Compositions: coating or plastic – Coating or plastic compositions – Molds and mold coating compositions
Reexamination Certificate
1998-12-07
2001-09-25
Moore, Margaret G. (Department: 1712)
Compositions: coating or plastic
Coating or plastic compositions
Molds and mold coating compositions
C528S030000, C528S038000, C528S043000
Reexamination Certificate
active
06294007
ABSTRACT:
TECHNICAL FIELD
The subject invention pertains to organopolysiloxane mold release compositions which display enhanced paintability.
BACKGROUND ART
Mold release compositions have long been used to facilitate the release of molded polymer parts from molds. Particularly in the case of parts having complex shapes or deep sections, and more particularly in the case of polymers which display aggressive adhesion to the mold surface, production of parts without an effective mold release would not be possible.
A wide variety of mold releases exist. Early mold releases relied on natural and synthetic waxes. Often, molds would have to be hand or machine buffed to obtain maximum release. Such mold release agents are not practical for modern high speed production rates. One advantage of such mold releases, however, is that they are often paintable without wiping or cleaning, and can be readily removed as well.
Aqueous soap solutions and dispersions are sometimes used as mold releases. However, soaps are not highly effective, and cannot be used with moisture sensitive molding compositions such as polyurethane RIM unless allowed to thoroughly dry. If still moist, surface defects and local foaming may occur in polyurethane RIM.
Polyurethane RIM has been especially problematic due to its natural tendency to adhere to molds. A considerable advance in RIM technology was the introduction of internal mold releases based on zinc stearate in conjunction with fatty substances such as fatty esters and epoxidized natural oils. These mold releases are incorporated into the reactive composition prior to molding. Unfortunately, in order to provide consistent, multiple releases, such internal mold releases must be used at high levels. For parts which must be painted, these high levels of use impair paintability. Decreasing the amount of internal mold release, however, increases the difficulty of release. Thus, such systems generally employ external mold releases in conjunction with internal mold releases.
Organopolysiloxanes such as trimethylsiloxy-terminated polydimethylsiloxane fluids have proven to be effective mold release agents, and when used in conjunction with aminoalkyl and thioalkyl-functional organopolysiloxanes, as disclosed in U.S. Pat. Nos. 4,251,277 and 3,883,628 provide extraordinary release.
Such organopolysiloxane fluids can be applied neat, in solution in organic solvent, or in the form of an aqueous emulsion. For pigmented moldings such as ski boots, roller blades, and the like, such mold releases are exemplary. Unfortunately, polydimethylsiloxane fluids are notorious for destroying paintability of molded parts, even after extensive wiping and washing operations. Common paint defects include uneven coverage, sometimes to the extent of large bare areas, orange peel, runs, sags, and particularly, fish eyes. The effects of such fluids on paintability is so severe, that some manufacturing plants ban all products containing polydimethylsiloxanes, even solid silicones such as gasketing material. Suppliers of O-ring seals and other products must frequently certify that their products contain no polydimethylsiloxanes.
Efforts to retain the advantages of polydimethylsiloxanes as mold release agents while retaining paintability have been only partially successful. Modification of these siloxanes by replacing a portion of the methyl groups with relatively hydrophobic hydrocarbon groups, e.g. C
4-30
alkyl groups, phenyl groups, and in particular, with &agr;-methylphenylethyl groups, has resulted in siloxane mold releases which are sometimes paintable immediately after demolding and without further post treatment such as wiping or washing, and which rather uniformly display good paintability after such post treatment. An example of such fluids is Wacker TN available from Wacker Silicones, Adrian, Mich. Similar mold releases are disclosed by Japanese Kokai JP 09012886 A2.
Unfortunately, while exhibiting enhanced paintability, the aforementioned modified siloxanes are not nearly as efficient in their mold release properties as straight polydimethylsiloxanes that contain aminoorgano- or thiolorgano-functional organopolysiloxane. This is particularly the case where deep sections and/or aggressively adhering polymer systems are involved.
It would be desirable to provide a mold release composition which is comparable in ease of mold release with polydimethylsiloxanes that contain aminoorgano- or thiolorgano-functional organopolysiloxane(s), while being paintable as well.
DISCLOSURE OF INVENTION
The present invention pertains to mixtures of organopolysiloxanes based on hydrophobically modified polydimethylsiloxane fluids and aminoorgano- and/or mercaptoorgano-functionalized organopolysiloxanes. These compositions provide both excellent release and paintability when prepared as stable compositions as described below. Surprisingly, unstable compositions which are not suitable as paintable mold releases by themselves are rendered highly effective when dissolved in organic solvent.
BEST MODE FOR CARRYING OUT THE INVENTION
The mold release compositions of the subject invention contain, as active ingredients, an organofunctional organopolysiloxane and a hydrophobic-modified polyorganosiloxane. The compositions may be applied neat, from solution, or as a dispersion. Neat products must display stability as hereinafter defined. The compositions may also include additional organopolysiloxanes, silanes, rheology control agents, surfactants, etc., but are very preferably devoid of polydimethylsilicone fluids, including silanol terminated polydimethyl fluids such as &agr;,&ohgr;-dihydroxylpolydimethylsiloxanes; and polydimethylsiloxanes having terminal or pendant hydrolyzable alkoxy or acetoxy groups. Alkoxy groups or other groups which are not hydrolyzable or hydrolyze only slowly may be acceptable for use as hydrophobicizing groups if these groups contain an appropriate hydrophobe.
The hydrophobic-modified polyorganosiloxane may be branched or linear, and contains moieties corresponding to:
R
a
R
b
1
SiO
1/2
(I)
R
a
R
b
1
SiO
2/2
(II)
R
a
R
b
1
SiO
3/2
(III)
and
SiO
4/2
(IV)
wherein
R is lower alkyl or alkylene, optionally interrupted by ether oxygen or thloether sulfur, such as methyl, n-propyl, i-propyl, n-butyl, vinyl, methoxymethlyl, methoxyethyl, ethoxymethyl, ethoxyethyl, methoxypropyl, and 2-thiobutyl. R preferably contains 4 carbon atoms or less, more preferably 3 or less carbon atoms, and in particular, 1 or 2 carbon atoms.
R
1
is a C
4
-C
30
hydrophobic group optionally containing not more than one ether oxygen or thioether sulfur when the carbon content is less than C
10
, and in general not more than two ether oxygen or thioether sulfur atoms for C
11
-C
30
groups, in any case insufficient interspersed —O— and/or —S— to defeat the hydrophobicity of the R
1
hydrophobicizing group. The hydrophobic nature of the R
1
groups containing interspersed —O— and —S— atoms may be assessed by evaluating the paintability of molded parts prepared employing a mold release containing organofunctional polysiloxane and the candidate —O— or —S— containing hydrophobic-modified polysiloxane.
Preferred examples of R
1
are C
4-30
, preferably C
6-20
alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl, alkaryl, and aralkyl groups. Non-limiting examples are 2-ethylhexyl, n-octyl, n-decyl, n-dodecyl, n-octadecyl, lauryl, stearyl, phenyl, tolyl, benzyl, phenylethyl, norbornenyl and particularly &agr;-methylphenylethyl. Also particularly suitlable are alkylated phenyl and napthyl groups, e.g. 4-nonylphenyl, 4-nonylphenylethyl, and 4-nonyl-2-methylphenylethyl, and the like, and alkyl-substituted cycloalkyl and cycloalkenyl such as 4-ethylcyclohexyl, 4-nonylcyclohexyl, 4-methylcyclohexyl, 2-cyclohexylhexyl, and the like.
The various R and R
1
groups may be substituted or unsubstituted. Examples of suitable substituents are alkoxy, cyano, and halo, preferably cyano and chloro substituents. Trifluoromethyl and other haloalkyl groups are also suitable.
It is possible that some of the R
Brooks & Kushman P.C.
Moore Margaret G.
Wacker Silicones Corporation
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