DE1900867A1 - Potting composition containing a urethane prepolymer - Google Patents

Abstract

Potting composition for encapsulating equipment is produced by mixing (I) a urethane prepolymer with free isocyanate groups, (II) a liquid polyol, (III) a petorleum oil with a viscosity-gravity constant of at least 0.95, and (IV) silicone dioxide. The potting composition is an excellent heat dissipator, a good sound suppressor, and is capable of withstanding powerful external conditions. The free isocyanate groups react with any moisture penetrating into the composition. The composition cures readily at room temp., and is relatively cheap.

Description

Heat Cast Curable Potting Compound This invention relates to a heat-cast curable potting compound for electrical devices.

Electrical devices such as transformers, coils, etc. must often relatively small in size. In general, these devices intended as components in an electrical device, such as a choke for a fluorescent lamp, which is usually enclosed in a metal case. One such application the components requires effective and adequate means to dissipate the heat, which during operation by the individual components within a ballast, such as a ballast transformer.

Usually a potting compound is used, which the core and the Includes coils. By using such potting compounds, the inside heat generated by the transformer to the exterior of the ballast housing be discharged, where it is released into the surrounding air.

In many applications, the ballast is exposed to harsh environmental conditions exposed, such as a humid and corrosive atmosphere and strongly changing temperatures, which can promote corrosion of the metal housing. In addition, the potting material begin to flow at high temperatures and there can be considerable absorption Moisture penetrate through the device. The occurrence of one or of A combination of these environmental conditions can eventually lead to premature electrical failure of the device.

According to the previous state of the art, asphalt-like Casting compounds used; however, resin compositions have recently been used. However, a major disadvantage of the resin compositions is their relatively high price in comparison been to the asphalt-like connections. This factor has made it economical is impractical to use resinous potting compounds in most cases where a large volume is to be filled.

Although the asphalt-like and the well-known resinous compounds in dungen Having proven to be technically satisfactory, they have some undesirable ones Properties. For example, many have not been particularly effective as heat sinks. Many have not been able to withstand excess moisture, which permanent damage to the electrical components inside the ballast could. Indeed, one of the real disadvantages of asphalt-type potting compounds is in that they crack after prolonged use and so do the electrical components the harmful effects of moisture and other harmful ones Expose environmental conditions.

In addition, the asphalt-like casting compounds must be used at high temperatures be poured into the ballast in liquid form, creating fuses and other temperature sensitive devices, which are usually at risk contained in a device such as a ballast. When using the previously known resin-like potting compounds must for the purpose of correct curing a high temperature can be maintained.

Another disadvantage of the casting compounds known from the prior art is discussed below. By the presence of, for example, transformers and other electrical components in the ballast, vibrations are generated, which cause an undesirable noise. It would therefore be very desirable to have a To use potting compound, which is the result of such an electrical device escaping sound vapor.

An improved resinous potting compound should come up against a comparison compared to all potting compounds known from the prior art, both the asphalt-like as well as resin-like prove to be beneficial. Obviously cost is a major consideration: a new resinous potting compound must be economically attractive compared to the cheap asphalt-like masses. In addition, the new resinous mass must have a good heat conductor and a good sound absorber and must be able to withstand severe environmental conditions. It was Another advantage of barz-like compounds was found in a new resinous potting compound should be used. Free isocyanate groups in resinous Compounds react with the remaining moisture in the environment and form a Gas. This is significant when including a device such as of a transformer where it is very important that the coils are free how possible from moisture. A new resinous potting compound should have this cleaning property Use to remove residual moisture from the coils.

The invention provides a potting compound which is an oil-extended Contains blended urethane elastomer. The manufacture of the stretched urethane elastomer comprises the mixture of a first component which is a urethane prepolymer with a contains a sufficient amount of free isocyanate groups and a second component, which contains a polyol. The second component also contains a petroleum-like one Ö1, which is a viscosity gravity constant of has at least 0.95. The second component contains a high proportion of one Silicon dioxide (Si 02), which has good thermal conductivity properties. The ones from the Mixing the two components resulting potting compound hardens at room temperature the end.

A preferred embodiment of the invention is as follows detailed description in connection with the attached illustration, which shows a front view of a ballast in which one wall of the housing of the ballast is removed.

The figure shows a ballast 1, suitable for use with electrical and electronic devices, which for example a Transformer 3 with a core 5 and a coil 7 contains. The core 5 and the coil 7 are arranged within an outer housing 9 for the ballast and are held at a distance from the housing 9 by the casting compound of the invention. The housing 9 for the ballast comprises a box made of sheet metal. The box is usually fitted with a lid 10 which can be removed to provide access to create the inside of the box. The potting compound is also used to the dissipate heat generated by the coil. In addition, the Potting compound to that of the vebrierenden components inside the housing for noise generated by the ballast. The core 5 consists of one suitable ferrous material and is stacked in a manner known per se Sheet metal or otherwise manufactured. The coil 7 comprises a plurality of layers made of wire or tape, which are wound on top of each other and carried out in a known manner suitable isolation are isolated from each other. In general, the core and the coil and the insulating material are impregnated with a varnish or a suitable resin. Electrical connection lines or taps 11 are generally from the Coil led out and to one end of the ballast where it usually is through the feed-through openings in the box 9.

In the figure, the potting compound 13 can also be seen, which the transformer 3 encloses and it at a distance from the walls of the housing 9 holds for the ballast. According to one embodiment of the present invention the casting compound was produced according to the following example: Example 1 Vorite 128 Isocyanate prepolymer 2.7% DB castor oil polyol 2.3% Dutrex 739 6.0% Dutrex 998 9.0% silicon dioxide, powder clear mesh size 0.0725 mm 80.0% (200 mesh) Das Vorite 128 isocyanate prepolymer forms a diisocyanate addition polymer based on ricin oleate, which has the following chemical and physical properties: color, visual Light, amber-colored NC0 content,% 10.4 - 11.1 Free tolylene diisocyanate (TDI)% 7.5 - 9.0 equivalent weight per NC0 group 378-404 specific weight at 250C 1.072-1.080 Viscosity at 25 ° C (Poise) 180 - 270 Refractive index at 25 C 1.5215-1.5235 The prepolymer can, for example, also be based on polyether be if so desired. The DB castor oil polyol consists of a modified one Castor oil polyol, although other polyols such as polyether-based polyols are also available from of this invention may be considered.

The potting compound is made as follows: by mixing the Dutrex 739 and the Dutrex 998 at 700 C a mixture of petroleum oils is made. 23 grams of the OIL DB castor polyol are added to this mixture. Then be at 70 ° C 27 grams of Vorite 128 isocyanate prepolymer added. The polyol and the isocyanate prepolymer are used in essentially stoichiometric amounts to make the urethane produce. Finally, a mixture of 480 grams of silicon dioxide (through a sieve with a clear mesh size of 0.84 - 0.44 mm (20 - 40mesh) screened) and made of 320 g silicon dioxide (through a sieve with a mesh size of 0.0725 mm (200 mesh) sieved) and, after it had been preheated to 70 O C, the above mixture added. The entire mixture is stirred until homogeneous.

As already stated, a group of oils has been found which is particularly suitable for stretching the polyurethanes. The group consists of oils that have a VGC viscosity gravity constant above 0.95. The viscosity-gravitational constant is a function of the chemical compound in which the oil is present and grows with the increase in the number of aromatic rings or naphene rings and can therefore be used as a measure of the aromaticity of the oil. The formula for calculating the VGC is: G-0.24 0.022 LOG (V1-35.5T / 0.755 G means the density at 15.56 ° C (600 F) and V1 is equal to the universal viscosity according to Sayboldt at 98.89 ° C (210 ° F), (Mill etal, Industrial and Engineering Chemistry, Volume 20, page 641 (1928)). Dutrex oils meet these requirements. With regard to the present invention, it has been found that the VGC is an important determinant of the compatibility of the oil with the urethane. Compatibility for this purpose can be defined as that property of a mixture of urethane and at least 75% by weight of a petroleum-based oil which leads to a mass which forms a gel and does not secrete any oil. In other words, compatibility is the characteristic of the compound that enables the oil to be retained and thus "stretched" the urethane. Significant is the apparent reduction in the cost of potting compounds, which have high compatibility, and this reduction makes the use of a potting compound with a urethane commercially feasible.

Below is a table showing the compatibility of Dutrex oils on the Based on petroleum with the prepolymer Vorite 128 and the DB oil polyol, as described in Example 1 is made.

Compatibility of polyurethanes based on Vorite 128 and DB-Ö1 with Dutrex petroleum oils.

Oil viscosity volatility aniline viscosity paraffinic degree of compatibility SUS 48.89 ° C% Loss (1) Point ° Gravitational Carbon- nity No. (210 ° F) ° C (° F) constant atoms% (2)% 275 35 7.9 31.94 (89.5) 0.939 27 50 298 40 6.5 - 5.28 (22.5) 0.967 27 75 (3) 315 44 0.8 42.22 (108) 0.920 38 50 357 47 0.6 12.78 (55) 0.961 42 85 419 49 4.6 - 11.11 (12) 0.986 26 85 739 107 0.4 - 10.56 (13) 0.999 (4) 85 757 124 0.1 28.33 (83) 0.943 43 50 (5) 898 271 0.4 - - (6) - 75 (3) 959 438 0.1 - - 1.006 (4) 75 (3) 985 783 0.1 55.0 (131) 0.912 45 50 998 2.443 0.1 - - 0.974 - 75 (3) 1726 85 0.2 40.56 (105) 0.931 38 50 1786 145 0.1 32.33 (90) 0.948 39 50 (1)% loss after 22 hours at 107, nu C (2250 F) (2) Method of S.S. Hurtz, et al, ANAT. Chem. 28, 1928 (1956) (3) The value represents the highest investigated concentration.

The maximum value can be greater.

(4) The content of aromatic compounds is not measurable because it is too high.

(5) Oil leaked after a week.

(6) The method is not suitable for oils that contain asphalt-like compounds contain, or oils that are too dark to determine the refractive index.

As can be seen from the table above, the present Petroleum-based oils used in the invention serve the viscosity-gravitational constant of at least 0.95.

This guarantees a tolerance of at least 75%.

This would generally change the oils used to the aromatic ones Restricting oils containing significant amounts of carbon atoms in aromatic Rings included.

It has also been found that oils of sufficient viscosity the need to individually seal the seams and feedthrough openings in the housing of the ballast to prevent the liquid from escaping during the curing of the resin, when the mixture is still in a liquid State excludes. Of course, the liquid resin should be a pretty have low viscosity when poured to ensure easy handling.

However, its viscosity should increase quickly after pouring, so that the leakage of resin from the housing for the ballast is prevented will. The petroleum based oils according to the present invention are disclosed in US Pat very satisfactory in this regard, since they are poured with a temperature of 700 C in a cold case have a viscosity of less than 500 cps, and their viscosity increases rapidly as the temperature drops. Indeed achieve these blends typically have viscosities in excess of 50,000 cps when they are themselves finally cool to 250 C so that the resin compound is sufficiently viscous to a To prevent leakage of the mass from the housing for the ballast.

A choke for a fluorescent lamp was made with the mixture of the Example 1 cast, in which the mixture at a temperature of 70 ° C in the Housing for the ballast was cast, which the electrical components contained. The entire ballast was left on for 16 hours at 250 ° C overnight allowed to stand to ensure gelatinization of the resin. A leak of liquid found at the feed-through openings or seams of the housing for the ballast not held. As previously discussed, the isocyanate groups in the resin act as a cleaning agent for the residual moisture in the bobbins before the geiatihierung and help therefore, to improve the overall operability of the ballast.

When determining the effectiveness of the casting compound according to the invention, im In contrast to conventional asphalt filling, for example in the Ballast manufactured in the above example on a trial basis with an asphalt-filled one Ballast compared under identical conditions. It was found out that the thermal conductivity of the ballast filled with urethange - 4 is a thermal conductivity of lOx10 cal / (sec.) (cm) (° C), in contrast to asphalt, which has thermal conductivity of 7x10 4 cal / (sec.) (cm) (OC). During a test to determine moisture absorption it was found that using a 90% relative humidity test for a period of 7 days the asphalt showed a weight gain of 0.05%, while the urethane-filled ballast showed a weight gain of 0.06 % occurred.

It was found that the new invention. Potting compound in has advantages over asphalt in other respects.

The water permeability of asphalt was tested in an immersion test with a test duration of 7 days with 0.004. determined. at a comparable test for the urethane potting compound was the water permeability determined to be 0.060%; this value is small enough to be of sufficient usefulness to ensure. Rain tests under specified conditions show that with Urethane filled ballast outperforms asphalt filled ballast. In a test which included 2 groups, one of 10 with urethane filled ballasts and a group of 10 filled with asphalt Ballasts, the average urethane-filled ballast lasted 551 cycles from to failure, whereas the ballast filled with asphalt endured an average of only 76 cycles before failure.

To the effectiveness of the new potting compound according to the present invention noise measurements were made for the ballast carried out. A noise measurement of the ballast with the casting compound of the Example 1 at normal working temperatures in an anechoic room gave one Noise level of 7.5 db. A noise measurement of the same ballast was carried out performed, which was potted and cured in a similar manner, however without the addition of silicon dioxide. This ballast had a noise level of 12.5 db, which is an increase in the noise level of 100% compared to the potting compound according to the present invention means. In addition, the seams and the Feedthrough openings are sealed separately in order to prevent the Prevent leakage of the synthetic resin.

In addition, a ballast ttr a fluorescent lamp of the same Model built into the case without resin or sand. This ballast had a noise level of 28.0 db, which is a 16-fold increase in the cuddled sound compared to the ballast filled with the new potting compound. It it can be seen that the silica-urethane potting compound of the present invention Invention is even more powerful than those known from the prior art only made of synthetic resin masses.

The following are two more examples of blends for making given the new casting compound: Example II% Vorite 128 2.7 DB-Ö1 2.3 Dutrex 739 6.0 Dutrex 998 9.0 silicon dioxide, powder clear mesh size 0.84 - 0.44 mm (20-40 mesh) (20-40 Wetron) 48.0 silicon dioxide, powder clear mesh size 0.0725 mm (200 mesh) (Oregon "800") 32.0 Properties Time to gel at 25 ° C 16 hours

Processing time at 700 C 45 min.

Time to gel formation at 700 C 185 min.

Viscosity at 70 ° C (Brookfield Spindle No. 6) 5 revolutions per Min. (5 RPM) - 38,400 cps 100 revolutions per minute (100 RPM) - 6,600 cps.

Viscosity at 250 C similar to putty. Example III Vorite 128 2.7 DB-Ö1 2.3 Dutrex 739 9.0 Dutrex 998 6.0 silicon oxide, powder, mesh size 0.1450-0.0725 mm, (100-200 mesh) (Oregon "800") 80.0 Properties duration until gel formation at 250 C for 16 hours

Processing time at 700 C 45 min.

Time until gel formation at 700C 185 min.

Viscosity at 700 C (Brookfield Spindle No. 6) 5 revolutions per minute (5 RPM) - 160,000 cps.

100 revolutions per minute (100 RPM) - 9,600 cps.

Viscosity at 260 C similar to putty. For example III it should be noted that that the extremely high viscosity of the mixture makes it necessary, the housing shake to ensure that the housing is properly filled.

The potting compound according to each of these examples was found to be extreme satisfactory and during the curing of the resin there was no seal Feed-through openings in the housing for the ballast required.

Although in all examples certain blends of petroleum based oils have been used, it goes without saying that these oils or others individually or can be used in various mixtures as long as the viscosity gravity constant remains above 0.95. In order to obtain the desired casting properties, however, summarize the preferred form of the invention mixtures in the eye, the viscosity of which is adjusted is that at 700 C viscosities below 500 epg and at 250 C viscosities above 50,000 cps. Of course, a wide variety of mixtures can be used which meet this latter requirement.

Claims (12)

Claims J Potting compound for potting electrical parts it is not noted that the reaction product is essentially stoichiometric Amounts of a urethane prepolymer with free isocyanate groups, with a liquid one Polyol, a petroleum-based oil that has a viscosity constant of gravity of at least 0.95 and contains silica. 2. Potting compound according to claim 1, d a d u r c h g e k e n nz e i c h n e t that the urethane prepolymer is a tolylene diisocyanate adduct based on ricinoleate contains. 3. Potting compound according to claim 1, d a d u r c h g e k e n nz e i c h Not that the liquid polyol comprises a modified castor oil polyol. 4. Potting compound according to claim 1, d a d u r c h g e k e n nz e i c h n e t that the petroleum based oil had a viscosity of less than 500 cps 70 ° C and at least 50,000 cps at 25 ° C. 5. Potting compound according to claim 1, d a d u r c h g e k e n n -z e i c h n t t that they are at least 5% by weight of the reaction product of the urethane prepolymer with the liquid polyol and at least 15% by weight of the petroleum-based oil. 6. Potting compound according to claim 1, d a d u r c h g e k e n nz e i c h n e t that the silicon dioxide preferably has a grain size corresponding to a clear Mesh size in the range of about 0.84 t1s 0.047 mm (20-300 mesh). 7. A method for producing the potting compound according to claim 1, d a it is noted that a urethane prepolymer with free isocyanate groups and a liquid polyol, a petroleum-based oil that has a viscosity gravity constant of at least 0.95 and a silica mixed together will. 8. The method according to claim 7, d a d u r c h g e k e n nz e i c h n e t that the petroleum-based oil has a viscosity of less than 500 cps 700 C and at least 50,000 cps at 250 C. 9. The method according to claim 7, d a d u r c h g e k e n nz e i c h n e t that the urethane prepolymer is a tolylene diisocyanate adduct based on ricinoleate contains. 10. The method according to claim 7, d a d u r c h g e k e n n -z e d c Note that the liquid polyol contains a modified castor oil polyol. 11. The method according to claim 7, d a d u r c h g e k e n n -z e i c h n e t that the silicon dioxide has a grain size corresponding to a clear mesh size from 0.84 to 0.047 mm (20-300 mesh). 12. The method according to claim 7, d a'd u r c h g e k e n nz e i c h n e t that at least 5 total.% of the reaction product of the urethane prepolymer with the liquid polyol and at least 15 gel.% of the oil based on petroleum can be used on the total weight of the casting compound. L e r s e i t e