CA2331448A1

CA2331448A1 - Acoustic dampening compositions containing recycled paint polymer

Info

Publication number: CA2331448A1
Application number: CA002331448A
Authority: CA
Inventors: Luke Strzegowski; James F. Hubert
Original assignee: Individual
Current assignee: Henkel Corp
Priority date: 1998-05-13
Filing date: 1999-05-07
Publication date: 1999-11-18
Also published as: AR016479A1; KR20010043567A; WO1999058597A1; BR9910374A; AU3859299A; TR200003311T2; EP1090067A1

Abstract

Acrylic resin-based plastisol compositions are improved by the incorporation of recycled paint polymer containing uncured resin (i.e., substances containing functional groups capable of undergoing chemical reaction). The compositions may be used to apply coatings to stiff articles having a tendency to vibrate such as metal automobile parts and the like. Such coatings are effective in suppressing mechanical vibration, reducing the noise of particle impact, and/or lowering the amount of air vibration in a cavity.

Description

ACOUSTIC DAMPENING COMPOSITIONS CONTAINING RECYCLED
PAINT POLYMER
Field of the Invention The present invention pertains to plastisol compositions based on acrylic resins such as polymethyl methacrylates which are capable of being sprayed onto automotive underbodies and the like. More particularly, the invention relates to the use of recycled paint polymer containing uncured resin to improve the acoustic dampening performance of such piastisols.
Nearly all vehicles, machines and appliances produced currently are comprised of relatively thin metal sheeting or plates. These thin plates often have a pronounced tendency to vibrate due to the effect of mechanically moving parts or running engines. Such vibration Leads to the undesirable generation of sound. Another source of noise, particularly in automobiles and other vehicles travelling on a road or other surface, is the debris such as gravel, sand, water and the like which is thrown up by the wheels of a vehicle against the wheel wells and the underbody of the vehicle. Sound may also be generated by the vibration of air within the cavities of a moving vehicle.
Numerous ways in which the noise associated with vibratory solid articles 2 o may be reduced have been proposed in the past. One common approach is to cover the thin metal plating used in vehicles, appliances and other machinery with a layer of a coating which deadens or absorbs sound. Visco-elastic coatings based on various polymers have often been employed for such purposes. Plastisols based on PVC (polyvinyl chloride), for example, have been modified to have better soundproofing properties in the working temperature range of -20°C to +60°C than conventional sprayable coating materials based on PVC resins (see, for example, U.S. Pat. No. 5,756,555). Acoustically active sprayable plastisol compositions based on styrene copolymers, alkyl methacrylate homopolymers, and/or methyl methacrylate copolymers are also known from U.S. Patent Number 5,741,824 (Butschbacher et al.). While such materials are effective as soundproofing coatings, there is still a need for further improvements in the field. For example, it would be desirable to develop alternative coating formulations which have a lower cost of production or which are even better at suppressing noise and vibration.
SUMMARY OF THE INVENTION
The invention provides a plastisol composition useful for suppressing mechanical vibration, reducing particle impact noise, or lowering air vibration in a cavity. The composition is comprised of one or more acrylic resins such as polymethyl methacrylate, recycled paint polymer containing uncured resin, one 2 0 or more plasticizers and one or more fillers. Damping constructions comprising at least one layer of the plastisol composition applied to a vibratory solid article are also provided. Additionally provided is a method of coating a vibratory solid article to suppress mechanical vibration, reduce particle impact noise; or lower air vibration in a cavity of said vibratory solid article, said method comprising applying at least one layer of the aforedescribed plastisol composition to said vibratory solid article and gelling (curing) said pfastisol composition, preferably by heating. Also furnished by the present invention is a coating obtained by gelling (curing) the plastisol composition.
Figure I is a graph showing the relationship between loss factor and temperature for the plastisol compositions discussed in Examples 1 and 2 and Comparative Examples 3 and 4. Figure 2 provides similar information for different thicknesses of the plastisof composition of Example 5.
The plastisol composition contains an effective amount of one or more acrylic resins, i.e., polymers formed by polymerization of monomers based on a,~i-unsaturated carboxylic acids. Such monomers may be homopolymerized or copolymerized, either with other monomers based on a,~i-unsaturated carboxylic acids or with other types of monomers such as olefins, vinyl esters, vinyl aromatics (e.g., styrene) and the like. Preferably, the monomer is an ester of an alpha, beta-unsaturated monocarboxylic acid, particularly a lower alkyl ester (e.g., methyl, ethyl, propyl, butyl, including both straight chain and branched isomers). The use of esters of acrylic acid and methacrylic acid is preferred, especially C, - C,o aliphatic esters. Particularly useful are methyl methacrylate homopolymers and copolymers (e.g., methyl methacrylate/butyl methacrylate copolymers). The acrylic resin is desirably a thermoplastic rather than a thermoset, although lightly cross-linked acrylic resins may also be employed. The glass transition temperature of the acrylic resin used in the invention is preferably at least about 80° C, more preferably at least about 100°
C, most preferably at least about 120° C. The acoustic damping properties of the cured plastisol composition generaliy improve as glass transition temperature increases. The use of acrylic resins having lower glass transition temperatures may, however, improve certain other properties such as elongation. The acrylic resin typically will have a number average molecular weight in the range of about 40,000 to 2,000,000 and may be made by conventional suspension or emulsion free radical polymerization. Preferably, the acrylic resin is in the form of fine particles or a powder when used to prepare the plastisol composition. The particle morphology (e.g., surface area, particle size and distribution, porosity) should be selected such that the resulting plastisol has acceptable stability prior to use (e.g., during storage). Particle sizes of from about 0.1 to about 500 microns are generally suitable.
While the amount of acrylic resin in the plastisol composition is not believed to be particularly critical, with the optimum amount varying greatly depending upon the acrylic resin selected, the relative amounts of the other 2 0 components as well as the properties desired in the cured plastisol, typically from about 10 to about 50% by weight of the plastisol composition will be acrylic resin.
A critical feature of the present invention is the incorporation of an amount of a recycled paint polymer containing uncured resin effective to improve the WO 99/58597 PG"f/US99/07027 acoustic activity of the plastisol composition as compared to a comparable plastisol composition containing an amount of acrylic resin equal to the total amount of acrylic resin plus recycled paint polymer in the plastisol composition of the present invention. Put a different way, sufficient recycled paint polymer 5 must be substituted for acrylic resin in the formulation so as to improve the sound deadening performance of the resulting plastisol composition when cured.
White this minimum amount will vary from one plastisol formulation to another depending upon a number of factors, typically at least about 1 % of the plastisol composition by weight will be recycled paint polymer. Generally speaking, no 1 o more than about 25% of the plastisol composition is recycled paint polymer, although higher levels could be utilized if so desired.
The recycled paint polymers containing uncured resin which are utilized in the plastisol compositions of this invention are well-known in the art and are more fully described, for example, in U.S. Patent Numbers 5,160,628, 5,254,263, and 5,880,218, the teachings of which are incorporated herein by reference in their entirety. Such materials are obtained from paint sludge, which is recovered from automotive painting operations and the like as described in the aforementioned patents. Paint sludge is a complex mixture, the chemical composition of which is difficult to describe in detail. Uncured polymer resins, 2o pigments, curing agents, surfactants, and other minor ingredients are known to be present, however, in addition to water and organic solvents. In the automotive industry, for example, paints which are commonly employed include thermosetting modified alkyd resins and acrylic resins. The.latter resins typically consist of acrylic-melamine or acrylic-isocyanic acid copolymers. The modified alkyd resins are generally obtained from polyalcohols, polybasic acids such as phthalic acids, and monobasic fatty acids and are used in combination with cross-linking agents such as amino resins (including urea and melamine resins).
Other paint resin systems frequently used in the automotive industry include phenolic resins, polyurethanes, epoxy resins, and hybrid systems such as acrylic/amino, acrylic/epoxy, alkyd/acrylic, alkyd/epoxy, and polyester/epoxy resin combinations. Automotive paints are described in more detail in the chapter entitled "Coatings" in Volume 3 of the Encyclor~edia of Polymer Science and Engine, Second Edition (published by Wiley-Interscience in 1985). In one embodiment of the present invention, the recycled paint polymer has been recovered from an automotive finishing operation and is comprised of an acrylic resin. Prior to use in the present invention, the paint sludge may be processed to remove, or reduce the level of, certain components. For example, the paint sludge may be detackified (i.e., treated with detackification agents) or concentrated or dried by heating or the like to remove water and other volatiles.
In one embodiment, the recycled paint polymer has a volatiles content of less than 1 % by weight. In another embodiment, the recycled paint polymer is in the form of a sludge powder. In yet another embodiment, the recycled paint polymer is in putty form (as descibed, for example, in U.S. Pat. No. 5,880,218). It is 2 o important, however, that this further processing not render the uncured resin in the recycled paint polymer unreactive. For this reason, the addition of a base to the recycled paint polymer in order to decatalyze said polymer, as described in U.S. Pat. No, 5,880,218, is preferably avoided.
Recycled paint polymer products suitable for use in the present invention are also available from commercial sources such as EPI of Toledo, Ohio, which markets such a material under the trademark "EPIMER 200P".
One or more plasticizers are also present in the plastisol composition and are used in an amount effective to provide a workable viscosity. That is, s sufficient plasticizer is utilized to permit the solid components of the composition (e.g., acrylic resin, fillers) to be applied as a coherent coating to, and to adhere to, a vibratory solid article by means of spraying, brushing, dipping or the like.
The amount and type of plasticizer(s) selected may also be readily varying to impart the desired acoustic and other properties to the final cured plastisol l0 coating. Typically, plasticizer levels will range from about 10% to about 60% by weight of the plastisol composition.
Suitable plasticizers are generally any of the plasticizers known in the art to be effective in plasticizing plastisol compositions. Phthalates, particularly alkyl and aryl phthalates such as dibutyl phthalate, dioctyl phthalate, benzylbutyl 15 phthalate, dibenzyl phthalate, diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), and diundecyl phthalate (DIUP) as well as benzoate esters such as dibenzoate esters of glycols are preferred. However, other known classes of plasticizers such as C3-C24 esters of adipic, azelaic, sebacic, trimellitic, citric and phosphoric acid, alkyl esters of fatty acids, alkyl sulfonic acid esters of 2 0 phenols, epoxidized triglycerides, dibenzyl toluene, or diphenylether are also suitable. Mixtures of plasticizers may also, of course, be used. The selection criteria for the plasticizers preferably used are determined on the one hand by the types and amounts of the acrylic resin, recycled paint polymer, and filler, and on the other hand by the viscosity and gelation conditions of the plastisof and by the acoustic properties and other characteristics desired in the cured coating.
The plastisol compositions of the present invention also will generally contain one or more different fillers. Fillers may be used to improve the weathering characteristics, reduce the surface tack, or increase the hardness of the fused plastisol film. Any of the known plastisol fillers may be employed including without limitation, titanium dioxide, diatomaceous earth, calcium carbonate (which may be coated, ground, and/or precipitated), calcium oxide (which may also function as a drying agent), mica, vermiculite, heavy spar, carbon black {which may also function as a pigment), silica (e.g., fumed sitica, sand), clay, talc, alumina, bentonite, glass (in the form of powder, fibers, beads, including hollow microspheres, or the like), expanded and/or expandable thermoplastic resin microspheres and the like. Typical filler levels will range from about 5 to about 50% by weight of the plastisol composition.
The plastisols according to the invention may also contain one or more reactive additives in addition to the recycled paint polymer (which may itself contain reactive components) such as, for example, thermosettabie resins such as epoxy resins, melamine-aldehyde resins, polyfunctional isocyanates, phenolic resins (e.g., phenol-aldehyde resins) and the like. Typical levels of reactive additives are from about 0.5 to about 5 percent by weight of the plastisol composition. Curatives, crosslinking agents and/or catalysts may be used to harden or cure the reactive additives. For example, polyfunctional amines and alcohols (e.g., diamines, glycols, polyether polyols, polyester polyols) may be utilized in combination with epoxy resins or polyfunctional isocyanates, while acid catalysts may be employed to cure melamine-aldehyde resins.

WO 99!58597 PCT/US99/07027 In addition, the plastisols may optionally contain other auxiliaries and additives typically encountered in plastisol technology, including, for example, adhesion promoters (silanes, titanates, zirconates), pigments, antiagers (stabilizers, antioxidants, corrosion inhibitors), flow aids (rheological control agents, surfactants), thixotropic agents, and blowing agents. The blowing agents are utilized when a foamed plastisol coating is desired. Foaming often can enhance the vibration-damping properties of the cured plastisol. Suitable blowing agents are any of the blowing agents known in the field, preferably organic chemical blowing agents selected from azo compounds, N-nitroso l o compounds, sulfonyl hydrazides, and sulfonyl semicarbazides. Blowing agent activators or accelerators which reduce the temperature at which the blowing agent is decomposed to release gas may additionally be incorporated into the plastisol composition.
The manner or order in which the aforedescribed components are combined with one another is not believed to be critical; any of the conventional plastisol preparation methods known in the art may be utilized. For example, the components may be added simultaneously or sequentially and admixed using a dispersion blade mixer, planetary mixer, kneader style mixer or the like until the desired consistency and uniformity are attained. While the mixing temperature 2 0 may be slightly elevated to reduce viscosity, temperatures high enough to cause premature fusion or gellation should obviously be avoided.
The plastisol compositions of this invention are suspensions of the acrylic resins) in the plasticizer(s). The suspensions are sufficiently fluid (i.e., flowable) to be applied at relatively low temperature by spraying, spreading, brushing, dipping, wiping or the like to a substrate to be coated, yet high enough in viscosity that a layer of the desired thickness may be readily achieved.
However, it is also possible to apply multiple layers of the plastisol, curing or increase the thickness of the coating by applying one layer, heating the applied 5 layer to induce gelation or curing, and similarly applying and curing one or more additional layers. The thickness of the coating will depend upon a number of factors, particularly the end-use application as well as the degree of noise reduction desired, but typically will be from about 0.05mm to about 100mm;
thicknesses of from about 0.5mm to about 25mm are also commonly employed.
1o The liquid plastisol which has been applied to the substrate is then converted to a visco-elastic material through exposure to heat or the like.
Temperatures of from about 50°C to 250°C (more preferably, about 100° C to 220° C) will generally suffice for such purpose. Heating is continued for a time effective to at least render the plastisol non-liquid or non-tacky and, more preferably, to fully develop the desired properties in the cured coating. This step may also be referred to as "gelling° or "curing". Without wishing to be bound by theory, it is believed that heating causes the suspended particles of acrylic resin to be fused or dissolved in the plasticizes. Some reaction of the uncured resin in the recycled paint polymer as well as any thermoset resin present in the 2 0 plastisol may also be taking place. Upon cooling, however, a solid coating is obtained which affords excellent sound deadening and exhibits good durability and adhesion to the substrate.
The plastisols according to the invention are particularly suitable as coatings for steel and other metal sheets. For example, they may be used as underbody coatings on automobiles, trucks, buses and other vehicles. In one particularly desirable application, the plastisol composition is sprayed onto the underside of an automobile (including, for example, the floor pan and wheel wells) and cured to provide a coating which effectively reduces the sound emission and mechanical vibration emanating from that area of the automobile during use. The plastisol composition may, of course, also be applied to an individual automotive part (e.g., fender, rocker panel) prior to assembly.
Example 1 and 2 illustrate embodiments of the acoustic dampening compositions of the present invention which differ primarily by the inclusion of a small amount of chemical blowing agent (oxybisbenzenesulfonyl hydrazide) in Example 2. The components of each of these examples are listed in Table 1.
The presence of the chemical blowing agent results in the composition expanding approximately 50% in volume when cured (gelled). The compositions were prepared using standard plastisol mixing procedures and cured using standard automotive paint conditions of 30 minutes at 130° C. The loss factor of each composition when cured was measured in accordance with ASTM E756.
Figure I is a plot of the loss factor over the temperature range -10°C
to +40°C.
For comparative purposes, an acoustic dampening composition which did not contain any recycled paint polymer was prepared and tested as described in Example 1 (comparative Example 3). The amounts of each of the polymethacrylate acrylic resins in the formulation were increased by 5 weight to compensate for the elimination of the recycled paint polymer. It may be readily seen from Figure I that the cured composition of Comparative Example 3 was significantly less effective in dampening noise, as measured by the loss factor, than the composition of Example 1 containing the recycled paint polymer.
Comparative Example 4 employed TPN 4869 PVC-based underbody coating, which is commercially available from Henkel Surface Technologies and which does not contain recycled paint polymer. While the TPN 4869 coating exhibited a higher loss factor than the compositions of Examples 1 and 2 at low temperatures, at room temperature and higher the compositions of the present invention were more effective in reducing noise.
to Example 5 illustrates yet another embodiment of the present invention which utilizes a melamine-formaldehyde resin instead of the epoxy resin used in Example 1 and 2, mica as a filler, glycol dibenzoate plasticizers instead of phthalate-based plasticizers as in Examples 1 and 2, a sulfonic acid curing agent, and different rheological control additives than were used in Examples and 2. Details of the formulation of Examples 5 were provided in Table 2.
Different thicknesses of the composition of Example 5 were prepared and tested in the same manner as in the prior examples. Figure 2 shows how the observed loss factor varies with both temperature and film thickness (tested at 200 Hz).

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Claims

We claim:

1. A composition useful for suppressing mechanical vibration, reducing particle impact noise, or lowering air vibration in a cavity, said composition being comprised of:
(a) one or more acrylic resins;
(b) recycled paint polymer containing uncured resin;
(c) one or more plasticizers; and (d) one or more fillers.

2. The composition of claim 1 additionally comprising one or more blowing agents.

3. The composition of claim 1 additionally comprising one or more adhesion promoters.

4. The composition of claim 1 additionally comprising one or more thermosettable resins.

5. The composition of claim 1 wherein at least one of the acrylic resins is selected from the group consisting of methyl methacrylate homopolymers and methyl methacrylate copolymers.

6. The composition of claim 1 wherein the uncured resin is comprised of an acrylic resin.

7. The composition of claim 1 wherein the recycled paint polymer containing uncured resin is in putty form.

8. The composition of claim 1 wherein the recycled paint polymer containing uncured resin has a volatiles content of less than 1% by weight.

9. The composition of claim 1 wherein the recycled paint polymer containing uncured resin is in powder form.

10. The composition of claim 1, characterised in being essentially free of vinyl chloride homopolymers and copolymers.

11. The composition of claim 1 wherein at least one of the plasticizers is a phthalate ester.

12. An acoustic dampening composition comprised of:
(a) about 10 to about 50% by weight of one or more acrylic resins, wherein at least one of said acrylic resins is selected from the group consisting of methyl methacrylate homopolymers and copolymers;
(b) about 1 to about 25% by weight of recycled paint polymer containing uncured resin;
(c) about 10 to about 60% by weight of one or more plasticizers; and (d) about 5 to about 50% by weight of one or more fillers.

13. The acoustic dampening composition of claim 12 additionally comprising one or more organic chemical blowing agents.

14. The acoustic dampening composition of claim 12 additionally comprising one or more adhesion promoters.

15. The acoustic dampening composition of claim 12 additionally comprising one or more thermosettable resins, at least one of said thermosettable resins being selected from the group consisting of epoxy resins and melamine-aldehyde resins.

16. The acoustic dampening composition of claim 12, characterized in being essentially free of vinyl chloride homopolymers and copolymers.

17. The acoustic dampening composition of claim 12 wherein the uncured resin is comprised of an acrylic resin.

18. The acoustic dampening composition of claim 12 wherein the recycled paint polymer is in putty form.

19. The acoustic dampening composition of claim 12 wherein the recycled paint polymer containing uncured resin has a volatiles content of less than 1 % by weight.

20. The acoustic dampening composition of claim 12 wherein the recycled paint polymer is in powder form.

21. A damping construction comprising at least one layer of the acoustic dampening composition of claim 1 applied to a vibratory solid article.

22. The damping construction of claim 21 wherein the vibratory solid article is a metal automotive component.

23. The damping construction of claim 21 wherein the layer of acoustic dampening composition has a thickness of from about 0.05mm to about 100mm.

24. The damping construction of claim 21 wherein the layer of acoustic dampening composition has been gelled by heating.

25. A damping construction comprising at least one layer of the acoustic dampening composition of claim 12 applied to a vibratory solid article and gelled by heating.

26. The damping construction of claim 25 wherein the vibratory solid article is a metal automotive component.

27. The damping construction of claim 25 wherein the layer of acoustic dampening composition has a thickness of from about 0.5mm to about 25mm.

28. A method of coating a vibratory solid article to suppress mechanical vibration, reduce particle impact noise, or lower air vibration in a cavity of said vibratory solid article, said method comprising applying at least one layer of the composition of claim 1 to said vibratory solid article and gelling said composition.

29. The method of claim 28 wherein the composition is applied by spraying.

30. The method of claim 28 wherein the composition is gelled by heating.

31. The method of claim 28 wherein the vibratory solid article is a metal automotive component.

32. The method of claim 28 wherein said layer of the composition has a thickness of from about 0.05mm to about 100mm.

33. A method of coating a metal automotive component to suppress mechanical vibration, reduce particle impact noise, or lower air vibration in a cavity of said metal automotive component, said method comprising spraying at least one layer of the composition of claim 12 onto said metal automotive component and gelling said composition by heating.

34. The method of claim 33 wherein said layer has a thickness of from about 0.5mm to about 25mm.

35. A coating obtained by gelling the composition of claim 1.

36. A coating obtained by heating the composition of claim 12 for a time and at a temperature effective to gel said composition.