JP2010105263A - Resin-coated metal sheet for container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin-coated metal sheet having fundamental properties required in materials of canned food and excellent designability of the surface of a can. <P>SOLUTION: The resin-coated metal sheet for container comprises polyester resin layers consisting mainly of polyethylene terephthalate on its two surfaces. By specifying a crystal structure of the polyester resin layer, the desired functionals can be obtained. For this purpose, a half-value width of a peak caused by C=0 stretching vibration around 1,730 cm<SP>-1</SP>obtained from a laser Raman spectroscopy method using direct polarized laser beam is set forth within a range of 16.0-24.0 cm<SP>-1</SP>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a resin-coated metal plate for containers used in, for example, can bodies and lids for canned foods.

Conventionally, tin-free steel (TFS), which is a material for canned food, and metal plates such as aluminum have been coated for the purpose of improving corrosion resistance, durability and weather resistance. However, this coating process has a problem that not only the baking process is complicated, but also a long processing time is required and a large amount of solvent is discharged.
Therefore, in order to solve these problems, instead of the coated steel sheet, a film laminated metal sheet was developed by laminating a thermoplastic resin film on a heated metal sheet, and is currently used industrially as a food canning material. Yes.

  In addition to basic characteristics such as processability and adhesiveness, food canning materials are also required to have design-related characteristics such as appearance color stability. When a metal plate coated with a conventional polyester resin is used so that the resin-coated surface is on the outer surface of food cans, the resin layer itself turns white and cloudy during retort sterilization (whitening phenomenon) ) Occurs. Since whitening greatly deteriorates the design of the outer surface of the can and lowers the consumer's willingness to purchase, several improvement techniques have been studied.

  For example, Patent Document 1 discloses a technique for controlling the crystal orientation of a resin layer not in contact with the crystallinity of a resin layer in contact with the metal plate when a polyester resin is laminated on the metal plate. The technique of Patent Document 1 is a technique obtained by estimating the whitening phenomenon as follows. That is, the rate at which the amorphous resin layer on the side in contact with the metal plate is crystallized by retort treatment differs between the dew condensation part and the non-condensation part on the surface of the metal plate. It is estimated that light scattering occurs and the surface appears whitened.

  Also, in Patent Document 2, since the crystallization rate of the polymer is slow during retort processing, the crystal grows slowly and becomes large, and this is considered to cause a whitening phenomenon, and the crystallization rate of the polymer during retort processing is increased. Has proposed to produce a large number of microcrystals.

However, in both Patent Documents 1 and 2, since the mechanism of the whitening phenomenon is not accurately grasped, the design is not sufficiently maintained, and cannot be said to be an appropriate improvement technique.
JP-A-6-155660 Japanese Patent Laid-Open No. 5-331302

  In view of such circumstances, the present invention is capable of dealing with many characteristics required for food canning materials, does not cause whitening even after retort treatment, and can maintain a design property on the outer surface of the can. The object is to provide a metal plate.

As a result of intensive studies by the present inventors for solving the problems, the following knowledge was obtained.
In a resin-coated metal plate that has a polyester resin layer composed mainly of polyethylene terephthalate on both sides, the crystal structure of the polyester resin layer is controlled within the range specified by laser Raman spectroscopy, deep drawing formability and processing It has been found that a resin-coated metal sheet for containers having many excellent functions such as performance relating to design properties in a retort processing environment in addition to basic properties such as post-adhesion can be obtained.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A resin-coated metal plate having a polyester resin layer mainly composed of polyethylene terephthalate on both sides, and a laser Raman spectroscopic analysis method using linearly polarized laser light in a cross section in the thickness direction of the polyester resin layer A resin-coated metal sheet for containers, wherein the half width of the peak due to C = 0 stretching vibration in the vicinity of 1730 cm ⁻¹ obtained from the above is in the range of 16.0 cm ^{−1 to} 24.0 cm ⁻¹ .
[2] A cross-section in the thickness direction of the polyester resin layer of the resin-coated metal sheet for containers subjected to a heat treatment for 5 seconds or more in a temperature range from the crystallization temperature of the polyester resin layer to the melting point or less in [1] The half width of the peak due to C = 0 stretching vibration near 1730 cm ^-1 obtained from laser Raman spectroscopy using linearly polarized laser light in the range of 16.0 cm ^{-1 to} 24.0 cm ^-1 A resin-coated metal plate for containers, characterized in that it exists.

  ADVANTAGE OF THE INVENTION According to this invention, in addition to the basic performance requested | required of a food canned raw material, the resin-coated metal plate for containers excellent in the design property of a can outer surface is obtained.

Hereinafter, the resin-coated metal plate for containers of the present invention will be described in detail.
First, the metal plate used by this invention is demonstrated.
As the metal plate of the present invention, an aluminum plate or a mild steel plate widely used as a can material can be used. In particular, a surface-treated steel sheet (hereinafter referred to as TFS) on which a two-layer film is formed, in which the lower layer is made of metallic chromium and the upper layer is made of chromium hydroxide, is optimal.
The amount of adhesion of the metal chromium layer and chromium hydroxide layer of TFS is not particularly limited, but from the viewpoint of adhesion after processing and corrosion resistance, both are in terms of Cr, 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.}

Next, a polyester resin layer mainly composed of polyethylene terephthalate on both surfaces of the metal plate will be described.
The polyester resin layer of the present invention contains polyethylene terephthalate as a main component. The term "polyethylene terephthalate" as a main component means a polyester in which 80 mol% or more of the structural units of the polyester are ethylene terephthalate units. More preferably, it is 85 mol% or more.
Although terephthalic acid as an acid component is essential from the viewpoint of mechanical strength, heat resistance, chemical resistance, and the like, further, flexibility, tear strength, and the like are improved by copolymerization with isophthalic acid. By copolymerizing the isophthalic acid component with respect to the terephthalic acid component in an amount of 10 to 15 mol%, it is preferable because deep drawability and post-processing adhesion are improved.
On the other hand, other dicarboxylic acid components and glycol components may be copolymerized as long as the above characteristics are not impaired. Examples of the dicarboxylic acid component include aromatic compounds such as diphenylcarboxylic acid, 5-sodium sulfoisophthalic acid, and phthalic acid. Dicarboxylic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, aliphatic dicarboxylic acid such as fumaric acid, aliphatic dicarboxylic acid such as cyclohexanedicarboxylic acid, oxycarboxylic acid such as p-oxybenzoic acid Etc. Examples of other glycol components include aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol, and neopentylglycol, finger ring glycols such as cyclohexanedimethanol, and aromatics such as bisphenol A and bisphenol S. Examples include glycol, diethylene glycol, and polyethylene glycol. These dicarboxylic acid components and glycol components may be used in combination of two or more. Moreover, as long as the effect of this invention is not inhibited, you may copolymerize polyfunctional compounds, such as trimellitic acid, trimesic acid, a trimethylol propane.

Furthermore, the polyester resin layer mainly composed of polyethylene terephthalate of the present invention is caused by C = O stretching vibration in the vicinity of 1730 cm ^{-1, which is} obtained from laser Raman spectroscopy using linearly polarized laser light, in the cross section in the thickness direction. The full width at half maximum of the peak is in the range of 16.0 cm ^{−1 to} 24.0 cm ⁻¹ . This is the most important requirement in the present invention. By defining the crystal structure of the polyester resin layer in this way, the designability after the retort sterilization treatment which is the object of the present invention can be ensured. The reason will be described below.
A.J.Melveger reported that the half-value width of the peak based on the C = O stretching vibration in the vicinity of 1730 cm ^-1 as determined by laser Raman spectroscopy is inversely proportional to the density of the polyester. (J. Polymer Sience 10,317,1972). It is known that there is a relationship of the following formula (1) between the resin density and the volume fraction crystallinity (polymer solid structure II (Kyoritsu Shuppan, 1984), 305).
Volume fraction crystallinity (%) = (ρ-ρa) / (ρc-ρa) × 100 (1)
However, ρ is a measured value of density, and ρc and ρa are the density of a complete crystal and a complete amorphous, respectively.
Therefore, by measuring the half width of the peak due to the C = O stretching vibration near the Raman shift of 1730 cm ^-1 , the density of the polyester irradiated with the laser beam can be obtained, and the above formula (1 ), The volume fraction crystallinity of the polyester (hereinafter referred to as crystallinity) can be determined.
Based on the above knowledge, the present inventors diligently investigated the relationship between the crystallinity and the retort whitening phenomenon.
First, in the examination, the measurement method of Raman spectroscopy used in the present invention will be described with reference to FIG. According to FIG. 1, the laser light 4 oscillated from the laser oscillator 3 is incident on the resin layer 2 laminated on the metal plate 1, and the scattered Raman scattered light 5 is dispersed by the spectroscope 6.
The beam diameter of the laser light irradiated by Raman spectroscopy can be changed by the lens 7, and the crystallinity of a necessary size region can be evaluated. Then, by narrowing the beam diameter of the irradiated laser light, it becomes possible to evaluate the degree of crystallinity in a minute region of the polyester resin layer.
The crystallinity at an arbitrary site in the cross section in the thickness direction of the polyester resin layer was evaluated by the Raman spectroscopy measurement method shown in FIG. The details of the measurement method are the same as in the examples described later.
Result, in the thickness direction of the cross section of the polyester resin layer, Raman shift With 16cm ^-1 ~24cm ^-1 the half width of peaks due to C = O stretching vibration of 1730 cm ^-1 vicinity retort whitening It was found that a resin-coated metal plate that can secure excellent design properties by suppressing the above and satisfy the characteristics required for food canning materials such as formability can be obtained. The reason is considered as follows.

When a food can made of a polyester resin-coated metal plate is subjected to a retort sterilization treatment, the outer resin layer is whitened. This is because fine bubbles are formed in the resin layer and light is scattered by the bubbles, resulting in a white turbid appearance. In addition, the bubbles formed in the resin layer have the following characteristics.
First, these bubbles are not formed even when the can is heated in a dry heat environment. Moreover, even if the retort sterilization process is performed without filling the contents into the can, no bubbles are formed. Bubbles are not observed over the entire thickness direction of the outer resin layer, but are observed near the interface in contact with the steel plate. From the above characteristics, it is considered that the formation of bubbles in the outer resin layer accompanying the retort sterilization treatment is caused by the following mechanism.

  From the beginning of the retort sterilization treatment, the can is exposed to high-temperature steam, and part of the steam penetrates into the inside of the outer resin layer and reaches the vicinity of the interface with the steel plate. At this time, since the vicinity of the interface between the outer resin layer and the steel plate is cooled from the inner surface by the contents, the water vapor that has entered the interface becomes condensed water. Next, as the retort sterilization time elapses, the temperature of the contents also rises, and the condensed water at the interface with the steel plate re-vaporizes. The vaporized water vapor escapes again through the resin layer, but it is presumed that the trace of condensed water at this time becomes bubbles.

  The reason why the bubbles are observed only near the interface with the steel sheet is that the place where the condensed water is formed is near the interface, and the resin near the interface has a soft amorphous structure, so it easily deforms. This is probably because bubbles are easily formed. The reason why the resin in the vicinity of the interface has an amorphous structure is that the resin melts at the time of heat fusion with the metal plate, and the crystal structure disappears.

  Therefore, in order to suppress retort whitening, 1) to improve the strength of the amorphous resin in the vicinity of the interface to suppress the formation of bubbles, 2) to suppress the penetration of water vapor into the resin layer, It is effective not to reach the vicinity. Therefore, as a result of intensive studies by the inventors, the most effective method for simultaneously achieving the above 1) and 2) was to increase the crystallinity of the resin layer.

  By crystallizing the amorphous resin layer in the vicinity of the interface, the mechanical strength (tensile strength, elastic modulus, etc.) of the resin is increased, and the formation of bubbles can be effectively prevented. Further, if the crystallinity of the entire resin layer increases, the amorphous region that is a water vapor permeation path decreases. In order for water vapor to penetrate inside the resin, it is necessary to bypass the crystal region, and the reach distance and reach time to the vicinity of the interface are greatly increased, and the formation of bubbles can be greatly reduced. .

Based on the above considerations, first, in the present invention, the half-value width of the Raman band based on the C = O stretching vibration near 1730 cm ^-1 in the cross section in the thickness direction of the resin layer as an index indicating the crystallinity. It was decided to use. Furthermore, in the present invention, in order to increase the crystallinity of the polyester resin layer and suppress retort whitening, the half width is defined as 24.0 cm ⁻¹ or less.
In addition, when obtaining the upper limit value (= lower limit value of crystallinity) defined in the present invention, the polarization plane of the laser beam (linearly polarized light) is the thickness of the resin layer as shown by 9 in FIG. It is preferable to measure by entering the resin layer cross section parallel to the direction.
When the polyester resin layer is a biaxially stretched film, most of the oriented crystals generated during the film stretching remain in the orientation perpendicular to the thickness direction of the resin layer. Therefore, the degree of crystallinity is higher than other orientations. Therefore, an orientation perpendicular to the thickness direction of the resin layer is inappropriate as an orientation for obtaining the lower limit value of the crystallinity (= the upper limit value of the half width). On the other hand, when the measurement is performed with the polarization plane parallel to the thickness direction, since the orientation is not affected by the film stretching, the existence density of oriented crystals is the lowest, and the lower limit of the crystallinity of the resin layer (= This is an appropriate orientation for obtaining the upper limit value of the half width.
As described above, by setting the half width to the above range and ensuring a certain degree of crystallinity in the resin, formation of bubbles that cause retort whitening can be reliably suppressed.
On the other hand, as the half width decreases, the retort whitening property becomes better, but the properties such as moldability and impact resistance tend to deteriorate. This is because as the half width decreases, the amorphous region rich in flexibility decreases and the rigid crystal region increases. Therefore, in consideration of these, in order to ensure the moldability and impact resistance required for food cans, the half band width of the Raman band based on C = O stretching vibration in the vicinity of 1730 cm ^-1 is set to 16.0 cm ^-1 It is necessary to stipulate above.
In the case of obtaining the lower limit value of the half width defined in the present invention (= upper limit value of crystallinity), linearly polarized laser light is used with the polarization plane perpendicular to the thickness direction of the resin layer, It is preferable to enter and measure the cross section of the resin layer. When the resin layer is a biaxially stretched film, when the laser beam polarization plane is measured perpendicular to the thickness direction of the resin layer, as described above, most of the oriented crystals generated during film stretching remain and crystallize. Since the degree becomes high, it is suitable as a measuring method for defining the upper limit value (= the lower limit value of the half width) of the crystallinity of the resin layer.

From the above, in order to obtain a polyester resin-coated metal sheet that can be used for food canning while improving retort whitening, the half value of the peak (Raman band) due to C = 0 stretching vibration in the vicinity of 1730 cm ^-1 The width is in the range of 16.0 cm ^{−1 to} 24.0 cm ⁻¹ .

As a method for controlling the crystallinity of the polyester resin layer within the range specified in the present invention, (1) a method for controlling the heat history at the time of heat fusion, and (2) heat at the time of post heating after heat fusion. There is a way to control the history.
In the case of the method (1), in order to ensure the adhesion between the resin layer and the metal plate, the resin layer in the vicinity of the interface is sufficiently melted at the time of heat-sealing and fluidized on the surface of the metal plate. It is necessary to increase the contact area with the plate. As a result, the resin layer and the metal plate are firmly adhered to each other by intermolecular force, hydrogen bonding, and anchoring action. Here, the resin layer in the vicinity of the interface with the metal plate is melted at the time of heat fusion, so that the crystal structure is largely broken, and it is highly possible that the resin layer remains as an amorphous region even after heat fusion. However, in order to obtain a crystal structure having a half-value width of 24.0 cm ⁻¹ or less as defined in the present invention, it is important to suppress melting and flow of the resin layer during heat fusion. On the other hand, when the flow on the surface of the metal plate is reduced, the adhesion may be deteriorated. Therefore, in order to ensure the retort whitening resistance while firmly securing the adhesion to the metal plate, it is necessary to strictly control the temperature history at the time of thermal fusion to balance both characteristics. This is not necessarily the best method for controlling the crystallinity of the layer within the range specified in the present invention.

  On the other hand, according to the method defined in the present invention, (2) the method of performing heat treatment again on the resin-coated metal plate after heat fusion, it is possible to suppress retort whitening without causing deterioration in adhesion. It is. That is, at the time of heat sealing, in order to ensure adhesion with the metal plate, the resin layer in the vicinity of the interface is sufficiently melted and then rapidly cooled to fix the structure of the polyester resin layer and ensure adhesion. . Thereafter, the resin layer in the vicinity of the interface is crystallized by performing heat treatment in an appropriate temperature range, and the crystallinity of the entire resin layer is increased to obtain a resin structure having excellent retort whitening resistance.

The heat treatment temperature and heat treatment time can be arbitrarily selected as long as the half-value width range specified in the present invention can be achieved, but it is carried out for 5 seconds or more in the temperature range from the crystallization temperature of the polyester resin layer to the melting point or less. It is desirable to do. Thereby, the crystal structure prescribed | regulated by this invention can be achieved easily.
When the heat treatment temperature is lower than the crystallization temperature of the polyester resin layer, crystallization does not proceed. Therefore, the degree of crystallinity in the direction parallel to the thickness direction, which is not affected by film stretching, cannot exceed the lower limit defined in the present invention. On the other hand, when the temperature exceeds the melting point of the polyester resin layer, the crystal structure is instantaneously destroyed and changed to an amorphous structure, so that it falls below the lower limit of the crystallinity specified in the present invention. Even if the heat treatment time is less than 5 seconds, the crystallinity specified in the present invention cannot be secured for the same reason, which is not suitable.
In addition, when the heat treatment temperature is set to a temperature range between the crystallization temperature of the polyester resin layer and the melting point or less, the crystallization degree of the resin layer increases with an increase in the heat treatment time. Therefore, the heat treatment time needs to be set in a range in which the crystallinity of the resin layer does not exceed the upper limit defined in the present invention.

  The polyethylene resin layer mainly composed of polyethylene terephthalate is preferably a biaxially stretched PET film from the viewpoint of heat resistance and taste characteristics. The biaxial stretching method may be simultaneous biaxial stretching or sequential biaxial stretching, but the stretching conditions and heat treatment conditions are specified, and the refractive index in the thickness direction of the film is 1.50 or more. Is preferable from the viewpoint of improving laminating properties and moldability. Furthermore, when the refractive index in the thickness direction is 1.51 or more, particularly 1.52 or more, the plane orientation coefficient is controlled within a specific range in order to achieve both formability and impact resistance even if there is some variation during lamination. This is more preferable because it can be performed.

  In addition, the biaxially stretched PET film is obtained by solid high-resolution NMR in terms of workability and impact resistance when processing the neck portion after receiving a thermal history of about 200 to 230 ° C. after drawing in the can making process. The relaxation time of the carbonyl moiety in the structural analysis is preferably 270 msec or more. More preferably, it is 280 msec or more, Most preferably, it is 300 msec or more. As long as the effects of the present invention are not hindered, other particles, for example, various amorphous externally added particles, internally precipitated particles, or various surface treatment agents may be used.

  The thickness of the polyester resin layer defined in the present invention is preferably 5 μm or more and 100 μm or less as a whole, more preferably 8 μm or more and 50 μm or less, and particularly preferably 10 μm or more and 25 μm or less.

Furthermore, colorants such as dyes and pigments can be added to the polyester resin layer of the present invention. By adding colorants such as dyes and pigments to the polyester resin layer, the underlying metal plate can be concealed and various colors unique to the resin can be imparted. For example, by adding carbon black as a black pigment, it is possible to conceal the metal color of the base and to impart a high-class feeling of black to food cans. The amount of carbon black added is desirably 5 PHR to 40 PHR. If it is less than 5 PHR, the blackness is insufficient, the color tone of the base metal cannot be concealed, and a high-quality design may not be imparted. On the other hand, even if it exceeds 40 PHR, the blackness does not change, so the effect of improving the design is not obtained, and the structure of the polyester resin becomes brittle, so that the resin layer may be easily broken during can manufacturing. is there. By making the addition amount in the range of 5 PHR to 40 PHR, it is possible to achieve both design properties and other required characteristics.
The particle size of the carbon black can be in the range of 5 to 50 nm, but the range of 5 to 30 nm is suitable in consideration of dispersibility and color developability in the polyester resin.
In addition to the black pigment, by adding a white pigment, the metallic luster of the base can be concealed, the printed surface can be sharpened, and a good appearance can be obtained. As a pigment to be added, it is necessary that an excellent design property can be exhibited after container molding. From such a viewpoint, inorganic pigments such as titanium dioxide can be used. Since the coloring power is strong and rich in spreadability, it is preferable because a good design property can be secured even after container molding. As for the addition amount of titanium dioxide, it is desirable that it is 5-30 mass% with respect to the object resin layer. If it is 5 mass% or more, sufficient whiteness will be obtained and favorable design property can be ensured. On the other hand, even if added over 30% by mass, the whiteness is saturated, so it is desirable to make it 30% by mass or less for economic reasons. More preferably, it is the range of 10-20 mass%. In addition, the addition amount of a coloring agent is a ratio with respect to the resin layer which added the coloring agent.
When a bright color is desired on the container surface, use of an azo pigment is also suitable. Although it is excellent in transparency, it has a strong coloring power and a high spreadability, so that a bright appearance can be obtained even after the container is molded. As an azo pigment that can be used in the present invention, the color index (name of CI registration) is at least one of pigment yellow 12, 13, 14, 16, 17, 55, 81, 83, 139, 180, 181. Can be mentioned. In particular, from the standpoints of vividness of color tone (bright color) and bleeding resistance in retort sterilization environment (inhibition ability against the phenomenon that pigments are deposited on the film surface), it has a large molecular weight and is soluble in polyester resin. A poor pigment is desirable. For example, CI Pigment Yellow 180 having a benzimidazolone structure having a molecular utilization of 700 or more is more preferably used.
The addition amount of the azo pigment is desirably 10 to 40 PHR with respect to the target resin layer. If the addition amount is 10 PHR or more, it is preferable because coloring is excellent. When the color is 40 PHR or less, the transparency becomes high and the color tone is rich.

Next, the manufacturing method of the polyester resin-coated metal plate for containers according to the present invention as described above will be described.
The polyester resin-coated metal plate for containers of the present invention is, for example, heated to a certain temperature or higher by a heating device (for example, metal band heating device 11 in FIG. 3), and a polyester film is crimped onto the surface 12 (hereinafter referred to as “lamilol”) and heat-sealing (hereinafter sometimes referred to as “laminate”). At this time, it is necessary that the coated surface is brought into contact with a metal plate using a press roll (hereinafter referred to as a laminate roll) and heat-sealed. Details of the lamination conditions will be described below.
The temperature of the metal plate at the start of heat fusion is desirably in the range of + 5 ° C. to + 30 ° C. based on the melting point of the polyester film. In order to ensure the interlayer adhesion between the metal plate and the polyester film by the heat fusion method, it is necessary to heat the polyester resin at the adhesion interface. By setting the temperature of the metal plate to a temperature range of + 5 ° C. or more based on the melting point of the polyester film, the resin in each layer is thermally fluidized, the wetting at the interface is mutually good, and excellent adhesion is achieved. Obtainable. The reason why the temperature is set to + 30 ° C. or lower is that even if the temperature exceeds + 30 ° C., further improvement in adhesion cannot be expected, the film is excessively melted, the surface is roughened by embossing on the surface of the roll, and the melt is transferred to the roll. This is because there is a concern that such a problem may occur.
It is desirable that the heat history received by the film at the time of lamination is not less than the melting point of the polyester film and not less than 5 msec. This is because wetting at the interface is good. Although the wettability improves with increasing time, when it exceeds 40 msec., Almost constant performance is exhibited and the effect is not recognized. Since there is a possibility of causing a decrease in productivity, it is desirable to set it to 40 msec or less. Therefore, the range of 5 to 40 msec is preferable.
In order to achieve such lamination conditions, in addition to high-speed operation of 150 mpm or more, cooling during heat sealing is also necessary. For example, the lami roll 12 in FIG. 3 is an internal water cooling type, and it can suppress that a film is heated too much by letting a cooling water pass. Furthermore, it is preferable because the thermal history of the polyester film can be controlled by changing the temperature of the cooling water.
The pressure of the lami roll 12 is preferably 9.8 to 294 N / cm ² (1 to 30 kgf / cm ² ) as the surface pressure. When the temperature is less than 9.8 N / cm ² , even if the temperature at the start of thermal fusion is not less than the melting point of the film + 5 ° C. and sufficient fluidity is ensured, the force to spread the resin on the metal surface is sufficient. Since it is weak, sufficient coverage cannot be obtained, and as a result, performance such as adhesion and corrosion resistance may be affected. On the other hand, if it exceeds 294 N / cm ^2, there is no inconvenience in the performance of the laminated metal plate, but it is uneconomical because the force applied to the lami roll is large and equipment strength is required, leading to an increase in the size of the apparatus. Therefore, the pressure of the lami roll is preferably 9.8 to 294 N / cm ² .

Examples of the present invention will be described below.

First, the polyester film which becomes a container inner surface side and a container outer surface side is manufactured. The polyester resin obtained by polymerizing the glycol component and the dicarboxylic acid component at the ratio shown in Table 1 was dried, melted and extruded, and cooled and solidified on a cooling drum to obtain an unstretched film. Subsequently, biaxial stretching and heat setting were performed to obtain a biaxially oriented polyester film.
About the polyester film obtained by the above, the crystallization temperature and melting | fusing point were measured with the following method. The measurement results are shown in Table 1 together with the resin components.
Crystallization temperature The crystallization temperature of the polyester resin layer in close contact with the surface of the metal plate was measured based on JIS K2454.
Melting | fusing point of polyester resin Melting | fusing point of the polyester resin layer closely_contact | adhered to the surface of a metal plate was measured based on JISK2454.

A chrome-plated steel plate was used as the metal plate. Cold rolling with a thickness of 0.18 mm and a width of 977 mm was annealed and tempered, degreased and pickled, and then chrome plated to produce a metal plate. Chromium plating was performed in a chromium plating bath containing CrO ₃ , F ⁻ , SO ₄ ²⁻ , and after chrome plating and intermediate rinsing, electrolysis was performed with a chemical conversion treatment solution containing CrO ₃ and F ⁻ . 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, using the metal strip laminating apparatus shown in FIG. 3, the chrome-plated steel sheet 10 obtained above is heated by the metal strip heating apparatus 11, and the container is formed on one surface of the chrome-plated steel sheet 10 with a lami roll 12 after the container is formed. As the polyester film that becomes the inner surface side, the film 13a prepared from Table 1 is laminated (heat fusion), and on the other surface, the film 13b prepared from Table 2 is laminated as the polyester film that becomes the outer surface side of the container after container molding. (Heat fusion). Thereafter, the metal band cooling device 14 was used for water cooling to produce a polyester resin-coated metal plate. FIG. 4 shows a cross-sectional structure of a polyester resin-coated metal plate.
The laminating roll 12 was an internal water-cooling type, and cooling water was forcibly circulated during laminating to perform cooling during film adhesion. Moreover, when laminating the resin film on the metal plate, the time during which the film temperature at the interface in contact with the metal plate was equal to or higher than the melting point of the film was set in the range of 1 to 20 msec.

Next, the polyester resin layer-coated metal plate obtained by the above method was subjected to heat treatment under the conditions shown in Table 2.
For the heat treatment, a batch-type drying furnace (made of SUS, heat source: 3.6 kW, 200 V, inner size: 600 × 600 × 600 mm) was used. Here, the heat treatment temperature is a set temperature of the drying furnace, and the heat treatment time is a time during which the resin-coated metal plate is held in the range of the set temperature of the drying furnace ± 2 ° C.
In addition, for the resin-coated metal plate after heat treatment, C = 0 stretching vibration in the vicinity of 1730 cm ⁻¹ obtained from laser Raman spectroscopy using linearly polarized laser light in the cross section in the thickness direction of the polyester resin layer The full width at half maximum of the peak was measured by the following method. The measurement results are shown in Table 2 together with the heat treatment conditions.
Half-width measurement of resin layer cross section by laser Raman spectroscopy About resin-coated metal plate after heat treatment, the cross section of the resin layer is buffed to make a measurement sample, and the resin layer cross section is obtained by laser Raman spectroscopy using linearly polarized laser light The half width measurement of was performed. Since the resin layer is a laminate of biaxially stretched films, the measurement is performed with the polarization plane of the laser beam perpendicular to the thickness direction of the resin layer, and the polarization plane with respect to the thickness direction of the resin layer. The half width was measured in two ways when measuring in parallel. The target half-value width is the half-value width of the peak due to the C = O stretching vibration near the Raman shift of 1730 cm-1.
For the measurement, a commercially available NRS-2000 laser Raman spectrometer manufactured by JASCO Corporation was used. For the incident light, an Ar + laser (wavelength 514.5 nm) was used, and the laser light was condensed to about 1 μm on the sample surface by a lens (× 100) and measured. The laser intensity was 2 mW on the sample surface. For the slit, slit 1 was set to 200 μm, slits 3 and 5 were set to 400 μm, and wave number resolution was set to 10.4 cm −1. The measurement time was 5 seconds × 2 per measurement point, and the aperture was 200 μm. The measurement was performed at a pitch of 1 μm with respect to the thickness direction of the film, and after repeating measurement three times for each measurement site, an average value was obtained and used as a measurement value. Since the laser beam emitted from the laser oscillator is highly linearly polarized light, a polarizer was not used in this measurement.

Further, the properties of the resin-coated metal plate after the heat treatment were measured and evaluated by the following methods, respectively.

A wax was applied to the polyester resin-coated metal plate after the heat treatment for formability, and then a disc having a diameter of 200 mm was punched out to obtain a shallow drawn can with a drawing ratio of 2.00. Next, the drawn can was processed at a drawing ratio of 2.20, and further drawn again to a drawing ratio of 2.50. Then, after performing doming forming according to a conventional method, 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 on the film after molding Δ: Molding is possible, but film damage is partially recognized ×: Can is broken and cannot be molded
Adhesiveness after molding Cans that were moldable (greater than or equal to) in the above-described evaluation of moldability were used. After filling the inside of the can with tap water, the lid was wrapped and sealed. Subsequently, a retort sterilization treatment was performed at 130 ° C. for 90 minutes, and a sample for peel test (width 15 mm, length 120 mm) was cut out from the can body. Part of the film is peeled off from the long side end of the cut sample. The peeled film was opened in the direction opposite to the peeled direction (angle: 180 °), and a peel test was performed at a tensile speed of 30 mm / min. Using a tensile tester to evaluate the adhesion force per 15 mm width. .
(Score)
○: 10.0 (N) / 15 (mm) or more Δ: 5.0 (N) / 15 (mm) or more, less than 10.0 (N) / 15 (mm) ×: 5.0 (N) / Less than 15 (mm)
Retort whitening resistance The bottom (can outer surface side) of the can that was moldable (or better) in the above-described moldability evaluation was targeted. After filling the can with room temperature tap water, the lid was wrapped and sealed. Then, it placed in a retort sterilization furnace with the bottom of the can facing downward, and a retort treatment was performed at 125 ° C. for 90 minutes. After the treatment, the change in the appearance of the outer surface of the bottom of the can was visually observed.
(About the score)
○: No change in appearance △: Faint cloudy appearance x: Appearance cloudy (whitening occurred)
The results obtained as described above are shown in Tables 3 and 4.

  From Tables 3 and 4, it can be seen that the inventive examples have good performance with respect to moldability, post-mold adhesion, and retort whitening resistance required for container materials. On the other hand, the comparative example outside the scope of the present invention is inferior in any of the characteristics.

  The resin-coated metal plate for containers of the present invention is excellent in the design of the outer surface of the can in addition to the basic performance required for food canned materials. It is a suitable material.

It is a figure which shows the measuring method of a laser Raman spectroscopy. It is a figure which shows the measuring method of a laser Raman spectroscopy. It is a figure which shows the principal part of the laminating apparatus of a metal plate. (Example 1) It is a figure which shows the cross-section of a resin coating metal plate. (Example 1)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal plate 2 Resin layer 3 Laser oscillator 4 Laser light 5 Raman scattered light 6 Spectrometer 7 Lens 8 Polarizing plane of laser light (perpendicular to resin thickness direction)
9 Polarization plane of the laser beam (parallel to the resin thickness direction)
10 Metal plate (chrome plated steel plate)
DESCRIPTION OF SYMBOLS 11 Metal strip heating apparatus 12 Lami roll 13a, 13b Film 14 Metal strip cooling apparatus

Claims (2)

A resin-coated metal plate having a polyester resin layer mainly composed of polyethylene terephthalate on both sides, and is obtained from laser Raman spectroscopy using linearly polarized laser light in a cross section in the thickness direction of the polyester resin layer. half width of peaks due to C = 0 stretching vibration of 1730 cm ^-1 vicinity, container resin-coated metal sheet, characterized in that in the range of 16.0cm ^-1 ~24.0cm ^-1. Using linearly polarized laser light in a cross section in the thickness direction of the polyester resin layer of a resin-coated metal plate for a container that has been heat-treated for 5 seconds or more in a temperature range from the crystallization temperature to the melting point of the polyester resin layer. The half-value width of a peak caused by C = 0 stretching vibration in the vicinity of 1730 cm ⁻¹ obtained from the measured laser Raman spectroscopy is in the range of 16.0 cm ^{−1 to} 24.0 cm ^−1. The resin-coated metal plate for containers as described.

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