JPH07314606A - Polyester film for coated metal sheet - Google Patents

Abstract

(57) [Abstract] [Purpose] Household appliances that show excellent moldability when used as a decorative metal plate, and also have excellent solvent resistance, stain resistance, heat resistance, designability and surface properties. Provided is a polyester film for a coated metal plate, which can be used for a decorative steel plate such as a sheet. [Structure] A biaxially stretched film having a melting point of 210 to 245 ° C. and a thickness of 5 to 100 μm, and the maximum value of the heat shrinkage stress in the longitudinal and transverse directions of the film is 130 to 300 gf / A polyester film for a coated metal plate, which is in the range of mm ² .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for coated metal sheets, and more specifically, it shows excellent moldability and excellent solvent resistance, stain resistance, heat resistance, designability and surface property. The present invention relates to a polyester film for a coated metal plate, which is useful as a decorative metal plate for home appliances and the like.

[0002]

2. Description of the Related Art A metal plate coated with a resin has been used for a long time because it is excellent in rust prevention. Especially, a metal plate such as a steel plate is coated with a vinyl chloride resin having a printed layer. The decorative steel plate (decorative metal plate) is widely used for building materials, home appliances, vehicles and the like.

However, in a decorative steel sheet coated with vinyl chloride resin, the vinyl chloride resin layer on the surface deteriorates due to the influence of ultraviolet rays, heat, moisture, etc., and the plasticizer in the vinyl chloride resin volatilizes with the passage of time. Therefore, there are drawbacks such that the surface characteristics are remarkably deteriorated, and the color changes significantly.

In order to improve such drawbacks, for example, a method of coating an acrylic resin layer on a coated vinyl chloride resin (Japanese Patent Laid-Open No. 3-32834) and a method of laminating an acrylic resin film (Japanese Patent Laid-open No. 56-56). -162649) or a method of applying a fluororesin paint (JP-A-63-63)
No. 293048) has been proposed.

A method using a polyolefin resin instead of a vinyl chloride resin (Japanese Patent Laid-Open No. 63-159028) has also been proposed.

However, the method of coating an acrylic resin layer or the method of laminating an acrylic resin film has a drawback that the solvent resistance of the acrylic resin is poor, and when a fluororesin is used, the characteristics as a resin are excellent, but it is economical. It has the disadvantage of being untargetable. Further, the method using a polyolefin resin has drawbacks such as poor heat resistance of the polyolefin resin.

Further, instead of the vinyl chloride resin, a method of laminating a biaxially stretched polyethylene terephthalate film having excellent properties such as solvent resistance, stain resistance, heat resistance, economy and surface property on a metal plate can be considered. . However, this polyethylene terephthalate film has a drawback that it is inferior in moldability because of its high rigidity.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the conventional resin for coated metal plate,
It is intended to provide a polyester film for a coated metal sheet, which satisfies all of molding processability, solvent resistance, stain resistance, heat resistance, designability and surface property in a well-balanced manner.

[0009]

The present inventors have arrived at the present invention as a result of extensive studies to develop a polyester film for a coated metal sheet which does not have the above-mentioned problems.

That is, the present invention has a melting point of 210 to 245.
Made of copolyester at ℃, thickness is 5-100μ
m biaxially stretched polyester film having a maximum thermal shrinkage stress of 130 in the machine and transverse directions.
It is a polyester film for a coated metal plate, which is in the range of up to 300 gf / mm ² .

The copolymerized polyester referred to in the present invention is a saturated polyester composed of a dicarboxylic acid component and a diol component, and has a melting point in the range of 210 to 245 ° C. A particularly preferable example is copolymerized polyethylene terephthalate. Can be mentioned as.

Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid and naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid. Examples thereof include alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Examples of the diol component include aliphatic diols such as ethylene glycol, butanediol and hexanediol, branched glycols such as neopentyl glycol, polyoxyalkylene glycols such as diethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol, and cyclohexanediene. Examples thereof include alicyclic diols such as methanol. These can be used as a component of the copolyester having a melting point of 210 to 245 ° C.

The proportion of the copolymerization component depends on the kind thereof, but as a result, the melting point of the polymer is 210 to 245 ° C., preferably 215 to 240 ° C., more preferably 220 to 235.
It is the ratio in the range of ° C. When the polymer melting point is less than 210 ° C, the heat resistance is poor. On the other hand, when the melting point of the polymer exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

The melting point of polyester is measured by Du
Pont Instruments 910 DSC
And a melting peak at a temperature rising rate of 20 ° C./min. The sample amount is about 20 mg.

The copolyester used in the present invention is not limited by its production method. For example, in order to produce a copolyester having ethylene terephthalate as a main constituent, an esterification reaction of terephthalic acid, ethylene glycol and a co-polymerization component is carried out, and the resulting reaction product is polycondensed to obtain a copolyester. Preferably used is a method or a method in which dimethyl terephthalate, ethylene glycol and a copolymerization component are subjected to transesterification reaction, and then the resulting reaction product is subjected to polycondensation reaction to obtain a copolymerized polyester.

In the production of the copolyester, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber and an antistatic agent can be added if necessary. Examples of such antioxidants include hindered phenol compounds, hindered amine compounds, sulfur atom-containing ester compounds, and the like, and examples of ultraviolet absorbers include benzophenone compounds and benzotriazole compounds.
Examples thereof include sacylate compounds.

The copolymerized polyester in the present invention preferably contains a lubricant such as inert particles in order to improve workability during film formation or handling of the laminate. Is, for example, Periodic Table IIA,
Inorganic fine particles containing IIB, IVA, and IVB elements (for example, kaolin, alumina, titanium oxide, calcium carbonate, silicon dioxide, etc.) or organic fine particles made of high heat-resistant polymer such as silicone resin and crosslinked polystyrene Etc. can be mentioned.

The content of such a lubricant is preferably such that the film can be easily wound in the film manufacturing process, or the workability in handling the laminate is improved. Generally, it is preferable to add a small amount of a lubricant having a large particle size and a large amount of a lubricant having a small particle size. For example, in the case of silica having an average particle size of 2.0 μm, about 0.05% by weight,
0.3% by weight for titanium dioxide with an average particle size of 0.3 μm
It is preferable to add to some extent. Further, the film can be made opaque by intentionally adjusting the content of the lubricant. For example, by adding 10 to 15% by weight of titanium dioxide, a white film having a good light-shielding property can be obtained.

The above-mentioned additives such as lubricants can be added to the polyester film by a method of adding during the polycondensation reaction of the copolyester or a method of adding the copolyester during the film formation of the film.

The polyester film of the present invention has a maximum thermal shrinkage stress of 130 in the machine direction and the transverse direction of the film.
In the range of up to 300 gf / mm ² , preferably 150
˜300 gf / mm ² .

This heat shrinkage stress was applied to a metal plate.
Affects the surface properties of the film. That is, in the vertical direction,
Thermal contraction stress is 130 gf / in either one of the lateral directions
mm ²If it is less than, the film is heated and pasted on the metal plate.
Since the heat shrinkage of the film is insufficient when matching, it is necessary to move to a metal plate.
Will be incompletely adhered, and the flat surface will have good surface properties.
It can't be pasted as an film. As a result, paste
Unevenness appears on the surface of the laminated film,
It becomes the surface with the skin-like unevenness of Yuzu called skin, and the surface
A product with good properties cannot be obtained.

On the other hand, when the heat shrinkage stress in either one of the longitudinal direction and the lateral direction of the film exceeds 300 gf / mm ² , the film is heated and attached to a metal plate (hereinafter sometimes referred to as "heat lamination"). ) At that time, the heat shrinkage of the film becomes too large, and wrinkles called wrinkle pattern (wrinkle) occur on the surface of the laminated film,
In addition, since it has a dull and dull surface, a good product cannot be obtained.

Further, the polyester film of the present invention is
The temperature at which the maximum value of the heat shrinkage stress in the vertical and horizontal directions (hereinafter sometimes referred to as "peak temperature") is 150 to 2.
It is preferable that the temperature is within the range of 05 ° C., and further 155-2.
It is preferably 00 ° C, particularly 160 to 195 ° C.

This peak temperature may affect the surface properties of the film heat-laminated on the metal plate. That is, in the heating laminate, the film heating temperature is usually 1
It is carried out at a temperature higher than 50 ° C, but peak temperature is
If the temperature is less than ℃, it is difficult to obtain an appropriate heat shrinkage stress at a normal heating temperature, and a good film cannot be obtained.
Further, in order to make the shrinkage stress of the film moderate, the film heating temperature at the time of heating laminating may be set to a temperature lower than 150 ° C. However, if the heating temperature is lowered to the above temperature, the film and the metal plate are not heated. Adhesive strength is insufficient and sufficient lamination cannot be performed.

When the peak temperature exceeds 205 ° C., the film heating temperature during heating lamination is set to a temperature exceeding 205 ° C. in order to obtain an appropriate heat shrinkage stress, but at such temperature, the film easily breaks. If the heating temperature of the film during heating laminating is lower than 205 ° C., the heat shrinkage stress of the film due to the heating during laminating does not reach the maximum, and a good film surface can be obtained. Can not.

The heat shrinkage stress and the peak temperature of the film are SINKU-RIKO ™ manufactured by Vacuum Riko Co., Ltd.
-3000 type THERMO-MECHANICAL
It can be determined by using an ANALYZER and heating the polyester film from room temperature to a temperature just before the polyester melts at a heating rate of 10 ° C./min and measuring. The size of the film used for measurement is 15 mm
× 5 mm.

Further, the polyester film of the present invention is
The heat shrinkage rate of the film when treated at 150 ° C. for 30 minutes is 3.0 to 5.0% in the longitudinal direction, particularly 3.0 to 4.5%.
Is preferable, and the lateral direction is preferably 0.5 to 3.0%, and particularly preferably 0.7 to 2.5%. If the heat shrinkage in the longitudinal direction is too small, it is difficult to utilize the heat shrinkage of the film when it is bonded to the metal plate, and it is difficult to bond it as a flat film having good surface properties. As a result, the surface of the film is likely to have an uneven skin-like texture, and it is difficult to obtain a good product. If the heat shrinkage in the longitudinal direction is too large, the heat shrinkage of the film becomes too large when it is attached to a metal plate, and it tends to result in shrinking wrinkle patterns or dull surface with no gloss, making it difficult to obtain a good product.

If the heat shrinkage in the lateral direction is too small, it is difficult to utilize the heat shrinkage of the film when it is bonded to the metal plate, and it is difficult to bond the film as a flat film having a good surface property. As a result, the surface of the film is likely to have an uneven skin-like texture, and it is difficult to obtain a good product. If the heat shrinkage in the lateral direction is too large, the heat shrinkage of the film becomes too large when it is attached to a metal plate, resulting in a shrink wrinkled surface, and it is difficult to obtain a good product. Further, the shrinkage of the film in the lateral direction becomes too large, so that the film cannot be properly attached to the edge portion of the metal plate, and there are many parts that are not products, resulting in poor productivity.

The heat shrinkage in the vertical direction of the film is preferably larger than the heat shrinkage in the horizontal direction. The reason for this is the process of heating and laminating the film on a metal plate.The film passes through the process with tension applied in the vertical direction to unwind and wind with a roll, while free in the horizontal direction. Therefore, in order to obtain a decorative metal plate having a good surface property, it is suitable to use the above films having different heat shrinkage rates.

The biaxially stretched film of the present invention can be manufactured by a conventionally known film forming method. For example, the copolyester is melt extruded into a sheet and rapidly cooled to prepare an unstretched film, which is heated by roll heating, infrared heating or the like and stretched in the longitudinal direction to obtain a longitudinally stretched film. This stretching in the machine direction is preferably performed by utilizing the peripheral speed difference between two or more rolls. The stretching temperature is preferably higher than the glass transition point (hereinafter sometimes referred to as “Tg”) of the copolyester, and more preferably 20 to 40 ° C. higher than Tg. The stretching ratio in the machine direction depends on the physical properties of the intended film, but is preferably 2.5 times or more and 3.6 times or less. When the stretching ratio is within this range, the unevenness in the thickness of the film becomes good, and it is difficult for the film to break during film formation, which is preferable.

The longitudinally stretched film is preferably stretched in the transverse direction and subjected to heat-setting and heat-relaxation treatments in order to obtain a biaxially stretched film. These treatments are carried out while the film is running. You can The transverse stretching is preferably started at a temperature 20 ° C. higher than the glass transition point of the copolyester, and the melting point of the polyester (hereinafter referred to as “T
m ”). The stretching start temperature is preferably (Tg + 40) ° C. or lower, and for example, in the case of polyethylene terephthalate obtained by copolymerizing 12 mol% of isophthalic acid, the temperature is preferably 73 to 113 ° C. Also, the maximum stretching temperature is 100-
It is preferable that the temperature is 40 ° C. lower.

The temperature rise in the transverse stretching process may be continuous or stepwise (sequential), and is usually performed sequentially. For example, the transverse stretching zone of the stenter is divided into a plurality of zones along the film running direction, and a heating medium having a predetermined temperature is flown in each zone to raise the temperature. If the stretching temperature in the transverse direction is too low, the film may break, which is not preferable. Further, if the maximum stretching temperature is lower than (Tm-120) ° C, the heat shrinkage of the film becomes large, and the uniformity of the physical properties in the width direction deteriorates, which is not preferable. On the other hand, the maximum stretching temperature is (Tm-
If the temperature is higher than 30) ° C., the film becomes soft and the film is torn due to disturbance or the like, which is not preferable.

The stretching ratio in the transverse direction depends on the physical properties of the intended film, but is preferably 2.7 times or more, more preferably 3.0 times or more, and preferably 4.0 times or less. . When the stretching ratio in the transverse direction is within this range, the thickness unevenness of the film becomes good and it is difficult to break during film formation, which is preferable.

In order to obtain the polyester film having the heat shrinkage in the machine direction and the transverse direction, the biaxial stretching in the machine direction and the transverse direction, especially when the biaxial stretching is sequentially performed. , The stretching ratio in the longitudinal direction is 2.5 to 3.6 times,
It is preferable that the stretching ratio in the transverse direction is 2.7 to 4.0 times and the heat setting temperature is 150 to 230 ° C.

The polyester film of the present invention has a thickness of 5 to 100 μm, preferably 7 to 75 μm, and more preferably 10 to 50 μm. If the thickness is less than 5 μm, breakage is likely to occur during processing, while 100 μm
Beyond is not only unnecessary for the purposes of the present invention, but also uneconomical.

As the metal plate to which the polyester film of the present invention is attached, steel, iron, aluminum, tin plate,
It is a plate generally called a metal plate such as stainless steel.

The decorative metal plate of the present invention is a decorative metal plate obtained by laminating the polyester film of the present invention on a metal plate, and it is preferable to use a polyester film having a printing layer on at least one surface. This printed layer is preferably provided on the surface of the polyester film laminated with the metal plate.

In the decorative metal plate of the present invention, a printing layer is provided on one side of the polyester film of the present invention, and a polyvinyl chloride film is laminated on the printing layer surface.
A decorative metal plate obtained by further laminating a metal plate on the polyvinyl chloride film is more preferable.

One side of the polyester film of the present invention is printed, and a polyvinyl chloride film is bonded as a base material with an adhesive to form a laminate, and the adhesive is used on the polyvinyl chloride film side of the laminate. A decorative metal plate obtained by sticking to a metal plate is particularly preferable because it has excellent durability.

The polyvinyl chloride in the present invention includes
Polyvinyl chloride conventionally used for decorative metal plates can be used. For example, polyvinyl chloride, or another monomer copolymerizable with vinyl chloride (for example, vinyl acetate, acrylate ester, etc.) and vinyl chloride The copolymers of

As the resin used in the printing ink for the decorative metal plate of the present invention, an acrylic resin, a rubber resin, an epoxy resin having an adhesive property to the polyester film,
It is preferable to contain one kind or two or more kinds of urethane resin, amino resin or polyester resin. As the pigment to be added to the printing ink, one kind or two or more kinds of an inorganic pigment, an organic pigment, and a metal powder, which are usually used as a pigment for ink, can be used.

The adhesive for the decorative metal plate of the present invention includes, for example, thermosetting resins such as polyurethane, phenol, furan, urea, melamine, polyester, epoxy and silicone, acetic acid. Vinyl, ethylene-vinyl acetate copolymer, and a partial hydrolyzate thereof,
One or two of ethylene-acrylic acid copolymer, acrylic resin, thermoplastic resin such as polyamide, butadiene-acrylonitrile rubber, neoprene, other rubber derivative, other glue, casein, natural resin, gum arabic, etc.
An adhesive containing at least one species as a main component can be mentioned.

[0043]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[Examples 1 to 4 and Comparative Examples 1 to 5] Copolymerized polyethylene terephthalate obtained by copolymerizing the components shown in Table 1 with the addition of 0.1% by weight of spherical monodisperse silica having an average particle size of 1.5 μm. Was melt-extruded at the temperature shown in Table 1 and rapidly solidified to obtain an unstretched film.

This unstretched film was stretched in the machine direction under the conditions shown in Table 1, then stretched in the transverse direction, and then heat set, and then relaxed by 4.5% in the transverse direction to form a biaxial film having a thickness of 25 μm. A stretched film was obtained.

[0046]

[Table 1]

A total of 9 kinds of films obtained in the above Examples 1 to 4 and Comparative Examples 1 to 5 were coated with an ester adhesive to form 1 film.
It is laminated with 00 μm vinyl chloride film to form a laminated film, and it is laminated on one side of a 0.5 mm thick galvanized steel sheet heated to about 200 ° C. with an epoxy adhesive, followed by mirror embossing with a mirror roll, followed by After cooling, a decorative metal plate was obtained. The obtained decorative metal plate was observed and evaluated according to the following criteria. The workability was also evaluated by the following method. The evaluation results of each are shown in Table 2.

(1) Gloss ◯: The film surface after lamination is glossy. Δ: The surface of the film after laminating is slightly glossy. X: The film surface after lamination is not glossy.

(2) Shrinkage wrinkles: No wrinkles are found on the surface of the film after lamination. Δ: Some wrinkles are observed on the film surface after lamination. X: Wrinkles are seen on the film surface after lamination.

(3) Yuzu skin ◯: Yuzu skin is not seen on the film surface after lamination. Δ: A little yuzu skin is seen on the film surface after lamination. X: Yuzu skin is seen on the film surface after lamination.

(4) Workability Based on JISK-5400, workability was evaluated by the breaking distance method of Erichsen value. That is, using an Erichsen tester, extruding a steel ball from the metal plate side of the film-coated decorative metal plate,
The extrusion distance until cracking and peeling of the film was measured when the test piece was deformed.

[0052]

[Table 2]

From the results shown in Table 2, it can be seen that the decorative metal plate using the film of the present invention is excellent in forming processability and surface property.

[0054]

The polyester film for a coated metal sheet of the present invention is excellent in moldability and surface property of a decorative metal sheet obtained by sticking to a metal sheet, and is extremely useful as a polyester film for a coated metal sheet. Is.

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Claims (5)

[Claims] 1. A biaxially stretched polyester film having a melting point of 210 to 245 ° C. and a thickness of 5 to 100 μm, and the maximum value of the heat shrinkage stress in the longitudinal and transverse directions of the film is 130. ~ 300gf / mm
^A polyester film for a coated metal sheet, which has a range of ² . 2. The temperature at which the maximum value of the heat shrinkage stress in the longitudinal and transverse directions is within the range of 150 to 205 ° C.
A polyester film for a coated metal sheet as described above. 3. The film has a longitudinal heat shrinkage of 3.0 to 5.0% and a transverse heat shrinkage of 0.5 to 3.0% when heat-shrinked at 150 ° C. for 30 minutes. Claim 1 or 2
A polyester film for a coated metal sheet as described above. 4. A decorative metal plate obtained by laminating the polyester film according to claim 1, 2 or 3 on one side of a metal plate. 5. The decorative metal plate according to claim 4, wherein a polyvinyl chloride film is laminated between the metal plate and the polyester film.