Patent Application
20110139959
This invention generally relates to mold sealer compositions that are effective for molding thermoplastic parts.
It is a common problem in the thermoplastic industry for molders to find that the efficiency of the semi-permanent release agent is sacrificed due to the use of high quality smooth mold surfaces, or highly filled thermoplastic compounds. In particular, the release agent cannot bond well onto the mold surfaces, particularly when chrome or nickel materials are employed as mold surfaces. The release agents are removed from the molds too easily, and as a result they do not perform very well over multiple releases from molds. This lack of adhesion can be demonstrated by rubbing the cured release agent off the mold surface.
It is also a common problem that the release number may be decreased due to the rubber flow or injection forces. In particular, the thermoplastic industry requires that mold coatings be highly durable, permitting a number of release cycles. However, most of the traditional release agents only last a few cycles before reapplication of release agent is needed. This problem increases the down time, the cost, and labor involved in reapplying the release agents.
Moreover, in addition to the need for mold sealers which have adequate release numbers, there is also a need for more effective from a performance standpoint as well as cost effective mold sealers.
The present invention is directed to mold sealer compositions, as well as methods for preparing such compositions and methods for applying such compositions to form mold sealer coatings and assemblies.
In one aspect of the invention there is provided mold sealer compositions which contain silanes having both amino and alkoxy functional groups, and having the formula:
In some embodiments of the invention, the mold sealer compositions may further contain a carrier and a cross-linking agent. Optionally, the molder sealer compositions of the present invention may contain additional additives, such as, e.g., slip agents (such as a functional or non-functional siloxanes), emulsifiers, pH modifiers, dyes, catalysts, biocides, cure modifying agents, fillers, viscosity modifying agents and combinations thereof.
The mold sealer compositions of the present invention may be curable by various mechanisms such as heat, moisture and/or ambient condensation. Desirably, the compositions are heat curable. When applied as a coating, the mold sealer compositions cure to a finish having a high durability permitting a number of releases (e.g., at least 3 releases, desirably at least 4 releases, and more desirably at least 5 releases), without transfer of the mold release composition to a part. The mold sealer compositions of the present invention are stable, e.g., having no or significantly reduced precipitation, separation, or performance deterioration for a substantial period, e.g., desirably for at least about six months, more desirably for about one year.
In another aspect of the invention there is provided a sealed mold assembly including a mold for forming a part having at least one surface and a coating on the at least one surface comprising the mold sealer composition of the present invention.
In another aspect of the invention there is provided a method for producing a durable seal on a mold, comprising the steps of:
(a) providing a mold for forming a part having at least one surface;
(b) applying a mold sealer composition onto said the at least one surface of the mold forming part, wherein the mold sealer composition includes:
(c) exposing said mold sealer composition to curing conditions for a time sufficient to effectuate at least partial cure, thereby forming a durable seal on the mold.
The present invention is directed to mold sealer compositions that are durable, cost effective, and permit multiple releases when applied as a coating. The present invention is also directed to sealed mold assemblies prepared with the mold sealer compositions of the present invention. Methods for preparing such compositions are also disclosed.
The mold sealer compositions of the present invention include a curable component, desirably, a heat curable component. The term “cure” or “curing,” as used herein, refers to a change in state, condition, and/or structure in a material that is usually, but not necessarily, induced by at least one variable, such as time, temperature, radiation, presence and quantity in such material of a curing catalyst or accelerator, or the like. The terms “cure” or “curing” cover partial as well as complete curing.
The curable component contains a silane that has both amino and alkoxy functional groups, a carrier, and a cross-linking agent. The silane has the general formula:
Non-limiting examples of useful silanes of the present invention include n-(2-aminoethyl)-3-aminoproplymethyldimethoxysilane, 3-aminopropyltriethoxysilane, methacryloxypropyltirmethoxysilane, methyltriethoxysilane, aminobutyltriethoxysilane, bis(3-trimethoxysilylpropyl)amine, aminopropylsilanetriol, 4-aminobutyltriethoxysilane, 3-aminopropylmethyldimethoxysilanc, n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropylsilanetriol, as well as oligomers of the above preformed or formed in situ from above monomers, as well as combinations thereof. These silanes are commercially available from sources such as Gelest, Dow Corning, Shin-Etsu Chemical, and Momentive Performance Materials.
The silane of the present invention is present in the mold sealer composition in an amount effective to obtain the desired bonding strength and release durability. Desirably, the silane is present in the mold sealer composition in an amount of 0.1-10 w/w %, more desirably, 0.3-5 w/w/%, and even more desirably 0.5-2 w/w %.
The mold sealer compositions may desirably contain cure components other than the silane of formula 1, as are known in the art. In particular, if a silane is not water soluble or only partially water soluble, an emulsifier or emulsifiers are advantageous for stability.
Additional silanes or crosslinking agents can be used with the aminosilane of formula (I) to modify the cross linking density of the sealer coating. Useful examples of such modifiers are tetra- or trialkoxy silanes. The addition of a crosslinking modifier is particularly useful when formula (I) has less than 3 crosslinking groups.
The heat curable component desirably includes a cross-linking agent, either formula (I) or a modifier. Cross-linking is the attachment of two or more chains of polymers by, for example, bridges and cross bridges, comprising either an element, a group, or a compound. Desirably, the cross-linking agent is selected from the group consisting of alkoxy functionalized si lanes and hydroxyl functionalized silanes.
Suitable cross-linking agents may be selected from a variety of crosslinkers, such as, but not limited to: a monomeric, cyclic, oligomeric or polymeric silazane, an enoxy-functional silazane, a silicon hydride, an alkoxy functional silane such as trialkoxy- and trialkoxysilanes, a methylethylketoxime functional silane, an acetoxy functional silane, an enoxy functional silane, an amino-functional silane, and combinations thereof. More specifically, suitable crosslinkers include, but are not limited to: tris methylamino functional silane, tris enoxy functional silane, hydride functional silane, and cyclic trisilazane. Particularly useful crosslinking modifiers are functionalized polydimethylsiloxane (PDMS), e.g. hydroxyl terminated PDMS.
Cross-linking agents desirably are present in the mold release compositions of the present invention in an amount from about 0.01% to about 10% w/w, more desirably from about 0.3% to about 3% w/w.
The mold sealer compositions contain a carrier. Suitable carriers include emulsion carriers, water based carriers and organic carriers. In a desirable aspect, the carrier is water, including, for example, as part of a solution or emulsion composition.
Examples of organic carriers include a non-VOC carrier component. Desirable non-VOC carriers include siloxane compounds, which may be branched, linear, or cyclic; or fluorinated alkane compounds, which also may be branched linear, or cyclic; and combinations thereof. Other useful non-VOC carriers include those non-reactive solvents that are environmentally friendly selected from the compounds listed by EPA as exempt from the definition of a Volatile Organic Compound in 40 C.F.R. §51.100, which is hereby expressly incorporated herein by reference in its entirety. It would be understood by those of ordinary skill in the art which solvents from EPA's list are non-reactive and environmentally friendly, and thus, would be suitable for use in the compositions of the present invention. In addition, solvents having a vapor pressure of less than 0.1 mm Hg, which are non-volatile, also are considered non-VOC solvents for purposes of the present invention.
In accordance with some aspects of the present invention, non-VOC solvents may be employed alone or in combination with other non-VOC solvents. In addition, it may be desirable to blend non-VOC solvents with VOC solvents as they evaporate slowly, thereby forming low-VOC carrier compositions. VOC organic carriers may include, for example, aliphatic or aromatic
C6-14 hydrocarbons.
Non-VOC carriers are present in the curable mold release compositions, for example, in an amount from about 1% to about 99.9% by weight of the total composition (w/w).
In some embodiments of the present invention, the mold sealer composition may contain a carrier composition that is a combination of a non-VOC carrier and a VOC carrier, thereby providing a low-VOC carrier composition, as described above. The VOC carrier component may be any conventional VOC solvent used in mold release compositions, such as, for example, C6 to C14 aliphatic, aromatic solvents, organic ether, acetate or mixtures thereof. Other VOC carrier components include alcohols, such as ethanol or propanol, in their pure form or mixed with water in any concentration. The VOC carrier may be present in amounts from about 0.1 to about 99.9% w/w.
The mold sealer compositions of the present invention may contain a number of other optional additives, such as, e.g., bases, catalysts, biocides, slip agents, dyes, cure modifying agents, fillers, viscosity modifying agents, and combinations thereof.
A slip agent used in the present invention may be a functional or a non-functional siloxane.
A base used in the present invention may be triethanolamine, triethy amine, KOH or any other suitable base. Any type of base known in the art may be used in accordance with this invention. Desirably, non-protonated amines may be used as suitable bases, as they may provide silanes with better bond-ability to metal/mold surfaces.
The function of the base may be useful for adjusting a pH to a basic region so that the amino group of the formula (I) is deprotonated.
Any conventional catalyst may be employed provided the mold release properties of the compositions are not compromised. Suitable catalysts that may be used include conventional organometallic catalysts, such as, water and solvent based organic titanium derivatives and organic tin derivatives, tertiary amine compounds, and certain early transition metal compounds. Generally, the catalyst is present in an amount from about 0 to 1.0% w/w. This concentration, however, may be varied depending upon the desired cure rate.
The pH of the mold sealer composition is desirably from about 3 to about 11, more desirably, from about 10 to about 11, and most desirably from about 10.5 to about 10.8. Lower pH may result in a more stable silanol having a longer shelf life, however, a sealer coating having a high pH is more effective in application (e.g., durability). Generally, the compositions may be formulated to achieve a balance between durability, i.e. the number of releases, ease of release and stability. The selection of pH in combination with other additives such as emulsifiers enhance the ability to achieve such a balance of properties.
The mold sealer composition may also contain a pH modifier. The pH modifier may be added, in an amount effective to improve the shelf life of the mold sealer composition and as a deprotonation agent. Desirably, the pH modifier is added to maintain the desired pH, such as, from about 3 to about 11, more desirably from about 10 to about 11, and most desirably from about 10.5 to about 10.8. Suitable pH modifiers include both acids and bases, as necessary to obtain the desired pH for the mold sealer composition. Examples of suitable pH modifiers include, e.g., triethanolamine, acetic acid, potassium hydroxide (KOH), sodium hydroxide (NaOH), and triethyl amine.
In accordance with the present invention, the mold sealer compositions desirably are applied to a part to form a mold sealer coating. Upon application, the compositions cure at ambient or elevated temperatures to form the mold sealer coatings. The application of heat is not necessary in some embodiments of the present invention, however temperature may desirably be used to affect curing speed. Thus, it may be desirable to apply heat, depending upon the components selected. In room temperature curing embodiments, cure time desirably ranges between about 2 minutes and about 48 hours. Examples of suitable heat applications, include, e.g., curing for 5 minutes at 400 F, curing for 10 minutes at 325 F, or curing 30 minutes at 200 F.
The cure time may be shortened upon addition of certain appropriate catalysts, as described above. The compositions desirably cure to a high durability finish that permits a number of releases without contaminating a released part by transfer of the release composition from the mold to the part. In one embodiment, the cured compositions permit at least 3 releases, desirably at least 4 releases, more desirably at least 5 releases, even more desirably at least 6-9 releases, and most desirably at least 10 releases.
Desirably, the cured mold sealer compositions of the present invention are stable, e.g., having no or significantly reduced precipitation, separation, or performance deterioration for a substantial period, e.g., desirably for at least about six months, more desirably for about at least one year. The presence of precipitation and separation can normally be determined by unaided observance, the naked eye.
The mold sealer compositions are applied to form a sealed mold assembly. The scaled mold assembly contains a mold forming a part having a least one surface, and a coating on the at least one surface, wherein the coating comprise the mold sealer composition of the present invention. The mold forming part may be composed of a material, such as, a metal selected from the group consisting of steel, stainless steel, chrome, cast iron, aluminum and nickel. The mold sealer composition may be chemically bonded to the at least one surface.
The present invention also contemplates sealed molds formed by the process of:
(a) providing a mold for forming a part, said mold having at least one surface;
(b) applying a mold sealer composition onto the at least one surface, said mold sealer composition including:
(i) a silane having the formula I:
(c) exposing said mold sealer composition to curing conditions for a time sufficient to effectuate at least partial cure, thereby forming a durable seal on said mold.
Any suitable curing conditions maybe be used, such as, e.g., heat curing (e.g., 400 F for 5 minutes, 325 F for 10 minutes, or 200 F for 30 minutes).
Table 1 shows the weight percent of five (5) inventive compositions:
1Triethylamine, a base was used.
2Silicone glycol copolymers sold under the trade name of Silwet 7605 (Momentive).
3Alcohol ethoxylate sold under the trade name of Tomadol 900 (Air Products).
4Ethoxylated fatty acids sold under the trade name of T-Maz 20 (BASF).
5Alkyl diphenyloxide disulfonate salts sold under the trade name of Dowfax 2A1 (Dow Chemical).
shows the weight percent of compositions 1, 2, 5 with the presence of the emulsifier and compositions 1A, 2A, and 5A without the emulsifier:
1Triethylamine, a base was used.
2Silicone glycol copolymers sold under the trade name of Silwet 7605 (Momentive).
3Alcohol ethoxylate sold under the trade name of Tomadol 900 (Air Products).
4Ethoxylated fatty acids sold under the trade name or T-Maz 20 (BASF).
5Alkyl diphenyloxide disulfonate salts sold under the trade name of Dowfax 2A1 (Dow Chemical).
The compositions 1, 2, and 5, which contain water-soluble silanes, were carried out with the presence of emulsifier(s) and without the presence of emulsifier(s). The results showed no observable differences with or without emulsifier(s) indicating that soluble silanes do not require emulsifiers.
Table 3 shows the weight percent of compositions 3 and 4 with the presence of the emulsifier and compositions 3A and 4A without the emulsifier:
1Triethylamine, a base was used.
2Silicone glycol copolymers sold under the trade name of Silwet 7605 (Momentive).
3Alcohol ethoxylate is sold under the trade name of Tomadol 900 (Air Products).
4Ethoxylated fatty acids sold under the trade name of T-Maz 20 (BASF).
5Alkyl diphenyloxide disulfonate salts sold under the trade name of Dowfax 2A1 (Dow Chemical).
In contrast with Table 2, compositions 3A and 4A, which contain silanes that are water-insoluble, when tested without emulsifier(s), could not be mixed to form a homogeneous solution. The silanes could be clearly seen floating on top of the water, even after extensive mixing. Therefore, there was no reliable way for compositions 3A and 4A to create a uniform coating on the mold surface, and as a result these formulas could not be tested for their effectiveness as a mold sealer.
Experiments were performed to evaluate the effectiveness (releasibility) of the seal of mold sealer compositions shown in Table 1 on various types of mold materials (stainless steel and/or chrome plated molds).
The following protocol was followed to test the releasibility:
1. Four coats of the inventive mold sealer composition were applied to a pair of metal panel using a spray gun, adjusted to spray 1 to 1.5 mL/second. After applying the inventive mold scaler composition, it was allowed to cure for 10 minutes at 325° F.
2. After the inventive mold sealer composition was cured, applied a commercially available silicone-based release agent (Frekote R-150, available from Henkel) was applied to the panels, using the same spray gun and allowed to cure for 10 minutes at 325° F.
3. After curing, the panels were tested for releasibilty by placing a small piece of uncured EPDM rubber between two of these panels, which was then placed into a hot press using an applied load of 5000 pounds and a temperature of 350° F. After 25 minutes the rubber was fully cured, and the panels were removed from the hot press.
4. The two panels were separated, and the cured rubber was removed.
The standard for assessing releasibility was based on a scale of 1 (worst) to 5 (best), as follows:
A value of 5 indicates an automatic release, with essentially no force required to release the rubber.
A value of 4 indicates that a small amount of force is required for release.
A value of 3 indicates that a moderate amount of force is required for release.
A value of 2 indicates that a high amount of force is required for release.
A value of 1 indicates no release at all: the rubber cannot be removed without being damaged.
Plus and minus signs were used to show slight differences in releasibility, e.g., a “4+” is slightly easier than a “4”, but not as easy as a “5+”.
Tests were performed on both steel and chrome molds, using Frekote R-150 with and without the mold sealer. The results were compared by counting the number of extremely easy, or “auto” releases that could be achieved—a value of “5” in the releasibility scale. Auto releases are defined as releases which require essentially no force at all to remove the cured rubber from the mold surface.
Following the above protocol, a comparison was made to test inventive mold sealer compositions nos. 1, 2, 3 and 5 on stainless steel.
Comparison tests were conducted to test the molds releasibility without sealer but with release agent, and releasibility without a sealer or a release agent. The release test was repeated multiple times, to determine how many easy releases could be obtained from a single application of each composition. The following results were obtained:
As illustrated in Table 2, the mold sealer compositions of the present invention obtained excellent releasibility properties on stainless steel as compared to the controls. As is also apparent from Table 2, the inventive compositions achieved at least 3.5-6 times as many releases cycles as the controls. When using the sealer on steel molds, it is possible to obtain 12 auto releases, where previously Frekote R-150 alone could only give one auto release.
Following the same protocol, a comparison was made to test inventive mold sealer compositions nos. 1, 2, 4 and 5 on chrome plated molds.
Comparison was made to a test without sealer but with release agent, and a test without sealer and release agent. The release test was repeated multiple times, to determine how many easy releases could be obtained from a single application of each formula. The following results were obtained:
As illustrated in Table 3, the mold sealer compositions of the present invention obtained excellent releasibility properties on chrome plated molds. As noted in some instances, the inventive mold sealer compositions achieved 2-4 times the number of release cycles as compared to the control (no sealer and no release agent compositions.) When using the sealer on chrome molds, it is possible to obtain 12 auto releases, where previously R-150 alone could only give one auto release.
The results on chrome and steel substrates depicted in the chart of
Mold: Chrome Molds
Molding parameters: Each of the inventive compositions 1-5 were tested over a period of 40 days of heat aging, which is approximately equal to 1 year at room temperature. 1 day of heat-aging is equivalent to 9 days of aging at room temperature.
Application: For each test during the shelf life study, the heat-aged samples of mold sealer were evaluated using the standard test method for rubber release. A heat-aged sample of mold sealer was removed from the oven and spray-applied to a chrome mold, using four coats. It was cured at 325° F. for 10 minutes. Next, Frekote R-150 was applied to the panel using the same spray gun and allowed to cure for 10 minutes at 325° F. Each panel was then tested for its ability to release EPDM rubber. The results were compared to determine how the performance of the mold sealer changes over time.
Test Results: The mold sealer was determined to have a shelf life of at least 1 year at room temperature (77° F., or 25° C.). The results are provided in
As indicated in the shelf life table in
The results in
Release agent Frekote R-150 was applied to sealed molds as a touch-up coat after 17-23 auto/good releases. Each touch-up coat provided approximately the same amount of releases as the original sealed mold (e.g. 17-23). There was no need to re-apply the sealer after the mold surface was already sealed by formula (I).
A simple test was performed to determine if the mold sealer would cause corrosive damage to metal molds, because this is a common problem for water-based formulas. An excess amount of the mold sealer was applied to a steel panel and allowed to air dry overnight at room temperature. On the same panel, the same test was also performed using water and using Frekote R-150.
The results indicated that the inventive mold sealer composition did not cause rust to form on steel molds, whereas using water in combination with Frekote R-150 alone did cause rust formation. This is due to its unique chemistry, which does not cause oxidative damage to take place at the mold surface.
The mold sealer was first cured at 325° F. for 10 minutes. After curing, the mold scaler was heated to 600° F. and held at that temperature for 1 hour. It was then cooled back down to 325° F., and Frekote R-150 was applied to the mold and cured for 10 minutes. After testing this panel for rubber release, it was able to give 20 auto releases, a significant improvement over the 12 auto releases which could be achieved without the secondary cure.
Example 6 describes tests that were performed in order to determine the optimal amount of silane to use in a mold sealer composition.
Water-based samples were prepared using 0.5%, 1.0%, and 1.5% aminopropyltriethoxysilane (abbreviated as APTES).
These samples were applied to chrome panels, and tested using Frekote R-150 release agent, as described in the test method given earlier.
The results were as follows:
These results show that the optimal concentration is approximately 1.0% silane. There is little to no benefit to using a higher amount, and using a lower amount results in decreased performance.
| Number | Date | Country | |
|---|---|---|---|
| 61090421 | Aug 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2009/054282 | Aug 2009 | US |
| Child | 13031399 | US |
