CA2083474A1

CA2083474A1 - Synthetic resin solid surface material and method of making same

Info

Publication number: CA2083474A1
Application number: CA 2083474
Authority: CA
Inventors: Douglas C. Turner
Original assignee: Individual
Current assignee: DURAGLAS PRODUCTS Ltd
Priority date: 1991-11-22
Filing date: 1992-11-20
Publication date: 1993-05-23
Also published as: GB2262469A; CN1074169A; GB9224583D0; CN1047345C; GB2262469B

Abstract

SYNTHETIC RESIN SOLID SURFACE MATERIAL
AND METHOD OF MAKING SAME

ABSTRACT OF THE DISCLOSURE

A synthetic resin solid surface material (10), such as cultured marble or onyx, and which is cast as a unitary structure, comprises a front or working surface formed by a first layer (16) of a synthetic resin, a rear surface formed by a second layer (18) of a synthetic resin and a layer of a core material (14) sandwiched between the first and second layers. A fibrous reinforcing material (22) is provided between the first layer (16) and the core (14). In one embodiment of the invention, the core material comprises plywood. In another embodiment, the core material comprises balsa wood with its grain arranged to extend between the first and second layers and including a further fibrous reinforcing layer (26) between the core (14) and the second layer (18). A two-step method for manufacturing the synthetic resin solid surface material comprises the steps of pouring a hardenable synthetic resin mixture into a mold (30) to form the first layer (16), allowing the first layer (16) at least partially to cure, proving a layer of fibrous reinforcing material (22) on top of the first layer (16), locating a layer of core material (14) on top of the layer of reinforcing material (22), pouring a hardenable synthetic resin mixture into the mold to form the second layer (18) on top of the core material (14) and allowing the resin to cure.

Description

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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 2~83~7~

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 2~83~7~

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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Claims

1. 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.

2. The material according to claim 1, further comprising an edge layer of synthetic resin bridging said core material between said first and second layers.

3. The material according to claim 2, wherein said first and second layers and said edge material are of the same synthetic resin and uniformly colored with a suitable colorant to provide a uniform appearance.

4. The material according to claim 1, wherein said first and second layers are differently colored.

5. The material according to claim 1, wherein the core material comprises one or more layers of plywood which are bonded together.

6. The material according to claim 1, wherein the core material comprises a sheet of balsa wood having a grain which is arranged so that it extends in a direction from said first layer to a said second layer.

7. The material according to claim 6, further comprising a second layer of fibrous reinforcing material embedded in said second layer along another side of said core material.

8. The material according to claim 1, wherein said first and second layers are substantially planar and substantially parallel with respect to one another.

9. The material according to claim 1, wherein said layer of core material is provided with holes therein extending between said first and said second layers.

10. A method of manufacturing a synthetic resin solid surface material comprising the steps of:

(a) pouring a hardenable synthetic 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) pouring 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.

11. The method according to claim 10, further comprising the step of providing a layer of reinforcing fibrous material between said first layer and said core material.

12. The method according to claim 11, wherein the layer of reinforcing material is applied to said first layer while the resin mixture is still in liquid form.

13. The method according to claim 11, wherein said first layer is first allowed to set prior to applying said reinforcing material and further comprising the step of providing a layer of hardenable synthetic resin between said first layer and said reinforcing layer to bond said reinforcing layer to said first layer.

14. The method according to claim 11, further comprising the step of providing a layer of hardenable synthetic resin between said reinforcing material and said core material for bonding said reinforcing material to said core material.

15. The method according to claim 10, wherein the core material comprises one or more layers of plywood which are bonded together.

16. The method according to claim 11, wherein the core material comprises a sheet of balsa wood having a grain which is arranged so that it extends in a direction from said first layer to a said second layer.

17. The method according to claim 16, further comprising the step of providing a layer of reinforcing fibrous material on top of said core material, prior to step (d).