Process for the production of polyurethane lens

Details Process for the production of polyurethane lens Process for the production of polyurethane lens

1999-04-30

2001-08-14

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C528S065000, C528S073000, C528S081000, C528S085000, C351S159000, C252S582000, C264S001100, C523S303000

Reexamination Certificate

active

06274694

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the production of a polyurethane lens.
2. Description of the Prior Art
It is disclosed in JP-A-63-130614 that, in the production of a polyurethane lens by reacting a polyisocyanate compound with a polythiol compound, a tetrafunctional poly t hid compound such as pentaerythritol tetrakis(mercaptoacetate) or pentaerythritol tetrakis-(mercaptopropionate) is used in combination with a difunctional polythiol compound having two thiol groups, for example, for increasing the crosslinking degree. It is also known that the reaction rate of one polythiol compound with a polyisocyanate compound differs from that of another. As a method of producing a polyurethane lens free of an optical strain from these two or more polythiol compounds, generally, there is employed a polymerization method in which the polymerization conditions are suited to a polythiol compound having a higher reaction rate with a polyisocyanate compound, the initial polymerization temperature is set at a low temperature and the polymerization temperature is gradually increased with taking time.
However, in the above polymerization method in which the polymerization conditions are suited to a polythiol compound having a higher reaction rate with a polyisocyanate compound, the initial polymerization temperature is set at a low temperature and the polymerization temperature is gradually increased with taking time, there is a problem in that the polymerization takes a long period of time to make the production efficiency poor. Further, when a lens having a large central thickness and a large marginal thickness is produced, for example, from pentaerythritol tetrakis(mercaptoacetate) (to be referred to as PETMA., hereinafter) which has a high reaction rate with a polyisocyanate compound, the amount of PETMA increases, and the reaction heat generated by the reaction with a polyisocyanate compound increases. It is hence difficult to prevent the occurrence of an optical strain and striae by controlling the polymerization heat alone. There is therefore a disadvantage in that the yield of lenses per a polymerization furnace is limited in mass production.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above problems. It is an object of the present invention to provide a process for the production of a polyurethane lens, which serves to decrease the polymerization time for producing a polyurethane lens from a polyisocyanate compound and polythiol compounds and which permits the production of a lens free of an optical strain and striae with good producibility in producing plastic lens having a large central thickness and a large marginal thickness.
The above object and advantages of the present invention is achieved by a process for the production of a polyurethane lens, which comprises the following steps (a) and (b).
step (a): providing a polyisocyanate compound and two or more polythiol compounds which have different reaction rates with the polyisocyanate compound, and adding an alkyltin halide compound of the general formula (I),
(R
1
)
c
—Sn—X
4−c
  (I)
wherein R
1
is methyl, ethyl, propyl or butyl, X is a fluorine atom, a chlorine atom or a bromine atom and c is an integer of 1 to 3,
to the above polyisocyanate compound, and
step (b): after the above step (a), mixing the polyisocyanate compound and the two or more polythiol compounds together with the alkyltin halide compound of the general formula (I) to allow them to react, and obtaining a polyurethane lens.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be detailed hereinafter.
The process of the present invention comprises the steps (a) and (b). In the step (a), a polyisocyanate compound and two or more polythiol compounds which have different reaction rates with the polyisocyanate compound are provided, and an alkyltin halide compound of the general formula (I),
(R
1
)
c
—Sn—X
4−c
  (I)
wherein R
1
is methyl, ethyl, propyl or butyl, X is a fluorine atom, a chlorine atom or a bromine atom and c is an integer of 1 to 3,
is added to the above polyisocyanate compound.
In the above step (a), it is required to add the alkyltin halide compound of the general formula (I) to a polyisocyanate compound. The reason therefor is as follows. A polyurethane lens having a large central thickness and a large marginal thickness has an optical strain when the alkyltin halide compound of the general formula (I) is added to a mixture of a polyisocyanate compound with polythiol compounds, while the above problem can be overcome when the alkyltin halide compound is added to a polyisocyanate compound before the polyisocyanate compound is mixed with polythiol compounds. Further, an alkyltin halide compound has poor solubility in a polythiol compound, while the alkyltin halide compound is easily soluble in a polyisocyanate compound. Therefore, the working is facilitated.
The polyisocyanate compound used in the step (a) is not specially limited. It can be properly selected from polyisocyanate compounds disclosed in JP-A-60-199016, JP-A-57-136601, JP-A-63-46213 and JP-A-1-302202.
Specific examples of the polyisocyanate compound include polyisocyanate compounds such as hexamethylene diisocyanate, isophorone diisocyanate, bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane diisocyanate, cyclohexane diisocyanate, bis(isocyanatomethyl)bicycloheptane, xylylene diisocyanate, tetramethylxylylene diisocyanate, lysine ester triisocyanate, tris(isocyanatomethyl)cyclohexane, mesitylene triisocyanate, bicycloheptane triisocyanate and hexamethylene triisocyanate; allophanate-modified products, buret-modified products and isocyanurate-modified products thereof; and adducts thereof with polyols or polythiols. These polyisocyanate compounds may be used alone or in combination. Other known isocyanate compounds may be used, while the isocyanate compound as a main component is required to be difunctional or higher. Halogen atoms such as Cl or Br may be introduced into a known aliphatic isocyanate compound having an aromatic ring in its molecule. As the polyisocyanate compound, particularly preferred are bis(isocyanatomethyl)cyclohexane, bis(isocyanatomethyl)bicycloheptane and xylylene diisocyanate and mesitylene triisocyanate.
Examples of the combination of the two or more polythiol compounds used in the present invention are as follows.
(i) A combination of a polythiol compound (S
1
) which is disclosed in JP-A-60-199016 and known to have a high reaction rate with a polyisocyanate compound, with a polythiol compound (S
2
) which is disclosed in JP-A-63-46213 and known to have a relatively moderate reaction rate with a polyisocyanate compound.
The above, polythiol compound (S
1
) includes ethylene glycol dithioglycolate, trimethylolpropane tris(thioglycolate) and pentaerythritol tetrakis(thiolycolate).
The above polythlol compound (S
2
) includes pentaerythritol tetrakis(mercaptopropionate). trimethylolpropane tris(mercaptopropionate), trimethylolethane tris(mercaptopropionate), dichioroneopentyl glycol bis(mercaptopropionate) and dibromoneopentyl glycol bis(mercaptopropionate).
(ii) A combination of the polythiol compound (S
3
) of the general formula (II)
(R
1
)
a
—C(CH
2
OCOCH
2
SH)
b
  (II)
wherein R
1
is methyl or ethyl, a is an integer of 0 or 1, b is an integer of 3 or 4, and a+b=4, or the formula (III),
with a polythiol compound (S
4
) which is disclosed in JP-A-3-236386 and has a relatively moderate reaction rate with a polyisocyanate compound.
The compound (S
3
) which has the general formula (II) includes trimethylolpropane tris-(mercaptoacetate), trimethylolethane tris(mercaproacetate) and pentaerythritol tetrakis(mercaptoacetate).
The compound (S
3
) which has the general formula (III) is dipentaerythritol hexakis-(mercaptoacetate).
The compound (S
4
) includes dimercaptomethyldithian.
The amount ratio of the two or more polythiol compounds which have different reaction rates with a polyisocyanate co

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