An Improvement in Electrical Insulating Sheet
Year: 1892

page_text: Date of Application, 1st June, 1892
Complete Specification Left, 17th Feb., 1893-Accepted, 1st Apr., 1893
PRUVIDIONAL DI MAT
"An Improvement in Electrical Insulating Sheet"
I, ROBERT WOOD, Secretary to the firm of Emmott and Company, Limited, 2, New
Bridge Street, Manchester, in the County of Lancaster, do hereby declare the nature
of this invention (which has been communicated to me from abroad, by Charles
Wilkin Jefferson, and Rupert Reginald St. John, both employed at the works
of the Edison General Electric Co., Schenectady, County of Schenectady, State of
New York, United States of America, electricians) to be as follows:-
My invention relates to an insulating material for electric conductors. The object
is to provide a sheet of material that is a good insulator, water-proof, non-combustible,
acid proof, and which will thoroughly protect electric conductors in all respects. It'
has long been known that mica is one of the best insulating materials, but its use has
been limited because of its inherent characteristics rendering it unfit for certain
applications, on account of its tendency to fracture on bending, pressing, &c.
My Invention consists in a so-called mica sheet formed of small irregular sheets,
and layers of thin mica fastened flatly together by means of a suitable adhesive
material, such as French varnish. Further, in order to make such a sheet, composed
of thin layers of irregular pieces of mica fastened flatly together, I face on one or
both sides, or in between the intervening layers of mica, with a thin fibrous material.
First, in order to make such a sheet composed of micaceous laminae as thin as
possible I use for the fibrous material a tissue paper having a long fibre, and
I find after a long series of tests, that the best tissue paper for this purpose is what
is known in the market as the Japanese tissue paper.
Secondly, in order to make such a sheet with more strength than is possible with
paper, and where the thickness is not an important matter, I take in the place of the
tissue paper a thin textile fabric for the fibrous material such as cotton gauze, India
lawn or silk fabric.
When a sheet of mica is required of greater thickness, I increase the number of
layers of the mica, or insert more layers of the tissue paper, or introduce more layers
of the textile fabric, or the two fibrous materials can be combined together in any
relation with the thin laminae of mica according to the requirements.

page_text: An Improvement in Electrical Insulating Sheet
I, ROBERT WOOD, secretary to the firm of Emmott & Co Limited, printers and
publishers of 2, New Bridge Street Manchester in the County of Lancaster, do hereby
declare the nature of this invention and in what manner the same is to be performed
to be particularly described and ascertained in and by the following statement :—
My invention relates to an insulating material for electric conductors. The object is
to provide a sheet of material that is a good insulator, water-proof, non-combustile,
acid proof, and which will thoroughly protect electric conductors in all respects. It
has long been known that mica is one of the best insulating materials, but its use
has been limited because of its inherent characteristics rendering it unfit for certain
applications, on account of its tendency to fracture on bending, pressing, &c.
My invention consists of small irregular sheets, i.e. scales and layers of such thin
non-comminuted mica with overlapping edges fastened flatly together by means of a
suitable adhesive material such as shellac. Further, in order to make such a sheet,
I face one or both sides, or in between the intervening layers of mica, with a thin
fibrous material.
First, in order to make such a sheet as thin as possible I use for the fibrous material
a tissue paper baving a long fiber, and I find after a long series of tests, that the best
tissue paper for this purpose is what is known in the market as the Japanese tissue
paper.
Secondly, in order to make such a sheet with more strength than is possible with
paper, and where the thickness is not an important matter, I take in the place of the
tissue paper a thin textile fabric for the fibrous material such as cotton gauze, India
lawn or silk fabric.
When a sheet of mica is required of greater thickness, I increase the number of
layers of the mica, or insert more layers of the tissue paper, or introduce more layers
of the textile fabric or the two fibrous materials can be combined together in any
relation with the thin laminae of mica according to the requirements.
I are am aware of similar articles of manufacture in which pulverized or com-
minuted mica is cemented to fibrous material, but I do not claim such a construction,
as it is objectionable for insulating purposes. The scales I employ are never less than
one or two square inches in area and generally five or six,-in short my invention
involves the use of non-comminuted mica only.
Having now particularly described and ascertained the nature of my said invention
(as communicated to me by my foreign correspondents) and in what manner the same
is to performed, I declare that what I claim is :-
1.An-electrical insulating-plate-consisting-of-alternate-laminae-of-non-comminated
mica;-eement-and-fibrous-material.
1 2-An electrical insulating plate consisting of a layer of cloth, paper or similar
fibrous material, such for example as Japanese tissue paper; a layer of elementary
non-comminuted mica scales having their edges overlapping and layers of an insulating
cement between the above named elements, substantially as described.
23-An electrical insulating plate consisting of the combination of elementary
non-comminuted mica scales of a given size and of irregular shape, overlapping
one another at their edges, electrically insulating cement between the said laminae,
and between the scales at their overlapping edges for the purpose described of holding
the same together; larger scales covering and cemented to the said smaller scales;
and fibrous sheets cemented to one or both sides of the micaceous sheet thus formed.
4-An-electrical-insulating-plate-consisting-of-a-core-of-fibrous-material-in-the-form
of-a-sheets-and-miea-sheets-applied-and-eemented-to-the-sides-thereof.

page_text: 5.-An-electrical-insulating-plate-consisting-of-the-combination- of--layers-of-miea
seales-of-a-given-size, fibrous-material-as-eloth-or-paper,-miea-seales; of-a-smaller-size
and-irregular-shapes-with-their-edges-overlapping-one-another another layer-of-cloth
or-paper;-and-another-layer-of-large-mien-seales-all-arranged-in-the-order-as-named-
Dated this 28th day of January 1893
Per Pro Emmott & Co. Limited,
ROBERT WOOD, Secretary,
Agents for the Applicants.