Apparatus and method for heat treating at least one lens body

Abstract

An apparatus (1) for heat treating at least one lens body (3), the apparatus (1) comprising:-at least one mould assembly (7) for casting a lens, each mould assembly (7) comprising a first mould member (9) and a second mould member (9), the first and second mould members (9) being arranged to hold the lens body (3) therebetween; -at least one induction coil (15) arranged so as to face the at least one mould assembly (7); and-a temperature control unit (17) configured to monitor a temperature in the mould assembly (7) wherein at least one of the first mould component (9) and the second mould component (9) comprises at least one metal part (11, 25, 29) made of a metal material, the induction coil (15) is configured to generate a magnetic field when supplied with a current and to generate heat in each metal part of each mold assembly (7).

Description

Technical Field

[0001] The invention relates to a device for heat-treating at least one lens body and a method for heat-treating using the device.

[0002] The invention also relates to an optical article comprising at least one lens body treated by such a method. Background Art

[0003] Ophthalmic lenses are conventionally manufactured by casting polymeric materials via a curing process of a polymerizable composition in a mold, thereby giving them the appropriate shape.

[0004] The curing time required for the material to fully harden is the limiting factor in the production rate of lenses.

[0005] In this document, the expression "lens body" is used to denote a finished lens, an unfinished lens such as a solid body intended to be further modified into a lens, or a fluid or gel material intended to be hardened and / or cured to form a lens.

[0006] The lens is, for example, an optical lens, preferably an ophthalmic lens.

[0007] The conventional casting process used in the ophthalmic industry typically includes the steps of mixing one or more monomers in a tank and adding eventual catalysts and additives to form a polymerizable composition, pouring this composition into mold assemblies, and then subjecting these filled mold assemblies to thermal cycles in an oven for a typical duration of 20 hours to polymerize and cure the composition.

[0008] Each mold assembly consists of two opposing glass mold members shaped to provide the front and back surfaces of the lens and an elastomeric gasket or tape for sealing the sides of the mold.

[0009] The initiation and propagation of the polymerization reaction is thermally activated. Furthermore, the reaction is generally exothermic and in order to avoid hot spots that cause irregularities in the cast lens, the temperature of each mold component needs to be controlled.

[0010] This thermal control is implemented in the oven during curing via a convection heating system of the oven's outer shell and at least one temperature sensor for implementing a feedback loop. The sensor can be used to monitor the overall temperature in the oven, or more preferably the individual temperature of each mold assembly.

[0011] These processes can be improved. In practice, the temperature control of the mold assembly is not precise, since the heating device has a high inertia and an accurate temperature control loop cannot be implemented. In addition, the energy efficiency of the heating device is low, and the energy efficiency of the casting process can therefore be improved. Together with reducing the duration of the casting phase, this allows reducing the energy requirements of the casting phase and the associated costs and increasing productivity. Summary of the invention

[0012] The present invention aims to solve these problems by providing an improved method for casting lenses. To this end, the present invention relates to an apparatus for heat treating at least one lens body, the apparatus comprising:

[0013] - at least one mold assembly for casting a lens, each mold assembly comprising a first mold member and a second mold member, the first mold member and the second mold member being arranged to hold the lens body therebetween,

[0014] - at least one induction coil, the at least one induction coil being arranged facing the at least one mould assembly, and

[0015] - a temperature control unit configured to monitor the temperature in the mold assembly,

[0016] Wherein, at least one of the first mold member and the second mold member includes at least one metal part made of a metal material, and the induction coil is configured to generate a magnetic field and generate heat in each metal part of each mold assembly when supplied with current.

[0017] Such an apparatus allows the use of an inductive heat source to temperature manipulate the lens body, thereby allowing for faster and more accurate heat generation and improved energy efficiency.

[0018] The apparatus may comprise at least one temperature sensor arranged to monitor the temperature in each mould assembly.

[0019] At least one of the first mold member and the second mold member may include a mold half made of a metal material as a metal part.

[0020] The mold half is, for example, a male mold component or a female mold component.

[0021] This feature enables good thermal contact between the metal part and the contents of the mold. The metal mold also exhibits desirable hardness and resistance properties.

[0022] One of the first mold member and the second mold member may include a mold half made of a metallic material and the other may include a mold half made of a transparent non-metallic material.

[0023] This feature enables visual control of the contents of the lens mold, for example to check for the presence of air bubbles.

[0024] An example of a transparent non-metallic material is glass.

[0025] The first mold member and the second mold member may each include a mold half made of a non-metallic material, and at least one of the first mold member and the second mold member further includes a retaining plate for the mold half as a metal part, the retaining plate being made of a metallic material and extending on an outer surface of the mold half.

[0026] This feature allows the use of interchangeable glass mold halves to adapt the apparatus to handle lenses of various shapes.

[0027] The first mold member and the second mold member may each include a mold half made of a non-metallic material, and at least one of the first mold member and the second mold member further includes a metal coating as a metal part, which is made of a metallic material and extends on an outer surface of the mold half.

[0028] This feature enables good thermal bonding between the non-metallic mold half and the metal part, as well as easy and fast preparation of the mold component by spraying a coating of metallic material on a glass mold, for example.

[0029] The metallic coating may present a thickness measured along a direction perpendicular to the outer surface comprised between 0,1 mm and 1 mm.

[0030] The metal part may extend over a portion of the outer surface of the half-mold, the portion comprising at least 80% of the total surface area of ​​the outer surface of the half-mold. This enables efficient heat transfer from the metal part to the half-mold.

[0031] Metal materials can show a temperature between 1×10 6 S / m and 2×10 7 Conductivity between S / m.

[0032] This feature allows improved heat generation through the Joule effect of the induced current.

[0033] The metallic material may comprise at least 50% by weight iron.

[0034] This feature allows the induced current to be generated efficiently and with sufficient resistance to generate heat.

[0035] The present invention also relates to a method for implementing the apparatus as described above to heat treat at least one lens body, the method comprising the following steps:

[0036] - holding the lens body between the first mold member and the second mold member of the mold assembly,

[0037] - generating a current in the induction coil and inducing a current in the metal parts of the mold assembly, thereby generating heat in the mold assembly via the Joule effect,

[0038] - processing the lens body in the mold assembly and monitoring the temperature in the mold assembly during processing, and

[0039] - Removing the processed lens body from the mold assembly.

[0040] This method enables a more energy efficient method of generating heat in a mold assembly containing a lens body. This enables faster heat treatment and / or less energy consumption during the heat treatment stage.

[0041] The method may include a preliminary step of preparing a mold assembly by depositing a metallic coating on an outer surface of a mold half made of a non-metallic material.

[0042] The coating may be deposited by spraying.

[0043] The heat treatment may be casting of the lens and includes heat-activated polymerization of a fluid or gel material contained in the mold assembly to produce a solid lens.

[0044] The casting process of lenses is long, energy demanding, and would highly benefit from improved energy efficiency.

[0045] The fluid or gel material may include a prepolymer.

[0046] The prepolymer is a solution including molecules each formed of a plurality of monomers, and thus shows a higher degree of polymerization than a monomer solution, but is not yet completely polymerized.

[0047] This type of material achieves faster polymerization, further speeding up the casting process.

[0048] Heat treatment may be performed to harden the coating applied to the lens body prior to placement in the mold assembly.

[0049] This type of process benefits from improved temperature control and energy efficiency to ensure better uniformity of the coating.

[0050] Heat treatment may include causing dye deposited on the lens body to migrate into the lens body prior to placement in the mold assembly.

[0051] This type of process is improved by the more accurate temperature monitoring permitted by the method of the present invention.

[0052] The invention further relates to an optical article comprising at least one lens obtained from a lens body treated by a method as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] - Figure 1 is a schematic representation of an apparatus for heat treating at least one lens body during a production step of a casting process according to a first embodiment of the present invention,

[0054] - Figure 2 is a partial schematic representation of an apparatus according to a second embodiment of the present invention,

[0055] - Figure 3 is a partial schematic representation of an apparatus according to a third embodiment of the invention, and

[0056] - Figure 4 is a schematic representation of an apparatus according to a fourth embodiment of the invention. DETAILED DESCRIPTION

[0057] Figure 1 Shown is a device 1 for heat treatment of at least one lens body 3. The device 1 is used for manufacturing lenses, for example by casting, as well as for other types of heat treatments, such as hardening of surface coatings activated by heat or migration of surface dyes into the lens.

[0058] The device 1 comprises a housing defining an internal volume 5 which is thermally insulated from the environment and which advantageously also provides at least partial electromagnetic shielding.

[0059] The apparatus 1 further comprises at least one mould assembly 7, preferably a plurality of mould assemblies 7, arranged in the housing 5. Each mould assembly 7 is designed to receive and hold a lens body 3 during the heat treatment.

[0060] In the case of a fluid or gel lens body, the sides of the mold assembly 7 are closed by using gaskets or tape.

[0061] The expression "lens body" is used to denote a finished lens, an unfinished lens such as a solid body intended to be further modified into a lens, or a fluid or gel material intended to be hardened and / or cured to form a lens.

[0062] For example, during the casting process, the lens body placed in the mold assembly is a polymerizable composition in a fluid or gel state.

[0063] Each mould assembly comprises two mould members 9 arranged facing each other to hold the lens body between them.

[0064] The mold members 9 each comprise a mold half 11 , such as a female mold or a male mold, and a holder 13 for the mold half 11 .

[0065] The female and male moulds comprise respectively a female moulding surface and a female moulding surface facing inwardly towards the lens body 3 and conforming to follow respectively the convex surface of the lens and the concave surface of the lens.

[0066] The holders 13 are, for example, clamps which are arranged to hold the mould half 11 in place during the heat treatment process.

[0067] exist Figure 1 In the embodiment shown, both mold halves 11 are made of metal material.

[0068] The metallic material is selected from metals and metal alloys to be compatible with induction based heat generation.

[0069] Preferably, the metal material exhibits a temperature between 1×10 6 S / m and 2×10 7 The electrical conductivity of the metal material is between 1000 S / m, providing efficient heat generation through the Joule effect of the induced current circulating in the metal material.

[0070] For example, metallic materials include ferrous metals such as cast iron, steel, chrome-plated steel, and stainless steel.

[0071] Preferably, the metallic material comprises at least 50% by weight ferrous metal, such as at least 50% by weight iron.

[0072] Steel is advantageous in that its specific heat is about two thirds that of glass, and therefore the mold assembly 7 requires less heat to raise the temperature of the lens body 3. In addition, the steel mold halves benefit from very high mechanical resistance to breakage and wear. Finally, in the event of surface damage to one of the molding surfaces of the mold halves, the surface can be regenerated via specific treatments, which is more difficult with glass.

[0073] The apparatus 1 further comprises at least one induction coil 15 arranged facing the mould assembly 7 and configured to generate a magnetic field when supplied with an electric current.

[0074] Preferably, the device 1 is for a metal part (such as Figure 1 Each mold member 9 of the two mold halves 11 in the example of FIG. 1 comprises such an induction coil 15 .

[0075] This increased number of induction coils 15 allows one such coil to be placed near each mold member 9 comprising a metal part and thus increases the efficiency of the induction heating in each mold assembly 7 .

[0076] Each induction coil 15 is linked to a control module 17, which is preferably arranged outside the housing 1 and includes a generator configured to supply a controlled current via the induction coil 15 and thereby generate a magnetic field and an induced current in the facing metal parts, thereby generating heat in the metal parts of the mold assembly 7. Then, the heat spreads to the entire mold assembly 7, thereby raising the temperature of the mold assembly 7 and the lens body 3.

[0077] Each control module 17 is further connected to at least one temperature sensor 19 configured to measure the temperature in the associated mold assembly 7 .

[0078] The control module 17 is configured to regulate the temperature in the mold assembly 7 by increasing or decreasing the intensity of the current supplied to the induction coil 15 and thereby increasing or decreasing the amount of heat generated by induction in the mold assembly 7 depending on the measured temperature and the temperature set point.

[0079] The control modules 17 are preferably linked together in a temperature control unit, which further comprises a user interface 17 through which a user can navigate all control modules 17 and assign heat treatment parameters.

[0080] Examples of such thermal treatment parameters include the temperature set point, the duration of the treatment, the rate of temperature change or even the temperature change profile over the duration of the treatment.

[0081] The use of induction heating rather than convection heating enables more efficient heat generation and, therefore, maintenance of curing temperatures at reduced energy costs. In fact, induction heat generation is generally considered to be about twice as efficient as conventional convection heat generation. In addition, curing times can be reduced via more precise control of curing temperatures, further reducing overall energy consumption.

[0082] Figure 2 A second embodiment of the apparatus 1 is shown, showing a single mould assembly 7 containing a lens body 3 and an associated induction coil 15. The apparatus 1 according to the second embodiment is similar to the apparatus described above, with the following differences.

[0083] The mould member 9 comprises a metal mould half 11 and a glass mould half 23. In the example shown, the glass mould half 23 is a female mould, but the reverse is equally possible.

[0084] The apparatus 11 includes a single induction coil 15 associated with the old assembly 7, as the glass mold half 23 is not electrically conductive and is therefore not suitable for generating heat via induction. This reduces the overall efficiency of heat generation, but provides the advantage of allowing visual inspection of the contents of the mold assembly 7 due to the optical transparency of the glass.

[0085] Therefore, the presence of bubbles in a lens body made of a fluid or gel material can be detected and corrected before the lens body 3 is cured.

[0086] Furthermore, this embodiment allows the use of a pre-existing glass mold half 23 , which is only partially replaced by a metal mold half 11 .

[0087] For the mold half 23 , other transparent materials than glass are conceivable, such as heat-resistant polymer materials.

[0088] Figure 3 A third embodiment of a device 1 according to the invention is partially shown. The device 1 according to the third embodiment is identical to the above described device except for the following.

[0089] In the third embodiment, both mould members 9 comprise a non-metallic mould half 23 , for example a glass mould half 23 .

[0090] Each holder 13 comprises a clamping plate 25 made of a metallic material conformable to come into contact with the outer surface 27 of each non-metallic mould half 23 and acting as a metal part of the mould member 9 for inductive heating.

[0091] The clamping plate 25 is in close contact with the outer surface of the non-metallic half-mold 23 to achieve efficient heat transfer.

[0092] Advantageously, the clamping plate 25 extends over a respective portion of the outer surface 27 of the half-mold 23 comprising at least 80% of the total surface area of ​​the outer surface 27 of the half-mold 23. This achieves a more efficient heat transfer and a more uniform heat flow over the surface of the lens body 3.

[0093] The device 1 advantageously comprises two induction coils 15 facing the clamping plate 25 for generating an induction current in the plate 25 .

[0094] Figure 4 A fourth embodiment of a device 1 according to the invention is partially shown. The device 1 according to the fourth embodiment is identical to the above described device except for the following.

[0095] In the fourth embodiment, both mould members 9 comprise a non-metallic mould half 23, for example a glass mould half 23. The non-metallic mould half 23 comprises a metal coating 29 extending on the outer surface 27 of the mould half and acting as a metal part of the mould member 9 for induction heating.

[0096] The coating layer 29 is made of the metal material as described above.

[0097] Preferably, the coating 29 extends over a portion of the outer surface 27 of the mold half 23 comprising at least 80% of the total surface area of ​​the outer surface 27 of the mold half 23. This achieves a more efficient heat transfer and a more uniform heat flow over the surface of the lens body 3.

[0098] For example, the coating 27 may be applied by spraying the outer surface 27 of each mold half 23 with a metal spray can prior to placing the lens body in the mold assembly 7 .

[0099] Alternatively, the coating may be deposited with a brush or by more specific methods such as electrodeposition.

[0100] This embodiment allows for the rapid modification of pre-existing glass mold halves for use with the induction heat treatment method according to the invention.

[0101] All the above embodiments can be freely combined with each other according to the technical knowledge of the skilled person.Furthermore, in any mould assembly the mould halves do not have to be of the same type and do not have to correspond to the same embodiment of the invention.

[0102] The invention also relates to a thermal treatment method implementing the device 1 as described above.

[0103] The method includes preliminary steps of preparing the lens body for thermal processing, such as mixing a monomer solution with a specific catalyst and additives to form a polymerizable composition to be poured into a mold assembly 7 and form the lens body 3.

[0104] Alternatively, this step may comprise applying a coating on at least one surface of the lens to produce a coating, the coated lens forming the lens body 3 .

[0105] Alternatively, this step may comprise applying a dye on at least one surface of the lens to migrate into the lens. Such a dry tinting method is described, for example, in document JP 2004 / 121434.

[0106] The method may comprise the step of preparing at least one glass mould half 23 by depositing a metal coating, for example by spraying, as disclosed in the fourth embodiment above.

[0107] Next, the method comprises the step of holding the lens body 3 between the first and second mold members 9, 9 of the mold assembly 7 for the entire duration of the heat treatment. If necessary, the sides of the mold assembly 7 may be closed with elastomeric gaskets or tape.

[0108] Next, the method includes the following steps: generating a current in the induction coil 15 under the control of each control module 17 and generating an induced current in the metal part of the associated mold assembly 7, thereby generating heat in the mold assembly 7 via the Joule effect.

[0109] The temperature in the mould assembly 7 is continuously monitored and the induction heating is adjusted to comply with the temperature set point or temperature profile input into the control unit.

[0110] The method finally comprises the step of removing the processed lens body from the mold assembly and obtaining a finished lens body which can be used for further processing procedures.

[0111] In a preferred embodiment, instead of monomers, the polymerizable composition comprises prepolymers (also called oligomers). Prepolymers are partially reacted monomers comprising molecules each formed from several of the same monomers.

[0112] The use of prepolymers helps to reduce cure time even further by enabling cure to begin from a partially polymerized composition, thereby further reducing overall energy costs.

[0113] Although the described apparatus and methods are primarily described in the context of heat activated polymerization, they can also be used in any lens polymerization process where heat is required as part of the process, such as UV-initiated polymerization where a heating step is required to complete the reaction.

[0114] Two comparative examples of implementing a conventional convection heating process and an induction heating process according to the present invention, respectively, are described below.

[0115] Example 1:

[0116] A catalyst solution containing 0,191 g of 18-crown-6, 0,048 g of KSCN and 0,318 g of thioethanol was prepared. Next, 10,00 g of NCO-terminated prepolymer made in a ratio of NCO / SH of 8 / 1 (viscosity equal to 0,071 Pa.s at 25° C.) was mixed with 9,39 g of SH-terminated prepolymer made in a ratio of SH / NCO of 8 / 1 (viscosity equal to 0,543 Pa.s at 25° C.), combined with the catalyst solution and the mixture was filled into a mold assembly containing a glass mold. Gel formation occurred in less than 10 minutes at room temperature and the reaction was completed in an air convection oven at 135° C. for 2 hours. The total energy used by the convection oven to complete the curing cycle was 2,7 kW.

[0117] Example 2:

[0118] A catalyst solution containing 0,191 g of 18-crown-6, 0,048 g of KSCN and 0,318 g of thioethanol was prepared. Next, 10,00 g of NCO-terminated prepolymer made in a ratio of NCO / SH of 8 / 1 (viscosity equal to 0,071 Pa.s at 25°C) was mixed with 9,39 g of SH-terminated prepolymer made in a ratio of SH / NCO of 8 / 1 (viscosity equal to 0.543 Pa.s at 25°C), combined with the catalyst solution and the mixture was filled into a mold assembly containing an iron metal mold. Gelation occurred in less than 10 minutes at room temperature and the reaction was completed in an induction oven at 135°C for 2 hours. The total energy used by the induction oven to complete the curing cycle was 1,5 kW, which is almost double the energy efficiency compared to Example 1.

Claims

1. A device (1) for heat treating at least one lens body (3), the device (1) comprising: - at least one mould assembly (7) for casting a lens, each mould assembly (7) comprising a first mould member (9) and a second mould member (9), said first mould member and said second mould member (9) being arranged to hold said lens body (3) therebetween, - at least one induction coil (15), said at least one induction coil being arranged facing said at least one mould assembly (7), and - a temperature control unit (17) configured to monitor the temperature in the mold assembly (7), Wherein, at least one of the first mold member (9) and the second mold member (9) includes at least one metal part (11, 25, 29) made of metal material, and the induction coil (15) is configured to generate a magnetic field and generate heat in each metal part of each mold assembly (7) when supplied with current.

2. The device (1) according to claim 1, wherein: At least one of the first mold member (9) and the second mold member (9) includes a mold half (11) made of a metal material as the metal part.

3. The device (1) according to claim 2, wherein: One of the first mold member (9) and the second mold member (9) comprises a mold half (11) made of a metallic material, and the other comprises a mold half (23) made of a transparent non-metallic material.

4. The device (1) according to claim 1, wherein: The first mold member (9) and the second mold member (9) each include a half mold (23) made of non-metallic material, and at least one of the first mold member (9) and the second mold member (9) further includes a retaining plate (25) for the half mold as the metal part, the retaining plate (25) being made of metal material and extending on the outer surface (27) of the half mold (23).

5. The device (1) according to claim 1, wherein The first mold member (9) and the second mold member (9) each include a half mold (23) made of a non-metallic material, and at least one of the first mold member (9) and the second mold member (9) further includes a metal coating (29) as the metal part, which is made of a metallic material and extends on the outer surface (27) of the half mold (23).

6. The device (1) according to claim 4 or 5, wherein: The metal part (25, 29) extends over a portion of the outer surface (27) of the half-mold (23), said portion comprising at least 80% of the total surface area of ​​the outer surface (27) of the half-mold (23).

7. The device (1) according to any one of the preceding claims, wherein: The metal material exhibits a temperature between 1×10 6 S / m and 2×10 7 Conductivity between S / m.

8. The device (1) according to any one of the preceding claims, wherein: The metallic material comprises at least 50% by weight iron.

9. A method for heat treating at least one lens body (3) using a device (1) according to any one of the preceding claims, the method comprising the following steps: - holding the lens body (3) between the first mold member (9) and the second mold member (9) of the mold assembly (7), - generating a current in the induction coil (15) and generating an induced current in the metal parts of the mold assembly (7), thereby generating heat in the mold assembly (7) via the Joule effect, - processing the lens body (3) in the mold assembly and monitoring the temperature in the mold assembly (7) during the processing, and - Removing the processed lens body (3) from the mold assembly (7).

10. The method according to claim 9, wherein: The method comprises a preliminary step of preparing the mould assembly (7) by depositing a metallic coating (29) on the outer surface (27) of a mould half (23) made of a non-metallic material.

11. The method according to claim 9 or 10, wherein: The heat treatment is the casting of the lens and comprises heat activated polymerization of the fluid or gel material contained in the mold assembly (7) to produce a solid lens.

12. The method according to claim 11, wherein: The fluid material includes a prepolymer.

13. The method according to claim 9 or 10, wherein: The heat treatment is to harden the coating applied on the lens body (3) before placing it in the mold assembly (7).

14. The method according to claim 9 or 10, wherein: The heat treatment includes causing the dye deposited on the lens body (3) to migrate into the lens body (3) and then place it in the mold assembly (7).

15. An optical article comprising at least one lens obtained from a lens body (3) treated by a method according to any one of claims 9 to 14.

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