Note: Descriptions are shown in the official language in which they were submitted.
WO 95112030 2 ~ 7 ~ Z 4 ~ PCT/DK94/00404
MODIFIED LATEX
This invention concerns a method for production of a binder solution making it
possible to produce a softer and stronger air-laid product having groups of fibers
5 bonded to other fibers and other groups of fibers. The soft and silky effect is obtained
tilrough a ' ~ of the binder making it possible to reduce the amount of binder
and easy to effect a ~ .y or at least a partly 1,~ ".li~ of the brittle bonds
which normally is provided in the form of cellulosic hydrogen bonds and/or casein
bonds.
It is a neccessity to apply SBR latex binders or other binders in an aqueous suspension
onto a dry laid product of fibrous material in order to form an effective bond between
individual fibers and groups of fibers. After the air-laying of the fibers onto a forming
surface the binder solution or suspension is applied onto the fibrous product. After the
15 applying of such solution or suspension in one or severai application stations the web
is normally ied through a drying unit and then through a curing unit leaving thehydrogen bond untouched in the dry formed paper.
When applying the binder solution a ' of brittle hydrogen bonds and elastic
20 bonds are necessarily provided together. The hydrogen bonds are valuable in a fibrous
product although they are generally an irritation to the human skin. However, the
hydrogen bonds are not brittle when they oniy stay in smail groups of few fiber-,~,~;1.. ,..,l;., ~ or between single fibers. These hydrogen bonds make the overall
product stronger. However, due to the brittleness of the hydrogen bonds the fibrous
25 product would appear as a rather stiff web having a poor hand and feel. Also the
drapability would be poorer than wanted.
The elasti~ h3tex bonds are valuable. However, since the latex is applied in a
suspension of water, therefore au;u~ ;ly, a hydrogen bond would also be provided30 together with a latex bond.
It is an object of the present invention tc provide a binder solution which makes it
WO gS/12030 21 7 S 2 ~ O PCT/DKg4/00404 ~
possible to .I. u.ur~ul~ a softer and more silky air-laid fibrous product in which the
fibers and groups of fibers are bonded together with other fibers or groups of fibers
via a ~,UIIIbill~ l of hydrogen bonds and elastic bonds, however, being illl~
so that it is possible at a following mechanical treatment of the product to divide the
hydrogen bond into separate groups of fibers being connected with other groups
through invisible minute lines containing elastic bonds. These invisible lines contain
only elastic bonds.
The mechanical treatment is preferably of the type which is described in copending
patent application filed with the United States Patent Office under the title "M~ ' '
partly I of hydrogen bonds for production of a softer and more silky air-
laid fibrous productn.
According to the present invention a method is provided wherein a " n~l ;r~ ,, of the
binder solution is effected by il~ a softener product into the binder suspensionbefore its application onto the fibrous product.
llil UdU~,~iUII/ '' '' ' ' of a softener product e.g. in the form of a SBR latex product
into the fibrous product makes it possible to reduce the amount of binder and
' 'S~ it is possible to obtain a product which, after a following mechanical
r ~ i. . of the hydrogen bonds, is more soft and silky and stronger. Thus all the
advantages obtained by the mechanical n Ij7~tirl-- is also obtained in a productaccording to the present invention, however, ~ ly the product will occur everl
more soft and silky than normal and also stronger than normal. These advantages are
25 described in the abo~c-,~ iu~,d United States Patent Application.
The surprising , u~. in the qualities is difficult to explain. However, it is
believed that the mechanical treatment of a latex bonded product will leave an elastic
~,...~-i. ;li. -1;ll.. between the fiber groups. S ' - IS/, the paper product will be
30 in a new quality. The hand and feel of the new product would be improved as
compared to the hand and feel of a product with which the hydrogen bonds throughthe whole product are making stiffness, and the mechanical 'i7~inn in very tiny
wo 95112030 ~ 1 7 o 2 ~ ~ pcrlDKs4Jno4o4
lines are according to the invention subject to a mrrl~onirZ-l n~ltr~li7z~tir,n process.
It is to be noted that the hydrogen bonds due to their brittleness and fragility are
normally not wanted in soft products used for hygienic purposes, diapers, wipers, etc.
A hydrogen bond is irritating to the skin as a dry formed product consists of fibers
5 arranged in groups in contact with or in connection with the other ~r~ups of fibers,
then the product will result as a product being stronger than a product having only
single fibers being in mutually contact or connection with other single fibers.
Accordingly, a product having small groups of fibers being illkll,ull. ,~ d through the
hydrogen bonds will not only be softer but also become stronger. This is due to the
10 fact that the groups will be , ~ by latex bonds which are not interrupted
with the m~rl~nirol method described below.
Hydrogen bond is unavoidable because the latex solution is suspended in so much
water that the hydrogen bond is all over and through the dry formed product.
15 According to this invention the hydrogen bond will remain in very small areas or
islands which have not been subjected to the 1i7~ti~n stretching process. Thus
the strongly coherence of the product will be maintained in said areas or islands and
in the connected islands.
20 The 1- ~i7otinn is effected by stretching the product at least in two directions,
however, also a stretching in three or four directions is possible. Thereby flexibility
lines are established in the bonds. Thus a more or less randomly orientated pattern is
obtained in which the hydrogen bonds have been fle~ible in mini lines. However, due
to tbe elasticity the latex bonds even after the stretched product, the product will all
25 over have a latex bond. With this method an aJv~ .O product is obtained having
groups of i..~., I fiber groups instead of single fibers. The final product willbe soft in quality, be strong and have a good hand and feel and a good drapability.
The effect of the 1 - of the hydrogen bonds in this mini line places is not
30 visible even in a three ~ . l ' uO~,u~, in the final products. They are almost
u~,u,ui~" however, the quality of the final product haO l~ new qualities.
Preferably the modifled SBR latex is used after a whipping process. Hereby the latex
WO 9S/12030 2 ~ ~ ~ 2 ~ ~ PCTII)IC94/00404 --
product is mixed intimately into the solution thereby ensuring a good di,L il~u~ .. of
the product through the fibrous product.
The mixing is done in the following way:
5 According to a specific . I.c..l; ~ blown castor oil is added to the SBR latex binder.
In such case the whipping process is adv.l~L~,_~u~, because it is an oxidation of the
castor oil which hereby will be blown. The use of blown castor oil is advantageous in
connection with a Styrene-Butadiene Rubber. It is preferred to add between 0.5 % and
1% by weight of the blown castor oil to the latex dry substance.
It is essential that the blown castor oil is added slowly to the Styrene-Butadiene Rubber
latex milk under an energetic whipping. Hereby, the advisably oxidation in the blown
oil remains.
15 According to a further possible i ' ' the SBR latex product may be provided
with milk which has given ! pl i~ ;ly good results. Thus, it is advantageous to use
milk having a content of fat of between 8 to 15% by weight, preferably having a
content of fat of 10% by weight. Such milk will also comprise casein. The caseincould occur in an amount of 2 to 3% by weight in the milk. The casein will also
20 provide good, however, brittle bonds. These brittle bonds may be compared with the
hydrogen bonds and would make the product strong. As it is known. casein is
insoluble in water. However, the casein bonds will be neutrali_ed to the extent wanted
together with the n~ tr~li7~tit)n of the hydrogen bonds by the stretching of the product.
It is believed that by stirringlwhipping in an oxygen containing air, as normal air, or
25 with little peroxide, the fat in the milk might be changed to a sort of blown oil.
If a Styrene-Butadiene Rubber latex is used it is adv~.A~,_~J~.,, to add between 2 to 5 %
by weight of natural latex in order to make the latex more elastic, and thereby making
it possible to obtain a higher degree of stretching. When obtaining such higher degree
30 of stretching a more fine pattern of invisible ~ LI.di~Liu.. lines is obtained.
It could be said that a is obtained in which each of the mosaic sections
contain small groups of fibers being i--~.~ d by the hydrogen bonds and
2 1 ~ 2 ~ OKT. lg~
possibly also the c~sein bonds. Said sectiorls being separated by a fine network of lines
in which tbe hydrogen bonds and possible also the casein bonds, if any, are neutralized
or released from their tension. Thereby a very strong and very soft product is obtained.
In EP-A-0 373 276 am apparatus is disclosed which comprises means for applying abinder solution onto a fibrous product and means for hf ~ ~ ~g~ of tbe binder
solution before this solution is introduced into the nozles. However, this apparatus does
not disclose means which makes it possible to effect a mixing of a softener product into
the binder solution. The apparatus neither discloses any separate means for suchsoftenerproduct.
The inveMion concerns also an apparatus for producing a soft and silky air-laid fibrous
product which includes forming means for dry-laying a fibrous web on a forming wire
positioned on a suction means, applicator means for applying a binder mixture onto the
-I 5 r~ fi6rous web so as to form brittle and elastic bonds in the fibrous web. This appartus
makes it possible to add th~ softener product to the binder solution in the mi~ing means.
The mixing means are preferably whipping means which make it possible to obtain an
intimate mixing.
20 Furtner features and advantages of the present invention will be understood by reference
to the attached drawings taken in, ; with the ensuing discussion.
DE.~CRrPTlON OF THl;. DRA~;VINGS
In the drawings,
Fig. 1-3 illustrate .i~ lly three f .. ~ of an apparatus according to the present invention,
Fig. 4 a . ~ ly enlarged view of a fibrous product ,.. lu.ur"~u,~
without the use of a method according to the present invention,
~ ,,t
~7s2~a
E~LACcMcNT SHEET
5A 1 3 OKT. ~95
Fig. S a view cvl~c~yul~lilg to the one shown in Fig. 4, however, having the
fibrous product produced by use of a binder 111 --Illr-. Il"G.1 by a method
according to the present invention, and
. Fig. 6 a ,. ~ ,. ., IA1;. lly view for illustrating the mini-mosaic of the irlvisible
flexibility line in the fibrous product illustrated ir~ Fig. 5.
Preferred .,.,~,v ~ for an apparatus according to the present invention is diaG~ram-
matically illustrated in Figs. l-3. In these Figures identical or ~,vllc~vll~ihlg elements
are designated with same reference numbers and will only be explairled in
~..lr ~ ,. ; _
wo 95112030 21~ ~ 2 ~ ~ PCT~DK94/00404
details in connection with Fig. 1.
The apparatus includes a fiber distributor 1, a suction box 2, and an endless
r..,~ i""..~ forming wire 3 passing there between the endless forming wire consisting
5 e.g. of a mesh net ~u.l~llu.,t~, I using bronze wires. The forming wire 3 is driven by
suitable means (not shown) so that it will ~ y pass between the distributor I
and the suction box 2. The forming wire 3 moves in direction of an arrow 4.
The suction box 2 includes a suction pipe 5 which is connected to a fan (not shown)
10 for the creation of a vacuum therein. The forming wire 3 passes through the nip of a
pair of rollers 6,7 and below a nozzle 8 spraying a binder solution onto the product
formed. The nozzle 8 is connected with a mixing box 10 according to the invention.
The mixing box 10 is connected with supplying means 11 and 12.
An endless band 13 is arranged in: of the forming wire 3. The band 13
is driven in direction of the arrow 14. A further endless band 15 is provided above the
forming wire 3 and the endless band 13. The endless band 13 is a gas permeable band
wounded on three rollers 16, 17, and 18. From the roller 17 a wall 19 is provided,
thereby dividing the interior space of the gas permeable band 15 into two compart-
ments 20 and 21. In the . 20 a vacuum is created through a fan (not
shown), thereby lifting the fibrous product 22 free of the forming wire 3. In the
WIII~ lt 21 an U.~ is created e.g. by means of the same fan which
creates the væuum in UUIIIIJ~ 11.._.1~ 20. Thereby, the fibrous product 22 is transferred
and deposited onto the endless band 13.
The apparatus also comprises two sets of rollers 23,24 and 25,26, respectively, and
a further nozzle 8 which is mounted between said sets of rollers and to which a binder
solution is supplied from the mixing box 10. The rollers 24 and 26 may preferably be
heated rollers. r... ~ ulc;~ the apparatus comprises a drying unit 27, a stretching unit
28, a curing unit 29, and a roller 30 for winding the final product.
The stretching unit 28 shown in Fig. 1 comprises a series of four bombarded rollers
1~ wo 95/12030 ~17 ~ 2 ~ ~ PCT~I)K94/00404
31. Between the bombarded rollers 31 turning and tightening rollers 32 are provided.
The turning and tightening rollers 32 are movable along the arrows 33 in order to urge
the fibrous product 22 against the bombarded rollers 31 with different forces, thereby
effecting different degrees of stretching.
The apparatus illustrated in Figs. 2 and 3 differs only from the apparatus illustrated
in Fig. I by the use of other stretching units 28.
The stretching unit in Fig. 2 comprises a single roller 34 having a surface provided
lO with small IJlU~Ub~ lllCeS thus providing a surface which cu--, r ' to the surface
known from a corncob, however, each ~)IU~Ub~,lclll~.G is much smaller as compared to
a corngrain. r.-.~ ....u.c;, the stretching unit 28 comprises two turning and tightening
rollers 35 being movable along arrows 36 in order to urge the fibrous product 22against the roller 34 with different forces thereby effecting different degrees of
lS stretching.
The stretching unit 28 illustrated in Fig. 3 comprises a series of four rollers 37 and
38. The rollers 37 and 38 comprise a left hand thread and a right hand thread,
respectively. The fibrous product 22 is led according to a sine-formed path through
20 the series of rollers 37,38 alternately being urged into contact with a left hand thread
and a right hand thread, thereby ci,~l~liZ,l.i..~ a stretch as the fibrous product 22 is
urged against the rollers 37,38 in a tightened manner. The threads provided on the
rollers 37,38 are rounded, thereby allowing the fibrous product 22 to slide on the top
of the threads.
The apparatus shown in different Figures operates in the following manner:
When the forming wire 3 is advanced in the abovc ' path a fiber material is
deposited on the forming wire 3 on which it is moved in direction of arrow 4 and30 forms a fiber layer when air is sucked away through the suction box 2. The flber layer
thus formed is rolled when passing the nip of the rollers 6,7. The binder material and
the softener product is mixed in the mixing box 10. Then the binder solution 9
WO 95/12030 ~ ~ ~ , PCT/DK94/00404
urd~ulcd according to the invention is the applied to one side of the layer by
means of the nozzle 8. The product thus formed has such a strength that it can be
removed from the forming wire 3 by means of the gas permeable endless band 15.
Due to the vacuum in the chamber 20 the fibrous product n is lifted free of the
5 forming wire 3 and is then deposited onto the band 13 due to the U._ll/IC~Ul~ in the
Cu..l~ ,.lL 21.
The fibrous product 22 is then passed through the set of rollers 23,24 and passes the
nozzle 28 at which a binder solution 9 is applied on the side of the product facing
0 dU..ll..~Lld~ on the forming wire 3. When the material has passed the set of rollers
25,26 it is led through a drying unit 27. The rollers 24 and 26 are preferably heate~
so as to remove a part of the moisture supplied together with the binder solution. Thus
is might be possible to obviate a use of a separate drying unit 27.
15 After having passed through the drying unit 27 the fibrous product 22 is led through
the stretching unit 28 in which the product is stretched at least in two directions. The
effect on the stretching would be explained in more detail below. Before the product
22 is wound on the roller 30 it is led through a curing unit 29.
20 If it is desired it is possible to provide a nozzle for adjusting the moisture content of
the product before it is wound on the roller 40.
The nozzles 8 are provided with a binder solution from a mixing box 10. The mixing
box 10 comprises preferably mrxing means in order to effect an intimaoe mixing by
25 a whipping process. The product to be mixed in the mixing box 10 is provided frorn
supply means 11 and 12.
The supply means 12 contain a latex binder which preferably is a SBR latex binder in
an aqueous suspension which is known in the art. It is noted that it is also possible to
30 use other binders which are well-known in the art.
The latex binder solution is modified by illLIudu~ a softener product from the
WO 95112030 2 1 7 ~ 2 4 0 PCr/l)K94/00~01
.
supply means 11. The illLIudu~,Livll of a softener product into the latex binder suspen-
sion has given ~l;a;llt,ly illl,UlV~ a in the qualities of the final product obtained
in that it is more soft and silky and also stronger than normal after the stretching
operation effecting in the shretching unit 28.
. S
According to a preferred ~ .l o~li.. the softener product is blown castor oil which
is whipped into a SBR latex binder solution. The whipping process is ~IVOIIL~-U~because of the oxidation of the castor oil which thereby is blown. It is preferred to add
between 0.5% and 1% by weight of the blown castor oil to a SBR latex dry substance.
According to another preferred ~..'..~.li,.,...; the softener product is milk having a
content of fat between 8 to 15% by weight, preferably a content of fat of 10% byweight. Moreover, between 2 to 5% of na~hural latex is added to SBR latex in order
to obtain a more elastic latex, and thereby making it possible to obtain a higher degree
15 of shretching. Such higher degree of shretching in the shretching unit 28 will provide
a more fine pahern of mini-mosaic lines in which the hydrogen bonds are neuhalized
as explained above.
The, ~ -.lir~ ll of the latex binder solution is essential in order to obtaiii the soft and
20 silky product which is provided according to the present invention.
The shretching unit 28 comprises bombarded rollers 31 which are well-known.
However, so far bombarded rollers 21 have been used for ~".."Jlh.. ,~ a fibrous
product. The fibrous product 22 is urged against the bombarded rollers 31 through the
25 influence from the turning and tightening rollers 32, thereby applying the fibrous
product 22 onto the rollers 31 with a force sufficient to effect a shretching. Preferably,
each succeeding bombarded roller is driven with a higher surface velocity than aprevious roller 31 in order to effect a shretching in the 1~1ngihl~1in~1 direction of the
product 22. Due to the s~hretching it is possible to obtain a fine pattern of invisible neu-
30 tralization lines to be explained below.
When using the corncob-shaped roller 34 illushated in Fig. 2 it is possible to obtain
WO 95112030 PCT/DK94/0040~ ~
2~
,, 10
a stretching around the smooth ~lu~ in the surface. The fibrous product æ
is also urged against the surface thereof by means of the turning and tightening rollers
35. Due to the great number of fine distributed and small IJlUIUb~,ldll~ a multi-di-
rectional stretching is obtained due to the force with which the fibrous product 22 is
5 urged against the surface of the roller 34.
If desired the roller 34 may be followed by one or more bombarded rollers for
effecting a: ' ~ However, such ,..louLh.,.l;..g process would not be necessary
for the production of most products. The roller 34 might have ~1U~ f~ having
10 a height of between 2 mm and 3 mm and having a mutual distance between
1"' ' of between 5 mm and 20 mm.
When using the thread-provided rollers 37,38 illustrated in Fig. 3 it is possible to
stretch the product in order to obtain said mosaic of ~ tinrl lines in the product
15 22. The thread is formed by a sine-shaped surface of the roller in which each sine-
wave has a height of between 5 and 10 mm and having a mutual distance between the
waves of between 10 and 15 mm. The roller may have a diameter of between 0.4 and0.6 m. The same diameters could also be used for the rollers 31 and 34.
20 In Fig. 4 a r ~ ' y enlarged view of a fibrous product 22 is illustrated. It is seen
that the single fibers 39 are distributed with a normal air-forming di~Llibu~iull of the
fibers 39 in all positions and with hydrogen bonds and latex bonds at cross-linking
points of the individual fibers.
25 Fig. 5 illustrates greatly enlarged a fibrous product 22 ~,u~ dil.6 to that illustrated
in Fig. 2, however, treated with a modified latex binder and subjected to a stretching
process as described above. In the view a mosaic of lines 41 is illustrated separating
the product in mosaic sections 42 in which the hydrogen bonds are ' In the
lines 41 the brittle hydrogen bonds and casein bonds are neutralized whereas the elastic
30 latex bonds are maintained even after the stretching of the product 22. The product
will all over its surface maintain the latex bonds. Thus the product is obtained having
groups of illL~l~u,,~ d fibers 39 in the mosaic sections 42 when said groups of fibers
~ wo9s/12030 21 7 5 2 ~ O PCT/DK94/0040~
are ;11~1~ ~ with other groups of fibers or single fibers through the latex bonds.
Accordingly, a final product is obtained having a good hand and feel and a good
drapability.
5 In Fig. 6 the mosaic pattern of the lines 41 is illustrated without the illustration of the
fibers 39. This is only for illustrative reasons as the lines 41 would be invisible in the
final product even if it is studied through a three-.li-- - O~ Illil,lUi~Wp~,.
