Note: Descriptions are shown in the official language in which they were submitted.
TRANSFER COATING FOR DECORATIVE LAMINATES
TECHNICAL FIELD
The present invention relates to polymeric film compositions
that are prepared on substrates having release properties. These
5 temporarily supported films find use in the manufacture of
decorative laminates wherein the laminate components are
consolidated under heat and pressure and the polymeric film
transfers to the surface of the laminate.
BACKGROUND ART
Heat and pressure consolidated decorative laminates have been
produced commercially for a number of years, and have found
widespread acceptance as mar-resistant surfaces for wallcoverings,
paneling, tabletops, countertops, and the like. These laminates
contain a number of laminae that are consolidated to form a unitary
15 structure carrying a surface decoration which can range from
something as simple as a solid color to something as complex as an
embossed simulated wood grain finish.
Although the methods of preparing such laminates and the
number and types of laminae can vary widely, the procedure for
~0 preparing such laminates generally involves the consolidation of one
or more sheets of core stock, depending primarily on the ultimate
thickness desired, in combination with a decorative or print sheet
and a top coat vr overlay. The core stock usually comprises an
unbleached kraft paper which has been impregnated with a relatively
')S inexpensive thermosetting resin, such as a phenolic resin, which
is easily cross-linked upon the application of pressure and heat.
In order to prevent sticking of the laminate to the press platens
specially treated caulstock or a release medium such as a paper
or foil with a release coating surface are used between the platens
30 and the laminate.
The decorative or print sheet has more stringent requirements
than the core stock. It is usually pigment filled, must be capable
of being impregnated with a noble thermosetting resin cross-linkable
~,
.
upon the application of heat and pressure, but exhibiting no color
deterioration upon the application of such heat and pressure, and it
must not allow any strike-through or bleeding of the resin used in
the core stock. In many instances, the decorative or print sheet
5 must also be capable of being printed with a design, such as
simulated wood grain, which survives the consolidation step intact.
Two of the most common noble thermosetting resins used to
impregnate the decorative or print sheet are urea-formaldehyde
resin condensates and melamine-formaldehyde resin condensates.
11) Other resins such as polyester resins have also been so employed.
In most instances an overlay sheet is superimposed over the
decorative or print sheet prior to consolidation of the laminae. The
overlay sheet is generally a thin, high-quality, alphacellulose paper
which is also impregnated with a noble thermosetting resin, usually
15 the same type in the decorative or print sheet. The overlay sheet
is usually transparentized during the consolidation step, thereby
enabling the decoration and/or printing which is present on the
decorative or print sheet to be readily seen in the finished
laminate, yet imparting a greater degree of mar and abrasion
20 resistance to the decorative laminate than would otherwise be
obtained without such an overlay.
An alternative to using an overlay sheet is to employ a
polymeric film between the decor sheet and the release medium.
U.S. Patent No. 3,616,0~1 discloses the use of a thermoplastic film
25 in this manner. Films used in this manner are likely to be
thermoplastic materials such as acrylics. Since the film is
self-supporting it is necessarily thick and because of its rigid
structure, the film is very brittle and handling of the film is
difficult. Contamination of the film is also a problem since dust is
30 picked up very easily by both sides of the film.
Another alternative to using an overlay sheet is to employ a
film of noble thermosetting resin on a substrate having release
properties. This approach provides compatibility between the
resins in the film and the resin in the decoratiYe
sheet, but not a reaction between the resins of the film
and the decorative sheet to produce a laminate with the
improved surface properties of the invention.
DISCLOSURE OF THE INVENTION
An aspect of this invention is as follows:
In a process for preparing a decorative laminate
comprising the steps ofo
tA) stacking together in an assembly
(a) one or more resin impregnated core
sheets,
(b) a decorative *ibrous sheet impregnated
with a noble thermosetting resin, and
(c) a releasing carrier surface coated with a
film composition in contact with the
decorative fibrous sheet;
~B) applying heat and pressure to consolidate the
assembly into a unitary structure; and
(C) separating the releasing carrier surface from
the unitary structure;
the improvement wherein said film composition comprises
polyvinyl butyral resin and melamine resin which reacts
with the noble thermosetting resin of the decorative
fibrous sheet during assembly consolidation.
The invention is also the decorative laminate
produced by the above described method.
Another aspect of this invention is as follows:
A releasing carrier having on its surface a
transferable film composition that is capable of
transferring to and reacting with noble thermosetting
resin impregnants of decorative fibrous sheets in a heat
and pressure laminating process wherein the film
composition is comprised of polyvinyl butyral resin and
melamine resin~
The present invention provides decorative laminates with
improved bond between the decorative fibrous shee-ts and the
superimposed film surfacing compositions because of the reactivity
between the two. It also can provide other desirable surface
5 properties, such as weather resistance or decorative effects,
without adversely affecting the bond properties.
The essential components of the film composition on the
releasing carrier surface are thermosetting polyvinyl butyral resin
and melamine resin. Polyvinyl butyral has the ability to thermoset
10 into a hard durable film and also reacts with melamine resin.
Polyvinyl butyral is a polyvinyl acetal prepared by reacting
butyraldehyde with polyvinyl alcohol.
Although polyvinyl acetal resins normally are thermoplastic and
soluble in a range of solvents, they may be cross-linked through
15 heating with a trace of mineral acid as a catalyst. Cross-linking is
thought to be caused by trans-acetalization, but may also involve
more c.omplex mechanisms such as a reaction between acetate or
hydroxyl groups on adjacent çhains. As a practical matter,
cross-linking of the polyvinyl acetals is carried out by reaction with
20 various thermosetting resins such as phenolics, epoxies, ureas,
diisocyanates and melamines. The availability of the functional
hydroxyl groups in vinyl acetals for condensations of this kind is
an important consideration of this application. Incorporation of
even a small amount of vinyl acetal resin into thermosetting
25 compositions markedly improves toughness, flexibility and adhesion
of the cured coating.
Vinyl acetal films by themselves are characterized by high
resistance to aliphatic hydrocarbons, mineral, animal and vegetable
oils (with the exception of castor and blown oils). They withstand
30 strong alkalis but are subject to some attack by strong acids.
However, when employed as components of cured coatings, their
stability to acids as well as solvents and other chemicals is
improved greatly.
æ~
The presence of hydroxyl groups in the acetal polymer
molecule not only enables good wetting of most substrates,
particularly important when applying the composition to a release
coated temporary carrier, but also furnishes reactive sites for
5 chemical combination with other thermosetting resins.
Thus, in the presence of an acidic catalyst such as p-toluene-
sulfonic acid, condensation reactions take place on heating among all
of the reactive functional groups of the polyvinyl acetal of the
transfer film, the melamine resin of the transfer film and the
10 melamine resin of the decorative sheet (groups such as hydroxy,
amine, methoxy and acetal) to produce a very strong, cross-linked
matrix. The reaction product is particularly stable when the
polyvinyl acetal resin of the present invention is employed, for this
resin has a long carbon chain backbone that would not be present
15 if only melamine-formaldehyde resins were used.
By including a melamine resin in the film composition, the
benefits are further enhanced since the kinetics of the reaction are
greatly improved due to the intimate mixing of the components. In
addition to participating in the foregoing reactions, melamine resin
20 improves the solvent resistance of the transfer film. It removes the
film from the thermoplastic state, and the entire film becomes one
that is basically thermoset. The mechanical properties of the film
are also greatly improved. It should be noted that when melamine
alone is used as a transfer film it is quite brittle and
25 unmanageable.
BEST MODE FOR CARRYING OUT THE INVENTION
In a preferred form for practicing the invention, the polyvinyl
acetal is dissolved in an appropriate solvent, such as mixture
of toluene and methanol. Following this, melamine resin combined
30 with the mixture. Cross-linking occurs as a natural reaction
but can be hastened by use of a catalyst. The film composition
is coated on a releasing carrier surface, such as a release paper,
and on drying a transfer film of polyvinyl acetal and partially
alkylated melamine resin is present as a clear transparent nonbrittle
film .
In this condition the film is ready for the laminating process.
As described earlier an assembly is prepared of phenolic resin
5 core sheets, and superimposed over this is a resin irrlpregnated
decorative sheet. Placed over the decorative sheet is the transfer
film on the release sheet with the film facing the decorative sheet.
Upon the application of heat and pressure in the laminating process
the film composition is able to react chemically with the resin of the
10 decorative sheet. In this way the transferred composition is
tjonded very tightly and irreversibly to the decorative sheet, and
the advantages of the invention are a direct consequence of this
strong bonding.
The reactive components of the transferable film composition
lS can be described by the :following general descriptions. .
Polvvinvl acetal resin- ` `
.
\ ~ ; -- _
2sl r- c ¦ CN2 ¦ ~ Curc
PV Acetal PV Alcohol PV Acetate
wherein R = C3H7
While this resin is composed of three groups, it is the
30 polyvinyl acetal and polyvinyl alcohol groups which are the most
reactive. The polyvinyl acetate group is present as an
unhydrolyzed residue from the parent polyvinyl acetate.
.
Tha melamine resin as used in the decorative sh~et and the
transfer film is represen-ted by the following general structure:
R R
\ N /
~ C~
N N
R I 1) R
1~ N _ C C_ N--
R~ ~ N~ --R
.
wherein R can be any combination of H, ~CH2OH or -CH2-O-CH3.
As stated earlier, in the presence of a catalyst, condensation
reactions take place on heating between all of the reactive
functional groups such as hydroxy, amine, methoxy and acetal of
both the polyvinyl acetal and the melamine resin.
In the practice of the invention the polyvinyl acetal of the film
20 composition will be polyvinyl butyral. The melamine resin in the
film composition will be a melamine-formaldehyde condensation
product. The film composition will be applied to the functional
surface of a reieasing carrier. There are a number of release papers
on the market suitable for the releasing carrier. It is well known
25 that they can be selected for the particular finish that they impart
to the decorative laminate and also for the degree of release
desired after the laminating operation. An example of a suitable
release paper is described in U.S. Patent No. 3,946,135.
The amounts of the various components used in the film
30 composition of this invention are not narrowly critical, and can
range, for example, from about 15 parts by weight (dry) to about
90 parts by weigh1: (dry) of polyvinyl butyral per 100 parts by
weight (dry) of coating, from about 10 parts by weight (dry) to
' ' ~,
--8--
about 85 parts by weight (dry) of melamine resin per 100 parts by
weight (dry) of coating and at least about 0.3 parts by weight
(dry) of acid catalyst per 100 parts by weight (dry) of coating.
The decorative sheet will be impregnated with a melamine resin
5 that is the same as or similar to the melamine resin used in the
transfer film composition. In the preparation of the decorative
sheet, the melamine has preferably not been fully cured prlor to
consolidating the laminate.
As is well-known in the art, additives may be combined wi-th
10 the film composition to impart their particular properties to the
finished laminate. These additives might be in the manner of those
to affect the physical appearance of the finished laminate or those
that might impart or improve the mechanical and chemical properties
of the finished laminate.
The following example is illustrative of the invention.
Example Parts by~.
Tol uene 80
Methanol 20
Mowital B 30H (polyvinyl butyral 25
manufactured by Hoechst Aktiengesellschaft)
Beetle resin 3735 (a 72% solution in 14
isopropanol of methylated melamine resin
manufactured by BIP Chemicals LTD)
para-toluene sulfonic acid (a catalyst) 0.6
Nacure 155 (dinonylnaphthalene 0.5
disulfonic acid, manufactured by
Kin~ Industries, as a 55% solution
in isobutanol, a catalyst)
I rganox 1010 (an antioxidant 0.35
manufactured by Ciba-Geigy)
The polyvinyl butyral was dissolved in the toluene-methanol
mixture under vigorous agitation. Following this, the melamine
ga
resin, the catalysts and the antioxidant were added. The solution
was well-stirred and further diluted with a mixture of toluene and
methanol in a ratio of 80 to 20, respectively, to attain the viscosity
necessary for a homogeneous coating.
The coating was applied by fountain-doctor roll coater onto the
surface of a silicone coated release paper. The coating was dried
in a ventilated oven at 120C - 140C for about 0.5 minutes and
upon drying was present as a clear transparent nonbrittle film on
the release paper.
A laminate assembly was then set up which was arranged with
3 core sheets impregnated with phenolic thermosetting resin on the
bottom. Superimposed over the core sheets was a decorative
fibrous sheet of alpha-cellulose paper impregnated with a
thermosetting melamine-formaldehyde resin. The film composition on
the release paper was placed over the decorative sheet with the film
composition in face-to-face relationship with the decorative sheet.
The entire assembly was placed in a laminating press where it was
consolidated into a unitary structure at a ternperature of 140C and
a pressure of about 100 Kg/cm2. Upon removal from the press, the
laminate was cooled and the release paper was stripped from the
lami nate .
There are a number of tests that can be performed on
decorative laminates to determine how they will withstand certain
conditions. Many of these are fully described and published by the
National Electrical Manufacturers Association in their Standards
Publication LD-3, 1985. Following is a brief description for some of
these tests:
Boiling Water: A section of laminate is subjected to boiling water
for a set period of time. The surface is later examined for
whitening or a change in surface texture. Results of the
examination are categorized as follows:
-10-
No effect: No changes on the surface of the laminate. There
is no whitening and no change in surface texture.
Slight effect: There is a change in color or surface texture
that is only visible when viewing the surface at certain
angles or from certain directors.
Moderate effect: There is a change in color or surface
texture visible at all angles and directions but it does not
appreciably alter the original condition of the sample.
Severe effect: There is a change in color or surface texture
which is obvious and markedly alters the original
condition of the sample, e.g., cracks, crazing, blisters,
discoloration, whitening or delamination.
In most cases, samples exhibiting no effect or slight effect are
acceptable .
High Temperature Resistance: A section of laminate is subjected to
heated wax (180C) for a set period of time. The surface is
later exalTined for whitening or a change in surface texture.
The specifications are the same as those categorized for the
Boiling Water test.
Scratch Resistance: This is a measurement taken on Teledyne
Taber Model 502 Shear/Scratch Tester. The force necessary
for a needle to scratch the laminate surface is recorded in
Newtons. A high value number indicates good scratch
resistance, and a low value indicates poor resistance.
Resistance to Steam: This is a hot condensation test in which the
laminate is used as a cover on a vessel containing constantly
boiling water for a period of two hours. The surface is later
examined for whitening or a change in surface texture. The
specifications are the same as those categorized for the Boiling
Water test.
Resistance to Chemicals: A sample of laminate is placed in a
special holder which provides for a certain amount of the
chemical under investigation to be in contact with the laminate
~.2~,
.
for 16 hours. The exposed laminate surface is then compared
to a reference unexposed laminate surface. The specifications
are the same as those categorized for the Boiling Water test.
5 The laminate prepared in the Example was tested along with the
only known commercial laminate which is of the type wherein an
acrylic film sandwiched between a release medium and the decorative
sheet is consolidated with the decorative sheet in the consolidation
p roces s .
The results summarized in the following table demonstrate the
superior laminate of the invention.
Known Commer-
Test Example cial Laminate
Boiling Water no effect severe effect
High Temperatureno effectsevere effect
Scratch Resistance 1 . 5 N 0. 5 N
Resistance to Steam no effect severe effect
Chemical Resistance
Acetone no effect severe effect
Ethanol " " " "
l-Propanol " " " "
Ethylacetate " " " "
Toluene " " " ~
Dichloromethane 11 .. .. ..
10O HCl moderate effect no effect
10% H2S4 no effect
10go NaOH " " " "
10% HNO3
10% CH3COOH " " " "
