JPH03138148A - Multilayered film - Google Patents

Abstract

PURPOSE:To improve the transparency, bleeding characteristics of additives, mechanical packaging characteristics and film strength by providing specified two surface layers and an inner layer consisting of a resin wherein a high pressure radical method low density polyethylene is a main ingredient. CONSTITUTION:Two surface layers consisting of a mixture of a mixed copolymer consisting of 80-35wt.% ethylene-alpha-olefin copolymer with a density of 0.900-0.925g/cm<3> and 20-65wt.% ethylene-vinyl acetate copolymer with a vinyl acetate content of 5-20wt.% and 0.2-5wt.% nonionic surface active agent and an inner layer consisting of a resin wherein a high pressure radical method low density polyethylene is a main ingredient are provided. The surface layer compsn. can be widely selected thereby in cope with the purpose of use and excellent characteristics can be obtd. thereby. In addition, it is possible to improve transparency, bleeding characteristics of additives, film strength and mechanical packaging characteristics by a synergistic effect of the surface layers and the inner layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a multilayer film made of ethylene resin suitable for shrink wrapping and the like.

[Prior Art] Conventionally, ethylene α-olefin copolymers and blends thereof have been used in various films. Ethylene α
- Olefin copolymer is an ionic copolymer of ethylene and α-olefins such as butene, hexene, octene, etc. using a Ziegler/Natsuta catalyst, etc., and has high density, medium density, and low density depending on the density. are categorized. Low-density polyethylene is called linear low-density polyethylene (LLDP).
VLDPE) and lower density linear very low density polyethylene (hereinafter referred to as VLDPE). These LLDPE and VLDPE have superior mechanical properties such as tensile strength, tear strength, and impact strength, as well as heat resistance, compared to conventional high-pressure low-density polyethylene (hereinafter referred to as LDPE for cars), but on the other hand, It has drawbacks such as a large load during melt extrusion and poor bleedability of organic additives onto the surface of the base material.

As a composition of such an ethylene α-olefin copolymer, LLDP is disclosed in JP-A-58-120654.
A composition comprising E and a small amount of ethylene vinyl acetate copolymer (hereinafter referred to as EV) has been disclosed to improve hot tack properties, mechanical strength, etc.

However, the film obtained from this composition does not have sufficient transparency, and also has the disadvantage that it is difficult to exhibit the effect when an antifogging agent or the like is added.

Further, JP-A-58-113237 discloses a composition in which heat sealability, rigidity, etc. are improved by using a composition consisting of EVA and a small amount of LLDPE. However, the film obtained from this composition does not have sufficient melt-cut sealing properties and has low suitability for mechanical packaging.

As compositions and films of ethylene α-olefin copolymers, EV
A composition and film comprising A, a small amount of LLDPE, and a tackifier are used to obtain a stretch film having excellent flexibility, mechanical strength, and clinging properties. However, when this film is used as a shrinkable film, its sealability is poor.

An example of using an ethylene α-olefin copolymer in a multilayer film suitable for shrink wrapping is disclosed in Japanese Patent Application Laid-Open No. 60-2404.
No. 51 discloses that a crosslinked film having two surface layers consisting of LLDPE, linear medium density polyethylene (hereinafter referred to as Ml), F and V8, and a core layer consisting of LLDPE has heat sealability. What is disclosed is an attempt to obtain a shrink film with an excellent, gentle shrink-temperature curve. However, this film has the drawback that its transparency, particularly after shrinkage, deteriorates, and also has poor antifogging agent bleed properties, making it difficult to impart antifogging properties.

Furthermore, in Japanese Patent Application Laid-open No. 62-80043, VLDPE
An attempt is made to obtain a film having excellent shrinkability and various sealing properties by using a film having a heat-sealing layer containing the following. However, this film was unable to satisfy all the requirements of transparency, additive bleedability, and mechanical packaging properties.

[Problems to be Solved by the Invention] It goes without saying that a film suitable for shrink wrapping is required to have excellent shrinkage properties, but it is also required to have the following properties.

(i) Excellent transparency (especially transparency after shrinkage).

(ii) Additives such as antifogging agents and antistatic agents bleed well, and their properties are fully exhibited.

(iii) It has excellent melt-cut sealing properties and can be mechanically packaged at high speed and stably.

(iv) Excellent strength such as tensile strength and impact strength.

However, although ethylene α-olefin copolymers generally have excellent strength in (1v) above,
The characteristics of ~(iii) cannot be said to be sufficient.

As mentioned above, at present, no film using an ethylene α-olefin copolymer that satisfies all of the properties required for shrink wrapping is available.

An object of the present invention is to provide a multilayer film that satisfies all the characteristics of transparency, additive bleedability, mechanical packaging suitability, and film strength.

[Means for solving the problem] That is, the present invention has a density of 0.900 to 0.925 g/
cm3 ethylene α-olefin copolymer 80-35v
+t% and 20 to 65 wt% of an ethylene vinyl acetate copolymer with a vinyl acetate content of 5 to 20 wt%. , relates to a multilayer film having an inner layer made of a resin mainly made of high-pressure radical-processed low-density polyethylene.

The ethylene α-olefin copolymer used for the surface layer in the present invention includes ethylene and, for example, butene-1,
Pentene-1, hexene-1,4-methylpentene-1
, octene-1, etc. (both are copolymerized with one kind of α-olefin), preferably hexene-1,4-methylpentene-1, octene-1, and 4-methylpentene-1 is more preferred. Preferable.The copolymerization ratio is indicated by the number of pendant methyl groups in the copolymer, and the number of carbon atoms is 1.
10 to 50 pieces per 000c is preferable, and 20 to 4 pieces per 000c.
0 pieces/100oc is more preferable, and 30 to 40 pieces/100oc is most preferable. The density of this ethylene α-olefin copolymer is 0.900 to 0.92
5g/cm”, preferably 0.905 to 0.91
5g/cm". If the density is less than 0.900g/cm", the film surface will be sticky, and the density will be 0.925g/cm.
If it is larger than m3, transparency decreases.

The EVA used in the surface layer of the present invention has a vinyl acetate content of 5 to 20 wt%, preferably 1O10N17%. Those with a vinyl acetate content of less than 5 wt% have poor transparency, and those with a vinyl acetate content of more than 20 wt% have poor extrudability and a strong acetic acid odor.

The ethylene α-olefin copolymer and E of the surface layer of the present invention
The ratio of VA is ethylene α-olefin copolymer 80~
EVA is 20 to 65 wt% compared to 35 wt%.

If the EVA ratio is less than 20 wt%, the kneading property with the nonionic surfactant and the bleeding property will be poor, resulting in poor antifogging properties. If the EVA ratio is more than 65 wt%, the sealing performance will be poor.

The resin used for the inner layer of the present invention is mainly made of high-pressure radical-processed low-density polyethylene. The high-pressure radical low-density polyethylene refers to ethylene homopolymers having long chain branches and ethylene copolymers that have been commercially available. Ethylene copolymer is ethylene and 10w
Copolymerized with t% or less of a copolymerizable comonomer,
For example, EVA has a vinyl acetate content of 10 wt% or less. "Mainly" means that the above-mentioned high-pressure radical low-density polyethylene has a ratio of at least 50 wt%, for example, high-density polyethylene, LLDP
E, olefin polymers such as ethylene propylene rubber and polypropylene may be mixed in an amount below 50 wt%.

The nonionic surfactants used in the present invention include, for example, polyhydric alcohol fatty acid esters such as glycerin fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, and their ethylene oxide adducts, polyoxyethylene fatty acid esters, and polyoxyethylene fatty acid esters. Ethylene alkyl ether, fatty acid jetanolamide, N, N
It is one type or a mixture of two or more types selected from '-bishydroxyethylalkylamine derivatives. This nonionic surfactant is used in the surface layer in a range of 0.2 to 5 wt%, preferably in a range of 0.5 to 4 wt%. 0.2
If it is less than 5 wt%, the effects such as antifogging and antistatic properties will not be sufficient, and if it is more than 5 wt%, kneading properties will become unstable, film formability will deteriorate, and the film surface will be contaminated. Furthermore, it is preferable to add the nonionic surfactant of the present invention to the inner layer as well. Since the high-pressure radical low-density polyethylene, which is the main component of the resin in the inner layer, has the effect of increasing the stiffness of the film and improving the weld sealability, it is not essential to use this additive. However, high-pressure radical-processed low-density polyethylene has excellent kneading and bleeding properties with the additive, so it exhibits properties such as antifogging and antistatic properties at an early stage, and further improves its durability. Adding the additive in a larger amount to the inner layer than the surface layer is
More preferred.

At this time, the amount of nonionic surfactant added to the inner layer is preferably 0.5 to 6 wt%.

The film of the present invention is a film of 3N or more. For example, in the case of a three-layer film, the preferred thickness ratio of each layer is selected from the range of 1/1/1 to 1/20/1 (surface layer/inner layer/surface layer). It will be done. In addition, other inner layers may be provided for the purpose of imparting gas barrier properties, improving film elasticity, improving interlayer adhesion, etc. In that case, the thickness of the other inner layers should be 30% or less of the entire film. It is preferable. There is no particular restriction on the method of multilayering in this case, and any method can be selected from conventionally used methods such as coextrusion, lamination, coating, etc., but coextrusion is particularly preferred. is preferred.

The multilayered film as described above may be used as it is without being stretched, or may be stretched and oriented if necessary. In particular, when trying to obtain a heat-shrinkable film, it is preferable to carry out stretching orientation, and according to a commonly used method, 2 to 2 to
It is preferable to stretch the film by about 10 times.

Furthermore, when trying to obtain a heat-shrinkable film, it is preferable to perform a crosslinking treatment before stretching. For example, α rays, β
It is preferable to crosslink the gel fraction of the film to 5 to 50% by irradiating the film with ionizing radiation such as rays, gamma rays, neutron beams, and accelerated electron beams.

Furthermore, the film of the present invention can be applied to each f! Additives such as antioxidants, antiblocking agents, slip agents, etc. may be included as desired.

[Example] The present invention will be explained in more detail using Examples below, but the present invention is not limited to these Examples in any way.

Note that the measurement methods and evaluation methods in Examples are as follows.

(1) Using hot air with a haze of 150℃ after shrinkage, the film has an area shrinkage rate of 30%.
After shrinking, it was measured using the ASTM-D-1003 method.

(2) Tensile modulus Measured according to ASTM-D-882-81 method.

(3) Melt index (MI) Measured by ASTM-D-1238 method (E condition).

(4) Gel fraction A sample was extracted with boiling limp-xylene, and the proportion of the insoluble portion was expressed by the following formula.

(5) Pendant Methyl Group Macromolecular Chemistry Labid Communication (Makromol, Chem, Rap
It was measured by the IR method according to the method described in idCommun, ) 9 (198g).

(6) Initial anti-fogging properties Cover a beaker containing 20°C water with the film that has been used for 3 days, and leave it in the refrigerator at 5°C for 1 hour. The condition of the water attached to the film is as follows. It was judged and evaluated according to the criteria.

5: Items with a mirror-like water film 4: Items with a slightly uneven water film 3: Items with spread water droplets 2: Items with small water droplets 1: White cloudy, contents confirmed Things that cannot be done (7) Repeated anti-fogging properties After measuring the initial anti-fogging properties, wash the film surface with water in a beaker, leave it for 1 hour, and then store it in a refrigerator at 5℃ for 1 hour.
Films left for an extended period of time were judged according to the same criteria as in (6).

(8) Melting seal strength Sentinel heat sealer 0.5Rx 280 f
Attach a fusing blade of 150℃, 30psi, 0.
Two stacked 15 mm wide films were fused and sealed for 5 seconds, and immediately after that, 1#h of the film was fixed, a load was applied to the other end, and the load when the seal was peeled off was taken as the strength.

(9) Fused seal temperature Attach a 0.5 Rx280 A fusing blade to the sentinel heat sealer and set the temperature to 25 at 30 psi% for 0.5 seconds.
A two-ply film with a width of 0 mm was cut and sealed, and the lower limit temperature of the cut and seal was evaluated from the following viewpoints.

◎: Completely fused at 150°C O: 80% or more fused in the width direction at 150°C △: Completely fused at 180°C Membrane stability The stability of the film when it was formed by inflation was evaluated according to the following criteria based on the size of the uneven thickness of the film.

0: Thickness unevenness of less than 10% and no bubble fluctuation O: Thickness unevenness of lO~20% and bubble fluctuation slightly Δ: Thickness unevenness of 20%
Bubble size and large bubble fluctuation ×: Inflatable non-inflatable A list of resins used in the examples is shown below.

VLDPE-a: (density=0.910g/cm",
MI=3.6 g/10 min.

Comonomer = 4-methylpentene-1, 234 pendant methyl groups/100OC) VLDPE-b: (Density = 0.912 g/am',
MI=3.3 g/lo min.

Comonomer=octene-1. Pendant methyl group = 18
pieces/100Oc>VLDPE-c: (density=0.915g/cm",
MI=2.0 g/10 min.

Comonomer = 4-methylpentene-1, pendant methyl group = 29/100OC) VLDPE-d: (Density - 0,9053/cm3.
Ml-0.8g/10min.

Comonomer rich octene-11 pendant methyl base 23
pieces/100OC) LLDPE-a: Cm degree -0,920g/cm',
MI・1.0 g/lo min.

Comonomer: octene-1, pendant methyl group = 14
pcs/100Oc1 00Oc) La: (Density - 0,935g/cm'
, Ml-2,5g/io min.

Comonomer rich octene-1, pendant methyl group = 7 pieces/100OC) EVA-a: (vinyl acetate content = 15 wt%, M
I=2.3g710min) EVA-b: (vinyl acetate content=25wt%, M
I=2.0g710min) EvA-c: (vinyl acetate content! 5 wt%,
Mlx 2.0g710min) EVA-d: (vinyl acetate content = 6wt%, MI =
0.3g710min) LDPE-a: (density -0,9193/cm',
Ml-2.0g/10min) LDPE-b: (Density-
0,928g/cm3. MI-0.5g/10min) First, the ratio of the ethylene α-olefin copolymer and EVA in the surface layer of the present invention was investigated using a single layer film, and based on the results, Examples and Comparative Examples were conducted. Ta.

Experimental Example I EVA-a was supplied to an extruder, and 2 wt% of diglycerin monooleate was added as a nonionic surfactant.
The mixture was poured into an extruder, kneaded, extruded through an annular gouer at 200° C., and rapidly cooled to form a tubular film with a thickness of 600 μm. This tubular film was flattened and cross-linked using an electron beam irradiation device (manufactured by Nissin High Voltage Co., Ltd.) to a gel fraction of 20%.
It was heated to 0° C. and blown to 7 times MD and 5.7 times TD to obtain a film with a thickness of 15 μm. Experiment N
Set it to 001.

Further, a film was obtained in the same manner as in Experiment No. 11 using the composition shown in Table 1. This will be referred to as Experiment No. 2-8. The physical properties of the films of Experiments No. 11 to 8 are also listed in Table 1, and are further shown as graphs in FIGS. 1 to 3.

The horizontal axis in Figures 1 to 3 represents the ratio of the raw resin composition,
The left end is 100% ethylene-olefin copolymer and EV
It is the A0% point, and the further to the right the EVA ratio increases,
The right end is the point of 100% EVA. The vertical axis is the initial anti-fogging property in Figure 1 and the fusing seal strength in Figure 2.
FIG. 3 shows the haze after shrinkage.

As is clear from Fig. 1, Experiment No. 6 (corresponding to the film using the composition of the prior art, JP-A-58-120654) had fair antifogging and melt-cut sealing properties, but after shrinkage The film turned white and had poor transparency. Experiment No. 7 (Prior art Japanese Unexamined Patent Publication No. 58-113237
No. 4,425,268 (corresponding to the film using the composition of US Pat. No. 4,425,268) had poor fusing sealability. Experiment No. 8 (Prior art, JP-A-60
- Compatible with films using the surface layer composition of Publication No. 240451) has low kneading properties with nonionic surfactants and is difficult to bleed, resulting in poor antifogging properties and poor transparency after shrinkage. It was said that it was also inferior.

VLDPE and EVA (7) Mixed system, that is, experiment No.
1 to 5, Experiment No. 5 (prior art, JP-A-62-8
0043) has poor kneading and bleeding properties with nonionic surfactants, and therefore has poor antifogging properties.

Examining the preferred range from Figure 1, the EVA ratio is 30 to 100% for initial anti-fogging properties (Figure 1), the εVA ratio is 0 to 50% for fusing sealability (Figure 2), and transparency (FIG. 3) shows good results in the entire range, and it is recognized that a well-balanced single-layer film that satisfies the evaluation from all three viewpoints can be obtained in the EVA ratio range of 30 to 50%.

Examples 1 to 3/Comparative Examples 1 to 4 40 wt% of VLDPE-a and εVA were used in the extruder for the surface layer.
-A 60 wt% mixture was added to the extruder for the inner layer using LDPE.
-a, extruded using a multilayer die, and rapidly cooled, surface layer/inner layer/surface layer=90μ/420μ/9
A tubular film with a total size of 600 μm was molded. At this time, as a nonionic surfactant, diglycerin monooleate was injected into an extruder in an amount of 2 wt% for the surface layer and 3 wt% for the inner layer, and kneaded. This tubular film was flattened and cross-linked to a gel fraction of 20% using an electron beam irradiation device, and then MD 7 times and TD
It was stretched 6.6 times to obtain a film with a thickness of 13 μm. This is referred to as Example 1.

In addition, a film was obtained in the same manner as in Example 1 according to the resin/nonionic surfactant ratio shown in Table 2. These are referred to as Examples 2 and 3 and Comparative Examples 1 to 4.

To explain the films listed in Table 2, Comparative Example 1
Examples 1 to 3 are single-layer films made of resins with different mixing ratios of EVA and VLDPE, and Examples 1 to 3 are multilayer films each having a surface layer made of the same resin composition as Comparative Examples 1 to 3. Comparative example 4 is the conventional technology, JP-A-60-24
This is a film corresponding to Publication No. 0451. In Table 2,
For these films, the results of evaluating the film-forming stability, antifogging properties, tensile modulus of elasticity, and fusing seal temperature, which are important characteristic values when performing mechanical packaging, are also described.

As is clear from Table 2, when comparing Example 3 and Comparative Example 3, Comparative Example 3, which is a single layer with a high proportion of VLDPH, has good fusing sealing properties, but its antifogging properties are poor and it cannot be used as a film. Although it was difficult, by using LDPE for the inner layer, the initial release and antifogging properties were dramatically improved. Also, when comparing Example 1 and Comparative Example 1, Comparative Example 1, which is a single layer with a high ratio of EV, has a fair anti-fog property, but
While there were some difficulties in properties related to mechanical packaging, such as fusing seal strength, multilayering improved the tensile modulus, which indicates the stiffness of the film, and the fusing seal temperature. Next, when comparing Example 2 and Comparative Example 2, the single-layer Comparative Example 2 was a relatively well-balanced film, but the characteristics of film forming stability, repeated fogging resistance, and tensile modulus were sufficient. On the other hand, the multilayer film Example 2 was an extremely excellent film with excellent film formation stability, high antifogging performance, firmness, and good fusing seal strength and temperature. be.

In this way, a film with high performance can now be obtained by using a resin composition for the surface layer, which had disadvantages and could not be used in a single layer, and by creating a multilayer structure.

Examples 4 to 6/Comparative Example 5 Using the same method as in Example 1, films with the configurations shown in Table 3 were obtained. Table 3 also lists the results of evaluating the physical properties and mechanical packaging suitability of these films and Example 2. Mechanical packaging tests and evaluations for evaluating the usefulness of the multilayer film of the present invention were conducted in the following manner.

(Evaluation of usefulness) Using a pillow shrink packaging machine (FP-280 model: Ibaraki Seiki Group), a packaging test was conducted using two cucumbers as contents and a packaging speed of 30 pieces/min. This packaging machine forms the film into a cylindrical shape, inserts the contents into the cylinder, fuses and seals the front and back, performs a rough packaging, and then shrinks the film with hot air to complete the tight packaging. It is a method. Packaging suitability was evaluated based on the following criteria.

(1) Running stability (Since poor running appears as a variation in the spacing between the fusing seals, this was used as the evaluation criterion.) 0: The spacing between the fusing seals is constant and stable. O: The spacing between the fusing seals is slightly uneven. △: Large variation in the interval between fusing seals ×: Film tearing occurs during packaging (2) Slip property 0: Film slides well with the machine and contents O: Film gets caught in the machine and makes abnormal noise △: The film gets caught in the machine and the packaging loss is 5% or more ×: The loss is 10% or more (3) Seal bank (seal opens when heated with hot air) 0: Seal bank occurs ○: Seal opening is less than 1% when heated with hot air Δ: Seal opening is 1% or more and less than 3% when heated with hot air Items that can be packaged tightly without wrinkles ○: Items with slightly sagging packaging that rarely occur: Items with slightly wrinkled packaging ×: Items with packaging full of wrinkles As is clear from Table 3, books The multilayer films of the invention, Examples 2 and 4 to 6, have excellent film forming stability, that is, high productivity (with little variation in film thickness, excellent transparency and antifogging properties, and It has a high display effect.It also has excellent properties such as melt-cut sealability and tensile modulus, which are important in mechanical packaging.As a result of actual packaging tests, the film has a firmness and is suitable for use as a slip agent. The effective nonionic surfactant bleeds out appropriately, has good running stability and slipperiness, and fuse-cut sealing is strong and stable, achieving tight packaging without wrinkles. On the other hand, the single-layer film of Comparative Example 5 is inferior to the above-mentioned properties, and as a result of packaging tests, stable packaging cannot be performed due to lack of film stiffness, etc., and there are large variations in fusing seal and shrinkage. , it was a film with low practicality).

(Margins below) 3-Table Figure 1 [Effects of the Invention] The multilayer film of the present invention allows the composition of the surface layer to be selected from a wide range depending on the purpose of use and to obtain excellent properties. Due to the synergistic effect of the film and the inner layer, it has excellent transparency, additive bleedability, and film strength, and has a high degree of suitability for mechanical packaging, as well as providing beautifully finished packages.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the film's raw resin ratio and initial Ω-proofing properties, Figure 2 is a graph showing the relationship between the film's raw resin ratio and fusing seal strength, and Figure 3 is a graph showing the relationship between the film's raw resin ratio and fusing seal strength. It is a graph showing the relationship between the ratio and the post-shrinkage haze.

Claims (1)

[Claims] (1) Mixture of 80 to 35 wt% of ethylene α-olefin copolymer having a density of 0.900 to 0.925 g/cm^3 and 20 to 65 wt% of ethylene vinyl acetate copolymer having a vinyl acetate content of 5 to 20 wt% A multilayer film having two surface layers made of a mixture of 0.2 to 5 wt% of a nonionic surfactant based on a copolymer, and an inner layer made of a resin mainly made of high-pressure radical low-density polyethylene.