Selection and analysis of molecular weight, raw materials and synthesis scheme of acrylic leveling agent

First,
Introduction
: the role of
leveling agent: powder coating in the melting flow usually, there are
"
liquid gas phase
"
and
"
liquid solid phase
"
two interfaces. The main molecular chain of the leveling agent can form a very thin single molecular layer on the surface of the melt, providing uniform surface pressure in the

Liquid Gas Phaseto help eliminate paint diseases such as pinholes and shrink holes; The ester base reduces the surface pressure of the melt coating in a controlled way, helping to immerse and dense the surface of the coating and the surface of the applied work pieceliquid solid phasewhile providing good wetting and paving of the substrate.
polypropylene butyl esters are one of the most commonly used low-cost materials for powder coatings
in
. Show strong surf activity, mainly because it has a more neat
"
-C-C-"
main chain has the characteristics of dredging resin, side chain is
"
butyl group
"
has pro-resin properties, such a structure allows it to freely orientation in the interface, and the liquid phase dissolves the part of the ester bond in-ion, the main chain floats in the interface to form a uniform single molecular layer, can be uniform surface stress. The polymerity
"
n"
the size of the molecular weight.
: What is the molecular weight of the liquid flow most reasonable?
According to reports from domestic and foreign experts, from the surface pressure, the softness of the main chain, the wetting of the substrate, the wetting and coating of pigment fillers, molecular fluidity and the operability of the synthesis process, the formation of coating luster, fullness, freshness and other perspectives, the conclusions generally tend to the following indicators:
Mn -
4
000 -
5
000
;Mw is 7000-10000
, the molecular weight distribution is
Mw/Mn is 1
.
5---2.
between
2, this is the ideal molecular structure indicator for polyacrylate butylate.
important point worth emphasizing: Mn is 3000---10000, and the molecular weight
Although Mw/Mn 1.5-
7.0 is also available, there are occasional problems, such as too many small and oversized molecules, pinholes, loss of light, non-interference, etc.
4000
or less molecules, because the molecules are too small and soluble too good, this will lose the leveling,
resulting in facing the light,
all small ripples;
less than 4000 and
more than 20,
20,000 liquid flow molecules, the less the better.
, synthetic materials
the molecular weight of the range once determined, the rest of the work is around this goal to find raw materials, fixed technology. The main materials are: acrylic butyl, xylene solvent, acetone
AIBN
catalyst, molecular weight regulator, in order to reduce costs, you can also add
3%-5%
Styrene copolymers are also modified with acrylic
2-
ethylhexylate, vinyl trimethyl sioxane, acrylic hydroxyethylate, acrylates or isocetones. Mainly to reduce surface stress to improve anti-jamming performance, these are beneficial innovations. Some factories in order to reduce costs directly in the

polypropylene orthobutyl esters
"
mixed with paracetam, parabens, fumarate, shunbutylene, epoxy soybean oil, etc., generally doped to about
20%
. These practices are not conducive to leveling and anti-jamming.
of solvents is varied. At the earliest stage, toluene (boiling point
110.63 degrees C)
was used, but due to toxicity and low boiling point, xylene (
138.5 to 141.5 degrees C
) was gradually adopted
. Ethyl glycol monoamyl ether (or ethylene glycol monomoethyl ether) is also a very ideal solvent, toxicity is lower than xylene, boiling point
124.6 degrees C
is also more reasonable, steaming solvent is more convenient, but easy to dissolve in water, not easy to remove water, not widely used in China, foreign use of mixture with xylene as a solvent method, is very worthy of reference. The boiling point is too low, the molecular weight of synthetic leveling agent is too large, tending to deflate, but the capacity is lost and foggy. The boiling point is too high solvent, because the steaming solvent temperature is too high, easy to make the finished product yellow oxide and the formation of large molecules, are not suitable for use. At present, the mainstream of the country is mixed xylene as a solvent, raw materials suitable, cheap, low toxicity, easy to store, easy to operate, good safety.
why the use of acetylene isodyl
AIBN
as a trigger, not a BPO
peroxide
? Two main factors are considered: First, the type and dosage of
triggers can affect the relative molecular mass and molecular structure of polymers, thus affecting the chemical and physical properties of resins. Acetronoxydyl (AIBN) and peroxybenzene (BPO) have different decomposition dynamics. AIBN chain transfer constant is small, the decomposition rate in different solvents is not much different, free-form activity is less than benzene free-form, chain transfer reaction is less, the resulting polymer has a narrower relative molecular mass distribution, with AIBN as a trigger can keep resin viscosity in a more appropriate range.
and BPO decomposition is easy to produce high-activity benzene free-forming, benzene free-forming easy to seize the monomer or polymer molecular chain of hydrogen atoms leading to branching and crosslinking, so that the relative molecular mass distribution is wider, the viscosity of the polymer significantly increased. Second, the polymerization formed by acetic nitrogen
AIBN
is (
CH
3
)
3
C-
, outdoor durability is better, and
BPO
causes polymer formation of the end base is a benzene ring, outdoor weather resistance is poor, long time will lead to the aging of the coating yellow.
generally believed that when the mass score of the trigger is greater than 4%, the mechanical properties, chemical properties, thermal stability, etc. of the polymer will be adversely affected. It has been proved that the
AIBN
dosage of 0.8%-1.2% is more appropriate and economical in the reaction of synthetic acrylates leveling agent.
4. Synthesis factors affecting molecular weight
(changes in reaction conditions mentioned in the table below, refers to fine-tuning of reaction conditions near normal production equilibrium points
reaction conditions
trend change trends
effects on the molecular weight of the final product
solvent varieties, boiling points, molecular polarity, molecular influence on the leveling agent.
high boiling point
≥
130
molecular weight tends to become smaller, the key is the temperature of the drop-plus time
(to be discussed)
boiling point low
≤
130
molecular weight increase
(to be discussed)
solvent ratio impact
solvent
/
single Body ratio
s (1.0-1.2): 1
appropriate increase solvent
molecular weight tends to be uniform, molecular distribution narrows
decreases
solvents less, the molecular multi-dispersion is wider, adverse
drop acceleration
accelerates the distribution of
molecules unevenly,
,
does not advocate too fast drop
slow down
the molecular weight tends to be more uniform,
2.5-3
hours after
drop plus temperature
113-118 degrees C
be appropriately raised
molecular weight is smaller, which is not conducive to uniformity.
temperature is too high and the temperature
.
appropriate reduction
molecular weight tends to be large
drop plus time
2.5-4.0
hours


too fast is not conducive to molecular uniformity
slow down,
yield is high
molecular weight is getting larger,
molecular weight distribution is narrowing, beneficial
auspicient nitrogen trigger dosage
0.8%-1.2% is ideal
appropriate addition
molecular weight is smaller


1%
more suitable
molecular weight regulator dosage
(
2,4-
diphenyl
-4-
methyl
-1-
ene
(α-MSD)
appropriate addition
molecules tend to be uniform,
tend to be excessive
reduction or do not use
molecular weight is getting longer, tending to be uneven
insulation time
2-3
hours
extension
is getting longer, the impact is small, but can eliminate small molecular groups
shortened
smaller, generally
should not be too short,
2-3
hours more appropriate
steaming solvent time
nitrogen agitation helps to steam quickly
extension
is getting larger, but the impact is not obvious
shortening
smaller,
advocates a short period of time, because the temperature is high yellow change
steaming solvent temperature
≤145
degrees optimal
increased temperature
getting larger,
does not recommend the use of high-temperature evaporation, can be slightly vacuum
reduce
smaller,
does not recommend more than
145
degrees steaming solvent
water content impact
(refers to the trace remaining in a monosome or solvent)
the
molecular weight becomes large or smaller,
has a
.
consumption of triggers, the amount of adsinthonate increases.
low
best not to contain water.
recommended to detect
s vacuum degree
mainly applied to the steaming solvent phase
increase
to increase,
recommended high vacuum but short time, nitrogen stirring
reduce
on the molecular weight of small impact, but affect flash point, volatile parts
nitrogen protection
nitrogen protection
color is low, good for molecular uniformity.
the use
nitrogen-free
tend to micro-yellow phase, but has little effect on molecular weight.
practice has proved that in the process of synthetic polyacrylate butylate leveling agent, there are several important points that need to be especially controlled:
1,
monomer total to solvent ratio
≈1
:
(1.0-1.2):
this ratio has a greater impact on the multidiscity of molecular weight, although the entire reaction process Is

crowding reaction, solvent is an excessive state, but with the increase in the amount of monoliths and the generation of reactants, the concentration of various components in the solvent has changed greatly, the less the proportion of the total solvent, the wider the molecular weight distribution, easy to produce some super-large molecules and super-small molecules, these on the surface tension negative effects, not conducive to the flat coating and satiety.
2,
drop acceleration: uniform, progressive drip acceleration is beneficial, chemical reactions are carried out in an instant, once the reaction conditions are reached, within one millionth of a second can be completed, drip acceleration on the molecular weight of the uniformity is very important, especially not when slow, casual. The multi-dispersion of molecular weight is greatly affected by it.
3,
monosome and solvent water content of the impact: monosomes and solvents will contain ≤5 per thousand of water, although not much, but because the solvent is recycled, water continued to accumulate, if not carefully ruled out in a timely manner, there will be a small amount of water with solvent or monosome into the reactor, after heating and xylene boiling, consumption of a large amount of adloid nitrogen
AIBN
, cost increase, more affect the molecular weight distribution, not conducive to later use.
4,
timing and rate of drip-added adestrous: The purpose of this operation is to enable small molecules or monons that are not fully reactive to continue to react, to prevent the late steaming solvent when the small molecules that are not fully reactive into the solvent, affecting the proportion of monosome concentration and molecular weight distribution of the next kettle. It is generally one-tenth of the total amount of triggers.
5,
insulation time, steaming solvent time on the molecular weight of the impact is not too large, but the temperature should not be too high, time should not be too long, low-temperature vacuum steaming solvent on the final product color is beneficial, if you expect to get better transparency of the product, the lower the temperature of the shorter the more favorable, of course, the premise is that the solvent to be fully steamed out.
6,
three-stage filtration: that is, the extraction of solvents and monosomes into the reactor and drip storage tank to filter, drop-added monosome into the kettle before filtration, finished product discharge packaging