JPH03277528A - Highly transparent film capable of longitudinal tearing - Google Patents

Abstract

PURPOSE:To obtain a film having an excellent transparency in which, in the case of tearing into an orthogonally directional strip with respect to the longitudinal direction thereof, it may be torn only into a parallel strip with respect to the longitudinal direction by performing a rolling process on a crystalline polyolefine resin film by means of a roll having a specific surface roughness. CONSTITUTION:The surface roughness of a roll used for manufacturing a film is set, ordinarily in 1S or below, preferably, 0.5 or below, and further preferably, 0.2S or below. It is preferable that the film is in the range of from 3 (g) to 200 (g) or below in its tearing strength obtained by an Elmendorf tearing test, and more preferably, set in the range of from 10 (g) to 100 (g). And, the film is 2% or below in its whole haze, and the haze difference (2.Hs-Hi) obtained from the inner Heyze (Hi) and surface haze (Hs) is selected to 1.5 or below, preferably, 1.3 or below therefor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a packaging film that is easy to tear into strips parallel to the longitudinal direction of the film and has excellent transparency.

[Prior Art] Packaging films are required to have the basic functions of protecting the contents, ease of handling, and transmitting product information.
Recently, in addition to these basic functions, there has been a growing trend for packaging materials to have strong functionality that is convenient for consumers to use.

Generally, packaging bags made of film are often opened by hand at the consumption stage, so it is an extremely important condition that they can be easily torn.

Furthermore, it is desired that the material is easy to tear and that the direction of tearing is linear and can be torn only in a fixed direction. Also,
Since it is strongly required to be able to confirm the actual color, shape, etc. of the contents through the packaging film, it is also very important to improve the transparency of the film.

From this point of view, there is a strong demand for transparent packaging materials that are easy to open, and various packaging materials and packaging forms have been developed to meet this demand.

A method for imparting unidirectional tearability and transparency to a crystalline polyolefin resin is generally a uniaxial stretching method. Films stretched in the longitudinal direction (film-forming direction) have improved transparency, while strips in the longitudinal direction (stretching direction) tend to tear easily.
It is known that cracks are difficult to form in the transverse direction, which is perpendicular to this direction.

[Problems to be Solved by the Invention] In the above-mentioned prior art, even if the film-like material obtained by the stretching method is torn into strips parallel to the longitudinal direction (stretching direction), it cannot be torn in the parallel direction only. The fissure may deviate laterally without the eye running.

If the contents are in liquid or powder form, if the tear goes in any direction other than the specified direction when opening, there is a risk of the contents scattering, so when resealing, fold the opening and reseal. It also becomes difficult.

Further, when a crystalline polyolefin resin film is highly stretched, the spherulites are destroyed to some extent, thereby improving the transparency inside the resin layer to some extent.

However, since the smoothness of the surface remains almost the same, the scattering of visible light does not decrease much. For this reason, the degree to which transparency can be improved by the stretching method is limited to a relatively low level. In other words, even if the transparency inside the resin layer is high,
If the surface smoothness of the resin layer is low, a large amount of visible light will be scattered on the surface of the resin layer, so that the high transparency inside the resin layer cannot contribute to the overall transparency at all. The present inventors have obtained a film-like product that has tearability that produces linear strips parallel to the longitudinal direction of the film, and that boasts extremely high transparency even though it is made of a crystalline polyolefin resin. As a result of intensive research into strategies, we have completed the present invention.

[Means for Solving the Problems] As a result, the present inventors found that when a crystalline polyopine resin film is rolled using a roll having a specific surface roughness, the film becomes longitudinally strip-like. We have discovered that the ease with which objects are torn is greatly improved, and that the scattering and reflection of visible light both inside and on the surface of the film-like object is extremely reduced, resulting in excellent transparency. The present invention was completed based on this knowledge.

As is clear from the above, the film-like product of the present invention is a film-like product suitable for packaging, which has excellent tearability that produces straight strips parallel to the longitudinal direction, and has extremely excellent transparency. be.

That is, the film-like material of the present invention has a tear strength of 3 (g) or more and 200 (g) to produce strips parallel to the longitudinal direction.
Within the following range, the total haze is 2% or less, and the Bayesian difference (
2.Hs-H1) is a film-like material made of a crystalline polyolefin resin of 1.5 or less. Moreover, even if an attempt is made to tear this film into strips in a direction perpendicular to the longitudinal direction, it can only be torn into strips parallel to the longitudinal direction, making it a film suitable for packaging.

The crystalline polyolefin resin used to create the film-like material of the present invention may be any polyolefin resin that has crystallinity (there are no restrictions on the type of raw material resin. Examples include: ・High-density polyethylene, medium-density polyethylene, or linear low-density polyethylene; ・Highly stereoregular homopolymerized polypropylene or copolymerized polypropylene; ・Polybutene-1, etc.; ・Ethylene or propylene as the main component; other α
- Crystalline polyolefin resins consisting of copolymers with olefins or polar vinyl monomers, and mixtures of two or more of these resins.

In addition, modified resins obtained by copolymerizing or grafting derivatives such as maleic acid, acrylic acid or methacrylic acid, unsaturated carboxylic acids such as fumarushun, other acid anhydrides or esters to the above resins, and the above-mentioned modified resins are also available. Modified resins obtained by treating the resin with ionizing radiation or crosslinking with a crosslinking agent can also be used depending on the purpose.

Among these various raw material resins, preferred ones include highly crystalline high-density polyethylene, medium-density polyethylene, and highly stereoregular propylene homopolymer.

In the present invention, the crystalline polyolefin resin includes:
Various fillers (or reinforcing materials) can be added to the extent that the transparency is not substantially reduced. Examples of fillers that can be used include fibrous fillers such as glass fiber, carbon fiber, wholly aromatic polyester fiber, wholly aromatic polyamide fiber, and vinylon fiber, flake fillers such as mica and talc, and spherical fillers such as glass peas. Examples include amorphous fillers such as calcium carbonate and wood chips.

The surface of these fillers (or reinforcing materials) is preferably subjected to a treatment that imparts affinity to the resin to be blended. Examples of such treatments include addition of unsaturated carboxylic acids or acid anhydrides, addition of unsaturated amines, and rubbery coating.

In addition to these fillers, moisture absorbers, extenders, colorants, flame retardants, deterioration inhibitors, antistatic agents, lubricants, etc. can be added.

In the present invention, the crystalline polyolefin resin is melt-kneaded and formed into a sheet or film (sometimes referred to as a "sheet-like material") by a known molding method such as a T-die method or an inflation method, The obtained rolling sheet or film (this may be referred to as a "rolling sheet material") is subjected to a rolling treatment.

Rolling in the present invention refers to rolling a sheet material made of the crystalline polyolefin resin described above at a specific rolling reduction rate between one or more pairs of rolls at a temperature below the melting point (defined later) of the resin. say. If rolling treatment is attempted on the sheet at a temperature higher than the melting point of the crystalline polyolefin resin, the sheet material for rolling will melt, so transparency cannot be improved, and the molten resin will adhere to the roll surface. Problems such as these are likely to occur. In the rolling process, the rolling operation may be repeated as necessary, the sheet may be preheated before rolling, or heat treatment may be performed after rolling.

The rolling reduction ratio r (%) in the present invention refers to the thickness of the material resin layer before rolling (h,) and the thickness of the film-like material after rolling (h2).
It can be expressed by the following equation.

r = 100 (hl - h2) / h The rolling reduction ratio of the rolled sheet or film (this may be referred to as a "rolled film material") is usually preferably in the range of 60% or more and 95% or less, more preferably is set in the range of 70% or more and 90% or less.

The surface roughness of the rolling roll used to create the film material suitable for the packaging of the present invention is usually set to IS or less, preferably 0.5S or less, and more preferably 0.2S or less. This is important in order to reduce the scattering of visible light on the surface of the rolled film.

The film material suitable for packaging of the present invention preferably has a tear strength of 3 (g) or more and 200 (g) or less, more preferably 10 (g) or more and 100 (g) or less, as determined by the Elmendorf tear test. shall be. If the tear strength is less than 2.5 (g), the strength of the film itself will be too low and its function as a packaging material to protect the contents will be insufficient. Tear strength is 210
(g) In the above cases, tearing by hand becomes difficult.

The film material suitable for packaging of the present invention has a gold haze of 2%.
Below, the haze difference (2·Hs-H1) calculated from the internal haze (H1) and the surface haze (f(s)) is selected to be 1.5 or less, preferably 1.3 or less.The gold haze is 2. If the haze difference is 5 or more, a highly transparent film cannot be obtained.Also, if the haze difference is 1.7 or more, the scattering of visible light due to the external haze becomes too large, so it is not possible to obtain a highly transparent film. It cannot be said that it is a film-like material.

The roughness of the roll surface used in the present invention is JISBO6
It was measured in accordance with the 01 test method.

[Preferred Embodiments] The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

The tearability evaluation shown in the table refers to the case where a film-like material is easily torn in a straight line in the vertical direction when it is torn by hand.
○", - The case where the tear did not occur in a straight line was expressed as "x".

Note that the characteristics of the film-like material were measured by the following method.

(1) Melting point of resin: represents the temperature at which the peak of the curve measured by DSC (differential scanning calorimeter) is located according to JIS K7121.

(i1) Tear strength: Measured according to ASTM 01922.

(ii1) Total Haze: Measured according to ASTM D1003.

(iv) Internal haze: Measured in the same manner as total haze by coating both sides of the film with liquid paraffin. (V) Surface haze: Calculated from the difference between total haze and internal haze.

Examples 1-2 and Comparative Examples 1-2 Two types of sheet-like materials for rolling [thickness 0.20 mm x width 25
0mm or thickness 0.15mm x width 250mm; Polypropylene homopolymer (abbreviated as rPPJ). Melt flow rate 1.Og/10 minutes, density 0.90g/cc,
melting point 162℃) roll diameter 300°trrmXfp
Each was supplied to rolling rolls with iA400■ and roughness of 0 and 2S, and the rolling reduction rate was 75 at a rolling roll temperature of 110°C.
% or 67%, two types of rolled film products with a thickness of 0.050 m+n were obtained.

Table 1 shows the total haze, internal haze, surface haze, and tear strength of each rolled film material.

In addition, when rolling was carried out under the same rolling conditions as Comparative Example 1 with a roll having a surface roughness of 2S, as in Comparative Example 2, the thickness was 0.050.
The results for the unrolled film of mm are shown in the first column.
Shown in the table.

Examples 3-4 and Comparative Examples 3-4 Two types of sheet-like materials for rolling [thickness 0.20 mm x width 25
0 mm or 0.15 mm x width 250 mm; ethylene-propylene random copolymer (abbreviated as rR-PPJ). Melt flow rate 2.2 g/10 min, density 0, 90
g/cc, melting point 142°C, ethylene content 4 mol% and propylene content 96%), rolling temperature 90°C.
Rolled in the same manner as in Example 1 to obtain a 0.045 mm thick sheet.
A rolled film of various types was obtained. However, the rolling reduction ratio was set to 78% or 70%, respectively.

Table 1 shows the total haze, internal haze, surface haze, and tear strength of each rolled film material.

In addition, as Comparative Example 3, when rolling was performed using a roll with a surface roughness of 2S under the same rolling conditions as in the above example,
As Comparative Example 4, the results for an unstretched film with a thickness of 0.045 mm are shown in Table 1.

Examples 5-6 and Comparative Examples 5-6 Two types of sheet-like materials for rolling [thickness 0.30 mm x width 2
501 or thickness 0.20mm x width 250mm; ethylene-brobylene block cobolimer (abbreviated as rB-PPJ). Melt flow rate 0.5g 710 minutes, density 0.
91 g/cc, melting point 160°C, ethylene content 8 mol%
and propylene content: 92 mol%)] was rolled in the same manner as in Example 1 at a rolling temperature of 110°C to a thickness of 0.
．． Two types of rolled film products of 0.050 mm were obtained. However, the rolling reduction ratio was set to 83% or 75%, respectively.

Table 1 shows the total haze, internal haze, surface haze, and tear strength of each rolled film material.

In addition, as Comparative Example 5, the surface roughness was 2S under the same rolling conditions.
Table 1 shows the results for a non-stretched film with a thickness of 0.050 mm as Comparative Example 6.

Examples 7 to 8 and Comparative Examples 7 to 8 Two types of sheet-like materials for rolling [thickness 0.30 mff1 x width 250 mm or thickness 0.22 mm x width 250 mmH high density polyethylene homopolymer (abbreviated as rPEJ), melt index 0. 8g/10 minutes, density 0.94g
/cc, melting point: 130°C)] at a rolling temperature of 90°C in the same manner as in Example 1 to obtain two types of rolled film products each having a thickness of 0.45 mm. However, the rolling reduction ratio was set to 85% or 80%, respectively.

Table 1 shows the total haze, internal haze, surface haze, and tear strength of each rolled film material.

Further, when rolling was performed using a roll with a surface roughness of 2S under the same rolling conditions as Comparative Example 7, the thickness was 0.
Table 1 shows the results for unstretched films of 0.045 mm.

[Effects of the Invention] The rolled film of the present invention has the characteristics of being easy to tear by hand and being tearable in a straight line and only in a certain direction.Although it is made of crystalline polyolefin resin, it has extremely high transparency. be.

The rolled film material of the present invention has the advantage of being easy to tear parallel to the longitudinal direction and having high transparency, and can be used for various packaging applications, such as general packaging, food packaging, pharmaceutical packaging, etc. It is suitable as a packaging material for medical products, etc.

Claims (1)

[Claims] (1) Tear strength parallel to the longitudinal direction is 3 (g) or more, 20
0 (g) or less, the total haze is 2% or less, and the haze difference (2・Hs-Hi) determined from the internal haze (H1) and the surface haze (Hs) is 1.5 or less. A highly transparent film-like material that can be longitudinally torn, characterized in that it is a film-like material made of polyolefin resin.