Patent Application
20240227330
An injection molding process with temperature control used in a manufacturing production environment for lenses.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In the manufacture of curved lenses, an injection molding process may be used in which a mold insert is compressed while material (e.g., plastic) is injected into the mold. However, in order to form microstructures, such as microlenses on a surface of the lens, the temperature of the insert should be tightly controlled while the insert is under a high compressive force.
The present disclosure relates to a method for injection-compression molding a lens into a mold insert including an internal cavity, a sidewall, and a gate, comprising injecting a polymer the internal cavity formed by a coupled first mold side and second mold side of the mold insert via the gate until a pressure of the internal cavity exceeds a predetermined force value, the first mold side being fixed and the second mold side being moveable and configured to apply a force generating the internal cavity pressure, wherein the method further comprises controlling a first temperature of the first mold side to be in a range of 4 degrees Fahrenheit to 10 degrees Fahrenheit greater than a second temperature of the second mold side and controlling a coining compression distance of the second mold side to be in a range of 0.008 inches to 0.018 inches. Advantageous aspects of the method according to the present disclosure are disclosed in claims 2 to 7.
The method further includes controlling the temperatures of the mold sides by flowing coolant at the first temperature through a first coolant channel in the first mold side; and/or flowing coolant at the second temperature through a second coolant channel in the second mold side. The present disclosure additionally relates to an injection-compression molding apparatus for molding a lens as disclosed in claim 8. Advantageous aspects of the injection-compression molding apparatus for molding a lens according to the present disclosure are disclosed in claims 9 to 13. The present disclosure additionally relates to an injection-compression molding system for molding a lens as disclosed in claim 14. Advantageous aspects of the injection-compression molding system for molding a lens according to the present disclosure are disclosed in claim 15.
Note that this summary section does not specify every feature and/or incrementally novel aspect of the present disclosure or claimed invention. Instead, this summary only provides a preliminary discussion of different embodiments and corresponding points of novelty. For additional details and/or possible perspectives of the invention and embodiments, the reader is directed to the Detailed Description section and corresponding figures of the present disclosure as further discussed below.
For a more complete understanding of the description provided herein and the advantages thereof, reference is now made to the brief descriptions below, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.
A lens which has microstructures such as microlenses (also known as “lenslets”) formed on the surface may provide prescriptive correction through a single vision zone and myopia correction through a constellation of aspherical lenslets in ring formations. This type of lens may create a volume of signal that slows down the elongation of the eye. The power on each ring may be designed to guarantee a volume of signal always in front of the retina and following its shape to achieve consistent myopia slowdown. A non-limiting example of a lens having aspherical lenslets in ring formation is a Stellest™ lens (See: “Essilor's Game-Changing Stellest™ Lens Shown To Slow Down Myopia Progression In Children By More Than 60%, After One-Year Interim Clinical Trial”, 28 Sep. 2020; Newsletter, Essilor, incorporated herein by reference in its entirety).
During the manufacturing process of microstructures such as microlenses, such as those associated with the Stellest™ lens, it is valuable to maintain and achieve an acceptable front curve design of the microlens and a targeted global power, and to monitor any potential departure of the micro-lens array from acceptable standards, to meet product specifications during and after the manufacturing process. Temperature control of the mold insert during injection is of high importance. However, previous work has not included using different temperatures for different regions of the mold insert.
The present disclosure is able to address shortcomings in the art, particularly with the solutions set forth in the claims.
In the description which follows the drawing figures are not necessarily to scale and certain features may be shown in generalized or schematic form in the interest of clarity and conciseness or for informational purposes. In addition, although making and using various embodiments are discussed in detail below, it should be appreciated that as described herein are provided many inventive concepts that may be embodied in a wide variety of contexts. Embodiments discussed herein are merely representative and do not limit the scope of the invention. It will also be obvious to one skilled in the art that all the technical features that are defined relative to a process can be transposed, individually or in combination, to a device and conversely, all the technical features relative to a device can be transposed, individually or in combination, to a process.
The following disclosure provides many different variations, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting nor inoperable together in any permutation. Unless indicated otherwise, the features and embodiments described herein are operable together in any permutation. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, spatially relative terms, such as “top,” “bottom,” “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. Inventive apparatuses may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
The order of discussion of the different steps as described herein has been presented for the sake of clarity. In general, these steps can be performed in any suitable order. Additionally, although each of the different features, techniques, configurations, etc. herein may be discussed in different places of this disclosure, it is intended that each of the concepts can be executed independently of each other or in combination with each other. Accordingly, the present invention can be embodied and viewed in many different ways.
In the present disclosure, the term “coining” refers to an injection-compression molding process which extends injection molding capabilities by compressing an injection mold.
The present disclosure describes a management system for injection molding process parameters, such as temperature, pressure and coining during manufacturing, which achieves both good front curve replication as well as a targeted average global power. These process parameters achieve an acceptable front curve and global power of the micro-lens within production process capability values, Cpk.
The mold insert has a front curvature and a back curvature, or base curve, which form the lens structure. The front curvature may include microlenses, such as described above for, but not limited to, myopia correction. The halves of the mold insert are closed by clamping while a resin such as polycarbonate resin is injected under pressure. As the injection pressure increases and subsides, the faces of the mold insert are vented until the mold can be fully closed.
Unlike some other thermoplastics, polycarbonate can undergo large plastic deformations without cracking or breaking. In a non-limiting example, the polycarbonate resin may be mixtures of polymers, such as polycarbonates, polycarbonate/copolyester blends, acrylics, such PMMA, cyclic olefin copolymers, amorphous polyamides, polyesters, copolyesters, polyurethanes, and the like. The resin may be made to color specifications, i.e., for colored lenses. In another non-limiting example, the polycarbonate resin may be Teijin 1270ZT, (See: Teijin Panlite 1250ZT, Sold by the Teijin company of Osaka, Japan.
Semi-finished single vision (SFSV) lenses are those marketed in bulk to opticians and eyeglass makers. The standard process parameters for SFSV lenses are relatively close to these process parameters (i.e., temperature, pressure and coining) and can potentially meet optic specifications (i.e., good front curve replication and targeted average global power), but stability of the process and the process capability (Cpk) can be lower than desired for production needs. A Cpk or Cp>1.0 indicates good reproducibility.
Table 1 shows process parameters for conventional SFSV lenses.
A Design of Experiments (DoE) was conducted to determine key process parameters that affect the base curve as well as the micro-lens global power.
Microstructures may include microlenses or microlenslets or any other type of structure or elements having physical Z deformation/height between 0.1 μm-50 μm and width/length between 0.5 μm-1.5 mm. These structures preferably have periodical or pseudo periodical layout, but may also have randomized positions. The preferred layout for microstructures is a grid with constant grid step, honeycomb layout, multiple concentric rings, contiguous e.g. no space in between microstructures. These structures may provide optical wave front modification in intensity, curvature, or light deviation, where the intensity of wave front is configured such that structures may be absorptive and may locally absorb wave front intensity with a range from 0% to 100%, where the curvature is configured such that the structure may locally modify wave front curvature with a range of +/−20 Diopters, and light deviation is configured such that the structure may locally scatter light with angle ranging from +/−1° to +/−30°.
In
The A side mold plate 106 has an internal concave curve which forms the convex side of the lens. The A side of the mold is held in place in a cylindrical housing by a locking mechanism inside the mold. A locking pin holds the A side of the mold within the cylindrical housing of the mold and can be released to change out the A side of the mold. The B side mold plate 138 has a convex surface which forms the concave side of the lens. Similarly, a locking pin holds the B side of the mold within the cylindrical housing of the mold and can be released to change out the B side of the mold. The pressure is released from the moveable side B of the apparatus to release the lens.
As shown in
Even a slight variation in the temperature of the mold insert during molding startup will affect the quality of the lenses. Temperature controllers preheat and keep the mold insert at a temperature set point by circulating coolant (water or oil) through the mold plates. As shown in
As seen in
Another important aspect is that the coining impacts the average global departure of the micro-lens (μL). Because of the large number of micro-lens on the lens surface, the difference between the nominal expected global power of the micro-lens and the measured value of the micro-lens is used to calculate the average global micro-lens departure.
The process of making a lens, such as the Stellest™ lens, was developed through a design of experiments to achieve not only a good front surface curve but also the global power of the micro-lens array to produce a lens within the specifications. The design of experiments has indicated the temperature of the mold, both the A-side and the B-side, plays an important role in achieving the front curve of the lens. As
The coining during the processing has also been found to be a factor that affects the global micro-lens power. A higher coining force becomes more critical when the B-side mold temperature is lower than 250 F, as seen in
The process parameters are designed to be used by injection molding production facilities in a mass production environment that would produce these specialty type lenses, such as the Stellest™ lens, that not only have a center front curve but also an array of microstructures such as micro-lenslets surrounding the center spherical front curve.
The process would be implemented at mass production facilities for injection molding ophthalmic lenses to support maintaining optic and global power within specification.
The process would be implemented at mass production facilities for injection molding ophthalmic lenses to achieve good reproducibility by keeping production process capability values, Cpk or Cp>1.0.
This set of process parameters can be used to help manage tighter specifications for optics/global power of future products.
If inserts are made within the given specification, then the developed process parameters shown in Table 2 will achieve a lens within optical and global power specifications.
An area for improvement may be adjustment in the process parameters when inserts have gone through significant production quantity with physical wear taking place on the insert. The design of experimental results may help in determining what key factors can potentially be used and adjusted to allow the worn inserts to produce lens that are still within optical and micro-lens global power specification.
Standard SFSV process conditions, as shown in Table 1, have been considered for producing the lens, since the lens design consists of the SFSV front curve as well as a micro-lens array surrounding the spherical center design.
In the preceding description, specific details have been set forth, such as a particular geometry of an injection molding system and descriptions of various components and processes used therein. It should be understood, however, that techniques herein may be practiced in other embodiments that depart from these specific details, and that such details are for purposes of explanation and not limitation. Embodiments disclosed herein have been described with reference to the accompanying drawings. Similarly, for purposes of explanation, specific numbers, materials, and configurations have been set forth in order to provide a thorough understanding. Nevertheless, embodiments may be practiced without such specific details. Components having substantially the same functional constructions are denoted by like reference characters, and thus any redundant descriptions may be omitted.
Various techniques have been described as multiple discrete operations to assist in understanding the various embodiments. The order of description should not be construed as to imply that these operations are necessarily order dependent. Indeed, these operations need not be performed in the order of presentation. Operations described may be performed in a different order than specifically described unless expressly indicated otherwise. Various additional operations may be performed and/or described operations may be omitted.
Those skilled in the art will also understand that there can be many variations made to the operations of the techniques explained above while still achieving the same objectives of the invention. Such variations are intended to be covered by the scope of this disclosure. As such, the foregoing descriptions of embodiments of the invention are not intended to be limiting. Rather, any limitations to embodiments of the invention are presented in the following claims.
Embodiments of the present disclosure may also be as set forth in the following parentheticals. (1) A method for injection-compression molding a lens into a mold insert including an internal cavity 160, a sidewall 108, and a gate 152, the method comprising injecting a polymer into the internal cavity formed by a coupled first mold side 106 and second mold side 138 of the mold insert via the gate until a pressure of the internal cavity exceeds a predetermined force value, the first mold side being fixed and the second mold side being moveable and configured to apply a force generating the internal cavity pressure; and wherein the method further comprises controlling a first temperature of the first mold side to be in a range of 4 degrees Fahrenheit to 10 degrees Fahrenheit greater than a second temperature of the second mold side and controlling a coining compression distance of the second mold side to be in a range of 0.008 inches to 0.018 inches.
(2) The method of (1), further comprising controlling the first temperature of the first mold side to be preferably in a range of 245 degrees Fahrenheit to 280 degrees Fahrenheit, more preferably in a range of 250 degrees Fahrenheit to 263 degrees Fahrenheit; and most preferably 255 degrees Fahrenheit; and controlling the second temperature of the second mold side to be preferably in a range of 240 degrees Fahrenheit to 275 degrees Fahrenheit, more preferably in a range of 250 degrees Fahrenheit to 257 degrees Fahrenheit; and most preferably 250 degrees Fahrenheit.
(3) The method of either (1) or (2), wherein the coining compression distance of the second mold side is inversely related to the second temperature of the second mold side. (As shown in
(4) The method of any of (1) to (3), flowing coolant at the first temperature through a first coolant channel in the first mold side; and flowing coolant at the second temperature through a second coolant channel in the second mold side.
(5) The method of any of (1) to (4), further comprising: selecting the predetermined force value from a range of preferably 9,000 psi to 15,000 psi, more preferably in a range of 10,000 psi to 13,000 psi, and most preferably 12,000 psi.
(6) The method of any of (1) to (5), further comprising: injecting the polymer for an injection time in a range of 20 seconds to 80 seconds, preferably 52 seconds; and cooling the polymer for a cooling time in a range of 200 seconds to 260 seconds, preferably 240 seconds.
(7) The method of any of (1) to (6), further comprising injecting and cooling the polymer in the internal cavity for an injection cycle time in a range of 220 seconds to 330 seconds, preferably 315 seconds.
(8) An injection-compression molding apparatus 100 for molding a lens, comprising: a mold insert having a first mold side 106, a second mold side 138 and an internal cavity 160 formed between the first mold side and the second mold side, the first mold side being fixed and the second mold side being moveable; a gate 152 connected to the internal cavity; an injection unit 150 connected to the gate, the injection unit configured to inject a polymer into the internal cavity 160;
a coolant channel in the first mold side 106 and/or in the second mold side 138; temperature controller circuitry 126 connected to the coolant channel and configured to control a temperature of a coolant in the coolant channel; springs and spacers configured to control a coining compression distance of the second mold side to be in a range of 0.008 inches to 0.018 inches.
(9) The injection-compression molding apparatus of (8), further comprising: a set of springs (1401, 1402) and metal spacers (142) enclosed by a retainer cup (136) and connected to the moveable side of the mold by the toggle body.
(10) The injection-compression molding apparatus of either (8) or (9), wherein the polymer is a polycarbonate resin.
(11) The injection-compression molding apparatus of any one of (8) to (10), further comprising an injection pressure sensor connected to the internal cavity, such that the injection pressure sensor is configured to measure an internal cavity pressure; and wherein the injection unit is configured to inject the polymer into the internal cavity until the internal cavity pressure exceeds a predetermined force value.
(12) The injection-compression molding apparatus of any one of (8) to (11), further comprising an injection controller configured to select the predetermined force value from a range of preferably 9,000 psi to 15,000 psi, more preferably a range of 10,000 psi to 13,000 psi, and most preferably 12,000 psi.
(13) The injection-compression molding apparatus of any one of (8) to (12), wherein the coolant channel is in the first mold side 106 as a first coolant channel 129 and in the second mold side 138 as a second coolant channel 128 and the first coolant channel has a first coolant 122 and the second coolant channel has a second coolant 120, the temperature controller circuitry is configured to control the first temperature of the first coolant 122 to be preferably in a range of 245 degrees Fahrenheit to 280 degrees Fahrenheit, more preferably in a range of 250 degrees Fahrenheit to 265 degrees Fahrenheit; and most preferably 255 degrees Fahrenheit; and the temperature controller is configured to control a second temperature of the second coolant 120 to be preferably in a range of 240 degrees Fahrenheit to 280 degrees Fahrenheit, more preferably in a range of 250 degrees Fahrenheit to 257 degrees Fahrenheit; and most preferably 250 degrees Fahrenheit.
(14) An injection-compression molding system for molding a lens, comprising: a mold insert having a first mold side 106, a second mold side 138 and an internal cavity 160 formed between the first mold side and the second mold side, the first mold side being fixed and the second mold side configured to be moveable; an injection unit 150 configured to inject a polymer into the internal cavity; a temperature controller connected to the first mold side, and the second mold side, wherein the temperature controller is configured to control a first temperature of the first mold side and to control a second temperature of the second mold side, wherein the first temperature is in a range of 4 degrees Fahrenheit to 10 degrees Fahrenheit higher than the second temperature; and springs and spacers body configured to control a coining compression distance of the second mold side to be in a range of 0.008 inches to 0.018 inches.
(15) The injection-compression molding system of (14), wherein the temperature controller is configured to control the first temperature of a first coolant (122) to be preferably in a range of 245 degrees Fahrenheit to 280 degrees Fahrenheit, more preferably in a range of 250 degrees Fahrenheit to 263 degrees Fahrenheit; and most preferably 255 degrees Fahrenheit; and the temperature controller is configured to control the second temperature of a second coolant 120 to be preferably in a range of 240 degrees Fahrenheit to 275 degrees Fahrenheit, more preferably in a range of 250 degrees Fahrenheit to 257 degrees Fahrenheit; and most preferably 250 degrees Fahrenheit.
Although representative processes and articles have been described in detail herein, those skilled in the art will recognize that various substitutions and modifications may be made without departing from the scope of what is described and defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21305658.3 | May 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/063342 | 5/17/2022 | WO |
