JPS6151392A - Stock composition for thermal transfer ink - Google Patents

Abstract

PURPOSE:To reduce the irregularity in the dots of a print image and to enhance the transparency and gloss of said image by preventing the flocculation and destruction of ink at the time of thermal transfer, by uniformly dispersing a colorant comprising pigment and/or a dye throughout heat-meltable ink containing wax as a main component and reducing the size of dispersed particles. CONSTITUTION:10-30pts.wt. of a colorant comprising pigment and/or a dye is mixed with 85-65pts.wt. of an alpha-olefin/maleic anhydride copolymer with an average MW of 2,000-30,000 and a m.p. of 60-90 deg.C, which is obtained by reacting by copolymerizing 20-60C alpha-olefin with maleic anhydride in a mol ratio of 1:1-1.5 and dispersed throughout the copolymer to prepare an ink stock composition which is, in turn, contained in heat-meltable ink in an amount of 30- 50wt%. The content of the ink stock composition occupying the heat-meltable ink is 30-50wt% and the main component of the remainder of 70-50wt% is wax and resin.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ink composition for a thermal transfer recording sheet used in a thermal transfer printer.

[Conventional technology]

In recent years, thermal transfer recording is non-impact and noiseless.

It is used in many fields such as facsimiles, computer terminals, recorders, and printers because it has features such as being maintenance-free, low cost, small and lightweight, and can be printed in color. In particular, the method of energizing thermal transfer using an energizing head is suitable for color recording with intermediate gradations.
This method is becoming more and more popular in the future. For details on current transfer recording, see, for example, "Nikkei Electronics", pages 64-6, June 25 issue, 1979.

The ink for thermal transfer recording sheets used in thermal transfer printers is heat-melting, and in order to achieve a sharp solid-melt-solid phase change during thermal transfer, the main component of the ink composition has traditionally been hydrocarbons. Colorants such as pigments and dyes are dispersed in natural wax or synthetic wax, and some synthetic resins and plasticizers are added to strengthen the film and improve adhesion.

However, it is a very difficult technique to crush and uniformly disperse pigments and dyes into the wax-based ink composition, which is the main component. there were. Traditionally, dispersion machines such as butterfly mixers and planetary mixers have been used to disperse pigments and dyes, but even when attempting to crush pigments and dyes by applying shearing force, the wax molecules tend to be slippery and are uniformly dispersed into a state close to secondary particles. Until recently, it was difficult to disperse pigments and dyes.

Non-uniform dispersion has caused various problems. 1st
The dots represent variations in the density of printed dots. In particular, in the case of full-color printing with intermediate gradations, the image quality is significantly degraded. The second point is that the transparency of the ink is low because the pigments and dyes are not pulverized close to primary particles. In this case as well, the transparency of the full-color print is low, resulting in an image with reduced detection accuracy. The third point is largely due to the non-uniform dispersibility of the agglomerated colorant in the ink. Because the cohesive force is small, cohesive failure occurs within the ink layer during transfer, and part of the ink is transferred to the recording paper, while the rest remains on the base material side of the thermal transfer sheet without being transferred to the recording paper. Put it away. Cohesive failure during transfer has had an adverse effect on image quality, such as causing density spots and significantly reducing the gloss of the print surface.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, the dispersion of pigments and dyes in ink compositions containing wax as a main component is uneven and the dispersed particle size is large, resulting in uneven dots of printed images, transparency, and cohesive failure of ink. , there were problems with gloss, etc.

The present invention is intended to solve these problems, and its purpose is to uniformly disperse pigments and/or dye colorants in hot-melt ink containing wax as a main component, and to disperse them. By reducing the particle size, the purpose is to prevent cohesive failure of the ink during thermal transfer, reduce dot variation in printed images, and improve transparency and gloss.

[Means for solving problems]

The present invention melts the heat-melting material by means of heat generation means,
As an ink raw material composition to be contained in a hot-melt ink to be used in a printer that transfers the ink to a recording paper to obtain a record, 10 to 30 parts by weight of a colorant such as a pigment and/or dye is mixed with a carbon atom having a carbon number of 20 to 60. The average molecular weight obtained by copolymerizing α-olefin and maleic anhydride at a molar ratio of 1:1 to 1.5 is 2.000 to s o, o o o,
α-olefin/maleic anhydride copolymer with a melting point of 60 to 90°C.

This is an ink raw material composition for thermal transfer, characterized in that the ink raw material composition is mixed and dispersed in an amount of 85 to 65 parts by weight, and the heat-melting ink contains 50 to 50% by weight of the ink raw material composition.

[Effect]

In order to uniformly disperse a pigment and/or dye colorant into fine particles, the present invention involves dispersing the colorant in the above-mentioned α-olefin/maleic anhydride copolymer and preparing an ink raw material composition (masterbatch). After that, mix the composition, wax, and some additives as necessary,
The mixture is kneaded to form the final hot-melt ink. It has been discovered that the colorant is very well dispersed in the copolymer described above. It has been discovered that the ink raw material composition thus obtained and the wax are well mixed and kneaded, and the colorant is uniformly dispersed in the final hot-melt ink with a small particle size.

Dispersion of the colorant into the above-mentioned α-olefin/maleic anhydride copolymer can be carried out using a conventional planetary mixer, butterfly mixer, sand mill, tank mixer, attritor, three-roll mill, or the like.

In addition, in the pigment manufacturing process, after manufacturing a filter cake obtained by filtering the aqueous slurry of the pigment without converting the pigment into a dry powder, the filter cake is
Through the so-called flushing step of adding the aforementioned α-olefin/maleic anhydride copolymer and vigorously mixing,
It can be used as the ink raw material composition of the present invention.

α-olefin/maleic anhydride copolymer (hereinafter referred to as MA
The amount of the pigment and/or dye coloring agent dispersed in the MA copolymer is 10 to 60 parts by weight per 85 to 65 parts by weight of the MA copolymer. About 5 parts by weight of plasticizer, viscosity modifier 2 dispersant,
Additives such as cohesive force improvers and adhesives may be added and dispersed.

If the content of the colorant exceeds 60 parts by weight, the dispersibility in the MA copolymer will deteriorate. On the other hand, when the amount of the colorant is less than 10 parts by weight, the dispersibility is good, but since the colorant content is low, wax, resin, etc. may be further added to the ink raw material composition of the present invention for dispersion. The colorant concentration of the final hot-melt ink is insufficient.

The MA copolymer used in the present invention can be obtained by solution polymerization or bulk polymerization in the presence of a radical catalyst by a conventionally known method by a copolymerization reaction of an α-olefin and maleic anhydride. The α-olefin preferably has 20 to 60 carbon atoms and is linear. If the number of carbon atoms is less than 20, the melting point of the MA copolymer will be higher than 90° C., and the viscosity will also be increased, and in printed images having intermediate gradations, dot omission will occur in transfer at low and medium densities. If the number of carbon atoms exceeds 60, the colorant will not be uniformly dispersed in the MA copolymer.

The reaction molar ratio of α-olefin and maleic anhydride is 1:1
~1.5. If the molar ratio of maleic anhydride to α-olefin is less than 1, a portion of the α-olefin remains unreacted, impairing the dispersibility of the colorant. On the other hand, if the molar ratio of maleic anhydride to α-olefin exceeds 1.5, the hue becomes yellow to brown, which adversely affects the hue and detectability of the ink.

The average molecular weight of the MA copolymer (evaluated by the GPO method using a standard polystyrene calibration curve) is 2.000 to 5.
It is 0.000. The average molecular weight is 2. If it is less than Cl00, the cohesive force of the final heat-melting ink will be weak, and the ink will be cut within the ink layer during thermal transfer. On the other hand, the average molecular weight is 30. If OOO is exceeded, the colorant will be poorly dispersed, the final hot-melt ink will have a high viscosity, and some dots will not be transferred.

The melting point of the MA copolymer is 60-90°C. The wax added later to the ink raw material composition of the present invention (D melting point is 6
Since the melting point of the MA copolymer used is in the range of 0 to 90°C, the melting point of the MA copolymer is also in the range of 60 to 90°C.

The content of the ink raw material composition of the present invention in the final hot-melt ink is 60 to 50% by weight.

The remaining 70 to 50% by weight of the main components are wax and arsenic resin. The waxes include clarified wax, microcrystalline wax, carnano wax, oxidized wax, and low molecular weight polyethylene wax, and the wax content in the final ink is 65 to 30% by weight. As a resin component, ethylene/vinyl acetate copolymer (lIfV
A), ethylene/ethyl acrylate copolymer (w x
A) Addition of 5 to 20% by weight of m-polyethylene, polybutyral, polyamide, polyester, etc. improves the cohesive force of the ink.

The thermal transfer ink raw material composition of the present invention has been described in detail above. The present invention will be explained below using examples. Of course,
The present invention is not limited thereby.

〔Example〕

Example 1 Maleic anhydride 401 was added to 300 t of xylene as a solvent to 250 vol of α-olefin of carbon i & 28 to 55,
Pour into a separable flask equipped with a condenser, heat and dissolve at 115°C under nitrogen atmosphere with stirring, and use as a catalyst.
t-butyl-octoacetate)alr was divided into 5 portions, added before the start of the reaction, 1 hour later, and 2 hours later, and the copolymerization reaction was carried out for 5 hours. After the reaction, the reaction was transferred to an evaporator and most of the xylene was distilled off under normal pressure, and then the remaining xylene and maleic anhydride were distilled off under reduced pressure to obtain the α-olefin/maleic anhydride copolymer of 2781 ( This was obtained (abbreviated as MA polymer).

The melting point of the MA copolymer is 75°C (DSC!, heating rate 1
0° C./min), and the average molecular weight was 8,500 (evaluated by GPO method and standard polyethylene calibration curve).

Examples 1 to 2 and Comparative Examples 1 to 6 The MA copolymer obtained in Example 1 was mixed with an organic pigment, phthalocyanine blue (cyan), in the proportions shown in Table 1, and dispersed using a dispersion machine. An ink raw material composition was prepared. As a comparative example, instead of the above MA copolymer, paraffin wax, microcrystalline wax, carnauba wax, oxidized wax (NPS9210 manufactured by Nippon Seiro Co., Ltd.), etc. were mixed with the above pigment and dispersed using a dispersion machine.

For mixing and dispersion, first, a preliminary portion was prepared using a planetary mixer at 120°C for 30 minutes), and after cooling and solidification, it was pulverized and then main dispersion was performed using a three-roll mill (the rear roll and middle roll were Passed 5 times at 70°C, cooling the rear roll with water).

The dispersibility of the dispersion was determined by observing the dispersion state of the pigment and the size of the dispersed particles using an optical microscope on a slide glass. The transparency of the dispersion was determined by applying the dispersion in a hot melt state to a polyester film (10 μm) using a bar coater (
The ink film obtained by elicoating a wire (with a wire diameter of 6 μm) was visually observed.

Comparative Example 1 has excellent dispersibility and transparency, but because the pigment content is low, when this ink raw material composition is later mixed and dispersed with wax to make the final hot-melt ink, the ink The concentration becomes diluted and the mixing ratio cannot be said to be appropriate.

In Table 1, O indicates excellent, Δ indicates medium, and X indicates poor.

Examples 1 and 2 were excellent in both dispersibility and transparency. On the other hand, as shown in Comparative Example 2, when the mixing ratio of pigment to MA copolymer exceeds a certain amount, even if MA
Even when dispersed in a copolymer, the dispersibility is poor and the transparency cannot be said to be excellent.

When the pigment is directly dispersed in carnauba wax (Comparative Example 5) or oxidized wax (Comparative Example 6), the dispersibility and transparency are moderate and inferior to those of the MA copolymer.

When the pigment is directly dispersed in paraffin wax (Comparative Example 5) and microcrystalline wax (Comparative Example 4),
It has very poor dispersibility and is almost impossible to disperse. It is also cloudy and opaque.

Examples 5 to 10 and Comparative Examples 7 to 10 The compositions of Example 2 and Comparative Example 6 were used as ink raw material compositions, and waxes and resins shown in Table 2 were added in various proportions. In addition, Planeta') -Miki-? −(1
The mixture was mixed and kneaded at 2D' (1 hour) to prepare the final hot-melt ink.

The above ink was used as the ink layer 4 of an electrically conductive thermal transfer sheet 1 as shown in FIG. PM! A binder containing carbon black particles is coated on one side of a T-biaxially stretched film (10 μm thick) 5 to form a current-carrying resistance layer 2 (resistance value 7.
5 KΩ/ron was formed, and an ink layer 4 (5 μm thick) was formed on the opposite side of the PET film using a bar coater using the above ink in a hot melt state.

A current-carrying head having a recording electrode 5 and a return electrode 6 was applied to the current-carrying thermal transfer sheet 1 using a thermal transfer paper (TT made by Mitsubishi Paper Industries Co., Ltd.).
Cyan gray scale printing was performed on R).

Head needle width: 60μ full, applied voltage: 25V.

Pulse width modulation; 50 μsec'2 m 5111c.

Regarding printed images, uniformity of dots (optical microscope) Transparency of one image (visual observation) Glossiness of one image (visual inspection) The ink layer is cohesive failure, and some of the dots remain on the transfer paper and the rest remain on the sheet. We observed the presence or absence (optical microscope) of these properties.These characteristic values were excellent.

In Table 2, even with the ink raw material composition of the present invention, when the content in the final ink is small, the characteristic values of the print are inferior in all cases (Comparative Example 7).

On the other hand, if the content of the ink raw material composition exceeds a certain amount, the uniformity and transparency of the dots will deteriorate.

The gloss becomes poor (Comparative Example 8).

When the MA copolymer used in the present invention was not used in the initial pigment dispersion (Comparative Examples 9 and 10), the characteristic values of the prints were all extremely poor.

In Examples 3 to 10, the ink raw material composition of the present invention was prepared using various waxes and resins, and the content of the ink raw material composition was 30%.
The final heat-melting ink was prepared by mixing and kneading to a concentration of ~50% by weight.
The characteristic values of the printed stamp images were all superior to those previously seen.

〔Effect of the invention〕

As described above, an ink raw material composition is prepared by mixing and dispersing a pigment and/or dye coloring agent with a specific α-olefin/maleic anhydride copolymer at a specific ratio, and this composition is used as a wax-based By including a specific amount in the heat-melting ink, the dispersibility of the colorant is made uniform and fine, the dot uniformity, transparency, and gloss of the heat-transferred image are improved, and cohesive failure of the ink is eliminated, etc. It has the effect of

The ink raw material composition for thermal transfer of the present invention can be used for thermal transfer using a conventional thermal head, such as energizing thermal transfer using an energizing head, etc.
Regardless of the principle, it can be applied to any type of printer as long as the principle is to transfer heat-fusible ink onto recording paper using heat application means to obtain a record.

[Brief explanation of the drawing]

FIG. 1 shows the structure of an energized thermal transfer sheet and a diagram of the principle of energizing it by a energizing head. 1; Electric thermal transfer sheet 3; Sheet support layer 4; Hot-melt ink layer 5; Recording electrode 6; Return electrode and above

Claims (1)

[Claims] As an ink raw material composition to be contained in a thermofusible ink to be used in a printer that obtains a record by melting the thermofusible ink using a heat generating means and transferring the ink to a recording paper, a pigment and/or dye colorant, 10- An average molecular weight of 2,000 to 30,000 and a melting point of 60 to 60, obtained by copolymerizing 30 parts by weight of an α-olefin having 20 to 60 carbon atoms and maleic anhydride at a molar ratio of 1:1 to 1.5. α at 90℃
- An ink raw material composition prepared by mixing and dispersing olefin/maleic anhydride copolymer in 85 to 65 parts by weight,
A raw material composition for thermal transfer ink, characterized in that it is contained in a heat-melting ink in an amount of 30 to 50% by weight.