JPH04202540A - Void-containing polyester film - Google Patents

Abstract

PURPOSE:To obtain a polyester film containing voids, having high surface-layer strength and suitable for recording paper, etc., having excellent drawing performance in high productivity by mixing a polyester with a thermoplastic resin incompatible with the polyester and orienting the mixture in at least one direction. CONSTITUTION:(A) A polyester preferably containing >=70mol% of ethylene terephthalate unit, butylene terephthalate unit or ethylene 2,6-naphthalate unit is mixed with (B) a thermoplastic resin incompatible with the component A [preferably a resin melting at <=300 deg.C and stable at the extrusion temperature (preferably polyolefin or polystyrene resin)]. The mixture is extruded in molten state and oriented in at least one direction to obtain the objective void- containing polyester film containing a number of voids and containing the component B in a state to have a major diameter of 1-50mum, a thickness of <=10mum and a major diameter to thickness ratio of 2-100.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is intended for use in films with improved wettability and adhesion of ink and coating agents when used for printing materials, posters, recording paper, packaging materials, etc. The present invention relates to a polyester film containing a large amount of fine cavities and having drawability.

(Conventional technology) Synthetic paper, which is made from synthetic resin as the main raw material and is a paper substitute, has better water resistance, moisture absorption dimensional stability, surface smoothness, gloss and clarity of printing, and mechanical strength than natural paper. Excellent in such things.

In recent years, applications that take advantage of these advantages have been developed.

Polyethylene, polypropylene, polyester, etc. are used as the main raw materials for synthetic paper, but among these, polyester, represented by polyethylene terephthalate, is superior in terms of high heat resistance and stiffness, and is widely used. It is possible to develop various uses.

Conventional methods for obtaining films made from polyester and having functions similar to those of paper include (1) incorporating a large amount of fine cavities inside the film, and (2-1) sandblasting a normal flat polyester film. or(
A method of roughening the surface by 2-2) chemical etching treatment and (2-3) matting treatment (a method of laminating a matting agent together with a binder) has been disclosed.

Among these, method (1), in which a large amount of fine cavities are contained inside the film, allows the film itself to be made lighter and has appropriate flexibility, making clear printing and transfer possible. There is an advantage.

Conventionally, as a method for creating fine cavities inside a film, a polymer that is incompatible with polyester is melt-kneaded in an extruder to obtain a sheet in which the polymer is dispersed in the form of fine particles in the polyester, and the sheet is further stretched. A method is disclosed for generating cavities around microparticles.

Examples of polymers that are incompatible with polyester used for generating cavities (hereinafter referred to as cavity forming agents) include polyolefin resins (for example, JP-A-49-134755) and polystyrene-based resins (for example, JP-A-49-134755).
16, Japanese Patent Publication No. 54-29550) and polyarylate resins (for example, Japanese Patent Publication No. 5B-28097). Among these, polystyrene and polypropylene are preferable because they are easy to form cavities and are inexpensive. However, a cavity-containing polyester film obtained using polystyrene or polypropylene as a cavity developing agent is difficult to use due to the cavity developing agent, the size of the cavities, If the thickness or the like is inappropriate, the film will break during film formation or the clips will come off in the tenter many times, resulting in a significant drop in productivity. Furthermore, since the strength of the film in the thickness direction is poor, there is also a drawback that when a tape or the like is attached and then removed, the surface layer of the film also comes off.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned drawbacks by improving the cavity developing agent, the size and thickness of the cavities inside the polyester film containing cavities, thereby improving productivity and improving the strength of the surface layer. The purpose is to provide a material suitable for recording paper with high drawing properties.

(Means for Solving the Problems) That is, the present invention has a large number of fine cavities manufactured by at least uniaxially orienting a polymer mixture in which polyester and a thermoplastic resin incompatible with the polyester are mixed. In the hollow-containing polyester film, the long axis diameter of the thermoplastic resin incompatible with the polyester present in the film is 1 to 50 μm, the thickness is 10 μm or less, and the ratio of long sleeve diameter to thickness is 2 to 100. The present invention relates to a cavity-containing polyester film characterized by the following.

Here, FIGS. 1 to 8 show cavities, thermoplastic resins that are incompatible with polyester, their major axis diameters, thicknesses, etc.

In the present invention, polyester is a polyester made by polycondensing aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalene dicarboxylic acid or their esters with glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, and neopentyl glycol. It is a polyester produced. These polyesters are produced by directly reacting aromatic dicarboxylic acids and glycols, or by polycondensation after transesterification of alkyl esters of aromatic dicarboxylic acids and glycols, or It is produced by a method such as polycondensation of glycol ester. Typical examples of such polyesters include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. This polyester may be a homopolymer or may be a copolymer of a third component. In any case, in the present invention, the content of ethylene terephthalate units, butylene terephthalate units, or ethylene-2,6-naphthalate units is 70 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more. Polyester is preferred.

The thermoplastic resin that is incompatible with the polyester used in the present invention can be used without any restriction as long as it is incompatible with the polyester described above, but it must be one that melts at 300°C or less and that cannot be extruded. Those having good stability at temperature are preferred.

Specifically, polyolefin resins such as polyethylene, polypropylene, and polymethylpentene, copolymerized polyolefin resins such as ionomer resin EP rubber, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, etc. Examples include polystyrene resins, polyarylate resins, polycarbonate resins, and polyacrylonitrile resins.

Among these, polyolefin resins and polystyrene resins are particularly suitable.

A polymer mixture of the polyester of the present invention and a thermoplastic resin that is incompatible with the polyester is, for example,
It is obtained by mixing chips of each resin, melting and kneading them in an extruder, and then extruding and solidifying. In addition, there is a method in which both resins are kneaded in advance using a mixer and then melted and extruded from an extruder to solidify, or a thermoplastic resin that is incompatible with polyester is added to the polyester in the polyester polymerization process, and the mixture is stirred. It can also be obtained by a method in which chips obtained by dispersion are melt-extruded and solidified. The polymer obtained by solidification is usually non-oriented or weakly oriented.

Further, a thermoplastic resin that is incompatible with the polyester is dispersed in the polyester in various shapes such as spherical, ellipsoidal, or thread-like shapes. The dispersion diameter is 0.1 to 30 μ- in a spherical shape. It is also possible to add pigments, colorants, light-fastening agents, fluorescent agents, antistatic agents, etc. to the polymer mixture depending on the application. The polymer mixture obtained in this way is further stretched between rolls with different speeds (roll stretching), stretched by being gripped with clips and spread (tentter stretching), or stretched by being spread by air pressure (inflated yoke). Orientation treatment is performed in at least one axis by, for example, stretching. At this time, peeling occurs at the interface between the polyester and the thermoplastic resin that is incompatible with the dispersed polyester, resulting in a large number of cavities in the polymer mixture.

Therefore, the amount of the thermoplastic resin that is incompatible with the polyester to be mixed with the polyester varies depending on the amount of cavities desired, but it is 1% to the entire polymer mixture.
% to 35% by weight is preferred. If it is less than 1% by weight, there is a limit to the amount of voids that can be generated, and the desired flexibility, lightness, and drawability cannot be obtained.On the other hand, if it is more than 40% by weight, the heat resistance of the polyester film is and strength is significantly impaired.

The most important point in the present invention is that the long axis diameter of the thermoplastic resin incompatible with the polyester present in the film is 1 to 50μ wide, the thickness is 10μ or less, and the ratio of the long sleeve diameter to the thickness is 2. ~100.

The major axis diameter of the thermoplastic resin that is incompatible with polyester is 50
If the thickness exceeds 10 μm or more, the cavities that develop become too large, resulting in poor strength in the thickness direction of the film, which may cause peeling of the surface layer of the film as described in the (Prior Art) section. , causing breakage during production. Furthermore, if the ratio of the long axis diameter to the thickness of the thermoplastic resin that is incompatible with polyester is less than 2, the bonding surface between the polyester and the thermoplastic resin that is incompatible with polyester becomes small, so that the thickness of the film decreases. This causes peeling of the surface layer of the film as described in the section ``Poor strength (prior art)''. Further, if the long axis diameter of the thermoplastic resin incompatible with polyester is less than 1 μm or if the ratio of long sleeve diameter to thickness is 100 or more, the void content rate will be low, which is not preferable.

The conditions for orienting the polymer mixture are closely related to the formation of cavities. Therefore, the conditions for achieving this purpose include, for example, the most commonly used sequential biaxial stretching process, in which a continuous sheet of the polymer mixture is stretched in the longitudinal direction with a roll and then stretched in the middle direction with a tenter. In the case of the sequential biaxial stretching method, the results are as follows. In order to generate a large number of cavities during roll stretching, the temperature is set to the secondary transition temperature of the thermoplastic resin that is incompatible with the polyester + 10°C.
Hereinafter, it is preferable to set the magnification to 1.2 to 5 times. In order to stably form a film without breaking during tenter stretching, the temperature is set to +10°C, the secondary transition temperature of the thermoplastic resin that is incompatible with the polyester. As mentioned above, it is preferable that the magnification is 1.2 to 5 times.

Therefore, the thermoplastic resin incompatible with the polyester to be mixed with the polyester has a secondary transition temperature of 70 to 1.
The temperature is preferably in the range of 30°C, and corresponding resins include, for example, polystyrene and polymethylpentene.

The dimensional stability at high temperatures can be improved by heat-setting the stretched and oriented cavity-containing film at 130°C or higher, preferably 180°C or higher.

Further, a cavity-containing film oriented only in the -axis direction is useful as a shrinkable film or an easily tearable film.

Since the present invention relates to a cavity-containing polyester film in which cavities are generated by an orientation treatment, it is necessary to orient the film in at least one axis.

(Function) In the present invention, the polyester mainly composed of repeating ethylene terephthalate units is used in order to satisfy the heat resistance and mechanical strength of the hollow polyester film.

In the present invention, a thermoplastic resin incompatible with the polyester is mixed with the polyester to obtain a polymer mixture by dispersing fine particles of a thermoplastic resin incompatible with the polyester in the polyester. This is to create the core of the cavity that will be generated by the next orientation process.

In the present invention, the reason why the polymer mixture is oriented in at least one axis is to generate a large number of fine cavities in the polymer mixture. By creating cavities, the weight of the film can be reduced, workability is improved, and the price per area is reduced. In addition, the inclusion of cavities increases flexibility, making it possible to print and print clearly during printing and transfer. Furthermore, by including cavities, light shielding properties and whiteness can be obtained. In addition, many protrusions derived from a thermoplastic resin incompatible with the polyester are formed on the surface of the film, making it possible to write with a pencil or ballpoint pen.

What is particularly important in the present invention is that the thermoplastic resin incompatible with the polyester present in the film has a long axis diameter of 1 to 50 μm, a thickness of 10 μm or less, and a ratio of the long axis diameter to the thickness. It should be between 2 and 100.

The major axis diameter of the thermoplastic resin that is incompatible with polyester is 50
If the thickness exceeds μ- or 10 μm or more, the cavities that develop become too large, resulting in poor strength in the thickness direction of the film, which may cause peeling of the surface layer of the film as described in the section (Prior Art). , causing breakage during production. Furthermore, if the ratio of the long axis diameter to the thickness of the thermoplastic resin that is incompatible with polyester is less than 2, the bonding surface between the polyester and the thermoplastic resin that is incompatible with polyester becomes small, so that the thickness of the film decreases. This causes peeling of the surface layer of the film as described in the section ``Poor strength (prior art)''.

Furthermore, if the major axis diameter of the thermoplastic resin incompatible with polyester is less than tμ or if the ratio of the major axis diameter to the thickness is 100 or more, the cavity content will be low, which is not preferable.

(Example) Next, Examples and Comparative Examples of the present invention will be shown.

The measurement and evaluation methods used in the present invention are shown below.

1) Intrinsic viscosity of polyester Polyester was dissolved in a mixed solvent of phenol (6 parts by weight) and tetrachloroethane (4 parts by weight) and measured at 30°C.

2) Long axis diameter, thickness, and ratio of long axis diameter to thickness of thermoplastic resin incompatible with polyester in the film The film was cut in the cross-sectional direction with a microtome, and ruthenium tetroxide (
A product stained with ruthenium chloride hydrite and sodium hypochlorite) was photographed at 20 locations using a transmission electron microscope (JEOL model JEM-200CX), and each was photographed using an image processing device called Luzenkus IID.
(manufactured by Reco) and tabulated. In this case, the difference between polyester, polystyrene, or polymethylpentene and the cavity was determined based on the difference in the degree of staining of ruthenium tetroxide as shown below.

Polyester...Light gray polystyrene...White polymethylpentene...Dark gray cavity...Black 3) Long axis diameter of the cavity Same as item 2) 4) Appearance of the film is 5.00ci+ specific gravity of the film X 5. Accurately cut out a square of OOc+i, measure its thickness at 50 points to obtain the average thickness tμ-, and measure its weight to the nearest 0.1■ wg
It was calculated using the following formula.

Appearance is specific gravity (-) = W/ 5 x 5 x t x1
00005) Void content of film was calculated by the following formula.

Cavity content ratio (volume %) - 100X (1 - true specific volume/apparent specific volume) However, true specific volume = xl/d++xz/dz+X3/d:++
- +

The true specific gravity values used in the calculations in the examples were polyethylene terephthalate 1.40, anatase titanium dioxide 3.90, and general polystyrene resin 1.40. o5, polymethylpentene resin 0.83 was used.

6) Surface peel strength of the film: Apply cellotape CT- manufactured by Chiban Co., Ltd. to the tape on the surface of the film.
Paste 51 of 18) and make sure it sticks well.

After that, hold the area around the tape with your hand to prevent the film from moving, and peel the tape in a direction parallel to the film. The films were ranked according to the ratio of the film adhesion area to the peeled tape area as follows.

○...0 to 10% Δ...11 to 70% ×...71% or more Example 1 Raw materials: (1) 90% by weight of polyethylene terephthalate resin with an intrinsic viscosity of 0.62 and (2) melt flow indene. 3', 0 was heated to 285°C using a T-die in a twin-screw extruder.
The material was melt extruded, electrostatically assimilated in close contact with a cooling rotary roll, and then longitudinally stretched 3.2 times in SO'C using a roll drawing machine, and then laterally stretched 3.4 times at 140°C in a tenter. This was then heat-set at 220°C to obtain a translucent polyester film.

The void content of this film was 11% by volume, and no peeling of the surface layer due to the tape occurred. Moreover, there was no breakage at all.

Example 2 In Example 1, polyethylene terephthalate resin was added to 9
A white opaque hollow-containing film was obtained in exactly the same manner except that 82% by weight was reduced from 0% by weight and 8% by weight of anatase titanium dioxide (previously kneaded with a part of the resin in (1)) was added. Ta. The void content of this was 18% by volume, and there was no breakage during film formation, which caused no peeling of the surface layer due to the tape. When observing the inside of the film, it was found that most of the cavities were filled with flat polystyrene, but there were also cavities containing titanium dioxide.

Example 3 In Example 2, polyethylene terephthalate resin was
A white opaque void-containing film was obtained in exactly the same manner except that the amount of general polystyrene was reduced from 2% by weight to 72% by weight and the amount of general polystyrene was increased from 10% by weight to 20% by weight. The void content of this film was 29% by volume, there was almost no peeling of the surface layer due to the tape, and there was almost no breakage during film formation. When the inside of the film was observed, there were many cavities in which polystyrene existed in a flat shape.

Example 4 A translucent polyester film was obtained in exactly the same manner as in Example 1, except that polymethylpentene was used instead of general polystyrene. The cavity content of this is 1
8% by volume, and no peeling of the surface layer due to the tape occurred. Further, there was no breakage at all during film formation.

Comparative Example 1 In Example 2, polyethylene terephthalate resin was
A void-containing film was obtained in exactly the same manner except that the amount of polystyrene was reduced from 0% by weight to 52% by weight, and the amount of general-purpose polystyrene was increased from 10% by weight to 40% by weight. The cavity content of this is 3
At 8% by weight, surface peeling occurred due to tape. In addition, there were many breaks during film formation. When observing the inside of the film, it was found that the long axis diameter of the polystyrene and cavities had become larger.

Comparative Example 2 A void-containing film was obtained in exactly the same manner as in Example 2, except that the temperature of the tenter was changed to 100''C.

The cavity content of this sample was 21% by weight, and peeling of the surface layer due to the tape occurred, although this was less than in Comparative Example 1.

When the inside of the film was observed, some pieces of polystyrene had a shape closer to spheres than in Example 2.

Comparative Example 3 A void-containing film was obtained in exactly the same manner as in Example 2, except that the temperature of the tenter was changed to 90°C.

The cavity content of this was 24% by weight, and the surface layer peeled off due to the tape. Moreover, during film formation, many breaks occurred.

When the inside of the film was observed, the polystyrene had a spherical shape compared to Example 2 and Comparative Example 2.

Comparative Example 4 A film containing no material was obtained except that the temperature of the tenter was changed to 100°C in Example 3. The cavity content of this is 28
The surface layer peeled off due to the tape at % by weight. Moreover, during film formation, many breaks occurred.

When observing the inside of the film, the thickness of polystyrene is 10μ
- and above were also observed, and the long axis diameter of the cavity was larger than that in Example 3.

Comparative Example 5 In Example 2, the temperature of the roll stretching machine was changed from 80°C to 1
A void-containing film was obtained in exactly the same manner except that the temperature was increased to 20"C. The void content was 3% by volume. When the inside of the film was observed, the polystyrene stretched in the longitudinal direction in the form of threads, with almost no voids. I couldn't see it.

(Effects of the Invention) The polyester film and the laminate thereof according to the present invention are similar to the cavity-containing polyester film obtained by using conventional polystyrene or polypropylene as a cavity developing agent, and the polyester film without voids. It has lightness, flexibility, concealability, matteness, drawability, etc. that are not found in other films, and it is also easier to manufacture than cavity-containing polyester films obtained by using conventional polystyrene or polypropylene as a cavity developer. The frequency of breakage during film formation and clip dislodgement during tenter is suppressed, and productivity is high, manufacturing can be done at low cost, and the cavity forming agent, cavity size, thickness, etc. are appropriate. It also has excellent drawing properties and does not cause peeling of the surface layer due to tape or the like.

Therefore, the hollow polyester film of the present invention can be used in an extremely wide range of fields such as labels, posters, recording paper, and packaging materials.

Margin below

[Brief explanation of the drawing]

FIG. 10 Schematic diagram of the cross-sectional direction of an unstretched sheet of the polymer mixture. FIG. 20 Schematic diagram of the cross-sectional direction of the unstretched sheet of FIG. 1 after stretching. Schematic diagram of the cross-sectional direction of the thermoplastic resin incompatible with polyester and the cavity in the stretched film. Schematic diagram of the cross-sectional direction of the thermoplastic resin incompatible with polyester in the stretched film Figure 50 Schematic diagram of the surface of the unstretched sheet of the polymer mixture Figure 6. Schematic diagram of the surface after stretching the unstretched sheet of View 5. Schematic diagram of a thermoplastic resin incompatible with polyester and the surface of a cavity in a stretched film.8. A schematic diagram of the surface of a thermoplastic resin incompatible with polyester in a stretched film. The symbols in the figure are defined as follows. 1. Polyester in the film 2. Thermoplastic resin incompatible with the polyester in the film 3. Cavity a in the film, diameter of the major axis of the cavity, thickness of the cavity C6 diameter of the minor axis of the cavity d, non-compatible with the polyester. Major axis diameter e of compatible thermoplastic resin, thickness f of thermoplastic resin incompatible with polyester, minor axis diameter X of thermoplastic resin incompatible with polyester, thickness direction Y of the film, Short axis direction Z, long axis direction of the film, where the long axis and short axis of the film are arbitrary directions, a≧c
, d≧f. Patent applicant: Toyobo Co., Ltd. March 27, 1991

Claims (1)

[Claims] At least one polymer mixture of polyester and a thermoplastic resin incompatible with the polyester is used.
In a cavity-containing polyester film having a large number of fine cavities obtained by axial orientation, a thermoplastic resin incompatible with the polyester present in the film has a long axis diameter of 1 to 50 μm and a thickness of 10 μm or less, A cavity-containing polyester film having a ratio of major axis diameter to thickness of 2 to 100.