JPH11152357A - White polyester-based film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a white polyester-based film excellent in softness by making the film mainly comprise polypropylene terephthalate and have a specified optical concn. SOLUTION: The objective film has an optical concn. of 0.3 or higher and pref. contains 10-50 vol.% closed voids inside. An optical concn. of 0.3 or higher is obtd. pref. by incorporating white inorg. or org. particles into a polyester or into a void-forming agent. Particles of titanium oxide, calcium carbonate, barium sulfate, and zinc sulfide are esp. pref. particles to be incorporated. 10-50 vol.% closed voids are formed in the film pref. by incorporating 3-30 wt.% void-forming thermoplastic resin (e.g. PS) incompatible with a polypropylene terephthalate resin and/or void-forming inorg. particles (e.g. titanium oxide) into the film and forming voids at the interface between resins or at the interface of the resin and the inorg. particle in the step of film stretching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly flexible white polyester film.

[0002]

2. Description of the Related Art Synthetic paper, which is a substitute for paper made from synthetic resin as a main material, is more water-resistant, hygroscopic, dimensionally stable, surface gloss, and glossiness of printed matter than paper made from natural pulp as a main material. Excellent in sharpness, mechanical strength, etc. For this reason, in recent years, various applications have been developed utilizing the characteristics.
As the main raw material of synthetic paper, those containing polyethylene terephthalate, which is a main component of polyolefin-based resin and polyester-based resin, have important characteristics required for synthetic paper such as high heat resistance and strong stiffness. As such, it is still quite widely used today.

Currently, the most effective method for obtaining a film having a function similar to that of natural paper using a synthetic resin as a main raw material is to form a myriad of fine cavities inside the film, thereby forming a film. This is a method that gives appropriate flexibility to itself and can be reduced in weight, as well as excellent writing properties and clear printing / transfer properties. As means for forming cavities inside the film, a resin incompatible with the matrix resin or inorganic or organic inactive particles is mixed into the raw material resin as a cavity forming agent, and formed into a film, and then mixed. This is a method in which voids are generated at the resin interface or at the interface with the particles by stretching.

[0004]

However, in the case of a film containing polyethylene terephthalate as a main component, there is a limit in the softening effect due to the formation of cavities, and studies have been made to obtain more excellent flexibility. For example, a method has been proposed in which a polyalkylene glycol component having a plasticizing effect on polyethylene terephthalate is mixed or copolymerized (JP-A-2-235942), but a sufficient softening effect cannot be obtained. Since polyether is extremely susceptible to thermal degradation, decomposition of polyether occurs in the step of drying the raw material or in the step of collecting and recycling resin melt lines or film waste. Decomposition of the polyether causes a reduction in the molecular weight of the polyester to significantly lower the film strength, a problem of coloring the film yellow, and a problem of a pungent odor due to the formation of aldehyde.

[0005] As described above, in the prior art, a white polyester film having sufficient flexibility has not been obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a white polyester film having excellent flexibility.

[0007]

The white polyester film of the present invention, which has solved the above problems, comprises polypropylene terephthalate as a main component and has an optical density of 0.3 or more. It is a white polyester film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The components of the present invention will be described below in order. First, the polypropylene terephthalate used in the present invention is a polyester containing terephthalic acid as a main acid component and 1,3-propanediol as a main glycol component.
Or a glycol component containing isophthalic acid, phthalic acid, diphenyl-4,4-dicarboxylic acid, naphthalene-2,6-
Dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid, diphenoxyethane-4,4-dicarboxylic acid, diphenylsulfone-4,4
Acid components such as dicarboxylic acid, diphenyl ether-4,4-dicarboxylic acid, malonic acid, 1,1-dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, decamethylene dicarboxylic acid, ethylene glycol and tetramethylene Glycol components such as glycol, neopentyl glycol, cyclohexane dimethanol, hydroquinone, and bisphenol A, and polyethylene glycol;
Polypropylene glycol, polytetramethylene glycol, a copolymer thereof, or the like may be copolymerized.

The method for producing the polyester in the present invention includes a method for directly obtaining a polyester by a reaction of a conventionally known dicarboxylic acid and glycol, and a method for transesterifying a lower alkyl ester of dicarboxylic acid with glycol, which is sodium, potassium, magnesium, or the like. Calcium, zinc,
A strontium, titanium, zirconium, manganese, and a compound containing one or more compounds containing cobalt are subjected to a heat reaction to obtain a low-polymerized polyester, and the obtained low-polymerized polyester is treated with a polymerization catalyst in the presence of ~
A method obtained by heating and polymerizing at 260 ° C. is exemplified.

Preferred polymerization catalysts include antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds and titanium compounds.

Examples of the titanium compound include tetraalkyl titanate, tetraaryl titanate, titanyl oxalate, titanyl oxalate, chelate compounds containing titanium, tetracarboxylate of titanium, and the like. Specific examples include tetraethyl titanate and tetrapropyl titanate. , Tetraphenyl titanate or partial hydrolysates thereof, titanyl ammonium oxalate, potassium titanyl oxalate, titanium triacetylacetonate and the like.

The white polyester film of the present invention comprises:
The optical density must be 0.3 or more as an essential component,
As a more preferred embodiment, 10 to 5
Preferably, it contains 0% by volume of independent cavities. This is because the function as synthetic paper can be exhibited by having these features. The void content is 10% by volume
If it is less than 5, sufficient flexibility as synthetic paper cannot be obtained, and 5
If it exceeds 0% by volume, it becomes too flexible, and handling as synthetic paper becomes difficult.

The method for obtaining the optical density of 0.3 or more is not particularly limited, but it is preferable to add white inorganic or organic particles having a hiding property to the polyester or the cavity-forming agent. preferable. Particles that can be added are not particularly limited, but particularly preferred particles include titanium oxide, calcium carbonate, barium sulfate, and zinc sulfide.

The method for incorporating 10 to 50% by volume of independent cavities inside the film is not particularly limited, but preferably, a void-forming thermoplastic resin which is incompatible with the polypropylene terephthalate resin which is a main component, and It is preferable to adopt a method of mixing 3 to 30% by weight of void-forming inorganic fine particles and forming voids (independent cavities) at the resin interface or the interface with the inorganic fine particles in the film stretching step.

The thermoplastic resin having void forming properties is not limited at all, but may be polystyrene resin, polyolefin resin, polyphenylene ether resin, polyacrylic resin, polycarbonate resin, polysulfone resin, or cellulose resin. And polyphenylene sulfide-based resins, cyclic olefin-based polymers, and ring-opened polymers thereof.

The void-forming particles are not limited, but those exemplified as particles for achieving an optical density can be used as they are.

The mixing amount of these void-forming resins or particles varies depending on the desired amount of cavities, but is preferably in the range of 3 to 30% by weight based on the whole film. This is because if it is less than 3% by weight, there is a limit in increasing the amount of cavities formed, and it is difficult to obtain a sufficient softening effect, and if it is more than 30% by weight, the stretchability of the film is significantly impaired. is there.

Further, the white polyester film of the present invention may have a nucleating agent, an antioxidant, a coloring inhibitor, a pigment, a dye, an ultraviolet absorber, a releasing agent, a lubricant, a flame retardant, You may mix | blend an inhibitor.

The white polyester film of the present invention comprises:
It is composed of the above-mentioned components, and may have a single-layer structure or a multi-layer structure of two or more layers.

The method for producing the white polyester film of the present invention is optional, and is not particularly limited.
A general method can be used in which after a mixture having the above composition is formed into a film to obtain an unstretched film, the unstretched film is stretched.

The conditions for stretching and orienting the unstretched sheet are closely related to the formation of cavities. In the following, an example of a sequential biaxial stretching method most preferably used, particularly a method of stretching an unstretched sheet in the longitudinal direction and then in the width direction will be described.
The alignment conditions will be described. First, in the first-stage longitudinal stretching step,
Stretching is performed between two or many rolls having different peripheral speeds. As a heating means at this time, a method using a heating roll, a method using a non-contact heating method may be used, or both may be used. However, in order to develop a large number of cavities at the interface of the incompatible resin, the film is stretched 3 to 5 times at a polyester transition temperature Tg + 50 ° C. or lower. Next, the uniaxially stretched film is introduced into a tenter, and at a temperature not higher than the melting point Tm-10 ° C. of the polyester in the width direction,
Stretch 2.5 to 5 times.

The biaxially stretched film thus obtained is subjected to a heat treatment as required. The heat treatment is preferably performed in a tenter, and the melting point of the polyester is Tm-50.
It is preferable to carry out in the range of ° C. to Tm.

The white polyester film of the present invention may have a coating layer on at least one of the surfaces. By providing a coating layer, it is possible to improve the wettability and adhesion of ink, a coating agent, and the like. Examples of the compound constituting the coating layer include a polyester-based resin and a polyurethane-based resin, but are not limited thereto.

As a method for providing a 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 is applied. it can. As the step of applying, any method such as a method of applying before stretching the film, a method of applying after longitudinal stretching, and a method of applying to the surface of the film after the orientation treatment is possible.

The white polyester film thus obtained is remarkably superior in flexibility to the void-containing film containing polyethylene terephthalate as a main component. For this reason, it is excellent in printing characteristics in various printers and can exhibit excellent characteristics as a marking film substrate.

[0026]

Next, examples of the present invention and comparative examples will be described.

The measurement and evaluation methods used in the present invention are described below.

1) Optical Density Using a Macbeth optical densitometer, the transmission density of white light was evaluated.

2) Cavity content Each of the unstretched film and the stretched film is 10 cm
Ten samples were cut out to a size of × 10 cm. The apparent specific gravity of the unstretched film (average of 10 sheets, d1) and the apparent specific gravity of the stretched film (average of 10 sheets, d2) were determined by measuring the thickness and weight. The void content was calculated from the following equation. Cavity content (%) = (d1 -d2) / d1 x 100

3) Flexibility 12.7 mm in width and 150 in length from any part of the film
5 mm were cut out, and the length of each sample was 127 mm, and the sample was fixed so as to protrude horizontally from the fixing table. Then, a 0.9 g weight was attached to the tip of the test piece and was hung down. 30 vertically from the horizontally fixed point
The distance a (mm) from the point below mm to the film hanging down in the horizontal direction was measured from the side surface of the test piece. Formula: ta
The sagging angle θ was calculated from nθ = a / 30. The average value of the five samples was used as the flexibility index. The smaller this value is, the better the flexibility is.

Example 1 81 parts by weight of terephthalic acid and 1,3-propanediol 7
4 parts by weight and 0.08 parts by weight of tetrabutyl titanate were charged into a reaction vessel, and the temperature in the vessel was increased from 150 ° C. to 190 ° C. for 30 minutes, and then increased to 230 ° C. over 3 hours to carry out an esterification reaction. To the obtained reaction product, 0.03 weight of tetrabutyl titanate was added, and the pressure was gradually reduced from 230 ° C. and the temperature was raised to reach 250 ° C. and 0.5 mmHg in 60 minutes, and the polymerization reaction was performed for 4.5 hours. went. The intrinsic viscosity of the obtained polymer was 0.83.

The above propylene terephthalate polymer 8
0% by weight of a polystyrene resin having a melt flow index of 2.0 (TOPOLEX 570- manufactured by Mitsui Toatsu Co., Ltd.)
57U) 3% by weight, polypropylene resin having a melt flow index of 1.7 (Noblen F manufactured by Mitsui Toatsu Co., Ltd.)
O-50F) 12% by weight and 5% by weight of anatase type titanium dioxide (TA-300 manufactured by Fuji Titanium Co., Ltd.) having an average particle size of 0.2 μm (electron microscopic method) were mixed and supplied to a vented twin-screw extruder. The mixture was sufficiently kneaded and extruded onto a cooling drum adjusted to 30 ° C. using a T-die to prepare an unstretched sheet. Subsequently, the obtained unstretched sheet was heated to 60 ° C. using a heating roll, and a longitudinal stretching of 3.4 times was performed between the rolls. Subsequently, the mixture was heated to 50 ° C. with a tenter to obtain 3.7.
The film was horizontally stretched twice, fixed in width, subjected to a heat treatment at 200 ° C. for 5 seconds, and further relaxed at 200 ° C. in the width direction by 4% to obtain a white polyester film having a thickness of 100 μm. The optical density of the obtained white polyester film was 0.9, the void content was 35%, and the flexibility index was 22 degrees.

COMPARATIVE EXAMPLE Polyethylene terephthalate chips having an intrinsic viscosity of 0.78 were mixed with polyethylene glycol flakes having a molecular weight of 20,000 at 10% by weight and a melt flow index of 10 g / g.
The raw material blended with 15% by weight of polypropylene chips for 10 minutes and melted and kneaded at 290 ° C. with an extruder is extruded into a slit shape on a cooling drum at 40 ° C. about 0.5 m.
An amorphous sheet having a thickness of m was obtained. Next, the film was stretched 3 times in the longitudinal direction and 3.2 times in the transverse direction, and heat-treated at 235 ° C. for 5 seconds to finally obtain a 100 μm-thick polyester film.
The resulting film had an optical density of 0.7, a void content of 45%, and a flexibility index of 30 degrees.

[0034]

As described above, it can be seen that the white polyester-based film of the present invention has superior flexibility to the polyethylene terephthalate-based void-containing film.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 67:02

Claims (2)

[Claims] 1. A white polyester film comprising polypropylene terephthalate as a main component and having an optical density of 0.3 or more. 2. The white polyester-based film according to claim 1, comprising polypropylene terephthalate as a main constituent and 10 to 50% by volume of independent cavities inside the film.