Plastic Injection Molded Parts – Surface Finishes

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By Jeremy Losek, Aug 25th, 2022

ICOMold Standard Surface Finishes


What Are Surface Finishes?

No amount of design work will help a product if it does not look and feel finished. That is why plastic finishes can make or break a product. Plastic surface finish is a critical part of the design process. The right plastic surface finish can take a product from plain and ordinary to amazing and extraordinary. Speak with the experts at ICOMold by Fathom to find out what plastic surface finish is best for your product.

Why Does Plastic Surface Finish Matter?

The overall success of a product will always come down to design. Not just the way the product looks, but maybe more importantly, how it feels. A product may have an outstanding design but it will never make it in the marketplace if it is unpleasant to hold.

The attractiveness of the exterior, the quality appearance of the surface, and the pleasantness of the feel are important factors and can mean the difference between customers choosing your product over someone else’s.

plastic textures

Surface finish also serves a practical purpose. The right plastic surface finish can hide many of the tooling marks left behind during the injection molding process. Flow lines, weld lines, sink marks, and shadow marks will be less obvious with the right surface finish or texture. Injection molding surface finish can also help improve paint adhesion and other post-processing operations. A part with a lightly textured surface will accept and hold paint more readily than a part with a completely smooth surface.

Plastic surface finish will enhance part functionality. Textured plastic finishes will help improve grip and give the item the proper feel when held in the customer’s hands. The proper surface texture is an important part of finishing a product.

Types of Plastic Surface Finish

There are two different ways to achieve a desired plastic surface finish. Texture can be tooled directly into the mold. This is an easy way to ensure every piece has the same finish. It will also reduce cost by eliminating the need for extra post processing. The other way to achieve the desired plastic surface finish is with post processing applications. This can include sanding, bead blasting, or etching.

In-mold texture is used to achieve a uniform plastic surface finish. Custom finishes can be tooled into the mold, whether it is a custom texture or texture in only certain places. Post processing through sanding, etching, or blasting can, in some circumstances, be used on specific sites of the part. A variety of textures and finishes can be achieved on any single part. In-mold texture and post processing are often used together to achieve the desired plastic surface finish.

Custom Plastic Surface Finish

ICOMold by Fathom only uses high-quality steel molds for plastic injection molding. Custom textures can be tooled directly into the steel mold. Aluminum molds do not allow for the same amount of customization. In fact, more surface finish options are available with a steel mold than with an aluminum mold. Steel can be polished to a high degree of smoothness to create a smoother surface finish. Steel molds also offer numerous options for surface finishes, including bead blast, etching, matte finish, leather grains, geometric, and graphics.

Finish vs. Texture

The mold tooling, the material characteristics of the injected plastic, and any post-processing will determine the final texture and finish of the part. Texture refers to the pattern in the plastic itself. The finish refers to the overall look of the plastic surface. Plastic surface finishes are typically broken down into four broad categories; dull, matte, semi-gloss, and gloss.

Dull: Rough and unpolished. Very little shine. Used for internal parts. Takes paint well.

Matte: Less rough. Some shine. Also used mostly for internal parts but can be used externally if desired. Takes paint well.

Semi-Gloss: Smooth and shiny appearance. Used for external parts or internal parts that slide or need to be smooth.

Gloss: Very smooth and shiny. Can have mirror-like appearance depending on the plastic material. Used for external parts.

Injection Molding Surface Finish Classifications

There are several different organizations and companies that have their own plastic surface finish grading scales. In the United States, the two most commonly used grading scales come from the Society of Plastics Industry (SPI) Europe, the widely used grading scale comes from the Society of German Engineers or Verein Deutscher Ingenieure (VDI). ICOMold by Fathom uses the Yick Sang Standard for plastic surface finish. Yick Sang is the Chinese equivalent of Mold-Tech or VDI. Any plastic surface finish grading scale will rate the plastic finishes from very smooth and reflective to dull and rough.

The experts at ICOMold can help you determine the best plastic surface finish for your product. See the plastic surface finish chart below for our standard surface finishes. ICOMold can also accommodate custom surface finishes.

Surface Finish Guide Typical Applications
Standard No Machine Mark Tool Marks Removed Low Cosmetic
SPI-C1 600 Stone Low Polish Parts
SPI-B1 600 Grit Paper Medium Polish Parts
SPI-A2 Grade #6 Diamond High Polish Parts
SPI-A1 Grade #3 Lens or Mirror
IM-1 Light Bead Blast Need 1 Degree Draft Angle
IM-2 Medium Bead Blast Need 1.5 Degree Draft Angle
IM-3 Heavy Bead Blast Need 3 Degree Draft Angle

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