JP5205340B2 - Polyethylene resin composition and inflation film comprising the same - Google Patents

Description

  The present invention relates to a polyethylene resin composition having excellent mechanical properties, transparency, and molding properties, and an inflation film comprising the same, and more particularly, even in a thin-walled film, the balance between impact resistance and rigidity is excellent. In addition, the present invention relates to a polyethylene resin composition suitable for production of a polyethylene film excellent in transparency and excellent in suitability for an automatic bag making machine, and an inflation film comprising the same.

Polyethylene blown films are often used for packaging applications. Recently, such a film is required to be thinner due to the influence of the enforcement of the Container Recycling Law.
However, if the film is made thinner in response to such a demand, the handling performance deteriorates due to the decrease in strength and rigidity, so that the basic performance required for a film such as a standard bag film is satisfied. Various studies have been conducted.

For example, in order to obtain a film with high impact strength, it is necessary to reduce the density of the resin, but if the density is lowered, the waist (stiffness) of the film becomes soft, and as a result, using an automatic bag making machine There is a problem that bags cannot be made at high speed.
In order to improve the balance between impact strength and rigidity, a composition comprising two kinds of ethylene / α-olefin copolymers having different densities and high-pressure radical polymerization method low-density polyethylene is already known (Patent Document 1). reference.). However, it does not fully satisfy the balance between strength and rigidity.

In addition, the resin composition comprising two kinds of ethylene / α-olefin copolymers having different molecular weight distributions is considerably improved in strength, but still does not sufficiently satisfy the balance between strength and rigidity. Furthermore, when the density is increased to obtain rigidity, there is a problem that transparency is deteriorated (see Patent Document 2).
As described above, in the conventional technique, it is difficult to sufficiently satisfy the basic performance required for a film such as a standard bag film.

Japanese Patent Application Laid-Open No. 7-149962 JP-A-9-31260

  An object of the present invention is to provide a polyethylene resin composition suitable for producing a polyethylene film having excellent balance between impact resistance and rigidity even when it is thin, excellent in transparency, and excellent in suitability for automatic bag making machines, and more To provide an inflation film.

  As a result of intensive studies to solve the above problems, the present inventors have identified two types of ethylene / α-olefin copolymers having different densities and a specific radical polymerization method branched low-density polyethylene. It has been found that a polyethylene resin composition blended so as to have an MFR and density of the above can solve the above problems, and has completed the present invention.

That is, according to the first invention of the present invention, 50 to 96% by weight of ethylene / α-olefin copolymer (A) and 2 to 30% by weight of ethylene / α-olefin copolymer (B) A polyethylene resin composition comprising 2 to 20% by weight of branched low-density polyethylene (C),
The ethylene / α-olefin copolymer (A) has (a-1) a temperature of 190 ° C., a melt flow rate (MFR) at a load of 2.16 kg of 0.5 to 5.0 g / 10 min, and (a-2). ) The density is 0.920-0.945 g / cm ³ ,
The ethylene / α-olefin copolymer (B) has (b-1) MFR of 0.5 to 5.0 g / 10 min, (b-2) density of 0.890 to 0.915 g / cm ³ , And (b-3) the molecular weight distribution (Q value: Mw / Mn) is 4.0 or less, and the density difference between the ethylene / α-olefin copolymer (A) and (B) is 0.015 g / cm. ³ or more
The branched low density polyethylene (C) is produced by a high-pressure radical method, and (c-1) MFR is 0.1 to 5.0 g / 10 minutes, and (c-2) density is 0.905 to 0.935 g. / Cm ³ , and (c-3) the melt tension (MT) at 190 ° C. (unit g) satisfies the following relational expression (1) with MFR (unit g / 10 minutes), and the polyethylene resin composition is: There is provided a polyethylene resin composition characterized in that (i) MFR is 0.4 to 5.0 g / 10 min, and (ii) density is 0.926 to 0.940 g / cm ³ .
MT> −8.74 × log MFR + 13.3 (1)

According to the second invention of the present invention, in the first invention, when a film having a thickness of 25 μm is formed, the polyethylene satisfies the following requirements (I) to (IV): A resin composition is provided.
(I) When the load at 1% tensile deformation in the MD direction is X (unit N) and the dart drop impact is Y (unit g), the following relational expression (2) is satisfied.
1.43 ≦ X + 0.48 × 10 ⁻² Y (2)
(II) X ≧ 1.00 (N)
(III) Y ≧ 43 (g)
(IV) Haze ≦ 7.0%

  According to a third aspect of the present invention, there is provided an inflation film comprising the polyethylene resin composition according to the first or second aspect of the invention.

  The polyethylene resin composition of the present invention is excellent in the balance between impact resistance and rigidity even if it is thin, and also has excellent transparency and is suitable for the production of a polyethylene film, particularly an inflation film, excellent in suitability for automatic bag making machines. The effect of being.

Hereinafter, the present invention will be described in detail for each item.
I. Components of polyethylene resin composition Ethylene / α-olefin copolymer (A)
The ethylene / α-olefin copolymer (A) used in the polyethylene resin composition of the present invention is a copolymer of ethylene and one or more α-olefins. The α-olefin preferably has 3 to 20 carbon atoms, more preferably 3 to 12 carbon atoms.
Specific examples include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene and the like. The total content of these α-olefins is usually 30 mol% or less, preferably 20 mol% or less.

  The melt flow rate (MFR) of the ethylene / α-olefin copolymer (A) is 0.5 to 5.0 g / 10 minutes, preferably 0.8 to 4 g / 10 minutes, and 1.0 to 3. 0 g / 10 min is more preferable. When the MFR is less than 0.5 g / 10 minutes, the moldability is inferior. On the other hand, when the MFR exceeds 5.0 g / 10 minutes, impact resistance, mechanical strength, etc. may be lowered. Here, the MFR of the ethylene / α-olefin copolymer (A) is compliant with JIS K7210 “Plastics—Test methods for melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics”. , 190 ° C., 21.18N (2.16 kg) when measured under load conditions.

The density of the ethylene / α-olefin copolymer (A) is 0.920 to 0.945 g / cm ³ , preferably 0.925 to 0.940 g / cm ³ , and 0.928 to 0.938 g. / Cm ³ is more preferable. When the density is within this range, the balance between impact resistance and rigidity and transparency are excellent. On the other hand, if the density is less than 0.920 g / cm ³ , the rigidity is lowered and the suitability of the automatic bag making machine may be impaired. On the other hand, if the density exceeds 0.945 g / cm ³ , impact resistance and transparency may be impaired. Here, the density of the ethylene / α-olefin copolymer (A) is a value measured by the following method.

  The pellets were hot-pressed to prepare a press sheet having a thickness of 2 mm. The sheet was placed in a beaker having a capacity of 1000 ml, filled with distilled water, capped with a watch glass, and heated with a mantle heater. After boiling boiling water for 60 minutes, the beaker was placed on a wooden table and allowed to cool. At this time, the boiling distilled water after boiling for 60 minutes was adjusted to 500 ml so that the time until reaching room temperature was not less than 60 minutes. Moreover, the test sheet was immersed in the substantially center part in water so that it might not contact a beaker and the water surface. After annealing the sheet at a temperature of 23 ° C. and a humidity of 50% within a period of 16 hours to 24 hours, the sheet was punched out to 2 mm in length and width, and the test temperature was 23 ° C. And a specific gravity measurement method ”.

2. Ethylene / α-olefin copolymer (B)
The ethylene / α-olefin copolymer (B) used in the polyethylene resin composition of the present invention is a copolymer of ethylene and one or more α-olefins selected from α-olefins having 3 to 20 carbon atoms. is there. The α-olefin having 3 to 20 carbon atoms is preferably one having 3 to 12 carbon atoms, specifically, propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1- Examples include hexene, 1-octene, 1-decene, 1-dodecene and the like. The total content of these α-olefins is usually 30 mol% or less, preferably 20 mol% or less.

  The MFR of the ethylene / α-olefin copolymer (B) is 0.5 to 5.0 g / 10 minutes, preferably 0.8 to 4 g / 10 minutes, and 1.0 to 3.0 g / 10 minutes. More preferred. When the MFR is less than 0.5 g / 10 minutes, the moldability is inferior. On the other hand, when the MFR exceeds 5.0 g / 10 minutes, impact resistance, mechanical strength, etc. may be lowered. Here, the MFR of the ethylene / α-olefin copolymer (B) is in accordance with JIS K7210 “Testing Methods for Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Plastic-Thermoplastic Plastic”. , 190 ° C., 21.18N (2.16 kg) when measured under load conditions.

The density of the ethylene · alpha-olefin copolymer (B) is a 0.890~0.915g / cm ^3, preferably 0.895~0.910g / cm ^3, 0.900~0.908g / Cm ³ is more preferable. When the density is within this range, the balance between impact resistance and rigidity and transparency are excellent. On the other hand, if the density is less than 0.890 g / cm ³ , the rigidity deteriorates. On the other hand, if the density exceeds 0.915 g / cm ³ , the effect of improving the impact resistance is not sufficient, and the balance between the impact resistance and the rigidity is insufficient. Is damaged. Here, the density of the ethylene / α-olefin copolymer (B) refers to a value measured by the same method as the method for measuring the density of the ethylene / α-olefin copolymer (A).
The difference between the density of the ethylene / α-olefin copolymer (B) and the density of the ethylene / α-olefin copolymer (A) used in the present invention is more preferably 0.015 g / cm ³ or more. By providing a density difference in this way, the balance between impact resistance and rigidity is further improved.

  Furthermore, the ratio (Q value: Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the ethylene / α-olefin copolymer (B) is 4.0 or less. If the Q value exceeds 4.0, the impact resistance improving effect is not sufficient, and the balance between impact resistance and rigidity is impaired. In view of the balance between impact resistance and rigidity, the upper limit of the Q value is preferably 3.0, more preferably 2.5, still more preferably 2.3, and particularly preferably 2.3. The lower limit of the Q value is preferably 1.5, more preferably 2.0.

  Here, the ratio (Q value: Mw / Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the ethylene / α-olefin copolymer (B) is determined by the following method (hereinafter referred to as “molecular weight distribution”). It is sometimes referred to as the “measurement method”.) Mw / Mn is defined by the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) measured by gel permeation chromatography (GPC).

Apparatus: GPC manufactured by Waters
150C type detector: MIRAN 1A infrared spectrophotometer (measurement wavelength: 3.42 μm)
Column: AD806M / S manufactured by Showa Denko Co., Ltd. (column calibration is performed by Tosoh monodisperse polystyrene (0.5 mg / ml solution of each of A500, A2500, F1, F2, F4, F10, F20, F40, and F288) Measurement was performed, and the logarithm of the elution volume and the molecular weight was approximated by a quadratic equation. The molecular weight of the sample was converted to polyethylene using the viscosity formula of polystyrene and polyethylene. Here, the coefficients of the viscosity formula of polystyrene are α = 0.723 and log K = −3.767, and polyethylene has α = 0.723 and log K = −3.407. ]
Measurement temperature: 140 ° C
Injection volume: 0.2ml
Concentration: 20 mg / 10 mL
Solvent: Orthodichlorobenzene Flow rate: 1.0 ml / min

The ethylene / α-olefin copolymer (B) uses a single-site catalyst as a polymerization catalyst, and is a one-stage or two-stage or more multistage by any one of gas phase polymerization, slurry polymerization, solution polymerization or high-pressure ion polymerization. And an ethylene / α-olefin copolymer obtained by copolymerizing ethylene and an α-olefin.
The single-site catalyst here is a catalyst that can form a uniform active species, and is usually adjusted by bringing a metallocene-based transition metal compound or a non-metallocene-based transition metal compound into contact with an activation co-catalyst. .

The single site catalyst is preferably a catalyst prepared by bringing a metallocene transition metal compound and an activation cocatalyst into contact with each other, more preferably a general formula:
ML _a X _n-a
(Wherein, M is a group 4 or lanthanide series transition metal atom of the periodic table of elements. L is a group having a cyclopentadiene-type anion skeleton or a group containing a hetero atom, and at least one Is a group having a cyclopentadiene type anion skeleton, a plurality of L may be bridged, X is a halogen atom, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, n is a transition Represents the valence of the metal atom M, and a is an integer satisfying 0 <a <n.)
A catalyst prepared by bringing a transition metal compound represented by the formula and an activating cocatalyst into contact with each other. These transition metal compounds may be used alone or in combination of two or more.

As an activation co-catalyst, it is used together with a metallocene transition metal compound or a nonmetallocene transition metal compound to give an olefin polymerization activity. An organoaluminum compound such as an alumoxane compound and / or triphenylmethyltetrakis ( Boron compounds such as pentafluorophenyl) borate and N, N-dimethylanilinium tetrakis (pentafluorophenyl) borate are used.
The single site catalyst may be used in combination with an inorganic carrier such as SiO ₂ and Al ₂ O _{3 and} a particulate carrier such as an organic polymer carrier such as a polymer such as ethylene and styrene.

3. Branched low density polyethylene (C)
The branched low density polyethylene (C) used in the polyethylene resin composition of the present invention is a polyethylene having a long chain branch, for example, a polyethylene obtained by polymerizing ethylene by a high pressure radical polymerization method. The polyethylene obtained by the high pressure radical polymerization method is also referred to as a high pressure method low density polyethylene.

  The branched low density polyethylene (C) has an MFR of preferably 0.1 to 5.0 g / 10 minutes, more preferably 0.3 to 4.0 g / 10 minutes, and further preferably 0.5 to 3.5 g / minute. 10 minutes. If it is this range, moldability will improve.

The branched low density polyethylene (C) preferably has a density of 0.905 to 0.935 g / cm ³ , more preferably 0.910 to 0.930 g / cm ³ . If it is this range, processability, such as drawdown property, draw resonance, stretchability, can be stably maintained.

Furthermore, in the branched low density polyethylene (C), the melt tension (MT) at 190 ° C. (unit g) and the melt flow rate (MFR) (unit g / 10 minutes) satisfy the following relational expression (1). Those are preferred. More preferably, it satisfies the relational expression (1a).
MT> −8.74 × log MFR + 13.3 (1)
MT> −8.74 × log MFR + 14.7 (1a)

  When the melt tension (MT) is within this range, processability such as draw-down property, draw resonance and stretchability can be stably maintained. Generally, when MFR increases, MT tends to decrease, but MT can be increased by increasing the amount of high molecular weight components and the amount of long chain branching by adjusting the polymerization temperature, multistage polymerization, etc. A branched low density polyethylene (C) satisfying the above relational expression can be obtained.

  Here, MT is measured using a capillograph manufactured by Toyo Seiki Seisakusho, cylinder temperature 190 ° C., orifice L / D = 8.1 / 2.095 (mm), piston speed 10 mm / min, take-off speed 4.0 m. / Min.

Further, the branched low density polyethylene (C) used in the present invention preferably has a η ₁ / η ₀ of 1.5 or more, more preferably 1.8 or more. η ₁ / η ₀ is obtained from a transient response curve of uniaxial extensional viscosity described later. When the branched low density polyethylene (C) satisfying the above is used, there is an advantage that high-speed molding processability is improved.

  The production method of the branched low density polyethylene (C) is not limited, and a known production method can be adopted. For example, a tubular process, an autoclave process, etc. are mentioned.

4). Next, the blending ratio of the resin component will be described.
The weight ratio of ethylene / α-olefin copolymer (A) / ethylene / α-olefin copolymer (B) / branched low density polyethylene (C) (total is 100% by weight) is (50 to 93) / (5-30) / (2-20), preferably (55-90) / (6-27) / (4-18), more preferably (60-86) / (8-25) / (6-15).
If the ethylene / α-olefin copolymer (A) is too much, the impact resistance is lowered, and if it is less, the rigidity is deteriorated. Moreover, when there are too many ethylene-alpha-olefin copolymers (B), rigidity will fall, and when few, tear strength and impact strength will not be improved. Further, if the branched low density polyethylene (C) is too much, the tearing strength is lowered, and if it is less, the molding processability such as the stability of the bubble is lowered at the time of film formation.

II. 1. Polyethylene resin composition Density The density of the polyethylene resin composition of the present invention consisting of the above components (A), (B) and (C) needs to be in the range of 0.926 to 0.940 g / cm ³ , preferably 0.926 to 0.936 g / cm ³ , more preferably 0.926 to 0.934 g / cm ³ .
When the density of the polyethylene resin composition is lower than 0.926 g / cm ³ , the rigidity of the film is lowered, and the suitability of the automatic bag making machine is deteriorated. Moreover, when the density of a polyethylene resin composition is higher than 0.940 g / cm < ³ >, the intensity | strength of a film will fall and transparency will also deteriorate.
Note that the approximate density of the polyethylene resin composition can be calculated from the respective densities and ratios of the components (A), (B), and (C) according to an addition rule.

2. MFR
The MFR of the polyethylene resin composition of the present invention comprising the above components (A), (B) and (C) needs to be in the range of 0.4 to 5.0 g / 10 min, preferably 0. 0.5 to 4.0 g / 10 min, more preferably 0.6 to 3.0 g / 10 min. If the MFR is lower than 0.4 g / 10 minutes, the fluidity is poor and the motor load of the extruder becomes too high. On the other hand, if the MFR is higher than 5.0 g / 10 minutes, the bubbles are not stable and difficult to mold. At the same time, the strength of the film is lowered.
The approximate MFR of the polyethylene resin composition can be calculated according to the addition rule from the respective MFRs and ratios of the components (A), (B), and (C).

3. Rheological properties The polyethylene resin composition of the present invention has a uniaxial extensional viscosity index (η ₀ ) of 60,000 Pa · sec or less, preferably 58,000 Pa · sec or less, more preferably 57,000 to 54,000 Pa · sec. It is preferable. When the uniaxial extensional viscosity index (η ₀ ) is 60,000 Pa · sec or less, the molten film is difficult to break, which is advantageous for improving the molding speed.

Further, the polyethylene resin composition of the present invention has a strain hardening degree (λ) of 1.5 or more, preferably 1.8 or more. When λ is 1.5 or more, draw resonance hardly occurs and excellent high-speed molding processability.
Here, the strain hardening degree (λ) is a quotient (λ = η ₁ / η ₀ ) obtained by dividing the uniaxial extension viscosity (η ₁ ) at a deformation time of 5 seconds by the uniaxial extension viscosity index (η ₀ ) in the measurement of uniaxial extension viscosity. ).
Hereinafter, η ₀ , η ₁ and λ will be described in more detail.

The uniaxial extensional viscosity index (η ₀ ) and the strain hardening degree (λ) are values obtained from a transient response curve of uniaxial extensional viscosity measured by a uniaxial extensional viscometer.

The strain hardening degree (λ) is an index representing the degree of increase of the uniaxial extensional viscosity in the region where the uniaxial extensional viscosity rises out of the linear region, and is measured as follows.
That is, first, using a uniaxial extension viscometer, a transient response of uniaxial extension viscosity at a measurement temperature of 180 ° C. and a strain rate of 1 second ⁻¹ is measured. η ₀ is a least square method for log (η) vs. log (t) from data of uniaxial extensional viscosity [η (Pa · second)] in a range where the deformation time is 1 to 2 seconds [t (second)]. Is a value extrapolated to the uniaxial extensional viscosity at a deformation time of 5 seconds. On the other hand, η1 was measured as a value of uniaxial extensional viscosity at a deformation time of 5 seconds, and the ratio (η ₁ / η ₀ ) was defined as the strain hardening degree (λ).

As a measuring device for uniaxial extensional viscosity, for example, a uniaxial extensional viscometer “trade name: RME” manufactured by Rheometric Scientific F.E. can be used. Although η ₁ / η ₀ is sometimes referred to as “extension viscosity ratio”, the term “degree of strain hardening (λ)” is used herein.

η ₀ is an index extrapolated from the linear region of uniaxial extensional viscosity, and can be controlled mainly by adjusting the MFR of the polyethylene resin.
Furthermore, the MFR of the polyethylene resin composition can be controlled by the MFR and composition of the ethylene / α-olefin copolymer and the branched low density polyethylene.

Moreover, η ₁ is an index of the nonlinear region. The branched low density polyethylene (C) generally has strong nonlinearity compared to the components (A) and (B), and is controlled by the type and amount of the branched low density polyethylene (C). be able to.
The relationship between the molecular weight, the molecular weight distribution, the degree of branching, the degree of branching distribution, etc., the non-linear starting point, and the degree of non-linearity is described in, for example, Journal of Japan Rheology Society, Vol. 19, pages 174 to 180 (1991) (by Kiyoto Koyama).

4). Other formulations etc. In the present invention, as long as the characteristics of the present invention are not essentially impaired, an antistatic agent, an antioxidant, an antiblocking agent, a nucleating agent, a lubricant, an antifogging agent, an organic or inorganic material, Known additives such as pigments, UV inhibitors and dispersants can be added.

  The polyethylene resin composition of the present invention includes the above-mentioned ethylene / α-olefin copolymer (A), ethylene / α-olefin copolymer (B), branched low-density polyethylene (C), and, if necessary, added Alternatively, various additives and resin components to be blended may be mixed using a Henschel mixer, a super mixer, a tumbler mixer, or the like, and then heated and kneaded with a single screw or twin screw extruder, a kneader or the like, and pelletized.

III. Use of polyethylene resin composition A polyethylene film formed by using the polyethylene resin composition of the present invention is excellent in impact resistance, strong in elasticity, and excellent in transparency. Suitable for production, it is used as a material for standard bags with dimensional standards such as inner bags and garbage bags.

As one of the indexes representing the transparency of the film, there is a haze value (Haze). The smaller this value, the better the transparency. For applications that require transparency, more transparent films are preferred.
The blown film according to the present invention molded using the polyethylene resin composition of the present invention has a haze value of 7% or less, preferably 5% or less.

The inflation film in the present invention has a value of 1% tensile deformation load in the MD direction of 1.0 N or more, preferably 1.05 N or more. If the value of 1% tensile deformation load is too low, the waist becomes soft, and handling properties such as automatic packaging suitability and openability are inferior.
The inflation film of the present invention has a sufficiently high load value at 1% tensile deformation, so that even if the thickness is reduced, the film is strong, has excellent automatic packaging suitability and openability, and is fundamental for achieving a thin film. It has requirements.

The inflation film in the present invention can form a film having a dart impact strength of 43 g or more, preferably 50 g or more, more preferably 70 g when a film having a thickness of 25 μm is formed.
In addition, the blown film in the present invention, when a film having a thickness of 25 μm is formed, when 1% tensile deformation load in the MD direction is X (unit N) and the dart drop impact is Y (unit g) It is preferable to satisfy the relational expression (2). More preferably, it satisfies the relational expression (2a).
1.43 ≦ X + 0.48 × 10 ⁻² Y (2)
1.45 ≦ X + 0.48 × 10 ⁻² Y (2a)

<Film forming method>
The film of the present invention is formed by inflation molding, but the specification and molding conditions of the inflation molding machine are not particularly limited, and conventionally known methods and conditions can be taken. For example, the diameter of the extruder is 10 to 600 mm, preferably 20 to 300 mm, more preferably 25 to 200 mm, and the ratio L / D of the diameter D to the length L from the bottom of the hopper to the cylinder tip is 8 to 45. , Preferably 12-36.
The die has a shape generally used for inflation molding, and has a flow path shape such as a spider type, a spiral type, a stacking type, etc., and has a diameter of 1 to 5000 mm, preferably 5 to 3000 mm, more preferably 10 to 1800 mm.
For cooling the bubble, a commonly used air ring can be used, and a known gas can be used as the cooling gas. Further, the temperature can be cooled by a chiller or the like, or heated by a heater or the like. I can do it. For the bubble cooling, a known method of applying cooling air from an external air ring or circulating a cooling gas inside can be used. The air ring is not limited to its shape and number, and one or a plurality of known ones such as a single slit type, a dual slit, and a chamber attached can be provided.

  As molding conditions, the resin extruded from the die has a temperature in the range of 140 to 260 ° C., preferably 180 to 240 ° C., and the average discharge speed determined by the discharge amount and the die shape is 1 mm / min to 10 m. / Min, preferably 5 mm / min to 5 m / min, more preferably 10 mm / min to 1 m / min. The bubble exiting the die is expanded by the internal gas, and the BUR represented by the ratio of the bubble diameter to the die aperture is in the range of 1.0 to 4.5, preferably 1.5 to 3.5. Yes, it can be molded under molding conditions such that the TUR represented by the ratio between the take-off speed and the average flow rate when extruded from the die is in the range of 2.0 to 200, preferably 10 to 100. The bubble is solidified by cooling, and the frost line height from the die outlet until the bubble is solidified varies depending on the film forming speed and the film thickness, but is 5 to 1800 mm, preferably 10 to 1200 mm, more preferably 20 to It is in the range of 800 mm.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist. In addition, the physical property measuring method etc. which were used in the Example are as follows.

[Physical property measurement method]
(1) Melt flow rate (MFR):
Based on JIS K7210, it measured on the conditions of 190 degreeC and a 21.18N (2.16kg) load.
(2) Density:
The pellets were hot-pressed to prepare a press sheet having a thickness of 2 mm. The sheet was placed in a beaker having a capacity of 1000 ml, filled with distilled water, covered with a watch glass, and heated with a mantle heater. After boiling boiling water for 60 minutes, the beaker was placed on a wooden table and allowed to cool. At this time, the boiling distilled water after boiling for 60 minutes was adjusted to 500 ml so that the time until reaching room temperature was not less than 60 minutes. Moreover, the test sheet was immersed in the substantially center part in water so that it might not contact a beaker and the water surface. The sheet was annealed at a temperature of 23 ° C. and a humidity of 50% for 16 hours or more and within 24 hours, then punched out to 2 mm in length and width, and measured at a test temperature of 23 ° C. in accordance with JIS K7112.
(3) Melt tension (MT):
Melting under the conditions of cylinder temperature 190 ° C., orifice L / D = 8.1 / 2.095 (mm), piston speed 10 mm / min, take-off speed 4.0 m / min using a capillograph manufactured by Toyo Seiki Seisakusho The tension (MT) was measured.
(4) Degree of strain hardening (λ):
The measurement was performed by the method described in the present specification.

[Film evaluation method]
(1) Dirt drop impact:
The film was fixed to a holder of a testing machine according to ASTM D1709, and was hit with a hemispherical penetrating portion of 38.1 mmφ, and the dart drop impact was measured.
(2) Tensile modulus:
Based on JIS K7127-1999, the tensile elastic modulus when deformed by 1% in the film processing direction (MD direction) and the film width direction (TD direction) was measured.
(3) 1% tensile deformation load:
Based on JIS K7127-1999, the film processing direction (MD direction) and the film width direction (TD direction) were pulled, and the load (N) when deformed by 1% was measured.
(4) Transparency (haze):
The measurement was performed according to JIS K7105-1981. It shows that it is excellent in transparency, so that this value is small.

[Inflation Film Molding Conditions and Formability Evaluation Method]
An inflation film was molded and evaluated under the following molding conditions using an inflation film film forming machine (molding apparatus) having the following 50 mmφ extruder.
Equipment: Inflation molding equipment (MK50 model, manufactured by Mitsubishi Heavy Industries, Ltd.)
Extruder screw diameter: 50mmφ
Die diameter: 75mmφ
Extrusion amount: 20kg / hr
Die outlet shear rate: 20 sec ^-1
Die lip gap: 3.0mm
Take-up speed: 40 m / min Blow-up ratio: 2.0
Molding resin temperature: 190 ° C
Film thickness: 25 μm, 30 μm
Cooling ring: Two-stage air cooling ring Frost line height: About 200-300mm

[Raw materials]
The raw materials used in the examples are as follows. The unit of density is g / cm ³ and the unit of MFR is g / 10 minutes.

(1) Ethylene / α-olefin copolymer (A):
LL-1: ethylene / butene-1 copolymer having a density of 0.936 and MFR 1.5 LL-2: ethylene / hexene-1 copolymer having a density of 0.928 and MFR 0.8 LL-3: a density of 0.920 , MFR1.0 ethylene-butene-1 copolymer LL-4: density 0.956, MFR 0.8 ethylene-butene-1 copolymer LL-5: density 0.930, MFR 1.5 ethylene-butene -1 copolymer

(2) Ethylene / α-olefin copolymer (B):
VL-1: Density 0.906, MFR 1.0, metallocene ethylene / hexene-1 copolymer having a ratio of weight average molecular weight to number average molecular weight of 2.2 VL-2: Density 0.906, MFR 1.0, Metallocene ethylene / hexene-1 copolymer having a weight average molecular weight to number average molecular weight ratio of 3.7 VL-3: density 0.880, MFR 2.2, ratio of weight average molecular weight to number average molecular weight 2.2 Metallocene-based ethylene / hexene-1 copolymer VL-4: Metallocene-based ethylene / hexene-1 copolymer having a density of 0.890, MFR 2.2, and a ratio of weight average molecular weight to number average molecular weight of 2.2

(3) Branched low density polyethylene (C):
LD-1: density 0.927, MFR 1.0, high density radical polymerization method low density polyethylene LD-2: density 0.925, MFR 6.0, high pressure radical polymerization method low density polyethylene LD-3: density 0.927, MFR0 .3, high-pressure radical polymerization method low-density polyethylene LD-4: density 0.920, MFR 4.0, high-pressure radical polymerization method low-density polyethylene

[Example 1]
100 parts by weight of a polyethylene resin composed of LL-1: 77% by weight, VL-1: 10% by weight, and LD-1: 13% by weight was mixed and homogenized by a mixer.
Next, the obtained mixture was melt-kneaded with a twin screw extruder, and the extrudate was solidified and granulated. About the granular polyethylene resin composition finally obtained, film moldability and film physical properties were evaluated by the methods described above. The evaluation results are shown in Table 1.

[Examples 2 to 7]
In Example 1, the types and blending amounts of the ethylene / α-olefin copolymer (A), the ethylene / α-olefin copolymer (B) and the branched low-density polyethylene (C) are as shown in Table 1. Except for the changes, a polyethylene resin composition was prepared in the same manner as in Example 1, and film formability and film physical properties were evaluated. The evaluation results are shown in Table 1.

[Comparative Examples 1-6]
In Example 1, the types and blending amounts of the ethylene / α-olefin copolymer (A), the ethylene / α-olefin copolymer (B) and the branched low-density polyethylene (C) are as shown in Table 2. Except for the changes, a polyethylene resin composition was prepared in the same manner as in Example 1, and film formability and film physical properties were evaluated. The evaluation results are shown in Table 2.

As is apparent from the evaluation results of Tables 1 and 2, Examples 1 to 7 in which the polyethylene resin composition satisfies the requirements of the present invention are ethylene / α-olefin copolymers (Examples 6 and 7). Although the molecular weight distribution of B) is relatively broad and the effect of improving the impact strength is somewhat small, all of them are improved in rigidity, impact strength, and transparency in a well-balanced manner.
On the other hand, in Comparative Examples 1 to 6, which lack at least some of the requirements of the present invention, the rigidity, impact strength, and transparency cannot be improved in a well-balanced manner.
For example, Comparative Example 1 is a case where the density of the ethylene / α-olefin copolymer (B) is not more than a specified lower limit, but the rigidity is remarkably reduced.
In Comparative Example 2 in which the blending amount of the ethylene / α-olefin copolymer (B) is not more than the specified lower limit, the impact strength is not improved and the strength is inferior.
Furthermore, in Comparative Example 3 in which the density of the composition (A) + B) + (C) is not more than the specified lower limit, the impact strength is good, but the rigidity is inferior and the balance between strength and rigidity is inferior.
Furthermore, in Comparative Example 4 where the density of the ethylene / α-olefin copolymer (A) is not less than the specified upper limit of density, the rigidity is good, but the impact strength and transparency are poor.
Further, in Comparative Example 5 in which the MFR of the ethylene / α-olefin copolymer (C) is equal to or higher than the prescribed upper limit, the MFR of the final composition is high, so that the impact strength, transparency, and molding stability are poor.
Further, although the MFR of the ethylene / α-olefin copolymer (C) is within the specified range, Comparative Example 6 in which the relationship between MFR and MT does not satisfy the relational expression (1) is excellent in the balance between impact strength and rigidity. Inferior in transparency and molding stability.

  According to the present invention, it is possible to provide a polyethylene resin composition suitable for the production of a polyethylene film which is excellent in balance between impact resistance and rigidity even when made thin, excellent in transparency, and excellent in suitability for automatic bag making machines. .

Claims (3)

50 to 96% by weight of ethylene / α-olefin copolymer (A), 2 to 30% by weight of ethylene / α-olefin copolymer (B), and 2 to 20% by weight of branched low density polyethylene ( C) and a polyethylene resin composition comprising
The ethylene / α-olefin copolymer (A) has (a-1) a temperature of 190 ° C., a melt flow rate (MFR) at a load of 2.16 kg of 0.5 to 5.0 g / 10 min, and (a-2). ) The density is 0.920-0.945 g / cm ³ ,
The ethylene / α-olefin copolymer (B) has (b-1) MFR of 0.5 to 5.0 g / 10 min, (b-2) density of 0.890 to 0.915 g / cm ³ , And (b-3) the molecular weight distribution (Q value: Mw / Mn) is 4.0 or less, and the density difference between the ethylene / α-olefin copolymer (A) and (B) is 0.015 g / cm. ³ or more
The branched low density polyethylene (C) is produced by a high-pressure radical method, and (c-1) MFR is 0.1 to 5.0 g / 10 minutes, and (c-2) density is 0.905 to 0.935 g. / Cm ³ , and (c-3) the melt tension (MT) at 190 ° C. (unit g) satisfies the following relational expression (1) with MFR (unit g / 10 minutes), and the polyethylene resin composition is: (I) MFR is 0.4-5.0 g / 10min, and (ii) density is 0.926-0.940 g / cm < ³ >, The polyethylene resin composition characterized by the above-mentioned.
MT> −8.74 × log MFR + 13.3 (1) 2. The polyethylene resin composition according to claim 1, wherein when a film having a thickness of 25 μm is formed, the following requirements (I) to (IV) are satisfied.
(I) When the load at 1% tensile deformation in the MD direction is X (unit N) and the dart drop impact is Y (unit g), the following relational expression (2) is satisfied.
1.43 ≦ X + 0.48 × 10 ⁻² Y (2)
(II) X ≧ 1.00 (N)
(III) Y ≧ 43 (g)
(IV) Haze ≦ 7.0%   An inflation film comprising the polyethylene resin composition according to claim 1.