Coloring Cast Urethane Parts

RAMPF provides a color-matching service for customers who purchase our polyurethanes.  (We do not offer this service for competitors’ products.)  However, before considering polyurethane pigmentation, there are many factors to consider.  For example, UV stability may be affected; polyurethane parts may change color after exposure to some lighting conditions or to elevated temperatures.  If it is important for the cast part to retain a specific color, painting surfaces may be the preferred option.  However, if the cast part walls must feature a consistent color throughout, eliminating the possibility of unsightly scratched on the surfaces, custom-colored polyurethanes are ideal.

Color Matching Requirements

When a customer decides that a color-matched polyurethane is required for a project, the beginning step is to notify RAMPF, providing the following information:

• The resin system being used Temperatures to which the casting will be exposed, including mold temperatures. The mass of the wall sections of the casting Appearance requirements for the cured part, i.e. opaque or translucent. A sample/swatch of the desired final part color and finish.  For example, if the part will have a matte finish, the color sample provided must also have a matte finish.  If a swatch is not available, a Pantone number is required.  (We maintain a current Pantone book for use in the process.)  NOTE:  This does not apply to clear tint matches.

Based on these details, RAMPF laboratory technicians will determine if the match is possible.  In some circumstances, for example, a fluorescent requirement is not attainable with a material that cures white in color.  Or, the colored polyurethane may exhibit a translucent appearance in thin sections when the desired appearance is opaque.  If it is determined that the color-matched results may not conform to the supplied project requirements, the customer will be notified.  RAMPF will recommend an alternate material that can be effectively colored or the customer can chose a different color.

RAMP’S Process

After a final decision is made, RAMPF will begin the matching process.  We begin by preparing colored polyurethane specimens and evaluating the cured samples under white light.  When a successful color-match is obtained, at least three samples are sent to the customer to ensure that the colored polyurethane meets all part specifications, including the desired appearance under anticipated lighting conditions.  Each sample is clearly marked with a TD number that can be used in referencing and ordering the color-matched material.

NOTE:  The customer can choose to waive the chip sample step.  However, if the customer does not examine and approve the colored specimen, RAMPF will not be responsible for dissatisfaction with the shade of the final product.  If a new match is required, the customer will be required to pay for a second match and approve the sample chips supplied by RAMPF.

RAMPF retains a duplicate of the color chips that are sent to the customer along with formulations for each specimen to ensure that the color approved for a project is duplicated with precision accuracy and quality.

When a final shade is selected, RAMPF can provide the pre-colored polyurethane to the customer for an additional 10% of the cost of the total material purchase.  Alternately, we can supply color and polyurethane components separately along with formulation guidelines for the customer to use in mixing the system in-house.

Frequently Asked Questions

Among the questions we are often asked about color-matched polyurethanes are:

1. Why is the gel time of my pre-colored polyurethane system slower now than it was when the material was originally received from RAMPF?

This issue is commonly found with pre-colored Shore A durometer hardness systems.  We recommend one the following two solutions:  incorporate a catalyst into the polyol to attain the original gel time OR rather than having the material pre-mixed, add the color immediately before use as each individual batch is prepared.

2. Why is the shade that I obtain when I mix polyurethane in the shop slightly different than the chip sample that I approved?

This color variation sometime occurs when a pigment that was purchased for a project is reused with a batch of polyurethane that has aged.  We recommend that the proper amount of material and colorant are ordered to complete an entire job because variances in base raw materials can produce slightly different shades with different batches of polyurethane.

In addition, care must be taken to ensure that colorant is fully stirred in its container before use OR the mixed, colored system is shaken to attain a uniform blend.  Colors “settle out” or separate from solution when stored for any length of time.

3. When we added color to our polyurethane, the mixed system was striated and the cured parts had “sticky”, wet areas.  What can we do?
Check the base of the colorant.  Liquid or paste colorants are created with blends of different fillers, such as carbon black, that are placed in a carrier or base.  The carrier should be compatible with the polyurethane system being used.  Many times when this problem arises, the user is adding epoxy color in a polyurethane based system.

4. What is the maximum amount of color that I can add to the system?
Color should represent no more than four percent of the total system mixture.  Higher levels of pigment can reduce the physical performance properties of the cured part.  Typically, a one to two percent load is sufficient to obtain the desired shade.

5. Should color be added to the polyurethane resin or hardener?
Always add color to the polyol portion of the polyurethane.  Different suppliers may label system components as Part A and Part B OR Resin and Hardener.  The recommended way to determine the correct “side” for adding color is to look at the MSDS and verify which component contains polyol ingredients.  When using RAMPF systems, color should be incorporated into the hardener and thoroughly mixed before adding the resin.

For further assistance with coloring urethane parts, contact RAMPF at 248.295.0223 or through e-mail at rgi-officestj@rampf-group.com.