JP3788320B2 - Air cooled inflation film - Google Patents

Description

【００３６】
【発明の効果】
本発明によれば、光学的性質、引裂強度および剛性に優れた空冷インフレーションフィルムが提供される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-cooled inflation film having an excellent balance of optical properties, tear strength and rigidity.
[0002]
[Prior art]
Air-cooled blown films can be produced with high productivity with a simple apparatus, and are therefore often used for packaging applications. Such an inflation film is required to have, for example, optical properties (transparency, gloss, etc.), tear strength and rigidity. Particularly recently, with the enforcement of the Container Recycling Law, there is a growing demand for thinning, and a film having excellent tear strength and rigidity is demanded.
[0003]
[Problems to be solved by the invention]
A low-density polyethylene (LDPE) air-cooled blown film produced by a high pressure radical polymerization method has excellent optical properties, but has a problem of poor tear strength. In contrast, an air-cooled blown film of linear low density polyethylene (LLDPE), which is a copolymer of ethylene and α-olefin, is excellent in tear strength but inferior in optical properties. Thus, it is often performed to improve the optical properties by blending about 10 to 30% of LDPE with LLDPE, but there is a problem that the tear strength is somewhat lowered.
[0004]
In addition, the rigidity of LLDPE and LDPE films is related to the density. Usually, the higher the density, the higher the rigidity. However, it tends to deteriorate the optical properties and decrease the tear strength. Compatibility with strength was difficult.
An object of the present invention is to provide an air-cooled inflation film excellent in optical properties, tear strength and rigidity, and a method for producing the same.
[0005]
[Means for Solving the Problems]
The present invention is a multi-layered film of three or more layers in which both surface layers are made of the following resin 1 and at least one intermediate layer is made of the following resin 2, and the surface morphology of the film is a spherulite having a diameter of 3 μm or more. And an air-cooled inflation film having an average surface roughness Ra of 30 nm or less .
(Resin 1) Linear low density polyethylene obtained by polymerization using a single site catalyst
(Resin 2) The linear low density polyethylene having a crystallization temperature higher than that of the resin 1 by 2 ° C. or more will be described in detail below.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The surface form of the film of the present invention has a spherulite structure. It is not preferable that the film surface form has an orientation structure such as a tatami structure because tear strength in the orientation direction is lowered. The spherulite structure as used herein refers to a crystal structure that grows in a sphere-symmetric growth mode centered on the crystal nucleus when the resin crystallizes. A simple spherulite structure may be a polyhedron shape). When such a spherulite structure appears on the surface of the film, the center part becomes a circular bulge (unevenness), so the surface morphology of the film is a spherulite structure by observing with an atomic force microscope or the like. I can confirm that there is.
[0007]
As for the size of the spherulite on the surface of the film (spherulite size), the larger the spherulite size, the greater the irregularities on the surface of the film, and the optical properties tend to deteriorate. Although the film has a spherulite structure in which spherulites having a diameter of 3 μm or more exist, the optical properties are excellent. The diameter is preferably 3 to 10 μm. The diameter is determined by measuring the unevenness of the film surface with an atomic force microscope. “The existence of spherulites having a diameter of 3 μm or more” means that spherulites having a diameter of 3 μm or more exist on any of the film surfaces. However, since the cooling of the film surface generally occurs almost uniformly, as described later, A field of view of 100 μm × 100 μm is observed with an atomic force microscope, and at least one spherulite having a diameter of 3 μm or more is required. Preferably it is 100-1000, More preferably, it is 300-1000 from a viewpoint of tear strength. Although one field of view may be observed, it is usually preferable to observe several places.
[0008]
Usually, when such irregularities are present on the surface of the film, the optical properties deteriorate due to light scattering on the surface of the film, but the average roughness Ra of the surface of the film of the present invention is 30 nm or less, and the present invention This film is excellent in optical properties while its surface morphology is a spherulite structure. The average roughness Ra of the surface of the film of the present invention is preferably as small as possible, and more preferably Ra is 27 nm or less.
In the present invention, as the average roughness Ra of the film surface, a value obtained by measuring the unevenness of the film surface with an atomic force microscope is adopted.
[0009]
As a preferred specific example of the air-cooled inflation film of the present invention, an air-cooled inflation film comprising a multilayer film having three or more layers, both surface layers comprising the following resin 1, and at least one intermediate layer comprising the following resin 2. Is mentioned.
(Resin 1) Linear low density polyethylene obtained by polymerization using a single site catalyst (Resin 2) Linear low density polyethylene having a crystallization temperature higher than that of the resin 1 by 2 ° C. or more, preferably this A specific example will be further described.
[0010]
Resin 1 is a linear low density polyethylene obtained by polymerization using a single site catalyst. 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.
By using a linear low density polyethylene obtained by polymerization using such a single site catalyst, the film of the present invention is superior in tear strength (particularly, tear strength in the MD direction) and is preferable.
[0011]
The single site catalyst used here is preferably a catalyst prepared by bringing a metallocene-based transition metal compound and an activating cocatalyst into contact with each other, more preferably a general formula ML _a X _na (wherein M is Group 4 or lanthanide series transition metal atom in the periodic table of elements L is a group having a cyclopentadiene type anion skeleton or a group containing a hetero atom, at least one having a cyclopentadiene type anion skeleton A plurality of L may be cross-linked, X is a halogen atom, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, n is a valence of a transition metal atom M, a is An integer satisfying 0 <a ≦ n.) A catalyst prepared by bringing a transition metal compound represented by the following formula into contact with an activating cocatalyst: Things used alone or in combination of two or more. As an activation co-catalyst, an olefin polymerization activity is provided by using it together with a metallocene transition metal compound or a nonmetallocene transition metal compound, and an organoaluminum compound containing an alumoxane compound and / or triphenylmethyltetrakis (penta Boron compounds such as fluorophenyl) borate and N, N-dimethylanilinium tetrakis (pentafluorophenyl) borate are used. The single-site catalyst may be used in combination with a particulate carrier including an inorganic carrier such as SiO ₂ and Al ₂ O _{3 and} an organic polymer carrier such as a polymer such as ethylene and styrene.
[0012]
The linear low density polyethylene referred to as the resin 1 or the resin 2 is a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, and has a polyethylene crystal structure. Examples of the α-olefin having 3 to 12 carbon atoms include propylene, butene-1,4-methylpentene-1, hexene-1, octene-1, and decene-1. From the viewpoint of tear strength, 4-methylpentene-1, hexene-1, octene-1, or decene-1 is particularly preferable.
[0013]
The MFR value of the resin 1 is preferably from 0.1 to 50 g / 10 minutes, more preferably from 0.5 to 10 g / 10 minutes, from the viewpoints of bubble stability and tear strength during film forming. If the MFR value is too low, the load on the extruder increases, which is not preferable. If the MFR value is too high, molding stability deteriorates, and blocking and tear strength may be lowered. MFR here means what was measured by the method prescribed | regulated to JIS-K7210.
[0014]
The density of the resin 1, the optical properties of bubble stability and film obtained at the time of film molding, from the viewpoint of tear strength, preferably 880~937kg / m ^3, more preferably 900~925kg / m ^3. If the density is too high, the optical properties are deteriorated, and the tear strength is also lowered. The density here means a density measured by a method defined in JISK6760-1981.
[0015]
The resin 2 is a linear low density polyethylene having a crystallization temperature 2 ° C. or more higher than that of the resin 1 and preferably has a crystallization temperature 4 to 20 ° C. higher than that of the resin 1. When the crystallization temperature of the resin 2 is sufficiently high, the unevenness of the film surface becomes small, the optical properties are good, and the tear strength and rigidity can be good. The surface is on both sides of the film, and different resins can be used for both surface layers as the resin 1, but the crystallization temperature of the resin 2 in that case is based on the resin 1 having a higher crystallization temperature. And
[0016]
The density of the resin 2, from the viewpoint of the rigidity of the bubble stability and film obtained at the time of film formation, preferably 900~940kg / m ^3, more preferably 920~935kg / m ^3.
The resin 2 is more preferably a linear low density polyethylene obtained by polymerization using a single site catalyst from the viewpoint of the tear strength of the film.
[0017]
The relationship between the MFR values of the resin 1 and the resin 2 is preferably such that the MFR value of the resin 2 is equal to or smaller than the MFR value of the resin 1. When the MFR value of the resin 2 is larger than the MFR value of the resin 1, the appearance of the film may be deteriorated. When the MFR values of the respective resins 1 on both surfaces are different, the lower MFR value is used as a reference.
[0018]
The layer ratio of the multilayer film is not particularly limited, but is preferably in the range of surface layer: intermediate layer = 4: 1 to 1: 4 from the viewpoint of productivity and physical property balance.
[0019]
In the case where the intermediate layer is composed of two or more layers, any one layer may satisfy the condition.
[0020]
The air-cooled blown film of the present invention is produced, for example, by using the above resin 1 for both surface layers and using the above resin 2 for at least one intermediate layer to process the film by the air-cooled inflation method. Is done.
The molding conditions are usually in the range of a processing temperature of 140 to 220 ° C., a blow ratio of 1.5 to 5.0, a take-off speed of 5 to 150 m / min, and a thickness of 10 to 200 μm.
[0021]
【Example】
Hereinafter, the present invention will be described in more detail based on examples.
The evaluation method was as follows.
[0022]
(A) Film surface average roughness Ra (unit: nm)
<Sampling>
After washing with acetone for 1 minute on the film surface, it was fixed on the sample stage with a double-sided adhesive seal. Thereafter, the static electricity of the sample was sufficiently removed with a static eliminator (DYNAC PB-160B manufactured by Fiesa Corporation).
<Measurement>
The unevenness of the sample surface was measured with an atomic force microscope (AFM) (measurement field: 100 μm × 100 μm).
○ Observation conditions / observation part: D3000 type large sample observation system (manufactured by Digital Instruments)
-Control part: NanoScope IIIa (manufactured by Digital Instruments; Ver.4.23r1)
・ Measurement mode: Tapping
-Data type: Height
・ Scan Rate: 0.5 to 1 Hz
• Number of lines: 512 lines • Number of data points: 512 points / line • Inclination correction: Inclination correction was performed using the “Real time Planefit” function (Line).
○ Probes used: TESP (Nanosensors)
-Material: Si single crystal-Cantilever shape: Single beam type-Cantilever spring constant: 21 to 78 N / m
・ Curve tip radius of curvature: 5 to 20 nm
・ Tip length: 10 to 15 μm
・ 1/2 cone angle of probe: around 18 degrees <data processing>
Curve correction and noise removal were performed using the “Flatten” function (Order 1) of the AFM control software.
The average roughness Ra of the film surface was calculated from the image obtained by performing curvature correction and noise removal using the measurement function “Roughness” of the AFM control software.
○ Software used / Name: NanoScope IIIa (Digital Instruments, Ver.4.23r1)
[0023]
(B) Surface morphology It was judged from the image obtained at the time of the Ra evaluation.
[0024]
(C) Spherulite size Measured from the image obtained at the time of the Ra evaluation.
[0025]
(D) Transparency: Evaluated by haze (unit:%).
Specifically, it measured by the method prescribed | regulated to JIS-K7210.
[0026]
(E) Tear strength (unit: kN / m)
It measured by the method prescribed | regulated to JIS-K7128.
[0027]
(F) Rigidity: 1% secant modulus (unit: MPa; hereinafter abbreviated as “1% SM”) was evaluated.
Specifically, a test piece having a width of 2 cm is cut out in the film processing direction (MD) or in the perpendicular direction (TD), attached to a tensile tester with a distance between chucks of 6 cm, and pulled at a speed of 5 mm / min, 1% 1% SM was obtained by calculating from the stress when stretched by the formula of 100 × (stress) / (cross-sectional area) [MPa].
[0028]
(G) Crystallization temperature (unit: ° C)
Using a differential scanning calorimeter (Perkin Elmer DSC), 10 mg of the sample was previously heated and melted at 150 ° C. for 4 minutes in a nitrogen atmosphere, and then the temperature was lowered to 40 ° C. at a rate of 5 ° C./min. The peak temperature of the maximum peak of the obtained curve was taken as the crystallization temperature.
[0029]
[Example 1]
Sumikacene E FV403 (density = 919 kg / m ³ , MFR = 4 g / 10 min, crystallization temperature = 104), which is a vapor phase metallocene ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd., on both surface layers. ), And the intermediate layer is Sumikasen E V404 (density = 927 kg / m ³ , MFR = 4 g / 10 minutes) which is a vapor phase metallocene ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd. Using an crystallization temperature = 109 ° C., an inflation film was produced under the following processing conditions.
(1) Inflation molding apparatus: Co-extrusion inflation molding machine manufactured by Placo Co., Ltd. (2) Die: 3 types, 3 layers coextrusion die diameter: 150 mmφ, lip gap: 2.0 mm
(3) Molding temperature: 150 ° C
(4) Extrusion amount: 40 kg / hr
(5) Total thickness: 50 μm
(6) Blow ratio: 2.2
(7) Take-up speed: 14m / min
(8) Layer ratio: Inner layer: Intermediate layer: Outer layer = 1: 2: 1
[0030]
[Example 2]
Sumikacene E FV403 (density = 919 kg / m ³ , MFR = 4 g / 10 min, crystallization temperature = 104), which is a vapor phase metallocene ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd., on both surface layers. The intermediate layer is Sumikacene α FZ203-0 (density = 931 kg / m ³ , MFR == multisite catalyst / high-pressure ion polymerization ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd.). An inflation film was produced under the same processing conditions as in Example 1 except that the molding temperature was set to 170 ° C. using 2 g / 10 minutes, the crystallization temperature = 111 ° C.).
[0031]
[Comparative Example 1]
Sumikacene E FV403 (density = 919 kg / m ³ , MFR = 4 g / 10 min, crystallization) which is a vapor phase metallocene ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd. is used for both surface layers and intermediate layers. Was used under the same processing conditions as in Example 1.
[0032]
[Comparative Example 2]
Sumikacene E FV403 (density = 919 kg / m ³ , MFR = 4 g / 10 min, crystallization) which is a vapor phase metallocene ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd. is used for both surface layers and intermediate layers. 80 parts by weight of temperature = 104 ° C. and 20 parts by weight of Sumikasen F200-0 (density = 923 kg / m ³ , MFR = 2 g / 10 min), a high-pressure radical polymerization method low-density polyethylene manufactured by Sumitomo Chemical Co., Ltd. Using the blended resin mixture, an inflation film was produced under the same processing conditions as in Example 1.
[0033]
[Comparative Example 3]
Sumikacene E FV403 (density = 919 kg / m ³ , MFR = 4 g / 10 min, crystallization temperature = 104), which is a vapor phase metallocene ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd., on both surface layers. The intermediate layer is Sumikacene E FV402 (density = 915 kg / m ³ , MFR = 4 g / 10 minutes), which is a vapor phase metallocene ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd. An inflation film was produced under the same processing conditions as in Example 1 using a crystallization temperature = 104 ° C.).
[0034]
[Comparative Example 4]
Sumikacene α FZ202-0 which is a multi-site catalyst / high-pressure ion polymerization ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd. (density = 921 kg / m ³ , MFR = 2 g / 10 minutes) The intermediate layer is Sumikacene α FZ203-0 which is a multi-site catalyst / high-pressure ion polymerization ethylene-hexene-1 copolymer manufactured by Sumitomo Chemical Co., Ltd. (density = 931 kg /). m ³ , MFR = 2 g / 10 min, crystallization temperature = 111 ° C.), and an inflation film was produced under the same processing conditions as in Example 1 except that the molding temperature was 170 ° C.
[0035]
Table 1 shows the evaluation results of the obtained films.
[Table 1]

[0036]
【The invention's effect】
According to the present invention, an air-cooled blown film excellent in optical properties, tear strength and rigidity is provided.

Claims (1)

Both surface layers are made of the following resin 1 and at least one of the intermediate layers is a multilayer film of 3 or more layers made of the following resin 2. An air-cooled inflation film having a crystal structure and an average surface roughness Ra of 30 nm or less.
(Resin 1) Linear low density polyethylene obtained by polymerization using a single site catalyst
(Resin 2) Linear low-density polyethylene having a crystallization temperature 2 ° C. higher than that of Resin 1