Note: Descriptions are shown in the official language in which they were submitted.
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The present inyention relates to a toner powder suitable for
developing latent electrostatic images and which can be fixed by heat,
essentially comprising finely divided coloured toner particles which include
thermoplastic material, colouring constituents and if desired a charge
regulator. The invention more particularly relates to a toner powder whose
thermoplastic material mainly comprises epoxy resin, whose original epoxy
groups have been blocked in a given manner and in a given percentage. The
invention also relates to a process for the preparation of such a toner powder,
a two-component developer containing such a toner powder and a single-
component developer containing such a toner powder.
Toner powders are widely used in the form of so-called single
and two-component developers for making visible latent electrostatic images
of the type formed on a suitable surface in electrography or electrophoto-
graphy.
Two-component developers have a toner powder whose toner particles
contain an insulating thermoplastic material mixed with relatively large
carrier particles. By contact with or friction against the carrier particles
the toner particles receive an electrostatic charge and consequently adhere
to the carrier particles. In general toner and carrier particles are matched
to one another in such a way that the toner particles assume a charge having
an opposite polarity to the latent electrostatic image to be developed.
When the developer is brought into contact with the image the toner particles
are torn loose from the c~rrier particles by the electrostatic charge of the
image and are deposited on the latent image so that it is rendered visible.
Examples of suitable carrier particles are~ inter alia, pulverulent
metal such as iron or nickel, metal oxide such as chromium oxide or aluminium
oxide and glass, sand or quartz. In practice, metal carrier particles,
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particularly iron particles, are widely used. Iron particles are in ~act
often used in powder developers for so-called magnetic brush developing in
which the developer is transferred to the electrostatic image to be developed
with magnetic transfer means in the form of a rotary powder brush.
Developers of the single-component type comprise a toner powder
which is either insulating or virtually insulating, i.e., it generally has a
specific resistance of >1012~ cm or is made conductive by applying finely
divided electrically conductive material to the surface of the powder grains
or homogeneously distributing same therein, so that its resistance is generally
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well below 10 ~ cm. Such developers are generally applied to the latent
image to be developed with the aid of a magnetic brush developer system. In
that case the toner powder contains a magnetisable iron pigment which can.
also serve as a dye.
Carbon black is generally added to the thermoplastic material
as the colouring constituent in the c~se of black toner powders, whereas
organic dyes are added in the case of coloured toner powders, e.g. for use in
electrographic multi-colour reproduction processes. Knot~ natural or
synthetic polymers or resins are used as the thermoplastic material. Examples
of suitable thermoplastic materials are polystyrene, copol~ners of styrene
with an acrylate and/or methacrylate, polyamides, modified phenol-formaldehyde
resins, polyester resins and epoxy resins.
The powder image formed during developing is fixed in the following
way. The procedure can take place directly on the surface on which it is
formed or after transfer to another receiving surface. Fixing generally takes
place by heating with the aid of r~diant heat or by a combination of heating
and pressure in a so-called contact fixing apparatus, the powder image being
bro~ht into contact with a heated surface such as a roller and/or belt.
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Toner powders mainly comprising epoxy resin whose original epoxy
groups have been blocked in a given way and in a given percentage are described
in the Applicant's Canadian Application Serial No. 277,8G2. The toner
powders described therein consist of at least 50% epoxy resin having an
epoxy molar mass of at least 10,000 achieved by blocking its original epoxy
groups partly by chemical reaction with a monofunctional carboxyllc acid
and/or a monofunctional phenol and partly by linking or bonding by means
of an intermolecular reaction or by means of a polyfunctional epoxy hardener.
By epoxy molar mass is meant the mass of resin in grams which contains one
gram equivalent of epoxy ~see pages 4-14 of "Handbook of Epoxy Resins" by
Lee and Neville, McGraw Hill Book Company, 1967).
The above-mentioned toner powders would appear to satisfy the
main requirements of a toner powder such as clearly defined polarity, good
eharge eharacteristies, adequate ehargeability, uniform eharge distribution,
charging stability and low light and temperature sensitivity, good fixing
properties, easily reprodueible fixing eharacteristics, thermal stability
and good per~anenee during prolonged use.
me glass transition temperature (Tg) and the position of the
melting range of the toner powder ean be signifieantly reduced by adding
eompounds sueh as those referred to in the Applicant's previously published
Dutch Patent Application 74.15325 as co-solvents, i.e., agents for aiding
the dissolving of given dyes in epoxy resins~during the preparation of the
toner powders described in the Applicant's Canadian Application Serial No.
277,802. In this way it is possible to obtain toner powders whose Tg is only
just above the mjnimum limit required for satisfactory use, generally
between 45 and 55C, whilst the lo~erlimit of their melting range starts
~ust above the Tg. Such toner powders can be satisfactorily rapidly fixed
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by a minimum of heat which results in important practical advantages.
However, the Applicant has found that the use of the above co-
solvents for the indicated purpose leads to a number of less desirable
secondary phenomena.
Even during the preparation of the toner powder to which the co-
solvent is added a not inconsiderable proportion thereof evaporates.
Furthermore, during the time the toner powder is in the copying apparatus
some of the co-solvent in the toner powder evaporates, resulting in a danger
of migration by the charge regulator and dirtying of the copying apparatus
and carrier particles.
The present invention provides toner powders based on blocked
epoxy resin having a low Tg and whose melting range starts just above the Tg,
without it being necessary to use a co-solvent and thus avoiding the above
disadvantages.
According to the present invention there is provided a heat-fixable
toner powder for developing latent electrostatic images which powder
comprises finely divided toner particles comprising
colouring constituents, and
thermoplastic material substantially comprising epoxy resin having
an epoxy molar mass (grams resin/grams equivalent of epoxy) ranging between
approximately 2,000 and 7,500,
the epoxy resin comprising
~a) a modified epoxy resin (A) obtained by blocking the epoxy groups
of an epoxy resin starting material (A') having a molar mass of a maximum of
approximately 1,000 and an epoxy molar mass of a maximum of approximately
700, in a proportion of approximately 25~95% by chemical reaction with one or
a combination of monofunctional reactants selected from the group consisting
of carboxylic acid, phenolic compounds and diaryl sulphonamide, and in
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a proportion of approximately 5-75% by intermolecular reaction with the
hydroxyl groups of the epoxy resin starting material (A') and/or by reaction
with an epoxy hardener, or
(b) a mixture of at least 20 parts by weight of the modified epoxy
resin (A) with a maximum of 80 parts by weight of a phenoxy resin and/or a
modified epoxy resin ~B) obtained by an at least 5% blocking of the epoxy
groups of an epoxy resin starting material (B') having a molar mass of at least
approximately 1,500 and an epoxy molar mass of at least approximately 900
by intermolecular reaction and/or by reaction with an epoxy hardener.
In the present invention the term epoxy resin is understood to
mean condensation products of a polyphenol, particularly bisphenol, with a
halohydrin and in particular epichlorohydrin. The term phenoxy resins refers
to products of the epoxy resin type in the preparation of which 4,4'-isopropy-
lidene-diphenol is used as the bifunctional epoxy hardener. In general they
have a linear structure and a molar mass between 10,000 and 80,000. One
commercially available phenoxy resin is Rùtapox 0717* (molar mass of 30,000)
of Messrs. Bakelite.
Examples of epoxy resins with a molar mass of a maximum of
l,000 and an epoxy molar mass of a maximum of 700 suitable for producing
the toner powder according to the invention are Epikote 1002* ~average molar
mass hereinafter M.M., of 1050 and epoxy molar mass hereinafter E.M.M. of 575-
700), Epikote 1001* (M.M. 900, E.M.M. 450-500), Epikote 828* (M.M. 370,
E.M.M. 184-194) and Epikote 827* (M.M. 360, E.M.M. 180-190).
Examples of epoxy resins with an M.M. of at least approximately 1,500
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and an E.M.M. of at least approximately 900 suitable for producing a toner
powder according to the invention are Epikote 1004~ (M.M. lLI00, E.M.M. 850-
940), Epikote 1006~ (M.M. 2,800, E.M.M. 1550-19nO) and Epikote 1009~ (M.M.
3750, E.M.M. 2300-3400). Epikote is a Shell trade mark and the M.M. and
E.M.M. values were supplied by the manufacturer.
In the preparation of a ~ner powder according to the invention
preference is given to the use of a modified epoxy resin obtained by blocking
the epoxy groups of a liquid epoxy resin with an M.M. of a maximum of
approxi~ately 500 and a~ E.M.M. of a maximum of approxi~ately 300 in a proportion
of approximately 50-95% by chemical reaction with a monofunctional carboxylic
acid, phenol or diaryl sulphonamide and in a proportion of approximately 5-50%
by bonding or linking by means of intermolecular reaction and~or an epoxy
hardener.
In this way it is possible to obtain toner powders whose Tg is between
appro.ximately 45 and 55C and having a wide melting range beginning immediatelyabove the Iatter value, preferably after mixing the modified epoxy resin described
above with phenoxy resin and/or with a modified epoxy resin obtained by blockingthe epoxy groups of an epoxy resin with an M.M. of at least approximately
2,500 and an E.M.M. of at least approximately 2,000 to a minimum extent of 5%
by linking and/or bonding by means of intermolecular reaction and~or an epoxy
hardener.
Such toner powders are particularly suitable for use in a high volume
copying apparatus with a contact fixing device. Compared with conventional
toners such as for example, toners based on styrene-acrylate polymers, they
can be excellently fixed at an extremely low temperature in a few hundredths
of a second.
The mono~unctional carboxylic acids, phenols or aryl sulphonamides
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used for blocking the epoxy resin or resins chosen as the starting product
must, apart from ~he carboxyl, hydroxy or amide group, contain no further
substituents which, under the conditions prevailing during the modification
process, can react with the reactive groups of the epoxy resin.
Carboxylic acids which can be used ~rith particular advantage are
aromatic carboxylic acids such as benzoic acid and those substituted by one
or more alkyl, aralkyl, cycloaIkyl, aryl, alkylaryl, alkoxy or aryloxy groups
and which under the conditions during modification are not or are scarcely
volatile. Exa~lples of such carboxylic acids are 2,4-dimethylbenzoic acid,
4-(~,~-dimethylbenzyl?-benzoic acid, 4-phenylbenzoic acid and 4-ethoxy-benzoic
acid. However, it is also possible to use aliphatic carboxylic acids such
as heptanoic, nonanoic, dodecanoic, isododecanoic, hexadecanoic and octa-
decanoic acids.
Examples of suitable phenol compounds are 4-n-butylphenol, 4-n-
pentylphenol, 2,3,4,6-tetramethylphenol, 2,3,5,6-tetramethylphenol, 4-(~
dimethyl)-benzylphenol, 4-cyclohexylphenol, 3-methoxyphenol, 4-methoxyphenol
and 4-ethoxyphenol. Of the above compounds, particular preference is given
to unsubstituted benzoic acid and 4~ -dimethyl)-benzylphenol.
Examples of suitable diaryl-sulphonamides are benzene-sulphonanilide
and derivatives thereof, such as those in which one or two benzene nuclei
carry one or more lower alkyl or alkoxy groups.
Although it is possible to separately block the epoxy resins chosen
as - starting products and then to prepare the toner powder with the aid of
modified epoxy resin or mixtures of modified epoxy resins thus obtained~
the blocking can however also take place during the preparation of the toner
pot~der, which leads to considerable time and t work ~avings. It has been
found that the blocking process can easily be kept under control and can be
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regulated as required. In this way it is possible to obtain a tailor-made
toner powder of particularly good quality. Another advantage of such a com-
bined preparation process is that when it is desired to prepare a toner
powder with a positive charge regulator of the amine type, in m~ny cases the
positive charge regulator can also serve to ensure a correct performance of
the blocking, thus obviating the necessit~ of a separate catalyst or any
other additions.
The toner powder according to the invention can be prepared with
the aid of methods generally known for the purpose of preparing toner powders
e.g. kneading extrusion or hot melting methods.
In the first two of these methods the resin, the colouring constituents,
and if desired other constituents, such as a charge regulator, can be mixed
together at temperatures of about 90-130C, whereas in the latter method
temperatures of about 150 to 250C are used. After cooling, the material
is ground into particles of the desired fineness, usually 2-50 ~m.
Of the three above-defined preparation methods, the hot melting
method has proved most suitable for the preparation of the toner powder accord-
ing to the invention, particularly if the blocking reactions are to take place
during the preparation of the toner powder, which is advantageous for the
reasons given hereinbefore. The toner powder prepared by this preferred
method appears to have even better properties than when the other two methods
are used and this particularly applies to the quality and reproducibility of
the charging, stability and fixing behaviour. This is helped by the fact that
with the preferred method it is easily possible to control and regulate the
tèmperatures and residence times.
If it is desired to prepare a toner powder whose modified epoxy
resin is obtained by starting partly with a liquid epoxy resin and partly with
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a solid epoxy resin, the two resins can be mixed together before performing
the blocking reaction. However, it is also possible in a first step to block
a certain proportion of the ultimately desired percentage and preferably
at least 70-80% thereof of the epoxy groups of the liquid epoxy resin chosen
as the starting material by reaction with one of the above-mentioned mono-
~unctional blocking agents, preferably in combination with the intermolecular
reaction. After this the solid epoxy resin or the mixture of epoxy resins
selected as the starting material or materials are added and blocking is per-
mitted to take place to the final desired percentage in a second step. m e
other desired constituentsare preferably added in the first step in order
to obtain maximum homogeneity of mixing.
~ le toner powders according to the invention generally charge in a
sufficiently negative manner with respect to conventional carriers such as e.g.
iron powder or iron-coa~ed powder, so that there is no need to add a charge
regulator for this purpose. However, if desired a negative charge regulator
can be added. A compound which can be used for this purpose is e.g. Atlac
382E (poly-4,4'-isopropylidene-diphenyl-propylene-oxide-fumarate), a trade
nark of Atlas Company.
m e toner powder can be mixed with special carriers known for this
purpose in order to obtain a two-component developer in which the toner powder
according to the invention acquires a positive charge. Such carriers are,
for example, described in British Patents Nos. 1,251,752; 1,342,748; 1,373,
000, 1,389,744 and 1,438,973.
Whenever the toner powder according to the invention is mixed with
a conventional carrier such as iron, nickel, metal oxide, glass, sand or quartz,
the powder must contain a positive charge regulator in order ror it to have
a sufficiently positive chargeability. For this purpose it is possible to use
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one of the conventional positi~e charge re~ukators, the best known of which
are ~igrosine base and Nigrosine-hydrochloride. HoT~Iever, the preferred
positive charge regulator for the toner FoW~er according to the invention is
an epoxy amine which is the chemical reaction product of an epoxy resin with
a basic amine.
One of the many types of commercially available epoxy resins can be
used in the preparation of such epoxy amines.
Ihe epoxy resin chosen as the starting resin preferably has an
M.M. of max. 1, 500 and an E.M.M. between 150 and 1,000, examples of such
commercial products being Epikote 828, 1001 and 1004~. The epoxy resin chosen
as the starting resin is reacted with a basicamine, which must be a primary
or a secondary mono- or polyfunctiona~ amine with a pKa-value ~ 3, and prefer-
ably between 8 and 11. The functionality of an amine is determined by the
number of hydrogen atoms on basic nitrogen atoms in the molecule. For the
meaning of the pKa - value, reference should be made to the book "Dissociation
Constants of Organic Bases in Aqueous Solution" by the International Union of
Pure and Applied Chemistry, 1965 Edition~ pages 1 and 2.
An additional advantage of using an epoxy amine as the positive
charge regulator is that by choosing a starting amine with a given pKa - value
it is possible to control the chargeability of the toner resin prepared with
it within certain limits. This leads to a greater freedom in the choice of
the carrier to be used in the developer and an increasing need is being found
for this.
In the preparation of the epoxy amine preference is given to the
use of substituted or unsubstituted low molecular weight aliphatic amines as
well as cycloaliphatic and heterocyclic amines. E~amples of advantageously
Usable unsubstituted monofunctional aliphatic amines are dipropyl, diisopropyl~
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dibutyl, dipentyl and dihexyl amines. P~rticularly good res~lts are obtained
with aliphatic hydroxy-alkylamines and in particular 2-methylamino-ethanol
and 2,2'-imino-diethanol. Examples of successf'ully tested polyfunctional amines
are 2-amino-ethanol, ethylene-diamine, diethylene-triamine and 2,2'-(ethylene-
diimino ) -diethanol .
me epoxy amines can be readily mixed with the toner resin due to
their structure being closely related to the modified epoxy resin and reveal
virtually no migration tendency. As a result the -toner powder prepared there-
with has a good uniform charge'ability and a good chargingstability. In view
of the fact that they are also virtually colourless, it is possible to prepare
therewith positively chargeable toner powders in any desired colour.
The quantitites of epoxy arnine to be used are generally between
0.01 and 1 equivalent base ~g of toner, being inter alia dependent on the
carrier to be used in the developer together with the toner powder. With the
hitherto used carriers the desired charging level is obtained in most cases
if between 0.025 and 0.25 equivalent base in the form of an epoxy amine is
present per kg of toner powder.
The toner powder according to the invention can also be used as
a single-component developer~'that is without carrier, for the purpose of
so-called unitary developing. Preferably there is then utili~ed the magnetic
brush developing method in which the toner powder is applied to the surface
to be developed by a powder brush formed on the rotary outer surface of a
developing roller having a ma~netic core. For this purpose finely divided
magnetisable material such as iron particles are homogeneously dispersed
in the toner particles. Said material is genercilly intimately mixed with the
toner resin during the preparation of the toner powder when it is still in the
liquid phase. Iron powder generally represents 30 to 80% by weight based on
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the resin.
A positive charge regulator is added to the toner powder for use in
developing negative electrostatic images.
The invention is further illustrated hereinafter by means of non-
limitative Examples.
Example 1
The following constituents are successively introduced into a mixing
kettle equipped with a stirrer and oil bath heating;
22.0 g of Epikote 828~ (E.M.M. = 185)
19.0 g of 4- a~a-dimethylbenzyl phenol
6.o g of a reaction product of Epikote 1001* with 2-methylamino-
ethanol as the positive charge regulator
6.0 g of carbon.
The mixture was then heated to 180C and stirred at thistemperature for 90 minutes. The phenolic blocking agent quantitatively
reacted with the epoxy resin, the residue being smaller than 0.1%. The E.M.M.
of the mixture was 3800, meaning that about 88% of the epoxy groups had
reacted. 47.0 g of Epikote 1009* (E.M.M. = 3150) was added and stirring
continued for 90 minutes at 200C. The E.M.M. of the mixture was now 4250,
meaning that about 82% of all the epoxy groups of the two epoxy resins had
reacted. m e cooled charge was ground and sieved giving particles in the
range approximately 8 to 24 ~m. The glass transition temperature (Tg) was
51C determined from the D.S.C.-thermogram recorded with the Du Pont 990
thermal analyzer. 4 parts of toner were mi~ed with 96 parts of oxidised iron
powder. m e charge was ~ 15uC/g and the permanence was > 100,000 copies.
When using the toner in a copying apparatus under practical conditions, there
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were not found to ~e any disadyantageous characteristics ~Ihich could beattributed to the presence of free epoxy groups.
The toner had a very fabourable fixing behaviour.
When used in a copying apparatus with a contact fixing device
provided with a silicone rubber-covered roller whose top coating had been
previously aged(hereinafter referred to as measuring arrangement A), a fixing
ran~e of 75 - 103C (28C) was found in the case of an effective contact time
i of 1.6 seconds. The lower limit of the fixing range is the temperature at
which the image is just adequately fixed. me upper limit is the temperature
at which so-called offset images first occur by transferring the image to the
fixing roller and from there back to the paper. The fixing range of a commercially
available toner powder based on styrene-butylacrylate copolymer was 102 -
133C.
m e toner powder prepared in the m~nner described hereinbefore
was per~ectly fixed in a contact fixing apparatus whose silicone rubber roller
was covered with a thin coating of silicone oil (hereinafter referred to as
measuring arranbement B) with an effective contact time of 0,03 seconds and
a contact roller temperature of 165C. A contact roller temperature of
210C was necessary to fix the prior art styrene-butylacrylate copolymer-
based toner powder in the same time.
Example 2
e process of Example 1 was repeated but in this case 47 g ofEpikote 1006* (E.M.M. = 1690) was used instead of Epikote 1009.
m e mixing time was 160 minutes and the Tg was 53C.
m e E.M.M. of the toner mixture was 5070 (87% of the epoxy groups
had reacted).
me characteristics of the toner were in accordance with those
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of Example 1.
Exam~le 3
Example 1 was repeated but in tnis case benzoic acid was used as
the blocking agent inst,ead of 4-a,a-dimethylbenzyl phenol. me mixing time
after adding the Epikote 1009~ was 40 minutes.
Ingredients:
26.0 g of Epikote 828-~ (E.M.M. = 185
12.0 g of benzoic acid
6.o g of Epilcote 1001~/2-methylamino-ethanol reaction product
6.o g of carbon
50.0 g of Epikote 1009~ (E.M.M. = 3150)
me Tg was 49C. rhe E.M.M. was 5600 (i.e. 88% of the epoxy groups
had reac`ted).
rhe melting range in measuring arrangement A was 88 - 122C
(34C).
m e lower limit in measuring arrangement B was 171C.
In a developer as described in E,cample 1 the toner polarity was
positive.
Exam~le 4
A mixture of:
28.7 g of Epikote 828~ (E.M.M. = 185)
24.3 g of 4-a~a-dimethylbenzyl phenol
6.0 g of Epikote 1001'~/2-methylamino-ethanol reaction product
were heated for 90 minutes accompanied by stirring at 180C, after which 41.0
g of Epikote 1009~ (E.M.M. = 3150) were added and mixing continued for 360
minutes at 200 C. m e charge was tra~sferred into a laboratory kneader
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and was mixed at the kneading e~uilibriu~ te~erature for 60 minutes with 100
g of magnetite (pigment).
The cooled charge was then ground,subjected to a per se known thermal
finishing treatment and sieved to a particle size distribution between
approximately 10 and 30 llm. The single-component toner can be used in
advantageous manner for developing negatively charged photoconductors (inter
alia those based on Zno) and can be fixed on plain paper with the fixing
arrangement specified in Example 1 (1.6 seconds contact time) between 93 and
125C.
The toner Tg was 47C.
The E.M.M., based on the organic substance (excluding magnetite)
was 5100, i.e., 88% of the epoxy groups had reacted.
Example 5
Example 1 was repeated but with the following ingredients:
25.3 g Or Epikote 828~ (E.M.M. = 185)
21.7 g of 4~ dimethylbenzyl phenol
0.5 g of tetramethyl ammonium chloride
6.o g of carbon
46.5 g of Epikote 1009~ (E.M.M. = 3150)
The thermal characteristics of the toner were approximately the
same as those of the toner of Example 1. The toner was given a negative
polarity when mixed with thermally blued iron powder in a ratio of 96 g iron:
4 g toner.
The Tg was 52C and the E.M.M. 4100.
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Example 6
A toner powder was prepared by mixing during 90 minutes in a
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mixing vessel:
45.4 g of hpikote 1001~ (E.M.M. = 495)
12.6 g of 4~ -dimethylbenzyl phenol
6.0 g of a reaction product of Epikote 1001~ with
2-methylamino-ethanol
8.o g of carbon.
Thereafter were added:
28.0 g of Epikote 1009~ (E.M.M. = 3500) and subsequently the
mixture was stirred at 200C for another 90 minutes. After cooling the charge
was ground and sieved giving particles in the range approximately 8 to 25 ~m.
me Tg was 63C and the E.M.M. = 5400 indicating that about 79% of the
original epoxy groups originally present in the starting ma-terial had been
blocked.
A developing powder comprising 4% by wt. of the toner powder so
prepared in admixture with 96% by wt. of an iron powder produced good copies
and showed a high permanence during prolonged use. m e toner powder could
be fixed at relatively low temperatures and had a high powder stability.
Example 7
Example 1 was repeated, but omitting the blocking agent 4~
dimethylbenzyl phenol. After mixing for two hours a rubbery mixture was
obtained which could not be ground and was no longer fixable.
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