Note: Descriptions are shown in the official language in which they were submitted.
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SYNTHETIC RESIN SOLID SURFACE MATERIAL
AND METHOD OF MA~ING SAME
FIELD OF THE INVENTION
This invention relates to a synthetic resin
solid surface material or artificial marble or onyx
product, such as is used for tabletops and countertops in
kitchens and bathrooms, and to a method of manufacturing
the product.
BACKGROUND OF THE INVENTION
Solid surface materials which are cast from
unsaturated polyesters or acrylic polymers and which in
some applications simulate marble or onyx, are known.
These materials can be heavy and costly. In
.P. O 188 440 Bl, a method of encasing a wooden core in a
coating of artificial marble is described. The core is
held in a mold and an artificial marble mix is poured into
the mou]d to envelop the core. Holes are provided through
the wooden core to promote the evacuation of air.
A disadvantage of a panel having a thin surface
layer of resin bonded to another material is the tendency
of the resin layer to crack upon exposure to extreme
temperatures or rapid temperature changes, or if subjected
to mechanical shock. This tendency increases in case of
delamination between the resin layer and the other
material.
It is accordingly an object of the present
invention to alleviate the above-mentioned difficulties.
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SUMMARY OF THE INVENTION
According to one aspect of the invention, there
is provided a synthetic resin solid surface material cast
as a unitary structure and comprising a front or working
surface formed by a first layer of a synthetic resin; a
rear surface formed by a second layer of a synthetic
resin; a layer of a core material sandwiched between said
first and second layers; and a fibrous reinforcing
material embedded in said first layer on one side of said
core.
According to another aspect of the invention,
there is provided a method of manufacturing a synthetic
resin solid surface material comprising the steps of:
(a~ pouring a hardenable synth~tic resin
mixture into a mold to form a first layer;
(b) allowing said first layer at least
partially to cure;
(c) locating a layer of core material on top of
said first layer;
(d) pourin~ a hardenable synthetic resin
mixture into the mold to form a second
layer on top of said core material; and
~e) allowing the resin to cure.
The synthetic resin mixture used may comprise a
synthetic resin and a filler material, such as a mineral
filler. Any suitable resin, such as a polyester, acrylic
polymer, epoxy or phenolic resin may be used.
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The core material may comprise any suitable
material, such as plywood, balsa wood, a plastic foam or
other commercial core materials, such as paper or aluminum
honeycombs. The preferred core material should provide
for expansion and contraction of the resin layers by being
compressible in length and width while retaining rigidity
in the vertical direction.
Further objects and advantages of the invention
will become apparent from the description of a preferred
embodiment of the invention below.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-section through a slab or
sheet of a solid surface material according to one aspect
of the invention;
Figure 2 is a cross-section through a mold
illustrating a method of manufacturing the material of
Figure l; and
Figure 3 is a cross-section through a mold
illustrating a method of manufacture of a slab of solid
surface material according to another embodiment of the
invention.
DETAILED DESCRIPTION
Figure 1 shows a cross-section through a slab 10
of a solid surface material according to one embodiment of
the invention. The slab 10 comprises a synthetic resin 12
which is cast around a core 14, which, in the present
example, comprises several layers of plywood, which are
bonded together. In particular, the slab 10 comprises a
first or top re~in layer 16, which, in use, serves as a
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working surface, e.g. in applications where the slab 10 is
installed as a tabletop or a countertop, a second or rear
layer 18 and edge layers 20. A layer of fibrous
reinforcing material 22 is provided between the core 14
and the top resin layer 16. Any suitable natural or
synthetic fibrous material may be used, such as glass
fibre, carbon fi~re, or aramid fibre, such as KEVLARTM
from DuPont. ~oles 24 are provided in the core 24 to
permit bonding between the layers 16 and 18, but these
holes are not essential.
The slab 10 is produced by means of a two-step
casting process in a mold 30, as illustrated in Figure 2,
using a suitable unsaturated polyester resin typical to
the cultured marble/onyx industry and having a viscosity
of about 2500 to 3000 cP and with a gel time of about 20
minutes at 70~F.
To the clear resin is added about 10% by weight
of styrene monomer to lower the viscosity to approximately
500 cP. A surface tension modifier, such as DOW CORNING
#7TM paint additive is added, to a concentration of 0.4%
by weightl to prevent foaming and to aid in the release of
air bubbles from the mixture. The mixture is coloured as
required using standard colorants compatible with
polyester-styrene mixtures. It is then blended in a high-
sheer mixer and heated to 110F. A mineral filler, such
as alumina trihydrate ground to about 200 U.S. mesh size,
is added to the mixture to a concentration of
approximately 55% by weight filler and ~5% by weight
resin. Finer grinds provide better stain resistance while
coarser grinds lower viscosity and make the material
easier to de-aerate and pump.
35The mixer is cycled on and off at approximately
10-minute intervals to allow the escape of air from the
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mixture. Provision of a vacuum of up to approximately 20
inches of mercury will aid in the evacuation of air.
However, care needs to be taken not to draw a higher
vacuum which can cause the styrene in the mixture to
gasify and create porosity in the finished product.
The mold 30, having a flat bottom and raised
sides, is prepared with a mold release agent, such as wax.
The mold 30 may be heated to speed up the curing process
but it should not be warmer than about 100F as this can
cause the product to cure too quickly and create stress.
The mixture 12 is catalysed at a ratio of 0.5 to
3.0% by weight with a suitable catalyst, such as methyl
ethyl ketone peroxide, and poured or pumped into the mold
30 to form the first layer 16 of the final product. The
layer 16 is poured to a depth approximately equal to the
desired thickness of the coating of the finished product,
for example 1/4 inch. The layer 16 is then allowed to
partially cure before the reinforcing fibre layer 22 is
applied. Thus, the reinforcing fibre layer 22 may be
added to the resin mixture while it is still in a liquid
state provided that the fibres are not pushed through to
the bottom of the mold 30. Further hardening of the layer
16 will then bond the reinforcing layer to the layer 16.
Alternatively, the layer 16 can be allowed to set before
the reinforcing layer 22 is added. In this instance,
additional resin mixture is added to the first layer 16 to
create a bond between the layer 16 and the reinforcing
layer 22.
During application of the reinforcing layer 22,
the fibres are spread on top of the resin layer 16. The
layer 22 may, for example, comprise glass fibres in random
orientation applied at a rate of about one ounce per
square foot.
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After the reinforcing layer 22 has been bonded
to the first layer 16, a small amount of reæin mixture is
added to the top of the reinforcing layer 22. This acts
as a bonding agent for the next layer of material forming
the core 14 and which is placed over the reinforcing layer
22.
The resin mixture used for the bonding is
similar to the first layer 16, applied at the rate of, for
example, 0.3 pounds per square foot.
In the present example, the core 14 is of
plywood which is placed on top of the second bonding resin
layer, and a downward pressure is applied to it to force
it into close contact with the entire second bonding resin
layer and to force the bonding layer to fill any small
voids or pockets. After the second bonding resin layer
has set sufficiently to hold the core 14 in place,
hardenable resin mixture 22 is pumped or poured into the
mold to encapsulate the core 14 and to cover its top to a
depth of, for example, 1/4 inch, thereby forming the
second layer 18 and the edge layers 20. After all the
resin in the mold has hardened, the material is removed
from the mold and sanded or polished to the desired
finish.
Post curing of the final product in an oven is
recommended to improve the physical properties of the
material by rapidly completing the chemical reactions.
The post curing process which has been found to be most
successful is to heat the product to approximately 100C
for 1 hour. The heating and cooling process should
include provisions for even heat distribution on all
surfaces until room temperature is achieved, as uneven
heating or cooling may result in warping of the product.
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According to another embodiment of the invention
and referring to Figure 3, a first resin layer 16 and a
reinforcing fibre layer 22 are formed in the mold 30, as
described above. In this case, however, the core 14
comprises a sheet of balsa wood with its grain
substantially perpendicular to the principal plane of the
sheet, or another suitable core, such as a honeycomb
structure. The balsa wood, serving as the core 14, may be
prepared by cutting pieces of balsa wood from the ends of
boards and holding them together by a backing layer of
fabric. After the core sheet has been placed in the mold
30, a second reinforcing fibre layer 26 is spread on top
of it. This second reinforcing fibre layer can be of the
same composition as, and be applied at the same rate, as
the first reinforcing fibre layer 22. Once the second
bonding resin layer has set sufficiently to hold the core
14 in place, resin mixture is poured into the mold to
encapsulate the core 14 and to form the second layer 18
and the edge layers 20.
The product prepared in according with the
second embodiment of the invention has particular ability
to withstand exposure to extreme temperatures,
particularly low temperatures. This ability derives from
the fact that the balsa wood core is readily compressible
in directions perpendicular to its grain. When the upper
and lower resin layers contract as their temperature is
lowered, the balsa wood core sheet presents relatively
little resistance to being compressed along the length and
width of the slab of material. However, it has sufficient
strength in the direction parallel to its grain, i.e.
across the thickness of the slab, to permit the
construction of a relatively strong slab of material
having relatively thin resin layers 16 and 18, provided
that a reinforcing fibre layer is present in both upper
and lower resin layers.
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The balsa wood, being light weight, reduces
overall product density, making it more functional in
areas where the weiqht of the conventional products may
be restrictive.
It has been found that the provision of the
fibre reinforcing layer 22 improves the resistance to
cracking during use, which has been a problem with some of
the conventional products.
Although in the specific example described
above, reference has been made to lowering the viscosity
of the resin, it is also possible in other applications to
raise the viscosity of the resin depending on
requirements. Thus, the viscosity can be increased so
long as it still remains a workable viscosity, e.g. air
can still be evacuated under vacuum and the mixture is
flowable enough to level when introduced into the mold.
The core material 14 may have its edges rounded
prior to placement in the mold. This will redistribute
some of the stress caused as the product expands or
contracts from ambient heat or cold or during the curing
process. It can also improve resistance to cracking on
impact. It further allows for reduced material usage at
the edges while maintaining the ability to shape the
edges. The core material can be of any suitable material
selected to provide a desired weight to strength ratio of
the final product.
While only preferred embodiments of the
invention have been described herein in detail, the
invention is not limited thereby and modifications can be
made within the scope of the attached claims.
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