JP3125542B2 - Laminated polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated polyester film containing a large amount of fine cavities inside a film used as a label, poster, recording paper, printing plate substrate, or packaging material. The present invention relates to a laminated polyester film which is also useful as a paper substitute having 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. Polyethylene, polypropylene, polyester, etc. are used as the main raw materials of synthetic paper. Among them, polyester represented by polyethylene terephthalate is excellent in terms of high heat resistance and strong rigidity, and Application development is possible.

[0003] As a method for obtaining a film having a function similar to that of paper using polyester as a main raw material, a method of incorporating a large amount of fine cavities into the film, a method of sandblasting a normal flat polyester film, and a method of chemical etching have been used. Alternatively, a method of roughening the surface by matting treatment (a method of laminating a matting agent with a binder) or the like is disclosed.

[0004] Among the above-mentioned methods, the method of containing a cavity in the inside of the film is advantageous in that the film itself can be reduced in weight,
There is an advantage that clear printing and transfer can be performed because appropriate flexibility can be imparted to the film. As a specific method for generating fine cavities inside the film,
A method in which a polymer incompatible with the polyester is melt-kneaded together with the polyester by an extruder to obtain a sheet in which the polymer is dispersed in fine particles in the polyester, and the sheet is further stretched to generate voids around the fine particles. Are known.

[0005] Polymers that are incompatible with the polyester used for cavitation (hereinafter referred to as cavitation agents)
Are polyolefin-based resins (for example,
No. 134755), polystyrene resins (for example, JP-B-49-2016, JP-B-54-29550) and polyacrylate resins (for example, JP-B-58-2).
Although many proposals have been made, such as polypropylene and polystyrene, they have been widely used because they are easy to develop cavities, have a low density, and are inexpensive.

Although such a film is used for commercial printing such as intaglio, letterpress, planographic printing and the like, and printing of an ink jet system or a thermal transfer system, the film substrate itself has almost no ink receptivity or water absorption. Because of this, processing such as providing a coating layer on the surface has been performed. However, it is necessary to increase the thickness of the coating layer or to increase the concentration of the processing agent, which raises problems such as an increase in cost and poor processing efficiency.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a film substrate having ink receptivity and water absorbability without surface treatment.

[0008]

The laminated polyester excellent in ink receptivity of the present invention is a laminated polyester film in which a polyester B layer containing inert particles is laminated on at least one surface of a polyester A layer, The polyester B layer has cracks in the thickness direction from the surface of the layer B. The cracks have a depth of 30% or more of the thickness of the layer B and have a depth of 1/100 μm or more in an arbitrary longitudinal cross-sectional area. It has a gist where it exists in proportion. Also,
It is a preferred embodiment of the present invention that the polyester A layer is a void containing polyester.

[0009]

In the present invention, the most important point is that a polyester B layer having a short groove-like crack on the film surface is laminated on at least one surface of the polyester A layer. The presence of these cracks has made it possible to impart ink receptivity and water absorbency to the film substrate itself. Hereinafter, the present invention will be described in detail.

[0010] The polyester in the present invention refers to an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid or an ester thereof and a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol or neopentyl glycol. Polyester produced by polycondensation. These polyesters are prepared by directly reacting an aromatic dicarboxylic acid and a glycol and then subjecting the alkyl ester of the aromatic dicarboxylic acid and a glycol to a transesterification reaction and then polycondensation, or a diglycol ester of an aromatic dicarboxylic acid. Can be produced by a known method such as polycondensation.

Representative examples of such polyesters include:
Examples thereof include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. The polyester may be a homopolymer or a copolymer of the third component.
In any case, in the present invention, the ethylene terephthalate unit, the butylene terephthalate unit or the ethylene-2,6-naphthalate unit contains 70 mol% or more, preferably 90 mol% or more, and more preferably 96 mol%.
Polyesters that are above are recommended.

In the present invention, in order to cause cracks in the layer B, inert particles must be contained. The inert particles mean inert particles that do not react with the polyester at all. In the present invention, any particles that do not melt up to about 300 ° C. can be used without particular limitation. Specifically, inorganic particles such as anatase type titanium dioxide, rutile type titanium dioxide, silicon dioxide, calcium carbonate, barium sulfate, aluminum oxide, strontium carbonate, synthetic zeolite particles, clay, kaolin, and talc, as well as crosslinked silicon resin particles And heat-resistant polymer fine particles such as cross-linked acrylic resin particles, cross-linked polystyrene particles, and epoxy resin particles.

[0013] These inert particles are the nuclei of cracks in the layer B, but cracks generated from a plurality of particles in the stretching process of the film unite to form cracks larger than the average primary particle diameter of the particles. It has been clarified by the present inventors and others that this will be the case. It is considered that ink or water enters between the cracks to impart ink receptivity or water absorption to the film.

According to the present invention, cracks having a depth of 30% or more of the thickness of the layer B are formed at a rate of 1/100 μm in an arbitrary longitudinal sectional area.
It is a necessary condition that it is present in a proportion of m or more. If the depth of the crack is smaller than 30% of the thickness of the layer B, and if the existing density is less than 1 piece / 100 μm, the effect of improving ink receptivity and water absorption is not observed. A more preferable crack existence ratio is 5/100 μm or more. In addition, the crack of 1/100 μm in an arbitrary vertical cross-sectional area means that, when the laminated polyester film is cut at an arbitrary position, in the film cross section, an arbitrary 100 μm in the cross-sectional direction (direction orthogonal to the depth direction). Means that there is one crack inside. Of course, 30% of the thickness of layer B
The presence of smaller cracks is acceptable.

Since such cracks are caused by coalescence of cracks generated around the inert particles, the size and amount of the cracks vary depending on the size and amount of the particles used.
The size of the inert particles should be adjusted according to the thickness of the layer (the surface roughness increases unless inert particles having a diameter smaller than the thickness of the B layer are used), and the diameter is usually 0.1 to 5 mm. .
It is preferable to use 0 μm particles in the B layer in an amount of 10 to 60% by weight or more. A more preferred amount is 20 to 50% by weight. If the inert particles are present in an amount exceeding 60% by weight, it is impossible to form the film itself, or even if the film can be formed, the amount of cracks is too large and the film strength is reduced. On the other hand, if the content is less than 10% by weight, the above-mentioned requirement for the numerical value of cracks cannot be satisfied. Inert particles are
Secondary, tertiary or higher aggregates may be formed inside the film. In addition, these inert particles,
You may mix | blend with a polyester A layer as needed.

In the present invention, the polyester A layer is preferably a void-containing polyester layer. If there are cavities, drawing properties and cushioning properties are improved. As a cavity developing agent,
Thermoplastic resin or inert inorganic particles which are incompatible with polyester are used. For example, polystyrene resin,
Thermoplastic resins such as polyolefin-based resins, polyacryl-based resins, polycarbonate resins, polysulfone-based resins, cellulose-based resins, polyamide-based resins, and the like, and inorganic particles exemplified as the inert particles. In particular, polyolefin resins such as polystyrene resins, polymethylpentene, and polypropylene are preferable.

The amount of cavities is 10 to 10 in the polyester A layer.
It may be present at 50% by volume, preferably 10 to 30% by volume. If it is more than 50% by volume, the stiffness of the film becomes weak. The required weight% of the void generating agent is almost the same as the volume% of the void content (of course, it is not exactly the same because it varies depending on the extrusion conditions and stretching conditions). Thus, the amount of the developing agent may be appropriately determined.

The polyester A layer is formed by mixing polyester and the above-mentioned void generating agent to form a sheet.
For example, a method in which chips of each resin are mixed and melt-kneaded in an extruder, and then extruded and solidified, a method in which both resins are kneaded in advance by a kneader, and a method in which the resin is melt-extruded and solidified by an extruder, or polymerization of polyester A sheet can be formed by adopting a method in which a cavity-forming agent is added in the step and chips obtained by stirring and dispersing are melt-extruded and solidified. The obtained unstretched sheet is usually in a non-oriented or weakly oriented state. Further, the cavity-forming agent is polyester A, and exists in a dispersed form in various shapes such as spherical, elliptical, or thread-like.

The above-mentioned polyester B layer containing inert particles is formed into a sheet by the same method.
The raw material of each layer and the polyester B layer are fed into independent separate extruders and co-extruded, and then laminated after stretching, preferably before stretching, and the laminated unstretched sheet is stretched in the longitudinal and / or transverse directions. By this means, the laminated polyester film of the present invention can be obtained.

The unstretched sheet extruded and laminated is known in the art such as a roll stretching method between rolls having a speed difference, a tenter stretching method in which the sheet is gripped and spread by clips, and an inflation method in which the sheet is circumferentially expanded by air pressure. Is oriented at least uniaxially. In this orientation treatment step, peeling occurs at the interface between the polyester and the void developing agent or the inert particles in the dispersed state, and many voids and cracks are generated in the stretched film.

The orientation treatment condition is an important point for generating a crack satisfying the above-mentioned prescribed condition.
The sequential biaxial stretching process most commonly performed will be described as an example. In the sequential biaxial stretching method in which an unstretched continuous sheet is roll-stretched in the longitudinal direction and then tenter-stretched in the width direction, the following conditions are used. Is recommended. First, in roll stretching (longitudinal stretching), a crack is generated in the B layer,
It is preferable to perform two-stage longitudinal stretching so that stretching can be performed stably. In the first stage, a crack is first formed in the B layer by setting the temperature at the time of stretching to the secondary transition temperature (Tg) of the raw material polyester + 15 ° C. or lower and the stretching ratio to 1.2 to 2.0.
In the subsequent second-stage longitudinal stretching, the raw material polyester is stretched 1.5 to 4.0 times at a secondary transition temperature (Tg) of +15 to + 40 ° C with emphasis on stretching stability. This may be followed by a third or more longitudinal stretching. In the next tenter stretching (transverse stretching), the stretching temperature is set at 11 so that a stable film can be formed without breaking.
The temperature is 0 to 150 ° C. and the magnification is 2.8 to 5 times. In other stretching methods, it may be appropriately changed according to the above conditions.

Further, in the present invention, it is desirable to carry out the heat treatment after the stretching by the following method. The heat treatment is performed at a temperature of 200 ° C. or more, preferably 220 ° C. after the completion of the stretching.
Above, more preferably at 230 ° C. or higher. At this time, it is preferable to perform heat setting while relaxing 3 to 8%. By performing the heat treatment in this manner, a void-containing film having a heat shrinkage at 150 ° C. of less than 2%, preferably less than 1.7%, and more preferably less than 1.5% can be obtained.

The laminated polyester film of the present invention can be produced through the above steps, and exhibits good ink receptivity due to the presence of the layer B. Although the ink receptivity is better as the B layer is thicker, the stretching stability is deteriorated when the B layer is thicker. Therefore, by providing a coating layer having a thickness not incompatible with the object of the present invention on the surface of the B layer, The wettability and adhesiveness of inks and coating agents can be further improved. Compared to the case where only the coating layer or only the layer B is provided on the film surface, further excellent ink receptivity can be obtained by the action of both layers. As the compound constituting the coating layer, a polyester-based resin is preferable, and in addition, a polyurethane resin, a polyester-urethane-based resin, an acrylic-based resin, and the like, which are generally used for improving the adhesiveness of a polyester film. Compounds are applicable.

As a method for providing these coating layers, there are known coating methods such as a gravure coating method, a kiss coating method, a dip method, a spray coating method, a curtain coating method, an air knife coating method, a blade coating method, a reverse roll coating method and the like. Can be adopted. As a step of applying, a method of applying in advance to the surface of an unstretched sheet before performing an orientation treatment, a method of applying the film to a surface of a laminated film oriented in an axial direction and further orienting it in a perpendicular direction, a lamination after the orientation treatment is completed Any method such as a method of coating on the film surface is possible.

Since the laminated polyester film of the present invention has better ink receptivity and water absorption than conventional films, when the laminated polyester film of the present invention is used as various substrates, it can be used for labels, posters, cards, Recording paper, packaging material, video printer receiving paper, barcode label, barcode printer receiving paper, thermal recording paper, map, dust-free paper, display board, white board, electronic white board, photographic paper, decorative paper, wallpaper, banknote, release paper , Origami, calendar, magnetic card, tracing paper, slip, delivery slip, pressure-sensitive recording paper,
Copying paper, clinical examination paper, building materials, antenna reflectors, film for capacitors, thermal insulation, decorative boxes, prepaid cards,
It can be suitably used for decorative displays, ink jet paper and the like.

[0026]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which do not limit the present invention.
Modifications and alterations that do not depart from the spirit described below are all included in the technical scope of the present invention.

The measurement and evaluation methods used in the examples are as follows. 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) Melt flow index of polypropylene resin The melt flow index was measured according to JIS-K6758-1981.

4) State of existence of cracks in layer B of laminated polyester The cross section of the film was examined with a scanning electron microscope (S-
After photographing 500 times with a (510 type), the number of cracks having a depth of 30% or more of the thickness of the B layer was counted per 300 μm width using an image processing device manufactured by Elionix. 5) Film density (g / cm ³ ) A film was accurately cut out to 5.00 cm × 5.00 cm to obtain a test piece, and its thickness was measured at 50 points to obtain an average thickness, and the weight of the test piece was 0.1 mg. It was measured and calculated. 6) Initial modulus of elasticity Measured according to ASTM D-882-81 (Method A).

7) Heat Shrinkage A film is taken to a width of 10 mm and a length of 250 mm,
Marks are made at mm intervals, and the distance A between the marks after fixing under a constant tension of 5 g is measured. Subsequently, 15 minutes under no tension for 30 minutes
The interval B between the marks after being placed in an oven in an atmosphere of 0 ° C. was determined, and the heat shrinkage was calculated by the following equation. (AB) / A × 100 (%) 8) Light transmittance According to JIS-K6714, Poick integrating sphere formula T.
The light transmittance of the film was measured using an R meter (manufactured by Nippon Seimitsu Kogaku). The smaller this value is, the higher the concealment property is. 9) Whiteness Using a color difference meter (N1001 manufactured by Nippon Denshoku Industries Co., Ltd.), J
It was measured by the B method (two-wavelength method) of IS-L1015-1981.

10) Surface roughness Using a surface roughness meter (manufactured by Tokyo Seimitsu: Surfcom 300A type) according to JIS-B0601-1982, stylus diameter 2 μm
m, the stylus pressure was 30 mg, and the cutoff was 0.8 mg, and the center line average thickness was measured. 11) Ink receptivity Shachihata stamp name 9 was stamped on the film surface, dried for 1 hour in an atmosphere of 25 ° C. and 65% RH, and then the imprint was lightly rubbed with a finger. When the character of the imprint was seen, it was evaluated as ○, and when it blurred so as not to be seen, it was evaluated as ×.

Example 1 Polyethylene terephthalate having an intrinsic viscosity of 0.62 was used as a raw material for the layer A, and as a raw material for the layer B, 60% by weight of polyethylene terephthalate and 40% by weight of anatase type titanium dioxide (average primary particle size 0.3 μm) were used. %, Respectively, and then put into separate twin-screw extruders, then melt-extruded from a T-die at 290 ° C. so as to obtain BAB, electrostatically tightly adhered to a cooling rotating roll, and solidified to about 1100 μm. An unstretched sheet was obtained. The unstretched sheet was subjected to 1.9-fold first-stage longitudinal stretching at 77 ° C. and further 1.9-fold second-stage longitudinal stretching at 100 ° C. using a roll stretching machine. Subsequently, the film was laterally stretched 3.4 times at 130 ° C. by a tenter, and then heat-treated at 235 ° C. while relaxing by 3% to obtain a cracked laminated polyester film. The thickness is B /
A / B = 5/90/5 μm. Table 2 shows the properties of the obtained film.

Example 2 The procedure of Example 1 was repeated except that 80% by weight of polyethylene terephthalate and 20% by weight of synthetic zeolite particles (JC-20, manufactured by Mizusawa Chemical Co., Ltd.) having an average particle size of 2.0 μm were used as raw materials for the layer B. Similarly, a laminated polyester film was obtained.

Examples 3 and 4 In Examples 1 and 2, the raw materials for the layer A were 80% by weight of polyethylene terephthalate, 15% by weight of polystyrene for general use (melt flow index: 2.0 g / 10 minutes), and anatase type dioxide. A laminated polyester film was obtained in the same manner as in Examples 1 and 2, except that a mixture of 5% by weight of titanium was used.

Example 5 A laminated polyester film was obtained in the same manner as in Example 1, except that 70% by weight of polyethylene terephthalate and 30% by weight of calcium carbonate having an average particle size of 0.6 μm were used as raw materials for the layer B.

Example 6 In Example 3, the thickness of the laminated film was changed to 2.5 / 20 /
A laminated film was obtained in the same manner except that the thickness was 2.5 μm. Example 7 In Example 3, a crystalline polypropylene (melt flow index: 5.5 g / 1) was used instead of polystyrene.
0 minutes) to obtain a laminated film in the same manner.

Comparative Examples 1 to 3 Laminated films were obtained in the same manner as in Example 3, except that the longitudinal stretching was changed as shown in Table 1. Comparative Examples 4 and 5 A laminated film was obtained in the same manner as in Example 3, except that the amount of titanium dioxide in Layer B was changed to 5, 70% by weight (residual polyethylene terephthalate). Table 1 shows the structures of the laminated polyester films of the above Examples and Comparative Examples.
Table 2 shows the results of evaluating the properties of the obtained film.

[0037]

[Table 1]

[0038]

[Table 2] The films of the examples were excellent in various properties and excellent in ink receptivity.

[0039]

The laminated polyester film of the present invention has
As well as conventional void-containing film, it has lightness, flexibility, concealment, matting, drawing properties, etc., and greatly improved ink receptivity and absorbency compared to conventional void-containing polyester film. Have been. Therefore, the laminated polyester film of the present invention can be used not only in extremely wide fields such as labels, posters, recording paper, slips, pressure-sensitive paper, copy paper, printer paper, and packaging materials, but also as ink jet paper and printing paper. It can be suitably used.

Continuation of the front page (56) References JP-A-3-132331 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 B29C 55/00-55 / 30 B41M 1/00-3/18

Claims (2)

(57) [Claims] Claims: 1. A polyester A layer, on at least one side,
A laminated polyester film in which a polyester B layer containing inert particles is laminated, wherein the polyester B layer has cracks in the thickness direction from the surface of the layer B, and the cracks are 30% of the thickness of the layer B. A laminated polyester film excellent in ink receptivity , having the above depth and being present at a ratio of 1 piece / 100 μm or more in an arbitrary longitudinal sectional area. 2. The multilayer polyester film having excellent ink receptivity according to claim 1, wherein the polyester A layer is a void-containing polyester.