nanoparticles

Typically, due to low polarity of MgO, its dispersibility into a non-polar solvent such as a hydrocarbon solvent is poor. When MgO is dispersed in hydrocarbon, MgO particles agglomerate, thus the particle diameter of the MgO particles observed in the solvent is much larger than the particle diameter of the actual MgO primary particles. It is observed that the MgO particles can be dispersed as primary particles in ethanol which is a polar solvent, however the dispersibility is low in heptane and the primary particles are agglomerated: When the MgO aggregate dispersed in the hydrocarbon solvent is used as a carrier for various functional substances, it is considered that the outer surface of the aggregate preferentially functions.

In general, preparation of MgO-based Ziegler-Natta catalyst using usual MgO, MgO is transformed into the catalyst with its agglomerated particle form maintained in a hydrocarbon solvent. Therefore, previously, the particle diameter of the MgO-based Ziegler-Natta catalyst has inevitably got almost the same with or larger than the particle diameter of the agglomerated MgO particles.

In the present invention, upon improving the method of producing MgO-based Ziegler-Natta catalyst, an attempt was made to prepare the catalyst in a condition in which the MgO carrier particles do not agglomerate. As a result, a MgO carrier that exhibits good dispersibility in a hydrocarbon solvent was acquired in a simple method, and a novel MgO nanoparticlebased Ziegler-Natta catalyst employing the improved MgO carrier was successfully obtained. The MgO nanoparticlebased Ziegler-Natta catalyst according to the present invention is easily prepared by modifying previous materials and processes. Nonetheless, the function and performance of the MgO nanoparticlebased Ziegler-Natta catalyst according to the present invention significantly exceed previous ones. The present invention provides novel MgO nanoparticlebased Ziegler-Natta catalyst and its application. The Ziegler-Natta catalyst according to the present invention is characterized in employing a MgO carrier material which is modified with a surfactant in a hydrocarbon solvent. The MgO carrier essential for the present invention is prepared through processes that particle aggregation, which is unavoidable in the production process of nomal Ziegler-Natta catalyst, is suppressed, and exists as nano-sized primary particles in a hydrocarbon solvent. Such the novel MgO carrier is named "well- dispersed MgO nanoparticles" in the present invention. The well-dispersed MgO nanoparticles may be typically prepared through the following Step 1 , 2 and 3 in this order.

(Stepl ) In Step 1 , MgO particles, a hydrocarbon solvent, and a surfactant are mixed. The mixing is usually done by stirring at room temperature. Regarding MgO particles, any types are applicable as far as they are classified in nanoparticle-type (or fine grade). Generally, MgO particles with a particle diameter in a range of ca. 10-300 nm, preferably 20-200 nm is generally used. As the hydrocarbon solvent, for example, heptane (b.p.99 °C), toluene (b.p.111 °C), or kerosene (b.p. ca. 150-160 °C) is employed.

As the surfactant, a non-ionic or a cationic surfactant is generally used, however a non-ionic surfactant such as polyalkylene glycol derivatives or sorbitan fatty acid ester derivatives is preferably used. A typical example of the surfactant employed in the present invention is epresented by the following formula.

(Formula 1 of surfactant) R in the follwoing fomulae represents a hydrocarbon group.)

[Chemi 1]

(CH ₂ CH ₂ 0) _m H (Formula 2 of surfactant) [Chemi 2]

(Formula 3 of surfactant) [Chemi 3]

Among these surfactants, the group of polyoxyethylene alkylamines represented by Formula 1 is preferable. Commercial product named ELEGAN S-100 (represented by Formula 1 with n:1-4, R:10- 14) by NOF Corporation is available as the preferable surfactant. (Step 2) In Step 2, the mixture obtained in Step 1 is subjecetd to heat treatment under being refluxed. The mixture is heated up to the temperature equal to or more than the boiling point of the hydrocarbon solvent, and is refluxed for a certain time in respond to the amount of the mixture, preferably half an hour to sevral hours. Through Step 1 and Step 2, the well-dispersed MgO nanoparticle is synthesized. (Step 3) In Step 3, the MgO particles obtained through Step 2 are separated and washed. There is no limitation over separating means. Any organic solvent generally used in a washing process is employable as the washing medium, however preferably heptane generally used in the following catalyst preparation. There is no limitation in the usage amount of the solvent and the repeating times of the washing as far as soluble substances to the organic solvent on the MgO can be sufficiently washed out.

In the method of producing the well-dispersed MgO nanoparticle according to the present invention, only Step 1 is added to the previous methods, thus a commercially available surfactant is newly added in the new material. With such a simple method, it is possible to produce the well- dispersed MgO nanoparticles according to the present invention. The method of producing the well- dispersed MgO nanoparticles according to the present invention is regarded highly efficient in view of industries.

Unmodified MgO particles were ununiformly dispered while agglomerating as secondary particles in a hydrocarbon solvent. Meanwhile, the well-dispersed MgO nanoparticles according to the present invention do not agglomerate in a non-polar solvent, and are well dispersed with the form of uniform sized extremely small particles (so-called "nanoparticles"). The well-dispersed MgO nanoparticle powder according to the present invention is a novel MgO particle in terms of its high dispersibility in the non-polar solvent.

[2] Producing of well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst

The method for producing the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst according to the present invention comprises a step of contacting the well-dispersed MgO nanoparticles obtained in the method above with titanium tetrachloride (TiCU), and typically comprises the following Steps 4, 5 and 6 in this order after Steps 1 , 2 and 3.

(Step 4) In Step 4, the well-dispersed MgO nanoparticles obtained through Step 3 are dispersed in a non-protic organic solvent, and titanium tetrachloride (TiCU) is added to the dispersion. As the solvent, a hydrocarbon solvent, preferably heptan is avalable. The amounts of the MgO, the solvent and the TiCI ₄ are arranged in accordance with a predetermined method. The temperature, etc. when contacting the well-dispersed MgO nanoparticles to the TiCU are also arranged in accordance with conventional conditions.

(Step 5) In Step 5, the mixture obtained throughStep 4 is heated at the temperature equal to or more than the boiling point of the organic solvent above in a refluxing condition. In case of using heptane as the organic solvent, the mixture is heated at the temperature equal to or more than the boiling point of heptane (99°C), preferably at the temperature of 100-180°C. Heating time is corrrespondant to the amount of the mixture, usually from half an hour to several hours, preferably one to five hours. Through Step 4 and Step 5, the surface layer part of the well-dispersed MgO nanoparticle is modified into catalyst component.

(Step 6) In Step 6, the catalyst particles obtained through Step 5 are washed. Any organic solvent usually used in a washing process is available in the washing medium, however preferably heptane generally preferably used for catalyst. There is no limitation in the amount of the the washing medium and repeating times of the washing as far as surplus substances are fully removed from the catalyst particles.

The particle from of the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst obtained through Step 1 to 6 depends on that of the well-dispersed MgO nanoparticle. Therefore, the particles also have a uniform particle diameter of under 1 μιη. The catalyst with such particle form is called as "well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst" in the present invention. The well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst composed of independent primary particles woukd be novel catalyst previously not available. Step 4, 5 and 6 are common to a processing step to the MgO nanoparticle-based conducted in producing the privious MgO-based Ziegler-Natta catalyst (Mgo/MgC /TiCU). Comparing the whole catalyst preparation processes, there is no difference in complication between the previous method and the mothod for producing the MgO-based Ziegler-Natta catalyst according to the present invention. The method for preparing the Ziegler-Natta catalyst according to the present invention enables to improve catalyst performance at low cost.

[3] Production of UHMWPE micro-fine particles

By polymerizating ethylene in the presence of the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst according to the present invention, it is possible to obtain ultra high molecular weight polyethylene (UHMWPE) in which the particle diameter depends on the form and the yield of the catalyst particle.

The well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst according to the present invention has the same handling property as that of the previous MgO-based Ziegler-Natta catalyst In producing UHMWPE. The UHMWPE micro-fine powder according to the present invention can be obtained by providing etylene under the same conditions of temperature and pressure in the presence of the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst according to the present invention. The UHMWPE micro-fine powder according to the present invention is a novel material which is previously unable to be produced, and which is a micro-fine having a uniform particle diameter less than 5 μιη, and appears insignificant agglomeration of primary particles. The activity in ethylene polymerization of the well-dispersed MgO nanoparticle-based Ziegler-

Natta catalyst according to the present invention is comparable to that of typical catalyst commercially produced. Therefore, it is possible to efficiently produce the UHMWPE micro-fine powder according to the present invention in the presence of the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst according to the present invention. [4] Molding product using UHMWPE micro-fine powder A molding product using the UHMWPE micro-fine powder according to the present invention is characterized by a lower fusion temperature, and good scratch resistance, in comparison with the conventional UHMWPE particle. Such UHMWPE micro-fine powder according to the present invention is useful as a material for compression-molding at lower temperature and a coating material. [Examples]

Examples according to the present invention and comparative examples are demonstrated as below. Note that in measuring particle diameter distribution, a laser scattering particle diameter distribution analyzer "Partica LA-950V2" by HORIBA Scientific, and a vacuum dispersion particle image analyzer "VD-200nano" by JASCO were used. In measuring titanium content, a ultraviolet- visible absorption spectrometer "V-670" by JASCO was used. The intrinsic viscosity ([η]) of UHMWPE was derived in accordance with ASTM 4020D, and the calculated [η] was converted to a viscosity average molecular weight (M _w ) in accordance with the following Margolies equation.

Μ _ν = 5.37 ^χ 10 ^4χ [η] ^{1 49}

[1] Production of well-dispersed MgO nanoparticles Commercial products of MgO powder having a 50 nm particle diameter (hereinafter called

"MgO(50)"), and a 200 nm particle diameter (hereinafter called "MgO(200)") are prepared.

2g of the MgO(50) and 8.0 ml of commercial product "ELEGAN S-100" by NOF Corporation were added into 25 mL of kerosene, and these materials were mixed (Step 1), and the mixture was heated at 160°C to reflux for one hour (Step 2). The solid product was washed several times with heptane (Step 3) and recovered. As proessed above, E-MgO(50), which is the well-dispersed MgO nanoparticle according to the present invention, was obtained.

Step 1 , 2 and 3 were also performed using 2g of the MgO(200), thereby E-MgO(200), which is the well-dispersed MgO nanoparticle according to the present invention, was obtained.

The particle diameter and particle diameter distribution of the E-MgO(50), the E-MgO(200), the unmodified MgO(50) (Comparative example 1-1 ) and the unmodified MgO(200) (Comparative example 1-2) were measured by laser scattering in n-heptane. Results are summarized in Table 1. Note that Dio, D50 and D90 represent particle diameters respectively corresponding to 10%, 50% and 90% in the cumulative volume-based particle diameter distribution. Especially, D50 is called "median diameter.". [Table 1]

Based on Table 1 , it is found that the E-MgO(50) and E-MgO(200) are well dispersed in heptane as so-called nanosize particles without agglomeration. These particle diameters are almost the same as those of unprocessed MgO dispersed in ethanol. Meanwhile, the particle diameters of the unmodified MgO(50) and MgO(200) is greatly larger than the corresponding primary particle diameter, threrby it is found that agglomeration (poor dispersibility) of the particles in heptane.

[2] Production of well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst

2g of the E-MgO(50) was suspended into 100 mL of heptane, and 30 mL of TiCI ₄ was added to this (Step 4). The mixture is refluxed for one hour while heated at 110°C (Step 5). Next, the solid product was washed several times with heptane (Step 6). As processed above, E-Cat50, which is the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst according to the present invention, was obtained.

Steps 4, 5 and 6 were also performed using 2g of the E-MgO(200), and E-Cat200 which is the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst according to the present invention was obtained.

Steps 4, 5 and 6 were applied to 2g of the MgO(50) and Cat50 as a comparative example of Ziegler-Natta catalyst was obtained. Steps 4, 5 and 6 were applied to 2g of the MgO(200) and Cat200 as a comparative example of Ziegler-Natta catalyst.

Further, as a comparative example, Ind-Cat as Ziegler-Natta catalyst for producing UHMWPE was prepared. The method for producing Ind-Cat is disclosed as Example 1 in the international patent publication, WO 2014/007765.

Table 2 shows results in which a titanium content(wt%) and the particle diameter and the particle diameter distribution measured regarding the E-Cat50, E-Cat200, Cat50, Cat200, and Ind-Cat measured by laser scattering in n-heptane. Fig.1 shows a particle diameter distribution curve for the E-Cat50, E-Cat200, CatSO and Ind-Cat.

[Table 2]

Based on Table 2 and Fig.1 , it is found that the well-dispersed MgO nanoparticle-based Ziegler- Natta catalyst according to the present invention has a very sharp particle diameter distribution curve around the particle diameter area below 1 μηη, corresponding to the narrow particle diameter distribution of the well-dispersed MgO nanoparticle.

The activity per unit gram of the catalyst is lower than that of the Ind-Cat, however, the activity per unit Ti amount of the catalyst is approximately equal to that of the Ind-Cat. Addtionally, in the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst in which a majority of components mainly consist of MgO, the residual chlorine content in produced UHMWPE can be significantly reduced in comparison with the conventional Ziegler-Natta catalyst.

[3] Production of UHMWPE Ethylene was polymerized in a 1 -litre stainless high-pressure reactor equipped with a mechanical stirrer function. 500 ml. of heptane as a solvent, 1.0 mmol of triethylaluminum as activator, and 10 mg of E-Cat50 were supplied into the reactor under nitrogen atmospher, and were stirred at 70°C and 750 rpm. Polymerization was started by supplying ethylenepressured at 0.8 MPa. After 2-hour long polymerization at the constant pressure and temperature, the polymerization was terminated by adding acidic ethanol consisting of ethanol and hydrochloric acid. The obtained white powder was filtrated, and dried at 60°C for six hours under reduced pressure. As processed above, powder E- PE50 composed of of the UHMWPE according to the present invention was obtained.

Ethylene is also polymerized in tha same condition using the Ind-Cat, thereby the Ind-PE which is a comparative example UHMWPE particle was obtained.

Table 3 shows properties of E-PE50 and Ind-PE. Note that the theoretical particle diameter (Dp _E ) was calculated by the following formula. In the formula, "dcat" denotes the density of catalyst, "d _PE " denotes the density of UHMWPE, Ύ" denotes the yield of UHMWPE per gram of catalyst, and "Dcat" denotes the particle diameter of the catalyst. [Formula 1]

Based on Table 3, the particle form of the E-PE50 shows the similar particle diameter theoretically derived from the particle form of the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst E- Cat50, and suggests single dispersion of the catalyst particles was throughly maintained during the ethylene polymerization. The particle diameter "1.3 μητι" of the E-PE50 is surprisingly small as UHMWPE micro-fine powder obtained in present of the catalyst advantageous in terms of cost. E- PE50 has the approximately same molecular weight and melting point as those of the conventional UHMWPE, therefore it is found that molecular structures which can be industrially satisfied are produced. [Table 3]

[4] Production of well-dispersed MgO nanoparticles with other sizes

The commercial product employed in the process [1] was replaced to one with the particle diameter of 20 nm or 100 nm. Thus, two more examples of the well-dispersed MgO nanoparticles according to the present invention named "E-MgO(20)" and "E-MgO(100)" were prepared. Table 4 shows properties of E-MgO(20), E-MgO(50), E-MgO(100) and E-MgO(200) in the same condition as the process [1]

[Table 4]

[5] Production of well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst with other sizes

The well-dispersed MgO nanoparticle-based Ziegler-Natta catalysts according to the present invention named "E-Cat20" and "E-Cat100" were produced in the same condition as the process [2]. Table 5 and Fig.2 show particle distribution of the E-Cat20, E-Cat50, E-Cat100 and E-Cat200.

Based on Table 4 and Table 5, it is found that the particle diameter of the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst belong to so-called nano-size, and is controlled by the particle diameter of the MgO carrier. Because the particle diameter of the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst corresponds to the particle diameter of the MgO carrier.

As shown in Table 5 and Fig.2, so-called nano-size of the particle diameter is attained in every case of E-Cat, E-Cat20, E-Cat50, E-Cat100 and E-Cat200. Based on Table 5, it is found that the titanium content in the catalyst was increased along with the increase of the surface area of the MgO carrier. This fact suggests that active catalytic components comprising titanium atoms were formed only on the surface layer of the well-dispersed MgO nanoparticles according to the present invention.

[Table 5]

[6] Fusion temperature of UHMWPE micro-fine powder

Powder of the E-PE50 was evenly spread in an aluminium mold with the dimensions of 5 cm (length) ^χ 5 cm (width) ^χ 500 jt/n (thickness). Subsequently, the upper side of the surface of the mold was pressed at 20 MPa therefore the E-PE50 powder is compressed, and then the mold was heated at a specified temperature for 6 minutes, and pressed at 20 MPa for 5 minutes after being heated. In the molded product, a transparent area was clearly observed on the E-PE50 sheet heated at press temperature 120°C, and this proves that the fusion of UHMWPE particles of E-PE50 has started. At 135°C when further heated, a majority of the E-PE50 sheet has beccme transparent. In comparison with this, upon attaining the same heating test using the Ind-PE powder, any transparent area was not observed on the Ind-PE sheet even when compression-moled at 135°C. At approximately 140°C above the melting temperature, a majority of the Ind-PE sheet became transparaent.

Fig.3 shows appearances of the E-PE50 and Ind-PE at 120°C, 130°C, 135°C and 140°C. Because a black background becomes visible via the sheet which becomes transparent, in Fig.3 a transparent part, that is a part where the fusion of the UHMWPE particles occurs can look black. In the appearances at 130 °C and 135 °C, it is found that there is a significant difference in the article fusion bonding states between the E-PE50 and the Ind-PE. A majority of the sheet of the E-PE50 became transparent at 130°C-135°C, while in the sheet of the Ind-PE, no transparent part is observed. Based on the results.it is found that in the micro-fine powder of the UHMWPE according to the present invention, its fusion among particles begins at 10°C -20°C lower temperature than that of the conventional UHMWPE powder. This means that the UHMWPE micro-fine powder according to the present invention can be compression-molded at lower temperature than before, or the adhesive property of the UHMWPE micro-fine powder according to the present invention is improved at the same temperature.

[7] Coating with UHMWPE micro-fine powder

Powder of the E-PE50 was spread on a high density polyethylene (HDPE) sheet. The sheet was pressed at 25 °C, then heated at 140 °C for 6 minutes and finally hot-pressed at 140 °C and 20 MPa for 5 minutes. After natural cooling, one surface of the HDPE sheet was coated by an UHMWPE layer. A laminate sheet is formed in the similar way using the Ind-PE for reference. Fig.4 shows appearance of the outer surface of the coating layer made of the E-PE50. Fig.5 shows appearance of the outer surface of the coating layer made of the Ind-PE.

Comparing the observed surface appearance each other, as shown in Fig.4 and Fig.5, the coating layer of the E-PE50 led to a smoother surface than that of the Ind-PE. Thus, a molding product made from the UHMWPE micro-fine powder according to the present invention can improve the surface smothness over conventional UHMWPE powder. The UHMWPE according to the present invention is useful as a coating material which can provide a smoother surface.

[8] Scratch resistance of UHMWPE layer The scratch resistance was compared between the coating layer from the E-PE50 and that from the Ind-PE. Fig.6 shows a surface of the coating layer of the E-PE50, which was scratched with a tweezer. Fig.7 shows a surface of the coating layer of the Ind-PE, which was scratched with a tweezer in the same way. Fig.8 shows a surface of the HDPE sheet scratched in the same way. The arrows on Fig.6, 7 and 8 represents each scratching direction. Based on Fig, 8, it is found that a wavy scratch pattern is clearly observed on the HDPE sheet in a direction perpendicular to a scratching direction. Althogh on the coating layer of the Ind-PE in Fig.7 there became less remarkable scracth, however minute scratch can be still observed. On the other hand, no such parabolic track is observed on the coating layer of the E-PE50 in Fig.6. These results indicate that a molding product composed of the UHMWPE micro-fine powder according to the present invention is useful as a coating material having good scratch resistance.

[Industrial applicability]

According to the present invention, it becomes possible produce the novel nano-sized Ziegler- Natta catalyst which employs the well-dispersed MgO nanoparticles as its carrier, and the novel UHMWPE micro-fine powder using this one. The well-dispersed MgO nanoparticle-based Ziegler- Natta catalyst according to the present invention is easily produced, additionally its particle diameter is easily controlled through the size of the MgO nanoparticles as its carrier. The ethylene polymerization using the well-dispersed MgO nanoparticle-based Ziegler-Natta catalyst according to the present invention is advantageous in reducing the amount of the chlorine residue in polyolefin. The UHMWPE micro-fine powder according to the present invention also has good fluidity because of its extremely small particle diameter of less than 5 μητι, or typically, approximately 1 μιη. Therefore, the UHMWPE micro-fine powder according to the present invention brings industrial advantages such as improved polymer purity and processability at the time of polymerizing or processing. Additionally, a molding product more favorable and more functionalized in its molding temperature, its surface smoothness, and its scratch resistance, etc., can be produced using the UHMWPE micro-fine powder according to the present invention as a material. The UHMWPE micro-fine powder according to the present invention is expected as an excellent polymer material which enables to expand conventional industrial application fields of the conventional UHMWPE.