Apparatus for preparing a synthetic resin plate of different colors

A synthetic resin plate having at least two different colors is prepared by a process having the steps of supplying at least two polymerizable liquid materials differing in the color from at least two inlets, passing them through at least two groups of flow paths alternately arranged, extruding and injecting the polymerizable liquid materials into a polymerization apparatus, polymerizing the liquid materials, and withdrawing a plate-shaped product having a striped pattern extending from the surface to the interior or a plate-shaped product having said striped pattern in which the boundary area between the adjacent stripe lines of different colors is gradated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process and apparatus for the 
preparation of a synthetic resin plate having at least two different 
colors. More particularly, it relates to a process and apparatus for the 
preparation of a synthetic resin plate having different colors, which 
comprises supplying a plurality of polymerizable liquid materials 
differing in color from at least two inlets, passing them through at least 
two groups of flow paths alternately arranged, extruding and injecting the 
polymerizable liquid materials into a polymerization apparatus, 
polymerizing the liquid materials, and withdrawing a plate-shaped product. 
The resulting product has a striped pattern extending from the surface to 
the interior or a striped pattern in which the boundary area between the 
adjacent stripe lines of different colors is gradated. 
2. Description of the Prior Art 
A plate of different colors having a color pattern only on the surface 
thereof has been known, and plates of this type are prepared according to 
various processes. For example, there can be mentioned a process in which 
a plate is formed and a pattern is printed on the plate by using paints 
differing in color, and a process in which a film having a color pattern 
printed thereon is bonded to a plate. Furthermore, plates of different 
colors in which the boundary area of the color pattern is gradated can be 
prepared according to a process in which paints differing in hue are 
applied to the surface of a plate by printing, spraying or dyeing or a 
process in which a film colored by printing, spraying or dyeing is bonded 
to the surface of a plate. However, these conventional plates of different 
colors are inferior as to durability and are defective in that the surface 
color film can be peeled from the surface of the plate by an external 
force or with the lapse of time. Moreover, when such a plate is subjected 
to heating or drawing processing, wrinkles are formed because of 
differences in the stretchability between the surface color film and the 
core plate, or the color is thinned in the drawn portion and the color 
difference between the drawn portion and the undrawn portion becomes 
prominent, resulting in a reduction of the aesthetic effect. 
Plates of different colors having a color pattern extending from the 
surface to the interior are disclosed in U.S. Pat. Nos. 3,488,246, 
3,529,325, 3,526,378, 3,570,056, 3,706,825 and 4,232,078. According to the 
teachings of these U.S. patents, a polymerizable liquid material including 
a filler and a colorant and having a high viscosity are appropriately 
mixed together by a three-stage mixing apparatus and the polymerizable 
liquid material is polymerized and cured to obtain an opaque plate-shaped 
product having a pattern resembling a marble pattern. The characteristic 
feature of this preparation process resides in appropriate mixing, and the 
pattern is changed according to the concentration, viscosity and flow rate 
of the starting material and the state of the mixer. Therefore, the 
probability of formation of a predictable pattern on the surface of the 
plate is low. It is thus difficult to produce an aesthetic color pattern 
with a good reproducibility. 
The technique disclosed in U.S. Pat. No. 4,232,078 is one developed by the 
inventor of the present invention. According to the technique of this 
patent, at least two polymerizable liquid materials differing in color are 
injected into a polymerization apparatus and are polymerized and cured to 
gradate the boundary area between the two liquids. In a plate of different 
colors prepared according to this process, the hue is changed only in the 
direction of the width but the hue is substantially uniform in the 
direction of the thickness. Accordingly, the formed pattern is relatively 
monotonous and lacks depth. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to provide a plate of 
different colors having a deep appearance in which the hue is changed not 
only in the direction of the width but also in the direction of the 
thickness by improving the technique disclosed in U.S. Pat. No. 4,232,078. 
That is, the invention provides a plate of different colors having a deep 
pattern of a plurality of lines extending from the surface to the interior 
or such a deep line pattern in which the boundary area is gradated. 
In accordance with the present invention, there is provided a process for 
the preparation of a synthetic resin plate having different colors, which 
comprises supplying at least two polymerizable liquid materials differing 
in the color from at least two inlets, passing them through at least two 
groups of flow paths alternately arranged, extruding and injecting the 
polymerizable liquid materials into a polymerization apparatus 
polymerizing the liquid materials and withdrawing a beautiful plate-shaped 
product having a striped pattern extending from the surface to the 
interior, or a beautiful plate-shaped product having the striped pattern 
in which the boundary area between the adjacent stripe lines of different 
colors is gradated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The synthetic resin plate having different colors according to the present 
invention may be preferably used as a surface decorating plate for a 
sanitary article such as a bathtub or a washstand and for room furniture, 
display stands and various partitions. 
The polymerizable liquid material used in the present invention is a 
polymerizable starting material comprising at least one monoethylenically 
unsaturated compound or polyfunctional compound, which is liquid under the 
normal pressure. As the monoethylenically unsaturated compound, there can 
be mentioned, for example, methacrylates such as methyl methacrylate, 
ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate and benzyl 
methacrylate, styrene, and halogen-substituted derivatives (such as 
chlorostyrene) and alkyl-substituted derivatives (such as 
.alpha.-methylstyrene) of styrene. Furthermore, a mixture comprising a 
substantial amount of such a methacrylate as mentioned above and an 
acrylate such as methyl acrylate as mentioned above and an acrylate such 
as methyl acrylate, ethyl acryate, butyl acrylate or 2-ethylhexyl 
acrylate, vinyl acetate, acrylonitrile or a derivative thereof may be 
used. As the polyfunctional compound, there can be mentioned, for example, 
glycol dimethacrylate, triallyl cyanurate, triallyl isocyanurate, 
poly(ethylene glycol) acrylate, poly(ethylene glycol) methacrylate, allyl 
acrylate, allyl methacrylate, divinylbenzene, diallyl methacrylate, 
diallyl phthalate and diethylene glycol bis-allylcarbonate. A mixture of 
methyl methacrylate as the main component and a comonomer copolymerizable 
therewith is most preferably used as the polymerizable liquid material in 
the present invention. 
A polymerization initiator is ordinarily incorporated into the 
polymerizable liquid material. For example, there may be used free radical 
polymerization initiators such as azobisisobutyronitrile, 
azobisdimethylvaleronitrile, benzoyl peroxide, lauroyl peroxide, acetyl 
peroxide, capryl peroxide, 2,4-dichlorobenzoyl peroxide, isopropyl 
peroxydicarbonate, isobutyl peroxide and acetylcyclohexylsulfonyl 
peroxide. Two or more or these initiators may be simultaneously used. 
A mixture of a monomer and a polymer may be used as the polymerizable 
liquid material, so far as the flowability is not lost. More specifically, 
there can be used a mixture formed by dissolving or suspending an 
appropriate amount of a polymer into a monomer such as mentioned above and 
monomer/polymer mixture obtained by partial polymerization. Various 
additives such as a stabilizer, a plasticizer, a polymerization regulator, 
a parting agent and a viscosity modifier may be added to the polymerizable 
liquid material, so far as polymerization is not extremely inhibited. 
The polymerizable liquid materials differing in color, which are used in 
the present invention, are polymerizable liquid materials differing in hue 
and/or saturation within the range covering colorless transparency, 
semitransparency and opacity. Dyes, pigments and coloring assistants used 
for the production of the polymerizable liquid materials differing in 
color may be selected from known products. When a transparent colored 
synthetic resin plate is prepared, at least one dye or a dispersion of at 
least one pigment in a dispersion medium is incorporated. When a 
semitransparent or opaque colored synthetic resin plate is prepared, a 
powdery or pasty pigment or dye is used. A granular processed pigment 
prepared by dispersing a pigment in the polymerizable liquid material, for 
example, methyl methacrylate or monomeric styrene, at a high 
concentration, adding a polymerization initiator to the dispersion, 
polymerizing the monomer and pulverizing the obtained colored polymer may 
be used as the pigment. This granular processed pigment is especially 
preferably used in the present invention. There may be adopted a simple 
method in which a powdery or pasty pigment is directly added to the 
polymerizable liquid material. In this case, however, color unevenness is 
caused by agglomeration or precipitation of the pigment, or uneven 
polymerization is caused by the activity of the pigment, resulting in a 
reduction of the quality or appearance of the product. In order to control 
the degree of transparency in a semitransparent product, it is preferred 
that an appropriate amount of a copolymer of methyl methacrylate and 
styrene prepared in advance be dissolved as the coloring assistant in the 
polymerizable liquid material to maintain the quality at a certain level. 
According to another method, an appropriate amount of monomeric styrene is 
added to the polymerizable liquid material. 
In the present invention, at least two polymerizable liquid materials 
differing in color are prepared according to the above-mentioned method. 
In the case where a dye is used as the colorant, it is preferred that the 
viscosities of the polymerizable liquid materials be controlled within the 
range of from 5 to 30 P (poise) at 20.degree. C. and the difference of the 
viscosity between the polymerizable liquid materials differing in color be 
not larger than 8 P. In the case where a pigment is used as the colorant, 
it is preferred that the viscosities of the polymerizable liquid materials 
be controlled within the range of from 3 to 30 P and the difference of the 
viscosity between the polymerizable liquid materials be not larger than 10 
P. 
For the production of a plate-shaped product having a striped pattern or a 
striped pattern in which the boundary area between the adjacent stripe 
lines of different colors is gradated according to the present invention, 
there may be adopted a process in which at least two groups of extrusion 
openings differing in sectional area and/or the number of the extrusion 
openings are alternately arranged, the polymerizable liquid materials 
colored in different hues are extruded at the same or different speeds 
from the respective groups of extrusion openings and are injected into a 
continuous polymerization apparatus of the confronting belt type for 
preparing and molding a resinous plate and the polymerizable liquid 
materials are polymerized. The striped pattern is formed when the 
polymerizable liquid materials are extruded from the respective groups of 
extrusion openings arranged alternately. The stripe line number and 
thickness of the striped pattern are determined by appropriately setting 
the sectional area and number of the extrusion openings. While 
polymerization is advanced in the continuous polymerization apparatus, the 
confronting belts are pressed by supporting rollers and the liquid 
materials differing in color are slightly mingled and diffused in the 
boundary area by the expanding force due to the weight and rigidity of the 
belts, with the result that the boundary area becomes gradated. The degree 
of gradation can be reduced by adjusting the viscosities of the liquid 
materials to 20 to 30 P and controlling the difference of the viscosity to 
0 to 5 P. The degree of gradation can be increased by adjusting the 
viscosities of the liquid materials to 3 to 30 P and controlling the 
difference of the viscosity to 5 to 10 P, and the effect is enhanced by 
the addition of a surface active agent. 
A striped pattern having thick and thin portions may be formed by injecting 
the polymerizable liquid materials differing in the color into a 
polymerization apparatus while extruding them at the same or different 
speeds. 
In the at least two groups of extrusion openings used in the process of the 
present invention, the total sectional area and sectional area of a single 
extrusion opening are not critical. In carrying out the process of the 
present invention, however, it is preferred that the sectional area be in 
the range of from 1 to 300 mm.sup.2. The sectional area ratio between the 
groups of extrusion openings may be in the range of from 1:99 to 99:1. The 
number of extrusion openings in each group may be 1 or an optional larger 
number, but in view of formation of the intended linear pattern of the 
present invention, it is preferred that the number of extrusion openings 
of each group be 5 to 500. The liquid materials are extruded from these 
extrusion openings in an amount corresponding to the capacity of the 
polymerization apparatus of the confronting belt type, that is, in an 
amount of 3 to 30 l/min, and the flow rate of each liquid material is 
adjusted to 0.1 to 10 m/min. In view of formation of the intended linear 
pattern, it is prefered that the ratio of the flow rates between the 
liquid materials be in the range of from 1:1 to 1:20. 
In carrying out the process of the present invention, the amount of 
polymerization initiator added for completion of polymerization of the 
liquid material is preferably adjusted to 0.05 to 0.3% in case of benzoyl 
peroxide or 0.02 to 0.2% in case of azobismethylvaleronitrile. 
The process of the present invention will now be described in detail with 
reference to the accompanying drawings. 
FIG. 1 is a longitudinal sectional view illustrating an embodiment of the 
apparatus in which three groups of extrusion openings are arranged and 
three polymerizable liquid materials differing the color are combined. 
Plates 5, 6 and 7 are sandwiched together, as by bolts 10 (FIG. 3). A 
conical gate 8 is connected to an upstream surface of the plate 5 and a 
conical gate 9 is connected to a downstream surface of plate 7. 
Polymerizable liquid materials differing in color are supplied at 
predetermined rates from inlets A, B and C, respectively, via metering 
pumps. The polymerizable liquid material supplied from the inlet A 
(hereinafter referred to as "liquid A") is guided to an outlet D through 
gate 8, extrusion openings 1, 1' . . . 1.sup.n in plates 5-7 and gate 9. 
The polymerizable liquid material supplied from the inlet B (hereinafter 
referred to as "liquid B") is guided to the outlet D through extrusion 
openings 2, 2' . . . 2.sup.n in plates 6 and 7 via the circumferential 
passage 4 and the spiral passages 2a in the plate 6. The polymerizable 
liquid material supplied from the inlet C (hereinafter referred to as 
"liquid C") is guided to the outlet D through extrusion openings 3, 3' . . 
. 3.sup.n in plate 7 via the circumferential passage 4' and the spiral 
passages 3a in the plate 7. If spacers 33 and 33' are arranged on eigher 
side of the sandwich formed by plates 5-7, the liquid flows are 
effectively prevented from being disturbed. The liquid materials coming 
from the outlet D are injected into a polymerization device while the 
formed striped pattern is maintained. 
FIG. 2 is a side view showing the groups of extrusion openings illustrated 
in FIG. 1. The liquid A passes through the first group of extrusion 
openings 1 in plates 5-7 from the left side face to the right side face in 
FIG. 1. The liquid B passes through the circumferential passage 4 from the 
inlet B and is distributed into the spiral passages 2a. The liquid B then 
passes through the second group of extrusion openings 2 formed in the 
spiral passages 2a and extending to the right in FIG. 1. The liquid C 
passes from inlet C through circumferential passage 4', additional spiral 
passages 3a, and then through the third group of extrusion openings 3 
formed in the spiral passages 3a and extending to the right from in FIG. 
1. Thus, the liquids A, B and C are combined and joined together while 
forming a striped pattern. The numbers and sizes of the extrusion openings 
1, 2 and 3 of the first, second and third groups shown in FIG. 2 may be 
determined according to the intended configuration of the striped pattern. 
Furthermore, the flow amounts and rates of the liquids A, B and C may 
optionally be set. For example, when only the liquid C among the liquids 
A, B and C is extruded at a high speed from the extrusion openings, since 
the line of the liquid C draws a different locus, a complicated pattern 
can be effectively formed. 
FIGS. 3, 4 and 5 show a combination of two groups of extrusion openings. 
FIG. 3 is an enlarged sectional view illustrating groups of extrusion 
openings in which liquids A and B are extruded from extrusion openings 1 
to 1.sup.n and extrusion openings 2 to 2.sup.n, respectively. FIGS. 4A and 
4B are plan and sectional views illustrating a part of the plate 5 shown 
in FIG. 3. FIGS. 5A and 5B are plan and sectional views illustrating a 
part of the plate 6 shown in FIG. 3. Circular plates are shown in FIGS. 2, 
4 and 5, but the plates that can be used in carrying out the present 
invention are not limited to such a circular plate. Referring to FIG. 3, 
the liquid B supplied from the inlet B passes through a passage 4 formed 
in the plate 6 and is extruded from extrusion openings 2 to 2.sup.n. The 
liquid B is then combined with the liquid A extruded from extrusion 
openings 1 to 1.sup.n and in this way a striped pattern is formed. 
FIG. 6 shows an embodiment of the continuous polymerization apparatus used 
in carrying out the process of the present invention. In FIG. 6, reference 
numerals 11 and 11' represent endless belts. Belts of a metal such as 
steel or stainless steel can be used as these belts. In order to obtain a 
plate excellent in surface appearance, these metal belts are carefully 
polished. The thickness of each metal belt is preferably 0.5 to 2 mm. The 
belts are respectively spread by main pulleys 12 and 13 and main pulleys 
12' and 13' to produce a predetermined tension in each belt. It is known 
to connect hydraulic cylinders to the main pulleys 12 and 12' and to 
adjust tensions on the belts by changing the hydraulic pressure in the 
cylinders. In order to improve the shape of the belts and increase the 
thickness precision of the plate, it is preferred that the tensions on the 
belts be high, but ordinarily, the belts are operated under tensions of 3 
to 15 Kg/cm.sup.2. The belts are moved by driving the main pulley 13', and 
meandering of the belts is prevented by adjusting angles of the main 
pulleys 12 and 13 and the main pulleys 12' and 13'. The angles of the main 
pulleys can be adjusted by changing the hydraulic pressures of the 
cylinders or by other mechanical means. Meandering of the belts can also 
be prevented by changing the angles of rolls 22 and 22' contacted with the 
back surfaces of the belts. 
The liquid materials are supplied from outlet D into a space between the 
confronting belts through a conduit 31 and an inclined plate 32 forming an 
injector. Injectors disclosed in Japanese Patent Publications No. 48-1276 
and No. 48-16056 and Japanese Patent Application No. 52-38890 may be used 
for injection of the liquid materials. In order to prevent the linear 
pattern from being disturbed, in the process of the present invention, it 
is preferred that the injector be brought as close to the lower belt 
surface as possible while preventing the injector from contacting the 
lower belt surface. 
Reference numerals 23 and 23' represent gaskets. The gaskets 23 and 23' 
travel with the belts in a state where the gaskets 23 (in FIG. 8) and 23' 
are each gripped between lateral edges of the confronting belts, whereby 
leakage of the liquid materials outside the belts is prevented. A gasket 
formed of soft polyvinyl chloride, polyethylene or the like material may 
be used, and a gasket having properties described in Japanese Patent 
Publication No. 47-49823 is preferably used. 
Rolls 14, 14' and 16, 16' are arranged to support the confronting belts 
from the back surfaces thereof. The rolls 16 should be arranged so that 
the liquid materials do not leak outside from the space defined by the 
confronting belts and the gaskets in the heated polymerization zones 15 
and 15'. The belts curve apart between adjacent rolls due to the hydraulic 
pressure of the liquid materials, the repulsive force of the gaskets and 
the weight of the belts. If the extent of this curvature is increased, the 
thickness precision of the plate-shaped product is reduced, and the linear 
pattern is disturbed with a resulting curve in the pattern lines or a 
change of the gradation state, resulting in a reduction of the aesthetic 
effect. 
This trouble is overcome by controlling the curvature of the belts to a low 
level. As means for controlling curving of the belts, the distance between 
adjacent rolls is narrowed and the belt tension is increased. For this 
purpose, the distance between rolls is adjusted to about 20 to about 100 
cm. The rolls are resiliently mounted so that even when the liquid 
materials are polymerized and contracted, the rolls are able to move in 
follow-up with this contraction and do not separate from the back surfaces 
of the belts. Instead of the above-mentioned roll system, there may be 
adopted a mechanism disclosed in Japanese Patent Publication No. 47-33498 
as the means for supporting the belts. Spray devices 17 and 17' are 
arranged in the polymerization zone to apply warm water to the belts for 
heating the belts. A temperature lower than 100.degree. C. may be used as 
the temperature of the warming water. Ordinarily, a temperature of 
65.degree. to 90.degree. C. is adopted for the warming water. Infrared ray 
heaters 18 and 18' are arranged in the second polymerization zone to heat 
the polymerized plate-shaped product at a temperature higher than 
100.degree. C. for removing the residual monomers. Another method, for 
example, a method using a hot air oven, may be adopted. Reference numerals 
19 and 20 respectively denote a zone for keeping warm and under 
appropriate conditions the plate-shaped product which has passed through 
the second polymerization zone and a zone for cooling the plate-shaped 
product under appropriate conditions. Reference numeral 21 represents a 
roll for supporting the belts in the zones 19 and 20. It is preferred that 
this roll 21 be cooled by a cooling fluid. Reference numeral 24 represents 
the obtained plate-shaped product, that is, the synthetic resin plate. 
FIG. 7 is a side view showing an embodiment of the apparatus for injecting 
the liquid materials into the space between the confronting belts. FIG. 8 
is a plan view showing this apparatus. In FIG. 7, reference numerals 11 
and 11' represent endless belts and reference numerals 12 and 12' 
represent the pulleys. The liquid materials are passed through the conduit 
31 and injected through the injector 32. In order not to disturb the 
striped pattern, it is preferred that the inclined plate of the injector 
32 should have such a width that it is brought close to the inner sides of 
the gaskets 23 (in FIG. 8) and 23'. Furthermore, in order to control 
disturbance of the striped pattern, it is preferred that the distance 
between the top end of the inclined plate and the lower belt 11' be as 
small as possible, so long as the top end is not brought into contact with 
the lower belt. It is ordinarily preferred that this distance be adjusted 
to 3 to 20 mm. 
The process of the present invention will now be described in detail with 
reference to the following examples. 
EXAMPLE 1 
A methyl methacrylate syrup, that is, a partially polymerized product of 
methyl methacrylate, having a viscosity of 20 P at 20.degree. C. and a 
polymerization degree of 24% was mixed with 500 ppm of 
azobisdimethylvaleronitrile as the polymerization initiator, 100 ppm of an 
ultraviolet ray absorber and 20 ppm of dioctyl sulfosuccinate as the 
parting agent to form a liquid material A. The same methyl methacrylate 
syrup as described above was mixed with 5% of monomeric methyl 
methacrylate to adjust the viscosity at 20.degree. C. to 14 P, and 200 ppm 
of an anthraquinone type blue dye was added to the syrup to form a liquid 
material B. A liquid material C was formed by adding 500 ppm of a cyanine 
type green dye dispersed in advance in a dispersing medium to the liquid 
material A. 
The liquid materials A, B and C were deaerated under a reduced pressure 
lower than 70 mmHg and injected at a total flow rate of 12.2 Kg/min at a 
ratio of 80:15:5 to extrusion opening groups A, B and C, respectively. The 
extrusion opening groups were arranged as shown in FIGS. 1 and 2. All of 
the extrusion openings were formed of stainless steel. The first extrusion 
opening group 1 comprised 24 holes, each having a diameter of 4 mm and a 
length of 66 mm. The second extrusion opening group 2 comprised 24 holes, 
each having a diameter of 2 mm and a length of 44 mm. The third extrusion 
opening group 3 comprised 24 holes, each having a diameter of 2 mm and a 
length of 22 mm. 
The liquid materials were passed through the extrusion openings to form a 
striped pattern and were passed through conduits connected to the outlet 
D, and they joined together at the point 31 shown in FIG. 6. Then, the 
liquid materials were continuously injected between the surfaces of the 
belts 11 and 11' through the injector 32 shown in the drawings. 
Each of the belts 11 and 11' was a polished endless belt of stainless steel 
having a thickness of 1.5 mm and a width of 1500 mm, and tensions were 
given to the belts by the main pulleys 12 and 12' and the tensions were 
adjusted to 10 Kg/cm.sup.2 by the hydraulic pressure. The distance between 
the upper and lower belts 11 and 11' was uniformly adjusted to 3 mm by the 
rollers 16 and 16' arranged at intervals of 400 mm. A hollow pipe of 
polyvinyl chloride containing dibutyl phthalate as the plasticizer in an 
amount of 60% based on the polymer, which had an outer diameter of 8 mm 
and a thickness of 0.6 mm, was used as the gasket 23. The length of the 
first polymerization zones 15 and 15' was 66 m, and the belts were heated 
by spraying warm water maintained at 80.degree. C. from the spray devices 
17 and 17' to the back surfaces of the belts. The length of the second 
polymerization zone was 10 m and the sheet was heated at 135.degree. C. by 
the infrared ray heaters 18 and 18'. The length of the keeping-warm zone 
19 was 10 m, and the belts were travelled within ducts surrounding the 
belts. The length of the cooling zone 20 was 2 m, and the polymerized and 
cured plate maintained at a temperature higher than 100.degree. C. at the 
inlet of the cooling zone was cooled to 100.degree. to 80.degree. C. by an 
air current and withdrawn from the belts. 
In the above-mentioned manner, a synthetic resin plate of different colors 
composed mainly of methyl methacrylate, which had a width of 1400 mm and a 
thickness of 3 mm, was continuously obtained. This synthetic resin plate 
had a beautiful appearance and a pattern of transparent blue and green 
lines extending from the surface of the colorless transparent plate to the 
interior thereof in parallel to the direction of advance of the belts, in 
which the boundary area between the two lines was gradated. 
EXAMPLE 2 
Processed pigments described below were added to a methyl methacrylate 
syrup having a viscosity at 20.degree. C. adjusted to 9 P to form a liquid 
material A. Namely, methyl methacrylate, styrene and barium sulfate were 
mixed at a ratio of 7:3:20, and 0.2% of benzoyl peroxide was added to the 
mixture and bulk polymerization was carried out. The obtained polymer was 
pulverized to obtain a granular processed pigment E. A cadmium sulfide 
type yellow pigment F was formed by the same processing as described above 
with respect to the pigment E, and a carbon black type pigment G was 
formed by the same processing as described above. The processed pigments 
E, F and G were incorporated into the methylmethacrylate syrup in amounts 
of 2.5%, 0.03% and 0.0015%, respectively. A liquid material B was prepared 
by adding the processed pigments E, F and G and a processed pigment H 
obtained by processing a cadmium sulfide type brown pigment in the same 
manner as described above with respect to the processed pigments E through 
G in amounts of 1.0%, 0.38%, 0.24 % and 0.28%, respectively, to a methyl 
methacrylate syrup having a viscosity of 20.degree. C. adjusted to 9 P. 
The viscosities at 20.degree. C. of the liquid materials A and B were 14 P 
and 12 P, respectively. Each of the liquid materials A and B was mixed 
with 500 ppm of azobisdimethylvaleronitrile as the polymerization 
initiator, 100 ppm of an ultraviolet ray absorber and 50 ppm of dioctyl 
sulfosuccinate as the parting agent. 
The liquid materials A and B were deaerated under a reduced pressure and 
injected at a flow rate of 8.1 Kg/min at a ratio of 8:2 into extrusion 
opening groups A and B shown in FIGS. 3-5 by metering pumps. All of the 
extrusion openings shown in FIGS. 3-5 were formed of stainless steel. The 
first extrusion opening group 1 comprised 80 circular holes, each having a 
diameter of 4 mm and a length of 44 mm, and the second extrusion opening 
group 2 comprised 80 stepped holes, each having a portion having a 
diameter of 4 mm and a length of 14 mm and a portion having a diameter of 
2 mm and a length of 3 mm. Both the liquids A and B were extruded at 
substantially the same flow rate from the groups of the extrusion openings 
and they were injected into the continuous polymerization apparatus of the 
confronting belt type shown in FIG. 6 while forming a linear pattern. 
Polymerization was effected in this apparatus. Thus, a synthetic resin 
plate of different colors composed mainly of methyl methacrylate, which 
had a width of 1400 mm and a thickness of 2 mm, was continuously prepared. 
This synthetic resin plate had a grained beautiful appearance in which a 
striped pattern of dense brown lines arranged in parallel to the direction 
of advance of the belts was formed in the thin brown semitransparent 
background. 
Obviously many modifications and variations of the present invention are 
possible in light of the above teachings. It is to be understood therefore 
that within the scope of the appended claims this invention may be 
practiced otherwise than as specifically described herein.