Transparent synthetic resin sheet or film, method for its production and applications thereof

A method for producing a sheet or film of a transparent synthetic resin, which comprises discharging onto a continuous substrate moving in one direction a synthetic resin material for the transparent synthetic resin from a discharge die having a linear outlet extending perpendicular to the moving direction of the substrate, casting and curing or solidifying the resin material on the substrate to form a sheet or film of the transparent synthetic resin, wherein the discharge die is continuously or intermittently reciprocated in a direction substantially perpendicular to the moving direction of the substrate.

The present invention relates to a method for producing a continuous sheet 
of a transparent synthetic resin suitable for the production of a 
laminated safety glazing product. 
A so-called laminated glass i.e. a laminate comprising a pair of inorganic 
glass sheets and an interlayer, is widely used as a safety glazing product 
for windshield for automobiles. On the other hand, attention has been 
drawn in recent years to a bilayer safety glazing product having a 
synthetic resin layer of a single or multi-layered structure provided on 
the inside surface (the interior side) of a laminated glass or an 
inorganic glass sheet. This bilayer safety glazing product is considered 
to have a higher level of safety than the laminated glass, since at the 
time of breakage, fragments of the inorganic glass are less likely to 
protrude to the interior side, and the possibility of injury to the human 
body by such fragments is small. Especially, a bilayer safety glazing 
material of this type wherein a sheet of inorganic glass is used, is more 
advantageous than the laminated glass, since it can be made to have a 
light weight. 
The bilayer safety glazing product of the above type (hereinafter referred 
to simply as BLW) is usually produced by laminating a film or sheet 
(hereinafter referred to simply as a sheet in the sense that this sheet 
includes a film) of a synthetic resin having excellent optical properties 
and good weather resistance on an inorganic glass sheet or on a laminated 
glass sheet. The synthetic resin sheet is a sheet having a single or 
multi-layered structure, and particularly the surface constituting the 
exposed surface is required to be hardly scratched, which is referred to 
as scratch resistance. In many cases, such a surface is formed of a hard 
coating film so-called hard coat, or a synthetic resin layer having a 
self-healing property i.e. a property whereby a scratch mark, if any, 
disappears as time passes. A single-layered synthetic resin sheet or each 
layer of a multi-layered synthetic resin sheet can be formed by casting or 
extrusion molding. The casting method is particularly suitable for the 
formation of a sheet or layer having excellent optical properties. In the 
case of a surface layer constituting the exposure surface of BLW or a 
single-layered synthetic resin sheet, it is made of a hard coating film or 
a cross-linked synthetic resin, whereby casting is substantially the only 
method for its molding. 
The casting is a method wherein a flowable material is cast on a substrate 
surface, followed by curing or solidifying to form a layer of a sheet- or 
film-form. The flowable material includes a solution or dispersion of a 
synthetic resin, a mixture of liquid reactive materials capable of 
reacting and curing to form a synthetic resin, and a solution or 
dispersion of a mixture of liquid or solid reactive materials. In the case 
of a solution or dispersion, the solvent or the dispersing medium is 
removed by e.g. evaporation for solidification, or in some cases, a 
reaction for curing takes place to form a solid synthetic resin. In the 
case of a mixture of liquid reactive materials which contains no solvent 
or dispersing medium, a reaction for curing takes place to form a 
synthetic resin. The cast material will have a flat smooth surface by its 
own weight and will be solidified or cured in that state to form a layer 
having excellent surfacial optical properties. 
A method for continuously molding a sheet for the production of a bilayer 
safety glazing product by casting is known and is disclosed in e.g. U.S. 
Pat. Nos. 4,643,944, 4,283,363, 4,605,528 and 4,590,030 and European 
Patent Nos. 38,760 and 133,090. This method is suitable particularly for 
the molding of a sheet of a polyurethane resin. In particular, by casting 
a reactive mixture capable of forming a polyurethane resin and containing 
no solvent, it is possible to mold a relatively thick sheet (e.g. 0.1 mm 
or thicker) in a one step casting. Further, by casting a flowable material 
on a preliminarily molded synthetic resin sheet, it is possible to produce 
a sheet having a multi-layered structure having a synthetic resin surface 
layer formed by the solidification or curing of the flowable material. In 
this case, the undercoating synthetic resin sheet may be formed by a 
casting method. Namely, a sheet having a multi-layered structure can be 
prepared by a so-called multi-step casting method. 
In a continuous casting method, it is common to employ a method wherein a 
flowable material is supplied onto the surface of a substrate moving in 
one direction. The formed sheet is usually a continuous sheet having 
substantially a constant width. Such a sheet is cut into a prescribed 
length for its lamination onto e.g. an inorganic glass sheet. A windshield 
for an automobile is usually bulged forward of the automobile and its 
longer sides are arcuate downwards. Accordingly, the sheet cut out from 
the continuous sheet has a fan shape with the longer sides being 
substantially arcuate. FIG. 2 shows a plan view of a continuous sheet. The 
continuous sheet 1 is continuous in the left-right direction in the 
Figure, and the sheet 2 cut out therefrom has a fan shape with its longer 
sides 3 and 4 being downwardly arcuate. With this shape, the upper central 
portion above the upper longer side of the cut out sheet 2 and both side 
portions below the lower longer side of the cut out sheet 2, of the 
continuous sheet 1 will be wasted without being used. These waste portions 
are not economically negligible. Particularly when the radius of curvature 
of the arcuate longer sides becomes small as the complexity in the shape 
of the windshield of an automobile advances in future, the area of these 
waste portions is considered to increase, and a certain measure will then 
be required. 
On the other hand, in order to reduce the glaring which the driver receives 
from the windshield of an automobile, it has been in practice to reduce 
the transmission of light by coloring the upper portion of the windshield. 
In the case of a laminated glass, such a windshield is produced by using 
an interlayer colored in a strip-shape along the upper portion. As 
mentioned above, the top side of the windshield is roughly arcuate, but as 
observed from the front, it is substantially linear on its appearance. For 
this purpose, the width of the strip-shaped colored portion of the cut out 
sheet is required to be substantially constant For example, in FIG. 2, the 
boundary line 5 between the colored strip portion and the non-colored 
portion is required to be downwardly arcuate in substantially parallel 
with the upper longer side 3. The portion between this boundary line 5 and 
the upper longer side 3 is a colored portion. In the case of an interlayer 
made of e.g. a polyvinyl butyral resin, a sheet having a linear colored 
strip portion is non-uniformly stretched so that the colored strip portion 
will be downwardly arcuate. For example, in FIG. 2, the sheet 1 having a 
linear boundary line 6 (the portion above the boundary line 6 is the 
colored portion) is non-uniformly stretched by using a conical roll in 
such a manner that the stretching ratio in the left-right direction in the 
Figure is small at the upper portion and large at the lower portion so 
that the boundary line 6 changes to a boundary line 5. 
In order to conduct such non-uniform stretching, the sheet 1 must be 
plastic. However, as mentioned above, in the case of a sheet for BLW, it 
is usual that at least the sheet constituting the exposed surface is a 
hard coat film or a cross-linked synthetic resin, which has low or little 
plasticity. Accordingly, it is hardly possible to obtain a sheet having an 
arcuate strip-shaped colored portion as mentioned above by non-uniform 
stretching from a sheet having a straight strip-shaped colored portion. 
It is possible to partially color the surface of the synthetic resin layer 
after the preparation of BLW, to obtain a partially colored BLW as 
mentioned above. However, this method of coloring leads to economical 
disadvantage since the productivity is thereby low. Further, with a view 
to improving the surface property such as the stain resistance of the 
surface of the synthetic resin layer, the permeability of a colarant may 
well be poor depending upon the material of the surface, whereby the 
subsequent coloring operation will be difficult. 
It is an object of the present invention to overcome the above problems in 
the casting method by reciprocating a discharge die for supplying a 
synthetic resin material in a direction substantially perpendicular to the 
direction of the movement of the continuous substrate. 
Thus, the present invention provides a method for producing a sheet or film 
of a transparent synthetic resin, which comprises discharging onto a 
continuous substrate moving in one direction a synthetic resin material 
for the transparent synthetic resin from a discharge die having a linear 
outlet extending perpendicular to the moving direction of the substrate, 
casting and curing or solidifying the resin material on the substrate to 
form a sheet or film of the transparent synthetic resin, wherein the 
discharge die is continuously or intermittently reciprocated in a 
direction substantially perpendicular to the moving direction of the 
substrate. 
The present invention also provides an elongated sheet or film of a 
transparent synthetic resin having a uniform thickness and smooth surface, 
which comprises a colored transparent strip zone (A) of a colored 
transparent synthetic resin (a) extending in the longitudinal direction of 
the sheet or film and a transparent strip zone (B) of a transparent 
synthetic resin (b) which is substantially the same as the colored 
transparent synthetic resin (a) except for the difference in color, the 
zone (B) extending in the longitudinal direction of the sheet or film, 
with the boundary of the zones (A) and (B) being partially curved. 
Furthermore, the present invention provides a laminated safety glass 
glazing product such as BLW wherein a sheet cut out from the elongated 
continuous sheet or film is employed. 
Now, the present invention will be described in further detail with 
reference to the preferred embodiments.

FIG. 1 is a diagrammatical plan view of a casting apparatus to be referred 
to for the description of the method of the present invention. Onto a 
continuous substrate 10 moving continuously to the right hand side 
direction in the Figure, a synthetic resin material 12 is supplied from a 
discharge die 11 having a linear outlet extending substantially 
perpendicular to the moving direction of the substrate. The synthetic 
resin material 12 is cast on the continuous substrate 10, followed by 
curing to form a smooth flat continuous sheet 13. The discharge die 11 
supplies the synthetic resin material while continuously or intermittently 
reciprocating in a direction substantially perpendicular (as shown) to the 
moving direction of the continuous substrate 10. If the discharge die 11 
is reciprocated in a simple harmonic motion relative to the continuous 
substrate 10 moving at a constant speed, the sheet thereby obtained will 
be a continuous sheet with a sine curve. Further, the curvature can be 
changed by changing the reciprocating speed of the discharge die 11. 
Furthermore, continuous sheets of various shapes may be prepared by 
temporarily stopping the reciprocation of the discharge die 11 or by 
changing the speed of the reciprocating movement thereof. FIG. 1 
illustrates the shape of a continuous sheet 13 in a case where the 
discharge die 11 was reciprocated in a simple harmonic motion except that 
it was temporarily stopped at the upper end in the Figure. 
By using the sheet obtained by the method of the present invention, the 
aforementioned problem can be solved. Namely, by approximating the upper 
and lower curves of the sheet 13 to the curves of the upper and lower 
longer sides 3 and 4 in FIG. 2, the waste portions of the sheet can be 
minimized, thus bringing about an economical advantage. Furthermore, there 
will be a significant advantage in that it is possible to obtain a sheet 
13 having a colored strip zone with a curved boundary line 14 by 
simultaneously supplying a colored synthetic resin material and 
non-colored synthetic resin material 12 from the discharge die 11 side by 
side along the longitudinal direction thereof onto the continuous 
substrate 10. 
FIG. 3 shows a cross section in the width direction (i.e. the top-bottom 
direction in the Figure) of the discharge die 11 of FIG. 1. To the 
discharge die 11 movable in the left-right direction in the Figure, a 
colored synthetic resin material (a') and a non-colored synthetic resin 
material (b') are supplied, and they are discharged from the front end 15 
onto the continuous substrate 10, whereby a continuous sheet comprising a 
colored portion (A) and a non-colored portion (B) side by side with a 
boundary line 14 will be obtained. The boundary line may preferably be not 
distinct. Namely, it is preferred to mix or overlap the two materials at 
the boundary region in the discharge die 11 so that the color density 
gradually decreases from the colored portion (A) to the non-colored 
portion (B) in order to form a so-called "gradation" portion. FIG. 4 shows 
a partial cross section of a discharge die having such a mixing section. 
By providing a mixing section as shown in the Figure, the colored 
synthetic resin material (a') and the non-colored synthetic resin material 
(b') are mixed at such a section and then discharged to form a boundary 
region 16 with a certain width. The mixing section is not limited to the 
illustrated static mixing means, and a forcible mixing means or a 
diffusion mixing means by taking a long contact time of the two materials, 
may also be employed. Further, instead of mixing, the two materials may be 
overlapped so that the ratio of the thicknesses of the two materials 
changes to form a similar boundary region. 
FIG. 5 is a diagrammatical plan view of a casting apparatus for 
illustrating another embodiment of the method for producing the synthetic 
resin sheet of the present invention. 
FIG. 6 is a side elevation thereof illustrating the apparatus in an 
enlarged scale in the thickness direction of the sheet. Onto a continuous 
substrate 20 moving continuously to the right hand side direction in the 
Figure, two types of synthetic resin materials (a') 23 and (b') 24 are 
supplied from a discharge die 22 having a linear outlet 21. The synthetic 
resin materials (a') 23 and (b') 24 are cast on the continuous substrate 
20 in a partially overlapped state, followed by curing in a heating 
furnace (not shown) to form an elongated transparent synthetic resin sheet 
25 having a uniform thickness and flat smooth surface. Thus, the sheet 25 
comprises a colored transparent strip zone (A) of a colored transparent 
synthetic resin (a) formed by the curing of the synthetic resin material 
(a') 23, a transparent strip zone (B) of a transparent synthetic resin (b) 
formed by the curing of the synthetic resin material (b') 24, and a 
transparent boundary strip zone (C) where the two synthetic resins are 
overlapped as illustrated. When the width of the spread of the synthetic 
resin material (a') 23 is designated as x, the width of the spread of the 
synthetic resin material (b') 24 is designated as y, and the width of the 
spread of the overlapping portion of the two materials is designated as z, 
as shown in FIG. 5, the width of the zone (A) is represented by x-z, and 
the width of the zone (B) is represented by y-z, and the width of the zone 
(C) is represented by z. 
The synthetic resin sheet 25 is an elongated sheet extending in the 
left-right direction in FIG. 5. This sheet 25 comprises the colored 
transparent strip zone (A), the transparent strip zone (B) and the 
transparent boundary strip zone (C) extending, respectively, in the 
longitudinal direction of the sheet, with their boundaries (i.e. the 
boundary between the zones (A) and (C) and the boundary between the zones 
(B) and (C)) being parallel to each other and curved. This transparent 
boundary strip zone (C) is the above-mentioned "gradation" portion. For 
example, when the transparent strip zone (B) is made of a colorless 
transparent synthetic resin, the color density in the transparent boundary 
strip zone (C) increases gradually in the width direction from the 
transparent strip zone (B) to the colored transparent strip zone (A). FIG. 
7 is an enlarged partial cross-sectional view showing the cross section 
taken along I--I' in FIG. 5. However, the cross section is enlarged more 
in the thickness direction than the width direction of the sheet. The 
colored transparent strip zone (A) is made of a colored transparent 
synthetic resin (a). The transparent strip zone (B) is made of a 
transparent synthetic resin (b) which is substantially the same as the 
colored transparent synthetic resin (a) except for the difference in 
color. This transparent synthetic resin (b) is preferably a colorless 
transparent synthetic resin or a colored transparent synthetic resin which 
is colored with a different color or with a different color density from 
the colored transparent synthetic resin (a). Particularly preferred is a 
colorless synthetic resin or a colored synthetic resin which is colored in 
a less degree with the same type of color as the colored transparent 
synthetic resin (a). The synthetic resins (a) and (b) are preferably 
substantially the same synthetic resins (substantially the same not only 
in the types but also in the compositions and physical properties), and 
more preferably they are the same synthetic resins except for the 
difference in color or in the presence or absence of the color. 
In the transparent boundary strip zone (C), the colored transparent 
synthetic resin (a) and the transparent synthetic resin (b) are overlapped 
to each other, as shown in FIG. 7. It is preferably a zone wherein the 
thickness of the layer of the colored transparent synthetic resin (a) and 
the thickness of the layer of the transparent synthetic resin (b) are 
gradually changed in the width direction (the left-right direction in the 
Figure) of the sheet. Namely, it is preferably a zone wherein the 
thickness of the layer of the colored transparent synthetic resin (a) 
becomes gradually thin and the thickness of the transparent synthetic 
resin (b) becomes gradually thick from the side where the zone (C) is in 
contact with the zone (A) towards the side where the zone (C) is in 
contact with the zone (B) (the total thickness of the two-layers being the 
same at any position). In the zone (C), either one of the layers of the 
colored synthetic resin (a) and the transparent synthetic resin (b) may be 
on the top of the other (although the two surfaces of the sheet may be 
distinguished in the sense that one of them is formed to be in contact 
with the substrate, and the other is formed to be not in contact with the 
substrate). 
The boundary surface (the cross section of which is represented by a dotted 
line in FIG. 7) in the transparent boundary strip zone (C) where the 
colored transparent synthetic resin (a) and the transparent synthetic 
resin (b) are in contact with each other is not necessarily distinct. This 
boundary surface is a surface formed by the contact of the two-types of 
flowing synthetic resin materials. Therefore, as microscopically observed, 
the two types of materials diffuse or mix at the boundary surface by the 
formation of turbulent flow. However, as observed macroscopically, the 
boundary surface exists, and the color is gradually changed in the zone 
(C). Further, this boundary surface is a boundary surface with respect to 
the color, and it is preferred that no substantial boundary surface exists 
with respect to the synthetic resin. Namely, it is preferred that the two 
types of the transparent synthetic resins (a) and (b) are in contact with 
each other without no substantial discontinuity even if they form a 
boundary surface where discontinuity in color exists. Particularly, no 
substantial discontinuity in the physical properties (such as strength) of 
the synthetic resins must exist at such a boundary surface. However, 
discontinuity in other properties may be permissible. For example, the 
colored transparent synthetic resin (a) is required to contain a coloring 
agent such as a dyestuff or pigment, while the transparent synthetic resin 
(b) may not contain a coloring agent or may contain a different type of a 
coloring agent. Further, for the purpose of preventing discoloration of 
the coloring agent, a stabilizer such as ultraviolet absorber may be 
incorporated in a substantial amount to the colored transparent synthetic 
resin (a), whereas no such a stabilizer or a less amount of such a 
stabilizer may be incorporated to the transparent synthetic resin (b). In 
such cases, there is a difference in the physical properties of the two 
types of transparent synthetic resins (a) and (b). The two types of 
transparent synthetic resins are most preferably substantially the same 
synthetic resins except for such a minor difference in the physical 
properties or the difference in the incorporation of a small amount of 
additives. This boundary surface may not be flat. For example, the cross 
section of the boundary surface as shown in FIG. 7 may be curved. 
FIG. 8a is a cross-sectional view of a discharge die 12, and FIG. 8b is an 
enlarged bottom view thereof. The cross section of the cross-sectional 
view of FIG. 8a is taken along line II--II'. The discharge die 22 has a 
first inlet 26, a second inlet 27, a first flowpath 28 enlarged in a 
fan-shape, a second flow path 29 enlarged in a fan-shape, a linear outlet 
21 and a partition wall 30 separating the first and second flow paths and 
extending with its end terminated immediately before the linear outlet 21. 
A synthetic resin material (a') 23 is introduced from the inlet 26, flow 
while spreading in the flow path 28 and is discharged from the linear 
outlet 21. Likewise, a synthetic resin material (b') 24 is introduced from 
the inlet 27, passes through the flow path 29 and is discharged from the 
linear outlet 21. The flow paths 28 and 29 join immediately before the 
linear outlet 21 to form a single flow stream, and they are divided by the 
partition wall 30 at the up-stream side. The width of the flow path is 
narrow (about x-z) at the front side at the cross sectional position 
(cross section along line II-II') of the cross-sectional view of FIG. 8a 
and wide at the back side (about x). Inversely, the width of the flow path 
29 is wide (about y) at the front side at the cross sectional position and 
narrow (about y-z) at the back side. The partition wall 30 is inclined 
relative to the thickness to the direction of the linear outlet 21, as 
shown by the bottom view of FIG. 8b. Namely, when the thickness direction 
of the linear outlet (the top-bottom direction in the Figure) is taken as 
0.degree. C. and the direction perpendicular thereto (the longitudinal 
direction of the linear outlet) is taken as 90.degree. C., the inclination 
angle .theta. is within a range of 0&lt;.theta.&lt;90. The closer the 
inclination angle to 90.degree. C., the wider the width of z. The closer 
the inclination angle to 0.degree. C., the narrower the width of z. The 
flows of the two types of synthetic resin materials (a') 23 and (b') 24 
overlap to each other at down-stream of the lower end of the partition 
wall 30 and they are discharged from the linear outlet 21 while 
maintaining the overlapping relation. The width of the lower end of the 
partition wall 30 is not necessarily the same as the width of z, because 
in many cases, the width of the overlapping portion changes more or less 
between the lower end of the partition wall 30 to the linear outlet 21 or 
before the synthetic resin materials discharged from the linear outlet 
become viscous and the flowability is lost (in most cases, the width of 
the overlapping portion is enlarged). 
In the present invention, the location or the shape of the partition wall 
30 in the discharge die 22 is not limited to the above embodiment. For 
example, the lower end of the partition wall 30 i.e. the terminal end in 
the down-stream direction, may extend to or beyond the linear outlet 21. 
In such a case, the flows of the two synthetic resin materials (a') 23 and 
(b') 24 join and overlap immediately after being discharged from the 
linear outlet 21 or at a further down-stream thereof. In a case where the 
two materials have relatively high viscosity and flow in the flow paths 
mainly by laminar flow, the terminal end of the partition wall may be 
located at a further up-stream side. 
In an extreme case, it is possible to provide a partition wall near the 
inlets of the discharge die so that the two flows are twisted before they 
are enlarged in a fan-shape and the two flows advance in a single 
fan-shaped flow path in a partially overlapping state and are discharged 
from the linear outlet. 
FIGS. 9a to 9d illustrate another embodiment of the discharge die. FIG. 9a 
is a partial plan view, FIG. 9b is a partial cross-sectional view, FIG. 9c 
is a cross-sectional view and FIG. 9d is a transverse cross-sectional 
view. The discharge die has an inlet 41 for introducing a synthetic resin 
material and a linear outlet 42 extending in the left-right direction in 
the Figure. It has a fan-shaped flow path 43 enlarged in the longitudinal 
direction of the linear outlet from the inlet 41 to the lineart outlet 42. 
The inlet 41 is divided by a partition wall 44. A first synthetic resin 
material (a') is introduced from one divided section 45, and a second 
synthetic resin material (b') is introduced from the other divided section 
46 in an amount substantially larger than the first material. As shown in 
FIG. 9a, the partition wall 44 is provided with an inclination at an angle 
between 0.degree. (the top-bottom direction in the Figure) i.e. the width 
direction of the linear outlet 42 and 90.degree. (the left-right 
direction) i.e. the longitudinal direction of the linear outlet. The flows 
of the two synthetic resin materials join to contact each other at the 
lower end of the partition wall 44, and further advance while enlarging 
the width of the flow to the linear outlet 42 and are discharged 
therefrom. 
As shown in FIG. 9c, the synthetic resin materials introduced from the 
inlet 41 flow downwards in the Figure while spreading in the left hand 
direction in the Figure and are then discharged from the linear outlet 42. 
The material introduced from the divided section 46 is in a larger amount 
than the material introduced from the other divided section 45, whereby 
the width of the discharge will be substantially wider than the width x of 
the other. Besides, the flows of the two materials are twisted by the 
inclined partition wall 44, whereby there will be a portion where the two 
materials are discharged in a overlapping manner, and the width of such a 
portion will be z. The cross sectional shape of the flow path 43 is as 
shown in FIG. 9d, whereby at the thick portion of the up-stream flow path 
for the materials, the respective materials mainly flow in the left-right 
direction in FIG. 9c and at the thin portion of the down-stream flow path, 
the materials mainly flow downwardly as shown in FIG. 9c. The boundaries 
of the respective materials will be as shown by the dotted lines in FIG. 
9c. 
FIGS. 10a and 10b show a partial plan view (10a) and a partial 
cross-sectional view (10b) of a further embodiment of the discharge die. 
The discharge die 50 has two inlets 51 and 52. A first synthetic resin 
material (a') is introduced from the first inlet 51, and a second 
synthetic resin material (b') is introduced from the second inlet 52 in an 
amount substantially larger than the first material. The partition wall 53 
extends from the first inlet to the right hand side in the FIG. 10a and 
its lower end reaches about the middle of a thick portion of the thick 
flow path as shown in FIG. 9d. The cross-sectional view taken along the 
lower end portion of this partition wall 53 is shown in FIG. 10b. In each 
Figure, the partition wall 53 is inclined relative to the linear outlet 54 
extending the left-right direction in the Figures. 
There is no particular restriction as to the shape of the above partition 
wall, so long as it is capable of bringing the two flows into an 
overlapping relation to each other. For example, in the partition wall as 
shown in FIG. 9, its cross sectional shape (the cross section in a 
direction perpendicular to the flow direction) may be not only linear as 
illustrated, but also in a S-shape to impart twisting to the flows in 
order to more effectively conduct the overlapping of the flows. The 
control of the width of the overlapping portion z may be conducted not 
only by the partition wall but also by changing the flow rate or the 
pressure of the two types of the synthetic resin materials. 
In the method of the present invention, a T-die having the above-mentioned 
structure is preferred as the discharge die. The T-die includes a straight 
manifold type, a coat hanger type and a fish tail type. Either one of such 
T-dies may be employed. It is particularly preferred to employ a T-die of 
a coat hanger type. 
In the method of the present invention, as the continuous substrate, it is 
preferred to employ a film or sheet having no adhesive property on its 
surface. For example, a film or sheet or a synthetic resin such as a 
polyethylene terephthalate resin or a steel belt having its surface 
treated for non-adhesiveness is suitable. Further, the continuous 
substrate may be a film or sheet constituting underlayer (or in some 
cases, an upper layer) of a multi-layered sheet. For example, in the case 
of BLW of a type wherein a polyethylene terephthalate resin film having a 
hard coating layer is laminated on an inorganic glass sheet by means of an 
adhesive synthetic resin, the continuous substrate may be made of this 
polyethylene terephthalate resin film (a supporting substrate fixed 
thereunder or movable together with this film may be provided) and a hard 
coating material is coated and cured thereon by the method of the present 
invention to obtain a hardcoat-provided film for BLW. 
Various means may be employed for moving the discharge die. For example, 
the discharge die may be driven by an electric motor or a servo motor 
provided with a screw. Such a driving means is preferably the one capable 
of controlling the speed of the movement and the cycle of the 
reciprocating movement as desired, whereby it is possible to produce a 
continuous sheet with the optimum shape or width depending upon the shape 
or size of BLW. 
The above described casting method is useful for producing a multi-layered 
sheet continuously. For example, a multi-layered sheet may be formed by a 
method wherein a second sheet may be laminated on a sheet formed by the 
above described method, or by a method wherein a second synthetic resin 
material is cast and cured thereon. It is particularly preferred to employ 
a multi-step casting method wherein a second synthetic resin material is 
cast and cured on the sheet formed by the above described method. 
FIGS. 11a and 11b illustrate a method for producing a two-layered sheet by 
a two-step casting method. FIG. 11a is a perspective view showing the 
two-step casting apparatus, and FIG. 11b is a cross-sectional view showing 
the cross section of the two-layered sheet thereby produced. Onto a 
continuous substrate 60, a synthetic resin material 62 is firstly 
discharged from a first discharge die 61. This first discharge die 61 is 
the discharge die illustrated in FIGS. 9a to 9b. This discharge die 61 
reciprocates in the left-right direction in the Figure and discharges 
synthetic resin materials 62 having different colors. The discharged 
synthetic resin materials 62 are cast and partially or completely cured 
while being passed through a heating furnace (not shown) to form a sheet 
63 made of the first synthetic resin. This sheet 63 made of the first 
synthetic resin has a colored transparent strip zone (A), a transparent 
strip zone (B) and a boundary strip zone (C) as mentioned in the 
foregoing. Then, onto the formed sheet 63, a second synthetic resin 
material 64 is supplied from a second discharge die 65. This second 
synthetic resin material is preferably a material capable of forming a 
colorless or uniformly colored synthetic resin. The second discharge die 
65 is preferably fixed. The discharge second synthetic resin material 64 
is cast and then cured. As shown in FIG. 11b, the resulting laminated 
sheet 66 has a double-layered structure, wherein the underlayer 67 as the 
colored transparent strip zone (A), the transparent strip zone (B) and the 
boundary strip zone (C) as shown in FIG. 7, and the upper layer 68 is made 
of a colorless or uniformly colored transparent synthetic resin. 
The preparation of the multi-layered sheet by a multi-step casting method 
is not restricted to the method shown in FIG. 11a. For example, in FIG. 
11a, a two-layered sheet may be produced by exchanging the positions of 
the first and the second discharge dies. Namely, onto the continuous 
substrate 60, the second synthetic resin material 64 is firstly discharged 
from the second discharge die 65, cast and cured, and then the first 
synthetic resin material 62 is discharged from the first discharge die 61, 
cast and cured to obtain a two-layered sheet having an underlayer made of 
the second synthetic resin and an upper layer made of the first synthetic 
resin (having a colored transparent strip zone (A)). 
The width of the continuous sheet (including the above-mentioned laminated 
sheet) of the synthetic resin in the present invention is preferably at 
least 50 cm depending upon the size of the glazing product for 
automobiles, as its main use. There is no particular restriction as to the 
upper limit of the width, but it is usually about 2 to 3 m. The thickness 
of the sheet is preferably from 0.04 to 4 mm, more preferably from 0.06 to 
2 mm. In the case of a laminated sheet, the overall thickness is 
preferably from 0.02 to 4 mm, more preferably from 0.4 to 2 mm, and the 
thickness of the thinner layer is preferably from 0.04 to 1 mm. The width 
of the strip zone (C) is preferably at most 1/3, more preferably at most 
1/5, of the width of the sheet. The lower limit is preferably about 1 cm, 
more preferably about 3 cm. 
The continuous sheet (inclusive of the above-mentioned laminated sheet) of 
a synthetic resin in the present invention is useful as a material for 
producing a laminated safety glazing product for automobiles or for 
building materials. Namely, from this continuous sheet, a sheet of a 
suitable size is cut out and directly or by means of an adhesive or 
together with other synthetic resin sheet or film, laminated on a 
transparent inorganic glass sheet or organ glass sheet to obtain a 
laminated safety glazing product. It is particularly suitable as a 
material for BLW which is used as a windshield for automobiles. 
When the continuous sheet in the present invention is a single layer 
synthetic resin, such a sheet will be used as the surface layer or inner 
layer of BLW. When used as the surface layer, the synthetic resin is 
preferably a cross-linked polyurethane resin having excellent self-healing 
properties. When used as an inner layer, the synthetic resin is preferably 
a thermoplastic or cross-linked polyurethane resin having high mechanical 
strength (which may have lower self-healing properties than the surface 
layer). 
When the continuous sheet of the present invention is used as the surface 
layer, the synthetic resin of the continuous sheet is preferably a 
cross-linked polyurethane resin having both excellent self-healing 
properties and high mechanical strength. The above-mentioned laminated 
sheet may be directly or by means of an adhesive layer laminated on the 
above-mentioned inorganic glass sheet with its one side as the surface 
layer and the other side as the bonding the surface, to obtain BLW. For 
this surface layer, it is preferred to employ a cross-linked polyurethane 
resin having excellent self-healing properties. This surface layer may be 
formed by the above-mentioned multi-step casting method as the upper-layer 
or underlayer of the laminated sheet. The layer which does not constitute 
the surface layer is preferably a thermoplastic or cross-linked 
polyurethane resin having high mechanical strength (which may have lower 
self-healing properties than the surface layer). By using the surface of 
this inner layer as the bonding surface, the laminated sheet is bonded to 
an organic glass sheet to obtain BLW. 
As the transparent synthetic resin, a polyurethane resin is particularly 
preferred. However, it may be a transparent synthetic resin formed by any 
other flowable synthetic resin material (a molten synthetic resin or a 
flowable mixture of reactive materials capable of forming a synthetic 
resin by reaction). As the polyurethane resin, a non-yellowing type 
polyurethane resin is used (a polyurethane resin obtained by using an 
aromatic polyisocyanate having an isocyanate group directly bonded to the 
aromatic nucleus is a yellowing type, and a polyurethane resin obtained by 
using an aliphatic polyisosianate, an alicyclic polyisocyanate and an 
aromatic polyisocyanate containing an isocyanate group not directly bonded 
to an aromatic nucleus is a non-yellowing type). The polyurethane resin 
may be a linear polyurethane resin having thermoplasticity or a 
cross-linked polyurethane resin (which may also be called a thermosetting 
polyurethane resin) having no thermoplasticity. Further, the polyurethane 
resin is preferably has excellent self-healing properties or high 
mechanical strength or both of such properties. The polyurethane resin 
having excellent self-healing properties is known and disclosed in e.g. 
U.S. Pat. Nos. 4,657,796, 4,684,694 or 3,979,548. The polyurethane resin 
having high mechanical strength is known and disclosed in e.g. European 
Patent No. 54491, Japanese Unexamined Patent Publication No. 135216/1984 
or U.S. Pat. No. 4,600,653. The polyurethane resin having both excellent 
self-healing properties and high mechanical strength is known and 
disclosed in e.g. European Paten No. 131,523, U.S. Pat. No. 4,683,171 or 
Japanese Unexamined Patent Publication No. 222249/1985 or No. 281118/1986. 
The casting method of the present invention is preferably conducted by 
using a mixture of reactive materials containing no substantial solvent, 
as the resin material (which may be called also as a bulk casting method). 
This mixture of reactive materials comprises a polyol and a polyisocyanate 
compound as the main components, and in many cases, further contains a 
chain extender such as a low molecular weight polyol or polyamine. 
Further, a small amount of a catalyst is usually incorporated. Further, a 
coloring agent is incorporated in at least one of the reactive material 
mixtures of the above-mentioned synthetic resin material (a') and the 
synthetic resin material (b'). If necessary, a stabilizer such as a 
ultraviolet absorber, an antioxidant, or a light stabilizer, or a 
moldability improving agent such as a leveling agent to improve the 
flowability or wettability of the mixture of reactive materials in 
casting, may be incorporated. However, it is undesirable to incorporate an 
additive which impairs the transparency of the synthetic resin, such as an 
inorganic filler. 
The above-mentioned polyol is preferably a polyester polyol, a 
polycarbonate polyol, a polyoxytetramethylene polyol or a combination 
thereof. Further, each polyol may be a combination of polyols having 
different molecular weights or different number of hydroxyl groups. The 
molecular weight is preferably from about 20 to 500, more preferably from 
40 to 400 as represented by the hydroxyl value. The number of hydroxyl 
groups is preferably from about 2 to 4, more preferably from about 2 to 3. 
When two or more polyols are used in combination, these values represent 
average values. When polyols having high molecular weights (i.e. low 
hydroxyl values) are used, it is preferred to incorporate a chain 
extender. The chain extender is a polyol having a relatively low molecular 
weight (usually not higher than 200) or a polyamine having a relatively 
low molecular weight. For example, it includes ethylene glycol, 
1,4-butanediol, 1,6-hexanediol, diethanolamine, dimethylol propionic acid, 
hexamethylenediamine and isophoronediamine. As the polyisocyanate, a 
polyisocyanate having no isocyanate group directly bonded to the aromatic 
nucleus as mentioned above, may be employed. Specifically, for example, 
methylenebis(cyclohexyl isocyanate), isophorone diisocyanate, 
hexamethylene diisocyanate or xylylene diisocyanate, or a modified product 
thereof such as an urea modified product, a prepolymer type modified 
product or an amide modified product may be mentioned. Particularly 
preferred is an alicyclic diisocyanate or an aliphatic diisocyanate, or a 
modified product thereof. A mixture obtained by mixing such reactive 
starting materials or mixing a prepolymer obtained by a partial reaction 
thereof, with the rest of materials, is subjected to reaction and curing 
to obtain a polyurethane resin.