Pulp molding die for molding shaped pulp articles, method, apparatus, and shaped pulp article

A pulp molding die for molding shaped articles from fiber pulp is disclosed. The die has a porous molding layer having a porosity of at least 5% and an average pore diameter in a range of 60 to 1000 .mu.m, the porous molding layer having a molding surface shaped to the configuration of the article to be molded; and a porous support layer disposed adjacent the porous molding layer on the opposite side thereof from the molding surface, the porous support layer having a porosity of at least 20% and an average pore diameter in a range of 0.6 to 10 mm, the average pore diameter being larger than that of the porous molding layer. The porous molding layer and/or the porous support layer have a pore structure for holding water. A method of molding shaped pulp articles from fiber pulp, has the steps of: (1) providing a pulp molding die as above; (2) molding a pulp article on the molding surface of the die by suction through the die; (3) removing the molded pulp article from the die; and (4) after repeating steps (2) and (3) at least once, applying cleaning water to the die to incorporate water in the pore structure of the die and thereafter applying air pressure to the die from inside the die to drive the incorporated water from the die, thereby removing fibers trapped in the die. An apparatus for molding shaped pulp articles from fiber pulp is disclosed.

BACKGROUND OF THE INVENTION 
This invention relates to a pulp molding die for molding pulp articles from 
used pulp and the like. Such pulp articles are suitably used as packaging 
and shock-absorbing materials, for example, egg boxes, fruit crates, 
packages for industrial products. This invention also relates to the 
method for molding such pulp articles. 
Conventionally, in Japan, plastic and Styrofoam containers have mainly been 
used for packing industrial products, or the like. However, such 
containers add to environmental problems since they are not biodegradable, 
they release hazardous gas upon incineration, and so on. Therefore, 
conversion to fiber containers using old pulp, which can be reused many 
times, has come to be investigated. 
The conventional pulp molding die consists of a main body and a wire mesh 
for the molding surface covering the main body. The wire mesh has a 
desired shape, which can be highly complex, of an article to be molded. 
The surface of the main body covered with the wire mesh also has 
complementary shape to the wire mesh. The main body is composed of 
aluminum blocks having numerous pores for water passage, and the blocks 
are joined together. The main body is joined to the wire mesh by 
connecting means such as bolts. The die may have a highly complex shape. 
Washing the conventional molding die of the wire-mesh type using a shower 
of water at each interval of molding can prevent, to some extent, the 
water passage from becoming clogged. However, washing complexly shaped 
dies is extremely time consuming. Moreover, there are problems such as (1) 
the need for time, skill, and experience in the production of molding dies 
having complex shapes, (2) the difficulty in eliminating unwanted marks of 
the joints and patterns of the wire mesh from the surface of the final 
product, and (3) the inability to form letters or minute designs since the 
wire conventionally used cannot produce precise edges and corners. 
Further, when the pores for water passage are clogged, the operation has 
to be stopped and the molding die is washed by pressurized water. 
Another type of a pulp molding die has been disclosed in Japanese Patent 
Laid-Open 60-9704. The die is composed of a single layer of particles 
forming the molding surface of a size chosen to provide a smooth surface. 
The particles, for example, made of ceramics, are bonded by a resin 
bonding agent, leaving pores. The thickness of this layer is 5-60 mm. 
There may be a backing plate (4 in FIG. 5); the specific example of this 
plate has a porosity of 7%. 
However, this type of a die has some problems. In actual use, this mold 
(with the plate 4) may clog, because large areas of the porous molding 
layer are directly backed by unapertured areas of the plate. Thus the 
continuous production of the pulp articles is interrupted for a declogging 
procedure. Moreover, the die is prone to distortion during mass 
production, which requires the die to withstand repeated decompression, 
since the molding die is bonded only by the resin. 
The present invention intends to solve the above-discussed conventional 
problems by providing a pulp molding die for molding pulp articles, which: 
(1) hardly experiences clogged pores, (2) can mold pulp articles having 
smooth surfaces, (3) is not prone to be damaged by repeated use, and (4) 
can be easily produced in a short amount of time. Moreover, the critical 
number of cycles in which molding a pulp article is continuously repeated 
without interruption can be greatly increased with the mold of the 
invention. The present invention is further intended to provide a pulp 
molding process, using the above-discussed pulp molding die, to greatly 
increase the critical number of possible continuous pulp moldings. 
SUMMARY OF THE INVENTION 
According to a first aspect of the invention, there is provided a pulp 
molding die for molding shaped articles from fiber pulp, comprising; a 
porous molding layer having a porosity of at least 5% and an average pore 
diameter in a range of 60 to 1000 .mu.m, the porous molding layer having a 
molding surface shaped to the configuration of the article to be molded; a 
porous support layer disposed adjacent the porous molding layer on the 
opposite side thereof from the molding surface, the porous support layer 
having a porosity of at least 20% and an average pore diameter in a range 
of 0.6 to 10 mm, the average pore diameter being larger than that of the 
porous molding layer; and means for holding water in the die by capillary 
attraction, the means comprising a pore structure defined by at east one 
of the porous molding layer and the porous support layer. 
Preferably at least one of the porous molding layer and the porous support 
layer has an interconnected pore structure. 
Preferably the die has an air flow characteristic such that when air 
pressure of 300 mm Aq is applied at the molding surface the air flow rate, 
Q, through the die is 50.ltoreq.Q.ltoreq.600, wherein Q is ml.A.sup.-1. 
s.sup.-1, A is the surface area of the molding surface in cm.sup.2, ml is 
the volume of air in cm.sup.3 that passes through the die, and s is 
seconds. 
The porous support layer may comprise means for allowing substantially 
uniform flow of air through the porous molding layer over the entire area 
of the opposite side thereof. 
Preferably the porous molding layer has a thickness in the range of 0.1 to 
20 mm. The porous molding layer may have a thickness in a range of 0.1 to 
5 mm. 
Preferably at least 80% of the pores of the porous molding layer have pore 
diameters in the range 25% less than the average pore diameter thereof to 
25% more than the average pore diameter thereof. Preferably the average 
pore diameter of the porous support layer is 1.5 to 10 times that of the 
porous molding layer. 
Preferably at least one of the porous molding layer and the porous support 
layer is composed of a plurality of water-insoluble particles bonded 
together. 
At least one of the porous molding layer and the porous support layer may 
be composed of a porous material formed by electroforming. 
At least one of the porous molding layer and the porous support layer may 
be composed of a honeycomb structure. 
At least one of the porous molding layer and the porous support layer may 
be composed of a perforated metal plate. 
According to a second aspect of the invention, there is provided a method 
of molding shaped pulp articles from fiber pulp, comprising the steps of: 
(1) providing a pulp molding die comprising a porous molding layer having 
a porosity of at least 5% and an average pore diameter in a range of 60 to 
1000 .mu.m, the porous molding layer having a molding surface shaped to 
the configuration of the article to be molded; a porous support layer 
disposed adjacent the porous molding layer on the opposite side thereof 
from the molding surface, the porous support layer having a porosity of at 
least 20% and an average pore diameter in a range of 0.6 to 10 mm, the 
average pore diameter being larger than that of the porous molding layer; 
and means for holding water in the die by capillary attraction, the means 
comprising a pore structure defined by at least one of the porous molding 
layer and the porous support layer; (2) molding a pulp article on the 
molding surface of the die by suction through the die; (3) removing the 
molded pulp article from the die; and (4) after repeating steps (2) and 
(3) at least once, applying cleaning water to the die to incorporate water 
in the pore structure of the die and thereafter applying air pressure to 
the die from inside the die to drive the incorporated water from the die, 
thereby removing fibers trapped in the die. 
Preferably the step (4) is performed in sequence each time after step (3). 
Preferably the air pressure is applied so as to give a maximum pressure of 
at least 1.0 gf/cm.sup.2 at the molding surface of the die. The air 
pressure may be applied as an impulse which rises to at least 1.0 
gf/cm.sup.2 at the molding surface of the die in less than 0.5 s. 
Preferably an above-mentioned method further comprises connecting the die 
to a volume of pre-compressed air to provide the air pressure. 
According to a third aspect of the invention, there is provided a shaped 
pulp article made by an above-mentioned method of molding shaped pulp 
articles from fiber pulp. 
According to a fourth aspect of the invention, there is provided an 
apparatus for molding shaped pulp articles from fiber pulp, comprising: a 
pulp molding die comprising a porous molding layer having a porosity of at 
least 5% and an average pore diameter in a range of 60 to 1000 .mu.m, the 
porous molding layer having a molding surface shaped to the configuration 
of the article to be molded; a porous support layer disposed adjacent the 
porous molding layer on the opposite side thereof from the molding 
surface, the porous support layer having a porosity of at least 20% and an 
average pore diameter in a range of 0.6 to 10 mm, the average pore 
diameter being larger than that of the porous molding layer; and means for 
holding water in the die by capillary attraction, the means comprising a 
pore structure defined by at least one of the porous molding layer and the 
porous support layer, the die having an inside surface remote from the 
molding surface; means for adding cleaning water to the die so that 
cleaning water is incorporated in the pore structure thereof; and means 
for applying air pressure to the inside surface of the die to drive water 
from the pore structure thereof. 
The means for adding cleaning water may comprises spraying means for 
spraying cleaning water onto the molding surface of the die. Preferably 
the means for applying air pressure comprises a container for compressed 
air, a conduit connecting the container to the inside surface of the die, 
and a valve in the conduit. 
A porosity in this specification refers to the volume ratio of the empty 
spaces in the porous molding layer and the porous support layer. For 
example, when either layer consists of particles, the total volume of the 
empty spaces between the particles determines the porosity. 
The pulp molding die according to the present invention has a porous 
molding layer having a specific porosity and a specific average pore 
diameter, and such a regulated molding layer gives numerous advantages. 
First of all fibers do not easily enter tile porous molding layer. 
Secondly even if fibers enter the porous molding layer, the fibers are not 
easily trapped in the porous molding layer. Thirdly even if fibers are 
trapped in the porous molding layer, the fibers are easily removed by 
backwashing so that pulp molding operations can continue without clogging 
the die. Moreover pulp articles made with the pulp molding die of the 
invention have a smooth, beautiful surface. Finally the mold has a 
sufficiently porous structure such that short fibers can pass through the 
mold, and thus the mold does not get clogged easily. 
The pulp molding die according to the present invention has a porous 
support layer adjacent to the porous molding layer on the opposite side 
thereof from the molding surface so that the die has a mechanical strength 
sufficient to withstand a pressure in a step of deposit a raw pulp 
material onto the die and another step of backwashing. 
The pulp molding die may have a rigid body, being integral to the porous 
support layer to hold the porous support layer. The rigid body may be made 
of a metal or a synthetic resin. The rigid body will prevent the die of 
the invention from bending or breaking. 
In a method for molding a pulp article, a die is introduced into a slurry 
containing fibers dispersed in a liquid. For example, the die is immersed 
in the slurry. 
Then fibers in the slurry are deposit onto the molding surface of the die 
by draining the fluid from the slurry through the molding die. For 
example, the die is immersed in a slurry, and the fluid from the slurry is 
drained through the die by reducing the pressure on the inside of the die, 
followed by removing the die from the slurry. In this example, water 
absorbed in the deposit on the die is preferably dried to a certain degree 
by reducing the pressure on the inside of the die, and then the pulp 
article is removed from the die. 
Fibers may be trapped in the porous molding layer in the die after molding 
a pulp article once or, more often than not, successively many times. To 
remove such trapped fibers, the die undergoes backwashing after every 
appropriate number of pulp molding operations. For example, the die may be 
backwashed every time after a pulp article is repeatedly molded twenty 
times. The backwashing of the die by water and air is accomplished by: 
applying cleaning water to the die after removal of a pulp article 
therefrom to incorporate water in the porous molding layer and/or the 
support layer of the die; and thereafter applying air pressure to the die 
from inside the die to drive the incorporated water from the die through 
the molding surface, thereby to remove fibers trapped in the die. A method 
of molding pulp articles according to the present invention includes this 
backwashing process so that the molding operations are smoothly repeated 
without clogging the die. 
An apparatus for molding shaped pulp articles from fiber pulp of the 
present invention can prevent the die from getting clogged and allow 
continuous operation of molding pulp articles without interruption.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1 the die has a porous molding layer 1, a support layer 2, and a 
rigid body 3. The porous molding layer 1 has a molding surface shaped to 
the desired configuration of the article to be molded. The porous molding 
layer 1 has an inside surface on the opposite side of the molding surface. 
A porous support layer 2 is adjacent to the inside surface of the porous 
molding layer 1. A rigid body 3 is integral to the porous support layer 2, 
and the rigid body 3 has drains 4. The rigid body 3 and a housing 5 define 
a chamber. The chamber is connected to a pressure chamber (not shown) and 
to a vacuum chamber (not shown ) through conduit 6 by means of 
solenoid-operated valves 7 and 8, respectively. 
The porous molding layer 1 has a porosity of at least 5%. When the molding 
layer 1 has a porosity less than 5%, the resulting die may not have 
sufficient drainage so that a molding operation becomes inefficient. 
Preferably the porous molding layer 1 has a porosity of at least 10%. 
Molding layer 1 has an average pore diameter in the range of 60 to 1000 
.mu.m. When the porous molding layer has an average pore diameter less 
than 60 .mu.m, fibers are prone to get trapped in such a molding layer and 
the trapped fibers are not easily removed by the backwash process. In 
contrast, when the porous molding layer has an average pore diameter 
greater than 1000 .mu.m, fibers are prone to get trapped in such a molding 
layer in a molding operation. Besides, a pulp article made with such a 
pulp molding die, has a rough surface. Preferably the molding layer 1 has 
an average pore diameter in the range of 120 to 700 .mu.m. 
Preferably at least 80% or, more preferably, at least 85% of the pores of 
the porous molding layer have pore diameters in the range of 25% less than 
the average pore diameter thereof to 25% more than the average pore 
diameter thereof. When pore diameters have large variance, a permeability 
of one part of a molding layer 1 may differ from that of the other part, 
and the molding die is more prone to clogging. 
Preferably the porous molding layer 1 has a thickness in the range of 0.1 
to 20 mm. Though a thin molding layer is favorable, a very thin molding 
layer having a thickness less than 0.1 mm may not have sufficient strength 
or stability in the long run. When the porous molding layer 1 has a 
thickness larger than 20 mm, the porous molding layer is more prone to 
have fibers trapped therein. Moreover, the porous molding layer may not be 
cleaned as efficiently by the backwash process. 
More preferably the porous molding layer 1 has a thickness in the range of 
0.1 to 10 mm. It is further preferable that a thickness of the porous 
molding layer 1 is at least 0.1 mm and less than 5 mm. 
A porous support layer 2 supports the porous molding layer 1, and the 
porous support layer 2 is adjacent to and may be bonded to the inside 
surface 1b of the porous molding layer 1. 
The porous support layer 2 has a porosity of at least 20%, preferably at 
least 25%, and an average pore diameter of the porous support layer 2 is 
larger than the average pore diameter of the porous molding layer 1. When 
a support layer has a porosity smaller than 20%, or when the average pore 
diameter of the porous support layer is smaller than the average pore 
diameter of the porous molding layer, the resulting die may not have 
sufficient drainage so that a molding operation becomes inefficient. 
Moreover, the porous molding layer may not be cleaned as efficiently by 
the backwash process so that the die is more prone to clogging. Preferably 
the average pore diameter of the porous support layer 2 is in the range 
0.6 to 10 mm, and further preferably in the range of 0.7 to 6 mm. 
The porous support layer 2 may be adapted to allow substantially uniform 
flow of air through the porous molding layer over the whole area thereof. 
When this condition is not met, in the backwash process the pressurized 
air may flow to areas with larger air flow and may not flow to areas with 
smaller air flow, and consequently, fibers trapped in the latter areas 
remain trapped. 
The porous support layer 2 has an average pore diameter ranging from 0.6 to 
10 mm, preferably from 0.7 to 6 mm. When the porous support layer has an 
average pore diameter larger than 10 mm, the porous support layer may not 
have sufficient mechanical strength to support the porous molding layer 1. 
Preferably the average pore diameter of the porous support layer 2 is 
1.5-10 times than that of the porous molding layer 1. When the average 
pore diameter of the porous support layer 2 is outside of this range, the 
resulting die may not have sufficient drainage so that a molding operation 
becomes inefficient. Moreover, the porous molding layer may not be 
efficiently cleaned by the backwash process, and the die is more prone to 
clogging. The porous support layer 2 may have an average pore diameter 
larger by two to six times an average pore diameter of the porous molding 
layer 1. 
The die of the present invention has, located in at least one of the porous 
molding layer and the porous support layer, an interconnected pore 
structure able to hold water. Preferably water is held by capillary 
action. The interconnected pore structure is quite efficient in drainage, 
allowing fibers in a slurry to deposit quickly on the die. 
Neither the porous molding layer 1 nor the porous support layer 2 has to 
have an upper limit in their porosity. However, either layer with too much 
porosity may not have sufficient mechanical strength. From this point of 
view, the porosity of the porous molding layer 1 and the porous support 
layer 2 should not exceed 95%. 
The porous molding layer 1 and the porous support layer 2 have certain 
ranges of porosity and average pore diameters as mentioned above. 
Moreover, the molding unit consisting of the porous molding layer 1 and 
the supporting layer 2 may have certain ranges of porosity and average 
pore diameters so that the molding unit has a certain air flow 
characteristic as a parameter for its permeability to air and liquid. 
Preferably the mold has an air flow characteristic such that when air 
pressure of 300 mm Aq is applied at the molding surface the air flow rate, 
Q, through the die is 50.ltoreq.Q.ltoreq.600, wherein Q is 
ml.A.sup.-1.s.sup.-1. A is the surface area of the molding surface in 
cm.sup.2, ml is the volume of air in cm.sup.3 that passes through said 
die, and s is seconds. 
When the air flow rate Q is less than 50 (ml.A.sup.-1.s.sup.-1), the 
molding unit may not have sufficient drainage so that a molding operation 
becomes inefficient. Moreover, the molding unit is more prone to clogging. 
On the other hand, when the air flow rate Q is larger than 600 
(ml.A.sup.-1.s.sup.-1), a backwash process does not work effectively, 
failing to prevent clogging of the molding unit. 
The porous molding layer 1 and the supporting layer 2 of the die may be 
composed of any material formed by any method as long as they have pores 
satisfying these characteristics mentioned above. Examples are shown as 
follows: 
(1) the porous molding layer 1 and/or the porous support layer 2 has a 
plurality of particles bonded together leaving empty spaces between the 
particles and the particles are insoluble to water; 
(2) the porous molding layer 1 and/or the porous support layer 2 has a 
porous material formed by electroforming; 
(3) the porous molding layer 1 and/or the porous support layer 2 has a 
honeycomb structure; and 
(4) the porous molding layer 1 and/or the porous support layer 2 has a 
perforated metal plate. 
FIGS. 1-5 show embodiments of the invention in which both the porous 
molding layer 1 and the porous support layer 2 have a plurality of 
particles bonded together. The particles are composed of any 
water-insoluble material, such as glass, ceramic, synthetic resin, metal 
and so on. Glass beads are preferable as the particles. It is easy to 
choose glass beads having desirable sizes, and thus it is easy to control 
porosity and pore diameters of the layer made of glass beads. 
The particles are preferably bonded by a resin bonding agent such as epoxy 
resin to form the porous molding layer 1 and the porous support layer 2. 
The bonding agent is not limited to epoxy resins, but it also includes 
resins that harden upon heat such as urethane resins, melamin resins, 
phenol resins, alkyd resins, etc. The bonding agent may be brazing filler 
metal such as brazing filler copper, brazing filler silver, and brazing 
filler nickel, etc. The bonding agent may be soldering materials to be 
soldered, frits, and thermoplastic resins. Alternatively the particles may 
be bonded together without any bonding agent; the particles may be bonded 
by, for example, sintering the particles. 
The mixture ratio of the resin bonding agent to particles is preferably 
3-15% by volume. When the ratio is lower than 3%, the bonding strength is 
not sufficient, resulting in increased possibility of damage. When the 
ratio is higher than 15%, enough space may not be available between the 
particles, and the permeability becomes lower, causing deterioration of 
the productivity. 
The die in which both the porous molding layer 1 and the porous support 
layer 2 are composed of water-insoluble particles are hereinafter 
described. 
The particles composing the porous molding layer may have an average 
diameter in the range of 0.2 to 1.0 mm. The molding layer may have a 
thickness larger by one to 20 times the average diameter of the particles. 
The average diameter of the particles for the porous molding layer 1 may 
range from 0.2-1.0 mm, preferably 0.4-0.9 mm, and, more preferably 0.6-0.8 
mm. When the particles are smaller than 0.2 mm in diameter, the empty 
spaces between each particle is so small that the necessary permeability 
cannot be obtained and the productivity in molding deteriorates. When the 
particles are larger than 1.0 mm in diameter, the empty spaces between 
each particle are so wide that fibers enter the molding die, resulting in 
protuberant roughness on the surface of the obtained pulp articles, 
facilitated clogging of the die, and increased difficulty in the 
separation of the pulp articles from the molding die. 
The particles forming the porous molding layer 1 have relatively uniform 
particle diameters. Preferably at least 80% of the particles have 
diameters in the range of .+-.0.2 mm from the average diameter of the 
particles. When the particle diameters do not meet this standard, empty 
spaces between particles may have varying sizes, resulting in an 
inhomogeneous surface of the molded fiber body. It is more preferable that 
at least 80% of the particles have diameters in the range of .+-.0.15 mm 
from the average diameter of the particles. 
Preferably the porous molding layer 1 has a thickness larger by 1 to 20 
times than the average diameter of the molding particles. The thickness of 
the layer needs to be at least the same as the average diameter of the 
particles forming the porous molding layer 1 to prevent the molded pulp 
articles from having a rough surface. When the thickness of the layer is 
larger than 20 times the average diameter of the molding particles, the 
porous molding layer is prone to clogging, and the backwashing does not 
work effectively. Specifically a thickness of the porous molding layer 1 
may range from 0.2 to 20 mm, preferably from 0.2 to 10 mm. It is further 
preferable that a thickness of the porous molding layer 1 is at least 0.1 
mm and less than 5 mm. 
The porous support layer 2, disposed on the inside surface of the porous 
molding layer 1, has sufficient mechanical strength and sufficient 
permeability toward air and water. For this purpose the porous support 
layer may be composed of bonded particles having an average diameter of 
1.0-10.0 mm, being larger than the average diameter of the particles in 
the porous molding layer 1, and having a thickness at least the same as 
the average diameter of the particles of the porous support layer 2. 
It is necessary for the particles of the porous support layer 2 to have a 
diameter of at least 1 mm so as to obtain the effect of washing the 
molding die. When the method of the present invention is applied, high 
effect of washing by a counter flow, i.e. backwashing, can be obtained by 
using the particles in the layer 2 preferably having an average diameter 
1.5 to 10 times, more preferably 2-5 times, larger than the average 
diameter of the particles in the layer 1. When the average diameter of the 
particles in the layer 2 is smaller than 1.5 times or 2 times that of the 
particles in layer 1, enough backwash pressure may not be obtained due to 
a pressure loss. 
On the other hand when the average diameter of the particles in the layer 2 
is larger than 10 times that of the particles in layer 1, particles in the 
porous molding layer 1 may be stuck between the particles of the porous 
support layer 2, causing the die to clog. 
Specifically the average diameter of the particles of the porous support 
layer 2 may be 1.0-10.0 mm, preferably 2.0-5.0 mm. 
Preferably the surface of the porous support layer 2 facing the porous 
molding layer 1, may have particles having diameters up to 5 mm. This 
limitation helps avoid potential inclusion of smaller particles of the 
porous molding layer 1 into empty spaces between larger particles of the 
porous support layer at their interface, which may lead to clogging, 
though the particles at the surface having diameters larger than 5 mm 
strengthen the bonding strength between the molding layer 1 and the porous 
support layer 2. 
The porous support layer 2 may have a thickness of at least the average 
diameter of the support particles in support layer 2, preferably 2-10 
times as thick as the average diameter thereof. When the porous support 
layer 2 is thinner than the average diameter of the particles thereof 2, 
the surface strength of the molding die cannot be ensured. Moreover, when 
the porous support layer 2 does not have a thickness of at least 2 times 
the average diameter of particles in that layer, some parts of the die may 
have a higher pressure than the other parts during a backwashing process 
so that the parts with less pressures are prone to leave some trapped 
fibers. This would also apply to a molding die having a rigid body having 
apertures. Therefore the thickness of the porous support layer should be 
at least twice the average diameter of the particles in the porous support 
layer 
On the other hand when the porous support layer 2 is thicker than 10 times 
the average diameter of the particles in the porous support layer 2, the 
pressure applied to the molding surface upon washing by a counter flow is 
not enough, thus causing clogging. 
Considering a pressure loss due to the porous support layer 2, it is 
preferable to make the porous support layer 2 thin, more preferably, 3-7 
times the average diameter of particles thereof. However, even if the 
porous support layer 2 should, for example, have a thickness about 10 
times the average diameter of particles thereof, the molding die can be 
washed just as effectively as when the thickness if 3-7 times, if the 
pressure from the inside is increased and apertures are added. 
Preferably the porous support layer 2 is integrally formed with a rigid 
body 3. The rigid body 3 can be made from any kind of material, such as 
metal or plastic, which can maintain a given strength to back up the 
porous support layer 2. It is also possible to have a back-up layer, as a 
rigid body 3, formed by bonding particles such as glass beads having a 
larger average particle diameter than the average diameter of particles in 
the porous support layer 2. 
When a metal plate, for example made of aluminium alloy, having a plurality 
of apertures, is used as the rigid body 3, the thickness is preferably at 
least 5 mm, more preferably 10-20 mm. When the thickness is less than 5 
mm, the rigidity of the body deteriorates and the layer 2 is prone to be 
damaged by distortion caused by repeated load upon molding pulp articles. 
Aluminium, which Young's modulus is about 7000 kgf/mm.sup.2, has far 
higher rigidity compared with a resin bonding material, which Young's 
modulus is 1000 kgf/mm.sup.2. By replenishing particles used in the porous 
support layer 2 in the apertures 4 of the rigid body, the bonding strength 
can be enhanced. It is possible that the frame has a structure having ribs 
to obtain both light weight and strength. 
Some embodiments of the invention may not require a rigid body 3 to be 
rigid. For example, the molding surface may have a small area and a 
pressure applied during molding pulp articles by suction is limited. In 
some cases a number of the pulp articles to be molded is limited. In these 
instances the strength of the molding die can be ensured by increasing the 
thickness of the layer 2, and the box-shaped frame as a rigid body can be 
used only in the peripheral part of the molding die and at the joint with 
chamber 5, on which pressure is easily applied. 
When the die has a box-shaped rigid body 3, the shape of the molding 
surface can be changed by replacement of a molding unit consisting of the 
porous molding layer 1 and the porous support layer 2, keeping the same 
rigid body 3. It makes the production of the pulp molding die easy, and 
the modification of the shape of the molding die easy. Therefore, the 
molding die can be produced at low cost. Further, in this type of pulp 
molding die, clogging can be eliminated easily by stopping the operation 
and washing the molding die by pressurized water in the same way as the 
conventional method. 
FIGS. 2-5 show embodiments of the die of the invention in which the porous 
molding layer 1 and the porous support layer 2 are integrated to the rigid 
body 3. FIG. 2 shows an embodiment in which a support layer 2 is 
maintained by a rigid body 3 adhered to the porous support layer 2 from 
below. 
FIG. 3 shows the die in which a rigid body 3 is a flat perforated plate, 
and some parts of the rigid body 3 do not contact the porous support layer 
2, leaving some empty spaces between the porous support layer 2 and the 
rigid body 3. One of the empty spaces between the porous support layer 2 
and the rigid body 3 is located at a center part of the rigid body. 
FIG. 4 shows the die which modifies the die of FIG. 3. The die of FIG. 4 
has a back-up layer 10 between the porous support layer 2 and the rigid 
body 3 in otherwise empty spaces in the molding die of FIG. 3. The back-up 
layer 10 may be composed of large particles, leaving enough pores for 
allowing sufficient flow of air or water. 
FIG. 5 shows a structure that the rigid body 3 of the molding die shown in 
FIG. 3 does not stretch to its center part unlike that of FIG. 3. 
Reference numeral 11 indicates an empty space. 
FIGS. 6(a), 6(b), 6(c), 7, and 8 show embodiments of the invention in which 
the porous molding layer 1 and/or the porous support layer 2 has a porous 
material 12 formed by electroforming. In FIGS. 6(a), 6(b), and 6(c) both 
molding layer 1 and support layer 2 are integrally formed by 
electroforming. The molding layer 1 has drains 13 having small apertures, 
and the supporting layer has drains 14 having large apertures. FIGS. 6(b) 
and 6(c) are cross sections that enlarge the A portion of FIG. 6 (a). In 
FIG. 7 molding layer 1 is formed by electroforming, and support layer 2 
consists of particles 15 bonded by a bonding agent. In FIG. 8 molding 
layer 1 consists of particles 20 bonded by a bonding agent, and support 
layer 2 is a porous article 21 formed by electroforming. By electroforming 
metal is electrically deposited onto an article to be treated to form a 
part having a desired shape. 
Alternatively the porous molding layer 1 and/or the porous support layer 2 
may have a honeycomb structure. In FIG. 9 support layer 2 has a honeycomb 
structure 16. In FIG. 9(b) a molding layer 1 consists of particles 17, 
while in FIG. 9(c) a molding layer 1 consists of a porous article 18 
formed by electroforming. 
As alternative embodiments, the porous molding layer 1 and/or the porous 
support layer 2 may be formed as a perforated metal plate. In FIGS. 10(a) 
and 10(b) a molding layer consists of particles 17, and a support layer 
consists of a perforated metal plate 19. 
A method of molding shaped pulp articles from fiber pulp is hereinafter 
described. 
The method for molding pulp articles of the present invention is 
characterized by a backwash process. In the process after the step of 
molding a pulp article, cleaning water is applied to either the porous 
molding layer 1 or the porous support layer, or preferably both the porous 
molding layer 1 and the porous support layer 2 so as to incorporate water 
in their pores, followed by applying air pressure to the die from inside 
the molding die by, for example, a volume of pre-compressed air. By this 
process, water and air pass though the porous support layer and the porous 
molding layer and fibers, stuck in the porous molding layer through 
molding pulp articles, are blown away to outside of the molding die 
through the molding surface. In the backwashing process of the invention 
water and air are applied sequentially. Preferably water is applied to the 
molding surface of the porous molding layer 1 to incorporate water in the 
pores in the layers. 
It is preferable that a pressure higher than atmospheric pressure is 
impulsively applied to the inside of the molding die in order to enhance 
the washing effect. The air pressure may be applied so as to give a 
maximum pressure at the molding surface of the die of at least 1.0 
gf/cm.sup.2, and, more preferably, at least 3.0 gf/cm.sup.2. Though the 
pressure on the molding surface is preferably high, the air pressure to 
give a pressure at the molding surface of the die up to 500 gf/cm.sup.2 is 
practical in view of enlargement of apparatus, the cost, and mechanical 
strength of the die. 1 gf is equivalent to 9.80665.times.10.sup.-3 N. 
Preferably the air pressure is applied as an impulse which rises to 1.0 
gf/cm.sup.2 in less than 0.5 seconds. It is far effective in removing 
trapped fibers to apply the pressure as an impulse, more effective by 
applying pressure as repeated impulses. 
This operation can be easily controlled by instantly opening the valve 26 
for backwashing, while maintaining the pressure of, for example, at least 
several atmospheric pressures in the compression chamber 28. Preferably 
the air pressure is applied as an impulse by connecting the die to a 
volume of precompressed air. 
Preferably the valve 26 for backwashing is an electromagnetic valve having 
a large capacity so that application of air pressure as an impulse is 
facilitated. For the same reason the volume of a compression chamber 11 is 
preferably much larger than that of the chamber of the molding apparatus 
22. Likewise the larger the inner diameter of a conduit 33, the better. 
A backwash process becomes more effective by the presence of a surfactant 
in the cleaning water. In addition to the backwashing process it is also 
preferable to wash a die in a conventional manner by applying a 
pressurized water to the molding surface of the die. 
A backwash process in accordance with the present invention can be 
performed in a short period such as several seconds after a molding 
operation. Therefore, it does not waste time in the molding cycle, and the 
effect of washing is greater than that of conventional washing methods. It 
is most effective that the washing is performed in every molding 
operation. However, it is possible to perform washing once in every 5-10 
molding operations when the shape of the molding die is simple or when the 
number of moldings is small. 
By adopting the method having the washing process mentioned above, the 
molding die can be prevented from clogging without decreasing its 
productivity. Particularly, by using the molding die of the present 
invention and adopting the method of the present invention, the eminent 
effect of washing can be obtained, and at least thousands of continuous 
moldings without clogging become possible. 
The molding die of the present invention has advantages such that: the die 
is not prone to clogging; the die gives a molded pulp article having a 
smooth surface; the die does not break after successive use; the mold can 
be prepared in a short period of time. 
The method according to the present invention includes a backwash process 
in which pressure is applied from inside the die subsequent to molding 
operations so that continuous molding operations become possible without 
interruption due to clogging of the die. The present invention enables one 
to easily form pulp articles made of pulps from recyclable used papers in 
a large quantity. 
EXAMPLES 
The present invention is hereinafter described in more detail with 
reference to Examples. However, the present invention is not limited to 
these Examples. 
FIG. 11 shows a molding die 30 consisting of a molding layer 1 and a 
support layer 2, and the molding die 30 has a shape of a disk having a 
diameter of 140 mm and a height of 25 mm. Both the porous molding layer 1 
and the porous support layer 2 are composed of glass beads having sphere 
shapes bonded by a water-resistant epoxy resin. To form the mold layer 1, 
8.7% by volume of the epoxy resin was used, while to form the support 
layer 1, 6.6% by volume of the epoxy resin was used. The porosity, the 
average pore diameter and the thickness of the porous molding layer 1 and 
the porous support layer 2 were chosen for each Example. 
The apparatus for molding shaped pulp articles from fiber pulp is shown in 
FIG. 11. A metallic chamber unit 22 has a holder 23 for holding a molding 
die 30, and drains 25, 29. The drain 25 for water and air is connected to 
a vacuum pump by means of a valve 24 and a vacuum chamber 35. 
The drain 29 is connected to a compression chamber, that is, a container 28 
for compressed air, by means of a pressure valve 26 for backwashing. The 
drain 29 is connected to a pressure valve 27 for removing a deposit cake. 
A compression chamber 28 was set to 1 kgf/cm.sup.2 (a gauge pressure). 
The molding die 30 was mounted to the chamber unit 22 through a packing 31 
by means of a lid 32 for pressing the die. The valve 24 disconnects a 
chamber inside the chamber unit 22 from the vacuum chamber 35. When the 
valve 24 is open, a pressure in the chamber inside the chamber unit 
decreases so as to suck a slurry containing fibers and to deposit fibers 
on the molding surface of the molding die 30. After a slurry is removed, 
opening the valve 24 dries the resulting fibrous deposit cake on the 
molding die. 
The valve 27 for removing a deposit cake has been closed in these steps to 
disconnect the chamber inside the chamber unit 22 from the compressed air 
provided by a compressor. Opening the valve 27 applies an air pressure to 
the chamber inside the chamber unit 22 to remove the fibrous deposit cake 
from the molding surface of the molding die 30. 
After removing the pulp article every time, water is showered over the 
molding surface of the molding die by a shower 34, disposed above the 
molding die 30, so as to incorporate water in pores in the die 30. 
A pressure valve 26 for backwashing has been closed in these steps, and 
disconnects the chamber inside the chamber unit 22 from pre-compressed air 
in the container 28 for compressed air. Opening the pressure valve 26 
provides a large volume of pre-compressed air to the chamber inside the 
chamber unit 22 so as to backwash the molding die 30. Thus the air passes 
through the die 30 in the direction of the molding surface, driving the 
incorporated water from the die 
The vacuum chamber 35 was kept under a pressure below 60 mm Hg. The 
container 28 for compressed air was kept at about one atmospheric 
pressure. 
The slurry used in this molding operation is prepared as follows. A pulp 
was made from the equal amount by weight of used newspapers and card 
boxes, and the pulp is dispersed in water to give the slurry containing 1% 
by weight of the pulp. 
Using this molding apparatus, a molding cycle consisting of eight steps 
shown in Table 1 was continuously repeated. It took about 20 seconds to 
complete each cycle. 
(TABLE 1) 
______________________________________ 
(1) A molding die is immersed into a slurry containing fibrous 
pulp. It takes one second to complete this step. 
(2) A vacuum valve 24 opens so as to reduce pressure in the 
chamber to deposit pulp on a molding surface of the die. It 
takes 1 to 3 second to complete this step. 
(3) The molding die is taken out of the slurry, keeping the valve 
24 open to dry the deposit through suction of air. It takes 
thirteen seconds to complete this step. 
(4) The vacuum valve 24 is closed 
(5) The compression valve 27 is open so as to remove the deposit 
from the molding die. It takes two seconds to complete this 
step. 
(6) Water is showered over the molding surface for one second. 
(7) The pressure valve 26 opens. 
(8) The pressure valve 26 is closed. It takes two seconds to open 
and close the pressure valve 26 once. 
(9) Go back to the step 1. 
______________________________________ 
A method for obtaining air flow characteristic of a molding die is 
described hereinafter. 
A molding die 30 was tested for its air flow characteristic which 
correlates air pressures applied to the die and air flow through the die. 
After a die in the molding apparatus underwent every 100 molding cycles, 
the die was taken out of the molding apparatus, and a molding die was 
dried by a dryer. Then the correlation of the die was measured by the 
permeability measuring apparatus shown in FIG. 12. 
The permeability measuring apparatus has a wind channel 36 to which a 
molding die 30 can be attached airtight. The molding surface of the 
molding die faces against the air flow. The apparatus has a pressure gauge 
37 for measuring a pressure of the upstream of the molding die 30, i.e. a 
pressure at the molding surface. The apparatus further includes an orifice 
plate 38 having an orifice, a differential pressure gauge 39, and a fan 
(not shown). 
A method for obtaining a "permeability ratio" is described hereinafter. 
As molding operations are repeated by the molding apparatus, a molding die 
30 loses its permeability due to an increased amount of fibers trapped in 
the die. A "permeability ratio" is defined as a parameter to indicate 
permeability of air through the die or, to be more exact, the extent of 
clogging of the die after repeated molding operations. 
The permeability ratio is defined as follows: 
the permeability ratio (%)=[Qx/Qi].times.100 wherein 
Qi is an initial air flow though a fresh die before a molding operation 
under an air pressure difference through the die of 300 mm Aq; and 
Qx is an air flow through the die after its successive molding operations 
of x times when an air pressure of 300 mm Aq is applied to the die; 
wherein 1 mmAq is equivalent to a pressure exerted by a pure water having a 
height of 1 mm under gravity, and usually x is 600. 
Since the ratio of air flows of the same die is taken, the effect on 
permeability due to its porosity, thickness, etc. would be cancelled out. 
Thus the loss of permeability during repeated molded operations of a die 
can be compared by this permeability ratio to another die. 
A "required molding time" is defined as a parameter to indicate 
permeability of water though a molding die. When a molding die is used to 
mold a pulp article of a certain thickness from a slurry, it takes time to 
deposit pulp fibers through suction, and the time depends on permeability 
of water through the molding die. In each of the examples described 
hereinafter, a time required to mold a disk shape pulp article having a 
diameter of 120 mm and a thickness of 3 mm is defined as a "required 
molding time." 
A porosity and an average pore diameter of the porous molding layer and the 
porous support layer is described hereinafter. 
Both an apparent specific gravity and a true specific gravity of a layer 
were measured and a porosity of the layer was calculated based on the two 
values. 
An average pore diameter and a pore diameter distribution were determined 
in the following three steps. 
In the first step a magnified photograph showing pores were taken of any 
part of the molding surface or any cross section of the porous molding 
layer and the porous support layer. However, when a layer consists of 
particles, sometimes it is difficult to take such a clear magnified 
photograph showing pores for water and air passage of the layer. On such 
occasions from the molding surface or from the surface of the cross 
section, particles appeared on the surfaces were removed so that pores 
were clearly recognized. Then the photograph on the surface was taken. 
In the second step pores in the photograph were painted black while the 
other parts were painted white to form a white-and-black pattern. The 
pores were defined as empty spaces among the particle on the utmost 
surface in the magnified photograph. 
In the last step the white-and-black pattern was treated with picture 
analysis so that a black pattern was approximated to circles. Then an 
average of the diameters of the circles was taken as an average pore 
diameter, and a distribution of the diameters of the circles was taken as 
a distribution of the pore diameters. 
Alternatively mercury porosimetry may be applied to the porous molding 
layer and the porous support layer having an average pore diameter up to 
300 .mu.m. 
EXAMPLE 1 
The porous molding layer 1 of the die of this Example had a porosity of 40% 
and a thickness of 4 mm. The porous support layer 2 had a porosity of 40%, 
an average pore diameter of 1.2 mm, and a thickness of 16 mm. 
The average diameter of the pores of the porous molding layer 1 was taken 
as a variable, and the permeability ratio, Q.sub.600 /Qi, of dies were 
obtained. The result is shown in FIG. 13. 
The die having the average pore diameter of the porous molding layer 1 of 
about 20 .mu.m, was clogged after molding operations were repeated 100 
times. Thus, the permeability ratio (%) on this point is taken as a ratio 
of Q.sub.100 over Qi wherein Q.sub.100 is the air flow at 300 mmAq after 
molding pulp articles 100 times with the die. 
The dies having their average pore diameters of the molding die of about 
500 .mu.m and 600 .mu.m were clogged after 300 successive molding 
operation. Thus, the permeability ratio (%) on these point are taken as 
ratios of Q.sub.300 over Qi wherein Q.sub.300 is the air flow at 300 mmAq 
of the die after 300 successive molding operation. 
EXAMPLE 2 
The porous molding layer 1 of the die of this Example had a porosity of 
40%, an average pore diameter of 480 .mu.m, and a thickness of 4 mm. The 
porous support layer 2 had a porosity of 40% and a thickness of 16 mm. 
The average diameter of the pores of the porous support layer 2 was taken 
as a variable. The other conditions were kept the same as those of Example 
1. The permeability ratio, Q.sub.600 /Qi, of dies were obtained. The 
result is shown in FIG. 14. 
EXAMPLE 3 
The porous molding layer 1 of the die of this Example had a porosity of 40% 
and a thickness of 4 mm. The porous support layer 2 had a porosity of 40% 
and a thickness of 16 mm. 
The average pore diameter of the porous molding layer 1 was taken as 80, 
280, and 480 .mu.m. The other conditions were kept the same as those of 
Example 1. For each average pore diameter, average pore diameters of the 
porous support layer were varied, and the permeability ratio, Q.sub.600 
/Qi, is plotted against the ratio of average pore diameters of the porous 
support layer over average pore diameters of the porous molding layer. The 
result is shown in FIG. 15. 
EXAMPLE 4 
The porous molding layer 1 of the die of this Example had an average pore 
diameter of 280 .mu.m and a thickness of 4 mm. The porous support layer 2 
had a porosity of 40%, an average pore diameter of 1.2 mm, and a thickness 
of 16 mm. A porosity of the porous molding layer was taken as a variable. 
The other conditions were kept the same as those of Example 1. 
A "required molding time" was measured to deposit pulp fibers to mold a 
disk shape pulp article having a diameter of 120 mm and a thickness of 3 
mm. The result is tabulated in Table 2. 
(TABLE 2) 
______________________________________ 
porosity of 
molding layer 
a required molding time 
(%) (seconds) 
______________________________________ 
3 -- 
12 15 
38 3 
59 1.5 
______________________________________ 
When a die having a porosity of the porous molding layer of 3% is used, 
even after 30 seconds the deposit cake did not reach to a thickness of 3 
mm. 
EXAMPLE 5 
The porous molding layer 1 of the die of this Example had an average pore 
diameter of 280 .mu.m a porosity of 40%, and a thickness of 4 mm. The 
porous support layer 2 had an average pore diameter of 1.2 mm and a 
thickness of 16 mm. A porosity of the support layer was taken as a 
variable. The other conditions were kept the same as those of Example 1. 
A "required molding time" was measured to deposit pulp fibers to mold a 
disk shape pulp article having a diameter of 120 mm and a thickness of 3 
mm. The result is tabulated in Table 3. 
(TABLE 3) 
______________________________________ 
porosity of 
support layer 
a required molding time 
(%) (seconds) 
______________________________________ 
18 15 
26 7 
42 3 
______________________________________ 
EXAMPLE 6 
The molding layers 1 of the dies of runs No. 1-4 of this Example had a 
thickness of 4 mm, and the porous support layer 2 a thickness of 16 mm. 
The average pore diameters and porosities of the porous molding layer and 
the support layer were varied as in Table 4. The other conditions were 
kept the same as those of Example 1. 
The die of run No. 5 is a conventional type as a comparative example in 
which a metallic net, as the porous molding layer is disposed on an 
aluminum plate with a thickness of 12 mm having apertures. 
The permeability ratio, Q.sub.600 /Qi, of dies were obtained, and the 
result is shown in Table 4. 
The die of run No. 1 was clogged after molding operations were repeated 250 
times. Thus, the permeability ratio (%) of the die is taken as a ratio of 
Q.sub.250 over Qi wherein Qi (ml/cm.sup.2.s) is an initial air flow though 
a fresh die before a molding operation when an air pressure of 300 mm Aq 
is applied to the die and; Q.sub.250 is an air flow through the die after 
its successive molding operations of 250 times when an air pressure of 300 
mm Aq is applied to the die. 
The die of run No. 5 uses a die of a conventional wire-mesh type in which a 
wire net serves as a molding layer and a main body composed of aluminum 
blocks serves as a support layer. 
(TABLE 4) 
______________________________________ 
molding layer support layer 
average pore 
poros- average pore flow rate 
diameter ity diameter porosity Q.sub.600 
(.mu.m) (%) (mm) (%) Qi Qi 
______________________________________ 
1 60 40 0.4 40 47 -- 
2 200 40 1.2 40 138 60 
3 280 40 1.2 40 218 85 
4 480 40 1.2 40 279 75 
5 560 70 3.0 15 628 50 
______________________________________ 
EXAMPLE 7 
The porous molding layer 1 of the die of this Example had an average pore 
diameter of 280 .mu.m and a porosity of 40%. The porous support layer 2 
had an average pore diameter of 1.2 mm, a porosity of 40%, and a thickness 
of 16 mm. A thickness of the molding layer was taken as a variable. The 
other conditions were kept the same as those of Example 1. The 
permeability ratio, Q.sub.600 /Qi, of dies were obtained. The result is 
tabulated in Table 5. 
(TABLE 5) 
______________________________________ 
thickness of 
molding layer 
the permeability ratio 
(mm) Q.sub.600 /Qi (%) 
______________________________________ 
0.05 -- (broken after 200 times) 
0.20 90 
5 75 
15 50 
25 35 
______________________________________ 
EXAMPLE 8 
The porous molding layer 1 of the die of this Example had an average pore 
diameter of 280 .mu.m, a porosity of 40%, and a thickness of 4 mm. The 
porous support layer 2 had an average pore diameter of 1.2 mm, a porosity 
of 40%, and a thickness of 16 mm. A thickness of the molding layer was 
taken as a variable. 
The percentage by volume of the pores of the porous molding layer having 
pore diameters in the range of 25% less than the average pore diameter 
thereof to 25% more than the average pore diameter thereof, was taken as a 
variable. The other conditions were kept the same as those of Example 1. 
The permeability ratios, Q.sub.600 /Qi, of dies was obtained. The result 
is tabulated in Table 6. 
(TABLE 6) 
______________________________________ 
the pores of the porous molding layer having pore 
permeability 
diameters in the range 25% less than the average 
ratio 
pore diameter thereof to 25% more than 
Q.sub.600 /Qi 
the average pore diameter thereof (%) 
(%) 
______________________________________ 
70 75 
85 85 
95 90 
______________________________________ 
EXAMPLE 9 
The porous molding layer 1 of the die of this Example had an average pore 
diameter of 280 .mu.m, a porosity of 40%, and a thickness of 4 mm. The 
porous support layer 2 had an average pore diameter of 1.2 mm, a porosity 
of 40%, and a thickness of 16 mm. 
An air pressure to the die during a backwash step was varied to give a 
varied maximum pressure of the molding surface of the die, and the other 
conditions were kept the same as those of Example 1. The permeability 
ratios, Q.sub.600 /Qi, of dies were obtained. The result is tabulated in 
Table 7. 
(TABLE 7) 
______________________________________ 
maximum pressure of the 
permeability ratios 
molding surface (gf/cm.sup.2) 
Q.sub.600 /Qi (%) 
______________________________________ 
0.8 45 
1 50 
3 60 
30 85 
______________________________________ 
EXAMPLE 10 
Numbers of successive 20-second cycles of molding operations of Table 1, 
using the die of FIG. 1, were determined, as a parameter of "moldability" 
of the die, until the molded articles began showing inhomogeneity in 
thickness due to clogging of the die. The molded article was made to have 
a thickness of 2 mm, and it was measured whether the molded article has a 
part having a thickness up to 0.5 mm. Thicknesses of molded articles were 
measured every 10 cycles up to 100 molding cycles, and after 100 molding 
cycles thicknesses of molded articles were measured in every 50 cycles. 
The molding surface of the die had letter imprints, and its transcription 
on the molded article was estimated. 
The die of FIG. 1 has a rigid body 3 having a thickness of 10 mm made of an 
aluminum alloy. The rigid body 3 has apertures 4 having square shapes with 
their edges of 20 mm for passing water. The rigid body 3 is connected to 
the housing 5 by bolts (not shown). The vacuum chamber was maintained at a 
pressure below 60 mmHg, and the compression chamber was maintained at one 
atmospheric pressure. After every molding operation, water is showered 
over the molding surface of the molding die. 
The molding surface 1 and the support surface 2 of the die are composed of 
glass beads bonded by 4% by volume of epoxy resin. The die has a square 
shape having its edges of 200 mm. The die has a protrusion in its center 
having horizontal cross sections of squares, leaving the length of a of 
FIG. 1 to be 50 mm. 
The glass beads of the porous molding layer 1 have a diameter distribution 
such that at least 80% of the beads have their diameters in the range 0.15 
mm less than the average diameter thereof to 0.15 mm more than the average 
pore diameter thereof. The thickness of the porous molding layer 1 
includes a contribution of particles of the porous molding layer 1 
incorporated between particles of the porous support layer 2. 
The glass beads of the porous support layer 2 have a diameter distribution 
such that substantially all the beads have their diameters in the range of 
30% less than the average diameter thereof to 30% more than the average 
pore diameter thereof. The thickness of the porous support layer 2 is 
about 25 mm. 
To prepare the die, onto a master mold made of a resin having a depression 
in its center, which has a surface shaped in the desired configuration, 
was laminated glass beads for the molding surface 1 mixed with an epoxy 
resin to a certain thickness. Then glass beads for the support surface 2 
mixed with the epoxy resin were laminated on the molding surface 1 to a 
thickness of 25 mm, followed by providing the rigid body 3 on the support 
surface 2. The molding surface 1 is bonded to the porous support layer 2 
by the epoxy resin, and the porous support layer 2 is bonded to the rigid 
body 3. The resulting die was removed from the master mold. 
Using these dies the number of continuous molding cycles was determined 
until the die got clogged by the method shown in Table 1. 
These results are tabulated in FIGS. 16-21. 
Transcription of the letters to molded articles by the present invention is 
satisfactory. 
The molding die having a specific property of the porous molding layer and 
the porous support layer is not prone to clogging, and the die gives a 
molded pulp article having a smooth surface without joints. Moreover, the 
method according to the invention prevents a die from clogging, and the 
permeability of the die does not deteriorate even after 600 molding cycles 
so that the method enables continuous molding operations. 
In contrast outside the scope of the invention the die does not have a 
sufficient permeability and is prone to clogging, resulting in a limited 
number of molding cycles. Moreover, molded pulp articles do not have a 
surface as smooth as those produced using the mold and process of the 
present invention.