JPH02164592A - Conductive film and transfer material for thermal recording - Google Patents

Abstract

PURPOSE:To improve heat resistance and the stabilities of electric characteristics by forming a film having specific surface resistivity and shrinkage stress from an aromatic polyamide or polyimide resin and a conductive filler. CONSTITUTION:A conductive filler is dispersed in a polymer-soluble solvent and this dispersion is added to and mixed with a solvent having an aromatic polyamide or polyimide resin dissolved therein to prepare a film forming raw solution. This raw solution is formed into a film according to a dry/wet method, a dry method or a wet method while the film is biaxially stretched to obtain a conductive film having surface resistivity RSO of 10<1>-10<4>OMEGA, surface resistivity RS after heating at 350 deg.C of 0.7<=RS/RSO<=1.2, shrinkage stress at 10-350 deg.C of 2kg/mm<2> or less and a thickness of 2-30mum. An ink layer is provided to one surface of this conductive film to form a transfer material for thermal recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a conductive film with excellent heat resistance, and a transfer body for heat-sensitive recording comprising an ink layer provided on one surface of the film.

[Prior art] Films made of aromatic polyamide or aromatic polyimide are used in electrical and electronic applications, information-related applications, etc. due to their excellent heat resistance. This film is a good heating element and its use is being considered. For example, JP-A-62-3
Typical examples include the base material of a transfer body using an electric transfer method such as 9288, and a planar heating element. These resins have good heat resistance, so they can raise the heat generation temperature, making it possible to print at high speeds in electrical transfer applications.

[Problem to be solved by the invention] These resins have a heat resistance of 300°C or higher for short periods of time and 150°C or higher for long-term use, and even films containing conductive fillers are heat resistant. is good, but
It has been found that when conventional conductive films are repeatedly used at high temperatures or used for long periods of time, the electrical properties of the films change.

That is, in electrical transfer applications, there is no problem when printing only once, but when the transfer body is heated many times because it is used many times, the resistance of the film changes and a problem arises in which the target printing density cannot be obtained. It has also been found that when the electrodes are attached and used for heating as a sheet heating element, there is a problem in that the resistance changes and the heating temperature changes.

The present invention solves the above problems and provides a conductive film with excellent heat resistance and stable electrical properties and a transfer body for heat-sensitive recording.

[Means for Solving the Problems] The present invention provides a film comprising at least an aromatic polyamide resin or an aromatic polyimide resin and a conductive filler, the film having a surface resistivity R8° of 1,01 to 104Ω, 350
Surface resistivity R5 after heating at °C is 0.7≦Rs/Rs
o≦1.2 and a shrinkage stress of 2 kg/m rd or less in a temperature range of 100 to 350°C, and a conductive film having a thickness of 2 to
This is a transfer body for heat-sensitive recording in which an ink layer is provided on one side of the conductive film having a thickness of 30 μm.

The aromatic polyamide of the present invention is preferably a polymer containing 70 mol% or more of repeating units represented by the general formula %.

Here, Ar, , and Ar2 contain at least one aromatic ring and may be the same or different, and representative examples thereof include the following.

In addition, some of the hydrogens on the aromatic rings are halogen groups (especially chlorine), nitro groups, 01 to C3 alkyl groups (
In particular, it also includes those substituted with substituents such as methyl group) and Cl-C5 alkoxy group. Moreover, X is -O--CH,-, -8o2-, -3-CO-, etc. These may be included alone or in copolymerized form.

The aromatic polyimide in the present invention is one that contains one or more aromatic rings and one or more imide rings in the repeating unit of the polymer, and is derived from this anhydride. Representative examples include the following:

End of conversation Nen Y-kai Here, Y is 10--CO--CH2 -5--5o2-, etc.

Furthermore, Ar is derived from tricarboxylic acid or its anhydride.

8r4 and Ar6 contain at least one aromatic ring and are derived from aromatic diamino or aromatic diisocyanate. Further, it may contain an amide bond, a urethane bond, or the like.

Typical examples of Ar4, Ar, etc. include the following.

Those containing 70 mol % or more of repeating units represented by are preferred.

Here, Ar3 + A r 5 contains at least one aromatic ring, and the two carbonyl groups forming the imide ring are bonded to adjacent carbon atoms on the aromatic ring.

This Ar3 is an aromatic tetracarboxylic acid or in which some of the hydrogens on these aromatic rings are halogen groups,
It also includes those substituted with substituents such as a nitro group, an 01-C3 alkyl group, and an 01-C3 alkoxy group. Z is
-0--CH2S-1SO□-1-CO- and the like.

These may be included alone or in copolymerized form.

Furthermore, the aromatic polyamide and aromatic polyimide of the present invention may be blended with lubricants, antioxidants, other additives, and other polymers to the extent that the physical properties of the film are not impaired.

The conductive filler of the present invention includes metals, metal oxides, carbon black, coatings with conductive substances on the surface,
Plated fillers such as silicon oxide, silicon carbide,
Examples include titanium oxide, calcium sulfate, aluminum oxide, etc. whose surface is plated with ALI, Ag, Ni, Cu, 2N, etc. 1. Shapes include spherical, amorphous, plate-like, and needle-like. Preferably, the size is spherical or amorphous, with a plate shape of 5 nm to 10 μm, and needle-shaped, with an average maximum length of 1100 nm to 50 μm. Among these, carbon black is preferred from the viewpoint of processability and dispersibility. Carbon black has a surface area (measured by nitrogen adsorption method) of 50 to 20,001 ('/g), an average particle size of -order particles of 5 to 500 nm, more preferably 10 to 1
00n, m. In addition, the legal adsorption amount is 50~2000■
/g, more preferably 100 to 1500 /g.

The amount of conductive filler added varies depending on the desired resistance, but is preferably 10 to 70 wj%, more preferably 10 to 5 Qwt%. When carbon black is used, it is preferably 10 to 40 wt%. If it is less than 10 wt%, no conductivity will be exhibited, and if it is more than 7 Qvt%, the conductivity will be too good, resulting in poor conversion efficiency to Joule heat or deterioration of the mechanical properties of the film. Note that in order to exhibit conductivity with a small amount added, it is preferable to combine two or more types of conductive fillers or to add a non-conductive filler.

The surface resistivity R5O of the present invention is 101 to 104 Ω, preferably 102 to 104 Ω. If it is smaller than 10', it will be difficult to convert into Joule heat, and if it is larger than 104Ω, the conductivity will be low and it will be difficult to generate heat from the film.

Furthermore, the film of the present invention can be heated for 1 minute at 350°C.
, the relationship between the surface resistivity Rs after heating and R3° before heating is 0. 7≦R, /R8,≦1.2, preferably 0.8
It must be within the range of ≦RS/R30≦1.1. If the product falls outside this range, problems may occur, such as the print density changing significantly when used repeatedly for electrical transfer, and the heat generation temperature gradually changing when used as a sheet heating element. , impractical.

In addition, the shrinkage stress of the film in the temperature range of 100 to 350°C is
Both require 2 kg/mn (the following is required.

Preferably 1kg/mrr? It is as follows. 2 kg/
mrr? If it is larger, the amount of deformation of the film due to heating becomes large, and when printing is repeated in electrical transfer applications, contact between the transfer body and the head deteriorates, causing problems such as uniform printing being impossible.

The film of the present invention has 7.
Is the strength of both sides 12kg/mrr? Above, it is more preferably 15 kg/m♂ or more. If the strength is less than 12 kg/mm, problems such as wrinkles or cuts are likely to occur during processing or use. Further, the elongation in at least one direction is preferably 10% or more, more preferably 15 to 100%, and the Young's modulus is 400 kg.
/mm or more is preferable.

Furthermore, the moisture absorption rate of the film (48% at 25°C and 175%RH)
(measured after standing for a period of time) is preferably 4w1% or less, more preferably 2wt% or less. If it is more than 4 wt%, the change in resistance will increase due to humidity, which is not preferable.

As one of the uses of the film of the present invention, a transfer body for heat-sensitive recording using an electric transfer method is suitable. The film thickness when used for this purpose is 2 to 30 μm. Preferably 3
~20 μm. If it is thinner than 2 μm, the strength will decrease and it will not be practical. Also, if it is thicker than 30 μm, local heating of the ink will not be possible and clear printing will not be obtained.
Furthermore, the energy required for printing increases, making it unsuitable for high-speed printing.

The ink layer provided on the transfer body is not particularly limited, but specific examples include melting ink and sublimation ink. Incidentally, the ink is composed of a coloring component and a binder component as main components, and additional components such as a softener, a flexibilizing agent, a smoothing agent, a dispersant, and a surface forming agent as required. The thickness of the ink layer is 0.2 to 20 μm, preferably 0.2 to 20 μm.
5~10! ! It is m.

As binder components, well-known waxes such as carnauba wax, paraffin wax, and ester wax, cellulose resins, vinyl resins, and various low-melting point polymers are useful.As coloring components, carbon black and various kinds of polymers are useful. Organic or inorganic pigments or dyes can be used, but the present invention is not limited thereto.

Next, the manufacturing method of the present invention will be explained, but it is not limited thereto. To achieve the present invention, aromatic polyamide or aromatic polyimide or polyamic acid (
It is formed by making a conductive filler exist in a solution of polyimide precursor) and forming a film from this solution.

First, aromatic polyamide is made from acid chloride and diamine, N-methylpyrrolidone (NMP)
, dimethylacetamide (DMAC), dimethylformamide (DMF), etc., by solution polymerization in an aprotic organic polar solvent, or by interfacial polymerization using an aqueous medium. Hydrogen chloride is produced as a by-product when acid chloride and cyamine are used as monomers, so to neutralize this, calcium hydroxide, calcium carbonate,
Add an inorganic neutralizing agent such as lithium carbonate or an organic neutralizing agent such as ethylene oxide, ammonia, triethylamine.

Further, the reaction between isocyanate and carboxylic acid is carried out in an aprotic organic polar solvent in the presence of a catalyst. These polymer solutions may be used as they are as a film-forming stock solution for forming a film, or the polymer may be isolated once and then redissolved in the solvent described in - to prepare a film-forming stock solution. Inorganic salts such as calcium chloride, magnesium chloride, lithium chloride, etc. may be added to the membrane forming stock solution as a solubilizing agent.

The polymer concentration in the film forming stock solution is preferably about 2 to 40 wt%.

On the other hand, a solution of aromatic polyimide or polyamic acid can be obtained as follows. That is, polyamic acid can be prepared by reacting a tetracarboxylic dianhydride with an aromatic diamine in an aprotic organic polar solvent such as N-methylpyrrolidone, dimethylacetamide, or dimethylformamide. Further, aromatic polyimide can be prepared by heating a solution containing the polyamic acid described above or adding an imidizing agent such as pyridine to obtain a polyimide powder, which is then dissolved again in a solvent. The polymer concentration in the membrane forming stock solution is preferably about 5 to 40W1%.

The conductive filler and polymer may be kneaded using the following methods, but are not limited to these methods.

(1) The conductive filler is dispersed in a solvent in which the polymer is soluble, and then added to the polymer solution, or the isolated polymer is added and dispersed in the dispersion solution.

(2) Conductive filler is dispersed in a polymerization solvent before polymerization, and then polymerization is performed.

(3) The conductive filler is added as a powder or together with a solvent to the polymer solution and dispersed.

Examples of the dispersion device include a colloid mill, three-roll mill, kneader, ultrasonic dispersion machine, sand mill, and ball mill.

The film-forming stock solution prepared as described above is formed into a film by a so-called solution casting method, but methods such as a dry-wet method, a dry method, and a wet method can be employed.

When forming a film by a wet method, the stock solution is extruded directly from a die into a film forming bath, or it is extruded onto a support such as a dot and then introduced into a wet bath together with the support. . This bath generally consists of an aqueous medium, and may contain an organic solvent, an inorganic salt, etc. in addition to water. The time it takes to pass through these wet baths depends on the thickness of the film, but it is
It is 0 seconds to 30 minutes. Furthermore, the film is stretched in the longitudinal direction. Next, drying, lateral stretching, and heat treatment are performed, and these treatments are generally performed at 100 to 500°C for a total time of 1 second to 30 minutes.

When forming a film by a wet-dry method, the stock solution is extruded from a die onto a support such as a drum or an endless belt to form a thin film, and then the solvent is scattered from the thin film layer and the film is dried until it has self-retention properties. Drying conditions are room temperature to 300℃, 60℃
Within minutes.

After the first dry process, the film is peeled off from the support and introduced into the first wet process, where it undergoes desalting, solvent removal, etc. in the same way as the wet process described above, and is further stretched, dried, and heat treated to form a film. Become.

When a dry process is employed, the film is dried on a drum or an endless belt, and the self-retaining film is peeled off from the support [7. The film is stretched in the longitudinal direction. Further, drying, stretching, and heat treatment are performed to remove residual solvent, and these treatments are performed at 100 to 500° C. for 1 second to 30 minutes.

The film formed as described above is stretched during the film forming process, and the stretching ratio is 0.9 to 3.0 in area ratio.
(Area magnification is defined as the value obtained by dividing the area of the film after stretching by the area of the film before stretching. 1 or less means relaxed.) Being within the range improves conductivity and mechanical properties. , which is preferable in terms of maintaining thermal properties. If the area magnification is greater than 3.0, the mechanical properties will improve, but the electrical conductivity will deteriorate significantly and the shrinkage stress will also increase, which is not preferable.

Please note that RS/RS. In order to keep this within the scope of the present invention, the heat treatment temperature is preferably 320°C or higher, preferably 350°C or higher, although it varies depending on the type of polymer and conductive filler used. Furthermore, after completing the steps described below, the area magnification is 0. 5 to 1.0, preferably in the range of 0.8 to 0.98, and when relaxing or annealing is performed at 320°C or higher, more preferably 350°C or higher, Rs/Rso
is preferred because it is stabilized. This relaxing or annealing can be done inline or offline.

Next, an ink layer is formed on the base film of the present invention obtained as described in 1. However, if necessary, pretreatment such as corona treatment or glow treatment may be performed. The inks include the ones mentioned above, and can be applied by hot-melt coating to one side of the above film, or by a general-purpose coating method such as gravure, reverse, or slit die as a solution dissolved in a solvent. .

The basic structure of the transfer body for thermal recording of the present invention consists of the above-mentioned base film and ink layer, and a conductive layer, such as AI, Ag, is provided between the film and the ink layer (referred to as an intermediate layer).
, Ni, C+, Co, Zn, Sn, V+o
, W, or their alloys, oxides, and nitrides.
00 to 5,000 people, preferably 400 to 3,000 people.

Providing a conductive layer as the intermediate layer is very effective in locally increasing the current density from Δ and Rad, and it is more preferable to use A1 as the intermediate layer. In addition, layers other than the conductive layer may be provided in the intermediate layer, such as a release layer, a slippery layer, a heat-resistant layer, etc., together with the conductive layer or without the conductive layer, or the film surface on the opposite side to which the ink layer is provided may have a slippery layer. The present invention is not hindered by the provision of layers, heat-resistant layers, etc.

[Effects of the Invention] The film of the present invention is mainly composed of a conductive filler and aromatic polyamide or aromatic polyimide, and the change in surface resistivity is extremely small even when heated at high temperatures.

Therefore, even when heated for a long time or repeatedly, the amount of heat generated is more stable than that of conventional conductive films, and reliability during high-temperature use and repeated use can be significantly improved. In particular, when the film of the present invention is applied to electrical transfer applications, it can be used many times and the amount of transfer sheet or transfer ribbon used can be significantly reduced, resulting in a very large economic effect.

[Measurement method and evaluation method of characteristics] (1) Surface resistivity R3o, R.

A circular main electrode with a diameter of 16 mm, an inner diameter of 30 mm, and an outer diameter of 34 mm.
Fix a ring-shaped counter electrode of mm so that the centers of the circles of each γ are the same, place it on the film surface with a load of 1 kg, read the resistance value when a current is passed through it, and calculate it using the formula below. do. Measurements are performed at 25° C. and 75% RH.

γ5=(P/g)xR γ3-Surface resistivity (KΩ) P: Effective circumference length of electrode (7.23cm) g: Distance between electrodes (0.7cm) R: Actual value of resistance (KΩ) Here , the obtained film was fixed to a frame, and this was heated to 350
γ, which was measured after being heated in an oven at ℃ for 1 minute, was defined as R3, and 75 before heating in the oven was defined as R3o.

■ Shrinkage stress Cut a sample to a sample width of 10 mm and sample length of 100 mm, apply an initial load of 0.25 kg/mrrr, and maintain the length at a constant value. This was heated in a heating furnace to 350° C. at a heating rate of 10° C./min, and the stress was plotted on a chart. Determine the shrinkage stress with the zero point before applying the initial load and (-).M
The D force direction and the TD force direction are measured, and the larger one is taken as the shrinkage stress of the film.

(3) Strength and elongation Strength when the film breaks when set in a tensilon type tensile testing machine according to ASTM-D-882 with a test width of 10 mm and a test length of 50 mm, and pulled at a tensile speed of 30.0 mm/min. , measure the elongation. Atmosphere is 25℃, 55%
It is RH.

(4) Young's modulus according to the method specified in JIS-Z-4702,
Using an Instron type tensile tester, test at 25°C, 5
Measured at 5% RH.

(5) Print quality A cyan sublimable ink solution having the following composition was coated on a film and dried to form an ink layer [7]. The ink layer thickness after drying is 2 μm.

Dye 4 parts Cellulose resin 6 parts Methyl ethyl ketone
40 parts toluene
40 parts Isobutyl alcohol 10 parts This transfer sheet was brought into close contact with an image-receiving paper, and printing was performed by applying a pulse of 5 msec using a current-carrying head of 10 lines/mm. Printing was performed on the same sheet five times, and the density of each resulting printed product was measured using a reflection densitometer. If the density change between the first and fifth printings was 20% or less, the print quality was judged as good (○), and if it exceeded 20%, it was judged as poor (x).

[Example] The present invention will be described below based on Examples, but is not limited thereto.

Example 1 82 moles of 2-chlorbala phenylene diamine (11,6
9 kg) and 4.4'-diaminodiphenyl ether 1
Polymerization was carried out in 300 kg of NMP using 8 mol (3.60 kg) as an amine component and 100 mol (23.75 kg) of 2-chloroterephthalic acid chloride as an acid component. Further, an equal amount of calcium hydroxide was added to the generated hydrogen chloride to complete neutralization and obtain a uniform polymer solution. A portion of this solution was taken, and carbon black having a particle size of 40 parts m was added thereto to give a concentration of 30 wt % to the formed film, and dispersed in a kneader for 10 hours.

This was uniformly cast onto an endless belt and dried until it had self-retention properties, and then peeled off from the belt and immersed in a water bath to extract the solvent and inorganic salt.

Note that the stretching in the longitudinal direction (MD force direction is 1.0 times).Furthermore, this is introduced into a tenter, and stretched at 300'C in the width direction (T
The stretching in the D force direction was set to 1.1 times, and the film was dried, heat treated, and wound up. Next, the tenter temperature was raised to 350°C, the wound film was passed through the tenter again, and the TD magnification was set to 0.
I relaxed as 9 times. The obtained film had a strength of 22 kg/m tn, an elongation of 20%, and a Young's modulus of 6.
The weight was 70 kg/mrrr, and it was a good film with well-balanced MDXTD physical properties. Also, the moisture absorption rate is 1.1w
t% and also RS/RS as shown in Table 1.

was close to 1, that is, the film showed a small change in surface resistivity even when heated at high temperatures. This film was coated with a sublimable dye and printed, but there was almost no change in print density even after multiple printings. In addition, when the film was separately made to generate heat under the same conditions as during printing and the temperature was measured, it was confirmed that it was 340 to 350°C.

Example 2 2-Chlorparaphenylenediamide 70 mol%, 44
Polymerization was carried out in NMP using 30 mol % of '-diaminodiphenylsulfone as an amine component and 100 mol % of terephthalic acid chloride as an acid component, and neutralized with calcium hydroxide to obtain a polymer solution.

Carbon black of 40 nm was added and dispersed to the concentration shown in Table 1 to obtain a uniform solution.

This was cast, dried, and introduced into a water bath in the same manner as in Example 1. Here, the MD force direction was stretched 1.1 times. Next, this was introduced into a tenter, dried and heat-treated at 280° C. while multiplying the TD force by 1.2, and then wound up.

Furthermore, the tenter was heated to 330℃ and the TD magnification was 0.9.
I tried to relax as much as possible. The obtained film is
Strength 25kg/mrd, elongation 25%, Young's modulus 700
kg/mrrf and excellent mechanical properties, and
The moisture absorption rate was 1.7wf%.

Furthermore, it had electrical properties as shown in Table 1.

When this was coated with a sublimable dye and a printing test was performed, it was confirmed that there was almost no change in print density and it was a good transfer material.

Example 3 A solution was obtained by adding 80 nm silver particles instead of carbon black to the same polymer solution as in Example 2. This was formed into a film under the same conditions as in Example 2, and further relaxed to obtain a film. The electrical properties and shrinkage stress of this film are shown in Table 1.

When a sublimable dye was applied to this and a printing test was performed, there was almost no change in color even after multiple printings.

Example 4 70 mol % of 44'-diaminodiphenyl ether and 30 mol 96 of para-phenylene diamine were used as amine components,
100 mol 96 of pyromellitic dianhydride was polymerized in DMAC. Furthermore, carbon black was added to obtain a uniform solution. This was cast onto an endless belt, dried until it had self-retention properties, and then peeled off from the belt.
The film was introduced into a tenter at 0°C and heat-treated while being stretched 1.1 times in the TD force direction. Note that the ME) stretching ratio before entering the tenter is 1.0. Then, the tenter was heated to 380℃ and TD
A film was obtained by relaxing so that the force in the direction was 0.8 times.

When this film was coated with a sublimable dye and a printing test was carried out, it was confirmed that there was no change in color even after multiple printings, indicating that it was a good transfer material.

Comparative Example 1 The carbon black-dispersed solution of Example 1 was cast onto a belt, dried, and desalted and solvent removed in a water bath.

The MD stretching ratio is 1.1 times.

The film was then introduced into a tenter at 280° C., dried and heat treated while being stretched 1° in the TD force direction, and heat treated to obtain a film. The characteristics of this film are as shown in Table 1, R3/Rso is small,
The resistance is significantly reduced by high-temperature heating.

When we applied a sublimable dye to this film and conducted a printing test, good printing density was obtained the first time, but
The density significantly decreased after the first printing, making it unsuitable for multiple printings.

Comparative Example 2 Example 1. A solution in which carbon black was dispersed was cast onto a belt, dried, and desalted and solvent removed in a water bath. Here, the MD stretching ratio was 1.4 times. 3 more
A film was obtained by drying and heat treatment while stretching 1°4 times in the TD force direction in a 00'C tenter. As shown in Table 1, this film had a small Rs/Rso and a large shrinkage stress.

When a sublimable dye was applied to this and a printing test was performed, there was a large change in printing density between the first and fifth printings, and uneven printing occurred. Looking at the film after printing, wrinkles had appeared on the film, but this is thought to be due to dimensional changes in the film during heating due to the large shrinkage stress.

Claims (2)

[Claims] (1) A film consisting of at least an aromatic polyamide resin or an aromatic polyimide resin and a conductive filler, and has a surface resistivity R_s_o of 10^1 to 10^4 Ω,
Surface resistivity R_s after heating at 350°C is 0.7≦R_s
/R_s_o≦1.2, and 100 to 35
A conductive film having a shrinkage stress of 2 kg/mm^2 or less in a temperature range of 0°C. (2) Claim No. 1 whose thickness is 2 to 30 μm
A transfer body for thermal recording, characterized in that an ink layer is provided on one side of the conductive film as described in item ).