JPS63230321A - Manufacture of high density polyethylene film - Google Patents

Abstract

PURPOSE:To enable a film excellent in mechanical property to be easily produced by heating and orientating the minimum width of the film having a specified weight average molecular weight and a specified molecular weight distribution continuously in order. CONSTITUTION:High density polyethylene film is used as raw material film, and unorientated and amorphous material is preferable, but low crystalline and low orientated material may be also used. For the physical property of the high density polyethylene resin of the raw material film, a resin in which its weight average molecular weight Mw is 100-200 thousands and molecular weight distribution (Mw/numerical average molecular weight Mn) is 2-7 and preferably 2.5-5 of narrow range thereof, is used. In this manufacture, the minimum part of a high density polyethylene film is heated and orientated under tension at the temperature equal to crystal dispersion temperature or higher and equal to melting point or lower. The minimum part of a product film is heated, and since the heated part is orientated by the tension always applied, a film excellent in molecular structure and various mechanical properties is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides zone heating and
This invention relates to a method for producing a film with extremely excellent mechanical properties that is produced by stretching.

[Conventional technology]

Highly oriented, highly elastic films are expected to be widely used in fields requiring excellent mechanical properties in the future, and as a result, research on higher-order structure rearrangement of general-purpose polymers is becoming more active.

Conventionally, the technology to make plastics highly elastic and strong is
Many of them target mN, and the following have been published for [t. That is, (a) high pressure extrusion method [for example, Journal of Polymer Science, Polymer Physics Edition (J, Polym, Sci.
, Polym, Phys, Ed) 12°635 (
(1974)), (b) die drawing method [for example, Journal of Polymer Engineering Science (J, of, Po1
Y, Eng, Sci) 20.1229 (1981
)), (c) gel spinning method (e.g. J, Smook a
nd A, J, Penn1nos, Polymer, B
ull, 975 (1983)), (d) Melting prevention method using high speed [e.g.
977)), (e) Zone/stretching, heat treatment methods [e.g.
of Applied Polymer Science (J, Pol
ym, Sci) Vol, 26.1951-196
0 (1981), IIM Journal Vol. 1.40.
No. 9 (1984), Special Publication No. 57-193513
Japanese Patent Publication No. 60-24852].

[Problem that the invention seeks to solve]

However, in the high pressure extrusion method (a) and the die stretching method (b), the tensile force is very small and auxiliary compared to the high pressure applied to the raw material side. Therefore, there is a concern that the molecular chains may become clogged in the form of threads near the mouthpiece, and orientation of the molecular chains is not easy.

The gel spinning method (C) uses an organic solvent in the melting process, making it very expensive. Also, since it uses a large amount of organic solvent, there are still problems with post-processing, and there is little possibility of mass production through industrialization. .

The melting prevention method using high speed (d) promotes the unfolding of molecular chains by high speed, freezing, etc., so the obtained fibers cannot form a stable crystalline structure and tend to have an amorphous structure. There are drawbacks.

The zone/stretch heat treatment method of (e) is
No. 52 describes a method for producing highly elastic and high-strength fibers by subjecting amorphous or as low-crystalline fibrils as possible to zone stretching and zone heat treatment. However, the method requires two operations, and furthermore, the modulus of elasticity of the obtained fiber remains low. In addition, the publications, including those published in the 4811 academic journal mentioned above, were originally laboratory-based, and it would be difficult to serialize them on an industrial scale. Furthermore, since a constant load is applied to the raw polymer rod to draw it, there is a problem that the cross-sectional area of the raw material rod is non-uniform, which causes the applied stress to become non-uniform, causing the cross-sectional area of the drawn fibers to vary or break. Ta.

All of these methods were developed for fibers, and it is impossible to apply them to films.Moreover, there are many difficulties in industrialization and product quality, such as problems with molecular orientation. The cost is also high, making industrialization unrealistic, and the current situation is that the goal has not been fully achieved.

In view of the above circumstances, the present invention has excellent mechanical properties,
The purpose of the present invention is to provide a method for producing a high-density polyethylene film that can be easily produced and is expected to have a wide range of uses in the future.

Means for Solving Problem C] The present invention has been made to achieve the above-mentioned object, and its gist is that a high-density polyethylene film is heated under tension and at a temperature higher than the crystal dispersion temperature of polyethylene, but at a temperature higher than the melting point. A method for producing a film that is heated and stretched at a temperature of:
The small average molecular weight (MW) of polyethylene is 100,000 to 200,000, and the number of molecules is 1 distribution [Mw/number average molecule 1f (H
n)) is from 2 to 7, and the method for producing a high-density polyethylene film involves sequentially and continuously heating and stretching the minimum width of the film.

[Specific structure and operation of the invention]

The present invention will be explained in detail below.

In the present invention, a high-density polyethylene film is used as a raw material film, and an unoriented amorphous film is preferred, but a low-crystalline and low-oriented film can also be used.

In addition, the physical properties of the high-density polyethylene resin of the raw material film are such that its weight average molecule lHw is 100,000 to 200,000, and its molecular weight distribution [Mw/number average molecule MHn] is 2 to 7, preferably 2.
．． A resin with a narrow molecular weight distribution of 5 to 5 is used. At this time, the density of the resin is 0.945g/C11? Above, preferably 0.945 to 0.975g/crf, especially 0.9
50 to 0.975 g/d is suitable.

Hw is 100,000 to 200,000, molecular weight distribution Hw/Hn is 2 to 7
If a high density polyethylene film other than the above is used as the base film, a highly oriented, highly elastic film with good material properties cannot be obtained.

Next, the present invention will be explained in detail.

The method of the present invention is made by heating and stretching a very small portion of a high-density polyethylene film under tension at a temperature above the crystal dispersion temperature but below the melting point of polyethylene.

1 and 2 show an example of an apparatus for producing the film of the present invention, and FIG. 1 is a schematic side view. Reference numerals 1 and 2 in the figure are a delivery roll and a take-up roll driven by a motor (not shown), respectively, and the difference in their rotational speeds applies tension to the raw material film 3 to continuously stretch it.

Now, set the feed speed by feed roll 1 to VCmm/
min, the winding speed by the winding roll 2 is V
When Dm/min, the stretching ratio λ for the raw material film 3 is given by the following equation.

λ-1+VD2 (Vo...(1) Therefore, in formula (1), by appropriately selecting VD for VC, a film with any stretching ratio can be obtained, but a highly oriented film can be obtained. It is preferable that λ>8.

Moreover, between the rolls 1 and 2, there is a very small plate heater 4.
is provided, and in the crystal dispersion temperature range, the raw material film 3
heats a very small part of the In order to minimize this heated portion, for example, a 2# plate heater 4 is used. Also,
Cooling units 5, 5 are provided on both sides of the heating unit 4' to prevent heat dispersion in the heating unit 4' caused by the plate heater 4 and to prevent the heating range of the raw material film 3 from expanding. As shown in an enlarged view in FIG. 2, the cooling medium 6, for example, vaporized cold air of liquid nitrogen, is introduced into the cooling section 5, and is discharged to the side opposite to the plate heater 4, and the cooling air is emitted from the heating section 4'. We try to keep heat dispersion to a minimum. Therefore, the applied stress can be concentrated in one line on the extremely small heating section. In this case, the width of the minimal heating section is preferably 20 seconds or less, preferably 10 mm or less, particularly 8 mm or less, and the heating temperature (stretching temperature) for the raw material film is suitably about 80 to 130°C. Moreover, the cooling scar of the cooling part 5 is adjusted by the injection amount and temperature of the cooling medium 6, but the molecular weight unfo
From the necessity of preventing relaxation of lding, it is desirable that the temperature be below O'C.

The film produced as described above is heated in its extremely small portion, and this heated portion is stretched under constant tension, resulting in a film with excellent molecular structure and various mechanical properties. can get. In particular, the elastic modulus of the film of the present invention is much higher than that of gel-spun fibers or conventional zone-stretched/heat-treated fibers;
It shows 5-60 Gpa.

Note that 7 and 8 in the figure are guide rollers. In addition, in the above explanation, a very small plate heater was used for heating and the device was a horizontal type, but there is no restriction on the heating means as long as a very small part can be heated.
Alternatively, the device may be of a vertical type.

〔Example〕

The present invention will be described below with reference to Examples and Comparative Examples.

In Examples and Comparative Examples, various physical properties such as mechanical properties of the films are measured and compared, and methods for measuring these physical properties are shown below.

(a) Measurement of tensile modulus of elasticity and breaking strength Measurement of tensile modulus of elasticity E and breaking strength was carried out under the following Tensilon conditions. The length of the sample was 20#9, the width was 6 trmr, and the crosshead tension speed was 20 mm/m.
The cross-sectional area of the sample was measured at least five times using a micrometer and a thickness gauge, and the average value was taken. Note that the breaking strength σb has a large error due to chuck breakage.
There is a strong possibility that it will come out smaller than the actual value, so it will probably be a perfect guess. The elastic modulus E was calculated from the initial slope of the stress-strain curve obtained from the tensile test.

(b) Bitter melon measurement Density measurement is performed using a water-methanol system dense surface gradient, etc.
It was measured by the float-sink method at ℃.

At this time, an aspirator was used in a water-methanol mixed solution.
The measurement was carried out after almost completely removing the air bubbles and introducing the tube into the gradient piping over a period of about 5 to 20 minutes.

The crystallinity XC was determined by the following formula (2) from the measured density. However, the crystal density ρC9 and the amorphous density ρa of polyethylene are ρC=1,000 and ρa=0.852.

When the measured density is ρ, ρ−,QCxρa +pa (1−Xc) (C) Birefringence measurement The birefringence of the sample was measured using a polarizing microscope equipped with a compensator using sodium as a light source.

Examples 1 and 2, Comparative Examples 1 to 3 Using the apparatus shown in Figure 1, the smallest part of the film was heated and
Stretched.

As the original film, five types of high-density polyethylene films A to F with different physical properties were used as shown in Table 1, in the T-die molded state with a width of 6.0 mm and a thickness of 0.6 mm. .

Table 1 In addition, the heating stone was set at 120°C for each sample, and the stretching ratio λ was approximately the maximum stretching ratio for each sample. However, the raw film was heated in the very small part and stretched smoothly without necking. It was done.

Each hard physical property was measured for these stretched films,
The results are shown in Table 2.

From Table 2, Hw is 150,000, and the value of Hw/Hn is 3.5.
The sample has the highest maximum stretching ratio, birefringence, and crystallization ratio, and the highest elastic modulus and breaking strength, but Hw
It can be seen that when a high-density polyethylene film having a Hw/Hn value of 100,000 to 200,000 and a Hw/Hn value of 3 to 5 is used, both the elastic modulus and the breaking strength become large.

The physical property values in the above range can be selected from ordinary high-density polyethylene.

Example 3 Minimal heating zone stretching was carried out in the same manner as in Example 1, except that the take-up roll speed VD and stretching humidity were changed to change the stretching ratio λ.

FIG. 3 shows a graph in which the dynamic elastic modulus E' measured at room temperature under each stretching condition is plotted against the stretching conditions. The dynamic elastic modulus E' at room temperature shown in FIG. 3 corresponds to the tensile elastic modulus E determined from the initial slope of the stress-strain curve by Tensilon.

In particular, it can be seen in FIG. 3 that the dynamic elastic modulus E' at room temperature has a peak at a stretching temperature of around 110 to 120 DEG C. for each stretching ratio. On the other hand, FIG. 4 shows a plot of the tensile modulus E determined from the initial slope of the stress-strain curve obtained by the Tensilon tensile test for each stretching condition.

The behavior of the tensile modulus E shown in FIG. 4 with respect to each stretching condition is almost the same as that of the dynamic modulus F'. The name of this case is also that it is stretched 20 times at a stretching temperature of 120℃. The elastic modulus of the sample was approximately 42.1 GPa, which is a fairly high tensile modulus.

〔effect〕

As mentioned above, the polyethylene film of the present invention is
It has extremely excellent mechanical strength, can be widely used for various purposes requiring strength, and is easy to manufacture, so its industrial value is extremely high.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an apparatus for manufacturing the film of the present invention, FIG. 2 is a partially enlarged view, and FIGS. 3 and 4 are
FIG. 3 is a diagram showing the relationship between the elastic modulus and stretching temperature of the film of the present invention, respectively. 1... Delivery roll, 2... Take-up roll, 3
...High-density polyethylene film (raw material film),
4...Plate heater, 4'...Heating part, 5...
Cooling section, 6... Cooling medium, 7, 8... Guide roll.

Claims (1)

[Scope of Claims] A method for producing a film in which a high-density polyethylene film is heated and stretched under tension at a temperature above the crystal dispersion temperature of polyethylene but below the melting point, the method comprising: ) is 100,000 to 200,000,
and the molecular weight distribution [Mw/number average molecular weight (Mn)] is 2 to
7, and furthermore, the method for producing a high-density polyethylene film is characterized in that the extremely small width of the film is successively heated and stretched.