JP2005125627A - Method for forming surface protecting layer with smooth surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a surface protecting layer 2 with a smooth surface, which can prevent an interference streak from occurring due to interference of reflected light on its front and back sides, even if a surface of the layer 2 is formed as the smooth surface such as a mirror surface, when the layer 2 composed of a transparent cured resin is formed on a surface of a base material 1, at least the surface of which is composed of a thermoplastic resin layer 11. <P>SOLUTION: The surface protecting layer 2, which is composed of the transparent cured resin, whose surface is rougher than a surface of the thermoplastic resin layer 11 and which has a finely uneven surface shape, is formed on the layer 11 with the smooth surface. After the layer 2 is cured, hot press treatment is applied from on the layer 2, so that the surface of the layer 2 can be smoothed, and so that concurrently with that, a finely uneven interface shape, wherein the surface shape of the layer 2 before the application of the hot press treatment is almost turned upside down, can be formed on an interface between the layer 2 and the layer 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a method for forming a surface protective layer made of a transparent curable resin for the purpose of improving surface hardness and wear resistance on the surface of a thermoplastic resin film or a thermoplastic resin molded body. The present invention relates to a method for forming a surface protective layer having a smooth surface that can prevent the occurrence of interference fringes due to interference of reflected light on the front and back surfaces even if the surface is a mirror-like smooth surface. A thermoplastic resin molded body having a surface protective layer formed according to this method is useful as an optical component such as an optical film or a lens, a surface protective film, a cosmetic material, or the like.

  Conventionally, a surface protective layer made of a transparent curable resin having a high hardness has been widely used on the surface of a substrate such as a transparent thermoplastic resin film or plastic molded body for the purpose of preventing scratches on the surface. ing. However, when the surface of the base material and the surface of the surface protective layer are highly smooth, the surface protective layer has a very slight amount unless the refractive index of the base material and the refractive index of the surface protective layer completely match. If the thickness is uneven, interference fringes will occur due to interference of reflected light on the front and back surfaces of the surface protective layer, which may hinder use in optical applications and unsightly design defects in design applications such as cosmetics. Therefore, there is a demand for a method for forming a surface protective layer that does not generate interference fringes.

  As a countermeasure against such a problem, for example, by adding metal oxide ultrafine particles having a refractive index higher than that of the substrate to the surface protective layer based on a resin having a refractive index lower than that of the substrate, the surface protective layer There is a proposal of a method of increasing the refractive index of the base material to match the refractive index of the substrate (see Patent Documents 1 and 2). However, this method uses extremely expensive metal oxide ultrafine particles at present, so an increase in the manufacturing cost of the product is inevitable, and a slight decrease in the transparency of the surface protective layer is inevitable. In order to match the refractive index perfectly, it is necessary to precisely control the blending amount of the metal oxide ultrafine particles, so the quality control of the coating solution is cumbersome and defective products are generated due to slight deviations in the blending amount. There are problems such as accidents being completely immune.

  On the other hand, the occurrence of interference fringes is based on the principle that the surface of the surface protective layer and the interface between the base material and the surface protective layer are both a unique phenomenon when the surface is a very smooth surface. There has already been proposed a method for preventing the generation of interference fringes by introducing a fine uneven shape at the interface between the substrate and the surface protective layer while maintaining the surface of the surface protective layer smooth. As a specific method, the surface of the base material is embossed in a fine uneven shape in advance, and a surface protective layer is formed on the surface so that the surface becomes a smooth surface (see Patent Document 3). And a method for roughening the surface of the substrate by the action of the solvent during coating by using a solvent that attacks the substrate as a solvent for the coating liquid for forming the surface protective layer (Patent Document 4) There is.

  However, the former may cause coating unevenness due to the influence of fine irregularities on the surface of the substrate during coating formation of the surface protective layer, which may impair the surface smoothness, especially solvent-type coating. When liquid is used, even if the surface is smooth immediately after coating, the effect of fine irregularities on the surface of the base material appears on the surface of the coating film due to evaporation and drying of the solvent. The latter, on the other hand, is affected by slight variations in coating conditions such as solvent concentration, viscosity, and drying speed of the coating liquid during coating, and the substrate and surface protective layer It is difficult to stabilize the state of the interface with the substrate, it is difficult to select a solvent depending on the combination of the material of the base material and the surface protective layer, and the solvent that erodes the base material swells the base material. It is likely to occur, or the surface of the base material is clouded to deteriorate transparency and design There are problems such that there is, none can say that universal way.

Prior art document information.
JP-A-7-151902 JP 2000-162403 A JP-A-8-197670 JP 2003-205563 A

  The present invention has been made to solve the above-described problems in the prior art, and at least a surface protective layer made of a transparent curable resin is formed on the surface of a base material made of a thermoplastic resin layer. When forming the surface protective layer, even if the surface of the surface protective layer is a smooth surface such as a mirror surface, the formation of a surface protective layer with a smooth surface that can prevent the occurrence of interference fringes due to interference of reflected light on the front and back surfaces Is to provide a method.

  In the present invention, at least the surface is made of a thermoplastic resin layer, the surface of the substrate having a smooth surface shape is made of a transparent curable resin, and the surface roughness is finer than the surface of the thermoplastic resin layer. After forming and curing a surface protective layer having an uneven surface shape, the surface of the surface protective layer is smoothed by subjecting the surface protective layer to a hot press process, and at the same time, The interface between the protective layer and the thermoplastic resin layer is characterized by forming a fine irregular interface shape that is substantially reversed from the surface shape of the surface protective layer prior to the hot-pressing treatment. This is a method for forming a surface protective layer having a smooth surface.

  Further, in the above method, the present invention provides that the surface roughness (JIS B 0601 (2001)) of the base material before formation of the surface protective layer is an arithmetic average roughness Ra of 1.0 μm or less, and a maximum height roughness. Rz is 10.0 μm, the surface roughness of the surface protective layer before the hot-pressing treatment is arithmetic average roughness Ra of 0.5 to 10.0 μm, and maximum height roughness Rz of 2.0 to The surface roughness of the surface protective layer after the hot pressing process is 30.0 μm, the arithmetic average roughness Ra is 1.0 μm or less, and the maximum height roughness Rz is 10.0 μm or less. It is what.

  According to the present invention, the surface of the surface protective layer is a mirror-like smooth surface excellent in optical properties and glossy design, while the interface between the surface protective layer and the substrate is a fine uneven interface. Since the shape is formed, the reflected light at the interface has a low coherence with the reflected light on the surface of the surface protective layer, and it is difficult to recognize interference fringes. This effect can be obtained even when the difference in refractive index between the base material and the surface protective layer is large, so that the resin can be freely designed for the surface protective layer without being restricted by the refractive index. In addition to facilitating the various functionalities required for the protective layer, it does not require special expensive additives, so it can be manufactured at low cost, and the solvent for coating the surface protective layer can be selected. Furthermore, even if some coating unevenness may occur during the coating of the surface protective layer, it is corrected by the hot-pressing process, so that an ideal surface product can be easily manufactured. Have various practical advantages.

  The substrate 1 used in the method of the present invention may be at least as long as the surface is made of the thermoplastic resin layer 11, may be entirely made of the thermoplastic resin layer 11, or may be made of surface thermoplasticity. A layer made of an arbitrary material may be laminated on the back surface of the resin layer 11. Furthermore, after the surface protective layer 2 is formed on the surface of the thermoplastic resin layer 11 according to the method of the present invention, another thermoplastic resin layer or a layer made of an arbitrary material may be laminated on the back surface arbitrarily. can do.

  The thermoplastic resin layer 11 on the surface of the base material 1 is not particularly limited in the present invention, but it is desirable that its surface shape be easily deformed during the hot-pressing process described later. Those having a low softening temperature are preferably used. Specifically, for example, polyolefin resins such as polyethylene and polypropylene, acrylic resins such as polymethyl methacrylate, amorphous polyester resins such as 1,4-cyclohexanedimethanol copolymerized polyester (so-called PET-G), poly A vinyl chloride resin etc. can be used conveniently. Further, it may be a mixture of a plurality of types of thermoplastic resins or a laminate composed of a plurality of thermoplastic resin layers. If the thickness of the thermoplastic resin layer 11 is too thin, it is difficult to perform the hot-pressing process.

  It is desirable that the surface of the substrate 1, that is, the surface of the thermoplastic resin layer 11, be as smooth as possible before the formation of the surface protective layer 2. Specifically, JIS B 0601 ( 2001) (the same shall apply hereinafter) arithmetic mean roughness Ra is preferably 1.0 μm or less, and maximum height roughness Rz is preferably 10.0 μm or less. If the surface roughness is rougher than this, when the surface protective layer 2 is provided, the thickness of the coating film of the surface protective layer 2 becomes extremely thin at the top of the convex shape of the surface of the thermoplastic resin layer 11, which is sufficient. Due to the inability to maintain the surface performance or the unevenness of the surface of the thermoplastic resin layer 11 itself and / or uneven coating of the surface protective layer 2 due to the size, the surface protective layer 2 can also be subjected to a subsequent hot press process. This is because it may be difficult to smooth the surface.

  The surface protective layer 2 formed on the surface of the thermoplastic resin layer 11 is formed of a curable resin so that the thickness of the surface protective layer 2 is not changed by a subsequent hot press process. The curable resin can be arbitrarily selected from various materials such as a polyurethane resin, a polyester resin, an acrylic resin, and the curing method is also a thermosetting type, for example, an ultraviolet ray or an electron beam. It can be arbitrarily selected from various methods such as ionizing radiation curing type. A plurality of types of resins may be mixed. However, if the curing rate is extremely high and the softening temperature of the cured resin is very high, sufficient surface smoothness may not be obtained after the hot-pressing process. Certain considerations are required in combination with pressure pressing conditions (temperature, pressure, etc.).

  Various additives are mixed in the curable resin forming the surface protective layer 2 for the purpose of imparting various functionalities such as scratch resistance, easy contamination removal, weather resistance, antistatic property and the like. May be. Examples of the method for forming the surface protective layer 2 include various known methods such as roll coating, gravure coating, knife coating, die coating, lip coating, comma coating, flow coating, dip coating, and spray coating. It can be arbitrarily selected from various coating methods. If the thickness of the surface protective layer 2 is too thin, the protective effect will be poor, and the fine uneven surface shape described later will not be sufficiently formed. If it is too thick, it will be difficult to smooth the surface by the hot press process described later. Therefore, in general, it is preferable to design appropriately within an average thickness range of about 2 to 50 μm.

  When the surface protective layer 2 is applied and formed, it is necessary to form a fine uneven surface shape with a rougher surface roughness than the surface of the thermoplastic resin layer 11 forming the surface of the substrate 1 on the surface. There is. Otherwise, it becomes difficult to form a fine uneven interface shape with the required roughness at the interface between the thermoplastic resin layer 11 and the surface protective layer 2 during the subsequent hot-pressing treatment. As a result, a sufficient interference fringe suppression effect cannot be obtained. On the other hand, when the surface roughness of the surface protective layer 2 formed by coating is excessive, the resistance to deformation of the surface protective layer 2 made of a curable resin is large, so that it is sufficient after the subsequent hot press process. There is a risk that it will not be possible to obtain a smooth surface. Considering such circumstances, the surface roughness of the surface protective layer 2 is such that the arithmetic average roughness Ra is in the range of 0.5 to 10.0 μm and the maximum height roughness Rz is in the range of 2.0 to 30.0 μm. It is desirable to form.

  As a method for forming the fine uneven surface shape as described above on the surface of the surface protective layer 2, any conventionally known method can be used. For example, a method of adjusting the viscosity of the coating liquid to be higher than usual to generate irregularities due to insufficient leveling after coating, a method of coating the entire surface uniformly, and then applying a fine pattern again, coating Adding organic or inorganic fine particles (so-called matting agent) to the liquid to roughen the surface of the coating film, spraying an airflow after coating to ripple the coating film surface, finely drying the coating film after touch For example, a method of applying an uneven embossing, a method of coating a release film having a fine uneven surface before solidification of the coating film, and peeling after solidification. When the substrate 1 is a thermoplastic resin film, the gravure coating method uses a coating liquid having a higher viscosity than usual, and there is no need to perform any other special process or treatment, and in a normal manner. There is an advantage that high-speed production is possible.

  After the coating of the surface protective layer 2, the surface protective layer 2 is cured at least to the extent that the surface protective layer 2 does not flow and change its thickness by the hot pressure pressing process before the hot pressing process. The degree of curing at this time does not necessarily need to be completely cured, and may be in a semi-cured state as long as the fluidity under the hot press processing conditions is lost. When the hardness of the surface protective layer 2 in the fully cured state is extremely high, it may be difficult to smooth the surface of the surface protective layer 2 by the hot pressing process. It is effective to perform a hot-pressing process in a state of being semi-cured to such an extent that it is lost, and then completely cure.

  The curing method may be selected from heating, ionizing radiation irradiation and the like according to the type of curable resin used for the surface protective layer 2. In particular, when a thermosetting resin and an ionizing radiation curable resin are used in combination, only one of them is cured into a semi-cured state, and after the hot press process, the other is cured and completely cured. In the fully cured state, it is possible to form a high-hardness surface protective layer 2 that is difficult or impossible to smooth by hot pressing, and the degree of cure in the semi-cured state is stable, so that the surface obtained There is an advantage that the surface smoothness of the protective layer 2 is also stabilized.

  As a method of the hot press process, a mirror surface embossing roll or a mirror surface embossing plate made of a hard material such as a metal whose surface is a mirror-like smooth surface is used. It is common to do this. In particular, when the substrate 1 has a web shape (continuous long shape), it is preferable to use a hot roll press method because of its excellent productivity. As processing conditions, it is necessary to heat at least a temperature at which the surface shape of the thermoplastic resin layer 11 on the surface of the substrate 1 can change, that is, generally a temperature equal to or higher than the thermal deformation temperature.

  By this hot pressing process, the surface protective layer 2 having the fine uneven surface shape is crushed by a smooth embossing roll or embossing plate, and the surface is smoothed. In places where the surface of the surface protective layer 2 was previously convex with respect to the surroundings, that is, where the surface protective layer 2 was locally thicker than the surroundings, the surface was leveled to the same height as the surroundings. Accordingly, the back surface, that is, the interface with the thermoplastic resin layer 11 moves downward so as to sink into the thermoplastic resin layer 11, and as a result, at the interface between the surface protective layer 2 and the thermoplastic resin layer 11. Is formed with a fine concavo-convex interface shape substantially corresponding to a shape obtained by inverting the surface shape of the surface protective layer 2 before the treatment.

  Thus, while the surface of the surface protective layer 2 becomes a mirror-like smooth surface, the interface between the surface protective layer 2 and the thermoplastic resin layer 11 becomes non-smooth so that the reflected light at the interface is scattered. The effect of reducing the interference with the reflected light on the surface of the surface protective layer 2 is produced. As a result, the width of the interference fringes observed from the surface side of the surface protective layer 2 is very small, and the interference fringes are very weak in intensity, so that it is difficult to confirm visually. Generation of interference fringes is suppressed.

  Here, the surface roughness of the surface protective layer 2 after the hot-pressing treatment is such that the arithmetic average roughness Ra is 1.0 μm or less and the maximum height so that the surface is sufficiently observed visually as a mirror-like smooth surface. It is desirable that the roughness Rz is 10.0 μm or less. In order to form such a smooth surface, a mirror surface embossing roll or a mirror surface embossing plate used in the hot-pressing process should have at least a surface smoothness equivalent to or higher than this (surface roughness is not more than the above). Needless to say, what should be done.

  In addition, when manufacturing a cosmetic material according to the manufacturing method of this invention, it is preferable that the surface definition Gd value of the surface after a hot press process is 0.8 or more. By doing so, an effect referred to as a so-called high gloss finish in which a reflected image of an object or the like is reflected on the surface of the decorative material without being greatly distorted is produced. Note that the Gd value is an index that represents the distinctness of image gloss set by the Japan Color Research Institute.

  When the method of the present invention is applied to the production of a decorative material, particularly a decorative sheet, for example, the surface protective layer 2 is formed by the method as described above using the transparent thermoplastic resin film as the thermoplastic resin layer 11 as the substrate 1. Then, the pattern layer 12 can be provided on the surface opposite to the surface protective layer 2 (FIG. 2). The pattern layer 12 may be directly printed by various printing methods, or the pattern layer 12 once provided on the release film may be applied to the back surface of the transparent thermoplastic resin film by a transfer method. The whole or part of the pattern layer 12 may be formed as a concealment layer.

  Further, another thermoplastic resin film 13 may be provided on the surface opposite to the surface protective layer 2 of the transparent thermoplastic resin film 11 as the thermoplastic resin layer 11 with or without the pattern layer 12 interposed therebetween. Good (Figure 3). This thermoplastic resin film 13 is provided for the purpose of improving the concealing property of the decorative sheet, increasing the sheet rigidity, improving the workability, etc. As the type of the thermoplastic resin, It can be arbitrarily selected from the same various materials as in the case of the thermoplastic resin layer 11 and may be transparent or colored.

  As a manufacturing procedure of the decorative sheet having such a configuration, after forming the surface protective layer 2 on the transparent thermoplastic resin film 11, the pattern layer 12 may be provided on the back surface, and another thermoplastic resin film 13 may be laminated. The thermoplastic resin film 13 provided with the pattern layer 12 on the surface in advance may be laminated on the back surface of the transparent thermoplastic resin film 11 provided with the surface protective layer 2. After the other thermoplastic resin film 13 is laminated on the back surface via the pattern layer 12, the surface protective layer 2 may be formed on the surface of the transparent thermoplastic resin film. Furthermore, you may provide a primer process in the back surface of the lower thermoplastic resin film 13 in order to improve the adhesiveness with the to-be-adhered base material of a decorative sheet.

  Note that the three steps of coating, curing, and hot-pressing in the formation of the surface protective layer 2 do not necessarily have to be carried out as continuous steps, and between the coating and curing and / or between curing and hot-pressing. Between these, other processes such as formation of the pattern layer 12 and lamination of other thermoplastic resin films 13 may be sandwiched. For example, when laminating the transparent thermoplastic resin film 11 and the other thermoplastic resin film 13 by the thermal laminating method, the surface protective layer 2 is previously formed on the surface by coating and curing, before the hot press process. When the transparent thermoplastic resin film 11 and the other thermoplastic resin film 13 are heat-laminated through the pattern layer 12 formed on one of them, as a pressure roll to be brought into contact with the surface protective layer 2 side, By using a mirror surface roll having a mirror-like smooth surface, the transparent thermoplastic resin film 11 and another thermoplastic resin film 13 are heat laminated and simultaneously the surface of the surface protective layer 2 is subjected to a hot press process. If the method to apply is employ | adopted, there exists an advantage which can manufacture simply and efficiently, without increasing a special process compared with the conventional manufacturing method.

  Silicone-modified isocyanate-cured polyurethane as a surface protective layer on one side of a transparent polymethylmethacrylate resin film “Sanduren” (manufactured by Kaneka Chemical Co., Ltd .; Ra = 0.2 μm, Rz = 1.2 μm) having a thickness of 200 μm The system resin “YL341” (manufactured by Toyo Ink Manufacturing Co., Ltd.) was applied by a direct gravure coating method using a gravure roll having a plate depth of 140 μm and dried and solidified. The surface roughness of the coating film at this time was Ra = 2.2 μm and Rz = 5.8 μm. Thereafter, using a cylindrical mirror surface embossing roll having a surface roughness of Ra = 0.1 μm and Rz = 0.9 μm, a hot press process was continuously performed under the condition that the film temperature was 125 ° C. . The surface roughness of the coating surface after the treatment was Ra = 0.4 μm and Rz = 1.4 μm. At this time, the average thickness of the surface protective layer was 9.2 μm.

  On the surface opposite to the surface protective layer side of the transparent film with the surface protective layer thus obtained, a pattern layer by gravure printing method is separately provided using urethane-based printing ink "Lamistor" (manufactured by Toyo Ink Manufacturing Co., Ltd.) The decorative layer was prepared by pasting the pattern layer surfaces of a colored polypropylene film having a thickness of 150 μm by a dry laminating method.

  Transparent acrylic polyester film “NAGASE A-PET” (manufactured by Nagase Sangyo Co., Ltd .; Ra = 0.4 μm, Rz = 2.1 μm) with a thickness of 300 μm and urethane acrylate UV curing as a surface protective layer While applying a mold resin (manufactured by Nippon Paint Co., Ltd.) by a direct reverse gravure coating method using a gravure roll with a plate depth of 200 μm, the film temperature is 140 on the same line. Under the conditions of a temperature of 0 ° C., a hot-pressing treatment was performed using a cylindrical mirror surface embossing roll having a surface roughness of Ra = 0.1 μm and Rz = 0.9 μm. At this time, the surface roughness of the coating film surface after irradiation with ultraviolet rays and before hot pressing is Ra = 2.1 μm, Rz = 12.5 μm, and after hot pressing, Ra = 0.2 μm, Rz = 1. .1 μm. At this time, the average thickness of the surface protective layer was 15.2 μm.

  A polyurethane-based resin “Lamistar” (manufactured by Toyo Ink Mfg. Co., Ltd.) added with 30% by weight of aluminum powder was applied to the back surface of the transparent film with a surface protective layer thus obtained by a direct gravure coating method. Produced.

[Comparative Example 1]
In Example 1 above, the coating condition of the surface protective layer is adjusted so that the smoothness of the coating film surface is the highest, and the transparent film with the surface protective layer is applied under the same conditions without performing the hot press process. As a result, the surface roughness of the surface protective layer was Ra = 0.4 μm, Rz = 1.5 μm, and the average thickness was 9.4 μm. Thereafter, a decorative sheet was produced in the same manner as in Example 1.

[Comparative Example 2]
In Example 2 above, the coating condition of the surface protective layer was adjusted so that the smoothness of the coating film surface was the highest, and the transparent film with the surface protective layer was applied under the same conditions without performing the hot press process. As a result, the surface roughness of the surface protective layer was Ra = 0.2 μm and Rz = 1.2 μm. Thereafter, a decorative sheet was produced in the same manner as in Example 2.

[Evaluation]
A decorative board produced by laminating the decorative sheets obtained in Examples 1 and 2 and Comparative Examples 1 and 2 on the surface of a medium density fiber board having a thickness of 24 mm is perpendicular to the floor surface under fluorescent lamp illumination. The maximum distance at which interference fringes can be recognized was measured by approaching the surface of the decorative board while visually confirming the surface of the decorative board from a position 10 m away from the front of the decorative board. The results are shown in the table below.

〔Evaluation results〕

Maximum interference fringe recognition distance Example 1 0.10 m
Example 2 0.08 m
Comparative Example 1 3.2 m
Comparative Example 2 2.9 m

Sectional drawing which shows embodiment of this invention method to process order. Sectional drawing of an example of the decorative sheet manufactured applying the method of this invention. Sectional drawing of an example of the decorative sheet manufactured applying the method of this invention.

Explanation of symbols

1 Base material 11 Thermoplastic resin layer (transparent thermoplastic resin film)
12 picture layer 13 thermoplastic resin film 2 surface protective layer

Claims (2)

  At least the surface is made of a thermoplastic resin layer, the surface of the substrate having a smooth surface shape is made of a transparent curable resin, the surface of the surface is rougher than the surface of the thermoplastic resin layer, and has a fine uneven shape. A surface protective layer having a surface shape is formed and cured, and then the surface protective layer is smoothed by applying a hot-pressing treatment on the surface protective layer. A smooth surface is characterized in that a fine uneven interface shape is formed at the interface with the thermoplastic resin layer by substantially inverting the surface shape of the surface protective layer before the hot-pressing treatment. A method for forming a surface protective layer.   The surface roughness (JIS B 0601 (2001)) of the base material before formation of the surface protective layer is such that the arithmetic average roughness Ra is 1.0 μm or less and the maximum height roughness Rz is 10.0 μm, The surface roughness of the surface protective layer before the hot-pressing treatment is such that the arithmetic average roughness Ra is 0.5 to 10.0 μm, the maximum height roughness Rz is 2.0 to 30.0 μm, The surface roughness of the surface protective layer after the press treatment is such that the arithmetic average roughness Ra is 1.0 μm or less and the maximum height roughness Rz is 10.0 μm or less. A method for forming a surface protective layer having a smooth surface.

Images