Suspension polymerization process of acrylic monomers

Details Suspension polymerization process of acrylic monomers Suspension polymerization process of acrylic monomers

1999-07-21

2001-12-25

Acquah, Samuel A. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S145000, C524S155000, C524S366000, C524S376000, C524S377000, C524S801000, C524S803000

Reexamination Certificate

active

06333379

ABSTRACT:

The present invention relates to a process for preparing antistatic acrylic polymers.
More specifically it relates to the production of acrylic (co)polymers beads having antistatic properties combined with optical properties comparable with those of the commercial acrylic copolymers, and with good mechanical and thermal properties.
It is known in the art that acrylic polymers do not show antistatic properties wherefore they easily attract dust and generally all the contaminants contained in the air. This represents a disadvantage for all the acrylic polymer applications where a particular cleanness and optical quality are required. As an example of these applications the vendor machine displays (distributing machines), dashboards, phones, etc., can be mentioned. Industrially, in order to avoid the presence of contaminants during the assembly, antistatic sprays or antistatic liquids which are mechanically distributed on the surface, are used. These systems have the inconvenience to increase the production costs, and the working times with pollution problems. Moreover the efficacy of these systems drastically decreases running the time, of the order of a few days, since they are easily removed from the surface due to any mechanical action. A further disadvantage of these systems is that the uniform distribution on the surface, also using sophisticated and expensive technologies, is not guaranteed. It is to be noted that these treatments are to be repeated during the time in order to maintain the acrylic polymer antistatic properties.
Processes to make antistatic acrylic polymers by preparing a compound in hot extruders or mixers (for instance Brabender) by addition of antistatic additives to the preformed polymer, are also known in the art. These systems have the drawback not to lead to compounds with a good additive distribution in the polymer. In order to obtain a good additive homogenization in the compound it is necessary to submit the additive to high temperatures for prolonged times. This operating way has the disadvantage to degrade the additive, to deactivate or volatilize it with consequent loss of antistatic properties. Tests carried out by the Applicant on pilot scale with extruders having about a 50 kg/h flow-rate have shown that with the known antistatic additives the acrylic polymer optical properties are worsened.
The need was felt to have available an industrial process for the production of antistatic acrylic polymers having anti-static properties combined with optical properties comparable with those of the commercial acrylic copolymers and with good mechanical and thermal properties wherein the antistatic additive is homogeneously distributed in the polymer.
It has been surprisingly and unexpectedly found by the Applicant a process to make the acrylic polymers antistatic which overcomes the disadvantage of the prior art and allows to obtain acrylic polymers with the combination of the above mentioned properties.
An object of the present invention is a process for preparing antistatic acrylic polymers wherein the acrylic monomers are polymerized in suspension, said acrylic monomers contain dissolved the antistatic additives selected from the following:
C
n
H
2n+1
CO—N(CH
2
CH
2
OH)
2
  (1)
wherein n is an intger ranging from 9 to 13, preferably n=11;
C
n′
H
2n′+1
N(CH
2
CH
2
OH)
2
  (2)
wherein n′ is an integer ranging from 8 to 14, preferably n′=12;
CH
2
(OR
1
)CH(OR
2
)CH
2
(OR
3
) or C(CH
2
OR
1
)(CH
2
OR
2
)(CH
2
OR
3
)(CH
2
OR
4
)  (3)
wherein R
1
, R
2
, R
3
, R
4
equal to or different from each other, are H or R, wherein R is a saturated or unsaturated C
12
-C
18
alkylcarboxylate, preferably saturated or monounsaturated C
18
, in class (3) monoesters are the preferred compounds; or their mixtures; the amount of total antistatic additive being in the range 0.2-15 phr (for 100 parts of monomers), preferably in the range 1-5 phr.
The product obtained in the form of beads, generally with size in the range 50-1,000 micron, is subsequently transformed into granules by extrusion with the same conventional techniques of the acrylic polymers. It has been surprisingly found that the antistatic additive does not undergo a degradation, modification or meaningful loss.
The so obtained granules can be used for the injection molding to obtain manufactured articles having antistatic properties which substantially remain unchanged during the time, combined with optical, mechanical and thermal properties, comparable with those of the starting acrylic polymers.
The suspension polymerization is well known and is a type of polymerization carried out in a system wherein the monomer is suspended under the form of little drops in a continuous phase and polymerized by using a radicalic type initiator soluble in the monomer. The continuous phase is generally water.
The ratio between the continuous phase (water) and the discontinuous phase (monomer) is generally in the range 1:1-3:1.
In the practical carrying out of this kind of process, it is necessary the use of suspension stabilizers which hinder the monomer little drops coalescence in the most advanced polymerization stages.
As suspension stabilizers, in the most common technique, hydrosoluble macromolecular compounds having an affinity towards the monomer are used. The stabilizer places itself at the interface between organic phase and aqueous phase, and forms a protective film which hinders the polymeric particle agglomeration.
At the end of the polymerization the suspending agent is removed from the polymer particle surface by washing with water.
See for example EP 457,356, herein incorporated by reference, wherein, as suspending and stabilizing agents of the aqueous suspension, polymers selected from the homopolymers of compounds having the formula
CH
2
═CR
a
—CO—A—CR
b
R
c
—CH
2
—SO
3
M  (I)
are used, wherein: R
a
═H, CH
3
; R
b
and R
c
, equal to or different, are H, C
1
-C
8
alkyls and M=alkaline, alkaline-earth metal or ammonium, A═NH, O or NCH
3
, or the copolymers of said compounds with acrylic monomers in amounts in the range 0-40% by weight.
As continuous phase instead of water the polymerization aqueous phase, totally or partially formed by the mother liquors obtained after the acrylic polymer separation, can be used, said mother liquors containing an organic phase comprising said suspending agent and other products obtained in polymerization, optionally added with an additional amount of said suspending agent so as to have a suspending medium containing at least 0.05% by weight and up to about 1% by weight of said suspending agent and at least 0.05% by weight, the maximum extent being up to about 5% by weight, of the above mentioned other products obtained in polymerization, preferably 0.1-0.5% by weight of the suspending agent and 0.1-1% by weight of the other products obtained in polymerization. This process is described in EP 683,182 in the name of the Applicant herein incorporated by reference.
As suspending agents which can be used in the suspension polymerization besides the suspending agents of formula (I), those known used in this kind of polymerization, such as polyvinylic alcohol, poly(meth)acrylic acid, etc., can be mentioned.
The acrylic polymer is separated from the mother liquors, for instance by centrifugation or filtration. The process can be carried out using the modalities known for the aqueous suspension polymerizations, that is, by operating with ratios between the aqueous phase and the acrylic monomers generally in the range 1:1-3:1, in the presence of suspending agents and of a radical polymerization initiator at temperatures at which the initiator decomposition occurs, generally in the range 50° C.-120° C. The aqueous phase is totally (100%) or partially formed, also in the range 30-50% by weight, by the mother liquors obtained by a previous polymerization provided that the above mentioned limits are observed. It is possible to recycle from 30 to 100% by weight of said mother l

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