JP7597630B2 - Polyethylene for film - Google Patents

Description

The present invention relates to polyethylene for film.

Polyethylene is processed and used as a wide variety of films, including heavy-duty bags, shrink wrap, general packaging, thin films, protective films, extrusion laminate films, extrusion molding films, and foam molding films. Among these, low-density polyethylene (LDPE), which is produced by high-pressure radical polymerization, is processed and used as extrusion laminate films and protective films. Protective films are laminated (attached) to optical materials and metal plates to protect them. For example, they are used as protective films to protect film-like etching resists (dry film resists (DFR)) used in circuit formation on substrates. In producing such films, a good balance between thinning of the polyethylene and ease of handling is required.

Patent Document 1 describes a protective film for DFR made of polyethylene obtained by high-pressure radical polymerization, and a protective film for DFR made of a polyethylene film in which the density of fisheyes present in the film is within a specific range.

JP 2002-60426 A

Under these circumstances, the problem that the present invention aims to solve is to provide polyethylene that is further improved in terms of thinness and ease of handling.

The present inventors have conducted intensive research in light of the above background and have completed the present invention.
That is, the present invention is as follows.
[1]
In an integral distribution curve of polyethylene evaluated by gel permeation chromatography, the weight fraction of components having a Log ₁₀ M exceeding 5.25 (W _Log10M>5.25 : unit is weight%) (M indicates a molecular weight in terms of polyethylene),
A polyethylene having a ratio (W _Log10M>5.25 /R _LS ) to a light scattering area ratio (R _LS ) represented by the following (Equation 1) of 5.7 or more and 6.7 or less.
R _LS = LS/LS' (Formula 1)
(In the formula, LS represents the light scattering area of a solution obtained by dissolving 40 mg of the polyethylene in 20 mL of orthodichlorobenzene.
LS' indicates the light scattering area of a solution in which 40 mg of standard polystyrene having a number average molecular weight of 1000 is dissolved in 20 mL of orthodichlorobenzene.

Below, [2] to [4] are each preferred aspects or embodiments of the present invention.
[2]
The polyethylene according to [1], wherein W _{Log10M > 5.25} / R _LS is 5.8 or more and 6.6 or less.
[3]
The polyethylene according to either [1] or [2], wherein the polyethylene is a high-pressure low-density polyethylene.
[4]
The polyethylene according to any one of [1] to [3], wherein the melt flow rate (MFR) of the polyethylene is 2 to 6 g/10 min.

According to the present invention, it is possible to provide a polyethylene with further improved thinning and ease of handling. The feature of the present invention is that it has been found that the ratio of the amount of medium to high molecular weight components and the amount of ultra-high molecular weight components in polyethylene is related to the balance between stretchability and haze, and the balance between stretchability and haze has been further improved to provide a polyethylene with further improved thinning and ease of handling. Thinning can be evaluated as the stretchability of the polyethylene, and ease of handling can be evaluated as the unevenness of the film surface, for example, the haze of the film. In the method and apparatus for producing polyethylene of the present invention, the pressure inside the reactor and the temperature difference in the reaction zone inside the reactor can be appropriately controlled.

FIG. 1 shows a schematic process diagram of one embodiment of the production flow of polyethylene of the present invention. FIG. 2 shows a schematic process diagram of one embodiment of the production flow of polyethylene of the present invention. FIG. 3 shows a schematic process diagram of one embodiment of the production flow of polyethylene of the present invention. FIG. 4 shows the relationship between haze and melt drawability (minimum thickness) of polyethylene films produced in the inventive and comparative examples. FIG. 5 shows GPC chromatograms (GPC integral distribution curves) for calculating the weight fractions of high molecular weight components of the polyethylenes produced in Example 1 and Comparative Example 1. FIG. 6 shows LS (light scattering detector) chromatograms for measuring the light scattering areas of the polyethylenes produced in Example 1 and Comparative Example 1.

<Polyethylene>
The polyethylene of the present invention is:
In an integral distribution curve of polyethylene evaluated by gel permeation chromatography, the weight fraction of components having a Log ₁₀ M exceeding 5.25 (W _Log10M>5.25 : unit is weight%) (M indicates a molecular weight in terms of polyethylene),
A polyethylene having a ratio (W _Log10M>5.25 /R _LS ) to a light scattering area ratio (R _LS ) represented by the following (Equation 1) of 5.7 or more and 6.7 or less.
R _LS = LS/LS' (Formula 1)
(In the formula, LS represents the light scattering area of a solution obtained by dissolving 40 mg of the polyethylene in 20 mL of orthodichlorobenzene.
LS' indicates the light scattering area of a solution in which 40 mg of standard polystyrene having a number average molecular weight of 1000 is dissolved in 20 mL of orthodichlorobenzene.
In a preferred aspect or embodiment of the present invention, W _Log10M>5.25 /R _LS is 5.8 or more and 6.6 or less.
The weight fraction of components having a Log ₁₀ M exceeding 5.25 (W _{Log 10 M > 5.25} : unit is weight %) and the light scattering area ratio (R _LS ) of the polyethylene of the present invention were measured according to the methods described below.

The polyethylene of the present invention can be various polyethylenes such as low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene, but low density polyethylene is preferred, and high pressure low density polyethylene is more preferred.

The melt flow rate (MFR, unit: g/10 min) of the polyethylene of the present invention is not particularly limited, but the melt flow rate measured by Method A under conditions of a load of 21.18 N and a temperature of 190°C in the method specified in JIS K7210-1995 is preferably 0.3 to 30 (g/10 min), more preferably 1 to 10, and even more preferably 2 to 6. If the MFR is low, it may be difficult to form a thin film, and if the MFR is high, it may be difficult to form a stable film.

The density (unit: kg/m ³ ) of the polyethylene of the present invention is not particularly limited, but is preferably 910 to 930 kg/m ³ , more preferably 918 to 930 kg/m ³ , and even more preferably 920 to 928 kg/m ³ . If the density is less than 910 kg/m ^{3 , the rigidity of the film may decrease, and the workability may become too poor. If the density exceeds 930 kg/m 3 ,} the flexibility of the film may decrease, and problems may arise in the adhesion of the film when used as a protective film.

The polyethylene of the present invention can be used for a wide variety of films, including heavy-duty bags, shrink films, general packaging, thin films, protective films, extrusion laminate films, extrusion molding films, and foam molding films. Among these, the preferred uses are extrusion laminate films and protective films, and the most preferred use is protective films.

A known film forming method can be used to produce a film (such as a protective film) from the polyethylene of the present invention. For example, any of the film forming methods such as the inflation method (air-cooling method, water-cooling method) and the T-die method can be used for film forming, and stretching such as uniaxial stretching and biaxial stretching can be added in some cases. There are no particular restrictions on the forming temperature and take-up speed in film forming, but a forming temperature of 130 to 230°C and a take-up speed of about 5 to 150 m/min are generally preferred. The film thickness is appropriately selected, but for films (such as protective films), a thickness of about 5 to 100 μm is generally preferred, and a thickness of 10 to 60 μm is even more preferred. A thickness of 12 to 25 μm is even more preferred. The polyethylene of the present invention may be blended with polyolefin resins such as linear low-density polyethylene, high-density polyethylene, ethylene-propylene copolymer, and ethylene-butene copolymer within a range in which the effects of the present invention are exerted. If necessary, additives normally used in polyolefins, specifically antioxidants, antiblocking agents, lubricants, antistatic agents, ultraviolet absorbers, etc., may be added. When polyethylene is produced in the presence of a radical polymerization inhibitor in the polymerization reaction system, a certain amount of the radical polymerization inhibitor present in the reaction system remains in the product. If this remaining radical polymerization inhibitor also has antioxidant properties and its concentration is sufficient, it is possible not to add an antioxidant to the polyethylene product.

<Production method of polyethylene>
The method for producing the polyethylene of the present invention is not particularly limited, and is, for example, as follows:
A method for producing polyethylene having the following requirements:
A method for producing polyethylene, comprising polymerizing high-pressure ethylene in the presence of a polymerization initiator using a tank reactor;
Within the tank reactor there are reaction zones with at least two different temperature regions;
A polymerization initiator and ethylene are supplied to a temperature region located upstream of the reaction zone in the tank reactor, and ethylene is polymerized to produce polyethylene;
The polyethylene produced in the temperature region at the upstream part within the tank-type reactor and unreacted ethylene are flowed into a temperature region located at a downstream part within the reaction zone of the reactor which is in communication with the upstream part, and polyethylene is further produced in the temperature region at the downstream part;
The difference (ΔT [°C]) between the temperature (T1 [°C]) of a temperature region located upstream of the reaction zone in the tank reactor to which the polymerization initiator is supplied and the temperature (T2 [°C]) of a temperature region located downstream of the reaction zone is 2.1°C or more and 8.4°C or less.

The pressure of ethylene used in the production method can be, for example, 100 to 280 MPa, preferably 100 to 250 MPa. More preferably, it is 156 to 174 MPa. If it is below the preferred range, the light scattering area and the weight fraction of components having a Log ₁₀ M exceeding 5.25 will be large, the haze will be high, and the melt drawability will be reduced. If it is above the preferred range, the light scattering area and the weight fraction of components having a Log ₁₀ M exceeding 5.25 will be small, the haze will be low, and the melt drawability will be improved.

The polymerization initiator used in this production method is not particularly limited, and examples thereof include diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, tert-butyl peroxypivalate, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, propionyl peroxide, tert-butyl peroxy-2-ethylhexanoate (t-butyl peroxy-2-ethylhexanoate), tert-butyl peroxyisobutyrate, tert-butyl peroxylaurate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, dicumyl peroxide, tert-butyl hydroperoxide, and di-tert-butyl peroxide.

The reactor used in this production method is a tank-type reactor. The number of reactors used is not particularly limited, and for example, two reactors, three reactors, or four or more reactors can be used. When two reactors are used, the two reactors are sometimes called the front-stage reactor and the rear-stage reactor, respectively.

In the reactor used in the process, there may be a reaction zone having at least two different temperature regions. The reaction zone may have three different temperature regions, four different temperature regions, or five or more different temperature regions. There may be more than two reaction zones in the reactor, such as two reaction zones, three reaction zones, or four or more reaction zones. The reaction zone may also be referred to as a reaction zone.

A polymerization initiator and ethylene are supplied to a temperature region located in the upstream part of the reaction zone in the reactor, and ethylene is polymerized to produce polyethylene. The polyethylene produced in the upstream temperature region in the reactor and unreacted ethylene are flowed to a temperature region located in the downstream part of the reaction zone in the reactor that is connected to the upstream part, and polyethylene can be further produced in the downstream temperature region. When the reactor is a vertical reactor (e.g., a tank reactor), the upstream part and the downstream part are sometimes called the upper part and the lower part, respectively.

The difference (ΔT [°C]) between the temperature (T1 [°C]) of the temperature region located upstream of the reaction zone in the reactor to which the polymerization initiator is supplied and the temperature (T2 [°C]) of the temperature region located downstream of the reaction zone can be 2.1°C or more and 8.4°C or less. Preferably, ΔT [°C] is 2.2°C or more and 8.0°C or less. Preferably, ΔT [°C] = T2 [°C] - T1 [°C].
When ΔT [° C.] is 8.4 or more or 2.1 or less, the weight fraction of components having a Log ₁₀ M value exceeding 5.25 increases, and the melt drawability decreases.

<Polyethylene manufacturing equipment>
The apparatus for producing the polyethylene of the present invention has similar features to the process for producing the polyethylene of the present invention described above.

<Specific examples of manufacturing methods and manufacturing devices>
The reaction apparatus, reaction conditions, etc. for the method and apparatus for producing the polyethylene of the present invention are not particularly limited, but examples include a production method having the reaction apparatus, reaction conditions, etc. described below.
In a process for polymerizing ethylene under high temperature and pressure, a composite reactor is used in which two or more tank reactors are connected in series by piping including a heat exchanger, a reaction mixture discharged from a first-stage tank reactor is cooled by the heat exchanger, and the cooled reaction mixture is again introduced into a second-stage tank reactor. Most of the raw material ethylene is injected into an upper reaction zone of a first-stage tank reactor having a lower reaction zone and a lower reaction zone, and the remaining raw material ethylene is injected into an upper reaction zone of a second-stage tank reactor having an upper reaction zone and a lower reaction zone. The raw material ethylene injected into the upper reaction zone of the first-stage tank reactor is polymerized in the presence of a polymerization initiator at a pressure of 100 to 280 MPa and a temperature of 130 to 200° C., and the reaction mixture thus obtained is a reaction mixture discharged from the end of the former-stage tank reactor is cooled to a temperature of 120°C or higher but 20°C or more lower than the reaction temperature in the lower reaction zone of the former-stage tank reactor by a heat exchanger installed between the former-stage tank reactor and the latter-stage tank reactor, and then injected into the latter-stage tank reactor and polymerized in the upper reaction zone of the latter-stage tank reactor in the presence of a polymerization initiator at a pressure of 100 to 280 MPa and a temperature of 130 to 200°C; and the reaction mixture thus obtained is introduced into the lower reaction zone of the latter-stage tank reactor and polymerized in the presence of a polymerization initiator at a temperature of 220 to 280°C.

When carrying out the polyethylene production method, for example, the number of injection points for the raw material ethylene and the polymerization initiator injected into the upper reaction zone of the front and/or rear tank reactors can be set to two or more along the length of the reactor. The polymerization initiator may be injected from the same injection point as the raw material ethylene, or from an injection point different from that of the raw material ethylene. There are various possible combinations of injection points for the raw material ethylene and the polymerization initiator injected into the upper reaction zone, but the optimal combination of positions can be determined appropriately by a person skilled in the art.

Most of the feed ethylene can be injected, for example, into the upper reaction zone of the upstream tank reactor, but most of the feed ethylene means 60% or more of the total feed ethylene.

The reaction pressure of ethylene can be, for example, 100 to 280 MPa, preferably 100 to 250 MPa. The maximum reaction pressure in the latter tank reactor is, for example, the reaction pressure in the former tank reactor minus the pressure loss in the piping leading to the latter tank reactor, but it can be adjusted within this range by the pressure control valve at the outlet of the former tank reactor.

The reaction temperature can be, for example, 130 to 250°C, preferably 140 to 250°C, in the upper reaction zone of the front and rear tank reactors, and can be, for example, 200 to 280°C, preferably 200 to 270°C, in the lower reaction zone. For example, the reaction temperature in the upper reaction zone may be different from that in the front or rear tank reactor. The same applies to the lower reaction zone.

For example, the polymerization initiator used in the upper reaction zones of the front and rear tank reactors is preferably one having a decomposition temperature of 40 to 80° C. to obtain a half-life of 10 hours. Specific examples of the polymerization initiator include diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, tert-butyl peroxypivalate, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, propionyl peroxide, tert-butylperoxy-2-ethylhexanoate (t-butylperoxy-2-ethylhexanoate), tert-butylperoxyisobutyrate, and the like.
For example, the amount of the polymerization initiator used in the polymerization of ethylene in the upper reaction zones in the front and rear stages may be 50 to 1000 parts by weight per 1,000,000 parts by weight of ethylene.
For example, the polymerization initiator used in the lower reaction zones of the front and rear tank reactors is preferably one having a decomposition temperature of 70 to 140° C. for obtaining a half-life of 10 hours, and specific examples thereof include tert-butylperoxy-2-ethylhexanoate (t-butylperoxy-2-ethylhexanoate), tert-butylperoxy isobutyrate, tert-butylperoxy laurate, tert-butylperoxy isopropyl carbonate, tert-butylperoxy acetate, tert-butylperoxybenzoate, dicumyl peroxide, tert-butyl hydroperoxide, and di-tert-butyl peroxide.
For example, the amount of the polymerization initiator used in the polymerization of ethylene in the front and rear lower reaction zones may be 5 to 500 parts by weight per 1,000,000 parts by weight of ethylene.
For example, the polymerization initiator may be used alone or in a mixture of two or more kinds in the first and second reaction zones or in the lower reaction zone of the first and second tank reactors.

The raw material ethylene gas may contain, for example, 0.1 to 10 mol % of a chain transfer agent relative to the ethylene.
As the chain transfer agent, one or a mixture of two or more of the following can be used: paraffins such as ethane, propane, butane, pentane, hexane, and heptane; α-olefins such as propylene, butene-1, hexene-1, and 3-methylpentene-1; aldehydes such as formaldehyde, acetaldehyde, and propionaldehyde; ketones such as acetone, methyl ethyl ketone, diethyl ketone, and cyclohexanone; and aromatic hydrocarbons such as benzene, toluene, and xylene.

<Specific example of the implementation in FIG. 1, FIG. 2 and FIG. 3 (production of polyethylene)>
In the implementation of FIG. 1 (Examples 1 to 3), the implementation of FIG. 2 (Examples 4 and 5), and the implementation of FIG. 3, for example, the following conditions can be adopted.
In the implementation of FIG.
The discharge pressure of the secondary compressor (line 9) can be, for example, 100 to 300 MPa, preferably 150 to 250 MPa;
The total feed rate of ethylene (gas rate of ethylene) (pipe 9) may be, for example, 5 to 30 tons/hour, preferably 10 to 20 tons/hour;
The feed rate of the raw material ethylene (pipe 10) at the top of the tank reactor 20 may be, for example, 1 to 15 tons/hour, preferably 3 to 10 tons/hour;
The feed rate of ethylene (pipe 11) to the lower part of the tank reactor 20 may be, for example, 1 to 20 tons/hour, preferably 5 to 10 tons/hour.
The feed rate of the raw material ethylene (pipe 12) at the upper part of the tank-type reactor 21 may be, for example, 1 to 15 tons/hour, preferably 3 to 10 tons/hour;
The amount of the polymerization initiator fed to the upper part of the tank reactor 20 (through the pipe 13) may be, for example, 1 to 10 kg/hour, preferably 2 to 8 kg/hour;
The polymerization initiator supply rate (pipe 14) at the bottom of the tank reactor 20 may be, for example, 1 to 10 kg/hour, preferably 2 to 8 kg/hour;
The polymerization initiator supply rate (pipe 15) at the top of the tank reactor 21 may be, for example, 1 to 10 kg/hour, preferably 1 to 8 kg/hour;
The polymerization initiator supply rate (pipe 16) at the bottom of the tank reactor 21 can be, for example, 0 to 10 kg/hour, preferably 0 to 8 kg/hour.

In the implementation of FIG.
The discharge pressure of the secondary compressor (pipe 5) can be, for example, 100 to 300 MPa, preferably 150 to 250 MPa;
The total feed rate of ethylene (gas rate of ethylene) (pipe 5) may be, for example, 5 to 30 tons/hour, preferably 10 to 20 tons/hour;
The feed rate of the raw material ethylene (pipe 6) at the upper part of the tank-type reactor 11 may be, for example, 1 to 15 tons/hour, preferably 3 to 10 tons/hour;
The feed rate of the raw material ethylene (pipe 7) at the bottom of the tank reactor 11 may be, for example, 1 to 20 tons/hour, preferably 5 to 10 tons/hour;
The amount of the polymerization initiator fed to the upper portion of the tank reactor 11 (through the pipe 8) may be, for example, 1 to 10 kg/hour, and preferably 2 to 8 kg/hour;
The polymerization initiator supply rate (pipe 9) at the bottom of the tank reactor 11 can be, for example, 1 to 10 kg/hour, and preferably 1 to 8 kg/hour.

In the implementation of FIG.
A total feed rate of raw material ethylene (e.g., 5 to 30 ton/hour, preferably 10 to 20 ton/hour, more preferably 14.0 to 18.0 ton/hour) compressed within a range of a discharge pressure of the secondary compressor (e.g., 100 to 300 MPa, preferably 150 to 250 MPa, more preferably 160 to 220 MPa) can be supplied from a pipe 3 to a temperature zone 1 of a tank-type reactor 6;
The pressure in the tank reactor 6 can be 155 to 215 MPa;
There are two temperature zones inside the tank reactor 6, and temperature zones 1 and 2 exist from the top, and a thermometer can be inserted into each temperature zone;
A polymerization initiator (e.g., t-butylperoxy-2-ethylhexanoate) can be supplied from a pipe 4 to the temperature zone 1 of the tank reactor 6 at a rate of, for example, 1 to 10 kg/hour, preferably 1 to 8 kg/hour, more preferably 3.0 to 6.0 kg/hour;
Ethylene is polymerized into temperature zone 1 of tank-type reactor 6 by raw material ethylene supplied from pipe 3 and a polymerization initiator (e.g., t-butylperoxy-2-ethylhexanoate) supplied from pipe 4 to produce polyethylene. The polyethylene produced in temperature zone 1 and unreacted ethylene are sent to temperature zone 2, where ethylene continues to be polymerized to produce polyethylene;
The polyethylene produced in temperature region 2 of the tank reactor 6 and unreacted ethylene are discharged from the bottom of the tank reactor 6 and passed through pressure regulating valve 5 to be introduced into a heat exchanger and a separator, where they are separated into the produced polyethylene and unreacted ethylene, thereby obtaining the produced polyethylene.

<Method of measuring physical properties of polyethylene>
The physical properties of the polyethylenes produced in the following Examples and Comparative Examples were measured according to the following methods.

(1) Melt flow rate (MFR, unit: g/10 min)
The melt flow rate was measured by Method A under conditions of a load of 21.18 N and a temperature of 190° C., in accordance with the method specified in JIS K7210-1995.

(2) Density (unit: kg/m ³ )
After carrying out annealing as specified in JIS K6922-2, the measurement was carried out by Method A according to the method specified in JIS K7112.

(3) Weight fraction of components having a Log ₁₀ M exceeding 5.25 (W _{Log 10 M > 5.25} , unit: weight%) (M indicates the molecular weight in terms of polyethylene)
The molecular weight distribution of polyethylene and various polyethylene-equivalent molecular weights (number average molecular weight Mn, weight average molecular weight Mw) are determined by gel permeation chromatography (GPC). GPC measurement is performed under the following conditions. Based on the description of ISO16014-1, the baseline on the chromatogram is specified and the peaks are designated. The weight fraction of components with Log ₁₀ M exceeding 5.25 (W _Log10M>5.25 [wt%]) (M indicates the polyethylene-equivalent molecular weight) is calculated from the integral distribution (see FIG. 5). W _Log10M>5.25 [wt%]=(integral value of the integral distribution curve of the part where Log ₁₀ M>5.25)/(integral value of the entire integral distribution curve).
(GPC Equipment and Software)
Apparatus: HLC-8321GPC/HT (manufactured by Tosoh Corporation)
(Measurement conditions)
GPC column: TSKgel GMHHR-H(S)HT 7.8 mm ID x 300 mm (Tosoh Corporation) x 3 Mobile phase: orthodichlorobenzene (Wako Pure Chemical Industries, Ltd., special grade) with dibutylhydroxytoluene (BHT) added at a concentration of 0.1 w/V, i.e., 0.1 g/100 mL Flow rate: 1 mL/min Column oven temperature: 140°C
Autosampler temperature: 140°C
System oven temperature: 40°C
Detection: Refractive Index Detector (RID)
RID cell temperature: 140°C
Sample solution injection volume: 300 μL
GPC column calibration standard material: Standard polystyrene manufactured by Tosoh Corporation was weighed out in the combinations shown in the table below, and 5 mL of orthodichlorobenzene (same composition as the mobile phase) was added, and the mixture was left to stand at room temperature for 120 minutes to dissolve.

(Sample solution preparation conditions)
Solvent: orthodichlorobenzene (special grade, manufactured by Wako Pure Chemical Industries, Ltd.) was used with BHT added at a concentration of 0.1 w/V (0.1 g/100 mL).
Sample solution concentration: 1 mg/mL
Automatic shaker for dissolution: DF-8020 (manufactured by Tosoh Corporation)
Dissolution conditions: 5 mg of a sample was sealed in a 1000 mesh SUS wire mesh bag, the wire mesh bag containing the sample was placed in a test tube, 5 mL of a solvent was added to the test tube, the test tube was covered with aluminum foil, the test tube was placed in a shaker, and the mixture was stirred at 140° C. for 120 minutes at a stirring speed of 60 reciprocations per minute.

(4) Calculation of Light Scattering Area Ratio (R _LS ) The light scattering area ratio was calculated from the following formula by measuring the light scattering area LS of a solution obtained by dissolving the polyethylene of each Example and Comparative Example in ortho-dichlorobenzene at a concentration of 2 mg/mL, and the light scattering area LS' of a solution obtained by dissolving standard polystyrene F10 manufactured by Tosoh Corporation ( having a weight average molecular weight of 9.64×104 as measured by the light scattering (LS) method ^and a weight average molecular weight of 9.89× ¹⁰⁴ as measured by the GPC method) in ortho-dichlorobenzene at a concentration of 2 mg/mL, using a liquid chromatography (LC) device equipped with a light scattering detector.
R _LS = LS/LS' (Formula 1)
A larger light scattering area ratio (R _LS ), that is, a larger light scattering area LS of a solution obtained by dissolving polyethylene in orthodichlorobenzene, indicates a larger amount of ultra-high molecular weight components in the polyethylene.

The measurement conditions are as follows.
・LC device: HLC-8121GPC/HT (manufactured by Tosoh Corporation)
Light scattering detector: PD2040 (Precision Detectors)
Laser light source: Wavelength 685 nm
GPC column: None Sample solution concentration: 2 mg/mL
Injection volume: 300 μL
・Measurement temperature: 140℃
Dissolution conditions: Stirring for 2 hours at 145°C Automatic shaker for dissolution: DF-8020 (manufactured by Tosoh Corporation)
Solvent and mobile phase: orthodichlorobenzene containing 0.1 w/V BHT (manufactured by Wako Pure Chemical Industries, Ltd., special grade)
・Mobile phase flow rate: 1.0mL/min

Specifically, a light scattering detector (LS) was connected to the LC device. The scattering angle used for light scattering detection was 90°. The LS was installed in the column oven of the LC device.
The dissolution of the sample was carried out in detail by the following procedure. First, 40.0 mg of sample and 20.0 mL of solvent were put into a 30 mL screw vial and sealed, the screw vial was set in DF-8020 (manufactured by Tosoh Corporation), and the sample was dissolved by stirring at 140 ° C for 2 hours. The sample solution obtained by the above method was filtered using a cylindrical filter paper with a pore size of 10 μm (Whatman cylindrical filter paper, diameter 18 mm x length 55 mm, model number: 2800-185) before analysis. Filtration was carried out at 140 ° C or higher to avoid precipitation of the sample, and the cylindrical filter paper was immersed in the sample solution and left to stand in the immersed state for 5 minutes to equilibrate, and the sample solution that had leached into the cylindrical filter paper was subjected to analysis. Filtration was carried out within 20 minutes to avoid changes in the concentration of the sample solution due to evaporation of the solvent.
In order to prevent ultra-high molecular weight components from being captured in the column, a GPC column and a guard column were not used. In order to obtain a chromatogram, a SUS pipe having an inner diameter of 0.75 mm and a length of 5 m was attached between the sample injection part and the LS detector, and the temperature of the sample injection part and each detector was set to 140°C.
The obtained LS chromatogram was subjected to baseline processing, and the light scattering area was calculated (see FIG. 6).
The light scattering area was determined using Malvern's data processing software OmniSEC (version 4.7).

(5) Evaluation of film formability of polyethylene An inflation film is produced under the following processing conditions. The take-up speed is gradually increased until the bubble breaks during molding processing, and the thickness and haze of the film produced at a take-up speed 0.5 m/min lower than the take-up speed at which the bubble breaks are measured.
Processing equipment: EX-50 model manufactured by Placo Co., Ltd. Screw diameter: 50 mm Φ
L/D: 28
Die diameter: 125 mm
Lip gap: 2.0mm
Set temperature: 150℃
BUR: 2.0
Take-off speed: 12m/min to 90m/min
Discharge amount: 23kg/h
Pulling machine: Tommy Machine Industry Co., Ltd. IFA-600
The tube is held at a constant take-up speed for 5 minutes, and if no bubble breakage occurs, the take-up speed is increased by 0.5 m/min. If the bubble breaks, the broken portion is sampled, and if fish eye (FE) nuclei are visually observed around the broken portion, it is determined that the breakage is due to FE and is evaluated again. The evaluation is repeated until no FE is observed and the bubble breaks.

(6) Haze The haze (unit: %) of the molded inflation film was measured in accordance with ASTM 1003. The larger the haze, the less the film will wrap around (stick to each other), and therefore the easier the film will be to handle.

(7) Thickness The thickness (unit: μm) of the molded inflation film was measured according to JIS Z1702. The thickness was measured around the circumference of the tubular film at 2 cm intervals in the direction perpendicular to the film take-up direction during film formation, and the average value was calculated. The smaller the measured thickness, the more the polyethylene is thinned, indicating that the polyethylene has excellent stretchability.

[Examples and Comparative Examples]
The present invention will be described below with reference to examples and comparative examples.

The physical properties of the polyethylenes produced in Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 1.


A larger haze indicates that the film is easier to handle, and a smaller thickness (i.e., a larger reciprocal of the thickness (1/thickness)) indicates that the film has better stretchability, so a larger "haze/thickness" ratio means that the balance between thinning (stretchability) and ease of handling (film haze) is better. As shown in Table 1A, in Examples 1 to 5, the "haze/thickness" is 1.2 or more, whereas in Comparative Examples 1 to 4, it is less than 1.2. It was confirmed that Examples 1 to 5 have a better balance between thinning (stretchability) and ease of handling (film haze) than Comparative Examples 1 to 4.

Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4 (Examples and Comparative Examples in FIG. 1)
1 , the feed ethylene compressed to a discharge pressure of 171.5 to 211.2 MPa (shown in Table 2) from the secondary compressor at a total feed rate of 16.0 to 17.7 ton/hour (shown in Table 2) is supplied from pipe 9 to temperature zone 1 of tank reactor 20 through pipe 10 at a feed ethylene feed rate of 4.0 to 4.4 ton/hour (shown in Table 2) at the upper part of the tank reactor 20, and is supplied to temperature zone 3 of the tank reactor 20 through pipe 11 at a feed ethylene feed rate of 8.0 to 8.9 ton/hour (shown in Table 2) at the lower part of the tank reactor 20. The remaining feed ethylene at a feed rate of 4.0 to 4.4 t/hour (shown in Table 2) at the upper part of the tank reactor 21 is supplied to temperature zone 5 of the tank reactor 21 through pipe 12.
The pressure in the tank reactor 20 is set to 155.1 to 197.3 MPa, and the pressure in the tank reactor 21 is set to 134.6 to 177.1 MPa.
There are four temperature zones inside the tank reactor 20, namely, temperature zones 1, 2, 3 and 4 from the top, and a thermometer is inserted in each temperature zone.
Furthermore, there are four temperature zones inside the tank-type reactor 21, namely, temperature zones 5, 6, 7, and 8 from the top, and a thermometer is inserted in each temperature zone.
To temperature zone 1 of tank reactor 20, t-butylperoxy-2-ethylhexanoate as a polymerization initiator is supplied from pipe 13 at a polymerization initiator supply rate of 3.5 to 5.1 kg/hour (shown in Table 2) to the upper part of tank reactor 20, and to temperature zone 3 of tank reactor 20, t-butylperoxy-2-ethylhexanoate as a polymerization initiator is supplied from pipe 14 at a polymerization initiator supply rate of 3.5 to 5.2 kg/hour (shown in Table 2) to the lower part of tank reactor 20.
Further, t-butylperoxy-2-ethylhexanoate as a polymerization initiator is supplied from pipe 15 to temperature zone 5 of tank reactor 21 at a polymerization initiator feed rate of 2.3 to 3.9 kg/hour (shown in Table 2) at the upper part of tank reactor 21, and t-butylperoxy-2-ethylhexanoate as a polymerization initiator is supplied from pipe 16 to temperature zone 7 of tank reactor 21 at a polymerization initiator feed rate of 0.0 to 1.7 kg/hour (shown in Table 2) at the lower part of tank reactor 21.

Ethylene is polymerized into temperature zone 1 of tank-type reactor 20 by raw material ethylene supplied from pipe 10 and polymerization initiator t-butylperoxy-2-ethylhexanoate supplied from pipe 13. The polyethylene produced in temperature zone 1 and unreacted ethylene are sent to temperature zone 2 and continue to be polymerized. The polyethylene produced in temperature zone 2 and unreacted ethylene are sent to temperature zone 3.
To temperature zone 3, raw material ethylene is further supplied from pipe 11 and a polymerization initiator t-butylperoxy-2-ethylhexanoate is further supplied from pipe 14, and ethylene continues to be polymerized to produce polyethylene. The polyethylene produced in temperature zone 3 and unreacted ethylene are sent to temperature zone 4, and ethylene continues to be polymerized to produce polyethylene.
The polyethylene produced in the temperature zone 4 of the tank reactor 20 and unreacted ethylene are discharged from the bottom of the tank reactor 20, passed through a pressure regulating valve 17, introduced into a heat exchanger 18, cooled in the heat exchanger 18, and supplied to the temperature zone 7 of the tank reactor 21.

Ethylene is polymerized into temperature region 5 of tank reactor 21 by the raw material ethylene supplied from pipe 12 and the polymerization initiator t-butylperoxy-2-ethylhexanoate supplied from pipe 15, to produce polyethylene.
The polyethylene and unreacted ethylene produced in the temperature zone 5 are sent to the temperature zone 6 where they are continuously polymerized. The polyethylene and unreacted ethylene produced in the temperature zone 6 are sent to the temperature zone 7.
To temperature zone 7 are supplied polyethylene and unreacted ethylene which have been discharged from the bottom of tank-type reactor 20, passed through pressure regulating valve 17, and introduced into heat exchanger 18 and cooled, and t-butylperoxy-2-ethylhexanoate as a polymerization initiator is further supplied from pipe 16, so that ethylene continues to be polymerized and polyethylene is produced. The polyethylene and unreacted ethylene produced in temperature zone 7 are sent to temperature zone 8, where ethylene continues to be polymerized and polyethylene is produced.

The polyethylene and unreacted ethylene produced in temperature zone 8 of the tank reactor 21 are discharged from the bottom of the tank reactor 21 and introduced into the heat exchanger and separator through the pressure control valve 19, where they are separated into the produced polyethylene and unreacted ethylene to obtain the produced polyethylene.

The production conditions for each of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 2.

The temperatures [°C] and temperature differences (ΔT) [°C] of the respective temperature regions in Examples 1, 2, and 3 are shown in Table 3.

The temperatures [°C] and temperature differences (ΔT) [°C] of the respective temperature regions for Comparative Examples 1, 2, 3, and 4 are shown in Table 4.

Examples 4 and 5 (Examples in FIG. 2)
In FIG. 2 , raw material ethylene compressed to a discharge pressure of 166.9 to 167.0 MPa (shown in Table 5) of the secondary compressor at a total supply rate of 14.3 to 17.0 ton/hour (shown in Table 5) is supplied from pipe 5 to temperature zone 1 of tank reactor 11 through pipe 6 at a raw material ethylene supply rate of 7.2 to 8.5 ton/hour (shown in Table 5) at the upper part of the tank reactor 11, and is supplied to temperature zone 3 of the tank reactor 11 through pipe 7 at a raw material ethylene supply rate of 7.2 to 8.5 kg/hour (shown in Table 5) at the lower part of the tank reactor 11.
The pressure in the tank reactor 11 is set to 164.2 MPa.
There are four temperature zones inside the tank-type reactor 11, namely, temperature zones 1, 2, 3 and 4 from the top, and a thermometer is inserted in each temperature zone.
To temperature zone 1 of the tank reactor 11, t-butylperoxy-2-ethylhexanoate as a polymerization initiator is supplied from pipe 8 at a polymerization initiator feed rate of 3.7 to 3.9 kg/hour (shown in Table 5) to the upper part of the tank reactor 11, and to temperature zone 3 of the tank reactor 11, t-butylperoxy-2-ethylhexanoate as a polymerization initiator is supplied from pipe 9 at a polymerization initiator feed rate of 2.2 to 2.6 kg/hour (shown in Table 5) to the lower part of the tank reactor 11.

In temperature zone 1 of the tank reactor 11, ethylene is polymerized with raw material ethylene supplied from pipe 6 and polymerization initiator t-butylperoxy-2-ethylhexanoate supplied from pipe 8 to produce polyethylene. The polyethylene and unreacted ethylene produced in temperature zone 1 are sent to temperature zone 2 where polymerization continues. The polyethylene and unreacted ethylene produced in temperature zone 2 are sent to temperature zone 3. Raw material ethylene is further supplied from pipe 7 to temperature zone 3, and polymerization initiator t-butylperoxy-2-ethylhexanoate is further supplied from pipe 9 to produce polyethylene. The polyethylene and unreacted ethylene produced in temperature zone 3 are sent to temperature zone 4, where ethylene continues to polymerize to produce polyethylene.

The polyethylene and unreacted ethylene produced in temperature zone 4 of the tank reactor 11 are discharged from the bottom of the tank reactor 11 and introduced into the heat exchanger and separator through the pressure control valve 10, where they are separated into the produced polyethylene and unreacted ethylene to obtain the produced polyethylene.

The production conditions for Examples 4 and 5 are shown in Table 5.

The temperatures [°C] and temperature differences (ΔT) [°C] in the respective temperature regions for Examples 4 and 5 are shown in Table 6.

According to the present invention, by setting the ratio of the medium to high molecular weight component and the ultra-high molecular weight component of the polyethylene within a specific range, it is possible to provide a polyethylene having an improved balance between thinning (stretchability) and ease of handling (irregularities on the film surface, for example, film haze).
The polyethylene of the present invention can be used for a wide variety of films, such as heavy-duty bags, shrink films, general packaging, thin films, protective films (protective films), extrusion laminate films, extrusion molded films, and foam molded films, and can be suitably used for applications such as various parts of home appliances, various housing equipment parts, various industrial parts, various building material parts, and various interior and exterior parts of automobiles, and has high applicability in various industrial fields, such as the electric and electronic industry, household products, transportation machinery industry, and building and construction industry.
In the method and apparatus for producing the polyethylene of the present invention, the pressure inside the reactor and the temperature difference in the reaction zone inside the reactor can be appropriately controlled.

Claims (4)

In an integral distribution curve of polyethylene evaluated by gel permeation chromatography, the weight fraction of components having a Log ₁₀ M exceeding 5.25 (W _Log10M>5.25 : unit is weight%) (M indicates a molecular weight in terms of polyethylene),
A polyethylene having a ratio (W _Log10M>5.25 /R _LS ) to a light scattering area ratio (R _LS ) represented by the following (Equation 1) of 5.7 or more and 6.7 or less.
R _LS = LS/LS' (Formula 1)
(In the formula, LS represents the light scattering area of a solution obtained by dissolving 40 mg of the polyethylene in 20 mL of orthodichlorobenzene.
LS' indicates the light scattering area of a solution in which 40 mg of standard polystyrene having a weight average molecular weight of 9.64 x 104 by the light scattering (LS) method ^and a weight average molecular weight of 9.89 x ¹⁰⁴ by the GPC method is dissolved in 20 mL of orthodichlorobenzene. The polyethylene according to claim 1, wherein W _{Log10M > 5.25} / R _LS is 5.8 or greater and 6.6 or less. The polyethylene according to claim 1 or claim 2, wherein the polyethylene is a high-pressure low-density polyethylene. The polyethylene according to any one of claims 1 to 3, wherein the polyethylene has a melt flow rate (MFR) of 2 to 6 g/10 min, the MFR being a melt flow rate measured by Method A under conditions of a load of 21.18 N and a temperature of 190°C in a method specified in JIS K7210-1995 .

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