Chemical mechanical polishing agent having a high removal rate for ophthalmic grinding, and method for polishing the outer surface of a plastic ophthalmic lens

Abstract

A formulation comprising an aqueous dispersion of abrasive particles and a surfactant, configured to polish the outer surface of a plastic ophthalmic lens, is provided, along with a method of polishing such a lens using such a formulation. The formulation has a viscosity of from about 1 cP to about 25 cP and a total solids content in the range of from about 15 wt% to about 40 wt%. The abrasive particles include a mixture of crystallized alpha alumina and theta alumina, wherein the alpha alumina is present in an amount ranging from 50 wt% to 80 wt% and the theta alumina is present in an amount ranging from 50 wt% to 20 wt%, based on the total weight of the abrasive particles.

Description

Technical Field

[0001] The present invention generally relates to ophthalmic polishing formulations. More particularly, the present disclosure relates to ophthalmic lens polishing formulations that provide enhanced or high levels of removal rates while maintaining low viscosity.

Background Art

[0002] The description in this section merely provides background information related to the present disclosure and does not necessarily constitute prior art.

[0003] When polishing plastic (e.g., polycarbonate) lenses, it is an important issue to control the viscosity exhibited by ophthalmic lens abrasives without adversely affecting the polishing performance. In conventional lens polishers, formulations having a high viscosity are not a problem as long as the formulation can maintain sufficient fluidity to flow through the pump and system at an appropriate rate. A formulation having a viscosity of 400 centipoise (cP) can flow through conventional polishing apparatuses without problems. However, recent digital polishing apparatuses cannot handle such viscous formulations, and when the viscosity is too high, an adverse effect on the performance across all metrics is recognized. Also, simply diluting cannot reduce the viscosity while maintaining the polishing performance. Rather, simply diluting reduces the viscosity to such an extent that the concentration of the polishing / active ingredient becomes too low to provide sufficient performance.

[0004] Another challenge in the development of ophthalmic lens polishing formulations for polishing plastic lenses is finding appropriate polishing components. Those skilled in the art will understand that most formulations employ the use of alpha alumina (α-Al 2 O 3 ) as the abrasive grains. However, when alumina is fired to form the alpha phase, it becomes hard and can have sufficient hardness to scratch the relatively soft surface of a plastic lens, even with brittle alumina abrasive grains.

[0005] The present disclosure generally provides a formulation comprising an aqueous dispersion of abrasive particles and a surfactant configured to polish the outer surface of a plastic ophthalmic lens. This polishing formulation has a viscosity of about 1 cP to about 25 cP and a total solids content that can be in the range of about 15 wt% to about 40 wt%. The abrasive particles include a mixture of crystallized alpha alumina and theta alumina, and alpha alumina is present in an amount ranging from 50 wt% to 80 wt% and theta alumina is present in an amount ranging from 50 wt% to 20 wt% based on the total weight of the abrasive particles. Optionally, the formulation can further include one or more of water-dispersible boehmite, an antifoaming agent, aluminum nitrate, and a cleaning aid.

[0006] According to one aspect of the present disclosure, the abrasive particles have a surface area in the range of about 10 m 2 / g to about 35 m 2 / g. The abrasive particles can also have an average particle size (D 50 ) in the range of about 1 micrometer (μm) to about 5 μm.

[0007] The abrasive particles can be present at a concentration in the range of about 15 wt% to about 30 wt% based on the total weight of the formulation. The amount of alpha alumina can be in the range of about 60 wt% to about 70 wt% and the amount of theta alumina can be in the range of about 40 wt% to about 30 wt% based on the total weight of the abrasive particles. Optionally, the abrasive particles can further include <1 wt% of gamma phase alumina or delta phase alumina.

[0008] According to another aspect of the present disclosure, the formulation has a pH between about 3 and about 5 and a viscosity that can be in the range of about 1 cP to about 10 cP. The surfactant can include a carboxy-functionalized or carboxylated polymer or a copolymer thereof.

[0009] Also, the boehmite has an average particle size (D 50 ) of less than about 0.5 μm and can be present in an amount up to 10 wt% based on the total weight of the formulation. The antifoaming agent present in the formulation can be a water-soluble silica-based antifoaming agent present at a concentration in the range of up to 1 wt% based on the total weight of the formulation.

[0010] According to still other aspects of the present disclosure, when measured with a conventional lens polisher using an uncut plastic ophthalmic lens, a removal rate of at least 8 mg / min is provided. The plastic ophthalmic lens may include polycarbonate.

[0011] According to other aspects of the present disclosure, a method of polishing the outer surface of a plastic ophthalmic lens is provided. The plastic ophthalmic lens may include polycarbonate. The method generally (a) providing a plurality of abrasive particles comprising a mixture of crystallized alpha alumina and theta alumina having an average particle size (D 50 ) in the range of about 1 micrometer (μm) to about 5 μm, wherein the alpha alumina is present in an amount in the range of 50 wt% to 80 wt% and the theta alumina is present in an amount in the range of 50 wt% to 20 wt% based on the total weight of the abrasive particles; (b) preparing a polishing composition comprising an aqueous dispersion of the abrasive particles and a surfactant, the polishing composition having a viscosity of about 1 cP to about 25 cP and a total solids content in the range of about 15 wt% to about 40 wt%; (c) applying the composition to the outer surface of the plastic ophthalmic lens; (d) mechanically rubbing the composition across the outer surface of the plastic ophthalmic lens to remove a layer of plastic material from the outer surface; and (e) removing the composition from the outer surface to obtain a polished surface.

[0012] In this method, the abrasive particles may be present in the composition at a concentration in the range of about 15 wt% to about 30 wt% based on the total weight of the composition, and the composition is configured to remove plastic material at a rate of at least 8 mg / min when measured with a conventional lens polisher using an uncut polycarbonate ophthalmic lens. Mechanically rubbing the composition across the outer surface of the plastic ophthalmic lens can be achieved by using conventional mechanical or manual polishing equipment, a digital polisher, or hand polishing.

[0013] According to another aspect of the present disclosure, the method comprises providing a plurality of abrasive particles, (a) preparing an aqueous mixture comprising 5 wt% to 30 wt% of non-crystallized boehmite and 0.5 wt% to 4 wt% of nitric acid, based on the total weight of the mixture; (b) placing the aqueous mixture into a sealed reaction vessel; (c) heating the sealed reaction vessel to a temperature in the range of 120 °C to 200 °C for 4 hours to 24 hours to form a slurry; (d) recovering and drying the slurry to obtain a powder; (e) further comprising firing the powder at a temperature in the range of 1,000 °C to 1,200 °C for about 1 hour to about 20 hours to form a mixture of crystallized alpha alumina and theta alumina.

[0014] Optionally, the mixture of crystallized alpha alumina and theta alumina may be further subjected to a particle size reduction using a grinding operation. The abrasive particles may further comprise <1 wt% of gamma phase alumina or delta phase alumina. Based on the total weight of the abrasive particles, the amount of alpha alumina is in the range of about 60 wt% to about 70 wt%, and the amount of theta alumina is in the range of about 40 wt% to about 30 wt%. The formulation may further comprise one or more of water-dispersible boehmite, defoamer, aluminum nitrate, and detergent aid. When present, the boehmite has an average particle size (D 50 ) of less than about 0.5 μm and is present in an amount of up to 10 wt% based on the total weight of the formulation. When present, the defoamer is present at a concentration in the range of up to 1 wt% based on the total weight of the formulation.

[0015] Applicable further fields will become apparent from the description given herein. The description and specific examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure.

[0016] In the following, various forms of the present disclosure will be described with reference to the accompanying drawings so that the present disclosure can be fully understood. The components of each drawing are not necessarily drawn to scale, but rather emphasis is placed on illustrating the principles of the present invention.

Brief Description of the Drawings

[0017]

Figure 1

[0018]

Figure 2

[0019]

Figure 3

[0020]

Figure 4

Modes for Carrying Out the Invention

[0021] The drawings described in this specification are for illustrative purposes only and are in no way intended to limit the scope of the present disclosure. Throughout the description and drawings, corresponding reference numerals should be understood to indicate similar or corresponding parts and features.

[0022] The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its applications and uses. The present disclosure generally provides an ophthalmic lens polishing formulation that exhibits improved removal rates while maintaining a low viscosity. This polishing formulation generally includes a water-soluble carboxy-functional copolymer and a mixture of crystallized alpha alumina and transitional phase alumina.

[0023] For purposes of the present disclosure, the terms "about" and "substantially," as used in connection with measurable values and ranges herein, denote the expected variations known to those of ordinary skill in the art (e.g., limitations and variability in measurements).

[0024] For purposes of the present disclosure, the terms "at least one" and "one or more" of an element may be used interchangeably and may have the same meaning. These terms indicate the inclusion of a single element or a plurality of elements, and may also be represented by the suffix "(s)" at the end of the element. For example, "at least one surfactant," "one or more surfactants," and "surfactant(s)" may be used interchangeably and are intended to have the same meaning.

[0025] According to one aspect of the present disclosure, the objective was to determine an additive that can reduce the viscosity of a polishing formulation without causing an adverse effect on performance, such as either surface quality or removal rate. This objective was achieved by incorporating one or more surfactants configured to interact with the abrasive particles to reduce the viscosity of the polishing formulation. Surprisingly, it has been found that the type of surfactant dramatically affects the performance of the formulation. Types of surfactants that can provide a low viscosity with little impact on the polishing performance of the polishing formulation include, but are not limited to, carboxy-functionalized or carboxylated polymers or copolymers such as short alkyl chain polyethylene glycol ether carboxylates, triblock carboxylic acid surfactants, carboxymethyl cellulose, and polycarboxylates. Examples of commercially available surfactants of this type include, but are not limited to, Carbosperse® K-XP228 (Lubrizol, Westlake, Ohio). The surfactant(s) may be present in an amount within the range of from 0.1 wt% to 5 wt%, or from about 0.5 wt% to about 3 wt%, or from about 1 wt% to about 2 wt% based on the total weight of the polishing formulation. Two or more carboxy-functionalized or carboxylated polymer or copolymer surfactants or dispersants may be used in combination as a mixture or blend without departing from the scope of the present disclosure.

[0026] The viscosity of a polishing formulation suitable for use in polishing a plastic lens is less than 30 centipoise (cP) and greater than 0.5 cP, or within the range of about 1 cP to about 25 cP, or about 1 cP to about 10 cP. The viscosity of the formulation can be determined by any method known in the art, including, but not limited to, the use of a parallel plate geometry, cone-plate geometry, Couette cell geometry, a rotational rheometer with a spindle (e.g., Brookfield viscometer), a viscosity cup, or a vibrating viscometer.

[0027] According to other aspects of the present disclosure, another objective was to determine a suitable polishing component for use in a polishing formulation that overcomes the drawbacks of the prior art. Surprisingly, it has been found that alumina containing a mixture of structural or transitional phases provides higher performance than pure alpha alumina over equivalent surface areas and phases. As described above, fully alpha alumina grains tend to scratch the surface of plastic lenses as their hardness increases upon firing. However, more gently fired alumina grains having the characteristics of both the alpha and theta phases provide an ideal hardness for polishing plastic lenses. The various phases of alumina can be quantitatively measured by X-ray diffraction (XRD). The combination of the alpha and theta phases provides a polishing medium that is soft enough to be difficult to scratch the plastic lens and hard enough to provide suitable polishing for grinding the surface of the lens.

[0028] Within the scope of the present disclosure, the term alpha / theta phase alumina is intended to mean a mixture of aluminum oxide particles in which some of the particles are present as the alpha (α) phase and some of the particles are present as the theta (θ) phase. Alpha-alumina particles generally exhibit a high density (i.e., 3.98 g / cm 3 ) and consist essentially of single crystals. On the other hand, theta-alumina particles generally exhibit a lower density (e.g., < 3.98 g / cm 3 ) and have low crystallinity.

[0029] Aluminum oxide (Al 2 O 3 ), i.e., alumina, is obtained by heating and dehydrating aluminum hydroxide such as gibbsite Al(OH) 3 or boehmite AlO(OH). As the temperature rises, various structural and transitional phases are formed. For example, when using boehmite as the starting material, the structural phases of the resulting alumina generally follow the order of γ-alumina (gamma) → Δ-alumina (delta) → θ-alumina (theta) → α-alumina (alpha). Boehmite, in the temperature range of 500 - 550 °C, with the removal of structural water, forms γ-Al 2 O3 It changes to metastable alumina. θ-Al 2 O 3 to α-Al 2 O 3 The change generally occurs when exposed to a temperature above 1050°C for a long time.

[0030] The polishing component in the polishing formulation of the present disclosure generally comprises, consists of, or consists essentially of a mixture of 50 - 80 wt% α-alumina and 50 - 20 wt% θ-alumina, and contains alpha / theta phase alumina. Alternatively, the amount of α-Al 2 O 3 present in the polishing component of the polishing formulation is in the range of about 55 to about 75 wt%, and the amount of θ-Al 2 O 3 present is in the range of about 45 to about 25 wt%. Alternatively, the amount of α-Al 2 O 3 present in the polishing component of the polishing formulation is in the range of about 60 to about 70 wt%, and the amount of θ-Al 2 O 3 present is in the range of about 40 to about 30 wt%. Alternatively, the amount of alpha / theta phase alumina present in the polishing component of the polishing formulation is within the range of 1:1 to 4:1, or within the range of about 1.25:1 to about 3:1, or within the range of about 1.5:1 to about 2.25:1 of θ-Al 2 O 3 to α-Al 2 O 3 ratio. The amount of other alumina phases such as γ-alumina and Δ-alumina in the polishing component can be negligible, or the presence of other alumina phases is ≤ 0.5 wt% or ≤ 1.0 wt% based on the weight of the polishing component.

[0031] The amount of each phase present in the alpha / theta phase alumina containing abrasive particles can be quantitatively measured using X-ray diffraction (XRD) measurements. Quantitative phase analysis represents the measurement of the relative proportion of elemental components or phases using an X-ray diffraction (XRD) pattern calibrated against either an internal or external standard. The intensity of the diffraction lines of a particular phase in a mixture depends on the relative amount of that phase in the mixture. Referring to FIGS. 1 and 2, the determination of the phase ratio between the alpha phase and the theta phase is based on the peak measured at ~33 degrees (refer to point T in FIG. 1) due to θ-Al 2 O 3 and the peak measured at ~38 degrees (refer to point A in FIGS. 1 & 2) due to α-Al 2 O 3 . The intensity ratio between them is measured. As shown in FIG. 1, it is shown that the abrasive particles used in the polishing formulations of Experimental Examples R-1 and R-2 and Comparative Example C-2 contain a mixture of the alpha alumina phase and the theta alumina phase. In comparison, as shown in FIG. 2, the abrasive particles used in the polishing formulations of Comparative Examples C-1 and C-2 contain only the alpha alumina phase.

[0032] The abrasive particles exhibit an average particle size (D 50 ) in the range from 0.5 micrometers (μm) to 7.5 μm, or from about 1 μm to about 5 μm, or from about 1.5 μm to about 3 μm. The average particle size and particle size distribution can be measured using any conventional techniques such as sieving, microscopy, Coulter counting, dynamic light scattering, particle image analysis, etc. Alternatively, a laser particle analyzer is used to determine the average particle size and its corresponding particle size distribution.

[0033] The abrasive particles also have a specific surface area in the range from 5 m 2 / g to 40 m 2 / g, or from about 10 m 2 / g to about 35 m 2 / g, or from about 15 m 2 / g to about 30 m 2It shows the surface area in the range up to / g. The measurement of the surface area of the abrasive particles can be achieved using any known technique including, but not limited to, microscopy, small-angle X-ray scattering, mercury porosimetry, and Brunauer-Emmett-Teller (BET) analysis. Alternatively, the surface area is determined using Brunauer-Emmett-Teller (BET) analysis.

[0034] If desired, the polishing formulation may incorporate one or more of water-dispersible boehmite, defoamer, aluminum nitrate, and cleaning aid. The amount of boehmite incorporated into the polishing formulation can range from greater than 0 wt% to 12 wt%, or up to 10 wt%, or 5 wt% or less. The boehmite particles can exhibit an average particle size of less than 0.75 μm, or about 0.5 μm or less, or 0.25 μm or less.

[0035] Examples of any defoamer in the polishing formulation include, but are not limited to, water-soluble silica-based defoamers present at a concentration in the range from greater than 0 wt% to 1.5 wt%, or 1 wt% or less. Examples of any cleaning aid incorporated into the formulation include, but are not limited to, any commercially available or known cleaning aid including polyvinylpyrrolidone (PVP).

[0036] The resulting polishing formulation contains an aqueous dispersion of abrasive particles and a surfactant as described above, and it has been found that the aqueous dispersion can effectively polish the outer surface of a plastic ophthalmic lens. This polishing formulation contains a total solids content of 10 wt% to 50 wt%, or about 15 wt% to about 40 wt%, or the total solids content is in the range from about 20 wt% to about 35 wt%. The amount of abrasive particles present in the polishing formulation is in the range from 10 wt% to 35 wt%, or about 15 wt% to about 30 wt%, or about 20 wt% to about 30 wt%.

[0037] Generally, the pH of the polishing formulation is essentially acidic, i.e., pH < 7, or a pH in the range from about 3 to 5, or a pH in the range from about 3 to about 4.

[0038] Plastic lenses that are polished on their surface by the complex may be any standard plastic poly(allyl diglycol carbonate) lenses (e.g., CR-39), polycarbonate lenses, trihybrid lenses, trivex lenses, high-index or ultra-high-index plastic lenses used in ophthalmic applications. Alternatively, the plastic lens is a polycarbonate lens.

[0039] According to yet another aspect of the present disclosure, a method for polishing the outer surface of a plastic ophthalmic lens is provided. Referring now to FIG. 3, this method 100 generally includes the following steps. First, provide 110 a plurality of polishing particles comprising, consisting of, or consisting essentially of a mixture of crystallized alpha alumina and theta alumina having an average particle size (D 50 ) in the range of about 1 micrometer (μm) to about 5 μm. Alpha alumina is present in an amount in the range of 50 wt% to 80 wt% and theta alumina is present in an amount in the range of 50 wt% to 20 wt% based on the total weight of the polishing particles. Prepare 120 a polishing formulation as defined above and further described herein. This formulation generally includes an aqueous dispersion of these polishing particles and a surfactant. This polishing formulation has a viscosity of about 1 cP to about 25 cP and a total solids content in the range of about 15 wt% to about 40 wt%. Apply 130 the formulation to the outer surface of the plastic ophthalmic lens and then mechanically rub it across the outer surface of the plastic ophthalmic lens to remove a layer of plastic material from the outer surface 140. Finally, remove the formulation from the outer surface to obtain a polished surface 150.

[0040] As used herein, the expression or term "polish" refers to making the surface of an ophthalmic lens smoother by removing material to remove the appearance of scratches and the haze thereby generated. In other words, making the surface of an ophthalmic lens smoother helps to hide or remove surface appearance defects and reduces the magnitude of specular reflection.

[0041] The mechanical rubbing 140 or polishing of the outer surface described in FIG. 3 can be achieved by any known polishing method used in ophthalmic lenses. Some examples of such polishing methods include, but are not limited to, conventional mechanical or manual polishers and polishing equipment, digital polishers, and hand polishing. The average amount of plastic material removed from the surface of the lens during polishing to effectively polish the lens surface is in the range of 8 mg / min to about 11 mg / min, or about 9 mg / min to about 10 mg / min, while maintaining the low viscosity as described above.

[0042] Referring now to FIG. 4, the step 110 of providing a plurality of abrasive particles may include the following steps. An aqueous mixture containing 5 wt% to 30 wt% of non-crystallized boehmite and 0.5 wt% to 4 wt% of nitric acid may be prepared 111 with respect to the total weight of the mixture. The aqueous mixture is placed in a sealed reaction vessel 113 and then heated to a temperature in the range of 120° C. to 200° C. for 4 hours to 24 hours to form a slurry 115. The slurry is recovered and dried to obtain a powder 117. Finally, the powder is fired at a temperature in the range of 1,000° C. to 1,200° C. for about 1 hour to about 20 hours to form a mixture of crystallized alpha alumina and theta alumina particles 119. If desired, the step 110 of providing a plurality of abrasive particles may subject the mixture of crystallized alpha alumina and theta alumina to particle size reduction using a grinding operation 122. Such grinding operations include, but are not limited to, the use of a sand mill, an attritor mill, and a horizontal bead mill.

[0043] (Example)

[0044] The specific examples provided in this disclosure are presented to illustrate various embodiments of the present invention and should not be construed as limiting the scope of the present disclosure. The embodiments are described so that a clear and concise specification is provided, but it is intended that the embodiments can be combined or divided in various forms without departing from the present invention. For example, it will be understood that all the preferred features described herein are applicable to all aspects of the present invention described herein.

[0045] All alumina used in the polishing formulations prepared in accordance with the teachings of the present disclosure, as well as those used as comparative examples, had an average particle size (D 50 ) found to be in the range of about 1.5 micrometers (μm) to about 3 μm. The abrasive particles having this average particle size (D 50 ) were obtained by grinding alumina using a horizontal bead mill at about 2000 rpm for about 2 hours with 1.25 mm yttria-stabilized zirconia grinding beads in an aqueous oxide solution at 40% oxide in water by volume. The particle size distribution was measured every 15 - 30 minutes until the measured average particle size (D 50 ) fell within the described range.

[0046] In the preparation of each of the following polishing formulations, the raw materials were combined and mixed until homogeneously dispersed. In each case, the raw materials were mixed at 600 rpm for 30 - 90 minutes using an overhead mixer equipped with an impeller-type blade.

[0047] Preparation of a polishing composition according to the present disclosure - In the first experimental example (R-1), an aqueous composition consisting of 20 wt% of polishing particles containing a mixture of crystallized alpha-phase alumina and theta-phase alumina, 2 wt% of aluminum nitrate, 2.5 wt% of a surfactant (KXP-228, Lubrizol, Westlake, Ohio), 0.5 wt% of a silica-based antifoaming agent, 2.5 wt% of water-dispersible boehmite, and the balance water was prepared. In this composition, the alpha / theta-phase alumina polishing particles contained approximately 35 wt% of theta-phase alumina and approximately 65 wt% of alpha-phase alumina (see Figure 1). These polishing particles had an average surface area of about 24 m 2 / g, and the pH of this composition was measured to be 3.5.

[0048] In the second experimental example (R-2), an aqueous composition consisting of 20 wt% of alpha / theta-phase alumina polishing particles, 2 wt% of aluminum nitrate, 2.5 wt% of a surfactant (KXP-228, Lubrizol, Westlake, Ohio), 0.5 wt% of a silica-based antifoaming agent, 2.5 wt% of polyvinylpyrrolidone (PVP), 2.5 wt% of water-dispersible boehmite, and the balance water was prepared. In this composition, the alpha / theta-phase alumina polishing particles contained approximately 35 wt% of theta-phase alumina and approximately 65 wt% of alpha-phase alumina (see Figure 1). These polishing particles had an average surface area of about 24 m 2 / g, and the pH of this composition was measured to be 3.9. The polyvinylpyrrolidone (PVP) used had an average molecular weight of 10,000 gms / mole.

[0049] Preparation of the comparative example composition - In Comparative Example C-1, an aqueous composition containing 25 wt% of non-crystallized alpha-alumina polishing particles, 2 wt% of aluminum nitrate, 2.5 wt% of 1,2-propanediol as a surfactant, 0.5 wt% of a silica-based antifoaming agent, 2.5 wt% of water-dispersible boehmite, and the balance water was prepared. In this comparative example (C-1), no theta-phase alumina was present (see Figure 2).

[0050] In Comparative Example C-2, an aqueous formulation was prepared consisting of 20 wt% polishing particles containing a mixture of crystallized alpha-phase alumina and theta-phase alumina, 2 wt% aluminum nitrate, 2.5 wt% surfactant (1,2-propanediol), 0.5 wt% silica-based defoamer, 2.5 wt% water-dispersible boehmite, and the balance water. In this formulation, the alpha / theta-phase alumina polishing particles contained approximately 35 wt% theta-phase alumina and approximately 65 wt% alpha-phase alumina (see Figure 1). These polishing particles had an average surface area of approximately 24 m 2 / g.

[0051] In Comparative Example C-3, an aqueous formulation was prepared containing 20 wt% non-crystallized alpha-alumina polishing particles, 2 wt% aluminum nitrate, 2 wt% surfactant (KXP-228, Lubrizol, Westlake, Ohio), 1 wt% silica-based defoamer, 1.5 wt% water-dispersible boehmite, and the balance water. In this comparative example (C-1), no theta-phase alumina was present (see Figure 2).

[0052] Tests of Experimental Runs and Comparative Examples - The viscosities and polishing characteristics (e.g., removal rate) exhibited by each polishing formulation were summarized in Table 1 below. The formulation C-1 of the comparative example showed a solids content of 20 - 35 wt%, a viscosity > 300 cP, and a removal rate of approximately 6 mg / min when tested against a conventional lens polisher. The formulation C-2 of the comparative example showed a solids content of 20 - 35 wt%, a viscosity > 300 cP, and a removal rate of approximately 9 mg / min. The formulation C-3 of the comparative example showed a solids content of 20 - 35 wt%, a viscosity < 20 cP, and a removal rate of approximately 7 mg / min. In comparison, the sample R-1 of the experimental example showed a solids content of 20 - 35 wt%, a viscosity < 20 cP, and a removal rate exceeding 9 mg / min. Similarly, the sample R-2 of the experimental example also showed a solids content of 20 - 35 wt%, a viscosity < 20 cP, and a removal rate exceeding 10 mg / min.

[0053]

Table 1

[0054] Comparative Examples C-1, C-2, and C-3 show formulations that do not contain a crystallized alpha / theta phase (see C-1, C-3), or have a viscosity of less than 25 centipoise (see C-1, C-2). Thus, these comparative examples provide a removal rate of less than 8 mg / min and / or a viscosity that is too high to provide the polish required for polycarbonate lenses. In contrast, Experimental Examples R-1 and R-2 show formulations prepared in accordance with the teachings of the present disclosure that include a mixture of alpha alumina and theta alumina crystallized as polishing particles and a surfactant or dispersant that reduces the viscosity to less than 25 centipoise (cP). Experimental Examples (R-1, R-2) provide both a low viscosity and a removal rate of greater than 8 mg / min required to effectively polish plastic lenses.

[0055] The conventional lens polisher used in these examples was the Toro-X-2S system from Satisloh and was various uncut plastic ophthalmic lenses such as CR39 lenses from GENTEX Optics. Viscosity was measured with a Brookfield DV1 viscometer, and pH was measured using a Mettler Toledo SevenCompact pH meter. Surface area was determined using the BET method with a Micromeretics TriStar II unit. X-ray diffraction patterns for phase determination were measured using a Rigaku MiniFlex II desktop X-Ray diffractometer. Reduction in the particle size of the alumina polishing grains was done by grinding in a horizontal bead mill from EMI. Particle size (granularity) distribution data was measured by the light scattering method with a Horiba LA930 particle size distribution measuring device.

[0056] The conditions used when operating the Toro-X-2S were to maintain the piston pressure at 0.5 bar and for the flow rate for polishing, to keep an amount high enough to maintain that the surface of the lens was always covered during operation. In the Toro-X-2S, this is a total flow rate of approximately 5 L / min. The operation was continued for 6 minutes, and the lens was washed with water and carefully dried using a clean microfiber cloth both before and after the operation. While recording the mass, the weight of the lens after cleaning was measured before and after polishing using a Mettler Toledo New Classic MS balance. Then, the change in mass before and after polishing was divided by the time (in minutes) the lens was polished to determine the mass / time removal rate. This process was repeated at least 5 times to obtain the average for each polishing formulation so as to ensure consistent and accurate results.

[0057] In this specification, embodiments have been described so that a clear and concise specification can be provided, but it is intended and should be understood that the embodiments can be combined or divided in various forms without departing from the present invention. For example, it will be understood that all the preferred features described herein are applicable to all aspects of the invention described herein.

[0058] Those skilled in the art will understand that, in view of the present disclosure, many changes are possible in the specific embodiments disclosed herein, and that similar results can be obtained without departing from or exceeding the spirit or scope of the present disclosure. Further, those skilled in the art will understand that any of the characteristics reported herein are characteristics that are measured regularly and obtained by a plurality of different methods. The methods described herein represent one such method, and other methods may be utilized without exceeding the scope of the present disclosure.

[0059] The foregoing description of various embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications and variations are possible in light of the above teaching. The described embodiments were chosen and described in order to best illustrate the principles of the invention and its practical application, to thereby enable others skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as defined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

1. A formulation comprising an aqueous dispersion of abrasive particles and a surfactant, configured to polish the outer surface of a plastic ophthalmic lens, wherein the polishing formulation has a viscosity of about 1 cP to about 25 cP and a total solids content in the range of about 15 wt% to about 40 wt%, wherein the abrasive particles include a mixture of crystallized alpha alumina and theta alumina, and wherein the alpha alumina is present in an amount ranging from 50 wt% to 80 wt% and the theta alumina is present in an amount ranging from 50 wt% to 20 wt% based on the total weight of the abrasive particles.

2. The formulation according to claim 1, further comprising one or more of water-dispersible boehmite, an antifoaming agent, aluminum nitrate, and a detergent aid.

3. The formulation according to claim 1 or 2, The abrasive particles are in a formulation having a surface area in the range of about 10 m ２ / g to about 35 m ２ / g.

4. The formulation according to any one of claims 1 to 3, The abrasive particles have an average particle size (D ５０ ) within the range of from about 1 micrometer (μm) to about 5 μm in the composition.

5. The formulation according to any one of claims 1 to 4, having a pH between about 3 and about 5.

6. The formulation according to any one of claims 1 to 5, wherein the surfactant includes a carboxy-functionalized or carboxylated polymer or copolymer.

7. The formulation according to any one of claims 1 to 6, wherein the abrasive particles are present at a concentration in the range of about 15 wt% to about 30 wt% based on the total weight of the formulation.

8. The formulation according to any one of claims 1 to 9, wherein the amount of alpha alumina is in the range of about 60 wt% to about 70 wt% and the amount of theta alumina is in the range of about 40 wt% to about 30 wt% based on the total weight of the abrasive particles.

9. The formulation according to claim 2, The boehmite has an average particle size (D ５０ ) of less than about 0.5 μm and is present in an amount of up to 10 wt% based on the total weight of the formulation.

10. The formulation according to claim 2, wherein the antifoaming agent is a water-soluble silica-based antifoaming agent present at a concentration in the range of up to 1 wt% based on the total weight of the formulation.

11. The formulation according to any one of claims 1 to 10, having a viscosity in the range of about 1 cP to about 10 cP.

12. The formulation according to any one of claims 1 to 11, providing a removal rate of at least 8 mg / min when measured with a conventional lens polisher using an uncut plastic ophthalmic lens.

13. The formulation according to any one of claims 1 to 12, wherein the plastic ophthalmic lens includes polycarbonate.

14. A formulation according to any one of claims 1 to 13, wherein the abrasive particles further comprise < 1 wt% of gamma-phase alumina or delta-phase alumina.

15. A method of polishing the outer surface of a plastic ophthalmic lens, An average particle size (D within the range of about 1 micrometer (μm) to about 5 μm ５０ ) of a mixture of crystallized alpha alumina and theta alumina, wherein the alpha alumina is present in an amount in the range of 50 wt% to 80 wt% and the theta alumina is present in an amount in the range of 50 wt% to 20 wt% based on the total weight of the abrasive particles, providing the plurality of abrasive particles; comprising the step of preparing a polishing formulation that is an aqueous dispersion of the abrasive particles and a surfactant, has a viscosity of about 1 cP to about 25 cP, and a total solids content in the range of about 15 wt% to about 40 wt%; the step of applying the formulation to the outer surface of the plastic ophthalmic lens; the step of mechanically rubbing the formulation across the outer surface of the plastic ophthalmic lens to remove a layer of plastic material from the outer surface; and the step of removing the formulation from the outer surface to obtain a polished surface.

16. The method according to claim 15, wherein the abrasive particles are present in the formulation at a concentration in the range of about 15 wt% to about 30 wt% based on the total weight of the formulation, and the formulation is configured to remove plastic material at a rate of at least 8 mg / min when measured with a conventional lens polisher using an uncut polycarbonate ophthalmic lens.

17. The method according to claim 15 or 16, wherein providing a plurality of abrasive particles comprises preparing an aqueous mixture comprising 5 wt% to 30 wt% of uncrystallized boehmite and 0.5 wt% to 4 wt% of nitric acid, based on the total weight of the mixture; placing the aqueous mixture into a sealed reaction vessel; heating the sealed reaction vessel to a temperature in the range of 120°C to 200°C for 4 hours to 24 hours to form a slurry; recovering and drying the slurry to obtain a powder; and firing the powder at a temperature in the range of 1,000°C to 1,200°C for about 1 hour to about 20 hours to form a mixture of crystallized alpha-alumina and theta-alumina.

18. The method according to claim 17, wherein the mixture of crystallized alpha-alumina and theta-alumina is further subjected to a particle size reduction using a grinding operation.

19. The method according to any one of claims 15 to 18, wherein the abrasive particles further comprise < 1 wt% of gamma-phase alumina or delta-phase alumina.

20. The method according to any one of claims 15 to 19, A method in which the plastic ophthalmic lens contains polycarbonate.

21. The method according to any one of claims 15 to 20, wherein the amount of alpha alumina is in the range of about 60 wt% to about 70 wt% and the amount of theta alumina is in the range of about 40 wt% to about 30 wt% with respect to the total weight of the abrasive particles.

22. The method according to any one of claims 15 to 21, wherein the formulation further comprises one or more of water-dispersible boehmite, an antifoaming agent, aluminum nitrate, and a cleaning aid.

23. The method according to claim 22, If present, the boehmite has an average particle size (D ５０ ) of less than about 0.5 μm and is present in an amount of up to 10 wt% based on the total weight of the formulation, wherein, when present, the antifoaming agent is a water-soluble silica-based antifoaming agent present at a concentration in the range of up to 1 wt% with respect to the total weight of the formulation.

24. The method according to any one of claims 15 to 23, wherein mechanically rubbing the formulation over the outer surface of the plastic ophthalmic lens is achieved by the use of conventional mechanical or manual polishing equipment, a digital polisher, or hand polishing.

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