JPH06218875A - Polyamide coated molded object and polyamide film used therein - Google Patents

Abstract

PURPOSE:To improve adhesiveness, moldability and impact resistance and to prevent the deterioration of the taste of content at the time of use as a molded can by coating at least the single surface of a steel panel with a polyamide film before molding the steel panel. CONSTITUTION:A steel panel molded object is obtained by coating at least the single surface of a steel panel with a polyamide film and subsequently molding the coated steel panel. The polyamide film pref. has relative viscosity etar of 2.5 or more, an m.p. of 180-235 deg.C and a thickness of 5-250mum. The polyamide film is pref., applied to the steel panel by bonding the polyamide film to the steel panel under heating and pressure by utilizing heat adhesiveness. The coated steel panel thus obtained is subjected to drawing, squeezing molding or drawing/squeezing molding using a jig such as a punch or a die. By this method a laminated steel panel excellent in the adhesion with the steel panel, moldability and impact resistance is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet molded body and a polyamide film used therefor. More specifically, it is drawn with a steel sheet during and after lamination.
Good adhesive, moldability when ironing,
The present invention relates to a steel sheet molded product that exhibits slipperiness and impact resistance, 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 polyamide film used therefor.

[0002]

2. Description of the Related Art Conventionally, a thermosetting paint is often applied to prevent corrosion of the inner and outer surfaces of a beverage metal can. On the other hand, it has been proposed to heat-laminate a thermoplastic resin film on a metal plate and draw it to form a can by drawing and ironing. As a thermoplastic resin film, a polyolefin film, a copolyester film, an adhesive-attached polyester film, etc. have been proposed. For example, Japanese Patent Publication No. 2-58094
The publication 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 non-oriented and the opposite side to remain biaxially oriented.

[0003]

However, the polyolefin film is inferior in heat resistance, corrosion resistance, and aroma retention, and in the case of the copolyester film, the film is stuck to the plug at the time of drawing or ironing, so that uniform molding cannot be performed. As a result, the film tends to crack, the plug does not come off easily, the molding speed does not increase, and the cost of laminating with an adhesive increases, and the drawability and ironing formability of the adhesive layer are poor, and cracking occurs and corrosion resistance There was a problem with. Further, in the method of thermally laminating a PET film, since it is necessary to set the laminating temperature high, damage to the metal plate, particularly damage to the plating layer such as a tin plate is large,
Further, since the PET itself has poor moldability, it has a big problem in dealing with deep drawing such as a general beverage can.

The present invention improves the suitability of a film for laminating a steel sheet and a steel sheet at the time of heat lamination, particularly slipperiness, in draw forming and ironing of such a film-coated steel sheet, and also improves adhesiveness, formability, and An object of the present invention is to provide a steel sheet molded article having good impact resistance, which does not change the taste of the filler when used as a molding can and has a good appearance, and a polyamide film used therefor.

[0005]

Means for Solving the Problems A steel sheet molded body of the present invention for this purpose is a steel sheet molded body which is formed by coating a polyamide film on at least one surface of a steel sheet, and the relative viscosity η _{r of the} polyamide used therein is 2 It is a polyamide film of 0.5 or more.

The polyamide in the present invention is a polymer having an amide bond in the main chain, which is obtained by ring-opening polymerization of lactam or condensation polymerization of dicarboxylic acid and diamine.
Polyamides containing aminobenzoic acid, p-aminomethylbenzoic acid and the like, and examples of dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid and azelaic acid. As the diamine, polyamide obtained from hexamethylenediamine, 2,4,4′trimethylhexamethylenediamine, meta or para-xylylenediamine, cyclohexanebismethylamine, bis (4aminophenyl) methane, paraaminocyclohexylmethane, etc. Can be given. A polymer obtained by copolymerizing one or more kinds of these caprolactam or dicarboxylic acid and diamine, and in the case of the present invention, particularly polyhexamethylene sebacamide (nylon 610), polyhexamethylene adipamide / caprolamide Copolymer (nylon 6,66), polycaprolamide (nylon 6), nylon 6,12 copolymer, nylon 12, polymethaxylylene adipamide (mXD6), nylon 6 / polyhexamethylene terephthalamide / isophthalamide Copolymers and their copolymers are preferred.

The relative viscosity η _r of the present polyamide film is 2.5 or more, preferably 3.0 or more, more preferably 3.5 or more. This is necessary for laminating suitability with a steel plate, formability after laminating, retort resistance, pinhole resistance, impact resistance, and preventing alteration of taste of contents.

The polyamide film of the present invention has a melting point of 180.
˜235 ° C., preferably 200 to 225 ° C. If the melting point exceeds 235 ° C., the heat adhesive strength between the steel sheet and the polyamide film becomes weak, and as a result, not only causes uneven molding and cracks, but also the steel sheet deteriorates especially in the case of tin-plated steel sheet. Not preferred because of On the contrary, if the melting point is less than 180 ° C., not only the adhesion to the metal becomes poor due to the retort treatment after the canning and the high temperature treatment in the baking step, but also the polyamide film layer shrinks and peels from the steel sheet.

The melting point of the polymer layer (II) must be 236 ° C. or higher, preferably 245 ° C. or higher, in order to improve the handling property such as baking at high temperature. The polymer of the polymer layer (II) is one or a mixture of two or more selected from polyamide, polyester, polyesteramide, polyetheramide, polyester ether, ethylene / vinyl alcohol copolymer, and the like. Polymers include nylon 66 and its copolymers, polyamides containing xylylenediamine, such as polyxylylene adipamide, polyamides containing terephthalic acid such as polyhexamethylene terephthalamide / isophthalamide copolymer (6I / 6T) and The copolymer (for example, 6 / 6I / 6T, 66 / 6I /
6T) and the like, polyethylene terephthalate (PET) and copolymers thereof such as polyethylene isophthalate / terephthalate copolymer, polyethylene naphthalate, polyesters such as polycyclohexanedimethylene terephthalate, and polymers of nylon 6 and PET. , A polymer of ethanolamine and terephthalic acid, adipic acid, etc., a polyesteramide such as a copolymer of PET and a diamine, and a copolymerized polyvinyl alcohol product having an ethylene content of 5 to 50 mol%, for example, "Eval" (manufactured by Kuraray), A typical example is "Sophical" (manufactured by Nippon Gosei).

Since these polymer (II) layers often come into direct contact with filling materials such as beverages after they are formed, it is important that the taste of the beverage does not change over time. It is considered that this may be due to selective adsorption or conversely gas generation from the film, and as one index thereof, the adsorbed amount of d-limonene is 20 μg / g or less and the volatile component is 5 μg / g or less. More preferably, the wetting tension of the film surface in contact with the content is 40 dy.
n / cm or more, preferably 45 dyn / cm or more, more preferably 50 dyn / cm or more, and known corona discharge treatment (in air, nitrogen, carbon dioxide gas, etc.) or plasma treatment (carbon dioxide gas, argon). Gas, etc.), flame treatment, chemical treatment, and even coating with polar polymer. Further, the higher the crystallinity of the film surface, the more difficult it is to adsorb, which is preferable. For this purpose, the metal plate and the film of the present invention are heated and softened at 180 to 230 ° C., brought into pressure contact with each other, and then gradually cooled without being excessively cooled, and in this process, mainly the polymer layer ( It is preferable to generate fine spherulites of about 1 μm or less in II) for crystallization. To refine the crystal, 0.01 as a crystal nucleating agent such as SiO _2.
It is preferable to add about 0.5%, and the crystallinity is 3
-50%, preferably 5-20%. In this way, by finely crystallization and increasing the surface wetting tension, taste components are not selectively adsorbed, and moreover, when the material is ironed and molded in the molding process, especially DI molding (Draw Ironing) It is preferable because uniform molding can be performed without causing slippage. It is estimated that this is mainly due to the improvement of the slipperiness between the ironing rod and the film of the present invention and the improvement of the toughness and rigidity of the film of the present invention.

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 preferably in the range of 0 to 50 μm. This is because if the thickness is less than 5 μm, the corrosion resistance and moldability are poor, and if it exceeds 250 μm, the moldability becomes poor. The thickness of the polymer layer (II) is preferably 0 to 8 μm, more preferably 0.5 to 3 μm. Furthermore, 25% or less based on the total thickness of the film of the present invention,
It is preferably in the range of 1 to 10%. This is because the characteristics such as handleability at high temperature, moldability, impact resistance, and pinhole resistance are satisfied. The thickness of the polyamide film is 10 to 200 μm, preferably 10 to 100
The thickness is preferably in the range of 10 μm, and more preferably in the range of 10 to 50 μm, in order to satisfy the adhesiveness with metal, impact resistance, retort resistance, moldability and the like.

Furthermore, the maximum surface roughness Rt of the polyamide film of the present invention is preferably 1 μm or less because it is possible to prevent air from being caught between the polyamide film and the metal.

The steel plate may be simply a metal plate containing iron as a main component, but an inorganic oxide coating layer for improving adhesion and corrosion resistance, such as chromic acid treatment, phosphoric acid treatment, chromic acid / phosphorus, is formed on the surface of the steel plate. Acid treatment, electrolytic chromic acid treatment, chromate treatment,
A chemical conversion treatment coating layer typified by chromium chromate treatment may be provided. Particularly, a chromium hydrated oxide having a chromium value of 6.5 to 150 mg / m ² in terms of metal chromium is preferable, and further spreadable metal plating. It will be appreciated that layers such as nickel, tin, zinc, aluminum, gunmetal, brass and the like may be provided. It is preferable to have a plating amount of 0.5 to 15 g / m ² for tin plating and 1.8 to 20 g / m ² for nickel or aluminum.

As a method for coating the steel sheet with the polyamide film, a method of thermocompression bonding utilizing the thermal adhesiveness of the polyamide film, a method of interposing another adhesive layer between the film and the steel sheet, and further adhering, In the present invention, the thermocompression bonding method is preferable.

The coated steel sheet thus obtained is drawn and ironed by a jig such as a punch and a die.
Squeeze ironing and forming. As a typical manufacturing method of a drawn and ironed can, that is, a side-seamless metal can (two-piece can), a coated steel plate is punched into a disk shape, and then drawn in a drawing process between a drawing die and a punch, In the redrawing process, the drawn cup-shaped molded product is redrawn or ironed between a redrawing die having a smaller diameter and a redrawing punch to form a deep-drawn or ironed cup-shaped molded product. . Of course, a lubricant can be used at the time of processing, and the third stage drawing process and ironing process are also possible.
In addition, the ironing rate in the one-step ironing process, that is,

[0016]

[Formula 1] It is preferably in the range of 10 to 50%, and 30 to 85% as a whole.

Next, a method for producing the polyamide-coated molded article of the present invention will be described, but the method is not limited thereto.

The coated steel sheet is obtained by directly heat-bonding the chemical conversion treated steel sheet and the polyamide film of the present invention, or by interposing another adhesive between them. Next, this coated steel sheet is subjected to ironing and / or drawing in multiple stages to obtain a cup-shaped compact.

A method for producing the ponoamide film of the present invention will be described, but the method is not limited thereto. Nylon 610 (melting point 215 ° C., relative viscosity η _r = 3.0) is used as the polyamide (I), and polyethylene terephthalate / isophthalate (melting point 245 ° C., intrinsic viscosity 1.0, 200 μm as an additive) is used as the polymer layer (II). 0.2% by weight of SiO ₂ ) and nylon 6 / 6I / 6T
(Melting point 240 ° C., relative viscosity η _r = 2.8, 0.15% by weight of Syloid 150 as an additive) is used, and after dehydration and drying by a known method, or without drying, a biaxial vent type is used. It is supplied to separate extruders to be melted, then laminated in two layers on a subsequent feed block, discharged from an ordinary die and cooled and solidified by a cooling drum to obtain a cast film. The two-layer laminated film thus obtained is subjected to heat aging or surface activation treatment, if necessary, and wound. This heat treatment and surface activation treatment are effective steps for preventing the gas dissolved in the film from scattering and selectively adsorbing the contents, and the volatile components in the treatment at 80 ° C. for 30 minutes are 5 μg / g or less Further, the adsorbed amount of d-limonene is set to 20 μg / g or less to prevent the deterioration of the taste of the filling.

The thickness of the polymer layer (II) thus obtained is reduced to 0.5 to 3 μm, while the thickness of the polyamide layer is increased to 10 to 50 μm to obtain a film having a total thickness of 20 to 50 μm.

The steel sheet laminating film of the present invention can be suitably used for coating the inner surface and the outer surface of a metal can produced by drawing or ironing. Further, it can be preferably used also for covering the lid portion of a two-piece can or the body, lid and bottom of a three-piece can because it has good metal adhesion and moldability. In particular, the colored film of the present invention can be used for coating the outer surface. For this purpose, the polyamide layer (I) and / or the polymer layer (I
A colorant can be added to the polymer of I). Most of the colorants are white, and titanium oxide Ti
A coloring agent selected from O ₂ , particularly rutile type titanium oxide, zinc white ZnO, and lithophone ZnSBaSO _{4 is} used in an amount of 10-5.
It is often added in an amount of 0% by weight, preferably 20 to 40% by weight. If the addition amount is less than 10% by weight, the whiteness and the hiding property are poor, which is not preferable. If necessary, a pinking agent or a bluing agent may be used in combination.

[0022]

[Method of evaluating physical properties]

(1) Moldability A copolymerized polyester film surface of a polyester film and a tin-plated tin metal plate are heated and pressure-laminated at a temperature of 180 to 230 ° C., and a press molding machine (manufactured by Semba Tekko KK, VAS-33P). Type) 100kg / cm
Cold forming with pressure of ² , diameter D is 100mm, depth h
To obtain a cup having a drawing ratio (h / D) of 1.3. A 1% saline solution was placed in this cup and the whole was heated to 80 ° C. and allowed to stand for 24 hours, after which the moldability was judged from the condition of rust generated in the can.

◯: No rust was generated Δ: 3 or less rusts with a size of 1 mm or less were generated ×: Many rusts were generated

(2) Melting point Tm, glass transition temperature Tg A scanning calorimeter (DSC-II type, manufactured by Perkin Elmer Co.) was set with 10 mg of a sample and heated under a nitrogen stream at a temperature rising rate of 20 ° C./min. The temperature was changed to Tg, which is the change temperature of the specific heat from the strangeness of the baseline due to the transition from the glass state to the rubber state, and the temperature was further raised, and the endothermic peak temperature due to the melting of the crystals was Tm.

(3) Impact resistance After forming the can in the above (1), after performing high pressure steam retort treatment at 125 ° C. for 30 minutes, the can side surface and the can bottom can be impacted with 5 punches from the can outer surface, and then (1) ), After leaving it in the same heated saline solution for 24 hours, observing and measuring the generation of rust in the part that was impacted by the punch, ○ when no rust was generated in that part, within 3 mm at sabiga 1 mm or less The case was marked with Δ, and the case where more rust was generated was marked with x.

(4) Volatile component (μg / g) 80 (25 μm × 150 mm × 450 mm) film
The components to be expelled by heating in a nitrogen stream at 30 ° C. for 30 minutes are quantified by gas chromatography. This gas amount (μg
/ G) was divided by the film weight (g).

(5) Adsorption of d-limonene on a film A film (25 μm × 150 mm × 450 mm) was d-
The film was immersed in an aqueous solution of limonene (20 ppm of 0.3% sugar ester added as a solubilizing agent) at room temperature for 5 days, and this film was heated in a nitrogen stream at 80 ° C. for 30 minutes to quantify the components displaced by gas chromatography. The unit is the gas amount (μg) divided by the film weight (g).

(6) Alteration of taste Although it is originally a sensory evaluation, in order to obtain reproducible and accurate data, the above (4) amount of the heating component generated and (5) the amount of adsorbed limonene adsorbed are Judged in.

◯: Heat-generated component amount less than 5, d-limonene adsorption amount less than 20 Δ: Heat-generated component amount of 5 or more, d-limonene adsorption amount less than 20 Δ: Heat-generated component amount less than 5, d-limonene adsorption amount 20 Above x: Amount of component generated by heating of 5 or more, Adsorption amount of d-limonene of 20 or more

(7) Surface wetting tension γ c (dyn / cm) 20 ° C. by the ASTM-D-2578-67T method,
The measurement was performed in a 65% RH atmosphere.

(8) Adhesiveness The copolymerized polyester film surface of the film of the present invention and the Sn-plated tin plate are fitted between a metal roll and a silicone rubber roll heated to 180 to 230 ° C., and a pressure of 20 is applied.
Pressure bonding was performed at kg / cm, and after bonding, it was cooled in air. The laminating adhesive strength of the laminated plate was determined by a peel test at an angle of 180 °, and the laminating adhesive strength was 250 g / c.
When it was m or more, it was evaluated as ◯, and when it was less than m, it was evaluated as x.

(9) Thickness of Interlayer Film After the film was aged and crystallized, a cross section was cut out with a microtome and measured with a phase contrast microscope.

(10) Intrinsic viscosity η, measured in orthochlorophenol at 25 ° C., dl
/ G.

(11) Relative viscosity η _r Concentrated sulfuric acid was used as a solvent for measurement.

[0035]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples.

Examples 1 to 8 Nylon 12 (η _r = 3.0), nylon 610 (η _r = 3.0), nylon 6,66 (η _r ) as a ponoamide.
= 2.9), nylon 6,12 (η _r = 3.2), and nylon 6I / 6T (η _r = 3.5), and polymetaxylylene having η _r = 2.8 as the polymer (II). Adipamide (mXD6), nylon 6/6 with η _r = 2.9
I / 6T, polyethylene terephthalate with η = 0.9 /
Using isophthalate (PET / I), each polymer was supplied to a twin-screw vent extruder and melted, and after two kinds of polymer melts were separated by a composite adapter, a two-layer laminated sheet was discharged from a die, and 110 A cast sheet was obtained while being gradually cooled on a sand bluff roll kept at ℃. The film thickness obtained was such that the polyamide layer had a thickness of 23μ and the polymer layer (II) had a thickness of 2μ, giving a total thickness of 25μ.

The mild steel plate hydrated chromium oxide layer as an upper layer on one side of (0.32mm) (28mg / m ² as chromium), it has a plating layer of metallic chromium layer (157 mg / m ²⁾ in the lower layer, other Layer (1.5g /
m ² ) a steel sheet having a plated layer of the malleable metal is heated by high-frequency heating, and the low melting point polyamide side of the laminated polyamide film is pressed onto the steel sheet to bond the steel sheet, and then rapidly cooled to obtain a coated steel sheet. It was Next, squeezing and ironing was performed at a total ironing rate of 68% so that the inner surface of the can became the film-coated surface. The moldability and impact resistance of the thus obtained molded product were evaluated.

[0038]

[Table 1]

[Table 2] Examples 9 to 12 Molded articles were obtained and evaluated in the same manner as in Example 1 except that the relative viscosity η _r of the polymer used in Example 1 was changed.

[0039]

[Table 3] Thus, the relative viscosity η _r of the polyamide is preferably 2.5 or more.

Examples 13 to 15 Molded articles were obtained in the same manner as in Example 1 except that the thickness constitution used in Example 1 was changed.

[0041]

[Table 4] Thus, the thickness of the polymer layer (II) which is the outer layer is 0 to
It can be seen that the range of 8 μm is preferable.

Comparative Example 1 A polyethylene terephthalate / isophthalate copolymer (83/17 mol%, η = 0.8) was fed to a twin-screw vent extruder and melted at 265 ° C., and then from a T-die die. It was discharged in a sheet form, and was brought into close contact with a cast drum kept at 25 ° C. to be cooled and solidified to obtain a film having a thickness of 25 μm.

The polyester film thus obtained was adhered to a plated steel sheet in the same manner as in Example 1 to obtain a coated steel sheet,
Then, ironing was performed.

[0044]

[Table 5] Thus, it can be seen that the polyester copolymer film is not suitable as an inner surface laminating film for can manufacturing.

[0045]

As the steel sheet laminating film of the present invention, a film obtained by laminating a high melting point polymer layer (II) thinly and a high viscosity, low melting point polyamide layer thickly is used. Not only is it excellent in moldability and impact resistance after retort treatment, but it has also become possible to maintain the taste of content fillings such as coffee and juice at high temperatures (60 ° C) without deterioration. Therefore, the film of the present invention can be used especially as an inner and outer burr film for a container such as a beverage can, and can be used for a DI ironing molding method or a DTR draw-molding can as a molding method.

Claims (8)

[Claims] 1. A polyamide-coated molded article, characterized in that at least one surface of a steel sheet is coated with a polyamide film and then molded. 2. The polyamide-coated molded article according to claim 1, which is obtained by a processing method selected from squeezing molding and / or ironing molding. 3. The polyamide-coated molded product according to claim 1 or 2, wherein the molded product is a beverage can. 4. The polyamide film used for the polyamide-coated molded article according to claim 1, wherein the polyamide film has a relative viscosity of 2.5 or more. 5. The polyamide film according to claim 4, which has a melting point of 180 to 235 ° C. 6. A polymer layer (II) having a melting point of 236 ° C. or higher, which is one kind or a mixture of two or more kinds selected from polyamide, polyester, polyester ether, polyester amide, polyether amide, and ethylene / vinyl alcohol copolymer. ) Is laminated | stacked on this poamide film, The polyamide film of Claim 4 or Claim 5 characterized by the above-mentioned. 7. The thickness of the polymer layer (II) is 0 to 8 μm.
The polyamide film according to claim 6, wherein 8. The colorant is blended in the polymer layer (II) and / or the polyamide layer.
Alternatively, the polyamide film according to claim 7.