Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-12-20
2003-08-19
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S024000, C560S302000, C525S474000, C525S451000
Reexamination Certificate
active
06608146
ABSTRACT:
The present invention relates to the use of unsaturated peroxides in cross-linking processes, such as the cross-linking of silicone rubbers and the curing of unsaturated polyester resins.
The use of peroxides for the radical cross-linking of silicone rubbers is well-known, particularly for use in hot air vulcanization systems. Typically, products like bis(2,4-dichlorobenzoyl) peroxide, bis (p-chlorobenzoyl) peroxide, 2,5-di-tert-butylperoxy hexane, tert-butyl cumyl peroxide, dicumyl peroxide, and di-tert-butyl peroxide were used. All of these products are known to result in blooming of low-molecular weight products or smell, the latter probably given off by decomposition products of the peroxide, which is highly undesired. Although a temperature treatment of the cross-linked silicone rubber may (partially) prevent blooming from occurring, because the low-molecular weight products are stripped away, such a treatment is undesired, since it is energy consuming and may lead to discolouration of the cured material.
In EP-A-0 282 130 it is disclosed to use bis(2-fluorobenzoyl) peroxide for the cross-linking of a silicone rubber in order to attain a good curing rate and to prevent decomposition products from blooming. Similarly, EP-A-0 235 537 proposes to use specific bis(4-alkylbenzoyl) peroxides for the cross-linking of silicone rubber. These bis(4-alkylbenzoyl) peroxides are said to give stable dispersions when formulated with silicone oils and not to result in discolouration of the cross-linked silicone rubber even when the dispersions have been stored for a prolonged period. However, the nature of these peroxides—they all have a dibenzoyl peroxide skeleton—inherently leads to the formation of aromatic decomposition products. Such products are undesired, since they are known to result in a bad smell of the cured product. DE-A-1 932 475 teaches to use tert-butylperoxy crotonate for the vulcanization of carbon black-filled organosiloxanes. However, the use of tert-butylperoxy crotonate was found to result in a silicone rubber with unacceptable properties, especially when cross-linking occurred at lower temperatures (below 150° C.).
For the radical curing/cross-linking of unsaturated polyester resins many peroxides are used, the selection typically being dependent on, inter alia, the composition of the formulation, processing temperatures, the desired reaction times, and residual monomer levels. For processes which are conducted at higher temperatures (>70° C.) very often di(4-tert-butylcyclohexylperoxy) peroxydicarbonate is used to get a quick gelation of the formulation. However, the product is not readily soluble in the unsaturated polyester resin and its use results in high residual styrene levels in the cured resin. Another frequently used peroxide is tert-butylperoxy benzoate. This peroxide, when used alone, leads to acceptably low residual styrene levels at curing temperatures above 110° C., but its use often results in too long gel times and it also contains the undesired benzoyl moiety, leading to benzene formation upon decomposition. A combination of di(4-tert-butylcyclohexyl) peroxydicarbonate and tert-butyl peroxybenzoate, which is known to be used, renders a system with acceptable gelation times and residual monomer levels. However, such a combination also suffers from the solubility and decomposition product problem. Many other combinations of peroxides have been proposed for use as cross-linking initiating systems. However, the use of combinations of peroxides is undesired since storage of two or more types of peroxides, typically with different storage temperature requirements, is troublesome and because handling and mixing is more time-consuming and metering a source of errors.
Therefore, there has been a continued search for alternatives and improved products for use in the field of cross-linking processes. More particularly, the industry is in need of new types of initiators that will give an effective cure of silicone rubbers and unsaturated polyester resins, comparable with the curing of conventional peroxides, but do not suffer from blooming, bad smell, solubility problems, and the like. Preferably, the alternatives can be used at conventional lower temperatures of up to 160° C. Also they are preferably used as the sole initiator, without that it is needed to combine them with other initiators.
Surprisingly, we have found that specific peroxides according to the invention can be used to fulfill this need. The specific peroxides are characterized by the formula
n=0 or 1,
R
1
, R
2
, and R
3
are independently selected from the group consisting of hydrogen, C
1
-C
20
alkyl, C
2
-C
20
alkenyl, C
2
-C
20
alkynyl, C
3
-C
20
cycloalkyl, C
3
-C
20
cycloalkenyl, C
6
-C
20
aryl, C
7
-C
20
aralkyl, and C
7
-C
20
alkaryl, which groups may include linear or branched alkyl moieties and which optionally are substituted with one or more groups selected from hydroxy, alkoxy, linear or branched polyalkyloxy, aryloxy, halogen, ester, ketone, carboxy, nitrile, and amido. Any pair of R
1
-R
2
, R
1
-R
3
, and R
2
-R
3
may be linked to form a cyclic structure. R
1
,R
2
, and R
3
may also be linked to form a polycyclic structure, and R
4
is selected from the group of radicals consisting of C
1
-C
20
alkyl, C
2
-C
20
alkenyl, C
2
-C
20
alkynyl, C
3
-C
20
cycloalkyl, C
3
-C
20
cycloalkenyl, C
6
-C
20
aryl, C
7
-C
20
aralkyl, and C
7
-C
20
alkaryl, which groups may include linear or branched alkyl moieties and which optionally are substituted with one or more groups selected from hydroxy, alkoxy, linear or branched polyalkyloxy, aryloxy, halogen, ester, ketone, carboxy, nitrile, and amido, and radicals of formulae II and III,
m=0 or 1,
R
5
is selected from C
1-20
alkylene, C
1-20
polyoxyalkylene, C
2-20
alkenylene, C
2-20
polyoxyalkenylene, C
2
-C
20
alkynylene, C
2-20
polyoxyalkynylene, C
3
-C
20
cycloalkylene, C
3
-C
20
cycloalkenylene, C
6
-C
20
arylene, C
7-20
aralkylene, and C
7-20
aralkenylene groups, which groups may include linear or branched alkyl moieties and all of which may optionally contain one or more hetero atoms, and wherein R
6
, R
7
, R
8
, and R
1′
, R
2′
, R
3′
are independently selected from the group consisting of compounds according to the definition of R
1
, R
2
, and R
3
, respectively.
Preferably, R
1
, R
2
, R
3
, R
1′
, R
2′
, R
3′
, R
6
, R
7
, and R
8
are independently selected from the group comprising hydrogen, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, pentyl, hexyl, heptyl, nonyl, and phenyl. The various R groups can be varied in such a way that a product with the desired properties is obtained, e.g. a certain melting point/range. Alternatively, mixtures of peroxides of formula I can be used that have the desired properties.
More preferably R
1
, R
2
, R
3
, R
1′
, R
2′
, R
3′
, R
6
, R
7
, and R
8
are selected such that one or more of the following moieties is formed:
H
3
C—CH═CH—CH═CH— (any isomer), and Alkyl—O—CO—CH═CH— (any isomer).
R
5
preferably is —C═C—C═C— (the residue of muconic acid) when n and m are 0, and C
2-12
alkylene or C
2-12
polyoxyalkylene, when both m and n are 1.
More preferred peroxides for use in the curing process of the present invention are:
di-2-butenoyl peroxide (all isomers)
di-2-methyl-2-butenoyl peroxide (all isomers)
di-3-methyl-2-butenoyl peroxide (all isomers)
(Z,Z′)-bis(4-butoxy-4-oxo-2-butenoyl) peroxide
di-2-butenoyl muconoyl peroxide of formula
2-butenoyl peroxy alkylcarbonates, of formula
and
di (2-butenoylperoxy) alkylenedicarbonates, such as
The peroxides of the invention can be produced in conventional ways by reacting the appropriate acid chloride(s), chloroformate, (mixed) anhydride, or the like, with sodium peroxide. How to use mixed anhydrides in the process to make the unsaturated peroxides is explained in more detail in non-prepublished PCT patent application PCT/EP00/09927.
Depending on the peroxide in question, it is possible that it can be used in
Jelenic Jernej
Meijer John
Navarro Charles Manuel
Akzo Nobel NV
Dawson Robert
Fennelly Richard P.
Peng Kim-Liang
LandOfFree
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