JPS61116521A - Inflation film molding process - Google Patents

Abstract

PURPOSE:To obtain effectively and stably the thin film with the excellent bal ance for longitudinal and transverse strengthes by molding polyethylene in which viscometric average molecular weight, fluidity ratio and molten surface tension is in a specified range, at specified cooling speed index and drawing index. CONSTITUTION:Polyethylene with 100,000-300,000 viscometric average molecular weight, 90-170 feuidity ratio and 3-10g molten surface tension, is inflation molded under the condition where the cooling speed index in a formula I [FLH; frost line height, V1; taking off speed (cm/sec), V0; the speed of molten material at the exit of a die] is 2-11, and the drawing index in a formula II [rhom; the density (g/cm<3>) of the resin extruded from a die slit, rhof; the density (g/cm<3>) of a film, G: the width (cm) of the die slit] is 1-4. Thus, the objective product is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a blown film forming method for highly efficiently producing a thin, high-strength blown film suitable for use as packaging bags and the like.

[Conventional technology and its drawbacks]

Conventionally, polyethylene, which has a viscosity average molecular weight of about 100,000-300,000, has a higher molecular weight than commonly used polyethylene, so it has poor fluidity and cannot be efficiently extruded, making inflation molding difficult. fc
The resulting film was also prone to vertical tearing, and its uses were limited and demand did not increase.

Therefore, when performing inflation molding using this high molecular weight polyethylene, it is necessary to increase the blow-up ratio, that is, the ratio of the product diameter to the circular slit of the die, to strongly cause molecular orientation in the lateral direction of the film.
Attempts have been made to improve the lateral strength.

Problems arose, such as bubbles not being stabilized during molding and product quality not improving much.

[Purpose of the invention]

The purpose of the present invention is to provide a method for efficiently and stably forming a thin film with good longitudinal and lateral strength balance when performing inflation molding using high molecular weight polyethylene.

[Structure of the invention]

The gist of the present invention is that the viscosity average molecular weight is from 10,000 to 300,000, and the flow ratio is from 90 to 70. A method for forming a blown film, characterized in that inflation molding is carried out under conditions where the melt tension Jl~ index is l~da.

F L HVt τ)--Zun 辷→ ・・・・・・・・・・・・(1)V
'+-V', V'.

ρmG 2=−・−・□Fist ψ・・・・・・−(n) ρf t
(BUR)” (Exist.

Polyethylene that can be applied to the method of the present invention has a viscosity average molecular weight of 700,000 to 300,000, and a fluidity ratio of ? O~lg0. #l Melt tension J
It is necessary to use a specific polyethylene of 11-109.

The viscosity average molecular weight was measured at Tetralin (130°C) using a Kubelohde-type improved viscometer, and was measured using the TungO formula (Cη).
=Hiroshi, io ,3
If it exceeds 0,000, the molding efficiency decreases.

The fluidity ratio is based on K4740 than J, and the extrusion rate (at 190℃, shear force IO @ die 77 cd (load 111377) and tcp dyne /, -d (load / / /J /lin)
11/lO min) was measured, and the value was determined by:

The fluidity ratio is a measure of molecular weight distribution; a small fluidity ratio value indicates a narrow molecular weight distribution, and a high fluidity ratio value indicates a wide molecular weight distribution.

In the method of the present invention, polyethylene with a fluidity ratio of less than 90 does not easily cause molecular orientation, making it difficult to obtain a film with good strength, and when the fluidity ratio exceeds /70, molecular orientation tends to occur and under normal molding conditions. If it becomes difficult to achieve the desired strength balance, it cannot be adopted.

Melt tension was measured from the nozzle used for melt index measurement at 6740 on polyethylene J-8 at 60°C 10
．． Ko! Extruded at a speed of I/m, /, jcorrrL/1oI
This is the tension (9) measured at a position a distance from the nozzle when the melt tension is taken at a speed of become unable. When the melt tension exceeds 101, bubbles tend to break and thin-wall formability becomes poor.

In the present invention, polyethylene may be an ethylene homopolymer, a copolymer of ethylene with other α-olefins such as propylene or butene-7, a copolymer of ethylene with vinyl acetate, etc. Any material may be used as long as it contains ethylene as a main component and has a viscosity average molecular weight, fL dynamic ratio, and melt tension within the above ranges.

In the method of the present invention, inflation molding is carried out using the above-mentioned specific polyethylene under specific conditions such as void formation.

The process is to mold the material.

The cooling rate index (τ) indicates the time (seconds) it takes for the film extruded from the goo to solidify.
) is expressed by the formula τ= Jn S−)
・・・・・・・・・・・・(1) V, -” is also v.

You can control it to a predetermined value by changing each requirement in the η. To change the value or L, use a take-off device.

It may be controlled by changing the extrusion i' of the extruder, and a predetermined cooling rate index (τ) is set by combining these '4I'.

If the cooling rate index (τ) is less than 1, the cooling is too strong and it is difficult to achieve a balanced orientation in the longitudinal and lateral directions of the film, and a film with excellent strength cannot be obtained; If the bubbles were not cooled properly, the bubbles became unstable, and the nine-molecule orientation was relaxed, resulting in a decrease in the strength of the film.

In the method of the present invention, it is still not possible to obtain a film with sufficiently excellent strength by controlling only the cooling rate index (τ) described above.

Furthermore, it is necessary to check the drawing index (χ).

Stretching index (2) is an index indicating 1 degree of stretching in the width direction of the film, and is expressed by (II) 2 below.

ρ f t (BUR)1
mam. (If) Stretching index (χ
) is required to be set at /% 44 K, and together with the above-mentioned cooling rate index (τ), it almost uniquely determines the film strength.

Stretching index <2) is determined by blow ratio, extrusion temperature, die slit width, product film thickness, etc.

If the stretching index (χ) is less than 1, it is difficult to achieve a well-balanced molecular orientation in the vertical and horizontal directions, and the molecular orientation is well-balanced even beyond the bow, so that K<.

〔Example〕

The method of the present invention will be explained in more detail by way of examples below, but the present invention is not limited to the following examples unless it goes beyond its gist.

Example 1 Viscosity average molecular weight (16,000), melt tension (9,!t) I,
High-density polyethylene (density (0, t) with flow ratio (tio)
j J) IIatl, melt index (o, o
r) I/10 minutes) using mA-4EO manufactured by Modern Machinery Co., Ltd.
(0wm1) Annular slit diameter (zO) tag on extruder
, using an inflation molding machine equipped with an inflation die and a cooling ring related to the lip clearing (/, 0), the resin temperature (coo>”cm and the extrusion amount ('0)
) 'Kg/hr% blowup (Bvx) ratio (j)
, take-off speed (13) m/min, 70 line height Cl0
) Under the condition of on, the film thickness, stiffness μ, folding diameter (3
6) A blown film was obtained. In addition, the melt velocity at the die exit/fi (V・2974m・t・D・G
It was calculated based on Q=extrusion amount, ρm=melt density, D=die diameter, G=clearance).

Further, the % film density was measured using J-Ko SK-4740.

The physical properties of the blown films thus obtained were measured, and the results are shown in Table 1. In addition,
Various physical property measurements were performed by the following methods.

Dart impact strength: A8TM-D/7 (79 (method A) Elmendorf tear strength: J engineering 13 Z-/70J example co-CJ) [In li example/, the inflation molding conditions were
! ! The same procedure as in Example 1 was carried out except that ti was changed as shown. The results are shown in Figure 1.

Comparative Examples 1 to (In Example 1, the inflation molding conditions were ag1
The same procedure as in Example 1 was carried out except for the changes shown in the table. The results are shown in Table 1.

However, the evaluation of film physical property measurement in the method of the present invention is as follows.

Film Formability 20 [Effects of the Invention] According to the method of the present invention, a thin and high-strength film can be obtained, which can be suitably used as bags for various packaging applications.

Sender: Mitsubishi Chemical Industries, Ltd. Representative Patent attorney required - (1 other person)

Claims (1)

[Claims] (1) Viscosity average molecular weight 100,000 to 300,000, fluidity ratio 90 to 1
70 and polyethylene with a melt tension of 3 g to 10 g as shown below (
I) A method for forming a blown film, characterized in that inflation molding is carried out under conditions in which the cooling rate index expressed by formula (II) is 2 to 11 and the stretching index expressed by formula (II) is 1 to 4. τ=FLH/(V_1-V_0)ln(V_1/V_0
)...(I) {FLH: Frost line height (cm) V_1: Take-up speed (cm/sec) V_0: Melt velocity at die exit (cm/sec)} χ=(ρm/ρf)・(G /t)・[1/(BUR)^
2]...(II) {ρm: Density of resin extruded from die slit (g/
cm^3) ρf: Density of film (g/cm^3) G: Width of die slit (cm) t: Thickness of film (cm) BUR: Blow ratio}