JP4604405B2 - Laminated polyester film for thermal lamination of metal plates - Google Patents

Description

【００５２】
（２）ブチレンテレフタレート単位を主体とするポリエステル樹脂（ＢＴ系樹脂）として以下の表８に記載の樹脂を使用した。
【００５３】
【表８】

【００５４】
（３）その他のポリエステル樹脂として以下の表９に記載の樹脂を使用した。
【００５５】
【表９】

【００５６】
参考例１〜９、実施例１〜３及び比較例１〜６
層（Ａ）、層（Ｂ）の原料として表１０〜１４に記載の割合で各ポリエステル樹脂を配合した後、それぞれ別々の押出機によりバレル温度２８０℃で押し出し、Ｔダイ内部で合流させ、２０℃の冷却ドラムで急冷して未延伸非晶化シートを得た。このシートを６０〜８０℃で縦方向に４．０倍延伸し、次いで、１２０℃で横方向に５．０倍延伸した後、１８０℃にて熱固定処理することにより、厚さ２５μｍのフィルムを得た。
【００５７】
得られたフィルムを前記の手順にてスチール鋼板上に熱ラミネート処理した後、絞りしごき成形してカップ成形した。カップについて種々評価を行った結果も表１０〜１４に記載した。
【００５８】
参考例１〜９および実施例１〜３の各評価においてＥＲＶ値は十分に小さく実用可能なレベルであり、実施例１〜１２のフィルムは、成形性、耐レトルト性、耐衝撃性に優れていることが分かった。
【００５９】
比較例１〜６の各評価において、ＥＲＶ値は大きく、成形性および耐レトルト性に劣っていることが分かった。
【００６０】
【表１０】

【００６１】
【表１１】

【００６２】
【表１２】

【００６３】
【表１３】

【００６４】
【表１４】

【００６５】
【発明の効果】
以上説明した本発明によれば、絞りしごき成形において充分な成形特性を有しながら、耐衝撃性、耐レトルト性、耐さび性にも優れた金属板熱ラミネート用積層ポリエステルフィルムが提供され、本発明の工業的価値は顕著である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laminated polyester film for metal plate heat laminating, specifically, a film that is heat laminated to a metal plate for producing a metal can subjected to drawing and ironing, like a two-piece metal beverage can, The present invention relates to a laminated polyester film for heat lamination of a metal plate, which has excellent processing characteristics as compared with conventionally used polyester films, and is excellent in impact resistance, retort resistance and rust resistance.
[0002]
[Prior art]
Conventionally, a method for producing a metal can has been proposed in which a polyethylene terephthalate film is bonded to a metal plate by heating and then made into a cup shape by drawing and ironing. Such polyester films for metal molded cans are roughly classified into two types. One is a laminated film composed of a biaxially oriented layer made of polyethylene terephthalate and an adhesive layer made of a lower melting point polyester resin, and the other is an amorphous or low-oriented polyester film. .
[0003]
However, the former laminated film is generally good in terms of protective properties such as retort resistance, impact resistance, and rust resistance, but the film may be cracked or wrinkled or whitened during molding. is there. On the other hand, the latter amorphous polyester film is excellent in molding process characteristics but inferior in protective characteristics. In addition, the low-orientation polyester film has intermediate performance in terms of protective properties and molding processing properties, and has not yet reached a sufficient level.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and its object is to provide a metal plate thermal laminate that has sufficient molding characteristics in draw ironing, but also has excellent impact resistance, retort resistance, and rust resistance. An object of the present invention is to provide a laminated polyester film.
[0005]
[Means for Solving the Problems]
As a result of intensive studies, the present inventor obtained knowledge that the above-mentioned object can be easily achieved by a laminated polyester film having specific physical properties, and has completed the present invention.
[0006]
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 comprises a polyester resin (A1) mainly composed of butylene terephthalate units and a polyester resin mainly composed of ethylene terephthalate units ( polyester resin composition for the A2) composed mainly (a) is composed of (but ratio of A1 to the total of A1 and A2 is the ratio of A2 in 5 to 55% by weight is 45 to 95% by weight), moreover , White pigment 5.0 to 30% by weight, the other layer (B) is a polyester resin (B1) mainly composed of butylene terephthalate units and a polyester resin (melting point 246 to 266 ° C. mainly composed of ethylene terephthalate) A polyester resin composition having B2) as a main component and having a glass transition temperature (Tg) of 60 ° C. or higher. B) is composed of (but the ratio of B1 to the total amount of B1 and B2 is from 10 to 70 wt%), melting point Tm (B2 melting point Tm (A2) is a polyester resin of the polyester resin (A2) (B2) 5) to 30 ° C lower than that of the laminated polyester film for metal plate thermal lamination.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. First, the polyester resin used in the laminated polyester film for metal plate thermal lamination of the present invention (hereinafter referred to as “film”) will be described.
[0008]
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. Further, two or more kinds of polyester resins obtained in the same manner and having different melting points can be mixed to form a composition.
[0009]
Examples of the polyvalent carboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, dodecadicarboxylic acid, cyclohexanedicarboxylic acid, and the like. Examples of the polyhydric alcohol component include ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentylglycol, 1,4-cyclohexanedimethanol, decanediol, and 2-ethyl-2-butyl. Examples include -1-propanediol and bisphenol A, but are not limited to these examples.
[0010]
Further, the polyester resin may be a copolymer of three or more types of polyvalent carboxylic acid or polyhydric alcohol, and is a copolymer with a monomer or polymer such as diethylene glycol, triethylene glycol, or polyethylene glycol. Also good.
[0011]
The film of the present invention is a laminated film composed of two layers of a layer (A) in contact with a metal and the other layer (B).
[0012]
First, the polyester resin composition (A) constituting the layer (A) will be described. The polyester resin composition (A) is a resin composition mainly composed of a polyester resin (A1) mainly composed of butylene terephthalate units and a polyester resin (A2) mainly composed of ethylene terephthalate units.
[0013]
Said polyester resin (A1) refers to resin which contains a butylene terephthalate unit normally 80 mol% or more, Preferably it is 85 mol% or more. As the copolymerization component, a polyvalent carboxylic acid and / or a polyhydric alcohol is used.
[0014]
The melting point Tm (A1) of the polyester resin (A1) is usually 190 to 225 ° C, preferably 195 to 225 ° C, more preferably 200 to 225 ° C, and particularly preferably 215 to 225 ° C. Incidentally, the melting point of polybutylene terephthalate homopolymer is 225 ° C. When melting | fusing point Tm (A1) is less than 190 degreeC, the ERV of the can after drawing ironing may deteriorate remarkably. 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.
[0015]
Said polyester resin (A2) refers to resin which ethylene terephthalate unit contains normally 60 mol% or more, Preferably it is 70 mol% or more, More preferably, it is 80 mol% or more. As the copolymerization component, a polyvalent carboxylic acid and / or a polyhydric alcohol is used.
[0016]
The melting point Tm (A2) of the polyester resin (A2) is usually 240 to 270 ° C., preferably 250 to 260 ° C. When the melting point Tm (A2) is less than 240 ° C., there is a behavior that the film sticks to the punch of the molding machine (= forming defect), the ERV of the drawn and ironed can can be remarkably deteriorated, or after the printing ink drying process, etc. In the high temperature heating process, wrinkles and scratches may occur on the film, or the film may float or peel off. On the other hand, when melting | fusing point Tm (a2) exceeds 270 degreeC, it may be inferior to the adhesiveness after film lamination to a steel plate, and a drawing ironing characteristic.
[0017]
In the polyester resin composition (A), the ratio of the resin (A1) to the total of the 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 proportion of the resin (A1) is less than 5% by weight or when the proportion of the resin (A1) exceeds 55% by weight, the ERV is remarkably 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.
[0018]
Next, a resin composition mainly comprising a polyester resin (B1) mainly composed of butylene terephthalate units and a polyester resin (B2) having a melting point of 240 to 265 ° C. mainly composed of ethylene terephthalate.
[0019]
Said polyester resin (B1) is the same as said polyester resin (A1). On the other hand, the polyester resin (B2) is the same as the polyester resin (A2) except that the melting point Tm (B2) is limited to 240 to 265 ° C. Melting | fusing point Tm (B2) becomes like this. Preferably it is 250-260 degreeC.
[0020]
When the melting point Tm (B2) is less than 246 ° C., there is a behavior that the film sticks to the punch of the molding machine (= forming defect), the ERV of the drawn and ironed can can be remarkably deteriorated, or after the printing ink drying process. In the high temperature heating process, wrinkles and scratches may occur on the film, or the film may float or peel off. On the other hand, when melting | fusing point Tm (a2) exceeds 266 degreeC, it may be inferior to the adhesiveness after film lamination to a steel plate, or a drawing ironing characteristic.
[0021]
In the polyester resin (B1), the ratio of the 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 it comes into contact with a punch, ring, or other mold of a drawing ironing machine that has been heated to a high temperature (60 to 65 ° C.) by continuous molding. ERV is significantly worsened. The upper limit of Tg is usually ° C. Moreover, the ratio of resin (B1) with respect to the total amount of resin (B1) and (B2) is 10 to 70 weight% normally, Preferably it is 20 to 60 weight%, More preferably, it is 25 to 55 weight%. When the proportion of the resin (B1) is less than 10% by weight, the moldability is remarkably lowered, and when it exceeds 70% by weight, it is difficult to make the Tg of the polyester resin (B1) 60 ° C. or higher.
[0022]
In the film of the present invention, in addition to the above conditions, it is important that the melting point Tm (A2) of the polyester resin (A2) is 5 to 30 ° C. lower than the melting point Tm (B2) of the polyester resin (B2). When the difference between the melting points Tm (A2) and Tm (B2) is less than 5 ° C, the film is scratched or distorted during thermal lamination, and when it exceeds 30 ° C, the layer (A) and the layer (B) There is a case where a difference in contraction occurs between the two and the end face is displaced.
[0023]
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 decrease. On the other hand, when [η] exceeds 1.5, productivity tends to be reduced, or uneven flow tends to occur during film formation. In particular, when the layer (B) contains a white pigment, color unevenness (white shading) occurs and the aesthetic appearance is impaired.
[0024]
In the film of the present invention, a white pigment can be contained in the layer (B) to obtain a white colored film. Such a white colored film is suitably used as a base film that is laminated on the outer surface of the molded can to improve the color of the printing ink.
[0025]
Although it does not restrict | limit especially as a white pigment, Usually, white pigments, such as a rutile type titanium oxide, an anatase type titanium oxide, and 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, and particularly preferably 15 to 19% by weight. When the white pigment is less than 5% by weight, the white hiding property is inferior and the color of the printing ink is insufficient. When the white pigment exceeds 30% by weight, the film tends to be broken during film formation. The impact resistance of the film is also significantly reduced.
[0026]
The film of the present invention contains an appropriate amount of a third component such as other polyester resins, other resins (for example, polyolefin resins and engineering plastics), inorganic fillers and the like within a range not impairing the characteristics of the present invention. May be.
[0027]
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 quantity of a lubricant particle is 0.01 to 1.5 weight% normally, Preferably it is 0.1 to 1.0 weight%.
[0028]
Although the manufacturing method of the film of this invention is not specifically limited, For example, the following methods are employ | adopted suitably. That is, the raw material polyester is melted in at least two extruders, coextruded from a T-die and laminated, then rapidly cooled with a cooling roll to be an amorphous sheet, and heated above the glass transition temperature of the raw material polyester, The film is stretched in the longitudinal direction, and then stretched in sequence with the transverse stretching or simultaneously biaxially stretched.
[0029]
In the film of the present invention, the ratio of the thickness d (B) of the layer (B) to the thickness d (A) of the layer (A) (d (B) / d (A)) is usually 0.01-2. 0.0, preferably 0.05 to 1.0.
[0030]
The thickness (total thickness) of the film of the present invention varies depending on the application. The thickness of the film when used in a metal can for beverages is usually 5 to 100 μm, preferably 10 to 75 μm. When the thickness of the film is less than 5 μm, the impact resistance is insufficient, and when it exceeds 100 μm, drawing and ironing may be difficult.
[0031]
The film of the present invention is mainly designed for squeezing and ironing cans, but after laminating to both sides or one side of a metal plate, the metal plate is cut to a desired size and canned by welding, For example, it is also suitable as a film for food cans typified by beverage cans, pail cans, tin plate 18L cans, steel drums, and the like. Moreover, the kind of raw material of a can material is not restrict | limited in particular, If it is a metal material generally used for can manufacturing, it can be used without a problem. Specific examples of the material of the can material include tinplate, TFS (chin-free steel), aluminum and the like.
[0032]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these examples at all unless the summary is exceeded. In addition, the evaluation method of the film of this invention is as follows.
[0033]
(1) Film lamination to a metal plate and production of a drawn ironing cup:
Using a laminating apparatus having two upper and lower rolls, the polyester film obtained in each example was pressure-laminated on both surfaces of a steel plate having a thickness of 0.19 mm to produce a laminated steel plate. The steel plate temperature at the time of bonding was 240 to 250 ° C., and the bonding speed was 10 m / min. However, about the film which added the white pigment to the layer (A), it laminated in the direction which becomes a cup outer surface. The obtained laminated steel sheet was heat-treated at 270 ° C. for 10 seconds using a hot air oven. Using a die and a punch, the laminated steel sheet was squeezed and formed at a rate of 30 strokes / minute into a forming container (hereinafter abbreviated as a cup) having a bottom diameter of 65 mm and a height of 250 mm in several steps. The thickness of the side wall near 200 mm in height from the bottom of the cup was reduced to about 35% of the original steel thickness. The obtained cup was evaluated by the following observations and tests.
[0034]
(2) Molding property evaluation:
(2-1) Cup film appearance:
The cup inner and outer surfaces after molding were visually observed and evaluated according to the criteria shown in Table 1 below.
[0035]
[Table 1]
(Inner film)
○: Wrinkles, scratches, and perforations are not recognized.
X: Wrinkles, scratches, and holes are generated.
(External film)
○: Wrinkles, scratches, perforations and white unevenness are not recognized.
X: Wrinkles, scratches, perforations, white unevenness, and insufficient whiteness occur.
[0036]
(2-2) ERV measurement:
0.8% by weight NaCl water was put into the cup after molding, the electrode was inserted, the current value was measured when a voltage of 6.0 V was applied with the can body as the anode, and according to the criteria shown in Table 2 below. The protective properties of the cup inner surface were evaluated. The number of tests was 100 cans.
[0037]
[Table 2]
A: The average value is less than 0.01 mA.
(Circle): The average value shows the value of 0.01-0.1 mA.
(Triangle | delta): An average value exceeds 0.1 mA and shows the value of 0.5 mA or less.
X: The value whose average value exceeds 0.5 mA is shown.
[0038]
(2-3) Heat resistance:
The appearance of the film when the cup after molding was processed in a heating oven at 200 ° 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.
[0040]
(2-4) Retort processing test:
The cup inner and outer surfaces after retort treatment (125 ° C., 30 minutes) were visually observed and evaluated according to the criteria shown in Table 4 below.
[0041]
[Table 4]
A: No change in film appearance.
○: Whitening of the inner film is somewhat conspicuous, but the outer surface is extremely whitened and practical.
(Triangle | delta): Although an outer surface film whitens in stripes, it is a practical use level.
X: Severe whitening or peeling is observed on the film.
[0042]
(2-5) ERV measurement after retort processing:
The cup was charged with 0.5 wt% NaCl water and evaluated according to the criteria shown in Table 5 below. The test was conducted for 100 cans.
[0043]
[Table 5]
A: The average value is less than 0.01 mA.
(Circle): The average value shows the value of 0.01-0.1 mA.
(Triangle | delta): An average value exceeds 0.1 mA and shows the value of 0.5 mA or less.
X: The value whose average value exceeds 0.5 mA is shown.
[0044]
(2-6) ERV measurement after drop test:
As an index of impact resistance, 350 g of water was put into a cup, dropped at an angle of 45 ° C. from a height of 50 cm, 0.5 wt% NaCl water was put into the cup, and the criteria shown in Table 6 below were applied. evaluated. The test was conducted for 100 cans.
[0045]
[Table 6]
A: The average value is less than 0.01 mA.
(Circle): The average value shows the value of 0.01-0.1 mA.
(Triangle | delta): An average value exceeds 0.1 mA and shows a value below 0.5 mA.
X: The value whose average value exceeds 0.5 mA is shown.
[0046]
(2-7) Rust resistance:
In (2-6), a 0.5 wt% NaCl aqueous solution was put into the cup after dropping and stored at 40 ° C. for 1 month, and then the corrosion state of the steel plate near the dents was observed.
[0047]
(3) Thermal properties of polyester:
About 10 mg of each layer sample is shaved from the film surface, using a DSC device “MDSC 2920 type” manufactured by TI Instruments, in a nitrogen atmosphere, at a temperature rising rate of 10 ° C./min, the melting point (Tm) of the polyester, glass The transition temperature (Tg) was measured.
[0048]
(4) Intrinsic viscosity [η]:
1 g of polymer was dissolved in 100 mL of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) and measured at 30 ° C.
[0049]
(5) Film thickness:
The cross section of the film was observed with a scanning electron microscope (SEM), and the thickness of each layer was measured.
[0050]
(6) Raw material polyester:
(1) Resins described in Table 7 below were used as polyester resins (ET-based resins) mainly composed of ethylene terephthalate units.
[0051]
[Table 7]

[0052]
(2) Resins listed in Table 8 below were used as polyester resins (BT-based resins) mainly composed of butylene terephthalate units.
[0053]
[Table 8]

[0054]
(3) Resins described in Table 9 below were used as other polyester resins.
[0055]
[Table 9]

[0056]
Reference Examples 1-9, Examples 1-3 and Comparative Examples 1-6
After blending each polyester resin as a raw material of the layer (A) and the layer (B) at a ratio shown in Tables 10 to 14, the polyester resin is extruded at a barrel temperature of 280 ° C. by a separate extruder, and merged inside the T die. Quenched with a cooling drum at 0 ° C., an unstretched amorphous sheet was obtained. The sheet was stretched 4.0 times in the longitudinal direction at 60 to 80 ° C., then stretched 5.0 times in the transverse direction at 120 ° C., and then heat-set at 180 ° C. to obtain a film having a thickness of 25 μm. Got.
[0057]
The obtained film was heat-laminated on the steel plate by the above procedure, and then drawn and ironed to form a cup. The results of various evaluations on the cups are also shown in Tables 10-14.
[0058]
In each evaluation of Reference Examples 1-9 and Examples 1-3 , the ERV value is a sufficiently small and practical level, and the films of Examples 1-12 are excellent in formability, retort resistance, and impact resistance. I found out.
[0059]
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 poor.
[0060]
[Table 10]

[0061]
[Table 11]

[0062]
[Table 12]

[0063]
[Table 13]

[0064]
[Table 14]

[0065]
【The invention's effect】
According to the present invention described above, there is provided a laminated polyester film for metal plate thermal lamination that has sufficient molding characteristics in drawing ironing and has excellent impact resistance, retort resistance, and rust resistance. The industrial value of the invention is significant.

Claims (2)

A polyester film mainly composed of a polyester resin (A1) mainly composed of a butylene terephthalate unit and a polyester resin (A2) mainly composed of an ethylene terephthalate unit. It is composed of the resin composition (A) (however, the ratio of A1 to the total of A1 and A2 is 5 to 55% by weight and the ratio of A2 is 45 to 95% by weight), and white pigment 5.0 to 30 The other layer (B) contains, as a main component, a polyester resin (B1) mainly composed of butylene terephthalate units and a polyester resin (B2) having a melting point of 246 to 266 ° C. mainly composed of ethylene terephthalate, and , it is composed of the polyester resin composition glass transition temperature (Tg) of 60 ° C. or higher (B) (provided that B1 ratio of the total amount of B1 and B2 is from 10 to 70 wt%), melting point Tm (A2 of the polyester resin (A2)) is 5 to 30 ° C. lower that the melting point Tm (B2) of the polyester resin (B2) A laminated polyester film for metal plate thermal lamination. The laminated polyester film for metal plate thermal lamination according to claim 1, which is for a molded can.