Plastic article or earthenware shaping or treating: apparatus – Plural female mold cavities cooperating with single press... – Roll press member coacting with endless surface having...
Reexamination Certificate
1999-08-25
2001-03-20
Dixon, Merrick (Department: 1774)
Plastic article or earthenware shaping or treating: apparatus
Plural female mold cavities cooperating with single press...
Roll press member coacting with endless surface having...
C425S356000, C425S367000, C425S365000, C425S373000, C425S374000, C425S355000
Reexamination Certificate
active
06203307
ABSTRACT:
FIELD OF THE INVENTION
The subject invention relates generally to hot soft nip calendering for producing a smooth and/or glossy finish on at least one surface of a sheet of paper.
BACKGROUND OF THE INVENTION
Paper mills transport a continuous web of paper through a complex array of rolls. Selected rolls in the paper mill are arranged in pairs and define a nip therebetween. Temperature, pressure, rotational speed and surface characteristics of the rolls determine the characteristics of the paper produced in the paper mill.
Many papers are required to have a smooth and/or glossy surface on at least one side. Hot soft nip calendering using a pair of specially covered rolls is commonly used in the prior art to impart a smooth or glossy finish to a surface of the paper being produced in the prior art paper mill. A prior art hot soft nip calender apparatus is identified generally by the numeral
100
in FIG.
1
and includes a pair of oppositely rotating rolls
102
and
104
defining a nip
106
therebetween. The roll
102
typically is formed from a metallic material, such as steel, and is a complex structure with passages
108
extending therethrough. A hot oil is circulated through the passages to heat the outer surface
110
of the roll
102
. A temperature of 400° F. often will be achieved in the nip
106
. Other prior art rolls, however, are gas fired and may attain surface temperatures above 500° F. The roll
104
in the prior art hot soft nip calender apparatus
100
includes a metallic shell
112
with a smooth soft outer cover
114
securely engaged or laminated thereon. The rolls
102
and
104
typically are disposed relative to one another to achieve an operating pressure on a paper web
116
therebetween in the range of 1,000-3,000 pounds per linear inch.
The high speed, high temperature and high pressure employed in the prior art hot soft nip calender apparatus
100
create a potential for failure of the cover
114
on the roll
104
. In particular, the cover
114
is known to delaminate from the metallic shell
112
to which the cover
114
is initially affixed. A replacement roll often will cost in the range of $300,000-$400,000 and an additional expensive roll must be maintained in inventory. This high cost is due to the complicated lamination of the cover
114
to the shell
112
in an effort to achieve a soft surface that willl withstand the high speeds, high pressures and high temperatures used in the prior art calender apparatus
100
described above. The delaminated cover
114
also can damage downstream equipment in the paper mill. Thus, the total cost for such a failure can exceed the significant cost of the soft calender roll
104
itself. Furthermore, the down-time for the paper mill can represent a substantial cost penalty independent of the replacement cost for the damaged roll.
Some aspects of paper finishing processees could be emhanced by using higher temperatures and/or pressure in the hot soft nip calender. For example, it often would be desireable to operate some such calenders at pressures approaching 2000 pounds per linear inch. It also would be desireable to achieve nip operating temperatures significantly higher than 400° F. However, these higher pressures and temperatures would exacerbate the problems of delamination of the soft cover
114
from the shell
112
of the prior art apparatus
100
.
In view of the above, it is an object of the subject invention to provide an improved hot soft nip calender.
It is another object of the subject invention to provide a hot soft nip calender where the soft smooth material of the nip can be substantially reduced in cost.
A further object of the subject invention is to provide a hot soft nip calender which enables higher operating temperatures and pressures in the nip.
An additional object of the subject invention is to provide an efficient hot soft nip calendering process.
SUMMARY OF THE INVENTION
The subject invention is directed to a hot soft nip calender apparatus which includes an elongated continuous belt of a suitably soft, smooth and strong material. The belt may include a substrate made by a textile weaving process. The substrate may be formed from Kevlar (DuPont), PEEK (DuPont), Ryton (Phillips), polyester or other such material known for its strength and high temperature capabilities. An exceptionally smooth outer layer is provided on the surface of the belt that will contact the paper. The smooth outer layer may comprise rubber, urethane or other such elastomeric material, as well as metallic materials that will perform well and maintain its characteristics after long term exposure to high temperature and pressure. The required degree of smoothness for the outer layer may be achieved by mechanical means including, but not limited to continuous casting, molding, extruding, metallizing, grinding and other precision machining processes. The opposed inner surface of the belt may be defined by the substrate, and may have a surface configuration to promote cooling or ventilation. The various layers of the belt are assembled by coating, lamination, needling or other such known process. The continuous loop of the belt preferably has a length selected to permit some cooling of the belt between successive passes through a nip as explained herein. For example, the belt may define a total length of approximately 35-90 feet, and preferably 35-50 feet.
The belt is removably mounted on an array of parallel belt carrier rolls. The belt carrier rolls are disposed to engage the inner surface of the belt and to circumferentially carry, support, tension and guide the belt.
The apparatus of the subject invention may further include a heated roll aligned parallel to the belt drive rolls and substantially adjacent the outer surface of the belt. The heated roll may be heated by hot oil, gas fired heaters or other such heating means.
The hot soft nip calender apparatus further includes pressure means adjacent the inner surface of the belt for urging the outer surface of the belt toward the heated roll and to define a nip therebetween. The pressure means may be defined by one of the belt drive rolls. Alternatively, the pressure means may be a non-rotating structure such as a pressure shoe. The dwell time of the paper passing through the nip can be extended substantially by having a pressure shoe defining essentially a line of contact through the nip. Alternatively, the nip can be extended by having several belt carrier rolls disposed circumferentially around the heated roll of the calender apparatus. Thus, the paper web will traverse a portion of the circumference of the heated roll. Hot soft nip calenders in accordance with the subject invention also may be used in tandem to alternately finish opposed surfaces of a web of paper.
The hot soft nip belt calender of the subject invention has several significant advantages over the prior art. First, the costly lamination of a cover onto a shell is entirely avoided. Thus, although a greater amount of the soft material is required for the belt than for the cover, the total cost of the belt is a fraction of the cost of having the roll recovered or the cost of a spare roll. The belt of the subject hot soft nip calender also allows for cooling of the belt material between successive passes of the belt through the nip. This periodic cooling contributes to a longer belt life and enables higher local temperatures and pressures to be employed in the nip. Additionally, the subject calender belt can be replaced readily in the event of damage or wear, or to achieve different surface characteristics for the paper being manufactured.
REFERENCES:
patent: 3032441 (1962-05-01), Beaumont et al.
patent: 3124480 (1964-03-01), Mahoney et al.
patent: 3124481 (1964-03-01), Mahoney
patent: 3124504 (1964-03-01), Mahoney et al.
patent: 4066548 (1978-01-01), Olson et al.
patent: 4323622 (1982-04-01), Gladh et al.
patent: 4457968 (1984-07-01), Harvey
patent: 4596633 (1986-06-01), Attwood
patent: 4624744 (1986-11-01), Vreeland
patent: 4710423 (1987-12-01), Imamura
patent: 4738197 (1988-04-01), Malk
Neider Thomas M.
Rudt Robert J.
Champion International Corporation
Dixon Merrick
LandOfFree
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