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Title:
POLYVINYL BUTYRAL AS ADHESION PROMOTER IN ELASTOMERIC ADHESIVE FORMULATIONS
Document Type and Number:
WIPO Patent Application WO/2019/134949
Kind Code:
A1
Abstract:
The invention is directed to an adhesive formulation comprising at least one polydiene and at least one polyvinyl acetal. The polydienes contain preferable isoprene, butadiene and maleic acid as repeating units. Use of the adhesive formulation as adhesive or sealant of coating for metals, fabric, wood, aluminum, textiles, fiber-reinforced composites, plastics, glass or fiber glass.

Inventors:
MUMMY, Florian (Beethovenplatz 5, Frankfurt am Main, 60325, DE)
SABEL, Thomas (Lindenstrasse 10, Bad Camberg, 65520, DE)
STEINBACH, Niklas (Peter-Fischer-Allee 23, Frankfurt, 65929, DE)
FRANK, Michael (Zur Traubenmühle 5a, Nieder-Olm, 55268, DE)
BÖHM, Ralph (Hattersheim, 65795, DE)
GRUENDKEN, Marcel (Hattersheim, 65795, DE)
Application Number:
EP2019/050122
Publication Date:
July 11, 2019
Filing Date:
January 04, 2019
Export Citation:
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Assignee:
KURARAY EUROPE GMBH (Phillip-Reis-Straße 4, Hattersheim, 65795, DE)
International Classes:
C09J109/00; C08F279/02; C09J151/00
Domestic Patent References:
WO2006058829A12006-06-08
Foreign References:
EP2610305A12013-07-03
Other References:
DATABASE WPI Week 201615, Derwent World Patents Index; AN 2015-731716, XP002782001
DATABASE WPI Week 201640, Derwent World Patents Index; AN 2016-180838, XP002782002
DATABASE WPI Week 201605, Derwent World Patents Index; AN 2015-68488D, XP002782003
None
Attorney, Agent or Firm:
KISTERS, Michael (Kuraray Europe GmbH, Mülheimer Strasse 26, Troisdorf, 53840, DE)
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Claims:
Claims

1 . Adhesive formulation comprising at least one polydiene and at least one polyvinyl acetal. 2. Adhesive formulation according to claim 1 , characterized in that the polydienes contain isoprene, butadiene and/or maleic acid as repeating units.

3. Adhesive formulation according to claim 1 , characterized in that the polydiens comprise 1 ,2-vinyl configurations from 5 to 90 mol.%.

4. Adhesive formulation according to any of the claim 1 to 3, characterized in that the polydiene has a molecular weight Mn in the range of 1 to 2.000 kg/mol. 5. Adhesive formulation according to any of the claim 1 to 4, characterized in that the composition contains 0,1 to 25 wt% polyvinyl acetal.

6. Adhesive formulation according to any of the claim 1 to 5, characterized in that the polyvinyl acetal has a degree of polymerization Pw between 100 and 1000.

7. Adhesive formulation according to any of the claim 1 to 6, characterized in that the polyvinyl acetal has a vinyl alcohol content in the range of 10 - 30 wt-%.

8. Adhesive formulation according to any of the claim 1 to 7, characterized in that the polydiene is a copolymer with repeating units of isoprene and maleic acid, wherein the average number of repeating units of maleic acid per molecule is between 1 and 12

9. Adhesive formulation according to any of the claim 1 to 7, characterized in that the polydiene is a copolymer with repeating units of butadiene and maleic acid, and wherein the average number of repeating units of maleic acid per molecule is between 1 and 12.

10. Adhesive formulation according to any of the claim 1 to 9, characterized in that the polydiene comprises polyisoprenes, polybutadiens or mixtures thereof. 1 1 . Adhesive formulation according to any of the claim 1 to 10, characterized in that the adhesive formulation comprises further inorganic fillers, process oil and/or vulcanizing agents.

12. Use of the adhesive formulation according to any of the claims 1 to 1 1 as adhesive or sealant of coating for metals, fabric, wood, aluminum, textiles, fiber-reinforced composites, plastics, glass or fiber glass.

Description:
Polyvinyl Butyral as Adhesion Promoter in Elastomeric Adhesive Formulations

The invention relates to adhesive formulations comprising polydiens like polyisoprenes or polybutadienes and polyvinyl acetal as adhesion promoter and the use of the preparation as curable adhesive. In automotive industry, it is a known technology to combine and/or seal metal parts with adhesives. Such adhesives need not only adhere firmly to the metal surfaces, but also need to exhibit flexibility to withstand temperature changes or vibrations.

The adhesion between the adhesive layer and the substrate is commonly considered as a weak part of a laminate. To improve the adhesion, polymers with functional groups are often found in adhesive formulation. Such functional groups include e.g. carboxyl, hydroxyl, maleic anhydride, epoxide or mercapto or silane groups. The person skilled in the art knows these polymers as so called“adhesion promoters”. In this respect, it is known to use curable polymer formulations comprising elastomers such a poly isoprene optionally in combination with acrylic monomers. However, especially in the case of difficult combinations of substrates like high polar surfaces to be combined with non-polar adhesives, dynamic stress applied to the adhesive may result in cracks. Commonly known adhesion promoters (e.g. polymers with carboxyl, hydroxyl, maleic anhydride, epoxide or mercapto or silane groups) only provide limited performance in this respect. Furthermore, high temperatures and environmental impacts accelerate the weakening of the adhesion layer.

Object of the invention was to enhance the adhesion of the known formulations on metal surfaces, especially on metal surfaces.

Detailed Description

It was found that the adhesion properties of polydiens can be enhanced significantly by addition of polyvinyl acetal as adhesion promotor. Furthermore, the failure rate of joined metal parts after exposure to salty and wet conditions (simulating wet winter conditions) is improved.

Accordingly, a first object of the invention is an adhesive formulation comprising at least one polydiene and at least one polyvinyl acetal. In the context of this patent application, polydienes may be any polymer containing isoprene, butadiene and/or maleic acid as repeating units. Preferable, the polydienes are liquid.

The polyvinyl acetal acts as adhesion promoter and/or gafting polymer for the polydienes.

The adhesive formulation according to the invention can be used as curable adhesive to combine different or similar kinds of substrates, especially metals. Accordingly, the adhesive formulation according to the invention can be used as sealing or coating to protect metals, fabrics, wood, aluminum, textiles, fiber-reinforced composites or plastics. Formulations according to the invention can be used to join e.g. thin walled metal sheets that are commonly used in the production of motor vehicles, machines and devices in order to reduce weight of the final car.

The adhesive formulation of the invention may comprise up to 60 wt% polydiens and 0,1 wt.% to 25 wt.%, preferable 0,1 wt.% to 5 wt.% of polyvinyl acetal, based on the overall formulation including all additives.

In a first embodiment, the adhesive formulation comprises polyisoprenes or polybutadiens or mixtures thereof as polydiene.

In a second embodiment, the adhesive formulation comprises as polydiene an copolymer with repeating units of isoprene and maleic acid, and wherein the average number of repeating units of maleic acid per molecule is between 1 and 12, preferable between 3 and 6. Such copolymers are hereinafter referred to as“functionalized polyisoprene”

In a third embodiment, the adhesive formulation comprises as polydiene an copolymer with repeating units of butadiene and maleic acid, and wherein the average number of repeating units of maleic acid per molecule is between 1 and 12, preferable between 3 and 6. Such copolymers are hereinafter referred to as“functionalized polybutadiene”.

The polydiens, especially polybutadienes and polyisoprenes comprise 1 ,2-vinyl configurations from 5 to 90 mol.%. and/or may have a molecular weight Mn in the range of 1 to 2.000 kg/mol. As polyvinyl acetal, especially poylvinylbutral or polyvinylacetacetal or polyvinyl(butral -co- acetacetal) is used. The degree of polymerization Pw is preferable between 100 and 1000 and/or the vinyl alcohol content in the range of 10 - 30 wt-%.

The adhesive formulation may further comprise inorganic fillers (e.g. calcium carbonate), process oil, and vulcanizing agents like sulfur, peroxides, phenolic crosslinking systems.

The process oil may be based on paraffinic, naphthenic or aromatic oil, or a vegetable oil e.g. derived from olive, palm, safflower, and sunflower. Preferred are triglycerides. The target concentration of the oil in the formulation is between 0 and 60 wt.% (based on the overall formulation).

The adhesive formulation may comprise up to 70 wt.% of inorganic filler. The filler can be ground CaCC>3 and/or treated and/or untreated CaCC>3.

The composition can be cured by adding curing or vulcanizing agents and subjecting the formulation applied to the substrates to temperatures greater than 120°C. Preferred curing agent is sulfur in combination with zinc oxide, stearic acid and accelerators. Other curing agents include of peroxides, phenols or benzochinondioxim for corresponding peroxide, phenolic or other crosslinking methods.

Without being bound to this theory, it is believed that the polyvinylacetal is cured to the polydienes, especially via groups originating from maleic acid repeating units. This leads to an increase of the molecular weight M n of the polymeric ingredients up to 100 kg/mol.

The formulation of the invention may be used as sealant and coating for metals like a car chassis, where the adhesive composition acts as a protective layer against environmental impacts. The formulation can be applied onto uncovered steel e.g. in limited accessible areas. Also important is the use as an adhesive between two parts, either or similar (e.g. metal-metal) or different kind joints (e.g. metal-plastics). Areas of use are in automotive and technical applications, often temperature sensitive areas and/or high dynamical stress. In general, the adhesive formulation according to the invention may be used as adhesive or sealant of coating for metals, fabrics, wood, aluminum, textiles, fiber- reinforced composites, plastics, glass or fiber glass.

Examples

Formulations C1 and C2 are comparative examples according the prior art (see table). Formulations E1 and E2 are according to the invention

The formulations were prepared with the ingredients as shown in table 1 by placing the polymers into a planetary mixer and homogenizing under a vacuum of about 200 mbar at a mixing rate of 150 rpm for at least 15 min. Then the fillers were

subsequently added and the resulting mixture was mixed with a rate of 50 rpm until homogeneous mixture was obtained. Then remaining material was added to the mixture and further mixed at 50 rpm until homogeneous mixture was obtained.

Once fillers were added, it was ensured that the heat of mixing did not cause the temperature to rise above 65°C.

Adhesive formulations C1/E1 and C2/E2 were further processed to adhesive formulations as shown in table 1 and evaluated in a tensile shear test and an artificial weathering test According to this procedure, the adhesive characteristic is indicated by the tensile adhesion strength relatively to 100 of the comparative example E2. A higher number means a better performance.

Table 1 Adhesive Formulations with

1 ) Buna CB 24 (high cis BR, min. 96 % cis 1 ,4, Mooney: 44), Arlanxeo

2) LIR-30, Kuraray Co.

3) LI R-403, Kuraray Co

4) Blend of 95 wt% cis-1 ,4 polyisoprene, molecular weight app. 28 kg/mol (Mn).

(Kuraray, LIR-30). 5 wt% polyvinyl butyral (Kuraray Europe GmbH, Mowital™ B 30 HH).

5) Blend of 95 wt% cis-1 ,4 polyisoprene-g-maleic anhydride, molecular weight app. 34 kg/mol (Mn), functionality F=3. (Kuraray Co, LI R-403). 5 wt% polyvinyl butyral (Kuraray Europe GmbH, mowital™ B 30 HH).

6) Sunthene 4240, Sunoco

7) Nocrac NS-6, Ouchi Shinko

8) Di(benzothiazol-2-yl) disulfide (MBTS), Vulkacit® DM Arlanxeo

9) Di-orto-tolylquanidine, DOTG, Acrochem

Shear Strength test

The adhesive formulation according to the invention was applied to steel sheets (width: 25 mm, thickness: 1 .6 mm, length: 100 mm). The steel sheets were coated with the adhesive formulation and brought into contact in such a way that an overlapping area of 12,5 mm was observed. The specimens were pressed to a thickness of about 25 pm and the steel sheets were secured then with clamps. Joints were cured for 30 min at 160°C.

The measurements were carried out after 48 hours after cooling down of the joints. Joints were stored over that time period under standard climatic conditions (50% rel. humidity and 23°C). Shear rate was set to 25 mm/min. Normalized measured values are summarized in Table 2.

Table 2

As shown in table 2, formulations according to the inventions have an enhanced shear strength as compared to formulations according to the prior art. Artificial weathering test

A Salt spray test was performed in an artificial atmosphere according to DIN ISO 9227:2012, wherein the neutral salt spray test was performed with an aqueous 5% sodium chloride solution with a pH value of 6.5 to 7.2 under specified conditions (35 ± 2) °C. Joint test samples as prepared as disclosed with the“shear strength test” were exposed to salt spray condition for a period of 1000 hours.

Afterwards samples were rinsed with deionized water for 5 minutes and were dried at room temperature for 6 hours.

Specimens were stored under standard conditions (23°C and 50 relative humidity) and measured after 48 hours being in the climatic chamber.

able 3, normalized values As shown in table 3, formulations according to the inventions have enhanced weathering properties as compared to formulations according to the prior art.