JPH1060135A - White polyester film for metal lamination and preparation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a white polyester film for metal lamination which possesses excellent heat lamination, strength, hiding power and the like by feeding three specified compsns. in a predetermined ratio into an extruder, extruding the combined compsn. into a sheet, and biaxially stretching the sheet. SOLUTION: A compsn. (A) prepd. by incorporating not less than 30wt.% TiO2 into a copolyester comprising 90 to 50mol% ethylene terephthalate units and 10 to 50mol% ethylene isophthalate units, a compsn. (B) prepd. by incorporating 0 to 15wt.% TiO2 into a copolyester comprising 85 to 95mol% ethylene terephthalate units and 15 to 5mol% ethylene isophthalate units, and a compsn. (C) prepd. by incorporating silicon oxide, a metal compd., phosphoric acid and the like into a polyester having the same compsn. as the polyester in the compsn. (B) are extruded into a sheet so that the content of the compsn. (C) is 1 to 20wt.%, the ethylene terephthalate unit content is 95 to 75mol%, the ethylene isophthalate unit content is 5 to 25mol%, and the TiO2 content is 20 to 40wt.%. The sheet is then biaxially stretched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white polyester film for metal lamination having excellent heat laminating properties, moldability and tensile strength, excellent concealing properties, and excellent whiteness. It is about.

[0002]

2. Description of the Related Art Food and beverage packaging includes steel cans,
Metal cans such as aluminum cans are used in large quantities. Conventionally, these metal cans are provided with corrosion resistance, printability, etc.
It has been used by applying a solvent type paint mainly composed of a thermosetting resin. However, the application of such a paint has poor productivity and has a problem of environmental pollution, etc. Recently, a biaxially stretched plastic film or a laminated film based on the biaxially stretched plastic film is laminated. The use of metal lamination has increased.

A metal can covered with a plastic film is manufactured by laminating a plastic film on a metal plate such as a steel plate or an aluminum plate (including a plate that has been subjected to a surface treatment such as plating), and forming a laminated metal plate. You. And the plastic film used here has good laminability with a metal plate, and is excellent in moldability.
No peeling, cracks, cracks, and pinholes of the film during molding
Numerous properties such as no water spots and white powder when retorted, excellent concealment properties and whiteness are required at the same time.

Therefore, in particular, as a film for the outer surface of a can,
Among the plastic films, a biaxially stretched film of polyethylene terephthalate (PET) or a copolymer thereof filled with titanium oxide at a high concentration has excellent physical and chemical properties, low production cost, and excellent cost performance. Used as a material.

In general, when a polyester film is manufactured by a flat method, a molten resin is extruded from a T-die and is cooled by being brought into contact with a cooling drum (cast roll).
Usually, at this time, a method of applying a high voltage (generally 5 to 10 kV) to the film, bringing the film into close contact with a cast roll by electrostatic force and rapidly cooling the film (referred to as an electrostatic pinning method) is employed.
However, polyester generally has a high specific resistance, causing aerial discharge when a high voltage is applied, or causing a problem that fine irregularities called pinning bubbles occur on the film surface due to uneven adhesion of the film to the cast roll. Sometimes. In order to prevent such a problem, it has been proposed to mix a specific metal compound with polyester to form a pinning master, and mix it with polyester to lower the specific resistance of polyester (Japanese Patent Publication No. 53-4).
No. 0231, JP-B-61-33855, JP-A-59-2146
No. 18, JP-A-60-11529).

However, in the case of producing a PET-based white copolyester film copolymerized with isophthalic acid used in the present invention, even if a conventionally used PET pinning master is blended, the generation of pinning bubbles and the like occur. Therefore, this solution has been sought.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and has excellent adhesiveness (thermal lamination property), mechanical strength, printability, and excellent concealing properties and whiteness. An object of the present invention is to provide a white copolyester film suitably used for laminating a metal can at an economical price.

[0008]

Means for Solving the Problems The inventors of the present invention prepared a white masterbatch of composition A in which a resin obtained by modifying PET at a specific copolymerization ratio with isophthalic acid and titanium oxide at a high concentration was used as a white masterbatch. Resin composition B having a low copolymerization ratio
By further diluting the composition, and blending the composition C in which a specific pinning agent is blended with the polyester having the same component composition ratio as the composition B, a high-quality white copolyester film is produced with good operability. They have found that they can do so and arrived at the present invention.

That is, the gist of the present invention is as follows. 1. Compositions A to C below, wherein composition C is 1 to 20% by weight,
The ethylene terephthalate unit is 95 to 75 mol%, the ethylene isophthalate unit is 5 to 25 mol%, and the titanium oxide content is 20 to 40% by weight. A method for producing a white polyester film for metal lamination, comprising biaxially stretching in a direction. Composition A: consisting of 90 to 50 mol% of ethylene terephthalate units and 10 to 50 mol% of ethylene isophthalate units,
Titanium oxide 30 in copolyester with intrinsic viscosity 0.5 or more
A composition that is blended by weight or more. Composition B: composed of 85 to 95 mol% of ethylene terephthalate units and 15 to 5 mol% of ethylene isophthalate units,
Polyester with an intrinsic viscosity of 0.5 or more and 0 titanium oxide
A composition containing 15% by weight. Composition C: 0.1 to 1.6% by weight of silicon oxide and an alkali metal compound selected from lithium, sodium and potassium are added to a polyester having the same composition ratio as that of composition B.
1.0 to 50 × 10 ^-4 mol / mol of acid component, metal compound selected from magnesium, calcium, manganese and zinc
1.0 to 50 × 10 ^-4 mol / acid component to 1 mole, and phosphoric acid, phosphorous acid or, these ester 1.0 to 50 × 10 ^-4 mol / acid component 1 mole composition containing. 2. 2. The method for producing a white polyester film for metal lamination according to claim 1, wherein the biaxial stretching method is a simultaneous biaxial stretching method. 3. 3. A white polyester film for metal laminate, having the following characteristics (1) to (6), obtained by the production method according to the above item 1 or 2. (1) Tensile strength 15kgf / mm ² or more (2) Thermal shrinkage at 160 ° C 5.0% or less (3) Optical density 0.3 or more (4) Gloss 10 or more (5) Whiteness 81.0 or more (6) Adhesive strength 300gf or more

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the present invention, the polyester constituting the film contains 95 to 75 mol% of ethylene terephthalate units.
And 5 to 25 mol% of ethylene isophthalate units.

If the proportion of the ethylene isophthalate unit is less than 5 mol%, the polyester lacks heat laminating properties, and if it exceeds 25 mol%, the strength is insufficient, which is not preferable.

The polyester resins in the composition A, the composition B and the composition C used in the present invention have an intrinsic viscosity.
It must be 0.5 or more, and if the intrinsic viscosity is smaller than this, the strength is insufficient. However, if the intrinsic viscosity is too large, not only will the quality be excessive,
On the contrary, the operability during the production of the film is deteriorated, and the heat laminating property is deteriorated. Particularly preferred are polyesters having an intrinsic viscosity of 0.6 to 1.2.

Further, the polyester preferably has a melting point of 200 to 240 ° C. for a crystalline copolyester and a glass transition point of 50 to 75 ° C. for an amorphous copolyester. If the ratio is out of the range, the heat resistance is insufficient or the heat laminating property is deteriorated, which is not preferable.

The polyester has a content of oligomers (linear or cyclic 1- to 9-mers mainly composed of a cyclic trimer) of 0.1 to 2% by weight and a content of acetaldehyde of 5 to 5% by weight.
A range of from 50 ppm to 50 ppm is preferable. If the range is out of these ranges, it is not preferable because it causes white powder, adversely affects taste, and increases production cost.

In the industrial production of polyester, a diethylene glycol component is inevitably produced as a by-product. However, it is desirable to control the content to be 1 to 3.5 mol% of the total glycol component. And the production cost becomes excessive, which is not preferable.

The polyester may be further copolymerized with components other than isophthalic acid within a range that does not impair the properties (usually 5 mol% or less). Specific examples of the copolymer component include phthalic acid, 2,6-naphthalenedicarboxylic acid,
-Dicarboxylic acids such as sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dodecane diacid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, and cyclohexanedicarboxylic acid Acid, 4-hydroxybenzoic acid,
ε-caprolactone, hydroxycarboxylic acids such as lactic acid,
Examples include diols such as 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, and ethylene oxide adducts of bisphenol A and bisphenol S. A tri- or higher functional compound such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, and pentaerythritol may be used in a small amount.

The polyester in the present invention can be produced by a conventional method. For example, a PET copolymer obtained by copolymerizing an isophthalic acid component can be produced as follows.

First, a slurry of terephthalic acid and ethylene glycol is continuously supplied to an esterification tank in which bis (β-hydroxyethyl) terephthalate and / or its low polymer is present, and the slurry is heated at a temperature of about 250 ° C. for 8 hours. The esterification reaction rate is about 95% to continuously obtain an esterified product. Transfer this to a polymerization vessel, add the required amount of isophthalic acid or its ethylene glycol ester, and polycondensate at a temperature of about 280 ° C under a reduced pressure of 1.3 hPa or less in the presence of a catalyst such as antimony trioxide or germanium dioxide. Perform the reaction.

The polyester thus obtained is
Since oligomers and acetaldehyde are contained in relatively large amounts, solid-phase polymerization at a temperature of 200 to 240 ° C (a temperature not exceeding the melting point of polyester) under reduced pressure or an inert gas flow is used to reduce these amounts. Further, it is desirable that the film is treated with steam or hot water, if necessary, and then subjected to a film forming process.

The amount of the ethylene isophthalate unit of the copolyester in the composition A is preferably from 10 to 50 mol%, and more preferably from 10 to 30 mol%. It is necessary to reduce the proportions of B and composition C, and the strength of the film decreases, and if it exceeds 50 mol%, the film-forming properties decrease. The amount of titanium oxide in the composition A is 30% by weight or more, preferably
Desirably, 30 to 70% by weight, and this amount is 30% by weight.
If it is less than the above, it is necessary to reduce the proportion of the composition B, and the strength of the film is reduced. If the amount is too large, the dispersibility in the copolyester is deteriorated, or the shape of the composition A chip is deteriorated. However, it is not preferable because biting failure occurs in the extruder.

The amount of ethylene isophthalate units of the copolyester in compositions B and C ranges from 15 to 5 mol%, preferably from 11 to 9 mol%. If it is less than 5 mol%, the adhesive strength will be insufficient, and if it is more than 15 mol%, the mechanical strength will be insufficient, which is not preferable. The titanium oxide concentration of composition B ranges from 0 to 15% by weight, preferably from 0 to 10% by weight, optimally from 0 to 5% by weight. If it is more than 15% by weight, the mechanical strength is insufficient, which is not preferable.

In the composition C of the present invention, the esterified product having an esterification reaction rate of about 95% is transferred to a polymerization vessel, a predetermined amount of isophthalic acid is added, and 0.1 to 1.6% by weight of silicon oxide is used as a lubricant. An alkali metal compound (hydroxide, acetate, carbonate, etc.) selected from lithium, sodium and potassium as a pinning agent is 1.0 to 50 × 10 ⁻⁴ mol / acid component 1 mol, magnesium, calcium, manganese, A metal compound selected from zinc (hydroxide, acetate, carbonate, etc.) in an amount of 1.0 to 50 × 10 ⁻⁴ mol / acid component 1 mol,
And phosphoric acid, phosphorous acid, or a lower fatty acid ester thereof, etc., in an amount of 1.0 to 50 × 10 ^-4 mol / mol of the acid component, and adding each component as a solution or slurry of ethylene glycol to form a catalyst. It can be obtained by melt polymerization to a desired viscosity in the presence at a temperature of about 280 ° C. under a reduced pressure of 1.3 hPa or less.

The titanium oxide used in the present invention is:
Rutile-type or anatase-type titanium oxide is used and may be used alone or as a mixture. Titanium oxide has a particle size of 0.5 μm or less, preferably 0.1 to 0.5
It is preferable that the particle diameter is larger than μm, and if the particle diameter is larger than this, the dispersibility in the polyester becomes poor, and the surface of the obtained film becomes uneven, resulting in low gloss.

The content of titanium oxide in the film is from 20 to
40% by weight, preferably 25-35% by weight, optimally 25-33% by weight. If the content is less than 20% by weight, the concealing properties and whiteness of the film are insufficient, and if it exceeds 40% by weight, the strength of the film is undesirably reduced.

The white film obtained according to the present invention comprises
It is necessary to satisfy the following characteristics (1) to (6). (1) Tensile strength 15 kgf / mm ² or more, preferably 18-25 kgf / mm
² (2) Thermal shrinkage at 160 ° C of 5.0% or less, preferably
4.0% or less (3) Optical density 0.3 or more, preferably 0.4 to 0.7 (4) Gloss 10 or more, preferably 10 to 20 (5) Whiteness 81.0 or more, preferably 85.0 to 95.0 (6) Adhesive strength 300 gf or more

When the tensile strength is less than 15 kgf / mm ^{2, the} strength is practically insufficient. When the heat shrinkage is more than 5%, the printing properties are poor. When the optical density is less than 0.3, the concealing property is poor. When the gloss is less than 10, the appearance of the film becomes poor, and when the whiteness is less than 81.0, the whiteness is practically insufficient, and when the adhesive strength is less than 300 gf, the lamination with metal is performed. Poor. The larger the characteristic value that defines the lower limit,
It is preferable that the characteristic value defining the upper limit is smaller, but if the quality is excessive, not only the cost is increased, but also the operability at the time of film production deteriorates, it is preferable to set the degree as the preferable range described above. Appropriate. The elongation may be in the range of usually 80 to 160% (mechanical direction: MD and direction perpendicular thereto: average of TD).

In the present invention, the compositions A, B, and C are supplied to a melt extruder at a predetermined ratio and extruded into a sheet.
It is biaxially stretched in the machine and transverse directions.

At this time, the composition ratio of the composition A, the composition B and the composition C is such that the composition of the polyester is 95 to 75 mol% of ethylene terephthalate units, 5 to 25 mol% of ethylene isophthalate units, and The content of titanium is 20-40
% Of the composition C, and 1 to 20% by weight based on the total weight of the compositions A to C.

In the method for producing a film in the present invention, a polyester composition containing titanium oxide is supplied to a melt extruder, extruded into a sheet at a temperature of 220 to 280 ° C., and placed on a cooling drum whose temperature is adjusted to a room temperature or lower. Let it adhere and cool,
A method of biaxially stretching the obtained unstretched sheet may be used. As the biaxial stretching method, a tenter-type biaxial stretching method such as a simultaneous biaxial stretching method and a sequential biaxial stretching method, and an inflation method can be used. In the present invention, the simultaneous biaxial stretching method is most preferable because a biaxially stretched film having a high concentration of titanium oxide can be stably produced.

At this time, it is necessary to select film-forming conditions so that the obtained film satisfies the above-mentioned properties. For example, when the simultaneous biaxial stretching method is used, the MD should be 1 to 1.2 if necessary. After pre-stretching about twice as many times, at the temperature of 50 to 150 ° C. with a tenter, simultaneous biaxial stretching is performed so that the MD and TD draw ratios are about 2 to 4 times, respectively, and then the relaxation rate of TD is several percent. Heat treatment at 80 to 200 ° C. for several seconds, and gradually cool to room temperature.

The heat treatment after stretching is a necessary step for reducing the heat shrinkage of the film.
It can be performed by a known method such as a method of blowing hot air, a method of irradiating infrared rays, or a method of irradiating microwaves, but the method of blowing hot air is optimal because heating can be performed uniformly and accurately.

The thickness of the film is suitably from 9 to 25 μm, and preferably from 12 to 17 μm, in order to secure the formability in drawing and ironing.

In order to improve the processability during film production and can production, an inorganic lubricant such as alumina or kaolin is used as a masterbatch in advance, and a necessary amount of this is added to form a film to form a film to impart slip properties to the film surface. It is desirable to do. Furthermore, in order to improve the appearance and printability of the film, for example, a silicone compound or the like can be contained.

The film of the present invention can be used for metal lamination as it is as a single-layer film. However, if necessary, it may be used as a laminate film with a film made of PET, polybutylene terephthalate, or a polyester mainly composed of these. It can also be used.

In the case of a laminated film, the monolayer film of the present invention and another film may be laminated in different steps.
When forming the film of the present invention, another film may be simultaneously extruded and laminated.

Further, the film of the present invention may be subjected to in-line coating during film production or post-coating after film production in order to further improve laminating properties with metal or further increase strength.
An optional coating layer such as an adhesive layer may be formed.

The film of the present invention is used by laminating with a metal. When the metal is a steel plate, a chemical conversion treatment such as chromic acid treatment, phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, nickel, tin, zinc, Aluminum, gunmetal, brass, and those subjected to various other plating treatments are preferably used.

The method for measuring the characteristic values of the film in the present invention is as follows. Intrinsic viscosity Measured at 20 ° C using an equal weight mixture of phenol and ethane tetrachloride as a solvent. Tensile strength Measure according to ASTM D882 on a sample with a width of 10 mm and a length of 10 cm. In addition, data is shown by the average value of MD and TD. Heat shrinkage A sample with a width of 10 mm and a length of 10 cm is left in an atmosphere of 160 ° C. for 15 minutes, and the dimensional change before and after being left is measured to obtain a percentage of the original length. In addition, data is shown by the average value of MD and TD. Optical density For a film having a thickness of 13 μm, using a transmission density meter TD 932 manufactured by Macbeth, setting the transmission nozzle diameter to 3 mm, calculating the incident light amount I ₀ and the transmitted light amount I, and calculating the transmission density D by the following equation:
This is defined as the optical density. D = −log (I ₀ / I) Gloss Measured according to ASTM D523. Whiteness JIS L 1015 7.11 Whiteness is measured by C method (Hunter's method). Adhesive force (Heat laminating property) Between a metal roll heated to 240 ° C and a silicone rubber roll, a sample film and a tin-free steel plate are superposed and inserted, and heated and bonded at a linear pressure of 10 kgf / cm. Using an autograph manufactured by Shimadzu Corporation, a 180 ° peel test is performed on a 25 mm wide specimen at a peel speed of 10 mm / min to measure the peel strength. And the peel strength is 300gf
The above case is regarded as pass (○), and the case where the peel strength is less than 300 gf is rejected (×).

Next, the present invention will be described specifically with reference to examples.

Example 1 An esterified product obtained by esterifying terephthalic acid and ethylene glycol by a known method and having an esterification reaction rate of 95% was transferred to a polymerization vessel, and isophthalic acid was added in an amount of 10 mol%. Silicon oxide as a lubricant
As a solution having a concentration of 1.0% by weight as a slurry by weight and a concentration of 1 mol / liter of ethylene glycol as a pinning agent, 15 × 10 ⁻⁴ mol of lithium acetate / 1 mol of an acid component, and 30 × 10 ⁻⁴ mol of magnesium acetate / acid component. 1 mol, 30 × 10 ^-4 mol of triethyl phosphate / 1 mol of an acid component are added,
Composition C having an intrinsic viscosity of 0.70 is melt-polymerized to a desired viscosity at a temperature of about 280 ° C. under a reduced pressure of 1.3 hPa or less in the presence of a catalyst.
Was prepared. From an extruder, titanium dioxide was added to a copolymerized PET (intrinsic viscosity 0.66) obtained by copolymerizing 22% by mole of isophthalic acid.
Composition A containing 50% by weight and isophthalic acid at 5 mol%
A composition B obtained by mixing 0.4% by weight of titanium dioxide with copolymerized PET (intrinsic viscosity 0.72) and a composition C were supplied to an extruder at a weight ratio of A / B / C shown in Table 1, Temperature 28
Extruded in a sheet form from a T-die at 0 ° C, a voltage of 7 kV was applied to the film with a pinning wire, and the surface temperature was 18 ° C.
Cooled by closely contacting the cooling drum, which has been controlled to a temperature of 130 μm, with good operability and no discharge or pinning bubbles.
m unstretched sheet was obtained. The obtained unstretched sheet is supplied to a tenter-type simultaneous biaxial stretching machine, and simultaneously biaxially stretched at a temperature of 80 ° C. with a stretching ratio of MD 3.0 and TD 3.3.
Was subjected to a heat treatment at a temperature of 210 ° C. for 4 seconds, then cooled and wound up to obtain a 13 μm thick white film. Table 1 shows the characteristic values and the like of the obtained film.
[In Table 1, IP% represents the ratio (mol%) of ethylene isophthalate units in the polyester. ]

Examples 2 to 7 and Comparative Examples 1 to 8 Composition A, composition B and composition C shown in Tables 1 and 2 were obtained by weight ratio of A / B / C shown in Table 1. A white film having a thickness of 13 μm was obtained in the same manner as in Example 1 except that the blended raw materials were used. Table 1 shows the characteristic values and the like of the obtained film.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

According to the present invention, an inexpensive metal which has excellent heat laminating properties (thermal adhesion), moldability and strength, and is preferably used for coating metal cans having excellent concealing properties and whiteness. A white polyester film for lamination is provided.

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location C08K 3/10 KJQ C08K 3/10 KJQ 3/22 KJR 3/22 KJR 3/32 3/32 3/36 KJS 3/36 KJS 5/521 KKD 5/521 KKD 5/524 5/524 C08L 67/02 LPD C08L 67/02 LPD // B29K 67:00 105: 16 B29L 7:00

Claims (3)

[Claims] A composition A comprising the following compositions A to C,
In terms of weight%, ethylene terephthalate units are 95 to 75 mol%, ethylene isophthalate units are 5 to 25 mol%, and titanium oxide content is 20 to 40% by weight. A method for producing a white polyester film for metal lamination, comprising: biaxially stretching in the vertical and horizontal directions. Composition A: consisting of 90 to 50 mol% of ethylene terephthalate units and 10 to 50 mol% of ethylene isophthalate units,
Titanium oxide 30 in copolyester with intrinsic viscosity 0.5 or more
A composition that is blended by weight or more. Composition B: composed of 85 to 95 mol% of ethylene terephthalate units and 15 to 5 mol% of ethylene isophthalate units,
Polyester with an intrinsic viscosity of 0.5 or more and 0 titanium oxide
A composition containing 15% by weight. Composition C: 0.1 to 1.6% by weight of silicon oxide and an alkali metal compound selected from lithium, sodium and potassium are added to a polyester having the same composition ratio as that of composition B.
1.0 to 50 × 10 ^-4 mol / mol of acid component, metal compound selected from magnesium, calcium, manganese and zinc
1.0 to 50 × 10 ^-4 mol / acid component to 1 mole, and phosphoric acid, phosphorous acid or, these ester 1.0 to 50 × 10 ^-4 mol / acid component 1 mole composition containing. 2. The method for producing a white polyester film for metal lamination according to claim 1, wherein the biaxial stretching method is a simultaneous biaxial stretching method. 3. A white polyester film for metal lamination, having the following characteristics (1) to (6), obtained by the production method according to claim 1. (1) Tensile strength 15kgf / mm ² or more (2) Thermal shrinkage at 160 ° C 5.0% or less (3) Optical density 0.3 or more (4) Gloss 10 or more (5) Whiteness 81.0 or more (6) Adhesive strength 300gf or more