i) Field of the Invention
The present invention relates to a car lighting fixture lens structure applied, for example, as an outer lens of a car head lamp, and a manufacturing method of the structure.
ii) Description of the Related Art
In general, this type of car lighting fixture lens structure is constituted of a lens body molded of a transparent resin material and attached to cover an opening of a lamp housing, and a transparent protective film laminated and formed on the outer surface of this lens body.
Specifically, the conventional car lighting fixture lens structure is provided with the lens body and a hard coat which functions as a protective film on the outer surface of the lens body.
Generally in this type of an apparatus for a car, a chamber is defined by a resin molded lens and housing. Moreover, a lens surface (the outer surface of the lens opposite to the inner surface disposed opposite to the chamber) is subjected to a hard coat treatment, that is, coated in order to protect the lens.
In a conventional apparatus for the car, since the lens surface is subjected to the hard coat treatment, the lens is easily damaged, broken, and attacked by chemicals. Moreover, lens broken pieces are sometimes scattered during lens breakage, and a problem also lies in adhesion to the lens. Furthermore, since a coating process is necessary, a problem also lies in productivity, and a facilities expense is high. Additionally, since organic solvents are used, an environmental problem also occurs.
Since polycarbonate having a molecular weight of 21000 to 25000 is used in a conventional lens body, a thickness of the lens body is of the order of 2.5 to 5 mm considering molding properties. The lens body is thus structured not to easily break.
Furthermore, for a purpose of securely preventing the lens broken pieces from being scattered during the lens breakage, the present applicant has filed an application of an invention in which the lens surface is doped with a thermoplastic urethane skin layer superior in elasticity (Japanese Patent Publication No. 2000-331525, filed on May 20, 1999, and laid open on Nov. 30, 2000).
However, the conventional lens body is formed not to easily break in this manner, and therefore it would fail to break when a predetermined impact at a traffic accident or the like is added. In consequence, a stress generated in the lens by the impact was difficult to be relieved.
An object of the present invention is to provide a car lighting fixture lens structure which can break under impact and relieve stress.
Another object of the present invention is to provide a manufacturing method of a car lighting fixture lens structure, in which formation can easily be performed without causing a high rise in a facilities expense or shape limitation of a lens body.
In order to achieve the aforementioned objects, according to the present invention, there is provided a car lighting fixture lens structure comprising: a lens body attached to cover an opening of a lamp housing and formed of a transparent resin material; and a transparent protective film laminated and formed on an outer surface of the lens body, the lens body is formed of a transparent thermoplastic resin material, and the transparent protective film is molded of a thermoplastic polyurethane.
According to the present invention, since the protective film is formed with the thermoplastic polyurethane, it is possible to protect the lens body from chipping, damage and breakage of an impact system by sand or the like, corrosion by a chemical, and the like.
Moreover, according to the present invention, since the protective film is formed with the thermoplastic polyurethane, it is possible to effectively prevent a broken piece from flying/scattering during lens body breakage.
Furthermore, according to the present invention, since the lens body breaks, it is possible to relieve stress generated by impact.
Additionally, according to the present invention, since the lens body and protective film are both formed of the thermoplastic resin material, recycling, for example, remolding of the lens structure is possible.
The car lighting fixture lens structure of the present invention is constituted in such a manner that the lens body is formed of a polycarbonate and the protective film is formed of an aliphatic thermoplastic urethane.
According to the present invention, since the aliphatic thermoplastic urethane superior particularly in wear resistance, strength, chemical resistance, and weathering resistance among thermoplastic elastomers is used to form the protective film, the lens body is effectively protected from the chipping, damage and breakage of the impact system by sand or the like, corrosion by the chemical, and the like.
Moreover, according to the present invention, since the aliphatic thermoplastic urethane is satisfactory in adhesion to the polycarbonate, the protective film of the aliphatic thermoplastic urethane can be formed to sufficiently adhere to the polycarbonate lens body. This can effectively prevent the broken piece from flying/scattering during lens body breakage.
The present invention is characterized in that the lens body is formed by disposing a character line of a groove portion dug in a thickness direction.
According to the present invention, when the stress is generated on the surface of the lens structure by the impact from the outside, the stress is concentrated on a portion with the character line formed therein and the lens body can easily be broken. This can relieve the stress generated in the lens body.
Moreover, according to the present invention, by appropriately selecting a character line sectional shape, forming depth and forming place to form the line, it is possible to control a breakage start point of the lens body during loading of the stress.
The present invention is characterized in that a molecular weight of the polycarbonate is 20000 or less.
According to the present invention, since the polycarbonate having a molecular weight of 20000 or less is used, and fluidity during injection into the metal mold is high, a lens with small thickness can be molded, therefore cost reduction can be realized. Moreover, since this polycarbonate has a low impact strength, breakage occurs under a predetermined impact. Therefore, when the impact of a traffic accident or the like is applied to the lens body formed by the polycarbonate, the lens breaks and it is possible to relieve the stress generated by the impact.
The present invention is characterized in that the lens structure is formed by a film in-mold molding method of injecting a polycarbonate in a metal mold with an aliphatic thermoplastic urethane film being set therein.
According to the present invention, it is possible to easily form the protective film of the aliphatic thermoplastic urethane film on the outer surface of the lens body of a polycarbonate with a sufficient adhesion force by the film in-mold molding method in which no organic solvent is used.
According to the present invention, the aliphatic thermoplastic urethane film is flexible, and high in follow-up property to the metal mold shape, and this enables three-dimensional shape in-mold molding which has been impossible with a hard coat sheet.
According to the present invention, since the lens structure is formed by the film in-mold molding method of injecting the polycarbonate in the metal mold with the aliphatic thermoplastic urethane film being set therein, the lens structure can easily be molded without causing deterioration of environment by the organic solvent, high rise of the facilities expense, or shape limitation of the lens body.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-85263, filed on Mar. 24, 2000, the disclosure of which expressly incorporated herein by reference in its entirety.