JP7170554B2 - thermal transfer media - Google Patents

Description

The present invention relates to thermal transfer media.

According to thermal transfer printing using a thermal transfer medium such as a thermal transfer ribbon, for example, it is possible to print white with concealability that cannot be obtained by printing using inkjet printing or electrophotography.
As a thermal transfer medium for white printing by thermal transfer printing, a white layer (ink layer) in which a white pigment is bound by a binder resin is laminated on a base material in a thermally transferable state. Common.

As the white pigment, an inorganic white pigment such as titanium oxide, which itself has a high hiding rate and brightness and is excellent in whiteness, is preferably used.
However, in the white layer using only titanium oxide as a white pigment, the thickness of the layer itself is generally small, the binder resin is colorless and transparent or colorless and translucent, and the particle shape of the titanium oxide is spherical. Concomitantly, light can easily pass through the gaps between the titanium oxides.

Then, light is transmitted through the gaps between the titanium oxides, particularly in the thickness direction of the white layer, which reduces the overall hiding power of the white layer. The whiteness of the print, which is evaluated from the lightness, tends to decrease.
In order to improve the overall opacity of the white layer, suppress the effect of the color of the base, and increase the whiteness of the print, the proportion of titanium oxide contained in the white layer is increased, It is conceivable to reduce the gap between titanium oxides.

However, in that case, the proportion of the binder resin is relatively low, so the white layer tends to have low flexibility and followability to the base material.
In addition, for example, when stress is applied during handling of the thermal transfer medium, there is a problem that the white layer is easily peeled off from the base material, which is a so-called overflow.
Especially when titanium oxide, which has a large specific gravity and is heavy, is used as the white pigment, such problems tend to occur.

Therefore, the thermal transfer medium is required to prevent the white layer from overflowing even when stress is applied.
In Patent Document 1, it is considered to use resin-made hollow fine particles together with a white pigment such as titanium oxide.
Since the hollow fine particles are made of resin and are hollow, they are lighter and more flexible than white pigments such as titanium oxide.

Hollow fine particles are basically made of a colorless transparent or colorless translucent resin. giving rise to a white color.
Therefore, by using hollow fine particles together with a white pigment, it is expected that the flexibility of the white layer and the conformability to the base material can be improved without significantly lowering the whiteness of the print, and the overflow can be suppressed.

However, when hollow fine particles are used together with a white pigment, a large amount of binder resin must be blended as described in Patent Document 1 in order to bind and retain both well.
Moreover, since the hollow fine particles are basically made of a colorless and transparent or colorless and translucent resin as described above, they themselves do not have concealing properties and transmit light.

Therefore, in the configuration of Patent Document 1, coupled with the relatively small proportion of the white pigment, it is still possible to prevent a decrease in the hiding power of the white layer as a whole and a decrease in the whiteness of the print. you can't.
Therefore, the thermal transfer medium is required to suppress the overflow of the white layer and to improve the concealability of the white layer and the degree of whiteness of printing.

Further, the thermal transfer medium is also required to prevent blurring in the printed thermal transfer area during thermal transfer printing.
In particular, when printing barcodes, QR codes (registered trademark), etc., the thin lines of barcodes and dots of QR codes (registered trademark) can be clearly printed without blurring in order to increase the accuracy of data reading. What you can do is needed.

Therefore, the thermal transfer medium is required to improve thermal sensitivity during thermal transfer printing to suppress blurring.
Further, in recent years, the use of thermal transfer media for printing on surfaces such as vinyl chloride resins, which are often used in outdoor applications where weather resistance is required, has been studied.
Therefore, the thermal transfer medium is also required to have excellent fixability of printing on the surface of the vinyl chloride resin or the like and excellent abrasion resistance.

However, the current state of the art is that conventional thermal transfer media cannot sufficiently meet these requirements, regardless of whether the white layer contains hollow fine particles or not.

JP-A-7-314908

The object of the present invention is to provide a white color that is less likely to overflow the white layer, is less likely to cause blurring, is clear, has a high degree of whiteness, and is particularly excellent in fixability and abrasion resistance to surfaces such as vinyl chloride resins. To provide a thermal transfer medium capable of printing on.

The present invention comprises a substrate and a thermally transferable white layer provided on the substrate, wherein the white layer contains kaolin, titanium oxide, and vinyl chloride-vinyl acetate copolymer resin. It is a thermal transfer medium.

According to the present invention, the white layer is less likely to overflow, is less likely to blur, is clear, and has a high degree of whiteness. It is possible to provide a thermal transfer medium capable of printing on.

As described above, the thermal transfer medium of the present invention includes a substrate and a thermally transferable white layer provided on the substrate, the white layer comprising kaolin, titanium oxide, and vinyl chloride-acetic acid. It is characterized by containing a vinyl-based copolymer resin (hereinafter sometimes abbreviated as "vinyl chloride-acetate-based resin").
In the thermal transfer medium of the present invention, kaolin, which is generally in the form of scales or flakes, is mainly affected by the stress applied during the formation of a white layer by coating a liquid coating material on the base material. are dispersed in the white layer while being oriented in the plane direction of the white layer.

The kaolin oriented and dispersed in the plane direction of the white layer is white in itself and has a hiding property. can be suppressed from transmitting in the thickness direction of the white layer.
Therefore, by using kaolin together, it is possible to improve the hiding power of the white layer without increasing the proportion of titanium oxide, and to print white with excellent whiteness.

In addition, the vinyl chloride resin used as the binder resin has excellent affinity for the surface of the vinyl chloride resin because the vinyl chloride component contained in the vinyl chloride resin has excellent affinity for the surface of the vinyl chloride resin. It is possible to improve the fixability of printing on the surface and the abrasion resistance.
In addition, the vinyl acetate component in the vinyl chloride resin enhances the flexibility, adhesiveness, adhesion, etc. of the vinyl chloride resin, and the adhesion of titanium oxide and kaolin, It functions to improve retention and increase overall flexibility of the white layer.

Therefore, even if titanium oxide and kaolin are fully blended in order to increase the whiteness of printing, the white layer can be prevented from overflowing.
Furthermore, the vinyl acetate component also functions to improve thermal sensitivity during thermal transfer printing and suppress blurring.
Therefore, according to the thermal transfer medium of the present invention, the white layer is less likely to overflow, is less likely to blur, is clear, and has a high degree of whiteness. It is possible to print in white which is excellent in terms of color.

"Base material"
Examples of the substrate include conventional films of resins such as polysulfone, polystyrene, polyamide, polyimide, polycarbonate, polypropylene, polyester and triacetate, thin paper such as condenser paper and glassine paper, and cellophane.
Among them, polyester films such as polyethylene terephthalate (PET) and polyethylene naphthalate are preferable from the standpoints of mechanical strength, dimensional stability, heat resistance, price and the like.

Although the thickness of the base material can be arbitrarily set according to the specifications of the thermal transfer printer, it is preferably 1 μm or more, particularly 2 μm or more, and 10 μm or less, particularly 8 μm or less.
By setting the thickness within this range, while ensuring the strength (tensile strength, etc.) of the base material, the heat applied from the back side of the base material by the thermal head of the thermal transfer printer is transferred to the white layer as efficiently as possible through the base material. It can be transmitted to improve thermal sensitivity during thermal transfer printing.

Therefore, blurring is less likely to occur, and clear printing can be performed.
The surface of the base material on which the white layer is to be formed may be subjected to a release treatment in the same manner as in the prior art.
《Back layer》
On the side opposite to the white layer (back side) of the base material, a back layer is formed in the same manner as before in order to improve the heat resistance, slipperiness, abrasion resistance, etc. of the back side that comes into contact with the thermal head. You may

The back layer can be formed conventionally.
That is, the back layer can be formed of a silicone resin, a fluororesin, a silicone/fluorocopolymer resin, a nitrocellulose resin, a silicone-modified urethane resin, a silicone-modified acrylic resin, or the like.
In addition, the back layer may contain a lubricant as necessary.

The back layer can be formed by applying a coating material obtained by dissolving or dispersing the above resin or the like in a solvent to the back side of the base material and then drying the coating material.
Also, by so-called hot-melt coating, the back layer can be formed by heating and melting a mixture of the above resins, applying the mixture to the back surface of the substrate, and then cooling and solidifying the mixture.
Although the thickness of the back layer can be set arbitrarily according to the specifications of the thermal transfer printer, it is preferably 0.05 g/m ² or more, particularly 0.1 g/m ² or more in terms of solid content per unit area. It is preferably 0.5 g/m ² or less, particularly preferably 0.4 g/m ² or less.

By setting the thickness to this range or more, a continuous layer that functions well as a back layer can be formed on the back of the base material, and the above-described effects of providing the back layer can be sufficiently ensured.
On the other hand, by setting the thickness of the back layer to the above range or less, the heat applied from the back side of the base material by the thermal head is transferred to the white layer as efficiently as possible through the back layer and the base material, thereby thermal transfer printing. It can improve the thermal sensitivity of the time.

Further, blurring is less likely to occur, and clear printing can be performed.
《Peeling layer》
The white layer may be directly laminated on the substrate by imparting thermal transferability to the white layer itself, or may be laminated on the substrate via a release layer having thermal transferability.
In particular, it is preferable to separate the functions as in the latter case and form a release layer and a white layer which are excellent in their respective functions.

As the release layer, as in the past, the white layer continues to be fixed to the surface of the substrate until the thermal transfer medium is used for thermal transfer printing, and is melted or softened by heating from the back side of the substrate with a thermal head. and a layer having a function of separating the white layer from the substrate.
Wax, thermoplastic resin, or the like can be used as the material for forming the release layer, as in the conventional case.

Examples of waxes include polyethylene wax, carnauba wax, paraffin wax, microcrystalline wax, and Fischer-Tropsch wax.
Examples of thermoplastic resins include polyethylene-based copolymers, poly(meth)acrylic acid esters, vinyl chloride-based (co)polymers, and polyester resins.

One or more of the above waxes, thermoplastic resins, and the like can be used.
Waxes are particularly preferred.
A thermoplastic resin such as ethylene vinyl acetate resin (EVA) may be added to the wax in order to prevent the white layer from overflowing before thermal transfer.
The release layer preferably has a melting point or softening point of 50° C. or higher, particularly 60° C. or higher, and preferably 150° C. or lower, particularly 120° C. or lower, in order to satisfactorily exhibit the functions described above.

In order to form a release layer having a melting point or softening point within the above range, a wax or thermoplastic resin having a melting point or softening point within the above range may be selected and used.
Also, two or more kinds of waxes and thermoplastic resins may be used in combination to adjust the melting point or softening point to fall within the above range.

The release layer may contain other components in addition to wax and thermoplastic resin.
Other components include, for example, one or more of organic or inorganic fillers, thermosetting resins, higher fatty acids, higher alcohols, higher fatty acid esters, amides, higher amines, oils, surfactants, and the like. mentioned.
Among them, the surfactant is for adjusting the peelability of the release layer, and examples of the surfactant include polyoxyethylene chain-containing compounds.

In addition, the release layer may contain a white pigment such as titanium oxide in order to assist the concealability of the white layer and the degree of whiteness of printing.
The release layer can be formed by applying a coating material prepared by dissolving or dispersing wax or the like in a solvent to the surface of the base material and then drying the coating material.
Alternatively, the release layer can be formed by hot-melt coating, in which the mixture of the wax or the like is heated and melted, applied to the surface of the substrate, and then cooled and solidified.

Although the thickness of the release layer can be arbitrarily set according to the specifications of the thermal transfer printer, it is preferably 0.1 g/m ² or more, particularly 0.2 g/m ² or more in terms of solid content per unit area. Preferably, it is 3 g/m ² or less, especially 2 g/m ² or less.
By setting the thickness to this range or more, a continuous layer that functions well as a release layer can be formed on the surface of the substrate.

Further, by setting the thickness of the release layer to the above range or less, the heat applied from the back surface side of the base material by the thermal head can be transmitted to the white layer through the release layer as efficiently as possible.
Therefore, by setting the thickness of the release layer within the above range, the thermal sensitivity during thermal transfer printing can be improved, and blurring is less likely to occur, and clear printing can be performed.

《White layer》
<Kaolin>
The kaolin contained in the white layer includes, for example, one or more of kaolinite, nacrite, dickite, halloysite, hydrated halloysite, etc., and is produced by purifying naturally occurring clay (white china clay, kaolin clay). and various kaolins used.

Specifically, for example, one or more of wet kaolin, calcined kaolin, dry kaolin, and the like classified according to the refining method can be used.
Among them, wet kaolin obtained by refining and bleaching with water to remove impurities, and calcined kaolin obtained by calcining the wet kaolin are preferable because of their excellent brightness and whiteness. Wet kaolin is preferred because it has excellent dispersibility in water.

Wet kaolin has better dispersibility in vinyl chloride resin than calcined kaolin because wet kaolin has a higher water content, so the water content and the chlorine atom that is the terminal group of vinyl chloride resin This is probably due to the good compatibility with
And, as is clear from the results of Examples described later, by selecting and using the wet kaolin, the wet kaolin can be dispersed well in the white layer, and the hiding property of the white layer and the whiteness of the printing can be improved. degree and can be further improved.

In addition, it is preferable to select and use kaolin having a large average particle size among the kaolins of the same type, that is, produced by the same refining method.
Among similar kaolins, the larger the average particle size, the more the gaps between the titanium oxides are blocked in the thickness direction of the white layer, as described above, and the transmission of light through the gaps in the thickness direction of the white layer is suppressed. This is because it is highly effective.

This is also clear from the results of Examples described later.
Specific examples of kaolin include, but are not limited to, the following various kaolins.
(wet kaolin)
BI kaolin (average particle size: 3 µm) and AA kaolin (average particle size: 5 µm) manufactured by Sanyo Clay Industry Co., Ltd.;

Among the Hydrite (registered trademark) series manufactured by Imerys Kaolin Co., TS90 (average particle size: 0.2 μm), TS90S (average particle size: 0.2 μm), UF90 (average particle size: 0.2 μm), UF90S (average particle size) diameter: 0.2 μm), PXNLC (average particle diameter: 0.4 μm), PXNLCS (average particle diameter: 0.4 μm), R (average particle diameter: 0.45 μm), RA (average particle diameter: 0.45 μm). 45 μm), RS (average particle size: 0.5 μm), RS-A (average particle size: 0.5 μm), 121S (average particle size: 1.0 μm), Flat D (average particle size: 4.0 μm), Flat DS (average particle size: 4.0 μm).

(calcined kaolin)
Imerys Kaolin Pole Star 400 (average particle size: 0.6 μm), NeoGen 2000 (average particle size: 0.7 μm), OpTiMax 0425 (average particle size: 0.8 μm), NeoGen MX (average particle size: 1 .1 μm), Glomax® LL (mean particle size: 1.5 μm).

Satintone No. manufactured by Takehara Chemical Industry Co., Ltd.; 5 (average particle size: 0.8 μm), Satintone W (average particle size: 1.4 μm), Glomax LL (average particle size: 1.5 μm).
One or more of the above kaolins can be used.
<Titanium oxide>
As titanium oxide (titanium dioxide, TiO ₂ ), for example, various titanium oxides such as rutile type and anatase type manufactured by a manufacturing method such as a sulfuric acid method and a chlorine method can be used.

However, in order to improve the hiding power of the white layer and print with a good degree of whiteness, it is preferable to select and use titanium oxide having an average particle size of 0.2 μm or more.
As mentioned above, since titanium oxide has a large specific gravity, in order to improve the dispersibility in the coating material that is the basis of the white layer and in the white layer, and to suppress the white layer from overflowing, It is preferable to select and use titanium oxide having an average particle size of 0.5 μm or less, which is smaller and lighter even within the above range .

Specific examples of titanium oxide include, but are not limited to, the following various grades of titanium oxide manufactured by Ishihara Sangyo Co., Ltd., all of which are of the rutile type.
(sulfuric acid method titanium oxide)
R-780 (average particle size: 0.24 μm), R-780-2 (average particle size: 0.24 μm), R-850 (average particle size: 0.24 μm), PF-736 (average particle size: 0 .24 μm), PF-737 (average particle size: 0.21 μm), PF-742 (average particle size: 0.25 μm), R-820 (average particle size: 0.26 μm), R-830 (average particle size : 0.25 μm), R-930 (average particle size: 0.25 μm), R-980 (average particle size: 0.24 μm), R-550 (average particle size: 0.24 μm), R-630 (average Particle size: 0.24 μm), R-680 (average particle size: 0.21 μm).

(Chlorine method titanium oxide)
CR-58 (average particle size: 0.28 μm), CR-58-2 (average particle size: 0.28 μm), CR-85 (average particle size: 0.25 μm), PF-690 (average particle size: 0 .21 μm), PF-691 (average particle size: 0.21 μm), PF-711 (average particle size: 0.25 μm), PF-739 (average particle size: 0.25 μm), PC-3 (average particle size : 0.21 μm), CR-95 (average particle size: 0.28 μm), CR-953 (average particle size: 0.28 μm), CR-97 (average particle size: 0.25 μm), UT771 (average particle size : 0.25 μm), PFC105 (average particle size: 0.28 μm), CR-60 (average particle size: 0.21 μm), CR-60-2 (average particle size: 0.21 μm), CR-63 (average particle size: 0.21 μm), CR-67 (average particle size: 0.21 μm), CR-50 (average particle size: 0.25 μm), CR-50-2 (average particle size: 0.25 μm), CR -57 (average particle size: 0.25 μm), CR-Super70 (average particle size: 0.25 μm), CR-80 (average particle size: 0.25 μm), CR-90 (average particle size: 0.25 μm) , CR-90-2 (average particle size: 0.25 μm), CR-93 (average particle size: 0.28 μm).

One or more of the above titanium oxides can be used.
〈Vinyl chloride resin〉
Various vinyl chloride-acetate resins containing at least vinyl chloride and vinyl acetate as repeating units can be used as the vinyl chloride-acetate-based resin.
Specific examples of the vinyl chloride-acetate resin include, but are not limited to, the following various grades of vinyl chloride-acetate-based resins of the Solbin (registered trademark) series manufactured by Nissin Chemical Industry Co., Ltd. .

(Type A)
A [composition: 92% by mass of vinyl chloride, 3% by mass of vinyl acetate, 5% by mass of vinyl alcohol, degree of polymerization: 420, weight average molecular weight Mw: 7.3 × 10 ⁴ , glass transition temperature Tg: 76°C], AL [ Composition: 93% by mass of vinyl chloride, 2% by mass of vinyl acetate, 5% by mass of vinyl alcohol, degree of polymerization: 300, weight average molecular weight Mw: 5.3×10 ⁴ , glass transition temperature Tg: 76° C.], TA5R [composition: 88% by mass of vinyl chloride, 1% by mass of vinyl acetate, 11% by mass of vinyl alcohol, degree of polymerization: 300, weight average molecular weight Mw: 6.1×10 ⁴ , glass transition temperature Tg: 78° C.], TAO [composition: vinyl chloride 91% by mass, 2% by mass of vinyl acetate, 7% by mass of vinyl alcohol, degree of polymerization: 360, weight average molecular weight Mw: 4.6×10 ⁴ , glass transition temperature Tg: 77° C.].

(C type)
C [composition: 87% by mass of vinyl chloride, 13% by mass of vinyl acetate, degree of polymerization: 420, weight average molecular weight Mw: 7.5 × 10 ⁴ , glass transition temperature Tg: 70°C], CL [composition: 86% by mass of vinyl chloride %, vinyl acetate 14% by mass, degree of polymerization: 300, weight average molecular weight Mw: 5×10 ⁴ , glass transition temperature Tg: 70° C.], CLL2 [composition: vinyl chloride 84% by mass, vinyl acetate 16% by mass, degree of polymerization : 260, weight average molecular weight Mw: 3.9 × 10 ⁴ , glass transition temperature Tg: 70°C], CH [composition: 86% by mass of vinyl chloride, 14% by mass of vinyl acetate, degree of polymerization: 650, weight average molecular weight Mw: 9.5×10 ⁴ , glass transition temperature Tg: 73° C.], CN [composition: 89% by mass of vinyl chloride, 11% by mass of vinyl acetate, degree of polymerization: 750, weight average molecular weight Mw: 9.9×10 ⁴ , glass transition temperature Tg: 75° C.], CNL [composition: 90% by mass of vinyl chloride, 10% by mass of vinyl acetate, degree of polymerization: 200, weight average molecular weight Mw: 3.5×10 ⁴ , glass transition temperature Tg: 76° C.], C5R [composition: 79% by mass of vinyl chloride, 21% by mass of vinyl acetate, degree of polymerization: 350, weight average molecular weight Mw: 5.8×10 ⁴ , glass transition temperature Tg: 68° C.].

(M type)
M5 [composition: 85 mass % vinyl chloride, 14 mass % vinyl acetate, 1 mass % dicarboxylic acid, degree of polymerization: 430, weight average molecular weight Mw: 6.9×10 ⁴ , glass transition temperature Tg: 69° C.].
(others)
TA3 [composition: 83% by mass of vinyl chloride, 4% by mass of vinyl acetate, 13% by mass of hydroxyalkyl acrylate, degree of polymerization: 350, weight average molecular weight Mw: 6.4×10 ⁴ , glass transition temperature Tg: 65° C.].

Among them, a vinyl chloride-vinyl acetate copolymer resin (hereinafter sometimes abbreviated as "vinyl chloride resin") containing only vinyl chloride and vinyl acetate without a third component as a repeating unit is preferable.
As the vinyl chloride resin, those having a vinyl acetate content of 5% by mass or more, especially 8% by mass or more, particularly 10% by mass or more, and 25% by mass or less, particularly 22% by mass or less, are selected and used. is preferred.

If the vinyl acetate content is less than this range, the vinyl acetate component may not provide the various effects described above.
That is, the function of improving the flexibility, adhesiveness, adhesion, etc. of vinyl chloride-acetate-based resins, improving the binding properties and holding properties of titanium oxide and kaolin, and the function of improving the flexibility of the white layer as a whole. becomes insufficient and the white layer tends to overflow.

In addition, the function of improving the thickness of the white layer and improving the thermal sensitivity during thermal transfer printing may also become insufficient, and blurring may easily occur.
On the other hand, when the vinyl acetate content exceeds the above range, the ratio of the vinyl chloride component is relatively small, so the vinyl chloride component improves the print fixability and scratch resistance on the surface of the vinyl chloride resin. In some cases, the effect of improving the

On the other hand, by selecting and using a vinyl chloride resin whose vinyl acetate content is within the above range, the white layer is less likely to overflow, less likely to be blurred, and the vinyl chloride resin, etc. It is possible to print with excellent fixability and abrasion resistance to the surface of the.
The polyvinyl chloride resin has a degree of polymerization of 200 or more and 450 or less, especially 350 or less, and a weight average molecular weight Mw of 3.5×10 ⁴ or more and 7.5×10 ⁴ or less, especially 5.8×. It is preferable to select and use one having a molecular weight of 10 ⁴ or less.

If the degree of polymerization and/or the weight-average molecular weight Mw is less than this range, the polyvinyl chloride resin may deteriorate the binding and retaining properties of titanium oxide and kaolin, and may tend to cause the white layer to overflow.
On the other hand, when the degree of polymerization and/or the weight-average molecular weight Mw exceeds the above ranges, the vinyl chloride acetate resin may have reduced thermal sensitivity during thermal transfer printing and may easily cause blurring.

In addition, the polyvinyl chloride resin having a degree of polymerization and/or a weight average molecular weight Mw exceeding the above range becomes difficult to dissolve in the solvent forming the white layer. In addition, the stability of the coating material that forms the basis of the white layer may be lowered, and deterioration over time may occur.
On the other hand, if a polyvinyl chloride resin having both the degree of polymerization and the weight average molecular weight Mw within the above ranges is selected and used, it is difficult to cause blurring, the image is clear, and the fixation and resistance to the surface of the vinyl chloride resin or the like is good. Printing with excellent abrasion resistance is also possible.

In addition, it is possible to make it more difficult to cause overflow, to make it easier to dissolve in the solvent that constitutes the white layer, and to improve the stability of the coating material that is the basis of the white layer, so that it is difficult to deteriorate with time.
<Proportion of each component>
The proportion of kaolin is preferably 2.5% by mass or more, particularly 4.5% by mass or more, and preferably 36% by mass or less, particularly 30% by mass or less, based on the total amount of kaolin and titanium oxide.

If the proportion of kaolin is less than this range, by using the kaolin in combination with titanium oxide, the hiding power of the white layer can be improved without increasing the proportion of titanium oxide, and white printing with excellent whiteness can be achieved. In some cases, the whiteness of the print may be lowered due to the insufficient effect to be obtained.
In addition, if the ratio of titanium oxide, which has a relatively large specific gravity, is increased in order to maintain the concealing property, the ability of the vinyl chloride-acetate-based resin to bind and hold is exceeded, and the white layer tends to overflow. In some cases.

On the other hand, if the proportion of kaolin exceeds the above range, the whiteness of the print may be lowered.
In other words, the brightness and whiteness of kaolin are lower than those of titanium oxide, the proportion of titanium oxide is relatively low, and a large amount of kaolin tends to aggregate in the white layer, causing uneven distribution. As a result, the whiteness of the print is lowered.

On the other hand, by setting the ratio of kaolin in the above range, it is possible to make it more difficult for the white layer to overflow, and the hiding property of the white layer is improved, so that white printing with excellent whiteness can be achieved. becomes possible.
The proportion of kaolin in the total amount of solids forming the white layer is preferably 2% by mass or more, especially 3% by mass or more, particularly preferably 4% by mass or more, and 30% by mass or less, especially 26% by mass or less. In particular, it is preferably 25% by mass or less.

In addition, the proportion of titanium oxide in the total amount of solids forming the white layer is preferably 50% by mass or more, especially 58% by mass or more, particularly preferably 60% by mass or more, and 90% by mass or less, particularly 88% by mass. The following are preferred.
Considering that the white layer is suppressed from overflowing due to the binding and retention properties of the vinyl chloride resin, and the white layer is improved in the fixability and scratch resistance of the surface of the vinyl chloride resin, etc., salt It is desirable that the proportion of the vinyl acetate resin is as large as possible.

However, in order to maintain the hiding power of the white layer and the degree of whiteness of the print, it is important to reduce the proportion of the vinyl chloride-acetate resin as much as possible in order to give priority to titanium oxide and kaolin. .
In order to balance these contradictory requirements, the proportion of the vinyl chloride-acetate resin should be 4.8% by mass or more, particularly 6% by mass or more, in the total amount of solids forming the white layer. It is preferably 22% by mass or less, particularly preferably 20% by mass or less.

If the ratio of the vinyl chloride-acetate resin is less than this range, the vinyl chloride-acetate resin has the function of improving the binding properties and retention of titanium oxide and kaolin, and the function of improving the flexibility of the white layer as a whole. becomes insufficient and the white layer tends to overflow.
In addition, the heat sensitivity during thermal transfer printing may be lowered, causing blurring, and the fixability and abrasion resistance of the white layer to the surface of vinyl chloride resin may be lowered.

On the other hand, if the proportion of the vinyl chloride-acetate resin exceeds the above range, the proportion of titanium oxide and kaolin will be relatively low, resulting in a decrease in the opacity of the white layer. may reduce the whiteness of
On the other hand, by setting the ratio of the vinyl chloride resin to the above range, the white layer is less likely to overflow, less likely to be blurred, clear, and fixable to the surface of the vinyl chloride resin, etc. , it is possible to print with excellent abrasion resistance.

In addition, it is possible to improve the concealing property of the white layer and perform white printing with an even higher degree of whiteness.
<Other ingredients>
A small amount of a pigment of any color other than white can also be added to the white layer in order to prepare a white tint.

In addition, as described above, when the white layer itself is to be imparted with thermal transferability, the white layer may be blended with wax or a thermoplastic resin that forms the release layer described above.
The proportions of pigments other than white, wax, thermoplastic resin, etc. can be set arbitrarily.
<Formation method, thickness>
The white layer is formed by applying a coating material obtained by dissolving or dispersing each of the above components in an arbitrary solvent on the release layer formed on the surface of the substrate or directly on the surface of the substrate and drying it. can do.

Although the thickness of the white layer can be set arbitrarily according to the use of the thermal transfer medium, it is preferably 2 g/m ² or more, particularly 3 g/m ² or more in solid content per unit area, and 6 g/m 2 or more. m ² or less, preferably 5 g/m ² or less.
By setting the thickness of the white layer to be more than this range, the white layer as a whole can improve the hiding property, suppress the effect of the base color, and increase the whiteness of the print.

Further, by setting the thickness of the white layer to be equal to or less than the above range, the thermal sensitivity of the white layer during thermal transfer printing is improved, and blurring is less likely to occur, and clear printing can be performed.
《Adhesive layer》
When printing on the surface of a resin such as vinyl chloride resin that has affinity and adhesiveness with vinyl chloride resin, the white layer can be directly thermally transferred and printed due to the function of vinyl chloride resin. No layers are required.

However, if the surface to be printed is a resin, glass, or metal surface that has low affinity and adhesiveness to vinyl chloride-acetate resin, it will show stickiness on the white layer due to the heat during thermal transfer printing. A heat-sensitive adhesive layer may be provided.
The heat-sensitive adhesive layer can be made of epoxy resin, for example.
In addition, the adhesive layer may contain a white pigment such as titanium oxide in order to assist the concealability of the white layer and the degree of whiteness of printing.

The construction of the thermal transfer medium of the present invention is not limited to the examples described above.
For example, the back layer and adhesive layer may be omitted.
Further, as described above, the white layer itself may be imparted with thermal transferability, and the peeling layer may be omitted.
In addition, various modifications can be made without departing from the gist of the present invention.

EXAMPLES The present invention will be further described below based on examples and comparative examples, but the configuration of the present invention is not limited to these examples.
<Example 1>
(base material and back layer)
As a base material, a PET film having a thickness of 5 μm and having a back layer made of a silicone-based resin formed on the back side was prepared.

(Release layer)
A coating material prepared by dissolving carnauba wax and EVA in a solvent was applied to the surface of the substrate opposite to the side on which the back layer was formed, and then dried to obtain a solid content per unit area of 1.5. A release layer was formed that was 0 g/m ² .
(white layer)
A coating material for a white layer was prepared by blending each of the following components with 30.0 parts by mass of methyl ethyl ketone (MEK) as a solvent.

Each component in Table 1 is as follows.
Kaolin: wet kaolin, BI kaolin manufactured by Sanyo Clay Industry Co., Ltd. (average particle size: 3 μm)
Titanium oxide: R-550 manufactured by Ishihara Sangyo Co., Ltd. (average particle size: 0.24 μm)
Vinyl chloride resin: Solbin CL manufactured by Nissin Chemical Industry Co., Ltd. [Vinyl chloride resin, composition: 86% by mass of vinyl chloride, 14% by mass of vinyl acetate, degree of polymerization: 300, weight average molecular weight Mw: 5 × 10 ⁴ , glass transition temperature Tg: 70°C]
Next, the above coating material was applied on the previously formed release layer and then dried to form a white layer having a solid content of 5 g/m ² per unit area to prepare a thermal transfer medium.

The ratio of kaolin in the white layer is 9.7% by mass of the total amount of kaolin and titanium oxide, 8.8% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 82.4% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Example 2>
A white layer was formed in the same manner as in Example 1, except that the same amount of a vinyl chloride resin (prototype) having a vinyl chloride content of 75% by mass and a vinyl acetate content of 25% by mass was blended as the vinyl chloride resin. A thermal transfer medium was produced.

The ratio of kaolin in the white layer is 9.7% by mass of the total amount of kaolin and titanium oxide, 8.8% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 82.4% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Example 3>
Solbin C5R manufactured by Nissin Chemical Industry Co., Ltd. [composition: 79% by mass of vinyl chloride, 21% by mass of vinyl acetate, degree of polymerization: 350, weight average molecular weight Mw: 5.8×10 ⁴ , A white layer was formed in the same manner as in Example 1, except that the same amount of glass transition temperature Tg: 68° C. was blended, and a thermal transfer medium was produced.

The ratio of kaolin in the white layer is 9.7% by mass of the total amount of kaolin and titanium oxide, 8.8% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 82.4% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Example 4>
Solbin CNL manufactured by Nissin Chemical Industry Co., Ltd. [Composition: 90% by mass of vinyl chloride, 10% by mass of vinyl acetate, degree of polymerization: 200, weight average molecular weight Mw: 3.5×10 ⁴ , A white layer was formed in the same manner as in Example 1, except that the same amount of the glass transition temperature Tg: 76° C. was added, and a thermal transfer medium was produced.

The ratio of kaolin in the white layer is 9.7% by mass of the total amount of kaolin and titanium oxide, 8.8% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 82.4% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Example 5>
A white layer was formed in the same manner as in Example 1, except that the same amount of a vinyl chloride resin (prototype) having a vinyl chloride content of 95% by mass and a vinyl acetate content of 5% by mass was blended as the vinyl chloride resin. A thermal transfer medium was produced.

The ratio of kaolin in the white layer is 9.7% by mass of the total amount of kaolin and titanium oxide, 8.8% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 82.4% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Comparative Example 1>
A white layer was formed in the same manner as in Example 1 except that the same amount of epoxy resin [JER (registered trademark) 1002 manufactured by Mitsubishi Chemical Corporation] was added in place of the vinyl chloride resin. A thermal transfer medium was produced.

The ratio of kaolin in the white layer is 9.7% by mass of the total amount of kaolin and titanium oxide, 8.8% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 82.4% by mass of the solid content, and the proportion of the epoxy resin was 8.8% by mass of the total solid content.
<Comparative Example 2>
A white layer was formed and a thermal transfer medium was produced in the same manner as in Example 1 except that kaolin was not blended and the amount of titanium oxide was changed to 15.5 parts by mass.

The ratio of kaolin in the white layer is 0.0% by mass, the ratio of titanium oxide is 91.2% by mass in the total amount of solids forming the white layer, and the ratio of vinyl chloride-acetate resin is in the total amount of solids. was 8.8% by mass.
<Example 6>
A white layer was formed in the same manner as in Example 1 except that the amount of kaolin was changed to 0.4 parts by mass and the amount of titanium oxide was changed to 15.1 parts by mass to prepare a thermal transfer medium.

The ratio of kaolin in the white layer is 2.6% by mass in the total amount of kaolin and titanium oxide, 2.4% by mass in the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 88.8% by mass of the total solid content, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total solid content.
<Example 7>
A white layer was formed in the same manner as in Example 1, except that the amount of kaolin was changed to 0.7 parts by mass and the amount of titanium oxide was changed to 14.8 parts by mass to prepare a thermal transfer medium.

The ratio of kaolin in the white layer is 4.5% by mass in the total amount of kaolin and titanium oxide, 4.1% by mass in the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 87.1% by mass of the total amount of solids, and the proportion of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Example 8>
A white layer was formed in the same manner as in Example 1 except that the amount of kaolin was changed to 4.5 parts by mass and the amount of titanium oxide was changed to 11.0 parts by mass to prepare a thermal transfer medium.

The ratio of kaolin in the white layer is 29.0% by mass in the total amount of kaolin and titanium oxide, 26.5% by mass in the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 64.7% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Example 9>
A white layer was formed in the same manner as in Example 1 except that the amount of kaolin was changed to 5.5 parts by mass and the amount of titanium oxide was changed to 10.0 parts by mass to prepare a thermal transfer medium.

The ratio of kaolin in the white layer is 35.5% by mass in the total amount of kaolin and titanium oxide, 32.4% by mass in the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 58.8% by mass of the total amount of the solid content, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total solid content.
<Comparative Example 3>
A white layer was formed in the same manner as in Example 1 except that the amount of kaolin was changed to 15.5 parts by mass and titanium oxide was not blended, and a thermal transfer medium was produced.

The ratio of kaolin in the white layer is 100.0% by mass in the total amount of kaolin and titanium oxide, 91.2% by mass in the total amount of solids forming the white layer, the ratio of titanium oxide is 0.0% by mass, The proportion of the vinyl chloride-acetate resin was 8.8% by mass of the total solid content.
<Example 10>
A white layer was formed in the same manner as in Example 1, except that the same amount of Hydrite TS90 (wet kaolin, average particle size: 0.2 μm) manufactured by Imerys Kaolin Co., Ltd. was added as kaolin to prepare a thermal transfer medium.

The ratio of kaolin in the white layer is 9.7% by mass of the total amount of kaolin and titanium oxide, 8.8% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 82.4% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Example 11>
A white layer was formed in the same manner as in Example 1, except that the same amount of NeoGen MX (calcined kaolin, average particle size: 1.1 μm) manufactured by Imerys Kaolin Co., Ltd. was added as kaolin to prepare a thermal transfer medium.

The ratio of kaolin in the white layer is 9.7% by mass of the total amount of kaolin and titanium oxide, 8.8% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 82.4% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Example 12>
A white layer was formed in the same manner as in Example 1, except that the same amount of NeoGen 2000 (calcined kaolin, average particle size: 0.7 μm) manufactured by Imerys Kaolin Co., Ltd. was added as kaolin to prepare a thermal transfer medium.

The ratio of kaolin in the white layer is 9.7% by mass of the total amount of kaolin and titanium oxide, 8.8% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 82.4% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 8.8% by mass of the total amount of solids.
<Comparative Example 4>
A white layer was formed and a thermal transfer medium was produced in the same manner as in Example 1, except that the same amount of scale-like precipitated calcium carbonate was added instead of kaolin.

The ratio of light calcium carbonate in the white layer is 9.7% by mass of the total amount of light calcium carbonate and titanium oxide, and 8.8% by mass of the total amount of solids forming the white layer. The proportion of the vinyl chloride-acetate-based resin was 82.4% by mass of the total solid content, and 8.8% by mass of the total solid content.
<Example 13>
A white layer was formed in the same manner as in Example 1 except that the amount of kaolin was 1.55 parts by mass, the amount of titanium oxide was 14.65 parts by mass, and the amount of vinyl chloride-acetate resin was 0.8 parts by mass. Then, a thermal transfer medium was produced.

The ratio of kaolin in the white layer is 9.6% by mass of the total amount of kaolin and titanium oxide, 9.1% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 86.2% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 4.7% by mass of the total amount of solids.
<Example 14>
A white layer was formed in the same manner as in Example 1 except that the amount of kaolin was 1.5 parts by mass, the amount of titanium oxide was 14.2 parts by mass, and the amount of vinyl chloride-acetate resin was 1.3 parts by mass. Then, a thermal transfer medium was produced.

The ratio of kaolin in the white layer is 9.6% by mass in the total amount of kaolin and titanium oxide, 8.8% by mass in the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 83.5% by mass of the total amount of solids, and the proportion of the vinyl chloride-acetate resin was 7.6% by mass of the total amount of solids.
<Example 15>
A white layer was formed in the same manner as in Example 1 except that the amount of kaolin was 1.35 parts by mass, the amount of titanium oxide was 12.35 parts by mass, and the amount of vinyl chloride-acetate resin was 3.3 parts by mass. Then, a thermal transfer medium was produced.

The ratio of kaolin in the white layer is 9.9% by mass of the total amount of kaolin and titanium oxide, 7.9% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 72.6% by mass of the total solid content, and the ratio of the vinyl chloride-acetate resin was 19.4% by mass of the total solid content.
<Example 16>
A white layer was formed in the same manner as in Example 1 except that the amount of kaolin was 1.3 parts by mass, the amount of titanium oxide was 12.0 parts by mass, and the amount of vinyl chloride-acetate resin was 3.7 parts by mass. Then, a thermal transfer medium was produced.

The ratio of kaolin in the white layer is 9.8% by mass of the total amount of kaolin and titanium oxide, 7.6% by mass of the total amount of solids forming the white layer, and the ratio of titanium oxide is the total amount of the above solids. 70.6% by mass of the total amount of solids, and the ratio of the vinyl chloride-acetate resin was 21.8% by mass of the total amount of solids.
<Comparative Example 5>
A white layer was formed in the same manner as in Example 1 except that kaolin was not blended, the amount of titanium oxide was 16.2 parts by mass, and the ratio of vinyl chloride acetate resin was 0.8 parts by mass. A medium was prepared.

The percentage of kaolin in the white layer is 0.0% by mass, the percentage of titanium oxide is 95.3% by mass in the total amount of solids forming the white layer, and the percentage of vinyl chloride-acetate resin is in the total amount of solids. was 4.7% by mass.
<Whiteness evaluation>
(Concealment rate measurement)
Each of the thermal transfer media prepared in Examples and Comparative Examples was used in a thermal transfer printer (Zebra 110Xi4 manufactured by Zebra Technologies Inc.) to thermal transfer print a white layer on the surface of a 5 μm-thick transparent PET film.

Next, with the thermal transfer printed white layer facing up, the PET film was tested according to Japanese Industrial Standards JIS K5600-4-1: 1999 "Paint general test method-Part 4: Square characteristics of paint-Section 1: Hiding power (for pale color paint)”, and fixed on the surface of the opacity test paper on which white and black portions are printed adjacently.
Then, a spectrophotometer [X-Rite eXact manufactured by Videojet X-Rite Co., Ltd.] is applied to each of four areas of the white layer on the PET film corresponding to the white part and the black part of the opacity test paper. The tristimulus value Y of the XYZ color system among the CIE color systems was obtained by performing colorimetry using the color system.

Next, the average value of the tristimulus values Y at the four locations corresponding to the white portion is Y _W , the average value of the tristimulus values Y at the four locations corresponding to the black portion is Y _B , and the concealment rate Y _B /Y _W is expressed as a percentage. calculated with
(brightness measurement)
The thermal transfer media prepared in the above Examples and Comparative Examples were used in the above thermal transfer printer, and a white layer was thermally transferred and printed on the surface of a transparent PET film having a thickness of 5 μm.

Next, the thermal transfer printed white layer was subjected to colorimetry using the above spectrophotometer to determine the L value in the CIE1976 (L*, a*, b*) color space.
(Whiteness evaluation)
Based on the hiding ratio _YB / _YW (%) and the L value, the whiteness of the thermal transfer printed white layer was evaluated according to the following criteria.

_A : Hiding ratio YB/ _YW was 70% or more, and L value was 90 or more.
○: The hiding rate Y _B /Y _W is 70% or more and the L value is 80 or more and less than 90, or the hiding rate Y _B /Y _W is 60% or more and less than 70% and the L value is 90 or more. there were.
Δ: Hiding ratio _YB / _YW was 60% or more and less than 70%, and L value was 80 or more and less than 90.

x: Hiding ratio _YB / _YW was less than 60% and/or L value was less than 80.
<Overflow evaluation>
After rubbing the white layer of the thermal transfer medium produced in each example and comparative example with a black cotton swab once, the black swab and the white layer were observed. Then, the resistance to overflow of the white layer was evaluated according to the following criteria.
x: Powder overflowing from the white layer adhered to the cotton swab, and streaks were observed in the white layer.

Δ: A small amount of powder overflowing from the white layer adhered to the cotton swab, but no change such as streaks was observed in the white layer.
◯: No powder adhered to the cotton swab, and no change such as streaks was observed in the white layer.
<Thermal sensitivity evaluation>
The thermal transfer media prepared in each example and comparative example were used in the thermal transfer printer described above, and the energy value applied to the thermal head was set to 15 (low and 30 (high value), and the bar code was printed at a printing speed of 4 inches/sec, and then the state of the bar code was observed.

The thermal sensitivity during thermal transfer printing was evaluated according to the following criteria.
◯: No blurring was observed in the printed bar code regardless of whether the energy applied to the thermal head was low or high.
Δ: When the energy applied to the thermal head is low, the printed barcode is blurred, but when the energy is high, the printed barcode is not blurred.

x: Even if the energy applied to the thermal head is high, the printed bar code is blurred.
<Evaluation of fixability and scratch resistance>
The thermal transfer media prepared in each example and comparative example are used in the above-described thermal transfer printer to print a barcode on the surface of the vinyl chloride resin. After rubbing several times, the state of the bar code was observed.

Then, the print fixability and scratch resistance were evaluated according to the following criteria.
◯: No change was observed in the state of the bar code before and after rubbing.
Δ: The bar code was slightly thinned by rubbing, but the above-mentioned whiteness evaluation was maintained at “Δ” or higher.
x: All or part of the bar code disappeared when rubbed.

The above results are shown in Tables 2-5.

From the results of Examples 1 to 16 and Comparative Examples 1 to 4 in Tables 2 to 5, by forming a white layer with at least kaolin, titanium oxide, and vinyl chloride-vinyl acetate copolymer resin, the white layer In addition to being less likely to overflow, it is excellent in heat sensitivity, less likely to be blurred, and has a high degree of whiteness, making it possible to print a white color that is particularly excellent in fixability and abrasion resistance on surfaces such as vinyl chloride resins. I found out.

However, from the results of Examples 1 to 5, considering that the above effect is further improved, the vinyl acetate content of the vinyl chloride resin is 5% by mass or more, especially 8% by mass or more, particularly 10% by mass. From the above, it has been found that it is preferable to select and use one having a content of 25% by mass or less, particularly 22% by mass or less.
Further, from the results of Examples 1 and 13 to 16, considering that the above effects are further improved, the proportion of the vinyl chloride resin is 4.8 mass in the total amount of solids forming the white layer. % or more, particularly 6 mass % or more, and 22 mass % or less, particularly 20 mass % or less.

From the results of Examples 1 and 6 to 9, especially considering further improvement of the whiteness of printing, the ratio of kaolin is 2.5% by mass or more in the total amount of kaolin and titanium oxide, especially 4 It has been found that the content is preferably at least 5% by mass , and preferably not more than 36% by mass, particularly preferably not more than 30% by mass.
Further, from the results of Examples 1 and 10 to 12, when considering further improving the whiteness of printing, wet kaolin and calcined kaolin, which are excellent in brightness and whiteness, are preferable as kaolin. It was found that wet kaolin is preferable because it is also excellent in dispersibility in resin, and that it is preferable to use kaolin of the same type with a large average particle size.

Claims (5)

A thermal transfer medium comprising a substrate and a thermally transferable white layer provided on the substrate, wherein the white layer contains kaolin, titanium oxide, and a vinyl chloride-vinyl acetate copolymer resin. 2. The thermal transfer medium according to claim 1, wherein the proportion of said kaolin is 5 mass % or more and 30 mass % or less of the total amount of said kaolin and titanium oxide. 3. The thermal transfer medium according to claim 1, wherein said kaolin is wet kaolin. 4. The sensor according to any one of claims 1 to 3, wherein the vinyl chloride-vinyl acetate copolymer resin is a vinyl chloride-vinyl acetate copolymer resin having a vinyl acetate content of 10% by mass or more and 22% by mass or less. Thermal transfer media. 5. The thermal transfer medium according to any one of claims 1 to 4, wherein the white layer is provided on the substrate via a release layer.