JP2003011309A - Laminated polyester film for heat-laminating metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated polyester film for heat-laminating a metal plate which has enough molding characteristics in stretch squeeze forming and is excellent in impact resistance, retort resistance, and rust resistance. SOLUTION: In the laminated film comprising two layers, a layer (A) to be contacted with a metal is formed from a polyester resin composition (A) containing a polyester resin (A1) having butylene terephthalate units as a main component and a polyester resin (A2) having ethylene terephthalate units as a main component, and the other layer (B) is formed from a polyester resin composition (B) which contains a polyester resin (B1) having butylene terephthalate units as a main component and a polyester resin (B2) mainly comprising ethylene terephthalate and having a melting point of 246-266 deg.C and has a glass transition temperature (Tg) of at least 60 deg.C. The melting point Tm (A2) of the polyester resin (A2) is lower by 5-30 deg.C than the melting point Tm (B2) of the polyester resin (B2).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated polyester film for heat-laminating metal plates, and more specifically, it is heat-laminated on a metal plate for producing metal cans, such as a two-piece metal beverage can, which is subjected to drawing and ironing. Laminated polyester film for heat-laminating metal sheets, which has excellent impact resistance, retort resistance, and rust resistance while having excellent molding and processing characteristics compared to conventionally used polyester films. Regarding

[0002]

2. Description of the Related Art Conventionally, as a method for producing a metal can, a method has been proposed in which a polyethylene terephthalate film is laminated on a metal plate by heating and then drawn into a cup shape by ironing. Such polyester films for metal forming cans are roughly classified into two types. one,
A laminated film composed of a biaxially oriented layer made of polyethylene terephthalate and an adhesive layer made of a polyester resin having a lower melting point, and the other is an amorphous or low oriented polyester film.

However, although the former laminated film is generally good in terms of protective properties such as retort resistance, impact resistance and rust resistance, cracks, wrinkles and whitening occur in the film during molding. There is a case. On the other hand, the latter amorphous polyester film is excellent in molding processing characteristics but inferior in protection characteristics. Further, the low orientation polyester film has an intermediate performance in terms of protection characteristics and molding processing characteristics, and has not yet reached a sufficient level.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide impact resistance, retort resistance, and rust resistance while having sufficient molding characteristics in drawing and ironing. Another object of the present invention is to provide a laminated polyester film for heat lamination of a metal plate, which has excellent properties.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventor has found that a laminated polyester film having specific physical properties can easily achieve the above object, and has completed the present invention. .

That is, the gist of the present invention is a laminated film composed of two layers, and the layer (A) in contact with the metal mainly contains a polyester resin (A1) mainly containing butylene terephthalate units and an ethylene terephthalate unit. It is composed of a polyester resin composition (A) containing a polyester resin (A2) as a main component (provided that the ratio of A1 to the total of A1 and A2 is 5 to 55% by weight and A2 is A2).
Is 45-95% by weight), the other layer (B)
Is a butylene terephthalate unit-based polyester resin (B1) and ethylene terephthalate-based melting point 246 to 266 ° C. polyester resin (B2).
With a glass transition temperature (Tg) of 6
It is composed of a polyester resin composition (B) having a temperature of 0 ° C. or higher, and the melting point Tm (A2) of the polyester resin (A2) is 5 to 5 than the melting point Tm (B2) of the polyester resin (B2).
It exists in a laminated polyester film for heat lamination of a metal plate, which is characterized by being 30 ° C. lower.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
First, the polyester resin used in the laminated polyester film for metal sheet thermal lamination (hereinafter referred to as "film") of the present invention will be described.

The polyester resin used in the present invention is obtained by a polycondensation reaction of a polyvalent carboxylic acid and a polyhydric alcohol by a conventional method. In addition, 2 obtained in the same manner and having different melting points
It is also possible to prepare a composition by mixing one or more polyester resins.

Examples of the above polycarboxylic acid component include
Examples of polyhydric alcohol components include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, dodecadicarboxylic acid and cyclohexanedicarboxylic acid. , Ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, decanediol, 2-ethyl-
2-butyl-1-propanediol, bisphenol A
However, the present invention is not limited to these examples.

Further, the above polyester resin may be a copolymer of three or more kinds of polyvalent carboxylic acids or polyhydric alcohols, and a copolymer with a monomer or polymer such as diethylene glycol, triethylene glycol or polyethylene glycol. May be

The film of the present invention is a laminated film comprising two layers, a layer (A) in contact with a metal and the other layer (B).

First, the polyester resin composition (A) constituting the layer (A) will be described. The polyester resin composition (A) is a resin composition containing, as main components, a polyester resin (A1) mainly containing butylene terephthalate units and a polyester resin (A2) mainly containing ethylene terephthalate units.

The above polyester resin (A1) refers to a resin containing a butylene terephthalate unit in an amount of usually 80 mol% or more, preferably 85 mol% or more. A polycarboxylic acid and / or a polyhydric alcohol is used as the copolymerization component.

Melting point Tm (A1) of polyester resin (A1)
1) is usually 190 to 225 ° C., preferably 195 to 2
The temperature is 25 ° C, more preferably 200 to 225 ° C, and particularly preferably 215 to 225 ° C. Incidentally, the melting point of the polybutylene terephthalate homopolymer is 225 ° C. If the melting point Tm (A1) is less than 190 ° C, the ERV of the can after drawing and ironing may be significantly deteriorated. Here, ERV means a current value when an electrode is inserted into the can content liquid and a voltage is applied with the can body as an anode, and is used as an index of film defects.

The above polyester resin (A2) refers to a resin containing ethylene terephthalate units in an amount of usually 60 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more. A polycarboxylic acid and / or a polyhydric alcohol is used as the copolymerization component.

Melting point Tm (A2) of polyester resin (A2)
2) is usually 240 to 270 ° C., preferably 25
It is 0-260 degreeC. When the melting point Tm (A2) is less than 240 ° C., the film sticks to the punch of the molding machine (=
If there is molding failure), the ERV of the squeezing and ironing can is significantly deteriorated, wrinkles or scratches occur on the film in the high temperature heating process such as after the printing ink drying process, or the film floats or peels. There is. On the other hand, the melting point Tm (a
If 2) exceeds 270 ° C., the adhesiveness after film lamination on a steel sheet and the draw and ironing forming characteristics may be poor.

In the polyester resin composition (A),
The ratio of the resin (A1) to the total of the above resins (A1) and (A2) is 5 to 55% by weight, and the ratio of the resin (A2) is 45 to 95% by weight. When the ratio of the resin (A1) is less than 5% by weight or the ratio of the resin (A1) is 55% by weight
In any case, the ERV is significantly deteriorated. The ratio of the resin (A1) to the total of the resins (A1) and (A2) is preferably 10 to 45% by weight, more preferably 12 to 40% by weight.

Next, a resin composition containing a polyester resin (B1) mainly containing butylene terephthalate units and a polyester resin (B2) mainly containing ethylene terephthalate and having a melting point of 240 to 265 ° C. is a main component.

The above polyester resin (B1) is the same as the above polyester resin (A1). On the other hand, the polyester resin (B2) has a melting point Tm (B2) of 24.
It is the same as the above polyester resin (A2) except that the temperature is limited to 0 to 265 ° C. The melting point Tm (B2) is preferably 250 to 260 ° C.

If the melting point Tm (B2) is less than 246 ° C., the film sticks to the punch of the molding machine (= molding failure), the ERV of the drawn and ironed can is significantly deteriorated, and the printing ink drying process Wrinkles and scratches may be generated on the film in the high temperature heating step such as later, and floating or peeling may occur on the film. On the other hand, when the melting point Tm (a2) exceeds 266 ° C., the adhesion after film laminating on a steel sheet and the draw and ironing forming property may be poor.

In the polyester resin (B1), the ratio of the above resins (B1) and (B2) is selected so that the glass transition temperature (Tg) of the polyester resin (B1) is 60 ° C. or higher. Tg is preferably 62 ° C. or higher, more preferably 64 ° C. or higher. When the Tg is less than 60 ° C, the film exhibits adhesive behavior when contacted with a die such as a punch or ring of a drawing and ironing machine that has become a high temperature (60 to 65 ° C) due to continuous molding, resulting in a molded can of ERV is significantly deteriorated. The upper limit of Tg is usually ° C. The ratio of the resin (B1) to the total amount of the resins (B1) and (B2) is usually 10 to 70% by weight, preferably 20 to 60%.
%, And more preferably 25 to 55% by weight. When the proportion of the resin (B1) is less than 10% by weight, the moldability is remarkably reduced, and when it exceeds 70% by weight, it is difficult to set the Tg of the polyester resin (B1) to 60 ° C. or higher.

In the film of the present invention, in addition to the above conditions, the melting point Tm (A2) of the polyester resin (A2) is 5 to 5% lower than the melting point Tm (B2) of the polyester resin (B2).
It is important that it is 30 ° C lower. Melting point Tm (A2) and Tm
If the difference from (B2) is less than 5 ° C, the film will be scratched or distorted during thermal lamination, and if it exceeds 30 ° C, a difference in shrinkage will occur between the layer (A) and the layer (B). , There may be a gap on the end face.

The intrinsic viscosity [η] of each of the polyester resins used in the present invention is usually in the range of 0.55 to 1.5. When [η] is less than 0.55, impact resistance and heat resistance tend to be lowered. On the other hand, when [η] exceeds 1.5, productivity tends to decrease, and flow unevenness tends to occur in the film during film formation. In particular, when the layer (B) contains a white pigment, color unevenness (white tint) occurs,
The aesthetics are spoiled.

In the film of the present invention, a white pigment can be contained in the layer (B) to give a white colored film. Such a white colored film is laminated on the outer surface of a molded can and is suitably used as a base film for improving the color development of printing ink.

The white pigment is not particularly limited,
Usually, rutile type titanium oxide, anatase type titanium oxide,
White pigments such as zinc sulfide are used. The white pigment content is usually 5 to 30% by weight, preferably 8 to 25% by weight,
More preferably 12 to 22% by weight, particularly preferably 15
-19% by weight. When the amount of the white pigment is less than 5% by weight, the white hiding property is poor and the color of the printing ink is insufficient. When the amount of the white pigment exceeds 30% by weight, the white ink tends to break during film formation, and after the can-making, The impact resistance of the film is also significantly reduced.

In the film of the present invention, an appropriate amount of a third component such as another polyester resin, another resin (for example, a polyolefin resin or engineering plastics), an inorganic filler or the like is used within a range that does not impair the characteristics of the present invention. May be included.

In particular, it is preferable to add lubricant particles to the film of the present invention to impart slipperiness to the film. The average particle size of the lubricant particles is usually 0.01 to 6.0 μm, preferably 0.05 to 5.0 μm. Moreover, the compounding amount of the lubricant particles is usually 0.01 to 1.5% by weight, preferably 0.1 to 1.0% by weight.

The method for producing the film of the present invention is not particularly limited, but for example, the following method is preferably adopted.
That is, the raw material polyester is melted by at least two extruders, co-extruded from a T die and laminated, and then rapidly cooled by a cooling roll to obtain an amorphous sheet, which is heated to the glass transition temperature of the raw material polyester or higher, Longitudinally stretched, then
Sequential stretching with transverse stretching or simultaneous biaxial stretching.

In the film of the present invention, the ratio (d) of the thickness d (B) of the layer (B) to the thickness d (A) of the layer (A).
(B) / d (A)) is usually 0.01 to 2.0, preferably 0.05 to 1.0.

The thickness (total thickness) of the film of the present invention is
It depends on the application. When used in a metal can for beverages, the thickness of the film is usually 5 to 100 μm, preferably 10
˜75 μm. When the thickness of the film is less than 5 μm, the impact resistance becomes insufficient, and when it exceeds 100 μm, drawing and ironing may be difficult.

The film of the present invention is designed mainly for drawing and ironing cans, but after laminating on both sides or one side of a metal plate, the metal plate is cut into a desired size and welded to make a can. What can be done, for example, canned foods represented by beverage cans, pail cans, tin plate 18L cans,
It is also suitable as a film such as a steel drum. Further, the kind of the material of the can material is not particularly limited, and any metal material generally used for can manufacturing can be used without any problem. Specific examples of the material of the can material include tin plate, TFS (chin-free steel), aluminum and the like.

[0032]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples as long as the gist thereof is not exceeded. The method for evaluating the film of the present invention is as follows.

(1) Lamination of a film on a metal plate and production of a squeezing and ironing molding cup: Using a laminating machine having two rolls, one on each side of a 0.19 mm thick steel plate. The polyester film was pressure laminated to produce a laminated steel plate. The temperature of the steel sheet during lamination was 240 to 250 ° C., and the lamination speed was 10 m / min. However, with respect to the film in which the white pigment was added to the layer (A), the film was laminated in the direction to the outer surface of the cup. The laminated steel sheet thus obtained is heated at 270 ° C. using a hot air oven.
And heat-treated for 10 seconds. Using a die and punch, in several steps, the above laminated steel plate, bottom diameter 65mm,
3 in a 250 mm high molded container (hereinafter abbreviated as cup)
It was drawn and ironed at a speed of 0 stroke / minute. The plate thickness of the side wall near the height of 200 mm from the bottom of the cup was reduced to about 35% of the original steel plate thickness. The obtained cups were evaluated by the following observations and tests.

(2) Evaluation of molding characteristics: (2-1) Appearance of film of cup: The inner and outer surfaces of the cup after molding were visually observed and evaluated according to the criteria shown in Table 1 below.

[0035]

[Table 1] (Inner film) O: No wrinkles, scratches or perforations are observed. X: Wrinkles, scratches, and holes are formed. (Outer film) Good: No wrinkles, scratches, holes, or white unevenness are observed. X: Wrinkles, scratches, holes, uneven whiteness, and insufficient whiteness occur.

(2-2) ERV measurement: 0.8% by weight NaCl water was put into a cup after molding, an electrode was inserted, and a current value was obtained when a voltage of 6.0 V was applied with the can body as an anode. The measurement was performed and the protection characteristics of the inner surface of the cup were evaluated according to the criteria shown in Table 2 below. The number of tests was 100 cans.

[0037]

[Table 2] A: The average value is less than 0.01 mA. ◯: Shows an average value of 0.01 to 0.1 mA. Δ: The average value exceeds 0.1 mA and is 0.5 mA or less. X: The average value exceeds 0.5 mA.

(2-3) Heat resistance: 20 cups after molding
The film appearance when processed in a heating oven at 0 ° C. for 120 seconds was visually observed and evaluated according to the criteria shown in Table 3 below. The number of tests was 100 cans.

[0039]

[Table 3] ○: No change at all X: Film distortion and edge shrinkage were recognized.

(2-4) Retort treatment test: The inner and outer surfaces of the cup after the retort treatment (125 ° C., 30 minutes) were visually observed and evaluated according to the criteria shown in Table 4 below.

[0041]

[Table 4] ⊚: No change in film appearance. ◯: The whitening of the inner film is slightly conspicuous, but the outer surface is extremely white and is at a practical level. Δ: The outer surface film is white in a striped pattern, but is at a practical level. X: Severe whitening and peeling are recognized on the film.

(2-5) ERV measurement after retort treatment:
0.5 wt% NaCl water was placed in the cup and evaluated according to the criteria shown in Table 5 below. The test was conducted on 100 cans.

[0043]

[Table 5] A: The average value is less than 0.01 mA. ◯: Shows an average value of 0.01 to 0.1 mA. Δ: The average value is more than 0.1 mA and 0.5 mA or less. X: The average value exceeds 0.5 mA.

(2-6) ERV measurement after drop test: As an index of impact resistance, 350 g of water was put in a cup and 5
After dropping from a height of 0 cm at an angle of 45 ° C., 0.5 wt% NaCl water was added to the cup, and evaluation was performed according to the criteria shown in Table 6 below. The test was conducted on 100 cans.

[0045]

[Table 6] A: The average value is less than 0.01 mA. ◯: Shows an average value of 0.01 to 0.1 mA. Δ: The average value is more than 0.1 mA and 0.5 mA or less. X: The average value exceeds 0.5 mA.

(2-7) Rust resistance: 0.5% by weight NaCl aqueous solution was added to the cup after falling in (2-6) and stored at 40 ° C. for 1 month, and then the steel plate near the dents was corroded. The condition was observed.

(3) Thermal properties of polyester: A sample of each layer was shaving about 10 mg from the film surface, and DSC device "MDSC2920 type" manufactured by TA Instruments.
Was used to measure the melting point (Tm) and glass transition temperature (Tg) of polyester at a temperature rising rate of 10 ° C./min in a nitrogen atmosphere.

(4) Intrinsic viscosity [η]: Phenol / tetrachloroethane = 50/50 (weight ratio) mixed solvent 10
1 g of polymer was melt | dissolved in 0 mL, and it measured at 30 degreeC.

(5) Film thickness: The film cross section was observed with a scanning electron microscope (SEM) to measure the thickness of each layer.

(6) Raw Material Polyester: (1) The resins shown in Table 7 below were used as the polyester resin (ET resin) mainly composed of ethylene terephthalate units.

[0051]

[Table 7]

(2) The resins shown in Table 8 below were used as the polyester resin (BT resin) mainly containing butylene terephthalate units.

[0053]

[Table 8]

(3) The resins shown in Table 9 below were used as other polyester resins.

[0055]

[Table 9]

Examples 1 to 12 and Comparative Examples 1 to 6 Each polyester resin was blended as a raw material for the layer (A) and the layer (B) at a ratio shown in Tables 10 to 14, and then barreled by separate extruders. It was extruded at a temperature of 280 ° C., merged inside the T die, and rapidly cooled with a cooling drum at 20 ° C. to obtain an unstretched amorphous sheet. This sheet was stretched 4.0 times in the machine direction at 60 to 80 ° C, and then in the transverse direction at 120 ° C to 5.
After stretching 0 times, the film was heat set at 180 ° C. to obtain a film having a thickness of 25 μm.

The obtained film was heat-laminated on a steel plate by the above-mentioned procedure, then drawn and ironed to form a cup. The results of various evaluations on the cups are also shown in Tables 10-14.

In each of the evaluations of Examples 1 to 12, the ERV value was sufficiently small and was at a practical level.
It was found that the film No. 2 was excellent in moldability, retort resistance and impact resistance.

In each evaluation of Comparative Examples 1 to 6, it was found that the ERV value was large and the moldability and retort resistance were inferior.

[0060]

[Table 10]

[0061]

[Table 11]

[0062]

[Table 12]

[0063]

[Table 13]

[0064]

[Table 14]

[0065]

EFFECT OF THE INVENTION According to the present invention described above, a laminated polyester film for heat lamination of a metal sheet, which has sufficient molding properties in drawing and ironing, and is also excellent in impact resistance, retort resistance and rust resistance. The industrial value of the present invention is remarkable.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3E061 AA16 AB04 AB21 AC09 AD01                       AD04 AD07 BA01 DA01 DB08                 4F100 AB01A AK41B AK41C AK42B                       AK42C AL05B AL05C BA03                       BA07 BA10A BA10B BA26                       CA13 EC03 EC032 EH20                       EH202 EH23 EH232 EJ18                       EJ183 EJ38 EJ382 EJ42                       EJ423 GB16 JA04C JA05C                       JB02 JJ03 JK10 JL10B                       YY00B YY00C                 4J002 CF06W CF07X GF00 GG01

Claims (3)

[Claims] 1. A laminated film comprising two layers, wherein the layer (A) in contact with the metal has a polyester resin (A1) mainly containing butylene terephthalate units and a polyester resin (A2) mainly containing ethylene terephthalate units.
Is composed of a polyester resin composition (A) whose main component is (provided that the proportion of A1 to the total of A1 and A2 is 5 to 55% by weight and the proportion of A2 is 45 to 95% by weight).
The other layer (B) contains, as a main component, a polyester resin (B1) mainly containing butylene terephthalate units and a polyester resin (B2) mainly containing ethylene terephthalate and having a melting point of 246 to 266 ° C. A polyester resin composition (B) having a transition temperature (Tg) of 60 ° C. or higher,
2. The laminated polyester film for thermal lamination of metal plates, wherein the melting point Tm (A2) of 2) is lower than the melting point Tm (B2) of the polyester resin (B2) by 5 to 30 ° C. 2. The laminated polyester film for heat lamination of a metal sheet according to claim 1, wherein the layer (A) contains 5.0 to 30% by weight of a white pigment. 3. The laminated polyester film for heat lamination of a metal plate according to claim 1, which is for a molded can.