Note: Descriptions are shown in the official language in which they were submitted.
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DIFFERENTIAL GLOSS RELEASE SHEET
BACRGROUND OF THE INVENTION
?ield of the In~ention
The present invention relates to coatings for paper and
ther types of ba5e sheets. More specifically, it relates to
05 oatings which are generally classified in the art as release
oatings and which are chara~terized by their ability to separate
ntact from a surface which is normally adherent.
istorv of the Prior Art
~ _ _ _ _ -
A nu~ber of processes exist in which a platic film or sheet
s formed on or against a release sheet and then separated from
he release sheet after taking steps, such as cooling or cur~ng,
o set the film or sheet. Curing, where necessary, may be
~ ~complished by heat or U.V~ radiation or by electron beam
; adiation. The release sheet provides a surface from which the
lastic material will readily release and imparts to the surface
f the plastic material the quality of finish of the release
urface. A textured surface can be provided on the surface of
he plastic material by using a release sheet having a textured
urface.
; One example of such forming processes is "casting", wherein
resino~s material, such as vinyl or urethane resins, in a
lowable fo~m and usually a plastisol, is deposited or "cast" on
he release sheet surface, heated, cured or cooled to consolidate
he plastic material into a continuous self-supporting film, and
tripped from the support.
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Another example of such orming processes is "panel pressingl'
f decorative plastic laminatesO In high pressure panel pressing,
ecorative laminates are conventionally prepared from an assembly
f a plurality of core sheets which are prepared by impregnating
05 web of paper with a resin material, such as phenolic resin.
he core sheets axe superimposed in a stacked relationship and
onsolidated with themselves and a decorative sheet under heat
nd pressure. The decorative sheet is positioned immediately
bove the core sheet assembly and is a resin saturated sheet
aving a solid color or a suitable design thereonl Superimposed
bove the decorative sheet is generally an overlay sheet which is
thin sheet of fine paper impregnated with a noble thermosetting
esi~, such as a melamine ~ormaldehyde resin or an unsaturated
olyester resin and the like (and is generally the same resin
sed to impregnate the decorative sheet). Hig ~ re laminates
fter being consolidated are usually further to a
tructural substrate, such as particlP board or plywood.
Low pressure panel pressed decorative laminates are made in
similar manner to high pressure laminates, but generally
nvolve lamination of the decorative sheet directly to particle
oard or other structural substrate. Other pressing processes
~here a plastic film or sheet is formed on or against a release
~ heet may not include lamination, but only texturing a moldable
! lastic ~urface which is already laminated. For example, a
- ~ ~5 lastic film could be coated directly onto particle board or
lywood and then textured by pressing against a release sheet.
When it is desixed to produce a textured surface on the
verlay sheet or the decorative sheet of a decorative plastic
aminate, various techniques can be used, such as using a textured
¦~r embossed 1 plate or resin stabiliæed board in the pressing
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peration. The desired embossed or textured pattern can also be
roduced on the release sheet for transfer to the pressed plastic
urface,which is a technique related to the present invention.
Release sheets can be any one of a number of commercially
05 ~vailable materials, such as a non-adherable paper, a non-adherable
luminum foil or a polished metal belt. To render them non-
dherable, the sheets can be coated, treated, or impregnated with
release coating of such materials as polymethylpentene, poly-
ropylene, polyfluoro%arbons~ silicone oil, thermoset silicone
esins, and others conventional release agents. Texturing can be
rovided by any one of a number of conventional techniques, such
s emboss~ng by mechanical means.
The use of textured or embossed release sheets for producing
~ textured pattern on a plastic sheet or film is quite useful for
`~ 15 oarse patterns, but not totally satisfactory for the production
f ~ine patterns. For one reason, the non-uniformity of the
aper surface can mask the embossing pattern. Also, in high
ressure pressing processes ther is a tendency for the embossed
attern to flatten out under pressure and thus create a smooth
urface. Furthermore, fine texture patterns formed by relief in
he surfàce are generally not highly visible on the formed
lastic surface, whether it be cast or pressed. The reason is
hat such texture is primarily visible as a result of shading or
;- hadows formed when 'ight falls upon the irregular surfaces, and
ery fine texture does not display shadowing or shading very
~ ~ ~rongly. As a result of this deficiency, it is sometimes
- ~ esirable to print shading or shadow patterns onto the cas-t or
ressed surface to highlight the textured surface by producing a
ifferential gloss effect. This can be accomplished by such
echniques as printing a dull coating material or ink onto the
igh points of the textured release sheet for transfer of the
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coating material into the depressed portions of the formed
plastic surface. Or in the alternative, a glossy coating
material or ink can be printed directly onto the raised
portions of the formed plastic surface. Another technique
sometimes employed is to polish the raised surace of the
; formed plastic surface to thereby impart a differential
gloss effect to the finished product.
The above-described prior art techniques for pro-
ducing a textured pattern on a formed piastic surface have
<~ 10 a number of disadvantages. For example, fine patterns can
, .
be difficult to transfer from an embossed release sheet
and, even when they do transfer, are not highly visible
~` on the formed plastic surface. When glossy or dull
, materials are printed either directly or indirectly on the ~ -
high or low parts of the formed plastic surface to produce
a differential gloss effect which highlights the texture
other disadvantages occur, such as the tendency for the
materials to rub off the plastic surface, the need for an
additional finishing step, and in the case of the material
being transferred from the release sheet, the inability
to reuse the release sheet.
SUMMARY OF THE INVENTION
It is an object of an aspect of the present inven-
tion to provide a formed plastic film or sheet having dif-
ferential gloss effect, the method of forming it against arelease sheet, the release sheet, and the method of making
the release sheet, all in a manner which avoids the above~
described disadvantages of the prior art.
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In accordance with one asFect of this invention there is
provided a release sheet for use in casting or panel pressing
comprising a base sheet suitable for use in casting or panel
pressing, a first gloss-producing layer provided by one of
said base sheet and a di.stinct continuous layer over said
base sheet; a second gloss-producing layer providing a
different gloss level from said first gloss-producing layer
and forming a distinct layer of a discontinuous pattern over
`~ said first gloss-producing layer; and a release surface
~` 10 provided one of said first gloss-producing layer, said first
and second gloss-producing layers, a distinct layer over
said first gloss-producing layer and a distinct layer over
said first and second gloss-producing layers, said release
surface at least including a material selected from the
group consisting of casting and panel pressing release
material; all of said distinct layers being permanently
secured to said base sheet so that they do not transfer
- from said release sheet when used for casting or panel press-
ing; said release sheet having a differential gloss pattern
which is reproducible on a plastic sheet or film cast on or
panel pressed against the release sheet, without transfer
of the materials forming the first and second gloss~
producing layers.
: In accordance with another aspect of this inven-
- 25 tion there is provided a method of producing a release
sheet of the type hereinbefore described in which the
. first gloss-producing layer is provided by a coating
. comprising a relatively high gloss film-forming resin,
and the second gloss producing layer is provided by a
relatively low gloss pigmented coating, which comprises:
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(a) providing a base sheet suitable for use in casting
or panel pressing with a first gloss-producing layer
uniformly overall on the surface; (b) embossing said base
sheet to provide an embossed pattern having raised portions;
(c) permanently applying over said first gloss-producing
layer in a discontinuous pattern said second gloss-
producing layer which provides a gloss level different
from said first gloss-producing layer, said second gloss-
producing layer being applied by tip printing said raised
portions of said embossed pattern; and (d) coating said
release sheet overall with a distinct layer of material
having release properties after step (a).
In accordance with another aspect of this inven-
"':`
tion there is provided a method of producing a release
sheet of the type hereinbefore described in which the
first gloss-producing layer is provided by a coating
comprising a relatively high gloss film-forming resin,
and the second gloss producing layer is provided by a
relatively low gloss pigmented coating, which comprises:
(a) providing a base sheet suitable for use in casting
or panel pressing with a first gloss-produclng layer
uniformly overall on the surface; (b~ embossing said base
sheet to provide an embossed pattern having raised portions;
and (c) permanently applying over said first gloss-
~, 25 producing layer in a discontinuous pattern said second
gloss-producing layer which provides a gloss level dif-
ferent from said first gloss-producing layer, said second
gloss-producing layer being applied by tip printing said
raised portions of said embossed pattern; at least one of said
~irst gloss-producing layer and said first and second
gloss-producing layers having release properties.
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In accordance with another aspect of this inven-
tion there is provided a method of producing a decorative
sheet product which comprises casting or panel pressing a
`. plastic sheet or film on or against the release sheet
referred to hereinabove, setting the plastic sheet or
film and then removing it from the release sheet.
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In addition to overcoming the above-stated disadvantages of
he prior art, the invention also offers the capability of producin
flat ~not having relief) finished product having the appearance
f relief, including the appearance of relief formed by difficult
05 atterns to transfer, such as fine leather or wood grain patterns,
sing a flat, unembossed, release sheet. Use of a flat release
heet provides more ~niform release than embossed release sheets.
lso, the flat surface of the finished product can be cleaned
asier than one which is actually embossed. Additionally, the
ifferential gloss surface produced on the finished product can
ave a more realistic textured appearance than one actually
extured.
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DETAILED DESCRIPTION OF THE PREFERRED EMBC)DIMENTS
In practicing the invention the various layers can be applied
y several different techniques. The starting material is a base
heet which can be provided by paper or other fibrous substrates
r such substrates as polished metal belts as metal foils. The
rinc;pal requirement for the substrate is that it have a smooth
_ urface to resist the penetration of the coating which provides
he release surface. Where the base sheet is provided by paper,
his rPquirement is typical~y met by pro~iding the paper with a
onventional base coating of a mineral pigment, such as clay,
xed with an adhesive. The base coating may in some cases be
he first gloss-producing layer, and in other cases, may be
~vercoated with the first gloss-producing layex. In some cases
7 he first gloss-producing layer can be provided by the actual
ase sheet, particularly where it is made from such materia~ as
etal foii or metal belts. If the release she~t is to be embossed,
t must be capable of being embossed without cracking.
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ThP second gloss-producing layer is applied over the first
loss-producing layer in a discontinuous (rather than overall)
attern to provide the differential gloss effect. The pattern in
which the second gloss-producing layer i5 applied can be almost
05 ny of a wide variety, such as wood grain, leather grain, marble-
zed, slate, geometric, clouds, artistic designs, or photographic
eproductions. It may be applied by tip printing, flexography,
. ravure printing, etc. rThe second gloss-producing layer can be
rovided by a coating of a wide variety of materials, but they
~ st produce a different gloss level from the first gloss-producing
ayer and must be compatible with and ~ anently adhere to the
irst gloss-producing layer~ In some cases, the coating material
f the second gloss producing layer can be provided by the same
aterial as the first gloss-producing layer, bu~ will have a
; 15 ifferent gloss level due to better "hold-up" (lack of penetration
~,~ nto the substrate) than the first gloss-producing layer.
The release surface is preferably provided by a distinct
ayer of a release agent coated over tha first and second gloss-
roducing layers. The differential gloss effect surprisingly
emains and is still transferable even with the release layer
$ laced on top. In some cases, the release surface may be provided
y the first and second gloss-producing layers themselves where
the coating materials chosen for such layers have adequate
~; elease properties. In other cases the release surface may be
rovided by a distinct layer coated over only the first gloss-
roducing layer and over which tha second gloss-producing layer
s applied. In this lakter case, the coating material of the
, econd gloss-producing layer must permanently adhere to the
;; elease surface and must ha~e adequate release properties itself,
r at least not substantially interfere (because of only a small
rea of surface being covered) with the release properties of the
elease surface.
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On~ of the advantages of the invention is the ability to
roduce a flat release sheet which will impart the appearance of
~n embossed pattern upon a plastic film formed on or against the
elease sheet~ This advantage is particularly valuable where the
05 ifferential gloss pattern is a very fine one, such as found in
~ood grain or leather grain. However, in other instances, par-
icularly where the differential gloss pattern is coarssr, the
nvention can be employed advantageously with an embossed release
heet. In such cases, it is particularly desirable to emboss the
elease sheet after applying the first gloss-producing layer and
o apply the second gloss-producing layer only on the raised
ortions ~f the embossed pattern. This method offers the advan-
ages of tip printing the raised portions of the embossed patterns,
which can be conveniently carried out by applying the coating
aterial of the second gloss-producing layer with a gravure roll
r some other offset printing apparatus positioned to lightly
ontact the raised portions of the embossed sheet. In such cases
he gravure roll would preferably have an overall pattern which
rovides the coating material to substantially the entire surface
f the gravure roll. One of the advantages of this technique is
hat the'second gloss-producing layer can be provided by a low-
loss pigmented coating which causes the recessed areas on the
lastic film or sheet formed on or against the release sheet to
;-ppear duller than the remaining surface (raised portions) of the
lastic film or sheet, thereby accentuating the embossed pattern.
` ~hen practicing this technique the release surface can be provided
i . y an ov~rall applied release agen~ after embossing and tip
rinting, or in some cases, it can be applied before embossing
nd tip printing~
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In the ~lternative, it may be desirable to print the second
loss-producing layer over the first gloss-producing layer prio~
o embossing the release sheet. In such cases, the embossing
attern may be identical to and registered with the differential
05 loss pattern to produce the same effect mentionad above. In
ther cases the differential gloss pattern may be different from
he embossed pattern to provide a particular appearance. In such
ases the two patterns ~ not register and there will be the
dvantage of no repeat in the combined pattPrns formed by the
mbossed pattern and the second gloss-producing pattern.
Although in most cases, the second gloss-producing layer
, ill have a lower gloss level than the first gloss-producing
ayer, there may be occasions where it is desirable to reverse
his.
The first gloss-producing layer can be provided by a variety
coating materials~ Where the invention employs a separate,
istinct layer for the release surface, the first gloss-producing
ayer can be provided by conventional pigment-binder coatings.
~ ical pigments useful in such coatings are silicas, barium
sulphate, precipitated ox unprecipitated calcium carbonate, and
alcined alumina. Typical binders are the natural glues such as
asein, protein, starches, and synthetic binders, such as latices,
;- olyvinyl alcohol, methylcellulose and othersO
Where no separate, distinct layer is employed for the release
urface, the irst gloss-producing layer will preferably include
mall additions of conventional release agents, such as silicone
esins, complexes of fatty acids and chromic chloride or poly-
nhydride fatty acid derivatives. The first gloss-producing
ayer is applied uniformly overall to the entire base sheet,
hich may or may not have been previously base coated with a
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11,Z61~1Z5
onventional pigment-binder coating, by conventional coating
echniques such as blade coating, air knife coating, or gravure
oll coating. The amount of coating applied for the first gloss-
roducing layer can vary over a wide range as long as overall
05 overage is obtained, from less than 1 pounds per ream to 15
ounds per ream being a suggested range.
The second gloss-producing layer is provided by a coating
at~rial which may be any one of the coating materials described
for the first gloss-producing layers, although it most likely
ould be one different than the particular one chosen for the
first gloss-producing layer. But, as previously mentioned, it
could be the same material as used for the first gloss-producing
layer. It is critical to the invention that the inherent gloss
roduced by the second gloss-producing layer be different f_om
hat produced by the first gloss-producing layer. It is generally
referred for the gloss level of the first gloss-producing layer
o be higher than that for the second gloss-producing layer.
owever, in some instances it may be desired to reverse this.
~he gloss level of either gloss-producing layer can be controlled
2a ~y the use of gloss control additives. A lower gloss level can
e provided by larger amounts o piyments and/or larger size
igments having greater flatting properties Such pigments are
lay, calcium carbonate, sand, barium sulfate etc. These pigments
re usually combinea with adhesives. Typical adhesives are
olyvinyl alcohol, methyl cellulose, starch, protein and styrene-
utadiene rubber~ Any of the binders may be used by itself as a
loss control additive, and they in general, would tend to raise
,~ ¦¦the gloss of coating.
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Gloss may be described as the characteristic of the surface
which causes light to reflect at a given angle in excess of the
iEfuse reflection at that angle~ There are a number of instru-
ents which measure an arbitrary value indicative of the gloss of
05 particular surface. The Gardner 60 gloss meter is one such
nstrument which is commonly used. The 60 angle is measured
from a line perpendicular to the paper, and is equivalent to a
0 angle from the plane of the paper surface. In practicing the
resent invention, it is critical that the gloss level produced
!~ 10 y the second gloss-producing layer be different from that
roduced by the first gloss-producing layer. It would be difficult
o place quantitative limits on this difference, but the difference
s such that the differential gloss appearance is quite noticable
o any observer.
15 Where a separate, distinct layer is employed for the release
urface, the coating material for the release surface may be
-ovided by any one o~ a number of conventional release materials~
uch as silicone resins or a complex of a fatty acid and chromic
hloride or polyanhydride fat~y acid derivatives. Such a coating
~a~ be applied by a number of techniques used to provide a
ontinuous coating layer. One particularly preferred technique
or coating an embossed sheet is use of an aix knife.
Having generally described the invention, the following
; ~ xamples are given to further illustrate preferred embodiments of
, 25 he invention.
'' . 'Q.
. EXAMPLE 1
A paper base sheet with a conventional clay and adhesive
ase coat (32 lbs./ream total basis weight) was coated overall
ith a first gloss-producing layer which was a mixture of the
ollowi~g:
.'
l ~ s
Dry Weight
styrenP-butadiene rubber latex
(Dow 620 from Dow Chemical Company) 15 parts
l soy protein, medium viscosity 15 parts
05 ¦ clay, coating grade 100 parts
¦ water to make 30% solids
¦ he coating mixture was applied by air knife in an amount of 5
I bs./ream, dried, and calendered to smooth the surface. The
¦ heet was then embossed between an etched steel roll and a cotton
¦ atrix backing roll in four different embossing patterns ranging
l from fine to medium leather yrain. The-hills of the embossed
¦ sheet were tip printed with a 150 line gravure roll using a
¦ oating mixture of the following:
¦ Dry Weight
15 ¦ Calcium carbonate, ground particles
at 50% 250 parts
polyvinyl alcohol (DuPont's
l Elvanol 71-30 at 10%, fully
¦ hydrolyzed, medium molecular
weight, medium viscosity) 75 parts
¦ Triton X-100 (Rohm and Haas welting
¦ agent, a non-ionic alkylaryl
I polye~her alcohol sulfonate at
_ ¦ 10%) 1.25 part
¦ wool green dye at 1% (for
observation purposes) 0.1
aqueous release coating of a complex of a stearic acid and
;- ¦chromium chloride and poly~inyl alcohol was then applied over the
,~ , ¦entire surface and dried.
¦ The gloss levels of the first gloss-providing layer and the
¦second gloss-producing layer of Example 1 were determined by
~- ~ king samples in a slightly varied manner. That is/ the second
~, ¦gloss-producing layer was coated overall on a large enough area
to take gloss readings. ~he 60 Gardner gloss readings obtained
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ere 19 for the first gloss-producting layer and 3 for the second
loss producing layer. These readings were taken after the
elease coating was applied, and they probably would have been a
ittle different if taken without the release coating, but the
05 ifference in gloss would be essentially the same.
A poly~inyl chloride plastisol was cast on the release
urface of the release sheet o Example 1 as a 4 mil wet film.
Over this was applied a 9 mil PVCl foam, and this was then
aminated to cotton fabric. This laminate was heated to expand
he foam and dried by known techniques. Upon separation of the
elease sheet from the cast product the film surface of the cast
roduct had the differential gloss effect of the release sheet.
he hills of the surface were glossy while the valleys were dull.
In another casting example a polyurethane was cast on the
elease surface of the release sheet of Example 1, and this 1 mil
ry layer was bonded to napped and shÇ red fabric using an adhesive
or the urethane. Upon separation of the release paper from the
rethane surface the same differential gloss effect on the
rethane surface was observed as above~ The hills of the surface
Pre glossy while the ~alleys were dull.
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~,~ EXAMPLE 2
;. A paper base sheet with a conventional clay and adhesive
ase coa~ (63 lbs./ream total basis weight) was coated overall
ith a mixtu of the follow ng:
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¦ hydroxyethyl cornstarch 16 parts
l tA. E. Staley Mfg. Co.)
¦ styrene-butadiene rubber latex 10 parts
05 ¦ (Dow 620 from Dow Chemical Company)
l polyvinyl alcohol (Vinol 107 K from
¦ Air Reduction Co.) 5 parts
¦- clay, coating grade 100 parts
~he coating mixture was applied by air knife in an amount of 6
~b~./ream, dried and calendered to~smooth the sheet. The sheet
~as then gravure printed with two different wood grain patterns
~o form the second gloss-producing layer-. The coating material
~sed for the second gloss-producing layer was the same as that
sed for the second gloss-producing layer in Example 1. the
heet was then top coated with a release coating of a release
gent, a monomeric polyhydric alcoholl and a cross-linkable
hermosetting resin o~ the formula set forth in Example 3 of U.S.
atent No. 3,946,135.
The release sheet of Example 2 was used in high pressure
anel pressing where it was placed against a melamina saturated
~verlay, which in turn, was against a melamine saturated and
rinted decorative sheet, which in turn, was against four phenolic
esin saturated core stock sheets.- The laminates were consoli-
ated at 1200 p.s.i. and 285 for 17 minutes. The relaase sheet
as stripped away from the panel and the panel exhibited gloss
ifferential and appeared to have grain structure in its surface
; ven though it was flat.
The release sheet of Example 2 was used in low pressure
anel pressing where it was placed against a melamlne saturated
nd printed decorative sheet, which in turn, was against a 3/4
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nch thick particle board~ The laminates were consolidated at
50 p.s~i. and 300F for ~ minutes. The release sheet was
tripped away, and the panel exhibited gloss differential and
ppeared to ha~e grain structure in its surface even though it
05 was flatO
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. EXAMPLE 3 -
A sheet of aluminum foil 5-8 mils thick, was coated in a
attern of a single wide strip from a gravure roll to provide a
eco~d gloss-producing layer of a coating like that of Example 1,
but with coating grade clay substitutPd fox the calcium carbonate.
o distinct release surface was applied over the seconcl gloss-
producing layer. The 60 Gardiner gloss readings for the foil
`- (which provided the first gloss-producing layer) was o~ scale
(100~) and was 19.0 for the second gloss-producing layer. A
olyvinyl chloride plastisol was cast on the oil ~elease sheet,
ried and stripped from the release sheet and displayed the
ifferential gloss effert of the release sheet.
Other examples were made like those of Example 1 and 2, but
ith different patterns ~such as marble, cloud prints, etc.) used
or the gecona gloss-producing layer and with vaxious release
oatings~ These examples were used in various casting and panel
ressing modes, providing the same observable gloss differential
;- s in Examples 1, 2 and 3.
. ''
EXAMPLES 4-18
As an illustration of the ability to vary the gloss level of
he first or second floss-producing layers by ~arying the materials
n ~he coating, the following examples are given. A conventional
lay/adhesive base coated paper was coated in a single strip
attern with the coating mixture of the second gloss producing
ayer in Example 1 with the noted variations and noted 60
ardiner gloss readings wPre obtained.
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~ 25
¦ Stearic Acid and
l Substituted Mo ReleaseSilicone type Chromic Chloriae
: I Material Coat Release Coat Release Coat
~ydroxyethyl corn- ~
05 ¦starch for PVA 3.0 6.0 3.0
. Isoy protein for PVA3.0-6.0 7.0-9.0 4.0
~ethyl cellulose
¦ for PVA . 5,0 9.0~9.5 5.0
. ~actic casein for
¦ PVA 2.5-3.0 7.0-9.0 ---
~yrene butadine
¦ rubber latex
¦ for PVA 2.5 8.5-10.0 3.0
~and ~or CaC03 --- 7.5 4.0-5.0
~inex, anhydrous
¦(Na, K) aluminum
silicate for
¦ CaC03 4-0 5.5-6.0 4.0
~lass beads for
¦ _ 3 24~0-25,0 19.0 22.0-24.0
play for CaC03 --- 14 . O .8 . O
: po pigment --- 20.0 29.O
. . ~tyrene butadiene
: I rubber latex
25 ¦ for PVA and no
pigment 48.0-52.0 37.0-39.0 45.0-47.0
: ethyl cellulose
for PVA and no -
. ` pigment 15.0 22.0-24.0 1600
i 30 actic casein for
:~ P~A and no
pigment 27.0-28.0 26.0 2~tO-26.0
ontrol (same as
; Ex. 1) - - 4.0 2.0
ase coated paper 32.0-35.0 20.0 18.0-20.0
Having described the invention generally and also in its
~ referred embodiments, variations within the scope of the inven-
.~ . ion will be obvious to -onè skilled in the art. For example, the
¦First gloss-p ducing layer is described as completely covering
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the surace of the base sheet, and this is highly préferred for
he convenience of coating and necessary where the second gloss-
roducing layer is in a fine pattern.
However, it is readily apparent that the first gloss-producing
05 layer does not have to cover the base sheet immediately beneath
. he second gloss-producing layer, and it can be absent in those
areas where the second gloss~producing layer is in a very coarse
. . attern. ~his variation is believed to be a functional equivalent
~f the prese invention in i=s broade~e form.
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