JP2002144513A - Polyester film for coating can material and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for coating a can material capable of rigidly adhering to a metal plate for a can by heating at a high temperature for a short time and clarifying a print in printing, and to provide a method for manufacturing the same. SOLUTION: The polyester film 1 comprises an adhesive layer 5a containing a polyester resin and an aminoplast resin by a weight ratio of 70/30 to 90/10 and provided on one side surface. The film 1 further comprises a cured overcoating layer 3 provided on its opposite surface. The film 1 also comprises a print layer 4 made of a polyester polyurethane resin and a polyisocyanate resin between a film 2 and the layer 5a and containing a pigment. The film 1 also comprises a size coating layer made of the same resin as that of the layer 4 between the layer 4 and the layer 4a and containing no pigment. In this case, the layer 5a may contain a titanium oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal plate for forming a can body of a can body, for example, a welded can body material such as a surface-treated steel sheet, which is heated and bonded via a thermosetting resin-based adhesive to form a protective coating layer. The present invention relates to a polyester film to be formed and a method for producing the same.

[0002]

2. Description of the Related Art As a metal can body used for containers of beverages and the like, a can body is formed by welding and joining both side edges of a can body blank obtained by cutting a surface-treated steel sheet for a can into strips. There is known a welded can body in which a separately manufactured can lid is double-wrapped around both ends of the can body. In the welded can body, in order to avoid that the flavor of the content is changed due to corrosion of the base metal or the eluted metal component due to contact between the content and the surface-treated steel sheet for the can, which is the base metal, the inner side of the can. Is coated with a paint such as an epoxy-phenol resin, and the outer surface of the can is coated with a paint for imparting aesthetic appeal.

Conventionally, the above-mentioned welded can body has been manufactured by baking with a heating oven every time the coating is performed on the inner and outer surfaces of the surface-treated steel sheet for cans. In the manufacturing method, the working environment tends to be harmed by the heat of the heating oven and the volatile organic solvent. In particular, on the outer surface side where multicolor printing is performed, baking by the heating oven is performed every time coating of 2 to 4 colors is performed. Therefore, the above tendency becomes stronger.

Accordingly, studies have been made to form a protective coating layer by coating the inner and outer surfaces of the surface-treated steel sheet for cans with a polyester film. According to this configuration, the corrosion of the surface-treated steel sheet can be prevented on the inner surface of the can, and in the can body in which the inner surface protective coating is applied and baked on the inner surface of the can, the component slightly elutes from the coating film. The flavor of the changing contents can be protected. In addition, by coating with a printed polyester film on the outer surface side of the can, it is possible to impart aesthetics and perform a required display without depending on painting. Therefore, by coating the inner and outer surfaces of the surface-treated steel sheet for cans with a polyester film to form a protective coating layer, the painting and baking steps in the conventional production method are not required, and it is expected to improve the working environment.

In order to cover the inner and outer surfaces of the surface-treated steel sheet for a can with a polyester film, a method of bonding the polyester film to a heated metal by pressing is considered.

[0006] However, it is not possible to obtain a sufficient adhesive force to the conventionally used surface-treated steel sheet for cans by simply pressing the polyester film for a short time under heating. Also, in order to bond the polyester film to the surface-treated steel sheet for a can through a normal thermosetting resin-based adhesive, there is a disadvantage that long-time heating at a high temperature is required to obtain a sufficient adhesive force. is there.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is possible to sufficiently heat a can body and a metal plate for forming a can body by heating at a high temperature for a short time. It is an object of the present invention to provide a polyester film for covering a can body material capable of obtaining a strong adhesive force and a method for producing the same.

Further, the present invention provides a polyester film capable of sharpening the printing on a can body formed from the metal plate when the polyester film is printed, and a method for producing the same. The purpose is to:

[0009]

In order to achieve the above object, a polyester film for covering a can body material according to the present invention comprises:
A polyester film which is heat-bonded to a metal plate for forming a can body of a can body via a thermosetting resin-based adhesive to form a protective coating layer, and a polyester resin and an aminoplast resin are formed on one surface of the polyester film. And 70/30
It is characterized in that an adhesive layer made of a resin containing at a weight ratio of up to 90/10 is provided.

The adhesive layer is made of the polyester resin 9
The amount of the aminoplast resin is 1 to 0 parts by weight.
If the amount is less than 0 parts by weight, it takes a long time to cure the adhesive layer even when heated at a high temperature, and if the amount of the aminoplast resin is more than 30 parts by weight with respect to 70 parts by weight of the polyester resin, the curing is performed. Undesirably progresses and the workability of the adhesive layer is reduced. As the polyester resin, a known polyester resin may be used alone,
An epoxy-modified polyester resin modified with an epoxy resin or the like may be used. As the aminoplast resin, a melamine resin, a benzoguanamine resin or the like can be used. In addition, the adhesive layer may use an epoxy resin together with the polyester resin and the aminoplast resin.

The polyester film is excellent in suitability for contents such as strength, transparency, and retention of flavor. What is required is a polyester obtained by polycondensation of a dicarboxylic acid component and a diol component. May be a polyester obtained by polycondensation of an aromatic dicarboxylic acid such as naphthalenedicarboxylic acid, terephthalic acid, or isophthalic acid, and a diol such as ethylene glycol, propylene glycol, or butylene glycol. Particularly preferred is a polyester obtained by polycondensation of naphthalenedicarboxylic acid and ethylene glycol (polyethylene naphthalate) or a polyester obtained by polycondensation of terephthalic acid and ethylene glycol (polyethylene terephthalate).

The polyester may contain another dicarboxylic acid component or diol component in the dicarboxylic acid component or diol component, if desired. Other preferable polyesters other than polyethylene terephthalate include JP-A-51-42786 and JP-A-64-70.
And polyesters described in JP-A No. 352 and JP-A-2-242738.

It is preferable that the surface of the polyester film to which the adhesive is applied is previously subjected to a surface oxidation treatment such as corona discharge or the like in order to improve the adhesive strength.

[0014] The polyester film is 5 to 5
Preferably, it has a thickness in the range of 0 μm. When the thickness of the polyester film is 5 μm or less, the polyester film is easily damaged during processing, pinholes and the like are generated, and the effect of preventing corrosion of the can and elution of metal may not be sufficiently obtained. Further, when the thickness is 50 μm or more, the residual stress becomes large, and the adhesion of the polyester film to the metal plate tends to decrease when a drawing process such as a neck-in process is performed on the can body.

Since the polyester film is heat-bonded to the metal plate for forming the can body of the can via the adhesive layer, the physical properties of the material are set to 150 ° C. in order to secure dimensional stability against heat treatment. A biaxially stretched polyester film having a heat shrinkage in the longitudinal direction of 1.2% or less and a heat shrinkage in the width direction of 0% when held for 30 minutes is preferable. Further, in order to secure the dimensional stability, heat treatment may be performed in advance at 160 ° C. for about 6 seconds, but a thermosetting resin is particularly formed on the side opposite to the surface on which the adhesive layer is provided. Preferably, a cured overcoat layer is provided. By providing the cured overcoat layer, the residual stress of the polyester film is reduced, the expansion and contraction of the film is regulated, the dimensional stability is secured, and the scratch resistance is improved. In the case of welding cans, after filling the contents, heat sterilization (retort sterilization)
Is usually carried out, but by providing the cured overcoat layer, it is possible to prevent the low polymerization degree component (oligomer) in the polyester film from being deposited on the surface during heat treatment such as retort sterilization treatment. , Improves the slipperiness.

The thermosetting resin forming the cured overcoat layer is preferably a resin capable of forming a cured film at high temperature and in a short time. For example, the thermosetting resin is composed of an epoxy resin and an aminoplast resin and is used as a short-time curing catalyst. Those containing an acid or an inorganic acid such as phosphoric acid or polyphosphoric acid are suitable. It is preferable that silicon or wax is added to the thermosetting resin in order to prevent oligomer precipitation and improve slipperiness.

When the polyester film is coated on the outer surface of the can of the metal plate, the polyester film may be printed so as to impart aesthetics to the can or to perform a required display. In such cases, strength for printing and dimensional stability against heat treatment when bonded to the metal plate are required, so that a heat-resistant polyester film such as polyethylene naphthalate, a uniaxially or biaxially stretched polyethylene terephthalate film Are preferred.

When printing is performed on the polyester film, a printing layer made of a resin composition containing a pigment is provided between the polyester film and the adhesive layer. The printing layer may be provided between the polyester film and the overcoat layer, but by being provided between the polyester film and the adhesive layer as described above, the printing layer is formed of a polyester film. It is preferred because it is protected from trauma. When performing multicolor printing for aesthetics and required display, the printing layer is formed by laminating the resin composition one color for each color of the pigment.

When the printing layer is subjected to the retort sterilization treatment after forming the welding can body and filling the contents, a whitened portion may be formed and the printing may become unclear. Therefore,
In order to prevent whitening due to the retort sterilization treatment, a size coat layer made of a resin composition obtained by removing the pigment from the resin composition forming the print layer is provided between the print layer and the adhesive layer. .

The resin composition for forming the printing layer forms an adhesive layer by heating at a high temperature for a short time to obtain a sufficient adhesive strength between the can body and the metal plate for forming the can body. It is preferable that the resin is selectively used depending on the type of the resin. That is, when the adhesive layer is made of a resin containing the polyester resin and the aminoplast resin in the weight ratio,
As the resin composition for forming the print layer, a resin composition comprising a polyester polyurethane resin and a polyisocyanate resin and containing a pigment is suitable.

The resin forming the adhesive layer preferably contains an inorganic or organic pigment for concealing the base of the metal plate, and titanium oxide is particularly preferred as the pigment. The titanium oxide has a weight ratio of 2 to the resin.
It is used in the range of 0/80 to 80/20.

When the polyester film covers the inner surface of the can of the metal plate, the polyester film may be plain, and there is no need for a cured overcoat layer and printing. In this case,
Since the strength, dimensional stability and the like are not strictly required, the polyester film may be a non-stretched polyester film, or may be a uniaxially or biaxially stretched polyester film. Polyethylene terephthalate film is suitable from the viewpoint of can quality when it becomes a body.

The polyester film for covering a can body material provided with the adhesive layer, the printing layer, and the cured overcoat layer is formed by applying a thermosetting resin to one surface of the polyester film and drying the cured overcoat. An overcoat layer forming step of forming a layer, a printing step of applying a resin composition containing a pigment to the other surface of the polyester film, and drying to form a printed layer, and forming a printed layer on the surface on which the printed layer is provided. An adhesive layer forming step of applying and drying a thermosetting resin-based adhesive to form an adhesive layer can be advantageously performed.

Either the overcoat layer forming step or the printing step may be performed first, but from the viewpoint of ensuring dimensional stability, the overcoat layer forming step is performed prior to the printing step.

When the size coat layer is formed between the printing layer and the adhesive layer, the manufacturing method includes the step of removing the pigment from the resin composition forming the printing layer following the printing step. A size coat layer forming step of forming a size coat layer by applying and drying the composition.

In the above-mentioned manufacturing method, each of the overcoat layer, print layer, size coat layer and adhesive layer is formed by gravure printing or coating.

[0027]

The polyester film for coating a can body material of the present invention comprises a polyester resin, an aminoplast resin and 70/3.
Since an adhesive layer made of a resin containing a weight ratio of 0 to 90/10 is provided, when the polyester film is bonded to the metal plate for forming the can body of the can body, it is heated at a high temperature for a short time. And a strong adhesive force can be obtained.

The polyester film for coating a can body material of the present invention has a cured overcoat layer made of a thermosetting resin provided on the side opposite to the surface on which the adhesive layer is provided, so that the When the polyester film is heat-bonded to the metal plate for forming the can body via the adhesive layer, the residual stress of the polyester film is reduced and expansion and contraction are regulated, so that dimensional stability against heat treatment is ensured. Further, by the cured overcoat layer, during the heating treatment such as retort sterilization treatment after filling the contents of the can body, precipitation of oligomers in the polyester film on the can surface, scratches on the film surface are prevented, and Slipperiness is improved.

In the polyester film for covering a can body material of the present invention, a printing layer made of a resin composition containing a pigment is provided between the polyester film and the adhesive layer, and is adhered by heating to the metal plate. Thereby, it is possible to impart aesthetics to the can body or perform a required display without depending on the coating printing. When the printing layer is provided, further, between the printing layer and the adhesive layer, by providing a size coat layer made of a resin composition obtained by removing the pigment from the resin composition forming the printing layer During the retort sterilization treatment after filling the contents in the can body, whitening of the printing layer is prevented, and the printing layer becomes clear.

As the printing ink used for forming the printing layer, conventionally known printing inks can be used. Examples of resin components include polyurethane resin, polyester polyurethane resin, epoxy resin, epoxy butyral resin, vinyl resin, and cellulose resin. And a resin composed of at least one of a polyisocyanate resin and a polyisocyanate resin.

The resin composition for forming the printing layer is obtained by using a resin composition comprising a polyester polyurethane resin and a polyisocyanate resin and containing a pigment.
When the polyester film is heat-bonded to the metal plate via the adhesive layer, a strong adhesive force can be similarly obtained by heating at a high temperature for a short time.

In the polyester film for covering a can body material of the present invention, the base material of the metal plate is concealed when the adhesive layer is heated and adhered to the metal plate because the adhesive layer contains titanium oxide as a pigment. The film surface becomes beautiful.
In particular, when the printing layer is provided, the printing is sharpened by using the adhesive layer containing the titanium oxide as a background.

According to the method for producing a polyester film for covering a can body material of the present invention, since the method includes the step of forming the overcoat layer, the residual stress of the polyester film is alleviated and the stretchability is regulated. The resulting polyester film has improved dimensional stability against heat treatment. The dimensional stability of the polyester film is further improved by performing the overcoat layer forming step prior to the printing step.

In the method for producing a polyester film for covering a can body material according to the present invention, after the printing step, a resin composition obtained by removing the pigment from the resin composition forming the print layer is applied and dried to form a size coat layer. By providing a size coat layer forming step of forming a polyester film, a polyester film that can prevent whitening of the printed layer due to retort sterilization treatment after can-making is obtained.

In the method for producing a polyester film for covering a can body material according to the present invention, each of the overcoat layer, the print layer, the size coat layer and the adhesive layer is formed by gravure printing and coating. It is formed to an even thickness.

[0036]

Embodiment 1 Next, the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory sectional view showing the structure of a polyester film for coating a can body material of the present invention, FIG. 2 is an explanatory sectional view showing the structure of a polyester film for covering a can body material coated on the inner surface side of a can, FIG. FIG. 4 is an explanatory cross-sectional view of a metal plate for forming a can body of a can body to which a polyester film for coating a can body material of the present invention is adhered by heating, and FIG. FIG. 5 is a plan view schematically showing a configuration example of a device for heating and bonding to a forming metal plate, and FIG. 5 is a side view of a transport path of the device in FIG.

In the present embodiment, the polyester film 1 for coating a can body material shown in FIG. 1 is used as the polyester film adhered to the outer surface of the can body forming metal plate. As shown in FIG. 1, the polyester film 1 is a biaxially stretched polyethylene terephthalate having a thickness of 12 μm (hereinafter, polyethylene terephthalate is abbreviated as PET).
A transparent cured overcoat layer 3 made of an epoxy resin and an aminoplast resin and made of a thermosetting resin to which a phosphoric acid catalyst is added is provided on one surface of the film 2, and a polyurethane polyester resin and a poly A printing layer 4 made of an isocyanate-based resin and printed with a printing ink containing a pigment is provided. The printing layer 4 is multicolor-printed in order to impart aesthetics to the outer surface of the can and to perform a required display, and is formed by laminating the printing inks containing pigments of the required colors for each color. I have.

A thermosetting resin-based adhesive layer 5a made of a resin containing a polyester resin and a melamine resin in a weight ratio of 85/15 is provided on the printing layer 4.

As the polyester film adhered to the inner surface of the can body forming metal plate, the polyester film 6 for coating the can body material shown in FIG. 2 is used. As shown in FIG. 2, the polyester film 6 is formed on a surface of a biaxially stretched PET film 2 having the same thickness as the polyester film 1 and having a thickness of 12 μm by a bisphenol-type epoxy resin obtained by a reaction between bisphenol and epichlorohydrin. An adhesive layer 5b made of a thermosetting resin-based adhesive containing an epoxy resin having a molecular weight of 10,000 and glycerol tristrimellitate anhydride as a trimellitic anhydride-based curing agent in a weight ratio of 95/5 is provided. The polyester film 6 is not printed and is plain, and the surface on which the adhesive layer 5b is provided has been subjected to corona discharge treatment in advance.

The polyester film 1a was manufactured as follows. First, a long biaxially stretched PET film 2 having one surface subjected to corona discharge treatment is drawn out, and a phosphoric acid catalyst made of an epoxy resin and an aminoplast resin is added to the surface not subjected to the corona discharge treatment. Solvent-based thermosetting resin was applied with a gravure roll,
The coating was dried at 60 ° C. for 8 seconds to form a cured overcoat layer 3 having a coating amount of 1.0 g / m ² , and was cooled to 50 ° C. or lower and wound up.

Next, a long biaxially stretched PET film 2 having the cured overcoat layer 3 formed thereon is pulled out, and a pigment made of a polyurethane polyester resin and a polyisocyanate resin is formed on the opposite surface of the cured overcoat layer 3. Was printed with a gravure roll and dried to form a print layer 4. The printing layer 4 is provided with a predetermined printing pattern for a single can body so as to impart aesthetics to the outer surface of the can and to perform a required display.
It is formed continuously in the longitudinal direction of the T film 2.

The printing layer 4 is formed so that the printing ink required for forming the printing pattern is printed for each color as described above, and the amount of applied ink is 1.0 g / m ² . After forming the printing layer 4, the long biaxially stretched PET film 2 was cooled, wound up, and aged for 2 days to cure the printing layer 4.

Next, the long two-sided printing paper on which the printing layer 4 is formed is formed.
Pull out the axially stretched PET film 2 and place it on the printed layer 4
Organic solution of the ester resin and melamine resin in the above weight ratio
Printing the resin solution dissolved in the agent with a gravure roll,
Dry and apply 2.0 g / m ^TwoThe thermosetting resin-based connection
After forming an adhesive layer 5a made of an adhesive and cooling, winding
Then, a polyester film 1 was obtained.

In the polyester film 1, the cured overcoat layer 3 is formed first, and then the print layer 4 is formed, so that the print pattern can be obtained with excellent dimensional accuracy.

The polyester film 6 was manufactured as follows. First, a long biaxially stretched PET film 2 similar to that used in the production of the polyester film 1 is drawn out, and one surface thereof is subjected to a corona discharge treatment,
A resin solution obtained by dissolving the epoxy resin and glycerol tristrimellitate anhydride in an organic solvent in the above-described weight ratio was applied thereon by gravure roll at a speed of 57 m / min. 1 so that the curing reaction of the adhesive does not proceed.
After drying at 20 ° C. for 10 seconds, the coating amount is 2.5 g / m ^2.
An adhesive layer 5b made of the above-mentioned thermosetting resin-based adhesive was formed, cooled, and wound up to obtain a polyester film 6.

Next, a welded can was manufactured using the polyester films 1 and 6. In the welding can body of this embodiment, FIG.
As shown, a polyester film 1 is heat-bonded to the outer surface of a can body forming metal plate 7 of a can body via an adhesive layer 5a to form a protective coating layer 9, and a polyester film is formed on the inner surface of the can. The film 6 is heat-bonded via the adhesive layer 5b to form the protective coating layer 10. In this embodiment, the metal plate 7 has a plate thickness of 0.22 mm and a nickel amount of 70 on the surface.
mg / m ² of nickel underlayer, on which a tin amount of 0.
Equipped with a tin layer of 8 g / m ² , the uppermost layer having a chromium content of 15
Using a tin-plated steel sheet further provided with a metallic chromium / chromium oxide layer of mg / m ^2, the above-mentioned heat bonding was carried out by the apparatus shown in FIGS.

In the above-described apparatus, first, as shown in FIG.
The strip-shaped metal plates 43 cut into a plurality of lengths of the can body blanks 42 are continuously supplied to a transport path 44.

As shown in the side view of FIG. 5, the transport path 44 is provided with a first heating means 45 such as a high-frequency heating device on the upstream side.
Is provided, and the strip-shaped metal plate 43 supplied to the transport path 44 is provided.
Is heated to 170 ° C. A printing film supply means 46 for supplying the long polyester film 1 printed as described above to the conveyance path 44 is provided below the conveyance path 44, and the plain and long printing film supply means 46 is provided above the conveyance path 44. A plain film supply means 47 for supplying the can inner surface coating film 6 to the transport path 44 is provided. The polyester films 1 and 6 produced as described above are wound after production, and are supplied to film supply means 46 and 4 respectively.
7 is provided.

The polyester films 1 and 6 are supplied to the transport path 44 by supply means 46 and 47 so as to contact the strip-shaped metal plate 43 on the side of the adhesive layers 5a and 5b. With the provided pressure roll 48, the strip-shaped metal plate 43 heated as described above is pressure-bonded to both surfaces of the strip-shaped metal plate 43 except for both side edges 49, 49, and is temporarily bonded via the adhesive layers 5a, 5b. . At this time, even if the polyester film 1 is wound around the supply means 46 as described above, the film does not stick to each other because the adhesive has good blocking resistance, and the cured overcoat layer 3 is further formed. As a result, the sliding property and the scratch resistance are good, and the sheet can be properly drawn from the supply means 46 and supplied to the transport path 44.

Since both of the polyester films 1 and 6 are long, the strip-shaped metal plate 43 is sandwiched between the temporarily bonded polyester films 1 and 6 and a plurality of the strips are connected in a long shape. Then, the strip-shaped metal plates 43 connected in a long shape are cut one by one by first cutting means 50 such as a knife cylinder provided at the end of the transport path 44.

Next, the strip-shaped metal plate 43 to which the polyester films 1 and 6 are temporarily bonded is discharged from the transport path 44 and supplied to a second heating means 51 such as a heating oven shown in FIG. The thermosetting resin-based adhesive of the adhesive layer 5a is cured by maintaining the temperature at 215 ° C. for 1 minute in the inside 51.
As a result, the polyester films 1 and 6 are completely adhered to the strip-shaped metal plate 43, and a strong adhesive force is obtained.

The strip-shaped metal plate 43 to which the polyester films 1 and 6 are adhered as described above is then cooled in a cooling means 52, and then supplied to a second cutting means 53 such as a slitter. It is cut for each can body blank 42. Since the cured overcoat layer 3 is formed on the polyester film 1 as described above, it is possible to maintain the dimensional accuracy of the initial printing even by heating during the temporary bonding or heating in the heating oven 51. it can. Therefore, the can body blank 42 can be cut in accordance with the print pattern of the print layer 4 accurately.

Next, the can body blank 42 obtained as described above is rounded with the printed polyester film 1 adhered to the outer surface of the can, and both side edges 49 are overlapped. The welded joint on the inner surface side of the can that was welded and not covered with the polyester film 6 was covered and corrected using an epoxyphenol resin-based correction paint to form a can body. Next, a neck-in process was applied to both ends of the can body, and an easy-open can lid having one end coated with an epoxy phenol resin on the inner surface side was double-tightened to produce a welded can body.

In the above welded cans, the adhesion of the polyester films 1 and 6 to the metal plate 7 was observed, and the enamel value of the cans was measured to determine the presence or absence of a metal exposed portion. Table 1 shows the results.

Next, the welded can body was filled with oolong tea as a content, and the open end of the welded can body was double-tightened with a can lid having a polyester film coated on the inner surface side of the can to heat sterilize. Processing (retort sterilization treatment) to produce canned, polyester film 1 after retort sterilization treatment
Was observed. In addition, the cans were stored at 37 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results.

[0056]

Example 2 The contents of the can obtained in Example 1 were
Filled with coffee, double-tightened a can lid coated with a polyester film on the inner side of the can at the open end of the welded can body and retort sterilized to produce a can, and the polyester after retort sterilized polyester The appearance of the film 1c was observed. In addition, the cans were stored at 37 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results.

[0057]

[Embodiment 3] In this embodiment, instead of the metal plate 7 of the embodiment 1, the thickness of chromium is 100 mg / m ^{2 on the} surface with a plate thickness of 0.22 mm.
Metal chromium underlayer with tin content of 0.2 g / m
² tin layer, and the uppermost layer is 12 mg / m ^{2 in} terms of chromium.
Polyester films 1 and 6 were heat-bonded to the thin tin-plated steel sheet in the same manner as in Example 1 except that a thin tin-plated steel sheet further provided with a metal chromium / chromium oxide layer was used.

Next, a can body was manufactured from the can body blank 42 in the same manner as in Example 1, the adhesion of the polyester films 1 and 6 to the thin tin plated steel sheet was observed, and the enamelizer value of the can body was observed. Was measured to determine the presence or absence of a metal exposed portion. Table 1 shows the results.

Next, a hot drink was filled into the can body as a content with a sports drink, and a can lid having a polyester film coated on the inner side of the can at the open end of the welded can body was double-tightened. A retort sterilization treatment was performed to produce a can, and the appearance of the polyester film 1 after the retort sterilization treatment was observed. In addition, the cans were stored at 37 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results.

[0060]

Embodiment 4 In this embodiment, instead of the metal plate 7 of Embodiment 1, a metal chromium base layer made of disc-like chromium having a plate thickness of 0.22 mm and a chromium amount of 60 mg / m ² and granular chromium is provided on the surface. In the same manner as in Example 1, except that a tin-free steel having a metal chromium / chromium oxide layer of 10 mg / m ^{2 in} terms of the amount of chromium was used, the polyester film 1 was added to the tin-free steel. 6 was adhered by heating.

When the tin-free steel is pressed against the welding electrode, the granular chromium is immersed in the base metal and the steel sheets are directly connected to each other. Therefore, regardless of the amount of tin on the surface of the base steel sheet. Can be welded.

Next, a can body was manufactured from the can body blank 42 in the same manner as in Example 1, the adhesion of the polyester films 1 and 6 to the tin-free steel was observed, and the enamelizer of the can body was observed. The value was measured to determine the presence or absence of a metal exposed portion. Table 1 shows the results.

Next, the can body was hot-packed with apple juice (juice 10%) as a content, and a can lid having a polyester film coated on the inner side of the can at the open end of the welded can body. The retort sterilization treatment was performed by double winding to produce a can, and the appearance of the polyester film 1 after the retort sterilization treatment was observed. In addition, 37
The container was stored at 6 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results.

[0064]

[Table 1]

The types of the surface-treated steel sheets described in Table 1 are as follows.

TNS is a nickel underlayer having a nickel amount of 70 mg / m ² , a tin layer having a tin amount of 0.8 g / m ² on the underlayer, and a metal layer having a chromium amount of 15 mg / m ^{2 on} the uppermost layer. It means a tin-plated steel sheet provided with a chromium / chromium oxide layer. The Cr / Sn system is a metal chromium underlayer having a chromium amount of 100 mg / m ² , a tin layer having a tin amount of 0.2 g / m ² on the underlayer, and a 12 mg / m ^{2 in} terms of chromium amount being formed on the uppermost layer. It means a thin tin plated steel sheet further provided with a metal chromium / chromium oxide layer. Board / granular chromium type means chromium content 60mg /
a metallic chromium underlayer made of a plate-like chromium and granular chromium m ^2, means a tin-free steel comprising a metallic chromium · chromium oxide layer of 10 mg / m ² of chromium amount in terms on the underlayer.

The curing agent in the adhesive section means glycerol tristrimellitate anhydride, and ERV is an abbreviation for enamel value.

From Table 1, it is clear that the polyester film for coating the can body material of the present invention is firmly adhered to the metal plate for forming the can body of the can body by heating at a high temperature for a short time. It is clear from the measured values that there is no exposed metal portion on the metal plate to which the polyester film is adhered.

As shown in Table 1, according to the polyester film for coating the can body material of the present invention, no abnormalities such as whitening were observed in the appearance even after the retort sterilization treatment, and the printing became clear. it is obvious. The whitening prevention effect is particularly remarkable when a size coat layer is provided. Further, when the adhesive layer 5a contains a white pigment of titanium oxide, the white adhesive layer 5a conceals the base of the metal plate 7, so that printing becomes clearer.

Further, from Table 1, according to the polyester film for coating the can body material of the present invention, the amount of iron eluted to the contents is extremely small, the adhesive strength is maintained even after long-term storage, and the can It is clear that corrosion of the metal plate for forming the body and change in the flavor of the contents can be prevented.

Further, from Table 1, it is apparent that the polyester film for coating the can body material of the present invention is firmly bonded irrespective of the type of the metal plate for forming the can body of the can body.

[0072]

As is apparent from the above, according to the polyester film for covering a can body material of the present invention, the polyester resin and the aminoplast resin are coated on one surface with a weight of 70/30 to 90/10. Since the adhesive layer made of the resin containing in the ratio is provided, the blocking resistance of the adhesive layer is good, and when the adhesive layer is adhered to the metal plate for forming the can body of the can body via the adhesive layer. A strong adhesive force can be obtained by heating at a high temperature for a short time. Since the polyester film for coating a can body material of the present invention is provided with a cured overcoat layer made of a thermosetting resin on the side opposite to the surface on which the adhesive layer is provided, the heat treatment at the time of the heat bonding is performed. In addition to being excellent in dimensional stability, precipitation of oligomers can be prevented, and scratch resistance and slipperiness of can materials and can bodies are improved.

The polyester film for covering a can body material of the present invention is provided with a printing layer made of a resin composition containing a pigment between the polyester film and the adhesive layer, and is adhered by heating to the metal plate. Thus, it is possible to impart aesthetics to the can body or perform a required display without depending on the painting. When the printing layer is provided, further,
Between the printing layer and the adhesive layer, by providing a size coat layer made of a resin composition obtained by removing the pigment from the resin composition forming the print layer, the can was filled with the contents. During the retort sterilization treatment, whitening of the printing layer can be prevented, and the sharpness of the printing layer can be maintained.

In the polyester film for coating a can body material of the present invention, the resin composition for forming the printing layer comprises a resin composition comprising a polyester polyurethane resin and a polyisocyanate resin and containing a pigment.
A strong adhesive force can be obtained by heating at a high temperature for a short time between the polyester film and the metal plate.

In the polyester film for coating a can body material of the present invention, since the adhesive layer contains titanium oxide as a pigment, the base material of the metal plate is concealed when heated and bonded to the metal plate. The film surface becomes beautiful.
In particular, when the printing layer is provided, the printing can be further sharpened by using the adhesive layer containing the titanium oxide as a background.

According to the method for producing a polyester film for covering a can body material of the present invention, since the overcoat layer forming step is provided, it is possible to obtain a polyester film having excellent dimensional stability against heat treatment in a subsequent step. it can. The dimensional stability of the polyester film can be further improved by performing the overcoat layer forming step prior to the printing step.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a configuration of a polyester film for coating a can body material of the present invention.

FIG. 2 is an explanatory sectional view showing a structure of a polyester film for coating a can body material coated on the inner surface side of the can.

FIG. 3 is an explanatory cross-sectional view of a metal plate for forming a can body of a can body to which a polyester film for coating a can body material according to the present invention is adhered by heating.

FIG. 4 is a plan view schematically showing a configuration example of an apparatus for heating and bonding the polyester film for coating a can body material of the present invention to a metal plate for forming a can body of a can body.

FIG. 5 is a side view of a transport path of the apparatus of FIG.

[Explanation of symbols]

2 ... polyester film, 4 ... printing ink, 5a ...
Thermosetting resin-based adhesive, 7 ... metal plate for forming a can body of a can body,
9 ... Protective coating layer.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B65D 8/16 C08J 5/12 CFD C08J 5/12 CFD C08L 67:00 // C08L 67:00 B65D 1 / 00 B (72) Inventor Hideyuki Yoshizawa 839-1 Shikamuro, Iwatsuki City, Saitama Prefecture Inside the Technical Headquarters of the Hokkai Seikan Co., Ltd. (72) Inventor Koji Matsushima 839-1 Shikamuro, Iwatsuki-shi, Saitama F-term (reference) 3E033 AA06 BA07 BA17 BB01 BB08 CA20 EA09 EA10 3E061 AA16 AB04 AB21 AC09 BA02 BB07 DB04 DB08 4F071 AA43 ABB CA01 CC02 CD07 4F100 AA21B AB01A AB03A AK01C AK01G AK35G AK41B AK41D AK41E AK41G AK42 AK51B AK51E AK53G AL01B AL01E AL05B AL05G BA04 BA05 BA07 BA10C BA10D CA13B CB00B CB00D CB00E EA011 EC012 EJ083 EJ182 EJ303 EJ38 EJ422 EJ423 EJ503 GB16 GB23 HB31B JB13B JB13C JL11

Claims (10)

[Claims] 1. A polyester film which is heat-bonded to a metal plate for forming a can body of a can body via a thermosetting resin-based adhesive to form a protective coating layer, wherein the polyester film has a polyester film on one surface. A polyester film for covering a can body material, comprising an adhesive layer made of a resin containing a resin and an aminoplast resin in a weight ratio of 70/30 to 90/10. 2. The can body according to claim 1, wherein a cured overcoat layer made of a thermosetting resin is provided on a side of the polyester film opposite to a surface on which the adhesive layer is provided. Polyester film for material coating. 3. The polyester film for coating a can body material according to claim 1, wherein a printing layer made of a resin composition containing a pigment is provided between the polyester film and the adhesive layer. 4. A size coat layer comprising a resin composition obtained by removing a pigment from a resin composition forming the print layer, is provided between the print layer and the adhesive layer. The polyester film for coating a can body material according to claim 1. 5. The polyester film for coating a can body material according to claim 1, wherein the resin composition for forming the printing layer comprises a polyester polyurethane resin and a polyisocyanate resin and contains a pigment. 6. The polyester film for coating a can body material according to claim 1, wherein the adhesive layer contains titanium oxide as a pigment. 7. A protective cover layer is formed by heating and bonding to a metal plate for forming a can body of a can body via a thermosetting resin-based adhesive, and a polyester resin and an aminoplast resin are formed on one surface of the can body. A method for producing a polyester film for coating a can body material provided with an adhesive layer made of a resin containing the resin in a weight ratio of 30/90 to 90/10, wherein a thermosetting resin is applied to one surface of the polyester film. An overcoat layer forming step of drying to form a cured overcoat layer; a printing step of applying a resin composition containing a pigment to the other surface of the polyester film and drying to form a print layer; Applying a thermosetting resin-based adhesive to the surface provided with the resin, and drying the same to form an adhesive layer. Manufacturing method. 8. The method for producing a polyester film for coating a can body material according to claim 7, wherein the overcoat layer forming step is performed prior to the printing step. 9. A method according to claim 9, further comprising a step of forming a size coat layer by applying and drying a resin composition obtained by removing a pigment from the resin composition forming the print layer, following the printing step. The method for producing a polyester film for coating a can body material according to claim 7, characterized in that: 10. The can according to claim 7, wherein each of the overcoat layer, print layer, size coat layer and adhesive layer is formed by gravure printing or coating. A method for producing a polyester film for covering a body material.