Satas D., Tracton A.A. (ed.). Coatings Technology Handbook

492

BLOMSTROM

both acids and bases. although they are slowly attacked by strong aqueous acids. Their

resistance

to

hydrocarbons and mineral oils is outstanding. Because

of

the residual hydro-

xyl groups

in

the polymers (Fig.

l),

they are readily cross-linked with a variety

of

widely

available crosslinking reagents that react with hydroxyl. Examples of the more common

cross-linking reagents are dialdehydes and phenolic, amino, isocyanate. and epoxy func-

tional resins. The butyral shows limited compatibility with other resins (e.g, alkyd. polyvi-

nyl

chloride, silicones. urea- and melamine-formaldehyde. cellulose acetate butyrate, and

ethyl cellulose) and excellent compatibility with nitrocellulose. epoxy. phenol-fonnalde-

hyde. isocyanate, and some rosin ester derivatives. The formal. being more polar than the

butyral. shows more limited compatibility with other resins.

It

is fully conlpatible with

most common isocyanate and epoxy resins, and shows limited compatibility with alkyd,

phenolic. melamine- and urea-formaldehyde resins. and silicones.

3.2

Physical and Chemical Properties

The physical and chemical properties of Butvar resins are shown in Table

I.

and the

mechanical, thermal, and electrical properties are given

in

Table

2.

Table

3

gives solubility

data for the Butvar resins in

a

variety

of

solvents. The physical and chemical properties

of

the Formvar resins are shown in Table

4;

the mechanical. thermal. and electrical proper-

ties are listed in Table

5.

Solubility data for the Formvar resins are given

in

Table

6.’.

Properties of Butvar dispersion BR are shown in Table

74.

The data given

in

Tables

1-7

are typical properties, not the manufacturer’s specifications. For actual product specifica-

tions, the nmwfacturer should be consulted. The polyvinyl formal grades are all chemically

identical: they differ only in molecular weight. The polyvinyl butyrals fall

into

two chemi-

cal groups, high

(17.5-21

wt

9’0)

residual polyvinyl alcohol, and low

(10.5-13

wt

96)

polyvinyl alcohol. Within each

of

these groups, molecular weight is also varied.

In

general,

as the percentage of polyvinyl alcohol increases. toughness, modulus. and adhesion

to

polar surfaces will increase. while the range of useful solvents decreases (conversely,

solvent resistance increases).

As

the percentage

of

polyvinyl alcohol decreases. the resins

become more broadly soluble, softer. and lower in glass transition temperature.

Within

a

given chemical group. increasing molecular weight results

in

a modest

increase in tensile strength and modulus, increased solution viscosity. and a modest in-

crease

in

solvent and chemical resistance. In general, even the lowest molecular weight

grades

of

these resins are high enough in molecular weight to be well within the chain

entanglement region

of

the

E‘

spectrum such that physical properties do not change drasti-

cally as molecular weight increases. Molecular weight variations can be used effectively

to control the rheology/viscosity

of

coatings formulations more than the properties

of

the

final coating.

3.3

Solution Viscosity

Solution viscosity is a function

of

chemical composition. molecular weight. and solvent

composition. Within

a

given chemical class, solution viscosity in a given solvent will

increase with molecular weight. The effect

of

solvent composition on solution viscosity

is more complex and not within the scope of this discussion. Solvent systems are often

chosen for

a

variety of reasons other than viscosity: drying rate. toxicity and other environ-

mental concerns, utility with other resins needed in a formulation. etc. Usually by judicious

experimentation. a compromise solvent system can be found, that will give a reasonable

mix of the required properties.

POLYVINYL ACETAL RESINS 493

Table

1

Typical Physical

and

Chemical Properties

of

Butvar Polyvinyl Butyral Resin

l3ut\:lr

rc\111\

,\.r S

M

Plopcrllc\

I11clllll'l"

13-72 7-1 B-73 B-70

1%

7')

H"J0

&')X

t.

I:

1'.

E

I:

E

3.4

Plasticizers

Plasticizers are often used to soften the films prepared from the polyvinyl acetals. Among

the suggested plasticizers for polyvinyl butyral are butyl benzyl phthalate, 2-ethylhexyl

diphenyl phosphate. dihexyl adipate, and

a

variety of other phosphate, phthalate. adipate.

sebacate, and ricinoleate esters. Rosin-based polyester, and blown linseed

oil

plasticizers

are

also used.

Diethyldiphenyl and dicyclohexyl phthalates. butyl benzyl phthalate and phosphate

esters including 2-ethylhexyl diphenyl phosphate polyester. chlorinated naphthalenic, and

494

BLOMSTROM

Table

2

Typical Mechanml. Thermal, and Electrical Properties

of

Bulvar Polyvinyl Butyral Resin

Properties

Bulvar resins

ASTM

method B-72 B-74 B-73 B-76 B-79 B-90 B-98

Mechanical"

Tensile strength. MPa

yield

break

Elongation.

(X-

yield

break

Modulus

of

elasticity

(apparnct). GPa

Flexural strength.

yleld. MPn

Hardness. Rockwell

M

E

Notched Izod Impact strength

(I

.25 cm

X

I

.25 cm), J/m

Thermal

("C)

Flow temperature,

Glass

temperature"

Heat distortion temperature

Heat-scaling temperature"

Dielectric constant

Electrical

50

Hz

1

kHz

I

MHz

10

MHz

Dissipatlon factor

X

IO3

50

Hz

1

kHz

1

MHz

IO

MHz

Diclectrlc strength. V/m

(3.2

mm

thlckness)

short titne

step by

step

D638-58T 47-54

D63X-58T 48-55

D638-58T

8

D638-58T 70

D638-58T 2.3-

2.4

D7Y0-59T 83-90

D785-51

115

D785-51 20

D256-56

59

D569-59 145-

155

72-78

D648-56 56-60

1

05

D 150-59T 3.2

D150-59T 3.0

D150-59T 2.8

D

150-59T 2.7

D150-59T 6.4

D150-59T 6.2

D 150-59T 27

D 150-59T

3

1

D149-59 17

D149-59

16

41-54

48-55

8

75

2.3-

2.4

83-90

I

15

20

59

135-

145

72-78

56-60

1

0s

3.2

3.0

2.8

2.1

6.4

6.3

27

31

17

16

45-52

4 1-48

8

80

2.2-

2.3

79-86

115

20

55

125-

I30

72-78

55-59

99

3.0

2.7

2.6

2.5

5.8

5.5

22

19

16

40-47

32-39

8

1

10

I

.9-

2.0

72-79

100

5

43

1

10-

I

15

62-72

50-54

93

2.7

2.6

2.5

5.0

3.9

13

15

I9

15

40-47

32-39

8

110

1.9-

2.0

72-79

100

5

43

110-

115

62-72

50-54

93

2.7

2.6

2.5

5

.0

3.9

13

15

19

15

43-50

49-46

8

100

2.1-

2.2

76-83

115

20

48

125-

130

72-78

52-56

205

3.2

3.0

2.8

2.7

6.6

5.9

22

23

18

l5

43-50

39-46

8

110

2.1-

2.2

76-83

1

10

20

37

1

05-

110

72-78

45-55

200

3.3

3.0

2.8

6.4

6.1

3-3

74

16

15

POLYVINYL ACETAL RESINS

495

Table

3

Solubility of Butvar Resins"

Butvar solutions agitated at room temperature for 24 h

5%

Solid Solution 10% Solids Solution

Solvent B-72, B-13, B-l4

B-16,

B-19, B-90, B-98

Acetic acid (glacial)

Acetonc

Butyl acetate

rt-Butyl alcohol

Butyl Cellusolve

Cyclohexanone

Diacetone alcohol

Diisobutyl ketone

N. N-Dimethylacetamide

N. N-Dirnethylformamide

Dimethyl sulfoxide

Ethyl acetate,

09%

Ethyl acetate,

85%

Ethyl alcohol,

959,

or

anhydrous

Ethylene dichloride

Ethylene glycol

Isophoronc

Isopropyl alcohol, 95%.

or

anhydrous

Isopropyl acetate

Methyl acetate

Methyl alcohol

Methyl ethyl kctonc

Methylene chloride

Mcthyl isobutyl kctonc

Naphtha (light solvent)

N-Mcthyl-2-pyrrolidonc

Propylene dichloride

Tetrnchlorcthylene

Tetrahydrofuran

Toluene

Toluene/ethyl alcohol

(95%)

(60:40 by weight)

1.

l,

1

-Trichloroethane

Xylene

S

1

I

S

PS

I

S

I

S

SW

I

PS

S

I

S

SW

PS

I

S

SW

S

I

S

SW

I

S

SW

S

I

S

SW

S

SW

S

SW

S

PS

S

PS

S

SW

PS

S

I

S

PS

S

SW

I

S

I

PS

S

PS

S

I

S

SW

S

SW

S

SW

~ ~~ ~~

~

l'

Key:

S

Completely

soluble:

PS

part~ally

soluble;

I

insoluhlc,

SW.

swells

(hazy. turbld).

Soutrr:

Ref.

3.

496

BLOMSTROM

Table

4

Typical Physical and Chemical Properties of Formvar Polyvinyl Formal Resin

Properties

Formvar resins

ASTM

Method"

Y95E

6/95E

7/95E

I

5/95E

Physical

Form

Volatiles. maximum,

'7c

Molecular weight

X

10-

'

(weight average)

Solution viscosity

15%

by wt, MPa+8

Resin viscosity

Specific gravity,

23"/23"

(2

0.002)

Burning rate, cnhin

Refractive index

(

2

0.0005)

Water absorption (24hs).

p/r

Hydroxyl content,

as

7r

polyvinyl alcohol

Acetate content,

;IS

%

polyvinyl acetate

as

Yr

polyvinyl formal, approx

Resistance

to

weak acids

strong acids

weak bases

strong bases

Organic solents

alcohols

chlorinated

aliphatic

aromatic

esters

kctones

Formal content,

Chemical"

(2)

D792-50

D635-56T

D542-50

D570-59aT

Dl

396-58

D 1396-58

DM-56T

D543-56T

D.543-56T

D543-56T

White. free-flowing powder

2.2

25-35

35-45

40-60

140-280

250-500

325-675

8-12

12-15

15-20

1.227

I

.227

1.227

2.0

2.3

I

,502

1.502

I

,502

1.2

5.0-6.5

9.5-13.0

82

E

G

P P P

E

G G G

G G

G

2.2

70-

I

50

1x00-3500

37-53

1.227

2.5

1

.so2

1.2

5.0-6.5

9.5-13.0

82

E

POLYVINYL ACETAL RESINS 497

Table

5

Typical Mechanical, Thermal. and Electrical Properties

of

Formvar Polyvinyl Formal Resin

Formvar resins

ASTM

Properties" Method 5195E 6195E 7195E

1

5195E

Mechanical

Tensile strength. MPa

yield

break

Elongation.

9

yield

break

Modulus of elasticity

(apparent). GPa

Flexural strength,

yield. MPa

Hardness, Rockwell

M

E

Notched lzod impact strength

(1.25 cm

X

1.25 cm).

Jlm

Thermal

("C)

6.9

MPa

Glass temperature

Heat distortion temperature

Heat-sealing temperature

Dielectric constant

Flow temperature.

Electrical

SO

Hz

1

kHz

I

MHz

IO

MHz

Dissipation factor

X

50

Hz

1

kHz

I

MHz

IO

MHz

Dielectric strength

short time

step by stcp

(3.2

mm thickness), Vlm

D638-58T

D790-59T

D785-5

1

D78.5-5

I

D256-56

D569-59

I2

D648-56

D 150-59T

D

I

50-59T

D 150-59T

D

1

50-59T

D 150-59T

D 149-59

59-66

52-59

7

50

2.7-3.

I

117-124

I

50

65

70

140-

1

50

103-1

13

83-87

96

3.2

3.3

3.1

3.0

8.1

IO

21

19

24

12

59-66

52-59

7

50

2.7-3.1

117-124

1

50

65

70

140-150

103-113

85-90

96

3.2

3.3

3.1

3.0

8.1

IO

21

19

13

12

59-66

52-59

7

50

2.7-3.

I

117-124

1

50

65

70

140-

1

50

103-1

13

85-90

99

3.2

3.3

3.

I

3.0

8.1

IO

21

19

13

12

59-66

52-59

7

50

2.7-3.1

117-124

1

50

65

70

160-

170

103-1

13

87-93

I07

3.4

3

.o

2.8

8.7

IO

21

18

12

13

"Converston factors:

MPo

X

145

=

psi;

GPa

X

145

X

IO'

=

psi;

Jlm

X

53.38

Ib-ft/in.

"

Glass

temperature

CT,)

was

determined

by

differentlal

scanning

calorlmeter.

'

Heat-sealing temperature

was

determined

on

a

3-5 m

dried

film

on

paper,

cast

from

a

10%'

solution

in

60:4O

ethanol.

A

dwell

time

of

1.5

seconds

at

414

kPa

(60

psi)

line

pressure

was

used

on

the

heat

sealer.

Sorrrcr:

Ref.

3.

498

BLOMSTROM

Table

6

Solubility

of

Formvar Resins"

Solvent

Formvar resins

15195E. 71958. 61958, 5I95E

Acetic acid (glacial)

Acetone

Aniline

Benzene

Butyl alcohols

Butyl acetate

Carbon disulfide

Cresylic acid

Cyclohexanone

Diacctone alcohol

Diisobutyl ketone

Dimethyl sulfoxide

N. N-Dimethylacetamide

N,

N-Dirncthylformamide

Ethyl acetate, 99%

Ethyl acetate, 85%

Ethyl nlcohol,

95%.

or anhydrous

Furfural

Hexane

Isopropyl alcohol. 95%, or anhydrous

Methyl acetate

Methyl alcohol

Methyl benzoate

Methyl butynol

Methyl Cellosolve acetate

Methyl ethyl ketone

Methyl isobutyl ketone

Methyl pentynol

N-Methyl-2-pyrrolidone

Nitropropane

Pentoxol

Propyl alcohols

Phenol

Propylene dichloride

Tetrachlorethane

Tetrahydrofuran

Toluene/cthyl alcohol (95%)

(6040

by weight)

Toluene

VMgLP Naphtha

Xylene-rz-butyl alcohol (60:40 by weight)

Xylcnc

S

1

S

I

1

S

I

S

I

l

I

S

I

S

I

1

I

S

I

S

I

S

I

"

Key:

S,

Completely

soluble;

I.

Insoluble

or

not

complctely

soluble

Source;

Ref.

3.

POLYVINYL ACETAL RESINS

499

Table

7

Properties

of

Butvar Dispcrsion BR

Property DescriptionNaluc

Form

Milk-white aqueous dispersion

of

plasticized

polyvinyl butyral

Total

solids 50.0-52%

Viscosity 500-

I500

mPa"

Particle sue

Most particles between 0.25 and

1.5

p

Particle charge

Anionic

Plasticizer content

40

parts per

100

parts

of

resin (28.6%

of

solids)

Pounds per gallon at 25°C

8.4

Grams pcr liter

1008

''

Determmed

on

n

Brookfield

vlscometer,

LVF,

no.

3

Spndle.

30

qm.

25°C.

PH

8.0-

10.5

adipate diesters are useful for polyvinyl formal. By proper choice of plasticizer type and

level, the physical-mechanical, chemical. and adhesion properties

of

these resins can be

tailored for

a

wide variety

of

applications. Fitzhugh and Crozier5 have studied the effect

of a number of plasticizers

on

the mechanical properties of polyvinyl acetal resins.

3.5 Toxicology

Butvar resins are regulated by the

U.S.

Food and Drug Administration under the Code of

Federal Regulations,

as

indirect food additives. Butvar resins have also been subjected

to

acute toxicity studies

on

laboratory animals. Subject to the appropriate regulations, they

are useful

in

a

number of packaging applications for both fatty and aqueous foods.

Both Butvar and Formvar resins have flash points

in

excess of 370°C. The lower

explosive limit

(LEL)

for Butvar dust in air is

20

g/m3. Although these materials are

considered to be nontoxic

in

ordinary everyday handling, good industrial hygienic practices

should be observed when using them.

4.0

SURFACE COATING APPLICATIONS

4.1

Polyvinyl

The inherent properties of adhesion

to

a

wide variety

of

surfaces, film toughness and

chemical/solvent resistance, and film clarity of the polyvinyl butyral resins makes them

the vehicle of choice in

a

wide variety of specialty coating applications. They adhere

tenaciously to most polar surfaces: wood, glass, metals, ceramics, pigments, etc. Their

high binding efficiency allows them

to

be used at very high pigment loadings. Ceramic

films are typically cast

in

thicknesses from fractions of

a

mil to several millimeters, using

4-5%

Butvar B-76

as

the sole binder"; most permanent coatings applications will require

considerably higher binder levels than this for adequate film strength. Polyvinyl butyral

resins have been used

as

the binder of choice in thermophotographic and photographic

coatings,' in photoconductive coatings, in electrophotographic coatings, and

as

a

coating

on optical recording disks,

all

of

which depend

on

film toughness, binder efficiency, and

optical clarity. Their toughness, chemical and heat resistance, and binding efficiency render

them useful in powder coatings and photothermographic coating applications.

500

BLOMSTROM

Table

8

Wcstern Pine Association Knot Sealer, WP578: Brush Application

Material

p/r

by weight

Butvar B-90 (Monsanto Chemical Co.)

Durite P-97 (Borden Chemical Co.)

SDA 3SA.

95%

ethanol

3.3

40.0

56.7

100.0

-

Polyvinyl butyrals are used extensively as wood coatings, where their resistance

to

natural wood oils makes them a primary choice for sealers and wash coats. An example

of an application

on

the Western Pine Association Knot Sealer number WP578 is given

in Table

8.

A well-known application of polyvinyl butyrals is

in

the manufacture of wash

primers for the priming of metal surfaces to be used

in

hostile environments (e.g., the

hulls

of

naval vessels). There are a number of formulations available, both single- and

two-package systems. Another example of a metal coating based on polyvinyl butyral is

Metal Coating

2009,

described

in

Table

9.

Other coating applications of the polyvinyl butyrals include solder masks for printed

circuit board manufacture, heat-fusible wire coatings, and zinc oxide-based photosensitive

paper coatings; they also serve as the bindedvehicle for iron oxide

in

the production of

magnetic recording tapes. They are widely used as

toughness/flexibility/adhesion

pro-

moters

in

the production

of

inks for letterpress, flexographic, and gravure printing, and

as

a component in toners for reprography.

4.2

Polyvinyl Butyral Dispersions

The dispersion

of

plasticized polyvinyl butyral

in

water, marketed by Monsanto as Butvar

Dispersion

BR.'

is widely used

as

a permanent surface size in critical textile applications

Table

9

Metal Coating 2009: Spray or Roller Application

Material

76

by weight

Diacetone alcohol 17.4

SDA-3SA.

95%

ethanol 7.1

Xylene 34.7

Mcthylon 75-

IO8

(Bakelite Thermosets, Ltd.)

S.

I

Epon 1007 (Shell Chemical Corp.)

13.0

Butvar B-90 (Monsanto Chemical Co.) 2.0

10%

Phosphoric acid (diluted with a portion

of

the given

-

2.7

solvent mixture) 100.0

Cure

cycle:

15

minute air dry

+

30 minutes at 190°F and

20

minutes at 400°F

S(JI~WC:

Ref.

3.

/l-Butanol 17.4

POLYVINYL ACETAL RESINS

501

e.g.. seat belt and parachute webbing). where the toughness of the butyral film lends

outstanding abrasion resistance to the fabric. The relatively high surfactant levels used

in

the manufacture of this dispersion reduce the inherent adhesion

of

the resin to most highly

polar surfaces such as metals and glass. This property is used to advantage

in

the prepara-

tion

of

removable coating for temporary protection of sensitive surfaces. This dispersion

is typically formulated with other dispersions/latex as extenders to reduce cost. Pigments

and plasticizers can be incorporated. as can small amounts of solvents to enhance adhesion

properties.

4.3

Polyvinyl

Formal’,8

Polyvinyl formal, available in several viscosity grades from Monsanto as Formvar, is

widely used as an oil-resistant insulating coating for magnetic wire. For this application

it

is normally cross-linked by formulating with phenolic, epoxy, or urethane resins to

enhance properties. These coatings are tough, strongly adhering, abrasion resistant. and

totally impervious

to

hydrocarbon oils and lubricants. Polyvinyl formal serves as the base

vehicle for coatings for printed circuit boards. both permanent and fugitive (e.g., solder

masking). for the surface treatment

of

glass fibers and boron filaments (abrasion resis-

tance), and

as

an antifog coating

on

glass.

It

finds application in photothermographic and

electrographic coatings. It is used as a binder

in

magnetic tape coatings. particularly for

the high performance chromium oxide coated tapes.

It

finds use as an

ink

binder and as

a lacquer to protect the surface of lithographic plates.

In

general, polyvinyl formal is higher

in

modulus and less susceptible to solvent

attack than is polyvinyl butyral. Conversely, solvent choices are more limited for the

formal. Films are somewhat yellow, reducing their utility

in

applications calling for a

colorless film.

REFERENCES

1.

2.

3.

4.

5.

6.

7.

8.

K. Toyoshima,

in

Po/yirlyl

Alcohol

C.

A.

Finch, Ed. New York: Wiley. 1973,

pp.

381-41

I.

T. P. Blomstrom, in

Blcyc/o/mfirr

of

Polyrrw

Scier~ce

trrld

D~~gir~eerir~,g.

2nd ed.,

Vol.

16.

J.

I.

Kroschwitz, Ed. New York: Wiley-Intcrscience, 1989.

EurwdFornlvor Brnchtre.

publication No 6070E, Montanto Chemical Company. Plastics and

Resins Division, 800 North Lindbergh Avenue, St. Louis, MO 63167.

Butvrrr

Dis/~er:~ior~s

ER

Drrfa

Sheet.

Monsanto Chemical Company. Plastics and Resins Division.

800 North Lindbcrgh Avenue, St. Louis,

MO

63 167.

A.

F.

Fitzhugh and R. N. Crozler,

J.

Polwl.

Sci..

K.

225 (1952);

9.

96

(1952).

K.

Hoshi,

S.

Tasaka, and

T.

Yoshimi,

Jpn.

Kokat. 62/46, 953 (1987): Taiyo Yudcn Co. Ltd.,

[

Cherrl.

ADstr..

/116(22), 18

I,

48

I

h.]

T.

Boersma.

J.

hr~tr,girrg

Techr~ol..

13(2), 75,

(

1987).

E. Lavin and

J.

A. Snelgrove, “Polyvinyl acetals,”

in

Erzc:\.c/o~pedit~

of

Cherrlicd

Tech~ology,

3rd ed.,

Vol.

23.

New

York: Wiley-lnterscicnce, 1983.

pp.

798-816.

Satas D., Tracton A.A. (ed.). Coatings Technology Handbook

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