PLASTISOLS WHICH PREVENT THE YELLOWING OF TOP COATS, PROCESS FOR THEIR PREPARATION AND THEIR USE

PLASTISOLS A PROPRIETE ANTI-JAUNISSEMENT DES COUCHES DE FINITION, PROCEDE DE PREPARATION ET UTILISATION DE CES PLASTISOLS

English Abstract

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Abstract
The invention relates to plastisols which prevent a yellowing of
top coats applied thereon, to a process for their preparation and
to their use. The plastisols based on PVC or methacryl contain, in
addition to basic adhesion promoters, aldehydes, ketones, their
derivatives, oligomers or mixtures of same.

Claims

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Patent claims
1. Plastisol characterized in that it contains only basic
adhesion promoter components and, as further additive, simple
aldehydes, ketones, their derivatives, oligomers or mixtures
of same.
2. Plastisol according to claim 1, characterized in that the
additive in the plastisol is contained in a quantity of more
than 0.001 wt-% relative to the total plastisol.
3. Plastisol according to any of claims 1 or 2, characterized in
that the content of this additive is 0.05 to 5 wt-%, particu-
larly 0.05 to 3 wt-%.
4. Plastisol according to any of claims 1 to 3, characterized in
that plastisols based on PVC or polymethacryl are involved.
5. Plastisol according to any of claims 1 to 4, characterized in
that it contains, as adhesion promoter, polyaminoamides
and/or vinyl imidazoles.
6. Plastisol according to any of claims 1 to 5, characterized in
that, as additive, simple monoaldehydes, ketones, their
derivatives, oligomers or mixtures of same are present.
7. Plastisol according to any of claims 1 to 6, characterized in
that the additive is formaldehyde, acetaldehyde, propionalde-
hyde and their derivatives or oligomers.
8. Plastisol according to any of claims 1 to 7, characterized in
that the additive is hexamethylenetetramine.

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9. Plastisol according to any of claims 1 to 8, characterized in
that the plastisol contains other usual aggregates.
10. Process for preparing plastisols according to any of claims 1
to 9, characterized in that the yellowing-inhibiting
additive, together with the other additives to be
incorporated, is mixed into the plastisol compound or the
individual additives are individually made into a paste with
the plasticizer prior to mixing with the plastisol compound
and added to the plastisol compound in this form.
11. Use of plastisols which, in addition to basic adhesion
promoters, contain aldehydes, ketones, their derivatives or
mixtures of same as additive, on steel parts or sheets primed
with electro-dip coats, which steel parts or sheets are
subsequently coated over.
12. Use according to claim 11, characterized in that the additive
in the plastisol is contained in a quantity of more than
0.001 wt-% relative to the total plastisol.
13. Use according to any of claims 11 or 12, characterized in
that the content of the additive is 0.05 to 5 wt-%,
particularly 0.05 to 3 wt-%.
14. Use according to any of claims 11 to 13, characterized in
that plastisols based on PVC or polymethacryl are involved.
15. Use according to any of claims 11 to 14, characterized in
that polyaminoamides and/or vinyl imidazoles are used as
adhesion promoter.

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16. Use according to any of claims 11 to 15, characterized in
that the additive is monoaldehydes and monoketones,
particularly formaldehyde, acetaldehyde, propionaldehyde and
their derivatives or oligomers.
17. Use according to any of claims 11 to 16, characterized in
that hexamethylenetetramine is used as additive.
18. Use according to any of claims 11 to 17, characterized in
that the plastisols contain further usual aggregates.

Description

210868~
lastisols which ~revent the Yellowina of to~ coats. ~rocess for
their Dre~aration and their use
The invention relates to plastisols which prevent yellowing of top
coats applied thereon, to a process for their preparation and their
use .
Plastisols are used in the car industry for undersealing and for
seam-closing and sealing. Depending on the application aim, further
aggregates are added to the plastisols, which are dispersions of
fine polymer particles in liquid plasticizers. Such aggregates are
flow-improvers, stabilizers, adhesion promoters, fillers and water-
absorbing substances. Adhesion promoters are added to the plasti-
8018 to produce long-life adhesion of the plastisols to steel or
galvanized, tin-plated or electro-dip coated steel sheets. As ad-
hesion promoters for PVC plastisols, basic compounds such as poly-
aminoamides (PAA) are used, for example. In contrast, as adhesion
promoters for polymethacrylic plastisols, usually basic vinyl
~midazoles are used, to which polyaminoamides are optionally added
additional adhesion promoter component. The other aqgregates are
likewise often basic compounds, e.g. calcium oxide, barium oxide
and calcium carbonate. With the final coating, the plastisols are
coated over at the same time.
Since electro-dip coats, particularly cathodic electro-dip coats
are used for pr~m~ng steel parts and sheets, it is observed that
the eoats applied to the plastisols yellow with time. Thl~ problem
partlcularly affect~ light, pastel-coloured and white coats, be-
e~u-- with the-- the di~coloratlon is more easily noticed, parti-
eularly if they are applied without an intermediate coat (filler).
llowinq is espeeially serious with white coats. Yellowing does
not in most ca~es appear ~mo~ately after stoving of the top
eo~ting, but only after some time. This is not a question of a

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yellowing of the plastisol itself, which could possibly appear
through the top-coat layer, but of a gradual discoloration of the
top coat itself.
To solve this problem, it was proposed in DE-A-38 21 926 to add as
additives to the plastisols acid cation exchangers, whose effect is
seen in that upon stoving they bind liberated amines. The addition
of acid substances however has the disadvantage tha~ they reduce or
even inhibit the effect of basic adhesion promoters. Further, acid
components react with other basic substances optionally present in
the plastisol such as calcium oxide and chalk, so that carbon di-
oxide and water form and the plastigels formed from the plastisols
become porous.
The aim of the invention is to prevent the yellowing of a top coat
which i9 applied to steel parts or metal sheets which have been
primed with an electro-dip coat and treated with plastisols, either
with or without an intermediate coat, without having to use acid
plastisol aggregates.
This aim i8 achieved with plastisols which, in addition to basic
adhesion promoters, and as further additive contain simple alde-
hydes, ketones, their derivatives, oligomers or mixtures of same.
Preferred embodiments of the invention are the sub~ect of the sub-
~idiary claims.
Partlcularly ~uitable as yellowing-inhibiting additlve are ali-
phatlc monoaldehydes ~uch aJ formaldehyde, acetaldehyde and pro-
pionaldohyde or simple aromatic aldehydes and ketones such as
ben~aldehyde, benzophenone or benzoquinone a8 well a8 their deri-
vatlve~. Re~amethylenetetramine ~urotropin or 1,3,5,7-tetra-aza-
adamantane)~ which splits off formaldehyde under the said condi-

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tions, has proved especially effective. However, al~o suitable arefor example di-, tri- or tetramers (oligomers) of the aldehydes
such as trioxymethylene (1,3,5-trioxane), paraldehyde (2,4,6-tri-
methyl-1,3,5-trioxane) or metaldehyde (a tetramer of acetalaldehyde
(C2H~O)~) -
The plastisols according to the invention already have a yellowing-
inhibiting effect from a content of approximately 0.001 % of "anti-
yellowing additive~. Preferably, the content of this additive is
0.05 to 5 %, a content of 0.1 to 3 % being especially preferred.
The yellowing-inhibiting effect becomes especially clear if, in
addition to the basic polyaminoamides usable for example as
adhesion promoter, several of the other basic aggregates are
present in the plastisol in relatively large amounts. Advanta-
geously the plastisols also contain only basic adhesion promoter
components. But even if these basic components are reduced to the
e~tent that is still ~ust necessary, no discoloration takes place
under very unfavourable circumstances (thick-layer electro-dip
coat$ng, warm, very humid atmosphere etc.) in the presence of the
yellowing-inhibiting addltive.
It is assumed that the yellowing substance is a basic compound
which could be captured with acid compounds. However, the use of
acid additive~ is to be avoided. Through the aldehyde or ketone,
~hich optionally must first be released from a derivative, the
concentration of the yellowing basic substance is presumably
lowered at least until yellowing is no longer observable.
Of cour~e, the pla~ti~ol can also contain other additives whose
if-ct~ are not ~mpaired by the anti-yellowinq additive.

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During preparation of the plastisol the yellowing-inhibiting addi-
tive is mixed in together with the other additives to be incorpo-
rated. The individual additives, however, can also be individually
made into a paste for example with the liquid plasticizer prior to
mixing to form the plastisol compound and added to the plastisol in
this form.
Embodiment~: ~lasti~ols
PVC ~lastisols
A~ A~ B. Bb
PVC homopolymer 20 20 30 30
(K value 70)
Plasticizer (DINP) 30 30 35 35
Thinner 5 5 _ _
(white spirit 180/210)
Filler (chalk) 43 44 29 30
C~O -- -- 1 1
TiO2 - - 2 2
SiO2 - - 0.5 0.5
Ba~ic lead sulphate - - O.5 0.5
Adhe~ion promoter (PAA)
Urotropin 1 - 1 -
100 100 100 100

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AcrYlate Dlastisols:
C~ Cb
Poly-MNA/BMA with 2 % vinyl imidazole 30 30
DINP 40 40
Cha~k 29.2 28.9
CaO
Urotropin 0.3
100 100
MMA = methyl methacrylate; BMA = butyl methacrylate
Pre w ration method~:
1. PVC plastisol A~ with all components directly mixed as one-pot
process.
PVC plastisol A~ without urotropin likewise.
2. PVC plastisol A~: urotropin is dispersed in plasticizer,
finely abraded on a roll and then added to the plastisol.
3. PVC plastisol B. ~in the case of Eb without urotropin)s mix
all solid additives (CaC03, CaO, TiO2 etc + urotropin) with a
little plasticizer, abrade and finally add the rest, i.e. PAA
and polymers.
4. Acrylic plastisols (C, and Cb) as 1.
During vehicle construction, after the sheets have been coated with
~n electro-dip coat and treated with plastisol, 8ay at occurring
weld ~eams, they are provided with a top coat. This coat is subse-
quently stovod.
For example, plastisol i8 applied to the sheets coated with elec-
tro-dip coat to achleve the effect according to the invention and
~ad- to qel at 140 C for 30 minute~. Then, optionally, filler

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coats are sprayed onto the sheet and onto the plastisol, ventilated
for 10 minutes and stoved at 130 oc. Subsequently the top coat is
sprayed on, dried for 10 minutes and stoved for 20 minutes at
130C.
To speed up determination of the degree of yellowin~ occurring with
sheets thus treated, test sheets were manufactured.
1. Pretreatment of the test sheets
2. Electro-dip coat coated sheets are laid on top of each other,
a distance of 1 mm between them being maintained with the aid
of interspersed spheres. The sheets are ~ecurely wrapped in
aluminium foil to maintain high condensate concentrations on
the inner surfaces of both sheets during the following 30
minute heat treatment at 180 oc. After cooling down, the
aluminium foil is removed and to better determine the effect
of the electro-dip coat a strip of 10 to 20 mm of the
electro-dip coat is removed from the centre of the sheet.
3. ~anufacture of the test sheets
The plastisol is applied as a bead, 0 to 4 mm high and 50 mm
long, to the inner side of the test sheet. Afterwards, the
plastisol is cro~slinked at the necessary temperature. The
white top coat is sprayed in a thickness of 30 to 40 ~m onto
the cooled sheet and cured under the necessary stoving
conditions (see Figure 1.).
4. Storage condltions
The test sheets are suspended in a securely closed box, whose
ba~e i~ covered wlth water (water depth 10 to 20 mm). The box
i~ ~tored at 60 C.
S. Evaluatlon
Accordlng to guallty, the flrst result~ can be obtained after
everal hours, days or a few weeks.

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The yellowing of the sheets is rated in each case with values of O
to 10, 0 ~ignifying a complete yellowing and 10 virtually no
yellowing.
Test results:
Plast~ol Prepared Tested
No. ~s per asper lea~ng Rating Appraisal
ql~iclc at room after s days
method temp.
l)A, 1 ~ 2 10
2)A~ 1 ~ 2 4
3)A, 1 ~c 6 10
4~Ab 1 ~c 6 2
S)A~ 2 ~ 2 10
6)u~, 2 s 6 10
~ 3 s 8 10
83~ 3 s 8 7
9)~, 3 s 40 10
3 s 40 2
ll)B. 1 s 6 10
lZ~, 1 s 6 3
~3)C, 4 s 6 10
~4)S 4 s 6 2
The formulation with b i8 alway~ prepared without urotropin.

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The results that can be seen from the Table clearly show that the
plastisols to which an anti-yellowing additive was added are supe-
rior to the conventional pla~tisols in terms of the yellowing phe-
nomenon. Even after relatively long weathering, no discoloration is
di~cernible.
The invention further comprises a process for preparing the plasti-
~ols according to the invention and their use on steel part~ and
~heets primed with electro-dip coat.

Representative Drawing