Note: Descriptions are shown in the official language in which they were submitted.
~ss~ln
Polypropyiene ~rticle with Improved Adhesion
This invention relates to polypropylene (PP) and particularly foils
of polypropylene with improved adhesion characteristlcs, and to a process
for its production.
For many areas in whlch they are employed, the wear characteristics
of materials have to be enhanced, e.g., by lacquering or by being coated
wlth or laminated to thin Einishing foils sheets or veneers. At the
present time, predominantly PVC and special papers are used for such
improvements especially for metal, wood, and cellulose materials.
When foils are used for surface improvement one proceeds from the
assumption that coating on carrier materials or on other films is to be
carried out at temperatures which are Erequently in excess of 100C and
that it is uneconomic to cool the laminate Ln the roller-coating
installation or press. A high level of thermal forming stability is also
necessary for coating which makes use of chemically active type adhesives
and which, because of the required level of storage stability, are best
selected so that the reaction proceeds at a temperature above 80C. This
is also necessary for coating with polymer films when no delamination
should take place at the temperature involved.
The physical characteristics, especially of thermal forming stability
and the good environmental characteristics, of polypropylene and its
co-polymerisates are particularly well suited to surface improvement.
However, a decisive disadvantage of polypropylene, results from its
surface engergy characteristics which prevent sufficiently good and
permanent adhesion of suitable lacquers, adhesives, and polymer films.
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i~n object o~ the present invention is to improve the adhesion
characteristics of polypropylene foils by modifying the surface energy
properties so as to ensure that suitable and permanent printing,
lacquering, and adhesion will be made possible.
Processes used to improve the adhesion characteristics of films,
especially polypropylene films, are already known. ~n example is corona
treatment (see Adhaesion, 1979, Volume 12, pp.381 - 389). Although this
treatment increases tlle surface tension temporarily, the effect diminishes
during storage and/or under the effects of high temperatures. An
alternative process involves flame treatment of such foils. The same
disadvantages arise as with the corona treatment. Chemical treatment
with ozone, fluorine, chlorine, etc., is also known. However a particular
disadvantage witll these and which may cause problems is their chemical
aggressiveness. ~ further known process is the irradiation with high
energy beams such as electron beams, ultra-violet rays, lasers, and the
like. Such processes are relatively costly and in most instances require
the additional use of seniti~ers and the durability of the effect varies.
~ permanent improvement in surface adhesion can be achieved by
chemical grafting using high energy beams. However, this process is too
costly to be suitable for the areas of application considered here.
In accordance with the present disclosure, a permanent increase in
surface tension and adhesion is achieved by providing a content of finely
divided cellulose in the polypropylene foil, which is then subjected to
known surface treatment methods for increasing surface tension, but which
to date have resulted in no permanent eEfects. The inventive idea is
based on the surprising fact that a content of finely divided cellulose in
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the polypropylene improves the effectiveness and the durability of the
surEace treatment. This effect c~ln be further increased if the cellulose
is added to a polyethylene batch. F~lrther favourable effects result from
the accompanying use of mineral Eillers.
Finely divided cellulose produced by the sulfite or sulfate processes
is suitable and preferred. Natural or recycled cellulose is also
suitable.
The amount of cellulose may be between 30 and 50 percent by weight of
~ the total weight of polypropylene and cellulose. If a content of 50
; 10 percent by weight is exceeded, the strength characteristics deteriorate
unduly.
l~hen the cellulose content is below 3 ~ by weight the desired
improvement of surface activation is insufficiently pronounced. It is
preferred that the material contain 3 to 30%-wt of cellulose.
The degree of fineness of the cellulose used in the foil lies between
1 to lQ0 um for a fibre thickness of 10 to 30 ym. If the particles are
more finely divided the expense rises unduly; larger particles lead to
problems in the production of smooth and thin foils. However, for natural
or regenerated cellulose particles of up to 100 ,um thick and with a
greatest mean length of 200 ~um can be used without difficulties in the
formation of the foil.
Commercial grades of polypropylene are suitable, including copolymers
with ~-olefins and graft copolymers with vinyl bonds. Random and block
copolymers with 1 to 10 mol-~ ethylene or mixtures with polyethylene (PE),
particularly with 5 to 20~ PE, that have a thermal resistance VSP/A above
100C are preferred.
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In addition, the new foils can also contain mineral fillers. Flllers
of this kind ~or polymer foils are already known. Mlca, talc, silicates
and silicic acld in their clifferent forms are especially suitable and for
~his reason are preferred. E~arnples of other usable mineral fillers are
carbonates, particularly calcium carbonate such as limestone and chalk,
and magnesium carbonate and the like.
Characteristics such as Shore hardness, vicat point, adhesion and
tensile strength can be influenced by the addition of suitable mineral
fillers. In the event that suitable mineral fillers of this kind are
present, it is desirable that the foil contain 3 to 30%-wt and preferrably
3 to 20~-wt, related to the sum of the weight of polyolefine and
cellulose.
The foils can also contain one or several organic modifying agents.
These serve to control the toughness, calendaring properties,
e~trudability and similiar characteristics. A group of materials
preferred for this purpose are blockpolymers of styrol with butadiene or
isobutylene or isoprene. Other suitable modifying agents are polymers
that are based on styrol-butadiene, methacrylate-butadiene-styrol.
Polyolefins, containing functional groups, are particularly suitable for
affecting the physical characteristics and adhesability. Modifying
additives of this kind are desirably present in the amount of 0.5 to
20~-wt, preferrably 2 to 10%-wt, with respect in each case to the sum of
the weights of the polyolefin and cellulose.
The use of wood dust in place of cellulose is not generally
recommended, because of its inherent color, insufficient cleanliness,
deficient resistance to light and that it changes color when affected by
temperature. Also the adhesive effect achieved is not as good.
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. . .
The relationship to cellulose content, of the increase in surface
tension from coroncl treatment and :its permanence, are shown in the test
results reproduced in Table I. In the ~nufacture of the foils tested,
the cellulose was Qdded by meclns of a tlD-PE~Masterbatch 1:1 (ilD-PE
Hostalen* GC7260).
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Table I
Proportion by I . Surface tension (dynes/cm)
weight cellulose I untreated I Corona treated after
in PP(l) I ll hr. 3 days 3 weeks . 3 mon~hs
0 1 25 1 46 38 28
5 1 25 1 52 50 50 45
20 1 25 1 58 52 52 52
l) PP Hostalen* PPN 1060
Since a higher surface tension does not always result simultaneously
in a higher level of adhesion for polypropylene (see Adhaesion 1979,
Volume 12, pages 381-389) the adhesion characteristics were tested by
means of a commercial urea-formaldehyde adhesive. The foil samples were
produced under identical conditions, corona treated and then pressed at
140C at lO kp/cm2 for 10 seconds. The durability of the adhesion was
assessed by storing for one day at 90C. The results are shown in Table
2.
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Table 2
Formulation l~urface tension I Scaling resistance
dynes/cm _I kp/2,4 c L
l hr. 20C 11 day 90C I 1 hr 20C 11 day 90C
PP+0 pts cellulose 1) 1 48 1 42 1 0.1 1 0
PP+20 pts cellulose 1~1 58 ¦ 52 1 1.2 ¦ 1.1
PP+20 pts cellulose 2)1 58 1 56 j 2.6 ¦ 1.9
(PE/cellulose batch)
1) PP Eltex* ~1 100
2) Batch: 50 pts/wt HD~PE Eltex* 2008
50 pts/wt Cellulose Arbocel* B 600/30
These results show that with a cellulose content the effect is not
only considerably longer lasting, but is also greatly increased,
particularly if the cellulose is added as a polyethylene batch.
further object of this disclosure is to provide a process for
manufacturing a polypropylene foil with improved adhesion
characteristics, making the foil by conventional methods and then giving a
surface activation treatment, and characterized in that fine-grained
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cellulose is added as a ~iller. It is preferred that 3 to 50%-wt,
particularly 3 to 30%-wt of cellulose be added, with respect to the sum of
the weights of polyolefin and the cellulose. Cellulose fibers are
suitable up to a length of 200 ~Im for a mean diameter of up to lOO,um.
The above statements apply for the preferred polypropylenes. Conventional
production methods and mlxing technologies known to those skilled in the
art are suitable for the production of the foils.
~ lineral fillers and/or modifying agents can be added in the
production of the foils. The foregoing data covering the composition of
the foils will apply accordingly.
The surface activation may be achieved by irradiation, or by flame
treatment or reaction with ozone. Preferred is corona treatment, or other
irradiation methods using electron beams, ultra-violet, or laser light.
The surface adhesion of polypropylene foils is considerably improved
by means of the new method and the new foils are particularly suitable for
coating, printing, enameling or lacquering, and adhesion, particularly in
thos~ present systems which use very short process times and the highest
possible temperatures, and in some instances such use is now possible for
the first time. When the new foils were cemented, for example, using
urea-formaldehyde resin there was no change in adhesion even after several
months. The resistance of surface activation to the effects of
temperature was also greatly improved. As an example, the adhesion of the
new foils which had been laminated by means of
urea-formaldehyde resin onto chipboard panels displayed no differences
over the range of coating temperatures from 80 to 140C. with a 30 second
press time.
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1 ~ S80 1~
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~rinting ink~, for exalnl)le those based on terpolymers of vlnyl
chloride - vinyl acetate - ~aleic aclds oE 0~l-group containing vinyl
polymers, and also conventional polyethlene printing inks show equally
good adhesion as ~eaction lacquers, for example, those based on
polyurethane~melamine resins and ultra-violet hardened polyester epoxide
and polyurethane acrylates. Even after l,000 hrs of xenotest weathering
and cropical testing it was not posslble to determine any change in
adilesion according to ~ST~I standard ~2142-63T (lattice~cut method).
The characteristics of the foils could be widely varied by the
addition of mineral fillers and organic modifying agents and the
advantageous adhesion characteristics could be partially improved by the
same method. As an example, the surface adhesion achieved by means of
corona treatment of a foil consisting of 95 parts of polypropylene and 5
parts of cellulose could be favourably improved by the addition of 20 or
30 parts of talc.
Conventional dyes and pigments are not disadvantageous.
The new foils can also be bonded directly to metals, wood, polymers
and copolymers with polymer groups and the like, by fusion without the ~Ise
of adhesives.
Coating is also possible at low temperatures, e.g., using epoxy
resins and polyurethanes as well as vinyl acetate-copolymers.
The following examples illustrate embodiments of the invention.
Example 1.
Polyethylene ~fI 190/2 = ~ (g/lO min) density 0.958 (Hostalen* GC
7260) and cellulose having a particle size less than 50 ~m (Arbocel* B
600/30) were mixed in a weight ratio of l : l, homogenized for 10 minutes
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at 160C in ~ rolling mi LI, cooled ancl then granulated. Ten parts by
weight of the bat~h obtained in this manner were mixed with 90 parts by
weight of PPI ~Ifl l90/5 ~ 3 (g/10 rnin) clensity 0.905 (g/cm3) Hostalen* PPN
1060 and extrude(l in tlle form o~ an 80 ~Im thick film at a mass temperature
of 220C.
The e~truded foil was subjected to corona treatment. The corona
treatment was carried out at full power on a Demes-VM pre-treatment device
and at a strip speed of 5 m/min. The treated foil displayed the following
characteristics:
Surface tension after 1 hour 52 dynes/cm
3 weeks 50 dynes/cm
3 months 48 dynes/cm
~ntreated 25 to 28 dynes/cm
Thermal forming resistance VSP/A 148C.
Hardness Shore D 69
Tensile Strength (longitudinal) 30 N/mm2
The treated foil was applied to a commercial chipboard panel. A
urea-formaldehyde resin of the following composition was used for
adhesion: 100 parts by weight Aerolite* 306
50 parts by weight W 170* hardener
70 parts by weight water
Pressing condition: Temperature 140C
Pressure 10 kp/cm2
Time 10 sec
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Tearing forces in the peeling test amounted to 1.6 kp/2.4 cm.
Example 2 (Comparison)
The polypropylene used in Example I was mixed in a proportion of S5:5
with HD-PE (Hostalen* GC 7260) without any other additives and then under
the previously given conditions was extruded, pre-treated and pressed.
Surface tension after 1 hour 48 dynes/cm
3 weeks 28 dynes/cm
3 months 25 dynes/cm
Untreated 25 dynes/cm
! 10 Thermal forming resistance VSP/A 145C
Hardness Shore D 68
Tensile Strength, longitudinal 28 N/mm2
Tear Strength in the peeling test 0.1 kg/2.4 cm
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E~;amp le
.~ mixture consisting of 80 parts by wei~ht of a polypropylene
copolymer ~IfI 230/2 = 1.8 g/lO min, dellsity 0.92 g/cm3 (Eltex* Kl lO0) and
20 parts by weight oE ce11ulose Arbocel* (~ 600/S0) and the usual
additives was calendared at 200C to a lOO~m thick foil. The
pre-treatment and adhesion were carried out according to Rxample I.
Tlle following values were measured:
Surface tension after 1 hour 58 dynes/cm
3 weeks 52 dynes/cm
3 months 52 dynes/cm
Untreated 25 dynes/cm
Thermal forming resistance VSP/A 150C
Hardness Shore D 72
Tensile Strength, longitudinal 32 M/mm2
Tear force in the peeling test 1.3 kp/2.4 cm
Example 4
A mixture consisting of 80 parts by weigh~ of polypropylene according
to Example 3 and 40 parts by weight of a batch consisting of 20 parts of
cellulose (Arbocel* BO 600/50) 20 parts HD-PE MfI 190/5 =1 (g/lO min)
density 0.950 g/cm3 (Eltex* B 2008) was calendared as in Example 3,
pre-treated and pressed.
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I:ls~oln
The following values resulted:
Surface tension aEter 1 hour 58 dynes/cm
3 weeks 58 dynes/cm
3 months 56 dynes/cm
IJntreated 25 dynes/cm
Thermal forming resistance VSP/A 148C
Hardness Shore D 67
Tensile Strength, longitudial 26 N/mm2
Tear force in the peeling test 2.6 kp/2.4 cm
O Example 5
A mixture consisting of 80 parts by weight of polypropylene according
to E~ample 3 and 20 parts by weight of cellulose (Arbocel* BO 600/50) and
20 parts by weights oE calcium carbonate (Omya* BSH) were calendared as in
Example 3 and pre-treated.
The following results were obtained:
Surface tension after l hour 58 dynes/cm
3 week 56 dynes/cm
3 months 56 dynes/cm
Untreated 25 dynes/cm
Thermal forming resistance VSP/A 155C
Hardness Shore D 72
Tensile strength, longitudinal 35 N/mm2
Tear force in the peeling test 2.6 kp/2.4 cm
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l~ssoln
Example 6
95 parts by weigllt of a mLxture according to Example 3 were aclded to
j parts by weight of SBS block copoLymer (C~lriflex* 1102) and processed
according to Example 3. On calendaring it was shown that a good foil
could still be produced at a speed that was 20% higher.
i The measured mechanical and adhesive characteristics were not
disadvantageously affected.
The foil obtained was coated with a conventional polyurethane lacquer
(Basis Desmophen* 1340 and Desmodur* Hl).
There was no separation of the lacquer layer in an adhesion tèst
according to AST~ D.2.1.4.1.-63.
! Example 7
.~ mixture consisting oE 80 parts by weight of a polypropylene
copolymer according to Example 3 (K1 100) 20% by weight of cellulose
(Arbocel B 600/50), and 20 parts by weight of talc and the usual additives
was calendared at 200~C to a 100 ~Im thick foil, activated according to
Example I and pressed by means of a 50 ~m thick foil of KR 2683 adhesive
agent at 130C, for 10 sec, and 10 kp/cm2. When the foil bond was removed
from the chipboard panel, chip tear out resulted.
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Example 8
.~ Eoil accord.in~ to Example 7 was pressed by means of an epoxy
adhesive (Daubert* Internationa~ 1 TDC 8160 BHV+l ~ DC 8160 AHV) at room
temperature and 5 kp/cL~I2 Eor 24 hours. The Eoil tore duriLIg the removal
test.
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