Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR PRODUCING S~IAPED ARTICLES
FROM VEGETABLE PARTICULATE MATERIALS
BACKGROUND OF THE INVENTION
This invention relates to a process for producing
flexible sheets or other shaped articles from vegetclble
particulate materials.
Japanese Laid Open Patent ~pplication ~Kokai) No.
106932/1984 discloses a process for producing sheets or other
shaped articles of vegetable particulate materials bonded
together with a binder resin by coating the particulates
with isocyanate terminated urethane prepolymers or poly-
isocyanate compounds and then rolling or otherwise shaping
the resultant mass under pressure. The urethane prepolymer
or polyisocyanate compound applied to the particulates cross-
links individual particles together through a chemical reac-
tion of the isocyanate group with atmospheric moisture or
active sites possessed by the particles. This process
requires relatively large amounts of binder prepolymer or
compound and is not suited for mass production of inexpensive
articles such as planter pots. Furthermore, relatively long
curing time and blocking to the mold prevent the process from
being applied to mass production o~ shaped articles on con-
ti~uous basis.
The process of this invention is distinguished from
the prior art in that it provides flexible sheets or articles
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in cost effec-tive manner.
SUMMARY OF THE INVENTION
According to the present invention, there is provided
a process for producing sheets or other shaped articles
comprising the steps of applying to vegetable particulate
materials an a~ueous mixture containing a urethane prepolymer
having a plurality of terminal free isocyanato groups formed
by reacting an excess of a polyisocyanate with a polyoxy-
alkylene polyol havlng at least two terminal hydroxyl groups
per molecule and an oxyethylene unit content of 10 to 90~ by
weight, said mixture containing a large excess of water;
shaping the resulting mass; curing and drying the resultant
articles. The aqueous mixture of said urethane prepolymer
~ay optionally contain an inert binder polymer.
The resultant article may be further compacted under
heat and pressure for improving strength properties.
DESCRIPTION OF PREPARED_EMBODIMENTS
The urethane prepolymer used in the present invention
may be prepared, as is well~known, by reacting an excess of
polyisocyanate compound with a polyoxyalkylene polyol having
at least two terminal hydroxyl groups per molecule and an
oxyethylene unit content of 10 to 90% by weight. The polyol
compound, in turn, may be prepared by addition-reacting an
alkylene oxide mixture with a starting active hydrogen
compound. Examples of starting active hydrogen compounds
which must have at least two active hydrogen atoms per
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molecule include ethylene glycol, propylene glycol, hydro-
quinone, bisphenol A, 1,6-hexanediol, neopentyl glycol,
glycerine, trimethylolpropane, 1,2,6-hexanetriol, penta-
erythritol, alpha-methylglycoside, sorbitol, sucrose, castor
oil, ethylenediamine, diethylenetriamine, piperazine, methyl-
amine, n-butylamine, aniline, xylylenediamine and the like.
Examples of alkylene oxides include e-thylene oxide, propylene
oxide, butylene oxide, styrene oxide, tetrahydroEuran and
the like. The proportion of ethylene oxide in the alkylene
oxide mixture should be 10 to 90% by weight. The addition-
reaction may be performed in known manner. rrhe resulting
polyether polyols preEerably have a molecular weight greater
than 1,000. The oxyethylene units present in each polyoxy-
alkylene chain may form a random or block copolymer. If the
oxyethylene unit content is greater than 90~, e.g. 100%, the
polyether polyols often occur as a solid at ambient temper-
ature or urethane prepolymers derived therefrom will cure
too rapidly into rigid states. Conversely, if the oxyethylene
unit content of the polyether polyols is less than 10%, the
urethane prepolymers derived therefrom tend to be less
hydrophilic than desirable.
Examples of polyisocyanate compounds include toluyl-
enediisocyanate (purified or crude T~I), disphenylmethane-
diisocyanate (MDI), polyethylenepolyphenylisocyanate, hexa-
methylenediisocyanate, xylylenediisocyanate, naphthalene-
diisocyanater isophoronediisocyanate, and mixtures thereof.
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The urethane prepolymer terminated with free iso-
cyanato groups may be prepared by reacting the polyisocyanate
compound and the polyether polyol at an NCO/OH equivalent
ratio of 1.5 to 100, preferably 2 to 20. The resulting
prepolymer may be easily dissolved or dispersed in a large
excess of water optionally together with a binder polymer to
form a binder liquid for bonding vegetable particulate
materials. Water acts as a chain extender o~ the urethane
prepolymer.
The binder liquid may optionally contain a solution
or emulsion of inert binder polymers. Examples of usable
water-soluble binder polymers include polyvinyl alcohol,
polyacrylic acid, polyacrylamide, water-soluble maleic acid
copolymers and the like. Examples of emulsions of binder
polymers include natural or synthetic rubber latexes such as
natural rubber, SBR, chloroprene rubber, acrylonitril-buta-
diene rubber, acrylate-butadiene rubber, isoprene rubber,
butyl rubber, ethylene-propylene rubber and the like.
~; Emulsions of other binder polymers such as polyvinyl acetate,
polyvinyl chloride, polyvinylidene chloride, vinyl chloride-
vinyl acetate copolymer, ethylene-vinyl acetate copolymer,
polyacrylate, aminoplast and phenol resins may also be used~
The proportion of water in the binder liquid is
preferably at least equal to but less than 50 times of the
combined solid contents of the urethane prepolymer and the
inert binder resin.
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Examples oE vegetable particulate materials include
but not limited -to saw dust, wood Eragments, cork powder,
rice bran, oil meal, soybean meaL, rice or other grain hulls,
straws, finely divided bark and the like.
In practicing the process of this invention, the
binder solution is first applied to vegetable particulate
materials such as by spraying. The resultant shaping com-
pound is immediately spread on a mat -to form a sh~t, all~w~d
to cure at room or an elevated temperature and dried.
Alternatively, said compound may be shaped into a desired
shape by mo]ding under pressure. Instead of applying the
premixed binder liquid, the vegetable particulate materials
may be wetted with a large amount of water and then mixed
with the remaining components.
The shaping compound may contain other conventional
; additives such as solvents, plasticizers, defoaming agents,
surfactants, coloring agents, fillers, curing catalysts and
the like.
The resulting sheets or other shaped articles may be
compacted by pressing under heat for further increasing
strength properties. This secondary processing is preferably
carried out at a pressure of 2 to 100 kg/cm2, more preferably
10 to 60 kg/cm2 and at a temperature of 70 to 200C, more
preferably 100 to 170C.
The present invention offers a process for producing
valuable sheets and other shaped articles having excellent
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Elexibility and other strength properties starting from waste
or less valuable materials in cost effective manner.
The following examples are offered for illustrative
purposes only. All parts and percents therein are by weight
unless otherwise indicated.
EXAMPLE 1
Preparation of urethane prepolymer
Urethane prepolymer solutions A, B and C shown in
Table 1 were prepared by reacting polyalkylene polyols and
polyisocyanates listed in Table 1 and diluted with ethyl
acetate to 70% concentration. The polyalkylene polyols ~ere
synthesized by addition-reacting a mixture of ethylene oxide
(EO) and propylene oxide ~PO) with a starting compound to
form a random copolymer.
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EXAMPLE 2
10 parts of urethane prepolymer solution A of Example
1 were mixed with 300 parts of water. The mixture was
sprayed on 50 parts of sawdust having a moisture content of
15% within 20 seconds. The resultiny mass was immediately
spread on a flat plate to a thickness of about 8 rnm and
~llowed to cure at 22C. The curing time was about 3 minutes
after spraying. The resulting sheet was dried in a dryer at
80C Eor 3 hours to obtain a flexible sheet having a thickness
~f about 8 mm. This sheet may be used as directory boards,
resilient floor coverings, etc.
EXAMPLE 3
10 parts of a 1:1 mixture of urethane prepolymers A
~nd B of Example 1 were mixed with 357 parts of water.
The mixture was sprayed on the same sawdust as used in Example
2 at a ratio of 514 parts per 100 parts of sawdust. After
spraying, the sawdust was immediately shaped into a sheet
having a thickness of about 1.5 mm, allowed to cure at 22C
and dried to obtain a thin flexible sheet. This sheet may
be used as packaginy materials for steel pipes and the like.
EXAMPLE 4
Sawdust of cedar and sypress trees obtained from
lumbermills having a moisture content of 5.9% and a particle
distribution of 20% of 60 mesh passing, 6.7~ of 60-52 mesh
passing, 5.3% of 52-48 mesh passing and 68% of 48 mesh
retenate was used. Sheets were made as in the preceding
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examples using 50 parts of this sawdust, 250 parts of water
and a varying amount of prepolymer solution C of Example 1
at 4, 5, 6, 7, 10, 15 and 20 parts, respectively, and tested
on tensile strength. The results obtained are shown in Fiy.
1. The tensile strength was approximately proportional to
the amount of urethane prepolymer.
EXAMPLE 5
Sheets were made as in Example 4 using 50 parts o~
sawdust, 10 parts urethane prepolymex solution C and a vary-
ing amount oE water at 150, 200, 250, 300 and 400 parts,
respectively, and tested on tensile strength. The results
obtained are shown in Fig. 2. The data indicate that an
optimum range of water lies between 200 to 300 parts per 10
parts of urethane prepolymer solution C and the tensile
strength decreases iL the amount of water is outslde thisrange.
EXAMPLE 6
Sheets were made as in Example 4 using 50 parts of
sawdust~ 250 parts of water and 7 parts (series A) or 10
parts (series B) of urethane prepolymer solution C. Sawdust
was used without sieving in run (1). In run (2) and run (3),
60 mesh retenate and 40 mesh retenate were used, respectively.
The results obtained are shown in Fig. 3. The data indicate
that the particle size distribution of sawdust has little
effect on the tensile strength. However, since the sheet
made ~rom 40 mesh retenate exhibited a decreased tensile
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strength, it may be preferable for the sawdust to have
relatively wide particle size distributions.
EXAMPLE 7
Sheets were made as in Example 4 using 50 parts of
sawdust, 7 parts of urethane prepolymer solution C and 250
parts of water, but the sawdust was blended with short fibers
(0.5-2 cm) or long fibers (3.0-6.0 cm) of cedar bark at
varying proportions. The results obtained are shown in
Fig. 4. Short fibers had no effect on the tensile strength
which decreased with increase in its proportion. Long fibers
had a significant effect on the strength but the fluidity of
shaping compound was decreased too much to make a sheed at
higher proportions.
EXAMPLE 8
i5 A shaping compound was prepared by spraying a mixture
of 5 parts of urethane prepolymer solution C of Example l and
250 parts of water onto 50 parts of sawdust used in Example
4. This compound was immediately compression-molded in a
; mold at a pressure of 45 kg/cm2 for 2 minutes, removed from
the mold and dried to obtain a planter pot of having a length
of 50 mm, a width of 150 mm, a depth of lO0 mm and a wall
thickness of lO mm. This planter pot was impermeable to
water but permeable to air. Therefore, this pot is more
suitable for growing plants than conventional plastic pots.
EXAMPLE 9
355 parts of aqueous mixture of urethane prepolymer
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used in Example 8 were sprayed on ]00 parts of a powdered
mixture of sawdust, rice bran, oil meal, soybean meal and
poultry feces. The resulting compound was immediately
compression-molded at a pressure of 35 kg/cm2, removed from
the mold and dried to obtain a planter pot. This pot is
particularly useful for agricultural purposes because when
seedlings grown in this pot are transplanted as such~ the
pot is decomposed by the action of water in the soil to a
Eertilizer.
EXAMPLE 10
100 parts of a mixture of oak sawdust (Q. rerrata t
Q. acutissima etc.) and rice bran containing a small amount
of Shiitake hypha (Lentinus edodes) were spray-coated with
375 parts of a mixture consisting of 5 parts of urethane
prepolymer solution C of Example 1 and 250 parts of water.
The resulting compound was compression-molded in a mold into
a bar having a length of 150 cm and a square cross section
of 10 X 10 cm2 at a pressure of 42 kg/cm2 for 2 minutes.
The shaped bar was removed from the mold and then dried~
This bar ma~ be used f~r culturing Shiitake as substitute
for natural bed logs~
EXAMPLE 11
50 parts of sawdust used in Example 4 were spray-
coated with a mixture of 7 parts of urethane prepolymer
solution C of Example 1 and 250 parts of water containing a
varylng amount of polyvinyl acetate (PVAc) emulsion (41~
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nonvolatile) at 0, 1, 5, 7 and 10 parts, respectively.
Sheets were made from respective compounds, dried and tested
on the -tensile strength. The results obtained are shown in
Fig. 5. The data indicate that the tensile strength may be
improved proportionally to the amount of polyvinyl acetate
emulsion. However, the sheet becomes more rigid and less
Elexible with the increase of the amount of polyvinyl ace~ate
emulsion.
EXAMPLE 12
The procedure of Example 11 was repeated except that
an ethylene-vinyl acetate copolymer (EVA) emulsion (~7% non-
volatile) was replaced for polyvinyl acetate emulsion.
The results obtained are shown in Fig. 6. The effect
of EVA emulsion on tensile strength was not so significant
as polyvinyl acetate emulsion but the flexibility was retained
sufficiently even at higher proportions of EVA emulsion.
EXAMPLE 13
The procedure of Example 11 was repeated except ~hat
an emulsion of ethylene-vinyl acetate-vinyl versatate copoly-
mer (50~ nonvolatile) was replaced for polyvinyl acetateemulsion.
The results obtained are shown in Fig. 7. The effect
of addition of ethylene-vinyl acetate-vinyl versatate copoly-
mer emulsion on the stren~th was between PVAc and EVA emul-
sions.
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EXAMPLE 14
Two shaped sheets obtained in Example 4 at a coating
amount of urethane prepolymer solution C of 20% and 30~,
respectively, by weight of sawdust were pressed at a pressure
of 50 kg/cm2 at 120C for 5 minutes. Initial tensile strength
values oE 530 g/cm2 and 1,100 g/cm2 were increased to 1,050
y/cm2 and 2,020 g/cm2, respectively.
EXAMPLE 15
Two shaped sheets obtained in Example 13 incorporat-
ing ethylene-vinyl acetate-vinyl versatate emulsion at 5~
and 10%, respectively, were pressed at a pressure of 150 kg/
cm2 at 120C for 5 minutesO Initial tensile values of 670 g/
cm2 and 875 g/cm2 were increased to 1,310 g/cm2 and 1,595 g/
cm2, respectively.
EXAMPLE 16
15 parts of urethane prepolymer solution A of Example
1 were mixed with 150 parts of water. The mixture was imme-
diatly thoroughly mixed with 100 parts of rice hulls within
20 seconds. The resulting mass was spread in a mold frame
to a thickness of about 20 mm and allowed to cure at 22C.
Curing was compIeted in 3 minutes after mixing the prepolymer
with water.
~ After standing 24 hours, the resulting sheet was
pressed at a pressure of 20 kg/cm2 at 100C for one minutes
to give a resilient sheet having a thickness of 10 mm, a
density of 0.50 g/cm3 and a flexural strength of 28 kg/cm2.
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