JP3298712B2 - Polyester film for 3-piece can coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyester film for coating three-piece cans.

[0002]

2. Description of the Related Art In recent years, there has been an increasing number of cases in which a thermoplastic resin film is coated on a metal plate and used as a material for a metal can. With a conventional metal plate coated with a thermosetting resin paint and baked and cured, it is difficult to completely eliminate metal exposure due to pinholes even if the amount of paint applied is large or double coating is performed. On the other hand, in the case of a coated metal plate coated with a thermoplastic resin, the metal exposure can be almost completely eliminated. In the case of painted boards, a large amount of solvent is used for coating and drying and baking,
This is because a printed layer can be provided by laminating a coating film that has been printed in advance. As a thermoplastic resin used for these coatings, a polyester excellent in heat resistance, workability, gas barrier properties and the like is generally used.

[0003] Polyethylene terephthalate, which is widely used as a raw material for plastic containers and stretched films, has excellent heat resistance, processability, gas barrier properties, and the like as a thermoplastic resin for metal coating. It is also used as a structure for beverage containers. However, when used by coating on a metal can, P
Unlike the case of an ET bottle or the like, it may be placed under high pressure and high temperature for the purpose of sterilization or the like in a state of being in contact with the liquid content which is substantially water. In this case, there is a possibility that the so-called retort-treated form is obtained and low-molecular-weight substances such as oligomers and aldehydes are extracted into the liquid content and come out, and the flavor of the filled content may be impaired. Yes, it was not preferable in terms of hygiene.

[0004]

The present invention has been made as a result of investigations to solve such problems. That is, the gist of the present invention is to laminate and coat a metal with an adhesive.
The terminal carboxyl group concentration after the can is made is 50 equivalent / t
Less than 2.0 μg per 1 cm ^{2 of} coated surface of low-molecular-weight substances extracted by retort treatment with pure water at 125 ° C. for 1 hour after lamination coating and can-making on metal with an adhesive And a polyester film for coating three-piece cans.

Hereinafter, the present invention will be described in detail. The three-piece can referred to in the present invention refers to a can body in which an exposed metal portion welded and joined is fused and coated with a coating film without using an adhesive or the like, for example, by a method described in JP-A-5-69485. The can lid and the can bottom are configured such that the side of the film-coated steel sheet that comes into contact with the contents becomes the coating layer. Examples of the metal plate used for such a purpose include a surface-treated steel plate and a light metal plate such as aluminum. In the case of a surface-treated steel sheet, a steel sheet coated with tin which has been passivated by a general chromium treatment, or plated with nickel or zinc may be used. In particular, electrolytic chromium-coated steel having two layers of chromium metal and chromium oxide is suitable. In the case of aluminum, pure aluminum may be used,
An alloy containing a small amount of manganese, magnesium, zinc, copper or the like may be used. Further, both pure aluminum and aluminum alloy may be subjected to chromic acid treatment or chromic acid / phosphoric acid treatment.

The polyester referred to in the present invention is an aromatic dicarboxylic acid or an ester-forming derivative thereof as a bifunctional acid component, specifically, terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, sebacic acid,
Adipic acid or one or more ester-forming derivatives thereof, and ethylene glycol, diethylene glycol, triethylene glycol, 1,3-
Propanediol, 1,4-butanediol, 1,4-
A polyester composed of one or more kinds such as cyclohexanedimethanol is preferred. Representative polyesters include polyethylene terephthalate and its copolymer, polyethylene 2,6-naphthalenedicarboxylate and its copolymer, polycyclohexane dimethylene terephthalate and its copolymer, and the like.

The polyester film of the present invention is usually made of the above-mentioned polyester, has been subjected to biaxial stretching or heat setting, and has a degree of plane orientation (ΔP) of at least 0.10.
0 to 0.200, more preferably 0.110 to 0.190, particularly preferably 0.130 to 0.180, and the crystallinity Δc
Is preferably at least 30 to 70%, more preferably 35 to 60%, particularly preferably 40 to 60%. If ΔP is less than 0.100, there is a tendency that sufficient gas barrier properties cannot be obtained. Similarly, when Δc is less than 30%, sufficient gas barrier properties tend not to be obtained. ΔP is 0.200
When the value exceeds χc or exceeds 70%, the rigidity of the film becomes too high, and after laminating on a metal plate, the film may peel off from the metal plate when forming and canning, or the film may crack. In some cases, the dent resistance after the metal can is reduced.

The polyester film of the present invention usually has a large number of surface protrusions formed by nuclei of a filler contained in the film, and has a dynamic friction coefficient μd of 0.02.
0.50, more preferably 0.05 to 0.45, especially 0.07
~ 0.40 is preferred. When μd is less than 0.02, the unevenness of the surface tends to increase, and the appearance may be impaired. When μd exceeds 0.50, blocking tends to occur when the portions coated with the film come into contact with each other in the can making process.

The most important features of the polyester film of the present invention are that the terminal carboxyl group concentration is low when the metal can is coated with a laminate, and the amount of low molecular weight substances extracted by immersion in water or ethanol aqueous solution and heating is extremely small. It is. That is, the concentration of terminal carboxyl groups after laminating and canning the metal with an adhesive is less than 50 equivalents / t, preferably less than 40 equivalents / t, and more preferably 3 equivalents.
It is less than 0 equivalent / t. Terminal carboxyl group concentration of 50
When the equivalent weight / t is exceeded, the number of terminal carboxyl groups which are the starting points of thermal degradation decomposition becomes too large, and if heated after coating cans, low molecular weight substances are newly generated, which is not preferable. After laminating and canning the metal with an adhesive and then subjecting it to retort treatment with pure water at 125 ° C. for 1 hour, a low-molecular-weight substance extracted from the polyester-coated metal is 1 cm ^2.
The amount is 2.0 μg or less, preferably 1.5 μg or less, more preferably 1.0 μg or less. The low molecular weight substance extracted by such retort treatment is polyester coated metal 1
If it exceeds 2.0 μg per cm ² , the flavor of the filled contents is impaired when heated for the purpose of sterilization or the like, which is not preferable in terms of hygiene.

[0010] As a method for reducing the amount of low molecular weight substances extracted by retort treatment, 1) a polyester film is composed of a polyester in which the amount of low molecular weight substances is reduced by solid phase polymerization during polycondensation; The polyester resin obtained in this way is preliminarily subjected to immersion treatment with hot water to constitute a polyester film from a polyester in which the amount of low molecular weight substances is reduced. 3) The polyester film obtained by a conventional method is subjected to a warm water immersion treatment to reduce Examples of the method include a method of reducing the amount of a molecular weight substance, and these methods are used alone or in combination of two or more to obtain the polyester film of the present invention. Further, each method will be described with reference to actual examples. The method of reducing low molecular weight substances by solid state polymerization is
In the production of ordinary polyester, where the polymerization is performed until the intrinsic viscosity [η] becomes 0.60 or more,
The polymerization is stopped at 0.40 to 0.50, and the obtained resin is heated at 240 ° C. for 10 hours under a high vacuum of 0.3 mmHg.

A method of preliminarily immersing the polyester in hot water to reduce the amount of low molecular weight substances is carried out by bringing the polyester into contact with water, steam, steam-containing inert gas, steam-containing air, or the like. The polyester is exposed to water at room temperature to 150 ° C. for 1 minute to 100 hours or longer, preferably 1 minute to 20 hours, more preferably 5 minutes to 20 hours.
It is performed by soaking for minutes to 10 hours. Preferably, the polyester is placed in hot water at 50 to 150 ° C. for 1 minute to 1 hour.
This is performed by immersing for 0 hour. More desirably, the polyester is immersed in hot water at 70 to 110 ° C for 3 minutes to 5 hours. Particularly preferably, it is carried out by immersing the polyester in hot water at 80 to 100 ° C for 5 minutes to 3 hours.

The contact of the polyester with steam or steam-containing gas or steam-containing air is usually carried out at room temperature to 150 ° C., preferably 50 to 150 ° C., more preferably 70 to 110 ° C. Alternatively, it is carried out by supplying steam-containing air, preferably in an amount of 0.5 g or more per 1 kg of polyester, or by bringing polyester into contact with steam in the presence thereof. The contact between the polyester and water vapor is usually performed for 1 minute to 50 hours, preferably 5 minutes to 10 hours. The method of reducing the intrinsic content of low molecular weight substances by subjecting the polyester film to hot water immersion is in accordance with the above-described hot water immersion applied to the polyester resin. Although the polyester film of the present invention is produced according to a conventional method,
An example is shown below.

First, a substantially amorphous sheet is obtained from a raw material polyester by a melt extrusion method. At this time, in order to suppress an increase in the content of low molecular weight substances due to thermal degradation, at least 3
Melt extrusion is performed at a melting temperature of 00 ° C or less, preferably 290 ° C or less, more preferably 280 ° C or less, with a residence time of at most 15 minutes, preferably 10 minutes, and more preferably 5 minutes. The obtained amorphous sheet was subjected to a glass transition point of polyester to 160 using a roll stretching machine.
Stretch in the machine direction at a temperature of ° C. The obtained uniaxially stretched film is coated with a coating liquid for improving various printing properties. Further, using a tenter stretching machine, the coating solution is dried at a temperature of longitudinal stretching temperature to 170 ° C. and stretched in the transverse direction while performing crosslinking polymerization.
Subsequently, heat treatment is performed at a temperature of 100 to 240 ° C. in a tenter to obtain a biaxially stretched film. If necessary, further longitudinal stretching using a roll stretching machine and a tenter stretching machine, respectively.
Re-lateral stretching is performed.

An example of a method for producing a three-piece can covered with the polyester film of the present invention will be described. Three-piece cans are roughly classified into solder cans, adhesive cans, and welded cans depending on the method of joining the can bodies. The polyester film of the present invention is particularly suitable for adhesive cans and welded cans. The adhesive can has been used in general cans for a long time, and is a method of injecting a molten adhesive into a bent portion. Examples of the method for producing a welding can include a conoweld method and a pseudoronic weld method. The former is based on TFS (Tin Free St).
eel) A method in which the chromium film on the surface is peeled off, and the steel base material is welded by a roll electrode. The latter is intended for tinplate, and is a method of welding using a copper wire as an intermediate electrode between a roll electrode and a tinplate without polishing the welding end face of the blank.

First, a polyester-coated steel sheet constituting a three-piece can is manufactured. The polyester film of the present invention is pressure-bonded to both surfaces of a chromium surface-treated steel plate, a tin-plated steel plate or an aluminum plate using various adhesives, for example, an epoxy resin adhesive. At this time, the steel plate for forming the can body may be coated with the film of the present invention on which various printings have been performed in advance. Polyester-coated chromium surface-treated steel sheet and tin-plated steel sheet are used as raw materials for can bodies and can bottoms, and aluminum sheets coated with polyester are used as raw materials for can lids. In any case, cut out to appropriate shape 3
Used as a component of a piece can. First, the coated steel sheet for a can body is rolled into a cylindrical shape, and a can body is formed by the above-described joining method.
A can bottom coated steel plate is attached to the can body. A rubber-based sealing compound is applied as a sealing material to the wrapped edge of the can body and dried, and the can bottom is double-wrapped. Normally, the molded body obtained in this way is filled with contents such as juice, and then a polyester-coated aluminum plate for a can lid is wound up into a three-piece can in the same manner as the can bottom.

[0016]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the scope of the invention. In addition, the evaluation method in an Example is as follows. In Examples and Comparative Examples, “parts” means “parts by weight”. (1) Intrinsic viscosity [η] 1 g of the polymer was phenol / tetrachloroethane = 50
/ 50 (weight ratio) in 100 ml of a mixed solvent.
It was measured at 0 ° C.

(2) Low molecular weight extract amount (μg / cm 2) The sample film was pressure-bonded to a chrome-plated steel sheet having a thickness of 0.30 mm using an epoxy resin adhesive to obtain a polyester-coated steel sheet. However, only one side of the steel sheet was covered with the resin. Japanese Patent Application Laid-Open (JP-A) No. 5-69, with the surface coated with polyester facing inside.
According to the method disclosed in Japanese Patent No. 485, a 350 ml juice can body is produced in which the exposed metal portion welded and joined is coated with a coating film without using an adhesive or the like. A can lid and a can bottom were manufactured such that the side in contact with the contents became a coating layer. A three-piece can consisting of the can body, can lid, and can bottom was manufactured, and 300 ml of pure water was sealed therein. The three-piece polyester-coated can is heated to 125 ° C. and retorted for 1 hour. The water after the retort treatment was collected, and the mass M (μg) of the nonvolatile matter obtained by distilling off the water was measured.
The value M / S (μg / cm ² ) divided by the internal surface area S (cm ² ) of the used three-piece sample can is defined as the amount of low molecular weight extract.

(3) Extraction Appearance Water after retort treatment was collected, and a Tyndall phenomenon was observed using a xenon lamp as a light source, and ranked according to the following criteria. ：: No turbidity of the optical path was observed immediately after the retort and one week after standing. ○: No turbidity of the optical path was observed immediately after the retort. : Tintal phenomenon is observed. △: Immediately after retort, it is transparent under the amount of indoor light,
The Tyndall phenomenon is observed in the xenon light path, and suspended matter in the water is observed with the naked eye even under indoor light after standing for one week. ×: Underwater with the naked eye under indoor light both immediately after retort and after standing for one week. Suspension is observed

(4) Terminal carboxyl group concentration (equivalent /
t) Makromol. chem. , 26, 226 (195
A. 8). Measured according to the method of Conix. (5) Plane orientation degree (ΔP) Using an Abbe refractometer manufactured by Atago Optical Co., the maximum value a and the minimum value b of the refractive index in the film surface and the refractive index c in the film thickness direction were measured. Was used to calculate the plane orientation. The measurement of the refractive index was performed at 23 ° C.
The test was performed in an atmosphere of 0 RH%. ΔP = (a + b) / 2−c

(6) Crystallinity Δc (%) A mixture of n-heptane and carbon tetrachloride, a standard density float is inserted between the density gradients having a density gradient, and the sample The density ρ of the sample depending on the position
And Substituting the obtained density ρ into the following equation, the crystallinity χc
I got

Χc = (ρ−1.335) × 100 / (1.4)
55-1.335) (7) Dynamic friction coefficient μd Two films cut to a width of 15 mm and a length of 150 mm are stacked on a smooth glass plate, a rubber plate is placed thereon, and a load is further placed thereon. With the contact pressure of the two films being 2 g / cm ² , the frictional force was measured by sliding the films at 20 mm / min, the frictional force was divided by the contact pressure, and then the frictional force was divided by the contact area. And The coefficient of friction at the point of sliding by 5 mm was defined as the dynamic friction coefficient μd.

Example 1 [Production of Polyester] (Polyester a) 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.1 part of calcium acetate monohydrate were placed in a reactor, and a transesterification reaction was carried out.
That is, the reaction start temperature was set to 170 ° C., and the reaction temperature was gradually increased with the distillation of methanol.
The temperature was raised to 0 ° C., thereby substantially terminating the transesterification reaction. Next, an ethylene glycol slurry containing amorphous silicon oxide having an average particle diameter of 3 μm and 0.04 part of phosphoric acid were added, and then 0.04 part of antimony trioxide was added, and a polycondensation reaction was performed by a conventional method. That is, the temperature was gradually increased and the pressure was gradually decreased, and after 2 hours, the temperature was 280.
The temperature and the pressure were set to 0.3 mmHg, and the reaction was stopped after 2 hours, to obtain a polyester containing 0.05 part of silicon oxide and having an intrinsic viscosity of 0.62.

(Polyester b) 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.1 part of calcium acetate monohydrate were placed in a reactor, and a transesterification reaction was carried out. That is, the reaction start temperature was set to 170 ° C., and the reaction temperature was gradually increased with the distillation of methanol. After 4 hours, the temperature was raised to 230 ° C. to substantially end the transesterification reaction. Next, an ethylene glycol slurry containing amorphous silicon oxide having an average particle size of 3 μm and phosphoric acid 0.1 g.
After adding 07 parts, 0.04 part of antimony trioxide was added, and a polycondensation reaction was performed by a conventional method. That is, the temperature was gradually increased and the pressure was gradually decreased. After 2 hours, the temperature was 280 ° C., the pressure was 0.3 mmHg, and the reaction was stopped after 1 hour, and 0.05 parts of silicon oxide was contained. A polyester having an intrinsic viscosity of 0.45 was obtained.
This polyester was further subjected to solid-state polymerization at 225 ° C. and 0.3 mmHg for 10 hours to obtain a polyester having an intrinsic viscosity [η] of 0.75.

(Polyester c) Polyester a is put into a pressure vessel containing pure water, the internal temperature is controlled at 90 ° C., and the immersion treatment is performed for 4 hours. I got

(Polyester d) Polyester b is placed in a pressure vessel containing pure water, the internal temperature is controlled at 90 ° C., and the immersion treatment is performed for 4 hours. I got

(Polyester e) Transesterification reaction was carried out in a reactor containing 78 parts of dimethyl terephthalate, 12 parts of dimethyl isophthalate, 60 parts of ethylene glycol and 0.1 part of calcium acetate monohydrate. That is, the reaction start temperature was set to 170 ° C., and the reaction temperature was gradually increased with the distillation of methanol. After 4 hours, the temperature was raised to 230 ° C. to substantially end the transesterification reaction. Then
After adding an ethylene glycol slurry containing amorphous silicon oxide having an average particle diameter of 3 μm and 0.04 part of phosphoric acid, 0.04 part of antimony trioxide was added, and a polycondensation reaction was performed by a conventional method. That is, the temperature was gradually increased and the pressure was gradually decreased. After 2 hours, the temperature was 280 ° C., the pressure was 0.3 mmHg, and the reaction was stopped after 2 hours, containing 0.05 part of silicon oxide. Intrinsic viscosity is 0.7
0 was obtained.

[Production of polyester film] Polyester b was melt-extruded at 280 ° C from a T-die at a residence time of 5 minutes.
Melt extruded in minutes. After being extruded from the T-die, it was quenched on a cast drum to a temperature below the glass transition point to obtain a substantially amorphous sheet. This sheet was stretched 3.6 times in the machine direction at 80 ° C. using a roll stretching machine. Next, using a tenter stretching machine, the film was stretched 4.2 times in the transverse direction at 100 ° C., and then heat-set at 230 ° C. in a tenter.
A film having a thickness of 25 μm was obtained. [Production of a three-piece can] The obtained film was chromium-plated using an epoxy resin adhesive to a thickness of 0.30.
mm, to obtain a polyester-coated steel sheet. However, only one side of the steel sheet was covered with the resin. The exposed metal portion welded and joined by a coating film without using an adhesive or the like according to the method described in Japanese Patent Application Laid-Open No. 5-69485, with the surface coated with the polyester facing inside. Done 35
A 0 ml juice can body was manufactured, and a can lid and a can bottom were manufactured separately from the above-mentioned polyester-coated steel sheet so that the side in contact with the contents became a coating layer. A three-piece can consisting of the can body, can lid and can bottom was manufactured.

Example 2 Example 1 was repeated except that polyester b was changed to polyester c.
In the same manner as in the above, a three-piece can was manufactured. Example 3 Example 1 was repeated except that polyester d was used instead of polyester b.
In the same manner as in the above, a three-piece can was manufactured. Example 4 In Example 3, the same as Example 3 except that after obtaining the film after biaxial stretching and heat setting, the film was immersed in pure water at 125 ° C. for 1 hour, dried and used. And then
A three-piece can was manufactured.

Comparative Example 1 Example 1 was repeated except that polyester a was used instead of polyester b.
In the same manner as in the above, a three-piece can was manufactured. Comparative Example 2 Example 1 except that polyester e was used instead of polyester b.
In the same manner as in the above, a three-piece can was manufactured. The results obtained above are shown in Table 1 below.

[0029]

[Table 1]

[0030]

The polyester film for coating three-piece cans of the present invention has a low extraction component with water or hot water,
It is excellent in hygiene and its industrial value is high.

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein the terminal carboxyl group concentration after laminating and canning the metal with the adhesive is less than 50 equivalents / t, and after the laminating and canning the metal with the adhesive at 125 ° C. The low molecular weight material extracted by retort treatment with pure water for 1 hour is 2.0% / cm ^{2 of the} coated surface.
A polyester film for coating a three-piece can, which is not more than μg.