JPS60124611A - Polypropylene film of good stretchability - Google Patents

Abstract

PURPOSE:A PP film low in unevenness of thickness and good in stretchability, obtained by molding a specified PP into a film. CONSTITUTION:Propylene is bulk-polymerized in the presence of a catalyst system comprising a MgCl2-carrying aluminum compound, an ester compound, etc., and low-stereoregularity PP is removed from the product by using a low-boiling hydrocarbon to obtain a PP having a limiting viscosity as determined in tetralin at 135 deg.C of 1.4-1.7dl/g, a ratio of MI10 to MI2>=18.5 (wherein MI2 is a melt index as determined at 230 deg.C and a load of 2.16kg, and MI10 is a melt index as determined at 230 deg.C and a load of 10kg) and a ratio of Mw to Mn>=6 (wherein Mw is a weight-average MW, and Mn is a number-average MW). A PP film obtained by melt-extruding the above PP and casting it in a cooling drum is longitudinally stretched at 120-150 deg.C and a ratio of 4-10, laterally stretched at 130-165 deg.C and a ratio of 4-15, and then heat-treated at 80-170 deg.C while it is given a lateral relaxation of 0-25%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polypropylene film which has good stretchability and whose quality is stable even when scraps are reused.

Stretched polypropylene film has excellent tensile strength, rigidity, and transparency, and has good heat resistance. It also has excellent oil resistance and electrical properties, making it suitable not only for various packaging films but also for industrial applications such as adhesive tapes. It is widely used as a film and in electrical parts such as capacitors.

Conventionally, stretched polypropylene films used for these purposes have been designed to have good stretchability and mechanical strength, so their intrinsic viscosity (17) (13
(measured in tetralin at 5°C) is 1.9-2.5 dl1
11 is generally used.

However, when obtaining a polypropylene film having such a degree of ω, the raw material displacement is relatively high, so the back pressure during extrusion is high and uniform sheeting becomes difficult. For this reason, sheeting is usually carried out by increasing the melt extrusion temperature and lowering the apparent viscosity. The difference becomes larger. For this reason,
When scraps obtained from both ends of the film are reused and formed into a film, the (5) of the raw material polypropylene and the scrap are different, resulting in uneven flow during extrusion. There was a problem in that the quality of the obtained film was inconsistent, such as uneven scratching.

On the other hand, if the purpose is simply to form a film, a polypropylene with a small value ((i)) is used; (iii) sheeting is possible at a relatively low temperature, so there is almost no difference in (5) between the raw material polypropylene and the film.

That is, even if scraps from both ends of the film are reused, the above problem does not occur. However, the stretchability of the thus obtained polypropylene film, especially the biaxial stretchability, was not stable, and there were problems in applying it to stretched film applications.

As a result of intensive studies under such circumstances, the present inventors found that polypropylene having specific physical properties is suitable for sheeting.
We have arrived at the present invention by discovering that there is almost no change in the film, and the stretchability of the obtained film is also good. ~1.7 dVll, (ti)
230 C (D temperature [-1', the ratio of the melt index (Mll) at & at a load of 2.16 to the melt index (MIso) at a load of 10 kl? M110/M
■2 is 18.5 or more, and (10 weight average molecular weight (acceptable) and number average molecular weight (Atsuji to Hokuma, <- is 6 or more It is.

In the present invention, (5) of polypropylene film measured in tetralin at 135°C is 1.4 to 1.7 dl.
/g, preferably 1.5 to 1.65 d&/11. If (5) is larger than 1.7 dl/11, the back pressure during extrusion will be large and the object of the present invention cannot be achieved. On the other hand, if @] is 1.4 d&/El,
The stretchability is poor, and the mechanical strength of the stretched film is not improved, which is not preferable.

In addition, in the present invention, a temperature of 230° C. and a load of 2.16 kl were measured according to Japanese Industrial Standards -7210 for polypropylene film. MI snow and load NlO boiled MI
l, the ratio (M11o/MI*) is 18. -5 or higher is required. This MI 1o /MI- is 18
．． If it is less than 5, the stretchability is poor. Also Mll. /
The upper limit of MI is not limited, but is preferably 35, more preferably 25.

Furthermore, in the present invention, the corner ξ is preferably 6 or more.
It needs to be 6.5 or higher. If the ratio is less than 6, the stretchability will be poor. Also MW/'MN
Although the upper limit of is not limited, it is preferably 10.

Note that the pubic area of the polypropylene film of the present invention is
For permeation chromatography, the column is 5
Hodex A-80M (1 bottle) was used, the solvent was orthodichlorobenzene, the temperature was 140°C, and the flow rate was 1. Measured with O1m1n. Sample concentration is 0.05
wt/vo1%. Molecular weight calibration was also performed using a monodisperse polystyrene molecular weight standard.

In the present invention, the above-mentioned
], MIs o/'hliI 2 and Mw/MN are almost the same measured values for the raw material polypropylene and the stretched polypropylene film. It is sufficient if any one of the measured values satisfies the above physical property values. Further, by measuring these physical properties of raw polypropylene, raw polypropylene that can be used to achieve the object of the present invention can be found, which is also a great advantage of the present invention.

The method for producing the polypropylene raw material used in the polypropylene film of the present invention is not particularly limited, but a preferred example is a titanium tetrachloride catalyst supported on magnesium chloride, an organoaluminum compound, an ester compound, etc. according to a known method. Polymerizing propylene by a bulk polymerization method using propylene itself as a solvent using a catalyst system consisting of a third component, and then removing polypropylene with low stereoregularity soluble in propylene with a low boiling point hydrocarbon such as propylene. obtained by. The polymer may contain any commonly used additives, if necessary.

The polypropylene raw material thus obtained is melt-extruded and then cast onto a cooling drum according to a conventional method to obtain the polypropylene film of the present invention with good stretchability.

This polypropylene film can be made into a stretched film by subjecting it to a conventionally known stretching machine. For example, to show a method for making a biaxially stretched film, the polypropylene film is fed to a longitudinal stretching machine, and the film temperature is 12
Stretched 4 to 10 times lengthwise at 0 to 15oC, then stretched 4 to 15 times in the transverse direction using a tenter at a film temperature of 13Q to 165C, allowing 0 to 25% relaxation in the transverse direction to 80 to 170C.
This method involves heat treatment.

Of course, it may be stretched again after these stretching steps.
A stretched film can also be obtained by stretching or rolling only along the -axis.

The thickness of the film of the present invention is not particularly limited, but! 3 to 150 for biaxially stretched film as a stretched film
In the case of a 1-axis stretched film, the thickness is preferably 10 μm to 10 μm.

Furthermore, in order to obtain the stretched polypropylene film of the present invention, it is of course possible to directly apply the polypropylene film produced from the raw material polypropylene to a stretching machine, which is also within the scope of the present invention. .

Furthermore, the amount of ash contained in this film was reduced to 100 p.
By keeping the content at pm or less, preferably 30 ppm or less, the resulting film has high dielectric breakdown voltage9 and excellent electrical properties, making it particularly preferable as an insulating material for capacitors.

Since the polypropylene film of the present invention has specific physical properties, it has the following excellent percentage characteristics.

(1) Because the melt of the raw material polypropylene flows easily,
A high-precision filter can be used during melting, and foreign matter in the film can be almost completely removed. Furthermore, there is little unevenness in the thickness of the obtained film.

(2) Because the melt of the raw material polypropylene flows easily,
Melt extrusion temperatures can be lower than those of conventional polymers. This not only saves energy, but also prevents thermal decomposition and gluing during extrusion, resulting in a high-quality film. Furthermore, there is little scattering from the die during extrusion, which not only provides an excellent working environment, but also prevents productivity from decreasing due to the adverse effects of scattering.

(3) Dodecylbenzene and condenser oil K vs. -J
- Its swelling resistance is superior to that of ordinary polypropylene film, and it exhibits excellent properties as an insulating material for oil-temperature condensers and oil-impregnated cables.

Embodiments of the present invention will be described below with reference to Examples and Comparative Examples.

Examples 1-4. Comparative Examples 1 to 3 Polypropylene having the HMI 1 o/MI z shown in Table 1 was extruded at the extrusion temperature and extrusion pressure 150 ki as shown in Table 1, and then pulled in a cooling drum at 30°C. I got the film.

Next, in step A, this film was guided to a stretching roll heated to a surface temperature of 135°C, longitudinally stretched 5 times, then transversely stretched 10 times in a tenter heated to 160°C. It is recommended to perform heat fixation treatment before relaxing.
The stretchability of the obtained stretched film was evaluated. ■l) + NIIy/vI of polypropylene film
Hr Mll (1/MI2, as well as the results of evaluations on lateral stretchability, lateral thickness unevenness, and foreign matter in the film are shown in Table 1.) These evaluations were performed as follows.

(1) Lateral stretchability: The number of breaks during horizontal stretching was calculated.

○: 1 time/hr or less, Δ: 2 to 5 times/hr %
6 times/hr or more (2) Thickness unevenness: Thickness unevenness measured over a length of 5 m in the lateral direction, according to the following classification.

085% or less, 615-20%, ×: 20% or more (3) Foreign matter: Directly fire two polarizing plates and insert the film between the two polarizing plates so that the measured total extinction position is reached. Light is incident from below perpendicular to the plane of polarization, and when viewed from above with the naked eye, the number of glittering pieces is counted and evaluated on the following three levels.

○; l Oi solid 70. 3 m2Jfi below, Δ
;1O-1oo pieces 10, 3 m2, x; ioo pieces/
0.3 m2 or more As is clear from Table 1, the film of the present invention not only has excellent film formability and stretchability, but also has excellent film quality such as thickness unevenness and foreign matter.

Claims (1)

[Claims] (i) Intrinsic viscosity measured in tetralin at xas°C (5)
is 1.4 to 1.7 d&/I, (ii) 230℃
Melt index at boiling temperature of 2.16 at load 2.16 (
Ml, ) and melt index at a load of 10 kg (
The ratio MIto/M11 with MIIO) is 18.5 or more, and GiD weight average molecule i1 (%) and number average molecule j1-(
A polypropylene film with good stretchability, characterized by having a ratio of 6 or more with respect to .