JPH11342577A - Polyester film for laminating steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve molding and printing characteristics by mixing a specific quantity of coherent lubricant particles into one of the surfaces of a laminated film comprising three-layers and mixing a specific quantity of a white pigment into an inner layer. SOLUTION: Coherent lubricant particles of 0.01-1 wt.% are mixed into at least one of the surface layers of a laminated film comprising three layers, and 11-50 wt.% of a white pigment is mixed into an inner layer thereof. And as the white pigment, titanium dioxide, calcium carbonate, barium sulfate, magnesium oxide, zinc white, zinc sulfate, lithopone, white lead, basic lead sulfate, etc., are used. And a primary particle diameter of the coherent lubricant particle is 5-100 nm, and degree of coherence is about 100-100,000. If the polyester film for laminating steel plates is laminated to a metal, a high whiteness degree can be obtained and hence printing characteristics can be improved. And when the film is applied to a metal container, abrasion resistance can be improved and further, wear of jig or tool can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for bonding steel sheets. Specifically, polyester film for bonding steel plates that has excellent whiteness after bonding with metal and exhibits good abrasion resistance when processed into metal containers, and further reduces shaving of jigs and tools to be processed It is about.

[0002]

2. Description of the Related Art Conventionally, the inner and outer surfaces of a metal food container are coated with a solution or dispersion of various thermosetting resins, such as epoxy or phenol, in a solvent to prevent corrosion. Coating has been widely practiced.
However, such a method of coating with a thermosetting resin requires a long time for drying the paint, and has unfavorable problems such as a decrease in productivity and environmental pollution due to a large amount of an organic solvent.

As a method for solving these problems, there is a method of bonding a polyester film to a steel plate, an aluminum plate, or a steel plate which has been subjected to various surface treatments such as plating on the metal plate as a material of the metal container. When a metal plate to which a film is attached is drawn and ironed to produce a metal container, the polyester film is required to have the following characteristics. (1) The film surface cannot be shaved during processing. (2) There is little shaving of the jigs and tools used for processing. (3) When printing on the film surface, the whiteness of the base white background is high. Many proposals have been made to satisfy these requirements. That is, (A) JP-A-6-49234 discloses that the particle size is 2.5 μm.
It contains 3 to 50% by weight of the following white pigment and has a melting point of 2
It has been proposed to use a polyester film having a temperature of 10 to 245C.

(B) Japanese Patent Application Laid-Open No. 5-33939 discloses a polyester film containing 3 to 50% by weight of rutile type titanium oxide particles having an average particle diameter of 0.5 μm or less and having a melting point of 210 to 245 ° C. It has been proposed to use.

However, in these methods, if the concentration of the white pigment in the film is increased in order to obtain a high whiteness, the white pigment falls off during the molding process and is mixed into the container.
In addition, shaving of the molding jig may occur due to the white pigment, making continuous production difficult. Conversely, if the concentration of the white pigment in the film is lowered, the color of the steel plate becomes transparent when molding after lamination with the steel plate, so that sufficient whiteness cannot be obtained and the print quality deteriorates.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a polyester film for bonding steel plates which is excellent in moldability and printing characteristics and is suitable for food containers. Is to provide.

[0007]

As a result of intensive studies to achieve the above object, a polyester film to be bonded to a steel plate has a laminated structure composed of three layers, and at least one surface layer contains cohesive lubricant particles. It was found that the white pigment should be contained in the inner layer at a high concentration, and the present invention was achieved. That is, according to the present invention, in a laminated film composed of three layers, at least one surface layer contains the cohesive lubricant particles in an amount of 0.1.
It is a polyester film for laminating steel plates, characterized in that the content is 0.01 to 1% by weight and the inner layer contains 11 to 50% by weight of a white pigment.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester constituting the polyester film in the present invention may be either a homopolyester or a copolyester. As typical examples of polyester, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate,
And polycyclohexanedimethyl terephthalate. These may be copolymerized, and the copolymer component may be an acid component or a glycol component. As the copolymerizing acid component, for example, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid,
Fatty acids such as aromatic dicarboxylic acids such as 5-sodium sulfoisophthalic acid and phthalic acid, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid and phthalic acid, and cyclohexyne dicarboxylic acid Oxycarboxylic acids such as cyclic dicarboxylic acids and p-oxybenzoic acid can be exemplified. Of these dicarboxylic acid components, isophthalic acid and naphthalenedicarboxylic acid can be exemplified, and glycol components to be copolymerized include aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol, and neopentyl glycol; Examples include alicyclic glycols such as methanol and aromatic glycols such as bisphenol A and bisphenol S. Note that two or more of these dicarboxylic acid components and glycol components may be used in combination. Among these, polyesters comprising 80% or more of ethylene terephthalate are preferred in terms of taste flavor when made into containers.

The white pigment used in the present invention may be inorganic or organic, but inorganic is preferred. Examples of the white inorganic particles include titanium dioxide, calcium carbonate, barium sulfate, magnesium oxide, zinc white, zinc sulfate, lithopone, lead white, and basic lead sulfate. In order to improve the whiteness of the film, the particle refractive index must be 1.5.
The above pigments are preferable, and the average particle size is 0.0
Those having a range of 1 to 2.0 μm are preferred. Here, if the particle size exceeds 2.0 μm, voids are likely to be generated around the particles during molding, and the particles are likely to fall off. The content of the white pigment in the inner layer needs to be 11 to 50% by weight. When the surface layer contains a white pigment, the content is preferably 10% by weight or less. If it exceeds 10% by weight,
The surface of the film is scraped, and the white pigment is easily dropped, and the jigs and tools used for the processing are easily scraped. When the content of the inner layer is lower than 11% by weight, the whiteness is reduced, and when the content is more than 50% by weight, film breakage occurs during molding.

In the present invention, it is necessary that at least one surface layer contains 0.01 to 1% by weight of cohesive lubricant particles. If the content is less than 0.01% by weight, the slip of the bonded steel sheets becomes poor, and the handling becomes poor. If the content exceeds 1% by weight, the slip property is saturated, so that the cost is increased and the film characteristics are deteriorated.

The primary particle size of the cohesive lubricant particles is 5 to 100 nm.
And the degree of aggregation is preferably 100 to 100,000. If the primary particle size is less than 5 nm, handling tends to be difficult. If the primary particle size is more than 100 nm, voids during molding and slipping of lubricant particles are likely to occur. If the cohesion degree is less than 100, the contribution of the jig for making the can to the prevention of damage is small, and if it exceeds 100,000, the agglomerates tend to be too large and the falling off during molding tends to increase. As the aggregated particles, silicon dioxide, alumina, calcium carbonate, mica, kaolin, clay and the like are preferable.

The thickness of the laminated film is 5 to 50 μm,
From the balance between the shaving prevention effect at the time of forming and the film whiteness, at least one surface layer is 0.0% of the thickness of the inner layer.
It is preferably 2 to 0.5 times. When the intrinsic viscosity of at least one surface layer is Va and the intrinsic viscosity of the inner layer is Vb, it is preferable that the following formulas are satisfied.

1.0 ≧ Va ≧ 0.6 0.6 ≧ Vb ≧ 0.4 Va is preferably 1.0 or less in terms of extrusion, and 0.6 or more in terms of cracking during molding. preferable. Vb is preferably 0.6 or less from the viewpoint of extrudability at the time of film formation, and is preferably 0.4 or more to prevent cracking due to crystallization of the film and facilitate bonding to a steel sheet.

The polyester film of the present invention may be an unstretched sheet such as a cast film, or a stretched film obtained by uniaxially or biaxially stretching the cast film as required. The polyester film of the present invention can be formed into a film using any conventionally known method.

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

The above-mentioned polyester for the surface layer is extruded from a twin-screw vent type extruder (the extrusion temperature is set to a melting point + 20 ° C.)
The polyester for the inner layer is similarly dried under reduced pressure at 150 ° C. for 4 hours, and then supplied to a usual single screw extruder to be melted. Next, two layers are stacked in a feed block, discharged from a normal T die, and then cooled and solidified in a cooling drum to obtain an amorphous film.

Further, a method of biaxially or simultaneously stretching the amorphous polyester film described above may be employed.
In the case of sequential biaxial stretching, stretching in the longitudinal direction or the width direction of the film can be performed twice or more. The stretching ratio in the longitudinal direction and the width direction of the film can be set according to the desired degree of orientation, strength and elastic modulus of the film, but is preferably 2.0 to 4.0 times.

Either the stretching ratio in the longitudinal direction or the width direction may be large, but the ratio of the stretching ratio in the width direction to the longitudinal direction is preferably 0.7 to 1.3, and more preferably 0.8 to 1.3. 2 range.

The stretching temperature may be any temperature within the range of the glass transition temperature of the polyester or more and the crystallization temperature or less, but is usually preferably 80 to 150 ° C. After the biaxial stretching, the film can be subjected to a heat treatment. Heat treatment temperature is above the crystallization temperature of polyester,
Any temperature below the softening point can be used, but it is preferably 120 to 240 ° C. The heat treatment time can be arbitrarily set, but it is usually preferable to perform the treatment for 5 to 120 seconds. The heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction.

The metal plate to be used in the present invention is not particularly limited, but a metal plate made of iron, aluminum or the like is preferable in view of formability. Furthermore, in the case of a metal plate made of iron, an inorganic oxide coating layer that improves the adhesiveness and corrosion resistance on the surface thereof, for example, chromic acid treatment, phosphoric acid treatment,
A chemical conversion coating layer represented by chromic acid / phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, or the like may be provided. In particular, 6.5 to 150 mg as chromium in terms of metal chromium
/ M ² chromium hydrated oxide is preferable, and a spreadable metal plating layer such as nickel, tin, zinc, aluminum, gunmetal, brass, etc. may be provided. It is preferable that tin plating has a plating amount of 0.5 to 15 mg / m ² , and nickel or aluminum has a plating amount of 1.8 to 20 g / m ² .

The polyester film for bonding steel sheets of the present invention can be suitably used for coating the outer surface of a two-piece metal can manufactured by drawing or ironing. Also, it can be used preferably for covering the lid portion of a two-piece can or for the body, lid, and bottom of a three-piece can because it has good adhesion and moldability to a metal plate.

The measuring method of each characteristic in the present invention is as follows. (1) Whiteness TFS (Tin Free S) heated to a temperature of 200 to 280 ° C
and the polyester film were pressure-bonded between two silicone rubber rolls at a pressure of 20 kg / cm, and immediately thereafter, rapidly cooled in a water tank to produce a film-bonded steel sheet. Color difference meter (SPECTRO PHOTOMETER NF99 made by Nippon Denshoku)
The whiteness (Hunter method) of the laminated steel sheets was measured in 9). (2) Degree of aggregation of aggregated lubricant particles The lubricant particles are exposed on the surface of the film using a plasma etching apparatus. A photograph (20,000 times) of the lubricant particles on the film surface is taken by SEM, and the degree of agglomeration is determined by the following equation.

Aggregation degree = number of primary particles / number of aggregates (3) Intrinsic viscosity of polyester
Was measured. (4) Sharpening of film and jig Shaving The film-bonded steel sheet prepared in (1) was pressed at 100 kg / c with a press-forming machine (VAS-33P, manufactured by Senba Tekko).
Molding is carried out at a temperature not lower than the glass transition temperature of the polyester film and not higher than the crystallization temperature at a pressure of m ² , and the diameter D is 100
A cup having a draw ratio (h / D) of 1.3 mm and a depth h of 130 mm was obtained.

After the 100 cans were continuously formed, the jig was removed from the press molding machine, and the degree of dirt adhered to the jig and the state of flaws were examined.

Regarding film shaving, the following ranking was performed based on the degree of contamination of the removed jig, and A and B were set to practical levels.

A: There is no white shavings on the jig.

B: Slight adherence of white shavings is observed on the jig.

C: White shavings adhere to the jig.

D: A large amount of white shavings adhere to the jig.

After the removed jig was washed with ion-exchanged water, the surface condition of the jig was observed with a metallographic microscope, and the jigs were ranked.

A: There is no flaw in the jig.

B Slight scratches are observed on the jig.

C: The jig is scratched.

D There are many scratches on the jig.

[0035]

The present invention will be described in more detail with reference to the following examples. Example 1 Polyethylene terephthalate copolymerized with 10 mol% of isophthalic acid (3.0% by weight of titanium dioxide, 0.1% by weight of cohesive silica, [Va] = 0.69) as a polyester for a surface layer,
As a polyester for the inner layer, polyethylene terephthalate copolymerized with 10 mol% of isophthalic acid (titanium dioxide 30.0%)
Wt.%, [Vb] = 0.52) and melted in a twin-screw vent type extruder (the temperature of the extruder is set to the melting point + 30 ° C, average residence time 8 minutes), and hot air at 150 ° C for 3 hours. After drying, the mixture is melted by a single screw extruder, then laminated in a feed block into three layers (lamination ratio surface layer: inner layer = 2: 11), discharged from a T die, cooled by a cooling drum, and cooled to 315 μm.
m cast film was obtained. The obtained cast film was stretched 3.2 times in the longitudinal direction at 90 ° C. This uniaxially stretched film is stretched 3.1 times in the width direction at 100 ° C. using a stenter, and heat-treated at 175 ° C. for 20 seconds under a constant length, and then wound into a roll to obtain a 35 μm thick laminated film. Was. Table 1 shows the physical properties of the three-layer laminated film thus obtained. Example 2 The same method as in Example 1 except that the content of titanium dioxide in the surface layer was 1.0% by weight, the concentration of titanium dioxide in the inner layer was 25.0% by weight, and the lamination ratio (inner layer: outer layer) was 2:13. To obtain a film. Example 3 The addition amount of the aggregated silica added to the surface layer was 0.08% by weight, the addition amount of titanium dioxide was 5.0% by weight, the titanium dioxide concentration of the inner layer was 25% by weight, and the lamination ratio (inner layer: outer layer) was 2: 1
A film was obtained in the same manner as in Example 1 except that the film thickness was changed to 3. Example 4 The type and amount of the white pigment added to the surface layer were changed to barium sulfate 5.0.
A film was obtained in the same manner as in Example 3 except that the amount of the aggregated silica was changed to 0.1% by weight. Example 5 The type and amount of white pigment added to the surface layer were changed to magnesium oxide.
A film was obtained in the same manner as in Example 4, except that the content was 5.0% by weight. Example 6 The type and amount of the white pigment to be added to the surface layer were changed to calcium carbonate 5.
A film was obtained in the same manner as in Example 4, except that the content was 0% by weight.

[0036]

[Table 1] Comparative Example 1 A film was obtained in the same manner as in Example 1, except that the titanium dioxide concentration in the inner layer was changed to 10.0% by weight. Comparative Example 2 A film was obtained in the same manner as in Example 2, except that no aggregated silica was added to the surface layer. Comparative Example 3 A film was obtained in the same manner as in Example 3, except that monodispersed spherical silica was used as the lubricant particles added to the surface layer. Comparative Example 4 A film was obtained in the same manner as in Example 3, except that the same resin as the inner layer, in which 25.0% by weight of titanium dioxide was added, was used.

[0037]

[Table 2]

[0038]

[Effect of the Invention] For laminating steel plates which have excellent whiteness and good wear resistance when processed into a metal container after lamination with metal, and further reduce shaving of jigs and tools to be processed. A polyester film is obtained.

Claims (7)

[Claims] 1. A laminated film having three layers, characterized in that at least one surface layer contains 0.01 to 1% by weight of cohesive lubricant particles and the inner layer contains 11 to 50% by weight of a white pigment. Polyester film for bonding steel sheets. 2. A method according to claim 1, wherein at least one surface layer contains white pigment at 0.0.
The polyester film for bonding steel sheets according to claim 1, wherein the polyester film contains 1 to 10% by weight. 3. The cohesive lubricant particles in at least one surface layer have a primary particle size of 5 to 100 nm and a cohesion degree of 100.
The polyester film for laminating steel plates according to claim 1 or 2, wherein the thickness is from 100,000 to 100,000. 4. The polyester according to claim 1, wherein at least 80% of the constituent units of the polyester are ethylene terephthalate.
4. The polyester film for bonding steel sheets according to any one of items 1 to 3. 5. The white pigment is any one of titanium dioxide, calcium carbonate, barium sulfate and magnesium oxide.
Alternatively, it is a mixture.
The polyester film for bonding steel sheets according to any one of the above. 6. The laminated film has a thickness of 5 to 50 μm,
At least one surface layer has a thickness of 0.02
The polyester film for laminating steel plates according to any one of claims 1 to 5, wherein the thickness is 0.5. 7. The intrinsic viscosity of a surface layer is defined as Va, and the intrinsic viscosity of an inner layer is defined as Va.
The polyester film for laminating steel sheets according to any one of claims 1 to 6, wherein the following formulas are satisfied when Vb is satisfied. 1.0 ≧ Va ≧ 0.6 0.6 ≧ Vb ≧ 0.4