JPH0249638B2 - INSATSUBUZAIOYOBISONOKEISEIHO - Google Patents

Description

[Detailed description of the invention] Printing members for intaglio printing, especially gravure printing,
Traditionally has a printed surface formed from copper. Recently, various proposals have been made for forming printing surfaces of other materials. For example, UK patent specification nos. 1465364, 1498819 and 1517714.
No. 3, it is proposed to form the printing surface of the surface of two materials, one material defining the cells of the required pattern of cells, and the other material filling the cells, and e.g. It is resin. Epoxy coatings have also been proposed in British Patent Specification No. 1544748.

GB Patent Specification No. 2034636 discloses a method whereby the printing surface of an intaglio printing element can be formed from certain polymeric materials and engraved by means of ion, electronic or laser beams to produce a sharp print without a rim around the engraved area. We have described how you can obtain it. The preferred polymeric material is polyacetal copolymer, but epoxy coatings have also been described. The printing surface is generally preformed as a sheet and then applied to a support. Unfortunately, it can be rather difficult to form a satisfactory surface with this technique. British Patent Specification No.
In 2071574 it is proposed to form a printed surface by powder spraying a coating composition of epoxy powder containing little or no filler.

Various types of epoxy resins are known. For example, it is common practice to provide powdered epoxy coating compositions based on the diglycidyl ether of bisphenol A. Cycloaliphatic epoxy coating compositions are also known. Another type of epoxy coating composition is an epoxy novolak composition. However, it is known that such compositions tend to form surfaces with inferior surface properties compared to many other types of epoxy resins. For example, epoxy novolak resin
It is known that there is a tendency to increase the likelihood of an effect known as the "orange peel effect" occurring.

The use of epoxy novolaks as components to improve the adhesion between a support and a layer to be bonded thereto is known (eg, as in US Pat. No. 4,210,569). It is also known to blend urethanes formed between novolacs and polyisocyanates with epoxy resins, as in GB 2031442. However, it does not form an epoxy novolak.

As in UK Patent Specification No. 2071574,
We have found that when using conventional powdered epoxy compositions, reasonably satisfactory properties are obtained if the filler content is kept low, but when using laser or other light beams, It would be desirable to be able to achieve sharper engravings. That is, these epoxies tend to produce engraved cells with slightly sloped or irregular sides, which can result in a lack of sharpness when the resulting surface is used for gravure printing. Also,
It would be desirable to improve the abrasion resistance of printed surfaces.

Despite the known drawbacks of epoxy novolac resins, it has surprisingly been discovered that improved results are obtained when the printing surface of a printing member is formed from a composition comprising an epoxy novolac resin. That is, despite the known drawbacks of epoxy novolac resins, they have very satisfactory engraving and printing properties, in particular improved engraving properties (especially when engraving by laser) and It has now been discovered that it is possible to obtain printed surfaces which can have very good abrasion resistance.

Known novolac resins are suitable for use in the present invention. The resin is applied to the support in an uncured or partially cured state and then cured on the support to form the desired cured continuous printed surface. The epoxy novolac to be cured consists of a blend of epoxy and novolac, which reacts during curing, or of a novolac resin containing epoxy groups, which crosslinks during curing.

One type of epoxy novolak useful for use in the present invention is made by reacting a novolak resin with epichlorohydrin so that the resulting novolak resin is substituted with at least two epoxy groups per molecule. You can get it. Thus, it can be considered a glycidyl ether of novolac resins. It is cured on the support in the presence of a curing agent or accelerator.

Another and preferred type of novolak resin for use in the present invention is a blend of an epoxy resin and at least 0.5 moles of novolak resin per mole of epoxy resin. applying the blend to a support and curing it on the support;
Complete the reaction between the epoxy resin and the novolak resin. The epoxy resin that reacts with the novolak resin is preferably based on bisphenol A, and is generally a reaction product of epichlorohydrin and bisphenol A. This reaction product contains other components,
For example, it can be further reacted with a dimeric carboxylic acid. The novolak resin is preferably used in an amount of at least 1 mole, more preferably 1.1 mole or more, of novolak resin per mole of epoxy. Best results are generally obtained with about 1.25 moles of novolac resin per mole of epoxy, but as discussed below, in some cases a few or more moles of novolac resin per mole of epoxy may be preferred. Sometimes.

These epoxy novolac compounded resins will generally contain additional curing agents or accelerators to promote final curing.

The phenolic groups forming the novolac resins can be derived from the phenols themselves or from substituted phenols, such as cresol. The phenol is further substituted in addition to the hydroxy groups required to form the novolak, preferably some or all of the benzene groups in the novolak are additional hydroxy or alkoxy groups,
Particular preference is generally given to substitution by methoxy groups.

The printing member is prepared by applying a curable epoxy novolak composition onto a support, then curing it to form the desired continuous printing surface, and then polishing the printing surface to impart non-printing properties. make. Generally, application is by powder coating of powdered epoxy novolak compositions.

The powdered composition, and the printed surface ultimately produced therefrom, preferably consists primarily of epoxy novolac, with an amount of epoxy novolac generally being at least 80%, preferably at least 90% of the composition. Become. The composition will contain any necessary hardeners or accelerators, such as acid anhydride or amine hardeners. The compositions may contain small amounts, generally up to 10%, of common flow agents such as waxes, soaps and alkali metal salts.

The composition may contain some filler, but the amount
It should be less than 20% by weight, preferably less than 15% by weight. In particular, the composition contains common fillers,
For example, it is preferably free of bauxite, alumina or barium sulfate. Although the compositions can contain small amounts of various fillers, it is particularly preferred to contain carbon black, generally in an amount of 0.5 to 10% by weight, most preferably 1 to 5% by weight, based on the total composition. As explained in our UK Patent Specification No. 2071574,
Carbon black reduces the limitations required for laser engraving, thus improving engraving quality and maintenance of non-printing properties between engraved cells.

The composition may also contain from 0.05 to 10% by weight, most preferably from 0.5 to 5%, of an additive selected from graphite, polytetrafluoroethylene and, most preferably, molybdenum disulfide.
As explained in our UK Patent Application No. 8133417 filed on 5 November 1981:
Such additives, especially molybdenum disulfide,
Reduces tool wear during diamond grinding,
and increases the abrasion resistance of the resulting printing surface during printing.

The powder composition can be deposited on the support by electrostatic coating, flock spraying, fluidized bed coating or, preferably, a combination of electrostatic and fluidized bed coating. This latter method is particularly advantageous. This is because electrostatic coating ensures a very uniform deposition of a layer of single particles, and the fluidized bed technique deposits this uniform underlayer into a layer of the desired thickness and with great uniformity. .

The support is generally preheated to a temperature at which the powder melts when it contacts the support or when it contacts the epoxy resin already deposited on the support. The composition must be cured by heating on the support. Temperature and heating time will be selected taking into account the particular epoxy novolak and curing agent used, and their amounts. Commercially available systems generally require curing for 0.5 to 6 hours, preferably 2 to 4 hours, at a temperature of 180 to 250C, preferably 210 to 240C. However, these temperatures and/or times can be decreased by increasing the amount of accelerator in the composition.

In one method, the support is heated to a temperature sufficient to melt the powdered composition and form an adhesive layer, but not to harden the composition. After the desired thickness of the epoxy novolak composition has been deposited on the support, the entire assembly is then heated to a higher temperature at which curing will occur. However, in a more preferred embodiment, the support is preheated to the curing temperature of the epoxy resin, the epoxy resin is powder coated onto the heated support, and the epoxy resin flows substantially without further heating. In the presence of the resin, it forms a uniform layer of resin that hardens. Thus, little or no external heating is applied and melting and curing result entirely from preheating of the support. This is highly advantageous as it eliminates the need for heating the printing member after the powder coating step. The powdered epoxy novolak composition must be formulated in a known manner so that it does not unacceptably sag or run at melting and curing temperatures.

The surface obtained by melting and curing the powdered composition is then polished to provide non-printing properties in intaglio printing. Generally, the support and printing surface are cylindrical and polishing is by diamond grinding, although various methods of imparting non-printing properties to the intaglio surface are effective and can be used.

The printing surface is then generally engraved with an ion or electron beam, preferably with a laser. The printing surface must be thick enough to be engraved to the desired depth. For example, if an intaglio printing surface is engraved to a depth of up to 30 microns, and the epoxy novolak layer is typically 0.2 to 1.5 mm, preferably
The thickness is between 0.4 and 1 mm, most preferably between 0.6 and 0.8 mm.

This is when the engraving results in waste that is easy to remove, as the rim around each cell or other location
As described in British Patent Specification No. 2071574:
It can be removed with solvents or chemical etching agents. Although the surface can then be subjected to electroless metal plating as described in the above specification, a particular advantage of the present invention is that the printed surface can be very well coated without plating. This means that it can have excellent abrasion and scratch resistance.

In particular, it has been found that by applying further heating steps it is possible to greatly increase the scratch and abrasion resistance of the hardened surface.

Curing conditions (prior to polishing) were selected to optimally cure the polymeric composition containing epoxy groups. It is well known that further curing of epoxy compositions by application of high temperatures is generally undesirable as it can result in stress cracking and deterioration.

The surprising improvement in properties that we obtained by further heating the polished surface is therefore particularly unexpected.

This further high temperature treatment or hardening, likened to "case hardening", can be applied to a polished surface before engraving, or it can be applied to an engraved surface. When it is applied to a polished surface before engraving, it is common to polish the surface before post-curing and after engraving.

Post-curing is accomplished by exposing the polished surface to elevated temperatures, generally higher than the curing temperature used prior to polishing. Temperature is generally 180-280
°C, preferably 200-260 °C, most preferably about
240°C and for 0.5 to 6 hours, preferably 1
Apply for ~3 hours. Heating appears to cause a condensation reaction between the phenolic groups of the novolak and the resulting removal of water. It appears that the reaction occurs only on the outer surface of the layer. Choosing the optimal conditions for heating is easy by routine experimentation and observation of the temperature that gives maximum hardness and scratch resistance after the polishing operation.

The effectiveness is greatest when the novolak epoxy resin contains reactive groups capable of participating in condensation reactions. Thus, novolac epoxy resins contain an excess of novolac, preferably at least 1.25 moles of novolac per mole of epoxy, and preferably:
It is desirable to contain significantly higher numbers of novolaks, eg, up to 2 or 3 moles or more per mole of epoxy. Another way to ensure particularly good final properties is to form novolaks from phenols containing more substituents than a single hydroxy group of the phenol, for example, the phenol component contains at least a secondary hydroxy group and It is preferable to contain/or an alkoxy group, preferably a methoxy group. Best results are obtained when the phenolic component of the novolac is a methoxy or other alkoxy substituted benzenediol and when the phenolic component is present in an amount of at least 1.2 moles per mole of epoxy.

This high degree of In order to ensure good adhesion between the more reactive epoxy novolak and the metal or other support on which the printed surface is formed, it may be desirable to use a less reactive epoxy novolak. For example, typically 50 to
A primer layer of 175 microns, and typically about 125 microns, is formed from a conventional relatively low functionality novolatile epoxy, followed by a 150-500 micron, typically 200-300 micron, more highly functional epoxy. A topcoat of high performance epoxy can be applied in which the novolac is present in greater amounts and/or formed from phenols containing additional hydroxy or other suitable substituents. The primer layer consists primarily of epoxy novolak and hardener, while the outer layer preferably includes carbon black, as described above. The increased wear resistance that can be obtained as a result of "case hardening" may be so high that the inclusion of molybdenum sulfide in the composition of the outer layer may be unnecessary.

It is highly undesirable to have water molecules trapped in successive layers of epoxy novolak compositions, especially when the powder coating or each powder coating is coated at low relative humidity.
It has been observed that it is desirable to operate under conditions of preferably 30% or less, most preferably 15% or less.

The following examples further illustrate the invention.

Example 1 A metal cylinder is heated to 200°C and, while grounded, a powdered epoxy composition is sprayed onto the cylinder using an electrostatic powder spray gun. The composition consists primarily of a phenol novolac epoxy formed by the reaction of a phenolic novolac and epichlorohydrin, but also contains other additives, excluding conventional hardeners and fillers, namely:
2 as an air release agent, based on the weight of the total composition.
% benzoin, 2% molybdenum sulfide and 5%
Contains % carbon black. When the desired coating thickness of about 0.8 mm was achieved, the cylinder and coating were heated to about 220° C. for 3 hours;
Melt and cure the coating. It is then diamond ground, laser engraved, optionally etched, and further etched as described in GB Patent Specification No. 2071574 and metallized. Glance.

Example 2 A cylinder is powder coated as in Example 1, but with two different compositions. The first composition is a phenol novolac epoxy applied to a thickness of 125 microns and formed by the reaction of 1.25 moles of phenolic novolac with epichlorohydrin, the phenolic component of the novolac being hydroxybenzene. . This primer composition also contains a curing agent and an air release agent. On top of the primer composition, apply a 250 micron thick layer of phenol novolac epoxy, which is formed by the reaction of 1.25 moles of phenolic novolac with epichlorohydrin, the phenolic component being It is methoxybenzenol. This outer layer also contains a hardening agent and 5
Contains % carbon black. Both compositions are sprayed under conditions of low relative humidity, approximately 15%.

The cylinder and coating are heated to about 220° C. for 3 hours to melt and harden the coating.
The coating is then diamond ground to its non-printing properties and then further heated to 240° C. for 2 hours. It is then laser engraved and, if necessary, etched. It can then be used for gravure printing.

Example 3 Bisphenol A epichlorohydrin resin is reacted with a dimeric acid and the reaction product 90
parts by weight are combined with 10 parts by weight of a low molecular weight novolac resin formed by the reaction of formaldehyde and dihydroxymonomethoxybenzene. The blend is heated to partially react, then cooled and solidified to stop the reaction and produce a powder. 100 parts of this powder are combined with 6 parts of carbon black, about 0.5 part of benzoin, and a small amount of a polyacrylic acid flow agent, trade name Modaflow.

The metal cylinder is heated to 220°C and the powdered epoxy composition is sprayed onto it by an electrostatic powder spray gun. If desired, the metal cylinder can be first coated with a primer as in Example 2. The powdered composition is applied to a coating thickness of about 0.8 mm and it cures on the support while the support cools to ambient temperature.

The coated support is then diamond ground and laser engraved to form an intaglio printing surface. Then it is heated to 240°C for 3 hours.

The resulting printing member can be used to test printing over a million copies.

EXAMPLE 4 The method of Example 3 is repeated but using a 7:3 epoxy:novolac weight ratio and additionally using a small amount of 2-methylimidazole as accelerator.

Claims (1)

[Claims] 1. The epoxy resin is an epoxy novolak.
A printing member having a printing surface of epoxy resin, characterized in that: 2. Epoxy novolaks are obtained by curing novolak resins substituted with at least two epoxy groups per molecule or by reacting epoxy resins with at least 0.5 moles of novolak resin per mole of epoxy resin. The printing member according to claim 1, which is made of resin. 3. The epoxy novolac is a resin obtained by reacting 1 mol of epichlorohydrin-bisphenol A epoxy resin with at least 1.1 mol of novolac resin. The printing member according to range 2. 4 Powder-coating epoxy resin powder onto a support,
The epoxy resin powder is an epoxy novolak composition in the process of forming a printed member by subsequently melting and curing the coating and polishing the printed surface to impart non-printing properties.
A method characterized by: 5 The epoxy novolak composition is a blend of a curing agent and a novolak resin substituted with at least two epoxy groups, or the epoxy resin is formulated with at least 0.5 moles of novolak resin per mole of epoxy resin. 5. A method according to claim 4, characterized in that it is obtained by: 6 Patent, characterized in that the epoxy novolak composition is a composition obtained by blending 1 mol of epichlorohydrin-bisphenol A epoxy resin with at least 1.1 mol of novolak resin. The method according to claim 5. 7. The method according to any one of claims 4 to 6, characterized in that after polishing the printed surface, it is heated to further harden the surface layer of the epoxy resin. 8. Heating after polishing is performed at a temperature of 200 to 260°C for 0.5 to 6 hours. The method according to claim 7. 9. Process according to claim 7 or 8, wherein the novolac resin is formed from a phenol substituted by at least one additional hydroxy group and/or by an alkoxy group. 10. The method according to claim 7 or 8, wherein the novolak resin is a methoxy-substituted monovalent or divalent phenol. 11 The epoxy resin is made from a resin of 1 mole of bisphenol A epichlorohydrin, and from 1.25 to
11. A method according to any of claims 7 to 10, formed from 3 moles of novolak resin. 12. The method according to any one of claims 7 to 11, wherein further heating is performed after engraving the surface. 13 Preheating the support to the curing temperature of the epoxy novolac resin and powder coating the resin powder onto the heated surface, the resin powder flowing into a uniform layer of the desired thickness and then substantially overlapping. 13. A method according to any one of claims 4 to 12, characterized in that the curing occurs in the absence of heating. 14 Claims 4 to 1, characterized in that the printing surface is engraved with a laser after being polished.
The method described in any of Section 3.