JP2001293832A - Laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film which makes a heat sealing property compatible with slippage, both properties being incompatible with each other, without sacrificing transparence. SOLUTION: A laminated polyester film comprises surfaces, at least one surface being composed of a low crystalline polyester, and a base material layer composed of a polyester having a melting point 10 deg.C or more higher than that of the low crystalline polyester, wherein the surface shows a dynamic friction coefficient of not more than 0.5 and the whole film shows a haze value of not more than 5%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film which is mainly used in the field of packaging by heat laminating a sheet-like material, for example, various polymer films, plastic sheets, metal foils, metal plates, paper and the like.

[0002]

2. Description of the Related Art Polyester films are widely used industrially because of their excellent mechanical properties, dimensional stability and heat resistance. In particular, in packaging applications, other materials are mainly used by laminating as a base material layer which is a structure. Normally, it is laminated with another material using an adhesive, but it is possible to omit a step of applying an adhesive by previously laminating a copolymer polyester having thermal adhesiveness to a polyester base layer. The use of film is also increasing. For example, a laminated polyester film disclosed in JP-A-2-252557 or the like corresponds to this.

In these laminated films, a heat treatment is performed in advance at a temperature lower than the melting point of the base material layer and higher than the melting point of the heat bonding layer in the film manufacturing process, so that the base material layer is thermally fixed and the heat bonding layer is simultaneously formed. Is generally melt-amorphized, but the heat-bonded amorphized layer has a remarkably poor slippage, which often causes troubles in handling the film.

[0004] Although the troubles related to the above-mentioned handling can be solved by setting the heat treatment temperature below the melting point of the heat bonding layer, the heat bonding layer must be melted during lamination. In addition to the necessary restrictions, the heat fixation of the base material layer becomes insufficient and the dimensional stability is impaired, so that the fundamental solution has not been reached.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to achieve both heat sealing properties and slip properties, which are contradictory properties, without impairing transparency. To provide a film.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above-mentioned problems, and as a result, have found that the above-mentioned problems can be easily solved by adopting a specific film structure, and have completed the present invention. .

That is, the gist of the present invention is a laminated film in which at least one surface is made of a low-crystalline polyester and the base material layer is made of polyester whose melting point is 10 ° C. or more higher than the melting point of the low-crystalline polyester. The laminated polyester film is characterized in that the dynamic friction coefficient of the surface is 0.5 or less and the haze of the entire film is 5% or less.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The polyester in the present invention refers to a polymer in which repeating units are connected by an ester bond. The repeating unit may have an ester bond. For example, a unit in which a polyvalent carboxylic acid and a polyhydric alcohol are condensed may be repeated.

Examples of polyvalent carboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 2,6-naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and tricarboxylic acids. Examples thereof include trivalent or higher polycarboxylic acids such as melitic acid and pyromellitic acid. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, trimethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, polyethylene glycol, Examples thereof include diols such as polytetramethylene glycol and polyhydric alcohols having a valency of 3 or more such as glycerin.

In addition to these, an oxycarboxylic acid such as p-hydroxybenzoic acid which can be a repeating unit by itself may be condensed.

The low crystalline polyester according to the present invention is:
When lowering the temperature at a constant speed from a molten state of 300 ° C by DSC,
It means a polyester in which a crystallization exothermic peak is not substantially observed at a cooling rate of 20 ° C./min or more.

The laminated film of the present invention has at least one surface composed of a low-crystalline polyester. In applications where thermal adhesion is required on both surfaces, both surfaces are made of a low-crystalline polyester, and in applications where thermal adhesion is required on only one surface, only one surface is made of a low-crystalline polyester.

In the laminated film of the present invention, the base layer functioning as a structure is made of a polyester having a melting point of 10 ° C. or more, preferably 20 ° C. or more, higher than the melting point of the low crystalline polyester forming the surface layer. The melting point difference is 10 ° C
If it is less than 1, a complete molecular orientation and a decrease in crystallinity are observed in the base material layer, and the surface layer becomes an obstacle in bonding.

The base layer of the laminated film of the present invention is preferably a biaxially oriented polyester layer having a function as a structure, and its composition is not particularly limited, but imparts appropriate strength. For this reason, it is recommended to mainly use a highly crystalline aromatic polyester such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate.

The haze of the laminated film of the present invention is 5% or less, preferably 4% or less. In packaging applications,
In general, various types of printing are performed before use. When the haze exceeds 5%, the printing becomes unclear, which is not preferable.

In the laminated film of the present invention, the coefficient of kinetic friction of the surface composed of the low crystalline polyester is 0.50 or less, preferably 0.40 or less. If the coefficient of kinetic friction exceeds 0.50, the handling of the film deteriorates, and the possibility of wrinkles occurring in operations such as winding is increased, which is not preferable.

As a method of reducing the dynamic friction coefficient of the surface composed of the low-crystalline polyester to 0.50 or less, a method of containing a large amount of particles can be mentioned. If the average particle size of the particles used is less than 1 μm, the effect of reducing the dynamic friction coefficient is small, so that a large amount of particles must be used, and as a result, the transparency of the film may be impaired. It is recommended to use particles having an average particle size of 1 μm or more. On the other hand, in the case of a large particle system having an average particle diameter of more than 4 μm, a large projection formed with such large particles as a nucleus cannot sufficiently adhere to an adherend, resulting in insufficient sealing strength. Therefore, it is recommended to use particles having an average particle size of 4 μm or less.

Examples of the lubricant particles include those conventionally used as lubricant particles for polyester films, such as silica, titania, alumina, kaolin, calcium carbonate, and crosslinked polymers. In particular, amorphous silica is recommended because of its relatively high slipperiness and transparency.

Even if the average particle size is controlled within a predetermined range, a surface layer made of a low-crystalline polyester containing particles capable of sufficiently improving the slipperiness causes a reduction in transparency. It is recommended to make the surface layer as thin as possible, but if it does not have a thickness of at least about 0.1 μm, it will not be possible to satisfy the characteristics in terms of thermal adhesion and slipperiness. The thickness of the surface layer composed of polyester is suitably about 0.3 to 3 μm.

In the laminated film of the present invention, various additives besides the lubricant particles are added to the surface layer, the base material layer and the other layers composed of the low-crystalline polyester in accordance with various applications as long as the properties are not impaired. An agent can be compounded.
For example, antistatic agents, flame retardants, ultraviolet absorbers, antiwear agents, dyes / pigments of each color, and the like may be added.

The laminated film of the present invention can be obtained by a conventional method. For example, the polyester constituting each layer is melted by a separate extruder, and coextruded from a T die is quenched on a cooling drum to form an amorphous sheet, and then Tg is increased by about 10 to 30 ° C. by a roll stretching machine. After stretching in the longitudinal direction at a temperature, it is further stretched in the transverse direction at a temperature about 5 to 20 ° C. higher than the roll stretching temperature in a tenter stretching machine,
Subsequently, heat setting is performed in a tenter stretching machine at a temperature lower than the melting point of the base material layer and higher than the melting point of the surface layer made of low crystalline polyester. Depending on the application, the heat shrinkage can be adjusted by relaxing before and after heat setting. Various in-line coatings may be applied before and after roll stretching.

[0023]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the following examples, “parts” means parts by weight. (1) Crystallinity As a differential scanning calorimeter, the following measurement was performed using MDSC-2920 manufactured by TA Instruments.

That is, after the 10 mg sample was equilibrated at 300 ° C., the temperature was measured at a rate of 20 ° C./min. The crystallization enthalpy per unit mass was determined from the area of the generated crystallization exothermic peak, and those having an enthalpy of 0.5 J / g or less were regarded as having low crystallinity. (2) Melting point The following measurement was performed using MDSC-2920 manufactured by TA Instruments as a differential scanning calorimeter.

That is, after sufficiently precrystallizing a 10 mg sample, the sample was equilibrated at 0 ° C.
Temperature rise measurement was performed at a temperature rise rate of ° C./min. The peak temperature of the crystal melting endothermic peak was defined as the melting point (° C.). (3) Coefficient of dynamic friction On a smooth glass plate, two films cut to a width of 15 mm and a length of 150 mm were put together with the surfaces made of low crystalline polyester together, and a rubber plate was placed on top of it. Place a 140g weight on top and 20m
The frictional force was measured by sliding the films at m / min. 5
The value obtained by dividing the frictional force at the time of sliding by mm by the load was defined as the dynamic friction coefficient. (4) Haze According to JIS K6714, the haze of the film (haze value;%) was measured with a spectroscopic turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd.
Was measured. (5) Seal Strength Seal strength (heat seal strength; N / 15 mm) was measured according to JIS Z1707. The heat sealing conditions were set to 100 MPa for 10 seconds at 150 ° C. for the surfaces made of low crystalline polyester. (Production of polyester) Polyester A 100 parts of dimethyl terephthalate, ethylene glycol 6
After charging 0 parts and purging with nitrogen, 225 mol of titanium tetrabutoxide was added as a titanium metal element, and the temperature was raised to 240 ° C. over 2 hours in a nitrogen atmosphere, and further maintained at 240 ° C. for 1 hour, and transesterification was performed. After that, an equimolar mixture of ethyl phosphate and diethyl phosphate is added in an amount of 440 mol as a phosphorus element, and subsequently, 370 mol of cobalt acetate tetrahydrate is added as a cobalt metal element, and germanium dioxide is converted into a germanium metal element. 300 as quantity
An appropriate amount of ethylene glycol slurry containing amorphous silica particles having a molar average particle size of 1.5 μm was added.

Thereafter, the pressure of the system was reduced to 1 mmHg in 1 hour and 25 minutes, the temperature was also increased 20 minutes after the start of the pressure reduction, and finally the polymerization reaction was carried out at 270 ° C. The polymerization was completed 3 hours 16 minutes after the start of the pressure reduction. The produced polyester was withdrawn as a strand, pelletized and collected to obtain polyester A. Polyester A has an intrinsic viscosity of 0.71
dl / g, the silica content was 0.5 part.

Polyester B Polyester A, except that no amorphous silica was added
Polyester B was obtained in the same manner as described above. Polyester B had an intrinsic viscosity of 0.70 dl / g.

Polyester C 78 parts of terephthalic acid was used instead of 100 parts of terephthalic acid.
Polyester C was obtained in the same manner as polyester A, except that isophthalic acid was 22 parts. Polyester C had an intrinsic viscosity of 0.71 dl / g and a silica content of 0.5 part.

Polyester D Polyester C except that amorphous silica was not added.
Polyester D was obtained in the same manner as described above. Polyester D had an intrinsic viscosity of 0.70 dl / g.

Example 1 Polyester B and polyester C were melted by separate extruders, the discharge ratio was 5: 1, and the melts were merged in a T-die so as to have a B / C stratification and co-extrusion. did. Immediately after extrusion, quenched immediately below the glass transition temperature on a cooling drum,
A substantially amorphous sheet was obtained. The obtained amorphous sheet is stretched 3.8 times in the longitudinal direction at 85 ° C. with a roll stretching machine, and further stretched in the transverse direction at 100 ° C. with a tenter stretching machine.
After performing 0-fold stretching, and subsequently performing heat setting at 240 ° C. with a constant width in a tenter stretching machine, while cooling to 160 ° C., relaxing 5% in the width direction, and cooling to room temperature to obtain a product. . The thickness of the obtained laminated film was 12 μm.

Example 2 A laminated film having a thickness of 12 μm was obtained in the same manner as in Example 1 except that the melts were merged so that the stratigraphy was C / B / C instead of B / C.

Example 3 A polyester having a thickness of 12 μm was prepared in the same manner as in Example 1 except that a mixed polyester I obtained by blending polyester A and polyester B at a weight ratio of 1: 5 was used instead of polyester B.
m was obtained.

Comparative Example 1 In place of polyester B, a mixed polyester II obtained by blending polyester A and polyester D at a weight ratio of 2: 9 was used, and the heat setting temperature was set to 200 ° C. Similarly, a laminated film having a thickness of 12 μm was obtained. The obtained film had poor seal strength.

Comparative Example 2 A laminated film having a thickness of 12 μm was obtained in the same manner as in Example 3 except that polyester D was used instead of polyester C. The resulting film was poor in slipperiness, wrinkled during processing, and was poor in handling properties.

Comparative Example 3 A film having a thickness of 12 μm was prepared in the same manner as in Example 3 except that the blend weight ratio of polyester A and polyester B was 1: 1.
Was obtained. When the obtained film was printed, it was unclear and not practical.

The results obtained are summarized in Table 1 below.

[0037]

[Table 1]

[0038]

The laminated polyester film of the present invention has
It has both heat sealing properties and slip properties, which are contradictory properties, without impairing transparency, and is suitable, for example, as a packaging film, and its industrial value is very high.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F100 AK41A AK41B AK41C BA02 BA03 BA06 BA10A BA10C BA26 GB15 JA04A JA04B JA04C JA11A JA11C JK16A JK16C JL12 JN01 YY00 YY00A YY00C

Claims (1)

[Claims] 1. A laminated film having at least one surface made of a low-crystalline polyester and a base layer made of a polyester having a melting point of the low-crystalline polyester higher by at least 10 ° C. A laminated polyester film having a coefficient of 0.5 or less and a haze of the whole film of 5% or less.