JPH0841219A - Polyester film for packaging food - Google Patents

Abstract

PURPOSE:To obtain the polyester film having a high UV rays-cutting property and an excellent gas barrier property, high in slipperiness and transparency, and used for packaging foods. CONSTITUTION:The polyester film comprises (A) an aromatic dicarboxylic acid component containing a naphthalene dicarboxylic acid or its ester-forming derivative and (B) a diol component consisting mainly of ethylene glycol as main components, further contains calcium element in an amount of 100-1000ppm, phosphorus element in an element ratio of 0.5-2.0 to the calcium element, and silica particles in an amount of 50-750ppm, and has a Tg of >100 deg.C, a Haze of <=2% and a dynamic friction coefficient of <=0.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for food packaging, and more specifically, it has a high UV blocking property and an excellent gas barrier property, and also has a good dynamic friction coefficient and a high transparency. The present invention relates to a polyester film useful for packaging foods such as products and retort foods.

[0002]

2. Description of the Related Art Polyester films represented by polyethylene terephthalate and the like are excellent in physical properties such as transparency, mechanical properties, dimensional stability and chemical properties such as chemical resistance. Therefore, it is widely used for magnetic tape and food packaging.

In particular, for food packaging, in recent years, a high degree of palatability is required for the contents, and the change in taste during the storage period has been taken up as a major problem. Techniques for satisfying these required physical properties have been studied so far, and generally, a film obtained by vapor deposition of aluminum on a polyolefin film such as polyethylene or polypropylene is used.

However, since these polyolefins have insufficient mechanical strength, dimensional stability and heat resistance, they are deformed during the storage period and peeled from the aluminum vapor deposition layer,
Or due to cracks in the aluminum vapor deposition layer,
It is known that the gas barrier property is greatly reduced.

As an improvement, the polyolefin film itself is modified to increase the vapor deposition strength of aluminum, or the side chains of olefins are --OH, --Cl,-.
It has been attempted to introduce a functional group such as CN to give a gas barrier property to the film itself, but its effect is small and a film suitable for practical use has not yet been obtained. It is difficult to obtain sufficient adhesiveness even with the adhesiveness to the aluminum vapor-deposited layer, and even if sufficient adhesive strength was obtained, the vapor-deposited layer could not be destroyed due to the deformation of the olefin film.

As a method for overcoming the above problems of polyolefins, an attempt has been made to use a polyester film represented by polyethylene terephthalate having a high gas barrier property as a resin itself. However, polyesters typified by polyethylene terephthalate have excellent mechanical strength, dimensional stability, and heat resistance, and also have a particularly high gas barrier, and are increasingly being used in applications that have been difficult to apply in the past. However, it is used for products that are displayed in stores as stores, or that are often stored for a long period of time, or where the taste of the contents is extremely strong and the value of the product is significantly impaired by slight oxygen transmission or ultraviolet irradiation. However, aluminum vapor-deposited polyethylene terephthalate film had to be used for these applications.

As a method of improving this drawback, that is, a method of imparting a high ultraviolet ray blocking property and a high gas barrier property without vapor-depositing aluminum, a resin having a high gas barrier property is used as an intermediate layer or a surface layer of a multilayer film. Methods such as arranging layers have been investigated. However, this method is very effective and can be widely used,
Since it has a multi-layer structure, the manufacturing cost is high and it is not suitable for food packaging.

On the other hand, polyethylene terephthalate which does not vapor-deposit aluminum can be used and is widely used at present for applications where high performances such as oxygen permeability and ultraviolet blocking property are not required. However,
Biaxially stretched polyester film with a thickness of about 20 μm, which is mainly used for food packaging, has high friction and lacks in slipperiness, so that defective winding shape, wrinkles, etc. are likely to occur in the film forming process and processing process, and thus slipperiness is improved. In order to impart it, generally, a slip agent mainly composed of an inorganic substance such as silica is added. However, although these slip agents are excellent in the effect of improving the frictional characteristics, they have a drawback that they reduce the transparency and make the printing unclear, especially in applications such as back printing, which greatly impairs their value as a product.

[0009]

In view of the above situation, the present inventors have a high UV blocking property and an excellent gas barrier property without aluminum vapor deposition, and have a good high slip property and a high transparency. As a result of earnest research on a polyester film for food packaging, the present invention has been achieved. That is, the present invention comprises (A) an aromatic dicarboxylic acid component containing 50 mol% or more of naphthalenedicarboxylic acid or its ester-forming derivative, and (B) a diol component containing ethylene glycol as a main component, as main constituent components. Which is a film made of a polyester resin containing 100 to 1000 ppm of calcium element,
The elemental ratio of phosphorus element to calcium element is 0.5 to
It contains internal particles in an amount of 2.0 and silica particles of 50 to 750 ppm, and has a glass transition temperature (hereinafter,
It is abbreviated as Tg. ) Is more than 100 ° C, haze is 2% or less, and dynamic friction coefficient is 0.5 or less.

The feature of the present invention is to use 2,6- or 1,4-naphthalenedicarboxylic acid or an ester-forming derivative thereof as an acid component in a specific amount and introduce it into the main chain to improve the physical properties of the resin. This is to greatly improve the mechanical properties such as elongation at break and elastic modulus, and to greatly improve the gas barrier property and the ultraviolet light blocking property, which are essential for food packaging applications. In addition, another feature of the present invention is that the internal particles containing the calcium element and the phosphorus element and the external particles composed of silica particles are used in combination as a means for imparting the slip property, thereby satisfying the sufficient slip property and the transparency at the same time. It is to let.

The polyester resin used in the polyester film for food packaging of the present invention comprises an aromatic dicarboxylic acid component containing naphthalenedicarboxylic acid or its ester-forming derivative as a main component, and a diol component containing ethylene glycol as a main component. It is composed of a polyester resin as a main component.

The naphthalenedicarboxylic acid or its ester-forming derivative used in the present invention is 5% in the acid component.
The content is 0 mol% or more, preferably 70 mol% or more.
This is because when the content of naphthalenedicarboxylic acid or its ester-forming derivative is less than 50 mol%, the ultraviolet resistance and gas barrier property of the formed polyester film are deteriorated and Tg is lowered to 100 ° C. or lower. Examples of ester-forming derivatives of naphthalenedicarboxylic acid include dialkyl esters and diaryl esters of naphthalenedicarboxylic acid.

Other aromatic dicarboxylic acids used in combination with naphthalene dicarboxylic acid or its ester-forming derivative include terephthalic acid, isophthalic acid, 5-sulfoisophthalic acid or their dialkyl esters, diaryl esters and the like. Among these, terephthalic acid or its dialkyl ester is particularly preferable. These aromatic dicarboxylic acids or their ester-forming derivatives account for 50 mol% or less of the total acid component of the polyester resin,
It is preferably used in the range of 30 mol% or less. Also,
In the present invention, if necessary, an aliphatic dicarboxylic acid such as glutaric acid, adipic acid, sebacic acid, oxalic acid, or succinic acid or an ester-forming derivative thereof is contained in the polyester resin in an amount of less than 20 mol%, preferably less than 20 mol%. 10
You may contain in the range less than mol%.

The diol component contains ethylene glycol as a main component, preferably in the range of 80 mol% or more, and more preferably 85% in the total diol component.
It is contained in the range of mol% or more. Further, in the present invention, as the diol component other than ethylene glycol,
One or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, triethylene glycol, an ethylene oxide adduct of a bisphenol compound or a derivative thereof can be used.

If desired, a polyfunctional third component such as trimellitic acid, trimesic acid and trimethylolpropane may be used in combination.

These polyester resins can be produced by a known direct polymerization method, transesterification method, or the like, and the degree of polymerization thereof is not particularly limited, but the intrinsic viscosity (phenol / Measured in a mixed solvent such as tetrachloroethane at 25 ° C) is 0.5 to
It is preferably 1.2 dl / g.

The polyester film for food packaging of the present invention is a polyester film produced from the polyester resin having the above-mentioned constitution, and contains internal particles containing calcium element and phosphorus element, and silica particles. . The internal particles containing calcium element and phosphorus element are fine particles deposited by the reaction of the calcium compound and phosphorus compound added to the reaction system during the production of polyester.

The calcium compound added to the reaction system includes inorganic compounds such as hydroxides, oxides, carbonates and hydrogen carbonates, and organic acid salts such as acetates, propionates, butyrates and stearates. And the like, and one or more of these compounds are used in combination. Calcium, which is added as a calcium compound, reacts with phosphorus to form the core of internal particles, so the slipperiness of the film improves as the content of calcium element increases, but on the other hand, calcium does not undergo thermal decomposition of the polymer. It is not preferable to add an excessive amount because it also promotes Therefore, the calcium compound is added so that the content of the calcium element contained in the film is 100 to 1000 ppm, preferably 300 to 600 ppm. This is because when the content of calcium element is less than 100 ppm, a film having sufficient slipperiness cannot be obtained, and when it exceeds 1000 ppm, thermal decomposition of the polymer is likely to occur in the polymerization step, and a polymer having a high degree of polymerization cannot be obtained. At the same time, the polymer becomes colored.

The elemental phosphorus is added to the reaction system as a phosphorus compound. Examples of the phosphorus compound include phosphoric acid, phosphorous acid or their esterified products such as trimethyl phosphate, triethyl phosphate, triphosphate. Phenyl, triethyl phosphite, triphenyl phosphite and the like,
These compounds can be used alone or in combination of two or more.

Since the internal particles are formed through the reaction between calcium and phosphorus, addition of a phosphorus compound in a certain amount or more with respect to the amount of elemental calcium causes a metal oxidation in which excess phosphorus is added as a condensation polymerization catalyst. Since the phosphorus compound also reacts with the substance and inhibits the polymerization, the phosphorus compound has an element amount ratio of 0.5 to 2.0, preferably 0.6 to 1.2, in terms of the element amount ratio to the calcium element. Is preferably added to. This is because when the element amount ratio to the calcium element is less than 0.5, the internal particles corresponding to the added calcium element are not formed, and the unreacted calcium element easily causes thermal decomposition of the polymer, resulting in a degree of polymerization. This is because there is a tendency that a polymer having a high viscosity cannot be obtained and the polymer may be colored. Further, when the elemental ratio of phosphorus element to calcium element exceeds 2.0, excess phosphorus also reacts with a metal oxide added as a polycondensation catalyst to inhibit polymerization, resulting in a polymer having a high degree of polymerization. This is because there is a tendency that the polymer cannot be obtained, the polymerization time becomes extremely long, the oxidative decomposition and thermal decomposition of the polymer are promoted, and the quality may be deteriorated.

The silica particles used in the present invention are
A silica having a refractive index close to that of polyester is preferable, and silica prepared by a wet method having a high affinity with polyester is preferable in order to prevent particles from falling off from the film surface.

The average particle diameter of the wet process silica used in the present invention is in the range of 1.0 to 5.0 μm,
If the thickness is less than 1.0 μm, the effect on the slipperiness is small, and if it exceeds 5.0 μm, the protrusion height is large, so that the slipperiness tends to decrease. It also develops defects such as eye.

Silica particles are added in the range of 50 to 750 ppm, preferably 100 to 300 ppm. This is because if the silica particles are less than 50 ppm, sufficient slipperiness cannot be obtained, and if it exceeds 750 ppm, the transparency of the film is lowered due to the formation of coarse particles. In the present invention, by incorporating silica particles as external particles together with the internal particles, it is possible to maintain sufficient slipperiness even when a high load is applied, without impairing the transparency of the film.

The method for producing the polyester film of the present invention is as follows:
Although not particularly limited, for example, it can be obtained by producing the polyester resin containing the above silica, the calcium element and the phosphorus element by a melt condensation method or the like and biaxially orienting the polyester resin. As the manufacturing method, a known manufacturing method, for example, first, after drying the polyester resin,
Melt extrusion is performed at a temperature of about 270 to 300 ° C., and a raw film is formed by a cast method, a calender method, or the like. Next, this raw film is stretched in the machine direction and the transverse direction at a temperature of about 80 to 120 ° C. The film is stretched by a method such as simultaneous biaxial stretching or sequential biaxial stretching, and either the longitudinal direction or the transverse direction may be stretched first. The biaxially stretched polyester film may have a thickness of 200 to 2 if necessary.
It can be obtained by performing a heat treatment at a temperature of 40 ° C. to fix the orientation by crystallization and improve the dimensional stability.

The thickness of the polyester film of the present invention is
Although not particularly limited, it is in the range of 6 to 380 μm.

It is important that the polyester film for food packaging of the present invention having the above constitution has a Tg of more than 100 ° C., a haze of 2% or less, and a dynamic friction coefficient of 0.5 or less. This is because when Tg is 100 ° C. or less, dimensional stability in boiling water is lowered, packaging of retort foods becomes impossible, and when haze exceeds 2%, the transparency of the film is lowered and the contents are sharp. It becomes impossible to see through and the printability deteriorates.
% Or less. Further, if the coefficient of dynamic friction exceeds 0.5, problems will occur in the film forming and processing steps, and the range is preferably 0.45 or less.

[0027]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Evaluations in Examples and Comparative Examples were performed by the following methods. The thickness of the film used for evaluation is 12 μm.

1. Glass transition temperature (Tg) A sample obtained by heating and melting in nitrogen at 280 ° C for 5 minutes and then rapidly cooled was used in a differential scanning calorimeter (manufactured by Shimadzu Corporation) at a temperature rising rate of 5 ° C / min in nitrogen. The shoulder temperature of the baseline change indicating the second-order transition point was measured and taken as Tg.

2. Haze The film thickness of 12 μm was measured with a haze meter manufactured by Tokyo Denshoku Co., Ltd. (MODEL TC-HIII), and the haze was converted per 10 μm of thickness.

3. Dynamic friction coefficient A surface tester manufactured by Shinto Kagaku Co., Ltd. was used and the thickness was 12μ.
The same film of m was attached to both the fixed part and the movable part to measure the dynamic friction coefficient.

4. Intrinsic viscosity 1 g of polymer is dissolved in 100 ml of phenol / tetrachloroethane 50/50 (weight ratio) mixed solution, and the temperature is 25 ° C.
It was measured at.

5. Gas barrier property A film having a thickness of 12 μm was measured with an oxygen permeability measuring device PX-TRAN manufactured by Mocon, and the oxygen permeability (ml / m ²
・ 24h) was measured.

6. Ultraviolet Transmittance (%) An ultraviolet measuring instrument was used to measure the transmittance at a wavelength of 350 μm. When the transmittance was less than 30%, it was evaluated as ◯, and when it was 30% or more, it was evaluated as x.

Example 1 25 mol parts of dimethyl terephthalate (hereinafter abbreviated as TPADM), 75 mol parts of dimethyl 2,6-naphthalenedicarboxylate (hereinafter abbreviated as NDCDM) and 200 mol parts of ethylene glycol were refined. Place in a reaction vessel equipped with a distillation column and a stirrer, and stir while stirring.
The temperature was gradually raised to 0 ° C., and transesterification was carried out while discharging distilled methanol out of the system. This was transferred to a polycondensation reaction vessel, and a 2 wt% ethylene glycol solution of calcium acetate monohydrate was added in an amount such that the elemental calcium temperature in the polymerization system was 225 ppm. After 10 minutes, 10% of trimethyl phosphate was added. Wt% ethylene glycol solution,
An amount was added so that the amount of elemental phosphorus in the polymerization system was 150 ppm. After a further 10 minutes, an ethylene glycol solution of antimony trioxide was added by a conventional method, and after a further 10 minutes, an ethylene glycol dispersion liquid of silica particles (manufactured by Fuji Silysia Chemical Ltd., Silysia # 310) synthesized by a wet method was used as silica. It was added so as to be 200 ppm in the polymerization system. After 30 minutes, pressure reduction and temperature increase were started, and the pressure was reduced to 3 mm at a vacuum degree of 1 mmHg or less and a temperature of 290 ° C.
After time condensation, polyethylene terephthalate having an intrinsic viscosity of 0.672 was obtained. The obtained polyethylene terenaphthalate was vacuum dried at 120 ° C. for 10 hours and then formed into a sheet having a thickness of 150 μm by a single type extruder. This sheet was stretched 3.5 times in the machine direction at a temperature of 90 ° C. using a stretching machine and then stretched 3.5 times in the transverse direction to obtain a 12 μm-thick polyester film. Table 1 shows the evaluation results of the obtained film.

Examples 2 to 7, Comparative Examples 1 to 4 Molar parts of TPADM and NDCDM, silica content,
The calcium content, the phosphorus content, and the element amount ratio of the phosphorus element to the calcium element were changed as shown in Table 1, and the method of Example 1 was repeated to obtain a thickness of 12 μm.
Was produced. Table 1 shows the evaluation results.

[0036]

EFFECT OF THE INVENTION The polyester film for food packaging of the present invention having the above-mentioned constitution has a high UV blocking property and an excellent gas barrier property, and also has good slipperiness and high transparency. , It is extremely useful for packaging foods such as luxury items and retort foods.

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location C08L 67/02 KJS (72) Inventor Shuji Ishiwata 2-3, Ushikawa-dori, 4-chome, Toyohashi City, Aichi Prefecture Ryo Rayon Co., Ltd. Toyohashi Office

Claims (1)

[Claims] 1. A main constituent component is (A) an aromatic dicarboxylic acid component containing 50 mol% or more of naphthalene dicarboxylic acid or its ester-forming derivative, and (B) a diol component containing ethylene glycol as a main component. A film made of a polyester resin, wherein the calcium element is 100 to 1000 ppm, and the phosphorus element is 0.5 to 2.0 in terms of the element amount ratio to the calcium element, and the silica particles are 50 to 750 ppm. Is included, the glass transition temperature exceeds 100 ° C.,
A polyester film for food packaging, which has a haze of 2% or less and a dynamic friction coefficient of 0.5 or less.