DE29520113U1 - Adhesive and sealant with vapor properties - Google Patents

Description

Adhesive and sealant with damping properties

The present invention relates to compositions for adhesives, sealants and/or coatings with damping properties which contain 3,4-polyisoprene. In particular, this invention relates to curable and non-curable compositions for adhesives, sealants and/or coatings which contain conventional polymer components and additionally 3,4-polyisoprene. These compositions are preferably used in the vehicle industry, in particular in the automotive industry.

In the manufacture and assembly of automobiles, adhesives, sealants and coatings are used for a variety of different purposes. Adhesives and sealants are selected primarily based on the following properties:

- Strength, i.e. tensile shear strength,
Peel strength

- Stretching, flexibility

- Ageing resistance

- easy to process.

For coatings, especially underbody protection coatings
abrasion resistance is another

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Selection criterion. In the automotive industry, efforts are being made to simplify the complexity of manufacturing processes in order to reduce manufacturing costs, among other things. There is therefore a need for "multifunctional" products, i.e. sealants, adhesives and/or coatings that can perform additional tasks in addition to their primary function.

In modern vehicle construction, machine and device construction, only very thin sheet metal thicknesses are used for metal structures. Moving machine or vehicle parts and running engines cause vibrations in these thin metal structures, and these vibrations generate noise. A number of methods are known for combating noise, but most of these methods require additional manufacturing steps and/or additional components whose sole function is to dampen vibrations. Highly filled bitumen mats are an example of such conventional vibration dampening products. These mats must be extruded, punched and formed in various individual steps. They often have to be heated immediately before use in order to adapt them to non-flat structures in the vehicle or machine so that they can then be glued to the body, machine or device. There have been numerous attempts to replace this complex and costly manual process with products that can be easily applied by robots. For example, EP-A-358598 or DE-A-3444863 describe plastisol compositions that fulfill the dual function of underbody protection (protection against abrasion) and acoustic damping. DE-A-4013318 describes a two-layer underbody protection coating that fulfills the dual function of protection against abrasion and damping of the

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Noise caused by impacting particles (stones, gravel, water, etc.). Although these products/processes are suitable for fulfilling the dual function of "underbody protection" and "noise dampening", there is a need to combine the functions of an adhesive and/or sealant with the function of noise dampening. This combination of properties is particularly desirable for those parts of a vehicle, machine or device that do not require a special coating for protection against abrasion, such as the bonnet, trunk lid, doors and bulkheads of a motor vehicle.

Adhesives and/or sealants used for these parts are preferably used early in the manufacturing process, in the so-called "body shell". In the body shell, these adhesives/or sealants are usually applied to the untreated, uncleaned metal; the sheet metal is often still coated with an anti-corrosive oil or deep-drawing oil. Plastisols, especially PVC plastisols, are also used in the body shell, but the plastisols described in EP-A-358598 or DE-A-3444863 are not suitable as adhesives/sealants on body shell. Plastisol compositions that are specifically suitable for use in the body shell have very poor or even no acoustic damping properties.

Adhesives/sealants preferably used in the bodyshell are based on rubber, in particular vulcanizable compositions based on 1,3-polybutadienes and/or 1,3-polyisoprenes. These preferably contain liquid, low-molecular polydienes, sulfur and, if necessary, accelerators for sulfur vulcanization. In addition, these formulations can contain solid, high-molecular rubber, with the liquid polydienes and/or solid rubbers additionally

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functional groups such as hydroxyl groups, carboxyl groups, anhydride groups or epoxy groups. These adhesives/sealants based on rubbers have already been the subject of numerous patent applications, e.g. EP-A-97394, EP-A-309903, DE-A-3834818, DE-A-4120502, DE-A-4122849, EP-A-181441 and EP-A-356715. DE-A-4122489 and EP-A-181441 mention a possible use of these compositions for damping vibrations and/or noise, but they do not provide any information on the efficiency of these compositions for vibration damping. As far as is known, these materials have not been used to simultaneously fulfill the function of an adhesive/sealant and vibration and/or noise damping material. FR-A-2255313 describes materials with high vibration damping coefficients, which essentially contain a polyisoprene with at least 60% 1,2 and 3,4 structures. According to the teaching of FR-A-2255313, however, the vibration damping materials are extruded in the form of flat structures, vulcanized and then glued to the metal structures. There is no information whatsoever that such compositions are suitable as adhesives and/or sealants and/or can be applied to metal structures in the uncured state. The use of 3,4-polyisoprenes for adhesives and/or sealants or coatings that are essentially free of volatile solvents has not yet been described, especially not when these compositions simultaneously have acoustic damping properties.

It has now been found that 3,4-polyisoprene can be combined with other curable and non-curable liquid and/or solid rubbers or liquid polyolefins and that these compositions form adhesives and/

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or sealants with excellent vibration damping properties. The inclusion of 3,4-polyisoprenes in adhesive/sealant formulations has, surprisingly, no adverse effect on other desirable properties of the formulations such as application behavior, curing speed, adhesion, strength and/or elasticity.

The adhesive/sealant compositions according to the present invention may contain at least one of the following components in addition to the 3,4-polyisoprene:

- one or more liquid or solid rubbers or elastomers

- thermoplastic polymers in the form of finely divided powders

- Fillers

- tackifying resins and/or adhesion promoters

- Plasticizer/Extender

- Curing agents (vulcanizing agents), accelerators, catalysts

- Stabilizers, antioxidants, anti-aging agents

- Tools to improve rheology.

3,4-polyisoprenes in the sense of this invention are polyisoprenes with a significant proportion of at least 30%, preferably 55 to 70% of 3,4-polyisoprene, the 3,4-polyisoprene content being determinable by NMR spectroscopy. Although the preferred 3,4-polyisoprenes are polymers with a high molecular weight, i.e. 200,000 and above, it may be advantageous for some formulations to use low molecular weight liquid 3,4-polyisoprenes, for example as an additive to conventional plastisols.

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The compositions according to the present invention can contain up to 40% by weight of 3,4-polyisoprene, preferably they contain less than 20% by weight and particularly preferably 5 to 15% by weight of 3,4-polyisoprene. The acoustic damping properties of the compositions according to the invention can be influenced by the proportion of 3,4-polyisoprene in the overall composition. The corresponding change in the loss factor serves as the measured variable. To a lesser extent, the content of 3,4-polyisoprene in the overall composition also determines the service temperature range in relation to the loss factor, by which is meant the temperature range in which a significant increase in the loss factor of the cured composition is observed due to the addition of 3,4-polyisoprene.

Examples of additional liquid rubbers or elastomers to be used are the following homo- and/or copolymers: polybutadienes, especially the 1,3- and 1,2-polybutadienes, which can have terminal and/or pendant functional groups such as hydroxy groups, carboxyl groups, carboxylic anhydride groups or epoxy groups; polybutenes; polyisobutylenes; 1,4-polyisoprenes; styrene-butadiene copolymers; butadiene-acrylonitrile copolymers; polyurethanes and polyepoxides. The molecular weight of the liquid rubbers is usually less than 20,000, preferably between 2,000 and 10,000. The content of liquid rubbers in the compositions according to the invention depends on the desired rheology of the uncured formulation and the desired mechanical properties and acoustic damping properties of the cured composition. In general, the content of liquid rubbers or elastomers is between 5 and 50 wt.%.

The suitable solid rubbers usually have a

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significantly higher molecular weight than the liquid rubbers (100,000 or higher), examples of suitable solid rubbers are polybutadiene (preferably with a high proportion of cis-1,4 configuration), styrene-butadiene rubber, butadiene rubber, butadiene-acrylonitrile rubber, isoprene rubber, butyl rubber and polyurethane rubber.

Examples of thermoplastic polymer powders are polypropylene, polyethylene, thermoplastic polyurethanes, methacrylate copolymers, styrene copolymers and PVC.

The fillers can be selected from a variety of materials, in particular chalk, natural ground or precipitated calcium carbonates, silicates, barite and carbon black. Fillers with a platelet structure such as vermiculite, mica, talc or similar layered silicates are also suitable. In some formulations, such fillers with a platelet structure show an improvement in the vibration damping properties. The total content of fillers in the formulation can vary between 10 and 70% by weight, with the preferred range being between 25 and 60% by weight.

If necessary, tackifiers and/or adhesion promoters can be added to the compositions according to the invention. Suitable examples include hydrocarbon resins, phenolic resins, terpene-phenolic resins, modified or unmodified abietic acids and their esters, polyamines, polyaminoamides, polyepoxy resins and anhydrides and copolymers containing anhydride groups. The type and amount of the tackifying resin(s) depends on the polymer composition of the adhesive/sealant, its strength in the cured state and the substrate to be bonded or sealed. Typical tackifying resins such as terpene-phenolic resins or abietic acid derivatives are

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usually used in amounts of 5 to 20 wt.% and preferably in the range between 7 and 15 wt.%. Typical adhesion promoters such as polyamines or polyaminoamides are normally used in the range between 0.5 and 10 wt.%. In the event that the compositions according to the invention contain plasticizers and/or extender oils, a large number of products are suitable for this purpose, for example C- to C11-dialkyl esters of phthalic acid and/or C- to C-dialkyl esters of C ₃ - to C ₀ -dicarboxylic acids, eg dioctyl adipate, or their

Mixtures, aliphatic, aromatic or naphthenic oils, low molecular weight polybutenes or polyisobutylenes, high boiling hydrocarbon fractions and mixtures of the aforementioned plasticizers and/or extender oils. Plasticizers and/or extender oils influence to a certain extent the rheological properties of the uncured composition and the mechanical properties including the damping properties of the cured composition. Plasticizers extenders are usually used in the range between 5 and 40 wt.%.

The crosslinking agents (hardeners), accelerators or catalysts to be used depend to a very large extent on the reactive and/or functional groups of the polymers selected. Sulfur-based vulcanization systems are used to crosslink the olefinic double bonds of liquid or solid rubbers, including 3,4-polyisoprene. In addition, a variety of organic and inorganic accelerators can be used in combination with sulfur or alone. Examples of such accelerators are mercaptobenzothiazoles, dithiocarbamates, sulfenamides, disulfides such as dibenzothiazole disulfide and/or thiuram disulfide, aldehyde-amine accelerators, guanidines and

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Metal oxides such as zinc oxide. In addition, other typical rubber vulcanization aids such as fatty acids (e.g. stearic acid) can be present in the formulations. The sulfur content can be within wide limits between 0 (in non-vulcanizable systems) to about 15% by weight, preferably up to about 10% by weight. Similarly, the range of the aforementioned accelerators can be between 0 and about 10% by weight. The content of metal oxides is generally between 0 and 10% by weight. Conventional stabilizers or anti-aging agents such as sterically hindered phenols or amines can be used to prevent thermal, thermo-oxidative or ozone degradation of the compositions according to the invention; typical amounts for these stabilizers are 0.1 to 5% by weight.

Although the rheology of the compositions according to the invention can normally be brought into the desired range by selecting the type and amount of fillers, conventional rheology aids such as pyrogenic silica or bentones can be used in an amount between 0.1 and 7% by weight. In addition, other conventional aids and additives can be used in the compositions according to the invention.

The effectiveness of the acoustic damping of the compositions according to the invention can be influenced to the specific needs of the application with respect to the position of the maximum of the loss factor and the temperature range in which a high acoustic damping is achieved.
The main influencing factors are the vulcanization system (sulfur content, vulcanization accelerator content) and the rubbers used. To a certain extent, the choice of fillers can also determine the maximum loss factor and the corresponding

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Temperature. The loss factor can also be influenced by the thickness of the material applied, and foamed materials are known to cause a higher loss factor than unfoamed materials. In cases where an adhesive with high tensile strength or tensile shear strength is required, foaming the material is naturally not applicable. In most applications, it is desirable for the maximum loss factor to be at room temperature (about ^{20 °} C) and for the region with a sufficiently high loss factor to extend over a wide temperature range. The vulcanization or curing conditions for the adhesive/sealant compositions according to the invention can be adapted to the specific applications. The composition usually cures in the temperature range between 80 ^° C and 240 ^° C in 10 to 35 minutes.

The invention will be explained in more detail in the following examples, whereby the selection of examples is not intended to represent a limitation of the scope of the subject matter of the invention.

The acoustic damping properties of the compositions were determined in the examples using the "Oberst method" as described in DIN 53440, Part 3, using coated steel strips. The coating was cured in a conventional laboratory drying cabinet. Unless otherwise stated, all parts in the following examples are parts by weight.

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Examples 1 to 5:

The following components were mixed in a laboratory kneader until homogeneous:

3,4-Polyisoprene ' 1
10 1
10 2
10 A
10 5
10 Chalk ² * 35 31.5 31 31 31 3 )
Precipitated calcium carbonate ' 24 25 25 25 24 41
Terpene Phenolic Resin ' 10 10 10 10 10 ·· 5)
Naphthenic Oil '
Polyisobutylene ' 5
15 5
15 5
15 5
15 5
15 Antioxidant ' 1 1 1 1 1 Calcium oxide ' 0 1 1 1 1 Zinc oxide, active 0 1 1 1 1 Sulphur powder 0 0 0.5 0 1.0 Dibenzothiazole disulfide (MBTS) 0 0.5 0.5 1.0 1.0 9)
Tensile shear strength ' 0.06 n/a. n/a. n/a. 1.2

1) 3,4-content (NMR) about 60%, Mooney viscosity 65/100 ⁰ C (ML4)

2) Natural, ground, average particle size 4.5μηι.

3) Stearate coated, average particle size 0.07 μm²

4) Dertophen T (trademark) softening point 93-97 ⁰ C (ring and ball method)

5) Nyflex 820 (trademark Nynas-Petroleum)

6) Oppanol B 10 (trademark, BASF)

7) N,N'-Di(1,4-dimethylpentyl)-1,4-phenylenediamine

8) Coated with stearic acid

9) 2mm layer thickness between steel sheet strips, hardened at 155°C/30 min, cohesive fracture - n.a. = not available .

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Comparison example 1

A PVC plastisol was prepared by mixing the following components:

Emulsion PVC, paste type 32.0

Dioctyl phthalate 30.0

Natural, ground chalk 16.5

Precipitated calcium carbonate 6.0

Calcium oxide 3.0

Metal oxides {colour pigments) 1.0

Soot 0.1

Stabilizers 1.0

Adhesion Promoter 2.0

Pyrogenic silica 0.4

Hydrocarbon extender 8.0

Example 6, 7 and comparative example 2 (Comp.2)

The following components were mixed until homogeneous in

mixed in a laboratory kneader:

Comp. 2 6_

Solid rubber ¹ * 2.7

2 )

3,4-Polyisoprene ' - 5.0 10.0

3 )
Liquid polybutadiene ' 8.9 8.9 7.0

Liquid polybutadiene ' 17.8 15.5 12.0

Carboxyl group-containing

Polybutadiene ⁵ ^ 8.9 8.9

Benzyl group-containing polybutadiene '

Precipitated calcium carbonate ' chalk ⁷ )

talc

Calcium oxide

soot

81
antioxidant ^;

— — 8.0 12.1 12.1 12.1 12.1 12.1 12.0 18.6 18.6 21.0 5.6 5.6 5.5 0.5 0.5 0.1 0.5 0.5 0.5

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Zinc oxide, active
Sulphur powder
Dibenzothiazole disulfide (MBTS)

Comp.2 3 4 6 7 4, 0 3 ,3 4.0 3, 0 5 ,0 2.5 in 4 1 ,0 5.3 1, ,5 1.2/1.8

Tensile shear strength '

1) Polybutadiene with high cis-l,4-content (98%), Mooney-

Viscosity 48/100 ⁰ C (ML4)

2) 3,4-content about 60% (NMR), Mooney viscosity 65/100 ⁰ C
(ML4)

3) Molecular weight about 1800, cis-l,4-content: about 72%

4) Molecular weight about 1800, vinyl content: about 40-50%
5a) Polybutadiene/maleic anhydride adduct, MW approx. 1700
5b) Polybutadiene with terminal benzyl groups, MW ca.900

6) Stearate coated, average particle size 0.07μηι

7) Natural, ground, average particle size 4.5jum

8) N,N'-Di(l,4-dimethylpentyl)1,4-phenylenediamine

9) 2mm layer between steel sheet strips, comparison example
2 and Example 6 cured at 155°C/30min,
Example 7 cured at 170°C/30min or 200°C/30min,
cohesive fracture pattern in all cases.

Acoustic damping properties

1 mm thick spring beam strips measuring 240 mm x 10 mm were coated on a 200 mm long section with a layer of the products from Examples 1 to 6 and Comparative Examples 1 and 2 in the layer thickness specified below. The coatings were then cured in a laboratory oven for 30 minutes at 190 ^° C (unless otherwise stated). The acoustic damping value (d-combi) was determined using the bending vibration test of DIN 53440, Part 3 at 200 Hz (Oberst method). As can be seen from Figures 1 to 3, the compositions that

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3,4-polyisoprene, a significantly high loss factor at normal service temperatures (-10° to 30 ⁰ C). In addition, Examples 2 and 5 clearly show that the temperature range with a high loss factor can be optimized to the desired range by making minor changes in the vulcanization system. Examples 6 and 7 show that the addition of 3,4-polyisoprene to conventionally vulcanizable rubber sealants/adhesives (Comparative Example 2) significantly improves the loss factor of these cured adhesives/sealants without having to compromise on the tensile shear strength.

Example 7 clearly shows that at higher curing temperatures the lap shear strength of the cured adhesive is increased, as expected. Surprisingly, the vibration damping measured by the Oberst method is also increased, in addition these compositions cured at the higher temperature show the high loss factor over a wider temperature range compared to the composition cured at the lower temperature, see Curve 14 compared to Curve 15 of Figure 3.

Explanation of figures 1 to 3

Figures 1 to 3 show a graphical representation of the combined loss factor at 200 Hz (d(combi)) of the coated steel strips as a function of temperature according to DIN 53440, Part 3. The test strips were produced as described above, with the majority of the test strips being produced at two different coating thicknesses in order to compensate for deviations in the layer thickness between different formulations.

Figure 1 shows the loss factor of a conventional

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PVC plastisol according to comparative example 1 (1/2) in comparison to a composition according to example 1 (3,4).

Curve Composition Layer Thickness

1: Comparison example 1 2.27 mm

2: Comparison example 1 4.52 mm

3: Example 1 2.2 mm

4: Example 1 4.5 mm

Figure 2 shows how the loss factor and the temperature range over which a significant loss factor (X) ₇ I) is observed can be varied by minor changes in the composition of the vulcanization system.

Curve composition Layer thickness 5: Example 2 2.0mm 6: Example 2 2.45mm 7: Example 3 2.6mm 8th: Example 3 3.5mm 9: Example 4 2.0mm 10: Example 4 2.65mm 11: Example 5 4.8mm

Figure 3 shows the loss factor of a cured rubber composition according to the prior art (Comparative Example 2). From this it can be seen that the loss factor of the composition according to Comparative Example 2 is negligible at the normal operating temperatures of a vehicle (-5 ⁰ C to 30 ⁰ C), while the inventive compositions of Examples 6 and 7 have a significant loss factor at the normal operating temperatures:

H1051 - 16 - Layer thickness Curve composition 3.0mm 12: Comparison example 2 3.1m 13: Example 6 2.3mm 14: Example 7 2.3mm 15: Example 7 4.4mm 16: Example 7

Note: The test strips for curves 15 and 16
were cured at 200 ⁰ C for 30 min, while the samples of curve 14 were cured at 170 ⁰ C for 30 min.

All adhesive/sealant compositions of Examples 1 to 7, in addition to their excellent damping properties, had the necessary properties to be used as adhesives or sealants for body-in-white applications in the automotive industry.

Claims (7)

H 1051 - 17 - Adhesive and sealant with damping properties Protection claims 1.) Compositions for use as adhesives, sealants or coating agents containing 5 to 40 wt.% 3,4-polyisoprene, characterized in that they additionally contain at least one liquid or solid rubber and contain at least one of the following substances: finely divided polymer powders, fillers, crosslinking or vulcanizing agents, adhesion promoters, plasticizers, liquid extenders. 2.) Compositions according to claim 1, characterized in that the liquid and/or solid rubbers are selected from the group of homo- or copolymers of polybutadiene, 1,4-polyisoprene, polyisobutylene, polybutene, styrene-butadiene rubber, polyurethanes and/or polyepoxides. 3.) Compositions according to at least one of the preceding claims, characterized in that the crosslinking agents are selected from the group of vulcanizing agents consisting of sulfur and/or at least one organic accelerator, dicyandiamide, carboxylic acid anhydrides and polyurethane catalysts. 4.) Compositions according to at least one of the preceding claims, characterized in that the plasticizer(s) and/or liquid extender(s) from the group of C- to C-dialkyl esters of - 18 Phthalic acid
or one or more C- to C- J O Dicarboxylic acid(s), aliphatic, aromatic or
naphthenic oils, low molecular weight polybutenes
and high boiling hydrocarbons selected
become. 5.) Compositions according to at least one of the preceding claims, characterized in that the adhesion promoter(s) is/are selected from the group of hydrocarbon resins, modified and/or unmodified abietic acid or its esters, phenolic resins, terpene-phenolic resins, epoxy resins, polyaminoamides, polyaminoethers or polymeric and/or
monomeric carboxylic acid anhydrides is selected. 6.) Crosslinked adhesive, sealant or coating according to at least one of the preceding claims, characterized in that it has been cured by heating to a temperature range between 8O ⁰ C and 24O ⁰ C. 7.) Adhesive, sealant or coating according to claim 6, characterized in that the loss factor d(combi) according to DIN 53440, Part 3 (Oberst method) at 20°C and a layer thickness of 2 mm is at least 0.1.