Technical Field:
[0001] The present invention relates to a pulp molded article which has a threaded part
and assures a good seal with a cap. More particularly, it relates to a pulp molded
article with a threaded part which part is an accurate reproduction of a molding surface
of a mold. The present invention also relates to a method of producing the pulp molded
article.
Background Art:
[0002] Pulp containers with a threaded part which are prepared by forming a thread on a
paper cylinder by a calender press are known. However, the shapes of the threads and
containers formed by a calender press are limited in nature of the method adopted
only to provide a poor seal with a cap, allowing the contents to leak during use.
In addition, the paper cylinder itself is not strong enough to assure durability for
repeated capping and uncapping.
[0003] JP-A-8-302600 discloses a pulp molded article having on its surface a projection
such as a thread. The projection is attached with an adhesive, etc. in a separate
step or formed in the step of drying a molded article. The method of forming a projection
in the step of drying is advantageous for efficient production of molded articles
since the step of making a projection and the step of attaching the projection are
carried out on the same molding line. Where a projection is formed in a drying step,
however, cases are met with, while depending on the shape of the projection, in which
the depression on the molding surface of a mold is not accurately transferred only
to make a rounded projection or a projection with a rough surface, or the resulting
projection fails to have an increased density for securing sufficient strength.
Disclosure of the Invention:
[0004] Accordingly, an object of the present invention is to provide a pulp molded article
with a threaded part which assures a good seal with a cap.
[0005] Another object of the present invention is to provide a pulp molded article with
a threaded part which has high durability for repeated capping and uncapping.
[0006] Still another object of the present invention is to provide a pulp molded article
with a threaded part which part is an accurate reproduction of a depression on the
molding surface of a mold and has sufficient strength.
[0007] The present invention accomplishes the above objects by providing a pulp molded article
comprising a neck portion and a thread provided on an outer surface of the neck portion,
and having an overrun torque of 1 N·m or higher between the neck portion and a threaded
cap screwed on the neck portion.
[0008] The present invention provides a preferred method for producing a pulp molded article
having a thread at the neck portion thereof. In the method of the present invention,
a papermaking mold. having a threaded part at the region corresponding to the neck
portion of the above pulp molded article is employed. The method comprises the step
of papermaking with the above papermaking mold to form a pulp molded article comprising
a neck portion and a thread provided on the outer surface of the neck portion.
Brief Description of the Drawings:
[0009]
Fig. 1 is a perspective showing an embodiment of the pulp molded article according
to the present invention.
Fig. 2 is an enlarged cross-section of the neck of the pulp molded article shown in
Fig. 1.
Fig. 3(a) is a perspective showing another embodiment of the pulp molded article according
to the present invention, with a part cut away.
Fig. 4 is a cross-section along line IV-IV of Fig. 3.
Fig. 5 is a cross-section of a thread along the width direction.
Fig. 6(a) shows the step of pouring a pulp slurry; Fig. 6(b) shows the step of dewatering
by feeding a pressurizing fluid. Fig. 6(c) shows the step of opening a papermaking
mold.
Fig. 7(a) shows the step of inserting a pressing member. Fig. 7(b) shows the step
of heat drying. Fig. 7(c) shows the step of opening a heating mold.
Best Mode for Carrying out the Invention:
[0010] The present invention will be described based on its preferred embodiments with reference
to the accompanying drawings. Fig. 1 is a perspective view of a pulp molded article
1. Fig. 2 gives an enlarged cross-sectional view of the neck portion thereof. Fig.
3 is a perspective view of a pulp molded article 1' according to another embodiment
different from Fig. 1, with a part cut away. The molded articles 1 and 1' each have
a cylindrical shape comprising an open neck 2 or 2' in the upper portion thereof,
a body 3 or 3', and a bottom 4 or 4'. The necks 2 and 2' have a smaller diameter than
the respective bodies 3 and 3'.
[0011] The molded articles 1 and 1' form right angles between their bodies 3 and 3' and
bottoms 4 and 4'. That is, the bodies 3 and 3' have a taper angle of 0°. The molded
articles 1 and 1' are at least 50 mm high, preferably at least 100 mm high. For some
uses of the molded articles 1 and 1', the bodies 3 and 3' do not need to make right
angles with their bottoms 4 and 4'.
[0012] The molded articles 1 and 1' have no seams nor thicker-walled parts which might have
resulted from joining and therefore ensure sufficient strength and a good appearance.
[0013] In the molded article 1 shown in Fig. 1, the neck 2 has a first neck portion 2a on
the side of its edge and a second neck portion 2b which is between the first neck
portion 2a and the body 3 and larger than the first neck portion 2a in diameter. The
first neck portion 2a and the second neck portion 2b connect to each other via a first
step 7a. The second neck portion 2b is connected to the body 3 via a second step 7b.
Thus, the neck 2 is step-shaped. On the other hand, the neck 2' of the molded article
1' shown in Fig. 3 has a straight cylindrical shape.
[0014] In the molded article 1 shown in Fig. 1, the first neck portion 2a of the neck 2
has a lip 8, formed by curling the edge outward and downward to make one turn. The
lip 8 makes a better seal with the reverse face of a cap hereinafter described. As
shown in Fig. 2, the inner surface of the molded article 1 is laminated with a resin
film 9 to impart water resistance to the molded article 1. The laminating resin film
and the lip 8 make the molded article 1 particularly suitable for containing liquid.
[0015] The molded articles 1 and 1' are made mainly of pulp. They can be made solely of
pulp. Where pulp is used in combination with other materials, the proportion of the
other materials is preferably 1 to 70% by weight, still preferably 5 to 50% by weight.
Other materials that can be used include inorganic substances such as talc and kaolinite,
inorganic fibers such as glass fiber and carbon fiber, powder or fiber of synthetic
resins such as polyolefins, non-wood or vegetable fibers, and polysaccharides.
[0016] The second neck portion 2b of the molded article 1 shown in Fig. 1 has a threaded
outer surface having a helical thread 5. The neck 2' of the molded article 1 shown
in Fig. 3 also has a threaded outer surface having a helical thread 5'. A cap (not
shown) having a thread that meshes with the thread 5 or 5' is screwed on the neck
2 or 2'.
[0017] The contour of the thread 5 (5') may be trapezoidal, triangular, squared, rounded,
etc. A proper thread contour is chosen according to the strength of the neck 2 (2')
and productivity of the molded article 1 (1') (e.g., drying capability or shaping
capability of the thread 5 (5')). For example, a rounded thread or a triangular thread
is preferred where ease of screwing a cap on and off is of importance or where a cap
is screwed on and off frequently. A trapezoidal thread is preferred where a cap is
screwed tight with a great torque, where a cap is required to hardly loosen, or where
a cap is required to be hardly pulled out. The threads used in the molded articles
1 and 1' are trapezoidal threads whose contour is a trapezoid as shown in Fig. 5.
[0018] With a threaded cap screwed on the neck 2 (2') of the molded article 1 (1'), the
overrun torque exerted between the neck 2 (2') and the cap is 1 N·m or more, preferably
1.2 N·m or more, still preferably 5 N·m or more. Such designing provides a good seal
of the neck 2 (2') with the cap so that the cap hardly loosens even by vibrations
during transportation, effectively preventing leakage of the contents contained in
the molded article 1 (1'). In particular, the molded article 1 shown in Fig. 1 assures
an improved seal with the cap owing to the lip 8 formed on the edge of the opening
as mentioned above. The seal of the neck 2 (2') with the cap is improved as the overrun
torque becomes higher above 1 N·m. In the practical use, a cap will not overrun where
the overrun torque value is 5 N·m. Taking into consideration the production method
of the molded articles 1 and 1', the composition of the molded articles 1 and 1',
and the like, the maximum overrun torque that could be reached by the state-of-the-art
techniques is about 10 N·m. The method of measuring an overrun torque will be described
later in Examples.
[0020] If S/W in relationship (1) exceeds 1.5, the thread 5 is liable to be broken during
dewatering or drying, or the thread 5 (5') tends to fail to have a smooth surface
or an increased density. If W exceeds 10t (mm) or 10 mm in relationships (2) or (3),
it is not easy to accumulate pulp fiber along the depression of a papermaking mold
from the viewpoint of available space, considering that a papermaking net is fitted
on the papermaking mold. Further, it is not easy to put the preform taken out of the
papermaking mold into a heating mold with a good registration.
[0021] Relationship (1) is preferably represented by relationship (1') in order to accurately
form thread 5 (5') in conformity to the depression of a mold, to prevent the thread
5 (5') from being broken, to improve the surface smoothness of the thread 5 (5'),
or to increase the density of the thread 5 (5').

[0022] In the present embodiment the width W of the thread (i.e., the length of the bottom
side of the trapezoid) is preferably 0.5 to 10 mm, still preferably 2 to 6 mm, for
exerting a sufficient clamping force and enjoying freedom of design (e.g., size and
shape) of the molded article 1.
[0023] The thickness t (mm) of the molded article 1(1') (i.e., the thickness of the neck
2 (2')) is determined appropriately according to the use, etc. of the molded article
1 (1') but, in general, preferably ranges from 0.2 to 10 mm, particularly 0.4 to 2
mm. Within this range, the neck 2 (2') will make a better seal with a cap, and durability
against frequent opening and closing will be improved further.
[0024] The flank angle θ of the thread 5' (see Fig. 5), the rising angle of the flank from
the base plane B of the neck 2 (2'), is preferably greater than 0° and smaller than
90°. If the flank angle exceeds 90°, shaping by expansion of a pressing member hereinafter
described is insufficient, and pressing of the preform by the pressing memer is insufficient.
[0025] Comers 5a (see Fig. 5) made by the base plane B of the neck 2 (2') and the flanks
are preferably radiused so as to facilitate transfer of the shape of the depression
of a heating mold hereinafter described. Specifically, the corners 5a preferably have
a curvature radius R of 0.1 mm or more, particularly 0.3 to 5 mm. The two corners
5a and 5a of the thread 5 (5') shown in Fig. 5 may have the same or different curvatures.
For example, where the thread 5 (5') contour is not trapezoidal (with equal flank
lengths) shown in Fig. 5 (for example, where the thread contour is like truncated
sawtooth), the two corners 5a often have different curvatures. In either case, it
is desirable for each of the two corners 5a to have a curvature falling within the
above-recited range.
[0026] The height H of the thread 5 (5') from the base plane 2a is appropriately determined
taking into account ease of molding the thread 5 (5'), the clamping force between
the thread 5 (5') and the cap, etc. In general, the thread 5 (5') preferably has a
height H of 0.3 mm or more, particularly 0.3 to 10 mm, especially 0.5 to 4 mm, for
producing a sufficient clamping force and assuring ease of opening and closing.
[0027] While pulp molded articles having a threaded part of the above-mentioned shape and
dimensions have been difficult to produce by conventional methods, they can be produced
easily by the preferred method described hereunder.
[0028] The effective number of turns of the threaded part is preferably 0.75 or more. With
an effective number of turns less than 0.75, a cap screwed on has reduced pull-out
strength and a reduced clamping force, tending to fail to provide a sufficient seal.
Further, with this preferred effective number of turns, the difference between clamping
torque in screwing a cap on the neck 2 (2') and opening torque in screwing the cap
off the neck is smaller than that obtained with the neck of a plastic container and
a plastic cap measured under the same conditions (as to, for example, the shape and
dimensions of the container and the cap). In short, so-called loss of torque is smaller.
This means that a cap screwed on a pulp molded container even with a small clamping
torque hardly becomes loose and that a pulp molded container can be sealed with a
cap with a smaller force without spilling the contents thereby assuring safety as
compared with a plastic container.
[0029] For obtaining a good seal by screw cap engagement and securing thread durability,
the threads per inch as measured according to JIS basic dimensions is preferably 2
to 64/25.4 mm, still preferably 4 to 12/25.4 mm. While an increased number of threads
could provide an improved seal, too many turns for clamping reduces convenience in
screwing a cap on and off.
[0030] Screw blocking projections 6 are provided near the junction between the second neck
portion 2b and the second step 7b of the molded article 1 shown in Fig. 1, by which
excessive engagement between the thread 5 constituting the threaded part of the neck
2 and the thread constituting the threaded part of a cap is prevented. The molded
article 1' shown in Fig. 3 also has screw blocking projections 6' near the junction
of the neck 2' and the body 3'. The screw blocking projections 6 (6') may be the type
to stop a cap on coming into contact the leading end of the cap's thread or the type
to stop a cap when the thread of the cap gets over the projection. Since the molded
articles 1 and 1' have four threads, four screw blocking projections 6 and 6' are
formed at a 90° interval. This design will further be described as for the molded
article 1' with reference to Fig. 4. As shown in Fig. 4, each screw blocking projection
6', when observed via a cross section of the neck 2', has a first surface 6a which
is parallel with the normal of the outer surface of the neck 2' and a second surface
6b which connects the first surface 6a and the outer surface of the neck 2' depicting
a smooth downward slope in the turning direction C of a cap. In mechanically clamping
a cap, the screw blocking projections 6 (6') effectively prevent the cap from overrunning.
As a result, the torque in mechanically clamping a cap is further increased. Such
screw blocking projections 6 (6') are not necessary where a sufficiently high torque
is obtained.
[0031] It is preferred for the neck 2 (2') inclusive of the thread 5 (5') to have a center-line
average roughness Ra (JIS B0601) of 50 µm or less, particularly 25 µm or less, especially
10 µm or less, which favors a better seal of the neck 2 (2') with a cap. The neck
2 (2') with such surface smoothness can be formed by, for example, a prescribed polishing
processing technique, but the production method hereinafter described is successful
in making the neck 2 (2') with high smoothness without involving such polishing. The
smaller the center-line average roughness, the better the seal of the neck 2 (2')
with a cap. A minimum center-line average roughness that could be achievable by the
state-of-the-art techniques is about 0.1 µm. For the same reason, the largest height
Ry (JIS B0601) of the neck 2 (2') inclusive of the thread 5 (5') is preferably 500
µm or less.
[0032] The neck 2 (2') inclusive of the thread 5 (5') preferably has a wax pick grade of
5A or higher, particularly 10A or higher, especially 16A or higher, which is a measure
of surface strength characteristics (resistance to picking, resistance to fiber rising
during use, and resistance to strength reduction of the neck) measured according to
the wax pick method (JIS P8129). With this preferred surface strength, the neck exhibits
improved durability against repeated capping and uncapping so that pulp fiber rising,
surface picking, paper dust fall-off, and like surface disturbances can be prevented
to maintain the appearance of the molded article 1 (1').
[0033] In order to obtain the above-recited surface hardness as graded by the wax pick method,
a method by adding a synthetic resin or a natural resin either externally or internally
can be adopted. Methods of externally adding the resin include laminating the neck
2 (2') inclusive of the thread 5 (5') with a resin film, coating the neck 2 (2') with
a resin liquid, and impregnating the neck 2 (2') with a resin liquid, and the like.
Methods of internally adding the resin include previous addition of a resin to a pulp
slurry as a stock for making the molding article 1 (1'). The resin film includes polyolefin
films and polyester films, with polyester shrinkable films being preferred. The resin
liquids which can be used for coating or impregnation or the resins which can be previously
added to a pulp slurry include liquids containing acrylic resins, styrene resins,
polyester resins, polyolefin resins, synthetic rubber resins, vinyl acetate resins,
polyvinyl alcohol resins, wax resins, polyacrylamide resins, polyamide epichlorohydrin
resins, starch resins, gum resins, viscous resins, epoxy resins, melamine resins,
phenolic resins, urea resins, polyurethane resins, fluorine resins, silicone resins,
etc. These resin liquids may be used either individually or as a mixture of two or
more thereof.
[0034] The engagement of the neck 2 (2') of the molded article 1 (1') with a cap is preferably
such that the pull-out strength of the cap is 5 N or greater, particularly 10 N or
greater, especially 20 N or greater, when the amount of engagement between the screw
thread of the neck 2 (2') and that of the cap is 0.5 mm, and the cap is given one
turn. With this preferred pull-out strength, the neck 2 (2') secures a better seal
with the cap to prevent the contents in the molded article 1 (1') from leaking more
effectively. Further, even when the molded article 1 (1') is lifted by the cap, the
cap does not come off, and the contents are prevented from leaking. Similarly to the
aforementioned overrun torque, the greater the pull-out strength, the better the seal
between the neck 2 (2') and the cap. The upper limit of the pull-out strength, which
is sufficient for the practical use, is about 700 N, while depending on the method
of producing the molded article 1 (1'), the composition of the molded article 1 (1'),
and the like. The details of the method of measuring pull-out strength will be described
in Examples hereinafter given.
[0035] It is preferred that the neck 2 (2') inclusive of the thread 5 (5') has a density
of 0.4 to 2.0 g/cm
3, particularly 0.6 to 1.5 g/cm
3, for assuring durability and sealing properties. The density is calculated from the
weight of a cut piece of arbitrary size sliced off the neck 2 (2') and the volume
of the piece measured from the size (area) and the thickness.
[0036] It is preferred for the neck 2 (2') inclusive of the thread 5 (5') to have a transverse
compressive strength of 20 N or higher, particularly 30 N or higher, for preventing
the neck 2 (2') from being buckled. The upper limit of the transverse compressive
strength, which is sufficient for practical use, is about 500 N. For the same effect,
it is preferred for the neck 2 (2') to have a vertical compressive strength of 100
N or higher, particularly 300 N or higher. The upper limit of the vertical compressive
strength, which is sufficient for practical use, is about 700 N. These compressive
strengths are measured by using a Tensilon tensile tester at a compression rate of
20 mm/min. It is preferred for the neck 2 (2') to have such drop strength that it
does not develop a crack or deformation when dropped once from a height of 1.2 m (JIS
Z1703). In measuring the drop strength, the molded article 1 (1') is dropped to land
on its neck 2 (2').
[0037] It is preferred for the neck 2 (2') inclusive of the thread 5 (5') to have a water
vapor transmission rate (JIS Z0208) of 100 g/(m
2·24 hrs) or lower, particularly 50 g/(m
2·24 hrs) or lower, for assuring preservability of the contents, for example, for preventing
a powdered detergent from absorbing moisture and caking.
[0038] It is preferred for the molded article 1 (1') according to the present embodiment
to have a vertical compressive strength of 100 N or higher, particularly 300 N or
higher, for preventing the molded article 1 (1') from being buckled. The upper limit
of the vertical compressive strength, which is sufficient for practical use, is about
700 N. The vertical compressive strength is measured in the same manner as described
above. It is preferred for the molded article 1 (1') to have such drop strength that
it does not develop a crack or deformation when dropped once from a height of 1.2
m (JIS Z1703) to land on its base, neck or side. In measuring the drop strength, the
molded article 1 (1') is filled with contents (basically full of water, or filled
with a prescribed amount of a commercially available product), and the neck 2 (2')
is sealed with a cap.
[0039] The preferred method of producing a molded article according to the present invention
will then be described with particular reference to the production of the molded article
1' shown in Fig. 3 while referring to Figs. 6(a) through 6(c). It is a matter of course
that the molded article 1 shown in Fig. 1 can be produced by the same method.
[0040] According to the method, a papermaking mold having a threaded part in the portion
mating with the threaded part of a molded article 1' is used to make a molded article
1' having a threaded part on the outer side of the neck 2'.
[0041] In more detail, a papermaking mold 10 is prepared. The papermaking mold 10 is made
up of two splits 11 and 11, the splits providing a cavity 12 of prescribed shape on
joining. The papermaking mold 10 has a thread 16 on its cavity wall in the portion
mating with the thread 5' of the molded article 1' (hereinafter referred to as a mating
thread 16). It is desirable for the mating thread 16 to satisfy relationships (4)
and (5) described later.
[0042] The cavity 12 of the papermaking mold 10 is connected to the outside via a slurry
pouring gate 15 open to the outside. The inner side of the cavity 12 is covered with
papermaking net having a prescribed mesh size (not shown). Each split 11 has a plurality
of interconnecting passageways 13 which connect the inside (i.e., the inner surface
of the cavity 12) to the outside. Each interconnecting passageway 13 is connected
to a suction means, such as a suction pump (not shown).
[0043] In this situation, a feed nozzle 17 is inserted through the slurry pouring gate 15,
and a predetermined amount of a pulp slurry is poured into the cavity 12 through the
feed nozzle 17. The pulp slurry concentration is usually 0.1 to 5% by weight. The
pulp slurry is either heated or not. Specifically, the temperature of the pulp slurry
can range from 0 to 90°C, preferably 10 to 70°C, still preferably 40 to 40°C. To heat
the pulp slurry to an elevated temperature is preferred for increasing dewatering
efficiency. Simultaneously with pouring the pulp slurry, the cavity 12 is evacuated
by suction through the interconnecting passageways 13 toward the outside of the papermaking
mold 10, whereby the water content of the pulp slurry is sucked up, and pulp fiber
is built up on the papermaking net covering the inner wall of the cavity 12. As a
result, there is formed a water-containing preform 1' as a deposit of pulp fiber on
the papermaking net. A predetermined amount of water (diluent water) can be injected
into the cavity 12 in the initial stage and/or the final stage of forming the preform
1' to thin the pulp slurry in the cavity 12 so as to prevent thickness unevenness
of the preform 1' effectively. The initial stage of forming is the stage when the
amount of pulp having been fed into the cavity 12 is not more than 30%, particularly
not more than 20%, of the total amount of pulp necessary for preform formation. The
final stage of forming is the stage when the amount of pulp having been fed into the
cavity 12 is at least 70%, particularly 80% or more, of the total amount of pulp necessary
for preform formation. The amount of diluent water to be fed is preferably such that
the concentration of the pulp slurry is reduced to 80% or lower, particularly 20 to
60%.
[0044] The feed nozzle 17 is used as a means for feeding the pulp slurry and also a pressurizing
fluid described later. The feed nozzle 17 has a fitting plate 17a, a nozzle 17b vertically
piercing the fitting plate, a three-way valve 17c attached to the upper end of the
nozzle 17b, and a slurry feed pipe 17d and a pressurizing fluid feed pipe 17e both
connected to the three-way valve 17c. On switching the three-way valve 17c, the nozzle
17b is connected to either the slurry feed pipe 17d or the pressurizing fluid feed
pipe 17e. While the pulp slurry is being poured into the cavity 12, the nozzle 17b
is connected to the slurry feed pipe 17d. The fitting plate 17a is fitted into the
slurry pouring gate 15 to close the slurry pouring gate 15.
[0045] The resulting preform 1' is subjected to a dewatering step. As shown in Fig. 6(b),
the papermaking mold 10 is sucked from the outside through the interconnecting passageways
13. In this state, with the feed nozzle 17 remaining fixed at the position for papermaking,
the three-way valve 17c is switched over to connect the nozzle 17b to the pressurizing
fluid feed pipe 17d, and a prescribed pressurizing fluid is supplied from a pressurizing
fluid source (not shown) to the cavity 12. As stated previously, since the slurry
pouring gate 15 is shut by the fitting plate 17a, the cavity 12 is hermetic. The term
"hermetic" as used herein does not mean that the cavity 12 is completely hermetic
but that the cavity 12 is airtight enough to increase its inner pressure above a specific
level described later by introducing a pressurizing fluid. The introduced pressurizing
fluid penetrates the preform 1' and is discharged outside through the interconnecting
passageways 13.
[0046] Pressurizing fluids which can be used include steam and superheated steam (hereinafter
inclusively referred to as steam). It is particularly preferred to use superheated
steam. By blowing steam, the temperature of water present in the preform 1' rises
instantaneously by the heat transfer in condensation of steam thereby to reduce the
viscosity and the surface tension of water. As a result, the water content in the
preform 1' is blown off instantaneously and very efficiently thereby achieving improved
dewatering efficiency. Not relying chiefly on heat exchange, this dewatering technique
is extremely energically advantageous. Moreover dewatering completes instantaneously,
providing a reduction of dewatering time. Because an elastic pressing member, which
is used in the heat drying step hereinafter described, is not used for dewatering,
the time for mechanical operations involved in using a pressing member, such as insertion
into the cavity, is omitted, resulting in a reduction of the time for mechanical operations.
Further, because the blowing pressure is lower than the pressure applied in press
dewatering, there is obtained an additional advantage that the papermaking net hardly
leaves its marks on the surface of the resulting preform 1' to provide a molded article
with a good appearance.
[0047] Steam is preferably introduced to increase the inner pressure of the cavity 12 to
98 kPa or greater, particularly 196 kPa or greater, especially 294 kPa or greater.
While better results are obtained with a higher inner pressure of the cavity 12, the
upper limit of the pressure that pays is about 980 kPa because the water removal efficiency
gradually approaches saturation with a pressure increase. The term "(inner) pressure
in the cavity 12" as used herein means a difference between the steam pressure at
the inlet and that at the outlet of the cavity 12.
[0048] It is preferable to start introducing steam while the slurry stays in the cavity
12 or while the diluent water, which has been fed into the cavity 12 in the final
stage of forming the preform 1', stays in the cavity 12, whereby the water content
in the cavity 12 is expelled out of the mold to shorten the dewatering time. Steam
is preferably blown for about 2 to 20 seconds, particularly about 3 to 15 seconds.
Dewatering completes in an extremely short time. By this dewatering step, the preform
that has had a water content of 75 to 80% by weight before dewatering is dewatered
to a water content of about 40 to 70% by weight.
[0049] Where superheated steam is used, a sufficient degree of superheating is such that
the inner pressure of the mold is increased to or above the above-specified value
and that the steam is not condensed before being blown into the mold. Steam may be
overheated sufficiently, but the dewatering effect is not improved correspondingly.
[0050] In addition to the above-mentioned steam, compressed air is also useful as a pressurizing
fluid for dewatering the preform 1'. By blowing compressed air, a physical mechanism
which does not chiefly rely on heat exchange works to remove the water content from
the wet preform 1' instantaneously. Compressed air is preferably blown to increase
the pressure of the cavity 12 to 196 kPa or higher, particularly 294 kPa or higher.
The upper limit of the pressure is about 1471 kPa for the same reasons as with steam.
The time for blowing compressed air is preferably 10 to 60 seconds, particularly 15
to 40 seconds. The pressure (initial pressure) of compressed air is not particularly
limited as long as the mold inner pressure may be increased to or above the above-recited
level. The detailed description concerning steam appropriately applies to the particulars
of compressed air that are not described here.
[0051] While steam and compressed air may be used individually, a combined use of both is
preferred for dewatering efficiency. It is particularly preferred to introduce steam
followed by compressed air for the following reason. If the steam blowing time is
long, there can result a large water content variation in the vertical direction of
the preform 1'. In order to avoid this, it is effective to first blow steam to sufficiently
elevate the temperature of water contained in the preform and then blow compressed
air. When steam and compressed air are blown in this order, steam are preferably blown
at a pressure of 98 kPa or higher, particularly 196 kPa or higher, especially 294
kPa or higher, for 2 to 20 seconds, particularly 3 to 15 seconds, and compressed air
is preferably blown at a pressure of 196 kPa or higher, particularly 294 kPa or higher,
for 2 to 25 seconds, particularly 5 to 20 seconds. It is preferred for dewatering
efficiency that blowing steam be continuously followed by blowing compressed air.
[0052] After the preform 1' is dewatered to a prescribed water content, the feed of the
pressurizing fluid is stopped, and the feed nozzle 17 is taken out of the papermaking
mold 10 as shown in Fig. 6(c). The papermaking mold 10 is opened, and the preform
1' having been dewatered to the prescribed water content is removed by means of a
prescribed handling unit. The resulting preform 1' has a thread formed on its neck.
A thread excellent in sealing performance and other characteristics can be formed
by dewatering the neck to a water content of 40 to 90% by weight, particularly 70
to 90% by weight (based on the dry weight).
[0053] The preform 1' taken out is then subjected to the step of heat drying. Figs. 7(a)
through 7(c) show the heat drying step in order. Fig. 7(a) is the step of inserting
a pressing member; Fig. 7(b) the step of heat drying; and Fig. 7(c) the step of opening
the heating mold.
[0054] A heating mold 20 which is made up of a pair of split pieces 21 and 21 is separately
prepared, the pieces 21 being joined together to form a cavity 22 having a shape in
conformity to the contour of a molded article 1' to be produced. The heating mold
is previously heated to a prescribed temperature. In this embodiment, the cavity shape
of the heating mold is the same as that of the papermaking mold. The water-containing
preform 1' having been dewatered to the prescribed water content is fitted into the
cavity of the heated heating mold by means of a prescribed handling unit. There is
not a net on the inner surface of the cavity 22. Each of the split pieces 21 has a
plurality of interconnecting passageways 23 which connect the inside thereof (the
inner wall of the cavity 22) and the outside. Each interconnecting passageway 23 is
connected to a suction means (not shown), such as a suction pump.
[0055] The heating mold has a thread 26 satisfying relationships (4) and (5) shown below
formed on its cavity wall in the portion mating with the thread 5' of the preform
1' (hereinafter referred to as a mating thread).
[0056] The mating thread 26 satisfy the following relationships (4) and (5), where the length
of the contour line of the mating thread observed via a cross-section along its width
direction is taken as s (mm), and the width of the thread as viewed via a plane is
taken as w (mm). By use of the heating mold 20 having the mating thread 26 satisfying
these relationships, the thread 5' can be formed in accurate conformity with the shape
of the mating thread 26, the thread 5' is prevented from breaking, the thread 5' can
be formed with a smooth surface, and the density of the thread 5' is increased.


[0057] It is still preferred for the mating thread 26 to satisfy relationship (4'):

[0058] The flank angle θ' of the mating thread 26, which is equivalent to the flank angle
θ of the thread 5' is preferably greater than 0° and smaller than 90°. The angle of
the mating thread 26 facing the corner 5a of the thread 5' (i.e., the angle made by
the mold inner surface facing the base plane B of the neck 2' of the molded article
and the flank of the mating thread 26) preferably has a radius curvature R' of 0.1
mm or more, particularly 0.3 to 5 mm.
[0059] An expandable hollow pressing member 24 is inserted in its shrunken state into the
preform 1' while evacuating the heating mold 20 as shown in Fig. 7(a). The term "expandable"
as used herein means that (1) the pressing member 24 elastically stretches and contracts
to change its capacity or (2) the pressing member 24 is not stretchable
per se but is capable of changing its capacity with a fluid fed inside thereof or discharged
outside. The former expandable member is made of an elastic material, such as natural
rubber, urethane rubber, fluororubber, silicone rubber and elastomers. The latter
expandable member can be of flexible materials, such as plastic materials (e.g., polyethylene
and polypropylene), films of such plastic materials having aluminum or silica deposited
thereon, films of such plastic materials laminated with aluminum foil, papers, fabrics,
and the like. In the present embodiment, a balloon-like bag made of an inflatable
elastic material is used as a pressing member 24.
[0060] As shown in Fig. 7(b), a prescribed pressurizing fluid is fed into the pressing member
24 to inflate the pressing member 24, and the inflated pressing member 24 presses
the wet preform 1' toward the inner surface of the heating mold 20, i.e., the inner
wall of the cavity 22. Thus the preform 1' is dried, and the inner shape of the cavity
22 is transferred to the preform 1' simultaneously. The mating thread 26 of the heating
mold 20 satisfying relationships (4) and (5), the pulp fiber layer deposited in the
grooves of the mating thread 26 is stretched to the length s of the contour line of
the mating thread 26. As a result, the deposited pulp fiber layer can be pressed sufficiently
without breakage even if the projections corresponding to the thread is formed in
the deposited pulp fiber layer. In addition, the shape of the mating thread 26 is
precisely transferred while increasing the density of the deposit pulp fiber layer
in the grooves of the mating thread 26. Therefore, the thread 5' of the resulting
molded article 1' is a satisfactory reproduction of the configuration of the mating
thread 26, the thread 5' has a smooth surface, and the thread 5' has increased strength.
[0061] The pressurizing fluid which can be used to expand the pressing member 24 includes
air (pressurizing air), hot air (heated pressurizing air), superheated steam, oil
(heated oil), and other various liquids. From the standpoint of operating convenience,
it is preferable to use air, hot air or superheated steam. The pressurizing fluid
is preferably fed under a pressure of 0.01 to 5 MPa, particularly 0.1 to 3 MPa.
[0062] It is effective for forming the thread 5' with excellent sealing properties and other
characteristics that the heating mold 20 has satisfactory capability of liberating
air (steam generated on heating) particularly in the portion corresponding to the
neck.
[0063] After the preform (molded article) 1' has been dried sufficiently, the fluid is withdrawn
from the pressing member 24, and the pressing member 24 is let to shrink and taken
out as shown in Fig. 7(c). The heating mold 20 is opened to take out the molded article
1' by means of a prescribed handling unit. The thread 5' on the neck 2' of the resulting
molded article 1' satisfies relationships (1) and (2) or (3), representing an accurate
reverse reproduction of the shape of the depressions on the heating mold. The thread
5' has a smooth surface, an increased density, and increased strength.
[0064] Another preferred method of producing the molded article according to the present
invention will then be described. The method will be described only with regard to
differences from the above-described one. The detailed description about the foregoing
method appropriately applies to the same particulars. The method comprises feeding
a pulp slurry to a cavity of a papermaking mold composed of a set of split pieces,
which are joined together to form a cavity of prescribed shape, to form a water-containing
preform on the cavity wall (molding surface of the cavity), inserting an expandable
hollow pressing member into the preform, and feeding a prescribed fluid into the pressing
member to expand the pressing member thereby pressing the preform by the expanded
preform toward the cavity wall (molding surface) to carry out dewatering.
[0065] The papermaking mold used in this method has the same structure as shown in Fig.
6(a), having a mating thread in the portion mating with the thread of the molded article.
The pressing member to be used for press dewatering the preform can be the same as
shown in Fig. 7(a). The fluid for expanding the pressing member and the fluid feed
pressure can be the same as in the above-described method.
[0066] After the preform is dewatered to a prescribed water content, and the shape of the
cavity wall is sufficiently transferred to the preform, the fluid is withdrawn from
the pressing member to let the pressing member to shrink. The shrunken pressing member
is removed from the preform. The papermaking mold is opened, and the wet preform having
the prescribed water content is taken out by means of a prescribed handling unit.
The resulting preform has a thread formed on its neck.
[0067] The preform thus taken out is then subjected to a heat drying step. The heat drying
step is carried out almost in the same manner as for the aforementioned press dewatering
step using a pressing member, except that papermaking and dewatering are not conducted,
and a heating mold heated to a prescribed temperature is used. That is, a heating
mold made up of a set of split pieces is separately prepared, the split pieces being
joined together to form a cavity having a shape in conformity to the contour of a
molded article to be produced. The heating mold is previously heated to a prescribed
temperature. The wet preform having been dewatered to a prescribed water content is
fitted into the cavity of the heated heating mold by means of a prescribed handling
unit.
[0068] A pressing member which is different from that used in the press dewatering step
in shape and/or material, etc. is inserted into the preform. A fluid is fed into the
pressing member to expand it. The expanded pressing member presses the preform onto
the cavity inner wall. The material of the pressing member and the fluid feed pressure
can be the same as those used in the press dewatering step. In this state, the preform
is dried by the heat. Thereafter, the same operations as in the aforementioned method
are followed.
[0069] The present invention is not limited to the above-mentioned embodiments. For example,
a pulp molded article satisfying relationships (1) and (2) or (3) can be produced
by methods other than the aforementioned ones. For example, while in the above-described
methods the screw thread is formed by completely filling the grooves of a mating thread
satisfying relationships (4) and (5) with pulp fiber by pressing with a pressing member,
it is possible to use a heating mold having a mating thread which satisfies relationship
(5) but has deeper grooves than the mating thread used in the aforesaid embodiments.
In this case, a molded article having a thread satisfying relationships (1) and (2)
or (3) can be produced by appropriately adjusting the degree of pressing pulp fiber
so that a thread may be formed with the grooves of the mating thread not being completely
filled with pulp fiber.
Examples:
[0070] The present invention will now be illustrated in greater detail by way of Examples,
but it is a matter of course that the scope of the present invention is not limited
thereto.
EXAMPLE 1
[0071] A pulp molded article was produced by the method shown in Figs. 6(a) to 6(c) and
7(a) to 7(c). A pulp slurry containing NBKP/LBKP (=50 wt%/50 wt%) was used. A paper
strengthening agent, aluminum sulfate, a sizing agent, a yield improving agent, and
the like were added to the slurry, and the concentration was adjusted to 1 wt%. The
contour and dimensions of the thread on the neck of the resulting molded article are
shown in Table 1.
EXAMPLES 2 TO 5
[0072] Pulp molded articles were produced in the same manner as in Example 1 with the following
exception. In Example 2, the neck of the molded article was laminated with a polyester
shrink film. In Example 3, the neck of the molded article was coated with an acrylic
resin emulsion. In Example 4, the neck of the molded article was impregnated with
a 50 wt%/50 wt% mixture of an acrylic resin emulsion and a melamine resin emulsion.
In Example 5, a pulp slurry containing 30 wt% polyethylene fiber was used. The contour
and dimensions of the thread on the neck of the resulting molded articles are shown
in Table 1.
COMPARATIVE EXAMPLE 1
[0073] A paper cylinder (available from Shofudo; outer diameter: 70 mm; number of turns:
1.25; number of threads: 6.23 mm; thread width: 3.5 mm) was used.
Evaluation of Performance:
[0074] The resulting molded articles were evaluated for overrun torque, pull-out strength,
center-line average roughness of the neck, surface strength of the neck by the wax
pick method, and durometer hardness of the neck in accordance with the following methods.
The transverse compressive strength and the density were measured according to the
previously described methods. The seal between the neck and a cap and the degree of
fiber rising on the neck after repeated capping and uncapping were measured by the
following methods. The results obtained are shown in Table 1.
1. Overrun torque
[0075] Measurement was made with a torque gauge (Mechanical Torque Meter 2-TM75, supplied
by TOHNICHI). The cap of "Wide Hiter" available from Kao Corp. was used. The cap was
screwed on by hand, and the overrun torque (clamping torque) of the cap was measured.
2. Pull-out strength
[0076] A jig attachable to a tensile tester was attached to the cap. The cap was screwed
on the molded article to a clamping torque of 3 N·m measured with the above-described
torque gauge and pulled by the tensile tester at a speed of 20 mm/min. The force when
the cap was pulled apart the molded article was measured.
3. Center-line average roughness of neck
[0077] Measured with a surface profilometer (Surfcom 120A, available from Tokyo Seimitsu
Co., Ltd.).
4. Surface strength of neck by wax pick method
[0078] The surface strength was measured in accordance with JIS P8129. Wax (rated 2A to
20A) was applied by fusion to the surface of the neck and pulled off when cool. The
highest number wax that did not disturb the surface of the neck was taken as a surface
strength grade. A higher wax number indicates higher surface strength. However, this
method is unapplicable to molded articles coated with a thermoplastic resin or impregnated
with a large amount of a thermoplastic resin.
5. Durometer hardness of neck
[0079] Durometer hardness is a measure of resistance to collapse of the part under test.
Here, it is used as a measure of resistance to strength reduction of the neck. Durometer
hardness was measured in accordance with JIS K7215. A rubber hardness tester (GS-809
available from Teclock Corp.; Shore A type) was used. The hardness was calculated
from formula (A):

where h represents the depth (mm) of penetration.
Method of measurement:
[0080] The molded article was set vertical. The indentor of the rubber hardness tester held
by hand was pressed horizontally to the outer peripheral surface of the threaded neck.
The depth (mm) of penetration in one second pressing was measured. An average depth
of penetration in 10 measurements (n=10) as calculated by formula (A) was taken as
a durometer hardness. In case where the molded article had a thin and soft wall, the
indentor was pressed onto a specimen cut out of the molded article and placed on a
glass plate. If necessary, a D type tester was used, or where the test piece is too
thin for measurement, a stack of several thicknesses was measured.
6. Seal between neck and cap
[0081] The molded article was filled with Wide Hiter (a trade name of a bleaching powder
available from Kao Corp.), and the cap was screwed on to a clamping torque of about
1.47 N·m (15 kgf·cm) measured with the torque gauge. The molded article held upside
down was given ten vertical shakings and placed on its base. The cap was screwed off,
and adhesion of powder to the outer surface of the neck of the molded article, the
threaded part of the inner surface of the cap, and the like was observed with the
naked eye.
7. Degree of fiber rising on neck after repeated capping and uncapping
[0082] The cap was screwed on and off repeatedly, and the degree of fiber rising on the
neck was observed with the naked eye.

[0083] As is apparent from the results shown in Table 1, the pulp molded articles of Examples
1 to 5 (the products of the present invention) exhibit a good seal between the neck
and the cap. It is seen, in particular, that the molded articles of Examples 2 to
5 having a resin added externally or internally to their neck are prevented from being
raised on their neck after repetition of capping and uncapping.
EXAMPLE 6
[0084] A plastic molded article of the same shape and size as the container of Example 1
was prepared. A plastic cap (the one used in Wide Hiter available from Kao Corp.)
was screwed on each of the pulp molded article of Example 1 and the plastic molded
article to a clamping torque of 2.0 N·m (20 kgf·cm) with the torque gauge. Immediately
thereafter, the opening torque was measured.
[0085] The opening torque of the pulp molded article of Example 1 was 1.96 to 2.45 N·m,
indicating a torque loss of 0.49 to 0.98 N·m (16 to 30%), whereas the opening torque
of the plastic molded article was 0.98 to 1.47 N·m, indicating a torque loss of 1.47
to 1.96 N·m (50 to 66%).
Industrial Applicability:
[0086] The pulp molded article according to the present invention secures a good seal with
a cap. The pulp molded article of the present invention exhibits improved durability
against repeated capping and uncapping.
[0087] The pulp molded article of the present invention assures an accurate reproduction
of the depressions on the molding surface of a mold and exhibits sufficiently high
strength in the threaded part thereof.