Application guide

Resin for Sheet Moulding Compound (SMC) Production

How SMC sheet is made and how a compounder chooses between the orthophthalic, isophthalic and terephthalic SMC resins in the range.

Choose the resin by the chemistry the compound requires.

Sheet moulding compound (SMC) is made as a sheet: a resin paste with filler and chopped glass, matured until it can be handled, then cut into charges for hot pressing. This guide covers making the sheet and choosing its resin; pressing the parts is covered in DMC and SMC compression moulding. The range offers three SMC resin routes: the orthophthalic DMC/SMC Resin, the isophthalic Isophthalic SMC Resin (SPR 301 SMC) and the terephthalic Terephthalic SMC Resin (SPR 401 SMC).

What manufacturers build

SMC producers make sheet compound that they press into parts themselves or sell to moulders. The catalogue lists SMC production, hot-mould and compression-moulding processes for SPR 301 SMC, and SMC production, compression-moulded composite components and hot-mould processing for SPR 401 SMC. The orthophthalic DMC/SMC Resin’s Technical Data Sheet lists moulding compounds, electrical housings, manhole covers, automotive panels, transport components, water tanks and sanitaryware. The two newer grades are explained in What Is Isophthalic SMC Resin? and What Is Terephthalic SMC Resin?.

Why this material suits the work

The catalogue’s guidance is to choose the family by the chemistry the compound requires: orthophthalic, isophthalic or terephthalic. The orthophthalic DMC/SMC Resin is published at 600 cPs at 25 °C with a 12–18 minute gel time and 35% styrene. SPR 301 SMC is an isophthalic resin for hot-mould SMC processing, at 800–1,400 cPs at 25 °C, a 12–18 minute gel time and 31–36% styrene; it shares one published specification with SPR 301 DMC but is a separate product. SPR 401 SMC is a terephthalic resin the catalogue describes with high heat resistance, good resistance to corrosive chemicals and strong mechanical and impact properties, at 800–1,500 cPs at 25 °C, a 12–18 minute ambient QC gel time and 32–38% styrene; that chemical-resistance wording describes intended service, not a compatibility chart. The decision rules are set out in Orthophthalic vs isophthalic vs terephthalic SMC resin.

Required resin characteristics

A resin chemistry matched to what the compound requires: orthophthalic, isophthalic or terephthalic
A viscosity the paste formulation is built around (typical 800–1,400 cPs for SPR 301 SMC and 800–1,500 cPs for SPR 401 SMC at 25 °C)
Non-accelerated supply, so the compounder sets the cure package for hot moulding
Compatibility with the compounder’s thickener, filler and additive package, confirmed by trial
Published specifications a downstream moulder can be shown

Process context

In general practice the resin is mixed with filler, thickener and the additive and cure package into a paste, which is spread onto a carrier film. Chopped glass rovings fall onto the paste, a second paste-coated film closes the sandwich, and compaction rollers work the paste into the glass. The sheet is then matured until it thickens to a handleable, mouldable state, cut into charges and pressed in heated tools. The catalogue reference cure for both SPR 301 SMC and SPR 401 SMC is MEKP 1.5% with cobalt octoate 0.4%, peroxide and cobalt added separately and never mixed directly. The cure package used in a hot-press compound, maturation, glass content and press conditions are the compounder’s and moulder’s decisions, set by their own trials.

Advantages

Three chemistries in the range let a compounder match the resin to what the compound requires
Each grade has a published typical specification on its product page
Non-accelerated supply across the SMC grades leaves cure control with the compounder
SPR 401 SMC is catalogued with high heat resistance, good corrosive-chemical resistance and strong mechanical and impact properties, for compounds that call for terephthalic chemistry

Common products

Sheet moulding compound for sale to moulders
Compression-moulded composite components
Electrical housings and enclosures
Automotive and transport panels
Manhole covers and utility products

Common questions

Which SMC resin chemistry should I choose?

The one the compound requires. If the part specification names a chemistry, follow it. Where heat or corrosive chemicals are part of the service, SPR 401 SMC is the grade the catalogue describes with those properties; confirm the choice by trial on your own compound.

Are SPR 301 SMC and SPR 301 DMC the same resin?

No. The catalogue publishes one shared typical specification for the two, but they are separately manufactured products. Order the SMC grade for sheet compound.

Is SMC resin the same as an FRP sheet-grade resin?

No. SMC here means sheet moulding compound, a compression-moulding route. The sheet-grade resins are a separate route for FRP sheets and panels, and data should not be carried between them.

Do you supply ready-made SMC sheet?

We supply the resin. The compound is made by whoever formulates it; if you need finished compound rather than resin, say so when you enquire, because that is a different purchase.

Producing SMC?

Tell us the compound you make, the chemistry it requires, the parts it feeds and the quantity you expect to take. Nepal price, packaging and lead time are confirmed on enquiry.

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