JPH0772239B2 - Twisted packaging film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a uniaxially stretched twist packaging film containing high density polyethylene as a main component. More specifically, it prevents breakage along the film orientation (stretching) direction (hereinafter referred to as vertical rupture) in horizontal twist packaging with the film orientation (stretching) direction as the twist axis, and at the same time has excellent horizontal twist retention and is transparent. Excellent in durability, rigidity and film forming (stretching), and bleeding (unsaturated fatty acid amide bleeds on the film surface,
The present invention relates to a twist packaging film having less bleeding property) and can be suitably used for candies, rice crackers and the like.

(Prior Art and Problems Thereof) In recent years, a uniaxially stretched high-density polyethylene film has been generally used in place of cellophane because a twist packaging film has excellent moisture resistance. However, since the uniaxially stretched high-density polyethylene film has a remarkably weak vertical tear strength, when used in a lateral twist package having a twisting axis in the film orientation (stretching) direction, which is called a lateral twist, a longitudinal break of the film occurs, which causes a lateral break. It can not be used for twist packaging, but it can only be used for vertical twist packaging with the twist axis in the direction perpendicular to the film,
There was a big limitation in use.

There are many reports as a film for twist packaging using high density polyethylene, for example, Japanese Patent Publication No. 52-794 has a density of 0.94 or more and a melt flow ratio (MI ₁₀ / MI
_2.16 ) discloses a method for producing a uniaxially stretched polyethylene film in which a high density polyethylene having 10 or less is used to form a film under specific conditions, and then an annealing treatment is performed, and JP-A-59-70521 discloses density. A high density polyethylene film with a melt flow ratio (MI ₁₀ / MI _2.16 ) of _7.5 to 15 and a surfactant of 0.05 to 2.0% by weight and uniaxially stretched 5 to 10 times is proposed. ing. However, these uniaxially stretched high density polyethylene films are not yet sufficient to improve the longitudinal tear strength to withstand transverse twist. Further, JP-A-60-233137 proposes a twist packaging film comprising 100 parts by weight of a specific high density polyethylene and 5 to 50 parts by weight of a linear low density polyethylene. Although the vertical tear strength of the film is improved due to the large mixing ratio with polyethylene, it is difficult to form a film and the retention of lateral twist is not yet sufficient.

The present inventors have earnestly studied in order to obtain a twist packaging film having lateral twisting suitability (preventing vertical breakage during horizontal twisting, and at the same time having excellent lateral twisting retention property), unlike the conventional vertical twisting. As a result, in order to obtain a twist-wrapping film having lateral twistability, it was found that a uniaxially stretched film is indispensable to have appropriate rigidity and elongation in the right angle direction. It has been found that a uniaxially stretched film using a composition containing a specific amount of a specific high-density polyethylene containing a specific amount and a specific amount of a specific linear ethylene-hexene-1 copolymer has excellent transverse twisting suitability. Was completed. As described above, the object of the present invention is to provide a film for twist packaging that can be used for vertical twist packaging, and that prevents vertical breakage even when used for horizontal twist packaging, and at the same time has horizontal twist holding property. That is.

(Means for Solving Problems) The present invention has the following configurations.

Unsaturated fatty acid amide having 18 to 22 carbon atoms 0.03 to 0.3% by weight
A high-density polyethylene having a melt index of 0.5 to 2 g / 10 minutes and a methyl branch number (X) of 0.5 ≦ X ≦ 4 per 1000 carbon atoms, and a linear ethylene-hexene having a melt index of 0.5 to 5 g / 10 minutes. -1 copolymer in the blending amount (Y)
Is 1 ≦ Y ≦ 4% by weight, and the product of X and Y is 0.5 ≦ XY ≦ 10
A twist packaging film using a composition formulated so that

The high-density polyethylene used in the present invention is a copolymer containing ethylene as a main component and a small amount of propylene, and is an ethylene-propylene copolymer obtained by copolymerizing propylene with ethylene at a partial pressure of 0.5 KgG / cm ² or less. It is a polymer and the number of methyl branches (X) (the number of methyl branches per 1000 carbon atoms is estimated by the absorbance at 1377 cm ^-1 by an infrared spectrophotometer)
Is 0.5 or more and 4 or less per 1000 carbons in the polymer, and the melt index (MI temperature 190 ℃, discharge amount of molten resin for 10 minutes under 2.16Kgf load) is 0.5 to 2g / 10.
Min, preferably 1.0-1.5 g / 10 min. The uniaxially stretched film obtained by using an ethylene-α-olefin copolymer, for example, an ethylene-butene copolymer, which contains a small amount of α-olefin other than propylene, has insufficient rigidity and poor lateral twist retention. Not preferable. When the number of methyl branches is less than 0.5, high-density polyethylene is used, and the resulting film has a weak vertical tear strength and vertical fracture occurs,
If the number of methyl branches exceeds 4, the rigidity of the obtained film is lowered too much and the lateral twist holding property is unfavorable. Moreover, when the high-density polyethylene having an MI of less than 0.5 g / 10 minutes is used, the stretchability of the obtained film is poor, and the MI is 2 g / 1.
The use of high-density polyethylene exceeding 0 minutes is not preferable because the transparency of the obtained film decreases.

The MI of the linear ethylene-hexene-1 copolymer used in the present invention is in the range of 0.5 to 5 g / 10 minutes, and the blending amount (Y) of the linear ethylene-hexene-1 copolymer is 1 ≦ Y ≦ 4% by weight, and the product XY of Y and the number of methyl branches X of high-density polyethylene is in the range of 0.5 ≦ XY ≦ 10, preferably 1 ≦ XY ≦ 5. In the present invention, it is important to use a linear ethylene-hexene-1 copolymer, and an ethylene-α-olefin copolymer containing a small amount of α-olefin other than hexene-1, such as butene-1. The film using the straight-chain ethylene-hexene-1 copolymer of (1) is unfavorable because the film has a weak vertical tearing strength and longitudinal breakage. The content of hexene-1 in the linear ethylene-hexene-1 copolymer used is not particularly limited, but generally 0.5 to 15% by weight is preferable. The MI of the linear ethylene-hexene-1 copolymer is 0.5 to 5 as described above.
It is in the range of g / 10 minutes, and when the MI is less than 0.5 g / 10 minutes, the compatibility with the high-density polyethylene is poor, so that stretch unevenness occurs during film formation and the stretchability deteriorates, and the MI is 5 g / 10 minutes. If it exceeds the range, uneven flow of the molten resin may occur and the transparency of the obtained film may be deteriorated, which is not preferable. The blending amount (Y) of the linear ethylene-hexene-1 copolymer is 1 ≦ Y ≦ 4% by weight as described above.
And the product XY of Y and the number of methyl branches X of high-density polyethylene must be in the range of 0.5≤XY≤10, preferably 1≤XY≤5. When Y is less than 1% by weight, the longitudinal tear strength of the obtained film is weak and vertical rupture occurs.
On the other hand, if the blending amount exceeds 4% by weight, the extrusion load and the resin pressure at the time of film formation will increase, making film formation difficult with ordinary equipment, and the printability and packaging processability of the obtained film. This is not preferable because it also causes a problem with the slip property. Even if Y is in the above range of 1 to 4% by weight, if XY is out of the above range, that is,
If XY is less than 0.5, the film vertical tear strength at the time of horizontal twist becomes weak and vertical breakage easily occurs, which is not preferable,
When XY exceeds 10, the rigidity of the obtained film decreases and the lateral twist holding property becomes poor, which is not preferable.

The unsaturated fatty acid amide contained in the high-density polyethylene used in the present invention has 18 to 22 carbon atoms (for example, oleic acid amide and erucic acid amide), and the high-density polyethylene and linear ethylene-hexene-1 It is a blend system of copolymers, and is essential to impart extrusion stability of the extruder and T-die, stretchability, and appropriate slip property to the film. The addition ratio of the unsaturated fatty acid amide is 0. with respect to the total amount of the unsaturated fatty acid amide and the high-density polyethylene.
It is from 03% by weight to 0.3% by weight. When the addition ratio of the unsaturated fatty acid amide is less than 0.03% by weight, the extrusion stability in the extruder and the resulting film lacks appropriate smoothness, and stretching unevenness occurs, resulting in poor stretchability, which is not preferable. On the other hand, if the proportion of unsaturated fatty acid amide added exceeds 0.3% by weight, bleeding on the surface of the obtained film will increase, resulting in poor transparency and lateral twisting retention. Further, in the case of unsaturated fatty acid amides having an unsaturated fatty acid amide having a carbon number other than 18 to 22, for example, undecylenic acid amide, the bleeding of the unsaturated fatty acid amide on the film surface increases, resulting in poor transparency and lateral twisting retention. It is not preferable. When a saturated fatty acid amide such as stearic acid amide or lauric acid amide is used, the amount of the saturated fatty acid amide that bleeds to the film surface increases, and transparency and horizontal twisting retention are impaired, which is not preferable.

The composition used for the twist packaging film of the present invention includes an antioxidant other than the above-mentioned unsaturated fatty acid amide, high-density polyethylene, and linear ethylene-hexene-1 copolymer,
An antiblocking agent, an antistatic agent, a nucleating agent, a colorant, or other polymer modifier may be added, and the use of the additive is particularly limited as long as the characteristics of the present invention are not impaired. Not a thing.

The method for producing the twist-wrapping film of the present invention is not particularly limited. For example, high-density polyethylene is mixed with predetermined amounts of unsaturated fatty acid amide and various antioxidants usually used in polyethylene, and the mixture is extruded. And so on 15
After melt-kneading at 0 to 280 ° C to form a granulated product, the granulated product and each predetermined amount of the linear ethylene-hexene-1 copolymer are mixed, and then an unstretched film is obtained by a known film forming method. The film forming method includes a T-die method, an inflation method and the like. Among them, the T-die method will be described. The film-like material extruded from the T-die at an extrusion temperature of 180 to 280 ° C. is heated to 60 to 120 ° C. The film is cooled and solidified to obtain an unstretched film (thickness 80 to 500 μm), and then this unstretched film is preheated with a preheating roll at a temperature of 80 to 120 ° C., a stretching speed of 30 to 120 m / min, and a stretching ratio of 4 to A method for obtaining a twist-wrapping film by uniaxially stretching at 10 times can be exemplified.

The twist-wrapping film of the present invention has a printability by corona discharge treatment, a surface treatment such as application of a surfactant, if necessary,
It is preferable to improve secondary processability such as antistatic property.

(Examples) Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples. The evaluation method of the present invention used in Examples and Comparative Examples was as follows.

(1) MI 190 ° C. The amount of molten resin discharged under a load of 2.16 Kgf for 10 minutes was measured according to JIS K6758.

(2) Transparency The transparency of the film sample is Haze (Haze) according to ASTM
Measured according to D1003.

(3) Bleedability A film sample was heat treated in an air oven at 40 ° C for 7 days, and then the transparency (Haze) of the film was measured, and the difference from the transparency (Haze) of the film immediately after film formation was calculated to determine the bleeding property. The sex was evaluated.

(4) Rigidity The tensile elastic modulus in the sample orientation (stretching) direction
Determined rigidity according to ASTM D882. The pulling speed is 50
mm / min.

(5) Elongation (TD) Based on ASTM D882, the tensile elongation at break in the direction perpendicular to the film (TD) was measured. The pulling speed was 50 mm / min.

(6) Suitability for horizontal twist The presence or absence of vertical breakage during horizontal twist and the ability to hold horizontal twist were checked.

The sample film was used to wrap the drops horizontally at 540 °, and it was observed whether or not the film had a vertical break.
In addition, a film that is twisted in a horizontal direction so that the film does not break vertically
It was left for 1 day at 0 ° C., and then the returning state was observed.

The following criteria ○ back angle 180 ° good △ back angle 180 to 300 ° using the lower limit × return angle 300 ° or more unusable ×× film is not available which vertical fracture (7) Peak methyl branches number infrared spectrophotometer 1377 cm ^- The transmittance (T) of ¹ is read and the absorbance (A) is calculated.

A = log ₁₀ (100 / T) Absorbance (A), thickness of sample film (1) Calculate concentration coefficient (C) from absorption coefficient (K) by C = A / K1, and calculate calibration curve from concentration coefficient C value in advance. Is prepared and the number of branches is estimated from the calibration curve.

(8) Stretchability The unstretched film was preheated with a preheating roll at a temperature of 80 to 120 ° C., uniaxially stretched at a stretching speed of 30 to 120 m / min and a stretching ratio of 3 to 9 and the stretched state (stretch unevenness) was observed.

Examples 1 to 4 and Comparative Examples 1 to 4 As Examples 1 to 4, an ethylene propylene copolymer having 0.5 to 2 methyl branches per 1000 carbon atoms described in Table 1 below was added to erucinamide. 0.25% by weight and 0.2% by weight of antioxidant are blended and mixed with a mixer with a high speed agitator. This mixture was melt-kneaded and granulated at an extrusion temperature of 250 ° C. to obtain a high-density polyethylene granulated product. This high-density polyethylene granule and MI are 3g / 10 minutes, hexene-1 content 4% by weight
The linear ethylene-hexene-1 copolymer of
After mixing with a tumbler mixer with the blending amount shown in the table, this mixture is extruded at a temperature of 220 ° C using an extruder with a 65 mm diameter T die, cooled by a chill roll at a temperature of 85 ° C, and solidified to give an unstretched film. Obtained. Then, this unstretched film is preheated with a preheating roll at a temperature of 100 ° C., and the speed is 60 m /
The film was stretched 6 times with a minute stretching roll to obtain a uniaxially stretched film. Further, as Comparative Examples 1 to 4, ethylene propylene copolymers shown in Table 1 below are mixed with erucinamide and an antioxidant in accordance with Examples 1 to 4, and melt-kneaded to form a high-density polyethylene granulated product. Got The high-density polyethylene granules and the same linear ethylene-hexene-1 copolymer as used in Examples 1 to 4 were mixed with a tumbler mixer in the blending amounts shown in Table 1 below. Then, this mixture was mixed according to Examples 1 to 4 and film-formed to obtain an unstretched film. Next, this unstretched film was stretched 6 times according to Examples 1 to 4 to obtain a uniaxially stretched film. Transparency (Haze), rigidity, and elongation (TD) of the uniaxially stretched film obtained in each Example and Comparative Example,
The lateral twist suitability was measured. The results are shown in Table 1.

Example 5, Comparative Examples 5 and 6 MI 1.0 g / 10 min described in Table 2 below, high density polyethylene having 2 methyl branches per 1000 carbon atoms 2 in erucic acid described in Table 2 below 0.02,0.3,0.5% by weight of amide
Was added and granulated according to Examples 1 to 4. 2% by weight of the obtained high-density polyethylene granules and the linear ethylene-hexene-1 copolymer were mixed according to Examples 1 to 4, and a film was formed to obtain an unstretched film. Then, this unstretched film was stretched in accordance with Examples 1 to 4 to evaluate its stretchability (the occurrence of stretching unevenness), and the unsaturated used on the film surface of a 6-fold stretched uniaxially stretched film having a thickness of 20 μm. The bleeding property and lateral twisting suitability of the fatty acid amide were investigated. The results are shown in Table 2.

Example 6, Comparative Examples 7 and 8 High-density polyethylene granules granulated according to Example 5 and linear ethylene-hexene-1 having MI of 0.3, 3, 7 shown in Table 3 below. 2% by weight of each of the copolymers was added, and Example 5 was used.
A film was formed according to the above procedure to obtain an unstretched film. Then, the unstretched film was examined under the conditions according to Example 5 for the stretchability (the occurrence of stretch unevenness) and the transparency of the 6-fold stretched uniaxially stretched film having a thickness of 20 μm.

The results are shown in Table 3.

(Effects of the Invention) As shown in Table 1 below, Examples 1 to 4 of the present invention have elongation (TD) while maintaining appropriate rigidity, and have good horizontal twist retention while preventing longitudinal breakage. It was found that the film was a uniaxially stretched film excellent in lateral twisting suitability. On the other hand, the film obtained in Comparative Example 1 in which the MI of the high-density polyethylene used exceeded the range of the present invention and the linear ethylene-hexene-1 copolymer exceeded the compounding range of the present invention, the rigidity was insufficient. However, the horizontal twisting retention is poor, and the methyl branch number X of high-density polyethylene and linear ethylene-hexene-
The product obtained in Comparative Example 2 in which the product XY with the compounding amount Y of 1 copolymer is out of the range of the present invention has insufficient rigidity and poor lateral twist holding property, and conversely linear ethylene-hexene. In Comparative Example 3 in which the -1 copolymer was not used, the film obtained had an insufficient elongation (TD), had a low longitudinal tear strength, and was longitudinally ruptured during lateral twist packaging. The film obtained in Comparative Example 4 in which the ethylene-butene copolymer was used instead of the ethylene-propylene copolymer had an appropriate elongation (TD), but the rigidity was insufficient and the lateral twist holding property was poor. Is.

Further, as shown in Table 2 described later, the film obtained in Example 6 of the present invention has good stretchability, bleeding property, and lateral twist holding property. On the contrary, the film obtained in Comparative Example 5 in which the amount of the unsaturated fatty acid amide added was out of the range of the present invention was 0.02% by weight, the bleeding property and the lateral twist holding property were good, but the unevenness in the drawing was caused during the drawing. Occurs and uniform stretching is difficult.
Further, the film obtained in Comparative Example 6 in which the amount of the unsaturated fatty acid amide added was outside the range of the present invention of 0.5% by weight was excellent in film forming property, but the obtained film was an unsaturated fatty acid on the film surface. Bleed of the amide was severe, and the ability to maintain the horizontal twist was impaired.

Furthermore, as shown in Table 3 below, in Comparative Example 7 using a linear ethylene-hexene-1 copolymer having an MI of 0.3, the stretchability of the obtained film was poor, and a linear chain having an MI of 7 was used. In Comparative Example 8 in which the ethylene-hexene-1 copolymer was used, uneven flow of the molten resin occurred in the flow direction of the obtained film, and a clear transparent film could not be obtained.

As described above, the twist packaging film of the present invention,
Even when used for horizontal twist packaging, it does not cause vertical breakage,
A film for twist packaging, which has excellent lateral twist holding properties, transparency, rigidity, film-forming (stretching) properties, and little bleeding of unsaturated fatty acid amide on the film surface, candy,
It can be suitably used as a twist packaging film used for packaging rice cakes and the like.

Claims (1)

[Claims] 1. An unsaturated fatty acid amide having 18 to 22 carbon atoms 0.03
Melt index 0.5 ~ 2g / 10 minutes, containing ~ 0.3 wt%,
Number of methyl branches (X) is 0.5 ≦ X ≦ 4 per 1000 carbon atoms
Melt index 0.5 to 5 per piece of high density polyethylene
The blending amount (Y) of the linear ethylene-hexene-1 copolymer of g / 10 minutes is 1 ≦ Y ≦ 4% by weight, and the product of X and Y is
A twist packaging film using a composition compounded so that 0.5 ≦ XY ≦ 10.