EP0484036A2

EP0484036A2 - Reinforced thermoplastic components for use in the manufacturing of ophthalmic lenses and methods of making such components

Info

Publication number: EP0484036A2
Application number: EP91309762A
Authority: EP
Inventors: Don H. Rotenberg; Ronald T. Hyslop; Milton Coleman
Original assignee: Coburn Optical Industries Inc; Pilkington Visioncare Inc
Current assignee: Gerber Coburn Optical Inc
Priority date: 1990-10-29
Filing date: 1991-10-22
Publication date: 1992-05-06
Also published as: CA2053999A1; JPH04300154A; MX9101663A; ZA918600B; BR9104682A; AU8682591A; EP0484036A3

Abstract

Components for use in the formation of a finished or partially finished ophthalmic lens, such as lens blocks (10) and prism rings and edging blocks and adapters for example, are formed from a carbon fiber reinforced crystalline thermoplastic containing at least 30% by weight carbon fiber based on the total weight of the component. The reinforced thermoplastic has a minimum tensile strength of at least about 20,000 psi, a minimum flexural strength of 2 x 10⁴ psi, a minimum flexural modulus of 2 x 10⁶ psi, and a specific gravity of less than 1.60. The lens block (10) includes a unique arrangement of ribs (18) to strengthen the block and increase its heat transfer properties. Metal finishing centers (44) are inserted into the block and are ultrasonically vibrated or heat staked in order to cause the plastic material to flow around and into serrations formed on the finishing centers.

Description

This invention relates to components for use in the manufacture of ophthalmic lenses, and in particular to lens surfacing blocks and prism rings, and edging blocks and adapters.
The manufacture of ophthalmic lenses on a commercial scale involves maintaining a high throughput of lenses. The processing equipment must be capable of operating for long periods with minimum shutdown times for maintenance and repair. This requirement is coupled with the need to ensure the equipment operates satisfactorily in the production of lenses.
In the case, for example, of equipment used for the surfacing of lens blanks, it is necessary to hold the blank firmly during grinding operations, such as surfacing, finishing, and polishing. The mounting means are known as lens blocks, and the majority of such blocks have heretofore been made of steel and have a diameter of about 43 mm. Larger diameter blocks of aluminum have also been used. The design of such blocks and their method of use is described in U.S. Patent 3,704,558.
Blocks made of steel or aluminum have been considered essential to ensure that the lens blanks are held rigidly to eliminate a distortion effect known as a blocking or surfacing wave, or to at least move this distortion effect to a region of the lens where it is of no serious consequence. Though all the requirements of maintaining rigidity and an unyielding support for the lens blank are met by metal blocks, their weight produces a high rate of wear of bearings on grinding machines, whereby the bearings must be replaced relatively frequently.
It would be desirable to provide a lens block which not only has rigidity and an unyielding support for the lens blank, but which will also reduces the degree of wear and tear on fining and polishing machines substantially below that experienced when using metal blocks.
A further consideration of the design of lens blocks relates to the manner of adhering a lens to the block. That is, the lens is typically adhered to the block by a blocking material which is introduced in a hot, flowable state into a cavity between the lens and block. Upon cooling, the blocking material hardens and adheres to both the lens and block. Originally a pitch-like blocking material was used for that purpose, but more recently the use of a low melting metal alloy has become prevalent. It is necessary that the block be capable of transferring the heat of the blocking alloy so that the latter will harden quickly enough to both minimize distortion of the lens and to permit rapid processing times. Therefore, a further requirement of block-forming materials is a high degree of thermal conductivity.
Yet another consideration involved in the fabrication of lens blocks involves the provision therein of centering recesses on a backside of the block opposite the lens-carrying side of the block. The centering recesses mate with fixed projections on grinding machines to establish a proper orientation of the lens. The centering recesses have been provided on the ends of cylindrical metal inserts or finishing centers which are press-fit into pre-formed holes in the backside of the lens block. However, such a press-fit installation step may distort aluminum blocks, and thereby adversely affect the ability of the block to properly position the lens.
Another component which must be made of a high strength to weight ratio material is a prism ring. Prism rings are critical components in fabricating certain types of ophthalmic lenses. They are required when finishing semi-finished lenses.
A lens blank having one of its two surfaces ground and polished or cast finished is termed a semi-finished lens. The subsequent generation of the opposite surface is a more exacting operation because the second surface must not only have the correct curvature, but must bear a relation to the previously finished surface, in order for the lens to have the ophthalmic properties required. This precise location of the second surface with respect to the first may require either or both of two adjustments or settings, one called "prism" and the other called "axis". Setting for prism involves a tilting of the second surface with respect to the first, and setting for axis involves a rotation of the second surface with respect to the first.
The problem of correctly relating the second surface to the first has been done by mounting a lens blank on a lens block in a conventional manner and then adjusting the block in the chuck of a generating machine by means of a shim-type or a cylinder-type of prism ring, so that the desired amount of prism at the correct meridian could be ground into the lens.
Alternatively, the desired amount of prism at the prescribed meridian can be incorporated directly into the lens block mounting so that when the block is mounted in a conventional manner in a grinding machine the desired prism is ground into the lens. The desired amount of prism is incorporated into the block by selecting the desired prism angle in a special prism blocking device by rotating the angled steel "prism rings" which provides the desired amount of tilt to the lens as it is presented to the mold. Thereafter, the molten alloy is introduced to adhere the lens to the block and incorporate the desired angle directly in the alloy block. This type of prism blocking process is described in copending U.S. Patent Application Serial No. 447,844 filed December 8, 1989.
The above-described shim-type, cylinder-type and rotating-type of prism rings are complicated and expensive to construct and maintain. In order to incorporate the desired amount of prism into the lens, a large inventory of shim and cylinder-type of prism rings is required to be kept on hand, and the constant handling thereof results in undesirable wear and a consequential cost penalty in replacing worn or damaged rings. Such rings have heretofore been made of steel bar stock or tube-stock of fabric impregnated thermoset phenolic resins. The manufacture of prism rings from these materials involves a lengthy and therefore costly multi-step lathing and machining process. There has been a need not only to find a material less susceptible to damage during handling but also whose use will simplify the manufacturing process for such rings.
An additional application where better materials and lower cost manufacturing processes would be desirable is the machined steel or investment cast zinc edging block and the machined brass or steel edging block adaptor. These components are used when finished lenses are edged to final shape. Such devices are costly to manufacture and can wear because of the soft nature of some of the metals.
The present invention provides a component for use in the formation of a finished or semi-finished ophthalmic lens, said component having been formed from a carbon fiber reinforced cyrstalline thermoplastic material containing at least 30% by weight carbon fiber based on the total weight of the component.
The present invention further provides a method of manufacturing a lens block for use in blocking an ophthalmic lens, comprising the steps of injection molding a body of carbon fiber reinforced crystalline thermoplastic material containing at least 30% by weight carbon fiber based on the total weight of the component, said body including a concave front surface and a rear surface having therein a plurality of holes, inserting finishing centers into respective ones of said holes while ultrasonically vibrating or heat-staking said centers whereby the said material forming walls of said holes flows against said centers and between outward projections of said centers.
According to the invention, there are provided components for use in the formation of a finished or partially finished ophthalmic lens. The components, such as a lens block, prism rings, and edging blocks and adapters, for example, are formed from a carbon fiber reinforced crystalline thermoplastic containing at least 30% by weight carbon fiber based on the total weight of the component. In a preferred embodiment the reinforced thermoplastic has at 73°F a minimum tensile strength of at least about 20,000 psi., a minimum flexural strength of 20,000 psi, a minimum flexural modulus of 2 x 10⁶ psi, a minimum compressive strength of 20,000 psi, and a specific gravity of less than 1.60.
The term crystalline thermoplastic includes polymeric materials which have a crystalline or semi-crystalline structure, and a unique melting point (crystalline melting temperature or Tm) below which the polymer tends to be crystalline and above which it is in a plastic state. Exemplary materials include polyesters such as polybutylene terephthalate (PBT), and polyethylene terephthalate (PET), polyetherketones (PEEK), polyphenylene sulphide (PPS), polyamideimides (PAI), and polyamides. Preferred are polyamides and polybutylene terephthalate. Combinations or alloys of two or more polymers can be used.
Certain components such as prism rings and blocks and edging blocks and adapters can be formed by injection molding in one step to a finished or semi-finished state. Prism rings can be made in a standard semi-finished form using the carbon filled thermoplastic, and then finished by one simple milling operation to the dimensions required to achieve a particular prism correction. This is in contrast to the use of glass fiber-containing materials which were found not to have the same ease of cutting during the milling step. The crystalline thermoplastics have good chemical resistance and are not affected by the oil and water based coolants used in the grinding and the water based slurries used in the polishing of lens blanks. When used for prism rings, carbon filled crystalline thermoplastics, unlike the prior art materials, do not gall or produce raised edges or a plow effect when scratched so as to interfere with the precision fit required for the prism ring in use.
A further advantage of the prism ring of the invention derives from its failure mode under compressive or bending stress. To produce lenses having a high amount of prism correction, the prism ring must have a portion with a very thin cross-section. Prior art metal prism rings fail by gradual bending of this thin portion. The amount of bending need not be great to cause the lenses produced to be incorrectly ground. Further, such defects in the ring may not be readily apparent, and a number of off-specification lenses could be produced before the problem is discovered.
By contrast, the prism rings produced by the invention can fail by catastrophic breakage, oftentimes the thinnest section of the ring breaking in two. Prior to breakage, however, the ring does not deform sufficiently to affect lens curvature, and hence no off-specification lenses are produced. The ring failure is also readily observable so that a defective ring is not in production for an extended period.
A totally unexpected advantage of the prism ring of the invention is that it can be left in lens production for a period of time after failure and still produce lenses within specification limits. The broken prism ring will lie flat as required between the generator chuck and the lens block and will continue to yield correct lenses until it can be replaced without disrupting lens production.
The crystalline thermoplastic can be used with other reinforcing materials present in addition to the carbon fiber, e.g., the addition of mica, kaolin, Wollastonite or other silicas or mineral fillers can help in assuring uniform or isotropic shrinkage during forming. A high filler or reinforcing material loading reduces shrinkage to low levels in any case. Preferably the thermoplastic composition has at least 30% by weight carbon fiber and when filler is added, this is in the form of fine particles, and quantities in the range 5% to 25% by weight can be used.
The use of carbon fiber as a reinforcing filler enables a material to be used, in a preferred embodiment, with a low specific gravity of the order of less than about 1.6, and most preferably less than about 1.5, a tensile strength of at least 20,000 psi, and flexural modulus of at least 2 X 10⁶ psi. This makes it possible to manufacture components which have high strength and rigidity while being ultralight in use. The term "carbon fiber" encompasses fiber materials made from pitch, polyacrylonitrile (PAN), or rayon fibers. Carbon fibers also provide increased thermal conductivity of the thermoplastic composition as compared to glass filled compositions employing the same thermoplastic polymers.
The preferred embodiment consists of carbon fiber made from polyacrylonitrile (PAN) by high temperature pyrolytic processes which yield carbon fibers of various tensile strengths. PAN derived carbon fiber of intermediate Young's modulus (stiffness) provides the filled plastic with the best combination of high tensile strength and high flexural modulus (rigidity), while at the same time yielding a filled plastic of relatively low specific gravity. These fibers are not in mat form or of "infinite" length. Instead they are cut relatively short so that the filled plastic will readily flow under the high temperature and pressure of the injection molding process.
In the case of blocks, a relatively thin block with a series of reinforcing ribs can be made. The ribs as well as providing rigidity and strength to the block also act as heat transfer fins. Good heat transfer properties are required when lenses are mounted on the blocks using low melting point alloys as it is necessary to transfer heat out of the alloy rapidly. This permits the alloy to solidify quickly, avoids harmful distortion of the lens blank, and allows the lens to be processed rapidly. Carbon fiber filled plastics are 2 to 5 times more thermally conductive than comparable materials filled with glass fiber, and 3 to 7 times more thermally conductive than unfilled plastics.
Thermal conductivity as used herein is defined as the rate thermal energy (heat) is transferred through a given material at a standard thickness in a unit time over a unit area and at unit temperature differential. For example, the thermal conductivity of an unfilled polybutylene terephthalate polymer (PBT) is reported as 1.1 BTU-in/hr-ft²-°F. A 40% glass filled PBT has a conductivity of 1.5; a 40% carbon fiber filled PBT has a conductivity of 3.5; and a 40% carbon fiber filled polyamide (nylon 6-6) has a conductivity of 8.0 BTU-in/hr-ft²-°F.
While carbon black, for example, will increase thermal conductivity of an organic plastic, carbon fiber is unique in producing the highest possible levels of thermal conductivity for an all-organic matrix, while yielding extremely high strength to weight ratios.
Generally, the higher the content of carbon fiber reinforcement, the higher the thermal conductivity of the plastic material. Carbon fiber content is advantageously as high as possible to obtain the highest thermal conductivity. At very high carbon fiber content, however, other physical properties are adversely affected, such as tensile strength, etc. Maintenance of these other physical properties dictates the upper limit to carbon fiber content.
The use of a plastic material for the lens block makes it simpler to fit a metal finishing center into the block. These are inverted cones into which the pins of a fining and polishing machine can fit. Such centers have been simply "press fitted" in the past. The centers for use with the blocks of the present invention have a serrated central portion which fits within the body of the plastic block. The steel center is ultrasonically vibrated as it is driven into the block and plastic material melts and flows around the steel center and holds it in place without stress or distortion. The invention also includes a block for holding lens blanks during processing, made from a carbon fiber reinforced crystalline thermoplastic material containing at least 30% by weight of carbon fiber, and having a minimum tensile strength of 20,000 psi, a minimum flexural strength of 2 x 10⁴ psi, a minimum flexural modulus of 20,000^psi, and a minimum compressive strength of 20,000 psi.
The invention further includes a block which is made from a carbon fiber crystalline thermoplastic material as described above, but which is provided with a metal finishing center which has been fixed in the block using ultrasonic or other rapid heating means.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which like numerals designate like elements, and in which:

Figure 1 is a rear view of a lens block according to the present invention;
Figure 2 is a side view of the lens block of Figure 1;
Figure 3 is a sectional view taken along the line 3-3 in Figure 1;
Figure 4 is a sectional view taken along the line 4-4 in Figure 1;
Figure 5 is an end view of a finishing center according to the present invention;
Figure 6 is a longitudinal sectional view through the finishing center of Figure 5;
Figure 7 is an end view of a cylinder-type prism ring in accordance with the present invention;
Figure 8 is a longitudinal sectional view through the prism ring of Figure 7, with a lens block depicted in phantom;
Figure 9 is an end view of a shim-type prism ring according to the present invention; and
Figure 10 is a longitudinal sectional view through the prism ring of Figure 9.

Depicted in the drawing are lens block and prism ring components for use in the manufacture of a finished or partly finished ophthalmic lens. The lens block 10, which will be described in connection with FIGS. 1-4 is of a novel shape, whereas the prism rings 60, 80 disclosed in connection with FIGS. 7-10, are of conventional shapes.
The lens block 10, which is injection molded of a plastic material to be hereinafter described, includes a concave front surface 12 bordered by a circular peripheral edge 14, and a back surface 16 which comprises a series of ribs and recesses. In particular, a plurality of generally radially oriented outer ribs 18 extends around the outer periphery of the back surface. The outer ribs 18 are circumferentially spaced apart to form outer recesses 20 therebetween. A circular annular rim 22 extends around the outer periphery of the back surface and interconnects the radially outer ends of the outer ribs 18. An alloy cavity 23 is defined in the front surface 12 by the annular rim 22. The depth of the cavity 23 is determined by the height of the rim 22. In general the alloy cavity is no more than about 2 mm in depth and is preferably at least about 1 mm in depth. Each outer rib 18 includes circumferentially facing surfaces 24 interconnected by an edge 26 which faces rearwardly and outwardly. Radially inner ends of the outer ribs 18 are joined to a first cylindrical projection 28, the latter being joined by a radial step 30 to a second cylindrical projection 32. The second projection includes a series of large recesses 34 and small recesses 36 which serve to reduce the weight of the block 10. Disposed between recesses 34, 36 is a network of inner ribs 40 which, like the outer ribs 18, serve to reinforce the block.
Extending forwardly through a thickest one 40 of the inner ribs is a through-hole 41 which passes completely through the block and thus through the concave front surface 12. That through-hole 41 conducts conventional molten alloy into a space defined between the front surface 12 and a lens when the lens is seated on the block. Upon hardening, the molten alloy adheres the lens to the block in the usual manner.
Extending partially through the network of inner ribs are three cylindrical holes 42 whose axes lie in a common plane bisecting the block. Those holes are formed at the time of forming the block and are sized to receive metal finishing centers 44 once the block has hardened. The finishing centers include pointed radial projections 46 which define a serrated cross section. Installation of the finishing centers 44 is performed by driving the centers 44 into respective holes 42 while the centers are ultrasonically vibrated by conventional vibrating equipment. As a result, a plastic material of which the block is formed is caused to melt and flow against the centers and between the projections 46 to secure the centers in place. Hence, the stresses imposed upon conventional centers upon being press fit into conventional metal blocks is avoided.
In another embodiment of the invention the cylindrical holes 42 are formed to be throughbores between the front and rear surfaces of the block. Such an arrangement enables the centers 44 to be easily removed when necessary by allowing the centers to be forced out of the throughbore towards the rear surface of the block. Once removed a new center can be inserted into the throughbore and ultrasonics are not required for this insertion.
It is not essential that the centers 44 are metallic. Centers formed from plastic are also suitable.
Turning now to the prism rings 60, 80, it is again pointed out that those rings are of conventional shape. Two types of prism rings are depicted, namely, a cylinder-type prism ring 60 depicted in FIGS. 7 and 8, and a shim-type prism ring 80 depicted in FIGS. 9 and 10.
The cylinder-type prism ring comprises a generally cylindrical section 62 which extends from an end section 64 of reduced inner diameter to form a seat 66. An opposite end 68 of the prism ring 60 lies in a plane 70 oriented non-perpendicularly to the longitudinal axis L of the cylindrical section 62.
The prism ring 60 is initially formed wherein the end 72 thereof lies in a plane perpendicular to the axis L (as shown in phantom in FIG. 8), and then the ring is machined to form the inclined end 68.
The prism 60 is utilized in combination with a conventional type of metal lens block B (shown in phantom in FIG. 8). A lens (not shown) is positioned on the block prior to the introduction of the metal alloy through the block B. The alloy thus adheres the lens to the block. The inclined end 68 of the prism ring is positioned over the block and alloy whereby the lens will be oriented in a proper position when the unit comprised of the lens, prism ring, and block is mounted against the chuck of a grinding machine.
The shim-type prism ring 80 is in the form of a wedge-shaped washer which is initially formed with both of its ends 82, 84 oriented perpendicular to the axis L. Thereafter, one of the ends 82 is machined to become inclined relative to the axis L.
The prism ring 80 is utilized as a shim when a blocked lens is being mounted on a grinding machine. That is, the prism ring 80 is placed between the shoulder of the larger style block and the surface of the chuck of the grinding machine in order to achieve a proper positioning of the lens.
Blocks so utilized with the carbon fiber filled prism rings can be the conventional steel 43 mm blocks and conventional 55, 63 or 68 mm aluminum blocks as described above, as well as carbon fiber filled crystalline thermoplastic 43, 55, 63, 68 or other sized blocks as also described above.
The crystalline thermoplastic polymeric materials useful in the invention include various polyesters, such as polybutylene and polyethylene terephthalate, polyphenylene sulphide, polyamides, polyamideimides, and polyetherketones. Preferred are the various polyamides and polybutylene terephthalate. The polyesters can be produced from aliphatic or aromatic dicarboxylic acids, and/or aliphatic or aromatic diols. Suitable aliphatic dicarboxylic acids and diols are those having from 2 to 10 carbon atoms. Useful aromatic polyesters are those formed from aromatic dicarboxylic acids and/or aromatic diols having from 8 to 20 carbon atoms. In addition to those mentioned above, examples include various naphthalene-based polyesters. A given polyester polymer can contain both aliphatic and aromatic monomeric components.
Of the polyamides, both aliphatic and aromatic polyamides can be used. Examples of aliphatic polymers include nylon 6, nylon 6-6 and nylon 6-12. Examples of aromatic polyamides include the various polyaramides such as Trogamide^R, a polyterephthalamide with a methyl substituted hexamethylenediamine.
Other thermoplastic polymers, such as polyacetals, can also be used provided that the physical properties of the compositions meet the requirements of the invention.
Table 1 summarizes the physical properties of representative materials, and their properties, useful in the invention. Table 2 summarizes the physical properties of materials that possess inadequate performance.
As can be seen by a comparison of Tables 1 and 2, the physical properties of carbon filled materials are superior to those of glass filled. For example, using polybutylene terephthalate (PBT), the tensile strength for materials with 30% carbon fiber is 25,000 psi, versus 17,300 psi for 30% glass filled PBT, the flexural strength is 40,000 psi versus 27,500 psi for 30% glass filled, and the thermal conductivity is 3.2 BTU-in/hr-ft²-°F versus 1.3 for 30% glass filled.
Comparable results are also achieved with nylon 6-6 and PPS.
The following examples illustrate the invention.

EXAMPLES 1-3 AND COMPARATIVE EXAMPLES 1-7

Lens blocks were prepared according to the invention as well as according to prior art techniques. In each case, the block was 68 mm in diameter. Both the design of the lens block and the compositions of the block were varied. The design variations were fourfold. In a first variation, a block having a smooth external shape (obtained by forming the block via injection molding through a die) and a "stepped" cavity was tested (Comparative Examples 1 and 2). The depth of the alloy cavity was greater than 2 mm. This design requires a large amount of alloy to fill the cavity and provide contact with the lens.
In a second design variation, a block was formed by machining to simulate the external shape of an aluminum block (Comparative Example 3). The machining provided for a "step" in the external surface. In the alloy cavity, the internal "step" was eliminated, thereby reducing the volume of alloy required. This resulted in an uniform internal design whereby a gap of approximately 2 mm was maintained at all points adjacent the outer surface of the lens.
In a third design variation, a molded block having a smooth outer surface was combined with an uniform internal design (Comparative Examples 4, 5, 6 and Example 1). In all three of these variations, the block was "solid", with no ribbing. A fourth variation combined the smooth external shape and uniform internal design with the ribbing (Examples 2 and 3).
The composition of the blocks was varied by using either carbon fiber or glass fiber. The glass fiber was used alone or in combination with mineral filler or ZnO filler. Finally, an aluminum block was included as a reference (Comparative Example 7). The lens blanks attached to the blocks were standard convex six-base-curve CR-39^R semi-finished blanks and all of the blocks had a matching concave six-base-curve surface to mate with the lens.
A Coburn #95-A Blocker was used in all examples without the brass "water-ring" cooling device. Lenses were at room temperature (75-77°F) and blocks were either at room temperature or had been cooled in a freezer for one hour at -2°F. The molten alloy showed pot temperatures in the blocker of 119-122°F, while the temperature of the alloy in the stem was 122-123°F.
Two process times were noted and are summarized in Table 3. The first is the removal time and is the minimum time required for the alloy to harden sufficiently so the operator can remove the blocked lens from the blocker, set it aside, and allow it to cool unattended (maintain integrity and not leak). The second time is the total time required for the alloy to completely solidify as observed by the appearance change (phase change) of the alloy from shiny to dull.
In Comparative Examples 1 and 2 (solid block with an internally stepped design), the block material was glass/mineral and glass filled PBT. Removal times were 75 and 60 seconds respectively for a block at room temperature. The removal times were high at least partially due to the stepped design of the block which required long cooling times for cooling the large quantity of alloy required.
The effect on cooling time of eliminating the internal step and replacing it with an uniform design is shown by Comparative Examples 3-6. Removal times were reduced to 55-45 sec for the case of Comparative Examples 3, 4, and 5, and "30⁺" sec for Comparative Example 6. The term "30⁺" means that the alloy was still too soft for proper handling. The 50% glass/ZnO filled material of Comparative Example 6 was too weak to survive chucking in the generator and was not useful.
Example 1 also had a removal time of 30+ seconds but the time for complete solidification was considerably reduced compared to the PBT/Glass/ZnO composition of Comparative Example 6.
The combination of ribbing and uniform design produced the lowest removal times - 28 and 25 sec respectively for 40% carbon filled PBT and nylon 6-6 as shown in Examples 2 and 3. Comparison of Examples 2 and 3 with Example 1 shows the additional improvement realized using a thin, lightweight, ribbed block design.
By comparison, an aluminum block with an uniform design resulted in removal times of 15-30 sec. A removal time of 30 sec or less is considered optimum.
Pre-cooling of the block to -2°F greatly reduces both removal times and complete solidification times as shown in Table 3. Additional steps are required, however, which significantly add to the cost of making the lens. This data indicates that removed times of about 30 sec or less can be obtained only through extraordinary means with blocks manufactured in accordance with the prior art.
Edging blocks and adaptors can also be made of the carbon-reinforced thermoplastic materials of the invention. As with the prism rings described above, the edging blocks and adaptors may be of conventional design but benefit from being constructed of thermoplastic materials.
Although the present invention has been described in connection with preferred embodiments of the invention, it will be appreciated by those skilled in the art that additions, substitutions, modifications, and deletions not specifically described, may be without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

A component for use in the formation of a finished or semi-finished ophthalmic lens, said component having been formed from a carbon fiber reinforced crystalline thermoplastic material containing at least 30% by weight carbon fiber based on the total weight of the component.
A component according to Claim 1, wherein the crystalline thermoplastic material is selected from the group consisting of polyesters, polyamides, polyetherketones, polyphenylene sulphide, and polyamideimides.
A component according to Claim 2, wherein the thermoplastic material is carbon fiber reinforced polybutylene terephthalate or a polyamide.
A component according to any one of Claims 1 to 3, wherein the component is a prism ring.
A component according to any one of Claims 1 to 3, wherein the component is a lens block, said lens block comprising a front surface of concave shape and a rear surface, said front surface including an alloy cavity for adhering a lens to the front surface of the block by filling the cavity with liquid alloy and solidifying the alloy by cooling, said rear surface including a plurality of ribs which serve to reinforce the block and enhance heat removal therefrom, a plurality of holes and finishing centers disposed in said holes, said finishing centers including at least one outwardly extending projection embedded in said carbon fiber reinforced crystalline thermoplastic material.
A component according to Claim 5, wherein when the block is heated from room temperature to an elevated temperature by the liquid alloy in the alloy cavity, the heat removal from the block in a room temperature environment and in the absence of additional cooling means is sufficient to allow removal of a lens and lens block assembly from a blocker after no more than about 30 seconds.
A method of manufacturing a lens block for use in blocking an ophthalmic lens, comprising the steps of injection molding a body of carbon fiber reinforced crystalline thermoplastic material containing at least 30% by weight carbon fiber based on the total weight of the component, said body including a concave front surface and a rear surface having therein a plurality of holes, inserting finishing centers into respective ones of said holes while ultrasonically vibrating or heat-staking said centers whereby said material forming walls of said holes flows against said centers and between outward projections of said centers.