JP2007253454A - Resin coated metal sheet for container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a resin coated metal sheet for a container excellent in the takeout properties of content, the adhesion with a metal sheet, heat resistance, molding processability, etc. <P>SOLUTION: The resin film becoming the inner surface side of the container comprises a resin layer based on a polyester and contains 0.1-30 mass% of a hydrophobic polymer with respect to the resin layer. Further, in order to set the distribution state of the hydrophobic polymer in the resin film to a proper range, the surface of the resin layer after the container is molded using the resin film and subjected to retort treatment is set so that a Raman band intensity ratio I<SB>2968</SB>/I<SB>3085</SB>is 0.10-1.0. Herein, I<SB>2968</SB>is the Raman band intensity in the vicinity of 2,968±5 cm<SP>-1</SP>originating from the C-H expansion and contraction of the glycol component of the polyester resin due to a laser Raman spectral method and I<SB>3085</SB>is the Raman band intensity in the vicinity of 3,085±5 cm<SP>-1</SP>originating from the C-H expansion and contraction of the benzene ring of the polyester resin due to the laser Raman spectral method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a resin-coated metal plate for containers. Specifically, the moldability and adhesion in the can making process are good, the impact resistance after filling the contents and the contents taking out after the retort treatment are excellent, and it is manufactured by a molding process such as drawing or ironing. The present invention relates to a polyester resin-coated metal plate suitable for a material of a lid or body of a metal can.

  Conventionally, a thermoplastic resin film is laminated on the inner surface and outer surface of a metal can using tin-free steel (TFS), aluminum or the like for the purpose of preventing corrosion of the metal plate. And many methods of laminating a thermoplastic resin film on a heated metal plate or a metal plate subjected to various surface treatments such as plating have been proposed.

For example, Patent Document 1 discloses a polyester film for laminating metal plates made of a biaxially oriented polyester film having a specific density and a plane orientation coefficient.
Patent Document 2 discloses a copolymerized polyester film for metal plate lamination, which is composed of a predetermined acid component and a glycol component and has a specific crystallinity.

  However, when the laminated metal plate proposed in Patent Documents 1 and 2 is used for food canning, the contents are firmly attached to the inner surface of the container when the contents are taken out from the container, and the contents are difficult to take out. There's a problem.

With respect to the above problem, Patent Document 3 defines the film surface after lamination by the contact angle with water in order to improve the content takeout property. However, in food canned applications, since the retort process is performed at around 120 ° C. as a sterilization process, the crystal structure of the polyester film is changed by this process and affects the takeout of the contents. However, sufficient effects are not always obtained. In addition, food cans are used in a wide variety of contents, handling a wide range of contents from hydrophilic to lipophilic, and it is necessary to ensure the removability of various contents. Satisfactory performance cannot always be obtained simply by defining the contact angle.
JP-A 64-22530 Japanese Patent Laid-Open No. 2-57339 JP 2004-168365 A

  The present invention has been made in view of such circumstances, and when used in food canning applications, is excellent in the ability to take out the contents even after retort processing, and further has good adhesion to metal plates, heat resistance, and molding. It aims at providing the resin-coated metal plate for containers excellent in workability.

In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, the following knowledge was obtained. Affinity between the hydrophobic polymer contained in the resin film and the polyester resin layer is important to prevent adhesion with food contents, and the affinity is greatly influenced by the crystal orientation of the polyester resin layer. Therefore, it is important to optimize the crystal orientation of the polyester resin layer, and using the Raman band intensity by the laser Raman method as an index representing the crystal orientation of the polyester resin layer, the benzene ring C of the polyester resin is used. Raman band intensity near 3085cm ^-1 ± ^{5cm -1} from -H stretch _{(I 3085)} and C-H stretch Raman band intensity near 2968cm ^-1 ± ^{5cm -1} from the glycol component of the polyester resin _{(I 2968)} By making the strength ratio of the material within an appropriate range and highly controlling the resin film structure, the contents can be taken out easily. Be above, we have found more.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A metal plate for a container that covers both sides of a resin film, and the resin film on the inner surface side of the container is a resin layer mainly composed of polyester and has a hydrophobicity of 0.1 to 30 mass% with respect to the resin layer. A container having a Raman band intensity ratio I ₂₉₆₈ / I ₃₀₈₅ of 0.10 or more and 1.0 or less on the surface of the resin layer after retort treatment. Resin coated metal plate.
_{However, I 2968} is the Raman band intensity near 2968cm ^-1 ± ^{5cm -1} from C-H stretching of glycol component of the polyester resin by the laser Raman _{spectroscopy, I 3085} is a benzene ring of the polyester resin by laser Raman C This is the Raman band intensity around 3085 cm ⁻¹ ± 5 cm ⁻¹ derived from −H stretching.
[2] In the above [1], the Raman band intensity ratio I ₂₉₆₈ / I ₃₀₈₅ in the longitudinal direction of the resin-coated metal plate for containers is 0.2 or more and 0.6 or less, and the resin-coated metal for containers The resin-coated metal plate for containers, wherein the Raman band intensity ratio I ₂₉₆₈ / I ₃₀₈₅ in the width direction of the plate is 0.10 or more and 0.5 or less.
[3] The resin-coated metal plate for containers according to [1] or [2], wherein the resin layer containing polyester as a main component has 80 mol% or more of the structural units of the polyester as ethylene terephthalate units. .
[4] In any one of [1] to [3], the resin layer mainly composed of the polyester is composed of two or more layers, and the hydrophobic polymer is added to only the layer in contact with the contents. . A resin-coated metal plate for containers, containing 1 to 30 mass%.
[5] In any one of [1] to [4], the region where the birefringence of the resin film on the inner surface side of the container is 0.02 or less is from the contact interface with the metal plate in the resin film thickness direction. A resin-coated metal plate for containers, characterized by being less than 5 μm.

  According to the present invention, it is possible to obtain a resin-coated metal plate for a container which is excellent in the content take-out property, and further excellent in impact resistance, adhesion to a metal plate, heat resistance and molding processability. Since the resin-coated metal plate for containers according to the present invention has the above-mentioned properties, it is suitable as a material for a lid or body of a metal can manufactured by a forming process such as drawing or ironing.

First, the main technical idea that led to the completion of the present invention will be described.
Even in the case of a film in which a hydrophobic polymer is applied and / or contained in a polyester resin at the same composition ratio, the contents can be taken out differently depending on the production conditions of the resin-coated metal sheet, the presence or absence of retorting, and the like. This is presumably because the affinity between the polyester resin layer and the hydrophobic polymer is different depending on the crystal orientation of the polyester resin layer, and as a result, the film surface state is different. Until now, examination of the content taking-out property which paid its attention to the surface state of a polyester resin layer is not made | formed. Therefore, first, a study was conducted on the relationship between the crystal orientation state of the polyester resin layer containing the hydrophobic polymer on the inner surface side of the container and the content take-out property.

  Canned foods contain proteins and fats as contents, and have polar groups such as amide groups, carboxyl groups, and hydroxyl groups. Therefore, these food contents have poor affinity with the hydrophobic polymer. On the other hand, a polyester resin mainly has a structure of a dicarboxylic acid component such as terephthalic acid and a divalent diol component such as ethylene glycol, a polar group such as a carboxyl group, an aromatic ring such as a benzene ring, and a fatty acid such as an ethylene chain. There are hydrophobic groups of the family. Therefore, the polyester resin alone has an affinity for food contents, and the contents easily adhere to the film surface. From the results of the above considerations, it is considered important to include a hydrophobic polymer in the polyester resin in order to inhibit the affinity with food contents and prevent the contents from adhering to the resin film surface. .

  Therefore, a hydrophobic polymer was included in the polyester resin, and the adhesion state with the food contents was examined. As a result, the hydrophobic polymer must be effectively present in the surface layer of the polyester resin in order to prevent adhesion with the food contents. For this purpose, the affinity between the hydrophobic polymer and the polyester resin layer is important. It was found that the affinity is greatly affected by the crystal orientation of the polyester resin layer.

As a method for investigating the crystal orientation state of the polyester resin layer, there is confocal laser Raman spectroscopy. The Raman band intensity (I ₂₉₈₆ ) in the vicinity of ₂₉₈₆ cm ⁻¹ ± 5 cm ⁻¹ by laser Raman spectroscopy reflects the arrangement of the C—H bonds of the glycol component in the polyester resin layer. The arrangement of the resin chains is in a relatively disordered state, and it is considered that there are many amorphous parts. The Raman band intensity (I ₃₀₈₅ ) around ₃₀₈₅ cm ⁻¹ ± 5 cm ⁻¹ by laser Raman spectroscopy reflects the arrangement of C—H bonds of the benzene rings in the resin layer. It is considered that the aromatic ring surface such as is parallel to the film surface direction, there are many crystal parts, and the crystals are oriented parallel to the film surface direction.

Based on the above, the strength ratio (I ₂₉₈₆ / I ₃₀₈₅ ) is considered to be an index indicating the crystalline orientation state of the polyester resin layer, that is, the affinity between the resin layer and the hydrophobic polymer. It was. As a result, it is clear that there is a correlation between the strength ratio (I ₂₉₆₈ / I ₃₀₈₅ ) of the two and the content take-out property, and further, when the strength ratio between the two after the retort treatment is defined within an appropriate range, the retort treatment is performed. The present inventors also found that excellent contents can be taken out even in food canned foods. The present invention is based on this finding.

Next, the reasons for limitation of the present invention will be described based on the above technical idea.
The present invention is a metal plate coated with a resin on both sides, and the resin film that becomes the inner surface of the container after molding the container is a resin layer containing polyester as a main component in order to obtain excellent content takeout properties. 0.1-30 mass% of hydrophobic polymer is contained. Further, the resin layer surface after being molded into a container and subjected to retorting treatment has a Raman band intensity ratio I ₂₉₆₈ / I ₃₀₈₅ of 0.10 or more and 1.0 or less. Note _{that, I 2968} is the Raman band intensity near 2968cm ^-1 ± ^{5cm -1} from C-H stretching of glycol component of the polyester resin by the laser Raman _{spectroscopy, I 3085} is a polyester resin by laser Raman 3085cm from the benzene ring C-H stretching ^-1 Raman band intensity near ± ^{5 cm -1.}

As described above, there is a correlation between the Raman band intensity ratio (I ₂₈₅₀ / I ₃₀₉₀ ) and the content take-out property. Therefore, in the present invention, it is important to define the intensity ratio between the two after retorting in an appropriate range. is there. From this point, first, the intensity ratio (I ₂₉₆₈ / I ₃₀₈₅ ) is set to 0.10 or more and 1.0 or less. If it is less than 0.10, the crystal orientation on the film surface becomes high, and film breakage and film cracking during can making occur, so that workability is reduced, and film cracking due to retort treatment occurs. On the other hand, if it exceeds 1.0, the crystal orientation on the film surface becomes small and the amorphous part increases. Therefore, the surface roughness of the film surface increases, and when retort treatment is performed, crystallization proceeds, the affinity between the polyester resin layer and the hydrophobic polymer decreases, and the contents can be easily removed. To do.

Further, the Raman band intensity ratio (I ₂₉₆₈ / I ₃₀₈₅ ) in the longitudinal direction (MD) of the resin-coated metal plate for containers is 0.2 or more and 0.6 or less, and the width direction of the resin-coated metal plate for containers The Raman band intensity ratio (I ₂₉₆₈ / I ₃₀₈₅ ) in (TD) is preferably 0.10 or more and 0.5 or less. Thus, by making the Raman band intensity (I ₂₉₆₈ / I ₃₀₈₅ ) in the longitudinal direction (MD) and the Raman band intensity ratio (I ₂₉₆₈ / I ₃₀₈₅ ) in the width direction (TD) within the optimum range, workability is improved. The affinity with the contents is effectively reduced, and the contents can be taken out more effectively.
The Raman band intensity ratio (I ₂₉₆₈ / I ₃₀₈₅ ) can be controlled by controlling the addition amount of the resin raw material catalyst, the intrinsic viscosity, the addition amount of the crystallization nucleating agent, the stretching conditions, or adjusting the lamination conditions. it can. For example, the Raman band intensity ratio can be reduced by increasing the amount of catalyst of the resin raw material, decreasing the intrinsic viscosity, increasing the amount of crystallization nucleating agent added, or adjusting the stretching conditions (such as increasing the stretching ratio). . Also, control of lamination conditions (such as lowering the metal plate temperature at the start of lamination, lowering the laminate roll temperature, lowering the laminate roll nip pressure, shortening the laminate roll nip time, shortening the time until cooling after lamination, etc.) Thus, the Raman band intensity ratio can be reduced. In addition, how to obtain | require the Raman band intensity ratio by confocal laser Raman spectroscopy is mentioned later in an Example.

  Next, the resin film which becomes a container inner surface side is demonstrated. The resin film contains polyester as a main component. And 0.1-30 mass% of hydrophobic polymer is contained with respect to the resin layer. The resin film may be a single layer or multiple layers. Moreover, polyester as a main component means that 70 mass% or more of polyester resin is contained with respect to the whole resin.

  Further, from the viewpoint of the required performance of content takeout properties, heat resistance and taste characteristics, it is preferable that 80 mol% or more of the structural unit of the polyester is the ethylene terephthalate unit in the polyester resin-based resin layer. As a result, particularly high contents can be taken out, heat resistance and taste characteristics can be obtained. When the ethylene terephthalate unit is less than 80 mol%, the crystallinity of the film is remarkably lowered, and the above characteristics may be deteriorated.

However, the polyester resin is not limited to the above, and may be one obtained by copolymerizing other dicarboxylic acid components and glycol components within a range not impairing heat resistance and taste characteristics. For example, dicarboxylic acid components include isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic acid and other aromatic dicarboxylic acids; oxalic acid, succinic acid Examples thereof include aliphatic dicarboxylic acids such as acid, adipic acid, sebacic acid, dimer acid, maleic acid and fumaric acid; alicyclic carboxylic acids such as cyclohexanedicarboxylic acid; oxycarboxylic acids such as p-oxybenzoic acid, and the like. These 1 type (s) or 2 or more types can be used.
Examples of the glycol component include aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol, and neopentyl glycol; alicyclic glycols such as cyclohexanedimethanol; aromatic glycols such as bisphenol A and bisphenol S. , Diethylene glycol and the like, and one or more of these can be used.
Furthermore, a polyfunctional compound such as trimellitic acid, trimesic acid, and trimethylolpropane may be copolymerized as long as the effects of the present invention are not impaired.
In the present invention, two or more of the above polymers can be blended and used. If necessary, an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a crystal nucleating agent, and the like can be blended.

  By containing the hydrophobic polymer in the resin film on the inner surface side of the container, (i) the surface free energy of the film is reduced, and (ii) lubricity is imparted to the film surface. Then, the content (i) makes it difficult for the contents to adhere to the film, and the effect (ii) reduces the coefficient of friction of the film surface, and can dramatically improve the take-out properties of the contents.

  When the content is less than 0.1 mass%, the effects (i) and (ii) described above become poor, and the contents can be taken out poorly. On the other hand, if it exceeds 30 mass%, the content takeout property is almost saturated due to the compatibility between the hydrophobic polymer and the polyester resin of the mother layer, and the effect due to the increase in the addition amount of the hydrophobic polymer is not seen. In the film production, productivity is lowered and disadvantageous in cost.

  Organic and inorganic lubricants can be used as the hydrophobic polymer component applied in the present invention. Polyolefin resins, paraffin waxes, montanic acid wax, montanic acid ester wax, silicone resins, fatty acids such as stearic acid, fatty acid amides such as stearic acid amide, esylamide, ethylenebisstearic acid amide, n-butyl stearate Organic lubricants such as fatty acid esters such as glycerin fatty acid esters, fatty alcohols and fluororesins are desirable, and in particular, polyethylene, polypropylene, polybutene, polypentene obtained by polymerizing one or more α-olefins. , Polymethylpentene, ethylene-propylene copolymer, ethylene-butene copolymer, stearic acid, hydroxystearic acid, stearic acid amide, ethylenebisstearic acid amide, oleic acid amide, tetrafluoroethylene resin But more desirable. These hydrophobic polymers can be used alone or in admixture of two or more. The polyolefin resin may be copolymerized with acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, maleic anhydride, or the like, as long as the olefin component is a main component.

  Moreover, as a resin film used as a container inner surface side, it does not ask | require whether it is a single layer and a multilayer as above-mentioned. In the case of a multi-layer structure, 0.1 to 30 mass% of a hydrophobic polymer may be added to each layer, but the film layer in contact with the contents is hydrophobic for the purpose of containing the hydrophobic polymer. It is necessary for the polymer to be contained. From this point, in consideration of economy and the like, it is preferable that 0.1 to 30 mass% of the hydrophobic polymer is contained only in the uppermost layer of the film. In addition, in this case, the application includes a hydrophobic polymer.

  Moreover, as for the resin film which becomes a container inner surface side after container shaping | molding, it is desirable that the area | region whose birefringence is 0.02 or less shall be less than 5 micrometers in a film thickness direction from a contact interface with a metal plate. The resin-coated metal plate is usually produced as follows. First, a film is brought into contact with a heated metal plate and pressed to melt the film resin at the metal plate interface. And a metal plate and a film are adhere | attached by wetting film resin to a metal plate. Therefore, in order to ensure the adhesion between the film and the metal plate, it is necessary that the film is melted, and the film birefringence of the portion in contact with the metal plate after the resin coating inevitably decreases. Become. Here, as specified in the present invention, if the film birefringence of the portion in contact with the metal plate after resin coating is 0.02 or less, it indicates that the film melt wetting at the time of resin coating is sufficient, It becomes possible to ensure excellent adhesion. The birefringence can be measured by a known method.

  Further, the resin film used in the present invention preferably has an intrinsic viscosity of 0.50 dl / g or more, more preferably 0.60 dl / g or more, particularly preferably from the viewpoint of improving mechanical properties, laminating properties and taste properties. It is 0.63 dl / g or more. When the intrinsic viscosity is less than 0.50 dl / g, taste characteristics may be deteriorated due to elution of oligomers.

  The resin film containing the hydrophobic polymer of the present invention may be prepared by applying a predetermined amount of the hydrophobic polymer to the polyester resin by a roll coat or the like, or by directly mixing in advance with a blender, a mixer or the like. Melting and kneading can be performed using a single-screw or twin-screw extruder, and the film can be manufactured by a normal film forming method.

  It does not specifically limit about the resin film which becomes a container outer surface side after container shaping | molding. For example, a resin layer mainly composed of a polyester resin can be used.

  The thickness of the resin film to be coated on both surfaces of the metal plate is 3 to 50 μm on both the inner surface side and the outer surface side in terms of formability after coating on the metal plate, metal coating property, impact resistance, and taste characteristics. It is preferable that the thickness is 8 to 30 μm.

Next, a method for coating the resin film on both surfaces of the metal plate will be described.
In the present invention, for example, a method is used in which a metal plate is heated to a temperature exceeding the melting point of the resin film, and the resin film is brought into contact with both surfaces using a pressure-bonding roll (hereinafter referred to as a laminate roll) and thermally fused. Can do.

The resin coating conditions are not particularly limited as long as the resin film structure specified in the present invention can be obtained. For example, the temperature at the start of resin coating is preferably 10 ° C. or more higher than the melting point temperature of the resin film, and the nip time (nip length / laminating speed) is preferably in the range of 5 to 50 msec. Furthermore, as the temperature history received by the resin film during resin coating, it is preferable that the time of contact at a temperature equal to or higher than the melting point of the resin film be in the range of 1 to 20 msec. In order to achieve such resin coating conditions, cooling during bonding is required in addition to high-speed resin coating. The pressure applied at the time of resin coating is not particularly specified, but the surface pressure is preferably 9.8 to 294 N / cm ² (1 to 30 kgf / cm ² ). If this value is too low, it is difficult to obtain sufficient adhesion because the time is short even if it is above the melting point. Also, if the pressure is large, there is no problem in the performance of the resin-coated metal plate, but it is uneconomical because the force applied to the laminate roll is large and the equipment strength is required, resulting in an increase in the size of the apparatus.

As the metal plate, an aluminum plate or a steel plate that is widely used as a material for cans can be used, and in particular, a surface-treated steel plate (two-layered film in which the lower layer is made of chromium metal and the upper layer is made of chromium hydroxide) For example, TFS) is optimal. The amount of adhesion of the metal chromium layer and the chromium hydroxide layer of TFS is not particularly limited, but from the viewpoint of adhesion and corrosion resistance after processing, both are in terms of Cr, and the metal chromium layer is 70 to 200 mg / m ² , chromium. hydroxide layer is preferably in the range of 10 to 30 mg / ^{m 2.}

A steel plate (thickness 0.18 mm, width 977 mm) subjected to cold rolling, annealing, and temper rolling was subjected to degreasing and pickling treatment, and then chrome plating treatment to produce a chrome plated steel plate (TFS). . Incidentally, the chromium plating _treatment, CrO ^3, F -, chromium plated with chromium plating bath containing _SO ^{4 2-,} after intermediate rinsing, _CrO 3, F ^-, electrolysis was chemical conversion treatment solution containing. At this time, electrolysis conditions adjusted to metallic chromium adhering amount and chromium hydroxide deposition amount (current density, the quantity of electricity, etc.), respectively Cr terms was adjusted to ^{120mg / m 2, 15mg / m} 2.

  Next, the chrome-plated steel sheet obtained above is heated with a metal band laminator using a metal band laminator, and then laminated with a laminating roll on both surfaces of the chrome-plated steel sheet (heat fusion). Thus, a resin-coated metal plate (laminated steel plate) was produced. The laminating roll was an internal water-cooling type, and cooling water was forcibly circulated during laminating to perform cooling during film adhesion. Moreover, the adjustment of the Raman band intensity ratio by laser Raman was performed by changing the laminating conditions to the metal band. The contents of the laminated resin film and the lamination conditions are shown in Table 1.

  For the laminated steel sheet produced as described above, the Raman band strength ratio, the birefringence of the polyester film (layer thickness with a birefringence of 0.02 or less), and contents are obtained by the following methods (1) to (5). The take-out property, moldability, adhesion and impact resistance were measured and evaluated. The obtained results are shown in Table 2.

(1) Raman band intensity ratio (R)
Cut laminated steel sheet from the bottom of the retort processed can inner, longitudinal laminated steel sheet (MD), with the width direction (TD), the following measurement conditions, Raman band near 3085cm ^-1 ± ^{5cm -1} by laser Raman and 2968cm Each Raman spectrum of the Raman band in the vicinity of ⁻¹ ± 5 cm ⁻¹ was measured, and the Raman band intensity ratio (R) was determined by the following formula.
<Measurement conditions>
Excitation light source: Ar laser (λ = 514.5 nm), output 2 mW
Microscopic magnification: x100
Longitudinal direction (MD): Laser light is incident so that the laser polarization plane is parallel to the longitudinal direction of the laminated steel sheet.
Width direction (TD): Laser light is incident so that the laser polarization plane is perpendicular to the longitudinal direction of the laminated steel sheet.
R = I ₂₉₆₈ / I ₃₀₈₅
I _2968: 2968cm ^-1 ± ^{5cm -1} vicinity of the Raman band intensity _I 3085: _3085cm ^-1 Raman band intensity near ± ^{5 cm -1} (2) layers of birefringence (birefringence than 0.02 of the polyester film Thickness)
The retardation in the cross-sectional direction of the film after removing the metal plate of the laminated steel sheet using a polarizing microscope was measured to determine the birefringence in the cross-sectional direction of the film.
The measurement method will be briefly described. Monochromatic light is converted into linearly polarized light by a polarizing plate. When this light is incident on the film, retardation is generated, so that it becomes elliptically polarized light after passing through the film layer. This elliptically polarized light becomes linearly polarized light having an angle of θ with respect to the vibration direction of the first linearly polarized light by the Senarmont type compensator. This θ is measured by rotating the polarizing plate. The relationship between retardation R and θ is defined by equation (1).
R = λ · θ / 180 (1)
λ: wavelength of monochromatic light The retardation R is defined by the formula (2).
Δn = R / d (2)
Δn: Birefringence index, d: Film layer thickness Therefore, the birefringence index Δn can be obtained from the formulas (1) and (2) by the following formula.
Δn = (θ · λ / 180) / d (3)
(3) Content takeout ability Using a drawing machine, the laminated steel sheet was cup-formed in a drawing step with a blank diameter: 100 mm and a drawing ratio (diameter before forming / diameter after forming): 1.88. Subsequently, the cup was filled with salted meat for luncheon meat, the lid was wrapped, and then retort processing (130 ° C. × 90 minutes) was performed. Thereafter, the lid was removed, the contents were taken out by turning the cup upside down, and then the degree of ease of taking out the contents was evaluated by observing the degree of contents remaining inside the cup.
(About the score)
○: The contents can be taken out only by turning the cup upside down (without shaking by hand), and when the inner surface of the cup after taking out is observed with the naked eye, the deposits are hardly confirmed.
Δ: The contents remain inside the cup only by turning the cup upside down, but the contents can be taken out by vibrating the cup up and down (such as shaking the cup by hand). When the inside of the cup after removal is observed with the naked eye, it is in a state where almost no deposits can be confirmed.
X: It is difficult to take out the contents only by vibrating the cup up and down (such as shaking the cup by hand). When the speed of vibrating up and down is extremely increased, or when the contents are forcibly removed using a spoon or other instrument and the inside of the cup is observed with the naked eye, the deposit can be clearly confirmed.

(4) Formability After applying wax to the coated metal plate, a disk having a diameter of 179 mm was punched out to obtain a shallow drawn can with a drawing ratio of 1.80. Next, the drawn can was redrawn at a drawing ratio of 2.20. Thereafter, in accordance with a conventional method, doming forming was performed, then trimming was performed, and then neck-in-flange processing was performed to form a deep drawn can. Focusing on the neck-in portion of the deep-drawn can thus obtained, the degree of film damage was visually observed.
(About the score)
○: No damage is observed in the film after molding Δ: Molding is possible, but film damage is partially recognized ×: Can is broken and cannot be molded (5) Adhesiveness In the above (4) A sample for peel test (width 15 mm × length 120 mm) was cut out from the can body portion of the can that was moldable. Part of the film is peeled off from the long side end of the cut sample, and the part of the film peeled off by the tensile tester is opened in the opposite direction (angle: 180 °) from the chrome-plated steel sheet from which the film has been peeled. A peel test was performed at a speed of 30 mm / min to evaluate the adhesion per 15 mm width. In addition, the contact | adhesion power measurement object surface was made into the can inner surface side.
(About the score)
A: 1.47 N / 15 mm or more (0.15 kgf / 15 mm or more).
A: 0.98 N / 15 mm or more and less than 1.47 N / 15 mm (0.10 kgf / 15 mm or more, less than 0.15 kgf / 15 mm).
X: Less than 0.98 N / 15 mm (less than 0.10 kgf / 15 mm).

(6) Impact resistance The can that was moldable in the above (4) was filled with water, and 10 pieces were dropped from a height of 1.25 m onto the PVC tile floor for each test, A voltage of 6 V was applied to the metal can, the current value after 3 seconds was read, and the average value after 10 cans was measured.
(About the score)
A: Less than 0.01 mA.
A: 0.01 mA or more and less than 0.1 mA.
X: 0.1 mA or more.

  From Tables 1 and 2, all of the invention examples within the scope of the present invention were excellent in quality stability and exhibited good characteristics. On the other hand, in the comparative example that is out of the scope of the present invention, any one or more of the contents take-out property, moldability, adhesion, and impact resistance is poor.

  The resin-coated metal plate for containers according to the present invention has excellent content take-out properties even after retorting, and has excellent adhesion, heat resistance, molding processability, and impact resistance with the metal plate. In addition to being optimal as a container material to be used, particularly as a food can container material, it can be used for applications that require the above characteristics.

Claims (5)

A metal plate for a container covering a resin film on both sides,
The resin film that becomes the inner surface of the container is a resin layer containing polyester as a main component, and contains 0.1 to 30 mass% of a hydrophobic polymer with respect to the resin layer,
Furthermore, the resin-coated metal sheet for containers, wherein the resin layer surface after being molded into a container and having a retort treatment has a Raman band intensity ratio I ₂₉₆₈ / I ₃₀₈₅ of 0.10 or more and 1.0 or less.
_{However, I 2968} is the Raman band intensity near 2968cm ^-1 ± ^{5cm -1} from C-H stretching of glycol component of the polyester resin by the laser Raman _{spectroscopy, I 3085} is a benzene ring of the polyester resin by laser Raman C This is the Raman band intensity around 3085 cm ⁻¹ ± 5 cm ⁻¹ derived from −H stretching. Further, the Raman band strength ratio I ₂₉₆₈ / I ₃₀₈₅ in the longitudinal direction of the resin-coated metal plate for containers is 0.2 or more and 0.6 or less, and the Raman band strength in the width direction of the resin-coated metal plate for containers. The resin-coated metal sheet for containers according to claim 1, wherein the ratio I ₂₉₆₈ / I ₃₀₈₅ is 0.10 or more and 0.5 or less.   3. The resin-coated metal sheet for containers according to claim 1, wherein in the resin layer containing polyester as a main component, 80 mol% or more of the structural units of the polyester are ethylene terephthalate units.   The said resin layer which has polyester as a main component is comprised from 2 or more layers, and contains 0.1-30 mass% of said hydrophobic polymer only in the layer which contact | connects the content. 4. The resin-coated metal plate for containers according to any one of 3 above.   The region where the birefringence in the resin film on the inner surface side of the container is 0.02 or less is less than 5 µm in the resin film thickness direction from the contact interface with the metal plate. A resin-coated metal plate for containers according to claim 1.