Method for surface treatment

Abstract: When machine works such as a honing processing, nicking processing or mirror finishing are applied on the surface 10a of the facing member of watches and clocks composed of Ti and Ti alloy, a layer of Ti oxide is formed to cause surface blackening. This oxide layer or other foreign substances are eliminated, for example, by a chemical etching or electropolishing by immersing in a etching solution, followed by forming a transparent protective layer on the surface 10a by coating, for example, with a glass coating solution and drying. The etching solution described above preferably comprises a mixed solution containing HF, HNO 3 and H 2 SO 4 . The arrangement prevents the surface of Ti and Ti alloy from contamination with fingerprints and being scratched, as well as enhancing the degree of whiteness and improving the quality of appearance.

Description: The present invention relates to a method of surface treatment, an ornament and to a device having such a treated surface or including such an ornament. As described in Japanese Unexamined Utility Model Publication No. 56-74060, Japanese Unexamined Patent Publication No. 58-96869 and Japanese Unexamined Patent Publication No. 62-263977, such methods are known in the art as to coat a metal surface such as aluminum with a rigid transparent coating film for the purpose of acquiring corrosion resistant, abrasion resistant and impact resistant properties. This transparent coating film is composed of a variety of organic resins and inorganic substances. Among these surface coating techniques, a transparent coating layer of rigid inorganic materials comprising aluminum oxide or aluminum silicon has been conventionally coated on the surface of facing cases composed of metals in the field of, for example, watches and clocks. In the case of wristwatches, machine works such as mirror finishing, nicking processing and honing processing are applied on the surface of facing cases comprising various kind of metals such as stainless steel, brass and other metals, thereby a transparent protective layer is formed on their surface. Recently, Ti that is a light and highly corrosion resistant material having a preventive effect for metal allergy has been noticed. However, there are some problems cited below when Ti is used for the facing case of wristwatches. Although honing processing (honing finish) is most frequently used for the surface finishing of the facing case made of Ti by taking the properties of Ti into considering, the surface layer of Ti is readily damaged and oxidized because the surface of Ti is bombarded with glass beads in the honing processing. Therefore, it is a problem that the surface becomes blackish besides contamination with fingerprints once adhered on the surface becomes difficult to be wiped off because the surface becomes uneven due to the honing processing. There is also another problem that the wristwatches are liable to suffer from small scratches since Ti has lower Vickers hardness of 150 or less than that of stainless steel (SUS) of 200. For the reasons described above, a transparent surface protective layer may be formed on the surface of the facing case made of Ti. However, when a coating for forming a protective layer is applied on the surface which has become blackish and uneven as a result of the honing processing, there would arise a problem on appearance of commodities that blackening further proceeds due to wetting phenomenon as seen when an uneven surface is wetted with water. This is a serious defect for the facing of watches which are intended to have a high ornamental value since such blackening generally gives the impression of an inferior product. When a layer of Ti oxide and foreign materials are present on the surface, the adhesion of a transparent protective layer is deteriorated. As a consequence, impact resistance and durability are decreased. GB 1116707A discloses the use of a protective, transparent coating consisting exclusively of potassium silicate on surfaces of titanium, zirconium or alloys thereof. The present invention seeks to mitigate at least some of the above mentioned disadvantages which arise with known arrangements. According to a first aspect of the present invention, there is provided a method of treating a titanium or titanium alloy surface of a metallic member for an ornament, the surface having been subjected to machine work by any of honing processing, nicking processing and mirror finishing, the method comprising: removing surface adhesion substances on said surface, adhering a glass coating liquid to form a transparent protective layer including glass composition, wherein the viscosity of said glass coating liquid is about 200 to 500 x 10 -3 Pa.s at 25°C when said machine work is either honing processing or nicking processing and the viscosity of said glass coating liquid is about 150 to 250 x 10 -3 Pa.s at 25°C when said machine work is mirror finishing, and drying said glass coating liquid. This invention can enable scratches and surface contaminations to be avoided while providing a good quality appearance. The appearance becomes whitish and glossy because a transparent protective layer is formed after removal of surface adhesion substances such as oxide layers. Thus, it is possible to provide an ornament with a superior ornamental value. The transparent protective layer has a high adhesive property and good durability. Since surface adhesion substances such as an oxide layer are liable to form when the machine works are applied, improvements in the quality of appearance are further effected. This effect is also displayed when any one of the machine works above is applied. This construction of the invention enables a surface to be formed with a sufficient amount of hardness having an excellent scratch resistance, protecting contaminations like adhesion of fingerprints and mechanical damage to a high level. It is preferable that the transparent protective layer is formed by allowing a glass coating liquid to adhere on the surface which has been subjected to the treatment of removing surface adhesion substances, followed by drying. This construction of the invention provides an easily formed transparent protective layer with a high adhesive property. It is preferable that the glass coating liquid is used after diluting its original liquid. It is especially preferable that the transparent protective layer is formed by allowing the glass coating liquid prepared by diluting its original liquid in a dilution ratio corresponding to the machine works to adhere, followed by drying. This construction of the invention enables to improve further the degree of whiteness and glossiness while maintaining a high degree of corrosion resistance, abrasion resistance and scratching resistance. This construction of the invention further improves corrosion resistance, abrasion resistance and scratching resistance. It is preferable that drying is carried out twice or more under different drying conditions. This construction of the invention improves film quality and the adhesive property of the transparent protective layer. It is preferable that the treatment for removing surface adhesion substances is a chemical polishing with an etching solution. This construction of the invention enables effective removal of the surface adhesion substances, especially a layer of Ti oxide. It is preferable that the etching solution comprises a mixed solution containing HF, HNO 3 and H 2 SO 4 . This construction of the invention enables the surface to be made white without roughening the surface of Ti or Ti alloys. It is preferable that the etching solution is an aqueous solution containing 1 to 10 vol% of HF, 15 to 40 vol% of HNO 3 and 30 to 60 vol% of H 2 SO 4 . This construction of the invention makes it possible to constantly produce an ornament having a high quality in appearance with a high productivity. It is preferable that the temperature of the etching solution is 30 to 75 °C and the treatment time with the etching solution is 5 to 60 seconds. This construction of the invention also makes it possible to obtain a better quality in appearance besides improving the productivity. It is preferable that the treatment for removing surface adhesion substances is an electropolishing. This construction of the invention enables effective removal of the surface adhesion substances, especially foreign materials and a layer of Ti oxide. It is preferable that the electrolyte solution used for the electropolishing contains H 3 PO 4 . This construction of the invention makes surface properties after the electrolysis treatment especially good. It is preferable that the electropolishing is carried out at an anodic current density of 0.5 to 10 A/cm 2 . This construction of the invention makes it possible to allow an electropolishing with a high whiteness and high quality in appearance to be rapidly carried out. It is preferable that the time for the electrolysis treatment is 3 seconds to 2 minutes. This construction of the invention makes it possible to sufficiently apply a required electropolishing without decreasing the productivity. It is preferable that the treatment for removing surface adhesion substances is a treatment at least containing surface washing. This construction of the invention enables easy removal of surface adhesion substances, especially surface contaminants and foreign materials having a weak adhering strength. It is preferable that the surface adhesion substances removed are those containing Ti oxide that causes blackening. This construction of the invention enhances the degree of whiteness, improving the quality in appearance. According to another aspect of the present invention, there is provided an ornament formed by the above-described method. These constructions of this invention enables damage prevention and contamination, providing an ornament having a high quality appearance. Because a transparent protective layer is applied after removing surface adhesion substances such as oxide layers, a whitish appearance can be obtained together with glossiness, giving a high class finish. It is preferable that the machine work is any one of honing processing, nicking processing or mirror finishing. When such machine works are applied, surface adhesion substances such as oxide layers are so liable to occur that the improvement gained in the quality of appearance is particularly high. When any one of the machine works above is applied, the effect described above can also be achieved. This construction of the invention enables a surface to be formed with a sufficient amount of hardness, highly preventing contamination such as adhesion of fingerprints and from other damage. It is preferable that the thickness of the transparent protective layer is 0.2 to 15 µm. This construction of the invention enables a sufficient amount of protective effect to be obtained as well as endowing the transparent protective group with a good film quality with few faults. It is preferable that the transparent protective layer has a Vickers hardness of 180 to 700. This construction of the invention further improves the abrasion resistance and scratching resistance of the transparent protective layer. It is preferable that the ornament is a facing member for watches and clocks. Since an especially excellent quality in appearance is required in the facing member of watches and clocks, this invention by which the foregoing effects are obtained can be advantageously applied. It is preferable that this invention is applied so as to provide an electronic device at least a portion of which is decorated with the ornament as described previously. It is preferable that the electronic device is a watch or a clock. Embodiments of the present invention will now be described in more detail, by way of example only and with reference to the accompanying drawings; in which:- Tables 1 to 7 set out details of certain examples, as described below; Fig. 1 is an illustration showing in concept surface conditions after the treatment process according to an embodiment of this invention. Fig. 2 is an another illustration showing in concept surface conditions after the treatment process according to an embodiment of this invention. Fig. 3 is a different illustration showing in concept surface conditions after the treatment process according to an embodiment of this invention. Fig. 4 is an another different illustration showing in concept surface conditions after the treatment process according to an embodiment of this invention. Fig. 5 is an another different illustration showing in concept surface conditions after the treatment process according to an embodiment of this invention. Fig. 6 is an another different illustration showing in concept surface conditions after the treatment process according to an embodiment of this invention. Embodiments to be described hereinafter are examples when this invention was applied for the facing cases of wristwatches (portable watches). The facing cases of the watch will be described first. The facing case of the watch is produced by assembling facing members of watches such as a case body, rear cover, cover glass and the like, a bezel being provided around the periphery of the cover glass in some watches. At least one of the case body and bezel of the facing members of watches may be produced with Ti (pure titanium) or titanium alloys. This invention is applicable to a facing member of watches made of Ti or Ti alloys. Ti alloys contain Ti as a main component in which one or two or more kinds of metals are incorporated. Examples of the metal to be incorporated into Ti are one or two or more kinds of metals such as Al, V, Mo, W, Fe, Co, Cr, Cu, Ag, Pt, Pd and Zn, but are not limited thereto. The content of these metals is not especially limited so long as the metals do not alter the intrinsic properties of Ti. The facing members of the wristwatch are produced by a press molding, casting, powder metallurgy process, lost wax process and metal injection molding (MIM) using the foregoing Ti or Ti alloy as a starting material. An appropriate cutting process is especially applied to the facing member produced by the press molding, if required. A machine work is applied, if necessary, on the surface of the facing member of watches. Examples of such machine work are a honing processing by blasting fine grains, a nicking processing and a mirror finishing by buff finishing or barrel finishing. Ti is a metal so liable to be oxidized that an oxide layer (color change layer) mainly comprising Ti oxide is often formed by surface oxidation. Formation of this oxide layer becomes evident when the machine works described above are applied. Formation of this oxide layer makes the surface blackish and deteriorates the quality in appearance, therefore it should be avoided as much as possible. Now, this invention is described with reference to Fig. 1 to Fig. 3. An oxide layer (damaged oxide layer) 11 generated by an oxidation of Ti is formed at the portion in the vicinity of the surface of the facing members 10 of watches made of Ti or a Ti alloy, where the surface suffers a mechanical damage due to the aforementioned machine works. Fig. 1 is an illustrative view of the surface of a facing member of a watch where a machine work described above, especially honing processing, has been applied. Since this oxide layer 11 causes blackening, allowing this portion to remain would affect the appearance of the facing case, thereby deteriorating a high class sense of the facing case of watches, even when a transparent protective layer 12 such as a glass coating is applied on the surface. Accordingly, the oxide layer 11 is removed from the surface 10a by applying, for example, a chemical polishing as shown in Fig. 2. This chemical polishing is carried out, for example, by allowing the surface 10a to contact an etching solution. Then, a transparent protective layer 12 is formed as shown in Fig. 3, on the surface 10a from which an oxide layer 11 has been removed, thereby an ornament (a facing member of watches) according to this invention is completed. A layer containing glass such as a glass coating layer is preferable as the transparent protective layer 12. This allows an wetting effect arising from refractive indices to be displayed, to make the appearance whitish and to give a high glossiness. Spoiling the appearance due to traces of fingerprints adhered to the surface 10a can be also prevented by this coating layer. The thickness of the transparent protective layer 12 represented by the glass coating layer is not especially limited, but a thickness of about 0.2 to 15 µm is preferable and a thickness of about 0.8 to 5.0 µm is more preferable. When the thickness of the transparent protective layer 12 is too large, cracks caused by an impact force are prone to be generated because the inner stress is enhanced in the transparent protective layer while, when it is too thin, the effects for preventing fingerprints from adhering and tiny scratches from appearing are diminished. Although the hardness of the transparent protective layer 12 is not especially limited, it is preferably in the range of 180 to 700 expressed by a Vickers hardness defined in JIS Z 2244, the range of 300 to 500 being more preferable. This enables to an excellent abrasion resistance and scratching resistance to be obtained. Now, the method for surface treatment according to this invention is described hereinafter. < 1 > Elimination of surface adhesion substances Foreign materials such as an oxide layer 11 and contaminants (these are generally referred to "surface adhesion substances") adhered in the vicinity of the surface 10a of the facing member 10 of watches, especially on the surface subjected to the machine works previously described, are eliminated. By this procedure, colors of the inherent substrate of the facing member of watches are displayed even if the surface has exhibited blackish color, thereby the degree of whiteness is enhanced besides giving a high degree of glossiness and improving the quality in appearance. Representative examples of treatments for removing the surface adhesion substances are 1 ○ chemical polishing with an etching solution, 2 ○ electropolishing and 3 ○ washing (washing with acids, alkali or water). These treatments will be described in turn hereinafter. 1 ○ Chemical polishing with an etching solution A chemical etching is carried out by allowing the facing member of watches to contact an etching solution, for example by immersing in the etching solution. Though the composition of the etching solution, temperature and immersing time are not especially limited, their preferable examples are described hereinafter. The etching solution preferably comprises a mixed solution containing HF, HNO 3 and H 2 SO 4 . A mixed solution of HF and HNO 3 may be used, but further adding H 2 SO 4 makes it possible to make the surface whitish without giving any roughness on the surface of Ti or Ti alloys. It is preferable that the etching solution is especially an aqueous solution containing 1 to 10 vol% of HF, 15 to 40 vol% of HNO 3 and 30 to 60 vol% of H 2 SO 4 . By selecting such composition range (referred to "optimum range" hereinafter), the surface of the facing member of watches can be processed to sufficiently whitish with glossiness within a comparative short treatment time, or with a high productivity, without causing any surface roughness (skin roughness). When either one of HF and HNO 3 is not present or contained in little amount, etching will not be substantially proceeded or slowly proceeds. When the content of HF is less than 1 vol% or the content of HNO 3 is less than 15 vol%, little etching effect can be obtained besides the treatment time is prolonged. When the content of HF is more than 10 vol% or the content of HNO 3 is more than 40 vol%, on the contrary, the surface roughness becomes liable to occur. The surface roughness also becomes liable to occur when the content of H 2 SO 4 is less than 30 vol% and, when the content is more than 60 vol%, the etching effect is diminished. Since surface roughness largely affects the facing member of watches to which a mirror finishing has been applied, it is more preferable to adjust the composition of the etching solution to 1 to 5 vol%, 15 to 35 vol% and 40 to 60 vol% for HF, HNO 3 and H 2 SO 4 , respectively. An example of the etching solution is prepared by mixing 5 vol% of commercially available 45 to 50 vol% HF (hydrofluoric acid), 45 vol% of commercially available 60 to 70 vol% HNO 3 (nitric acid) and 50 vol% of commercially available 98 vol% H 2 SO 4 (conc. sulfuric acid). The composition of this etching solution is 2.25 to 2.5 vol% of HF, 27 to 31.5 vol% of HNO 3 and 49 vol% of H 2 SO 4 with a balance of water, satisfying the optimum range. The facing member of watches is immersed in this etching solution for, for example, about 30 seconds for a chemical etching. As shown in Example 8 to 14 below, a good appearance could be obtained by appropriately adjusting the immersion time in the etching solution or other conditions such as the temperature of the solution even when the composition of the etching solution is out of the optimum range described above. Therefore, the composition of the etching solution to be used in this invention is not necessarily limited to the optimum range. The quality in appearance of the polished face was investigated, after washing with water, by variously changing the composition of the etching solution and immersion time in the etching solution. The results are listed in Table 1 below together with the etching conditions. The substrate for the facing member of watches was a sintered body formed by a metal powder injection molding, the constituting material being an alloy containing 6 wt% of Ti and 1 wt% of Al. A honing processing was applied on the entire surface of the facing member. The etching temperature was 70°C in all cases. Table 1 - refer to the drawings herein The quality in appearance after etching in Table 1 was visually evaluated and classified into the following 5 ranks. A: Very good appearance (a very high degree of whiteness) B: Good appearance (a high degree of whiteness) C: Normal appearance (a middle class of whiteness, slight roughness on the surface) D: Rather bad appearance (blackish, roughness on the surface) E: Bad appearance (evidently blackish, evident roughness on the surface) The product evaluated as rank A and B have no problem at all when they are used for commercial commodities while the product of rank C are applicable without any problem for the product except those for which an especially high grade of quality is required like a high class commodity. Examples 1 to 7 correspond to the products produced using the etching solution within the optimum range and Examples 8 to 14 correspond to the product produced using the etching solution out of the optimum range. The products in Examples 1 to 7 have superior quality in appearance to the products in Examples 8 to 14. A most excellent appearance was obtained in Examples 1, 2, 4 and 7 when the immersion time in the etching solution was relatively longer time of 30 seconds or 60 seconds, whereas a most excellent appearance was obtained in Examples 3, 5 and 6 when the immersion time in the etching solution was relatively shorter time of 5 seconds or 30 seconds. In Example 8, a good appearance was obtained when the immersion time in the etching solution is as long as 60 seconds because the content of HF is relatively small. On the other hand, the content of HF is relatively so large in Example 9 that a good appearance was obtained when the immersion time in the etching solution is as short as 5 seconds. In Example 10, a good appearance was obtained when the immersion time in the etching solution is as long as 60 seconds because the content of HNO 3 is relatively small. On the other hand, the content of HNO 3 is relatively so large in Example 11 that a good appearance was obtained when the immersion time in the etching solution is as short as 5 seconds. In Example 12, a good appearance was obtained when the immersion time in the etching solution is as short as 5 seconds because the content of H 2 SO 4 is relatively small. On the other hand, the content of H 2 SO 4 is relatively so large in Example 11 that a good appearance was obtained when the immersion time in the etching solution is as long as 60 seconds. In Example 14, the appearance becomes normal at an immersion time of up to 60 seconds because H 2 SO 4 is not added, but a longer immersion time results in a good appearance. In the Comparative Example 1 where any chemical polishing by etching is applied, on the contrary, the quality in appearance is bad. The quality in appearance was investigated by changing the treatment time (immersion time) against the facing member of watches (subjected to a honing processing) as described previously with a constant solution temperature by using a etching solution having the same composition as in Example 3 of Table 1. The results are listed in Table 2 below. The quality in appearance was investigated by changing the solution temperature against the facing member of watches (subjected to a honing processing) as described previously with a constant treatment time (immersion time) by using a etching solution having the same composition as in Example 3 of Table 1. The results are listed in Table 3 below. The evaluation methods for the quality in appearance in Table 2 and Table 3 are the same as listed in Table 1. Table 2 - refer to the drawings herein Table 3 - refer to the drawings herein As shown in Table 2, a most excellent quality in appearance was obtained at a temperature of the etching solution of 70°C with an immersion time of 5 seconds to 50 seconds, gradually showing a tendency to cause surface roughening when the treatment time is 70 seconds or longer. Accordingly, the preferable treatment time (immersion time) is 5 to 50 seconds, a treatment time of 5 to 30 seconds being more preferable, when it is taken into account to obtain a best surface aspect thus attempting to improve productivity. Although a most excellent quality in appearance was obtained for a treatment time of 30 seconds at a temperature range of 30 to 75°C as shown in Table 3, the whiteness slightly decreases when the solution temperature is as low as 25°C while, when the temperature is as high as 80°C, the etching effect is so enhanced that there is a tendency to exhibit a little roughness. Therefore, the preferable solution temperature is 30 to 75°C and more preferable temperature is 30 to 60°C when it is taken into account to obtain a best surface appearance and to treat at as low a temperature as possible for the reason of safety. 2 ○ Electropolishing An electropolishing is applied to the facing member of watches comprising Ti or Ti alloys. This electropolishing is carried out by allowing the facing member of watches to dissolve (anode dissolution) in an electrolyte solution by using the facing member as an anode. Electropolishing is described hereinafter referring to Fig. 4 to Fig. 6. Foreign substances 13 other than the substrate metals of the facing member of watches 10 adhere on the surface 10a made of Ti or Ti alloys by applying the machine works described previously. Especially, foreign substances bombarded into the surface are present in the case of the facing member of watches 10 after being subjected to a honing processing. The adhesive property of a transparent protective layer 12 will be decreased and durability is deteriorated when the transparent protective layer 12 such as a coating glass layer is formed if this foreign substances 13 are allowed to remain on the surface 10a. Therefore, a transparent protective layer 12 is formed on the surface 10a from which this foreign material 13 has been removed by applying an electropolishing as shown in Fig. 5, thereby completing a facing member of watches according to this invention. When an oxide layer previously described has been formed on the surface 10a, the oxide layer can be removed together with the foreign substances 13. According to the method described above, the film quality and adhesive property to the surface 10a of the transparent protective layer 12 can be improved by making the surface 10a uniform and substantially smooth after the foreign materials 13 have been removed from the surface 10a. Accordingly, a transparent protective layer 12 being excellent in fingerprint adhesion preventing property and scratching resistant property can be formed with a high durability. The composition of the etching solution (etching treatment solution), temperature, electric current density and treatment time are not especially limited, but their suitable examples will be described below. The composition of the electrolyte solution is not especially limited but it is preferable that the solution contains H 3 PO 4 (phosphoric acid). The electrolyte solution containing H 3 PO 4 is especially suitable for the electrolysis treatment for Ti or Ti containing alloys, making the surface after the treatment good. The preferable concentration in the electrolyte solution in this case is 8 to 12 vol%. When the concentration of H 3 PO 4 is too low, foreign substances are not fully eliminated within a short time since polishing strength is lowered while, when the concentration is too high, the polishing strength is so enhanced that the appearance is easily subjected to color changes. pH of the electrolyte solution is not limited but the preferable range is usually 1.0 to 1.2, pH range of 1.05 to 1.1 being more preferable. The temperature of the electrolyte solution is not especially limited and it may be in the range of 25 to 30°C . The electrolysis treatment time is not especially limited and is determined depending on the composition of the electrolyte solution and electric current density. The preferable time is usually 3 seconds to 2 minutes but more preferable time is 5 seconds to 1 minute. When the electrolysis time is too short, the electropoishing will be insufficient while, even when the electrolysis treatment time is made longer than the foregoing time, the effect is not improved lowering the productivity. The anode electric current density in the electropolishing is not especially limited, but a current density of 0.5 to 10 a/cm 2 is preferable and a density of 1 to 5 a/cm 2 is more preferable. When the current density is too low, a sufficient electropolishing can not be carried out in a short time while, when the current density is too low, the color of the surface 10a of the facing member of watches 10 is often changed (turn to yellow) lowering its whiteness especially when the time for the electropolishing treatment is prolonged. It is needless to say that the conditions such as the composition of the electrolyte solution, pH and electric current density are not limited to the conditions described above. Examples of the elctropolishing will be described hereinafter. A facing member of watches was produced via a press processing and cutting processing and a honing processing was applied on the entire surface of the member. The composition of the metal substrate of this facing member of watches is pure Ti. After subjecting the facing member of watches to an alkaline degreasing and acid neutralization treatment in this order, electropolishing was applied to the member by changing the anode electric current density and electrolysis treatment time using two kinds of electrolyte solutions followed by washing with warm water (70°C). The quality in appearance of the facing member of watches was evaluated. The composition of the electrolyte solution and other electrolysis conditions are listed in Table 4 below and the experimental results are shown in Table 5 below. Table 4 - refer to the drawings herein Table 5 - refer to the draings herein The quality in appearance after etching was visually evaluated and classified into the following 5 ranks as shown in Table 5. A: Very good appearance (a very high degree of whiteness) B: Good appearance (a high degree of whiteness) C: Normal appearance (a middle class of whiteness, slight color change to yellow) D: Rather bad appearance (, a little) E: Bad appearance (evidently yellow change, foreign substances remain) The product evaluated as rank A and B have no problem at all when they are used for commercial commodities while the product of rank C are applicable without any problem for the product except those for which an especially high grade of quality is required like a high class commodity. Products having a good quality in appearance were obtained in all Examples 15 to 28. Of these, the product in which the anodic electric current density and electrolysis treatment time were made optimum gave a most excellent quality in appearance. When the electric current density is relatively low (Examples 15 and 22), a good quality of appearance is obtained by making the concentration of phosphoric acid high or the electrolysis treatment time slightly long. When the electric current density is relatively high (Examples 20, 21, 26, 27 and 28), a good quality of appearance is obtained by making the concentration of phosphoric acid low or the electrolysis treatment time slightly short. On the contrary, the quality of appearance becomes wrong in Comparative Example 2 where an electropolishing is not applied. 3 ○ Washing Washing methods include acid washing, alkaline washing (including alkaline degreasing and neutralization with an acid), water washing, warm water washing, washing with organic solvents such as alcohol and oil washing. One of these methods or an appropriate combination of two or more kind of these method can be used. The acid washing solution for the foregoing acid washing that can be properly used is, for example, 3 to 5 % of sulfuric acid while the alkaline solution for the foregoing alkaline washing that can be properly used is, for example, 3.5 to 5 % of Deepsol 41C (made by Deepsol Co.). The method for washing is not especially limited but any one of shower washing, jet washing, ultrasonic washing, precision washing, or simply immersing in a washing solution or immersing in the washing solution with stirring can be used. The temperature of the washing solution is also not especially limited and any temperature ranging from room temperature washing to a high temperature washing at about 100°C may be used. 4 ○ Combination of aforementioned 1 ○ to 3 ○ The treatments in 1 ○ to 3 ○ can be used by an arbitrary times of combination in any order of them. For example, 3 ○ may applied after applying 1 ○ or 2 ○, thereby the appearance of the surface 10a can be made good or more clean. By using these different kind of treatment together, the appearance of the surface 10a can be delicately adjusted, thereby improving the adhesive property of the transparent protective layer 12 to be described hereinafter. < 2 > Formation of transparent protective group After removing the surface adhesion substances described above, a transparent protective layer 12 is formed on the surface 10a of the facing member of watches 10 as shown in Fig. 3 and Fig. 6. The transparent protective layer 12 is constructed with a glass coating layer. The method for forming the layer will be described hereinafter. A glass coating liquid is allowed to adhere on the surface of the surface 10a of the facing member of watches 10 by, for example, a coating method followed by drying, thereby a transparent glass coating layer is formed. A glass coating liquid comprising a product obtained by dissolving an alkali silicate as a main component and fine granular silica with heating (a transparent glass coating agent made by Okuno Seiyaku Kogyo Co., trade name CRM Coat 100) can be used. This kind of glass coating liquid (an original liquid) is produced by dissolving 100 part by weight (as converted to solid fraction) of an alkali silicate such as sodium silicate or potassium silicate and 5 to 100 part by weight of fine granular silica having a mean grain diameter of 40 µm preferably with heating at 50 to 100°C, more preferably at 80 to 100°C, for about 1 to 2 hours to allow the fine granular silica to dissolve (disperse) into the alkali silicate. Water may be added at an upper limit of 600 part by weight against 100 part by weight of the total solid fraction described above, which makes dissolution easy and rapid. While the inorganic transparent glass coating liquid can be used as an original liquid or by diluting with a diluting solvent, it is preferable to use a solution diluted with a diluting solvent. This not only enhances the workability of the coating process but also improves the film quality of the transparent protective layer, especially hardness and corrosion resistance of the film. The dilution ratio of the glass coating liquid is preferably selected depending on the kind of the machine works applied to the facing member of watches, i. e. a honing processing, nicking processing or mirror finishing. This will enable to improve color tones such as degree of whiteness and glossiness while keeping the corrosion resistant, abrasion resistant and scratch resistant properties of the transparent protective layer to a high level. The preferable range of the dilution ratio depending on the kind of the machine works is as follows. There would be also a preferable range in the viscosity of the glass coating liquid to be coated. This viscosity range corresponds to the dilution ratio described above and the former is described hereinafter together with the latter. Honing processing The preferable dilution ratio is 85 % or less and the ratio of 30 to 70% is more preferable. For example, the dilution ratio can be adjusted to 70% (water : original liquid (volume ratio) = 70 : 30) by adding water to the original liquid. The viscosity of the diluted solution is preferably 150 x 10 -3 Pa.s (150 cps) at 25°C or more, the viscosity of 200 x 10 -3 Pa.s to 500 x 10 -3 Pa.s (200 to 500 cps) at 25°C being more preferable. Nicking processing The preferable dilution ratio is 85% or less and the ratio of 30 to 70% is more preferable. For example, the dilution ratio can be adjusted to 70% (water : original liquid (volume ratio) = 70 : 30) by adding water to the original liquid. The viscosity of the diluted solution is preferably 150 x 10 -3 Pa.s (150 cps) at 25°C or more, the viscosity of 200 x 10 -3 Pa.s to 500 x 10 -3 Pa.s (200 to 500 cps) at 25°C being more preferable. Mirror finishing The preferable dilution ratio is 50 to 98% and the ratio of 90 to 98% is more preferable. For example, the dilution ratio can be adjusted to 95% (water : original liquid (volume ratio) = 95 : 5) by adding water to the original liquid. The viscosity of the diluted solution is preferably 150 to 400 x 10 -3 Pa.s (150 to 400cps) at 25°C or more, the viscosity of 150 x 10 -3 Pa.s to 250 x 10 -3 Pa.s (150 to 250cps) at 25°C being more preferable. When the dilution ratio is too high (the viscosity is too low), the corrosion resistant property and abrasion resistant property of the transparent protective layer obtained from the glass coating liquid may be sometimes decreased while, when the dilution ratio is too low (the viscosity is too high), the degree of whiteness or glossiness is decreased especially in the members being subjected to a mirror finishing. When the transparent protective layer is composed of a material other than the glass material such as an organic coating film, the dilution solvent applicable for coating is organic solvents other than water such as alcohols, benzene and toluene. These organic solvents can be used by mixing with water. Examples of the coating methods of the glass coating liquid include immersion (dipping), spraying, roll coating and coating with a brush. The coating liquid coated on the surface 10a is then dried. The drying condition is not especially limited, but it is preferable that the drying is usually carried out at a temperature of room temperature to 250°C for 1 to 20 minutes, the temperature range of 150 to 230°C for 5 to 15 minutes being more preferable. Such drying may be carried out twice or more under the same or different drying conditions. When drying is carried out twice or more under the different conditions (at least one condition of the drying method, drying temperature and drying time (drying speed) is different), the method contributes to the film qualities (especially denseness, homogeneity and uniformity of thickness) and adhesive property of the transparent protective layer 12. Suppose that a cycle of coating of the glass coating liquid and its drying is counted as 1 step, this step may be repeated several times. One example of this steps is that; the coating liquid that has been diluted to a desired dilution ratio is sprayed on the front surface 10a of the wristwatch case using a spray gun followed by a temporary drying at 150°C for 10 minutes. Then, the same glass coating liquid is also sprayed on the rear surface (inner surface) 10a followed by a temporary drying at 150°C for 10 minutes. Next, the coated case is subjected to a final drying at 180°C for 10 minutes by allowing a drying fan and ventilation fan to operate, thereby a transparent protective layer made of a glass layer is formed. This transparent protective layer has a good corrosion resistance, abrasion resistance, scratching resistance, impact resistance, fingerprint adhesion preventing property and adhesive property. For the purpose of more enhancing the corrosion resistance, abrasion resistance and scratching resistance owing to the transparent protective layer, a plurality of coating with the glass coating liquid (coating liquid) may be repeated. Examples of this coating will be described hereinafter. A concentrate of the glass coating liquid was obtained by dissolving 100 part by weight (as converted to a solid fraction) of sodium silicate and 50 part by weight of fine granular silica having a mean grain diameter of 30 µm at 85°C with heating followed by stirring for about 1 hour to dissolve (disperse) the fine granular silica into alkali silicate, thereby an original liquid for a glass coating liquid is obtained. This original liquid of the glass coating liquid was diluted with water to prepare the glass coating solutions by variously changing their dilution ratio and viscosity (25° C) as shown in Table 6 below. Each glass coating solution was coated on the surface of the facing member of watches obtained in aforementioned Example 1 (immersion time in the etching solution = 30 seconds) by a spray method and dried, thereby a transparent protective layer having a thickness (a mean value) shown in Table 6 was formed. A temporary drying at 160°C for 8 minutes and a final drying at 185°C for 10 minutes were carried out. The quality in appearance of the face on which a transparent protective layer was formed, Vickers hardness, fingerprint adhesion resistance (difficulty for adhering fingerprints), scratching resistance and adhesion property of the transparent protective layer were investigated with respect to each facing member of watches. The results are listed in Table 6. Table 6 - refer to the drawings herein In the column of the evaluation of the quality in appearance in Table 6, the reference character H, S and M correspond to honing processing, nicking processing and mirror finishing, respectively. The quality in appearance was visually evaluated and classified into 5 ranks. A: Very good appearance (a very high degree of whiteness and glossiness) B: Good appearance (a high degree of whiteness and glossiness) C: Normal appearance (a middle class of whiteness and glossiness) D: Rather bad appearance (a little whiteness and glossiness) E: Bad appearance (no whiteness and glossiness) The product evaluated as rank A and B have no problem at all when they are used for commercial commodities while the product of rank C are applicable without any problem for the product except those for which an especially high grade of quality is required like a high class commodity. The fingerprint adhesion resistance in Table 6 was evaluated by the degree of fingerprint adhesion by a light touch of fingers when the machine works corresponds to H and M were applied, and the results were classified into 4 ranks below. no adhesion of fingerprint O little adhesion of fingerprint Δ a little adhesion of fingerprint X obvious adhesion of fingerprint The scratching resistance in Table 6 was investigated when the mechanical work corresponds to H. Test 1 indicates the result of 1.5 H 10 4 times of scratching test with a sheet of cowhide under an applied pressure of 500 g/cm 2 . Test 2 indicates the result of a scratching test with an A1 piece. Test 3 indicate the result of a scratch test with BS steel. Test 4 indicates the result of a scratch test with stainless steel wire. The results were evaluated by classifying into the following 4 ranks. no trace of scratching O little trace of scratching Δ a little trace of scratching X obvious trace of scratching The adhesive property of the transparent protective layer in the case of the machine work defined by S and M in Table 6 was judged by the degree of peeling of the transparent protective layer when an adhering tape adhered on the layer was peeled off. The adhesive property was evaluated by classifying into the following 4 ranks. no peeling of the transparent protective layer O little peeling of the transparent protective layer Δ a little peeling of the transparent protective layer X obvious peeling of the transparent protective layer As shown in Table 6, an excellent quality in appearance, finger print adhesion resistance, scratching resistance and adhesion property of the transparent protective layer were obtained in all of Example 29 to 35. Especially, selection of a proper dilution ratio in accordance with the kind of the machine works (H, S and M) allows whiteness and glossiness to be enhanced while improving the quality in appearance. On the contrary, Comparative Example 3 where no transparent protective layer has not been formed has a bad fingerprint adhesion resistance and scratching resistance. In Comparative Example 4 where a transparent protective layer is formed without applying any electropolishing (treatment for removing surface adhesion substances) has a bad quality in appearance besides being inferior in the adhesion property of the transparent protective layer. The quality in appearance of the transparent protective layer, Vickers hardness (Hv), finger print adhesion resistance (difficulty in adhering fingerprints), scratching resistance and adhesion property of the transparent protective layer were investigated with respect to the sample prepared by the same method as described previously, except that a transparent protective layer was formed on the surface of the facing member of watches obtained in foregoing Example 18 (electrolysis treatment time = 30 seconds). The results are shown in Table 7 below. Table 7 - refer to the drawings herein As shown in Table 7, an excellent quality in appearance, fingerprint adhesion resistance, scratching resistance and adhesion property of the transparent protective layer were obtained in all of Example 36 to 42. Especially, selection of a proper dilution ratio in accordance with the kind of the machine works (H, S and M) allows whiteness and glossiness to be enhanced while improving the quality in appearance. On the contrary, Comparative Example 5 where no transparent protective layer has not been formed has a bad fingerprint adhesion resistance and scratching resistance. In Comparative Example 6 where a transparent protective layer is formed without applying any electropolishing (treatment for removing surface adhesion substances) has a bad quality in appearance besides being inferior in the adhesion property of the transparent protective layer. The coating liquid for forming the transparent protective layer is not limited to those previously described, but any condition such as composition of the coating liquid, temperature, dilution ratio viscosity, methods of coating can be adopted. For example, various kinds of coating liquids containing inorganic substances such as aluminum oxide, silicon oxide or water glass can be used. The transparent protective group is not limited to inorganic substances but it may be composed of a polymer material (an organic film) such as a rigid resin. The method for forming the transparent protective layer is not limited to the coating method (coating) described above but the layer may be formed by various kind of wet plating or dry plating (for example: evaporation, spattering, ion plating and CVD). It is usually preferable to form the transparent protective layer within 144 hours after completing the elimination step of the surface adhesion substances described above. This is because an oxidation film starts to be formed on the surface when the time lapse exceeds 144 hours, having a possibility to start slight color changes. Applications of this invention are not limited to coating of the approximately entire surface of the facing member of watches or the facing case constructed by assembling the same with a transparent protective layer, but a transparent protective layer such as a glass coating layer may be formed on the surface or a part of the surface, or at a plurality of portions on the surface, of the facing member of watches, facing case or other ornaments. When a treatment for forming a transparent protective layer is applied by providing a masking on the inner face of the facing case of watches, the transparent protective layer is not formed on the inner face of the facing case of watches. Accordingly, a precise positioning of mechanical parts (movements) is made possible when the mechanical parts are assembled and fixed in the case, thereby a bad influence of the component of the transparent protective layer on the mechanical parts can be prevented. For example, there is a possibility that driving of the mechanical parts are disturbed to cause retardation or halt by being invaded with debris of the transparent protective layer into engaging faces of the case or rear cover in snap-fixing the rear cover to the case. Such inconvenience can be prevented by avoiding to form a transparent protective layer on the engaging face between the rear cover and case. Application of this invention is not limited to the product where a transparent protective layer is formed on the substrate of Ti or Ti alloys, but the transparent protective layer may be formed on layers of Ti or Ti alloy that has been formed on a desired substrate. While this invention is not only applicable for the facing case of wristwatches, band or completed watches using thereof, but also to other kind of watches and clocks such as a portable watch, table clock or wall clock as well. Applications other than clocks and watches are eye glass frames, tiepins, cuff links, lighters or their cases, pens, rings, necklaces, bracelets, brooches, pendants, earrings, piercing rings, coronets, ornaments, decorations, decorative goods such as interior products (being more or less decorative) and accessories. The object of this invention is also electronic devices a part of which is provided with ornaments (ornaments used for at least displaying an decorative effect at a part of the device). Examples of such electronic devices are electronic watches and clocks, portable phones, pocket bells, calculators, personal computers, word processors, printers, copy machines, cameras, video equipments, televisions, audio equipments, electronic toys and a variety of measuring apparatus. This invention is applicable not only to ornaments, accessories and electronic devices but also to various kind of members made of Ti or Ti alloys. According to the foregoing descriptions, this invention may provide the following effects. An excellent scratching resistance and fingerprint adhesion resistance can be obtained by forming a transparent protective layer. Forming the transparent protective layer with a layer containing a glass like a glass coating layer makes it possible to easily form a transparent protective layer as well as forming a highly rigid transparent protective layer being excellent in corrosion resistance and abrasion resistance. Prior to forming such transparent protective layer, surface adhesion substances, especially those that cause color changes, are eliminated by applying, for example, a chemical polishing or electropolishing with an etching solution on the surface of Ti or Ti alloys, thereby the inherent colors of Ti or Ti alloys can be displayed with a high degree of whiteness and glossiness together with improvement in the quality of appearance. Therefore, ornaments are endowed with a high class sense, increasing their commercial value. An appropriate selection of the component of the etching solution or other treatment conditions makes it possible to make the polished face white without causing any roughening when the chemical polishing is carried out with an etching solution. A proper selection of the composition of the electrolyte solution, electric current density and other treatment conditions makes it possible to obtain a smooth and good surface, improving its degree of whiteness. Even when machine works such as a honing processing, nicking processing or mirror finishing have been applied to the surface of Ti or Ti alloys, an excellent surface quality as described previously can be obtained. The aforegoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention, as defined in the appended claims. Paragraphs of Advantage 1. A method for surface treatment characterized by forming a transparent protective layer after applying a treatment for removing surface adhesion substances on the surface of Ti or Ti alloy. 2. A method for surface treatment characterized by forming a transparent protective layer after applying a treatment removing surface adhesion substances on the surface of Ti or Ti alloy subjected to machine works. 3. A method for surface treatment according to Paragraph 2, wherein said machine work is any one of honing processing, nicking processing or mirror finishing. 4. A method for surface treatment according to any one of Paragraphs 1 to 3, wherein said transparent protective layer is a layer containing a glass. 5. A method for surface treatment according to any one of Paragraphs 1 to 4, wherein said transparent protective layer is formed by adhering a glass coating liquid on the surface subjected to said treatment for removing surface adhesion substances, followed by drying. 6. A method for surface treatment according to Paragraph 5, wherein said glass coating liquid is used after diluting its original liquid with a diluting solvent. 7. A method for surface treatment according to Paragraph 2 or 3, wherein said transparent protective layer is formed by allowing the glass coating liquid diluted to a dilution ratio corresponding to said machine works to adhere, followed by drying. 8. A method for surface treatment according to Paragraph 7, wherein the viscosity of said glass coating liquid is 150 cps (25°C) or more. 9. A method for surface treatment according to Paragraph 7 or 8, wherein said drying is carried out twice or more under different drying conditions. 10. A method for surface treatment according to any one of Paragraphs 1 to 9, wherein said treatment for removing surface adhesion substances is a chemical polishing with an etching solution. 11. A method for surface treatment according to Paragraph 10, wherein said etching solution comprises a mixed solution containing HF, HNO 3 and H 2 SO 4 . 12. A method for surface treatment according to Paragraph 10, wherein said etching solution is an aqueous solution containing 1 to 10 vol% of HF, 15 to 40 vol% of HNO 3 and 30 to 60 vol% of H 2 SO 4 . 13. A method for surface treatment according to any one of Paragraphs 10 to 12, wherein the temperature of said etching solution is 30 to 75°C and the treatment time with said etching solution is 5 to 60 seconds. 14. A method for surface treatment according to any one of Paragraphs 1 to 9, wherein the treatment for removing said surface adhesion substances is an electropolishing. 15. A method for surface treatment according to Paragraph 14, wherein the electrolyte solution used for said electropolishing contains H 3 PO 4 . 16. A method for surface treatment according to Paragraph 14 or 15, wherein said electropolishing is carried out at an anodic current density of 0.5 to 10 A/cm 2 . 17. A method for surface treatment according to any one of Paragraphs 14 to 16, wherein the time for electrolysis treatment is 3 seconds to 2 minutes. 18. A method for surface treatment according to any one of Paragraphs 1 to 17, wherein the treatment for removing said surface adhesion substances is a treatment containing at least surface washing. 19. A method for surface treatment according to any one of Paragraphs 1 to 18, wherein said surface adhesion substances contain Ti oxides that cause blackening. 20. An ornament comprising a transparent protective layer formed on the surface of a metallic member comprising Ti or Ti alloy where surface adhesion substances have been removed. 21. An ornament characterized in that a transparent protective layer is formed on the surface of a metalic member where contaminants have been chemically removed, wherein machine working is first applied on the metallic member which comprises Ti or Ti alloy. 22. An ornament according to Paragraph 21, wherein said machine working is any one of honing processing, nicking processing or mirror finishing. 23. An ornament according to any one of Paragraphs 20 to 22, wherein said transparent protective layer is a layer containing glass components. 24. An ornament according to any one of Paragraphs 20 to 23, wherein the thickness of said transparent protective layer is 0.2 to 15 µm. 25. An ornament according to any one of Paragraphs 20 to 24, wherein said transparent protective layer has a Vickers hardness of 180 to 700. 26. An ornament according to any one of Paragraphs 20 to Paragraph 25, wherein said ornament is a facing member for watches or clocks. 27. An electronic device at least a portion of which is decorated with an ornament according to any one of Paragraphs 20 to 25. 28. An electronic device according to Paragraph 27, wherein said electronic device is an watch or a clock.

Claims: A method of treating a titanium or titanium alloy surface of a metallic member for an ornament, the surface having been subjected to machine work by any of honing processing, nicking processing and mirror finishing, the method comprising: removing surface adhesion substances on said surface, adhering a glass coating liquid to form a transparent protective layer including glass composition, wherein the viscosity of said glass coating liquid is about 200 to 500 x 10 -3 Pa.s at 25°C when said machine work is either honing processing or nicking processing and the viscosity of said glass coating liquid is about 150 to 250 x 10 -3 Pa.s at 25°C when said machine work is mirror finishing, and drying said glass coating liquid. A method according to claim 1, further comprising washing said surface before removing the surface adhesion substances. A method according to claim 1 or claim 2, wherein the glass coating liquid is adhered within 144 hours after removing surface adhesion substances is finished. A method according to any one of claims 1 to 3, wherein the transparent protective layer has a Vickers hardness of 180 to 700 after drying. A method according to any one of claims 1 to 4, wherein said glass coating liquid is used after diluting its original liquid with a diluting solvent. A method according to any one of claims 1 to 5, wherein said drying is carried out twice or more under different drying conditions. A method according to any one of claims 1 to 6, wherein the removing of surface adhesion substances is performed by chemical polishing with an etching solution. A method according to any one of claims 1 to 6, wherein the removing of surface adhesion substances is performed by electropolishing. An ornament formed by a method according to any one of claims 1 to 8.

Inventors: UCHIYAMA AKIRA, UCHIYAMA, AKIRA
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1998
Main classification: C23D5
IPC codes: G04B37, C23D3, C25F3, C23D5, C25F1, C23F1