U.S. patent application number 14/596304 was filed with the patent office on 2016-07-14 for wet-strength corrugated fiberboard.
The applicant listed for this patent is BASF SE. Invention is credited to Rainer Blum, Jurgen Keck, Hubertus Kroner, Gabriel Skupin.
Application Number | 20160201270 14/596304 |
Document ID | / |
Family ID | 56367130 |
Filed Date | 2016-07-14 |
United States Patent
Application |
20160201270 |
Kind Code |
A1 |
Blum; Rainer ; et
al. |
July 14, 2016 |
WET-STRENGTH CORRUGATED FIBERBOARD
Abstract
The present invention relates to single face or double faced
corrugated fiberboard comprising one or more corrugated plies,
wherein at least one of the linerboard plies or corrugated plies is
a paper-film assembly comprising: i) a 30 to 600 g/m.sup.2 grammage
papery material of construction, ii) a biodegradable polymeric
coating from 1 to 100 .mu.m in thickness. More particularly, the
present invention relates to single face or double faced and/or
corrugated fiberboard comprising one or more corrugated plies,
wherein at least one of the linerboard plies or corrugated plies is
a paper-film assembly comprising: i) a 30 to 600 g/m.sup.2 grammage
papery material of construction as outer layer, ii) a biodegradable
polymeric coating from 1 to 100 .mu.m in thickness as interlayer,
and iii) a 30 to 600 g/m.sup.2 grammage papery material of
construction as inner layer. The present invention further relates
to methods of producing this corrugated fiberboard.
Inventors: |
Blum; Rainer; (Mannheim,
DE) ; Skupin; Gabriel; (Speyer, DE) ; Kroner;
Hubertus; (Neustadt, DE) ; Keck; Jurgen;
(Speyer, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen |
|
DE |
|
|
Family ID: |
56367130 |
Appl. No.: |
14/596304 |
Filed: |
January 14, 2015 |
Current U.S.
Class: |
162/125 |
Current CPC
Class: |
D21H 19/28 20130101;
D21H 11/14 20130101; D21H 27/38 20130101; D21H 19/74 20130101 |
International
Class: |
D21H 27/38 20060101
D21H027/38; D21H 19/74 20060101 D21H019/74; D21H 11/14 20060101
D21H011/14; D21H 19/28 20060101 D21H019/28 |
Claims
1.-7. (canceled)
8. A method of producing a paper film assembly for the manufacture
of corrugated fiberboard that includes one or more linerboard plies
and one or more corrugated plies, the method comprising laminating
preheated webs of paper with a polymeric film with or without a
lamination adhesive, wherein the paper film assembly comprises; i)
a 30 to 600 g/m.sup.2 grammage papery material of construction as a
layer, and ii) a biodegradable polymeric coating with a thickness
from 1 to 100 .mu.m.
9. The method of claim 8, wherein the laminating includes the
lamination adhesive.
10. The method of claim 8, wherein the grammage papery material of
construction is 50 to 150 g/m.sup.2, and the thickness of the
biodegradable polymeric coating is from 10 to 60 .mu.m.
11. The method of claim 8, wherein the polymeric coating is
selected from an aliphatic/aromatic polyester prepared from
butanediol, terephthalic acid or one or more C.sub.6-C.sub.18
dicarboxylic acids.
12. The method of claim 8, wherein the polymeric coating is a
copolymer mixture comprising: 30% to 50% by weight of a
biodegradable, aliphatic-aromatic polyester; 70% to 50% by weight
of one or more polymers selected from the group consisting of
polylactic acid and polyhydroxyalkanoate; and 0% to 2% by weight of
an epoxy-containing poly(meth)acrylate.
13. The method of claim 8, wherein said layer i) comprises
wastepaper in the range from 10 to 100%.
14. A method of producing a paper film assembly for the manufacture
of corrugated fiberboard that includes one or more linerboard plies
and one or more corrugated plies, the method comprising laminating
preheated webs of paper with a polymeric film with or without a
lamination adhesive, wherein the paper film assembly comprises; i)
a 30 to 600 g/m.sup.2 grammage papery material of construction as
an outer layer, ii) a biodegradable polymeric coating with a
thickness from 1 to 100 .mu.m as an interlayer, and iii) a 30 to
600 g/m.sup.2 grammage papery material of construction as an inner
layer.
15. The method of claim 14, wherein the laminating includes the
lamination adhesive.
16. The method of claim 14, wherein the outer layer, grammage
papery material of construction is 50 to 150 g/m.sup.2, the
thickness of the biodegradable polymeric coating is from 10 to 60
.mu.m, and the inner layer, grammage papery material of
construction is 50 to 150 g/m.sup.2
17. The method of claim 14, wherein the polymeric coating is
selected from an aliphatic/aromatic polyester prepared from
butanediol, terephthalic acid or one or more C.sub.6-C.sub.18
dicarboxylic acids.
18. The method of claim 14, wherein the polymeric coating is a
copolymer mixture comprising: 30% to 50% by weight of a
biodegradable, aliphatic-aromatic polyester; 70% to 50% by weight
of one or more polymers selected from the group consisting of
polylactic acid and polyhydroxyalkanoate; and 0% to 2% by weight of
an epoxy-containing poly(meth)acrylate.
19. The method of claim 14, wherein said layer i) and said layer
iii) comprises wastepaper in the range from 10 to 100%.
20. The method of claim 8, wherein the biodegradable polymeric
coating is applied as a hot melt with an extrusion coating.
21. The method of claim 20, wherein the polymeric coating as a
hotmelt is pumped from a stock reservoir vessel preheated to a
temperature from 150 to 200.degree. C. into a wind-slot die as the
paper web travels directly past the die lip at a high rate of speed
to provide coatings of from 1 to 5 g/m.sup.2.
22. The method of claim 14 wherein the biodegradable polymeric
coating is applied as a hot melt in an extrusion coating.
24. The method of claim 22, wherein the polymeric coating as a
hotmelt is pumped from a stock reservoir vessel preheated to a
temperature from 150 to 200.degree. C. into a wind-slot die as the
paper web travels directly past the die lip at a high rate of speed
to provide coatings of from 1 to 5 g/m.sup.2.
Description
[0001] The present invention relates to single face or double faced
corrugated fiberboard comprising one or more corrugated plies,
wherein at least one of the linerboard plies or corrugated plies is
a paper-film assembly comprising:
i) a 30 to 600 g/m.sup.2 grammage paper-based construction
material, ii) a biodegradable polymeric coating from 1 to 100 .mu.m
in thickness.
[0002] More particularly, the present invention relates to single
face or double faced corrugated fiberboard comprising one or more
corrugated plies, wherein at least one of the linerboard plies or
corrugated plies is a paper-film assembly comprising:
i) a 30 to 600 g/m.sup.2 grammage paper-based construction material
as outer layer, ii) a biodegradable polymeric coating from 1 to 100
.mu.m in thickness as interlayer, and iii) a 30 to 600 g/m.sup.2
grammage paper-based construction material as inner layer.
[0003] The present invention further relates to methods of
producing this corrugated fiberboard.
[0004] Polymer-coated paper-based products have numerous
applications, more particularly in paper varieties whose ink jet
printability can be improved by the polymeric coating, i.e., all
graphic papers, natural papers, paperboard and cardboard. In all
these applications, the surface of the paper-based construction
material is altered, as is indeed desired for the abovementioned
applications such as printability or barrier properties.
Paper-based products coated with biodegradable polymer (blends) are
known from WO2010/034712.
[0005] However, there are numerous applications where the surface
properties of the paper are actually desired. In corrugated
fiberboard production, the untreated surface of paper has distinct
advantages. When the corrugated plies are produced on the so-called
fluted rows, the untreated surfaces of paper do not adhere. On the
other hand, untreated papery materials of construction have
insufficient wet strength or oil resistance for numerous
applications. Subsequent impregnation or waxing of the papers leads
to issues in the recycling of the papery materials of
construction.
[0006] German Laid-Open Specification DOS 2124092 describes
wet-strength corrugated fiberboards having a corrugation with a
paper/polyethylene/paper construction. This embodiment is
disadvantageous in that the paper/polyethylene assembly is not
simple to recycle using customary methods (e.g., deinking in the
case of newspaper by the method described in EO 09174077.9).
[0007] The problem addressed by the present invention was
accordingly that of providing corrugated fiberboard that has
surface properties comparable to paper, but at the same time has
wet strength, oil resistance, a higher moisture resistance and is
also simple to recycle.
[0008] This problem is solved by the corrugated fiberboard of the
present invention. The inner and outer surfaces are of an untreated
paper-based construction material. The structural reinforcement
resides in the interior of the assembly and improves the barrier
properties such as moisture resistance, wet strength, water vapor
resistance and oil resistance of the entire assembly.
[0009] The corrugated fiberboard of the present invention also has
distinct advantages in recycling and can be recycled by the method
described in EP 09174077.9. The corrugated fiberboard is initially
charged in an aqueous wastepaper suspension which
a) is pulped in the presence of at least one hydrolase, b) is
pulped in an alkaline medium, and/or c) is treated in an alkaline
medium in a deinking process, and the polymeric film is
subsequently separated from the wastepaper suspension. The method
is preferably carried out in only one of the described embodiments
a), b) or c). But it is also possible to carry out any desired
combinations of at least two embodiments. In general, however, one
of the embodiments mentioned will be sufficient to achieve complete
separation of biodegradable polymers from the papery fiber.
[0010] Wastepaper and the recovery of the wastepaper from
paper-based products are of particular economic significance in the
paper industry, since resources (cellulosic pulp) can be protected
in this way. The term "wastepaper" is based on German standard
specification DIN 6730 and is accordingly defined as paper or
paperboard which are to be recycled in used or unused form from
production or processing and are to be returned as half-stuffs to a
manufacturing process. In Germany alone, the wastepaper feed rate,
i.e., the proportion of total domestic paper production accounted
for by wastepaper, was 65% in 2003. Usually, wastepaper is used as
a secondary raw material in paper and paperboard production.
However, wastepaper cannot be recycled infinitely often. With every
use cycle, the fibers are shortened by the mechanical stress and
after about 4 to 6 cycles lose the ability to re-form into a sheet,
and this in turn has adverse consequences for paper strength.
Corrugated fiberboard production utilizes papers comprising new-
and high-grade papery fibers. This is why the wastepaper fraction
is very small in the case of corrugated fiberboard. We have now
found that the proportion of wastepaper in the corrugated
fiberboard of the present invention can be distinctly increased
while at the same time the properties of the assembly such as the
strength of the paper can be maintained at a high level. In the
paper-based assembly it is the inner coating of polymer or rather
polymeric sheet which assumes an important structural function.
[0011] The term "paper-based products" for the purposes of the
present invention subsumes all species of paper and more
particularly paperboard and cardboard.
[0012] As fibrous materials for producing these paper-based
products there come into consideration all qualities customary for
this purpose, e.g., mechanical pulp, bleached and unbleached
chemical pulp, paper-based stocks from all annual plants and also
wastepaper (also in the form of broke, both coated and uncoated).
These fibrous materials can be used either alone or in any desired
mixture with one another for the production of the pulps from which
the paper-based products are produced. Mechanical pulp includes for
example groundwood, thermomechanical pulp (TMP),
chemothermomechanical pulp (CTMP), pressure groundwood,
semichemical pulp, high-yield chemical pulp and refiner mechanical
pulp (RMP). As chemical pulp there come into consideration for
example sulfate, sulfite and soda pulps. Suitable annual plants for
production of papery stocks are for example rice, wheat, sugarcane
and kenaf.
[0013] The pulps are typically admixed with sizing agents in an
amount of 0.01% to 3% by weight and preferably 0.05% to 1% by
weight, solids in each case, based on dry paper stock, and they
depend on the degree of sizing desired for the papers to be sized.
The paper-based construction material may further comprise further
substances, for example starch, pigments, dyes, optical
brighteners, biocides, strength enhancers for paper, fixatives,
defoamers, retention aids and/or drainage aids.
[0014] The central polymeric layer may comprise any biodegradable
polymer customary for paper coating.
[0015] Biodegradable polymers are already known to a person skilled
in the art and are disclosed inter alia in Ullmann's Encyclopedia
of Industrial Chemistry (online-Version 2009), Polymers,
Biodegradable, Wiley-VCH Verlag GmbH & Co. KG, Weinheim, 2009,
pages 131. More particularly, the term "biodegradable polymers" for
the purposes of the present invention subsumes: polylactic acid
(PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA),
polyalkylene carbonate such as polypropylene carbonate (PPC) or
polyethylene carbonate (PEC), chitosan and gluten and one or more
polyesters based on aliphatic diols and aliphatic/aromatic
dicarboxylic acids such as, for example, polybutylene succinate
(PBS), polybutylene succinate adipate (PBSA), polybutylene
succinate sebacate (PBSSe), polybutylene adipate-co-terephthalate
(PBAT), polybutylene sebacate-co-terephthalate (PBSeT),
polybutylene succinate-co-terephthalate (PBST). Also suitable are
compounds of one or more of the biodegradable polymers mentioned
with natural polymers, such as starch, glucose, oligomeric
glucosene, cellulose, cellulose derivatives, lignins, chitosan,
gluten, collagen, zein and copolyesters thereof.
[0016] As biodegradable polymers it is more particularly partly
aromatic polyesters which are suitable for the central polymeric
layer. By partly aromatic polyesters based on aliphatic diols and
aliphatic/aromatic dicarboxylic acids are also meant polyester
derivatives such as polyether esters, polyester amides or polyether
ester amides. Partly aromatic polyesters include linear polyesters
which are not chain extended (WO 92/09654 A1). Aliphatic/aromatic
polyesters formed from butanediol, terephthalic acid and aliphatic
C.sub.6-C.sub.18 dicarboxylic acids such as adipic acid, suberic
acid, azelaic acid, sebacic acid and brassylic acid (as described
in WO 2006/097353 to 56 for example) are suitable blending partners
in particular. Preference is given to chain-extended and/or
branched partly aromatic polyesters. The latter are known from
documents WO 96/15173 to 15176, 21689 to 21692, 25446, 25448 or WO
98/12242, which are expressly incorporated herein by reference.
Mixtures of different partly aromatic polyesters similarly come
into consideration.
[0017] Partly aromatic polyesters particularly suitable for the
central polymeric film are constructed as follows: [0018] i) from
40 to 70 mol %, based on the components i to ii, of one or more
dicarboxylic acid derivatives or dicarboxylic acids selected from
the group consisting of succinic acid, adipic acid, sebacic acid,
azelaic acid and brassylic acid, [0019] ii) from 60 to 30 mol %,
based on the components i to ii, of a terephthalic acid derivative,
[0020] iii) from 98 to 102 mol %, based on the components i to ii,
of a C.sub.2-C.sub.8 alkylene diol or C.sub.2-C.sub.6 oxyalkylene
diol, [0021] iv) from 0.00% to 2% by weight, based on the total
weight of components i to iii, of a chain extender and/or
crosslinker selected from the group consisting of a di- or
polyfunctional isocyanate, isocyanurate, oxazoline, epoxide,
carboxylic anhydride and/or a brancher capable of forming three
ester and/or amide bonds at least, [0022] v) 0.00% to 50% by
weight, based on the total weight of components i to iv, of an
organic filler selected from the group consisting of native or
plastified starch, natural fibers, woodmeal and/or of an inorganic
filler selected from the group consisting of chalk, precipitated
calcium carbonate, graphite, gypsum, conductivity carbon black,
iron oxide, calcium chloride, dolomite, kaolin, silicon dioxide
(quartz), sodium carbonate, titanium dioxide, silicate,
wollastonite, mica, montmorillonites, talc, glass fibers and
mineral fibers, and [0023] vi) from 0.00% to 2% by weight, based on
the total weight of components i to iv, of at least one stabilizer,
nucleator, slip and release agent, surfactant, wax, antistat,
antifogant, dye, pigment, UV absorber, UV stabilizer or other
plastic additive.
[0024] Partly aromatic polyesters of the abovementioned composition
are supremely recyclable by the method described in EP 09174077.9,
optionally in mixtures with polylactic acid.
[0025] Particularly suitable are partly aromatic polyesters having
a melt volume rate (MVR) to EN ISO 1133 (190.degree. C., 2.16 kg
weight) of 5 to 50 cm.sup.3/10 min, more particularly of 5 to 25
cm.sup.3/10 min and more preferably of 5 to 12 cm.sup.3/10 min.
[0026] Suitable for the central polymeric layer are further in
particular the following copolymer mixtures of the composition:
[0027] (a) from 5% to 95% by weight, preferably from 30% to 90% by
weight and more preferably from 40% to 70% by weight of a
biodegradable, aliphatic-aromatic polyester, and [0028] (b) from
95% to 5% by weight, preferably from 70% to 10% by weight and more
preferably from 60% to 30% by weight of one or more polymers
selected from the group consisting of polylactic acid,
polycaprolactone, polyhydroxyalkanoate, chitosan and gluten and one
or more polyesters based on aliphatic diols and aliphatic/aromatic
dicarboxylic acids such as, for example, polybutylene succinate
(PBS), polybutylene succinate adipate (PBSA), polybutylene
succinate sebacate (PBSSe), polybutylene terephthalate-co-adipate
(PBTA) and [0029] (c) from 0% to 2% by weight of a
compatibilizer.
[0030] Compatibilizers of group (c) are carboxylic anhydrides such
as maleic anhydride and more particularly epoxy-containing
copolymers based on styrene, acrylic esters and/or methacrylic
esters. The epoxy-bearing units are preferably glycidyl
(meth)acrylates. Epoxy-containing copolymers of the abovementioned
type are marketed for example by BASF Resins B.V. under the
Joncryl.RTM. ADR brand. Joncryl.RTM. ADR 4368 for example is
particularly useful as compatibilizer.
[0031] Particularly preferred copolymer mixtures therefore comprise
[0032] (a) from 20% to 90% by weight, preferably from 30% to 50% by
weight and more preferably from 35% to 45% by weight of a
biodegradable, aliphatic-aromatic polyester, [0033] (b) from 80% to
10% by weight, preferably from 70% to 50% by weight and more
preferably from 65% to 55% by weight of one or more polymers
selected from the group consisting of polylactic acid and
polyhydroxyalkanoate, and [0034] (c) from 0% to 2% by weight of an
epoxy-containing poly(meth)acrylate.
[0035] As polylactic acid of group (b) it is preferable to use one
that has the following profile of properties: [0036] an MVR melt
volume rate at 190.degree. C. and 2.16 kg to EN ISO 1133 of 0.5 to
100 ml/10 min, preferably 5 to 70 ml/10 min and more preferably 9
to 50 ml/10 min, [0037] a melting point below 240.degree. C.,
[0038] a glass transition point (Tg) above 55.degree. C., [0039] a
water content of below 1000 ppm, [0040] a residual monomer content
(lactide) of below 0.3% by weight, and [0041] a molecular weight of
above 10 000 daltons.
[0042] Preferred polylactic acids are for example
NatureWorks.RTM.6201 D, 6202 D, 6251 D, 3051 D and more
particularly 3251 D (polylactic acid from NatureWorks). Polylactic
acids may also comprise the sole polymeric substituent of the
polymeric layer.
[0043] Polyhydroxyalkanoates of group (b) are primarily
poly-4-hydroxybutyrates and poly-3-hydroxybutyrates, copolyesters
of the aforementioned hydroxybutyrates with 3-hydroxyvalerates or
3-hydroxyhexanoate. Poly-3-hydroxybutyrate-co-4-hydroxybutyrates
are known from Metabolix in particular. They are marketed under the
trade name Mirel.RTM..
Poly-3-hydroxybutyrate-co-3-hydroxyhexanoates are known from
P&G or Kaneka. Poly-3-hydroxybutyrates are marketed for example
by PHB Industrial under the brand name Biocycle.RTM. and by Tianan
under the name Enmat.RTM..
[0044] The molecular weight M.sub.w of the polyhydroxyalkanoates is
generally in the range from 100 000 to 1 000 000 daltons and
preferably in the range from 300 000 to 600 000 daltons. The
polyhydroxyalkanoates may also comprise the sole polymeric
constituent of the polymeric film.
[0045] Polycaprolactone is marketed for example by Daicel under the
product name Placcel.RTM.. It can be used in the polymeric layer
alone or preferably in polymer blends. The polycaprolactone can be
used as component b) or comprise the sole polymeric constituent of
the polymeric layer.
[0046] Polyalkylene carbonate is to be understood as meaning more
particularly polyethylene carbonate and polypropylene carbonate.
Polyethylene carbonate is a polymer formed from ethylene oxide and
carbon dioxide. Polypropylene carbonate is a polymer formed from
propylene oxide and carbon dioxide. Polypropylene carbonate is
particularly preferred and can be used in the polymeric layer alone
or in combination with other biodegradable polymers.
[0047] It will be appreciated that other biodegradable polymers can
also be used for the polymeric layer--alone or in admixture with
other polymers. It will be found advantageous in this connection
for these polymers likewise to have a high flowability.
[0048] For example, polylactic acid having a melt volume rate (MVR)
to EN ISO 1133 (190.degree. C., 2.16 kg weight) of 5 to 70
cm.sup.3/10 min, more preferably of 9 to 50 cm.sup.3/10 min and
even more preferably of 5 to 25 cm.sup.3/10 min will be found to be
an advantageous blending partner in such polymer blends. Blends of
flowable polyesters with the aforementioned flowable polymer blends
are also suitable for the paper coating.
[0049] As mentioned, the biodegradable aliphatic-aromatic
polyesters and polymer blends are known from WO 2010034712. This
document and the references cited therein is hereby expressly
incorporated herein by reference not only for the composition of
these polyesters but also for their methods of making.
[0050] The "biodegradable" feature shall for the purposes of the
present invention be considered satisfied for any one material or
composition of matter when this material or composition of matter
has a DIN EN 13432 percentage degree of biodegradation equal to at
least 90%.
[0051] The general effect of biodegradability is that the polymers
and polymer blends (hereinafter also referred to as polymer
(blends) for short) decompose within an appropriate and verifiable
interval. Degradation may be effected enzymatically hydrolytically,
oxidatively and/or through action of electromagnetic radiation, for
example UV radiation, and may be predominantly due to the action of
microorganisms such as bacteria, yeasts, fungi and algae.
Biodegradability can be quantified, for example, by polymer
(blends) being mixed with compost and stored for a certain time.
According to DIN EN 13432, for example, CO.sub.2-free air is flowed
through ripened compost during composting and the treated compost
subjected to a defined temperature program. Biodegradability here
is defined via the ratio of the net CO.sub.2 released by the sample
(after deduction of the CO.sub.2 released by the compost without
sample) to the maximum amount of CO.sub.2 releasable by the sample
(reckoned from the carbon content of the sample) as a percentage
degree of biodegradation. Biodegradable polymer (blends) typically
show clear signs of degradation, such as fungal growth, cracking
and holing, after just a few days of composting.
[0052] Other methods of determining biodegradability are described
in ASTM D 5338 and ASTM D 6400-4 for example.
[0053] Corrugated fiberboard consists of one or two linerboard
plies, the corrugated plies and, in the case of multi-ply species
of corrugated fiberboard, of one or more interplies. Depending on
the number of linerboard plies/interplies and corrugated plies
present, single face corrugated fiberboard consists of one ply of
corrugated paper adhered to paper or cardboard. Single-flute double
faced corrugated fiberboard consists of one ply of corrugated paper
adhered between two plies of paper and cardboard. Two-flute
corrugated fiberboard consists of two plies of corrugated paper
which are adhered together by a ply of paper or cardboard and the
free outside surfaces of which are each likewise adhered to a ply
of paper or cardboard. Corrugated fiberboard with more flutes has a
similar construction. The strength/resistance properties are
subdivided into varieties and can be reviewed in DIN 55468.
[0054] Sea transportation in particular utilizes corrugated
fiberboards comprising a wet-strength adhesive and wet-strength
papers. Wet-strength papers are either waxed or impregnated and/or
body admixed with sizes or wet-strength resins. Papers endowed with
wet strength in this way cannot be recycled. Recycling is prevented
by the waxes or, respectively, sizes. Especially the kraft liners
used for the linerboard plies and interplies have a low recycled
content. On the other hand, it is especially for the production of
the kraft liners that high- and new-grade paper fibers are used,
and it would be economically very interesting to be able to recover
these paper fibers.
[0055] The corrugated fiberboard of the present invention
preferably includes, as corrugated' ply and interply or else as
linerboard ply, kraft liners having the construction paper-based
construction material/polymeric layer comprising biodegradable
polymers or preferably paper-based construction material/polymeric
layer comprising biodegradable polymers/paper-based construction
material.
[0056] The kraft liners used are preferably constructed as follows:
[0057] i) a 30 to 600 g/m.sup.2, preferably 40 to 400 and more
preferably 50 to 150 g/m.sup.2 grammage paper-based construction
material, [0058] ii) a biodegradable polymeric coating from 1 to
100 .mu.m, preferably 5 to 80 .mu.m and more preferably 10 to 60
.mu.m in thickness.
[0059] Particular preference is given to kraft liners having the
following construction: [0060] i) a 30 to 600 g/m.sup.2, preferably
40 to 400 and more preferably 50 to 150 g/m.sup.2 grammage
paper-based construction material as outer layer, [0061] ii) a
biodegradable polymeric coating from 1 to 100 .mu.m, preferably 5
to 80 .mu.m and more preferably 10 to 60 .mu.m in thickness as
interlayer, and [0062] iii) a 30 to 600 g/m.sup.2, preferably 40 to
400 and more preferably 50 to 150 g/m.sup.2 grammage paper-based
construction material as inner layer.
[0063] The two- or more-layered paper assembly (kraft liner) is
preferably produced using lamination and extrusion processes. An
explicit reference shall be made in this connection to WO
2010/034712 and the processes described therein, including
coextrusion processes.
[0064] It is additionally possible for the polymers or compounds to
be extruded as a film. The methods of tubular film extrusion and
chill-roll extrusion come into consideration here for film
production.
[0065] In the case of thin layers, the application of a hotmelt
also comes into consideration, as a special case of extrusion
coating or dispersion application. This process is described in
Ullmann, TSE Troller Coating. The hotmelt is pumped from a stock
reservoir vessel preheated to about 150-200.degree. C., into the
die from which the surface application takes place. In the case of
a wind-slot die, the paper web travels directly past the die lip at
a high rate of speed. The gap, the web guidance, the web speed and
the uniformity of the melt stream determine the quality of the
polymeric layer. Coatings of 1 to 5 g/m.sup.2 are
customary--depending on the smoothness of the substrate. Very thin
extrusion coatings can be applied in this way.
[0066] Dispersion coatings do not require any heating prior to
application. The application technology is comparable to that of
the hotmelt in the case of planar coatings. Web speeds are the
highest at up to 3000 m/min. This means that dispersion coatings
are also possible online on paper machines.
[0067] The coating with polymers such as polypropylene carbonate
can also be effected using solutions of the polymers in alcohols
for example.
[0068] Single- and multi-layered assemblies of paper-based and
polymeric layers in every layer (corrugated layer or surface layer)
are possible and sensible in order to minimize swelling of the
cardboard layers.
[0069] The thickness of the polymeric layer in the corrugated web
is not subject to any special restriction. The basis weight of the
polymeric layer is in the range from 1 to 100 g/m.sup.2 for
example.
[0070] The paper-based layers of the corrugated web can utilize a
wide variety of materials, for example white or brown kraft liner,
half-stuff, wastepaper, corrugatable stock or ream wrappers. The
thicknesses of these paper-based layers can vary within wide limits
and be, for example, up to 300 g/m.sup.2 or higher.
[0071] In general, the paper-film assembly has an overall thickness
of 31 to 1000 g/m.sup.2. A paper-film assembly of 80 to 500 .mu.m
is preferably obtainable by lamination and of 50 to 300 .mu.m more
preferably by extrusion coating.
[0072] The corrugated web thus obtained is then adhered in
conventional manner with one or two linerboard webs to obtain
single face or double faced corrugated fiberboard, although a
doubled or triple corrugated fiberboard with two or three
corrugated webs and one or, respectively, two intermediate
linerboard webs is also possible of course.
[0073] The polymer-reinforced corrugated fiberboard produced
according to the present invention has numerous advantages over
conventional corrugated fiberboard: [0074] The corrugated
fiberboard has extremely high stack compression values, breaking
strength and puncture resistance, especially after exposure to
moist atmospheric conditions, are very greatly enhanced. [0075]
Bursting strength, especially after exposure to moist atmospheric
conditions, is very greatly enhanced.
[0076] The corrugated ply can be produced in two stages. In this
case, a first step comprises coating a paper web as described with
a biodegradable and recyclable polymer by extrusion coating,
hotmelt application or dispersion coating.
[0077] In the second step, one or more coated paper plies are
fluted in a machine between 2 broad toothed wheels (fluting rolls)
with wave-shaped teeth at about 100 to 200.degree. C. and
preferably at 160-180.degree. C. at high speed to endow them with
the typical wave shape. Shaping and conveying of the corrugated
material are effected in one operation by the intermeshing toothed
wheels.
[0078] Three-layered corrugated plies (paper/polymer/paper) can be
produced from the already extruded or laminated kraft liners on
conventional equipment using fluted rolls as described in German
Laid-Open Specification DOS 2124092 for example. It is advantageous
to produce the multi-layered corrugated web by heat sealing in one
operation with the fluting on the corrugated fiberboard machine
(see DE 2842869).
[0079] When a polymeric layer is at the surface, the polymer may
stick to the fluting teeth. In this case, the polymeric layer is
protected by Teflon coating of the toothed wheels, or by an
accompanying film which is readily separable from the polymeric
layer, against direct influence of heat to prevent any sticking.
The film can be executed for example in about 10-50 .mu.m PP or
HDPE, since the homopolymers of these two polyolefins have only
very low adherence to biodegradable plastics (e.g., polylactic
acid, PLA, PBAT, PBSeT, PBSSe, PHA, PCL, PPC).
[0080] After fluting, the tips of the flutes are coated, via a
sizing unit, with hot starch solution at about 80.degree. C., with
which the corrugated surface is subsequently joined to the upper
linerboard layer. The same operation is subsequently carried out
for the lower linerboard layer.
[0081] Further adhering operations to further combinations of
linerboard layer and corrugated ply can follow to produce
high-strength cardboards having multiple corrugated plies.
[0082] Instead of using starch it is also possible to use mixtures
of starch and/or a filmable biodegradable dispersion such as a
polyester-polyurethane dispersion (e.g., Luphen.RTM. D DS 3585) for
the adhering. A further possibility consists in using a hotmelt
adhesive instead of the starch system. Such corrugated fiberboards
make it possible to improve the moisture resistance of the
corrugated bond.
[0083] The bond between the corrugated web and the linerboard layer
can also be produced using a corrugated ply whose outer layers are
polymer coated. In such a case, it is merely the thermally induced
adhering or welding of the polymeric surface of the corrugated web
to the papery or polymeric surface of the linerboard layer which is
possible.
[0084] The final cardboard web is subsequently cut into
production-appropriate dimensions using automated cutting devices,
folded, die-cut and processed into cardboard packaging.
[0085] The examples which follow elucidate the present invention
without limiting it.
EXAMPLE 1
Two-Ply Flute
A) Production of Coated Paper:
[0086] The semicommercial coating rig (ER-WE-PA) consisted of a
main extruder A (Reifenhauser, 80 mm diameter--30 D) and 3
extruders (B, C, D) of 60 mm diameter/25 D length. With Ecoflex F
BX 7011 (a polybutylene terephthalate adipate from BASF SE having
an MVR of about 2.5 cm.sup.3/10 min, all the MVR values used in
what follows were determined to EN ISO 1133 (190.degree. C., 2.16
kg weight) it was possible to achieve a throughput of about 90 kg/h
at 81 1/min. The throughput of the main extruder (Reifenhauser, 80
mm diameter--30 D) was 190 kg/h at a speed of 77 1/min. The
throughput of the extruders was varied to achieve very thin
layers.
[0087] The coextrusion rig included a tool for die coextrusion
which permitted a coextrusion of up to 7 layers at a die width of
1000 mm and an adjustable gap width of 0.5 mm. By means of inserts
in the melt channel, different layers could be used together. The
rig was equipped with a two-layer adapter insert (from Cloeren,
with edge encapsulation) of the form AAABBBB with the main extruder
as extruder A and a 60 extruder as extruder B. The outer layer A
was run with 40% of the overall thickness, the inner layer B on the
cardboard with 60% of the overall thickness.
[0088] The paper used was a corrugatable paper based on 100%
wastepaper.
[0089] The paper was activated by a flame ionization unit (gas
burner) or a corona discharge rig before coming into contact with
the molten polymer.
[0090] All the coatings were extruded onto the cardboard at a melt
temperature of 250.degree. C. and a normal contact pressure on the
chill roll of 4 bar. The web speed was varied between 30 m/min and
200 m/min. Higher speeds led to melt resonance on the
semicommercial rig depending on the product.
Polyesters Used:
Polyester 1
[0091] Ecoflex.RTM. F BX 7011 (a polybutylene adipate
coterephthalate from BASF SE) with an MVR of 2.5 cm.sup.3/10
min.
Polyester 2
[0092] A polybutylene terephthalate sebacate with an MVR of 6.4
cm.sup.3/10 min.
Polylactic Acid
[0093] NatureWorks.RTM. 3251 D from NatureWorks with an MVR
(190.degree. C., 2.16 kg to ISO1133) of 30 ml/10 min.
Extrusion Coating
[0094] A compound of 24% polyester 2 16% polyester 1 and 60%
polylactic acid was used in main and secondary extruders A and B.
Melt temperature was 258.degree. C.
[0095] At a maximum web speed of 170 m/min, an average layer
thickness of 16.5 .mu.m (-48% of the reference layer thickness) was
obtained. The coating could only be detached with fiber rupture in
the cardboard matrix. Flow instabilities such as increase and
decrease of the throughput or dynamic variation of the melt web
width (melt resonance) only occurred from 240 m/min. A particularly
low neck-in was observed.
B) Production of Corrugated Ply
[0096] The paper-film assembly described under A) was fluted on a
PTI Austria Huwell 2 corrugation rig using two intermeshing toothed
wheels of the type A flute. For fluting, the polymeric layer was
protected from direct effect of heat by Teflon coating to avoid any
sticking of the film assembly to the toothed wheel. Fluting was
done at 170.degree. C.
Performance Characteristics
[0097] The moisture resistance of the flute was determined via the
DIN EN ISO 7263 flat crush resistance (CMC) under a DIN EN 20187
standard atmosphere. The samples had the dimensions 160.times.12.7
mm and were measured with and without conditioning, i.e., 48 hours'
storage at 30.degree. C. and 90% relative humidity.
TABLE-US-00001 TABLE 1 Flat crush resistance Sample CMT (N)
Strength loss Uncoated paper measured 70.7 directly Uncoated paper
37.7 47% conditioned Example 1 93.0 measured directly Example 1
64.0 32% conditioned
[0098] The results in the table show that even the flute first
single face coated with biodegradable polymer has distinctly higher
wet strength than that without coating. In addition, the starting
point is distinctly higher, so that altogether a distinctly
stronger flute is obtained.
* * * * *