PROCESS FOR MOLDING SOLID SURFACE MATERIALS

Abstract: A process for molding parts essentially containing solid surface materials into shapes and/or textured designs is described. A product containing relief pattern on at least one surface can be made by the present molding process without machine or gluing.

Description: TITLE PROCESS FOR MOLDING SOLID SURFACE MATERIALS CROSS REFERENCE TO RELATED APPLICATION 5 This application claims the benefit of pending U.S. Application No. 09/565,166 filed 4 May 2000. BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a process for molding solid surface materials. l o More particularly, it relates to a process for molding a part containing solid surface material to form a shape, a relief pattern in the surface, or a combination thereof. Description of the Related Art Solid surface materials are composites of finely divided mineral fillers 15 dispersed in an organic polymer matrix. These materials are usually manufactured by thermoset processing, such as sheet casting, cell casting or bulk molding. The solid surface materials are generally very stiff and may be somewhat brittle. They have a high heat capacity. Overheating such materials can cause surface defects and whitening in colored materials. 20 It is known to form visual patterns within the solid surface material. This can be accomplished by mixing and blending different colored fillers within the matrix. The resultant product has a smooth rather than a texture surface. It is also known to form the materials into curved shapes, such as sinks and tubs, using heat and vacuum. Such processes have been disclosed in, e.g., Ford, U.S. Patent 25 5,236,658, and Minghetti et al., U.S. Patent 5,521,243. These heat-and-vacuum processes can result in a high degree of waste and may not be suitable for forming articles having intricate shapes. It is known to alter the surface of solid surface materials. For example, it is possible to machine patterns into the surface of the materials or to form raised patterns by gluing pieces onto the surface of the 30 materials. However, both of these surface altering processes are time consuming and result in a high level of waste. Additionally, it is difficult to obtain a molded article having a design with intricate details. It is therefore desirable to be able to form solid surface materials in shapes and/or with raised or imprinted relief patterns more efficiently and with less waste. SUMMARY OF THE INVENTION The present invention relates to a process for molding solid surface materials to form a shape, a relief pattern in the surface, or a combination thereof. The process comprises the application of both heat and pressure to a part 5 containing solid surface material in a mold having a mold form which will produce the desired part shape and/or relief pattern. In one embodiment of the invention, the process comprises: providing a mold form having on at least one mold form surface a relief pattern, a shape, or a combinations thereof; l o providing the part having a first part surface area; heating the part to a conformable temperature; forming a pattern on the heated part by applying a molding pressure greater than atmospheric pressure to the mold form containing the heated part and maintaining the molding pressure for a predetermined amount of time to obtain a molded part. 15 In one embodiment of the invention, the process comprises applying pressure to the part by providing a multiplier board on the part, wherein the multiplier board has a applied pressure surface with a surface area greater than that of the part's surface adjacent to the multiplier board. In another embodiment of the invention, vacuum as well as pressure can 20 be used to form the pattern on the heated part. A vacuum enclosure can be provided prior to applying the molding pressure, after applying the molding pressure, or at the same time as the application of the molding pressure. In yet another example, the vacuum enclosure step comprises placing the part containing solid surface material in a mold form, covering the part with an 5 air impermeable material, providing a matching mold over the part, applying vacuum to the mold form and applying pressure to the matching mold. The invention also relates to a product containing at least one solid surface material comprising a desired relief pattern made by the process of the invention. BRIEF DESCRIPTION OF THE DRA WINGS 0 Figure 1 is a cross-sectional view of a core mold. Figure 2 is a cross-sectional view of a cavity mold. Figure 3 is a perspective view of a mold with a pressure box. Figure 4 is a cross-sectional view a part in a mold to which vacuum can be applied. 5 Figure 5 is a perspective view of a mold in a vacuum box and a pressure box. Figure 6 is a cross-sectional view of a part in a mold with a multiplier board that can be evacuated to form a pressurized vacuum enclosure. Figure 7 is a schematic diagram of the part in Figure 4 or Figure 6 after molding. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a process for molding a part containing solid surface material to form a shape, a relief pattern on at least one surface, or a combination thereof. The process includes providing a heated part containing at least one solid surface material in a molded form and applying pressure for a predetermined time to obtain a molded part. In some embodiments, vacuum may also be used to form a molded part. As used herein, the term "mold form surface" refers to the surface of a mold form into which or over which the part is molded. The shape can be a simple shape, such as a bowl, or a complex shape. The term "relief patterns" is intended to encompass overall textured patterns, imprinted surface designs, and raised exterior surface designs. The relief pattern can be an overall texture such as a wood grain or pebble surface; an imprinted surface design in which the height of the design is less than the overall height of the sheet of solid surface material; and/or raised exterior relief. In addition, the present invention can provide relief patterns that penetrate through a portion or the entire depth of the part. The relief pattern can be a combination of designs and patterns. The term "conformable" describes a physical state at which the material is capable of yielding to the shape of the molding form, with the assistance of an applied pressure, thereby forming an intimate mirror image of the molding form shape. The value associated with "vacuum" applied in the process of this invention refers to the vacuum pump reading under 1 atmosphere of pressure. Similarly, the value associated with gauge "pressure" applied in the process of this invention refers to the pressure pump gauge reading. It is understood that when structure component A is stated to be "adjacent to" a first surface of structure component B, it is meant that structure component A is closer to the first surface of structure component B than it is to a second surface of structure component B, such second surface being disposed opposite of the first surface. As used herein, the word "adjacent" does not necessarily mean that structure component A is immediately next to the first surface of structure component B. Thus, it is possible that a structure component C is disposed between structure component A and structure component B, and it is still true that structure component A is adjacent to the first surface of structure component B. The term "air impermeable" container refers to a container, or a material is forms a container, that is capable of holding a vacuum of at least 5 inches of Hg (0.17 atm) for at least 10 minutes under atmospheric pressure. Conversely, the term "air permeable" refers to container, or a material that forms a container, that 5 is not capable of holding a vacuum of at least 5 in. of Hg (0.17 atm) for at least 10 minutes under atmospheric pressure. The Mold Form One of the first steps in the process of the invention is to provide a mold form (or mold) having a shape, a surface relief pattern, or a combination thereof. o The mold form can be a core mold 10, as best seen in Figure 1 , or it can be a cavity mold 20, as best seen in Figure 2. When a core mold 10 is used, a part containing solid surface material (not shown), through the molding process, will conform over a core surface 12. When a cavity mold 20 is used, a part containing solid surface material (not shown), through the molding process, will conform to5 the cavity surface 22. The mold form surface 12, 22 of either a core mold 10 or a cavity mold 20 can have a relief pattern (not shown). It is understood that the mold relief pattern on mold form surface 12, 22 will have the opposite or mirror image of the relief pattern desired (i.e.: corresponds to the desired relief pattern) in the part. That is, if the desired relief pattern includes a raised exterior relief, o the mold form surface will have an imprinted relief pattern on the mold relief form surface. Similarly, where the part is to have an imprinted relief, the mold will have a raised exterior relief. The mold form 10 or 20 can be made from any material with sufficient structural integrity to maintain its shape under the vacuum, pressure, and 5 temperature conditions of the molding process. Molds are typically made from materials such as wood, epoxy, filled epoxy, resin-impregnated fiberglass, steel and aluminum. The relief pattern in the mold can be made by any conventional process, such as cutting or machining. As further discussed below, the air permeability of the mold form depends upon the enclosure configuration. 0 Typically there is a high degree of friction between the mold form surface 12, 22 and the part to be molded. This can make it difficult to properly position the part in the mold. To overcome the friction problem, a release layer may be placed on the mold form surface 12, 22. Materials such as poly(vinyl)fluoride, poly(tetrafluoroethylene), and other fluorinated polymers can be used. A wax5 coating, such as paraffin wax, may also be provided on the mold form surface 12, 22. The release material can be added as a heated film and vacuum formed into the mold form surface 12, 22 to conform to the mold shape. Alternatively, the mold form surface 12, 22 can be dusted with a powdered material, such as talc, prior to adding the part. Excess talc powder should be wiped off from the mold form surface 12, 22, since too much talc may affect the surface texture of the finished part and may cause damage to the equipment used to draw the vacuum, e.g., a vacuum pump. The Part A part that can be processed by the present invention essentially contains at least one solid surface material. The part may be, for example, a composite containing solid surface material or a thermoplastic matrix material containing solid surface material as fillers. By "essentially contains," it is meant that the part's physical characteristics are dominated by the solid surface material component(s). In other words, while the part may contain other materials, the part's glass transition temperature (Tg), heat capacity, brittleness and stiffness are dictated by the solid surface material component(s). The solid surface material is a composite of finely divided mineral fillers dispersed in an organic polymer matrix. The part can be of any shape that is contained by the mold geometry. The overall size of a part is limited only by the size of the mold form and the ability to handle the material. In many cases the part can be a self-supporting preformed sheet of essentially solid surface material. Thicknesses in the range of from about 0.125 to 1.0 inch (0.32 to 2.54 cm) are typical, although this is not a limitation, as discussed above. Examples of suitable polymer matrices include polymerized and/or crosslinked vinyl compounds, particularly acrylics; polyesters; urethanes; epoxies; phenolics, including novolacs; amino resins, including urea resins; and the like. Preferred polymers include epoxy resins, unsaturated polyester resins, and acrylic resins. Epoxy resins useful in the present invention include those based on epoxide groups having certain reactivity. Such materials may include resins of bisphenol type A, bisphenol type F, phenol novolacs, alicyclic epoxy, halogenated epoxy, and cycloaliphatic epoxy resins. Unsaturated polyester resins useful in the present invention include those wherein the reactivity is based on the presence of double or triple bonds in the carbon chain. Unsaturated polyester resins are formed by the reaction of molar amounts of unsaturated and saturated dibasic acids or anhydrides with glycols. The unsaturation sites can then be used to crosslink the polyester chains, via vinyl containing monomers such as styrene, into a thermoset plastic state. Acrylic resins useful in the present invention are not particularly limited and include various kinds of conventional polymers and copolymers of acrylic and methacrylic acids and esters. (Meth)acrylate esters are preferred. The terms "(meth)acrylic" and "(meth)acrylate" are intended to mean "acrylic and/or methacrylic" and "acrylate and/or methacrylate", respectively. Examples of suitable (meth)acrylate esters include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, glycidyl (meth)acrylate, and the like. The filler is generally a finely divided mineral material having a particle size less than about 200 microns. Examples of suitable fillers include alumina trihydrate, alumina monohydrate, Bayer hydrate, silica, magnesium hydroxide, calcium carbonate, and barium sulfate. Other additives may also be present in the solid surface material. Examples of other additives include pigments, dyes, flame retardant agents, parting agents, fluidizing agents, viscosity control agents, curing agents, antioxidants, and the like, as is well known in the art. Crosslinking agents may also be incorporated into the solid surface material. However, crosslinking agents should be used sparingly because this component may affect the formability of the part. For example, the higher the amount of crosslinkers, the less formable the solid surface material will be. Preferably, at most 3 wt % of crosslinking agent, based upon the weight of the monomer component of the solid surface material, is present. A preferred solid surface sheet material comprises an acrylic material, including a poly(methylmethacrylate) resin with alumina trihydrate as a filler. Such compositions have been described in, for example, U.S. Patents 3,847,865 and 4,085,246, the contents of which are incorporated herein by reference. The part containing solid surface sheet material can be formed by any conventional process well known in the art. These conventional processes include sheet casting, cell casting and bulk molding a thermally curable composition. In addition, the part can be formed by molding a liquid, chemically curable composition, as disclosed in co-pending U.S. Application Serial No. 08/995,888 assigned to the same assignee. Heating The Part Another step in the process of the invention is to heat the part containing solid surface material to a temperature (conformable temperature) at which the shape and/or the relief pattern can be formed, i.e., a temperature at which the part is sufficiently softened to take on the shape and/or relief pattern contours. In general, the conformable temperature is above the Tg of the polymer matrix material of the part. However, the temperature should not be so high as to cause degradation of any compositional component. The temperature chosen, therefore, will depend on for example, components, composition (e.g., polymer and fillers) in the part, the nature of the polymeric material and the filler distribution density, filler type, filler particle size and filler content. In general, temperatures that are from about 20°C to about 80°C, preferably from about 20 to about 40°C, above the Tg are preferred. For parts containing acrylic systems, the preferred temperature is in the range of from about 110° to about 220°C preferably between 120° and 190°C. The part can be pre-heated (i.e., heated prior to placing it into the mold form) by any conventional means, including ovens, resistance heaters, infrared heaters and hot air blowers. For example, part can be placed between two metal plates which are heated. Where the part is pre-heated, an unheated mold (i.e., one that does not employ a heating source, or one in which the heating source is not activated) is used. It is also possible to use a heating mold (i.e., one employing a heating source) and heat the part directly in the mold. A heating mold can be heated prior to placement of the part in the mold, or the mold can be at room temperature and heated after the part is added. The part should be heated for a time sufficient to bring the part to the desired conformable temperature. The part should be supported during the heating to prevent it from sagging or distorting. Where the part is heated prior to placement into the mold form and it is not supported directly by the heating device, the part can be generally supported on a screen which then can be used to transport the sheet to the mold. Where the part is heated in a heating mold, the heating source should be turned off after the part reaches the desired conformable temperature before or during the pattern forming step. Turning off the heating mold allows the mold form surface cool so that the part surface adjacent to the mold form surface can "freeze," (i.e.: cool to retain) the relief pattern. Pattern Formation The pattern formation step of the invention involves the application of pressure and, optionally, forming a vacuum enclosure. The pressure can be locally applied through mechanical means or applied with a pressurized fluid, or applied with a combination of mechanical means and pressurized fluid. Pressure can be locally applied to the heated part by placing a platen or a mechanical, hydraulic or pneumatic press over the heated part, by placing a second matching mold half over the heated part, by placing a multiplier board over the heated part or a combination thereof. Pressure can be applied with a pressurized fluid by means of, for example, a hydraulic chamber, or a compressed gas chamber, having a compliant diaphragm or bladder, as best seen in Figure 3. The pressure box 200 can be pressurized by means of a compressed gas or liquid. As best seen in figure 3 mold form 30 is in a support structure 100. A part (not shown) is placed in the mold 30. Over this mold 30 is placed pressure box 200 with diaphragm 210 resting against the part (not shown). The box is pressurized by means of pressure inlet 220 through which compressed gas or fluid is pumped. Direct pressure can be effectively provided by placing a platen or press over the part, especially where the part has a sheet geometry. Pressure can then be applied to the platen or press by any conventional means including mechanical clamps, a pneumatic press or a hydraulic press. If the press in any way sticks to the hot or cooled part, a release layer or film can be used between the part and the press. A release layer can be applied to one side of the press or a separate release film can be placed between the press and the part. Any release material which can withstand the temperature of the heated solid surface material can be used. Examples of suitable materials include fluoropolymers, such as polytetrafluoro- ethylene, and silicones. In another embodiment, the part can be placed between two matched mold halves. By "matched" is meant that the two halves are complementary and, when closed together, form the desired shape for the part. Preferably, the part used is a sheet material. The two components of the mold forms are frequently referred to as a male and female or core and cavity. There will be a gap between the two halves which is the thickness of the solid surface material to be molded. Either or both mold halves can have a relief pattern. Pressure can be applied to the mold by any conventional means including for example, mechamcal clamps, a pneumatic press, or a hydraulic press. Optionally, the second mold half may be formed, for example, by a rubber diaphragm, air bladder or fluid bladder, so that it is compliant and can be pressurized by a compressed gas or liquid. The mold form may be flat to result in a sheet which may have surface relief. Alternatively, the mold form may be shaped to result in a shaped solid surface material which may have surface relief. For example, the mold form can have a curved shape profile such that a sheet of solid surface material is formed into a bowl shape having surface relief on the exterior and/or interior surface(s). Where the desired design includes a complex shape, it is preferred to inflate the air impermeable blanket to stretch the blanket over the shape before applying pressure. This pre-stretch pressure forming is especially useful when a desired shape has a locally deep draw so that portions of the part is required to stretch significantly (e.g., 10%) more than other portions of the part. To pre- stretch the heated part, a pressure box with two halves can be used. Pressure (first half pressure) is then applied through the first half, which is adjacent to the mold form surface, to stretch the part into a dome shape. The first half pressure is then removed from the first half. Pressure (second half pressure) can then be applied through the second half to deflate the dome shape and conform pre-stretched part into the mold form surface. The second half pressure should be greater than the first half pressure, preferably from 1.5 to 6 times greater, more preferably from 1.5 to 3 times greater. In another embodiment (pre-stretch vacuum forming), the part can be stretched with a first pressure, after which, instead of applying pressure through the second half, a vacuum can be drawn from the first half. Preferably, this embodiment is used to form a complex shape without much textured pattern. Alternatively, the pressure can be applied by placing a multiplier board over the part, as best seen in Figure 6. Figure 6 shows a multiplier board 70 having a first board surface 72 and a second board surface 74 (applied pressure surface ~ i.e.: the side of the board onto which pressure is applied) that is opposite the first board surface 72. A compliant volume provider 80 is adjacent to the multiplier board 70. The compliant volume provider 80 has a first compliant surface 84 adjacent to the first board surface 72 and a second compliant surface 82 adjacent to a first part surface 52 of the part 50. The board 70, compliant volume provider 80, and part 50 are enclosed in a vacuum system provided by an impermeable blanket 60. The part 50 is placed on mold form 40 which is on support 100. When a vacuum is used, it is drawn through one or more (not shown) vacuum port(s) 120. The board 70 is a sheet of material with the first board surface 72 with a surface area significantly greater than the surface area of the part surface 52 of the part 50 to be molded. The greater board surface area provides a greater pressure force to the part than if the board surface area is equal to that of the part surface 52. The desired ratio of the surface area of the surfaces 52, 72 depends upon the complexity of the relief pattern: the greater the complexity, the greater the desired ratio. Generally, the ratio of the surface area of the surfaces 52, 72 ranges between 1.5 to 1 and 10 tol . Where the compliant volume provider is not present, the effective pressure (P e f f )on the mold part 50 can be expressed by Equation (I) below: peff = [SA 74 /SA 52 ] x P applied Equation (I) wherein: Papplied = pressure applied to the board 70; SA 52 = surface area of part surface 52; S A74 = surface area of surface 74. In a preferred embodiment, a compliant volume provider 80 is placed between the board surface 72 and the part surface 52. "Compliant volume provider" includes any material with a fixed volume that disperses pressure from the multiplier board 70 to the part 50 and conforms to the configuration of the part 50 as the part is molded and returns to its original shape upon removal from the mold. Compliant volume providers can be compressible or incompressible materials. Examples of compliant volume providers useful in the invention includes elastomers, rubbers, any gas contained in an elastic or rubber housing, any liquid contained in an elastic or rubber housing, and combinations thereof. Although not required by the invention, this compliant volume provider facilitates even distribution of pressure over an irregular surface, thus providing a more detailed pattern texture. Where the compliant volume provider is present, the effective pressure (P e ffi)on the mold part 50 can be expressed by Equation (II) below: Peff 1 = [SA 74 /SA effSurf ] x P applied Equation (II) wherein: Papplied = pressure applied to the board 70; SAeffSurf ~ surface area of the effective surface, which in this case, is the compliant surface 82 or the part surface 52, whichever has the smaller surface area; S A74 = surface area of surface 74. The dimensions of the compliant volume provider depends upon the dimension of the desired design. For example, if the dimension of a texture design is much smaller than the dimension of the part, then the compliant volume provider should have dimensions a little greater than those of the texture design, but not as large as the dimensions of the part. In both Equations (I) and (II) above, the pressure applied to the board 70 can be pressure from fluidized pressure or pressure by local means; pressure from rubber blanket when vacuum is drawn, or a combination of such. In a preferred embodiment, the multiplier board 70 is used in conjunction with a vacuum enclosure, as best seen in Figure 6. The board 70 is placed on the part 50 prior to enclosing the vacuum system. In Figure 6, the system is enclosed with air impermeable blanket 60. However, other enclosing means can be used, as 5 further discussed below. The part 50 and the multiplier board 70 are then enclosed and a vacuum is drawn. Where vacuum is not applied to the system containing a multiplier board, the multiplier board can be used to magnify the pressure on the part applied by the before-described fluidized pressure or local means. l o The multiplier board can be made of any rigid material that is sufficiently strong to withstand the pressure when a vacuum is drawn. The board is typically made of wood or fiberboard. Other materials such as sheets of metals, fiberglass, fiberglass composites, and rigid polymers can also be used. If the multiplier board sticks to either the heated or the cooled solid surface material, a release layer or 15 sheet can be used as discussed above. The pressure is maintained for a time sufficient to ensure that the solid surface material conforms to the shape of the mold form surface. Simultaneously, the mold is allowed to cool to a pattern-freeze temperature below Tg of the part, so that the part is freeze to retain the relief pattern. While the pattern-freeze 20 temperature depends upon the composition of the part, generally, this temperature is in the range of from 40°C to 100°C. For a part essentially containing acrylic solid surface materials, the pattern-freeze temperature is generally in the range of from 85°C to 90°C. To reach the desired pattern-freeze temperature, generally, where a sheet part is used, a time of about two minutes per millimeter of sheet 25 thickness is sufficient for an unheated mold (i.e., mold without a heating source) with a pre-heated part. For heated molds with a pre-heated part, the time can be somewhat shorter. The pressure is then removed and the part is allowed to cool in the mold. In general, the part is cooled to a temperature of about 20-40°C below the Tg before removing the part from the mold form. For parts containing acrylic 30 solid surface materials, it is preferred that the temperature is below 85°C before the molded part is removed from the mold form. The semi-cooled molded part can then be removed from the mold and allowed to continue cooling, if necessary. It is generally necessary to support the part during the last cooling in order to prevent it from warping or distorting. The 35 sheet material can be left in the mold until it is completely cool, but generally is removed prior to that to improve cycle time. In a preferred embodiment, the mold part is allowed to cool uniformly on all sides of the part and the part is fully supported during cooling. A "cookie cooling rack" or a supported screen can be used. Alternatively, the part can be clamped into a frame, such as an aluminum perimeter frame, and hung vertically in water or circulating air to cool. Slow cooling in an insulated container is more preferred. Vacuum Enclosure In another embodiment of the invention, a vacuum enclosure is formed in addition to pressure. A vacuum can be drawn after the part is placed in the mold and the mold form is heated to the desired molding temperature. The vacuum enclosure can be formed by enclosing the part and the mold form in an air impermeable enclosure and evacuating the enclosure. This enclosure can be formed in various ways. One major factor that determines how the enclosure is formed is the air permeability of the mold form. For example, where the mold form is made of an air permeable material, the mold form can be placed in an air impermeable container to form the air impermeable enclosure. On the other hand, where the mold form is made of an air impermeable material, the mold form itself can be used to form a portion of the air impermeable enclosure, thus, an air impermeable blanket can be used to seal the mold form to complete the air impermeable enclosure. It is understood that the configuration and/or dimensions of the part can also affect the method for forming the air impermeable enclosure. For example, where the thickness of the part is greater than the depth of the mold cavity opening, while the length and width that can be encompassed by the mold cavity opening, an air impermeable container may be used even if the mold cavity itself is made of air impermeable material. The part and mold form can be enclosed using a simple vacuum bag, by applying an air impermeable blanket over the part and mold, or in a vacuum forming machine. When the blanket is used, it covers the part and seals around the mold form. The air impermeable blanket can be made of any material which is sufficiently air impermeable to allow a vacuum to be drawn under it. The material should have sufficient flexibility to be able to seal to the mold edges and conform to the part's surfaces (without breakage) when the vacuum is drawn. Examples of suitable materials include rubbers, particularly silicone rubbers due to their high temperature stability. The rubber materials will typically have a durometer (also known as Shore A hardness) above 30. If the blanket material sticks to the hot or cooled part, a release layer or film may be used. A release layer can be applied to one side of the blanket or the part, or a separate release film can be placed between the blanket and the part. Any release material which can withstand the temperature of the heated solid surface material can be used. Examples of suitable materials include fluoropolymers, such as polytetrafluoroethylene, and silicones. The air impermeable container can be made of same materials as the blanket. After the impermeable enclosure is formed, a vacuum can be drawn around the sheet material and mold form, prior to applying pressure. The vacuum can be drawn by any conventional means, generally a vacuum pump. A vacuum of from about 5 to about 29 in. Hg (0.17 to 1 atm) is generally sufficient. A preferred vacuum is 10-29 in. Hg (0.34 to 1 atm), more preferably 20-29 in. Hg (0.69-1 atm). The air is evacuated generally by means of small holes either in the mold itself or in the underlying support structure, as best seen in Figure 4. A part containing solid surface material, 50, is placed in mold 40, having an indentation relief pattern 42. Openings 44 at the bottom of the mold form 40 are provided for drawing a vacuum. Silicone blanket 60 is placed over part 50, overhanging the mold so as to completely enclose the part and mold. A vacuum is drawn through at least one opening 120 shown here on support 100. Preferably, the openings 44 are in the mold form 40 itself, particularly for fine details. Air removal should be accomplished in all areas of the mold form. Narrow slots (not shown) can be used as a time-saving alternative to vacuum holes. A porous disc (not shown) can be used to cover the openings 44 to provide support for the part 50. Such porous discs can be made of composite copper, stainless steel or aluminum. Alternatively, discs containing screen, slots or vents (not shown) can also be used to cover the openings 44. Such porous discs, screens, slots, or vents are available from Freeman Products of Mt. Joy, PA. Alternatively, porous metal molds (not shown) of, for example, composite copper, stainless steel or aluminum, can be used which eliminate the need for either slots or holes. One method of applying vacuum and pressure using a vacuum box and a pressure box is illustrated in Figure 5. Mold 30 is in vacuum box 300. The part containing solid surface material (not shown) is placed in mold 30. The part and mold are covered with an air impermeable blanket 60 (shown partially). In this embodiment the air impermeable blanket forms the vacuum enclosure, rather than the part forming the seal for the vacuum. Thus it is not necessary to clamp the part in place. This is advantageous in that it eliminates the clamped edges which are waste. Once the part and the air impermeable blanket are in place, the pressure box 200 is placed over the part such that diaphragm 210 is resting against the part. The vacuum box is then evacuated by means of vacuum port 320, and pressure is applied by means of pressure inlet 220 through which compressed gas or fluid is pumped. The pressure and vacuum are held for a time sufficient to ensure that the sheet material completely conforms to the mold relief pattern. Generally, a time of about two minutes per millimeter of part thickness is sufficient for an unheated mold. For heated molds, the time can be somewhat shorter. After sufficient time has passed to complete the molding, the pressure is removed and the part is allowed to partially cool while under vacuum. When the part is at least partially cooled as discussed above, the vacuum is removed and the part is removed from the mold. Additional cooling, if needed, is carried out as discussed above. Figure 7 shows the system of Figures 4 or 6 after the molding process. The part 55 has conformed with the mold relief pattern (not shown) of mold form 40 (shown on support 100). It is surprising and unexpected that a part containing solid surface material, which material is rigid and stiff and have a high heat capacity, can be formed with surface relief. Such materials are known to tear and discolor when forced to bend over small radii. With the process of the invention, it is possible to form a raised relief on a solid surface material that is higher than the thickness of the solid surface. For example, using the process of the invention it has been possible to form solid surface sheet materials having a thickness of 1/2 inch (1.27 cm) and a raised relief of 1.5 inches (3.8 cm). The surface relief pattern can be designed to exceed the allowable forming stress of the solid surface material so that the material will whiten in the relief areas. This creates a relief in a contrasting (whiter) color. Alternatively, a raised relief pattern can be selectively sanded to give a different gloss appearance. EXAMPLES The invention can be further described by the following examples which are illustrative and not intended to be limiting. Comparative Example - Vacuum Only The part used was a sheet of alumina trihydrate filled acrylic (Corian® Genesis from E. I. du Pont de Nemours and Company, Inc., Wilmington, DE) which was 10 x 30 inches (25.4 x 76.2 cm) with a thickness of 0.5 inches (1.3 cm). The mold was a collection of loose stones on a MDF (medium density fiberboard) board. The board was placed on a table that can be covered with an elastic silicone blanket sealing around the edges. The Corian sheet material was heated until the surface temperature of the sheet reached 170°C. The sheet was then removed and placed on the mold (stones) and covered with a silicone blanket, forming a seal around with the table beyond the edge of the mold. A vacuum was then drawn under the silicone blanket by means of a standard vacuum pump connected to the table base. Air is evacuated from under the blanket, Corian® and stones through a manifold running around the perimeter of the table or through holes in the table base. The vacuum was maintained for about 6-12 minutes. Prior to removing the vacuum, cooling fans can be used to shorten the cooling time. When the silicone blanket temperature reached 88°C, the vacuum was removed and the solid surface sheet material was removed from the mold and placed on a cookie cooling rack. The resulting part was a sheet of material having a very dimensional, detailed surface imprinted the shape of the random stones placed on the board. EXAMPLE 1 Vacuum with pressure applied by multiplier board The process steps followed in the Comparative Example were followed with the following exceptions : - Mold - The mold was made by casting a liquid polymer resin onto a thin PVA (polyvinyl alcohol) film. To make the mold the film was held down over a flat board that had various leaves (from trees) arranged on the board. When the Corian ® polymer resin had cured, it had a very detailed duplication of the leaves in the surface of a 0.75 inch (1.9 cm) thick Corian® board. The Corian® board was thus a flat mold containing leaf impressions. The mold was then placed on a table that could be covered with an elastic silicone blanket sealing around the edges. - Forming - The 10 x 30 inch (25.4 x 76.2 cm) Corian® sheet material was heated until the surface temperature of the sheet reached 170°C. The Corian® sheet was placed on the leaf mold. Then a multiplier board having dimensions of 30 x 40 inch (76.2 x 101.6 cm) and 5.5 inch (13.97 cm) thick was placed on the Corian® sheet. The thickness of the multiplier board is dictated by the need for the board to withstand the bending load created by the vacuum. A 1-inch (2.54 cm) thick, 40 durometer silicone pad is placed between the bottom surface of the multiplier board and the Corian® sheet to distribute the force of the board over an uneven textured surface. The ratio of the multiplier board and Corian® surface areas determined the amount the forming pressure is increased. In this example, the multiplier board increased the effective pressure of the vacuum by 4 times. So a vacuum of 27 in. Hg (0.93 atm) created 4 atm (56 psi) forcing the Corian® sheet onto the mold for much better definition. The mold, sheet and multiplier board were then covered with a silicone blanket, forming a seal around with the table beyond the edge of the mold. A vacuum was then drawn under the silicone blanket by means of a standard vacuum pump connected to the table base. Air is evacuated from under the blanket, Corian® and mold through a manifold running around the perimeter of the table or through holes in the table base. The resultant Corian® sheet had a leaf texture that is raised on the sheet. EXAMPLES 2-5 Pressure forming The three parts made of solid surface material were used to form articles having a wood-grain design. Each part was a sheet of alumina trihydrate filled acrylic (Corian® Genesis from E. I. du Pont de Nemours and Company, Inc., Wilmington, DE) which was 10 x 30 inches (25.4 x 76.2 cm) with a thickness of 0.5 inches (1.3 cm). The mold used for these three parts was made from a 0.75 inches (1.9 cm) thick oak board with a well defined, attractive grain pattern. For each of the three parts, the following molding steps were followed: The wood grain pattern was created by sand blasting the surface to remove the softer material and leave a raised, more pronounced grain. The board was placed in a pressure forming mold box. The box was a two part, top and bottom assembly that sealed into a top and bottom chamber when brought together. The top and bottom were separated with an elastic silicone blanket that sealed around the edges. A hardware cloth was installed in clamp frames having an opening 13 x 33 inches (33 x 84 cm). The frame opening was 3 inches (7.6 cm) larger than the sheet size in both dimensions to minimize edge effects in heating. Each of the parts was placed on the cloth and the frame and sheet were placed in an oven. It was heated until the surface temperature of the sheet reached 188°C. The frame and sheet were then removed from the oven for 45 seconds to allow the sheet surface and core to equilibrate. The frame and sheet were then returned to the oven and heated until the surface was again 188°C. Care was taken to avoid overheating which will cause the material to bubble and become unusable. The frame and sheet material were then removed from the oven. The frame clamps were then opened and the hardware cloth removed. The Corian® material was picked up and placed on the mold, which had been preheated to a temperature of 75-85°C. A 0.125 inch thick silicone rubber blanket was placed over the Corian® sheet, extending out beyond the perimeter of the lower pressure box. The top pressure box was lowered down to tightly seal with the lower box by pinching the silicone blanket. A vacuum of 22 in. Hg (0.76 atm) was then drawn in the lower box which contained the oak mold and Corian® sheet. Pressure was applied to the top box at the same time to create a larger pressure differential between the top and bottom pressure box. This pressure differential acted to press the Corian® sheet firmly0 against the wood grain mold. This pressure differential was maintained for 6-12 minutes to allow the Corian® sheet material to cool down to 85°C. The pressure and vacuum were then released, the boxes separated, the silicone rubber blanket removed and the molded Corian® sheet removed. The pressure applied to the top box in making each of the parts are listed5 in Table 1 below. TABLE 1 All three parts included an oak grain pattern on one side. It was observed that the o greater the pressure applied resulted in a deeper detail in the oak grain pattern. EXAMPLE 6 Pre-stretch Pressure Forming The solid surface material that can be used is a sheet of alumina trihydrate filled acrylic (Corian® Genesis from E. I. du Pont de Nemours and Company,5 Inc., Wilmington, DE). The dimensions of this part can be 20 x 24 inches (25.4 x 76.2 cm) with a thickness of 0.5 inches (1.3 cm). The mold can bemade from MDF (medium density fiberboard). The MDF mold can made by gluing 4 layers of 0.75 inch board to create a 3.9 inch thick block. The MDF can then be machined to create pockets in the board, similar to small bowls. The board can be0 placed in a pressure forming mold box. The box will have a two-part, top and bottom assembly that seals into a top and bottom chamber when brought together. The top and bottom will be separated by the Corian® sheet, which will be larger than the boxes and is pinched as the seal around the edges. The Corian® sheet will then be placed in a perimeter clamp frame and the clamps actuated to positively hold the sheet. Then the sheet and clamp frame will be placed in an oven. The sheet will be heated until the surface temperature of the sheet reached 188°C. The frame and sheet will then be removed from the oven for 45 seconds to allow the sheet surface and core to equilibrate, so that the temperature of the part's surface is essentially equal to the temperature at the center of the part. The frame and sheet will then be returned to the oven and heated until the surface was again 188°C. Care will be taken to avoid overheating which will cause the material to bubble and become unusable. The frame and sheet material will then be removed from the oven. The Corian® sheet, extending out beyond the perimeter of the lower pressure box was positioned directly over the bottom pressure box. The top pressure box will be lowered down to tightly seal with the lower box by pinching the Corian® sheet. Air pressure of from about 5 to about 10 psi will then be introduced in the lower box for about 10 seconds to stretch the Corian® sheet material uniformly like a stadium dome. This allows greater forming depths by effectively spreading the draw out over the entire sheet rather than locally in pockets. The pressure will then be exhaustedfrom the lower box which contained the MDF mold. The top box will be pressurized at the same time to create a larger pressure differential between the top and bottom pressure box. This pressure differential will act to press the Corian® sheet firmly against the MDF mold. This pressure differential will be maintained for 6-12 minutes to allow the Corian® sheet material to cool down to 85°C. The pressure and vacuum will then be released, the boxes separated and the Corian® sheet removed having crisp, well defined bowl patterns in the sheet. EXAMPLE 7 Pre-stretch Pressure forming bowl The solid surface material used was a sheet of alumina trihydrate filled acrylic (Corian® Genesis from E. I. du Pont de Nemours and Company, Inc., Wilmington, DE) which was 24 x 30 inches (61 x 76.2 cm) with a thickness of 0.5 inches (1.3 cm). The mold was made from cast aluminum. The mold was two small 8" x 8" x 5" sink shapes that the material is formed into. The mold was placed in a pressure forming mold box. The box was a two part, top and bottom assembly that sealed into a top and bottom chamber when brought together. The top and bottom were separated by the Corian® sheet, which was larger than the boxes and was pinched at the seal around the edges. The Corian® sheet was placed in a perimeter clamp frame and the clamps actuated to positively hold the sheet. Then the sheet and clamp frame were placed in an oven. The sheet was heated until the surface temperature of the sheet reached 188°C. The frame and sheet were then removed from the oven for 45 seconds to allow the sheet surface and core to equilibrate or soak. The frame and sheet were then returned to the oven and heated until the surface was again 188°C. Care was taken to avoid overheating which will cause the material to bubble and become unusable. The frame and sheet material were removed from the oven. The Corian® sheet, extending out beyond the perimeter of the lower pressure box was positioned directly over the bottom pressure box. The top pressure box was lowered down to tightly seal with the lower box by pinching the Corian® sheet. Air pressure of 10 psi was then introduced in the lower box for about 10 seconds to stretch the Corian® sheet material uniformly like a stadium dome. This allows greater forming depths by effectively spreading the draw out over the entire sheet rather than locally in pockets. The pressure was then exhausted and a vacuum of 20 in. Hg (0.70 atm) was drawn in the lower box which contained the double sink mold. A pressure of 4 atm was applied to the top box at the same time to create a larger pressure differential between the top and bottom pressure box. This pressure differential acted to press the Corian® sheet firmly into the sink mold. This pressure differential was maintained for 6-12 minutes to allow the Corian® sheet material to cool down to 85°C. The pressure and vacuum were then released, the boxes separated and the Corian ® sheet removed having two well defined bowl patterns in the sheet.

Claims: What is claimed is: 1. A process for molding a part containing solid surface material, the process comprising: providing a mold form having on at least one mold form surface a relief pattern, a shape, or a combination thereof; providing the part; heating the part to a conformable temperature in a range from 110°C and 220°C; forming a desired relief pattern on the heated part by applying a molding pressure greater than atmospheric pressure to the mold form containing the heated part and maintaining the molding pressure for a predetermined time to obtain a molded part wherein the part and the mold form is enclosed by an air impermeable blanket which overhangs the mold on all sides. 2. The process of Claim 1 wherein the blanket is a silicone rubber having a durometer greater than 40. 3. The process of Claim 1 wherein the solid surface material is a filled acrylic material and the part is in sheet form. 4. The process of Claim 3 wherein the conformable temperature is between 120 and 190°C. 5. The process of Claim 1 wherein the pattern formation step further comprises the step of providing a vacuum enclosure by evacuating the mold form containing the part. 6. The process of Claim 1 wherein: the part has a first surface with first part surface area; the molding pressure is at least partially applied by providing a multiplier board having a applied pressure surface and a board surface opposite the applied pressure surface, the board surface disposed adjacent to the first part surface, the applied pressure multiplier board having a having a board surface area greater than the first part surface area.

Inventors: HANNON JOHN L, HANNON, JOHN, L.
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 2000
Main classification: B29C59
IPC codes: B29C43, B29C51, B29C59