JP2876651B2 - Antistatic white polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to paper substitutes, that is, cards, labels, stickers, home delivery slips, video printer receiving papers, posters, maps, dust-free papers, display plates, and white boards. , Printing paper, copy paper, etc., as a base material, especially printing paper that requires antistatic properties,
The present invention relates to an antistatic white polyester film used for copy paper and the like.

[Prior Art] A plastic film used for the above-mentioned application as a paper substitute is required to be white and opaque. Conventionally, polyolefin resins based on polyolefin resins such as those obtained by adding calcium carbonate to polyolefin resins (JP-B 63-64310) are known. However, these films are susceptible to heat and have poor mechanical strength. There is. In order to improve these drawbacks, a polyester film having fine cells based on polyester and added with polypropylene has been reported (for example, see JP-A-63-16 / 1988).
8441 etc.).

However, when an antistatic agent is added to a conventional polyester film in order to have an antistatic property, there has been a problem that the antistatic agent is trapped in fine bubbles and a sufficient antistatic effect cannot be obtained. Further, if the polyester layer containing the antistatic agent is merely laminated on the white polyester layer, the antistatic agent migrates to the inner layer and is trapped, so that a sufficient antistatic effect cannot be obtained.

[Problems to be Solved by the Invention] Accordingly, an object of the present invention is to provide a white polyester film having a small apparent density, low cost, and excellent antistatic properties.

[Means for Solving the Problems] As a result of earnest studies, the present inventors have found that when the apparent density of the film is smaller than 0.5, the amount of fine bubbles is too large and the antistatic agent is trapped. Further, when forming fine bubbles in a white polyester film, it is possible to prevent the antistatic agent from being trapped by adding a polyalkylene glucose or a copolymer thereof to make the average diameter of the fine bubbles preferably 50 μm or less. And completed the present invention.

That is, the present invention has at least a white polyester layer, an apparent density of 0.5 g / cm ³ or more and less than 1.0 g / cm ³ , and an antistatic white polyester having a surface resistivity of 10 ¹¹ Ω or less. Provide a film.

[Effects of the Invention] According to the present invention, a low-density polyester film having excellent antistatic properties and whiteness is provided. As a result, it is possible to obtain a low-cost film free of printing troubles due to charging as a substitute for paper.

[Specific description of the invention] The apparent density of the white polyester film of the present invention is as follows:
0.5 g / cm ³ or more 1.0 g / cm less than ^3, preferably 0.6 g / cm ³ or more zero.
Less than 95 g / cm ^3, more preferably 0.7 g / cm ³ or more 0.9 g / cm ³
Is less than. If the apparent density is 1.0 g / cm ³ or more, the cost becomes higher with respect to paper, and the competitiveness as a substitute for paper is lost. On the other hand, if the apparent density is less than 0.5 g / cm ³ , the amount of microbubbles inside becomes too large and the antistatic agent is trapped, so that a sufficient antistatic effect cannot be obtained, and the mechanical strength is also weak.

The surface resistivity of the white polyester film of the present invention is 10 ¹¹ Ω or less, preferably 10 ¹⁰ Ω or less. If the surface specific resistance is larger than 10 ¹¹ Ω, paper feeding failure or the like due to charging during printing may be caused.

The white polyester layer of the present invention contains a myriad of fine air bubbles in a layer made of polyester, and the light is scattered by these air bubbles to render the white polyester opaque.

The polyester used in the present invention may be any polyester that can form a film, for example,
Polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-o-oxybenzoate,
Examples thereof include poly-1,4-cyclohexylene dimethylene terephthalate and polyethylene 2,6-naphthalenedicarboxylate. Of course, these polyesters may be homopolyesters or copolyesters. As the copolymerization component, diol components such as diethylene glycol, neopentyl glycol and polyalkylene glycol and adipic acid, sebacic acid,
Examples thereof include dicarboxylic acid components such as phthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium sulfoisophthalic acid. Among them, polyethylene terephthalate has excellent water resistance, durability, chemical resistance, and the like when formed into a film, and is preferred as the polyester used in the present invention.

In the present invention, a polymer of a polyolefin resin is added in order to provide whiteness and reduce the density by including bubbles in the white polyester layer. The polyolefin resin to be added may be any resin that can be mixed with polyester to form a film, and examples thereof include low-density polyethylene, high-density polyethylene, and polymethylpentene. Further, the copolymer is not necessarily limited to a homopolymer, and may be a copolymer thereof. Among them, polypropylene and polymethylpentene, which are polyolefins having a small critical surface tension, are preferred. In particular, polymethylpentene has good releasability from polyester,
It is preferable because fine bubbles are easily formed during stretching.

The addition amount of the polyolefin resin is preferably 3 to
The content is 30% by weight, more preferably 5 to 20% by weight. If the amount is less than 3% by weight, the amount of fine bubbles generated is small, and the apparent density of the white polyester film of the present invention cannot be easily obtained. On the other hand, if the amount exceeds 30% by weight, the stretchability of the film deteriorates, and the film-forming properties deteriorate.

Further, by adding polyalkylene glycol or a copolymer thereof, the dispersion state of the polyolefin resin can be made finer, whereby the size of the bubbles can be adjusted to prevent the antistatic agent from being trapped. The average diameter of the fine bubbles is preferably 50 μm or less, more preferably 40 μm or less.
By setting the thickness to μm or less, a surface resistivity within the range of the present invention can be achieved.

Polyalkylene glycol or a copolymer thereof used in the present invention include polyethylene glycol, polypropylene glycol, a 1: 1 copolymer of ethylene glycol and propylene glycol, methoxy polyethylene glycol, and the like, but are not limited thereto. . In general, even when a surfactant is added, the dispersion state of the polyolefin resin can be further reduced,
In this case, the adhesion between the polyolefin resin and the polyester is increased, and the generation of bubbles during stretching is inhibited. However, surprisingly, when polyalkylene glycol or a copolymer thereof is added, not only the dispersion state of the polyolefin resin is refined to promote the generation of fine bubbles, but also the cleavage strength is improved.

The addition amount of the polyalkylene glycol or the copolymer thereof in the present invention is preferably 0.5 to 5% by weight, more preferably 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 reduced, and almost no improvement in cleavage strength is recognized. Also,
The average diameter of the microbubbles increases, and when the antistatic agent is added, the bubbles are trapped and the antistatic effect is considerably lost. If the amount exceeds 5% by weight, the thermal stability becomes poor and the white polyester layer becomes yellowish in color.

In particular, the polyalkylene glycol has a molecular weight in consideration of the stretchability of the film and the promotion of generation of fine bubbles.
Preferred are polyethylene glycols of 500 to 30,000, 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 is weak. When the molecular weight exceeds 30,000, the cleavage strength becomes weak.

Furthermore, in order to impart antistatic properties to the white polyester film of the present invention, it is preferable to add an antistatic agent at 3% by weight or less. When the addition amount exceeds 3% by weight, deterioration of the mechanical properties of the film is recognized. When the white polyester film is a single-layer film composed of only a white polyester layer, it is preferable to add the antistatic agent in an amount of 0.1% by weight or more, since good antistatic properties can be obtained.

Preferred examples of the antistatic agent used in the present invention include dodecylbenzenesulfonate, bis [octylpolyoxyethylene] phosphate soda, phosphonium dodecylbenzenesulfonate, and phosphonium alkylsulfonate. Among them, dodecylbenzenesulfonate is particularly preferred. The effect is further enhanced by using polyalkyl glycerin in combination.

The antistatic agent can be obtained not only when it is added to the white polyester layer but also when it is added to the polyester layer A to be described later laminated thereon. The addition amount is preferably 0.1% by weight to 3% by weight for the same reason as described above. In the present invention, when the white polyester film is composed of a composite film described later, it is preferable to add at least the antistatic agent to the outermost layer in order to obtain good antistatic properties. However, for example, when the antistatic agent is not added to the white polyester layer, it is added only to the polyester layer A on both sides thereof, and when the average diameter of the fine bubbles in the white polyester layer exceeds 50 μm, the polyester layer A It is not preferable because the antistatic agent migrates to the white polyester layer and is trapped. Therefore, most preferably, by adding to the entire polyester layer, the migration of the antistatic agent of the polyester layer A to the white polyester layer can be prevented, and a further antistatic effect can be obtained.

The cleavage strength of the white polyester film of the present invention is preferably at least 250 g / 15 mm, more preferably at least 300 g / 15 mm. When the cleavage strength is less than 250 g / 15 mm, the film is easily broken when it is peeled off again when used for applications such as labels and seals.

In order to increase the whiteness and optical density of the white polyester film of the present invention, inorganic particles are added to the white polyester layer in an amount of 0.2.
It is preferable to add 05 to 25% by weight, preferably 0.5 to 15% by weight. Examples of the inorganic particles include talc, magnesium oxide, gypsum, barium sulfate, and magnesium carbonate. It is also preferable to add 0.001 to 0.5% by weight of a fluorescent whitening agent in order to increase the whiteness.

The optical density of the white polyester film of the present invention is 0.
It is 7 or more and 1.6 or less, preferably 0.8 or more and 1.6 or less. If the optical density is less than 0.7, the back side of the film can be seen through because the concealability of the film is small, which is not preferable. On the other hand, 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 white polyester film of the present invention is preferably 80% or more and 110% or less, more preferably 8% or less.
5% or more and 105% or less. When the whiteness is less than 80%, the film becomes yellowish and impairs the high-grade appearance of printing. On the other hand, if the whiteness exceeds 110%, a bluish tint is imparted, which also impairs a sense of quality.

The white polyester film of the present invention may be a single-layer film composed of only the white polyester layer or a composite film with another film. When forming a composite film, it is preferable to laminate a polyester layer A to which no polyolefin resin is added on at least one surface of the white polyester layer to form a composite film. When this polyester layer A is laminated on a white polyester layer to which polyalkylene glycol or a copolymer thereof has not been added,
The cleavage strength does not change much, but when laminated on a white polyester layer to which polyalkylene glycol or a copolymer thereof is added, the cleavage strength is dramatically improved by interaction with the polyalkylene glycol or the copolymer thereof. In the case of a single-layer film, the adhesion of the surface is reduced due to the presence of the polyolefin resin on the surface of the white polyester layer. However, the provision of the polyester layer A on the surface can prevent the adhesion from decreasing.

The thickness of the laminated polyester layer A is 10 μm
The following is preferred. If it exceeds 10 μm, separation at the interface between the laminated polyester layer A and the fine bubble-containing layer tends to occur.

In the present invention, by adding inorganic particles to the laminated polyester layer A, the smoothness of the film surface is improved, and by lowering the gloss, a polyester film closer to paper can be obtained. Examples of the inorganic particles include calcium carbonate, silicon dioxide, titanium dioxide, barium sulfate and the like. The addition amount of the inorganic particles is preferably 0.05 to 25% by weight. If the addition amount is less than 0.05% by weight, the slip of the film becomes worse as compared with paper, and the productivity in post-processing such as printing is not good. If the addition amount exceeds 25% by weight, the surface of the film becomes weak and troubles such as paper dust easily occur during post-processing.

Next, a method for producing the polyester film of the present invention will be described, but the present invention is not limited thereto.

A polyester chip, an antistatic agent and a polyalkylene glycol or a copolymer thereof are added to the polyester during the polymerization reaction or at the completion of the polymerization, and the obtained master chip is sufficiently vacuum-dried, and then the polyolefin resin chip is mixed. It can be supplied to an extruder heated to 270 to 300 ° C. and formed into a sheet from a T-die. The polyalkylene glycol or its copolymer is preferably added at the time of polyester polymerization or at the completion of polymerization to form a master chip, but the three components may be kneaded in advance with a pelletizer or the like. When laminating the polyester layer A,
Separately dried polyester chips can be supplied to another extruder and laminated with a white polyester film in a T-die to form a sheet. Further, at this time, a master chip of inorganic particles and / or an antistatic agent may be mixed with a chip of polyester and dried under vacuum.

The sheet-like film obtained as described above has a temperature of
After being cooled and solidified with a cooling drum at 10 to 60 ° C to form an unstretched film, it is guided to a group of rolls heated to 80 to 120 ° C, stretched longitudinally in the longitudinal direction, cooled with a group of rolls at 20 to 30 ° C, and then uniaxially stretched. Can be obtained.

Next, the uniaxially stretched film is guided to a tenter while gripping both ends of the film with clips, and is transversely stretched in a width direction perpendicular to the longitudinal direction in an atmosphere heated to 90 to 140 ° C. to obtain a biaxially stretched film. The stretching ratio is 2 to 5 times each in the vertical and horizontal directions, but the area ratio (longitudinal stretching ratio × lateral stretching ratio) is 4
A factor of 2 to 25 is preferred. When the area magnification is less than 4 times, the whiteness of the obtained film is poor, and when it exceeds 25 times, the film tends to be broken at the time of stretching and the film forming property is poor.

The biaxially stretched film obtained as described above can be heat-set at 150 to 235 ° C. in a tenter to have flatness and dimensional stability. The heat-fixed film is gradually and uniformly cooled to room temperature, and the film is wound up to obtain the polyester film of the present invention.

Hereinafter, methods for measuring the physical properties of the polyester film of the present invention will be described.

(1) Apparent density Measured using a carbon tetrachloride-n-heptane-based density gradient tube. More specifically, a density gradient tube is prepared in a constant temperature bath at 25 ° C., and a value obtained when a measurement sample is charged and left for 24 hours is used.

(2) Surface specific resistance The main electrode (50 mmφ), the main electrode when a sheet is sandwiched between the card electrode (inner diameter 70 mmφ, outer diameter 80 mmφ) and the counter electrode (80 mm) and a voltage of 1 kV is applied. The resistance is determined from the value of the current flowing from the electrode to the guard electrode, and multiplied by 60π to obtain the surface specific resistance.

(3) Average diameter of microbubbles Take a photograph of a cross section cut in the mechanical direction or the vertical direction of the film forming process at a magnification of 1,000 to 5,000 times with a scanning electron microscope, and take at least the specified thickness range. Ten
Zero or more voids are applied to an image analyzer to determine the distribution of the diameter of a circle corresponding to the surface of the void. The volume average diameter of this distribution is defined as the average diameter of the fine bubbles.

(4) Cleavage strength A polyurethane primer is applied to the film to form a coating film having a thickness of 2 μm, and an unstretched polypropylene film (100 μm thickness, manufactured by Toray Gosei Co., Ltd.) is bonded at 50 ° C. After aging at 48 ° C for 48 hours, width 15mm
Then, one end is peeled off and attached to Tensilon. The cleavage film is maintained at a right angle to the part where the bonded part is peeled off, and the average value of five film tapes having the strength when the measurement film and the unstretched film are peeled off is defined as the cleavage strength. However, this does not exclude the case where the film was not broken and was peeled off with the adhesive layer. At this time, the peeling speed is 300 mm / min.

(5) Breaking strength A film is cut into a width of 10 mm, attached to Tensilon at an interval of 50 mm, and stretched at a stretching speed of 300 mm / min. The tension at the moment when the film breaks is defined as breaking strength. Take the average value of five film tapes.

(6) Whiteness When the reflectance at wavelengths of 450 nm and 550 nm is B% and G%, respectively, according to JIS-L-1015, whiteness (%) = 4B-3G.

(7) Optical Density The films are stacked so as to have a thickness of about 150 μm, and the transmission density is measured using an optical densitometer (TE927, manufactured by Macbeth). Blot film thickness and optical density,
The optical density corresponding to a thickness of 0 μm is determined.

[Examples] The present invention will be described more specifically with reference to examples, but examples of the present invention are not limited thereto.

Examples 1 to 6, Comparative Examples 1 to 4 A polyethylene terephthalate (intrinsic viscosity: 0.65) chip was mixed with an antistatic agent and a 6% by weight master chip of polyethylene glycol so as to have a ratio shown in Table 1, and the mixture was heated at 180 ° C. After vacuum drying for 3 hours, a predetermined amount of each polyolefin resin was mixed as shown in Table 1 and supplied to an extruder heated to 280 ° C. The film extruded into a sheet from the T-die was cooled and solidified by a cooling drum having a surface temperature of 25 ° C. The obtained unstretched film was guided to a group of rolls heated to 90 ° C., longitudinally stretched 3.0 times in the longitudinal direction, and then cooled by a group of rolls at 25 ° C. Next, the film stretched in the longitudinal direction was guided to a tenter while gripping both ends of the film with clips, and transversely stretched 3.0 times in the width direction in an atmosphere heated to 100 ° C. The obtained biaxially stretched film was heat-set at 220 ° C. in a tenter, and then gradually cooled to obtain a polyester film having a thickness of 50 μm.

The physical properties of the obtained polyester film are as shown in Table 1. As can be seen from Table 1, the apparent density is 0.5 g / c.
antistatic effect is less than m ³ does not appear. Also, without adding polyethylene glycol, the average diameter of fine bubbles is 50μ
It can be seen that a sufficient antistatic effect cannot be obtained even when m exceeds m. When polyethylene glycol is added in an amount exceeding 3% by weight, the whiteness becomes poor and the breaking strength also decreases.

Examples 7 to 9 A polyethylene terephthalate (intrinsic viscosity: 0.65) chip was mixed with a polyethylene glycol 6% by weight master chip so that polyethylene glycol was 1.0% by weight, and further 10% by weight of polymethylpentene and 10% by weight of dodecylbenzenesulfonic acid. The soda was mixed at the ratio shown in Table 2, dried under vacuum at 180 ° C for 3 hours, and then supplied to an extruder heated to 280 ° C. The melt-extruded sheet-like film was formed into a sheet by laminating a film of polyethylene terephthalate mixed with a predetermined amount of sodium dodecylbenzenesulfonate on both sides in a T-die and a film extruded by another extruder. The obtained laminated film was stretched in the same manner as in the above Examples and the like, and then heat-set to obtain a laminated film having a thickness of 50 μm.

The physical properties of the obtained laminated film are as shown in Table 2. Even if it is added to the inner layer or the outer layer of the polyester film, the same antistatic property can be obtained because the average diameter of the microbubbles is sufficiently small. Strength can be obtained. The antistatic property is dramatically improved by adding an antistatic agent to both the inner and outer layers.

Continuation of the front page (51) Int.Cl. ⁶ identification code FIB29L 7:00 9:00 C08L 67:00 (56) References JP-A-60-38123 (JP, A) JP-A-63-193822 (JP) , A) JP-A-2-80456 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08J 5/18 C08J 9/00-9/42 B29C 55/00-55/20 B29K 67:00 B29L 7:00 B29L 9:00 C08L 67/00

Claims (7)

(57) [Claims] (1) having at least a white polyester layer, an apparent density of 0.5 g / cm ³ or more and less than 1.0 g / cm ³ , and a surface resistivity of
An antistatic white polyester film having a resistivity of 10 ¹¹ Ω or less. 2. A white polyester layer containing an antistatic agent in an amount of 0.1 to 0.1%.
2. The antistatic white polyester film according to claim 1, comprising 3% by weight. 3. The antistatic white polyester film according to claim 1, further comprising a polyester layer A laminated on at least one side of the white polyester layer. 4. The polyester layer A contains an antistatic agent in an amount of 0.1 to 3%.
The antistatic white polyester film according to claim 3, which is contained by weight. 5. The antistatic white polyester film according to claim 3, wherein the polyester layer A contains 0.05 to 25% by weight of inorganic particles. 6. The antistatic white polyester film according to claim 1, having a cleavage strength of 250 g / 15 mm or more. 7. An optical density of 0.7 to 1.6 and a whiteness of 80%.
The antistatic white polyester film according to any one of claims 1 to 6, wherein the content is at least 110%.