JP3646333B2 - Photographic paper for thermal transfer - Google Patents

Description

（式中、Ｒ¹は水素又はメチル基、エチル基、プロピル基などの低級アルキル基であり、Ｒ²はメチル基などの低級アルキル基でありｘ、ｙ及びｚは数式（Ｉ）
【００２２】
【数２】
［アセタール化度（％）］＝｛ｘ／（ｘ＋ｙ＋ｚ）｝×１００ （Ｉ）
で定義されるアセタール化度が５０％以上となる０以上の数である。）
で表される化合物を好ましく挙げることができる。特に好ましいポリビニルアセタールとしてはＲ²がメチル基であって、Ｒ¹が水素であるポリビニルホルマール、Ｒ¹がメチル基であるポリビニルエタナール、Ｒ¹がエチル基であるポリビニルプロパナール、Ｒ¹がプロピル基であるポリビニルブタナール等を挙げることができる。
【００２３】
なお、ポリビニルアセタールとしては、ｘとｙとｚとの和である重合度が小さすぎると膜が脆くなり成膜性が不十分となり、大きすぎると基材への接着力が不十分となるので、好ましくは５００〜３０００、より好ましくは１５００〜３０００の重合度のものを使用する。
【００２４】
本発明において使用する多官能イソシアネート化合物としては、分子中に２以上のイソシアネート基を有する無黄変タイプの化合物を好ましく挙げることができ、例えば、ヘキサメチレンジイソシアネート（ＨＤＩ）、ビウレット等の脂肪族ポリイソシアネートや、トルエンジイソシアネート（ＴＤＩ）、キシレンジイソシアネート（ＸＤＩ）等の芳香族ポリイソシアネートを挙げることができる。これらは、単独で使用してもよく複数種を併用してもよい。
【００２５】
また、ポリビニルアセタールと多官能イソシアネート化合物とから架橋反応物を形成する場合、紫外線照射や加熱などの種々の手段により行うことができるが、製造コストや架橋操作の点から加熱により架橋させることが好ましい。
【００２６】
このような架橋反応物において、上述したポリビニルアセタール及び多官能イソシアネート化合物の配合割合については、ポリビニルアセタール１００重量部に対し、多官能イソシアネート化合物を１００〜２００重量部とすることが好ましい。多官能イソシアネート化合物の配合割合が多すぎると、バックコート層４を形成するためにこれらを混合調製した塗料のポットライフが短くなり、逆に少なすぎると架橋密度が低下して本発明の効果が得られなくなるので好ましくない。
【００２７】
また、バックコート層４における架橋反応物の含有量は、少なすぎると本発明の効果が得られないので、少なくとも５０重量％以上とする。
【００２８】
なお、バックコート層４には上述のポリビニルアセタール及び多官能イソシアネート化合物の他、必要に応じて種々の添加剤を配合することができる。例えば、有機又は無機フィラー等の摩擦係数調整剤；ポリエチレンワックス、アミドワックス、テフロンパウダー等の固形ワックス類、フッ素系界面活性剤、リン酸エステル系界面活性剤、シリコーンオイル、高融点シリコーンワックス等の離型剤；陽イオン型界面活性剤（第４級アンモニウム塩、ポリアミン等）、陰イオン型界面活性剤（アルキルベンゼンスルホネート、アルキル硫酸エステルナトリウム塩等）、両性イオン型界面活性剤、非イオン型界面活性剤等の帯電防止剤；ポリアルキレングリコール、ポリビニルアルコール、ポリビニルピロリドン等の水性インキ筆記性向上剤等を適宜配合することができる。なお、このような帯電防止剤は、バックコート層４内に含有させる他、バックコート層４の表面にコーティング等により塗布してもよい。
【００２９】
本発明の熱転写用印画紙において、基材２や染料受容層３は従来の熱転写用印画紙と同様に構成することができる。
【００３０】
例えば、基材２としては、上質紙、コート紙の紙類、種々のプラスチックシート、合成紙あるいはこれらの複合シート等を使用することができる。
【００３１】
また、染料受容層３としては、ポリエステル、セルロースエステル、ポリビニルブチラール、ポリカーボネート、ポリ塩化ビニル等の染着性樹脂から形成することができる。
【００３２】
なお、染料受容層３にも必要に応じて種々の添加剤を含有させることができる。例えば、染料受容層３の白色度を向上させて転写画像の鮮明度を高め、また画像表面に筆記性を付与し、さらにまた転写画像の再転写を防止するために、蛍光増白剤や白色顔料を含有させることができる。ここで、白色顔料としては、酸化チタン、酸化亜鉛、カオリン、クレー、炭酸カルシウム、微粉末シリカ等を使用することができる。
【００３３】
また、染料受容層３には、転写画像の耐光性を向上させるために、紫外線吸収剤、光安定剤、酸化防止剤等を添加することができる。また、熱転写時のインクリボンとの離型性を向上させるために離型剤を添加することができる。離型剤としては、ポリエチレンワックス、アミドワックス、テフロンパウダー等の固形ワックス類、フッ素系界面活性剤、リン酸エステル系界面活性剤、シリコーンオイル、高融点シリコーンワックス等を使用することができる。なかでも、離型性、耐久性の点からシリコーンオイルを使用することが好ましい。
【００３４】
更に、染料受容層３には、静電気の発生を抑制するために、帯電防止剤を添加することができる。帯電防止剤としては、陽イオン型界面活性剤（第４級アンモニウム塩、ポリアミン等）、陰イオン型界面活性剤（アルキルベンゼンスルホネート、アルキル硫酸エステルナトリウム塩等）、両性イオン型界面活性剤、非イオン型界面活性剤等の種々の界面活性剤を使用することができる。なお、このような帯電防止剤は、染料受容層３内に含有させる他、染料受容層３の表面にコーティング等により塗布してもよい。
【００３５】
本発明の熱転写用印画紙は常法により製造することができ、例えば、ポリビニルアセタールと多官能イソシアネート化合物とを含有するバックコート層形成用塗料を調製し、それを常法により基材２の裏面に塗工し、キュアリングしてバックコート層４を形成し、更に、基材２の表面に染料受容層形成用塗料を塗布し、キュアリングを行い染料受容層３を形成することにより製造することができる。また、先に染料受容層３を形成した後にバックコート層４を形成することにより製造することもできる。
【００３６】
本発明の熱転写用印画紙に対する画像形成方法には特に制限はなく、例えば、昇華型熱転写記録用インクリボンを使用し、市販のビデオプリンター等により、昇華型熱転写記録を行うことができる。特に、親油性染料を用いる画像形成方法に使用する場合に、画像の裏移りを有効に防止することができる。
【００３７】
【作用】
本発明の熱転写用印画紙においては、バックコート層が高度にアセタール化がされたポリビニルアセタールと多官能イソシアネート化合物との架橋反応物を含有する。この架橋反応物は、十分な耐水性を有し、また、染料に染着されにくく、しかも基材への良好な接着力を示す。従って、そのような架橋反応物から構成されるバックコート層は、染料の裏移りとインクリボンとの融着が抑制され、しかも基材に対して十分な接着力を有するものとなる。
【００３８】
【実施例】
以下、本発明を実施例に基づいて具体的に説明する。
【００３９】
実施例１〜２０及び比較例１〜４
シート状基材として、１５０μｍ厚の合成紙（王子油化（株）製、ＦＰＧ−１５０）を用意し、この表面に乾燥膜厚が１０μｍとなるように表１の組成の染料受容層形成用塗料を塗布し、１２０℃で２分間乾燥させることにより、基材の表面に染料受容層を形成した。
【００４０】
【表１】

次に、シート状基材の裏面に表２〜表６の組成のバックコート層形成用塗料を乾燥膜厚が１μｍとなるように塗布し、キュアリング（条件：５０℃／２日間）させバックコート層を形成することにより熱転写用印画紙を作製した。
【００４１】
なお、実施例又は比較例で使用した成分の商品名と入手先は以下の通りである。
【００４２】
多官能イソシアネート系化合物(*1)： コロネートＬ、日本ポリウレタン社製
多官能イソシアネート系化合物(*2)： コロネートＨＬ、日本ポリウレタン社製
多官能イソシアネート系化合物(*3)： タケネートＤ−１０２、武田薬品工業社製
シリコーンオイル(*4)： ＳＦ−８４２７、東レ・ダウコーニング社製
導電剤(*5)： サフトマーＳＴ−１０００、三菱油化社製
ポリエステル樹脂(*6)： バイロン２００、東洋紡績社製
塩化ビニル共重合体樹脂(*7)： ＭＲ１１０、日本ゼオン社製
アクリル酸エステル共重合体(*8)： プライコールWL81、ロームアンドハース社製。
【００４３】
（評価）
作製した熱転写用印画紙に対し、バックコート層の基材への「接着性」、染料のバックコート層への「耐裏移り性」、熱転写用印画紙のプリンターでの「重送現象」、熱転写用印画紙の裏面（バックコート層）に印字した場合の「インクリボンの融着」及びバックコート層の「耐水性」について以下に説明するように試験し評価した。これらの結果を表２〜表６に示す。
【００４４】
バックコート層の基材への「接着性」試験
熱転写用印画紙のバックコート層に粘着テープ（セロテープ、ニチバン社製）を手でいったん貼り付けた後に引き剥がした際のバックコート層の剥がれの程度を、以下の評価基準に従って目視にて評価した。
【００４５】
「接着性」評価基準
ランク 状態
○： バックコート層が剥離しない場合
△： バックコート層の剥離が生じるが、実用上支障のない程度である場合
×： 実用上問題のある程度にバックコート層が剥離する場合。
【００４６】
「耐裏移り性」試験
作製した熱転写用印画紙と昇華型熱転写インクリボン（ＶＰＭ３０ＳＴＡ、ソニー（株）製）とを使用し、プリンター（ＣＶＰ−Ｇ７、ソニー（株）製）でＭＡＸ濃度２．３でベタ印画を行った。得られた熱転写用印画紙の染料受容層に、同種の熱転写用印画紙のバックコート層面を重ね合わせ、６０℃で２日間、５０ｇ／ｃｍ²の荷重を印加した。その後、重ね合わせたバックコート層へ移行した染料の光学濃度をマクベス反射濃度計を用いて測定した。この場合、数値が小さい程、染料の移行が少なく、耐裏移り性が良好であることを意味する。実用上、この数値が０．１５以下となることが望まれている。
【００４７】
「重送現象」試験
５０枚の熱転写用印画紙に対し、上述の「耐裏移り性」試験と同様の印画を連続的に行い、その際の重送現象の有無を調べた。
【００４８】
「インクリボンの融着」試験
熱転写印画紙の表裏を逆にしてプリンターに装着する以外は、上述の「耐裏移り性」試験と同様に、熱転写用印画紙のバックコート層に印画を行い、その際にインクリボンとバックコート層との融着の有無を調べた。
【００４９】
「耐水性」試験
画像を形成した熱転写用印画紙を水に浸した後、熱転写用印画紙を水から引上げ、そのバックコート層をベンコットを用いて１０回拭き、その際のバックコート層の剥がれの程度を、以下の評価基準に従って目視にて評価した。
【００５０】
「耐水性」評価基準
ランク 状態
○： バックコート層が剥離しない場合
△： バックコート層の剥離が生じるが、実用上支障のない程度である場合
×： 実用上問題のある程度にバックコート層が剥離する場合
【００５１】
【表２】

【００５２】
【表３】

【００５３】
【表４】

【００５４】
【表５】

【００５５】
【表６】

【００５６】
表１〜表５から、アセタール化度が５０％以上のポリビニルアセタールと多官能イソシアネート化合物との架橋反応物から構成されるバックコート層を有する実施例１〜２０の転写用印画紙は、「接着性」、「耐裏移り性」、「重送現象」、「インクリボンの融着」及び「耐水性」のすべての評価項目について、優れた結果を示していることがわかる。
【００５７】
一方、表６に示したように、バックコート層にポリビニルアセタールを使用していない比較例１〜３の熱転写用印画紙は、いずれもバックコート層に染料が移行しやすく、移行した染料画像の光学濃度がいずれも０．１５を大きく超え、従って、染料の「耐裏移り性」の点で実用上問題を有していた。従って、バックコート層にはポリビニルアセタールを使用することが必要であることがわかる。しかも、ポリビニルアセタール以外の樹脂を使用した場合には、その樹脂の種類に応じて、染料の「耐裏移り性」だけでなく「重送現象」や「インクリボン融着」の点で不十分な結果となることがわかる。
【００５８】
また、ポリビニルアセタールやポリエステル樹脂などの成膜成分を用いずに、主として多官能イソシアネート化合物で成膜したバックコート層を有する比較例４の熱転写用印画紙の場合には、「接着性」及び「インクリボン融着」の点で不満足となった。
【００５９】
従って、ポリビニルアセタール及び多官能イソシアネート化合物の双方を使用して、それらから形成される架橋反応物からバックコート層を形成することが必要であることがわかる。
【００６０】
【発明の効果】
本発明の熱転写用印画紙によれば、重送現象を抑制でき、また、印画紙を表裏逆にしてプリンターに誤送した場合でもインクリボンとの融着を抑制することができ、更に耐水性を低下させることなく染料の裏移りを大きく低減させることができる。
【図面の簡単な説明】
【図１】一般的な熱転写用印画紙の断面図である。
【符号の説明】
１ 熱転写用印画紙
２ 基材
３ 染料受容層
４ バックコート層[0001]
[Industrial application fields]
The present invention relates to a thermal transfer photographic paper having a backcoat layer. More specifically, the present invention relates to a thermal transfer photographic paper that can be suitably used for sublimation thermal transfer recording, and improves the runnability in the printer to suppress the double feed phenomenon and to reverse the dye. In addition, the present invention relates to a photographic paper for thermal transfer having a back coat layer having high water resistance and high adhesion to a substrate.
[0002]
[Prior art]
An ink ribbon having an ink layer made of a sublimable or heat diffusible dye and a photographic paper having a dye receiving layer are superposed, and the ink layer is heated according to image information by a thermal head or the like, and printed from the ink layer. A sublimation thermal transfer recording method is known in which an image is formed by transferring a dye to a paper dye-receiving layer. According to this method, a continuous color full-color image can be formed. Therefore, the method is attracting attention as a method for hard-copying a video image.
[0003]
FIG. 1 is a cross-sectional view of a general thermal transfer photographic paper 1 used for sublimation thermal transfer recording. As shown in the figure, this thermal transfer photographic paper 1 has a dye-receiving layer 3 on one side of a sheet-like substrate 2 and a backcoat layer 4 on the other side.
[0004]
Here, the dye receiving layer 3 is a layer that receives the dye transferred from the ink ribbon at the time of thermal transfer recording and holds the dye image formed thereby. Such a dye-receiving layer 3 is formed from a thermoplastic resin such as polyester, cellulose ester, polycarbonate, polyvinyl chloride, etc., which is conventionally easily dyed by a dye.
[0005]
In addition, the back coat layer 4 reduces the friction of the photographic paper in the printer that performs thermal transfer recording and improves the running performance, so that a plurality of photographic papers that should be sent to the printer one by one are sent to the printer in layers. In order to suppress the double feed phenomenon and even if the photographic paper is mistakenly sent to the printer with the front and back sides of the photographic paper turned upside down, the photographic paper will not be fused with the ink ribbon in the printer. It is provided in order to suppress the occurrence of mechanical troubles in the interior. As such a back coat layer 4, a layer formed of an acrylic resin is generally used.
[0006]
[Problems to be solved by the invention]
However, in a conventional thermal transfer photographic paper having a backcoat layer, when another photographic paper is placed on top of the photographic paper on which the image is formed, the image of the photographic paper on which the image is formed (the dye) There has been a problem that the dye is transferred from the receiving layer) to the back surface (back coat layer) of the photographic paper placed thereon.
[0007]
In order to solve this problem, in consideration of the fact that the dye forming the image is oleophilic, the back coat layer is formed of a hydrophilic resin such as polyvinyl alcohol having low compatibility with the oleophilic dye. However, when the back coat layer is formed of a hydrophilic resin, there arises a problem that the water resistance of the back coat layer is lowered.
[0008]
For this reason, in order to provide water resistance to polyvinyl alcohol, it is considered that polyvinyl alcohol is highly acetalized with an aldehyde compound. For example, it is conceivable to acetalize so that the degree of acetalization is 50% or more. Thereby, it is expected that the problems of the see-through property of the dye and the water resistance can be solved. However, the backcoat layer composed of polyvinyl acetal highly acetalized in this way increases the degree of lipophilicity, so if you print the paper incorrectly by feeding it to the printer upside down, the ink ribbon Therefore, there is a problem in that it causes a mechanical trouble of the printer. Furthermore, considering the film formability, it is desired that the degree of polymerization of the polyvinyl acetal is about 500 or more. However, the polyvinyl acetal having such a degree of polymerization has a problem that the adhesive force to the substrate is not sufficient.
[0009]
The present invention is intended to solve the above-described problems of the prior art, and suppresses double feeding phenomenon and dye set-off, has good water resistance, and at the same time has high adhesion to a substrate. In addition, an object of the present invention is to form a backcoat layer on a thermal transfer photographic paper which is difficult to fuse with an ink ribbon even when the photographic paper is reversed and fed to a printer and printed.
[0010]
[Means for Solving the Problems]
The present inventor has found that the above object can be achieved by constituting the backcoat layer of the thermal transfer photographic paper from a cross-linked reaction product of a polyvinyl acetal having a degree of acetalization of 50% or more and a polyfunctional isocyanate compound. The invention has been completed.
[0011]
That is, the present invention relates to a thermal transfer photographic paper having a dye-receiving layer on one side of a substrate and a backcoat layer on the other side, wherein the backcoat layer comprises polyvinyl acetal having an acetalization degree of 50% or more. A thermal transfer printing comprising a cross-linking reaction product with a polyfunctional isocyanate compound, wherein the cross-linking reaction product is obtained by cross-linking reaction of 100 to 200 parts by weight of a polyfunctional isocyanate compound with respect to 100 parts by weight of polyvinyl acetal. Provide paper.
[0012]
Hereinafter, the present invention will be described in detail.
[0013]
The thermal transfer photographic paper of the present invention is basically formed on a sheet-like base material 2, a dye receiving layer 3 formed on the surface thereof, and a back surface, similarly to the thermal transfer photographic paper 1 shown in FIG. And a laminated structure with the back coat layer 4 formed.
[0014]
Here, the thermal transfer photographic paper of the present invention is obtained by applying a crosslinking reaction product obtained by crosslinking a polyfunctional isocyanate compound to a polyvinyl acetal having a degree of acetalization of 50% or more, preferably 60% or more. It is characterized by containing.
[0015]
Here, the reason for using polyvinyl acetal is that polyvinyl acetal has low oil-based dye-dyeing property, and therefore can effectively prevent the dye see-off phenomenon.
[0016]
Further, the reason for using a polyvinyl acetal having an acetalization degree of 50% or more is that water resistance of an acetalization degree of less than 50% is not sufficient. In addition, since the thing of 90% or more of acetalization degree is difficult to obtain practically, in this invention, it is preferable to use a thing of 90% or less of acetalization degree.
[0017]
By the way, highly acetalized polyvinyl acetal increases the degree of lipophilicity. This increase does not greatly increase the set-off of the dye, but causes a problem that the ink ribbon is easily fused to the backcoat layer 4. Further, when the degree of polymerization of polyvinyl acetal is set to 500 or more in consideration of film formability, there arises a problem that the adhesiveness of the back coat layer 4 to the substrate 2 is lowered. Therefore, in the present invention, in order to increase the cohesive force of the backcoat layer itself and suppress the fusion with the ink ribbon, the polymerization degree of the polyvinyl acetal is sufficiently increased to maintain the good film formability. In order to increase the adhesive strength to the material, it is necessary to cause the polyvinyl acetal to undergo a crosslinking reaction using a crosslinking agent.
[0018]
In this case, a polyfunctional isocyanate compound is used as the crosslinking agent in this case. Thereby, the fusion | bonding to the ink ribbon of the backcoat layer 4 can be suppressed effectively, and the favorable adhesive force to a base material can be provided. In addition, good water resistance can be imparted to the backcoat layer 4.
[0019]
Furthermore, the friction coefficient of the backcoat layer 4 can be adjusted to an appropriate range by forming the backcoat layer 4 from the above-mentioned crosslinking reaction product and a lubricant added as appropriate. Therefore, the double feeding phenomenon can be suppressed.
[0020]
As the polyvinyl acetal used in the present invention, chemical structural formula (A)
[0021]
[Chemical formula 2]

(Wherein R ¹ is hydrogen or a lower alkyl group such as a methyl group, an ethyl group, or a propyl group; R ² is a lower alkyl group such as a methyl group; and x, y, and z are formulas (I)
[0022]
[Expression 2]
[Degree of acetalization (%)] = {x / (x + y + z)} × 100 (I)
The degree of acetalization defined by is a number of 0 or more at which the degree of acetalization is 50% or more. )
Preferred examples include compounds represented by: Particularly preferred polyvinyl acetals are polyvinyl formal in which R ² is a methyl group and R ¹ is hydrogen, polyvinyl ethanal in which R ¹ is a methyl group, polyvinyl propanal in which R ¹ is an ethyl group, and R ¹ is propyl. Examples thereof include polyvinyl butanal which is a group.
[0023]
As polyvinyl acetal, if the degree of polymerization, which is the sum of x, y, and z, is too small, the film becomes brittle and the film formability is insufficient, and if it is too large, the adhesion to the substrate is insufficient. The polymerization degree is preferably 500 to 3000, more preferably 1500 to 3000.
[0024]
As the polyfunctional isocyanate compound used in the present invention, a non-yellowing type compound having two or more isocyanate groups in the molecule can be preferably exemplified. For example, aliphatic polymethylene such as hexamethylene diisocyanate (HDI), biuret, etc. Mention may be made of aromatic polyisocyanates such as isocyanate, toluene diisocyanate (TDI) and xylene diisocyanate (XDI). These may be used alone or in combination of two or more.
[0025]
Moreover, when forming a crosslinking reaction product from polyvinyl acetal and a polyfunctional isocyanate compound, it can be carried out by various means such as ultraviolet irradiation or heating, but is preferably crosslinked by heating from the viewpoint of production cost and crosslinking operation. .
[0026]
In such a cross-linked reaction product, the blending ratio of the polyvinyl acetal and the polyfunctional isocyanate compound is preferably 100 to 200 parts by weight of the polyfunctional isocyanate compound with respect to 100 parts by weight of the polyvinyl acetal. When the blending ratio of the polyfunctional isocyanate compound is too large, the pot life of the paint prepared by mixing them to form the backcoat layer 4 is shortened. Conversely, when the blending ratio is too small, the crosslinking density is lowered and the effect of the present invention is reduced. Since it cannot be obtained, it is not preferable.
[0027]
Moreover, since the effect of this invention will not be acquired if there is too little content of the crosslinking reaction product in the backcoat layer 4, it shall be 50 weight% or more.
[0028]
In addition to the above-mentioned polyvinyl acetal and polyfunctional isocyanate compound, various additives can be blended in the back coat layer 4 as necessary. For example, friction coefficient modifiers such as organic or inorganic fillers; solid waxes such as polyethylene wax, amide wax, Teflon powder, fluorine surfactants, phosphate ester surfactants, silicone oils, high melting point silicone waxes, etc. Release agent: cationic surfactant (quaternary ammonium salt, polyamine, etc.), anionic surfactant (alkylbenzene sulfonate, alkyl sulfate sodium salt, etc.), amphoteric surfactant, nonionic interface An antistatic agent such as an activator; a water-based ink writability improver such as polyalkylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone can be appropriately blended. Such an antistatic agent may be applied to the surface of the backcoat layer 4 by coating or the like in addition to being contained in the backcoat layer 4.
[0029]
In the thermal transfer photographic paper of the present invention, the substrate 2 and the dye receiving layer 3 can be configured in the same manner as conventional thermal transfer photographic paper.
[0030]
For example, as the base material 2, high-quality paper, coated paper, various plastic sheets, synthetic paper, or a composite sheet thereof can be used.
[0031]
The dye-receiving layer 3 can be formed from a dyeing resin such as polyester, cellulose ester, polyvinyl butyral, polycarbonate, polyvinyl chloride.
[0032]
The dye receiving layer 3 can contain various additives as required. For example, in order to improve the whiteness of the dye-receiving layer 3 to increase the sharpness of the transferred image, to impart writing properties to the image surface, and to prevent retransfer of the transferred image, a fluorescent whitening agent or white Pigments can be included. Here, as the white pigment, titanium oxide, zinc oxide, kaolin, clay, calcium carbonate, fine powder silica and the like can be used.
[0033]
In addition, an ultraviolet absorber, a light stabilizer, an antioxidant, and the like can be added to the dye receiving layer 3 in order to improve the light resistance of the transferred image. Further, a release agent can be added in order to improve releasability from the ink ribbon at the time of thermal transfer. As the mold release agent, solid waxes such as polyethylene wax, amide wax, and Teflon powder, fluorine surfactants, phosphate ester surfactants, silicone oil, high melting point silicone wax, and the like can be used. Among these, it is preferable to use silicone oil from the viewpoint of releasability and durability.
[0034]
Furthermore, an antistatic agent can be added to the dye receiving layer 3 in order to suppress the generation of static electricity. Antistatic agents include cationic surfactants (quaternary ammonium salts, polyamines, etc.), anionic surfactants (alkylbenzene sulfonates, alkyl sulfate sodium salts, etc.), zwitterionic surfactants, nonionics Various surfactants such as type surfactants can be used. Such an antistatic agent may be applied to the surface of the dye receiving layer 3 by coating or the like in addition to being contained in the dye receiving layer 3.
[0035]
The thermal transfer photographic paper of the present invention can be produced by a conventional method. For example, a backcoat layer-forming coating material containing polyvinyl acetal and a polyfunctional isocyanate compound is prepared, and this is applied to the back surface of the substrate 2 by a conventional method. And coating to form a back coat layer 4. Further, a dye receiving layer forming coating is applied to the surface of the substrate 2, and the dye receiving layer 3 is formed by curing. be able to. Moreover, it can also manufacture by forming the backcoat layer 4 after forming the dye receiving layer 3 previously.
[0036]
The image forming method for the thermal transfer photographic paper of the present invention is not particularly limited, and for example, sublimation thermal transfer recording can be performed with a commercially available video printer using a sublimation thermal transfer recording ink ribbon. In particular, when used in an image forming method using a lipophilic dye, it is possible to effectively prevent the image from seeing off.
[0037]
[Action]
In the photographic paper for thermal transfer of the present invention, the back coat layer contains a cross-linked reaction product of a highly acetalized polyvinyl acetal and a polyfunctional isocyanate compound. This cross-linked reaction product has sufficient water resistance, is hardly dyed by a dye, and exhibits good adhesion to a substrate. Therefore, the backcoat layer composed of such a cross-linked reaction product has a sufficient adhesion to the base material while suppressing the back-off of the dye and the ink ribbon.
[0038]
【Example】
Hereinafter, the present invention will be specifically described based on examples.
[0039]
Examples 1-20 and Comparative Examples 1-4
As a sheet-like base material, 150 μm-thick synthetic paper (FPG-150, manufactured by Oji Yuka Co., Ltd.) is prepared. For forming a dye-receiving layer having the composition shown in Table 1 so that the dry film thickness is 10 μm on the surface. The paint was applied and dried at 120 ° C. for 2 minutes to form a dye-receiving layer on the surface of the substrate.
[0040]
[Table 1]

Next, a backcoat layer-forming paint having the composition shown in Tables 2 to 6 is applied to the back surface of the sheet-like base material so that the dry film thickness becomes 1 μm, and cured (condition: 50 ° C./2 days) for back A thermal transfer photographic paper was prepared by forming a coat layer.
[0041]
In addition, the brand name and acquisition place of the component used in the Example or the comparative example are as follows.
[0042]
Polyfunctional isocyanate compound (* 1): Coronate L, polyfunctional isocyanate compound produced by Nippon Polyurethane Co., Ltd. (* 2): Coronate HL, polyfunctional isocyanate compound produced by Nippon Polyurethane Co., Ltd. (* 3): Takenate D-102, Takeda Silicone oil manufactured by Yakuhin Kogyo Co., Ltd. (* 4): SF-8427, Conductive agent manufactured by Toray Dow Corning Co., Ltd. (* 5): Saftmer ST-1000, Polyester resin manufactured by Mitsubishi Yuka Co., Ltd. (* 6): Byron 200, Toyobo Vinyl chloride copolymer resin (* 7): MR110, acrylic ester copolymer (* 8) manufactured by Nippon Zeon Co., Ltd. Plycol WL81, manufactured by Rohm and Haas.
[0043]
(Evaluation)
"Adhesion" to the base material of the backcoat layer, "anti-set-off resistance" to the backcoat layer of the dye, "double feed phenomenon" in the printer of the thermal transfer photographic paper, The “ink ribbon fusion” and the “water resistance” of the backcoat layer when printed on the back surface (backcoat layer) of the thermal transfer photographic paper were tested and evaluated as described below. These results are shown in Tables 2-6.
[0044]
"Adhesion" test of backcoat layer to substrate <br/> Backcoat when the adhesive tape (cello tape, manufactured by Nichiban Co., Ltd.) is once applied to the backcoat layer of thermal transfer photographic paper and then peeled off. The degree of layer peeling was visually evaluated according to the following evaluation criteria.
[0045]
"Adhesiveness" evaluation criteria Rank State ○: When the backcoat layer does not peel △: When the backcoat layer peels off, but there is no practical problem ×: Back to the extent of practical problems When the coat layer peels off.
[0046]
"Back-off resistance" test Using the produced thermal transfer printing paper and sublimation thermal transfer ink ribbon (VPM30STA, manufactured by Sony Corporation), using a printer (CVP-G7, manufactured by Sony Corporation) Solid printing was performed at a MAX density of 2.3. The backcoat layer surface of the same kind of thermal transfer printing paper was superimposed on the dye receiving layer of the obtained thermal transfer printing paper, and a load of 50 g / cm ² was applied at 60 ° C. for 2 days. Thereafter, the optical density of the dye transferred to the overlaid backcoat layer was measured using a Macbeth reflection densitometer. In this case, the smaller the value, the less dye transfer and the better the reverse resistance. In practice, it is desired that this value be 0.15 or less.
[0047]
“Double Feed Phenomenon” Test 50 sheets of thermal transfer printing paper were continuously subjected to the same printing as the above-mentioned “back-off resistance” test, and the presence or absence of the double feed phenomenon was examined.
[0048]
“Ink ribbon fusing” test <br/> Similar to the above-mentioned “back-off resistance” test, except that the thermal transfer photographic paper is mounted on the printer with the front and back sides reversed. Printing was performed, and the presence or absence of fusion between the ink ribbon and the backcoat layer was examined.
[0049]
"Water resistance" test After immersing the thermal transfer photographic paper on which the image is formed in water, the thermal transfer photographic paper is pulled up from the water, and the backcoat layer is wiped 10 times with a bencot. The degree of peeling of the coat layer was visually evaluated according to the following evaluation criteria.
[0050]
"Water resistance" evaluation criteria Rank State ○: When the backcoat layer does not peel △: When the backcoat layer peels off, but there is no practical problem ×: Back to some extent for practical problems When the coat layer peels off [0051]
[Table 2]

[0052]
[Table 3]

[0053]
[Table 4]

[0054]
[Table 5]

[0055]
[Table 6]

[0056]
From Tables 1 to 5, the transfer photographic papers of Examples 1 to 20 having a back coat layer composed of a cross-linked reaction product of a polyvinyl acetal having a degree of acetalization of 50% or more and a polyfunctional isocyanate compound are “adhesive” It can be seen that excellent results are shown for all the evaluation items of “Resistance”, “Set-off resistance”, “Double feed phenomenon”, “Ink ribbon fusion” and “Water resistance”.
[0057]
On the other hand, as shown in Table 6, the thermal transfer photographic papers of Comparative Examples 1 to 3 in which no polyvinyl acetal is used in the backcoat layer, the dye easily migrates to the backcoat layer. Each of the optical densities greatly exceeded 0.15, and therefore there was a practical problem in terms of “back-off resistance” of the dye. Therefore, it can be seen that it is necessary to use polyvinyl acetal for the backcoat layer. Moreover, if a resin other than polyvinyl acetal is used, depending on the type of resin, not only the “transfer resistance” of the dye but also the “double feed phenomenon” and “ink ribbon fusion” are insufficient. It turns out that it becomes a result.
[0058]
Further, in the case of the photographic paper for thermal transfer of Comparative Example 4 having a back coat layer mainly formed of a polyfunctional isocyanate compound without using film forming components such as polyvinyl acetal and polyester resin, “adhesiveness” and “ It was unsatisfactory in terms of “ink ribbon fusion”.
[0059]
Therefore, it turns out that it is necessary to use both a polyvinyl acetal and a polyfunctional isocyanate compound, and to form a backcoat layer from the crosslinking reaction product formed from them.
[0060]
【The invention's effect】
According to the photographic paper for thermal transfer of the present invention, the double feeding phenomenon can be suppressed, and even when the photographic paper is reversely fed to the printer, the fusion with the ink ribbon can be suppressed. The set-off of the dye can be greatly reduced without lowering.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a general thermal transfer photographic paper.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Printing paper for thermal transfer 2 Base material 3 Dye receiving layer 4 Backcoat layer

Claims (3)

In thermal transfer printing paper having a dye-receiving layer on one side of the substrate and a backcoat layer on the other side,
The back coat layer contains a cross-linked reaction product of a polyfunctional isocyanate compound with a polyvinyl acetal having a degree of acetalization of 50% or more ,
A thermal transfer photographic paper , wherein the cross-linked reaction product is obtained by cross-linking reaction of 100 to 200 parts by weight of a polyfunctional isocyanate compound with respect to 100 parts by weight of polyvinyl acetal . Polyvinyl acetal has the chemical structural formula (A)

(Wherein R ¹ is hydrogen or a lower alkyl group, R ² is a lower alkyl, and x, y and z are represented by formula (I)
[Expression 1]
[Degree of acetalization (%)] = {x / (x + y + z)} × 100 (I)
The degree of acetalization defined by is a number of 0 or more at which the degree of acetalization is 50% or more. The thermal transfer photographic paper according to claim 1 , which is a compound represented by the formula: The photographic paper for thermal transfer according to claim 2 , wherein the polyvinyl acetal is polyvinyl formal, polyvinyl ethanal, polyvinyl propanal or polyvinyl butanal.

Images