JPH11291420A - Multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film having excellent force recovery properties or particularly excellent indentation recovery properties even at a low temperature of about 0 deg.C while maintaining retarded recovery properties and excellent chilliness resistance. SOLUTION: In the film adapted particularly to a stretched packaging for a food or the like by a hand packaging or a machine packaging, comprising both surface layers (S layers) each made of a polyolefin resin composition having a melting point of 100 deg.C or lower, and at least one heat resistant layer (C layer); the heat resistant layer is formed of 10 to 90 wt.% of a polypropylene resin having a melting point of 140 deg.C or higher and 10 to 90 wt.% of an ethylene-styrene random copolymer having a glass transition point (Tg) of 0 deg.C or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer film, and more particularly to a film suitable for stretch packaging of food or the like by hand packaging or machine packaging.

[0002]

2. Description of the Related Art Polystyrene-based elastomers (hereinafter referred to as T
PS) and a resin comprising a block copolymer of styrene and a conjugated diene, or a random copolymer or a hydrogenated composition thereof alone, or a polypropylene-based polymer having a melting point of 140 ° C. or more. Compositions and multilayer stretch films using these as an intermediate layer and an ethylene-vinyl acetate copolymer (EVA) as both surface layers are already known (JP-B-59-47670, JP-B-5-47670). 5
No. 9822, Japanese Patent Application Laid-Open No. 6-179783, Japanese Patent Application Laid-Open No. 8-119319, U.S. Pat. No. 4,835,218.
No.).

[0003] In these methods, attention is paid to the property of TPS, that is, not the instantaneous recovery of a polyolefin-based elastomer, but the property of a plasticized vinyl chloride film that slowly recovers (referred to as delayed recovery). However, by using this resin, it has succeeded in imparting delay recovery properties that could not be imparted by using only the polyolefin resin.

[0004] Example 5 of JP-A-8-119319
More specifically, this film is made of a hydrogenated derivative of a styrene-isoprene-styrene triblock copolymer (Tg = −19 determined by dynamic viscoelasticity).
℃) 49% by weight and softening point 125 ℃ (Tg = 81 ℃)
A mixed composition comprising 21% by weight of a hydrogenated petroleum resin and 30% by weight of a propylene-based copolymer was mixed with an intermediate layer (C).
S / C / with EVA as both surface layers (S layers)
It is a co-extruded blown film of S = 2/11/2 (μm), and describes that the film has excellent resilience (recovery in the present invention).

[0005] Here, the recoverability required for the film for stretch packaging can be roughly classified into a) push-in recoverability and b) delayed recovery property. Products such as food are placed on a container made of expanded polystyrene (generally called a PSP tray) or a molded container (tray) made of polypropylene or polystyrene, and wrapped while stretching a film for packaging (hereinafter referred to as tray packaging). ) After that, it is displayed at the store in an open showcase or the like set at 0 to 10 ° C. "A) Indentation recovery" means that when a consumer picks up a product displayed at a store and checks it, even if the user pushes a finger or the like from above the film, no indentation mark of the finger or the like remains. As described above, it is preferable that the film recovers as quickly as possible because of the property of recovering the deformation of the film.

[0006] On the other hand, the "a) delay recovery property" is a property of slowly returning to the original size as described above. For example, there is a process of cutting a film when packaging the film by a machine. In order to cut the film with a cutter while tension is applied to the film, when the film is cut, the tension is released and the film tries to return to the original state. In the case of a film having characteristics that recover instantaneously, the film returns too much at this time, and the film folds and adheres, so that the film length becomes insufficient even if the film is cut to a predetermined size.
Also, when packaging both hand and machine packaging in trays,
In films with delayed recovery properties, even if there are some wrinkles or looseness immediately after packaging, there is a tendency for the wrinkles and looseness to gradually disappear due to the slowly recovering characteristics, and there is a tendency to finish neatly even if the packaging work is performed roughly to some extent It is in.

[0007] As a recent trend of food packaging, low-temperature distribution and low-temperature display are being implemented as measures for maintaining freshness and as a measure against food poisoning represented by O-157. 0-30 during transportation
In an open showcase where the temperature is controlled to about 0 ° C. and displayed, the setting is generally set to about 0 ° C.

[0008]

On the other hand, the above-mentioned film has too much indentation recoverability in consideration of delay recovery, especially when it is displayed in an open showcase set at a low temperature of about 0 ° C. However, it tends to be inferior to polyolefin resin films. In addition, it has been pointed out that the strength is significantly reduced at 0 ° C. or lower, and that the products packaged in trays are rubbed against each other to easily form holes. Therefore, the present invention provides a film having excellent indentation recovery properties, especially at low temperatures of about 0 ° C., and excellent cold and cold resistance, while maintaining the delayed recovery properties characteristic of conventional films. As an issue.

[0009]

The present invention has a melting point of 100 ° C.
Both surface layers (S layers) made of the following polyolefin resin composition, and at least one heat-resistant layer (C layer), wherein the heat-resistant layer has 10 to 90% by weight of a polypropylene resin having a melting point of 140 ° C. or more. Glass transition point (Tg) is 0 ° C
The following ethylene-styrene random copolymers 10-9
0% by weight.

Hereinafter, the present invention will be described in detail. The present invention differs from the prior art in that an ethylene-styrene random copolymer having a glass transition point (Tg) of 0 ° C. or lower (abbreviated as ESR) is used as a polystyrene-based elastomer (TPS). First, the fact that the present invention is superior to the prior art will be described with reference to Table 1. In Table 1, the film of Example 1 has a TPS of “ethylene-styrene /“ random ”copolymer (ES having a Tg of 0 ° C. or less).
R) ", and the film of Comparative Example 1 is a conventional film using" hydrogenated derivative of styrene-isoprene-styrene / "triblock" copolymer "as TPS. Is a stretch film made of only a polyolefin resin without using TPS as the film of Comparative Example 2.

From Table 1, the film of the present invention is evaluated as “◎” in the overall evaluation, whereas the conventional film and TP
It can be seen that the overall evaluation of the stretch film made of only the polyolefin-based resin without using S was “x”.
Comparing the film of Example 1 with the film of Comparative Example 1, the film of Comparative Example 1 was inferior to the film of Example 1 in indentation recovery at low temperature and dart strength.

As a factor, the above result cannot be explained by simply comparing Tg, which is considered to determine low-temperature characteristics. This has been achieved for the first time by using a random copolymerization type having no styrene segment as TPS as in the present invention. Regarding the strength deterioration at low temperature, it is equivalent to the stretch packaging film of only the polyolefin resin of the film of Comparative Example 2, and the temperature dependence of the film property is obtained by copolymerizing a styrene copolymer having an aromatic ring structure. Despite the use, a film that behaves in the same manner as a film made of only a polyolefin-based resin was obtained.

[0013] From the above, as TPS, "Tg is 0
It can be seen that the film of the present invention using the “ethylene-styrene / random copolymer having a temperature of not more than 0 ° C.” is superior to a conventional film using a block-type TPS and a polyolefin-based resin film not using TPS. Therefore, in the present invention, the ethylene-styrene copolymer needs to be a random copolymer as TPS.

As described above, when styrene forms a block, the apparent Tg measured by dynamic viscoelasticity or the like is 0.
Even when the temperature was lower than 0 ° C, it was not possible to obtain a film having excellent indentation recoverability, particularly at a low temperature of about 0 ° C and excellent dart strength at a temperature of about -30 ° C. Here, the definition of "random copolymer" is, in a narrow sense, a completely random copolymer of ethylene and styrene.
In the present invention, there are polystyrene segments that do not exist and do not form a block copolymer (pseudo random), and those that do not have a sea-island structure as described in the morphology of a polypropylene-based block copolymer described below. Shall be considered.

The fact that the copolymerization is random means that ¹³ C-NM
It is confirmed by the R spectrum,
It can be confirmed from the Tg and the melting peak in the measurement. For example, in the case of ESR, if the styrene content is in the range of 0 to 25 mol%, the melting point (Tm: ° C) and the styrene content (x: mol%) satisfy the following relationship. Tm ≒ 126.37 × exp (−0.0504x) (Formula 1) When the styrene content is more than 25 mol%, almost no melting peak is observed, but the DS at Tg
A clear inflection will be recognized in the C curve. The following relationship exists between Tg (unit: ° C.) and styrene content (x: mol%). Tg ≒ 0.0092 × ² + 0.3553 × −23.803 (Formula 2) If a segment containing only styrene is present, a DSC curve due to the segment should appear around 105 ° C.

Therefore, in the present invention, the DSC
The copolymer was confirmed to be a random copolymer by the melting point and Tg of the copolymer obtained by the method. Further, the Tg of the random copolymer (ESR) must be 0 ° C. or less. Table 2 shows a comparison between Examples 1 to 5 and Comparative Example 3 described later.
As shown in Table 2, the film of Comparative Example 3 having an ESR Tg of 22 ° C. or higher than 0 ° C. was inferior in indentation recovery at low temperature and dart strength at low temperature even if TPS was a random copolymer.

Tg is preferably −22 ° C. or more from the viewpoint of delay recovery, as can be seen from a comparison between Example 2 and Example 3. Further, Tg between Example 4 and Example 5 is described later. As can be seen from the comparison, the case where Tg is −22 to −14 ° C. is more preferable in order to provide indentation recovery and cold / cold resistance in a lower temperature range of −10 ° C. ESR is
JP-A-7-70223, JP-A-7-324106
For example, those polymerized by a Ziegler-Natta type catalyst or a metallocene catalyst, preferably a bis-Cp type metallocene catalyst can be exemplified.

As described above, the styrene content is determined by ESR T
In order for the ESR Tg to be 0 ° C. or less, the above-mentioned (Equation 2) should be about 39 mol% (about 70% by weight) or less. The styrene preferably has a styrene content of about 6 mol% (about 20% by weight) or more. Further, in order to reduce Tg to -14 ° C or less, 18 mol%
(About 45% by weight) or less.

Here, styrene is described as a constituent monomer in the above copolymer, but a vinylidene aromatic monomer may be used in addition to styrene. For example, α-methylstyrene, alkyl- or phenyl-ring-substituted derivatives of styrene having 1 to 4 carbon atoms such as ortho-, meta-, and para-methylstyrene, or mixtures thereof, ring-halogenated styrene, vinylbenzocyclobutane And divinylbenzene.

Further, an α-olefin may be copolymerized therewith. Examples of the α-olefin include propylene, 1-butene, 1-hexene, and 1-octene having 3 to 12 carbon atoms.
Α-olefins can be exemplified. The ratio of the α-olefin may be appropriately determined in the range of about 1 to 30 mol%,
When the styrene content is as low as about 6 mol%, it is preferable to set the ratio of the α-olefin to be higher from the viewpoint of transparency. However, the styrene content is the same as in the case of ESR. Further, a peroxide or the like may be added to the copolymer to dynamically crosslink in an extruder. In this case, the rubber elasticity tends to increase, and in some cases, the effect of improving the indentation recovery may be seen.

In the film of the present invention, the heat-resistant layer (C
Melting point (T) of the polypropylene resin used as the layer)
m) must be 140 ° C. or higher. In comparison between Example 1 and Comparative Example 4 described below, the film of Comparative Example 4 had a Tm of 137 ° C. of the polypropylene resin,
The heat resistance of the heat-resistant layer is insufficient and a melt hole is easily formed, and the sealable temperature is 115 to 130 ° C. (Example 1 is 115
145 ° C) and the temperature range (R) was only 15 ° C.
As a result, as shown in Table 3, the sealability was "x".
The reason for the lack of heat resistance is that when the ethylene content is increased in the case of a propylene-ethylene random copolymer, T
It is considered that the difference in heat resistance was higher than Tm of the polypropylene-based resin as compared with Example 1 because m decreased and the crystallinity also decreased.

Specific examples of the polypropylene resin having a melting point of 140 ° C. or higher include homo isotactic polypropylene resin, random copolymers and block copolymers with other α-olefins except propylene. Can be Preferred are block copolymers. As a more specific example of the random copolymer, in the case of a random copolymer of ethylene and propylene, those having an ethylene content of about 1.7 mol% (about 2.3% by weight) or less are preferable. Further, from the viewpoint of transparency and indentation recovery, the ethylene content is more preferably about 0.7 mol% (about 1.0 wt%) or more.

Next, as a heat-resistant resin having heat resistance and flexibility (which can improve indentation recovery property), a polypropylene block copolymer can be mentioned. In comparison between Example 1 and Example 6 described below, the film of Example 1 uses a propylene-ethylene random copolymer having a Tm of 142 ° C., and has a sealable temperature of 115 to 115 ° C.
In contrast to 145 ° C. (R = 30 ° C.), the film of Example 6 uses a polypropylene block copolymer having a Tm of 165 ° C. and has a sealable temperature of 115 to 165.
° C (R = 50 ° C), and the sealable temperature range is greatly expanded.

Among the polypropylene block copolymers, the main chain having a high melting point is preferably a homopolypropylene as described above. The soft component is a random copolymer of propylene and an α-olefin except propylene, and in the case of a random copolymer of ethylene and propylene as the soft component, the ethylene content is 10 to 10.
90 mol%, more preferably 20 to 80 mol% is preferable in terms of recoverability and transparency. The morphology of the block copolymer is described in "Okayama, New Catalyst and New Polymer Alloy by Gas-Phase Polymerization, Chemical Economics, 19
96 / October issue, 11 ('96) ", it generally has a sea-island structure, but those with a large dispersion diameter of the island structure generally have a roughened film surface when formed into a film. It tends to deteriorate optical properties such as transparency and glossiness.

Therefore, of the block copolymers,
As is clear from the comparison between Example 6 and Example 7 described later, the soft component (island structure) is also used in the block copolymer.
Are uniformly dispersed with a particle diameter of 1 μ or less.
For example, a reactor T using a polymerization process of two or more stages
Montelu-JPO's "Cataroy" called PO,
Tokuyama's "PER", Chisso's "NEWCON"
And the like. In some cases, a polypropylene resin having a melting point of 140 ° C. or more and a polyolefin resin elastomer are melt-kneaded by an extruder or the like, and dynamically crosslinked with a peroxide or the like may be used in some cases.

In the film of the present invention, the heat-resistant layer (C
The proportion of the polypropylene resin having a melting point of 140 ° C. or more in the layer) is 10 to 90% by weight, and the ethylene-styrene random copolymer (ESR) having a Tg of 0 ° C. or less is 10 to 9% by weight.
It must be 0% by weight. In a comparison between Example 11 described later and Comparative Example 5, the film of Comparative Example 5 was inferior in delay recovery property when the proportion of the polypropylene resin was less than 10% by weight. On the other hand, when the content exceeds 90% by weight, the film becomes unsuitable as a stretch film as described in Example 8 and Comparative Example 5 to be described later, or a bubble bulges during stretching. The film formation became unstable. In addition, in comparison between Example 10 and Example 11,
The film of Example 9 is more excellent in the delay recovery property. Therefore, from the viewpoint of the delay recovery property, the content of the polypropylene resin is preferably 25% by weight or more.

In comparison between Example 8 and Comparative Example 2 described later, the film of Comparative Example 2 had an ESR ratio of 10%.
When the amount was less than% by weight, the delayed recovery property and the indentation recovery property were poor.
In comparison with Example 8 and Comparative Example 5, the film of Comparative Example 5 having an ESR of more than 90% by weight was inferior in delay recovery. Further, in comparison between Example 8 and Example 9, the film of Example 10 is more excellent in the indentation recovery property. Therefore, from the viewpoint of the indentation recovery property, the ESR is preferably 25% by weight or more.

The heat-resistant layer (C layer) has an ethylene-α having a density of 0.900 g / cm ³ or less for the purpose of improving indentation recovery and cold / cold resistance in addition to the polypropylene resin and ESR.・ Olefin copolymer and melting point 90 ℃
The following polybutene-1 polymer (preferably butene-1)
-Propylene random copolymer), 1,2-polybutadiene and the like may be blended in a range of 30% by weight or less.
Furthermore, petroleum resins, dicyclopentadiene resins, terpene resins, hydrogenated derivatives thereof and the like may be blended in the range of 20% by weight in order to improve optical properties and delay recovery properties. In addition, blending a liquid additive such as a mineral oil or a process oil in a range of 10% by weight or less may improve the transparency, cold / cold resistance and delayed recovery of the film.

In the film of the present invention, both surface layers (S
The layer) imparts surface properties such as sealability, anti-fogging property, transparency and glossiness, and needs to be a polyolefin resin composition having a melting point (Tm) of 100 ° C. or less. In the comparison between Example 13 and Comparative Example 6, which will be described later, the film of Example 13 uses VL1 having a Tm of 99 ° C for the S layer and thus has a sealable temperature of 115 to 145 ° C. The film of Example 6 had a Tm higher than 100 ° C. in the S layer (Tm =
116 ° C) The sealable temperature is 130 because VL2 is used.
The lowest sealable temperature was increased to １４145 ° C., and thus the sealability was “x”.

Specific examples of the resin used for both surface layers (S layers) include, for example, those having a density of 0.87 to 0.91 g / cm.
^3, an ethylene-α-olefin copolymer, a copolymer of aliphatic monocarboxylic acid or its ester and ethylene, or a partially saponified polymer thereof,
a, Zn, Mg and the like, which are ion-bonded by metal ions. Of these, vinyl acetate content is 10
EVA of 15% by weight and HAO (higher α-olefin) such as 1-hexene or 1-octene as α-olefin were copolymerized with ethylene using a metallocene catalyst to have a density of 0.875 to 0.905 g / cm ^3. And the molecular weight distribution (Mw
/ Mn) is preferably 3.0 or less in view of sealability and strength.

The film of Example 1 using EVA for the S layer described later, Example 13 using the ethylene-octene-1 copolymer polymerized with the metallocene catalyst, and ethylene-polymerized with the Ziegler catalyst Tear strength of each film of Comparative Example 6 using butene-1 copolymer (JIS P81
16 (according to 16), the MD (vertical direction) /
TD (lateral direction) = 10/10 (g), 100/80
(G), 20/30 (g), indicating that the copolymer of HAO and ethylene polymerized using a metallocene catalyst was excellent in strength.

In addition, antifogging agents such as nonionic surfactants and anionic surfactants, inorganic particles such as fatty acid amide and silica, organic particles such as PMMA, lubricants such as silicone oil, antistatic agents, etc. An antioxidant, an ultraviolet absorber and the like may be added. Note that another layer (B layer) may be provided in addition to the S layer and the C layer. For example, ethylene-α having a density of 0.87 to 0.91 g / cm ³ for the purpose of imparting strength
-An olefin copolymer can be used, or a resin obtained by collecting and repelleting a film can be used.

Similarly to the S layer, the B layer has an antifogging agent such as a nonionic surfactant or an anionic surfactant, inorganic particles such as fatty acid amide or silica, organic particles such as PMMA, and silicone. A lubricant such as oil, an antistatic agent, an antioxidant, and an ultraviolet absorber may be added. Where S
The thickness ratio of the layer, the C layer and the B layer is generally 10 to 35 in order.
%, 30-80%, 0-50%. Its configuration is S
/ C / S, S / C / B / S, S / C / B / C / S, S /
B / C / B / S and the like are preferable, but those having a symmetric structure with respect to the central layer are preferable. Incidentally, the film thickness is generally 5 to 20 μ, preferably 8 to 15 μ.

Next, since the film of the present invention is used for stretch packaging, the 100% elongation load, which is an index of the stretchability, is 10% in both the machine direction (MD) and the transverse direction (TD).
The width is preferably 0 to 500 g / cm, and more preferably the 200% elongation load is 100 to 1 for both MD and TD.
000 g / cm width. As a particularly preferred range,
100% elongation load of MD is 100-500 g / cm width, 200% elongation load is 200-600 g / cm width, and TD 100% elongation load is 200-100 g / cm width.
% Elongation load is 110 to 350 g / cm width, and M
D is the case where the elongation load is larger than TD. The breaking elongation is preferably 200% or more for both MD and TD.

Next, examples of the film forming method of the present invention include a co-extrusion T-die casting method, a co-extrusion direct inflation method, a co-extrusion double bubble inflation method, and a laminating method. Extrusion direct inflation and coextrusion double bubble inflation. Hereinafter, the extrusion double bubble inflation method, which is one of the preferred film forming methods, will be described in detail.

First, the resin composition for both surface layers (S layer), the resin composition for heat-resistant layer (C layer), and preferably the resin composition for intermediate layer (B layer) are melted by separate extruders. The mixture is kneaded, extruded from a multilayer circular die, quenched and solidified by a coolant such as water, and then the tubular raw material is folded and taken up. Thereafter, a cross-linking treatment may be performed with high-energy radiation such as an electron beam. Next, the raw material is filled with a gas such as air and inflated, heated to a temperature of 60 to 140 ° C., and then heated to 50 to 11 ° C.
Stretched at a temperature of about 0 ° C. at an area magnification of 2-36 times,
Cool with cold air of below ℃, fold with converging roll and take off. Further, the film may be subjected to relaxation heat treatment with hot air or roll heat treatment with a large number of roll pairs. From the viewpoint of the dimensional stability of the film, it is preferable to perform the heat treatment in a state where the MD and TD are relaxed in a range of 30% or less.

Here, the evaluation method in the present invention will be described below. (1) Randomness According to JIS K-7121, transition temperatures (Tg and Tm) were measured using DSC-7 manufactured by PerkinElmer. The sample amount is about 5 mg, and the heating rate and the cooling rate are 1
0 ° C / min, measurement temperature -70 to 200 ° C, holding time 5
Minutes. The randomness was evaluated based on whether the transition temperature coincided with (Equation 1) and (Equation 2), and further, whether Tg and Tm of the homopolymer of each monomer were not expressed. (2) Tg The transition temperatures (Tg and Tm) were measured using DSC-7 manufactured by Perkin Elmer, in accordance with JIS K-7121. The sample amount is about 5 mg, and the heating rate and the cooling rate are 1
0 ° C / min, measurement temperature -70 to 200 ° C, holding time 5
Minutes. (3) MI and MFR Measured under condition 4 (190 ° C., load = 2.16 kg) in accordance with JIS K-7210, MI, condition 14
(230 ° C., load = 2.16 kg)
Shown as FR.

(4) Delay recovery property Evaluation method In an atmosphere of 15 ° C. and 60% RH, a film sample is cut into a size of 1200 mm in MD and 350 mm in TD, and the standard is set at 100 mm inside from both short sides of the sample. I drew a line. One end of this sample was fixed at the reference line, and 175 g (0.5 g /
cm width). This weight is for preventing the film from jumping up during the measurement. In this state, the tension is pulled to 10% (100 mm) MD based on the reference line, released 30 seconds later, and the difference between the lengths 0.5 seconds and 2 seconds later is measured. L (%) was obtained by dividing.・ Evaluation criteria Scale Symbol Remarks L ≧ 1.3 ◎ Excellent delay recovery 1.0 ≦ L <1.3 ○ Level with no practical problem (passed above) 0.5 ≦ L <1.0 △ Linear packaging L <0.5 × not applicable to the machine L <0.5 × There is a problem even with the upright type packaging machine (5) Indentation recovery ・ Evaluation method Press the film pasted on the frame at the specified stretch rate with the pushing rod and push it. After the removal, it was evaluated whether or not an indentation mark remains.

Specifically, the film is 125 × 125 m
Stretch rate 2% for MD, 2% for TD, 5%
% And 10%. The center point of the film is 15mmφ and the tip is rounded. The depth is 15mm and 20m at a speed of 1m / min.
After maintaining the state of being pushed for 2 minutes under five conditions of m, 25 mm, 30 mm and 35 mm, the pushing rod was pulled out at a speed of 1 m / min. Starting from the start of sampling, 30
After standing for a minute, it was confirmed that no indentation marks remained. The measurement was performed at 23 ° C. and 0 ° C.

The evaluation was carried out based on how many of the 15 conditions of the combination of the three conditions of the stretch ratio of the film and the five conditions of the indentation depth recover without leaving any indentation marks.・ Evaluation criteria Scale Symbol Remarks Recovery under 10 conditions or more ◎ Recovery under 8 conditions or more ○ Level that has no practical problem (passed) Recovery under 6 conditions or more △ Can be used in some applications 5 conditions or less (6) Dart strength ・ Evaluation method The dart strength was measured by RDT manufactured by Toyo Seiki with a thermostat.
The film breaking energy ENG (unit: J) was determined using -5000 / DART. Dart type is SMA
LL ALUMINIUM DART (3.75 kg)
The dirt diameter is 5/8 inch (15.88 mmφ), the maximum load of the cell is 100 pounds (45.53 kgf), the inner diameter of the receiving die is 2.5 inches (63.5 mmφ), and the dart falling speed is 3.87 m. / Second (fall height is 76cm)
The temperature was adjusted to 23 ° C. and −30 ° C.・ Evaluation criteria Scale Symbol Remarks ENG ≧ 0.1 ◎ 0.05 ≦ ENG <0.1 ○ Level with no practical problem (passed above) 0.01 ≦ ENG <0.05 △ Holes are easily formed with sharp objects Drill level ENG <0.01 × It is brittle and easily makes a hole

(7) 100% elongation load, 200% elongation load, and elongation at break 10 mm width × 100 mm in the MD and TD of the sample film.
The sample was cut into a length of 100 mm, and a 100% elongation load, a 200% load and a breaking elongation were measured by a tensile tester equipped with a load cell. The measurement was performed at a chuck distance of 50 mm, a pulling speed of 200 mm / min, and a measurement temperature of 23 ° C. (8) Optical properties-Evaluation method HAZE (%) was measured in accordance with ASTM D-1003.・ Evaluation criteria Scale Symbol Remarks HAZE ≦ 1.5 ◎ Excellent transparency 1.5 <HAZ ≦ 2.0 ○ Practically acceptable level (passed above) 2.0 <HAZ ≦ 3.0 △ Whiteness of film HAZE> 3.0 × Not suitable for practical use (9) Sealability ・ Evaluation method Cut out a film sample into 30 cm × 30 cm. Chuo Chemical's PP tray CH15-11 (150 mm length x
A 200 g aluminum plate is placed on a 114 mm width × 26 mm height), and the sample film is cut out and wrapped from the long side first, and then wrapped from the short side. In this case, on the bottom surface of the tray, a portion in a single state is formed without overlapping the portion where the film is folded.

Next, while setting a hot plate which can be controlled within ± 1 ° C. in steps of 5 ° C. from 90 ° C., the package wrapped as described above is placed on the hot plate so that the tray bottom side contacts the hot plate. Immediately observe the heat sealing state of the film on the bottom side of the tray with the contact time being 2 seconds. If the folded portion is to be peeled off, the film is fused to such an extent that the film is torn, and no melt hole is generated in one film of the film. R, ° C).・ Evaluation criteria Scale Symbol Remarks R ≧ 35 ◎ Excellent sealability 25 ≦ R <35 ○ Level with no practical problems (passed above) 15 ≦ R <25 △ Level that can be used if packaging is performed carefully R <15 × Not practical

(10) Wrapping property Evaluation method The following three types, in which 200 g of clay was placed on a film which was slit into a width of 400 mm and rolled into a roll using an upside-down packaging machine Wmini-ZERO1 manufactured by Ishida Co., Ltd. 30 PSP trays were packaged, and 25 or more PSP trays were judged to be acceptable if they could be packed neatly without wrinkles or tears. Chuo Kagaku SK20F: 194 x 155 x 30 (mm) ... standard tray Chuo Kagaku C-12: 281 x 131 x 22 (mm) ... slender tray FP18 LY18-25: 248 x 180 x 25 (mm) )… Large trays ・ Evaluation criteria Scale Symbol Remarks All three trays passed ◎ Tray with difficult shape can be packed Two trays passed ○ Normal use is possible (more than acceptable level) 1) One kind of tray has passed △ Only those that can be easily packaged can be used All have failed × Not suitable for practical use

(11) Comprehensive evaluation: Evaluation method Delay recovery, indentation recovery at 23 ° C. and 0 ° C., 23
Eight items of dart strength, optical properties, sealing properties, and packaging properties at ℃ and -30 ℃ were comprehensively evaluated.・ Evaluation criteria Scale Symbol Remarks All 8 items are “「 ”or more and 7 items or more are“ ◎ ”◎ Excellent as stretch film. All eight items are “◎” or “○” ○ Level that has no practical problem (passed above) There is no “×”, but even one item has “△” △ Restricted use One item is “×” Is at a level where there is a practical problem

[0045]

EXAMPLES First, the polymers used in this example are shown below. ESR1: styrene content of 10.3 mol% (30.0
Wt%) ethylene-styrene random copolymer [density = 0.942 g / cm ³ , Tg = −18 ° C., Tm = 71
° C, MI = 0.8] ESR2: Styrene content is 18.4 mol% (45.5
Wt%) ethylene-styrene random copolymer [density = 0.952 g / cm ³ , Tg = -14 ° C, Tm = 58
° C, MI = 1.0] ESR3: an ethylene-styrene random copolymer having a styrene content of 6.3 mol% (20.0% by weight) [density =
0.940 g / cm ³ , Tg = −22 ° C., Tm = 88
° C, MI = 1.2] ESR4: Ethylene-styrene random copolymer having a styrene content of 0.8 mol% (3.0% by weight) [density =
0.937 g / cm ³ , Tg = −25 ° C., Tm = 120
° C, MI = 0.9] ESR5: styrene content is 38.6 mol% (70.0 mol%
Wt.%) Ethylene-styrene random copolymer [density = 1.015 g / cm ³ , Tg = 0 ° C., amorphous, MI =
0.6] ESR6: styrene content of 54.3 mol% (81.5 mol%)
Ethylene wt%) - styrene random copolymer [density ^{= 1.035g / cm 3, Tg =} 22, amorphous, MI =
0.6] (In all of the above ESR1 to ESR6, no inflection derived from the styrene segment was observed at around 105 ° C. in the DSC curve.) H-SIS: styrene-isoprene-styrene-triblock Hydrogenated derivative of a polymer [20% by weight of styrene, 80% by weight of polyisoprene having a 3,4-bond ratio of 55%, density = 0.94 g / cm ³ Tg = −19
° C, amorphous, MI = 0.7 (Kuraray “HIBLER H”
SV-3 "equivalent)] EVA1: Ethylene having a vinyl acetate content of 15% by weight
Vinyl acetate copolymer [density = 0.934 g / cm ³ , T
m = 92 ° C., MI = 2.2] VL1: 1-ethylene having an octene content of 12% by weight
Octene-1 copolymer [density = 0.902 g / cm ³ ,
Tm = 99 ° C., MI = 3.0 (“AF manufactured by Dow Chemical Company”
FINITY FW1650 "or equivalent)] VL2: ethylene-butene-1 copolymer [density = 0.
900 g / cm ³ , Tm = 116 ° C., MI = 1.0 (equivalent to “DFDA1209” manufactured by Nippon Unicar)] UL: 1-octene-ethylene-octene-1 copolymer having a content of 24% by weight [density = 0.870 g / cm ³ , T
m = 58 ° C., MI = 1.0 (“ENG” manufactured by Dow Chemical Company)
AGE EG8100 ") KS: 65% of amorphous ethylene-propylene copolymer
Wt.% Polypropylene block copolymer (reactor TPO) [density = 0.88 g / cm ³ , Tm = 16
At 2 ° C., MFR = 0.8, the amorphous ethylene-propylene copolymer has a dispersion diameter of submicron order and is uniformly dispersed (“CATAROY KS” manufactured by Montell-JPO).
081P ")) PP1: Propylene-ethylene random copolymer having an ethylene content of 1.61 mol% [density = 0.90 g / cm
³ , Tm = 142 ° C., MFR = 6.5 (JPO “J
-REX-F4460 ") PP2: Propylene-ethylene random copolymer having an ethylene content of 1.82 mol% [density = 0.90 g / cm
³ , Tm = 137 ° C., MFR = 7.0 (“F” manufactured by Chisso Corporation)
M821 "equivalent)] PP3: Amorphous ethylene-propylene copolymer 2
Polypropylene block copolymer containing 2% by weight [density = 0.90 g / cm ³ , Tm = 165 ° C., MFR = 12
(Equivalent to “J-REX-PM881X” manufactured by JPO)]

[0046]

Example 1 EVA1 was used as a skin layer (S layer), and diglycerin / coconut fatty acid monoester (equivalent to “L-71D” manufactured by Riken Vitamin Co.) / Polyoxyethylene stearate = 70/30 (% by weight) Was used as a heat-resistant layer (C layer) by adding 3% by weight of a mixture of
Using a mixture of 1 / PP1 / UL = 50/30/20 (% by weight), melted in a layer configuration of S / C / S = 35/30/35 (%) from a multilayer circular die set at 220 ° C. After being extruded and quenched with cold water at 15 ° C., it was folded with a converging rack to obtain a raw material having a thickness of 100 μm and a width of 280 mm. Here, about 2 mg / m ² of coconut fatty acid K was applied to the inner surface of the raw material tube by dry weight. Further, the raw material is taken out, guided between two pairs of differential rolls, heated to 120 ° C. in a state where air is injected and formed into a tube again, and 2.7 times in the longitudinal direction in a stretching zone where the ambient temperature is 110 ° C. The film was stretched 3.5 times in the lateral direction, and folded with a converging rack having an opening of 45 degrees while blowing cold air at 15 ° C. Next, 2% in the vertical direction in an oven set at 60 ° C.
A 5% relaxation heat treatment was performed in the lateral direction, and both ends of the film were cut off and wound as two films. The thickness of the resulting film was about 11μ. About the obtained film, the physical property measurement of the film and the evaluation of the film were performed by the method of a text.

[0047]

Comparative Examples 1 and 2 H-SIS /
In a mixture of PP1 / UL = 50/30/20 (% by weight) (Comparative Example 1) and PP1 / UL = 30/70 (% by weight)
(Comparative Example 2) The same operation as in Example 1 was performed, except that the mixture was used. Table 1 shows the physical properties and evaluation results of the films of Example 1 and Comparative Examples 1 and 2 described above. The fact that the present invention is superior to the prior art will be described with reference to Table 1. In Table 1, the film of Example 1 is a film of the present invention using “an ethylene-styrene /“ random ”copolymer (ESR) having a Tg of 0 ° C. or less” as a polystyrene-based elastomer (TPS). 1 film is TP
S is a conventional film using “hydrogenated derivative of styrene-isoprene-styrene ·“ triblock ”copolymer” as S. Further, the film of Comparative Example 2 was TP
This is a stretch film made of only a polyolefin resin without using S.

Table 1 shows that the film of the present invention was evaluated as “「 ”in the overall evaluation, whereas the conventional film and TP
The stretch film made of only the polyolefin-based resin without using S had an overall evaluation of “x”. Comparing the film of Example 1 with the film of Comparative Example 1, the film of Comparative Example 1 was inferior to the film of Example 1 in indentation recovery at low temperature and dart strength. As a factor, the above result cannot be explained simply by comparing Tg, which is considered to determine low-temperature characteristics. According to the present invention, it can be achieved for the first time by using a random copolymer type having no styrene segment as TPS.

The strength degradation at low temperature is equivalent to that of the film of Comparative Example 2 which is a stretch wrapping film made of only the polyolefin resin, and the temperature dependence of the film properties is obtained by copolymerizing styrene having an aromatic ring structure. Despite the use of such a resin, a film having the same behavior as a film made of only a polyolefin resin was obtained. From the above, the film of the present invention using “an ethylene-styrene random copolymer having a Tg of 0 ° C. or less” as a TPS is a conventional film using a block type TPS or a polyolefin not using TPS. It turns out that it is excellent compared with a system resin film.

[0050]

Examples 2 to 5 The polystyrene-based elastomer used for the heat-resistant layer (C layer) was ESR4 (Example 2), ESR3
(Example 3) The same operation as in Example 1 was repeated except that ESR2 (Example 4) and ESR5 (Example 5) were used instead.

[0051]

Comparative Example 3 The same operation as in Example 1 was repeated, except that the polystyrene-based elastomer used for the heat-resistant layer (C layer) was changed to ESR6. Example 1 and Examples 2 to 5 above
Table 2 shows the physical properties and evaluation results of the films of Comparative Example 3 and Comparative Example 3. The necessity that the ESR Tg is 0 ° C. or lower will be described with reference to Table 2. In Table 2, the films of the examples were all “「 ”or more in the overall evaluation. In contrast, the film of Comparative Example 3 had an ESR of Tg of 2
Since 2 ° C. and higher than 0 ° C. were used, the indentation recovery at low temperature and the dart strength at low temperature were inferior. From the above, it is understood that the Tg of the ESR needs to be 0 ° C. or lower.

It should be noted that comparing Example 2 and Example 3,
Example 3 (Tg of ESR = −22 ° C.) is the same as Example 2 (Tg of ESR).
g = −25 ° C.), indicating that the TSR of ESR is preferably −22 ° C. or higher. When the indentation recovery at -10 ° C. was evaluated for the films of Example 4 and Example 5, Example 4 was “○” and Example 5 was “X”. Therefore, it is understood that when the demand for indentation recovery extends to a lower temperature range of about −10 ° C., the Tg of the ESR is preferably −14 ° C. or less.

[0053]

Examples 6 and 7 The same operation as in Example 1 was performed except that the polypropylene resin used for the heat-resistant layer (C layer) was changed to PP3 (Example 6) and KS (Example 7).

[0054]

Comparative Example 4 The same operation as in Example 1 was performed except that the polypropylene resin used for the heat-resistant layer (C layer) was changed to PP2. Table 3 shows the physical properties and evaluation results of the films of Example 1 and Examples 6 and 7 and Comparative Example 4. Using Table 3, the melting point (Tm) of the polypropylene resin of the heat-resistant layer (C layer)
Is required to be 140 ° C. or higher. In Table 3, Example 1 (Tm of polypropylene-based resin =
142 ° C.), Example 6 (Tm = 165 ° C.), Example 7
(Tm = 162 ° C.) was excellent in sealing properties, and therefore, the overall evaluation was “◎”.

On the other hand, in the film of Comparative Example 4, the Tm of the polypropylene resin was 137 ° C., the heat resistance of the heat-resistant layer was insufficient, a melt hole was easily formed, and the sealable temperature was 115 to 130 ° C. (Example 1 is 115-145 ° C)
And the temperature range (R) was only 15. This is because, in the case of the propylene-ethylene random copolymer, when the ethylene content is increased, the Tm is lowered and the crystallinity is also lowered. It is thought to have appeared.

From the above, it is understood that the melting point (Tm) of the polypropylene resin of the heat-resistant layer (C layer) needs to be 140 ° C. or more. Here, in comparison of Example 1 and Example 6, the film of Example 1 uses a propylene-ethylene random copolymer having a Tm of 142 ° C., and has a sealable temperature of 115 to 145 ° C. (R = 30 ° C.) On the other hand, the film of Example 6 uses a propylene-based block copolymer having a Tm of 165 ° C. and has a sealable temperature of 115 to 165 ° C. (R = 50 ° C.). This indicates that it is preferable to use a propylene-based block copolymer. Further, in Table 3, the films of Example 7 using the reactor TPO KS as the polypropylene-based resin had all the evaluation results of “◎”, which is one of the most excellent films among the films of the present invention.

[0057]

Embodiments 8 to 11 In the embodiment 1, the ESR1 / PP
The same operation as in Example 1 except that the ratio of 1 / UL was changed as shown in Table 4 and the thickness ratio between the S layer and the C layer was changed as shown in Table 4 from the relation of film forming property and elongation load. Was repeated. still,
The same operation as in Example 1 was performed to form a film at the ratio in the heat-resistant layer of Example 8, and the 100% elongation load was MD / TD = 800/300 (g / cm width), 200
% Elongation load is MD / TD = 1400/700 (g / cm
Width) and elongation at break were MD / TD = 120/200 (%), and only a film which was not suitable for practical use as a stretch film was obtained. In addition, the same operation as in Example 1 was attempted to form a film at the ratio in the heat-resistant layer of Example 11, but the bubble was partially swollen and immediately punctured, and the film could not be formed.

[0058]

Comparative Example 5 In Example 1, ESR1 / PP1 / U
The ratio of L was changed to 95/5/0 (%), and the thickness ratio of the S / C / S layer was 10/80/10 (%) in view of the film forming property.
The same operation as in Example 1 was repeated, except that the operation was changed to. still,
The ratio of ESR1 / PP1 / UL was changed to 5/95/0 (%), and the thickness ratio of the C layer was reduced in the same manner as in Example 8 to reduce S.
An attempt was made to form a film by performing the same operation as in Example 1 except that / C / S was changed to 47.5 / 5 / 47.5 (%), but the bubbles were blistered and punctured immediately. The film could not be formed.

The above Example 1, Comparative Example 2, and Examples 8 to
Table 4 shows the physical properties and evaluation results of the films 10 and Comparative Example 5. According to Table 4, the heat-resistant layer (C layer) is 10 to 90% by weight of the polypropylene resin and 10 to 90% by weight of the ESR.
The necessity to be described will be described. In Table 4, all the films of the present invention were evaluated as “総 合” or more in the overall evaluation. On the other hand, the film of Comparative Example 5 containing less than 10% by weight of the polypropylene resin was inferior in the delay recovery property and the sealing property (heat resistance). A film having the same ratio exceeding 90% by weight could not be formed as described above. Further, the film of Comparative Example 2 having an ESR of less than 10% by weight was inferior in delay recovery property and indentation recovery property. Further, the film of Comparative Example 5 having an ESR of more than 90% by weight was inferior in delay recovery properties and sealing properties (heat resistance).

From the above, it is understood that the polypropylene resin needs to be 10 to 90% by weight and the ESR needs to be 10 to 90% by weight. Also, in Table 4, Examples 10 and 1 were used.
Compared with Example 1, Example 10 is more excellent in delay recovery property, and the content of the polypropylene resin is preferably 25% by weight or more. Furthermore, comparing Example 8 with Example 9, Example 9 is more excellent in indentation recovery, and preferably has an ESR of 25% by weight or more.

[0061]

Embodiments 12 and 13 The surface layer (S layer) was UL (embodiment 1).
The same operation as in Example 1 was repeated except that 2) and VL1 (Example 13) were used.

[0062]

Comparative Example 6 The same operation as in Example 1 was repeated except that the surface layer (S layer) was changed to VL2. Table 5 shows the physical properties and evaluation results of the films of Example 1 and Examples 12 and 13 and Comparative Example 6. The necessity that the surface layer (S layer) is made of a polyolefin-based resin composition having a melting point (Tm) of 100 ° C. or lower will be described with reference to Table 5.

In Table 5, the films of all Examples had overall evaluations of “「 ”or more. On the other hand, the film of Comparative Example 6 has a sealable temperature of 130 to 145 ° C (115 to 145 ° C in Example 1) and a minimum sealable temperature because VL2 having a Tm higher than 100 ° C is used for the S layer. And the sealing property was “x”. Therefore, it is understood that the surface layer (S layer) needs to be made of a polyolefin resin composition having a melting point (Tm) of 100 ° C. or less. Here, in Example 12, the sealable temperature was 60 to 145 ° C. (R = 85 ° C.), and the sealing property was excellent, since UL having a Tm of 58 ° C. was used for the S layer.

[0064]

Example 14 In Example 2, UL was replaced with a hydrogenated terpene resin ("Clearon P125" manufactured by Yashara Chemical Company).
The same operation as in Example 2 was repeated, except for changing to. The physical properties of the film of Example 14 were such that the 100% elongation load was 140
/ 100 (g / cm width), 200% elongation load is 300 /
220 (g / cm width), elongation at break is 300/420
(%), And all the evaluation results were “◎”. Compared with Example 2, the delay recovery property and the optical characteristics were particularly improved. The film of Example 14 had self-adhesion in hand packaging.

[0065]

Fifteenth Embodiment In the fifth embodiment, UL was replaced with a natural oil ("Smoyl P70" manufactured by Matsumura Oil Research Institute) (Example 1).
The same operation as in Example 2 was repeated except for changing to 5).
The physical properties of the film of Example 15 were such that the 100% elongation load was 2
00/90 (g / cm width), 200% elongation load 300
/ 150 (g / cm width) and elongation at break is 350/420
(%) And a film which was more easily stretched than that of Example 5.

The evaluation results are all “◎”, and the results are shown in Example 5.
In comparison with the above, the indentation recovery property at a low temperature and the dart strength at a low temperature are improved. In addition, HAZE is particularly excellent in optical properties.
And the value of GLOSS (based on JIS K-7105)
While the film of Example 5 had 1.2% and 130% in order, the film of Example 14 had 0.9% and
140%.

[0067]

Example 16 EVA1 as a skin layer (S layer), diglycerin / coconut fatty acid monoester (equivalent to "L-71D" manufactured by Riken Vitamin Co.) / Glycene oleate (equivalent to "OL-100" manufactured by Riken Vitamin Co.) Product) = 3% by weight of a mixture (weight ratio) was used, and a mixture of ESR1 / KS / the above mineral oil = 25/70/5 (% by weight) was used as a heat-resistant layer (C layer). As the B layer, S / B / C / B / S = 10/30 / using VL1 to which 1% by weight of diglycerin / coconut fatty acid monoester (equivalent to L-71D manufactured by Riken Vitamin Co.) was added. 20
The same operation as in Example 1 was repeated, except that a five-layer configuration of / 30/10 (%) was used. The physical properties of the film of Example 16 were such that the 100% elongation load was 150/90 (g / cm width),
When the 200% elongation load is 300/120 (g / cm width),
The elongation at break was 350/420 (%), and the evaluation results were all “◎”.

[0068]

Example 17 A skin layer (S layer) obtained by adding 1% by weight of diglycerin / coconut fatty acid monoester (equivalent to L-71D manufactured by Riken Vitamin Co.) to EVA1 was used.
As C layer, ESR2 / PP (propylene homopolymer at Tm = 162 ° C .; Y1300 manufactured by JPO) / UL / EV
A / PB-1 (butene-1-propylene copolymer; TAFMER BL2481 manufactured by Mitsui Chemicals, Inc.) = 25/10/15 /
Using a mixture of 50/10 (% by weight) and further using a mixture of PP / PB-1 = 50/50 (% by weight) as the B layer, S / C / B / C / S = 10/35/10/35/10
(%), Melt-extruded, quenched with cold water at 15 ° C, and then folded on a converging rack to have a thickness of 50μ.
An 280 mm wide raw material was obtained. Here, about 2 mg / m ² of coconut fatty acid K was applied to the inner surface of the raw material tube by dry weight. Further, the raw material is taken out and guided between two pairs of differential rolls, air is injected, the tube is again heated to 50 ° C in a state of being formed into a tube, and 2.7 times in the vertical direction while being blown with 5 ° C cold air. The film was stretched 4.0 times in the direction, and folded with a converging rack having an opening of 60 degrees.

Next, a heat treatment for relaxing 20% in the vertical direction and 47% in the horizontal direction was performed in an oven set at 60 ° C., and both ends of the film were cut off and wound as two films.
The thickness of the resulting film was about 11μ. About the obtained film, the physical property measurement of the film and the evaluation of the film were performed by the method of a text. The physical properties of the film of Example 16 were such that the 100% elongation load was 450/130 (g / c).
m width), 200% elongation load is 800/250 (g / cm
Width) and the elongation at break were 220/350 (%), and the evaluation results were all “除 い” except for the packaging property. Regarding the wrapping property, the large tray LY18-25 could not be packaged due to the large elongation load and small breaking elongation.
Met.

[0070]

[Table 1]

[0071]

[Table 2]

[0072]

[Table 3]

[0073]

[Table 4]

[0074]

[Table 5]

[0075]

According to the present invention, the indentation recovery property, in particular, zero recovery property, is maintained while maintaining the delay recovery property characteristic of the conventional film.
Excellent indentation recovery even at a low temperature of about ℃, and -30
Even at a low temperature of ° C., a film having strength such as dart strength can be obtained for the first time.

Claims (1)

[Claims] 1. A heat-resistant layer comprising a surface layer (S layer) comprising a polyolefin resin composition having a melting point of 100 ° C. or lower and at least one heat-resistant layer (C layer), wherein said heat-resistant layer has a melting point of 140 ° C.
A multilayer film comprising 10 to 90% by weight of a polypropylene resin having a temperature of not lower than 0 ° C and 10 to 90% by weight of an ethylene-styrene random copolymer having a glass transition point (Tg) of not higher than 0 ° C.