JPH0832499B2 - Heat resistant polyester film for transfer film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is excellent in deep drawability, flatness and heat resistance, and has very few coarse particles, and is extremely excellent as a base film for transfer film. Regarding polyester film.

[Problems to be Solved by Prior Art and Invention]

Conventionally, various methods have been used as a printing method for a molded article, and a transfer printing method is one of the typical methods. In recent years, what has been highlighted as one of the printing methods is a so-called molding transfer method in which transfer is performed simultaneously with molding.

The transfer method will be briefly described with reference to FIG. A layer 4 including a printing layer, such as a release layer, a printing layer, and an adhesive layer, which are sequentially laminated in advance, and the base film 3 are positioned between the injection machine 2 and the mold 1. The film is heated, if necessary, and then preformed by vacuum or compressed air, and then a resin is injected from the injection machine 2. The layer 4 including the printing layer is transferred to the surface of the molded product by the pressure during the molding, and after molding, the base film 3 is peeled off from the molded product to complete both molding and printing.

Compared with the conventional method of printing after molding, such a transfer method enables a significant cost reduction by omitting steps.
Further, it is possible to print on a quadratic or cubic curved surface, not limited to a flat surface, extremely accurately and quickly.

As a base film used in the transfer method, a polyester film or a vinyl chloride resin film has been conventionally used. However, the conventional polyester film has a very small elongation rate of the film in the above molding step, and when the mold is deeper or has a complicated shape, film breakage frequently occurs in the step, and transfer is practically impossible. Become. Therefore, the polyester film,
At present, it is used only in molding transfer using a mold having a shallow bottom and a simple shape.

On the other hand, a vinyl chloride resin film is very excellent in moldability (hereinafter referred to as deep drawability) for a mold having a deep bottom or a complicated shape as described above, but the flatness of the film is higher than that of a polyester film. And the number of coarse particles present on the film surface or inside is extremely large,
It was unsuitable as a base film for accurate and clear transfer printing.

The shapes of molded products have become more and more diverse in recent years, and the demand for molding transfer requiring the above-mentioned deep drawability is increasing.
Therefore, it has been desired to obtain a film which is a base film of a transfer film while maintaining the flatness and the small number of fish eyes of a polyester film and having an excellent deep drawability of a vinyl chloride resin film.

In view of the above problems, the present inventors have previously proposed that the above problems can be improved by imparting certain specific physical properties to a film of an isophthalic acid copolymer of biaxially oriented polyester. However, when unevenness or grooves were added to the mold and the height or depth was low and smooth, good results were obtained with the proposed film, but the unevenness was sharp or thin and deep. In some cases, there was a problem of breaking at that part.

[Means for solving problems]

Therefore, the present inventors have arrived at the present invention as a result of intensive studies to solve the above problems.

That is, the gist of the present invention is that the second-order transition temperature of the film is 70 ° C.
And above, and the average refractive index of the film is 1.598 or less,
A heat-resistant polyester film for a transfer film, which has a degree of plane orientation of 0.050 or more and 0.140 or less and a heat of fusion of the film of 8 cal / g or less.

 The present invention will be described in detail below.

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 one or more dicarboxylic acids, and as the diol component, ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycol, 1,4-cyclohexane. Although any polyester or copolymerized polyester thereof composed of one or more known diol components such as dimethanol and neopentyl glycol may be used, in the present invention, Polyethylene terephthalate Te, polybutylene terephthalate, polyethylene-2,6
Copolymers of polyesters consisting of naphthalate, terephthalic acid and 1,4-cyclohexanedimethanol are preferred. Above all, a copolymer of polyethylene terephthalate is particularly preferable in terms of cost.

However, the film must have a second-order transition temperature (Tg) of 70 ° C. or higher in the film state. By the way, the temperature of polyethylene terephthalate is 69 ° C, and that of polyethylene-2,6-naphthalate is 113 ° C.

The film of the present invention may be a copolyester as described below as long as the above conditions are satisfied. For example, oxycarboxylic acid such as p-oxybenzoic acid and p-oxyethoxybenzoic acid, benzoic acid,
Use of monofunctional compounds such as benzoylbenzoic acid and methoxypolyalkylene glycol, and polyfunctional compounds such as glycerin, pentaerythritol, and trimethylenepropane, as long as the product retains a substantially linear polymer. You can do it.

As the polyester of the present invention satisfying the above conditions,
A copolyester obtained by copolymerizing polyethylene terephthalate as a main component with neopentyl glycol and 1,4-cyclohexanedimethanol as a diol component is industrially inexpensive and is particularly preferable.

The content of neopentyl glycol and 1,4-cyclohexanedimethanol in all the diol components in the above copolymerized polyester may be any proportion as long as the second-order transition temperature is 70 ° C. or higher, but is preferably 5 mol%. More than 50
It is not more than mol%, more preferably not less than 5 mol% and not more than 30 mol%.

On the other hand, the proportion of the polyethylene terephthalate component in the above copolyester is preferably 50 mol%, more preferably 70 mol%.

When the content of polyethylene terephthalate is less than 50 mol%, the strength and heat resistance of a film are significantly reduced, which is not preferable.

Further, in order to improve the slipperiness of the film, it is also preferable to contain fine particles such as an organic lubricant and an inorganic lubricant. Further, it may contain additives such as a stabilizer, a colorant, an antioxidant, an antifoaming agent and an antistatic agent, if necessary. 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 polyester, such as internal particles formed inside the polymer during the production of polyester by an alkali metal compound or an alkaline earth metal compound. The fine particles contained in the film are 0.005 to 0.9
The weight percent and the average particle diameter are preferably 0.001 to 3.5 μm.

The polyester of the present invention preferably has an intrinsic viscosity in a film of 0.40 or more, more preferably 0.50 or more. When the intrinsic viscosity of the film is less than 0.40, sufficient strength and deep drawability cannot be obtained, which is not preferable.

The desired film in the present invention can be obtained by stretching such a polyester to give specific film physical properties.

Further, as one of important constitutional requirements in the present invention, it is necessary that the degree of plane orientation ΔP represented by the following formula in the polyester film of the present invention is 0.050 or more and 0.140 or less, preferably 0.050 or more and 0.130 or less, and further preferably Is preferably 0.050 or more and 0.120 or less.

In the above formula, n _γ , n _β and n _α represent the maximum refractive index in the film plane, the refractive index in the direction orthogonal thereto and the refractive index in the thickness direction, respectively.

A film having a degree of plane orientation ΔP of more than 0.140 is not preferable because the deep drawability is insufficient and the film breaks frequently during molding transfer. Although the cause of this is not clear, it is estimated by the present inventors that a film having a degree of plane orientation ΔP of more than 0.140 has a high degree of orientation of molecular chains in the plane of the film,
It seems that there is no room for giving sufficient elongation to the film during deep drawing molding transfer.

On the other hand, a film having a degree of plane orientation ΔP of less than 0.050 is not preferable because the degree of orientation in the plane of the film becomes insufficient and the strength of the film decreases and the flatness of the film deteriorates.

However, although the deep drawability during molding transfer was improved to some extent by controlling the surface orientation degree ΔP within the above range, the deep drawability has not yet reached a completely satisfactory level.

On the other hand, the present inventors have found that the average refractive index of the film and the heat of fusion of the film have a great influence on the deep drawability of the film during molding transfer.

That is, in the film of the present invention, the average refractive index of the film represented by the following formula is required to be 1.598 or less, preferably 1.597 or less, more preferably
It is desirable that it is 1.580 or more and 1.597 or less.

This value correlates with the crystallinity of the film,
The higher the crystallinity, the higher. In the present invention, when the film number exceeds 1.598, the crystallinity of the film becomes high, and the film is frequently broken during molding transfer, which is not preferable.

On the other hand, even if the crystallinity of the original film is in the proper range, if the film is crystallized by heating before molding transfer or during molding transfer, the film is likely to break during molding transfer for the same reason as above. I think that the.

In the present invention, one of the important constituents is that the heat of fusion of the film is 8 cal / g or less, preferably 6 cal / g
Hereafter, it is more preferably 2 to 6 cal / g.

Generally, a film having a high heat of fusion has high crystallinity, and the crystallinity tends to increase. In the present invention, when the heat of fusion of the film exceeds 8 cal / g, crystallization of the film proceeds due to heating before or during molding transfer, and the film is frequently broken during molding transfer, which is not preferable. Further, the film having a heat of fusion of less than 2 cal / g has no problem in deep drawing at the time of molding transfer, but in the raw material drying step during film formation, crystallization is extremely difficult, and thus a complicated step such as vacuum drying Is required.

In the film of the present invention, the unevenness of the film thickness is preferably 20% or less, more preferably 10% or less. When the thickness unevenness of the film exceeds 20%, the flatness of the film is not sufficient, and distortion or the like is likely to occur in the pattern when the printing layer is formed, which is not preferable.

Further, in the film of the present invention, the number of coarse particles having a maximum diameter of 1.0 mm or more present on the film surface or inside is 100 cm ²
The number of hits is preferably 5 or less, more preferably 2 or less. A film in which the number of the coarse particles exceeds 5 per 100 cm ² is not preferable because the print layer has a gap and a so-called print gap occurs after transfer.

In the film of the present invention, the shrinkage in the longitudinal and transverse directions under the conditions of 150 ° C. and 3 minutes in air is preferably 10% or less,
More preferably, it is 5% or less. A film having a shrinkage ratio of more than 10% has a shrinkage in the longitudinal direction or a shrinkage in the lateral direction of the film in the heating section in the processing step, for example, in the drying step after the printing layer is formed, which causes distortion of the printed pattern. Is not preferred.

The Young's modulus in the machine direction and the transverse direction of the film of the present invention is preferably 300 kg / mm ² or more, more preferably 350 kg / mm ² or more. The Young's modulus is 300 kg
A film having a thickness of less than / mm ² is not preferable, because when the film is subjected to a winding tension in the molding step, the film is likely to be stretched and the design of the printing layer is distorted.

In the film of the present invention, the birefringence of the film is preferably 0.025 or less, more preferably 0.020 or less, and particularly preferably 0.015 or less. The birefringence of the film is
When it exceeds 0.025, the anisotropy of the film becomes large, and the deep drawability of the film at the time of molding transfer is deteriorated, which is not preferable.

The thickness of the film thus obtained is not particularly limited, but the thickness preferably used as a film for molding transfer is 5 to 200 μm, more preferably 10 to 150 μm.

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

The polyester of the present invention containing an appropriate amount of inorganic particles or the like as a slip agent, a hopper dryer, a paddle dryer, a commonly used dryer such as an oven,
Alternatively, it is dried using a vacuum dryer or the like and then extruded at 200 to 320 ° C. At the time of extrusion, any existing method such as a T-die method or a tubular method may be adopted.

Although the amorphous sheet is obtained by rapid cooling after extrusion, it is preferable to use an electrostatic application method at the time of rapid cooling because the thickness unevenness of the amorphous sheet is improved.

Next, the amorphous sheet is stretched in the machine direction and the transverse direction so that the area ratio is at least 6 times or more, preferably 9 times or more to obtain a biaxially oriented film, and if necessary, the film is longitudinally and / or transversely. After re-stretching to, preferably
Heat treatment is performed at a temperature in the range of 150 to 220 ° C. to obtain the desired film.

In the heat treatment step, relaxation of 0.1 to 30% in the transverse direction and / or the longitudinal direction in the cooling zone at the maximum temperature of the heat treatment and / or the cooling zone at the heat treatment outlet is also a preferred embodiment of the present invention. . Further, in the heat treatment step, a two-step heat treatment may be performed.

During or after the stretching step, adhesiveness to the film,
A coating layer may be formed on one side or both sides of the film, or a corona discharge treatment or the like may be performed in order to impart antistatic properties, slip properties, and the like.

As described above, according to the present invention, it is possible to obtain a polyester film which is excellent in deep drawability, flatness and heat resistance, and which has very few coarse particles and which is extremely suitable as a base for a transfer film.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to these examples as long as the gist thereof is not exceeded.

 The evaluation method of the film is shown below.

(1) 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., Ltd. and a sodium lamp as a light source.

The maximum refractive index n _γ in the film plane, the refractive index n _{β in the} direction orthogonal thereto, and the refractive index n _α in the thickness direction are obtained, and the average refractive index (), plane orientation degree (ΔP), and birefringence index (Δ
n) was calculated according to the following formula.

Δn = n _γ −n _β (2) Second-order transition temperature of film The film was held at 300 ° C. for 5 minutes in a nitrogen atmosphere to melt, and then rapidly cooled to obtain a substantially amorphous sample. The second-order transition temperature of the sample was measured with a differential scanning calorimeter DSC-1B manufactured by Perkin Elmer at a temperature rising rate of 4 ° C./min, and this was used as the second-order transition temperature of the film.

(3) Heat of melting of film Differential scanning calorimeter DSC-1B manufactured by Perkin Elmer Co., Ltd.
The area of the peak accompanying the melting of the crystal of the sample measured at a temperature rising rate of 16 ° C./min was calculated by the above, and calculated according to the following formula.

Where A: heat of fusion per unit area (cal / cm ² ) on the chart when indium was measured under the same conditions S: area of melting peak of sample (cm ² ) m: weight of sample (g) (4) Intrinsic viscosity (η) 200 mg sample is phenol / tetrachloroethane = 50/50
Add to 20 ml of mixed solvent and heat at about 110 ℃ for 30 minutes, then at 30 ℃
It was measured at.

(5) Thickness unevenness of film The continuous film thickness measuring instrument (using an electronic micrometer) manufactured by Anritsu Electric Co., Ltd. was used to measure the length of the film along the lengthwise direction of 5 m, and the thickness unevenness was calculated by the following formula. .

(6) Number of Coarse Films Using a polarizing microscope with a magnification of 10 times, the number of coarse products having a maximum diameter of 1.0 mm or more existing on the surface and inside of the film under polarized light was converted into the number per 100 cm ² of film area.

(7) Heat Shrinkage of Film The film was heat shrunk in a geared oven at a temperature of 150 ± 2 ° C. for 3 minutes with no load applied, and the heat shrinkage in the longitudinal and transverse directions was determined according to the following formula.

However, l ₀ : Original length 10 cm l: Length after shrinkage (8) Deep drawability of film Use a mold with a length of 10 cm, a width of 10 cm, and a maximum depth of 1.8 cm. After preforming, the heated resin was injected to perform molding. The deep drawability of the film was evaluated as follows based on the frequency of film breakage during the molding.

◯: There is no breakage of the film.

Δ: Film breakage sometimes occurs at 1 to 2 places, which causes trouble during continuous operation.

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

(9) Suitability as transfer film After forming the release layer, the printing layer and the adhesive layer of the film, molding transfer was actually continuously carried out by the method of (8) above. The film was evaluated as ◯ when it could be operated continuously without breakage of the film at the time of molding, and when the printing on the molded product showed almost no distortion of the design, omission of printing, etc., and x when it was not.

Comparative Example 1 80 mol% of terephthalic acid unit as a digalvic acid component
And a pre-crystallized copolyester containing 600 ppm of amorphous silica having an average particle size of 1.2 μm and comprising 20 mol% of isophthalic acid unit, 98 mol% of ethylene glycol unit and 2 mol% of diethylene glycol unit as diol components after precrystallization with a paddle dryer. It was dried, extruded from an extruder at 285 ° C., then rapidly cooled and solidified to obtain an amorphous sheet. The intrinsic viscosity (η) of the amorphous sheet was 0.66.

The amorphous sheet is placed between a heating roll and a cooling roll by IR
After using a heater together and stretching 3.5 times in the machine direction at 85 ° C,
Then, it was stretched 3.8 times in the transverse direction at 110 ° C. and heat-treated at 180 ° C. while being relaxed by 15% in the width direction. The obtained film had a second-order transition point of 66 ° C. and a thickness of 50 μm.

Example 1 The dicarboxylic acid component was composed of terephthalic acid units, and the diol component was 1,4-cyclohexanedimethanol unit 33 m
ol% and ethylene glycol unit 67mol% copolyester and polyethylene terephthalate weight ratio
After blending at 70/30, it was dried, extruded and quenched to obtain an amorphous sheet. The amorphous sheet at 90 ° C in the longitudinal direction 3.7
After the double stretching, the film was stretched 4.0 times in the transverse direction at 120 ° C., and then heat-treated at 200 ° C. while performing 10% relaxation in the width direction. The obtained film had a thickness of 50 μm, a second-order transition temperature of 80 ° C., and an intrinsic viscosity of 0.72.

Comparative Example 2 Using the amorphous sheet of Example 1, the same procedure as in Example 1 was used to draw at 90 ° C. in the machine direction 2.0 times, and then in the transverse direction 2.5.
After the double stretching, heat treatment was performed under the same conditions as in Example 1 to obtain a thickness of 50.
A film of μm was obtained.

Comparative Example 3 Using the amorphous sheet of Example 1, the heat treatment temperature was 225 ° C.
Stretch film formation was performed in exactly the same manner as in Example 1 except that
A film having a thickness of 50 μm was obtained.

Example 2 The dicarboxylic acid component was 98 mol% of terephthalic acid units and o
-Using a vacuum dryer, a copolyester containing 1000 ppm of calcium carbonate fine particles having an average particle size of 0.9 µm and consisting of 2 mol% of phthalic acid unit, 90 mol% of diol component and 10 mol% of neopentyl glycol unit, After drying, the film was extruded and stretched in the same manner as in Example 1 to obtain a film having a thickness of 30 μm. The film thus obtained had a second-order transition temperature of 75 ° C. and an intrinsic viscosity of 0.70.

Comparative Example 4 Using the amorphous sheet of Example 2, the film was stretched 4.4 times in the machine direction between a heating roll and a cooling roll at 78 ° C., and then stretched at 100 with a tenter.
The film was stretched 4.8 times at ℃ and heat-treated in the same manner as in Example 2 to obtain a film having a thickness of 30 μm.

Table 1 shows the physical properties and evaluation results of the films obtained in the above Examples and Comparative Examples.

The film of Comparative Example 1 had a low second-order transition temperature of the film and was not yet completely excellent in deep drawability. On the other hand, the films of Examples 1 and 2 showed good deep drawability. On the other hand, in Comparative Examples 2, 3 and 4, it can be seen that in Examples 1 and 2, the average refractive index, the degree of plane orientation, etc. deviate from the specific ranges, resulting in defects.

[Effects of the Invention] As described above, a film satisfying the conditions of the present invention is excellent in deep drawability, flatness, heat resistance and the like, and is extremely useful as a base film of a transfer film.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an outline of a molding transfer method in which transfer is performed simultaneously with molding. In the figure, 1 is a mold, 2 is an injection machine, 3 is a base film, and 4 is a layer including a printing layer.

Claims (1)

[Claims] 1. The second-order transition temperature of the film is 70 ° C. or higher, the average refractive index of the film is 1.598 or lower, the degree of plane orientation is 0.050 to 0.140 and the heat of fusion of the film is 8 cal / g.
A heat-resistant polyester film for a transfer film, which is characterized in that: