Nozzle plate for spinning glass fibres

A nozzle plate for spinning glass fiber including a flat plate portion and a multiplicity of nozzles projecting from the flat plate portion. Each of the nozzles comprises a greater diameter portion located at its flat plate portion side and a smaller diameter portion located at its tip side. The smaller diameter portion has an inner diameter of 0.3 mm to 1.0 mm and a length of 0.5 mm to 2.0 mm, and the greater diameter portion has an inner diameter of 1.1 mm to 2.5 mm, and the length of the nozzle projecting from the flat plate portion is in range of 4.0 mm to 6.0 mm. By use of this nozzle plate for spining glass fiber, a fine glass fiber having a diameter smaller than 3 .mu.m can be manufactured in a stable manner.

BACKGROUND OF THE INVENTION 
1. FIELD OF THE INVENTION 
The present invention relates to a nozzle plate for spinning glass fibres 
used in a glass fibre manufacturing apparatus. 
2. DESCRIPTION OF THE PRIOR ART 
Glass fibres having diameter of 9 to 23 .mu.m are used in large quantities 
in form of glass cloth or glass mat as a basic material for FRP or printed 
circuit boards. These glass fibres are manufactured through a method in 
which molten glass is extruded through nozzle holes formed in a nozzle 
plate for spinning glass fibres and taken up with a predetermined speed by 
means of a take-up device. As partly shown in FIG. 3, the nozzle plate 
used here is formed with a nozzle 2 projecting from a flat plate portion 
1, and the nozzle 2 is formed with a straight nozzle hole 3. The molten 
glass 4 flows out through the nozzle hole 3 and forms a cone 5 at the tip 
of the nozzle, and the cone is drawn downwards, thereby attenuating the 
glass flow and producing a glass fibre 6. Usually, the diameter d of the 
nozzle hole is in range of 1.0 mm to 2.5 mm, the length l of the straight 
portion of the nozzle hole is in range of 2 mm to 6 mm, the nozzle 
projecting length L is in range 3 mm to 6 mm, and the thickness t of the 
nozzle is about 0.3 mm. 
Recently, by virtue of the advance in the glass fibre making art, it become 
possible to manufacture a glass fibre of about 3 .mu.m by use of a glass 
fibre spinning nozzle of a straight type of a prior art such as shown in 
FIG. 3. However, it is difficult to manufacture a glass fibre thinner than 
the above, which can be used as a spacer for a liquid crystal display. 
The manufacturing difficulity is caused not only by the fact that the glass 
fibre itself is fine and easily broken, but also by problems included in 
the fibre attenuating method. For obtaining a thinner fibre, there are 
methods such as a method in which the diameter of the nozzle hole is 
decreased for decreasing the flow rate of the molten glass, another method 
in which the spinning speed (drawing speed) of the glass fibre is 
increased, and a combination of these methods. 
Although the diameter of the fibre can be decreased by increasing the 
spinning speed, the fibre is frequently broken in spinning at a high 
speed, because the fibre is formed by drawing the cone of the molten glass 
at high speed, which molten glass flows out through the nozzle at low 
speed, and the strength of each fibre is low. Therefore, actually, the 
spinning speed can not be increased beyond 2,500 m/min and a limit exists 
in decreasing the diameter of the fibre manufactured by use of a nozzle 
hole having a rather greater diameter. 
On the other hand, in the method in which the diameter of the nozzle hole 
is decreased for decreasing the flow rate of the molten glass, the molten 
glass is apt to be influenced by environmental conditions when the molten 
glass passes through the narrow nozzle. For example, there is caused a 
problem that the molten glass is rapidly cooled under the influence of the 
disturbed air around the nozzle and stops to flow out through the nozzle, 
thereby causing a breakdown of the glass fibre. When the glass fibre drawn 
from the nozzle hole has broken, the molten glass flowing out through the 
nozzle hole forms a drop at the tip of the nozzle, and when the drop grows 
up to a certain amount, the drop separates from the tip of the nozzle and 
falls down, thereby forming a cone of the molten glass at the tip of the 
nozzle and producing again a glass fibre continuous to the cone. In case 
of the nozzle of decreased hole diameter, the flow rate of the molten 
glass is small, and it takes a long time for the drop of the molten glass 
to grow to an amount sufficient to fall down. In this process, the molten 
glass 4 adheres even to the outer surface of the nozzle 2 as shown in FIG. 
4, and does not easily fall down. In an extreme case, the molten glass 
extends over the outer surface of the nozzle up to the flat plate portion 
of the nozzle, and forms no drop, but adheres totally to the lower surface 
of the nozzle plate. As a result, the glass fibre spinning process can not 
be reopened. In case of reopening the glass fibre spinning process by 
high-handedly separating the molten glass adhered to the top of the nozzle 
from the nozzle by using such as tweezers, as shown in FIG. 5, the outer 
diameter of the cone 5, become greater due to the molten glass wetting the 
outer surface of the nozzle, and the molten glass stays on the outer 
peripheral portion of the cone. This staying molten glass is cooled by the 
atmospheric air, and the viscosity of the glass become greater. Since the 
molten glass thus having high viscosity mixes intermittently with the 
glass flow for forming a fibre, the cone become unstable and the fibre has 
a great fluctuation in its diameter and is apt to be easily broken. 
SUMMARY OF THE INVENTION 
The present invention is intended to solve the above-mentioned problems of 
prior arts, and to provide a nozzle plate for spinning glass fibre capable 
of stably producing a glass fibre having a diameter smaller than 3 .mu.m. 
The inventor of the present invention has noticed that the molten glass 
flows in a stable manner by making the nozzle narrow only at its tip 
portion, even if the flow rate of the glass is small, and the forming of 
the drop of the molten glass and falling down of the same are stabilized 
by providing an outer surface of the nozzle which is difficult to be 
wetted by the molten glass. The present invention has been developed based 
on this discovery. 
According to the present invention, there is provided a nozzle plate for 
spinning glass fibres which includes a multiplicity of nozzles projecting 
from a flat plate portion of the plate, and each of the nozzles is 
composed of a greater diameter portion located on its flat plate portion 
side and a smaller diameter portion located on its tip side, the smaller 
diameter portion having an inner diameter in range of 0.3 mm to 1.0 mm and 
a length in range of 0.5 mm to 2.0 mm, the greater diameter portion having 
an inner diameter in range of 1.1 mm to 2.5 mm, and the length of the 
nozzle projecting from the flat plate portion being in range of 4.0 mm to 
6.0 mm. 
In the nozzle plate having the above-mentioned structural features, it is 
preferred to cover the peripheral portion of the nozzle exit and the 
nozzle peripheral portion adjacent thereto with a metallic material having 
a contact angle greater than 58 degrees against the molten glass in 
temperature range of 1100.degree. C. to 1500.degree. C. 
The present invention will be described further in detail by referring to 
the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is an enlarged sectional view of a nozzle portion of a nozzle plate 
according to the present invention. The nozzle plate indicated as a whole 
with reference numeral 10 comprises a flat plate portion 11 and a 
multiplicity of nozzles 12 (one of them is only shown in the figure) 
projecting from the flat plate portion. The nozzle 12 is composed of a 
greater diameter portion 13 located on the flat plate portion side and a 
smaller diameter portion 14 located on the nozzle tip side. The greater 
diameter portion 13 includes a straight nozzle hole 13a of a greater 
diameter, and the smaller diameter portion 14 includes a straight nozzle 
hole 14a of a smaller diameter adjacent to the nozzle hole 13a. 
The smaller diameter portion 14 is provided for suppressing the flow rate 
of the molten glass flowing out from the nozzle 12, and the inner diameter 
d.sub.1 of the nozzle hole 14a of the smaller diameter portion 14 is 
determined to be smaller than the diameter of the nozzle hole of the 
conventional nozzle. However, if the inner diameter d.sub.1 is excessively 
small, the flow feature of the molten glass is deteriorated too much, and 
in addition, the fabrication of the nozzle hole become difficult. In 
consideration of these circumstances, the inner diameter d.sub.1 of the 
nozzle hole 14a is determined in range of 0.3 mm to 1.0 mm. Further, if 
the length 11 of the smaller diameter portion 14 is excessively long, the 
flow resistance become too great, and the molten glass passing through 
this portion is apt to be easily influenced by the atmosphere. Therefore, 
the length 11 is usually determined smaller than 2 mm. The lower limit of 
the length 11 will be described later. 
The greater diameter portion 13 is provided for decreasing the flow 
resistance and passing the molten glass at a flow rate sufficient to 
protect the molten glass from the fluctuating cooling effect from the 
outside. The inner diameter d.sub.2 of the nozzle hole 13a is determined 
greater than that of the nozzle hole 14a of the smaller diameter portion, 
of course, and usually, greater than 1.1 mm. However, if the diameter 
d.sub.2 is excessively great, the amount of the molten glass staying in 
the nozzle become excessively great. For preventing this phenomenon, the 
inner diameter d.sub.2 is 25 selected to be smaller than 2.5 mm. 
The outer diameter of the smaller portion 14 is determined as small as 
possible for the purpose of decreasing the contact area between the tip of 
the nozzle and the molten glass drop formed at the tip of the nozzle, when 
the glass fibre spinning process starts, and of making it easy for the 
drop to fall down in a rapid and sure manner. Therefore, the thickness t 
of the nozzle is determined as thin as possible in a range permissible 
from the strength view point. For example, the thickness is about 0.3 mm 
in case the nozzle plate is made from platinum-rhodium alloy. The length 
1.sub.1 of the smaller diameter portion 14 is required to be greater than 
0.5 mm for the purpose of preventing the molten glass adhered to the outer 
surface of the nozzle from staying in the region between the smaller 
diameter portion and the greater diameter portion and disturbing a 
formation of a stable cone. 
The length 1.sub.2 of the nozzle 12 projecting from the flat plate portion 
11 is determined in range of 4 mm to 6 mm. In case of the length 12 
greater than 6 mm, the flow resistance of the molten glass increases and 
the molten glass is apt to be influenced by the atmosphere, while in case 
of the length 12 smaller than 4 mm, when operated for a long time, the 
molten glass adhered to the outer surfaces of the adjacent nozzles is 
connected with each other and fill the gap between the nozzles, and in the 
worst case, the lower surface of the nozzle plate is wholly covered by the 
molten glass, thereby making it impossible to make spinning. 
In the nozzle 12 which satisfies the above-mentioned requirements, the 
molten glass flows in a stable manner in spite of the small flow rate, and 
accordingly, a stable cone is formed at the tip of the nozzle. As a 
result, a fine glass fibre 17 can be produced without requiring any 
excessively high speed spinning. 
As for the material composing the nozzle plate 10, there is no special 
limitation, but platinum-rhodium alloy can be used similarly to in the 
prior arts. However, the platinum-rhodium alloy (for example, 10% Rh --90% 
Pt) has a rather small contact angle in range of 31.degree. to 35.degree. 
at the temperature of 1100.degree. C. to 1500.degree. C. against molten 
glass, and accordingly, is apt to be wetted by molten glass. As a result, 
when operated for a long time, the outer surface of the nozzle is 
gradually wetted by the glass, thereby disturbing a stable forming of a 
cone. Further, at a start of glass fibre spinning, the molten glass 
adheres to the surface of the nozzle as forming a drop of the molten glass 
at the tip of the nozzle, as shown in FIG. 4, thereby possibly making it 
impossible for the drop to fall down and for the fibre to be made. For 
preventing this phenomenon, a material difficult to be wetted by molten 
glass is preferred as the material for the nozzle plate, for example, such 
as platinum-gold-rhodium alloy (refer to GB Pat. No. 1,242,921 or U.S. 
Pat. No. 3,672,880) or platinum-gold-palladium alloy (refer to Japanese 
Pat. Publication No. 53-35854). 
Instead of making the nozzle plate wholly from a material difficult to be 
wetted by molten glass, it may be also possible to make the nozzle plate 
itself from a usual platinum-rhodium alloy, and to provide a covering 
layer 18 made of a metallic material difficult to be wetted by molten 
glass only at the region around the exit of the nozzle 12 and at the outer 
peripheral portion of the nozzle adjacent to said region. By providing the 
covering layer 18, the use of high cost material can be decreased and the 
cost of the nozzle plate can be also decreased as a whole. 
As for the material used for the covering larger, there is preferred a 
material which has a significantly greater wetting resistance against 
molten glass in comparison to platinum-rhodium alloy and a contact angle 
greater than 58 degrees against molten glass at the temperature range of 
1100.degree. C. to 1500.degree. C. As the material for the covering layer 
18, gold alloys such as the above-mentioned platinum-gold-rhodium alloy or 
platinum-gold-palladium alloy can be used, and further a single gold can 
also be used. The reason why the covering layer made of gold has a wetting 
resistance against molten glass is as follows. At the beginning of the 
operation, the gold on the nozzle surface is in a molten state, because 
the melting point of gold is 1063.degree. C., and the nozzle surface is 
never wetted by the glass. After then, the gold and the nozzle metal 
together produces an alloy under the function of the heat generated in the 
operation, and the contact angle against molten glass become greater than 
60 degrees similarly to in case of platinum-rhodium alloy containing gold. 
Needless to say, materials other than the above-mentioned ones can be 
used. 
The covering layer 18 can be formed by a known method such as vacuum 
deposition, spattering or plating. The thickness of the covering layer 18 
is determined in range of 50 .mu.m to 400 .mu.m, preferably 100 .mu.m to 
300 .mu.m. In case of the thickness smaller than 50 .mu.m, the effect can 
not be maintained for a long time, and even if the thickness is made 
greater than 400 .mu.m, the continuation of the effect does not have a 
significant change. 
For improving the close adhesion between the covering layer 18 and the 
nozzle surface, the covering layer may be baked for a short time at a 
temperature higher than the spinning temperature by 50.degree. C. to 
100.degree. C. 
Since, in a nozzle plate for spinning glass fibre according to the present 
invention, a nozzle hole 14a of a smaller diameter is provided below a 
nozzle hole of a greater diameter as shown in FIG. 1, the flow rate of the 
molten glass can be made small, and the molten glass passing through the 
nozzle hole is not easily influenced by the environmental conditions. As a 
result, the flow of the molten glass is stable and a stable cone is formed 
at the tip of the nozzle. Further, since the flow rate of the molten glass 
is suppressed at a low level, a fine fibre can be obtained without 
increasing the spinning speed. Thus, a fine glass fibre of high quality 
having a diameter smaller than 3 .mu.m can be manufactured without 
suffering any trouble such as a breakaway of the fibre. 
Further, in case where the nozzle surface is covered by a metallic material 
difficult to be wetted as shown in FIG. 2, the molten glass rarely spreads 
on the outer surface of the nozzle, when the spinning is started or 
restarted and the molten glass flows out from the nozzle tip and forms a 
drop, and as soon as a small drop 19 is formed as shown in FIG. 2, the 
drop quickly falls down and a glass fibre surely connected with the cone 
produced at the nozzle portion can be formed. In consequence, in spite of 
the decreased flow rate of the molten glass through the nozzle, the 
spinning operation can be easily started. In addition since the glass drop 
quickly falls down, the molten glass contacts with the outer surface only 
for a short time and wets the nozzle in a limited area, thereby assuring a 
long and stable operation. 
Examples according to the present invention are described below. 
EXAMPLE 1 
The nozzle tip portion of the nozzle plate made from platinum-rhodium alloy 
and having a shape known in FIG. 1 (inner diameter d.sub.1 of the smaller 
diameter portion : 0.6 mm, outer diameter of the smaller portion : 1.2 mm, 
length 1.sub.1 of the smaller diameter portion : 0.8 mm, inner diameter 
d.sub.2 of the greater diameter portion : 1.2 mm, nozzle length 1.sub. :2 
5 mm) is plated by gold through electroplating with a plating thickness of 
200 .mu.m, thereby forming a covering layer 18 as shown in FIG. 2. Glass 
fibres have been manufactured by using the above-mentioned nozzle plate 
under conditions in which the depth of the molten E-glass is 10 m, the 
spinning speed is 2500 m/min, and the spinning temperatures are 
1320.degree. C., 1250.degree. C., and 1220.degree. C. corresponding to the 
fibre diameters 2.5 .mu.m, 2.0 .mu.m, and 1.8 .mu.m, respectively. The 
result is shown in Table 1. 
EXAMPLE 2 
The tip portion of the same nozzle plate as in Example 1 is coated with 
gold of 100 .mu.m thickness through vacuum deposition, and then, heated at 
1350.degree. C. for 0.5 hour, thereby forming a covering layer of 
platinum-gold alloy on the surface of the nozzle. Fibres of E-glass have 
been manufactured by use of this nozzle plate under the same condition as 
in Example 1. The result is shown in Table 1. 
EXAMPLE 3 
No covering layer is provided on the nozzle of the nozzle plate which is 
the same as in Example 1. Glass fibres have been manufactured under the 
same condition as in Example 1, and the result is shown in Table 1. 
REFERENCE EXAMPLE 1 
By use of a nozzle plate having a shaped shown in FIG. 3 and made of 
platinum-rhodium family alloy (nozzle inner diameter d : 1.3 mm, tip outer 
diameter : 1.9 mm, nozzle length L : 5 mm), glass fibres have been 
manufactured under the same condition as in Example 1. The result is shown 
in Table 1. 
TABLE 1 
______________________________________ 
Diameter of Manufactured Fibre (.mu.m) 
2.5 2.0 1.8 
______________________________________ 
Example 1 O O .DELTA. 
Example 2 O O .DELTA. 
Example 3 O .DELTA. X 
Reference .DELTA. X X 
Example 1 
______________________________________ 
O: stable spinning is possible 
.DELTA.: spinning is possible, but a little unstable 
X: spinning is impossible 
Since, as mentioned above, each nozzle on the nozzle plate according to the 
present invention is composed of a greater diameter portion and a smaller 
diameter portion adjacent thereto, the molten glass can be flowed with a 
small flow rate in a stable manner, and a fine glass fibre can be 
manufactured without requiring a high spinning speed. As a result, a fine, 
for example, thinner than 3 .mu.m, glass fibre of high quality can be 
manufactured without suffering frequent breakdown of the fibre. 
If a covering layer having a great wetting resistance against the molten 
glass is provided at the tip of the nozzle, it prevents the drop of the 
molten glass from spreading on the outer surface of the nozzle when a 
spinning is started or restarted, thereby assuring a fall down of the drop 
and a start of the spinning. Further, since the molten glass does not wet 
the exit of the nozzle, there is no fear that the glass adhered around the 
nozzle disturbs the flow of the molten glass in making a glass fibre, and 
a stable condition for making glass fibre is assured. This advantage is 
specially helpful when a fine glass fibre is to be manufactured. Further, 
since there is almost no fear that the molten glass spreads on the outer 
surface of the nozzle, the space between the adjacent nozzles can be 
smaller. Since the amount of the material of the covering layer to be used 
is small, the cost of the nozzle plate can be suppressed, even if the 
price of the material is high.