JPS6040229A - Low temperature heat shrinkable film - Google Patents

Abstract

PURPOSE:To provide the titled film with a large shrinkage stress and excellent in the transparency by empolying a linear low-density polyethylene resin (LLDPE) with a specified density. CONSTITUTION:This is a LLDPE film which is less than 5% in the haze value, more than 30% in the M-direction heat shrinkage stress (90 deg.C), less than 5% in the T-direction heat shrinkage (90 deg.C) and more than 300g/mm.<2> in the M-direction shrinkage stress (90 deg.C). Said low temperature heat shrinking film is produced as follows: LLDPE with the density of below 0.935g/cm<2> is made to be a thick film with a better transparency by the 2-stage air-cooling (or water cooling) inflation or chill roll method and then, uniaxially stretched at a high factor (about 3-6) in the M-direction at about 90 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-temperature heat-shrinkable film, and in particular, it has high heat-shrinkability at low temperatures, high shrinkage stress (and excellent transparency compared to conventional shrink films). The present invention relates to a low-temperature heat-shrinkable film with outstanding features.

Conventional heat-shrinkable films usually start shrinking at around 100°C and exhibit a large shrinkage rate of 50 to 70% at around 130°C. However, in general, high-pressure low-density polyethylene (r, DPE) resin is used as a film raw material, and the melting point of this resin is 1[)0 to 110°C, so the above-mentioned 130°C It is impossible to obtain a large shrinkage stress at around shrinkage temperatures, and even if shrink wrapping is performed, there is a drawback that the tension is insufficient.

In addition, as a low-temperature heat-shrinkable film, the above-mentioned high-pressure method LD
Attempts have also been made to slightly stretch PR at a low magnification to provide low Ti1A shrinkage. but.

General high-pressure LDPE has many long chain branches and therefore has extremely poor stretchability, resulting in stretching breakage in one shot, making it difficult to stretch the film sufficiently to make it uniform. In addition, this film has transparency, which is a very important element as a packaging film because high-pressure LDPK is stretched non-uniformly at a low magnification (2 to 2.5 times). Haze on 11 (
The haze value (haze) was also unfavorable at around 10%.

- The present invention was completed as a result of YTR+ research in order to improve the above-mentioned drawbacks. 1 To illustrate the outline of the present invention, 1 In the present invention, the low density polyethylene resin used as a raw material is Density 0.9 that can be stretched uniformly up to high magnification (3 to 6 times) in place of high-pressure polyethylene
3511/Sono Linear polyethylene resin (hereinafter referred to as LLDPE) having short chain branches of 3 or less is used, and the film is formed using the conventional air-cooling inflation method. J: '), 2-stage air-cooled inflation method, water-cooling inflation method, chill-roll method, etc. The same LLDPE is sufficiently cooled to produce a thick film with good transparency, and the film is heated at around 90°C with a Sekiba skewer ( 3
By uniformly stretching the film in the M direction (up to 6 times), a film with extremely excellent transparency (Haze value of 5% or less) was obtained.

In addition, the heat shrinkage rate of the same film is 60% in the M direction at 90°C.
The shrinkage stress in the T direction is 5% or less and the shrinkage stress in the M direction at 90°C is so o g7#I! A low-temperature heat-shrinkable film having two or more excellent features was obtained.

To illustrate the LLDPE used in the present invention.

Ethylene and a-olefins having 3 to 12 carbon atoms, such as propylene, butene-1, hexene-1゜4-methyl-1-
A small amount of pentene, octene-1, decene-1, etc. is produced by a conventionally known medium-low pressure method or high-pressure method in the presence of a Ziegler type catalyst.Furthermore,
The medium and low pressure method may be any method such as a gas phase method, a slurry method, or a solution method.

The LLDPI used in the present invention is made by blending the polyethylene resin with ethylene-vinyl acetate copolymer, butene-based rubber, high-pressure low-density polyethylene having long chain branches, etc., preferably at 40 wt% or less. Blends are also included.

In the above-mentioned LLDPE, if the density exceeds 0.93511/3, sufficient low-temperature heat shrinkability cannot be obtained, which is not preferable.

The melt index (MI) of LLDPE is not particularly limited, but it is appropriate that it is Oj ~ 81 / 10 min, preferably 0.5 ~ 5 jl / 10 min, and if it is less than 0.31710 min, it will not be a good quality film due to melt fracture etc. was not obtained, and 8.9710
If it exceeds min, the strength of the obtained film decreases, which is not preferable for this purpose. There is no particular restriction on the molecular weight distribution, but it is preferable to use one with a narrow molecular weight distribution in order to improve the quality, especially the transparency, of the obtained film.
Mw: weight average molecular weight measured by GPO, Mn: GPC
It is preferable that the measured number average molecular weight is 3.0 to 5.0.

As mentioned above, by use of the LLDPH of the present invention.

The stretching ratio of the film can be made as high as 6.0 to 6.0 times, and a uniform film without uneven thickness can be obtained by uniform stretching.

Since the stretching ratio can be made as high as 3 times or more, a film with sharply improved transparency was obtained beyond this point. At this time, if the stretching ratio is less than 3.0 times, stretching unevenness becomes thick (thickness unevenness, etc.) becomes a problem.

In addition, the transparency is poor, and if the stretching ratio exceeds 6.0 times, stretch breakage tends to occur, making stable production difficult and making it difficult to obtain a film having the desired film properties of the present invention.

In the film forming method, it is possible to use the conventional air-cooling inflation method, which involves blowing air around the circumference of an extruded tube and then allowing it to cool naturally to create a blank tube-shaped film, but there is no method that can provide sufficient cooling. By employing methods such as the water-cooled inflation method, which is commonly used as a well-known rapid cooling method, in which the tube is cooled by bringing it into direct contact with water, and the Yoruchiru O-/I/ method for cooling rolls (chill rolls), it is possible to achieve even greater transparency. An improved film can be obtained.

The stretching temperature for producing the low-temperature heat-shrinkable film of the present invention is not particularly limited, but is around 90'C.

Preferably, it exhibits excellent low-temperature heat shrinkage properties at 80 to 100°C.

Conventionally, films with outstanding transparency and excellent low-temperature shrinkability were not polyethylene resins, but polyvinyl chloride (PVL), stretched polypropylene (PP), and the like were used in this field.

However, the film of the present invention retains the excellent properties of polyethylene (low-temperature heat-sealability, flexibility, food integrity, etc.), has excellent transparency comparable to PVC or stretched PP film, and has excellent thermal properties. It is a film with shrinkage properties.

The present invention will be explained below with reference to Examples and Comparative Examples.

The physical properties of the film were measured as follows.

*1) Haze (%); ASTM D-1005*
2) Heat shrinkage rate (%); JIS Z1709 (90″C
, 100°C] Shrinkage stress (9/v + tail 2): Using a Tensilon (equipped with an elevating and lowering vortex tank), record the shrinkage tension while raising the temperature at 3°C/min.

Test Saito film 50 m/m wide, chuck distance 100 m/m (rectangular shape) Installation Install a strip-shaped film (50 m/m width) set at a chuck distance of 100 m/m on a Tensilon with zero tension. set.

Ambient temperature at 6℃/min from room temperature Increase the temperature and calculate the contraction tension generated at each temperature. Shrinkage divided by original film cross-sectional area Expressed as stress.

Example 1 A linear low-density polyethylene resin having short chain branches with a density of 0.91711/tooth 3 was used, and the resin was sufficiently cooled by an air cooling inflation method to obtain a film with good transparency. was stretched in the M direction at a stretching ratio of 6.5 times and a stretching degree of 90°C to form a stretched film (thickness 40μ).
I got it.

Table 1 shows the results of measuring the physical properties of the stretched film.

Examples 2 to 6 Stretched films were obtained in the same manner as in Example 1 except that the resins shown in Table 1 were used. The results are shown in Table 1.

((i L , Example 6 was carried out by the water-cooled inflation method.

11/Example 1 A stretched film (thickness = -4
0 μ) was obtained. However, the stretching ratio was set to 6.0 as in Example 1.
When the stretching was carried out at 5 times, stretching breakage occurred, so the stretching ratio was kept at 2.2 times.

, ¥l+j is shown in Table 1.

Comparative Example 2 Stretching was carried out (same as Comparative Example 1 except that it was different).
I got frum. The results are shown in Table 1.

Comparative Example 6 ':'River! :II-1,65j9 /(yn' pvc
A stretched film was obtained in the same manner as for comparison (+u1) except that 1':1!

Comparative Example 4 A film (i) was prepared in the same manner as Comparative Example 6 except that no stretching was performed. The results are shown in Table 1.

Comparative Example 5 A stretched film was obtained in the same manner as Comparative Example 1 except that pp having a density of 0.900 was used. The results are shown in Table 1.

Claims (1)

[Claims] A linear polyethylene resin with short chain branches with a density of 0.955117OR3 or less is used, and the film properties include a haze value of 5% or less and a heat shrinkage rate in the M direction at 90°C of 6.
A low-temperature heat-shrinkable film characterized by having a heat shrinkage rate of 0% or more, a heat shrinkage rate in the T direction of 5% or less, and a shrinkage stress in the M direction at 90° C. of 300'9/fat2 or more.