Room temperature fast curable composition

Details Room temperature fast curable composition Room temperature fast curable composition

2000-02-24

2001-10-23

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S017000, C528S026000, C528S021000, C528S901000, C528S034000

Reexamination Certificate

active

06306998

ABSTRACT:

This invention relates to room temperature fast curable compositions, and more particularly, to condensation curing type compositions which are fast and deeply curable at room temperature.
BACKGROUND OF THE INVENTION
Room temperature fast curable organopolysiloxane compositions of the condensation curing type known in the art include compositions of one part type comprising a both end hydroxy-terminated organopolysiloxane as a base polymer and a crosslinking agent in an amount minimized so as to increase the crosslinking rate through hydrolysis, and compositions of two part type wherein a both end hydroxy-terminated organopolysiloxane as a base polymer and a crosslinking agent are separately packed.
The compositions of one part type, however, are not regarded as fast curing since they merely have a high curing rate from the surface and require a certain time for deep curing. By contrast, the compositions of two part type are relatively fast in depth curing, but are difficult to handle on account of a mixing ratio of the two parts departing from 1:1 and thus inapplicable to an automatic mixing dispenser. In order to drive complete curing to depths, the quantity of hydroxyl at both ends of organopolysiloxane or polyoxyalkylene polymer and the quantity of crosslinking agent added must be strictly controlled, or water must be further added as a deep curing agent.
On the other hand, organopolysiloxane compositions of the addition curing type are efficient to work with since the two parts are mixed in a ratio of 1:1. However, the working environment is limited since a heating oven is generally necessary for curing and the curing catalyst can be poisoned in the presence of an addition poison.
To solve these problems, we proposed in U.S. Pat. No. 5,319,050 a composition comprising a diorganopolysiloxane blocked with a hydrolyzable silyl group at either end of its molecular chain, 0.001 to 1 mol of an organic compound having at least one C═O group in a molecule, and 0.001 to 1 mol of an organic compound having at least one NH
2
group in a molecule. This is a room temperature fast curable organopolysiloxane composition which utilizes water formed as a by-product by ketimine forming reaction between C═O and NH
2
groups. Continuing investigations, we found that when the diorganopolysiloxane as the base polymer is end-blocked with a hydrolyzable silyl group, the composition maintains storage stability etc., but its fast curing property does not significantly exceed that of conventional well-known two part type compositions wherein a both end hydroxy-terminated organopolysiloxane and a crosslinking agent are separately packed.
JP-A 61-204289 discloses a humidity-curable sealing composition comprising a polyoxyalkylene ether backbone polymer having a hydrolyzable silicon group at an end of its molecular chain and the reaction product between an amine compound and a carbonyl compound with water removed. Since water has been removed from the reaction product, the composition cannot be fast curing.
SUMMARY OF THE INVENTION
An object of the invention is to provide a room temperature fast curable composition of the condensation curing type which is fast and deeply curable at room temperature.
We have found that a room temperature fast curable composition is obtained by blending (A) a diorganopolysiloxane blocked with a hydroxyl group at both ends of its molecular chain and having a viscosity of 25 to 1,000,000 centistokes at 25° C., (B) a hydrolyzable silane of the formula (1) defined below or a partial hydrolyzate thereof, (C) an organic compound having at least one C═O group in a molecule, and (D) an organic compound having at least one NH
2
group in a molecule. The composition cures in the presence of water in air. At the same time as curing, reaction occurs between carbonyl and NH
2
groups that components (C) and (D) possess at &bgr;-position, to form water at depths, which water facilitates the fast and deep curing of the composition so that curing takes place not only from the surface, but also from the deep interior. Furthermore, since the both terminals of the base oil as component (A) are changed from the hydrolyzable groups to the hydroxyl groups, condensation reaction between these hydroxyl groups and hydrolyzable groups on the crosslinking agent takes place at the same time. These reactions cooperate to achieve outstanding improvements in fast curing and deep curing capabilities. The composition is thus a room temperature fast curable composition which is especially effective as the one part type.
Accordingly the invention provides a room temperature fast curable composition comprising:
(A) 100 parts by weight of a diorganopolysiloxane blocked with a hydroxyl group at both ends of its molecular chain and having a viscosity of 25 to 1,000,000 centistokes (cSt) at 25° C.,
(B) 2 to 50 parts by weight of a hydrolyzable silane of the following general formula (1):
R
1
4−n
SiX
n
  (1)
wherein R
1
is a monovalent hydrocarbon group, X is independently selected from the group consisting of ketoxime, alkoxy, acyloxy, amide, and amino groups, and n is an integer of 2 to 4, or a partial hydrolyzate thereof,
(C) an organic compound having at least one C═O group in a molecule, In an amount to give 0.001 to 1 mol of the C═O group per 100 parts by weight of component (A), and
(D) an organic compound having at least one NH
2
group in a molecule, in an amount to give 0.001 to 1 mol of the NH
2
group per 100 parts by weight of component (A).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Briefly stated, the room temperature fast curable composition of the invention contains as essential components (A) a diorganopolysiloxane blocked with a hydroxyl group at both ends of its molecular chain and having a viscosity of 25 to 1,000,000 centistokes at 25° C., (B) a hydrolyzable silane of the formula (1) or a partial hydrolyzate thereof, (C) an organic compound having at least one C═O group in a molecule, and (D) an organic compound having at least one NH
2
group in a molecule.
Component (A) serving as the base polymer is a diorganopolysiloxane which should be blocked with a hydroxyl group at both ends of its molecular chain. On account of the presence of hydroxyl groups, the diorganopolysiloxane (A) can condense with the hydrolyzable silane or partial hydrolyzate thereof (B) to form a cured product in the form of a rubber elastomer.
One preferred diorganopolysiloxane is a both end hydroxyl-blocked diorganopolysiloxane of the average compositional formula shown below.
Herein, R is independently a substituted or unsubstituted monovalent hydrocarbon group, and m is such a number that the diorganopolysiloxane may have a viscosity of 25 to 1,000,000 cSt at 25° C.
In the above formula, R may be the same or different and is preferably selected from substituted or unsubstituted monovalent hydrocarbon groups of 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl and butyl, cycloalkyl groups such as cyclohexyl, alkenyl groups such as vinyl and allyl, aryl groups such as phenyl and tolyl, aralkyl groups such as benzyl and phenylethyl, and substituted ones of these groups in which some of the hydrogen atoms are replaced by halogen atoms or cyano groups, such as chloromethyl, 3,3,3-trifluoropropyl and cyanoethyl. Of these groups, methyl, phenyl and 3,3,3-trifluoropropyl groups are preferable, with methyl being most preferable.
The diorganopolysiloxane as component (A) or base polymer should have a viscosity of 25 to 1,000,000 cSt at 25° C. and preferably 100 to 200,000 cSt at 25° C. Outside this range, there arise such problems as inefficient working and the difficulty to form a cured rubber having satisfactory properties.
Component (B) is a hydrolyzable silane of the general formula (1) or a partial hydrolyzate thereof.
R
1
4−n
SiX
n
  (1)
In formula (1), R
1
is a monovalent hydrocarbon group preferably of 1 to 10 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, bu

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