Patent Application
20070077322
This application is based on Japanese patent application No. 2005-285905, the content of which is incorporated herewith by reference.
1. Field of the Invention
The present invention relates to a resin molding apparatus and more particularly to a resin molding apparatus which is suited for molding of small optical elements such as lenses.
2. Description of Related Art
In a resin molding apparatus, generally, a movable mold is moved to come into contact with and separate from a fixed mold (for clamping and opening). Specifically, the movable mold is supported by a movable platen, and the movable platen slides on a tie bar which is fixed to a fixed platen. In this case, it is required to have good slidability between the tie bar and a bush bearing provided for the movable platen.
Conventionally, as Japanese Patent Laid-Open Publication No. 2001-246627 discloses, a lubricant (grease) is filled between the tie bar and the bush bearing. However, the use of a lubricating oil requires periodical oil supplies, and the oil supplies may cause an axial gap between the fixed mold and the movable. Even when an automatic oil supplying method is adopted, it is likely that each automatic oil supply causes a change in the axial gap between the fixed mold and the movable mold. The axial gap prevents smooth opening/closing of the molds, causes uneven distribution of clamping force on a separating surface and causes deformation of molding spaces. Especially in molding very small optical elements such as microlenses, the axial gap between the fixed mold and the movable mold may result in an axial gap between surfaces of each of the molded microlenses. Therefore, it is very difficult to obtain molded products with stable optical performance.
Japanese Utility Model Laid-Open Publication No. 7-11322 discloses that the bush bearing of the movable platen has a porous ceramic layer impregnated with a lubricant. This is to implement the idea of automatic oil supplies. However, problems such as durability, etc. are left unsolved.
An object of the present invention is to provide a resin molding apparatus which performs smooth opening/closing of molds without using a lubricant and which produces molded products of high quality.
In order to attain the object, a resin molding apparatus according to the present invention comprises a movable platen for supporting a movable mold, a fixed platen for supporting a fixed mold, a tie bar for connecting the movable platen to the fixed platen and a bush bearing fixed to the movable platen at a position to be in contact with the tie bar such that the movable platen is movable along the tie bar via the bush bearing. In the apparatus, a low friction surface treatment is applied to at least one of a surface of the tie bar in contact with the bush bearing and a surface of the bush bearing in contact with the tie bar.
The tie bar may pierce through the bush bearing, and in this case, the low friction surface treatment may be applied to an outer circumference of the tie bar or an inner surface of the bush bearing.
The low friction surface treatment is preferably forming a hard lubricating layer made of diamond-like carbon, forming a hard lubricating layer made of diamond-like carbon containing an additive or forming a hard lubricating layer made of CrN.
In the resin molding apparatus according to the present invention, a low friction surface treatment is applied to at least either the outer circumference of the tie bar or the inner circumference of the bush bearing provided for the movable platen. Therefore, the opening/closing motions of the molds are smooth, and occurrences of axial gaps due to oil supplies can be avoided. Also, the posture of the movable platen during an opening/closing motion is stable, and the clamping force is distributed evenly. Therefore, deformation of the separating surface can be minimized. Thereby, the accuracy of the molded products is improved, and it is possible to mold especially very small optical elements without any problems such as an axial gap between surfaces, etc. When the resin molding apparatus is of a type which molds a plural number of products at a time, that is, when the apparatus has a plural number of molding spaces, variations among the plural number of molding spaces in deformation can be minimized. Accordingly, there is no fear that the molded products may vary in performance. Further, since no lubricants are used, the clearance between the tie bar and the bush bearing can be filled to the utmost, which is very effective to prevent an axial gap between the movable mold and the fixed mold.
This and other objects and features of the present invention will be apparent from the following description with reference to the accompanying drawings in which:
Embodiments of a resin molding apparatus according to the present invention will be described with reference to the accompanying drawings.
The movable platen 35 is driven to move horizontally by a driving mechanism (not shown). When the movable platen 35 is moving in the direction A, the molds 20 and 30 are clamped, and when the movable platen 35 is moving in the direction A′, the molds 20 and 30 are opened. In the first embodiment, the clamping force is designed within a range from 5 tons to 15 tons.
A runner 52 is connected to each of the molding spaces 51 via a gate 53. An injection unit (not shown) extends from the direction X to the rear side of the fixed mold 20 via the inside of a locating ring 61 (which will be described later), and melted resin ejected from the injection unit is injected into the molding spaces 51 via the respective runners 52 and gates 53.
Each of the tie bars 40 is fixed to the fixed platen 25 at one end and fixed to a rear platen (not shown) at the other end. The movable platen 35 is fitted to the tie bars 40 via bush bearings 36 such that the movable platen 35 slides on the tie bars 40 via the bush bearings 36. A low friction surface treatment is applied to at least either the outer circumferences of the tie bars 40 or the inner circumferences of the bush bearings 36. It is not necessary to apply the low friction surface treatment to the tie bars 40 entirely, and it is necessary to apply the low friction surface treatment to merely the parts where the bush bearings 36 slide.
It is sufficient if the low friction surface treatment is as effective as a lubricant conventionally used for an improvement in the slidability. The low friction surface treatment is, for example, forming a hard lubricating layer made of DLC (diamond-like carbon), forming a hard lubricating layer made of DLC containing an additive or forming a hard lubricating layer made of CrN. These hard lubricating layers are effective enough to improve the slidability and the durability. Although it is preferred that such hard lubricating layers are formed on both the outer circumferences of the tie bars 40 and the inner circumferences of the bush bearings 36 by the low friction surface treatment, it is sufficient to form hard lubricating layers either the outer circumferences of the tie bars 40 or the inner circumferences of the bush bearings 36.
According to this embodiment, at least either the outer circumferences of the tie bars 40 or the inner circumferences of the bush bearings 36 provided for the movable platen 35 are subjected to the low friction surface treatment, and smooth opening/closing of the molds 20 and 30 is possible without using a lubricant. Therefore, an axial gap due to an oil supply can be avoided. Also, the posture of the movable platen 35 during an opening/closing motion is stable, and an even distribution of clamping force can be achieved even during a continuous molding operation. Therefore, deformation of the separating surface between the molds 20 and 30 can be minimized. Thereby, the quality of molded products can be improved, and very small optical elements without any problems such as an axial gap between surfaces, etc. can be obtained.
Also, variations among the molding spaces 51 in deformation can be minimized, and accordingly, variations among the molded products in performance can be minimized. Further, since a lubricant is not used, the clearances of the tie bars 40 and the clearances of the bush bearings 36 can be filled to the utmost, which is very effective for prevention of an axial gap.
The detailed structures of the fixed platen and the movable platen and the structures of the platens may be designed arbitrarily.
Although the present invention has been described in connection with the preferred embodiment, it is to be noted that various changes and modifications are possible to those who are skilled in the art. Such changes and modifications are to be understood as being within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2005-285905 | Sep 2005 | JP | national |
