DE2339990C2 - Coating compositions for paper and their use - Google Patents

Description

Recently, significant advances have been made in high-performance, multi-color offset printing. For this high-performance printing process, there is an urgent need for a pigment binder with improved Properties for processing and coating paper. For this purpose, Binders starch, casein and latices made from copolymers are used.

For offset printing of paper webs, latices are required which have excellent wet absorption properties and resistance to blistering, among other properties. That coated Paper for offset printing is delivered in the form of a roll? ·. » and differs from coated paper that is to be printed on in individual sheets and that in Plan sheet is delivered. A variety of improved synthetic copolymers have already been made studied and widely used in the manufacture of pigment coated paper, e.g. B.

Copolymers of butadiene, styrene and an olefinically unsaturated carboxylic acid and copolymers Butadiene, methyl methacrylate and an olefinically unsaturated carboxylic acid. These copolymers have however, various disadvantages, which is why they are used as a binder for coating paper webs for offset printing are unsuitable. For example, some conventional synthetic copolymer latexes are inexpensive Water resistance and good recording resistance, but they are unsatisfactory in terms of offset ink transfer and bubble resistance. Some other synthetic copolymer latices have good offset ink transferability and satisfactory bubble resistance, but very good poor water and absorption resistance.

When printing, the ink transferability Im generally influenced by the type and amount of pigment binder and the roughness of the pigment, and it depends on the properties of the coating layer on the paper. For large pigment particles the surface of the coated paper becomes porous, reducing the gloss and smoothness of the coated paper Surface suffers. This can lead to increased penetration of the printing ink into the coated paper and to it lead to a larger amount of the transferred ink, on the other hand, the printing ink transferability also becomes irregular. As the pigment binder content increases, so does the amount of ink transferred and the amount of ink penetrating the paper is reduced. This means that Art each as a pigment binder for Paplerbeschlchtungsmassen The latex used from a synthetic copolymer is very dependent on the absorption of water through the coated paper and the porosity of the size layer. So the

*> ° Latex plays an important role in terms of transferability and the penetration speed of the printing ink,

When offset printing paper webs, the printed Ink dry virtually instantly after application. Therefore offset printing machines are for printing paper webs In contrast to offset printing machines for printing flat sheets with at high temperatures and in high speed working dryers. The drying

The ink printed with these dryers can cause bubbles to form on both sides of the with printed paper. This phenomenon is particularly observed when using high temperatures on the printed paper at the same time the water in the coated paper evaporates, whereby the vapor pressure is greater than the internal strength of the coated paper. If when printing If bubbles are formed in the paper, the quality of the paper will deteriorate. The formation of vesicles depends in large part Extent of the porosity of the coated layer on the paper, the water content in the paper and / or the internal strength of the coated paper. When the internal strength of the paper is greater than that of the When the paper dries, it creates vapor pressure, usually only a few bubbles form. About the internal strength however, to increase the size of the paper, very good quality pulp must be used. It would also be useful to have the To reduce the water content in the paper and thus also the internal vapor pressure when using a Dryer generates s1rd. However, this attempt would not be entirely satisfactory because it is difficult Is to deliver the paper made in this way in well-formed rolls and the low water content the dimensional accuracy of the paper also deteriorates. The use of pigment with coarse particles can die Improve the porosity of the paper and thus also allow a decrease in the internal vapor pressure, but would be its gloss, the brilliance of the print and the resistance to wet pick-up to be worsened. To improve the prevention of blistering of the On coated paper, it is therefore more important and more useful to use a pigment binder with better resistance to use against vesicle bleeding than to increase the strength of the paper itself and / or to use a special pigment.

In DE-OS 2161408 a latex composition is for Treatment of fibrous materials described. This latex mass is said to have the bond strength of fibrous Products while improving the appearance and absorption properties of the treated fiber products change as little as possible.

In DE-OS 14 95 428, a Mlschpolymerlsat latex is described as a carrier for coating compositions with improved odor and improved viscosity.

The object of the invention is to provide a coating compound for paper that have favorable properties in terms of preventing the formation of bubbles Has ink transfer in multi-color offset printing, water resistance and recording resistance. This object is achieved by the coating composition for paper according to the invention.

The invention thus relates to the claims featured item.

The gel content of the copolymer is preferably at most 40 wt. 56.

The copolymer consists of a sol part, which is soluble in benzene, and a gel part, which is in benzene Is insoluble. The gel content of the copolymer is the content of the gel fraction in% by weight based on the Weight of the copolymer, d. H. understood the total weight of the sol part and gel part.

To determine the gel content of the copolymer, the sol content of a latex film is determined and from this the gel content of the copolymer is calculated. A latex film (1 g), which by drying the copolymer at Room temperature was obtained, is dissolved in 400 ml of benzene. After standing for 48 hours, the solution becomes filtered with a No. 2 filter paper, the gel portion remaining in the filter. The Filtrai is dried at 70 ° C and the sol content is determined. The difference between the weight of the latex film (1 g) and the sol content results the gel content.

The coating composition of the invention has improved properties, particularly in terms of its prevention for the formation of bubbles, the transfer of multicolor olfactory printing ink, the water resistance

ίο and persistence of recording.

The diolefin component of the copolymer is preferably butadiene or isoprene. This monomer will used in an amount of 24.5 to 50 parts by weight to produce a copolymer with the appropriate elasticity properties to surrender. If smaller amounts of monomer are used, the required amount will not be achieved Preserved elasticity, as a result of which the adhesive strength of the copolymer suffers. When using larger quantities on the diolefin component, the copolymer becomes too soft, so that it has the required water resistance does not own.

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 of the dicarboxylic acids can also be used will. This carboxylic acid component improves the adhesive properties of the coating and the mechanical strength of the latex increased. In general, a conventional

JO means to be used for waterproofing, which reacts with the carboxylic acid to form a cross-linked structure and a water-impermeable one Coating creates. The carboxylic acid component is preferably used in an amount of about 0.5-10

Jt parts by weight used.

The olefinically unsaturated monomer copolymerizable with the diolefin and the carboxylic acid is z. B. a monomeric aromatic vinyl compound such as styrene, iZ-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 will preferably in an amount of about 40 to 75 parts

'"is used by weight. Preferably, styrene or Methyl methacrylate or a mixture thereof in an amount of at least about 80% by weight, based on the Total weight of the monomer component, used.

For the production of those used according to the invention

■ '·' · Copolymer latex a chain transfer agent is used, which not only regulates the molecular weight of the copolymer, but also the formation of a three-dimensional one Structure between the double bonds In the starting monomers and in the

^bn th polymer prevented. By using these chain transfer agents, it is also possible to regulate the gel content of the copolymer, which results in a coating composition with excellent properties with regard to the prevention of bubble formation and water resistance

^{b1 is obtained} in the offset printing of paper webs. Examples of suitable chain transfer agents are acrolein, methacrolein, allyl alcohol, 2-ethylhexyl thioglycolate, mercaptans such as octyl mercaptan, n-dodecyl mercap-

tan, tert-dodecyl mercaptan, n-hexadecyl mercaptan and mixed tert-mercaptans, sulfides of the thiuram type such as tetraethylthiuram sulfide, dipentamethylene thiuram hexasulfide, Haloalkanes such as carbon tetrachloride, methylene chloride, carbon tetrabromide and ethylene bromide, and hydrocarbons such as pentaphenylethane. The chain transfer agent can either be used alone or as a mixture used and added simultaneously or continuously during the polymerization. The chain transmitter can also be used in a mixture with one of the monomers used.

The amount of chain transfer agent is of particularly great importance for reducing the gel content of the copolymer used in the invention. When using a larger amount the chain carrier increases the gel content decreases. However, since the gel content also depends on various other factors, such as the polymerization temperature, the conversion and the type of feed depends on the monomers, the other factors must also be considered. For example, the Use an amount of about 0.6 to 0.8 parts by weight or more of a chain sub-carrier such as dodecyl mercaptan per 100 parts by weight of the total amount of monomers sufficient when the polymerization at at a temperature of about 50 to 70 ° C and at a conversion of about 95 to 100 percent. The use of about 0.1 to 0.2 parts by weight of this chain transfer agent can be sufficient when the polymerization carried out at a temperature of about -5 to + 10 ° C and at a conversion of about 60 percent will. At a higher polymerization temperature, the amount of chain transfer agent used also generally increases elevated. At a lower conversion, the amount of chain transfer agent used can generally also be used be reduced.

In this context it must be pointed out that such copolymers with low Gel content, as used according to the invention, was not used for coating paper. Below is the violin content of commercially available polytos merlatices for paper coating summarized:

45

50

SB. 023

Note: All latlces contain a modified carboxylic acid as the main component Styrene-butadlene copolymer.

An emulsifier can also be used to produce the polymer latices used according to the invention. Suitable emulsifiers are anionic wetting agents such as alkali metal salts of alkyl sulfates and alkyl aryl sulfonates or sulfonated alkyl esters. Specific examples of these known emulsifiers are sodium dodecylbenzenesulfonate, Sodium lauryl sulfate, sodium di-sec-butylnaphthallnjul'onate, Sodium dloctyl sulfosuccinate, sodium dodecyldlphenyl ether disulfonate and dlo Sulfuric acid esters:; rer fatty alcohols, alkylarylsullo-

Trade Gel content, Manufacturer Surname % Dow ®iaiex 620 86 , Oow Chemical Dow ® Iatex 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 F.mulslnr rhndnnas ®81 Rhone Poulence

nates, alkylnaphthalene sulfonates and their derivatives, alkyl sulfonates, sulfonic acid salts of alkyl succinates and sulfonic acid esters and phosphoric acid esters of nonionic emulsifiers. Non-ionic emulsifiers such as Polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenol ethers and polyethylene glycols can be used with the anionic emulsifiers.

As polymerization initiators, for. B. Persulfates, inorganic peroxides such as hydrogen peroxide, organic peroxides such as cumene hydroperoxide, lauroyl peroxide or Diisobuiylbenzoylperoxid and so-called redox catalysts can be used in which an oxidizing agent is used together with a reducing agent such as Sodium hyposulfite or rongaiite is used. Together with the emulsifiers and / or polymerization initiators can also use a wide variety of electrolytes, polymerization accelerators or complexing agents used as they are used for the production of synthetic coperimer latices.

The polymerization can be carried out at low temperatures when an Rc-iox polymerization initiator is used, or at high temperatures, when other polymerization initiators are used. The monomers and / or the emulsifiers can be fed in during the polymerization. The order in which the reactants are fed and the reagents are, however, not of critical importance in this polymerization process. It depends on the type of connections used.

As soon as the monomers have polymerized to a corresponding conversion, the polymerization is terminated, and the reaction mixture can be controlled with a polymerization interrupter the pH value and / or a stabilizer. After stripping off the unreacted monomers the obtained copolymer latex can be stored in a container.

The use of a polymeric sun breaker Is generally preferred because it increases the gel content after polymerization, e.g. B. suppressed during recovery of the unreacted monomers, during storage or during shipping will. Examples of polymerization interrupters that can be used are carbamate or thiuram compounds, Sodium thiosulfate, hydroxylamine sulfate, hydroquinone and thiourea. When a polymerization interrupter is not used, the gel content may vary depending on the storage conditions before use Values above 60 percent increase, 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 Pifcinont, a pigment binder and / or a common means for improving the water resistance and / or other means for Coating paper can be used. As a pigment, for. B. clay, titanium dioxide, a mixture of plaster and Aluminum oxide, a mixture of calcium sulfate and aluminum sulfate, calcium carbonate, aluminum hydroxide or zinc oxide can be used. B. Casein,. Starch and Starch derivatives 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 stand out thereby from. that in the offset printing of paper webs

no blistering occurs. Furthermore, the properties in terms of water resistance and transmission of printing ink in the Olfset printing of paper webs is much better than with printing paper, the one with conventional ones Coating mass was coated.

The examples illustrate the invention. Parts are by weight unless otherwise stated lsi.

example 1

3 In a 10 liter autoclave, 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 parts of sodium bicarbonate, 0.8 parts of potassium persullate, 100 parts

len water. 1.3 parts of a sodium alkylbenzenesulfonate and a chain transfer agent indicated below are charged. The mixture is heated to 60 ° C. for 14 hours and stirred. A copolymer latex is obtained. The conversion is 98 percent and no coagulate has formed. The average particle size of the copolymer in the aqueous dispersion is about 2.0 × 10 " ⁷ m .

In Table I are the printing properties of various types Summarized Beschlchtungsmassen coated paper. Included in the table below the copolymer latlces the following chain transfer agents in the specified amounts:

Copolymer chain transfer agent latex

A.
B.
C.
D.
E.

*) added at intervals.

Parts by weight

n-uodecyl mercaptan 0.3

tert-dodecyl mercaptan 0.6

tert-dodecyl mercaptan 1,2

Octyl mercaptan *) 1,2

The latex E is produced at a temperature of 60 ° C. with the same components as the latexes A to D, but without a chain transfer agent. The latex E has a size of about 2.8 10 ⁷ and a gel content of 95 percent. The copolymer latex F is a commercial product. Latices A, E and F were used for comparison.

Coating compounds are made using these latices made from the following components:

Components

Weight table

kaolin

Aluminum hydroxide

denatured starch

latex

Means of Increase.

the water resistance

Dispersants

80
20th
7th
12th
0.35

0.25

The coating compositions are adjusted to a solids content of 45 percent and then on applied to bleached sulfate paper. The coated paper is dried and calendered. After that it will Paper examined for its various properties. The results are summarized in Table I.

Table I.

properties

Copolymer latices
ABC

Gel content, %

Resistance to
Wet pickup

Resistance to
Dry absorption

Ink transferability

Resistance to
Blistering

Pressure Giance, %

Air permeability,
ml / mln

85 55 40 14th 95 90 2.8 2.4 2.4 2.0 4.0 2.8 2.2 2.2 2.2 2.4 4.5 2.4 2.6 2.4 2.4 2.4 3.0 3.0 4.3 3.0 2.2 1.5 3.5 4.7 76 77 79 78 72 77 17th 18th 18th 19th 25th 17th

The unarmed eye of the extent is used to determine the resistance to wet ingestion determines in which the wet pick-up of the coating takes place. These experiments are done with a strip of paper carried out as a sample coated with the copolymer latex on which an offset printing ink was applied relatively high adhesive value with a printing machine of the RI type was printed, namely unmiitelbai after the coated paper has been moistened by a moistening roller.

The resistance to dry absorption is with the unarmed eye as the adhesive strength of the coating with regard to the extent, in from which the printed area was removed. This experiment is carried out on coated paper, which was printed with a commercially available offset printing ink in an RI-type printing machine.

The transferability of printing ink in offset printing is determined with the naked eye on the basis of the density of the printed ink. The printing is as well as when testing the resistance to wet ingestion with a printing ink with a very low Adhesive value carried out so as not to produce any decrease in printing ink.

The resistance to bubble formation in offset printing of paper webs is detected with the naked eye. Paper strelfen are 2 days beforehand conditioned at 90 percent relative humidity. Then the moistened paper with one in the Heat-drying printing ink and printed immediately then in an improved pendulum type testing device for the determination of bubbles W. A. Wlnk, Tappi, 50 (7); 102A (1967)]. This tester is with a heater to heat the sample to 350 ° C within about 1 second. With this

Table II

10

The temperature is set to 180 ± 5 "C. The The drying time is 1.0 ± 0.1 seconds. The paper tested has a moisture content of 7.5 ± 0.5 percent. The test results are averages of 6 samples.

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

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

The air permeability is measured with an Emilgryner porosity knife determined according to the Japanese industrial inspection standard JISC-2I1I.

As can be seen from Table I. If a paper coated with the coating composition according to the invention, in which a copolymer with a low gel content is used, is significantly better in terms of its resistance to wet ingestion and blistering than the papers which have been coated with conventional sizing compositions. The papers coated with the coating compound A and the commercially available latex F have poor resistance to the formation of bubbles. The substrate coated with the coating composition E paper has a favorable air permeability and very good resistance to blistering is, '<-Yes extremely unsatisfactory in terms of its resistance to Naßaulnahme and Trockenaulnahme and print gloss quality.

Example 2

According to Example 1, the following copolymers are prepared from the ingredients given in Table II:

Components,
Parts by weight

Copolymer latices G H

Butadiene 34 34 34 36 40 Styrene 52.75 51.5 55.5 _ 56.5 Methyl methacrylate 10 10 12th 62.5 - 2-hydroxyethyl acrylate 2 - - - - Glycidyl methacrylate - 2 - - - Fumaric acid 0.75 1.5 1.5 - 1.5 Acrylic acid 0.5 • 1.0 1.0 1.5 2.0 tert-dodecyl mercaptan 1.3 - 1.0 - 1.0 Mixture of - 1.2 - - - tertiary mercaptans Octyl mercaptan - - - 0.4 - Gel content, % 15th 28 21 5 45

The five polymer latices obtained are examined in accordance with 55 in the manner described above. Example 1 Coating Compounds Prepared With Which The results are shown in Table III. Paper coated and in terms of its properties

ii

Table III

properties

Copolymer latices G Fl 1

Gel content, % 15th 28 21 5 45 90 Resistance to 2.0 1.8 1.7 3.0 3.7 2.8 Wet-out Bests-dlgkelt against 1.8 1.4 1.7 2.0 1.3 2.4 Truck pickup Printing inks 1.6 1.8 2.0 1.5 2.3 3.0 Transferable Resistance to 1.3 2.0 1.8 1.0 2.7 4.7 Blistering Print gloss, % 78 79 79 78 78 77 Air permeability, ml / mln 20th 18th 19th 19th 18th 17th

From Table III it can be seen that a decrease in the gel content of the polymer latices leads to unexpectedly better properties. 2t)

Example 1 was used to determine the gel content of the latex compositions described in DE-OS 21 61 408 reworked of this publication. The gel content of the latex copolymer was 71 percent. Of the The gel content is therefore clearly above the upper> s limit for the latex copolymer according to the invention. In a further experiment, the proportion of tertiary

mlajMaii vuii υιομπι ^ ι ι

increased from 0.5 to 1.0 parts. In the example 1 the DE-OS 2161408 produced latex copolymer the gel content changed within certain time intervals as shown below.

Days after the Manufacturing

Direct

after manufacture 10

30th

Gel content, %

52 66

83

From the values determined it can be seen that the gel has already been considerably retained after 10 days Immediately after manufacture, although it rose below. the maximum limit in accordance with the invention is, however, 35

Claims (12)

Patent claims: 1. Coating compound For paper with increased resistance to the formation of bubbles in offset printing, wherein the binder base is made from a copolymer A. at least one aliphatic conjugated diolefin, B. at least one olefinically unsaturated carboxylic acid and C. at least one further olefinic copolymerizable with the diolefin and the carboxylic acid unsaturated monomers, together with customary coating pigments, characterized in that the copolymer consists 24.5 to 50 parts by weight (A),
0.5 to 10 parts by weight (B) and
40 to 75 parts by weight (C) and has a Geigehail of at most 60% by weight, using a chain transfer agent known per se and a polymerization interruptor known per se was set during the polymerization. 2. Coating composition according to claim 1, characterized in that the copolymer has a gel content of at most 40 wt .- *. 3. Coating composition according to claim 1, characterized in that the Dlolefin component (A) of the Copolymers is butadiene or isoprene. 4. Coating composition according to claim 1, characterized in that the carboxylic acid component (B) of the copolymer acrylic acid, methacrylic acid, maleic acid, fumaric acid or itaconic acid or that Is anhydride or a monoalkyl ester of maleic acid, fumaric acid or itaconic acid. 5. Coating composition according to claim 1, characterized in that the monomer component (C) of the copolymer is an aromatic vinyl compound, an acrylic or methacrylic compound, acrylamide, Is N-methylolacrylamide or acrylonitrile. 6. Coating composition according to claim 1, characterized in that the monomer component (C) contains about 10 to 60 parts by weight of styrene per 40 to 75 parts by weight. 7. Coating composition according to claim 1, characterized in that the monomer component (C) Styrene and / or methyl methacrylate in an amount of at least 80% by weight, based on the Weight of the monomer component. 8. Coating composition according to claim 1, characterized in that the monomer component (C) 1 to 5 parts by weight of 2-Hydroxyäthylacryl <n and or or contains glycldyl methacrylate. 9. Coating composition according to claim 1, characterized in that the pigment is a mixture 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 I, characterized by an additional content of a common binder. 11. Coating compound according to claim 1, characterized by an additional content of a polymeric ion breaker. 12. Use of the coating compound after Claim 1 for coating paper for offset printing.