JPH08253610A - White polyester film - Google Patents

Abstract

PURPOSE: To obtain the subject film having high cleavage strength, mechanical strength, heat-resistance and whiteness and useful as a substitute for paper by adding a polyolefin resin and a polyethylene glycol to a polyester at prescribed ratios. CONSTITUTION: This biaxially drawn film having a cleavage strength of >=300g/15mm and composed of a polyester layer containing innumerable fine bubbles is produced by incorporating (A) a polyester with (B) <=30wt.% of a polyolefin resin and further (C) 0.5-5wt.% of a polyethylene glycol. Preferably, the component B is polymethylpentene or polypropylene and the layer contains inorganic particles.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel white polyester film having good whiteness and excellent mechanical properties.

More specifically, paper substitutes, that is, cards, labels, stickers, courier slips, video printer image receiving paper, bar code printer image receiving paper, posters, maps, dust-free paper, display boards, white boards, photographic paper. The present invention relates to a white polyester film which can be favorably used as a base material for copy paper and the like.

[0003]

2. Description of the Related Art Generally, printed matter that is used outdoors is not resistant to wind and rain when paper is used, and conventionally water resistant paper or plastic film has been used. Further, a plastic film is used because the adhesive paper such as a label and a seal is torn when the paper is peeled after being attached.

Films used for such applications are
Whiteness and opacity are required. For example, as a conventional product, there is one in which calcium carbonate is added to a polyolefin resin (Japanese Patent Publication No. 63-64310), but since it is based on polyolefin, it is weak against heat and There is also a problem in mechanical strength. In order to improve these drawbacks, polyester-based polypropylene added with polypropylene (for example, JP-A-63-1168).
441).

However, these conventional films have the following disadvantages.

Films based on polyolefins lack heat resistance and have poor mechanical strength.

The color tone of the film is yellowish,
Impairs the beautiful whiteness and luxury.

Those based on polyester are expensive.

In order to reduce the cost per area of the film, fine bubbles are formed inside the film, and the film having a reduced apparent density is likely to be cleaved. In order to suppress cleavage, it is necessary to reduce internal fine bubbles, that is, to keep the density high.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above problems in the prior art, exhibits a beautiful white color, is difficult to cleave despite the existence of innumerable fine bubbles, and has a high breaking strength. The object is to provide a large new white polyester film.

[0011]

The white polyester film of the present invention which achieves the above-mentioned object is composed of the following (1)-
It has the configuration of (4).

That is, (1) Polyester resin is added to polyester in an amount not exceeding 30% by weight, and polyethylene glycol is added in an amount of 0.5 to 5% by weight. It becomes biaxially stretched, and the cleavage strength is 300 g / 15
It is a white polyester film having a thickness of at least mm. More preferably, (2) the polyolefin resin is polymethylpentene, which is the white polyester film described in 1 above.

Preferably, (3) the polyolefin resin is polypropylene, and the above-mentioned 1 is provided.
It is the described white polyester film.

More preferably, the above (1) or (2) is characterized in that (4) the polyester layer contains inorganic particles.
Alternatively, it is the white polyester film described in 3.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The white polyester film of the present invention will be described in more detail below.

The white polyester film of the present invention comprises a polyester and a polyolefin resin in an amount of 3% by weight or more and 30% by weight or more.
Weight% or less, and polyethylene glycol 0.5 to
It is composed of a layer of polyester added with 5% by weight and containing countless fine bubbles.

The polyester referred to in the present invention may be any one as long as it can form a film, for example, polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-o-oxybenzoate, poly-1,4-. Cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, etc. can be used. Of course, these polyesters may be homopolyesters or may be copolyesters, and examples of the copolymerization component include diethylene glycol, neopentyl glycol,
A diol component such as polyalkylene glycol and a dicarboxylic acid component such as adipic acid, cepasic acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and 5-sodium sulfoisophthalic acid can be used.

The polyester used in the present invention is preferably polyethylene terephthalate. This is because the polyethylene terephthalate film is excellent in water resistance, durability and chemical resistance.

The white polyester layer in the present invention is a layer made of polyester containing innumerable fine air bubbles, and these fine air bubbles scatter light to make it white and opaque. Has been done. At this time, it is preferable to add inorganic particles to the polyester in order to increase whiteness and optical density.

As the inorganic particles, talc, magnesium oxide, gypsum, barium sulfate, magnesium carbonate and the like can be used, but calcium carbonate, titanium dioxide, barium sulfate and the like are particularly preferable as the inorganic particles. It is also preferable to add a fluorescent whitening agent in order to further increase the whiteness.

The optical density of the white polyester film in the present invention is preferably 0.7 or more and 1.6 or less. More preferably, it is 0.8 or more and 1.6 or less. When the optical density is less than 0.7, the back side can be seen through because the hiding property of the film is small, which is not preferable. Further, if the optical density exceeds 1.6, a large amount of fine bubbles must be contained, and the strength of the film becomes weak, which is not preferable.

The whiteness of the preferably constructed white polyester film of the present invention is generally 80% or more and 110% or more.
It has excellent whiteness as shown below. It is more preferably 85% or more and 105% or less. If the whiteness is less than 80%, the film becomes yellowish and spoils the high-grade feeling of printing, which is not desirable. Further, when the whiteness exceeds 110%, it becomes bluish, and the high-grade feeling tends to deteriorate.

As the polyolefin resin to be added to the white polyester layer in the present invention, any one can be used as long as it can be mixed with polyester to form a film, and examples thereof include low density polyethylene, high density polyethylene, polypropylene and polybutene. It is practical to use polymethylpentene or the like. Further, it is not necessarily limited to homopolymers, and may be copolymers thereof.

Among them, polyolefins having a small critical surface tension are preferable, and polypropylene and polymethylpentene are preferable. In particular, polymethylpentene is the most desirable because it has good releasability from polyester and easily forms fine bubbles during stretching. In the white polyester film of the present invention, the amount of the polyolefin resin added to the polyester is an important factor, and it is important that it does not exceed 30% by weight, and it is practically within the range of 1 to 30% by weight. It is more preferably in the range of 5 to 20% by weight. When the amount of addition is small, the amount of fine bubbles generated is small, the apparent density of the white polyester film is large, and it is not suitable for fields requiring lightness.

On the other hand, if the amount added exceeds 30% by weight, the stretchability of the film is generally poor and the film-forming property is generally poor.

The apparent density of the white polyester film according to the present invention is determined by the amount of fine bubbles produced. According to the knowledge of the present inventors, although not particularly limited, the film of the present invention generally has an apparent density of 0.5 g /
The values are from cm ³ or more to around 1 g / cm ³ . If it exceeds 1 g / cm ³ , it is difficult to reduce the cost, and the competitiveness against paper becomes small except for some fields, which is not desirable.

When the apparent density is less than 0.5 g / cm ³ , the amount of fine air bubbles inside is very large, and it becomes generally difficult to make the cleavage strength 300 g / 15 mm or more, and further the film strength. Be careful because it tends to be weak and brittle. One of the features of the white polyester film of the present invention is that the cleavage strength thereof is 300 g / 15 mm or more. Particularly preferably, the molded product exhibits a high level of 350 g / 15 mm or more. This is largely due to the achievement of finer formation of air bubbles inside the film.

Incidentally, the cleavage strength is, for example, 250
If it is a low level such as less than g / 15 mm, there is generally a problem that the film is easily broken when it is peeled off again when it is used for a label or a seal.

In the present invention, the action and effect of adding polyethylene glycol are remarkable, and in particular, the action of adding polyethylene glycol can make the dispersed state of the added polyolefin resin finer. It is what makes up.

Although it is possible to make the dispersed state of the polyolefin resin fine even when a generally-known surfactant or another polyalkylene glycol is added, the present inventors have found that, for example, in the case of a surfactant. In addition, the adhesiveness between the polyolefin resin and the polyester becomes high, and this has the effect of inhibiting the generation of fine bubbles during stretching, which is not preferable. Further, when other polyalkylene glycol is added, although the effect of refining the dispersed state of the polyolefin resin and the effect of not inhibiting the generation of fine bubbles are recognized, the effect is not as great as when polyethylene glycol is used. Subtly inferior. In particular, compared with the case of adding other polyalkylene glycol, when polyethylene glycol is added, the stretchability of the film is obviously good, and good generation of fine bubbles can be promoted.

In the present invention, the technical life of determining the value of the film is to generate fine air bubbles as desired, so that the use of polyethylene glycol is actually more effective in industry and such fine air bubbles are used. It is possible to achieve a high level of improvement in the cleaving strength of the formed film because it is possible to form innumerably good conditions.

In the present invention, it is essential that the amount of polyethylene glycol added be within the range of 0.5 to 5% by weight. More preferably, it is 0.5 to 3% by weight. If the addition amount is less than 0.5% by weight, the effect of finely dispersing the polyolefin resin tends to be poor, and the effect of improving the cleavage strength is not recognized. If the amount added exceeds 5% by weight, the thermal stability becomes poor and the white polyester layer becomes a yellowish color, which is not preferable.

Particularly, polyethylene glycol has a molecular weight of 500 to 30,000, preferably 1,000.
~ 10,000 is good. When the molecular weight is less than 500, the white polyester layer tends to have a yellowish color, and the cleavage strength becomes weaker. If it exceeds 30,000, the cleavage strength will be weakened.

The white polyester film of the present invention may be used as it is as a single layer film comprising the white polyester film, or
Further, it may be used as a composite film laminated with another layer.

In the case of forming a composite film, it is preferable to form a composite film in which a normal polyester layer having no polyolefin resin, polyalkylene glycol or a copolymer thereof added to at least one surface of the white polyester layer. .

Next, an example of a method for producing the white polyester film according to the present invention will be described.

After sufficiently vacuum-drying a master chip prepared by adding polyester chips and polyethylene glycol to polyester during the polymerization reaction or at the time of completion of polymerization, polyolefin resin chips are mixed to obtain 270-270.
It is supplied to an extruder heated to 300 ° C. and molded into a sheet from a T die. When laminating the polyester layer A, separately dried polyester chips are fed to another extruder and laminated in a T die to form a sheet. At this time, when adding the inorganic particles, a polyester chip is mixed with a master chip of the inorganic particles, vacuum-dried, and supplied to the extruder. Polyethylene glycol is preferably added at the time of polyester polymerization or at the completion of polymerization to form a master chip, but this is not necessarily the case. Alternatively, the three components may be kneaded in advance with a pelletizer or the like.

Further, an unstretched film obtained by cooling and solidifying the film in a cooling drum having a surface temperature of 10 to 60 ° C. is 80 to 12
Lead to rolls heated to 0 ° C, longitudinally stretch in the longitudinal direction,
It cools with a 20-30 degreeC roll group.

Subsequently, both ends of the longitudinally stretched film are guided to a tenter while holding both ends with clips, and transversely stretched in a direction perpendicular to the longitudinal direction in an atmosphere heated to 90 to 140 ° C.

The stretching ratio is 2 to 5 times in each of the length and width, but the area ratio (longitudinal stretching ratio × horizontal stretching ratio) needs to be 4 to 25 times. If the area ratio is less than 4 times, the resulting film will have a poor easy-cutting property. On the contrary, if it exceeds 25 times, the film will tend to be broken during stretching and the film-forming property will be poor.

In order to impart flatness and dimensional stability to the biaxially stretched film thus obtained, 150 in a tenter.
It is possible to produce the white polyester film of the present invention by carrying out heat setting at ˜235 ° C., uniformly cooling gradually, then cooling to room temperature and winding.

[Method of Measuring Physical Properties and Method of Evaluating Effect] (1) Apparent Density A carbon tetrachloride-n-heptane type density gradient tube was used.

(2) Cleavage strength A polyurethane primer is applied to the film to be measured to form a coating film having a thickness of 2 μm, and an unstretched polypropylene film (thickness 100 μm, manufactured by Toray Synthetic Film Co., Ltd.) at a temperature of 50 ° C. After bonding and aging at 40 ° C for 48 hours, cut into a width of 15 mm, peel off one end and attach to Tensilon, keep the bonded part at a right angle to the peeled part, strength when peeling the measurement film and unstretched film Is the cleavage strength. The peeling speed at this time is 300 mm /
Minutes. At this time, an average value of 5 films was taken excluding those in which the film was not broken and peeled off by the adhesive layer.

(3) Optical Density Films are stacked so as to have a thickness in the vicinity of 150 μm,
The transmission density is measured with an optical densitometer (TR927 manufactured by Macbeth). Plot thickness and optical density, 150
The optical density corresponding to the thickness of μm was determined.

(4) Whiteness Based on JIS-L-1015, whiteness = 4B-3G (%), where B% is the reflectance at a wavelength of 450 nm and G% is a reflectance at a wavelength of 550 nm. Sought as.

(5) Cellophane tape peeling strength Cellophane tape (18 m width made by Nichiban Co., Ltd.) on the film surface
m) is attached to a length of 10 cm, a load of 1 kg / cm ^{2 is} applied for 10 seconds, and then the film is momentarily peeled by hand in the direction perpendicular to the film. The state of adhesion to the film surface and the cellophane tape at this time was divided into the following four levels for evaluation.

A: In the case where it was carried out 5 times, the surface of the film was not changed in all 5 times, and there was no deposit on the cellophane tape.

B: When the cellophane tape has no deposits, although it is floated on the film surface and fluffed at least once after 5 times.

C: When 5 times were performed and at least once, a part of the film surface was destroyed and adhered to the cellophane tape.

D: 5 times, and at least once, almost the entire surface of the film adhered to the cellophane tape.

(6) Stretchability The following judgment was made from the state during film formation.

◯: A state in which a uniform film can be collected without causing breakage in the longitudinal stretching and breakage in the transverse stretching during film formation and without unevenness in the stretching.

Δ: A state in which lateral stretching breakage occurs during film formation, but the tearing can be easily repaired, and a homogeneous film having no stretching unevenness can be collected.

X: Breakage in transverse stretching or breakage in longitudinal stretching frequently occurs, and uneven stretching occurs even when stretching is possible.

[0055]

EXAMPLES The present invention will be described based on examples.

Example 1 and Comparative Example 1 A polyethylene terephthalate chip was mixed with a master chip of 6% by weight of polyethylene glycol in the proportion shown in Table 1 and vacuum dried at 180 ° C. for 3 hours. The polyolefin resin (polymethylpentene resin) shown in Table 1 was mixed in a ratio, supplied to an extruder heated to 270 to 300 ° C., and molded into a sheet from a T die. Further, the unstretched film obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. is guided to a roll group heated to 80 to 98 ° C., stretched 3 times in the longitudinal direction, and 25 ° C.
It cooled with the roll group. Subsequently, both ends of the longitudinally stretched film were introduced into a tenter while holding both ends with clips, and laterally stretched 3 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. Then, heat setting was carried out at 220 ° C. in a tenter, and the film was gradually cooled and wound up to obtain a film having a thickness of 50 μm.

The physical properties of the obtained film are shown in Table 1. When the amount of the polyolefin resin added was more than 30% by weight, the film forming property was deteriorated and the desired film could not be obtained (Comparative Example 1).

The white polyester film according to the present invention has a high cleaving strength of 570 g / 15 mm in spite of the existence of innumerable fine bubbles, and has a whiteness of 81%, which is a high level, which is unprecedented. (Example 1).

[0059]

[Table 1]

[0060]

According to the present invention, a novel white polyester film having high cleavage strength, excellent mechanical strength and heat resistance, and excellent whiteness is provided.

Claims (4)

[Claims] 1. Polyester and polyolefin resin 3
It is added in an amount not exceeding 0% by weight, and further, polyethylene glycol is added in an amount of 0.5 to 5% by weight, which is composed of a polyester layer containing innumerable fine bubbles and is biaxially stretched and has a cleavage strength of 300 g / 15 mm. The above is the white polyester film characterized by the above. 2. The white polyester film according to claim 1, wherein the polyolefin resin is polymethylpentene. 3. The white polyester film according to claim 1, wherein the polyolefin resin is polypropylene. 4. The white polyester film according to claim 1, 2 or 3, wherein the polyester layer contains inorganic particles.