JP3314820B2 - Gas barrier void-containing polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when used in labels, posters, recording paper, packaging materials, etc., contains a large amount of fine cavities inside a film with improved surface peel strength, opacity, whiteness, etc. And a polyester film having good gas barrier properties.

[0002]

2. Description of the Related Art Synthetic paper, which is a paper substitute made of synthetic resin as a main raw material, has a higher water resistance, a greater moisture absorption dimensional stability, and a higher stability than natural paper.
Excellent in surface stability, gloss and sharpness of printing, mechanical strength, etc. In recent years, application development utilizing these advantages has been promoted. As a method for obtaining a film having a function similar to paper made of polyester as a main raw material, a method of containing a large amount of fine cavities inside the film can provide a point that the film itself can be reduced in weight and impart appropriate flexibility. ,
There is an advantage that clear printing and transfer become possible.

[0003] As a method of forming fine cavities inside a film, conventionally, a polymer incompatible with polyester is melt-kneaded with an extruder, and a sheet in which the polymer is dispersed in fine particles in polyester is obtained. A method of generating a cavity around fine particles by stretching is disclosed. Examples of the polymer incompatible with the polyester used for the cavity (hereinafter, referred to as a cavity developing agent) include polyolefin resins (for example, JP-A-49-13).
No. 4755) and polystyrene resins (for example, JP-B-49-2016 and JP-B-54-29550) are preferable.

[0004] So far, the void-containing polyester film has excellent properties such as light weight, concealing property, and stiffness, but no void-containing polyester film having good gas barrier properties .

[0005]

[SUMMARY OF THE INVENTION The present invention, the disadvantages, i.e., by suitability of the distribution cavity, printing or printing, copying, etc. There are vivid and durable, concealing property and whiteness, It is an object of the present invention to provide a substrate having excellent surface strength and good gas barrier properties.

[0006]

That is, the present invention comprises a fine cavity formed by orienting at least one axis a polymer mixture obtained by mixing a polyester with a thermoplastic resin incompatible with the polyester. Void-containing polyester film ( C) provided with a layer (B) made of a thermoplastic resin on at least one surface of the polyester layer (A) to be formed
The further provides a at least organic and / or gas barrier properties void-containing polyester film having a gas barrier layer made of an inorganic substance on one side, 3 from the surface of the A layer
the void content contained up to 8 μm is 8% by volume or less;
And the average void content of the entire film (C) is 10% by volume.
The present invention relates to a gas-blocking void-containing polyester film having a content of at least 50% by volume.

The polyester of the present invention and a polymer mixture obtained by mixing the polyester with an incompatible thermoplastic resin may be obtained, for example, by mixing chips of each resin, melt-kneading in an extruder, and then extruding and solidifying. A method obtained by kneading both resins with a kneading machine in advance, and a method of solidifying by extruding the mixture further by an extruder, or adding a thermoplastic resin incompatible with polyester in a polyester polymerization step, stirring and dispersing. It can also be obtained by a method of melt-extruding the chips obtained and solidifying them.

[0008] To the polymer mixture, a coloring agent, a light-proofing agent, a fluorescent agent, an antistatic agent and the like can be added according to the use. The obtained polymer mixture is further stretched between rolls having different speeds (roll stretching), stretched by gripping and spreading with a clip (tenter stretching), or stretched by air pressure (inflation stretching). At least one axis orientation treatment is performed by such as. By the orientation treatment, peeling occurs at the interface between the polyester and the cavity developing agent, and cavities are developed.

Therefore, the amount of the thermoplastic resin which is incompatible with the polyester and which is mixed with the polyester depends on the amount of the target cavity, but is preferably 3% by weight to 35% by weight based on the whole polymer mixture. . If the content is less than 3% by weight, there is a limit in increasing the amount of cavities formed, and the desired flexibility, lightness and drawing property cannot be obtained. Conversely, 40
If the amount is more than the weight percentage, the heat resistance and strength of the polyester film are significantly impaired.

In order to reduce the amount of cavities only in the surface layer,
It is effective to make the dispersed particles of the thermoplastic resin in the polymer mixture finer near the surface layer than near the center,
It can be obtained by selecting the melt viscosity characteristics of the polyester and the thermoplastic resin and the conditions for melt extrusion from an extruder. The conditions for orienting the polymer mixture are closely related to the formation of cavities. Therefore, the conditions for achieving this object are, for example, the most commonly performed sequential biaxial stretching step, for example, taking a continuous sheet of the polymer mixture as a roll in the longitudinal direction and then stretching in the width direction. In the case of the sequential biaxial stretching method in which tenter stretching is performed, the following is performed. In the roll stretching, it is preferable that the temperature is not higher than the biaxial stretching temperature of the polyester + 30 ° C. and the magnification is 1.2 to 5 times in order to generate many cavities. In tenter stretching, the temperature is set to 80 to 140 for stable film formation without breaking.
It is preferable that the temperature and the magnification are 1.2 to 5 times.

[0011] The void-containing film subjected to the stretching orientation treatment is
When heat setting is performed at 30 degrees or more, preferably 180 degrees or more, dimensional stability at high temperatures can be improved. In the present invention, a so-called composite film in which a surface layer and a center layer are laminated must be used. The method is not particularly limited. However, in consideration of productivity, the raw materials of the surface layer and the center layer are extruded from separate extruders, guided to one die to obtain an unstretched sheet, and then oriented at least uniaxially.
Lamination by the so-called coextrusion method is most preferred.

The void-containing polyester film thus obtained has a void content of not more than 8% by volume in the layer from the surface of the layer A to a depth of 3 μm, and an average void content of the entire layer of 10% by volume. It is necessary to be above. When the thermoplastic resin B layer is not provided, or when the surface layer from the surface of the layer A to the depth of 3 μm contains more than 8% by volume of cavities, a material having particularly good surface strength cannot be obtained. The thickness of the surface layer portion of the cavity ratio A layer be not more than 8% by volume 3
When the thickness is smaller than μm , a material having particularly good surface strength cannot be obtained. If the average porosity of the entire film layer is less than 10% by volume , the flexibility inherent in the void-containing polyester film becomes insufficient, and the drawing properties and cushioning properties also become insufficient.

In the present invention, gas barrier properties can be provided by providing a gas barrier layer on at least one side of the above-mentioned film. Examples of the gas barrier layer include vinylidene chloride, vinylidene chloride-acrylonitrile copolymer, vinylidene chloride-acrylic acid copolymer, vinylidene chloride-acrylate copolymer, and vinylidene chloride.
At least one of vinyl alcohol copolymer, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, etc. Known methods such as a method of applying more than one kind, a method of forming these resins into a laminated film by coextrusion or laminating, and a method of evaporating an inorganic substance such as silicon dioxide, calcium carbonate, titanium dioxide, and aluminum oxide (for example, 48-48480, 52-98
074) can be used and is not limited.

[0014]

In the present invention, polyester is used for
This is for satisfying the heat resistance and mechanical strength of the void-containing polyester film. In the present invention, mixing a thermoplastic resin incompatible with the polyester to the polyester, to obtain a polymer mixture, by dispersing fine particles of the thermoplastic resin incompatible with the polyester in the polyester, This is because the nuclei of the cavities generated by the next alignment treatment are formed.

In the present invention, the reason why the thermoplastic resin B layer is provided and the amount of cavities contained in the surface layer portion 3 μm of the A layer is set to 8% by volume or less is to increase the surface strength. On the other hand, the reason why the average void content of the entire layer is set to 10% by volume or more is to provide appropriate drawing properties and cushioning properties. The reason why the gas barrier layer is provided in the invention is to improve the gas barrier property.

The void-containing polyester film thus obtained satisfies the surface strength and gas barrier properties particularly required for applications such as packaging materials.

[0017]

Next, examples of the present invention will be described. 1) Intrinsic viscosity of polyester The polyester was dissolved in a mixed solvent of phenol (6 parts by weight) and tetrachloroethane (4 parts by weight) and measured at 30 ° C. 2) Melt flow index of polystyrene resin Measured at 200 ° C. under a load of 5 kg according to JIS-K7210. 3) Density The film was cut out into a square of 5.00 cm x 5.00 cm, and its thickness was measured at 50 points to obtain an average thickness of tμm.
The weight was measured up to 0.1 mg and defined as wg, which was calculated by the following equation.

[0018]

(Equation 1)

4) Average porosity of film Calculated by the following equation.

In the present invention, the reason why the thermoplastic resin B layer is provided and the amount of cavities contained in the surface layer portion 3 μm of the A layer is set to 8% by volume or less is that the surface strength is further increased. On the other hand, the reason why the average void content of the entire layer is set to 10% by volume or more is to provide appropriate drawing properties and cushioning properties. In the present invention, to use a water-soluble resin and water insoluble polyester copolymer is order to improve the adhesion of both hydrophilic resin and a hydrophobic resin.

However,

[0022]

Next, examples of the present invention will be described. 1) Intrinsic viscosity of polyester The polyester was dissolved in a mixed solvent of phenol (6 parts by weight) and tetrachloroethane (4 parts by weight) and measured at 30 ° C. 2) Melt flow index of polystyrene resin Measured at 200 ° C. under a load of 5 kg according to JIS-K7210. 3) Apparent specific gravity of the film The film was accurately cut into a square of 5.00 cm × 5.00 cm, the thickness was measured at 50 points, and the average thickness was tμ.
m, its weight is measured to 0.1 mg and wg,
The apparent density of the film was calculated by the following equation. Apparent density (g / cm ³ ) = w / (5 × 5 × t) × 10000 The specific gravity of the solid is the density of the solid and the density of water at 4 ° C.
(0.999973 g / cm ³ ) and generally defined as
It is the density of water and substantially 1.00 g / cm ³ Minaseruko
From the apparent density of the film divided by the density of water
And the apparent specific gravity of the film is calculated as follows.

Apparent specific gravity (−) = w / (5 × 5 × t) × 10000

4) Average porosity of film Calculated by the following equation. Cavity content (volume%) = 100 × (1-true specific volume / apparent specific volume)

Where true specific volume = x1 / d1 + x2 / d2 + x3 / d3 +... + Xi / di +.

Apparent specific volume = 1 / apparent specific gravity of film In the above formula, xi represents the weight fraction of the i component, and di represents the true specific gravity of the i component. The values of the true specific gravity used in the calculations in the examples were polyethylene terephthalate 1.40, general-purpose polystyrene 1.05, and anatase-type titanium dioxide 3.9.
Was used.

The cross section of the unstretched sheet of the polymer mixture of this example was observed with a scanning electron microscope. The average particle size of the polystyrene dispersed in the center was 5.0 μm, whereas the average particle size of the polystyrene dispersed in the center was 5.0 μm. The average particle size was 0.7 μm. The apparent specific gravity is 1.10, and the porosity of the surface layer of the A layer is 2
The volume%, the total average porosity was 21% by volume, the light transmittance was 13%, and the thickness was 50 μm.

Linear copolyester polymerized by using 80 mol% of terephthalic acid and 20 mol% of sebacic acid as an acid component and 60 mol% of ethylene glycol and 40 mol% of neopentyl glycol as a glycol component in this film. Isocyanate compound consisting of a reaction product of 1 mol of tolylene diisocyanate and 3 mol of trimethylolpropane in a ratio of 95: 5 to tetrahydrofuran 5
% Solution dissolved in an applicator (gap 1/1)
000 inches) and heated in a hot air drier at 115 ° C for 40
Dried for seconds. Further, the coated surface was overcoated with vinylidene chloride resin and dried at 115 ° C. for 40 seconds. At this time, the applied amount of the solid content was 4.6 g / cm. ASTM at this time
The gas permeation amount of oxygen according to the -D1484-68 method is 11.
5 (cc / m ² · 24 hr · 1 atm) was good.

[0029]

The void-containing polyester film of the present invention has the same light weight, flexibility, concealing properties, matting properties, and drawing properties as the conventional void-containing polyester film obtained using polystyrene or polyolefin as a void-generating agent. In addition to having the properties, compared to the conventional void-containing polyester film , excellent opacity, whiteness, surface strength,
In addition, there is an effect that it has good adhesiveness to both hydrophilic and hydrophobic resins. Therefore, the void-containing polyester film of the present invention can be used for labels, posters, recording paper,
Packaging materials, heat-sensitive recording material, can be used in a very wide range of fields, such as photographic paper.

Claims (1)

(57) [Claims] At least one surface of a polyester layer (A) containing fine cavities formed by at least uniaxially orienting a polymer mixture of a polyester and a thermoplastic resin incompatible with the polyester. A gas-blocking cavity in which a cavity-containing polyester film ( C) provided with a layer (B) made of a thermoplastic resin , and a gas barrier layer made of an organic and / or inorganic material provided on at least one surface thereof. A polyester film comprising:
Gas barrier properties characterized in that the content of voids contained within 3 μm from the surface of the layer is not more than 8% by volume and the average content of voids in the entire film (C) is not less than 10% by volume and not more than 50% by volume. Void-containing polyester film.