JP2013060006A - Tube-like ethylene resin multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer film that has superior tear strength and impact strength and has a moderate slipperiness.SOLUTION: A tube-like ethylene resin multilayer film which comprises: a core layer that contains 50-100 wt.% of (B) an ethylene-a-olefin copolymer which satisfies the conditions (b1), (b2) and (b3) and 0-50 wt.% of (C) an ethylene-vinyl acetate copolymer which contains 3-40 wt.% of a monomer unit derived from vinyl acetate and has a MFR of 0.1-7 g/10 minutes; and two surface layers that contains (A) an ethylene resin that satisfies the conditions (a1), (a2) and (a3). (a1) NC5 is less than 0.1 per 1,000 carbon atoms. (a2) Ea is ≥40 kJ/mol. (a3) The density is 900-925 kg/m. (b1) Ea is less than 40 kJ/mol. (b2) MFR is 0.1-2 g/10 minutes. (b3) The density is 900-925 kg/m.

Description

  The present invention relates to a tubular ethylene-based resin multilayer film.

  Conventionally, cargo placed on a pallet is stretched in four directions in a tubular film that is smaller than the pallet or cargo using a pallet stretch packaging system, and this is covered with the pallet and cargo, and the cargo is bound together with the pallet. Wrapped by and it is transported or stored. The stretch hood film used for such a packaging means has a force to firmly bind the cargo and the pallet from a sufficiently stretched state to a size capable of binding the cargo and the pallet together. For example, Patent Document 1 discloses a stretch hood film made of an ethylene-vinyl acetate copolymer, and Patent Document 2 discloses a stretch hood film made of an ethylene-α-olefin copolymer.

JP-A-6-345880 JP 2010-254963 A

  In recent years, stretch hood films have the same rate of recovery for recovery from stretched dimensions to the size that allows cargo and pallets to be bound together, as well as the ability to recover from tight binding, as well as conventional films. Tear strength and high impact strength may be required. Moreover, when the inner surfaces of the stretch hood film are blocked from each other, or the inner surface is too slippery, it may be difficult to widen the mouth of the stretch hood film with the pallet stretch packaging system. Under such circumstances, the problem to be solved by the present invention is to provide a tubular ethylene-based resin multilayer film which is excellent in tear strength and impact strength and has appropriate slipperiness.

That is, the present invention has a monomer unit based on ethylene and a monomer unit based on an α-olefin having 4 to 20 carbon atoms, and satisfies all of the following requirements (b1), (b2) and (b3). Satisfactory ethylene-α-olefin copolymer (B) 50-100% by weight,
And a monomer unit based on ethylene and a monomer unit based on vinyl acetate, the content of the monomer unit based on vinyl acetate is 3 to 40% by weight, and the melt flow rate (MFR) is 0. 0.1-7 g / 10 min ethylene-vinyl acetate copolymer (C) (provided that the weight of ethylene-vinyl acetate copolymer (C) is 100 wt%) 0-50 wt%
(However, the total amount of the ethylene-α-olefin copolymer (B) and the ethylene-vinyl acetate copolymer (C) is 100% by weight),
Having two surface layers containing an ethylene-based resin (A) satisfying all of the following requirements (a1), (a2) and (a3);
It is a tubular ethylene-based resin multilayer film in which a core layer is disposed between two surface layers.
Ethylene resin (A)
(A1): The number of branches of 5 carbon atoms (N _C5 ) measured by ¹³ C-NMR is less than 0.1 per 1000 carbon atoms (a2): the flow activation energy (Ea) is 40 kJ / (a3): ethylene-α-olefin copolymer (B) having a density of 900 to 925 kg / m ³
(B1): Flow activation energy (Ea) is less than 40 kJ / mol (b2): Melt flow rate (MFR) is 0.1-2 g / 10 min (b3): Density is 900-925 kg / m ³

  According to the present invention, it is possible to provide a tubular ethylene-based resin multilayer film that is excellent in tear strength and impact strength and has appropriate slipperiness.

The ethylene resin (A) is a polymer having a monomer unit based on ethylene as a main unit, and the content of the monomer unit based on ethylene is the total weight (100% by weight) of the ethylene resin (A). The amount of the polymer is 50% by weight or more. Examples of the ethylene resin (A) include a high-pressure low-density polyethylene produced by a high-pressure radical polymerization method and an ethylene-α-olefin copolymer produced by a coordination polymerization method. The ethylene-based resin (A) is preferably an ethylene-α-olefin copolymer having a monomer unit based on ethylene and a monomer unit based on an α-olefin having 3 to 20 carbon atoms. The content of the monomer unit based on ethylene in the ethylene-α-olefin copolymer is usually 50 to 99% by weight with respect to the total weight (100% by weight) of the ethylene-α-olefin copolymer. The content of the monomer unit based on the α-olefin having 3 to 20 carbon atoms is usually 1 to 50% by weight.
The ethylene-α-olefin copolymer can be obtained by copolymerizing ethylene and an α-olefin having 3 to 20 carbon atoms. Examples of the α-olefin having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 4 -Methyl-1-pentene, 4-methyl-1-hexene and the like are mentioned, and 1-hexene and 1-octene are preferable. Moreover, said C3-C20 alpha olefin may be used independently and may use 2 or more types together.

  Examples of the ethylene-α-olefin copolymer include an ethylene-propylene copolymer, an ethylene-1-butene copolymer, an ethylene-1-hexene copolymer, an ethylene-1-octene copolymer, and an ethylene-1 -Butene-1-hexene copolymer, ethylene-1-butene-1-octene copolymer and the like, preferably ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-1 -Butene-1-hexene copolymer and ethylene-1-butene-1-octene copolymer.

The ethylene resin (A) has a carbon atom number of 5 branches (hereinafter sometimes referred to as “N _C5 ”) measured by ¹³ C-NMR from the viewpoint of increasing tear strength and impact strength. Less than 0.1 per 1000 atoms. N _C5 is preferably less than 0.05 per 1000 carbon atoms, more preferably less than 0.01 and most preferably zero.

N _C5 of the ethylene-based resin (A) should be adjusted according to the polymerization conditions such as the selection of the production method such as gas phase polymerization and slurry polymerization, the selection of the polymerization catalyst, the polymerization temperature, the polymerization pressure, the type and addition amount of the comonomer. Can do.

N _C5 can be obtained by the following method. In a ¹³ C-NMR spectrum in which exponential is applied to the window function, the sum of all peaks observed at 5 to 50 ppm is 1000, and the peak area of a peak having a peak top in the vicinity of 32.5 to 32.7 ppm is Asked. The peak area is a value corresponding to the number of branched methylene carbons having 5 carbon atoms (C ^** in the following structural formula).
・ ・ ・ ・ CH ₂ -CH-CH ₂ -...
└CH ₂ -CH ₂ -C ^** H ₂ -CH ₂ -CH ₃
In addition, since the position of the peak derived from the methine carbon to which the branch having 5 or more carbon atoms is bonded may be shifted depending on the measurement apparatus and measurement conditions, the standard is usually measured for each measurement apparatus and measurement conditions. Go and decide. In the spectrum analysis, it is preferable to use a negative exponential function as the window function.

  Since it is easy to produce a film, the molecular weight distribution (Mw / Mn) of the ethylene-based resin (A) is preferably 5 or more, more preferably 6 or more, and even more preferably 7 or more. Further, from the viewpoint of impact strength, tear strength, elongation recovery rate, and elongation recovery force, the molecular weight distribution of the ethylene-based resin (A) is preferably 25 or less, more preferably 20 or less. The molecular weight distribution (Mw / Mn) is represented by the ratio of the weight average molecular weight to the number average molecular weight, and the weight average molecular weight (Mw) in terms of polystyrene and the number average molecular weight (by gel permeation chromatography) Mn) and Mw divided by Mn (Mw / Mn). The Mw / Mn can be changed, for example, depending on the hydrogen concentration or polymerization temperature during polymerization. When the hydrogen concentration or polymerization temperature is increased, an ethylene resin (A) having a large Mw / Mn is obtained.

  From the viewpoint of improving the film elongation recovery rate, the elongation recovery force, and the slipperiness of the film, the flow activation energy (Ea) of the ethylene-based resin (A) is 40 kJ / mol or more, preferably 50 kJ / mol or more. More preferably, it is 55 kJ / mol or more, More preferably, it is 60 kJ / mol or more. From the viewpoint of tear strength and impact strength, Ea is preferably 100 kJ / mol or less, more preferably 90 kJ / mol or less. The Ea can be changed by, for example, the hydrogen concentration or ethylene pressure during polymerization, and when the hydrogen concentration or ethylene pressure is lowered, an ethylene resin (A) having a large Ea is obtained.

The flow activation energy (Ea) is a master curve showing the dependence of the melt complex viscosity (unit: Pa · sec) at 190 ° C. on the angular frequency (unit: rad / sec) based on the temperature-time superposition principle. Is a numerical value calculated by the Arrhenius equation from the shift factor (a _T ) at the time of creating the value, and is a value obtained by the following method. First, melting complex viscosity-angular frequency curve of ethylene-based resin at temperatures of 130 ° C., 150 ° C., 170 ° C. and 190 ° C. (T, unit: ° C.) Is rad / sec). Next, based on the temperature-time superposition principle, the melt complex viscosity-angular frequency curve at each temperature (T) is superimposed on the melt complex viscosity-angular frequency curve of the ethylene copolymer at 190 ° C. determine the shift factor (a _T) at a temperature (T). A respective temperature (T), from a shift factor (a _T) at each temperature (T), by the method of least squares [ln (a _T)] and [1 / (T + 273.16) ] and the primary approximate expression (Equation (I) below) is calculated. Next, Ea is obtained from the slope m of the linear expression and the following expression (II).
ln (a _T ) = m (1 / (T + 273.16)) + n (I)
Ea = | 0.008314 × m | (II)
a _T : Shift factor Ea: Activation energy of flow (unit: kJ / mol)
T: Temperature (unit: ° C)
For the calculation, commercially available calculation software may be used. As the calculation software, Rheos V. manufactured by Rheometrics is used. 4.4.4.
The shift factor (a _T ) is obtained by moving the logarithmic curve of the melt complex viscosity-angular frequency at each temperature (T) in the log (Y) = − log (X) axis direction (however, the Y axis Is the complex viscosity of the melt, and the X axis is the angular frequency.), And the amount of movement when superposed on the melt complex viscosity-angular frequency curve at 190 ° C., in the superposition, melting at each temperature (T) The logarithmic curve of complex viscosity-angular frequency shifts the angular frequency by a _T times and the melt complex viscosity by 1 / a _T times for each curve. Moreover, the correlation coefficient when calculating | requiring (I) Formula by the least squares method from the value of four points | pieces, 130 degreeC, 150 degreeC, 170 degreeC, and 190 degreeC is usually 0.99 or more.

  The melt complex viscosity-angular frequency curve is measured using a viscoelasticity measuring apparatus (for example, Rheometrics Mechanical Spectrometer RMS-800 manufactured by Rheometrics), and usually geometry: parallel plate, plate diameter: 25 mm, plate interval: 1. It is performed under the conditions of 5 to 2 mm, strain: 5%, angular frequency: 0.1 to 100 rad / sec. The measurement is performed in a nitrogen atmosphere, and it is preferable that an appropriate amount (for example, 1000 ppm) of an antioxidant is added to the measurement sample in advance.

The density of the ethylene-based resin (A), elongation recovery rate, elongation recovery force, in view of enhancing the tear strength and impact strength, is ^{900kg / m 3 ~925kg / m 3} , preferably 905kg / m ³ ~921kg / m ^3, more preferably from ^{910kg / m 3 ~915kg / m 3} . In addition, this density is measured according to the A method (underwater substitution method) prescribed | regulated to JISK7112-1995 using the sample which annealed as described in JISK6760-1995.

  The melt flow rate (MFR) of the ethylene-based resin (A) is usually 0.1 to 50 g / 10 minutes, and 2 g / 10 from the viewpoint of improving tear strength, impact strength, film slipperiness, and stretch recovery force. Preferably it is less than or equal to minutes. The MFR is measured by the A method according to JIS K7210-1995 under conditions of a temperature of 190 ° C. and a load of 21.18N.

The ethylene resin (A) preferably has a g * defined by the following formula (II) of 0.70 to 0.95.
g * = [η] / ([η] _GPC × g _SCB *) (II)
[Wherein [η] represents the intrinsic viscosity (unit: dl / g) of the ethylene resin and is defined by the following formula (II-I). [Η] _GPC is defined by the following formula (II-II). g _SCB * is defined by the following formula (II-III).
[Η] = 23.3 × log (ηrel) (II-I)
(In the formula, ηrel represents the relative viscosity of the ethylene-based resin.)
[Η] _GPC = 0.00046 × Mv ^0.725 (II-II)
(In the formula, Mv represents the viscosity average molecular weight of the ethylene-based resin.)
g _SCB * = (1-A) ^1.725 (II-III)
(In the formula, A is defined by the following formula (II-V).
A = ((12 * n + 2n + 1) * y) / ((1000-2y-2) * 14 + (y + 2) * 15 + y * 13) (II-V)
In the formula, n represents the number of carbon atoms constituting the short chain branch contained in the ethylene-based resin (for example, n = 2 when butene is used as the α-olefin, n = 4 when hexene is used), y Represents the number of short chain branches per 1000 carbon atoms determined by NMR or infrared spectroscopy. ]]
Regarding g *, the following literature was referred to: Developments in Polymer Characterisation-4, JV. Dawkins, Ed., Applied Science, London, 1983, Chapter. I, “Characterization. Long Chain Branching in Polymers, "by Th. G. Scholte

[Η] _GPC is the intrinsic viscosity (unit: dl / g) of a hypothetical polymer that has the same molecular weight distribution as the molecular weight distribution of the ethylene-based resin whose intrinsic viscosity is measured and the molecular chain is assumed to be linear. ).
g _SCB * represents the contribution to g * caused by introducing short chain branching into the ethylene-based resin.
Formula (II-II) is described in Journal of Polymer Science, 36, 130 (1959) pp. 287-294 by LH Tung.

  The relative viscosity (ηrel) of the ethylene resin can be measured by the following method. A sample solution is prepared by dissolving 100 mg of an ethylene-based resin at 135 ° C. in 100 ml of tetralin containing 0.5% by weight of butylhydroxytoluene (BHT) as a thermal degradation inhibitor. The relative viscosity (ηrel) of the ethylene resin is calculated from the falling time of the sample solution measured using an Ubbelohde viscometer and the falling time of a blank solution made of tetralin containing only 0.5 wt% BHT. .

で定義され、a＝０．７２５とした。 The viscosity average molecular weight (Mv) of the ethylene resin is expressed by the following formula (II-IV)

And a = 0.725.

  g * is an index representing the degree of contraction of a molecule in a solution caused by long chain branching. When the amount of long chain branching per molecular chain is large, the contraction of the molecular chain increases. Get smaller. The g * of the ethylene-based resin is preferably 0.70 to 0.95, more preferably 0.75 to 0.90, from the viewpoints of elongation recovery rate, elongation recovery force, tear strength, and impact strength. More preferably, it is 0.75-0.85. It is preferable that g * is 0.95 or less because the elongation recovery rate is excellent. In addition, when g * is 0.70 or more, the molecular chain spreads sufficiently when the crystal is formed, so the probability of tie molecule formation is high, the relaxation time of the molecular chain is short, and the stretch recovery force It is excellent in tear strength and impact strength.

  Examples of the ethylene resin preferably used as the ethylene resin (A) include ethylene resins described in JP-A-2008-106264.

  The ethylene-α-olefin copolymer (B) is a copolymer having a monomer unit based on ethylene and a monomer unit based on an α-olefin having 4 to 20 carbon atoms. The ethylene-α-olefin copolymer (B) can be obtained by copolymerizing ethylene and an α-olefin having 4 to 20 carbon atoms using an olefin polymerization catalyst. Examples of the ethylene-α-olefin copolymer (B) include an ethylene-1-butene copolymer, an ethylene-1-hexene copolymer, an ethylene-1-octene copolymer, and ethylene-1-butene-1. -Hexene copolymer, ethylene-1-butene-1-octene copolymer, and the like. From the viewpoint of increasing tear strength and impact strength, ethylene-1-hexene copolymer, ethylene-1-octene copolymer are preferable. It is a polymer.

  The content of the monomer unit based on ethylene in the ethylene-α-olefin copolymer (B) is usually 50 with respect to the total weight (100% by weight) of the ethylene-α-olefin copolymer (B). ~ 99% by weight. The content of the monomer unit based on the α-olefin having 4 to 20 carbon atoms is usually 1 to 50% by weight with respect to the total weight (100% by weight) of the ethylene-α-olefin copolymer.

  From the viewpoint of increasing the elongation recovery force, impact strength, and tear strength, the flow activation energy (Ea) of the ethylene-α-olefin copolymer (B) is less than 40 kJ / mol, preferably less than 38 kJ / mol. It is. The flow activation energy (Ea) is obtained by the same method as the flow activation energy (Ea) of the ethylene-based resin (A).

The density of the ethylene-α-olefin copolymer (B) is 900 to 925 kg / m ³ , and is preferably less than 922 kg / m ³ from the viewpoint of enhancing the flexibility of the film and the elongation recovery rate, and more preferably Is less than 915 kg / m ³ . The density is measured by the same method as the density of the ethylene resin (A).

  The melt flow rate (MFR) of the ethylene-α-olefin copolymer (B) is 0.1 to 2 g / 10 minutes, and preferably 1 g / 10 minutes or more from the viewpoint of improving workability and tear strength. . The MFR is measured by the A method according to JIS K7210-1995 under conditions of a temperature of 190 ° C. and a load of 21.18N.

  The ethylene-α-olefin copolymer (B) can be produced by, for example, a solution polymerization method, a slurry polymerization method, a gas phase polymerization method, a high-pressure ion polymerization method, or the like.

The multilayer film of the present invention has a core layer containing the ethylene-α-olefin copolymer (B). The core layer may use the ethylene-α-olefin copolymer (B) alone as a resin component, and may further contain other resins.

  As a preferable example of the core layer when the core layer of the multilayer film of the present invention contains another resin, the ethylene-α-olefin copolymer (B), a monomer unit based on ethylene, and a single unit based on vinyl acetate are used. An ethylene-vinyl acetate copolymer having a monomer unit content of 3 to 40% by weight based on vinyl acetate and a melt flow rate (MFR) of 0.1 to 7 g / 10 min. And a layer containing the polymer (C) (however, the weight of the ethylene-vinyl acetate copolymer (C) is 100% by weight). A film having such a core layer is also excellent in stretch recovery rate while maintaining a high stretch recovery force.

  The content of the monomer unit based on vinyl acetate in the ethylene-vinyl acetate copolymer (C) is preferably 10% by weight or more, more preferably from the viewpoint of enhancing the flexibility of the film and the elongation recovery rate. 15% by weight or more. When the content of monomer units based on vinyl acetate contained in the ethylene-vinyl acetate copolymer is 40% by weight or less, the film has excellent stretch recovery ability.

  The melt flow rate (MFR) of the ethylene-vinyl acetate copolymer (C) is 7 g / 10 min or less from the viewpoint of enhancing the film strength and the stretch recovery force. The MFR is measured by the A method according to JIS K7210-1995 under conditions of a temperature of 190 ° C. and a load of 21.18N.

  The ethylene-vinyl acetate copolymer (C) is produced by polymerizing ethylene and vinyl acetate using a catalyst. Examples thereof include a bulk polymerization method using a radical initiator and a solution polymerization method.

  The tubular multilayer film of the present invention comprises a core layer (provided that the ethylene-α-olefin copolymer (B) is contained in an amount of 50 to 100% by weight and the ethylene-vinyl acetate copolymer (C) is contained in an amount of 0 to 50% by weight. The total amount of the ethylene-α-olefin copolymer (B) and the ethylene-vinyl acetate copolymer (C) is 100% by weight). When the content of the ethylene-α-olefin copolymer (B) contained in the core layer is increased, the tear strength, impact strength, and flexibility are more excellent.

  The tubular multilayer film of the present invention comprises two surface layers containing the ethylene resin (A), 50 to 100% by weight of the ethylene-α-olefin copolymer (B), and the ethylene-vinyl acetate copolymer. It is a film having a core layer containing 0 to 50% by weight of combined (C) and having a core layer disposed between two surface layers. Specific layer configurations include surface layer / core layer / surface layer, surface layer / layer (α) / core layer / surface layer, surface layer / layer (α) / core layer / layer (β) / surface layer, etc. Is mentioned. Here, the layer (α) and the layer (β) represent layers other than the surface layer and the core layer of the present invention. Preferably, at least one surface layer is arranged adjacent to the core layer. More preferably, the structure is a surface layer / core layer / surface layer.

The content of the ethylene-based resin (A) contained in the surface layer is preferably 70% by weight or more, more preferably 80% by weight, with the total amount of components contained in the surface layer being 100% by weight. That's it. The surface layer may contain a resin different from the ethylene resin (A), various additives described later, and the like.
The total amount of the ethylene-α-olefin copolymer (B) and the ethylene-vinyl acetate copolymer (C) contained in the core layer is 100% by weight based on the total amount of the constituent components contained in the core layer. Preferably, it is 80 weight% or more, More preferably, it is 90 weight% or more. The total amount of the constituent components contained in the core layer is 100% by weight, and in the core layer, a resin different from the ethylene-α-olefin copolymer (B) and the ethylene-vinyl acetate copolymer (C), and various types described later Additives and the like may be included. The core layer may contain an ethylene resin (A) as a resin different from the ethylene-α-olefin copolymer (B) and the ethylene-vinyl acetate copolymer (C).

  The thickness of the tubular multilayer film of the present invention is preferably 0.01 mm or more from the viewpoint of increasing tear strength and impact strength. In addition, from the viewpoint of coating workability of the film, it is preferably 0.3 mm or less, and more preferably in the range of 0.03 to 0.25 mm.

  The ratio of the thickness of the core layer to the entire thickness of the tubular multilayer film of the present invention is preferably 30% or more and less than 90% from the viewpoint of enhancing the extrusion moldability, transparency of the resulting film, and heat sealability. Yes, more preferably 50% or more and less than 80%.

  In the multilayer film of the present invention, an antioxidant, a light stabilizer, an ultraviolet absorber, a lubricant, an antiblocking agent, an antistatic agent, other resins, and the like are blended in the core layer and the surface layer as necessary. These may be used alone or in combination of two or more.

  Examples of the antioxidant include trivalent phosphorus atoms such as so-called hindered phenol compounds such as 2,6-dialkylphenol derivatives and 2-alkylphenol derivatives, phosphite compounds, and phosphonite compounds. A phosphorus ester compound is mentioned. These antioxidants may be used alone or in combination of two or more. From the viewpoint that the film of the present invention is hardly colored, it is preferable to use a hindered phenol compound and a phosphorus ester compound in combination. In each layer containing an antioxidant, when the weight of the resin in the layer is 100 parts by weight, the layer preferably contains 0.01 to 1 part by weight of an antioxidant, preferably 0.03 to 0 More preferably, 5 parts by weight is contained. The antioxidant is preferably contained in both the core layer and the two surface layers.

  Examples of the light stabilizer include hindered amine compounds having the structure described in JP-A-8-73667, and specific examples thereof include trade names of tinuvin 622-LD, chimasorb 944-LD (above Ciba. Specialty Chemicals Co., Ltd.), Hostabin N30, VP Sanduvor PR-31 (manufactured by Clariant, Inc.), Saiyasorb UV3529, Saiyasorb UV3346 (manufactured by Cytec, Inc.), and the like. Furthermore, a sterically hindered amine ether compound having a structure described in JP-A-11-315067 can be mentioned, and specifically, trade name Tinuvin NOR371 (manufactured by Ciba Specialty Chemicals) can be mentioned. In each layer containing the light stabilizer, when the weight of the resin in the layer is 100 parts by weight, the layer preferably contains 0.01 to 3 parts by weight of the light stabilizer. More preferably, it is contained in an amount of 0.1 to 1 part by weight. The light stabilizer is preferably contained in both the core layer and the two surface layers.

  Examples of the ultraviolet absorber include benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, benzoate ultraviolet absorbers, and cyanoacrylate ultraviolet absorbers, and these may be used alone or in two types. You may use the above together. In each layer containing the ultraviolet absorber, when the weight of the resin of the layer is 100 parts by weight, the layer preferably contains 0.01 to 3 parts by weight of the ultraviolet absorber, and 0.03 to 2 More preferably, it is contained in parts by weight. The ultraviolet absorber is preferably contained in both the core layer and the two surface layers.

  Examples of the lubricant include fatty acids such as stearic acid, oleic acid, and lauric acid; fatty acid amides such as oleylamide, erucylamide, ricinolamide, and behenamide; glycerin esters of higher fatty acids; fatty acid esters such as sorbitan ester and n-butyl stearate Etc. can be used. The content of the lubricant contained in the multilayer film of the present invention is such that the ethylene resin (A), the ethylene-α-olefin copolymer (B), and the ethylene-vinyl acetate copolymer contained in the multilayer film. When the total weight with (C) is 100 parts by weight, it is preferably less than 0.02 parts by weight. Moreover, the multilayer film of this invention does not need to contain a lubricant.

  Examples of the anti-blocking agent include synthetic silica such as dry silica and wet silica; natural silica such as diatomaceous earth; silicon resin; polymethyl methacrylate and the like. In each layer containing the antiblocking agent, when the weight of the resin of the layer is 100 parts by weight, the layer preferably contains 0.2 to 5 parts by weight of the antiblocking agent. The anti-blocking agent is preferably contained in one surface layer or both surface layers.

  When there are a plurality of components constituting each layer, these components are mixed and / or melt-kneaded and then made into a film by the production method described later. Examples of the mixing method include a method of mixing them with a tumbler blender, a Henschel mixer or the like. Examples of the melt-kneading method include a method of melt-kneading them with a single screw extruder or a multi-screw extruder, a method of melt-kneading them with a kneader, a Banbury mixer, or the like.

  Examples of the method for producing the tube-shaped multilayer film of the present invention include a coextrusion blown film forming method and a coextrusion T-die cast film forming method, and the coextrusion blown film forming method is preferable.

  When performing extrusion molding such as an inflation molding method or a T-die cast molding method as a film production method, the extrusion molding temperature is usually 110 to 250 ° C. From the viewpoint of improving the adhesion between the film and the packaged body, the temperature is preferably 130 ° C or higher, and more preferably 140 ° C or higher. Moreover, from a viewpoint of suppressing the thermal deterioration of a film, Preferably it is 240 degrees C or less, More preferably, it is 220 degrees C or less, More preferably, it is 190 degrees C or less.

The tubular multilayer film of the present invention is excellent in elongation recovery rate and elongation recovery force. Specifically, it is preferable that the stretch recovery force in the direction perpendicular to the film forming direction (hereinafter referred to as TD direction) is 23 N / 50 mm width or more, and the stretch recovery rate of the dimensions is 70% or more.
The elongation recovery force and the elongation recovery rate are values obtained by the following methods, respectively.
[Elongation recovery power]
A test piece having a width of 50 mm and a length of 140 mm is prepared so that the longitudinal direction is the TD direction, and two parallel marked lines are attached to the center of the test piece at a distance of 100 mm. Using two chucks of the tensile tester, hold the test piece at the marked line (with the chuck spacing of 100 mm), and stretch the test piece at room temperature at a tensile speed of 1000 mm / min until the chuck spacing is 200 mm. (Stretching ratio: 2.0 times) After holding for 5 seconds, the gap between the chucks is returned to 185 mm so that the stretching ratio is 1.85 times. The tension 1 minute after returning the gap between the chucks to 185 mm is taken as the extension recovery force.
[Elongation recovery rate]
After measuring the extension recovery force, the test piece is removed from the chuck, the distance (L) between the marked lines after releasing the load is measured, and the extension recovery rate is calculated by the following equation.
Elongation recovery rate (%) = (1− (L−100) / 100) × 100
The stretch recovery rate is an index indicating how much the length of the film has been restored after measuring the stretch recovery force and releasing the load.

  If the film has a recovery rate of 70% or more in the TD direction, it is difficult for gaps to form between the film and heavy cargo during transportation and storage of heavy pallets. It is hard to cause collapse.

  When the elongation recovery rate in the TD direction is 70% or more and the elongation recovery force is 23 N / 50 mm width or more, the bundled heavy cargoes can be tightly fixed, so during transportation or storage Less likely to collapse.

The tubular multilayer film of the present invention has moderate slipperiness even without a lubricant. Specifically, the value of the dynamic friction coefficient (hereinafter referred to as μk) of the inner surface of the tubular multilayer film is preferably 0.30 or more and less than 0.70. When the dynamic friction coefficient (μk) is 0.30 or more, when the pallet stretch wrapping machine automatically widens the mouth of the film, the film does not slip too much and the mouth is easy to widen. Moreover, when the coefficient of dynamic friction (μk) is less than 0.70, the films are difficult to block each other and the mouth is easily spread.
The dynamic friction coefficient (μk) is measured according to ASTM D-1894.

  The tubular multilayer film of the present invention is useful as a stretch food film.

Hereinafter, the present invention will be described with reference to examples and comparative examples.
The physical properties of Examples and Comparative Examples were measured according to the following methods.

(1) Melt flow rate (MFR, unit: g / 10 minutes)
According to the method defined in JIS K 7210-1995, the measurement was performed by the A method under the conditions of a load of 21.18 N and a temperature of 190 ° C.

(2) Density (Unit: kg / m ³ )
It measured according to the method prescribed | regulated to A method among JISK7112-1995. In addition, the measurement sample piece was annealed according to the method of low density polyethylene described in JIS K6760-1995 and used for measurement.

(3) Molecular weight distribution (Mw / Mn, unit:-)
Using a gel permeation chromatograph (GPC) method, the weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured under the following conditions (1) to (9), and the molecular weight distribution (Mw / Mn) was determined.
Measurement condition
(1) Equipment: 150CV ALC / GPC manufactured by Waters
(2) Separation column: Shodex GPC AT-806MS manufactured by Showa Denko KK
(3) Temperature: 140 ° C
(4) Solvent: o-dichlorobenzene
(5) Elution solvent flow rate: 1.0 ml / min
(6) Sample concentration: 1 mg / ml
(7) Measurement injection volume: 400 μl
(8) Molecular weight standard substance: Standard polystyrene (manufactured by Tosoh Corporation; molecular weight = 6000000 to 500)
(9) Detector: Differential refraction

(4) Flow activation energy (Ea, unit: kJ / mol)
Using a viscoelasticity measuring device (Rheometrics Mechanical Spectrometer RMS-800 manufactured by Rheometrics), melt complex viscosity-angular frequency curves were measured under the following measurement conditions at temperatures of 130 ° C., 150 ° C., 170 ° C. and 190 ° C. Next, from the obtained melt complex viscosity-angular frequency curve, Rheometrics R. The activation energy (Ea) was determined using 4.4.4.
<Measurement conditions>
Geometry: Parallel plate Plate diameter: 25mm
Plate spacing: 1.5-2mm
Strain: 5%
Angular frequency: 0.1-100 rad / sec Measurement atmosphere: Under nitrogen

(5) g *
g * = [η] / ([η] _GPC × g _SCB *) (II)
G * was determined by the formula (II).
[Η] was determined by the following method. First, a sample solution was prepared by dissolving 100 mg of an ethylene-based resin at 135 ° C. in 100 ml of tetralin containing 0.5% by weight of butylhydroxytoluene (BHT) as a thermal degradation inhibitor. The relative viscosity (ηrel) of the ethylene-based resin is calculated from the falling time of the sample solution measured using an Ubbelohde viscometer and the falling time of a blank solution made of tetralin containing only 0.5% by weight of BHT. did. The calculated relative viscosity (ηrel) was substituted into the formula (II-I) to obtain [η].
[Η] = 23.3 × log (ηrel) (II-I)
(In the formula, ηrel represents the relative viscosity of the ethylene-based resin.)
[Η] _GPC was determined by the following method. The viscosity average molecular weight (Mv) was calculated from the measurement result of (3) molecular weight distribution. The calculated Mv was substituted into the formula (II-II) to obtain [η] _GPC .
[Η] _GPC = 0.00046 × Mv ^0.725 (II-II)
(In the formula, Mv represents the viscosity average molecular weight of the ethylene-based resin.)
g _SCB * was obtained by substituting A obtained by the formula (II-V) into the formula (II-III). g _SCB * = (1-A) ^1.725 (II-III)
(In the formula, A is defined by the following formula (II-V).
A = ((12 * n + 2n + 1) * y) / ((1000-2y-2) * 14 + (y + 2) * 15 + y * 13) (II-V)
In the formula, n represents the number of carbon atoms constituting the short chain branch contained in the ethylene-based resin, and y represents the number of short chain branches per 1000 carbon atoms. ]]
In addition, the measurement and calculation of the number n of short-chain branches and the number y of short-chain branches per 1000 carbon atoms contained in the ethylene resin are described in the literature (Die Makromoleculare Chemie, 177, 449 (1976) McRae, MA, Madams, WF), and carried out using characteristic absorption derived from α-olefin. The infrared absorption spectrum was measured using an infrared spectrophotometer (FT-IR7300 manufactured by JASCO Corporation).

(6) Calculation method of N _C5 A carbon nuclear magnetic resonance spectrum ( ¹³ C-NMR) was measured by a carbon nuclear magnetic resonance method under the following measurement conditions, and was determined by the following calculation method.
<Measurement conditions>
Apparatus: AVANCE600 manufactured by Bruker
Measuring probe: 10 mm cryoprobe Measuring solvent: 1,2-dichlorobenzene / 1,2-dichlorobenzene-d4
= 75/25 (volume ratio) mixed liquid Measurement temperature: 130 ° C
Measurement method: proton decoupling method Pulse width: 45 degrees Pulse repetition time: 4 seconds Measurement standard: Tetramethylsilane Window function: Exponential or Gaussian Integration count: 2500 times <Branch degree calculation method>
Calculation method of the number of branches having 5 carbon atoms (N _C5 , unit: 1 / 1000C)
In a ¹³ C-NMR spectrum in which exponential is applied to the window function, the peak area of a peak having a peak top in the vicinity of 32.5 to 32.7 ppm is defined by assuming that the sum of all peaks observed at 5 to 50 ppm is 1000. Asked.

[Physical properties of film]
(7) Coefficient of dynamic friction (unit: none)
The dynamic friction coefficient of the tube inner surface was measured according to ASTM D-1894.

(8) Rigidity (1% SM) (Unit: MPa)
A strip test piece having a width of 20 mm and a length of 120 mm was sampled so that the longitudinal direction was a film take-up direction (MD) and a direction (TD) perpendicular to the MD direction, and the test piece was used. A tensile test was performed under conditions of a chuck distance of 60 mm and a tensile speed of 5 mm / min to measure a stress-strain curve. From the stress-strain curve, the load at 1% elongation (unit: N) was determined, and 1% SM was determined from the following formula, which was used as the film rigidity.
1% SM = [F / (t × l)] / [s / L0] / 10 ⁶
F: Load at 1% elongation (unit: N)
t: Test piece thickness (unit: m)
l: Specimen width (Unit: m, 0.02)
L0: Distance between chucks (Unit: m, 0.06)
s: 1% distortion (Unit: m, 0.0006)

(9) Tear strength (unit: kN / m 2)
The measurement was performed according to the method defined in ASTM D1922.

(10) Impact strength (unit: kJ / m)
Using a pendulum impact tester (manufactured by Toyo Seiki Seisakusho), the impact energy was determined as the impact strength when the impact ball punched out the center of the 67 mmφ impact surface using an impact ball (15 mmφ hemisphere).

(11) Elongation recovery force (unit: N / 50mm width)
A test piece having a width of 50 mm and a length of 140 mm was produced from the film formed so that the longitudinal direction was a direction (TD) perpendicular to the take-up direction. Two parallel marked lines were attached to the center of the test piece at a distance of 100 mm. Using two chucks of a tensile tester, hold the test piece at the marked line (with the chuck spacing of 100 mm), and stretch the test piece at room temperature under a tensile speed of 1000 mm / min until the chuck spacing is 200 mm. (Drawing ratio: 2.0 times), and held for 5 seconds as it was, the gap between the chucks was returned to 185 mm, and the drawing ratio was 1.85 times. The tension 1 minute after returning the gap between the chucks to 185 mm was defined as the elongation recovery force.

(12) Growth recovery rate (unit:%)
After measuring the elongation recovery force, the test piece was removed from the chuck, the distance (L) between the marked lines after releasing the load was measured, and the elongation recovery rate was calculated by the following equation.
Elongation recovery rate (%) = (1− (L−100) / 100) × 100

[Example 1]
(1) Preparation of co-catalyst support Silica (Sypolol 948 manufactured by Devison Corp .; 50% volume average particle size = 55 μm; pore capacity = 1.67 ml / g; specific surface area = 325 m ² / g) 2.8 kg and 24 kg of toluene were added and stirred. Thereafter, after cooling to 5 ° C., a mixed solution of 0.9 kg of 1,1,1,3,3,3-hexamethyldisilazane and 1.4 kg of toluene was maintained for 30 minutes while maintaining the reactor temperature at 5 ° C. It was dripped at. After completion of dropping, the mixture was stirred at 5 ° C. for 1 hour, then heated to 95 ° C., stirred at 95 ° C. for 3 hours, and filtered. The obtained solid product was washed 6 times with 20.8 kg of toluene. Thereafter, 7.1 kg of toluene was added to form a slurry, which was allowed to stand overnight.

  To the slurry obtained above, 3.46 kg of diethylzinc in hexane (diethylzinc concentration: 50% by weight) and 2.05 kg of hexane were added and stirred. Then, after cooling to 5 ° C., a mixed solution of 1.54 kg of 3,4,5-trifluorophenol and 2.88 kg of toluene was added dropwise over 60 minutes while maintaining the temperature of the reactor at 5 ° C. After completion of dropping, the mixture was stirred at 5 ° C. for 1 hour, then heated to 40 ° C. and stirred at 40 ° C. for 1 hour. Then, it cooled to 5 degreeC and 0.221 kg of water was dripped in 1.5 hours, keeping the temperature of a reactor at 5 degreeC. After completion of dropping, the mixture was stirred at 5 ° C for 1.5 hours, then heated to 40 ° C, stirred at 40 ° C for 2 hours, further heated to 80 ° C, and stirred at 80 ° C for 2 hours. After stirring, the supernatant was withdrawn at room temperature until the remaining amount reached 16 L, 11.6 kg of toluene was added, and then the temperature was raised to 95 ° C. and stirred for 4 hours. After stirring, the supernatant liquid was extracted at room temperature to obtain a solid product. The obtained solid product was washed 4 times with 20.8 kg of toluene and 3 times with 24 liters of hexane. Thereafter, drying was performed to obtain a solid component (hereinafter referred to as a promoter support (a)).

(2) Preparation of prepolymerization catalyst component (1) Into an autoclave with a stirrer having an internal volume of 210 liters that had been previously purged with nitrogen, 80 liters of butane was added, and then 144 mmol of racemic-ethylenebis (1-indenyl) zirconium diphenoxide was added. The autoclave was heated to 50 ° C. and stirred for 2 hours. Next, 0.5 kg of the promoter support (a) was added, and the temperature of the autoclave was lowered to 31 ° C. After the system was stabilized, 0.1 kg of ethylene and 0.1 liter of hydrogen (room temperature and normal pressure volume) were charged, and then 207 mmol of triisobutylaluminum was added to initiate polymerization. After 30 minutes while continuously supplying ethylene and hydrogen at 0.6 kg / hour and 0.5 liter (room temperature and normal pressure volume) / hour, respectively, the temperature was raised to 50 ° C. and ethylene was fed at 3.6 kg / hour, A total of 6 hours of prepolymerization was carried out by continuously supplying hydrogen at 10.9 liters (room temperature and normal pressure volume) / hour. After the polymerization was completed, ethylene, butane, hydrogen and the like were purged and the remaining solid was vacuum dried at room temperature to obtain a prepolymerized catalyst component (1) containing 37 g of polyethylene per 1 g of the promoter support (a).

(3) Production of ethylene-1-hexene copolymer Ethylene and 1-hexene were copolymerized in a continuous fluidized bed gas phase polymerization apparatus using the prepolymerization catalyst component (1). The polymerization conditions were a temperature of 80 ° C., a total pressure of 2 MPa, a molar ratio of hydrogen to ethylene of 1.48%, and a molar ratio of 1-hexene to ethylene of 1.70%. During the polymerization, ethylene, 1-hexene and hydrogen were continuously supplied in order to keep the gas composition constant. Further, the pre-polymerization catalyst component (1) and triisobutylaluminum were continuously supplied at a constant ratio so that the total powder weight of the fluidized bed was maintained at 80 kg and the average polymerization time was 4 hours. By polymerization, a powder of an ethylene-1-hexene copolymer (hereinafter referred to as PE-1) was obtained at a polymerization efficiency of 20.3 kg / hour.

(4) Granulation of ethylene-1-hexene copolymer powder The PE-1 powder obtained above was fed with an extruder (LCM50, manufactured by Kobe Steel, Ltd.) at a feed rate of 50 kg / hour, a screw rotation speed of 450 rpm, and a gate. Granulation was performed under the conditions of an opening degree of 4.2 mm, a suction pressure of 0.2 MPa, and a resin temperature of 200 to 230 ° C. to obtain PE-2 pellets. The evaluation results of PE-1 pellets are shown in Table 1.

(5) Film molding Inflation molding was performed under the following conditions using a three-layer coextrusion inflation molding machine (die diameter: 100 mm, lip opening: 1.2 mm) consisting of three extruders having a screw diameter of 40 mmφ. The above PE-1 pellets 85% by weight and the anti-blocking agent master batch (anti-blocking agent concentration 10% by weight, hereinafter referred to as AB-MB) 15% by weight are uniformly mixed using a tumbler mixer. did. The obtained pellet mixture was introduced into an outer layer extruder and an inner layer extruder, and a commercially available ethylene-1-hexene copolymer (Sumikasen E FV203 manufactured by Sumitomo Chemical Co., Ltd. [MFR = 2 g / 10 min, density = 912 kg / m ³ , molecular weight distribution = 2.0]: hereinafter referred to as LL-1, the basic physical properties of LL-1 are shown in Table 1.) 100 wt% was introduced into an extruder for the intermediate layer and extruded. Machine, die set temperature is 180 ° C, extrusion rate of inner layer, intermediate layer and outer layer is 3kg / hr, 9kg / hr, 3kg / hr, respectively, and blow-up ratio (BUR) is 2.0 with co-extrusion Inflation molding was performed to obtain a multilayer film having a thickness of 100 μm. Table 2 shows the physical property evaluation results of the obtained multilayer film.

(6) Anti-blocking agent masterbatch (AB-MB) used for the above film forming
As an anti-blocking agent master batch (AB-MB), a commercially available ethylene-1-hexene copolymer (Sumitomo Chemical Co., Ltd. Sumikasen E FV402 [MFR = 4 g / 10 min, density = 915 kg / m ³ , molecular weight distribution = 3 .2]: hereinafter referred to as LL-2, the basic physical properties of LL-2 are shown in Table 1.) A resin composition comprising 90% by weight and 10% by weight of an antiblocking agent was used.

[Example 2]
In inflation molding, the resin to be introduced into the intermediate layer extruder is 75% by weight of LL-1 pellets and a commercially available ethylene-vinyl acetate copolymer (Evatate H2020 manufactured by Sumitomo Chemical Co., Ltd. [MFR = 1.5 g / 10 min. The vinyl acetate content was 15% by weight, and the mixture was made in the same manner as in Example 1 except that it was made into a mixture with 25% by weight of pellets.

[Comparative Example 1]
The above LL-2 pellets 95% by weight and AB-MB 5% by weight were uniformly mixed with a tumbler mixer.
Pellets of 99% by weight of PE-1 and 1% by weight of a lubricant master batch (lubricant concentration of 4% by weight, hereinafter referred to as SA-MB) were uniformly mixed with a tumbler mixer.
Comparison was made except that a mixture of LL-2 pellets and AB-MB was introduced into an outer layer extruder and an inner layer extruder, and a mixture of PE-1 pellets and SA-MB was introduced into an intermediate layer extruder. Inflation molding was performed in the same manner as in Example 1. The evaluation results of the obtained film are shown in Table 2. At this time, the lubricant content in the film is 0.024% by weight when the weight of the film is 100% by weight.
As a lubricant masterbatch (SA-MB), a resin composition comprising 96% by weight of LL-2 and 4% by weight of lubricant was used.

Claims (4)

Ethylene-α having a monomer unit based on ethylene and a monomer unit based on an α-olefin having 4 to 20 carbon atoms and satisfying all of the following requirements (b1), (b2) and (b3) -Olefin copolymer (B) 50-100 weight%,
And a monomer unit based on ethylene and a monomer unit based on vinyl acetate, the content of the monomer unit based on vinyl acetate is 3 to 40% by weight, and the melt flow rate (MFR) is 0. 0.1-7 g / 10 min ethylene-vinyl acetate copolymer (C) (provided that the weight of ethylene-vinyl acetate copolymer (C) is 100 wt%) 0-50 wt%
(However, the total amount of the ethylene-α-olefin copolymer (B) and the ethylene-vinyl acetate copolymer (C) is 100% by weight),
Having two surface layers containing an ethylene-based resin (A) satisfying all of the following requirements (a1), (a2) and (a3);
A tubular ethylene resin multilayer film in which a core layer is disposed between two surface layers.
Ethylene resin (A)
(A1): The number of 5 carbon atoms measured by ¹³ C-NMR is less than 0.1 per 1000 carbon atoms (a2): the activation energy of flow is 40 kJ / mol or more (a3) : Ethylene-α-olefin copolymer (B) having a density of 900 to 925 kg / m ³
(B1): Flow activation energy is less than 40 kJ / mol (b2): Melt flow measured by method A under conditions of a load of 21.18 N and a temperature of 190 ° C. according to the method defined in JIS K 7210-1995 The rate is 0.1 to 2 g / 10 min (b3): the density is 900 to 925 kg / m ³ The ethylene-based resin (A) has a monomer unit based on ethylene and a monomer unit based on an α-olefin having 3 to 20 carbon atoms, and satisfies the following requirement (a4): ethylene-α- The tubular ethylene resin multilayer film according to claim 1, which is an olefin copolymer.
(A4): The molecular weight distribution represented by the ratio of the weight average molecular weight to the number average molecular weight is 5 to 25 The total weight of the ethylene resin (A), the ethylene-α-olefin copolymer (B), and the ethylene-vinyl acetate copolymer (C) contained in the tubular ethylene resin multilayer film is The tubular ethylene-based resin multilayer film according to claim 1 or 2, wherein when the content is 100 parts by weight, the content of the lubricant contained in the tubular ethylene-based resin multilayer film is less than 0.02 parts by weight. The stretch food film which consists of a tubular ethylene-type resin multilayer film as described in any one of Claims 1-3.