JPH05107803A - Toner resin - Google Patents

Abstract

PURPOSE:To obtain a toner resin which can give a toner excellent in fixing property, anti-offset property, blocking resistance and picture image characteristics which enables rapid printing in a copy machine, printer, etc. CONSTITUTION:This toner resin consists of a styrene-base copolymer synthesized from styrene monomers and vinyl monomers, or mixture of these copolymers. The chromatogram of this resin measured by gel permeation chromatography shows at least one max. in each mol.wt. region from 10<3> to 7X10<4> and from 10 to 2X10<6> and a shoulder in >5X10<5> mol.wt. region which includes the max. of the largest mol.wt. The resin has 3X10<3>-10<5> Pa S melting viscosity at 120 deg.C, 50-68 deg.C glass transition point, and 0.5-20mgK0H/g acid value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin for toner which is used in electrophotography, electrostatic printing and the like and which is excellent in non-offset property, fixing property, blocking resistance and image characteristics.

[0002]

2. Description of the Related Art A typical image forming process in electrophotography or electrostatic printing is to uniformly charge a photoconductive insulating layer, expose the insulating layer, and then charge the exposed portion. To form an electric latent image by dissipating the latent image, and to make the latent image visible by attaching a fine powder toner having an electric charge to the latent image. The obtained visible image is transferred to a transfer material such as transfer paper. It comprises a transfer step of transferring and a fixing step of permanently fixing by heating or pressing.

Toners and resins for toners used in such electrophotographic methods or electrostatic printing methods are required to have various performances in the above respective steps. For example, in the developing process, the toner and the resin for the toner retain a charge amount suitable for the copying machine without being affected by the surrounding environment such as temperature and humidity in order to attach the toner to the electric latent image. Must-have. Further, in the fixing step by the heat roller fixing method, the non-offset property that does not adhere to the heat roller and the fixability on paper must be good.
Further, blocking resistance that toner does not block during storage in a copying machine is also required.

Conventionally, styrene-acrylic resins have been widely used as toner resins, and linear type resins and crosslinked type resins have been used. As a linear type resin, a resin in which a high molecular weight substance and a low molecular weight substance are mixed to improve the fixing property and the non-offset property is known. Also,
The cross-linking type resin has a broader molecular weight distribution due to cross-linking to improve fixing property and non-offset property. In particular, research on linear type resins has been advanced, and attempts have been made to improve the fixability and non-offset property by controlling the molecular weight of the resin.

[0005]

However, the speeding up of printing by a copying machine is advancing year by year, and it is attempted to improve the fixing property by further reducing the molecular weight of the low molecular weight material. The toner using the modified toner resin has weak mechanical strength, and the toner during frictional charging with the carrier during high-speed printing is excessively pulverized, causing problems such as fogging in the image after printing. Have

In this regard, as described in Japanese Patent Publication No. 3-48506, a polymer having a relatively high molecular weight is mixed to suppress over-pulverization of the toner, and a polymer having an ultrahigh molecular weight is mixed. Attempting to improve the non-offset property and improve the fixing property by mixing a low molecular weight polymer. However, since a polymer having a relatively high molecular weight and a polymer having an ultrahigh molecular weight are mixed, the fixability is not sufficiently satisfactory. Therefore, an object of the present invention is to provide a resin for toner which has an excellent balance between fixing property and non-offset property, and which has excellent blocking resistance and image characteristics.

[0007]

In view of such circumstances, the inventors of the present invention have made earnest studies on the resin for toner, and as a result, as a result of balancing the molecular weight and viscosity of the resin for toner, non-offset property and fixing The present invention has been accomplished, and it has been found that the toner has excellent properties and can achieve a good balance between them, and that the image characteristics can be improved by further controlling the acid value of the resin for toner.

That is, the toner resin of the present invention comprises a styrene-based copolymer synthesized from a styrene-based monomer and a vinyl-based monomer or a mixture of the copolymers, and measured by gel permeation chromatography. In the chromatogram, the molecular weight is 10 ^{3 to} 7 ×
The molecular weight of the molecular weight distribution ⁵ has at least one local maximum in the region of 10 ⁴ and at least one local maximum in the region of molecular weight 10 ⁵ to 2 × 10 ⁶ , and exhibits the maximum of the maximum molecular weight. It has shoulders in the area of × 10 ⁵ or more, and 1
Melt viscosity at 20 ° C. is 3 × 10 ³ to 10 ⁵ Pa.
S, glass transition temperature 50 to 68 ° C., acid value 0.5 to 2
It is characterized in that it is 0 mgKOH / g.

Examples of the styrene-based monomer used in the styrene-based copolymer of the present invention include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene and α.
-Methyl styrene, p-ethyl styrene, 2,4-dimethyl styrene, pn-butyl styrene, p-tert
-Butylstyrene, pn-hexylstyrene, pn
-Octyl styrene, pn-nonyl styrene, pn
-Densyl styrene, pn-dodecyl styrene, p-
Methoxy styrene, p-phenyl styrene, 3,4-diclosyl styrene and the like can be mentioned.

The vinyl-based monomer of the present invention may be any monomer containing the above-mentioned styrene-based monomer and capable of radical polymerization. For example, acrylic acid, ethyl acrylate, methyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, methacrylic acid, ethyl methacrylate, methyl methacrylate. , N-butyl methacrylate, isobutyl methacrylate, propyl methacrylate, methacrylic acid 2
-Ethylhexyl, stearyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, maleic acid, butyl maleate, methyl maleate, dimethyl maleate, fumaric acid, butyl fumarate, dibutyl fumarate, diisobutyl fumarate. ,
Examples thereof include dimethyl fumarate and diethyl fumarate.

Further, in the present invention, a chain transfer agent may be used to adjust the molecular weight. Examples of the chain transfer agent include α-methylstyrene dimer, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate, and n-octyl mercaptan.

The styrenic copolymer of the present invention obtained from the above components has the following chromatogram measured by gel permeation chromatography:
Molecular weight of 10 ^{3 to} 7 × 10 ⁴ and molecular weight of 10 ⁵ to
It is necessary to have at least one local maximum in each of the 2 × 10 ⁶ regions, and to have a shoulder in the region of 5 × 10 ⁵ or more in the molecular weight distribution showing the maximum of the maximum high molecular weight. The polymer having a molecular weight distribution having a maximum value in the molecular weight range of 10 ^{3 to} 7 × 10 ⁴ improves the fixing property of the toner, and has a maximum value in the molecular weight range of 10 ⁵ to 2 × 10 ^6. The polymer (1) improves the non-offset property of the toner and prevents the toner from being excessively pulverized. Further, the polymer having a molecular weight distribution having a shoulder in a region having a molecular weight of 5 × 10 ⁵ or more improves the non-offset property of the toner.

In the present invention, the shoulder having a molecular weight distribution of 5 × 10 ⁵ or more in the molecular weight distribution showing the maximum value of the maximum molecular weight means the location of the inflection point excluding the maximum value and the minimum value. And having a shoulder in the region of 6 × 10 ^{5 to} 2 × 10 ⁶ , and particularly 6 × 10 ⁵ to
The range of 10 ⁶ is more preferable because it has an excellent balance of fixing property and non-offset property.

Further, in the styrene-based copolymer of the present invention,
Molecular weight of 10 ^{3 to} 7 × 10 ⁴ and molecular weight of 10 ⁵ to 2 ×
The ratio to the region of 10 ⁶ is preferably in the range of 75:35 to 90:10 from the viewpoint of toner characteristics. This is because when the ratio with the region having a molecular weight of 10 ^{5 to} 2 × 10 ⁶ is less than 10, the shoulder does not exist in the molecular weight distribution and the non-offset property is impaired.

Further, in the toner resin of the present invention, 12
Melt viscosity at 0 ° C. is 3 × 10 ³ to 10 ⁵ Pa · S
Therefore, it is necessary that the acid value is 0.5 to 20 mgKOH / g and the glass transition temperature is 50 to 68 ° C. This is because by using a resin having a melt viscosity in this range, it is possible to prevent the toner from being excessively pulverized while being excellent in the fixing property of the toner. By controlling the acid value of the resin within the above range, the toner This is because image fogging is prevented and image characteristics are excellent. Further, when the glass transition temperature of the resin is in the above range, the blocking resistance of the toner is excellent.

In the present invention, the method for producing the toner resin is not particularly limited, and polymers having respective molecular weight distributions may be mixed and melt-kneaded with an extruder or a mixer. It may be produced by a polymerization method such as a suspension polymerization method, a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, or a combination thereof.

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, the glass transition temperature (Tg) was determined by the temperature at the intersection of the baseline of the chart measured by a differential calorimeter at a temperature rising rate of 10 ° C./min and the tangent of the endothermic curve near Tg. Melt viscosity is 1.0 mmφ x
Using a flow tester (CFT-500 manufactured by Shimadzu Corporation) having a 10 mm nozzle, under a load of 30 Kgf,
The measurement was performed under a constant temperature increase rate of 3 ° C./min. The acid value was determined by a titration method using KOH in a toluene solvent. The molecular weight was measured by HCL-8020 manufactured by Tosoh Corporation and calculated in terms of polystyrene.

The fixing property and non-offset property were evaluated by using a copying machine capable of freely changing the copying speed and setting the copying speed at 70 sheets / minute. The image characteristics were evaluated by using the same copying machine and the occurrence of fog in the image after copying 5000 sheets. The blocking resistance was evaluated based on the aggregation state of the toner when 50 g of the toner was put in a sample bottle, put in a hot air dryer kept at 50 ° C. and left for about 48 hours, and then the taken out sample bottle was inverted.

Example 1 The weight ratio of styrene to n-butyl acrylate was 85:15.
And the solid content is 14.3% and the weight average molecular weight is 10,000.
1400 parts by weight of the emulsion of No. 00 was charged into a reaction vessel equipped with a distillation column, a stirrer and a thermometer and stirred at a stirring rotation speed of 100 rpm, and 800 parts by weight of deionized water and 6.4 parts by weight of polyvinyl alcohol were added. A solution prepared by dissolving 8 parts by weight of sodium sulfate was added. Then, 696 parts by weight of styrene, 104 parts by weight of acrylic acid ester and 16 parts by weight of α-methylstyrene dimer were charged into a reaction vessel, and the stirring speed was 300 r.p.m. p. m and the temperature inside the container was 40 ° C., and the mixture was stirred and mixed for about 1 hour. Next, 16 parts by weight of benzoyl peroxide was added to the reaction vessel,
The temperature inside the vessel was raised to 90 ° C. and suspension polymerization was carried out for about 3 hours. After the suspension polymerization was completed, a silicone antifoaming agent (KM-70 manufactured by Shin-Etsu Chemical Co., Ltd.) equipped with a Liebig cooling tube was added, and the temperature inside the container was raised to 100 ° C. to remove residual monomers. Then, cool the temperature inside the container to 90 ° C,
16 parts by weight of caustic soda was placed in the reaction vessel and held for about 30 minutes. Further, after cooling the reaction system to room temperature, the resin was taken out and dried at 50 ° C. for about 12 hours.

The resin obtained has an acid value of 1.5 mg KOH.
/ G, melt viscosity at 120 ° C. is 1.8 × 10 ⁴ Pa · S,
The glass transition temperature was 64.5 ° C. The molecular weight distribution by gel permeation chromatography is
It has a maximum value at a molecular weight of 8.5 × 10 ⁵ , this peak is the maximum molecular weight, and the molecular weight of this distribution is 1.39 ×.
He had a shoulder at 10 ⁶ . Furthermore, the molecular weight 1.
It had a maximum value at 6 × 10 ⁴ .

Next, 91 parts by weight of the obtained resin, 5 parts by weight of carbon black, 1 part by weight of a caustic control agent (Bontron S-34 manufactured by Orient Chemical Co., Ltd.) and 3 parts by weight of low molecular weight polypropylene wax were mixed with a Henschel mixer. Then 13
The mixture was kneaded with a twin-screw extruder at 0 ° C. After that, fine pulverization and classification were repeated until the particle size became 10 to 20 μm to obtain a toner. The obtained toner was excellent in fixing property, non-offset property and blocking resistance, and the image was clear without fog and was excellent in image characteristics.

Example 2 The weight ratio of styrene to n-butyl acrylate was 65:35.
And the solid content is 14.3% and the weight average molecular weight is 59000.
1752 parts by weight of 0 emulsion, 75 deionized water
A solution prepared by dissolving 0 part by weight, 6 parts by weight of polyvinyl alcohol and 7.5 parts by weight of sodium sulfate was put into a reaction vessel. Then, 645 parts by weight of styrene, 97.5 parts by weight of ethyl acrylate, 7.5 parts by weight of methacrylic acid, 15 parts by weight of α-methylstyrene dimer and 60 parts by weight of benzoyl peroxide were charged into a reaction vessel, and Example 1 and Suspension polymerization was performed by the same method.

The resin obtained has an acid value of 5.3 mg KOH.
/ G, melt viscosity at 120 ° C. is 3.0 × 10 ⁴ Pa · S,
The glass transition temperature was 62.0 ° C. The molecular weight distribution by gel permeation chromatography is
It has a maximum value at a molecular weight of 4.8 × 10 ⁵ , this peak is the maximum molecular weight, and the molecular weight of this distribution is 7.0 × 1.
He had a shoulder at 0 ⁵ . Furthermore, the molecular weight is 1.5
It had a maximum value at 8 × 10 ⁴ .

Next, a toner was obtained from the obtained resin in the same manner as in Example 1. The obtained toner was excellent in fixability, non-offset property, and blocking resistance, and particularly, the balance between fixability and non-offset property was good. Further, the image was clear without fog and was excellent in image characteristics.

Example 3 The weight ratio of styrene to n-butyl acrylate was 85:15.
And the solid content is 14.3% and the weight average molecular weight is 1.2 × 1.
0 emulsion 1960 parts by weight of ^6, deionized water 7
A solution prepared by dissolving 20 parts by weight, 5.8 parts by weight of polyvinyl alcohol and 7.2 parts by weight of sodium sulfate was placed in a reaction vessel. Next, 590 parts by weight of styrene, 108 parts by weight of ethyl acrylate, 21.6 parts by weight of methacrylic acid,
14.4 parts by weight of α-methylstyrene dimer and 57.6 parts by weight of benzoyl peroxide were placed in a reaction vessel, and suspension polymerization was carried out in the same manner as in Example 1.

The obtained resin has an acid value of 18.3 mgKOH.
/ G, melt viscosity at 120 ° C. is 4.0 × 10 ⁴ Pa · S,
The glass transition temperature was 66.0 ° C. The molecular weight distribution by gel permeation chromatography is
It has a maximum value at a molecular weight of 1.0 × 10 ⁶ , this peak is the maximum molecular weight, and the molecular weight of this distribution is 1.5 × 1.
0 had a shoulder to ⁶ at the. Furthermore, the molecular weight is 1.8
It had a maximum value at 8 × 10 ⁴ .

Next, a toner was obtained from the obtained resin in the same manner as in Example 1. The obtained toner was excellent in fixing property, non-offset property and blocking resistance, and the image was clear without fog and was excellent in image characteristics.

Example 4 1050 parts by weight of the emulsion used in Example 2, 850 parts by weight of deionized water, 6.8 parts by weight of polyvinyl alcohol and 8.5 parts by weight of sodium sulfate were dissolved and charged into a reaction vessel. Next, 722 parts by weight of styrene, 128 parts by weight of n-butyl acrylate, 12.8 parts by weight of α-methylstyrene dimer and 42.% of benzoyl peroxide.
5 parts by weight were placed in a reaction vessel, and suspension polymerization was carried out in the same manner as in Example 1.

The obtained resin has an acid value of 1.0 mgKOH.
/ G, melt viscosity at 120 ° C. is 2.1 × 10 ⁴ Pa · S,
The glass transition temperature was 61.0 ° C. The molecular weight distribution by gel permeation chromatography is
It has a maximum value at a molecular weight of 4.8 × 10 ⁵ , this peak is the maximum molecular weight, and the molecular weight of this distribution is 7.0 × 1.
He had a shoulder at 0 ⁵ . Furthermore, the molecular weight is 3.2
It had a maximum value at 8 × 10 ⁴ .

Next, a toner was obtained from the obtained resin in the same manner as in Example 1. The obtained toner was excellent in fixability, non-offset property, and blocking resistance, and particularly, the balance between fixability and non-offset property was good. Further, the image was clear without fog and was excellent in image characteristics.

Example 5 240 parts by weight of styrene, 60 parts by weight of n-butyl acrylate and 0.3 parts by weight of 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane were mixed and distilled. Charge the reaction vessel equipped with a tower, stirrer and thermometer,
After performing N ₂ substitution for 1 hour, the stirring speed was kept at 50 rpm, the temperature inside the container was raised to 92 ° C. while flowing N ₂ gas, and after polymerizing to 70% of these vinyl polymers by bulk polymerization, 457 parts by weight of xylene was added and the temperature inside the container was raised to 140 ° C. Then xylene 68
Parts by weight, 312 parts by weight of styrene, 80 parts by weight of n-butyl acrylate, 8 parts by weight of methacrylic acid, 9.8 parts by weight of α-methylstyrene dimer and 29.4 parts by weight of azobisisobutylnitrile for about 6 hours. Was added dropwise and solution polymerization was carried out. After the suspension polymerization was completed, xylene was removed under a high vacuum of 50 mmHg or less, and when the solvent removal was completed, it was cooled to obtain a solid resin.

The obtained resin has an acid value of 8.4 mgKOH /
g, the melt viscosity at 120 ° C. was 8.0 × 10 ³ Pa · S, and the glass transition temperature was 58.0 ° C. Further, the molecular weight distribution by gel permeation chromatography has a maximum value at a molecular weight of 5.8 × 10 ⁵ , and this peak is the maximum molecular weight. The molecular weight of this distribution is 1.35 × 1.
0 had a shoulder to ⁶ at the. Furthermore, the molecular weight is 4.0
It had a maximum value at × 10 ³ .

Next, a toner was obtained from the obtained resin in the same manner as in Example 1. The obtained toner was excellent in fixing property, non-offset property and blocking resistance, and the image was clear without fog and was excellent in image characteristics.

Example 6 The weight ratio of styrene, n-butyl acrylate and methacrylic acid was 78: 20: 2 and the weight average molecular weight was 8.0 ×.
⁵ parts by weight of a copolymer having a molecular weight of 10 ⁵ and a weight average molecular weight of 7.
20 parts by weight of a copolymer of 0 × 10 ⁵ and 70 parts by weight of a copolymer of styrene and n-butyl acrylate in a weight ratio of 78:12 and a weight average molecular weight of 6.0 × 10 ^5. And were mixed to obtain a solid resin.

The resin thus obtained has an acid value of 3.2 mgKOH.
/ G, melt viscosity at 120 ° C. is 8.0 × 10 ⁴ Pa · S,
The glass transition temperature was 55.0 ° C. The molecular weight distribution by gel permeation chromatography is
It has a maximum value at a molecular weight of 5.8 × 10 ⁵ , this peak is the maximum molecular weight, and the molecular weight of this distribution is 8.0 × 1.
He had a shoulder at 0 ⁵ . Furthermore, the molecular weight is 5.8.
It had a maximum value at × 10 ⁴ .

Next, a toner was obtained from the obtained resin in the same manner as in Example 1. The obtained toner was excellent in fixability, non-offset property, and blocking resistance, and particularly, the balance between fixability and non-offset property was good. Further, the image was clear without fog and was excellent in image characteristics.

Comparative Example 1 The weight ratio of styrene to n-butyl acrylate was 80:20.
Then, a solid resin was obtained in the same manner as in Example 1 except that an emulsion having a weight average molecular weight of 4.0 × 10 ⁵ was used.

The resin obtained has an acid value of 1.2 mg KOH.
/ G, melt viscosity at 120 ° C. is 1.0 × 10 ⁴ Pa · S,
The glass transition temperature was 63.5 ° C. The molecular weight distribution by gel permeation chromatography is
It has a maximum value at a molecular weight of 3.0 × 10 ⁵ , this peak is the maximum molecular weight, and the molecular weight of this distribution is 4.0 × 1.
He had a shoulder at 0 ⁵ . Furthermore, molecular weight 1.2
It had a maximum value at × 10 ⁴ .

Next, a toner was obtained from the obtained resin in the same manner as in Example 1. The obtained toner was excellent in fixability, blocking resistance, and image characteristics, but was inferior in non-offset property.

Comparative Example 2 The weight ratio of styrene to n-butyl acrylate was 80:20.
Then, a solid resin was obtained in the same manner as in Example 2 except that 3500 parts by weight of the emulsion having a weight average molecular weight of 2.6 × 10 ⁶ was used.

The obtained resin has an acid value of 3.5 mgKOH.
/ G, melt viscosity at 120 ° C. is 1.0 × 10 ⁵ Pa · S,
The glass transition temperature was 70.0 ° C. The molecular weight distribution by gel permeation chromatography is
It has a maximum value at a molecular weight of 2.45 × 10 ⁶ , this peak is the maximum molecular weight, and the molecular weight of this distribution is 2.6 ×.
He had a shoulder at 10 ⁶ . Furthermore, the molecular weight 1.
It had a maximum value at 68 × 10 ⁴ .

Next, a toner was obtained from the obtained resin in the same manner as in Example 1. The obtained toner was excellent in non-offset properties, blocking resistance, and image characteristics, but was inferior in fixability.

Comparative Example 3 A solid resin was obtained in the same manner as in Example 2 except that 276.5 parts by weight of the emulsion of Example 2 was used.

The obtained resin has an acid value of 5.8 mgKOH.
/ G, melt viscosity at 120 ° C. is 2.0 × 10 ³ Pa · S,
The glass transition temperature was 56.0 ° C. The molecular weight distribution by gel permeation chromatography is
It had a maximum value at a molecular weight of 4.8 × 10 ⁵ , and this peak was the maximum molecular weight. However, there was no shoulder in this distribution. Further, it had a maximum value at a molecular weight of 1.8 × 10 ⁴ .

Next, a toner was obtained from the obtained resin in the same manner as in Example 1. The obtained toner was excellent in fixability and blocking resistance, but poor in non-offset property,
The image had fog and a clear image could not be obtained.

Comparative Example 4 The weight ratio of styrene to n-butyl acrylate was 70:30.
Then, suspension polymerization was carried out in the same manner as in Example 1 except that 1752 parts by weight of an emulsion having a weight average molecular weight of 1.61 × 10 ⁶ , 525 parts by weight of styrene, and 225 parts by weight of n-butyl acrylate were used. I went.

The obtained resin has an acid value of 1.5 mgKOH.
/ G, melt viscosity at 120 ° C. is 2.1 × 10 ⁴ Pa · S,
The glass transition temperature was 41.5 ° C. The molecular weight distribution by gel permeation chromatography is
It has a maximum value at a molecular weight of 1.42 × 10 ⁶ , this peak is the maximum molecular weight, and the molecular weight of this distribution is 1.6 ×.
He had a shoulder at 10 ⁶ . Furthermore, the molecular weight 1.
It had a maximum value at 48 × 10 ⁴ .

Next, a toner was obtained from the obtained resin in the same manner as in Example 1. The obtained toner was excellent in fixability, non-offset property, and image characteristics, but was inferior in blocking resistance.

[0049]

By controlling the molecular weight, viscosity, acid value and glass transition temperature, the resin for toner of the present invention can provide a toner excellent in fixability, non-offset property, blocking resistance and image characteristics. In addition, it is possible to speed up printing by a copy machine, a printer, or the like.

Claims (1)

[Claims] 1. A chromatogram measured by gel permeation chromatography, which comprises a styrene-based copolymer synthesized from a styrene-based monomer and a vinyl-based monomer or a mixture of the copolymers.
It has at least one maximum in the region of molecular weight 10 ^{3 to} 7 × 10 ⁴ , has at least one maximum in the region of molecular weight 10 ⁵ to 2 × 10 ⁶ , and has a maximum of the maximum molecular weight. In addition to having a shoulder in a region having a molecular weight of 5 × 10 ⁵ or more in the molecular weight distribution shown, the melt viscosity at 120 ° C. is 3 × 10 5.
³ to 10 ⁵ Pa · S, glass transition temperature 50 to 68 ° C.,
A resin for toner, which has an acid value of 0.5 to 20 mgKOH / g.