JP2535803C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a label, a poster, a recording paper, a packaging material, and the like, which has sufficient waist strength and a large amount of fine cavities inside a film. And a drawing-containing polyester film. [0002] Synthetic paper, which is a paper substitute using synthetic resin as a main raw material, is more water-resistant than natural paper.
Excellent in moisture absorption dimensional stability, surface stability, print gloss and sharpness, mechanical strength, etc. In recent years, application development utilizing these advantages has been promoted. As a main raw material of synthetic paper, polyethylene, polypropylene, polyester, etc. are used. Among them, polyester typified by polyethylene terephthalate is excellent in that it has high heat resistance and is stiff, and is widely used. Applications can be developed. As a method for obtaining a film having a function similar to that of paper using polyester as a main raw material, there are conventionally (1) a method in which a large amount of fine cavities are contained in the inside of the film, or a conventional flat polyester film using (2-1) sandplast. There is disclosed a method of roughening the surface by a treatment, (2-2) chemical etching treatment, (2-3) matting treatment (a method of laminating a matting agent with a binder), and the like. Among them, the method of (1) in which a large amount of fine cavities are contained in the film can provide a point that the film itself can be reduced in weight and appropriate flexibility, thereby enabling clear printing and transfer. There is an advantage. Conventionally, as a method of forming fine cavities inside a film, a polymer incompatible with polyester is melt-kneaded with an extruder, a sheet in which the polymer is dispersed in fine particles in polyester is obtained, and the sheet is further stretched. Discloses a method for generating a cavity around fine particles. Examples of the polymer incompatible with the polyester used for the cavity (hereinafter, referred to as a cavity developing agent) include a polyolefin-based resin (for example, JP-A-49-134755).
Japanese Patent Publication No. JP-B-49-2016 and Japanese Patent Publication No. 54-29550, and polyarylate resins (for example, Japanese Patent Publication No. 58-280).
No. 97 publication). Among them, polypropylene and polystyrene are particularly preferable in that they easily form cavities, have a low density, and are inexpensive. However, conventional films containing many cavities become weaker, causing troubles and operability in post-processing processes such as surface treatment and printing, especially in the process of continuously processing wound films. A problem such as a decrease has occurred. In addition, the present invention has a shortage of heat resistance. SUMMARY OF THE INVENTION According to the present invention, printing and printing can be performed by optimizing the above-mentioned drawbacks, namely, the type and size of the cavity developing agent. It is an object of the present invention to provide a base material suitable for strong labels, posters, recording paper, etc., which are sharp and durable for printing, copying, etc., and have good operability in post-processing of the film. [0004] That is, the gist of the present invention as a means for solving these problems is to provide an oriented polyester film having an apparent density of 0.7 to 1.3 g / cm ^3. Has an initial elastic modulus of 300 kg / mm ² or more and a heat shrinkage factor (150 ° C., 30
Min) is less than 1.7%. The polyester in the present invention is produced by polycondensing an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, or naphthalenedicarboxylic acid or an ester thereof with a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol, or neopentyl glycol. Polyester. These polyesters react directly with the aromatic dicarboxylic acid and glycol,
It is produced by a method such as transesterification of an alkyl ester of an aromatic dicarboxylic acid and glycol followed by polycondensation, or polycondensation of a diglycol ester of an aromatic dicarboxylic acid. Representative examples of such polyesters include polyethylene terephthalate, polyethylene butylene terephthalate, and polyethylene 2,6 naphthalate. This polyester may be a homopolymer or a copolymer of the third component. In any case, in the present invention, a polyester having an ethylene terephthalate unit, a butylene terephthalate unit or an ethylene-2,6-naphthalate unit of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more is preferable. The thermoplastic resin incompatible with the polyester used in the present invention must be incompatible with the polyester described above. Specifically, polystyrene resin, polyolefin resin, polyacrylic resin, polycarbonate resin, polysulfone resin and the like can be mentioned. In particular, polyolefin resins such as polystyrene resins, polymethylpentene, and polypropylene are preferable. An important point in the present invention is that the apparent density is 0.7 to 1.3 g / cm ³ , preferably 0.8 to 1.3 g / cm ³ , and more preferably 0.9 to 1.3 g / cm ³ . That is. When the apparent density is less than 0.7 g / cm ³ , rupture frequently occurs during film formation, and the productivity is reduced. When the apparent density is more than 1.3 g / cm ³ , drawing properties and cushioning properties are lost. The point more important in the present invention, preferably one of the initial modulus 300 kg / mm ² or more, 305 kg / mm ² or more, more preferably, more preferably 310 kg / mm ² by the 320 kg / mm ² or more is there. If it is less than 300 kg / mm ^{2, the} rigidity of the polyester is lost, so that troubles and operability occur in post-processing steps such as a surface treatment step and a printing step, particularly in a step of continuously processing a wound film. A problem such as reduction occurs. Also, the heat shrinkage at 150 ° C must be less than 1.7%, preferably less than 1.5%. If it is 1.7% or more, the operability in post-processing at a high temperature is reduced. The cavity-containing film of the present invention has a surface roughness of 1.0 μm or less, preferably 0.3 μm.
m is desirable. If the thickness exceeds 1.0 μm, it is likely to cause printing failure when printing with a printer or the like. The polymer mixture of the present invention obtained by mixing the polyester and the thermoplastic resin incompatible with the polyester 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 from an extruder, or adding a thermoplastic resin incompatible with the polyester in the polyester polymerization step, stirring and dispersing. It can also be obtained by a method of melt-extruding the chips obtained and solidifying them. The polymer (unstretched sheet) obtained by solidification is usually in a non-oriented or weakly oriented state. In addition, the thermoplastic resin incompatible with the polyester exists in a form dispersed in the polyester in various shapes such as a spherical shape, an elliptical spherical shape, and a thread shape. [0007] The polymer mixture may contain inorganic particles as needed to improve concealment and drawing properties. Examples of the inorganic particles therefor include titanium dioxide, silicon dioxide, calcium carbonate, barium sulfate, aluminum oxide, kaolin, and talc, but are not particularly limited. To the polymer mixture, a coloring agent, a light-fast agent, a fluorescent agent, an antistatic agent, and the like can be added according to the application. The polymer mixture thus obtained is further stretched between rolls having different speeds (roll stretching), stretched by gripping and expanding with clips (tenter stretching), or stretched by air pressure (inflation stretching). At least one axis orientation treatment is performed by such as. At this time, exfoliation occurs at the interface between the thermoplastic resin incompatible with the dispersed polyester and the polyester, and many cavities are generated in the polymer mixture. Therefore, the amount of the thermoplastic resin incompatible with the polyester to be mixed with the polyester depends on the amount of the target cavity, but is preferably 3% by weight to 39% by weight, particularly preferably 8% by weight, based on the whole polymer mixture. ~ 35% by weight is preferred. 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. On the other hand, when the content is 40% by weight or more, the heat resistance and strength of the polyester film, particularly the stiffness, are significantly impaired. [0008] Furthermore, by providing a coating layer on the film surface, the wettability and adhesion of ink, coating agent and the like are improved. As the compound constituting the coating layer, a polyester-based resin is preferable, but in addition, a polyurethane resin, a polyester-urethane resin, and a means for improving the adhesiveness of a normal polyester film such as an acrylic-based resin are disclosed. Compounds are applicable. As a method for providing the coating layer, a commonly used method 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, and a reverse roll coating method can be applied. As a step of applying, a method of applying in advance to the surface of the mixed polymer material before performing the orientation treatment, a method of applying the film to the surface of the cavity-containing film oriented in the axial direction, and further orienting it in the perpendicular direction, Any method such as a method of coating the finished void-containing film surface is possible. In the present invention, a so-called composite film in which a surface layer and a center layer are laminated as necessary may be used. The method is not particularly limited. However, in consideration of productivity, the so-called co-extrusion lamination is most preferable, in which the raw materials for the surface layer and the center layer are extruded from separate extruders, led to one die to obtain an unstretched sheet, and then oriented at least uniaxially. . The conditions for orienting the polymer mixture are an important point for obtaining a stiff and void-containing film. Therefore, the conditions for achieving this purpose are, for example,
The most commonly performed sequential biaxial stretching step is exemplified by a sequential biaxial stretching method in which a continuous sheet of the polymer mixture is roll-stretched in the longitudinal direction and then tenter-stretched in the width direction. Become like In the roll stretching (longitudinal stretching), the secondary transition temperature of the polyester is + 30 ° C. or lower. In the tenter stretching (lateral stretching), the temperature is 80 to 150 ° C., and the magnification is 2.8 to 5 in order to form a stable film without breaking. Double it.
Further, in order to obtain a void-containing film having an initial elastic modulus of 300 kg / mm ² , the condition of the longitudinal stretching ratio becomes important. The first draw ratio must be 2.5 to 5.0 times to obtain a moderately large number of cavities. If it is less than 2.5 times, a moderately large number of cavities cannot be obtained. When the ratio is 5.0 times or more, the cavity is excessively developed, so that the initial elastic modulus is less than 300 kg / mm ^2, and the heat shrinkage at 150 ° C. is less than 1.7%, preferably less than 1.5%. . In addition, after stretching vertically and horizontally, 1.0
The film is longitudinally stretched 5 times or more, and the longitudinal stretching (first time × second time) is 3.5 times, preferably 3.65 times.
Must be more than double. If this condition is not satisfied, the initial elastic modulus is 300 kg /
A void-containing film having a heat shrinkage of less than 1.7%, preferably less than 1.5% at 150 ° C. in mm ² cannot be obtained. An important point in the present invention lies in heat treatment conditions after stretching. The heat treatment must be performed at 200 ° C. or higher, preferably 220 ° C. or higher, more preferably 230 ° C. or higher after the completion of stretching. At this time, the heat setting must be performed while relaxing by 3 to 8%. If the temperature is less than 200 ° C or less than 3%, the initial elastic modulus is 300k.
A void-containing film having a heat shrinkage at g / mm ² or 150 ° C. of less than 1.7%, preferably less than 1.5%, cannot be obtained. In the present invention, polyester is used in order to satisfy 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 that the polymer mixture is oriented at least uniaxially is to generate a large number of fine cavities in the polymer mixture. By forming cavities, the film can be reduced in weight, workability is improved, and the cost per area is reduced. Further, by containing the cavity, flexibility is increased, and clear printing and printing can be performed when performing printing and transfer. Further, by containing a cavity, light opacity and whiteness can be obtained. Further, a large number of protrusions derived from a thermoplastic resin incompatible with the polyester are formed on the film surface, and writing with a pencil or a ballpoint pen becomes possible. The void-containing polyester film thus obtained has excellent heat resistance and mechanical strength required for applications such as posters, labels, delivery slips, barcode labels, and receiving paper, and is strong enough to be operable during post-processing. Was obtained. Examples Next, examples of the present invention and comparative examples will be described. The measurement / evaluation method used in the present invention will be described below. 1) Density A film was cut out into a square of 5.00 cm x 5.00 cm, and the thickness was measured at 50 points, the average thickness was set to tμm, and the weight was measured to 0.1 mg and the wg was measured.
And calculated by the following equation. ## EQU1 ## Apparent density (g / cm ³ ) = (w / 5 × 5 × t) × 10000 2) Cavity content Calculated by the following equation. ## EQU2 ## Cavity content (volume%) = 100 × (1-true specific volume / apparent specific volume) where: true specific volume = x1 / d1 + x2 / d2 + x3 / d3 +... + Xi ## EQU00004 ## 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 value of the true specific gravity used in the calculations in Examples was polyethylene terephthalate 1
. 40, general-purpose polystyrene 1.05, polypropylene 0.91, and anatase-type titanium dioxide 3.9 were used. [0018] 3) initial modulus film width 10mm and attached to the tensile tester in the length interval 40 mm (Shimadzu Autograph), 200 mm / pulled at a rate of strength against the rise of elongation kg / mm ² units I asked for it. 4) Heat shrinkage Take a film 10mm wide and 250mm long, mark at 200mm intervals and 5g
Is fixed under a constant tension, and the mark interval A is measured. Subsequently, a load of 3 g was applied for 30 minutes.
The interval B between the marks after being placed in an oven in an atmosphere at 150 ° C. was determined, and was determined as the heat shrinkage rate by the following equation. ## EQU5 ## Thermal Shrinkage (%) = (AB) × 100 / A 5) Light Transmittance According to JIS-K6714, a Poick integrating sphere formula H.V. T. The light transmittance of the film was measured using an R meter (manufactured by Nippon Seimitsu Kogaku). The smaller the value, the higher the concealment property. 6) Surface roughness According to JIS-B0601-1982, using a Surfcom 300A type surface roughness meter (manufactured by Tokyo Seimitsu Co., Ltd.), center line average with a stylus diameter of 2 μm, a stylus pressure of 30 mg, a measurement pressure of 30 mg, and a cutoff of 0.8 mg. The thickness was measured. 7) Waist strength Free rolls having a diameter of 10 cm are placed in parallel at intervals of 20 cm, and one end of the continuous film is fed at 2 m / min from one roll as shown in FIG. At this time, FIG.
Is passed if it passes over the roll as shown in FIG. 3, and it is rejected if it falls just before the other roll as shown in FIG. This test was repeated 10 times, and the test was evaluated as ○ if all 10 tests were passed, and × if it was not passed even once. Examples 1 and 2 A polyethylene terephthalate resin having an intrinsic viscosity of 0.60 and a melt flow index of 3.0 g / 10 min.
It is melt-extruded at 290 ° C. from a T-die with an axial screw extruder, solidified electrostatically in close contact with a cooling rotating roll, and subsequently longitudinally stretched 3.1 times at 90 ° C. with a roll stretching machine, and subsequently at 130 ° C. with a tenter. After stretching 3.0 times in the transverse direction,
. The film was longitudinally stretched two times and heat-treated at 235 ° C. while relaxing by 5% to obtain a polyester film containing a large number of cavities inside. It was a good thing with strong waist. Example 3 A polyethylene terephthalate resin was used as a raw material and a melt flow index was used.
A void-containing polyester film was obtained in exactly the same manner as in Example 1, except that 14% by weight of the crystalline polypropylene was contained at 7 g / 10 minutes. It was a good thing with strong waist. Example 4 A void-containing polyester film was obtained in exactly the same manner as in Example 1, except that 5% by weight of titanium dioxide was added. It was strong and had good whiteness. Example 5 The sheet of Example 1 was used as a central layer A, and a polymer mixture containing 80% by weight of a polyethylene terephthalate resin and 20% by weight of anatase type titanium dioxide was used as a surface layer B on both sides thereof, and B / A / B Were laminated so that the final thickness became 3/54/3 μm, and the film was stretched in the same manner as in Example 1 to obtain a laminated void-containing polyester film. Comparative Example 1 A void-containing polyester film was obtained in exactly the same manner as in Example 1 except that the first longitudinal stretching ratio was 2.2 times. The film had a low waist having an initial elastic modulus in the longitudinal direction of less than 300 kg / mm ² . Comparative Example 2 A void-containing polyester film was obtained in exactly the same manner as in Example 1, except that the first-time longitudinal stretching ratio was 3.7, and the second-time stretching was not performed. A large number of cavities appeared, and the film had a weak waist whose initial elastic modulus in the longitudinal direction was less than 300 kg / mm ² . Comparative Examples 3 and 4 A void-containing polyester film was obtained in exactly the same manner as in Example 1 except that the heat treatment conditions were changed as shown in Table 1. It can be seen that the initial elastic modulus or heat shrinkage does not satisfy the conditions in the text. Comparative Example 5 The same procedure as in Example 1 was carried out except that 41% by weight of general-purpose polystyrene was added to polyethylene terephthalate resin as a raw material, but the film was frequently broken and film formation was impossible. Comparative Example 6 The procedure was performed in exactly the same manner as in Example 1 except that polyethylene terephthalate resin was used as a raw material and polystyrene for general use was 1% by weight. The polyester film had no void inside. The void-containing polyester film of the present invention has the same lightness, flexibility, concealing properties, and matte as the void-containing polyester film obtained by using a conventional polystyrene or polyolefin as a void developing agent. In addition to having the properties and drawing properties, it is stiffer than conventional void-containing polyester films, has excellent heat resistance, and has high operability in processing steps and the like. Therefore, the void-containing polyester film of the present invention is inexpensive and can be used in a very wide range of fields such as labels, posters, recording paper, and packaging materials. [Table 1] [Table 2]

[Brief description of the drawings]   FIG.   FIG. 1 shows an apparatus for evaluating the stiffness of a film using a free roll.   FIG. 2   FIG. 2 shows an apparatus for evaluating the stiffness of a film using a free roll.   FIG. 3   FIG. 3 shows an apparatus for evaluating the stiffness of a film using a free roll.   [Explanation of symbols]   In FIGS. 1, 2, and 3, 1 is a free roll and 2 is a film.

Claims (1)

Claims: 1. An oriented polyester film having an apparent density of 0.7 to 1.3 g / cm ³ , one of which has an initial elastic modulus of 300 kg / mm ² or more,
And a heat-shrinkage ratio (150 ° C., 30 minutes) of less than 1.7%. 3. A film comprising a thermoplastic resin on at least one surface of the film of claim 1. 3. A void-containing polyester film characterized by laminating B). 3. A void-containing polyester film comprising the layer B of claim 2 containing 0.5 to 30% by weight of inorganic particles. the film