The present invention relates to a process for the surface treatment
of an aluminum support for printing plate as a lithographic printing plate support.
More particularly, the present invention relates to a process for the surface treatment
of an aluminum support for printing plate which operates at a reduced running
cost with a drastic reduction of industrial waste.
As a support for lithographic printing plate there has heretofore
been widely used an aluminum plate. This aluminum support for lithographic printing
plate is subjected to roughening to enhance the adhesion to the photosensitive
layer provided thereon. This roughening is carried out by continuously graining
an aluminum support, e.g., by rubbing the aluminum support with an abrasive slurry
(normally a mixture of pumice or pumicite obtained from igneous rock or alumina
with water) under a rotating brush.
However, in order to maintain a predetermined grain, it is necessary
to keep the grain size of the abrasive in a predetermined distribution. To this
end, the abrasive which has been worn and ground to have a smaller grain size than
the desired value needs to be discharged from the system through a classifier.
Thus, it has taken a great cost to dispose of the abrasive used.
On the other hand, it has been practiced to etch the surface of the
aluminum support for printing plate with caustic soda before or after mechanical
or electrochemical roughening of the surface of the aluminum support. However,
since the aluminum ion concentration in the etching solution has an extremely great
effect on the quality of the aluminum support for printing plate, it is important
to keep the aluminum ion concentration in the etching solution at a predetermined
value.
Further, various surface treatments such as anodization with sulfuric
acid have been practiced. Therefore, it is also necessary to neutralize the waste
liquid to produce an aluminum hydroxide sludge from which aluminum hydroxide is
recovered.
The inventors proposed as a mechanical roughening method a method
involving brush graining in EP0734883A1 which corresponds to JP-A-8-324143 (The
term "JP-A" as used herein means an "unexamined published Japanese patent application").
In accordance with the surface treatment method disclosed in the above cited patent,
the disadvantages of brush graining method can be eliminated. Thus, fill-in and
scumming can be eliminated to provide a printing plate having improved printing
properties. However, since this method employs aluminum hydroxide, which exhibits
a low hardness, as an abrasive, a new problem arises that it requires the consumption
of a great amount of the abrasive.
As mentioned above, when it is desired to maintain a good abrasion
in the surface treatment of an aluminum support for printing plate, a consequence
must be encountered that the mechanical surface treatment (surface roughening)
is accompanied by the discharge of an increased amount of waste abrasive, which
in turn is accompanied by the use of an increased amount of a new abrasive.
Further, when an aluminum support for printing plate is chemically
or electrochemically roughened (surface-treated), the surface treatment is accompanied
by the discharge of a great amount of waste. Another consequence is that the amount
of chemicals required for the surface treatment is increased. Therefore, the disposal
of waste requires complicated procedure and raised cost. For example, the expenses
for abrasive and chemicals are drastically increased.
EP-A-771760 discloses a process for the purification of aluminum hydroxide
character-ized in that crystalline aluminum hydroxide which is ground and etched
is used as an original seed crystal. A process for the surface treatment of aluminum
plate utilizing said purification process is also disclosed.
An object of the present invention is to provide a process for the
surface treatment of an aluminum support for printing plate which can operate stably
at an extremely low cost as compared with the prior art by reducing the amount
of waste discharged from the step of surface treatment of an aluminum plate as
a support for lithographic printing plate and the amount of chemicals and abrasive
to be used in the surface treatment.
The foregoing object of the present invention is accomplished by
the following process for the surface treatment of an aluminum support for printing
plate according to the present invention.
- (1) A process for the surface treatment of an aluminum support for printing
plate which comprises a step of brush-graining with an abrasive brush and an abrasive
slurry, characterized in that:
- as said abrasive there is used aluminum hydroxide;
- said aluminum hydroxide which has been used in graining is dissolved in a sodium
aluminate solution;
- said sodium aluminate solution having a raised supersaturation degree; and
- said aluminum hydroxide which has been left undissolved and seed crystal aluminum
hydroxide undergo hydrolysis reaction to produce crystalline aluminum hydroxide
which is then purified and partially supplied as a regenerated abrasive.
- (2) The process for the surface treatment of an aluminum support for printing
plate according to Clause (1), wherein the percent dissolution of said aluminum
hydroxide which has been used in abrasion in a sodium aluminate solution is from
15% to 100%.
- (3) A process for the surface treatment of an aluminum support for printing
plate which comprises:
- preparing a part of a treatment liquid containing a sodium aluminate solution
to be recycled for surface etching as a supersaturated sodium aluminate solution;
or
- mixing a part of said treatment liquid with an aluminum sludge mainly composed
of amorphous aluminum hydroxide produced by the neutralization of waste acid liquid
and waste alkaline liquid discharged from the step of surface treatment of an
aluminum support to prepare a supersaturated sodium aluminate solution; and then
- allowing said sodium aluminate solution to undergo hydrolysis reaction to crystallize
aluminum hydroxide which is then purified and recycled as an abrasive,
characterized in that
- aluminum hydroxide which has been used in abrasion is dissolved in said supersaturated
sodium aluminate solution; and
- said aluminum hydroxide which has been used in abrasion but which has been left
undissolved and seed crystal aluminum hydroxide undergo hydrolysis reaction to
produce crystalline aluminum hydroxide which is then purified and partially supplied
as an abrasive again.
- (4) The process for the surface treatment of an aluminum support for printing
plate according to Clause (3), wherein the percent dissolution of said aluminum
hydroxide which has been used in abrasion in a sodium aluminate solution is from
15% to 100%.
- (5) The process for the surface treatment of an aluminum support for printing
plate according to Clause (3), wherein the waste acid liquid and waste alkaline
liquid discharged from the step of surface treatment of an aluminum support for
printing plate were adjusted to a pH value of from not less than 5.0 to less than
9.0 when neutralized.
- Fig. 1 is a schematic flow chart of treatment procedure illustrating the first
embodiment of the process for the surface treatment of an aluminum support for
printing plate according to the present invention;
- Fig. 2 is a diagram illustrating a part of a schematic flow chart of treatment
procedure of the second embodiment of the process for the surface treatment of
an aluminum support for printing plate according to the present invention; and
- Fig. 3 is a diagram illustrating the other part of a schematic flow chart of
treatment procedure of the second embodiment of the process for the surface treatment
of an aluminum support for printing plate according to the present invention.
A first embodiment of the process for the surface treatment of an
aluminum support for printing plate will be described hereinafter in connection
with Fig. 1.
In the present embodiment of the process for the surface treatment
of an aluminum support for printing plate, an aluminum support 1 is mechanically
surface-treated with an abrasive slurry 4 as an abrasive which has been properly
supplied under abrasive brushes 3 disposed at a predetermined interval while running
through a predetermined route, supported by a plurality of pass rollers 2, as
shown in Fig. 1.
The abrasive slurry 4 is supplied onto the surface of the aluminum
support 1 by the action of a circulating pump 6 while being rubbed against the
aluminum support 1 under the abrasive brushes 3, and then returned to a circulating
tank 5 through an abrasive slurry return line 7. In the surface treatment by brush
graining, the abrasive slurry which has been used for surface treatment is liable
to gradual reduction of grain diameter of abrasive if it continues to be used,
disabling the desired surface treatment.
Accordingly, the circulating tank 5 is replenished with a new batch
of the abrasive 12 and water 13.
The replenishment with the abrasive 12 and water 13 causes part of
the abrasive slurry to flow into an overflow tank 5a. The abrasive slurry which
has thus overflown is supplied into a cyclon 8 by a pump 9 and then subjected to
classification by the cyclone 8. The abrasive slurry which has been classified
into a group having a great grain diameter is then returned to the circulating
tank 5. On the other hand, the abrasive slurry which has been classified into
a group having a small grain diameter is passed through an abrasive slurry discharge
line 10 to a centrifugal separator 11 where it is then dehydrated to obtain a used
abrasive 14 in powder form. Sodium hydroxide 15 and water 16 are supplied to a
tank 17 in order to control the liquid concentration in the tank 17.
Aluminum hydroxide 21 is then recovered from part of the used abrasive.
The used abrasive is also partially charged into a tank 17 for dissolving used
aluminum hydroxide. The aluminum hydroxide 21 thus recovered can be used as starting
material for other purposes. In this case, the aluminum hydroxide 21 is valuable.
The percent dissolution of said aluminum hydroxide which has been
used in abrasion in a sodium aluminate solution is from 15% to 100%, preferably
from 50% to 80%. At the upper limit or more, it become difficult to dissolve said
aluminum hydroxide and increase initial cost or running cost for operating the
system.
The abrasive which has been charged into the aluminum hydroxide dissolution
tank 17 is then stirred with sodium aluminate which has been heated by steam for
a predetermined period of time so that it is dissolved in sodium aluminate. The
sodium aluminate solution which has thus aluminum hydroxide dissolved therein to
have a raised supersaturation degree is properly cooled by a cooler 30, and then
passed to a crystallization tank 18. In the crystallization tank 18, crystallization
reaction occurs to produce crystalline aluminum hydroxide again which is then subjected
to solid-liquid separation by a dehydrator 19 to obtain crystalline aluminum hydroxide
in powder form.
The aluminum hydroxide which has thus been subjected to solid-liquid
separation by the dehydrator 19 is partially supplied into the circulating tank
5 as a regenerated abrasive aluminum hydroxide 20 as necessary. The remainder of
the aluminum hydroxide thus withdrawn may be supplied into the crystallization
tank 18 as seed crystal. It may be withdrawn as aluminum hydroxide 21 which is
then reused as starting material for other purposes.
In the tank 17 for dissolving used aluminum hydroxide, the liquid
temperature, liquid concentration (T-NAOH), stirring intensity (crushing action
thereby) and retention time can be controlled to adjust the percent dissolution
of used aluminum hydroxide.
A second embodiment of the process for the surface treatment of an
aluminum support for printing plate according to the present invention will be
described hereinafter in connection with Figs. 2 and 3. Figs. 2 and 3 form a continuous
treatment process. The two parts are connected at A, B and C.
As shown in Figs. 2 and 3, in the step of surface treatment of an
aluminum support for printing plate in the present embodiment, an aluminum support
1 is subjected to mechanical surface treatment with an abrasive under an abrasive
brush 3, supported by a pass roll 2, in the same manner as in the first embodiment.
An abrasive slurry 4 is supplied onto the surface of the aluminum support by the
action of a circulating pump 6 while being rubbed against the aluminum support
1 under the abrasive brushes 3, and then returned to a circulating tank 5 through
an abrasive slurry return line 7.
In the surface treatment by brush graining, the abrasive slurry which
has been used for surface treatment is liable to gradual reduction of grain diameter
of abrasive if it continues to be used, disabling the desired surface treatment.
Accordingly, the circulating tank 5 is replenished with a new batch of the abrasive
12 and water 13. This replenishment causes part of the abrasive slurry to flow
into an overflow tank 5a. The abrasive slurry which has thus overflown is supplied
into a cyclon 8 by a pump 9 and then subjected to classification by the cyclone
8.
The abrasive slurry which has been classified into a group having
a great grain diameter is then returned to the circulating tank 5. On the other
hand, the abrasive slurry which has been classified into a group having a small
grain diameter is passed through an abrasive slurry discharge line 10 to a centrifugal
separator 11 where it is then dehydrated to obtain a used abrasive 14 in powder
form. The used abrasive 14 is then partially charged into a tank 17 for dissolving
used aluminum hydroxide.
The used abrasive which has thus been charged into the tank 17 is
then stirred with sodium aluminate which has been heated in the dissolution tank
17 for a predetermined period of time so that it is dissolved in sodium aluminate.
The sodium aluminate solution which has thus aluminum hydroxide dissolved therein
to have a raised supersaturation degree is then passed to a crystallization tank
18. During the feed of the sodium aluminate solution is properly cooled by a cooler
30.
In the crystallization tank 18, crystallization reaction occurs to
produce crystalline aluminum hydroxide again which is then subjected to solid-liquid
separation by a dehydrator 19 to obtain crystalline aluminum hydroxide in powder
form.
The aluminum hydroxide thus withdrawn is then partially supplied
as an abrasive again. In other words, it is supplied into the circulating tank
as a regenerated aluminum hydroxide 20 as necessary. The remainder of the aluminum
hydroxide thus withdrawn (part other than used for replenishment) is then withdrawn
as a valuable aluminum hydroxide 21 which is then reused as starting material for
other purposes.
In the tank 17 for dissolving used aluminum hydroxide, the liquid
temperature, liquid concentration (T-NAOH), stirring intensity (crushing action
thereby) and retention time can be controlled to adjust the percent dissolution
of used aluminum hydroxide. In the present embodiment, the control over liquid
temperature is carried out by steam heating. The stirring can be accomplished
by means of a screw which is properly driven.
On the other hand, waste acid liquid and waste alkaline liquid which
have been discharged from rinsing tanks 40, 41, 42 and 43, an electrolytic tank
50 and an anodization tank 60 of the step of surface treatment of the aluminum
support 1 are neutralized at a pH adjustment tank 70, and then passed to a cohesion
and sedimentation tank 80 where amorphous aluminum hydroxide (aluminum hydroxide
sludge) flock is produced. The amorphous aluminum hydroxide flock is then concentrated,
and then dehydrated at a filter press 81.
The aluminum hydroxide sludge thus dehydrated is then charged into
a sludge dissolution tank 82 so that it is dissolved in a sodium aluminate solution.
As a result, the supersaturation degree of the sodium aluminate solution is raised.
The sodium aluminate solution is passed to a separator 83 where insoluble components
are then separated therefrom. The liquid thus separated is charged into the crystallization
tank 18 where it is subjected to hydrolysis reaction to purify aluminum hydroxide.
The aluminum hydroxide thus purified is then subjected to solid-liquid
separation by the dehydrator 19 (vacuum filter). The filtrate is partially passed
to a liquid preparation tank 45 so that it is used as an etching solution. The
remainder of the filtrate is then passed to the tank 17 for dissolving used aluminum
hydroxide and a sludge dissolution tank 82 as a dissolving liquid. The liquid in
the liquid preparation tank 45 is passed to the sludge dissolution tank 82 through
a concentrating apparatus 84. In Fig. 2, the reference numeral 46 indicates an
etching tank in which the liquid thus prepared can be properly sprayed onto the
aluminum support, and in Fig. 3, the reference numeral 59 indicates an anodization
and power supply tank in which electrodes are properly arranged.
Examples of the process for the surface treatment of an aluminum
support for printing plate according to the present invention will be described
hereinafter.
EXAMPLE 1
In Example 1, treatment was effected in accordance with the process
for the surface treatment of an aluminum support for printing plate shown in Fig.
1.
The treatment conditions in Example 1 are as set forth in Table 1.
Treatment conditions in Example 1
Conditions of mechanical roughening of aluminum support
Width of aluminum support
1,000 mm
Treatment speed
50 m/min.
Abrasive
Crystalline aluminum hydroxide; average grain diameter: 30
µm
Abrasive concentration
200 g/l
Used abrasive
Crystalline aluminum hydroxide; average grain diameter: 15
µm
Conditions of dissolution of abrasive aluminum hydroxide
Solution concentration
T-NAOH: 120 g/l; Al: 28 g/l
Solution temperature
95°C
Solution retention time
5 hours
Solution temperature before charging into crystallization tank
55°C
Conditions of crystallization reaction
Crystallization solution concentration
T-NAOH: 120 g/l; Al: 24 g/l
Crystallization solution temperature
55°C
Seed crystal concentration in crystallization tank
150 g/l
COMPARATIVE EXAMPLE 1
On the other hand, in Comparative Example 1 as opposed to Example
1, the dissolution and crystallization of used aluminum hydroxide were not effected.
The used aluminum hydroxide thus produced was sold as a valuable. As the abrasive
to be supplied as replenisher there was used aluminum hydroxide used as an industrial
starting material.
These results show that Example 1 allows stable treatment in a process
for the surface treatment of an aluminum support by mechanical roughening with
crystalline aluminum hydroxide as an abrasive and recycling of the abrasive from
the step of surface treatment of an aluminum plate as printing plate support as
compared with Comparative Example 1, making it possible to reduce the cost of
abrasive and the discharged amount of waste.
In other words, Example 1 provided results satisfying Claims 1 and
2 according to the present invention.
EXAMPLE 2
In Example 2, treatment was effected in accordance with the process
for the surface treatment of an aluminum support for printing plate shown in Figs.
2 and 3.
The treatment conditions in Example 2 are as set forth in Table 2.
Treatment conditions in Example 2
Conditions of mechanical roughening of aluminum support
Width of aluminum support
1,000 mm
Treatment speed
50 m/min.
Abrasive
Crystalline aluminum hydroxide; average grain diameter: 30
µm
Abrasive concentration
200 g/l
Used abrasive
Crystalline aluminum hydroxide; average grain diameter: 15
µm
Conditions of dissolution of abrasive aluminum hydroxide
Solution concentration
T-NAOH: 120 g/l; Al: 28 g/l
Solution temperature
95°C
Solution retention time
5 hours
Solution temperature before charging into crystallization tank
55°C
Conditions of crystallization reaction
Crystallization solution concentration
T-NAOH: 120 g/l; Al: 24 g/l
Crystallization solution temperature
55°C
Seed crystal concentration in crystallization tank
150 g/l
EXAMPLE 3
In Example 3, treatment was effected in accordance with the process
for the surface treatment of an aluminum support for printing plate shown in Figs.
2 and 3 in the same manner as in Example 2.
The treatment conditions of Example 3 were the same as used in Example
2 except for those set forth in Table 3 below.
Treatment conditions in Example 3
Conditions of treatment of waste liquid from the surface treatment of aluminum support
pH adjustment tank
7.0
Water content in aluminum hydroxide sludge
80%
Conditions of dissolution of aluminum hydroxide sludge
Solution concentration
T-NAOH: 120 g/l; Al: 28 g/l
Solution temperature
70°C
Solution retention time
30 min.
Solution temperature before charging into crystallization tank
55°C
COMPARATIVE EXAMPLE 2
In Comparative Example 2 as opposed to Examples 2 and 3, the dissolution
and crystallization of used aluminum hydroxide were not effected. The used aluminum
hydroxide thus produced was sold as a valuable. As the abrasive to be supplied
as replenisher there was used aluminum hydroxide used as an industrial starting
material.
These results show that Examples 2 and 3 allow stable treatment in
a process for the surface treatment of an aluminum support by mechanical roughening
with crystalline aluminum hydroxide as an abrasive and reduction of the discharged
amount of waste from the step of surface treatment of an aluminum plate as lithographic
printing plate support and the used amount of chemicals and abrasive as compared
with Comparative Example 2. In some detail, Example 2, in addition to the effects
of Example 1, makes it possible to reduce the discharged amount of aluminum hydroxide
sludge (waste) and the used amount of the etching caustic soda (i.e., chemicals
used). Further, Example 3, in addition to the effects of Example 2, makes it possible
to stabilize the quality of aluminum hydroxide sludge thus produced.
In other words, Example 2 provided results satisfying the above-described
Clauses (3) and (4), and Example 3 provided results satisfying the above-described
Clauses (3) and (5).
As mentioned above, in accordance with the process for the surface
treatment of an aluminum support for printing plate of the present invention, in
a process for the surface treatment of an aluminum support involving mechanical
roughening with crystalline aluminum hydroxide as an abrasive, the abrasive can
be effectively used and the resulting abrasion quality can be stabilized. Further,
the discharged amount of waste from the step of surface treatment of an aluminum
plate as a lithographic printing plate support and the used amount of chemicals
and abrasive can be reduced from that of the prior art.
As a result, the reduction of the running cost in the surface treatment
step can be realized, enabling stable provision of a high quality aluminum support
for printing plate at a low cost.