Opaque and Translucent Painting

p/n 33-D215 Rev A

 

Opaque and Translucent Painting

 

It is often advantageous to add color to a part or parts within an assembly. To color a very complex part a dying process is recommended as this is able to uniformly coat complex features without impacting movement or interface geometry. However, some user applications require final-quality, production-looking parts. For example, is common for manufacturers to produce injection-molded parts in high volume with a base color plastic and subsequently paint the parts with a two-part polyurethane for critical-to-function surface durability and aesthetic requirements. It is important to be able to prototype this type of part during the design cycle. Painting can also be required to simulate a metal finish, create translucent colored parts like for automotive lenses, create a high-gloss chrome-plated look, or simply for specialty engineering or aesthetic purposes.  With most prototyping technologies, this can be difficult to achieve due to objectionable layer lines and/or surface quality issues due to support contacts and/or surface roughness.  3D Systems MultiJet Printing (MJP) technology utilizes a high-resolution printing process that places over 1 billion individual droplet per cubic inch of part volume. This is combined with a melt-away support technology that produces no support marks on the part and results in very good surface quality. Therefore, MJP parts are easily painted with both professional coatings and consumer spray paint.

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Numerous customer use cases require high optical clarity including automotive lenses, bottles, jars and containers, as well as flow visualization and for purely aesthetic purposes

 

MJP Opaque Painting Overview

The ProJet MultiJet Printer (MJP) 2500 is designed to be used by an individual user up to a large group and offers numerous materials for a wide variety of customer needs. The Rigid materials are relatively strong and stiff materials with tensile strength 35-70 MPa, a modulus of up to 3000 MPa, and can achieve an elongation before break of up to 30%. The engineering materials M2G-CL (Armor) and M2G-DUR (Proflex) maintain the high quality and fidelity of MJP, but are designed especially for the most aggressive engineering applications including high impact strength, complex snap fits, and living hinges. The Armor material is designed to have ABS-like properties to simulate injection-molded plastic parts. Armor has an impact strength of 40-50 J/m, and yet still maintains a tensile strength of 30-35 MPa, stiffness modulus of 1500-2000 MPa and elongation before break between 55 to 65%. The ProFlex material is designed to have Polyproplyene-like properties. It has an impact strength of 70-80 J/m, and is much more flexible with a stiffness of 250 to 350 MPa and elongation before break up to 65-75%. All of these materials can be easily painted with a high-quality, professional result using the same simple process.

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The ProJet 2500 offers a wide range of rigid and engineering materials that span from strong and stiff, to tough and flexible.  All of these materials can be easily painted

 

Painting MJP Parts

For most applications, the ProJet 2500 is able to produce paintable surface quality right out of the printer with no needed filling, sanding, or bead blasting. All MJP parts to be painted should be processed normally with the EasyClean system or an oven to remove the bulk wax and with mineral oil. If EZ Rince-C is used in the post processing, one should wipe the parts down with isopropyl alcohol prior to painting to insure sufficient surface cure. If mineral oil is used no special process is needed prior to painting. Use dawn soap to remove all the mineral oil residue from the surface. Follow normal post processing recommendations. For very complex parts it may be advantageous to apply the dawn soap directly to the part and use a brush to insure all the mineral oil is removed. A good water rinse and drying should be used as the final cleaning step.

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For MJP painted parts apply the Dawn soap directly to the part and use a brush if needed

 

As-printed part surface uniformity is improved somewhat by aggressively brushing the surface with a stiff nylon brush or a buffing wheel; however, typically this is not needed.

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A Stiff nylon brush can be used to improve surface optical clarity 

 

Paint Type and Application Process

Painting can be done by a professional shop using a two-part polyurethane with a paint and catalyst or with standard enamel/acrylic paint that can be found at most hardware or hobby stores or on-line at locations like Amazon.com, McMaster-Carr or Walmart.com. Very good results can be achieved without the need for professional skills or equipment. All color and type of paints can be used. For example, all Rust-Oleum® & Krylon® spray paints are good choices. Painting should be done according to the recommendations on the can. Use an overhead light that enables good visualization of the part surfaces. Hold the can 10-12 inches away from the part and apply paint until a uniform coat is achieved. Start painting the surfaces that are the hardest to reach.  Other more accessible surfaces will get coated naturally as these difficult areas are painted. After the difficult areas are coated with a uniform layer, touch up any of the easier to reach areas. It is typically good to start with a thin, light layer and then build a solid coat through multiple applications. The goal is to create a uniform layer on all surfaces without resulting in any dripping or running of the paint. To achieve a glossy surface, the final coat needs to be thick enough to cover the entire surface uniformly, but thin enough to avoid any drips or runs. Proper technique will often result in a lot of wasted paint. Three or four coats are typically needed. Apply the coats in rapid succession with 3-5 minutes between coats. If the paint is allowed to dry for a longer time, it is typically recommended to let it sit overnight and apply the remaining coats the next day. If drips or runs are formed during painting, it is best to let it dry completely and attempt to sand the drips off these surfaces. Subsequent coats will typically hide most over- or under-coverage issues and reprocessing sanding marks in the paint but will not hide large drips of paint. There are specially designed paints that are commonly available and are made to simulate metal surfaces. One can also use numerous metallic-type paints that are available from many vendors to create metal-looking surfaces and other professional effects.

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ProJet M2R-GRY Rigid material parts painted with metallic-type spray paints to achieve a metal-like surface texture and color 

 

Hammered-type paints can also be used to simulate a metal finish. These paints create a natural texture that has professional aesthetic qualities and tends to hide defects.

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ProJet M2R-CL rigid clear material painted with hammered-type spray paints 

 

There are numerous brands and families of paint, each that can produce a different effect. All work equally well when using a 3D Systems Projet 2500 MJP printer.

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ProJet M2R-TAN material painted with stone-type spray paints 

 

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M2G-DUR (ProFlex) clear material with flat matte chalky-finish spray paints

 

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M2G-CL (Armor) clear material with bright neon-finish spray paint

 

If you have your parts professionally painted with a two-part polyurethane (like an automotive-type or plastic injection molded-type formulation), try a 7-1-2 mixture of paint, catalyst and thinner. Use three coats applied in rapid succession.

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M2R-CL and M2R-GRY parts professionally painted with a two-part polyurethane 7-1-2 paint/catalyst/thinner – 3 coats in rapid succession

 

Sanding and/or Blasting to Achieve Painted Translucent Colored Parts

There are special spray paints that create a colored translucent effect. This is needed for certain applications like creating automotive lenses.

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Transparent clear and spray painted automotive lenses can be made in Rigid Clear, Armor, and ProFlex.

 

One of the clear materials must be used to create this type of painted translucent effect. Additional processing steps are also required. A bead blasting or a sanding process on the surfaces of the parts followed by painting is highly recommended in order to achieve the best quality. Hand sanding is best applied to flat surfaces where bead blasting is best for complex surfaces. A wet sandpaper like 3M Wetordry is recommended for sanding MJP parts. Wet sanding is highly recommended using a progression of finer grit sandpaper. Set the sandpaper on a flat surface preferably near a sink. Apply water to the part and the sandpaper. Push the part against the paper and sand the part either in long strokes or in a circulatory motion. Move the part to un-used portions of the paper often. Rotate the part 90 degree periodically attempting to sand the entire surface uniformly.

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3M Wetordry sandpaper

 

Apply force during sanding in a way to equally distribute the pressure across the surface of the part being sanded. Wash debris off the part and sandpaper often by running cold water over them. Don’t let the debris build as it can cause surface defects and impede the normal sanding process. Start with 240 grit and sand the surface until it is uniformly finished and flat. Don’t proceed if the surface has high or low spots or curvature. If the part has printed natural curvature that you want to maintain, hold the part in your hand and sand it with a folded piece of paper that allows compliance over the surface of curvature. Periodically dry the part and look at it in reflected light to visualize areas that are not being sanded sufficiently. After the 240 grit, move to 600 grit and then to finer 1200, 1500 or 2000 grit using the same procedure with water and washing away debris often. The finer grit sanding should go relatively fast as long as the initial 240 grit achieved a flat and uniform surface. 

For complex shaped surfaces, a faster and high quality surface preparation for colored translucent coating can be achieved by using a dry glass bead blasting after the post process. Use 40 to 90 nominal diameter micron range small glass beads with a 60-80 psi pressure on the entire surface.

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Dry Glass Bead Blasting

For higher volume processing of parts, one might consider the use a water vapor blasting system. Also known as “wet abrasive”, “dustless blasting”, or “water honing” it is an abrasive blasting technique that mixes the blasting media with water. 

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Water Vapor Blasting

 

 

The addition of water buffers and lubricates the particle providing a cushion that can protect both the media and the surface from excess damage. This method also increases the effectiveness of the media by lowering media breakdown and by preventing impregnation of foreign materials into the surface.

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Dry vs. Wet blasting (water vapor blasting)

Dry and wet blasting are both commonly used to process 3D printed parts for many technologies including Selective Laser Sintering and Stereolithography parts. An industrial wet blasting machine is able to process a larger of volume of parts with less effort compared to a dry bead blasting. After sanding and/or dry or wet blasting, the part should be thoroughly rinsed and dried and is then ready to be painted. Again, these sanding and/or blasting steps are the most important steps that must be done to a sufficient degree in order to achieve good painted optical clarity.

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Transparent clear but colored parts can be created with “glass” type translucent acrylic paints  

For certain types of translucent or metallic paints, a different color effect is created depending on the base material that is used. For example, the two rows in these sets of parts were painted with the same paint, but with different base material. The left row in each set was made with Rigid white and the right row was made with Rigid Gray.

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Base material impact on color asthetic between white (M2R-WT) and gray (M2R-GRY) materials

Left set:  Translucent paints on white material (left) and gray material (right) materials

Right set:  Metallic paints on white material (left) and gray material (right) materials

 

 

MJP Opaque and Translucent Painted Part Examples

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Statue as printed (right) and hand painted (left)

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M2R-GRY professionally hand painted

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M2R-GRY statue as printed (right) and spray painted (left)

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M2R-GRY statue figurine spray painted

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M2R-CL Rigid Clear parts painted with glossy metallic spray paints

 

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M2R-GRY Rigid Gray part painted with glossy metallic spray paints