Process for producing crosslinked, melt-shaped articles
Crosslinked, melt-shaped articles are manufactured by a process that does not require the use of post-shaping external heat or moisture, the process comprising the steps of: A. Forming a crosslinkable mixture of a 1. Organopolysiloxane containing one or more functional end groups; and 2. Silane-grafted or silane-copolymerized polyolefin; and B. Melt-shaping and partially crosslinking the mixture; and C. Cooling and continuing crosslinking the melt-shaped article. Crosslinking is promoted by the addition of a catalyst to the mixture before or during melt-shaping or to the melt-shaped article.
1. A process for the manufacture of crosslinked, melt-shaped articles, the process comprising the steps of:
A. Forming a crosslinkable mixture comprising:
1. at most 10 wt %, based on the total weight of the crosslinkable mixture, of an organopolysiloxane containing two functional end groups which are hydroxyl groups, wherein the organopolysiloxane is a polydimethylsiloxane of the formula
wherein Me is methyl and n is from 10 to 400; and
2. Silane-grafted polyethylene;
B. Melt-shaping and partially crosslinking the mixture into an article; and
C. Cooling the melt-shaped article; and
D. Storing the melt-shaped article and continuing crosslinking without external moisture diffusion,
wherein a crosslinking catalyst is added to the mixture before or during melt-shaping or to the melt-shaped article,
wherein the melt-shaped article has a thickness of greater than 0.2 mm, and
wherein the crosslinked, melt-shaped article passes the hot creep test (100% elongation) measured at 200° C., 0.2 MPa load held for 15 minutes in accordance with IEC 60811-2-1.
2. The process of claim 1 in which the catalyst is a Lewis or Bronsted acid or base.
3. The process of claim 1 in which the crosslinkable mixture comprises, based on the weight of the mixture:
i. 0.5 to 10 wt % of the organopolysiloxane; and
ii. 0.01 to 0.2 wt % of the crosslinking catalyst.
4. The process of claim 1 in which at least one of the crosslinkable mixture or a component of the mixture is subjected to drying conditions prior to melt shaping the crosslinkable mixture.
5. The process of claim 1 in which at least one of the organopolysiloxane and crosslinking catalyst is at least partially soaked into the silane-grafted polyethylene at a temperature below the melting temperature of the silane-grafted polyethylene prior to melt-shaping the mixture.
6. The process of claim 1 in which the crosslinking catalyst is a Bronsted acid.
7. The process of claim 6 in which the crosslinking catalyst is sulfonic acid.
8. The process of claim 1 in which the melt-shaped article is a cable coating.