Technical Field
[0001] The present invention relates to heat-sensitive recording paper and more specifically
to heat-sensitive recording paper which is cheap and excellent in storage stability
and which has high reliability to the thermal head. Background Art
[0002] The heat-sensitive recording system which makes use of a basic colorless dye and
an acidic substance capable of causing the color-development of the basic colorless
dye upon heating shows various characteristic properties. For instance, the system
does not require the use of any developing process and the maintenance of the hard
thereof is very easy. For this reason, such a heat-sensitive recording system has
widely been used in a variety of fields such as facsimiles, printers and recorders
for measuring machinery and tools.
[0003] As substrates for the heat-sensitive recording paper, there have presently been used
wood-free paper which does not contain any waste paper, but it is assumed that the
waste paper will be more frequently used in the substrates for the heat-sensitive
recording paper because of the increasing demand for the reduction in the cost of
the heat-sensitive recording paper and reuse or recycling of paper-making pulp.
[0004] Incidentally, when waste paper is incorporated into the substrates for the heat-sensitive
recording paper, the resulting recording paper suffers from a variety of problems.
For instance, the color-printing density thereof is reduced (discoloration) during
storage under a high humidity condition, fogging of the white ground thereof is caused
during storage under a high temperature condition and further when a long term running
test is performed, there is observed the dot-missing of a thermal head (partial breakage
of the thermal head).
[0005] Accordingly, the object of the present invention is to provide heat-sensitive recording
paper which is cheap, makes it possible to save resources, is excellent in storage
stability and exhibits high reliability to the thermal head.
[0006] The inventors of this invention have conducted various studies to achieve the foregoing
object and as a result have found out that the aforementioned object of the present
invention can effectively be achieved if the amount of the surfactants remaining in
a substrate for heat-sensitive recording paper can be reduced to a level of not more
than 1,000 ppm in the case where the substrates for the heat-sensitive recording paper
comprise waste paper. Moreover, the inventors have also found out that a more excellent
effect can be attained by disposing a barrier layer between the foregoing substrate
and a heat-sensitive recording layer.
[0007] In general, waste paper is prepared according to any combination of the following
three processes:
(1) Defibration Process · · · · waste paper is treated mechanically and with a chemical
to loosen into fibrous state and to thus peel off printing ink from the fibers.
(2) Process for Removing Dusts · · · · foreign substances (such as plastics) and dusts
are removed.
(3) Process for Deinking · · · · the printing ink peeled off from the fibers is removed
outside the system according to a floatation method or a washing method.
[0008] If the waste paper thus obtained is simply incorporated into a substrate for the
heat-sensitive recording paper, the resulting recording paper is greatly affected
by surfactants as deinking agents which are used in the foregoing deinking process
(3). Thus, the recording paper causes discoloration during storage under a high humidity
condition, fogging of the white ground thereof during storage under a high temperature
condition and the dot-missing of the thermal head. The inventors of this invention
have investigated the influence of these surfactants on the properties of the substrate
containing the waste paper and have found out that if the deinking agent comprises,
for instance, nonionic surfactants such as polyoxyethylene alkyl phenyl ethers, polyoxyethylene
alkyl ethers or polyoxyethylene polyoxypropylene block polymers; or cationic surfactants
such as quaternary ammonium salts, alkyltrimethylammonium chloride, cetyltrimethylammonium
chloride and alkylbenzylmethylammonium chloride, the substrate containing the waste
paper causes discoloration during storage under a high humidity condition and fogging
of the white ground thereof during storage under a high temperature condition, while
if the deinking agent comprises, for instance, anionic surfactants such as fatty acid
soaps, alkylbenzenesulfonic acid salts, salts of higher alcohol sulfuric acid ester,
α-olefinsulfonates and dialkylsulfosuccinates, the reliability of the substrate to
the thermal head is greatly impaired. The present invention has been completed on
the basis of the foregoing findings.
[0009] Consequently, the present invention relates to heat-sensitive recording paper which
comprises a substrate provided thereon with a heat-sensitive recording layer, which
comprises a basic colorless dye and an acidic substance capable of color-developing
the basic colorless dye upon heating, wherein the substrate comprises waste paper
and the amount of surfactants remaining in the substrate is controlled to not more
than 1,000 ppm.
[0010] The present invention will hereinafter be explained in more detail.
[0011] In the heat-sensitive recording paper, there is used a substrate comprising waste
paper.
[0012] The term "waste papers" is a generic name which enbraces used paper, paper board
or cutting scraps thereof.
[0013] The substrate used in the present invention may be completely composed of waste paper,
but it preferably comprises waste paper in an amount of not more than 60%. If the
waste paper is incorporated into the substrate in an amount of greater than 60%, the
strength of the substrate is liable to be impaired and it is apt to cause a decrease
in whiteness.
[0014] In addition, the content of the surfactants remaining in the substrate must be in
general controlled to not more than 1,000 ppm and preferably not more than 800 ppm.
The storage stability of the substrate is impaired and the dot-missing of the thermal
head is apt to cause as the content of the remaining surfactants increases.
[0015] As the basic colorless dyes which may be used in the heat-sensitive recording paper
of the present invention, there may be mentioned, for instance, triarylmethane type
dyes such as 3,3-bis(p-dimethylaminophenyl)- 6-dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)phthalide,
3-(p-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(2-methylindol-3-yl)phthalide,
3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide, 3,3-bis(1,2-dimethylindol-3-yl)-6-dimethylaminophthalide,
3,3-bis(9-ethylcarbazol-3-yl)-6-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl)-6-dimethylaminophthalide
and 3-p-dimethylaminophenyl-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide; diphenylmethane
type dyes such as 4,4' -bis-dimethylaminobenzhydryl benzyl ether, N-halophenyl-leucoauramine
and N-2,4,5-trichlorophenyl leucoauramine; thiazine type dyes such as benzoyl leucomethylene
blue and p-nitrobenzoyl leucomethylene blue; spiro type dyes such as 3-methyl-spiro-dinaphthopyran,
3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran,
3-methyl-naphtho(6'-methoxybenzo)spiropyran and 3-propyl-spiro-dibenzopyran; lactam
type dyes such as rhodamine-B-anilinolactam, rhodamine(p-nitroanilino)lactam and rhodamine(o-chloroanilino)lactam;
and fluoran type dyes such as 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran,
3-diethylamino-7-methoxyfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran,
3-diethylamino-6,7-dimethylfluoran, 3-(N-ethyl-p-toluidino)-7-methylfluoran, 3-diethylamino-7-N-acetyl-N-methylaminofluoran,
3-diethylamino-7-N-methylaminofluoran, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-N-methyl-N-benzylaminofluoran,
3-diethylamino-7-N-chloroethyl-N-methylaminofluora n, 3-diethylamino-7-N-diethylaminofluoran,
3-(N-ethyl-p-toluidino)-6-methyl-7-phenylaminofluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluoran,
3-diethylamino-6-methyl-7-phenylaminofluoran, 3-diethylamino-7-(2-carbomethoxy-phenylamino)fluoran,
3-(N-ethyl-N-isoamylamino)-6-methyl-7-phenylaminofluoran, 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran,
3-pyrrolidino-6-methyl-7-phenylaminofluoran, 3-piperidino-6-methyl-7-phenylaminofluoran,
3-diethylamino-6-methyl-7-xylidinofluoran, 3-diethylamino-7-(o-chlorophenylamino)fluoran,
3-dibutylamino-7-(o-chlorophenylamino) fluoran, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluoran,
3-diethylamino-6-methyl-7-anilinofluoran, 3-butylamino-6-methyl-7-anilinofluoran and
3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran.
[0016] As the inorganic or organic acidic substance capable of color-developing the basic
colorless dyes by heating, a variety of compounds have been known and examples thereof
include inorganic acidic substances such as active china clay, acidic china clay,
attapulgite, bentonite, colloidal silica and aluminum silicate; and organic acidic
compounds, for instance, phenolic compounds such as 4-tert-butylphenol, 4-hydroxydiphenoxide,
α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4-tert-octylcatechol, 2,2'-dihydroxydiphenol,
2, 2'-methylenebis (4-methyl-6-tert-isobutylphenol), 4,4'-isopropylidenebis(2-tert-butylphenol),
4,4'-sec-butylidenephenol, 4-phenylphenol, 4,4'-isopropylidenediphenol (bisphenol
A), 2,2'-methylenebis(4-chlorophenol), hydroquinone, 4,4'-cyclohexylidenediphe nol,
benzyl 4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, hydroquinone monobenzyl ether,
novolak type phenol resin and phenolic polymer; aromatic carboxylic acids such as
benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid,
3-sec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic
acid, salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic
acid, 3-(α-methylbenzyl)salicylic acid, 3-chloro-5-(α-methylbenzyl)salicylic acid,
3,5-di-tert-butylsalicylic acid, 3-phenyl-5-( α, α-dimethylbenzyl)salicylic acid and
3,5-di-α-methylbenzylsalicylic acid; and salts of these phenolic compounds or aromatic
carboxylic acids with multivalent metals such as zinc, magnesium, aluminum, calcium,
titanium, manganese, tin and nickel.
[0017] The ratio of the amount of the basic colorless dye to that of the acidic substance
in the heat-sensitive recording layer is appropriately selected depending on the kinds
of these basic colorless dyes and the acidic substances employed, but in general the
acidic substance is used in an amount ranging from 1 to 50 parts by weight and preferably
in the order of 1 to 10 parts by weight per 1 part by weight of the basic colorless
dye.
[0018] A coating solution containing these substances is prepared by simultaneously or separately
dispersing the basic colorless dye and the acidic substance in a dispersion medium
which is usually water utilizing an apparatus for agitation · pulverization such as
a ball mill, an attritor and a sand grinder to thus give a coating solution. In this
case, the particle size of the dispersed particles are desirably as small as possible
and more specifically this dispersion process is desirably continued till the size
of the dispersed particles reaches not more than 2µm.
[0019] Such a coating solution may comprise, as an adhesive, starches, hydroxyethyl cellulose,
methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl
alcohol, salts of diisobutylene · maleic anhydride copolymers, salts of styrene ·
maleic anhydride copolymers, salts of ethylene· acrylic acid copolymers, salts of
styrene · acrylic acid copolymers and styrene · butadiene copolymer emulsion in an
amount ranging from 10 to 40% by weight and preferably 15 to 30% by weight on the
basis of the total weight of the solid content of the solution.
[0020] In addition, the coating solution may further comprise a variety of auxiliary agents,
for instance, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate,
lauryl alcohol sulfuric acid ester·
sodium salts, alginic acid salts and metal salts of fatty acids; and ultraviolet light
absorbers such as benzophenol type and triazole type ultraviolet light absorbers;
as well as other additives such as antifoaming agents, fluorescent dyes and coloring
dyes.
[0021] Moreover, it is also possible to optionally add, to the coating solution, for instance,
lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax,
paraffin wax and ester wax; inorganic pigments such as kaolin, clay, talc, cacium
carbonate, calcined clay, titanium oxide, diatomaceous earth, finely pulverized anhydrous
silica and active china clay; sensitizing agents such as stearic acid amide, stearic
acid methylenebisamide, oleic acid amide, palmitic acid amide, sperm oil oleic acid
amide, coconut oil fatty acid amide, meta-terphenyl, p-benzylbiphenyl, ester derivatives
of hydroxynaphthoic acid, dibenzyl terephthalate and tribenzylamine.
[0022] In the present invention, it is preferred to dispose a barrier layer between the
substrate and the heat-sensitive recording layer. The presence of such a barrier layer
makes it possible to reduce the influence of the surfactants included in the substrate
and to provide an improved heat-sensitive recording paper which does not show any
discoloration and fogging of the white ground during storage and whose reliability
to the thermal head is further enhanced.
[0023] The barrier layer can be formed from, for instance, film-forming polymeric compounds
and examples thereof include casein, polyvinyl alcohol, ammonium alginate, methyl
cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, maleic anhydride copolymers,
styrene · maleic anhydride copolymers and styrene · butadiene copolymers. These polymeric
compounds are in general used in the form of an emulsion. In addition, the amount
thereof to be coated in general ranges from 0.3 g/m² to 5.0 g/m² and preferably 0.5
g/m² to 2.0 g/m². This is because, if the coated amount of the polymer is less than
0.3 g/m², the effect of lowering the influence of the surfactants is impaired, while
if it exceeds5.0 g/m², the resulting images are apt to have insufficient quality.
[0024] Moreover, a protective layer may optionally be applied onto the heat-sensitive recording
layer.
[0025] Furthermore, an intermediate layer containing a pigment may also be applied onto
the foregoing barrier layer. (Examples)
[0026] The present invention will hereinafter be explained in more detail with reference
to the following Examples.
Preparation of Coating Solution for Heat-sensitive Recording Layer
[0027]
[0028] Each of the solutions A and B was dispersed using a sand grinder so that the average
particle size of the dispersed particles therein reached not more than 2 µm.
[0029] The solution C was dispersed with a homomixer for 10 minutes.
[0030] A coating solution for heat-sensitive recording layer was prepared by mixing 54.7
parts by weight of the solution A, 155.3 parts by weight of the solution B and 50
parts by weight of the solution C and then adding, to the resulting mixture, 33.3
parts by weight of a 30% dispersion of zinc stearate, 100 parts by weight of a 12%
aqueous solution of polyvinyl alcohol and 130 parts by weight of water.
Example 1
[0031] The foregoing coating solution for heat-sensitive recording layer was applied onto
base paper having a waste paper content of 40%, an amount of a remaining surfactant
(sodium alkylbenzenesulfonate) of 240 ppm and a basis weight of 50 g/m² so that the
coated amount thereof (weighed after drying) was equal to 5 g/m², dried and further
subjected to calendering to thus give heat-sensitive recording paper whose recording
surface has a Bekk smoothness of 600 seconds.
Example 2
[0032] Heat-sensitive recording paper was prepared in the same manner used in Example 1
except that base paper having a waste paper content of 50%, an amount of a remaining
nonionic surfactant (polyoxyethylene-alkylphenyl ether) of 430 ppm and a basis weight
of 50 g/m² was used as a substrate.
Example 3
[0033] Heat-sensitive recording paper was prepared in the same manner used in Example 1
except that base paper having a waste paper content of 60%, an amount of a remaining
nonionic surfactant (polyoxyethylene-alkylphenyl ether) of 510 ppm and a basis weight
of 50 g/m² was used as a substrate.
Example 4
[0034] Heat-sensitive recording paper was prepared in the same manner used in Example 1
except that base paper having a waste paper content of 50%, an amount of a remaining
cationic surfactant (alkyltrimethyl ammonium chloride) of 700 ppm and a basis weight
of 50 g/m² was used as a substrate.
Example 5
[0035] Heat-sensitive recording paper was prepared in the same manner used in Example 1
except that base paper having a waste paper content of 50%, an amount of a remaining
anionic surfactant (sodium alkylbenzenesulfonate) of 950 ppm and a basis weight of
50 g/m² was used as a substrate.
Comparative Example 1
[0036] Heat-sensitive recording paper was prepared in the same manner used in Example 1
except that base paper having a waste paper content of 50%, an amount of a remaining
anionic surfactant (sodium alkylbenzenesulfonate) of 1200 ppm and a basis weight of
50 g/m² was used as a substrate.
Comparative Example 2
[0037] Heat-sensitive recording paper was prepared in the same manner used in Example 1
except that base paper having a waste paper content of 50%, an amount of a remaining
nonionic surfactant (polyoxyethylene-alkylphenyl ether) of 1400 ppm and a basis weight
of 50 g/m² was used as a substrate.
Comparative Example 3
[0038] Heat-sensitive recording paper was prepared in the same manner used in Example 1
except that base paper having a waste paper content of 50%, an amount of a remaining
cationic surfactant (alkyltrimethyl ammonium chloride) of 1500 ppm and a basis weight
of 50 g/m² was used as a substrate.
Comparative Example 4
[0039] Heat-sensitive recording paper was prepared in the same manner used in Example 1
except that base paper having a waste paper content of 40%, an amount of a remaining
nonionic surfactant (polyoxyethylene-alkylphenyl ether) of 1500 ppm and a basis weight
of 50 g/m² was used as a substrate.
Example 6
[0040] Heat-sensitive recording paper was prepared in the same manner used in Example 4
except that polyvinyl alcohol was applied onto the base paper in an amount of 1 g/m².
Example 7
[0041] Heat-sensitive recording paper was prepared in the same manner used in Example 5
except that polyvinyl alcohol was applied onto the base paper in an amount of 1 g/m².
Example 8
[0042] Heat-sensitive recording paper was prepared in the same manner used in Example 7
except that the amount of polyvinyl alcohol coated was changed to 2 g/m².
[0043] Then the heat-sensitive recording paper obtained in Examples 1 to 8 and Comparative
Examples 1 to 4 were subjected to the following tests and the results thus obtained
were summarized in the following Table 1.
(1) Storability
[0044] A test pattern was printed and recorded on each heat-sensitive recording paper with
a heat-sensitive facsimile FF 621C (available from Fujitsu Limited) and the density
of the white ground and the printed portion thereof were determined by a Mcbeth densitometer
RD-514. Further, the samples which had been printed with the facsimile FF 621C were
used in the following storability test.
a) Resistance to Humidity
[0045] Each sample was stored under a high humidity condition of 40 °C-90% RH for 24 hours
and after the storage, the density of the white ground and the printed portion of
the sample were determined by a Macbeth densitometer RD-514.
b) Heat Resistance
[0046] Each sample was stored under a high temperature and dry condition of 60 °C for 24
hours and after the storage, the density of the white ground and the printed portion
thereof were likewise determined by a Macbeth densitometer RD-514.
(2) Thermal Head Breakage Test
[0047] Each heat-sensitive recording paper was wound around a platen roll, the platen roll
and a thermal head (KJT-216-8MGF1) commercially available from Kyocera Corp. were
fixed (0.15 kgf/cm), stored in an environment of 80 °C-85% RH for 20 hours while applying
a voltage to the thermal head and then subjected to a solid printing operation to
determine the rate of the dot-missing of the thermal head.
Evaluation
[0048]
- ○:
- the rate of the dot-missing is not more than 5%.
- △:
- the rate of the dot-missing is more than 5% and not more than 10%.
- ×:
- the rate of the dot-missing is more than 10%.
[0049] As seen from the results listed in Table 1, improved heat-sensitive recording paper
can be obtained by controlling the amount of the remaining surfactants to not more
than 1,000 ppm, the resulting recording paper being cheap, making it possible to save
resources, being excellent in storage stability and exhibiting high reliability to
the thermal head, though waste paper is incorporated into the substrate of the recording
paper. In addition, it is also found that the quality of the recording paper can further
be improved by disposing a barrier layer between the substrate and the heat-sensitive
recording layer.