JP2574058B2 - Polyester film for metal lamination processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a polyester film for metal laminating and forming, and more particularly, an excellent forming when laminating to a metal plate and performing can forming such as drawing. The present invention relates to a polyester film for metal laminating and forming capable of producing metal cans, such as beverage cans, food cans, and the like, which have excellent heat resistance and fragrance retention.

<Prior art and its problems> Metal cans are generally coated to prevent corrosion on the inner and outer surfaces. Recently, organic solvents have not been used for the purpose of simplifying the process, improving hygiene, and preventing pollution. Development of a method for obtaining rust resistance has been promoted, and as one of the methods, coating with a thermoplastic resin film has been attempted. That is, a method of laminating a thermoplastic resin film on a metal plate of tin, tin-free steel, aluminum, or the like, followed by drawing, etc., has been studied. Polyolefin films and polyamide films have been tried as this thermoplastic resin film, but they do not satisfy all of the moldability, heat resistance and fragrance retention.

On the other hand, polyester films, especially polyethylene terephthalate films, have attracted attention as having balanced properties, and several proposals based on these have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal plate via a low-melting-point polyester adhesive layer and used as a can-making material (JP-A-56-10451, JP-A-1-192546).

(B) An amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a can-making material (JP-A-1-192545, JP-A-2-57339).

(C) A biaxially oriented polyethylene terephthalate film having low orientation and heat set is laminated on a metal plate and used as a material for can production (JP-A-64-22530).

However, examinations by the present inventors have revealed that sufficient characteristics cannot be obtained in any case, and that each has the following problems.

Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention, but is insufficient in moldability and whitening of the film (generation of minute cracks) in canning with large deformation. Breakage occurs.

Regarding (B), since it is an amorphous or extremely low-crystalline aromatic polyester film, the moldability is good, but the fragrance retention is inferior, and after printing after can-making, retort sterilization, etc. The film is easily embrittled by the treatment and is easily broken by the impact from the outside of the can.

As for (C), the effect is not exerted in the intermediate region between the above (A) and (B). However, since the isotropy of the film surface is not ensured, it can be used as in can making (deep drawing). When deformation is performed in all directions, the formability in a specific direction of the film may be insufficient.

<Means for Solving the Problems> The present inventors have further conducted intensive studies to develop a polyester film for can-making without these problems.
The present invention has been reached.

That is, the present invention contains spherical particles having an average particle diameter of 2.5 μm or less, a relative standard deviation of 0.3 or less, and a particle diameter (major axis / minor axis) of 1.0 to 1.2, and a melting point of 210 to 1.2. Two
It is made of 45 ° C copolymerized polyester, the refractive index in the film thickness direction is 1.505 to 1.545, the refractive index in the film surface direction is 1.61 to 1.66 in all directions, and the subpeak by DSC is 150 to 205 ° C. It is a polyester film for metal lamination forming.

Representative examples of the copolymerized polyester in the present invention include copolymerized polyethylene terephthalate.
This copolymer component may be an acid component or an alcohol component.
Examples of the acid component include aromatic dibasic acids such as isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid; and alicyclic rings such as cyclohexanedicarboxylic acid. Examples of the alcohol component include aliphatic diols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These can be used alone or in combination of two or more.

The proportion of the copolymer component depends on the type thereof, and as a result, the polymer melting point is in the range of 210 to 245 ° C, preferably 215 to 240 ° C, and more preferably 220 to 235 ° C. When the melting point of the polymer is less than 210 ° C., the heat resistance is inferior, so that it cannot withstand the heating in printing after can production. On the other hand, the polymer melting point
When the temperature exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of polyester is measured by Du Pont Instru
The method is to determine the melting peak at a heating rate of 20 ° C./min using ments 910 DSC. The sample amount is about 20 mg.

The copolymer polyester in the present invention has an average particle size of 2.
It contains spherical particles (spherical lubricant) having a particle size ratio (major axis / minor axis) of 1.0 to 1.2 with a relative standard deviation of 0.3 or less at 5 μm or less.

If the average particle size exceeds 2.5 μm, coarse particles (for example, 10 μm
The above particles) serve as a starting point, which is not preferable because pinholes are formed or broken in some cases.

The particle size ratio (major axis / minor axis) of the lubricant particles is 1.0 to 1.2, and this particle size ratio improves the pinhole resistance as well as the average particle size of 2.5 μm or less. Examples of such a spherical lubricant include spherical silica, spherical titanium oxide, spherical zirconium, and spherical silicone particles.

Here, the average particle size and the particle size ratio of the lubricant particles are, for example, 10,000-
The major axis, the minor axis, and the area circle equivalent diameter are obtained from the image magnified 30,000 times, and are then calculated by applying these to the following equation.

Average particle diameter = total area circle equivalent diameter of measurement particles / number of measurement particles Particle diameter ratio = average major diameter of particles / average minor diameter of the particles Also, the spherical lubricant particles preferably have a sharp particle size distribution, The relative standard deviation, which represents the steepness of the distribution, is 0.3
It is as follows.

 This relative standard deviation is expressed by the following equation.

Here, Di: area circle equivalent diameter (μm) of each particle: average value of area circle equivalent diameter n: represents the number of particles.

The amount of the spherical lubricant in the copolymerized polyester may be determined according to the winding property in the film production process. Generally, it is preferable to add a small amount of particles having a large particle diameter and a large amount of particles having a small particle diameter. For example, it is preferable to add about 0.05% by weight for monodispersed spherical silica having an average particle diameter of 2.0 μm, and about 0.3% by weight for monodispersed spherical titanium dioxide having an average particle diameter of 0.3 μm. Also, by intentionally adjusting the content of the lubricant,
The film can be made opaque. For example, a white film can be obtained by adding 10 to 15% by weight of spherical titanium dioxide.

The copolymerized polyester in the present invention is not limited by its production method. For example, a method of subjecting terephthalic acid, ethylene glycol and a copolymer component to an esterification reaction and then subjecting the resulting reaction product to a polycondensation reaction to obtain a copolymerized polyester, or a method of transesterifying dimethyl terephthalate, ethylene glycol and a copolymer component. A method of reacting and then subjecting the resulting reaction product to a polycondensation reaction to form a copolymerized polyester is preferably used. In the production of the copolymerized polyester, if necessary, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent and the like can be added.

The polyester film of the present invention is obtained by melting the above-mentioned lubricant-containing copolymerized polyester, discharging it from a die, forming it into a film, biaxially stretching and heat setting. And this film has the following requirements (1), (2) and (3)
Must be provided.

(1) The refractive index in the thickness direction of the film is 1.505 or more and 1.545
Below, preferably more than 1.510 and 1.540 or less, more preferably more than 1.510 and 1.530 or less. This refractive index is 1.50
If it is less than 5, the moldability will be insufficient, while if it exceeds 1.545 (that is, if the orientation is excessively low), the structure will be close to amorphous and the heat resistance will be insufficient.

(2) The refractive index in the film surface direction is 1.61 in all directions
It is in the range of not less than 1.66 and preferably not more than 1.615 and not more than 1.655. In deep drawing or drawing-ironing, which is frequently used in can manufacturing, deformation must be performed uniformly in all directions, and any part of the film must be able to follow this deformation. In the direction where the film surface refractive index is less than 1.61, the formability is good, but the heat resistance is inferior. On the other hand, in the direction where the refractive index exceeds 1.66, the formability is poor. Occur. In addition, the refractive index in the film thickness direction and the surface direction is measured as follows.

A polarizing plate analyzer is attached to the eyepiece side of the Abbe refractometer, and each refractive index is measured with a monochromatic NaD line.
The mounting solution uses methylene iodide, and the measurement temperature is 25 ° C. For the measurement of the refractive index distribution in the thickness direction and the refractive index distribution in the plane direction, the total width of the film when the film that has been heat-set is released is set to 1, and the width of 0.8 times this is cut out symmetrically with respect to the center of the film. It went about the end part when it was.

(3) DSC sub-peak is 150-205 ° C, preferably 155-200 ° C, more preferably 160-195 ° C. This sub-peak contributes to the stability of film quality after heat lamination on a metal plate.If this sub-peak is lower than 150 ° C, raising the heating lamination temperature with the metal plate makes the bottom of the can become brittle, while increasing the heating lamination temperature. If the temperature is lowered, the film breaks during processing, and a good can cannot be produced by adjusting the heating lamination temperature. If the sub-peak exceeds 205 ° C., the film breaks during can making at any heating lamination temperature, making can making impossible.

The measurement of the sub-peak temperature is carried out by the same method and under the same conditions as the measurement of the melting point of polyester. That is, Du Pont Instru
Using ments 910DSC, obtain a sub-peak at a heating rate of 20 ° C / min. The film sample is about 20 mg. The relationship between the sub-peak and the melting point can be understood, for example, from FIG.

In order to obtain the film characteristics in the present invention, the longitudinal stretching ratio is preferably from 2.5 to 3.6 in the biaxial stretching treatment, particularly in the sequential biaxial stretching treatment.
Times, transverse stretching ratio 2.7-3.6 times, heat setting temperature 150-230 ℃
From the conditions of stretching heat treatment, the refractive index in the thickness direction is 1.505 or more and 1.545 or less, the refractive index distribution of the film surface is 1.61
Is not more than 1.66 and the sub peak by DSC is 150 ~
It is advisable to conduct a biaxial stretching heat setting treatment under the condition of 205 ° C. In particular, JP-A-58-160122, JP-A-59-115812, and JP-A-59-114028 disclose a method for controlling the refractive index distribution (the maximum value and the minimum value of the refractive index). May be used, or the following method may be used.

The copolyester is melt-extruded into a sheet and quenched to form an unstretched film, which is heated by roll heating, infrared heating, or the like, and stretched in the machine direction to obtain a stretched film. This stretching is preferably performed by utilizing the peripheral speed difference between two or more rolls. The stretching temperature is higher than the glass transition point (Tg) of the copolyester, and 20-40 ° C higher than Tg
Preferably, the temperature is high. The stretching ratio depends on the physical properties of the final film, but is preferably 2.5 times or more. This magnification is further preferably 3.6 times or less.

The longitudinally stretched film is successively subjected to transverse stretching, heat setting, and heat relaxation to give a biaxially oriented film. These processes are performed while the film is running. The transverse stretching process is started at a temperature higher than the glass transition point (Tg) of the copolymerized polyester by 20 ° C. or more. And the melting point of the polyester (T
m) while the temperature is raised to a temperature lower by (120 to 30) ° C. The stretching start temperature is preferably (Tg + 40) ° C. or lower. For example, in the case of polyethylene terephthalate copolymerized with 12% by mole of isophthalic acid, the temperature is preferably in the temperature range of 73 to 113 ° C. The maximum stretching temperature is from Tm (100 ~ 4
0) Preferably, the temperature is lower by 0 ° C.

The temperature rise in the transverse stretching process may be continuous or stepwise (sequential). Usually the temperature is raised sequentially. For example, the transverse stretching zone of the stenter is divided into a plurality of sections along the film running direction, and the temperature is raised by flowing a heating medium of a predetermined temperature in each zone.
If the transverse stretching start temperature is too low, the film will break,
Not preferred. On the other hand, if the maximum stretching temperature is lower than (Tm-120) ° C., the heat yield of the film increases, and the ratio of uniformity of physical properties in the width direction decreases, which is not preferable. On the other hand, if the maximum stretching temperature is higher than (Tm−30) ° C., the film becomes soft and breaks due to disturbance or the like, which is not preferable.

The transverse stretching ratio depends on the physical properties of the final film,
It is preferably at least 2.7 times, more preferably at least 3.0 times. This magnification is further preferably 3.6 times or less.

The heat setting process is performed after the horizontal stretching, but is started from the temperature at the end of the horizontal stretching. Then, the film is stretched by 2 to 20% in the film width direction and at a temperature of (Tm−20) ° C. or lower. This stretching is commonly referred to as toe-out and is preferably 5-15%. Further, the difference between the temperature at the end of the heat setting and the temperature at the start of the heat setting is preferably 40 ° C. or less, more preferably 30 ° C. or less. In some cases, the temperature difference may be 1 ° C., but 5 ° C. or more, and further 10 ° C.
It is preferable to make the above. If the elongation in the heat setting is less than 5%, the isotropic region in the film width direction becomes small, which is not preferable. On the other hand, if the elongation is more than 20%, not only is the heat yield in the lateral direction markedly increased, but also the film tends to break, which is not preferable.

The heat-set film is once cooled to a temperature below the glass transition point (Tg) of the polyester, slit at a predetermined width at the end of the film, separated, and then subjected to a heat relaxation treatment as required.

The heat relaxation treatment does not restrict the film width direction, and 4 ~ 10
It is carried out at a temperature of (Tg + 30) to (Tg + 80) ° C. for 0.3 to 20 seconds under a running tension as low as kg / cm ² . The thickness of the film subjected to the thermal relaxation treatment is preferably 6 to 75 μm, more preferably 10 to 75 μm. The width of the film is preferably 1 m or more. The above treatment temperature is, for example, about 103 to 153 ° C. in the case of a 12 mol% isophthalic acid copolymerized polyester. The thermal relaxation treatment is preferably performed using a heating and floating treatment device. As a medium for heating and floating the film, a heated inert gas, particularly, heated air is preferably used. According to the heating and floating treatment, the heat relaxation treatment can be efficiently performed while maintaining stable film running.

The object of the present invention is achieved only when all of the above five requirements of the melting point, the lubricant, the refractive index in the thickness direction, the refractive index distribution, and the sub-peak temperature by DSC are satisfied. For example, a polyethylene terephthalate homopolymer is used. Even if the requirements for lubricant, thickness direction refractive index, refractive index distribution, and sub-peak temperature by DSC are satisfied, good can workability (deep drawability) cannot be obtained, and the average particle size of lubricant exceeds 2.5 μm. If the other four requirements are met, a pinhole will occur,
It causes trouble. If the sub-peak temperature by DSC is not in the range of 150 to 205 ° C., good can quality cannot be obtained even if the other four requirements are satisfied.

The polyester film of the present invention preferably has a thickness of 6 to 75 μm. 10 to 75 μm, especially 15 to 50 μm
It is preferred that If the thickness is less than 6 μm, breakage or the like is likely to occur during processing, while if it exceeds 75 μm, the quality is excessive and uneconomical.

As a metal plate for cans to which the polyester film of the present invention is bonded, a plate of tin, tin-free steel, aluminum or the like is suitable. The bonding of the polyester film to the metal plate can be performed, for example, by the following method.

The metal plate is heated to a temperature equal to or higher than the melting point of the film, the film is bonded, and then rapidly cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered.

The adhesive layer is primer-coated on the film in advance, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive such as an epoxy-based adhesive, an epoxy-ester-based adhesive, an alkyd-based adhesive, or the like can be used.

<Example> Hereinafter, the present invention will be further described with reference to examples.

Examples 1 to 4 and Comparative Examples 1 to 3 Spherical monodisperse silica having an average particle size of 1.5 μm or 2.0 μm (particle size ratio 1.07, relative standard deviation 0.1) was added and the components shown in Table 1 were copolymerized. The copolymerized polyethylene terephthalate (intrinsic viscosity: 0.60) was melt-extruded at the temperature shown in the same table and solidified rapidly to obtain an unstretched film.

Next, the unstretched film was stretched longitudinally and transversely under the conditions shown in the same table, and then heat-set to obtain a biaxially oriented film having a thickness of 25 μm.

 Table 4 shows the characteristics of this film.

Comparative Example 4 12 mol% copolymerized polyethylene terephthalate (intrinsic viscosity: 0.60) containing the bulk silica shown in Table 2 was melt-extruded at 280 ° C., quenched and solidified to obtain an unstretched film, and then the unstretched film The longitudinal stretching temperature is 100
The film was successively biaxially stretched at 30 ° C., a longitudinal stretching ratio of 3.0 times, a transverse stretching start temperature of 110 ° C., a transverse stretching end temperature of 160 ° C., and a transverse stretching ratio of 3.1 times, and then heat-set at a heat setting temperature of 190 ° C. and an elongation of 10%.

 Table 4 shows the properties of the obtained biaxially oriented film.

Comparative Examples 5 to 9 12 mol% of isophthalic acid copolymerized polyethylene terephthalate containing 0.05% by weight of spherical monodisperse silica having an average particle size of 2.0 μm (particle size ratio 1.07, relative standard deviation 0.1) (melting point
(229 ° C, intrinsic viscosity 0.60) was melt-extruded at 280 ° C and quenched and solidified to obtain an unstretched film. Next, the unstretched film was stretched longitudinally and transversely under the conditions shown in Table 3 and then heat-set to obtain a biaxially oriented film.

Here, ordinary sequential biaxial stretching was performed without taking the method for isotropy.

A total of 14 kinds of films obtained in the above Examples 1 to 5 and Comparative Examples 1 to 9 were bonded to both sides of a 0.25 mm thick tin-free steel heated to 260 ° C., cooled with water, and then cooled to a 150 mm diameter disk. It was cut into two pieces and deep-drawn in two stages using a drawing die and a punch to prepare a 55 mm-diameter side seamless container (hereinafter abbreviated as can).

The following observations and tests were performed on the cans, and the cans were evaluated according to the following criteria.

(1) Deep drawing workability-1 ○: Both inner and outer surfaces are processed into films without any abnormality, and no whitening or breakage is observed in the films on the inner and outer surfaces of the can.

Δ: Whitening was observed on the top of the film inside and outside of the can.

X: Film breakage is observed in a part of the film on the inner and outer surfaces of the can.

(2) Deep drawing workability-2 ○: The inner and outer surfaces were processed without any abnormality, and the rust prevention test of the film surface in the can (1% NaCl water was put in the can, the electrode was inserted, and the can body was used as the anode. Measure the current value when a voltage of 6 V is applied.

×: There is no abnormality in the film on both the inner and outer surfaces, but the current value is 0.2 mA or more in the ERV test. When the energized portion is observed under magnification, pinhole-shaped cracks starting from the coarse lubricant are observed in the film.

(3) Impact cracking resistance For cans with good deep drawing, pour water thoroughly, drop 10 pieces for each test from a height of 1 m onto a PVC tile floor, and conduct an ERV test in the can. Result: 0.2: 0.2 mA or less for all 10 samples.

Δ: 0.2 mA or more for 1 to 5 pieces.

C: 0.2 mA or more for 6 or more.

Alternatively, the film was already cracked after falling.

(4) Heat embrittlement resistance The can which had been subjected to good deep drawing was heated and maintained at 210 ° C. for 5 minutes, and then subjected to the impact cracking resistance evaluation described in (3). It was less than 0.2 mA.

Δ: 0.2 mA or more for 1 to 5 pieces.

C: 0.2 mA or more for 6 or more.

Alternatively, after heating at 210 ° C. for 5 minutes, cracking of the film was already observed.

 Table 4 shows the above four types of evaluation results.

From the results shown in Table 4, the film of the example was found to have deep drawability,
It turns out that it is excellent in all of the impact cracking resistance and the heat resistance.

In addition, when the heating temperature of the tin-free steel was changed variously for the films of Comparative Examples 5 and 9, no area where the overall evaluation was good (で) was found even if the heating temperature was increased or decreased.

<Effect of the Invention> The polyester film for metal laminating and forming of the present invention can be subjected to can drawing after laminating with a metal plate, for example, in deep drawing to form a metal can. It has excellent impact resistance and heat resistance, and is extremely useful for metal containers.

[Brief description of the drawings]

Figure 1 is an example of a DSC chart, where A is melting point, B
Indicates a sub-peak temperature.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication C08L 67:02 (72) Inventor Yoji Murakami 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture Teijin Limited Sagamihara Research Center (56) References JP-A-3-87249 (JP, A)

Claims (1)

(57) [Claims] An average particle diameter of 2.5 μm or less, a relative standard deviation of 0.3 or less, and a particle diameter ratio (major axis / minor axis) of 1.0 to 1.
2, which comprises a copolymerized polyester having a melting point of 210 to 245 ° C. and a refractive index in the film thickness direction of 1.
505 to 1.545, the refractive index in the film plane direction is 1.61 to 1.66 in all directions, and the sub peak by DSC is 150
A polyester film for metal lamination molding, which is at a temperature of up to 205 ° C.