Modified felt seam

This invention relates to A press felt for a paper making machine comprising a batt layer portion adapted to be positioned on a paper making machine juxtaposed the path of a paper web and a base weave portion designed to receive water from the paper sheet and to carry the batt layer, and means for jointing first and second ends of the felt to form a continuous belt, wherein the felt is provided at a first end portion with a flap in which the batt layer of the felt is configured to form a flap and at a second end portion, is configured to cooperate with said flap end portion characterized in that at least one of said end portions is coated with a hot melt adhesive whereby on the bringing of the first and second end portions into juxtaposition, the application of heat and pressure to bond said ends permits the formation of a seam in which the flap element overlays the remainder of the join in the felt.

DESCRIPTION 
This invention relates to seamed press felts and has particular reference 
to a seamed press felt modified to reduce or substantially eliminate 
marking of a paper sheet by the felt during production of the paper. 
In a paper making machine, when a newly formed sheet leaves the forming 
section, it has a moisture content typically between 70 and 80% depending 
on the type of paper making machine employed. On leaving the forming 
section, the thus formed sheet is passed through the press section where 
the sheet is advanced on a press felt through the press nip between press 
rolls where further water is expressed from the sheet. The press section 
includes several press nips in order to remove the maximum amount of 
remaining water in this section of the paper making machine. 
A typical press felt comprises a soft surface batt layer portion which is 
positioned juxtaposed the paper web and serves to protect the latter, and 
a less compressible base weave portion designed to receive water from the 
paper sheet and carry it away in a press nip. Such a felt is hereinafter 
referred to as a "felt of the kind described". The essential features of a 
press felt are that it should be substantially uniform in properties to 
prevent any kind of marking of the paper during formation and pressing. 
It will be appreciated that difficulty arises in the jointing of press 
felts since either the felts are made in a tubular fashion, or felts are 
made in longitudinal lengths and which need to be joined. Hitherto, only 
felts which are woven as endless felts have been acceptable since this 
tends to overcome the substantial discontinuity occasioned by other types 
of press felt joints. As an alternative to endless felts, loop seams in 
press felts have been proposed, for example, in U.S. Pat. Nos. 2,883,734 
and 2,907,093, but because of the nature of the loops and seam area it is 
self-evident that woven, single layer felts where there is little 
protection between the seam loops and a paper web, marking of the paper 
web is as it passes a nip almost inevitable. 
Straight joints have also been proposed by securing butt edges with a 
backing sheet, but again this produces a hardness in the nip which causes 
the marking of the paper. 
Seamed press felts are gaining popularity in the paper industry because 
they allow for easier installation and reduce paper machine down time. 
However, their utility has been limited due to the tendency of flap wear 
and sheet marking. 
According to the present invention, there is provided a press felt of the 
kind described having at a first end portion, a flap in which the batt 
layer of the felt is configured to form a flap, and a second end portion 
configured to cooperate with said flap end portion, characterised in that 
at least one of said end portions is coated with a hot melt adhesive 
whereby on the bringing of the first and second ends into juxtaposition, 
the application of heat and pressure to bond the said ends, permits the 
formation of a seam in which the flap element overlays the remainder of 
the join in the felt. 
In another aspect of the present invention, the felt may be installed with 
a flap portion trailing in the machine direction of travel. The adhesive 
may be a polyamide hot melt adhesive and may typically be applied in a 
solution for example, by spraying. Where the adhesive is a polyamide hot 
melt adhesive, the solvent may be a methylene chloride/methanol mixture. 
The adhesive may typically be activated using a steam iron. 
After such a felt has been installed on a paper mill, the hot melt adhesive 
may be activated via a hot air gun or steam iron, followed by pressure on 
the seam; the felt may thereafter be run. Tests have been conducted to 
show that the sprayed bonded seam in accordance with the present invention 
shows reduced wear when compared with an untreated control seam. In 
particular the Applicants have found that a press felt in accordance with 
the present invention, in which the hot melt adhesive is applied by 
solvent spraying, permits careful control of the quantity of adhesive 
which can be applied sufficient to obtain an adequate bond for the seam 
and at the same time, reduce or substantially eliminate the marking effect 
of the seam.

EXAMPLE 1 
A 10% solution of a Bostik nylon (S319-72) hot melt solution in 1:1 
methylene chloride:methanol was sprayed onto one half of the flap and 
trailing edge of a seam before seaming. A sprayer unit and multiple 
applications were used for this procedure. 
The felt was seamed after installation on the experimental press section. 
The hot melt was activated using a steam iron, Setting 4. 
In order to test for reduced flap wear, the felt described above was 
subject to a an accelerated test on an experimental press section. The 
press running conditions were as follows: speed--2000 ft/min; oscillating 
needle showers at 280 psi at 15.degree. angle into the face of the felt; 
nip pressure--450 psi; and a double slotted vacuum box at 15" Hg. The 
sprayed/bonded portion of the seam prepared by the method described above 
showed reduced wear when compared to the untreated control portion of the 
seam after 4 hours of accelerated testing on an experimental press. This 
is shown in FIG. 2 of the accompanying drawings. 
From the figures it will be seen that the wear apparent on the control 
section of the seam is much more pronounced than that from the section 
marked "adhesive" in accordance with the present invention. 
EXAMPLE 2 
A 16% solution of a Bostik nylon (S319-72) hot melt adhesive in 1:1 
methylene chloride:methanol was applied (two times) by atomizer spray unit 
in part of the seam area of a felt sample. The hot melt was activated 
using a steam iron, Setting 4. 
The remainder of the seam was made up in a conventional manner and the 
sample and control areas were conditioned in the wet state by subjecting 
them to 500 compression cycles at 1000 psi. Both areas were subsequently 
evaluated for sheet marking utilizing Beloit carbon impressions at 500 and 
1000 psi, and a dynamic press nip simulator using 100 g/m.sup.2 bleached 
softwood kraft handsheets. The sample yielded reduced marking when 
compared to the untreated control. This is shown in FIG. 1. 
From FIG. 1 it will be seen that the marking from the sample marked 
"adhesive" in accordance with the present invention is less pronounced 
than that of the control.