JP2001294678A - Heat-shrinkable polypropylene-based film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a heat-shrinkable polypropylene-based film satisfying both low temperature shrinksbility and transparency. SOLUTION: This heat-shrinkable polypropylene-based film is made from a polypropylene-based resin, has <=1.0 specific gravity and is characterized by having <=8% haze after heat treatment and >=30% heat shrinkage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polypropylene film which is excellent in transparency and low-temperature shrinkability and which can be separated from polyethylene terephthalate by a specific gravity method.

[0002]

2. Description of the Related Art In recent years, for the purpose of improving the appearance of a packaged article, packaging for avoiding direct impact of the contents, tight packaging, label packaging for protecting glass bottles or plastic bottles and labeling products, etc. , Shrink labels are widely used. The printing is often gravure printing, usually 3 to 5 colors, and sometimes 7 or more colors. When the final product (label) is formed, the printed surface becomes the inner surface of the label, and the printed surface is viewed through the film, which causes a problem that the haze is high (opaque).
If the low-temperature shrinkage is inferior, the label set on the bottle does not fit firmly when finishing through a shrink tunnel, which causes a problem of uneven finish.

[0003] As plastic materials used for these purposes, polyvinyl chloride, polystyrene, polyethylene terephthalate, polyolefin and the like are known.
However, although the polyvinyl chloride label is excellent in shrink characteristics, it generates chlorine gas at the time of incineration and has a problem such as environmental pollution. Polystyrene and polyethylene terephthalate labels have good heat shrinkability, but the specific gravity of the polyethylene terephthalate bottle is close to the value, so that floating separation becomes difficult and the recyclability of the polyethylene terephthalate bottle is hindered.

[0004] Polypropylene has a low specific gravity and can be easily stretched, and the film is a film having good transparency.
Therefore, the heat-shrinkable film made of the polypropylene-based resin is easily float-separated from the polyethylene terephthalate bottle. However, conventional polypropylene films are inferior in low-temperature shrinkage, and therefore have a major drawback as commercial wrap films and shrink wrapping films.

As a measure to solve these drawbacks, a propylene-ethylene random copolymer obtained by copolymerizing about 3 to 5% by weight of ethylene, 1 to 3% by weight of ethylene, and 3 to 10% by weight of butene-1.
% Copolymerized propylene-ethylene-butene-1 ternary random copolymer has a biaxially stretched film, but is transparent, has excellent gloss, but has the disadvantage of inferior low-temperature shrinkage. I have. Therefore, if the amount of copolymerization is increased in order to improve the low-temperature shrinkability, the transparency will be poor.

In addition, JP-A-58-166049 discloses a multilayer shrinkable film having a linear polyethylene resin as a core layer and a propylene-ethylene copolymer as both skin layers. However, according to the findings of the present inventors, it is true that both the advantages of the linear polyethylene resin and the propylene-ethylene copolymer are combined, the transparency and the gloss are excellent, and the tear resistance is also improved to some extent. However, the low-temperature shrinkage was insufficient.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-shrinkable polypropylene resin which can satisfy low-temperature shrinkage and transparency and can be separated from polyethylene terephthalate by a specific gravity method. It is to provide a film.

[0008]

The inventors of the present invention have made intensive efforts, studies, studies, and studies to improve the above-mentioned problems of transparency and low-temperature shrinkability, and have finally completed the present invention. That is, the present invention provides a shrink label having a specific gravity of 1.0 or less, wherein a haze after heat treatment is not more than 8% and a heat shrinkage at 90 ° C. for 10 seconds is not less than 30% in a film made of a polypropylene resin. Film, preferably the polypropylene resin is propylene
A film for shrink labels, which is a 1-butene random copolymer. More preferably, the propylene-1
-The content of 1-butene unit in the butene random copolymer is 5 to
A heat-shrinkable polypropylene film characterized by being in a range of 50 mol%.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polypropylene film for shrink labels of the present invention is composed of a single layer or a laminate.
Examples of the resin in the present invention include those composed of a propylene homopolymer and those obtained by copolymerizing propylene with ethylene, butene and the like, and are preferably composed of a propylene-1-butene random copolymer.

[0010] The propylene-1-butene random copolymer uses 1-butene as a comonomer, and the content of 1-butene unit is 5 to 50 mol%, preferably 10 to 40 mol%. 1
-Butene units are determined from the characteristic absorption at 770 cm-1 using an infrared spectrophotometer. In addition, the measurement with an infrared spectrophotometer was performed for the propylene-1-butene random copolymer,
A calibration curve was prepared and quantified using quantitative values obtained by -NMR. Cold xylene soluble part of propylene-1-butene random copolymer
(CXS) is 1 to 60% by weight, more preferably 2 to 50% by weight.

Melt flow rate (MFR) of the above copolymer
Is usually 3 to 15 g / 10 minutes, preferably 4 to 10 g / 10 minutes.
The melting point of the copolymer is usually 100 to 150 ° C, preferably 110 to 140 ° C. Specifically, the melting point is about 10 m cut out from a 0.5 mm thick sheet produced by hot pressing.
g sample into a DSC measurement sample, pre-heated at 230 ° C, cooled to room temperature, held for 5 minutes, heated at a rate of 5 ° C / min, quantified from the thermograph, and measured. You.
The copolymer is, for example, a catalyst for stereoregular polymerization of an α-olefin known as a catalyst system, a so-called Ziegler-Natta catalyst, i.e., a transition metal compound belonging to Groups 4 to 8 of the periodic table and a first element of the periodic table. It can be obtained by polymerization using a compound comprising an organic compound of a Group III to 3 metal and preferably a third component of an electron donor compound.

Examples of the polymerization method include a solvent polymerization method in which polymerization is performed in a solvent and a gas phase polymerization method in which polymerization is performed in a gas phase. The method for obtaining the resin composition is not particularly limited, and includes any known method such as an extrusion melt blending method and a Banbury blending method.

The film according to the present invention may contain, for example, an antistatic agent, an anti-blocking agent,
Additives such as lubricants, cloud inhibitors, stabilizers and nucleating agents may be included.

The polypropylene film for a shrink label of the present invention can be obtained by subjecting a sheet formed by a T-die casting method using a die to at least a uniaxial direction, for example, a TD direction or an MD direction, by a known stretching method such as a tenter method or roll stretching. It is obtained by stretching. If the polypropylene film for shrink labels of the present invention is not stretched at least in the uniaxial direction, the finished surface of the container and packaging will be defective. In particular, in order to obtain a film having good low-temperature shrinkability, the film needs to be sufficiently oriented by stretching. To that end, the stretching temperature of the film is a very important factor.

When the film is stretched at a temperature ranging from 40 ° C. to a temperature lower by 10 ° C. than the melting point of the resin, preferably 40 ° C. or more, the film is sufficiently oriented and a stretched film having good low-temperature shrinkability can be obtained. However, as a result of examining stretching conditions and heat treatment conditions from the viewpoint of transparency, it is possible to achieve both low-temperature shrinkage and transparency by changing the stretching temperature, stretching ratio, and stretching speed, preferably stretching. Magnification is 4
~ 9 times.

In the present invention, the heat shrinkage is at least 30%, preferably at least 40%. If it is less than 3%, the label moldability is poor. The haze after the heat treatment is 8% or less, preferably 5% or less. If it exceeds 8%, the print is difficult to see.

[0017]

Hereinafter, the present invention will be described based on examples.
The present invention is not limited to these examples. Data and evaluation in Examples and Comparative Examples were performed according to the following methods. (1) Heat shrinkage Measure the dimensions before and after heating in the MD direction (direction perpendicular to stretching) or TD direction (stretching direction) when a sample having a length of 100 mm × 100 mm is immersed in hot water at 90 ° C for 10 seconds, and The heat shrinkage was calculated based on the equation. Heat shrinkage (%) = ((dimension before heating−dimension after heating) / dimension before heating) × 100 Measurement was performed in accordance with JIS Z 1709. (2) Haze Heat treatment was performed at 90 ° C. for 10 seconds, and the measurement was performed using a haze meter NDH1001DP manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K 7105. (3) Melting point of polymer Measurement was performed using an externally heated DSC using PTC-10A of Thermoflex series manufactured by Rigaku Denki KK as a temperature controller. (4) Measurement was performed based on MFR JIS K7210. (5) Amount of butene The 1-butene unit was measured using an infrared spectrophotometer.

Example 1 Propylene-1-butene random copolymer (manufactured by Sumitomo Chemical Co., Ltd., Sumitomo Noblene, content of 1-butene unit 27 mol%, melting point 130 ° C., melt flow rate 5 g / min.) ) A resin composition containing 100% by weight is extruded from a T-die at 220 ° C, wound around a cooling drum at 15 ° C, quenched,
An unstretched sheet was produced. After heating this sheet at 50 ° C, it is stretched 6 times in the TD direction at 60 ° C, and the stretching speed is 2000%
/ Min, to obtain a 60 μm thick uniaxially stretched shrink label film. By heat-treating the obtained film at 90 ° C for 10 seconds, the heat shrinkage is 5% in the vertical direction and 42% in the horizontal direction,
With a haze of 4.8%, a label with good low-temperature shrinkage and transparency was obtained.

Comparative Example 1 Propylene-ethylene-1-butene random copolymer (Sumitomo Chemical Co., Ltd., Sumitomo Noblene, ethylene unit content 2.1% by weight, 1-butene unit content 5.7% by weight) , Melting point 138 ° C, melt flow rate 5g / min) 1
The resin composition containing 00% by weight was extruded from a T-die at 240 ° C., wound around a cooling drum at 15 ° C., and quenched to prepare an unstretched sheet. After heating this sheet at 80 ° C, 40-80
When the film was stretched in the TD direction at ℃, the film was broken at any temperature and could not be stretched.

[0020]

Industrial Applicability The film of the present invention can provide a polypropylene film for shrink labels which has good low-temperature shrinkability and excellent transparency. Further, the polypropylene film for a shrink label of the present invention is preferable because it does not have environmental problems such as polyvinyl chloride. Furthermore, specific gravity is 1.
Since it is 0 or less, the suspension separation from the polyethylene terephthalate bottle is easily performed, and the recyclability can be improved.

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Claims (3)

[Claims] 1. A film comprising a polypropylene resin, wherein the haze after heat treatment is 8% or less and 90 ° C.
A heat-shrinkable polypropylene film having a specific gravity of 1.0 or less, wherein the heat-shrinkage rate for 10 seconds is 30% or more. 2. A heat-shrinkable polypropylene film, wherein the polypropylene resin according to claim 1 is a propylene-1-butene random copolymer. 3. The heat as claimed in claim 2, wherein the content of 1-butene unit in the propylene-1-butene random copolymer according to claim 2 is in the range of 5 to 50 mol% based on the whole polypropylene resin. Shrinkable polypropylene film.