JPH10175279A - White laminated polyester film for metal plate bonding - Google Patents

Abstract

(57) [Problem] To provide a white laminated polyester film which is useful for forming and forming the outer surface of a container after bonding to a metal plate. SOLUTION: A copolyester layer (layer B) containing a rutile type titanium oxide having a specific average particle diameter and having a specific range of melting point and intrinsic viscosity is used as a core layer, and is laminated on one surface of the layer B. A film comprising a copolymerized polyester layer (layer A) and a copolymerized polyester layer (layer C) laminated as necessary on the other surface of layer B, wherein the following formulas (1) to (3) are A white laminated polyester film for bonding metal plates, characterized by satisfying.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white laminated polyester film for laminating a metal plate, and more particularly, to a biaxially useful biaxially useful film formed on a metal plate so that the film becomes the outer surface of the container. It relates to an oriented white laminated polyester film.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion of the inner and outer surfaces. Recently, coating with a thermoplastic resin film has been attempted as a means for imparting rust prevention without using an organic solvent for the purpose of simplifying the process, improving hygiene, and preventing pollution. 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 did not satisfy all of moldability, heat resistance and fragrance retention.

[0003] Accordingly, attention has been paid to polyester films, particularly polyethylene terephthalate films, because of their well-balanced properties, and several proposals based on these have been made. That is, (1) a biaxially oriented polyethylene terephthalate film is laminated on a metal plate and used as a material for can production (JP-A-56-10451, JP-A-1-192546). (2) An amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a material for producing a can (JP-A-1-192545, JP-A-2-5-5).
No. 7339). (3) A biaxially oriented polyethylene terephthalate film having a low orientation and thermally fixed is laminated on a metal plate and used as a can-making material (JP-A-64-22530).

[0004] However, none of them have sufficient characteristics.
Each has the following problems: Regarding (1), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention, but has insufficient molding processability. In such cases, breakage occurs.

[0005] As for (2), since it is an amorphous or extremely low-crystalline aromatic polyester film, its moldability is good but its fragrance retention is inferior. It may be easily embrittled by post-treatment and further long-term storage, and may be transformed into a film which is easily broken by an impact from the outside of the can.

[0006] As for (3), the effect is not exerted in the intermediate region between the above (1) and (2), but it has not yet reached a low orientation applicable to can processing.

[0007] In general, printing is performed on the outer surface of the metal container. When printing, a white paint is preliminarily applied for the purpose of shading before printing. By using a white light-shielding film as the thermoplastic resin film to be laminated on the metal plate, it is possible to omit the undercoating of the white paint, but in the methods (1), (2) and (3) above, In the case of a white film produced by adding a film, the respective disadvantages cannot be eliminated, and in the case of a white film containing titanium oxide at a high concentration for improving concealing properties, abrasion of a roll used at the time of film formation becomes a problem.

[0008]

DISCLOSURE OF THE INVENTION The present inventors have intensively studied to develop a white polyester film for can processing, which is excellent in concealing property and hardly causes roll abrasion. As a result, the present inventors have reached the present invention.

[0009]

According to the present invention, a rutile type titanium oxide having an average particle size of 0.1 to 0.5 .mu.m is used for 10 to 50 days.
wt.%, the melting point is 210 to 245 ° C., and the intrinsic viscosity of the polymer portion is 0.46 to 0.66. The copolymer polyester layer (B layer) has an average particle size laminated on one surface of the B layer. 0.1 to 0.5 μm rutile type titanium oxide
15 wt%, average melting point of the copolymerized polyester layer (A layer) having a melting point of 210 to 245 ° C. and an intrinsic viscosity of the polymer portion satisfying the formula (1), and optionally, the other surface of the B layer. It contains 0 to 15 wt% of rutile type titanium oxide having a particle size of 0.1 to 0.5 μm, and has a melting point of 210
A laminated polyester film comprising a copolymerized polyester layer (C layer) having a temperature of about 245 ° C. and an intrinsic viscosity of a polymer part satisfying the formula (2), and the apparent density (ρ) of the film is represented by the formula (3). A white laminated polyester film for laminating a metal plate, characterized by satisfying the conditions.

[0010]

[Equation 3] | η _A −η _B | <0.15 --- (1) | η _C −η _B | <0.15 --- (2)

In the formulas (1) and (2), η _A is the intrinsic viscosity of the polymer portion of the copolymerized polyester layer (A layer), and η _B is the polymer portion of the copolymerized polyester layer (B layer). the intrinsic viscosity of, eta _C represents the intrinsic viscosity of the polymer part of the copolyester layer (C layer).

[0012]

(Equation 4)

Here, in the formula (3), ρ is the apparent density (g / cm ³ ) of the whole white laminated polyester film, ρ ₀
Is the calculated density (true density) of the entire white laminated polyester film (g / cm ³ ), ρ _i is the density of the polymer portion of each copolymerized polyester layer (g / cm ³ ), and ρ _t is the density of the rutile type titanium oxide ( g / cm ³ ), X _i is the thickness (μm) of each copolyester layer, W _i is the titanium oxide concentration (wt%) in each copolyester layer, and n is the number of copolyester layers.

In the present invention, the copolymerized polyester constituting the layers A, B, and C includes polyethylene terephthalate copolymer, polyethylene isophthalate copolymer, polyethylene-2,6-naphthalate copolymer, polybutylene terephthalate. And copolymers. Among these, a polyethylene terephthalate copolymer is preferred.

The copolymer component of the copolymer polyester 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 2,6-naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decane dicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. An alicyclic dicarboxylic acid such as an acid can be exemplified, and the alcohol component is 1,4-butanediol, 1,6-
Examples thereof include aliphatic diols such as hexanediol and alicyclic diols such as 1,4-cyclohexanedimethanol. These can be used alone or in combination of two or more.

The proportion of the copolymer component depends on the kind thereof, and as a result, the melting point of the polymer is in the range of 210 to 245 ° C., preferably 215 to 235 ° C. When the melting point of the polymer is less than 210 ° C., the heat resistance is inferior, so that it is not preferable because it cannot withstand heating in printing after can-making. On the other hand, if the melting point of the polymer exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired, which is not preferable.

The copolymerized polyesters constituting the layers A, B and C may have the same or different proportions of the copolymerization components or copolymerization components, but are preferably the same.

Here, the melting point of the copolyester was measured using Du Pont Instruments 910.
A method in which a melting peak is determined at a heating rate of 20 ° C./min using DSC. The sample amount is about 20 mg.

The copolymerized polyester of the present invention can be produced by a known method. For example, as a method for producing a copolymerized polyethylene terephthalate, terephthalic acid, ethylene glycol and a copolymer component are subjected to an esterification reaction,
Then, the obtained reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyethylene terephthalate, or dimethyl terephthalate, ethylene glycol and a copolymer component are subjected to a transesterification reaction, and then the obtained reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyethylene terephthalate. Can be preferably cited. In the production of the copolymerized polyester, other additives such as a fluorescent whitening agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent and the like can be added as required. In particular, when the whiteness is to be improved, the addition of a fluorescent whitening agent is effective.

In the present invention, the intrinsic viscosity of the polymer portion constituting the layer B is from 0.46 to 0.66, preferably from 0.48 to 0.64. When this intrinsic viscosity is less than 0.46, the film breakage at the time of stretching the film is increased, and when the obtained biaxially oriented white polyester film is laminated on a metal plate and then molded into a container, the film tends to be broken. . On the other hand, those exceeding 0.66 are of excessive quality and are uneconomical because the productivity of the raw material polymer is lowered.

Next, the difference (| η _A −η _B |) between the intrinsic viscosity (η _A ) of the polymer portion constituting the A layer and the intrinsic viscosity (η _B ) of the polymer portion constituting the B layer is 0. .15. This difference is preferably less than 0.12, more preferably less than 0.1. This difference (| η _A −η _B
When |) is larger than 0.15, a large difference in orientation occurs between the front and back sides of the film, making it difficult to handle the film during lamination, and further causing lamination wrinkles and the like.

The difference (| η _C −η _B |) between the intrinsic viscosity (η _C ) of the polymer portion constituting the C layer and the intrinsic viscosity (η _B ) of the polymer portion constituting the B layer is 0. It is necessary to be less than 15. This difference is preferably less than 0.12, more preferably less than 0.1. This difference (| η _C −η _B
When |) is larger than 0.15, a large difference in orientation occurs between the front and back sides of the film, making it difficult to handle the film during lamination, and further causing lamination wrinkles and the like.

Here, the intrinsic viscosity of the polymer portion of the film was measured at a temperature of 35 ° C. after dissolving in o-chlorophenol, removing the filler such as titanium oxide by a centrifuge.

In the present invention, the rutile-type titanium oxide contained in the copolymerized polyester has an average particle size of 0.1 μm or less.
0.5 μm rutile type titanium oxide. This average particle size is preferably from 0.2 to 0.4 μm. When the average particle size is less than 0.1 μm, it is difficult to uniformly disperse the copolymer in the copolymerized polyester, and the white concealing property becomes poor. On the other hand, it is difficult to produce rutile-type titanium oxide having an average particle diameter of more than 0.5 μm, and the produced titanium oxide is not preferable because it has many coarse particles.

The rutile type titanium oxide has a purity of 95
% Or more is preferable. When the purity is less than 95%, when added at a high concentration, the dispersibility is poor, and the molecular weight of the polyester is remarkably reduced.

In the present invention, the content of the rutile type titanium oxide to the copolymerized polyester constituting the layer B is 10%.
-50 wt%, preferably 15-40 wt%. If this content is less than 10 wt%, the white opacity of the film is not sufficient, while if it exceeds 50 wt%, the white opacity is saturated, and no further improvement in the effect is seen. And the resulting biaxially oriented white polyester film is apt to break when laminated to a metal plate and then molded into a container.

The content of the rutile type titanium oxide added to the copolymerized polyester constituting the layers A and C is from 0 to 1
5 wt%, preferably 0 to 10 wt%, more preferably 0 to 6 wt%. If the content exceeds 15% by weight, roll abrasion occurs in the film forming step, which is not preferable.

In the present invention, other white pigments such as alumina, calcium carbonate, silica, barium sulfate, anatase type titanium oxide and the like can be used together with rutile type titanium oxide.

Before adding the rutile type titanium oxide in the present invention to the copolymerized polyester, it is preferable to adjust the particle size and remove coarse particles by using a purification process. As an industrial means of the purification process, a pulverizing means includes, for example, a dry or wet centrifuge. Of course, these means may be used in combination of two or more, and may be purified stepwise.

Various methods can be used for adding rutile type titanium oxide to the copolymerized polyester. A typical method is as follows. (A) A method of adding before the end of transesterification or esterification at the time of synthesizing the copolyester, or adding before the start of the polycondensation reaction. (A) A method of adding to the copolymerized polyester and melt-kneading. (C) In the above methods (A) and (A), a master pellet containing a large amount of rutile-type titanium oxide is produced,
A method of kneading with the copolyester containing no titanium oxide and containing a predetermined amount of rutile type titanium oxide. In addition, when using the method of (a) in which rutile-type titanium oxide is added at the time of polyester synthesis, it is desirable to add the rutile-type titanium oxide to a reaction system as a slurry in which glycol is dispersed.

In the present invention, the density (ρ) of the white laminated film must satisfy the following expression.

[0032]

(Equation 5)

Here, in equation (3), ρ is the apparent density (g / cm ³ ) of the laminated film, and ρ ₀ is the calculated density (true density).
(G / cm ³ ), ρ _i is the density of the polymer portion of each copolymerized polyester layer (g / cm ³ ), ρ _t is the density of rutile titanium oxide (g / cm ³ ), and X _i is the density of each polyester layer. thickness (μm), W _i is a titanium oxide concentration of the polyester layer (wt%), n represents each number of the polyester layer.

When ρ / ρ ₀ <0.65, the number of voids in the film becomes too large, the film breakage during film stretching increases, and the obtained biaxially oriented white laminated polyester film is laminated to a metal plate. After that, when molded into a container, it is not preferable because it is easily broken.

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

In the white laminated polyester film of the present invention, the polyester constituting each layer is separately melted, co-extruded from a die, laminated and fused before solidification, and immediately quenched to obtain a substantially amorphous copolymer. Obtain a polyester sheet. Next, the sheet is heated in a roll, an infrared ray 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 copolymerized polyester, and the stretching ratio is preferably 2.7 to 3.6 times. The stretching in the transverse direction starts at a temperature 20 ° C. or more higher than Tg, and is 10 ° higher than the melting point (Tm) of the copolyester.
It is preferable to perform the heating while raising the temperature to a temperature lower by 0 to 130 ° C. It is preferable that the magnification of the transverse stretching is 2.8 to 3.7 times. The heat setting temperature is preferably selected from the range of 150 ° C. to 205 ° C. so as to adjust the film quality according to the melting point (Tm) of the copolymerized polyester. In addition, each copolymerized polyester can be separately melted, extruded to form a film, stretched by an unstretched state or stretched by the stretching method, and then laminated and fused.

The thickness of the white laminated polyester film of the present invention is preferably from 6 to 75 μm. 10 to 10
It is preferably 75 μm, particularly preferably 15 to 50 μm.
If the thickness is less than 6 μm, cracks or the like are likely to occur during processing, while if it exceeds 75 μm, the quality is excessive and uneconomical.

The white laminated polyester film of the present invention has a two-layer structure in which layer B is used as a core layer, layer A is laminated on one surface of layer B, and layer C is optionally laminated on the other surface of layer B. Alternatively, it is a film having a three-layer laminated structure.

In the above white laminated polyester film, the ratio (X) of the thickness of layer _A (X _A ) to the thickness of layer _B (X _B )
The ratio of the _A / X _B) and C layer having a thickness (X _C) and B layer having a thickness _{(X B) (X C /} X B) is preferably about 0.05 to 1.0, respectively, and further 0 .1 to 0.7 are preferred.

As a metal plate to which the white laminated polyester film of the present invention is bonded, in particular, a metal plate for can making, a plate of tin, tin-free steel, aluminum or the like is suitable. Lamination of polyester film on metal plate
For example, it can be performed 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 laminated, and then cooled. The surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered. An 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, epoxy-
Ester-based adhesives, alkyd-based adhesives, and the like can be used.

[0041]

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

Examples 1 to 7 and Comparative Examples 1 to 6 Rutile-type titanium oxide having an average particle size shown in the table was added to a copolymerized polyethylene terephthalate obtained by copolymerizing the components shown in Table 1 at the concentrations shown in the table. Thus, polyesters for the A layer, the B layer, and the C layer were obtained. These polyesters were separately melted under the film-forming conditions shown in Table 3, then co-pressed from dies adjacent to each other, laminated and fused, quenched and solidified to form an unstretched film, and then the unstretched film was cured. The film was stretched longitudinally and transversely under the conditions shown in Table 3 and then heat-set to obtain a biaxially oriented white laminated film having a thickness of 20 μm. The characteristics of this film are shown in Table 4.

[Comparative Examples 7 and 8] 12 mol of isophthalic acid
% Of rutile-type titanium oxide, calcium carbonate, and barium sulfate having the average particle sizes shown in Table 2 were added to the copolymerized polyethylene terephthalate to obtain polyesters for the A layer, the B layer, and the C layer. These polyesters are listed in Table 3 below.
The film was melt-extruded under the film-forming conditions shown in Table 1 and solidified by quenching to obtain an unstretched film. The unstretched film was stretched longitudinally, stretched horizontally, and then heat-set to obtain a biaxially oriented film having a thickness of 20 μm. The characteristics of this film are shown in Table 4.

The characteristics of each film obtained in the above Examples and Comparative Examples were evaluated by the following observations and tests, and evaluated according to the following criteria.

(1) Intrinsic Viscosity The intrinsic viscosity of the polymer portion of the film was measured at a temperature of 35 ° C. after dissolving in o-chlorophenol, removing the filler such as titanium oxide by a centrifuge. The intrinsic viscosity of each layer is the intrinsic viscosity of an unstretched film obtained by extruding the polyester of each layer independently.

(2) Abrasion A non-stretched film obtained by individually extruding polyester of each layer cut to a width of 1/2 inch in an environment of a temperature of 20 ° C. and a humidity of 60% is bladed (industrial manufactured by GKI, UK). A blade of a razor testing machine) is vertically applied, and further pressed into contact with 1.5 mm to make it run at a speed of 60 m / min and an entrance tension of 60 g. 50 films
m, the amount of wear of the blade after running (W, unit: μ)
m ³ ) was measured with an SEM, and determined based on the following criteria. 〇: W <4.0 × 10 ⁴ μm ³ ×: W ≧ 4.0 × 10 ⁴ μm ³ The films obtained in the above Examples and Comparative Examples were subjected to 260 ° C.
It is laminated on both sides of a 0.25 mm thick tin-free steel plate, cooled with water, cut into a 150 mm diameter disk, and deep-drawn in three stages using a drawing die and punch. A seam (hereinafter abbreviated as can) was created. The following observations and tests were performed on the cans, and each was determined according to the following criteria.

(3) Appropriate lamination A: Laminable without wrinkles. X: Wrinkles occur during lamination.

(4) Deep drawing processability -1 と も: Both inner and outer surfaces are processed into a film without any excess, and fine cracks and breaks are not recognized in the film on the inner and outer surfaces of the can. X: Film breakage is observed in a part of the film on the inner and outer surfaces of the can.

(5) Deep drawing workability-2 ○: The inner and outer surfaces were processed without any abnormality, and the rust prevention test of the film surface on the inner surface of the can (1% NaCl water was put in the can, the electrode was inserted, and the can was The current value is measured when a voltage of 6 V is applied to the anode, and the current value is 0.2 mA at ERV.
The following is shown. ×: There is no abnormality on the inner and outer surfaces, but the current value is 0.2 mA or more in the ERV test, and when the energized portion is observed under magnification, pinhole-shaped cracks starting from the coarse lubricant are observed in the film.

(6) Impact cracking resistance The cans with good drawability were filled with water and 10 pieces of each test were dropped from a height of 30 cm on a PVC tile floor for each test. The evaluation was performed according to the following criteria. ：: 0.2 mA or less for all 10 pieces. Δ: 0.2 mA or more for 1 to 5 pieces. X: 0.2 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(7) Heat Embrittlement Resistance The can which had been subjected to good deep drawing was heated and held at 210 ° C. for 5 minutes, and then the impact cracking resistance described in (6) was evaluated. . ：: 0.2 mA or less for all 10 pieces. Δ: 0.2 mA or more for 1 to 5 pieces. X: 0.2 mA or more for 6 or more or 210
After heating at 5 ° C. for 5 minutes, cracks are already observed.

(8) Whiteness of can outer surface Before laminating the white film and tin-free steel, the tin-free steel surface, which becomes the outer surface of the can after can making,
Using Karasuguchi, length 50mm, width 0.2m each
m, a black line of 1.4 mm was entered, and after making the can, the black line was observed through a white film. The evaluation was performed as follows. ：: Neither of the black lines can be seen. Δ: One black line looks faint, but the other black line is not visible. ×: One black line is visible, and the other black line is also faint. Table 4 shows the results of the above seven evaluations.

From the results shown in Table 4, it can be seen that the films of Examples are excellent in all of abrasion resistance, proper lamination, deep drawing workability, impact cracking resistance, heat resistance, and can outer whiteness.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

[0057]

[Table 4]

[0058]

The white laminated polyester film of the present invention for laminating a metal plate is suitable for lamination and abrasion resistance in forming a metal can by, for example, deep drawing to form a metal can after laminating to a metal plate. It is excellent in deep drawability, impact resistance after can production, heat resistance, and whiteness on the outer surface of the can, and is extremely useful as a coating material for the outer surface of a metal container.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tetsuo Yoshida 3-37-19 Koyama, Sagamihara-shi, Kanagawa Pref.

Claims (2)

[Claims] 1. A rutile-type titanium oxide having an average particle diameter of 0.1 to 0.5 μm is contained in an amount of 10 to 50 wt% and a melting point of 210
２245 ° C. and the intrinsic viscosity of the polymer part is 0.4
6 to 0.66 of a copolyester layer (layer B), 0 to 15 wt% of rutile type titanium oxide having an average particle size of 0.1 to 0.5 μm laminated on one surface of layer B, and having a melting point of 2
The average particle size of the copolymer polyester layer (A layer) which is 10 to 245 ° C. and the intrinsic viscosity of the polymer portion satisfies the formula (1) and, if desired, is laminated on the other surface of the B layer is 0.1 to 0.5 μm rutile-type titanium oxide in 0 to 15 w
a laminated polyester film comprising a copolymerized polyester layer (C layer) having a melting point of from 210 to 245 ° C. and an intrinsic viscosity of a polymer portion satisfying the formula (2), wherein the apparent density ( ρ) satisfies the condition of the expression (3). | Η _A −η _B | <0.15 --- (1) | η _C −η _B | <0.15 --- (2) Here, Equations (1) and (2) In the formula, η _A is the intrinsic viscosity of the polymer portion of the copolymerized polyester layer (layer A), η _B is the intrinsic viscosity of the polymer portion of the copolymerized polyester layer (layer B), and η _C is the copolymerized polyester layer (layer C). Represents the intrinsic viscosity of the polymer part. (Equation 2) Here, in the formula (3), ρ is the apparent density (g / cm ³ ) of the whole white laminated polyester film, and ρ ₀ is the calculated density (true density) of the whole white laminated polyester film (g / c).
m ³ ), ρ _i is the density of the polymer portion of each copolymerized polyester layer (g / cm ³ ), ρ _t is the density of rutile type titanium oxide (g / cm ³ ), and X _i is the thickness of each copolymerized polyester layer (μm), W _i is a titanium oxide concentration of each copolyester layer (wt%), n represents the number of copolyester layers. 2. The white laminated polyester film for laminating a metal plate according to claim 1, wherein the film is laminated on a surface of the metal plate to be an outer surface of the container.