DE2016676A1 - Damping material - Google Patents

Description

Dr. Ing, E. BERKENFELD. Dipl.-Ing. M. BERKENFELD, patent attorneys, Cologne Attachment · File number

β. April 1970 Sch // ^Mpm · ^dAnm · Lord Corporation

Damping material

This invention relates to damping covers, particularly to polymeric materials used as damping covers and cores for brittle metal, plastic and other building materials to absorb resonance vibration.

Cushioning treatments using polymeric materials for Deflecting mechanical vibration energy is used to monitor the resonance behavior of sioh bending surfaces. They weaken or eliminate the radiance disrupt * the noise from vibrating surfaces as well as the transmission of undesired vibrations and increase the fatigue strength of the Construction materials.

A common damping method used is that coating the surface of the metal or material to be damped with a polymeric damping material. Damping materials used in this way have been called extensional damping materials and are usually characterized by high values of their dynamic properties Loss modulus, E, at the temperatures and frequencies of interest. The theoretical analysis of the resonance behavior a cantilever beam which is coated with a viscoelastic damping material is known. It was found that the Loss factor (the ratio of the deflected energy to the stored energy per vibration period) of the composite beam for practical purposes (including the application of light-weight coatings) are primarily a function of the proportions of the volume modula of the vlskoelastic material to the

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Storage modulus of the metal (or non-lossy material) and of the Ratio of the thickness of damping material and metal. if the dynamic properties of the damping material as a function the frequency and temperature are known "it is therefore possible to determine the dynamic behavior of a coated bar of any length" calculate. The theory was used to guide the development of damping materials for thin plates and other more complex structures.

It is currently possible to determine the position of the peak attenuation at eirxr desired temperature and frequency to a limited degree, to deliver. However, the temperature and frequency ranges over which a high spread is achieved are due to the limited Temperature and frequency bandwidths of the loss modulus of the damping materials available up to now are limited. This temperature bandwidth limitation, together with the requirement of a low additional weight, has the fields of application for additional damping treatments in aviation Storey, restricted traffic, ships, freezers, home appliances, and mason enclosures.

Another dampening method currently in use in structures employs viscoelastic polymeric materials, which are sandwiched between skins made of metal, plastic or other building material. Polymers used in this way are referred to as constrained layer damping materials. The relationships between the loss factor of the composite laminate and the viscoelastic properties of the core material and the geometrical conditions of the laminate are somewhat compared to the case of expansion damping more complicated, but the theoretical analysis was developed to calculate the dynamic properties of the layer structure, if the properties of the viscoelastic core are known. Polymeric substances for this application should generally be one high loss factor over the broadest possible temperature and Have frequency range. It is also possible to match the elastic Sohermodule to the geometrical given of the Sohiohtstoffes adjust to get optimal cushioning.

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So far, the properties of the damping materials have been direct. obtained by the fact that the loss behavior in dynamic-mechanical Testing watched. These include torsion pendulums, complex module flexible shaft devices (this device works with Beam diffraction for testing physical properties of elastomers) dynamic mechanical spectrometers and the like. Electric Conductivity measurements with direct current became apparent Not used to identify potential damping materials.

The use of dielectric methods to study potential mechanical damping ability in a polymer has heretofore been limited. This follows from the fact that efforts at direct Relationship of dielectric data with dynamic-mechanical relationships were successful in only a few cases. There were now certain techniques and parameters of dielectric measurements | and found values that provide a clear, beneficial measurement of the Create damping efficiency of polymeric materials.

Certain * polymeric substances have also been found which, especially as expansion damping coatings, have an unusual damping efficiency and the previously known Ma -? ---- ~ V materials are far in excess. These materials also possess superior Properties in the case of forced layer damping application, but to a less pronounced degree than in the case of expansion damping coatings the case is. It should be emphasized, however, that both expansion and forced layering applications the substances according to the invention are far superior to previously available materials.

For damping applications, as considered here, is it is important to have a wide temperature and frequency range of the To have cushioning. One of the problems of previous damping. materials was the lack of high attenuation magnitude over such a wide temperature and frequency range.

The relatively small temperature range of the previously known * vibration damping materials - around 12 ° C if the reference value η c «0.1 (m ₂ / m.« 0.3) is used - is a decided disadvantage for a large number of industrial applications. The after-L 66/2 _ ₅ _

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The question of improved damping materials is particularly evident in the field of modern transport, for example motor vehicles, aircraft, railway wagons, etc. Such vehicles are currently treated with damping materials whose maximum effect is set to room temperature (21 ^° C.). Be one drives these vehicles on cold winter days (for example, -235 ⁰ C) lowered or in hot zones (for example, with outdoor temperatures of 38 ⁰ C), then the Vibrationsdämpfungswirküng to an unacceptably small size. It is quite obvious that, particularly in the case of rapidly moving means of transport, good vibratory damping means are required which cover wide temperature ranges.

Another example are machine systems with thin-walled plate constructions, which heat up quickly during operation. A particularly good example of such a system is the home washing machine with a thin-walled plate housing, the normal operating temperature range of these machines is about 49 to 6O ⁰ C. Since it is required that the machines working noise both at start-up (at about 21 ⁰ C) as well as in continuous operation, a satisfactory vibration damping material needs to sweep over the entire range of about 21 ⁰ C to 6o ° C with its Vibrationsdämpfungswirküng. One can also find a compromise solution for machines. try this type by using a dampening agent which is effective at an intermediate temperature within the desired range. For the range mentioned in the latter example, an agent with maximum effect at a temperature of 41 C would have the greatest dampening effect in the middle of the desired temperature band, but it would remain unsatisfactory at the limits of the range, especially at the upper limit where the greatest There is a requirement for vibration damping effect.

A particularly difficult case exists in modern aircraft, which may leave the ground at a temperature of 29 ⁰ C and is located in a few minutes at an altitude of 10,000 meters and Tempeifturen of -40 ° C. In such cases, the previous materials are completely unsatisfactory. The substances according to the invention create a much broader temperature and frequency range than with conventional materials used in damping applications.-L 66/2 _4_

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th polymers can be achieved and solve many of these so far unsolvable problem-e of damping a vibration.

It has been found that cushioning coatings and sealants on the basis of polymers, which are derived from the monomers of the homologous methacrylate series, give compounds which high Attenuation expansion over considerably greater temperature and frequency ranges than any other known expansion dampening material. It has been found that homopolymers of the methacrylates and copolymers of the monomers of the methacrylate series with other monomers, especially styrene, and physical Mixtures of homopolymers of the methacrylate series with other homopolymers, especially polystyrene, these excellent damping, possess properties. Polymers of methacrylic acid esters show im ™ general multi-course damping mechanisms, a peak of mechanical loss in connection with movements of the polymer chain structure, a secondary peak which is generally attributed to the movements of the side chains of the ester. The two Loss peaks are usually resolvable in the neat polymer, although portions of the peaks overlap. This won't achieved with polymers that do not have secondary loss mechanisms own. It has been found that by adding plasticizers the main transient loss peak after low temperatures (Measurements carried out at constant frequency) with faster Speed is shifted as the secondary peak and at Plasticizer content, which is used for expansion damping applications | are of interest, this tends to add the two peaks together to give a wide temperature range over which provide high damping, especially in expansion damping applications, can occur.

The molecular structure and the concentrations of various plasticizers and fillers affect the temperature and frequency bandwidths of the damping connections. These effects seem however, to be separable from the polymer build-up effects observed in the methaorylate series of polymers leading to the much more effective temperature ranges for cushioning compounds prepared from these polymers. the Methaorylate series of damping materials is therefore not limited to one L 66/2 ■ - -5-

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special plasticizer or filler type limited. Cushioning covers differ from common colored or protective covers in that they must have a minimum thickness which is greater than that of ordinary paint coatings. Ordinary Paint coatings are of the order of a dried film with a thickness of 0.025-0.050 mm, while the minimum thickness for the effectiveness of a perceptible damping is 0.25 mm.

As a measure of the relative effectiveness of dampening coatings, a standard steel cantilever beam was coated on one side with the damping coating and the loss factor ^ c of the composite was measured using known techniques at various temperatures and frequencies. With the same mass ratios of coating to metal (the ratio of 0.3 as a standard counter was used) show coatings according to the invention in the assembled structure has a loss factor of 0.1 or greater over the temperature ranges from 69 to 86 ° F (20.6 ⁰ C to 30, ^{0 0} C), compared to a temperature range (determined in the same way) of 45 to 50 ⁰ F (7.22 ° C to 10.0 ⁰ C) for other known materials. They also show a composite loss factor of 0.2 or greater over a temperature range of 30 to 35 ° F (1.1t ° C to 1.67 ⁰ C), compared to 10 to 15 ° F (^ 12.2 ⁰ C to -9.44 ° C) for other known substances.

These damping covers are prepared in the following catfish: Plastic materials are made with a suitable plasticizer to define the region of maximum cushioning (in conjunction with the glass transition) in the desired temperature and frequency range softened. (Dielectric loss and DC conductivity measurements can be used to quickly determine the correct plasticizer content, which is required to determine the temperature of the peak attenuation). then filler is added to increase the dynamic loss modulus of the coating (a necessary requirement for non-enforced Damping pulls). It can also be possible, not To use softened polymer materials, which are already at their maximum Damping properties in the usual temperature and frequency range have by merely adding suitable fillers'. .5.

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+ Glass transition = glass transition.

This expression is explained on page 356 of the book "Synthetic Rubber "issued by John Wiley & Sons, Inc., New York; Chapman & Hall, Limited, London.

Damping materials based on methacrylate polymers, however preferably prepared in slightly different ways, are also equally effective in applications of forced layer damping (three-layer Schiohtstoffe). Since lower moduli are often required for damping materials, which for forced If shock absorption treatments are suitable, they will be filler-free or prepared with fillers of such type and quantity that the optimum module results. Fillers are also added around the temperature range (with a bit of flow, peak attenuation) ^ to widen. Plasticizers are forced in applications " Layer attenuation needed to set the temperature of the peak attenuation and control the module.

The subject of the invention is with reference to the special Example of damping materials according to the invention and under Hinwels more clearly understandable on the attached drawings.

Fig. 1 shows a curve of the loss factor of the composite structure as a function of the temperature for a test stick, which is coated with a composition according to the invention, in comparison to similar test sticks to those with previously available Damping agents are coated. |

Figures 2 to 7 show curves of the loss factor of the composite Structure as a function of the temperature for various compositions according to the invention.

FIGS. 8 to 11 show comparative curves of dielectric "tan cT" depending on the temperature for different Materials.

Figures 12 and 1> show curves of the volume stability in Dependence on the temperature for different substances.

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Below is an example of its special embodiments of the invention given.

Example 1 Qewioht parts

67/33 methyl methacrylate-styrene 100 copolymers

Plasticizer, butyl benzyl phthalate 60 Dixon Graphit 1101 I50

The damping properties of this connection are shown in Flg. 1 shown and there with typical, commercially available damping covers. compared which are currently in use and under the names LD 400 and LD 403 are sold.

From the comparison curves it can be seen that the effective temperature range of the inventive material is wider than that of both previous materials in combination.

Example 2 weight center Polymethyl methacrylate 100

Plasticizer, butyl benzyl phthalate 60 Dixon Graphit 1101 I50

Pig. 2 shows the damping properties of this preparation.

Example 3 Weight point Polystyrene 33 Polymethyl methacrylate 67 Plasticizer, butyl benzyl phthalate 60 Dixon graphite 1101 150

Pig. 3 shows the damping properties of the preparations.

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Example 4 Qewioht parts Polyethylene methaorylate 100 Celluflex GEP-Welohmacher 50 Dixon graphite 1101

Parts by weight 100 60 too 390

4 shows the damping properties of this preparation. Example 5

67/33 methyl methacrylate-styrene copolymers'

Plasticizer, butyl benzyl phthalate Vermiculite τυυ λ Methylene chloride (volatile solution

middle)

The foregoing example illustrates a spray coating wet.

Fig. 5 shows the damping properties of this preparation. Example 6 parts by weight

Poly-n-butyl methacrylate .100 Plasticizer! Butyl-benzyl-phthalite 20 Dixon oraphite 1101 150 6 shows the damping properties of this preparation.

The previous six examples illustrate materials which are particularly suitable for expansion steam applications are. The following example shows a slightly modified mass, which is particularly suitable for use with forced sole damping suitable

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ORlGiNA INSPECTED Example 7 weight parts -

67/53 methyl methacrylate-styrene-100

Copolymers Weichmaoher, butyl-benzyl-phthalate 60 Flg. 7 shows the Däflipfungselgensohaften of this preparation.

All of the above formulations were made on a two-roll Oummi mill. The polymer, plasticizer and filler were weighed out in the correct proportions and added directly to the mill. The mill wading were typically heated (to 38-121 ⁰ C _4, depending on the particular formulation) "is a fusion of the polymer with the Weichmaoher effect.

Example 5 * A solvent bath system for spray application was prepared as above and then in methylene chloride (Solvent) dissolved. It can also be prepared by the solid components are added directly to the solvent and everything is put together in a mixer (e.g. Baker-Perkins mixer) mixed.

Test samples are made by removing the coating (or core) binds in a form under heat and pressure directly to the metal base or bases. The samples are cooled under pressure to cause deformation prior to removal from the mold impede. Other processing methods (e.g. calendering, spraying, application with a spatula, extrusion, etc.) are possible. All samples are tested for their dynamic damping properties on a complex module apparatus from Bruel and Kjaer of the type 3930.

" The end-

The near dielectric loss behavior can be used to study the effects of polymer structure on molecular motion. It is known that polymefchyl methaorylate has two loss peaks, which are referred to as alpha and beta splits. The alpha peak occurs at the higher temperature and is added to the movement as long as the main chain includes polymers. The beta tip on the lower Tenpera-L 66/2. ₁₀ -

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The movement is assigned to the movement insofar as it includes the polar ester side groups, which are attached to the main chain of the polymer. It is also known that the same molekula-'re process that is responsible alpha-process for the alpha-loss peak, which in the main GlasUbergangszon'e ^+, as determined by dynamic mechanical and dielectric ^ testing, occurs. It has now been found that a study of the alpha process by dielectric methods can give valuable information about the chain dynamics in connection with the dynamic-mechanical behavior, especially in the case of polymeric materials based on methyl methacrylate and its homologues.

In addition, the dielectric method can also provide information about the Bearing the temperature and the temperature range indicate which is associated with the primary alpha loss peak and the secondary beta loss peak. The dielectric loss behavior of the The alpha process in a methyl methaurylate-styrene 67/35 copolymer is particularly striking. This copolymer shows an alpha process with a deflection or scattering factor, (tan ^ f) peak, which is considerably more intense than the alpha process in polymethyl methaorylate bmw. in polystyrene. Such behavior (which resembles a synergistic effect) indicates that the configuration of the copolymer is more favorable for energy dispersion. This example is shown in FIG.

+ Main glass transition zone.

This expression is explained in the book "Synthetic Rubber", out-

given by John Wiley * Sons, Inc., New York; Chapmann & Hall, ™ Limited, London.

As has already been emphasized, the addition of a stabilizer to a polymer has an effect on the intensity and temperature of the tan «f peak in connection with the alpha process. In the case of methyl methacrylate-based polymers, the additive is of a plasticizer sufficient to .zu the alpha peak temperature move to a lower temperature. If sufficient ·. When plasticizer is added, the alpha tip can converge with the lower temperature beta tip. The tan «f rent is increased and the loss curve widens

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in the temperature range considerably when this convergence takes place. The merging of the alpha and beta peaks also leads to a broadening of the temperature range in the dynamic mechanical loss behavior. Fig. 9 compares the dielectric Tan values of polymethyl methacrylate with and without 60 parts per 100 butyl benzyl phthalate plasticizers.

Figure 10 shows a similar comparison for the methyl methacrylate-styrene 67/63 copolymer. Figure 11 shows the same comparison for a physical mixture of polymethyl methacrylate and polystyrene in the ratio 2/1.

Measurements of DC conductivity (resistance) in polymeric materials through their glass transition zones have been indicated. In such previous reports, the points of conductivity (resistance) plotted against temperature only a change in slope in the glass transition zone.

It has now been found that conductivity studies which are carried out with dynamic Temperature sensing and continuous current monitoring - can lead to unusual behavior in the glass transition zone, which differs from a simple Changing the slope makes a difference. In particular, examples of reversal and gradual (plateau) behavior were given in the Glass transition zone of polymeric substances based on methyl methacrylate and its homologues.

The on Methylmethaci ⁱ ylat Styro-67 / J53 Copolymer conducted dc conductivity studies show a clear difference in response, compared with polymethyl methacrylate and polystyrene. This is illustrated in FIG. 12. The methyl methacrylate-styrene-67/33 copolymer shows a reversal of the course in the transition zone.

The addition of 60 parts of butyl benzyl phthalate as a softener to the polymer causes changes in the behavior of the direct current conductivity. This is shown in FIG. 1j5. The softened methyl methaorylate-styrene-67 / j53-copolymer shows a course, which a broad, stepwise (plateau) region in the glass transition-L 66/2 -12- .. '

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zone. As in the case of the dielectric measurements, the plasticizer has been added the glass transition zone shifted to a lower temperature range. Fig. 1j5 also shows the curve for Weiohgemaehtes ELymethyl methacrylate and the plasticized phy-. ; sikalische mixture of two parts and polymethylmethaoryiat one part polystyrene.

Similar observations of the reversal or of the step-by-step behavior in the glass transition zone in studies of the conductivity of oil currents with continuous monitoring of the current were found for other polymers, including polyethylene methacrylate, poly-n-butyl methacrylate, polyisobutyl methacrylate, polymethyl acrylate, copolymers of methyl methacrylate and methyl methacrylate Lund butyl methacrylate, copolymers of methyl methacrylate and the like η-butyl acrylate, the terpolymer of methyl methacrylate, methyl acrylate and styrene.

These reversals and the childlike behavior could be called Signs of the configurational mobility of the polar groups in reaction to the applied electric field when crossing the. Glass transition zone can be explained. If you find a reversal or a step or a step instead of the simple change in Drop in the application of the resistance to the temperature profile for polymethyl methacrylate, this is explained by that the network of the polymer is looser. A loosening of the polymer network can be done by softening from the outside or by structural softening through copolymerization or higher Ho- ™ mologe within a family, like methacrylates.

It has been found that these peculiar properties for the materials adapted for use in accordance with the invention are characteristic and can be applied to materials set up which are suitable for use according to the invention are/

In carrying out the invention, it is preferred to use polymeric substances which have glass and secondary transition points which are less than 139 ^° C., in most cases less

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than 111 ⁰ C, from each other.

It has been found that the amount of plasticizer should not exceed about 50 # of the total mass and preferably about 50 # should be. It has also been found that any conventional plasticizer can be used, which is suitable for the particular vehicle in Talking about polymers works as plasticizers.

Fillers of lower density are preferred as fillers in the damping masses according to the invention in order to maximize hassle / To achieve mass coefficients with the Netall to be damped. It has been found that graphite, carbon black, mixtures of graphite and carbon black, Silica, talc, and vermiculite are particularly satisfactory.

It has been found that the polymer to be used according to the invention expand two properties »ufl. Ss only polar function and have a secondary transition point below T. Further It has been found that methacrylate and acrylates are the most satisfactory basic starting materials for the invention.

The invention is not limited to the embodiments shown here by way of example. Within the scope of the invention are On the contrary, the Fadnann was given various changes without further ado.

Claims

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Claims (7)

Dr. Ing. E. BERKENFELD · Dipl.-Ing. H. BERKENFELDf Patentanwälte, KSIn Annex "'File number for entry from 6th 1. Damping material layer in combination with a Stiffening material consisting of pressure layers and fillers, characterized in that the damping material made of a polymeric material such as methacrylate, acrylate and Methacylate ester polymers and copolymers, which polar functions and in the solid state "clearly defined, im Having spaced apart glass and secondary transition points, and the polymeric material with a Plasticizer is mixed, which moves the two transition points together for the purpose of creating a combined transition effect, and the layer has a thickness of at least 0.25 mm. 2. Damping material layer according to claim 1, characterized in that the layer is sufficiently thick to cause a loss factor of 0.1 or more ^{in a temperature range of 20 - JO 0 C.} j5. Damping material layer according to claim 1, characterized characterized in that the polymeric material is disposed between constraining stiffening layers. 4. damping material layer according to claim 1, characterized characterized in that the polymer is polymethyl methacrylate, folymethaoryl acid or polyethyl methacrylate. L 66/2 -15- 109808 / 20SS 5. damping material layer according to claim 1, characterized in that the polymer is a copolymer of a homologue is of the methacrylate series and styrene. 6. damping material layer according to claim 1, characterized in that the polymer is a copolymer of homologues of the methacrylate series, which has glass and secondary transition points within 121 ⁰ C of each other. 7. damping material layer according to claim 1, characterized in that a filler is added which the material Gives stiffness. L 66/2 -16- 109808/2055 Blank page