PATENT DOCUMENT

Publication Number: US-8562886-B2
Application Number: US-87588510-A
Country: US
Kind Code: B2

Title: Composite laminate having an improved cosmetic surface and method of making same

Abstract:
A composite laminate includes a plurality of sheets of prepreg stacked one over another, and a scrim layer provided on an exterior surface of the sheets of prepreg. Each prepreg sheet is formed of fibers preimpregnated with resin. The scrim layer and the sheets of prepreg form a composite laminate whereby the scrim layer constitutes an outer, exposed surface of the composite laminate. The scrim layer may be a nonwoven carbon or glass fiber scrim that has absorbed resin from the sheets of prepreg. A method of making a composite laminate includes placing into a mold a scrim and a plurality of sheets of prepreg, with the scrim extending between an exterior surface of the sheets of prepreg and an inner surface of the mold; forming a composite laminate whereby the scrim is adhered to the sheets of prepreg; and removing the composite laminate from the mold. An outer layer of the composite laminate includes the scrim.

Claims:
What is claimed is: 
     
       1. A method of making a composite laminate, comprising:
 placing into a mold a scrim and a plurality of sheets of prepreg, each sheet of prepreg including fibers preimpregnated with resin, wherein the scrim extends between an exterior surface of the plurality of sheets of prepreg and an inner surface of the mold, wherein:
 the scrim is made of a nonwoven mat of randomly oriented fibers, 
 the fibers of each sheet of prepreg are substantially parallel carbon fibers, and 
 the carbon fibers in adjacent sheets of prepreg are disposed at an angle relative to one another; 
 
 forming a composite laminate whereby the scrim is adhered to the sheets of prepreg and the fibers of at least one sheet of the plurality of sheets of prepreg are at least partially visible through the scrim; and 
 removing the composite laminate from the mold, wherein an outer layer of the composite laminate includes the scrim and forms an outer, exposed surface of the composite laminate. 
 
     
     
       2. The method of  claim 1 , wherein the step of forming the composite laminate causes the scrim to absorb resin from the sheets of prepreg, whereby the resin and scrim constitute the outer layer of the composite laminate. 
     
     
       3. The method of  claim 1 , wherein the fibers of the scrim are carbon fibers. 
     
     
       4. The method of  claim 1 , wherein the step of placing the scrim and the plurality of sheets of prepreg into the mold comprises:
 placing the scrim into the mold; and 
 placing the sheets of prepreg into the mold over the scrim after the scrim has been placed into the mold. 
 
     
     
       5. The method of  claim 1 , wherein the step of forming the composite laminate includes subjecting the scrim and the sheets of prepreg to heat and pressure. 
     
     
       6. The method of  claim 1 , further comprising:
 placing a second scrim into the mold so that the sheets of prepreg are disposed between the first scrim and the second scrim, wherein the step of forming the composite laminate includes causing the second scrim to absorb the resin from the sheets of prepreg, whereby the resin and the scrim form a second outer layer of the composite laminate, the sheets of prepreg being sandwiched between the first and second outer layers. 
 
     
     
       7. The method of  claim 6 , wherein at least one of the first and second scrims is formed of carbon fibers. 
     
     
       8. The method of  claim 6 , wherein at least one of the first and second scrims is formed of glass fibers. 
     
     
       9. The method of  claim 6 , wherein the resin in each sheet of prepreg is pigmented. 
     
     
       10. The method of  claim 6 , wherein at least one of the first and second scrims is formed of carbon fibers and another is formed of glass fibers. 
     
     
       11. The method of  claim 1 , wherein the outer, exposed surface of the composite laminate is textured, wherein an inner surface of the mold has a texture which is transferred to the resin during forming of the composite laminate. 
     
     
       12. A method of making a composite laminate, comprising:
 placing a first scrim into a mold, wherein the first scrim is made of a nonwoven mat of randomly oriented fibers; and 
 placing a plurality of sheets of prepreg over the first scrim in the mold, each sheet of prepreg including fibers preimpregnated with resin, wherein:
 the first scrim extends between an exterior surface of the plurality of sheets of prepreg and an inner surface of the mold, 
 the fibers of each sheet of prepreg are substantially parallel carbon fibers, and 
 the carbon fibers in adjacent sheets of prepreg are disposed at an angle relative to one another; 
 
 placing a second scrim into the mold so that the sheets of prepreg are disposed between the first scrim and the second scrim; 
 forming a composite laminate by causing the first and second scrims to absorb the resin from the sheets of prepreg whereby the first and second scrims are adhered to the sheets of prepreg and the fibers of at least one sheet of the plurality of sheets of prepreg are at least partially visible through at least one of the first scrim or the second scrim; and 
 removing the composite laminate from the mold, wherein the resin and the first scrim constitute a first outer layer that forms an outer, exposed surface of the composite laminate, and wherein the resin and the second scrim form a second outer layer of the composite laminate, the sheets of prepreg being sandwiched between the first and second outer layers. 
 
     
     
       13. The method of  claim 12 , wherein at least one of the first and second scrims is formed of carbon fibers or glass fibers. 
     
     
       14. The method of  claim 12 , wherein one of the first or second scrims is formed of carbon fibers and the other of the second or first scrims is formed of glass fibers. 
     
     
       15. The method of  claim 12 , wherein the resin in the sheets of prepreg is pigmented. 
     
     
       16. The method of  claim 12 , wherein the outer, exposed surface of the composite laminate is textured, wherein an inner surface of the mold has a texture which is transferred to the resin during forming of the composite laminate. 
     
     
       17. The method of  claim 12 , wherein the fibers of each sheet of prepreg are nonwoven.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional of U.S. application Ser. No. 11/932,244, filed Oct. 31, 2007, the entire disclosure of which is incorporated herein by reference thereto. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to composite laminates, and more particularly, the present invention relates to composite laminates prepared from fiber reinforced resin impregnated materials. 
     2. Background Art 
     Many products are formed of plastics because they are light weight and can be readily shaped and styled. Electrical equipment enclosures, such as enclosures for computers and portable electronic devices, for example, are typically formed of plastic materials to make aesthetic, functional housings. Plastic housings for electronic equipment can be both rigid and lightweight, and can be durable without being bulky. Electronic equipment enclosures also typically provide shielding against electromagnetic pollution, such as that which emanates from the electronic device or exists in the surrounding environment. 
     Plastic housings for electronic equipment may be prepared from plastic material reinforced with carbon fiber. Carbon fiber reinforced plastic, also referred to as carbon fiber composites, provide a very strong, lightweight material for forming housings for electronic equipment. Carbon fiber composites may be formed by layering sheets of carbon fiber material into a mold that is the shape of the desired product. The mold may then be filled with a thermosetting resin (e.g., an epoxy resin prior to being cured) and the resin cured to thermoset the resin (e.g., autoclave cured and/or vacuum bagged). The mold may also be filled with a thermoplastic resin that is then “cured” in the sense that after the resin conforms to the shape of the mold, it is cooled until the thermoplastic resin is below its glass transition temperature and therefore maintains its shape. Another method of producing carbon fiber composites is by layering sheets of carbon fiber material that has been preimpregnated with thermoplastic resin or partially cured thermosetting resin (or has a layer of thermoplastic resin or partially cured thermosetting resin layered over each sheet) into a mold that is in the shape of the desired product. This assembly may then be placed in a vacuum or is subject to thermal compression until the resin fully cures. 
     Despite the many benefits of carbon fiber composites, such composites are typically black and the carbon fibers are typically visible on the composite surface. In addition, the fibers (either as a unidirectional, woven, or nonwoven substrate) are typically variable in their construction and therefore are variable in their surface presentation. As a result, the resulting carbon fiber composite can have cosmetic imperfections that reduce the aesthetic appearance of the molded article formed therefrom. Further, carbon fiber composites, often being black, provide a narrow range of surface appearance to the molded article and therefore may give a “tired”, unexciting look. 
     BRIEF SUMMARY OF THE INVENTION 
     A composite laminate having an improved cosmetic surface is presented herein. The composite laminate includes a plurality of sheets of preimpregnated material, or prepreg, stacked one over another and a scrim layer provided on an exterior surface of the sheets of prepreg. The scrim layer and the sheets of prepreg form a composite laminate whereby the scrim layer constitutes an outer, exposed surface of the composite laminate. Each sheet of prepreg is made from fibers preimpregnated with resin, and the fibers of the prepreg may be substantially parallel or woven carbon fibers. The scrim layer may be a glass fiber or carbon fiber scrim, or veil, that has absorbed resin from the sheets of prepreg during a molding process. In another embodiment, the composite laminate includes a plurality of sheets of prepreg stacked one over another and first and second scrim layers provided on opposing exterior surfaces of the sheets of prepreg, whereby the sheets of prepreg are sandwiched between the first and second scrim layers. The first and second scrim layers constitute exposed surfaces of the composite laminate. 
     A method of making a composite laminate having an improved cosmetic surface includes the steps of placing into a mold a scrim and a plurality of sheets of prepreg, with the scrim extending between the sheets of prepreg and an inner surface of the mold; forming a composite laminate whereby the scrim is adhered to the sheets of prepreg; and removing the composite laminate from the mold. An outer layer of the composite laminate includes the scrim. In one embodiment, the forming step includes causing the scrim to absorb the resin from the sheets of prepreg, whereby the resin and the scrim form the outer layer of the composite laminate. 
     Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below, with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention. In the drawings, like reference numbers, letters, or renderings indicate identical or functionally similar elements. 
         FIG. 1A  is a cross-sectional schematic view of a composite laminate for forming a molded article, in accordance with one embodiment of the present invention; 
         FIG. 1B  is an enlarged view of a portion of the composite laminate of  FIG. 1A ; 
         FIG. 2  is a exploded, schematic view of stacked sheets of resin impregnated material and a scrim used to form the composite laminate of  FIG. 1A ; 
         FIG. 3  is a cross-sectional schematic view of the material of  FIG. 2  placed in a mold for preparation of a molded article formed of the composite laminate of  FIG. 1A , in accordance with one embodiment of the present invention; and 
         FIG. 4  is a cross-sectional schematic view of another composite laminate for forming a molded article, in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A molded article in accordance with one embodiment of the present invention may be formed of a composite laminate  10 , illustrated in  FIGS. 1A and 1B . Composite laminate  10  has opposing first and second surfaces  12  and  14 , respectively, and is formed of a composite  30  and a scrim layer  20 . Surface  12  is formed on the exterior of scrim layer  20 . Surface  14  is formed on the exterior of composite  30 . Composite  30  is formed of a plurality of sheets of prepreg  30   a - 30   g  that are fused together during a molding process. An exemplary molding process for making composite laminate  10  is provided below with reference to  FIGS. 2 and 3 . In the embodiment illustrated in  FIG. 1A , eight sheets of prepreg ( 30   a - 30   g ) form composite  30 . However, it should be understood that any number of sheets of prepreg may be used. For example, in one embodiment, between 5 and 8 sheets may be used, and in another embodiment, 20 sheets may be used. Further, the sheets of prepreg can vary in thickness. For example, a sheet of prepreg can have a thickness in a range of about 25-200 μm. Therefore, a designer may choose to use more or less sheets of prepreg depending on the thicknesses of the sheets and the strength the composite laminate that is desired. 
     As used herein, the term “prepreg” refers to fibers preimpregnated with resin, such as a combination of a fibrous substrate (such as a mat, fiber, or cloth material) with resin impregnated on and into the substrate. Each sheet of prepreg  30   a, b, . . . g  is a substantially planar sheet of fibers impregnated with a resin that is initially ready for curing. During the molding process for forming composite laminate  10 , the resin of prepreg sheets  30   a - 30   g  are cured. There are many types of resins that may be used in prepreg sheets  30   a - 30   g , including, but not limited to, conventional thermoplastic resins and conventional thermosetting resins such as epoxies. The resin is typically at an intermediate stage prior to becoming fully cured. The fibers of the prepreg sheets  30   a - 30   g  sheets may be, for example, carbon fibers. To produce a sheet of prepreg, continuous fibers formed from bundles of filaments may be linearly oriented to produce a sheet of unidirectional fibers, or the fibers may be woven to produce a woven sheet, as known to one of skill in the relevant art(s). These fibrous sheets are then impregnated with resin to form sheets of prepreg. Sheets of prepreg  30   a - 30   g  can be formed using conventional methods for impregnating fibers with resin. For example, one method of manufacturing a sheet of prepreg is disclosed in U.S. Pat. No. 5,201,979, which is incorporated herein in its entirety by reference thereto. 
     As shown in  FIG. 1B , scrim layer  20  is formed of a scrim  22  and resin  23 . During the molding process, excess resin  23  from the plurality of sheets of prepreg  30   a - 30   g  seeps through and is absorbed by scrim  22 , such that surface  14  of composite laminate  10  includes resin  23  and scrim  22 . Scrim  22  is thin (e.g., about 50 μm thickness), and may be made of a nonwoven mat of fibers, randomly oriented, similar to felt. The fibers of scrim  22  may be carbon fibers, glass fibers, and synthetic resin fibers (e.g., aramid fiber). The fibers may also be inorganic fibers such as metal fibers (e.g., aluminum fibers or titanium fibers). In one embodiment, scrim  22  may be a nonwoven glass fiber scrim, and in another embodiment scrim  22  may be a nonwoven carbon fiber scrim, such as Part #1064 produced by Fibre Glast Developments Corp. of Brookville, Ohio. Also, in one embodiment, scrim  22  may be impregnated with resin. 
     Since glass fiber is less stiff than carbon fiber, composite laminate  10  having a glass fiber scrim has improved impact resistance over a like composite laminate incorporating a carbon fiber scrim. Scrim  22  extends over composite  30  and hides the reinforcing fibers of prepreg sheets  30   a - 30   g . Since scrim  22  absorbs resin  23  of the composite  30 , scrim  22  takes on the cosmetic properties and color of resin  23 . Also, as noted above, scrim  22  is very thin, and it is translucent, and the underlying fibers of composite  30  are partially visible therethrough. The combination of resin  23  and scrim  22  forming scrim layer  20  imparts a depth to surface  12  of composite laminate  10 , thereby providing an improved cosmetic surface of a molded article formed therefrom that is not only consistent in appearance, but is also aesthetically pleasing. 
     Resin  23  may be clear or pigmented. Clear resin would provide the most visibility of scrim  22  and the underlying fibers of composite  30 , and therefore provides a greater perception of depth to surface  12  than pigmented resin. For example, pigmented resin would produce a translucent, colored surface, altering the apparent depth of surface  12  of composite laminate  10  and providing further variation to the cosmetic surface of the molded article. Moreover, if a clear glass fiber scrim is used as part of scrim layer  20 , scrim  22  would be transparent, such that pigmented resin has a greater impact on the color and apparent depth of surface  12  of composite laminate  10 . To provide further variation to the appearance of surface  12 , the thickness of the scrim may be varied. In one embodiment, the scrim may be just thick enough to be substantially opaque, whereby the underlying fibers of prepreg sheets  30   a - 30   g  are not visible therethrough. 
     Composite laminate  10  may be provided with a smooth and/or textured surface. A textured surface may be achieved by applying a texture to the inner surface of a mold, which is then transferred to resin  23  during the molding process. As such, the several embodiments of the present invention described herein provide a designer with the opportunity to produce molded articles that have the advantageous properties of carbon fiber composites, without being limited to its black color or its imperfections in appearance. Composite laminate  10  may form any shape of molded article. In one embodiment, the molded article is an enclosure, such as a housing for an electronic device, with first surface  12  being the outer, exposed surface of the molded article, and second surface  14  constituting an inner, hidden surface thereof. In this instance, scrim layer  20  imparts the enclosure with a consistent and pleasing cosmetic surface. Further, in molded articles having irregular curved portions, such as curved corners of an enclosure, the underlying fibers of the prepreg sheets are most likely to be inconsistently oriented and are therefore less likely to provide the molded article with a uniform appearance. Therefore, the presence of scrim layer  20  provides congruency between the appearance of the irregular curved portions of the enclosure. 
     A method of making composite laminate  10  will now be described with reference to  FIGS. 2 and 3 .  FIG. 2  shows an exploded, schematic view of a plurality of sheets of prepreg  30   a - 30   g  and a scrim  22 , prior to being laminated together to form composite laminate  10  shown in  FIG. 1A . In the schematic of  FIG. 2 , each sheet of prepreg  30   a, b  . . . g, may be formed of woven, nonwoven or parallel (i.e., unidirectional) fibers. In one embodiment, the fibers of at least one sheet of prepreg may be substantially woven. In another embodiment, the fibers of at least one sheet of prepreg of composite  30  may be substantially parallel carbon fibers. In another embodiment, all sheets of prepreg that form composite  30  may be formed of substantially parallel carbon fibers. Further, in one embodiment, fibers of adjacent sheets  30   a, b . . . g  may be disposed at an angle to one another, such as illustrated in  FIG. 2 . Typically, the orientation of the fibers of the adjacent sheets of prepreg are varied to improve the strength of the molded article formed therefrom. 
     Extending over a face of composite  30  is a scrim  22 . In the embodiment of  FIG. 2 , scrim  22  extends beneath prepreg sheet  30   a , and scrim  22  and sheets  30   a - 30   g  form an assembly  40  that may then be placed in a mold all at once.  FIG. 3  shows assembly  40  placed in a mold  50  such that scrim  22  extends between an inner surface of mold  50  and the bottom-most prepreg sheet (i.e., sheet  30   a ) of composite  30 , with prepreg sheets  30   a - 30   g  stacked over scrim  22 . Alternatively, assembly  40  may be formed directly in mold  50  by placing scrim  22  in mold  50  and thereafter placing individual prepreg sheets  30   a, b . . . g  in mold  50 . 
     Scrim  22  is then adhered to composite  30  during a molding process conventional in the relevant art, for example, by applying heat and/or pressure so as to laminate together scrim  22  and prepreg sheets  30   a - 30   g  and cure resin  23 . When assembly  40  is laminated together to form composite laminate  10 , scrim  22  absorbs excess resin  23  of prepreg sheets  30   a - 30   g , thereby forming scrim layer  20  which is unitary with composite  30 , as illustrated in  FIGS. 1A and 1B . Thereafter, the laminated prepreg sheets  30   a - 30   g  and scrim layer  20  are removed from mold  50 , with scrim layer  20  forming surface  12  of composite laminate  10 . 
     In another embodiment, depicted in  FIG. 4 , a composite laminate  60  may be formed in which the plurality of prepreg sheets  30   a - 30   g  of composite  30  are sandwiched between scrim layer  20  and a second scrim layer  80 , which constitute an outer surface  62  and an inner surface  64 , respectively, of composite laminate  60 . As such, both inner and outer surfaces of a molded article formed from composite laminate  60  are provided with a consistent, aesthetically pleasing appearance, which may be especially desired when both the inner and outer surfaces of the molded article are visible to a user. 
     Composite laminate  60  may be formed similar to composite laminate  10 , but with assembly  40  of  FIG. 3  including another scrim extending over the upper-most prepreg sheet (i.e., sheet  30   g ) of composite  30 . During a compression molding process, excess resin from prepreg sheets  30   a - 30   g  would also seep through the scrim over prepreg sheet  30   g , adhering the scrim to composite  30 . The resin and scrim forms scrim layer  80 . The scrims of scrim layers  20  and  80  may be formed of like materials (e.g., both scrims are carbon fiber scrims), or the scrims may be formed of different materials (e.g., scrim  22  may be a glass fiber scrim while the scrim of scrim layer  80  is a carbon fiber scrim). It should therefore be apparent that various modifications to scrim layers  20  and/or  80  of composite laminate  60  may be employed so as to achieve molded articles having a variety of cosmetic surfaces in accordance with the present invention. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Metadata:
Filing Date: 20100903
Publication Date: 20131022
Grant Date: 20131022
Priority Date: 20071031
Inventors: DIFONZO JOHN
LIGTENBERG CHRIS
Assignee: APPLE INC
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Family ID: 40583198