JPH07145257A - Void-containing polyester film - Google Patents

Abstract

PURPOSE:To provide a void-containing polyester film excellent in stiffness and foldability and having a sufficient strength even after it is folded. CONSTITUTION:This is a void-containing polyester film containing a thermoplastic resin incompatible to the polyester and oriented in one or two directions. The void content (P1) in a region (X) from the film surface to H/20 in the thickness direction is 0 to 5 vol% when the whole thickness of the film is expressed by (H). The void content (P2) in a region (Y) of H/20 to H/4 continued from that region is 5 to 25vol% and the void content (P3) in a region (Z) from H/4 to H/2 is 10 to 30vol%. Further, (P3) is larger by 5 to 20vol% than (P2).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film containing a large amount of fine voids inside a film used as a label, a poster, a recording paper, a printing plate base material, and a packaging material. The present invention relates to a polyester film having high strength, good bending property, and sufficient strength even after bending.

[0002]

2. Description of the Related Art Synthetic paper, which is a paper substitute mainly made of synthetic resin, has a higher water resistance, a 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. Polyethylene, polypropylene, polyester, etc. are used as the main raw materials for synthetic paper. Among them, polyester typified by polyethylene terephthalate is excellent in that it has high heat resistance and is strong and has a wide range of properties. It can be used for various purposes.

As a method for obtaining a film having a function similar to that of paper by using polyester as a main raw material, conventionally, a method of containing a large amount of fine voids in the film, or an ordinary flat polyester film is sandblasted or chemically etched. Alternatively, a method of roughening the surface by a matting treatment (a method of laminating a matting agent with a binder) or the like is disclosed.

Among the above methods, the method of containing a cavity inside the film can reduce the weight of the film itself,
There is an advantage that clear printing and transfer are possible because appropriate flexibility can be given to the film. As a specific method for generating minute cavities inside the film,
A method in which a polymer incompatible with polyester is melt-kneaded together with polyester in an extruder to obtain a sheet in which the polymer is finely dispersed in polyester, and the sheet is further stretched to generate voids around the fine particles is known. Are known.

A polymer that is incompatible with the polyester used to generate cavities (hereinafter referred to as cavity-developing agent)
The polyolefin resin (for example, JP-A-49-
134755), polystyrene resins (for example, Japanese Patent Publication No. 49-2016, Japanese Patent Publication No. 54-29550), and polyacrylate resins (for example, Japanese Patent Publication 58-2).
8097), but polypropylene and polystyrene have been widely used because they easily cause voids, have a low density, and are inexpensive.

However, it is difficult for the conventional film to balance the rigidity and strength of the film with the void content for making paper-like, and it is difficult to maintain the crease or the bending angle after folding the film and the bending line. There was a problem in strength. That is, if the rigidity of the film is too high, it will return to the original flat state immediately even if the film is bent, but if the film is made too flexible by expressing a lot of cavities, the durability of the bent part will be poor. is there. For this reason, sufficient processing suitability has not been obtained in applications where the film is folded and used, for example, printing plates such as planographic printing plates, letterpress printing plates, intaglio printing plates, and applications such as boxes.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art by providing a void-containing polyester film having a high rigidity, good bendability, and sufficient strength even after bending. It is intended to be provided.

[0008]

SUMMARY OF THE INVENTION The present invention is an at least uniaxially oriented void-containing polyester film containing a thermoplastic resin incompatible with polyester, the total thickness of the film being H. And the void content P _{1 in} the region X from the film surface to H / 20 in the thickness direction is 0 to 5% by volume, and the void content P _{2 in} the region Y in the subsequent H / 20 to H / 4 is P ₂ 5-25% by volume, further H /
The gist is that the void content P _{3 in} the region Z of 4 to H / 2 is 10 to 30% by volume, and P ₃ is 5 to 20% by volume larger than P ₂ .

[0009]

In the present invention, the maximum point is that the void content of the polyester film has a gradient in the thickness cross-sectional direction of the film. Generally, by creating cavities in the film, weight reduction can be achieved, workability is improved, and the price per area is also reduced.
There is an advantage that the flexibility of the film is increased and clear printing or printing is possible when printing / transferring. In addition, the presence of cavities provides a light shielding property and whiteness, and a large number of protrusions derived from the cavities are formed on the film surface, which enables writing with a pencil or a ballpoint pen. The present inventors have succeeded in remarkably improving bendability, durability and the like by changing the cavity distribution of such a cavity-containing film in the film thickness direction, and arrived at the invention. Hereinafter, the present invention will be described in detail.

The polyester used in the present invention is 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. It is a polyester produced by polycondensation. These polyesters are obtained by directly reacting an aromatic dicarboxylic acid with a glycol, and then subjecting an alkyl ester of an aromatic dicarboxylic acid to a glycol with an ester exchange reaction followed by polycondensation, or a diglycol ester of an aromatic dicarboxylic acid. Can be produced by a known method such as polycondensing.

As a typical example of such polyester,
Examples thereof include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. This polyester may be a homopolymer or a copolymer of a third component.
In any case, in the present invention, the ethylene terephthalate unit, the butylene terephthalate unit or the ethylene-2,6-naphthalate unit is 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol%.
The above polyesters are recommended.

The thermoplastic resin incompatible with the polyester used as the cavity developing agent in the present invention is not particularly limited as long as it is incompatible with the above-mentioned polyester. Specifically, polystyrene resin, polyolefin resin, polyacrylic resin, polycarbonate resin, polysulfone resin, cellulose resin,
Examples thereof include polyamide resins. In particular, polystyrene resins, polyolefin resins such as polymethylpentene and polypropylene are preferable.

In the present invention, the polyester and the cavity developing agent are mixed to form a sheet. For example, after chips of respective resins are mixed and melt-kneaded in an extruder,
A method of extruding and solidifying, a method of melt-extruding a mixture of both resins previously kneaded by a kneader and solidifying it, and adding a cavity-developing agent in the polyester polymerization step, and stirring and dispersing the mixture were obtained. A sheet can be formed by adopting a method of melt-extruding and solidifying chips. The obtained unstretched sheet is usually in a non-oriented or weakly oriented state. In addition, the cavity-developing agent is polyester, which is present in a dispersed form in various shapes such as spherical shape, elliptic spherical shape, and thread shape.

An important point in the present invention is that a gradient of void content is provided in the thickness direction of the polyester film. That is, in a film in which the unstretched sheet obtained as described above is oriented at least uniaxially, when the total thickness of the film is H, as shown in FIG. The void content P ₁ of the region X up to 20 is 0 to 5% by volume, followed by H
The void content P ₂ of the region Y of / 20 to H / 4 is 5 to 25% by volume, and the void content P ₃ of the region Z of H / 4 to H / 2 is P ₃
Is 10 to 30% by volume, and P ₃ is 5 to ₂ more than P _2.
Must be 0% by volume greater.

Cavity content rate P in region X₁ Is more than 5% by volume
If not, the film surface strength is inferior, which is preferable.
No In addition, P in area Y₂ Is 5% by volume, P in area Z
₃ Is less than 10% by volume, the film has high rigidity.
The bending angle (in Figure 2
Angle formed by two facing surfaces a and b after valley-folding the film
Degree θ) exceeds 90 ° (the field on the right in Fig. 2)
Go). On the other hand, P in area Y ₂ Is 25% by volume,
P₃ Is more than 30% by volume, the strength of the film is low.
It becomes unfavorable. And P₃ -P₂ Is 5% by volume
If it is less than or more than 20% by volume, folding
It is possible to achieve both bending angle and film strength after bending.
I can't come.

In order to obtain such a film structure, the respective layers of the regions X, Y, and Z are prepared by introducing separate raw materials having different amounts of the cavity developing agent into three independent extruders. Means for forming by extrusion and laminating after stretching, preferably before stretching, and stretching the laminated unstretched sheet in the machine direction and / or the transverse direction can be adopted. In the present invention, since the void content P _1, P _2, P ₃ (volume%) becomes lower as it gets closer to the film surface, X, Y,
It is preferable that the weight of the cavity-developing agent contained in the raw material polyester for forming the Z layer is Z ≧ Y ≧ X. Also, by increasing the shear stress during melt extrusion, the void developing agent can be finely dispersed to lower the void developing rate, and the film temperature during stretching can be lowered near the center rather than near the film surface. It is also possible to change the cavity expression rate by adopting the method.

The amount of the thermoplastic resin which is incompatible with the polyester which is the void-developing agent varies depending on the amount of the target voids, but is 3% by weight to 39% by weight with respect to the entire raw material mixture.
Weight% is preferable, and 8-35 weight% is especially preferable. Three
If the content is less than 10% by weight, there is a limit to increase the amount of cavities, and the flexibility, lightness, drawability and strength of the target film, particularly the strength of the waist, are significantly impaired. Further, if the void-developing agent is blended in an amount exceeding 39% by weight, the heat resistance and the film strength will be poor. As for the amount of the cavity developing agent in the raw material in each region, the total amount may be distributed as Z ≧ Y ≧ X as described above. The preferred amount of the cavity developing agent is 0 to 20% by weight in the X layer, 5 to 20% by weight in the Y layer, and 5 to 5% in the Z layer.
It is 30% by weight.

By setting the void content as described above, the bending angle of the film can be set to 30 to 90 °.
A more preferable bending angle is 60 to 90 °. If the bending angle is less than 30 ° or more than 90 °, the adhesion will be poor when used by being folded and brought into close contact with a roll or the like such as a printing plate. Further, the film strength after bending is preferably 10 kg / mm ² or more,
If it is smaller than this, it lacks durability when used by bending. The initial elastic modulus of the film is 300 kg / mm ²
It is preferable that it is above, and if it is smaller than this, the film becomes weak.

In the present invention, if necessary, the raw material may contain inorganic particles in order to improve the hiding property and the drawing property. The inorganic particles include titanium dioxide, silicon dioxide,
Examples thereof include calcium carbonate, barium sulfate, aluminum oxide, kaolin, and talc, but are not particularly limited. Of course, since these inorganic particles also have the effect of developing cavities by stretching, they can be used as cavities expressing agents. Furthermore, the raw material mixture may have a
It is also possible to add a colorant, a light fastness agent, a fluorescent agent, an antistatic agent and the like.

The unstretched sheet that is extruded and laminated is publicly known such as a roll stretching method between rolls having a speed difference, a tenter stretching method in which a sheet is held by a clip to expand it, and an inflation method in which it is expanded in the circumferential direction by air pressure. Orientation treatment is performed at least uniaxially by the stretching method. In this orientation treatment step, peeling occurs at the interface between the void-developing agent and the polyester, which were in a dispersed state, and many voids are generated in the stretched film.

The orientation treatment conditions are important points for obtaining a film containing voids having a strong elasticity. The most commonly used sequential biaxial stretching step 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. Orientation treatment is preferable. First, in roll stretching (longitudinal stretching), the temperature during stretching is set to the second-order transition temperature (Tg) of the raw material polyester in order to develop a large number of cavities.
The stretching temperature is 80 to 150 ° C. and the stretching ratio is 2.8 to 5 so that stable film formation can be achieved without breaking in tenter stretching (transverse stretching) at + 30 ° C. or less and a stretching ratio of 2.0 to 5.0. Double. Other stretching methods may be appropriately changed according to the above conditions.

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

The void-containing polyester film of the present invention can be produced through the above steps, but by providing a coating layer on the film surface, the wettability and adhesiveness of ink, coating agent and the like can be further improved. You can also As the compound constituting the coating layer, a polyester resin is preferable, but a polyurethane resin,
A compound usually used for improving the adhesiveness of the polyester film, such as a polyester-urethane resin and an acrylic resin, can be applied.

Known coating methods such as a gravure coating method, a kiss coating method, a dipping method, a spray coating method, a curtain coating method, an air knife coating method, a blade coating method and a reverse roll coating method can be used to form these coating layers. Can be adopted. As the step of applying, a method of previously applying to the surface of the unstretched sheet before performing the orientation treatment, a method of applying to the surface of the uniaxially oriented cavity-containing film and further orienting it in the perpendicular direction, the orientation treatment is completed. Any method such as coating on the surface of the void-containing film is possible.

The void-containing polyester film of the present invention has a surface strength, a strength against cleavage, and a bending property, which are higher than those of conventional films having no distribution of void content.
Excellent strength after bending. Therefore, when using the void-containing polyester film of the present invention as various substrates, not only a printing plate or box, but also a label, a poster, a card,
Recording paper, packaging material, video printer image receiving paper, bar code label, bar code printer image receiving paper, thermal recording paper, map, dust-free paper, display board, white board, electronic white board, photographic paper,
It can be suitably used for decorative paper, wallpaper, banknotes, release paper, origami, calendars, magnetic cards, tracing paper, slips, delivery slips, pressure-sensitive recording paper, copying paper, clinical inspection paper, parabolic antenna reflectors, etc. .

[0026]

The present invention will be described in more detail with reference to the following examples, but the following examples do not limit the present invention.
All modifications and implementations that do not depart from the spirit of the description below are included in the technical scope of the present invention.

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

4) Void content in each region of the X, Y, and Z layers of the void-containing film: The vicinity of the surface of the film cross section was photographed with a scanning electron microscope (Hitachi: S-510 type), and then each region was photographed. The cavity was traced on a tracing film, and the figure in which the cavity was painted was image-processed with an image analyzer (Luzex IID, manufactured by Nireco Corporation), and the cavity content rate was calculated as an area rate. Was displayed. 5) Bending angle A film having a width of 15 mm and a length of 40 mm was bent so that a crease was formed in the width direction. A thermal inclination tester (HG-100, manufactured by Toyo Seiki Co., Ltd.) was used for bending at 1.5 ° C at 25 ° C.
A load of kgf / mm ² was applied for 1 minute. After removing the load, leave it in an environment of 25 ° C and RH 65% for 5 minutes,
The angle formed by the film facing surface after bending was determined.

6) Film strength after bending: A film having a width of 15 mm and a length of 100 mm was bent under the conditions of 5), the film was flattened, and the chuck gap length was 40 using an autograph (Shimadzu: HG-3000).
mm, and the tensile speed was 200 mm / min, and the strength at break was determined. 7) Initial elastic modulus It was measured by ASTM D-882-81 (method A). 8) Heat shrinkage The film is set to a width of 10 mm and a length of 250 mm,
Marks are made at intervals of mm, and after fixing under a constant tension of 5 g, the distance A between the marks is measured. Then, 15 minutes without tension for 15 minutes
The space B between the marks after being placed in an oven in an atmosphere of 0 ° C. was determined, and the heat shrinkage rate was calculated by the following formula. (A-B) / A x 100 (%)

9) Light Transmittance According to JIS-K6714, Poic integrating sphere type H.264. T.
The light transmittance of the film was measured using an R meter (manufactured by Nippon Seimitsu Optical Co., Ltd.). The smaller this value, the higher the concealing property. 10) 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 peel angle keeps the void-containing film flat and is about 150.
It was done in the ° direction. The area of the void-containing film attached to the cellophane tape side was differentiated as follows. Class 1: No peeling at all. Class 2 ... Almost no peeling. Class 3 ... About half peeled off. Class 4 ... almost peeled off. Class 5 ... The whole peeled.

11) Bendability When the plate was mounted on the plate copper of a TEXEL AR01 type offset printing machine manufactured by Shinanomenshi Co., Ltd., the adhesion to the plate copper was determined as follows. ○: The plate is completely adhered from the mouth to the plate copper. B: A slight gap is recognized between the plate and the copper plate from the gripper to the copper plate. X: A gap is recognized between the plate and the copper plate from the gripping portion to the copper plate. 12) Durability of printed matter 20,000 sheets of four colors were printed using a TEXEL AR01 type offset printing machine manufactured by Shinanomenshi Co., Ltd., and judged as follows. O: There was no color shift and printing was possible to the end. ×: The plate was torn in the middle of the grip and printing was stopped.

Example 1 Polyethylene terephthalate having an intrinsic viscosity of 0.62 was used as a raw material for the X layer, 85 wt% of polyethylene terephthalate was used as a raw material for the Y layer, and general-purpose polystyrene (melt flow index: 2.0 g / 10 minutes) 10 5% by weight and anatase type titanium dioxide having an average particle size of 0.3 μm
A mixture of 80% by weight of polyethylene terephthalate, 15% by weight of general-purpose polystyrene (same as above), and 5% by weight of anatase type titanium dioxide having an average particle size of 0.3 μm as a raw material for the Z layer. Used,
Each of them is melt-extruded from T-die by separate twin-screw extruder at 290 ° C. so as to be XYZ-Y-X, electrostatically adhered to a cooling rotary roll and solidified to about 110.
An unstretched sheet of 0 μm was obtained. This unstretched sheet was longitudinally stretched 3.5 times at 83 ° C. by a roll stretching machine,
After stretching 3.5 times horizontally at 140 ° C with a tenter,
Heat treatment was carried out at 235 ° C. with 4% relaxation to obtain a void-containing polyester film. The thickness of each layer is X / Y / Z /
Y / X = 5/20/50/20/5 μm. The characteristics of the obtained film are shown in Table 2.

Examples 2 to 6 and Comparative Examples 1 to 4 Example 1 except that the raw materials were changed as shown in Table 1.
A void-containing film was obtained in the same manner as described above. The evaluation results of the film are shown in Table 2.

[0034]

[Table 1]

[0035]

[Table 2]

The films of the examples were excellent in each characteristic and had good adhesion to rolls when used as an offset printing plate, and were easy to use.

[0037]

INDUSTRIAL APPLICABILITY The void-containing polyester film of the present invention, like the conventional void-containing polyester film, has light weight, flexibility, hiding power, matteness, drawability, etc. As compared with the contained polyester film, a film having excellent bending property and bending resistance can be obtained. Therefore, the void-containing polyester film of the present invention can be used not only in a very wide range of fields such as labels, posters, recording papers, slips, pressure-sensitive papers, copying papers, printer papers, packaging materials, but also offset printing plates, boxes, etc. A film was obtained which was particularly useful for the application.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross section of a film and is a view for explaining each region of X, Y, and Z.

FIG. 2 is a diagram illustrating a bending angle.

Claims (1)

[Claims] 1. A at least uniaxially oriented void-containing polyester film containing a thermoplastic resin incompatible with polyester, wherein the total thickness of the film is H, in the thickness direction. Cavity content P _{1 in} the region X from the film surface to H / 20 is 0 to 5% by volume, followed by H / 2
The void content P ₂ of the region Y of 0 to H / 4 is 5 to 25% by volume, the void content P ₃ of the region Z of H / 4 to H / 2 is 10 to 30% by volume, and P ₃ Is 5 to ₂ more than P _2.
A void-containing polyester-based film, characterized in that it is 0% by volume.