CA2001077A1

CA2001077A1 - Heat-vulcanizable adhesive and a method for bonding

Info

Publication number: CA2001077A1
Application number: CA002001077A
Authority: CA
Inventors: Hans-Juergen Buecken; Julius Herold; Peter Hofmann
Original assignee: Individual
Current assignee: Henkel AG and Co KGaA
Priority date: 1988-10-20
Filing date: 1989-10-20
Publication date: 1990-04-20
Also published as: ZA897928B; KR0133529B1; EP0369165A1; JPH02169683A; DE3835740A1; KR900006471A

Abstract

ABSTRACT OF THE DISCLOSURE

A heat-vulcanizable adhesive for the surface-bonding of solids is described, which contains polybutadiene or a polybutadiene mixture, and/or copolymer of butadiene with olefins and/or diolefins, and optionally other vulcanizable polymer components. Said adhesive is characterized by a content of at least 0.5 weight% (based on the vulcanizable polymers) metal salt from the group of drying agents for drying oils functioning as a hardening catalyst. The adhesive is particularly useful in vehicle assembly: a protective skin, which imparts washer resistance to the adhesive, is formed in less than 5 hours under prevailing working conditions.

Description

20~077 PATENT
Case D8272 HEAT-WLCANIZABLE ADHESIVE AND A METHOD FOR BONDING

Backaround of the Invention The invention concerns heat-vulcanizable adhesives for the bonding of solids. The adhesives contain polybutadiene or polybutadiene mixtures, and/or copolymers of butadiene with olefins and/or diolefins, and optionally other vulcanizable polymer components. The invention also concerns the application of the heat-vulcanizable adhesives in a method for the bonding of solids, particularly steel sheet for vehicle or automobile assembly.
In vehicle or automobile assembly, and particularly in assembly of automotive bodies, steel sheet components are often adhesively bonded using unfinished steel sheet. The adhesive used for this purpose is subsequently hardened in the lacquer drying ovens. Prior to adhesive hardening in the lacquer drying ovens, the bonded workpiece passes through cleaning, phosphatizing, and dip-priming stages.
The agents used in these stages can wash the adhesive from the glued seams. Various measures are known for preventing wash-out of the adhesive. For example, thermal-inductive prehardening of the adhesive, use of a solvent-containing adhesive formulation, use of a two-component formulation, or use of a strip or a round cord form have been attempted to prevent wash-out. These measures suffer from specific disadvantages or require the installation of special equipment.
EP-A 0 097 394 discloses heat-vulcanizable, polybutadiene-based adhesives which contain, in addition to polybutadiene or a polybutadiene mixture, sulfur, fillers, water-binding agents (particularly calcium oxide), vulcanization auxiliaries, and vulcanization accelerators. These adhesives have a particularly poor resistance to being washed from the glue seam during the aqueous cleaning, phosphatizing, and dip-priming.
The invention is an improved heat-vulcanizable, polybutadiene-based adhesive which can be processed using application equipment commonly available in the industry and which, due to their content of a special hardening catalyst, form a skin shortly after application under normal working conditions without fully hardening, wherein this skin protects the adhesive from the effects of the cleaning, phosphatizinq, and dip-priming ag~nts.

Brief Description of the Invention In accordance with the invention, heat-vulcanizable adhesives are provided which contain, as hardening catalyst, at least 0.5 weight% (based on vulcanizable polymers) of at least one metal salt from the group of drying agents for drying oils, wherein the type and amount of said metal salt is selected such that a skin forms on the surface of the adhesive within less than 5 hours at room temperature in the presence of atmospheric oxygen.
The adhesives of the invention are suitable for bonding the surfaces of solids such as metal (particularly steel), glass, ceramics, and the like to form composites of like or different materials.

Dètailed_~esçription of the Invention The metal salts present according to the invention are themselves known as drying agents for drying oils; see Ullmann, Encyclopedia of Industrial Chemistry, 5th Edition, Volume A9, (1987), pp. 63/64 as well as the 4th Edition (in German), Volume 23, (1984), pp. 421-424 S (Verlag Chemie Weinheim). These drying agents include in particular the oil-soluble metal salts of organic acids.
The acid moiety of the metal salts can be, for example, a monocarboxylic or polycarboxylic acid. Preferred within the context of the invention are the salts of monocarboxylic acids, particularly of naphthenic and/or isooctanoic acids. In a preferred embodiment of the invention, the hardening catalyst contains metal salts having cobalt, lead, zinc, manganese, cerium, and/or zirconium as the metal cation. However, skin formation -as desired within the framework of the present invention -is in fact undesirable during the drying of drying oils.
Therefore, in the prior art compositions, these metal salts were used at very low concentrations, and generally in combination with agents to prevent skin formation.
The specialist can easily determine the upper limit to be observed according to the invention for the addition of hardening catalyst. This limit is preferably lies up to about 10 weight%: additional quantities of the catalyst either will not increase or will only insignificantly increase the rate of skin formation on the surface of ~he adhesives used.
The air surrounding the workpiece supplies the oxygen necessary for skin formation after application of the adhesive. The ambient temperature to which the workpiece should be exposed after adhesive application and until skin formation as a general matter corresponds to room temperature of, for example, the assembly shop, and between about 15 and about 35 degrees Centigrade. Thus, skinning according to the invention advantageously proceeds under normal working conditions.

Z0~1077 Within the framework of the invention, polybutadiene refers to the different, structurally isomeric homopolymers of 1,3-butadiene. Butadiene homopolymers occur in two structurally isomeric forms, that is, as 1,4-polybutadiene and 1,2-polybutadiene.
1,4-polybutadienes are linear and unbranched and contain main-chain double bonds which can have a cis or trans configuration. 1,2-Polybutadienes contain side groups with a vinylic double bond.
All of the aforementioned polybutadiene isomers are suitable for use in the adhesives of the invention. A
preferred embodiment of the invention contains 1,4-polybutadiene, particularly cis-1,4-polybutadiene having at least 70% double bonds in the cis configuration.
Polybutadienes having 80 or even 98% double bonds in the cis configuration are particularly useful. These polybutadienes are commercially available. It is known that cis-1,4-polybutadienes have excellent hardening properties, with the result that these materials are particularly preferred when rapid skinning is required.
Furthermore, within the context of the invention, 1,4-polybutadiene can be used which contains more than 50%
trans double bonds, for example, products having 60 to 98%
trans double bonds. Poly-1,2-butadienes, i. e., substances with vinylic double bonds, can also be used. Products having 20 to 99% pendant double bonds, for example, products containing more than 40%, more than 80%, or even more than 90% of these double bonds, are very suitable as starting material.
In most cases, mixtures of isomers of polybutadiene -so-called polybutadiene mixtures are used for the adhesives of the invention. For example, 1,4-polybutadienes can be used which contain 20 to 70% cis double bonds and/or 20 to 50% trans double bonds and which can also contain 0 to 3%, or 3 to 30%, or more pendant 200~077 vinylic double bonds. Polybutadienes can be produced in the different configurations according to methods known in polymer chemistry, see, for example, H. G. Elias, '~Macromolecules", 4th Edition, Huethig & Wepf Publishing Company, Basel, Heidelberg, New York, p. 676 ("Cis" to "Trans" Configuration Change) and pp. 744-746 and 1012 ff.
In a particularly preferred embodiment of the invention, at least one of the polybutadienes making up the polybutadiene mixture contains at least 70% double bonds in the cis configuration and comprises at least 50 weight% of the polybutadiene mixture.
In another preferred embodiment of the invention, the polybutadiene or polybutadiene mixture has a number-average molecular weight in the range of 1,000 to 10,000.
Copolymers of butadiene with olefins and/or diolefins, for example, with styrene or acrylonitrile, can also be used in the heat-vulcanizable adhesives of the invention in place of polybutadiene or in mixture with polybutadiene.
Preferred butadiene copolymers contain at least 40 weight%
and particularly at least 60 weight% butadiene.
Furthermore, the adhesives of the invention can contain other vulcanizable components, for example, polychlorobutadiene, polyisoprene, EPDM rubber, butyl rubber, acrylate rubber, as well as chlorobutyl rubber and bromobutyl rubber. These other vulcanizable components are preferably used in minor quantities relative to the polybutadiene mixture.
In another preferred embodiment of the invention, the heat-vulcanizable adhesives of the invention contain sulfur and/or sulfur-containing vulcanization agents.
Sulfur-containing w lcanization agents are defined in Ullmann, Encyclopedia of Industrial Chemistrv, 4th Edition, Volume 13, pp. 639-640, Verlag Chemie Weinheim (1977), which is incorporated herein by reference. Typical examples of sulfur-containing vulcanization agents, known 20010~7 as sulfur donors, are dimorpholyl disulfide, 2-morpholinodithiobenzothiazole, caprolactam disulfide, and dipentamethylenethiuram tetrasulfide, as well as the thioplasts.
In another preferred embodiment of the invention, the heat-vulcanizable adhesives contain vulcanization accelerators and vulcanization auxiliaries. These are familiar to the specialist in the field of rubber vulcanization, see Ullmann, loc. cit., pp. 639-644; the lo same holds for ageing and fatigue inhibitors, pp. 644-6s0.
Zinc oxide is a particularly preferred vulcanization auxiliary within the context of the invention. Some preferred vulcanization accelerators are, for example 2-mercaptobenzothiazole, dibenzothiazyl disulfide, the zinc salt of 2-mercaptobenzothiazole, benzothiazyl-2-cyclohexylsulfenamide, benzothiazyl-2-tert-butylsulfenamide, benzothiazyl-2-sulfene morpholide, benzothiazyldicyclohexylsulfenamide, diphenylguanidine, di-ortho-tolylguanidine, ortho-tolylbiguanide, tetramethylthiuram disulfide, tetramethylthiuram monosulfide, zinc N-dimethyldithiocarbamate, zinc N-diethyldithiocarbamate, zinc N-dibutyldithiocarbamate, zinc N-ethylphenyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, ethylenethiourea, diethylthiourea, and diphenylthiourea.
In another preferred embodiment of the invention, the heat-vulcanizable adhesives can contain fillers which are well known to the rubber specialist, for example, calcium carbonate, talc, pyrogenic silica, and carbon black.
Pigments with a filler character are also included among useable fillers. Other suitable fillers can be found in the aforementioned Ullmann, 4th Edition, Volume 13, pp.
650-654.
According to another preferred embodiment of the invention, the heat-vulcanizable adhesives contain a water-binding agent which functions to prevent pore formation in the adhesive during hardening by water which may be present. Calcium oxide is a particularly preferred ` water-binding agent for the adhesives of the invention.
The adhesives of the invention can also contain additives commonly used in vulcanizable compositions, such as aging and fatigue inhibitors, for example, as are described in greater detail in the aforementioned Ullmann, 4th Edition, Volume 13, pp. 644-650. The vulcanizable adhesive has the following composition in another preferred embodiment of the invention:
a) 20 to 50 weight parts polybutadiene or polybutadiene mixture, b) 1 to 8 weight parts sulfur and/or sulfur-containing vulcanization agent, c) 30 to 70 weight parts filler, d) 1 to 10 weight parts water-binding agent, e) 2 to 8 weight parts vulcanization auxiliary, f) 1 to 6 weight parts vulcanization accelerator, g) 0.5 to 10 weight% (based on vulcanizable components) metal salt as hardening catalyst, and, optionally, h) commonly used additives such as aging inhibitors and/or fatigue inhibitors.
Particularly preferred are heat-vulcanizable adhesives of the following composition:
a) 20 to 50 weight parts polybutadiene or polybutadiene mixture, b) 4 to 6 weight parts ~ulfur, c) 40 to 60 weight parts filler from the group comprising calcium carbonate, talc, and carbon black, d) 3 to 8 weight parts calcium oxide as water-binding agent, e) 3 to 5 weight parts zinc oxide as vulcanization auxiliary, f) 2 to 5 weight parts vulcanization accelerator, g) 0.5 to 10 weight% (based on vulcanizable components) of a metal salt as hardening catalyst, and, optionally, h) typical additives such as aging inhibitors and/or fatigue inhibitors.
The invention also comprises a method for the bonding of solids, particularly steel sheet for vehicle assembly, using a heat-vulcanizable adhesive which contains polybutadiene or a polybutadiene mixture, and/or copolymers of butadiene with olefins and/or diolefins, and, optionally, other vulcanizable components, and as a hardening catalyst at least 0.5 weight% (based on vulcanizable components) of a metal salt from the group of drying agents for drying oils. The type and quantity of the hardening catalyst is selected such that a skin forms on the surface of the adhesive in less than five hours in the presence of atmospheric oxygen. The adhesive is applied to the surface of at least one solid element, the surfaces to be bonded are joined, and the adhesive is hardened under the effect of heat. In a particularly advantageous method, the solids to be bonded, whose surfaces may carry impurities, particularly greases or oils, are cleaned, phosphatized, and/or dip-primed only after application of the adhesive, joining of the parts, and formation of a skin on the surface of the adhesive.
The adhesive is then hardened under the action of heat, as desired during enamelling.

Examples The invention is explained in greater detail using the 1~ following preferred examples.

Examples 1 to 4 The components listed in Table 1 were mixed for one hour in a commercial planetary paddle mixer with a 500 kg capacity.
Table 1 also lists the formulation used for the comparison test, as well as the skin formation time (hours) and tensile shear strength for all formulations.
The time (in hours) required at room temperature in the presence of atmospheric oxygen to form a skin which stabilized the applied adhesive against the effects of washing, phosphatizing, and dip-priming ("washer resistance") was used as the "skin formation time". Washer resistance must be achieved within 2 to 5 hours. This corresponds to the time between application of the adhesive on the workpiece and the appearance of washer resistance.
As can be seen from the comparison test, an adhesive lacking drving agent according to the invention does form a skin after a considerably longer period of time (more than 72 hours), but this skin remains very thin due to the absence of a thorough drying. Protection of the adhesive is not achieved.
The washer resistance was determined by spraying hot water on and/or between applied qlue lines according to the following test method:

Z00107~
Two glue lines (250 x 30 x 2 mm) were applied at a distance of 50 mm from one another on an oiled steel sheet (300 x 300 mm). After a prescribed standing time at room temperature, the horizontally positioned sample was exposed to a water jet at 50 degrees Centigrade ~5 degrees Centigrade at a pressure of 68 kN/m2 through a No. 1/2 GG-25 Full Jet nozzle from the Spraying System Company. The distance between sample and nozzle was 250 mm. The water jet was directed between the lines for one minute. The degree of deformation or shift in the glue line was subsequently evaluated and the quantity of cooled adhesive was determined gravimetrically. There was no shift in the glue lines or loss of adhesive at the indicated skin formation times.
The tensile shear strength was measured according to DIN 53 283 on a 2 mm or 0.3 mm thick layer after a hardening time of 30 minutes at 180 degrees Centigrade in an air-circulation oven.
Table 1 demonstrates that the adhesives of the invention formed the desired stabilizing skin after 2 or 3.5 hours. The adhesive of the comparison formulation took over 72 hours to form a very thin skin which did not provide washer resistance.
The formulations of the Examples are shown as parts by weight in Table 1.

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Claims

1. Heat-vulcanizable adhesive for the bonding of solid substrates comprising vulcanizable polymers comprising polybutadiene or a polybutadiene mixture, and/or copolymer of butadiene with olefins and/or diolefins, and at least 0.5% by weight, based on the weight of the vulcanizable polymers, of a hardening catalyst, metal salt selected from the group consisting of drying agents for drying oils, wherein an amount of the hardening catalyst is provided so that a skin forms on the surface of the adhesive in less than five hours at room temperature in the presence of atmospheric oxygen.

2. A heat-vulcanizable adhesive of Claim 1, wherein the adhesive contains up to 10 weight% hardening catalyst (based on the vulcanizable polymers).

3. A heat-vulcanizable adhesive of Claim 1 or 2, wherein the hardening catalyst comprises at least one metal salt having cobalt, lead, zinc, manganese, cerium, and/or zirconium as the metal cation.

4. A heat-vulcanizable adhesive of Claim 1 or 2, wherein the hardening catalyst comprises at least one oil-soluble metal salt of an organic acid.

5. A heat-vulcanizable adhesive of Claim 4 wherein the oil-soluble initial salt of an organic acid is a salt of a monocarboxylic acid.

6. A heat-vulcanizable adhesive of claim 5 wherein the oil-soluble metal salt of an organic acid is a metal salt of naphthenic or isooctanoic acid.

7. A heat-vulcanizable adhesive of claim 1 or 2 wherein the adhesive contains 1,4-polybutadiene having at least 70% double bonds in the cis configuration.

8. A heat-vulcanizable adhesive of Claim 1 or 2 wherein the adhesive contains a polybutadiene mixture wherein at least one polybutadiene in the polybutadiene mixture contains at least 70% double bonds in the cis configuration and comprises at least 50 weight% of the polybutadiene mixture.

9. A heat-vulcanizable adhesive of Claim 1 or 2 wherein the polybutadiene has a number-average molecular weight in the range of 1,000 to 10,000.

10. A heat-vulcanizable adhesive of Claim 1 or 2 containing a copolymer of butadiene with olefins and/or diolefins wherein the copolymer contains at least 40 and preferably at least 60 weight% butadiene.

11. A heat-vulcanizable adhesive of Claim 1 or 2, wherein the adhesive contains a vulcanization accelerator, vulcanization auxiliary, filler, water-binding agent, and sulfur and/or sulfur-containing vulcanization agent.

12. A heat-vulcanizable adhesive of Claim 1 or 2 wherein the adhesive contains ageing and/or fatigue inhibitors.

13. A heat-vulcanizable adhesive of Claim 1 or 2, comprising:
a) 20 to 50 parts by weight polybutadiene or polybutadiene mixture;

b) 1 to 8 parts by weight sulfur and/or sulfur-containing vulcanization agent;
c) 30 to 70 parts by weight filler;
d) 1 to 10 parts by weight water-binding agent, e) 2 to 8 parts by weight vulcanization auxiliary;
f) 1 to 6 parts by weight vulcanization accelerator;
g) 0.5 to 10 weight% (based on vulcanizable polymers) of at least one metal salt as hardening catalyst;
and, h) 0-10 parts by weight of commonly used additives such as ageing inhibitors and/or fatigue inhibitors.

14. A heat-vulcanizable adhesive of Claim 1 or 2 comprising:
a) 20 to 50 parts by weight polybutadiene or polybutadiene mixture;
b) 4 to 6 parts by weight sulfur;
c) 40 to 60 parts by weight of a filler selected from the group comprising calcium carbonate, talc, pyrogenic silica, and carbon black;
d) 3 to 8 parts by weight calcium oxide as a water-binding agent;
e) 3 to 5 parts by weight zinc oxide as a vulcanization auxiliary;
f) 2 to 5 parts by weight vulcanization accelerator;
g) 0.5 to 10 % weight (based on vulcanizable polymers) of at least one metal salt hardening catalyst;
and h) 0-10 parts by weight commonly used additives such as ageing inhibitors and/or fatigue inhibitors.

15. A method for the bonding of solids, particularly steel sheet for vehicle assembly, which comprises: applying an adhesive which contains polybutadiene or a polybutadiene mixture, and/or copolymer of butadiene with olefins and/or diolefins, and optionally other vulcanizable polymer components and, as hardening catalyst, at least 0.5% by weight (based on the vulcanizable polymers) of at least one metal salt from the group consisting of drying agents for drying oils, the amount of the hardening catalyst being provided such that a skin forms on the surface of the adhesive in less than five hours at room temperature in the presence of atmospheric oxygen; joining the solids to be bonded; and hardening the adhesive under the effect of heat.

16. A method of Claim 12, where after joining of the solids to be bonded and a skin has formed on the surface of the adhesive, the joined solids are cleaned, phosphatized, and/or dip-primed before hardening of the adhesive under the effect of heat.