JPH0277066A - Electrostatic charge image developing toner - Google Patents

Abstract

PURPOSE:To improve the fixing and the offset resisting properties of the subject toner by incorporating a specified copolymer contg. a main constituting unit of alpha,beta-unsatd. ethylenic monomer, as a main resin component in the toner. CONSTITUTION:The copolymer which contains the alpha,beta-unsatd. ethylenic monomer as the main constituting unit and has the ratio of a weight average mol.wt. to a number average mol.wt. of 45-100, is incorporated in the toner as the main resin component. The weight average mol.wt. and the number average mol.wt. mean value that the copolymer is separated (classified) by mol.wt. by a gel permeation chromatography using a THF solvent, and the copolymers classified are detected by a differential refractometer method, and are represented by the conversion value of a standard mol.wt. polystyrene, respectively. Thus, the application of an oil on a heating roller and the addition of an anti-sticking substance such as wax or olefins, etc., to the toner is obviated, whereby the fixing and the offset resisting properties of the toner are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new toner for developing electrostatic images in electrophotography, electrostatic printing, electrostatic recording, and the like.

The novel toner for developing electrostatic images of the present invention is a fine powder developer used in the so-called dry development method, and is suitable for use in dry development methods such as the cascade method, bristle brush method, magnetic brush method, impression method, and powder cloud method. It is characterized by containing an α,β-unsaturated ethylenic monomer as the main structural unit and a polymer having Mw/Mn of 45 to +00 as the main resin component. .

As is well known, toners for developing electrostatic images generally include a resin component, a colorant component consisting of a pigment or dye, a plasticizer,
It is composed of additive components such as a charge control agent, and as the resin component, natural or synthetic resins are used alone or in an appropriate mixture.

Many improvements have been proposed regarding the resin components of toners suitable for dry development methods, which have undergone rapid technological development in recent years. Electronic copying, especially for the purpose of high-speed copying,
In photocopiers, a heated roller constant deposition method is used.
After the toner image obtained by development on the electrostatic recording medium (photosensitive drum) is once transferred to a transfer sheet such as paper, the transfer sheet is passed through a fixing roller that performs heat and pressure bonding to fuse the toner image to the sheet. Fixation is performed. However, because the surface of the fixing roll and the toner image come into pressure contact in a heated and molten state, a portion of the toner forming the image adheres to and is transferred to the fixing roll, and this is transferred again onto the next sheet to be fixed, resulting in the so-called "offset phenomenon". Therefore, there has been a long-awaited resin component that will prevent toner from adhering to the surface of the fixing roller even in high-speed copying and will allow sufficient fixing.

Japanese Patent Publication No. 51-23354 discloses a resin containing 0.005 to 20% by weight of a crosslinking agent based on the monomer as a resin component for a toner that has so-called "offset resistance" that does not cause such an offset phenomenon. The use of ingredients is proposed. Also, Special Publication No. 55-6895 1↓, weight average molecule f
(hereinafter referred to as Mil+)/number average molecular weight (hereinafter referred to as Mn) uses a polystyrene resin as the main resin component, and provides a toner for developing electrostatic images with excellent fixing properties and anti-offset properties. Discloses that the

However, as copying speeds have become faster and faster in recent years, and the desire for clear and stable copies has become more pronounced,
There has been a strong demand for toners that have even better fixing properties and anti-offset properties than those of the prior art described above. As a result of extensive research into toner resin components that can meet these demands, the present inventor has finally completed the invention of a toner with better fixing properties and anti-offset properties than those of the prior art. I ended up doing it.

The electrostatic image developing toner of the present invention contains an α,β-unsaturated ethylenic monomer as a main structural unit, and has Mw/
It contains a polymer having an Mn of 45 to 100 as a main resin component. As used herein, the term "mainly" used as the main structural unit means that the σ,β-unsaturated ethylenic monomer is contained in an amount of 50% by weight or more, preferably 80% by weight or more, based on the polymer.

In addition, in this specification, =Mw, Mn are gel permulation chromatography (hereinafter referred to as G, P, and C).
The product separated using THF as a solvent was detected using a differential refractometer (SHODEX 5E-11) to determine the weight average molecular weight and number average, respectively, expressed as standard molecular weight polystyrene (Waters polystyrene standard) equivalent values. Means molecular weight. On the other hand, in this specification, the term "main resin component" refers to a resin component that accounts for at least 70% by weight of the resin components blended in the toner for developing electrostatic images.

Therefore, the toner for developing an electrostatic image according to the present invention has excellent fixing properties and anti-offset properties compared to conventional toners, and also has excellent blocking resistance and pulverizability. .

In order to have such excellent performance, a polymer constituting the main resin component should have an Mv/Mn of 45 to 100, preferably 50 to 85, and more preferably 60 to 80. If M w / M n is too small, less than 45, the excellent offset properties of the present invention cannot be obtained;
If it is too large, the fixability and pulverizability will be poor, which is not preferable.

In the past, various efforts have been made to improve offset resistance (for example, crosslinked polymer in Japanese Patent Publication No. 51-23354, Mw/Mn3.5 in Japanese Patent Publication No. 55-6895).
-40 polymer) has now achieved satisfactory offset resistance only after measures such as applying silicone oil to the heating roller and adding non-adhesive substances such as wax and olefin to the toner have been added. Currently, the copying machine has a built-in oil application device, which forces the entire device to become larger, or sometimes the oil cannot be supplied stably.
This causes an offset phenomenon and causes machine failure.

However, when wax, olefin, etc. are added, the flow performance deteriorates when the toner is subjected to flow frictional charging, resulting in the problem that charging is not performed uniformly and clear images cannot be obtained.

The toner of the present invention does not require oil to be applied to a heating roller, and has excellent offset resistance without adding non-stick substances such as wax or olefin.

Further, the electrostatic image developing toner of the present invention has surprising anti-blocking performance. Conventionally, in order to improve fixing performance, the thermal melting temperature of the binder resin that forms the toner has been designed to be as low as possible, but when the melting temperature is lowered,
During storage or fluid frictional charging, it aggregates into a cake-like shape and loses its performance as a toner. Generally, the glass transition temperature (Tg) is used to express this lower limit thermal melting temperature.
is being used effectively. In conventional toners, a blocking phenomenon occurs when the Tg of the binder resin is below 55°C and the toner is not used, but with the toner of the present invention, when the Tg of the binder resin is below 55°C.
Since the following toners also have anti-blocking performance, it is possible to design a thermal melting temperature lower than that of conventional toners. Therefore, a toner with good fixing performance and excellent blocking resistance was obtained.

Furthermore, the toner for electrostatic images of the present invention has excellent pulverizability in addition to the above-mentioned excellent properties.

Here, the pulverizability refers to the property of being efficiently pulverized into a desired particle size distribution when the additives described below are added to the main resin component and pulverized. This has made it possible to produce toners with excellent properties economically and advantageously on an industrial scale.

α is the main structural unit of the main resin component of the present invention.

Examples of β-unsaturated ethylenic monomers include styrenes such as styrene, 0-1m-5p-methylstyrene, p-ethylstyrene, and pt-butylstyrene, vinylnaphthalenes, ethylene, propylene, butylene, Ethylenically unsaturated monoolefins such as inbutylene, vinyl chloride, vinyl fluoride, vinyl acetate, vinyl esters such as vinyl butyrate, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, acrylic acid Ethylene monocarboxylic acids such as n-octyl, ethylhexyl acrylate, chloroethyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobunal methacrylate, n-octyl methacrylate, dodecyl methacrylate, stearyl methacrylate, etc. Ethylene monocarboxylic acid derivatives such as esters, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, dimethyl maleate, diethyl maleate, dibutyl maleate, etc. ethylenic dicarboxylic acids and their derivatives, vinyl methyl ketones, vinyl hexyl ketones, vinylidene halides such as vinylidene chloride, vinylidene chlorofluoride, N-
Examples include N-vinyl compounds such as vinylpyrrole, N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone.

Examples of compounds having two or more non-coherent double bonds, which are constituent units of the polymer constituting the main resin component of the electrostatic image developing toner of the present invention, include aromatic divinylbenzene, divinylnaphthalene, etc. Compounds, diethylene carboxylic acid esters such as ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1.3 butanediol dimethacrylate, aryl methacrylate, N,N divinylaniline,
Examples include divinyl ether and divinyl sulfide. Divinylbenzene and ethylene glycol dimethacrylate are preferably used.

One preferred embodiment of the polymer constituting the main resin component of the electrostatic image developing toner of the present invention is 30 to 90% by weight of styrene.
(meth)acrylic acid alkyl ester 10-70% by weight
, a compound having two or more non-conjoint double bonds 0,05~
A copolymer containing 2% by weight, preferably 50 to 80% by weight of styrene, 20 to 50% by weight of an alkyl (meth)acrylate, and a compound containing two or more non-coterminous double bonds. It is a copolymer containing .1-1% by weight. If the amount of styrene is too small (less than 30% by weight), appropriate pulverizability cannot be obtained, which is not preferable, and if it is too large, exceeding 90% by weight, the fixing temperature becomes high, which is not preferable. In addition, the number of compounds with two or more common type 2 bonds is 0.0
If it is too small, such as less than 5% by weight, the Mw/Mn will not reach 45 or more, which is not preferable, and if it is too large, exceeding 2% by weight, the copolymer of the present invention will not be obtained because it will become insoluble.

Examples of such alkyl (meth)acrylates include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, Examples include isobutyl methacrylate, lauryl methacrylate, stearyl methacrylate, and particularly preferred are mn-butyl acrylate, ethylhexyl 1 acrylate, n-butyl methacrylate, and lauryl methacrylate. Compounds with two or more non-mutant double bonds include divinylbenzene, ethylene glycol,
Among them, dimethacrylate and the like are particularly preferred, and divinylbenzene is particularly preferred.

The MW of such polymers is between 1,000 and 30°000.
Those having a molecular weight of 2.000 to 15.000 are particularly preferably used. If Mn is too small (less than 1°000), the agglomeration resistance during toner storage and triboelectrification will deteriorate, which is undesirable, and if it is too large (more than 30.000), fixing properties and pulverizability will deteriorate. So I don't like it.

Another preferred embodiment of the polymer constituting the main resin component of the electrostatic charge developing toner of the present invention is obtained by graft polymerizing the above α,β-unsaturated ethylenic monomer to a rubber elastic polymer. It is a copolymer that can be used as a copolymer.

The term "U rubber elastomer" as used herein refers to so-called diene-based elastomers containing a compound having a common double bond as a constituent unit and so-called non-diene-based elastomers that can easily undergo dehydrogenation and crosslinking. Refers to elastomer. Examples of the former include butadiene rubber, styrene-butadiene rubber, nitrile rubber, natural rubber, synthetic imprene rubber, chloroprene rubber, etc.; examples of the latter include ethylene-propylene rubber, butyl rubber, acrylic rubber, ethylene-vinyl acetate rubber, and chlorosulfonated rubber. polyethylene, chlorinated polyethylene, polyisobutylene, polyester rubber,
Examples include epichlorohydrin rubber and chlorinated butyl rubber, but styrene-butadiene rubber, butadiene rubber, nitrile rubber, and ethylene-propylene rubber are preferred, with styrene-butadiene rubber being particularly preferred.

These rubber elastic polymers have a polymerization degree MW of 500°000.
Below, those having a molecular weight of 300,000 or less are preferably used. If the degree of polymerization is too large, exceeding 500,000, the graft copolymer will become insoluble, which is not preferred.

On the other hand, α is graft polymerized to the rubber elastic polymer.

β-copolymerizable ethylene monomers, generally the above-mentioned styrenes, ethylenically unsaturated monoolefins, vinyl esters, ethylenic monocarboxylic acids, esters thereof,
Examples include ethylenic monocarboxylic acid derivatives, vinyl ethers, ethylenic dicarboxylic acids, derivatives thereof, vinyl ketones, vinylidene halogen compounds, and N-vinyl compounds, but styrene and alkyl (meth)acrylates are preferable. Esters, particularly preferably styrene, methyl acrylate, ethyl acrylate, acrylic acid n
-butyl, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate,
n-butyl methacrylate, isobutyl methacrylate, lauryl methacrylate, stearyl methacrylate, most preferably styrene, n-butyl acrylate, ethylhexyl acrylate, n-butyl methacrylate, lauryl methacrylate.

A preferred embodiment of such a graft copolymer constituting the main resin component of the toner for developing electrostatic images of the present invention includes 0.1 to 20% by weight of rubber elastic polymer, 30 to 90% by weight of styrene, (
A copolymer containing 10 to 70% by weight of meth)acrylic acid alkyl ester, preferably 0% rubber elastic polymer.
-5 to 5% by weight, 50 to 80% by weight of styrene, (meth)
20 to 50% by weight of acrylic acid alkyl ester is used. If the amount of the rubber elastic polymer is too small (less than 0.1), M w / M n will not be 45 or more, which is not preferable, and if it is too large, exceeding 20% by weight, the graft copolymer will become insoluble, which is not preferable. do not have. Also, styrene is 30
If it is too small (less than 90% by weight), it is undesirable because appropriate pulverization properties cannot be obtained, and if it is too large (more than 90% by weight), the fixing temperature becomes high (undesirable).

The polymer constituting the main resin component of the toner of the present invention is suitably produced by the following method.

When the polymer has a compound containing two or more non-coterminous double bonds (hereinafter referred to as a crosslinkable monomer) as a constituent unit, a radical polymerization method is adopted, and the radical polymerization initiator is It is preferable to use the radical polymerization initiator in an amount that satisfies the relationship expressed by the number of moles of generated radicals. Under such conditions, polymerization methods such as bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization are employed, and emulsion polymerization and suspension polymerization are preferred. Also, when containing a rubber elastic polymer, the radical polymerization method is adopted, and the radical polymerization initiator is used in an amount that satisfies the relationship shown by the number of generated radical moles of the radical polymerization initiator in the following formula. preferable. In the case of a so-called non-diene elastomer in which the rubber elastic polymer can easily undergo dehydrogenation and crosslinking, the copolymerization reaction is carried out under conditions known as a hydrogen abstraction reaction. Under such conditions, bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc. are employed, and emulsion polymerization and suspension polymerization are preferred.

The toner for developing an electrostatic image according to the present invention has the above-mentioned resin as the main resin component, but other polymers may be mixed as necessary in addition to the main resin component. I can do it. Other polymers that may be mixed and used in this manner include phenol formaldehyde resins, epoxy resins, polyurethane resins, cellulose resins, polyether resins, xylene resins, and the like.

Further, an appropriate pigment or dye is blended as a coloring agent in the toner for developing an electrostatic image according to the present invention.

Examples of such pigments or dyes include carbon black, self-oil blue, DuPont oil red, phthalocyanine blue, aniline blue, nigrosine dye, ultramarine blue, quinoline yellow, malachite green offsalate, rose bengal, etc. There are mixtures such as, and the amount necessary for coloring the toner is blended.

Furthermore, the toner for developing electrostatic images according to the present invention may further contain a release agent, if necessary. Such compounds include, for example, Cd of stearic acid.

Ba, Ni1 Co, SL, Cu, MgS Ca salt, Z nSM n1F es CoSCus of oleic acid
P bs M g salt, Zn of palmitic acid, C0
% Cus rvtg, SL Ca salt, Zn, Co, Ca salt of linoleic acid, Za or Cd salt of ricinoleic acid, Pb salt of caprylic acid, Pb salt of caproic acid, etc. Metal salts and natural and synthetic higher fatty acids. Examples include paraffins, fatty acid esters or partially cocooned products thereof, alkylene bis fatty acid amides, etc., and one or more of these compounds may be mixed as appropriate in the toner of the present invention.

Further, the toner for developing an electrostatic image according to the present invention may further contain other types of toner additives such as a charge control agent and a plasticizer, if necessary.

Thus, the toner for developing electrostatic images according to the present invention has excellent fixing properties and excellent offset resistance in high-speed electrophotographic copying, and also has excellent t-blocking resistance. Surprisingly, it has been found that the present invention also has the completely unexpected effect of having excellent pulverizability during toner production.

Toner is made into a final product by blending the above-mentioned additives with the main resin components, uniformly mixing and melting the mixture, cooling the molten mixture, crushing it as necessary, and then finely pulverizing it with a jet mill, etc. Conventionally, it has not always been easy to efficiently obtain a final product (toner) having a desired particle size distribution with an average particle size of 10 to 15 μm. It is possible to crush it. The present invention will be explained in detail below using examples.

Reference Example 1 (Preparation of Resin A) In a 5012 polymerization machine, 8 kg of styrene, 2 units of n-butyl acrylate, di-vinylbenzene (purity 56%) 602,
Add benzoyl peroxide °8001, mix and dissolve, then add polyvinyl alcohol (Gohsenol KH-17) 1
20 IKg of an aqueous solution of deionized water in which 02 was dissolved was added. Next, the inside of the polymerization machine was heated to 90°C and kept under stirring for 12 hours, then 50% caustic soda aqueous solution 1602 was added, and the inside of the polymerization machine was heated and kept at 120°C under pressure for 5 hours to complete the polymerization reaction. Ta. The obtained polymer slurry was cooled, dehydrated, washed repeatedly, and dried to obtain a heath-like resin A9.8ky. The obtained resin Mn was 4,000 and uw/un was 45.

Reference Example 2 (Preparation of Resin B) Reference Example fi1m8 and the amount of divinylbenzene was 902
The polymerization reaction was carried out in exactly the same manner except that [n
Resin B having a Mw/Mn of 4,800 and an Mw/Mn of 72 was obtained.

Reference Example 3 (Preparation of Resin C) In Reference Example 1, 2 parts of n-butyl acrylate was changed to 2 parts of lauryl methacrylate, and the amount of divinylbenzene was changed to 1 part.
The polymerization reaction was carried out in exactly the same manner except that 209 was used, and resin C with Mn of 5,600 and MW/IVin of 98 was used.
I got it.

Reference Example 4 (Preparation of resin resin) Trisodium phosphate (12 hydrate) 4. ? , sodium bicarbonate 42, potassium persulfate 8'J1 anionic emulsifier (D
OWfax-2A I) 8I? , Dissolve UPOL pE62) 329 in water 4902 as a nonionic emulsifier and add 2Q
The mixture was placed in a pressure-resistant glass flask, and the desired element was blown into the system to adjust the oxygen content to 0.2%.

Next, styrene 2902 and butadiene 160j? were mixed by measurement in a nitrogen atmosphere. , a mixed solution of n-lauryl mercaptan 12 was added to the above flask, and the inside of the flask was heated.
It was brought to 0°C and kept under stirring for 5 hours. After cooling, the resin emulsion was reprecipitated in methyl alcohol (5a) and separated, and after drying, a flaky resin 2502 was obtained. Mn of the above resin is 6
2,000, and Mw/Mn was 4.0.

Exactly the same polymerization reaction as in Reference Example 1 was carried out except that divinylbenzene 602 was changed to the above resin 2001.
A resin adhesive was obtained.

Reference Example 5 (Preparation of Resin E) Styrene 6.4 in a 50Q polymerization machine! ? Acrylic acid n-
16 kg of butyl and 2-mercaptoethanol 1309 were charged, and the inside of the polymerization machine was heated to 90°C while blowing air at 2 Q/l 1 lin from a blowing tube with an inner diameter of 2 mm.
A time polymerization reaction was performed.

Next is styrene 1.6! g n-butyl acrylate 40
After adding a mixed solution of 02, divinylbenzene 52 (purity 56%), and benzoyl peroxide 1002 to the above reaction product, 20 koji of an aqueous solution of deionized water in which Gohsenol KH-17102 was dissolved was added to clean the inside of the polymerization machine. under stirring 80
The polymerization reaction was completed by keeping at °C for 12 hours. Mn6 of resin E obtained by separating the polymer slurry from water and drying it
．． 500, M W / M n is 43 and ivy.

Reference Example 6 (Preparation of Resin F) Styrene 3.2- and methyl methacrylate 800. ? , 2-mercaptoethanol 3202 were charged, and while blowing air at 2 Q/min from a blowing tube with an inner diameter of 2 mm, the inside of the polymerizer was set to 90''O and a polymerization reaction was carried out for 10 hours.

Next, styrene 1.8 to 9, methyl methacrylate 2.7
After adding a mixed solution of 1.5 parts n-butyl acrylate and 127 parts lauryl peroxide to the above reaction product, Gohsenol KH-1710,? An aqueous solution of deionized water dissolved in
The polymerization reaction was completed after a certain period of time. Mn2,100, Mn of resin F obtained by separating the polymer slurry from water and drying it
w/Mn was 103.

Reference Example 7 (Preparation of Resin G) In a 50Q polymerization machine, 7 parts of styrene, 3 parts of n-protyl methacrylate, and 982 parts of ethylene glycol dimethacrylate were added.
, n-lauryl mercaptan 91jl, azobisisobutyronitrile 200. ? After preparing a mixed solution, 20ml of an aqueous solution of deionized water in which Gohsenol KH-17log was dissolved was added, and the inside of the polymerization machine was kept at 80°C for 12 hours with stirring to carry out a polymerization reaction. Resin G obtained by separating the polymer monomer slurry from water and drying it is insoluble in THF,
It is impossible to measure molecular weight.

Reference example 8 (preparation of resins H and
After heating to ℃, pivalic acid peroxide (-butyl 4009,
Styrene solution mixed and dissolved with benzoyl peroxide 4002 10.81. i was ignited in the polymerization machine for 4 hours. After continuing the polymerization reaction at the same temperature for 2 hours, the resulting polymer solution was cooled to 50° C. and reprecipitated into 100Q methanol to separate the flaky resin H. This product had an Hn of 8°500 and an rvw/rvn of 4.5.

Separately, instead of the above styrene solution, 8°2 styrene,
n-butyl methacrylate 1.8, pivalic peroxide (-
Butyl 4007. Exactly the same polymerization and post-treatment operations were performed except that a mixed solution of benzoyl peroxide 4002 1098- was used, and Mn was 82500, M v / M n
obtained a resin ■ of 4.3.

Example 1 100 parts of resin A manufactured in Reference Example 1 and 10 parts of carbon black (Diablack SH) were mixed and heated to 140°C.
The mixture was thoroughly kneaded for 20 minutes using a hot roll.

After cooling, it is coarsely crushed into a powder of approximately 300 μm using a jet mill (I
DS-2 type), air pressure 5ka/Cm” supply amount 3゜5k
g/Hr to obtain a fine powder with an average particle size of 15μ,
This was used as toner. When this toner was stored in a constant temperature room at 55° C. for 8 hours, no blocking occurred.

When a copying test was conducted using the above toner with a commercially available copying machine (Ubitx 3500 manufactured by Roku Konishi Photo Industry Co., Ltd.), image fixation was possible from 120°C, and even at 250°C, due to the offset of the toner to the heat roll. No stains 2
Even after 0,000 copies, clear images without stains were obtained.

Examples 2 to 4 The resins produced in Reference Examples 2 to 4 were used to form toners in the same manner as in Example 1, and a copying test was conducted.
Shown in the table.

Comparative Examples 1 to 3 The resins produced in Reference Examples 5 to 7 were made into toners in the same manner as in Example 1, and a copying test was conducted.
Shown in the table. Incidentally, Comparative Example 3 corresponds to a supplementary test of Example 1 of Japanese Patent Publication No. 51-2334.

Comparative Example 4 (Additional test to Example 8 of Japanese Patent Publication No. 55-6895) Except that 50 parts of each of the resins H and ■ produced in Reference Example 8 were mixed and used. The results of the copying test are shown in Table 1.

Claims (1)

[Scope of Claims] 1. A graft copolymer of an α/β-unsaturated ethylenic monomer onto a rubber elastic polymer, wherein the α/β-unsaturated ethylenic monomer is the main component. Contained as a structural unit and @M@
A toner for developing an electrostatic image, comprising a copolymer having w/@M@n of 45 to 100 as a main resin component. 2. The toner according to claim 1, wherein the rubber elastic polymer is contained in an amount of 0.1 to 20% by weight based on the copolymer.