JPH0455866B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a laminated plastic film and a method for manufacturing the same. Specifically, the present invention relates to a plastic film whose surface layer is coated with an extremely thin thermosetting resin coating with little coating unevenness, and a high-speed coating method thereof. In more detail, the thickness unevenness of the laminated resin layer was measured by optical interferometry using parallel white light by ±30%.
% or less, and as a high-speed manufacturing method, a roller with a specific curvature and smoothness is brought into contact with the coating liquid surface when the coating liquid is metered onto the film and wetted, and the film and roller surfaces are This paper proposes a coating method that smoothes the coating film by limiting the relative speed of the coating. Generally, plastic films are widely coated with various resins in order to impart properties such as slipperiness, antistatic properties, easy adhesion, abrasion resistance, and gas barrier properties. The coating resin is usually applied without a solvent, in the form of a solution or dispersion, and is dried or cured to be integrated with the base film.
The method of coating the coating liquid is also selected depending on the properties of the coating liquid, the coating thickness, and the purpose of coating, and various methods are employed. However, in recent years, due to the increasing sophistication of various properties required for coating films and the desire to save resources, thin films with high surface precision of 1μ or less are required, and coating methods are also required to be coated at high speeds to increase productivity. There have been cases where the known methods are not satisfactory. When a plastic film is coated with a transparent resin coating of 1μ or less, the refractive index of the coating usually does not perfectly match that of the base film, resulting in a rainbow pattern due to light interference, and slight coating unevenness can impair the appearance. becomes. This rainbow pattern becomes noticeable when the coating thickness is less than 1μ and the thickness unevenness is ±30% or more when measured by optical interferometry using parallel white light. It is necessary to suppress coating unevenness to ±30% or less. Regarding the coating speed, it is extremely difficult to coat the surface of plastic film with a uniform thin film of 1μ or less of transparent thermosetting resin at high speed. At present, we have no choice but to modify the coating film at the expense of Furthermore, the productivity of a series of various processing operations on a film on a production line is often limited by the coating speed. For example, a polyester film is coated with a 0.5μ thick melamine-containing alkyd resin for 200m/200m.
The coating conditions in various methods when carried out at a speed of min are as follows. (1) Gravure coating method - The gravure pattern becomes a rainbow pattern. (2) Offset gravure coating method - An arrow pattern is generated, and a rainbow pattern is also generated due to microbubbles generated at the edge of the roller. (3) Air knife coating method - High air pressure is required to reduce the amount of coating applied, and magatad-like wind patterns appear on the coated surface in a rainbow pattern. (4) Bar coating method - It is difficult to adjust the coating amount, and vertical striped rainbow patterns frequently occur in the length direction due to fluctuations in film tension. (5) Knife coat method - Same as bar coat method. (6) Reverse roll coating method - It is difficult to stably transfer the thin coating film on the roller without drying it, the range of conditions is narrow, and high precision coating cannot be maintained for a long period of time. (7) Squeeze coat (inverse roll coat)
Process: Microbubbles are generated at the edge of the roller, and the spotted pattern becomes a rainbow pattern. (8) Transfer roll coating method - The disadvantages seen in reverse roll coating method and squeeze coating method both occur. (9) Bead coating method - high speed coating of 50m/min or higher is not possible. (10) Spray coating method - A smooth coated surface cannot be obtained. Regarding the method of smoothing the coating surface, the conventionally used smoothing bar is effective in low-speed coating, but at speeds of 150 m/min or more, it disturbs the coating surface and causes forward and reverse rotation. Or, even when using two stages, the rainbow pattern cannot be reduced. Furthermore, even with the so-called film smoothing method in which a flexible film is applied to the surface of the coating liquid to smooth the coating surface, microbubbles are generated at the tip of the film at high speeds, resulting in a rainbow pattern with vertical stripes. The present inventors have invented a laminated film with improved adhesiveness and a good appearance, and have also conducted extensive research into a high-speed production method for the same, and have finally arrived at the present invention. That is, (A) a mixture of alkyd resin and melamine and/or urea resin; (B) a mixture of acrylic resin and melamine and/or urea resin;
or mixture with urea resin, (C) 100% modulus
A laminate of a thermosetting resin layer with a thickness of 1μ or less selected from any urethane resin having a weight of 80Kg/cm2 or ^more and a thermoplastic resin layer, wherein the thickness unevenness of the thermosetting resin layer is , is a laminated film that is ±30% or less when measured by optical interferometry using parallel white light,
As a high-speed production method, a plastic film that can run at a speed of 150 m/min or more is used to produce (A) a mixture of alkyd resin and melamine and/or urea resin, and (B) a mixture of acrylic resin and melamine and/or urea resin. , (C) 100% modulus 80
After applying a thermosetting resin solution or dispersion selected from urethane resins of Kg/cm ² or more, when the coating liquid is wet, apply a mirror roller with a diameter of 80 mm or more and a surface roughness of 0.4 μ or less to the coating liquid surface. The relative speed between the film and the roller surface is 10 to 100 m/min.
This is a high-speed thin film coating method by rotating the roller to smooth the coating film so that the final coating film thickness is 1.0 μm or less. The plastic film in the present invention is an unstretched, uniaxially stretched or biaxially stretched film made of thermoplastic synthetic resin such as polyamide resin, polyester resin, polyolefin resin, polyvinyl chloride resin, etc., and is used to improve the adhesion of the coating film. This includes those that have been pretreated such as corona discharge treatment or fire treatment. The coating agent used in the present invention is a so-called thermosetting resin solution or dispersion that undergoes a curing reaction at room temperature or by heating after coating film formation, and includes, for example, alkyd resins, melamine resins, urea resins, acrylic resins, reactive urethane resins, and These compounds are listed. The present invention is not necessary for coating agents that have been modified to such an extent that no optical interference pattern occurs by ordinary coating methods. For example, in the case of reactive urethane resin, the inventors' experience shows that the 100% modulus of the coating film is 80.
This method is especially necessary for so-called hard coatings of Kg/cm ² or more. Here, 100% modulus is
This is a value measured in accordance with JIS K6301. In addition,
Antistatic agents, stabilizers, antiblocking agents, and/or colorants may be added to the coating agent as long as they do not substantially impair the transparency of the coating film. Furthermore, the measurement method by optical interference method using parallel white light rays as used in the present invention is the following measurement method. Generally, the measurement of film thickness can be roughly divided into two types: a contact measurement method using a dial gauge, etc., and an optical measurement method using optical absorption or interference. Among these measurement methods, there are two methods: one is to keep the wavelength of the light constant and change the angle of incidence on the film, and the other is to fix the film and change the wavelength of the light. Both methods utilize the phenomenon of optical interference. This is what I did. These methods can accurately measure extremely small areas on the film while the film is stationary, but in order to measure the overall thickness unevenness of the film, a moving part is required in the optical system. Moreover, since precise movement is required, measurement errors are likely to occur in practice, and this method is particularly inapplicable to measurements of interference rainbow patterns with thickness irregularities of 1 μm or less. In the case of films, an important factor other than mechanical performance is good appearance, but in the case of films with a thickness of 1 μm or less, conventionally the only way to judge this was by visual inspection, making it difficult to make an objective evaluation. It was hot. The present inventors investigated this evaluation method and found that the interference method using parallel white light is the most suitable. That is, in this method, a parallel white light beam is irradiated onto a traveling film, and the wavelength intensity distribution of the light beam transmitted through the film or reflected by the film is detected to measure the film thickness. When white light is irradiated onto a film, in addition to the light that directly passes through the film, there is also light that is reflected several times between both surfaces of the film and then exits.These light beams interfere with each other and produce specific wavelengths. A phenomenon occurs in which light of certain wavelengths becomes stronger and light of a specific wavelength becomes weaker. In other words, the wavelength intensity distribution of the radiant energy of the light (hereinafter referred to as the spectrum of light) before it enters the film changes as it passes through the film. This change depends on the film thickness d and the refractive index n if the incident angle of the light beam is constant. Therefore, by irradiating a film with white parallel light and measuring the spectrum of the light transmitted through the film, the thickness of the film can be determined from the previously measured refractive index of the film. The light used as a light source should be approximately white, that is, it should have almost constant radiant energy regardless of wavelength in the visible region, and the spectrum of the light source should have a distribution that does not cause misidentification of maxima and minima due to interference of transmitted light. It's okay to have it. There is no particular limit to the wavelength range of the light source, but visible light is most suitable as the film does not have extreme absorption at a specific wavelength, and the wavelength is approximately 3000 to 8000 Å, preferably 4000 to 8000 Å. . If a wavelength in this range is used, it is possible to measure a film with a thickness of about 0.5 to 10 microns with extremely high accuracy by utilizing the interference of an optical path difference of about the wavelength to several tens of times the wavelength. In the present invention, in order to detect the spectrum of transmitted light or reflected light, a light source of parallel white light and a detection section are arranged opposite each other, and a film is run through the space between the light source and the detection section, that is, the irradiation section. The traveling film may be irradiated with parallel white light from a light source, and the reflected light may be received by the detection section. To explain how to calculate the thickness of a film from its spectrum, generally speaking, when a film is irradiated with white light, the light that passes through the film directly, or the light that passes through the film and then reflects once on the inside of the film and exits the film. There is light that is reflected several times between the two surfaces and exits. These two types of light interfere with each other, and as a result, light with a specific wavelength becomes stronger and light with a specific wavelength becomes weaker. In other words, the wavelength intensity distribution of the radiant energy of the light (hereinafter referred to as the spectrum of light) before it enters the film changes as it passes through the film. This change depends on the film thickness d and the refractive index n if the incident angle of the light beam is constant. Therefore, by irradiating a film with white parallel light and measuring the spectrum of the light transmitted or reflected by the film, the thickness of the film can be determined from this and the previously measured refractive index of the film. The maximum value of the light spectrum can only be obtained when the optical path difference between the two types of light mentioned above is an integral number (order of interference) times the wavelength of the light.
If the wavelength showing the maximum is λ, then the film thickness d
can be expressed by the following formula. d=1/2n cosθm・λ (where θ is the angle of refraction and m is the order of interference) When measuring the spectrum of transparent light, the detection section uses a spectrometer, for example, to separate the spectra, and then uses a linear light receiving element as a light receiving element. Light receiving element (linear image sensor)
By receiving light using a sensor, the spectrum can be measured all at once. In the case of a laminated film, the above equation holds true for each layer, and the combined spectrum is detected, so it is necessary to separate them numerically. If the film thickness of each layer is similar, separation is difficult, but if the thickness of the laminated part is 1 μm or less as in the present invention, the difference from the base film is large, so separation is easy. The present inventors made various films with different thickness unevenness in the laminated parts, and conducted a study by comparing the visual appearance evaluation with the thickness unevenness measurement results by optical interferometry using parallel white light beams. It was found that when the thickness is less than 1 μm, interference fringes become noticeable when the thickness unevenness is ±20% or more, and they can be particularly clearly identified when the thickness exceeds ±30%. Therefore, in order not to impair the appearance, it is necessary to reduce the thickness unevenness to ±30% or less, preferably ±20% or less when measured by optical interferometry using parallel white light. In the coating method of the present invention, the method of measuring and applying the film coating liquid is not particularly limited.
Regardless of the accuracy of the coated surface, any known method that can coat the target coating amount can be used. A diameter of 80 mm or more, preferably 120 mm, is obtained when the measured coating liquid is wetted, that is, before the film formation starts by drying.
A mirror roller with a surface roughness of 0.4 μm or more and a surface roughness of 0.4 μ or less is brought into contact with the coating liquid surface, and the relative speed between the film and the roller surface is 10 to 100 m/min, preferably 10 to 50 m/min.
The roller is rotated so that the coating liquid surface is smoothed. If the roller is brought into contact with the coating after the coating liquid film has started to form, no smoothing effect will be obtained, and instead, horizontal step-like coating unevenness will occur. Furthermore, if the diameter of the smoothing roller is smaller than 80 mm, the coating film will be disturbed when the roller leaves, regardless of the rotational speed of the roller, and a coating film free of optical interference patterns will not be obtained. Furthermore, if the roller surface roughness exceeds 0.4μ, a slight streak pattern will remain on the coating film, especially in thin coatings of 0.5μ or less. In the present invention, the relative speed between the film and the roller surface is (film speed) - (circumferential speed of the roller)
is the speed defined by , and is particularly important. When the speed of the roller surface is around the same speed as the film, the coating film is disturbed, and the relative speed with the film is 10 to 100 m/min.
The coating film is well smoothed within the range of
When the speed exceeds 100 m/min, vertical striped patterns tend to occur. If the coating film is thin, the relative speed is 10 to 50.
m/min is preferred. According to the present invention, by simply installing a mirror rotating roller that satisfies the above conditions before drying the existing coating equipment, the problem of coating unevenness caused by light interference can be eliminated by coating a transparent thermosetting resin coating of 1μ or less. It can be applied uniformly and at high speed until it runs out, and can be widely used for various surface modification of films with good appearance. Further, when the present invention is employed for in-line coating of unstretched or uniaxially stretched film during the plastic stretched film manufacturing process,
We have created a pre-coated biaxially stretched film that has a good appearance without reducing the productivity of the entire process, and even if the thickness of the coating film becomes thinner due to stretching after coating, defects due to optical interference will not be a problem. It is particularly effective because it can be produced with high efficiency. Next, the present invention will be explained in more detail based on Examples, but the present invention is not limited thereto. Comparative experiment example One side of a 12μ thick biaxially stretched polyester film, Emblem #1200 (manufactured by Unitika KK), was coated with various thermosetting resin coating liquids shown below under various conditions, and the coated surface was measured using reflected natural light. Comparative observations were made. The results are shown in Table 1. Coating liquid A Aminoalkyd resin coating liquid Phthalkyd M641-50 (manufactured by Hitachi Chemical KK)/
A resin mixture consisting of Melan 20 (manufactured by Hitachi Chemical KK)/nitrocellulose in a weight ratio of 63/27/10 was mixed with toluene/ethyl acetate/cyclohexanone in a 6/6/20 weight ratio.
Solid content concentration 15 in mixed solvent consisting of 2/2 weight ratio
Coating liquid obtained by dissolving it so that it becomes %. B Thermosetting acrylic resin coating liquid Hitaroid 2405/Hitaroid 2602/Melan 20
(all manufactured by Hitachi Chemical KK) in a 40/30/30 weight ratio toluene/xylene/
A coating liquid obtained by dissolving n-butanol in a mixed solvent with a weight ratio of 1/1/1 to a solid content concentration of 10%. C Solvent type urethane resin coating liquid Desmofene 800 (Japan Polyurethane KK)
Coronate HL) was dissolved in ethyl acetate.
(manufactured by Nippon Polyurethane KK) and blended so that the isocyanate group/hydroxyl group ratio is 1.2 and the solid content concentration is 6%. The 100% modulus of the coating film is 150Kg/cm ² . D Water-dispersed urethane resin coating liquid INPRANIL DLH, an anionic aliphatic polyester urethane water dispersion
(manufactured by Bayer AG, solid content 40%) 700 parts by weight of ion-exchanged water was added to 100 parts by weight, and the mixture was thoroughly stirred to obtain a coating solution with a solid content of 5%. The 100% modulus of the coating film is 50
kg/ ^cm2 . E Water-dispersed urethane resin emulsion 6 parts by weight of a 5% aqueous solution of trimethoxymelamine was added to 100 parts by weight of the coating solution D, and the mixture was thoroughly stirred to obtain a coating solution with a solid content of 5%. The 100% modulus of the coating film is 85Kg/cm ² . As is clear from Table 1, in high-speed coating of thermosetting resin coating liquids, it is not possible to obtain a coating film of 1μ or less without rainbow patterns caused by light interference using known methods; The coating method of the present invention is extremely effective. Regarding polyurethane resin coating agents, the present invention is not necessary if the coating film has a low 100% modulus, but such coating agents generally contain relatively long chain pre-coating agents that already have urethane bonds in the molecule. The polymer is the target unit of the curing reaction, and the blocking resistance and heat resistance are poor. In coatings that require these performances, there are many reaction sites at the coating film curing stage, that is,
Since a hard coating agent is required, the coating method of the present invention has no choice but to be used.

【table】

[Table] The coating liquid was smoothed.
Examples 1 to 4 Biaxially stretched nylon film “Emblem” (Unitika) with a thickness of 15 μm that was subjected to corona discharge treatment on one side
Coating liquid A used in the comparative experiment example on the treated surface of (manufactured by KK)
was applied at a speed of 150 m/min with a 175-mesh gravure, and the diameter was 120 mm and the surface roughness was
A 0.3μ mirror surface roller was brought into contact with the film, and the film was rotated at a relative speed of 50 m/min to smooth the coating film and then dried. Similarly, coating solutions B and C were each coated and dried. The coating thicknesses of these laminated films were measured by optical interference method using parallel white light beams with wavelengths of 3000 to 8000 Å, and were found to be 0.5μ±0.1μ and 0.3μ, respectively.
±0.05μ and 0.1±0.03μ, both of which were films with good appearance and no noticeable interference fringes. Examples 5-8 Melt extrusion of polyethylene terephthalate
An unstretched film was formed on a drum cooled to 40°C while applying electrostatic charge, and then stretched 3.5 times in the longitudinal direction using a peripheral speed difference between metal rollers heated to 90°C, and then stretched at a speed of 200 m/min. Coating agents A, B, D, and E used in the comparative experiment were each applied to one side of the longitudinally stretched film while it was running with a gravure roll of 175 mesh, and the diameter was 230 mm and the surface roughness was 230 mm.
A 0.15μ mirror roller was brought into contact with the coating surface while rotating at a relative speed of 50 m/min to the film to smooth it, and then dried. The coating film was then fed into a stenter at the same speed, preheated to 105°C, stretched 3.5 times in the transverse direction, heat treated in an atmosphere of 230°C for 4 seconds, cooled and rolled up.
The thickness of the substrate of the obtained stretched film was 12μ, and the thickness of the coating film was measured by optical interferometry using parallel white light with a wavelength of 3000 to 8000Å.
A0.08μ±0.02μ, B0.08μ±0.02μ, D0.04μ±0.01μ
,
and E0.04μ±0.01μ. The coated surfaces of these films had excellent appearance, with no rainbow pattern due to reflected light.

Claims (1)

[Claims] 1 (A) A mixture of alkyd resin and melamine and/or urea resin, (B) A mixture of acrylic resin and melamine and/or urea resin, (C) 100% modulus of 80 kg/cm ² or more A laminated film consisting of a thermosetting resin layer with a thickness of 1.0μ or less selected from any of the urethane resins and a thermoplastic resin layer with a thickness of 2μ or more. 2. The laminated film according to claim 1, wherein the thickness unevenness of the thermosetting resin layer is ±30% or less as measured by optical interference method using parallel white light. 3 A plastic film that can run at a speed of 150 m/min or more, (A) a mixture of alkyd resin and melamine and/or urea resin, (B) a mixture of acrylic resin and melamine and/or urea resin,
(C) After applying a thermosetting resin solution or dispersion selected from urethane resins with a 100% modulus of 80 kg/cm ² or more, the diameter is 80 mm when the coating liquid is wetted.
As described above, a mirror roller with a surface roughness of 0.4μ or less is brought into contact with the coating liquid surface, and the roller is rotated so that the relative speed between the film and the roller surface is 10 to 100 m/min to smooth the coating film and final Coating film thickness
A method for producing a laminated film characterized by coating a thin film of 1.0μ or less at high speed. 4. The method for producing a laminated film according to claim 3, wherein the laminated film during the manufacturing process is an unstretched film or a uniaxially stretched film, and is stretched in at least one direction after coating.