JPH08176329A - 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, a cushioning property, a drawing property, 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 crystalline polystyrene resin having a crystal melt peak of >=1cal/g determined with a differential scanning calorimeter, preferably the polystyrene resin mainly having a syndiotactic structure, 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.

Among these, the most effective of these is that the polyester resin film has a large number of minute cavities formed therein, thereby imparting appropriate flexibility to the film itself, as well as excellent writability and vividness. It is a method of providing excellent printability 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.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and its object is the cavity expression rate observed when a polystyrene resin is used as a cavity developing agent. Provide a void-containing polyester resin film or sheet that solves the shortage and gives a high void content according to the draw ratio even when a small amount of polystyrene-based resin is blended, and is excellent in lightness, cushioning property, drawability, etc. It is what

[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. A void-containing polyester-based 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. The gist is that the crystalline polystyrene resin having a crystal melting peak of 1 cal / g or more as determined by a calorimeter is used. The void-containing polyester resin film according to the present invention has an apparent specific gravity of 0.6 to 1.
3. By setting the light transmittance to 40% or less, the center line average roughness of the surface to 1.0 μm or less, and the heat shrinkage rate at 150 ° C. to 2% or less, the performance as a synthetic paper is further improved. can do. Further, as the crystalline polystyrene resin used as the cavity developing agent in the present invention, those having a structure mainly composed of syndiotactic are recommended as being particularly preferable.

[0009]

As described above, the void-containing polyester resin film or sheet of the present invention (hereinafter, represented by a film again) is a polystyrene resin blended with the polyester resin as a void-developing agent by a differential scanning calorimeter. A crystalline polystyrene resin having a required crystal melting peak of 1 cal / g or more is used, and such a highly crystalline polystyrene resin is uniformly dispersed in a polyester resin as a base resin in a dispersed state. After being mixed and melt-extruded, when it is cooled and solidified, it rapidly crystallizes in a state of being dispersed in the polyester resin film, and the crystal melting does not occur even by heating during stretching. As a result, in the subsequent stretching step, despite the deformation of the polyester resin constituting the matrix, the crystallized polystyrene resin was hardly deformed,
Therefore, in this stretching step, interfacial peeling occurs between the matrix resin and the crystallized polystyrene resin, and a cavity corresponding to the stretching ratio is surely formed in that portion.

In order to effectively exert such a cavity-producing effect, the crystal melting peak of polystyrene resin determined by the differential scanning calorimeter as described above is 1 ca.
It was confirmed that a crystalline polystyrene resin having a l / g or more should be selectively used. By the way, in the case of an amorphous polystyrene resin or a polystyrene resin having a crystalline melting peak of less than 1 cal / g even if it is crystalline, it is dispersed in a polyester resin and formed into a film in a stretching step, Since the polystyrene resin particles are deformed or melted and simultaneously deformed in the stretching direction, cavities corresponding to the stretching ratio are not formed and the object of the present invention cannot be achieved.

Therefore, in the present invention, it is an essential requirement that a crystalline polystyrene resin satisfying the above-mentioned crystal melting peak is used as a cavity-developing agent, and further additional requirements are not particularly required. For example, a resin mainly having an isotactic structure or a resin mainly having a syndiotactic structure can be used, and among them, a crystalline polystyrene resin mainly having a syndiotactic structure is particularly preferable. That is, the syndiotactic structure is a polymer structure having a stereo structure in which a phenyl group or a substituted phenyl group, which is a side chain, is alternately located in the opposite direction with respect to a main chain composed of carbon-carbon bonds, and has a stereoregular structure. It exhibits higher crystallinity than polystyrene-based resin with atactic structure, which has no property, and crystallizes rapidly in a short time after melt extrusion, and the crystal does not melt or deform even under high temperature conditions of 100 ° C or higher, and is stretched. It exhibits outstanding performance as a cavity-developing agent. The molecular weight of the crystalline polystyrene resin 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.

Specific examples of the polystyrene resin include styrene homopolymer, styrene and o-methylstyrene, p-methylstyrene, m-methylstyrene,
Alkyl styrenes such as 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, p-tert-butylstyrene, halogenated styrenes, halogenated alkylstyrenes and alkyl ethers. Styrene-based copolymers obtained by copolymerizing copolymerizable monomers such as styrene and ethyl vinylbenzene sulfonate can be used, but it is preferable to copolymerize an appropriate amount of the above-mentioned copolymerizable monomers. It is a styrene copolymer having a lower melting point and improved kneadability with a polyester resin. However, these styrene-based copolymers must also be crystalline with a crystal melting peak of 1 cal / g or more as determined by a differential scanning calorimeter, and the structure thereof is syndiotactic for the reasons described above. A structure is preferable.

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. Representative 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 the crystalline polystyrene resin is prepared by, for example, mixing chips of each resin, melting and kneading in an extruder, and then extruding and solidifying.
A method in which both resins are previously kneaded by a kneader is melt-extruded from an extruder and solidified, and a chip obtained by adding polystyrene resin in a polymerization step to produce a polyester resin and stirring and dispersing It can be obtained by a method such as melt extrusion and solidification. The preferable blending amount of the crystalline polystyrene-based resin with respect to the polyester-based resin at this time varies depending on the amount of cavity formation and the stretching conditions required for the film finally obtained, but is usually a ratio in the total amount of the resin. In 5
˜50% by weight, more preferably 8 to 35% by weight. However, if it is less than 5% by weight, the amount of voids generated in the stretching step becomes insufficient, and it becomes difficult to obtain satisfactory lightness, flexibility, drawability, and writability.
If it exceeds the above range, the stretchability may be significantly reduced, and the heat resistance, strength, waist strength, etc. may be impaired.

In the present invention, in addition to the above polyester resin and crystalline polystyrene resin, it is also effective to add fine particles of inorganic or organic substance to impart a concealing property (impermeable or whiteness) to the film. Is.
Such fine particles include silica, kaolin, talc,
Examples include inorganic fine powders such as calcium carbonate, magnesium carbonate, strontium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, titanium oxide and barium sulfate, or organic fine powders such as crosslinked polymers and organic white pigments. However, two or more of these 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, and has a myriad of minute voids formed therein by uniaxial or biaxial stretching, and has a layered structure. Although it may be a single layer or a multi-layer structure of 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.
The heat shrinkage is preferably 0.1% to 1.0 μm and more 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 especially writability with a 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 used as synthetic paper, the light transmittance tends to cause so-called ghosting due to a decrease in the hiding power of more than 40%. % Or less is preferable.

The preferred centerline average roughness also varies depending on the use, but the standard preferred roughness is 1.0 μm or less, more preferably 0.1 to 1.0 μm, and 0.1
If the thickness is less than μm, the drawability tends to be insufficient especially when used as synthetic paper, and if the thickness exceeds 1.0 μm, a problem occurs in the sharpness of a printed image. 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 crystalline polystyrene resin as described above, for example, a chip of each resin is melted in an extruder. A method of extruding the mixed mixture into a film or a sheet, a method of kneading both resins in advance with a kneader and the like and a method of melt extruding with an extruder, and adding a crystalline polystyrene resin in the polymerization step when producing polyester Alternatively, a method of producing a mixture in which a crystalline polystyrene resin is mixed in a dispersed state and performing melt extrusion molding using this as a raw material can be adopted.

In melt extrusion, the specific conditions are not particularly limited as long as the crystalline polystyrene resin can be finely and uniformly dispersed in the polyester resin. By mixing and extruding a crystalline polystyrene resin into a film or sheet, the film or sheet has a fine spherical crystalline polystyrene resin in a polyester resin matrix, an ellipse, a single fiber,
Alternatively, a non-oriented or weakly oriented film or sheet uniformly dispersed as another irregular shape can be 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 gripped and spread by clips. 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-based resin and the crystalline polystyrene-based resin that form the matrix, and fine voids are formed in that portion. At this time, since the crystalline polystyrene resin is crystallized in the unstretched state as described above and crystal melting does not occur under the stretching temperature condition, plastic deformation of the crystalline polystyrene resin hardly occurs in the stretching step. The cavities are surely formed according to the draw ratio.

The preferable conditions for stretching vary depending on the target void content, the compounding amount of the crystalline polystyrene resin, and the like, and therefore cannot be uniformly defined.
If shown as standard conditions, the longitudinal stretching ratio is 1.
2 to 4.0 times, the stretching temperature is in the range of 95 to 140 ° C., and if the longitudinal stretching ratio is less than 1.2 times, the void formation rate tends to be insufficient and the weight reduction, flexibility and cushioning property are sufficiently improved. In addition to the above, the strength also tends to be insufficient. On the other hand, when it exceeds 4.0 times, it becomes difficult to perform lateral stretching which is often performed thereafter. 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 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, if the film is then stretched in the transverse direction using a tenter, etc., the film's anisotropy is eliminated and the film becomes isotropic, and tear resistance is improved. When the film is stretched, the void ratio is increased and a film or sheet having a high void content can be obtained.

A preferable condition for the transverse stretching is that the stretching ratio is 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 has a relatively small blending amount by selectively using a crystalline polystyrene resin having a specified crystal melting peak as a void-developing agent. Sufficient cavities can be formed, and it is further improved in flexibility, cushioning property, drawing property, writability, etc. as compared with a cavity-containing polyester resin film or sheet using ordinary polypropylene or polystyrene as a cavity developing agent. It becomes a thing.

It is also effective to form a coating layer on the one or both sides of the void-containing polyester resin film or sheet according to the present invention to improve wettability with ink or the like or adhesiveness. Is. 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 additives such as the inorganic particles, the antistatic agent, the ultraviolet absorber, the fluorescent whitening agent and the antioxidant are changed to different ones for the surface layer and the central layer, respectively, the required characteristics can be met. It becomes easy to obtain a multilayer film. For example, in order to achieve both slipping property and hiding property (opacity), the surface layer may contain particles having a larger particle size than the central layer, or in order to achieve both the ultraviolet protection effect and the hiding property, the surface layer may be provided with an ultraviolet protection agent. And surface-treated rutile titanium dioxide, and the central layer may contain titanium dioxide, calcium carbonate, or the like.

The fine void-containing polyester resin film thus obtained has extremely excellent flexibility, cushioning property, drawing property, writing property, etc., as compared with the conventional void-containing polyester resin film, and is water resistant. , Excellent hygroscopicity, dimensional stability, surface stability, gloss and sharpness of printed matter, and mechanical strength. Therefore, this film or sheet is a label, a sticker, a poster, a card, a recording paper, a packaging material, a video printer image receiving paper, a bar code label, a bar code printer image receiving paper, a thermal transfer image receiving paper, a thermal recording paper, a sublimation transfer image receiving paper, Inkjet image receiving paper, offset printing paper, foam printing paper, map, dust-free paper, sign board, white board,
Electronic whiteboard, photographic paper, decorative paper, wallpaper, building materials, banknotes, release paper, origami, calendars, magnetic cards, tracing paper, slips, delivery slips, pressure-sensitive recording paper, copying paper, clinical test paper, and parabolic antennas. It can be effectively used for various applications such as a base material for a reflector or a display reflector.

[0033]

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.

Example 1 90 parts of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 10 parts by weight of a syndiotactic polystyrene copolymer resin having a weight average molecular weight of 290,000 were melt-mixed uniformly, and 285 ° C. from a T-die. Was melt-extruded and cooled and drawn while electrostatically adhering to a cooling roll to obtain an unstretched sheet.

The syndiotactic polystyrene copolymer resin used here was a 96/4 (molar ratio) copolymer of styrene and p-methylstyrene, and the syndiotacticity was 89%. The copolymer resin used a differential scanning calorimeter (“DSC-10A” manufactured by Rigaku Denki Co., Ltd.) and the heat of fusion at 250 ° C. when the temperature was raised at 20 ° C./min.
It is crystalline with a melting peak of 7 Cal / g.

This sheet was stretched 3.3 times in the longitudinal direction at 85 ° C. by utilizing the peripheral speed difference of the rolls, and subsequently stretched 3.5 times in the transverse direction at 140 ° C. by a tenter. Then 2
It was heat-set by a 4% relaxation treatment at 50 ° C., and finally a 100 μm void-containing polyester resin film was obtained.

Example 2 As a raw material resin for the layer A, 80 parts by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, 15 parts by weight of the syndiotactic polystyrene copolymer resin used in Example 1 and an average particle diameter of 0.35 μm were used. A mixture of 5 parts by weight of anatase type titanium dioxide was used, and 98 parts by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.64 and spherical zeolite particles ("J" manufactured by Mizusawa Chemical Co., Ltd.
C-20 ") 2 parts by weight of the mixture are used, these are melt mixed in separate melt extruders, then coextruded from a T-die and drawn exactly as in Example 1 below to obtain the final A void-containing laminated polyester resin film having a thickness ratio of B / A / B = 5/90/5 was obtained.

Example 3 In Example 1, instead of the syndiotactic polystyrene copolymer resin, syndiotacticity was 98%.
10 parts by weight of a crystalline polystyrene resin consisting essentially of styrene and 3 parts by weight of a general polystyrene resin (“T-500-57U” manufactured by Mitsui Toatsu Chemicals, Inc.) are used, and the extrusion conditions are the melting part of the extruder. Cylinder temperature of 305
A void-containing polyester resin film was obtained in exactly the same manner, except that the temperature of C and the temperature of the T-die were 285 ° C.

Comparative Example 1 In place of the syndiotactic polystyrene copolymer resin of Example 1, a general atactic polystyrene resin ("T-500-57U" manufactured by Mitsui Toatsu Chemicals, Inc.) was used. Similarly, a void-containing polyester resin film was obtained. The atactic polystyrene resin was an amorphous resin having no crystalline melting peak. The obtained void-containing polyester resin film,
The void content was lower than that of the film of Example 1 and the drawability was poor.

Comparative Example 2 A copolymer resin of styrene / p-methylstyrene = 70/30 (an amorphous resin having no crystal melting peak) was used in place of the syndiotactic polystyrene copolymer resin in Example 1 above. A void-containing polyester resin film was obtained in the same manner except that was used. The void content of this product was low, and the drawability was poor.

Table 1 shows the apparent specific gravity, void content, light transmittance, crystal melting peak of the void developing agent used, thermal shrinkage, surface roughness and pencil drawability of each film obtained in the above Examples and Comparative Examples. Collectively shown.

[0045]

[Table 1]

As is clear from Table 1, the void-containing polyester resin film of the present invention in which a crystalline polystyrene resin having a high crystal melting peak is used as a void-developing agent has a void relative to an apparent specific gravity. The content is high, and the fine cavities are efficiently formed over the entire area. 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, it can be seen that the pencil drawability is remarkably improved by roughening the surface by the efficient formation of the fine cavities.

[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 has become possible to provide a void-containing polyester resin film or sheet that can be formed uniformly and efficiently throughout and has further excellent properties in terms of lightness, cushioning properties, drawing properties, and the like.

 ─────────────────────────────────────────────────── ─── 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 number of fine cavities are formed inside by melt-extruding a mixture containing a polyester resin and a thermoplastic resin incompatible with the polyester resin and then stretching the mixture in at least one axial direction. In the void-containing polyester resin film or sheet formed, a crystalline polystyrene resin having a crystal melting peak of 1 cal / g or more determined by a differential scanning calorimeter is used as the thermoplastic resin. Characteristic void-containing polyester resin film 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 crystalline polystyrene resin has a syndiotactic main structure.