JPH05261810A - Manufacture of inflation film - Google Patents

Abstract

PURPOSE:To establish a method of film with a stability of bubble and a high productivity in the case of manufacturing a film of low melt-viscosity LLDPE through air-cooling inflation. CONSTITUTION:The manufacture of a long-neck type film is as follows; a linear low density polyethylene with a density of 0.91-0.94g/cm<3> is used, wherein the lip gaps are made 2.5-10.0mm, a stabilizer with a diameter smaller than that of a die is provided on the die surface, the dies temperature is kept at 170-210 deg.C, an air layer is formed between the bubble and the stabilizer, and further these are maintained not in contact with each other, a frost line 3 is allowed to be 4-20 times of the die 1 diameter and the expansion ratio is made 2-5 times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a blown film of a linear low density polyethylene (hereinafter referred to as LLDPE) having excellent transparency with high productivity.

[0002]

2. Description of the Related Art There have been many proposals for producing an inflation film by an air-cooling method, and the shape of a resin bubble for forming a film by these proposals is Japanese Patent Publication No.
2180, it is roughly divided into three or four types (FIGS. 2 to 4).

Factors that determine this shape include air cooling capacity, film take-up speed, molten resin temperature, etc., and medium density polyethylene (hereinafter referred to as MDPE),
High-density polyethylene (henceforth HDPE), etc.
For linear polyethylene with high density, so-called long-neck type bubble molding as shown in Fig. 1 is mostly adopted, and it is supplied in large quantities to shopping bags and other fields as a high-strength balance film. ..

On the other hand, the molecular structure of LLDPE is higher than that of high-pressure process low-density polyethylene (hereinafter referred to as LDPE).
Even though it is similar to PE, it has a low density, and because it does not contain an ultra-high molecular weight component, its melt viscosity is much smaller than that of HDPE for balance films, so its rheology is H.
Unlike DPE, it is prone to rough skin due to melt fracture, and the stability of the bubble is poor, making it difficult to form the bubble into a shape such as a long neck type. Usually, it is a type or c type bubble shape. (JP-A-57-34920).

However, the biggest problem in the production of blown film due to the shape of the bubble is that the high take-up speed is difficult and the productivity is limited, and the strength is increased because there is no sudden expansion portion of the bubble. Was impossible.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides LLDPE in the production of a film by an air-cooled inflation method.
Eliminates the instability of bubbles due to the low melt viscosity of
The goal was to stabilize the bubble and establish a highly productive LLDPE film manufacturing method.

[0007]

The present invention is a linear copolymer having a density of 0.91 to 0.94 g / cm ³ , which is a copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms. Low density polyethylene with a stabilizer having a diameter smaller than the die diameter on the die surface and a lip gap of 2.5 to 10.0.
Extruded from a die having a diameter of 170 mm at 170 ° C to 210 ° C to form an air layer between the bubble and the stabilizer, without bringing the bubble into contact with the stabilizer, and setting the frost line distance to the die diameter of 4 to 20.
The above object could be achieved by developing a method for producing an inflation film which is characterized in that the expansion ratio is expanded to 2 to 5 and taken over while keeping the double ratio.

The LLDPE which can be used in the present invention uses a transition metal catalyst in a high pressure method or a low pressure method and has 3 to 10 carbon atoms.
Is a copolymer of α-olefin and ethylene and has a density of about 0.91 to 0.94 g / cm ³ . Generally, the density varies depending on the content of α-olefin, but when butene-1 is used as a comonomer, it has 10 carbon atoms.
If the number of side chains is 20 to 25, then about 0.91,
If the number of side chains is 3 to 5, it is said to be 0.94, which is within this range. Examples of the α-olefin in this case include propylene, butene-1, hexene-1, 4-methylpentene-1, octene-1 and the like. The density is 0.
When it exceeds 94 g / cm ² , the transparency of the film is deteriorated, which is not preferable.

JIS of LLDPE which is the object of the present invention
The melt flow rate (hereinafter referred to as MFR) measured by the method of condition 1 in Table 1 of K-7210 is not limited, but is applicable to about 0.3 to 5.0 g / 10 min. Especially 0.4-3.0g / 10th place LLD
It is preferably applied to PE.

The molecular weight distribution of this LLDPE (M _W /
It is generally represented by M _N. ), Smaller than commercially available HDPE for balance film, usually LLDPE
Is commercially available as long as it is about 2.0 to 10.0.

It should be noted that, for this LLDPE, 1000-
Density 0.91 obtained by polymerizing in the presence of a free radical generator such as peroxide under a high pressure of 3500 Kg / cm ^2.
~0.93g / cm ³ about, MFR is 0.3~5.0g
/ 10 min high pressure low density polyethylene (hereinafter LDPE
Say. 50% by weight or less of the total weight may be blended.

Blending of LDPE in excess of this proportion should be avoided as it will result in a marked reduction in impact strength of the product film. The effect of lowering the pressure at the tip of the extruder can be clearly observed in LLDPE containing 5% or more of this LDPE.

The raw material LLDPE used in the present invention is, of course, an additive such as an antioxidant, an ultraviolet absorber, a slip agent, an antiblocking agent, and a colorant, which are blended with polyethylene which is a usual film raw material. Alternatively, an antistatic agent or the like may be blended.

As shown in FIG. 1, the apparatus used for producing the blown film of the present invention may be either upward or downward except that the die 1 has a large lip gap of 2.5 to 10 mm. You can use almost the same as the HDPE inflation device.

In the production of LLDPE film, it is a long neck type, and it is possible to increase the transparency by expanding the lip gap, and especially the high frost line 3
It is a new discovery that transparency can be secured even in molding in. It was thought that the high frost line slows the molten resin as compared with the low frost line, resulting in poor transparency, but it was surprising that this effect is almost negligible.

During operation, means such as lowering the extrusion temperature so that the bubble shape becomes the shape of the long neck shown in FIG. 1, lowering the temperature of the cooling air 2 at the die outlet, increasing the air volume, and increasing the take-up speed. Must be adjusted according to.

The stabilizer 4 is provided with an air inlet / outlet 5 (an outlet when the film is running in the same direction, an inlet when the film is made to flow backward) at its tip, and an air inlet / outlet 7 at the base or die surface of the stabilizer. (Corresponding to the air inlet / outlet at the tip of the stabilizer) is provided to create an air layer by circulating air between the bubble and the stabilizer to prevent contact between the bubble and the stabilizer of LLDPE having a low resin melt viscosity. To do. Shape of the stabilizer,
The material does not come into contact with bubbles during normal operation, so it is relatively free as long as it does not take an extreme shape, and it may have a shape like a cylinder, cone, disk or skewered dumpling. Considering the contact of bubbles and the stability of air flow, it is preferable that the surface has a cylindrical shape having a diameter smaller than the diameter of the die, such as a conical shape.

The air is supplied and discharged through an air inlet / outlet at the top of the stabilizer and an air inlet / outlet provided on the stabilizer base or on the die surface, and the supplied air passes between the bubble and the stabilizer. Is discharged. This air may be circulated and used, but in some cases the required amount of air is small, so it may simply be passed in one direction.

The preferable extrusion temperature of the resin varies depending on the resin, but it should be set to 170 to 210 ° C., which is slightly lower than the normal temperature of 220 ° C.
It is preferable to set the temperature as low as possible so long as melt fracture does not occur so as not to have the shape of c type in FIG.

If a slight melt fracture occurs, the problem can be avoided by increasing the lip gap.

Since LLDPE is a resin having the property of being extremely susceptible to melt fracture, the lip gap is much larger than that of general HDPE and is 2.5 to 10 mm.
It is necessary to make it preferably 4 to 8 mm. If this lip gap is less than 2.5 mm, the transparency will decrease,
If it is larger than 10 mm, it becomes difficult to adjust the uneven thickness of the film. Also, when skin roughness due to melt fracture is observed, it is avoided by increasing the lip gap. If it is still unavoidable, take measures such as raising the resin temperature.

Also in LLDPE, HDPE or MD
As with PE, the actual expansion ratio (the ratio of the bubble diameter at the temperature lower than the frost line to the diameter at the expansion start point) has an effect on the impact strength of the film. When this is small or large, the strength balance is lost. 2 to 5 is usually caused because the vertical tearing property becomes strong and it causes ring breakage.
, Preferably between 2.8 and 3.8.

The frost line (line for crystallizing the molten resin) 3 is 4 to 20 times, preferably 5 to 12 times, and more preferably 7 times the diameter of the die at a distance from the die surface.
Adjust the cooling air so that it is between about 12 times. If the length is shorter than 4 times, it is necessary to strongly apply the cooling air, the bubbles are shaken, the operation becomes unstable, and the thickness of the film varies. On the other hand, making it longer than 20 times will reduce the impact strength, so it should be avoided.

When operated under such conditions, the stability of the bubble is increased due to the influence of the stabilizer even if it is a long-neck type bubble, and high-speed take-up becomes possible, which is 40 m / m faster than the conventional LLDPE inflation speed. m
Stable operation became possible even if it was more than in.

[0025]

The melt viscosity of LLDPE is lower than that of HDPE, and it has not been adopted to form a bubble with a long neck in the film production by the ordinary inflation method. Therefore, the stability of the bubble is not good, and the fluctuation of the bubble and the unevenness of the film thickness are caused when the high-speed molding is performed, so that it has not been adopted as an industrial production method.

According to the present invention, the extrusion temperature is set as low as possible, and the die lip gap is 2.5 to 10 mm.
We succeeded in making the shape of the bubble a long neck by keeping it large, and by further providing a stabilizer on the die surface and bringing the bubble into contact with it and rapidly expanding it, high-speed molding (take-off speed It is possible to establish a method for producing a film that stabilizes bubbles even at a higher speed than before, has good transparency, has sufficient strength, and has less uneven thickness.

At this time, it is also an effective method to reduce the thickness of the stabilizer to increase the substantial expansion ratio.

[0028]

The present invention will be described in more detail with reference to Examples and Comparative Examples. The impact strength is JIS K-721.
1. Haze gloss and image clarity are JIS K-710
5 was measured.

(Example 1) Density is 0.922 g / cm
³ , an ethylene-butene-1 copolymer (LLDPE) having an MFR of 0.80 g / 10 min was used, and the extruder bore diameter was 50.
mmφ, die diameter 80 mmφ, stabilizer diameter 70 mm,
Using a die lip gap 3.0 mm molding machine,
Resin temperature 190 ° C, film thickness 30 μm, folding width 40
Molding was performed at 0 mm, a take-up speed of 40 m / min, and a frost line distance of 457 mm. The results are shown in Table 1.

(Example 2) LLDPE used in Example 1
Of 80% by weight and MFR of 2.50 g / 10 min LDPE
A film of the same size was obtained under the same molding conditions as in Example 1 except that 20% by weight of the composition was used. The results are shown in Table 1.

(Example 3) A film having the same size and the same resin composition as in Example 2 was obtained under the same molding conditions as in Example 2 except that the lip gap was 5.0 mm and the take-up speed was 70 m / min. The results are shown in Table 1.

(Example 4) Density of 0.9 as LLDPE
22 g / cm ³ , MFR 0.30 g / 10 min 80% by weight of ethylene-butene-1 copolymer, MFR 2.50
Using a resin composition consisting of 20 parts by weight of LDPE of g / 10 min, lip gap 5.0 mm, take-up speed 50
A film of the same size was obtained under the same molding conditions as in Example 2 except that the film was molded at m / min. The results are shown in Table 1.

Example 5 A resin composition was obtained except that the extrusion temperature was 230 ° C. and the take-up speed was 40 m / min, and other molding conditions were the same as in Example 4 to obtain a film of the same size. The results are shown in Table 1.

(Example 6) Density of 0.9 as LLDPE
25 g / cm ³ , 80 parts by weight of ethylene-hexene-1 copolymer having an MFR of 1.00 g / 10 min and an MFR of 2.50.
Film formation was performed under the same conditions as in Example 1 except that a resin composition consisting of 20 parts by weight of LDPE of g / 10 minutes was used. The results are shown in Table 1.

(Embodiment 7) The frost line distance is set to 640.
A film having the same size was obtained under the same molding conditions and using the same resin composition as in Example 2 except that the thickness was changed to mm. The results are shown in Table 1.

Example 8 Using the same resin composition as in Example 2 except that the expansion ratio was 2.5, a film of the same size was obtained under the same molding conditions. The results are shown in Table 1.

(Comparative Example 1) A film of the same size was obtained under the same molding conditions using the same resin composition as in Example 2 except that the lip gap of the die was 1.0 mm and the take-up speed was 30 m / min. .. The results are shown in Table 1.

(Comparative Example 2) The frost line distance was set to 240.
A film was formed under the same conditions as in Example 2 except that the thickness was 0 mm. The results are shown in Table 1.

Comparative Example 3 The resin composition used in Example 2 was used, and a take-up speed of 25 m / m was used without using a stabilizer.
Film formation was performed at min. The frost line at this time was about 455 mm. The film thickness is 30 μm
Is. In this case, the bubbles were unstable and the operation was difficult, and there was a large variation in the film thickness. Table 1 shows the properties of the film obtained in a relatively stable manner.

(Comparative Example 4) Take-up speed 40 m / min
However, since the pressure at the tip of the extruder was high and it felt dangerous, it was not possible to sample under stable operating conditions.

[0041]

[Table 1]

[0042]

EFFECT OF THE INVENTION LLDPE is LDPE even if it has a low density.
It is known that it has a higher strength than H.P. and is superior in transparency (haze and clarity) to HDPE.
The present invention has developed a method for producing an inflation film that takes advantage of this characteristic.

According to the method of the present invention, LL having a low melt viscosity
Even with DPE, a thin air layer is provided between the bubble and the stabilizer, so the bubble is stable, and the longitudinal and lateral strengths of the resulting film are balanced even at high speeds, resulting in high production. You can secure the sex. Especially because it is a long-neck type, it may have a good horizontal and vertical balance, or it may be a useful material for transparent packaging due to its excellent clarity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view when a method of the present invention is carried out.

FIG. 2 is a sectional view of a bubble shape according to a conventional method.

FIG. 3 is a sectional view of a bubble shape according to a conventional method.

FIG. 4 is a cross-sectional view of a bubble shape according to a conventional method.

[Explanation of symbols]

 1 Die 2 Air ring 3 Frost line 4 Stabilizer 5 Air outlet 6 Neck point 7 Air inlet

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Bamba Takeshi Kawasaki-ku, Kawasaki-ku, Kanagawa 3-2 Chidori-cho, Showa Denko KK Kawasaki Resin Research Laboratory (72) Inventor Masashi Chide 3-2 Showa Denko KK Kawasaki Resin Research Laboratory

Claims (3)

[Claims] 1. A copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms and having a density of 0.91 to 0.9.
170 g of linear low density polyethylene of 4 g / cm ³ with a stabilizer having a diameter smaller than the die diameter on the die surface and a lip gap of 2.5 to 10.0 mm
Extruded at ℃ ~ 210 ℃, to create an air layer between the bubble and the stabilizer, without contacting the bubble with the bubble, keeping the frost line distance 4 to 20 times the die diameter, the expansion ratio 2 ~
5. A method for producing an inflation film, which comprises expanding to 5 and collecting. 2. The linear low-density polyethylene is a linear low-density polyethylene containing 50% by weight or less of high-pressure low-density polyethylene, and has an MFR of 0.3 to 5.0 g.
It is / 10 minutes, The manufacturing method of the inflation film of Claim 1. 3. An air inlet / outlet is provided at a tip of the stabilizer and a base or a die of the stabilizer to form an air layer between the bubble and the stabilizer, and the air is allowed to flow between the bubble and the stabilizer. Of manufacturing blown film.