MXPA99008378A - Postcure treatment for reaction injection molded polyurethanes - Google Patents

Abstract

A method of treating reaction injection molded polyurethane, polyurethane/urea and polyurea polymers comprising exposing a reaction injection molded polyurethane, polyurethane/urea or polyurea polymer to an amount of infrared energy sufficient to increase the temperature of the polymer to at least 180°C, and then maintaining the temperature of the polymer at or above that temperature, for a time sufficient to increase the Gardner impact property, as measured using ASTMD-3029, when compared to the same polymer which has been heated to the same temperature and maintained thereat for the same time in a convection oven. The invention produces marked improvements in impact, heat sag and heat distortion temperature properties, and thus is particularly suited to rapid preparation of parts using a mass production conveyor and is particularly well-suited to preparation of parts whichare to be subjected to later high temperature processes, such as the"E-coat"process.

Description

TREATMENT OF POST CU RADO FOR POLY U RETANS MOLDED BY INJECTION REACTION The present invention relates to the field of injection molded polyurethanes, and particularly to a post curing treatment thereof which provides improvements in properties.

It is generally known that injection molded polymers, which are generally referred to as polyurethane polymers (polyurea and polyurethane / polyurea), benefit from a post cure treatment after being removed from the mold. The post curing treatments generally serve to react residual isocyanate with unreacted polyol and polyamines to complete the polyurethane and polyurea reaction, allow the evolution of trapped gases for improved ability to be painted, and allow the formation of a hydrogen bonded network of lower energy than that found in the uncured polymer. This improves the heat distortion properties that result in better end-use performance. Post curing also reduces the amount of time a part needs to react and degas from 3 days to a few hours. In most of this industry, and particularly in the portion of automotive parts thereof, this cured post has typically been achieved by extended exposure (usually 1 hour) to heat in a convection oven. Furnace temperatures of 140 ° C are commonly used to cure the selected polymers to prepare automotive fascia. This is obviously relatively time-consuming and energy-intensive, but significant improvements in the properties noted hereinbefore have strongly supported the continuation of manufacturing methods incorporating this post-curing treatment. However, an application for these polymers which is expanding is common and rapidly is in the area of vertical body panels. The body panels which have been made up to now mainly of steel, must be fastened generally even a pre-painted process in-line, widely used known as "E-layer", in which an anticorrosive epoxy resin is applied to the steel surfaces and are then subjected to oven curing at a much higher temperature, generally in the range of 180-200 ° C. The use of polymeric body panels presents new challenges, because, unless the body panel is cured sufficiently before this layer process ^ E, the higher temperature required for this E-layer process can adversely affect the dimensional stability of the panels. However, fastening the panels to two separate sequential elevated temperature processes - a post cure treatment after molding, and a heat treatment as part of the E-coating process - is extremely expensive. This is because the convection ovens required in the conveyor lines for such an approach have to be extremely large and have to be actually heated to temperatures even higher than 200 ° C due to the inherent problems associated with convection heating. For example, as the temperature of the substrate begins to approach the air temperature, the transfer of heat to the part drops dramatically. This, however, can lead to another problem which is that using such a higher air temperature to ensure that the core of the part reaches the desired temperature can result in degradation of the part surface. Thus, it is difficult to post properly cure using such high temperature transport lines without encountering problems in polymer quality and without risking poor curing which leads to loss of dimensional stability in subsequent E-layer processing. The alternative, which is to place parts in furnaces without a conveyor, is not efficient either. The industrial manufacturer needs, therefore, a method to perform the post cure without relying on high temperature convection ovens, which method can be carried out on transported parts, and which results in a post cure such that subsequent exposure in high temperature convection ovens will not result in Unacceptable dimensional changes in the part. The present invention offers such a method, and also offers unexpected and surprising improvements in polymer properties as well. It is a method to treat polyurethane, polyurethane / urea and polyurea polymers injection-molded reaction comprising exposing a polyurethane polymer, polyurethane / urea or polyurea injection-molded reaction to an amount of infrared energy sufficient to increase the polymer temperature by at least 180 ° C, and then maintain the temperature of the polymer at or above that temperature, for a time sufficient to increase the Gardner impact property, as measured using ASTMD-3029, when compared to the same polymer that has been heated to the same temperature and kept in it for the same time in a convection oven. Preferably, the Gardner impact property is increased by at least 25 percent when compared to the same polymer which has been heated to the same temperature and maintained therein for the same time in a convection oven. More preferably, the Gardner impact property is increased by at least 35 percent when compared to the same polymer which has been heated to the same temperature and maintained therein for the same time in a convection oven. Preferably, the polymer is maintained at the desired target temperature (at least 180 ° C) for 20 to 35 minutes, and also preferably the temperature of the polymer is increased such that it reaches a level of at least -10 ° C. greater than the highest temperature at which the polymer will be exposed in any subsequent processing, such as the E-layer process. The preferred wavelength is from 0.76 to 2 microns. The use of the present invention improves important mechanical properties such as impact, heat shrinkage and heat distortion temperature. It is also significantly faster and less expensive when compared to convection heating. Finally, it does not result in degradation of the part surface, since the entire polymer mass is essentially simultaneously heated.

The present invention surprisingly uses infrared radiation, which is the form of electromagnetic radiation that falls between visible light and radio waves in the electromagnetic spectrum, for its post-curing treatment. Infrared radiation is known to provide the highest heat transfer profile, in general, of all types of electromagnetic radiation. Its character is divided into wavelengths, designated as short, medium and long, and the wavelength for maximum intensity is the "short" wavelength area (known as "high intensity") from 0.76 to 2 microns. The mechanism of operation in this new approach is the absorption of radiation within this limited range of wavelength. This absorption by an organic molecule resulted in the excitation of the molecule to a higher energy state, and the return of the molecule to its fundamental energy state resulted in the release of energy, mainly as heat. Although the authors also experimented with exposures to broadband IR (wavelengths concentrated mainly in the range of 2.5-15 microns, but with over-tone bands ranging from 1 to 100 microns), the performance suggested a strong preference for wavelengths from 0.76 to 2 microns. The effect of this IR radiation is that the temperature of the polymer rises much more quickly than is possible using a convection oven alone, and this rapid rise in temperature, followed by the maintenance of the temperature afterwards for a short time, usually 20 to 35 minutes, results in a fully cured polymer exhibiting superior properties, for example impact resistance and dimensional stability measured by heat-setting, when compared to an identical polymer that has been post-cured without IR treatment, but which instead it has been placed in a convection oven for a sufficient time to reach the target temperature, and then maintained at that same temperature for the same amount of time as the polymer treated with I R. In most applications the source of IR is able to raise the temperature of the polymer to the desired post curing temperature in 2% minutes, compared to 15 to 30 minutes using a convection oven. This reduces the size of the furnace required to process body panel parts, which is extremely important for use with conveyor lines and allows the use of either the IR source or conventional convection means to carry out the maintenance portion of the furnace. temperature of the process that follows the initial heating. Typically, the IR source and convection oven are combined in an apparatus to perform both portions of the process more or less simultaneously. The reaction injection polymers to which the infrared radiation is applied include in particular those known as "polyureas" and "polyurethane / ureas", which generally include reaction injection molded, rigid elastomers used in automotive and durable materials, including furniture, toys , team accommodations. Because there is some controversy in the amount of polyurea content present in many polymers otherwise simply classified as "polyurethanes", "polyurethanes" as such are also included in embodiments of the present invention.

These polymers have urea groups, urethane groups and / or mixtures thereof. That is, the polymers can be prepared from materials that include or react to form only polyurethane or polyurea groups, or the polymers of the present invention can be prepared from materials that include or react to form both polyurethane and polyurea groups. Other polymer ligatures can be formed in the practice of the present invention, also, for example, a polymer having polyurethane groups can be prepared., polyurea and isocyanurate. In general, these polymers are prepared via the reaction of an isocyanate, an isocyanate-reactive material, such as a polyol, and a chain extender, with additional materials included depending on the desired end result. Also included are polyurea / polyurethane polymers prepared from formulations including a polyisocyanate, polyisocyanate-reactive compounds (including polyols and polyamines) and a polyepoxide. These formulations, when post-cured at more than 150 ° C, exhibit improved heat stability and are described, for example, in US Pat. No. 5,525,681. The primary isocyanate-reactive material selected for the preparation of injection-reaction molded polyurethanes is specifically a hydroxy-functional material, called a polyol. Polyols used herein include those prepared from alkylene oxides and an aromatic amine or alkylene oxide initiator. Suitable aromatic amines for preparing these materials can include any di-, or polyfunctional aromatic amine.

Suitable aromatic amines for initiators include: toluene diamine (TDA) isomers, which include 2,6-TDA, and 2,4-TDA, for example; methylene diamine isomers, (MDA) which include, for example, 2,2'-MDA, 2,4'-MDA, and 4,4'-MDA; MDA oligomers including, for example, mixtures of isomeric compounds having from 3 to 6 aromatic rings; alkyl derivatives of aromatic amines such as 4-methyl-2,6-TDA, and dimethyl-MDA isomers; halogenated derivatives of TDA such as 3-chloro-2,4-TDA; compounds similar to any of these. Suitable alkylene oxides for use include oxides having from 2 to 8 carbon atoms, preferably from 2 to 4 carbon atoms. For example, suitable alkylene oxides may be ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, styrene oxide, epichlorohydrin, 3-methyl-1,2-butylene oxide. , similar compounds and their mixtures. In the present invention, polymers and copolymers of propylene oxide are preferred. The chain extender preferably included in the formulations used in the present invention are preferably selected from low molecular weight diols and triols. Ethylene glycol is particularly useful, but other similar compounds can also be used. Propylene glycol, ethylene glycol, are also suitable for use in the present invention. Particularly preferred, however, is an amine-containing material, which may be aliphatic or aromatic, but is preferably aromatic in nature. This component can be selected from amine-terminated polyamines and polyols. Diamines having molecular weights of less than 800, preferably less than 500 are conventionally employed. Preferred compounds containing amino groups include the sterically hindered aromatic diamines containing at least one linear or branched alkyl substituent in the ortho position to the first amino group and at least one, preferably two, linear or branched alkyl substituent which contains minus one, preferably one to three carbon atoms in the ortho position to the second amino group. These aromatic diamines include 1-methyl-3,5-diethyl-2,4-diamino benzene, 1-methyl-3,5-diethyl-2,6-diaminobenzene, 1, 3,5-trimethyl-2,4-diamino benzene, 1-methyl-5-t-butyl-2,4-diaminobenzene, 1-methyl-5-t-butyl-2,6-diaminobenzene, 1, 3,5-triethyl-2,4-diaminobenzene, 1-methyl-5-t-butyl-2,4-diaminobenzene, 1-methyl-5-t-butyl-2,6-diaminobenzene, 1, 3,5-triethyl-2,4-d-aminobenzene, 3, 5 , 3 ', 5'-tetraethyl-4,4'-diaminodifenylmethane, 3, 5,3', 5'-tetraisopropyl-4,4'-diaminodifeni I methane, 3,5-diethyl-3 ', 5' -diisopropyl-4,4'-diamino diphenyl methane, 3,3'-diethyl-5,5 > -diisopropyl-414'-diamino diphenyl methane, 1-methyl-2,6-diamino-4-isopropylbenzene, and mixtures of the above diamines. Most preferred are mixtures of 1-methyl-3,5-diethyl-2,4-diaminobenzene and 1-methyl-3,5-diethyl-2,6-diatninobenzene in a weight ratio between 50:50 and 85:15. , preferably 65:35 to 80:20. Non-clogged aromatic polyamines can be used with sterically clogged chain extenders and include 2,4- and / or 2,6-diaminotoluene, 2,4- and / or 2,6-diaminodiphenylmethane, 1,2'- and 1, 4- phenylene diamine, naphthalene-1, 5-diamine and triphenyl methane-4,4 ', 4"-triamine.The difunctional and polyfunctional aromatic amine compounds may also exclusively or partially contain secondary amino groups such as 4,4'-dihydroxyphene. (methylamino) -diphenylmethane or 1-methyl-2-methylamino-4-aminobenzene Also suitable are liquid mixtures of polyphenyl polymethylene polyamines of the type obtained by condensation of aniline with formaldehyde. Generally, aromatic diamines and polyamines which are not sterically clogged are very reactive to provide sufficient processing time in the preparation of polymers such as RIM polyurethanes and polyureas Consequently, these diamines and polyamines must be used in combination with one or more of the diammonically clogged diamines. e mentioned previously. An exception to this is the case of methoxychloroaniline. This particular diamineAlthough it is not sterically clogged, it is a suitable material for preparing RIM polyurethanes / polyureas. The polymer composition also generally includes a polyisocyanate. Any polyisocyanate or mixture of polyisocyanates known in the art is suitable for the practice of the present invention. Useful polyisocyanates are described in U.S. Patent No. 4,785,027, for example. The polyisocyanate can be aliphatic or aromatic. Suitable aromatic polyisocyanates for use herein include: phenyl diisocyanate; 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; toluene diisocyanate; Naphthalene 1,4-diisocyanate; 2,4'- and / or 4,4'-diphenylmethane diisocyanate (MDl); polymethylene polyphenylene polyisocyanates (polymeric MD1); similar compounds and their mixtures. Suitable aliphatic polyisocyanates include: 1,6-hexamethylene diisocyanate; isophorone diisocyanate; 1,4-cyclohexyl diisocyanate; similar compounds and their mixtures. The prepolymers prepared by reacting a polyol or chain extender with a polyisocyanate are also suitable. The polyisocyanate can be used in a suitable amount to prepare the injection molded composition reaction with an isocyanate index of 90 to 130. Preferably, the index is from 100, more preferably 105, to 130, more preferably 1 10. The index of isocyanate is determined by dividing the number of isocyanate equivalents by the number of equivalents of isocyanate-reactive material, and multiplying the ratio obtained by 100. A polyisocyanate of the present invention may have an average nominal functionality of 2.0, preferably from 2.5, more preferably 2.6, to 3.5, more preferably 3.3, and more preferably 3.0. Frequently included in the preparation of a reaction injection polymer suitable for use in the present invention is one or more optional components. Such may include, for example, one or more copolymer polyols, polyester polyols, catalysts, fillers, crosslinkers, surfactants, mold release agents, and / or flame retardants. Although not required, it is customary to include at least one interlayer, catalyst and mold release agent, since these materials promote the establishment of good physical properties, including raw strength, and increase the ability of the manufacturer to prepare quickly and easily a succession of parties with limited need to intervene in process steps.

Polyurethane catalysts are also suitably used with the present invention. The catalyst is preferably incorporated into the formulation in a suitable amount to increase the reaction rate between the isocyanate groups of the composition of the present invention and a hydroxyl-reactive species. Although a wide variety of materials useful for this purpose are known, the most widely used and preferred catalysts are tertiary amine catalysts and organotin catalysts. Examples of suitable polyurethane catalysts for preparing a polymer which is useful in the present invention are tertiary amine catalysts such as: triethylenediamine; N-methyl morpholine; dimethylethanolamine; pentamethyldimethylenetriamine; N-ethyl morpholine; diethyethanolamine; N-coco morpholine; 1-methyl-4-dimethylaminoethyl piperazine; bis (N, N-dimethylaminoethyl) ether; similar compounds and mixtures of any of these. The amine catalysts are usually used in an amount from 0.1 to 5, preferably from 0.2 to 3 parts per 100 parts of polyol composition, by weight. Organometallic catalysts are also suitable, and examples include organoplomo, organofierro, organomercurio, organobismuto, and preferably organotin compounds. Most preferred are organotin compounds such as dibutyltin dilaurate, dimethyltin dilaurate, stannous octoate, stannous chloride and the like. The organometallic compounds are usually used in an amount from 0.05 to 0.5 parts per 100 parts, by weight, of polyol composition. Examples of tertiary amine catalysts include, for example, triethylenediamine, N-methyl morpholine, N-ethyl morpholine, diethyl ethanolamine, N-coco morpholine, 1-methyl-4-dimethylaminoethyl piperazine, 3-methoxy-N-dimethylpropylamine, N, N-diethyl-3-diethyl aminopropylamine, dimethylbenzyl amine. Tertiary amine catalysts are advantageously employed in an amount from 0.01 to 2 weight percent of the polyol formulation. Examples of organotin catalysts include dimethyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, stannous octoate. Other examples of effective catalysts include those taught in, for example, U.S. Patent No. 2,846,408. Preferably the organotin catalyst is employed in an amount from 0.001 to 0.5 weight percent of the polyol formulation. The polymers of the present invention may also be mixtures of polymers and polymer interpenetrating network polymers. For example, a polyurethane of the present invention can be mixed with another polymer such as, for example, an acrylonitrile-butadiene-styrene polymer and then be painted electrostatically. Other miscible polymers useful with the present invention include, but are not limited to, nylon, polyethylene terephthalate, and polyacrylate. Interpenetrating network polymers can be prepared with polymers of the present invention with materials such as epoxy resins and polycarbonate resins. The network polymers can be prepared by including one or more monomers in the formulations of the present invention such that the materials of a segregated phase or co-continuous polymer network in situ. Preferably, polymers containing urea / urethane groups are the predominant component of multiple polymer compositions of the present invention. The preferred means for forming the polyurethane / polyurea polymers of the present invention is by means of injection molding reaction (RIM). The preparation of RIM polymers is well known in the art, but generally includes the steps of introducing at least two streams of reactive materials mutually through a mixing head into a mold wherein the materials polymerize to produce a molded polymer article. . It is conventional for one stream to be the isocyanate component, and the other to be the polyol, chain extender and any additional optional materials such as catalyst, fillers, mold release agents, and so on.; however, in some cases additional optional materials may be added to the isocyanate component. Processing of the RIM polymer is typically done in the mold for a period of time ranging from 1 to 5 minutes, followed by demolding. The polymer is then ready to be treated with infrared radiation to effect the post curing of the present invention.

The infrared equipment used preferably can be any source of infrared radiation capable of emitting the designated radiation wavelength. Preferably such equipment is controlled via a non-manual chronometric means, to use the commercial processing, and such chronometric means is determined by temperature measurement. The incorporation of an optical pyrometer to determine the temperature is preferred. The following examples are included to more fully illustrate the present invention; however, they are not intended to be, nor should they be constructed as being, limiting their scope in any way. Unless otherwise indicated, all parts and percentages are by weight. The ASTM designations for the test protocols referenced for property determinations are as follows: Specific Gravity ASTM D-792 Flex Module ASTM D-790 Percent Load (weight) ASTM D-297 Heat Bagging ASTM D-3769 Impact Gardner ASTM D-3029 Example 1 A panel was molded into a plate mold using a Cincinnatti-Milcron HT Reaction Injection Molding machine (R. I.M.). The polymer formulation was SPECTRIM HH * with 20 percent wollastonite RRIMGLOS1 **. [* SPECTRIM HH is a registered trademark of The Dow Chemical Company. ** RRIMGLOS1 is a registered trademark of Nyco Co.]. Following the demolding, one of the panels was then cured by heating it to 190 ° C and maintaining the temperature at 190 ° C for 1 minute using an ITW BGK infrared oven, model # 2516-48 HP. The wavelength of the energy of I R varied in the range of 0.76 to 2.0 microns. The temperature was monitored by an internal optical pyrometer with an internal feedback control circuit. Then, the panel was placed in a convection oven for 30 minutes at 190 ° C and then allowed to cool. The resulting properties of the cooled panel are: specific gravity 1.25, load percent 20.23, flexural modulus (parallel) 17.007 kg / cm2, flexural modulus (perpendicular) 8.270 kg / cm2, heat-shielding 1.0 mm, Gardner impact 8.22 cm-kg.

Example 2 (Comparative) Another panel prepared by the same procedure was post-cured and using the same formulation as in Example 1 in a convection oven.After 30 minutes in the oven, the panel reached a temperature of 190 ° C and then it was allowed to remain in the oven for 30 minutes at 190 ° C. The resulting properties of the cooled comparative panel were: specific gravity 1.25, load percent 20.23, flexural modulus (parallel) 18.009 kg / cm2, flexural modulus ( perpendicular) 8,595 kg / cm2, heat bagging 1 .3 mm, Gardner impact 5.72 cm-kg.

Example 3 A panel was molded in a reaction injection molding machine (R.I.M.) Cincinnatti Milcron HT using a plate mold using the procedure used in Example 1 and Example 2 (comparative).

The panel was post-cured in an ITW BGK post-curing infrared oven Model # 2516-48 HP. The panel reached the post curing temperature of 190 ° C in 2 minutes and 20 seconds and then maintained at that temperature for 30 minutes. The panel was removed from the oven, cooled and the properties were determined. They were: specific gravity 1.21, load percent 19.9, flexural modulus (parallel) 15.618 kg / cm2, heat bagging 9.3 mm, Gardner impact 8.22 cm-kg. A panel that had been post-cured at the same time was then held at 185 ° C for 40 minutes in a convection oven to simulate E-layer conditions. The resulting properties after cooling were: specific gravity 1.23, load percent 20.3, flexural modulus (parallel) 15.217 kg / cm2, heat bagging 3.7 mm, Gardner impact 264.65 cm-kg.

Example 4 Panels molded in the same manner as in the previous examples and comparative example were post-cured in a convection oven. The panels reached 190 ° C in 30 minutes and were then kept at this temperature for 30 minutes. The panels were removed from the oven and cooled. The physical properties were determined to be: specific gravity 1.23, load percent 20.0, flexural modulus (parallel) 16.282 kg / cm2, heat sag 9.7 mm, Gardner impact 5.0 cm-kg. Another panel, prepared at the same time and post-cured in a convection oven was subjected to an E-layer simulation of 185 ° C for 40 minutes. The panels were cooled and it was then determined that they have the following properties: specific gravity 1.21, load percent 20.0, flexural modulus (parallel) 15,738 kg / cm2, heat bagging 6.7 mm, Gardner impact 3.22 cm-kg.

Claims (8)

1. REIVIN DICATIONS 1. A method for treating polyurethane, polyurethane / urea and polyurea polymers injection-molded reaction comprising exposing a polyurethane polymer, polyurethane / urea or polyurea injection-molded reaction to an amount of infrared energy sufficient to increase the temperature of the polymer to at least 175 ° C, and then maintaining the temperature of the polymer at or above that temperature, for a time sufficient to increase the Gardner impact property, as measured using ASTM D-3029, when compared to the same polymer that has been heated to the same temperature and kept in it for the same time in a convection oven. The method of claim 1 wherein the Gardner impact property is increased by at least 25 percent when compared to the same polymer that has been heated to the same temperature and maintained therein for the same time in an oven of convection. The method of claim 2 wherein the Gardner impact property is increased by at least 35 percent when compared to the same polymer that has been heated to the same temperature and maintained therein for the same time in an oven of convection. 4. The method of claim 1 wherein the temperature of the polymer is raised to at least 175 ° C and is maintained therein for at least 20 minutes. 5. The method of claim 4 wherein the temperature of the polymer is elevated to at least 196 ° C. The method of claim 1 wherein the polymer is moved to make contact with infrared energy by means of a conveyor. The method of claim 1 wherein the temperature of the polymer is maintained by convection oven for at least 30 minutes. 8. The method of claim 7 wherein the temperature of the polymer is elevated to at least 196 ° C. RESU MEN A method for treating polyurethane, polyurethane / urea and polyurea polymers injection-molded reaction comprising exposing a polyurethane polymer, polyurethane / urea or polyurea injection-molded reaction to an amount of infrared energy sufficient to increase the temperature of the polymer to at least 180 ° C, and then maintaining the temperature of the polymer at or above that temperature, for a time sufficient to increase the Gardner impact property, as measured using ASTM D-3029, when compared to the same polymer which has been heated to the same temperature and kept in it for the same time in a convection oven. The invention produces marked improvements in impact properties, heat shrinkage and heat distortion temperature, and. thus it is particularly suitable for rapid preparation of parts using a conveyor for mass production and is particularly suitable for preparation of parts which are to be subjected to a high temperature process later, such as the "E-layer" process. .