MXPA97005664A - Structural adhesives, with rubber base, for lines without revestimie - Google Patents

Abstract

The present invention relates to a composition that hardens with heat, of a component, based on liquid rubbers, characterized in that it contains fine particle powders of thermoplastic polymers and, in its hardened state, has an elongation at break of more than 1.

Description

STRUCTURAL ADHESIVES, WITH RUBBER BASE, FOR COATING WITHOUT COATING This invention relates to compositions that harden with heat, one component, based on liquid rubbers and thermoplastic polymers in powder form of fine particles, and their production and use as structural adhesives, with an elongation at break of more than 15% . In modern assembly techniques for joining metal components in the construction of machines, vehicles or equipment manufacturing, more specifically in the manufacture of automobiles, conventional methods of assembly such as beading, bolting or welding, are increasingly replaced by the adhesion. Especially electric welding, which is a source of future corrosion, is being replaced, when possible, or applied in combination with structural adhesives. For this reason, there is a growing demand for high strength structural adhesives. For reasons of assembly, these adhesives have to be used in the stage known as lining without coating in the manufacture of automobiles, that is, the adhesives are usually applied to the metal surface without pickling. These surfaces are usually covered with various corrosion-inhibiting oils and oil soluble for deep-drawing, so that the adhesives used should not be affected functionally by these oils. In addition, the adhesives must be able to withstand - preferably without pre-freezing - the different wash baths and installations and the high temperatures of up to around 240 ° C prevailing in the cooking ovens during electrocoating and must also harden at temperatures of this order. Moreover, adhesives are required to have good aging-resistant adhesion for various galvanized steels, for example, for electrolytically galvanized steel plates, galvanized hot-dip galvanized steel plates and corresponding annealed and galvanized steel plates or Galvanized and then phosphatized steel plates. The structural adhesives for these applications must also have a minimum strength of around 15 MPa. In the interest of uniform operation in the assembly line, only materials that are capable of being transported by pumps and applied by machines are suitable. Taking into account the demanding strength requirements, one-component thermoset epoxy adhesives have been used primarily for these applications in the past. However, apart from the advantages of high tensile strength, epoxy adhesives have numerous important disadvantages. One-component, thermosetting, paste-like epoxy adhesives do not show adequate resistance to washing in the wash and phosphating baths, so that the corresponding joints normally have to be pre-gelled by thermoinduction or in special ovens. Unfortunately, this implies an additional stage. Attempts have been made to overcome this situation by developing one-component, thermoset epoxy adhesives that resemble the melts in character. Unfortunately, these adhesives require special application systems since they have to be applied hot. Another general disadvantage of epoxy adhesives is their tendency to absorb moisture under the effect of high atmospheric humidity, which can give rise to corrosion phenomena and weakening of the joint at the junction line. Although epoxy adhesives are distinguished by their high tensile strength, their elongation at break is usually very bad; even epoxy adhesives flexibilized by rubber adhesion have a breaking elongation of less than 5%. In addition, the use of epoxy adhesives based on low molecular weight expóxicos compounds (molecular weight <700) is undesirable in industrial hygiene areas, since these low molecular weight epoxies can initiate allergic or sensitization reactions in contact with the skin. For some time, compositions based on vulcanizable rubbers have been used as an alternative. EP-B-97 394 discloses an adhesive mixture based on liquid polybutadiene rubber, sulfur in powder form, organic accelerators and optionally solid rubber. According to B. D. Ludbrook, Int. J. Adhesion and Adhesives, vol. 4, No. 4, pages 148-150, the corresponding adhesives based on liquid polybutadienes are able to achieve levels of resistance equivalent to the felxibilized epoxy adhesives through a suitable choice of the amount of sulfur and accelerators. While these formulations have good hardening properties and show high resistance to aging and still adhere in an acceptable manner to normal lubricated steel plates, their utility for different galvanized steel plates is limited, in addition to which the breaking elongation of these high strength rubber adhesives. To improve the adhesion, the patent DE-C-38 34 818 proposes the use of polybutadienes terminated in OH for liquid rubber. According to EP-B-441 244, homopolymers or copolymers containing diol, amino, aido, carboxyl, epoxy, isocyanate, anhydride or acetoxy groups can be used in addition to hydroxy-functional homopolymers or copolymers such as functional rubber polymer, although the hardened adhesive mixture has an elongation at break of not more than 15%. According to EP-B-309,903 and DE-C-40 27 064, the polyfunctional epoxy compounds can be added to adhesive mixtures based on liquid rubbers to improve adhesion and tensile shear strength. Regardless of the fact that it is undesirable for the reasons explained in the above to use adhesive compositions containing epoxy resins, the adhesive compositions described in the last two documents are not suitable as structural adhesives because they only reach a very low level of resistance at the earliest. 3 MPa. Accordingly, the problem referred to by the present invention was to provide adhesives and sealing liquids which could be used with advantage to join metal parts of automobile linings ("unlined linings") and which: show adequate permanent adhesion on various metal surfaces currently used without any need for pre-treatment of desalting or pickling. - which can be used as structural adhesives (structural adhesives in the context of the invention are adhesives that achieve a strength of at least 15 MPa in tensile cutting tests), which have an elongation at break according to DIN 53504 of more than 15% and preferably more than 20%, in addition that the materials consist of a component that hardens with heat and that hardens at temperatures of 160 ° C to 240 ° C, that its resistance properties are not sigificatively affected by the hardening temperature apart from normal, lubricated steel plates, the substrates on which adhesion must be obtained includes, in particular, the various galvanized and lubricated steel plates and aluminum plates.

According to B. D. Ludbrook loe. cit., the strength values of vulcanized rubber adhesives can be significantly increased by the amount of sulfur and accelerator, but always to the detriment of the elongation at break. It has surprisingly been found that adhesion of fine particle powders of thermoplastic polymers to liquid rubber based adhesives not only increases tensile shear strength, it also significantly improves the elongation at break. Given the other properties, for example the resistance to aging and the adhesive behavior on the aforementioned substrates, are not affected by the adhesion of the thermoplastic polymer powder, the adhesives in question are much more universal in their utility. In this way, the structural adhesives can still be used for the first time where, until now, it has only been possible to use adhesives with lower strength levels taking into account the high necessary elasticity, as is the case, for example, with coating adhesives to join internal panels to external loaves in the manufacture of automobiles where high rigidity of the torsion is required for structural reasons. The sealant adhesive compositions according to the invention contain at least one of the following substances. one or more liquid rubbers and / or solid rubbers or elastomers. fine particle powders of vulcanization agents of thermoplastic polymers, vulcanization accelerators, catalysts. filling materials and / or primers. auxiliary oils - auxiliary anti-aging for flow The liquid rubbers or elastomers can be selected from the following group of homopolymers and / or copolymers: polybutadienes, more particularly 1,4- and 1,2-polybutadienes, polybutenes, polyisobutylenes, 1,4- and 3,4-polyisoprenes, copolymers of styrene / butadiene, butadiene / acrylonitrile copolymers, these polymers may have terminal and / or lateral functional groups (statistically distributed). Examples of these functional groups are hydroxy, amino, carboxyl, carboxylic anhydride or epoxy groups. The molecular weight of these liquid rubbers is usually less than 20,000 and preferably between 900 and 10,000. The percentage content of liquid rubber in the composition as a whole depends on the required rheology of the unvulcanized composition and the required mechanical properties of the hardened composition. This percentage content of the liquid rubber or elastomer usually varies between 5 and 50% by weight based on the formulation as a whole. In this sense, it has been shown that it is useful to use mixtures of different liquid rubbers both in their molecular weight and in their configuration in relation to the remaining double bonds. To achieve optimum adhesion on the various substrates, a liquid rubber component containing hydroxyl groups or anhydride groups is used in the particularly preferred formulations. At least one of the liquid rubbers should have a percentage content of cis-1 double bonds, 4, while the other liquid rubber must have a high percentage of vinyl double bonds. By comparison with liquid rubbers, suitable solid rubbers have a significantly higher molecular weight (MW = 100,000 or greater). Examples of suitable rubbers are polybutadiene, preferably with a very high percentage of cis-1,4 double bonds (usually above 95%), styrene / butadiene rubber, butadiene / acrylonitrile rubber, synthetic isoprene rubber or natural, butyl rubber or polyurethane rubber. The addition of thermoplastic polymer powders into fine particles produces a significant improvement in tensile shear strenwhile maintaining a very high elongation of fracture hitherto uncommon for structural adhesives. In this way, resistance to constant tensile stress of more than 15 MPa can be achieved for breaking extensions well above 15% and, very often, above 20%. The structural adhesives with high strenhitherto conventionally used were based on epoxy resins that only had fracture elongations of less than 5%, even as flexibilized adhesive formulations. The combination of high tensile shear strenvalues with high elongation at break is attributed to the adduction of thermoplastic polymer powders according to the invention. According to the invention, various thermoplastic polymer powders are suitable adhesives, in which are included, for example, vinyl acetate in the form of a homopolymer or in the form of a copolymer with ethylene and other olefins and derivatives of acrylic acid , polyvinyl chloride, vinyl chloride / vinyl acetate copolymers, styrene copolymers of the type described, for example, in DE-A-40 34 725, polymethyl methacrylate and copolymers thereof with other (meth) acrylates and functional comonomers, for example, of the type described in DE-C-24 54 235, or polyvinyl acetals, for example, polyvinyl butyral. Although the size of the particle, or rather, the particle size distribution of the polymer powders does not appear to be particularly crucial, the average particle size must be below 1 mm, preferably below 350 microns and more preferred between 100 and 20 microns. Polyvinyl acetate and ethylene / vinyl acetate (EVA) based copolymers are more particularly preferred. The amount of the thermoplastic polymer powder that is added is determined by the range of strenrequired and is between 2 and 20% by weight based on the composition as a whole, with a range of 10 to 15% being particularly preferred. Since the crosslinking or hardening reaction of the rubber composition has a significant influence on the tensile shear strenand the elongation at break of the hardened adhesive composition, the vulcanization system has to be selected and adapted with extreme care. The various vulcanization systems based on elemental sulfur and vulcanization system without free sulfur can be used. The vulcanization systems without free sulfur include those based on thiuram disulfides, organic peroxides, polyfunctional amines, quinones, p-benzoquinone dioxime, p-nitrosobenzene and dinitrosobenzene and also systems crosslinked with diisocyanates (block). Vulcanization systems based on elemental sulfur and accelerators of vulcanization, organic and also zinc compounds are most particularly preferred. Sulfur in the form of powder is used in amounts of 4 to 15% by weight based on the total composition, with 6 to 8% being particularly preferred. Suitable organic accelerators are dithiocarbamates (in the form of their ammonium or metal salts), xanthogenates, thiuram compounds (monosulfides and disulfides), thiazole compounds, aldehyde / amine accelerators (for example, hexamethylene tetramine) and also guanidine accelerators, dibenzothiazyl disulfide (MBTS) being particularly preferred. These organic accelerators are used in amounts of 2 to 8% by weight, based on the formulation as a whole and preferably in quantities of 3 to 6%. In the case of zinc compounds which act as accelerators, an option may be made between the zinc salts of the fatty acids, zinc dithiocarbamates, basic zinc carbonate and, in particular, zinc oxide in fine particles. The content of the zinc compounds is in the range of 1 to 10% by weight and preferably in the range of 3 to 7% by weight. In addition, other common vulcanization agents of the rubber, eg, fatty acids (eg, stearic acid) may be present in the formulation. Although, in general, the compositions according to the invention already show very good adhesion to the substrates to which they are to be joined by virtue of the presence of the liquid rubber containing the functional groups, when necessary, it is possible to add binders and / or primers. . Suitable binders and / or primers are, for example, hydrocarbon resins, phenolic resins, terpene / phenol resins, resorcinol resins or derivatives thereof, modified or unmodified resin acids or esters (abietic acid derivatives), polyamides, polyaminoamides, anhydrides and copolymers containing anhydride. The addition of polyepoxic resins in small amounts (<1% by weight) can also improve adhesion on some substrates. In this case, however, preferably solid epoxy resins with a molecular weight well above 700 in finely ground form are used so that the formulations are still substantially free of epoxy resins, especially those with molecular weights less than 700. If glueings or primers are used, the type and amount used will depend on the composition of the adhesive / sealant polymer, the strength required of the hardened composition and the substrate to which the composition is to be applied. Common (sticky) sizing resins, for example terpene / phenol resins or resin acid derivatives are normally used in concentrations of 5 to 20% by weight while common primers, such as polyamides, polyaminoamides or resorcinol derivatives are used in concentrations of 0.1 to 10% by weight. The compositions according to the invention are preferably free of plasticizers for the thermoplastic polymer. More particularly, they are free of phthalic acid esters. However, it may be necessary to influence the rheology of the unvulcanized composition and / or the mechanical properties of the vulcanized composition by adhesion of the so-called extender oils, ie the aliphatic, aromatic or naphthenic oils. However, this preference influence is exerted by the suitable choice of low molecular weight liquid rubbers or through the use of low molecular weight polybutenes or polyisobutylenes. If the extender oils are used, they are used in quantities of 2 to 15% by weight. The fillers can be selected from a number of materials, which include in particular limestone, ground or precipitated natural calcium carbonates, calcium or magnesium carbonates, silicates, barium sulfate and also carbon black. Lamellar fillers, for example vermiculite, mica, talc or similar stratiform silicates, are also suitable as fillers. It can be useful for loading materials, be at least partially pretreated on its surface. The coating with stearic acid to reduce the introduced moisture and prevent the hardened composition from becoming sensitive to moisture has proved particularly useful for the various calcium carbonates and limestones. In addition, the compositions according to the invention generally contain between 1 and 5% by weight of calcium oxide. The total content of the filler materials in the formulation can vary from 10 to 70% by weight and is preferably in the range of from 25 to 60% by weight. Conventional stabilizers, for example sterically hindered phenols and amine derivatives can be used to prevent thermal, thermooxidative or ozone degradation of the compositions according to the invention, these stabilizers are usually used in amounts of 0.1 to 5% by weight. Although the rheology of the compositions according to the invention can normally be brought to the required range through the choice of the fillers and the proportion of the quantity of the low molecular weight liquid rubbers, the conventional rheology auxiliaries, For example, pyrogenic silicas, Bentones or cut fibers converted into pulp or fibrillated can be added in amounts of 0.1 to 7%. In addition, other auxiliaries and conventional additives can be used in the compositions according to the invention. As mentioned at the beginning, the preferred application for the one-component binder / sealant composition, according to the invention, is in the assembly of uncoated liners in the automotive industry, so that the compositions must be cured for 10 minutes. at 35 minutes at temperatures of 80 to 240 ° C, with temperatures from 160 ° C to 200 ° C being preferable for application during assembly of the liner without coating. The compositions according to the invention have the advantage over epoxy adhesives, that they run hot, that they need to be heated only slightly around 30 to 45 ° C for pumping and application, in addition to which their wetting power for cold substrates is considerably better than that of the epoxy melts, by virtue, among other things, of its inherent greater tackiness. The following examples are proposed to illustrate the invention without limiting it in any way. To determine the tensile shear strength, strips of 1.5 mm thickness of a 14 05 steel of 25 x 100 mm were bonded with the adhesives with a coating of 25 x 20 mm; the thickness of the adhesive layer was 0.2 mm. The steel strips had been lubricated in advance with ASTM Oil No. 1, the weight of the coating from 3 to 4 g / m2. The elongation at break and the tear strength were determined in a test sample S2 according to DIN 53 504, the thickness of the layer 2 mm. A tension tester was used, laboratory, conventional for both tensile tests (feed rate 50 mm / min). The adhesives were hardened in a laboratory oven with circulating air, hardening time: 30 min at 180 ° C. In an evacuable laboratory mixer, the compositions identified in the following tables were mixed in vacuo until they were homogeneous. Unless otherwise indicated, all parts in the Examples are parts by weight.

Table 1 Example 1 Basic axis Comparative example 1 Comparative 2 Polybutadiene 5.0 5.0 5.0 Solid (1) Polybutadiene 5.0 5.0 5.0 Liquid (2) Polybutadiene 15.0 15.0 15.0 Liquid (3) Polybutadiene 5.0 5.0 5.0 Liquid (4) Zinc Oxide 4.0 4.0 4.0 Active Sulfur in 7.0 5.0 7.0 Disulfide powder 5.0 5.0 5.0 dibenzothiazil (MBTS) 10.0 - polyvinyl acetate powder (5) Carbonate of 41.0 53.0 51.0 calcium oxide of 2.5 2.5 2.5 calcium Antioxidant 0.5 0.5 0.5 Resistance to 18.3 MPa 8 .2 MPa 14.7MPa shear stress by stretching Lengthening 26.0% 57.3% 4.96% breakage Resistance to 16.5 MPa 7.0 MPa 14.5 MPa tear (1) cis-1,4 at least 98%, viscosity Mooney 48 (ML4- 100) (2) PM around 1800, cis-1,4 around 72% (3) MW around 1800, vinyl around 40-50% (4) addition products polybutadiene / maleic anhydride, MW around 1700 (5) EVA Tg copolymer around 23 ° C Table 2 Example 2 Example 3 Example 4 Comparative example 1 Polybutadiene 5.0 5.0 5.0 5.0 Solid (1) Polybutadiene 5.0 5.0 5.0 5.0 Liquid (2) Polybutadiene 15.0 15.0 15.0 15.0 Liquid (3) Polybutadiene 5.0 5.0 5.0 5.0 Liquid (4) Zinc Oxide 4.0 4.0 4.0 4.0 Active Sulfur Powder 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 disulfide dibenzothiazil (MBTS) 10.0 polyvinyl chloride (5) styrene-10.0 methacrylate (6) - 10.0 polymethyl methacrylate (7) 43.0 43.0 43.0 43.0 calcium carbonate Calcium oxide 2.5 2.5 2.5 2.5 Antioxidant 0.5 0.5 0.5 0.5 Resistance to 9.8 MPa 9.8 MPa 11.9 MPa 8.2 Shear stress for traction Lengthening of 46.7% 34.1% 29.5% 57.3 rupture Resistance to 8.2 MPa 7.0 MPa 9.9 MPa 7.0 MPa tear (1) cis-1,4 at least 98%, viscosity Mooney 48 (ML4- 100) (2) MW around 1800, cis-1,4 around 72% (3) MW around 1800, vinyl around 40-50% (4) addition products polybutadiene / maleic anhydride, PM about 1700 (5) PVC in emulsion, value K 70 (6) styrene copolymer according to DE-A-40 34 725, 7.5% methacrylic acid (7) PMMA containing copolymerized vinyl imidazole In the test of resistance to constant effort by traction, a failure in the cohesion with all the samples of the test was observed. The only plate thicknesses available to determine the adhesion behavior on galvanized steel were the 0.8 mm plate thicknesses commonly used in the automotive industry. However, the high strength structural adhesives of the present examples are already in the range of strength of these thin steel plates, so that the adhesion behavior on these substrates could only be evaluated by a qualitative peeling test. For this purpose, steel plates were lubricated with ASTM Oil No. 1, hardened in the oven as described above and then evaluated in a manual desquamation test. The following substrates were tested: steel plates galvanized by electrolytic means, hot dip galvanized, galvanized and phosphated and annealed and galvanized. In all cases, cohesive failures were observed. As can be seen in a comparison of Comparative Example 1 with Comparative Example 2, the tensile shear strength or tear strength of the rubber based adhesives according to the prior art can be significantly increased only by a higher content of sulfur, although at the same time there is a drastic reduction in elongation at break. The addition of the polyvinyl acetate copolymer (Example 1) according to the invention produces a significant increase in tensile shear strength, but at the same time maintains the elongation at break at a higher level (26%). As can be seen from the comparison of Comparative Example 1 (without addition of the thermoplastic powder) to Examples 2 to 4, the tensile shear strength can be significantly increased with this addition, despite the low sulfur content, to through the addition of the various thermoplastic powders only with a very slight reduction in the elongation at break.

Claims (1)

1. CLAIMS A one-component, heat-curing composition based on liquid rubbers, characterized in that it contains fine particle powders of thermoplastic polymers and, in its hardened state, has an elongation at break of more than 15%. The heat hardening composition according to claim 1 is characterized in that it additionally contains at least one solid rubber in an amount of 1.5 to 9% by weight and preferably in an amount of 4 to 6% by weight based on in the whole composition. The heat hardening composition according to claim 1 or 2 is characterized in that it is substantially free of epoxy resins. The heat hardening composition, as claimed in at least one of the preceding claims, is characterized in that a vulcanization system with sulfur, organic accelerators for vulcanization and zinc compounds is used for curing. The heat hardening composition, as claimed in claim 3, is characterized in that the vulcanization system consists of 4% by weight at 15% by weight and preferably 5% by weight at 10% by weight of sulfur in the form of powder, 2% by weight at 8% by weight and preferably 3% by weight at 6% by weight of organic accelerator and 1% by weight at 8% by weight and preferably 2% by weight at 6% by weight of zinc compounds, preferably zinc oxide, the percentages by weight are based on the composition as a whole. The heat hardening composition according to at least one of the preceding claims is characterized in that the thermoplastic polymer powder is a vinyl acetate homopolymer or copolymer, an ethylene / vinyl acetate copolymer, a homopolymer or copolymer of vinyl chloride, a styrene homopolymer or copolymer, a homopolymer or copolymer of (meth) acrylate or a polyvinyl butyral or a mixture of two or more of these polymers and has an average particle size below 1 mm, preferably below of 350 microns and more preferably below 100 microns. The heat hardening composition, as claimed in at least one of the preceding claims, is characterized in that the composition is free of plasticizers for the thermoplastic polymer (s). The composition as claimed in at least one of the preceding claims is characterized in that it additionally contains fillers, auxiliaries for rheology, extender oils, primers and anti-vents. 9. The production of a reactive composition that hardens with heat, as claimed in at least one of the preceding claims, by the super-sharp mixing of the components. The use of the compositions, claimed in at least one of the preceding claims, as a component thermosetting structural adhesive. 11. The use, according to claim 10, for the assembly of a liner without coating in the manufacture of automobiles. 12. A process for joining metal parts and / or for sealing joints between metal parts, is characterized in that at least one one-piece surface is covered with the compositions claimed in at least one of the preceding claims, - the pieces, which are to be joined, are placed together, and the pieces together are optionally heated after the mechanical assembly, for harden the reactive composition. 13. A process for coating the structural components by spraying or extruding the claimed compositions into at least one of claims 1 to 8 on the surface of the piece and heating the coated piece to harden the composition. A process for coating, joining and / or sealing structural components is characterized in that an extruded film, an extruded cord or an extruded tape produced from the composition claimed in at least one of claims 1 to 8 applies in at least one structural component, the components are optionally placed together and then heated to harden the composition.