JPH011776A - Thermal transfer dye sheets and supporting substrate coating compositions for their manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to thermal transfer dye sheets for thermal transfer printing and compositions used to coat support substrates in making thermal transfer dye sheets.

Thermal transfer printing is a technique that uses electrical signals to print by heating selected areas of a dye sheet and transferring the dye to an image receiving sheet adjacent to the dye sheet. The heated areas of the thermal transfer sheet are selected according to electrical signals in a suitable transfer printing device and provide individual pixels, which are then joined together to form a print corresponding to said electrical signals. do.

This print can be in the form of recorded data consisting of monochromatic letters, numbers and graphics, for example, but the technique can be applied to any suitable image, such as the signal obtained from a video or electronic still camera, by using a plurality of suitable dyes and small pixels. Color printing can be made from electrical signals.

Generally, thermal transfer dye sheets consist of a support substrate coated with a composition of thermal transferable dye uniformly dispersed in a matrix of binder.

The supporting substrate is usually a thin polymeric film, such as a biaxially oriented polyester film, and the matrix of binder in which the dye is dispersed is typically a silicone or cellulosic material. However, matrices of other binders can also be used. However, dye sheets are produced by co-casing, in which a dye and a binder dissolved in a common solvent are poured together onto the surface of a support film to form a film.
ting) and a sufficiently uniform coating from the beginning.
g), but at least one drawback common to most such coating systems is that the uniformity of the coating is only temporary. After a period of time, the dispersed dye molecules tend to aggregate and form a separate phase in the form of small crystals. This tendency causes the surface of the dye sheet to become rough and the resolution
), but the latter reduction in resolution is only a problem if printing with photographic standard resolution or near-photographic standard resolution is required. A more common problem is that the dye sheet tends to become messy and some of the dye easily rubs off or otherwise falls off and transfers from the dye sheet during handling of the dye sheet. That's what it means.

The present inventors have now found a means to improve coating compositions for thermal transfer dye sheets in order to solve the problems described above.

That is, according to the first aspect of the present invention, in a thermal transfer sheet comprising a support substrate coated with a composition comprising a thermally transferable dye uniformly dispersed in a matrix comprising a polymeric binder, also contains a crystallization inhibitor, and the structure of the crystallization inhibitor includes a polymeric skeleton, and the thermal transferable dye or a substantial portion thereof is attached to the polymeric skeleton. -60, which has a molecular structure formed by chemically bonding a large number of groups having substantially the same shape, charge distribution, and hydrogen bonding pattern as -60 is provided.

According to a second aspect of the present invention, there is provided a composition comprising a thermally transferable dye, a polymeric binder, and a crystallization inhibitor, wherein the molecular structure of the crystallization inhibitor is a polymeric skeleton. and in which a number of groups having substantially the same shape, charge distribution, and hydrogen bonding mode as the thermally transferable dye or a substantial portion thereof are chemically bonded to the polymeric backbone. Provided is a support substrate coating composition for producing a thermal transfer dye sheet, characterized in that the composition has the following characteristics:

The preferred plurality of groups attached to the polymeric backbone of the crystallization inhibitor differ only in the position in which the individual dye molecules are attached to the polymeric backbone; A group that is essentially identical to an individual dye molecule. If the nature of the dye is such that the introduction of some minor substituents does not significantly affect the shape, charge distribution and hydrogen bonding mode or parameters of the dye, the above-mentioned A number of groups can substitute for the dye moiety itself.

The inventors have discovered that even if a small portion of the dye molecule is completely shed, the remaining substantial portion can act to prevent dye crystallization when attached to a polymeric backbone. I discovered that. In other words, in the present invention, from this relationship, the above-mentioned "substantial portion of the dye" refers to a material that mimics the crystallization behavior of the TI-released dye.
ic) refers to the portion of the dye that is sufficient to do so. However, it is particularly advantageous to substituent groups of one of the dyes with other groups of similar shape but different electron affinities, in order to compensate for the change in charge distribution due to the presence of the polymeric backbone. It may be advantageous to introduce instead of one substituent. Furthermore, when a large number of the above-mentioned groups are bonded to a polymer-like skeleton via a flexible bonding group, a greater degree of conformational freedom is obtained than is possible when a large number of groups are bonded directly. However, the effectiveness of doing so will be highly dependent on the matrix of both the polymeric backbone and the groups attached to it.

The inventors have added materials that are compatible with a matrix of polymeric binders containing dispersed dyes to form stable blends. I prefer to select and use it as a skeleton. Although this can provide a high crystallization prevention effect, it does not seem to be necessary to achieve at least some improvement in the coating film regarding the problem of dye molecule aggregation mentioned above. do not have.

A preferred thermal transfer dye sheet of the present invention is one in which the crystallization inhibitor is present in an amount of 0.01 to 10% by weight of the thermal transfer dye.

(Example) The invention will be illustrated by the following examples.

To evaluate the additive materials of the present invention for use as anti-crystallization agents for thermal transfer dye sheets, various dye sheet coating compositions were prepared and compared. In these first series of comparative tests, several different additives were used in varying amounts, but the dyes and binders used were different in order to make accurate comparisons between the different additives. was held constant. That is, the dye used was a red anthraquinone dye having the following structure, and the binder was a thermosetting silicone resin. The following tests (excluding the control test in Example 1) were carried out at room temperature without the heat curing process normally used in practice, in order to evaluate the blending effects of the above additives within a convenient test time. I did it. Both the dyes and silicone binders mentioned above are materials that are known to cause crystallization problems when used in thermal transfer sheets.

When used together, dyes of the above type and silicone binders provide particularly unstable systems that give rise to rapid crystallization, thereby making it easier to compare the effectiveness of the crystallization inhibitors of the present invention. I found what I could do. These are the reasons for choosing the particular dyes and silicones mentioned above as models to illustrate the use of anti-crystallization agents according to the invention.

Example 1 (Control Test-A) As a control, i.e. without the addition of anti-crystallization agent, on the surface of the substrate of Melinex (trade name) polyester film, the basic dye was combined with the above-mentioned basic dye. A film of a dye and a binder was obtained by pouring a solution of a composition consisting of a dye and a binder to form a film.

This solution was in methyl ethyl ketone, a common solvent for both dye and binder. Upon removal of the solvent, the film formed as a layer of an amorphous, featureless mixture of polymer (binder) and dye. However, before completing heat curing, the red dye was seen to crystallize. Large crystal growths that appeared to be spherulite-like when made into bulk powder appeared as two-dimensional rosettes several tens of microns in diameter in the binder film about one micron thick. Such films are messy in that such rosette images are transferred to the receiver sheet during the printing process during thermal transfer, and furthermore, the red dye is transferred to one's hands when handling the dye sheet. be.

The coating composition according to the present invention was prepared by copolymerizing p-vinylphenol and styrene and grafting an anthraquinone chromophore onto the backbone of the resulting copolymer.

1-Vinylphenol Report: p-vinylphenol was produced as follows.

15.6 g of p-hydroxycinnamic acid to 15 m of quinoline
fl, 0.6 g of copper powder, and 1.1 g of hydroquinone were mixed into a slurry. The mixture was heated in an oil bath at 200°C for 15 minutes.

After that, the generation of CO□ almost stopped. The reaction mixture was then cooled, distilled under rotary pump vacuum, and p
-Vinylphenol and quinoline, boiling point 60°C ~ 8
0°C (boiling point, quinoline = 114°C/15 mmHg
; p-vinylphenol-1 engineering 5°C/16 (Foundation) Hg
) was collected. The distilled fraction was dissolved in hot diethyl ether and the solution was neutralized by successive washings with H(l) and distilled water and then dried over MgSO4. After removal of the solvent, the residue was dissolved in hot petroleum ether (40~ 60°C).By cooling this solution, colorless plate crystals 1.3
6 g was obtained. Yield 11.76%. The crystals were recrystallized from petroleum ether prior to copolymerization.

Preparation of styrene: Styrene was purified by vacuum distillation to remove the inhibitor.

Bulk polymerizations of p-vinylphenol and styrene were carried out four times using the monomer feed ratios listed in Table 1 (expressed as mole fraction of p-vinylphenol in the monomer feed). All polymerization equipment systems were degassed with nitrogen and sealed under an inert atmosphere before being placed in a 60°C bath. The polymerization initiator used was azoisobutyronitrile (
AIBN) and the polymerization continued for 50 hours. The copolymer was recovered by dissolving the reaction mixture in methyl ethyl ketone (MEK) and precipitating with methanol. Each copolymer was purified using the same solvent-nonsolvent system.

Table 1: In order to graft the anthraquinone moiety onto the molecular backbone of the copolymer, a reaction similar to that commonly used in the synthesis of low-molecular block anthraquinone dyes was used. there was. That is, as a typical example, 0.78 g of the previously produced copolymer is used in an amount of 1.1 mol.

of 1-amino-2-promo-4-hydroxy-anthraquinone and 2 molar equivalents of sodium carbonate in dry N-methylpyrrolidone (NMP).

The solution was stirred continuously at 135° C. under static nitrogen gas, and the progress of the grafting reaction was monitored by withdrawing a portion of the solution at regular intervals and examining it by thin layer chromatography. The reaction lasted approximately 20 hours in total. Table 2 shows the experimental conditions for three experiments in which an anthraquinone chromophore was grafted onto a styrene-p-vinylphenol copolymer.

After the reaction, the grafted copolymer was recovered by precipitation with methanol. The recovered graft copolymer was further purified either by methanol extraction or by methanol precipitation from the MEK solution. lastly,
The graft copolymer was dried under vacuum at 40°C overnight and stored in the dark in the refrigerator.

Table 1 *AQBr=l-amino-2-bromo-4-hydroxy-anthraquinone dye 2-bond 1 set methyl ethyl ketone (MEK) was coated as a solution on the surface of a 6 μm Melinex support film with a red dye and a silicone binder. The film was deposited using a manual 1-bar coater (co-ca coater).
st) did. After removing the solvent, binder
) had a final thickness of approximately 1 μm. In this test, a stock solution of dye and binder in MEK was prepared according to the following composition: 20.8 g MEK 0.080 g red dye, i.e. without crosslinker and curing agent for silicone;
Prepared. 2.5 ml of this was used for each experiment, to which was added 1 part of the graft copolymer described above. The weight of the chromophore of the anthraquinone moiety present in the additive was calculated and expressed as the weight of the dye content of each dye-binder system. The correlation between crystallization rate and weight percent of additive was then compared. The results obtained are shown in Table 3.

Two further comparative tests were conducted. First, the same anthraquinone dye [1-amino-4-hydroxy-2
A low molecular weight derivative of -(4-t-butylphenoxy)-anthraquinone 1 (designated L?'lWD) was added to the coating composition. On the other hand, a high molecular weight material (polystyrene) without grafted dye moieties was added. These additives were used in a wide range of different concentrations. Beyond the range protected by the grafted additive, ie, below about 5% of the dye, little effect was observed, and when polystyrene was added, little effect was observed even at high concentrations. However, a similar good reduction in crystallization rate was obtained by increasing the amount of low molecular weight derivative (LMWD) to even higher levels than using the grafted polymeric backbone of the present invention. However, no effect of reducing nucleation per unit area was observed. These results, including comparisons, are shown in Table 3 below.

Table 3 In the second set of experiments, a different polymeric binder, ethyl hydroxyethyl cellulose (denoted as EHEC), was used, and other polymeric crystallization modifiers were used in the experiments. Synthesized for. The dye used was the same red anthraquinone dye used in the previous example.

Polymeric crystallization inhibitor (modif) in the binder polymer
fer) to promote a more intimate mixing between the additive and the binder. Finally this second
The grafted polymeric additives in the test series were polymeric binders, II! It was manufactured to have a chemical structure similar to HEC.

Then, using hydroxypropyl cellulose (referred to as RPC), random ink was added to the backbone of NPC.
Chemical synthesis was performed to add an anthraquinone dye structure to the desired position. In this second set of tests, the grafted chromophore 1-amino-2-bromo-4-hydroxyanthraquinone sheds a substantial portion of the molecular structure (as defined above) of the free dye, i.e., the terminal phenoxy group. It consists only of what was made. 1-amino-2-bromo-
4-Hydroxyanthraquinone is attached to the cellulose backbone via flexible bonds provided by hydroxypropyl units already present in IIPC.

A graft polymer was produced using the stage and conditions shown in Table 4.

The final synthesis of each additive was performed in the same manner.

That is, 11 PCs were dried overnight at 60°C in a vacuum oven to remove moisture and stored in a desiccator.
10 g of freshly distilled N-methylpyrrolid-2-one (denoted as NMP) in a round-bottomed flask.
Added to 100c. This mixture was heated to approximately 85°C. At that temperature the polymer melts. An appropriate amount of 1-amino-2-bromo-4-hydroxyanthraquinone (AQB
r) and sodium carbonate as a catalyst were added to a flask equipped with a condenser. Clamp the device
It was placed in an oil bath maintained at a constant temperature of 135°C. Stirring was then started and the reaction was allowed to proceed for a specified period of time until the grafting reaction was completed.

The progress of the reaction was monitored by thin layer chromatography. Aliquots (1 quot) of the reaction mixture were taken every hour, and the reaction was judged to be complete when free dye stopped rising through the thin layer by analysis of the chromatogram. A strong purple dot remained at the origin R,=0.

After each reaction was completed, the graft polymer was recovered. The viscous purple liquid obtained from each synthesis reaction was added dropwise to a beaker equipped with an electric stirrer containing approximately 1 drrr of diethyl ether. A sticky purple solid formed which appeared to contain residual NMP. Free dye remaining in the sample was removed with diethyl ether. The diethyl ether was then allowed to stand and the resulting polymer was placed in a vacuum oven at 60°C overnight. Next, take this sample out of the oven and add methanol 150 c+d.
and added dropwise to a beaker containing 1-5 drrr of ethyl acetate.

A fibrous precipitate formed. The solution was filtered and the resulting fibrous polymer was dried in a vacuum oven at 60''C. The polymer was purified by redissolution and reprecipitation before further analysis and experiments.

Four polymers synthesized by grafting reactions involving amino-2-promo-4-hydroxyanthraquinone and hydroxypropylcellulose were characterized using various techniques.

Dish Z Visible Separation Methanol solutions of known concentrations of each graft copolymer were prepared and UV spectra of each sample were taken. The device is a Pye-Un operated in the frequency range 400-700 nm.
icam PU8800 was used.

NMR light proton NMR is Jeol operated at 100MHz.
Anthraquinone levels in each synthesized polymer were measured using an FX-100 instrument. Spectra were taken in deuterated DMSO and symmetrical tetrachloroethane.

TMS was used as an internal standard. Actual grafted dye levels include additives gHPC-5, gHPC-10,
They were 4.9%, 5.3%, 10.0% and 1014% for gHPC-15 and gllPc-20, respectively. These are the d aromatic proton range (chemical shift δ-7 to 8.5) of 1-amino-2-bromo-4-hydroxyanthraquinone, and the aliphatic proton range (chemical shift δ = 1) of the polymer hydroxypropyl cellulose. .5-3
．． It was calculated by measuring the peak integral value (concentrated at 3 ppm).

GPC measurements were performed on all grafted RPC samples. A column with a length of 600 mm and an inner diameter of 7.5 m was packed with 5 μm grade MTOGEL as a packing material and operated at 60°C. DMF containing 1% Liar as solvent
The column was passed through the column using a flow rate of 10.6 ml/min. Molecular weights were calculated on polystyrene standards.

A glossy amorphous film was prepared by preparing and casting a standard solution of ethyl hydroxyethyl cellulose (EIIEC) binder and red anthraquinone dye. A -bar coater was used to cast the above solution onto a 6 μm Melinex support film surface. Details of the solvent system, which is a mixture of methylene chloride, methanol and cyclohexanone, are given in Table 5.

A small amount of cyclohexanone helped to reduce haze in the solvent system, which either results from layer separation or appears in the film cast if it is not present in the solvent system. This solvent system was chosen because it dissolves all components used in Form 1 of the film, namely the EHEC1 dye and the four graft polymers. Several standard solutions were prepared, but the optimal solution containing the highest possible proportion of dye in the solvent system and at the same time producing high quality amorphous films was a dye mixture with the following composition:

EIIEC (grade - top quality) 0.3g red dye
0.05 g solvent 10
On average, six fills 4 were cast from the above standard solution.

Then a modified system
was developed with a standard solution, and grafted polymer g-RPC-15 was added to all to prepare six different solutions.
It was used. A solution of additives and solvent was first prepared, filtered, and then added to a standard dye-binder system: 0.05 g of dye and 2 g of EflEICO. The compositions of these solutions are shown in Table 6.

Six films were cast from each solution using the same procedure. The thickness of the binder in the resulting film was approximately 1 μm.

Another series of sheets was EHECed in the solvent system listed in Table 5.
It was molded from a solution consisting only of a polymer and a polymeric additive. The resulting film showed no evidence of layer separation on the 1 micron scale.

Table 5 Composition of the solvent mixture used in the dye-binder system Table 6 Graft polymer and solvent content in the modified system 1) Accelerated aging test Amorphous selected from standard solutions and dye sheets of solution kl~3 Film samples were subjected to Fisons Envi under conditions of constant temperature (40°C) and constant relative humidity (60%).
Aging was performed using a weather meter manufactured by Ronment Equipment. Samples were removed from the weather meter after 24 hours.

2) Microscopic measurement under hot stage A small piece of the standard solution that appeared amorphous to the naked eye and a small piece of fill prepared from solutions Nos. 1 to 3, which had not been subjected to a weather meter, was selected as the sample. The sample is heated to high temperature conditions and the crystallization rate is measured by rosettes in the dye-binder film.
Observation was made by recording the growth of ea). This operation is performed using a Zeiss optical microscope and a Panasonic (Panasonic)
(nasonic) Observation was made using a continuous video recorder. The sample was heated from a temperature of about 40°C to 100°C at a constant heating rate of 30°C per minute. Sufficient crystallization was determined to have occurred when no trace of the initial uncrystallized dye remained in the microscopic field of view. The photographs captured sufficient crystallization from the amorphous films obtained from the standard and three modified systems.

Table 7: Actual level of grafting calculated by proton NMR analysis Table 8: When crystallized sheets of the standard system and modified system are heated to 100°C, crystal nucleation is rapid at first; It has been found that the presence of a coalesced anti-crystallization agent significantly slows subsequent crystallization. In the presence of the additive, the crystallization rate was roughly halved.

These results demonstrate that the use of a polymeric additive containing pendant dye groups in the backbone of the polymeric additive prevents crystallization of free dye in the dye sheet as shown in the first example. However, by using additives that can be more intimately mixed with the binder polymer, it has been shown that the anti-crystallization effect can be achieved with even smaller amounts of additive.

In the first, second and third set of experiments, a specially designed dye was used to prevent crystallization of the organic thermal transfer dye in the dye sheet.
The applicabilit of the more general principle for the use of polymeric additives
The experiment was repeated except that a different dye was used to illustrate the principle.

Dye sheets were produced by molding as described above from solutions prepared according to the following composition.

Binder: Ethyl hydroxyethyl cellulose (EHEC) 1.6 g dyeing
Material=1-〇-butyl-5-(4-chlorophenylazo)
-3-cyano→→〒Boo-6-hydroxy-4-methylpyrid-2-one 0.53 g Solvent: Tetrahydrofuran 15.6 g・12
- based again on a cellulose structure that has been modified to include a wide variety of chemical bonding moieties.

That is, hydroxypropyl cellulose (RPC) prepared as described above was dissolved in 25 ml of anhydrous pyridine. Add the acid derivative of the dye, i.e. 1-n-butyl-5-(4-carboxyphenylazo), to this stirred solution at room temperature.
-3-cyano-6-hydroxy-4-methylpyrido-2
-one acid chloride, 1 g was added.

The mixture was further stirred at room temperature for 3 hours, and the modified polymer was then recovered by precipitation with ethyl acetate. This yellow polymer was purified by repeated dissolution in chloroform and precipitation with ethyl acetate.
Finally, it was dried at 40°C under reduced pressure.

The HPC grafted in this example was characterized by NMR, FTIR and UV/visible spectroscopy. All these techniques confirmed the success of the chemical reaction and the degree of grafting to the polymer was calculated from the NMR integrals. The grafting rate, expressed as the ratio of the weight of the dye newly chemically bonded to the polymer to the weight of the polymer, is 6.
% (weight).

Dye 2 System A number of dye sheets were prepared by spreading a solution of dye, EHEC and polymeric additives dissolved in tetrahydrofuran onto the surface of a polyester film. Details of the solutions used are shown in Table 9 below.

Dynamic Aging Test 1) Accelerated Aging Test Each dye sheet sample produced was heated at 135°C in air.
and heated for various specified times. Recovery revealed that the yellow dye had aggregated and crystallized in the dye sheet in varying amounts. Unit area of dye sheet (50cffl)
The number of nuclei per sample was recorded for each sample.

2) Microscopic observation at high temperatures A small piece of each dye sheet was heated from room temperature to 140°C at a heating rate of 20°C per minute, and the growth of dye crystals in the dye sheet was observed using a video camera attached to an optical microscope. observed by recorder. The crystallization rate of the yellow dye was then determined at 140°C. The crystallization measurement results are shown in the table below.

The results obtained show that under the selected conditions the rate of crystallization of the yellow dye in the dye sheet is only slightly influenced by the presence of the polymeric additive.

However, nucleation is sensitive to the presence of additives. This effect was achieved by grafting (grafting) unmodified RP instead of IPC additives.
This was not observed when using an equivalent level of C.

This third example further demonstrates the principles of designing polymeric crystallization inhibitors by attaching groups to the polymeric backbone that are structurally similar to the crystallized organic dyes in TTP dye sheets. illustrates its general applicability to all dyes contained in the polymeric environment before and during use.

Procedural amendment (formality) %formula% 1. Display of incident 1988 Patent Application No. 137609 2, Title of Invention 3. Person who makes corrections 4. Agent

Claims (1)

[Scope of Claims] 1. A thermal transfer sheet comprising a support substrate coated with a composition comprising a thermal transferable dye uniformly dispersed in a matrix comprising a polymeric binder, wherein said composition prevents crystallization. The anti-crystallization agent has a molecular structure that includes a polymeric skeleton, and the crystallization inhibitor has a polymeric skeleton, and the thermal transferable dye or a substantial portion thereof and a substantial portion thereof. 1. A thermal transfer dye sheet characterized in that it essentially has a molecular structure formed by chemically bonding a large number of groups having the same shape, charge distribution, and hydrogen bonding pattern. 2. A dye sheet according to claim 1, wherein the polymeric backbone is compatible with the polymeric binder. 3. The plurality of groups bonded to the polymeric backbone have essentially the same chemical structure as the individual thermally transferable dye molecules, and have chemical 3. The dye sheet according to claim 1, wherein only the substituent for forming a bond is substituted. 4. A dye sheet according to claims 1-2, wherein said plurality of groups are bonded to the polymeric backbone by flexible bonding substituents. 5. The dye sheet according to claims 1 to 4, wherein the crystallization inhibitor is present in an amount of 0.01 to 10% by weight of the heat transferable dye. 6. A composition comprising a thermally transferable dye, a polymeric binder, and a crystallization inhibitor, wherein the molecular structure of the crystallization inhibitor includes a polymeric skeleton, and It essentially has a molecular structure in which a large number of groups having substantially the same shape, charge distribution, and hydrogen bonding pattern as the thermal transferable dye or a substantial portion thereof are chemically bonded to the skeleton. A coating composition used for coating a supporting substrate in the production of a thermal transfer dye sheet, characterized in that 7. A coating composition according to claim 6, comprising a solution of a thermally transferable dye, a polymeric binder material and an anti-crystallization agent in a common solvent or a mixture of solvents.