JPH0232400B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel paper coating agent based on a synthetic resin emulsion. When preparing a synthetic resin emulsion used as a paper coating agent, the method differs somewhat depending on the type of resin, but in all cases it is essential to use an emulsifier or a protective colloid.
For example, to prepare an emulsion of a vinyl polymer such as vinyl acetate, acrylic ester, or vinyl chloride, the monomer is emulsion polymerized in the presence of an emulsifier or a protective colloid, and a polyester resin emulsion, To prepare epoxy resin emulsions, silicone resin emulsions, etc., the above resin in solution or molten form is dropped into an aqueous solution containing an emulsifier or protective colloid and stirred to form an emulsion, or the emulsifier and the above molten resin are added. An aqueous solution of a protective colloid is added dropwise and stirred to form an emulsion. As typical emulsifiers or protective colloids, nonionic surfactants and anionic surfactants are used alone or in combination, and polyvinyl alcohol (PVA) is used, but surfactant-based In use, there are many problems in terms of mechanical stability of the emulsion obtained, so
The use of PVA-based materials has become mainstream. However
When using a partially saponified PVA with an average degree of saponification of about 88 mol%, an emulsion with high structural viscosity, low temperature dependence of viscosity, and good freeze stability or storage stability at low temperatures is produced. However, if a completely saponified type with an average degree of saponification of about 99 mol% is used, an emulsion that is water resistant, large, and has a small structural viscosity index can be obtained, but the temperature dependence of the viscosity is poor. It is known that the freezing stability and storage stability at low temperatures are significantly inferior, and each type of emulsion is used depending on the purpose of the emulsion. However, with the advancement of technology, emulsions with the above-mentioned properties alone are no longer satisfactory, and the performance of both emulsions using partially saponified PVA and completely saponified PVA has been improved. There is a need for an emulsion that has a suitable structural viscosity index, excellent water resistance, low temperature dependence of viscosity, and good freeze stability and storage stability at low temperatures. In order to obtain an emulsion with such performance, it is possible to use a mixture of partially saponified PVA and completely saponified PVA, but in this case, each
In many cases, the characteristics of PVA cancel each other out, and rather the drawbacks of each PVA become more apparent. However, the present inventors have conducted various studies on emulsifiers or protective colloids that can simultaneously satisfy these various properties of emulsions, and have found that by using acetoacetylated PVA as an emulsifier or protective colloid, emulsions with excellent properties can be obtained. was obtained and found to be extremely useful as a paper coating agent, leading to the completion of the present invention. According to the present invention, the following remarkable effects can be obtained. (1) The emulsion's low-temperature storage stability and freeze-thaw stability are improved, as well as the film's water resistance. (2) Emulsions with high viscosity can be obtained even at low concentrations.
(3) Water resistance can be more easily enhanced by using in combination with a crosslinking agent (aldehydes, amines, metal salts, etc.). (4) It can be used in the same way as when PVA is used as an emulsifier, and it can also be used in a wide range of ways, such as in combination with a surfactant. (5) Since it has excellent cohesiveness with clay minerals, strong water resistance can be achieved by using clay minerals together in the pigment coating. (6) Wastewater containing the emulsion can be easily treated by coagulation and precipitation using clay or the like. The acetoacetylated PVA used in the present invention is
Obtained by reacting PVA and diketene. (The chemical reaction formula is

It is shown by [Formula]. ) For example, PVA is dispersed in an acetic acid solvent,
One method is to add diketene to this, and the other is to dissolve PVA in a solvent such as dimethylformamide or dioxane in advance and add diketene to it. It is also possible to obtain acetoacetylated PVA by directly contacting PVA with diketene gas or liquid diketene. use here
PVA can be used not only in saponified polyvinyl acetate, but also in PVA that has been slightly modified with carboxyl groups, amide groups, nitro groups, carboxylic acid ester groups, hydrocarbon residues, sulfonic acid (salt) groups, etc. It is. The average degree of saponification and average degree of polymerization of acetoacetylated PVA are not particularly limited, but from the viewpoint of effectiveness as a protective colloid, the residual acetate group should be 0.1 to 0.1.
It is preferably 15 mol% and the average degree of polymerization is in the range of 500 to 2,600. The content of acetoacetyl groups is suitably in the range of 0.05 to 25 mol%, preferably 1 to 15 mol%.
If it is less than 0.05 mol%, the contribution to the water resistance, stability, and thickening property of the emulsion is small and undesirable;
If it exceeds 15 mol%, the emulsion will be destroyed and it will be difficult to obtain a homogeneous emulsion. To prepare the acetoacetylated PVA-containing synthetic resin emulsion of the present invention, monomers are emulsion polymerized using acetoacetylated PVA as an emulsifier or protective colloid, and a synthetic resin solution or melt is prepared in the presence of acetoacetylated PVA. The above three cases include adding acetoacetylated PVA to a synthetic resin emulsion obtained by an arbitrary method to produce a more stable emulsion. Each case will be specifically explained below. Method using emulsion polymerization method This method is usually suitably carried out when producing a polymer emulsion of a vinyl compound.
During emulsion polymerization, water, acetoacetylation
A conventional emulsion polymerization method can be carried out, in which a vinyl compound is added once or continuously in the presence of PVA and a polymerization catalyst, followed by heating and stirring. The appropriate amount of acetoacetylated PVA to be used is about 0.1 to 30% by weight, preferably about 2 to 20% by weight, based on the solid content of the polymer. If it is less than 2% by weight, no sufficient effect will be obtained, and if it is more than 20% by weight, the effect will not increase in proportion to the amount used. The acetoacetylated PVA
Although it is possible to add the compound at any time, such as at the beginning, during or after the emulsion polymerization, it is usually added at the beginning or during the emulsion polymerization. Vinyl compounds used in this method include vinyl acetate, vinyl propionate, acrylic ester, methacrylic ester, vinyl chloride, vinylidene chloride, acrylonitrile,
methacrylonitrile, styrene, ethylene,
Glycidyl group-containing compounds such as propylene, glycidyl acrylate, glycidyl methacrylate, glycidyl divinyl ether, glycidyl vinyl ether, methylol group-containing compounds such as N-methylolacrylamide and N-methylolmethacrylamide, and alkoxy group-containing derivatives thereof, acrylamide, methacrylamide, etc. Carboxylic acid amides, carboxylic acids such as acrylic acid and methacrylic acid, divinyl adipate,
Divinyl succinate, triallyl cyanurate, diallyl fumarate, triallyl citrate, diallyl maleate, vinyl versatate,
These include homopolymerization or copolymerization. In particular, monopolymerization or copolymerization using vinyl acetate, styrene, etc. is preferable. When a vinyl compound containing an N-methylol group or a glycidyl group is used, a self-crosslinking emulsion can be produced, and a coating agent with good water resistance can be prepared. As the emulsion polymerization catalyst, a catalyst used in normal emulsion polymerization is used. Redox catalysts are particularly preferred; specific examples include hydrogen peroxide and formaldehyde, zinc sulfoxylate, glyoxalic acid/zinc sulfoxylate, glyoxylic acid/zinc sulfoxylate, hydrogen peroxide,
Combinations of ammonium persulfate or potassium persulfate with sodium metabisulfite, sodium bisulfite, ferrous sulfate, dimethylaniline, formaldehyde zinc sulfoxylate or formaldehyde sodium sulfoxylate may be mentioned. Furthermore, nonionic surfactants and ionic surfactants can also be used in combination with acetoacetylated PVA. Furthermore, other emulsifiers, such as PVA cellulose derivatives (carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, etc.), polyacrylic acid derivatives, (anhydrous) maleic acid-vinyl ether copolymers, (anhydrous) maleic acid-
Vinyl acetate copolymers, saponified vinyl acetate-(meth)allylsulfonic acid (salt) copolymers, and the like can also be used in combination as appropriate. Other various additives, regulators, etc. used in ordinary emulsion polymerization can also be used as appropriate. Method by post-emulsification This method is suitably carried out when preparing a synthetic resin emulsion that is difficult to produce by emulsion polymerization. In this method, acetoacetylated PVA may be dissolved in water, and a solution or molten resin may be added dropwise to the solution and stirred, or an aqueous solution of acetoacetylated PVA may be dropped into the molten resin and stirred. There is no particular need for heating to form an emulsion, but if necessary, it may be heated to about 45 to 85°C. The substances to be emulsified are not particularly limited, and include epoxy resins, urethane resins, urea-formalin initial condensates, phenol-formaldehyde initial condensates, alkyd resins, polyester resins,
Examples include ketene dimer, silicone resin, wax, polypropylene, polyethylene, and the like. The amount of acetoacetylated PVA to be used varies somewhat depending on the resin content of the required emulsion, etc., but it is usually selected from the range of 0.1 to 30% by weight, preferably 1 to 25% by weight based on the material to be emulsified. . If necessary, a nonionic activator such as a polyoxyethylene-alkyl ether type, a polyoxyethylene-alkyl phenol type, a polyhydric alcohol ester type, or a cationic activator such as a higher alkyl amine salt is used in combination with the resin. You can also. It is also possible to mix these active agents into the object to be emulsified. Post-addition method This method is carried out by adding acetoacetylated PVA to a synthetic resin emulsion obtained by any method for the purpose of further improving stability or thickening. Targeted emulsions include styrene/butadiene emulsions, cis-1,4 polyisoprene emulsions, chloroprene emulsions, acrylonitrile/butadiene emulsions, vinylpyridine emulsions, methyl methacrylate/butadiene emulsions, polyurethane emulsions, and acrylic esters. emulsions, vinyl acetate emulsions, ethylene/vinyl acetate emulsions, vinyl chloride emulsions, polystyrene emulsions, polyethylene emulsions, silicone emulsions, polybutene emulsions, thiol emulsions, and the like. When adding and mixing acetoacetylated PVA to an emulsion, when adding the PVA as an aqueous solution, it is sufficient to simply add the aqueous solution to the emulsion while stirring the emulsion at room temperature, but when adding the PVA powder, , add the powder while stirring the emulsion, stirring for 60 to 80 minutes.
It is preferable to heat the mixture to ℃ because uniform mixing can be completed in a short time. The amount of acetoacetylated PVA used is approximately 0.1 to 0.1 to the solid content of the emulsion.
3.0% by weight, preferably in the range of 0.1-10% by weight. When using acetoacetylated PVA with a low degree of acetoacetylation, increase the amount added.
Acetoacetylation with a large degree of acetoacetylation
When using PVA, a small amount will produce effects such as thickening. That is, the viscosity increasing effect and the stability improving effect are approximately proportional to the degree of acetoacetylation and the amount added. Therefore, it is desirable to understand these relationships and then select the degree of acetoacetylation and the amount added depending on the purpose. Thus, the emulsion obtained can be used as it is or, if necessary, may be further treated with a plasticizer, a film-forming agent such as a high-boiling solvent, clay, calcium carbonate,
Extender pigments such as kaolin and diatomaceous earth, colored pigments such as titanium oxide, preservatives, insect repellents, rust preventives, thickeners, etc. are appropriately blended and used. In particular, metal compounds,
(Beryllium, zirconium, titanium, chromium, calcium, magnesium, zinc, barium, strontium, aluminum, bismuth,
Oxides, hydroxides, basic salts, acidic salts, neutral salts, amine complexes, etc. of antimony, cobalt, iron, nickel, etc.) Formaldehyde, glyoxal, dimethylolated products of urea or melamine, isocyanate compounds, epichlorohydrin, ethylene glycol The combined use of curing agents such as various epoxy compounds such as diglycidyl ether, glycerol di- or triglycidyl ether has the effect of further improving the water-resistant adhesive strength. Preferred metal compounds include zinc acetate, zinc oxide, zinc glycinate, chromium nitrate, titanyl sulfate, zinc carbonate, aluminum chloride, zinc benzoate, zinc salicylate, zinc glycolate, calcium hydroxide, magnesium oxide, titanium lactate, and the like. It will be done. It is also possible to add a water-soluble polymer substance for the purpose of increasing viscosity. The amount added is usually in the range of 5 to 500% in terms of solid content based on the emulsion. Such water-soluble polymer substances include:
PVA derivatives such as acid-modified PVA, acetoacetylated PVA, olefin-modified PVA, alkyl vinyl ether-modified PVA, Beova-modified PVA, etc., PVA,
Starch, CMC, hydroxymethylcellulose,
Examples include hydroxyethyl cellulose, methyl cellulose, casein, etc., and these can be mixed in any form such as an aqueous solution or powder form. In preparing the paper coating liquid of the present invention, the solid content concentration is usually 2 to 60% in consideration of workability etc.
It is selected within a range of about % by weight. There are no particular limitations on the paper to be coated with the paper coating agent of the present invention, but examples include paperboard such as manila ball, white ball, and liner, general high-quality paper, printing paper such as gravure paper, thermal recording paper, and inkjet recording paper. Various types of recording paper are preferably used. In applying the coating liquid to such paper, any known method such as a roll coater method, an air doctor method, a blade coater method, etc. may be employed. However, the amount of coating liquid applied is
It is appropriate that the amount is about 0.5 to 30 g/m ² , especially 1 to 20 g/m ² . In the coating liquid, polyvalent ions of heavy metal salts of water resistance agents such as glyoxal and melamine-formaldehyde resins are used as necessary. Known additives such as plasticizers such as glycols and glycerin, antifoaming agents, mold release agents, and surfactants can also be added. Further, although the coating liquid is generally suitably used for clear coating of paper, it can also be used for pigment coating by adding pigments such as clay, titanium dioxide, and satin white as appropriate. Next, the present invention will be specifically explained with reference to Examples. In the examples, "parts" or "%" represent "parts by weight" or "% by weight." Example 1 Acetoacetylated PVA with an average degree of polymerization of 1700, residual acetate group 1 mol%, and degree of acetoacetylation 2.3 mol%
An emulsion was obtained in the following manner. In a separate flask equipped with a stirrer, reflux condenser, addition funnel, and thermometer, add 131.3 parts of the above water.
11.5 parts of PVA and 10 parts of vinyl acetate monomer were charged, and the temperature inside the flask was raised to 60°C while stirring. During this time, while replacing the inside of the flask with nitrogen gas.
Polymerization was initiated by adding 2 ml of 10% H ₂ O ₂ water and 3 ml of 10% tartaric acid. Initial polymerization was carried out for 30 minutes, and the remaining 90 parts of vinyl acetate monomer was added dropwise over 3 hours.
All the monomers were charged, and the mixture was aged at 70°C for 1 hour and then cooled. The obtained emulsion had good fluidity. Table 1 shows various characteristics. Control example 1 Acetoacetylation used in Example 1
Instead of PVA, use regular PVA (average degree of polymerization 1700,
An emulsion was obtained in the same manner as in Example 1 using 1 mol % of residual acetic acid groups. Table 1 shows various properties of the emulsion. Example 2 Acetoacetylated PVA with average degree of polymerization of 1800, residual acetic acid groups of 12 mol%, and degree of acetoacetylation of 1.6 mol%
An emulsion was obtained in the following manner. In the same apparatus as in Example 1, 155.5 parts of water and the
Initial polymerization was carried out in the same manner as in Example except that 7.0 parts of PVA and 10 parts of vinyl acetate monomer were used. Thereafter, the remaining 90 parts of vinyl acetate monomer was added dropwise over 2 hours, and after completion of the addition, the mixture was aged at 75°C for 1 hour and then cooled. Table 1 shows various characteristics. Control example 2 Acetoacetylation used in Example 2
Instead of PVA, use regular PVA (average degree of polymerization 1800,
An emulsion was obtained in the same manner as in Example 2 using 12 mol % of residual acetic acid groups. Table 1 shows various properties of the emulsion. Example 3 Acetoacetylated PVA with an average degree of polymerization of 1400, residual acetic acid group 1 mol%, and degree of acetoacetylation 8.9 mol%
An emulsion was obtained in the following manner. 11.0 parts of the above PVA, 0.5 parts of Emulgen 950 (polyoxyethylene nonylphenol ether, manufactured by Kao Seiken), 70 parts of vinyl acetate monomer, 30 parts of butyl acrylate, and 101.5 parts of water were charged into the same apparatus as above, and 5 parts of ammonium persulfate was charged. % aqueous solution 5ml,
5 ml of a 5% aqueous solution of sodium bisulfite was added, and emulsion polymerization was carried out at 40-50°C for 30 minutes and at 180-85°C for 3 hours under a nitrogen gas atmosphere. Table 1 shows various characteristics. Control example 3 Acetoacetylation used in Example 3
In place of PVA, average degree of polymerization 1400, residual acetate group 1
An emulsion was obtained in the same manner as in the example except that mol % of PVA was used. Table 1 shows various characteristics. Example 4 Acetoacetylated PVA with average degree of polymerization of 1800, residual acetic acid groups/mol%, and degree of acetoacetylation of 3.5 mol%
An ethylene/vinyl acetate/vinyl chloride copolymer emulsion was obtained in the following manner. Add 100 parts of water and the above to the autoclave for polymerization.
Charge 8 parts of PVA, raise the internal temperature to 65℃ and PVA
Then, ethylene was introduced under pressure to maintain the temperature at 30Kg/ ^cm2 , the internal temperature was raised to 75℃, and 40 parts of vinyl chloride and
Emulsion polymerization was carried out by dropping 45 parts of vinyl acetate and 8 parts of a 5% aqueous solution of ammonium persulfate over 5 hours, the ethylene pressure was returned to normal pressure, and after further aging for 1 hour, the concentration was adjusted to 50%. . Table 1 shows various characteristics. Example 5 Using the same acetoacetylated PVA as in Example 4, a vinyl acetate/veova (vinyl ester of carboxylic acid branched at the α-position: trade name of Ciel Chemical) copolymer emulsion was obtained in the following manner. Charge 100 parts of water and 8 parts of the above PVA into a polymerization container, raise the internal temperature to 65°C to dissolve the PVA, further raise the temperature to 75°C, and then add 50 parts of PEOVA and vinyl acetate.
50 parts and 8 parts of a 5% aqueous solution of ammonium persulfate were simultaneously added dropwise over 3.5 hours to carry out emulsion polymerization, and after further aging for 1 hour, the concentration was adjusted to 50%. Table 1 shows various characteristics. Example 6 Using the same acetoacetylated PVA as in Example 4, a butyl acrylate/styrene copolymer emulsion was obtained in the following manner. An emulsion having a concentration of 50% was obtained in the same manner as in Example 5, except that the monomers were changed to 60 parts of butyl acrylate and 40 parts of styrene, and 0.2 parts of dodecyl mercaptan was added as a chain transfer agent.
Table 1 shows various characteristics.

【table】

[Table] Example 7 100 parts of ethylene-vinyl acetate copolymer emulsion (resin content 50%, viscosity 530 cps), polymerization degree 1700,
2.5 parts of acetoacetylated PVA with residual acetate groups of 1 mol % and degree of acetoacetylation of 5.4 mol % were added and mixed. The characteristic values of this emulsion are shown in Table 2. Examples 8 to 13 10.0 parts of vinyl acetate resin emulsion (resin content 50%, viscosity 7400 cps), polymerization degree 1700, residual acetic acid group 1
In Example 8, 1 part of acetoacetylated PVA with a degree of acetoacetylation of 2.3 mol% and in Example 9
In Example 10, 2 parts were added, and in Example 10, 6 parts were added and mixed. Further, to 100 parts of the above emulsion, acetoacetylated PVA with a degree of polymerization of 1800, a residual acetic acid group of 12 mol%, and a degree of acetoacetylation of 1.6 mol% was added in Example 11, 1 part, Example 12, 2 parts, and Example 13, 6 parts. Add and mix.
The properties of the obtained emulsion are shown in Table 2. Comparative Examples 4 to 6 Comparative Example 4 was the same as Example 7 except that PVA (degree of polymerization 1700, residual acetic acid group 1 mol%) was used, and PVA (degree of polymerization 1700, residual acetic acid group 1 mol%) was used in Example 9. In Comparative Example 5 and Example 12, PVA (polymerization degree
Comparative Example 6 was a case in which the same procedure was carried out except that 1800 and 12 mol % of residual acetic acid groups were used, and the emulsion properties of each are shown in Table 2.

[Table] Example 14 Acetoacetylated PVA with a degree of polymerization of 500, a residual acetic acid group of 1.3 mol%, and a degree of acetoacetylation of 2.3 mol% was produced. Dissolve 4.0g of the above PVA in 31.0g of 50℃ warm water,
Next, 65 g of Epikote 828 (liquid bisphenol A type epoxy resin, manufactured by Ciel Chemical Co., Ltd.) previously heated to about 50° C. was gradually added and vigorously stirred with a high-speed mixer to obtain an epoxy resin emulsion. The properties of the emulsion are shown in Table 3. Control Example 7 The same experiment as in Example 14 was carried out, except that PVA with a residual acetate group of 1.3 mol % and a degree of polymerization of 500 was used instead of the above PVA. The results are also shown in Table 3. Example 15 8 parts of acetoacetylated PVA having a degree of polymerization of 1700, a residual acetic acid group of 1.9 mol %, and a degree of acetoacetylation of 3 mol % was dissolved in 82 parts of water and kept at 65°C. Next, pre-molten hexadecyl ketene dimer was gradually added dropwise, and emulsion was formed using a homogenizer to obtain a ketene dimer emulsion. The performance of the emulsion is shown in Table 3. Control Example 8 The same experiment as in the above example was carried out except that PVA having a residual acetate group of 1.9 mol % and a degree of polymerization of 1700 was used in place of the above PVA. The results are also shown in Table 3. Example 16 15 parts of the emulsifier used in Example 15, 15 parts of water, 100 parts of atactic polypropylene (average molecular weight 18,000)
A small amount of octadecylamine acetate was kneaded in a pressure kneader at a temperature of 90° C. for 20 minutes. Water was added to obtain a polypropylene emulsion with a solids content of 30%. The results are shown in Table 3.

【table】

[Table] Performance evaluation test 1 to 2 as a paper coating agent Vinyl acetate/vinyl versatate/acrylic acid (88/
16/4) Copolymer emulsion and EVA (70/30
molar ratio) An emulsion was produced. Pigment coating was performed using the emulsion. Using a Dickson type coater, the coating was applied to a base paper with a basis weight of 85 g/m ² at a speed of 10 m/min so that the coating amount was 20 g/m ² , and then the surface temperature was 60°C and the linear pressure was 100
Finishing was carried out using a super calender roll at a speed of 7.5 m/min and a speed of 7.5 m/min. The surface properties (water resistance, whiteness, gloss) of the obtained coated paper were measured. The results are shown in the table. Note; EVA; ethylene/vinyl acetate copolymer

【table】

【table】

Claims (1)

[Claims] 1. A paper coating agent made of a synthetic resin emulsion containing acetoacetylated polyvinyl alcohol as a protective colloid.