Patent Publication Number: US-2009226619-A1

Title: Texturing of molding dies

Description:
FIELD 
     The present disclosure relates to molding dies and more particularly to texturing molding dies to improve the paintability of molded components. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Some paints, such as water based paints, do not adhere particularly well to certain untreated polymeric surfaces, especially molded polypropylene. For instance, polypropylene is generally known in the art to be very difficult to successfully paint with water based paint. The paint often peels and/or separates from polypropylene substrates. 
     The low surface tension of many molded components (especially polypropylene) may cause liquids, such as paint, to bead up on the surface of the component rather than wetting the material and adhering thereto. Low surface tension in the material results in a high contact angle between the surface of the material and the liquid paint. 
     Liquid droplets may exhibit contact angles greater than 90 degrees on hydrophobic surfaces. This high contact angle causes the liquid paint to form compact droplets on the molded component. Intermolecular forces within the liquid paint droplets may act to maintain the droplet form, resisting the paint&#39;s ability to spread and wet the material, thereby hindering adhesion. 
     Thus, it can be difficult to achieve adequate adhesion of paint (e.g., water based paint) to molded components, especially polypropylene and other polymeric components, while maintaining streamlined and efficient manufacturing processes, consistent with lean manufacturing principles. 
     SUMMARY 
     A method of adhering paint to a molded component may entail providing a molding die adapted to mold the molded component, forming the molded component in the molding die, forming a texture including a plurality of recesses onto the molded component, and applying a paint to the molded component and into the plurality of recesses. 
     In another embodiment, a method of adhering paint to a polypropylene component may entail forming a molding die adapted to shape a polypropylene component, sandblasting a texture into a surface of the molding die, the texture including a plurality of recesses, molding the polypropylene component in the molding die, the texture imprinting onto a surface of the polypropylene component, and applying a paint to the surface of the polypropylene component. The texture increases a surface tension of the polypropylene component to facilitate adhesion of the paint to the surface of the polypropylene component. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a flowchart illustrating an embodiment of a method of adhering paint to a component according to the principles of the present disclosure; 
         FIG. 2  is a perspective view of a component and a molding die having a texture according to the principles of the present disclosure; 
         FIG. 3  is a detail view of a partially painted surface of the component of  FIG. 2  having a texture imprinted thereon according to the principles of the present disclosure; and 
         FIG. 4  is a perspective view of a component being sandblasted to form a texture thereon. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     With reference to  FIGS. 1-3 , one embodiment of a method of adhering paint to a component is illustrated at  FIG. 1  and is generally indicated by reference numeral  100 . As will be discussed in greater detail below, the method of adhering paint to a component  100  (hereinafter “the method”) may increase a surface tension of the component  10 , which may decrease a contact angle between the component  10  and paint  12 . Liquid droplets may exhibit contact angles greater than 90 degrees, for example, on surfaces of hydrophobic materials (such as, for example, polypropylene and other polymers). The contact angle between a liquid and a hydrophobic surface decreases as the surface tension is increased. Decreasing the contact angle to below 90 degrees may allow the paint  12  to spread and wet the component  10 , allowing the paint  12  to adhere to the component  10  (see  FIG. 3 ), rather than beading up thereon. 
     The component  10  may be an instrument cluster frame ( FIG. 2 ), for example, molded to house and display instruments in a vehicle, such as, for example, a speedometer, a tachometer, a fuel gauge, and/or other gauges and instruments that may display information to a driver of the vehicle. The component  10  may be formed from any material, especially polypropylene and other polymeric materials. It should be appreciated that the component  10  could be any molded component formed from any suitable material without departing from the scope of the present disclosure. 
     With continued reference to  FIGS. 1-3 , the method  100  will be described in detail. First, block  110  entails providing a molding die  14 . More specifically, providing a molding die (or die)  14  may entail forming a cavity within a block of material, the cavity having a plurality of surfaces  15  which may form a negative (or inverse) of the shape of the component  10  (see  FIG. 2 ), such that a liquid polymer (or other material) may solidify within the die  14  to form the component  10 , as is known in the art. The die  14  may be machined or otherwise formed from steel, iron, aluminum, or any other suitable material. 
     Block  120  may entail applying a texture  16  to the surfaces  15  of the die  14 . The texture  16  may include a plurality of recesses, e.g., scratches and/or other deformations and imperfections. A grade of the texture  16  should be sufficient to raise a surface tension of the component  10  (described in detail below) to within a required range. In one embodiment, the grade of the texture  16  may be about TH-110 (or WN3015) or equivalent. It should be appreciated that the texture  16  could be applied to the die  14  concurrently with forming the die  14 , i.e., blocks  110  and  120  could occur simultaneously. 
     The texture  16  may be applied to the die  14  by a sandblasting process, in which standard shop air (e.g., about 60 to about 80 psi) may be utilized to cause blasting media to impact surfaces of the die  14  at high speeds. The blasting media size, shape and material can be rated to yield the texture grade of about TH-110. It should be appreciated that applying the texture  16  to the die  14  is not limited to sandblasting processes and may be accomplished by any of several other suitable processes, including filing, sanding, chiseling, acid etching, and/or any other process capable of applying a suitable texture to the die  14 . 
     The next step, block  130 , may include forming the component  10  in the die  14  (i.e., molding the component  10 ). Liquefied material may be inserted into the die  14  and may solidify therein (according to the principles of known molding, casting, and/or forming processes) to produce the shape of the component  10 . The component  10  may be formed by injection molding, blow molding, extrusion, or any other molding, forming or casting process known in the art to be suitable for shaping components in the die  14 . 
     Block  140  may entail imprinting the texture  16  of the molding die  14  into the component  10 . More specifically, the inverse of the texture  16  may be imprinted onto the component  10  during the steps of block  130 , causing the formation of a texture  18  on the component  10  ( FIG. 3 ), i.e., forming the texture  18  onto the component  10  may occur simultaneously with forming the component  10  in the molding die  14 . The texture  18  may have a grade of about TH-110 to increase a surface tension of the component  10  to at least about 30 dynes per centimeter or between about 30 dynes per centimeter to about 34 dynes per centimeter. 
     The next step, block  150 , may entail applying the paint  12  to the component  10 . The paint  12  may be applied to the component  10  by any suitable means known in the art, such as, for example, spraying, brushing, or submerging the component in the paint  12 . The paint  12  may be a water based paint such as, for example, Red Spot® paint, or any other paint suitable for application to polymeric surfaces. 
     A surface tension within about 30-34 dynes per centimeter may be sufficient to reduce the contact angle between the paint  12  and surfaces of the component  10  to below 90 degrees, for example, thereby inducing the paint  12  to wet the component  10 . Significant wetting of the surface of the component  10  causes the paint  12  to adhere thereto (see  FIG. 3 ). 
     The paint  12  may be applied to the component  10  to substantially fill the plurality of recesses of the texture  18 , giving the painted surface of the component  10  a smooth and aesthetically pleasing appearance ( FIG. 3 ). 
     With reference to  FIG. 4 , the method  100  could include forming the texture  18  onto the component  10  after the molding process  130  particularly for prototype and/or low volume production of the component  10 . For example, each component  10  may be sandblasted (as shown in  FIG. 4 ), sanded, or otherwise abraded and/or textured to achieve the requisite surface tension. 
     Referring now to  FIGS. 1-4 , there are multiple advantages to the teachings of the present disclosure. The methods of adhering paint (e.g., water based paint) to the component according to the present disclosure solves the long felt, but unresolved need for an efficient method of adhering paint to certain materials, including polypropylene and other polymers. 
     Imprinting the texture  16  onto the component  10  directly from the die  14  renders each component  10  ready for painting (i.e., each component has the requisite surface tension to facilitate paint adhesion) without an additional step after the molding process. In this manner, components may be mass produced without adding steps in the production process, as only the molding die  14  is treated, thereby only adding one step to the tooling preparation process. The added step to the tooling preparation process may be more readily absorbed through production of multiple components  10 , as the additional tooling costs will be spread out thereover. 
     Imprinting the texture  16  into the component  10  via the molding die  14  as described above with reference to block  140  also improves the reliability and repeatability of the texturing process. The method  100  may reduce variances in the texture  18  of the component  10 , when each component  10  is molded from the same molding die  14 . 
     However, as described above, the embodiment of the method  100  wherein the texture  18  is formed onto the component  10  after the component  10  is molded may be well suited for low volume production of the component  10 . Additionally or alternatively, forming the texture  18  after molding the component  10  may allow customization of the method  100  for individual components, for example, if the painted portions of the component  10  differ for each production run. One of ordinary skill in the art will appreciate from the present disclosure that a variety of other reasons may render this embodiment (i.e., forming the texture  18  after molding the component  10 ) more suitable than the former embodiment (i.e., simultaneously forming the texture  18  and molding the component  10 ) described herein. 
     The description of the present disclosure is merely exemplary in nature and, thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.