WO2007088556A1

WO2007088556A1 - An improved lens of diethyleνε glycol bis allyl carbonate cr-39 and a process for preparation thereof

Info

Publication number: WO2007088556A1
Application number: PCT/IN2006/000159
Authority: WO
Inventors: Rakesh Kumar Khandal; Geeta Seshadri; Gourishanker Jha
Original assignee: Shriram Institute For Industrial Research
Priority date: 2006-01-31
Filing date: 2006-05-10
Publication date: 2007-08-09
Also published as: CN101180553A; CN101180553B

Abstract

An improved lens comprising CR-39 and polytoiol in the ratio of 30-50% of CR-39, 70-50% of polythiol and total weight of TDI and CR-39 is 25-50% by weight of the total material and wherein CR-39, Polythiol and TDI is present preferably in the ratio of 31-32%, 31-32% and 36-38% respectively wherein the Refractive Index of the lens is in the order of 1.59-1.65.

Description

TITLE

An improved lens of diethylene glycol bis aliyl carbonate CR-39 and a process for preparation thereof.

FIELD OF INVENTION

This invention relates to an improved lens of diethylene glycol bis aliyl carbonate CR-39 and a proems for preparation thereof

BACKGROUND OF INVENTION

Plastic lenses are classified based on their refractive index, and the refractive index defines the power of the leas. Thus, if a lens having a low refractive index is used for a higher power, the lens would need to be of substandard thickness, which adds discomfort to a wearer due to the weight of such a lens. In swell aa instance, it is preferable louse a lens having a high refractive index.

Hitherto. lenses having a high refractive index of 1.6 and above is normally made from a polythiol. The process consisted the first preparing a dioi from mercaptσih, efhanσl and epichlorohydrin in the presence of triethylaumine as a catalyst. The ratio of the catalyst raid active ingredients was 1:1 and the reaction is carried out at a temperature of above 40°C. The did is then reacted with anhydrous sodium sulphide to give a tetrol, The tetro 1 is reacted with thiourea and concentrated hydrochloric and for a period of 9 hours at 12O⁰C to produce a salt of isothiouroniu, such a salt is reacted with ammonia in toluene as a solvent to produce poly thiol.

Several disadvantages are associated with such a knows process. One suoh distinct disadvantage is that of km yields. Yet another disadvantage is that the yield, even though low, is obtained at high temperature, A further disadvantage is the time of synthesis.

The p Q Iy thiol prepared is such a manner has been used to improve the refractive index of a low refractive index regin, diethylene glycol bis allyl carbonate Le CR-39.

Even though CR-39 has very good properties of clarity, in adi in ability and dy ©ability, it is characterized by a low refractive index ie 1.49,

As such process for preparation of lens is known in art which employs polym erization of CR-39 resin, in the presence of DiisoPropyl peroxide (DIPP) for a time period of 17-20 hours, which is time consuming. Further, the catalyst (DIPP) being sensitive to temperature has to be stored at low temperature. OBJECT OF THE INVENTION

An object of this invention is to prepare a lens of CS-39 with high refractive index of less than 1.60 and a process for preparation thereof, which has good optical properties.

Another object of this invention is to propose an improved lens and a process for preparation thereof, which is less time consuming than the time required for CR-39,

Still another object of this invention is to propose an improved lens and a process for preparation thereof, which is cost effective.

Yet another object of this invention is to propose a process for the tailor making of refractive index,

Further object of this invention is to propose an improved lens and a process for preparation thereof, which can be conducted at room temperature.

STATEMENT QF INVENTION

According to this invention there is provided an improved lens comprising CR-39 and polythiol in the ratio of 30-50% of CR-39, 70-50% of polythiol and total weight of TDI and CR-39 is 25-50% by weight of the total material and wherein CR-39_? Polytfiiol and TDI is present preferably in the ratio of 31-32%, 31-32% and 36-38% respectively wherein the Refractive Index of the lens is in the order of 1.55-1.65.

Further acϋording to this invention there is provided a process for preparation of an improved lens comprising the steps of;-

degassing of p o lyth io 1 m ised with a catalyst, mixing of CR-39 with the polythiol obtained by the first etep, addition of Toluene diisoeynate (TDI) followed by degassing so as to obtain a mixture for lens, pouring of the mixture into a m ould, heating of the mould followed by curing.

DETAIL DESCRIPTION OF THE INVENTION

In accordance with the present invention, polythiol is mixed with 0.04- 0.06% of a catalyst which is Bibuiyl Tin dilaurate (DBTDL). The polythiol imparts good optical properties to the lens produced therefrom, The m ixture thus obtained by the first step is subjected to the step of degassing at a temperature of 60-80⁰C and pressure of 1-5 mm of Hg for a tim e period of 0,5-3 hours followed by cooling to a temperature of 20-3θ°C, This is followed by addition of CR-39 with poly thiol and in a ratio of 40:60 to 60:40 at a temperature of 25-6O⁰C and pressure of 1 mm -5mm Hg for 5 fflinutes-i hour with stirring. Thereafter, Toulene diisocynatβ is added in an am ount of 25-50%, which is degassed under the pressure of 1-5 mm Hg for 10-40 m inutes so as obtain the required mixture for lens. The same is poured into a mould made of₅ for example, stainless stell and glass which is kept in an oven maintained at a temperature of 40-80⁰C for a time period of 5-14 hours, After removal from the oven, the m ould is cured in the oven at a temperature of 40-80°C for a tim e period of 3-6 hours.

The p o Iy thiol used in the present invention m ay be prepared by the process of our eopendiπg patent application no.2342/Del/2GG4 and comprising in the first step of the preparation of the diol. However, in the preparation of the diol in accordance with the aforesaid patent application, the reactant epichiorohydrin is added dropwise to mereapto ethanol in the presence of a catalyst so as to main tain the reaotion mixture at room temperature. However, depending upon the catalyst, the reaction mixture may be heated at 2O⁰C to 50⁰C. Preferably the ratio of more apto ethanol to epichiorohydrin is 1:1 to 1:1.5, The catalyst is selected from trbthaiiolam ine. Epichiorohydrin is added to ethanol such that,, the reaction mixture is maintained at a temperature of 2O⁰C to 35⁰C. Heating of the reaction may be carried at 35⁰C for half hour, if necessary. The diol produced by the first step is subjected to a second step to produce tetrol. Thus, diol is reacted with solution of sodium sulphide. It has been found that sodium sulphide ia a hydrate form in distinction to an anhydrous form of the known art has definite advantages. Hydrated sodium sulphide helpg in the reaction as the reaction is quicker. Sodium sulphide is added dropwise and the temperature is maintained at 20 to 5O⁰C. The reaction is completed within 1 to 1 V₂ hours in comparison to 3 hours of the known art.

The third step consists in reacting tetrol with hydrochloric acid at 90 tQ IDO⁰C for 9 to 12 hours for the formation of isothiouronium salt.

Finally the salt of isothiouronium is reacted with amm onia in toluene to produce polythiols.

The lens produced by the process described herein above comprises CR-39 and polythiol in the ratio of 30-50% of CR-39, 70-50% of polythiol and total weight of TDΪ and CR-39 is 25-50% by weight of the total material and wherein CR-39, Polythiol and TDI is present preferably in the ratio of 31- 32%, 31-32% and 36-38% respectively. The lens of the present invention was subjected to property evaluation,, which generated the following:

Refractive index is in the order of 1.59 to 1.65 in comparison to the low Refractive Index of CR-39 of 1.49 Tran sm ittaii ce is 90-93%

Resistant to impact

Go o d m ach in ab ility an d dy eab ility .

Further, it is to be noted that, the lens is upto FDA standards.

The invention will now be illustrated with respect to an example which is intended to be an illustrative specific example and is not intended to be taken restrictively to imply any limitation on the scope of the present invention,

EXAMPLE

For the preparation of lens, 7 gm of polythiol is mixed with 0.04 gm of DBTDL₅ which is degassed at a temperature of 6O⁰C and pressure of 2 mm Hg for 1 hours. The sam e is cooled to room temperature Le 3O⁰C, which is added with 3 gra of CR-39 and subjected to a step of degassing at a temperature of 3O⁰C and pressure of 2 mm Hg for 10 m inutes. To this 8 gm of TDI is added, which is further degassed for 10 minutes at a temperature of 25⁰C and pressure of 2 nm Hg.

The mixture thus obtained is injected into glass blanks fitted in a rubber gasket. The blank filled with the mixture is placed in a hot air oven at 5O⁰C for 12 hours. Thereafter, the same is rem oved for curing in the sam e oven for 3 hours. It is to be understood that the present invention is susceptible to m odification, changes, adaptations by those skilled in the art. Such modification Sj changes and adaptations are intended to be within the scope of the present invention, which is further set forth under the following claims:

Claims

WE CLAIM;

L An improved lens comprising CR-39 and polythiol in the ratio of 30-50% of CR-39, 70-50% of polythiol and total weight of TDI and CR-39 is 25-50% by weight of the total material and wherein CR-39, Polythiol and TDI is present preferably in the ratio of 31- 32%, 31-32% and 36-38% respectively wherein the Refractive Index of the lens is in the order of 1,59-1,65.

2. An improved lens as claimed in claim 1 wherein CR-39 is present preferably in the amount of 32% by wt, polythiol is present preferably in the amount of 32% by wt. and Toluene diisocynate (TDI) is present preferably in the am ount of 36% by wt.

3. A process for preparation of an improved lens comprising the steps of: degassing of polythiol mixed with a catalyst, mixing of CR-39 with the polythiol obtained by first step, addition of Toluene diisocynate (TDI) followed by degasiiπg so as to obtain a m ixture for lens. pouring of the mixture into a mould, heating of the mould followed by curing.

4. The process as claim ed in claim 3 wherein the polythiol is prepared by a process comprising in the steps of:-

(a) preparing a diol from ethanol and epichlorohydrin at 20° to 4O⁰C in the presence of a catalyst wherein the ratio between ethanol and epichlorohydrin is 1:1 to 1:1.5. (b)reactiπg the diol with a solution of sodium sulphide to obtain a tetrol, (e) preparing a salt of isothiouronium by reacting the tetrol with liydroϋhlorio acid and thiurea. (d) reacting the salt with amm onia in solution to obtain the p o Iy thiol.

5. The process as claimed in claim 3 and 4 wherein the degassing is carried out at a temperature of (SO-SO⁰C and pressure of 1-5 mm Hg for 0,5-3hours.

6. The process as claimed in any of the preceding claims wherein the catalyst is Dibutyl Tin dilayrate (DBTDL)₃ which is 0.04-0.06% in amount.

7. The process as claimed in any of the preceding claims wherein the ratio between CR39 and ploythioi is 30:70 to 60:40.

8. The process as claimed in any of the preceding claim s wherein Toluene diisocyπate is 25-50% and further degassing is done at a pressure of l-3mm Hg for 10-40 m inutes.

9. The process as claimed in any of the preceding claims wherein the m oulded mixture is heated at a temperature of 40-SO⁰C for a tim e period of 5-14 hours,

10. The process as claimed in any of the preceding claims wherein curing is performed at a temperature of 40-80⁰C for 3-6 hours,