JP5348944B2 - Longitudinal uniaxially stretched polyester film for metal cans, its production method, resin-laminated metal plate - Google Patents

Description

  The present invention relates to a specific resin composition, a longitudinally uniaxially stretched film for a metal can having specific resin properties, a method for producing the same, and a metal plate coated with the resin, which are useful for coating a metal plate.

  The most important performance required for beverage cans and food cans is the shelf life of the contents, and it is important to maintain the flavor over a long period of time and at the same time prevent corrosion of the metal. Under these circumstances, many methods have already been proposed for laminating a resin film on a metal plate and producing a drawn can and a drawn and ironed can using this material. For example, in Patent Document 1, a biaxially stretched film made of a polyester resin is laminated on a metal plate by thermal fusion, and in the coated resin layer after lamination, the crystallization state in the resin layer near the metal plate and non-nearness It is disclosed to provide a can material having excellent workability and work adhesion by controlling the orientation state in the resin layer within an appropriate range. However, in order to obtain this characteristic, it is necessary to appropriately control the degree of biaxial orientation of the coating resin layer, and thus there is a troublesome task of strictly managing the heat fusion conditions between the metal plate and the biaxially stretched film.

  In addition, the biaxially stretched film is generally formed by reheating a sheet extruded from a T-die and solidified with a cooling roll, stretching in the longitudinal direction, stretching in the width direction, and It is manufactured in a process of winding on a roll. For stretching in the machine direction, the film may be heated with a heating roll and stretched at a difference in peripheral speed between a plurality of rolls. However, since transverse stretching is performed by grasping both ends of the film to maintain a suitable stretching temperature. A large heating furnace is required. Furthermore, in order to guarantee the thermal stability of the film, a heating furnace for heat setting after stretching is also required, and a large amount of energy is used. In addition, although the thermal stability of the film is improved as the heat setting is performed, the contradictory phenomenon that the heat fusion property with the metal plate is lowered due to the progress of crystallization of the film occurs. It was not the most suitable film for laminating metal plates.

  Thus, conventionally, as a resin-coated metal plate for metal cans, a biaxially stretched resin film obtained by thermally bonding a resin film with orientation imparted to the resin film has been used. In order to improve the workability, it has become necessary to make it non-oriented in a state where it is coated on a metal plate. Therefore, for example, Patent Document 2 discloses a resin film for coating a metal plate that is easy to cover a metal plate in a non-oriented state and tries to prevent damage to the film due to the can.

  In Patent Document 2, a thermoplastic resin is heated and melted, extruded continuously from a T-die in a band shape, cooled and solidified, and then stretched in a low temperature range, and then a stretched film is formed without heat fixing. Thus, a method for producing a resin film for coating a metal plate that can be heat-sealed to a metal plate has been disclosed, but since it is stretched in a relatively low temperature range of Tg to Tg + 80 ° C., it tends to shrink after stretching. The tendency to do becomes strong. For this reason, winding tightening may occur during long-term storage, and wrinkles and blocking troubles may occur. Heat fixing is required, or the draw ratio is 1.5. Although there is a description that it is preferable to set to about 2.5 times, in the case of trying to form a film from a composition such as a polybutylene terephthalate resin, in particular, by the method disclosed therein Since the glass transition temperature Tg of the resin is low, the tendency to shrink after stretching is further increased. Therefore, the problems as described above have become serious, and it has not always been optimal as a method for producing a resin film-coated metal plate.

JP-A-6-155660 JP 2002-120278 A

  In order to solve the above problems, the present invention has a specific resin composition suitable for squeezed cans and squeezed and squeezed cans as a film structure, excellent in adhesion and laminating properties, and heat-set in a film forming process. (Cannot be heat set), and the rolled roll is a uniaxially stretched film for a metal can excellent in appearance without wrinkles, a method for manufacturing the same, and a metal can coated with the resin and excellent in can manufacturing An object of the present invention is to provide a resin laminated metal plate.

According to the first aspect of the present invention, the dicarboxylic acid component is composed of terephthalic acid, the glycol component is composed of 1,4-butanediol, 50 to 70% by weight of the polyester (a), the dicarboxylic acid component is composed of terephthalic acid, and the glycol component is composed of A longitudinally uniaxially stretched film composed of a polyester resin composition comprising 50 to 30% by weight of a polyester (b) made of ethylene glycol,
(1) In-plane refractive index difference (difference between the vertical refractive index and the horizontal refractive index of the film) ΔN is 60 × 10 ⁻³ or more,
(2) The crystallization fraction is 50% or less,
(3) Heat shrinkage under conditions of 150 ° C. × 30 minutes is 25% or less in the longitudinal direction (MD direction) of the film, 8% or less in the lateral direction (TD direction) of the film,
The present invention relates to a longitudinally uniaxially stretched polyester film for metal cans.
2nd of this invention is a method of manufacturing the polyester film of Claim 1, Comprising: Polyester (a) 50-70 whose dicarboxylic acid component consists of terephthalic acid and whose glycol component consists of 1, 4- butanediol. A polyester resin composition consisting of 50% by weight and a polyester (b) 50 to 30% by weight of a dicarboxylic acid component consisting of terephthalic acid and a glycol component consisting of ethylene glycol is extruded from a T die using an extruder, and a molten resin Is cooled and solidified to form a sheet on a cast roll, and then when the glass transition temperature of the polyester (a) is Tg (a), the sheet is [Tg (a) + 80 ° C.] or more and [Tg ( vertically 3-4.5 fold by the peripheral speed difference between a) + 100 ℃] before stretching is a heating control temperature range below the roll and draw roll after Next, the peripheral speed ratio between the roll after stretching and the guide roll continuous thereafter is controlled in the range of 100: 97.0 to 100: 99.6 without performing heat setting, and the guide roll continuous after the roll after stretching. The present invention relates to a method for producing a longitudinally uniaxially stretched polyester film for covering a metal plate, wherein the tension of the film is relaxed to relieve the internal stress of the stretched film.
3rd of this invention is a manufacturing method of the longitudinally uniaxially stretched polyester film for metal plate coating | coated of Claim 2, Comprising: Controlling the peripheral speed ratio of the roll after extending | stretching and several guide rolls connected after that, it is a step. In particular, the present invention relates to a method for producing a longitudinally uniaxially stretched polyester film for coating a metal plate, characterized by relaxing the tension of the film.
4th of this invention is a manufacturing method of the vertical uniaxial polyester film for metal plate coating | coated in any one of Claim 2 or 3, Comprising: After longitudinal stretching, the glass transition temperature of the said polyester (a) is set to Tg (a In the temperature range of Tg (a) to Tg (b) when the glass transition temperature of the polyester (b) is Tg (b), the total amount of tension relaxation in the longitudinal direction is determined using a plurality of guide rolls. The present invention relates to a method for producing a longitudinally uniaxially stretched polyester film for coating a metal plate, comprising a step of controlling the content to be 0.4% or more.
A fifth aspect of the present invention is a resin-laminated metal plate for a metal can in which the film according to claim 1 is coated directly or on one side or both sides via an organic resin film layer, and the crystalline state of the coated resin film Relates to a resin-laminated metal plate characterized in that the crystallization fraction does not exceed 35%.

  Hereinafter, the present invention will be described in detail. The polyester film constituting the film of the present invention comprises a polyester (a) 50 to 70% by weight of a dicarboxylic acid component made of terephthalic acid, a glycol component made of 1,4-butanediol, and a dicarboxylic acid component made of terephthalic acid. These are two types of blended polyester films having a blending ratio of 50 to 30% by weight of the polyester (b) whose glycol component is ethylene glycol.

In the resin composition, the polyester (a) in which the dicarboxylic acid component is composed of terephthalic acid and the glycol component is composed of 1,4-butanediol is in the range of 50 to 70% by weight, more preferably 55 to 65% by weight. It is. When the composition ratio of the polyester (a) exceeds 70% by weight of the resin composition, the adhesion with the metal plate is lowered and it is not suitable for a material to be molded into a metal can. Moreover, when the composition ratio of polyester (a) is less than 50% by weight of the resin composition, the coating resin becomes milky and deteriorates in appearance by heat treatment such as retort sterilization treatment of the metal can.
The polyester (a) in the present invention may be appropriately copolymerized with other components as long as the effects of the present invention are not impaired. For that purpose, terephthalic acid and 1,4-butanediol are each 90 mol%. It is preferable to exist above.

Examples of the acid component as a copolymerization component of the polyester (a) include isophthalic acid, (anhydrous) phthalic acid, aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, oxalic acid, succinic acid, adipic acid, and sebacic acid. , Dimer acids having 20 to 60 carbon atoms, aliphatic dicarboxylic acids such as (anhydrous) maleic acid, fumaric acid and itaconic acid, alicyclic dicarboxylic acids such as (anhydrous) hexahydrophthalic acid and hexahydroterephthalic acid, and other hydroxy groups Carboxylic acid and polyfunctional carboxylic acid can be mentioned.
Examples of the alcohol component as a copolymerization component of the polyester (a) include aliphatic glycols such as ethylene glycol, diethylene glycol, triethylene glycol, and 1,2-propanediol, 1,4-cyclohexanedimethanol, and 1,4. -Alicyclic diols such as cyclohexanediethanol, aromatic diols, polyfunctional alcohols and the like.

In the resin composition, the polyester (b) in which the dicarboxylic acid component is made of terephthalic acid and the glycol component is made of ethylene glycol is in the range of 50 to 30% by weight, more preferably 45 to 35% by weight. When the composition ratio of the polyester (b) exceeds 50% by weight of the resin composition, the coating resin becomes milky and deteriorates in appearance by heat treatment such as retort sterilization treatment of the metal can. Moreover, if the composition ratio of polyester (b) is less than 30% by weight of the resin composition, the adhesion to the metal plate is reduced, making it unsuitable for a material to be molded into a metal can.
The polyester (b) in the present invention may be appropriately copolymerized with other components similar to those in the case of the polyester (a) as long as the effects of the present invention are not impaired. For that purpose, terephthalic acid and ethylene glycol are used. Are preferably present in an amount of 90 mol% or more.

  Examples of the acid component and the alcohol component as the copolymerization component of the polyester (b) include the same as the polyester (a).

  In addition, you may add an appropriate amount of a pigment, an antiblocking agent, antioxidant, a stabilizer, etc. to a resin composition as needed.

In the present invention, the polyester (a) and the polyester (b) are substantially incompatible.
The polyester (a) is preferably selected in the range of a melting point of 212 to 224 ° C. and an intrinsic viscosity of 0.78 to 1.45 dl / g.
The polyester (b) is preferably selected in the range of a melting point of 246 to 255 ° C. and an intrinsic viscosity of 0.66 to 0.99 dl / g.

In the film of the present invention, the lower limit of the in-plane refractive index difference ΔN, which is the difference between the longitudinal refractive index and the lateral refractive index of the film, is 60 × 10 ⁻³ or more, preferably 100 × 10 ⁻³ or more. is there. Here, ΔN is defined by the following equation.
[Equation 1]
ΔN = Nx−Ny (1)
However, Nx is a value of a refractive index measured by an Abbe refractometer in the longitudinal direction (MD direction: machine direction) and Ny is a lateral direction (TD direction: traverse direction).
In the case of a film having an in-plane refractive index difference ΔN of less than 60 × 10 ⁻³ , either MD direction stretching is insufficient or TD direction stretching is too strong. In the invention, since the transverse stretching in the TD direction is not performed, the stretching in the MD direction is insufficient. If the stretching in the MD direction is insufficient, the tension control becomes difficult in the process of laminating on the metal plate, wrinkles are easily generated, the end of the film protrudes from the metal plate, or the width of the film in the TD direction It becomes unstable and it becomes difficult for the film edge part to stick together in a predetermined position. In this sense, the film of the present invention has an in-plane refractive index difference ΔN of 60 × 10 ⁻³ or more.
The upper limit of the refractive index difference ΔN is not particularly limited, but is set to such an extent that no curling occurs and preferably does not exceed 200 × 10 ⁻³ .

The crystallization fraction of the film of the present invention is 50% or less, preferably 30% or less. When the crystallization fraction exceeds 50%, the adhesion to the metal plate tends to be lowered, and it becomes difficult to obtain a good laminated metal plate. The lower limit of the crystallization fraction is 0.5% from the viewpoint of industrial productivity.
The crystallization fraction of the film affects the adhesion between the film and the metal plate when the film is laminated on the metal plate, and affects the moldability of the can and the quality of the can after lamination.
The crystallization fraction of the film before lamination in the present invention is determined by the following method.
(1) The film formed was designated as sample a.
(2) The film formed was melted by heating at 270 ° C. for 1 minute in a nitrogen atmosphere and immediately put into water cooled to 5 ° C. as sample b.
(3) The film formed was heated and melted at 270 ° C. for 1 minute in a nitrogen atmosphere, and then gradually cooled to 50 ° C. over 3 hours to obtain a sample c.
(4) The density of these samples a, b and c is measured by a known method using a density gradient tube, and the value obtained by calculating with the following formula is defined as the crystallization fraction (%).
[Equation 2]
Crystallization fraction (%) = {(Da−Db) / (Dc−Db)} × 100 (2)
In addition, Da, Db, and Dc in a formula show the density of samples a, b, and c, respectively.

Furthermore, the film of the present invention has a heat shrinkage rate of 150 ° C. × 30 minutes in the MD direction of 25% or less, preferably 23% or less. The TD direction is 8% or less, preferably 6% or less.
The reason is that the heat shrinkage rate in the MD direction is first, but if the heat shrinkage rate exceeds 25%, the film shrinks due to the influence of radiant heat from the preheated metal plate when the film is bonded to the metal plate. As a result, the tension control becomes unstable, and as a result, it becomes difficult to obtain a good laminated metal plate. The lower limit in the MD direction is preferably 0.5% or more from the viewpoint of industrial productivity.
On the other hand, in the heat shrinkage rate in the TD direction, if the heat shrinkage rate exceeds 8%, the dimension in the width direction of the film becomes unstable, and it becomes difficult to bond the film to a predetermined position of the metal plate. The lower limit of the TD direction is preferably 0.1% from the viewpoint of industrial productivity.

The heat shrinkage was measured as follows.
When measuring the heat shrinkage rate in the MD direction from the film, it is cut into a strip shape having a dimension of 150 mm in the longitudinal direction and 20 mm in the width direction, and when measuring the heat shrinkage rate in the TD direction, 20 mm in the longitudinal direction. A test specimen was cut into a strip shape having a dimension of 150 mm in the width direction. After storing the test piece at 23 ± 2 ° C. all day and night, put two marked lines so that the distance between marked lines becomes 100 mm. The test piece was put in an electric oven at 150 ° C., heated for 15 minutes, taken out and left at room temperature for 30 minutes, and then the distance between marked lines was measured to calculate the heat shrinkage rate.
[Equation 3]
[Heat shrinkage ratio] (%) = [100 mm- (distance between marked lines after heating)] / 100 mm × 100
... (3)

  The thickness of the film of the present invention is suitably in the range of 6 to 40 μm, and more preferably in the range of 8 to 30 μm. If the thickness is less than 6 μm, the mechanical strength of the film is low, so that it is difficult to control the tension during lamination, and workability is reduced. Even if the thickness exceeds 40 μm, the workability is not improved and the material is useless, which is not economical.

The film manufacturing method of the resin composition of this invention is demonstrated below. After manufacturing a sheet to a predetermined thickness by a known method of cooling on a cast roll using an extruder equipped with a T die, the sheet is converted into a glass transition temperature Tg (a ), The difference in peripheral speed between the roll before stretching and the roll after stretching, which is heated to a temperature range of [Tg (a) + 80 ° C.] or more and [Tg (a) + 100 ° C.] or less, is 3 to 4.5 times. It is important to relax the internal stress of the stretched film by longitudinally stretching the film and then relaxing the tension between the post-stretching roll and the guide roll following the post-stretching roll without heat setting. Preferably, the ratio of the peripheral speed between the roll after stretching and the guide roll that follows the roll is controlled in the range of 100: 97.0 to 100: 99.6, and the amount of relaxation of the film tension in the machine direction is 0.4% (100 : 99.6) to 3% (100: 97). More preferably, after longitudinal stretching, Tg (a) to Tg (b) [Tg (b) is the glass transition temperature of the polyester (b). The guide roll in the temperature range is gradually decelerated so that the peripheral speed ratio of the last guide roll falls within the above range. For example, the relationship between the post-stretching roll and the plurality of guide rolls connected thereto is set such that the peripheral speed ratio of each of the four guide rolls to the post-stretching roll 100 is 99.9, 99.8, 99.6, 99. The longitudinal tension of the stretched film is relaxed by decelerating stepwise so as to be 4. As described above, the film shrinkage rate in the film plane is more uniform when the longitudinal tension of the stretched film is gradually relaxed using a plurality of guide rolls in the temperature range of Tg (a) to Tg (b). This is a preferred embodiment because it is possible to achieve a stable film. Moreover, the guide roll for loosening the tension | tensile_strength of a stretched film in steps will not be limited to four if it is in said range. The upper limit of the amount of tension relaxation in the longitudinal direction should not exceed 3% (100: 97) because the roll when the film is wound should not be wrinkled .

In producing the film of the resin composition of the present invention, if the temperature of the roll before stretching is less than [Tg (a) + 80 ° C.], the internal strain of the film after stretching becomes large, and the heat shrinkage in the MD direction is 25% or less. It becomes difficult to make. Moreover, when it exceeds [Tg (a) +100 degreeC], crystallization of a film will advance and the crystallization fraction of the film after extending | stretching will exceed 50%.
Further, when the peripheral speed ratio between the stretched roll and the next guide roll (or a group of guide rolls continuous thereafter) is more than 100: 99.6 after stretching, the film has no relaxing effect after stretching, and heating in the MD direction. When the shrinkage rate exceeds 25% and the film is bonded to the metal plate, the film shrinks due to the radiant heat from the preheated metal plate, resulting in unstable tension control of the film, and as a result It may be difficult to obtain a good laminated metal plate (wrinkles in the vertical direction).
Even if the peripheral speed ratio is less than 100: 97, the relaxation effect is not improved, the productivity is lowered, and it is not economical. Here, the relaxation effect means that some of the stress of the elastically deformed portion is relaxed mainly among the elastically deformed portion and the plastically deformed portion of the strain received by the resin film.
In addition, the temperature of the roll after extending | stretching does not have a restriction | limiting in particular, What is necessary is just below the temperature of the roll before extending | stretching.
Thus, after extending | stretching, the ear | edge part of both sides is slit and it winds up by a well-known method, and becomes a roll-shaped product.

Moreover, in the film manufacture of this invention, the heat setting after an extending process is not performed. When heat-fixed, the crystallization rate of the polybutylene terephthalate resin, which is the main component, is high, so the crystallization fraction of the film exceeds 50%, and the heat-fusibility is lowered. A relatively high temperature is required. As a result, since the film is softened due to the influence of radiant heat from the metal plate, it is difficult to bond the film to a predetermined position on the metal plate.
When the film is laminated on a metal plate by pressing the crystallized fraction of the longitudinally uniaxially stretched film composed of the polyester resin composition to 50% or less without performing heat setting after stretching in this way. Even without strictly controlling the roll temperature or controlling the ambient temperature, the film width is stable and can be bonded in place, providing excellent adhesion. Good laminating properties.
Moreover, it is not necessary to provide the heat setting process for heat-setting after a extending process at a film forming process, and the energy cost for it can be reduced.

Next, a method for laminating the resin composition film of the present invention on a metal plate will be described below.
The metal plate used as the base material for the resin-coated metal plate for can manufacturing is not particularly limited, and is an aluminum plate, an aluminum alloy plate, a nickel-plated steel plate, a tin-plated steel plate, an ultrathin tin-plated steel plate, an electrolysis plate, or the like. It is appropriately selected from conventionally known metal plates for can manufacturing such as surface-treated steel sheets such as chromic acid-treated steel sheets and galvanized steel sheets, and is in close contact with thermosetting resins and thermoplastic resins. It is preferable to perform a surface treatment rich in properties.
Specifically, as a metal plate for a seamless can subjected to squeezing and ironing, etc., for an aluminum alloy plate having a thickness of 0.24 to 0.38 mm, the amount of adhesion on one side is 1 to 40 mg / m ² . Examples thereof include those subjected to chemical conversion treatment such as a phosphoric acid chromate treatment to which chromium is adhered or a zirconium phosphate treatment to which 4 to 17 mg / m ² of zirconium is adhered. Further, as the surface-treated steel sheet, the thickness (thickness of the surface-treated steel sheet itself) is 0.15 to 0.25 mm, a lower layer made of metal chromium with a coating amount of 10 to ²⁰⁰ mg / m ² , and 1 to 3 in terms of chromium. TFS (Tin Free Steel), in which a two-layer coating with an upper layer made of chromium hydrated oxide of 30 mg / m ² is formed on a steel sheet, is preferable from the viewpoints of resin adhesion and corrosion resistance. In addition, for nickel-plated steel sheets, a chemical conversion coating layer mainly composed of an organic resin of 1 to 100 mg / m ² as the amount of C is formed on both sides on the nickel plating layer of ^{20 to} 2000 mg / m ² as the amount of adhesion on one side. What you gave.

As a method of laminating the resin composition film of the present invention on a metal plate, the metal plate is preheated, and the resin composition film is pressed and bonded to one side or both sides of the metal plate with a rubber roll. As a method for heating the metal plate, a known method such as a hot air heating method, an electric heating roll heating method, a high frequency heating method, an infrared heating method or the like can be suitably used, and the heating temperature is the melting point of polyester (a), which is the main component, ± 10 ° C. Is suitable.
After laminating the metal plate and the film, heat the polyester (b) from the melting point to the melting point + 40 ° C. in a heating furnace to melt the film, and immediately quench in a water bath or by blowing cooling air. Therefore, it is necessary to break the oriented crystal structure of the coated resin film and make it amorphous to a crystallization fraction of 35% or less.
The reason for this is that if the crystallization fraction exceeds 35%, the coated resin film is insufficiently stretched and formed by drawing and ironing, so that the coated resin film cracks and the quality of the can is maintained. This is because it disappears. The lower limit of the crystallization fraction is determined in consideration of the energy cost required for cooling and the size of the equipment, and is preferably 3% or more.

  By carrying out like this, the resin laminated metal plate for metal cans coated on one side or both sides of the film directly or through an organic resin film layer, the crystal state of this coated resin film is 35% in terms of crystallization fraction. Therefore, it is suitable for use in metal cans that require severe processing such as drawing and ironing, and there are molding troubles such as peeling during drawing and ironing. No defects such as cracks occur in the film on the inner surface side of the metal can. Moreover, the flavor of the food and drink in the can is maintained for a long period of time, and the inner surface of the metal can that has been made is of high quality without causing the corrosion reaction of the metal, and without damaging the appearance at the sterilization temperature after filling. It can be set as the resin film covering metal plate suitable for a can material.

  As described above, it is a requirement necessary for producing a metal can that the crystal state of the film covering the metal plate does not exceed 35% in terms of crystallization fraction. Therefore, the crystal state of the longitudinally uniaxially stretched film before being bonded to the metal plate is important. The necessity for setting the crystallization fraction of the longitudinally uniaxially stretched film before being bonded to the metal plate to 50% or less is as described above. In addition, the crystallization fraction of the film, which is a requirement of the present invention, is 50. A longitudinally uniaxially stretched film that deviates from the condition of% or less is less susceptible to thermal melting than that of a film having a crystallization fraction of 50% or less. Therefore, when using such a film, since it is necessary to completely collapse the crystal structure of the film attached to the metal plate, the melting point of the polyester (b) + 40 ° C. is used as the heating and melting temperature of the film. A heating temperature exceeding that (the temperature of the heated film itself) is required, and a holding time of about 5 seconds is required at that temperature. For this reason, it becomes difficult to make the crystallization fraction amorphous to 35% or less without thermal degradation of the resin. Thermal degradation of the coating resin is not preferable because it causes the formation of low molecular weight components and adversely affects the flavor properties of the metal can, and thermal degradation should be prevented as much as possible. In this sense, the longitudinal uniaxially stretched film used to coat the metal plate is used to make the crystal state of the film covering the metal plate not exceed 35% in terms of crystallization fraction. The rate needs to be 50% or less.

In the present invention, the crystallization fraction of the coating resin coating the laminated metal plate is determined by the following method.
(1) A resin film scraped from the surface of the resin-coated metal plate was used as sample aa.
(2) The film formed was melted by heating at 270 ° C. for 1 minute in a nitrogen atmosphere and immediately put into water cooled to 5 ° C. as sample b.
(3) The film formed was heated and melted at 270 ° C. for 1 minute in a nitrogen atmosphere, and then gradually cooled to 50 ° C. over 3 hours to obtain a sample c.
(4) The density of these samples aa, b, and c is measured by a known method using a density gradient tube, and the value obtained by calculating the following formula is defined as the crystallization fraction (%).
[Equation 4]
Crystallization fraction (%) = {(Daa−Db) / (Dc−Db)} × 100 (4)
In addition, Daa, Db, and Dc in a formula show the density of samples aa, b, and c, respectively.

The resin composition film of the present invention can be directly bonded to a metal plate, but can also be bonded through an organic resin film (adhesive). Examples of the organic resin film that can be suitably used in the present invention include alkyd resin paints, epoxy resin paints, acrylic resin paints, urea resin paints, phenol resin paints, polyurethane resin paints, and the like. Can be used in combination. Coating is performed by a known technique, and the coating amount is preferably 0.6 to 6 μm in thickness.
The adhesive may be applied to the thermoplastic resin film side to form an adhesive layer, or may be applied to the metal plate side to form an adhesive layer. Moreover, you may make it add a white pigment (titanium oxide) with an average particle diameter of 0.1-0.5 micrometer to an adhesive agent as needed.

Below, the metal can manufactured by well-known manufacturing methods, such as drawing forming and drawing ironing, using the above-mentioned resin composition coating metal plate is described. The metal can has a workability because the resin composition film of the can body portion stretched in the vertical direction of the metal can by drawing and ironing inevitably produces oriented crystals and increases the crystallization fraction. Easy to block. Therefore, in order to avoid this crystalline state, the can body is placed in the resin film in the process of heating at the end of the process of manufacturing a known two-piece metal can, that is, the process of printing the outer surface and the heat curing of the clear paint. It is important to heat the polyester (b) from the melting point to the melting point + 40 ° C. and quench with cold air to eliminate the oriented crystals and reduce the crystallization fraction to 50% or less.
If the crystallization fraction exceeds 50% at the stage of the can, cracks will occur and the metal part will be exposed and corroded when subjected to impact deformation in the distribution process after the metal can is filled with the contents. May lead to a connection.

In the present invention, in the metal can, the crystallization fraction of the coating resin after extinguishing the oriented crystals is obtained by the following method.
(1) The resin film scraped from the thin part of the can body of the resin-coated metal can was used as sample aaa.
(2) The film formed was melted by heating at 270 ° C. for 1 minute in a nitrogen atmosphere and immediately put into water cooled to 5 ° C. as sample b.
(3) The film formed was heated and melted at 270 ° C. for 1 minute in a nitrogen atmosphere, and then gradually cooled to 50 ° C. over 3 hours to obtain a sample c.
(4) The density of these samples aaa, b, and c is measured by a known method using a density gradient tube, and the value obtained by calculating the following formula is defined as the crystallization fraction (%).
[Equation 5]
Crystallization fraction (%) = {(Daa-Db) / (Dc-Db)} × 100 (5)
In addition, Daaa, Db, and Dc in a formula show the density of samples aaa, b, and c, respectively.

  According to the present invention, the laminate adhesiveness with the metal plate is excellent, the tension is applied in the longitudinal direction, the laminating suitability with small shrinkage in the lateral direction is excellent, and the wound roll is excellent in appearance without wrinkles. The film can be produced without requiring a heat setting step in the film forming step. As a result, a good laminated metal plate can be obtained without strict process control. By controlling the coating resin to a predetermined crystallization fraction, a laminated metal plate with excellent canability can be stabilized. The effect that it can manufacture automatically is produced.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited thereto. Moreover, although the result of each Example and each comparative example is shown in Table 1 and Table 2, (-) in Table 2 shows that the sample which deserves evaluation was not obtained. Further, “lateral stretching ratio of 1” in the examples and comparative examples other than Comparative Example 2 means that the width direction is not restricted and the lateral stretching is not performed.

In the following examples and comparative examples, the following raw resin and metal plate were used.
Polyester (a) (hereinafter referred to as PBT):
Polybutylene terephthalate (PBT) resin polyester (b) having an intrinsic viscosity of 1.10 dl / g, a melting point of 222 ° C., and a Tg of 23 ° C. (hereinafter referred to as PET):
Polyethylene terephthalate (PET) resin metal plate (hereinafter referred to as an aluminum plate) having an intrinsic viscosity of 0.73 dl / g, a melting point of 253 ° C., and a Tg of 73 ° C .:
JIS 3000 series aluminum alloy plate with a thickness of 0.3mm, with phosphoric acid chromate treatment on the surface

Example 1
PBT resin pellets and PET resin pellets were mixed at a weight ratio of 60:40, charged into an extruder equipped with a T die, and heated and melted at a temperature of about 280 ° C. The melted resin was fed into a T-die, formed into a sheet form from a nozzle, extruded, cooled and solidified on a cast roll, and formed into an 80 μm thick sheet. This sheet was heated with a roll before stretching heated to [Tg + 87 ° C.] = (110 ° C.) of PBT, longitudinally stretched 4 times by the peripheral speed difference from the roll after stretching, and then the roll after stretching without heat setting. And the following guide rolls are controlled so that the peripheral speed ratio is 100: 99.4, respectively, and the film tension is relaxed, and then both ends of the film are wound while removing the slits to obtain a thickness of 20 μm. A test film was obtained. The evaluation results of the film are shown in Table 1.

The film is sandwiched between a pair of crimping rolls on both sides of an aluminum plate heated to 220 ° C., and then put in a heating furnace at 290 ° C., and the film crimped on both sides of the aluminum plate is heat-melted and immediately cooled. Air was blown and rapidly cooled to 120 ° C. or less within 5 seconds to obtain a laminated metal plate in which the coating film was amorphous and non-oriented. A wax-based lubricant was applied to the laminated metal plate, punched out into a disk having a diameter of 155 mm, and then subjected to shallow drawing (drawing ratio: 1.60) into the disk with a punch mold having a diameter of 95 mm to obtain a shallow drawn cup. Next, this shallow drawn cup was redrawn with a die punch having a diameter of 66 mm (drawing ratio: 1.44), and the obtained redrawn cup was ironed (the ironing ratio of the can body side wall: 56%). A deep drawing-ironing can body was obtained. This deep-drawn and ironed can body was domed with respect to the bottom of the can according to a conventional method, and the opening end portion was trimmed so that the can height was 124 mm.
Next, the body is printed and painted, and the can temperature at the time of baking is heated to 260 ° C., and air-cooled so that the can temperature reaches 60 ° C. in 4 seconds after reaching the temperature. After extinguishing, a two-piece metal can for 350 ml was obtained by neck-forming and flange-forming the open end by a known method. The evaluation results of the metal can obtained are shown in Table 1.

However, the ironing rate of the side wall of the can body is
[Equation 6]
(T ₀ −t ₁ ) / t ₀ × 100 (6)
Calculate from
Here, t ₀ is the thickness before processing, t ₁ is the thickness of the can body side wall portion after processing.

Each evaluation method is shown below.
(Film roll appearance characteristics)
The appearance characteristics of a film roll wound with a longitudinally uniaxially stretched film were examined.
The roll in which the film was wound was not marked with wrinkles (◯), and the roll was marked with (x). Each evaluation result is shown in Table 1.
(Laminate)
The appearance of the film thermocompression bonded to the metal plate and the positional relationship between the metal plate and the film were examined.
In terms of appearance, those without film wrinkles were marked with (◯), and those with wrinkles on the film were marked with (x).
In addition, regarding the positional relationship, when the end portion of the film is not in a predetermined position such as protruding from the metal plate (± 1 mm or more with respect to the set position), it was determined as impossible (×).
In addition, the phenomenon that the film peeled off from the metal plate during processing such as drawing, redrawing, and ironing using the film-laminated metal plate was also defined as (x).
(Can manufacturing)
The damage of the film by drawing and ironing was examined visually.
After processing, the film was not damaged (O), when film peeling was observed (F), and when damage such as film peeling was observed (X).
(Inner grade of metal can)
A 1% saline solution was put in a metal can, and a copper wire electrode was immersed in the metal can as a cathode, a part of the film on the outer surface of the can body was scraped off and used as an anode, and a voltage of +6 V was applied between both electrodes for 3 seconds. The maximum current (mA) was measured. The smaller the current that flows, the better. If the leakage current is less than 7 mA (◯), 7 mA or more was taken as (x).
(Shock resistance of metal cans)
A metal can is filled with water, sealed, subjected to a retort treatment at 125 ° C. for 30 minutes, and a V-shaped hitting core is placed on the side wall of the can body cooled to 5 ° C. Aiming at the strike center, a 500 g weight is dropped from a height of 15 cm to give a deformation with impact to the side wall of the can body. The deformed can was examined by the same method as the inner surface quality evaluation. The smaller the current that flows, the better. If the leakage current is less than 7 mA (◯), 7 mA or more was taken as (x).
(Appearance after heat sterilization of metal can)
The metal can was filled with water, sealed, subjected to a retort treatment at 125 ° C. for 30 minutes, and then the appearance was visually examined. When the film appearance was normal (◯), when the film had a polka-dot blot or whitening, it was determined not to be possible (×).

(Example 2)
The same test as in Example 1 was performed except that the resin composition in which the blending of the PBT resin pellets and the PET resin pellets was a weight ratio of 70:30 was used. The results are shown in Table 1.

(Example 3)
The same test as in Example 1 was performed except that the blend of the PBT resin pellet and the PET resin pellet was changed to a resin composition having a weight ratio of 50:50. The results are shown in Table 1.

Example 4
The laminate described in Example 1 was put in a heating furnace at 290 ° C. and the film bonded to both surfaces of the aluminum plate was melted by heat. The flow rate of the cooling air to be sprayed was slightly weaker than that in Example 1, and within 120 seconds at 120 ° C. The same test as in Example 1 was performed except that the cooling conditions were changed so as to be as follows. The results are shown in Table 1.

(Example 5)
Example of Example 1 except that after the molding process of Example 1, the temperature reached at the can temperature at the time of baking after printing and painting was 260 ° C., and the air cooling conditions were changed so that the can temperature would be 50 ° C. or less after 6 seconds. The same test as 1 was conducted. The results are shown in Table 1.

(Example 6)
The same test as in Example 1 was performed except that the resin composition of Example 1 was made into a sheet, and then the draw ratio was set to 3 times. The results are shown in Table 1.

(Example 7)
The same test as in Example 1 was performed except that the resin composition of Example 1 was made into a sheet, and then the draw ratio was 4.5 times. The results are shown in Table 1.

(Example 8)
The same test as in Example 1 was performed, except that the resin composition of Example 1 was made into a sheet, and then the roll temperature before stretching was lowered to [Tg + 82 ° C.] = (105 ° C.) of PBT. The results are shown in Table 1.

Example 9
The same test as in Example 1 was performed, except that the resin composition of Example 1 was made into a sheet, and then the roll temperature before stretching was increased to [Tg + 100 ° C.] = (123 ° C.) of PBT. The results are shown in Table 1.

(Example 10)
When the resin composition of Example 1 is made into a sheet and stretched under the temperature conditions of Example 1, and the peripheral speed of the roll after stretching is set to 100, the four guide rolls connected thereto are respectively 99.9, 99.8, The same test as in Example 1 was performed except that the speed was gradually decreased at a ratio of 99.6 and 99.4. The results are shown in Table 1.

(Comparative Example 1)
The same test as in Example 1 was performed except that the blend of PBT resin pellets and PET resin pellets was changed to a resin composition having a weight ratio of 90:10. The results are shown in Table 2.
The PBT resin has a high crystallization rate and its composition ratio is too high, so that the crystallization fraction of the film exceeds 50%. As a result, the adhesion between the film and the metal plate was reduced, and the film could not withstand the processing for forming a metal can, resulting in peeling.

(Comparative Example 2)
The same test as in Example 1 was carried out except that the resin composition of Example 1 was made into a sheet, and then the longitudinal stretch ratio was 3 times and the lateral stretch ratio was 3 times. The results are shown in Table 2.
Since the sheet was stretched 3 times in both the vertical and horizontal directions, the in-plane refractive index difference ΔN was 53 × 10 ⁻³ , and as a result, the heat shrinkage rate in the horizontal direction exceeded 8%, and the film was laminated to a metal plate. At that time, the edge of the film meandered with respect to the edge portion of the metal plate, and exceeded the limit of the predetermined position. As a result, the film protrudes from the metal plate, and the film of the part that protrudes by heat melting of the laminated film swells in a ball shape. Occurred.

(Comparative Example 3)
The same test as in Example 1 was performed except that the blend of the PBT resin pellet and the PET resin pellet was changed to a resin composition having a weight ratio of 45:55. The results are shown in Table 2.
Although there were no problems in the laminating process and the can manufacturing process, the film surface was whitened in a spot shape and damaged in appearance by retort sterilization (125 ° C, 20 minutes) of a metal can filled and sealed with water. . This is a phenomenon that occurs when the composition ratio of PBT is less than 50%.

(Comparative Example 4)
The same test as in Example 1 was performed except that the stretched film of Example 1 was heat set (heat-set) under the conditions of 150 ° C. × 15 seconds. The results are shown in Table 2.
Although there is a merit that heat-shrinking is difficult by heat setting the film, the heat causes the crystallization fraction of the film to exceed 50%. As a result, the adhesion between the film and the metal plate was reduced, and the film could not withstand the processing for forming a metal can, resulting in peeling.

(Comparative Example 5)
After stretching in Example 1, the same test as in Example 1 was performed except that the circumferential speed of the roll after stretching and the next roll was changed to a circumferential speed ratio of 100: 99.8. The results are shown in Table 2.
The relaxation effect after stretching became insufficient, and the heat shrinkage in the MD direction of the film exceeded 25%. As a result, at the time of lamination, the film contracted due to radiant heat from the preheated metal plate, the tension control became unstable, and the laminate finished with wrinkles in the vertical direction.

(Comparative Example 6)
The same test as in Example 1 was performed except that the resin composition of Example 1 was made into a sheet, and then the stretching ratio in the longitudinal direction was 5 times. The results are shown in Table 2.
When the stretching ratio in the machine direction was set to 5 times and a film having a heat shrinkage ratio in the MD direction of the film exceeding 25% was produced and laminated, the same phenomenon as in Comparative Example 5 occurred.

(Comparative Example 7)
The same test as in Example 1 was performed, except that the resin composition of Example 1 was made into a sheet, and then the roll temperature before stretching was lowered to [Tg + 74 ° C.] = (97 ° C.) of PBT. The results are shown in Table 2.
Since the stretching temperature was less than [Tg + 80 ° C.] = (103 ° C.), the internal strain of the film after stretching increased, and the heat shrinkage ratio exceeded 25%. As a result, the same phenomenon as in Comparative Example 5 occurred.

(Comparative Example 8)
The same test as in Example 1 was performed, except that the resin composition of Example 1 was made into a sheet, and then the roll temperature before stretching was increased to [Tg + 105 ° C.] = (128 ° C.) of PBT. The results are shown in Table 2.
The stretching temperature exceeded [Tg + 100 ° C.] = (123 ° C.), crystallization of the resin proceeded with the heat, and the crystallinity of the stretched film exceeded 50%. As a result, the same phenomenon as in Comparative Example 4 occurred.

(Comparative Example 9)
Laminate as described in Example 1, put in a heating furnace at 290 ° C., heat melt the film pressed on both sides of the aluminum plate, weaken the flow rate of the cooling air to be blown so that it becomes 120 ° C. or less within 12 seconds. Except that the cooling conditions were changed, the same test as in Example 1 was performed to obtain a resin-laminated metal plate. The results are shown in Table 2.
The heat-melted resin film is gradually cooled, crystallization of the resin film proceeds, and the crystallization fraction is less than 35%, which is the condition defined in claim 5, and The crystallization fraction has exceeded 35%. As a result, the elongation characteristic of the resin film was deteriorated, peeling of the film was observed by drawing ironing, and the inner surface quality of the final product metal can was 10 to 18 mA.

(Comparative Example 10)
The blend of PBT resin pellets and PET resin pellets is changed to a resin composition having a weight ratio of 70:30, and the resin composition is made into a sheet. Thereafter, the roll temperature before stretching is set to [Tg + 99 ° C.] = (PBT). 122 ° C.), the stretching ratio was set to 3 times, and the same test as in Example 1 was performed except that the peripheral speed of the roll after stretching and the peripheral speed of the next roll were changed to a peripheral speed ratio of 100: 96.0 respectively. did.
As a result, since the difference in the peripheral speed of the roll was too large, the difference in the refractive index in the film surface became 55 × 10 ⁻³ , and the tension control in the vicinity of the rear winding was destabilized. Film wrinkles began to erupt and could not be used. The results are shown in Table 2.

Claims (5)

Polyester (a) 50 to 70% by weight of a dicarboxylic acid component made of terephthalic acid and a glycol component made of 1,4-butanediol, a polyester (b) made of terephthalic acid and a glycol component made of ethylene glycol (b) A longitudinally uniaxially stretched film composed of a polyester resin composition comprising 50 to 30% by weight,
(1) In-plane refractive index difference (difference between the vertical refractive index and the horizontal refractive index of the film) ΔN is 60 × 10 ⁻³ or more,
(2) The crystallization fraction is 50% or less,
(3) Heat shrinkage under conditions of 150 ° C. × 30 minutes is 25% or less in the longitudinal direction (MD direction) of the film, 8% or less in the lateral direction (TD direction) of the film,
A vertically uniaxially stretched polyester film for metal cans. A method for producing a polyester film according to claim 1, wherein the dicarboxylic acid component is made of terephthalic acid and the glycol component is made of 1,4-butanediol. A polyester resin composition comprising 50 to 30% by weight of a polyester (b) comprising terephthalic acid and a glycol component comprising ethylene glycol is extruded from a T-die using an extruder, and the molten resin is formed into a sheet on a cast roll. Then, when the glass transition temperature of the polyester (a) is Tg (a), the sheet is [Tg (a) + 80 ° C.] or more and [Tg (a) + 100 ° C.] or less. the peripheral speed difference between the roll before heating controlled stretching of the temperature range and after stretching rolls longitudinally stretched 3 to 4.5 times, then heat The peripheral speed ratio between the post-stretching roll and the subsequent guide rolls is controlled in the range of 100: 97.0 to 100: 99.6 without performing the adjustment, and the film is placed between the guide rolls following the post-stretching roll. A method for producing a longitudinally uniaxially stretched polyester film for coating a metal plate, wherein the tension is relaxed and the internal stress of the stretched film is relaxed.   It is a manufacturing method of the longitudinally uniaxially stretched polyester film for metal plate coating | coated of Claim 2, Comprising: The tension | tensile_strength of a film is relieve | moderated in steps by controlling the peripheral speed ratio of a post-stretch roll and a plurality of guide rolls connected thereafter. A method for producing a longitudinally uniaxially stretched polyester film for coating a metal plate.   It is a manufacturing method of the vertical uniaxial polyester film for metal plate coating | cover in any one of Claim 2 or 3, Comprising: After longitudinal stretch, the glass transition temperature of the said polyester (a) is Tg (a), and polyester (b) When the glass transition temperature of Tg (b) is Tg (b), the total amount of tension relaxation in the longitudinal direction is 0.4% or more using a plurality of guide rolls in the temperature range of Tg (a) to Tg (b). The manufacturing method of the longitudinally uniaxially-stretched polyester film for metal plate coating | cover characterized by including the process controlled so   The film according to claim 1 is a resin laminated metal plate for a metal can, which is coated directly or on one side or both sides via an organic resin film layer. The crystal state of the coated resin film is 35 in terms of crystallization fraction. % Resin laminated metal sheet characterized by not exceeding%.