Reinforced plastic products with decorated surfaces

Quadruple-layer reinforced plastic products having decorative surface designs resembling marble, onyx or the like. Each product comprises four layers: (a) a gel coat layer of clear thermosetting resin, (b) a printed fabric, woven or nonwoven, made of glass fiber or polyester fiber and impregnated with a clear thermosetting resin, (c) a background layer comprised of a thermosetting resin in which an inorganic pigment has been dispersed and (d) a backup layer of FRP.

BACKGROUND OF THE INVENTION 
1. Summary of the Invention 
This invention relates to reinforced plastic products with decorative 
surfaces having attractive and depth designs resembling the surfaces of 
onyx and marble. More particularly, this invention relates to reinforced 
plastic products which display excellent performance characteristics 
particularly in applications where their surfaces are contacted with cold 
or/and hot water, such as bathtubs, wash basins, waterproof pans to be 
employed as the prefabricated bathroom floor, rowboat hulls, etc. 
2. Description of the Prior Art 
The great majority of reinforced plastic products heretofore available are 
uni-colored. However, because such uni-colored products cannot fully meet 
the consumer's requirements, much development effort has been made in 
recent years to manufacture reinforced plastic products having an 
aesthetic appearance. 
To decorate the surface of such a product, the printing method and the 
method involving the use of impregnated paper are known. In the case of 
the printing method, however, the decorative effect attainable is rather 
prosaic and only superficial, lacking in the sense of depth which is 
associated, for instance, with onyx or marble. Moreover, the decorative 
surfaces obtained by printing are inadequate in water resistance and, 
particularly when the products are contacted with hot water, are ready to 
become discolored or faded. 
The method of producing a design on the surface of plywood using an 
impregnated paper, that is the method which comprises superimposing a 
printing paper saturated with a clear synthetic resin on the surface of a 
plywood and applying both pressure and heat to the assembly over the 
paper, has also been found to be unsatisfactory in the manufacture of 
articles, the surfaces of which are to be contacted with hot water in 
service, such as bathtubs and wash basins, because of the following and 
other disadvantages. The first disadvantage is that because the 
impregnated paper is made of cellulosic fiber, it is inadequate in 
resistance to hot water. The cellulosic fiber, which is organic, gains in 
volume when contacted with hot water and, consequently, the exposed 
surface of the product is roughened with time. Experiments have shown that 
surface defects are encountered when such products are boiled in water for 
100 hours on ends. The second disadvantage is that because the paper has a 
very dense structure, impregnation with an unsaturated polyester resin 
cannot be thorough enough and removal of air pockets in the resin 
impregnation step is also inadequate, with the result that fine blisters 
of the order of 0.1 to 10 mm are produced on the product surface as 
demonstrated by the boiling resistance test which is normally performed 
for checking products of this kind for quality, such blisters detracting 
from the serviceable life of the product. 
This invention provides solutions to the foregoing problems. It is, 
therefore, an object of this invention to provide a reinforced plastic 
product comprising, either as a whole or in part, a quadruple-layer 
construction having a surface presenting one of attractive and shimmering 
effects resembling the rippling surface of marble or the streaked surface 
pattern of onyx. 
It is another object of this invention to provide an aesthetically 
decorative reinforced plastic product such that its backing FRP layer is 
not visible from the face side, with only the aforementioned decorative 
surface effect being clearly visible from the depth of the construction. 
It is still another object of this invention to provide a decorative 
reinforced plastic product having a protective surface layer which is 
substantially impermeable to cold and hot water and, hence, free from 
discoloration or changes in color, besides being highly resistant to 
impact. 
It is another yet object of the invention to provide a decorated plastic 
product incorporating as a decorative layer a woven, or non-woven fabric 
which is readily susceptible to impregnation with a synthetic resin and to 
removal of air pockets. 
It is a further object of the invention to provide a decorative reinforced 
plastic product which is lightweight, tough and durable. 
The above and other objects as well as the numerous advantages of this 
invention will become apparent from the following detailed description 
made with reference to the accompanying drawing.

DETAILED DESCRIPTION OF THE INVENTION 
The illustrated bathtub, except for its ancillary components such as a 
girder 5, a handrail 6 and an overflow cap 7, consists of a 
quadruple-layer structure which is hereinafter described in detail. 
Thus, of the layers constituting said quadruple-layer structure, the 
uppermost layer is a gel coat layer 1 comprised of a clear thermosetting 
resin. As examples of said clear synthetic thermosetting resin which is to 
be employed for the formation of said gel coat layer 1 may be mentioned 
unsaturated polyester resins in the bisphenol or isophthalic acid series, 
vinyl ester resins, epoxy resins, etc. The gel coat layer 1 has a 
thickness in the range of 0.1 to 0.5 millimeter, which protects a 
decorative layer (2) disposed on the inner side thereof. This gel coat 
layer 1 is not only impact-resistant but also resistant to hot water. The 
term `resistance to hot water` as used throughout this specification means 
that no surface change occurs even when the product is immersed in hot 
water over 90.degree. centigrade for a consecutive 500 hours. 
Laid up on the inner side of said gel coat layer is a decorated fabric or 
web 2 which is made of glass fiber or polyester fiber, on which a design 
generally associatable, for example, with onyx or marble has been printed, 
and which has been impregnated with a clear thermosetting resin. While the 
aforesaid fabric made of glass fiber may be one of the conventional woven 
fabrics, the fabric made of polyester fiber is desirably a nonwoven 
fabric. The nonwoven polyester fabric is more advantageous than a woven 
version as will be explained hereinafter, although the latter may also be 
employed. Insofar as it still lends itself to printing, the fabric 2 is 
preferably as sheer as possible, normally about 0.1 millimeter in 
thickness. Made of glass fiber or polyester fiber as aforesaid, the fabric 
2 is resistant to hot water. The glass fiber is any of those fibers which 
are generally employed as reinforcements for FRP articles. Because such 
materials are previously treated with a coupling agent, they are well 
compatible with the thermosetting resin with which they are to be 
impregnated, thus being convenient to employ. Of course, polyester fibers 
offer excellent compatibility with thermosetting resins. Whether the 
fabric 2 is made of glass fiber or polyester fiber, the clear 
thermosetting resin therefore penetrates well into the fabric 2. Moreover, 
because the fabric 2 has a relatively coarse or open-mesh structure than 
paper, it is more readily and more thoroughly impregnated with a synthetic 
resin and lends better to degassing in the course of layup. The clear 
thermosetting resin is normally selected from among unsaturated polyester 
resins, vinyl ester resins, epoxy resins and other resins which are 
resistant to hot water. 
On the inner side of the second layer, i.e. fabric 2, is layed up on an 
opaque or translucent background layer 3 made of a thermosetting resin in 
which an inorganic pigment has been dispersed. Generally, the 
thermosetting resin employed for the formation of this layer is also 
selected from among unsaturated polyester resins, vinylester resins, epoxy 
resins, etc. The pigment is preferably one which is inert to the other 
materials employed. The particular type of pigment used is a determinant 
of what is the background color of the design. Since, normally, the 
background is preferably white, the pigment is selected from among such 
materials as titanium oxide, silica, etc. 
The fabric 2 as such is opaque but after it has been impregnated with a 
clear synthetic resin as mentioned hereinbefore, all the design-free areas 
are clear. Therefore, if the FRP layer described hereinafter is directly 
laid up on the inner side of the fabric 2, the fiber construction of the 
FRP layer becomes visible from the face side of the article through the 
design-free areas to weaken the contrast of the printed design on the 
fabric 2 against the background, thus failing to impart a desired 
aesthetic appearance to the final product. 
However, in accordance with this invention, because a background layer 3 is 
laid up on the inner side of said fabric 2, the fiber pattern in a backup 
layer 4, which is disposed further on the inner side of layer 3, is not 
visible through the outer layers, with the printed design on the fabric 
layer 2 alone being vividly and clearly visible. Normally, said background 
layer 3 has a thickness in the range of about 0.1 to 0.5 millimeter. 
Further laid up on the background layer 3 is a backup layer 4 which 
constitutes the innermost layer. This layer 4 is made of a 
fiber-reinforced plastic material comprising a reinforcement such as 
chopped strand mat and a thermosetting resin such as an unsaturated 
polyester resin, vinyl ester resin, epoxy resin or the like. 
Because the strength of the quadruple-layer structure of this invention is 
primarily accounted for by this backup layer 4, the thickness of the layer 
4 depends upon the kind of article to be produced. In the case of a 
bathtub, for instance, the backup layer 4 may be about 3 millimeters thick 
but the thickness must be increased to about 10 millimeters when the final 
product is a rowboat hull, for instance. Thus, one may additionally use a 
different type of reinforcement in lieu of increasing the thickness of 
said fiber-reinforced plastic layer or employ a backup layer which, as a 
whole, is a conventional "sandwich" FRP construction. 
The illustrated bathtub may hold 260 l of water and measures 460 
millimeters high by 800 millimeters wide by 1510 millimeters long. This 
bathtub is fabricated by the following procedure. First, a gel coat layer 
1 is built up on a mold 8 by the spray-up method. This layer 1 is made of 
a bisphenol-type unsaturated polyester resin corresponding to Grade UP-CEE 
of JIS K-6919 (JIS for Japanese Industrial Standard; the same applies 
wherever it appears hereinafter). The gel coat layer 1 is formed by 
spraying up a total of 900 grams of said resin in a couple of 
installments. Then, on this gel coat layer 1 is superimposed a decorative 
fabric 2 which has been impregnated with 900 grams of the same 
bisphenol-type unsaturated polyester resin as above. The fabric 2 in the 
illustrated embodiment is a printed cloth of glass, the substrate glass 
cloth corresponding to Grade EF-063 of JIS R-3416 and being 0.1 .+-. 0.01 
mm thick, with a density of 60 fibers/25 mm and a weight of 107 
g/m.sup.2. Prior to the superimposition of said fabric 2, one-half of the 
aforesaid impregnating resin is coated onto the underside of the gel coat 
layer 1. Following said superimposition, the remaining half of the resin 
is coated onto the superimposed fabric 2. The fabric 2 has been previously 
cut to the shapes of a bottom wall 9, four inner side walls 10a, 10b, 10c 
and 10d, four top walls 11a, 11b, 11c and 11d, and two apron walls 12a and 
12b. These fabric pieces are applied over the corresponding areas and held 
securely in position by means of jigs. The above operation is carried out 
exercising care to ensure that there will be no residual air pockets 
between the fabric 2 and the corresponding surface and that the printed 
design will not appear twisted or deformed. Additional care is required 
when, at the abutting areas of the fabric pieces, a continuity of the 
design is desired. 
On a curved surface with a small radius of curvature, many wrinkles are 
formed and, therefore, the printed design tends to be distorted. In such 
areas, a geometric or orderly printed design is difficult to reproduce. 
The fairly coarse construction of a nonwoven polyester fabric facilitates 
a re-distribution of porosity. Stated differently, by spreading wrinkles 
to coarse areas, all the undesirable wrinkles can be absorbed. It follows, 
then, that it is worthwhile to contemplate using a nonwoven polyester 
material in curved areas. The idea of putting a decorative design must be 
abandoned for curved areas in which the contemplated design cannot be 
obtained even by such a procedure. Of course, some products may be such 
that localized designs alone are sufficient to accomplish an aesthetically 
satisfactory effect. Therefore, the reinforced plastic products according 
to this invention include products such that only a portion of the article 
consists in a decorated quadruple-layer structure such as the one 
described hereinbefore, with the remainder which comprises one or more 
curved surfaces adjoining and merging with the first-mentioned portion 
being a dual-layer structure consisting of a gel coat layer and a FRP 
layer just like the conventional reinforced plastic product. If the design 
is such that it does not require alignments of its elements, particularly 
in the case of a psychedelic design, all the aforementioned problems may 
be solved by using said nonwoven fabric for the curved surfaces, thus 
enabling one to produce the desired reinforced plastic product. 
In the above fabrication of a bathtub, an opaque or translucent background 
layer of thermosetting resin is laid up on the resin-impregnated fabric 2. 
This layer 3 is formed by coating a mixture of 800 grams of an isophthalic 
acid-type unsaturated polyester resin corresponding to Grade UP-CM of JIS 
K-6919 and 80 grams of rutile-type titanium oxide in a couple of 
installments. 
Finally, on the background layer 3 is laid up a backup layer 4 consisting 
of two chopped strand mats corresponding to Grade EM-450 of JIS R-341 
using 7 kg of the same isophthalic acid-type unsaturated polyester resin. 
To the reverse side of the bathtub is attached a thermal insulating 
material not shown. A girder 5 is secured to the reverse side of the 
bathtub and a handrail 6 is attached to the top wall 11b, with an overflow 
cap 7 being attached to the inner wall 10c. A drain-hole 13 is formed 
through bottom wall 9, while reinforcing plates 14a and 14b are installed 
across the spaces between the respective side walls as shown. 
The bathtubs fabricated in the above manner have passed all the tests and 
met all the requirements as specified in JIS A 5704, i.e. the appearance 
test, determination of the thickness of the gel coat layer, a gel coat 
layer cracking test, a gel coat toughness test, boiling resistance test, 
water absorption test, tensile test, determination of the degree of 
cross-linking, deformation test under water-filled conditions, sand bag 
impact test, poise impact test and hydrochloric acid resistance test. The 
foregoing description is particularly directed to a bathtub but it should 
be understood that one skilled in the art may apply the principles of this 
invention without undue effort to other reinforced plastic products within 
the principle and scope of the claims appended hereto.