Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1997-11-12
1999-03-30
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C08K 310
Patent
active
058891072
DESCRIPTION:
BRIEF SUMMARY
The invention relates to hydrosols of metal complex salts, comprising surface-active substances, and to a special process for the free-radical emulsion polymerization of vinyl esters in the presence of these hydrosols as seed base. The invention additionally relates to the use of polyvinyl ester dispersions prepared in this way as adhesives for porous or semiporous substrates.
Aqueous dispersions of polyvinyl esters, especially those of polyvinyl acetate, are used as so-called white glues for bonding wood and other porous substrates. Adhesives of this kind have been described in the literature, for example in Handbook of Adhesives, 3rd edition, chapter 21, Van Nostrand Reinhold, New York, 1990 and in Wood Adhesives--Chemistry and Technology, volume 1, chapter 7, Marcel Dekker, New York, 1983.
These adhesives are usually prepared by free-radical emulsion polymerization of the vinyl esters in the presence of polymeric stabilizers, so-called protective colloids, especially polyvinyl alcohol. A review of this process, which is treated extensively in the technical literature, can be found, for example, in Wood Adhesives--Chemistry and Technology, volume 2, chapter 2, Marcel Dekker, New York, 1989.
The emulsion polymerization of vinyl esters, especially vinyl acetate, in the presence of polyvinyl alcohol usually produces dispersions of relatively high viscosity. Also, compared with dispersions stabilized only with the aid of pure emulsifiers, the particle-size distributions are broader. Depending on the polymerization process, the type of initiator, the type of stabilizer and other parameters it is also common, furthermore, to observe instances of particle agglomeration. This phenomenon is the cause in particular of a further increase in the viscosity of the dispersions, going as far as to produce a pastelike consistency and to impair flow. This also causes a loss in shear stability and, in general, adversely affects the reproducible preparation of dispersions within narrow viscosity limits.
A subgroup of polyvinyl ester dispersions is formed by those whose adhesive bonds are of enhanced water resistance. In these dispersions, the hydrophilicity of the polyvinyl alcohol used as protective colloid is often reduced by copolymerization with vinyl compounds having a crosslinking action, such as N-methylol(meth)acrylamide.
Such a method is proposed, for example, in the documents U.S. Pat. No. 3,301,809, DE-C 26 20 738 and DE-A 39 42 628. In combination with acidic curing agents, such as aqueous mineral acids or acidic metal salts, for example aqueous solutions of aluminum chloride, water-resistant adhesives are obtained.
A known disadvantage of the process is that the copolymerization of increasing quantities of the crosslinking agent, N-methylol(meth)acrylamide, results in a further drastic increase in viscosity being observed. Moreover, on storage, the dispersions--especially in the acid-catalyzed form--tend to show an increase in viscosity and structure. The pot life of the acid-catalyzed glue formulations, therefore, is usually short.
The documents DE-C 26 20 738 and DE-A 39 42 628 describe a two-stage polymerization process in which part of a monomer mixture is included in the aqueous initial charge and part is metered in. The monomers involved are principally vinyl esters of acetic acid, pivalic acid and .RTM.Versatic acids (.alpha.,.alpha.-dialkylcarboxylic acids, Shell-Chemie) and also N-methylolacrylamide. Depending on the nature of the vinyl esters and the nature of the acidic catalysts added subsequently, glue formulations are obtained which have pot lives of at least 4 weeks.
In U.S. Pat. No. 4 085 074, volatile nitrogen bases such as ammonia, mono-, di- or trialkyl(ol)amines, especially triethanolamine, are proposed as crosslinking inhibitors for the acidic metal salts such as aluminum chloride. The bases are added to the glue formulations subsequently. The stability of formulations modified in this way, on storage, exceeds 3 months, although their viscosities prior to storage, at <1.5 Pa.cndot.s, are
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"Polyvinyl Acetate Emulsions for Adhesives", Handbook of Adhesives, 3rd Edition, Chapter 21, Van Nostrand Reinhold, New York, 1990.
"The Chemistry of PVA", Wood Adhesives--Chemistry and Technology, vol. 1, Chapter 7, Marcel Dekker, New York, 1983.
"Polyvinyl Acetate Wood Adhesives", Wood Adhesives--Chemistry and Technology, vol. 2, Chapter 2, Marcel Dekker, New York, 1989.
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Hennemann Heinz
Jakob Martin
Matz Volker
Cain Edward J.
Clariant GmbH
McCann Philip P.
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