JPH0892467A - Polyester film - Google Patents

Abstract

(57) [Summary] [Purpose] High glass transition temperature and excellent hiding power.
Provided is a polyester film having light transmittance, dimensional stability in boiling water, and gas barrier properties. [Structure] In a polyester film made of a polyester resin having a dicarboxylic acid component containing naphthalenedicarboxylic acid or an ester-forming derivative thereof as a main component and a diol component containing ethylene glycol as a main component, the average particle diameter is Is 1.5 to 5 μm, the pore volume of the particle surface is 0.6 to 1.7 ml / g, and the average pore diameter is 6
It contains 0.1 to 8% by weight of silica particles of 0 to 200Å, glass transition temperature of 100 ° C or higher, haze of 60% or higher, total light transmittance of 70% or higher, and oxygen transmittance of 300 ml / m. A film that is ² / 24h or less.

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 industry. More specifically, it has excellent concealing properties and light transmittance, and can be used in boiling water. The present invention relates to a polyester film having a low oxygen permeability and suitable for storing fresh food.

[0002]

2. Description of the Related Art Polyester films typified by polyethylene terephthalate have physical properties such as transparency, mechanical properties and dimensional stability.
In addition, since it has excellent chemical properties such as chemical resistance, it is widely used for magnetic tapes, general industries, food packaging and the like.

In particular, for food packaging, the taste of the contents has become high-grade in recent years, and fruits for gifts,
Individual packaging of snacks is becoming popular. Papers are generally used for these purposes, and have been used for protecting products and imparting aesthetic appeal. However, since these papers have low mechanical strength, they are often damaged during transportation of goods or during the period of display at stores.Although the papers are moisture-proof, they are not It has low water resistance and water resistance, so it is easily damaged by high humidity such as during the rainy season or when it is exposed to water during rainfall, and even when damage does not occur, the shape is significantly deformed, greatly reducing the value as a packaging material for products. It was something that was. Further, papers have little effect in applications where they are sealed with a packaging material and used for the purpose of preventing oxidation due to oxygen in the air, such as snacks, and the storage period is significantly limited.

On the other hand, a plastic film packaging material containing a polyester film is used as a food packaging material because it overcomes various drawbacks of the above-mentioned papers such as mechanical strength, gas barrier property, and water / moisture resistance. In many cases, it is becoming popular. As the plastic film, a film obtained from a polyolefin resin such as polypropylene or polyethylene is most often used, and subsequently, a film obtained from a polyvinyl chloride resin or a polystyrene resin is often used. Further, as a laminated product of these films, a film having a resin film having a high gas barrier property on three intermediate layers, or a heat-sealing property and a gas barrier property on the back surface of a two-layer bag when making a bag are provided. Films and the like have been used.

However, films obtained from resins such as polypropylene and polyethylene have low mechanical strength and high crystallinity, and polyvinyl chloride resin films generate hydrogen chloride due to incineration during disposal. Is not preferable in terms of environmental protection, and because polystyrene resin film has low heat resistance, distortion due to deformation at room temperature tends to occur, and use is restricted due to high combustion heat at incineration. The tendency is being increased. A polyester film has been attracting attention as a material for compensating for the drawbacks of these general-purpose films, and a polyester film has been used in increasing amounts in recent years. Polyester film has excellent properties with respect to these resins in terms of mechanical strength, gas barrier property, heat resistance, and chemical resistance, and it has been confirmed that it has extremely preferable properties as a packaging material, and the case to be used is It is increasing.

However, in recent years, individual packaging of products has become widespread against the backdrop of a situation in which the taste of high-quality products to be packaged is increasing, and the concealing property of a plastic film is used as a method of imparting a high-class feeling. Boosting is becoming more commonly used. For example, this is used for individual packaging of fruits for gifts or exhibitions, or individual packaging of snacks, especially for multicolor printing. In addition, examples of general industrial applications include synthetic papers,
It has been used in some parts such as tracing paper.

In the plastic film used for these purposes, a method of incorporating a large amount of inorganic particles having a refractive index greatly different from that of the resin into the film has hitherto been adopted, and rutile or anatase-type oxidation as the inorganic particles. Titanium, kaolin, and wet or dry silica are used.

However, films having a concealing property and a suitable light transmittance and which are mainly used for food packaging have been diversified in recent years due to their material suitability, and applications where importance is attached to color and taste, and long-term use of fresh foods. The fields of application are expanding, such as applications for storage, and applications that can withstand retort food processing in boiling water.

However, in consideration of such use, a film having excellent hiding property and light transmittance can be obtained by adopting a conventional method. It has not been found yet about a film which is neither deformed nor damaged by a treatment in boiling water exceeding 100 ° C. and has a high gas barrier property.

[0010]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above-mentioned circumstances, and as a result, by containing a specific amount of silica particles having a specific structure in a polyester film composed of specific components, The inventors have found that the above problems can be solved and have reached the present invention.

That is, the present invention is a film made of a polyester resin containing a dicarboxylic acid component containing naphthalenedicarboxylic acid or an ester-forming derivative thereof in an amount of 50 mol% or more and a diol component containing ethylene glycol as a main component. In the film, the average particle size is 1.5 to 5 μm, and the pore volume on the particle surface is 0.6 to
Silica particles having 1.7 ml / g and an average pore diameter of 60 to 220Å are contained in an amount of 0.1 to 8% by weight, a glass transition temperature of 100 ° C or higher, a haze of 60% or higher, and a total light transmission. Rate is 70% or more, oxygen permeability is 300m
The polyester film is characterized in that it is 1 / m ² · 24 h or less.

The polyester resin used in the polyester film of the present invention comprises a 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. .

The naphthalenedicarboxylic acid component used to obtain the polyester resin is 2,6- or 1,4-
The main component is naphthalenedicarboxylic acid such as naphthalenedicarboxylic acid or its ester-forming derivative, and is incorporated in the main chain of polyester as an acid component,
It not only enhances the mechanical properties of the resin, but also has the effect of greatly improving the gas barrier properties essential for food packaging 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%.

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,
Diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, an ethylene oxide adduct of a bisphenol compound or its derivative, and the like can be used.

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

In the polyester resin composed of the above dicarboxylic acid component and diol component used in the present invention, it is preferable that 80 mol% or more of its repeating units are naphthalene terephthalate units.

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 [η ] (Measured in a mixed solution of phenol / tetrachloroethane and the like at 25 ° C.) of about 0.5 to 1.2 dl / g is preferable.

The polyester film of the present invention is a polyester film obtained from the polyester resin having the above-mentioned constitution, and contains silica particles having a specific structure.

A feature of the present invention is that a polyester film has silica particles having a specific structure, that is, an average particle diameter of 1.5 to 5 μm and a pore volume of 0.6 on the particle surface.
-1.7 ml / g and by containing a specific amount of silica particles having an average pore diameter in the range of 60 to 220Å, the film has a high hiding effect and an elegant appearance, and the film passes through the film forming process. It has been found that a film having good properties can be obtained.

The silica used in the present invention has a bulky structure in which the surface and the inside of the particles are made porous to form cavities. Therefore, the masking property obtained with respect to the added amount is high, and it becomes possible to exhibit a high masking effect with a smaller added amount than that of conventional silica. In the present invention,
As the silica particles to be used, by using porous silica particles having a porous surface and the inside thereof,
The silica particles are made bulky to enhance the hiding power of the film with respect to the content of the particles. However, when the porous silica particles are added to the polyester polymerization system, it is carried out by adding a dispersion liquid in which silica particles are dispersed in a solvent such as ethylene glycol, but the solvent content on the particle surface is When it becomes higher, the viscosity of the dispersion increases, the dispersibility of the silica particles tends to decrease, and the process passability tends to decrease.

Therefore, the silica particles used in the present invention have an average particle size (measured by the Coulter counter method) of 1.5 to 5 μm and a pore volume of the particle surface of 0.
6 to 1.7 ml / g, the average pore diameter of the particle surface is 60 to 2
It is necessary to be in the range of 20Å. By using such silica particles, it is possible to obtain a film having a great hiding property and an elegant appearance without impairing the dispersibility of the particles and the process passability. It is a thing.

The particle size of the silica particles affects the haze of the film, and the average particle size of the silica particles is 1.5 μm.
When the average particle size exceeds 5 μm, the hiding property of the film increases, but defects such as voids are likely to occur in the film, and the hiding property of the film tends to occur at the time of stretching. This is because vertical tearing may occur. The average particle size of the silica particles is preferably in the range of 2.5 to 4.5 μm.

Further, the pore volume of the surface of the silica particles affects the bulkiness of the particles, and the pore volume is 0.6 ml /
If it is less than g, the hiding property of the film does not decrease unless a large amount is added. Further, when the pore volume of the particle surface exceeds 1.7 ml / g, the hiding property of the film increases, but the apparent density difference between the silica particles and the solvent becomes large and it becomes difficult to adjust the dispersion liquid, and the particle surface The solvent viscosity increases and gelation of the dispersion and aggregation of silica particles are likely to occur, resulting in poor processability, and the particle dispersibility decreases, and a uniform film cannot be obtained. The pore volume of the silica particle surface is
The range is preferably 0.8 to 1.6 ml / g, and more preferably 1.0 to 1.4 ml / g.

Further, when the average pore size of the silica particles on the particle surface is less than 60Å, friction between the silica particles and the solvent is increased, the viscosity of the solvent is increased, and gelation of the dispersion liquid or aggregation of the silica particles is likely to occur. The passability is poor, and the dispersibility of the particles is low, so that a uniform film cannot be obtained. On the other hand, if the average pore diameter exceeds 220 Å, the roundness of the silica particles is lowered, making it difficult to prepare a uniform dispersion, and the hiding property of the film is lowered. The average pore diameter of the silica particles is preferably in the range of 70 to 210Å, more preferably 100 to 180Å.

The content of silica particles in the polyester film is in the range of 0.1 to 8% by weight. If the content is less than 0.1% by weight, the hiding property is not sufficient, and if it exceeds 8% by weight, the total light transmittance is high. When the product is packaged low, it becomes impossible to see through the object to be packaged, and the viscosity of the dispersion increases in the polymerization process, resulting in poor processability and a uniform film cannot be obtained. As the silica particles having such a specific structure, siloid-based silica particles by a dry method or a wet method or silica particles by a gelling method are suitable, and gelling silica particles are particularly suitable.

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 a polyester resin containing the above-mentioned constituent components containing the above-mentioned silica particles by a melt condensation method or the like and biaxially orienting it. As the production method, a known production method, for example, after melt-extruding a resin at 270 to 300 ° C.,
A substantially non-oriented sheet obtained by cooling and solidifying at -80 ° C is biaxially stretched in the vertical and horizontal directions at the same time in the longitudinal or transverse direction at 80 to 120 ° C, or in the longitudinal direction, and then in a tenter in the transverse direction in one or more stages. The method of utilizing the so-called sequential stretching, further, after the transverse stretching is substantially completed, heat treatment is performed at 200 to 240 ° C. in a drawing tenter to fix the orientation by crystallization to stabilize the dimension. It can be obtained by utilizing a method for improving sex.

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.

If necessary, the polyester film of the present invention may be added with necessary amounts of antioxidants, pigments and the like which are usually used.

With the above constitution, the polyester film of the present invention has a glass transition temperature of 100 ° C. or more, haze of 60% or more, total light transmittance of 70% or more, and oxygen transmittance of 300 ml / in a film having a thickness of 17 μm. m ² · 24
It is important that h or less.

(1) If the glass transition temperature is less than 100 ° C., the dimensional stability in boiling water is insufficient, and retort food cannot be packaged. (2) When the haze is less than 60%, high hiding property cannot be exhibited. (3) If the total light transmittance is less than 70%, the amount of light passing through the film is reduced, the film surface becomes dark, and the elegant appearance is not exhibited. (4) Oxygen permeability of 300 ml / m ²
・ If it exceeds 24 hours, the commercial value of the contents will be impaired by the permeation of oxygen. It is due to the reason such as.

[0033]

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.

1. Haze (%) The haze of a film having a thickness of 17 μm was measured with a haze meter (MODEL TC-HIII) manufactured by Tokyo Denshoku Co., Ltd.

2. Total Light Transmittance According to ASTM D 1003, the total light transmittance of a film having a thickness of 17 μm was measured.

3. Glass transition temperature (Tg) A sample obtained by melting at 280 ° C for 5 minutes and then quenching with dry ice was a nitrogen flow at a heating rate of 5 ° C / min using a heat flow rate differential scanning calorimeter manufactured by Shimadzu Corporation. Measured below. The glass shoulder transition temperature (Tg) was taken as the shoulder shoulder value.

4. Gas barrier property Oxygen permeability (ml / m ² · 2 of 17 μm thick film)
4h) is made by Mocon, oxygen permeability measuring device PX-T
It was measured by RAN.

5. Dimensional stability in boiling water A film having a thickness of 17 μm was immersed in boiling water at 95 ° C. or higher for 1 minute without applying tension, then taken out from the boiling water and allowed to stand at room temperature for 30 seconds to measure the shrinkage rate. . ○: Shrinkage of less than 7% ×: Shrinkage of 7% or more

Examples 1 to 8 and Comparative Examples 1 to 8 Dimethyl terephthalate (DMT) and dimethyl 2,6-naphthalenedicarboxylate (NDC) were charged in the amount ratio shown in Table 1, and further 2 to the dicarboxylic acid component. .2 mole ratio ethylene glycol (EG) and manganese acetate as a catalyst were charged into a reaction vessel equipped with a rectification column and a stirrer, and the temperature was gradually raised to 260 ° C while stirring,
While distilling out the distilled methanol out of the system, transesterification was carried out to obtain a reaction product having a reaction rate of 93%. The obtained reaction product was transferred to a polycondensation reaction vessel, and antimony trioxide was used as a catalyst.
After adding trimethyl phosphate as a stabilizer, various silica particles shown in Table 1 (manufactured by Fuji Sylysia Ltd., Sylysia # 430) prepared in advance as an ethylene glycol dispersion solution were added. After stirring for 20 minutes to distill off excess ethylene glycol, the degree of vacuum was reduced to 1 mmHg or less in 30 minutes, and the temperature was raised to 290 ° C. for polycondensation to obtain a polyester resin having a predetermined degree of polymerization. This polyester resin was vacuum-dried at 120 ° C. for 10 hours, and then formed into a 150 μm sheet by a T-die casting type film forming machine, and then stretched 3.0 times in each of the longitudinal and transverse directions and heat-treated to form a film with a thickness of 17 μm. Got The glass transition temperature (Tg), haze, total light transmittance, oxygen transmittance, and dimensional stability in boiling water of this film were measured. The evaluation results are shown in Table 1.

[0040]

[Table 1]

[0041]

The polyester film of the present invention having the above-mentioned constitution has a high glass transition temperature, and has excellent concealing property, light transmitting property, dimensional stability in boiling water and gas barrier property. Therefore, it can be widely used for industrial applications including food packaging.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location B29K 105: 16 (72) Inventor Seisuke Tanaka 2 Sanbishi, 4-1, Ushikawa-dori, Toyohashi City, Aichi Prefecture Rayon Co., Ltd. Toyohashi Office

Claims (1)

[Claims] 1. A film made of a polyester resin comprising a dicarboxylic acid component containing 50 mol% or more of naphthalenedicarboxylic acid or an ester-forming derivative thereof and a diol component containing ethylene glycol as a main component, the polyester resin comprising: The average particle size in the film is 1.5-5μ
m, the volume of pores on the particle surface is 0.6 to 1.7 ml / g, and the average pore diameter is 60 to 220Å.
The glass transition temperature is 100 ° C or higher, the haze is 60% or higher, the total light transmittance is 70% or higher, and the oxygen transmittance is 300 ml / m ² · 24h or lower. A polyester film characterized by.