Note: Descriptions are shown in the official language in which they were submitted.
STD 501 PI ~ 452
PRESSURE BOI~ G ADHESIVE AND
ADXES~ VE COATED PRODUCT
Backqround of the InventiorL
This invention relate3 to a pressure bonding adhesive for u3e
5 on paper product3 which are subj ected to high temperature
condition3, and more particularly to an adhe8ive for use on
documents such as mailer forms produced by laser printing.
The use of ~lself" adhesives for use in mailer forms is well
known. In the past, heat ~;eal adhesives were u3ed on form3 which
10 were not 3ubj ected to heat and pre33ure until the f inal printed
form wa3 3ealed by applying heat to the adhe3ive. However, new
adhe3ive3 were required with the advent of la3er printer3, which
generally u3e heat and pres3ure - (fu3er roll3) for adhering toner
image3 to paper. The3e ad~le3ive3 need to form 3trong bond3 under
pre33ure alone and be able to with3tand fu3er roll temperature3 of
up to 232 C without becoming tacky .
Much effort ha3 been made to adapt "3elf" adhe3ive3 3uch a3
natural rubber latex coating3 to the need3 of la3er printer3.
The3e coating3 generally are adherent with other coating3 of the
3ame material but are not adherent toward other surfaces. The
pre33ure 3eal3 made after printing in la3er printer3 u3ing 3uch
"3elf" adhe3ive3 have not been entirely 3ati3factory for 3everal
rea30n3. Fir3t, 3uch adhe3ive3 have adhered to the fu3er roll3,
cau3ing fouling or jamming. Second, 3ilicone oil3 which are
commonly applied to fu3er roll 3urfaces have tran3ferred to the
adhe3ive3, preventing formation of 3trong self-adhesive bonds.
Third, adhesive coated form3 are 3tored in 3tack3, pack3 or roll3
prior to printing and "blocking" often occur3, which cau3e3 the
adjacent pile3 to 3tick to~ether, thu3 preventing proper feeding.
Finally, 3uch prior adhe3ive coating3 103e bond-forming ability
with age.
Some ef forts have been made to correct these problems using
adhesives such as the one d:isclosed in U.S. patent 4,918,128. This
adhesive is composed of a graft polymerized natural rubber latex
with styrene and methyl methacrylate comonomers and a non-
thermopla3tic particulate solid.
Still, there remains a need in the art for a pressure bonding
adhesive which will not become tacky under high temperatures, lose
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adheeive properties due to contact with silicone oils, "block" when
stacked prior to printing, or lose bond-forming ability with age.
SummarY of the Invention
The present invention meets that need by providing a pressure
bonding adhesive for use on laser printed documents which combines
non-thermoplastic pigment particles and a compound selected from
the group consisting of a natural rubber latex, a ~[raf t copolymer
of natural rubber and acrylic monomer and a blend of the natural
rubber latex and the graf t copolymer . These compounds produce an
adhesive capable of withstanding the heat and pressure conditions
of the fuser rolls in sheet fed and web fed laser printers such as
the Xerox 4050, the SiemenE; 2140, the IBM 3800 and 3900 and still
form a secure bond under pressure alone.
The adhesive comprises non-thermoplastic pigment particles,
a compound selected from the group consisting of unmodified natural
rubber latex, a graf t copolymer of natural rubber and acrylic
monomer and a blend of the ~nmodified natural rubber latex and the
graft copolymer and optionally one or more compounds selected from
the group consisting of chloroprene-methacrylic acid copolymer
latex and a vinyl-methacry~ ic acid copolymer latex. The adhesive
has a glass transition tem~?erature (Tg) in the range of -10 to
-78C and a green strength of 0 . 05 to 0 . 75 p . s . i . .
In a preferred embodiment, the acrylic monomer used in the
graft copolymer is choseII from the group consisting of ethyl
acrylate, methyl methacrylate and ethyl methacrylate. In addition,
the graft copolymer contains the acrylic monomer in a weight
percent of 30 to 50% and has a glass transition temperature of from
about -60 to -65C. When present, the optional chloroprene-
methacrylic acid copolymer latex should have a glass transition
temperature of about -45C and be used in the adhesive in a weight
percent of from 10 to 40%. It is also desirable for the optional
vinyl-methacrylic acid copolymer latex when present to have a glass
transition temperature in the range of from -14 to -25C and be
used in the adhesive in a ~ieight percent of from 10 to 40%.
The natural rubber la~ex and the graft copolymer of natural
rubber and acrylic monomer of the present invention give the
adhesive the properties necessary for effective pressure bonding.
The graft copolymer also reduces tack, which prevents blocking.
The non-thermoplastic pigment also reduces surface tack to prevent
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blocking and absorbs the s:ilicone oils ueed on fuser rolls. The
optional chluL ,~Lelle-methacrylic acid copolymer latex and vinyl-
methacrylic acid copolymer latex help to prevent premature drying
of the adhesive during the application of the adhesive to a
3ubstrate.
Accordingly, it is an obj ect of the present invention to
provide an adhesive which will not become tacky under high
temperatures, loee adhesive properties due to contact with silicone
oils, "block" when stacked prior to printing, or lose bond-forming
ability with age.
Brief Deecription of the D~awinqs
Fig. 1 illustrates a typical cellulosic substrate which has
been coated with a pressure bonding adhesive in accordance with the
present invention.
Detailed Deec~i~tion of the Preferred Embodimente
Fig. 1 illustrates a typical embodiment of the adhesive coated
product of the present invention. A single sheet of paper 10 is
used to make a mailer document 12. The adhesive is applied to the
mailer at lines 70, 72, 80 and 82.
The adhesive may be applied to any suitable cellulosic
substrate and plastic sub3trates, preferably those having porous
surfaces that would allow the adhesive to adhere securely such as
Tyvek polyolefins. In a preferred embodiment, the adhesive is
applied to the substrate to provide a thickness when dry of from
0.3 to 0 7 mil, and most preferably about 0.5 mil. The adhesive
may be used to form various mailer products or envelopes which
require adhesives.
In its preferred form, the adhesive of the present invention
comprises a blend of a non- thermoplastic pigment particle such as
silica which has a particle size of 1-40 microns, a natural rubber
latex which is not chemically modified, and a graft copolymer of
natural rubber and acrylic monomer, the monomer being selected from
the group consisting of ethyl acrylate, methyl methacrylate and
ethyl methacrylate. The adhesive also optionally contains a
chloroprene-methacrylic acid copolymer latex and a vinyl-
methacrylic acid copolymer latex. The required physical
characteristic~ of the final adhesive are a glass transition
temperature (Tg) in the range of -10 to -78C and a green strength
of 0.05 to 0.75 p.s.i
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The non-thermoplastic filler pigment may be any convenient
organlc or inorganic hard-particle pigment such as, for example,
silica gel. It is used in a solids weight percent of 1 to 10%,
most preferably about 2~. The effect the pigment has on the dried
5 adheGive film is to reduce surface tack, which prevents blocking
and improves feeding of forms having the adhesive. It also absorbs
the silicone oils uæed on many printer fuser rolls.
The unmodif ied natural rubber latex is a natural product
obtained from rubber trees. It can be used in a solids weight
10 percent of 0 to 99~, and ntost preferably in an aqueous emulsion
, r nt~;n~ng about 559~ rubber solids. It is comprised mainly of cis
1,4-polyi#oprene (93-95 wt 96), moigture (0.3-1.0 wt ~), acetone
soluble residue (1 . 5-4 . 5 wt ~), proteins (2 . 0-3 . 0 wt ~), and ash
(0.2-0.5 wt ~). The nominal properties of a dried film of natural
15 rubber are a glass transition temperature of -72C, a dielectric
constant of 2 . 3 7 and a green strength of 0 . 72 p . 8 . i . .
The graft polymerized natural rubber latex is produced by
reacting the natural latex with an acrylic monomer. This result~
in random and block copolynterization of the acrylic monomer with
20 the natural rubber of pol~isoprene. This treatment provides a
dried film adhesive with increasing hardness, reducing tack and
blocking tendency, raises the glass transition temperature from
about -72C to about -60 to -65C, and decreases the bond strength
formed when two films are joined by pressure. At some ratios, the
25 resultant copolymer may sho~r two glass transition temperatures, one
due to the natural rubber alld one due to the added copolymer. The
graft copolymers used in the present invention contain from 30~ to
5096 of the acrylic comonomer based on the weight of the copolymer.
The latex is preferably used a~ an aqueous emulsion of about 589~
30 solids. However, the graft copolymer can be used in a solids
weight percent of from 0 to 999~.
The optional chloroprene-methacrylic acid copolymer latex
preferably has a glass tra~lsition temperature of about -45C and
is present in the adhesive in a weight percent of from 10 to 40~.
35 A satisfactory chloroprene-methacrylic acid copolymer for use in
the present invention is Neoprene 115 from du Pont, which is
supplied as a 45~6 solids content composition.
The optional vinyl-methacrylic acid copolyrner latex has a
glass transition temperature in the range of from -14 to -25C and
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is present in the adhesive in a weight percent of from 10 to 40%.
An example of a vinyl-methacrylic acid copolymer latex which can
be used in the present invention is Haloflex 320 from Zeneca
Resins, a division of ICI.
The final adhesive may also contain water, and lesser amounts
of ammonia, defoamer and dye. The water helps to prevent premature
drying and can be present in a weight percent of 1 to 10% in
addition to the water already present in the aqueous latex
emulsions. The ammonia helps to stabilize the rubber latex and
provide a basic pH. It carL be used in a weight percent of 0.1 to
1. 0% . The defoamer is used to prevent foaming of the adhesive in
use and during application. It can be used in a weight percent of
o to 0.2%. The dye is used for aesthetic reasons to make the
adhesive more visible to the user and can be any color. The dye
should be water-soluble and can be used in a weight percent of 0
to 0.2%.
In order that the invention may be more readily understood,
reference is made to the following example which is intended to
illustrate the invention, but not limit the scope thereof.
Exam~le 1
A pressure bonding adhesive composition was prepared in
accordance with the present invention by blending 75% (weight
percentage) unmodified natural rubber latex (55% solids), 17% of
a graft copolymer of natural rubber and methyl methacrylate (58%
solids), 5.1% water, 2% inorganic CabosiI silica pigment particles
from Cabot, 0.4% ammonia, 0.01% water soluble dye and 0.019~
defoamer The composition was applied by a Flexo Analox roll at
a thickness of from 0.25 to 0.5 mil to a cellulosic substrate and
then dried using a radio frequency dryer. The dried film adhesive
exhibited satisfactory stability under high temperatures and did
not lose adhesive properties due to contact with silicone oils,
~block" when stacked prior to printing, or lose bond-forming
ability with age.
