JPH075763B2 - White polyester film - Google Patents

Description

The present invention relates to a white biaxially stretched polyester film having a highly improved light resistance.

<Problems to be Solved by Conventional Technology and Invention> Polyester typified by polyethylene terephthalate is used for information recording materials because of its excellent mechanical properties, electrical properties, chemical resistance, and dimensional stability. For capacitors,
It is used as a base material in many fields such as packaging, plate making, electricity loss, and photographic film applications.

Taking advantage of the excellent properties of such polyester films in recent years, whiteboards for electronic white boards and, for example, credit cards, telephone cards, are widely used for financial cards such as Japanese National Railways cards, communications, transportation institutions, etc. The range of use is expanding.

However, in such applications, the polyester film used as the base material turns yellow over a long period of time because it is used while being affected by the sunlight outside or the ultraviolet rays from indoor fluorescent lamps. Or, there is a problem that the mechanical strength is likely to decrease.

In particular, the former is a serious problem, but it is known that this is a phenomenon based on deterioration yellowing of titanium dioxide contained as a white masking agent in the white polyester film due to ultraviolet rays. In order to improve these properties required of the white polyester film, a UV absorber is generally contained in the white polyester film. This makes it possible to prevent deterioration of the white polyester film to some extent.

However, conventionally used ultraviolet absorbers are organic ultraviolet absorbers such as benzophenone type, benzotriazole type, and hydroquinone type, and these organic ultraviolet absorbers are generally easily decomposed by heat or oxidatively. Moreover, some sublime at high temperatures.

On the other hand, a polyester film, such as polyethylene terephthalate, is formed at 270 to 300 ° C. Therefore, even if such an organic ultraviolet absorber is added at the time of film formation, the ultraviolet absorber undergoes thermal decomposition or sublimation and its ultraviolet absorption ability is increased. Is significantly reduced.

Further, if the amount of the ultraviolet absorber added is increased to compensate for the decrease in the ultraviolet absorbing ability, the hue of the obtained film may be reduced or accumulated in the film forming machine, which causes various troubles.

Furthermore, some of such organic UV absorbers have a harmful effect on the human body.

As described above, at present, it is very difficult to maintain sufficient light resistance and whiteness even if the organic ultraviolet absorber is blended with the white polyester film.

<Means for Solving Problems> The present inventors have made earnest studies in order to achieve such an object in view of a situation in which demands for improvement of light resistance to white light of a white polyester film and maintenance of whiteness are becoming strict. As a result of stacking, it was found that light resistance to ultraviolet rays and maintenance of whiteness of the white polyester film can be achieved for the first time by using fine particles of anatase type titanium dioxide containing a zinc compound, and arrived at the present invention.

That is, the gist of the present invention is characterized in that anatase type titanium dioxide containing 0.1 to 2.0% by weight of zinc compound in terms of zinc element to titanium dioxide is added to polyester in an amount of 2.0 to 30% by weight. It exists in a biaxially stretched polyester film.

Hereinafter, the present invention will be described in detail.

The polyester referred to in the present invention means an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, or its ester and ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol, etc. It is a polyester that can be obtained by polycondensing such a glycol.

This polyester can be obtained by directly polycondensing an aromatic dicarboxylic acid and a glycol, or by subjecting an aromatic dicarboxylic acid dialkyl ester and a glycol to an ester exchange reaction and then polycondensation, or by diluting an aromatic dicarboxylic acid diester. It can also be obtained by a method such as polycondensation.

Typical examples of such polymers include polyethylene terephthalate and polyethylene-2,6 naphthalate. This polymer may be a homopolymer or may be a copolymer of a third component. In any case, in the present invention, the ethylene terephthalate unit and / or the ethylene-2,6 naphthalate unit is 80 mol%.
The polyester having the above is preferable.

In the present invention, a specific amount of anatase titanium dioxide containing a specific amount of a zinc compound is blended with the polyester.

As the zinc compound contained in the anatase type titanium dioxide, zinc acetate, zinc benzoate, zinc oxide, zinc carbonate,
Examples thereof include zinc chloride, zinc hydroxide, zinc lactate, zinc phosphate, zinc sulfate, zinc nitrate, etc., but are not limited thereto. Of these, zinc compounds having good heat resistance are preferable.

The zinc compound-containing anatase titanium dioxide used in the present invention preferably has an average particle size of 0.1 to 1.0 μm, and more preferably 0.2 to 0.5 μm. Average particle size 0.1
If it is less than μm, the light transmittance becomes large and the white hiding effect becomes insufficient, which is not preferable. Conversely, the average particle size is 1.0 μm
If it exceeds, the original whiteness of the anatase type titanium dioxide decreases, which is not preferable.

The amount of zinc compound contained in the anatase type titanium dioxide is 0.1 to 2.0% by weight in terms of zinc element.
It is preferably about 1.0% by weight. The amount of zinc compound contained in anatase type titanium dioxide is calculated in terms of zinc element
If it is less than 0.1% by weight, the effect of improving the light resistance becomes insufficient, which is not preferable. On the other hand, if the amount of zinc compound contained in the anatase type titanium dioxide exceeds 2.0% by weight in terms of zinc element, the thermal stability of the polyester will decrease and problems such as film rupture during film formation tend to occur. Not preferable.

The content of zinc compound-containing anatase type titanium dioxide is 2.0 to 30% by weight with respect to the polyester.
It is preferably about 20% by weight. If the compounding amount of the zinc compound-containing anatase type titanium dioxide is less than 2.0% by weight, the light transmittance becomes large and the white hiding effect becomes insufficient, which is not preferable. On the other hand, if this amount exceeds 30% by weight, the mechanical strength of the polyester is lowered and problems such as breakage of the film during film formation occur, which is not preferable.

The zinc compound-containing anatase type titanium dioxide used in the present invention is not limited in its production method as long as it satisfies the conditions defined above. As a method of incorporating such a zinc compound into anatase titanium dioxide, a predetermined amount of zinc compound such as zinc oxide, zinc hydroxide, zinc carbonate, zinc chloride may be added and blended at the time of producing anatase titanium dioxide, or commercially available. The anatase type titanium dioxide may be surface-treated with a zinc compound such as zinc oxide, zinc hydroxide, zinc carbonate or zinc chloride.

The zinc compound may be contained inside the anatase-type titanium dioxide or may be present on the surface, but it is more preferable to be present on the surface in order to improve the initial whiteness.

In the present invention, the zinc compound-containing anatase type titanium dioxide can be compounded at any stage up to the production of the polyester film. That is, the zinc compound-containing anatase type titanium dioxide may be blended, for example, as a glycol slurry or as a powder as it is at any stage before the start of polycondensation, during the polycondensation reaction, and after the end of the polycondensation reaction. Alternatively, the polyester resin and the zinc compound-containing anatase type titanium dioxide may be melt-mixed in an extruder to form a chip. It should be noted that a so-called master battip containing zinc compound-containing anatase titanium dioxide at a high concentration is produced, and this master battip does not contain zinc compound-containing anatase titanium dioxide or contains a small amount thereof, if necessary. It is also possible to produce a polyester film having a predetermined amount by mixing with polyester.

In the present invention, the initial whiteness, if necessary, does not adversely affect the light resistance, does not increase the number of coarse particles, and has an average particle size and content that does not adversely affect the smoothness of the polyester film surface. If necessary, inert particles other than the zinc compound-containing anatase type titanium oxide may be used in combination. In addition to the above-mentioned inert particles, so-called precipitation type fine particles precipitated by the reaction of the catalyst residue and the phosphorus compound in the reaction system can be used together.

In any case, the biaxially stretched polyester film containing a specific amount of anatase type titanium dioxide containing a specific amount of a zinc compound satisfies the initial whiteness and light resistance targeted by the present invention.

A publicly known method can be adopted for the polycondensation of the polyester in the present invention. For example, one or more antimony compounds, germanium compounds, titanium compounds and the like are used as a catalyst for the polycondensation reaction, heated to about 230 to 300 ° C., and the reaction is advanced by distilling glycol under reduced pressure. A known method can be used for forming the chip and the master chip. For example, the raw material polyester chips and the particles are melt-mixed by an extruder at 270 to 300 ° C., and after cooling, formed into chips. Further, a known film forming method can be adopted for forming the film. For example, after melt-extruding a raw material polyester chip containing anatase type titanium dioxide containing a zinc compound at 270 to 300 ° C into a film, cooling it at 40 to 70 ° C and solidifying it to form an amorphous sheet, and then lengthwise (2.5 to 3.5 times ), Sideways (2.
(5 to 3.5 times) or sequential biaxial stretching or simultaneous biaxial stretching 160 to 2
A method such as heat treatment at 70 ° C. (for example, the method described in JP-B-30-5639) can be adopted.

<Examples> The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Various physical properties and characteristics are measured or defined as follows. In the examples, "part" means "part by weight" and "%" means "% by weight".

(1) Average particle size Centrifugal sedimentation type particle size distribution measuring device (SA-CP3 manufactured by Shimadzu Corporation
The value of the integrated (weight basis) 50% in the equivalent spherical distribution measured by (type) is used.

(2) Thermal stability 7 g of polymer was put in a test tube, vacuum dried at 160 ° C- / mmHg for 2 hours, then recompressed to 100 mmHg with nitrogen gas, and then 290 ° C 2
The heat-melting heat treatment was carried out for an hour, and the degree of retention of the degree of polymerization was evaluated from the retention rate of the intrinsic viscosity [η] of the polymer before and after the treatment, which was measured by the method (3) below.

(3) Intrinsic viscosity [η] 1 g of polymer is phenol / tetrachloroethane = 50/50
It was dissolved in 100 ml of a mixed solvent (weight ratio) and measured at 30 ° C.

(4) Dispersibility in polymer 8.5 kg / h using 1000 mesh filter with filtration area of 30 cm ²
Extruded amount until the pressure at the inlet of the filter reaches 150 kg / cm ² when the molten polymer is extruded at r (converted to ton / m ² ).
Expressed as The larger this value, the better the filter filtration property, and the better the polymer dispersibility.
The dispersibility in the polymer at that time was judged as follows.

> 40 (tons / m ² ) …… ○ 20-40 (tons / m ² ) …… △ <20 (tons / m ² ) …… × (5) Film-forming property of film at 270-300 ℃ 40 ~ 70 after melt extruding
After cooling and solidifying at ℃ to make an amorphous sheet, lengthwise (3.0 times),
Biaxial stretching was sequentially carried out horizontally (3.0 times), and the frequency of breakage at that time was judged as follows.

Not broken at all …… ○ Sometimes broken …… △ Frequently broken …… × (6) Initial whiteness of the film Measured using a Tokyo Denshoku color difference meter (TC-5D type).
The whiteness of the film is represented by the b value, and the smaller the value, the higher the whiteness. The larger the b value, the stronger the yellowish tint and the yellowing.

(7) Concealment Degree The density of transmitted light under a G filter was measured using a Macbeth densitometer (TD-904 type). The larger this value is, the higher the hiding power is.

(8) Evaluation of light resistance UV long life fade meter (FA
L-3 type) was used, and after irradiating with ultraviolet rays at 63 ° C. ± 3 ° C. for 300 hours, the b value was measured using the color difference meter (TC-5D type) of the above (6). The smaller the change (Δb value) between the initial b value and the b value after 300 hours, the better the light resistance.

<Example 1> (Production method of polyester chip) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol
Parts and 0.07 parts of calcium acetate-hydrate in a reactor, the temperature of the mixture is increased by heating, the methanol is distilled off to carry out the transesterification reaction, and it takes about 4 and a half hours after the reaction is started to reach 230 ° C. The transesterification reaction was completed.

Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added, and polymerization was carried out according to a conventional method. That is, the reaction temperature was gradually increased to finally 280 ° C., while the pressure was gradually reduced to finally 0.5 mmHg. After 4 hours, the reaction was completed,
A polyester (A) was obtained by chipping according to a conventional method. At that time, the viscosity [η] was 0.702.

(Manufacturing method of master batch) 60 parts of the obtained polyester (A) and 40 parts of anatase type titanium dioxide containing zinc oxide (0.3% in terms of zinc element) having an average particle size of 0.3 μm manufactured by a conventional method are processed by a conventional method. 29 in extruder
Melt mixing was performed at 0 ° C. to obtain a master batch chip (B).

(Film Forming Method) The polyester (A) and the polyester (B) were blended at 62.5: 37.5 so that the blending amount of the titanium dioxide was 15%, followed by drying at 180 ° C. for 5 hours and at 290 ° C. according to a conventional method. The film was melt-extruded, cooled at 50 ° C. and solidified to form an amorphous sheet, which was sequentially biaxially stretched lengthwise and widthwise and heat-treated at 230 ° C. to obtain a white biaxially stretched film having a thickness of 250 μm.

The characteristics of the obtained white polyester film are shown in Table 1. As shown in Table 1, the initial whiteness and light resistance of the obtained white polyester film are very good and have very satisfactory characteristics.

<Example 2> Zinc hydroxide having an average particle size of 0.3 μm (0.3% in terms of zinc element) was used instead of the anatase type titanium dioxide containing zinc oxide (0.3% in terms of zinc element) having an average particle size of 0.3 μm used in Example 1.
Example 1 except that the contained anatase type titanium dioxide was used
A white biaxially stretched film was obtained by the same method as described above. The characteristics of the obtained white polyester film are shown in Table 1. The white polyester film thus obtained has very satisfactory properties as in Example 1.

<Example 3> A white biaxially stretched film was obtained in the same manner as in Example 1 except that zinc oxide (0.6% in terms of zinc element) -containing anatase type titanium dioxide having an average particle size of 0.3 µm was used. The characteristics of the obtained white polyester film are shown in Table 1. The white polyester film thus obtained has very satisfactory properties as in Example 1.

<Example 4> White in the same manner as in Example 1 except that anatase type titanium dioxide containing zinc oxide (0.6% in terms of zinc element) having an average particle size of 0.3 µm was compounded so that the compounding amount was 20%. A biaxially stretched film was obtained. The characteristics of the obtained white polyester film are shown in Table 1. The white polyester film thus obtained has very satisfactory properties as in Example 1.

Comparative Example 1 A white biaxially stretched film was obtained in the same manner as in Example 1 except that anatase type titanium dioxide having an average particle size of 0.3 μm was used. The characteristics of the obtained white polyester film are shown in Table 1. As shown in Table 1, since it does not contain a zinc compound, it is inferior in light resistance and is inadequate as a characteristic of the white polyester film.

Comparative Example 2 A white biaxially stretched film was obtained in the same manner as in Example 1, except that zinc oxide (0.07% in terms of zinc element) -containing anatase type titanium dioxide having an average particle size of 0.3 μm was used. The characteristics of the obtained white polyester film are shown in Table 1. First
As shown in the table, the content of zinc oxide is 0.1 in terms of zinc element.
%, The light resistance is poor and the properties of the white polyester film are insufficient.

Comparative Example 3 A white biaxially stretched film was obtained in the same manner as in Example 1 except that anatase titanium dioxide containing zinc oxide (2.5% in terms of zinc element) having an average particle size of 0.3 μm was used. It was not possible to obtain a white polyester film because the dispersibility in the polymer and the thermal stability of the polymer were poor.

<Comparative Example 4> White by the same method as in Example 1 except that anatase type titanium dioxide containing zinc oxide (0.6% in terms of zinc element) having an average particle size of 0.3 μm was blended so that the blending amount was 1%. A biaxially stretched film was obtained. The characteristics of the obtained white polyester film are shown in Table 1. As shown in Table 1, the hiding power is inferior and the properties of the white polyester film are insufficient.

<Comparative Example 5> White color was obtained in the same manner as in Example 1 except that anatase titanium dioxide containing zinc oxide (0.6% in terms of zinc element) having an average particle size of 0.3 μm was blended so that the blending amount was 35%. An attempt was made to obtain a biaxially stretched film, but since the content of the titanium dioxide was too large, the mechanical strength of the polyester film was lowered and the film forming property was poor, and a white polyester film could not be obtained.

Comparative Example 6 A white biaxially stretched film was obtained in the same manner as in Example 1 except that rutile titanium dioxide containing zinc oxide (0.6% in terms of zinc element) having an average particle size of 0.4 μm was used. The characteristics of the obtained white polyester film are shown in Table 1. As shown in Table 1, since rutile type titanium dioxide is used, the initial whiteness is inferior and the characteristics of the white polyester film are insufficient.

<Effects of the Invention> As described in detail above, the white biaxially stretched polyester film of the present invention contains a specific amount of zinc compound-containing anatase type titanium dioxide, and is used as a whiteboard for electronic whiteboards and magnetic cards. Excellent light resistance required. Further, the use of zinc compound-containing anatase type titanium dioxide has a feature that the initial whiteness is also improved at the same time.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area B29L 7:00

Claims (2)

[Claims] 1. Titanium dioxide is 0.1 in terms of zinc element.
A white biaxially stretched polyester film comprising 2.0 to 30% by weight of anatase type titanium dioxide containing 2.0 to 30% by weight of a zinc compound with respect to polyester. 2. The average particle size of anatase titanium dioxide is 0.
The white biaxially stretched polyester film according to claim 1, which is in the range of 1 to 1.0 μm.