JPH05345398A - Heat-sealable cavity-containing polyester film - Google Patents

Abstract

PURPOSE:To provide a polyester film especially suitable for a packing material imparting sharp printing or duplication, having durability and excellent in concealability, whiteness and heat sealability by rationalizing the size of cavities. CONSTITUTION:A layer (B) composed of a thermoplastic resin is provided on at least the single surface of a fine cavity-containing polyester layer (A) formed by at least uniaxially orienting a polymer mixture of polyester and a thermoplastic resin incompatible with polyester to form a cavity-containing polyester film characterized by that the content of cavities contained in the A-layer up to a depth of 3mum from the surface thereof is 8vol.% or less and the average content of cavities in the whole of the film is 10-50vol.%. A heat-sealable layer is provided to at least the single surface of this polyester film.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention, when used for labels, posters, recording papers, packaging materials, etc., contains a large amount of fine voids inside a film having improved surface peel strength, hiding power, whiteness and the like. The present invention relates to a polyester film having heat sealability.

[0002]

2. Description of the Related Art Synthetic paper, which is a paper substitute mainly made of synthetic resin, has a higher water resistance, higher dimensional stability in moisture absorption, and a higher dimensional stability than natural paper.
It has excellent surface stability, gloss and clarity of printing, and mechanical strength. In recent years, application development has been promoted by making use of these advantages. As a method of obtaining a film having a function similar to paper using polyester as a main raw material, a method of containing a large amount of fine voids inside the film can give a point that the film itself can be lightened and an appropriate flexibility can be imparted. ,
There is an advantage that clear printing and transfer are possible. Conventionally, as a method of generating minute cavities inside the film,
A method is disclosed in which a polymer incompatible with polyester is melt-kneaded with an extruder to obtain a sheet in which the polymer is dispersed in fine particles in polyester, and the sheet is further stretched to generate voids around the fine particles. There is. As the polymer incompatible with the polyester used for the cavities (hereinafter referred to as the cavity developing agent), a polyolefin resin (for example, JP-A-49-134755) or a polystyrene resin (for example, JP-B-49-2016) is used. JP-B No. 54-29550). Conventional void-containing polyester films are lightweight,
Although it had excellent properties such as concealability and firmness, it did not have heat-sealing properties and had poor processing characteristics such as bag making.

[0003]

DISCLOSURE OF THE INVENTION The present invention has the drawbacks of the previous term, namely, by optimizing the distribution of cavities, it is clear and durable for printing, printing, copying, etc. It is intended to provide a base material having excellent strength and heat sealability.

[0004]

That is, the present invention provides a fine cavity produced by orienting at least uniaxially a polymer mixture obtained by mixing a polyester with a thermoplastic resin incompatible with the polyester. In the polyester film containing a large number, the content of cavities included in the surface layer from the surface to a depth of 3 μm is 4% by volume or less, and the average content of cavities in the entire layer is 8% by volume or more and 50% by volume or less. The present invention relates to a void-containing polyester film having a heat-sealing layer made of a copolyester on at least one surface of a film.

A polymer mixture obtained by mixing the polyester of the present invention and an incompatible thermoplastic resin with the polyester is prepared by, for example, mixing chips of each resin, melt-kneading in an extruder, and then extruding and solidifying. Method, or a method in which both resins are kneaded in advance by a kneader to be melt-extruded and solidified by an extruder, or an incompatible thermoplastic resin is added to the polyester in the polyester polymerization step and dispersed by stirring. It can also be obtained by a method of melt-extruding and solidifying the obtained chips. It is possible to add a colorant, a light-proofing agent, a fluorescent agent, an antistatic agent, etc. to the polymer mixture depending on the application. The resulting polymer mixture is further stretched between rolls having different speeds (roll stretch), stretched by gripping and expanding with a clip (tenter stretch), and stretched by expanding by air pressure (inflation stretch). Orientation processing is performed on at least one axis by such as. By the orientation treatment, peeling occurs at the interface between the polyester and the void developing agent to develop voids. Therefore, the amount of the thermoplastic resin that is incompatible with the polyester and mixed with the polyester varies depending on the amount of the target voids, but is preferably 3% by weight to 35% by weight with respect to the entire polymer mixture. 3% by weight
Below, there is a limit to increase the amount of cavities,
The desired flexibility, lightness and drawability cannot be obtained. Conversely, 4
When it is 0% by weight or more, the heat resistance and strength of the polyester film are significantly impaired.

The conditions for orienting the polymer mixture are closely related to the formation of cavities. Therefore, the conditions for achieving the object are, for example, the most commonly performed sequential biaxial stretching step, and a continuous sheet of the polymer mixture is roll-stretched in the longitudinal direction and then in the width direction. In the case of the sequential biaxial stretching method in which tenter stretching is performed, it is as follows. In the roll stretching, it is preferable that the temperature is not more than the biaxial stretching temperature of polyester + 30 ° C. and the magnification is 1.2 to 5 times in order to generate a large number of voids. In the 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. The void-containing film that has been stretched and oriented can be improved in dimensional stability at high temperatures when heat-set at 130 ° C. or higher, preferably 180 ° C. or higher. In the present invention, a so-called composite film in which the surface layer and the center layer are laminated must be formed. The method is not particularly limited. However, from the viewpoint of productivity, it is most preferable to use the so-called coextrusion method in which the raw materials for the surface layer and the central layer are extruded from different extruders, introduced into one die to obtain an unstretched sheet, and then oriented at least uniaxially. ..

The void-containing polyester film thus obtained is provided with a thermoplastic resin B layer and has a void content of 8% by volume in the layer from the surface of layer A to a depth of 3 μm.
It is necessary that the average porosity is not more than 10% by volume. If the thermoplastic resin B layer is not provided, or if the surface layer from the surface of the A layer to a depth of 3 μm contains more than 8% by volume of cavities, particularly good surface strength cannot be obtained. Further, when the surface layer portion of the layer A having a porosity of 4% by volume or less is thinner than 3 μm, particularly good surface strength cannot be obtained. Therefore, in the present invention,
The surface layer of layer A, which has less cavities than the center, has a depth of 3μ.
m or more, and the void content contained therein must be 4% by volume. Further, the entire layer needs to have an average void content of 10% by volume or more. If the average porosity of the entire layer is less than 10% by volume, the flexibility peculiar to the void-containing polyester film becomes insufficient, and the drawing property and cushioning property also become insufficient.

In order to reduce the amount of voids only in the surface layer of layer A, it is effective to make the dispersed particles of the thermoplastic resin in the polymer mixture finer near the surface layer of layer A than around the center. It is obtained by selecting the melt viscosity characteristics of the polyester and the thermoplastic resin and the conditions for melt extrusion from the extruder. In the film of the present invention, the void-containing polyester film is provided with a heat-sealing layer containing at least one copolymerized polyester on at least one side. The copolyester as used herein is a polymer which is soluble in an organic solvent, in which 95 to 50 mol% of the acidic component is terephthalic acid residue and 20 to 70 mol% of the alcohol component is ethylene glycol residue. The remaining 5 to 50 mol% of the acidic component consists of residues of adipic acid, sebacic acid and other aliphatic dibasic acids, isophthalic acid, orthophthalic acid, diphenyldicarboxylic acid and the like. The remaining 80 to 30 mol% of the alcohol component is 1.2-propylene glycol, 1.3-propylene glycol, 1
-Consisting of glycol residues such as 3-butanediol, 1.4-butanediol, diethylene glycol, triethylene glycol, dipropylene glycol and neopentyl glycol. The copolyester of the present invention may be melted in an organic solvent such as chloroform, toluene or xylene and then applied on at least one side of the film, or may be a laminated film formed by coextrusion.

[0009]

In the present invention, the polyester is used
This is because the heat resistance and mechanical strength of the void-containing polyester film are satisfied. In the present invention, the polyester is mixed with the polyester incompatible thermoplastic resin, to obtain a polymer mixture, by dispersing fine particles of the polyester incompatible thermoplastic resin in the polyester, This is to form a nucleus of a cavity generated by the next alignment treatment. In the present invention, the reason why the thermoplastic resin B layer is provided and the amount of the cavities contained in the surface layer portion 3 μm of the A layer is 8% by volume or less is because the surface strength becomes particularly strong. On the other hand, the reason why the average void content of the entire layer is 10% by volume or more is to provide appropriate drawing properties and cushioning properties. The void-containing polyester film thus obtained was excellent in surface strength and had heat sealability.

[0010]

EXAMPLES Examples of the present invention will be described below. 1) Intrinsic viscosity of polyester 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 is cut into a square of 5.00 cm × 5.00 cm, and its thickness is measured at 50 points, and the average thickness is t μm.
Was calculated, and the weight thereof was measured up to 0.1 mg to be wg, which was calculated by the following formula.

[0011]

[Equation 1] 4) Average porosity of film Calculated by the following formula.

[0012]

[Equation 2] However,

[0013]

[Equation 3]

[0014]

[Equation 4] In the above equation, xi represents the weight fraction of the i component, and di represents the true specific gravity of the i component. The true specific gravity values used in the calculations in the examples are polyethylene terephthalate 1.40, general-purpose polystyrene 1.05, anatase type titanium dioxide 3.
9. Rutile type titanium dioxide 4.2 was used. 5) Porosity of the surface layer of the void-containing film After taking a photograph of the surface layer near the surface of the cross section of the film with a scanning electron microscope, trace the voids in the region from the surface layer to a depth of 3 μm on a tracing film and analyze the image. Image processing was performed by the device, the void ratio was calculated as an area ratio, and this value was directly displayed as volume%. -Scanning electron microscope used S-510 scanning electron microscope manufactured by Hitachi Ltd.-Image analysis processor used Luzex IID (Nireco Corporation)

6) Light transmittance According to JIS-K6714, the Poick integrating sphere type H. T.
The light transmittance of the film was measured using an R meter (manufactured by Nippon Seimitsu Optical Co., Ltd.). The smaller this value is, the higher the hiding property is.

7) Surface Peel Strength Using cellophane tape (18 mm width, made by Nichiban), the surface peel strength was evaluated by a cellophane tape peel test. The peeling angle was in the direction of about 150 degrees while keeping the void-containing film flat. The area of the peeled void-containing film was differentiated as follows. Class 5 ... Peeled off entirely Class 4 ... Almost peeled off Class 3 ... About half peeled off Class 2 ... Almost peeled off Class 1 ... No peeled off at all

Example 1 As a raw material, 80% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 was added to a melt flow index of 2.0.
g / 10 minutes General-purpose polystyrene 15% by weight, anatase-type titanium dioxide 5% by weight having an average particle size of 0.3 μm is used as a raw material of the A layer, and polyethylene terephthalate resin is 95% by weight as a raw material of the B layer, average particle diameter of 0.3 μm. Of 5% by weight of rutile type titanium dioxide are melt-extruded from T-dies at 290 ° C. by separate twin-screw extruders, electrostatically adhered and solidified on a cooling rotary roll, and each layer is B / A / B.
= 30/440/30 μm of an unstretched sheet of the polymer mixture was obtained. At this time, the T-die slit interval is 1.0 mm
Then, the average flow velocity of the melt of the polymer mixture in that portion is 8.
It was 8 m / sec. Subsequently, the unstretched sheet was longitudinally stretched 3.5 times with a roll stretching machine at 83 ° C., and then horizontally stretched 3.5 times with a tenter at 130 ° C. and then 4% at 235 ° C.
Heat treatment was carried out while relaxing to obtain a polyester film containing a large number of cavities inside. Thickness is B / A / B = 3 /
It was 44/3 μm. The porosity of the surface layer portion of the layer A of the obtained film was 2% by volume, and the whole was 21% by volume. The portion with few cavities was present from the surface layer to a depth of about 3 μm. The surface strength of the void-containing film obtained in this example was class 1. When the cross section of the unstretched sheet of the polymer mixture of this example was observed with a scanning electron microscope, the average dispersed polystyrene particle size of polystyrene was 5.
The average particle size of the dispersed particles near the surface layer is 0.
It was 7 μm. The apparent specific gravity is 1.10, the porosity of the surface layer of layer A is 2% by volume, and the average porosity of the whole is 21% by volume.
The light transmittance was 13% and the thickness was 50 μm.

A linear copolymerized polyester (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 were used on one surface of this film ( Softening point 125 ° C) and vinylidene chloride-acrylonitrile copolymer (Saran resin F216 made by Asahi Dow ┷) are mixed at 50/50 (weight ratio), and solvent (tetrahydrofuran / toluene = 70/30 (weight ratio) mixed solution) The solution melted by heating at 60 ° C. for 2 hours was 2.38.
A coating film was prepared by applying g / m @ 2 and drying at 80 DEG C. for 30 seconds. The adhesive strength was 115 g / cm, the heat-sealing strength was 95 g / cm, and the heat-sealing property was good, and blocking was not caused even when the coating film was wound and then rewound. The adhesive strength was measured by sticking a Nichiban cellophane tape to the coated surface and measuring the strength when the stop phrase was peeled off from the base film with a tensile tester. The pulling rate was 200 mm / min, the peeling angle was 180 °, and the width was 1 cm.
Heat sealing strength is the two films at a temperature of 150 ℃,
The film heat-sealed at a pressure of 5 kg / cm ² is left at room temperature for 24 hours, then 180
It was evaluated by the force applied when peeled at an angle of ° at a speed of 200 mm / min.

[0019]

INDUSTRIAL APPLICABILITY The void-containing polyester film of the present invention, like the void-containing polyester film obtained by using conventional polystyrene or polyolefin as a void-developing agent, is lightweight, flexible, concealable, delusterable, and drawable. In addition to the properties of the void-containing polyester film, the heat-sealing property of the polyester film is superior to that of the conventional void-containing polyester film, so that it has excellent specific gravity, whiteness, and surface wettability. Therefore, the void-containing polyester film of the present invention is a label,
It can be used in an extremely wide range of fields such as posters, recording paper, and packaging materials.

Claims (1)

[Claims] 1. A polyester layer (A) containing fine cavities formed by orienting at least uniaxially a polymer mixture obtained by mixing a polyester with an incompatible thermoplastic resin. , A layer (B) made of a thermoplastic resin is provided, and 3 μm from the surface of the A layer.
To 8% by volume or less, and the average void content of the entire film is 10% by volume or more and 50% by volume or less. A film having a heat seal layer made of polymerized polyester.