DK146896B - PHOTOSENSIBLE RESIN MATERIAL FOR PREPARING A FLEXOGRAPHIC PRINT PLATE - Google Patents

Description

146896

The present invention relates to a photosensitive resin material for the production of a flexographic printing plate which has improved properties, particularly with respect to liquids, such as aqueous or alcoholic colors commonly used in the printing range.

Flexography is a letterpress area that requires the sheet material used for it to have elasticity just like rubber materials.

In flexography, aqueous or alcoholic inks are usually used for printing, so that sheet materials are required which possess -o such properties that they are not transformed or swelled upon continuous contact with such inks. To date, flexographic printing plates have usually been manufactured in one of two ways. In one method, a metal master plate is first prepared from a negative and a matrix which is constituted by a phenol-formaldehyde condensate, e.g. "Bakelite®11 is made from the master plate, and raw rubber is poured onto the matrix and then vulcanized. This process is so complicated that improvements have long been desired. Another method requires specialized work, creating relief patterns directly by cutting or engraving the rubber sheets.

In order to improve such methods, a method using photosensitive materials has also been proposed. In this process, the material is cured by irradiation with light through a negative with transparent image areas, and the uncured areas are washed out with liquids such as water, alkaline solutions or alcohols. Accordingly, this process requires the use of photosensitive materials which are soluble in such liquids. The materials commonly used for this purpose are resistant to such liquids which are insufficient to meet the requirement of printing a rather large number of paper.

The plates employing these materials may be subject to swelling, thereby deteriorating the quality of the printed designs. Conventional photosensitive resins are not satisfactory in terms of elasticity, hardness and elongation and thus cannot replace rubber materials.

It is also known that a syndiotactic polymer of 1,2-butadiene can be used as photo-curable material in combination with a photosensitizer because it can be readily cross-linked by ultraviolet irradiation due to the double bonds in the side chains as described in ACS Symposium Series, No. 4, pp. 26-35 (1974) and Japanese Publication Nos. 10521/1976 and 28041/1977. It is stated therein that the combination of a syndiotactic polymer of 1,2-butadiene and a photosensitizer can be used as a resin matrix prepared by pressing it onto a master plate and then curing by the action of ultraviolet radiation. However, it is to be noted that the pure combination of the syndiotactic polymer of 1,2-butadiene with the photosensitizer does not possess sufficient sensitivity to light irradiation and cannot provide cured image areas with a satisfactory cure rate. The lack of sufficient hardness will cause the cured image areas of the printing plate to swell upon washing with xylene and that some portions of the cured areas, preferably fine contours, will be destroyed and washed out. This is an exceedingly great disadvantage and renders such a material useless as a printing pad.

It has now been found that the addition of an ethylenically unsaturated monomer and a photopolymerization initiator to a syndiotactic polymer of 1,2-butadiene can improve light sensitivity. The advantages presented by using the syndiotactic polymer of 1,2-butadiene are the rubbery properties, the high resistance to liquids such as water and alcohols, and the low cost of materials. Accordingly, the syndiotactic polymer of 1,2-butadiene in this combination can produce flexographic printing plates with advantageous properties which are valuable for this purpose without having the disadvantages of the known materials.

The invention thus relates to a photosensitive resin material for producing a flexographic printing plate and containing a syndiotactic polymer of 1,2-butadiene, which resin material is characterized in that it is in the form of at least one syndiotactic polymer of 1,2-butadiene. an ethylenically unsaturated monomer and a photopolymerization initiator, the syndiotactic polymer of 1,2-butadiene having an average molecular weight of from ca. 10,000 to 300,000, a content of units derived from 1,2-butadiene of at least approx.

35 and a crystallinity of approx. 10 to 30%, the ethylenically unsaturated monomer is an acrylic or methacrylic acid ester having an alkanol having from 4 to 20 carbon atoms, and the photopolymerization initiator is benzoin and / or an alkyl ether thereof. It should be noted that combining the monomer and initiator with the polymer of 1,2-butadiene can significantly increase the sensitivity to light and prevent swelling of image areas during leaching of the uncured 05 areas with xylene, thereby producing excellent patterns which provide excellent overall sharpness. It is known that a photosensitive resin can be prepared from such a polymeric binder by the addition of an ethylenically unsaturated monomer of the commonly used type.

However, it is extremely difficult to thoroughly and uniformly mix a syndiotactic polymer of 1,2-butadiene with such ethylenically unsaturated monomer as acrylic acid, methacrylic acid and esters thereof, e.g. acrylates or methacrylates, due to the poor solubility of the polymer of 1,2-butadiene in aliphatic hydrocarbons and the insolubility in ketones and alcohols.

It has now been found that a certain type of ethylenically unsaturated mono has better compatibility with the syndiotactic polymer of 1,2-butadiene and is uniformly mixed with it. This type of ethylenically unsaturated monomer does not require the use of any solvent for mixing, so that the resin material can be easily melted into 20 sheets or sheets. This is extremely advantageous in the manufacture of large-scale, low-cost flexographic graphics sheets or plates.

The use of a photopolymerization initiator with good solubility in the monomer serves to prevent the initiator from being separated from the shaped sheet products.

The syndiotactic polymer of 1,2-butadiene used according to the present invention is any polymer of 1,2-butadiene which has an average molecular weight of from approx. 10,000 to 300,000, a content of units derived from 1,2-butadiene of approx. 80 to 100 percent and a crystallinity of from approx. 10 to 30 percent.

Especially such polymers of 1,2-butadiene, which have an average molecular weight of from approx. 100,000 to 200,000 ,, a content of units derived from 1,2-butadiene of approx. 90 to 100 percent and a crystallinity of from approx. 15 to 25 percent, possess properties that make them suitable for flexographic printing plates by virtue of their rubbery elasticity and their resistance to liquids such as water or alcohols. The syndiotactic polymers of 1,2-butadiene generally have a melting point in the range of about 65 to 110 ° C. This is extremely advantageous in forming the material into sheets or sheets because the thermal polymerization of the ethylenically unsaturated monomers does not take place at this temperature range during melt formation.

The ethylenically unsaturated monomers for use in accordance with the present invention are esters of acrylic acid or methacrylic acid having an alkanol containing from 4 to 20 carbon atoms. Examples of the esters include butyl acrylate, isobutyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, neopentylacrylat, octyl acrylate, lauryl acrylate, stearyl rylacrylat, butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, 10 2-ethyl hexyl methacrylate, neopentyl methacrylate, octyl methacrylate, lauryl methacrylate, stearyl methacrylate, 1.6 -hexyldiacrylate, neopentyl diacrylate, 1,6-hexyldimethacrylate or neopentyl dimethacrylate. The ethylenically unsaturated monomers can be used alone or in combination with each other. They can be used in an amount in the range of from approx. 15 to 300, preferably from 5 to 150 parts by weight per unit weight. 100 parts by weight of the syndiotactic polymer of 1,2-butadiene. Additional unsaturated monomers, i.e. other than said ethylenically unsaturated monomers, may also be used in combination with the latter, but only in such an amount that they do not adversely affect the compatibility of the 20 ethylenically unsaturated monomers with the polymer of 1,2-butadiene because the further unsaturated monomers of itself lacks the necessary compatibility thereby. Examples of such monomers are e.g. ethylene glycol diacrylate or dimethacrylate, trimethylol propane triacrylate or trimethacrylate, trimethylolethane triacrylate or trimethacrylate, acrylamide, methacrylamide or Ν, meth-methyl bisacrylamide or bismeth acrylamide.

The photopolymer initiator for use according to the invention is benzoin or an alkyl ether thereof, the alkyl portion of the ether preferably having from 1 to 8 carbon atoms. The alkyl moiety may be a straight-chain or branched aliphatic alkyl group and comprises e.g. methyl, ethyl, isopropyl, n-butyl or octyl. The benzoin and the alkyl ether thereof do not undergo pyrolysis at temperatures below ca. 100 ° C, and no dark reaction occurs during molding of the sheet or sheet material. This means that the resin material containing the photopolymer initiator does not undergo a phenomenon whereby the material is cured by the application of heat during the forming step. The photopolymerization initiator can be used in an amount of from approx. 0.025 to 30, for incrementally from ca. 0.1 to 15 parts by weight relative to 100 parts by weight of the syndiotactic polymer of 1,2-butadiene.

Also, photosensitizers can be added to the photosensitive resin materials of the invention to further increase their sensitivity to light by photopolymerization. Such photosensitizers may e.g. include anthracene, p-dinitrobenzene, 2-chloro-4-nitroaniline, 9-antranylaldehyde, benzophenone, benzil, ρ, ρ'-tetramethyldiaminobenzo-phenone, 1,2-benzanthraquinone, 1,2-naphthoquinone or 4-naphthoene. quinone.

The flexographic printing plates made from the photosensitive resin materials of the invention usually have the same hardness as rubber materials of the type used for flexographic purposes and can therefore be used as a replacement for the previously known flexographic rubber sheets. The flexographic printing plates must necessarily have different hardnesses and elasticities depending on the type of materials to be printed and the inks. When the resin material of the invention alone cannot provide a flexographic plate of sufficient hardness or elasticity, it is possible to further employ a plasticizer such as a polymeric plasticizer containing at least one of the compounds ethylene, isoprene and butadiene as the polymer component or a liquid. plasticizer. Examples of such polymeric plasticizers are polyisobutylene, polybutene, polyisoprene rubber, ethylene-propylene rubber, other polybutadiene rubber, styrene-butadiene rubber, or ethylene-vinyl acetate copolymer. The liquid plasticizers are those which have an alkyl substituent in the side chain and a boiling point higher than ca. At normal pressure and may include dialkyl phthalates, dialkyl adipates, trialkyl trimellites and alkyl vinyl ethers, the alkyl moieties being the same or different and containing from four to twenty 30 carbon atoms. Examples of liquid plasticizers are e.g. dibutyl, dihexyl, di-2-ethylhexyl, diheptyl, diocetyl, dinonyl or diisodecyl phthalate, di-2-ethylhexyl, dioctyl or diisodecyl adipate, trioctyl or triisodecyl trimethyl lithyl and octyl or lyl . These plasticizers have such a low degree of solubility in water or alcohols that they do not adversely affect the color resistance of the resulting flexographic printing plates.

The addition of such plasticizers does not adversely affect the quality of the resulting plates in terms of solubility. The plasticizers can be added in an amount of from approx. 5 to 150, preferably from ca. 10 to 100 parts by weight per unit weight. 100 parts by weight of the syndiotactic polymer of 1,2-butadiene and they can be selected 05 depending on the hardness required by the flexographic printing plate for use. The plasticizers can be used alone or in combination with each other. An additive may be added for the purpose of controlling photosensitivity, improving wavelength selectivity, and / or preventing the light reflectance phenomenon, and may include a polymerization inhibitor, a dye, a stretch pigment and a filler. Examples of such inhibitors are hydroquinone, p-methoxyphenol, tert-butyl catechol or 2,6-di-tert.-butyl-β-cresol. Dyes such as eosin, rose bengal, methyl violet, methylene blue and malachite green can also be added in any ratio. Further, stretching pigments or fillers such as glass fibers, polyethylene and polymethyl methaacrylate, preferably in powder form, may also be added.

The photosensitive resin materials of the invention can be prepared by admixing the syndiotactic polymer of 1,2-butadiene, the ethylenically unsaturated monomer and the photopolymerization initiator. With the resin material, a plate with relief pattern for use as a fiexographic plate can be prepared as follows. For example, a suitable amount of pills of syndiotactic polymer of 1,2-butadiene is mixed with a solution of a given amount of the photopolymerization initiator in a suitable amount of the ethylenically unsaturated monomer 25 by means of a mixer. A temperature at which the mixture is effected may preferably be from room temperature to approx. 60 ° C. The mixture allows the solution to penetrate into the pillars to form pills with a uniform distribution of the solution therein. When the polymeric plasticizer is used, it is milled with the syndiotactic polymer of 1,2-butadiene and formed into pellets. The liquid plasticizer can be used in the form of a solution in the ethylenically unsaturated monomer. The soaked pellets are then melted at a temperature of approx. 90 ° C or more, e.g. up to approx. 160 ° C, in conventional manner, for sheets having a thickness of approx. 0.1 to 10 mm. The molding process may be pressing, extrusion or injection molding. The products thus formed can be used, as they are, for flexographic purposes. When the shaped sheets or sheets are too thin, it is preferable to use a support for the sheet or sheet.

Such support may e.g. include a sheet of polyester, nylon or a synthetic rubber.

The shaped sheets or sheets can be further processed to use O5 as flexographic sheets. The surface of the shaped sheets or sheets is slightly sticky, as is characteristic of rubber materials, so it may sometimes be difficult to bring a negative into close and uniform contact with the surface of the sheet. In order to avoid this difficulty and to facilitate the close contact of a negative with the formed sheet 10 or the shaped plate, the surface of the shaped product may optionally be subjected to a side treatment that the molten resin material is formed into sheets or sheets on a polyester sheet which is treated by grinding. The polyester sheet is then removed after being cooled. This treatment can give the shaped product the same effect as if the abrasive treatment had been carried out directly on the surface thereof. The sheet thus treated may allow a uniform and close contact with the negative. This treatment may also serve to facilitate the printing ink retention capability.

2® In preparing a flexographic printing plate from the master plate of the photosensitive resin material of the invention, the master plate is brought into close contact with a negative film by a vacuum pressure device and exposed by ultraviolet radiation from a suitable source commonly used in this field. , Such as a high-pressure mercury lamp, a chemical lamp, or a carbon arc lamp for a predetermined period of time. After the negative film is removed, the master plate is then subjected to treatment with an aromatic hydrocarbon such as xylene or toluene or a halogenated hydrocarbon such as chloroform, trichloroethane, trichloroethylene or tetrachloroethylene, thereby washing out the uncured areas. These hydrocarbons can be used alone or in combination with alcohols, ketones or ethers.

This treatment can be carried out in a conventional manner, e.g. by brushing the surface of the master plate into the liquid or by spraying the liquid against the surface of the plate. The thus treated master plate, after drying, can be further subjected to re-exposure by ultraviolet radiation. The resulting flexographic printing plate bears patterns having edges that are sharp and clear and resistant to aqueous or alcoholic printing in combination with good rubbery elasticity.

The following examples illustrate the present invention. Parts are on a weight basis.

Example 1

A photosensitive resin material consisted of the following ingredients: Syndiotactic polymer of 1,2-butadiene "JSR RB 810", content of units derived from 1,2-butadiene 90%, crystallinity 15% 100 parts 10 Neopentylglycol dimethacrylate 30 parts

Lauryl methacrylate 10 parts

Benzoin isopropyl ether 3 parts

The last three ingredients were mixed together to form a solution which was then again mixed with the pills of the syndiotactic polymer of 1,2-butadiene for approx. 1 hour at 40 ° C by means of a mixer, whereby the solution was uniformly contained therein. Next, the pellets were formed into sheets with a thickness of 2 mm on a polyester sheet with a 2 mm spacer, which sheet was previously subjected to abrasive treatment on both sides by means of a press at a temperature of 110 ° C and a pressure of 10 kg per cm for a period of approx. 50 seconds. After the sheet had cooled, the polyester sheet was removed from its surface. The shaped sheet was then brought into close contact with a negative film by means of a vacuum pressure device and irradiated with a 3 kilowatt high pressure mercury lamp for 5 minutes at a distance of 25 80 cm. After the exposure was completed, the negative was removed and the xylene was sprayed onto the exposed surface at a pressure of 2 kg / cm for 4 minutes, leaving a relief pattern with a depth of approx.

700 µ was produced. The sheet was dried using a drying device and again subjected to exposure with the mercury lamp for 3 minutes.

The resulting printing plate could reproduce a very clear pattern of the negative. It was also found that the plate had a sufficient hardness of 90 degrees measured by a "Shore A Durometer".

Example 2

A photosensitive resin material consisted of the following ingredients:

35 Syndiotactic polymer of 1,2-butadiene "JSR

RB 810 ", 100 parts

Lauryl methacrylate 18 parts

Trimethylol propane trimethacrylate 4 parts

Benzoin isopropyl ether 3 parts 146896 9

These ingredients were treated in the same manner as in Example 1 to produce a printing plate of sufficient rubber elasticity and with a hardness of approx. 75 degrees.

Example 30 A resin material consisted of the following ingredients:

Syndiotactic polymer of 1,2-butadiene "JSR RB 820", content of units derived from 1,2-butadiene 92%; crystallinity 25% 100 parts 2-ethylhexylmethacrylate 60 parts 10 Benzoin isopropyl ether 2 parts

These ingredients were treated in the same manner as in Example 1 to produce a printing plate. This plate was found to have a hardness of 85 degrees with sufficient rubber elasticity.

Example 4 A resin material consisted of the following ingredients:

Syndiotactic polymer of 1,2-butadiene "JSR RB 810", 100 parts

Neopentylglycol acrylate 10 parts

Diisodecyl phthalate 30 parts 20 Benzoin isopropyl ether 3 parts p-methoxyphenol 0.05 parts

These ingredients were treated in the same manner as in Example 1 to produce a printing plate. This plate was found to have a hardness of 65 degrees with sufficient rubber elasticity.

Example 5

A resin material consisted of the following ingredients:

Syndiotactic polymer of 1,2-butadiene "JSR RB 810", 100 parts

Neopentyl glycol dimethacrylate 10 parts 30 Stearyl vinyl ether 30 parts

Benzoin isopropyl ether 3 parts p-methoxyphenol 0.05 parts

These ingredients were treated in the same manner as in Example 1. The resulting printing plate was found to have a hardness of 60 to 35 degrees with sufficient rubber elasticity.

146896 10

Example 6

A resin material consisting of the following ingredients was prepared:

Syndiotactic polymer of 1,2-butadiene 05 "JSR RB 810", 100 parts

Polyisoprene Rubber "JS IR 2200" 30 parts

Neopentyl glycol dimethacrylate 10 parts

Lauryl methacrylate 30 parts

Benzomisopropyl ether 3 parts 10 p-methoxyphenol 0.05 parts

A mixture of syndiotactic polymer of 1,2-butadiene and polyisoprene rubber was rolled on a rolling mill with a surface temperature of 140 ° C and cut into paste. Then the pastes were mixed with the other ingredients by a mixer and the mixture was treated in the same manner as in Example 1. This gave a printing plate having a 50 degree rubber hardness and a good rubber elasticity.

reference Example

A mixture of 100 parts of syndiotactic polymer of 1,2-butadiene "JSR RB 810" and 3 parts of benzomisopropyl ether was roll formed on a 20 mill with a surface temperature of 140 ° C and then treated in the same manner as in Example 1 by means of a press and thereby providing a resin master plate.

The resin master plate was compared with resin master plates made from the materials of Examples 1-6 with respect to properties 25 as printing plate.

The property survey was conducted as follows:

Each of the resin master plates was exposed through identical test card negatives by ultraviolet irradiation for 5 minutes (Examples 1-6) and 10 minutes (Reference Example), and the uncured 30 areas were removed by spraying xyi to the exposed surface of the plate with a spray pressure of 2 kg. per. cm. Next, the plate was dried and exposed again by ultraviolet radiation. The plate thus treated was examined in terms of relief depth, minimum line width, halftone point and solubility.

35 The halftone point study was conducted to determine whether points with a diameter of approx. 30 µ in lines drawn with 26 lines per cm remains or not after xylene treatment. In the subsequent table, "good" means that all the points present on the survey card negative used are left, and "bad" means that nothing or little remains of such points.

jj; 05 Resin Relief - Minimum Halftone Resolution Material Depth Line Width Point Ability_

Ex. 1 0.7 mm 100 µ good 59

Ex. 2 0.7 mm 100 µ good 33

Ex. 3 0.7 mm 110 µ good 33 10 Ex. 4 0.8 mm 150 µ good 52

Ex. 5 0.8 mm 150 µ good 52

Ex. 6 0.7 mm 150 µ good 52

Reference Example 0.6 mm 300 μ poor 26 15 __ $ The value of the solubility is expressed in lines per cm.

This value discussed above means that even lines drawn at 26 lines per cm does not dissolve; the hardened 20 areas were partially dissolved and made uneven.

The table indicates that the photosensitive resin material of the present invention exhibits excellent overall properties.

Claims (7)

146896 1. Photosensitive Resin Material for Preparation of a Flexographic Fish Printing Pad Containing a Syndiotactic Polymer of 1,2-Butadiene, CHARACTERIZED IN THE FORM OF AT LEAST ONE SYNDIOTACTIC POLYMER OF 1,2-BUTADINE, AN ETHYLENICALLY UNSATURED monomer and a photo-polymerization initiator, the syndiotactic polymer of 1,2-butadiene having an average molecular weight of from ca. 10,000 to 300,000, a content of units derived from 1,2-butadiene pi at least. 10 approx. 80% and a crystallinity pi. 10 to 30%, the ethylenically unsaturated monomer is an acrylic or methacrylic acid ester having an alkanol having from 4 to 20 carbon atoms, and the photopolymerization initiator is benzoin and / or an alkyl ether thereof. 2. A photosensitive resin material according to claim 1, characterized in that the ethylenically unsaturated monomer is present in an amount of pi from ca. 5 to 300 parts by weight, preferably from ca. 5 to 150 parts by weight, and the photopolymerization initiator is present in an amount of from approx. 0.025 to 30 parts by weight, preferably from ca. 0.1 to 15 parts by weight, per 100 parts by weight of the syndiotactic polymer of 1,2-butadiene. 3. A photosensitive resin material according to claim 1, characterized in that the syndiotactic polymer of 1,2-butadiene has an average molecular weight of from approx. 100,000 to 200,000, a content of units derived from 1,2-butadiene of at least approx. 90% and a crystallinity of approx. 15 to 25%. 4. Photosensitive resin material according to claim 1, characterized in that the ethylenically unsaturated monomer is an alkyl acrylate, alkyl methacrylate, alkyl diacrylate or alkyl dimethacrylate. 5. Photosensitive resin material according to claim 1, characterized in that the photopolymer initiator is an alkyl ether of benzoin, wherein the alkyl moiety is a straight or branched aliphatic alkyl group having from 1 to 8 carbon atoms. 6. Photosensitive resin material according to claim 1, characterized in that it contains a plasticizer. 7. Photosensitive resin material according to claim 6, characterized in that the plasticizer material is contained in an amount of from approx. 5 to 150 parts by weight, preferably approx. 10 to 100 parts by weight, per 100 parts by weight of the syndiotactic polymer of 1,2-butadiene.