JP4943753B2 - Stretch film and manufacturing method thereof - Google Patents

Description

The present invention relates to a stretch film and a method for producing the same.

Stretch films for prepacks are known in which foods such as fruits and vegetables, fresh fish, meat, and side dishes are placed directly on trays or placed on lightweight plastic trays such as polystyrene paper (PSP) to overlap the films. This stretch film for prepack is used for the operation of packaging food by an automatic packaging machine or manually (see Patent Documents 1 to 5, etc.).

In food packaging using an automatic packaging machine, there is a method called super stretch, in which the film is stretched 1.5 to several times before packaging, the food is wrapped in a stretch film, and the edges of the film are automatically weaved and packaged. Widely used.

Stretch films for prepacks are required to have high adhesion to a conveyor belt when stretched in an automatic packaging machine, do not whiten during stretching, and do not recover instantaneously when woven.

As a stretch film for prepack, it is a copolymer of a vinyl aromatic compound and a conjugated diene or a hydrogenated derivative thereof, and has at least one layer containing a resin having a glass transition temperature of −20 ° C. or higher. A film having a storage elastic modulus (E ′) measured at a frequency of 10 Hz and a temperature of 20 ° C. by a viscoelasticity measurement of 5 × 10 ^{8 to} 5 × 10 ⁹ dyn / cm ² and a loss tangent (tan δ) in the range of 0.2 to 0.8. It is known (see Patent Document 1).

In cold districts, the workplace temperature is 5 to 15 ° C. At such low temperatures, the film is not flexible enough to cause defects such as wrinkles during packaging, tearing during packaging, and whitening. was there.

JP 09-165492 A JP 10-119205 A Japanese Patent Laid-Open No. 08-003384 Japanese Patent Application Laid-Open No. 08-224842

A stretch film and a method for producing the same are provided.

The present invention comprises an intermediate layer comprising a resin composition containing a petroleum resin, a propylene-based resin, and an ethylene-vinyl acetate copolymer, wherein the amount of petroleum resin added is 6 to 40% by mass, and an ethylene-vinyl acetate copolymer. It is the stretch film formed by laminating | stacking the surface layer containing coalescence, and its manufacturing method.

The stretch film of the present invention has sufficient flexibility even at a low temperature, and has the effect that wrinkles, tears, and defects due to whitening are less likely to occur during packaging.

The present invention includes a petroleum resin, a propylene-based resin, and an ethylene-vinyl acetate copolymer, an intermediate layer comprising a resin composition in which the amount of petroleum resin added is 6 to 40% by mass, and an ethylene-vinyl acetate copolymer It is a stretch film formed by laminating a surface layer containing, and a production method thereof.

<Petroleum resin>
Petroleum resins, for example, C ₅ system (aliphatic), C ₉ type (aromatic), cyclopentadiene, terpenes, terpene derivatives, rosin and rosin derivatives, and hydrogenated products of these resins can be used. Petroleum resins can be used as mixtures or copolymers. Hydrogenated petroleum resins are preferred because they have good compatibility with propylene resins and ethylene-vinyl acetate copolymers and can increase the transparency of the film.

The amount of petroleum resin used in the resin composition constituting the intermediate layer is 6 to 40% by mass. If the amount of petroleum resin used in the intermediate layer is small, the film may instantly recover when folded using the super stretch method, resulting in poor folding. If used excessively, the film will become hard and used in cold regions. In some cases, whitening may occur easily during stretching.

<Propylene-based resin>
Examples of the propylene resin include polypropylene homopolymers, ethylene-propylene copolymers, propylene-butene copolymers, copolymers such as ethylene-propylene-butene, propylene-α olefin copolymers, and propylene-based resins thereof. A mixture of resins can be used. In these propylene resins, propylene-α olefin copolymers are preferably used.

<Ethylene-vinyl acetate copolymer (EVA)>
The ratio of ethylene and vinyl acetate in the ethylene-vinyl acetate copolymer is not particularly limited, but the vinyl acetate unit content is preferably 5 to 25% by mass, and more preferably 10 to 20% by mass. When the vinyl acetate unit content is 5 to 25% by mass, the melt flow ratio (MFR) is 0.2 to 2 g / 10 min (190 ° C, 2.16 kg load), and it has excellent strength and flexibility in cold regions, and can be processed into a film. An easy stretch film can be obtained.

The ethylene-vinyl acetate copolymer has an effect of imparting adhesion to the conveyor belt. The content of vinyl acetate in the component is 5 to 25% by mass, preferably 10 to 20% by mass, and the melt flow ratio (MFR) is 0.2 to 2 g / 10 min (190 ° C., 2.16 kg load). It is suitable in terms of film forming processability.

It is desirable from the viewpoint of production efficiency that the ethylene-vinyl acetate copolymer used for the intermediate layer and the surface layer has the same monomer composition.

The two surface layers laminated on the front and back of the intermediate layer are preferably the same. However, if the two surface layers both contain an ethylene-vinyl acetate copolymer, the two layers are not necessarily the same. Additives and the like may be different.

Various additives such as antioxidants, fillers, antifogging agents, antistatic agents, nucleating agents, flame retardants and the like may be used for the intermediate layer and the surface layer.

The stretch film preferably has a peak temperature of a temperature dependence curve of loss tangent in a range of −10 ° C. to 15 ° C. by a dynamic viscoelastic device. The temperature degree dependence curve of the loss tangent is measured at a frequency of 10 Hz by a dynamic viscoelastic device.

If the peak temperature of the temperature dependence curve of the loss tangent is low, plastic deformation is likely to occur at work temperatures (5 to 15 ° C) in cold regions, and when the film is folded by the super stretch method, the film instantly recovers and folds Defects may occur. If the peak temperature of the loss tangent is high, the stretch film may become hard and difficult to stretch at the work place temperature in a cold region, or may be easily whitened during stretching.

The value at the peak of loss tangent measured at a frequency of 10 Hz by dynamic viscoelasticity measurement is preferably 0.2 or more. If the loss tangent peak value is 0.2 or less, the film's restoring behavior is instantaneous, so when used in super stretch packaging, the film will be restored in a short time before folding into the bottom of the tray, causing poor folding. In some cases, the stretch film on the back side of the tray may become wrinkled without overlapping, and the sealing performance may be reduced.

(Example 1)
Using an inflation extruder consisting of three extruders: a 55mm single-screw extruder for the surface layer and a 100mm single-screw extruder for the intermediate layer, with a set temperature of 180-195 ° C and a winding speed of 70m / min, ethylene -97% by weight of vinyl acetate copolymer and 3% by weight of antifogging agent are used as the front and back layers, 8% by weight of petroleum resin, 63% by weight of propylene resin, 26% by weight of ethylene-vinyl acetate copolymer and antifogging agent A stretch film having a layer composition ratio of 1: 2: 1 with 3% by mass as an intermediate layer was obtained.

(Materials used)
Ethylene-vinyl acetate copolymer: vinyl acetate monomer unit content 20% by mass, commercially available product.
Petroleum resin: cyclopentadiene, commercially available.
Propylene resin: ethylene-propylene-butene copolymer, commercially available product.

(Example 2-4)
According to the recipe shown in Table 1, a stretch film was obtained in the same manner as in Example 1 except for the points shown in Table 1.

(Comparative Example 1-3)
The raw material composition was changed. Except for the points shown in Table 2, it was the same as Example 1.
(Comparative Example 4)
The surface layer was the same as Example 1 except that the ethylene-acrylic acid copolymer was 97% by mass and the antifogging agent was 3% by mass.

(Evaluation)
The properties and performance of the film and the state during film formation were measured by the following methods to evaluate the stretch film.
1) Loss tangent in dynamic viscoelasticity measurement Using a viscoelasticity analyzer RSA-II manufactured by Rheometrics, at a vibration frequency of 10 Hz, at a temperature of −30 to 50 ° C., at a rate of temperature increase of 1 ° C./min, The temperature dependence of loss tangent was measured based on JIS K6253 standard.
2) Stretch packaging suitability
Using a stretch film with a width of 360 mm, a PSP tray (length 282 mm, width 212 mm, height 30 mm) was wrapped with an automatic packaging machine (AW-4600 manufactured by Teraoka Seiko Co., Ltd.), and the items shown in Table 3 were evaluated. .

The stretch film of the present invention has sufficient flexibility even at a low temperature, and has the effect that wrinkles and tears during packaging and the occurrence of defects due to whitening are less likely to occur. Therefore, the stretch film is suitably used for super stretch packaging in cold regions.

Claims (3)

An intermediate layer comprising a resin composition containing a petroleum resin, an ethylene-propylene-butene copolymer, and an ethylene-vinyl acetate copolymer, wherein the addition amount of each resin component is the following (1) to (3): , ethylene - Ri Na by laminating a surface layer containing a vinyl acetate copolymer, a peak with respect to the temperature dependency of the loss tangent measured by dynamic viscoelasticity measurement by JIS K6253 method (tan [delta) is in the -10 ° C. to 15 ° C. A stretch film that exists and has a loss tangent value at the peak of 0.2 or more .
(1) Petroleum resin: 8-35% by mass
(2) Ethylene-propylene-butene copolymer: 36 to 63% by mass
(3) Ethylene-vinyl acetate copolymer: 15 to 35% by mass The stretch film according to claim 1, wherein the ethylene-vinyl acetate copolymer used for the intermediate layer and the surface layer has the same monomer composition. The manufacturing method of the stretch film of Claim 1 or Claim 2 which used the inflation extrusion method.