JP2003246869A - Film for metallic can cover lamination - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film for metallic can cover lamination which excels in the protection of the contents, particularly excels in the preservation of taste and flavor and long-term storage, has good cover-production processability and, simultaneously, does not cause corrosion at the scoring-provided portion even when maintained at high temperatures. <P>SOLUTION: The film for metallic can cover lamination is composed of a polyethylene terephthalate polymer containing a titanium element and a phosphorus element, and the titanium element is derived from the catalyst and is dissolved and present in the polymer, and its content as the metallic element is 2-10 mmol%, and the polymer meets formula (1): 2≤P/Ti≤15, and formula (2): 5≤Ti+P≤100 [wherein Ti is a titanium element concentration (mmol%) in the polymer; and P is a phosphorus element concentration (mmol%) in the polymer] as the contents of the titanium element and the phosphorus element, and substantially does not contain any metallic element other than the titanium element. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a film for laminating metal can lids, and more particularly to a film for laminating metal can easy open lids.

[0002]

2. Description of the Related Art As a metal can lid that can be opened without using a can opener, a so-called pull-top type, a stion tab type or a stion tab type easy open can lid is widely used. This metal can lid is made of aluminum, tinplate, tin-free steel (TFS), etc. as a metal material, and has a coating on the inner surface for anticorrosion, and then a score is provided in the thickness direction with a metal plate to make it easy open. It is the one.

[0003] In this score processing, a correction coating is generally applied because scratches and cracks are formed in the coating film on the inner surface. As a method of omitting this correction coating, a specific polyester film is used by being attached to a metal material (JP-A-62-5).
2045, JP 63-12445, JP 1-124551, JP 1-182248, JP 3-63124).

The characteristics required for these films are:
For example, it has excellent laminating properties on metal plates, the polyester film does not peel or crack due to impact on a metal can, pinholes do not occur, and the metal in the scored part does not corrode, especially beverages. It is important that no corrosion occurs when kept at a high temperature (60 ° C or higher) before eating. Recently, for example, by reducing the amount of metal catalyst components in the contents of metal cans and the impurity components mixed in the metal catalyst components, there is an increasing demand to prevent changes in the taste characteristics of the contents and maintain long-term storage stability. ing.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to protect contents, particularly to preserve flavor and aroma, to have long-term storability, to have good lid-making workability, and to score even when kept at high temperature. It is intended to provide a film for laminating a metal can lid which does not cause corrosion in a processed part.

[0006]

That is, the present invention comprises a polyethylene terephthalate polymer containing a titanium element and a phosphorus element, the titanium element being derived from a catalyst,
It exists in the state of being dissolved in a polymer and its content is 2 as a metal element.
10 to 10 mmol%, the polymer satisfies the following formulas (1) and / or (2) as the content of titanium element and phosphorus element, and is substantially free of metal elements other than titanium element. It is a film for laminating metal can lids. 2 ≦ P / Ti ≦ 15 (1) 5 ≦ Ti + P ≦ 100 (2) (where Ti is the concentration of titanium element in the polymer (mmol%), P is the phosphorus in the polymer) Represents the concentration of an element (mmol%).)

The present invention will be described in detail below. [Polyethylene terephthalate polymer] In the present invention, the film is composed of a polyethylene terephthalate polymer. The polyethylene terephthalate polymer is a linear polyester composed of terephthalic acid as a dicarboxylic acid component and ethylene glycol as a diol component.

Among the polyethylene terephthalates, those having a melting point of 270 ° C. or less are preferable since it is easy to industrially produce a film, particularly a biaxially stretched film.

The polyethylene terephthalate polymer may be a copolymer. When it is a copolymer, the copolymerization component may be contained as a dicarboxylic acid component, may be contained as a diol component, or may be contained in both the dicarboxylic acid component and the diol component. Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid; alicyclic compounds such as cyclohexanedicarboxylic acid. Mention may be made of dicarboxylic acids. Examples of the diol component include aliphatic diols such as butanediol and hexanediol; and alicyclic diols such as cyclohexanedimethanol.

It is preferable to use isophthalic acid and / or naphthalene-2,6-dicarboxylic acid as a copolymerization component in order to achieve the object of the present invention. The copolymerization components may be used alone or in combination of two or more.

When polyethylene terephthalate is a copolymer, the proportion of the copolymer component depends on the type of the copolymer component, but as a result, the melting point of the polymer is preferably 270 ° C. or lower. Here, the melting point of the polymer is determined by a method using a differential scanning calorimeter (910 DSC manufactured by Du Pont Instruments) with a sample amount of 20 mg and a melting peak at a temperature rising rate of 20 ° C./min.

In order to obtain a polymer having such a melting point, the amount of the copolymerization component with respect to the total dicarboxylic acid component is 0.1 to 18 mol% when isophthalic acid is used, and 0.1 when naphthalene dicarboxylic acid is used. It may be -18 mol%.

This polymer can be produced, for example, by a method of subjecting terephthalic acid and ethylene glycol and optionally a copolymerization component to an esterification reaction, and then subjecting the resulting reaction product to a polycondensation reaction to obtain a polyester polymer. it can. Alternatively, it can be produced by a method of subjecting dimethyl terephthalate and ethylene glycol and optionally a copolymerization component to an ester exchange reaction, and then subjecting the obtained reaction product to a polycondensation reaction to obtain a polyester.

In the case of using a copolymer, a plurality of polyesters such as polyethylene isophthalate, polyethylene-2,6-naphthalate and polybutylene terephthalate are mixed and melted with polyethylene terephthalate, and the copolymerization polymer is utilized by utilizing a transesterification reaction. May be

A titanium compound is used as a polymerization catalyst for the polymer so that the contents retain excellent flavor and aroma when used in a can. As the polymerization catalyst of polyester, for example, antimony compounds and germanium compounds have been used in addition to titanium compounds, but if the antimony element or germanium element resulting from them is contained in the polymer, the content is kept It is not suitable for this application because it has poor aroma retention, especially the flavor retention and aroma retention after retort treatment. Therefore, in the present invention, it is necessary that the polymer contains only titanium element as the metal element derived from the catalyst and does not substantially contain metal elements other than titanium element. In the present invention, the titanium element is derived from the titanium compound of the catalyst, is present in a dissolved state in the polymer, and the content is 2-1 as the metal element.
It is 0 mmol%. As the titanium compound, titanium tetrabutoxide and titanium acetate are preferably used. If the content of the elemental titanium is less than 2 mmol%, the polymerization reaction rate becomes slow, and if it exceeds 10 mmol%, dry heat deterioration is likely to occur during melt extrusion, which is not preferable. A phosphorus compound is added to the polymer as a heat stabilizer. Therefore, the polymer contains elemental phosphorus. Phosphoric acid and phosphorous acid are preferable as the phosphorus compound.

The polymer is an additive such as an optical brightener,
Antioxidants, heat stabilizers, UV absorbers and antistatic agents may be added.

The titanium element and the phosphorus element contained in the polymer satisfy the following formulas (1) and / or (2). 2 ≦ P / Ti ≦ 15 (1) 5 ≦ Ti + P ≦ 100 (2) (where Ti is the concentration of titanium element in the polymer (mmol%), P is the phosphorus in the polymer) Represents the concentration of an element (mmol%).)

If this condition is satisfied, good taste characteristics, especially long-term storage stability can be obtained. In particular, if the concentration of titanium element is higher than the above range, the amount of metal transferred from the film to the contents increases, and the flavor retention and long-term storability of the contents deteriorate. If the concentration of the titanium element is less than the above range, the polymerization reaction rate of the polyester will decrease, and a polyester having a predetermined intrinsic viscosity cannot be produced.

The intrinsic viscosity of the polymer is preferably 0.50.
Is about 0.64 dl / g. Intrinsic viscosity is 0.50dl /
If it is less than g, the film is frequently broken during melt extrusion of the polymer and biaxial stretching, which is not preferable.
When the intrinsic viscosity exceeds 0.64 dl / g, the workability during score processing is deteriorated, which is not preferable.

[Lubricant] The film of the present invention preferably contains a lubricant. The lubricant may be either an inorganic lubricant or an organic lubricant. As the inorganic lubricant, fine particles of an inorganic compound such as silica, alumina, titanium dioxide, calcium carbonate, barium sulfate can be used.

As the organic lubricant, fine particles of resin such as crosslinked silicone resin and crosslinked polystyrene resin can be used.

The lubricant preferably has an average particle size of 0.001 to
The thickness is 2.5 μm, more preferably 0.01 to 2.0 μm. If the average particle size of the lubricant exceeds 2.5 μm, coarse lubricant particles, for example, particles having a size of 10 μm or more, are generated as a starting point at the time of score processing by the lid-making process, and this pinhole is generated, causing corrosion in the score processing portion. Not preferred because of If the average particle size is less than 0.001 μm, the slipperiness of the film is insufficient during film formation, and it becomes difficult to smoothly manufacture the film. In order to prevent the occurrence of pinholes, the lubricant is preferably a monodisperse spherical lubricant. The particle size ratio (major axis / minor axis) of the spherical lubricant here is 1.0 to 1.2.
Is. Examples of such a lubricant include spherical silica, spherical silicon, and spherical calcium carbonate.

The amount of lubricant contained in the film is preferably 0.01 to 5.0% by weight. It is preferable to add a small amount of particles having a large particle size and a large amount of particles having a small particle size. For example, in the case of spherical silica having an average particle diameter of about 2.3 μm, it is preferable to add about 0.05% by weight, and in the case of spherical silica having an average particle diameter of about 1.5 μm, it is preferable to add about 0.1% by weight. The lubricant is usually used by externally adding it to the film.

[Film] The film of the present invention preferably has a plane orientation coefficient in the range of 0.115 to 0.140. When the plane orientation coefficient is less than 0.115, the unevenness in the thickness of the film is poor, the processability of the film varies, and the corrosivity is affected, which is not preferable. Plane orientation coefficient is 0.14
When it exceeds 0, it becomes difficult to bond the metal material and perform molding, which is not preferable.

The film of the present invention has a differential scanning calorimeter (D
SC) shows two or more endothermic peaks in the range of 170 to 270 ° C, and preferably two or more endothermic peaks in the temperature range of 180 to 270 ° C. Here, the endothermic peak of the film is a differential scanning calorimeter (Du Pont Ins).
910 DSC manufactured by Trents Inc.), the sample amount is 20 mg, and the melting peak is determined at a temperature rising rate of 20 ° C./min.

The endothermic peak includes an endothermic peak due to melting of the polymer, that is, an endothermic peak at the melting point.
The endothermic peak of this melting point is usually measured as the endothermic peak on the high temperature side, and the other endothermic peaks are usually measured as the endothermic peak on the lower temperature side. If the temperature of the endothermic peak on the low temperature side is less than 170 ° C, the biaxial orientation of the film is not sufficiently fixed by heat, and wrinkles may occur during thermocompression bonding to the metal material or the strength for bonding may be insufficient. Or

The thickness of the film of the present invention is preferably 6
˜50 μm, more preferably 10 to 40 μm.
If the thickness is less than 6 μm, tearing is likely to occur during processing such as lid making, which is not preferable. Those exceeding 50 μm are uneconomical because of excessive quality.

As the metal plate for the lid used for laminating with the film of the present invention, tin plate, tin-free steel (T
FS) and aluminum plates are preferred. Tin-free steel and aluminum plates are particularly preferable.

For laminating the film on the metal plate, for example,
A method in which a metal plate is heated to a temperature equal to or higher than the melting point of the film and then the films are bonded together and rapidly cooled, and the surface layer portion of the film in contact with the metal plate is amorphized and adhered, and the film is pre-coated with an adhesive layer as a primer. Then, this surface may be attached to a metal plate, and a resin adhesive such as an epoxy adhesive, an epoxy-ester adhesive, or an alkyd adhesive may be used as the adhesive layer.

[Production Method] The film of the present invention can be produced, for example, by the following method.

The polyethylene terephthalate polymer is melt extruded at a temperature higher than the melting point by 30 to 60 ° C. and rapidly solidified on a rotating drum to obtain an unstretched film. Then, this unstretched film is stretched at 100 to 140 ° C. in the longitudinal direction by
It was stretched 4.0 times and then stretched 2.5 to 4.0 times in the transverse direction at a temperature 10 to 40 ° C. higher than the longitudinal stretching temperature, and then 170
Heat fixing at ~ 210 ° C to obtain a metal can lid laminating film.

From the obtained film, a film-bonded metal plate can be obtained by heating the film to a temperature 10 to 40 ° C. higher than the melting point of the polymer, press-bonding it to TFS, and then rapidly cooling it.

[0033]

EXAMPLES The present invention will be described in more detail with reference to examples. The characteristics were measured and evaluated by the following methods.

(1) Intrinsic viscosity The film was dissolved in orthochlorophenol and the intrinsic viscosity was measured at 35 ° C.

(2) Surface orientation coefficient Using an Abbe refractometer, the refractive index nMD in the longitudinal direction of the film with respect to the sodium D line, the refractive index nTD in the width direction,
The refractive index nZ in the thickness direction was measured at 23 ° C. The surface orientation coefficient was calculated from these refractive indices by the following formula. Plane orientation coefficient = (nMD + nTD) / 2-nZ

(3) Amount of metal element and amount of phosphorus element The film is heated to 240 ° C. and melted to form a circular disk, and the amount of metal element and amount of phosphorus element contained in the film are measured by X-ray fluorescence analysis. I asked. For the quantification, a calibration curve by fluorescent X-ray obtained from a sample in which the addition amount of each metal element was changed in advance was used.

(4) Flavor-preserving and aroma-retaining property A film prepared by the following method was added to purified water in 60 cc of water.
On the other hand, the film area was soaked in a glass container at a ratio of 48 cm ² . Heat treatment was performed on the sealed glass container at 60 ° C. for 1 hour, and the purified water obtained was evaluated by 30 panelists based on the following criteria. As the comparison liquid, purified water that was not subjected to any treatment was used. ◯: 3 or less out of 30 people felt a change in taste and aroma as compared with the comparative solution. Δ: 4 to 9 out of 30 people felt a change in taste and aroma as compared with the comparative solution. X: 10 or more out of 30 people felt a change in taste and aroma as compared with the comparative liquid.

(5) Long-term storability A glass container containing purified water in which the above-mentioned film was dipped was sealed and heat-treated at 60 ° C. for 4 weeks. It was judged by the method.

(6) Workability The film was laminated on a metal plate by the method described in the following examples to prepare a film-bonded metal plate, and the presence or absence of defects was visually inspected at the stage of molding into a lid. In this visual inspection, the presence or absence of defects such as wrinkles in the film and breakage of the film in the processed portion was checked. Those with no defects were marked with ◯, and those with defects were marked with x.

(7) Corrosion After the sample capped by the method described in the following example was immersed in purified water and heat-treated at 60 ° C. for 4 weeks, there was no change such as corrosion in the scored portion. Was visually inspected. Those with no change are marked with ○, and those with change are marked with ×
And

(8) Endothermic peak The endothermic peak of the film is measured by a differential scanning calorimeter (Du Po
nt Instruments 910 DSC)
With a sample amount of 20 mg and a heating rate of 20 ° C.
It was measured by a method of obtaining a melting peak in / min.

Example 1 0.05% by weight of spherical silica having an average particle size of 1.0 μm was used, and titanium isobutoxide was used as a polymerization catalyst and phosphoric acid was used as a heat stabilizer. Mol%, naphthalene-2,6
Polyethylene terephthalate (melting point 230 ° C.) copolymerized with 6 mol% of dicarboxylic acid component was melt extruded at 280 ° C. and rapidly solidified on a rotating drum to obtain an unstretched film. Next, this unstretched film was stretched 3.2 times in the longitudinal direction at 120 ° C., then stretched 3.3 times in the lateral direction at 130 ° C., and then heat-set at 195 ° C. for laminating a metal can lid with a thickness of 20 μm. I got a film. Table 1 shows the intrinsic viscosity, the plane orientation coefficient and the DSC peak temperature of the obtained film.

The obtained film was heated to 250 ° C., pressure-bonded to one side of TFS having a thickness of 100 μm for 2 seconds and then rapidly cooled to obtain a film-bonded metal plate. Further, this metal plate was punched into a disc shape in a press molding process and formed into a desired lid shape. Then, in the score marking step, a score was used to score the score from the outer surface side of the lid so that the score reaches the middle of the metal material. The residual thickness of the metal material in the score was 50 μm.

Subsequently, in the rivet forming step, a rivet forming die is used to form a rivet projecting outward on the score opening portion, and the opening tab is adhered to the rivet in the tab attaching step, and the tab is struck and tabbed. Fixed. Such a sample was kept in water at 60 ° C. for 4 weeks, but no change such as corrosion was observed in the score processed portion. The results are shown in Table 2.

[0045]

[Table 1]

[0046]

[Table 2]

Examples 2 to 5 and Comparative Examples 1 to 6 The same as Example 1 except that the polyester and the catalyst metal shown in Table 1 were used, and the film was formed under the film forming conditions shown in Table 1. A polyester film was obtained and a lid corrosion test was further conducted. The properties of the obtained film and the results of the corrosion test are shown in Table 2.

As is clear from the results shown in Table 2, the film of the present invention has excellent processability and corrosion resistance for bonding metal can lids.

[0049]

EFFECTS OF THE INVENTION According to the present invention, the contents are excellent in protection properties, particularly flavor retention and aroma preservation property, and long-term storage property, and have good lid-making workability, and the score-processed portion is corroded even when kept at high temperature. It is possible to provide a metal can lid laminating film that does not cause

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichiro Okada             3-37-19 Oyama, Sagamihara City, Kanagawa Prefecture             People DuPont Films Co., Ltd. Sagamihara Research Center             In the center F-term (reference) 3E086 AB01 AD30 BA02 BA15 BA35                       BB77 BB90 CA01                 4F071 AA46 AH04 BA01 BB06 BB07                       BC01                 4F100 AB01B AB03B AK42A BA01                       BA02 GB16 GB23 JA06A                       JA20A YY00A                 4J029 AA03 AC01 AD10 AE03 BA03                       CB06A CC06A JA103 JB131                       JF321 JF413

Claims (2)

[Claims] 1. A polyethylene terephthalate polymer containing a titanium element and a phosphorus element, wherein the titanium element is derived from a catalyst and is present in a dissolved state in the polymer, and the content is 2 to 10 mmol% as a metal element. Is a film for laminating metal can lids, which satisfies the following formulas (1) and / or (2) as the content of titanium element and phosphorus element and contains substantially no metal element other than titanium element. 2 ≦ P / Ti ≦ 15 (1) 5 ≦ Ti + P ≦ 100 (2) (where Ti is the concentration of titanium element in the polymer (mmol%), P is the phosphorus in the polymer) Represents the concentration of an element (mmol%).) 2. The film has a plane orientation coefficient of 0.115 to.
0.140, which is 1 when measured with a differential scanning calorimeter.
Shows two or more endothermic peaks in the range of 70 to 270 ° C.,
The intrinsic viscosity of the polymer forming the film is 0.50
The metal can lid laminating film according to claim 1, having a content of 0.64 dl / g.