JPH0323098B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Fields) Polyester films are used for various purposes depending on their characteristics. Among these, the present invention relates to a surface-coated polyester film, particularly a surface-modified film with excellent solvent resistance for secondary processing. (Prior Art) Several proposals have already been made regarding methods for modifying the surface of a biaxially stretched polyester film by coating it with a primer during the film forming process. For example, as a method for improving adhesion to ink etc., Japanese Patent Publication No. 48-17382 discloses a method of coating a composition comprising an acrylic or methacrylic resin and an aminoaldehyde condensate or a ureide polymer complex; Examples include a method of coating with a composition consisting of an aqueous polyurethane dispersion and a surfactant as disclosed in JP-A-58-5227, and a method of coating with an aqueous solution, emulsion or dispersion of a polyester resin as disclosed in JP-A-58-5227. be able to.
In addition, as a method for imparting an antistatic effect, JP-A-50-146670 discloses coating an aqueous coating composition of polyethylene oxide, alkali metal salt of acrylic copolymer, sulfonated polystyrene, polyvinyl sulfonic acid, etc. A method is disclosed. Furthermore, JP-A-54-96590 discloses that an acrylic polymer composition having a quaternary ammonium salt in its side chain that is soluble in water or an aliphatic lower alcohol is coated with an acrylic polymer composition that improves ink adhesion and antistatic properties. JP-A No. 56-127450 discloses a method of imparting slipperiness and adhesion by coating with a specific acrylic polymer. Although each of these methods is effective in imparting desired properties to polyester films, they have the following drawbacks. That is, it has low resistance to organic solvents such as toluene, isopropyl alcohol, ethyl acetate, and methyl ethyl ketone used in film secondary processing, such as printing, coating, and lamination. To give a specific example, if printing is continued for a long time using a printing ink diluted with a mixed solvent containing methyl ethyl ketone, isopropyl alcohol, etc. as the main ingredients, which is commonly used in printing processes, the coating film may be removed by the gravure roll. It is easy to cause plate jams and print defects. In addition, in dry lamination processing in which a large amount of adhesive is applied, adhesion failure is likely to occur, particularly in boiling sterilization or high-temperature hot water treatment such as retort treatment, which tends to cause a decrease in adhesive strength. (Problems to be Solved by the Invention) As a result of intensive studies aimed at solving these drawbacks, the present inventors have found that the above-mentioned drawbacks are not observed at all in the coating film having the following solvent resistance. . In other words, in a so-called rubbing test where absorbent cotton is soaked in an organic solvent commonly used in secondary processing and rubbed on the surface of the coating, the coating will not peel off even if the coating is rubbed 10 times or more. The organic solvents commonly used in secondary processing include methanol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl ketone, and mixed solvents thereof. The present invention is aimed at such a coated film, and was achieved as a result of various tests. That is, on at least one side of an unstretched or uniaxially stretched polyester film, at least 20% by weight of an etherified methylolmelamine in its solid content and 5 to 30 parts by weight of an organic acid per 100 parts by weight of the melamine component are added. A water-soluble or water-dispersible resin composition containing an ammonium salt or amine salt of It is an excellent surface-coated polyester film. In the present invention, polyester is a linear saturated polyester synthesized from an aromatic dibasic acid or its ester-forming derivative and a diol or its ester-forming derivative. For example, polyethylene terephthalate, its copolymer, or a blend of these and a small proportion of other resins. The coating composition is applied to an unstretched film produced by melt extruding these resins and formed into a film by a conventional method, or to a uniaxially stretched film further stretched in only one direction. (Means for solving the problems) The coating liquid used in the present invention will be explained.
The coating liquid used in the present invention is an aqueous solution or aqueous dispersion of a resin composition containing an etherified product of methylolmelamine and an ammonium salt or amine salt of an organic acid as essential components. First, the etherified product of methylolmelamine used in the present invention is a compound obtained by reacting a lower alcohol with a methylolmelamine derivative obtained by condensing melamine and formaldehyde to etherify it, and a mixture thereof. Examples of methylolmelamine derivatives include monomethylolmelamine,
Dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, hexamethylol melamine, etc. can be mentioned, but trimethylol melamine or higher is preferable from the viewpoint of crosslinking properties. Also included are condensates consisting of two or three monomers of the above derivatives. Lower alcohols used for etherification include methyl alcohol,
Examples include ethyl alcohol and isopropyl alcohol, but methyl alcohol is most preferred from the viewpoint of reactivity of the etherified product and solubility in water. The degree of etherification of the methylolmelamine of the present invention is
It is preferably 50% to 90%. If the degree of etherification is less than 50%, the reactivity of the etherified methylolmelamine becomes too high, and some of the crosslinking reaction proceeds during storage of the coating solution, resulting in a crosslinked structure of the final film. defects occur. Furthermore, the storage stability of the coating solution also deteriorates. On the other hand, if the degree of etherification exceeds 90%, the reactivity of the melamine component decreases, and the degree of crosslinking of the final film obtained becomes insufficient. Furthermore, at least 20% by weight of the solid content of the water-soluble or water-dispersible resin composition used in the present invention must be the etherified product of methylolmelamine. 20 melamine ingredients
If the amount is less than % by weight, the degree of crosslinking of the coating will be insufficient and the desired solvent resistance will not be obtained. (Function) The ammonium salt or amine salt of an organic acid used in the present invention refers to an ammonium salt or amine salt of an organic compound that is soluble in 5 to 10% sodium hydroxide. The ammonium salt or amine salt of the organic acid is a component that acts as a catalyst for the crosslinking reaction of the etherified methylolmelamine,
It has the characteristic of being a latent catalyst. In other words, it shows almost no catalytic activity under temperature conditions around room temperature, and begins to show activity at around 100°C.
It has the property of rapidly demonstrating its catalytic ability when the temperature exceeds ℃. The purpose of using such a latent catalyst in the present invention is to suppress the reaction of the melamine component during the storage of the coating liquid and the drying process after coating, and to quickly carry out the crosslinking reaction in the stretching heat setting process, especially in the heat setting process. It's about tightening. Examples of ammonium salts or amine salts of organic acids preferred in the present invention include ammonium salts or amine salts of organic compounds having a relatively strongly acidic carboxylic acid group, sulfonic acid group, or sulfine group. Among these, ammonium salts and amine salts of aromatic sulfonic acids such as para-toluenesulfonic acid and dodecylbenzenesulfonic acid are most preferred in terms of catalytic ability, stability, and compatibility with resin components. The amines used to form salts with organic acids are compounds with a structure in which the hydrogen atom of ammonia is replaced with a hydrocarbon group, and because they are easily soluble in water, methylamine, dimethylamine, trimethylamine, ethylamine, and diethylamine are used. , triethylamine and the like are preferred. By the way, the latent catalytic property of ammonium salts or amine salts of organic acids is a property that can only be demonstrated when they are made into salts consisting of the acid and the base.For example, when inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, etc. When used, the etherified product of methylolmelamine reacts quickly at room temperature and is precipitated and separated in the coating solution. Also ammonium salt or amine salt, sodium salt, potassium salt, magnesium salt,
150℃ when replaced with metal salts such as calcium salts
Even if heated to a higher temperature, the crosslinking reaction does not proceed easily. Furthermore, the amount of the ammonium salt or amine salt of the organic acid used in the present invention is difficult to determine unconditionally since the crosslinking promotion effect varies depending on the type of catalyst.
5 to 30 parts by weight per 100 parts by weight of the melamine component,
Preferably it is 10 to 20 parts by weight. The pH of the coating liquid used in the present invention is preferably in the range of 4 to 10. If the pH is less than 4, the reaction of the melamine component will partially proceed during storage of the coating solution, resulting in a decrease in storage stability of the coating solution and defects in the crosslinked structure of the final coating film. Further, if the pH is higher than 10, the reactivity of the melamine component decreases, and the degree of crosslinking of the final coating becomes insufficient. Further, the amount of free formalin contained in the coating liquid used in the present invention is preferably 0.5 to 9 parts per 100 parts of the melamine component. If the amount of free formalin is less than 0.5 parts, the reactivity of melamine will decrease and the degree of crosslinking of the final coating will be insufficient, and if it is more than 9 parts, the reaction of the melamine component will partially proceed during storage of the coating solution. , the storage stability of the coating solution decreases, and defects occur in the crosslinked structure of the final coating. The components other than the etherified product of methylolmelamine and the ammonium salt or amine salt of organic acid in the water-soluble or water-dispersible resin composition used in the present invention have a pH of 4 to 10.
Any water-soluble or water-dispersible polymer substance that is stable within this range may be used, and the type thereof is not particularly limited. Examples include polyolefins, polyesters, polyamides, polyvinyl alcohols, epoxy resins, acrylic resins, urine resins, polyurethanes, cellulose resins, polyvinyl acetate, polyethers, modified products thereof, primers, and the like. It may also be a mixture of two or more types of polymeric substances. In addition, various additives such as emulsifiers, antistatic agents, antiblocking agents, colorants, heat stabilizers, plasticizers, ultraviolet absorbers, and viscosity modifiers can be added as appropriate depending on the purpose. Furthermore, if necessary, alcoholic solvents, etheric solvents, etc. may be added to the extent that they do not significantly affect the stability of the coating solution or the environment during the film forming process. The viscosity of the coating liquid used in the present invention is preferably 200 centipoise (20°C) or less.
If a coating with a voltage exceeding 200 centipoise is used, uneven coating is likely to occur. In addition, the solid content concentration of the coating liquid is usually 10 wt% or less. Further, the coating thickness is not particularly limited, but it is appropriate that the thickness of the final coating film be about 0.01 to 0.5 μm. Any known coating method can be used to apply the water-soluble or water-dispersible resin composition to the surface of the unstretched or uniaxially stretched polyester film. For example, gravure roll method,
A metering bar method, an air knife method, a reverse roll method, and a spray method may be applied independently or in combination. The coating process is applied to an unstretched film that has just been casted by melt extruding the polymer, or to a uniaxially stretched film that has just been stretched in either the vertical or horizontal direction. Drying after coating should be carried out under temperature conditions that do not allow the reaction of the melamine component to proceed, and it is preferable that the coating temperature does not exceed 100°C. If the reaction of the melamine component proceeds during the drying process, defects will occur in the crosslinked structure of the final coating film. After coating on an unstretched film, if it is stretched both vertically and horizontally at the same time, or if it is coated after being stretched vertically and then stretched horizontally, it is supplied to a tenter without drying after coating and is dried using the preheating and stretching process. may be applied. The heat setting conditions after stretching are important in that, in this step, a crosslinking reaction proceeds mainly between the melamine components or between the melamine component and other resin components having crosslinking points. As for this condition, it is preferable that the heat treatment be performed at 180° C. or higher for 4 seconds or longer. Among the above in-line coating methods, a method in which an unstretched film is coated, then vertically stretched and then horizontally stretched, a method in which an unstretched film is coated, then horizontally stretched and then vertically stretched, and an unstretched film is horizontally stretched and then coated, The method of vertical stretching is not preferred because the coating layer may adhere to the stretching rolls or conveyance rolls or coating defects may occur during the vertical stretching. Therefore, it is appropriate to use a method in which an unstretched film is coated and then stretched simultaneously in the vertical and horizontal directions, or a method in which the unstretched film is uniaxially stretched in the vertical direction, then coated, and then stretched in the horizontal direction. Further, in a method of coating a film after biaxial stretching, which is outside the scope of the present invention, it is impossible to obtain the solvent resistance achieved by the method of the present invention even if the same heat treatment is performed. Although the reason for this is not completely clear, it is thought that it is because the adhesion between the coating layer and the base material is inferior to that of the coating film obtained by the in-line method as in the present invention. (Example) Hereinafter, a detailed explanation will be given by giving examples. Note that the solvent resistance test, which is a measurement item in the examples, was conducted in the following manner. Absorbent cotton was impregnated with five types of organic solvents: methyl alcohol, isopropyl alcohol, toluene, ethyl acetate, and methyl ethyl ketone, and the coated surface was rubbed. The strength of solvent resistance was determined by the number of times the coating was rubbed until the coating peeled off. Comparative Example 1 Water-dispersible polyester resin (manufactured by Dainippon Ink Co., Ltd.) Finetex ES-670 (solid content 22wt%)
was diluted with water to obtain an aqueous dispersion with a solid content of 6 wt%. Polyethylene terephthalate resin was extruded from a die using an extruder, and casted on a drum at 60°C to obtain an unstretched film with a thickness of 150μ.
Subsequently, this film was stretched 3.5 times in the extrusion direction using a vertical stretching machine consisting of a roller system heated to 80 to 90°C and having different circumferential speeds. Next, the water dispersibility of the resin described above was applied using the reverse roll method, and the water was heated at 50°C.
After drying, it was stretched 3.5 times in a tenter at 110℃ in the direction perpendicular to the initial stretching direction, and 5.5 times at 210℃ to 230℃.
A coated biaxially stretched film (symbol A) having a thickness of 12.2 microns was obtained by heat setting for seconds. Comparative Example 2 A polyethylene terephthalate resin was extruded from a die using an extruder, and casted on a drum at 60°C to obtain an unstretched film with a thickness of 150μ. Subsequently, the aqueous dispersion used in Comparative Example 1 was applied to this film by a reverse roll method, dried at 50°C, and then stretched 3.0 times in the extrusion direction using a simultaneous biaxial stretching machine at a stretching temperature of 110°C. After stretching 3.5 times in the perpendicular direction, heat setting was performed at 210 DEG C. to 230 DEG C. for 5.5 seconds to obtain a coated biaxially stretched polyester film (symbol B) having a thickness of 12.2 microns. Example 1 100 parts of Finetex ES-670 (solid content 22%) were mixed with 8.2 parts of 65% methyl etherified hexamethylolmelamine (solid content 70%, containing 5% free formalin) and para-toluenesulfonic acid. 0.9 parts of ammonium salt was added, and water was further added and stirred to obtain a water-dispersible resin composition with a solid content of 6%.
This aqueous dispersion had a pH of 7 and a viscosity of 1.4 centipoise. This water-dispersible resin composition was in-line coated in the same manner as in Comparative Example 1 to obtain a coated biaxially stretched polyester film (symbol C). Example 2 The water-dispersible resin composition used for in-line coating in Example 1 was in-line coated in the same manner as in Comparative Example 2 to obtain a coated biaxially stretched polyester film (symbol D). Comparative Example 3 A water-dispersible acrylic resin (manufactured by Miki Riken Co., Ltd.), Riken Resin MC-10B (solid content 45%), was diluted with water to obtain an aqueous dispersion with a solid content of 6%. This dispersion was inline coated in the same manner as in Comparative Example 1 to obtain a coated biaxially stretched polyester film (symbol E). Comparative Example 4 The aqueous dispersion used in Comparative Example 3 was inline coated in the same manner as in Comparative Example 2 to obtain a coated biaxially stretched polyester film (symbol F). Example 3 To 100 parts of Riken Resin MC-10B (solid content 45%), 16.7 parts of an aqueous solution of 60% methyl etherified hexamethylolmelamine (solid content 70%, containing 5% free formalin) and para-toluenesulfonic acid were added. 1.8 parts of ammonium salt was added, and water was further added and stirred to obtain a water-dispersible resin composition with a solid content of 6%.
This aqueous dispersion had a pH of 6.2 and a viscosity of 1.5 centipoise. This water-dispersible resin composition was in-line coated in the same manner as in Comparative Example 1 to obtain a coated biaxially stretched film (symbol G). Example 4 The water-dispersible resin composition used in Example 3 was in-line coated by the method of Comparative Example 2 to obtain a coated biaxially stretched polyester film (symbol H). Comparative Example 5 A polyethylene terephthalate resin was extruded from a die using an extruder and casted on a drum at 60°C to obtain an unstretched film with a thickness of 150μ. Subsequently, this film was stretched 3.5 times in the extrusion direction using a vertical stretching machine consisting of a roller system heated to 80 to 90°C and having different circumferential speeds. followed by tenter
The film was stretched 3.5 times in a direction perpendicular to the initial stretching direction at a temperature of 110°C and heat set for 5.5 seconds at 210°C to 230°C to obtain a biaxially stretched polyester film with a thickness of 12.2μ. The water-dispersible resin composition used in Example 1 was applied to this film by a reverse roll method, and the film was heated to 50°C.
After drying at , heat treatment was performed at 210°C to 230°C for 5.5 seconds to obtain a coated biaxially stretched polyester film (symbol I). Comparative Example 6 The water-dispersible resin composition used in Example 3 was coated by the method of Comparative Example 5 to obtain a coated biaxially stretched polyester film (symbol J). A solvent resistance test was conducted on the coated biaxially stretched polyester films A to J obtained in Examples 1 to 4 and Comparative Examples 1 to 6. The results are shown in Table 1. The numbers shown in the table are the number of times the coating was rubbed before it flaked off. Further, for each coated stretched film obtained in Examples 1 to 4 and Comparative Examples 1 to 6, a 100% stock solution of Lamiace 165 Beni (manufactured by Toyo Ink Co., Ltd.), a general-purpose gravure printing ink containing PVC/urethane resin as the main binder, was added. Parts of methyl ethyl ketone/toluene/isopropyl alcohol = 45/
When a continuous semi-continuous printing test was conducted using ink diluted with 30 parts of a 45/10 mixed solution, printing defects due to plate jamming occurred at a distance of 400 m or less in all comparative examples, but printing defects occurred at a distance of 50,000 m or less in all examples. No plate jams occurred during printing. Table 1 shows the results.
Shown below.

[Table] (Effects of the invention) The surface-coated polyester film produced as described above was able to withstand being rubbed more than 10 times in a so-called rubbing test in which absorbent cotton is soaked in an organic solvent commonly used in secondary processing and the coating surface is rubbed. It has the effect of preventing the coating from peeling off, and has come to offer great industrial advantages.

Claims (1)

[Claims] 1 At least one side of an unstretched or uniaxially stretched polyester film contains at least 20% by weight of an etherified methylolated melamine in its solid content, and 5 to 30 parts by weight per 100 parts by weight of the melamine component. A water-soluble or water-dispersible resin composition containing an ammonium salt or an amine salt of an organic acid is applied, dried, and then stretched biaxially or in a direction perpendicular to the initial stretching direction and heat set.
The resulting surface-coated polyester film has excellent solvent resistance.