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Description  |
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FIELD OF THE INVENTION
The invention relates to a starch based adhesive composition that can be
used to form corrugated board. More particularly the invention relates to
a starch based adhesive that rapidly increases in viscosity to form high
strength green bonds under conditions of heat and pressure resulting in
increased manufacturing rates of corrugated board.
BACKGROUND OF THE INVENTION
Corrugated paper board or liner board is commonly prepared by first forming
a corrugated element or medium by passing a cellulosic sheet between
corrugating rolls forming a substantially sinusoidal or serpentine
cross-section in the sheet. An adhesive is commonly applied to the tips of
the thus formed sinusoidal portion called flutes and a noncorrugated or
planar cellulosic liner is applied against the adhesive coated flutes of
the corrugated elements as the corrugated sheet passes between a
corrugating roll and a pressure roll. The resulting paper product having
the corrugating medium on one side and the planar liner on another side is
called a single-faced element. The single-faced element may be used as is
in certain applications as a liner or buffer material within a container.
More commonly adhesive is applied to the flute tips of the single-faced
element and a second liner sheet is subsequently applied to the adhesive
liner in a "double facer" operation. The second liner sheet is exposed to
conditions of heat and pressure during its contact with the adhesive. In a
so-called "hotplate" dryer section a continuously moving belt with a
hotplate or platen surface is used to partially remove water from the
adhesive bond line and establish a cured adhesive bond at elevated
temperatures such as 300.degree.-400.degree. F.
The adhesives which have been developed to form the corrugated board or
paper board are generally starch base adhesives. The earliest corrugating
board adhesive patent, U.S. Pat. No. 2,102,937, discloses an adhesive
composition comprising gelatinized starch, ungelatinized starch, alkali
and borax in a water base. This adhesive has formed the basis for the
manufacture of essentially all corrugated paper board to date. This
adhesive is a carrier adhesive, wherein a portion of the starch forms a
carrier gelatinized phase and the balance of the starch forms an
ungelatinized phase. Under conditions of heat and pressure the
ungelatinized starch rapidly gelatinizes, absorbs water and causes a rapid
increase in viscosity and adhesivity of the starch-adhesive composition.
Borax increases the level of viscosity as well during final
gelatinization.
The use of additives in starch based corrugating board and other types of
adhesives has been the subject of substantial research in recent years.
One useful adhesive additive is various polymers of polyvinyl alcohol. On
the whole, the use of soluble polyvinyl alcohol polymers has been avoided
since soluble polyvinyl alcohol has been believed to interact with borax
in the presence of alkali and starch to form useless gels. In order to
avoid these difficulties a variety of patents have taught that by varying
such parameters as the pH of the adhesive of the solubility of the
polyvinyl alcohol, a stable polyvinyl alcohol containing adhesive can be
formed. For example, Nickerson, U.S. Pat. No. 3,720,633 teaches that at
acid pH's polyvinyl alcohols can be used in adhesive compositions in the
presence of polyhydroxy compounds without the formation of substantial
gels. Czerwin, U.S. Pat. No. 4,094,718 and Imoto, Japanese Pat.
Publication No. 45-19600 teach that polyvinyl alcohol can be used in
corrugating board adhesives containing starch, alkali and borax only if
the polyvinyl alcohol compositions are substantially insoluble and
prevented from reacting with the adhesive components until the adhesive is
applied to the corrugating medium and heated past the gel temperature of
the starch. Not only does Nickerson indicate that the use of soluble
polyvinyl alcohols can result in the formation of intractable gels but
Czerwin treats the insoluble polyvinyl alcohol in order to remove soluble
polyvinyl alcohol that could solubilize and interact with the adhesive
components and form a gel. However Czerwin teaches that some soluble
polyvinyl alcohol tends to be present in the adhesive. In Krankkala, U.S.
Pat. No. 4,600,739, certain types of partially hydrolyzed soluble
polyvinyl alcohol composition below a certain concentration were found to
be compatible with corrugated board adhesives containing starch, alkali
and borax. The addition of the controlled amounts of a specific soluble
polyvinyl alcohol was found to substantially increase green bond strength
and rate of manufacture of the corrugated board. The amounts of the
soluble polyvinyl alcohol that can be used is limited by the fact that at
higher concentrations than claimed the soluble polyvinyl alcohols tend to
form the gels recognized in Czerwin and Imoto. Further, soluble. polyvinyl
alcohol tends not to provide any substantial water resistance to the glue
line since the polyvinyl alcohol composition is stable.
The speed at which corrugating machines can be run is limited by the
rapidity of viscosity increase in the bond line between the liner and
corrugated medium. As the viscosity of the adhesive rises under conditions
of heat and pressure in the corrugating machine, a "green bond" is formed
which holds the components together until the adhesive system forms the
final heat-cured corrugated bond. The green bond relies solely on the
viscosity of the product to maintain the integrity of the product during
curing.
Conventional starch based adhesives rely on the response of borax and
ungelatinized starch under conditions of heat and pressure to increase the
viscosity of the adhesive during green bond formation. More recent
corrugating adhesives containing the additionally insoluble polyvinyl
alcohol utilize the increase in viscosity that results as the polyvinyl
alcohol is solubilized at high temperature. However, both the conventional
and the solid polyvinyl alcohol containing conventional adhesives increase
viscosity at a rate that leaves substantial room for improvement. If the
rate at which viscosity increase occurs in the bond line can be increased,
then the corrugating machines can be run at a substantial increase in
speed resulting in an increase in productivity.
Accordingly a substantial need exists for a corrugating adhesive having a
faster set or a substantial increase in the rate of viscosity development
or in the rate of green bond formation during the manufacture of
corrugated board.
BRIEF DESCRIPTION OF THE INVENTION
We have learned that problems relating to the incompatibility of polyvinyl
alcohol compositions can be solved and an adhesive having a substantially
improved green bond strength, and fast set or increase in the rate of
viscosity increase can be achieved by adding to a corrugating adhesive
comprising starch, alkali base, boric acid and water, an amount of a fully
hydrolyzed cold water insoluble polyvinyl alcohol composition wherein the
polyvinyl alcohol is in solution not suspension. Preferably the polyvinyl
alcohol is added to the adhesive in the form of a solution of the
polyvinyl alcohol in water. We have found that, contrary to the teachings
of the art, that the incompatibility of polyvinyl alcohol compositions can
be controlled by carefully controlling the amount of polyvinyl alcohol in
relation to boric acid in the final adhesive composition and by selecting
a fully hydrolyzed polyvinyl alcohol composition of appropriate molecular
weight. Further a selection of a preferred lower molecular weight
polyvinyl alcohol can improve the compatibility of the adhesive and the
polyvinyl alcohol.
While we do not wish to be held to a theory of action of the invention, we
believe that the problems relating to phase separation and gelling in
polyvinyl alcohol containing adhesive is directly related to an
interaction between the hydroxyl groups of the starch or boric acid with
hydroxyl groups of the polyvinyl alcohol. We have further found that in
formulating corrugating adhesives with the partially hydrolyzed polyvinyl
alcohol that there is a threshold concentration of the fully hydrolyzed
soluble polyvinyl alcohol above which substantial gelling or
incompatibility results. However, below the threshold polyvinyl alcohol
acts to substantially increase fast set and strength of the green bond
during corrugating board manufacture. Since the polyvinyl alcohol is in
solution, the rate of green bond formation is increased by the presence of
the alcohol, but is not limited by the rate of dissolution of a solid
polyvinyl alcohol. Since green bond formation is increased corrugating
machine speeds can be increased proportionately. Still further, we have
found that the fully hydrolyzed polyvinyl alcohol adds to the water
resistance of the corrugated board since the polymer is water insoluble at
typical use temperatures.
DETAILED DESCRIPTION OF THE INVENTION
Briefly, the novel water-resistant corrugated board adhesives of this
invention are prepared by forming an aqueous emulsion, having an alkaline
pH containing a solubilized fully hydrolyzed PVOH, starch, a strong alkali
metal hydroxide base and a boric acid compound and optionally a basically
reacting crosslinking resin, and wax. The corrugated paper board adhesive
of this invention is preferably formed from a suspension of starch
particles in water. The viscosity and solids content are important factors
influencing the speed with which the paper board machine can be operated
and also effects the quality of the finished paper board. The suspending
paste or carrier medium must be sufficiently viscous to maintain a smooth
suspension of the starch particles, but not so viscous as to interfere
with the application of the adhesive to the paper board. The nature and
proportion of dissolved solids in the carrier medium influences both pot
life and the speed with which a given paper stock absorbs water from the
applied adhesive. The water content of the adhesive affects adhesive
properties. A small degree of water absorption from the adhesive to the
paper is desirable in forming strong bonds between the paper plies.
Absorption of water beyond that required to give good bonding is
undesirable since it robs the adhesive of water needed to complete the
gelatinization of the suspended starch upon heating in the corrugator and
leads to inferior bonding.
POLYVINYL ALCOHOL
The cold water insoluble polyvinyl alcohol (PVOH), a polyhydroxy polymer
having a polymethylene backbone with pendent hydroxy groups, is a
synthetic resin that removes better than 98.5% of the acetyl group and in
certain grades of polymer better than 99% of the acetyl groups. It is
produced by the hydrolysis of polyvinyl acetate. The theoretical monomer:
##STR1##
does not exist. It is commonly available as a dry solid and is available
in granular or powdered form. PVOH grades include a "super" hydrolyzed
form (99.3% plus removal of the acetate group), and a fully hydrolyzed
form (99% +removal of the acetate group). The properties of the resins
vary according to the molecular weight of the parent polymer and the
degree of hydrolysis. Polyvinyl alcohols are commonly produced in nominal
number average molecular weights that range from about 20,000 to 100,000.
Commonly the molecular weight of commercial polyvinyl alcohol grades is
reflected in the viscosity of a 4 wt-% solution measured in centipoise
(cP) at 20.degree. C. with a Brookfield viscometer. The viscosity of a 4%
solution can range from about 5 to about 65 cP. Variation in film
flexibility, water sensitivity, ease of solvation, viscosity, block
resistance, adhesive strength, dispersing power can all be varied by
adjusting molecular weight or degree of hydrolysis. Solutions of polyvinyl
alcohol in water can be made with large quantities of lower alcoholic
cosolvents and salt cosolutes. Polyvinyl alcohols can react with aldehydes
to form acetals, can be reacted with acrylonitrile to form cyanoethyl
groups, and can be reacted with ethylene or propylene oxide to form
hydroxy alkylene groups. Polyvinyl alcohols can be readily crosslinked and
can be borated to effect gellation.
Polyvinyl alcohol is made by first forming poly-vinyl acetate or a vinyl
acetate containing copolymers such as an ethylene vinyl acetate copolymers
and removing the acetate groups using a base catalyzed alkanolysis. The
production of polyvinyl acetate or a vinyl acetate copolymer can be done
by conventional processes which controls the ultimate molecular weight.
Catalyst selection temperatures, solvent selection and chain transfer
agents can be used by persons skilled in the art to control molecular
weight. The degree of hydrolysis is controlled by preventing the
completion of the alkanolysis reaction. Polyvinyl alcohol is made in the
United States by Air Products & Chemicals, Inc. under the tradename
VINOL.RTM., by duPont under the trade name ELVANOL.RTM. and by Monsanto
under the trade name GELVITOL.RTM..
The preferred polyvinyl alcohol compositions for use in this invention
comprise polyvinyl alcohol made from a homopolymer or interpolymer of
vinyl acetate that is fully hydrolyzed, i.e. greater than about 98.5 to
99% of the hydroxyl groups are free of acetate or super hydrolyzed,
greater than 99.3% of hydrolysis. The preferred fully hydrolyzed polyvinyl
alcohol is available in low, medium or high molecular weight variations
characterized by the Brookfield viscosity of a 4 wt-% aqueous solution at
20 degrees. The low molecular weight polyvinyl alcohol (MW 11,000 to
31,000) has a viscosity of about 4-10 cP, the medium molecular weight
composition (MW =77,000 to 79,000) has a viscosity of about 15-30 cP and a
high molecular weight composition (MW 106,000 to 110,000) has a viscosity
of about 35-60 cP. The preferred polyvinyl alcohol compositions have a
reduced particle size adapting the composition for rapid dissolution. The
particle size of the most preferred polyvinyl alcohol is such that 99+% of
the product will pass through a -80 mesh screen.
The most preferred polyvinyl alcohol composition is made from a low to
medium molecular weight homopolymer of vinyl acetate that is fully
hydrolyzed. The use of higher molecular weight polymers are more likely to
gel at higher concentrations.
STARCH
The starch based adhesives of this invention are commonly characterized as
being either a carrier adhesive, a no carrier adhesive, or a carrier/no
carrier adhesive. The term carrier adhesive implies the presence of a thin
base of gelatinized starch in which ungelatinized or nonhydrated starch
particles are emulsified or suspended. The term no carrier adhesive
implies the substantial absence of gelatinized or hydrated starch in the
adhesive emulsion. The term carrier/no carrier adhesive implies that the
distinction between gelatinized starch and ungelatinized starch is not
clear in the adhesive composition. Generally carrier/no carrier adhesives
are prepared in a way that a substantial amount of partly hydrated or
partly gelatinized starch is formed. These terms are imprecise since
during the preparation of the starch based adhesives some starch
inherently becomes gelatinized during processing at any temperature.
However substantial proportions of starch remain ungelatinized and
nonhydrated during preparation which can gelatinize and interact with
PVOH, and borax during green bond formation.
The starch used in both the carrier phase and suspended starch phase is a
commodity chemical produced from a number of root, stem or fruit, plant
sources. Starch is a high molecular weight polymeric carbohydrate
polysaccharide, most commonly composed of six carbon monosaccharide units
joined by alpha-glycan linkages having an approximate molecular formula of
(C.sub.6 H.sub.10 O.sub.5).sub.n, wherein n equals 10hu 2to 10.sup.6.
Starch occurs naturally in the form of white granules and comprise linear
and branched polysaccharide polymers. Starch is commonly manufactured by
first soaking and grinding the plant starch source, and separating the
starch from waste matter. The starch is commonly reslurried and processed
into a finished dried starch product. Commercial starch often has the form
of a pearl starch, powdered starch, high amylose starch, precooked or
gelatinized starch, etc. Preferably pearl starch is used in making both
the carrier phase and the particulate starch suspended in the carrier.
BASE
The novel adhesive compositions of the invention contain a strong base
which promotes the production of crosslinking species from the resin and
acts to cure the adhesive. Essentially any strong base can be used,
however preferred bases are alkali metal hydroxides. The most preferred
strong bases include sodium and potassium hydroxide. The strong base also
lowers the gel point of the starch, which increases the rate of hydration
of the starch during curing of the glue line.
BORIC ACID COMPOUND
The novel adhesive compositions of the invention include a boric acid
compound which cooperates with the gelatinized and nongelatinized starch
during heating and curing by reacting with available hydroxyl groups of
the starch, forming a starch borax complex which aids in gelling the
carrier starch molecules and the suspended starch molecules. The
cooperative reaction increases the tack of the adhesive and produces
strong bonds. Any boric acid compound having free hydroxyl groups attached
to the boron atom can be used, however commercial boric acid (orthoboric
acid, H.sub.3 BO.sub.3 and its hydrated forms H.sub.3 BO.sub.3 -H.sub.2 O)
and borax (sodium tetraborate decahydrate, Na.sub.2 B.sub.4 O.sub.7
-XH.sub.2 O and other hydrate and anhydrous forms) are commonly used. For
a discussion of boric acid compounds such as boron oxides, boric acids and
borates, see Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition,
Vol. 3, pp. 608-652. The boric acid compound increases the tackiness,
viscosity, and cohesive strength of the adhesive. As the adhesive cures in
the glue line, a gel structure forms between the hydroxyl group of the
polysaccharide, the basic acid compound and the PVOH. The exact mechanism
of the crosslinking reaction between these compounds is unknown. Further,
the borax buffers the caustic nature of the base used in the adhesive
stabilizing the adhesive to the hydrolytic effect of the base.
CROSSLINKING RESINS
Resins that can be used in the novel adhesive compositions of this
invention include resins that upon heating in basic media generate
crosslinking species that react with and crosslink the hydroxyls in
adjacent starch molecules. The crosslinking reagent tends to reduce the
hydrophilic nature and the water solubility of the starch molecules by
effectively removing the availability of hydroxyl groups to water and by
introducing aliphatic alkylene-type crosslinking moieties.
A preferred class of crosslinking resins comprise well known condensation
products of the reaction of a ketone and an aldehyde compound. These
resins are characterized as a polyether polymer but can contain a variety
of other monomers such as urea, melamine, etc. In the presence of heat and
base, they commonly decompose to produce species that effectively
crosslink the starch molecules. Preferred resins are acetone-formaldehyde
resins, acetone-urea-formaldehyde resins, acetone-melamine-formaldehyde
resins comprising 15 to 30 wt-% acetone, about 5 to 50 wt-% formaldehyde
and 0 to 15 wt-% of third monomer. One example of the preferred
crosslinking resin embodiment of this invention comprises the Ketack
series of resins manufactured by American Cyanamide.
WAX
The term wax is used very broadly and is applied to a wide variety of
materials. The materials can have properties resembling certain well known
waxes or can be used to provide physical properties similar to those
associated with well known properties of wax such as sealing, polishing,
candle making, etc. Many waxy substances have been found in nature and
have been known to be useful for many years.
Historically waxes include substances that are natural products. Chemically
natural waxes are esters of fatty acids and monohydric fatty alcohols.
Physically waxes are water repellant solids having a useful degree of
plastic character. However, modern waxes include various synthetic
substances that can replace natural waxes in many preparations. The
composition of natural waxes generally comprise an ester of a saturated
fatty acid and a long chain monohydric alcohol. Long chain fatty acids
often include acids having greater than 16 carbon atoms and most commonly
about 26 carbon atoms. The aliphatic monohydric alcohol commonly has at
least 14 and can range as high as 36 carbon atoms. Petroleum, mineral or
other synthetic waxes often consist of saturated hydrocarb having
aliphatic or open chain structures with relatively low branching or side
chains.
Particularly preferable waxes for the water resistant corrugated board
adhesive are waxes such as petroleum waxes, candelilla wax, beeswax, etc.
Particularly preferred waxes are the petroleum waxes such as
microcrystalline waxes, slack waxes and paraffin waxes.
In somewhat greater detail, the novel fast set corrugating adhesives of
this invention can made by combining the ingredients in water and heating
the mixture until a smooth uniform composition is formed. Preferably the
adhesive is made by combining a starch slurry with a solution of the base
in water heating the mixture to at least partially gelatinized the starch
and then adding the remaining components under conditions of mixing to
form the smooth corrugated adhesive. Since the polyvinyl alcohol is cold
water insoluble, it must be exposed to heat in the presence of free water
to be solubilized. Preferably, a water solution of the polymer is premade
by adding the polyvinyl alcohol to water and then heating with stirring
until dissolved. The adhesive can contain from about 5 to 75 parts of
starch and about 0.1 to about 10 parts of base per 100 parts of the
adhesive composition. In "carrier" adhesives the carrier phase comprises
about 1 to 25 parts of starch and the ungelatinized phase comprises 5 to
50 parts of starch per each 100 parts of adhesive. The adhesive can
contain about 0.1 to 5 parts of boric acid per each 100 parts of water and
optionally about 0.1 to 5 parts of basically reacting crosslinking resin
per 100 parts of water and about 0.1 to 5 parts of wax in an emulsion form
per each 100 parts of water.
The fast setting adhesive of this invention contain about 0.01 to 2.0 parts
of polyvinyl alcohol per each 100 parts of adhesive. Preferably the
adhesive contains about 0.1 to 1.5 parts of polyvinyl alcohol and most
preferably for reasons of rapid set and compatibility with the adhesive
components about 0.25 to 1.25 parts of polyvinyl alcohol per 100 parts of
adhesive. The ratio of polyvinyl alcohol to boric acid is important in the
invention since the interaction between polyvinyl alcohol and boric acid
can cause substantial gelling problems and the manufacture of the
adhesive. Accordingly, polyvinyl alcohol is used in a ratio of less than 9
parts by weight of polyvinyl alcohol per each part of boric acid,
preferably 1 to 8 parts of polyvinyl alcohol per part of boric acid and
most preferably 2 to 7 parts of polyvinyl alcohol per each part of boric
acid for reasons of obtaining a fast setting adhesive free of unacceptable
component interactions.
EXAMPLE I
Into a 1200 milliliter stainless steel beaker immersed in a 200.degree. F.
water bath equipped with an electrically driven blade mixer was placed 800
grams of deionized water. Into the water was placed 100 grams of a fully
hydrolyzed low molecular weight polyvinyl alcohol composition (VINOL 107
Air Products). The contents of the beaker were stirred until dissolution
was complete. Sufficient deionized water was added to the beaker to
prepare 1 liter of solution.
EXAMPLE II
Into an about 6 liter stainless steel steam heated vessel having an
inverted trapezoid cross-section equipped with an electrically drive
propeller blade mixer was placed 1,668 kilograms of water. 791.2 grams of
pearl (corn) starch was added to the water. The contents were mixed until
uniform for 5 minutes and into the starch suspension was , added slowly,
drop-wise over a 15-minute period, a solution of 24 grams of sodium
hydroxide in 416 grams of water. After the addition of the sodium
hydroxide solution, the mixture was heated to about 96.degree. F.
resulting in a viscosity of 20 #5 Zahn cup seconds. Into the blended,
smooth emulsion of starch was added 10 grams of boric acid. The resulting
starch based adhesive was 27.6 wt-% solids. The mixture was stirred for 10
minutes until uniform and 88.4 grams of a 10 wt-% solution of a fully
hydrolyzed low molecular weight polyvinyl alcohol (VINOL 107) was added.
The mixture was stirred for 15 minutes. The product had a viscosity of
11.4 #5 Zahn cup seconds.
EXAMPLE III
Into a stainless steel beaker in a heated water bath equipped with an
electrically driven blade mixer was placed 25.5 grams of deionized water.
Into the water was placed 12.5 grams of Clinton 121B starch. The mixture
was stirred and heated to 130.degree. F. When the starch suspension became
uniform, a pre-mix solution of 27.0 grams of sodium hydroxide and 62.5
grams of deionized water was added drop-wise over a 5 minute period. After
addition was complete the suspension was mixed for 15 minutes. After
mixing 437.8 grams of water was added to the primary stainless steel
beaker to cool the solution. The resulting solution was mixed until
uniform.
In a secondary stainless steel beaker in the water bath equipped with an
electrically driven blade mixer was added 2081.2 grams of deionized water.
The water was heated to a temperature of 90.degree. F. and into the water
was added 1050.0 grams of Clinton 121B starch along with 12.6 grams of
5-mol borax. The contents of the secondary stainless steel beaker were
mixed for 10 minutes and the contents of the primary beaker was added to
the secondary beaker drop-wise over a 30 minute period. After the addition
was complete the mixing was continued until the contents of the beaker was
smooth. Into the smooth suspension was added 120.0 grams of a 10 wt-%
solution of a low molecular weight, fully hydrolyzed polyvinyl alcohol
(Air Products VINOL 107). After the addition of the polyvinyl alcohol
solution the mixture was stirred until uniform. The fully formulated
corrugating adhesive had a viscosity of 9.0 #5 Zahn cup seconds.
EXAMPLE IV
A stock solution of sodium hydroxide, 5-mol borax and water was prepared
which is representative of a corrugating adhesive mixture without the
starch.
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Water 4160 g
NaOH 38 g
5-mol Borax 17 g
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To a 500 g aliquot of the stock solution was added solutions of various
polyvinyl alcohols. The amount of alcohol initially added to the stock
solution is equivalent to the amount of PVOH added to a starch corrugating
adhesive.
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Experi-
ment PVOH Added Time Observations
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1 19 g 10% V-425 0 Clear, no gel
2 1 + 19 g 10% V-425
8 min. Clear, no gel
3 2 + 19 g 10% V-425
20 min. Clear, no gel
4 57 g 10% V-425 0 Clear, no gel
5 19 g 10% V-107 0 Clear, no gel
6 5 + 19 g 10% V-107
13 min. Clear, no gel
7 6 + 19 g 10% V-107
35 min. Clear, no gel
8 57 g 10% V-107 0 Clear, no gel
9 19 g 10% V-350* 0 Gel particles
10 19 g 10% V-350 + 19
0 Clear, no gel
g H.sub.2 O
11 10 + 19 g 10% V-350 +
10 min. Clear, no gel
19 g H.sub.2 O
12 11 + 38 g 5% V-350
20 min. Clear, no gel
13 114 g 5% V-350 -- Clear, no gel
14 28.5 g 7.5% V-325
0 Clear, no gel
15 14 + 28.5 g 7.5% V-325
10 min. Small gel
particles
16 15 + 28.5 g 7.5% V-325
28 min. Small gel
particles
17 85.5 g 7.5% V-325
0 Small gel
particles
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A 10% solution of VINOL 325 formed large gel particles upon addition to the
stock solution.
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18 3.1 g 20% V-205, 9.5
0 Clear, no gel
g 10% V-107
19 18 + 20% V-205, 9.5 g
20 min. Clear, no gel
10% V-107
20 19 + 20% V-205, 9.5 g
25 min. Clear, no gel
10% V-107
21 9.3 g V-205, 28.5 g
0 Clear, no gel
V-107
22 3.1 g 20% V-205, 9.5
0 Slightly cloudy,
g V-325, 5 g H.sub.2 O no gel
23 22 + 20% V-205, 9.5 g
6 min. Slightly cloudy,
V-325, 5 g H.sub.2 O no gel
24 23 + 20% V-205, 9.5 g
15 min. Slightly cloudy,
V-325, 5 g H.sub.2 O no gel
25 9.3 g 20% V-205, 28.5
0 Slightly cloudy,
g V-325, 15 g H.sub.2 O no gel
______________________________________
*High molecular weight fully hydrolyzed
The table of data shows that the amount of the high molecular weight fully
hydrolyzed PVOH placed in solution must be carefully controlled to avoid
gellation and compatibility problems.
______________________________________
Polyvinyl Molecular wt
______________________________________
V-107 about 28,000-44,000
V-203 about 17,000-26,000
V-205 about 33,000
V-350 about 212,000
V-425 about 135,000
V-523 about 43,000 to 103,000
V-540 about 127,500
______________________________________
The above discussion, Examples and data illustrate our current
understanding of the invention. However, since many variations of the
invention can be made without departing from the spirit and scope of the
invention, the invention resides wholly in the claims hereinafter appended
.
* * * * *
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