U.S. patent application number 15/670503 was filed with the patent office on 2017-11-23 for nonwoven/film laminates.
This patent application is currently assigned to RKW SE. The applicant listed for this patent is RKW SE. Invention is credited to Ludwig BORMANN, Gunter SCHREINER.
Application Number | 20170333264 15/670503 |
Document ID | / |
Family ID | 35385914 |
Filed Date | 2017-11-23 |
United States Patent
Application |
20170333264 |
Kind Code |
A1 |
BORMANN; Ludwig ; et
al. |
November 23, 2017 |
NONWOVEN/FILM LAMINATES
Abstract
The invention relates to a method for producing nonwoven/film
laminates for personal hygiene articles, from an initial film web
consisting of a thermoplastic polymer and an initial nonwoven web.
According to said method, the initial film web and the initial non
woven web, whose melting point lies above the crystallite melting
point of the polymer, are heated to a temperature that exceeds the
crystallite melting point of the polymer and lies below the melting
point of the initial nonwoven web. The laminate is then guided
through a cooled nip and is cooled to a temperature that lies below
the crystallite melting point of the initial film web. The
invention also relates to laminates that can be produced by said
method.
Inventors: |
BORMANN; Ludwig; (Babensham,
DE) ; SCHREINER; Gunter; (Schnaitsee, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RKW SE |
FRANKENTHAL |
|
DE |
|
|
Assignee: |
RKW SE
FRANKENTHAL
DE
|
Family ID: |
35385914 |
Appl. No.: |
15/670503 |
Filed: |
August 7, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13013469 |
Jan 25, 2011 |
9750649 |
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15670503 |
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11574535 |
Apr 3, 2007 |
7947147 |
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PCT/EP05/08903 |
Aug 17, 2005 |
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13013469 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 66/7294 20130101;
B32B 27/12 20130101; B32B 38/0012 20130101; Y10T 428/24942
20150115; Y10T 442/678 20150401; Y10T 156/10 20150115; A61F 13/514
20130101; B32B 2270/00 20130101; B32B 37/203 20130101; B32B 2305/20
20130101; B32B 2307/724 20130101; B32B 37/08 20130101; B32B 2555/00
20130101; B32B 2250/02 20130101; B32B 2309/02 20130101; Y10T
428/31504 20150401; Y10T 442/674 20150401; B32B 37/04 20130101;
B32B 5/022 20130101; B32B 2307/51 20130101; B32B 27/32 20130101;
B32B 2307/7265 20130101 |
International
Class: |
A61F 13/514 20060101
A61F013/514; B32B 5/02 20060101 B32B005/02; B32B 27/12 20060101
B32B027/12; B32B 37/04 20060101 B32B037/04; B32B 27/32 20060101
B32B027/32 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 2, 2004 |
DE |
10 2004 042 405.5 |
Claims
1-11. (canceled)
12. A nonwoven-film laminate useful as backsheet for personal
hygiene articles, obtained by a method comprising: a) providing a
film web made of at least one thermoplastic polymer; b) providing a
nonwoven web, wherein the nonwoven web has a melting point in
excess of the crystallite melting point of the thermoplastic
polymer; c) jointly heating the film web and the nonwoven web to a
temperature above the crystallite melting point of the
thermoplastic polymer and below the melting point of the nonwoven
web, in order to heat the entire film web to at least a molten
state of the thermoplastic polymer and form the nonwoven-film
laminate; and d) guiding the nonwoven-film laminate through a
cooled nip in order to cool the nonwoven-film laminate below the
crystallite melting point of the film web, wherein the heating
comprises heating the film web and the nonwoven web with a heating
cylinder and further heating the film web and the nonwoven web with
another heating method so that the film web is heated to the molten
state.
13. The nonwoven-film laminate according to claim 12, wherein the
another heating method comprises heating with radiant heat.
14. The nonwoven-film laminate according to claim 12, where the
another heating method comprises heating with an infrared
radiator.
15. The nonwoven-film laminate according to claim 12, wherein the
cooled nip is formed by a stamping roller and a rubber roller,
wherein the embossed texture of the stamping roller reduces the
degree of gloss of the laminate.
16. The nonwoven-film laminate according to claim 12, wherein the
cooled laminate is subjected to a stretching step in machine
direction or crossways direction or in machine direction and
crossways direction.
17. The nonwoven-film laminate according to claim 12, wherein the
film web is blow-extruded.
18. The nonwoven-film laminate according to claim 12, wherein the
film web is printed.
19. The nonwoven-film laminate according to claim 12, wherein the
film web is stretched in machine direction or crossways direction
or in machine direction and crossways direction.
20. The nonwoven-film laminate of claim 12, wherein the nonwoven
web is in direct contact with the heating cylinder.
21. The nonwoven-film laminate according to claim 12, wherein the
film web consists of a mixture of LDPE and LLDPE or of a mixture of
LDPE, LLDPE and PP.
22. The nonwoven-film laminate according to claim 12, wherein the
nonwoven web consists of PP or PE.
23. The nonwoven-film laminate according to claim 12, wherein a
low-melting component is contained in the nonwoven web and/or the
film web, wherein the nonwoven web contains at least one component
which comprises a melting temperature above the crystallite melting
temperature of the low-melting component of the film web.
24. The nonwoven-film laminate according to claim 12, wherein the
film web further comprises a filler material.
25. The nonwoven-film laminate according to claim 24, wherein the
filler material is chalk.
26. The nonwoven-film laminate according to claim 12, wherein the
film web comprises a second thermoplastic polymer, wherein the
second thermoplastic polymer has a melting point in excess of the
crystallite melting point of the thermoplastic polymer.
27. A nonwoven-film laminate for personal hygiene articles
consisting of a film web made of a thermoplastic polymer and a
nonwoven web, obtained by a method comprising: a) providing a film
web made of a thermoplastic polymer; b) providing a nonwoven web,
wherein the nonwoven web has a melting point in excess of the
crystallite melting point of the thermoplastic polymer; c) jointly
heating the film web and the nonwoven web to a temperature above
the crystallite melting point of the thermoplastic polymer and
below the melting point of the nonwoven web, in order to heat the
film web to a molten state and form the nonwoven-film laminate; and
d) guiding the nonwoven-film laminate through a cooled nip in order
to cool the nonwoven-film laminate below the crystallite melting
point of the film web, wherein the heating comprises wrapping the
film web and the nonwoven web around a heating cylinder a wrap
distance so that the film web is heated to the molten state.
28. The method according to claim 27, wherein the cooled nip is
formed by a stamping roller and a rubber roller, wherein the
embossed texture of the stamping roller reduces the degree of gloss
of the laminate.
29. The method according to claim 27, wherein the cooled laminate
is subjected to a stretching step in machine direction or crossways
direction or in machine direction and crossways direction.
30. The method according to claim 27, wherein the film web is
blow-extruded.
31. The method according to claim 27, wherein the film web is
printed.
32. The method according to claim 27, wherein the film web is
stretched in machine direction or crossways direction or in machine
direction and crossways direction.
33. The method of claim 27, wherein the nonwoven web is in direct
contact with the heating cylinder.
34. The nonwoven-film laminate according to claim 27, wherein the
film web consists of a mixture of LDPE and LLDPE or of a mixture of
LDPE, LLDPE and PP.
35. The nonwoven-film laminate according to claim 27, wherein the
nonwoven web consists of PP or PE.
36. The nonwoven-film laminate according to claim 27, wherein a
low-melting component is contained in the nonwoven web and/or the
film web, wherein the nonwoven web contains at least one component
which comprises a melting temperature above the crystallite melting
temperature of the low-melting component of the film web.
37. The nonwoven-film laminate according to claim 27, wherein the
film web further comprises a filler material.
38. The nonwoven-film laminate according to claim 37, wherein the
filler material is chalk.
39. The nonwoven-film laminate according to claim 27, wherein the
film web comprises a second thermoplastic polymer, wherein the
second thermoplastic polymer has a melting point in excess of the
crystallite melting point of the thermoplastic polymer.
Description
[0001] The invention relates to improved nonwoven-film laminates
and to a method for the production, thereof.
[0002] Being a waterproof material and, if desired, a material that
is breathable at the same time, plastic films have become
in-dispensable in a multitude of technical fields and daily life.
An broad field of application relates to personal hygiene articles,
such as diapers.
[0003] While known films meet the requirements for tightness,
lightness and breathability to a satisfactory extent, their
stability and, above all, their surface condition which is also
referred to as "grip" fail to be optimal. In particular, breathable
films exhibit poor tear resistance, and the use of thicker and,
thus, more stable films increases the cost incurred. As regards the
grip, the smooth glossy surface of plastic films is felt to be
unpleasant. Particularly the internal surface of personal hygiene
articles, which is sitting directly on the skin, and the external
surface as well should be felt to be soft and, if possible, give a
feeling similar to textile. Smooth films give the impression of
clinging to the skin, even if they are breathable films.
[0004] A further problem is the development of noise, also referred
to as "rustling", which is, in particular, caused by thin films in
personal hygiene articles during movements of the wearer. Such
rustling should be avoided as far as possible since, otherwise, the
acceptance of the personal hygiene article would be impaired.
[0005] In order to overcome the above problems, innumerable
suggestions have been made for a modification of the films as such
and also for the application of laminates made of films containing
woven or nonwoven fabrics.
[0006] For example, DE 195 38 049 describes a method for the
production of a film web which, on the one hand, exhibits improved
transverse elasticity and puncture resistance and, on the other
hand, improved softness and reduced rustling. Therein, an initial
film web consisting of a thermoplastic polymer is heated up to the
molten state and above the crystallite melting point of the polymer
by means of one or more heating cylinders and is subsequently
guided through a cooled nip.
[0007] Wide-spread use is also made of laminates consisting of
non-woven or woven fabrics or films, since these combine the
waterproofness of the film with the textile like surface of woven
or nonwoven fabrics. Nonwoven fabrics are used primarily. In the
most simple case, the laminates consist of a film and a nonwoven
fabric, which can be combined with each other in various manners.
Thermobonding, adhesive bonding and direct extrusion (cast method)
are the most current methods.
[0008] In thermobonding, a stamping roller (=engraved steel roller)
is used, mostly together with a smooth steel roller as a second
roller, to fuse the material of the film and/or nonwoven fabric in
a localized manner by means of high temperature and pressure, with
the result that the two material webs are bonded to each other. The
method has the disadvantage that, owing to the conditions
prevailing during bonding, the film may be damaged and may,
therein, lose its liquid tightness, this also being referred to as
pinholing. In addition, the bonds are only localized, this having
an adverse effect on the composite strength.
[0009] U.S. Pat. No. 5,837,352 discloses an example, describing
laminates consisting of a film and nonwoven fabric, which may be
bonded through thermobonding or ultrasonic or other methods.
[0010] Although with adhesive bonding there is achieved a bonding
across the entire surface, it results in a deterioration of the
breathability of breathable films. What is more, bonding agents
cause additional cost and are, in part, suspected of being harmful
to health. If, however, localized bonding instead of full-surface
bonding is chosen in order to preserve breathability, the composite
strength will suffer.
[0011] As an alternative to adhesive bonding, films and/or nonwoven
layers may be provided or additives may be introduced in the film
and/or nonwoven, this allowing bonding at substantially lower
temperatures, if the thermobonding method is used. U.S. Pat. No.
5,695,868 describes an example, where a component referred to as
bonding agent is contained in either the film or the non-woven or
even in both. This component allows thermobonding below the melting
point of the film and nonwoven, with the result that the
breathability of the film is preserved, and bonding remains
localized.
[0012] Direct extrusion is a cost-effective method for
non-breathable laminates, ensuring a reliable compound strength,
but causing poor softness and a high pinholing risk. If breathable
laminates are desired, breathability can only be achieved in a
second step through reworking of the composite. For this purpose,
either fillers causing the formation of pores thereon when the
laminate is stretched are contained in the film, or the laminate is
provided with pores through needling.
[0013] For example, U.S. Pat. No. 5,865,926 discloses a film which
is extruded on a nonwoven web and, subsequently, the composite is
stretched (ring-rolled) by means of surface-textured rollers in
order to make the composite breathable.
[0014] Finally, use is also made of methods where nonwoven fabrics
are provided with a coating, in order to achieve the desired
tightness against liquids with simultaneous permeability to water
vapor. An example thereof is described in U.S. Pat. No.
5,879,341.
[0015] None of the known methods is able to meet all requirements
in an optimum manner. For that reason, there is a constant demand
for improved laminates and improved methods for the production of
laminates.
[0016] Surprisingly, it has now been found that laminates with
excellent breathability, softness and rustling values can be
produced by heating a film up to the molten state and combining
said film with a nonwoven at this temperature and by then guiding
the composite through a cooled nip.
[0017] Thus, the aforementioned problems are solved by a method for
the production of a laminate from an precursor film web and a
precursor nonwoven web, wherein the precursor film web consisting
of a thermoplastic polymer and the precursor nonwoven web whose
melting point is in excess of the crystallite melting point of the
polymer are heated up to a temperature above the crystallite
melting point of the polymer, with the laminate then being guided
through a cooled nip. The aforementioned problems are also solved
by laminates produced by said method.
[0018] Surprisingly, the molten polymer of the film web adheres to
the non-molten nonwoven web. This composite is fixed in the
subsequent cooled nip.
[0019] The precursor film web is produced in known manner, e.g. by
blow extrusion. In general, all thermoplastic polymers can be used
as materials for the film. A multitude of commercial products is
available on the market. Preferrably, use is made of LDPE (low
density polyethylene), LLDPE (linear low density polyethylene),
MDPE (medium density polyethylene), HDPE (high density
polyethylene), and various PPs (polypropylene) as well as copolymer
of ethylene or propylene with other comonomers. These polymers are
either used in their pure form or as polymer mixtures. Usual
formulations for hygiene films are, for example, mixtures of 10 to
90% by weight of LDPE, 10 to 90% by weight of LLDPE and 0 to 50%
MDPE, such as a mixture of 80% LDPE, 20% LLDPE and pigments meeting
the particular requirements. Commercial polymers for hygiene films
have the melting ranges or crystallite melting points listed
below:
[0020] LDPE=112 to 114.degree. C.
[0021] LLDPE=119 to 125.degree. C.
[0022] MDPE=125 to 128.degree. C.
[0023] Usually, hygiene films are dyed, e.g. white with titanium
dioxide. In addition, they are provided with usual additives and
processing agents, some of which are the molder's trade secret.
[0024] Further suitable substances are ethylene vinyl acetate
(EVA), ethylene acrylate (EEA), ethylene ethyl acrylate (EEA),
ethylene acrylic acid (EAA), ethylene methyl acrylate (EMA),
ethylene butyl acrylate (EBA), polyester (PET), polyamide (PA), for
example nylon, ethylene vinyl alcohols (EVOH), polystyrene (PS),
polyurethane (PU), and thermoplastic olefin elastomers.
[0025] Preferred materials for the precursor film web are
polyolefins, such as LDPE, LLDPE and PP. Most preferred materials
are mixtures of these polymers, such as mixtures of LDPE and LLDPE,
mixtures of LDPE or LLDPE and PP, or mixtures of PE or PP with
different melting points.
[0026] The precursor nonwoven web is also produced in known manner.
All nonwoven fabrics containing at least one formulation component
based on a thermoplastic polymer are useful. The non-wovens may
contain fibers of PE, PP, PET, Rayon, cellulose, PA, and mixtures
of these fibers. It is also possible to use bicomponent or
multicomponent fibers. Most preferred materials are, for example,
nonwovens made of spun or staple fibers based on PP, PE or PET, as
well as nonwovens made of mixtures of PP and PE or mixtures of PET
and PP or PE.
[0027] In general, the thermal lamination method according to the
invention can be utilized with all thermoplastic formulations,
wherein the melting points and raw materials must be coordinated
with each other, as is the case with the thermobonding method. In
general, the webs to be laminated must comprise a similar
morphology in at least one formulation component, in order to
achieve a reliable basis for adequate composite adhesion through
temperature.
[0028] The number of webs to be laminated is not limited; however,
the necessary heating of the webs, for example through a heating
cylinder, must be ensured before said webs reach the cooled nip. It
is not only possible to laminate nonwovens with films, but also any
conceivable combination (e.g. non-woven-nonwoven;
nonwoven-film-nonwoven; film-film; etc.).
[0029] The precursor webs may have been produced by any known
method, but must contain thermoplastic components. Here, it is
important to coordinate the materials of film and nonwoven with
each other, on the one hand by choosing crystallite melting points
which are sufficiently spaced apart from each other and, on the
other hand, by choosing materials which are sufficiently compatible
with each other to allow bonding. The appropriate material
combinations are known to those skilled in the art and can also be
determined by means of a few orienting tests.
[0030] The difference in the crystallite melting point of the
precursor film web or the low-melting component of the precursor
film web should be at least about 5.degree. C., preferrably at
least about 10.degree. C., and most preferrably at least about
20.degree. C. below the melting temperature of the precursor
nonwoven web or below the melting temperature of the high-melting
component of the precursor nonwoven web.
[0031] To achieve a better compatibility, a low-melting component
may be contained in the precursor film web or the precursor
nonwoven web or in both thereof. Herein, it must be ensured that at
least one component of the precursor nonwoven web comprises a
melting point above the crystallite melting temperature of the
precursor film web or of the lower-melting component in the
precursor film web.
[0032] To improve material compatibility, it is also possible to
use two-layer or multi-layer nonwovens where the layer in the
laminate that is in contact with the precursor film web consists of
a lower-melting material or contains a lower-melting material than
the further layer(s).
[0033] According to the invention, the precursor film web and the
precursor nonwoven web are jointly heated through a preferrably
antistick-coated heating cylinder and are then guided through a
cooled nip. As a matter of course, it is also possible to use a
plurality of heating cylinders or other heating methods, such as
infrared radiators. For reasons of clarity, however, the invention
will be described below with regard to one heating cylinder
only.
[0034] In a preferred embodiment, the precursor nonwoven web is in
direct contact with the surface of the heating cylinder. The
precursor film web is carried along on top thereof. The temperature
of the heating cylinder is selected such that the precursor film
web is heated up to the molten state across the wrap distance of
the heating cylinder, however, such that this temperature does not
yet initiate the molten state for the carried-along precursor
nonwoven web, i.e. this temperature must be below the crystallite
melting point of the precursor nonwoven web.
[0035] Since the nonwoven web that is not in the molten state yet
bears on the heating cylinder, it is ensured that the molten film
web resting on top thereof can be detached in an easy manner that
is highly stable with regard to the process.
[0036] It is, however, also possible to apply the method with the
film web having direct contact to an antistick-coated heating
cylinder and a nonwoven web arranged on top thereof.
[0037] In the following cooled nip, the laminate is cooled to
temperatures below the crystallite melting point of the film web.
Preferrably, the cooled nip consists of a steel roller and a
counterpressure rubber roller. The steel roller is, preferrably,
provided with a textile-type engraving which further supports the
textile appearance of the laminate surface. The preferrably used
embossed texture of the steel roller reduces the degree of gloss of
the laminate.
[0038] Contrary to known thermobonding lamination methods wherein
two heated steel rollers (raised engraved roller and smooth
counterpressure roller) are used to guide a film web and a nonwoven
web and the composite is created through temperature and very high
pressures in a localized manner only, the thermal lamination method
according to the invention provides full-surface lamination.
Similar to the known adhesive lamination methods, this is to
advantage in that, owing to low pressures in the lamination process
(pressureless heating, lamination step in the cooled nip over the
entire surface and with soft rubber roller as counterpressure
roller), very soft laminates (similar to adhesive laminates) are
created without use of adhesives and, on the other hand, the risk
of material damage (perforations, pinholes) incurred with
thermobonded laminates is excluded.
[0039] The composite adhesion between nonwoven and film can very
easily be controlled through the degree of heating. The higher the
temperature of the surface of the heating cylinder, the higher the
composite values between nonwoven and film. The heating process
window at the minimum temperature is provided through the
absolutely necessary molten state of the raw material component
responsible for composite adhesion. The upper heating limit is
provided through the crystallite melting point of the nonwoven web.
If heating goes beyond the crystallite melting point of the
nonwoven web, the resulting laminates will have an indestructible
bond between the nonwoven web and the film web; however, the high
softness of the laminate will be lost, causing the risk of holes
similar to the direct extrusion or thermobonding methods.
[0040] Contrary to the known adhesive lamination methods, the
thermal lamination method according to the invention is to
advantage in that a high softness of the products is achieved
without the use of an adhesive. Moreover, said method allows the
production of trilaminates (nonwoven-film-nonwoven) without
requiring major modifications to the plant. In this case, it is
only necessary to carry along a second nonwoven web over the two
initial webs and to also heat said web through a heating cylinder
or heating cylinders.
[0041] As compared with the classic thermobonding method, the
thermal lamination method is to advantage in that the produced
laminates have a higher softness and material damage caused by high
pressures and temperatures is avoided. As a result, these laminates
are not associated with the risk of perforations or microholes
("pinholes") which represent a considerable defect in personal
hygiene articles (leaky diapers), for example when such laminates
are used as backsheets.
[0042] As compared with laminates produced according to the known
direct extrusion method, the combined nonwoven-film laminates
provide a higher softness while the risk of defective spots
(perforations, pinholes) is clearly reduced. With direct extrusion,
the melt film is applied to the nonwoven directly downstream of the
slot die and at extrusion temperature. The nonwoven-film web
composite is produced in a subsequent cooled nip. Owing to the
necessary high extrusion temperatures (e.g. approx. 230.degree. C.
for LDPE-LLDPE-PP mixtures, corresponding to approx. 70.degree. C.
above the crystallite melting point of the highest-melting
formulation component), the molten film web has a very low
viscosity when it is applied to the nonwoven web. In combination
with the subsequent cooled pressure-controlled nip, the
low-viscosity film web penetrates the nonwoven web to a very high
extent. As a result, the laminate is hardened and the nonwoven
filaments pierce the film web, this in turn being a cause of
perforations and pinholes in the finished product.
[0043] Contrary thereto, the invention allows highly precise
adjustment of the viscosity of the molten film web by means of the
heating cylinder. By decoupling the extrusion and lamination
procedure, the high extrusion temperatures can be restricted to
this procedure and substantially lower temperatures can be used for
the lamination procedure. Contrary to the direct extrusion method
(with identical formulations), the invention, hence, allows
lamination with the composite values usually required for personal
hygiene articles (>0.10 N/cm) as early as when the crystallite
melting point of the raw material component in the film web
responsible for the lamination behavior is reached.
[0044] As compared with direct extrusion lamination, the present
invention is further to advantage in that the laminates produced
according to the invention can be printed. According to the
invention, the film can be printed after the extrusion procedure
and before the lamination procedure. This allows printing on the
film side which will be covered by the non-woven in the future
laminate. This results in an excellent printing quality, because it
is possible to print on the smooth film web. The nonwoven which, in
the finished laminate, will be arranged directly on top of said
smooth film web affects the print image only to an inconsiderable
degree, but will prevent abrasion of the printing ink in the
finished product. If the laminates printed according to the
invention are, for example, used as backsheets for diapers, the
surround cannot become dirty through abrasion of the printing ink,
since the latter is covered by the nonwoven.
[0045] As regards breathable laminates, this embodiment is further
to advantage in that the stretching step for creating the
breathability in filler-containing films is, preferrably, also
achieved before the printing and lamination procedures. This
prevents the print subjects from being distorted while stretching
is in progress.
[0046] With direct extrusion (the molten film web is bonded to the
nonwoven web directly downstream of the slot die), it is not
possible to print on the film web nor to cover same with the
nonwoven web. With this method, it is either possible to print on
the nonwoven side (=external surface of the various finished
products (e.g. diapers)), this allowing only a highly restricted
printing quality and posing the danger of printing ink abrasion in
the finished product. Or the side facing the film can be printed
before the film is applied, but then the printing quality will
remain poor and printing on the nonwoven requires a great amount of
printing ink. Further, direct extrusion laminates can be printed by
printing on the film side according to what is called the counter
print method. Therein, the print subject is visible through the
nonwoven and film layers in the finished product. In this case, the
print subject can be seen to a limited degree only or not at all;
this is particularly applicable to strongly dyed opaque films (for
example chalk-filled breathable films).
[0047] As a matter of course, the method according to the invention
can immediately follow the production of the precursor film web,
for example by extruding a film web through a slot system and
cooling by means of a stamping unit, a chill-roll system or even a
cooling roller or cooling rollers only. Such a system is then
equipped with one or more downstream heating cylinders according to
the invention with subsequent cooled nip. If desired, a printing
unit is installed upstream of the heating cylinder(s) according to
the invention.
[0048] In a further preferred embodiment, the nonwoven-film
combination is, after the lamination procedure, subjected to a
ring-rolling step in crossways direction to the web. On the one
hand, this stretching in crossways direction (CD) reduces the base
weight of the laminate, broadens the web in crossways direction and
increases the softness of the finished product. These described
changes in property can be easily manipulated through the geometry
used and through the degree of engagement of the ring-rolling
rollers. As a matter of course, the laminates can also be subjected
to a ring-rolling step in machine direction (MD) or in crossways
and machine direction (CD+MD). Since the depth of penetration of
the film web into the nonwoven web can be easily controlled through
the heating cylinder, the formation of perforations and/or pinholes
in the stretching procedure can be easily prevented.
[0049] FIG. 1 is a schematic diagram of the thermal lamination
method according to the invention. A precursor nonwoven web 2 is
guided over the deflection roller 3 and a precursor film web 1 is
guided over the deflection and impression roller 4. Said webs 2 and
1 are both guided onto a heating cylinder 5. There, the two webs
are jointly heated to a temperature above the crystallite melting
point of the precursor film web and below the crystallite melting
point of the precursor nonwoven web. Therein, the nonwoven web is
bearing on the cylinder 5. Subsequently, the composite formed on
the heating cylinder 5 is fixed and cooled in the stamping unit
which consists of the stamping roller 6 and the rubber roller 7.
The composite is guided over the deflection rollers 8 and 9 and is
then subjected to a stretching step which is achieved in crossways
direction through the ring-rolling rollers 10 and 11. Thereafter,
the finished laminate can be further processed in known manner.
[0050] The examples following below are intended to illustrate the
invention, however without restricting it thereto.
EXAMPLE 1
Nonwoven-Film Laminate (Non-Vreathable)
[0051] A precursor film web consisting of 30% polypropylene
(melting point ranging from 137 to 143.degree. C.), 60% LDPE and
10% LLDPE is blow-extruded in 14 g/m.sup.2. Thereafter, the
precursor film web and a precursor nonwoven web (14 g/m.sup.2)
based on polypropylene are jointly fed to a system, such as it is
schematically represented in FIG. 1. The polypropylene of the film
web differs from the polypropylene of the precursor nonwoven web in
that its DSC crystallite melting point is approx. 20.degree. C.
lower. The precursor nonwoven web is in direct contact with the
surface of the heating cylinder. The precursor film web is carried
along on top thereof. The temperature of the heating cylinder is
selected such that, over the wrap distance of the heating cylinder,
the precursor film web is heated up to the molten state at a
temperature ranging from 137 to 143.degree. C. At this temperature,
the carried-along precursor nonwoven web does not reach the molten
state yet. In the subsequent cooled nip, the laminate is cooled
down to a value below the crystallite melting point of the film
web.
[0052] The laminate showed composite values of >0.10 N/cm as
required for personal hygiene articles.
EXAMPLE 2
Nonwoven-Film Laminate (Non-Breathable)
[0053] A precursor film web consisting of 70% LDPE (melting point
ranging from 108 to 113.degree. C.) and 30% LLDPE (117 to
124.degree. C.) is blow-extruded in 14 g/m.sup.2. Thereafter, the
precursor film web and a precursor nonwoven web (14 g/m.sup.2,
melting point ranging from 131 to 135.degree. C.) based on
polypropylene are jointly fed to a system, such as it is
schematically represented in FIG. 1. The LDPE of the film web
differs from the polypropylene of the precursor nonwoven web in
that its DSC crystallite melting point is approx. 20.degree. C.
lower. The precursor nonwoven web is in direct contact with the
surface of the heating cylinder. The precursor film web is carried
along on top thereof. The temperature of the heating cylinder is
selected such that, over the wrap distance of the heating cylinder,
the precursor film web is heated up to the molten state at a
temperature ranging from 114 to 125.degree. C., either in part
(above LDPE melting point) or as a whole (above LDPE and LLDPE
melting points). At this temperature, the carried-along precursor
nonwoven web does not reach the molten state yet. In the subsequent
cooled nip, the laminate is cooled down to a value below the
crystallite melting point of the film web. To achieve an
appropriate composite, the molten state of the LDPE formulation
component is already sufficient.
[0054] The laminate showed composite values of >0.10 N/cm as
required for personal hygiene articles.
EXAMPLE 3
Nonwoven-Film Laminate (Breathable)
[0055] A precursor film web (precursor film) is blow-extruded. The
formulation of the film web consists of 70% polypropylene compound
(melting point ranging from 137 to 143.degree. C.) and 30% LLDPE
compound (117 to 124.degree. C.) wherein the compounds each consist
of a mixture of raw material plus 60% CaCO.sub.3 (chalk).
Thereafter, the precursor film web and a precursor nonwoven web (14
g/m.sup.2) based on polypropylene are jointly fed to a system, such
as it is schematically represented in FIG. 1. The polypropylene
present in the film web differs from the polypropylene of the
precursor nonwoven web in that its DSC crystallite melting point is
approx. 20.degree. C. lower. The two webs are jointly heated
through an antistick-coated heating cylinder and then guided
through a cooled nip (stamping roller and a counterpressure rubber
roller) The precursor nonwoven web is in direct contact with the
surface of the heating cylinder. The precursor film web is carried
along on top thereof. The temperature of the heating cylinder is
selected such that, over the wrap distance of the heating cylinder,
the precursor film web is heated up to the molten state at a
temperature ranging from 137 to 143.degree. C., but that the
carried-along precursor nonwoven web does not reach the molten
state yet at this temperature. In the subsequent cooled nip, the
laminate is cooled down to a value below the crystallite melting
point of the film web.
[0056] In the present exemplary embodiment, the nonwoven-film
combination is, after the lamination procedure, additionally
subjected to a ring-rolling step in crossways direction to the
material web. This stretching step is intended to generate
breathability. That means that fine pores are formed around the
chalk grains (mean particle size ranging from 0.8 to 3.0 pm) for
achieving breathability, the maximum permissible size of said pores
being approx. 1 pm to preserve liquid tightness. The measurement as
to ASTM E 398 (38.degree. C., 90% relative air humidity, measuring
instrument LYSSY L 80-5000 Lyssy AG, CH) resulted in a permeability
to water vapor ranging from 2200 to 2500 g/m.sup.2 in 24 h.
[0057] Depending on the size of the chalk grains used and the
ring-rolling penetration depth, a permeability to water vapor
ranging from 500 to 3500 g/m.sup.2 in 24 h can be achieved.
Example 4
Nonwoven-Film Laminate (Highly Breathable)
[0058] In a first step, a precursor film web (precursor film) is
blow-extruded. The formulation of the film web consists of 70%
low-melting polypropylene compound (melting point approx. at
130.degree. C.) and 30% high-melting polypropylene compound
(melting point ranging from 158 to 164.degree. C.). The compounds
each consist of a mixture of raw material plus 55% CaCO.sub.3
(chalk).
[0059] After the so-called precursor film has been blow-extruded,
the film is stretched in machine direction in a monoaxial MDO
stretching unit. Therein, 100% of the film web is stretched in
machine direction with the stretching degree ranging from 1:1.5 to
1:4.0, thus producing breathability. Contrary to partial stretching
in ring-rolling, MDO stretching allows to reach very high
breathabilities without posing the risk of perforations or pinholes
and, thus, of film webs that are permeable to liquid; this is
achieved by means of high stretching degrees and owing to the fact
that the entire film web area is available for stretching.
[0060] After completion of the stretching step, the breathable film
web can be very easily printed if desired, using the usual methods.
The smooth film surface provides the basis of highly precise print
images on the film web, and the print subjects are preserved,
showing no distortions caused by the previous stretching step. For
example, breathable direct extrusion laminates (nonwoven-film
laminates) are not stretched before printing on the nonwoven web
and the lamination procedure are completed. Therein, the print
subjects are distorted through this following stretching step.
[0061] Subsequently, the breathable film web and a precursor
non-woven web (14 g/m.sup.2) based on polypropylene are jointly
heated through an antistick-coated heating cylinder and then guided
through a cooled nip. The polypropylene present in the film web
differs from the high-melting polypropylene of the precursor
nonwoven web in that its DSC crystallite melting point is approx.
20.degree. C. lower. In two nonwoven layers, the formulation of the
three-layer precursor nonwoven web consists of a high-melting
polypropylene (crystallite melting point ranging from approx. 150
to 165.degree. C.). Similar to the film web, the third nonwoven
layer (=external surface=lamination side facing the film) was made
of a polypropylene having a melting point of approx. 130.degree.
C.
[0062] The precursor nonwoven web is in direct contact with the
surface of the heating cylinder, wherein the nonwoven layer having
the reduced melting point faces the precursor film web. The
precursor film web is carried along on top thereof. The temperature
of the heating cylinder is selected such that, over the wrap
distance of the heating cylinder, the precursor film web is, in
part, heated up to the molten state of the low-melting PP compound,
but such that this temperature (ranging from 130 to 140.degree. C.)
does not cause the carried-along precursor nonwoven web to reach
the molten state of the two high-melting PP nonwoven layers yet.
Therein, the third low-melting PP nonwoven layer is heated up to
the crystallite melting point. This nonwoven layer is in direct
contact with the precursor film web and supports an appropriate
composite (>0.10 N/cm) through the molten state. In the
subsequent cooled nip, the laminate is cooled down to a value below
the crystallite melting point of all formulation components of the
film and nonwoven webs. A permeability to water vapor ranging from
2000 to 3500 g/m.sup.2 in 24 h has been measured.
[0063] As in example 2, it is also possible to manipulate the
permeability to water vapor by means of the parameters of filler
particle sizes and ring-rolling penetration depth. Values ranging
from 500 to 5000 g/m.sup.2 are possible.
[0064] Additional ring-rolling in crossways direction further
increases the softness and the permeability to water vapor.
* * * * *