JPS60181178A - Composition for aqueous printing ink - Google Patents

Abstract

PURPOSE:The titled composition for ink suitable especially as aqueous flexographic ink or aqueous gravure ink, having improved pigment dispersibility, printability, and water resistance, obtained by copolymerizing specific monomers to give an acrylic copolymer of alkali soluble type, neutralizing it with a basic substance. CONSTITUTION:(A) 5-60wt% (meth)acrylic ester monomer [e.g., (meth)acrylic acid octyl ester, etc.] containing 8-18C long-chain alkyl is copolymerized with (B) 5-30 alpha,beta-monoethylenic unsaturated carboxylic acid monomer [most preferably (meth)acrylic acid] and 10-90wt% another copolymerizable monomer (e.g., styrene, etc.), to give an acrylic copolymer, which is neutralized with a volatile basic substance (e.g., ammonia water, etc.), to give the desired composition for ink.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composition suitable for water-based printing inks, particularly water-based flexo inks or water-based gravure inks, and more specifically, the present invention relates to a composition that contains a specific alkali-soluble copolymer as its main binder resin. The present invention relates to a composition for water-based printing ink, which is characterized by comprising:

The inks used in gravure printing and flexographic printing are
Most of them are oil-based inks that contain large amounts of organic solvents, but in recent years there have been problems with pollution such as air pollution, health and safety in the working environment, dangers such as ignition, etc. Water-based ink has attracted attention as a method, and in fact, it is already used in large quantities for printing on paper such as general wrapping paper and corrugated poles, and is also used for some applications on plastic films, and the ratio of water-based ink is increasing. is on the rise.

However, although water-based inks are essentially superior in terms of the above problems, there are some issues regarding the suitability of the inks for manufacturing and printing.
The performance of ink@film after printing has many disadvantages compared to oil-based inks, and it is currently difficult to say that it is necessarily sufficient.

In general, the main properties that gravure or flexographic printing inks should have are: (1) good ink fluidity, (2) good storage stability, (3) excellent printability, and (4) excellent pigment dispersibility. , the print surface has a good finish (
5) In printed matter, the ink film adheres well to the film, etc., and there is little damage or change due to light, heat, water, oil, chemicals, friction, bending, etc. Ease of manufacture is also important.

Most of these performances depend on the binder used in the ink, and therefore, the key to obtaining an excellent ink is what composition is used as the binder.

Seven chic has been used as a binder for water-based inks since ancient times.

In addition to natural resins such as casein, synthetic resins such as rosin-modified maleic acid resins, petroleum resins, styrene/maleic acid resins, and acrylic copolymers have been used.

Among these, styrene/maleic acid resins have been preferred because they have excellent pigment dispersibility and good ink fluidity and storage stability. However, on the other hand, the dry ink coating film is hard and brittle, which limits its uses, and it cannot be applied to plastic films or the like. On the other hand, acrylic copolymers used in water-based inks are broadly divided into emulsion type and alkali-soluble type, both of which have excellent weather resistance and can easily produce relatively flexible coatings. In terms of suitability for film, it is superior to styrene/maleic acid resins.

However, because emulsion-type acrylic copolymers contain a large amount of hydrophilic emulsifier, they have poor ink drying properties and water resistance of the coating film, lack stability against mechanical shear during printing, and partially gel. In addition, it tends to foam, resulting in partially dried gels, and since these gels and dried films are difficult to re-dissolve, they can be mixed in the ink and significantly deteriorate the printing finish. There are drawbacks such as. On the other hand, alkali-soluble acrylic copolymers are inferior to oil-based inks in terms of pigment dispersibility, water resistance, chemical resistance, and printability, and although they can be applied to paper, they cannot be used for plastic films, etc. be.

As described above, the various binder compositions conventionally used in water-based inks have their advantages and disadvantages, and no one has yet been found that satisfies all the performance requirements.

Therefore, as a result of intensive research, the present inventors have discovered that by copolymerizing the monomers specified in the present invention with an alkali-soluble acrylic copolymer, we have achieved We succeeded in significantly improving pigment dispersibility, printability, and water resistance without sacrificing any of the characteristics.

In particular, the present invention has shown excellent suitability for gravure and flexible printing of plastic films.

That is, in the present invention, tAl has a long chain alkyl group having 8 to 18 carbon atoms (
At least one type of meth)acrylic acid ester monomer5-
60% by weight (B) At least one type of α,β-monoethylenically unsaturated carboxylic acid monomer 5 to 30% by weight At least one type of other copolymerizable monomer on Ic 10 to 90% by weight % of an acrylic copolymer is neutralized with a volatile basic substance to provide an aqueous printing ink composition.

Next, specific examples of the monomers used in the present invention are listed below.

(A1) In the present invention, the (meth)acrylic acid ester monomer having a long chain alkyl group having 8 to 18 carbon atoms includes (meth)acrylic acid octyl ester, (meth)acrylic acid 2-ethylhexyl ester, ( Meth)acrylic acid nonyl ester, (meth)acrylic acid decyl ester, (meth)acrylic acid undecyl ester, (meth)acrylic acid ester, (meth)acrylic acid tridecyl ester, (meth)acrylic acid myristyl ester , (meth)acrylic acid cetyl ester, (meth)acrylic acid stearyl ester, and the like.
Those having 2 to 18 long chain alkyl groups are preferred.

tB) The α,β-monoethylenically unsaturated carboxylic acid monomer referred to in the present invention refers to (meth)acrylic acid, itaconic acid, crotonic acid, fumaric acid, (anhydride)maleic acid, and the carbon number of maleic anhydride. Examples include hafesters containing 1 to 4 lower alcohols, but (meth)acrylic acid is particularly preferred in terms of water resistance, pigment dispersibility, and copolymerizability.

(C) Other copolymerizable monomers referred to in the present invention include aromatic monomers such as styrene, vinyltoluene, α-methylstyrene, (meth)acrylic acid methyl ester, (meth)acrylic acid Lower alkyl esters of (meth)acrylic acid such as ethyl ester, (iso)propyl (meth)acrylate, (iso)butyl (meth)acrylate, and tert-butyl (meth)acrylate; 2-hydroxyethyl Examples include polymerizable alcohols such as (meth)acrylate, hydroxypropyl (meth)acrylate, and (meth)allyl alcohol.

Furthermore, the volatile basic substances used to neutralize the copolymer in the present invention include aqueous ammonia, triethylamine, diethylamine, monoethylamine, tributylamine, dimethylethanolamine, monoethanolamine, morpholine, N -Methylmorpholine, 2-amino-
Examples include 2-methy/I/-1-propertool.

The amount of the (meth)acrylic acid ester monomer having a long chain alkyl group having 8 to 18 carbon atoms used in the copolymer is 5 to 60 M%, and if the amount of such needles is less than 5% by weight, Pigment dispersibility and printing workability are not sufficient, and on the other hand, if it exceeds 60% by weight, the film becomes soft, resulting in poor drying properties and film strength, making it impractical.

Further, the amount of the α,β-monoethylenically unsaturated carboxylic acid monomer is 5 to 30% by weight, and the amount is 5% by weight.
If it is less than 30% by weight, the water solubility of the copolymer will be poor, while if it exceeds 30% by weight, the water resistance and alkali resistance of the ink film will be poor, which is not preferable.

The alkali-soluble copolymer of the present invention can be easily obtained by polymerizing the monomer mixture described above in the presence of a conventional radical generator, such as benzoyl peroxide, tert-butyl peroxybenzoate, etc. However,
In this case, the molecular weight may be adjusted using a commonly used chain transfer agent.

As a practical polymerization method for such a copolymer, solution polymerization is the most suitable method, and the solvent used in this case, in light of the purpose of the present invention, is a water-miscible organic solvent and a small amount of alcohol. For example, methanol, ethanol, ingropanol, normal propatool, methyl cellosolve, ethyl selonlube, inglovir cellosolve, normal propyl cellosolve, normal butyl cellosolve, inbutyl cellosolve, tertiary butyl cellosolve, etc. are suitable.

To prepare a water-based printing ink using the acrylic copolymer thus obtained, the copolymer is first neutralized with a volatile basic substance such as aqueous ammonia or an organic amine, and then pigments and dyes are added to the copolymer. , water, a water-miscible organic solvent, a wax, an antifoaming agent, etc. are added as necessary, and mixing is carried out in accordance with the treatment of ordinary water-based printing inks. When a pigment is used, its type and amount are not particularly limited, but a suitable mixing ratio is such that the amount of the copolymer is 50 parts by volume or more per 100 parts by volume of the pigment.

If the amount of the copolymer is less than 50 parts by volume, practical performance required for ordinary printed matter may be lacking, such as slight fading of color when the printed surface is rubbed. Depending on the design of the printed matter, the ink can be used as an ink with a high pigment content, an ink with a very low pigment content, or an overprint varnish that does not contain a pigment for protection or cosmetic purposes.

The composition of the present invention can also be used in combination with aqueous binders conventionally used in aqueous printing inks. For example, natural resins such as shellac and casein, rosin-modified maleic acid resins,
Water-based varnishes using petroleum resins, styrene/maleic acid resins, acrylic emulsions, acrylic/styrene emulsions, etc. can be used.

The ink obtained using the composition of the present invention has a viscosity (
Zahn cup A3) is usually 16 to 25 for gravure printing.
22 to 30 seconds is sufficient for 7 seconds and 7 lexo printing, but generally 10 to 30 seconds, preferably 14 to 20 seconds is suitable in consideration of various printing suitability.

Next, the present invention will be further explained with reference to examples. In addition, parts and percentages in the examples are based on weight unless otherwise specified.

Example 1 80 parts of butyl cellosolve was charged into a No. 11 reaction vessel equipped with a stirrer, a reflux condenser, a temperature control device, and a nitrogen gas introduction tube, and the temperature was maintained at 100'C in a nitrogen gas atmosphere.

To this, 1 part of butyl peroxy 2-ethylhexanoate (part name: Perbutyl O manufactured by NOF ■), 40 parts of lauryl methacrylate, 10 parts of styrene, 21 parts of methyl methacrylate, 2 parts of ethyl acrylate, methacrylic acid 9 parts were added dropwise over 4 hours. After the dropwise addition was completed, stirring was continued at the same temperature for 3 hours and cooled to 40°C, and then 21 parts of butyl cellosolve, 1 part of 25% ammonia, and 15 parts of water were added.
45% non-volatile content, weight average molecular weight 52. D 0
0.

An aqueous resin having a polymer specific gravity of 0.929 was obtained.

Example 2 80 parts of ethanol is charged into a reaction vessel similar to Example 1, and the temperature is maintained at 78° C. in a nitrogen gas atmosphere.

To this, 1 part of tert-butylperoxy 2-ethylhexanoate, 33 parts of SLMA (part name: Acrylic Ester 5L manufactured by Mitsubishi Rayon ■), 37 parts of methyl methacrylate,
23 parts of butyl acrylate and 10 parts of methacrylic acid were added dropwise over a period of 4 hours.

After the dropwise addition was completed, stirring was continued at the same temperature for 3 hours and cooled to 40'C, then 21 parts of ethanol, 8 parts of 25% aqueous solution, and 14 parts of water were added to give a mixture with a non-volatile content of 45% and a weight average. Molecular weight 65. ODD, an aqueous resin having a polymer specific gravity of 0.927 was obtained.

Example 6 80 parts of Improvil alcohol is charged into a reaction vessel similar to that in Example 1, and the temperature is maintained at 80° C. in a nitrogen gas atmosphere.

To this was added 3 parts of tert-butylperoxy 2-ethylhexanoate, 15 parts of stearyl methacrylate, 10 parts of styrene, 32 parts of methyl/I/methacrylate, 34 parts of butyl acrylate, and 9 parts of methacrylic acid over a period of 4 hours. and dripped it.

After the dropwise addition was completed, stirring was continued for 6 hours at the same temperature and cooled to 40°C, followed by 26 parts of Improvil alcohol, 25%
Add 7 parts of ammonia water and 16 parts of water, non-volatile content 45%,
Weight average molecule [35, ODD, polymer specific gravity 0.928
An aqueous resin was obtained.

80 parts of ethanol is charged into a reaction vessel similar to that in Example 1, and the temperature is maintained at 78° C. in a nitrogen gas atmosphere.

To this, 3 parts of tert-butylperoxy 2-ethylhexanoate, 21 parts of styrene, 20 parts of methyl methacrylate.
1, 50 parts of butyl acrylate, and 9 parts of methacrylic acid were added dropwise over a period of 4 hours.

After the dropwise addition was completed, stirring was continued at the same temperature for 6 hours and cooled to 40°C, and then 23 parts of ethanol, 7 parts of 25% aqueous ammonia, and 16 parts of water were added to achieve a non-volatile content of 45% and a weight average molecule.
An aqueous resin having a polymer specific gravity of 38,000 and a polymer specific gravity of 0.929 was obtained.

This comparative example shows a carbon number of 8 to 1, which is an essential component of the present invention.
This is an alkali-soluble acrylic copolymer containing no acrylic acid or methacrylic acid ester monomer having eight long-chain alkyl groups.

<Application test> Using the water-soluble resins obtained in Examples 1 to 3 and comparative examples, mix the following formulations [A] and formulation (B), add steel poles of the same capacity, and shake in a high-speed shaker. The base ink was adjusted by kneading for 2 hours.

[Formulation A]

(Total: 100 parts) [Formulation B] (Total: 100 parts) To 100 parts of these base inks, 20 parts of the water-soluble resin used for the base ink paste was blended, water was added as a diluent, and the mixture was added to Zahnkapp/I66. The time was adjusted to 18 to 20 seconds.

The ink thus obtained was applied using a bar coater to a milky white high density polyethylene film surface-treated by corona discharge, and the performance was evaluated one day later to obtain the results shown in Table 1.

(a) The particle size of the pigment was measured using a grind gauge after 1 hour and 2 hours of grinding with the pigment-dispersible paste ink, and the degree of crushing was determined.

◎: Good kneading property after 1 hour ○: Not enough after 1 hour, but good kneading property after 2 hours △: Not sufficient after 2 hours ×: Poor kneading property even after 2 hours (B) Gloss Measurement value using a crossmeter (reflection angle 60 degrees) ← → Adhesion After pasting cellophane tape (made of polyethylene terephthalate) on the printed surface, it was peeled off 180 degrees and the peeling state of the ink film was observed. It was evaluated as follows.

◎: No peeling, very good ○: Slight peeling, good △: Approximately % of the area peeled off, slightly poor The ink film was rubbed with a constant force and the number of times it was rubbed until the ink film peeled off was measured.

(e) Oil-resistant Soybean white squeezed oil was soaked in absorbent cotton and evaluated in the same way as in the previous section.

(f) Create an acid-resistant 5% acetic acid aqueous solution, drop a few drops of this onto the printed surface using a dropper, leave it for 5 minutes, wipe it off with absorbent cotton, observe the damage to the ink film, and observe the following: It was evaluated as follows.

◎; No change. Very good ○: The coating film did not dissolve or disappear, but the gloss decreased. Good △: Part of the coating film dissolved and disappeared. Slightly poor X: The coating film completely disappeared. Defective (G) Alkali Resistance A 0.05% aqueous solution of caustic soda was prepared, a few drops of this was put into the printed surface using a dropper, and after being left for 5 minutes, it was evaluated in the same manner as in the previous section.

(Finishing of printed matter) Printed on low-density polyethylene, biaxially oriented polypropylene, and polyethylene terephthalate films using a small gravure printing machine, observing the sharpness of fine letters and patterns on multiple sides of the finished product, and evaluating it as shown below. did.

- One clear, very good 0: Fine letters and patterns are unclear. Good △; some parts are clear; poor ×; unclear. defective

Claims (1)

[Scope of Claims] (N 5 to 6 at least one type of (meth)acrylic acid ester monomer having a long chain alkyl group having 8 to 18 carbon atoms
0% by weight (B) At least one type of α,β-monoethylenically unsaturated carboxylic acid monomer 5 to 30 weight%
An aqueous printing ink oil or composition obtained by neutralizing a copolymer obtained from 0 to 90% by weight with a volatile basic substance.