Stock material or miscellaneous articles – Structurally defined web or sheet – Physical dimension specified
Patent
1987-07-07
1990-09-04
Lesmes, George F.
Stock material or miscellaneous articles
Structurally defined web or sheet
Physical dimension specified
428409, 525240, 264564, C08L 2304
Patent
active
049543911
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a high density polyethylene type film with a remarkably superior transparency and a process for production thereof, more particularly, it relates to a transparent high density polyethylene type film with a good balance of strength in the M (machine) direction and T (transverse) direction, a remarkably high impact strength of the film, and a large Young's modulus, and a process for production thereof.
The present invention further relates to a high density polyethylene type film having a high strength, superior transparency, and good heat sealability, and a process for production thereof.
BACKGROUND ART
In the past, to obtain a high density polyethylene (hereinafter referred to as "HDPE") transparent film, the general practice has been to pass a molten resin through a slit die and cool it rapidly by chill rolls or water. However, with this method, to improve the formability, use has been made of resins with low molecular weights. Therefore, the transparent film obtained has had a relatively weak strength.
To obtain a strong film through the use of high molecular weight HDPE in forming a film, the general practice has been to use air-cooled inflation. With this method, it has been possible to obtain a film with superior strength through balancing the molecular orientation with the blow ratio, but since air is used for the cooling, only translucent or semitransparent films have been obtainable.
Attempts have been made to achieve a certain degree of transparency (haze of about 15%) even with high molecular weight HDPE by passing the film through heated rolls having a surface gloss, so as to enhance the surface smoothness, but a transparency of a haze of 10% or less has not been obtained.
To make an HDPE film transparent, it is known to uniaxially draw a semitransparent HDPE film to a ratio of 5 to 10 and press it between rolls. The film obtained by this method does indeed have a superior transparency, but features a remarkable orientation in the drawing direction or rolling direction, and thus there is remarkable directionality in the aspect of film strength, resulting in a tendency to easy tearing, the obtaining of an insufficient strength, an uneven heat contraction, warping in the film, heat sealing inability, and other defects.
In the past, to obtain a high strength film from an HDPE film, the primary practice has been to use the inflation process. In inflation forming to obtain a high density film, as disclosed in Japanese Examined Patent Publication (Kokoku) No. 56-5172 and Japanese Unexamined Patent Publication (Kokai) No. 60-15122, it has been necessary to obtain a balance in the longitudinal and lateral orientation.
That is, if the orientation in the longitudinal direction is too great, longitudinal tearing easily occurs and if the orientation in the lateral direction is too great, a high strength film can not be obtained. Therefore, in general, in inflation forming, consideration is given to the ratio of the inflation ratio of the bubble and the diameter of the die, i.e., the blow ratio, the take up speed, and the frost line height. However, although it has been possible to impart strength to a film with a balance in the longitudinal and lateral orientations, in the case of a high density polyethylene, the transparency is poor, and thus the applications are limited at the present stage.
To improve the transparency of high density polyethylene type film, several other methods have been proposed.
For example, Japanese Unexamined Patent Publication (Kokai) No. 53-31768 proposes the technique of passing an original material thermoplastic resin film between a pair of rollers set to a clearance smaller than the thickness of the film and having a surface roughness of 0.5 s or less, at a temperature lower than the melting point or the softening point of the film, or lower, for rolling to obtain a film having a thickness smaller than the thickness of the original material film and a transparency of a haze of 4% or less. This technique is particularly character
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Journal of Polymer Science, vol. 20, No. 94, Apr., 1956, pp. 209-211, New York; J. J. Keane et al.: "Light Scattering from Oriented Polyethylene Films".
O. J. Sweeting: "The Science and Technology of Polymer Films", vol. 2, 1971, pp. 152-155, Chapter 2, Wiley, New York; O. J. Sweeting: "Polyethylene".
Chemical Abstracts, vol. 91, No. 24, 12/10/79, p. 13, Abstracts No. 193826j; A. Yoshino et al.: "Formation of Oriented-Extended-Chain Crystals on high-density Polyethylene and Their Transparency"; & Kobunshi Ronbunshu 1979, 36 (9), 581-7.
Kotani Terumitsu
Saito Yoshimasa
Taka Toshio
Lesmes George F.
Showa Denko Kabushiki Kaisha
Zirker D. R.
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