A UV-curable resin composition, which comprises blending urethane acrylate with tris(2-acryloxyethyl)isocyanurate, or with tris(2-acryloxyethyl)isocyanurate and with diacrylate, which composition has a low viscosity and a good drawing workability before curing and cures rapidly by ultraviolet radiation to give cured products having a high elastic modulus, a high elongation and a low water-absorption.

BACKGROUND OF THE INVENTION 
The present invention relates to ultraviolet rays (UV)-curable resin 
compositions, which provide cured products having high elastic moduli, 
high elongations, low water-absorption and low viscosities. These 
UV-curable resin compositions are utilized as coating material and are 
especially effective as secondary coating material for optical fibers. 
Optical fibers are in general subjected to coating with resin along with 
the drawing operation, since possible minute defects on the surface of 
fibers may give rise to a drop in the intensity of light. The coating 
generally comprises two layers, consisting of a primary coating material 
having a lower modulus for direct protection of the surface of fibers and 
a secondary coating material having a higher modulus to render strengths 
to fibers. Furthermore, UV-curable resins have increasingly been utilized 
in recent years as coating material for increasing drawing speed to 
improve productivity. 
Among other properties required for the secondary coating materials, 
appropriate elastic modulus and elongation are required in order to 
maintain mechanical strengths, thereby preventing increase in optical 
transmission loss due to microbending. In addition, from the viewpoint of 
preventing humidity and water, they are required to have a low 
water-absorption. Furthermore, to increase drawing speed at processing 
operation, thereby improving productivity, a high curing rate is required. 
Hitherto, as the secondary coating material for optical fiber, such 
materials which have elastic modulus of more than 10 kg/mm.sup.2 and 
elongations of more than 10% have been used to maintain mechanical 
strengths and to prevent increase in optical transmission loss due to 
microbending. Further, to maintain water-resisting and humidity-resisting 
properties, materials having a water-absorption of less than 4% are used. 
Furthermore, for the purpose of improving productivity by drawing optical 
fibers at high speeds, materials which have viscosities less than 15000 
cps at normal temperature (25.degree. C.) are preferably used so far. 
However, these coating materials have some defects. For example, some of 
them have higher water-absorptions, though elastic moduli thereof are 
satisfactory, and the other ones have satisfactory elastic moduli and 
elongations, but viscosities thereof are high and furthermore curing rates 
are slow. There have been no materials which satisfy all of these 
characteristic properties properly. 
Furthermore, the secondary coating layer becomes thinner as the diameters 
of optical fibers are reduced step by step, and therefore coating 
materials which have higher elastic moduli and elongations, sufficient 
toughness and well-balanced properties are required. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide UV-curable resin compositions, 
which have higher elastic moduli, higher elongations, lower 
water-absorptions and lower viscosities, and which cure rapidly, and is 
particularly to provide UV-curable resin compositions, which have 
especially higher elastic moduli, higher elongations, sufficient toughness 
and well-balanced properties. These compositions are particularly used 
efficiently as secondary coating material for optical fibers. 
To attain this object, the present invention provides a UV-curable resin 
composition which comprises blending 100 parts by weight of a urethane 
acrylate, which has been prepared by reacting hydrogenated 
4,4'-diphenylmethane diisocyanate (4,4,'-dicyclohexylmethane diisocyanate) 
with both ends of polytetramethylene glycol having a molecular weight of 
650-1300 and then reacting the reaction product with a compound having a 
hydroxyl group and an acryloyl group in one molecule, with 10-140 parts by 
weight of a compound having the below-mentioned formula (1) or of a 
compound having the formula (1) and a compound having the below-mentioned 
formula (2) (hereinafter referred to as Composition A). 
The gist of the invention resides also in a UV-curable resin composition 
which comprises blending 100 parts by weight of a urethane acrylate, which 
has been prepared by reacting hydrogenated 4,4'-diphenylmethane 
diisocyanate with both ends of polytetramethylene glycol having a 
molecular weight of 650-1300 and then reacting the reaction product with a 
compound having a hydroxyl group and an acryloyl group in one molecule, 
with 10-140 parts by weight of a compound having the formula (1) or of a 
compound having the formula (1) and a compound having the formula (2), and 
further with 1-40 parts by weight of N-vinylpyrrolidone (hereinafter 
referred to as Composition B). 
In addition, the gist of the invention resides in a UV-curable resin 
composition which comprises blending 100 parts by weight of a urethane 
acrylate, which has been prepared by reacting hydrogenated 
4,4'-diphenylmethane diisocyanate with both ends of polytetramethylene 
glycol having a molecular weight of 650-1300 and then reacting the 
reaction product with a compound having a hydroxyl group and an acryloyl 
group in one molecule, with 10-140 parts by weight of a compound having 
the formula (1) or of a compound having the formula (1) and a compound 
having the formula (2), and further with 1-40 parts by weight of one or 
more of acryloyl morpholine and dicyclopentanyl acrylate (hereinafter 
referred to as Composition C). 
Furthermore, the gist of the invention resides in a UV-curable resin 
composition which comprises blending 100 parts by weight of a urethane 
acrylate, which has been prepared by reacting hydrogenated 
4,4'-diphenylmethane diisocyanate with both ends of polytetramethylene 
glycol having a molecular weight of 650-1300 and then reacting the 
reaction product with a compound having a hydroxyl group and an acryloyl 
group in one molecule, with 10-140 parts by weight of a compound having 
the formula (1) or of a compound having the formula (1) and a compound 
having the formula (2), with 1-40 parts by weight of one or more of 
acryloyl morpholine and dicyclopentanyl acrylate, and further with 1-40 
parts by weight of N-vinylpyrrolidone (hereinafter referred to as 
Composition D). 
##STR1## 
The above and other related objects and features of the invention will be 
apparent from a reading of the following description of the disclosure.

THE PREFERRED EMBODIMENTS 
(A) Composition A. 
(a) Urethane acrylate. 
This is an acrylic oligomer obtained by reacting hydrogenated 
4,4'-diphenylmethane diisocyanate (hydrogenated MDI) with both ends of 
polytetramethylene glycol (molecular weight 650-1300) and then reacting 
the reaction product with a compound having a hydroxyl group and an 
acryloyl group in one molecule. Here, by compounds having a hydroxyl group 
and an acryloyl group in one molecule are meant those compounds such as 
2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate. As examples of 
isocyanate compounds, mention is made of MDI (diphenylmethane 
diisocyanate), TDI (tolylene diisocyanate), IPDI (isophorone 
diisocyanate), HDI (hexamethylene diisocyanate), hydrogenated MDI and the 
like. In the present invention, hydrogenated MDI is used since it is most 
preferable for obtaining compositions which cure rapidly. 
Among glycol components such as polyester glycol and polypropylene glycol, 
polytetramethylene glycol is used in this invention for the purpose of 
improving water-resistant and heat-resistant properties in resulting 
compositions. As to molecular weights of the glycol, molecular weights 
between 650 and 1300 are preferred for affording sufficient elastic 
modulus and elongations to resulting compositions. With molecular weights 
less than 650, enough elongations can not be obtained, while with 
molecular weights over 1300, enough elastic modulus can not be attained. 
(b) Tris(2-acryloxyethyl)isocyanurate [aforementioned formula (1)], 
diacrylate [aforementioned formula (2)]. 
Of these compounds, use is made of compound (1) alone or of compound (1) 
and compound (2) in combination. The use of these compounds is important 
for cured products, which are obtained by curing the resulting composition 
with ultraviolet rays, to increase elastic modulus without changing 
elongations and to give a lower water-absorption. The proportion of said 
compounds is 10-140 parts by weight, preferably 30-100 parts by weight, to 
100 parts by weight of urethane acrylate. With a proportion less than 10 
parts by weight, elastic modulus of cured products become less than 10 
kg/mm.sup.2, whereas with a proportion over 140 parts by weight, the cured 
products show elongations less than 10%, resulting in poor mechanical 
properties which are necessary for the secondary coating on optical fiber. 
Furthermore, when both compounds are used, of 10-140 parts by weight of 
tris(2-acryloxyethyl)isocyanurate [formula (1)] and diacrylate [formula 
(2)], the proportion of diacrylate represented by the formula 2 should be 
less than 20 parts by weight. It is preferable for resin compositions to 
contain diacrylate represented by formula (2) of less than 20 parts by 
weight, in order to improve such properties as viscosity, crystallization 
and the like, although the compositions may contain no diacrylate. The 
upper limit of the diacrylate is 20 parts by weight, and beyond this 
limit, the resulting resin compositions cure very slowly and it is 
unfavorable. 
The use of these two types of acrylates is important to obtain cured 
products with a low water-absorption, since a high water-absorption 
renders the strength of optical fiber low. 
(B) Composition B. 
The above-mentioned Composition A is as such satisfactorily used for the 
secondary coating for optical fibers. However, to meet demand for higher 
drawing speeds of optical fibers and for improving productivity, the 
present invention makes it possible to increase curing rate of the resin 
compositions without altering other characteristic properties, by blending 
Composition A with N-vinylpyrrolidone. Thus, the invention also provides a 
UV-curable resin composition which comprises 100 parts by weight of 
urethane acrylate, 10-140 parts by weight of 
tris(2-acryloxyethyl)isocyanurate represented by the formula (1) alone or 
in combination with diacrylate represented by the formula (2) [provided 
that the diacrylate represented by the formula (2) is present in an amount 
of less than 20 parts by weight] and 1-40 parts by weight of 
N-vinylpyrrolidone. 
The bending proportion of N-vinylpyrrolidone is 1-40 parts by weight, 
preferably 3-20 parts by weight. With blending proportion less than one 
part by weight, no change is noticed in curing rate, and with blending 
proportion over 40 parts by weight, water-absorption becomes more than 4%, 
resulting in the cured products which are unfavorable as the secondary 
coating. In using N-vinylpyrrolidone, it is preferable to use it in 
combination with tris(2-acryloxyethyl)isocyanurate represented by the 
formula (1) and diacrylate represented by the formula (2), in order to 
keep a balance among characteristic properties such as elastic modulus, 
elongation, water-absorption and curing rate. This is especially important 
to keep water-absorption low. 
(C) Composition C. 
Composition A comprising the compounds (a) and (b) can be as such 
satisfactorily used as material for the secondary coating on optical 
fibers. However, there are demand for material having higher elastic 
modulus and higher elongations, in order to attain sufficient strength 
even in case of optical fibers with extremely fine diameter. 
To meet such requirements, the present invention makes it possible to 
obtain materials having higher elastic modulus and higher elongations 
without altering other characteristic properties, by blending the 
above-mentioned Composition A with one or more of acryloyl morpholine 
having the below-mentioned formula (i) and dicyclopentanyl acrylate having 
the below mentioned formula (ii) (concretely speaking, elastic modulus 
more than 60 kg/mm.sup.2, elongations more than 30%). 
##STR2## 
Thus, the invention also provides a UV-curable resin composition comprises 
100 parts by weight of urethane acrylate, 10-140 parts by weight of 
tris(2-acryloxyethyl)isocyanurate represented by the formula (1) alone or 
in combination with diacrylate represented by the formula (2) [provided 
that the diacrylate represented by the formula (2) is present in an amount 
of less than 20 parts by weight] and 1-40 parts by weight of one or more 
of acryloyl morpholine and dicyclopentanyl acrylate. 
The blending proportion of the acrylate(s) selected from the group of 
acryloyl morpholine and dicyclopentanyl acrylate is 1-40 parts by weight, 
preferably 3-20 parts by weight. The content of the acrylate less than one 
part by weight does not favorably affect the elastic modulus and if the 
content of the acrylate is more than 40 parts by weight, the cured 
products show a high water-absorption and this is unfavorable for the 
secondary coating on optical fiber. In using acryloyl morpholine and 
dicyclopentanyl acrylate, it is preferable to use them in combination with 
tris(2-acryloxyethyl)isocyanurate represented by the formula (1) and 
diacrylate represented by the formula (2), in order to keep a balance of 
characteristics such as higher elastic modulus, elongation, water 
absorption and curing rate. Especially, this is important to maintain a 
high elastic modulus (more than 60 kg/mm.sup.2) and a high elongation 
(more than 30%). 
(D) Composition D. 
Although the above-mentioned Composition C is as such satisfactorily usable 
as secondary coating material, it is required to have a lower viscosity 
when a further improvement in the drawing processability is desired. 
According to the invention, this problem is solved by blending the 
Composition C with N-vinylpyrrolidone. So, by blending Composition C with 
N-vinylpyrrolidone, it is possible to increase the curing rate without 
affording the other properties. By utilizing this characteristic feature, 
the addition of said compound to Composition C makes it possible to attain 
a lower viscosity without lowering the curing rate. This improves the 
drawing processability. 
The content of N-vinylpyrrolidone is 1-40 parts by weight. Thus, the 
invention also provides a UV-curable resin composition comprises 100 parts 
by weight urethane acrylate, 10-140 parts by weight of 
tris(2-acryloxyethyl)isocyanurate represented by the formula (1) alone or 
in combination with diacrylate represented by the formula (2) [provided 
that the content of the diacrylate represented by the formula (2) is less 
than 20 parts by weight, of 10-140 parts by weight], 1-40 parts by weight 
of one or more of acryloyl morphorine and dicyclopentanyl acrylate and 
further 1-40 parts by weight of N-vinylpyrrolidone. With the content of 
N-vinylpyrrolidone less than one part by weight, no effect is obtained and 
with the content more than 40 parts by weight, the cured product shows a 
higher water absorption and is unfavorable for the secondary coating on 
optical fiber. Furthermore, in using N-vinylpyrrolidone, it is preferable 
to use in combination with tris(2-acryloxyethyl)isocyanurate represented 
by the formula (1) and diacrylate represented by the formula (2), in order 
to keep a balance of characteristic properties such as elastic modulus, 
elongation, water absorption and curing rate. This is especially important 
for maintaining a high elastic modulus (more than 60 kg/mm.sup.2) and a 
high elongation (more than 30%). 
(E) For the compositions as mentioned above, a variety of reactive diluents 
can be blended with the compositions to adjust their viscosities and to 
improve their workabilities. As reactive diluents, various mono acrylates 
are used, which include 2-ethylhexyl acrylate, lauryl acrylate, 
2-hydroxyethyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 
2-butoxyethyl acrylate, 2-phenoxyethyl acrylate, dicyclopentanyl acrylate, 
dicyclopentanyloxyethyl acrylate, isobornyl acrylate, tetrahydrofurfuryl 
acrylate, phenoxydiethyleneglycol acrylate, and nonylphenoxyethyleneglycol 
acrylate. Especially, phenoxyethyl acrylate, isobornyl acrylate, 
phenoxydiethyleneglycol acrylate and dicyclopentanyloxyethyl acrylate. 
These can be alone or as a combination of two or more. The proportion of 
these monoacrylates is preferably less than 60 parts by weight per 100 
parts by weight of urethane acrylate for the purpose of not impairing 
characteristic properties such as elastic modulus, elongation, and 
water-absorption causing from urethane acrylate, 
tris(2-acryloxyethyl)isocyanulate and diacrylate of formula (2). 
Furthermore, a photopolymerization initiator is blended. Radical cleavage 
type, hydrogen-abstraction type and other any type of initiators can be 
used. For example, 2,2-dimethoxy-2-phenylacetophenone, 
1-hydroxycyclohexylphenyl ketone, benzoin, benzoin methyl ether, benzoin 
ethyl ether, benzoin isopropyl ether, 2-hydroxy-2-methylpropiophenone, 
benzil, benzophenone, 
2-methyl[4(methylthio)phenyl]-2-morpholino-1-propanone, 
2-methylanthraquinone, 2,4-diethylthioxanthone and the like are 
effectively used. The amount to be used less than 0.5-10% by weight, 
preferably less than 1-5% by weight. 
Furthermore, the compositions according to the present invention may 
contain various types of additives, such as antioxidants, polymerization 
inhibitors, levelling agents, antifoaming agents and the like. 
The UV-curable resin compositions according to the invention so obtained 
can cure more rapidly into a cured products having well-balanced 
characteristic properties, resulting in effective use as the secondary 
coating material on optical fiber. 
Hereinafter working examples and comparative examples are shown. 
EXAMPLES AND COMATIVE EXAMPLES: 
(I) The resin compositions were prepared by blending the below-mentioned 
compounds in the blending proportions (parts by weight) shown in Tables 1, 
2 and 3; 
1. Urethane acrylate of the formula (3): 
##STR3## 
2. Phenoxyethyl acrylate of the formula (4): 
##STR4## 
3. Tris (2-acryloxyethyl)isocyanurate of the formula (1): 
##STR5## 
4. Diacrylate of the formula (2): 
##STR6## 
The physical properties of the cured products were determined by curing the 
above-mentioned resin compositions by giving a predetermined energy from a 
UV lamp (80 W/cm.sup.2, 1 k.W metal halide lamp) and forming a sheet with 
a thickness of 200 .mu.m. The values of elastic modulus and elongation 
were determined in accordance with JIS K7113, using samples which were 
obtained by punching out with No. 2 plastics dumbbell from the sheet, 
which had been prepared by exposing the resin composition to ultraviolet 
rays of 1000 m J/cm.sup.2 energy. Curing velocities were determined by 
measuring elastic modulus for samples of sheets having a thickness of 200 
.mu.m which had been made by exposing said resin composition to 
ultraviolet rays of 100 m J/cm.sup.2 and 1000 m J/cm.sup.2, respectively, 
and by calculating the percentage of the modulus at 100 m J/cm.sup.2 as 
compared with the value of the modulus at 1000 m J/cm.sup.2 of 100%. 
Water-absorptions were determined in accordance with JIS K 7209B method, 
using sheets cured at 1000 m J/cm.sup.2. These results are shown in Tables 
1, 2 and 3. 
TABLE 1 
__________________________________________________________________________ 
Com- Com- Com- Com- Com- 
parative 
parative 
parative 
parative 
parative 
Example 
Example 
Example 
Example 
Example 
Example 
Example 
Example 
Example 
Example 
Example 
1 2 3 4 5 6 1 2 3 4 5 
__________________________________________________________________________ 
Urethane 
100 100 100 100 100 100 100.sup.(1) 
100.sup.(2) 
100.sup.(3) 
100 100 
acrylate 
Compound of 
20 40 60 80 100 120 40 40 40 5 150 
the formula 
(1) 
Phenoxyethyl 
30 35 40 45 50 55 35 35 35 26 63 
acrylate 
Photopoly- 
5 5 5 5 5 5 5 5 5 5 5 
merization 
initiator 
Elastic 14.3 35.1 46.3 55.6 58.0 65.0 34.7 32.0 32.5 5.2 77.0 
modulus 
(kg/mm.sup.2) 
Elongation 
55 45 33 28 24 15 47 45 45 58 9 
(%) 
Curing rate 
68 70 80 85 80 84 55 54 55 65 85 
(%) 
Water- 1.0 1.2 1.2 1.5 2.0 2.3 1.5 1.5 1.3 0.9 2.5 
absorption 
(%) 
__________________________________________________________________________ 
Notes: 
.sup.(1) PTMG850/MDI/2HEA 
.sup.(2) PTMG850/TDI/2HEA 
.sup.(3) PTMG850/IPDI/2HEA 
PTMG850 Polytetramethylene glycol (average molecular weight: 850) 
MDI Diphenylmethane diisocyanate 
TDI Tolylene diisocyanate 
IPDI Isophorone diisocyanate 
2HEA 2hydroxyethyl acrylate 
In Examples 1-6 and Comparative Examples 1, 2, 3, 4 and 5 on Table 1, 
elastic modulus, elongations, water absorption and curing velocities were 
determined, using resin compositions containing phenoxyethyl acrylate with 
a photopolymerization initiator dissolved therein in combination with 
predetermined amounts of tris(2-acryloxyethyl)isocyanurate and urethane 
acrylate. In Examples 1-6, elastic modulus and elongations are more than 
10 kg/mm.sup.2 and more than 10%, respectively. However, as is seen from 
Comparative Example 4, when the content of Compound (1) is less than 10 
parts by weight, elastic modulus obtained becomes less than 10 
kg/mm.sup.2. On the contrary, as is seen from Comparative Example 5, when 
the content of Compound (1) is over 140 parts by weight, elongations 
become less than 10%. These cases show that the resulting products are 
unsatisfactory as material for the secondary coating. 
In Comparative Example 1, a urethane acrylate is used, which has been 
obtained by reacting MDI (diphenylmethane diisocyanate) with both ends of 
polytetramethylene glycol (molecular weight 850) and then reacting the 
resulting product 2HEA (2-hydroxyethyl acrylate). 
In Comparative Examples 2 and 3, similarly, a urethane acrylate is used, 
which has been obtained by reacting TDI (tolylene diisocyanate) and IPDI 
(isophorone diisocyanate), respectively with both ends of 
polytetramethylene glycol and then reacting the resulting product with 
2HEA. As is seen from the comparison with Example 2, the curing velocities 
are slow in both cases, and this proves that hydrogenated MDI is most 
preferable as isocyanate. 
TABLE 2 
__________________________________________________________________________ 
Example 
Example 
Example 
Example 
Example 
Example 
Comparative 
Comparative 
7 8 9 10 11 12 Example 6 
Example 7 
__________________________________________________________________________ 
Urethane 100 100 100 100 100 100 100 .sup.(1) 100 
acrylate 
Compound of the 
5 20 40 60 80 120 30 35 
formula (1) 
Compound of the 
20 20 20 20 20 20 30 20 
formula (2) 
Phenoxyethyl 
31 35 40 45 50 60 40 30 
acrylate 
Photopoly- 
5 5 5 5 5 5 5 5 
merization 
initiator 
Elastic modulus 
18.0 30.1 43.4 50.1 66.5 72.0 41.3 35.5 
(kg/mm.sup.2) 
Elongation 
45 35 30 28 22 10 30 35 
(%) 
Curing rate 
70 75 80 82 82 85 60 53 
(%) 
water- 0.9 1.0 1.2 1.5 1.7 2.0 1.2 1.9 
absorption 
(%) 
__________________________________________________________________________ 
Note: 
.sup.(1) PTMG850/MDI/2HEA. 
In Table 2, in Examples 7-12 and Comparative Examples 6 and 7, using 
Compound (1) and Compound (2) similarly as in Table 1, urethane acrylate, 
phenoxyethyl acrylate and a photopolymerization initiator are mixed, and 
elastic modulus, elongations, water-absorption and curing velocity are 
determined. In Table 2, in Examples 7-12, wherein 20 parts by weight of 
diacrylate are used, elastic modulus of more than 10 kg/mm.sup.2 and 
elongations of more than 10%. However, as is shown in Comparative Example 
6, when 30 parts by weight of diacrylate represented by the formula (2) 
are used, the curing velocity becomes 60%, this is not favorable from the 
point view of curing velocity. In Comparative Example 7, urethane acrylate 
is used which has been obtained by reacting MDI (diphenylmethane 
diisocyanate) with both ends of polytetramethylene glycol (molecular 
weight 850) and then reacting 2-HEA (2-hydroxyethyl acrylate) with the 
resulting product. As is apparent from the comparison with Examples 8 and 
9, it is better to use urethane acrylate represented by the formula (3) in 
place of this urethane acrylate, for the purpose of speeding up of curing 
velocity. 
TABLE 3 
__________________________________________________________________________ 
Example 
Example 
Example 
Example 
Example 
Comparative 
13 14 15 16 17 Example 8 
__________________________________________________________________________ 
Urethane 
100 100 100 100 100 100 
acrylate 
Compound of 
50 50 50 50 50 50 
the formula 
(1) 
Compound of 
10 10 10 10 10 10 
the formula 
(2) 
Phenoxyethyl 
41 41 43 45 48 40 
acrylate 
N--vinyl- 
3 6 10 20 30 45 
pyrrolidone 
Photopoly- 
5 5 5 5 5 5 
merization 
initiator 
Elastic 46.8 48.6 50.9 57.5 63.9 68.0 
modulus 
(kg/mm.sup.2) 
Elongation 
30 30 30 35 33 36 
(%) 
Curing rate 
81 83 85 90 90 92 
(%) 
Water- 1.1 1.2 1.6 2.0 2.7 4.2 
absorption 
(%) 
__________________________________________________________________________ 
In Table 3, the components mixed in a similar method as in Tables 1 and 2 
were blended with N-vinylpyrrolidone in various proportions. As is seen 
from Examples 13-17, with elastic modulus of over 10 kg/mm.sup.2, 
elongations of over 10% and water-absorption of less than 4%, the curing 
velocity is also considerably rapid (more than 80%). As is shown in 
Comparative Example 8, when the content of N-vinylpyrrolidone is 45 parts 
by weight, water-absorption becomes over 4%, giving unfavorable results. 
FIG. 1 is a graph showing the relationship between blending proportions (in 
parts by weight) of the compound of the formula (1) or of the combination 
of the compound of the formula (1) with that of the formula (2) per 100 
parts by weight of urethane acrylate and elastic modulus and elongations. 
From FIG. 1, it is apparent that in order to attain elastic modulus of 
over 10 kg/mm.sup.2 and elongations of over 10%, it is preferable to use 
10-140 parts by weight of the compound (1) or a combination of the 
compound (1) and the compound (2) per 100 parts by weight of urethane 
acrylate. Further in FIG. 1, the reference character, a white circle (o) 
designates the case of the compound (1) and a black circle (.cndot.) the 
combination of the compounds (1) and (2). 
FIG. 2 is a graph showing the relationship between the proportions parts by 
weight of N-vinylpyrrolidone and the curing velocity and the 
water-absorption. From FIG. 2, it is apparent that, in order to attain 
curing velocity of over 80% and water-absorption of less than 4%, the 
addition of 1-40 parts by weight of N-vinylpyrrolidone to the blend which 
comprises 100 parts by weight of urethane acrylate and 10-140 parts by 
weight of the compound (1) alone or of the compounds (1) and (2) is 
preferable. 
Next, on an optical fiber, which had been spun up to 125 m.phi. at a 
drawing speed of 200 m/min, a UV-curable resin composition having a 
Young's modulus of 0.1 kg/mm.sup.2 was coated as the primary coating up to 
250 .mu.m.phi. and then cured by a metal halide lamp of 3 kW, and 
subsequently the resin composition according to Example 14 was coated up 
to 400 m.phi. and then cured by exposing to ultraviolet radiation by a 
metal halide lamp of 3 kW. An optical fiber obtained showed no increase in 
optical transmission loss and had a strength of 6 kg. Furthermore, the 
coated optical fiber showed no increase in optical transmission loss and 
no deterioration in strength, even after 60 days of 95% RH humidity-heat 
test at 60.degree. C. 
(II) Resin compositions were prepared by blending the below-mentioned 
compounds at the blending proportions (parts by weight) shown in Tables 4 
and 5: 
1. Urethane acrylate represented by the formula (3): 
##STR7## 
2. Phenoxyethyl acrylate represented by the formula (4): 
##STR8## 
3. Acryloyl morpholine represented by the formula (i): 
##STR9## 
4. Dicyclopentanyl acrylate represented by the formula (ii): 
##STR10## 
5. Tris (2-acryloxyethyl)isocyanurate represented by the formula (1): 
##STR11## 
6. Diacrylate represented by the formula (2): 
##STR12## 
The physical properties of the cured products were determined by curing the 
above-mentioned resin compositions by exposing to a predetermined energy 
from a UV lamp (80 W/cm.sup.2, 1 kW metal halide lamp), and forming a 
sheet with a thickness of 200 um. The values of elastic modulus and 
elongations were determined in accordance with JIS K7113, using samples 
which were obtained by punching out with No. 2 plastics dumbbell from the 
sheet, which had been prepared by exposing the resin composition to 
ultraviolet rays of 100 m J/cm.sup.2. Curing velocities were determined by 
measuring elastic modulus for samples of sheets with a thickness of 200 
.mu.m which had been made by exposing said resin composition to 
ultraviolet rays of 100 m J/cm.sup.2 and 1000 m J/cm.sup.2, respectively, 
and by calculating the percentage of the modulus at 100 m J/cm.sup.2 as 
compared with the value of the modulus at 1000 m J/cm.sup.2 of 100%. 
Water-absorptions were determined in accordance with JIS K7209B method, 
using sheets cured at 1000 m J/cm.sup.2. These results are shown in Tables 
4 and 5. 
TABLE 4 
__________________________________________________________________________ 
Com- Com- Com- Com- Com- 
Ex- 
Ex- 
Ex- 
Ex- 
Ex- 
Ex- 
Ex- 
Ex- 
Ex- 
Ex- 
parative 
parative 
parative 
parative 
parative 
am- 
am- 
am- 
am- 
am- 
am- 
am- 
am- 
am- 
am- 
Example 
Example 
Example 
Example 
Example 
ple 
ple 
ple 
ple 
ple 
ple 
ple 
ple 
ple 
ple 
9 10 11 12 13 
18 19 20 21 22 23 24 25 26 27 *A *B *C *A *A 
__________________________________________________________________________ 
Urethane 
100 
100 
100 
100 
100 
100 
100 
100 
100 
100 
100 100 100 100 100 
acrylate 
Compound of 
40 40 40 20 20 20 40 20 40 20 40 40 40 40 20 
the formula 
(1) 
Compound of 20 20 20 20 20 30 20 
the formula 
(2) 
Acryloyl 
35 20 35 20 35 35 35 35 35 
morpholine 
Dicyclo- 35 15 35 15 
pentanyl 
acrylate 
N--vinyl- 35 35 
pyrrolidone 
Phenoxyethyl 35 35 
acrylate 
Photopoly- 
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 
merization 
initiator 
Elastic 
68 70 68 70 71 70 35.1 
30.1 
54 58 67 68 68 70 70 
modulus 
(kg/mm.sup.2) 
Elongation 
38 37 37 37 37 37 45 35 40 35 37 37 37 37 37 
(%) 
Curing rate 
87 86 87 90 88 88 70 75 90 90 55 54 55 60 58 
(%) 
Water- 1.8 
1.8 
1.8 
1.7 
1.7 
1.7 
1.2 
1.0 
3.5 
3.2 
1.9 1.9 1.9 1.8 1.8 
absorption 
(%) 
__________________________________________________________________________ 
Note: 
(A) PTMG850/MDI/2HEA. 
(B) PTMG850/TDI/2HEA. 
(C) PTMG850/IPDI/2HEA. 
PTMG850: Polytetramethyleneglycol 
##STR13## 
MDI: Diphenylmethane diisocyanate 
TDI: Tolylene diisocyanate 
IPDI: Isophorone diisocyanate 
In Examples 18, 19 and 20 on Table 4, acryloyl morpholine and 
dicyclopentanyl acrylate were used. As is apparent from comparing with 
Example 24, when one or more than one of acryloyl morpholine and 
dicyclopentanyl acrylate are used, elastic modulus of more than 60 
kg/mm.sup.2 and elongations of more than 30% are attained in each case. 
As is seen from comparing with Example 25, Examples 21, 22 and 23, wherein 
the Compound (2) was used, show that even in these cases where acryloyl 
morpholine and dicyclopentanyl acrylate are used, elastic modulus are more 
than 69 kg/mm.sup.2 and elongations more than 30%. 
As is apparent from comparing Example 21 with Comparative Example 12, it is 
also shown that the content of the compound (2) less than 20 parts by 
weight is essential for improving curing velocity. 
Comparative Examples 9, 10, 11 and 13 are examples wherein a urethane 
acrylate varying in isocyanate structure thereof was used. As is seen from 
the comparison of Comparative Examples 9, 10 and 11 with Example 18, it is 
apparent that, as to the isocyanate structure in urethane acrylate to be 
used, hydrogenated diphenylmethane diisocyanate is most favorable in 
attaining rapid curing rate. 
Furthermore, as is apparent from the comparison of Examples 18 and 19 with 
Example 26, and of Examples 21 and 22 with Example 27, when 
N-vinylpyrrolidone is added elastic modulus become less than 60 
kg/mm.sup.2 and water-absorptions are also high. In this case, it is shown 
that the use of one or more of acryloyl morpholine and dicyclopentanyl 
acrylate is important for obtaining an optical fiber coating material, 
which has a high elastic modulus and high elongations and is 
well-balanced. 
TABLE 5 
__________________________________________________________________________ 
Ex- 
Ex- 
Ex- Ex- 
Ex- Ex- Ex- 
am- 
am- 
am- 
Ex- am- 
am- am- 
Ex- Ex- am- 
ple 
ple 
ple 
ample 
ple 
ple 
Comparative 
Comparative 
ple 
ample 
ample 
ple 
Comparative 
28 29 30 31 32 33 Example 14 
Example 15 
34 35 36 37 Example 
__________________________________________________________________________ 
16 
Urethane 100 
100 
100 
100 100 
100 
100 100 100 
100 100 100 
100 
acrylate 
Compound of the 
40 40 40 40 40 40 40 20 40 40 40 40 40 
formula (1) 
Compound of the 
12 12 12 12 12 12 12 12 12 12 12 12 12 
formula (2) 
Acryloyl 10 20 40 50 10 20 40 40 
morpholine 
Dicyclopentanyl 10 20 40 50 
acrylate 
N--vinyl- 
10 10 10 10 10 10 10 10 10 45 
pyrrolidone 
Phenoxyethyl 20 
acrylate 
Photopoly- 
5 5 5 5 5 5 5 5 5 5 5 5 5 
merization 
initiator 
Elastic modulus 
72 70 62 71 66 61 55 56 45 68 65 60 80 
(kg/mm.sup.2) 
Elongation 
30 35 37 30 35 37 42 42 40 35 35 37 35 
(%) 
Curing rate 
88 90 90 87 87 87 85 85 85 80 80 80 90 
(%) 
Water- 1.8 
1.8 
1.8 
1.7 1.7 
1.7 
1.8 1.8 1.6 
1.5 1.5 1.6 
4.5 
absorption 
(%) 
Viscosity 
9000 
8000 
5400 
10000 
7200 
4900 
6000 5800 7000 
12000 
11000 
6800 
4500 
(cps) @ 25.degree. C. 
__________________________________________________________________________ 
In Table 5, limitations are shown when acryloyl morpholine and 
dicyclopentanyl acrylate are used. As is seen from the comparison of 
Examples 28, 29 and 30 with Comparative Example 14, when the content of 
acryloyl morpholine is more than 40 parts by weight, elastic modulus 
becomes less than 60 kg/mm.sup.2, showing that proportion less than 40 
parts by weight is preferable. Similarly, when dicyclopentanyl acrylate is 
used, contents of less than 40 parts by weight are favorable, as is seen 
from the comparison of Examples 31, 32 and 33 with Comparative Example 15. 
As is seen from the comparison of Examples 29 and 32 with Example 34, even 
when the compositions comprise compounds (1) and (2) and 
N-vinylpyrrolidone, it is apparent that the addition of acryloyl 
morpholine and dicyclopentanyl acrylate serves to attain a higher elastic 
modulus. 
Furthermore, as is apparent from the comparison of Examples 28, 29 and 30 
with Examples 35, 36 and 37 in the Table 5, the addition of 
N-vinylpyrrolidone to the resin compositions according to the invention 
serves to reduce the viscosity of the composition, resulting in 
facilitating the coating operation. In addition, Comparative Examples 
17-20 show that the use of N-vinylpyrrolidone serves to provide lower 
viscosity without almost reducing curing speed. As to blending rate 
thereof, a content less than 40 parts by weight is preferable and as shown 
by Comparative Example 16 a content less than 40 parts by weight leads to 
higher water-absorption, resulting in an unfavorable material for coating 
optical fiber. 
Next, on an optical fiber, which had been spun up to 125 .mu.m.phi. at a 
drawing speed of 200 m/min, a UV-curable resin composition having a 
Young's modulus of 0.1 kg/mm.sup.2 was coated as the primary coating 
material up to 250 .mu.m.phi. and then cured by a metal halide lamp of 3 
kW, and subsequently the resin composition according to Example 29 was 
coated up to 400 .mu.m.phi. and then cured by exposing to ultraviolet 
radiation by a metal halide lamp of 3 kW. An optical fiber obtained showed 
no increase in transmission loss and had a strength of 6 kg. Furthermore, 
the coated optical fiber showed no increase in optical transmission loss 
and no deterioration in strength, even after 60 days of 95% RH 
humidity-heat test at 60.degree. C. 
As is explained in the above, according to UV-curable resin composition of 
the invention, cured products can be obtained, which have elastic modulus 
of more than 10 kg/mm.sup.2, elongations of more than 30% and 
water-absorption of less than 4%. The composition can be effectively used 
as the secondary coating material on optical fiber, since it cures 
sufficiently rapidly.