Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-06-10
2001-06-26
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S429000
Reexamination Certificate
active
06251523
ABSTRACT:
FIELD OF THE ART
The present invention relates to a reflection prevention glass plate, especially a glass plate suitable for use as windows of an automobile having small visible light reflectivity, and to a method for producing the same. The invention also relates to coating compositions for forming a reflection preventing film.
BACKGROUND ART
Conventionally, provision of reflection preventive treatment on the surface of the glass product has been practiced to prevent loss of fluoroscopic property and light permeability or dazzling due to the reflection of visible light on the surface of a glass plate or other glass product.
There is known, for example, a low refractive index reflection preventive film made by coating a coating liquid comprising a silica sol having a particle size of 5 to 30 nm and a hydrolyzate of alkoxy silane contained in the solvent and cured (Japanese Patent Laid-open Publication No. H8-122501).
In the front glass of an automobile, there is a problem of lowering a driver's visibility of front area by reflection images of inner panel (instrument panel) inside a car and dash board coming into driver's view. This problem is due to the reflection of the light incident from the inner panel and dash board and surroundings thereof upon the surface of the front window glass. The light incident from inner panel and dash board income with quite a high incident angle upon the front window glass and get into the driver's eyes. In order to improve the visibility, reflectivity upon the front window glass at the high incident angle (60° for example) is required to be lowered. With the above low refractive index reflection preventive film it is still insufficient to realize reduction of reflectivity at high incident angle, and it cannot be commented that the visibility is sufficiently high.
An object of the present invention is to provide a glass plate suitable for windows of an automobile having small reflectivity of visible light at high incident angle and improved visibility.
DISCLOSURE OF THE INVENTION
The present invention provides a glass plate for visible light reflection prevention with the film comprising chain silica fine particles and silica of 5 to 30% by weight based on the weight of said chain silica fine particles, and having thickness of 110 to 250 nm coated on at least one surface of the glass substrate, and dents and projections being formed on the surface of the film.
Further, the present invention provides a glass plate for visible light reflection prevention having small reflectivity at high incident angle, with the film comprising chain silica fine particles and silica, and having thickness of 110 to 250 nm coated on at least one of surface the glass substrate, space being formed between the mutually adjacent chain silica fine particles in the film, said film having refractive index of 1.25 to 1.40, and dents and projections being formed on the surface of the film.
In the present invention, the glass substrate surface is coated with a reflection preventive film comprising the chain silica fine particles and silica, and the film surface is provided with dents and projections caused by the projection of chain silica fine particles.
The above film comprises the chain silica fine particles and a smaller amount of silica, preferably 5 to 30% by weight of silica based on the weight of the chain silica fine particles which does not have the form of fine particles, wherein the silica serves as a binder for mutual adhesion between the chain silica fine particles and adhesion between the silica fine particles and the glass substrate surface.
As to the above mentioned chain silica fine particles, straight linear shaped ones may be used, but two-dimensionally, more preferably three-dimensionally curved shaped ones are most preferably used. By using the chain shaped silica fine particles, there are formed a large number of gaps of 5 to 20 nm width between the adjacent chain fine particles in the film. These large numbers of gaps have exceedingly large gross volume in comparison with the gaps made on supposition of using the same amount of spherical silica fine particles in place of the chain silica fine particles. Moreover, because the amount of silica used as binder for adhering the chain fine particles one another is small, the above gaps are not filled by the silica binder, and a majority of the gaps remain as voids occupied by air or gas. Due to the existence of such voids, the refractive index value of the film as a whole becomes smaller than the refractive index of silica (about 1.45) to become 1.25 to 1.40. The refractive index of the film at which reflective prevention theoretically becomes zero is the square root value of the refractive index of the glass substrate (1.50), i.e. 1.225, and the refractive index of the present invention can get closer to this index.
When the amount of silica as a binder in the film is too scarce, if it is less than 5% by weight to that of chain silica fine particles for example, the adhesion of the chain silica fine particles becomes insufficient to cause lowering of the mechanical strength of the film. Inversely, when the amount of silica is too large, if it is more than 30% by weight to that of chain silica fine particles for example, the gaps between the chain fine particles are fully filled by the silica to leave no void, so that the refractivity of the film cannot be made small, and the reflectivity cannot be lowered. The volume of the above-mentioned voids is between 50 to 80% of the volume of the entire film when the refractive index of the latter film is compared to the refractive index of a film made of silica without voids (about 1.45).
On the film surface, there are formed small dents and projections mainly by the projection surface of the chain silica fine particles, which serve to prevent reflection images by diffusing the reflection lights, and not to lower the resolution of the penetration images. When the amount of silica as the binder in the film is too large, the whole chain silica fine particles submerge under the silica. Because of this, the arithmetic mean roughness (Ra) of the film surface to be described later becomes less than 5 nm, and the mean interval (Sm) of the dents and projections on the film surface is apt to exceed 300 nm, and it becomes impossible to prevent practical reflection of the reflective images. Accordingly, for the purpose of lowering the refractive index of the film without lowering mechanical strength of the film, and moreover, to form the above mentioned dents and projections on the film surface, the amount of silica in the film is preferably made to 5 to 30% by weight, more preferably to 10 to 20% by weight, based on the weight of the chain silica fine particles.
The size of the chain silica fine particles is preferably of an average diameter of 10 to 20 nm and an average length of 60 to 200 nm. Herein, the average diameter means a value obtained by measuring each diameter of 100 samples with electron microscope, and the weights are given to the measured values in proportion to the volume. Similarly, the average length means that the respective lengths of 100 samples (in case of the sample being curved, the length taken along the curve) are measured with electron microscope, and the weights are given to the measured values in proportion to the volume and the average values are obtained.
When the average diameter is less than 10 nm or the average length is less than 60 nm, (1) the total volume of the voids between the adjacent fine particles becomes and accordingly that of the voids of the total volume becomes small, so that it becomes impossible to make the value of refractive index as a film small. Also, (2) the arithmetic mean roughness (Ra) of the resulting film surface becomes less than 5 nm, whereby it becomes impossible to form enough of the effective dents and projections to prevent the interference of the reflection images and undesirable. In case of the average diameter exceeding 20 nm or the average length exceeding 200 nm, the arithmetic mean roughn
Okamoto Hideki
Takahashi Kouji
Conlin David G.
Dike Bronstein Roberts & Cushman IP Group
Edwards & Angell LLP
Jones Deborah
McNeil Jennifer
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