Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1995-11-13
2001-11-20
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S087000, C156S333000, C156S338000, C427S426000, C428S317700, C524S405000, C524S501000
Reexamination Certificate
active
06319352
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a sprayable dispersion based on an acrylic acid ester copolymer and a colloidal chloroprene polymerisate. The invention also concerns a process for the elastic adhesion of two substrate surfaces, of which at least one is porous in structure, using this dispersion. Here and below the term acrylic acid ester copolymer also comprises an acrylic acid ester styrene copolymer.
Acrylic acid ester copolymers are for example the substances ACRONAL 310S, S600 or DS3382 by the company BASF, chloroprene polymerisates are the substances DISPERCOLL C74 or C84 by the company BAYER.
When two substrate surfaces are coated with an adhesive and pressed together after the adhesive has dried, the adhesive is called a contact adhesive. This can only develop its effect when the solvent or water has evaporated. If only one of the two substrate surfaces to be joined is coated with an adhesive and the other substrate surface pressed on after evaporation of the solvent or water, we have a bonding adhesive. Of particular importance are contact adhesives based on polychloroprene, resins and organic solvents. The solid content is usually only 10-25 w. %, the organic solvents predominate by far.
Contact adhesives dissolved in highly volatile organic solvents can be processed quickly. This advantage is however largely or even predominantly eliminated by a number of disadvantages. The organic solvents which escape on spraying and drying represent a significant loss in economic terms. The volatile solvents are also inflammable, harmful to health and/or the environment. Therefore special systems must always be constructed and precautions taken to prevent or at least reduce the uncontrolled escape of solvents. EP, A1 0470928 describes a process for elastic adhesion of two substrate surfaces. At least one of these is porous in structure. A rubber-containing first dispersion with an acrylic acid ester copolymer and a colloidal second dispersion of a chloroprene polymerisate are applied to at least one of the substrate surfaces after prior or with simultaneous mixing. The substrate surfaces to be glued are then, immediately afterwards or later, laid against each other with the adhesive dispersions wet, and pressed together. The two substrate surfaces adhere with a high initial force even at room temperature and achieve a high final force. No organic solvents are required, but only low quantities of waste water occur which can easily be cleaned and disposed of. The spectrum of applications is broad but lies in particular in the adhesion of foams.
SUMMARY OF THE INVENTION
The inventors have faced the task of creating a sprayable dispersion and a process for elastic adhesion of two substrate surfaces with a dispersion of the type described initially, which further improves the initial adhesion force of the substrate surfaces laid against each other wet, also guarantees a high final adhesion force and in particular a long processing time after application of the dispersion, without loss of the ecological and economic advantages.
In relation to the sprayable dispersion, the task according to the invention is solved in that it contains boric acid which is mixed into the dispersion.
The sprayable dispersions can be used as contact or bonding adhesives. A high initial adhesion force absolutely comparable to those of solvent-containing adhesives can be achieved in seconds after application if the two substrate surfaces are laid against each other wet and pressed together. A similarly high initial adhesion force, which is even higher for a longer time, is achieved if the applied dispersions are first ventilated and then the substrate surfaces laid against each other wet. No production stoppages occur as the machine stoppage is shorter, and the applied dispersion remains wet for a long time.
The adhesion dispersions are pressure-sensitive. Immediately after pressing together, the actual bonding process begins without water being emitted. This is of great practical significance as wet surfaces coated with dispersion can be pressed together and immediately achieve the initial adhesion force necessary for further processing and/or transport. This force rapidly increases after processing and achieves for example the limit of tear for a foam of medium hardness.
The dispersions are produced in a mixer of conventional type where the chloroprene polymerisate is preferably added at the end. A mixed dispersion can be stored under airtight conditions for several months without coagulating.
Acrylic acid ester copolymers, including acrylic acid ester styrene copolymers as stated, can for example be made to contain rubber by the addition of natural unvulcanized latex. The chloroprene polymerisate can contain smaller quantities of monomers other than chloroprene, for example other dienes, acrylic acid or methacrylic acid. In total however the quantity of the other monomers added preferably does not exceed 30 w. % in relation to the chloroprene polymerisate. The mean particle size of the acrylic acid ester copolymer and the chloroprene polymerisate is preferably in the sub-micron range, in particular approximately 0.2 &mgr;m.
Watery dispersions of the, acrylic acid ester copolymer and the chloroprene polymerisate have for example a solid content of 30-70 w. %, in particular 40 to 65 w. %.
The isolated ratio of the acrylic acid ester copolymer to the colloidal chloroprene polymerisate can vary within a relatively broad band, preferably from 10 w. % acrylic acid ester copolymer: 90 w. % chloroprene polymerisate up to 60 w. % acrylic acid ester copolymer: 40 w. % chloroprene polymerisate. In other words, the weight ratio of acrylic acid ester copolymer to chloroprene polymerisate preferably lies in the range between 1:10 and 1.5:1. In practice the mixing ratio is usually around 50:50 w. % and, by deviation, as a trend more chloroprene polymerisate is added. The data on the mixing ratios always relates to the solid content.
For a general setting of the pH values and addition of secondary substances, see EP, A1 0470928 page 4 lines 22 to 33.
The addition of boric acid (H
3
BO
3
) to the dispersion, essential to the invention, preferably takes place in a quantity of 0.1 to 10 w. %, in particular 0.5 to 5 w. % in relation to the solid content. The addition of boric acid drastically improves the initial adhesion force of the sprayable dispersion even after a longer ventilation time.
With a high boric acid concentration, the boric acid is preferably first dissolved in glycerine.
Apart from the boric acid, sodium lauryl sulphate can be added, preferably in a concentration of 0.1 to 3 w. % in relation to the finished mixture. This improves the mechanical properties, in particular the processability, of the preferred sprays.
Organic components can also be added which specifically promote required properties of the dispersion: N-alkylpyrrolidone, for example in the form of N-methyl-2-pyrrolidone up to 15 w. % in relation to the solid content and/or N-octyl-2-pyrrolidone or N-dodecyl-2-pyrrolidone, in each case up to 10 w. % again in relation to the solid content.
N-methyl-2-pyrrolidone can also be mixed with N-octyl-2-pyrrolidone or N-dodecyl-2-pyrrolidone, with unchanged weight ratios. N-methyl-2-pyrrolidone is a softening agent, the two other pyrrolidones promote the coagulation ability and wetting.
With the aim of softening, improving adhesion, heat resistance and storage stability, in addition to boric acid, dimethylphthalate or diisobutylphthalate can be added as other components, preferably at up to 20 w. % again in relation to the solid content.
As indicated above, fine grain filler materials can be mixed in, preferably ZnO, MgO and/or colour pigments.
In relation to the process, the task is solved by the invention in that the dispersion is applied to at least one of the substrate surfaces, the substrate surfaces to be glued are applied to each other wet and pressed together with at least 0.1 N/cm
2
for approximately 0.5 seconds.
When the dispersion leaves a spray device, a spray nozzle, spray
Simmler Emil
Simmler Thomas
Alfa Klebstoffe AG
Bachman & LaPointe P.C.
Gallagher John J.
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