JPH05287090A - Biaxially oriented polyester film for metal sheet laminate - Google Patents

Abstract

PURPOSE:To provide the title film which has specified characteristics and hence is suitable for laminating with a metal sheet to give a laminate formable into a container by incorporating TiO2 and a pigment into a specific copolyester. CONSTITUTION:The title film is made from a copolyester having an m.p. of 210-245 deg.C (e.g. polyethylene terephthalate prepd. by using isophthalic acid as a comonomer), contains TiO2 having a mean particle diameter of 0.5mum or lower and at least one pigment (e.g. quinacridone), and has a degree of crystal orientation in the thickness direction of 0.2-0.6, a total light transmittance of 40% or lower, and a color which has a hue angle H deg., a lightness value L*, and a chroma C* in the L*/a*/b* color specification system satisfying the following relations: -60 deg.<=H<=60 deg., L*>=60, C*>=3, and 2L*+C*>=200, wherein H deg.=tan<-1>b*/a* (wherein a*>0) and C*={(a*)<2>+(b*)<2>]1/2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film for laminating metal plates, and more particularly to a biaxially oriented copolyester film useful for forming a container after being laminated on a metal plate.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion on the inside and outside. Recently, for the purpose of simplifying the process, improving hygiene, preventing pollution, etc., coating with a thermoplastic resin film has been attempted as a method of imparting rust preventive properties without using an organic solvent.

That is, a method of making a can by laminating a thermoplastic resin film on a metal plate such as tin plate, tin-free steel, aluminum or the like and then making a can is under study.

Polyolefin film and polyamide film have been tried as this thermoplastic resin film.
Moldability, heat resistance, and aroma retention are not all satisfied.

On the other hand, a polyester film, especially a polyethylene terephthalate film, has been noted as having balanced properties, and several proposals based on this have been made. That is,

(A) A biaxially oriented polyethylene terephthalate film is laminated on a metal plate via an adhesive layer of low melting point polyester 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 and JP-A-2-573).
39). (C) A low orientation, heat-set, biaxially oriented polyethylene terephthalate film which is heat-fixed is laminated on a metal plate and used as a can-making material (Japanese Patent Laid-Open No. 64-22530).

[0007]

However, as a result of the study by the present inventors, it has been clarified that neither of the sufficient characteristics is obtained, and the following problems are involved.

Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and aroma retention,
Molding processability is insufficient and minute cracks occur in the film during can manufacturing that involves large deformation, and in extreme cases fracture occurs.

Regarding (B), since it is an amorphous or extremely low crystalline aromatic polyester film, it has good moldability, but has poor flavor retention, and printing after can-making and retort sterilization treatment. After treatment such as the above, and further storage for a long period of time, the film is liable to be brittle, and there is a possibility that the film may deteriorate due to an impact from the outside of the can.

Regarding (C), although it is intended to exert its effect in the intermediate region between (A) and (B), it has not yet reached the low orientation applicable to can manufacturing.

Further, printing is generally performed on the outer surface of the metal container, but a white paint is pre-coated for the purpose of shading at the time of printing, and then printing is performed. When the thermoplastic resin film laminated on the metal plate is a white light-shielding film, the undercoating of the white paint can be omitted. In the methods (A), (B) and (C), the white pigment is used. In the case of the white film produced by adding the above, the respective drawbacks cannot be eliminated and the purpose of the outer surface of the can cannot be achieved.

Further, when a white pigment is added to the polyester film alone, when it is laminated on a metal plate, it becomes dull white due to the influence of the color of the underlying metal plate, which makes color matching during printing difficult. ..

An object of the present invention is to provide a polyester film for laminating metal plates, which is excellent in moldability, light-shielding property, color tone, and coloring property of printing ink.

[0014]

The inventor of the present invention arrived at the present invention as a result of extensive studies to achieve the above object.

That is, the present invention comprises a copolymerized polyester containing titanium dioxide having an average particle size of 0.5 μm or less and at least one other coloring agent, and having a melting point in the range of 210 to 245 ° C. Has a degree of crystal orientation in the thickness direction of 0.2 to 0.6 and a total light transmittance of 4
0% or less, the hue angle H ° in the L * / a * / b * color system, the lightness L *, and the saturation C * have a color satisfying the following expressions (1) to (4). A biaxially oriented polyester film for laminating metal plates.

[0016]

[Equation 2]

A typical example of the copolymerized polyester in the present invention is a copolymerized polyalkylene terephthalate. The copolymerization component may be an acid component or an alcohol component. Examples of the acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid, and alicyclic compounds such as cyclohexanedicarboxylic acid. Examples thereof include group dicarboxylic acids. Examples of the alcohol component include aliphatic diols such as ethylene glycol, butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These may be used alone or in combination of two or more. Further, two or more kinds of copolyesters may be blended and used.

The proportion of the copolymerization component and the proportion of the blend of the copolyester depend on the kind, but as a result, the melting point of the polymer is 210 to 245 ° C., preferably 215.
The ratio is in the range of ˜235 ° C. Polymer melting point is 2
If the temperature is lower than 10 ° C, the heat resistance is inferior, and therefore, the heating in printing after can making cannot be endured. On the other hand, the polymer melting point is 245
When the temperature exceeds ℃, the crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of the copolymerized polyester is measured by a method using a Du Pont Instruments 910 DSC to obtain a melting peak at a temperature rising rate of 20 ° C./min. The sample amount is about 20 mg.

Titanium dioxide contained in the copolyester of the present invention is crystalline in anatase type,
Any of rutile type may be used. Further, for the purpose of improving the dispersibility of titanium dioxide in polyester, titanium dioxide whose surface is treated with an oxide such as aluminum, silicon or zinc or various organic substances can also be used.

The average particle size of titanium dioxide is 0.5 μm or less, preferably 0.05 to 0.4 μm. Here, the average particle diameter means the “equivalent spherical diameter” of particles at a point of 50% by weight of all measured particles. Further, the “equivalent spherical diameter” means the diameter of an imaginary sphere having the same volume as the particle, and can be calculated from the measurement by a usual sedimentation method or the like. When the average particle size of titanium dioxide is larger than 0.5 μm, generally, there are many coarse particles and the light-shielding property becomes poor, which is not preferable.

The content of titanium dioxide added to the polyester is not particularly limited as long as the total light transmittance of the film is 40% or less and the color of the film satisfies the following formulas (1) to (4). It is preferably 5 to 30% by weight, more preferably 10 to 25% by weight. When the content of titanium dioxide is less than 5% by weight, the light-shielding property becomes insufficient. On the other hand, when it exceeds 30% by weight, the film breaks at the time of stretching the film and the breakage occurs during deep drawing, which is not preferable.

In the present invention, another coloring agent used in combination with titanium dioxide is an inorganic type if the total light transmittance of the film is 40% or less and the color of the film satisfies the following formulas (1) to (4). The organic type may be used, and the dye or pigment may be used, but those having heat resistance and weather resistance are preferable. Examples of this inorganic pigment include red iron oxide, cadmium red, cobalt blue, and the like, examples of this organic dye include Samaron blue, indico, rose bengal, and the like, and as this organic pigment, quinacridone red, quinacridone violet. , Chromophthal red, perylene red, phthalocyanine blue, and the like. These may be added alone or in combination of two or more.

The content of the other colorant added is not particularly limited as long as the total light transmittance of the film is 40% or less and the color of the film satisfies the following expressions (1) to (4).

The color of the film in the present invention satisfies the following expressions (1) to (4).

[0026]

[Equation 3]

If the hue angle H ° does not satisfy the expression (1), it is impossible to eliminate the influence of the color of the metal plate when the film is attached to the metal plate. Also, lightness L * and saturation C *
When does not satisfy the expressions (2) to (4), the color of the film itself becomes dark.

Here, the total light transmittance of the film is measured by a Poic integrating sphere light transmittance meter. L * value, a *
The value and b * value are Y = 94.95, X = 93.63, Z = 112.3 by the Nippon Denshoku Industries SZ-Σ90 color difference meter.
The measurement is performed with 10 films placed on a white standard plate having a tristimulus value of 2. In addition, L * value, a * value,
b * value is L * / a * / b * defined in CIE1976
This is due to the color system.

The copolyester used in the present invention is not limited by its production method. For example, a method of subjecting terephthalic acid, ethylene glycol and a copolymerization component to an esterification reaction, and then subjecting the resulting reaction product to a polycondensation reaction to form a copolymerized polyester, or a transesterification reaction of dimethyl terephthalate, ethylene glycol and a copolymerization component. Then, the resulting reaction product is subjected to a polycondensation reaction to obtain a copolyester, which is preferably used. In the production of the copolyester, it is preferable to add titanium dioxide and other colorants, and if necessary, other additives such as optical brighteners, antioxidants, heat stabilizers, UV absorbers, electrostatic agents. Inhibitors and the like can also be added. The addition of a fluorescent whitening agent is particularly effective in order to improve whiteness.

The titanium dioxide and other colorants in the present invention are preferably subjected to a particle size adjustment and coarse particle removal using a refining process before being added to the copolyester. As the industrial means of the refining process, examples of the pulverizing means include a jet mill and a ball mill, and examples of the classifying means include a dry or wet centrifuge. In addition, these means combine two or more kinds,
Of course, it may be purified stepwise.

Various methods can be used to incorporate titanium dioxide and other colorants into the copolyester. The following methods can be given as typical methods.

(A) A method of adding before the completion of the transesterification reaction or the esterification reaction during the synthesis of the copolyester, or before the start of the polycondensation reaction.

(A) A method of adding to the copolyester and melt-kneading.

(C) In the above-mentioned methods (a) and (a), master pellets containing a large amount of titanium dioxide and other coloring agents are produced, and kneaded with a copolymerized polyester containing no such additives to give a predetermined amount. The method of including the additive of.

When the method (a) of adding the polyester during the synthesis is used, it is preferable to add it to the reaction system as a slurry in which titanium dioxide or another coloring agent is dispersed in glycol.

The biaxially oriented polyester film of the present invention is obtained by melting the above-mentioned copolymerized polyester containing titanium dioxide and another colorant, discharging it from a die to form a film, and biaxially stretching and heat-setting. Is. The degree of crystal orientation in the thickness direction of this film is in the range of 0.2 to 0.6, preferably 0.25 to 0.55. When the crystal orientation degree exceeds 0.6, the moldability becomes insufficient and the film is liable to break during deep drawing. On the other hand, when the crystal orientation is less than 0.2, that is, when the orientation is excessively low, the heat resistance becomes insufficient.

The degree of crystal orientation is measured as follows.

Using an X-ray diffractometer, the crystal orientation index <cos ² Φ _j , 1 in the three directions (longitudinal direction MD, width direction TD, thickness direction ND) of the film crystal plane (100).
00>, and the crystal orientation degree f ^{i, k} is calculated from the following equation.

F ^{i, k} = 2/3 <cos ² Φ _{j, k} > −1/2 (where i = MD, TD or ND, k = 100) where the crystal orientation in the three directions is Rigaku Denki Measure using a pole-making sample stand.

However, since the reflection peaks due to the titanium dioxide particles are near an anatase (101) and a rutile (110) of the copolyester (100), (100) of the copolyester of α = 0 in the pole figure. ) _Is the reflection intensity of titanium dioxide (I _TiO2, α _{= 0} )
As a result, the crystal orientation degree is calculated by subtracting I _TiO2, α _{= 0} from the intensities at all α and β positions up to α = 90 °.

Here, I _TiO2, α _{= 0} = 1/2 (I _TiO2, α
_{= 0} , _MD + I _TiO2, α _{= 0} , _TD ).

In the above, α is the pole sample stand, and α = 9
0 ° represents the case where (100) is arranged in parallel with the film surface, and α = 0 ° represents the case where it is arranged perpendicularly to the film surface. Further, β represents the method in the MD and TD planes of the film, and β = 0 is the MD and β = 90 ° is the TD direction. In the present invention, the crystal orientation is N in the thickness direction.
It is represented by the value of D.

As an example of a method for producing a film satisfying such requirements, a biaxial stretching method, particularly a sequential biaxial stretching method will be described below, but the present invention is not limited to this method. ..

As described above, the copolyester containing titanium dioxide and another colorant is melted, discharged from a die to be formed into a film, and immediately cooled to obtain a substantially amorphous copolyester sheet. obtain. Next, this sheet is heated by roll heating, infrared heating or the like and stretched in the longitudinal direction. At this time, the stretching temperature is preferably 20 to 40 ° C. higher than the glass transition point (Tg) of the copolyester, and the stretching ratio is preferably 2.7 to 3.6 times. Stretching in the transverse direction is preferably carried out while starting at a temperature higher than Tg by 20 ° C. or more and raising the temperature to 100 to 130 ° C. lower than the melting point (Tm) of the copolyester. The transverse stretching ratio is preferably 2.8 to 3.7 times. Further, the heat setting temperature is selected in the range of 150 to 205 ° C. to adjust the film quality according to the melting point (Tm) of the copolyester polymer.

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

The object of the present invention is achieved only when the above-mentioned six conditions of titanium dioxide and other colorants, as well as the melting point of polyester, the crystal orientation of film, the total light transmittance and the color are satisfied. It is something. When all of the six conditions are satisfied, it becomes possible to obtain a biaxially oriented polyester film for laminating metal plates, which is excellent in moldability, light-shielding property, color tone, and coloring property of printing ink.

As the metal plate to which the biaxially oriented polyester film of the present invention is laminated, particularly as a metal plate for can manufacturing, tin, tin-free steel, aluminum and the like plates are suitable. The biaxially oriented polyester film can be attached to the metal plate by, for example, the following method.

The metal plate is heated above the melting point of the film, the films are laminated and then cooled, and the surface layer portion (thin layer portion) of the film in contact with the metal plate is made amorphous and adhered.

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

[0050]

EXAMPLES The present invention will be further described below with reference to examples.

[0051]

Examples 1 to 6 and Comparative Examples 1 to 11 Copolymerized polyethylene terephthalate (intrinsic viscosity 0.64) obtained by copolymerizing the components shown in Table 1 with the white pigments and colorants having the particle sizes shown in the same table. Using the pellets added and contained in the concentration shown in, melt-extruded under the film forming conditions shown in the same table, rapidly cooled and solidified to an unstretched film, and then the unstretched film was longitudinally stretched under the conditions shown in the same table, and laterally stretched. And then heat set to a thickness of 20 μm
A biaxially oriented film of was obtained.

The characteristics of this film are shown in Table 2.

A total of 17 kinds of films obtained in Examples 1 to 6 and Comparative Examples 1 to 11 were laminated on both sides of a 0.25 mm thick tin-free steel heated to 260 ° C., and after cooling with water. A disk having a diameter of 150 mm was cut out, and deep drawing was performed in three steps using a drawing die and a punch to prepare a side surface seamless container (hereinafter, abbreviated as a can) having a diameter of 55 mm.

The following observations and tests were carried out on this container, and each container was evaluated according to the following criteria.

(1) Deep drawing workability-1 ○: Both the inner and outer surfaces of the film were processed without any abnormalities, and no microcracks or fractures were found in the film on the inner or outer surface of the can. Δ: Film rupture is recognized in a part of the film inside and outside 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 inside the can (1% NaCl water was put in the can, the electrode was inserted, and the can body was The current value is measured when an anode is applied with a voltage of 6 V. 0.2 mA in ERV test)
The following is shown. X: 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, and pinhole-like cracks originating from the film coarse lubricant are observed when the energized portion is enlarged and observed.

(3) Impact crack resistance With respect to cans with good deep-drawing, water was fully poured, and 10 bottles for each test were dropped from a height of 30 cm onto the PVC tile floor surface, and then the ERV test in the cans was conducted. As a result, ◯: 0.2 mA or less for all 10 pieces. (Triangle | delta): It is 0.2 mA or more about 1-5 pieces. X: 0.2 mA or more for 6 or more, or cracks of the film are already observed after dropping.

(4) Heat embrittlement resistance After the cans, which had been well drawn by deep drawing, were heated and held at 210 ° C. for 5 minutes, the impact crack resistance evaluation as described in (3) above was carried out. It is 0.2 mA or less for all 10 pieces. (Triangle | delta): It is 0.2 mA or more about 1-5 pieces. ×: 0.2 mA or more for 6 or more, or cracks of the film are already observed after heating at 210 ° C. for 5 minutes.

(5) Before bonding the light-shielding film and the tin-free steel, the tin-free steel surface, which is the outer surface of the can after making the can, is provided with a crow mouth to have a length of 50 mm, a width of 0.1 mm, and a width of 0.1 mm, respectively. A line was entered, and this black line was observed through the film after can making. The evaluation was performed as follows. ◯: Both black lines with a width of 1 mm and 0.1 mm are invisible. Δ: A black line with a width of 1 mm is slightly visible, but a black line with a width of 0.1 mm is not visible. X: A black line with a width of 1 mm is visible, and a black line with a width of 0.1 mm is also faintly visible.

(6) Print Sharpness A circle having a diameter of 5 mm of magenta, yellow, cyan and black was printed on the outer surface of the can with printing ink, and the color was observed. The evaluation was performed as follows. ○: All colors look vivid. X: There is a dull color.

Table 2 shows the evaluation results of the above six types.

[0062]

[Table 1]

[0063]

[Table 2]

From the results shown in Table 2, it is understood that the films of Examples are excellent in all of deep drawing workability, impact crack resistance, heat resistance, light shielding property, and print definition.

[0065]

INDUSTRIAL APPLICABILITY The biaxially oriented polyester film for laminating metal plates of the present invention has a deep drawing workability and a can-making property when it is formed into a metal can by, for example, deep-drawing after forming it into a can. It is excellent in impact resistance, heat resistance, light-shielding property and printing clarity afterward, and is extremely useful as a metal container.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Reference number in the agency FI Technical display location B32B 27/20 A 6122-4F Z 6122-4F 27/36 7016-4F B65D 1/09 1/28 7445-3E C08K 3/20 C08L 67/02 KJR 8933-4J // C08J 5/12 CFD 9267-4F B29K 67:00 105: 16 B29L 9:00 4F (72) Inventor Gen Izumi 3-37 Oyama, Sagamihara-shi, Kanagawa No.19 inside Sagamihara Research Center, Teijin Limited

Claims (2)

[Claims] 1. A titanium dioxide having an average particle size of 0.5 μm or less and at least one other colorant, and a melting point of 2
It is composed of a copolyester in the range of 10 to 245 ° C. and has a crystal orientation in the thickness direction of the film of 0.2 to 0.6.
, The total light transmittance is 40% or less, L
* / A * / b * Hue angle H °, lightness L in color system
A biaxially oriented polyester film for laminating metal plates, which has a color whose saturation C * satisfies the following formulas (1) to (4). [Equation 1] 2. The biaxially oriented polyester film for laminating metal plates according to claim 1, which is formed into a container after the film is laminated on a metal plate.