Reaction Injection Molding - American Chemical Society

10 Nylon 6 RIM R. M. HEDRICK, J. D. GABBERT, and M. H. WOHL

Downloaded by UNIV OF MINNESOTA on July 28, 2013 | http://pubs.acs.org Publication Date: January 8, 1985 | doi: 10.1021/bk-1985-0270.ch010

Monsanto Company, St. Louis, MO 63166 The successful utilization of Reaction Injection Molding (RIM) to fabricate complex polyurethane shapes in a single step from relatively low viscosity streams has led to a search for other chemical systems which can be fabricated by the RIM process. The rapid polymerization of molten caprolactam by anionic catalysis has been utilized to develop attractive nylon RIM systems. The incorporation of a rubber segment in the polymer chain allows the fabrication of high impact or even elastomeric nylon parts. The combination of a rubber phase with the high melting (215°C) crystalline nylon phase provides useful properties at low temperatures as well as at elevated temperatures. Equipment is now commercially-available for nylon RIM and while process conditions are different from those required for urethane RIM, cycle times are competitive. No postcure is required. The

success of

search which

for

urethane

other

can yield

Lactams,

reaction

chemistry products

with

with

injection suitable

molding

useful properties

especially caprolactam,

(RIM)

has l e d to

characteristics

for

and good

are potentially

a

RIM

economics.

interesting

candi-

dates. Caprolactam Molten five

minutes

merization brium

is

caprolactam with

is

amount

commercially-available at

low exotherm

essentially of

(approximately

a reasonable p r i c e .

c a n be p o l y m e r i z e d by a n i o n i c to

complete i n

monomer r e m a i n s

catalysis

produce a s o l i d that

time,

part. although

dependent upon the

two p e r c e n t monomer a t

160°C)·

in

The

one to poly-

an

equili-

temperature

No p o s t c u r e

is

necessary. The nylon

product

6,

melting

at

permitted extreme products for

of

the anionic

a crystalline 215°C.

of

tough

on the other

RIM p r o d u c t s ,

excellent

The development o f

the range

through

polymerization

polymer with properties

to

nylon

extreme. block

In

caprolactam

block

products

addition

copolymers has

to

to

copolymers o f f e r

is

properties,

be extended from nylon

engineering-type

these

of

mechanical

soft

improved some

6 on one

elastomeric properties

process

0097-6156/85/0270-0135$07.75/0 © 1985 American Chemical Society

In Reaction Injection Molding; Kresta, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

136

REACTION INJECTION M O L D I N G

a d v a n t a g e s o v e r n y l o n 6 RIM. These advantages i n c l u d e lower mold temperatures, reduced shrinkage i n the mold and perhaps f a s t e r m o l d ing c y c l e s . When c o m p a r e d t o u r e t h a n e R I M s y s t e m s , t h e s e p r o d u c t s o f f a r an improved balance of s t i f f n e s s and toughness, better chemic a l and temperature r e s i s t a n c e , lower t o x i c i t y and simpler p r o c e s s ing requirements.

Anionic Joyce

Polymerization

and R i t t e r

polymerization


small

amount

(1)

of

of

of

in

Caprolactam

1941

obtained a patent

caprolactam.

sodium or

They

other

alkali

sodium caprolactam and the

rapid,

caprolactam above

form molten

merization amide

to

is

the

the

rapid

are

clearly

product

of

exothermic

The tion

of

in

polymer most

controlling

the to

it

the

for of

reducing

early

the

melt

the

for

polymerization

of

polymer.

the

The

form

poly-

low v i s c o s i t y

a reaction

cyclic

polyamide. a molten

polymer,

polyamide product

injection

molecular weight desired

levels

of

always

a n d was

molding

high

the

the

light

of

later

did ring-opening

the of

nylon not

Figure

1)

In

understood use

in

the

fiber

or

polymer produced

plastic

the

or

Surprisingly,

6 p r e p a r e d by the of

and prepara-

c o n c e n t r a t e d on

polymerization.

knowledge,

polymerization

giving

rise

to

the

1955,

Monsanto

a n i o n i c method sodium

capro-

of

the shown

in

Italian

patent

580069 w h i c h was

H.

K.

(3)

DuPont

Hall

of

a n i s m w h i c h was tested

by

the

polymerization In

not

The

shown

an a c y l a m i n o end group the

absence

Polymerization

stops

amount w h i c h

polymerization occur

which

controls

of

route

with

the

thermal

the

number

1958.

casting

in

the

Figure

results

initiated

initiation chains

The at

in

initiator,

to

very

occurs,

the

of

is

reduced

the

with

to

1.

reaction. an

equili-

condensation

high molecular Below

initiator

caproFigure

termination

and thus

five

chain

no

The

rapid

polymerization

initiated

polymerization.

started

Very

four

amino end group is

mech-

acyllactam

160°C.

temperature. in

(2)

m e c h a n i s m was

resulted

monomer l e v e l of

published

1958.

2 produces a nylon

there

the

28,

acyllactam

impurities,

the

postulated

proposed an i d e n t i c a l

the

which

of

July

acyllactam

a function

this

issued

and without

when

is

r e s e a r c h on

adding a pre-formed

mechanism f o r

lactam polymerization In

the

(see chains

well.

first

December,

not

A two-stage mechanism

sodium caprolactam of

end group

was

nylon

that chain

combinations of

p r o p o s e d m e c h a n i s m was

procedure of

absence

each

anionic polymerization

in

and a s o l i d

that

exploratory

subsequently

containing

the

occur.

This

published

simple

caprolactam

minutes.

1.

of

lactams.

for

Figure

but

mechanism as

as

in

can be p o s t u l a t e d

and one a c y l l a c t a m

Company b e g a n

thermally-initiated

it

occur,

possibility

catalyzed polymerization

cannot

not its

decade

a function

a condensation polymerization

brium

next

the

after

formed had one amino end group

base

was for

concentration.

In only

very

was

application, i.e.,

during

molecular weight

lactam

system

process

work

the

at

to

t e c h n o l o g y was

polymerization

anionic

was

did

of

a

caprolactam

and h i g h m o l e c u l a r weight

qualities

mechanism f o r

interest

moldings,

to

nylon

base c a t a l y z e d

r e a c t i o n of

system.

since

by

in

high molecular weight

this

polymerization desirable

metal

an i s o m e r i z a t i o n

a high viscosity,

Although

(RIM)

200°C to

reaction

on the

d e s c r i b e d the

weight

temperatures

concentration

molecular


weight.

HEDRICK ET A L .

Nylon 6 RIM

0^ INITIATION

+ lia

137

0 θ

N

{^^

if

/

-

N(CH ) — c—!f

Ν

9

CATALYST REGENERATION

Ό

+ Na


PROPAGRATION a

/ \

HN(CH Κ - Ν

e/ )

Τι

+ Na Ν

?

©

c

^ v

» H *(CH )-C-N 9

}

9

Na AMIDE ANION

IMIDE POLYMER

AMIDE ANION

IMIDE

N(CH )-Î-f H - 5 9

NYLON 6 Figure 1. Proposed mechanism f o r the p o l y m e r i z a t i o n of c a p r o l a c t a m .

Œ

2 ^ ^ ^ ^ INITIATOR

a

y^^J CATALYST

thermally

initiated

Na( K^ ^-(CH )-C0

anionic

Ο

Caprolactam

F i g u r e 2. Acyllactam i n i t i a t e d caprolactam.

anionic

polymerization


of

R E A C T I O N INJECTION M O L D I N G

138 A branching product

of

reaction higher

centration. amount ing

addition

equivalent

reaction

molecular range. tne

The

the

and l i n e a r

of

is

a c h i e v e d by

shown i n

neither

a p p r e c i a b l e amine or

patents

were

issued

amine

to

R

Figure

(5)

0

0

II

II

the

The

where

C—N—C

to

3.

react The

anionic

in

the

distribution

a

weight

with acyllactams,

and the

weight product

A number

detail

the

has

of

structural

polymerization

important

an

branch

of

molecular

formulation

most

give

broad molecular

Company w h i c h

for

to

aniline

eliminate

c a r b o x y l end g r o u p s .

Monsanto

use.

chains

such as to

a very

known

stoichiometric

initiators

is

are

of

p r e d i c t e d by a c y l l a c t a m c o n

w i t h a normal

amines

is

initiator

combination than

a primary

polymer

primary

probable reaction

l a c t a m and t h e i r

the

acyllactam appears

control

for

in

weight

can be prepared over

Since

requirements


to

weights

(4)

results

molecular

structure

of

capro

for

the

R"

R'

I R" cannot

be a hydrogen.

a n d R"

and have the

The

most

structure

commonly-used i n i t i a t o r s

of

an a c y l l a c t a m

combine

R

1

0

ο II

II

R c—* ι Examples

of

this

type

are

a c e t y l c a p r o l a c t a m and a d i p o y l b i s c a p r o -

lactam. A convenient reacting

an

method f o r

isocyanate with

R Ν C 0

Use

of

+ HN

diisocyanate

growing

at

both

which

weight

usually

crosslinked

are

most

sodium

latter

•

allows

product.

in

R N—C—Ν

produces an i n i t i a t o r

ends,

lightly

an i n i t i a t o r

situ

is

>

molecule capable

faster

polymerization

With d i i n i t i a t o r s

due to

a branching

commonly-used c a t a l y s t s

for

the

of

rate

c a n b e made b y r e a c t i n g

for

product

a

is

reaction.

caprolactam

polymerization

c a p r o l a c t a m and c a p r o l a c t a m magnesium b r o m i d e .

catalyst

by

c a p r o l a c t a m monomer.

J

given molecular The

forming the

a Grignard

The

reagent

with

caprolactam. The

anionic

polymerization

depth by W i c h t e r l e of

Macromolecular Chemistry

Nylon The

6 Reactive

use

of

directly the

production

viscosity, was

is

anionic

low

Corporation. the

of

lactams

Prague.

has

been explored

co-workers

at

the

in

great

Institute

(6-8)

Molding

initiated

Polymer

feed

in

polymerization

f r o m c a p r o l a c t a m was

the

of

and Sebenda and t h e i r

large

initial

and the

pieces rate

heat

commercialized in

The

of

of

to

c o m m e r c i a l i z e d In t e c h n o l o g y was since

the

increase

United

monomer

viscosity

polymerization is

Germany by B a y e r .

the

particularly

molten of

produce cast

low.

of

shapes States

useful is

of

the

A similar

(9)


by for

low

catalyzed system


HEDRICK ET AL.

Nylon 6 RIM

F i g u r e 3 . Use of a n i l i n e to c o n t r o l m o l e c u l a r weight distribution.

and


REACTION INJECTION MOLDING

140 The

adaptation of

casting

and r e a c t i o n

undoubtedly here

proceeded at

reports

the

work w i t h which In culate

1962,

low

cost,

forcement

and y i e l d s

to


silicates, to

dry.

Moisture

disrupts

the

properties silanes,

which

are

severely

such as

s t i l l

nylon

plasticized

destroyed In

I960's

by m o i s t u r e ,

products ment

are

of

which

the into

taining

dispensed

into

mold. the

the

abrasive

than is

to

best

sale

faces, Methods

Since

rein-

high

loading

with

In

order For

the nylon

are

polymer

system

is

or

very

and bonds

completely

and the

mechanical

Functional

provides While

an

the

effective

nylon

matrix

is

not

maintained.

and commercialized for

RIM

as

molding.

this

several

well The

as

properties

was

before

a

product of

the

develop-

d e s i g n e d and

fresh

charge of

c a p r o l a c t a m was

diluting

built

the

slurry

con-

automatically

any remaining

d i d not

was

typical

catalyzed

proceed

until

the

added. in

the

were

the

an

viscosity

small

if

percent

weight.

very or

abrasive

extrusion

c a p r o l a c t a m w e r e pumped the

injection

clay

is

mineral

much

molding.

particles

to

a product,

of

pigmented c h a i r

less

reinforced

e s p e c i a l l y impact in

a c i c u l a r shaped W o l l a s t o n i t e

stiffness

by

Wollastonite

is

molding

Calcined

properties, mineral

60

(Si02) ,

silica

injection

preferred

combination of

to

Although low

and i s

30

quartz

in

the

range of ground

be p o s t - p r o c e s s e d by

The

is

completely

readily

degraded.

polymerization

clay.

in

to it

silica

bond between phases

injection,

is

fibrous

reinforcement,

range of

excessive abrasion.

silica

greater

impact

sometimes

the

strength,

range of

particles with

a

one

consacrifice

strength.

Hundreds for

used

minerals

microns.

tributed of

that

obtained with very two

I.

The

vessel,

slurries

without

to

the

It

than

a polar

as

injection

Vykan.

be t o l e r a t e d

and c a s t

was

is

tailored

holding

and c a l c i n e d

could not

The

6

are

and m o l t e n

were

polymer

for

After

Minerals

resin,

the

mineral

c h a r g e was

useful

obtainable

b a t c h - c a t a l y z e d , degassed and i n j e c t e d

catalyst most

6

Table

sufficiently

(CaSi03> and

the

initiator,

material

The

in

of

i m p i n g e m e n t m i x - h e a d , e q u i p m e n t was

automatically

charge

next

trademark

given

stiffness

surface.

developed

nylon

the

partimineral

coupling agents

long

properties

mineral-reinforced

the

or

triethoxysilane

formulations

under

as

through

mineral-reinforced sold

silane

and s i l i c a t e

Monsanto

is

of

coupling agents.

and i r r e v e r s i b l y

and r e i n f o r c e d

the

that

use

uncoupled reinforcements

3-aminopropyl

bond between the is

to

the

caprolactam.

nylon

mineral

permeates

adhesion

in

particulate

functional

silicate

since

has

presented

particulate

i n c r e a s e of

with

A polyamide such as

a polar

Company

pumpable s l u r r i e s

mineral

organic

progress

i m p a c t much l e s s

with

to

familiar.

such as molten

the

lactams

d o e s h a v e some a d v a n t a g e s .

multiaxial readily

The

Although

the

it

properties

treat

the

effective.

provide

of

commercial products

by Monsanto

polymers.

monomers

reinforced

necessary

well

the

Monsanto

initiated

of

does not

low-viscosity obtain

at

of

companies.

a r e most

reinforcement,

reduces

molding

several

authors

w o r k was

fibrous


activities the

reinforcement

reinforcement with

the

injection

by

of

this

sink-marks were

thousands method. or

other

Since

all

surface

developed which

surfaces defects

shells were

could not

compensated for

were

produced

appearance be

sur-

tolerated.

polymerization



load

hrs

3

psi

16-19

92-100

10

0.25

0.1-0.8

120

hrs

M-Scale

Hardness

Strain

24

12-14

0.2-018

D-785-65

D-695

Monsanto ll->45

8->45

ft-lbs

%

Monsanto 4-65

4-30

ft-lbs

psi

R-Scale

Rockwell

@ 1%

Compressive

Stress

122°F,

4000

psi,

122°F,

2000 p s i ,

under

Ball

Falling

Deformation

Dart

Falling

Impact

24

D-790 3.3-8

5

10

8-17

Modulus

Flexural

psi

D-790

3

10

9-15

5

10 18-25

Strength

Flexural

Modulus

D-638

Tensile

5-8

D-638

8-17

6.90-8.80

D-638

Procedure

ASTM

6-12

8.50-14.7

8.70^-14.8

H20

3- 7 psi

psi

-1.3%

Fail

%

3

as

Fabricated

Dry,

2- 3

10

Units

M e c h a n i c a l P r o p e r t i e s of Vykan A ( M i n e r a l -- R e i n f o r c e d N y l o n 6 )

Yield

Tensile

Fail

Elongation

Strength

Yield

Tensile

Property

Table I .



142 shrinkage desks, hundred

for

The process

cycle

three

to

been p u b l i s h e d ,

large

time

for

minutes.

the

of headboards,

produced for

as

individual

four the

production

terminated of

in

thirty-five

a

twelve-

pounds

were

parts.

mineral-reinforced While

technology is

of

1971.

details

of

contained in

properties

by

injection

Block

then

o b t a i n a b l e from

through

reaction

cast mineral-reinforced

R e s e a r c h was

caprolactam

Nylon

of

as

consisting

was

nylon

6

this

casting

system

a number

have

of

(10)

The range

Furniture

Castings

a variety

total was

patents.


defects.

and luggage racks

room m o t e l .

produced

not

without

and chests

nylon

nylon

directed at

the

6 products

expanding


b l o c k copolymers and t h e i r

was

the of

fabrication

molding.

Copolymers

Chemistry Nylon

b l o c k copolymers were

polymerization polymers.

(11)

diisocyanates groups

which

l a c t a m was the

of

basis

The

with polyether

used for

to

of

initiation

the

prepolymers,

initiated

prepared from

glycols,

c a t a l y z e the

from the

of

anionic

polyurethane the

reaction

This

nylon

block copolymers are

capro

research.

from The

is

(12)

stoichiometric

and caprolactam using

described previously.

end

Sodium

copolymer system

6 RIM

formed

preof

contained isocyanate

reaction.

areas

polymeric polyols w h i c h was

synthesized

presence of

caprolactam polymerization.

some c u r r e n t

NYRIM n y l o n mixtures

previously

caprolactam in

poly

acyllactam

reactions

are

as

follows:

A)

Prepolymer

Formation Χ H0~\/0H

+ X +

1

POLYOL

I—C

I NH ( C H ) — C — 0 · ν ν / * 0 — C ( C H ) 2

5

2

POLYETHER POLYESTERAMIDE In which also of

normally functions

acts to is

the

inert

reaction,

as

so The

presence of The

copolymerization

that

multifunctional

for

the

resulting

reaction

occurs

reaction.

or

in

prepolymer

slowly

catalyst

may b e p r e p a r e d i n

solvents,

acyllactam

caprolactam polymerization,

polymeric polyol moeities.

an a l k a l i n e

prepolymer

organic

PREPOLYMER the

initiator

combine the used

by a c y l l a c t a m . in

seconds. of

prepolymer

acyllactam

ated but

the

is

See R e a c t i o n

with heat

excess

termin (13),

completed within

mass

c a p r o l a c t a m as

An

is

or part

in of

the

presence

the

B.


total


8.

8 L

Reaction

B.

2

5

— a

Formation.

[

0

- o-\c

POLYETHER

—0 Jb

11

c—C

->

5

PREPOLYMER

POLYAMIDE

1

NH(CH )

2

0

0

2

5

(CH ) — N H ^ C

*

—C(CH ) —NH—C—R—C-j-NF

POLYETHER POLYESTERAMIDE

2

(CH ) —U—0.

L CLJfl —R—C

Copolymer

5

C(CH ) —NH

È-—ij—C—R—C--NH

8

R

^

0


2

5

C4h N H ( C H ) ( !

CAPROLACTAM

H] Y

0 II

CATALYST

144 In

REACTION INJECTION MOLDING the

anionic

acyllactam the

polymerization

initiates

At

the

same t i m e ,

as

weak

t a m may i n s e r t The

result the

sented

more

equally groups

at

these

would

of

divided so

if

that

ting

structure

used

a method

in

the

block copolymer, from

the

throughout

the

of

w

See

nylon normal

the

ends

of

The

=

n

selective weight

determine

mer.

These parameters

final

resin

copolymer blocks

determine

product.

are

polyol

The

determined in

exercised

the

over

of

the

addition

molecular

final

weight Thus,

weight

alkaline

catalyst

systems

suitable

for

the

reactions.

The

preferred

prepared

reaction

NYRIM c o p o l y m e r s , catalyst

make up

the

Most

a

of

catalyst

Grignard

two

reactive

such as

that

of

nylon

and by the

nylon

percentage

good c o n t r o l of

can be

copolymers.

caprolactam polymeriza-

and

copolymerization

c a p r o l a c t a m magnesium with

is

the block

caprolactam.

used—reactive

bromide, With

prepolymer

polyether

or

hydrocarbon

to

give

polyester

useful

so

individual

weight

for

in

nylon

as

of

sites

the

polyol

final

such

types

transfer

of

the

to

prepoly-

reaction

the

multiple

polyol

resulting

to

streams.

polyols

yield

of

residues.

caprolactam

in

The

blocks

in

or

to

Kurz

dissolved

glycols

polymers.

is

of

alterna-

(14)

are

may b e u s e d

reaction

used

reagent

These

diols

polyols

of

very

two-package system

concentrate.

of

is

condensa-

the

nylon

ratio

of

of

polyol

amount

prepolymer

only

pre-

same for

Kurz.

and p r o p e r t i e s

The

both

the

weight

molecular

polymer.

E.

weight

to

the

curve

resulting

and the

molecular

is

and a c y l l a c t a m

elucidation

degradation

by p o l y o l

molecular

are

J.

polyol

occurred

copolymerization all

molecular

chain.

147.

for

blocks

the

back-

instead

structure

ester

The

are

by

page

by

of

in

The

fully

the

the

A(BA)

prepolymer

2/1).

d e s c r i b e d more

molecular

prepolymer

that polycaprolac-

prepolymer

distribution

b l o c k copolymer and a n a l y z e d

bisacyllactam

the

end groups.

active

the

M /M

the

so

caprolactam polymerization

resulting

(i.e.,

along

sites

b l o c k copolymer or

schematic.

within

is

linkages

transfer

caprolactam available

between

weight

polymers

and

or

points

occur

clearly

tion

tion

ester

an a l t e r n a t i n g

amount

molecular

nylon

the

initiation

acyllactam initiating

The


is

ABA w h i c h

from

of

form nylon

prepolymer.

bone a c t

of

to

caprolactam polymerization

resins, ester

block copolymers.

polyols

but

may b e u s e d

these

linkages

in

will

not

in

give

polyester

act

a random copolymer

is

obtained.

block copolymers

are

determined

Other

the block co-

as

multiple

to

the

Properties The

properties

greatest which

extent

play

weight,

an

by

in

s e e n when

range

Table the

polyol

are

type

II.

polyol

of The

nylon

to

polyol

polyamide.

type,

and r e a c t a n t

Other

polyol

ratios

factors

molecular

as

well

content glycol

of

is

of

rubber

varied

phase

from

2000-molecular

with

decreased hardness, modulus

b l o c k copolymer p r o p e r t i e s

effect

changes o c c u r r i n g

are

flexural

of

as

the

conditions.

polypropylene

expected phase

role

coupler-activator

A typical

data,

ratio

important

polymerization trated

the

to

60%.

weight

increased polyether

tensile

accompanied by

0

strength,

increases

in

is

illus-

concentration

tear

tensile

For

was soft

is

these

used.

The

block

strength

and

elongation,


10.

recovery

and Impact

strength

is

an e f f e c t of

small

which i s amounts for

low l e v e l s

combination In better in

that


decrease

in

tensile

higher

of

as well

polyol,

and high

strength

higher

6 is

impact

end of

through

polyols

strength.

contribute

modulus,

the physical

to a

particularly property

2000 a r e r e q u i r e d ,

improvements as p o l y o l m o l e c u l a r weight Multifunctional

notch

strength.

polyols

at least

in

impact

obtained which has a

and f l e x u r a l

modulus of

Incorporation

as multiaxial

molecular weight

impact

strength.

i n a dramatic decrease

polyol a modified nylon

Molecular weights

level.

erties

Izod

o f h i g h modulus

the lower

the impact

polyol result

increased

of

balance

further

The f i v e - f o l d

reflected in

of

general,

spectrum.

strength.

accompanied by a n e i g h t e e n - f o l d i n c r e a s e i n e l o n g a t i o n —

sensitivity At

145

Nylon 6 RIM

HEDRICK ET A L .

also

is

with

increased

contribute

beyond

to better

prop-

crosslinking.

Table I I .

Effect

o f P o l y o l Content on NBC

Property Dry

as Molded

Percent

Polyol

0

10

20

40

84

83

78

62

37

10,800

7,800

6,400

5 ,300

2,100

% Elongation

30

35

285

490

530

% Recovery

30

30

30

60

80

1, 3 0 0

800

410

220,000

3 1, 0 0 0

Shore

D Hardness

Tensile

Strength

PSI

Tear

60

Strength

Flexural

PLI

1,800

Modulus

PSI

390,000

Notched

280,000

Izod

Impact Ft The

Lbs./In. effects

balance

for

graphically strength ether

0.6 of

polyether

a different in

Figure

content

is

This

impact

Izod

occurs

linear

in

ether,

the impact rate

14% a n d h i g h e r impact

N.B.

strength/stiffness

are

illustrated

and Izod

polyether

N.B.

impact

content.

modulus e x h i b i t s

u p t o 30% p o l y e t h e r .

range.

But in

starting

This

copolymers as well

A t t h e same also

occurring at a

modulus.

Thus,

a much b e t t e r

phenomenon o c c u r s

as other

poly-

a t a b o u t 14% p o l y -

impact

flexural

copolymers have

and s t i f f n e s s .

As

an expected

The i n c r e a s e i s

an increase i n

the decrease

polyether,the

strength

of

increases.

c u r v e shows

nylon block

modulus

flexural

linearly

strength

than

copolymer

Flexural

the low polyether

much h i g h e r of

4.

increased,

time,

5.7

content on the impact polyether

a r e shown a s a f u n c t i o n

decrease.

polyol

1.6

at

balance

with

other

rubber-reinforced

resins.


146


Structure While

and Morphology

the polyether

and g r e a t e r continue in

to provide

high

phase r e s u l t s

elongation,

crystallinity

polymer melting

points

scanning calorimeter block

(polyether)

a n d a t 45 t o 5 0 ° C

temperatures

216°C

(nylon The

are

6 T ) m

function

of

content

copolymers is

0 to

deflection

in

These

on

-70°C

transitions

occur

content.

Melt-

copolymer to

similar

to,

the t

g

for

pendulum d a t a

o f NBCs

ranging

representing

in

polyether

9 a n d 18%

but not identical

polyether

with nylon

The copolymer c u r v e s

polyether.

changes i n

This

the nylon

(14)

(G*) as a

deflection t

region

g

6,

show

a

becomes

a t 45

to

are not apparent. F r o m t h e same d a t a ,

function

of

temperature

ether

were

nylon

t g a r e more

from

deleted for

37 t o

while which

This

tends

amount

Another ether,

clarity.

clearly

due to n y l o n

In

Figure

is

is

content

regions

becomes

by the nylon

region

which

tration,

nylon

becomes

phase.

elastic

give

for

increased

to

In In

stiffen

of

temperature

to

the

the range

decrease transition.

in

the

polyether the nylon

the polyether

copoly-

0 t o 20% p o l y -

the mid-range of

phase with

to

more

crystallinity

and also rise

and a t higher

the dispersed

acting as crosslinks

is

poly-

p e a k s become more p r o n o u n c e d , these

content.

the continuous

as a

9 a n d 56%

the changes i n morphology o c c u r r i n g

changes i n polyether

nylon

plotted for

6 the damping peaks

As p o l y e t h e r

6 in

amorphous m a t e r i a l

(G") i s

The curves

to broaden the t r a n s i t i o n of

a r e b e c o m i n g more

Heat

6.

shown.

polymers lites

modulus

Figure

may b e e x p l a i n e d i n p a r t

reason

mer w i t h

the loss in

66%, t h e - 6 0 ° C p o l y e t h e r

the change

diffuse. the

a t -60 to

polyether

torsion

a series

The c u r v e s

much more p r o n o u n c e d w h i l e 50°C

resulting

pendulum s t u d i e s

complex modulus

the dashed c u r v e .

at -60°C,

phase

to heat s a g .

65% p o l y e t h e r

from

5 a n d show for

66%.

are quite

shown

curves

Figure

temperature

from

block

strength

blocks

20% p o l y e t h e r .

dynamic modulus

reproduced i n

which

for

6).

range of

from 1 9 5 ° f o r

impact

nylon

resistance

transitions

(nylon

the entire

range

the hard

and t o r s i o n

c o p o l y m e r s show

a l l copolymers f o r

ing

for

and high

linear

nylon

in higher

the high melting

Differential

in


rubber

tensile

37%, t h e concencrystal-

rubber

phase.

Resistance

Table

III

shows

copolymers modulus range polyol

with

ratio

the effect polyol

at

even though is

contents

- 2 9 ° / 7 0 ° C shows t h e modulus

i n c r e a s e d from

in

on f l e x u r a l

the mid-range

only

slight

modulus

20-40%.

change

shows a n e i g h t e e n - f o l d

over

for

The l o w the p o l y o l

decrease

20-40%.


as

HEDRICK ET AL.

Nylon 6 RIM

Λ Τ

POLYETHER

^χ_χ_χ_χ_χ_χ_0-0-0-0-Χ-Χ-Χ-Χ-Χ-Χ-0-0-0-0-0-Χ-Χ-Χ-Χ-Χ-Χ-0-0-0-0-Χ-Χ-Χ-Χ-Χ-Χ'^ NYLON BLOCK COPOLYMER SEGMENT

400 ^/^IZOD 300


i-12 Δ

g

200

V \

FLEXURAL MODULUS

as g

w 100

L

4

1-2 10

20

30

50

40

COPOLYMER % POLYOL

F i g u r e 4 . Modulus-impact balance f o r n y l o n b l o c k (dry-as-molded).

copolymer

9.0

8.0

-100

-50

0

50

100

150

200

Temp. (°C)

Figure 5 .

Dynamic modulus curves f o r n y l o n b l o c k

(complex modulus

^^^ CfliàfCll Society Library 1155 1«h 8t N. w. W a shington. 0. C 20036 In Reaction Injection Molding; Kresta, J.; v e r

copolymer

a

ACS Symposium Series; American Chemical Society: Washington, DC, 1985.



Figure

6.

Loss

modulus

versus

temperature

for

nylon

block

copolymer.


10.

Nylon 6 RIM

HEDRICK ET AL.

Table

III.

149

NBC T e m p e r a t u r e - M o d u l u s Polyol

20 Flexural


Content

35

30

40~

Modulus

@ -20°C

296,000

80,000

54,000

28,000

23°C

197,000

42,000

22,000

11,000

70°C

71,000

21,000

17,000

9,000

Modulus

Ratio

-29 /70°C

4 2

Q

The and

contribution

soft-block to

C as

Even

163

at

quite

to

crystalline

sag e x h i b i t e d

these

very

low

low

heat

which

painting

steel

heat

values end of

are the

sag values

withstand

an a b i l i t y line

the

3^2 high melting

are

also

by NBC.

to

automotive

could

relate

to

assembly

eliminate

the

o p e r a t i o n and permit

IV.

Flexural PSI

.125" Moisture

6

blocks

the

the

heat

modulus.

sag values

were

the

ability

line

paint

requirement

use

of

the

of

fabricated

bake-oven for

cycles—

a separate

same p a i n t s

used

off for

NBC H e a t

Sag/Flexural

Modulus

Modulus

Heat

Sag

163°C

@ 230C

-

0.1

115,000

.06

60,100

0.15

33,500

0.15

24,700

0.2

11,000

0.34

thick

in.

specimen 4"

overhang

-

60

minutes

Effect

effect

of

documented.

moisture (15)

copolymers to

requirements

applications nylon

shows

flexural

spectrum,

169,000

block

IV

the

in

components. Table

The

nylon

reflected

Table

related modulus

3Λ

low. The

parts

the

of

hard-phase separation

sag

at

3^8

1

resistance

of

Response

block

for

on n y l o n

Because of

6 resins

this,

the

is

well-known

susceptibility

moisture

absorption

was

exterior

automotive

body p a n e l s and

requiring

dimensional

copolymer formulations

expected.

and of

wellnylon

Evaluation other

stability

indicated that

would not

meet

early

specifications


150


with in

regard

to

not

sufficient The

in

use

moisture

tion not

creased fiber meet

total

moisture

the

rate give

absorption but

in

of

the

stability

of

of

relative

8.

the

end-use,

60%

the

Figure

9.

of

The

glass

by r e i n f o r c e m e n t

values

appear

applications Molding

parts

our in

resin

purposes,

which

they

two

e.g.,

reaction more

In

ment part, ments

can be

resin

fully

for is

decreased

well. to

The

nylon

6.

The

be s u f f i c i e n t

for

copolymers

30%

improvement

while of the

in

Polyol

C gave

milled

glass

immersion

reinforced reduced

to

glass for

is

humidity

resin

exterior

dimensional

reflects

a maximum

fiber.

fiber

growth of

These automotive

stability.

transfer

the

as

impart

much h i g h e r required

injection

static

set

up

to

low-

d e f i n e d as

are

or

carried

molding,

molding

streams

parts

produce

casting.

are

and i n j e c t e d

RIM

to

can be

rotational is

a

combined and mixed

into

form a p l a s t i c

mold with

molding,

mold and the

impregnate to

are

injection

molding,

device

systems

prepolymers

reaction

rapidly

the

or

a c l o s e d mold

part.

To

foamed to

compensate

some

dynamic mixers

compensate for

degree.

a r e employed

polymerization

additional material.

Thus,

a

produced.

percentages of

In

to

significant

only

relative

in

parameters

reactive

casting,

by p a c k i n g

into

so

to

pumping systems

part

placed

as

three

of

milled

requiring

shrinkage,

low-pressure

shrinkage solid

1/16"

transfer

or

polymerize

polymerization the

as

fiber.

nylon-based polymer

an impingement mixing

In

C not

Improvement

f r o m monomers

processes;

casting,

For

of

directly

several

pressure

where

glass

almost

values

within

glass

insufficient

identical

on the

Expansion

areas

polymerization

finished

process

be w e l l other

is

gave a f u r t h e r

illustrated

25%

with

Β

in

Processes

Anionic by

to or

with

of

A and

stability,

Polyol

with

added

range of

was

absorp

greatly

C)

C gave

C is

fiber.

but

of

NBC f o r m u l a t i o n

The

with Polyol

of

types

Polyols

Reinforcement

conditions

Polyol

improvement.

three

absorption

humidity

the

original

effect

for

copolymer appears to

Figure

of

large

of

effect

orientation

to

rate

in

over

The

dimensional

C c o p o l y m e r was

Under

7

improvement

Use

The

of

6.

copolymer.

well. in

decrease

stability.

absorption,

(Curve

this

The

reinforcement

applications.

expansion.

Polyol

of

degree of

critical

a b s o r b e d , but

reinforcement

and

the

polyol variation

rate

as

fiber

NBC g a v e u n e x p e c t e d i n c r e a s e

Figure

20%

improvement

for

moisture

in

when r e i n f o r c e d

nearly

a

of

further

below,

third

typical

in

nylon

i n c r e a s e d the

expansion

with

of

applications,

shown

0.3%

blocks

that was

dimensional

data

over

absorption.

glass

dimensional

level

absorption most

required

rubber

expansion

of

Polyol

amount

for

polyol

specifications A

the

use

shown

will

decrease

out

give

moisture

the

is

illustrated


of

from

absorption

blocks.

only

the

to

on l i n e a r

polyol

as

e x p a n s i o n due to

expansion r e s u l t i n g

for

c l o s e d mold which

the

possible

RIM

casting, rotates

or

the

long

short

mat the

fiber to

fiber

is

injected use

so of

reinforce

the

molded

reinforce

processes.

reactant

around

or

is

permits

and toughness

with

casting

the

stream

This

fiber

maximum s t i f f n e s s is

reinforcing

liquid

reinforcement.

heavy continuous

than

rotational

the

a preformed

reacting

one o r

mixture

is

more axes

introduced so

as

to


into

produce

HEDRICK ET A L .

Nylon 6 RIM


3.0

5

10

15

20

25

36

Days Water Immersion 72 F F i g u r e 7. copolymer.

Effect

of water immersion on e x p a n s i o n

of n y l o n




3.0L

% Relative Figure 8. Effect b l o c k copolymer.

Humidity

of r e l a t i v e h u m i d i t y on e x p a n s i o n of n y l o n


HEDRICK ET AL.

Nylon 6 RIM


2.0l

S

10

Days

IS

20

23

Immersion

F i g u r e 9 . E f f e c t of water immersion on r e i n f o r c e d f o r c e d n y l o n b l o c k copolymer ( P o l y o l C ) .

and

unrein-


154


a uniform l a y e r of polymer on the hollow part is produced. The

last

Reaction

important

First,

processes are not

Injection

Nylon-based molding

two

RIM

from urethane

RIM

systems

the

RIM

equipment and

found most


points

at

heated

tanks,

pumps,

accomplished

or

water

by

urethane

two

not,

streams.

are are of

operating

chemically is

used, that

typically

required

pressure

lines

Third, those

of

versus for very are

gel

5

to

30

temperatures stability.

At

pot

the

life

of

tures

from

typically Thus, the

of

reactants

This of

part

to

of

longer

time

caprolactam,

urethanes.

nylon on is

are

hot

they

contain

of

This

allows

temperatures,

of

45

to

is

the

Second, 90°F

the

lower

order part

of

rate

5-10

surface

are normally temperatures,

seconds for

also 3-4

than

reasons until

reactants the

mold

parts

difference

mold

of

about

is

the

temperature

a result

of

the

low

at

gel

and For

and tempera

times

are

thickness.

reauired

for

by c o n d u c t i v e h e a t i n g . very

Kcai/mole versus exotherm

run

1/8-inch time

is

minutes.

quality

these

is

low-

seconds,

than

molds

only

of

systems.

several

At

to

one-tenth use

monomer

polymerization

on the

generation,

time

is

120

RIM

gel

pressures

hydraulic

nylon

rise

energy

for

and 3 2 5 ° F .

60

streams

a r e much l o n g e r

in

to

normal

since both

There are

30

and

their

required

horsepower

attained.

viscosities

they

This

soluble

the

l a c t a m monomer,

range.

systems

rubber

typical

Carbide,

over

be

spots.

energy c o n s e r v a t i o n and product

A typical reaction

NYRIM 2000 n y l o n

preferred

mixxng n e a d

i.iie o r d e r

temperatures or

the

psig

urethanes.

polymer

mixed stream

the to

of

from Union

Thus,

oil

resistance

are

compared w i t h

in

this

hot

temperature-controlled

Additionally,

and lower

times

tool,

in

practice,

circulating

a comparison of

systems.

typically

these

them have

whether

xmpingemenL

materials

equipment must

methods

solutions

are

making

and l a c k

2700

150-300

the

urethane

reasons

the

30

the

and

these

equipment w i t h two

for

in

the

b e t w e e n 250

10 RIM

low

optimum p h y s i c a l p r o p e r t y release

several

systems

commercial

viscosity

comparable.

held at for

in

are

high molecular weights typically

in

polyol

RIM,

copolymer from Monsanto,

seconds for

First,

In

streams,

and so

for

urethanes,

this.

control

system,

and v a l v e s

rhe

the

of

low

RIM

hardware

first

systems

low

RIM

liquid

equipment w i t h

temperatures.

quite

quite

nylon

Thf

See F i g u r e

n y l o n - b a s e d RIM

mixing

the

reactive

block

nylon the

urethane

and molds.

are very

a t y p i c a l urethane of

Thus,

tracing

uniformity

the

or

in

by e n c l o s i n g the

NYFTM 2 0 0 0 n y l o n in

lines

electrically

Second,

ranges

common u s e

hands and t a p e s . their

for

Unlike

1 5 8 ° F and 3 2 0 ° F r e s p e c t i v e l y ,

by j a c k e t i n g

systems,

modifiers of

in of

useful

lactam.

room t e m p e r a t u r e .

is

design of

conditions.

monomers

solids

A

urethanes.

Impact

isocyanate materials

of

with

cavity,

differ

have m e l t i n g

cause

the

systems

the

or

practiced

of

Molding

ε-caprolactam and l a u r y l

ovens

surface

aspects which

process

heating

inner

is

low

18-20 shown

heat

of

kcal/mole in

Figure

reaction for 11

block copolymer.


for

H E D R I C K ET A L .

Nylon 6 RIM


ιο,οοα

Figure

10.

Viscosity

of

urethane

a n d NYRIM

raw m a t e r i a l

streams




Figure 1 1 . In-mold reactant made from NYRIM 2 0 0 0 .

temperature d u r i n g c u r e of a p a r t


10.

The in

net

nylon

less

effect

RIM.

part

jection although

is

This as

rates

method of

as

high

foaming.

as

In

tion

systems.

density the also

of

optimum

Blowing

frequently

1.0-1.4

added

to

systems

the

and urethane reactant

in

external

used. lb

In-

parts,

the

systems

streams

tanks

density

the

in

the

typically

b y means o f

microcellular

Freon

is

are

p i p e l i n e mixers

of

such as

control

are

be used and produces

common o n 3 - 4

measure and c o n t r o l

agents,

to

l b s / s e c o n d can be u s e d .

control

to

rates

pumping u n i t s

lb/second are

by f r o t h i n g

gauges are used

tanks.

injection

smaller

between n y l o n

by use

For

lower of

urethanes,

nucleated with nitrogen or

use

0.1

difference

speed a g i t a t o r s

permit

when f i b e r - r e i n f o r c e d

low

as

A fourth

to

permits

anisotropy

rates

157

Nylon 6 RIM

H E D R I C K ET AL.

high-

recircula-

foams, froth

nuclear

density

in

chloro-fluorocarbons, and shrinkage

values

are

of


urethanes. Nylon

RIM

gen content blanket

used

soluble

in

The

nylon

upon

systems

is to

the

inert

foam i s

throttling

the

and

material

produced

as

hold

The

fact

no

is

comes

out

RIM

have a l s o

in

Chemical

been

is

quite

required.

the

reactants

and

the

streams

nitro-

is

orifices

the

simpler.

of

of

nitrogen

Nitrogen

soluble

nylon

the

frothing

much l e s s

that

control

of

tanks.

impingement mixer

nitrogen

but

pressure

by gas which

the

nucleating agents

Accurate target ties,

in

only

to

blend of

achieve

during

polymer

are

than

liquids,

blowing

successfully

rate,

not

that

ratio

either

kinetics

Internal

not

agents

used

in

nylon

require

a p p l i c a t i o n of

urethane

the

urethane

build-up tating

in use

every

reactant

head.

mold,

urethane release internal

third

Newer shots

spray

to to

high

as

The

All

Nylon

affect

show

the

determined the

stream

systems

proper-

of

contains

will

well.

of

physical

second

5% d o n o t

for

a mold r e l e a s e streams

or

These

agent,

to

the

tanks

reactions

even with

internal

well

contains

only

can be

formu-

any e f f e c t

developed

urethanes.

on

the

because

mold r e l e a s e

quality

tool. that smooth

Monsanto's is

RIM

a

react

to

with

problems

of

necessiSome

newer

introduce mold r e l e a s e at systems nylon

paintable.

show

they

have caused

permit

b e made b e t w e e n a p p l i c a t i o n s o f the

a soap or

mold s u r f a c e s .

to

nylon

urethanes

cannot be added

spray-on mold r e l e a s e s ,

scrub

for

Most

a wax,

Many m o l d r e l e a s e s

component stream

mold r e l e a s e

a high

stream which

technology is

shot.

chemicals.

a

the

being developed

p e r i o d i c shutdowns

systems

where

is

the

part

as

0.5%

essentially

being o f f - r a t i o

as

systems

within

properties.

mold r e l e a s e

after

in

are

components.

Thus,

changes

while

the

materials

made

to

finished

nylon

RIM

nylon

isocyanate ratio.

physical properties.

or

it

desired

modifier

systems

silicone,

the

with

be h e l d

to

solution.

lated

important

typically

sensitive

materials

reaction so

of

and rubber

catalyst

less

must

being very

properties

initiator

is

ratios

order

these

the

metering

stream

physical

mix

the

systems.

Urethane

by

nitrogen-blown

makes a c c u r a t e m e t e r i n g

solid

RIM

the

through

monomer.

froths,

also

c a p r o l a c t a m monomer a n d s o

polymerization, in

are

p r o v i d e d by s e t t i n g

surface

In is

RIM

from

external system

certain required

0

to

the

50

mold

contains

an

applications on a p a r t ,


a

158


thermosetting the

reverse

tial

release

part

to

face

quality

result

systems

from

the

tool

of

in

lies

surface, of

then

in

tool.

the

extent

of

reacts are

The

state

with

fully of

the

allowing tool

the

urethane breaks

tool

after

each

comes

out

between urethane are

quite

used for

shots,

urethane

similar surface

the

RIM.

results off

shot. need

means t h a t in

be u s e d . RIM

mold.

Many

mold to

generate

the

part.

reaction before the in

Parts

atmospheric

part.

Nylon for

cycle

spite

of

Nylon

RIM

which

is

be manually flash

the

is

much

part.

This

mold r e l e a s e a p p l i c a t i o n times

the

Commercial

flash

and must

completely with

and the

comparable,

the

sur-

A

may a l s o

the

of

reverse

and n y l o n

isocyanate in

the

from

surface

mold.

which

and t y p i c a l l y

operation,

lower

enough i n

produces differen-

maximizing

replication.

a 5°F

complete the

tougher

in

show

demolding and h a n d l i n g

removed

difference

the

the

mold r e l e a s e s

far

that

provides

surface,

between urethane

residual

cure of

surface

This

cure obtained in

for

cured in

weak a n d b r i t t l e ,

tool

surface

Silicone

difference

green-strength

parts

fairly

the major

oven post-cured to

moisture

time

the part.

the

tool

are polymerized just

sufficient

parts

the

adhere to

and f i d e l i t y

last

urethanes


u s e d on

can be o b t a i n e d by m a i n t a i n i n g

The

RIM

is

unseen surface

preferentially

temperature

are

mold r e l e a s e

or

for

nylon

and

urethane

shorter closed-mold

cycles

of

2.5

minutes

are

common. Equipment As

Requirements

a result

machines

of

the

system

can be simpler

The

nylon machines, of

insulated,

but

tion

and have l e s s

rates The

tionally, lids

they

tanks

anchor-type valve

differences

and lower

for

the

need

if

should

any

should

be h e a t e d to

which might

plug

pressure and l i d

ethylene-propylene should

be both

The This

avoids

should

clean

out.

to

and

and l i n e s of

where

flexible

are

jacketed,

it

preferred

side

Should

streams, the

oil

nylon

then than

RIM

ers

of

RIM

for

nylon

of

the

it

is

visa

reaction

be set

occur more

versa. speed

of

of

to

avoid

occur.

Tank

l a c t a m monomer

Teflon the

resin

or

monomer.

to

allow

material when

Tanks

that

the

jackets

oil

pumps

that

to

jacket

the

stainless

Where

these

the

to

oil

will

lines the pressures

leak

into

affect

Many m a n u f a c t u r -

valves

steel.

Teflon

reactant

adversely

and p h y s i c a l p r o p e r t i e s .

m a c h i n e s b e made o f

with

keep

and All

machine

lined

and the

reactants

tanks,

lines

be coupled

contamination w i l l all

the

are used.

simplify

required.

likely Oil

to

hoses

are

between the

recirculation. in

they

lines

equipment recommend t h a t RIM

up

the

materials

recirculating

leakage

type

speed

Addi-

pressurization/degassing

be s e l f - d r a i n i n g

preferred

low.

slow

be u s e d .

flush

be of

surfaced flexible

are

suction

or

injec-

vacuum-capable.

be d e s i g n e d to

is

valves

control

inside

to

reinforcement

a v o i d a t t a c k by

reinforcing

Smooth

are

the

RIM

control.

be a g i t a t e d w i t h

be of

should

should

temperature

settling

lines

rubber

pressure

tanks

improves

relief

have lower

ratio

avoid sublimation

seals

nylon

heated and

units,

systems of

outlined,

urethane machines.

be w e l l

accurate

settling

also

Agitator

for

reinforced

bottom v a l v e s

than

pressure

nylon machines should

should

ports.

previously cost

c o u r s e , must

can be lower

agitators

plugging

in

and

Mild

fittings steel


and

10.

HEDRICK ET AL.

galvanized

Nylon 6 RIM

steel

tanks

have been

copper

and brass

lines

and f i t t i n g s

of

the

material

mately

painted.

was

Both rotary for

nylon

forced

not

an i s s u e

Tank

b e made with

the

however,

parts

metering

piston

to

be

volumes

of

nitrogen

is

gas

were

units

units

have

color

be

u l t i -

to

are

are

as

the

suitable

best

for

rein-

the

in

the

tank

Molds

for

nylon

materials

plating

resistance

of

epoxy

a few

is

parts

30

psig

mix

incorporation

tanks

adjusted

of

of

all

less

storage

than

are used,

also

before

tends

and

5 ppm

is

depending upon

of

used

failing.

large

dissolved pressure.

improve At

that

variety

and n i c k e l .

to

materials.

demonstrated

the

from a wide

kirksite

been widely

fiberglass

carry

nitrogen

c a n b e made

softer

when

to

degassing,

aluminum,

been

required

by c o n t r o l

systems

steel,

has

is

Following

made o f

system

to

the

RIM

has

molds

tooling

0

inerting

content

its mix.

including

and n i c k e l

gas

produced.

used as

into

dry

from

Vacuum d e g a s s i n g o f reinforcement

for

a moisture

pressures

foam d e n s i t y

than

used,

a p p l i c a t i o n s where

because

Displacement lance

Nitrogen

suitable.

of

in

systems.

tanks.

the

successfully

pump a n d p i s t o n - t y p e

RIM.

P r o v i s i o n must hold


159

this

will

Development work

Chrome

the

scratch

writing,

produce

no

more

continues

in

this

area. In used

most

for

lines

should

done a t means or

respects,

urethanes. be

Reaction Injection Molding - American Chemical Society

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