WO2006090003A1

WO2006090003A1 - Method for manufacturing lenses for optical products, such as cameras, spectacles, sunglasses, mobile phones etc.

Info

Publication number: WO2006090003A1
Application number: PCT/FI2006/000067
Authority: WO
Inventors: Jari Ruuttu
Original assignee: Fortiondesignit Oy
Priority date: 2005-02-23
Filing date: 2006-02-23
Publication date: 2006-08-31
Also published as: FI20050218A0

Abstract

A method for manufacturing optical products, such as lenses for cameras, spectacles, sunglasses or mobile phones, in which the product is connected to a frame or a body. The product is detached from the blank and a specific bevelled edge is formed at an angle of 10-80 °, preferably approximately 30 °, the edge engaging an opening comprising an edge bevelled at a corresponding angle in the frame or body (6).

Description

Method for manufacturing lenses for optical products, such as cameras, spectacles, sunglasses, mobile phones etc.

The manufacture of optical products in particular and combining them with the actual product, such as the casing of a mobile phone, involve many problems.

Regarding manufacture, the problem resides in the fact that the product, such as e.g. the lens of a mobile phone, has so far been made by injection moulding in a separate cavity, resulting in high stresses and optical errors, such as aurora borealis, and also in deformation of the optical surface.

Considering the coating processes required for the optical product to meet the demands posed on it, including at least an anti-reflective coating (AR coating), ordinary coating and scratch-free coating (SF coating), production problems increase substantially.

Coating processes are known, such as e.g. a vacuum coating process and a chemical process.

After all the processes mentioned above, the finished optical product should be combined with the product proper. This is a most complicated, costly and time- consuming operation when conventional methods are used, and in addition, the joint will have poor quality.

The method of the invention provides a solution to the problems above:

1. By the method of the invention, an optical product is manufactured in an injection-moulding process using a CD-DVD method.

2. By the method of the invention, coating, i.e. anti-reflective coating and scratch- free coating, is performed under vacuum by means of laser.

3. By the method of the invention, the products are detached from the blanks and a specific bevelled edge is formed at an angle of ~ 30 °.

4. By the method of the invention, connection is primarily performed by laser welding, but secondly also by ultrasonic welding. Operations 1-4 defined above yield a complete entity without incurring higher costs. The overall process will be appreciably less expensive than with known methods.

In addition to yielding manufacture at lower cost, the method of the invention also provides substantially higher quality. Atoms having a speed in the range ~ 25,000 - 100,000 m/s will be extremely densely packed when settling on the surface of their object, and then adhesion and surface hardness properties will be considerably improved compared to currently known methods.

The method of the invention differs substantially from prior art methods for manufacturing optical products.

1. Prior art products have been produced as individual units, i.e. melted plastic has been injection moulded in a cavity comprising the physical shape of one specific product. There have been no prior art suggestions to produce an optical product by injection moulding a large blank comprising a plurality of products, as is done in the CD disc application of the method of the invention.

Prior art methods have not allowed for further processing operations, such as coating and attachment.

The remarks above also apply to prior art methods for manufacturing spectacles, even though coating is crucial in such manufacture, since there have been no technical means for other procedures.

Individually made workpieces involve problems impairing their quality:

a) high stresses b) aurora borealis c) refraction errors d) complex mould e) extremely difficult further processing

A method implementing CD manufacture is free of such problems. 2. Coating of optical products by prior art methods differs from the coating in accordance with the method of the invention.

In prior art methods, only spectacles and CD-DVD discs are coated, however, using different methods for the two; this is natural, since they have different purposes of use.

CD-DVD discs have a vacuum-evaporated thin metal coating of ~ 350 nm, e.g. aluminium coated directly on plastic, and on top of this, a chemical hard lacquer coating, and there have not even been any efforts to achieve an actual scratch- free or anti-reflective coating, since this has not been considered necessary.

Nowadays it is known that especially CD-DVD recordings, which are meant to store information over periods of more than 10 years, do not yet have adequate quality. The problem of such recordings is specifically oxidation of the metal surface, whereby the data are lost in their totality. None of the prior art methods has provided a solution to the problem, whereas the method of the invention has resolved the problem.

Spectacles constitute the largest single product category in which scratch-free and anti-reflective coatings are provided.

Optical products, which are subject to strong wear and should have anti-reflective features, should meet the following requirements:

Firstly, they should be wear resistant.

Secondly, the product should be provided with an anti-reflective coating with the primary purpose of eliminating reflection; yet with the coating in the outer-most layer, i.e. beyond the hard coating, it also plays an important part in the scratch- free function of the product.

For the following reasons, prior art manufacturing methods do not provide techniques that could be successful even theoretically.

1. The plastic from which the products are made has an impact as such on the end result, which is partly determined by the plastic hardness and the lacquers used. Since an optical product is considered here, the plastic is also required to have excellent optical properties, such as light transmittance.

As a rule, optical products made of plastic have always been coated with hard lacquer by chemical means so as to achieve a hard surface, which can subsequently be subjected to vacuum coating.

2. Vacuum coating is specifically used for achieving anti-reflective coatings, which play an essential part in the scratch-free feature.

Consequently, in prior art methods, the operation mentioned last, i.e. vacuum coating processes, constitute the major problem.

The outermost anti-reflective coating is made up of a plurality of layers and materials, as illustrated in figure 8, 43-48. The coating materials usually comprise oxides, such as silica, titanium, chromium etc., however, prior art methods also use magnesium fluoride MgF₂ to a substantial extent.

The problem does not reside in the coating material itself, but in the very work processes, i.e. in the manner of evaporating these materials. Prior at methods also involve the problem of their work processes not allowing the use of new materials, such as carbon, in the manufacture of a diamond coating.

Prior art vacuum methods are mainly based on thermal evaporation, the optimal applications having implemented ionic bombardment in order to increase the energy charge of the atom, and this has had a favourable effect on the atom speed.

In this case, the evaporated material has a temperature only in the range ~ 2,000 ° - 3,000 °, resulting in very low energy charge of the atom, which, in turn, entails a very low atom speed of 100-150 m/s.

Under the laws of physics, the atom speed of an evaporated material affects the density of the coating thus produced, and this, again correlates with the hardness of the coating.

Commercially notable prior art methods do not achieve an atom speed higher than the range 100-150 m/s during evaporation. To resolve the problems defined above, one has examined the applicability of known lasers to vacuum processes. Such lasers are Nd-Yag pulse or solid-state lasers, whose pulse lengths always have a longer duration than of the order of a nanosecond. Pulses of such long duration have achieved but small improvements compared to thermal evaporation.

Known lasers have achieved atom speeds of approximately ~ 500 m/s, which consequently is not sufficient; there is also the additional problem of the laser power being consistently too low, typically ~10-200 watts.

Prior art laser methods do not provide a solution to the basic problem, i.e. achieving a higher atom speed. In addition, they yield poor quality due to the long pulse duration, and known laser devices do not produce adequate power.

Thermal evaporation involves the problem of the evaporated material melting before evaporating. This results in the generation of an abundance of heat that has not been bound to the atom to be evaporated, and thus the temperature of the vacuum space and the evaporated body will increase critically.

Solid-state and long-pulse laser applications have exactly the same results as thermal evaporation.

In both the cases, the material is evaporated in large clusters, resulting in poor surface quality.

The invention relates to a method comprising primarily injection moulding of a "blank" using a CD-DVD process, forming areas in which the lens can be cut open, preferably by forming a distinctly slanted surface cut at an angle of 10-70 ° using a laser, for instance.

The invention has the advantage that the lens can be fixed optimally with a strong joint to the matching oblique surface of the casing member using laser welding, ultrasonic welding, glue or the like.

In accordance with the invention, the lens can also be cut from a PMMA, PC, PA planar sheet, preferably using laser, however, mechanical milling or water cut operations are equally well applicable. It is essential that the workpiece (lens) be made without being placed in the cavity at the manufacturing stage, as is done in injection-moulding processes. When a lens is formed from a planar sheet, this problem will evidently not occur, however, three-dimensional shapes/surfaces cannot either be produced.

Fl Patent Application 20010239 discloses the use of a CD-DVD injection moulding method in the manufacture of optical products.

The difference between the method of the invention and that of Fl Patent Application 20010239 resides in the fact that the known CD-DVD method forms workpieces, lenses, in a physical form, which are connected with the inner plane and the outer periphery over projections alone.

The invention, comprising a CD-DVD manufacturing method as one application, does not include separate mould cavities, in which individual physical workpieces could be produced, but they are seamless integrated parts of the CD-DVD disc, even though they may have three-dimensional designs.

The mould construction and the methods are quite identical to those of any method for producing CD-DVD discs.

The method of the invention yields the following benefits: superior quality of the workpiece, i.e. the lens, which is totally free from aurea borealis and stresses, no optical deformation, extremely high dimensional accuracy maintained throughout the further processing operations. The mould has inexpensive and rapid manufacture, no ejection pins are needed, and the mould base is readily replaced.

In addition, this is the only method that allows fully automated further processing, regardless of the dimensioning and shape of the workpiece, since the workpiece, i.e. the lens, is always only a part of an integral CD-DVD disc, which has constant dimensions and always comprises the same amount of raw material.

It should be noted that the injection moulding process is but one way of further processing an optical workpiece. Other processes comprise chemical UV-cured lacquering including lacquer application by piezo, spraying, spinning or other means, vacuum coating, antireflective treatment and scratch-free coating treatments, hard coatings produced by piezo or tampo means or laser, cutting open the workpiece (lens) by laser, milling or water cutting operations.

The work processes above require that a CD-DVD containing 1-30 workpieces is transferred, stored and shifted between and during the operations. Then, in the last actual operation, the workpiece is cut open and forms a slanted surface at an angle of 10-80 °, typically 30°. If the workpiece can be connected to the frame with an adhesive tape or by mechanical means, the cut surface may be straight, i.e. at an angle of 90+5 °.

Comparison with prior art methods

The lens edge is most typically a graded level, with two vertical surfaces forming at the edge of the lens with a maximum cant of +5 ° if the workpiece, i.e. the lens, is injection moulded.

Especially injection moulding involves the problem of generating stresses that have a negative impact on the optical coating proper. This requires a mould cavity and ejection pins. The process is slow, since the injection speed cannot be high (in order to avoid aurea borealis) and the cooling period is long. All of the further processing operations are very difficult with the workpieces being apart from each other.

When a lens is connected to the frame, the planar surface alone is utilised, since there is no method for connecting the vertical surfaces to the frame.

Ultrasonic welding is typically used, but adhesive and tape attachments also occur. Laser welding is a new way of attachment, yielding optimal quality and a rapid work process.

A laser beam is usable for welding the pieces together, but it can be used only on planar surfaces, in other words, precisely in the weakest area of the workpiece.

Workpieces may be positioned in abutting and opposite relationship, spaced by an interstice with high dimensioning accuracy, a seam, since without such accuracy the pieces cannot be joined. Ultrasonic welding and gluing are excluded in such an application, by contrast, laser welding could be operative, provided that the workpieces are positioned in abutment with sufficient accuracy, which means that there should be no physical gap in reality.

In this case, a laser beam is not usable, but instead, a means of laser beam type with an oblique angle of incidence; otherwise the body will not be melted nor welded over the entire material thickness.

There still remains the real problem of poor resistance to mechanical stress and also to stresses of bending type.

Fl 20010239 cited above represents the closest related prior art, but in this method the workpieces are in a physically finished form in the very injection-moulding step, whereas the workpieces of the present invention form an integral entity without seams, with the components formed only in the step of cutting up the entity.

An exemplifying case of the invention comprises the lens of a mobile phone having a edge bevelled at an angle of 10-80 °, most typically 30 °, as illustrated in the figure. The bezels of the counter-piece represent the display.

In an example of the invention, the bevelled edges of the frame and the lens are placed inversely, i.e. with cants towards the display, and then mounting is performed through the bottom.

In a typical embodiment of the invention, the lens is positioned in the frame with the slanted surfaces (edges) of the two workpieces facing each other in the natural state.

In a preferred embodiment of the invention, the laser beam is directed from a laser fibre head to the junction at the location of the slanted surfaces. It should be noted that the laser beam is in an advantageous position owing precisely to the slanted surfaces, i.e. the angle of incidence of the beam is favourable, even though the beam were directed from one single spot, referred to as spherical ball scanner in professional language.

A preferred embodiment of the invention comprises production of an optical product, such as a display lens, a camera lens or any optical product by the CD- DVD injection moulding method. The CD-DVD plane has a constant standard appearance and dimension, and so does the central hole. An injection moulding process is optimal in the manufacture of high-precision optical products requiring further processing.

A viscous substance, typically PMMA, PC, PA or the like, is injected through the centre, from where it spreads simultaneously towards the outer periphery in the direction indicated by the arrows.

It is essential not to have discrete components, and hence no separate cavities, but instead, all of the workpieces form a homogenously integrated part of the CD- DVD disc, even in the case of three-dimensional surfaces.

This ensures a short cycle time of ~ 33 s for a CD disc size and of 6 s for a DVD disc size, i.e. one fifth of the size in prior art methods.

The invention uses an integral CD-DVD disc comprising the three-dimensional geometries desired for the products, but without forming any separate cavity, whereas the entire space between the central hole and the outer periphery of the CD-DVD disc is a uniform and continuous space, as is the case in a standard CD- DVD disc.

The separate workpieces are not formed until the cutting is performed by laser, mechanical or water means at an angle of 30 °, for instance, thus enabling optimal connection using e.g. laser welding.

One embodiment of the invention comprises an optimal application for joining a lens and a frame by means of laser, the workpieces to be joined being provided with the bevelled edges of the invention.

In this embodiment, the laser beam is directed to an optical lens system, referred to in professional language as an optically compensated flatbed scanner, allowing for evaporation of a wide surface, having e.g. a width of 50 mm, with the correct beam spot focus.

This allows the laser to be directed at the same angle in each case, e.g. perpendicularly, following the junctions between the workpieces, thus yielding a high-precision and high-quality result. A preferred embodiment of the invention comprises typical surfaces, which are indispensable in order to obtain anti-reflective and scratch-free features in the optical products.

The frame of the optical product may be made of glass or plastic, with specific coatings on both sides, the coatings being typically made of oxides and having mutually different refraction indexes.

We may cite as examples silicon oxide (SiO₁ Siθ₂), titanium oxide (TiO, TiO2), chromium oxide (CrO, CrO₂) or metals, such as silver (Ag).

The coating of the new application may be made of any material or material group, such as nitrides, borides, fluorides, metals, oxides and carbon, used for forming a diamond coating.

If its is desirable to provide, besides anti-reflective and scratch-free characteristics, a reflection density varying in accordance with light intensity, such a feature being useful in sunglasses, there may be a different number of layers 44-48.

In purely optical products, such as a camera or mobile phone lenses, only anti- reflective and scratch-free features are desirable.

In a preferred optical product, the plastic frame is first coated with a chemical hard coating, e.g. UV cured hard lacquer. Then different materials are coated on top of each other using the picosecond laser-vacuum method of the invention.

The layers may be coated in the following order: titanium oxide, silicon oxide titanium oxide and diamond coating.

This procedure combines the anti-reflective and scratch-free features so that light reflection will be only ~ 0.1 % and about 99.9% of the light will be transmitted through the optical product, while still yielding a totally scratch-free end product as the end result.

A prerequisite for this is the use of picosecond laser of the new method, combining adequate power with a vacuum process. The laser of the invention has the following parameters:

a) power - 100-10,000 watt b) pulse length 1-50 ps (picoseconds) c) pulse energy 1-10 μJ d) pulse power 50-10,000 kW e) pulse repetition frequency 1-10 MHz.

Figure 4 illustrates the manufacture, cutting, coating and assembling of an optical product, such as a mobile phone lens or the like.

In the first step of the method of the invention, the lens blank of figure 4 is injection moulded using the CD method.

Some of the areas in the product are not separated by walls, i.e. the products have no separate recesses, but instead, this particular area has been provided with a mould coating corresponding to the three-dimensional shapes of the product.

This allows melted viscous material, such as plastic, to move freely from the centre, through which it is injected, towards the outer periphery in the direction indicated by the arrows.

The end result will consist of a flawless and stress-free plastic blank, which can be further processed as such, regardless of the different products comprised in the blank.

The automated line carries out hard lacquering, vacuum coating by picosecond laser and impression or laser pattern engraving, if necessary.

The last work step comprises cutting of the actual products from the lens blank using e.g. laser or mechanical engraving.

A product produced as described above is advantageously fixed by laser welding.

As defined above regarding the method of the invention, the optical product, such as a mobile phone lens, is preferably provided with a bevelled edge. In this case, the counter-piece, such as the casing, should have an identical bevelled edge for the bevelled edges of the two pieces to match.

In order to avoid unnecessary and complex jigs, which are otherwise required both in ultrasonic welding and laser welding, a projection is preferably formed in accordance with the invention.

The lens and the product can be locked together by means of the projection, without using mechanical jigs.

The projection is initially melted by a laser beam so that the area starts getting filled.

The projection melts under the action of the laser beam, forming a locking that does not allow the lens to be removed.

The actual laser welding of the main surfaces is performed only after this.

Detailed description of the invention

The invention relates to a method for manufacturing optical products having a maximum thickness of 3 mm, such as lenses for spectacles, sunglasses or mobile phones, in which the product is connected to a frame or a body by detaching the optical product from the blank and by forming a specific edge bevelled at an angle of 10-80 °, preferably approximately 30 °, which engages an opening comprising an edge at a corresponding angle in the frame or body.

In a preferred embodiment of the invention, the components are joined by means of laser welding.

In a second preferred embodiment of the invention, the components are joined by means of ultrasonic welding.

In a further preferred embodiment of the invention, the components are joined by gluing.

Before being joined, the surface/surfaces of the product in the method of the invention can be provided with anti-reflective coating. In a second preferred embodiment of the invention, the surface/surfaces of the product are provided with scratch-free coating before being joined.

In accordance with the invention, the edge of the frame or body comprises a projection, with the aid of which the product is attached e.g. by laser welding to the frame or body before the product in its totality is connected to the frame or body by laser welding.

In a particularly preferred embodiment of the invention, the blank is a workpiece of the type of a CD disc.

The invention also relates to a product produced by the method.

Claims

1. A method for manufacturing optical products having a maximum thickness of 3 mm, such as lenses for spectacles, sunglasses or mobile phones, in which the product is connected to a frame or a body, characterised in that the optical product is detached from the blank and a specific bevelled edge is formed at an angle of 10-80°, preferably approximately 30°, the edge engaging an opening comprising an edge at a corresponding angle in the frame or body.

2. A method as defined in claim 1 , characterised in that the components are joined by means of laser welding.

3. A method as defined in claim 1, characterised in that the components are joined by means of ultrasonic welding.

4. A method as defined in claim 1 , characterised in that the components are joined by gluing.

5. A method as defined in any of the preceding claims, characterised in that before being joined, the surface/surfaces of the product are provided with anti- reflective coating.

6. A method as defined in any of the preceding claims, characterised in that before being joined, the surface/surfaces of the product are provided with scratch- free coating.

7. A method as defined in any of the preceding claims, characterised in that the edge of the frame or body comprises a projection, with the aid of which the product is attached e.g. by laser welding to the frame or body before the product in its totality is connected to the frame or body by laser welding.

8. A method as defined in claim 1 , characterised in that the blank is a workpiece of the type of a CD disc.