APPLICATION INFORMATION
ADDITIVES FOR SHEET MOLDING COMPOUNDS (SMC)

TS-A 10

02

SMC technology

Contents
03 Introduction

14 Processing additives

04 Advantages and examples of SMC

18 Coupling agents

06 SMC systems and production process

19	Additives with fiber wetting

08	A wide variety of different raw
materials – an extract
10 Wetting and dispersing additives
13 Anti-separation additives

properties
20 Air release
21 Additives overview

03

Introduction
Fiber reinforced composites such as SMC (Sheet Molding Compound) haveshown remarkable growth in the automotive, electrical, and constructionindustries since their introduction in 1960s. SMC parts are based on amatrix system, fillers, and fibers. By adding BYK additives, these parts areable to meet the latest requirements of the industry and a broader variety
of manufactured components (e.g. several parts for cars, trucks, and trains)
can be produced.
Through the continuous development of raw materials, fibers, andprocesses, a wide range of applications for sheet molding compounds has
been established. Using a glass-fiber-reinforced SMC results in signficant
weight savings compared to steel parts. In addition, resistance to corrosion
and chemicals is increased. The use of carbon fibers can further increase
the focus on “lightweight applications” and high mechanical strength.
Reducing the weight of components is of particular interest in, for example,
aerospace and automotive industries, where environmental aspects likeemission reduction and lower fuel consumption is of high interest.

Note
To ensure the best appearance
and full functionality, please
open in Adobe Acrobat.

For additional information
on additives and technical
topics, please contact us:
Thermosets.BYK@altana.com

04

SMC technology

Advantages and examples of SMC
The advantages of SMC parts lie in a more robust, faster, andcost-efficient process. Sheet molding compounds allow moredesign freedom, and a higher number of manufactured parts
can be produced using a wear-free production process.
Compared to steel, fiber-reinforced composites have a lower
density and therefore the weight of the final part can be
decreased. In addition to the weight advantage, composites
have a better resistance to corrosion and chemicals, and ahigher stiffness.

Amount of parts
Parts/year
100,000
10,000
1,000
100
10
1
Fiber spraying

Hand layup

RTM,
infusion

SMC/BMC
molding

BMC injection
molding

Thermoplastic
injection molding

Al/Mg/Zn
die-casting

LFT

Sheet metal
forming
G.01

05

SMC technology / Advantages and examples of SMC

Examples of SMC applications:• Automotive: trucks, cars, and othercommercial and agricultural vehicles• Mass transit: trams, trains,light railways, and monorails• Electrical & electronic: housings,
fuses, and switchgears• Building & construction: civilengineering and household fixtures• Sanitary: washrooms, bathtubs andhygienic surfaces

06

SMC technology

SMC systems and production process
To identify the different types of SMC systems, a distinction
is made between standard, low shrink (LS), and low profile(LP) formulations. The differences between these three
types can be created by variations in the composition of
the compound, resulting in different shrinkage and surface
appearances.

Standard systems with high waviness are mainly used for
low-cost applications. Low shrink (LS) systems are often
used in industrial, transportation, or sanitary applications.
For an excellent surface with almost no waviness inautomotive class A applications, low profile (LP) systems
show the best performance in regard to visual appearance.

The differences between the systems and their advantages
Formulation

Surface

Shrinkage

Pigmentation

Application

Standard

Waviness> 0.15 %Pigmentable

Low cost

LS (Low shrink)

Improved wavinessand surface appearance

0.05 – 0.15 %Pigmentable• Electrical• Sanitary• Transportation• High flame retardancy

LP (Low profile)

Excellent surface appearance,nearly no waviness< 0.05 – (– 0.20) %Not pigmentable• Automotive• Class A
T.01

07

SMC technology / SMC systems and production process

SMC production process – the four steps

1. Preparation of the SMC paste

2. SMC production

3. Maturation

4. Cutting and molding

The raw materials, including all liquidcomponents and fillers, are mixed
homogeneously to prepare the paste.

The SMC paste is applied to the SMC
line in doctor boxes that determine
the thickness of the formulation.
Fibers are added automatically on theline during this process step. The fiber
weight content is adjusted via the
speed of the SMC line.

Due to the addition of a thickening
agent, SMC maturates over time; thiscan be done at elevated temperatures.
Usually SMC has a shelf life of several
weeks to several months from thedate of production.

After maturation, the SMC can be
cut to the desired size and molded
under pressure and temperature.

Doctor box with
SMC paste

An animation of the
SMC process can befound online.

Fiber cutter

Carrier film

Doctor box with
SMC paste

Impregnation zone

Carrier film

SMC roll

G. 02

08

SMC technology

A wide variety of different
raw materials – an extract

28 %The fiber-reinforced matrix can be formulated to meet themost demanding chemical, flame-retardant, electrical, andenvironmental conditions.

Fibers• Glass fibers• Carbon fibers• Other fibers

42 %Fillers and pigment pastes:• Calcium carbonate• Aluminium trihydrate (ATH)• Pigment pastes• Hollow glass spheres

5%

Additives andthickening agents:

Typical SMC formulation
G. 03

25 %

Resins and cure system:• Unsaturated polyesters• Epoxy resins• Vinyl esters• Hybrid resins• Wetting and dispersing additives• Anti-separation additives• Processing additives• Coupling additives• Additives with fiber wetting properties• Air release additives

09

SMC technology / A wide variety of different raw materials – an extract

Additives and thickening agents
Widely used additive groups are:• Wetting and dispersing additives• Anti-separation additives• Processing additives• Coupling additives• Additives with fiber wetting properties• Air release additives
Resins and cure systems
Unsaturated polyesters have a universal
use and are low cost matrix systems.
By comparison, vinyl ester systems areoften used for improved mechanicalproperties and chemical resistance. The
newest matrix systems are epoxies, which
are often used in combination with carbon
fibers. Epoxy systems provide very goodmechanical properties and good chemical
resistance. The cure system depends on theresin that is used in the SMC formulation.
Curing agents can be e.g. peroxides with
inhibitors for unsaturated polyesters andvinyl ester resin systems.

Thickening agents are added for maturationand to improve the processability of the
SMC formulation.

FibersFillers and pigment pastes
Fillers have a significant impact on theproperties of the SMC parts. Calcium
carbonate is a low-cost filler that ensures agood surface appearance in the final part.
Formulations can also be highly filled with
ATH (aluminium trihydrate) to improve theflame retardancy in applications such astransportation. Hollow glass spheres can
reduce the density of the SMC but are
difficult to process. They can cause surface
defects after sanding of the molded part.
Common pigment pastes with carbon black,titanium dioxide or other pigments arewidely used in SMC. A good filler particle
distribution is very important as it has ahuge impact on such aspects as the surface,color, and mechanical properties of themolded part.

A variety of fibers can be used in SMC applications. The mostcommonly used are glass fibers as they provide a good costperformance ratio with a moderate density. Carbon fibers havea lower density and very good mechanical properties but are
cost intensive compared to glass fibers and can have a poorer
impregnation. Other fiber materials such as natural or aramid
fibers are less common. Natural fibers also have a low density andgood mechanical properties but can have a high moisture content.
In special applications, orientated fibers in the form of fabrics,
such as unidirectional or biaxial materials, can have a positive
impact on the mechanical properties.

Selection of additives andhow they work
You will find more information in
our multimedia brochures, which
provide interactive graphics,
fascinating animations, and videos.

10

SMC technology

Wetting and dispersing additives
The use of BYK‘s wetting and dispersing additives results
in a fine and homogeneous distribution of solid particles inliquid media and ensures the long-term stability of such
systems. The additives stabilize fillers and pigments.
Wetting and dispersing additives improve the wetting ofsolids and stabilize them in the system.

The wetting and dispersing additives provide the freedom tocreate formulations with great variety in the quantity of fillers
and pigments, coarser or finer filler particle sizes, constantimpregnation viscosity, and a good flow behavior of the pasteon the SMC line. In order to ensure optimum performance,
the additive should be added before the solids.

The wetting and dispersing process
Wetting

Dispersing

Stabilizing

without additive

with additive
G. 04

11

SMC technology / Wetting and dispersing additives

The use of wetting and dispersing additives can result ina lower viscosity of the paste. In addition, it is possible toadjust the filler load while still maintaining the same
viscosity (G.05).

the quality of the surface is reduced, or it leads to poor
mechanical properties. A lower viscosity of the compound
therefore becomes a key factor when it comes to thepossibility of using higher filler loads. No extra styrene isneeded when using wetting and dispersing additives.

Extra styrene can be added to the resin system to decrease
the viscosity of the SMC formulation (G.06). Using
more solvent for the viscosity reduction decreases theperformance of the final part. The shrinkage is increased,

Application example for wetting and dispering additives
Viscosity

Viscosity
Increasing the filler load while
maintaining the viscosity

Reduction of viscosity

Strong reduction of viscosity

Filler loadWithout additive  

Formulation including wetting and dispersing additive

G. 05

Additive amount
Formulation including additional styrene  

Formulation including wetting and dispersing additive

G. 06

12

SMC technology / Wetting and dispersing additives

Additives overview
Product

Resin system
UP

DosageVE

EP

BYK-W 903

1.0 –2.0 % b.o.f.

BYK-W 995

1.0 –2.0 % b.o.f.

BYK-W 996

1.0 –2.0 % b.o.f.

BYK-W 9010

0.5 –1.0 % b.o.f.

BYK-W 9011

0.5 –1.0 % b.o.f.

BYK-W 9012

0.5 –1.0 % b.o.f.

b.o.f. = based on filler

T.02

13

SMC technology

Anti-separation additives
Anti-separation additives improve the homogeneity of theresin system and keep the system stable in the filled state.
BYK‘s anti-separation additives compatibilize the differencein the molecular weight of the components and improvecolor homogeneity and color depth of the compound.
Without using such anti-separation additives, the welldispersed shrink control particles can reagglomerate andseparate again.
A non-homogeneous SMC will also result in nonhomogeneous molded parts. Defects such as productwarpage or non homogenous surfaces can be expected,
which may result in paint or bonding problems.

Additives overview
Product

Resin system

DosageRemarks

BYK-9076

1.0 – 2.0 phr

Solvent-free

BYK-W 972

1.0 – 2.0 phr

BYK-W 974

1.0 – 2.0 phr

DISPERBYK-170

1.0 phrOnly for UP with polystyrene

DISPERBYK-185

1.0 phrOnly for UP with polystyreneUP

phr = per hundred resin

VE

T.03

14

SMC technology

Processing additives
Processing additives from BYK are used in several plastics
applications. BYK processing additives have generally
positive influences on a wide range of processing
parameters and the properties of the final productcompared to standard internal release agents. Due tothe liquid delivery form of the additives they are easier
to incorporate into the SMC formulation.

Benefits of BYK processing additives

Releaseagent

Release
agent

Color
homogeneity

Monofunctional
standard
additive

Shrinkagedecrease

Anti-separation
properties

Gloss
increase

Multifunctional
processing
additive

Haze
reduction

Perfect surface
appearance

G. 07

15

SMC technology / Processing additives

Perfect surface appearance
Using BYK processing additives results in an
improved flow behavior, which in turn leads tosmoother surfaces. This can clearly be seen on
larger molded parts.

Without processing additive

With processing additive

16

SMC technology / Processing additives

Color homogeneity
The processing additives replace the classic
stearates that are the main cause for manyof the defects in pigmented compounds.

With zinc stearate

With processing additive

17

SMC technology / Processing additives

Additives overview

Low shrink formulations

BYK-P 9080​

4.0 – 5.0 phr

Low profile formulations

BYK-P 9085​

4.0 – 6.0 phr

Low profile formulations, only for chrome plated molds

BYK-P 9912​

1.0 – 3.0 phr

Flow ​behavior​

2.5 – 3.0 phr

Decreased shrinkage

BYK-P 9065​

Color ​homogenity​

Low shrink formulations

Water ​resistance​

3.0 – 4.0 phr

Mechanical ​properties​

BYK-P 9060​

Bonding ​properties​

Remarks

Surface appearance​

Dosagephr = per hundred resin  	

Resin system

Paintability

EffectMold ​release

Product

UP

VE

Fiber

EP

GF

CF

T.04

18

SMC technology

Coupling agents
In SMC systems, the condition of interfaces is a significant
influencing variable for the efficiency in the final application.
Interfaces are developed where solids and liquids or different
solid structures meet. A multitude of molecular and physicalforces determine how strong the bond is between thesephases.

The coupling effectNo coupling effectCoupling effect

Adhesive failure

Cohesive failure in the matrix

The objective of coupling agents is to create as many
stable additional bonds between the liquid and the solid
components to improve the mechanical properties.
Coupling agents can improve both the static and the
dynamic resilience of the component through improved
filler/ fiber-matrix bonding.

G.08

Mode of action
Additives overview
Product

Resin system
UP

G.09

VE

Fiber
EP

GF

DosageCF

BYK-C 8001

1.0 – 5.0 %b.o.l.

BYK-C 8013

3.0 – 5.0 phr

BYK-C 8014

3.0 – 5.0 phr

phr = per hundred resin   b.o.l. = based on liquid

Remarks

Also suitable for MDI/
isocyanate thickening
T.05

19

SMC technology

Additives with fiber
wetting properties

Improved fiber impregnation
Without additive

With additive

Additives with fiber wetting properties are used to optimize
the wetting process of resin systems on different fibers. An
enhanced wet-out of the fibers leads to a better quality of
the final compound. By using these additives, an improved
fiber impregnation with no dry spots and no air entrapment
can be achieved.

G.10

Additives overview
Product

Product group

EffectAir release

Resin system
Wetting of fiber

UP

VE

Fiber
EP

GF

DosageCF

BYK-9076

Wetting and dispersing additives

1.0 – 3.0 phr in UP/VE
1.0 – 3.0 % b.o.l. in EP

BYK-A 560

Air release additives

1.0 phr

BYK-P 9920

Processing additives

1.0 – 3.0 % b.o.l.

BYK-S 732

Surface additives

0.25 –1.0 phr

phr = per hundred resin   b.o.l. = based on liquid  	

Remarks

Crosslinking with EP matrix possible

T.06

20

SMC technology

Air release

Additives overview
Product

Air bubbles can develop into pinholes,
which increases porosity and dramaticallyreduces the overall performance of the final
part. BYK’s air release agents or defoamers
prevent and destroy these air bubbles andenable improved processing, a perfectsurface, and optimum product properties.

Resin system
UP

DosageVE

RemarksEP

BYK-A 525

0.5 – 1.0 phr

BYK-A 530

0.5 – 1.0 phr

BYK-A 555

0.5 – 1.0 phr

BYK-A 560

0.5 – 1.0 phr

BYK-P 9920

1.0 – 3.0 % b.o.l.

Crosslinking with EP matrix possible

phr = per hundred resin   b.o.l. = based on liquid

T.07

Defoaming and air release

Foam on the surface.
Defoamers destabilize the foam bubbles.

Air incorporation within the system.
Air release agents accelerate the migration of the bubbles to the surface.

G.11

21

SMC technology

Additives overview (1/3)

Flow behavior

Decreased shrinkage​

Color ​homogenity

Water ​resistance​

Mechanical properties​

Bonding ​properties​

Surface ​appearance​

Paintability

Mold ​release​

Wetting of filler

Wetting of fiber

Resin system

Coupling

EffectAnti-​separation​

Product group

Air release

Product

UP

VE

Fiber

EP

GF

DosageCF

BYK-A 525

Air release additives

0.5 – 1.0 phr​

BYK-A 530

Air release additives

0.5 – 1.0 phr​

BYK-A 555

Air release additives

0.5 – 1.0 phr​

BYK-A 560

Air release additives

Air release:
0.5 – 1.0 phr​​Fiber wetting:
1.0 phr​

BYK-C 8001

Coupling agents

1.0 – 5.0 % b.o.l.

BYK-C 8013

Coupling agents

3.0 – 5.0 phr​

BYK-C 8014

Coupling agents

3.0 – 5.0 phr​

phr = per hundred resin   b.o.l. = based on liquid   b.o.f. = based on filler  	

Remarks

Also suitable for MDI/
isocyanate thickening
T.08

22

SMC technology

Additives overview (2/3)

Flow behavior

Decreased shrinkage​

Color ​homogenity

Water ​resistance​

Mechanical properties​

Bonding ​properties​

Surface ​appearance​

Paintability

Mold ​release​

Wetting of filler

Wetting of fiber

Resin system

Coupling

EffectAnti-​separation​

Product group

Air release

Product

UP

VE

Fiber

EP

GF

DosageRemarksCF

BYK-P 9060

Processing additives

3.0 – 4.0 phr​Low shrink formulations​

BYK-P 9065

Processing additives

2.5 – 3.0 phr​Low shrink formulations​

BYK-P 9080

Processing additives

4.0 – 5.0 phr​

Low profile formulations

BYK-P 9085

Processing additives

4.0 – 6.0 phr​

Low profile formulations,only for chrome plated molds

BYK-P 9912

Processing additives

BYK-P 9920

Processing additives

BYK-S 732

Surface additives

phr = per hundred resin   b.o.l. = based on liquid   b.o.f. = based on filler  	

1.0 – 3.0 phr​
1.0 – 3.0 % b.o.l.

Crosslinking with EP
matrix possible

0.25 – 1.0 phr​
T.08

23

SMC technology

Additives overview (3/3)

Flow behavior

Decreased shrinkage​

Color ​homogenity

Water ​resistance​

Mechanical properties​

Bonding ​properties​

Surface ​appearance​

Paintability

Mold ​release​

Wetting of filler

Wetting of fiber

Resin system

Coupling

EffectAnti-​separation​

Product group

Air release

Product

UP

VE

Fiber

EP

GF

DosageRemarks

CF

BYK-9076

Wetting and dispersing additives

Anti-separation:​
1.0 – 2.0 phr
Fiber wetting:
1.0 – 3.0 phr in
UP/VE 1.0 – 3.0 %b.o.l. in EP​

BYK-W 903

Wetting and dispersing additives

1.0 – 2.0 % b.o.f.

BYK-W 972

Wetting and dispersing additives

1.0 – 2.0 phr​

BYK-W 974

Wetting and dispersing additives

1.0 – 2.0 phr​

BYK-W 995

Wetting and dispersing additives

1.0 – 2.0 % b.o.f.​

BYK-W 996

Wetting and dispersing additives

1.0 – 2.0 % b.o.f.​

BYK-W 9010

Wetting and dispersing additives

0.5 – 1.0 % b.o.f.​

BYK-W 9011

Wetting and dispersing additives

0.5 – 1.0 % b.o.f.​

BYK-W 9012

Wetting and dispersing additives

0.5 – 1.0 % b.o.f.​

DISPERBYK-170

Wetting and dispersing additives

1.0 phr​Only for UP with polystyrene​

DISPERBYK-185

Wetting and dispersing additives

1.0 phr​Only for UP with polystyrene​

phr = per hundred resin   b.o.l. = based on liquid   b.o.f. = based on filler  	

T.08

02/2022
TS-A 10BYK-Chemie GmbH
P.O. Box 10 02 45
46462 Wesel
GermanyTel +49 281 670-0
Fax +49 281 65735

ADD-MAX®, ADD-VANCE®, ADJUST®, ADVITROL®, ANTI-TERRA®, AQUACER®, AQUAMAT®, AQUATIX®, BENTOLITE®, BYK®, BYK®-DYNWET®,
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The information herein is based on our present knowledge and experience. The information merely describes the properties of our products but noguarantee of properties in the legal sense shall be implied. We recommend testing our products as to their suitability for your envisaged purpose
prior to use. No warranties of any kind, either express or implied, including warranties of merchantability or fitness for a particular purpose, are maderegarding any products mentioned herein and data or information set forth, or that such products, data or information may be used without infringing
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This issue replaces all previous versions.