KR19980068302A - Method for producing biaxially oriented polyester film for metal plate laminate - Google Patents

Abstract

The present invention relates to a method for producing a biaxially oriented polyester film used for metal sheet lamination during the production of beverage pipes, food pipes, etc., and is intended to improve physical properties such as molding processability.

Specifically, the present invention is prepared by using single or mixed antimony trioxide and germanium compound as a polycondensation reaction catalyst when preparing a copolymer polyester having a melting point of 205 to 245 ° C. with polyethylene terephthalate as a main chain, and average particles of the copolymer polyester. The present invention relates to a method for producing a polyester film comprising the addition of a combination of two kinds of inert fine particles of different diameters. Excellent performance in crack resistance and peeling resistance.

Description

Method for producing biaxially oriented polyester film for metal plate laminate

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a polyester film for forming a plated steel sheet laminate which is subjected to various electroplating such as tin or chromium. More specifically, a tube for making a beverage tube, food tube, etc. by laminating the polyester film according to the present invention on a metal plate. The present invention relates to a biaxially oriented polyester film for metal plate laminate molding processing, which has excellent molding processability during processing, and has excellent adhesion, crack resistance, and peeling resistance with a metal plate after molding.

Conventionally, in order to prevent corrosion of the inner and outer surfaces of metal tubes, various methods of dissolving or dispersing various thermosetting resins such as epoxy and phenol in a solvent, and then coating and coating a metal surface are widely used.

However, the method of coating such a thermosetting resin requires a long time of about 10 minutes to 20 minutes at 180 ° C. to 220 ° C. for drying the coated paint, so that the productivity is relatively low and occurs when a large amount of organic solvent is used and dried. There is a problem that is accompanied by environmental pollution by carbon dioxide, a large amount of waste water generated during the cleaning.

In order to solve this problem, laminating a thermoplastic resin film such as polyolefin and polyamide on a steel plate, an aluminum plate, or a metal plate that has been subjected to various treatments such as plating on the surface of each metal plate in recent years, and then forming a punching or draw process. Although a method of passing through is proposed, polyolefin or polyamide does not completely satisfy molding processability, heat resistance, and impact resistance.

On the other hand, thermoplastic polyesters, which are widely used in food containers such as drinking water and cooking oil, particularly polyethylene terephthalate, have excellent moldability, retort resistance, and mechanical strength, and many proposals to use them as base films have been proposed.

For example, a method (1) of joining a metal plate with a biaxially oriented polyethylene terephthalate film through an adhesive layer of polyester having a low melting point and producing a can using the obtained laminate as a material is disclosed in Japanese Patent Laid-Open No. 10,451 / 1981. No. 2 and No. 192,546 / 1989, a method (2) of joining a metal plate with a film of aromatic polyester which is amorphous or of very low crystallinity and producing a can using the obtained lamination as a material Patent Publications 192,545 / 1989 and 57,339 / 1990 and the like.

In addition, a method (3) of joining a metal plate with a heat-set biaxially oriented polyethylene terephthalate film having a low degree of orientation and using the obtained laminate as a material is disclosed in Japanese Patent Laid-Open No. 22,530 / 1989 and the like. The first layer formed of the first aromatic co-polyester and the second layer formed of the polyester composition obtained by melting and mixing the second aromatic copolyester and the third aromatic polyester, and the bonded metal plate is excellent A method for producing a can (4) to exhibit moldability is shown in Japanese Patent Publication Nos. 13,920 / 1993 and 25,392 / 1994 and the like.

In the conventional technique as described above, in the case of (1), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and supplemental complementary property, but the molding processability is insufficient, causing whitening (causing microcracks) or rupture and a large amount of deformation during the can manufacturing process. In the case of (2), the film used is an amorphous or very low crystallinity aromatic polyester film. It is susceptible to embrittlement when it is carried out or when the can is subjected to post-treatment for retort treatment or when the can is stored for a long time, and the embrittled film is susceptible to rupture due to external impact.

In addition, in the case of (3), the laminated film has an advantage of being able to be molded in a region of low deformation, whereas the film is subjected to retort treatment for later printing or sterilizing can contents in a can. It is easy to be embrittled, and the embrittled film has a problem of being easily ruptured due to external impact, and the method described in (4) shows that the laminated film used has good winding property, heat resistance, retort resistance, anti-avoidance and impact resistance. This relatively good but not satisfactory level, in particular, in the drawing process during the can manufacturing, there is a problem that pinholes easily occur due to particle dropping on the film, the film is easily broken.

It is an object of the present invention to provide a biaxially oriented polyester film having excellent performance in various physical properties such as molding processability as a film to be bonded to a metal plate.

Still another object of the present invention is to provide a good stretchability when forming a co-polyester having a certain level of melting point by using a conventional biaxial stretching method to ensure that the elongation of the film has an appropriate range after heat bonding to a metal plate. It is to provide a laminated polyester film for joining a metal plate to reduce the deterioration of the adhesive force due to the improvement of the problem that peeling and cracking of the film occurs during the tube forming.

The present invention is prepared by using a single or mixed antimony trioxide or germanium compound as a catalyst for the polycondensation reaction in the production of copolymer polyester having a melting point of 205-245 ° C. with polyethylene terephthalate as a main chain, the average particle in the copolymer polyester Characterized in that the first inert fine particles having a diameter (d1) of 0.01-0.4 μm and the second inert fine particles having an average particle diameter (d2) of 0.1-3.0 μm are added so that d1 / d2 is 2.5 or more. It relates to a method for producing a polyester film.

The main dicarboxylic acid components used in the preparation of the copolyester in the present invention include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, sebacic acid and maleic acid. Among them, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and the like are advantageous in heat resistance, retort resistance, impact resistance and the like. Examples of the diol component include aliphatic glycols such as ethylene glycol, diethylene glycol, butylene glycol, and cyclohexane dimethanol, aromatic glycols such as hydroquinone and bisphenol A, and the like. The dicarboxylic acid and diol component enumerated above can be used individually or in combination of 2 or more types.

As described above, the copolyester used in the present invention includes polyethylene terephthalate, polyethylene naphthalate, and the like as its main chain, and isophthalic acid as the copolymerization component is most suitable for the purpose of the present invention. It is preferable to use 5-20 mol%, more preferably 7-15 mol% of copolymerization components with respect to all acid components from a viewpoint of molding processability, low temperature impact resistance, retort resistance, heat resistance, etc. In addition, diethylene glycol or the like may be used as the copolymerization component of the diol component within the range that does not impair the properties of the copolyester. However, the present invention does not exceed 5 mol%, preferably 3 mol%, based on the total diol component. It is effective in the invention.

The degree of polymerization of the copolyester is preferably in the range of intrinsic viscosity of 0.06 to 0.85, more preferably 0.64 to 0.08 of the polymer after liquid phase polymerization or solid phase polymerization, in view of molding processability and low temperature impact resistance during the production process. When the intrinsic viscosity is less than 0.60, breakage or cracking of the film is likely to occur due to punching, draw, or the like during the production process, and in particular, low temperature impact resistance is lowered, which is not a preferred method. On the other hand, if the intrinsic viscosity exceeds 0.85, it is not preferable in terms of polymerization process and cost.

Melting point of the copolyester is in the range of 205 ~ 240 ℃, more preferably in the range of 215 ℃ to 230 ℃ suitable for the purpose of the present invention, when the melting point is less than 205 ℃ processability during steel pipe processing, but heat resistance and retort resistance, etc. Deterioration is not preferable, and if it exceeds 240 ℃, heat resistance and retort resistance is improved, but the crystallinity of the polymer is increased, the heat adhesive force is lowered, the film peeling occurs during the manufacturing of the steel tube after lamination on the metal plate, The moldability deteriorates, which is not preferable, and moreover, the production cost is increased because of excessive energy consumption requiring high temperature when preheating the metal plate.

On the other hand, it is suitable for the object of the present invention that the copolyester has an elongation of 115 to 185% in the longitudinal direction and 85 to 115% of the longitudinal elongation in the lateral direction using a conventional biaxial stretching method. More preferably, the case where the longitudinal elongation is 125 to 175% and the transverse elongation is 90 to 100% of the longitudinal elongation is suitable for the purpose of the present invention. If the longitudinal elongation is less than 115% or the transverse elongation is less than 85% of the longitudinal elongation, it is not preferable because the stretch adhesive strength of the film decreases and the peeling or cracking of the film occurs when the film is thermally bonded to the metal plate. On the contrary, when the film exceeds 185% or the transverse elongation exceeds 115% of the longitudinal elongation, the peeling or cracking of the film is considerably reduced, but it is difficult to maintain the thickness of the film uniformly.

The copolyester used in the present invention is obtained by subjecting a reaction product obtained by esterifying or transesterifying terephthalic acid, ethylene glycol and isophthalic acid or a copolymerization component to a polycondensation reaction. Reaction catalysts usable in the transesterification reaction include manganese acetate, magnesium acetate, calcium acetate, potassium acetate, tetrabutyl titanate, and the like, and may be added at the beginning or at any stage of the reaction.

In addition, in the polycondensation reaction step, antimony trioxide or germanium compound is added as a polycondensation catalyst at the beginning of the polycondensation reaction, and in the present invention, a mixed catalyst of antimony trioxide and germanium dioxide is most preferably used. On the other hand, in the present invention, lubricants, fluorescent brighteners, antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents and the like can be added as necessary.

In the present invention, the copolyester contains inert fine particles, wherein the inert fine particles used include first inert fine particles having an average particle diameter (d1) of 0.01 to 0.4 µm and an average particle diameter (d2) of 0.1 to Preferred are combinations of second inert particulates of 3.0 μm. The average particle diameter d1 of the first inert fine particles is more preferably 0.05 to 0.3 μm, and the average particle diameter d2 of the second inert fine particles is more preferably 0.3 to 2.0 μm.

The ratio of the average particle diameter d2 of the second inert particles to the average particle diameter d1 of the first inert particles is 2.5 or more, more preferably 3.0 or more.

The material of the first inert fine particles may be inorganic or organic, with inorganic being more preferred. Examples of the material of the inorganic inert particles include silica, alumina, kaolin, titanium dioxide, calcium carbonate and barium sulfate. Crosslinked silicone resin particles or crosslinked polystyrene particles are used as the organic inert fine particles.

The first impurity fine particles may be one kind or a combination of two or more kinds of the inert fine particles, and may be used in combination with other inert fine particles as necessary.

The content of the first inert fine particles in the copolyester is preferably 0.01 to 3% by weight, more preferably 0.1 to 1.0% by weight, particularly preferably 0.2 to 0.5% by weight.

The content of the second inert fine particles in the copolyester is preferably 0.001 to 0.3% by weight, more preferably 0.01 to 0.2% by weight, particularly preferably 0.05 to 0.1% by weight.

The copolyester film used in the present invention is melted to a temperature above the melting point in the extruder, and then extruded, cooled, and solidified through a die, followed by conditions such as the temperature and draw ratio of the longitudinal stretching and transverse stretching, and the temperature of the heat setting process. It can be prepared by adjusting. In addition, the final thickness of the produced film is 12 to 40 µm (more preferably 15 to 30 µm) is advantageous for the purposes of the present invention. If the thickness of the film is less than 12㎛, breakage is likely to occur in the film during the steelmaking process, and if it exceeds 40㎛, it is uneconomical because it has excessive quality characteristics.

Metal plates bonded to the co-polyester film of the present invention, in particular, metal plates for can production include tin-plated steel sheets, tin-free steel sheets and aluminum plates and chromium-plated steel sheets.

In the method of bonding the laminated polyester film on the metal plate, the metal plate is heated to a temperature above the melting point of the film, the film is bonded thereto, the obtained lamination is cooled and the surface layer portion (thin layer portion) of the film in contact with the metal plate is brought into an amorphous state. To adhere to the metal plate or to bond the film to the film, and to bond the substrate and the metal plate to each other, where known adhesives such as epoxy adhesives, epoxy-ester adhesives and alkyd adhesives can be used. Resin adhesive can be used.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, and the physical properties measured herein were used in the following method.

(1) intrinsic viscosity

2.0 g of each copolyester was dissolved in a 1,1,2,2, -tetrachloroethane / phenol (60/40 weight percent) mixed solvent and measured at 25 ° C.

(2) glass transition temperature and melting point

A 6.0 mg sample of copolyester was obtained using a DuPont 9100 differential scanning calorimetry at a rate of 20 ° C./min, and the melting point was taken as the peak temperature.

(3) Deep processing

Machinability was evaluated according to the following 3 grade system.

(Circle): A sample film can be deep-processed without abnormality to both the inside and the outer surface of a metal can, and the film on this surface does not show opacity or rupture.

(Triangle | delta): Opacity of a film is observed in the upper part of a metal can.

X: A tear is observed in a part of film.

(4) film elongation

The prepared co-polyester film was measured for the longitudinal and transverse elongation of the film using an Instron's tensile strength tester, respectively.

(5) thermal adhesion

The copolyester film was sandwiched between plated steel sheets and heated at a constant pressure using a heating press, and then the size of the adhesive force was evaluated by the ATM D1876 method.

(6) drawing adhesion

After thermally bonding the copolyester film to the metal plate, the metal plate was cut with a tensile strength test piece to observe the degree of peeling of the film according to the tensile rate of the tensile strength tester. The tensile rate at the time point at which the peeling of the film began to occur by scratching the surface of the film with a spiral tester and peeling it with 3M tape was expressed as the stretch adhesive force of the film.

(7) retort resistance

After filling the cans with good deep water, retort treatment at 120 ° C. for 1 hour in steam sterilizer, and maintaining them at 50 ° C. for 30 days, and then, each group of 10 cans was polyvinyl chloride at 1m height. Dropped onto tile floor and ERV tested.

○ All 10 cans show a current value of 0.1 mA or less.

Δ 1 to 5 cans exhibit a current value of 0.1 mA or more.

Cracks are already observed in the film after at least 6 cans exhibit or drop a current value of 0.1 mA or more.

Examples 1-5 and Comparative Examples 1-5

The copolyesters having an additional copolymer unit derived from the components shown in Table 1 (containing 0.3 wt% of calcium carbonate having an average particle diameter of 0.3 μm) and the polyester compositions shown in Table 1 were individually dried, melted and Extruded through adjacent dies according to a conventional method and solidified by quenching to produce a copolyester film having polyethylene terephthalate as the main chain, and then stretching the unstretched film to the longitudinal and transverse stretching ratios shown in Table 1. Thermal curing at the heat setting temperature shown in 1 to obtain a biaxially oriented film having a thickness of 25㎛, it is shown in Table 2 to evaluate the physical properties.

TABLE 1a

Copolymerization component Melting Point (℃) Intrinsic viscosity Elongation ratio Lateral draw ratio Heat setting temperature Furtherance mole% Example 1 Isophthalic acid 18 212 0.72 3.2 3.3 195 ℃ Example 2 Isophthalic acid 12 224 0.69 3.4 3.3 190 ℃ Example 3 Isophthalic acid 8 234 0.68 3.4 3.5 195 ℃ Example 4 Sebacic acid 5 244 0.70 3.3 3.4 190 ℃ Example 5 Isophthalic acid 12 224 0.69 3.3 3.3 195 ℃

TABLE 1b

Copolymerization component Melting Point (℃) Intrinsic viscosity Elongation ratio Lateral draw ratio Heat setting temperature Furtherance mole% Comparative Example 1 Isophthalic acid 20 202 0.72 3.6 3.8 170 ℃ Comparative Example 2 Isophthalic acid - 248 0.68 3.2 3.4 240 ℃ Comparative Example 3 Sebacic acid 9 234 0.69 3.5 3.8 165 ℃ Comparative Example 4 Isophthalic acid 8 234 0.68 3.9 4.3 195 ℃ Comparative Example 5 Isophthalic acid 12 224 0.69 4.0 4.4 210 ℃

TABLE 2

Deep Processing Film Elongation (%) Elongation Thermal Adhesion (N / ℓn ² ) Retort Resistance Longitudinal direction Transverse Example 1 ○ 150.5 105.2 50% 161 ○ Example 2 ○ 141.2 144.3 34% 143 ○ Example 3 ○ 145.2 141.9 32% 141 ○ Example 4 △ 143.3 142.1 29% 140 ○ Example 5 ○ 146.8 147.4 46% 160 ○ Comparative Example 1 △ 99.8 87.2 19% 140 ○ Comparative Example 2 × 155.5 140.1 11% 95 × Comparative Example 3 △ 111.4 105.1 25% 142 △ Comparative Example 4 ○ 105.2 103.3 42% 167 △ Comparative Example 5 ○ 143.3 145.2 52% 170 ○

As confirmed in the above examples and comparative examples, the polyester film according to the present invention is laminated on a metal plate, and has excellent molding processability during the steelmaking process for making foods, beverage tubes, etc., but also adhesion and crack resistance with the metal plate after molding. It shows excellent performance in peeling resistance.

Claims (5)

In the preparation of a biaxially oriented polyester film prepared by producing a copolymer polyester having a melting point of 205 to 245 ° C. with a polyethylene terephthalate as a main chain and then extruding, cooling, solidifying and biaxially stretching, the average particle diameter ( It is characterized by using a copolyester added by combining the first inert fine particles having a d1) of 0.01 to 0.4 μm and the second inert fine particles having an average particle diameter (d2) of 0.1 to 3.0 μm so that d1 / d2 is 2.5 or more. A method for producing a biaxially oriented polyester film for metal plate laminate. The method according to claim 1, wherein the content of the first inert fine particles is 0.01 to 3% by weight. The method of claim 1, wherein the content of the second inert fine particles is 0.001 to 0.3% by weight. 2. The method for producing a biaxially oriented polyester film for metal plate laminate according to claim 1, wherein the biaxial orientation is performed in the longitudinal direction from 115 to 185% and in the transverse direction from 85 to 115%. The method for producing a biaxially oriented polyester film for metal plate laminate according to claim 1, wherein antimony trioxide and germanium compound are used singly or in combination as a catalyst for polycondensation reaction during the production of copolyester.