JPH07421B2 - Multiple print type pressure sensitive transfer recording medium - Google Patents

Description

The present invention relates to a multiple-print type pressure-sensitive transfer recording medium, and more particularly to a multiple-print type pressure-sensitive transfer recording medium used for overstrike or multi-strike in impact type typewriters and printers.

BACKGROUND ART Conventional multi-print type pressure-sensitive transfer recording media of this type include:
For example, as shown in Japanese Patent Application Laid-Open No. 58-29694, a structure is known in which a plastic film substrate and a microporous layer impregnated with ink paste are bonded together by an adhesive layer made of a vinyl chloride-vinyl acetate copolymer.

This type of pressure-sensitive transfer recording medium has the problem that, although this problem occurs both at room temperature and at high temperatures, when printing is repeated particularly at low temperatures, the microporous layer itself peels off from the film substrate and is transferred, making further printing impossible.

An object of the present invention is to provide a pressure-sensitive transfer recording medium of the multiple print type which allows repeated printing at the same location on the recording medium not only in normal temperature and high temperature environments but also in low temperature environments.

DISCLOSURE OF THE INVENTION The present invention provides a multiple-print type pressure-sensitive transfer recording medium having a microporous layer formed on the surface of a substrate, the microporous layer comprising microporous particles and a binder agent that bonds the particles together, and the microporous layer containing a liquid pink paste that is incompatible with the binder agent, wherein the substrate is a plastic film, and the substrate and the microporous layer are bonded together by an adhesive layer formed by crosslinking a vinyl chloride-vinyl acetate copolymer having hydroxyl groups with an isocyanate compound.

The recording medium of the present invention can be used not only in normal temperature and high temperature environments (for example, up to 45°C), but also in low temperature environments, for example, in a 0°C atmosphere.
Even if the same location is repeatedly printed 20 times or more,
The porous layer does not peel off from the substrate film, and printing can be performed satisfactorily.

This effect does not change even after the recording medium of the present invention is left standing at -20°C for one week or at 60°C for one week.

The present invention is characterized in that the adhesive layer that bonds the microporous layer and the substrate in the recording medium is improved.

The adhesive layer in the present invention is made of a vinyl chloride-containing polymer having a hydroxyl group.
This adhesive is made of a vinyl acetate copolymer crosslinked with an isocyanate compound, and has excellent adhesive properties, especially at low temperatures.

The vinyl chloride-vinyl acetate copolymer having a hydroxyl group is and This is obtained by partially saponifying a vinyl chloride-vinyl acetate copolymer.

The vinyl chloride-vinyl acetate copolymer preferably contains 5-15% by weight of vinyl alcohol units, 85-93% by weight of vinyl chloride units, and 0.5-3% by weight of vinyl acetate units. If the content of vinyl alcohol units is less than 5% by weight, the adhesion between the microporous layer and the substrate decreases, and if it exceeds 15% by weight, the solubility in solvents decreases significantly and the pressure-sensitive transferability of the liquid ink paste decreases. The copolymer preferably has an average degree of polymerization of 300-700. If the average degree of polymerization is greater than 700, the adhesive layer becomes too hard and easily becomes brittle at low temperatures, while if it is less than 30%, the adhesive layer becomes too hard and easily becomes brittle at low temperatures.
If it is less than 0, the adhesive strength will be insufficient.

The isocyanate compound used in the present invention is a polyisocyanate, i.e., a difunctional or trifunctional or higher isocyanate. There are no particular limitations on the polyisocyanate, and any of the usual ones, such as those used in polyurethane adhesives, can be used. Typical examples of such polyisocyanates include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane-4,4'-diisocyanate, triphenylmethane-p,
Examples of the isocyanate compound used in the present invention include p',p"-triisocyanate and hexamethylene diisocyanate. As the isocyanate compound, a urethane prepolymer having terminal NCO groups, which is a partial reaction product of the above-mentioned polyisocyanate and a polyhydroxy compound (for example, trimethylolpropane, propylene glycol, etc.), is also preferably used. The above isocyanate compounds may be used alone or in combination of two or more. When a mixture of isocyanate compounds having different numbers of NCO groups is used, it is preferable to use one having an average number of NCO groups per molecule of 1.8 or more.

The vinyl chloride-vinyl acetate copolymer having a hydroxyl group reacts with an isocyanate compound to crosslink as shown in the following formula:

The amount of the isocyanate compound added is preferably 1 to 6 parts per 20 parts (parts by weight, the same applies hereinafter) of the vinyl chloride-vinyl acetate copolymer having hydroxyl groups. If the amount is less than 1 part, the effect of improving adhesion is insufficient, and if it exceeds 6 parts, the pot life of the ink is shortened.
The printability deteriorates and the print density becomes weaker after repeated printing.
The molar ratio is about 0.25 to 1.50.

Examples of the solvent used to prepare the adhesive solution include methyl ethyl ketone, methyl isobutyl ketone, and acetone.

The adhesive may further contain other adhesives such as polyurethane adhesives, polyester adhesives, and acrylic adhesives.

The adhesive layer is formed by applying the adhesive to one side of the substrate with a coater in an amount of 1 to 4 g/ ^m2 (amount applied after drying, the same applies hereinafter), preferably 2 to 3 g/ ^m2 . If the amount applied is less than 1 g/ ^m2 , the adhesiveness decreases, and if it exceeds 4 g/ ^m2 , the ink retention becomes too strong, resulting in a decrease in print density.

As the substrate, a plastic film of polyester, polypropylene, polyamide or the like having a thickness of about 3 to 50 μm can be suitably used.

Next, liquid ink paste components such as colorants and viscosity modifiers are mixed, and this is kneaded and mixed with components constituting the microporous layer such as porous powder and binder, and a volatile solvent, etc. The dispersion thus obtained is applied to the top surface of the adhesive layer of the substrate using a coater at a rate of, for example, 10 to 30 g/ ^m2 , preferably 15 to 30 g/ ^m2 , and then dried. In this way, a layer containing the liquid ink paste consisting of the colorants, viscosity modifiers, etc., and the microporous layer composed of the porous powder and binder is formed on the adhesive layer, and the pressure-sensitive transfer recording medium of the present invention is obtained.

As the colorant, any of the colorants used in this type of recording medium, such as dyes and pigments, can be used, but it is preferable to use a solution of an oil-soluble dye dissolved in a liquid fatty acid together with a pigment, since this can significantly reduce the decrease in print density due to repeated printing. Here, as the liquid fatty acid, one or a mixture of two or more of oleic acid, isostearic acid or similar liquid fatty acids can be used, and the amount of the liquid fatty acid used is 1 to 30% of the total amount of the ink paste components.
It is preferable to blend it in the range of % by weight.

As the oil-soluble dye, Nigrosine base, Spirit Black, Special Black, Victoria Blue base, Methyl Violet base, etc. can be suitably used alone or in mixtures of two or more thereof, and it is preferable to blend them in the range of 1 to 10% by weight of the total amount of the ink paste.

Examples of the pigment include Printex 25 (a trade name of a color carbon black manufactured by Degussa), Mogul L (a trade name of a color carbon black manufactured by Cabot Corporation), and Raven 1255 (a trade name of a color carbon black manufactured by Columbia Ribbon and Carbon Manufacturing Co.).
One or more kinds of carbon black, black toner, etc. can be appropriately used, and 1 of the total amount of the ink paste can be used.
The blending amount is preferably in the range of up to 40% by weight, particularly 20 to 40% by weight.

Any of the conventionally known viscosity modifiers can be used as the viscosity modifier, but particularly preferred are vegetable oils such as rapeseed oil, soybean oil, and castor oil; mineral oils such as vitreous oil and jet oil;
Di(2-ethylhexyl) adipate (hereinafter referred to as DOA), di(2-ethylhexyl) sebacate (hereinafter referred to as DO
The viscosity modifier may be one or more of the following: a cold-resistant plasticizer such as di(2-ethylhexyl)azelate (hereinafter referred to as DOZ); a hydrocarbon such as Lipolube oil; an α-olefin oligomer; etc. The viscosity modifier is used to adjust the viscosity of the liquid ink paste at 25°C, preferably 4,
The viscosity may be less than 1,000 cP (preferably 3,600 cP or less) or more than 300 cP, and it is particularly preferable to use an amount in the range of 20 to 50% by weight of the total ink paste. When a liquid fatty acid and an oil-soluble dye are used as the colorant in a weight ratio of 20:1 to 2:1, good repeatability can be obtained even at a viscosity of 2,000 to 10,000 cP.

The liquid ink paste may further contain a wetting agent.

Any of the conventionally known wetting agents can be used as the wetting agent, and in particular, one or more of sorbitan fatty acid esters such as sorbitan monostearate, sorbitan monoisostearate, and sorbitan monooleate, lecithin, or similar substances can be suitably used, and it is preferable to incorporate them in an amount of 3 to 30% by weight (particularly 5 to 25% by weight) of the total amount of the ink paste.

The porous powder may be one or more of inorganic porous powders such as diatomaceous earth, zeolite, porous silica, activated carbon, etc., or organic porous powders such as urethane foam powder, etc., having an average porosity of 50 to 97%, preferably 60 to 93%, and an average particle size of 1 to 20 μm. The amount of porous powder used is preferably 1 to 4 parts, preferably 2 to 3 parts, per 10 parts of the liquid ink paste.

The binder may be one or more of the following resins that are incompatible with the liquid ink paste components but are compatible with the volatile solvents listed below and have adhesive properties for the porous powder listed below: vinyl chloride-vinyl acetate copolymer, polyester resin, cellulose acetate butyrate resin, etc. The amount of binder used is preferably 1 to 10 parts, and more preferably 2 to 7 parts, per 10 parts of the liquid ink paste.

Among these binders, a vinyl chloride-vinyl acetate copolymer, in which the ratio of vinyl chloride is 4 to 7 parts, is particularly preferred in order to obtain uniform, clear printing.
If the ratio is less than 4 parts per 5 parts of vinyl acetate, it becomes difficult to manufacture the resin.
If the ratio is more than 5 parts, the microporous layer becomes hard and easily broken. For this reason, when the ratio of vinyl chloride is 4 to 7 parts per 5 parts of vinyl acetate, the resin can be easily produced and a microporous layer that is not easily broken can be obtained.

Furthermore, if the average degree of polymerization of the specific vinyl chloride-vinyl acetate copolymer is less than 700, the heat resistance decreases, and there is a risk that the liquid ink paste will flow out when the ambient temperature exceeds 60°C. Furthermore, if the average degree of polymerization exceeds 950, production becomes difficult. Therefore, it is preferable to set the average degree of polymerization to 700 to 950, especially 800 to 900.

The volatile solvent may be methyl ethyl ketone (hereinafter,
One or more of the following may be suitably used: MEK, acetone, methyl isobutyl ketone, toluene, IP Solvent (a trade name for an isoparaffinic hydrocarbon oil manufactured by Idemitsu Petrochemical Co., Ltd.).

Best Mode for Carrying Out the Invention The present invention will now be described with reference to examples.

EXAMPLES Four types of adhesives, Nos. 1 to 4, having the compositions shown in Table 1 were prepared.

Next, each of these adhesives was applied to a polyethylene terephthalate film (thickness: 7 μm) using a blade coater so that the thickness after drying would be 2 g/m ² , and the temperature was 9
The coating was dried in a drying apparatus at 0°C for 1 minute to allow the crosslinking reaction to occur.

Then, eight kinds of liquid ink pastes No. 1 to No. 8 shown in Table 2 and 15 kinds of liquid ink pastes No. 1 to No. 15 shown in Table 3 were applied to the adhesive layer.
The thickness of the microporous layer after drying is 7 μm.
An ink-containing microporous layer having a thickness of 1/2 mm was formed to obtain a transfer recording medium.

Each of the recording media thus obtained was printed at 0°C using an AP-500 electronic typewriter manufactured by Canon Inc.
When repeated printing tests were conducted in this atmosphere, the same spot was printed more than 20 times on all recording media.
The microporous layer did not peel off from the substrate, and the print had sufficient density for image reading.

The multiple print type pressure-sensitive transfer recording medium of the present invention has the effect of being able to obtain prints having a density sufficient for image reading even when the same location is repeatedly printed in a low temperature atmosphere.

Claims (6)

[Claims] [Claim 1] A multiple-print type pressure-sensitive transfer recording medium in which a microporous layer consisting of microporous particles and a binder agent that bonds the particles to each other is provided on the surface of a substrate, and a liquid ink paste that is incompatible with the binder agent is contained in the microporous layer, wherein the substrate is a plastic film, and the substrate and the microporous layer are bonded together by an adhesive layer made of a vinyl chloride-vinyl acetate copolymer having hydroxyl groups crosslinked with an isocyanate compound. 2. The recording medium according to claim 1, wherein the vinyl chloride-vinyl acetate copolymer having hydroxyl groups comprises vinyl alcohol units, vinyl chloride units and vinyl acetate units. 3. The copolymer of claim 1, wherein the copolymer contains 5 to 10 vinyl alcohol units.
3. The recording medium of claim 2, which comprises 15% by weight of vinyl chloride units, 85 to 93% by weight of vinyl chloride units, and 0.5 to 3% by weight of vinyl acetate units. 4. The recording medium according to claim 1, wherein the amount of the isocyanate compound used is 1 to 6 parts by weight per 20 parts by weight of said copolymer. 5. The recording medium according to claim 1, wherein said plastic film is at least one of a polyester film and a polyamide film. 6. The microporous layer is made of a porous powder selected from the group consisting of diatomaceous earth, calcium carbonate, and porous silica powder, and a vinyl chloride-based binder consisting of 5 parts by weight of vinyl acetate and 4 to 7 parts by weight of vinyl chloride.
2. The recording medium according to claim 1, which comprises a vinyl acetate copolymer.