JPH0785922B2 - Easy tear film and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an easily tearable film that is easily torn and a method for producing the same, and can be used as a seal base film for packaging bags for foods, medicines and the like. it can.

BACKGROUND ART In recent years, a linear low-density polyethylene (L-LDPE) film has been widely used as a sealing base material (sealant) film for laminating packaging bags for foods, medicines and the like. This L-
Since the LDPE film is excellent in mechanical strength, sealing strength and sealing performance, the package contents are sufficiently protected.

The following is used as this L-LDPE film. For example, including 1-butene as a conomer
C4-based L-LDPE film, monomers other than 1-butene (eg, 4-methyl-1-pentene having 6 carbon atoms, 8 carbon atoms)
1-octene) as a conomer, C6 series, C8 series L-
LDPE film and the like.

On the other hand, in recent packaging bags, in addition to the above sealing strength,
There is a demand for easy tearing so that it can be easily opened by hand without using an opening means such as scissors or a kitchen knife. Conventionally, in order to impart this easily tearable property to the packaging bag, it has been practiced to form a notch such as a V-cut in the opening portion of the bag.

[Problems to be Solved by the Invention] According to the above-mentioned conventional sealing substrate film, since the film is generally liable to be stretched, when the packaging bag using the film is opened, even if there is preparation, it is torn and opened by hand. It was difficult to do, and I had to use scissors or a kitchen knife.

In particular, the C6 and C8 L-LDPE films have a problem of extremely poor tearability. Even if the draft ratio during film formation is increased, good tearability cannot be obtained. Even if the film is uniaxially stretched, satisfactory tearability is not obtained.

When the C4 type L-LDPE film is used, the tearability is considerably improved, but there is a drawback that the cut line is not linear. When the draft ratio at the time of film formation is increased, the tearability is improved, but the good linear cut property is still not obtained. Further, even if the film is uniaxially stretched, similar improvement in tearability can be obtained, but good linear cutability cannot be obtained.

The present invention is easy to tear, has a linear cutability,
Moreover, it is an object of the present invention to provide an easily tearable film having excellent heat sealability in a wide temperature range.

[Means and Actions for Solving the Problem] The easily tearable film according to the present invention has a linear low-density polyethylene (L-LDPE) having a 1-butene content of 1 to 10 mol%.
A base layer composed of 98 to 70% by weight and 2 to 30% by weight of a propylene-α-olefin random copolymer (random PP), and a content of one or two or more α-olefins having 6 or 8 carbon atoms. A film in which a seal layer made of 1 to 10 mol% L-LDPE is laminated, and the infrared dichroic ratio D _{720 cm} ^-1 (A⊥ / A) of the film is 1.07 or more. And Where A⊥ is the absorbance when the film pulling direction or stretching direction is perpendicular to the infrared deflection direction, A
Is the absorbance when the film drawing direction or stretching direction is parallel to the infrared deflection direction.

When the proportion of 1-butene contained in L-LDPE constituting the base layer is less than 1 mol%, it becomes close to that of HDPE (high density polyethylene), and the sealing performance and film physical properties of L-LDPE are impaired. On the other hand, if it exceeds 10 mol%, the crystallinity becomes too low to be practically usable as a film.

If the proportion of random PP in the base layer is less than 2% by weight, the linear cut property is deteriorated,
When it is larger, the physical properties of the film are deteriorated. Preferably, the proportion of random PP is 5 to 20% by weight. Examples of the α-olefin constituting the random PP include ethylene, propylene, 1-butene and the like.

The L-LDPE containing 1-butene has a melt index (MI) of 0.1 to 30 g / 10 minutes, preferably 1 to 10 g / 10 minutes. If the MI is less than 0.1 g / 10 minutes, the melt viscosity will be high and extrusion will be difficult. If the MI is more than 30 g / 10 minutes, the physical properties of the film will deteriorate. The density is 0.900 to 0.950.
g / cm ³ If it is less than 0.900 g / cm ³ , the crystallinity is low, so the effect of uniaxial stretching cannot be obtained, and if it is more than 0.950 g / cm ³ , the properties as L-LDPE cannot be obtained.

Examples of the α-olefin having 6 or 8 carbon atoms forming the seal layer include 4-methyl-1-pentene, 1-hexene, and 1-octene.

Infrared two-color ratio D _720cm ^-1 as an index of molecular orientation in the film
(A⊥ / A) is measured, and the easily tearable film according to the present invention is limited to those having this value of 1.07 or more. When the infrared dichroic ratio is less than 1.07, good easy tearability cannot be obtained.

If the base layer is L-LDPE containing an α-olefin having 6 or 8 carbon atoms, the tearability will be poor. On the contrary, when the sealing layer is made of C4 type L-LDPE alone, the heat sealing strength becomes low and the physical properties of the film become poor. In addition, this seal layer is C4 series, C6 series, C8 series.
When the mixture of the system and random PP is used, the physical properties of the film become poor.

In this easily tearable film, the thickness ratio of the base layer and the seal layer is preferably 1: 1 to 10: 1.
When [the thickness of the base layer / the thickness of the seal layer] is less than 1, the tearability is poor, and when it is more than 10, the sealing temperature range is narrow.

The method for producing the easily tearable film in the present invention is 1-
Butene content 1-10 mol% L-LDPE 98-70 wt%
And propylene-α-olefin random copolymer 2 to
After coextruding a mixed resin consisting of 30% by weight and L-LDPE containing 1 to 10 mol% of one or more α-olefins having 6 or 8 carbon atoms from a T die, uniaxially It is characterized by stretching.

As the T die for coextrusion molding, for example, a multi-manifold type or a feed block type can be used.

The uniaxial stretching can be performed by longitudinal uniaxial stretching using a hot roll method.

The conditions for this uniaxial stretching are as follows, for example.

The heating and stretching temperatures are 70 ° C to 110 ° C, preferably around 90 ° C. If the temperature is lower than 70 ° C, heating is insufficient and uniform stretching becomes difficult. On the other hand, if the temperature exceeds 110 ° C, the film sticks to the roll and stretching becomes impossible.

The preheating temperature is 50 ° C to 110 ° C, preferably around 80 ° C. Five
If the temperature is lower than 0 ° C, heating becomes insufficient and uniform stretching becomes difficult. On the other hand, if the temperature exceeds 110 ° C, the film sticks to the roll and stretching becomes impossible.

The annealing temperature is 70 ° C to 110 ° C, preferably around 90 ° C. Below 70 ° C, the dimensional stability of the film is poor. Also,
If it exceeds 110 ° C, the crystal orientation is relaxed and the linear cut property deteriorates.

The draw ratio is 1.1 or more, preferably 1.3 or more.

[Examples] Examples 1 to 10 A resin to be a base layer and a resin to be a seal layer were made into a molten resin at 240 ° C in an extruder, and this molten resin was coextruded from a multi-manifold type T die to form a base layer. And a sealing layer were laminated to form a film. Subsequently, the film was cooled by contacting it with a chill roll at 40 ° C. Table 1 below shows the resin used as the base layer and the resin used as the seal layer, and the thickness ratio of the base layer and the seal layer used in each example.

C4 system L-LDPE, C6 used in each example and the following comparative examples
Specific examples of the system L-LDPE, the C8 system L-LDPE, and the random PP are as follows.

C4 L-LDPE: Idemitsu Polyethylene-L, 1014T (trade name) ... 1-butene content 5.5 mol%, MI 10 g / 10 min, density
0.910 C4 type L-LDPE: Idemitsu Polyethylene-L, 0464R (trade name) ... 1-butene content 1.5 mol%, MI 4.5 g / 10 minutes, density
0.935 C4 L-LDPE: Idemitsu Polyethylene-L, 0684R (trade name) ... 1-butene content 0.5 mol%, MI 7.0 g / 10 min, density
0.943 C6 series L-LDPE: Mitsui Petrochemical Ultzex, 1020L (trade name) ... 4-methyl-1-pentene content 4.8 mol%, MI
2.1 g / 10 minutes, density 0.910 C6 series L-LDPE: Mitsui Petrochemical Ultzex, 2020L (trade name) ... 4-methyl-1-pentene content 4.8 mol%, MI
2.1 g / 10 minutes, density 0.920 C6 system L-LDPE: Mitsui Petrochemical Ultzex, 3520L (trade name) ... 4-Methyl-1-pentene content 1.2 mol%, MI
2.1g / 10min, Density 0.935 C8 series L-LDPE: Idemitsu Moretec, 1018CN (trade name) ...
1-octene content 5.6 mol%, MI 8.0 g / 10 min, density 0.91
0 C8 series L-LDPE: Idemitsu Moretec, 0438CN (trade name) ...
1-octene content 4.5 mol%, MI 4.0 g / 10 min, density 0.91
6 C8 series L-LDPE: Idemitsu Moretec, 0258CN (trade name) ...
1-octene content 2.0 mol%, MI 2.1 g / 10 minutes, density 0.93
1 Random PP: Idemitsu Polypro, F-730N (trade name) ... Ethylene content 3.0 mol%, MI 7.0g / 10min, density 0.900 Was used for uniaxial stretching to produce the easily tearable film of each example. The conditions during this stretching are as follows.

Preheating roll temperature …… 80 ℃ Heating roll temperature …… 90 ℃ Drawing roll temperature …… 90 ℃ Annealing roll temperature …… 90 ℃ Inlet line speed …… 10m / min Exit line speed …… 11 ～ 20m / min Stretching ratio …… 1.1 to 2.0 Regarding the easily tearable film produced in each example, infrared ray 2
Table 1 below shows the results obtained by measuring and evaluating the color ratio, the tear strength in the stretching direction, the linearity of the tear portion, the seal temperature, and the seal strength.

As for the infrared dichroic ratio, the infrared dichroic ratio at 720 cm ^-1 was measured using a FTIR-7000 model manufactured by JASCO Corporation.

The tear strength in the stretching direction of the film was measured by measuring the elemental tear strength (kg / cm) according to JIS-Z1702.

The linearity of the tear portion is an evaluation of the state after tearing. In the column of linearity of tearing part in the table, ○ is good (there is no waviness in the tearing part, the tearing direction is linear),
Δ indicates a little good (there is some waviness in the tearing part and the tearing direction is slightly inclined), and x is poor (the waviness in the tearing part is large and tearing occurs in the oblique direction).

The sealing temperature of the biaxially stretched nylon film and the film of each example was dry-laminated with an adhesive and heat-sealed at ² kg / cm ² for 1 second, and the tensile strength reached 300 g / 15 mm width. The heat seal temperature at that time was measured. The biaxially stretched nylon film used at this time was Idemitsu Unilon G-100.
(Product name). As the adhesive, a two-component adhesive [AD-308A, AD-308B (trade name)] manufactured by Toyo Morton Co., Ltd. was used.

The seal strength is a value obtained by measuring the tensile strength (kg / 15 mm width) of the dry laminated film heat-sealed with a seal bar under the conditions of 160 ° C., 2 kg / cm ² , and 1 second.

Comparative Examples 1 to 11 A base layer and a seal layer were laminated and formed in the same manner as in the above-mentioned examples, and uniaxially stretched films according to Comparative Examples were produced. Properties such as tear strength in the stretching direction were measured and evaluated. The results are also shown in Table 1 below.

From Table-1, the easily tearable films according to Examples 1 to 10 are C4.
A film in which a base layer composed of a system L-LDPE and a random PP having a content of 5 to 20% by weight and a seal layer composed of a C6 system L-LDPE or a C8 system L-LDPE are laminated and having an infrared dichroic ratio. Is 1.97 to 2.01, it can be seen that good results are obtained for all characteristics. That is, as for the tear strength in the stretching direction, a low value of 4.2 to 6.1 kg / cm is obtained, and it is possible to easily tear in one direction. Regarding the linearity of the tear portion, in all cases, there was no waviness and it was linear, which was good. About seal temperature, 300g / 15m
Heat seal temperature of 97 to obtain tensile strength of m width is 97
It is ~ 104 ° C, and a film excellent in heat sealability can be obtained in a wide temperature range. For seal strength, see 4.1-
Good results of 5.3kg / 15mm width were obtained. Therefore, the films according to the above examples are excellent in tearability, so when the packaging bag is manufactured as the base film for lamination, tearing and opening of the bag by hand is easy, and the tearing line is linear. And looks good. Moreover, since the heat-sealing property is excellent in a wide temperature range, the function of protecting the package contents is good.

On the other hand, according to Comparative Examples 1 and 2, the base layer and the seal layer have the same structure as that of the present invention, but the stretch ratio is 1.
It is 0, which indicates that the infrared dichroic ratio is 1.04, which is lower than 1.07 defined in the present invention, and therefore the tear strength in the stretching direction and the linearity of the tear portion are poor. That is,
Since the tear strength in the stretching direction is high, it cannot be easily torn by hand, and the tear portion is largely wavy, and tears also occur in the oblique direction. Further, according to Comparative Examples 3 to 6, since the content of the random PP in the base layer is out of the range of 2 to 30% by weight according to the present invention, at least one of the tear strength and the seal strength in the stretching direction. It turns out that one is bad. According to Comparative Examples 7 to 10, since the base resin of the base layer uses C6 series and C8 series L-LDPE other than the C4 series according to the present invention, the tear strength in the stretching direction and the linearity of the tear part are It can be seen that all are defective. According to Comparative Example 11, the resin of the seal layer is the C6 type or C8 type L-LD according to the present invention.
Since it is not PE, it can be seen that the tear strength and seal strength in the stretching direction are inferior.

EFFECTS OF THE INVENTION According to the present invention, an easily tearable film that can be easily torn in a straight line and has excellent heat-sealing property in a wide temperature range is obtained.

Claims (3)

[Claims] 1. A linear low-density polyethylene having a 1-butene content of 1 to 10 mol%, 98 to 70% by weight, and propylene-α.
-A base layer comprising 2 to 30% by weight of an olefin random copolymer, and a linear low density polyethylene containing 1 to 10 mol% of one or more α-olefins having 6 or 8 carbon atoms A film in which a sealing layer is formed, and the infrared dichroic ratio D _720cm ^-1 (A⊥ / A) of this film is 1.07.
The easily tearable film as described above (where A⊥ is the absorbance when the film drawing direction or stretching direction and the infrared deflection direction are perpendicular to each other, and A is the film drawing direction or stretching direction and the infrared deflection direction). It is the absorbance when the direction is parallel to). 2. The easily tearable film according to claim 1, wherein the thickness ratio of the base layer to the seal layer is 1: 1 to 10: 1.
Easy tear film. 3. A linear low density polyethylene having a 1-butene content of 1 to 10 mol%, 98 to 70% by weight, and propylene-α.
A mixed resin composed of 2 to 30% by weight of an olefin random copolymer, and a linear low-density polyethylene containing 1 to 10 mol% of one or more α-olefins having 6 or 8 carbon atoms. Is coextruded from a T-die, and then uniaxially stretched, which is a method for producing an easily tearable film.