Three piece mold assembly for making an ocular device

Abstract: A mold assembly (10) for making an ocular device such as a contact lens, an intraocular lens or a lens blank has three pieces which include a sleeve (12), a first mold segment (14) and a second mold segment (16). The first mold segment includes a peripheral skirt extends away from a mold cavity and which terminates in an end portion which is in interference fit engagement with the sleeve for establishing a leak-resistant fluid seal.

Description: Background of the Invention 1. Field of the Invention The present invention relates to a mold assembly for making an ocular device such as a contact lens, an intraocular lens or a blank which is later lathed to make a lens. 2. Description of the Related Art Certain mold assemblies for making ocular devices such as contact lenses, intraocular lenses or lens blanks consist of two pieces that include a male mold segment and a female mold segment. Typically, such assemblies include frustoconical or tapered walls on one of the segments to align the segments as the latter are brought together during a molding operation. Examples of two-piece mold assemblies are described in U.S. Patent Nos. 4,121,896 and 4,197,266. Other types of mold assemblies for making ocular devices consist of three pieces which include a sleeve and two segments that fit within the sleeve. Examples of three-piece mold assemblies are described in U.S. Patent Nos. 3,761,208, 4,166,088 and 4,836,960. However, the quality of a molded ocular lens is dependent upon the mold assembly that is used to make the lens. A mold assembly that is dimensionally accurate and stable during use facilitates the manufacture of a dimensionally accurate and thus optically correct lens. A precision mold assembly may be made from metallic materials which can be machined to precise tolerances. It has also been proposed to reduce the cost of lens assemblies by making the assemblies of plastic materials which can be injection molded. However, typical plastic lens mold assemblies are less rigid than corresponding assemblies made of metallic materials and may cause the finished lens to assume an incorrect contour or dimension. In some instances, it is desirable to use a mold assembly that has a tracking segment which moves during curing of the molding material to maintain contact with the latter as the material expands or contracts. Often, a flexible gasket or rim is placed between the segments in an attempt to contain the liquid lens molding material within the mold cavity during tracking, while also forming the edge of the molded lens. However, it is sometimes difficult to ensure that the gasket or rim has sufficient flexibility to permit free, unhindered tracking, while still maintaining a proper pinch-off and seal in order to contain the mold material within the liquid cavity. Summary of the Invention The present invention is directed toward a mold assembly for making an ocular device, and comprises a sleeve having a passage, a first mold segment removably received in the passage, and a second mold segment removably received in the passage at a location spaced from the first mold segment to present a mold cavity therebetween. The first mold segment has a base adjacent the mold cavity and a peripheral skirt extending in a direction away from the mold cavity. The base and the skirt define an open recess. The sleeve extends along the skirt and is in contact with the skirt for aligning the first mold section with the sleeve. The skirt includes an end portion remote from the base. The passage next to the end portion has a cross-sectional area slightly less than the cross-sectional area of the end portion in order to establish a leak-resistant fluid seal. Advantageously, the skirt facilitates precise alignment of the first mold segment with the sleeve in order to help ensure that the first mold segment is in proper alignment with the second mold segment. The interference fit engagement between the skirt and the sleeve, being located remote from the base of the first mold segment, avoids undue distortion of the shape of the base, yet rigidly secures the first mold segment to the sleeve in order to permit the second mold segment to track the curing material if desired. The interference fit engagement between the first mold segment and the sleeve also enables the first mold segment to be removed from the sleeve when desired after a molding operation in order to gain access to the molded ocular device. Brief Description of the Drawings Fig. 1 is a fragmentary side cross-sectional view of a mold assembly constructed in accordance with the invention; Fig. 2 is a reduced, side cross-sectional view of a sleeve of the assembly of Fig. 1, additionally showing a sprue connection for making the sleeve; Fig. 3 is a reduced, side cross-sectional view of a first mold segment of the assembly shown in Fig. 1, additionally illustrating a sprue connection for making the segment; Fig. 4 is a reduced, side cross-sectional view of a second mold segment of the assembly shown in Fig. 1, along with a sprue connection for molding the segment; Fig. 5 is a reduced, cross-sectional view of the assembly shown in Fig. 1, except that mold material for making an ocular device has been placed in the assembly and the second mold segment is shown in its initial stages of movement toward the first mold segment; Fig. 6 is a view similar to Fig. 5 except that the second mold segment has moved to a certain position to define a mold cavity, and a source of radiation (shown schematically) has been activated to initiate curing of the mold material; Fig. 7 is a reduced view somewhat similar to Fig. 6 except that the sleeve has been placed next to a holding jig, and an ejector is in contact with the first mold segment for pushing both the first mold segment and the second mold segment out of the sleeve in order to recover the cured product; Fig. 8 is a fragmentary view of part of the assembly shown in Fig. 1 along with a closure mechanism for use when the assembly is used in a tracking mode; and Fig. 9 is a view somewhat similar to Fig. 8 except that a different closure mechanism is shown which is useful when the assembly is used in a non-tracking mode. Detailed Description of the Preferred Embodiment A mold assembly 10 for making an ocular device is shown in Figs. 1 and 5-7 and includes a sleeve 12, a first mold segment 14 and a second mold segment 16 that are shown individually in Figs. 2-4 respectively. The sleeve 12 has a central, elongated passage 18 which removably receives the segments 14, 16 to make the molded ocular device. Referring now to Figs. 1 and 2, the sleeve 12 is generally cylindrical and includes an inwardly extending, ring-shaped flange 20 that is formed along the entire circumference of the passage 18. The sleeve 12 also has a first frustoconical surface 22 next to the passage 18 and positioned such that its smallest diameter is adjacent the flange 20. The sleeve 12 includes a second frustoconical surface 24 along with a cylindrical section 26 that interconnects the surfaces 22, 24. The cylindrical section 26 has a central longitudinal axis that coincides with a central longitudinal axis 30 of the passage 18. The sleeve 12 has a frustoconical surface portion 32 next to the passage 18 and remote from the flange 20. The frustoconical portion 32 extends at a non-zero angle relative to the axis 30. The sleeve 12 also has an outer, flat, annular end 36 which extends in a plane perpendicular to the axis 30, along with a radially-extending shoulder 38 which integrally connects the frustoconical portion 32 to the second frustoconical surface 24. Turning now to Figs. 1 and 3, the first mold segment 14 has a window or base 40 that is integrally connected to a depending, cylindrical skirt 42 which is hollow to provide a central recess 44. Normally, an end portion 46 of the skirt 42 has an outer diameter equal to the outer diameter of the remainder of the skirt 42 as shown in Fig. 3. However, when the first mold segment 14 is received in the passage 18 as shown in Fig. 1, the end portion 46 is deflected slightly inwardly in a radial direction by the surface 22 and is in interference fit relationship (shown exaggerated) with the surface 22 to thereby establish a leak-resistant fluid seal remote from the base 40. In practice, the skirt 42 is in engagement with the sleeve 12 along its axial length and circumferential extent, but the most effective fluid seal is established next to the first frustoconical surface 22 due to the interference fit. The base 40 has a precisely curved face 48 for molding one side of an ocular device, and the length of the skirt 42 and resulting remoteness of the interference fit of the end portion 46 from the base 40 helps to avoid distortion of the contour of the face 48 when the first mold segment 14 is pulled into the passage 18 abutting the flange 20. The second mold segment 16 (see Fig. 4) includes a central section 50 with a curved face 52 opposite the face 48 of the first mold segment 14. The second mold segment 16 is movable in the passage 18 to a certain position that is shown in Fig. 1 (as well as Fig. 6) spaced from the first mold segment 14 to define a mold cavity 54 that is bounded by the face 48, the face 52 and part of the cylindrical section 26 of the sleeve 12. The faces 48, 52 form opposite sides of an ocular device that is made from polymer lens molding material which is received and cured in the mold cavity 54. The second mold segment 16 includes a tubular section 56 integrally connected with the central section 50. An outer cylindrical section 60 of the tubular section 56 has a central axis that coincides with the axis 30 when the second mold segment 16 is in the position shown in Fig. 1. The second mold segment 16 is circumscribed by an outwardly extending cylindrical portion 62 having an outer cylindrical wall 63 that has a larger diameter than the outer diameter of the cylindrical section 60. When the second mold segment 16 is in the position shown in Fig. 1, part of a lower, radially-extending, annular surface 65 of the cylindrical portion 62 and part of the cylindrical section 60 of the segment 16 along with the second frustoconical surface 24, the shoulder 38 and a lower part of the frustoconical portion 32 of the sleeve 12 combine to define a reservoir chamber 64 for excess material. An outer end section 66 of the second mold segment 16 has an outermost, flat, annular end 68 which extends in a plane perpendicular to the central axis of the second mold segment 16. The outer end section 66 also includes an outwardly facing cylindrical surface 70 located between the end 68 and the cylindrical portion 62. An inner wall 72 of the tubular section 56 faces a central recess 74 of the second mold segment 16. The wall 72 is frustoconical and preferably in the shape of a female zero Morse taper that is sized to fit a zero Morse taper pin which has been shortened from 5 cm to 2.5 cm. (A female zero Morse taper is made by using a finishing reamer having a flute length of 5.7 cm, a large end diameter of 9.3 mm and a small end diameter of 6.4 mm.) Figs. 5-7 are exemplary of the steps undertaken in using the assembly 10 to make an ocular device. First, the first mold segment 14 is inserted in the sleeve 12 starting at the end 36 and is advanced along the passage 18 until the outer end of the end portion 46 contacts the upper surface of the flange 20. As the end portion 46 of the skirt 42 reaches the position shown in Fig. 5, the end portion 46 is deflected radially inwardly by the first frustoconical surface 22 (Figs. 1-2) in order to form an interference fit that (1) establishes a leak-resistant fluid seal, and (2) releasably locks the first mold segment 14 in place. Next, a measured quantity of liquid molding material 76 is placed on top of the face 48 as shown in Fig. 5. The second mold segment 16 is then brought into position over the sleeve 12 and above the end 36 such that the central axis of the second mold segment 16 is in rough alignment with the longitudinal axis 30 of the passage 18. Next, the second mold segment 16 is advanced toward the first mold segment 14 and into the passage 18 whereupon, in all likelihood, the cylindrical portion 62 (see Figs. 1 and 4) of the segment 16 contacts one lateral side of the frustoconical portion 32 of the sleeve 12. As the second mold segment 16 continues to advance toward the first mold segment 14, the frustoconical portion 32 functions as an alignment means to shift the second mold segment 16 in a direction perpendicular to the axis 30 as may be necessary to precisely align the central axis of the second mold segment 16 with the axis 30 of the sleeve 12 as the second mold segment 16 continues to advance. By the time that the cylindrical section 60 of the second mold segment reaches the cylindrical section 26 of the sleeve 12, the longitudinal axis of the second mold segment 16 is precisely aligned with the axis 30. As such, the curved face 52 does not come into contact with the sleeve 12 such as the shoulder 38, and damage to the face 52 is largely avoided even in instances where the second mold segment 16 is initially unaligned with the axis 30. In this regard, the second frustoconical surface 24 is inclined at a greater angle relative to the axis 30 than the angle of inclination of the frustoconical portion 32 in order to avoid contact with the face 52. Next, as the second mold segment 16 continues to move toward the first mold segment 14, the cylindrical sections 26, 60 telescopically engage each other and function as a guide means to prohibit shifting of the second mold segment 16 in a direction perpendicular to the axis 30. As the second mold segment 16 moves to the certain position that is shown in Fig. 6 (also shown in Fig. 8), the material 76 is spread throughout the cavity 54, and a portion of the material 76 moves along the sliding cylindrical sections 26, 60 (which are in communication with the cavity 54) in order to lubricate the latter. Excess material is displaced to the reservoir chamber 64. Next, a light source 78 shown schematically in Fig. 6 is activated to begin curing of the material 76 which includes a photoinitiator that is effective at the wavelength of the light source 78. As the material 76 cures, the material 76 may shrink or expand; however, the lubricated cylindrical sections 26, 60 permit the second mold segment 16 to track such expansion or contraction in a manner that facilitates full contact of the faces 48, 52 with the material 76 at all times so that the surface of the curing material 76 accurately replicates the faces 48, 52. The axial length of sliding contact of the cylindrical sections 26, 60 need only be about 100 microns before the segment 16 reaches the certain position shown in Figs. 6 and 8. Preferably, the frustoconical portion 32 is inclined at a taper of 0.25 degrees per side relative to the axis 30. The inclination permits air to escape without undue hindrance as the segment 16 advances. Additionally, the cylindrical wall 63 is sized to present a radial clearance of 0.005 mm with the frustoconical portion 32 when the second mold segment 16 is in its lowest expected position (such as that shown in Figs. 6 and 8), in order to provide a gross containment or restriction between the reservoir chamber 64 and the atmosphere external of the assembly 10. The restriction permits air to be vented to the atmosphere, but generally prevents escape of material 76. As this restriction is established, advancement of the segment 16 creates a slight back pressure on the material 76 and encourages the latter to remain in the cavity 54. However, the clearance between the cylindrical wall 63 and the frustoconical portion 32 is sufficient to prevent undue resistance to tracking movement of the cylindrical sections 26, 60 as the material 76 cures. The use of a three-piece assembly permits the sleeve 12, the first mold segment 14 and the second mold segment 16 to be molded from different plastic materials. The sleeve 12, the first mold segment 14 and the second mold segment 16 are molded from plastic materials which are selected to provide the base 40 with an overall light transmittance value that is greater than the light transmittance value of the sleeve 12 and the second mold segment 16. As a result, photoinitiation of the material 76 generally occurs only in the mold cavity 54, while material in the reservoir chamber 64 and between the interengaged cylindrical sections 26, 60 remains substantially uncured and in a liquid state so as to avoid hindering movement of the second mold segment 16 and provide, if necessary, a source of additional liquid material to the cavity 54. In practice, the second mold segment 16 and the sleeve 12 are opaque, while the first mold segment 14 including the base 40 are translucent in order to admit light to the cavity 54. The lower surface of the base 40 (viewing Figs. 1 and 3) may be flat to facilitate curing of the material 76 from the center of the cavity 54 and then outwardly in a radial direction. The light source 78 is deactivated once the material 76 in the cavity 54 has substantially polymerized, and the assembly 10 is subsequently placed in an oven. The material 76 also includes a thermal initiator, so that the flash (i.e., the material in the chamber 64 along with material adjacent the cylindrical surfaces 26, 60) is thermally initiated and polymerized as the assembly 10 is heated while the ocular device 80 (see Fig. 7) is postcured and/or annealed. Then assembly 10 can be subsequently taken apart without contacting a significant quantity, if any, of uncured liquid material 76. The assembly 10 is then placed against a jig 82 such that the end 36 of the sleeve 12 contacts edge portions of the jig 82 surrounding an orifice 84. Next, a cylindrical ejector 85 is guided through the flange 20 and into the recess 44 of the skirt 42, and contacts the bottom of the base 40. Continued movement of the ejector 85 in the direction shown in the arrow in Fig. 7 moves the first and second mold segments 14, 16 out of the passage 18, whereupon the ocular device 80 can be recovered. A chuck, tightened around the skirt 42, will loosen the segment 14 from the device 80 while enabling the device 80 to remain attached to the segment 16. The three-piece mold assembly 10 also permits the selection of particular plastic materials for the segments 14, 16 which have a greater or lesser affinity as desired for the cured mold material of the ocular device 80. For example, if the device 80 is a lens blank which is to be later lathed into the shape of a lens, it may be preferable to have the device 80 remain fixed to the second mold segment 16 and release from the first mold segment 14 as the segments 14, 16 are moved apart after removal from the sleeve 12, so that subsequent lathing can be carried out using the second mold segment 16 as a mount. In such a situation, the second mold segment 16 could be made of a material such as amorphous nylon, while the first mold segment 14 may be made of a material such as polymethylpentene. The assembly 10 may be used in either a tracking mode or a non-tracking mode. When used in a tracking mode, clearance between the cylindrical section 26 and the cylindrical section 60 should range from -0.01 to +0.01 mm (per side). If desired, the end 68 of the second mold segment 16 may be used as a reference guide to determine the spacing between the faces 48, 52. As one example, the assembly 10 may be dimensioned such that the distance between the faces 48, 52 and thus the thickness of the ocular device 80 is a certain dimension when the end 68 is coplanar with the end 36. In Fig. 8, a closure mechanism 94 has a boss 95 that contacts the end 36. The mechanism also carries an adjustment plate 96 which bears against the end 68. The plate 96 is vertically adjustable relative to the boss 95 in order to vary the thickness of the device 80. When the molding material 76 comprises a perfluoroether monomer, the material 76 contracts during polymerization when the light source 78 is activated. To permit free tracking movement, the distance "A" in Fig. 8 should be equal to or greater than the shrinkage of the material 76 in a vertical direction (viewing Fig. 8) between the faces 48, 52. When the assembly 10 is used in a non-tracking mode, the second mold segment 16 is held in a fixed position relative to the sleeve 12. In the non-tracking mode, the clearance between sections 26, 60 should range from 0.00 to 0.01 mm per side to permit the material 76 to flow as needed between the reservoir chamber 64 and the cavity 54, such that the material 76 remains in contact with the faces 48, 52 during curing. Fig. 9 shows a closure mechanism 98 that bears against the end 68 while the sleeve 12 is supported in a fixed position. The tubular section 56 is dimensioned to enable the surface 65 to seat against the shoulder 38 when spacing between the faces 48, 52 is equal to the desired thickness of the ocular device 80. Figs. 2-4 illustrate preferred locations for various sprue connections used to make the assembly 10. Fig. 2 shows a sprue 86 and a disc-shaped diaphragm gate 87 coupled to an inner surface of the flange 20 of sleeve 12. Unlike other areas of the sleeve 12, the shape of the inner wall of the flange 20 is not critical and provides an ideal location for the gate 87. Figs. 3 and 4 show sprues 88, 90 for making the first and second mold segments 14, 16 respectively. The position of the sprues 88, 90 and accompanying gates normally provides even distribution of the material during injection molding in order to provide accurate contours on the faces 48, 52 as well as on the critical side surfaces of the segments 14, 16. Additionally, the sprue 88 functions as a handle for pulling the first mold segment 14 into the sleeve 12 so that damaging contact with the face 48 can be avoided. Using this method, a pliers-like tool used for pulling the sprue 88 could include nippers for cutting the sprue 88 and accompanying gate subsequent to installation of the segment 14 in the sleeve 12. If the ocular device 80 is a lens, it may be preferable to degate the segment 14 immediately after the segment 14 is molded, since the thickness of the sprue 88 might otherwise cause increased shrinkage in the center of the base 40 and thereby impair the lens optics as the segment 14 cools after molding. The degated segment 14 is drawn into the sleeve 12 by a pin such as the ejector 85 using a vacuum assist in order to seat the segment 14 against the flange 20 without contact with the contoured face 48.

Claims: A mold assembly for making an ocular device comprising: a sleeve (12) having a passage (18); a first mold segment (14) removably received in said passage; and a second mold segment (16) removably received in said passage at a location spaced from said first mold segment to present a mold cavity therebetween, said first mold segment having a base (40) adjacent said mold cavity and a peripheral skirt (42) extending in a direction away from said mold cavity, said base and said skirt defining an open recess (44), said sleeve extending along said skirt and being in contact with said skirt for aligning said first mold section with said sleeve, said skirt including an end portion (46) remote from said base, said passage next to said end portion having a cross-sectional area slightly less than the cross-sectional area of said end portion in order to establish a leak-resistant fluid seal. The assembly of claim 1, wherein said passage (18) is substantially cylindrical adjacent said skirt (42), and wherein said skirt extends continuously along the circumference of said passage. The assembly of claim 1, wherein said skirt (42) is substantially cylindrical. The assembly of claim 1, wherein said sleeve (12) includes a flange (20) extending inwardly toward said passage to limit movement of said first mold segment (14) away from said mold cavity. The assembly of claim 4, wherein said passage (18) is substantially cylindrical, and wherein said flange is ring-shaped and extends along the circumference of said passage. The assembly of claim 1, wherein said skirt (42) is generally cylindrical, and said passage has a cross-sectional area adjacent said end portion which is slightly less than the cross-sectional area of said passage adjacent said base, thereby establishing said interference fit engagement. The assembly of claim 1, wherein said sleeve (12) and said second mold segment (16) each include mating, cylindrical wall sections telescopically engageable with each other when said second mold segment is at said location in order to permit tracking of said second mold segment during curing of molding material. The assembly of claim 1, wherein said base (40) has a certain light transmittance value, and wherein said sleeve and said second mold segment each have a light transmittance value which is less than said light transmittance value of said base. The assembly of claim 1, wherein said first mold segment (14) is releasably fixed to said sleeve. The assembly of claim 1, wherein said base (40) includes a central region with a removable molding sprue. The assembly of claim 1, wherein said second mold segment includes a central section adjacent said mold cavity and a tubular wall section extending away from said mold cavity, said tubular wall section having a central recess, and wherein said central section includes a sprue connection (90) in the center of said recess. The assembly of claim 1, wherein said sleeve (12) includes a flange extending inwardly towards said passage, wherein said flange is in contact with said skirt, and wherein said sleeve and said second mold segment each include respective ends which are substantially coplanar when said second mold segment is at said location. The assembly of claim 1, wherein said sleeve (12) is substantially cylindrical and has an inwardly extending flange engagable with said skirt, and wherein said flange includes a removable disc-shaped diaphragm molding gate.

Inventors: FOGARTY TERENCE M C O MINNESOT, FOGARTY, TERENCE M., C/O MINNESOTA MINING AND
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1991
Main classification: B29C33
IPC codes: B29L11, A61F2, B29C33, G02C7, B29D11, B29C43, B29C39, G02C13