JPH08176330A - Void-containing polyester resin film and sheet - Google Patents

Abstract

PURPOSE: To obtain a void-containing polyester resin film such as synthetic paper, capable of evenly and efficiently forming fine voids in the whole of the film, excellent in a lightweight property, etc., and well compatible with an ink, etc., by using a crystalline polystyrene resin specified in the crystal melt peak as a void-developing agent. CONSTITUTION: A mixture containing (A) a polyester resin and (B) a thermoplastic resin incompatible with the component A is melted and extruded to obtain the objective film or sheet. Therein, a polyolefin resin having a molecular structure mainly comprising a syndiotactic structure, preferably polypropylene and/or polymethylpentene, is used as the component B. The obtained film or sheet has an apparent specific gravity of 0.6-1.3, a light transmittance of <=40%, a surface central line average roughness of <=1.0μm, and a heat sprinkage of <=2% at 150 deg.C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cavity-containing polyester resin film or sheet (hereinafter referred to as a film) which is further improved in lightness, cushioning property, drawing property and the like required when used as, for example, synthetic paper. With respect to (1), this film can be widely used as a base material for magnetic recording cards, various reflection plates, and the like, as well as synthetic paper for various purposes.

[0002]

2. Description of the Related Art Synthetic paper, which is a paper substitute made of synthetic resin as a main raw material, is more water-resistant, absorbs moisture, has dimensional stability, surface stability, and glossiness of printed matter than paper made from natural pulp. In recent years, various applications have been promoted by taking advantage of its characteristics because of its excellent clarity, mechanical strength, and the like.

[0003] The main raw materials of synthetic paper include polyolefin resins such as polyethylene and polypropylene, and polyester resins. Among them, polyester resins represented by polyethylene terephthalate have high heat resistance and high rigidity. Since it has important characteristics required for paper, it is still widely used at present.

As a method of obtaining a film having a function similar to that of natural paper using a polyester resin as a main raw material, a method of blending an inorganic pigment such as titanium dioxide or calcium carbonate into the film as a whitening means, a resin film By forming countless cavities inside, lightness and flexibility, waist,
Methods such as improving the drawability, roughening the surface of the resin film with a flat surface by sandblasting, chemical etching, matting (a method of attaching a matting agent for surface roughening together with a binder) to the surface, etc. Are known.

Of these, the most effective ones at present are the formation of countless fine voids inside the polyester resin film, which gives the film proper flexibility and excellent writability and writability. It is a method that gives clear printing and transferability. As a means for forming fine voids inside the film, a resin that is incompatible with the polyester resin (sometimes called an incompatible resin or a void developing agent) is mixed in the raw material resin, This is a method in which the film is formed into a shape and then stretched in the longitudinal and transverse directions.

As the incompatible resin (cavity-developing agent) blended in the polyester-based resin for forming a cavity, a polyolefin-based resin (JP-A-49-134755, etc.),
A large number of polystyrene-based resins (Japanese Patent Laid-Open No. 49-2016 and Japanese Patent Publication No. 54-29550), polyarylate-based resins (Japanese Patent Publication No. 58-28097, etc.), etc. have been proposed. Among these, polypropylene and polystyrene have characteristics such as excellent cavity expression, low density, and low cost. Among them, a film using polystyrene as a cavity-developing agent is a strong one. Therefore, it is preferable. However, according to what the present inventors have confirmed, when polystyrene or polypropylene etc. is used as the cavity-developing agent, those resin particles dispersed in the polyester-based resin are in the transverse stretching step for cavity formation. Because it deforms in the stretching direction,
We have found that it is not possible to develop cavities according to the draw ratio, and as a result, it is not possible to satisfactorily enhance the lightness and cushioning properties. Moreover, in the case where the ordinary polyolefin resin is used as the cavity developing agent,
The wettability of the obtained void-containing polyester resin film surface is deteriorated, which causes a problem that the coating agent, the ink and the like are repelled.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and the purpose thereof is to develop a cavity which is particularly observed when a polyolefin resin is used as a cavity developing agent. In addition to eliminating the shortage rate, it improves the wettability with coating agents and inks, and even with a small amount of cavity-developing resin, it gives a high cavity content rate according to the draw ratio, and is excellent in lightness, cushioning property, drawability, etc. Another object of the present invention is to provide a void-containing polyester resin film or sheet.

[0008]

The structure of the void-containing polyester-based resin film or sheet according to the present invention, which was able to solve the above-mentioned problems, comprises a polyester-based resin and a heat incompatible with the polyester-based resin. In a void-containing polyester resin film or sheet having innumerable fine cavities formed therein by melt-extruding a mixture containing a plastic resin and then stretching the mixture in at least one axial direction, syndiotactic as the thermoplastic resin. The gist is that it uses a polyolefin resin having a molecular structure mainly composed of tic structure. The void-containing polyester resin film according to the present invention has an apparent specific gravity of 0.6 to 1.3, a light transmittance of 40% or less, a center line average roughness of 1.0 μm or less, and a heat shrinkage rate at 150 ° C. When it is 2% or less, the performance as a synthetic paper can be further improved. Further, as the polyolefin resin having a molecular structure mainly composed of syndiotactic structure, which is used as a cavity-developing agent in the present invention, polypropylene and / or polymethylpentene are particularly preferable.

[0009]

As described above, the void-containing polyester-based resin film or sheet of the present invention (hereinafter, represented by a film again) is mainly composed of a syndiotactic structure as a resin to be blended as a void-developing agent in the polyester-based resin. A polyolefin resin having a molecular structure of, preferably polypropylene and / or polymethylpentene is used.

That is, a polyolefin resin having a molecular structure mainly composed of syndiotactic structure (hereinafter sometimes abbreviated as syndiotactic PO) means an alkyl which is a side chain with respect to a main chain composed of carbon-carbon bonds. It is a resin having a three-dimensional molecular structure in which groups are alternately located in opposite directions, and has higher crystallinity and glass transition temperature than a resin having a molecular structure mainly composed of an atactic structure. for that reason,
Syndiotactic PO dispersed in polyester resin matrix by melt mixing with polyester resin
Is rapidly crystallized by cooling after being extruded into a film, and is not melted and deformed even by heating during stretching. As a result, in the stretching step, the deformation of the syndiotactic PO hardly occurs despite the deformation of the polyester resin constituting the matrix. Therefore, in this stretching step, the matrix resin and the syndiotactic PO are not deformed. Interfacial peeling easily occurs and a cavity corresponding to the draw ratio is surely formed in that portion.
Therefore, in the present invention, those having a molecular structure preferably consisting of all syndiotactic structures are preferable, but syndiotacticity is about 80% or more, more preferably 9%.
If it is 0% or more, more preferably about 95% or more, the effect intended by the present invention is sufficiently exhibited.

Since a polyolefin resin having a molecular structure mainly composed of an atactic structure has poor crystallinity and a low glass transition temperature, it may be dispersed in a polyester resin and formed into a film in a stretching step. Since the atactic resin particles are deformed or melted and easily deformed in the stretching direction along with the stretching of the polyester resin matrix, cavities depending on the stretching ratio are not formed,
The object of the present invention cannot be achieved.

Therefore, in the present invention, the use of syndiotactic PO as a cavity-developing agent is an essential requirement, and specific examples of such syndiotactic PO include the carbons at the 1st and 2nd positions in the ethylene molecule. Although various polyolefins having various substituents can be mentioned, polypropylene and / or polymethylpentene are particularly preferable among them, and their homopolymers or copolymers, or blends thereof are used. be able to. Among these, particularly preferred examples of polypropylene having a syndiotactic structure are, for example, JP-A-2-41303, JP-A-2-41305, and JP-A-2-41305.
No. 25514, No. 4-80214, No. 4-2147
No. 09, No. 4-21814, etc. are mentioned.

The polyolefin-based resin mainly having a syndiotactic structure as described above has less low-molecular-weight components than the ordinary polyolefin-based resin mainly having an atactic structure, and when this is used as a cavity-developing agent, a cavity-containing polyester obtained. It is also possible to enjoy the advantage that the surface of the resin sheet or film becomes more compatible with the coating agent or ink and the repellency is eliminated to improve the adhesiveness.

As described above, the polyolefin-based resin mainly composed of the syndiotactic PO structure exhibits higher crystallinity than the polyolefin-based resin having the atactic structure having no stereoregularity, and is rapidly crystallized in a short time after the melt extrusion. In addition, the crystals do not melt or deform even under a high temperature condition of about 100 ° C. or more, and exhibit excellent performance as a void-developing agent during stretching. The molecular weight of the syndiotactic PO is not particularly limited, but the weight average molecular weight is preferably 10,000 to 3,000,000, more preferably 10,000 to 1,000,000.

Next, as the polyester constituting the polyester resin which is the base resin of the film of the present invention,
A polyester obtained by polycondensing an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, or naphthalenedicarboxylic acid or an ester thereof, and a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol or neopentyl glycol, These polyesters can be obtained by directly reacting an aromatic dicarboxylic acid with a glycol, or by subjecting an alkyl ester of an aromatic dicarboxylic acid and a glycol to an ester exchange reaction followed by polycondensation, or a diglycol of an aromatic dicarboxylic acid. It can also be produced by a method such as polycondensation of ester.

Typical examples of such polyesters include polyethylene terephthalate, polyethylene / butylene terephthalate, and polyethylene-2,6-naphthalate. These polyesters may be homopolymers or copolymers obtained by copolymerizing the third component, but in any case, in the present invention, ethylene terephthalate units and butylene terephthalate units are used. Alternatively, a polyester in which the proportion of ethylene-2,6-naphthalate units is 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more is preferable.

The mixture of the polyester resin and syndiotactic PO is prepared by, for example, mixing chips of each resin, melt-kneading in an extruder, and then extruding and solidifying.
A method in which both resins are previously kneaded by a kneading machine and further melt-extruded from an extruder to solidify, and chips obtained by adding syndiotactic PO in a polymerization step for producing a polyester resin and stirring and dispersing. Can be obtained by melt-extruding and solidifying.

At this time, the preferable blending amount of the syndiotactic PO with respect to the polyester resin varies depending on the amount of void formation required for the film finally obtained and the stretching conditions, but it is usually in the total amount of the resin. It is selected from the range of 5 to 50% by weight, more preferably 8 to 35% by weight. If it is less than 5% by weight, however, the amount of voids generated in the stretching step becomes insufficient, and it becomes difficult to obtain satisfactory lightness, flexibility, drawability, and writability. On the other hand, if it exceeds 50%, it becomes excessive. In that case, the stretchability may be remarkably lowered, and the heat resistance, strength, waist strength, etc. may be impaired.

In the present invention, in addition to the above polyester resin and syndiotactic PO, it is also effective to add inorganic or organic fine particles to impart a concealing property (impermeable or whiteness) to the film. is there. Examples of such fine particles include silica, kaolin, talc, calcium carbonate, magnesium carbonate, strontium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, titanium oxide, barium sulfate, and other inorganic fine powder, or crosslinked polymer. Organic fine powders such as and organic white pigments are exemplified, and two or more kinds of them can be added in combination if necessary. If necessary, an antistatic agent, an ultraviolet absorber, an antioxidant, an optical brightening agent, a coloring agent and the like may be contained in appropriate amounts as other components.

The void-containing polyester resin film according to the present invention is composed of the above-mentioned components, has a large number of fine voids formed therein by uniaxial or biaxial stretching, and has a single layer structure. Although it may be a layer or a multi-layer structure having two or more layers, the void content is 10 to 50% by volume, more preferably 15 to 30% by volume, and the apparent specific gravity is 0.6 to 1 .3, more preferably 0.
9 to 1.25, light transmittance is 40% or less, more preferably 20% or less, center line average roughness of the surface is 1.0 μm or less, more preferably 0.1 to 1.0 μm, heat shrinkage at 150 ° C. The ratio is preferably 2% or less, more preferably 1.5% or less, still more preferably 1.0% or less.

However, if the void content is less than 10% by volume, flexibility and cushioning properties tend to be inadequate, and writability with a particularly hard pencil becomes insufficient, while 50% by volume.
When it exceeds, the film becomes inferior in initial elastic modulus, strength, waist and the like. Further, if the apparent specific gravity is less than 0.6, the void ratio is too high, resulting in weakness and weakness, and if it exceeds 1.3, the lightness, cushioning property, flexibility, and drawability tend to be insufficient due to lack of voids. The tendency is to become Although the preferable light transmittance varies depending on the use, especially when it is used as a synthetic paper, if the light transmittance exceeds 40%, the hiding property tends to be lowered and so-called character transfer tends to occur. , 40% or less is preferable.

The preferred center line average roughness also varies depending on the use, but it should normally be 1.0 μm or less, more preferably 0.1 to 1.0 μm,
If it exceeds 1.0 μm, a problem arises in the sharpness of the printed image. When the thickness is less than 0.1 μm, the drawability tends to be insufficient especially when used as synthetic paper. The heat shrinkage rate at 150 ° C is a characteristic that particularly affects the thermal dimensional stability as a film, and if it exceeds 2%, insufficient dimensional stability at high temperatures poses a problem when applied to various applications. May be. However, as long as the film or sheet meets the above-mentioned characteristic range, it can be used without any problems not only as a synthetic paper but also in various other applications.

In producing the void-containing polyester resin film of the present invention, a mixture containing the polyester resin as described above and the syndiotactic PO as described above, for example, chips of each resin are melt-mixed in an extruder. A method of extruding the mixture into a film or a sheet, a method of pre-kneading both resins with a kneader and the like and then melt-extruding with an extruder, and adding Sondiotactic PO in the polymerization step during the production of polyester. Alternatively, a method in which a mixture in which syndiotactic PO is mixed in a dispersed state is manufactured and melt extrusion molding is performed using this as a raw material can be adopted.

In melt extrusion, the specific conditions are not particularly limited as long as the syndiotactic PO can be finely and uniformly dispersed in the polyester resin. The film or sheet is prepared by mixing the tactic PO and extruding the mixture into a film or sheet, whereby the syndiotactic PO is finely spherical, elliptical, monofilament-shaped, or any other shape in the polyester resin matrix. A non-oriented or weakly oriented film or sheet uniformly dispersed as a shape is obtained.

The unstretched film or sheet thus obtained is subsequently stretched between two or a plurality of rolls having different peripheral speeds, or a tenter stretching method in which both sides of the film are held by clips and spread. Or by an inflation stretching method or the like in which stretching is performed by expanding using air pressure or the like.
Stretching in the axial direction, preferably biaxial direction. In this stretching step, interfacial peeling occurs between the polyester resin that constitutes the matrix and the syndiotactic PO, and fine voids are formed in that portion. At this time, since the syndiotactic PO is crystallized in the unstretched state as described above and crystal melting does not occur under the stretching temperature condition, plasticizing deformation of the syndiotactic PO hardly occurs in the stretching step, Cavities are surely formed according to the draw ratio.

The preferred conditions for the stretching cannot be specified uniformly because they vary depending on the target void content, the amount of syndiotactic PO compounded, etc. Direction draw ratio is 1.2
~ 4.0 times, the stretching temperature is in the range of 95 ~ 140 ℃,
If the longitudinal stretching ratio is less than 1.2 times, the void formation rate tends to be insufficient, weight reduction, flexibility and cushioning properties will not be sufficiently improved, and the strength will also be insufficient, while if it exceeds 4.0 times, Lateral stretching often becomes difficult. When the stretching temperature is lower than 95 ° C, the softening of the film or sheet is insufficient, so that stable stretching cannot be performed. On the other hand, when the stretching temperature is higher than 140 ° C, crystallization progresses during stretching and subsequent lateral stretching. Sex is significantly impaired.

For heating during stretching, any method such as roll heating or infrared heating may be adopted. Further, it is possible to provide a guide roll, a nip roll, or the like at an arbitrary position of the preheating or stretching roll.

After the above-mentioned longitudinal stretching, it is desirable to perform a relaxation treatment if necessary and then stretch in the transverse direction. However, by only stretching in the machine direction, not only the anisotropy of the obtained film becomes too strong and the tear resistance deteriorates, but also the cavity formed is stretched only in the machine direction.
This is because it is difficult to sufficiently improve the weight reduction effect, flexibility, cushioning properties, and the like. However, when the film is laterally stretched with a tenter or the like thereafter, the anisotropy of the film is eliminated to make it isotropic and tear resistance is improved, and the cavity stretched in the longitudinal direction in the longitudinal stretching step is further expanded in the lateral direction. When the film is stretched, the void ratio is increased and a film or sheet having a high void content can be obtained.

The preferred conditions for transverse stretching are a stretching ratio of 1.
The stretching temperature is in the range of 2 to 4.0 and the stretching temperature is in the range of 100 to 160 ° C. If it is less than 1.2 times, the effect of improving the anisotropy will be insufficient and the void ratio will not be sufficiently increased, and conversely 4. When it exceeds 0 times, the stretching in the transverse direction becomes dominant and anisotropy in the transverse direction occurs, and tears and the like easily occur in the transverse stretching process. On the other hand, if the stretching temperature is less than 100 ° C, the softening of the film will be insufficient and the stretching operability will be poor, and if the stretching temperature exceeds 160 ° C, the film will be excessively softened and may be broken.

After the longitudinal / transverse stretching is performed as described above, it is preferable to heat-set by heating to 170 to 240 ° C., preferably 200 to 240 ° C. At this time, it is preferable to perform a relaxation treatment of about 2% in the longitudinal / horizontal direction in parallel, since a void-containing polyester resin film or sheet having more stable various physical properties can be obtained.

The void-containing polyester resin film or sheet according to the present invention thus obtained can form sufficient voids with a relatively small amount by selecting and using syndiotactic PO as a void-developing agent. Therefore, the flexibility, cushioning property, drawing property, writing property, and the like are further improved as compared with a cavity-containing polyester resin film or sheet using a usual cavity-developing agent such as polypropylene or polystyrene.
Moreover, the repellency of the coating agent and the ink, which is seen when a polyolefin resin mainly composed of atactic structure is used as a cavity-developing agent, is also prevented, and it is well compatible with these coating agents and inks, and their adhesiveness and adhesiveness Is also increased. In consideration of processability and the like, this film preferably has an initial elastic modulus of 250 kg / mm ² or more. If the initial elastic modulus is insufficient, problems may occur during post-processing such as printing. .

The void-containing polyester resin film or sheet according to the present invention has improved adhesiveness as described above by selecting the void-developing agent, but if necessary, one or both of the surfaces may be further added. It is also effective to form a coating layer for improving adhesion. As a main constituent of the coating layer, a polyester resin having a good affinity with the film is preferable, but other than the usual polyester resin film such as polyurethane resin, polyester / urethane resin, acrylic resin, etc. The resin used for improving the adhesiveness can be appropriately selected and used. As a method for forming such a coating layer, any method such as a gravure coating method, a kiss coating method, a dip coating method, a spray coating method, a curtain coating method, an air knife coating method, a grade coating method and a reverse coating method can be adopted. it can. The coating may be performed in any of the unstretched state before the stretching treatment, after the longitudinal stretching or the longitudinal relaxation treatment, and after the lateral stretching or the lateral relaxation.

The film or sheet of the present invention is one in which fine cavities are formed by using the specific cavity-developing agent as described above, and it is as described above that it includes a single layer or multiple layers. However, examples thereof include a biaxially stretched void-containing polyester resin film on which at least one surface is laminated with various resin films or melt-extruded and laminated.

In this case, a multilayer film may be formed by laminating a layer made of another material on at least one surface of the basic void-containing polyester resin layer. The method is not particularly limited, and for example, a method of laminating a molten thermoplastic resin on at least one surface of a biaxially stretched void-containing film, a method of laminating a molten thermoplastic resin on at least one surface of the uniaxially stretched film, A method of further stretching the laminate in the perpendicular direction, a method of laminating another already stretched film using an adhesive or a pressure-sensitive adhesive, and the like can be adopted. However, in view of productivity, the raw materials for the surface layer and the central layer are extruded from different extruders, respectively, and introduced into one die to obtain an unstretched sheet, and then at least 1
Most preferred is a lamination by a so-called co-extrusion method of orienting in the axial direction.

In this case, if the surface layer and the central layer contain different additives such as inorganic particles, antistatic agents, ultraviolet absorbers, optical brighteners, and antioxidants, the required characteristics can be met. It becomes easy to obtain a laminated film. For example,
In order to achieve both slipperiness and hiding power (opacity), the surface layer contains particles with a particle size larger than that of the central layer. Examples include a method in which treated rutile titanium dioxide and the central layer contain titanium dioxide, calcium carbonate, or the like.

The thus obtained fine void-containing polyester resin film is very excellent in flexibility, cushioning property, drawing property, writability, adhesiveness of coating agent and ink, etc. as compared with the conventional void-containing polyester resin film. In addition, it has excellent performances such as water resistance, moisture absorption, dimensional stability, surface stability, gloss and sharpness of printed matter, and mechanical strength. This film or sheet is therefore a label, sticker, poster,
Cards, recording paper, packaging materials, video printer image receiving paper, bar code labels, bar code printer image receiving paper,
Thermal transfer image receiving paper, thermal recording paper, sublimation transfer image receiving paper, inkjet image receiving paper, offset printing paper, foam printing paper, map, dust-free paper, sign board, white board, electronic white board, photographic paper,
Decorative paper, wallpaper, building materials, banknotes, release paper, origami, calendars, magnetic cards, tracing paper, slips, delivery slips, pressure-sensitive recording paper, copy paper, clinical test paper, and parabolic antenna reflectors and display reflectors. It can be effectively used for various purposes such as a base material of.

[0037]

EXAMPLES Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and may be appropriately applied within a range compatible with the gist of the above and the following. Modifications can be made and they are all included in the technical scope of the present invention. The measurement and evaluation methods employed in the following examples are as follows. (Apparent specific gravity) The film was accurately cut into a square of 5.0 cm × 5.0 cm, the thickness was measured at 50 points, the average thickness was taken as t (μm), and the weight thereof was accurately measured to 0.1 mg. Then, the apparent specific gravity is calculated by the following formula. Apparent specific gravity = w / 5 × 5 × t × 10000

(Average void content) Calculated by the following formula. Average void content (volume%) = 100 × (1-true specific volume /
Apparent specific volume) However, true specific volume = x1 / d1 + x2 / d2 + x3 / d3 + …… xi / di Apparent specific volume = 1 / Apparent specific gravity of film xi is the weight fraction of i component, di is the i component True Specific Gravity The value of true specific gravity in the examples is polystyrene 1.05,
Anatase type titanium dioxide 3.9, spherical zeolite 2.
4, polyethylene terephthalate 1.4 was used.

(Centerline average roughness) JIS-B601-1
Measured by 982. The measurement length is 2.5 mm, the cutoff is 0.8 mg, and the measurement speed is 0.3 mm. (Heat Shrinkage) The film is cut into a width of 10 mm and a length of 250 mm, marked at intervals of 200 mm, fixed with a constant tension of 5 g, and the distance A between the marks is measured. Then, put it in an oven in an atmosphere of 150 ° C. for 30 minutes under no tension and leave the mark B
Is measured, and the heat shrinkage rate is calculated by the following formula. Heat shrinkage rate (%) = [(A−B) / A] × 100

(Light transmittance) In accordance with JIS-K6714, Poic integrating sphere type H.264. T. Using an R meter (manufactured by Nippon Seimitsu Optical Co., Ltd.), measure the light transmittance of the film. The smaller this value, the higher the concealing property. (Pencil drawability) Characters were written on the film with a pencil having a hardness of 2H, and those clearly visible were marked with ◯, and unclear ones were marked with x.

(Ink repelling) On the surface of the film, a solvent type polyester resin adhesive (manufactured by Toyobo Co., Ltd.) and a polyurethane curing agent (Takenate D110 manufactured by Takeda Pharmaceutical Co., Ltd.) are used.
N ") in a solids weight ratio of 200: 1.
It was coated using a gravure coater so that the dry thickness would be 0.2 μm. After that, a water-based ink (“Aqua Color 39 Indigo” manufactured by Toyo Ink Co., Ltd.) was applied by gravure coating so that the dry thickness was 2 μm, and the ink repelling at this time was recognized as ×, not recognized. Was marked as ○.

Example 1 85 parts by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, 10 parts by weight of a syndiotactic polypropylene copolymer resin having a syndiotacticity of 95% and a weight average molecular weight of 430,000 and titanium dioxide (Fuji Titanium). (“TA-300” manufactured by the company), 5 parts by weight are uniformly melt mixed,
Melt extrusion was performed from a T-die at 290 ° C., and cooling and drawing were performed while electrostatically adhering to a cooling roll to obtain an unstretched sheet.

This sheet was longitudinally stretched 3.3 times at 98 ° C. by utilizing the peripheral speed difference of the rolls, and subsequently stretched 3.5 times laterally at 140 ° C. by a tenter.
Then, it was heat-set at 250 ° C. while being subjected to a 4% relaxation treatment to finally obtain a 100 μm void-containing polyester resin film.

Comparative Example 1 A cavity-containing polyester resin film was obtained in the same manner as in Example 1 except that atactic polypropylene (“WF5088” manufactured by Union Polymer Co., Ltd.) was used instead of syndiotactic polypropylene. It was The apparent specific gravity, void content, light transmittance, heat shrinkage, pencil drawability, and ink repellency of the films obtained in the above Examples and Comparative Examples were examined, and the results shown in Table 1 were obtained.

[0045]

[Table 1]

As is clear from Table 1, the void-containing polyester resin film of the present invention using polypropylene having a syndiotactic structure as a void-developing agent has a void content ratio relative to the apparent specific gravity of the comparative film. Tall and minute cavities are efficiently formed all over, and this is also reflected in the tendency that the light transmittance is relatively small.

The films of the examples have a larger surface roughness than the comparative films, but both have a surface roughness of 1.0 μm or less, and there is no problem in appearance. However, the pencil drawability is rather enhanced due to the roughened surface due to the efficient formation of minute cavities. Further, the film of the present invention has better compatibility with the ink than the comparative film, and excellent results are obtained in repelling the ink.

[0048]

EFFECTS OF THE INVENTION The present invention is configured as described above, and by using a crystalline polystyrene resin having a specified crystal melting peak as a cavity-developing agent, it is possible to form fine voids in the polyester resin as a whole. It can be formed evenly and efficiently throughout, and has excellent properties such as light weight, cushioning property, drawing property, etc., and it is well compatible with coating agents and inks, and its repelling is suppressed and excellent adhesion It has become possible to provide a void-containing polyester-based resin film or sheet exhibiting properties.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshitake Suzuki 2-1-1 Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd.

Claims (3)

[Claims] 1. A large number of fine voids are formed inside by melt-extruding a mixture containing a polyester-based resin and a thermoplastic resin incompatible with the polyester-based resin and then stretching the mixture in at least one axial direction. A void-containing polyester resin film or sheet formed by using a polyolefin resin having a syndiotactic structure-based molecular structure as the thermoplastic resin. Or sheet. 2. The apparent specific gravity is 0.6 to 1.3, the light transmittance is 40% or less, the center line average roughness of the surface is 1.0 μm or less, and the thermal shrinkage at 150 ° C. is 2% or less. Item 2. The void-containing polyester resin film or sheet according to Item 1. 3. The void-containing polyester resin film or sheet according to claim 1, wherein the polyolefin resin is polypropylene and / or polymethylpentene.