WO2007138168A1

WO2007138168A1 - A vibration damping system

Info

Publication number: WO2007138168A1
Application number: PCT/FI2007/050307
Authority: WO
Inventors: Kari Saarinen; Lasse Lamula; Pasi Kosonen; Samu Aalto; Tomi Lindroos
Original assignee: VTT Technical Research Centre of Finland Ltd
Current assignee: VTT Technical Research Centre of Finland Ltd
Priority date: 2006-05-30
Filing date: 2007-05-29
Publication date: 2007-12-06
Anticipated expiration: 2008-11-30
Also published as: FI20065364A0

Abstract

A method for manufacturing an epoxy material for vibration damping, in which method the ratios of the components of the epoxy material are selected so that the Tg region of the epoxy material corresponds to the temperature and the vibration frequency of the vibrating body. The epoxy material comprises at least one epoxy resin mixed in a stoichiometric ratio with at least one flexibilizing curing agent in order to achieve the maximum of the mechanical damping within the Tg region.

Description

A VIBRATION DAMPING SYSTEM

Field of the Invention

The present invention relates to a method for manufacturing an elastic epoxy material for vibration damping and a vibration damping system which comprises a vibrating body and an elastic epoxy material in association with the vibrating body.

Background of the Invention

Noise and vibration problems in machines are often generated by vibrating surfaces of components that exhibit low inherent material damping. Vibration damping is usually divided into five different damping mechanisms. They include internal material damping, interface damping (friction damping), radiation damping, energy losses occurring as a result of reflection at discontinuities of structures, and viscous damping caused by viscoelastic material or by surrounding fluid.

Internal material damping, the transformation of mechanical energy into heat, is often described using a quantity called the loss factor, which indicates the fraction of the vibratory energy lost in one cycle of the vibration (L. Cremer, M. Heckl, E. E. Ungar, Structure-Borne Sound, Springer- Verlag, Berlin, 1988). This damping mechanism, as all the other damping mechanisms, is dependent on various factors like frequency, temperature and material composition.

Material damping is often presented as a single value in handbooks. These values can be used only for the rough comparison of different materials. In scientific papers the damping values are typically measured using various methods, which are not properly documented. The effect of specimen mounting, type of excitation and sensors are not examined. Furthermore the measurements are carried out at a single frequency. Several measures are introduced to describe the amount of damping. Loss factor (77), damping ratio {ζ), viscous damping (c), critical damping (c_c), specific damping capacity {ψ ), half power bandwidth (£>), logarithmic decrement [A), sharpness of resonance (O), tan delta and decay time [T) are the most common ones. Interrelations of these measures are as follows

9 ^- η = ,

where /is the natural frequency.

In this application, the terms loss factor or tan delta are used and their values are equal. The values are presented in decimal numbers, not in percentages.

Damping materials can be used for a wide variety of noise and vibration applications. Polymer based damping treatments are one of the most common methods to increase damping of the structure and thereby to decrease resonant vibration and noise. In practice, by using only polymer-based coatings on the surface of the structure, the desired reduction in vibration and noise cannot be achieved, or the thickness of the damping layer becomes impractically thick. The properties of polymers are highly dependent on temperature and also on excitation frequency, and as a result, one damping material cannot cover all of the needs.

A number of formulations of epoxy based damping materials are presented in articles and patent publications of prior art. In these publications enhanced damping capacity is based on the use of plasticizers, elastic resins, thermoplastic polymers or fillers. The use of plasticizers like phthalates, sebacates, and phosphates to adjust damping properties has generally been unsatisfactory with epoxies. Although plasticizers are fully compatible during curing, they separate from the resin onto the surface after the curing.

Typical flexible resins are epoxies derived from acidic functional oils (e.g. dimer acid, cashew nut shell oil, and castor oil), or polyalkylene glycols, such as polyethylene or polypropylene glycol. These flexible resins are generally used only as modifying resins, at levels of 10-30% wt. of the total epoxy content. Because these materials become part of the polymer, the effect on other properties is not as deleterious as using plasticizers, but separating from the resin is still effected. Usually, flexibility of epoxy materials is based on the use of this kind of flexible resins. Typical compositions for vibration damping based on flexible resins are disclosed e.g. in document WO02/50184.

Thermoplastic polymer additions can be separated into three classes: those that exist as a separate phase (e.g. amine terminated acrylonitrile-butadiene [ATBN] rubbers16), those that separate into a second phase during curing (e.g. carboxyl terminated butadiene- acrylonitrile [CTBN] rubbers17), and those that remain soluble throughout. It has been shown that these additions have a stronger effect on toughness than on elastic properties.

The above mentioned elastic epoxy materials contain volatile constituents and thus they are not stable materials. The adjustment of the glass transition region (Tg) of these materials at desired temperature range is challenging, and in practice it is impossible. The Tg region can be adjusted substantially correct, but the pinpoint adjustment of the Tg region on the temperature of the vibrating body is not specified in advance.

Summary of the Invention

The object of the present invention is to disclose a novel epoxy material for vibration damping, which provides high mechanical damping properties in the glass transition region (Tg) and is relatively easy to adjust with regard to the location of the glass transition region by altering the ratios of the components of the epoxy material. To achieve these aims, the method according to the invention is characterized in that at least one epoxy resin is mixed in a stoichiometric ratio with at least one flexibilizing curing agent in order to achieve the maximum of the mechanical damping within Tg region.

In epoxy materials prepared by the method according to invention, it is possible to optimize the damping capacity (loss factor and tensile modulus) of epoxy material in a desired operating environment, i.e. the Tg region of the epoxy material corresponds to the temperature and the typical vibration frequency range and amplitude of the vibrating body and its environment.

These epoxy material systems provide high mechanical damping properties at a desired temperature, the loss factor of the epoxy based damping material being greater than 1.0, preferably greater than 1 .2 within the Tg region. It has been found that the chemical composition of the epoxy material is one of the substantial factors by which high mechanical vibration damping is achieved within the Tg region. Especially, these high damping properties are based on the use of curing agents that yield increased elasticity and controllable visco- elastic damping properties. The use of these flexibilizing curing agents, i.e. modified oligomeric, polyamide-type and polyamidoamine-type curing agents, provides enhanced visco-elastic behaviour while the performance of the other properties of the epoxy system are maintained in acceptable level. Previously, these types of epoxy-amine systems have been utilized successfully in high flexibility coatings such as floorings, but in vibration damping applications such epoxy materials are not known.

Consequently, the elasticity of the epoxy material according to the invention is based on the use of the flexibilizing curing agent. In known elastic epoxy damping materials, the elasticity is based on flexible resins or fillers. The use of the epoxy-functionalized modificator in stoichtiometric mixture ratio with the epoxy resin also affects the elasticity of the epoxy material according to the invention, but it affects more the control of the location of the Tg region than the elasticity.

The main idea of the invention is that the epoxy systems are relatively easy to adjust with regard to the location of the glass transition region by altering the ratios of epoxy resins and modifiers and then adding a stoichiometric amount of curing agent, and the location of the Tg region can be predefined. The epoxy material comprises at least one epoxy resin and one flexibilizing curing agent, but preferably at least one modificator is also added to the epoxy material. A filler or fillers and additive agents such as fire retardants can also be added to the epoxy material. All the used components, except fillers, take part in cross- linking reactions and are nominally fully reactive, and they do not contain any volatile constituents. Thus, the epoxy materials prepared by the method according to the invention contain flexible macromolecule networks which are the explanation for a stabile structure of the material.

The location of the Tg region can be modified by using the same components of the epoxy material in the different mixture ratios. This type of a formulation principle results in families of generic materials where elasticity, the location of the glass transition region and the mechanical damping properties can be modified. Thus, the properties of the epoxy materials can be easily altered by various resins, curing agents and other reactive modifiers and by varying their stoichiometric concentrations. This has been shown to be an efficient method for the control of mechanical vibration damping.

Another object of the invention is to present the use of an epoxy material comprising a flexibilizing curing agent for vibration damping of a vibrating body as is described above.

Yet another object of the present invention is to disclose a vibration damping system comprising a vibrating body and an elastic vibration damping material in association with the vibrating body. The vibration damping system according to the invention is characterized in that a flexibilizing curing agent of the epoxy material has been mixed in a stoichiometric ratio with an epoxy resin so that the Tg region of the epoxy material corresponds to the temperature and the vibration frequency of the vibrating body.

In the epoxy material systems according to the invention, it is possible to exploit the maximum mechanical damping capacity around the Tg- peak at a desired temperature. The maximum of the mechanical damping can be adjusted by ± 10 ⁰C, preferably ± 5 ⁰C of the temperature of the vibrating body. The epoxy materials according to the invention provide an excellent vibration damping performance over a wide temperature and vibration frequency range. The temperature range from +0 ⁰C to +100 ⁰C is covered with different material combinations, where a loss factor greater than 1.0 is achieved.

The cross-linked elastic epoxy systems according to the invention are promising polymeric materials for various engineering applications in which high damping and elasticity but also high mechanical values and ease of processing of isotropic material are needed. Especially interesting is that the modification of the properties is relatively easy and results in generic properties, and the processing can take place on site. These epoxy materials are easily castable in between the surface layers and provide good adhesion on many surfaces. Furthermore, these materials are relatively cheap.

Epoxy systems are versatile because of the large number of potential epoxy resin, curing agent and modificator combinations. Examples of typical applications of epoxy materials include adhesives, functional joints, high damping constrained layers and shock absorbing pads, abrasion resistant coatings and flexible laminates. These formulations can also be used to modify existing formulated epoxy systems.

Brief Description of the Drawings

In the following, one embodiment of the invention will be described in detail. The appended drawings are part of the description. In the drawings, Fig. 1 shows DMTA testing of a series of elastic epoxy systems aiming at high damping between 15 -50 ⁰C, Fig. 2 shows a series of DMA curves for EEP021 used for a master curve construction, Fig. 3 shows a master curve of EEP021 displayed as a function of storage modulus E' and reduced frequency, and Fig. 4 shows a master curve of EEP021 displayed as a function of loss factor Tan delta and reduced frequency.

Detailed Description of the Invention

In this application, the terms epoxy material and epoxy systems are synonyms for each other. Furthermore, as previously mentioned, the values of loss factor and tan delta are equal. The term "maximum of mechanical damping" also refers to loss factor.

The epoxy materials according to the invention are purpose-made functional materials which contain at least two main components: an epoxy resin and a flexibilizing curing agent. These two components formulate one stoichiometric mixture, which covers a certain Tg region. The location of the glass transition region (Tg) can be adjusted by altering the ratios of epoxies and modificators and then adding stoichiometric amounts of curing agents. By varying the stoichiometric quantities of different modificators and curing agents with base epoxy resins, it is possible to adjust the glass transition region accurately to exploit peak loss factors at desired operating temperature, frequency and amplitude. The stoichiometric mixture ratio is dependent on the used components and it has to be determined separately for each epoxy system.

The design principle of the most suitable epoxy system contains two main steps:

1. Measurement of the temperature or temperature range of the vibrating body or structure, followed by the selection of the epoxy system having Tg at the higher temperature limit of the desired temperature range. After that, the suitable materials are selected by using databases and the know-how of the person skilled in the art.

2. Measurement of the typical vibration frequencies and amplitudes of the vibrating body, followed by the fine tuning of the dynamic Tg of the damping material by using modifiers. Recorded master curves for different epoxy systems can be used in this step.

Generally, the uniform quality and experienced selection of the starting materials are the key factors to constructing this kind of an epoxy system. The successful pinpointing of performance with regard to the measured temperature and strain rate is the result of a specialist's extensive knowledge on the chemical and physical properties of resins, modifiers and curing agents.

According to the first principle, the peak Tg temperature decreases with an increased amount of the modificator in stoichiometric mixtures. This effect is usually quite linear. This kind of a modification principle will set the maximum starting temperature, which is the peak Tg location of the plain mixture of epoxy resin and flexibilizing curing agent. Addition of the modificator will decrease the Tg temperature associated with the peak damping value. The peak Tg temperature is increased by adding non-flexibilizing curing agent to the mixture, the modificator is also used in epoxy materials for higher Tg temperatures.

According to the second principle, there are one epoxy resin, one modificator and two curing agents (flexibilizing and non-flexibilizing curing agent). The peak Tg temperature is adjusted principally by premixing two curing agents. The Tg is adjusted by mixing the ratio of these curing agents. Flexibilizing curing agent is needed here to maintain the Tg peak tan delta value, i.e. loss factor, above 1.0.

Preferably, epoxy material is a composition of three components comprising an epoxy resin, a flexibilizing curing agent and a modificator, but the epoxy material can be a composition of over 10 different components. The number of the components is dependent on the Tg temperature as is shown above. The different Tg region can be achieved by using same components of the epoxy material in different mixture ratios. This type of a formulation principle results in families of generic materials, wherein one epoxy system corresponds to the one Tg temperature. Alternatively, the adjustment of the Tg region can be used by altering various resins, curing agents and other reactive modifiers and varying their stoichiometric concentrations.

The first reactive component of the material, i.e. the epoxy resin, can be selected from the following: epoxy resins of the bisphenol A type, epoxy resins of the novolac type, epoxy resins of the bisphenol F type, alicyclic epoxy resins, epoxy resins of the glycidyl type, epoxy resins of the biphenyl type, epoxy resins containing a naphthalene ring, epoxy resins containing a cyclopentadiene group, polyfunctional epoxy resins, and any combination of these.

The second reactive component of the material, i.e. the flexibilizing curing agent, can be selected from amine-functionalized elastomers and oligomeric polyamides or oligomeric polyamidoamines.

The third reactive component of the material, i.e. the modificator or adduct, can be selected from the following: epoxy-functionalized polyetherpolyols, epoxy-functionalized oils such as epoxidized castor oil, epoxidized linseed oil, epoxidized soybean oil, carboxyl- functionalized butadiene-acrylnitrile elastomers, and epoxidized polysiloxane copolymers.

The non-flexibilizing curing agent i.e. rigid curing agent can be any kind of non-flexibilizing curing agent, which is synergistic. For example aliphatic amines and cycloaliphatic amides are potential non- flexibilizing curing agents for increasing the peak Tg temperature.

All the abovementioned components of the epoxy material take part in cross-linking reactions and they are chemically fully reactive and achieve a thermodynamic equilibrium.

Furthermore, the epoxy material may include specific filler(s) and additive agents. The addition of the non-reactive filler or additive agent affects only the stiffness or strength properties of the epoxy material. The location of the Tg region is not dependent on them, and thus any kind of non-reactive filler or additive agent can be added to mixture if it enables some other desired properties for the epoxy material. On the basis of that, for example solid antibacterial agents, fire retardants and agents affect strength and tensile properties, but they are neutral in relation to the location of the Tg region. However, all reactive additive agents, which e.g. take part in cross-linking reactions and affect thermodynamic equilibrium, have to be taken into account in stoichiometric mixture ratio. Examples of these reactive additive agents are various oils and waxes, solvents and compounds reacting with amines or amides. Preferably, elastic epoxy systems are unfilled.

The various elastomeric polymer chains could be functionalized with various reactive chemical groups applicable in epoxy formulations, providing essentially high inherent elasticity and toughness for a cured system. In addition, suitable functionalization of polymers increased inherent compatibility as well as significantly reduced migration and blistering.

The components of the specially designed purpose-built epoxy material are mixed and cured. These elastic epoxy systems are curable at room temperature. However, they can be prepared from their components at an elevated temperature as well, for example from 70 to 120 degrees Celsius. One advantage of the material is that its components, including the modificator, are reactive and form a fully cured epoxy- based elastomer material. Non-reactive softeners or plasticizers or other modifying agents that would migrate or leak out or evaporate from the material will not be needed.

These epoxy materials, which contain the flexibilizing curing agent, provide high mechanical damping properties at a desired temperature, the loss factor of the elastomeric vibration damping material being greater than 1.0, preferably greater than 1.2. A high maximum loss factor value in the glass transition region is a consequence of a thermodynamic equilibrium between molecules. A loss factor greater than 1.0 is achieved in the temperature the range from + 0 ⁰C to +100 ⁰C, preferably in range from + 10 ⁰C to +80 ⁰C. The maximum of the mechanical damping can be adjusted by ± 10 ⁰C, preferably ± 5 ⁰C of the temperature of the vibrating body.

The viscosity of the system can be adjusted to facilitate processing by e.g. vacuum resin infusion, spray coating as well as compression, injection or resin transfer moulding. The viscosity of the epoxy system is preferably adjusted between 500 and 100,000 cPs.

These epoxy materials approved good adhesion on many surfaces, and they are easily castable in various forms in different closed and open moulds. Thus they can be used for vibration damping systems, where an elastic vibration damping material is associated with the vibrating body. The epoxy materials manufactured at different temperature ranges can be put together to establish so-called sandwich structures. After curing, the epoxy material can be formed by mechanical processing methods like conventional epoxy materials.

The present invention is illustrated by the following example, which is included for illustrative purposes only and in no way intended to limit the present invention.

A series of six generic epoxy systems where Tg location is controlled by different stoichiometric concentrations of starting material is presented in this example. The Tg region was adjusted by altering the ratios of epoxies and modifiers and then adding a stoichiometric amount of flexibilizing curing agent.

Stoichiometric mixtures of bisphenol A/F epoxy resin blend, difunctionalized epoxidized alcohol, diglycidyl ether of polypropylene oxide and elastomer functionalized polyamide curing agent were prepared. The aim of this series of experiments was to adjust the peak

Tg to room temperature. The series of samples was named as EEP019

- EEP024.

Recipes given in parts per hundred (phr) are shown in the following table.

The viscosity values between resins, adducts and curing agents are very different, and thus the selection of correct parameters for mixing is very important. The mixing of the system components has to be completed fast enough but still by avoiding high shear and bubble disintegration. In addition, selecting the correct curing schedule is important due to the preferred level of phase separation for functionalized elastomeric component.

The cured samples were cut into specimens and tested for dynamic modulus and damping properties with Polymer Laboratories MK N-III DMTA (Fig. 1 ). As a result, it was found to be possible to exploit maximum mechanical damping capacity around Tg-peak at the desired temperature. Addition of the modifier gradually decreased the Tg from 44.1 ⁰C to 18.6 ⁰C. The best recipe for room temperature application was EEP023, which had a peak Tg temperature at 24.2 ⁰C and tan delta of 1.27.

Measurement and calculation of frequency dependent master curves are shown in Figures 2 to 4. In this case, the measurement was carried out using 01 dB Metravib Viscoanalyzer VA4000.

In Fig. 2, the mixture EEP021 presented in Fig. 1 is separately measured in the Viscoanalyzer VA4000 over a range of base measurement frequencies. This kind of a measurement is used in master curve construction based on Williams-Landell-Ferry (WLF) equations. The WLF master curves estimate the frequency response of the storage modulus and loss factor well beyond the measured frequency range, as is well known by a person skilled in the art.

In Figs. 3 and 4, the examples of the master curves are based on the measurement shown in Fig. 2. The storage modulus E^' is shown as a function of reduced frequency in Fig. 3, and the loss factor tan delta in Fig. 4. As optimal damping performance for certain applications may be a compromise between maximum storage modulus and loss factor, a reference temperature of 20 ⁰C was chosen for the master curve calculation.

Tensile testing was performed with an lnstron 4505 universal testing machine. Testing was done at ambient conditions. For EEP019 - EEP024 the testing speed was maintained at 25mm/min (1.04%/s nominal strain rate) for all samples. Tensile modulus determination was performed between 0.1 and 0.3 MPa of tensile strength.

The following table shows the results of the generic set off materials, where the set itself was designed to pass over the Tg region at room temperature.

On the grounds of the data presented above, it can be concluded that the use of the flexibilizing curing agent enables the loss factor above 1 .0. By mixing epoxy resin, flexibilizing curing agent and modificator, the peak Tg temperature can be adjusted at the desired temperature range. The invention is not restricted to the example and compositions of the above description, but it can be modified within the scope of the inventive idea presented in the claims.

Claims

Claims:

1 . A method for manufacturing an epoxy material for vibration damping, in which method the ratios of the components of the epoxy material are selected so that the Tg region of the epoxy material corresponds to the temperature and the vibration frequency of the vibrating body, characterized in that at least one epoxy resin is mixed in a stoichiometric ratio with at least one flexibilizing curing agent in order to achieve the maximum of the mechanical damping within the Tg region.

2. The method according to claim 1 , characterized in that the maximum of the mechanical damping i.e. loss factor is greater than 1.0, preferably greater than 1.2 within the Tg region.

3. The method according to claim 1 or 2, characterized in that the Tg region of the epoxy material is adjusted by adding a modificator to the epoxy material.

4. The method according to claim 3, characterized in that the addition of the modificator decreases the peak Tg temperature.

5. The method according to any of the preceding claims, characterized in that the Tg region of the epoxy material is adjusted by adding a non-flexibilizing curing agent to the epoxy material.

6. The method according to claim 5, characterized in that the addition of the non-flexibilizing curing agent increases the peak Tg temperature.

7. The method according to any of the preceding claims, characterized in that a filler or fillers are added to the epoxy material.

8. The method according to any of the preceding claims, characterized in that additive agents, such as fire retardants or other additive agents, are added to the epoxy material.

9. The method according to any of the preceding claims, characterized in that the maximum of the mechanical damping is ± 10 ⁰C, preferably ± 5 ⁰C of the temperature of the vibrating body.

10. The method according to any of the preceding claims, characterized in that the loss factor greater than 1.0 is achieved at the temperature range from +0 ⁰C to +100 ⁰C.

1 1. Use of an epoxy material comprising a flexibilizing curing agent for vibration damping of a vibrating body.

12. The use according to claim 1 1 , characterized in that the epoxy material comprises at least one epoxy resin and one flexibilizing curing agent.

13. The use according to claim 1 1 or 12, characterized in that the epoxy material comprises at least one reactive modificator.

14. The use according to any of the preceding claims 1 1 -13, characterized in that the epoxy material comprises at least one non- flexibilizing curing agent.

15. The use according to any of the preceding claims 1 1 -14, characterized in that the flexibilizing curing agent is a curing agent of the oligomeric polyamide type or oligomeric polyamidoamine type.

16. The use according to any of the preceding claims 1 1 -15, characterized in that the epoxy resin is selected from the following: epoxy resins of the bisphenol A type, epoxy resins of the novolac type, epoxy resins of the bisphenol F type, alicyclic epoxy resins, epoxy resins of the glycidyl type, epoxy resins of the biphenyl type, epoxy resins containing a naphthalene ring, epoxy resins containing a cyclopentadiene group, polyfunctional epoxy resins, and any combination of these.

17. The use according to any of the preceding claims 13-16, characterized in that the modificator is selected from the following: epoxy-functionalized polyetherpolyols, epoxy-functionalized oils such as epoxidized castor oil, epoxidized linseed oil, epoxidized soybean oil, carboxyl-functionalized butadiene-acrylnitrile elastomers, epoxidized polysiloxane copolymers.

18. The use according to any of the preceding claims 1 1 -17, characterized in that the epoxy material comprises additive agents such as fire retardants or other additive agents.

19. The use according to any of the preceding claims 1 1 -18, characterized in that the components of the epoxy material are chemically fully reactive.

20. The use according to any of the preceding claims 12-19, characterized in that the loss factor of the epoxy material is greater than 1.0, preferably greater than 1 .2 within the Tg region.

21. A vibration damping system comprising: - a vibrating body, and - an elastic vibration damping material in association with the vibrating body, characterized in that a flexibilizing curing agent of the epoxy material has been mixed in a stoichiometric ratio with an epoxy resin so that the Tg region of the epoxy material corresponds to the temperature and the vibration frequency of the vibrating body.

22. The vibration damping system according to claim 21 , characterized in that the loss factor of the epoxy material is greater than 1.0, preferably greater than 1 .2 within the Tg region.