U.S. patent application number 10/816848 was filed with the patent office on 2004-09-30 for molding base paper and molded paper vessel produced from it.
This patent application is currently assigned to OJI PAPER CO., LTD.. Invention is credited to Asayama, Yoshiyuki, Mikado, Hideyuki.
Application Number | 20040191437 10/816848 |
Document ID | / |
Family ID | 27481331 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040191437 |
Kind Code |
A1 |
Asayama, Yoshiyuki ; et
al. |
September 30, 2004 |
Molding base paper and molded paper vessel produced from it
Abstract
A molding base paper used for forming paper vessels such as a
cup or tray for foods and various industrial products is disclosed
which satisfies the following conditions (1) to (4): (1) a tensile
strength (JIS-P 8113) of at least 2.0 kN/m, (2) an elongation at
break (JIS-P 8113) of at least 1.5 %, (3) a critical compression
stress, defined by the following formula, in the range of 1 to 10
MPa: critical compression stress =A/B wherein A represents the
compression strength determined by JIS-P 8126, and B represents the
area of loaded part of the test piece in the determination of the
compression strength, and (4) an amount of the compression
deformation, caused by applying compression stress of 20
kgf/cm.sup.2in thickness direction, of at least 10%. The paper
vessels are prepared by controlling the water content of the
molding base paper at 10 to 20% and then drawing the molding base
paper at 100 to 150.degree. C.
Inventors: |
Asayama, Yoshiyuki; (Tokyo,
JP) ; Mikado, Hideyuki; (Tokyo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
OJI PAPER CO., LTD.
7-5, Ginza 4-chome
Chuo-ku
JP
|
Family ID: |
27481331 |
Appl. No.: |
10/816848 |
Filed: |
April 5, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10816848 |
Apr 5, 2004 |
|
|
|
09867629 |
May 31, 2001 |
|
|
|
Current U.S.
Class: |
428/34.2 |
Current CPC
Class: |
D21H 11/08 20130101;
D21H 11/02 20130101; D21H 27/38 20130101; Y10T 428/1303 20150115;
D21H 19/00 20130101; B31F 1/0077 20130101 |
Class at
Publication: |
428/034.2 |
International
Class: |
B65D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2000 |
JP |
2000-162889 |
May 31, 2000 |
JP |
2000-162890 |
Oct 3, 2000 |
JP |
2000-341167 |
Oct 23, 2000 |
JP |
2000-323065 |
Claims
17. A process for preparing a molded paper vessel, comprising
draw-molding under heat and pressure, a molding base paper having
the following conditions (1) to (4): (1) a tensile strength (JIS-P
8113) of at least 2.0 kN/m, (2) an elongation at break (JIS-P 8113)
of at least 1.5%, (3) a critical compression stress, defined by the
following formula, in the range of 1 to 10 MPa:Critical compression
stress =A/B wherein A represents the compression strength
determined by JIS-P 8126, and B represents the area of loaded part
of the test piece in the determination of the compression strength,
and (4) an amount of compression deformation, caused by applying
compression stress of 20 kgf/cm.sup.2 in thickness direction, of at
least 10%, so as to form a vessel which satisfies the following
formula (5):0.15.ltoreq.H/(S1).sup.1/2 (5) wherein S1 represents
the bottom area of the vessel and H represents the height
thereof.
18. The process according to claim 17, wherein said molding base
paper comprises a mechanical pulp selected from the group
consisting of ground wood pulp, refiner ground wood pulp and
thermomechanical pulp.
19. The process according to claim 18, wherein said molding base
paper comprises a mechanical pulp in an amount of 20 to 80%.
20. The process according to claim 17, wherein said molding base
paper further comprises a synthetic resin layer on at least one
surface thereof.
21. A process for preparing a molded paper vessel, comprising
draw-molding a molding base paper under heat and pressure, so as to
form a molded paper vessel which satisfies the following formula
(1):0.15.ltoreq.N/(S1).sup.1/2 (1)wherein S1 represents the bottom
area of the vessel and H represents the height thereof, said
molding base paper comprising a high density layer having a density
of 0.7 to 0.9 g/cm.sup.3 and a low density layer having a density
of lower than 0.7 g/cm.sup.3, and said molding base paper having a
basis weight of 100 to 500 g/cm.sup.2 and a density of 0.40 to 0.70
g/cm.sup.3.
22. The process of claim 21, wherein said low density paper is
mainly comprised of mechanical pulp.
23. The process of claim 22, wherein said mechanical pulp is
thermomechanical pulp.
24. The process according to claim 21, wherein said molding base
paper further comprises a synthetic resin layer on at least one
surface thereof.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a molding base paper, which
is used as a material for various packing vessels for industrial
products or the like. The vessels are also usable for keeping fresh
foods such as meats, vegetables and fishes, and various processed
foods such as lunches, side dishes, frozen foods, cakes and
noodles. In particular, the present invention relates to a molding
base paper, which causes only a low environmental load upon
disposal and which is particularly suitable for press molding.
[0002] Plastic vessels have been used in a large amount as food
vessels or packing materials for various industrial products
because they can be easily molded, they can be mass-produced and
the production costs of them are low.
[0003] Examples of the plastic vessels widely used are foamed
styrol vessels obtained by molding foaming polystyrene beads or by
press-molding foaming polystyrene sheets; polypropylene vessels,
polyethylene terephthalate vessels and polyvinyl chloride
vessels.
[0004] However, these plastic vessels have a problem in that, when
they are thrown away, the environment is burdened with a heavy
load. Namely, when the plastic vessels are buried in the ground,
they are semipermanently kept in the ground without being
decomposed. Further, when they are incinerated, the incinerator is
damaged because of a high incineration calorie thereof; they cannot
be easily and perfectly combusted and particularly, when polyvinyl
chloride is incinerated, gaseous hydrogen chloride having a strong
corroding effect might be formed.
[0005] Under these circumstances, recyclable, biodegradable vessels
made of a pulp causing only a low environmental load, and having
only a low incineration calorie are recently demanded in place of
the plastic vessels, taking the environmental problems, recycling
problems and saving of resources into consideration.
[0006] As for three-dimensional moldings made of pulp only or a
material mainly comprising pulp, pulp molded vessels have been
used.
[0007] The pulp molded vessels have been widely used as packing
vessels. The pulp molded vessels were produced by a method which
comprises preparing a net mold having concave and convex
corresponding to the shape of the intended vessel, making paper
using a pulp slurry on the net mold under suction and drying it. By
this method, the starting pulp material can be molded in a desired
shape. Thus, the vessel obtained by this method has a shape which
can be selected in a considerably wide range. However, the
production of the pulp mold takes a time and it has a problem in
the productivity.
[0008] Further, it is difficult to impart sufficient water
resistance and oil resistance, which are often demanded of tray
vessels for foods, to the pulp molded vessels. This technique
increases the cost.
[0009] For the production of moldings mainly composed of pulp other
than pulp moldings, a process wherein a base sheet mainly composed
of pulp such as a paperboard is press-molded under heating.
[0010] In this method, the base sheet having score lines is placed
between male and female molds and then pressed under heating.
[0011] This press molding method has a very high productivity
because the molding can be obtained by one pressing operation.
[0012] However, the base sheet mainly composed of paper pulp
generally has poor drawing property, extensibility and elasticity
unlike resins and metals. Therefore, when a deep press molding is
conducted for the purpose of obtaining a tray having a certain
deepness, such as 40 mm or deeper, the base sheet cannot bear the
drawing and might be broken.
[0013] Thus, when an ordinary board paper or the like was used as
the base material, only shallow vessels, so-called paper plates
having a deepness as shallow as 20 mm, could be produced. Thus, the
shape of the obtained moldings was limited in the prior art.
[0014] In addition, even when the vessels were not broken, the
folds at the score lines become uneven and the vessel surface
cannot be easily smoothened. In case the flange or rim of a tray,
which extends horizontally and outwardly from the upper edge of the
side wall of the tray, is uneven, a gap is formed due to the
unevenness when the tray is covered with a lid or when it is sealed
with a film or the like and accordingly the sealing is lowered.
Further, a breaking point at the fold causes of lowering of the
strength of the tray.
[0015] Methods for solving those problems were proposed. For
example, Japanese Patent (hereinafter referred to as "J. P") KOKAI
No. Hei 5-286023 discloses a method wherein a corrugated paper
prepared by providing many bent portions on a paper material in a
wave form to make it extensible is compressed in a mold under
heating; J. P. KOKAI No. Hei 6-134898 discloses a method wherein a
paper material having the whole concavo-convex surface to make it
extensible is moistened and then press-molded under heating; and J.
P. KOKAI No. Hei 7-214705 discloses a method wherein two or more
sheets of moistened base paper are laminated by means of an
adhesive, and the obtained laminate is corrugated and then
press-molded.
[0016] In all of these methods, however, the base sheets are
previously corrugated and thereby made extensible so that
press-processability is imparted to them and, then they are
pressed. Thus, the corrugation step is necessitated before the
pressing step and the corrugation still remains in the pressed
vessel to impair the appearance of the vessel and also to make the
strength of the vessel insufficient.
[0017] J. P. KOKAI No. Hei 7-315358 discloses a method wherein a
corrugated sheet is pressed under heating in a metal mold. In this
method, the corrugated sheet is used as the base material so that a
distortion caused by the pressing is absorbed to some extent by the
fluted structure thereof.
[0018] However, this method, wherein the corrugated sheet should be
used as the base sheet, cannot be employed when an ordinary base
material such as a paperboard is used. In addition, the creases
caused by the pressing cannot be completely removed.
[0019] J. P. KOKAI Hei 6-239334 discloses a method wherein pulp
fibers are impregnated with an olefin resin, a sheet thus having
extensibility is obtained from the mixture and then the sheet is
pressed. J. P. KOKAI Hei 10-8393 discloses a method wherein a sheet
having an improved extensibility is obtained from a mixture of
thermoplastic resin fibers and pulp fibers and then the sheet is
pressed under heating.
[0020] However, these methods are to impart press processability to
the base sheet mainly comprising paper by adding the thermoplastic
resin thereto. These references do not disclose to impart press
processability to the base sheet by controlling the physical
properties of the base paper and by constituting the specific layer
structures. In addition, the use of the thermoplastic resins in a
large amount may result in a large problem in lowering
recyclability and increasing the environmental load when it is
thrown away.
[0021] The base sheets obtained by the above-described methods have
the following defect: When a molding obtained by pressing them
under pressure has a curved part of a serious distortion, the
unevenness of the creases is serious in the curved part and it
cannot be removed by the pressing. The moldability was thus not
good.
[0022] When vessels are to be used for moist foods, drinks, soups
and noodles in soup, and for various other purposes, molded plastic
vessels having side walls higher than those of the tray-shaped
vessels and cup-shaped molded vessels are used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows a flow diagram which shows how to mold a paper
blank sheet 3 by a pair of molds 1, 2. FIG. 1A shows the state
where a blank paper sheet is set on a female mold before the
pressing. FIG. 1B shows the state where a paper molded product
exists on the concave portion of the female mold after the
pressing.
[0024] FIG. 2 is a perspective view of a paper tray showing the
shape of one example of the paper vessels.
[0025] FIG. 3 a perspective view of a paper tray showing the shape
of a different example of the paper vessels.
[0026] FIG. 4 is a cross-sectional view of a paper tray taken along
the line a-a in FIG. 2 or line b-b in FIG. 3, wherein a taper angle
(.phi.) and a radius of curvature (r) are shown.
[0027] FIG. 5 is a perspective view of a paper tray having a round
bottom.
[0028] FIG. 6 is a cross-sectional view of a paper tray, wherein a
projected bottom area (S3) of the tray is indicated.
[0029] FIG. 7 is a cross-sectional view of a paper tray having a
round bottom, wherein a virtual bottom area (S4) of the tray is
indicated.
[0030] FIG. 8 shows a plan view of a blank sheet wherein score
lines are formed both sides.
[0031] FIG. 9 shows a perspective view of a molded vessel using the
blank sheet shown in FIG. 8.
[0032] FIG. 10 shows perspective views of a rectangular molded
vessel obtained in Example 3-1 taken from different angles.
[0033] FIG. 11 shows perspective views of a square molded vessel
obtained in Example 3-2.
[0034] FIG. 12 shows perspective views of a round molded vessel
obtained in Example 3-3.
[0035] FIG. 13 shows perspective views of a round molded vessel
obtained in Example 4.
SUMMARY OF THE INVENTION
[0036] The object of the present invention is to provide a base
paper suitable for press molding. The base paper mainly comprises a
pulp and it also has such an excellent moldability in that the base
material is not easily cracked and no unevenness is formed on the
creased parts at the folding parts in the pressing step, and has a
high productivity.
[0037] Another object of the present invention is to provide paper
vessels produced by a drawing method (deep drawing vessel) and
usable as relatively deep trays and cups, such as those having a
depth of 40 mm or higher, and a method for producing them.
[0038] Still another object of the present invention is to provide
paper vessels produced by the deep drawing method, which are light
in weight and free from swelling at the body and bottom thereof and
which also have a high stiffness.
[0039] For attaining the above-described objects, the present
invention provides a molding base paper satisfying the following
conditions (1) to (4):
[0040] (1) a tensile strength (JIS-P 8113) of at least 2.0
kN/m,
[0041] (2) an elongation at break (JIS-P 8113) of at least
1.5%,
[0042] (3) a critical compression stress, defined by the following
formula, in the range of 1 to 10 MPa:
Critical compression stress=A/B
[0043] wherein A represents the compression strength determined by
JIS-P 8126, and B represents the area of loaded part of the test
piece in the determination of the compression strength, and
[0044] (4) an amount of the compression deformation, caused by
applying compression stress of 20 kgf/cm.sup.2 in thickness
direction, of at least 10%.
[0045] The present invention also provides a molding base paper
having a high-density layer having a density of 0.7 to 0.9
g/cm.sup.3 and a low-density layer having a density of lower than
0.7 g/cm.sup.3, and also having a whole basis weight of 100 to 500
g/cm.sup.2 and a whole density of 0.4 to 0.7 g/cm.sup.3, wherein
the low-density layer is mainly composed of at least one pulp
selected from among mechanical pulps, curled fibers and mercerized
pulps.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] Natural pulp fibers for forming the molding base paper
according to the present invention are, for example, wood fibers
(chemical pulps and mechanical pulps), non-wood fibers and waste
paper pulps. They are suitably selected as required.
[0047] The wood fibers include fibers from coniferous trees and
broad leaf trees. Among the wood fibers, the chemical pulps include
kraft pulps produced by using sodium hydroxide and sodium sulfide
in the step of digesting wood chips, and also sulfite pulp produced
by using a sulfurous acid and a hydrogensulfite. These pulps may be
either unbleached or bleached.
[0048] Such kraft pulps include coniferous kraft pulps and broad
leaf kraft pulps. Depending on whether the pulps are bleached or
unbleached, the pulps can be classified into bleached kraft pulps
such as coniferous bleached kraft pulps (NBKP) and broad leaf
bleached kraft pulps (LBKP) and unbleached kraft pulps such as
coniferous unbleached kraft pulps (NUKP) and broad leaf unbleached
kraft pulps (LUKP).
[0049] The mechanical pulps include ground wood pulp (GP) obtained
by grinding logs with a grinder, refiner ground wood pulp (RGP)
obtained by refining waste woods from lumbermills, and
thermomechanical pulp (TMP) obtained by heating and refining wood
chips.
[0050] In those mechanical pulps, TMP is preferred in view of the
bulkiness and strength of the resultant sheets. TMP also includes
C-TMP obtained by the chemical treatment of the wood chips followed
by the refining under pressure, and BC-TMP obtained by additional
bleaching treatment.
[0051] It is preferable that TMP is generally used in an amount of
10 to 100%, more preferably 20 to 80% on the basis of the mass of
the pulp of the molding base paper.
[0052] In those wood fiber pulps, those having long fibers obtained
from conifers such as pine, larch, cedar, fir and Japanese cypress
are suitable for improving the extensibility and strength of the
base papers.
[0053] Pulps of short fibers obtained from broad leaf trees such as
birch, beech, maple, elm and chestnut trees are also usable in
combination with the trees of long fibers so far as the effect of
the present invention is not impaired.
[0054] Non-wood fibers usable in the present invention include bast
fibers such as paper mulberry, paper bush, ganpi, flax, hemp,
kenaf, ramie, jute and Sunn hemp; seed fibers such as cotton and
cotton linters; leaf fibers such as Manila hemp, sisal and esparto;
and stem fibers such as bamboo, rice straw, wheat straw and
sugarcane bagasse.
[0055] In particular, paper mulberry, paper bush, kenaf, Manila
hemp, sisal, cotton and cotton linters are preferred because they
have long fibers and they are capable of improving the
extensibility and strength of the base paper of the present
invention.
[0056] The non-wood fibers can be digested in the same manner as
that for the wood fibers.
[0057] The waste paper pulps usable in the present invention
include, for example, waste corrugated papers and papers of waste
magazines. The waste corrugated papers are particularly preferred
because they are capable of improving the extensibility and
strength of paper sheets.
[0058] These pulp fibers are usable either alone or in combination
of two or more kinds of them.
[0059] If necessary, synthetic resin fibers can be mixed with the
fibers so far as the effect of the present invention is not
impaired. The synthetic resin fibers usable herein are, for
example, polyethylene fibers, polypropylene fibers, polyamide
fibers, polyethylene terephthalate fibers and polybutylene
terephthalate fibers. However, the amount of the synthetic fibers
to be used should be as small as possible in view of the recycling
property of the molding base paper and of lowering the
environmental load. For example, if used, it would be suitable that
the amount would be up to 10%, based on the total fibers in the
molding base paper.
[0060] The molding base paper, made of the above-described pulp
fibers, preferably has a tensile strength (JIS-P 8113) of at least
2.0 kN/m. The molding base paper preferably has an elongation at
break (JIS-P 8113) of at least 1.5%, more preferably at least 2.0%.
When the molding base paper has a tensile strength of less than 2.0
kN/m or an elongation at break of lower than 1.5%, the
extensibility of the base paper is low and the base paper is broken
at the time of press molding.
[0061] The properties of the base paper can be controlled in these
ranges by known methods such as a method wherein the base paper is
prepared in a plural layers and at least one of these layers is
made of NBKP or a method wherein a strength additive is
incorporated thereinto.
[0062] When the press mold has a curved part of a high distortion
(or larger curvature), it is necessary to absorb the distortion by
forming folding creases in the curved part in the press-molding
step. In this case, the creased part is tucked like an accordion in
the plane direction to form an uneven surface and then the uneven
surface is compressed in the thickness direction by the pressing.
Therefore, for obtaining a higher moldability, it is preferred to
control the critical compression stress as determined by the
following formula in the range of 1 to 10 MPa, preferably 3 to 9
MPa and the compressibility in the thickness direction is 10% or
higher, preferably 15% or higher. In this case, the term
"compressibility" means that in a thickness direction when a
compression stress of 20 kgf/cm.sup.2 is imposed.
Critical compression stress=A/B
[0063] wherein A represents the compression stress determined by
JIS-P 8126, and B represents the area of loaded part of the test
piece in the determination of the compression strength.
[0064] When the critical compression stress is larger than 10 MPa,
the creased part is not sufficiently tucked. When the
compressibility is lower than 10%, the compression molding in the
creased part becomes insufficient. Thus, the excellent moldability
cannot be obtained in these cases.
[0065] For controlling the critical compression stress and the
compressibility in the thickness direction in the above-described
ranges, the density of the molding base paper should be kept low.
For this purpose, rigid pulp fibers are preferred. Generally, pulp
fibers are beaten to obtain a paper sheet having a uniform
formation (namely, a mechanical external force is applied to the
pulp fibers to partially fibrillate the cellular walls of the
fibers). However, in the present invention, the beating should be
controlled to be light so as to keep the stiffness of the fibers.
For example, the degree of the beating is preferably controlled so
that the freeness (Tappi T-227 Canadian standard) of chemical pulps
should be at least 500 mlcsf, that of mechanical pulps should be at
least 180 mlcsf, that of hemp pulp and kenaf should be at least 500
mlcsf and that of waste corrugate paper pulp should be at least 500
mlcsf. For beating the pulp fibers, a beater, conical refiner,
drum-type refiner, disc-type refiner or the like is used.
[0066] A foaming agent can be incorporated into the molding base
paper to lower the density thereof so far as the effect of the
present invention is not impaired.
[0067] Heat-expanding microcapsules containing a low-boiling
solvent can be used as the foaming agent. The microcapsules are in
the form of particles having an average diameter of 10 to 30 .mu.m,
which expand to about 4 to 5 times larger diameter and about 50 to
100 times larger volume by heating to a relatively low temperature
of 80 to 200.degree. C. for a short period of time. Each
microcapsule comprises a volatile organic solvent (expanding agent)
such as isobutane, pentane, petroleum ether, hexane, a low-boiling
halogenated hydrocarbon or methylsilane covered with a
thermoplastic resin comprising a copolymer of vinylidene chloride,
acrylonitrile, an acrylic ester, etc. When the capsules are heated
to a temperature above the softening point of the polymer, the
polymer membrane starts to be softened and gradually the vapor
pressure of the expanding agent contained therein is elevated to
expand the membrane and thereby to expand the capsules. The foaming
agent is added to a pulp slurry and foams in the heating and drying
step in the production of the molding base paper or the foaming
agent foams when the molding base paper containing it is passed
through water having a high temperature. Further, light pigments
such as shirasu balloons can be added to the pulp slurry to lower
the density of the base paper in the step of making it.
[0068] Chemicals usable for producing the base paper of the present
invention are sizing agent, strength additive, yield improver, etc.
which are the same as those usually used for making paper. They are
usable if necessary.
[0069] The sizing agents usable herein include inner sizing agents
such as alkyl ketene dimers, styrene/acrylic resin and rosin. The
strength additives and yield improvers include organic compounds
such as polyacrylamide resin, polyamide epichlorohydrin resin,
polyethyleneimine and derivatives thereof, polyethylene oxide,
polyamine, polyamide, polyamide polyamine and derivatives thereof,
cationic and amphoteric starches, oxidized starch,
carboxymethylated starch, vegetable gum and polyvinyl alcohol; and
inorganic compounds such as alumina sulfate, alumina sol, colloidal
silica and bentonite. They can be used in a suitably combined
form.
[0070] These additives can be added by spraying between the paper
layers in the paper making step or by applying them to the base
paper surface in the course of or after making the paper.
[0071] A filler can be used in the course of making paper in the
present invention. The fillers include inorganic fillers such as
talc, kaolin, calcined kaolin, clay, diatomite, heavy calcium
carbonate, magnesium carbonate, aluminum hydroxide, titanium
dioxide, magnesium sulfate, silica, aluminosilicates and kaolin;
and organic synthetic fillers such as polystyrene particles and
urea/formalin resin particles. They can be used in a suitably
combined form.
[0072] In addition, paper making assistants such as a dye, a pH
regulator, a slime controller, a defoaming agent and a thickener
are suitably usable depending on the purpose.
[0073] In the paper making method of the present invention, pH is
suitably selected in the range of about 4.5 (acidic paper making
method) to about 6 to 8 (neutralized paper making method) as the
occasion demands.
[0074] Th present molding base paper is made from a slurry
comprising the above-described starting materials and chemicals by
an ordinary method. The paper machine is not particularly limited,
and an ordinary paper machine such as Fourdrinier machine, a
cylinder paper machine, a tanmo machine, an inclined paper making
machine or a paper machine of a suitable combination type is
usable.
[0075] The sheet of paper can be dried with an ordinary
multicylinder dryer, Yankee dryer or through dryer. The dryer is
not particularly limited.
[0076] The molding base paper of the present invention may be
comprised of a single layer or may be a multi-layer paper in a
multi-layer structure comprising more than two layers. The
multi-layer paper may be easily obtained by a multiple paper making
method.
[0077] The molding base paper thus obtained has a basis weight in
the range of preferably 100 to 500 g/m.sup.2, more preferably 200
to 400 g/m.sup.2. When the basis weight is below 100 g/m.sup.2, the
molded product obtained after the press molding cannot have a
sufficient strength. On the contrary, when the basis weight is
above 500 g/m.sup.2, the moldability of the creased part is reduced
unfavorably.
[0078] It is suitable that the density of the molding base paper is
preferably 0.4 to 0.7 g/cm.sup.3, more preferably 0.50 to 0.65
g/cm.sup.3.
[0079] The paper satisfying the conditions (1) to (4) of the
present invention as stated above can be prepared by the
above-described method. For well-balancing the strength,
elongation, stiffness and compressibility, it is suitable that the
molding base paper should be prepared by using a high density layer
and a low density layer in combination.
[0080] The present molding base paper is desirably a multi-layer
paper wherein a low density layer is used as an intermediate layer
and high density layers are used as outer layers sandwiching the
intermediate layer. By constructing the base paper this way, the
resultant base paper becomes bulky and has a high stiffness. The
low density layer and high density layer may be respectively
constructed by two or more layers The density of the high density
layer used in the molding base paper in a multi-paper form is
suitably 0.7 to 0.9 g/cm.sup.3, preferably 0.75 to 0.85 g/cm.sup.3.
The high density layer is preferably and mainly composed of kraft
pulp or high-quality waste paper. By constructing the base paper
this manner, the strength, elongation, stiffness and
compressibility of the resultant base paper is well balanced.
[0081] The density of the low density layer used in the molding
base paper in a multi-paper form is suitably less than 0.7
g/cm.sup.3, preferably less than 0.2 to 0.6 g/cm.sup.3.
[0082] The stiffness of the sheet of paper, paper board or the like
is represented as follows (supposing the sheet to be a
cantilever):
S=E.multidot.I/B.multidot.W=E.multidot.T.sup.3/12.multidot.W
[0083] wherein E represents Young's modulus (MPa), I represents
geometrical moment of inertia (N.multidot.cm.sup.2), B represents
the width of sample (mm), W represents the weight of the sample
(kg), and T represents the thickness of the sample (mm).
[0084] Namely, the stiffness S can be considered to be proportional
to Young's modulus and the cube of the sheet thickness.
[0085] As for the stiffness of a sheet having a multi-layer
structure like the paper board, A. T. Luey reported as follows in
Tappi November 1963, Vol. 46, No. 11: The value of the stiffness in
each layer is determined from Young's modulus and geometrical
moment of inertia of each layer. Then, the total of the values of
the stiffness in the respective layers is calculated to determine
the stiffness of the whole sheet. According to this idea, the
stiffness becomes higher as the distance from the center of the
paper thickness becomes longer or, in other words, as the paper is
thickened. Therefore, the intermediate layer is desirably bulky.
Because the stiffness is represented by (thickness).sup.3
.times.(Youngs modulus), the higher Young's modulus in the outer
layer, the more effective in the improvement in the stiffness.
[0086] Therefore, it is suitable that the density of the
intermediate layer is 0.2 to 0.6 g/cm.sup.3, preferably 0.3 to 0.5
g/cm.sup.3. When the density of the intermediate layer is below 0.2
g/cm.sup.3, the interlaminer strength is seriously lowered and, on
the contrary, when it exceeds 0.6 g/cm.sup.3, the density of the
whole base paper cannot be controlled at 0.4 to 0.7 g/cm.sup.3.
[0087] In the present invention, the density of the outer layer
should be 0.7 to 0.9 g/cm.sup.3. When the density of the outer
layer is below 0.7 g/cm.sup.3, the Young's modulus of the external
layer is low and the improvement in the stiffness of the present
invention cannot be expected. On the contrary, when the density
exceeds 0.9 g/cm.sup.3, the surface of the outer layer of the base
paper becomes excessively tense. Therefore, it is substantially
difficult to obtain a layer having a higher density in the paper
making step and, in addition, a suitable press moldability cannot
be obtained.
[0088] Although the variety of the pulp used for forming the high
density layer is not particularly limited, a pulp obtained by a
high degree of beating of conifer tree pulp such as NUKP and NBKP
to keep its stiffness is particularly desirable. For obtaining the
effect of the present invention, the basis weight of the outer
layer (a high density layer) is desirably 15 to 100 g/m.sup.2. When
the basis weight is less than 15 g/m.sup.2, it may be difficult to
obtain the layer having a high Young's modulus and also to make the
paper itself. On the contrary, when the basis weight of the outer
layer exceeds 100 g/m.sup.2, the basis weight of the low-density
layer is relatively reduced and, as a result, the density of the
whole base paper is increased to make it difficult to control it in
the range of 0.4 to 0.7 g/cm.sup.3.
[0089] In the present invention, the multi-layer base paper is
produced with a multi-layer combination former like in the
production of ordinary paper boards. For example, the pulp slurry
in an amount corresponding to a dry basis weight of several ten
g/m.sup.2 is successively laminated on wire parts of about 10
stations to form a wet sheet.
[0090] Concretely, at first, about 40 g/m.sup.2 of a pulp layer is
formed on a wire part for forming a paper layer to be the outer
layer. It is then dehydrated and moved on a blanket. Then, a paper
layer to be the intermediate layer is also formed in another wire
part repeatedly in the same manner as that described above. A
necessary number of the intermediate layers are thus placed on the
outer layer. Finally, another outer paper layer is formed to obtain
the molding base paper of the present invention.
[0091] The pulp to be used in the present invention for forming the
low density layer is that having a freeness of 200 to 650 ml,
preferably 250 to 550 ml in a re-dissociated state according to
Canadian standard of JIS-P 8121. When the freeness is below 200 ml,
the pulp fibers cannot be efficiently dehydrated and, therefore,
the squeezed sheet will have a dense structure. This fact makes the
production of a paper layer structure of a low density difficult.
On the contrary, when the freeness is over 650 ml, the density of
the sheet is excessively low and, therefore, the ply separation is
caused in the pressing step in the paper making process to cause
balloon-like swelling.
[0092] A stock having a freeness of 200 to 650 ml in the
re-dissociated form can be adjusted to a freeness of Canadian
standard of 250 to 700 ml irrespective of the pulp used as the
starting material. The determination of the freeness of the pulp by
re-dissociating the base paper is effective for determining
necessary pulp properties from a product having excellent operation
properties in a short time. It is more preferable that any of
mechanical pulp, mercerized pulp and curled fibers is contained in
an amount of 50% or higher based on the total pulp.
[0093] The pulp material used for forming the low density layer is
mainly a pulp material capable of easily foaming a paper layer of a
low density. Concretely, these pulps are mechanical pulps. The
mechanical pulps are usually obtained by mechanically breaking
woods, particularly coniferous woods and then dissociating them.
GP, TMP, RGP, etc are usable. In them, TMP and RGP are preferred.
In particular, pulps obtained from monterey pine, southern pine,
Douglas fir or the like are preferred for obtaining a paper layer
of a low density because their fibers are rigid and they are not
easily deformed. In addition, when they are used, lowering in the
density is only slight in the press-molding step. Non-wood
materials such as kenaf, reed, bamboo and bagasse (crushed sugar
cane from which sugar has been removed) are also usable. Pulps
obtained by a partial chemical treatment such as pulps obtained by
the mechanical crushing in the presence of a chemical and bleached
pulps are also included in the mechanical pulps.
[0094] Further, pulp materials used for preparing a low density
layer may contain having a density reduced by a chemical treatment
such as mercerized pulp and curled fibers are also preferably
used.
[0095] In the present invention, the above-described pulps are
mainly used for forming the low-density layer. They can be used in
the form of a suitable mixture with pulps prepared from ordinary
woods and also chemical pulps prepared from various non-wood
materials such as kenaf, reed, bamboo and bagasse.
[0096] It is effective to form an outermost layer (hereinafter
referred to as "crack preventing layer") of a paper sheet having an
elongation at break (JIS-P 8113) of at least 5% (in respect of at
least one direction of the MD and CD direction) on at least one
surface of all of the above-described molded base papers for the
purpose of preventing formation of cracks on the surface of the
resultant vessel in the course of the deep drawing process.
[0097] Moldings produced by the deep drawing technique are more
stretched than those produced by shallow drawing technique in the
molding step. In particular, a paper layer which forms the outer
side of the molding is stretched in an extent higher than a layer
which form the inner side. Thus, the outer side should have a
higher elongation at break. Preferably, the elongation at break of
the outer layer is at least 6%, more preferably 7% or higher.
[0098] The pulps usable for forming the outermost layer are those
described above. In the wood fiber pulps, those having long fibers
obtained from conifers such as pine, larch, cedar, fir and Japanese
cypress are suitable for improving the extensibility and strength
of the paper sheets.
[0099] In non-wood fibers, paper mulberry, paper bush, kenaf,
Manila hemp, sisal, cotton and cotton linters are preferred because
they have long fibers and they are capable of improving the
extensibility and strength of the paper sheet.
[0100] The chemicals usable for making papers are ordinary
chemicals used for making the molding base paper of the present
invention. They are suitably selected from among sizing agents,
strength additives, yield improvers, mineral fillers, organic rigid
fillers, dyes, pH regulators, slime controlling agents, defoaming
agents and thickening agents.
[0101] A paper sheet for the crack preventing layer having a high
elongation at break can be prepared from a slurry containing the
above-described starting materials and chemicals by the following
steps: an apparatus for press-rotating an endless, thick rubber
belt through nip rolls is applied to a part of a dryer roll in a
wet paper making machine. A wet paper is passed between the dryer
and the belt. The paper is shrunk by shrinking the previously
extended belt. This method is called Clupak method. In another
method, a paper sheet is peeled from a press roll, cylinder dryer
or Yankee dryer of a paper making machine or processing machine
with a doctor to form wrinkles. This method is called "crepe
method." The crepe method can be conducted in various ways with
various devices, such as doctor devices, depending on the position
of the crapes. For example, in duo-stress method, the crepe is
provided with a doctor in a press part of a paper machine and then
the paper is extended lengthwise and breadthwise by passing it
through grooved rolls in a middle part of the dryer.
[0102] The paper sheet for the crack preventing layer obtained in
the above-described paper-making step is not only a monolayer sheet
and it can also be a combination board having two or more layers in
the present invention.
[0103] The basis weight of the paper sheet for forming the crack
preventing layer is preferably in the range of 40 to 300 g/m.sup.2,
more preferably 50 to 150 g/m.sup.2. When the basis weight of this
paper sheet is below 40 g/m.sup.2, the tensile strength of the
sheet is insufficient and the sheet is easily broken in the molding
step and, on the contrary, when it exceeds 300 g/m.sup.2, the
density of the molding base paper obtained by the lamination with
this paper sheet as the crack preventing layer is increased to
lower the moldability of the creased part of the molding
unfavorably.
[0104] The paper sheet for forming the crack preventing layer,
obtained by this method, can be laminated with the molding base
paper by an adhesive. The lamination method is not particularly
limited. The lamination can be conducted by a wet lamination method
wherein an aqueous adhesive such as a synthetic resin emulsion,
starch or PVA is applied to the base paper and then the crack
preventing layer is pressed on the base paper through nip rolls; a
hot melt lamination method wherein a hot melt adhesive molten by
heating is applied to the base paper and then the crack preventing
layer is pressed on the base paper through nip rolls; or an
extrusion lamination method wherein a thermoplastic resin such as
polyethylene or polypropylene molten by heating is spread in the
form of a film on the base paper and then the crack preventing
layer is pressed on the base paper through nip rolls.
[0105] If necessary, a pigment coating layer comprising a pigment
and an adhesive can be formed on one or both surfaces of the
molding base paper of the present invention. By forming the coating
layer, a high printability can be imparted to the surface of the
molding base paper.
[0106] Further, a printed layer can be formed by using an ink such
as dye ink or a pigment ink with an ordinary printing machine.
[0107] The pigment used for forming the coating layer can be
suitably selected from known pigments such as calcium carbonate,
kaolin, clay, talc, titanium oxide and plastic pigments.
[0108] The adhesives used for forming the coating layer can be
suitably selected from known adhesives such as starch, casein, SBR
latex and polyvinyl alcohol.
[0109] The coating layer may be either a singly layer or multiple
layers. The amount of the coating is desirably about 20 to 30
g/m.sup.2 in total.
[0110] When such a coating layer is to be formed, the layer
directly under the coating layer preferably has an increased
freeness and smoothened surface.
[0111] The coating layer can be formed with a coating apparatus
suitably selected from various known apparatuses. It is also
possible to further form a printing layer on the coating layer.
[0112] If necessary, a water-resistant film can be formed on one or
both surfaces of the molding base paper of the present invention
for the purpose of keeping the paper from impregnation with a
liquid or leak. The water-resistant film can be formed directly on
the base paper or on the coating layer or printing layer as
desired.
[0113] The water-resistant film can be formed by coating a
water-resistant coating or by laminating a synthetic resin. The
method for the formation of the water-resistant film can be
suitably selected according to the conditions.
[0114] The coatings to be applied to the surface of the base paper
to make it water resistant include emulsions such as
microcrystalline waxes and paraffin waxes; latices such as SBR
latex and polyvinylidene chloride latex; and synthetic resin
emulsions such as acrylic resin emulsions, self-emulsifiable
polyolefin emulsions and polyethylene copolymer resin emulsions.
The apparatus for applying the water-resistant coatings is not
particularly limited, and it is suitably selected from among
ordinary bar coater, air-knife coater, roll coater, blade coater,
gate roll and size press. The coating amount of the coating after
drying is preferably about 1.0 to 20.0 g/m.sup.2 in total. The
coating layer may be either monolayered or multilayered.
[0115] The synthetic resin layer to be formed on the surface of the
base paper may be made of polyolefin resins such as polyethylene,
polypropylene and polymethylpentene; saturated polyester resins
such as polyethylene terephthalate and polybutylene terephthalate;
polyamide resins such as nylon; ethylene/vinyl alcohol copolymer;
polystyrene resin; and polyacrylonitrile resin. The base paper is
laminated or coated with one of these synthetic resins or a mixture
of two or more of them to form a water-resistant film. The method
for the lamination of the synthetic resin layer is not particularly
limited, and it is usually selected from among wet lamination, hot
melt lamination, extrusion lamination, dry lamination and thermal
lamination methods.
[0116] When the drawing is conducted by pressing under a very high
pressure, non-uniformity in color is caused along the score line
parts, in which the folding creases are formed, of the molding base
paper which will be the surface of the vessel. The color
non-uniformity seriously damages the appearance of the product to
reduce the commercial value thereof.
[0117] It is effective for solving this problem by incorporating a
pigment into the synthetic resin layer.
[0118] The amount of the pigment in the synthetic layer is
preferably in the range of 3 to 40% by weight. When it is below 30%
by weight, a sufficient effect of concealing the color
non-uniformity would not be obtained. On the contrary, when it is
larger than 40% by weight, the physical and chemical stability of
the synthetic resin is lowered to make it difficult to form a
stable synthetic resin layer on the base paper.
[0119] In particular, neck-in of the molten film occurs in T-die,
and the synthetic resin layer partially lacks because of
insufficiency in spreadability of the synthetic resin layer.
[0120] When the synthetic resin used is a polyolefinic resin and
the pigment is titanium oxide, the amount of titanium oxide is
preferably 5 to 10% by weight and the basis weight is preferably 15
to 60 g/m.sup.2.
[0121] The water-resistant coatings or synthetic resins described
above may be biodegradable thermoplastic resins.
[0122] The biodegradable thermoplastic resins are not particularly
limited so far as they have a biodegradability equal to that of
paper or higher. They include aliphatic polyesters such as
3-hydroxybutyrate/3-hydroxyvale- rate copolymer, 3-hydroxybutyrate
polymer and polycaprolactone; polyglycolides such as polylactic
acid; polyvinyl alcohol; polyvinyl alcohol/starch composite; and
cellulose derivatives such as cellulose acetate. Synthetic and/or
natural resins can be used either alone or in the form of a mixture
of them.
[0123] In those biodegradable thermoplastic resins, those
particularly preferred in the present invention are aliphatic
polyesters. The biodegradable aliphatic polyesters are excellent in
the processability when they are to be laminated with the base
paper and also in water resistance of the obtained product.
[0124] Biodegradable or non-biodegradable resins and additives may
be added to these thermoplastic resins in order to improve the
processability and physical properties of them. When the
non-biodegradable resins and additives are added, the amount of
them is desirably not heavier than the thermoplastic resins. When
the former is heavier than the latter, a bad influence would be
exerted on the biodegradability of the tray or vessel itself.
[0125] Then, the description will be made on the press molding of
the molding base paper.
[0126] <Molding Method>
[0127] Control of Water Content of Base Paper
[0128] The molded paper vessels of the present invention are
produced by so-called drawing method wherein the blank sheets for
vessels are stamped out of the base paper, the sheets are scored
with lines at necessitated parts, and each of the blank sheets is
placed between male and female molds of a press and pressed under
heating. In this process, the water content of the molding base
paper should be previously controlled.
[0129] Water content of the base paper should be in the range of 10
to 20%, preferably 11 to 17% and most preferably 12 to 15%. The
term "water content of the base paper" herein indicates weight % of
water based on the oven dry weight of the whole pulp in the molding
base paper.
[0130] When the water content of the base paper is kept in this
preferred range, the paper is plasticized to improve the
moldability thereof and also to reduce the breaking of the paper
layer in the course of the molding. As a result, the vessel
obtained by the drawing has an increased deepness, smooth and
beautiful appearance and a high stiffness.
[0131] When the water content of the base paper is below 10%, the
molding having a sufficient stiffness cannot be obtained. On the
other hand, when it exceeds 20%, the molding base paper is
blistered and the layers of the base paper are peeled off and, in
addition, a long time is necessitated for drying because the water
content is high and, as a result, the productivity is lowered
unfavorably.
[0132] The water content of the base paper can be controlled by a
method wherein water is supplied to the base paper immediately
before the press molding, or a method wherein the paper is
moistened after it is delivered from a dryer in the paper making
process and the paper is transported and stored while its water
content is kept.
[0133] Molding Method
[0134] Description will be made on the step of producing the molded
vessel from the blank sheet made of the molding base sheet of the
present invention.
[0135] According to the present invention, the drawing is conducted
with a pair of press molds. As shown in FIG. 1, a pair of press
molds are a male mold (convex mold) 1, which is a concave form and
has a shape corresponding to the inner surface of the molding to be
obtained and a female mold (concave mold) 2 which is a convex form
and has a shape corresponding to the outer surface of the molding.
In FIG. 1, the convex mold 1 moves toward the concave mold 2
downwardly, to press the blank sheet 3. In this case, the direction
in movement of the molds including a relative movement of the molds
is not limited and is readily obvious to a person skilled in the
art. For convenience for illustration, the convex mold is referred
to as a upper mold and a concave mold is referred to as a lower
mold and the description will be made with reference to the case
where the upper mold moves toward the lower mold to press the blank
sheet.
[0136] The blank sheet 3 can be heated by, for example, high
frequency heating method, hot air heating method, infrared heating
method or the like. The whole mold may be previously heated. In
this case, a means of heating the mold is necessitated. In an
ordinary heating means, the press mold is heated with an electric
heating device. In another method, the press mold is connected with
a high-frequency generator to heat the base sheet with the high
frequency heating. A combination of the electric heating with the
high frequency heating is also possible.
[0137] The heating temperature in the molding step is such that the
temperature of the heated molding base paper is in the range of
preferably 100 to 150.degree. C., more preferably 110 to
140.degree. C. When the temperature of the heated molding base
paper is below 100.degree. C., a long time is taken for the molding
to lower the productivity and, on the contrary, when the
temperature is higher than 150.degree. C., the base paper is easily
blistered particularly when it has a high water content.
[0138] The molding base paper can be controlled at the
above-described, predetermined temperature by setting it in the
heated pressing machine. In another method, the molding base paper
containing water is heated with electromagnetic waves such as
microwaves and then placed in the pressing machine.
[0139] The vessel molded from the blank sheet is taken out of the
mold. Although the vessel taken out of the mold may be air-dried,
the high-temperature vessel is preferably kept in a cooling mold
for a predetermined time to cool it.
[0140] The heat pressing mold is made of a well-known material such
as aluminum, an aluminum alloy, brass, iron, stainless steel or
ceramic.
[0141] The mold can be operated by means of any of hydraulic press,
air cylinder and cam mechanism. The clearance between the upper
mold and the lower mold can be controlled by hydraulic or air
pressure method. The pressure can be controlled by a computer
depending on the thickness of the molding, or by adjusting the
position of a stopper. In the cam mechanism, the clearance can be
controlled depending on the previously designed shape of the cam
and the descending speed of the mold.
[0142] In the press molding, the pressure is preferably in the
range of 10 to 100 kgf/cm.sup.2. When it is smaller than 10
kgf/cm.sup.2, the compression deformation in the scored part is
insufficient and, on the contrary, when it exceeds 100
kgf/cm.sup.2, the paper layer is broken at the folding creased
portions unfavorably.
[0143] The pressing time in the press molding step is preferably in
the range of 2 to 30 seconds from the viewpoints of the moldability
and workability.
[0144] <Shape of the Vessel>
[0145] The vessel of the present invention is generally open at the
upper edge and has a flange or rim at the upper edge thereof (FIGS.
2, 3 and 5). The flange may be curled.
[0146] The plan view of the vessel may be square, rectangular,
round, oval or the like. When it is rectangular, the corner is
usually round.
[0147] FIGS. 2 and 3 show examples of the vessels of the present
invention prepared by the drawing method. FIG. 2 shows a vessel in
an oval form. FIG. 3 shows a vessel in a rectangular form.
[0148] The vessel has a bottom and a side wall extending upwardly
from the bottom. The bottom is typically flat. In FIGS. 2 and 3,
the side wall upstanding from the flat bottom is not perpendicular
to the bottom but is inclined outwardly or, in other words, it is
tapered. When the side wall is perpendicular to the bottom, the
vessels cannot be piled up one by one.
[0149] FIG. 4 is a cross-sectional view of the vessel taken along
the a-a line in FIG. 2 or the b-b line in FIG. 3. In this case, the
cross-sectional view is the same between the vessels shown in FIGS.
2 and 3.
[0150] In FIG. 4, a taper angle .phi.is the angle defined by the
bottom and the side wall inside the vessel. The taper angle is
preferably 95 to 130.degree.. The radius of curvature at the corner
of the vessel defined by the bottom and the side wall is indicated
by (r) in FIG. 4.
[0151] In the paper vessel of the present invention, the corner
between the bottom and the side wall is not folded but curved. When
the radius of curvature is small, the paper is easily broken at the
corner, particularly at the four angular corners and, in addition,
wrinkles at the corner between the side walls are easily
increased.
[0152] When the radius of curvature is large, a deep vessel cannot
be obtained by the drawing and, the efficiency of the use of the
material is low. When the area of the flat bottom is, for example,
10 cm.times.10 cm, the radius of curvature is preferably about 0.5
to 2 cm. The radius of curvature should be exactly determined
according to the area of the bottom. When the value determined by
dividing the radius of curvature (r) by the square root of the
bottom area (S1) is 0.05 to 0.2, a deep vessel free from the
breakage of the paper can be obtained by the drawing.
[0153] In the present invention, vessels not having the flat bottom
can be obtained in addition to the above-described vessels having
the roughly flat bottom and roughly flat sidewall. For example, as
shown in FIG. 5, a semispherical vessel can be produced. A part of
the bottom of the vessel as shown in FIG. 5 can be turned over
inside the vessel with another pressing machine after the molding,
so that the placing of the vessel can be stabilized.
[0154] <Area of the Bottom>
[0155] The area of the bottom (S1) is the area of a part of the
vessel which part is brought into contact with a flat surface when
the vessel is placed on the flat surface. When the area of the
bottom is not easily determined, either projection bottom area S3
or virtual bottom area S4 as explained by the following methods (A)
and (B) can be employed.
[0156] (A) When the sidewall is almost flat, the projection bottom
area is the area of a part surrounded by a line drawn by the
intersection of a line of a sidewall ridge rectangular to the edge
and a line extending from the flat surface of the bottom. The
projection bottom area S3 is shown in FIG. 6. FIG. 6 is a
cross-sectional view similar to FIG. 4.
[0157] (B) The internal cubic volume V of the vessel is determined.
The open area S2 at the top of the vessel is determined. The
virtual bottom area S4 was determined according to the formula:
V=(S4+S2).times.H/2.
[0158] In this case, S2 is the area surrounded by the peripheral
edge of the open side of the vessel as shown in FIG. 7, which is a
cross-sectional view like FIG. 4.
[0159] <Height of Vessel>
[0160] The paper vessel obtained by the drawing is relatively deep
in the present invention. The depth (height of the vessel) should
be decided depending on the area of the bottom of the vessel.
[0161] Namely, the paper vessel obtained by the drawing in the
present invention is characterized by satisfying the following
formula (1):
0.2.ltoreq.H/(S1).sup.1/2 (1)
[0162] wherein S1 represents the bottom area of the vessel and H
represents the height thereof.
[0163] S1 is as described above. If necessary, the value of S3 or
S4 described above can be employed as the bottom area S1.
[0164] The value obtained by dividing the height H by the square
root of the bottom area S1 according to formula (1) is preferably
0.3 to 1.2. Particularly when it is 0.4 or above, the vessel can be
in the form of a cup.
[0165] When the value is below 0.2, it is suggested that a
sufficient drawing could not be attained. The obtained vessel is
unsuitable for receiving materials having a high water content or
for liquids. In addition, in such a case, the effect of the side
wall for increasing the stiffness of the vessel is
insufficient.
[0166] When the value is larger than 1.2, the vessel obtained by
the deep drawing is too deep to keep the base paper from being
broken in the molding step.
[0167] When the vessel does not have the substantially plane
bottom, it is preferable that the following formula (2) should be
satisfied in the relationship between the height H and the opening
area S2:
0.15.ltoreq.H/(S2).sup.1/2 (2)
[0168] The shape of the vessel is the same as that in FIG. 5. S2 in
FIG. 5 is the same as that in FIG. 7.
[0169] <Walls of Molded Vessels>
[0170] For obtaining the vessel having the above-described shape
and a practically necessitated stiffness while the breakage in the
curved area thereof is prevented, a molding base paper having a low
density and a high strength must be used as a material for vessel
wall to be formed by the drawing. For obtaining such a base paper,
mechanical pulp containing a large amount of lignin remaining
therein is preferred. The amount of the mechanical pulp in the
whole paper can be determined by determining Kappa number according
to JIS P-8211.
[0171] Namely, Kappa number of the whole pulp used for forming the
vessel of the present invention is preferably 40 to 160.
[0172] The molding base paper of the present invention contains
natural pulp as the main component, and its moldability is superior
to that of conventional molding base papers.
[0173] The following Examples will further illustrate the present
invention, which by no means limit the scope of the present
invention. Unless otherwise stated, parts are given by weight of
the solid.
EXAMPLE 1-1
[0174] With a disc refiner, commercially available NBKP was beaten
to 550 mlcsf (Tappi T-227, Canadian standard), monterey pine TMP
was beaten to 300 mlcsf and commercially available NUKP was beaten
to 550 mlcsf.
[0175] From these stocks, a paper board composed of three layers,
i.e. the first layer of 40 g/m.sup.2 NBKP, the second layer of 250
g/m.sup.2 TMP and the third layer of 40 g/m.sup.2 NUKP, was
prepared with a multi-layer combination paper machine. The paper
board was used as the molding paper base.
[0176] The tensile strength, elongation at break, critical
compression stress and compression deformation in thickness
direction of the base paper were determined by methods described
below.
[0177] The base paper thus obtained was used to form a tray, and
the moldability thereof was evaluated.
EXAMPLE 1-2
[0178] A stock composed of 80 parts of commercial LBKP beaten to
500 mlcsf with a disc refiner, 20 parts of commercial NBKP beaten
to 500 mlcsf and 10 parts of foaming microcapsules (trade name:
Matsumoto Microsphere F-30D; a product of Matsumoto Yushi Seiyaku
Co., Ltd.) was prepared.
[0179] A sheet of paper having a basis weight of 150 g/m.sup.2 was
made from the stock with an experimental machine for making
hand-made paper, and then dried with a rotary drier at 110.degree.
C. The hand-made paper was used as the molding base paper and
evaluated in the same manner as that of Example 1-1.
EXAMPLE 1-3
[0180] Commercial NBKP was beaten to 600 mlcsf with a disc refiner
to obtain a stock. A sheet of paper having a basis weight of 260
g/m.sup.2 was made from the stock with an experimental machine for
making hand-made paper, and then dried with a rotary drier at
110.degree. C. The hand-made paper was used as the molding base
paper and evaluated in the same manner as that of Example 1-1.
EXAMPLE 1-4
[0181] Monterey pine TMP was beaten to 300 mlcsf with a disc
refiner to obtain a stock. A sheet of paper having a basis weight
of 280 g/m.sup.2 was made from the stock with an experimental
machine for making hand-made paper, and then dried with a rotary
drier at 110.degree. C. The hand-made paper was used as the molding
base paper and evaluated in the same manner as that of Example
1-1.
Comparative Example 1-1
[0182] 50 parts by weight of curled fiber (a product of
Weyerhaeuser Co.) and 50 parts by weight of monterey pine TMP were
dissociated and mixed together without beating to obtain a stock. A
sheet of paper having a basis weight of 290 g/m.sup.2 was made from
the stock with an experimental machine for making hand-made paper.
The paper was used as the molding base paper and evaluated in the
same manner as that of Example 1-1.
Comparative Example 1-2
[0183] The evaluation was conducted in the same manner as that of
Example 1-1 except that the molding base paper was replaced with a
production filter paper (trade name: Standard Filter Paper No. 2; a
product of Advantech Toyo (KK); basis weight: 125 g/m.sup.2).
Comparative Example 1-3
[0184] The evaluation was conducted in the same manner as that of
Example 1-1 except that the molding base paper was replaced with K
liner (trade name: NRK 280; a product of Oji Paper Co., Ltd.; basis
weight: 280 g/m.sup.2).
Comparative Example 1-4
[0185] The evaluation was conducted in the same manner as that of
Example 1-1 except that the molding base paper was replaced with a
base paper for cups (a product of Shin-Fuji Seishi (KK); basis
weight: 290 g/m.sup.2).
[0186] (Evaluation Methods)
[0187] (1) Tensile Strength
[0188] Test pieces obtained by cutting a test paper to a width of
15 mm and length of 250 mm respectively in the flow direction and
the cross direction were kept under conditions of 23.degree. C. and
50% RH for at least 24 hours to control the moisture thereof. Then,
the tensile strength of the test pieces was determined with
Strograph M2 tester (a product of Toyo Seiki Seisaku-sho, Ltd.) at
a rate of pulling of 20 mm/min according to JIS-P 8113.
[0189] (2) Elongation at Break
[0190] Test pieces obtained by cutting a test paper to a width of
15 mm and length of 250 mm respectively in the flow direction and
the cross direction were kept under conditions of 23.degree. C. and
50% RH for at least 24 hours to control the moisture thereof. Then,
the elongation at break of the test pieces was determined with
Strograph M2 tester (a product of Toyo Seiki Seisaku-sho, Ltd.) at
a rate of pulling of 20 mm/min according to JIS-P 8113.
[0191] (3) Critical Compression Stress
[0192] Test pieces obtained by cutting a test paper to a width of
12.7 mm and length of 152.4 mm respectively in the flow direction
and the cross direction were kept under conditions of 23.degree. C.
and 50% RH for at least 24 hours to control the moisture thereof.
Then, the compression strength A of the test pieces was determined
with digital ring crush tester X-1104 (a product of (KK) Orientech)
according to JIS-P 8126. Further, the area B of the loaded part of
the test piece in the step of determining compression strength was
determined. The critical compression stress was calculated
according to the following formula:
Critical compression stress=A/B
[0193] wherein the unit of critical compression stress is MPa, unit
of compression strength is N, and the area of the loaded part of
the test piece is calculated by the formula:
(thickness of test piece)(mm).times.152.4 mm
[0194] wherein the thickness of the test piece was determined
according to JIS-P 8118 by using a sample having a moisture
controlled under conditions of 23.degree. C. and 50% RH for at
least 24 hours.
[0195] (4) Compression Deformation
[0196] The moisture of 50 mm.times.50 mm test pieces was controlled
under conditions of 23.degree. C. and 50% RH for at least 24 hours.
Each test piece was pressed in the thickness direction with
Strograph M2 tester (a product of Toyo Seiki Seisaku-sho, Ltd.) at
a compression rate of 1.0 mm/min to draw a stress-distortion curve
to determine the compression (distortion) under a compression
stress of 20 kgf/cm.sup.2.
[0197] (5) Moldability
[0198] A molding base paper was scored with 24 lines to form a
molding blank sheet as shown in FIG. 8. The blank sheet was molded
into a tray with the molds and a press molding machine under
conditions comprising a press pressure of 35 kgf/cm.sup.2, press
temperature of 150.degree. C. and press time of 5 seconds to form a
tray (having a major axis of about 20 cm, a 5 minor axis of about
14 cm and a height of about 4 cm) as shown in FIG. 9.
[0199] The moldability was evaluated according to the following
three criteria:
[0200] .largecircle.: The sheet could be molded in a tray shape and
the obtained product had the smooth surface.
[0201] .DELTA.: Although the sheet could be molded in the tray
shape, the obtained product had the rough surface particularly in
the folding creased part.
[0202] X: The blank was broken in the molding step to make the
molding in the tray shape impossible.
[0203] The results of the evaluation are shown in Tables 1 and
2.
1 TABLE 1 Basis weight Molding base paper (g/m.sup.2) Example 1-1
NBKP/TMP/NUKP 336 Example 1-2 LBKP + NBKP + foaming agent 156
Example 1-3 NBKP hand-made paper 255 Example 1-4 TMP hand-made
paper 282 Comp. Ex. 1-1 Curled fiber/TMP 290 Comp. Ex. 1-2 No. 2
filter paper 132 Comp. Ex. 1-3 NRK 280 274 Comp. Ex. 1-4 Base paper
for cups 289 Thickness Basis weight of Density of (mm) Density each
layer each layer Example 1-1 0.642 0.52 NBKP 0.70 TMP 0.48 NUKP
0.70 Example 1-2 0.997 0.16 Example 1-3 0.493 0.52 Example 1-4
0.970 0.29 Comp. Ex. 1-1 1.040 0.28 Comp. Ex. 1-2 0.281 0.47 Comp.
Ex. 1-3 0.335 0.82 Comp. Ex. 1-4 0.327 0.88
[0204]
2 TABLE 2 Tensile Elongation Critical strength at break compression
Compression (kN/m) (%) stress (MPa) deformation MD CD MD CD MD CD
(%) Moldability Example 1-1 19.7 9.4 2.4 5.7 7.8 5.7 17
.largecircle. Example 1-2 2.4 2.8 1.1 74 .largecircle. Example 1-3
7.3 4.4 3.5 11 .largecircle. Example 1-4 6.4 2.7 1.7 20
.largecircle. Comp. Ex. 1-1 6.2 3.4 1.4 3.0 1.9 1.4 36 X Comp. Ex.
1-2 3.4 1.7 1.4 3.3 3.7 2.6 22 X Comp. Ex. 1-3 16.8 7.3 2.4 6.5
14.8 11.0 10 .DELTA. Comp. Ex. 4 23.1 9.9 2.6 8.3 15.8 11.6 8.4
.DELTA.
[0205] It is clear from Tables 1 and 2 that the molding base paper
sheets of the present invention have excellent moldability because
they are not cracked and the folding creased parts thereof do not
become uneven in the molding step.
EXAMPLE 2-1
[0206] The following three kinds of pulps (1) to (3) were combined
together in the following order at a wire speed of 300 m/min with
an experimental orientation paper machine of Kumagai Riki Kogyo to
make a combined paper.
[0207] (1) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0208] (2) Monterey pine TMP having 350 mlcsf, 180 g/m.sup.2
[0209] (3) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0210] (These Stocks were Beaten to a Predetermined Freeness with
KRK high-concentration Disc Refiner-type Beater of Kumagai Riki
Kogyo)
[0211] In the lamination, a 2.0% aqueous dispersion of starch
(ONL510: a product of Oji Corn Starch) was sprayed on the surface
(felt side) of each layer in such an amount that 1.0 g/m.sup.2 of
the solid would be applied thereto. The layers were combined
together to form a laminate.
[0212] The wet laminate sheet thus obtained was placed between
monoplastic canvas sheets (product of Shikishima Canvas Co.) and
pressed with a calender (product of Yuri Roll Machine) at a rate of
30 m/min under a nipping pressure of 10 kg/cm.
[0213] Then, the sheet was dried with a ferrotype cylindrical
heating dryer.
[0214] The moisture of the sheet was controlled under conditions of
20.degree. C. and 65% RH and treated with a calender (product of
Yuri Roru Kikai) at a rate of 20 m/min under a nipping pressure of
20 kg/cm. 8.0% PVA (Kuraray POVAL PVA-KL 118; a product of Kuraray
Co., Ltd.) was applied to the sheet by hand in an coating amount of
2.0 g/m.sup.2. Then, the sheet was treated with a calender (product
of Yuri Roll Machine) at 120.degree. C. at a rate of 20 m/min under
a nipping pressure of 40 kg/cm to obtain the molding base
paper.
[0215] The moisture of the molding base paper was controlled under
conditions of 20.degree. C. and 65% RH, and then the basis weight,
thickness, density and Z strength Taber stiffness thereof were
determined.
[0216] Further, a polypropylene film having a thickness of 40 .mu.m
was laminated on the surface of the molding base paper by melt
extrusion to obtain a sheet for producing a molded paper
vessel.
[0217] An oval-shaped blank sheet was stamped out of the sheet. The
blank sheet was radially provided with score lines 10 at both sides
as shown in FIG. 8.
[0218] The blank sheet thus obtained was heat-pressed between a
pair of upper and lower molds for forming an oval-shaped tray with
a test press molding machine (a product of Dai-Ichi Koki) at
130.degree. C. under 35 kg/cm.sup.2 to obtain paper vessels having
a major axis of about 20 cm, a minor axis of about 14 cm and a
height of about 4 cm (see FIG. 9).
[0219] A gelatinized liquid obtained by gelatinizing 7% starch (Oji
Ace A; a product of Oji Corn Starch Co.) in water at 70.degree. C.
was cooled to ambient temperature was used in place of a food. 250
g of the gelatinized liquid was fed into the molded paper vessel.
After confirming that the molded paper vessel containing the
gelatinized liquid was apparently free from swelling in the body
and the bottom and that the shape of the vessel was normal, the
open edge of the vessel was covered with a polyethylene film and
placed in a refrigerator. After leaving the vessel to stand at
5.degree. C. for 12 hours, the extents of the swelling in the body
and bottom of the molded paper vessel were judged by a method
described below.
EXAMPLE 2-2
[0220] A combined paper was made in the same manner as that of
Example 2-1 except that three kinds of pulps shown below were used,
that a coating liquid shown below was applied to the surface with
Mayer bar by hand so that 9.0 g/m.sup.2 of an undercoating and 10.0
g/m.sup.2 of a topcoating were formed after drying, and that the
laminated paper was dried at 105.degree. C. in a hot air dryer (a
product of Advantech KK) for 60 seconds.
[0221] (1) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0222] (2) Monterey pine TMP having 300 mlcsf/commercial NBKP
having, 150 mlcsf (70/30), freeness after the combination: 280
mlcsf, 230 g/m.sup.2
[0223] (3) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0224] [Coating Composition]
[0225] Topcoating: Kaolin (Ultrawhite 90; Engelheart Co.)/calcium
carbonate (Brilliant 15; Shiraishi Kogyo)/titanium oxide (TCA 333;
Tokemu Product)=50/35/15 and latex (L1410; Asahi Chemical Industry
Co., Ltd.)/urea starch phosphate (MS 4600; Nihon Shokuhin Kako Co.,
Ltd.)=15/5 (parts by weight of the solid; the same shall apply
hereinafter).
[0226] Undercoating: Kaolin (Kaobright; Thiele Co.)/calcium
carbonate (Softon 2200; Bihoku-Funka)=50/50 and latex (0668:
JSR)/urea starch phosphate (MS 4600; Nihon Shokuhin Kako Co.,
Ltd.)=15/5.
[0227] The molding base paper and then the molded paper vessel were
produced in the same manner as that of Example 2-1. The
determination and evaluation were conducted in the same manner as
that described above.
EXAMPLE 2-3
[0228] A combined paper was made in the same manner as that of
Example 1 except that three kinds of pulps shown below were
used:
[0229] (1) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0230] (2) Commercial mercerized pulp having 300 mlcsf/commercial
NBKP having 150 mlcsf (70/30), freeness after the combination: 250
mlcsf, 200 g/m.sup.2
[0231] (3) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0232] The molding base paper and then the molded paper vessel were
produced in the same manner as that of Example 2-1. The
determination and evaluation were conducted in the same manner as
that described above.
EXAMPLE 2-4
[0233] A combined paper was made in the same manner as that of
Example 1 except that three kinds of pulps shown below were
used:
[0234] (1) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0235] (2) Commercial NBKP having 150 mlcsf/curled fibers
(Weyerhauser) having 750 mlcsf (70/30), freeness after the
combination: 300 mlcsf, 160 g/m.sup.2
[0236] (3) commercial NBKP having 450 mlcsf, 40 g/m.sup.2
[0237] The molding base paper and then the molded paper vessel were
produced in the same manner as that of Example 2-1. The
determination and evaluation were conducted in the same manner as
that described above.
EXAMPLE 2-5
[0238] A combined paper was made in the same manner as that of
Example 2-1 except that three kinds of pulps shown below were
used:
[0239] (1) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0240] (2) Kenaf TMP having 350 mlcsf, 185 g/m.sup.2
[0241] (3) Commercial NBKP having 380 mlcsf, 50 g/m.sup.2
[0242] The molding base paper and then the molded paper vessel were
produced in the same manner as that of Example 2-1. The
determination and evaluation were conducted in the same manner as
that described above.
Reference Example 2-1
[0243] A paper was made in the same manner as that of Example 2-1
except that only one kind of pulp shown below was used to form only
one layer:
[0244] (1) Commercial NBKP having 450 mlcsf, 350 g/m.sup.2
[0245] The molding base paper and then the molded paper vessel were
produced in the same manner as that of Example 2-1. The
determination and evaluation were conducted in the same manner as
that described above.
Reference Example 2-2
[0246] A paper was made in the same manner as that of Example 2-1
except that two kinds of pulps shown below were used to form 2
layers:
[0247] (1) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0248] (2) Monterey pine TMP having 350 mlcsf, 250 g/m.sup.2
[0249] The molding base paper and then the molded paper vessel were
produced in the same manner as that of Example 2-1. The
determination and evaluation were conducted in the same manner as
that described above.
Reference Example 2-3
[0250] A paper was made in the same manner as that of Example 1
except that only one kind of pulp shown below was used to form only
one layer:
[0251] (1) Commercial NBKP having 450 mlcsf, 360 g/m.sup.2
[0252] The molding base paper and then the molded paper vessel were
produced in the same manner as that of Example 2-1. The
determination and evaluation were conducted in the same manner as
that described above.
[0253] The results of the determination and evaluation obtained in
above Examples and Comparative Examples are shown in Tables 3 and
4.
[0254] The evaluation methods were as follows:
[0255] [Density of each Paper Layer]
[0256] The layers were separated from each other by an interlaminar
peeling method stated in interlaminar peeling strength test of
combined paper board according to JIS P 8139, and thickness (mm)
and basis weight (g/m.sup.2) of each of them were determined.
[0257] Because each of the peeled layers was fluffy and thicker
than the actual thickness due to the fluff, a correction factor was
calculated according to the following formula to correct the
thickness of each peeled layer, and the density of the layer was
calculated:
Correction factor=(the whole layer thickness before peeling)/(total
thickness of the layers after peeling)
[0258] When the peeling of the layers by the interlaminar peeling
method stated in interlaminar peeling strength test of laminated
paper board according to JIS P 8139 was difficult, the combined
sheet sample was immersed in 60.degree. C. water for 1 hour and
then the sample was divided into the surface layer, intermediate
layer and back layer by peeling. The respective layers thus
obtained were dried and the thickness (mm) and basis weight
(g/m.sup.2) of each of them were determined. Then, the correction
factor was calculated as described above, and the thickness of each
layer was corrected, and the density of the layer was
calculated.
[0259] [Judgement of Body Swelling Rate]
[0260] The periphery of the middle of body of the paper tray was
measured. The difference in the periphery measured in the normal
state before the test and that measured 12 hours after was
calculated and then the body welling rate was calculated.
Body swelling rate (%)=[(periphery of middle of the body 12 hours
after)-(periphery of middle of the body before evaluation
test)]/(periphery of middle of the body before evaluation test)
[0261] The body swelling rate higher than 3.0% was judged to be X
X, that in the range of 1.5 to 3.0% was judged to be X, and that
below 1.5% was judged to be .largecircle..
3 TABLE 3 Total basis Example Molding Pulp weight No. method Layer
combination (g/m.sup.2) 2-1 press top NBKP 310 intermediate TMP
back NBKP 2-2 press top NBKP 330 intermediate N material TMP + NBKP
back NBKP 2-3 press top NBKP 310 intermediate mercerized pulp +
NBKP back NBKP 2-4 press top NBKP 260 intermediate NBKP + CF back
NBKP 2-5 press top NBKP 290 intermediate kenaf TMP back NBKP Basis
weight of Density of Density of Example each layer whole layers
each layer Stiffness Body No. (g/m.sup.2) (g/cm.sup.3) (g/cm.sup.3)
MD (g .multidot. cm) swelling 2-1 50 0.55 0.80 410 .largecircle.
200 0.50 50 0.80 2-2 50 0.60 0.80 375 .largecircle. 200 0.52 50
0.80 2-3 50 0.60 0.80 360 .largecircle. 200 0.52 50 0.80 2-4 50
0.55 0.80 285 .largecircle. 160 0.50 40 0.80 2-5 50 0.55 0.80 410
.largecircle. 185 0.50 50 0.80 Note: "N material" means a
coniferous tree material.
[0262]
4TABLE 4 Total basis Reference Molding Pulp weight Example No.
method Layer combination (g/m.sup.2) 2-1 press top NBKP 360
intermediate none back none 2-2 press top NBKP 260 intermediate
NBKP back none 2-3 press top NBKP 370 intermediate none back none
Basis weight of each Density of Density of Example layer whole
layers each layer Stiffness Body No. (g/m.sup.2) (g/m.sup.3)
(g/m.sup.3) MD (g .multidot. cm) swelling 2-1 350 0.80 0.80 200 X
none none none none 2-2 50 0.80 0.80 150 X 200 0.80 none none 2-3
360 0.80 0.80 210 X none none none none
EXAMPLE 3-1
[0263] The molding base paper obtained in the same manner as that
of Example 2-1 was treated with water vapor to control the water
content thereof at 12%. An oval-shaped blank sheet was stamped out
of the base paper. The blank sheet was radially provided with score
lines at both sides as shown in FIG. 8.
[0264] The blank sheet thus obtained was heat-pressed between a
pair of upper and lower molds for forming a paper tray with a test
press molding machine (a product of Dai-Ichi Koki) at 130.degree.
C. under 35 kg/cm.sup.2 to obtain paper tray having a height of 4
cm and an opening of an almost rectangular shape having a length of
18.6 cm and a width of 12.6 cm as shown in FIG. 10. It also had a
flange having a width of 0.7 cm. The tray vessel thus obtained by
the drawing had a curved side wall and also a curved area between
the side wall and the bottom.
[0265] The obtained tray had a taper angle (.phi.) of 115.degree.,
radius of curvature (r) of 2 cm and bottom area (S1) of 72
cm.sup.2. Accordingly, H/(S1).sup.1/2 was 0.47, r/(S1).sup.1/2 was
0.24, and H/(S2).sup.1/2 was 0.26.
[0266] The degree of swelling in the body of the tray obtained by
the drawing was also determined as described below.
EXAMPLE 3-2
[0267] A molding base paper was obtained in the same manner as that
of Example 2-2.
[0268] A blank sheet was obtained in the same manner as that of
Example 3-1 except that the shape of the blank sheet was roughly
square, that the corners thereof were round, that a pair of upper
and lower molds for forming a square vessel was used, that the
water content of the blank sheet was 15% and that the molding
temperature was 140.degree. C.
[0269] Thus, almost square tray was obtained by the drawing as
shown in FIG. 11. This tray had a height of 2.8 cm and an opening
of an almost rectangular shape having a length of each side of the
opening of 8 cm. It also had a flange or rim having a width of 1
cm, and a curved side wall and also a curved area between the side
wall and the bottom.
[0270] The tray had a taper angle (.phi.) of 113.degree., radius of
curvature (r) of 1.3 cm and bottom surface (S1) of 20 cm.sup.2.
Accordingly, H/(S1).sup.1/2 was 0.62, r/(S1).sup.1/2 was 0.29, and
H/(S2).sup.1/2 was 0.35.
[0271] The tray thus obtained by drawing was evaluated in the same
manner as that of Example 3-1.
EXAMPLE 3-3
[0272] A combined paper was made in the same manner as that of
Example 3-1 except that three kinds of pulps shown below were
used:
[0273] (1) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0274] (2) Monterey pine TMP having 350 mlcsf/commercial LBKP
having 350 mlcsf (70/30), freeness after the combination: 350
mlcsf, 200 g/m.sup.2
[0275] (3) Commercial NBKP having 380 mlcsf, 50 g/m.sup.2
[0276] The molding base paper was produced in the same manner as
that of Example 3-1. After controlling the moisture under
conditions of 20.degree. C. and 65% RH, the basis weight, thickness
and density of the paper were determined.
[0277] The surface of the base paper (inner surface of the vessel)
was laminated with a polypropylene film having a thickness of 40
.mu.m in the same manner as that of Example 3-1 to obtain a blank
sheer for forming a vessel.
[0278] Then, the blank sheet was molded in the same manner as that
of Example 1 except that the blank sheet was round, that the mold
was bowl-shaped, that the water content of the blank sheet was 13%
and that the molding temperature was 120.degree. C. The bowl-shaped
vessel thus obtained by the drawing had a height of 5.5 cm and an
opening of a diameter of 12 cm as shown in FIG. 12. It also had a
flange or rim having a width of 0.8 cm, and a curved side wall and
also a curved area between the side wall and the bottom.
[0279] The vessel had a taper angle (.phi.) of 114.degree., radius
of curvature (r) of 1 cm and bottom surface (S1) of 28 cm.sup.2.
Accordingly, H/(S1).sup.1/2 was 1.03, r/(S1).sup.1/2 was 0.19, and
H/(S2).sup.1/2 was 0.52.
[0280] The results of the evaluation in Examples 3-1 to 3-3 are
shown in Table 5.
5TABLE 5 Total basis Example Pulp weight No. Layer combination
(g/m.sup.2) 3-1 top NBKP 310 intermediate TMP back NBKP 3-2 top
NBKP 330 intermediate N material TMP + NBKP back NBKP 3-3 top NBKP
310 intermediate N material TMP + LBKP back NBKP Basis weight
Density of Density of each whole of each Elongation Example layer
layers layer Body at break No. (g/m.sup.2) (g/cm.sup.3)
(g/cm.sup.3) swelling (MD/CD) (%) 3-1 50 0.55 0.80 .largecircle.
3.4/6.9 200 0.50 50 0.80 3-2 50 0.60 0.80 .largecircle. 2.9/6.3 200
0.52 50 0.80 3-3 50 0.60 0.80 .largecircle. 2.4/5.2 200 0.52 50
0.72
Example 4-1
Effect of Outer layer on Base Paper
[0281] With a disc refiner, commercially available NBKP was beaten
to 550 mlcsf (Tappi T-227, Canadian standard) and monterey pine TMP
was beaten to 300 mlcsf. From these stocks, a paper support
composed of two layers, i.e. the first layer of 40 g/m.sup.2 NBKP
and the second layer of 250 g/m.sup.2 TMP, was prepared with a
multi-layer combination paper machine. A bleached, stretching kraft
paper (Oji Paper Co., Ltd., basis weight: 75 g/m.sup.2) was applied
as an outer layer sheet to the paper support to obtain a molding
base paper. The combination was conducted as follows: 20 g/m.sup.2
(in terms of solid) of an EVA emulsion-type adhesive (trade name:
Vinisol 1412 KAI; Daido Kasei) was applied to the TMP layer surface
of the paper board with Mayer bar. Immediately thereafter, the
bleached, stretching draft paper was pressed on the undried coating
layer with a hand roll. After drying with a hot air dryer at
110.degree. C. for 20 seconds, the molding base paper thus obtained
was subjected to the tests described below to examine its
elongation at break and moldability.
[0282] In this case, the multi-layer base paper without the outer
layer has the following layer construction.
6 kind of density base weight pulp (g/cm.sup.3) (g/m.sup.2) top
layer NBKP 0.70 40 back layer TMP 0.48 250 Total layer -- 0.50
290
EXAMPLE 4-2
[0283] A molding base paper was prepared and evaluated in the same
manner as that of Example 4-1 except that the outer layer sheet to
be applied to the paper support was replaced with an unbleached
stretching kraft paper for cement bags (Oji Paper Co., Ltd., basis
weight: 83 g/m.sup.2).
EXAMPLE 4-3
[0284] A molding base paper was prepared and evaluated in the same
manner as that of Example 4-1 except that the second layer of the
paper support contained 180 g/m.sup.2 of TMP and the outer layer
sheet to be applied to the paper support was replaced with a
stretching kraft paper for adhesive tapes.
[0285] (Evaluation Methods)
[0286] (1) Elongation at Break
[0287] A blank sheet obtained by cutting the resultant test paper
to a width of 15 mm and length of 250 mm respectively in both the
flow direction and cross direction were kept under conditions of
23.degree. C. and 50% RH for at least 24 hours to control the
moisture thereof. Then, the elongation at break of the blank sheet
was determined with Strograph M2 tester (a product of Toyo Seiki
Seisaku-sho, Ltd.) at a rate of pulling of 20 mm/min according to
JIS-P 8113.
[0288] (2) Moldability
[0289] The moisture of the sheet was controlled at 12% by the
treatment with water vapor. Circular blank sheet was stamped out of
the sheet. The blank sheet was radially scored with lines. The
blank sheet thus obtained was heat-pressed between a pair of upper
and lower molds for forming a cup-shaped tray with a test press
molding machine (a product of Dai-Ichi Koki) at 130.degree. C.
under 35 kg/cm.sup.2 to obtain a cup-shaped paper vessel having a
height of 7 cm, a circular opening having a diameter of 12 cm and a
circular bottom having a diameter of 6 cm. It also had a flange or
rim having a width of 0.8 cm, and a curved side wall and also a
curved area between the side wall and the bottom as shown in FIG.
13. The molding was conducted in such a manner that the outer layer
side of the sheet formed was the outside of the vessel. The
moldability was evaluated as follows:
[0290] .largecircle.: The sheet could be molded into cups, the
outer layer of each molding was not broken and the molding surface
was smooth.
[0291] .DELTA.: The sheet could be molded into a cup but the outer
layer of the cup was broken.
[0292] X: The blank sheet was broken in the molding step and it
could not be molded into a cup.
[0293] The evaluation results are shown in Table 6.
7 TABLE 6 Example 4-1 Example 4-2 Example 4-3 Outer Kind Bleached
Unbleached Unbleached layer stretching stretching stretching sheet
kraft paper kraft paper for kraft paper cement bag for adhesive
tape Basis weight 75 83 73 (g/m.sup.2) Density 0.72 0.60 0.68
(g/cm.sup.3) Elongation at break (%) MD 9.0 6.5 7.4 CD 7.9 7.9 8.9
Basis weight of base 292 292 225 paper (g/m.sup.2) Total base Basis
weight 387 396 320 paper (g/m.sup.2) Density 0.56 0.54 0.60
(g/cm.sup.3) Moldability .largecircle. .largecircle.
.largecircle.
[0294] It is clear from Table 6 that the molding base paper of the
present invention is excellent in moldability because when it is
used even for deep molding to form a cup or the like, the outer
paper layer surface is not cracked or broken in the molding
step.
EXAMPLE 5-1
[0295] A molding base paper was obtained in the same manner as that
of Example 2-1.
[0296] [Determination of Outer Layer Density]
[0297] The layers were separated from each other by an interlaminar
peeling method stated in interlaminar peeling strength test of
combined paper board according to JIS P 8139, and thickness (mm)
and basis weight (g/m.sup.2) of each of them were determined.
[0298] Because each of the peeled layers was fluffy and thicker
than the actual thickness due to the fluff, a correction factor was
calculated according to the following formula to correct the
thickness of each peeled layer, and the density of the layer was
calculated:
Correction factor=(the whole layer thickness before peeling)/(total
thickness of the layers after peeling)
[0299] When the peeling of the layers by the interlaminar peeling
method stated in interlaminar peeling strength test of laminated
paper board according to JIS P 8139 was difficult, the combined
sheet sample was immersed in 60.degree. C. water for 1 hour and
then the sample was divided into the surface layer, intermediate
layer and back layer by peeling. The respective layers thus
obtained were dried and the thickness (mm) and basis weight
(g/m.sup.2) of each of them were determined. Then, the correction
factor was calculated as described above, and the thickness of each
layer was corrected, and the density of the layer was
calculated.
[0300] [Extrusion Lamination Method]
[0301] Titanium oxide was incorporated into a polypropylene
(SunAllomer: a product of MSS) with Labo-plastomill (Toyo Seiki
Co., Ltd.) so that the titanium oxide content would be 10% by
weight. The obtained mixture was applied to the surface of the base
paper to form a synthetic resin layer having a thickness of 30
.mu.m by melt extrusion method. Thus, a base paper for forming
vessels was obtained.
[0302] An oval-shaped blank sheet was stamped out of the base
paper. The blank sheet was radially scored with lines as shown in
FIG. 8.
[0303] The blank sheet thus obtained was heat-pressed between a
pair of upper and lower molds for forming an oval-shaped vessel
with a test press molding machine (a product of Dai-Ichi Koki) at
130.degree. C. under 35 kg/cm.sup.2to obtain a vessel having a
major axis of about 20 cm, minor axis of about 14 cm and height of
about 4 cm as shown in FIG. 9.
EXAMPLE 5-2
[0304] A molding base paper and then molded paper vessel were
produced in the same manner as that of Example 5-1 except that the
following three kinds of pulps (1) to (3) were used, that titanium
oxide content was changed to 8% by weight, and that the synthetic
resin layer having a thickness of 40 .mu.m was formed:
[0305] (1) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
[0306] (2) Monterey pine TMP having 300 mlcsf/commercial NBKP
having 150 mlcsf (70/30), freeness after the combination: 280
mlcsf, 200 g/m.sup.2
[0307] (3) Commercial NBKP having 450 mlcsf, 50 g/m.sup.2
Reference Example 5-1
[0308] The molding base paper and then molded paper vessel were
produced in the same manner as that of Example 5-1 except that only
the polypropylene (SunAllomer: a product of MSS) was used without
titanium oxide to form a synthetic resin layer having a thickness
of 30 .mu.m.
[0309] The molded vessel obtained in the Examples and Reference
Example were evaluated by the following method:
[0310] <Surface Evaluation Method>
[0311] The flange or rim of each molded vessel was sampled. A part
(20 mm in longitudinal direction) thereof was tested with a micro
color difference meter R-30 (Nippon Denshoku Kokyo). The color
difference (WB value) was determined at 10 points. The spot
diameter was 0.6 mm. When R value (difference between the maximum
and the minimum) was 10 points or above, the results were shown by
X, and when it was less than 10 points, the results were shown by
.largecircle..
8 TABLE 7 Base paper Density Density Basis (outer (the weight
layer) whole) Synthetic TiO.sub.2 g/m.sup.2 g/cm.sup.3 g/cm.sup.3
resin (wt. %) Surface Ex. 5-1 250 0.80 0.50 PP 10 .largecircle. Ex.
5-2 300 0.80 0.60 PP 8 .largecircle. Ref. 250 0.80 0.50 PP 0 X Ex.
1
EXAMPLE 6-1
[0312] A molding base paper was obtained in the same manner as that
of Example 2-1. An aliphatic polyester sheet (trade name: Bionolle,
Showa Highpolymer Co., Ltd.) having a thickness of 40 .mu.m was
applied to the surface of this base paper by melt extrusion method
to form a laminate to be used as a sheet for molding paper
vessels.
[0313] An oval-shaped blank sheet was stamped out of the base
paper. The blank sheet was radially scored with lines as shown in
FIG. 8.
[0314] The blank sheet was heat-pressed between a pair of upper and
lower molds for forming an oval-shaped paper tray with a test press
molding machine (a product of Dai-Ichi Koki) at 130.degree. C.
under 35 kg/cm.sup.2 to obtain a vessel having a major axis of
about 20 cm, minor axis of about 14 cm and height of about 4 cm as
shown in FIG. 9.
Reference Example 6-1
[0315] A molding paper vessels was obtained in the same manner as
that of Example 6-1 except that the aliphatic polyester applied to
the surface of the molding base paper to form the laminate was
replaced with polypropylene.
[0316] The results of the determination and evaluation in the above
Example and Comparative Example are shown in Table 8.
[0317] The evaluation method was as follows:
[0318] [Biodegradability]
[0319] The molded paper vessels were buried in the ground in a farm
for 6 months and then they were taken out and degree of the
decomposition of them was observed.
9TABLE 8 Laminate State after keeping in the ground for resin 6
months Example 6-1 Aliphatic The vessel retained only a small
polyester amount of paper fibers but nothing of its original form.
Ref. Ex. 6-1 Polypropylene The paper partially decomposed and the
laminate layer completely remained.
[0320] As shown in Table 8 above, it is clear that the use of a
biodegradable resin as an outer layer for the present base sheet
reduces environmental load. Claim 1-16 (Canceled).
* * * * *