JPH039879A - Thermal recording paper - Google Patents

Abstract

PURPOSE:To eliminate the curl at the times of high and low humidities and to obtain recording of high sensitivity by using base paper prepared from dry pulp under such a condition that the heating degree of the pulp is set to a specific range by a papermaking process as a support. CONSTITUTION:When heating degree as Canadian Standard Freeness advances to 250cc (CSF) or less, the entanglement of fibers is enhanced and contact points increase even when dry pulp is used and, therefore, the extensibility of paper increases and heat insulating effect becomes poor because of the reduction of voids in a paper layer. Therefore, the heating degree is set to 250cc (CSF). Contrarily, since voids increase excessively in an unbeaten state, a coating solution passes through the paper layer when a thermal layer is applied to be bonded to and accumulated on a backing roll and paper becomes easy to cut. Therefore, dry pulp is beaten to 550cc (CSF) or less. When thermal paper is prepared by applying a thermal coating solution to the base paper using this dry pulp directly or through an intermediate layer, the curl of thermal paper is almost eliminated because the extensibility of the base paper is low even when humidity changes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to thermal recording paper. In particular, it relates to thermal recording paper that curls little even when environmental humidity changes and has high sensitivity.

[Conventional technology]

A variety of heat-sensitive recording materials have been published so far that utilize a color-forming reaction under heating between at least one colorless or light-colored basic dye and phenols, organic acids, etc.
-14039 public rights, etc.) have been widely put into practical use.

These heat-sensitive recording materials are used in a wide range of fields, including measurement recorders, computers and information communication terminals, facsimile machines, and automatic ticket vending machines. These recording devices are equipped with thermal elements such as thermal heads or thermal pens,
By heating this element, it can be colored and records can be obtained.

Recently, applications have become more diversified and equipment has become more sophisticated, and along with this, the quality required for thermal recording paper has also become more advanced.

For example, facsimile machines can now record A4 size paper in less than one minute, whereas it previously took several minutes, but thermal recording paper is now required to have significantly higher recording sensitivity than before.

Many proposals have been made to meet this demand, but most of them involve a combination of a colorless or light-colored basic dye and a coloring agent, generally consisting of a phenol or an organic acid.
Furthermore, it relates to the combined use of a thermofusible substance (generally referred to as a sensitizer).

[Problem that the invention seeks to solve]

In recent years, facsimile machines that use heat-sensitive recording paper have become rapidly popular, and are increasingly being used in ordinary households. The reason for this is that facsimile machines have become smaller,
Moreover, it has become cheaper. Such popular facsimile machines require so-called high-sensitivity thermal recording paper that can achieve sufficiently high recording density with as little energy as possible.

In order to achieve high sensitivity in heat-sensitive recording paper, the total amount of basic dye, coloring agent, and sensitizer in the heat-sensitive recording layer has become as large as possible. These ingredients (
The coloring components (coloring components) melt and develop color due to the heat from the thermal head, but if the amount of the compound is too large, the molten material will inevitably adhere to the head, creating so-called head scum, which will cause paper feeding problems (sticking, printing noise). Printing problems (streaks and scratches on the printing surface) become a problem.

It is known that one method to prevent dust from adhering to the head is to incorporate fine powder such as calcium carbonate, magnesium carbonate, talc, clay silica, calcium silicate, or aluminum silicate into the heat-sensitive layer. However, in the case of high-sensitivity thermal paper containing a large amount of color-forming components, the problem of residue adhesion cannot be completely solved.

As another means of solving the problem of residue adhering to the head, attempts have been made to incorporate wax, etc., but this cannot be said to be completely effective in the case of high-sensitivity thermal recording paper, which contains a large amount of color-forming components. .

After all, in order to eliminate the problem of head sludge, it is desired to reduce the amount of color-forming components in the heat-sensitive recording paper layer as much as possible and still achieve a high sensitivity that is sufficient to obtain the required sufficient recording density.

On the other hand, as facsimile machines become popular in ordinary households, there is an increasing demand for reducing the curling of thermal recording paper due to humidity.

In other words, in ordinary homes, air conditioning equipment is not yet fully equipped, and during high humidity such as the rainy season, the base paper that is the support stretches, but the heat-sensitive recording layer side does not stretch, so the heat-sensitive recording layer side curls, causing severe damage. If it is, it will become cylindrical.

On the other hand, when the humidity is low, such as in winter, curling occurs with the paper side facing inside, which also poses a practical problem.

Curl-free thermal recording paper is becoming more and more important, not only for general household use, but also for use in places without air conditioning, and increasingly in overseas environments, where the number of uses has increased in recent years. .

[Means for solving problems]

As a result of repeated research in order to achieve this objective, the present inventors used dry pulp and found that the softness of the pulp (
We have discovered that by using a base paper made from 250 cc to 550 cc of CSF as a support, it is possible to obtain high-sensitivity recording with almost no curling at high or low humidity, and have arrived at the present invention. It is something that

Pulp is usually produced by cooking and bleaching materials containing cellulose fibers such as wood, bagasse, and rice straw, but after bleaching, pulp is processed into a slurry or thick porridge that is beaten and then sent to the papermaking process, which is called wet pulp. It's called slush pulp.

On the other hand, after bleaching, it dries and becomes a sheet.
When making paper, pulp is first loosened with water (disintegrated), made into a slurry, and then beaten, and the pulp used is called dry pulp.

After dry pulp is bleached, it dries once, causing internal bonds within the fibers and becoming keratinized, so when this is re-disaggregated and paper is made, a paper layer with fewer contact points is formed.

It is well known that in ordinary machine-made paper, the fibers are blended in the machine's machine direction (longitudinal grain), so expansion and contraction due to moisture is smaller in the longitudinal direction and greater in the lateral direction. This is due to the property that the expansion and contraction of pulp fibers due to adsorption and desilvering is greater in the diameter direction than in the length direction.

Paper made using dry pulp has fewer contact points between fibers, so even if the thickness of the fibers changes due to moisture, it is thought that this change is less likely to appear as an elongation of the paper itself, especially in the lateral direction. Once dried, fibers become less swellable due to keratinization (see ``Paper and Pulp: Chemistry and Technology of Paper Manufacturing Volume 2'', translated and supervised by Rei Oe, published by Chugai Sangyo Research Group). A similar phenomenon is also observed when waste paper is reused.

On the other hand, paper using wet pulp has many contact points between the fibers, and changes in fiber thickness due to increases and decreases in moisture are likely to be added to the paper, resulting in significant elongation of the paper, especially in the lateral direction.

Therefore, if you make thermal paper by applying a thermal coating liquid directly to base paper using dry pulp or after providing an intermediate layer, the thermal paper will curl because the expansion and contraction of the base paper itself is small even when the humidity changes. will almost disappear.

On the other hand, heat-sensitive recording paper obtained using a base paper using dry pulp as a support has considerably higher sensitivity than when using wet pulp. The reason for this is that base paper made from dry pulp has fewer contact points between fibers, forming a paper layer with many voids, and these voids act as a heat insulating layer, allowing the heat transferred from the heat-sensitive layer to It is thought that diffusion into the base paper is reduced and coloring efficiency is improved.

The degree of beating is usually Canadian standard filter wood bark (CSF).

JIS P-2181), the freeness is 250.
When it progresses to below cc (CSF), even if dry pulp is used, the entanglement of the fibers becomes stronger and the number of contact points increases, so as the value of the freeness decreases, the expansion and contraction of the paper gradually increases. Furthermore, since the voids in the paper layer are reduced, the insulation effect becomes poor. Therefore, the freeness is 250c
c (CSF) or more, preferably 300 cc (C8F) or more is required.

On the other hand, the upper limit of the beating degree is the unbeaten state, but in such a state there are too many voids, so the coating machine uses an intermediate layer to
Alternatively, when a heat-sensitive layer is applied without using an intermediate layer, there are many problems such as the coating liquid passing through the paper layer and adhering to and depositing on the packing roll, and the paper being weak in strength, making it easy to tear the paper, which is not practical.

Therefore, the dry pulp used for the base paper according to the present invention is 550 cc (CSF) or less, preferably 500 cc (CSF) or less, and preferably 500 cc (CSF) or less.
SF) It is necessary to beat the following.

As the type of dry pulp, pulp made from hardwood and N pulp made from softwood may be used alone or in combination. Further, waste paper pulp obtained by disintegrating waste paper may be used in combination.

These pulps may be beaten individually or in combination.

Although it is possible to use a small amount of wet pulp in combination with the dry pulp, in view of the purpose of the present invention, the wet pulp should be about 20% or less, preferably 5% or less of the total pulp.

When making the base paper of the present invention, internal size chemicals such as rosin, alkyl ketene dimer alkenyl succinic acid, and fillers such as clay talc and calcium carbonate may be used as necessary.

In addition, paper strength agents such as polyacrylamide and starch,
Moisture-resistant resin or the like may be added.

Further, PVA, starch, SBR, styrene maleic anhydride, etc. may be used to size or coat the surface.

The heat-sensitive recording paper according to the present invention has a heat-sensitive recording layer formed on one side of a support directly or via an intermediate layer.

Any commonly used heat-sensitive color former, color former, binder, etc. can be used to form the heat-sensitive recording layer. A coating solution for forming a heat-sensitive recording layer is applied onto a support, and smoothing treatment is performed using a super calender or the like, if necessary.

The color-forming substance contained in the heat-sensitive recording layer is an organic compound (dye) that is colorless or light-colored before heat-sensitive treatment, and develops color by reacting with an organic acid or phenol compound (coloring agent) during heat-sensitive treatment. be. Such coloring substances include various leuco dyes such as triphenylmethane, triphenylmethane-phthalide, fluoran, diphenylmethane, leucoauramine, spiropyran, indoline, and indigo dyes. can.

In addition, there are many practical examples of phenolic compounds as coloring agents.
Monophenols such as P-hydroxybenzoic acid derivatives, phthalic acid derivatives, naphthoic acid derivatives, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) and sono-similar compounds, bisphenol sulfone,
Any of diphenols such as bisphenol sulfide, gallic acid derivatives, and other triphenols can be used. Of course, other things are also possible.

As the binder used in the present invention, generally known water-soluble resins can be used. Specifically, polyvinyl alcohol, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, gum arabic, gelatin, casein, starch, polyvinylpyrrolidone, styrene-maleic anhydride copolymer, polyacrylate, polyacrylic acid copolymer, etc. Can be mentioned.

Alternatively, an aqueous emulsion such as styrene or butadiene latex may be used.

When preparing a coating solution for forming a heat-sensitive recording layer, a surfactant such as a dispersant or an antifoaming agent may be added as a dispersion aid if necessary, and a whitening agent or a surfactant may be added to prevent the coating material from adhering to the thermal head. , talc, clay, calcium carbonate,
Fillers such as titanium oxide or starch can be added.

It is also effective to add antifoaming agents to suppress foaming during coating, surfactants to improve coating properties, and the like.

In addition, as lubricants, mold release agents, and sensitivity regulators, animal, vegetable, and mineral waxes such as paraffin wax, microcrystalline wax, polyolefin wax, and carnauba wax, fatty acids and their metal salts, polyhydric alcohol esters of higher fatty acids, A condensate of a higher fatty acid and an amine can be used in combination.

〔Example〕

Examples of the present invention are shown below, but the following examples do not limit the present invention. Parts in each example and comparative example indicate parts by weight.

Example I Liquid A (dye dispersion) 10% Polyvinyl alcohol water Liquid B Bisphenol A Rosebenzylbiphenyl 10% Polyvinyl alcohol water 40 parts 40 parts 5 parts 5 parts 0 parts 0 parts The above two liquids A and B were prepared separately. It was ground to an average particle size of 1 μm using a sand glider. Next, the dispersion liquid was mixed in the following proportions to prepare a coating liquid.

A liquid
l O part B liquid
15 parts calcium carbonate (50% dispersion)
8 parts lO% polyvinyl alcohol 30
1 part zinc stearate (30% dispersion) 2 parts paraffin wax (30% dispersion) 2 parts Next, 20 parts of NBKP was used as the pulp, and 80 parts of P was used as the LB (both dry pulp), and 1% of the pulp was used. rosin,
A base paper of 45 g/m'' was made by adding 2% sulfuric acid. The softness of the pulp at this time is as shown in Table 1.

Each of the base papers was coated with the above heat-sensitive coating liquid using a Mayer bar so that the coated amount after drying was 7 g/m'. Further, this was adjusted using a super calendar so that the Bekk smoothness of the coated surface of the heat-sensitive layer was 800 seconds.

[Comparative Example 1] In the above example, Pl and L were added to the NB of the dry pulp.
The procedure was exactly the same as in Example 1 except that the freeness of BKP was 230 cc (CSF) in each case.

[Comparative example 2] Dry pulp NBKP according to Example 2 above.

and 12 to wet pulp NO instead of LBKP.
0 parts, wet pulp LBKF 80 parts, both 3
The entire procedure was carried out in the same manner as in Example 1, except that the volume was 80 cc (CSF).

The thermal recording papers obtained in these Examples and Comparative Examples were subjected to measurement of recording sensitivity and evaluation of curl, and the results are shown in Table 1.

The recording sensitivity was measured using a Toyo Seiki thermal gradient tester, and the sample was heated to 100m5e at a temperature of 120℃ + 2.5kg/cm2.
c Heating and measuring the color density using a Macbeth densitometer RD-914.
It was measured with

Curl was visually evaluated after cutting the sample into an A-4 size (with the grain of the paper in the vertical direction) and leaving it for 10 minutes under the temperature and humidity conditions shown in Table 1.

As described above, it is clear that the heat-sensitive recording paper of the present invention has excellent properties such as high sensitivity and almost no curling even at high and low humidity.

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Claims (1)

[Claims] 1. A thermosensitive recording paper in which a thermosensitive coloring layer is provided on a support using a coloring reaction between a colorless or light-colored dye and a coloring agent, and a dry pulp is used. ) in a range of 250 cc to 550 cc, using a base paper as a support.