Back to EveryPatent.com
| United States Patent |
6,048,624
|
|
Alba
, et al.
|
April 11, 2000
|
Coated dummy plates
Abstract
A dummy plate is provided for offset printing which essentially consists of
a plate-, sheet- or band-form, mechanically and/or electro-chemically
roughened, anodically oxidized and optionally hydrophilized aluminium
support and a non-photosensitive, water-soluble protective layer applied
thereto, characterized in that the layer contains a water-soluble organic
compound which contains at least one OH- or NH-acidic group having a pKa
value of .ltoreq.8 as acid or salt, and has a layer thickness which is
smaller than the average roughness ra of the support material, determined
by optical means. Even after extended storage at elevated temperature, the
dummy plate can easily be used without an additional development step and
exhibits no tendency to stick.
| Inventors:
|
Alba; Cornelia (Ingelheim, DE);
Elsasser; Andreas (Idstein, DE);
Grabley; Fritz-Feo (Kelkheim, DE);
Jorg; Klaus (Ingelheim, DE);
Lehmann; Peter (Kelkheim, DE)
|
| Assignee:
|
AGFA-Gevaert (Mortsel, BE)
|
| Appl. No.:
|
126422 |
| Filed:
|
July 30, 1998 |
Foreign Application Priority Data
| Intern'l Class: |
B32B 015/04; B05D 003/00; B41N 001/00 |
| Field of Search: |
428/469,457,459,461,472.2,336,500,913
427/156,327,379,384,402
|
References Cited
U.S. Patent Documents
| 5474885 | Dec., 1995 | Michiels et al. | 430/539.
|
| 5786127 | Jul., 1998 | Madoux et al. | 430/273.
|
| 5908706 | Jun., 1999 | Lehmann et al. | 428/469.
|
Primary Examiner: Yamnitzky; Marie
Attorney, Agent or Firm: Foley & Lardner
Claims
We claim:
1. Dummy plate for offset printing comprising a plate-, sheet- or
band-form, mechanically and/or electrochemically roughened, anodically
oxidized and optionally hydrophilized aluminum support and a
non-photosensitive, water-soluble protective layer applied thereto,
wherein the layer contains a water-soluble organic compound which contains
at least one OH- or NH-acidic group having a pKa value of .ltoreq.8 as
acid or salt, and has a layer thickness which is smaller than the average
roughness ra of the aluminum support.
2. Dummy plate according to claim 1, wherein the pH of the protective layer
is 2-8.
3. Dummy plate according to claim 1, wherein the ra value of the aluminum
support is between 0.5 and 1.5 .mu.m.
4. Dummy plate according to claim 1, wherein the anodization is followed by
hydrophilizing treatment with an organic polymer containing
phosphorus-containing groups.
5. Dummy plate according to claim 1, wherein the organic compound contains
at least 3 acidic groups.
6. Dummy plate according to claim 1, wherein the acidic group is a
phosphonic or sulphonic acid unit.
7. Dummy plate according to claim 1, wherein the content of organic
compound is at least 5%.
8. Dummy plate according to claim 7, wherein the content of organic
compound is at least 10%.
9. Dummy plate according to claim 8, wherein the content of organic
compound is at least 20%.
10. Dummy plate according to claim 1, wherein the protective layer contains
a biocide.
11. Dummy plate according to claim 1, wherein the protective layer contains
a sequestering agent.
12. Dummy plate according to claim 1, wherein the protective layer
additionally contains a polymeric, water-soluble film former.
13. A process for producing the dummy plate of claim 1, comprising applying
a coating solution at least twice and drying each coat.
14. A process according to claim 13, comprising applying the coating
solution twice.
15. Dummy plate for offset printing consisting of a plate-, sheet- or
band-form, mechanically and/or electrochemically roughened, anodically
oxidized and optionally hydrophilized aluminum support and a
non-photosensitive, water-soluble protective layer applied thereto,
wherein the layer contains a water-soluble organic compound which contains
at least one OH- or NH-acidic group having a pKa value of .ltoreq.8 as
acid or salt, and has a layer thickness which is smaller than the average
roughness ra of the aluminum support.
Description
TECHNICAL AREA OF THE INVENTION
The invention relates to a dummy plate for offset printing which
essentially consists of a mechanically and/or electrochemically roughened
anodically oxidized and aluminium support and a non-photosensitive,
water-soluble layer applied thereto, and to a process for the production
thereof.
PRIOR ART
In a printing machine, a plurality of plates are generally clamped
alongside one another and in succession on a printing cylinder. Dummy
plates are planographic printing plates without ink-carrying areas. They
are used where the paper band is not to be printed completely. A dummy
plate has the task of transferring damping solution applied over the
entire width of the cylinder to the paper band. At the same time, the
dummy plate must not take up the printing ink, so that this is not
transferred to the paper ("smearing"). A particularly large number of
dummy plates are necessary if, in multicolour offset printing, individual
colours are not needed on all pages and the respective inking systems are
then not supposed to transfer ink.
Dummy plates are usually roughened and anodically oxidized aluminium
plates. If desired, they can also be subjected to hydrophilizing
treatment, for example with phosphorus-containing compounds, as described
in DE 4423140. The disadvantage of these dummy plates is that they react
very sensitively to fingerprints and other external influences.
Fingerprints result, for example, in ink take-up and thus smearing in the
printing machine. In addition, it is found that the hydrophilicity of such
dummy plates worsens with time, and they therefore take up ink in the
printing machine and cause smearing. This effect is particularly
pronounced if the dummy plates have been exposed to the room air without
protection for an extended period and have taken up, for example,
moisture, dust or traces of oil. In order to eliminate the consequences of
fingerprints and to restore the hydrophilicity of the aluminium surface to
the original value, dummy plates are subjected to the normal development
process with subsequent gumming. The development cleans and hydrophilizes
the surface of the printing plate. Subsequent gumming protects the
surface. The dummy plates treated in this way have a significantly lower
tendency towards smearing in the printing machine.
EP 96200429 describes dummy plates which do not require a development step
before use in the printing machine. These dummy plates consist of an
aluminium support of the abovementioned type which has a
non-photosensitive, water-soluble protective layer of a water-soluble
polymer and an acidic inorganic substance. Preference is given to mixtures
of polyvinyl alcohol and inorganic phosphates/sulphates. However, it is
found that these materials lose their ink-repellent action after extended
storage at elevated temperature--which can be simulated by a forced
storage test for 24 hours at 100.degree. C.--and likewise result in
smearing during printing. It has furthermore been found that the
protective layers become tacky under moist storage conditions.
OBJECT OF THE INVENTION
The object of the invention is therefore to provide a dummy plate in which,
even after extended storage at elevated temperature, a development step is
not absolutely necessary in order to ensure a sufficiently ink-repellent
action during printing and which does not develop a tendency to stick
during storage at high atmospheric humidity levels. In addition, it should
be processable without problems in an automatic development unit with
developer and subsequent gumming. This additional requirement therefore
means that, in automatic printing-plate processing units, all plates,
including the dummy plates, are subjected to the normal development
conditions.
BRIEF DESCRIPTION OF THE INVENTION
The object is achieved by a dummy plate for offset printing which
essentially consists of a plate-, sheet- or band-form, mechanically and/or
electro-chemically roughened, anodically oxidized and optionally
hydrophilized aluminium support and a non-photosensitive, water-soluble
layer applied thereto. The layer is characterized in that it has a
water-soluble organic compound which contains at least one OH- or
NH-acidic group having a pKa value of .ltoreq.8 as acid or salt, and has a
layer thickness which is smaller than the average roughness ra of the
support material, determined by optical means.
DETAILED DESCRIPTION OF THE INVENTION
The organic compound preferably contains at least 3 acidic groups,
particularly preference being given to phosphonic acid and/or sulphonic
acid units. This compound can be a defined organic compound or a mixture
and/or polymer thereof. In the case of a salt, the counterions are
preferably monovalent cations, in particular sodium, potassium or
ammonium, the proportion of acidic groups in the form of a salt or free
acid also depending, besides on the pKa value, on the pH of the coatings,
which is preferably set to 2-8. The salt formation can also take place
intra-molecularly. The proportion of these organic compounds in the
protective layers is at least 5%, preferably >10%, particularly preferably
>20%.
The layer can furthermore contain, in particular, a water-soluble polymeric
film former. Examples thereof are polyvinyl alcohols, polyamides, such as
polyvinylpyrrolidone, starch derivatives, such as gum arabic, etc. The
proportion of these film formers is between 0 and 80%. In the case of the
use of polymeric organic compounds containing acidic units which have
film-forming properties, for example sulphonated polystyrene, the addition
of such film formers is not absolutely necessary.
The protective layer preferably also contains a sequestering agent. In
particular, sequestering agents are used whose structure corresponds to
the above-described organic compounds containing acidic units. Examples
which may be mentioned are aminocarboxylic acids and aminophosphonic
acids. The proportion of these additives is between 0 and 20%, preferably
between 5 and 15%.
The protective layers preferably contain a biocide as preservative.
Examples which may be mentioned are derivatives of 4-isothiazolin-3-one,
such as 2-methyl-4,5-trimethylene-, 5-chloro-2-methyl- and
2-methyl-4-isothiazolin-3-one, furthermore 2-bromo-2-nitro-1,3-propanediol
or chloroacetamide. The proportion of these additives is between 0 and 2%,
preferably between 0.01 and 1%.
Something which is not necessary for the function as a dummy plate, but is
advantageous in manufacturing the material, is the addition of surfactants
and dyes. Surfactants improve the coating behaviour. Dye additives
simplify inspection of the finished material. The amounts added are
generally less than 5%.
In the production of the novel dummy plates, a dilute aqueous solution
containing said constituents is generally applied to the roughened and
optionally hydrophilized aluminium support. The proportion of non-volatile
constituents in this coating solution varies depending on the coating
method; in the case of flow coating, solids contents of between 0.05 and
5% give good results.
The thickness of the water-soluble protective layer after drying is less
than the average roughness ra of the support material, determined by
optical means. At higher layer thicknesses, a tendency to stick when
stored under moist conditions is evident in these coatings. In the case of
support materials having roughness values ra of between 0.5 and 1.5 .mu.m,
films having densities of .gtoreq.1 g/ml give the best results at layer
weights of from 0.15 to 0.5 g/m.sup.2.
The aluminium plates, sheets or bands from which the novel dummy plates are
produced consist of aluminium or an alloy thereof. They are mechanically
and/or electrochemically roughened. The roughening is preferably carried
out electrochemically in dilute hydrochloric acid or nitric acid. During
the subsequent anodic oxidation, preferably in dilute sulphuric acid, an
oxide layer forms on the aluminium. The oxidation is preferably controlled
in such a way that the oxide layer has a weight of from 1 to 5 g/m.sup.2.
The aluminium material prepared in this way is then subjected, if desired,
to hydrophilizing treatment. The hydrophilization is preferably carried
out using phosphorus-containing compounds. Particular preference is given
here to organic polymers containing phosphorus-containing groups, in
particular phosphinic acid or phosphonic acid groups. Polymers of this
type are described, for example, in EP-A 069 320 and EP-A 069 318.
Particular preference is given to polyvinylphosphonic acid, also in the
form of a combination post-treatment, as described in DE 4423140. The
hydrophilization is generally carried out within a few seconds using
aqueous solution at elevated temperature.
The novel dummy plate does not have to be subjected to the development
process, even after extended storage at elevated temperature, but instead
can, after edging, be clamped directly onto the printing cylinder of the
printing machine. The water-soluble layer is removed by the damping
solution, producing the ink-repellent action.
During application of the protective layer, coating faults can occur which
cause undesired smearing during printing. Such faults can be avoided by
applying the aqueous coating solution to the aluminium support material in
at least two applications and drying each coat, so that the coating faults
occurring during the preceding application are compensated. Preferably, an
aqueous coating solution is applied twice and dried each time. Uncoated
areas which later result in smearing are reliably avoided in this way.
EXAMPLES
The examples below describe embodiments of the invention. Comparative
examples are denoted by an *.
The density of the films is in all cases >1 g/ml.
Example 1
An aluminium band which has been roughened electrochemically in
hydrochloric acid (ra value 1.25 .mu.m, determined using an optical
microprobe having a measurement spot radius of 1 .mu.m) and anodized in
sulphuric acid (oxide layer weight: 3 g/m.sup.2) and hydrophilized using a
0.2% aqueous polyvinylphosphonic acid solution at 60.degree. C. in 10
seconds is coated with in each case 1% aqueous solutions of the following
composition by means of a double application using a flow coater at a rate
of 0.35 g/m.sup.2 :
1-1*:
80% by weight of polyvinyl alcohol having a degree of hydrolysis of 75-79
mol % and a degree of polymerization P.sub.n of 300
4% by weight C.sub.12 -C.sub.14 -fatty acid ethoxylate containing 20 EO
units
16% by weight of 85% phosphoric acid
1-2*:
as for 1-1, but
16% by weight of ammonium dihydrogenphosphate (NH.sub.4 H.sub.2 PO.sub.4)
instead of the phosphoric acid
1-3:
40% by weight of the disodium salt of dodecyldiphenyl ether disulphonic
acid (surfactant)
25% by weight of the sodium salt of benzene-1,3-di-sulphonic acid,
9.8% by weight of citric acid monohydrate (sequestering agent),
25% by weight of the sodium salt of polystyrene-sulphonic acid
0.2% by weight of chloroacetamide as biocide.
The pH is adjusted to 7 using NaOH
1-4:
40% by weight of polyvinyl alcohol having a degree of hydrolysis of 75-79
mol % and a degree of polymerization P.sub.n of 300
25% by weight of the sodium salt of benzene-1,3-di-sulphonic acid,
9.8% by weight of citric acid monohydrate (sequestering agent)
25% by weight of the sodium salt of polystyrene-sulphonic acid,
0.2% by weight of chloroacetamide as biocide.
The pH is adjusted to 6 using NaOH.
1-5:
40% by weight of dextrin,
25% by weight of the sodium salt of benzene-1,3-di-sulphonic acid,
9.8% by weight of the trisodium salt of aminotris-methylenephosphonic acid
(sequestering agent)
25% by weight of the sodium salt of polystyrene-sulphonic acid
0.2% by weight of 2-methyl-4,5-trimethylene-4-iso-thiazolin-3-one as
biocide.
The pH is adjusted to 5 using NaOH.
1-6:
70% by weight of dextrin,
19.8% by weight of the trisodium salt of aminotris-methylenephosphonic acid
(sequestering agent)
10% by weight of polyvinylphosphonic acid
0.2% by weight of 2-bromo-2-nitro-1,3-propanediol as biocide.
The pH is adjusted to 5 using NaOH.
The sulphonic and phosphonic acids used in
Examples 1-3 to 1-6 have pKa values of .ltoreq.8.
1-7*:
Comparative plate without a protective layer
Plates 1-1 to 1-7 are stored a) for 20 hours at room temperature, b) for 20
hours at 100.degree. C. and an atmospheric humidity of <20% r.h and c) for
20 hours at 40.degree. C. and an atmospheric humidity of approximately 80%
r.h.
The plates were then proofed in a Roland-Favorit II printing machine with
Dahlgreen damping system and it is checked whether the dummy plates run
freely with less than 50 sheets (+=free after less than 50
sheets,-=smearing even after 50 sheets).
The results are shown in Table 1.
TABLE 1
______________________________________
Example Storage a) Storage b)
Storage c)
______________________________________
1-1* + - +
1-2* + - +
1-3 + + +
1-4 + + +
1-5 + + +
1-6 + + +
1-7* - - -
______________________________________
In addition, dummy plate samples 1-3 to 1-6 are developed in a development
unit at 24.degree. C. and a processing rate of 1.0 m/min in the following
negative developers:
______________________________________
2.0 parts by weight of sodium phenylsulphonate
1.4 parts by weight of NaOH
1.5 parts by weight of Graham salt
4.0 parts by weight of pelargonic acid
3.0 parts by weight of polyvinylmethylacetamide
4.0 parts by weight of benzyl alcohol
0.5 part by weight of potassium borate
rest to 100 parts by weight of demineralized water.
______________________________________
The results of the subsequent proofing test as described above are shown in
Table 2:
TABLE 2
______________________________________
Example Storage a) Storage b)
Storage c)
______________________________________
1-3 + + +
1-4 + + +
1-5 + + +
1-6 + + +
______________________________________
Example 2
An aluminium band which has been electro-chemically roughened in nitric
acid (ra value 0.95 .mu.m, determined using an optical microprobe having a
measurement spot radius of 1 .mu.m) and anodized in sulphuric acid (oxide
layer weight: 2 g m.sup.2) and hydrophilized firstly using a 0.1% aqueous
solution of phosphonomethylated polyethylenimine and subsequently with a
0.2% aqueous polyvinylphosphonic acid solution, in each case at 60.degree.
C. for 10 seconds, is coated with in each case 0.8% aqueous solutions of
the following composition by means of a double application using a flow
coater at a rate of 0.40 g/m.sup.2 :
2-1:
40% by weight of polyvinyl alcohol having a degree of hydrolysis of 75-79
mol % and a degree of polymerization P.sub.n of 300
40% by weight of dextrin
4% by weight of C.sub.12 -C.sub.14 -fatty acid ethoxylate containing 20 EO
units
16% by weight of 85% phosphoric acid
2-2*:
as for 2-1, but
16% by weight of ammonium dihydrogenphosphate (NH.sub.4 H.sub.2 PO.sub.4)
instead of the phosphoric acid
2-3:
20% by weight of the sodium salt of dioctyl-sulphosuccinate (surfactant)
25% by weight of the sodium salt of benzene-1,3-di-sulphonic acid,
4.8% by weight of the trisodium salt of
N,N-bis-carboxy-methyl-.beta.-alanine (sequestering agent)
49% by weight of the sodium salt of polystyrene-sulphonic acid
1.0% by weight of Acid Red 52, C.I. 45100
0.2% by weight of chloroacetamide as biocide
The pH is adjusted to 7 using NaOH.
2-4:
40% by weight of polyvinyl alcohol having a degree of hydrolysis of 75-79
mol % and a degree of polymerization P.sub.n of 300
20% by weight of dextrin
10% by weight of the sodium salt of phenylphosphonic acid
4.8% by weight of the trisodium salt of
N,N-bis-carboxymethyl-.beta.-alanine (sequestering agent)
24% by weight of the sodium salt of polystyrene-sulphonic acid
1.0% by weight of Acid Red 52, C.I. 45100
0.2% by weight of chloroacetamide as biocide
The pH is adjusted to 6 using NaOH.
2-5:
40% by weight of dextrin,
25% by weight of the sodium salt of phenylphosphonic acid,
9.8% by weight of the trisodium salt of aminotris-methylenecarboxylic acid
(sequestering agent)
24% by weight of the sodium salt of N-phosphono-methyl-polyethylenimine
0.2% by weight of 2-methyl-4,5-trimethylene-4-iso-thiazolin-3-one as
biocide.
1.0 % by weight of Acid Red 52, C.I. 45100
The pH is adjusted to 5 using NaOH.
2-6:
69% by weight of dextrin,
19.8% by weight of the trisodium salt of aminotris-methylenephosphonic acid
(sequestering agent)
10% by weight polyvinylmethylphosphinic acid
0.2% by weight of 2-bromo-2-nitro-1,3-propanediol as biocide.
1.0% by weight of Acid Red 52, C.I. 45100
The pH is adjusted to 5 using NaOH.
The sulphonic/phosphonic/phosphinic acids used in Examples 2-3 to 2-6 have
pKa values of .gtoreq.8.
2-7*:
Comparative plate without a protective layer
Plates 2-1 to 2-7 are stored a) for 20 hours at room temperature, b) for 20
hours at 100.degree. C. and an atmospheric humidity of <20% and c) for 20
hours at 40.degree. C. and an atmospheric humidity of about 80%.
The plates were subsequently proofed in a Roland-Favorit II printing
machine with Dahlgreen damping system and examined and set as in Example
1.
The results are shown in Table 3.
TABLE 3
______________________________________
Example Storage a) Storage b)
Storage c)
______________________________________
2-1* + - +
2-2* + - +
2-3 + + +
2-4 + + +
2-5 + + +
2-6 + + +
2-7* - - -
______________________________________
In addition, dummy plate samples 2-3 to 2-6 are developed in a development
unit at 24.degree. C. and a processing rate of 1.0 m/min in the following
negative developer:
______________________________________
1.0 part by weight of sodium cumenesulphonate
2.8 parts by weight of 1-amino-2-propanol
1.5 parts by weight of trisodium citrate
1.0 part by weight of Na.sub.2 SiO.sub.3
2.0 parts by weight of C.sub.12 -C.sub.14 -fatty acid
ethoxylate containing 15 EO units
remainder to 100 parts by weight of demineralized
water.
______________________________________
The results of the subsequent proofing test as described above are shown in
Table 4:
TABLE 4
______________________________________
Example Storage a) Storage b)
Storage c)
______________________________________
2-3 + + +
2-4 + + +
2-5 + + +
2-6 + + +
______________________________________
Example 3
An aluminium band is roughened (ra value 0.8 .mu.m) using a 40% aqueous
slurry of aluminosilicate having an average particle size of 40 .mu.m,
anodized in sulphuric acid (oxide layer weight: 1.8 g/m.sup.2) and
hydrophilized using a 0.2% aqueous polyvinylphosphonic acid solution at
60.degree. C. for 10 seconds.
The subsequent protective layer is applied in various thicknesses (see
Table 5) as a 0.8% aqueous solution:
______________________________________
70% by weight of dextrin,
18.8% by weight of the trisodium salt of aminotris-
methylenephosphonic acid
(seguestering agent)
10% by weight of polyvinylphosphonic acid
1.0% by weight of Acid Red 52, C.I. 45100
0.2% by weight of 2-bromo-2-nitro-1,3-propanediol
(biocide)
______________________________________
The pH is adjusted to 4.5 using NaOH.
The finished plates are stored as described in Example 1, and the plates
stored as in c) are firstly investigated for tendency to stick. (Table 5:
+=no evident tendency to stick, -=sticking of the plate samples).
TABLE 5
______________________________________
Example Layer thickness (.mu.m)
Adhesion test
______________________________________
3-1 0.2 +
3-2 0.4 +
3-3* 1.2 -
______________________________________
A proofing test is then carried out as described above. The results are
shown in Table 6:
TABLE 6
______________________________________
Example Storage a) Storage b)
Storage c)
______________________________________
3-1 + + +
3-2 + + +
3-3* + + - x)
______________________________________
x)=smearing tendency in the areas where the protective layer has been
damaged by adhesion.
Top