JPS62122741A - Transparent film made of high density polyethylene - Google Patents

Abstract

PURPOSE:To make a film highly transparent without inhibiting its strength, by specifying the characteristics of the film formed from a thermoplastic resin which contains more than required ratio a high density polyethylene having density more than a specific value. CONSTITUTION:By using a thermoplastic resin containing a high density polyethylene having density more than 0.935g/cm<3> in more than 70%, there is formed a transparent high density polyethylenic film of haze value less than 10% having the following properties; a) surface roughness less than 0.1mu at the film of thickness less than 200mum, b) C axis orientation function (Fc) of the crystal in the film more than 0, 1, and c) the difference of refractive indices DELTAn between the non-crystalline part and the crystalline part in the film less than 0.1070. Surface haze is caused from the light scattering owing to minute structural unevenness which occurs by the crystallization of film surface layer, and is extremely improved as the roughness of the film surface is made less than 0.1mum. Also the transparency of the film inside is better as Fc is larger and DELTAn is smaller. So when Fc is larger than 0.1 and DELTAn is smaller than 0.1070, the transparency of the HDPE film which has a smooth surface having roughness less than 0.1mu is more extremely improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high-density polyethylene film with outstanding transparency, and in particular, the film has a good balance in the M direction and the T direction, and has an extremely high impact strength. The present invention also relates to a transparent high-density polyethylene film having a large Young's modulus.

[Conventional technology]

Conventionally, to obtain a high-density polyethylene (hereinafter sometimes referred to as HDPE) transparent film, a method has generally been used in which a molten resin is passed through a slit die and rapidly cooled with a chill roll or water. However, in this method, the resin used has a low molecular weight in order to improve processability, and therefore the strength of the resulting transparent film is relatively low.

In addition, the air-cooled inflation method is generally used to form films using high-molecular-weight HDPK in order to obtain film strength. However, because of the cooling in air, only opaque or translucent films can be obtained.

In addition, by passing this film between heated rolls with a glossy surface to improve its surface smoothness, even polymeric fit HDPE can be coated with a haze (HaZ6).
) Value: about t5X] K Crab, Haze, for which attempts have been made to make it transparent It is impossible to obtain excellent transparency with a value of 10% or less.

In addition, in order to make the HDPK film transparent, it is necessary to uniaxially stretch the HDPE film obtained from Ushi-transparency by 3 to 5 times.
A method of rolling between rolls is known. However, although the films obtained by these methods certainly have excellent transparency, the films obtained are significantly oriented in the stretching and rolling directions, resulting in significant directional properties in terms of film strength. The disadvantages were that it was easy to tear, that it did not have sufficient strength, and that the heat shrinkability was uneven, causing distortion in the film.

[Problem that the invention seeks to solve]

The present invention solves the drawbacks of the prior art, and provides a highly transparent film with good balance in the M and T directions, high impact strength, and a high Young's modulus. The overall purpose is to provide HDPE-based films.

[Means for resolving problems] and [Operation] The present invention provides a film having a thickness of 200 μm or less made of a thermoplastic resin containing at least 70% of high-density polyethylene with a density of 0.9 s s ti 7 cm 5 or more. The surface roughness of the film is 0.1μ or less, the C-axis orientation function (Fc) of the crystals in the film is 0.1 or more, and the difference Δn in the refractive index between the amorphous part and the crystal part in the film is is 0.107
A transparent high-density polyethylene film having a haze value of 10% or less and a haze value of 0 or less.

To explain the effects of the present invention together with its outline, the transparency of a film can be divided into the surface and internal transparency of the film. HDP molded using air-cooled inflation method
K film (for example, 40 μ thick [melt flow index (M I ) = 0.0411/10 min
As a result of measuring the transparency of the density (DJ = 0.94927 crrr') by dividing into surface factors and internal factors, the total haze value (hereinafter sometimes simply referred to as haze) of this film was, for example, 75%. Of these, the surface haze can be separated into 60% and the internal haze is 15%.As a special case, this surface haze is caused by scattering of light due to the unevenness of the micro-a structure that occurs during the crystallization of the film surface layer. In other words, by making the entire surface smooth, it is possible to significantly improve the surface roughness of the film to 0.1μ or less in the present invention. This is the same principle that can be made transparent by pasting cellophane tape, and an example of this application is H.
Methods of laminating highly transparent resins on both sides of a DPE film or coextrusion molding are known.

However, as mentioned earlier, this method is only a method of reducing scattering on the surface of the film, and sufficient transparency cannot be obtained by this method alone.

Therefore, unless the internal haze is eliminated, it is impossible to obtain an excellent transparent film with a haze of 15% or less in the above case.

Therefore, the present inventors thoroughly investigated the factors that cause this internal haze, and found that the cause of internal haze is due to fluctuations in the refractive index of the crystal lattice axis orientation (a, b, c@l of polyethylene). , and the fluctuation of the refractive index resulting from the difference Δn in the refractive index between the amorphous layer (part) and the crystalline layer (part).The orientation of the crystal lattice axis is determined from the orientation function Fc, and Δn f Lolanz
- As a result of researching the film transparency function using the Lolanz equation and various data, it was found that Fc and Δn are closely related to the internal transparency of the film.

That is, it has been found that the larger pc is (the C-axis orientation becomes more uniform) and the smaller Δn is, the lower the transparency inside the film becomes.

As a result, Fc
The inventors have discovered that when Δn is 0.1 or more and Δn is 0.1070 or less, the transparency of HD PE films with a smooth surface with a surface roughness of 0.1 μ or less is even more significantly improved, leading to the present invention. .

Here, the C-axis orientation function FC is determined from the polarized infrared spectrum according to 5ta1n. (Macromolec
ulθFa = (D 7 s o-' ) / (v7
s o +z ) Fb = (D, 2o-') / (
D, 2o + Z) Fa +Fb -1-Fc = 0 However, D730% D72° is 7501: M, 7
The infrared dichroic ratio at 20 m-', Fa, Fb, and Fc are the orientation functions of the a, b, and c axes of the crystal, and the difference Δn in the refractive index between crystal and amorphous is Lolenz −L
Variant of OLENZ (Plastic Vol. 51)
A 2P34) 6 n ρ where n is the refractive index of the film, which was measured using an Atsube refractometer.

ρ is the film density, which was obtained from density piping.

Δρ is the density difference between crystal and amorphous, and the following literature value was used.

Crystal density: 1.011/crW5E, RoWai
ter:J, PolymarSci 2 1 56
1°19 amorphous density: 0.851/ffi'A
, in-Doolittla: J.

App, Phys, 22 1471 °19Haz
Measurement of e is based on ASTM D-1003.

Furthermore, the surface roughness, which indicates the smoothness of the film surface, is determined by JIS
It was measured in accordance with the BO601-55 test method.

The reason why the resin in the present invention is a thermoplastic resin containing at least 70% of HDPEtl with a density of 0.95511/cm3 or more is because it has excellent properties as an HDPK film, such as stiffness, Young's modulus, and barrier properties (moisture resistance).
, density 0.955.9 as a property having impact strength etc.
/1M1' or more, and even if various additives, extenders, blending resins, etc. are blended to modify the resin, the above! (This is to take advantage of these properties by containing at least 70% DPE.

In addition, in the present invention, the film surface roughness is set to 0.1μ or less, and the external unevenness is large in the case of HDPE, and scattering of light on the surface causes worsening of external haze. This is because this is one of the conditions under which the desired highly transparent film of the present invention can be achieved.

The high-density polyethylene film of the present invention may be passed between a pair of rolls having a smooth surface at a temperature below the melting point so that the original film has a thickness of less than that. Instead of passing the material between rolls at the same temperature, it is preferable to use three heated rolls, with a temperature difference between the rolls, and then rapidly cool.

For example, a raw film made of high-density polyethylene having a density of 0.9551/- or more is passed between three heated rolls under the following temperature conditions, and then cooled.

The temperature conditions of the three heating rolls are as follows: the first heating roll (hereinafter referred to as R1), the second heating roll (hereinafter referred to as R2), and the third heating roll (hereinafter referred to as R2) according to the order in which the raw film passes through the three heating rolls. Assuming a heated roll (hereinafter referred to as R3), the temperature of R2 is higher than the temperatures of R4 and R3, and R
The temperature in step 2 is preferably 1050 or higher and below the melting point of the film.

For example, a metal roll having a hard chrome plating layer on its surface is used as each heating roll. It's good to be well-educated.

Others have been processed or finished to have a mirror-like luster. Rolls with smooth surfaces can be used.

The heating roll needs to have a temperature higher than that of its second roll (R2), the other first roll (R1), and the third roll (R3). That is, the raw film is preferably passed between heating rolls consisting of a system of R1, R2, and R3, with the middle part set at the highest temperature and a temperature difference between the rolls.

The temperature of R1 is preferably below the melting point.

If the temperature of R1 exceeds 90C', the neck-in of the film becomes large and a good film cannot be obtained.From this point of view, the temperature of R1 is preferably 90C or less. The temperature of R3 is preferably 80C or more and 120C or less. When the temperature of R3 exceeds 120C, it is difficult to obtain good transparency, and when it is below 80C, the film adheres to the ridge 20, making it difficult to obtain sufficient transparency.

The original film is passed through the gap between the three heating rolls, which has a thickness equal to or less than the original film thickness, to form a transparent film having a thickness equal to or less than the original film thickness.

It is preferable that the rolling magnification is larger than Fi1 and smaller than Fi1.

The film after passing through the heating roll is then cooled. For example, it is cooled by two chill rolls (hereinafter referred to as R4 and R5). The temperature of these chill rolls is not particularly limited, but is preferably 70C or lower and 30C or higher.

When it exceeds 70C, it is difficult to function as a chill roll, and when it is below 50C, it is difficult to obtain sufficient flatness of the film.

[Actual beam example]

The present invention will be explained below using actual frame examples and comparative examples.

For actual frame examples and comparative examples, HDPK (D=0.949
i/crII5, MI==0.04 JI/IO minutes) by the inflation method to produce a 50μ raw film, and pass the raw film between heated rolls with surface gloss at a temperature below the melting point of the resin. Films with an upper surface roughness of 0.1 μm or less and varying Fc and Δn were produced, and the physical properties of the films are shown in Table 1.

However, in Example 3 and Comparative Example 4, HDPK and low density polyethylene (LDPR, D = 0.921, M I = 1.5
) The procedure was the same as above except that the blend system was used.

Molded material 65φEXt, die 100φ spiral 2) Temperature C1=02=C3=:H=D=190c3) Take-up speed 15m/! 1Iin reflow ratio (B, V
, R) = 4.05) Film thickness 50μ [Effects of the invention] According to the present invention, as shown in the above-mentioned actual winding example, a high-density polyethylene film with a small haze value and excellent transparency can be obtained. The film also has both transparency and film strength. Conventionally, with high-density polyethylene films, it was difficult to make them highly transparent without impairing the film strength, but the present invention improves this. What has been achieved has great industrial significance.

Claims (1)

[Claims] In a film having a thickness of 200μ or less made of a thermoplastic resin containing at least 70% of high-density polyethylene with a density of 0.935g/cm^3 or more, the surface roughness of the film is 0.1μ or less, and crystals within the film are A transparent high-density film with a haze value of 10% or less, which has a C-axis orientation function (Fc) of 0.1 or more, and a difference Δn in the refractive index between the amorphous part and the crystalline part in the film is 0.1070 or less. Polyethylene film.