JP2013213082A - Easily tearable surface-roughened biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-roughened biaxially oriented polyester film which exhibits straightness of tear, has reduced haze value unevenness in the machine direction and enables homogenization of the roughened surface.SOLUTION: An easily tearable surface-roughened biaxially oriented polyester film is produced using a starting material prepared by mixing 58-89 pts.mass of a thermoplastic polyester resin (A), 6-12 pts.mass of an amorphous polyamide (B) having a higher glass transition temperature than the thermoplastic polyester resin (A), and 5-30 pts.mass of a polybutylene terephthalate (C) containing 5-20 mass% of a polytetramethylene glycol unit so that the total of (A) to (C) is made 100 pts.mass, wherein the film is characterized in that a variation of haze value measured at intervals of 100 m in the machine direction (MD) is ≤3%.

Description

  The present invention relates to an easily tearable roughened biaxially stretched polyester film having a controlled flow direction (MD) surface roughness and useful in fields such as magnetic tapes, capacitors, and packaging.

  Biaxially stretched polyester films represented by polyethylene terephthalate have excellent physical and chemical properties and are used in many applications such as magnetic recording materials, packaging materials, photosensitive materials, and various photographic materials. These polyester films have different required properties depending on their applications, and it is necessary to roughen the surface from the viewpoints of process passability during production, processing, workability during handling, and writing properties.

  As a method for roughening the film surface, Patent Document 1 discloses that a thermoplastic polyester resin is 90 to 96% by mass and a thermoplastic resin having a high glass transition temperature (Tg) such as an amorphous polyamide resin is 10 to 4% by mass. A biaxially stretched roughened film and a method for producing the same are disclosed.

  The biaxially stretched polyester film can be increased in production line width and film width (for example, 5 m or more) due to advances in equipment and manufacturing technology. On the other hand, it becomes difficult to produce a stretched film having uniform physical properties as the stretcher becomes larger. When the maximum value of the haze in the width direction of the stretched film is Hmax, and the haze of other portions in the width direction other than Hmax is H, the stretch start point of the film corresponding to the position of the haze H (preheating zone and It is patented that the haze in the width direction of the stretched film can be made uniform by adjusting the temperature at the boundary point of the stretching zone) higher than the temperature at the stretching start point of the film corresponding to the position of Hmax and simultaneously biaxially stretching. It is disclosed in Document 2. However, this method makes the haze uniform only in the width direction, and a haze fluctuation of about 8% occurs in the MD direction.

JP-A-6-206291 Japanese Patent Laid-Open No. 10-211649

  An object of the present invention is to solve the above problems in a roughened biaxially stretched polyether film.

  As a result of intensive studies to solve the above problems, the present inventor mixed a suitable amount of polybutylene terephthalate containing a polytetramethylene glycol unit into a roughened biaxially stretched polyester film having a conventional composition, whereby the flow direction ( It was found that the non-uniformity in the haze of MD) can be reduced, and the present invention has been achieved. The summary is as follows.

  58 to 89 parts by mass of the thermoplastic polyester resin (A), 6 to 12 parts by mass of an amorphous polyamide (B) having a glass transition temperature higher than that of the thermoplastic polyester resin (A), and 5 to 20 parts by mass of polytetramethylene glycol units. % Of polybutylene terephthalate (C) containing 5 to 30 parts by mass and (A) to (C) is a film manufactured using a raw material with a total of 100 parts by mass, in the flow direction (MD) An easily tearable roughened biaxially stretched polyester film having a haze variation rate of 3% or less measured every 100 m.

  According to the present invention, by blending a predetermined amount of the modified PBT in the roughened biaxially stretched polyester film, not only the expression of straightness of tearing but also the haze unevenness in the flow direction is reduced and the rough surface can be homogenized. An unexpected remarkable effect is obtained, and the industrial utility value of the present invention is high.

Hereinafter, the present invention will be described in more detail.
The thermoplastic polyester resin (A) used in the present invention is a polycondensate such as dicarboxylic acid, diol, or oxycarboxylic acid.

  Examples of the diol component include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, and 2,6-naphthalene dicarboxylic acid. An acid etc. are mentioned. Examples of the oxycarboxylic acid include p-oxybenzoic acid.

  Specific thermoplastic polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), poly-1,4-cyclohexylenedimethylene terephthalate (PCT), poly-p-ethylene. Oxybenzoate (PEBO) and copolymers or mixtures thereof are preferably used.

  The Tg of the thermoplastic polyester resin (A) preferably used is measured by a differential thermal analysis (DSC) method. PET is about 70 ° C., PBT is about 50 ° C., PEN is about 120 ° C., PCT is about 95 ° C., PEBO About 60 ° C. is a general value.

  The amorphous polyamide (B) is required to have a higher Tg than the thermoplastic polyester resin (A), and is a thermoplastic resin having a critical surface tension different by 0.1 mN / m or more. Is preferred. The requirement for the value of Tg and critical surface tension is as follows. That is, within a range satisfying the predetermined Tg value and critical surface tension value, the amorphous polyamide (B) is melt-mixed, whereby the thermoplastic polyester resin (A) becomes a sea component, and the amorphous polyamide (B) becomes easy to form an island component. That is, it becomes a composition in which the amorphous polyamide (B) is dispersed in the form of particles in the thermoplastic polyester resin (A), which is extruded into a film and further stretched to form a roughened film. When the critical surface tension of the amorphous polyamide (B) is the same as or close to the critical surface tension of the thermoplastic polyester resin (A), compatibility is recognized and the film is not sufficiently roughened. . Further, if the Tg of the amorphous polyamide (B) is lower than that of the thermoplastic polyester resin (A), the amorphous polyamide (B) is deformed together with the thermoplastic polyester resin (A) during stretching, and the amorphous polyamide (B) becomes a nucleus. It is difficult to generate protrusions on the film surface. The difference in critical surface tension between the thermoplastic polyester resin (A) and the amorphous polyamide (B) is preferably 0.1 mN / m or more, more preferably 0.5 mN / m or more. The difference in Tg between the thermoplastic polyester resin (A) and the amorphous polyamide (B) is preferably 10 ° C. or higher, more preferably 20 ° C. or higher.

The amorphous polyamide (B) preferably has a melt viscosity of 50 to 5000 Pa · s at a temperature of 280 ° C. and a shear rate of 10 ² sec ⁻¹ . When the melt viscosity is less than 50 Pa · s, the particles of the amorphous polyamide (B) dispersed in the matrix of the thermoplastic polyester resin (A) become small, and the film surface protrusion formation degree and the concealability become insufficient. On the other hand, when it exceeds 5000 Pa · s, the dispersed particles of the amorphous polyamide (B) become too large, the operability is deteriorated, and the physical properties of the obtained film are impaired.

  The form of the amorphous polyamide (B) dispersed in the thermoplastic polyester resin (A) is desired to be spherical, preferably the average particle size is in the range of 0.5 to 6.0 μm, more preferably 1 It is preferable to be in the range of 0.0 to 5.0 μm.

  In the roughened film of the present invention, the amorphous polyamide (B) serves as a nucleus to form fine protrusions on the film surface, and the surface roughness of the film is 0.05 to The range is 0.12 μm, and the ten-point average roughness (SRz) is in the range of 0.8 to 2.5 μm, preferably in the range of 1.00 to 2.00 μm. When SRa is 0.05 μm or less and SRz is 0.8 μm or less, the degree of protrusion and concealment on the film surface is insufficient, and when SRa is 0.3 μm or more and SRz is 2.5 μm or more, film quality and mechanical performance are obtained. Is insufficient.

The higher the Tg of the amorphous polyamide (B), the easier it is to exhibit the roughening effect, but it is preferably 200 ° C. or lower in consideration of the workability during polycondensation or melt molding.
The composition of the amorphous polyamide (B) is not particularly limited. For example, hexamethylenediamine and bis (4-amino-3-methylcyclohexylmethane) are used as the diamine component, and terephthalic acid and isophthalic acid are used as the dicarboxylic acid component. A thing can be preferably used. Examples of commercially available products include Grivory XE3038, XE3653, and TR55 manufactured by EMS.

  In the present invention, polybutylene terephthalate (C) (hereinafter referred to as modified PBT) containing 5 to 20% by mass of polytetramethylene glycol (PTMG) units is obtained by copolymerizing PBT and PTMG.

  The modified PBT used in the present invention is obtained by copolymerizing an appropriate amount of PTMG with general PBT obtained by polycondensation of terephthalic acid (or dimethyl terephthalate) and 1,4-butanediol. The content of the PTMG unit in the modified PBT is 5 to 20% by mass, preferably 10 to 20% by mass, and more preferably 10 to 15% by mass. When the PTMG content is less than 5% by mass, the resulting film has poor mechanical strength, dimensional stability, haze, and the like, and it is difficult to obtain stable film straightness. Become. In addition, when the content of PTMG exceeds 20% by mass, a phenomenon in which the film pulsates during extrusion (so-called ballast phenomenon) may be manifested particularly when produced on a mass production scale, and the film thickness unevenness increases. End up.

  The molecular weight of PTMG used in the present invention is preferably 600 to 4000, more preferably 1000 to 3000. When the molecular weight is less than 600, the mechanical properties of the film deteriorate, and when it exceeds 4000, the film tends to be difficult to stretch.

  In order to produce the polyester film in the present invention, the mixing ratio of the thermoplastic polyester resin (A), the amorphous polyamide (B), and the modified PBT (C) in 100 parts by mass of the film raw material is (A) = 58. -89 parts by mass, (B) = 6-12 parts by mass, (C) = 5-30 parts by mass, preferably (A) = 70-82 parts by mass, (B) = 6- It is good to set it as the range of 12 mass parts and (C) = 12-18 mass parts. When the mixing ratio of the modified PBT (C) is less than 5 parts by mass, straight tearability cannot be obtained, and when it exceeds 30 parts by mass, the performance such as mechanical strength, dimensional stability, and haze is reduced. In addition to problems in practical performance, thickness unevenness increases and tear straightness also decreases. Furthermore, when the modified PBT mixing ratio is less than 5 parts by mass, the degree of reduction in kneading unevenness due to the addition of the screw feeder is insufficient, and the haze fluctuation in the MD direction remains large. Moreover, when amorphous polyamide (B) is less than 6 mass parts, roughening is inadequate and sufficient cloudiness cannot be provided to a film. On the other hand, when the amount exceeds 12 parts by mass, roughening becomes remarkable and the film has a too high haze.

  In the present invention, first, an unstretched film is formed by a conventional method using a mixture of thermoplastic polyester resin (A), amorphous polyamide (B), and modified PBT (C) in a predetermined ratio. That is, the mixture of (A) to (C) is melt-kneaded with a single-screw or twin-screw extruder to finely add amorphous polyamide (B) and modified PBT (C) into the thermoplastic polyester resin (A). Disperse, extrude into a film form from a T-die and cool with a casting roller. The unstretched film thus obtained has relatively smooth surface irregularities, but the irregularities appear by being biaxially stretched. In this case, the stretching temperature is preferably a temperature within the range of Tg of the thermoplastic polyester resin (A) to Tg of the amorphous polyamide (B). When the temperature is lower than the Tg of the thermoplastic polyester resin (A), the stretchability is poor, and when the temperature is higher than the Tg of the amorphous polyamide (B), good surface unevenness is hardly exhibited. The biaxial stretching is preferably performed 1.5 times or more in the longitudinal and lateral directions. The thickness of the film by stretching is preferably not less than the dispersed particle diameter of the amorphous polyamide (B), and is in the range of 6 to 25 μm, preferably in the range of 10 to 20 μm. When the film thickness is 25 μm or more, the haze increases. The method for stretching the film is not particularly limited, and sequential biaxial stretching, simultaneous biaxial stretching, and the like can be applied. Moreover, the variation rate of the haze measured for every 100 m in the MD direction of the film of the present invention is 3% or less, and it is necessary that the film has tear straightness.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

[Reference Example 1: Synthesis of thermoplastic polyester resin]
A slurry of terephthalic acid and ethylene glycol (ethylene glycol / terephthalic acid molar ratio 1.6) is continuously fed to an esterification reactor in which bis (β-hydroxyethyl) terephthalate and / or its oligomer is present, at 250 ° C. The esterification reaction was carried out under pressure for a residence time of 6 hours, and the esterification product was continuously obtained. Next, this was transferred to a 100 parts by mass polymerization tank and heated to 280 ° C. At this time it was added 2 × 10 ^-4 mol of magnesium acetate against total acid component 1 mol of constituting the polyester, relative to the acid component 1 mol of a catalyst of antimony trioxide 2 × 10 ^-4 mol, respectively, start the vacuum And polycondensation reaction to obtain polyethylene terephthalate (PET).
The intrinsic viscosity of this resin measured at a temperature of 20 ° C. was 0.78, the critical surface tension was 41 mN / m, and the Tg was 70 ° C., using an equal mass mixture of phenol and ethane tetrachloride as a solvent.

[Reference Example 2: Synthesis of amorphous polyamide 1]
Raw material 10 in a proportion of 45 mol% isophthalic acid, 5 mol% terephthalic acid, 42.5 mol% hexamethylenediamine, 7.5 mol% bis (4-amino-3-methylcyclohexylmethane), 0.015 mol% acetic acid A mass part was charged into a reaction tank together with 8 parts by mass of pure water, and the air in the reaction tank was purged with nitrogen several times. After raising the temperature to 90 ° C. and reacting for about 5 hours, the reaction temperature was gradually raised to 280 ° C. over 10 hours while stirring in the tank under pressure (1800 kPa). Then, after releasing the pressure and reducing the pressure to atmospheric pressure, polymerization was further performed at the same temperature for 6 hours. After the reaction was completed, nylon was discharged from the reaction vessel and cut to obtain pellets. The obtained amorphous polyamide 1 had a Tg of 150 ° C. and a critical surface tension of 46 mN / m.

[Reference Example 3: Synthesis of amorphous polyamide 2]
In Reference Example 2, the raw material ratio was 50 mol% hexamethylenediamine, 20 mol% bis (3-methyl-4-amino-cyclohexyl) methane, 10 mol% isophthalic acid, and 20 mol% lauryl lactam. Except for the above, the same operation was performed to obtain amorphous polyamide 2 having a Tg of 45 ° C.

[Reference Example 4: Synthesis of modified PBT]
194 parts by mass of dimethyl terephthalate, 108 parts by mass of 1,4-butanediol, and 80 ppm of tetrabutyl titanate (value converted to the mass of titanium metal with respect to the polymer) were added, and the temperature was increased from 150 ° C. to 210 ° C. while heating to 2.5 ° C. The transesterification reaction was performed for a time. After 85 parts by mass of the obtained transesterification reaction product was transferred to a polymerization vessel and 40 ppm of tetrabutyl titanate was added, 15 parts by mass of PTMG having a molecular weight of 1100 was added and pressure reduction was started, and finally the pressure was reduced to 1 hPa. The temperature was raised from 210 ° C., and finally, melt polymerization was performed at a temperature of 245 ° C. to obtain a PTMG copolymerized PBT having a relative viscosity of 1.60 (solvent: tetrachloroethane: phenol = 50: 50 (mass ratio)).

  Next, the measurement method used for evaluation of an Example and a comparative example is shown below.

(A) Haze measurement Using a haze meter (NDH-2000) manufactured by Nippon Denshoku Industries Co., Ltd., in accordance with ASTM D1003-61, measurement is performed for the central portion in the width direction of the film every flow direction (MD) 100 m. went. The practical haze range is about 40 to 60%, preferably 45 to 55%.
The rate of change was calculated by the following formula using the maximum value, the minimum value, and the average value of all measurement points in the flow direction.
Fluctuation rate = (maximum value-minimum value) / average value x 100 (%)

(B) Straightness of tearing From the both ends of the film roll, the sample is sampled in A4 size so that the MD direction becomes the longitudinal direction, and three 50 mm incisions are made every 20 mm in the TD direction from the sample end. One side of this notch was held by the chuck part of the load cell, and the amount of TD deviation was measured when it was torn 150 mm in a direction 30 ° from the MD horizontal direction at a tensile speed of 2.5 m / min. A total of 6 points were measured for each sample: 3 points in the right front direction and 3 points in the left front direction, and the average value was taken as the measurement value. When the measured value was less than 3 mm, it was judged that there was tear straightness (◯), and when it was 3 mm or more, there was no tear straightness (×).

(C) Glass transition temperature The glass transition temperature was measured using a differential scanning calorimeter (manufactured by Perkin Elmer). The crushed specimen was placed in a sealed state so that it did not protrude into a predetermined aluminum cell, and a sample for measurement was obtained. The measurement range was 50 ° C. to 270 ° C., and the temperature increase rate was 20 ° C./min. The temperature of the endothermic peak first seen in the temperature raising process was read, and the temperature was defined as the glass transition temperature (Tg).

(D) Critical surface tension Measure the solid surface contact angle (Θ) using the same series of liquids with known surface tension (γ), and give the value of γ giving cos Θ = 1 in the solid / liquid contact angle, The critical surface tension was used.
Contact-Angle-Meter manufactured by Kyowa Interface Science Co., Ltd. was used for contact angle measurement. The reagent was sucked with a syringe, pressurized and expanded to a predetermined size, and the sample was brought into contact with the expanded liquid reagent and slowly released. After detachment, an operation of drawing a tangent at the end of the water droplet and reading the angle (Θ) was continued until cos Θ = 1, and the value of γ at that time was defined as the critical surface tension.

Example 1
A mixture of 15.0 parts by mass of modified PBT prepared in Reference Example 4, 77.0 parts by mass of PET prepared in Reference Example 1, and 8.0 parts by mass of “amorphous polyamide 1” prepared in Reference Example 2 was used as a single screw extruder. And melt-kneaded at a temperature of 280 ° C. and extruded from a T die using a 90 mmφ extruder to obtain an unstretched film having a thickness of 120 μm and a width of 1.5 m. Next, a simultaneous biaxial stretching machine was used for this unstretched film, and the stretching ratio was 3.0. Double, horizontal 3.3. The film was biaxially stretched as a double and wound on an 8000 m roll. At this time, the temperature of the film at the stretching start point was 90 ° C. over the entire width. As a result of measuring the haze of the obtained biaxially stretched polyester film roll at 81 points every 100 m in the MD direction, the variation rate was 3% or less.

Examples 2-6, Comparative Examples 1-7
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the mixing ratio of PET, amorphous polyamide 1 and modified PBT was changed to the values described in Table 1. Modified PBT having different copolymerization ratios were obtained by changing the ratio of the transesterification product and PTMG in the same synthesis method as in Reference Example 3.

Example 7
A biaxially stretched polyester film was obtained under the same conditions and method as in Example 1 except that TR55 (Tg 155 ° C.) manufactured by EMS was used as an amorphous polyamide having a Tg higher than those in Examples 1 to 6. .

Comparative Example 8
A biaxially stretched polyester film was obtained under the same conditions and method as in Example 1 except that amorphous polyamide 2 was used in place of amorphous polyamide 1.

  Table 1 summarizes the characteristic values of the biaxially stretched polyester films obtained in the above Examples and Comparative Examples.

  With the compositions of the examples, an easily tearable and roughened biaxially stretched polyester film having good tear straightness and small fluctuation in haze is obtained.

  On the other hand, the biaxially stretched polyester film produced with the composition of Comparative Example 1 to which no modified PBT was added did not have tear straightness, and the haze fluctuation was about three times as large as that of each Example. It was.

  With respect to the compositions of Comparative Examples 2 and 3, the haze fluctuation is suppressed by the modified PBT addition effect, but the tear straightness is inferior to the Examples.

  Regarding the compositions of Comparative Examples 4 and 5 in which the mixing ratio of PBT and PTMG in the modified PBT was changed, both the straightness of tearing and the haze fluctuation rate are inferior to those of the examples.

  Regarding the compositions of Comparative Examples 6 and 7 in which the amount of amorphous polyamide added was changed, the composition had easy tearing and the haze fluctuation was suppressed, but the haze level was outside the allowable range.

Regarding the composition of Comparative Example 8 using an amorphous polyamide having a Tg lower than that of the thermoplastic polyester resin, the same results as in Comparative Examples 6 and 7 were obtained.

Claims (2)

58 to 89 parts by mass of the thermoplastic polyester resin (A), 6 to 12 parts by mass of an amorphous polyamide (B) having a glass transition temperature higher than that of the thermoplastic polyester resin (A), and 5 to 20 parts by mass of polytetramethylene glycol units. % Of polybutylene terephthalate (C) containing 5 to 30 parts by mass and (A) to (C) is a film manufactured using a raw material with a total of 100 parts by mass, in the flow direction (MD) An easily tearable roughened biaxially stretched polyester film having a haze variation rate of 3% or less measured every 100 m. The easily tearable roughened biaxially stretched polyester film according to claim 1, wherein the average value of the haze measured every MD 100 m is 40 to 60%.