NO142404B - HYDRAULIZED, COLD WATER SOLUBLE, GRANULES, STARCH-BASED GUM, AND PROCEDURES FOR PRODUCING THEREOF - Google Patents

Description

The invention relates to starch-based rubber which can serve

as a substitute for gum arabic and which is particularly suitable as a film former on coated pills and as a gum base in cosmetic mid-

laughing. It has relatively low viscosity at high concentrations,

high resolution stability and clarity and also forms films of excellent clarity. These gums are similar to gum arabic in terms of film forming and viscosity properties. In certain applications, these starch-based gums work better than gum arabic. Lithographic films and solutions formed with these starch-based gums are significantly more stable than similar films and solutions containing gum arabic.

Gum arabic is widely used in lithography

due to its relatively low viscosity and its good rheological properties in concentrated solutions. It is obtained from acacia trees in subtropical and tropical regions and is found in limited quantities. The price of gum arabic is increasing, as both its production costs

nings and demand is increasing, so that a replacement of this material with a readily available starch-based product is highly desirable.

Gum arabic with consistently good properties is difficult to obtain due to certain seasonal variations.

The rubber is sold in a number of grades, depending on purity and

colour. For many applications, gum arabic must be purified by dissolving it in water and filtering the solution to remove coarse impurities.

Furthermore, the use of gum arabic is associated with stability problems due to the naturally occurring hydrolytic enzyme residue which reduces the viscosity of gum arabic during storage. For certain applications, further purification by ion exchange treatment is needed, which increases material costs. This problem does not occur with the starch-based gums according to the present invention.

Conventional sensitizing solutions for deep etched lithographic plates are prepared from combinations of gum arabic and dichromate, and the resulting films are rendered insoluble by exposure to light. Purified gum arabic is first dissolved in water, and ammonium dichloronate is added. The solution is then made alkaline with ammonium hydroxide. The sensitizing solution is then coated on a metal plate as a thin film which emits ammonia as it dries, with a resulting lowering of the pH. The dichromate solutions are kept alkaline for stability, but the film formed on the plate must have an acidic pH for proper development of a photosensitive image. The lifespan of such plates that use gum arabic as a film former is so short that in the past it was thought that it was impractical to produce plates just before they were to be used. This causes considerable difficulty and inefficient work for the lithographer who has to plan and program plate production just before the images are to be produced (which is usually accompanied by a final typing deadline).

The starch-based gums according to the invention provide for the first time a completely satisfactory replacement for gum arabic in lithography. Attempts have previously been made to use starches as gum arabic substitutes for lithographic use. For example, adhesive carboxymethyl starches are described in US Patent 2,589,313. These starches do not have the necessary film-forming properties due to the presence of low molecular weight compounds which are not easily removed. These starch products are formed under alkaline conditions and are sold as salts with a high content of impurities that will corrode lithographic plates after a short contact time, and which also tend to react with the ingredients of lithographic solutions and thereby interfere with their proper function during the lithography process.

Many proposals have been made during the last 50 years to make starch derivatives which have similar properties to water-soluble natural gums. See: Whistler, among others Industrial

Gums, ch XXXI, Academic Press, N.Y. (1959), page 727 mm. However, none of the products described there have received any bigger ones

commercial success. US Patents 2,516,634, 2,733,238, 2,802,000

and 2,845,417 describes some of these starch derivatives. None of these patents, however, suggest the use of starch-based gums in lithography to replace gum arabic.'

Many attempts have been made to produce synthetic ones

gum arabic substitutes. US patent 2,250,516 mentions araboga-lactan as a substitute for gum arabic in lithographic desensitizing solutions. US Patent 2,520,161 mentions carboxyalkyl esters of carbohydrate gums such as galactomannan, glucomannan, tragacanth gum, gum arabic and karaya gum. None of these gums mentioned in the patents are readily available, and they are all more expensive than the starch-based gums according to the invention.

US patent 2,589,313 relates to the use of carboxymethyl ethers

of cellulose, starch and water-soluble gums for processing lithographic plates, but the cleaning method is not described. Carboxy ethers are formed with an alkaline solution of sodium hydroxide or trimethylammonium hydroxide, and the indicated reagents include chloroacetic acid, chloromaleic acid, chloromalonic acid and chloropropionic acid. Excess alkali is neutralized after the reaction with phosphoric acid or another mineral acid, and the ether is precipitated in alcohol or acetone as an alkali salt. The cleaning method, which is very important, is not described, and it turns out that the remaining salt residues and other reaction by-products can cause significant storage and corrosion problems when you want to store film-coated lithographic plates for a longer time.

British patent 1,171,893 describes gum-like hydroxypropyl derivatives of amylopectin obtained primarily by enzyme hydrolysis. Amylopectin-rich starch fractions are dissolved by heating in water of at least 110°C. These starch fractions are then enzymatically depolymerized and dried. The British patent mentions that acid hydrolysed (ie diluted) starches do not represent satisfactory rubber substitutes because they are very unstable and after a short time increase in viscosity and gel. (See British Patent 1,171,893, p. 1, lines 55-57). The UK enzymatic depolymerisation process for pre-glued amylopectin does not allow the removal of low molecular weight components and impurities from the depolymerised starch. Although the patent mentions that acid hydrolysis is also possible, it mentions that enzyme hydrolysis is preferred, and only examples of enzyme hydrolysis are given.

The high temperature of 110°C recommended in the British patent for the hydrolysis process is well above the pasting temperature of the starch. The patent describes the pasting of this starch before the dilution, and the indicated miniraum viscosity is significantly higher (250 cP) than the minimum viscosity (10 cP) obtained by the present invention. It is believed that the British patent intentionally limits the minimum viscosity that can be achieved by introducing a chain-forming enzyme (1,4-1,6 transglucosidase) into the pre-pasted product. Only the use of the product as a foodstuff is mentioned in the patent document, and in such applications low molecular weight salts and other contaminants do not interfere as they do in lithographic applications.

The invention relates to starch-based gums which constitute

an excellent substitute for gum arabic and which are particularly advantageous for lithographic use. The new starch-based gums have a high degree of solubility, excellent solution clarity, relatively low viscosity at high concentrations and high solution stability, more than 6 months. They have excellent film-forming properties and can be easily prepared by the acid dilution and selective substitution steps described below. It has been found that carboxyl and amino substituents placed in the starch molecule increase the photosensitivity when these gums are used in sensitizing solutions for lithographic plates. It has been found that also amidoalkyl substituents which have hydrogen on the nitrogen atom increase the photosensitivity in sensitizing solutions.

The present invention thus provides a hydrolyzed, cold water soluble, granular, starch-based gum which is treated with amylase and comprises at least one non-ionic substituent having a degree of substitution of 0.1-0.3, which gum has improved film-forming properties and improved stability in aqueous solution when stored for over 1 month, the aqueous solution having 24 to 27% solids and an initial Brookfield viscosity of 10-249 cP as measured with spindle No. 1 at 20 rpm. minute at 27°C, and essentially retains this viscosity even when stored for over 1 month.

The starch-based gum according to the invention

is characterized in that the non-ionic substituent is an alkyl, hydroxyalkyl, cyanoalkyl, aminoalkyl or amidoalkyl group where the alkyl group has 1-6 C atoms, or an acyl group selected from acetyl, propionyl and butyryl, and the rubber is obtained by first diluting a granular starch with acid, preferably oxidatively,

then reacting the diluted granular starch with a nonionic substitution agent, washing the crude granular reaction product with water to remove most of the low molecular weight components and remaining sodium sulfate, sodium chloride, and organic solubles from the crude granular reaction product for obtaining a uniformly substituted starch-based gum, gelatinizing the starch-based gum, and filtering the gelatinized starch-based gum to remove substantially all residual impurities.

The invention also provides a method for producing a starch-based rubber as described above. In the method, a starch with an amylose content of 30% by weight or less is first diluted with acid so that a granular starch is obtained which has a viscosity of from 10 to 249 cP measured at a concentration of 24 to 27% solids at 27°C in a Brookfield viscometer with spindle No. 1 at 20 rpm. minute. The diluted starch is then treated with a substitution agent to a degree of substitution of 0.1 to 0.3 using a substituent selected from among alkyl, hydroxyalkyl, cyanoalkyl, aminoalkyl, amidoalkyl and acyl groups with 1-4 carbon atoms. The resulting granular starch-based gum is then washed to remove virtually all low molecular weight components including solubilized starch, sodium sulfate, sodium chloride, propylene chlorohydrins, propylene glycol and its polymers, after which the granular starch derivative is boiled and finally the cooked starch derivative is treated with amylase .

In the method according to the invention, care is taken to maintain the granular structure of the starch, and after acid dilution, derivatives of the granular starch are produced using monofunctional reagents, such as propylene oxide, vinyl acetate or acrylamide to a degree of substitution of 0.1- 0.3. During the derivatization step, the viscosity of the starch remains

then essentially constant. Low molecular weight material is then removed from the granular, partially diluted starch derivative material by washing with water, and the starch derivative is boiled and treated with amylase to solubilize any remaining granule fragments or recrystallized amylose fragments. Enzyme action can be terminated by heating or by lowering the pH of the cooked starch, and it is then filtered to remove any remaining insoluble materials. The filtered starch liquor can be brought to 14°Bé (24 to 27% solids) as

liquid, or it can be spray-dried and sold as a dry powder.

If desired, the granular, partially diluted, starch derivative-based rubber product may be further treated prior to boiling, by bleaching with oxidizing agents such as hypochlorite solutions followed by washing. Hydrogen peroxide deoxidation followed by removal of excess hydrogen peroxide by catalase is an alternative bleaching process that is more advantageous for food applications. Bleaching causes the color of the starch-rubber product to become lighter and gives a more pleasant appearance. Although it is preferred to bleach the product while it is in granular form, it can also be bleached after cooking.

These starch derivatives according to the invention are i

substantially free of low molecular weight contaminants, and they can be converted into hydrosols having a solids ratio almost identical to gum arabic hydrosols. The starch-based gums produced according to the invention can be used in various phases of the lithography technique as a complete replacement for gum arabic, and the viscosity can be carefully regulated to meet the viscosity requirements required by a particular lithographic application. The largest number of potential areas of use for the product is at 14° Bé (24 to 27% solids),

and for this reason the boiled, liquid product is adjusted to this solids content.

Granular, waxy corn starch is normally used

as base starch, and it is either acid hydrolysed first to the desired viscosity, or it is diluted with acid and then subjected to hypochlorite oxidation to achieve the desired viscosity. The diluted product is then treated with propylene oxide. In contrast to previously known amylopectin-based gums, the waxy corn-based gums according to the invention form stable, very clear, non-sticky solutions with excellent stability. Viscosity can be as low as 10 cP at 20 rpm. minute (Brookfield).

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Other starches, including corn and potato starch,

can also be used instead of waxy maize starch, provided that the amylose content of the starch in question does not exceed 30%• Waxy maize starch contains no or little amylose and usually requires a lower degree of substitution than amylose-containing starches to ensure stable viscosity. These waxy cornstarch-based gums also form films with great clarity. The degree of starch dilution prior to the substitution step is dependent on the desired final viscosity and is determined by the intended use of the starch-based rubber product.

A derivative of the acid-diluted starch is then formed by etherification or esterification which introduces non-ionic substituents consisting of starch ether or starch ester groups. Alkyl ether groups, such as methyl or ethyl groups, and substituted alkyl ether groups, such as hydroxyethyl, hydroxypropyl, cyanoethyl, aminoethyl or amidoethyl groups can be used. Acyl groups, for example acetyl can also be used, and also other acyl groups.

Hydroxyethyl and hydroxypropyl groups are the preferred hydrophilic substituents, as they have a high degree of solubility and solution stability when used in lithographic solutions. Hydroxypropyl substitution using propylene oxide is particularly preferred, because propylene oxide is cheap, easy to handle, because the reaction can be more easily controlled under the existing production conditions. Aqueous solutions of this product exhibit excellent stability when stored for longer than 6 months.

Amidoalkyl substituents containing active hydrogen on the nitrogen atom promote the photosensitivity of dichromate-sensitized films used for lithographic imaging. Suitable amidoalkyl substituents can be introduced by treating the starch under alkaline conditions with acrylamide, N-methylacrylamide or methacrylamide, all of which have molecular weights below 90.

Any nonionic substituent which increases the solubility of the starch may be used, provided it does not impart to the starch properties incompatible with lithographic requirements. For example, starches having hydrophobic substituents can be separated from solutions, e.g. from bichromate photosensitizing solutions, and excessive hydrophobic substitution can cause dry films with an irregular surface and thus poor image quality.

The starch-based gums according to the invention must have a minimum degree of substitution of non-ionic substituents of 0.1,

and the maximum degree of substitution can be as high as 0.3. Increasing the substitution, particularly with hydrophilic substituents, such as with hydroxypropyl and amidoalkyl groups, appears to increase the swelling tendency of the starch, thereby interfering with the removal of low molecular weight contaminants by washing with water. This purification is particularly important when the starch-based gums are to be used for the production of lithographic films, as components with low molecular weight have a detrimental effect on film quality and storage stability.

In order to achieve the desired substitution, slurried starch is reacted with propylene oxide under conditions which preserve the granular structure of the starch. The reaction product is then separated and washed with water to remove low molecular weight by-products, for example starch cleavage products (oligosaccharides) formed during the acid dilution step, and electrolytes resulting from the use of alkaline catalysts used in the substitution step. It is important to remove by-products with low molecular weight, as they impair the film-forming properties of starches according to the invention, particularly in lithographic applications. The presence of large amounts of salts is also disadvantageous because of their corrosive effect on lithographic plates and equipment. These by-products are effectively removed by the water washing described above.

The desired substitution can also be achieved by a dry granular reaction of the starch with propylene oxide under substantially non-aqueous conditions. It is, for example, possible to carry out hydroxypropylation of diluted starch using known hydroxypropylation of starch suspended in aliphatic ketones, as described in US patent 3,135,733, or by dry conversion of catalyst-impregnated starch with propylene oxide, as described in US Patent 2,516,632. Washing the starch derivative with water is the most convenient and safest way to remove low molecular weight by-products. The hydroxypropyl substitution reaction of acid-hydrolyzed aqueous starch slurries followed by water washing seems today to represent the best method for producing starch-based gums according to the invention.

The new hydrolyzed, non-ionically derivatized starch-based gums described herein represent an excellent substitute for gum arabic in all major areas of lithography technique. As mentioned above, amidoalkyl-substituted starches which have active hydrogen on the nitrogen atom will form films with increased photosensitivity. Increased photosensitivity that allows faster image formation can also be achieved by introducing ionizing groups, for example carboxyl groups and amino substituents in the starch molecule, and the choice depends on whether one wants to achieve

an anionic or a cationic product. Up to 3% by weight of carboxyl (anionic) can be added to the starch, although as little as 1% by weight or less of carboxyl content causes an increased light sensitivity of starch-based films.

Limited amounts of carboxyl groups can be added to the starch molecule by means of oxidizing reagents, for example by controlled hypochlorite oxidation of the starch, taking care to avoid excessive dilution. When adding carboxyl groups in this way, consideration should be given to the starch-diluting effect that the oxidizing agent will have on the viscosity of the final product. For easier viscosity regulation, carboxylation by hypochlorite treatment can be carried out as part of the first dilution operation which takes place before carrying out the substitution reaction.

Light-sensitizing amino groups can be introduced using the method according to US patent 2,813,093, which describes a method for introducing dialkylaminoethyl ether groups. Aminoethyl ether groups can be introduced by treating the starch in a dry state, or by slurrying the starch with ethyleneimine. Addition of an aminoethyl substituent to the starch is easy and simple, and this substituent is particularly effective in increasing the photosensitivity of starch films formed from the product. The ethyleneimine treatment of starch esters can cause a cleavage of ester groups and should be avoided. Sodium hypochlorite treatment of aminoethyl starches should also be avoided as it destroys the amino groups.

As mentioned above, the photosensitivity of the starches according to the invention can also be increased by means of amidoalkylation, so that starch ethers are formed which have hydrogen on amidonitrogen atoms. These amido groups can likewise be attacked by the hypochlorite reagent, and hypochlorite bleaching of amidoalkyl-substituted starches should be avoided.

Before storage and shipment, the washed, granular starch-based gums can be dried. For most applications, it is more advantageous to boil the starch product, treat it with amylase, filter it, and adjust the solids content to 14° Bé (24 to 27% solids) for shipment and use. The pre-boiled, liquid product can be spray-dried too

to make the shipment more convenient. In any case, the pre-cooked product is more convenient to use. No further boiling is required. Boiling is advantageously carried out in a jet cooker as described in US patent 3,067,067. The cooked starch mass is then spray-dried or dried on hot rollers. A cooked starch product can also be obtained by drying slurried starch on hot rollers without

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some separate pasting step (drum drying) .

The clarity of the starch solutions depends on

pH during - the pasting and also dependent on the treatment with α-amylase enzyme. To obtain starch solutions with the highest clear-

het, the pre-pasting should be carried out at a pH of 5 to 7.5, preferably a pH of 6 to 7. The treatment with amylase enzyme after jet boiling and before the filtration step provides a true °PP~ solution of excellent clarity. Clarity is not improved by-; r sticking at a pH below 5, and the starches are exposed to oxidative instability at pH values above 7.5.

The hypochlorite treatment of the starch derivative can be used to achieve improved filterability and should be carried out in stages. The hypochlorite bleaching agent first reacts with the protein fraction that is usually found in natural starch, and only small additional amounts of hypochlorite are needed to achieve the improved filtering ability of the starch, during the hypochlorite treatment a small oxidation of the starch can occur, and it can thereby forming smaller amounts of carboxyl groups which usually do not exceed 0.1 to 0.2% by weight of carboxyl groups, based on the weight of the starch,

and which do not cause any problems in terms of the film-forming properties of the starch-based product.

In an alternative way of working, the starches according to the invention can be bleached using small amounts of hydrogen peroxide, at a pH above 7, preferably a pH of 7.5 to 8.5, either in a slurry or in a pasty state. It is usually advantageous to use 1% of a 35% hydrogen peroxide solution for every 100g of the starch. Bleaching is carried out at 37°C for 2 hours. Bleaching with hydrogen peroxide can be carried out with aqueous starch at any suitable temperature above the freezing point of water. The treatment time varies in a known manner with the temperature and with

the amounts of hydrogen peroxide used.

At the end of the bleaching step, there is usually unreacted hydrogen peroxide which should be destroyed to prevent a possible oxidative decomposition of the starch product during storage. It is convenient to destroy excess hydrogen peroxide by treating the bleached starch mixture with catalase, for example "Fermeolase", a fungus catalase. When 10 Baker units of catalase per grams consumed 35% hydrogen peroxide is added to the starch mixture, the iodine stain test for hydrogen peroxide is usually negative after

stirring the mixture for 30 to 60 minutes at room temperature.

Bleaching with hydrogen peroxide is preferred, because any

residues are compatible with the use of the new starch-based gums according to the invention in foodstuffs, pharmaceuticals and cosmetics.

The starch-based gums described here will form completely clear aqueous solutions with 25% solids and higher concentrations, and they have a very stable solution viscosity. Solutions with 14° Be (24 to 27% solids) prepared according to the invention were stored at room temperature for 1

to 6 months, and even longer than 12 months, without any change in viscosity. One can therefore prepare loads of these starch-based rubber solutions for lithographic use and store them for a longer period of time before they are actually used, which greatly facilitates the lithography work.

These starch-based gums have all those properties

which are needed to replace gum arabic in lithographic applications, and they are superior in several respects to gum arabic in lithographic applications. Solutions of gum arabic and dichromate for deep etching must be made alkaline to achieve stable storage, as they are unstable at lower pH ranges. However, the imaging of gum arabic/dichromate films can only be carried out at acidic pH. Therefore, ammonia must be removed from gum arabic dichromate films before they can be irradiated. Similar solutions using starch-based gums of the invention and dichromate are stable at pH below 7, and starch/dichromate can be successfully irradiated without any further pH adjustment. Because of this, very satisfactory and stable acidic starch/sodium dichromate solutions can be prepared long in advance, while gum arabic based solutions used for the same purpose lose their stability and usability after only one day.

If lithographic plates coated with gum arabic/dichromate films are stored for some time, the films will harden even when stored in the dark (dark aging). This problem is particularly evident when storage takes place at high temperatures and humidity.

These cured films are not particularly suitable for development processes used in lithography. "Dark aging" can occur within 1 hour of coating a lithographic plate, and this problem severely limits the conditions under which these plates can be stored and the possible storage times.

Depending on the humidity conditions, gum arabic-based sheets that have been stored for only half a day will

"dark ages" to such an extent that excessive irradiation is needed

■to form images that have sufficient image contrast. Gum arabic coated plates are normally not used for deep etching purposes after 2 days as they have lost their sensitivity. Only a very limited supply of gum arabic-coated plates can be advantageously produced and stored before they are to be used.

In contrast, the starch-based rubber/dichromate-coated plates according to the invention retain their image sensitivity and are completely satisfactory even when used after a storage time of up to 30 days. As a result, a large number of coated lithographic plates can be prepared in advance long before they are to be used, greatly improving the efficiency of plate making.

Carboxyl or aminoalkyl groups can be added to increase photosensitivity, and such starch-based gums are less resistant to dark aging, but even films made from these modified starch-based gums are more stable than gum arabic-based films. The improvement in light sensitivity that is possible by adding these groups must, however, be assessed in relation to the reduced storage time.

"Press-ready" lithographic plates are usually protected during storage with an outer coating of gum arabic. If such a coating is used, the coating must be removed before the plates can be used for pressure..To remove this protective coating, the plates are run "as if for pressure" and approximately 10 to 12 plate revolutions are required to remove the protective coating. In contrast, coatings using the starch-based gums of the invention can be removed much more easily after only a few "as if for pressure" revolutions.

When gum arabic solutions are used in desensitizing solutions (fountain solutions), the necessary pumping can cause foaming, which is undesirable. The starch-based gums according to the invention do not exhibit this foaming effect and are therefore much better suited for desensitizing solutions.

The starch-based gums thus have properties that are as good or better than natural gum arabic, especially for use in lithography. These starch-based gums can be easily and cheaply produced from relatively unlimited supplies of rich

equal starches, while the world's supply of gum arabic is rapidly diminishing.

Due to their excellent film-forming properties, these starch-based gums can also be used for food and other purposes, such as candy coating and in cosmetics.

The following examples illustrate preferred embodiments of the invention.

Example 1

Starch hydrolysis was carried out in the following way: One

21° Be slurry of waxy corn starch (100 parts) was prepared in water at 16°C. The temperature of the slurry was then raised to 52°C, and 6 parts of 77.7% sulfuric acid diluted to 30 Be (density 1.26) was added to the slurry. The acidified slurry was brought to an alkaline fluidity 66 at 52°C (20 g starch, 2 n sodium hydroxide) which requires 18 hours. The slurry was adjusted to a pH of 4.5 to 5.0 by adding a 6% (8.8 Be) solution of 35 parts sodium hydroxide. The alkali fluidity test method is described immediately below

according to example 17.

Hydroxypropylation, by reaction of propylene oxide

with the acid diluted starch, was carried out under continuous stirring according to the following method: Anhydrous sodium sulfate (3.25 parts) was first added to the nearly neutralized slurry and stirred until a solution formed. 1 part of 6% sodium hydroxide solution was gradually added over 45 minutes. The gas space in the reaction chamber was then filled with nitrogen gas, and propylene oxide (10 parts) was added to the slurry. The reaction lasted for 8 hours at 82 to 44°C. Another portion of propylene oxide (5 parts) was now added, and the mixture was left to react at the same temperature for a further 15 hours.

The hydroxypropylated starch thus formed

had a hydroxypropyl content of 4.0% calculated on dry substance.

The hydroxypropylated granular starch product was adjusted to an 18° Be slurry. The starch product was there-

after being made soluble by jet cooking as described in US patent no. ■ 3 067 067. The jet cooking equipment is the same as described in the above-mentioned patent. The jetted starch was adjusted to pH 7 with 10% sulfuric acid, temperature 90 to 96°C. An amyl-

containing enzyme (α-amylase in this example) was added to the cooked starch in a ratio of 15 parts α-amylase to 100 parts starch, on a dry matter basis. The temperature was held for 15 minutes at 90 to 96°C. After the 15 minute enzyme purification step, the pH of the cooked starch was adjusted to 4 with 10% sulfuric acid to terminate the enzyme activity. The amylase enzyme dissolves all starch fragments that remain after the starch product is jet-cooked. It is also possible that some amylose recrystallizes as a result of the jet cooking step, and this recrystallized amylose is also made soluble by enzyme treatment. A number of different amylase enzymes can be used. An α-amylase, "Ban 120", sold by Novo Corporation, Mamaroneck, N.Y., was used in this example, but the following enzymes may be used: fungus α-amylase ("Asperzyme" - sold by Enzyme Dev. Corp., NYC and Japan), p-amylase (powder from diastatic brewer's malt - "Formalt" sold by Star Malt Company, Milwaukee, Wisconsin), malt concentrate containing high-diastatic, viscous (3-amylase, sold by Malt Diastase Co., Brooklyn N.Y.; amylase " Rhozyme H-39" (Rohm &Haas); amylase "Miles Ht 1000" derived from Bacillus subtilis and sold by Miles Laboratories, Inc., Elkhart, Indiana. In principle, the amylase enzyme can be derived from the following sources: animal; - saliva - and pancreatic secretions; vegetable: - barley malt, wheat bran and soybeans; bacterial sources: - Bacillus subtilis, Bacillus lichenformis and fungus sources including Aspergillus niger and Aspergillus oryzae.

After the enzyme activity had ended, it was

boiled starch product filtered hot. The solids content can be adjusted to 14° Bé (24 to 27% solids), and the product is ready for sale and can be used for typical lithographic purposes, such as for desensitizing and adhesive solutions and sensitizing solutions. A liquid product with 14° Bé is a product with a typical solids content for most lithographic purposes, and is most often chosen by buyers. Formaldehyde and sodium benzoate (0.1-1%) are optional preservatives.

The enzyme-treated starch-based gums produced according to the invention can also be spray-dried and sold as spray-dried powder. Water to form the desired solution can be added when the product is to be used. This dry product has the same benefits as a pre-cooked product, but the shipping and handling costs are less. Both the pre-gelatinized and the spray-dried products can be used to form fluff-

free desensitizing and gumming solutions with great clarity that remain stable for longer periods of time, over 12 months

(normal room temperature 21°C, pH 7.5).

Example 2

Example 1 was repeated, except that the acid hydrolysis

was carried out to an end point of alkali fluidity 68 (20 g starch, 2 n sodium hydroxide). The starch was preheated, washed, reslurried and heated above pH 9.1 with 3% (added as sodium hypochlorite) until all active chlorine was used up (about 3

hours). Reaction with propylene oxide was carried out as described in example 1. The liquid product was treated with enzymes after boiling as described above. The cooked product can also be spray-dried and sold dry to be dissolved when it is to be used. In the case of liquid pregelatinized products, it is advantageous

like adding a small amount of chemical preservative,

for example sodium benzoate, to prevent microbial attack. Pro-

the duct can be used to prepare desensitizing and gumming solutions.

Example 3

The method from example 3 was repeated, except that hypochlorite bleaching (5.5% added in portions) was used to

reduce the viscosity to an alkali fluidity of 66 (20 g starch,

2n sodium hydroxide), which required 8 hours. The slurry was adjusted to pH 4.5 to 5 by addition of 6% (8.8° Be) solution of 35 parts sodium hydroxide. The hydroxypropylation was carried out as in Example 1. Solutions of this product were advantageously used for various lithographic applications, including for sensitizing solutions, desensitizing solutions and gumming solutions.

Example 4

An acid hydrolyzed, waxy corn starch was slurried at 37°C to 20° Baumé and pH increased to 10.8 - 11.1 with 6% NaOH. 4.1 liters of hypochlorite bleach were then added

(3% CI2" based on the weight of the starch, calculated on dry matter),

and allowed to react until all Cl2 was used up (shown by a negative KJ test). When this starch was cooked, it had a viscosity

of 110 cP (27°C at 25.5% solids content). Anhydrous sodium sulfate (7% based on the weight of the starch, calculated on dry substance) was added, and the pH was adjusted to 11.1 - 11.4 with 6% NaOH. Propylene oxide (15% based on

the weight of the starch, calculated on dry substance) and allowed to react with the starch for 18 hours at 43°C with stirring. The pH was then adjusted to 5-7 with 30° Baumé sulfuric acid, and the starch product was filtered and washed to remove solutes. The product is still in granular form so that it is possible to remove all low molecular weight impurities and salts that may interfere with the use of the product for lithographic purposes.

The washed starch product was then slurried and boiled at •> 93°C for 10 minutes with approx. 30% solids, the pH being maintained at 6.0 to 7.5 with 30° Baume-j^SO^ The temperature was maintained at 90 to 96°C, and 0.05% α-amylase enzyme ("Ban 120 " from Novo Corp., Mamaroneck, N.Y.) was added with stirring and allowed to react for 15 minutes. The pH was then adjusted to 3.5 - 4 and the temperature was increased to 99°C for 5 minutes to inactivate the enzyme. The starch mass was then heat-filtered using "Solkafloc" as filter medium (> 60°C). The pH was then adjusted to 7 with 6% NaOH and the solids content adjusted to approx. 14° Baumé (24 to 27% solids). The solution is very clear and it remained free of flecks and stable for longer than 12 months when stored at room temperature (21°C).

Example 5

Bleaching of the starch derivative prepared according to example 1 was carried out in the following way: The slurry resulting from the hydroxypropylation was treated with hypochlorite solution, using a bleaching solution containing 0.1 g of chlorine per ml obtained by passing 3.0 parts chlorine into an aqueous solution of 4.0 parts sodium hydroxide and allowing the mixture to react for 1 hour at 42 to 50°C, followed by 0.25 part sodium metabisulphite which allowed to react for 15 minutes at the same temperature. The slurry was filtered at pH 3, the starch was again slurried at pH 6 which was adjusted with ammonium hydroxide, filtered, washed and dried. When this was done with dichromate in a sensitizing solution using the amounts mentioned in Example 10, the sensitized films prepared from the solution on a gravure plate could be used for imaging for more than 1 month, while similar gum arabic-based films

could not be used for image forming after less than 1 week.

Example 6

A starch prepared as in Example 1 was bleached

and jet-boiled as follows: To an 18° Baumé slurry of granulated, hydroxypropylated, acid-diluted starch derivative was added 1 part of 35% hydrogen peroxide per 100 parts starch. The mixture was stirred at 43°C for 2 hours, and then the oxidation reaction was stopped by adding catalase (10 Baker units of Fermolase catalase per gram of hydrogen peroxide used) to the stirred off-

cooled slurry, and stirring was continued for 30 minutes.

At the end of this time, the iodine stain test for excess hydrogen peroxide was negative. The slurry was filtered, the starch washed with water, reslurried and the slurry adjusted to pH 7 with dilute sulfuric acid. The neutral slurry was made soluble by jet boiling.

When the soluble starch was used as described

in Example 15 to form a protective coating on a ready-to-print image plate, the image was not faded and the protective plate printed correct copies after only a few revolutions, whereas similar gum arabic protected plates required printing several times as many copies before obtaining correct copies.

Example 7

Example 1 was repeated using potato starch instead of corn starch: The product obtained from potato starch was substantially equivalent to the product obtained from corn starch and worked equally well as a protective coating. The potato starch-based derivative was also satisfactory when used in a photosensitizing solution following the method described in Example 13.

Example 8

Hydrolyzed waxy corn starch was amidoalkylated

by means of acrylamide in the following way: Waxy corn starch was prepared as described in example 1. The hydrolysis mixture was neutralized with sodium hydroxide solution and filtered. The starch was washed with water and dried to 9.5% moisture content. The dried starch (1500 parts on a dry basis) was slurried in 2400

parts of water which contained 150 parts of anhydrous sodium sulfate and 15.5 parts of sodium hydroxide. Acrylamide (150 parts) was added to

the slurry with stirring, and the slurry was stirred at 46°C for 16 hours. At the end of this reaction time, the mixture was adjusted to pH 6.0 with 30° Baumé sulfuric acid and filtered and washed to remove all low molecular weight impurities. After air drying, the starch had 9.5% moisture and 1.12% nitrogen content (dry basis).

The amidoalkylated starch was prepared as a light-sensitive coating by using the quantities of components indicated in Example 13. The resulting film required only half the development time for acceptable images required with the starch of Example 1.

Example 9

Acetylation of hydrolyzed starch using vinyl acetate was carried out as follows: Waxy corn starch was prepared as described in Example 1, and the final slurry was filtered, washed and dried. The dried starch contained 9.5% moisture.

A starch slurry containing 2500 parts of water and 1000 parts (dry basis) of hydrolyzed waxy corn starch was prepared. Sodium carbonate (50 parts) was added and dissolved in the stirred slurry. Vinyl acetate (150 parts) was added to the slurry which was stirred for 5 minutes, adjusted to pH 4.0 with dilute sulfuric acid and filtered. The filter cake was washed with water, reslurried in water and filtered. After air drying, the starch contained 9.5% moisture and 7.3% acetyl. This acetylated starch derivative was particularly advantageous as a protective coating for preprinted lithographic plates and was also very effective when used in a desensitizing solution by the method and in the amounts described in Example 14.

Example 10

A carboxyethylated propylene oxide treated starch was obtained by treating 100 parts of the slurry starch product from Example 1 in 2200 parts of water containing 20 parts of dissolved sodium hydroxide and 400 parts of dissolved sodium sulfate, with 80 parts of ethyl acrylate. The slurry was maintained at 46°C with stirring and ethyl acrylate was added and the slurry maintained at a pH of 11-11.4 by gradual addition of an aqueous solution containing 5% sodium hydroxide and 10% sodium sulfate. The reaction of ethyl acrylate with the starch slurry was allowed to last for 2 hours, after which the reaction mixture was adjusted to pH 4.5 with dilute sulfuric acid, filtered, the filter cake washed with water, re-slurried, adjusted to pH 4.5 with dilute sulfuric acid solution and the re-slurried starch was then filtered, washed and dried. The starch product contained 0.58% carboxyl. Light-sensitive, dichromate-containing films based on this starch required only half the exposure time necessary to form images as similar films based on the starch of Example 1.

Example 11

The hydrolyzed, propylene oxide-treated starch from example 1 was treated with ethyleneimine in the following way: The dried starch product from example 1 (100 parts) was placed in a pressure bottle, and 1.85 parts of ethyleneimine dissolved in 20 parts of water were added. Glass balls were then placed in the pressure bottle as a stirring aid. The bottles were capped and rolled in a constant temperature bath of 82°C for 2 hours. At the end of the reaction time, the bottle contents were removed and sieved to separate glass beads and minor amounts of agglomerated starch from the resulting amino-substituted starch product which was washed and dried.

The analysis of the starch derivative showed 0.3% by weight of nitrogen, and it was suitable as a protective coating. When the derivative was used in the quantities indicated in Example 13, it could form images after much shorter light exposure times than the starch derivative from Example 1 which was treated in the same way.

Example 12

Example 5 was repeated until the metabisulphite treatment. The resulting starch product was sieved, washed and reslurried. The slurry was adjusted to pH 6.0 with dilute sulfuric acid and boiled in a jet cooker at 149°C. The resulting mass was cooled to 16°C, filtered, and spray-dried. The dried starch product was readily soluble in cold water and suitable for lithographic use, such as for gumming, light-sensitive films and for desensitizing solutions.

Example 13

A solution of a sensitizer was prepared containing 20 parts of a starch derivative prepared according to Example 12, 4 parts ammonium dichromate, 3 parts ammonium hydroxide (28% concentration), 0.1 part Kiton blue dye and 80 parts water. A plate was coated with this sensitizing solution on a centrifuge. After storage in the dark for 30 days, the plate was exposed through glass. The plate required a development time of 6 minutes. For comparison, a plate coated with an identical sensitizing solution, containing gum arabic instead of starch, was stored in the dark under identical conditions for 7 days and then exposed through glass. The plate had been dark-aged to such a high degree that it could not be developed.

Example 14

A sensitizing solution containing 20 parts of starch derivative prepared according to Example 2, 4 parts of sodium dichromate and 80 parts of water was adjusted to pH 5.0 by means of lactic acid. A lithographic plate was coated with this sensitizing solution and exposed through glass. The exposed plate required a development time of 5 minutes, the same as an analogous plate obtained by coating with a sensitizing solution containing 20 parts starch derivative, 4.0 parts ammonium dichromate and 3 parts ammonium hydroxide (28% concentration). The quality of the finished plate was exactly the same as that of a plate prepared with the above-described sensitizing solutions based on ammonium dichromate.

Example 15

A press-ready deep etching plate was rubberized with a rubberizing solution containing the starch-based gum according to the invention on half of the plate, and with gum arabic on the other half of the plate. The gumming solutions contain up to 25% solids. After storage for 30 days, the plate was mounted in a lithographic printing press and the rubber removed conventionally by contact with a water roller. After 5 impressions, the page previously gummed with the starch derivative gave correct images, while the page previously gummed with gum arabic had unclear parts of the image after 25 impressions.

Example 16

Two similar ammonium dichromate-based sensitizing solutions were prepared, one of which contained gum arabic and the other a starch derivative prepared according to example 5, and these were then mixed in a sensitizing solution in the conditions specified in example 13. Each solution was applied to a plate and the plates were stored in the dark at 37°C and 90% relative humidity for 1 hour. The plates were then exposed through glass in the usual way. During storage, the development time of the gum arabic-coated exposed plate increased from 4 to 12 minutes, while the exposed starch-based gum-coated plate had an unchanged development time of 4 minutes.

Example 17

A desensitizing solution based on the starch derivative according to the invention was used for printing and circulated by means of a pump in a conventional manner. Such solutions normally comprise water and water/alcohol mixtures in different proportions.

It was found that the solution foamed very little and to a negligible extent. Similarly prepared gum arabic solutions can, under the same conditions, foam very vigorously.

Alkali fluidity test method

1. Non-neutralized slurry method. A 20 g sample (dry basis, corrected) of the starch slurry was pipetted

in a fluidity beaker. Then 75 ml of 8.0% (2n) sodium hydroxide was added. The mixture was stirred for 3 minutes for pasting of the starch. The stirred mass was then transferred to an alkali fluidity funnel, and the temperature of the mass was noted. The alkali fluidity was then determined using the following method: The alkali fluidity test method is generally described in US patent 3,238,193, columns 7 and 8, lines 40-61 resp. 1-9.

The funnel used for the experiment has a specific "water time" between

30 and 40 seconds. The "water time" of the funnel is checked at the beginning of each trial by passing 100 ml of clean water through the funnel and noting the time. This total time is calculated. for each' sample of alkali-treated starch slurry to be examined. The alkali fluidity is the total amount of the starch sample in ml that passes through the funnel in the "water time" defined above.

The alkali fluidity funnel used for the alkali fluidity test described above comprises 2 main parts, a funnel body and a funnel tip which is screwed onto the body. A simple, conical piston-type valve on a glass rod can be used to manually regulate the flow through the funnel opening. The funnel parts are precision machined from stainless steel and polished,

so that they have very smooth surfaces on all parts that come into contact with the test pieces.

The funnel body forms a largely conical container

which form 60° angles between opposite converging funnel walls. The height of the funnel body is sufficient to hold at least one 100 mL sample, and a 0.7 mm orifice and fluid passage is provided at the narrowest part of the funnel for connection to the funnel tip. The fluid passage has a length of 2.5 to 1.25 cm from the opening to the narrow end of the funnel body. The opposite, wide opening of the funnel body is directed upwards, and the cone-shaped valve is introduced from above down into the narrower opening during the experiment. The operation of this valve in relation to the "water time" of the funnel gives the test readings. The funnel tip is a cup-shaped part that is screwed onto the narrow end of the funnel body. The inner chamber of the funnel tip is hemispherical in shape and has a diameter of

4.5 mm with a lower central opening of 1.7 mm with a length of 1.25 mm. The total height of the lower end of the funnel body passage to the lower outer opening of the funnel tip includes the height of the ball chamber (2.5 mm) and the length (1.25 mm) of the opening of the funnel tip.

The above-described, composite apparatus is placed vertically above a measuring cylinder to carry out the experiments. At the beginning of each trial, the "water time" of the apparatus is checked by letting 100 ml of clean water flow through the funnel and noting the required time. The "water time" then becomes the time in relation to which each sample is examined.

As mentioned above in Example 1, the alkali fluidity test is used to monitor the acid conversion step of the process. When the desired alkali fluidity is reached, the acid conversion step is stopped. The alkali fluidity is then corrected to 25°C using a table based on experience.

2. Neutralized slurry method. A 20 g sample (dry basis, corrected) of the starch slurry was pipetted into a fluidity beaker after the slurry had first been neutralized to pH 5, filtered and washed. 75 ml of 8.0%-ig is added

(2n) sodium hydroxide, and the slurry is stirred for exactly 3

minutes. The stirred mass is then immediately transferred to an alkali fluidity funnel (as described above) and the temperature of the mass is measured and corrected to 25°C using a table based on experience.

Summary

The granular reaction method for producing starch-based gums according to the invention is important, because it is possible to wash out almost all the water-soluble components with low molecular weight from the raw, granular starch derivative. It is particularly important to remove low molecular weight components such as sodium sulfate and propylene glycols (in some cases including di- and tripropylene glycols) because they interfere with lithographic work. It is difficult to define precisely the amount of each low molecular weight byproduct that may be present. It is and-

so important to remove syrups that have a dextrose equivalent higher than 15 T Propylene chlorohydrins may be present if hypochlorite bleaching is used.

The content of residual salts (primarily sodium

sulfate and sodium chloride) should be 2% or less, calculated on

dry substance, based on the weight of the washed starch derivative.

The total propylene chlorohydrin residue should not exceed 0.0005

% by weight, based on the weight of the washed starch derivative and calculated on dry substance, and the propylene glycol residue should not exceed 3

% by weight calculated on the weight of the starch.

The starch-based gum according to the invention has the best aesthetic appearance when it is treated with amylase to solubilize the recrystallized amylose and other floc-forming starch fragments.

The more stable, clear solutions are obtained when one

uses a thicker, acid hydrolyzed starting starch. An acid-hydrolyzed starch oxidized with 2 to 4% Cl 2 (as NaOCl) is then reacted with 15% propylene oxide, filtered and well washed to remove salts. The product is then cooked as described in detail in Example-1. The intermediate is then treated with α-amylase enzyme (> 0.01%) at pH 6.5 to 7.5. The enzyme fairy action is terminated by adjusting the pH to 3.7 - 4.2, while keeping the temperature above 90°C. The resulting product is clear after filtration and remains clear for at least 6 months (>5 pH).

The starch-based gum according to the invention is an excellent and cheap substitute for gum arabic, especially for lithographic applications where you want to have a uniform quality

tet and stability of the sensitization and desensitisation solution. The product is preferably boiled and, after boiling, is soluble in cold water so that you get very clear solutions (normally with 25% solids) which have excellent film-forming properties and a much greater storage stability than similar solutions that use gum arabic . Raw materials for these starch-based gums are not dependent on random changes in world trade, which, for example, have a major impact on acacia gum which is already rare and is beginning to disappear completely due to political and economic unrest in the parts of the world where it occurs.

Claims (13)

1. Hydrolyzed, cold water soluble, granular, starch-based gum which is treated with amylase and comprises at least one nonionic substituent having a degree of substitution of 0.1 to 0.3, which gum has..improved film-forming properties and improved stability in aqueous solution when stored for more than 1 month, the aqueous solution containing 24 to 27% solids and having an initial Brookfield viscosity of from 10 to 249 cP, measured with a No. 1 spindle at 20 rpm. minute at 27°C, and largely retains this viscosity even after being stored for over 1 month, characterized in that the non-ionic substituent is an alkyl, hydroxyalkyl, cyanoalkyl, aminoalkyl or amidoalkyl group where the alkyl group has 1- 6 C atoms, or an acyl group selected from acetyl, propionyl and butyryl, and the rubber is obtained by first diluting a granular starch with acid, preferably oxidatively, then reacting the diluted granular starch with a non-ionic substitution agent, washing the crude , granular reaction product with water to remove the majority of low molecular weight components including residual sodium sulfate, sodium chloride and organic soluble substances from the raw granular reaction product to obtain a uniformly substituted starch-based gum, gelatinize the starch-based gum, and filter the gelatinized starch-based gum to remove substantially all remaining contaminants. 2. Starch-based gum as stated in claim 1, characterized in that the non-ionic substituent is hydroxypropyl, and that the starch-based gum is derived from waxy corn starch. 3. Rubber as specified in claims 1 and 2, characterized in that it comprises added carboxyl groups up to a degree of substitution of 0.1, the viscosity properties of the starch-based rubber remaining largely unchanged after the addition of carboxyl groups. 4. Rubber as specified in claim 3, characterized in that the carboxyl groups originate from hypochlorite oxidation of the starch derivative, the rubber being essentially free of propylene chlorohydrins. 5. Rubber as stated in claims 1 and 2, characterized in that it contains added aminoalkyl groups up to a degree of substitution of 0.1, the viscosity properties of the starch-based rubber remaining essentially unchanged after the addition of aminoalkyl groups. 6. Gum as stated in claims 1 to 5, characterized in that the granular starch derivative is boiled, and that the boiled starch is treated with an amylase which dissolves all starch fragments and recrystallized amylose that are present after the boiling. 7. Gum as stated in claim 6, characterized in that the amylase is α-amylase, 3-amylase or a combination thereof originating from vegetable and animal sources. 8. Process for the production of a starch-based rubber as stated in claim 1, characterized by the following steps: a) a starch with an amylose content of 30% by weight or less is diluted with acid to obtain a granular starch having a viscosity of from 10 to 249 cP measured at a concentration of 24 to 27% solids at 27°C in a Brookfield viscometer with a No. 1 spindle at 20 rpm. minute, b) the diluted starch is treated with a substitution agent to a degree of substitution of 0.1 to 0.3 by means of a substituent selected from alkyl, hydroxyalkyl, cyanoalkyl, aminoalkyl, amidoalkyl and acyl groups with 1-4 carbon atoms , c) the resulting granular starch-based gum is washed to remove virtually all low molecular weight components including solubilized starch, sodium sulfate, sodium chloride, propylene chlorohydrins, propylene glycol and its polymers, d) the granular starch derivative is boiled and e) the boiled starch derivative is treated with amylase. 9. Method as stated in claim 8, characterized in that the starch derivative is boiled and then treated with an amylase selected from α-amylase, β-amylase or a combination thereof originating from animal and vegetable sources. 10. Method as stated in claim 8, characterized in that the pH of the cooked starch derivative is set to 5.5-8.5 at a temperature from 90 to 96°C and that the α-amylase enzyme is then added to the cooked starch in a amount of 5 parts α-amylase per 100 parts of the starch derivative, on a dry matter basis, whereby all starch fragments and fragments of recrystallized amylase are solubilized within 15 minutes, then the pH is adjusted to 3.7-4.2 to terminate the enzyme activity, then the boiled starch derivative and the liquid product are hot-filtered set to 14° Baumé (24-2*7% solids). 11. Method as stated in claims 8 to 10, characterized in that an aqueous solution of the starch-based rubber is formed, the aqueous solution of rubber is separated from insoluble components and water is removed from the aqueous solution to obtain a dried, starch-based rubber with a moisture content of 5 to 15%. 12. Method as stated in claims 8 to 11, characterized in that a starch is used where the substituent is hydroxyalkyl and that the granular, acid-hydrolyzed starch is treated with a hypochlorite solution containing up to 5% by weight of active chlorine, in order to obtain an easily filterable , aqueous solution of the starch. 13. Method as stated in claims 8 to 11, characterized in that a starch is used where the substituent is hydroxypropyl and that the granular, hydrolyzed starch is treated with hydrogen peroxide to improve the color and obtain an easier filterable, aqueous solution of the starch-based gum.