KR100256593B1 - Heat adhesive polyester film for metal lamination - Google Patents

Abstract

PURPOSE: A hot sealing polyester film for metal lamination is provided, to improve the hot sealing property without the deterioration of the mechanical strength and the size stability. CONSTITUTION: The polyester film comprises the first polymer resin layer which comprises the copolymeric polyester containing 80-90 wt.% of terephthalic acid and 10-20 wt.% of isophthalic acid as an acid repeating unit; and the second polymer resin layer which comprises the copolymeric polyester containing 90 wt.% of terephthalic acid or more and 10 wt.% of isophthalic acid or less as an acid repeating unit, and 0.02-0.15 wt.% of one or more kinds of spherical silica with the mean particle size of 0.05-2.0 micrometers. The first and second polymer resin layers comprise 0.005-0.2 wt.% of phosphoric acid-based compound based on the weight of the polymer resin layer, respectively. Preferably the copolymeric polyester of the first polymer resin layer has the limiting viscosity of 0.55-0.75 dl/g, and the melting point of 150-230 deg.C; and the copolymeric polyester of the second polymer resin layer has the melting point of 200-250 deg.C.

Description

Heat adhesive polyester film for metal lamination

The present invention relates to a heat-adhesive polyester film for metal lamination, and in detail, the polyester film itself is provided with adhesiveness without being coated or laminated with an adhesive or other resin to be heated and pressed to the metal to be continuously bonded. And a heat-adhesive polyester film for metal lamination.

It is well known that there is a growing concern and concern over global environmental pollution. Most countries around the world apply strict standards on environmental pollution, and therefore, there is an urgent need for the development of environmentally friendly technologies and production processes in industrial and industrial fields. In conjunction with this situation, the elimination of pollution factors in new products and new technology processes is emerging as not only an environmental consideration, but also an important issue that determines industrial success.

As a conventional metal plate material, after the resin coating and printing on the metal material such as tin and TFS (Tin Free Steel) several times, it is baked and fired and plated, or press-molded and degreased and washed. Products manufactured by printing and painting treatment have been mainly used. However, the products have a problem in that the manufacturing process, because a large amount of organic solvents are inevitably used to harm workers due to deterioration of the working environment, as well as the environment such as air pollution due to carbon gas discharged after the process It had a fatal weakness that the problem could not be avoided.

Therefore, there has been a growing interest in new materials for metal plates, in which the pollution factor is minimized, resources and energy can be reduced, and stability can be secured. As a result of many studies, polyester laminate metal plates have been born. . The polyester laminated metal sheet can significantly reduce the amount of carbon dioxide generated in the manufacturing process, and much better environmental friendliness than the conventional metal plate manufacturing process that emits a large amount of carbon dioxide, which is the main cause of global warming, after the process is performed. Have

The polyester laminated metal sheet is manufactured by laminating a polyester film on a steel sheet, an aluminum sheet or a steel sheet surface-treated with various paints, and then performing drawing molding and ironing on the metal sheet. It is common. The polyester laminated metal sheet is a situation that the demand is explodingly increased, such as containers of metal cans.

On the other hand, the following conditions are mentioned as conditions which each unit material used for the said polyester laminated metal plate should have especially. First, in the case of a metal plate, strength, corrosion resistance, coating property of an organic material, secondary work adhesion and workability, etc. are required, and in the case of a polyester film laminated and coated on the metal plate, on the other hand, processability, hygiene and contents Excellent corrosion protection is required.

Various studies have been conducted on materials capable of satisfying the above conditions, but materials that satisfy all of the various required characteristics according to various processing methods or kinds of food, which are the contents of cans, have not been developed yet. The present invention particularly relates to a polyester film having excellent heat adhesion to a metal plate.

As the industrial structure becomes more complex, the necessity for materials that can satisfy a variety of applications is increasing, and interest in excellent polymer properties and light polymer resins is increasing, and various polymer resins having advantages in different physical properties are copolymerized and co-processed. Due to the advantage that it can be made into a final film having excellent physical properties through processing such as extrusion, research and development on this is active.

In particular, the polyester resin represented by polyethylene terephthalate is widely used in various industrial products because of its physical and chemical stability, high mechanical strength, excellent heat resistance, durability, chemical resistance, dimensional stability, and the like. In particular, when used by laminating on a steel sheet or an aluminum plate, transparency and high gloss that can represent the appearance of a painted or printed metal plate is a great advantage. In addition, since it also has hygiene, it is highly stable even when reprocessing a metal plate for environmental protection, and is used in place of other conventional synthetic resins as an industrial film.

However, the existing polyester film does not have thermal adhesiveness, so in order to be used for applications requiring thermal adhesiveness, a process of coating or laminating an adhesive or other resin on the polyester film to impart thermal adhesiveness is required. It was. However, it is difficult to maintain the adhesion improvement effect of the final film at a desirable level only by coating with an adhesive or other resin, and in the case of lamination, it is excellent in terms of thermal adhesiveness but requires a complicated lamination process. Although the unit cost is high, it is not preferable in terms of economics, and heat adhesiveness is imparted, but there is also a problem that the inherent properties of the polyester resin as the base film are weakened.

The technical problem to be achieved by the present invention is to maintain the inherent properties of polyester film, such as mechanical strength, dimensional stability, and the like to solve the above problems, excellent heat adhesion, and is manufactured in the form of cans to preserve the taste when storing food It is desirable to provide a heat-adhesive polyester film for metal lamination.

In order to achieve the above technical problem, in the present invention, a first polymer resin layer formed of a copolymerized polyester comprising 80 to 90% by weight of terephthalic acid and 10 to 20% by weight of isophthalic acid as an acid component in a repeating unit and repetition 0.02 to 0.15% by weight of at least one spherical silica formed from a copolyester comprising 90% by weight or more of terephthalic acid and 10% by weight of isophthalic acid as the acid component in the unit, and having an average particle diameter of 0.05 to 2.0 µm. There is provided a heat-adhesive polyester film for metal lamination having a second polymer resin layer comprising.

Preferably, the intrinsic viscosity of the copolyester forming the first polymer resin layer is 0.55 to 0.75 dl / g and the melting point is 150 to 230 ° C. It is preferable that melting | fusing point of the copolyester which forms the said 2nd polymer resin layer is 200-250 degreeC.

In addition, according to one embodiment of the polyester film of the present invention, the spherical silica contained in the second polymer resin layer preferably has a long diameter to short diameter ratio of 1.1 or less. In addition, the spherical silica is preferably a mixture of two kinds of particles having different sizes _{, in which} the average radius of the small particles is 0.05≤D _{50, a} ≤0.3 and the average radius of the large particles is 0.5≤D _{50, b} ≤2.0. (The above D _{50, a} and D _{50, b} represent the average radius of small particles and large particles, respectively).

According to a preferred embodiment of the present invention, both the first polymer resin layer and the second polymer resin layer further include a phosphoric acid compound.

In the polyester film of the present invention, the copolyester constituting the first polymer resin layer and the second polymer resin layer is at least one selected from the group consisting of ethylene glycol and butylene glycol in the alcohol component of the repeating unit. Is preferably a dihydric alcohol.

In the present invention, it is preferable that the thickness of the polyester film is 10 to 38 µm, and the thickness ratio of the first polymer resin layer and the second polymer resin layer is adjusted to be 1: 4 to 1: 8.

Hereinafter, the present invention will be described in more detail.

In the present invention, the first polymer is formed of a copolyester comprising 80 to 90% by weight of terephthalic acid and 10 to 20% by weight of isophthalic acid as the acid component in the repeating unit in order to impart thermal adhesion to the polyester film. It is formed of a copolyester comprising 90 wt% or more of terephthalic acid and 10 wt% or less of isophthalic acid as the acid component in the resin and the repeating unit, and contains 0.02 to 0.15 wt% of spherical silica having an average particle diameter of 0.05 to 2.0 µm. Each of the second polymer resins is formed, and each of them is melted at a temperature higher than 30 ° C above the melting point, and then laminated in two layers in the feed block and discharged through an extrusion die. Subsequently, the cooling drum is cooled while electrostatically applying the first polymer resin layer to the drum surface. The sheet thus produced is sequentially stretched biaxially according to the draw ratio required for the product according to the application. In addition, in some cases, the step of heat setting may be further performed. In the polyester film manufactured through the above steps, the second polymer resin layer retains the physical properties of the existing polyester film, while the first polymer resin layer is easily bonded at an appropriate temperature and pressure and has excellent adhesion. Will have

In the polyester film of the present invention, the copolyester forming the first polymer resin layer uses 80 to 90% by weight of terephthalic acid and 10 to 20% by weight of isophthalic acid as the acid component, and ethylene glycol or the polyhydric alcohol component. It is prepared by esterification or transesterification using butylene glycol and polycondensation under high temperature and high pressure.

When the content of isophthalic acid is maintained in the above range, not only the heat adhesion to the base material such as a metal iron plate for cans is easy, but also the adherend and the second polymer resin layer may be firmly adhered after the heat adhesion. If the content of isophthalic acid is less than 10% by weight, a large amount of heat is required for adhesion with the metal plate, and crystallization is accelerated during the can manufacturing process, and it is easy to peel off from the adherend. In addition, if the content of isophthalic acid is more than 20% by weight, the melting point is too low, the impact resistance and film forming processability is increased. At this time, it is preferable that the intrinsic viscosity of the copolyester is 0.55 to 0.75 dl / g. The reason is that when the intrinsic viscosity is lower than 0.55 dl / g, the problem of crystallization of the polymer proceeds too fast. Is higher than 0.75 dl / g, the molecular weight of the polymer is so large that it is difficult to manufacture the resin itself, it is difficult to obtain a uniform sheet due to the high viscosity during film molding.

Copolymerized polyester of the second polymer resin layer is also prepared by the same method as described above, except that the final laminated polyester plate has an adhesive property even after molding and at the same time moderately crystallized between food and metal plate to preserve taste and It is necessary to properly adjust the dose of isophthalic acid so that impact resistance can be maintained. The amount of isophthalic acid should be added less than in the case of preparing the first polymer resin layer, but is preferably within 10% by weight, preferably 3 to 8% by weight. On the other hand, it is necessary to adjust the average roughness of one side of the film to 0.005 to 0.1㎛ or less for handling and post-lamination of the film, for this purpose, it is preferable to add 0.02 to 0.15% by weight of inorganic fine particles having an average particle diameter of 0.05 to 2.0㎛. . If the size of the particles is too large and large, the defects of the film increase in post-processing, and the characteristics for metal lamination are lost.

As the inorganic fine particles, materials commonly known in the art, including titanium dioxide, calcium carbonate, kaolin, barium sulfate, silica, talc, zeolite, and the like are used. Among them, silica, particularly spherical silica, is particularly preferable because of its high affinity with the resin, and thus, void formation is suppressed as much as possible, impact resistance is strong, and a role of suppressing the generation of pinholes during can molding is particularly preferable. Also, among the spherical silicas, particles having a uniform size and distribution of silica and having a long diameter to short diameter ratio of 1.1 or less are suitable. Preferably, the average radius of the small particles is 0.05 ≦ D _{50, a} ≦ 0.3 and the average radius of the large particles is Two kinds of particles of 0.5 ≦ D _{50 and b} ≦ 2.0 are mixed and added.

In addition, it is preferable that the phosphoric acid compound is further added in the step of preparing the copolyester forming each resin layer. As the phosphate compound, a phosphate or phosphite compound is used, which serves to prevent the formation of a complex or thermal decomposition by a metal catalyst and to decompose the peroxide in the secondary thermal oxidation reaction. The phosphoric acid compound is preferably added in an amount of 0.005 to 0.2% by weight based on the weight of the composition for forming each resin layer. If the added amount is less than 0.005% by weight, the effect of improving heat resistance is hardly exhibited. If the added amount is more than 0.2% by weight, the effect of increasing the thermal stability is insignificant, but the strength of the resin itself is reduced. There is a fear that a whitish film is obtained.

Preferred examples of the phosphate-based compound include trifetyl phosphate, trixylene phosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, trigylenyl phosphate, xylenyl phosphate, cresyl diphenyl phosphate, and distearyl pentaerythritol disi. Phosphate, bis-2,4-di-t-butyl pentylerythritol disphosphate or tris-2,4-di-t-butylphenyl phosphate. By using the phosphoric acid-based compound, it is possible to prevent side effects such as deterioration of the intrinsic viscosity of the resin, change of resin color due to deterioration, and deformation or discoloration of the heat-induced portion during the heat processing.

In addition to the phosphoric acid compound, conventional additives such as a polycondensation catalyst, a dispersant, an electrostatic agent, an antiblocking agent, and the like may be added within a range that does not impair the effects of the present invention.

On the other hand, the thickness of the polyester film prepared as described above is not particularly limited, but may vary depending on the type of adherend, the thermal bonding temperature, the thermal bonding pressure and the like adhesion method. It is preferable that the thickness of a film is 10-38 micrometers in consideration of moldability and impact resistance. On the other hand, the thickness ratio of the first polymer resin layer and the second polymer resin layer is not particularly limited, but in view of the physical properties of the adhesive and the polyester film, the thickness ratio of the two layers is 1: 4 to 1: It is preferable that it is eight.

In preparing the heat-adhesive polyester film of the present invention, the stretching step influences the adhesion and physical properties of the finally obtained polyester film, and in particular, both surfaces appearing due to the molecular orientation constituting the surface structure and the surface structure of the film. Determining the density is an important step. Therefore, not only the draw ratios in the length and width directions, but also proper adjustment of the drawing conditions including the drawing speed is necessary, and heat setting temperature, heat setting time and cooling conditions are also important. The draw ratio is set in consideration of the degree of orientation, strength, elastic modulus, etc. of the film, but usually 2 to 5 times is appropriate. In the case of carrying out the widthwise stretching after longitudinal stretching according to the sequential stretching, the longitudinal stretching temperature is generally preferably 90 to 100 ° C. If the stretching temperature is lower than this, the stretching of the second polymer resin layer is uneven. Orientation is excessive, and when the stretching temperature is higher than this, the stretching of the first polymer resin layer is nonuniform and the thermal adhesive force is significantly decreased.

In the stretching in the width direction after the stretching in the longitudinal direction, the stretching temperature should be appropriately matched with the stretching direction in the longitudinal direction, but is preferably adjusted to 120 to 140 ° C. In addition, the heat setting step is a step carried out to maintain the heat stability, crystallinity and heat adhesion of the polyester film obtained at a desirable level, it is preferably carried out for 5 to 10 seconds at 180 to 250 ℃.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, it goes without saying that the scope of the present invention is not limited by the following examples. In the following examples, ethylene glycol was used as the polyhydric alcohol component for convenience.

<Example 1>

After mixing terephthalic acid and isophthalic acid at a weight ratio of 84:16 to constitute an acid component, and mixing two components in an equivalent ratio of 1: 2 using ethylene glycol as a diol component, antimony dioxide was added as a polycondensation catalyst to the mixture. And bis-2,4-di-t-butylpentylerythritol disphosphate and triphenyl phosphate, respectively, 0.02% by weight is added to a polycondensation reaction to form a copolymer polyester having an intrinsic viscosity of 0.65 dl / g. A polymer resin was prepared.

Terephthalic acid and isophthalic acid were mixed in a weight ratio of 94: 6 to form an acid component, ethylene glycol was used as a diol component, and the two components were mixed in an equivalent ratio of 1: 2. Then, antimony dioxide was added as a polycondensation catalyst to the mixture. 0.1% by weight of spherical silica having an average particle diameter of 1.5 µm, and 0.02% by weight of bis-2,4-di-t-butylpentylerythritol disphosphate and triphenylphosphate, respectively, were subjected to a polycondensation reaction to give an intrinsic viscosity of 0.63. A second polymer resin formed from co-polyester of dl / g was prepared.

The copolyester is melted and extruded through two extruders, and then laminated in two layers in a feed block, followed by stretching in a longitudinal drawing ratio of 3.5 times and a widthwise drawing ratio of 3.2 times using a conventional T-die and a biaxial stretching apparatus. Heat setting was carried out at 200 ° C. to prepare a biaxially stretched polyester film. The properties of the prepared polyester film were evaluated and shown in Table 1 below. Evaluation of the characteristic of the film was performed by the following method.

(1) melting temperature

It measured by heating up at 20 degree-C / min in nitrogen atmosphere using the differential thermal analyzer (the DSC-7 by a Perkin Elmer company).

(2) Copolymerization Ratio of Copolyester

¹³ C-NMR spectra were obtained by using a nuclear magnetic resonance spectrometer (JNM-LA300, manufactured by JEOL).

(3) intrinsic viscosity of PET

It was obtained by dissolving the copolymer in ortho-chlorophenol and measuring the relative viscosity at 30 ° C.

(4) surface density (surface crystallinity)

973 & 1504 cm ^-1 was compared using the infrared spectrometer (FTS-60 by DIGILAB company), and the crystallinity degree of the surface was measured.

(5) breaking strength

The tensile strength of the film was measured using an Instron tensile tester (ASTM D882).

(6) average particle diameter

After the surface layer is removed from the surface of the film using an ion etching machine, the size of the particles is observed with an electron microscope (SEM). The average particle diameter is obtained by measuring 100 or more and averaging it.

(7) film roughness

Five measurements are taken using a two-dimensional illuminometer (KOSAKA SE-30D) and then averaged.

(8) Thermal adhesive force measurement (laminate characteristics; peel force)

The first polymer resin layer of the polyester film of the present invention, which has been given thermal adhesion, is brought into contact with the TFS heated to a temperature of 180 to 240 ° C., and a pressure of 100 kg / cm ² is applied between the rubber roll and the steel roll made of silicon. After laminating in an applied state, it was quenched and subjected to 180 ° peeling experiment.

(9) Moldability

The steel plate laminated with TFS at 210 degreeC was shape | molded by the draw molding machine, and the draw & redraw can was made. 1% saline solution was added to the can, and the lamination defects according to the molding process were evaluated as current values flowing under a voltage of 6V. At this time, if the average of 10 cans is 0.1 mA or less, it can evaluate as a preferable thing.

(10) Hot Water Resistance (Retort Resistance)

After steam retort or dip retort, changes in appearance (whether bleaching occurred) were evaluated.

(11) impact resistance

After the shock was deformed by the can, 1% saline solution was added thereto, and the shock resistance was evaluated as a current value flowing under a voltage of 6V. At this time, if the average of 10 cans is 0.1 mA or less, it can evaluate as a preferable thing.

<Examples 2 to 7>

Except changing the concentration of the isophthalic acid of the first polymer resin layer, the isophthalic acid concentration of the second polymer resin layer, the amount of the inorganic additive, the thickness of the first polymer resin layer and the stretching conditions as shown in Table 1, A polyester film was prepared in the same manner as in Example 1. The properties of the prepared film were measured and the results are shown in Table 1.

<Comparative Examples 1 to 5>

Except for changing the concentration of isophthalic acid in the first polymer resin layer, the concentration of isophthalic acid in the second polymer resin layer, the type and amount of the inorganic additive, the thickness and the stretching conditions of the first polymer resin layer as shown in Table 1 The polyester film was manufactured by the method similar to Example 1. The properties of the prepared film were measured and the results are shown in Table 1.

As can be seen from the above, in order to manufacture a heat-adhesive film for metal lamination suitable for food storage, the type and content of the acid component included in the first polymer resin layer, the acid component of the second polymer resin layer It is necessary to control the type and content, the type, content and particle size distribution of the inorganic fine particles. In addition, in order to maintain the intrinsic properties of the conventional polyester film as it is, to provide heat adhesion, and to enable uniform stretching during engraving, surface crystallinity and molecular orientation of the adhesive surface must be controlled. This is possible by setting the stretching conditions in consideration of the fixed and cooling temperatures. As such, it is possible to produce various co-extrusion films for metal lamination suitable for the lamination method by adjusting the composition and stretching conditions of each resin layer.

Claims (6)

A first polymer resin layer formed of a copolyester comprising 80 to 90 wt% of terephthalic acid and 10 to 20 wt% of isophthalic acid as the acid component in the repeating unit; And 0.02-1 or 2 or more types of spherical silicas formed from the copolyester containing 90 weight% or more of terephthalic acid and 10 weight% or less of isophthalic acid as an acid component in a repeating unit, and whose average particle diameter is 0.05-2.0 micrometers. And a second polymer resin layer containing 0.15% by weight, wherein the first polymer resin layer and the second polymer resin layer both contain 0.005 to 0.2% by weight of the phosphoric acid compound based on each polymer resin layer. Thermal adhesive polyester film for metal lamination. The heat-adhesive polyester film for metal lamination according to claim 1, wherein the copolyester forming the first polymer resin layer has an intrinsic viscosity of 0.55 to 0.75 dl / g and a melting point of 150 to 230 ° C. The heat-adhesive polyester film for metal lamination according to claim 1, wherein the copolyester forming the second polymer resin layer has a melting point of 200 to 250 ° C. The method according to claim 1, wherein the spherical silica has a ratio of long diameter to short diameter of 1.1 or less, the average radius of the small particles is 0.05≤D _{50, a} ≤0.3 and the average radius of the large particles is 0.5≤D _{50, b} ≤2.0, It is a mixture of 2 types of particles, The heat-adhesive polyester film for metal laminations. The method of claim 1, wherein the phosphate compound is trifetyl phosphate, trixylene phosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, trigylenyl phosphate, xylenyl phosphate, cresyl diphenyl phosphate, distearyl pentaerytate At least one compound selected from the group consisting of rititol disphosphate, bis-2,4-di-t-butyl pentylerythritol disphosphate and tris-2,4-di-t-butylphenyl phosphate A heat-adhesive polyester film for metal lamination. According to claim 1, wherein the total thickness of the film is 10 to 38㎛, the thickness ratio of the first polymer resin layer and the second polymer resin layer is 1: 4 to 1: 8 thermal bonding for metal lamination, characterized in that Sex polyester film.