JP2794893B2 - Biaxially oriented polyester film for molding - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film for molding having excellent moldability, uneven thickness and heat resistance.

[Problems to be solved by conventional technology and invention]

Hitherto, biaxially stretched polyester films have excellent strength and heat resistance and have been widely applied to various industrial uses. For example, vacuum, compressed air, overhang, cold, injection, in-mold,
The use of polyester film as a raw material or auxiliary material for embossing, etc. has been studied, and the application of the processed polyester film to molding transfer, molding containers, electrical discharge, packaging, decoration, etc. Are being considered.

However, the biaxially stretched polyester film is inferior in moldability as compared with the vinyl chloride resin, and thus has been difficult to apply in these applications. In particular, improvement of moldability has been demanded as a base film for molding transfer and molding containers.

The present inventors have proposed biaxially stretched polyester films in which various moldability has been improved in response to the above requirements.

However, when the moldability is improved, unevenness in the thickness of the film is greatly deteriorated, and various problems occur during processing. For example, when the thickness unevenness of the film for forming and transferring is poor, not only the flatness of the film is deteriorated, but also the elongation of the film becomes uneven at the time of forming and transferring, so that the accuracy of the transferred design is reduced. Further, if the thickness unevenness of the film for a molded container is poor, the moldability becomes non-uniform, so that there is a tendency that the film is broken or partial delamination occurs during lamination.

Thus, in the polyester film for molding,
In addition to heat resistance, which is a basic required characteristic, it has been required to satisfy the phenomenon of binarization, that is, improvement in moldability and thickness unevenness.

[Means for solving the problem]

In view of the above problems, the present inventors have conducted intensive studies,
The inventors have found that a polyester film having certain specific properties has excellent moldability, uneven thickness and heat resistance, and have completed the present invention.

That is, the gist of the present invention resides in a biaxially stretched polyester film for molding, which satisfies the following formulas at the same time.

Gs (60 °) ≧ 60… 55 ≦ X ₁₀₀ ≦ 80… 1.575 ≦≦ 1.595… 1.5 ・ (−1.563) ≦ ΔP ≦ 1.5 ・ (−1.543)… Hereinafter, the present invention will be described in detail.

Polyester used in the present invention, as a dicarboxylic acid component, terephthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenylether dicarboxylic acid, aliphatic Dicarboxylic acid and the like, consisting of one or more known dicarboxylic acids, and as a diol component, ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycol, It is a polyester comprising one or more known diol components such as 1,4-cyclohexanedimethanol and neopentyl glycol.

In the polyester of the present invention, copolymerizable components include, for example, oxycarboxylic acids such as p-oxybenzoic acid, monofunctional compounds such as benzoic acid, benzoylbenzoic acid, and methoxypolyalkylene glycol; and polyfunctional compounds such as glycerin and pentaerythritol. Functional compounds can also be used to the extent that the product can retain a substantially linear polymer.

In the polyester constituting the film of the present invention,
The proportion of polyethylene terephthalate is preferably at least 50% by mole, more preferably at least 70% by mole. If the polyethylene terephthalate content is less than 50 mol%, the strength and heat resistance of the film are undesirably reduced.

In the polyester constituting the film of the present invention,
As an acid component, an aliphatic dicarboxylic acid component is preferably 1 to
By containing 20 mol%, more preferably 1 to 10 mol%, it becomes possible to improve the film formability, heat resistance and unevenness of thickness.

In the polyester constituting the film of the present invention, the content of the aliphatic dicarboxylic acid component in all the acid components is 20 mol.
%, The heat resistance is reduced and the thickness unevenness is deteriorated. On the other hand, if the content is less than 1 mol%, the above characteristics are not improved, which is not preferable.

As the aliphatic zirconic acid component contained in the polyester constituting the film of the present invention, C4-12,
Preferably an aliphatic dicarboxylic acid component having 6 to 12 carbon atoms,
The moldability, heat resistance and thickness unevenness can be further improved, which is preferable.

Further, in order to improve the lubricity of the film, it is also preferable to contain fine particles such as an organic lubricant and an inorganic lubricant, and, if necessary, a stabilizer, a coloring agent, an antioxidant, an antifoaming agent, and an antistatic agent. And the like. Known fine external particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, lithium fluoride, and carbon black, and the melting of polyester resin are given as fine particles imparting slipperiness. Internal particles formed inside the polymer at the time of polyester production by a high melting point organic compound which is insoluble during film formation, a crosslinked polymer, and a metal compound catalyst used at the time of polyester synthesis, such as an alkali metal compound and an alkaline earth metal compound. The content of fine particles contained in the film is usually
0.002 to 0.9% by weight, average particle size is 0.001 to 10
It is preferably in the range of μm.

The polyester of the present invention has an intrinsic viscosity in the film of preferably 0.50 or more, more preferably 0.60 or more. When the intrinsic viscosity of the film is less than 0.50, sufficient strength and moldability cannot be obtained, which is not preferable.

In the film of the present invention, the glossiness Gs of the film (60
Ii) is at least 60%, preferably at least 80%, more preferably at least 90%. Films having a gloss Gs (60 °) of less than 60% are not preferred because after molding, the molded article becomes cloudy or the transparency is impaired.

In the film of the present invention, the crystallite size (X ₁₀₀₎
Is in the range of 55-80 °, preferably in the range of 60-80 °, more preferably in the range of 65-75 °.

The crystallite size (X ₁₀₀ ) referred to in the present invention is defined by the half width of the (100) diffraction peak measured by X-ray diffraction.
This is the crystallite size obtained using the equation of er.

According to our findings, the crystallite size (X ₁₀₀ )
It is closely related to the heat resistance and strength of the film, and if the crystallite size (X ₁₀₀ ) is less than 55 °, the heat resistance of the film is undesirably reduced. The crystallite size (X
_A film with ₁₀₀ ) exceeding 80 ° is not preferable because the strength of the film is reduced and the flatness is deteriorated.

In the film of the present invention, the film average refractive index is in the range of 1.575 to 1.595, preferably 1.580 to 1.5
The range is 90. In the case of a film having a value of more than 1.595, a film having good moldability cannot be obtained, which is inappropriate. 1.
Films less than 575 are not suitable because of poor strength and poor flatness of the film.

The plane orientation degree ΔP of the film of the present invention is 1.5 · (−1.5
63) to 1.5 · (−1.543), and preferably 1.5 · (−1.560) to 1.5 · (−1.54).
5) range. Films outside this range are moldable,
Poor thickness and poor heat resistance make it unpractical.

In the present invention, the heat of fusion of the film is preferably in the range of 1 to 8 cal / g, more preferably 1 to 6 cal / g.
Films having a heat of fusion of more than 8 cal / g are not preferred because moldability decreases. On the other hand, films with a heat of fusion of less than 1 cal / g
In particular, when recycling the ears and the like, since crystallization is extremely difficult in the raw material drying step such as film formation, a complicated step such as vacuum drying is necessary, which is not preferable, and the thickness unevenness of the film is also deteriorated, which is preferable. Absent.

Regarding the shrinkage properties of the film of the present invention,
The shrinkage in the longitudinal and transverse directions after the minute treatment is preferably 10% or less, more preferably 5% or less.

A film having a shrinkage ratio of more than 10% in the vertical or horizontal direction is not preferable because the film shrinks greatly in a heating section during the processing step. In particular, in the use of a transfer film, the shrinkage in the horizontal direction under the above conditions is preferably 0% or less (when the film expands, the shrinkage is set to minus). In the case of a film having a lateral shrinkage of more than 0%, when used for forming and transferring, the film shrinks in the drying step after the formation of the print layer, which is not preferable.

In the film of the present invention, the thickness unevenness of the film is preferably 30% or less, more preferably 20% or less, and most preferably 15% or less. In the case of a film having a thickness unevenness of more than 30%, the moldability and the elongation at the time of molding become non-uniform, and the pattern is distorted at the time of molding transfer, which is not preferable.

Regarding the mechanical strength of the film of the present invention, the Young's modulus in the longitudinal and transverse directions of the film is preferably 300 kg / mm
^{It is 2} or more, more preferably 350 kg / mm ² or more. A film having a Young's modulus of less than 300 kg / mm ² is not preferable because the film tends to elongate in the forming step.

Although the thickness of the film of the present invention is not particularly limited, the thickness preferably used as a film for molding transfer is 5 to 5.
It is 500 μm, more preferably 5 to 300 μm.

Next, the production method of the film of the present invention will be specifically described, but is not limited to the following examples as long as the constitutional requirements of the present invention are satisfied.

The polyester of the present invention containing an appropriate amount of inorganic particles and the like as a slipping agent, if necessary, is dried using a commonly used dryer or vacuum dryer such as a hopper dryer, a paddle dryer, and an oven, and then heated to 200 to 320 ° C. And extrude. When extruding, any existing method such as a T-die method and a tubular method may be employed.

After extrusion, the amorphous sheet is quenched to obtain an amorphous sheet, but it is preferable to use an electrostatic application method during the quenching because unevenness in the thickness of the amorphous sheet is improved.

The resulting amorphous sheet is then at least 3.
The film is stretched 0 times or more, preferably 3.2 times or more, more preferably 3.3 times or more, and has a longitudinal birefringence Δn of 0.040 or more, preferably 0.050 or more, and more preferably 0.055 or more. If the stretching ratio in the longitudinal direction is less than 3.0 times, the unevenness in the thickness of the film in the longitudinal direction is unfavorably deteriorated. Next, the obtained vertically stretched film is stretched 3.0 to 3.5 times in the transverse direction to form a biaxially oriented film. When the stretching ratio in the longitudinal direction is less than 3.0 times, the unevenness in the thickness in the transverse direction is unfavorably deteriorated. The transverse stretching ratio is preferably 3.2 to 5.0 times, and more preferably 3.4 to 5.0 times.

Next, the obtained biaxially oriented film is subjected to heat treatment, and this heat treatment step is important for obtaining the film of the present invention. When the melting point of the film is Tm (° C), the heat treatment temperature is preferably in the range of (Tm-40) to (Tm-5) ° C, more preferably (Tm-35) to (Tm-10) ° C, particularly Preferably, it is in the range of (Tm-30) to (Tm-15) ° C. If the heat treatment temperature is lower than (Tm-40) ° C., the relaxation of the orientation of the film is insufficient, and the moldability and heat resistance of the film are poor, which is not preferable. The heat treatment temperature of the film is (Tm
If the temperature exceeds -5) ° C., not only is the moldability of the film deteriorated, but also breakage during film formation occurs, which is not preferable.

 The heat treatment time is usually 1 second to 10 minutes.

In the heat treatment step, relaxation of 0.1 to 30% in the transverse direction and / or the longitudinal direction in the zone of the highest temperature of the heat treatment and / or the cooling zone at the exit of the heat treatment is also one of the preferable embodiments in the present invention. In particular, it is preferable to perform 5 to 30% relaxation in the horizontal direction. In the heat treatment step, a two-step heat treatment may be performed.

During or after the stretching step, in order to impart adhesiveness, antistatic properties, slipperiness, mold release properties, etc. to the film, a coating layer is formed on one or both sides of the film, or a corona discharge treatment or the like is performed. It does not matter.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples.
The present invention is not limited to these examples unless it exceeds the gist.

 In addition, the evaluation method of a film is shown below.

(1) Gloss of Film Gs (60 °) Using a VGS-1001DP glossy watch manufactured by Nippon Denshoku Industries Co., Ltd., the 60 ° specular gloss Gs (60 °) was measured according to JIS Z 8741. That is, the reflectance of the sample was determined based on the reflectance of the black standard plate at an incident angle and a reflection angle of 60 degrees, and the gloss was determined.

(2) X-ray diffraction measurement: X ₁₀₀ samples in film-form by (average crystallite size) X-ray automatic diffractometer 2θ
From the half width of the (100) plane peak near = 26 ゜, the following equation (Schel
The crystallite size X ₁₀₀ was calculated by the equation of ler). The X-ray output was performed at 30 kv and 15 mA.

K = 0.94 (rad) [Sherrer constant] λ = 1.5418 (Å) [wavelength of X-ray] Hc = half width (rad) (3) Average refractive index of film (), degree of plane orientation (Δ
P), birefringence (Δn) The refractive index of the film was measured using an Abbe refractometer manufactured by Atago Co., and using a sodium lamp as a light source.

Δn = _n γ -n β Note that represents the maximum refractive index, the refractive index and the thickness direction of the refractive index in the direction perpendicular to that of the above formula n _gamma, n _beta and n _alpha Each film plane.

(4) Heat of dissolution of film ΔHm (cal / g) The area of the peak accompanying the melting of the crystal of the sample, measured at a heating rate of 16 ° C./min, using a differential scanning calorimeter DSC-1B manufactured by PerkinElmer, Inc. Was calculated according to the following equation.

A: Heat of fusion per unit area on the chart when measuring indium under the same conditions (cal / cm ² ) S: Area of melting peak of sample (cm ² ) m: Weight of sample (g) (5) Film thickness unevenness The film thickness was measured at a length of 5 m along the longitudinal direction of the film using a continuous film thickness measuring device manufactured by Anritsu Electric Co. (using an electronic micrometer), and the thickness unevenness was calculated by the following formula.

(6) Intrinsic viscosity (η) 200 mg of sample was phenol / tetrachloroethane = 50/50
After heating for 30 minutes at about 110 ° C, add
Was measured.

(7) Heat shrinkage of film (%) Heat shrink the film in a gard oven at a temperature of 150 ± 2 ° C under no load for 3 minutes, and calculate the heat shrinkage in the vertical and horizontal directions according to the following formula. Was.

However, l _0: original length 10 cm l: length after shrinkage (8) transfer and while suitability thermal drying as a film film (3) on the release layer to form a print layer and adhesive layer, FIG. 1 As shown in the vertical 10cm, horizontal 10cm,
Using a mold (I) having a maximum depth of 5.0 cm, the film was preformed inside the mold under vacuum and pressure, and then the heated resin was injected to continuously perform molding transfer. With respect to the frequency of breakage of the film during molding, the shape of the injection molded product, and the finish of printing of the formed product, the suitability as a transfer film was evaluated as follows.

A: There is no breakage of the film, and the shape of the formed product and the finish of printing are beautiful.

：: There is no breakage of the film at all, but a defective product sometimes occurs in the shape of the molded product or the finish of printing.

Δ: Occasionally, film breakage occurs in one or two places, which hinders continuous operation.

×: The film is frequently broken and cannot be used.

Example 1 80 mol% of terephthalic acid units as a dicarboxylic acid component,
It is composed of 16 mol% of isophthalic acid units and 4 mol% of sebacic acid units.
mol%, 2 mol% of diethylene glycol, pre-crystallized copolymer polyester containing 500 ppm of amorphous silica fine particles having an average particle size of 1.4 μm, followed by main drying, extrusion at 280 ° C. using an extruder having a T die, and rapid cooling. It was solidified to obtain an amorphous sheet. The obtained sheet is stretched 3.5 times at 75 ° C. in the horizontal direction between the heating roll and the cooling roll, and then stretched 3.6 times at 95 ° C. in the horizontal direction.
Heat treatment was performed at 190 ° C. with 0.5% relaxation. The average thickness of the obtained film is 50 μm, and the intrinsic viscosity is 0.66.
And the melting point was 220 ° C.

Example 2 The heat treatment temperature was 200 ° C. using the amorphous sheet of Example 1.
The film was drawn in the same manner as in Example 1 except that the film thickness was changed to obtain a film having an average thickness of 50 μm.

Example 3 Using the amorphous sheet of Example 1, stretching was carried out in exactly the same manner as in Example 1 except that the longitudinal stretching ratio was 3.0 times, to obtain a film having an average thickness of 50 μm.

Comparative Example 1 Using the amorphous sheet of Example 1, the longitudinal stretch ratio was 3.0.
A film was drawn in the same manner as in Example 1 except that the heat treatment temperature was changed to 175 ° C. and a film having an average thickness of 50 μm was obtained.

Comparative Example 2 80 mol% of terephthalic acid units as a dicarboxylic acid component
After pre-crystallizing a copolyester comprising 20 mol% of isophthalic acid units and 500 ppm of amorphous silica fine particles having an average particle size of 1.4 μm and consisting of 98 mol% of ethylene glycol units and 2 mol% of diethylene glycol units as diol components, followed by main drying, 280 using extruder with T die
Extruded at ℃ and quenched and solidified to obtain an amorphous sheet. The resulting sheet is placed between the heating roll and the cooling roll in the vertical direction for 85
After stretching 3.2 times at 110 ° C., the film was stretched 3.6 times at 110 ° C. in the horizontal direction, and heat-treated at 180 ° C. while performing 15% relaxation in the horizontal direction and 0.5% relaxation in the vertical direction. The average thickness of the obtained film was 50 μm, the intrinsic viscosity was 0.66, and the melting point was 210 ° C.

 The results obtained above are shown in Table 1 below.

[Effects of the Invention] The film of the present invention has excellent moldability, heat resistance and unevenness in thickness, is suitable for molding, especially as a base film for molding transfer and molding containers, and its industrial value is high.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a molding transfer method in which transfer is performed simultaneously with molding. In the figure, 1 denotes a mold, 2 denotes an injection machine, 3 denotes a base film, and 4 denotes a layer including a printing layer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B29C 55/12-55/16 C08J 5/18

Claims (3)

(57) [Claims] 1. A biaxially oriented polyester film for forming, characterized by simultaneously satisfying the following formulas (1) to (3). Gs (60 °) ≧ 60… 55 ≦ X ₁₀₀ ≦ 80… 1.575 ≦≦ 1.595… 1.5 ・ (−1.563) ≦ ΔP ≦ 1.5 ・ (−1.543)… (However, in the above formula, Gs (60 °) is gloss of the film (%), crystallite size X ₁₀₀ is measured by X-ray diffraction (Å), the average refractive index, [Delta] P represents the degree of planar orientation) 2. The biaxially stretched polyester film for molding according to claim 1, wherein both the shrinkage in the longitudinal and transverse directions of the film after treatment at 150 ° C. for 3 minutes are 10% or less. 3. The biaxially oriented polyester film for molding according to claim 1, wherein the thickness unevenness of the film is 30% or less.