JPS6327535A - Shrinkable polyester film - Google Patents

Abstract

PURPOSE:To provide the titled shrinkable film having specific heat of fusion, birefringence and shrinkage of the film and suitable as a label for a PET bottle for refreshing drink. CONSTITUTION:The objective film has a heat of fusion of >=3cal/g, a birefringence of 0.005-0.050, an average refractive index of <=1.595 and a shrinkage of >=40% along a direction and <=15% along the other direction after the treatment in a 100 deg.C air oven for 5min. The film is produced from a crystalline polyester obtained by the polycondensation of (A) a dicarboxylic acid component containing >=85% terephthalic acid and (B) a glycol component containing >=85% ethylene glycol.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an inexpensive polyester shrink film that has good heat shrinkage properties and shrink properties.

[Problems to be solved by conventional technology and invention] Conventionally,
Shrink films mainly made of vinyl chloride are widely used in shrink applications for labels. However, now that PET bottles are being used as containers for soft drinks, etc., there is a social demand for collecting and reusing the bottles.

However, if the bottle and label have different compositions, it is difficult to separate them, so polynisder-based shrink films are desired for label applications as well, so that the bottle and label can be reused without being separated.

On the other hand, conventionally, amorphous copolyester or this amorphous copolyester and P! ! T or P
It has been proposed that a film with excellent heat sealability and shrinkability can be obtained by uniaxially stretching a composition comprising a blend of BT in the longitudinal or transverse direction. (Titr from JP-A-37-≠272, JP-A-Sho! 7-)
Publication and JP-A-Sho! However, these films include various problems. First, it cannot be dried under the same drying conditions as ordinary polyethylene terephthalate, and the polymer composition is complex and the polymer cost is high, making the film extremely expensive compared to PVC film. Although it is good, the reality is that it is not yet used in the market. Therefore, it is desired to obtain a shrink film using polyethylene terephthalate units, which are currently used in large quantities for biaxially oriented films, FIIEn products, bottles, etc. and are available at extremely low prices, or polyesters modified to some extent. .

However, since the above-mentioned polymer is crystalline, it crystallizes when uniaxially stretched or the like, and it has been considered impossible to obtain the necessary shrinkage characteristics.

[Means for solving the problem'].

The inventors of the present invention have conducted extensive research to answer the above-mentioned requirements, and have discovered that it is possible to obtain satisfactory shrinkage characteristics as a shrinkable film by imparting specific physical properties even to crystalline polyester. This is what became.

That is, the gist of the present invention is that the heat of fusion of the film is J ca
A film made of crystalline polyester of l / 9 or more, whose birefringence Δn is o, oor or more 01
010 or less, an average refractive index n of Hj9j or less, and a shrinkage rate in one direction for j minutes in an air oven of ≠O% or more and the other /j% or less Exists in shrink film. ' Hereinafter, the present invention will be explained in detail.

The crystalline polyester of the present invention is one that has crystallinity with a heat of fusion of J cab / J' or more, and contains terephthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid as a dicarboxylic acid component. , azelaic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl ether dicarboxylic acid, etc., and consists of one or more types of known dicarboxylic acids, and also contains ethylene glycol, propylene glycol, trimethylene glycol as a diol component. , tetramethylene glycol, hexamethylene glycol, diethylene glycol, polyalkylene glycol, 1. Any polyester or copolyester consisting of one or more known diol components such as ≠-cyclohexane dimetatool may be used, but mainly polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6 - Naphthalate, terephthalate II and/
, 4(-cyclohexane dimetatool), and copolymers thereof are preferred. Particularly,
Polyethylene terephthalate is particularly preferred because it is inexpensive.

The copolymerized polyester includes a dicarboxylic acid component and/or
Alternatively, those obtained by substituting a part of the glycol component with other dicarboxylic acids or glycol components can be used, but of course, other components, such as p-oxybenzoic acid, p-oxybenzoic acid, etc. Oxycarboxylic acids such as ethoxybenzoic acid, benzoic acid, benzoylbenzoic acid, monofunctional compounds such as methoxypolyalkylene glycols, polyfunctional compounds such as glycerin, pentaerythryltole, trimethylol, trimethylenepropane are also produced. It can be used as long as it can maintain a substantially linear polymer.

Here, in the copolymerized polyester iζ whose main component is polyethylene terephthalate, the tr of the dicarboxylic acid component is
At least y must be terephthalic acid, and at least 3 rj moles of the glycol component must be ethylene glycol. Terephthalic acid and/or ethylene glycol!
If it is less than molar S, crystallinity will substantially disappear and it is unsuitable.

Further, the above-mentioned polyester may be one in which other polymers are added or mixed in addition to the polyester, as long as the amount is 20 mol% or less.

In addition, in order to improve the slipperiness of the film, organic lubricants,
It is also preferable to contain fine particles such as an inorganic lubricant.

Additionally, it may contain additives such as stabilizers, eyebrow coloring agents, antioxidants, antifoaming agents, etc., if necessary. Fine particles that impart slipperiness include known inert external particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, and lithium fluoride, and when forming polyester resin into a melt film. They can be internal particles formed inside the polymer during polyester production by insoluble high melting point organic compounds, crosslinked polymers, and metal compound catalysts used during polyester synthesis, such as alkali metal compounds, alkaline earth metal compounds, etc. The fine particles contained in the film have a weight of O.oar to 1% and an average particle diameter of 0.0/-3.14 m.

The film of the present invention has a heat of fusion of J cab / JF
Above, preferably jca1/11 or more, more preferably 70al 711 or more. If the heat of fusion of the film is less than j cab / 11, the drying method normally used for polyethylene terephthalate cannot be used in the drying process before extrusion film formation, and a new dryer will need to be installed, increasing costs. It is unsuitable because it becomes a factor.

The film of the present invention has a refractive index Δn of o, ooz or more and 0. OjO or less, and the average refractive index (stone) is /, J9!
Hereinafter, preferably less than or equal to Ij, more preferably less than or equal to
Must be less than or equal to 0. In the case of a film with a refractive index of less than 0.004- or more than o, czo, and/or with a film with an average refractive index i of more than 8tO'0, it is not possible to make the yield in one direction more than UO3. It is not available because it cannot satisfy the characteristics of a shrink film.

In order to use the film thus obtained as a shrink film, it must be shrink processed in one direction.

X or more, preferably 1O or more, the other yield rate is 71%
Below, it should preferably be 1% or less. If the shrinkage in at least one direction is not more than aopg, it may not adhere tightly to the bottle when used as a label.
Unsuitable because it does not shrink. Also, the one-way convergence iig is u
If the yield rate of the other side exceeds 71 g even if the yield rate is more than Oji, the decoy handle will shift in this case as well, making it unsuitable.

Next, a method for manufacturing the film of the present invention will be specifically described.

A crystalline polyester containing an appropriate amount of inorganic particles as a slip agent is dried under the same drying conditions as ordinary polyethylene terephthalate or its copolymer, and then extruded to obtain an unstretched film. The unstretched film is uniaxially stretched in the longitudinal or transverse direction. In this case, the stretching ratio is 7 times or more and 3.0 times or less. As long as thickness unevenness does not worsen, a low stretching temperature is preferable. Stretching methods include not only vertical-axis stretching with rolls and horizontal uniaxial stretching with a tenter, but also known biaxial stretching, in which strong stretching is performed in either the vertical or horizontal direction and minimal stretching in the other direction. ζ is also possible. The film thus obtained is heated to 100°C as necessary.
After heat fixing, the product is rolled up.ζAccording to the present invention, it is possible to obtain a polyester shrink film with excellent heat sealability and shrink properties by using existing Mfil and using an inexpensive polymer. It has excellent industrial value when it can be reused.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, and the present invention is not limited to these Examples unless it exceeds the gist thereof. .

The method for evaluating the film is shown below.

(11) Yield rate was determined according to the following formula by heat shrinking for 1 minute in a no-load state in a Gad oven at a temperature of 100°C ± J'C.

(2) Heat of fusion of film (caV, 9) Sensitivity and heating rate/A by PerkinElmer DEIC-/B
The area of the peak associated with crystal melting of the sample measured at 'C/m and chart speed uOws/- was calculated according to the following formula.

Heat of fusion of film - 08-1 (31 Birefringence Δn Retardation was measured using a polarizing microscope manufactured by Carl Zeiss, and the birefringence (Δn) was determined by the following formula.

Δn = R/ d (4) Average refraction 2 using Hyakuatsube's refraction gt (manufactured by Atago Co., Ltd.)
The value for the Na-D line measured at 3°C was determined.

The average refractive index is given by i=V3 (nq+n/+nr) where the refractive index nα in the thickness direction, the refractive index nr in the main orientation direction, and the refractive index n and y in the direction perpendicular to the main orientation direction. 'Example 18 and Comparative Example 7%--Polyethylene terephthalate having an intrinsic viscosity of 2 degrees of 0.12 was dried and extruded according to a conventional method to obtain an unstretched film. The unstretched film was passed 1. between a stretching roll and a cooling roll at t3°C. - times (comparative example 1), 2.0 times (example/), j, 0
The film was stretched twice (Comparative Example 2) to obtain a wound film. Table 1 shows the physical properties of the film. Also shown are the results when these films were shrunk and attached to a cylindrical soft drink PIT bottle as a shrink label.

At that time, those with good flatness of the design and label were marked with O, and those with poor flatness were marked with x.

Example 3 and Comparative Example 3, ≠ A copolymerized polyester consisting of 0 mol % of terephthalic acid in the dicarboxylic acid component and 10 mol % of isophthalic acid and ethylene glycol with an intrinsic viscosity of 0.70 obtained by solid phase polymerization was carried out. In the same manner as in Example 1, the M film was stretched by λ times, 2 times, and 3.0 times to obtain a shrink film for labels. Comparative example J1
Example 2 and Comparative Example Hiro. These results are also shown in the table/
Shown below.

Example 3 and Comparative Example j%6 The unstretched film of Example- was directly guided through a tenter and rz
Stretch 2.3 times in the transverse direction at 0°C, io°C, 2
After heat fixing at 00°C, it was rolled up. The physical properties of this film and the results as a shrink film for labels are shown below.
Indicated.

From the above results, it can be seen that the films and films that satisfy the conditions of the present invention are extremely suitable as shrink films.

Claims (2)

[Claims] (1) A film made of crystalline polyester whose heat of fusion is 3 cal/g or more, whose birefringence Δn is 0.005 or more and 0.050 or less, and whose average refractive index @
A polyester shrink film characterized in that n@ is 1.595 or less, and the shrinkage rate after 5 minutes in an air oven at 100° C. is 40% or more in one direction and 15% or less in the other direction. (2) 85 mol% or more of the dicarboxylic acid component of the crystalline polyester is terephthalic acid or a derivative thereof, and 85 mol% or more of the diol component is ethylene glycol. Polyester shrink film.