JP2615931B2 - Film production method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a film having excellent tear strength, impact strength, rigidity and tensile strength in the longitudinal direction (stretching direction) of the film. More specifically, the present invention relates to a method for producing a packaging film mainly composed of linear polyethylene, which can be made thinner than conventional films, and which is suitable for packaging relatively heavy articles such as rice grains, fertilizers, and resin pellets. Things.

[Conventional technology and its problems]

Conventionally, a film formed by molding a linear polyethylene resin by the T-die method or the inflation method is inferior in rigidity and tensile strength, and it has been necessary to use a relatively thick film in order to use it as a packaging film for heavy goods.

Therefore, it has been proposed to stretch the film to impart rigidity and tensile strength.

Therefore, it is conceivable to biaxially stretch the raw material. However, since the biaxial stretching apparatus has a high equipment cost and a narrow range of stretching conditions, the operation management is strict, and it is used only in a very small number of fields.

In addition, although the longitudinal uniaxial stretching apparatus, which has been widely used in the past, has a low equipment cost and is easy to operate and manage, the anisotropy of the physical properties of the film, particularly the tear strength and the surface strength in the longitudinal direction (stretching direction) remain. No satisfactory film was obtained.

Therefore, the present invention solves the drawbacks of the prior art, and as a result of intensive studies to produce a thin film having excellent strength properties from linear polyethylene, as a result, an original film obtained by inflation molding a specific linear polyethylene resin under specific conditions. We found that a film with excellent tear strength can be made even if it is molded at the same BUR (blow-up ratio) as in the past inflation molding by stretching the web under specific conditions in the longitudinal and uniaxial directions, and complete the present invention. Reached.

[Means for solving the problem]

The gist of the present invention is that the melt index is 2 g / 10 minutes or less, and the density is 50% of linear polyethylene having a density of 0.910 to 0.965.
For inflation molding of a resin containing at least one weight percent, a die is provided that can rotate either the movable die lip or the core through an annular slit or rotate both in opposite directions. Using an inflation molding device, the movable die lip and the core are simultaneously rotated in the opposite direction or in only one direction at a rotation speed equal to or higher than the rotation index (S) shown by the following formula (I), and the rotation index (S)
Inflation molding while rotating at a rotation speed of 10 times or less of the obtained film, the stretching temperature in the film take-off direction is the melting point of the resin -70 ~ -20 ℃, stretch ratio 1.5 ~
(8) The method for producing a film, wherein the film is uniaxially stretched under the conditions described in (8).

Where G: width of annular slit (m / m) MI: melt index of the above resin (g / 10 minutes) t: film thickness (m / m) BUR: blow-up ratio D: diameter of annular slit (m / m m) Hereinafter, the present invention will be described in detail.

0.91 ~ as linear polyethylene used in the present invention
Linear low density polyethylene or 0.965 g / cm ³ or less of high density polyethylene 0.95 g / cm ³ is used.

The linear low-density polyethylene refers to ethylene and other α.
-It is a copolymer with an olefin and is different from a branched low-density polyethylene resin produced by a conventional high-pressure method.
Linear low density polyethylene is, for example, ethylene and other α
An olefin obtained by copolymerizing about 4 to 17% by weight, preferably about 5 to 15% by weight of butene, hexene, octene, decene, 4-methylpentene-1 or the like; Is manufactured using a type catalyst or a Philip type catalyst,
A conventional high-density polyethylene and short branched structure by the copolymerization component, density is obtained by this use of short chain branching suitably reduced by 0.91~0.95g / cm ³ or so, conventional branched low density polyethylene It is a polyethylene having a more linear structure and a structure with more branches than a high-density polyethylene.

The high-density polyethylene is an ethylene homopolymer obtained by polymerizing ethylene alone using a Ziegler-type catalyst or a Phillips-type catalyst, and has a density of 0.965 g / c.
m ³ or less of what is used.

The above linear polyethylene has a melt index of 2g / 1
Those having a length of 0 minutes or less, preferably in the range of 1 g / 10 minutes to 0.001 g / 10 minutes, are suitably used. If the melt index is higher than the upper limit, the surface strength is undesirably reduced. Further, the linear polyethylene has a density of 0.910 to 0.965 g / cm ³ , preferably 0.915 to 0.940 g / cm ³ . If the density is higher than the upper limit, the impact resistance is significantly reduced, and if the density is lower than the lower limit, the rigidity and the tensile strength are undesirably reduced.

In the method of the present invention, the melt index is JIS K676
Is a value measured in compliance with condition 4 in Table 1 of JIS K7210 is a normative reference 0, the flow ratio, using the melt index instrument, shearing force 10 ⁶ dynes / cm ² (Load 11131
g) and 10 ⁵ dynes / cm ² (load 1113 g) (g / 10 min)
And Is calculated. The density is a value measured according to JIS K6760.

In the present invention, only the above-described linear polyethylene may be used, but the linear polyethylene may be used as a main component, and a branched low-density polyethylene or the like may be blended in less than 50% by weight.

The branched low-density polyethylene contained in the linear polyethylene includes an ethylene homopolymer and a copolymer of ethylene and another copolymer component.

Vinyl copolymers such as vinyl acetate, ethyl acrylate and methyl acrylate, hexene,
Examples thereof include olefins having 3 or more carbon atoms such as propylene, octene, and 4-methylpentene-1. The copolymerization amount of the copolymerization component is 0.5 to 18% by weight, preferably 2 to 10% by weight.
% By weight. These low-density polyethylenes are desirably obtained by radical polymerization using a radical generator such as oxygen or an organic peroxide by an ordinary high-pressure method (1000 to 3000 kg / cm ² ).

The branched low-density polyethylene having a melt index of 2 g / 10 min or less, preferably 1 g / 10 min to 0.01 g / 10 min is used. If the melt index is higher than the above range, the surface strength of the film is undesirably reduced. Further, the above-mentioned branched low-density polyethylene has a density of 0.
930 g / cm ³ or less, and particularly in the range of 0.915~0.925g / cm ^3, preferably from the viewpoint of improving the surface strength.

The blending amount of the linear polyethylene and the branched low-density polyethylene is 100 to 50 parts by weight of the linear low-density polyethylene, preferably 90 to 70 parts by weight to 0 to 50 parts by weight of the branched low-density polyethylene, and preferably 10 to 50 parts by weight. Used within the range of 30 parts by weight.

Further, about 0.10 part by weight or less of a radical generator may be added to this composition. For example, dicumyl peroxide, 2,5-dimethyl-2,5 di (t-butylperoxy)
Hexane, 2,5-dimethyl-2,5 di (t-butylperoxy) hexyne-3, α, α'-bis (t-butylperoxyisopropyl) benzene, dibenzoyl peroxide, di-t-butylper Oxide and the like.

By reacting the linear polyethylene or a mixture of the linear polyethylene and the branched low-density polyethylene with a radical generator, the polyethylenes cause molecular coupling to increase the high molecular weight component, and the melt index decreases. A modified polyethylene is obtained. The modified polyethylene is more likely to be oriented in the transverse direction at the time of inflation molding than the unmodified linear polyethylene or a blend of the linear polyethylene and the branched low-density polyethylene. In addition, the vertical tear strength and impact strength are significantly improved.

Antioxidants, UV absorbers, if necessary,
Known additives usually used for polyethylene, such as an antistatic agent and a lubricant, may be added.

In addition, as the blown film forming apparatus used in the present invention, any type of blown film can be used, but the forming die is different from a normal circular die, and is one of an annular die and a core. A rotatable die is used, which is rotatable or can rotate in opposite directions to each other. FIG. 1 shows an example of a die used in the present invention.

In FIG. 1, a movable die lip (2) in which the dies can be rotated in opposite directions via an annular slit (1).
And a core (3), and a resin flow path (4) for supplying a resin to the annular slit (1).

In the present invention, the above-mentioned resin is molded under specific molding conditions using an inflation film molding apparatus equipped with the above-mentioned rotary die.

First, in the blown film molding equipment,
Since one or both of the movable die lip (2) and the core (3) are rotated in opposite directions, the film extruded from the annular slit (1) must be oriented in a combined direction of the extrusion direction and the rotation direction. Therefore, a film having oblique molecular orientation can be obtained as a whole film. The degree of molecular orientation of the film is appropriately selected and determined by adjusting the rotational speed of the movable die lip and the core, the extrusion speed and the take-up speed of the resin, and the like.

In the present invention, in order to produce a film excellent in impact strength and longitudinal tear strength of the film, the number of rotations of the movable die lip (2) and the core (3) (movable die lip,
And when the core is rotated simultaneously in the opposite direction, the sum of the rotation speeds of both, or when only one of them is rotated, the rotation speed) is calculated by the rotation index (S) of the following formula (I). Not less than 10 times and not more than 10 times the S value
The adjustment is performed within the range of 1.2 to 10 times the value.

Here, S: rotation index G: width of annular slit (m / m) MI: melt index of the above resin (g / 10 minutes) t: film thickness (m / m) BUR: blow-up ratio D: annular slit Of diameter (m / m).

The above-mentioned rotation index (S) is an important index of the molding operation conditions of the present invention, and the fluidity (MI) of the resin used, the film thickness (t), the blow-up ratio (BUR), the slit width of the die used. The required minimum total number of revolutions (rpm) is defined by (G) and the slit diameter (D).

When the rotation speed specified above is lower than the rotation index (S), the strength of the obtained film is not much different from that of a molded product with a conventional high blow-up ratio, and the effect of the present invention is sufficiently exhibited. I can't. Also, the rotation speed is a rotation index (S).
If it is more than 10 times, there is no demerit in physical properties of the obtained film, but there is a possibility that it may cause a slight problem from the viewpoint of the durability of the molding apparatus, which is not preferable.

In addition, the extrusion speed and take-off speed of the resin are set to such a level as to be usually performed in inflation molding.

By using the inflation method, it is possible to impart a horizontal orientation with a lower BUR than when using the conventional inflation method, and the stability of bubbles during the forming of the raw material is greatly improved.

The unstretched film is then uniaxially stretched in the machine direction at a stretching temperature of the melting point of the resin composition (modified polyethylene) -70 to -20 ° C and a stretching ratio of 1.5 to 8 times.

The stretching temperature is preferably −20 ° C. or lower and −70 ° C. or higher, more preferably −30 ° C. to −60 ° C. Below the range, stretch unevenness occurs in the film, and above the range, the impact strength of the film is greatly reduced.

The stretching ratio is preferably 1.5 to 8 times, and more preferably 2 to 5 times. Stretching ratio is 1.5
If the ratio is less than twice, the effect of stretching is insufficient, and the rigidity and tensile strength of the film are not sufficient. Also 8
If it is twice or more, the stretched film has an excessive molecular orientation in the longitudinal direction, and the longitudinal tear strength of the film is undesirably reduced.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples,
The present invention is not limited to the following examples unless it exceeds the gist.

 The evaluation method in the examples is as follows.

(B) Strength of the obtained film Elmendorf tear strength-JIS P8116 Dart drop impact (DDI)-ASTM D1709 (b) Finger pull-out strength test A finger pull-out strength test was performed to examine the tensile strength of the film.

The test method is to cut the longitudinally stretched film obtained above into 760 mm in the stretching direction and 1000 m in the transverse direction (the width direction of the film).
/ m (If the film width is small, cut it to 10mm width so that the overlapped part will be 10mm, cut it in the horizontal direction so that the overlapped part will be 10mm, and apply hot melt adhesive to the overlapped part. (Grade HX-960 manufactured by Nitta Gelatin Co., Ltd.) is applied, and the overlapped portion is heated and adhered with a hot gun to form a cylindrical body.
After heat-sealing using a 22B-Z type heat sealer, the obtained bag was filled with 20 kg of fertilizer, and the opening was heat-sealed to obtain a test packaging bag. The heat-sealed portion of the 20 kg fertilizer bag was the floor. It was lifted by hand so as to be parallel to the surface, and the situation where the finger bites into the film surface of the bag was observed.

Evaluation A: Fingers did not bite at all, no problem B: Fingers bite, but no problem C: Fingers bite, problematic The results are shown in Table 1.

Example 1 (1) Linear low-density polyethylene {melt index (MI): 0.5 g / 10 min, flow ratio: 20, density: 0.921 g / cm ³ } was 80
Parts by weight and high pressure method branched low density polyethylene ｛MI: 0.4g / 10
Min, flow ratio: 45, density: 0.922 g / cm ³ド ラ イ dry blended 20 parts by weight, and this was put into a modern machine Delser (trade name) 65φ type extruder with an annular slit diameter: 250 mmφ, annular slit width (die lip) Gap): Formed using an inflation molding machine with a 4.0 mm spiral die (rotary die of the shape shown in Fig. 1) equipped with a spiral rotary die (rotary die of the shape shown in Fig. 1) that can rotate the die lip and the core in opposite directions through an annular slit. Under the conditions of a temperature of 190 ° C., a blow-up ratio (BUR) of 1.7 and the number of rotations shown in Table 1, a 200 μm blown film was obtained.

The raw film was slit in the film take-off direction, and a longitudinally uniaxially stretched film having a thickness of 80 μm was produced using a roll stretching apparatus under the conditions of a stretching temperature of 80 ° C. and a stretching ratio (3 times in the longitudinal direction). . Table 1 shows the evaluation results.

Examples 2 and 3, Comparative Examples 1 to 4 As shown in Table 1, a film was obtained and evaluated in the same manner as in Example 1 except that the molding conditions, the resin composition and the like were changed.
The results are shown in Table 1.

[Effect of the Invention] The film obtained by the method of the present invention is excellent in tear strength, impact strength, rigidity and tensile strength, can be made thinner, and is a suitable film to be used for heavy-weight packaging bags and the like. .

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an example of a die used in the present invention. In the figure, 1 is an annular slit, 2 is a die lip, and 3 is a core.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-158221 (JP, A) JP-A-63-173620 (JP, A) JP-A-52-37983 (JP, A)

Claims (1)

(57) [Claims] A linear polyethylene having a melt index of 2 g / 10 minutes or less and a density of 0.910 to 0.965 is 50% by weight.
In inflation molding of the resin contained above, either one of the movable die lip and the core can be rotated through an annular slit, or an inflation molding provided with a die adapted to rotate both of them in opposite directions. Using the device, the movable die lip and the core are simultaneously rotated in the opposite direction or only one of them at a rotation speed not less than the value of the rotation index (S) represented by the following formula (I), and the rotation index (S) is 10 or more.
Inflation molding while rotating at a rotation speed of not more than 2 times, the obtained film is uniaxially stretched under the conditions of a stretching temperature in the film take-off direction of a melting point of the resin -70 to -20 ° C and a stretching ratio of 1.5 to 8 A method for producing a film, comprising: However, G: width of annular slit (m / m) MI: melt index of the above resin (g / 10 minutes) t: film thickness (m / m) BUR: blow-up ratio D: diameter of annular slit (m / m) )