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...
Reexamination Certificate
2002-04-30
2004-04-20
Yoon, Tae H. (Department: 1714)
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...
C524S819000, C524S821000, C524S823000, C524S834000, C523S201000, C523S205000
Reexamination Certificate
active
06723779
ABSTRACT:
The invention relates to the field of surface treatment and in particular to hydrophobic thermoplastic films for surface coatings and more particularly to films obtained by low-temperature drying of a latex containing neither volatile organic compounds nor coalescents.
BACKGROUND OF THE INVENTION
In the context of the invention, the term “latex” should be understood to mean an aqueous dispersion of polymer particles which can be obtained by the emulsion polymerization of one or more monomers.
Many latices are intended for the building, paper, textile and leather industries and are used in the surface treatments of various materials, particularly as paints, varnishes, adhesives and mastics. More generally, such latices are required to have a minimum film-forming temperature, called hereafter MFT, as low as possible. The MFT is the lowest temperature at which the particles form a continuous film after the water has been evaporated.
When the polymers constituting the particles dispersed in a latex have a relatively low glass transition temperature, denoted by T
g
, it is easy for the latex to form a film at room temperature but the films obtained are tacky and their mechanical integrity is poor. On the other hand, if the polymers have a high T
g
, the films will be of better quality but film formation at room temperature would require the addition of a coalescents. The latter is generally a volatile organic compound which evaporates during application and film formation, as described in U.S. Pat. Nos. 4,455,402 and 5,021,469.
For obvious environmental-friendliness and cost-reduction reasons, it is desirable to develop latices containing neither volatile organic compounds nor coalescents, having a relatively low MFT and able to give films at low temperature which have no surface tack and are of good mechanical quality.
To achieve this objective, EP 466,409 proposes a solution based on a mixture of two latices, one having a low T
g
, generally called a “soft” latex providing film formation and the other having a high T
g
, generally called a “hard” latex providing mechanical integrity. U.S. Pat. No. 263,193 describes a solution based on a shell/core latex with a shell having a “soft” character and a core having a “hard” character. Unlike the previous document, EP 609,756 describes a latex, prepared in two steps, having a “soft” core with a T
g
ranging from −5° C. to −55° C. and a “hard” shell with a T
g
of less than 50° C.
Likewise, FR 2,090,483 describes a latex, obtained by two-step polymerization, consisting of 35 to 50% of a polymer, obtained in the first step, having a T
g
of less than 10° C. and of 50 to 65% of a polymer, obtained in the second step, having a T
g
of greater than 60° C., the first-step polymer being crosslinked and fastened to the second.
DETAILED DESCRIPTION OF THE INVENTION AND BRIEF DESCRIPTION OF DRAWINGS
Applicant has found that an ingenious solution to the problem described above entails a latex containing particles of hydrophobic polymers having a core/shell structure. With a so-termed “soft” core having a T
g
of less than 20° C. and a so-termed “hard” shell having a T
g
of greater than 50° C. The Applicant has in fact discovered that, as long as the mass contribution of the shell to the total weight of the polymer particles does not exceed 30%, such a latex applied to any surface gives, after drying at low temperature, and without the use of coalescents or volatile organic compounds, a continuous film which has a structure in the form of soft parts dispersed in a hard matrix, is homogeneous, has no surface tack and has good mechanical integrity.
In general, hydrophobicity is the non-solubility in water or the lack of affinity with respect to water. According to the invention, this lack of affinity may be hierarchized. This is because the hydrophobicity according to the invention is defined by the solubility parameter; (delta) as described in “Properties of polymers” by D. W. Van Krevelen, 1990, 3rd edition, page 220. This parameter makes it possible to classify various polymers according to their affinities with respect to water. According to the invention, a polymer is hydrophobic if its (delta) is less than 26. In addition, if (delta1) of a polymer 1 is less than (delta2) of a polymer 2, then 1 is more hydrophobic than 2.
One of the subjects of the invention is a hydrophobic thermoplastic film consisting of 70 to 90% by weight of a polymer (P
1
) with a soft character having a T
g
of less than 20° C. dispersed in 10 to 30% of a polymer (P2) with a hard character having a T
g
of greater than 50° C.
The polymer P1 is dispersed in the form of individualized nodules in the matrix consisting of the polymer P2.
The film of the invention is hydrophobic in the context of the invention defined above; in addition, P1 is more hydrophobic than P2.
Preferably, P1 has a T
g
of less than 0° C. and P2 a T
g
of greater than 60° C.
REFERENCES:
patent: 3808180 (1974-04-01), Owens
patent: 5082732 (1992-01-01), Ueda et al.
patent: 5403884 (1995-04-01), Tsai et al.
patent: 5403894 (1995-04-01), Tsai et al.
patent: 5424341 (1995-06-01), Ogoe et al.
patent: 5500457 (1996-03-01), Sarkar et al.
patent: 5631323 (1997-05-01), Guntherberg et al.
patent: 5866657 (1999-02-01), Tominaga et al.
patent: 41 39 382 (1992-08-01), None
patent: 0 522 791 (1993-01-01), None
patent: 2 729 150 (1996-07-01), None
Polymer Handbook, “Glass Transition Temperatures of Polymers”, J. Brandrup & E.H Immergut. pp. III-66 to 71, Interscience Publishers, 1966.
Domingues Dos Santos Fabrice
Drujon Xavier
Fabre Pascale
Leibler Ludwik
Meunier Gilles
Elf Atochem S.A.
Smith , Gambrell & Russell, LLP
Yoon Tae H.
LandOfFree
Low-temperature film-forming latex based on hydrophobic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low-temperature film-forming latex based on hydrophobic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low-temperature film-forming latex based on hydrophobic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3224845