JPS5845444B2 - Kamihifukuyou Yuukiganryyouno Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing an emulsifier-free organic pigment for coating polystyrene paper.

More specifically, the present invention involves the copolymerization of methacrylic acid and styrene or a monomer containing styrene as a main component in an aqueous medium in the absence of an emulsifier. A polymer latex is provided.

Conventionally, inorganic pigments such as clay or titanium dioxide have been mainly used as pigments for paper coatings, but in recent years, as demands for paper quality such as printing paper have increased, the amount of pigments used for paper coatings has increased. As a result, the weight increase of printed materials using coated paper cannot be ignored.

Therefore, in order to reduce the weight of coated paper, polymers with lower density than inorganic pigments have been used as organic pigments.

As such an organic pigment, a polymer latex produced by an emulsion polymerization method has been proposed, but it has the drawback that the emulsifier used during polymerization reduces the water resistance strength of the coated paper.

Emulsion polymerization is one of the industrially important polymerization methods, and emulsifiers and protective colloids are used to obtain stable polymer latex.

In particular, when polymerizing hydrophobic monomers such as styrene and butadiene, it is essential to use an emulsifier not only to maintain the stability of the latex produced, but also to carry out the polymerization reaction itself, and it usually has a coefficient of 1 to several. surfactants are used.

However, the emulsifier used in the polymerization reaction is inevitably mixed into the polymer latex and gives the latex foaming properties.
Further, as mentioned above, in addition to reducing the water resistance of the dried film, it also has disadvantages such as causing coloration and reducing adhesiveness.

Therefore, it has been desired to reduce the amount of emulsifier used as much as possible.

In addition, the usefulness of using polystyrene polymer latex as an organic pigment for paper coating was published in Japanese Patent Publication No. 46-652.
It is known from Publication No. 4.

That is, when a composition containing an organic pigment is applied to paper, it reduces the weight of the paper and behaves as an opaque white pigment with a high degree of gloss.

Although this publication does not contain a detailed description of the method for producing organic pigments, U.S. Patent No. 3,819,557 by the same applicant describes an embodiment in which polystyrene polymer latex is produced using an emulsifier during polymerization. There is.

However, when polystyrene polymer latex produced in the presence of an emulsifier according to such conventional methods is used, only coating films with poor water resistance are obtained.

In addition, when an emulsifier is used, the surface tension of the polymer latex decreases and foaming occurs during the production of the polymer latex or during the preparation process of the coating solution, resulting in a decrease in workability.

The surface tension of polymer latex is 50 dyne/crr
If it is at least L, preferably at least 60 dyne/cm, the foaming property will be low and the workability will be extremely good.

The method of obtaining latex by polymerizing or copolymerizing various monomers without using an emulsifier has already been reported by Matsumoto et al.
7DO1, 57DO2), JP-A-49-30472, C, W, CESKA (J, Appl.

Polymer Sci, 18 427-437 (1
974)).

However, with these methods, the stability of the latex during polymerization is poor and coagulation is likely to occur, and the particle size cannot be controlled to 0.3 μm or more.

It has drawbacks such as long polymerization time and poor productivity.

As a result of various studies on the production method of polystyrene polymer latex which is stable and has a uniform particle size and can be suitably used as an organic pigment for paper coating, the present inventors found that methacrylic acid and styrene in a specific composition ratio, or styrene When polymerizing by continuously adding a mixture with a monomer mainly composed of
Moreover, the particle size is uniform, and a stable polymer latex with high surface tension can be obtained. When this polymer particle is used as an organic pigment for paper coating, it can replace part or all of the inorganic pigment, and it has an excellent coating film. It has been found that these pigment dispersions have excellent optical properties and have excellent water resistance, and that these pigment dispersions exhibit good workability due to their low foaming properties.

The present invention was achieved based on these findings, and 100 parts by weight of a monomer mixture consisting of 3 to 8 parts by weight of methacrylic acid and 97 to 92 parts by weight of styrene or a monomer mainly composed of styrene, 0.5 to 2.5 parts by weight of alkyl mercaptan are mixed, and the mixture is mixed with 5 parts by weight containing persulfate.
This is a method for producing an organic pigment for paper coating, which does not contain an emulsifier, and is characterized in that it is continuously added to an aqueous medium at a temperature of 0 to 100°C for 3 to 8 hours and polymerized.

When a mixture of a binder and an inorganic pigment is used for paper coating, part or all of the inorganic pigment can be replaced with an organic pigment to provide a coating that is lightweight and has excellent white gloss, while also improving water resistance, which is a disadvantage of organic pigments. Obtaining a coating with little degradation was achieved for the first time by using the polystyrene polymer latex produced by the method of the invention as an organic pigment.

That is, according to the present invention, it is possible to stably produce a polystyrene polymer latex that has a high surface tension, is stable, has a relatively large particle size, and has a uniform particle size, and a binder using this as an organic pigment can be produced. The IA+-A coating, which is made of a mixture with inorganic pigments, has excellent water resistance, mechanical properties, and optical properties, and the polymer latex is stable up to a polymer concentration of about 60% by weight.

In the present invention, methacrylic acid is essential for producing polystyrene polymer latex, and if methacrylic acid is not included, the polymerization rate of styrene or a hydrophobic monomer mainly composed of styrene will be extremely slow.

If the amount of methacrylic acid used is less than 3 weights of all monomers,
Coagulates tend to form during polymerization, and when the weight exceeds 8 weight, coagulates tend to form, and when the amount of methacrylic acid used increases, the particle size of the polymer becomes smaller.
Furthermore, the water resistance of the coating decreases and it loses its effectiveness as an organic pigment.

Therefore, the amount of methacrylic acid used is 3 to 8 weight φ of the total monomers.
is appropriate.

α other than methacrylic acid. In the case of β-unsaturated oxycarboxylic acid, it is necessary to use 100 parts by weight in order to obtain a stable polymer latex, and coatings using this polymer have the drawback of significantly lowering the water resistance strength.

Among the monomers copolymerized with methacrylic acid, styrene is used to increase the heat distortion temperature of the organic pigment and further increase the refractive index of the particles.

The higher the refractive index, the better the optical properties such as the whiteness of the coating film.

The monomers used in the polymerization may be only methacrylic acid and styrene, but a third monomer copolymerizable with these may be used in combination.

As the third monomer, aromatic vinyl compounds such as vinyltoluene, α-methylstyrene, chlorostyrene, and divinylbenzene, as well as methyl acrylate, ethyl acrylate, methyl methacrylate, acrylonitrile, butadiene, and the like are used.

The third monomer is used in an amount within about 20 weight φ of styrene in order to maintain the heat distortion temperature of the resulting polymer at 50'C or higher.

The purpose of using the third monomer, in addition to improving the stability of the latex, is to obtain particles with a certain heat distortion temperature.

It is desired that the heat distortion temperature is higher than the drying temperature during coating, preferably 50°C or higher.

The amount of water used for polymerization is 90 parts by weight per 100 parts by weight of monomer.
0 to 60 parts by weight, preferably 230 to 60 parts by weight are used.

Next, an alkyl mercaptan is mixed into these monomer mixtures.

The amount of alkyl mercaptan used is 1.00 of the monomer mixture.
The amount is 0.5 to 2.5 parts by weight.

Alkyl mercaptans are necessary to stably produce polymer latexes.

If it is less than 0.5 parts by weight, coagulates will be formed during polymerization, and 2.5 parts by weight will result.
Even if an amount that raises parts by weight is added, coagulum is likely to be formed during polymerization.

Specifically, the alkyl mercaptan is preferably a long-chain alkyl mercaptan such as tert-dodecyl mercaptan or n-dodecyl mercaptan, and a stable polymer latex is not suitable for lower alkyl xanthogens and halogenated hydrocarbons, which are usually used as chain transfer agents. Not generated.

The mixture of monomer and alkyl mercaptan is continuously added to water containing persulfate at a temperature of 50-100° C. over a period of 3 to 8 hours and polymerized.

Examples of persulfates include ammonium persulfate and potassium persulfate.

Further, a reducing agent such as sodium thiosulfate or ferrous chloride can be added to the persulfate.

The amount of persulfate used is 0.3 to 3 parts by weight per 100 parts by weight of the monomer.

The temperature of the aqueous medium is 50-100°C, preferably 60-9
It is 0°C.

At temperatures lower than 50'C, the polymerization rate is slow and coagulum is formed during polymerization.

It is necessary to add the mixture of monomer and alkylmercapkun continuously.

A coagulum forms when the mixture is added for less than 3 hours.

Also, sometimes when the entire amount is added, a large amount of coagulum is generated.

The longer the monomer addition time, the larger the polymer particles will be, but adding a time longer than 8 hours will not only lengthen the polymerization time and be meaningless, but also cause coagulation to occur.

The addition of the mixture of monomer and alkyl mercaptan is carried out continuously.

The addition may be carried out by dropping or flowing down from above the surface of the polymerization solution, or may be injected from below the surface of the polymerization solution.

Further, the mixture may be added evenly and continuously within a predetermined period of time, or may be added intermittently to the extent that it can be considered as substantially continuous addition.

The particle size of the polymer latex produced in the above process is 0.3μ or more, which is required for a pigment, and the particle size is uniform, and the latex is stable despite its high surface tension.

The polymerization is carried out by adjusting the polymer concentration in the latex to 100 parts by weight or more, preferably 30 to 60 parts by weight.

After the polymerization is completed, stripping for demolding the polymer or dilution or concentration for adjusting the concentration can be carried out if necessary.

When preparing a paper coating composition using a polymer latex, the polymer latex is on the acidic side of pH 2-3, so before mixing with the binder or even with the inorganic pigment, in order to increase the stability during mixing, If necessary, a basic substance such as ammonia, sodium hydroxide or potassium hydroxide may be added to adjust the pH to 7-10.

When using the organic pigment of the present invention as a paper coating composition, binders include starch, modified starch, soybean protein, natural binders such as casein, styrene-butadiene copolymer latex, and carboxy-modified copolymer latex. , polyvinyl acetate latex, polychloroprene,
Synthetic binders such as latex and polyvinyl alcohol, used alone or in combination.

Inorganic pigments include kaolin clay, calcium carbonate,
Titanium oxide (rutile, anatase), etc. are used.

The mixing ratio of pigment and binder is usually 10 in terms of dry weight.
0 to 5-25.

In the pigment, the mixing ratio of organic pigment and inorganic pigment used is between 1/99 and 10010 in dry weight ratio.

Coating the paper substrate is carried out by known techniques, such as air knives, trailing blades, inverted blades, roll coaters.

After coating, the surface is dried and finished by calendering, etc.

Application, drying and finishing temperatures must not exceed the softening temperature of the organic pigment.

It is also necessary that the organic pigment is not softened by the binder.

Next, the present invention will be explained in more detail using actual examples, but the present invention is not limited to these examples unless the gist thereof is exceeded.

Example 1 A stainless steel reactor (capacity 1OOl) equipped with a stirrer, cooling coil, temperature detector, jacket, etc. was replaced with nitrogen and 51ky of water was charged, and the temperature was raised to 80°C while stirring.
I made it.

A solution of 0.15 to 9 ammonium persulfate in 1.5 units of water was charged into a reactor, followed by a mixture of 28.5 kg of styrene, 1.5 to 9 of methacrylic acid, and 0.3 ky of tert dodecyl mercaptan for 5 hours. was added continuously to the reactor.

After the monomer addition was completed, the temperature of the reactor was raised to 90°C, and inoculation was continued for an additional 3 hours.

The solid content concentration of the obtained polymer latex was 36.9 or more.
The pH was 1.9, and the conversion rate was too high.

When this latex was filtered through a 200-mesh stainless steel wire mesh and the residue was measured, it was found that the coagulated product was polymer 1.
It was very low at 0.026F per 00g.

Further, the surface tension when the pH was adjusted to 8.3 with ammonia water (concentration 28%) was 66.7 dyne/crrL.

The average particle size determined by electron microscopy was 0.63μ, and the particle sizes were well aligned.

(Hereinafter, this will be referred to as latex A.

) When measuring the performance of the organic pigment of the present invention, the performance of the organic pigment of the present invention to which a conventional emulsifier was added and a commercially available organic pigment were measured in order to examine the influence of the emulsifier.

The formulation of the paper coating composition and the conditions for preparing the organic pigment sample are shown in Tables 1 and 2.

Samples (2) to (5) are comparative samples * Na salt of lauryl alcohol sulfate These blended compositions were coated on high-quality paper with a bar coater at 11.0
Apply to a temperature of ±1.1 and heat at 120'C.

Dry for 1 minute and 70'C115kg/CI? Calendar running was performed twice under L conditions.

Table 3 shows the results of testing according to the usual coated paper evaluation method.

As is clear from Table 3, compared to the evaluation results of Formulation A of the conventional method that does not use organic pigments, those that use organic pigments in combination are significantly superior in white paper gloss, but are inferior in water resistance strength.

Especially samples with added emulsifier (2), (3),
In (4), it can be seen that the water resistance strength decreases in proportion to the amount of emulsifier added.

Further, commercially available organic pigments also have poor water resistance, but when the organic pigment of the present invention is used, there is little decrease in water resistance, indicating that the water resistance is excellent.

Example 2 Comparison of mercaptan amount Stirrer, cooling pipe, thermometer made of glass 11 Separable 4
Replace the two-flask with nitrogen and add 476g of water.
The temperature was raised to 'c.

Next, 1.4 g of ammonium persulfate was dissolved in 1.4 g of water and charged.

Next, a monomer solution containing styrene 2665i' (95% by weight), methacrylic acid 14F (5% by weight), and tert-dodecylmercaptan (by weight) was added over 3 hours.
continuously added to the reactor.

After the addition of the 7-mer, the temperature was raised to 90°C and polymerization was continued for an additional 2 hours.

The resulting emulsion was filtered through a 200-mesh stainless steel wire gauze to determine the amount of coagulum produced.

The results are shown in Table 4.

Table 4 shows that polymerization stability is good when the amount of mercaptan is within the range of 0.5 to 2.5 PHM.

Note that experiment number 2.7 is a comparative example.

Example 3 Comparison of methacrylic acid amount A 11 separable flask similar to that in Example 2 was purged with nitrogen, 476 g of water was charged, and the temperature was raised to 80°C.

1.4 g of ammonium persulfate was dissolved in 14 cI** of water and charged.

Subsequently, a mixture of styrene and methacrylic acid 281 and ter
2.8 g of t-dodecyl mercaptan was mixed and added continuously to the reactor over 5 hours.

After the monomer addition was completed, the temperature was raised to 90'C and polymerization was continued for an additional 2 hours.

The obtained latex was filtered through a 200-mesh stainless steel wire gauze to determine the amount of formed coagulum.

The results are shown in Table 5.

From Table 5, it can be seen that the amount of methacrylic acid is preferably 3 to 8 weight φ.

Note that experiment numbers 8 and 12 are comparative examples.

Example 4 Comparison of monomer bath addition time A 11 separable flask similar to Example 2 was purged with nitrogen, 476 g of water was charged, and the temperature was raised to 80°C.

Next, 1.4 g of ammonium persulfate was dissolved in 14 g of water and charged.

Next, 266 g of styrene 14 g of methacrylic acid, ter
2.8 g of t-dodecyl mercaptan was mixed and added continuously to the reactor over a predetermined period of time.

After the monomer addition was completed, the temperature was raised to 90° C. and polymerization was continued for an additional 2 hours.

Table 6 shows the properties of the obtained emulsion.

Table 6 shows that the monomer addition time is preferably 3 to 8 hours.

Note that experiment numbers 13, 14, and 18 are comparative examples.

Example 5 Example of use of third monomer A 11 separable flask similar to Example 2 was purged with nitrogen, 476 g of water was charged, and the temperature was raised to SO'C.

Next, 1.4 g of ammonium persulfate was dissolved in 1=H' of water and charged.

Next is Styrene 252? (90 weight φ), methyl methacrylate 14F (5 weight φ), methacrylic acid 14F (
5% by weight) and 2.1 liters of tert-dodecyl mercaptan were mixed and added continuously to the reactor over 4 hours.

After the monomer addition was completed, the temperature was raised to 90'C and polymerization was continued for an additional 2 hours.

The conversion rate was 100%. When the residue was measured by filtration through a 200-mesh stainless steel wire gauze, the coagulated product was 0.065 F/oog of polymer.

Also, when the pH is adjusted to 7.7 with 28φ ammonia water, the surface tension is 57 dyne/crIL1 and the average particle size is 0.
．． It was 45μ.

This latex is designated as sample (6).

Using the same polymerization procedure, the monomer composition dropped was changed to 252 g of styrene.
(90 weight), ethyl acrylate 14g (5 weight)
, methacrylic acid 14'i (5% by weight), tert-
Polymerization was carried out as 2.8 g of dodecyl mercaptan.

The conversion of the latex obtained was 100%, with a product coagulum of 0.07:l (per 101 polymer).

When the pH was adjusted to 8.1 with 28 cups of ammonia water, the surface tension was 57 dyne/crn and the average particle size was 0.42μ.
Met.

This latex is called Sampu no Koro 7).

[Comparison of performance of organic pigments] Comparison of performance as organic pigments was conducted in the same manner as in Example 1.

That is, Sampno 6) and sample (7) were tested using formulations C and D of Example (2).

The results are shown in Table 7. Comparative Example 1 A pressure-resistant bottle having an internal volume of 340 TLl was purged with nitrogen, and the polymerization composition shown in Table 8 was charged therein and polymerized at 70° C. for 6 hours.

It can be seen that when polymerization is carried out using a method in which monomers are added all at once at the start of polymerization without using alkyl mercaptan, the polymerization stability is poor and the particle size of the obtained latex is also small.

Comparative Example 2 Example using acrylic acid instead of methacrylic acid Example 2
11 Separable flask similar to 11 was replaced with nitrogen and water was added to 47
6g was charged and the temperature was raised to 80°C.

Next, 1.4 g of ammonium persulfate was dissolved in 14 g of water and added.

Subsequently, a mixture of styrene and acrylic acid 281i' and te
2.8 g of rt-dodecyl mercaptan was mixed and added continuously to the reactor over 4 hours.

After the monomer addition was completed, the temperature was raised to 90°C and polymerization was continued for an additional 2 hours.

The obtained latex was filtered through a 200-mesh stainless steel wire gauze to determine the amount of coagulum produced.

The results are shown in Table 9.

Table 9 shows that when acrylic acid is used instead of methacrylic acid, polymerization stability is poor and coagulation is likely to occur.

Claims (1)

[Claims] 1. Mix 0.5 to 2.5 parts by weight of alkyl mercaptan to 100 parts by weight of a monomer mixture consisting of 3 to 8 parts by weight of methacrylic acid and 97 to 92 parts by weight of styrene or a monomer mainly composed of styrene. A method for producing an organic pigment for paper coating that does not contain an emulsifier, characterized in that the mixed solution is continuously added to an aqueous medium containing a persulfate at a temperature of 50 to 100°C for polymerization over a period of 3 to 8 hours. .