JPH0892391A - Polyester film - Google Patents

Abstract

PURPOSE: To obtain polyester film having a high glass transition point, adhesion, gas barrier properties and excellent dimensional stability in boiling water. CONSTITUTION: This polyester film mainly comprises (A) the dicarboxylic acid components containing more than 50 mole% of naphthalenedicarboxylic acid or its ester-forming derivative, (B) the diol component containing 1-10wt.% of diethylene glycol, (C) 0.1-10wt.% of-polyethylene glycol component of 1,000-20,000 number-average molecular weight and has a glass transition point higher than 100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film used for food packaging and general industrial applications. More specifically, it has a high affinity with hot-melt or dry laminating adhesives and is used for retort applications. The present invention relates to a polyester film which has high dimensional stability even when used in boiling water and is useful as various packaging materials.

[0002]

2. Description of the Related Art Polyester films represented by polyethylene terephthalate have been widely used for packaging and magnetic recording media because of their excellent heat resistance, mechanical properties and chemical resistance. However, while the polyester film has such excellent characteristics, it has a low affinity for hot melt or dry laminating adhesives,
It has a drawback that the peel strength between films after lamination is low and sufficient performance cannot be exhibited. Such characteristics are also due to solvent resistance, which is an advantage of polyethylene terephthalate, but essentially, the molecular chain that constitutes polyethylene terephthalate is rigid, and in addition to having a high molecular weight, the manufacturing process thereof is also high. In the above, it can be considered that there is a synergistic effect of crystallization caused by the high temperature heat treatment performed for imparting dimensional stability.

Attempts have been made to improve these drawbacks from the aspect of inks or adhesives. For example, a method using UV ink has been studied, but UV ink has a large stress strain at the time of curing and it is present at the polyester film interface. Surface destruction occurs. Further, as a practical property, durability against shear stress such as scratching by nails is important.

Further, formation of a primer layer on the film surface has been studied, and it has been proposed and used to use an acrylic resin, a melamine resin or the like as a primer. However, although these resins have excellent adhesion as an ink layer, they have the drawback that they are easily peeled off at the interface with the polyester film. Therefore, there is a demand for the development of a primer resin having a high adhesive force at the two interfaces between the polyester film and the ink layer, but a resin having a practically sufficient performance has not yet been obtained.

Further, as a method for increasing the affinity with the adhesive, it has been studied to increase the activity of the film surface by corona treatment, flame treatment, ultraviolet treatment, etc., but all of them have a small effect and a practical level of effect is obtained. I couldn't.

On the other hand, it has been attempted to add a large amount of inorganic particles to form fine irregularities on the film surface for the purpose of an anchoring effect, but the irregularity surface formed has a contact rather than an improvement in adhesive strength due to the anchoring effect. The larger the area, the more the effect of lowering the adhesiveness occurs, and this point also needs to be resolved.

Further, the conventional film is made to contain inorganic particles such as silica and kaolin in order to impart the slipperiness required in the film forming and processing steps, and to form the unevenness on the film surface to reduce the contact area. It was a general method to give slipperiness by using. However, since such a method remarkably increases the haze of the film, it is not suitable for printing applications or applications requiring transparency.

As a result of studying such problems, the present inventors first found that isophthalic acid, diethylene glycol,
It was also found that a film made of polyethylene glycol having a specific number average molecular weight improves the affinity for the laminating adhesive and the peel strength of the laminating film is increased (Japanese Patent Application No. 5-208006). However, in recent years, with the diversification of packaging materials, physical properties that have not been conventionally required have been required. Part 1
One is the direct heating of food filling containers due to the spread of microwave ovens. In this case, heat content is required because the water content is brought to a boiling state by heating. In addition, the polyester film is increasingly used in so-called retort foods, which are directly immersed in boiling water in a packaged state and heated, and in this case as well, heat resistance of 100 ° C or higher is required. is there.

[0009]

The object of the present invention is to modify a resin without using a complicated and costly method such as formation of a primer layer on the film surface and use of a UV curable ink. It is an object of the present invention to provide a polyester film capable of increasing the affinity with an adhesive and having high heat resistance which has not been obtained by conventional films.

[0010]

The present inventors have arrived at the present invention as a result of intensive research to achieve the above-mentioned object.

That is, in the present invention, 50 mol% of (A) naphthalenedicarboxylic acid or its ester-forming derivative is used.
A dicarboxylic acid component containing an aromatic dicarboxylic acid as a main component, (B) a diol component containing 1 to 10% by weight of diethylene glycol, and (C) 0.1 to 10
A polyester film containing, as a main component, a polyethylene glycol having a number average molecular weight of 1,000 to 20,000 in an amount of 1% by weight and having a glass transition temperature of 1
A polyester film having a temperature of 00 ° C. or higher.

A feature of the present invention is that, as the polyester constituting the film, naphthalenedicarboxylic acid or its ester-forming derivative, a specific amount of diethylene glycol and a specific amount of polyethylene glycol having a specific number average molecular weight are used as constituents, and hot This is to obtain a heat-resistant film having a high affinity with an adhesive for melt or dry laminating and having high dimensional stability even when used in boiling water for retort applications.

The naphthalenedicarboxylic acid component used to form the polyester film of the present invention comprises 2,6
-Or 1,4-naphthalenedicarboxylic acid or other naphthalenedicarboxylic acid or its ester-forming derivative as a main component, is incorporated into the main chain of polyester as an acid component, enhances the mechanical properties of the resin, food packaging It has the effect of greatly improving the gas barrier properties essential for applications and the dimensional stability in boiling water.

The naphthalenedicarboxylic acid or its ester-forming derivative used as the acid component (A) in the present invention is preferably 50 mol% or more, more preferably 70 mol% or more in the acid component. This is because when the naphthalenedicarboxylic acid or its ester-forming derivative is less than 50 mol% in the acid component, the mechanical strength of the formed polyester film tends to decrease, and the gas barrier property and the dimensional stability in boiling water tend to decrease. This is because you cannot get 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 naphthalenedicarboxylic 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 are used in an amount of 50 mol% or less, preferably 30 mol% or less, based on the total acid components of the polyester resin. Further, 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%, It may be contained preferably in the range of less than 10 mol%.

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

Further, the diol component (B) in the present invention
As a diol compound containing 1 to 10% by weight of diethylene glycol based on the obtained polymer.
When the amount of diethylene glycol is less than 1% by weight, the effect of adding diethylene glycol does not substantially appear. On the other hand, when it exceeds 10% by weight, heat resistance and dimensional stability in boiling water decrease. become. Preferably 1
~ 5% by weight. Examples of diol compounds used in combination with diethylene glycol include ethylene glycol, propylene glycol, butanediol, 1,4
-One or more of cyclohexanedimethanol, neopentyl glycol, triethylene glycol, ethylene oxide adducts of bisphenol compounds or their derivatives can be used. Of these, use of ethylene glycol is preferred. The amount used is preferably in the range of 80 mol% or more, more preferably 85 mol% or more in the total diol component.

The film of the present invention must contain a polyethylene glycol component (C) in addition to the above acid component (A) and diol component (B).

In the present invention, the fact that the polyethylene glycol is contained in the polyester in a finely dispersed manner can impart flexibility to the film without deteriorating the thermal physical properties such as the melting point of the polyester. preferable. The polyester constituting the film of the present invention does not have a structure in which polyethylene glycol is randomly copolymerized with the polyester, but has a structure in which polyethylene glycol is block-bonded to a part of the main chain terminal of the polyester. Therefore, since polyethylene glycol having a low elastic modulus is not incorporated in the main chain of polyester and is finely dispersed in the polyester in a bulk state, flexibility can be imparted without lowering the heat resistance of the film. Furthermore, since polyethylene glycol is block-bonded to the end of the main chain of polyester, polyethylene glycol, which has a low compatibility with polyester, does not aggregate and grow locally as a lump, and the homogeneity due to poor dispersion and Does not cause deterioration of physical properties.

In order to block-bond polyethylene glycol to a part of the polyester main chain terminal, for example,
This can be achieved by using polyethylene glycol having a specific number average molecular weight. That is, by using polyethylene glycol having a number average molecular weight in the range of 1,000 to 20,000, the polyethylene glycol can be block-bonded to a part of the polyester main chain terminal without random copolymerization with the polyester.

In the present invention, it is important that the polyethylene glycol used has its molecular weight and addition amount within the specified ranges. This is because the presence state of polyethylene glycol in the polyester constituting the obtained film changes depending on the molecular weight and the addition amount of polyethylene glycol, and in order to obtain a preferable structure in terms of physical property expression, the molecular weight and addition amount may be set within a specific range. This is because it is necessary.

The polyethylene glycol has a number average molecular weight of 1000 to 20000, preferably 6000 to 1.
It is in the range of 5000. If the number average molecular weight is less than 1000, it will be incorporated in the main chain of the polyester and cause the melting point to be lowered. On the other hand, if it exceeds 20,000, the terminals will not react substantially, and there is a high probability of existing in bulk form. As a result, haze is increased, which results in impairing the sharpness of printing in printing applications.

The addition amount is preferably in the range of 0.1 to 10% by weight, and more preferably in the range of 1 to 5% by weight, based on the obtained polymer. If it is less than 0.1% by weight, the substantial effect due to the addition of polyethylene glycol does not appear. On the other hand, if it exceeds 10% by weight, the glass transition temperature is lowered and the haze is increased and the film is formed. In some cases, bleeding out from the surface may result in undesirable results.

Further, in the present invention, various additives may be blended in order to impart a specific performance to the film. Examples of the additives include inorganic particles such as silica, talc, kaolin and calcium carbonate, pigments such as titanium oxide, ultraviolet absorbers, release agents and flame retardants.

The method for obtaining the polyester resin constituting the polyester film of the present invention is not particularly limited, but, for example, (A) a naphthalenedicarboxylic acid or an aromatic dicarboxylic acid containing an ester-forming derivative thereof as a main component is used. After the esterification or transesterification reaction of the acid component and (B) a diol component containing ethylene glycol as a main component containing a specific amount of diethylene glycol, a polyethylene glycol having a predetermined degree of polymerization in the condensation polymerization step of polyester. After adding a predetermined amount of the above, polycondensation is subsequently performed under normal conditions, and when the predetermined degree of polymerization is reached, the reaction is stopped, and the mixture can be discharged, pelletized, or the like.

The method for producing the polyester film of the present invention is not particularly limited. For example, the polyester resin is produced by the above-mentioned melt polycondensation and cast by a usual film forming machine having a T die, and then biaxially produced. It can be obtained by stretching and orientation. As a method for producing the same, a known means, for example, a resin that is melt-extruded at 270 to 300 ° C. and then cooled and solidified at 40 to 80 ° C. to obtain a substantially non-oriented sheet is prepared at 80 to 120 ° C. At the same time in the longitudinal and transverse biaxial, or longitudinally stretched, then stretched in the transverse direction in one step or multiple steps in the tenter, a method utilizing a so-called sequential stretching method, further after the transverse direction stretching is substantially completed,
It can be obtained by subsequently performing a heat treatment at 200 to 240 ° C. in a tenter to fix the orientation by crystallization and improve the dimensional stability. Further, in order to impart a specific performance to the film, a conventionally known processing such as application of resin such as vinylidene chloride, polyvinyl alcohol, polyamide, polyolefin or the like, lamination, or vapor deposition of metal may be performed.

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 of the present invention thus obtained has a glass transition temperature of 100 ° C. or higher. This has a glass transition temperature of 100 ° C.
If it is less than 1, the heat resistance is lowered and the dimensional stability in boiling water is lowered.

[0029]

EXAMPLES The present invention will be described in more detail with reference to examples and comparative examples. The performance was evaluated by the following method. (1) Glass transition temperature (Tg) A sample obtained by melting at 280 ° C. for 5 minutes and then quenching with dry ice was a heating rate of 5 ° C./minute using a heat flow rate differential scanning calorimeter manufactured by Shimadzu Corporation. Was measured under a nitrogen stream. The glass shoulder transition temperature (Tg) was taken as the shoulder shoulder value. (2) Gas barrier property Oxygen permeability (ml / m ² · 2 of 12 μm thick film)
4h) is made by Mocon, oxygen permeability measuring device PX-T
It was measured by RAN. (3) Adhesiveness A polybutadiene-based coating agent was uniformly applied to the surface of a polyester film having a thickness of 12 μm with a bar coater, dried at room temperature for a certain period of time to remove the solvent, and the adhesive strength was evaluated by tape peeling. The adhesiveness was judged according to the following criteria. A: No peeling is observed. B: The peeled area is within 10% of the whole. C ... The peeled area exceeds 10% of the whole. (4) Dimensional stability in boiling water A film having a thickness of 12 μm was immersed in boiling water at 95 ° C. or higher for 1 minute without applying tension, and then taken out from the boiling water.
The shrinkage rate was measured after standing for 30 seconds at room temperature ..... Shrinkage rate of less than 7% ..... Shrinkage rate of 7% or more.

Examples 1 to 9 and Comparative Examples 1 to 5 Dimethyl 2,6-naphthalenedicarboxylate (NDC), dimethyl terephthalate (DMT) and diethylene glycol (DEG) in the amounts shown in Table 1 were added to the dicarboxylic acid component. On the other hand, a 2.2-fold molar ratio of ethylene glycol (EG) was charged into a reaction vessel equipped with a rectification column and a stirrer, and manganese acetate was added thereto while stirring 260
The temperature was gradually raised to 0 ° C., and transesterification was carried out while discharging distilled methanol out of the system to obtain an esterified product having a reaction rate of 93%. The obtained esterified product was transferred to a polycondensation reaction vessel, and antimony trioxide as a polycondensation catalyst, trimethyl phosphate as a stabilizer, and polyethylene glycol (P having a number average molecular weight shown in Table 1) were used.
EG) was added in the amount shown in Table 1, and the mixture was stirred for 20 minutes to distill off excess ethylene glycol. Then, the degree of vacuum is reduced to 1 mmHg or less for 30 minutes, and the polycondensation reaction is carried out by raising the temperature to 290 ° C. and the intrinsic viscosity (measured at 25 ° C. in a mixture of phenol / tetrachloroethane and the like by weight).
A polyester resin of 7 dl / g was obtained. Next, the obtained polyester resin was vacuum-dried until the water content became 100 ppm or less, and then formed into a film with a film forming machine to obtain a raw sheet having a thickness of 150 μm. After stretching this raw sheet 3.5 times in the longitudinal direction and the transverse direction,
Heat treatment was carried out at 230 ° C. to obtain a polyester film having a thickness of 12 μm. The glass transition temperature (Tg), adhesiveness, oxygen permeability and dimensional stability in boiling water of the obtained film were measured. The results are shown in Table 1.

[0031]

[Table 1]

[0032]

EFFECT OF THE INVENTION The polyester film of the present invention has a high glass transition temperature and is excellent in adhesiveness, gas barrier property and dimensional stability in boiling water, so that it is suitable for general industrial applications including food packaging applications. It can be widely used.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seisuke Tanaka 2-4-1, Ushikawa-dori, Toyohashi-shi, Aichi Sanryo Rayon Co., Ltd. Toyohashi Plant

Claims (1)

[Claims] 1. A dicarboxylic acid component containing as a main component an aromatic dicarboxylic acid containing (A) naphthalenedicarboxylic acid or an ester-forming derivative thereof in an amount of 50 mol% or more,
A polyester film comprising (B) a diol component containing 1 to 10% by weight of diethylene glycol and (C) a polyethylene glycol having a number average molecular weight of 1,000 to 20,000 of 0.1 to 10% by weight as main components. A polyester film having a glass transition temperature of 100 ° C. or higher.