DE2339990A1 - COATING COMPOUNDS FOR PAPER AND THEIR USE - Google Patents

Description

^w Coating compositions for paper and their use "Priority: August 7, 1972, Japan, No. 78 936/72

The invention relates to a coating composition for paper which is characterized by a content of a pigment and a latex of a copolymer of 24.5 to 50 parts by weight at least one aliphatic conjugated diolefin, 0.5 to 10 parts by weight of at least one olefinically unsaturated Carboxylic acid and 40 to 75 parts by weight of at least one olefinically unsaturated monomer, which with the diolefin and the Carboxylic acid is copolymerizable, and a gel content of

as a binder

at most about 60 percent by weight ^ - as well as the use of the coating compound for coating paper, especially for

Offset printing or flat printing. The gel content is preferably of the copolymer not more than 40 percent by weight.

The coating composition of the invention has improved properties, especially with regard to their prevention of the formation of bubbles, the transfer of multi-color offset printing inks, the water resistance and the absorption resistance.

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There have been significant advances in offset more recently color printing achieved with high printing performance. For this high-performance printing process there is an urgent need for one

ver
Pigment binder with improved properties for processing and coating paper. For this purpose, starch, casein and latices made from copolymers were used as binders. '

For offset printing of paper webs, latices are required which have excellent wet absorption properties and resistance to Must have blistering among other properties. The coated paper for offset printing is in the form of Shipped on rolls and differs from coated paper, which is to be printed on in individual sheets, and that is delivered in planar form. A large number of improved synthetic copolymers have already been investigated and Widely used in the manufacture of pigment-coated paper, e.g. copolymers of butadiene, styrene, as well as an olefinically unsaturated carboxylic acid and copolymers of butadiene, methyl methacrylate and an olefinically unsaturated one Carboxylic acid. However, these copolymers have

Different disadvantages as a binder for coating paper webs, which is why they / for offset printing

are unsuitable. For example, some conventional latexes made from synthetic copolymers have a favorable one Water resistance and good recording resistance, but they are unsatisfactory in terms of offset ink transfer and bubble resistance. Some other latexes made from synthetic copolymers have good offset ink transferability and satisfactory blowing height resistance, but a J

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very poor water and absorption resistance.

In printing, ink transferability is generally determined by the type and amount of the pigment binder and the roughness of the pigment and it depends on the properties of the coating layer on the paper. With big ones Pigment particles become the surface of the coated paper porous, as a result of which the gloss and smoothness of the coated surface suffer. This can lead to increased penetration

a bigger one

Printing ink in the coated paper and to / amount of transferred On the other hand, ink transferability also becomes irregular. With increasing pigment binder content the amount of ink transferred decreases and the amount of ink penetrating the paper becomes

Type of

decreased. This means that the, each as a pigment binder latex used for paper coating compositions synthetic copolymer is very dependent on the absorption

duxch

tion of water / the coated paper and the porosity the coating layer. So the latex plays one important role with regard to the transferability and the rate of penetration of the printing ink.

When offset printing paper webs, the printed ink has to dry practically immediately after application. Therefore offset printing machines are used for printing paper webs in contrast to offset printing machines for printing flat sheets equipped with high temperature and high speed dryers. The drying of the printed Ink with these dryers can cause blisters to form

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on both sides of the printed paper. This phenomenon is particularly observed when, when high temperatures are applied to the printed paper, the water in the coated paper evaporates at the same time, as a result of which the vapor pressure is greater than the internal strength of the coated paper. If bubbles are formed in the paper during printing, the quality of the paper will deteriorate. The formation of bubbles depends to a large extent on the porosity of the coated layer on the paper, the water content in the paper and / or the internal strength of the coated paper. If the internal strength of the paper is greater than the vapor pressure generated when the paper is dried, only a few bubbles tend to form. However, in order to increase the internal strength of the paper, paper pulp of very good quality must be used. It would also be useful to reduce the water content in the paper and thus also the internal vapor pressure that is generated when a dryer is used. However, this attempt would not be entirely satisfactory because it is difficult to deliver the paper produced in this way in well-formed rolls and the low water content also impairs the dimensional stability of the paper. The use of pigment with coarse particles can improve the porosity of the paper and thus also allow the internal vapor pressure to be reduced, but its gloss, the brilliance of the print and the wet pick-up resistance would be impaired. In order to improve the prevention of the formation of bubbles in the coated paper, it is therefore more important and expedient to use a pigment binder with more favorable resistance to the formation of bubbles than to increase the strength of the paper itself and / or a _j

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use special pigment.

The object of the invention is therefore to create a coating composition for paper that has favorable properties in terms of Prevention of ink transfer blistering in multi-color offset printing, water resistance and recording resistance owns. This object is achieved by the above-mentioned coating composition for paper.

The diolefin component of the copolymer is preferred Butadiene or isoprene. This monomer is used in an amount of about 24.5 to 50 parts by weight to form a copolymer with the corresponding elasticity properties. Using smaller amounts of monomer will not the required. Preserved elasticity, as a result of which the adhesive strength of the copolymer suffers. When using larger quantities the copolymer becomes too soft on the diolefin component, so that it does not have the required water resistance.

Specific examples of the carboxylic acid component of the copolymer are acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid. The anhydrides and monoalkyl esters can also be used of the dicarboxylic acids can be used. This carboxylic acid component enhances the adhesive property of the coating and increases the mechanical strength of the latex. In general, a conventional one can also be used in the coating composition A waterproofing agent can be used which reacts with the carboxylic acid to form a crosslinked structure and creates a waterproof coating. The carbon

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Acid component is preferably used in an amount of about 0.5 to 10 parts by weight used.

The olefinically unsaturated monomer copolymerizable with the diolefin and the carboxylic acid is, for example, a monomeric one aromatic vinyl compound such as styrene, α-methylstyrene or Vinyl toluene, a 'monomeric acrylate, such as methyl acrylate, ethyl acrylate, Butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate or glycidyl acrylate, a monomeric methacrylate, such as methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate or glycidyl methacrylate, acrylamide, N-methylol acrylamide or acrylonitrile. These monomers can easily be copolymerized with the diolefin and the carboxylic acid. the Monomer component is preferably used in an amount of about 40 to 75 parts by weight. Preferably styrene or Methyl methacrylate or a mixture thereof in an amount of at least about 80 percent by weight based on the total weight of the monomer component is used.

For the production of the copolymer latex used according to the invention a chain transfer agent is used, which not only determines the molecular weight of the copolymer, but also its formation a three-dimensional structure between the double bonds in the starting monomers and in the one formed during the polymerization Polymer prevents. By using these chain transfer agents, the gel content of the copolymer can also be regulated, whereby a coating compound with excellent properties

_L th with regard to the prevention of the formation of bubbles and water-j

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resistance in offset printing of paper webs is obtained. Examples of suitable chain transfer agents are acrolein, methacrolein, allyl alcohol, 2-ethylhexyl thioglycolate, Mercaptans, like. Octylmereaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan, n-hexadecyl mercaptan and mixed tert-mercaptans, Thiuram-type sulfides, such as tetraethylthiuram sulfide, dipentamethylene thiuram hexasulfide, Haloalkanes, such as carbon tetrachloride, methylene chloride, carbon tetrabromide and ethylene bromide, as well as hydrocarbons such as pentaphenyl ethers. The chain transfer agent can be used either alone or in admixture and at. the polymerization can be added simultaneously or continuously. The chain transmitter can also be mixed with one of the monomers used can be used.

The amount of chain transfer agent is of particularly great importance for reducing the gel content of the copolymer used according to the invention. If a larger amount of the chain transfer agent is used, the gel content decreases. However, since the gel content also depends on various other factors such as the polymerization temperature, the conversion and the manner in which the monomers are fed, the other factors must also be taken into account. For example, the use of an amount of about 0.6 to 0.8 parts by weight or more of a chain transfer agent such as dodecyl mercaptan per 100 parts by weight of the total amount of monomers is sufficient when the polymerization is carried out at a temperature of about 50 to 70 ⁰ C and at a Conversion of about 95 to 100 percent is carried out. The use of about 0.1-0.2 parts by weight of this chain transfer agent

_L may be sufficient if the polymerization takes place at a temperature

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from about -5 to +10 C and with a conversion of about 60 percent. At a higher polymerization temperature also generally increases the amount of chain transfer agent used. In the case of a lower conversion, the amount can generally also be used of the chain transfer device used can be reduced.

In this connection it must be pointed out that such copolymers with a low gel content, as used according to the invention, were not used for coating paper. The gel content of commercially available polymer latices for paper coating is summarized below: trade name gel content, % manufacturer

Dow latex 620 86 Dow Chemical Dow latex 636 89 Dow Chemical Dow latex 680 83 Dow Chemical JSR 0692 85 Japan synthetic rubber JSR 0668 92 Japan synthetic rubber Naugatex 2752 93 Uniroyal Emulsion rhodopas
SB.023 81 Rhone Poulence

Note: All latices contain as a major component a styrene-butadiene copolymer modified with an unsaturated carboxylic acid.

An emulsifier can also be used to produce the polymer latices used according to the invention. Suitable emulsifiers are anion-active wetting agents, such as alkali metal salts of alkyl sulfates, Alkyl aryl sulfonates or sulfonated alkyl esters. Specific examples of these known emulsifiers are sodium dodecylbenzenesulfonate, Sodium lauryl sulfate, sodium di-sec.,

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butylnaphthalene sulfonate, sodium dioctyl sulfosuccinate, disodium dodecyldiphenyl ether disulfonate and the sulfuric acid esters of higher fatty alcohols, alkylarylsulfonates, alkylnaphthalene sulfonates and their derivatives, alkyl sulfonates, sulfonic acid salts of Alkyl succinates and sulfonic acid esters and phosphoric acid esters of non-ionic emulsifiers. Non-ibnian emulsifiers, such as Polyoxyäthylenalkyläther, Polyoxyäthylenalkylphenoläther and polyethylene glycols can be used together with the anion-active Emulsifiers are used.

Polymerization initiators that can be used are, for example, persulfates, inorganic Peroxides, such as hydrogen peroxide, organic peroxides, such as cumene hydroperoxide, lauroyl peroxide or diisobutylbenzoyl peroxide, and so-called redox catalysts are used, where an oxidizing agent is used together with a reducing agent such as sodium hyposulfite or rongalite. Together with the emulsifiers and / or polymerization initiators A wide variety of electrolytes, polymerization accelerators or complexing agents can also be used, how they are used to make synthetic copolymer latices.

The polymerization can be carried out at low temperatures when a redox polymerization initiator is used or at high temperatures if other polymerization initiators are used. The monomers and resp. or the emulsifiers can be fed in during the polymerization will. However, the order in which the reactants and the reagents are fed in is

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sation procedure is not critical. She hangs on the type of connections used.

As soon as the monomers polymerized to a corresponding conversion the polymerization is terminated and the reaction mixture can be stopped with a polymerization interrupter, a pH control agent and / or a stabilizer be moved. After stripping off the unreacted monomers, the copolymer latex obtained can be placed in a container be kept.

The use of a polymerization interrupter is generally preferred because it suppresses an increase in the gel content after polymerization, for example during recovery of the unreacted monomers, during storage or shipping. Examples of polymerization interrupters which can be used are carbamate or thiuram compounds, sodium thiosulfate, hydroxylamine sulfate, hydroquinone and thiourea. If a polymerization interrupter is not used, the gel content can rise to values above 60 percent, depending on the storage conditions before use, so that this binder is unsuitable for the purposes of the invention.

The copolymer produced by the process according to the invention can be mixed with a pigment, a pigment binder and / or a conventional agent to improve the Water resistance and / or other means for coating paper can be used. Clay, titanium dioxide, a mixture of plaster of paris and alumina, a mixture j

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of calcium sulfate and aluminum sulfate, calcium carbonate, aluminum hydroxide or zinc oxide can be used. Casein, starch and starch derivatives, for example, can be used as additional pigment binders or polyvinyl alcohol can be used. Examples of agents for increasing water resistance are melamine-formaldehyde condensates, Urea-formaldehyde condensates and polyamide resins. . ·

. The coating compositions of the invention are characterized by that no bubble formation occurs in the offset printing of paper webs. Furthermore, the properties are in terms of water resistance and transfer of printing ink with offset printing of paper webs is much better than with printing paper that is made with conventional ones Coating compositions was coated.

The examples illustrate the invention. Parts refer to the weight, unless otherwise stated.

Example i

. A 10 liter autoclave is filled with 32 parts of butadiene, 55 parts of styrene, 10 parts of methyl methacrylate, 1.5 parts of acrylic acid, 1.5 parts of fumaric acid, 0.7 part of sodium bicarbonate, 0.8 part of potassium persulfate, 100 parts of water, 1.3 parts a sodium alkylbenzenesulfonate and a chain transfer agent indicated below. The mixture is 14 hours heated to 60 ° C and stirred. A copolymer latex is obtained. The conversion is 98 percent and it hasn't Coagulate formed. The average particle size of the copolymer in the aqueous dispersion is about 2000 S.

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Table I summarizes the printing properties of paper coated with various coating compositions. In the The following table contains the copolymer latices as follows Chain transmitter in the specified quantities:

Chain transmitter Parts by weight A. n-dodecyl mercaptan 0.3 B. tert-dodecyl mercaptan 0.6 C. tert-dodecyl mercaptan 1.2 D.
E. Octyl mercaptan * 1.2

■ *) added at intervals ¹ .

The latex Ξ is made at a temperature of 60 C with the same Ingredients like the latices A to D, but without a chain transfer agent. The latex E has a particle size of about 2800 A and a gel content of 95 percent. The copolymer latex F is a commercial product. Latices A, E and F were used for comparison.

Using these latices, coating compounds are produced from the following components:

Components parts by weight

Ultra-White 90 (kaolin) 80

Aluminum hydroxide 20

denatured starch 7

Latex 12

Means to increase the water _

resistance ^υ * ^

Dispersant 0.25

The coating compositions are to a solids content of

l_ 45 percent adjusted and then on bleached sulfate paper _j

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applied. The coated paper is dried and calendered. After that the paper is on its different Properties examined. The results are summarized in Table I.

Table I. Characteristic copolymer latices

AB C DEF

Gel content, % 85 55 40 14 95 90

Resistance to _{2 Q} «. _{24 2Q} . _{Q 2}

Wet pick-up ^ ' ^ö ** * ^ ^' ^{u 4} U} ^ »

Resistance to _{22 22 22 2} . . ,. ₂

Dry absorption * »* *» * ^ * ^ ^ '^ ^ ^{i :?} ^ ^>

Ink transfer _{26 2} , ₂ . ₂₄ , _Q ,

availability ^ '°' ^ ' ⁴ ^' ^ ' ^υ ^'

Resistance to ". _{,, 0 ?? 1 ς} , _{ς 4}

Blistering ^? - ⁵ ^ * ⁰ ^ '*''^^' ⁵ ^ '

Print gloss,% 76 77 79 78 72 77

Air permeability,
m. /

To determine the gel content of the copolymer, the solution is

The content of a latex film is determined and the gel content of the copolymer is determined from this calculated. A latex film (1 g) obtained by drying the copolymer latex at room temperature is shown in 400 ml of benzene dissolved. After standing for 48 hours, the solution is filtered with No. 2 filter paper. The Filtrafc will dried at 70 ° C. and the sol content determined.

To determine the resistance to wet absorption, the extent to which the wet absorption is determined with the naked eye the coating takes place. These tests are carried out with a paper strip as a sample, the one with the copolymer latex is coated, on which an offset printing ink with various

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relatively high bond value with an RI-type printing machine was printed immediately after the coated paper was moistened by a moistening roller.

Resistance to dry intake is increased with the unarmed Eye is determined as the adhesive strength of the coating in terms of the extent to which the printed area has decreased became. This experiment is carried out on coated paper that is combined with a commercially available offset printing ink RI-type printing machine was printed.

The transferability of printing ink in offset printing becomes visible to the naked eye due to the density of the printed Printing color determined. Printing is the same as when testing for resistance to wet pick-up with a printing ink carried out with a very low adhesive value in order not to produce any decrease in printing ink.

The resistance to the formation of bubbles in the offset printing of paper webs is determined with the naked eye. Paper strips become 90 percent relative before 2 days Humidity, conditioned. The moistened paper is then printed with a heat-drying printing ink

of the Pendelfcyps

and immediately afterwards dried in an improved test device for the determination of bubbles (W, A. Wink, Tappi, 50 (7); 102A (1967)) Heat 1 sc 'mde to 350 ° C. In the case of diadem / request, the temperature is set to 180 £ 5 ⁰ G. The Troüknunasäaiier is 1.0 + J

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0.1 seconds. The examined paper has a moisture content of 7.5 +. 0.5 percent, the test results are average values of 6 samples.

The results obtained are expressed by rating numbers from 1 to 5. "1" means best results, "5" means very much bad results.

The print gloss is determined with a gloss meter on coated paper that with a printing machine of the RI type 0.4 ml. Of a commercially available offset printing ink has been printed. The printed paper is stored for 1 day and then examined.

The air permeability is measured with an Emilgryner porosity meter determined according to the Japanese industrial test standard JIS C-2111 .

As can be seen from Table I, is one with the invention Coating compound coated paper in which a copolymer with a low gel content is used, much better in terms of its. Resistance to wet pickup and Blistering than the papers made with conventional coating sma ssen were coated. The papers coated with the coating compound A and the commercially available latex F. have poor bubble resistance. The paper coated with the coating compound E has a favorable air permeability and fairly good blistering resistance, however, is extremely unsatisfactory in terms of its resistance to wet pick-up and dry pick-up

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take and print gloss quality.

Example 2

According to Example 1, the following copolymers are produced from the components given in Table II:

Table II

Components, parts by weight G Cop oil merlatices I. J K 34 H 34 36- 40 Butadiene 52.75 34 55.5 ' - 56.5 Styrene 10 51.5 12th 62.5 - Methyl methacrylate 2 10 - - - 2-hydroxyethyl acrylate - - - - Glycidyl methacrylate 0.75 2 1.5 - 1.5 Fumaric acid 0.5 1.5 1.0 1.5 2.0 Acrylic acid 1.3 1.0 1.0 - 1.0 tert-dodecyl mercaptan _ « - - _ Mixture of tert-mercap 1.2 tan - - 0.4 - Octyl mercaptan 15th - 21st 5 45 Gel content, % 28

With the five polymer latices obtained, according to Example 1 Coating compositions produced with which paper is coated and, with regard to its properties, to those described above Way is examined. The results are shown in Table III.

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Table III H CoTDolvmerlatices J K F. properties 28 I. 5 45 90 G- 1.8 21st 3.0 3.7 2.8 Gel content, % 15th 1.4 1.7 2.0 1.3 2.4 Resistance to
Wet pickup 2.0 1.8 1.7 1.5 2.3 3.0 Resistance to
Dry absorption 1.8 2.0 2.0 1.0 2.7 4.7 Ink transfer
availability 1.6 79 1.8 78 78 77 Resistance to
Blistering 1.3 18th 79 19th 18th 17th Print gloss, % 78 19th Air permeability, 20th

From Table III it can be seen that a decrease in gel content the polymer latices lead to unexpectedly better properties.

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Claims (14)

Claims . Uy coating compound for paper, marked by a content of a pigment and a latex of a copolymer of 24.5 to 50 parts by weight of at least one aliphatic conjugated diolefin, 0.5 to 10 parts by weight of at least one olefinically unsaturated carboxylic acid and 40 up to 75 parts by weight of at least one olefinically unsaturated monomer which is copolymerizable with the diolefin and the carboxylic acid and a gel content of at most about 60 percent by weight. 2. Coating composition according to claim 1, characterized in that the copolymer has a gel content of at most 40 percent by weight having. 3. Coating compound according to claim 1, characterized in that that the diolefin component of the copolymer or butadiene Isoprene is. 4. Coating composition according to claim 1, characterized in that the carboxylic acid component of the copolymer acrylic acid, Methacrylic acid, maleic acid, fumaric acid or itaconic acid acid or anhydride or a monoalkyl ester of maleic acid, Is fumaric acid or itaconic acid. 5. Coating compound according to claim 1, characterized in that that the monomer component of the copolymer is an aromatic . see vinyl compound, an acrylic or methacrylic compound, 409807/0934 - -19 is acrylamide, N-methylolacrylamide or acrylonitrile. 6. Coating compound according to claim 1, characterized in that that the monomer component is about 10 to 60 parts by weight of styrene Per contains 40 to 75 parts by weight. 7. Coating compound according to claim 1, characterized in that that the monomer component is based on styrene and / or methyl methacrylate in an amount of at least 80 percent by weight based on the weight of the monomer component. 8. Coating composition according to claim 1, characterized in that the monomer component is 1 to 5 parts by weight of 2-hydroxyethyl acrylate and / or contains glycidyl methacrylate. 9. Coating composition according to claim 1, characterized in that the pigment is a Geraisch made of gypsum and aluminum oxide, a mixture of calcium sulfate and aluminum sulfate, or calcium carbonate, Aluminum hydroxide, zinc oxide or clay. 10. Coating composition according to claim 1, characterized by an additional content of a further binder. 11. Coating compound according to claim 10, characterized in that that the additionally used binding agent modified starch, casein, soybean protein, carboxymethyl cellulose, Polyvinyl alcohol, a polyvinyl acetate emulsion, an acrylic copolymer emulsion, an ethylene vinyl acetate copolymer Is emulsion, hydroxyethyl cellulose or sodium alginate, 409807/0934 12. Coating composition according to claim 1, characterized by an additional content of a polymer disruptor. 13 Coating compound according to Claim 12, characterized in that that the polymerization interrupter is a carbamate or thiuram compound, sodium thiosulfate, hydroxylamine sulfate, Is hydroquinone or thiourea. 14. Use of the coating composition according to claim 1 for coating of paper for offset printing. 409607/0934