Active energy beam-curable composition containing particles and coated optical fiber

This invention provides: PA0 (i) an acitve energy beam-curable composition for coating the surface of optical fibers therewith, the composition comprising about 100 parts by weight of an active energy beam-curable substance, about 0.5 to about 100 parts by weight of a particulate substance having a mean particle size of about 0.2 to about 200 .mu.m and optionally a photopolymerization initiator; PA0 (ii) a coated optical fiber prepared by applying the composition of item (i) to the surface of an optical fiber and curing the coating; PA0 (iii) a bundle-type optical fiber cable prepared using the coated optical fiber of item (ii); PA0 (iv) an optical fiber unit of the tape type prepared by applying the composition of item (i) to optical fibers and curing the coating; and PA0 (v) an optical fiber prepared using the optical fiber unit of item (iv).

The present invention relates to an active energy beam-curable composition 
and more particularly to an active energy beam-curable composition capable 
of forming a coating of proper slip property on the outer surface of 
optical fibers. 
Optical fiber units of the tape type for transmitting optical signals are 
known which comprise two or more optical fibers arranged in parallel with 
each other and covered with an outer coat (unit coat) comprising one or 
more layers to provide an integral assembly. Optical cables formed with 
optical fiber units of the tape type pose the following problem. If high 
frictional resistance exists between the optical fiber units or between 
the unit and a structural material for holding the units in the cable, the 
optical fiber cable when bent during the manufacture or during the 
installation of the cable undergoes insufficient relaxation of elongation 
or contraction so that stress is locally applied on the cable, resulting 
in the occurrence of micro-bends and the increase of transmission loss. 
On the other hand, optical fiber cables of the bundle type incur the 
following disadvantage. If there is high frictional resistance between the 
optical fibers or between the fiber and the structural material for 
retaining the fibers in the cable, an optical fiber cable of the bundle 
type when bent is locally subjected to stress because of the poor slip 
property of optical fibers and is broken. 
To avoid the problems resulting from the poor slip property and the 
friction, various techniques have been usually used which include, for 
example, the application of fine powder to the surface of optical fibers 
or optical fiber units of the tape type, the application of silicone-type 
or fluorine-type oil to the surface thereof and the increase of the 
surface hardness of optical fibers or optical fiber units. 
However, these techniques give the following disadvantages. The application 
of fine powder onto the optical fibers or optical fiber units of the tape 
type necessitates a procedure for applying the fine powder thereover, and 
faces the risk of polluting the work environment in view of use of fine 
powder during application, hence a serious obstacle to production of 
optical fibers in a pollution-free environment. 
The application of silicone-type or fluorine-type oil on the surface of 
optical fibers or optical fiber units of the tape type for increase of 
slip property requires an additional procedure for application of oil, and 
disadvantageously renders the surface sticky. 
The increase of surface hardness of optical fibers generally reduces the 
elongation ratio of coating and impairs the elasticity of optical fibers, 
optical fiber units of the tape type or the like. 
It is an object of the present invention to provide a curable composition 
capable of giving a coating of suitable slip property on the outer surface 
of optical fibers. 
It is another object of the invention to provide a curable composition 
which can easily form a coating on the outer surface of optical fibers 
without polluting the work environment during the application of the 
composition. 
Other objects and features of the invention will become apparent from the 
following description. 
According to the invention, there is provided an active energy beam-curable 
composition for coating the surface of optical fibers therewith, the 
composition comprising about 100 parts by weight of an active energy 
beam-curable substance, about 0.5 to about 100 parts by weight of a 
particulate substance having a mean particle size of about 0.2 to about 
200 .mu.m and optionally a photopolymerization initiator. 
The curable composition of the present invention is curable by application 
of active energy beams such as electron beams, ultraviolet rays or the 
like, and thus can easily form a coating over the outer surface of optical 
fibers. The coating formed from the composition of the invention has a 
surface finely projected and dented by the presence of particulate 
substance of specific particle size and is suitably elastic, therefore 
slippery. 
The active energy beam-curable substance for use in the invention is at 
least one substance selected from active energy beam-curable resins, 
active energy beam-curable vinyl monomers and active energy beam-curable 
oligomers. 
Examples of active energy beam-curable resins useful in the invention are 
resins prepared by condensing a polyester and acrylic or methacrylic acid, 
ethylenically unsaturated group-containing polyurethane resins, 
ethylenically unsaturated group-containing epoxy resins, ethylenically 
unsaturated group-containing phosphorus-containing epoxy resins, 
ethylenically unsaturated group-containing acrylic resins, ethylenically 
unsaturated group-containing silicone resins, ethylenically unsaturated 
group-containing melamine resins and like ethylenically unsaturated 
group-containing resins. 
Ethylenically unsaturated group-containing resins include, for example, 
those having preferably about 0.1 to about 5.0 moles, more preferably 
about 0.3 to about 3.0 moles, of ethylenically unsaturated groups per 
1,000 g of the resin. 
Polymerizable unsaturated monomers can be used as the active energy 
beam-curable vinyl monomers. Examples of useful polymerizable unsaturated 
monomers are esterification products of acrylic or methacrylic acid with a 
monohydric alcohol having 1 to 28 carbon atoms such as methyl acrylate, 
methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, 
n-butyl methacrylate, iso-butyl acrylate, iso-butyl methacrylate, 
tert-butyl acrylate, tert-butyl methacrylate, propyl acrylate, propyl 
methacrylate, hexyl acrylate, hexyl methacrylate, octyl acrylate, octyl 
methacrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 
2-ethylhexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, 
stearyl acrylate, stearyl methacrylate and the like; vinyl aromatic 
compounds such as styrene, vinyltoluene, methylstyrene, chlorostyrene, 
divinylbenzene and the like; carboxyl-containing monomers such as acrylic 
acid, methacrylic acid and the like; hydroxyl-containing monomers such as 
2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl 
acrylate, 2-hydroxypropyl methacrylate and the like; adducts of the above 
hydroxyl-containing monomer with such polyisocyanate as butyl isocyanate, 
phenyl isocyanate or the like; adducts of the above hydroxyl-containing 
monomer with phosphoric acid; unsaturated monomers having a 
nitrogen-containing heterocyclic ring such as vinylpyrrolidone, 
vinylpyridine and the like; and other vinyl compounds such as vinyl 
acetate, vinyl chloride, vinyl isobutyl ether, methyl vinyl ether, 
acrylonitrile, 2-ethylhexyl vinyl ether and the like. 
Useful active energy beam-curable oligomers are polymerizable unsaturated 
oligomers and include, for example, diethylene glycol diacrylate, 
diethylene glycol dimethacrylate, polyethylene glycol diacrylate, 
polyethylene glycol dimethacrylate, propylene glycol diacrylate, propylene 
glycol dimethacrylate, 1,3-butanediol diacrylate, 1,3-butanediol 
dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 
neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, 
1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 
trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 
pentaerythritol triacrylate, pentaerythritol trimethacrylate, 
pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate and like 
di-, tri- or tetra-vinyl compounds; reaction products prepared by reacting 
acrylic and/or methacrylic acid with an adduct of the above polyhydric 
alcohol with ethylene oxide; reaction products prepared by reacting 
acrylic and/or methacrylic acid with an adduct of the above polyhydric 
alcohol with propylene oxide; reaction products prepared by reacting 
acrylic and/or methacrylic acid with an adduct of the above polyhydric 
alcohol with .epsilon.-caprolactone; phosphorus-containing polymerizable 
unsaturated oligomers; etc. 
According to the present invention, the above active energy beam-curable 
resins, vinyl monomers and oligomers are usable singly or at least two of 
them can be used in mixture as the active energy beam-curable substance. 
Preferably the active energy beam-curable resin is used in mixture with at 
least one of the active energy beam-curable vinyl monomer and oligomer in 
a ratio by weight of the resin to the latter in the range of from about 20 
: about 80 to about 90 : about 10. 
The particulate substance for use herein has a mean particle size of about 
0.2 to about 200 .mu.m, preferably about 1 to about 50 .mu.m, and can be 
either inorganic or organic. 
Examples of useful inorganic particulate substances are particles of 
silica, calcium carbonate, talc, mica, clay, barium sulfate, ceramics or 
metallic oxides. 
Organic resin particles useful in the invention can be any of particles of 
polyamide, acrylic resin, polyethylene, polypropylene, polycarbonate, 
polyurethane, epoxy resin, polyethylene terephthalate, polyvinylidene 
fluoride, polytetrafluoroethylene, silicone resin and like resins. The 
resins insoluble in the active energy beam-curable substance are suitable 
to achieve the objects of the invention. 
Use of particulate substance having a particle size of less than 0.2 .mu.m 
imparts a poor slip property, whereas use of particulate substance with a 
particle size of over 200 .mu.m aggravates the surface irregularities of 
coating, causing high transmission loss by the lateral pressure, hence 
unsuitable to achieve the objects of the invention. It is more desirable 
that the particle size of the particulate substance be in the range of 
1/20 to 1 times the dry thickness of the coating. 
Preferably the Young's modulus of particulate substance for use herein is 
equal to or close to that of the binder portion of the coating formed by 
curing the active energy beam-curable substance. If the Young's modulus of 
the particulate substance is too low, the Young's modulus of the coating 
is markedly reduced and the coating strength is decreased. On the other 
hand, if the Young's modulus of the particulate substance is too high, the 
Young's modulus of the coating is greatly increased, and the elongation 
ratio is decreased. It is desirable that the particulate substance 
generally have a Young's modulus of about 0.5 to about 500 kgf/mm.sup.2. 
The surface of the particulate substance for use herein may be coated with 
a coupling agent or activated to enhance the adhesion to the binder and to 
increase the strength of the coating. 
Useful coupling agents include those heretofore known such as silicone type 
agent, metal chelate type agent containing titanium, aluminum, zirconium 
or like metals, etc. The activation can be done by treatment using plasma, 
ozone, acid, alkali or the like or by exposure to corpuscular radiation. 
The amount of the particulate substance used is about 0.5 to about 100 
parts by weight per 100 parts by weight of the active energy beam-curable 
substance. Use of less than 0.5 part by weight of the particulate 
substance imparts reduced slip property, whereas use of more than 100 
parts by weight of the particulate substance gives a brittle coating, 
hence unsuitable. 
The composition of the invention is curable by application of electron 
beams, ultraviolet rays or like active energy beams. When the composition 
is cured by exposure to ultraviolet rays, the composition needs to contain 
a photopolymerization initiator. Examples of useful photopolymerization 
initiators include those commonly employed which produce radicals on 
excitation by ultraviolet-ray irradiation such as benzoin, benzoin methyl 
ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl 
ether, benzoin n-butyl ether, .alpha.-hydroxyisobutyl phenone, 
benzophenone, p-methylbenzophenone, Michler's ketone, anthraquinone, 
2-methylanthraquinone, phenyldisulfide, 2-nitrofluorene and the like. 
These photopolymerization initiators are usable singly or at least two of 
them can be used in mixture. The amount of the initiator used is about 0.1 
to about 10 parts by weight per 100 parts by weight of the active energy 
beam-curable substance. 
A photosensitization accelerator may be used conjointly with the 
photopolymerization initiator to accelerate the photopolymerization 
reaction initiated by the initiator. The photosensitization accelerator 
for use herein include, for example, triethylamine, triethanolamine, 
2-dimethylaminoethanol and like tertiary amine type accelerators; 
triphenylphosphine and like alkylphosphine type accelerators; and 
.beta.-thiodiglycol and like thioether type accelerators; etc. These 
photosensitization accelerators are usable singly or at least two of them 
can be used in mixture. The amount of the photosensitization accelerator 
used is preferably about 0.1 to about 10 parts by weight per 100 parts by 
weight of the active energy beam-curable substance. 
When the composition is cured by exposure to electron beams, the 
photopolymerization initiator and the photosensitization accelerator need 
not be used. 
When required, the composition of the invention may contain an agent for 
improving the slip property and silicone-type or fluorine-type additives, 
and may further incorporate therein a coloring pigment, saturated resin, 
solvent and the like in an amount which does not adversely affect the 
curing of the composition. 
Usable slip property improvers are silicone-type, fluorine-type, 
polyethylene wax-type, polypropylene wax-type and like slipping agents 
commonly employed. Specific examples of silicone-type slipping agents are 
BYK-300 (product of Bic Marinecrot Co., Ltd.) and TSF4700 (product of 
Toshiba Silicone Co., Ltd.). Specific examples of fluorine-type slipping 
agents are "Unidyne DS402" (trademark, product of Daikin Industries, Ltd.) 
and the like. The slip property improver is preferably used in an amount 
of about 0.01 to about 10 parts by weight per 100 parts by weight of the 
active energy beam-curable substance. 
The composition of the invention is curable by exposure to electron beams, 
ultraviolet rays or like active energy beams. 
Electron beam sources for curing the composition by electron beam 
irradiation are electron beam generators such as Cockcroft, 
Cockcroft-Walton, van de Graaff, resonance transformer, transformer, 
insulating core transformer, dynamitron, linear filament and 
high-frequency Electron beam generators, etc. In this case, a suitable 
dose of electron beam to be applied is about 1 to about 20 megarads 
although variable depending on the film thickness and the like. Preferably 
electron the beam is irradiated in an inert gas atmosphere. 
Useful ultraviolet ray sources include a mercury lamp, xenon lamp, carbon 
arc, metal halide lamp, sunlight and the like. While ultraviolet rays can 
be applied without any specific limitation on conditions, preferably light 
beams containing ultraviolet rays at a wavelength of about 150 to about 
450 nm are applied in air or in an inert gas atmosphere. 
The composition of the invention is suitably usable for forming a coating 
on the outer surface of optical fibers which require a slip property. For 
example, in case of optical fiber units of the tape type, the composition 
is used for covering optical fibers or for forming a unit coat on the 
outer surface of arranged optical fibers to be formed into a optical fiber 
unit of the tape type. In case of optical fiber cables of the bundle type, 
the composition is used for coating the outer surface of optical fibers. 
The thickness of the coating formed from the composition, which is not 
specifically limited, is suitably about 2 to about 500 .mu.m in coating an 
optical fiber and about 5 to about 500 .mu.m in forming a unit coat for a 
optical fiber unit of the tape type. 
The composition of the invention is cured by application of active energy 
beams and can easily form a coating on the outer surface of optical fibers 
without polluting the work environment. The coating from the composition 
has a suitable elasticity and fine surface irregularities, and exhibits an 
adequate slip property which would prevent partial build-up of stress. 
Therefore the optical fibers with the outer surface coated with the 
composition involve only low transmission loss and would be unlikely to 
break and be high in durability, even when bent during the manufacture or 
the installation of optical cables.

The present invention will be described below in greater detail with 
reference to the following Examples and Comparison Examples in which the 
parts are all by weight unless otherwise specified. 
EXAMPLE 1 
An ultraviolet ray-curable composition (I) was prepared by mixing together 
70 parts of Gohselack UV-7000B (trade name for active energy beam-curable 
urethane acrylate resin, product of The Nippon Synthetic Chemical Industry 
Co., Ltd.), 30 parts of trimethylolpropane triacrylate, 4 parts of 
1-hydroxy-1-cyclohexylacetophenone as a photopolymerization initiator and 
10 parts of talc particles having a mean particle size of about 10 .mu.m. 
The obtained ultraviolet ray-curable composition (I) was applied onto five 
optical fibers to form a unit coat thereon, the five optical fibers being 
arranged in parallel with each other to form an integral assembly of the 
tape type, each optical fiber having an outside diameter of 300 .mu.m, 
comprising a core of 5 .mu.m diameter and a cladding of 130 .mu.m diameter 
and being covered with a primary coat and a secondary coat and externally 
colored. The unit coat was cured by exposure to ultraviolet ray from a 
metal halide lamp at a dose of 10 mJ/cm.sup.2 in an atmosphere containing 
oxygen in a concentration of up to 500 ppm, giving a coated optical fiber 
unit of the tape type having a width of 1.6 mm and a thickness of 0.4 mm. 
The obtained optical fiber units of the tape type showed an excellent slip 
property when superposed on each other. 
An optical cable was produced which had at each of six positions four 
optical fiber units of the tape type superposed on each other, namely the 
cable being composed of 120 optical fibers. Two transmission loss tests 
were carried out using a 100 m length of the obtained fiber cable wound 
into a coil of 1 m diameter and using the same length of cable in a 
straight state. The test results showed that the wound cable caused 
transmission loss higher by 0.2 dB/km, i.e. only slightly higher, than the 
straight cable. 
EXAMPLE 2 
The same procedure as in Example 1 was repeated with the exception of using 
10 parts of Orgasol 2002D (trade name for Nylon 12, about 20 .mu.m in mean 
particle size, about 200 kgf/mm.sup.2 in Young's modulus, product of Ato 
Chem, France) in place of 10 parts of talc used in Example 1, giving an 
ultraviolet ray-curable composition (II). 
The ultraviolet ray-curable composition (II) was applied by a die coater to 
optical fibers each comprising a core of 90 .mu.m diameter and a cladding 
of 100 .mu.m diameter to form a coating of about 30 .mu.m thickness. The 
coating was cured by exposure to ultraviolet ray from a high pressure 
mercury lamp at a dose of 5 mJ/cm.sup.2 in an atmosphere of nitrogen gas, 
giving an optical fiber covered with a single coat. 
A optical fiber cable of the bundle type (2 m length) was produced from the 
obtained optical fiber for use as an image fiber in forming images 
consisting of 3000 picture elements. The fiber cable was subjected to a 
test of 100 cycles, each cycle consisting of winding the cable into a coil 
of 300 mm diameter and unwinding the cable to a straight state. After the 
test, the optical fiber cable remained entirely unbroken, hence 
satisfactory in durability. 
EXAMPLE 3 
An ultraviolet ray-curable composition (III) was prepared in the same 
manner as in Example 2 with the exception of further adding 0.5 part of 
BYK-300 (trade name for a silicone-type slip property improver, product of 
Bic.Marinecrot Co., Ltd.). 
The same subsequent procedure as in Example 1 was repeated with the 
exception of using the ultraviolet ray-curable composition (III) in place 
of the ultraviolet ray-curable composition (I) used in Example 1, giving a 
optical fiber unit of the tape type. The obtained optical fiber units 
showed a good slip property when superposed over each other. 
An optical fiber cable comprising 120 optical fibers was produced in the 
same manner as in Example 1 with the exception of using the obtained 
optical fiber unit of the tape type. Two transmission loss tests were 
conducted using a 100 m length of the cable wound into a coil of 1 m 
diameter and using the same length of the cable in a straight state. The 
wound cable caused transmission loss higher by 0.1 dB/km, i.e. only 
slightly higher, than the straight cable. 
EXAMPLE 4 
An electron beam-curable composition (IV) was produced in the same manner 
as in Example 2 with the exception of not using 
1-hydroxy-1-cyclohexylacetophenone as a photopolymerization initiator. 
The electron beam-curable composition (IV) was applied by a die coater to 
an optical fiber comprising a core of 90 .mu.m diameter and a cladding of 
100 .mu.m diameter r. to a thickness of about 30 .mu.m. The coating was 
cured by exposure to electron beams at an accelerating voltage of 150 KV 
at a dose of 1 megarad in an atmosphere of nitrogen gas, giving an optical 
fiber covered with a single coat. 
An optical fiber cable of the bundle type (2 m length) was produced from 
the obtained optical fiber for use as an image fiber in forming images 
consisting of 3000 picture elements. The cable was subjected to a test of 
100 cycles, each cycle consisting of winding the cable into a coil of 300 
mm diameter and unwinding the cable to a straight state. After the test, 
the optical fiber cable remained entirely unbroken, hence satisfactory in 
durability. 
COMISON EXAMPLE 1 
An ultraviolet ray-curable composition (V) was prepared in the same manner 
as in Example 1 with the exception of not using 10 parts of talc. The same 
subsequent procedure as in Example 1 was repeated with the exception of 
using the ultraviolet ray-curable composition (V) in lieu of the 
ultraviolet ray-curable composition (I), giving an optical fiber unit of 
the tape type. The optical fiber units of the tape type exhibited poor 
slip property when superposed over each other. An optical fiber cable 
comprising 120 optical fibers was produced in the same manner as in 
Example 1 with the exception of using the obtained optical fiber unit of 
the tape type. Two transmission loss tests were carried out using a 100 m 
length of the obtained fiber cable wound into a coil of 1 m diameter and 
using the same length of cable in a straight state. The test results 
showed that the wound cable caused transmission loss higher by 3 dB/km, 
i.e. much higher, than the straight cable, hence defective in contrast 
with the cables tested in Examples 1 to 4. 
COMISON EXAMPLE 2 
The same procedure as in Example 2 was repeated with the exception of using 
the ultraviolet ray-curable composition (V) prepared in Comparison Example 
1 in place of the ultraviolet ray-curable composition (II), giving an 
optical fiber cable of the bundle type having a length of 2 m for use as 
an image fiber for forming images consisting of 3000 picture elements. The 
cable was subjected to a test of 100 cycles, each cycle consisting of 
winding the cable around a 300 mm diameter and unwinding the cable to a 
straight state. The cable was found to have broken at a ratio of 3%, hence 
defective.