JP3318954B2 - Film for metal lamination and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for metal laminating and a method for producing the same, and more particularly, to a good adhesive, moldability and slippage when drawing and ironing at the time of lamination with metal and after lamination. The present invention relates to a film for metal laminating, which exhibits excellent properties, does not deteriorate the taste of the filling when used as a beverage can or a food can, and has a good appearance, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, thermosetting paints are often applied to prevent corrosion of the inner and outer surfaces of metal beverage cans. On the other hand, it has been proposed that a thermoplastic resin film is heat-laminated on a metal plate and then formed into a can shape by drawing or ironing. As a thermoplastic resin film, a polyolefin film, a copolymerized polyester film, a polyester film with an adhesive, and the like have been proposed. For example, Japanese Patent Publication No. 2-58094 discloses a method for producing a film-coated metal plate in which a polyethylene terephthalate (PET) film is heat-laminated and then rapidly cooled to leave the metal laminate side unoriented and the other side to remain biaxially oriented. Is disclosed.

[0003]

However, polyolefin films are inferior in heat resistance, corrosion resistance, and fragrance retention. Copolymerized polyester films adhere to the plugs at the time of drawing or ironing, making uniform molding impossible. As a result, the film is apt to crack or the plug is hard to be pulled out, so the molding speed does not increase.In addition, the cost of laminating with an adhesive increases, the drawability and ironing formability of the adhesive layer is poor, and the film is cracked and corrosion resistant. There was a problem. In the method of laminating a PET film by heat, the lamination temperature needs to be set high, so that the metal plate is damaged, especially the plating layer of a tin plate, etc.
In addition, since PET alone has poor moldability itself, there has been a large problem in coping with deep drawing like a general beverage can.

[0004] The present invention is to improve the suitability of the film for metal lamination and the metal plate in the heat lamination, especially the slipperiness, and to improve the adhesiveness and the molding property in the drawing and ironing of such a film-coated metal plate. It is an object of the present invention to provide a film for metal lamination which has good properties, does not deteriorate the taste of the filling when used as a molded can, and has a good appearance, and a method for producing the same.

[0005]

According to the present invention, there is provided a film for metal lamination according to the present invention, wherein a glass transition temperature Tg is set on a film made of a copolymerized polyester having a melting point of 140 to 200 ° C. on a side in contact with a metal. Polybutylene terephthalate having a temperature of 45 ° C. or higher (however, a glass transition temperature of 8
(Excluding those at 5 ° C. or higher) .

[0006] The copolyester in the present invention is:
A copolymer obtained by polycondensation of a dicarboxylic acid and a diol, and examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, and azelaic acid. Is, butylene glycol, hexanediol, cyclohexane dimethanol,
Neopentyl glycol and the like. In the present invention, a copolymer containing at least 50 mol% of polybutylene terephthalate and polyhexamethylene terephthalate is a polymer obtained by copolymerizing at least one of these dicarboxylic acids and diols.

Representative copolymers include polybutylene (terephthalate / isophthalate), poly (butylene / hexamethylene) terephthalate, polybutylene (terephthalate / naphthalate) and the like.
The melting temperature (melting point) Tm of this copolyester is 140-
200 ° C., preferably 150-180 ° C.
The one in the range of ° C is preferred. If Tm is lower than 140 ° C., the adhesive strength to metal is greatly reduced by retort treatment after canning, and if Tm exceeds 200 ° C., the adhesive strength to metal is weakened, and the adhesion between metal and the film of the present invention is poor. Air is trapped in the gap, which causes molding unevenness and cracks, which is not preferable.

The copolyester must be excellent in hydrolysis resistance. For this purpose, it is necessary that the ester group concentration is relatively low, and ethylene glycol is essentially contained in the diol component. And the number of carbon atoms between the ester groups must be 3 or more, preferably 4 or more.

Further, the copolyester needs to have a high degree of crystallinity and glass transition point to some extent, and it is preferable that the degree of crystallinity is about 5 to 30%, and the glass transition point is 30 ° C. or higher, preferably 30 ° C. or more. The temperature is preferably 35 ° C. or higher because of excellent hydrolysis resistance.

Furthermore, the maximum surface roughness Rt of the copolymerized polyester film of the present invention is preferably 1 μm or less, since it is possible to prevent air from entering the metal.

Next, polybutylene terephthalate having a glass transition temperature Tg of 45 ° C. or higher (provided that the glass transition temperature
Is a polymer mainly composed of polybutylene terephthalate homopolymer, polybutylene terephthalate, dicarboxylic acid such as sebacic acid, adipic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and hexamethylene. Glycol, bisphenol A or another diol copolymerized by one or more, and furthermore, an alloy of polybutylene terephthalate with a polymer such as polycyclohexane dimethylene terephthalate, polycarbonate, polyethylene naphthalate, or phenoxy resin, and Its crystal melting point is 2
It is a polymer whose temperature exceeds 00 ° C.

When the crystal melting point is less than 200 ° C., the handling property of the film is significantly poor, and when the glass transition temperature Tg is lower than 45 ° C., the taste of the content filling after canning is about 60 ° C. It is easy to deteriorate by heating for a long time. This is considered to be mainly due to the selective adsorption of taste components and, conversely, the generation of gas from the film. One of the indicators is that the amount of adsorbed d-limonene is 20 μg / g or less and the volatile component is 5 μg / g. It should be: For this purpose, the wetting tension of the film surface in contact with the contents is 5
It is preferably at least 0 dyn / cm, preferably at least 60 dyn / cm, more preferably at least 65 dyn / cm, and may be a known corona discharge treatment (in a gas such as air, nitrogen, or carbon dioxide) or a plasma treatment (carbon dioxide, argon). In a gas such as, for example, flame treatment, chemical treatment, and even coating of a polar polymer.
Further, it is preferable that the crystallinity of the film surface be high, because it is difficult to adsorb. For this purpose, the metal plate and the film of the present invention are heated and softened at 180 to 230 ° C., pressed and adhered, and then cooled while gradually cooling without quenching. It is preferable to generate and crystallize fine spherulites of about 1 μm or less. 0.01 and SiO ₂ as a crystal nucleating agent in order to refine the crystal
It is preferable to add about 0.5%, and the crystallinity is 10%.
６０60%, preferably 20-50%. By increasing the fine crystallization and increasing the surface wetting tension in this way, the taste components are not selectively adsorbed, and furthermore, the molding process, especially DI molding (Draw Ironi)
When the material is iron-formed as in ng), it is preferable because the material can be uniformly formed without stick-slip or the like. It is presumed that this is mainly due to the improvement of the sliding property between the ironing rod and the film of the present invention and the improvement of the rigidity of the film of the present invention. Furthermore, the higher the intrinsic viscosity [η] of the film of the present invention is 0.9 to 2.0, preferably 1.0 to 1.6, it may be excellent in moldability, impact resistance, prevention of deterioration of taste and the like.

Next, a method for producing the film of the present invention will be described, but the present invention is not limited thereto. A copolyester and a nucleating agent as an additive, for example, an average particle size of 0.25
A polybutylene terephthalate homopolymer to which μm of SiO ₂ has been added is dehydrated and dried by a known method, or is supplied to a separate extruder of a twin-screw vent type without being dried and melted. At 2
After the layers are stacked and discharged from a normal die, they are cooled and solidified by a cooling drum to obtain a cast film. The thus obtained two-layer laminated film is introduced into an oven heated to 100 to 200 ° C., heat-treated for about 0.1 to 10 minutes, then surface-activated and wound up, and the glass transition temperature Tg
To obtain a laminated film having a polybutylene terephthalate film layer having a temperature of 45 ° C. or higher. The heat treatment and the surface activation treatment are steps necessary to prevent gas dissolved in the film, for example, gas such as tetrahydrofuran or butadiene from being scattered, or to prevent selective adsorption of the contents. 5 μg / g of volatile components after 30 minutes treatment
Further, by changing the amount of adsorbed d-limonene to 20 μg / g or less, deterioration of the taste of the filler is prevented.

The thickness of the film of the present invention is 5 to 250 μm.
m, preferably 15 to 100 μm, more preferably 2
It is in the range of 0 to 50 μm. If the thickness is less than 5 μm, the corrosion resistance, moldability and the like will be poor if the thickness is less than 250 μm, and the moldability will be inferior if the thickness exceeds 250 μm. The thickness composition ratios are as follows: a copolymerized polyester film layer and a polybutylene terephthalate polymer layer having a glass transition temperature Tg of 45 ° C. or higher (excluding those having a glass transition temperature of 85 ° C. or higher).
Preferably the thickness ratio of Ku) is 1 / 30-30 / 1, and more preferably in the range of 1 / 10-10 / 1.
The thickness of the copolymerized polyester film layer is 1 μm
As described above, the thickness is preferably 3 μm or more, which is necessary to make the thickness more than twice the maximum surface roughness Rt of the metal plate. For example, in the case of a 30 μm thick film, the thickness of the copolymer polyester film layer is preferably 3 to 27 μm. The copolymerized polyester film layer is mainly determined by adhesiveness, impact resistance, retort resistance, moldability, and the like, and the high Tg polybutylene terephthalate polymer film layer is mainly used to alter the taste, moldability, handleability,
Determined by thermal deformability.

In order to control various characteristics such as crystallinity of each film layer in the above-mentioned production process, a combination of a cooling drum temperature, stretching conditions and heat treatment conditions is appropriately selected according to the characteristics of the selected polyester. can do.

The film for metal lamination of the present invention can be suitably used for coating the inner and outer surfaces of a metal can manufactured by drawing or ironing. Also, it can be preferably used for covering the lid portion of a two-piece can or the body, lid, and bottom of a three-piece can because of its good metal adhesion and moldability. In particular, a colored film of the present invention can be used for coating the outer surface. For this purpose, a colorant can be blended with a polymer mainly composed of copolymerized polyester and / or polybutylene terephthalate. Many colorants are white, and include 10-50% by weight, preferably 20-40% by weight of a colorant selected from titanium oxide TiO ₂ , especially rutile type titanium oxide, zinc oxide ZnO, lithophon ZnSBaSO _{4 and the} like. %
Often added. If the addition amount is less than 10% by weight, whiteness and hiding properties are inferior, so that it is not preferable. If necessary, a pinking agent or a bluing agent may be used in combination.

[Evaluation Methods of Physical Properties] (1) Crystallinity The cross section of the sheet was cut out, and the half width of the detected intensity of each layer in the sheet was measured by the laser Raman emission method. The amorphous state and the crystalline state of the polyester resin were obtained. The degree of crystallinity was calculated from the half-value width of the above. After dissolution with the metal plate, the density of the film was measured using a density gradient tube, and the degree of crystallinity was calculated from the densities of the amorphous state and the crystalline state of the polyester resin.

(2) Average surface roughness (Ra) and maximum surface roughness (Rt) A stylus type surface roughness meter HO specified in DIN4768.
Expressed as the center line average roughness (Ra) and the maximum roughness (Rt) at a cutoff of 0.25 mm, as measured by MMEL-TESTER-T10.

(3) The coefficient of friction of the sample film having a coefficient of friction of 80 × 150 mm is high Tg.
The chrome-plated steel sheet heated to 100 ° C is superimposed on the film surface, a load of 200 g is put on the film, and the tension when the lower steel sheet is pulled at a speed of 200 mm / min is divided by the load of 200 g to determine the friction. Coefficient was used. When this value was less than 5, it was evaluated as ○, and when it exceeded 5, it was evaluated as x.

(4) Moldability Copolymerized polyester film The surface of the polyester film and the tin-plated tin metal plate are heated and press-laminated to a temperature of 180 to 230 ° C., and a press forming machine (manufactured by Senba Iron Works Co., Ltd.) VAS-33P type) 100kg / cm
Cold forming is performed at a pressure of ² and the diameter D is 100 mm and the depth is h.
Was obtained with a draw ratio of 1.3 mm (h / D) of 1.3 mm. A 1% saline solution was put in the cup, the whole was heated to 80 ° C., left for 24 hours, and the mold name was judged from the condition of rust generated in the can. ：: No rust was generated. △: Less than 3 rusts of 1 mm or less were generated. X: Many rusts occurred.

(5) Melting point Tm, glass transition temperature Tg A sample of 10 mgr was set in a scanning calorimeter (DSC-II, manufactured by PerkinElmer), and the temperature was raised at a rate of 20 ° C./min under a nitrogen stream. The temperature was raised, the temperature at which the specific heat changed from the change in the baseline based on the transition from the glassy state to the rubbery state was Tg, and the temperature was further raised, and the endothermic peak temperature based on the melting of the crystal was Tm.

(6) Adhesiveness Between the metal roll and the silicone rubber roll heated to 180 to 230 ° C., the surface of the copolymerized polyester film of the film of the present invention and the Sn-plated tin plate were put together, and the pressure was 20
They were bonded under pressure at kg / cm, and cooled in air after bonding. The laminating adhesive strength of the laminate was determined by a peel test at an angle of 180 °, and the laminating adhesive strength was 250 g / c.
When it was not less than m, it was evaluated as ○, and when it was less than m, it was evaluated as x.

(7) Impact resistance After forming the can in the above (4), after high-pressure steam / retort treatment at 125 ° C. for 30 minutes, impact was applied to the side and bottom of the can with a punch from the outer surface of the can at five locations. After standing for 24 hours in the same heated saline solution as in 4), the occurrence of rust was observed and measured in the area where the punch was given an impact.と き,
When rust occurred more than that, it was evaluated as x.

(8) Deterioration of taste Originally a sensory evaluation, but in order to obtain reproducible and accurate data, as shown in Table 1 below, the amount of components generated when heated at 80 ° C. for 30 minutes And the adsorption amount of d-limonene.

[0025]

[Table 1]

(9) Volatile component (μg / g) A film (25 μm × 150 mm × 450 mm)
The components removed by heating in a nitrogen stream at 30 ° C. for 30 minutes are quantified by gas chromatography. This gas amount (μg
/ G) divided by the film weight (g).

(10) Adsorption of d-limonene on film The film (25 μm × 150 mm × 450 mm) is adsorbed on d-limonene.
The film is immersed in an aqueous solution of limonene (20 ppm) at room temperature for 5 days, and this film is heated at 80 ° C. for 30 minutes in a nitrogen stream to determine the components to be expelled by gas chromatography. The unit is the gas amount (μg) divided by the film weight (g).

(11) Surface wetting tension γ _c (dyn / c
m) According to the ASTM-D-2578-67T method,
It was measured under a 65% RH atmosphere.

[0029]

The present invention will be described below more specifically with reference to examples and comparative examples. Examples 1 to 5, Comparative Examples 1 to 3 Polybutylene (terephthalate / isophthalate) PBT / I, poly (butylene /
Hexamethylene) terephthalate PB / HT, polyethylene (terephthalate / isophthalate) PET / I, and a polybutylene terephthalate homopolymer PB as a polymer mainly composed of polybutylene terephthalate which becomes a film having a glass transition temperature Tg of 45 ° C. or higher
T, polybutylene (terephthalate / naphthalate) P
An alloy obtained by blending bisphenol A type polycarbonate PC with BT / N and PBT was used. Each polymer was fed to a twin-screw vented extruder, melted, and two types of polymer melts were combined with a composite adapter.
The layer-laminated sheet was discharged, adhered to a cooling drum maintained at 20 to 60 ° C., and cooled and solidified to obtain a cast sheet. The sheet was further heat-treated in an oven at 150 ° C. for 10 seconds, subjected to plasma treatment under a normal pressure in a mixed gas of argon and carbon dioxide on the surface of the polybutylene terephthalate film, and then wound up. The thickness was fixed at 25 μm and the thickness was set at 5/20. The polybutylene terephthalate film was added with 0.1% by weight of Aerosil SiO ₂ (average particle size: 0.2 μm) as an additive (however, it was not added to Comparative Examples 1 and 2). In Example 3, the heat treatment and the normal pressure plasma treatment were not performed.

The copolyester surface (crystallinity 15 to 25%, maximum surface roughness Rt = 0.1 to 0.5 μm) of the thus obtained two-layer laminated sheet and a tin plate (Sn) Plate thickness 300μm, maximum surface roughness Rt = 1μ
m), and after heating and compression bonding at 200 ° C., crystallized by slow cooling, and cold-formed to a draw ratio of 1.5 to form a can. The can thus obtained was evaluated for moldability, impact resistance, taste deterioration, and the like.
The result was as follows.

As described above, if the Tg of the film in contact with the filling of the can is not higher than 45 ° C., the taste is changed, and the adhesiveness, impact resistance and hydrolysis resistance of polyethylene terephthalate are poor. When the polymer is used, not only the moldability but also the impact resistance is weak, and it is found that the polymer is not practical. Of course, even if the same polymer is used, the heat treatment and the surface activation treatment do not change the taste, and the addition of the nucleating agent improves the impact resistance, probably because the spherulite size is smaller. . In addition, it was also confirmed that even after heat treatment at 195 ° C. after biaxial stretching of Comparative Example 3 three times vertically and three times horizontally, moldability and impact resistance were not improved at all.

[0032]

[Table 2]

Examples 6 to 13 A PBT homopolymer having an intrinsic viscosity [η] of 1.2 and rutile-type titanium oxide (average particle size: 0.25 μm) were quantitatively supplied to a twin-screw vented extruder. Melted. Also,
A polybutylene (terephthalate / isophthalate) copolymer as a copolymerized polyester was supplied to a twin-screw vented extruder and melted at 280 ° C. in the same manner as described above. After merging the melts of the two polymers with a composite adapter, 2
The layer-laminated sheet was discharged, and was tightly cooled and solidified on a cooling drum maintained at 45 ° C. to obtain a cast sheet having a thickness of 25 μm. The copolyester surface of the two-layer laminated sheet thus obtained and the copolyester surface of the two-layer laminated sheet used in Example 2 were each TFS (Tin Fre).
e Steel: tin-free iron) plates were heated and laminated at 200 ° C. on both sides, then drawn and formed to a draw ratio of 1.3 to form a can. At this time, the outer surface was made to be a white film. Table 3 shows the evaluation results of the cans thus obtained. It can be seen that it is necessary to add 10% by weight or more, preferably 20% by weight, of TiO _{2 in} order to provide whiteness and excellent concealing properties for eliminating the blackness of the underlying TFS plate.

[0034]

[Table 3]

[0035]

As the film for metal lamination of the present invention, a polybutylene terephthalate film layer having a high Tg is laminated on a low melting point copolymerized polyester film having a specific composition, followed by heat treatment and surface treatment. As a result, not only is it excellent in adhesion to a metal plate, moldability, impact resistance after retort treatment, etc., it is also possible to maintain the taste of content filling such as coffee and juice at a high temperature (60 ° C.) It has become possible not to deteriorate. Therefore, the film of the present invention can be used as an inner and outer film for containers such as beverage cans and food cans. As for the molding method, it can also be used for the DI ironing method and the DTR draw forming can.

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁷ Identification code FI B29K 67:00 B29K 67:00 (56) References JP-A-5-254065 (JP, A) JP-A-3-176144 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 47/00-47/96 B32B 1/00-1/10 B32B 15/08 104 B32B 27/00-27/42

Claims (10)

(57) [Claims] 1. A melting point of 140 to 20 on a side in contact with a metal.
A polybutylene terephthalate having a glass transition temperature Tg of 45 ° C. or higher (but a glass transition temperature of 85 ° C. or higher) is placed on a 0 ° C. copolyester film.
A film for metal laminating is formed by laminating a film composed mainly of a polymer excluding) . 2. The film for metal lamination according to claim 1, wherein said copolymerized polyester contains polybutylene terephthalate or polyhexamethylene terephthalate as a main component. 3. A polybutylene terephthalate having a glass transition temperature Tg of 45 ° C. or higher (however, the glass transition temperature
Excluding those at 85 ° C or higher)
3. A polybutylene terephthalate homopolymer, a polybutylene terephthalate copolymer, or an alloy of polybutylene terephthalate and another polymer, wherein the polymer has a crystal melting point of more than 200 ° C.
Film for metal lamination. 4. The film for metal lamination according to claim 1, wherein a colorant is blended with the polymer mainly composed of the copolymerized polyester and / or polybutylene terephthalate. 5. The film for metal lamination according to claim 4, wherein the colorant contains a colorant selected from titanium oxide TiO ₂ , zinc oxide ZnO and lithophon ZnSBaSO _{4 in} an amount of 10 to 50% by weight. 6. The film for metal lamination according to claim 1, wherein the surface wetting tension of at least one side of the metal laminate film is 50 dym / cm or more. 7. The film for metal lamination according to claim 1, wherein a volatile component when heated at 80 ° C. for 30 minutes is 5 μg / g or less. 8. The film for metal lamination according to claim 1, wherein the adsorption of d-limonene is 20 μg / g or less. 9. The copolymerized polyester and polybutylene terephthalate having a glass transition temperature Tg of 45 ° C. or higher .
After co-extrusion cast and soup glass transition temperature as a main component except rather) of not less than 85 ° C. polymers, 100-20
9. A heat treatment at 0 ° C.
The method for producing a film for metal laminate according to any one of the above. 10. The method for producing a metal laminate film according to claim 1, wherein a metal plate is directly adhered to the surface of the copolymerized polyester film by heating and then gradually cooled to finely crystallize. Method.