JPS6223117B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to surface sizing agents for paper. Conventionally, polyvinyl alcohol containing carboxyl groups (hereinafter referred to simply as polyvinyl alcohol)
Abbreviated as PVA, polyvinyl alcohol containing carboxyl groups is simply modified with carboxyl groups.
There have been various reports (for example, Japanese Patent Publication No. 50-9882) regarding the production and use of PVA (abbreviated as PVA), but carboxyl group-modified PVA produced by these known methods has been used as a surface sizing agent for paper. When used, satisfactory performance is not always achieved. The reason for this is not fully clear, but carboxyl group-modified PVA produced by conventional production methods does not exhibit the typical performance expected as a characteristic of carboxyl groups, such as weak or no reactivity with metal ions. It is possible that there is a relationship. When increasing the degree of modification to bring out the characteristics of carboxyl groups, the original
The problem was that the excellent properties characteristic of PVA, such as film-forming ability and coating strength, were drastically reduced. The present invention solves these problems, and the weight ratio of vinyl acetate and ethylenically unsaturated dicarboxylic acid in the polymerization system is always 100 in the presence of alcohol.
homogeneous solution copolymerization in the presence of alcohol so that the ratio is in the range of 0.01 to 5 and almost constant, and the resulting copolymer is added to the ethylenically unsaturated dicarboxylic acid units in the copolymer in alcohol. Paper containing carboxyl group-modified PVA obtained by saponification using a total amount of alkali of 2 molar equivalents for the vinyl acetate units and 0.001 to 1.0 molar equivalents of the alkali for the vinyl acetate units in the copolymer. surface sizing agent. In the present invention, by using carboxyl group-modified PVA obtained by such a special method, it is possible to obtain sizing paper with excellent surface strength and barrier properties, as is clear from the examples described below. . In addition, since the carboxyl group-modified PVA used in the present invention has high reactivity with metal ions, if a compound containing metal ions such as aluminum sulfate is contained in the layer or surface of the paper to be sized, the surface A sizing paper with excellent strength and barrier properties can be obtained. The use of ethylenically unsaturated dicarboxylic acid as a modifying monomer in the production of carboxyl group-modified PVA has already been proposed in literature and is well known. However, since all ethylenically unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid are not substantially soluble in vinyl acetate, monoesters of the dicarboxylic acid monomers are used instead of dicarboxylic acid monomers in the homogeneous polymerization method. (maleic acid monoalkyl ester,
fumaric acid monoalkyl ester, itaconic acid monoalkyl ester, etc.), diesters (maleic acid dialkyl ester, fumaric acid dialkyl ester, itaconic acid dialkyl ester, etc.), or anhydrides (maleic anhydride, itaconic anhydride, etc.)
It has been a common practice to substitute monomers with high solubility in vinyl acetate, such as vinyl acetate. When ethylenically unsaturated dicarboxylic acids are used, emulsion polymerization is usually used. However, the present inventor has discovered that homogeneous solution copolymerization can be carried out by controlling the weight ratio of vinyl acetate and ethylenically unsaturated dicarboxylic acid in the polymerization system to always be in the range of 0.01 to 5 to 100 in the presence of alcohol. When the copolymer is further saponified under specific conditions, it exhibits unique behavior that is thought to be based on molecular structural factors, and has excellent performance as a surface sizing agent for paper. It was discovered that carboxyl group-modified PVA can be obtained. Carboxyl group modification exhibiting such peculiar behavior
PVA can never be obtained by using conventional manufacturing methods by replacing ethylenically unsaturated dicarboxylic acids with their monoesters, diesters, or anhydrides; This cannot be obtained even when esters are used. Also,
monoester of ethylenically unsaturated dicarboxylic acid,
When a diester or anhydride is used, depending on the saponification conditions, the saponified product of the copolymer becomes insolubilized during drying, producing modified PVA that is completely insoluble in water and therefore useless as a surface sizing agent for paper. However, according to the manufacturing method of the present invention, such inconvenience does not occur at all. When the amount of ethylenically unsaturated dicarboxylic acid during copolymerization is 0.01 part or less per 100 parts of vinyl acetate, the amount of carboxyl groups contained in the product PVA is too small to exhibit the characteristics of the PVA of the present invention. figure,
In addition, if the amount is 5 parts or more, it may not dissolve in the polymerization system and homogeneous solution copolymerization may not be carried out smoothly.
Also, from an economic point of view, there is no need to use more than five copies. In addition, in the present invention, when saponifying the copolymer, 2 molar equivalents of alkali are added to the ethylenically unsaturated dicarboxylic acid units in the copolymer in alcohol and 0.001 to 0.001 to 0.001 to 0.001 to the vinyl acetate units in the copolymer are added.
If it is necessary to saponify using alkali in the range of total amount with 1.0 molar equivalent of alkali, and if a smaller amount of alkali is used than this range,
The performance shown in the present invention cannot be achieved. In addition, if a larger amount of alkali is used than this range, the alkali will remain in the resulting modified PVA, causing problems such as coloring. In this way, when ethylenically unsaturated dicarboxylic acid is copolymerized with vinyl acetate under specific conditions, and then the copolymer is saponified under specific conditions, the production process of carboxyl group-modified PVA that has been conventionally adopted can be improved. Previous knowledge has shown that it is possible to obtain carboxyl group-modified PVA that does not cause the insolubilization that tends to occur in PVA, has remarkable reactivity with metal ions, and has excellent performance as a surface sizing agent for paper. This was completely unexpected. Examples of the ethylenically unsaturated dicarboxylic acids used in the method of the present invention include maleic acid, fumaric acid, and itaconic acid, but itaconic acid is particularly excellent in terms of performance. The weight ratio of these ethylenically unsaturated dicarboxylic acids to 100 parts of vinyl acetate in the polymerization system is always in the range of 0.01 to 5 and should be kept constant during the copolymerization. Approximately 0.1 to 50 mol% in the copolymer depending on these polymerization conditions.
of ethylenically unsaturated dicarboxylic acid units. As the copolymerization method in the present invention, both a batch method and a continuous method can be carried out, as is clear from the Examples described later. In the case of batch method,
The monomer composition changes with the polymerization rate according to the comonomer reactivity ratio (r ₁ , r ₂ ), but in producing the copolymer targeted by the present invention, on the one hand, Alternatively, a so-called semi-batch method is adopted in which both monomers are added, so that the weight ratio of vinyl acetate and ethylenically unsaturated dicarboxylic acid in the polymerization system is always 100:0.01.
5, and it is necessary to control the ratio so that it is approximately constant. An example of how to calculate the amount added in this case is RJHanna as shown in Example 1 below.
Industrial and Engineering Chemistry;
The formula submitted in Vo1.49, No.2, 208-209 (1957) is mentioned. In one-column continuous polymerization, the weight ratio of vinyl acetate and ethylenically unsaturated dicarboxylic acid can be controlled to be approximately constant by carrying out steady-state polymerization. In addition, in the case of multi-column continuous copolymerization, similar to the batch method, monomers are added to the second and subsequent columns to combine vinyl acetate and ethylenically unsaturated dicarboxylic acid in the polymerization system in each column. It is necessary to control the weight ratio so that it is always in the range of 0.01 to 5:100 and that the ratio is almost constant. As shown in Example 2 of Japanese Patent Publication No. 40-14862, even if the weight ratio of vinyl acetate and ethylenically unsaturated dicarboxylic acid is initially in the range of 0.01 to 5 to 100, the batch polymerization is carried out as it is. Since the ratio of both monomers in the polymerization system varies greatly, it is not possible to produce carboxyl group-modified PVA with excellent performance as a surface sizing agent for paper, which is the object of the present invention. Methanol, ethanol, etc. are usually used as the alcohol coexisting in the copolymerization system. Further, as an initiator for the copolymerization reaction, known initiators for radical polymerization such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, acetyl peroxide, etc. can be used. The reaction temperature is usually selected from the range of 50°C to the boiling point. Methanol and ethanol are usually used as alcohols during saponification. The alcohol may be anhydrous, or may optionally contain water or an organic solvent such as methyl acetate or ethyl acetate. The concentration of the copolymer in the alcohol is not particularly limited, but is usually selected from a range of 5 to 50% by weight. The alkali used for saponification is selected from hydroxides of alkali metal salts such as sodium hydroxide and potassium hydroxide, alcoholates such as sodium methylate and potassium methylate, and ammonia. The saponification temperature is not particularly limited, but is usually selected from the range of 10 to 50°C. The saponification time varies depending on conditions such as the concentration of the copolymer, the amount of alkali, and the temperature, but is usually 3 hours or less. The degree of saponification of the modified PVA of the present invention is not particularly limited, and the modified PVA can have any saponification degree depending on the purpose.
Can be PVA. As the saponification reaction progresses, a white gel or precipitate is produced, as in the case of ordinary PVA, and white PVA powder can be obtained by crushing, washing, and drying this. The surface sizing agent for paper made of modified PVA of the present invention has excellent solubility in water, good viscosity stability in highly concentrated liquids, and excellent fluidity. The remarkable property of the modified PVA of the present invention of high reactivity with metal ions is of particular importance in paper surface sizing agents. That is, by using the carboxyl group-modified PVA of the present invention as a surface sizing agent for paper, it causes a chemical reaction with aluminum sulfate contained in a normal paper layer to form a strong coating film, improving surface strength, etc. The effect of improving paper strength is remarkable, and as the content of aluminum sulfate in the paper layer increases, the coating film becomes stronger and can impart high barrier properties to the paper layer. The present invention will be specifically explained below with reference to production examples, control examples, examples, and reference examples of carboxyl group-modified PVA. Production example of modified PVA 1 In a polymerization tank equipped with a reflux condenser, stirrer, thermometer, nitrogen inlet tube, post-addition liquid, charging port, and pump, add 2800 g of vinyl acetate, 370 g of methanol, and a 10% methanol solution of maleic acid. I prepared 140g of. While stirring the polymerization solution, the system was replaced with nitrogen and heated in a constant temperature bath, and when the temperature reached 60℃, 2.2'-
3.36g of azobisisobutyronitrile in methanol
It was added together with 200 g to start polymerization. From the start of polymerization, a 10% methanol solution of maleic acid was added to RJHanna while analyzing the solid content concentration of the polymerization system.
(Industrial and Engineering Chemistry, Vo1
49, No. 2, pp. 208-209 (1957)), the polymerization was allowed to proceed dropwise. After dropping 190 g of a 10% methanol solution of maleic acid almost uniformly over a period of 5 hours and 30 minutes, thiourea was added to stop the polymerization. The solid content concentration immediately before the termination of polymerization was 35%. Methanol vapor was blown into this polymerization paste to remove unreacted vinyl acetate monomer, thereby obtaining a methanol solution of a vinyl acetate-maleic acid copolymer having a maleic acid unit content of 5.1 mol %. Next, the copolymer concentration of the solution was adjusted to 30% with methanol.
44 ml of a 10% methanol solution of sodium hydroxide was added to 167 g of the prepared solution while stirring at 40°C for saponification. The gel-like material was ground with a household mixer, washed with methanol, and dried at 100° C. for 5 hours to obtain a white powder of modified PVA (degree of saponification of vinyl acetate units: 97.9 mol%). This 4% aqueous solution of PVA
The Bruckfield viscosity at 20°C was 21.5 cp. Example 2 Into a polymerization reactor similar to Example 1, 3500 g of vinyl acetate, 403 g of methanol, and 20 g of a 25% methanol solution of itaconic acid were charged, and after performing operations of nitrogen substitution, stirring, and heating, 2,2'-azobisiso Butyronitrile
2.45g was added together with 200g of methanol to initiate polymerization at 60°C. After 248 g of a 25% methanol solution of itaconic acid was uniformly dropped over a period of 3 hours and 15 minutes from the start, thiourea was added to stop the polymerization. The solid content concentration immediately before the termination of polymerization was 30%. Unreacted vinyl acetate monomer was removed by a conventional method to obtain a methanol solution of vinyl acetate-itaconic acid copolymer having an itaconic acid content of 3.0 mol %. While stirring 167 g of the solution whose concentration was adjusted to 30% at 40°C, 32 g of a 10% methanol solution of sodium hydroxide was added.
ml was added and saponified. A white gel-like substance was obtained in 5 minutes and 30 seconds. After grinding, washing and drying, the modified PVA becomes a white powder (degree of saponification of vinyl acetate unit: 99.1 mol%)
I got it. The Brookfield viscosity of this 4% aqueous solution of modified PVA at 20°C was 42.0 cp. Example 3 Vinyl acetate/
Itaconic acid/methanol/2.2'-azobisisobutyronitrile was continuously charged at a weight ratio of 100/4.1/34.7/0.07, and the residence time was set to 5 hours.
Continuous copolymerization was carried out at 60°C. The weight ratio of unreacted vinyl acetate to itaconic acid in the continuously taken out reaction solution was 100:0.24. The polymerization rate of vinyl acetate was 50%, and that of itaconic acid was 97%. Next, the liquid coming out of the polymerization reactor is introduced into a vinyl acetate expulsion step, where the vinyl acetate is expelled by methanol vapor, and a methanol solution (copolymer) of vinyl acetate-itaconic acid copolymer with an itaconic acid unit content of 5.0 mol% is introduced. A polymer concentration of 30%) was obtained. This solution 100
Kg/hour, 5% methanol solution of sodium hydroxide was charged into the mixer at a rate of 52.2/hour, and the saponification reaction was carried out on a rotary belt for 20 minutes. The produced white PVA gel was passed through the steps of pulverization, washing, and drying to obtain a white PVA powder (degree of saponification of vinyl acetate units: 98.7 mol%). Example 4 Polymerization in the same manner as in Example 2 using 3000 g of vinyl acetate, 545 g of methanol, 7 g of 25% methanol solution of itaconic acid and 1.5 g of 2,2'-azobisisobutyronitrile with 200 g of methanol. started. During the polymerization period of 3 hours, 116 g of a 25% methanol solution of itaconic acid was uniformly added dropwise. The solid content concentration at the time of termination of polymerization was 40%. This copolymer contained 1.3 mol% itaconic acid. 30% methanol solution of copolymer 167
22 ml of 10% methanol solution of sodium hydroxide was added and saponified to obtain modified PVA (degree of saponification of vinyl acetate units: 99.3 mol%). Control Example 1 Copolymerization and saponification were carried out in the same manner as in Example 1, except that maleic anhydride was used instead of maleic acid, and a yellow PVA powder (Saponification degree of vinyl acetate unit: 97.0 mol) was obtained. %) was obtained. The polymer structure was 91.7 mol% vinyl alcohol, 2.8 mol% vinyl acetate, and 5.5 mol% maleic acid units. Control Examples 2 and 3 Copolymerization and saponification were carried out in the same manner as in Example 1, except that monomethyl maleate (Control Example 2) or dimethyl maleate (Control Example 3) was used instead of maleic acid. PVA powder {saponification degree of vinyl acetate units: 97.0 mol% (Control Example 2), 96.7 mol% (Control Example 3)} was obtained. Control Example 4 White PVA powder (degree of saponification of vinyl acetate units: 98.4 mol%) was obtained by copolymerization and saponification in the same manner as in Example 2, except that dimethyl itaconate was used instead of itaconic acid. Ta. Control Examples 5 and 6 PVA powder {vinyl acetate unit Saponification degrees of 99.1 mol% (Control Example 5) and 98.9 mol% (Control Example 6) were obtained. Control Examples 7 and 8 PVA powder {saponification degree of vinyl acetate unit 98.5 mol% (Comparative Example 7), 99.1 mol% (Comparative Example 8)}. Control Example 9 Using the same reactor as in Example 1, vinyl acetate
900g of itaconic acid, 30g of itaconic acid, 200g of methanol, and 0.5g of 2,2'-azobisisobutyronitrile were mixed all at once, and polymerization was carried out at 60°C for 7 hours. The copolymer was saponified in the same manner as in Example 1 to obtain PVA powder. (Itaconic acid content: 2.7 mol%) Control example 10 An unmodified, normal,
Obtained PVA powder. Control Example 11 A modified PVA powder was obtained in the same manner as in Control Example 1, except that the amount of alkali during saponification was half the amount used in Control Example 1. However, this polymer was not soluble in water and merely exhibited swelling, so it could not be used as a surface sizing agent for paper. Control Example 12 Modified PVA (vinyl acetate) was prepared in the same manner as in Example 1, except that instead of using 44 ml of a 10% methanol solution of sodium hydroxide as the saponification condition, 26.3 ml was used for saponification. The degree of saponification of the units was 50 mol%, and the content of maleic acid units was 5.1 mol%). Examples 1 to 4 and Comparative Examples 1 to 10 Carboxyl group-modified PVA prepared in Examples 1 to 4
A paper surface sizing test was conducted using As a comparative example, modified PVA prepared in Control Examples 1 to 10
A surface sizing test using unmodified PVA was also conducted. The test procedure and results are shown below. 1 Surface sizing test (1) Target paper: High-quality paper base paper (paper without surface sizing), basis weight 66.9 g/m ² , tightness 0.68
g/ ^cm3 thickness 98μ, aluminum sulfate content 1.29% (2) Sizing liquid; various types listed in the table and
4% by weight aqueous solution of PVA resin (3) Size press: Surface sizing of paper was carried out using a test size press manufactured by Kumagai Riki Kogyo Co., Ltd. (Squeezing pressure 10Kg/cm ² , speed
(60 m/min, sizing liquid temperature 50°C) The foaming properties of the sizing liquid were observed during the size press. (4) Drying: Drying was performed at 105°C for 1 minute using a rotating drum dryer. (5) Calendaring: Calendar the paper after drying at speed 10.
m/min, pressure 50Kg/cm, temperature 50℃ 2
Calendar processing was performed twice. (6) Conditioning: The paper was conditioned by being left at 20° C. and 65% RH for 3 days before being subjected to physical property measurements. 2 Paper property test (1) IGT printing strength (fuzz onset speed) Measured using an IGT printing tester at a printing pressure of 35 kg/cm ² and using picking oil M. The higher the value, the higher the surface strength. (2) RI conduit picks Using an RI tester made by Mei Seisakusho, a printing test was conducted using TV20 (black) ink made by Dainippon Ink, and the conduit picks were counted. The smaller the number of picks, the higher the paper strength. (3) Air permeability (barrier property) Measured according to JIS P8117-1963. The higher the number, the better the barrier properties are. 3 Measurement Results The paper physical property measurement results are summarized in the table below. From these results, it is understood that the carboxyl group-modified PVA of the present invention is a surface sizing agent that provides better surface strength and barrier properties than conventionally known polyvinyl alcohol resins.

【table】

[Table] Examples 5 to 7 and Comparative Examples 11 to 13 The paper used in Example 1 was coated with an aluminum sulfate aqueous solution to increase the content of aluminum sulfate in the paper layer, and the paper obtained in Example 2 was coated with an aluminum sulfate aqueous solution to increase the content of aluminum sulfate in the paper layer. Apply a carboxyl-modified PVA aqueous solution to the liquid (toluene/
The barrier properties of n-heptane mixture were investigated.
The results are shown in the table. Barrier properties are toluene/n-heptane (50/
50) The mixed solution was dropped onto coated paper, and judgment was made by whether or not it was transmitted in 30 seconds. That is, we created many samples with different amounts of PVA coating, and determined the lower limit of the amount of coating that would not allow the above-mentioned mixed solution to pass through. Therefore, the lower the value, the higher the barrier properties of PVA.

[Table] Reference Examples Each modification obtained in Examples 1 to 4, Control Examples 1 to 9 and 12
Various metal salt powders were added to and mixed with 10% aqueous solutions of PVA and unmodified PVA (Kuraray Poval 117), and the reactivity with the metal salts was investigated.
However, when aluminum sulfate is used in powder form, it also gels unmodified PVA, so add 1.5 ml of a 10% solution of aluminum sulfate [Al ₂ (SO ₄ ) ₃ 18H ₂ O].
The results of dropping and observing the condition are shown in the table. It was confirmed that all of the carboxyl group-modified PVA used in the paper surface sizing agent of the present invention form gels or insoluble substances with many metal salts and have significantly high reactivity with metal ions.

【table】

【table】

Claims (1)

[Claims] 1. In the presence of alcohol, the weight ratio of vinyl acetate to ethylenically unsaturated dicarboxylic acid in the polymerization system is always in the range of 0.01 to 5 to 100 and is uniform so that it is almost constant. The copolymer obtained by solution copolymerization is mixed with an alkali in an amount of 2 molar equivalents based on the ethylenically unsaturated dicarboxylic acid units in the copolymer and the vinyl acetate units in the copolymer in alcohol. A surface sizing agent for paper containing carboxyl group-modified polyvinyl alcohol obtained by saponification using an alkali in a total amount in the range of 0.001 to 1.0 molar equivalent. 2. The surface sizing agent for paper according to claim 1, wherein the unsaturated dicarboxylic acid is itaconic acid.