JPH10110045A - White polyester film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white polyester film having excellent surface smoothness, reduced defective transfer, good traveling on a printer, a low apparent density and an interlaminar breaking strength high enough to prevent easy split even when re-released and to provide a method for producing the same. SOLUTION: This film has at least a white polyester layer (A), at least either of the surfaces of which has protrusions formed by the addition of an incompatible resin or inorganic particles and which has a three-dimensional surface roughness index in a range simultaneously satisfying the following formulas (1) to (4): (1) 0μm<Ra<=0.1μm, (2) 0.05μm<=Wca<=1μm, (3) 1<Wca/ Ra<=10 and (4) μs<1 (wherein Ra is the center line average roughness, Wca is the waviness of center line of filtered wave, and μs in the coefficient of friction between films).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white polyester film having low white density and high smoothness, and a method for producing the same. More specifically, the present invention relates to paper substitutes: cards, labels, stickers, courier slips,
Video printer receiving paper, bar code printer receiving paper, poster, map, dust-free paper, display board, white board, photographic paper,
The present invention relates to a white polyester film used as a base material for printing or printing on a surface such as copy paper, especially a color gradation printing substrate, and a method for producing the same.

[0002]

2. Description of the Related Art Waterproof papers or plastic films have conventionally been used for printed materials used outdoors because they cannot withstand wind and rain using paper. Further, in the case of an adhesive paper such as a label or a sticker, the paper is torn when it is peeled off after being attached, and thus a plastic film is also used for such an application. Films used in such applications are required to be white and opaque. For example, there is a film obtained by adding calcium carbonate to a polyolefin resin (Japanese Patent Publication No. 63-64310). Therefore, it has been considered that it is weak to heat and has a problem in mechanical strength. As an improvement over these drawbacks, a polyester base and a polypropylene added thereto (for example, JP-A-63-168441), and a thermal transfer for which the surface smoothness is defined by an air leak index. Receiving paper (Tokuhei 4-1
No. 6078).

[0003]

However, these films have the following problems.

[0004] Polyolefin-based films are:
Lack of heat resistance and low mechanical strength.

[0005] The color tone of the film is yellowish, which impairs the sense of quality.

[0006] Those based on polyester are expensive.

[0007] In order to reduce the cost per area of the film, fine bubbles are formed inside the film, and the film whose apparent density is lowered is easily cleaved. To suppress cleavage, it was necessary to reduce the number of microbubbles inside, that is, to keep the density high.

The properties to be provided as the receiving paper for printing include:
That is, the surface has a certain degree of smoothness. The Beck smoothness, which is generally used as surface smoothness, is too macroscopic when used as a thermal transfer image-receiving sheet, and is not suitable for discussing the relationship with the uniformity of the gradation image. When the maximum height (Rmax) and the center line average roughness (Ra) shown in JIS-B-0601 were small, there was no transfer omission and the uniformity of the image was good. It was found that the coefficient increased and the film running property in the printer became extremely poor, and conversely, the running property was significantly deteriorated.

The present invention solves the above-mentioned problems, and provides a white polyester having excellent surface smoothness, little transfer omission, good printer runnability, low apparent density, and high breaking strength between layers which are not easily cleaved. It is an object to provide a film and a method for producing the film.

[0010]

The above-mentioned white polyester film of the present invention is a polyester film having at least a white polyester layer (A) and having at least one surface having fine projections. Having a three-dimensional surface roughness index of the following formula (1):
It is characterized by being within a range that simultaneously satisfies the expression (4).

0 μm ≦ Ra ≦ 0.1 μm (1) 0.05 μm ≦ Wca ≦ 1 μm (2) 1 <Wca / Ra ≦ 10 (3) μs <1 (4) (Where Ra is the center line average roughness, Wca is the wave center line undulation, and μs is the coefficient of friction between the films.) The white polyester film of the present invention includes the following preferred embodiments.

(A) At least one surface is a polyester film having projections formed by adding an incompatible resin or particles, and the three-dimensional surface roughness index of the surface having projections is represented by the following formula (4): And (5) must be simultaneously satisfied.

0.7 <μs (MD) / μs (TD) <1.3 (4) 0.01 μm <Rmax <1 μm (5) (However, μs (MD) and μs (TD) Is the coefficient of friction between films in the MD and TD directions, and Rmax is the maximum height.) (B) Apparent density is 0.5 g / cm ³ or more and 1.3 g / c.
m ³ , cleaving strength 200 g / 15 mm or more, 150
0 g / 15 mm or less.

(C) The average dispersion diameter (H) of the incompatible resin is in a range satisfying the following expression (6). 1 μm ≦ H ≦ 100 μm (6) (d) The average particle diameter (M) of the particles must be within the range satisfying the following expression (7).

0.01 μm ≦ M ≦ 5 μm (7) (e) The white polyester layer is formed by adding an incompatible resin to the polyester in an amount of 0.5% by weight or more and 30% by weight or less, and further adding at least one kind of It is obtained by adding an antistatic agent in an amount of 0.5% by weight or more and 30% by weight or less and performing biaxial stretching.

(F) The white polyester film is used for receiving paper for printing.

(G) In the production method in which the white polyester film of the present invention is subjected to heat treatment with hot air at least once after stretching the unstretched polyester film in at least one direction, the heat treatment is carried out at an atmosphere temperature not lower than the melting point of the polyester. Manufactured.

Hereinafter, the present invention will be described in detail.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The white polyester film of the present invention is basically composed of polyester, and the polyester in the present invention may be any film as long as it can form a film. Examples include polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-o-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, and polyethylene-2,6-naphthalenedicarboxylate. These polyesters may be a homopolyester or a copolyester, and as the copolymerization component, for example, diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, Examples include dicarboxylic acid components such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium sulfoisophthalic acid. As the polyester used in the present invention, polyethylene terephthalate is preferable in terms of water resistance, durability, chemical resistance and the like.

The white polyester film of the present invention has at least a white polyester layer (A). The white polyester layer (A) in the present invention is a layer in which countless fine bubbles are contained in a layer made of the polyester, and the fine bubbles scatter light to make the layer white and opaque.

In order to form such fine bubbles, a method is preferred in which a polyester in which an incompatible resin or particles are dispersed is stretched so that a crack is generated at the interface and fine bubbles are generated in the polyester. . At this time, it is preferable to simultaneously use the immiscible resin and the particles in order to further increase the whiteness and the optical density.

The particles used in the present invention include organic particles and inorganic particles. The organic particles include acrylic acid, styrene and the like as constituent components, and specific examples include cross-linked polystyrene particles and cross-linked acrylic particles. Examples of the inorganic particles include talc, magnesium oxide, gypsum, barium sulfate, and magnesium carbonate, and calcium carbonate, titanium dioxide, and barium sulfate are particularly preferable.

The addition amount of the particles in the white polyester layer (A) of the present invention is preferably 0.5 to 10% by weight, more preferably 2 to 6% by weight, based on the polyester. If the amount of added particles is small, small projections intended by the present invention may not be obtained, and if too large, surface smoothness may not be obtained. In the present invention, it is also preferable to add a fluorescent whitening agent to further increase the whiteness.

The white polyester layer (A) in the present invention
As the incompatible resin to be added, polystyrene, polyolefin resin and the like are preferable. As the polyolefin resin, any resin 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, polybutene, and polymethylpentene. Further, the copolymer is not necessarily limited to a homopolymer, and may be a copolymer thereof. Among them, polyolefins having a small critical surface tension are preferred, and polypropylene and polymethylpentene are preferred. Polymethylpentene is particularly preferred because of its good releasability from polyester and easy formation of microbubbles during stretching.

The amount of the immiscible resin of the present invention is preferably 0.5 to 30% by weight, more preferably 5 to 30% by weight.
20% by weight. If the amount of the immiscible resin is small, the generation amount of fine bubbles is small, the whiteness of the white polyester film is insufficient, and the apparent density is 1.3 g / cm.
May not be less than ³ . On the other hand, if the amount is too large, the stretchability of the film tends to be poor and the film-forming properties tend to be poor.

The optical density of the white polyester film in the present invention is preferably 0.5 or more and 1.6 or less. More preferably, it is 0.8 or more and 1.6 or less. If the optical density is low, the back side of the film may show through because the concealability of the film is small, which is not preferable. Further, in order to increase the optical density, a large amount of fine bubbles must be contained, and the strength of the film is undesirably reduced.

In the present invention, the white color of the white polyester film means a film having a whiteness of 30% or more.
The whiteness is preferably 50% or more, more preferably 85% or more.
% Or more. The upper limit is desirably 110%. If the whiteness is less than 80%, the film is yellowish,
The print quality may be impaired. In addition, the whiteness is 11
If it exceeds 0%, it tends to be bluish, and similarly, the sense of quality may deteriorate.

In the white polyester film of the present invention, the projections on the surface are preferably formed by adding an incompatible resin or particles.

In the present invention, the center line average roughness Ra, which is one of the three-dimensional surface roughness indexes, is defined as JIS-B-060.
It is a numerical value defined as 1 and represents a surface irregularity (projection) with a relatively small period, and it is necessary to satisfy the following expression (1).

0 μm <Ra ≦ 0.1 μm (1) The center line average roughness Ra is preferably 0.05 μm ≦ Ra ≦
0.09 μm, particularly preferably 0.05 μm ≦ R
a ≦ 0.08 μm. If it exceeds 0.1 μm, transfer omission is likely to occur.

The film-to-film coefficient of friction μ of the present invention
s needs to satisfy the following equation (4).

Μs <1 (4) Film-to-film friction coefficient μs is more preferably μ
s <0.7, most preferably μs <0.5. The larger the value, the worse the slipperiness of the film,
Printer runnability deteriorates. Conversely, the smaller this value is, the more preferable it is. However, the lower limit value of μs is about 0.2 which can be manufactured.

The white polyester film of the present invention has a longitudinal friction coefficient (μs (M
D)) is preferably 0.7 to 1.3 times, more preferably 0.9 to 1.3 times the coefficient of friction (μs (TD)) in the width direction.
It is 1.1 times. If this value is too small, it tends to slip too much in the horizontal direction and the end face of the roll is likely to shift, while if this value is too large, wrinkles on the nodule are likely to occur in the vertical direction and the winding appearance is likely to deteriorate. In order to keep the balance between μs (MD) and μs (TD) within an appropriate range, the MD / TD orientation ratio of the polyester within 1 μm from the surface is set to 0.7 to 1.3, and the surface layer is made of polyester. It can be obtained by either heat treatment at a temperature not lower than the melting point.

In the present invention, the wave center line undulation (Wc
a) is a numerical value defined in JIS-B-0610, and represents surface irregularities (undulations) with a relatively large period,
It is necessary to satisfy the following expression (2).

0.05 μm ≦ Wca ≦ 1 μm (2) The wave center line undulation Wca is preferably 0.05 μm ≦
Wca ≦ 0.5 μm, particularly preferably 0.1 μm
≦ Wca ≦ 0.3 μm. When Wca exceeds 1 μm, when a transfer receiving layer or the like is applied, coating uniformity is poor, which is not preferable. On the other hand, if Wca is less than 0.05, the running property of the printer is inferior.

Further, in the present invention, the ratio between Wca and Ra needs to satisfy the following equation (3).

1 <Wca / Ra ≦ 10 (3) The ratio of Wca to Ra is preferably 1 <Wca / Ra ≦
3. It is very difficult with our knowledge to obtain a white polyester film with a large undulation such that the Wca / Ra ratio exceeds 10. Therefore, the expression (3) means that the undulation height having a large period is larger than the projection height having a small period. Although the reason is not clear, when such conditions are satisfied, the effect of the undulation is substantially greater than the effect of the small projections. Therefore, a white polyester film having this surface structure has good gradation transferability and is slippery. It has good properties.

As a method for forming fine projections on at least one surface in the present invention, a method in which an incompatible resin or particles controlled to a specific dispersion diameter is added, stretched, and then heat-treated at a high temperature, A method of laminating a layer to which fine particles are added to an extremely thin layer, a method of thermally crystallizing and stretching a polyester in a surface layer portion to which substantially no particles are added, and a method of combining them are preferable. A method of adding an incompatible resin or particles controlled to a specific dispersion diameter and stretching the film is particularly preferable.

In general, in order to reduce the center line average roughness Ra, it is necessary to reduce the dispersion diameter of the immiscible resin, to add particles having a small particle size, to reduce the amount of addition, Heat-treated above the melting point of the polyester, and by combining them. However, generally, when Ra is reduced, there arises a problem that the slipperiness of the film becomes extremely poor. This is because the contact area of the film becomes large when viewed microscopically, but in the present invention, the contact area of the film was reduced by adjusting the undulation to an appropriate range in order to improve the slipperiness, and this conflict was solved. .

That is, in order to obtain a white polyester film having fine projections, which is the object of the present invention, particles are used in combination with an incompatible resin having a controlled relative dispersion diameter, or particles are substantially added to the outer layer. The unstretched film is laminated with an ultra-thin layer, the unstretched film is previously unevenly stretched with an embossing roll and stretched, the surface layer is heat-treated at a temperature equal to or higher than the melting point of the polyester after stretching, and the coarse protrusions are physically removed by calendering or the like. It is obtained by appropriately combining the above.

In the present invention, the maximum roughness (Rmax), which is one of the three-dimensional surface roughness indexes, is defined by JIS-B-060.
It is a numerical value defined as 1, and it is preferable that the smaller this value is, the less the transfer omission is, and it is preferable to satisfy the following expression (5).

0.01 μm <Rmax <1 μm (5) The maximum roughness Rmax is particularly preferably 0.05 μm <R.
max <0.5 μm. When Rmax exceeds 1 μm, transfer omissions often occur, and when it is 0.01 μm or less, it may be difficult to make the friction coefficient μs smaller than 1. In order to reduce Rmax, a method of removing coarse particles by a method such as a filter, a method of adding particles having a small particle size, a method of reducing the amount of added particles, and a method of physically increasing coarse protrusions on the film surface by calendering Obtained by combining any of the methods for removing the above.

The apparent density of the white polyester film is preferably 0.5 g / cm ³ or more and less than 1.3 g / cm ³ . More preferably, 0.7 g / cm ³ or more, 1.1 g / cm ³
less than cm ³ . If the apparent density is too large, the concealing property will be low and the film will be seen through, or the film will be strong and the softness of the film peculiar to the internal bubble-containing film will be reduced. On the other hand, if the apparent density is too small, the amount of fine bubbles inside is too large, so that the cleavage strength tends to be low, and the strength of the film tends to be weak and brittle.

The cleavage strength of the white polyester film in the present invention is preferably 200 g / 15 mm or more. It is more preferably at least 500 g / 15 mm, most preferably at least 600 g / 15 mm. Cleavage strength 200g /
If it is less than 15 mm, the film surface will be cleaved when it is peeled off when used for strongly adhesive labels and seals, and if it is severe, the film will be easily broken.

The average particle size (H) of the incompatible resin in the white polyester film layer (A) preferably satisfies the following expression (6).

1 μm ≦ H ≦ 100 μm (6) If the average particle size H of the incompatible resin exceeds 100 μm, the film may be broken, and if it is less than 1 μm, sufficient whiteness cannot be obtained. There are cases.

Further, a white polyester film layer (A)
It is preferable that the average particle diameter (M) of the medium particles satisfies the following expression (7).

0.01 μm ≦ M ≦ 5 μm (7) If the average particle diameter M of the particles exceeds 5 μm, the film may be broken, and if it is less than 0.01 μm, sufficient whiteness can be obtained. May not be.

Further, in the present invention, when the incompatible resin and the particles are used together in the white polyester film layer (A), the ratio of the average particle diameter H of the incompatible resin to the average particle diameter M of the particles is as follows. (8) is preferably satisfied.

2 <H / M ≦ 20 (8) In the present invention, by taking such a relationship, a white polyester film having many small protrusions by particles and a large swelling by an incompatible resin. Is easy to manufacture.

When the ratio H / M of the average particle size H of the incompatible resin to the average particle size M of the particles exceeds 20, the gradation transferability may be deteriorated. When H / M is 2 or less, the obtained white polyester film may not be able to satisfy the relationships of the above-described formulas (1) to (4).

The white polyester film of the present invention may be a single-layer film consisting of only the white polyester layer (A) or a laminated film having at least this layer. Examples of the layer to be laminated on the white polyester layer (A) include films such as polyolefin, polyester, and paper, and a preferable laminate is a polyester film. Particles may be added to the laminated polyester film. By adding the particles, the slip on the film surface can be improved, and the glossiness can be eliminated.

When a polyester film is laminated, it is preferable to form a laminated film in which a polyester layer (B) containing no incompatible resin and no antistatic agent is laminated on at least one surface of the white polyester layer (A). . In this case, it is more preferable to laminate the polyester layer (B) on the white polyester layer (A) to which the antistatic agent is added, because the cleavage strength is dramatically improved. Further, by laminating the polyester layer (B), there is also an effect of improving the adhesiveness of the surface.

In the case of a laminated film, preferred lamination structures include a combination of A / B, A / B / C, B / A / B, A / B / A, and the like. Here, A is a white polyester layer (A), B is a polyester layer (B), and C is a polyester layer (C) different from B in thickness composition or composition such as added particles.

When a laminated film is used in the present invention,
The lamination thickness is desirably 15 μm or less so as not to lose the effect of the undulation of the white polyester layer (A). It is more preferably at most 5 μm, most preferably at most 1 μm. The lower limit is 0.1 μm.

It is also desirable that the average particle size (M) of the particles in the polyester film resin to be laminated also satisfies the expression (7). The amount of the particles added to the polyester film resin to be laminated is preferably 0.05 to 25% by weight. As the particles, calcium carbonate, silicon dioxide,
Examples include titanium dioxide and barium sulfate. When the addition amount is small, the number of small protrusions on the film surface decreases, and the lubricity tends to be poor. If the added amount is too large, troubles such as powder dropping may occur during post-processing.

In the present invention, at least one kind of antistatic agent or a copolymer thereof is added to the white polyester layer (A) in an amount of 0.5 to 30% by weight.
Axial stretching is preferred. Preferred examples of the antistatic agent include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. A low-molecular type or a high-molecular type can be selected depending on the application, but a high-molecular type is more preferable in view of durability and surface contamination. Particularly preferably used are nonionic polymer type surfactants, and specifically, plastic age (page 136,
May, 1995), polyethers, quaternary ammonium salts, sulfonic acids, betaines, polymer charge transfer conjugates, and the like. Among them, polyethers and copolymers thereof are particularly preferred.

Preferred polyethers and copolymers thereof include, but are not limited to, polyethylene glycol, polypropylene glycol, a 1: 1 copolymer of ethylene glycol and propylene glycol, and methoxy polyethylene glycol. .
By adding these antistatic agents, the dispersion diameter of the incompatible resin becomes uniform and fine. If the addition amount of the antistatic agent is small, the effect of uniform fine dispersion of the incompatible resin is small,
Further, the cleavage strength tends to be insufficiently improved. If the addition amount is too large, the thermal stability deteriorates, and the white polyester layer tends to have a yellowish color, which is not preferable.

A particularly preferred polyether is polyethylene glycol. The molecular weight of the polyethylene glycol is from 500 to 30,000, preferably from 1,000 to 10,000. When the molecular weight is small, the white polyester layer tends to have a yellowish color, and the cleavage strength tends to be weak. If the molecular weight is too large, the cleavage strength tends to be weak. In addition, polyethylene glycol has better stretchability when added than other polyalkylene glycols, and has the effect of promoting the generation of fine bubbles.

In the present invention, those further copolymerized with a polyester are most preferable in order to improve durability and stain resistance of the surface. Examples of the polyester copolymerized with the polyether include polyethylene terephthalate and polybutylene terephthalate.

In the method for producing a white polyester film of the present invention, the polyester composition is melted and extruded by an extruder, and the sheet extruded from the T-die is cooled and solidified by a cooling drum having a surface temperature of 10 to 60 ° C. A method of forming an unstretched film is preferably used. This cooling and solidification preferably uses an electrostatic application method. In order to obtain a preferable swelling, it is also quenched on a cooling drum having an embossed surface to form a sheet. As for the uneven pattern on the surface of the metal roll, the density of the convex portions is at least 2/5 mm in at least one direction, and the uneven pattern can be selected from various shapes such as silk, turtle shell, satin finish, and lattice. The projection height of the metal roll surface is preferably 5 μm or more and 500 μm or less in Rmax value.

In the present invention, after the film is stretched in at least one direction, it is preferable that the film is heat-treated with hot air at least once. The ambient temperature for this heat treatment is equal to or higher than the melting point of the polyester. At this time, in order to obtain the white polyester film of the present invention without fusing the white polyester film, it is preferable that only the melting point of the polyester is adjusted to be higher than the melting point of the polyester only at the surface layer of the film.

The heat transfer coefficient of air is smaller than that of water and the like, and the thermal conductivity of polyester is about 0.17 kcal / m
Since the temperature is as low as hr · ° C., the film is heated from the surface by heating using hot air or the like with air as a medium, and a temperature distribution occurs in the thickness direction of the film. In particular, in the case of a laminated white polyester film in which the inner layer contains voids and the thermal conductivity is reduced, the polyester resin temperature of the extreme surface layer is reduced by passing the heat treatment atmosphere through an oven or a tenter in which the atmosphere temperature is equal to or higher than the melting point of the polyester for a short time. The melting point is set to the melting point or more, and the internal polyester resin temperature can be controlled to be lower than the melting point.

In order to maximize the effect of this heat treatment, a polyester resin having a lower melting point than that of the inner layer polyester may be selected as the outer layer polyester resin. By this special heat treatment, the surface smoothness is improved by reducing the number of coarse projections and increasing the number of fine projections while maintaining the undulation property. As a result, the three-dimensional surface roughness index is as described in the above (1) to (3).
It becomes easier to obtain a white polyester film having a surface satisfying the expression (3) at the same time.

Next, a preferred method for producing the film of the present invention will be described. The polyester chip and the master chip obtained by adding polyethylene glycol to the polyester during the polymerization reaction or at the completion of the polymerization are sufficiently vacuum-dried, and then the polyolefin resin chip is mixed.
It is supplied to an extruder heated to 70 to 300 ° C. and formed into a sheet shape from a T-die.

In the case of laminating the polyester layer (B), separately dried polyester chips are supplied to another extruder and laminated in a T-die to form a sheet.
At this time, when adding inorganic particles, a polyester chip mixed with an inorganic particle master chip and dried under vacuum,
Feed to the extruder. The polyalkylene glycol is preferably added at the time of polymerization of the polyester or at the completion of the polymerization to form a master chip, but this is not always necessary. Further, the three components may be previously kneaded with a pelletizer or the like. Further, the sheet extruded from the T die is cooled and solidified by a cooling drum having a surface temperature of 10 to 60 ° C. to obtain an unstretched film. This unstretched film is guided to a group of rolls heated to 80 to 120 ° C., stretched in the longitudinal direction, and stretched to 20 to 3
Cool with rolls at 0 ° C. Subsequently, the film was guided to a tenter while holding both ends of the longitudinally stretched film with clips.
The film is stretched in a direction perpendicular to the longitudinal direction in an atmosphere heated to 140 ° C.

The stretching ratio is 2 to 5 times in each of the vertical and horizontal directions, and the area ratio (longitudinal stretching ratio × lateral stretching ratio) is preferably 4 to 25 times. In order to impart flatness, dimensional stability and surface smoothness to the biaxially stretched film thus obtained, 150 to 300 in a tenter.
The heat treatment of ° C is performed. At this time, the tenter is preferably divided into two or more chambers, but the ambient temperature of at least one chamber is controlled to a temperature equal to or higher than the melting point of the polyester. The heat-treated film is then quenched uniformly, cooled to room temperature, and wound up.

Further, in the present invention, the film wound continuously as required was adjusted in advance so that the atmosphere temperature in the front chamber of the oven was 240 to 300 ° C. and the atmosphere temperature in the rear chamber of the oven was 20 ° C. 0.1 in each oven
A method in which heat treatment is performed by passing through for 1 second is also used.

[Method of Measuring Physical Properties and Evaluation of Effect]
The method for measuring physical properties and the method for evaluating effects in the present invention are as follows.

(1) Apparent density A density gradient tube of carbon tetrachloride-n-heptane 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 (100 μm thickness, manufactured by Toray Gosei Co., Ltd.) is formed at a temperature of 50 ° C. After lamination and aging at 40 ° C. for 48 hours, cut into 15 mm width, peeled off one end, attached to Tensilon, and kept at right angles to the part where the bonded part was peeled off,
The strength when the measurement film and the unstretched film are peeled off is defined as the cleavage strength. The peeling speed at this time is 300 mm / min. At this time, the average value of the five films is taken except for those in which the film is not broken and is peeled off by the adhesive layer.

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

(4) Whiteness Based on JIS-L-1015, the reflectance at a wavelength of 450 nm is B%, and the reflectance at a wavelength of 550 nm is G%.
The degree of whiteness was determined from 4B-3G (%).

(5) Cellophane tape re-peeling strength Cellophane tape (Nichiban Co., Ltd., width 1)
8 mm) for 10 cm in length, apply a load of 1 kg / cm ² for 10 seconds, and then instantaneously peel off the film perpendicularly by hand. This operation is performed three times in the same place, and the following four levels are classified based on the state of adhesion to the film surface and the cellophane tape at this time. A and B levels are considered acceptable.

A = 5 times, no change on the film surface and no adhesion to the cellophane tape.

B = 5 times, when the film floats on the film surface at least once, and fuzzing is observed, but there is no adhesion on the cellophane tape.

C = 5 times, at least once, when a part of the film surface was broken and adhered to the cellophane tape.

D = 5 times, at least once, when almost the entire surface of the film adheres to the cellophane tape.

(6) Cushion ratio (%) A standard gauge 90930 is used for the dial gauge No. 2109-10 of Mitoyo Seisakusho Co., Ltd., and the dial gauge stand No. 7001D is used.
Using the GS-M, dial gage holding partial load 50g and 5
00g and the thickness d of each film
It was determined from the following formula from 50 and d 500 and evaluated in four steps. ◎, △, and Δ are in a good range in which cushioning properties are felt.

Cushion rate = 100 × (d50−d5)
00) / d 50 ◎ ・ ・ ・ 15% or more ○ ・ ・ ・ 10% or more and less than 15% △ ・ ・ ・ 5% or more and less than 10% × ・ ・ ・ less than 5% (7) Surface roughness index Center line average roughness The surface Ra, the maximum height Rmax, and the wave center line undulation Wca The film surface is measured with a stylus type surface roughness meter (SE-3C, manufactured by Kosaka Laboratories) in accordance with JIS B-0601.
The measurement is performed over a measurement length of 4 mm with a cutoff value of 0.8 mm in the longitudinal direction of the film under the conditions of a needle radius of 2 μm and a load of 70 mg. Such measurement is performed 150 times continuously at 2 μm intervals in the lateral direction of the film, that is, over 0.3 mm in the lateral direction of the film.

Ra means that a portion of the measured length L is extracted from the roughness curve in the direction of its center line, the center line of the extracted portion is set as the X axis, and the direction of the longitudinal magnification is set as the Y axis. When Y = f (x), the value given by the following equation is expressed in μm.

[0082]

(Equation 1) Rmax represents a value in μm in which the maximum peak and the deepest valley of a portion extracted by the reference length from the cross-sectional curve are sandwiched between two straight lines parallel to the center line, and the interval divided by the vertical magnification is expressed in μm. The wave undulation curve is a curve obtained by removing a small uneven component from the cross-sectional curve with a low-pass filter having a predetermined high-frequency cutoff value.

Wca is a wave center line obtained by removing a component having a large interval corresponding to an irregular shape such as straightness from a wave undulation curve by a high-pass filter having a predetermined low-frequency cutoff value. The average value of the center line of the undulation curve is expressed in μm.

The surface of the film was measured according to JIS B-0610 by using a stylus type surface roughness meter (SE-3C, manufactured by Kosaka Laboratories).
Measure with. The measurement is performed over a measurement length of 20 mm in the longitudinal direction of the film under the conditions of a needle radius of 2 μm and a load of 70 mg. Such measurement is performed 150 times continuously at 2 μm intervals in the lateral direction of the film, that is, over 0.3 mm in the lateral direction of the film.

(8) Average Particle Size of Inorganic Particles The inorganic particles are dispersed in ethanol, and measured using a centrifugal sedimentation type particle size distribution measuring apparatus (CAPA500, manufactured by HORIBA, Ltd.). Diameter.

(9) Average Particle Size (a) and Shape Factor of Dispersion The mechanical direction (MD) of the film or its perpendicular direction (T
The cross section cut in D) is 1000 to 50 with a scanning electron microscope.
A photograph enlarged by a factor of 00 is taken, and at least 100 or more incompatible polymer dispersions in a specified thickness range are subjected to an image analyzer to determine the distribution of the diameter of a circle corresponding to the area of the dispersion. The area average diameter of this distribution is defined as the average diameter (dispersion diameter) of the dispersion. In addition, 100 major diameters /
The ratio of the minor axis is defined as the shape factor of the dispersion.

(10) Gradation As a color printer, "Professional Color Point
2 "(manufactured by Seiko Denshi Kogyo Co., Ltd.), and a thermal transfer ink ribbon, CH705 (yellow, magenta, cyan, manufactured by Seiko I Supply Co., Ltd.) were used to test the thermal transfer recording image receiving sheet of the present invention. Pattern printed. Then, the gradation of the printing surface is visually determined, and the following 3
Grading was performed. A and B were evaluated as good. The printing at this time was performed in a "PALMIX" mode (8 gradations) which is gradation printing.

A: Five or more gradations can be reproduced.

B: Three or more gradations can be reproduced.

C: No gradation.

(11) Melting point (Tm) and glass transition temperature (Tg) of polyester Measured using a differential thermal scanning DSC2 (manufactured by Perkielmer). 300mg of sample 10mg by nitrogen gas flow,
The melt was held for 5 minutes and then quenched with liquid nitrogen. In the process of raising the temperature of the obtained sample at a rate of 10 ° C./min, the specific heat change based on the transition from the glassy state to the rubbery state was read, and this temperature was taken as the glass transition temperature (Tg). The melting temperature (Tm) was taken as the melting point.

(12) Coefficient of friction (μs, μs (MD),
μs (TD)) Measured at 25 ° C. and 65% RH using a slip tester according to the method specified in ASTM-D1894-63.

Μs = 0.5 × (μs (MD) + μs (TD))

[0094]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

(Example 1 and Comparative Example 1) A polyethylene terephthalate chip in which polymethylpentene and titanium dioxide were mixed so as to have the ratio shown in Table 1 was used to obtain 18 chips.
After vacuum drying at 0 ° C. for 3 hours, the mixture was supplied to an extruder heated to 270 to 300 ° C. and formed into a sheet by a T-die. The unstretched film cooled and solidified by a cooling drum having a surface temperature of 25 ° C. is guided to a group of rolls heated to 80 to 98 ° C., and stretched three times in the longitudinal direction.
Of the roll group. Subsequently, the longitudinally stretched film was guided to a tenter while gripping both ends of the film with clips, and horizontally stretched three times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. Thereafter, the film was heat-set at 210 ° C. in a tenter, uniformly cooled, and wound up (Comparative Example 1). Subsequently, the wound film was previously heated at an ambient temperature of 28
Each sample was passed through an oven in which the atmosphere temperature in the rear chamber of the oven was adjusted to 20 ° C. at 0 ° C. for 0.5 seconds to perform heat treatment (Example 1). The film thickness was 100 μm. Tables 1 to 3 summarize the physical properties and the like of the obtained films.

Example 2 A polyethylene terephthalate chip in which polymethylpentene, titanium dioxide and dodecylbenzenesulfonic acid (DBS) were mixed so as to have the ratio shown in Table 1 was vacuum-dried at 180.degree. To an extruder heated to ~ 300 ° C,
It was formed into a sheet with a die. Further, an unstretched film was obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. At this time, the cooling drum had a pyramid-shaped unevenness having a length of 0.66 mm, a width of 0.66 mm and a height of 100 μm.
A metal drum with a surface of 40 mesh having 225 pieces per cm 2 was used. This unstretched film is
Lead to a group of rolls heated to ℃, stretched three times in the longitudinal direction,
It cooled with the roll group of 25 degreeC. Subsequently, the film was guided to a tenter while gripping both ends of the longitudinally stretched film with clips.
3.3 in a direction perpendicular to the longitudinal direction in an atmosphere heated to 0 ° C.
The film was stretched twice. Thereafter, the film was heat-set at 230 ° C. in a tenter and uniformly cooled, and then wound up. Film thickness is 100
μm. Tables 1 to 3 summarize the physical properties and the like of the obtained films.

(Examples 3 to 5) A polyethylene terephthalate chip obtained by mixing polymethylpentene, calcium carbonate and polyethylene glycol (PEG) so as to have the ratio shown in Table 1 was vacuum-dried at 180 ° C. for 3 hours, and then dried at 270 ° C. Feed to extruder (A) heated to ~ 300 ° C and extrude polyethylene terephthalate mixed with calcium carbonate from other extruder (B) to the ratio shown in Table 1 and apply both sides in T-die The sheets were laminated (B / A / B) and formed into a sheet surface. Further, the film is heated to a surface temperature of 25.
The unstretched film cooled and solidified by the cooling drum at
It was led to a group of rolls heated to ９８98 ° C., stretched three times in the longitudinal direction, and cooled by a group of rolls at 25 ° C. Subsequently, the longitudinally stretched film was guided to a tenter while gripping both ends of the film with clips, and horizontally stretched three times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. Thereafter, the film was heat-fixed in a tenter at 220 ° C., and then gradually cooled, and then wound up.
After passing through an oven in which the ambient temperature of the oven was adjusted to 20 ° C. for 0.5 seconds, heat treatment was performed in the oven. The thickness of the film was 100 μm, and the film lamination ratio was B / A / B = 1/98/1. Tables 1 to 3 summarize the physical properties and the like of the obtained films.

However, in Example 4, the heat treatment in the oven performed after the heat treatment in the tenter in Example 3 was not performed. In Example 5, polystyrene sulfonic acid sodium salt having a molecular weight of 70,000 was used instead of PEG.

(Comparative Example 2) PM used in Example 1
A film was obtained in the same manner as in Example 1 except that P was not added.

(Comparative Example 3) Film lamination ratio was B / A / B
A film was obtained in the same manner as in Example 4, except that = 1/8/1.

Comparative Example 4 A film was obtained in the same manner as in Example 4 except that the amount of polymethylpentene in the white polyester layer (A) used in Example 4 was changed.

The results are summarized in Tables 1 to 3.

[0103]

[Table 1]

[Table 2]

[Table 3] By comparing Example 1, Example 2 and Comparative Example 1, the three-dimensional roughness index of the surface can be precisely controlled within the range of the present invention by heat-treating the surface layer at a temperature equal to or higher than the melting point or by appropriately adding an antistatic agent. It can be seen that by controlling, a white polyester film having excellent print gradation is obtained.

From the results of Comparative Examples 2 and 3, the three-dimensional roughness of the surface was determined when the thickness of the film to be laminated was not appropriate and when the amount of the incompatible resin added to the white polyester layer (A) was small. It can be seen that when the index is not controlled within the range of the present invention, it is difficult to obtain a white polyester film having excellent print gradation.

[0105]

According to the present invention, the incompatible resin or particles in the white polyester layer are dispersed and preferably the dispersion diameter is controlled, or the surface layer is heat-treated to a temperature higher than the melting point of the polyester to obtain a three-dimensional surface. By precisely controlling the roughness index within a predetermined value range, in particular, printing gradation,
A white polyester film having excellent color printability can be obtained.

Also, the surface smoothness is excellent, the transfer loss is small, the printer running property is good, and the apparent density is small.
In addition, a white polyester film having high breaking strength between layers which is not easily cleaved can be obtained.

The thus obtained white polyester film of the present invention can be used for cards, labels, stickers, courier slips, receiving paper for video printers, receiving paper for barcode printers, posters, maps, dust-free paper, display boards , White board, photographic paper, copy paper, etc., and particularly suitable for a substrate for printing or printing on the surface, especially a color gradation printing substrate.

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

Claims (8)

[Claims] 1. A polyester film having at least a white polyester layer (A) and having at least one surface having fine projections, wherein the three-dimensional surface roughness index of the surface having fine projections is as follows: 1) A white polyester film characterized by satisfying the expressions (1) to (4) at the same time. 0 μm <Ra ≦ 0.1 μm (1) 0.05 μm ≦ Wca ≦ 1 μm (2) 1 <Wca / Ra ≦ 10 (3) μs <1 (4) (However, , Ra is the center line average roughness, Wca is the wave center line undulation, and μs is the coefficient of friction between films.) 2. A polyester film having projections formed on at least one surface by adding an incompatible resin or particles, wherein the surface having projections has a three-dimensional surface roughness index represented by the following formula (4): 2. The white polyester film according to claim 1, wherein the value satisfies the expression (5) at the same time. 0.7 <μs (MD) / μs (TD) <1.3 (4) 0.01 μm <Rmax <1 μm (5) (However, μs (MD) and μs (TD) are MD, respectively) The coefficient of friction between film and film in the TD and TD directions, Rmax, is the maximum height.) 3. An apparent density of 0.5 g / cm ³ or more,
Less than 1.3 g / cm ³ , cleavage strength 200 g / 15 mm
The white polyester film according to claim 1 or 2, wherein the weight is 1500 g / 15 mm or less. 4. The white polyester film according to claim 2, wherein the average dispersion diameter (H) of the incompatible resin is in a range satisfying the following expression (6). 1 μm ≦ H ≦ 100 μm (6) 5. An average particle diameter (M) of the particles is as follows:
5. A method according to claim 2, wherein said expression is satisfied.
The white polyester film according to any one of the above. 0.01 μm ≦ M ≦ 5 μm (7) 6. The white polyester layer, wherein an incompatible resin is added to the polyester in an amount of 0.5% by weight or more and 30% by weight or less, and at least one antistatic agent is added in an amount of 0.5% by weight or more and 30% by weight. % Or less and biaxially stretched. 7. The white polyester film according to claim 1, which is used for a receiving paper for printing. 8. A production method in which an unstretched polyester film is stretched in at least one direction and then heat-treated at least once, wherein the heat treatment temperature is equal to or higher than the melting point of the polyester. A method for producing a white polyester film according to the above-mentioned item.