JP2880538B2 - Transparent paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [A] Industrial Application Field The present invention relates to a transparent paper, and more particularly to a transparent paper in which a base paper impregnated with a radiation-curable resin is cured by irradiation to improve the physical properties of the paper. is there.

[B] Prior Art In order to increase the transparency of paper, a method of increasing the degree of beating of pulp fibers and an impregnation method of filling the space of the base paper with resins have been applied. Particularly in the latter case, it has been practiced to improve the physical properties of the paper, for example, strength, rigidity, water resistance, moisture resistance, etc., by selecting the resin to be filled.

Further, as disclosed in Japanese Patent Publication No. Sho 50-30163, JP-A-55-67097 and JP-A-56-63097, a method using a resin which can be polymerized and cured by radiation has been used.

In particular, Japanese Patent Publication No. Sho 50-30163 attempts to improve the physical properties such as dimensional stability and heat resistance by impregnating with an acrylate having four ethylene oxide chains and curing it by irradiation with radiation. .

[C] Problems to be Solved by the Invention However, the transparent paper obtained by using such a method does not yet show a sufficient improvement in physical properties, particularly has a large shrinkage due to heat, and has a dimension in dry copy. Stability is a problem.

[D] Means for Solving the Problems The present inventor has earnestly studied means for solving the above problems, and as a result, has reached the following invention.

That is, the invention is a transparent paper with improved heat shrinkage, characterized by impregnating a base paper with an acrylate having eight or more ethylene oxide chains without solvent or as an aqueous solution and curing by irradiation with radiation. The details of the present invention will be described below.

In the present invention, as a base paper used as a support, ordinary natural pulp paper, a so-called nonwoven fabric made of synthetic fibers can be used, but softwood pulp, hardwood pulp, and softwood mixed pulp wood pulp as a main component are used. Natural pulp paper is advantageously used.

The radiation-curable resin used in the present invention is a compound having a carbon-carbon unsaturated bond, particularly an acrylate having an ethylene oxide chain represented by the following general formula.

_{CH 2 = CHCO- (OCH 2 CH} 2) n -OCOCH = CH 2 (n 8 or more) Speaking under the trade name (manufactured by Toagosei Chemical Industry Co., Ltd.), Aronix M-245, A-400, A- 600 (manufactured by Shin-Nakamura Chemical Co., Ltd.), PEG-400DA (manufactured by Nippon Kayaku Co., Ltd.),
9EG-A, 14EG-A (Kyoeisha Yushi Kagaku Kogyo Co., Ltd.)
Manufactured).

Since these radiation-curable resins are water-soluble and can be easily made into an aqueous solution, they can be used not only as a solvent-free but also as an aqueous solution. Compounds having n less than 8 are not preferred because the effect of suppressing heat shrinkage is not only extremely small compared to compounds having n of 8 or more, and they are insoluble in water and cannot be used as an aqueous solution. These radiation-curable resins may be used alone or as a mixture.

As long as the heat shrinkage suppressing effect is not impaired as necessary, the radiation curable resin having an ethylene oxide chain may be polymerized by radiation other than the general formula having one or more widely used carbon-carbon unsaturated bonds. Possible resins, ie compounds containing acryloyl groups, methacryloyl groups, acrylamide groups, allyl groups, vinyl ether groups, vinyl thioether groups and the like or compounds having one or more epoxy rings can be added.

Further, an antistatic agent, an antifoaming agent, a fluorescent dye, a filler, and the like can be added as long as the heat shrinkage suppressing effect is not impaired.

In the present invention, when the resin is cured by irradiation with ultraviolet rays, a photopolymerization initiator is mixed and used in the radiation-curable resin. As the photopolymerization initiator, ethyl anthraquinone,
Methylbenzoyl formate, 1-hydroxycyclohexyl phenyl ketone, acetophenone, diethoxyacetophenone, acetophenones such as di and trichloroacetophenone, o-benzoylmethyl benzoate, benzophenone, Michler's ketone, benzyl, benzoin, benzoin alkyl ether, benzyl dimethyl ketal, There are tetramethylthiuram monosulfide, xanthone, thioxanthones, azo compounds and the like, and the amount of the photopolymerization initiator used is usually in the range of 0.1 to 10% by weight based on the ultraviolet curable resin. A storage stabilizer such as hydroquinone may be used in combination with the photopolymerization initiator.

The radiation curable resin is impregnated into the base paper. The impregnation is
At the stage of base paper production, by adding a radiation-curable resin in the process of forming a slurry composed of pulp and various additives, or dipping the base paper after papermaking in a solution containing these radiation-curable resins Alternatively, it can be carried out by tubing or applying a solution containing these resins to the base paper.

The impregnation amount of the radiation-curable resin is not particularly limited, but that of the impregnated paper is 3 to 50% based on the total weight after impregnation.
% Is preferred. If the impregnation amount is less than 3%, the transparency is low and the performance of the present invention cannot be sufficiently exhibited. The upper limit depends on the space ratio in the paper, but generally 50%
If it exceeds, the amount of resin component adhering to the paper increases, and the paper texture is lost or becomes brittle.

The radiation of the present invention includes α-rays, β-rays, γ-rays, X-rays, electron beams, and ultraviolet rays. From the viewpoint of danger to the human body and handling, it is preferable to use widely used electron beams and ultraviolet rays. As an electron beam accelerator used for electron beam irradiation, a scan method or a curtain method can be adopted, but a curtain method which is relatively inexpensive and easily provides a large output is preferable. The accelerating voltage of the electron beam is 100 to 1000 kV, preferably 150 to 300 kV, and the absorbed dose is 0.5 to 20 Mrad, preferably 1 to 10 Mrad. If the accelerating voltage is less than 100 kV, the amount of transmitted energy is insufficient. If the accelerating voltage is more than 1000 kV, the energy efficiency is reduced and it is not economical. If the absorbed dose is less than 0.5 Mrad, the curing reaction becomes insufficient. If it exceeds 20 Mrad, not only does energy efficiency decrease, but also the object to be irradiated generates heat and paper properties deteriorate significantly, which is not preferable.

Since curing by electron beam irradiation is a radical reaction and depends on the oxygen concentration in the atmosphere, it is replaced by an inert gas such as nitrogen, helium, or carbon dioxide to reduce the oxygen concentration.
Irradiation is preferably performed in an atmosphere in which the concentration is controlled to 600 ppm or less, preferably 400 ppm or less.

Examples of the ultraviolet irradiation device include a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, and a metal halide lamp.
There is also an ozone-less type that generates less ozone. Generally, a plurality of lamps having an output of 30 w / cm or more are used in parallel.

[E] Action The transparent paper according to the present invention is obtained by impregnating a base paper with an acrylate having 8 or more ethylene oxide chains without solvent or as an aqueous solution, and curing by irradiation with radiation. Very good dimensional stability.

[F] Examples Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the content of the present invention is not limited to Examples.

 In addition, all "%" in an example shows "weight%."

Example 1 A pulp made from 50% NBKP and 50% LBKP was beaten to 40 ° SR, and a base paper having a basis weight of 50 g / m ² and a transparency of 32% was made of polyethylene oxide diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.). A-400: about 9 ethyleneoside chains, average molecular weight
508) and irradiated with an electron beam using an electron beam irradiation device (Nissin High Voltage Co., Ltd., Curetron) under the conditions of an oxygen concentration of 400 ppm, an acceleration voltage of 200 kV, and an absorbed dose of 2 Mrad to obtain a transparent paper sample. Was.

Example 2 On the same base paper as in Example 1, the acrylate of Example 1 was used.
After impregnated with a 50% aqueous solution and air-dried, electron beam irradiation was performed in the same manner as in Example 1 to obtain a transparent paper sample.

Example 3 The same base paper as in Example 1 was impregnated with a 50% aqueous solution of polyethylene oxide diacrylate (A-600, manufactured by Shin-Nakamura Chemical Co., Ltd .: about 14 ethylene oxide chains, average molecular weight 708), and air-dried. Electron beam irradiation was performed in the same manner as in Example 1 to obtain a transparent paper sample.

Example 4 The same base paper as in Example 1 was impregnated with a 66% aqueous solution of polyethylene oxide diacrylate (PEG-400DA, manufactured by Nippon Kayaku Co., Ltd .: about 9 ethylene oxide chains, average molecular weight 522), air-dried, and Electron beam irradiation was performed in the same manner as in Example 1 to obtain a transparent paper sample.

Comparative Example 1 A base paper similar to that of Example 1 was impregnated with tetraethylene oxide diacrylate (A-200, manufactured by Shin-Nakamura Chemical Co., Ltd .: about 4 ethylene oxide chains, average molecular weight 308), and a method similar to that of Example 1 was used. The sample was irradiated with an electron beam to obtain a transparent paper sample.

Comparative Example 2 The same base paper as in Example 1 was impregnated with tripropylene oxide diacrylate (M-220, manufactured by Toa Gosei Chemical Industry Co., Ltd.), and irradiated with an electron beam in the same manner as in Example 1 to obtain a transparent paper. A sample was obtained.

Comparative Example 3 The same base paper as in Example 1 was impregnated with a 50% acetone solution of isocyanuric acid triacrylate (M-325, manufactured by Toagosei Chemical Industry Co., Ltd.), and irradiated with an electron beam in the same manner as in Example 1. And a transparent paper sample was obtained.

The properties of the samples and base paper of Examples 1 to 4 and Comparative Examples 1 to 3 were determined by the following measurement methods and are shown in Table 1.

 The impregnation rate was determined from the following equation.

Transparency is measured in JIS p with a Hunter reflectometer
Opacity based on -8138 was measured and determined by subtracting that value from 100.

The heat shrinkage is measured by applying a 120 g tensile load to a 5 cm long paper, irradiating an infrared lamp for 8 minutes from a distance of 20 cm from the paper, heating the paper to 30 ° C, and measuring the shrinkage with a micrometer. The shrinkage relative to the original length was expressed as a percentage of shrinkage.

[G] Effects of the invention As is clear from the table, the paper of the comparative example has good transparency, but has a large heat shrinkage of 0.33% or more in the CD direction and 0.13% or more in the MD direction. That is, heat shrinkage of the paper is not significantly improved. On the other hand, the paper according to the present invention has a heat shrinkage of 0.27% or less in the CD
It can be seen that the thermal shrinkage in the direction is 0.12% or less, the change in shrinkage after heating is small, and the transparency can be changed by selecting the resin concentration and type.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) D21H 21/26

Claims (2)

(57) [Claims] 1. A transparent paper characterized in that base paper is impregnated with an acrylate having eight or more ethylene oxide chains, cured by irradiation, and has a heat shrinkage in the CD direction of 0.27% or less. 2. The transparent paper according to claim 1, wherein the base paper is impregnated with an acrylate having an ethylene oxide chain as an aqueous solution.