JPH0737098B2 - Laminated white polyester film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a laminated white polyester film having a low density and rich whiteness. More specifically, paper substitutes, that is, cards, labels, stickers, courier slips, image receiving paper for video printers, image receiving paper for bar code printers, posters, maps, dust-free paper, display boards, white boards, photographic paper, copy paper. The present invention relates to a laminated white polyester film used as a base material such as.

[Prior Art] Printed materials used outdoors cannot withstand wind and rain when paper is used, and conventionally water-resistant paper or plastic film has been used. Also, with adhesive paper such as labels and stickers, the plastic film is used for such applications because the paper is torn when it is peeled off after being attached. Films used for such applications are required to have white opacity. For example, there is a polyolefin resin with calcium carbonate added (Japanese Patent Publication No. 63-64310), but since it is based on polyolefin, it is weak against heat. Also, it has been said that there is a problem in mechanical strength. In addition, those with polypropylene added as a base to improve these drawbacks (for example,
JP-A-63-168441).

[Problems to be Solved by the Invention] These films have the following problems.

Films based on polyolefins lack heat resistance and weak mechanical strength.

The color tone of the film has a yellowish tint, which impairs the sense of quality.

 Those based on polyester are expensive.

In order to reduce the cost per area of the film, fine bubbles are created inside the film, and the film with a lower apparent density is easy to cleave. In order to suppress the cleavage, it was necessary to reduce the internal fine bubbles, that is, to keep the density high.

The present invention solves such a problem and has a small apparent density,
Moreover, it is an object of the present invention to provide a laminated white film having a large breaking strength between layers.

[Means for Solving the Problems] The present invention comprises a composite film obtained by laminating a polyester layer A on at least one surface of a white polyester layer, and has an apparent density of 0.5 g / cm ³ or more and less than 1.0 g / cm ³ . Cleavage strength is 25
The present invention relates to a laminated white polyester film having a weight of 0 g / 15 mm or more.

The apparent density of the laminated white polyester film in the present invention must be 0.5 g / cm ³ or more and less than 1.0 g / cm ³ .
It is preferably 0.6 g / cm ³ or more and less than 0.95 g / cm ³ , and more preferably 0.7 g / cm ³ or more and less than 0.9 g / cm ³ . If the apparent density is 1.0 g / cm ³ or more, the cost does not become low, and the paper has no competitiveness. Also, the apparent density is 0.5g
If it is less than / cm ³ , the amount of fine bubbles inside is too large, so that the cleavage strength does not reach 250 g / 15 mm or more, and the strength of the film becomes weak, resulting in fragility.

The cleavage strength of the laminated white polyester film in the present invention needs to be 250 g / 15 mm or more. It is preferably 300 g / 15 mm or more, more preferably 350 g / 15 mm or more. When the cleavage strength is less than 250 g / 15 mm, the film is easily broken when it is peeled off again when it is used for a label or a seal.

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

Polyethylene terephthalate is preferable as the polyester used in the present invention. 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 countless fine bubbles, and light is scattered by the fine bubbles to make the layer white and opaque. At this time, it is preferable to add inorganic particles to the polyester in order to increase whiteness and optical density. As inorganic particles, talc, magnesium oxide,
Gypsum, barium sulfate, magnesium carbonate and the like are available, but calcium carbonate, titanium dioxide, barium sulfate and the like are preferred as the inorganic particles. It is also preferable to add a fluorescent whitening agent to increase the whiteness.

The optical density of the laminated 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. Optical density 0.7
When it is less than the above range, the hiding property of the film is small, and the back side can be seen through. 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 laminated white polyester film is 80%.
It is preferably 110% or less. It is more preferably 85% or more and 105% or less. When the whiteness is less than 80%, the film has a yellowish tint, which impairs the high quality printing. Further, when the whiteness exceeds 110%, it becomes bluish, and similarly, the high-class feeling is deteriorated.

The polyolefin resin added to the white polyester layer in the present invention may be any as long as it can be mixed with polyester to form a film, for example, low density polyethylene, high density polyethylene, polypropylene, Examples include polybutene and polymethylpentene. Further, it is not necessarily limited to homopolymers, and may be copolymers thereof. Among them, polyolefin having a small critical surface tension is preferable, and polypropylene and polymethylpentene are preferable.
In particular, polymethylpentene is particularly preferable because it has good releasability from polyester and easily forms fine bubbles during stretching.

The addition amount of the polyolefin resin of the present invention is 3 to 30% by weight, preferably 5 to 20% by weight. When the amount added is less than 3% by weight, the amount of fine bubbles generated is small and the apparent density of the laminated white polyester film does not become less than 1.0 g / cm ³ . On the other hand, if the amount added exceeds 30% by weight, the stretchability of the film deteriorates and the film-forming property deteriorates.

Examples of the polyalkylene glycol or the copolymer thereof in the present invention include, but are not limited to, polyethylene glycol, polypropylene glycol, a 1: 1 copolymer of ethylene glycol and propylene glycol, methoxy polyethylene glycol and the like. . By adding these polyalkylene glycols, the dispersed state of the polyolefin resin can be made fine. Even when a generally-known surfactant is added, the dispersed state of the polyolefin resin can be made finer, but in this case, the adhesiveness between the polyolefin resin and the polyester becomes high, which hinders the formation of fine bubbles during stretching. However, surprisingly, when the polyalkylene glycol is added, the dispersed state of the polyolefin resin is made finer and the generation of fine bubbles is not hindered.
Furthermore, it promotes the generation of fine bubbles. Even more surprising is the improvement in cleaving strength observed with the addition of polyalkylene glycol.

The amount of polyalkylene glycol added in the present invention is preferably 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 is not obtained, and the cleavage strength is not improved. 5% by weight
If it exceeds, the heat stability becomes poor and the white polyester layer becomes a yellowish color, which is not preferable.

Polyethylene glycol is particularly preferable as the polyalkylene glycol. The molecular weight is 500-30,000,
It is preferably 1,000 to 10,000. 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. In addition, polyethylene glycol has better stretchability of the film when added than other polyalkylene glycols, and promotes generation of fine bubbles.

It is a composite film in which the polyester layer A is laminated on at least one surface of the white polyester layer of the present invention. It is preferable to use a laminated film in which a polyolefin resin and a polyester layer A to which a polyalkylene glycol or a copolymer thereof is not added are laminated on at least one surface of a white polyester layer. When the polyester layer A is laminated on the white polyester layer to which the polyalkylene glycol is not added, the cleavage strength is not so strong. By the way, when the polyester layer A is laminated on the white polyester layer to which polyalkylene glycol is added, the cleavage strength is dramatically improved by the synergistic action with the polyalkylene glycol, which is more preferable. Further, when the polyester layer A is not present, the polyolefin resin is also present on the surface of the white polyester layer, so that the adhesive strength of the surface is worse than that of polyester, but by laminating the polyester layer A on the surface,
It is possible to prevent the deterioration of the adhesive strength.

Further, the thickness of the laminate is preferably 10 μm or less. 10μ
When it exceeds m, peeling easily occurs at the interface between the laminated polyester layer A and the fine bubble-containing layer inside.

In the present invention, inorganic particles may be added to the laminated polyester layer A. By adding inorganic particles, it is possible to improve the slipperiness of the film surface and eliminate the glossy feeling. The addition amount of the inorganic particles is preferably 0.05 to 25% by weight. Examples of the inorganic particles include calcium carbonate, silicon dioxide, titanium dioxide, barium sulfate and the like. If the amount added is less than 0.05% by weight, the slippage of the film will be worse than that of paper, and the productivity in post-processing such as printing will be poor. If the amount added exceeds 25% by weight, the surface of the film becomes weak and problems such as paper dust are likely to occur during post processing.

Next, the method for producing the film of the present invention will be described.
It is not limited to such an example.

After sufficiently vacuum-drying the polyester chips and the master chips in which the polyalkylene glycol was added to the polyester during the polymerization reaction or at the time of completion of the polymerization, the chips of the polyolefin resin were mixed and the extruder A heated to 270 to 300 ° C was used. In order to supply and laminate the polyester layer A, another dried polyester chip is supplied to another extruder B 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. The polyalkylene glycol is preferably added at the time of polyester polymerization or at the completion of polymerization to prepare a master chip, but this is not always the case. Alternatively, the three components may be kneaded in advance with a pelletizer or the like.

Further, the unstretched film obtained by cooling and solidifying the film with a cooling drum having a surface temperature of 10 to 60 ° C. is guided to a roll group heated to 80 to 120 ° C., longitudinally stretched in the longitudinal direction, and cooled by a roll group of 20 to 30 ° C.

Then, the both ends of the longitudinally stretched film are guided to a tenter while gripping 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 x horizontal stretching ratio) needs to be 4 to 25 times. The area ratio is less than 4 times. Thus, the resulting film becomes poor in easy-cutting property. On the contrary, when it exceeds 25 times, the film tends to be broken during stretching, resulting in poor film-forming property.

The flatness of the biaxially stretched film thus obtained, in order to impart dimensional stability, heat setting is performed at 150 to 235 ° C. in a tenter, and after uniform slow cooling, the film of the present invention is cooled by cooling to room temperature. obtain.

[Method of measuring physical properties and method of evaluating effects] (1) Apparent density A carbon tetrachloride-n-heptane density gradient tube was used.

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

(3) Optical Density Films are stacked so as to have a thickness near 150 μm, and the transmission density is measured with an optical densitometer (TR927 manufactured by Macbeth Co.). The thickness and the optical density were plotted to determine the optical density corresponding to a thickness of 150 μm.

(4) Whiteness Based on JIS-L-1015, reflectivity at wavelength 450nm is B
%, When the reflectance at the wavelength of 550 nm is G% Whiteness = 4B-3G% (5) Cellophane tape peeling strength Cellophane tape on the film surface (Nichiban width 18 mm)
10 cm in length, apply a load of 1 kg / cm ² for 10 seconds, and then momentarily peel it by hand in the direction perpendicular to the film. The state of adhesion to the film surface and cellophane tape at this time is divided into the following 4 levels: A: When 5 times are performed, the film surface does not change after 5 times, and there is no adhered matter on the cellophane tape.

B: Repeated 5 times, at least once, floated on the film surface, fluff, etc., but there was no adhered substance on the cellophane tape.

C: When 5 times are performed and at least once, a part of the film surface is broken and adheres to the cellophane tape.

D: 5 times, at least once, almost all of the film surface adheres to the cellophane tape.

(6) Stretchability Judgment was made as follows from the state during film formation.

◯: A state in which a uniform film having no stretching unevenness and no lateral stretching breakage during film formation and no stretching unevenness can be collected.

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

×: Frequent lateral stretching break or longitudinal stretching breakage,
Even if it can be stretched, it has uneven stretching.

[Examples] The present invention will be described based on Examples.

Comparative Examples 1 and 2 A polyethylene terephthalate chip was mixed with a 6% by weight master chip of polyethylene glycol in the proportion shown in Table 1 and vacuum-dried at 180 ° C. for 3 hours.
The polyolefin resins shown in Table 1 were mixed in the proportions shown in the table, supplied to an extruder heated to 270 to 300 ° C., and formed into a sheet from a T die. Furthermore, the surface temperature of this film
The unstretched film that has been cooled and solidified with a cooling drum at 25 ° C
It was introduced into a roll group heated to ˜98 ° C., stretched 3 times in the longitudinal direction, and cooled with a roll group at 25 ° C. Then, while holding both ends of the longitudinally stretched film with clips, guide it to the tenter.
In the atmosphere heated to 0 ° C., the film was transversely stretched 3 times in the direction perpendicular to the longitudinal direction. 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 as shown in Table 1. It can be seen that when the amount of the polyolefin resin added exceeds 30% by weight, the film forming property becomes poor. If the addition amount is less than 3% by weight, the apparent density exceeds 1.0. Further, it can be seen that among the polyolefin resins, polymethylpentene has a small apparent density with a small addition amount and can maintain a high cleavage strength.

Examples 1 and 2 and Comparative Examples 3 to 5 Polyethylene terephthalate chips were added with 10% by weight of polymethylpentene, and 6% by weight of the compatibilizing agent shown in Table 1 was added to the master chips in the proportions shown in Table 1. Polyethylene terephthalate extruded from the extruder as described above and extruded from another extruder was laminated on both surfaces in a T-die to form a sheet. After that, a film having a thickness of 50 μm was obtained by the method as described above.

The physical properties of the obtained film are as shown in Table 1. If the amount of polyalkylene glycol added is less than 0.5% by weight, the cleavage strength will be less than 250 g / 15 mm. When a compound other than polyalkylene glycol is used as the compatibilizer, no improvement in cleavage strength is observed.

In addition, the density is lower when polyethylene glycol is used.

Examples 3 and 4 Polyethylene terephthalate extruded from the extruder as described above in the proportions shown in Table 1 and extruded from other extruders were laminated in a T die to form a sheet. After that, a film having a thickness of 50 μm was obtained by the method as described above.

The physical properties of the obtained film are as shown in Table 1. It can be seen that the cleaving strength increases as the thickness of the laminate increases. [Advantages of the Invention] The present invention provides a film excellent in heat resistance, mechanical strength, and whiteness, which has fine bubbles inside and low density. It is possible to obtain a film having a high cleavage strength by reducing the cost.

Claims (5)

[Claims] 1. A composite film comprising a polyester layer A laminated on at least one side of a white polyester layer,
Apparent density is 0.5g / cm ³ or more, less than 1.0g / cm ³ , and cleavage strength is
A laminated white polyester film characterized by having a weight of 250 g / 15 mm or more. 2. The polyester layer A contains inorganic particles in an amount of 0.05 to 25.
The laminated white polyester film according to claim (1), characterized in that the laminated white polyester film is contained in a weight percentage. 3. An optical density of 0.7 to 1.6, a whiteness of 80.
% Or more and 110% or less, The laminated white polyester film according to claim (1) or (2). 4. A white polyester layer comprising 3% by weight or more and 30% by weight or less of a polyolefin resin added to polyester, and 0.5% by weight or more and 5% by weight or less of at least one polyalkylene glycol or a copolymer thereof. The laminated white polyester film according to any one of claims (1) to (3), which is obtained by adding and biaxially stretching. 5. The laminated white polyester film according to claim 4, wherein the polyolefin resin is polymethylpentene.