WO1997034199A1

WO1997034199A1 - Photosensitive resin composition and coating comprising said composition

Info

Publication number: WO1997034199A1
Application number: PCT/NL1997/000126
Authority: WO
Inventors: Stuart Arthur Harris; Theodorus Kessler; Albertus Koster; Gerardus Franciscus Joseph Pouwels
Original assignee: Stork Screens B.V.
Priority date: 1996-03-15
Filing date: 1997-03-12
Publication date: 1997-09-18
Also published as: AU2046197A; NL1002628C2; ID20061A

Abstract

A photosensitive base resin composition for a photoresist to be used in screen printing comprises a photopolymer and an alkyd resin. Such a composition affords a nontacky coating layer. If required, other resins such as an amino resin and/or phenol resin can be incorporated in the composition, if this is required for chemical resistance. In particular, the composition comprises 5-30 % of a poly(vinylalcohol), which has been grafted with stilbazolium, as a photopolymer, 20-80 % alkyd resin and 10-70 % of one more other resins (percentages given as solid matter of base composition).

Description

Photosensitive resin composition and coating comprising said composition

The invention relates to a photosensitive resin composition which comprises a photopolymer and a polyester resin.

Such a composition is known, for example, from EP-B1- 0 130 804. This known composition contains four components, namely a photopolymer from a water-soluble vinyl acetate polymer having certain styrylpyridinium or styrylquinolinium grafting groups, a second polymer component selected from water-dispersible or hydrophobic polymers such as polyurethane or a dispersion of polyester resin, a third component of a photopolymerizable, unsaturated compound having at least one ethylenically unsaturated group, for example a UV aerylate or an unsaturated polyester, and a photopolymerization initiator as the fourth component. Such a composition can be used in a photosensitive coating (photoresist) for printing plates or printing screens.

According to this publication, in particular, the third component and the associated initiator are required to achieve good wet strength after development with water as well as good chemical resistance of the final coating. This composition has better characteristics, compared with the photopolymers disclosed by GB-B-2030575.

It was found, however, that the composition disclosed by EP-B-0 130 804 although it exhibits the abovementioned characteristics, does have a distinct drawback. The fact is that this composition results in a tacky coating which adheres to the film applied thereto during operation. As a result, some of the coating is transferred to the film and consequently the coating layer is damaged. Moreover, as a result, the film which often needs to be stored becomes unusable for reuse. To avoid this drawback it had previously been proposed that talcum powder be sprinkled on the coating layer applied.

It is an object of the present invention to reduce the tackiness of the photosensitive composition while at least retaining the other good characteristics.

The photosensitive resin composition of the type described according to the invention is characterized in that the polyester resin is an alkyd resin.

It was found, surprisingly, that the choice of an alkyd resin together with a photopolymer improves the tackiness-related characteristic. It is assumed that this beneficial property is the result, inter alia, of the third component from the above-described known composition, in particular the UV aerylate, being replaced by alkyd resin. The coating obtained from such a composition not only has the improved characteristics with respect to tackiness, but also good wet strength, stability, chemical resistance and photosensitivity, which are at least equal to those of the known compositions. As usual, the composition may include a photoinitiator, whose presence is not required, however, which may afford an economic advantage.

Examples of photopolymers which can be employed in the composition according to the invention are those which are described in the British Patent GB-B-2 030 575 and the European Patents EP-B-0 130 804, 0 313 220, 0 313 221 and 0 373 537. All these publications disclose photopolymers of poly(vinyl alcohols) or poly(vinyl acetates) having diffe- rent grafting groups and methods of preparation thereof. The preferred photopolymers are those according to GB-B-2 030 575 and EP-B-0 313 220 and 0 313 221 which are hereinafter referred to as stilbazolium-grafted poly(vinyl alcohols) .

The dry solids content of the preferred photopolymer in the base composition is generally in the range of 5-30%, preferably in the range of 9-17%. If the content is less than 5% inadequate emulsification takes place because not enough protective colloid is present, which gives rise to an unstable and tacky coating. Moreover, if the content is that low, insufficient stilbazolium groups are present for the reaction under the influence of light, the wet strength not being optimal as a result. If the content exceeds the upper limit of 30%, then the composition is relatively expensive and the chemical resistance to the printing inks applied during a printing process is reduced.

Alkyd resins (also known as oil-modified polyesters) can be prepared, as known in the art, from three components, i.e. 1) polyhydric alcohols or mixtures thereof, such as, for example, propylene glycol, ethylene glycol, glycerol, pentaerythritol, polyglycerol, dimethanolpropionic acid, sorbitol, mannitol and neopentylglycol with 2) polybasic acids, anhydrides or mixtures thereof, such as, for example, tri- or higher polybasic acids such as unsaturated fatty acids maleated with citric acid, maleated colophonium, trimellitic acid, benzophenonetetracarboxylic acid, dibasic acids such as phthalic acid, isophthalic acid, adipic acid, succinic acid, azelaic acid, sebacic acid and 3) monobasic acid or mixtures thereof such as, for example, saturated or unsaturated fatty acids or oils thereof such as, for example, coconut oil, (dehydrated) castor oil, soya oil, linseed oil, tall oil and sunflower oil. The alkyd resin may be of the oxidatively drying type or of the stoving type.

Examples of alkyd resins which can be used in the composition according to the invention are available, inter alia, under the trade names Crodakyd, Uralac, Alftalat, Sacolyd, Novalkyd, Sintal, Jagalyd and Worleekyd. These alkyd resins are typically prepared from phthalic anhydride

(25-70%) or isophthalic anhydride (10-20%) . The oil content (30-80%) is based on a wide variety of fatty acids (for example linseed oil, tall oil, coconut oil, castor oil or synthetic acids) . The fatty acids containing a nonconjugated unsaturated bond are particularly preferred. Examples thereof comprise coconut oil, castor oil, grape seed oil, linseed oil, palm oil, safflower oil, sunflower oil, soya oil and tall oil. The oil content is preferably in the range of 30-55%. Also of interest is the hydroxyl content of the alkyd resin, which is preferably in the range of 3-7.5%.

With a view to stability, preference is given to the use of alkyd resins having an acid value of less than 25, although alkyd resins having acid values up to 50 mg of KOH/g of solid of the alkyd resin have proved suitable.

The choice of the components depends on the characteristics aimed for, both with respect to processing and to the characteristics of the end product. The dry solids content of the alkyd resin in the base composition is generally in the range of 20-80%, preferably 40-75%. If the content is higher, the chemical resistance is inadequate and, on the other hand, not enough amino resin may be present to achieve good cross-linking, whereas with a lower content the flexibility is too low and a brittle layer is formed. The use of alkyd resins which contain drying or semi-drying (unsaturated) oils or fatty acids is especially preferred. In addition to the alkyd resin, other resins compatible therewith, such as those described in the abovementioned European Patent EP-B1-0 130 804, for example, can be used in the composition according to the invention. A particular resin combination, suitable in stability terms, consists of alkyd resin with amino resin and/or phenolic resin, the amino resin being the most preferred.

Amino resins are well known per se in the coating sector. Examples include mela ine formaldehyde resin and (single) benzoguanamine resin, the latter being particularly preferred in terms of storability. The amino resin enables joint curing (drying) of the polyester resin, in particular an alkyd resin, during stoving. Suitable amino resins which can be used according to the invention are commercially available under the trade names Luwipal, Beetle, Maprenal, Cy el and Resimene.

If the alkyd resin is accompanied by one or more other resins in the composition according to the invention, the dry solids content thereof is generally 10-70% of the total composition, preferably 15-50%. In the case of an amino resin, the upper limit is determined by the flexibility, while the lower limit is determined by the chemical resistance. The invention further relates to a photosensitive coating (photoresist) for screen printing which contains, as an essential component, the photosensitive resin composition according to the invention, in addition to conventional solvents. The photosensitive coating according to the invention preferably comprises 35-50% of base composition, 40-75% of water and 5-15% of organic solvent, the best results being achieved with a coating which comprises approximately 45% of base composition, 45% of water and 10% of organic solvent.

The solvents suitable for use in the coating according to the invention comprise, in particular, the lower alkyl alcohols and alkyl acetates or glycols or mixtures thereof, such as isobutanol, propanol and butylglycol and preferably butyl acetate, butylalcohol or a mixture thereof. If a mixture of organic solvents is used, the ratio of the various components thereof is not critical and can be determined by those skilled in the art depending on the specific application requirements. As already indicated above, the coating is employed in the printing industry, in particular for screen printing. This involves a layer of the coating according to the invention being applied to a screen, for example, a cylindrical screen and being dried at a slightly elevated temperature, for example approximately 35°C, over a sufficient period of time, for example around 30 minutes. Obviously, the correct drying conditions will depend on the type and quantities of the components in the coating and the coating thickness applied. On top of the dried coating a patterned film is then applied which is exposed to light and then removed, together with the unexposed coating layer, the screen as a result being provided with the correct printing pattern and the actual printing being able to commence.

The invention is explained below with reference to the following examples.

Comparative Example 1. A glass beaker is charged with 54.5 g of liquid epoxy resin, formed from bisphenol A and epichlorohydrin, the contents then being heated to 115°C and an amine curing agent then being added. The mixture thus obtained was allowed to cool to 50°C. Another glass beaker was charged with 59.4 g of urethaneacrylate oligomer (85% in 1,6- hexanediol acrylate) , which was heated to 50°C and 0.6 g of photoinitiator Irgacure 369 (Ciba Geigy) was then added. The mixtures were combined and, until further processing, kept at 50°C.

100 g of the above warm resin phase was then emulsi¬ fied in a mixture of 48 g of photopolymer LS400 (Toyo Gosei, Japan; a 13% aqueous solution of a polyvinyl derivative, consisting of 88% saponified poly(vinyl acetate) having a degree of polymerization of 500, and modified with 4.2 mol% of styrylpyridinium groups) and 192 g of a 10% aqueous solution of an 88% saponified poly(vinyl acetate) having a degree of polymerization of 3300. The photoe ulsion thus obtained was then diluted with water and ethanol and coloured by means of a water-soluble dye.

This photoemulsion was further diluted with water and then applied to a nickel screen for rotary-screen printing, by means of dip coating. After drying for 40 minutes at 35°C, the still tacky emulsion was treated with talc to achieve a nontacky coating. The screen was then exposed through a negative film, a gallium-doped low-pressure mercury lamp being used, and then developed with water. After polymerization for 1 hour at 180°C, the coating was no longer tacky. However, the photoemulsion exhibited poor wet strength and chemical resistance.

The results of this comparative example and of the examples described hereinafter are summarized in Table 1.

Comparative Example 2. To reduce tackiness of the dry film, a different photoemulsion was prepared for comparison. The resin phase herein was modified by reducing the amount of tacky UV aerylate oligomer.

68 g of the epoxy resin employed in Comparative Example 1 were heated to 115°C, and 7 g of amine curing agent were then added. Separately, 29 g of urethaneacrylate oligomer and 1 g of photoinitiator Irgacure 369 were blended, i.e. the quantity of urethane- acrylate oligomer was half of that in Comparative Example 1. Combining the two mixtures afforded 105 g of warm resin phase which was emulsified, in the same manner as in Comparative Example 1, in the same mixture of photopolymer and poly(vinyl alcohol) solution. The photoemulsion thus obtained was somewhat less tacky. The wet strength, however, was extraordinarily poor, and after development with water, all the photoemulsion applied to the screen re-emulsified.

Example 1.

A glass beaker was charged with a mixture of 150 g of alkyd resin having a short oil chain length (a so-called "short oil alkyd") and 150 g of alkylated benzoguanamine resin. This mixture was then heated, with stirring, to 65°C. The alkyd resin is a 65% solution in butyl acetate. The alkyd resin has a castor oil content of 42% and a maximum acid value of 15 mg of KOH per g of solid of the resin, and a hydroxyl content of 4% (OH equivalent) . The benzoguanamine resin, which is described as a non-plasticizing benzoguanamine formaldehyde resin is an 80% solution in n- butanol.

The warm mixture was then emulsified in 200 g of photopolymer (photopolymer SPP H13 from Toyo Gosei (JP) ; a 13% aqueous solution of a poly(vinyl alcohol) derivative, consisting of 88% saponified poly(vinyl acetate) with a degree of polymerization of 1700, modified with 1.3 mol% of styrylpyridinium groups) with the aid of a high-shear blender. The emulsion thus obtained was diluted with 80 g of water, neutralized with the aid of a 33% solution of DMEA in water, and coloured by means of 1 g of a water-soluble dye, to form a photoemulsion. The photoemulsion had a solids content of 42% and a solvent phase which comprised 44% of water, 9% of butanol and 5% of n-butanol.

This emulsion was left to stand for 1 week, and was then further diluted with water. The coating composition obtained was applied to a rotary nickel screen. After drying at 35°C for 40 minutes, the non-tacky photoemulsion was exposed through a negative film, a Ga-doped low-pressure Hg lamp being used. The screen was then developed with water and the unexposed coating was readily redispersed, while the coating cross-linked under the influence of light exhibited good wet strength. After polymerization for 1 hour at 180°C, the rotary screen was ready for use. The coating exhibited good wet strength and good chemical resistance to a wide variety of chemicals.

Example 2.

With the same starting materials as in Example 1 being used, 185 g of alkyd resin were blended with 125 g of benzoguanamine resin. The mixture was then emulsified in 200 g of photopolymer and processed in accordance with Example 1 to give a photoemulsion. The composition of the photoemulsion thus obtained was as follows: solids content 42%, butyl acetate 11% and n-butanol 4%. The ultimate coating exhibited improved flexibility, albeit somewhat at the expense of the chemical resistance.

Example 3.

With the same starting materials as in Example 1 being used, 115 g of alkyd resin were blended with 150 g of benzoguanamine resin. The mixture was then emulsified in 345 g of photopolymer. The ultimate coating exhibited good wet strength, reasonable flexibility and good chemical resistance. Example 4. With the same starting materials as in the preceding examples being used, 163 g of alkyd resin were blended with 132 g of benzoguanamine resin and the mixture was then emulsified in 273 g of photopolymer. The photoemulsion had moderate wet strength, good chemical resistance to solvents and acids and reasonable flexibility.

Example 5. In this example, 150 g of alkyd resin having a short oil chain length (42% of coconut oil, 30% of phthalic anhydride, acid value <10, solids content 80% in isopropanol) were blended with 150 g of the above benzoguanamine resin and heated to 75°C. The warm mixture was emulsified in 200 g of photopolymer SPP H13. This photoemulsion exhibited good wet strength and good chemical resistance.

Example 6. The same warm mixture of alkyd resin and benzoguanamine resin as in Example 5 was emulsified in 200 g of photopolymer SPP S10 (likewise available from Toyo Gosei (JP) ) . This photopolymer is an 11% aqueous solution of a polyvinyl derivative, consisting of 88% saponified poly(vinyl acetate) with a degree of polymerization of 2300, modified with 1.1 mol% of styrylpyridinium groups. The results obtained were comparable with those of Example 5.

Example 7. The same warm mixture of alkyd resin and benzoguanamine resin as in Example 5 was emulsified in 200 g of photopolymer SPP S13 (likewise available from Toyo Gosei (JP) ) . This photopolymer is an 11% aqueous solution of a polyvinyl derivative, consisting of 88% saponified poly(vinyl acetate) with a degree of polymerization of 2300, modified with 1.37 mol% of styrylpyridinium groups. The results obtained with the aid of this photopolymer were comparable with those of Examples 5 and 6.

Example 8.

In this example, 117 g of alkyd resin having a long oil chain length (83% mixed acids, 13% of phthalic anhydride, acid value <7, solids content 99%) were blended with 145 g of benzoguanamine resin. This preblend was heated to 75°C and then emulsified in 200 g of photopolymer SPP H13. The presence of this alkyd resin having a long oil chain length resulted in an improvement of the flexibility of the ultimately obtained coating.

Example 9.

150 g of alkyd resin having a short oil chain length (35% of special acids, 25% of phthalic anhydride, acid value <10, hydroxyl content 4.4%, solids content 80% in isobutyl acetate) were blended with 150 g of benzoguanamine resin, then heated and emulsified with 200 g of photopolymer SPP H13. This led to a photoemulsion having excellent chemical resistance to bases, albeit at the expense of the wet strength and chemical resistance to solvents.

Example 10.

84 g of benzoguanamine resin were blended with 197 g of alkyd resin (50% of non-drying oil, acid value <50, solids content 75% in n-butanol/butyl glycol) , then heated and emulsified in 200 g of photopolymer SPP H13. The result was a photoemulsion having excellent flexibility, wet strength and very good chemical resistance.

Example 11.

206 g of the same alkyd resin as in Example 10 were blended with 67 g of benzoguanamine resin (esterified with methanol, solids content 75% in isobutanol) , heated and then emulsified in 200 g of photopolymer SPP H13. This afforded eminently well-balanced characteristics. Example 12 .

Example 11 was repeated, except that 209 g of alkyd resin were blended with 89 g of benzoguanamine resin. The results obtained with this photoemulsion were comparable with those of Example 11, except that the chemical resistance to bases was somewhat lower.

Example 13.

Example 11 was repeated, employing 180 g of alkyd resin and 120 g of benzoguanamine resin. Again, the same favourable characteristics were obtained, except that the flexibility and chemical resistance to bases was somewhat lower.

Example 14.

To a glass beaker was added a mixture of 150 g of the same short oil alkyd resin as used in Example 1 and 97.5 g of a fully etherified melamine formaldehyde resin of the "HMMM" type, mainly consisting of hexamethoxymethyl melamine. This mixture was then heated to 65°C with stirring.

This blend was then emulsified with a high shear mixer into 200 g of photopolymer SPP H13, neutralised using a 33% DMAE and coloured using 1 g of a water-soluble dye to give a photoemulsion.

After standing for 1 week this photoemulsion was further diluted with water, filtered and then coated onto a rotary nickel screen. After drying for 40 minutes at 35 °C the non-tacky photoemulsion was exposed through a photo- negative film using a Ga doped low pressure Hg lamp. The screen was then developed using water, whereby the non- irradiated coating was readily re-emulsified in water, whilst the photo cross-linked coating exhibited good wet strength. After polymerisation for 1 hour at 180 °c the rotary screen was ready for use.

Table 1 below summarizes the results of the above comparative examples and examples. Table 1 . Resul ts

Example Tacki- Wet Chemical resistance to Flexi¬ ness strength bility solvents acids bases

Comp. 1 very - - - - poor

Comp. 2 poor -

1 adequate + ++ + * / -

2 dry * / - + +/- - ^♦/-

3 dry + ++ ++ +/- +/-

4 dry +/- ++ ++ -

5 adequate + +/- ++ */ - ^♦/-

6 adequate + + ++ +/- * / ^•

7 adequate ++ + ++ * / - */ -

8 dry - ++ + +

9 dry + ++

10 dry ++ ++ ++ + ++

11 dry ++ ++ ++ ++ ++

12 dry ++ ++ ++ + ++

13 dry ++ ++ ++ + +

14 dry ^♦/- + + + +/-

++ excellent; + = good; +/- « adequate; = inadequate; - ■= poor; -- ^« very poor,

1, The solvents tested were acetone, butyl acetate, cyclohexane, ethanσl and xylene.

The acids tested were 5% acetic acid and 5% sulphuric acid. The base tested was 5% sodium hydroxide.

Claims

1. Photosensitive resin composition which comprises a photopolymer and a polyester resin, characterized in that the polyester resin is an alkyd resin.

2. Photosensitive resin composition according to claim 5 1, characterized in that the photopolymer is a poly(vinyl)alcohol grafted with stilbazolium.

3. Composition according to claim 1 or 2, characterized in that the alkyd resin is selected from an oxidatively drying alkyd resin and/or stoving alkyd resin.

10 4. Composition according to any one of claims 1-3, characterized in that the composition comprises 5-30% of photopolymer, 20-80% of alkyd resin and, if required, 10-70% of other resins, the percentages being expressed as percentage of solids of the total composition.

15 5. Composition according to any one of the preceding claims 1-4, characterized in that the other resins are selected from amino resin and/or phenol resin.

6. Composition according to any one of the preceding claims 4 or 5, characterized in that the composition

20 comprises 40-75% of alkyd resin, 15-50% of amino resin and 9-17% of photopolymer.

7. Composition according to claim 5 or 6, characterized in that the amino resin is benzoguanamine resin.

258. Photosensitive coating for screen-printing, characterized in that the coating comprises 35-50% of the photosensitive composition according to any one of claims 1- 7, as well as 40-75% of water and 5-15% of organic solvent.

9. Photosensitive coating according to claim 8, 30 characterized in that the organic solvent is selected from the group consisting of alcohols, acetates, glycols and mixtures thereof.

10. Photosensitive coating according to claim 8 or 9, characterized in that the coating contains about 45% of the

35 base composition according to any one of claims 1-7, about 45% of water and about 10% of organic solvent.

11. Screen-printing stencil comprising a support and thereon a photosensitive film of the photosensitive coating according to any one of claims 8-10.