EP3512711B1

EP3512711B1 - Medium for thermal transfer printing

Info

Publication number: EP3512711B1
Application number: EP17777982.4A
Authority: EP
Inventors: Katsushi Shishido; Yuta OKABE
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2016-09-15
Filing date: 2017-09-14
Publication date: 2020-11-04
Anticipated expiration: 2037-09-14
Also published as: EP3512711A1; JP2018047696A

Description

[Technical Field]

The present disclosure relates to a medium for thermal transfer printing.

[Background Art]

Hitherto, thermal transfer ink ribbons have been widely used as media for thermal transfer printing, in order to print characters and barcodes on plastic films used as, for example, nameplates and labels.
Commercially available plastic films used as labels include many types. Among these types, there are films having different chemical polarities such as low-polarity films (e.g., polyethylene films and polypropylene films) and high-polarity films (e.g., polyethylene terephthalate (PET) films). It is desirable to use thermal transfer ink ribbons formed of ink materials suitable for these plastic films.
The print quality and fixability of existing thermal transfer ink ribbons are improved for the plastic films individually. For example, there has been proposed a thermal transfer ink ribbon including a thermally fusible ink layer containing a reactive functional group-containing acrylic-based copolymer and having thermal transferability to low-polarity and high-polarity plastic films (see, e.g., PTL 1). Reference is also made to JP 2014-091324 , which discloses a thermal transfer sheet.

[Citation List]

[Patent Literature]

[PTL 1] Japanese Unexamined Patent Application Publication No. 10-264535

[Summary of Invention]

[Technical Problem]

The present disclosure has an object to provide a medium for thermal transfer printing, the medium having a good thermal transferability to at least both of a film having a low chemical polarity and a film having a high chemical polarity and capable of providing an image excellent in scratch resistance and alcohol resistance.

[Solution to Problem]

According to one aspect of the present disclosure, a medium for thermal transfer printing of the present disclosure includes a support, a release layer provided over the support, and a thermally fusible ink layer provided over the release layer. The release layer contains a first styrene resin. The thermally fusible ink layer contains a second styrene resin and a polyester resin. The content ratio of the second styrene resin in the thermally fusible ink layer is higher than the content ratio of the first styrene resin in the release layer.

Advantageous Effects of Invention

The present disclosure can provide a medium for thermal transfer printing, the medium having a good thermal transferability to at least both of a film having a low chemical polarity and a film having a high chemical polarity and capable of providing an image excellent in scratch resistance and alcohol resistance.

Brief Description of Drawings

[fig.1]FIG. 1 is a schematic view illustrating an example of a medium for thermal transfer printing of the present disclosure.

Description of Embodiments

(Medium for thermal transfer printing)

A medium for thermal transfer printing of the present disclosure includes a support, a release layer provided over the support, and a thermally fusible ink layer provided over the release layer.
The release layer contains a first styrene resin.
The thermally fusible ink layer contains a second styrene resin and a polyester resin.
The content ratio of the second styrene resin in the thermally fusible ink layer is higher than the content ratio of the first styrene resin in the release layer.
The medium for thermal transfer printing further includes other layers as needed.
The medium for thermal transfer printing of the present disclosure is based on a finding that existing media for thermal transfer printing have been improved to some degree in thermal transferability to a film having a low chemical polarity and a film having a high chemical polarity, but have been poor in scratch resistance and alcohol resistance.
The medium for thermal transfer printing of the present disclosure has the following two features.
First, the thermally fusible ink layer contains a second styrene resin and a polyester resin.
The reason why it is difficult for media for thermal transfer printing to provide good transferred images on both of a low-polarity film and a high-polarity film is that materials suitable for these kinds of films respectively are not compatibilized with each other well but become phase-separated when contained at the same time in the thermally fusible ink layer. The second styrene resin and the polyester resin contained in the thermally fusible ink layer have solubility parameters (SP values) of 9.1 and 10.7 respectively. Generally, there is a tendency that materials having a SP value difference of a degree corresponding to the difference between about 9 and about 11 have a poor compatibility with each other and do not mix with each other uniformly at normal temperature.
The present inventors have found that a polyester resin obtained by condensation polymerization of an aromatic dicarboxylic acid and a diol compound, and a styrene resin, which is likewise in the aromatic series, can be compatibilized with each other even though the SP values of these resins are apart. Meanwhile, the SP values of a polyethylene (PE) film and a polypropylene (PP) film (with a SP value of about 8.1), which have a low polarity, are close to the SP value of a styrene resin. The SP value of a polyethylene terephthalate (PET) film is close to the SP value of a polyester resin having a similar structure. Therefore, these resins can provide a medium for thermal transfer printing having an excellent thermal transferability to both of a low-polarity film and a high-polarity film.
Second, the release layer contains a first styrene resin, and the thermally fusible ink layer contains a second styrene resin. The first styrene resin in the release layer and the second styrene resin in the thermally fusible ink layer may be the same as or different from each other.
By the release layer containing a first styrene resin, it is possible to improve thermal transferability to a low-polarity film such as a polyethylene (PE) film and a polypropylene (PP) film without spoiling thermal transferability to a high-polarity film such as a polyethylene terephthalate (PET) film. This is considered to be because when heat is applied to the release layer and the thermally fusible ink layer from a thermal head of a thermal transfer printer during thermal transfer, the release layer and the thermally fusible ink layer become compatibilized with each other to more effectively improve wettability of the ink when the ink contacts the surface of a low-polarity film, leading to an improved thermal transferability. On the other hand, if the thermally fusible ink layer contains a second styrene resin in a large amount from the very beginning, the thermally fusible ink layer has a poor close adhesiveness with a high-polarity film such as a PET film. Therefore, not only can the thermally fusible ink layer not be thermally transferred sufficiently, but also the strength of the image may be spoiled.
To solve the problem described above, the present inventors conducted a series of earnest studies, paying attention to the resins to be contained in the release layer and the thermally fusible ink layer of the medium for thermal transfer printing. As a result, it was found possible to obtain a good thermal transferability regardless of the chemical polarity of films, which are transfer targets, and to obtain an image excellent in scratch resistance and alcohol resistance, by adding styrene resins having a low chemical polarity like, for example, a polypropylene film, which is a transfer target, in both of the release layer and the thermally fusible ink layer as the first styrene resin and the second styrene resin respectively with the content ratio (% by mass) of the second styrene resin in the thermally fusible ink layer higher than the content ratio (% by mass) of the first styrene resin in the release layer, and by adding a polyester resin having a high chemical polarity like, for example, a polyester film, which is a transfer target, in only the thermally fusible ink layer. The first styrene resin in the release layer and the second styrene resin in the thermally fusible ink layer may be the same as or different from each other.
Hence, the medium for thermal transfer printing of the present disclosure is characterized in that the content ratio of the second styrene resin in the thermally fusible ink layer is higher than the content ratio of the first styrene resin in the release layer. It is preferable that the content ratio of the second styrene resin in the thermally fusible ink layer be higher than the content ratio of the first styrene resin in the release layer by 2% by mass or greater. By the content ratio of the second styrene resin in the thermally fusible ink layer being higher than the content ratio of the first styrene resin in the release layer, it is possible to obtain a good thermal transferability to both of a film having a low chemical polarity and a film having a high chemical polarity, and to obtain an image excellent in scratch resistance and alcohol resistance.

The support is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the support include various plastic films such as a polyethylene terephthalate (PET) film, a polyester film, a polycarbonate film, a polyimide film, a polyamide film, a polystyrene film, a polysulfone film, a polypropylene film, a polyethylene film, and a cellulose acetate film. Among these supports, a polyethylene terephthalate (PET) film excellent in strength, heat resistance, and thermal conductivity is preferable.
The average thickness of the support is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably 3 micrometers or greater but 10 micrometers or less.

The release layer is a layer provided for facilitating separation between the support and the thermally fusible ink layer when heat is applied. Therefore, the release layer is formed of components that melt and become a low-viscosity liquid when heat is applied by a thermal head.
It is preferable to adjust the components to be contained in the release layer, so as for the layer to be easily torn at about the interface between a heated portion and a non-heated portion.
The release layer contains a first styrene resin, preferably contains a wax, and further contains other components as needed.

-First styrene resin for the release layer-

The first styrene resin is a polymer containing styrene as a monomer, and is contained in order to improve thermal transferability and resolution.
The first styrene resin may be a homopolymer of styrene or a copolymer of styrene with another aliphatic compound monomer or aromatic compound monomer.
The number average molecular weight of the first styrene resin is preferably 10,000 or less and more preferably 500 or greater but 5,000 or less. When the number average molecular weight of the first styrene resin is 10,000 or less, there is an advantage that the first styrene resin softens in a short time and hence has a high sensitivity.
The number average molecular weight of the first styrene resin can be measured by, for example, a gel permeation chromatography (GPC) method.
The softening point of the first styrene resin is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably 90 degrees C or higher but 150 degrees C or lower.
The softening point can be controlled by appropriately adjusting the degree of polymerization of the first styrene resin, and can be measured by, for example, a ring and ball method (JIS K2531).
The first styrene resin may be an appropriately synthesized product or a commercially available product. Examples of the commercially available product include YS RESIN SX100 (available from Yasuhara Chemical Co., Ltd.), and FTR8100 (available from Mitsui Chemicals, Inc.).
The content ratio of the first styrene resin in the release layer is preferably 10% by mass or greater but 30% by mass or less and more preferably 10% by mass or greater but 20% by mass or less. When the content ratio of the first styrene resin is 10% by mass or greater but 30% by mass or less, there is an advantage that thermal transferability to a low-polarity film such as a polyethylene (PE) film and a polypropylene (PP) film can be improved without spoiling thermal transferability to a high-polarity film represented by a polyethylene terephthalate (PET) film.

-Wax-

The wax is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the wax include: natural waxes such as a beeswax, cetaceum, a Japan wax, a rice bran wax, a carnauba wax, a candelilla wax, and a montan wax; synthetic waxes such as a paraffin wax, a microcrystalline wax, an oxide wax, ozokerite, ceresin, an ester wax, and a polyethylene wax; higher saturated fatty acids such as margaric acid, lauric acid, myristic acid, palmitic acid, stearic acid, furoic acid, and behenic acid; higher saturated monovalent alcohols such as stearyl alcohol and behenyl alcohol; higher esters such as fatty acid ester of sorbitan; and higher fatty acid amides such as stearic acid amide and oleic amide. One of these waxes may be used alone or two or more of these waxes may be used in combination. Among these waxes, a carnauba wax and a polyethylene wax are preferable.

-Other components-

Examples of the other components include a rubber, a resin other than the styrene resin, and a solvent.
The rubber is added in order to impart elasticity to the release layer and provide a good close adhesiveness between the medium for thermal transfer printing and the transfer target.
Examples of the rubber include isoprene rubbers, butadiene rubbers, ethylene propylene rubbers, butyl rubbers, and nitrile rubbers.
Examples of the resin other than the styrene resin include resins having a strong adhesiveness in order to prevent detachment of the release layer.
The release layer can be formed by coating a release layer coating liquid containing the first styrene resin and the wax, and, as needed, the other components over the support by a coating method such as a hot melt coating method, a gravure coater, a wire bar coater, and a roll coater, and drying the release layer coating liquid.
The average thickness of the release layer is preferably 0.2 micrometers or greater but 3.0 micrometers or less and more preferably 0.5 micrometers or greater but 2.0 micrometers or less.

The thermally fusible ink layer contains a second styrene resin and a polyester resin, and further contains other components as needed.

-Polyester resin-

The polyester resin is contained for transferability to a polyethylene terephthalate (PET) film and image durability.
As the polyester resin, a condensation polymerization product of an aromatic dicarboxylic acid and a diol compound is preferable.
Examples of the aromatic dicarboxylic acid include phthalic acid, isophthalic acid, and terephthalic acid.
Examples of the diol compound include: aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, and neopentyl glycol; aromatic alcohols such as bisphenol A-alkylene oxide adducts such as polyoxypropylene-2,2-bis(4-hydroxyphenyl)propane and polyoxyethylene-2,2-bis(4-hydroxyphenyl)propane; and hydrogenated bisphenol A or alkylene (containing from 2 through 4 carbon atoms) oxide adducts (with an average number of added moles of from 1 through 16) of hydrogenated bisphenol A.
It is possible to add an aliphatic polybasic acid to the polyester resin in order to improve fluidity.
Examples of the aliphatic polybasic acid include: saturated aliphatic dicarboxylic acids such as succinic acid, succinic anhydride, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecane diacid, and 1,4-cyclohexane dicarboxylic acid; unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, citraconic acid, and citraconic anhydride; and trifunctional or higher aliphatic carboxylic acids such as 1,2,3,4-butanetetracarboxylic acid.
The glass transition temperature of the polyester resin is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably 40 degrees C or higher but 80 degrees C or lower.
The glass transition temperature can be measured by, for example, a differential scanning calorimetry (DSC) method.
The number average molecular weight of the polyester resin is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably 30,000 or less and more preferably 1,000 or greater but 10,000 or less.
The number average molecular weight can be measured by, for example, a gel permeation chromatography (GPC) method.
The polyester resin may be an appropriately synthesized product or a commercially available product. Examples of the commercially available product include VYLON series (available from Toyobo Co., Ltd.) and ELIETEL series (available from Unitika Ltd.).
The content ratio of the polyester resin in the thermally fusible ink layer is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably 20% by mass or greater but 60% by mass or less and more preferably 30% by mass or greater but 50% by mass or less.

-Second styrene resin for the thermally fusible ink layer-

As the second styrene resin, a similar resin to the resin described in the description of the first styrene resin in the release layer can be used. It is preferable to use a styrene resin appropriately selected from styrene resins raised as the examples of the first styrene resin.
The content ratio of the second styrene resin in the thermally fusible ink layer is preferably 10% by mass or greater but 40% by mass or less and more preferably 12% by mass or greater but 30% by mass or less. When the content ratio of the second styrene resin is 10% by mass or greater but 40% by mass or less, there is an advantage that thermal transferability to a film having a low chemical polarity is improved without inhibiting conflicting thermal transferability to a film having a high chemical polarity.
The ratio (A:B) by mass between the content ratio A of the second styrene resin and the content ratio B of the polyester resin in the thermally fusible ink layer is preferably from 1:0.50 through 1:5 and more preferably from 1:0.50 through 1:2. When the ratio (A:B) by mass is from 1:0.50 through 1:5, a medium for thermal transfer printing good for both of a film having a low chemical polarity and a film having a high chemical polarity can be obtained.

-Other components-

The other components are not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the other components include a colorant, a wax, an oil, a resin other than the polyester resin and the styrene resin, and a lubricant.

--Colorant--

The colorant is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the colorant include carbon black, azo-dyes and pigments, phthalocyanine, quinacridone, anthraquinone, perylene, quinophthalone, aniline black, titanium oxide, zinc oxide, and chromium oxide. One of these colorants may be used alone or two or more of these colorants may be used in combination.

--Wax--

The wax is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the wax include a paraffin wax, a microcrystalline wax, a paraffin oxide wax, a candelilla wax, a carnauba wax, a rice wax, a montan wax, a ceresin wax, a polyethylene wax, a polyethylene oxide wax, a castor wax, a hydrogenated beef tallow oil, lanolin, a Japan wax, sorbitan stearate, sorbitan palmitate, stearyl alcohol, a polyamide wax, oleylamide, stearyl amide, hydroxystearic acid, and a synthetic ester wax. One of these waxes may be used alone or two or more of these waxes may be used in combination.
Examples of the oil include silicone oils and perfluoroalkyl ether.
Examples of the resin other than the polyester resin and the styrene resin include silicone resins, tetrafluoroethylene resins, and fluoroalkyl ether resins.
Examples of the lubricant include silicon carbide and silica.
The thermally fusible ink layer can be formed by coating a thermally fusible ink layer coating liquid containing the polyester resin and the second styrene resin, and, as needed, the other components over the release layer by a coating method such as a hot melt coating method, a gravure coater, a wire bar coater, and a roll coater, and drying the thermally fusible ink layer coating liquid.
The average thickness of the thermally fusible ink layer is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably 0.5 micrometers or greater but 3.0 micrometers or less and more preferably 0.8 micrometers or greater but 2.0 micrometers or less.

The other layers are not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the other layers include a back layer and an overcoat layer.

-Back layer-

As needed, the medium for thermal transfer printing of the present disclosure may include a back layer over a surface (back surface) of the support at a side at which the thermally fusible ink layer is not provided.
The back layer is intended for protecting the support from a high temperature when heat from a thermal head is applied. The back layer contains a resin, and further contains other components as needed.
Examples of the resin include thermoplastic resins and thermosetting resins that have a high heat resistance, and ultraviolet-ray-curable resins and electron-beam-curable resins. Specific examples of the resin include fluororesins, silicone resins, polyimide resins, epoxy resins, phenol resins, and melamine resins.
Examples of the other components include particles and a lubricant.
By providing the back layer, it is possible to significantly improve the heat resistance of the support. Therefore, by providing the back layer, it becomes possible to use supports that hitherto have been inappropriate.

-Overcoat layer-

The medium for thermal transfer printing may include an overcoat layer over the thermally fusible ink layer in order to obtain a greater background smear resistance. When the overcoat layer is provided, the overall thickness of the ink surface will increase. Therefore, it is preferable to provide the overcoat layer in a manner that efficient application of heat to the thermally fusible ink layer by a thermal head is not inhibited.
The constitution of the overcoat layer is free of a coloring component. As needed, it is possible to appropriately select constituent components.
The average thickness of the overcoat layer is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably 0.2 micrometers or greater but 1.0 micrometer or less.
FIG. 1 is a schematic diagram illustrating an example of a medium for thermal transfer printing of the present disclosure. The medium 10 for thermal transfer printing of FIG. 1 includes a support 1, a release layer 2 provided over the support 1, and a thermally fusible ink layer 3 provided over the release layer 2. A back layer 4 may be provided over a surface of the support 1 at a side at which the thermally fusible ink layer 3 is not provided. An overcoat layer may be provided over the thermally fusible ink layer 3.

A thermal transfer method for a medium for thermal transfer printing used in the present disclosure is a thermal transfer method for thermally transferring the thermally fusible ink layer of the medium for thermal transfer printing of the present disclosure onto a transfer target.
It is preferable that the transfer target be at least one selected from the group consisting of a polyethylene film, a polypropylene film, and a polyethylene terephthalate film. It is preferable that the thermal transfer be performed with a heating unit. Examples of the heating unit include a serial thermal head and a line-type thermal head.

Examples

The present disclosure will be described below by way of Examples. The present disclosure should not construed as being limited to these Examples.

(Preparation example 1)

Carbon black (available from Mitsubishi Chemical Corporation, #44) (13 parts by mass), a polyester resin (with a weight average molecular weight of 8,000 and a glass transition temperature (Tg) of 49 degrees C, available from Unitika Ltd., ELIETEL UE-3300) (6 parts by mass), a magnesium chelate dispersant (available from Kawaken Fine Chemicals Co., Ltd., M118) (1 part by mass), and methyl ethyl ketone (MEK) (80 parts by mass) were mixed, to prepare a carbon black dispersion liquid (with a solid content of 20% by mass).

(Example 1)

The following components were mixed to prepare a thermally fusible ink layer coating liquid with a solid content of 23% by mass.

The carbon black dispersion liquid (with a solid content of 20% by mass): 38 parts by mass,
A polyester resin toluene solution (with a solid content of 30% by mass) (an aromatic carboxylic acid: terephthalic acid/isophthalic acid, a diol compound: ethylene glycol/neopentyl glycol, with a number average molecular weight of about 5,000 and a glass transition temperature (Tg) of 45 degrees C): 38.3 parts by mass,
A toluene solution of a styrene resin (i) (with a solid content of 30% by mass) (available from Yasuhara Chemical Co., Ltd., product name: SX100, with a number average molecular weight of about 2,000 and a softening point of from 95 degrees C through 105 degrees C) : 9.2 parts by mass,
A polyethylene oxide wax dispersion liquid (product name: HI-WAX 210MP, available from Mitsui Chemicals, Inc., with a number average molecular weight of 2,000 and a solid content of 10% by mass) : 11.5 parts by mass, and
Methyl ethyl ketone (MEK) : 3 parts by mass

-Preparation of wax dispersion liquid-

The components in the composition described below were mixed (mass ratio of carnauba wax and polyethylene wax is carnauba wax:polyethylene wax=1:1) and dispersed by a usual method to prepare a wax dispersion liquid with a volume average particle diameter of 3 micrometers and a solid content of 10% by mass.

Carnauba wax (available from Kato & Co., with a melting point of 84 degrees C): 5 parts by mass
Polyethylene wax (available from Mitsui Chemicals, Inc., HI-WAX 200PF, with a melting point of 122 degrees C): 5 parts by mass
Toluene: 90 parts by mass

-Preparation of release layer coating liquid-

The following components were mixed to prepare a release layer coating liquid with a solid content of 10% by mass.

The wax dispersion liquid (with a solid content of 10% by mass): 86 parts by mass,
A toluene solution of the styrene resin (i) (with a solid content of 30% by mass) (available from Yasuhara Chemical Co., Ltd., product name: SX-100, with a number average molecular weight of about 2,000 and a softening point of from 95 degrees C through 105 degrees C): 3.33 parts by mass,
A styrene-butadiene block copolymer toluene solution (with a solid content of 30% by mass) (product name: TR-2000, available from JSR Corporation): 1.33 parts by mass, and
Toluene: 9.34 parts by mass

The following components were mixed to obtain a back layer coating liquid.

A silicone rubber dispersion liquid (KS-779H, available from Shin-Etsu Chemical Co., Ltd., with a solid content of 30% by mass): 6 parts by mass,
A platinum catalyst: 0.1 parts by mass, and
Toluene: 94 parts by mass

The back layer coating liquid was coated over one surface of a support, which was a polyethylene terephthalate film having an average thickness of 4.5 micrometers, such that the amount of the back layer coating liquid to be attached after dried would be 0.05 g/m², and dried, to provide a back layer.
Next, the release layer coating liquid was coated over a surface of the polyethylene terephthalate film at a side at which the back layer was not provided, such that the amount of the release layer coating liquid to be attached after dried would be 1.0 g/m², and dried, to form a release layer having an average thickness of 1 micrometer. Next, the thermally fusible ink layer coating liquid was coated over the release layer such that the amount of the thermally fusible ink layer coating liquid to be attached after dried would be 1.0 g/m², and dried, to form a thermally fusible ink layer having an average thickness of 1 micrometer. In the way described above, a medium for thermal transfer printing was produced.

(Examples 2 to 7 and Comparative Examples 1 to 5)

Media for thermal transfer printing of Examples 2 to 7 and Comparative Examples 1 to 5 were produced in the same manner as in Example 1, except that the components and blending amounts of the release layer coating liquid and the thermally fusible ink layer coating liquid of Example 1 were changed as presented in Table 1, Table 2, and Table 3.

(Example 8)

A medium for thermal transfer printing of Example 8 was produced in the same manner as in Example 1, except that unlike in Example 1, a toluene solution of a styrene resin (ii) (with a solid content of 30% by mass) (available from Mitsui Chemicals, Inc., a styrene/aliphatic monomer copolymer, product name: FTR6110, with a number average molecular weight of about 1,000 and a softening point of 110 degrees C) was used instead of the toluene solution of the styrene resin (i) in the thermally fusible ink layer coating liquid, as presented in Table 2.

[Table 1]

		Ex. 1	Ex. 2	Ex. 3	Ex. 4	Ex. 5
Release layer coating liquid	Wax dispersion liquid (solid content: 10% by mass)	86	86	86	76	66
	Toluene solution of styrene resin (i) (solid content: 30% by mass), number average molecular weight: about 2,000	3.33	3.33	3.33	6.67	10
	Styrene-butadiene block copolymer toluene solution (solid content: 30% by mass)	1.33	1.33	1.33	1.33	1.33
	Toluene	9.34	9.34	9.34	16	22.67
Total (part by mass)		100	100	100	100	100
Thermally fusible ink layer coating liquid	Carbon black dispersion liquid (solid content: 20% by mass)	38	38	38	38	38
	Polyester resin toluene solution (solid content: 30% by mass)	38.3	29.1	19.9	29.1	19.9
	Acid component: terephthalic acid/isophthalic acid
	Diol component: ethylene glycol/neopentyl glycol
	Number average molecular weight: about 5,000
	Tg: 45 degrees C
	Toluene solution of styrene resin (i) (solid content: 30% by mass), number average molecular weight: about 2,000	9.2	18.4	27.6	18.4	27.6
	Toluene solution of styrene resin (ii) (solid content: 30% by mass), number average molecular weight: about 1,000					-
	Polyethylene oxide wax dispersion liquid (solid content: 10% by mass)	11.5	11.5	11.5	11.5	11.5
	Methyl ethyl ketone (MEK)	3	3	3	3	3
Total (part by mass)		100	100	100	100	100
Content ratio (% by mass) of first styrene resin in release layer		10	10	10	20	30
Content ratio A (% by mass) of second styrene resin in thermally fusible ink layer		12	24	36	24	36
Content ratio B (% by mass) of polyester resin in thermally fusible ink layer		50	38	26	38	26
Ratio (A:B) by mass		1 :4.17	1:1.58	1:0.72	1:1.58	1 : 0. 72

[Table 2]

		Ex. 6	Ex. 7	Ex. 8
Release layer coating liquid	Wax dispersion liquid (solid content: 10% by mass)	76	91	86
	Toluene solution of styrene resin (i) (solid content: 30% by mass), number average molecular weight: about 2,000	6.67	1.67	3.33
	Styrene-butadiene block copolymer toluene solution (solid content: 30% by mass)	1.33	1.33	1.33
	Toluene	16	6	9.34
Total (part by mass)		100	100	100
Thermally fusible ink layer coating liquid	Carbon black dispersion liquid (solid content: 20% by mass)	38	38	38
	Polyester resin toluene solution (solid content: 30% by mass)	15.3	29.1	38.3
	Acid component: terephthalic acid/isophthalic acid
	Diol component: ethylene glycol/neopentyl glycol
	Number average molecular weight: about 5,000
	Tg: 45 degrees C
	Toluene solution of styrene resin (i) (solid content: 30% by mass), number average molecular weight: about 2,000	32.2	18.4	-
	Toluene solution of styrene resin (ii) (solid content: 30% by mass), number average molecular weight: about 1,000	-	-	9.2
	Polyethylene oxide wax dispersion liquid (solid content: 10% by mass)	11.5	11.5	11.5
	Methyl ethyl ketone (MEK)	3	3	3
Total (part by mass)		100	100	100
Content ratio (% by mass) of first styrene resin in release layer		20	5	10
Content ratio A (% by mass) of second styrene resin in thermally fusible ink layer		42	24	12
Content ratio B (% by mass) of polyester resin in thermally fusible ink layer		20	38	50
Ratio (A:B) by mass		1:0.48	1:1.58	1:4.17

[Table 3]

		Comp. Ex. 1	Comp. Ex. 2	Comp. Ex. 3	Comp. Ex. 4	Comp. Ex. 5
Release layer coating liquid	Wax dispersion liquid (solid content: 10% by mass)	86	96	66	86	76
	Toluene solution of styrene resin (i) (solid content: 30% by mass), number average molecular weight: about 2,000	3.33	-	10	3.33	6.67
	Styrene-butadiene block copolymer toluene solution (solid content: 30% by mass)	1.33	1.33	1.33	1.33	1.33
	Toluene Total	9.34	3.07	22.67	9.34	16
(part by mass)		100	100	100	100	100
Thermally fusible ink layer coating liquid	Carbon black dispersion liquid (solid content: 20% by mass)	38	38	38	38	38
	Polyester resin toluene solution (solid content: 30% by mass)	47.5	29.1	29.1	-	41.4
	Acid component: terephthalic acid/isophthalic acid
	Diol component: ethylene glycol/neopentyl glycol
	Number average molecular weight: about 5,000
	Tg: 45 degrees C
	Toluene solution of styrene resin (i) (solid content: 30% by mass), number average molecular weight: about 2,000	-	18.4	18.4	47.5	6.1
	Toluene solution of styrene resin (ii) (solid content: 30% by mass), number average molecular weight: about 1,000	-	-	-	-	-
	Polyethylene oxide wax dispersion liquid (solid content: 10% by mass)	11.5	11.5	11.5	11.5	11.5
	Methyl ethyl ketone (MEK)	3	3	3	3	3
Total (part by mass)		100	100	100	100	100
Content ratio (% by mass) of first styrene resin in release layer		10	-	30	10	20
Content ratio A (% by mass) of second styrene resin in thermally fusible ink layer		-	24	24	62	8
Content ratio B (% by mass) of polyester resin in thermally fusible ink layer		62	38	38	-	54
Ratio (A:B) by mass		-	1:1.58	1:1.58	-	1:6.75

Next, thermal transferability, scratch resistance, and alcohol resistance of the obtained media for thermal transfer printing were evaluated in the manners described below. The results are presented in Table 4.

(1) White polyethylene terephthalate (PET) label (hereinafter referred to as "PET label")

A vertical Code 39 barcode (3 dots) was printed over a white PET label (available from Avery Products Corporation, product number: 72825) under the printing conditions described below. An ANSI grade value [indicating a barcode reading rate (an error infrequency rate) by 5 grades including 0, 1, 2, 3, 4] of the barcode portion was read and evaluated according to the criteria described below. A higher value means a better thermal transferability.

Printer: ZEBRA 105SL (300 dpi) (available from Zebra Technologies Corporation)
Printing speed: 150 mm/second
Printing density setting value: 20

A: The ANSI grade value was 3.0 or greater.
B: The ANSI grade value was 1.5 or greater but less than 3.0.
C: The ANSI grade value was less than 1.5.

(2) Transparent polypropylene (PP) label (hereinafter referred to as "PP label") A 4-pt alphabet letter was printed over a transparent PP label (available from Toyobo Co., Ltd., product number: P2161) under the printing conditions described below, and thermal transferability was evaluated according to the criteria described below.

Printer: ZEBRA 105SL (300 dpi) (available from Zebra Technologies Corporation)
Printing speed: 100 mm/second
Printing density setting value: 22

A: Printing was possible with no missing portion.
B: Some portion was missing.
C: Untransferable.

A vertical Code 39 barcode (5 dots) was printed over a white PET label (available from Avery Products Corporation, product number: 72825) and a transparent PP label (available from Toyobo Co., Ltd., product number: P2161) under the printing conditions described below, to obtain test images.
Next, using a friction tester available from Suga Test Instruments Co., Ltd., the white PET label was scratched 1,000 times and the transparent PP label 200 times with a barcode pen scanner loaded by 750 g. The images after scratched were evaluated for scratch resistance according to the criteria described below.

Printer: ZEBRA105SL (300 dpi) (available from Zebra Technologies Corporation)
Printing speed: 100 mm/second
printing density setting value: 24

Printer: ZEBRA105SL (300 dpi) (available from Zebra Technologies Corporation)
Printing speed: 100 mm/second
printing density setting value: 28

A: No change was observed in the image after tested.
B: The image had no missing portion, and only ink contamination/bleeding was observed in a peripheral portion of the image.
C: The image of a scratched portion was missing.

A vertical Code 39 barcode (5 dots) was printed over a white PET label (available from Avery Products Corporation, product number: 72825) and a transparent PP label (available from Toyobo Co., Ltd., product number: P2161) under the same printing conditions as used for the scratch resistance, to obtain test images.
Next, using a friction tester available from Suga Test Instruments Co., Ltd., the white PET label was scratched 400 times and the transparent PP label 140 times with a cotton cloth wetted with ethanol and loaded by 750 g. ANSI grade values of the images after scratched were measured, to evaluate alcohol resistance according to the criteria described below.

A: The ANSI grade value was 0.6 or greater.
B: The ANSI grade value was 0.1 or greater but less than 0.6.
C: The ANSI grade value was less than 0.1.

[Table 4]

	Thermal transferability		Scratch resistance		Alcohol resistance
	PET label	PP label	PET label	PP label	PET label	PP label
Ex. 1	A	B	A	A	A	B
Ex. 2	A	B	A	A	A	B
Ex. 3	B	A	A	A	B	A
Ex. 4	B	A	A	A	B	B
Ex. 5	B	A	B	A	B	B
Ex. 6	B	A	B	B	B	B
Ex. 7	B	B	A	B	B	B
Ex. 8	A	B	A	A	A	B
Comp. Ex. 1	A	C	A	C	A	C
Comp. Ex. 2	A	C	B	C	A	B
Comp. Ex. 3	C	A	C	A	C	B
Comp. Ex. 4	C	A	C	B	C	B
Comp. Ex. 5	A	C	A	C	A	C

From the results of Table 4, it was found that Examples 1 to 8 obtained better results than Comparative Examples 1 to 5 in any of the evaluation items.
As compared, it was found that Comparative Examples 1 and 2 in which either the thermally fusible ink layer or the release layer was free of a styrene resin were poor in thermal transferability and scratch resistance on the PP label.
It was found that Comparative Example 3 in which the content ratio of the first styrene resin in the release layer was higher than the content ratio of the second styrene resin in the thermally fusible ink layer was poor in thermal transferability, scratch resistance, and alcohol resistance on the PET label.
It was found that Comparative Example 4 in which the thermally fusible ink layer was free of a polyester resin was poor in thermal transferability, scratch resistance, and alcohol resistance on PET label.
What improve thermal transferability to the PP label are that the thermally fusible ink layer contains a polyester resin and a second styrene resin and that the release layer contains a first styrene resin. However, when the content ratio of the first styrene resin in the release layer was higher than the content ratio of the second styrene resin in the thermally fusible ink layer, there was a tendency that thermal transferability to the PET label was poor. It was found that there was a need that the content ratio of the second styrene resin in the thermally fusible ink layer be higher than the content ratio of the first styrene resin in the release layer, in order to enable favorable thermal transfer to the PP label and the PET label.
On the other hand, when the content ratio of the second styrene resin in the thermally fusible ink layer was lower than 10% by mass as in Comparative Example 5, the function of the polyester resin became dominant, which may make it impossible to obtain the effect on the PP label.

Description of the Reference Numeral

1:: support
2:: release layer
3:: thermally fusible ink layer
4:: back layer
10:: medium for thermal transfer printing

Claims

A medium (10) for thermal transfer printing, the medium comprising:
a support (1);

a release layer (2) provided over the support (1); and

a thermally fusible ink layer (3) provided over the release layer (2),

wherein the release layer (2) comprises a first styrene resin,

wherein the thermally fusible ink layer (3) comprises a second styrene resin and a polyester resin, and

wherein a content ratio of the second styrene resin in the thermally fusible ink layer (3) is higher than a content ratio of the first styrene resin in the release layer (2).
The medium (10) for thermal transfer printing according to claim 1,
wherein the polyester resin comprises a condensation polymerization product of an aromatic dicarboxylic acid and a diol compound.
The medium (10) for thermal transfer printing according to claim 1 or 2,
wherein a number average molecular weight of at least any one of the first styrene resin and the second styrene resin is 10,000 or less.
The medium (10) for thermal transfer printing according to any one of claims 1 to 3,
wherein the content ratio of the second styrene resin in the thermally fusible ink layer (3) is 10% by mass or greater but 40% by mass or less.
The medium (10) for thermal transfer printing according to any one of claims 1 to 4,
wherein the content ratio of the first styrene resin in the release layer (2) is 10% by mass or greater but 30% by mass or less.
The medium (10) for thermal transfer printing according to any one of claims 1 to 5,
wherein a ratio (A:B) by mass between content ratio A of the second styrene resin and content ratio B of the polyester resin in the thermally fusible ink layer (3) is from 1:0.50 through 1:5.
The medium (10) for thermal transfer printing according to any one of claims 1 to 6,
wherein the release layer (2) further comprises a wax.