JP2692310B2 - Biaxially oriented polyester film for molding - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially stretched white polyester film for molding, which has a high hiding power and a low glossiness and is excellent in moldability.

[Conventional technology and problems to be solved]

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,
Considering the use of polyester film as a raw material or auxiliary material for embossing, etc., and considering the application of the processed polyester film to molding transfer, molding containers, electrification, packaging, decoration, etc. Have been.

As such a film, for example, Japanese Patent Laid-Open No. 64-1182
As disclosed in JP-A No. 0, JP-A-64-16650, JP-A-64-22530, JP-A-64-40400, JP-A-64-45699, isophthalic acid, sebacic acid A biaxially stretched and heat-fixed film of a film obtained by combining and copolymerizing diethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol and the like is known.
Further, in order to improve the moldability, the longitudinal and lateral orientation during biaxial stretching is lowered, the method for reducing the plane orientation coefficient of the film, the method for lowering the heat setting temperature, the method for relaxing in the longitudinal and lateral directions, etc. There is known a method of properly combining.

However, there is a demand for a film for molding which has a higher added value to meet the expanding applications.

[Means for solving the problem]

The present inventors have conducted extensive studies in view of the above-mentioned requirements, and as a result, found that a film having a high-class feeling can be obtained by further increasing moldability by adding another polymer to polyester and foaming the same, It came to completion.

That is, the gist of the present invention is that the apparent specific gravity is 0.4 to 1.3, the degree of hiding is 0.2 or more, and in an atmosphere of 150 ° C, 10
The biaxially stretched polyester film for molding is characterized in that the film strength F ₁₀₀ at 0% elongation is 0.5 to 5.0 kg / mm ² .

 Hereinafter, the present invention will be described in detail.

The polyester used in the present invention is known as a dicarboxylic acid component, such as terephthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and diphenyl ether dicarboxylic acid. Of dicarboxylic acid of 1 or more types, and ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycol, 1,4-cyclohexane as a diol component. A polyester comprising one or more known diol components such as dimethanol and neopentyl glycol.

As the copolymerization component in the polyester of the present invention, for example, an oxycarboxylic acid such as p-oxybenzoic acid, benzoic acid, benzoylbenzoic acid, a monofunctional compound such as methoxypolyalkylene glycol, glycerin, pentaerythritol, etc. Polyfunctional compounds can also be used to the extent that the product retains a substantially linear macromolecule.

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

1 to 20 mol of the aliphatic dicarboxylic acid component as the acid component of the polyester constituting the film of the present invention in the total acid component
%, Preferably 1 to 10 mol%. A film in which the content of the aliphatic dicarboxylic acid component in the total acid components exceeds 20 mol% is not preferable because the heat resistance is lowered and the thickness unevenness is deteriorated.

Further, if the content is less than 1 mol%, the above-mentioned characteristics are not improved, which is not preferable.

As the aliphatic dicarboxylic acid component to be contained in the polyester constituting the film of the present invention, the aliphatic dicarboxylic acid component having 4 to 12 carbon atoms, preferably 6 to 12 carbon atoms is the above-mentioned moldability, heat resistance and thickness unevenness. Can be improved, which is preferable.

Further, in order to improve the lubricity of the film, it is also preferable to include 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. As fine particles imparting lubricity, known inert external particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, lithium fluoride and carbon black, melting of polyester resin Examples include high melting point organic compounds insoluble during film formation, crosslinked polymers, and metal compound catalysts used in the synthesis of polyesters, such as internal particles formed inside the polymers during the production of polyesters by alkali metal compounds, alkaline earth metal compounds and the like. The content of the fine particles contained in the film is usually
The average particle size is 0.001 to 0.9% by weight.
It is preferably in the range of 3.5 mμ.

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. If the intrinsic viscosity of the film is less than 0.50, it is not preferable because sufficient strength and moldability cannot be obtained.

In the film of the present invention, 1 at 150 ℃ atmosphere
The film strength F ₁₀₀ at 00% elongation must be in the range of 0.5 to 5 kg / mm ² . In the present invention, F ₁₀₀ is the average value of the strength in the machine and transverse directions of the film at 100% elongation at 150 ° C. The F ₁₀₀ value is preferably in the range 0.5 to 3 kg / mm ² .

According to the results of our study, the strength F ₁₀₀ value is closely related to the formability of the film, and a film having an F ₁₀₀ of more than 5 kg / mm ² is not preferable because the formability is lowered. Also, F ₁₀₀
When the film is less than 0.5 kg / mm ^2, the film is deformed non-uniformly at the time of molding. For example, in the case of a transfer film, the transferred pattern is undesirably deformed. In addition, the difference in strength between the longitudinal and transverse directions of a film when stretched at 150 ° C and 100% is usually 3 kg / mm.
² or less, preferably 2 kg / mm ² or less, more preferably
1kg / mm ² or less. If the difference exceeds 3 kg / mm ² , the anisotropy becomes large and the formability deteriorates.

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 the ears and the like are recycled, crystallization becomes extremely difficult in the raw material drying step during film formation, and a complicated step is required during vacuum drying, which is not preferable and the thickness unevenness of the film is deteriorated.

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). For a film whose lateral shrinkage exceeds 0%,
When used for molding transfer, the film shrinks in width in the drying step after forming the printing layer, which is not preferable.

On the other hand, the film of the present invention is preferably a film having a structure having fine closed cells on the surface and inside thereof, the apparent specific gravity of the film of the present invention is required to be in the range of 0.4 to 1.3, preferably Is in the range of 0.6 to 1.3, more preferably 0.8 to 1.2. If the apparent specific gravity is less than 0.4, the mechanical strength of the film becomes insufficient, which is not preferable.

Further, the hiding degree of the film of the present invention needs to be 0.2 or more, preferably 0.3 or more. The degree of concealment
When it is less than 0.2, the diameter of the closed cells existing in the film becomes large and the mechanical strength is lowered, and when it is used as a white film, a large amount of pigment is inevitably added, which is not preferable.

The film of the present invention is required to have the above-mentioned characteristics, but the manufacturing method thereof is not particularly limited as long as such characteristics and requirements are not impaired.

For example, as one of the methods for obtaining the polyester film for molding of the present invention, there is a method of blending polyester with a specific polypropylene, extrusion-molding into a sheet, and then biaxially stretching the sheet to form a film. For more information,
Melt flow index (hereinafter MFI
Abbreviated as 0.2) to 120% of crystalline polypropylene homopolymer in an amount of 3 to 20 wt% and melt-extruded to form a substantially amorphous sheet, which is then stretched biaxially at an area ratio of 4 times or more. This is a method for forming a film, and forming a polyester film containing numerous fine closed cells on the surface and inside thereof.

By adopting such a method, a biaxially stretched film having an apparent specific gravity of the film of the present invention of 0.4 to 1.3 and a hiding power of 0.2 or more can be easily obtained. Moreover, the film can be produced under ordinary film forming conditions for the stretched polyester film without modifying the conventional film forming apparatus.

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.

〔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) Film strength at 100% elongation in an atmosphere of 150 ° C F ₁₀₀ (kg / mm ² ) Intesco 20
A 01-type thermostat was set at 150 ° C., a film having a width of 15 mm was set so that the gap between the chucks was 50 mm, left for 2 minutes, and then the strength at 100% elongation was measured at a tensile speed of 200 mm / min. Measurements performed on longitudinal and transverse directions of the film, and the average value was defined as the F _100. In addition, about the film which ruptures before 100% extension, it converted according to the following formula.

(2) Film thickness unevenness A continuous film thickness measuring device (using an electronic micrometer) manufactured by Anritsu Electric Co., Ltd. was used to measure the film length of 5 m along the longitudinal direction of the film, and the thickness unevenness was calculated by the following formula. .

(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 fusion of film (cal / g) The area of the peak associated with the melting of the crystal of the sample measured at a temperature rising rate of 16 ° C./min was determined by a differential scanning calorimeter DSC-1B manufactured by Perkin Elmer Co., It was calculated according to the following formula.

A: Heat of fusion per unit area on the chart when indium was measured under the same conditions (cal / cm ² S: Area of melting peak of sample (cm ² ) m: Weight of sample (g) (5) Limit Viscosity (η) 200 mg sample is phenol-tetrachloroethane = 50/50
After heating for 30 minutes at about 110 ° C, add
Was measured.

(6) Heat shrinkage rate (%) of the film The film was heat shrunk for 3 minutes with no load during the guard open at a temperature of 150 ± 2 ° C., and the heat shrinkage rate in the longitudinal and transverse directions was calculated according to the following formula. It was

However, l ₀ : Original length 10 cm l: Length after shrinkage (7) Formability as a transfer film Length 10 cm, width 10 cm, maximum depth 2.0 cm Using a mold, the film is vacuum and compressed. After pre-molding inside, molding was performed by injecting a heated resin. The formability of the film was evaluated as follows based on the frequency of film breakage during molding.

：: No break in the film.

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

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

(8) Suitability as a film for molding container A 16 μm polyester film is laminated with an unstretched polypropylene film of 70 μm via an adhesive, preheated, and then vacuumed using a mold with an opening diameter of 10 cm and a depth of 3 cm. A plastic tray was prepared by pressure molding. Delamination occurs between the polyester film and polypropylene film at the time of molding, or those that frequently break are ×
Those that could be molded without any particular problems were marked with a circle.

(9) Apparent specific gravity A sample of 10 cm × 10 cm is cut out from an arbitrary portion of the film, the average thickness at 9 arbitrary points is measured with a micrometer to determine the volume, and then the weight of the sample is weighed to obtain 1
The weight per cm ³ was determined. The number of measurements was performed on five samples, and the average value was used as the apparent specific gravity.

(10) Concealment Degree The density of transmitted light under a G filter was measured using a Macbeth densitometer TD-904 type. The larger this value, the higher the hiding power. The number of measurements was three, and the average value was taken as the degree of hiding.

(11) Melt flow index (MFI) (g / 10min) It was measured according to the method of JIS K-6758-1981. The lower this value is, the higher the melt viscosity is.

(12) Glossiness (%) A gloss meter VG-107 type manufactured by Nippon Denshoku Co., Ltd. was used and measured according to the method of JIS Z-874. The value at an incident angle / reflection angle of 60 ° was measured with the black standard plate as a reference. The number of measurements was n = 3, and the average value was taken as the glossiness.

Example: 80 mol% terephthalic acid unit as a dicarboxylic acid component,
Consists of 16 mol% of isophthalic acid unit and 4 mol% of sebacic acid unit. As diol component, ethylene glycol unit 98
After pre-crystallizing a copolyester chip containing 500 ppm of amorphous silica fine particles having an average particle size of 1.4 μm and comprising 500 mol% and 2 mol% of diethylene glycol unit, a crystalline polypropylene homopolymer with a melt flow index (MFI) of 5 is applied to the chip. Polymer chips were blended at 10 wt% and blended uniformly. The mixed polymer was finally dried, extruded at 280 ° C. using an extruder having a T die, and rapidly solidified to obtain an amorphous sheet. The obtained sheet was stretched 3.0 times at 75 ° C in the longitudinal direction between the heating roll and the cooling roll, and then 3.4 times at 95 ° C in the transverse direction, with 12% transverse relaxation and 0.3%.
Was heat-treated at 175 ° C while relaxing in the vertical direction. The obtained film had an average thickness of 38 μm and an intrinsic viscosity of 0.63.

The physical properties and characteristics of the obtained film are shown in Table 1 below.

[Effects of the Invention] The film of the present invention is a white film having a high degree of hiding and a low gloss, and is useful as a high-quality molding film, and has a high industrial value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-204020 (JP, A) JP-A 2-16130 (JP, A) JP-A 64-9244 (JP, A)

Claims (1)

(57) [Claims] 1. An apparent specific gravity of 0.4 to 1.3 and a degree of concealment of 0.
A biaxially stretched polyester film for molding, which has a film strength F ₁₀₀ of 100% stretched in an atmosphere of 2 or more at 150 ° C. of 0.5 to 5.0 kg / mm ² .