KR20200064691A - Low density polyethylene resin with ecellent processability and preparation method thereof - Google Patents

Abstract

The present invention relates to a low-density polyethylene resin, particularly to a low-density polyethylene resin having excellent processability and a method for preparing the same. The low-density polyethylene resin has a relatively high low-molecular weight region of MWD (molecular weight distribution) and suitable balance of neck-in properties with draw-down properties based on extrusion processability and melt tension to provide excellent processability, and thus may be useful for extrusion coating or lamination. In addition, the method for preparing a low-density polyethylene resin includes multiple steps of carrying out an autoclaving process and a tubular process sequentially, and thus can broaden the width of a decrease in high-molecular weight region controlled by a modifier in the state of MWD of low-density polyethylene resin increased to the highest level. Therefore, it is possible to control MWD with ease and to reduce processing sensitivity, thereby providing improved processability and productivity as compared to a single autoclaving or tubular process.

Description

LOW DENSITY POLYETHYLENE RESIN WITH ECELLENT PROCESSABILITY AND PREPARATION METHOD THEREOF}

The present invention relates to a low-density polyethylene resin, specifically, to a low-density polyethylene resin excellent in processability and a method for manufacturing the same.

Low-density polyethylene and ethylene vinyl acetate resins for general extrusion coating or lamination are widely used for paper coating, kraft paper coating, etc. for waterproofing purposes, and plastic films for laminating and thermal bonding. In the manufacture of the resin for extrusion coating or lamination, the higher the molecular weight distribution due to the molecular weight distribution (MWD) characteristic of the resin, the lower the extrusion load due to the lower molecular weight, thus showing relatively stable flow characteristics in the extruder. Due to its high molecular weight, it has a high melt tension when casting a T-die, so it has a tendency to have excellent neck-in properties. However, since the draw-down property tends to be inhibited by the high molecular weight, it is important to balance the high molecular weight to control the properties of the resin.

As a conventional technique, a low-density polyethylene resin for extrusion coating is manufactured by adding a modifier such as isobutene for the purpose of increasing the draw-down characteristics and controlling the melt index and density, but to adjust the balance between the draw-down characteristics and the melt tension. Having difficulty.

In addition, in the case of the low-density polyethylene resin provided by the autoclave process, there is an advantage that it can be advantageously designed in terms of neck-in properties due to melt tension or extrusion processability due to relatively wide MWD, but there is a problem in that relatively low draw-down properties are inferior. . In order to reinforce this, it is possible to adjust the properties of the corresponding part by adding a modifier, but likewise, it is difficult to balance, and there is a limit to widening to a low molecular weight region in order to reinforce the flowability of extrusion processing.

On the other hand, in the case of the low density polyethylene resin provided by the tubular process, the MWD is relatively low for excellent drawdown characteristics, but the coating processability, such as neck-in characteristics, is poor due to poor melt tension compared to the resin provided in the autoclave process. have.

Republic of Korea Patent No. 10-0798624 (published on January 21, 2008) relates to a mixed resin composition of low-density polyethylene and polypropylene produced by a single autoclave process, and the low-density polyethylene according to the pressure, temperature, and initiator of the autoclave reactor Although molecular weight distribution control is disclosed, it is limited to a single autoclave process.

Republic of Korea Patent Publication No. 10-2014-0085579 (2014.07.07 published) relates to a mixed resin composition of a low-density polyethylene and ethylene vinyl acetate copolymer having a MWD of more than 15 produced by a single tubular process, according to the initiator activity Although process control is disclosed, it is limited to a single tubular process.

Japanese Patent Publication No. 2008-531831 (published on August 14, 2008) relates to a low-density polyethylene resin composition, which discloses that it can be produced in a multi-process, but does not disclose the control of specific processes, melt index, melt strength And molecular weight distribution.

Japanese Patent Publication No. 2009-197225 (2009.09.03 publication) relates to an ethylene homopolymer or copolymer, which discloses an ethylene polymer with improved neck-in and draw-down properties, but does not disclose control of a specific process. , Melt index, density, melt tension, shear viscosity, branching water, and the like.

Republic of Korea Registered Patent No. 10-0798624 Republic of Korea Patent Publication No. 10-2014-0085579 Japanese Patent Publication No. 2008-531831 Japanese Patent Publication No. 2009-197225

The present invention is to solve the above problems, has a relatively high low molecular weight MWD, low-density polyethylene resin excellent in workability, due to the balance of the extrusion characteristics and the melt-in neck-in characteristics and draw-down characteristics by tension The purpose is to provide. In addition, the present invention by applying a multi-process sequentially proceeding the autoclave process and the tubular process, through the control of the chain length and the high molecular weight reduction by the modifier in the state of increasing the molecular weight distribution (MWD) of the low-density polyethylene resin as much as possible, An object of the present invention is to provide a method for producing a low-density polyethylene resin having excellent processability with a reduced high molecular weight region and a relatively low molecular weight region.

The present invention has a melt index (190°C, 2.16 kg load) of 3-15 g/10 min, a density of 0.910-0.925 g/cm ³ , and a molecular weight distribution (MWD) expressed as Mw/Mn 8 ~ 11, and provides a low-density polyethylene resin characterized in that the Z average molecular weight is 500,000 to 700,000.

In addition, the present invention

(a) polymerizing ethylene gas in an autoclave reactor; And

(b) continuously polymerizing the low-density polyethylene resin polymerized in step (a) in a tubular reactor;

It provides a method for producing the low-density polyethylene resin comprising a.

The low-density polyethylene resin according to the present invention has a relatively high low-molecular-weight MWD, and is excellent in processability due to an appropriate balance of extrusion processing characteristics and neck-in characteristics and draw-down characteristics due to melt tension, so for extrusion coating or lamination It can be useful.

In addition, the method for manufacturing a low-density polyethylene resin according to the present invention includes a multi-step process in which the autoclave process and the tubular process are sequentially performed, thereby reducing the high molecular weight region by the modifier in the state where the MWD of the low-density polyethylene resin is raised as much as possible. The MWD can be easily adjusted because the adjustment width can be widened, and the process sensitivity is reduced, thereby improving processability and productivity compared to a single autoclave or tubular process.

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

In the present invention, when a part “includes” a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated.

<Low density polyethylene resin>

An aspect of the present invention has a melt index (190° C., 2.16 kg load) of 3 to 15 g/10 min, a density of 0.910 to 0.925 g/cm ³ , and a molecular weight distribution (MWD) expressed as Mw/Mn. ) Is 8 to 11, and Z average molecular weight is 500,000 to 700,000.

The low-density polyethylene resin according to the present invention has a melt index of 3-15 g/10 min, preferably 3.5-14 g/10 min, more preferably 4-12 g/10 min. Specifically, if the melt index is less than the above range, the neck-in property is excellent, but the draw-down property is greatly deteriorated, and thus the processing stability is lowered during T-die coating, so high-speed processing may be difficult. The down characteristic is greatly improved, but the productivity of the T-die coating process may decrease due to the inferior neck-in characteristic.

The low density polyethylene resin according to the present invention has a density of 0.910 to 0.925 g/cm ³ , preferably 0.912 to 0.923 g/cm ³ , and more preferably 0.915 to 0.920 g/cm ³ . Specifically, if the density is less than the above range, it is difficult to manufacture in a high pressure autoclave reactor, there is a possibility that the barrier properties are deteriorated, and if it is more than the above range, there is a possibility that heat sealing and adhesion are poor and unsuitable for coating application.

The low density polyethylene resin according to the present invention has a molecular weight distribution (MWD) expressed by Mw/Mn of 8 to 11, preferably 8 to 10.5, and more preferably 8 to 10. Specifically, if the molecular weight distribution is less than the above range, the extrusion load increases during extrusion, and there is a possibility that the neck-in characteristic in the workability is lowered, and if it is more than the above range, the draw-down characteristic in the workability may be lowered.

The low-density polyethylene resin according to the present invention has a Z average molecular weight of 500,000 to 700,000, preferably 520,000 to 700,000, and more preferably 540,000 to 700,000. Specifically, if the Z average molecular weight is less than the above range, there is a possibility that the neck-in characteristic is lowered, and if it is more than the above range, there is a possibility that the draw-down characteristic is lowered.

The low-density polyethylene resin according to the present invention may preferably be for extrusion coating or lamination from the viewpoint of excellent balance of neck-in characteristics and draw-down characteristics.

The extrusion coating or lamination can be done using conventional extrusion coating techniques. Specifically, the low-density polyethylene resin may be introduced into an extrusion device and discharged as a melt into a T-die to coat the substrate traveling through the cooling roll and nip roll below. At this time, the resin temperature in the extruder is preferably 270°C to 350°C, more preferably 280 to 350°C, most preferably 300 to 350°C, and the temperature of the T-die equipment is preferably May be 270°C to 350°C, more preferably 280°C to 350°C, and most preferably 300°C to 350°C. The substrate traveling through the cooling roll and nip roll may be selected from one or more of paper, metal film, plastic film, and tarpaulin, and the traveling speed may be variously set to 80 to 500 m/min.

The low-density polyethylene resin according to the present invention can be applied by being classified according to the processing speed conditions when applied to extrusion coating or lamination. The low-density low-density polyethylene resin for medium and low speed, which can be provided over a running speed of 80 to 150 m/min, preferably has a melt index of 3 to 6 g/10 min and a density of 0.910 to 0.925 g/cm ³ in the resin provided under the polymerization conditions. Can be In addition, a low-density polyethylene resin for high speed, which can be provided over a running speed of 150 to 500 m/min, preferably has a melt index of 6 to 15 g/10 min and a density of 0.910 to 0.925 g/ in the resin provided under the polymerization conditions. It can be ³ cm.

When the low-density polyethylene resin according to the present invention is extrusion-coated on a biaxially stretched polypropylene film at a die temperature of 320°C using a 65 mm∮ single-axis extrusion coating machine having a T-die width of 600 mm, the coating is performed at an extrusion coating line speed of 60 m/min. When molding to a thickness of 20 μm, the neck-in ratio to die width is preferably 10% or less, more preferably 9% or less, and most preferably 8.5% or less, at 35 rpm of the screw of the extrusion coating machine. The maximum line speed of may be preferably 100 m/min or more, more preferably 110 m/min or more, and most preferably 115 m/min or more.

<Molded product>

Another aspect of the invention is a molded article comprising the low density polyethylene resin according to the invention.

The molded article can be manufactured by various molding methods using the low-density polyethylene resin of the present invention, and the shape, size, etc. of the molded article can be appropriately determined.

Examples of the method for manufacturing the molded article include an injection molding method, a press molding method, a vacuum molding method, a foam molding method, an extrusion molding method, etc., which are commonly used in industry, and, depending on the purpose, the same or different from the low-density polyethylene resin of the present invention. And a molding method in which the polyethylene-based resin and other resins are bonded together, a method of coextrusion molding, and the like. The molded article according to the present invention may preferably be manufactured by extrusion coating or laminating the low-density polyethylene resin according to the present invention.

<Method for manufacturing low density polyethylene resin>

Another aspect of the invention,

(a) polymerizing ethylene gas in an autoclave reactor; And

(b) continuously polymerizing the low-density polyethylene resin polymerized in step (a) in a tubular reactor;

It is a method for producing a low-density polyethylene resin according to the invention comprising a.

(a) Autoclave reactor stage

The method for producing a low density polyethylene resin according to the present invention includes the step of polymerizing ethylene gas in an autoclave reactor.

The autoclave reactor according to the present invention may have a pressure of preferably 1,700 to 1,900 kgf/cm ² , more preferably 1,725 to 1,875 kgf/cm ² , and most preferably 1,750 to 1,850 kgf/cm ² . Specifically, when the pressure of the autoclave reactor is less than the above range, many long-chain branches of low-density polyethylene are generated, and the Z-average molecular weight is large, and there is a possibility that the draw-down characteristic is deteriorated in processability. It decreases and the Z average molecular weight becomes small, and there is a possibility that the neck-in characteristic in workability is lowered.

The autoclave reactor according to the present invention may have an upper temperature of preferably 220 to 250°C, more preferably 225 to 245°C, and most preferably 230 to 240°C. Specifically, when the upper temperature of the autoclave reactor is less than the above range, the long-chain branching of low-density polyethylene decreases, and the Z average molecular weight becomes small, and there is a possibility that the neck-in characteristic in the processability decreases. There is a possibility that the Z-average molecular weight increases due to the increase in branching, and the draw-down characteristics of the workability decrease.

The autoclave reactor according to the present invention may have a lower temperature of preferably 250 to 275°C, more preferably 260 to 275°C, and most preferably 265 to 275°C. Specifically, if the lower temperature of the autoclave reactor is less than the above range, there is a possibility that the production load falls, and if it is more than the above range, there is a possibility that the risk of explosion of the reactor increases.

Two or more kinds of peroxides may be added to the autoclave reactor according to the present invention, preferably as polymerization initiators at the top and bottom. The polymerization initiator is preferably t-butyl peroxybenzoate at the top of the reactor and di-t-butyl peroxide (di-t-) at the bottom of the reactor. butyl peroxide) can be added.

The autoclave reactor according to the present invention may preferably be added with a modifier for controlling the molecular weight distribution. From the viewpoint of using the C4 series in terms of the reactor, C4 series hydrocarbons may be added as the modifier, and more preferably, n-butane, isobutane or isobutylene ( iso-butylene).

In addition, the hourly input amount of the modifier according to the present invention may be preferably 10-40 kg/hr, more preferably 15-40 kg/hr, most preferably 15-30 kg/hr. Specifically, if the hourly input amount of the modifier is less than the above range, there is a possibility that the molecular weight distribution control by the modifier is insignificant, and if it is more than the above range, the generation of low molecules is maximized to increase the melt index, increase the density, and decrease the Z average molecular weight. Thereby, there is a possibility that the neck-in characteristic is deteriorated in processability.

(b) tubular reactor stage

The method for producing a low-density polyethylene resin according to the present invention includes the step of continuously polymerizing the low-density polyethylene resin polymerized in the autoclave reactor step (a) according to the present invention in a tubular reactor.

The tubular reactor according to the present invention is installed at the rear end of the autoclave reactor so that the process can be continuously performed.

The tubular reactor according to the present invention may have a pressure of preferably 1,700 to 1,900 kgf/cm ² , more preferably 1,725 to 1,875 kgf/cm ² , and most preferably 1,750 to 1,850 kgf/cm ² . Specifically, when the pressure of the tubular reactor is less than the above range, long-chain branching of low-density polyethylene is generated, and the Z average molecular weight is large, and there is a possibility that the draw-down characteristic is deteriorated in the processability. It decreases and the Z average molecular weight becomes small, and there is a possibility that the neck-in characteristic in workability is lowered.

The tubular reactor according to the present invention may have a temperature of preferably 230 to 280°C, more preferably 240 to 280°C, and most preferably 245 to 280°C. Specifically, if the temperature of the tubular reactor is less than the above range, the reaction activity may drop, improving the properties and increasing the production load due to further reaction, and if it is more than the above range, the reaction activity is not stable, and high pressure, high temperature There is a possibility of explosion due to reaction.

Two or more kinds of peroxides may be added to the tubular reactor according to the present invention, preferably as a polymerization initiator. The polymerization initiator is preferably t-butyl peroxy-2-ethylhexanoate, t-butyl peroxy-3,5, from the viewpoint of optimum activity suitable for the reaction temperature. 5-Trimethylhexanoate, or di-t-butyl peroxide can be added.

The manufacturing method of the low-density polyethylene resin according to the present invention includes a multi-process in which an autoclave process and a tubular process are continuously performed, so process sensitivity is reduced, and thus processability and productivity can be improved. Specifically, the production method according to the present invention preferably produces 1 to 20 hours per hour compared to a single process that polymerizes only in step (a) using an autoclave reactor or a single process that polymerizes only in step (b) using a tubular reactor. %, more preferably 2-20%, most preferably 3-20%.

Hereinafter, examples will be described in detail to specifically describe the present specification. However, the embodiments according to the present specification may be modified in various other forms, and the scope of the present specification is not interpreted to be limited to the embodiments described below. The embodiments of the present specification are provided to more fully describe the present specification to those skilled in the art. In addition, "%" and "part" which represents content below are on a weight basis unless otherwise specified.

Examples and comparative examples

First, ethylene gas was compressed at high pressure. Specifically, the pressure was compressed to 50 kgf/cm ² while recirculating gas was introduced through a purge gas compressor, and the pressure was 250 kgf/cm ² while ethylene was introduced from a primary compressor. And compressed at high pressure while maintaining the state of 1,600 kgf/cm ² in a secondary compressor (Hyper Compressor).

Low-density polyethylene resins of Examples 1 to 3 and Comparative Examples 1 to 5 were prepared according to the conditions described in Tables 1 and 2 below using compressed ethylene gas. Specifically, compressed ethylene gas was introduced into an autoclave reactor, and after setting the autoclave reactor pressure, upper temperature, and lower temperature, n-butane was introduced as a modifier. In the autoclave reactor, a polymerization initiator was added by diluting t-butyl peroxybenzoate at the top of the reactor with di-t-butyl peroxide at the bottom of the hydrocarbon. The low-density polyethylene polymer and unreacted ethylene gas from the autoclave reactor were directly introduced into the tubular reactor, and after setting the tubular reactor pressure and temperature, further reactions were performed. In the tubular reactor, di-t-butyl peroxide, t-butyl peroxy-2-ethylhexanoate, and t-butyl peroxy-3,5,5-trimethylhexanoate were added as polymerization initiators.

The prepared low-density polyethylene resin was coated on a biaxially stretched polypropylene film at a die temperature of 320° C. using a 65 mm∮ single screw extrusion coating machine having a T-die width of 600 mm.

unit Example 1 Example 2 Example 3 Five
Sat
Clo
re
this
Eve Reactor
pressure kgf/cm ² 1,850 1,800 1,750 Reactor
Top
Temperature ℃ 235 235 235 Lower reactor
Temperature ℃ 270 270 270 Modifier Kg/hr 30 20 10 Tu
BL
la Reactor
pressure kgf/cm ² 1,850 1,800 1,750 Reactor
Temperature ℃ 270 270 270 Production load MT/hr 16 16 16 MI g/10min 8.0 7.0 5.0 density g/cm ³ 0.919 0.918 0.918 Molecular weight distribution (MWD) - 8.8 8.3 8.1 Z average molecular weight - 578,500 601,200 611,500 Neck-in ratio % 9 8 7 Drawdown m/min 200 160 120

unit Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Five
Sat
Clo
re
this
Eve Reactor
pressure kgf/cm ² 1,650 1,700 1,780 1,780 1,760 Reactor
Top
Temperature ℃ 256 256 229 235 235 Lower reactor
Temperature ℃ 270 270 248 270 270 Modifier Kg/hr - - 30 20 - Tu
BL
la Reactor
pressure kgf/cm ² 1,650 1,700 1,780 - - Reactor
Temperature ℃ 270 270 270 - - Production load MT/hr 16 16 16 13.5 13.5 MI g/10min 8.0 5.5 24.0 12.0 5.0 density g/cm ³ 0.919 0.916 0.924 0.919 0.918 Molecular weight distribution (MWD) - 10.2 10.8 6.5 7.5 12.0 Z average molecular weight - 756,500 801,400 398,600 482,300 965,500 Neck-in ratio % 6 5 19 15 4 Draw down m/min 70 60 400 300 50

Experimental Example

The resins prepared according to the Examples and Comparative Examples were evaluated by the following methods, and the results are shown in Tables 1 and 2.

[Assessment Methods]

1) Melt flow index (MI): measured according to ASTM D1238.

2) Density: Measured according to ASTM D792.

3) Molecular weight characteristics (molecular weight distribution (MWD), Z average molecular weight): measured by GPC analysis according to ASTM D3536.

4) Neck-in ratio: The neck-in ratio when the molding was performed at an extrusion coating line speed of 60 m/min with a coating thickness of 20 μm was measured to confirm the neck-in ratio to die width.

5) Drawdown: The maximum line speed at 35 rpm of the screw of the extrusion coating machine was measured.

6) Production load: The hourly production was calculated.

As a result, as shown in Table 1, Examples 1 to 3 satisfies the properties suitable for the purpose of the present invention and exhibits an appropriate balance in the neck-in ratio and draw-down characteristics. However, as shown in Table 2, Comparative Examples 1 and 2, the autoclave and tubular reactor pressure, the autoclave upper temperature, and whether the modifier was added were out of the required range of the present invention, thereby resulting in molecular weight distribution and Z average molecular weight This target property was not satisfied, and as a result, the neck-in ratio was excellent, but the drawdown characteristics were inferior. In addition, in Comparative Example 3, the upper and lower temperatures of the reactor were out of the required range of the present invention, and as a result, the molecular weight distribution and the Z average molecular weight did not satisfy the target physical properties, and as a result, the drawdown characteristics were excellent but the neck-in ratio. This resulted in falling. Comparative Examples 4 and 5 are produced by a single autoclave reactor process without a continuous process of the tubular reactor, and the molecular weight distribution and the Z average molecular weight are rapidly changed depending on whether a modifier is added, and the production load is also autoclave. And about 15.6% compared to the tubular continuous process. Therefore, it was found that the sensitivity of the molecular weight distribution change by the modifier is minimized by the autoclave and tubular continuous processes, thereby increasing the processability and increasing productivity.

Claims (4)

Melt index (190℃, 2.16kg load) is 3~15 g/10 min, density is 0.910~0.925 g/cm ³ , and molecular weight distribution (MWD) expressed as Mw/Mn is 8~11 , Z low molecular weight polyethylene resin, characterized in that the average molecular weight is 500,000 ~ 700,000. According to claim 1,
The low-density polyethylene resin is a low-density polyethylene resin for extrusion coating or lamination. (a) polymerizing ethylene gas in an autoclave reactor; And
(b) continuously polymerizing the low-density polyethylene resin polymerized in step (a) in a tubular reactor;
A method for producing the low-density polyethylene resin according to any one of claims 1 to 2 comprising a. According to claim 3,
Method for producing a low-density polyethylene resin, characterized in that in the step (a) C ₄ series hydrocarbon modifier is added.