KR20080093723A - Polyethylene resin, preparation method thereof and cross-linked polyethylene pipe made from the same - Google Patents

Abstract

A method for preparing a polyethylene resin, a polyethylene resin prepared by the method, and a crosslinked polyethylene pipe using the resin are provided to inhibit the generation of a volatile low molecular weight polyethylene and to reduce the generation of bubbles. A method for preparing a polyethylene resin comprises the steps of contacting an ethylene monomer with a catalyst diluted with a solvent in the presence of hydrogen as a molecular weight controller to polymerize it; and discharging the gaseous component of a reactor when the conversion rate of polymerization is 95-99.5 wt% and polymerizing the unreacted ethylene monomer, wherein the difference between the pressure ratio(P_H2/P_C2) of the gaseous hydrogen and ethylene at the first step and the pressure ratio(P_H2/P_C2) of the gaseous hydrogen and ethylene at the second step is 0.01-0.2.

Description

POLYETHYLENE RESIN, PREPARATION METHOD THEREOF AND CROSS-LINKED POLYETHYLENE PIPE MADE FROM THE SAME

The present invention relates to a polyethylene resin, a method for producing the same, and a tube for a crosslinked polyethylene pipe produced therefrom. More specifically, the manufacturing process is simple, and the production of volatile low molecular weight polyethylene is suppressed, and thus The present invention relates to a polyethylene resin having a significantly low bubble generation frequency during processing, a method for producing the same, and a crosslinked polyethylene pipe having a low amount of bubbles, having excellent pressure resistance characteristics.

Polyethylene is light, high toughness, heat-adhesive and easy to install, and when applied to the water supply pipe is excellent in chemical resistance against chlorine contained in the water, etc., is now widely used as a pipe.

Recently, polyethylene pipes are often used as sewage pipes instead of concrete pipes, and are also used in drain pipes, underground buried conduits, water pipes, gas pipes, or hoses and ondol pipes for transferring water. It's growing.

As a conventional method for producing a polyethylene resin for pipes, there is a method of having a molecular weight distribution that is easily extrudable by using a chromium-based catalyst as one polymerization reactor, but has a problem of requiring a high catalytic technology.

Another conventional manufacturing method (US Patent No. 6225421, published on May 1, 2001) connects two polymerization reactors in series to produce a low molecular weight polymer in the first reactor, and transfers the slurry of the prepared polymer to the second reactor. There is a method for producing a high molecular weight polymer again to have a molecular weight distribution that is easy to extrude, but there is a problem that requires an additional device, the process is complicated.

The molecular weight distribution has a bimodal molecular weight curve form, the polymer of the low molecular weight portion increases the extrusion processability during the molding process, the polymer of the high molecular weight portion serves to increase the mechanical properties.

Since the polyethylene resin itself is not good in heat resistance, pressure resistance and environmental stress cracking resistance to be used as plastic pipes such as water supply pipes, the polyethylene resin is used by improving the physical properties insufficient by chemical crosslinking or water crosslinking.

In the water-crosslinking method, a silane compound such as vinyl ethoxysilane, an organic peroxide, and a silanol condensation catalyst are mixed with polyethylene, and the obtained composition is extruded into a pipe while heating the obtained composition, and the formed pipe is exposed to an environment containing water to produce a silane. It is a method of advancing crosslinking.

The silane crosslinked pipe formed by the water crosslinking method has a problem such as odor generated from unsaturated silane compound and the like during use, and there is a problem that long-term extrusion work is difficult because a large amount of die is generated even during pipe extrusion.

The chemical crosslinking method is extrusion molding into a pipe shape while heating the polyethylene to a decomposition temperature of an organic peroxide such as dicumyl peroxide, and the organic peroxide is thermally decomposed into organic radicals. Radicals are generated and crosslinking proceeds.

The chemical crosslinking method using the organic peroxide is a crosslinking method of the polyethylene resin most used industrially.

The chemically crosslinked polyethylene pipes are produced while the polyethylene resin is crosslinked in contact with the peroxide at high temperature to form a three-dimensional network. In most of these processes, the polyethylene resin in powder form and the peroxide crosslinking agent are mixed to allow peroxide to penetrate into the particle pores and then processed into a pipe in an Engel extruder (ram extruder).

Due to the volatile low molecular weight material contained in the resin during the processing of the polyethylene pipe, the final pipe product may include bubbles. This is an important cause of weakening the local strength of the pipe and lowering the pressure resistance characteristic.

Therefore, there is a need for the development of polyethylene resins having low bubble generation frequency when processed into crosslinked pipes and simple manufacturing process without requiring high catalyst technology.

In order to solve the problems of the prior art as described above, the present invention provides a method for producing a polyethylene resin that is simple in the manufacturing process, suppresses the production of volatile low molecular weight polyethylene, and has a significantly low bubble generation frequency when processed into a crosslinked pipe or the like. It aims to provide.

In addition, an object of the present invention is to provide a polyethylene resin according to the above production method.

In addition, an object of the present invention is to provide a crosslinked polyethylene pipe excellent in pressure resistance characteristics because the amount of bubbles produced from the polyethylene resin is remarkably small.

The above and other objects of the present invention can be achieved by the present invention described below.

In order to achieve the above object, the present invention is a method for producing a polyethylene resin by reacting an ethylene monomer with a catalyst diluted in a solvent under hydrogen as a molecular weight regulator in a continuous stirred reactor,

Iii) contacting the ethylene monomer with a catalyst to polymerize; And ii) discharging the gas component in the reactor at the time when the polymerization conversion rate of step iii) is 95 to 99.5% by weight, and polymerizing the unreacted ethylene monomer.

Polyethylene resin, characterized in that the pressure ratio (P_H ₂ / P_C ₂ ) of the hydrogen and ethylene in the gas phase of step iii) and the pressure ratio (P_H ₂ / P_C ₂ ) of hydrogen and ethylene in the gas phase of step ii) of 0.01 to 0.2 It provides a method of manufacturing.

In addition, the present invention provides a polyethylene resin according to the above production method.

The present invention also provides a crosslinked polyethylene pipe prepared by reacting the polyethylene resin and the peroxide crosslinking agent.

Hereinafter, the present invention will be described in detail.

The present inventors have recognized that the presence of air bubbles in pipe products may be reduced in thickness, thereby lowering local pressure resistance characteristics, and that there may be rupture when using the product for a long time. As a result, in the process of polymerizing up to 95 to 99.5% by weight of the total amount of ethylene monomer to the main reactor of the continuous stirring reactor (CSTR) and moving it to the co-reactor to polymerize unreacted 0.5 to 5% by weight of ethylene monomer When the polyethylene resin is prepared by adjusting the pressure ratio difference between hydrogen and ethylene in the gaseous phase of the main reactor and the secondary reactor to 0.01 to 0.2, the crosslinked pipe product made of the prepared polyethylene resin is compared with the conventional crosslinked pipe product. It is confirmed that the amount of bubbles is significantly reduced, and based on this, to complete the present invention The.

The method for producing a polyethylene resin of the present invention is a method for producing a polyethylene resin by reacting an ethylene monomer with a catalyst diluted in a solvent under hydrogen as a molecular weight regulator in a continuous stirred reactor.

Iii) contacting the ethylene monomer with a catalyst to polymerize; And ii) discharging the gas component in the reactor at the time when the polymerization conversion rate of step iii) is 95 to 99.5% by weight, and polymerizing the unreacted ethylene monomer.

Further characterized in that the ⅰ) pressure ratio between hydrogen and ethylene in the gas phase of step (P_H ₂ / P_C ₂₎ and ⅱ) pressure ratio between hydrogen and ethylene in the gas phase of step (P_H ₂ / P_C ₂₎ differ from 0.01 to 0.2.

In the step iii), all of the ethylene monomers to be reacted are added and contacted with a catalyst under hydrogen so that 95 to 99.5% by weight of the added ethylene monomer is polymerized.

The pressure ratio (P_H ₂ / P_C ₂ ) of the gaseous hydrogen and ethylene monomer of step (iii) is preferably 0.1 to 0.5, but is not limited thereto.

In the slurry process in which ethylene is polymerized using a catalyst diluted in a solvent in the continuous stirred reactor, polyethylene having a desired molecular weight in solution is controlled by controlling the concentration or pressure ratio (P_H ₂ / P_C ₂ ) of hydrogen and ethylene monomers in the gas phase in the reactor. It can manufacture. The higher the pressure ratio, the lower the molecular weight is polymerized, and the lower the higher the molecular weight is.

As the catalyst, a Ziegler-Natta catalyst may be used, which is a typical Ziegler-Natta catalyst including a main catalyst composed of a halogenated complex of magnesium and titanium and a cocatalyst composed of an organometallic compound of group II or III of the periodic table. The Ziegler-Natta catalyst is preferably a catalyst having a titanium content of 10 to 30% by weight and a Ti ⁺³ conversion of 30 to 60%.

As the organometallic compound, it is preferable to use trialkyl aluminum, dialkyl aluminum halide, alkyl aluminum dihalide, aluminum dialkyl hydride or alkyl aluminum sesqui halide, and more preferably Al (C ₂ H ₅ ). ₃ , Al (C ₂ H ₅ ) ₂ H, Al (C ₃ H ₇ ) ₃ , Al (C ₃ H ₇ ) ₂ H, Al (iC ₄ H ₉ ) ₂ H, Al (C ₈ H ₁₇ ) ₃ , Al (C ₁₂ H ₂₅ ) ₃ , Al (C ₂ H ₅ ) (C ₁₂ H ₂₅ ) ₂ , Al (iC ₄ H ₉ ) (C ₁₂ H ₂₅ ) ₂ , Al (iC ₄ H ₉ ) ₂ H, Al (iC ₄ H ₉ ) ₃ , (C ₂ H ₅ ) ₂ AlCl, (iC ₃ H ₉ ) ₂ AlCl, (C ₂ H ₅ ) ₃ Al ₂ Cl ₃ , and the like.

The organometallic compounds may be mixed and used, preferably a mixture of Al (C ₂ H ₅ ) ₃ and Al (iC ₄ H ₉ ) ₃ , Al (C ₂ H ₁₇ ) ₃ , Al (C ₂ H ₅ ) A mixture of ₃ and Al (C ₈ H ₁₇ ) ₃ , a mixture of Al (C ₄ H ₉ ) ₂ H and Al (C ₈ H ₁₇ ) ₃ , Al (iC ₄ H ₉ ) ₃ and Al (C ₈ H ₁₇ ) A mixture of ₃ , a mixture of Al (C ₂ H ₅ ) ₃ and Al (C ₁₂ H ₂₅ ) ₃ , a mixture of Al (iC ₄ H ₉ ) ₃ and Al (C ₁₂ H ₂₅ ) ₃ , Al (C ₂ H ₅ ) ₃ and Al (C ₁₆ H _{33) 3} of the mixture, or Al (C ₃ H _{7) 3} and Al (C ₁₈ H ₃₇₎ is the use of such a mixture of ₂ (iC ₄ H _9).

The catalyst may be injected by dilution in the form of a slurry in an aliphatic hydrocarbon solvent having 5 to 12 carbon atoms such as pentane, hexane, heptane, nonane, decane or an isomer thereof, or an aromatic hydrocarbon solvent such as toluene or benzene. .

The ethylene monomer dissolved in the solvent causes a polymerization reaction with the catalyst present in the form of a slurry.

The polymerization of step iii) is preferably performed at 2 to 10 atm, and 70 to 90 ° C., and the melt index (MFR) of the polyethylene resin prepared therefrom is preferably 0.03 to 0.1.

Step ii) is a step of polymerizing 0.5 to 5% by weight of ethylene monomer remaining without polymerization in step iii).

In step ii), the gas is discharged without any further reactants, and the polymerization is performed under conditions where the pressure ratio (P_H ₂ / P_C ₂ ) of hydrogen and ethylene monomers is 0.11 to 0.7, but is not limited thereto. .

Step ii) increases the molecular weight of the polyethylene polymerized by adjusting the pressure ratio (P_H ₂ / P_C ₂ ) between hydrogen and ethylene monomer, and suppresses the production of low molecular weight polyethylene, thereby suppressing the formation of bubbles during processing in pipes and the like. Has an effect. In addition, since no further reactants are administered in the co-reactor, it has the effect of simplifying the reaction process.

 Since the gas component of step ii) is composed almost of hydrogen when considering only ethylene monomer and hydrogen, the amount of hydrogen can be controlled by discharging a certain amount of gas component.

When the ethylene monomer dissolved in the solvent is consumed by the polymerization reaction, since the ethylene monomer in the gas phase is easily dissolved in the solvent, when considering only the ethylene monomer and hydrogen, the gas component of the co-reactor is mostly hydrogen, and the unreacted ethylene monomer is Most of them are dissolved in a solvent. Therefore, when the gas component is discharged from the co-reactor, most of the hydrogen is discharged. After discharge, part of the ethylene monomer dissolved in the liquid phase is vaporized into the gas phase, and the pressure ratio of hydrogen and ethylene monomer of the gas phase in the co-reactor (P_H ₂ / P_C ₂ ) Can be adjusted.

The polymerization of the step ii) is preferably carried out at 0.2 to 5 atm, and 70 to 90 ℃ condition, the melt index (MFR) of the polyethylene resin finally produced through the polymerization of steps i) and ii) is 0.03 It is preferable that it is to 0.1.

The ⅰ) pressure ratio between hydrogen and ethylene in the gas phase of step (P_H ₂ / P_C ₂₎ and ⅱ) pressure ratio between hydrogen and ethylene in the gas phase in step (P_H ₂ / P_C ₂₎ is preferably a difference of 0.03 to 0.2.

When the pressure ratio difference is less than 0.01, there is an effect of disturbing the flow of the fluid transported by the pressure difference between each reactor, when the pressure exceeds 0.2 has an effect of rapidly increasing the bubble generation rate during the pipe extrusion process.

The continuous stirred reactor may be one commonly used in ethylene polymerization, and may preferably include a main reactor in which step iii) is carried out and an auxiliary reactor in which step ii) is connected in series.

At the end of step iii) in the main reactor, the reactants are transferred to the auxiliary reactor to start step ii).

Discharge of the gas component may be carried out in a tube or a secondary reactor connecting the main reactor and the secondary reactor.

The co-reactor may be located at the rear end of the main reactor to further polymerize 0.5 to 5% by weight of the remaining ethylene monomer without reaction in the main reactor to maximize the ethylene polymerization yield.

The polyethylene resin of the present invention is characterized in that it is prepared according to the above production method.

The polyethylene resin preferably has a melt index (MFR) of 0.03 to 0.1 and a density of 0.945 to 0.955 kg / L.

The polyethylene resin may be used for the crosslinked pipe, but is not limited thereto.

The crosslinked polyethylene pipe of the present invention is prepared by reacting the polyethylene resin for crosslinked pipe and the peroxide crosslinking agent.

The peroxide can be brought into contact with the polyethylene resin to cause crosslinking, and a three-dimensional network can be formed to produce a crosslinked polyethylene pipe.

The pipe manufacturing process may include a process of mixing the polyethylene resin and the peroxide crosslinking agent in powder form to allow peroxide to penetrate into the particle pores and then processing the pipe through an Engel extruder (ram extruder).

When the peroxide crosslinked polyethylene pipe is processed using the polyethylene resin, a low molecular weight material is contained in the polyethylene resin, thereby greatly reducing the amount of bubbles included in the final pipe product. This prevents the local thickness reduction of the pipe and maintains the strength and pressure resistance properties uniformly throughout the pipe.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the appended claims.

[ Example ]

Example  One

< Ziegler Nata  Preparation of Catalyst

Tetrachloride titanium (TiCl ₄ ) was added to a hexane suspension of magnesium alkoxide so that the molar ratio of titanium to magnesium (Ti / Mg) was 0.27 to prepare a reaction mixture, and the reaction mixture was heated to 85 ° C., and then 5.5 hours. The resulting precipitate was filtered off and washed five times with hexane. Thereafter, triethylaluminum was reacted at a molar ratio of 0.5 to perform preactivation to prepare a Ziegler-Natta catalyst. Was Ti ^{3 +} ratio of the prepared catalyst was 40%.

<Production of Polyethylene Resin>

In a continuous stirred reactor (CSTR type reactor) in a 200 L main reactor, 40 kg / hr of nucleic acid as solvent, 2 mM Ti / hr of Ziegler-Natta catalyst prepared above, and triethylaluminum 70 mM / as cocatalyst. Injected at a flow rate of hr. 12 kg / hr of ethylene monomer and 2.5 g / hr of hydrogen were added to the molecular weight control agent so that the pressure ratio between hydrogen and ethylene monomer in the gas component of the main reactor was 0.24, and polymerization was carried out at 82 ° C. and 5 atm conditions. At the time when the polymerization conversion rate was 98% by weight, the entire reactant was transferred to a 200 L co-reactor having a volume connected in series with the main reactor. Without adding additional catalyst, cocatalyst and ethylene monomer to the co-reactor, the pressure ratio of hydrogen and ethylene monomer in the gaseous phase of the co-reactor is 0.25, and the main reactor at 78 ° C and 1.5 atm conditions. The polyethylene resin was prepared by reacting 2% by weight of the remaining ethylene monomer without reacting.

<Production of Polyethylene Pipes>

0.6 wt% of ditertbutyl peroxide (DTBP) was mixed with the prepared polyethylene resin and a crosslinking agent, and a polyethylene pipe was manufactured under the conditions of 160 ° C. using an Engel extruder.

Example  2

Except that the pressure ratio of hydrogen and ethylene in the gas phase of the auxiliary reactor in Example 1 was adjusted to 0.34 was carried out in the same manner as in Example 1.

Comparative example  One

Except that the pressure ratio of hydrogen and ethylene in the gas phase of the auxiliary reactor in Example 1 was adjusted to 0.74 was carried out in the same manner as in Example 1.

Comparative example  2

Except that the pressure ratio of hydrogen and ethylene in the gas phase of the auxiliary reactor in Example 1 was adjusted to 0.64 was carried out in the same manner as in Example 1.

Comparative example  3

Except that the pressure ratio of hydrogen and ethylene in the gas phase of the auxiliary reactor in Example 1 was adjusted to 0.54 was carried out in the same manner as in Example 1.

The physical properties of the pipes prepared in Examples 1 to 2 and Comparative Examples 1 to 3 were measured by the following method, and the results are shown in Table 1 below.

* Melt Index (MFR)-measured at 190 ° C by 2.16 kg load in accordance with ASTM D1238 method.

Number of bubbles-The number of bubbles contained in a 10 m long pipe was visually measured.

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Main reactor % Polymerization conversion 98 98 98 98 98 P_H ₂ / P_C ₂ of the main reactor 0.24 0.24 0.24 0.24 0.24 P_H ₂ / P_C ₂ of the co-reactor 0.25 0.34 0.74 0.64 0.54 P_H ₂ / P_C ₂ between reactors Difference 0.01 0.1 0.5 0.4 0.3 Melt index 2.3 2.2 2.4 2.3 2.2 Number of bubbles (average value) 3 5 15 14 11

As shown in Table 1, the crosslinked polyethylene pipes according to the present invention (Examples 1 and 2) have a large difference between P_H ₂ / P_C ₂ of the main reactor and P_H ₂ / P_C ₂ of the secondary reactor (comparative example). It was confirmed that the number of bubbles was remarkably small as compared with 1 to 3).

As described above, according to the present invention, the manufacturing process is simple by adding no further reactants in step ii) (secondary reactor), and the gas phase of steps (iii) (main reactor) and ii) (secondary reactor) By controlling the pressure ratio of hydrogen and ethylene monomers, the production of volatile low molecular weight polyethylene is suppressed, and polyethylene resin with a low frequency of foaming when processing with crosslinked pipes, its manufacturing method, and the amount of bubbles produced therefrom have significantly lower pressure resistance characteristics. There is an effect of providing this excellent crosslinked polyethylene pipe.

Claims (12)

A method for preparing polyethylene resin by reacting an ethylene monomer with a catalyst diluted in a solvent under hydrogen as a molecular weight regulator in a continuous stirred reactor, Iii) contacting the ethylene monomer with a catalyst to polymerize; And ii) discharging the gas component in the reactor at the time when the polymerization conversion rate of step iii) is 95 to 99.5% by weight, and polymerizing the unreacted ethylene monomer. The ⅰ) of the step of vapor phase hydrogen and ethylene pressure ratio (P_H ₂ / P_C ₂₎ and ⅱ) in the step of vapor phase hydrogen and ethylene pressure ratio (P_H ₂ / P_C ₂₎ the difference, characterized in that 0.01 to 0.2 Method for producing polyethylene resin. The method of claim 1, The catalyst is a Ziegler-Natta catalyst comprising a main catalyst consisting of a halogenated complex of magnesium and titanium, and a promoter consisting of an organometallic compound of group II or III of the periodic table. Method for producing polyethylene resin. The method of claim 2, The Ziegler-Natta catalyst, characterized in that the titanium content of 10 to 30% by weight, Ti ⁺³ conversion of 30 to 60% Method for producing polyethylene resin. The method of claim 1, The solvent is an aliphatic hydrocarbon or aromatic hydrocarbon solvent having 5 to 12 carbon atoms, characterized in that Method for producing polyethylene resin. The method of claim 1, Step iii) is characterized in that the pressure ratio (P_H ₂ / P_C ₂ ) of hydrogen and ethylene in the gas phase is 0.1 to 0.5. Method for producing polyethylene resin. The method of claim 1, Step ii), the pressure ratio of hydrogen and ethylene in the gas phase (P_H ₂ / P_C ₂ ) is characterized in that 0.11 to 0.7 Method for producing polyethylene resin. The method of claim 6, The pressure ratio of hydrogen and ethylene in the gas phase is controlled by discharging a gas component. Method for producing polyethylene resin. The method of claim 1, The polymerization of step iii) is carried out at 2 to 10 atm and 70 to 90 ℃ condition, the polymerization of step ii) is carried out at 0.2 to 5 atm and 70 to 90 ℃ condition Method for producing polyethylene resin. The method of claim 1, The polyethylene resin is characterized in that the melt index is 0.03 to 0.1 Method for producing polyethylene resin. The method of claim 1, The continuous stirred reactor is characterized in that the main reactor in which the step iii) polymerization is carried out and the auxiliary reactor in which the ii) step polymerization is carried out in series. Method for producing polyethylene resin. Polyethylene resin prepared according to any one of claims 1 to 10. Prepared by reacting the polyethylene resin of claim 11 and a peroxide crosslinking agent Crosslinked polyethylene pipe.