JPH05345476A - Cavity-containing polyester film for thermal recording - Google Patents

Abstract

PURPOSE:To provide a cavity-containing film for thermal recording imparting sharp thermal recording printing having durability, excellent in concealability and whiteness and having sufficient heat resistance, stiffness strength and surface strength by rationalizing the size of cavities. CONSTITUTION:A cavity-containing polyester film is constituted by providing a layer (B) composed of a thermoplastic resin 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 and characterized by that the content of cavities contained in an 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 thermal recording layer containing a colorless or light-colored basic dye and a developer heated and melted to come into contact with the basic dye to develop a color is provided on the cavity-containing polyester film.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention contains a large amount of fine voids inside a film, which has improved surface peel strength, hiding power, whiteness, etc. when used for a thermal recording label, a thermal recording paper and the like. The present invention relates to a polyester film for heat-sensitive recording.

[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 that has a function similar to paper mainly made of polyester or polypropylene, a method of containing a large amount of fine voids inside the film gives a point that the film itself can be made lightweight and appropriate flexibility. The advantage is that clear printing and thermal recording are possible. Conventionally, a heat-sensitive recording material using a void-containing film as a base paper has been widely disclosed. (JP-A-62-14
829, JP-A-1-198388). However, conventional void-containing films for heat-sensitive recording not only have problems in heat resistance and strength of the waist, but also have insufficient surface strength and are therefore used as heat-sensitive recording labels. In that case, there was a drawback that handling was poor.

[0003]

DISCLOSURE OF THE INVENTION The present invention has solved the drawbacks of the previous term, that is, by optimizing the size of the cavity, the heat-sensitive recording print is clear and durable, and hiding and whiteness It is intended to provide a void-containing film for heat-sensitive recording which has not only excellent heat resistance but also has sufficient heat resistance, waist strength and surface strength.

[0004]

A polyester layer (A) containing fine cavities produced by orienting at least uniaxially a polymer mixture obtained by mixing polyester with a thermoplastic resin incompatible with the polyester. A layer (B) made of a thermoplastic resin is provided on at least one surface of the layer A, the content of voids contained in the layer A up to 3 μm is 8% by volume or less, and the average content of voids in the entire film is 10% by volume. % Or more and 50% by volume or less, on at least one surface of the void-containing polyester film, a colorless or light-colored basic dye and a coloring agent capable of being colored by heating and melting contact with the basic dye. The present invention relates to a void-containing polyester film having a heat-sensitive recording layer.

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 used. 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 has a void content of 8% by volume or less in the layer from the surface of the layer A to a depth of 3 μm, and the average void content of the entire layer is 10% by volume. It is necessary to be above. A
8 cavities contained in the surface layer from the surface of the layer to a depth of 3 μm
When the content is more than the volume%, 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 portion of the layer A having less voids than the central portion has a depth of 3 μm or more, and the void content contained therein needs to be 4% by volume. Furthermore, as the whole layer, the average content of cavities is 10
It must be at least volume%. Average porosity of the whole layer is 1
When it is less than 0% by volume, the flexibility peculiar to the void-containing polyester film becomes insufficient and the sharpness of the heat-sensitive recorded image becomes 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. The film of the present invention comprises a void-containing polyester film provided with a thermosensitive recording layer containing a colorless or light-colored basic dye and a coloring agent capable of developing a color by heating and melting contact with the basic dye on at least one side. is there. As the colorless or light-colored basic dye, various compounds known in the field of thermal recording materials can be used, and examples thereof include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide. Triallylmethane dyes and 3-diethylamino-6-methyl-7
Examples thereof include fluorane dyes such as phenylaminofluorane. Similarly, various compounds known in the field of thermal recording materials can be used as the color-developing agent.
4'-isopropylidene diphenol, 4,4'-cyclohexylidene diphenol, 4-hydroxybenzoic acid benzyl ester, etc. are illustrated. The heat-sensitive recording layer is usually formed by applying a coating liquid containing a binder, an inorganic pigment, various auxiliaries and the like in addition to the above compounds to the void-containing film. The coating amount is not particularly limited. An overcoat layer can be provided on the heat-sensitive recording layer, and various undercoat layers can be provided for the purpose of improving the adhesiveness with the void-containing film. Various known techniques in the field of manufacturing a thermal recording material can be added.

[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, a thermoplastic resin B layer is provided,
In addition, the amount of cavities contained in the surface layer portion 3 μm of the layer A is set to 8
The reason why the content is less than or equal to volume% is to further increase the surface strength, and the higher surface strength also improves the resistance to cleavage. On the other hand, the reason why the average porosity of the entire layer is 10% by volume or more is to obtain flexibility so that a clear thermosensitive recording image can be obtained.

[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 A photograph of the surface of the cross section of the film near the surface layer was taken with a scanning electron microscope, and then the voids in the region from the surface layer to a depth of 3 μm were traced on a tracing film and painted. Was subjected to image processing with an image analyzer, and the void ratio was obtained 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. On one side of this film, 3-diethylamino-6 was used as a basic dye.
-Methyl-7-phenylaminofluorane, 4,4'-isopropylidenediphenol as a coloring agent, and amorphous silica on fine particles together with oxidized precipitate, a coating liquid having a dry weight of 7.0 g / m 2 was dispersed in water. Apply and dry to be ² ,
A coated film was produced. The coated film was passed through a heat-sensitive facsimile. The recording density measured by a Macbeth densitometer was 1.05.

[0019]

INDUSTRIAL APPLICABILITY The void-containing polyester film for heat-sensitive recording of the present invention has the same lightness, flexibility, hiding power and matteness as the void-containing polyester film obtained by using conventional polystyrene or polyolefin as a void-developing agent. The film is suitable for use as a thermal recording label because of its excellent recording properties after coating with a thermal recording layer, and particularly excellent surface peel strength, as well as excellent properties, drawing properties, etc. ..

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, at least one side of the void-containing polyester film is colorless. Or a thermosensitive recording layer containing a light-colored basic dye and a colorant capable of developing a color by heating and melting contact with the basic dye.