Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2000-09-11
2002-03-12
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C525S066000, C525S474000, C528S029000, C528S032000, C528S075000, C528S905000, C428S339000, C428S343000, C428S3550CN, C428S3550EN
Reexamination Certificate
active
06355760
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to polyurethane adhesives having improved shear strength.
(ii) Description of the Related Art
Polyurethanes are polymers resulting from the polycondensation of polyisocyanates on polyols. They comprise a large number of compounds having widely varied properties. A feature common to polyurethanes is excellent tensile, tear and abrasion strength and stability with respect to chemical agents and temperature.
The Applicant Company has now found new polyurethane adhesives having improved shear strength. These polyurethanes are obtained by polycondensation reaction of diisocyanates on a mixture containing at least one polyol including polyether grafts and at least one short-chain alcohol.
Polyurethane adhesives containing grafted polymers are already known.
JP-B-01014021 describes a composition which is permeable to water vapour and consists of a hydrophobic polyurethane and a hydrophilic polyurethane. The hydrophilic polyurethane is obtained by reaction of a hydrophobic polyol, a diisocyanate and a chain extender having ethylenic unsaturations, followed by a step of copolymerization in the presence of ionic and nonionic hydrophilic monomers (for example polyoxyethylene).
JP-A-62020578 discloses an adhesive which consists of a mixture of a thermoplastic polyurethane having grafted vinyl units, a polyoxyalkylene ether polyol and an isocyanate.
GB-A-2197657 describes a mastic obtained by reaction of a grafted low molecular weight polymer, a polyol and a polyisocyanate.
JP-A-06172539 proposes a process for preparing thermoplastic polymers including polyoxyethylene grafts by polymerization of a polymer containing hydrophilic units with a halogenated hydrophobic rubber.
SUMMARY OF THE INVENTION
The polyurethane adhesives according to the present invention have high shear strength, in particular when two elements formed by the polyurethane of the invention are superimposed. The combination thus formed is found to have very high shear strength although it has substantially no cleavage strength. The polyurethanes of the invention furthermore have the following advantages:
they are not tacky in nature,
they can be transferred from one support to another at will (repositionable nature),
they can be cleaned, for example with alcohols (reactivatable nature).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In the present description, the term “polyurethanes having high shear strength” is intended to mean polyurethanes having a shear strength in excess of 1 daN (measured according to standard NFT76-107).
In view of the fact that it is not feasible to determine their structure precisely, the polyurethanes of the present invention will be defined by the process with which they are obtained. This process involves the polycondensation of a mixture containing at least one polyol including at least one polyether graft per chain and at least one short-chain alcohol on a diisocyanate. For the sake of clarity, the term “grafted polyol” will be used below to denote the polyol including at least one polyether graft per chain.
The grafted polyol involved in the formation of the polyurethane according to the invention may be any polyhydroxylated polymer whose main chain carries at least one graft of the formula:
in which:
R
1
and R
2
, which are identical or different, represent a straight-chain or branched C
1
-C
10
alkyl radical,
R
3
represents a straight-chain or branched C
1
-C
4
alkylene radical,
R
4
represents a straight-chain or branched C
1
-C
9
alkyl radical,
R
5
represents H or a methyl radical,
x is a whole number between 1 and 11 inclusive,
y is a whole number between 3 and 50.
The preferred grafted polyols are selected from hydroxytelechelic polybutadienes and hydroxytelechelic polyisoprenes.
They advantageously satisfy the formula:
in which:
R
1
and R
2
represent a straight-chain or branched C
1
-C
10
alkyl radical,
R
3
represents a straight-chain or branched C
1
-C
4
alkylene radical,
R
4
represents a straight-chain or branched C
1
-C
9
alkyl radical,
R
5
, R
6
and R
7
, which are identical or different, represent H or a methyl radical,
x is a whole number between 1 and 11 inclusive,
y is a whole number between 3 and 50,
m, n and p, which are identical or different, represent the average numbers of the various repeat units provided statistically, these numbers being connected with one another by the relationships:
(m+n+p) is between 30 and 100
p/(m+n+p) is between 0.2 and 0.8
n/(n+m) is between 0.1 and 1.
In the polyols of formula (II) it is to be understood that the repeat units having a pendant vinyl unsaturation may be identical or different, depending on the nature of R
5
and R
6
. The same is true as regards the repeat units carrying the polyether graft.
Even more advantageously, the grafted polyols satisfy the aforementioned formula, in which
R
1
and R
2
represent a methyl radical,
R
3
represents an ethylene or propylene radical,
R
4
represents a methyl or ethyl radical,
R
5
, R
6
and R
7
represent a hydrogen atom,
x is a whole number between 4 and 11 inclusive,
y is a whole number between 5 and 20,
(m+n+p) is between 30 and 100
p/(m+n+p) is between 0.2 and 0.8
n/(n+m) is between 0.1 and 1.
The grafted polyols employed according to the invention can be prepared according to the process described below, this process consisting in:
a) reacting, in the presence of a hydrosilylation catalyst, apsolyol including ethylenic unsaturations with a haloalkyl (diorgano)silane of formula:
in which:
X represents Br or Cl,
R
1
, R
2
and x have the meaning given above,
b) separating the polymer from the reaction medium,
c) reacting the precipitated polymer with a polyether compound of formula:
in which R
3
, R
4
and y have the meaning given above, in the presence of a compound which is capable of forming the alcoholate of the compound of formula (IV), and
d) separating the resulting polymer from the reaction medium.
The starting polymer employed in step a) is generally selected from polyols containing ethylenic unsaturations of the pendant vinyl type and/or unsaturations carried by the carbon atoms constituting the chain of the polyol.
By way of example of polyols which can be used for the invention, mention may be made of the polyols obtained by polymerization or copolymerization of diene compounds in which a part contains hydroxyl groups such as hydroxylated polybutadienes or hydroxylated polyisoprenes.
The polyols are preferably selected from hydroxytelechelic polybutadienes containing pendant vinyl unsaturations, for example with -1,2 and -1,4 polymerizations, and hydroxytelechelic polyisoprenes containing pendant vinyl unsaturations, for example with -1,2, -3,4 and -1,4 polymerizations.
The halogenated silane of formula (III) is capable of reacting with the ethylenic and pendant vinyl unsaturations carried by the initial polyol when the temperature exceeds 40° C. Under the preferred process conditions, that is to say at a temperature of less than 80° C., only the pendant vinyl unsaturations react, partly or completely, and the ethylenic unsaturations do not react substantially with the halogenated silane (III).
The preferred halogenated silane satisfies the formula (III) in which:
X represents Br,
R
1
and R
2
represent a methyl radical,
x is a whole number between 4 and 11.
In general, the amount of halogenated silane (III) employed depends on the number of pendant vinyl unsaturations on which it is to be added. The procedure is advantageously carried out in the presence of an excess of between 5 and 60% by mole with respect to the stoichiometric amount needed to convert the desired number of vinyl bonds.
The hydrosilylation catalyst is generally selected from platinum-based catalysts such as hexachloroplatinic acid, optionally in hydrated form, metal carbonyls such as cobalt carbonyl or nickel carbonyl. Hexachloroplatinic acid is preferably used.
The catalyst is generally employed in an amount of 0.1 to 0.5% by mole with respe
Papon Eric
Tordjeman Philippe
Villenave Jean-Jacques
Bostik Findley
Hunton & Williams
Sergent Rabon
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