JPH06313295A - Production of easily disaggregative moisture-proof paper - Google Patents

Abstract

PURPOSE:To provide a method for producing an easily disaggregative moisture- proof' paper excellent in the moisture proof, extremely easily disaggregative on its regeneration, and enabling to reduce the using amount of a moisture-proof composition. CONSTITUTION:The characteristic of this method for producing moisture-proof paper is comprises coating a substrate such as paper sheet, paper board or corrugated paper board with a moisture-proof composition. containing a low mol.wt. wax and a flexible synthetic resin in a solid content ratio of 90:10 to 50:50, drying the coated substrate, and subsequently heating and aging the coated paper at a temperature of 30 deg.C to the melting point of the wax.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is used as a moisture-proof wrapping paper for moisture-proof packaging of industrial and industrial products, and other fields requiring moisture proofness, and is recovered after use. The present invention relates to a moisture-proof paper which is extremely easy to reuse and has an excellent disintegration property, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a polyethylene film or an inexpensive kraft paper laminated with a polyethylene film has been widely used for simple moisture-proof packaging of industrial products. However, due to the recent tendency to value the global environment, it is difficult to recycle polyethylene-based moisture-proof materials, and most of them are either incinerated or landfilled as waste, and pollution is inevitable. There is an urgent need to develop a moisture-proof paper that can be recycled or is easily recycled in this field.

Polyethylene has a large production scale and is a hydrophobic substance by itself, so that it has a high moisture-proof property, and if it has a good disintegrating property, it is the most suitable synthetic resin for obtaining a moisture-proof paper at a low cost. Therefore, a wax-based composition having a moisture resistance comparable to that of polyethylene and attracting attention as a composition having a better disintegration property than polyethylene is a wax composition having a low molecular weight and similar in composition to polyethylene.

Wax-processed paper in which wax is applied to paper has been used effectively as a moisture-proof paper for a long time, while waxes have high crystallinity and poor flexibility, so that they have poor film-forming properties and creases on the processed paper. If it adheres, the wax coating film will be cracked and moisture resistance will be reduced. Therefore, as an attempt to increase flexibility, in the case of paraffin wax, microcrystalline microcrystalline wax or low molecular weight polyethylene is added, but it is still more difficult to fold and moisture than the high molecular weight polyethylene laminate. However, if a large amount of microcrystalline wax is added, blocking may occur.

When a water-based wax emulsion is used, a synthetic resin latex can be used for improving flexibility, and effective synthetic resins are preferably flexible synthetic resins and rubber-based ones. Therefore, in the case of a moisture-proof paper having good recyclability, some conventional techniques have been disclosed as a method of applying a mixture of a synthetic resin-based latex and a wax-based emulsion to paper, paperboard, corrugated board or the like.

For example, in JP-B-55-22597 and JP-A-59-66598, a synthetic rubber latex is used as a synthetic resin latex, and an aqueous emulsion containing a wax emulsion is applied to the latex. Kaisho 56-148997 and Japanese Patent Fair 2-1
671 discloses an example in which an acrylic emulsion is used and a mixture thereof is used with a wax emulsion. Further, JP-A-5-25796 discloses the use of a styrene-acrylic copolymer as a coating agent for the purpose of improving heat resistance as compared with a mixture thereof.

[0007]

However, the moisture-proof paper obtained by adding the synthetic resin latex to the wax emulsion in the pretreatment of the present invention is an amorphous flexible synthetic resin having a poor moisture-proof property with respect to a crystalline wax. Since rubber type latex is added, flexibility is partially improved, but moisture resistance is not sufficiently improved. Therefore, in order to obtain moisture resistance equivalent to that of high molecular weight polyethylene, the amount of wax to be applied must be increased, resulting in high cost and poor price competitiveness. Focusing on this point, the present invention further improves the moisture resistance of the wax-based moisture-proof paper, and at the same time, how can the coating amount be reduced so as to sufficiently compete with polyethylene in terms of the price of the product. Was made as an issue.

[0008]

The present invention has the following structure as a method for solving the above problems. That is, a moisture-proof composition obtained by mixing waxes and a synthetic resin having flexibility in a solid content of 90 to 50:10 to 50 is applied to a base material such as paper, paperboard and corrugated board and dried. A method for producing a moisture-proof paper excellent in moisture resistance and easily disintegrating, characterized in that the coated paper obtained is heated and aged at a temperature not lower than 30 ° C. and not higher than the melting point of wax.

Wax is basically a hydrocarbon or a compound consisting of carbon, hydrogen and oxygen, and is a hydrophobic organic compound. Generally, at room temperature, many are solid and crystalline, melt at relatively low temperatures and show low viscosity, from the most abundant types of petroleum wax to plant-based, animal-based, mineral-based, as well as synthetic wax It is a composition that exists in a wide range.

As mentioned above, the wax is generally crystalline as described above, and it is immediately crystallized to be moisture-proof by being melted by heating and then cooling after coating, or by cooling after heating and drying after coating the emulsion. Manifest the sex. When wax alone is used, the crystallization time is extremely short, and crystallization progresses with cooling and almost completes when the temperature reaches room temperature, so even if the coated paper is repeatedly heated and cooled, the coating film will be damaged. But unless it's there, it doesn't affect moisture resistance.

However, the moisture-proof paper coated with a wax containing a synthetic resin has improved flexibility, but has high moisture permeability, and thus has another difficulty in moisture-proofness. However, if the product that was once cooled and used as the final stage in the conventional product is heated again and held at a temperature condition below the melting point of the wax for a predetermined time and then cooled, surprisingly, the moisture resistance is better than that before reheating. It has been found that the phenomenon is much improved, and this phenomenon is completely unexpected, and the present invention has been reached by clarifying this phenomenon.

The waxes that can be used in the present invention have been described above. Specifically, paraffin wax, microcrystalline wax, etc. as petroleum wax, beeswax, lanolin etc. Examples thereof include wood wax, carnauba wax, candelilla wax and the like, mineral substances such as montan wax, ozokerite, ceresin and the like, and synthetic waxes such as montan type Hoechst wax, polyethylene wax and Fischer-Tropsch wax.

The synthetic resin to be mixed is preferably an amorphous resin or a rubber-based resin in order to improve the flexibility of the wax, and examples of the amorphous resin include acrylic esters such as acrylic acid ester and methacrylic acid ester. (Co) polymers of homopolymers or their modified products, crosslinked polymers in which functional groups are introduced, maleinized or fumarized rosin or petroleum resin, or esterified with polyhydric alcohol Those having the same effect can be preferably used. When these are used in an aqueous system, a surfactant may be newly used for emulsification, but it is customary to use an emulsion that participates in emulsion polymerization during polymerization.

As the rubber type, a polymer obtained by polymerizing two or more kinds of a butadiene monomer or a monomer having two or more kinds of double bonds and a monomer having another double bond, and further a functional group added thereto. Examples include those introduced.

The moisture-proof composition used in the present invention is not only a synthetic resin having flexibility with wax, but also a resin such as styrene-maleic acid copolymer which functions as a dispersant for promoting uniform mixing of both. It is also possible to mix a water-soluble resin such as a maleic acid-modified resin for imparting water solubility useful for disaggregation.
Further, as the base paper for coating the moisture-proof composition, paper,
Paperboard, corrugated board and the like are appropriately selected and used as necessary, but the most commonly used paper is unbleached kraft paper. Whether or not the surface of the coated paper is calendered and whether or not the surface size is present is not particularly limited.

As a coating method, in the case of a solid moisture-proof composition, a hot melt coater or a wax coater may be usually used. It may be heated and melted to coat a predetermined amount on the paper surface and then cooled. When the moisture-proof composition is in a liquid state, any ordinary roll coater, kiss coater, rod coater, blade coater, air knife coater, gravure coater, size press, calender size or the like can be applied. After coating a predetermined amount on the surface of the base paper with these facilities, it is heated and dried to obtain a coated paper. The reheating temperature of the coated paper is preferably higher as long as it is equal to or lower than the melting point of the wax used, and may be cooled after being kept at a constant temperature for a certain period of time after reheating, and if the cooling rate is slow, immediately after reheating. You can start cooling.

[0017]

[Function] Moisture resistance is basically a property of preventing water molecules from passing between molecules of a substance, and the molecule of a substance is hydrophobic and allows water molecules to pass through. Difficult or
Alternatively, if the intermolecular distance is smaller than that of water molecules, it means that the moisture resistance is good. Crystallization is due to the fact that molecules are arranged in order and the intermolecular distance becomes dense, and the higher the degree of crystallinity, the better the moisture resistance. However, in order for the molecules to be arranged in order, it is necessary for the molecules to move easily, and for that reason, the smaller the molecular weight is, the easier the molecules move and the more easily they are crystallized.

Since wax has a relatively low melting point and thus has a small molecular weight and is easily crystallized, synthetic resins generally have a higher molecular weight than wax, so that the molecules do not move easily, and the crystallization rate is slow even when crystallized. Therefore, when treated with wax alone, crystallization was completed within the cooling time to normal temperature after coating, but when blended with synthetic resin, high-molecular substances that are difficult to crystallize coexist, which impedes crystallization. There is a possibility that cooling will be completed as it is. Crystallization occurs below the melting point, but the crystallization rate is better if it is below the melting point.
Therefore, it is considered that when the coated paper that is not sufficiently crystallized is heated again to the melting point or lower, the crystallization is promoted and the moisture resistance is improved.

The embodiment of the present invention is characterized in that a coated paper obtained by coating a wax-based moisture-proof composition on paper is subjected to a heat aging treatment. Therefore, a melting method is used as a means for applying the moisture-proof composition. It does not matter whether it is a water-based or solvent-based liquid. Therefore, in the water system, the wax emulsion and the synthetic resin emulsion can be mixed and used.

Next, details of the present invention will be described based on embodiments.

Example 1 A wax emulsion obtained by emulsifying 135 ° F. paraffin wax was used as a wax, and an acrylic resin emulsion was added to the wax emulsion at a solid content of 75:25.
The moisture-proof composition obtained by mixing at a ratio of 70 g / m ²
The unbleached kraft paper was coated to a solid content of 10 g / m ² and then dried by heating to obtain a coated paper. Table 1 shows the water vapor transmission rate and the disintegration property at this time. This coated paper was heated again to 40 ° C. and aged for 2 days. The water vapor transmission rate and disintegration property at this time are shown in Table 1.

Example 2 A moisture-proof composition was applied to unbleached kraft paper at a solid content of 6%.
All were performed under the same conditions as in Example 1 except that the coating was performed so as to have g / m ² . The results are shown in Table 1.

[0021]

COMPARATIVE EXAMPLE 1 The same conditions as in Example 1 were used except that the temperature and time for heating and aging the coated paper again were 70 ° C. for 5 hours. The results are shown in Table 1.

[Comparative Example 2] The same conditions as in Example 2 were repeated except that the temperature and time for heating and aging the coated paper again were 70 ° C for 5 hours. The results are shown in Table 1.

[0022]

[Table 1] Test method in the table Water vapor transmission rate; JIS K 7129-1992 Item 3 Method A Unit g / m ² · 24h Test condition 40 ° C, 90% RH Degradability; Coated paper test piece 60g cut into 2.5 cm square Four
Add water at 20 ℃ so that the concentration will be 150% for 150 minutes.
Stir at 0 rpm to disaggregate. After the disaggregation, the paper is handmade with a handsheet making machine so that the disintegration property of the sheet is visually determined to be 80 g / m ² . The case where there was no binding or lump was rated as ◯, and the case where unseparated binding was present in the sheet was rated as x.

[0023]

INDUSTRIAL APPLICABILITY In the present invention, a coated paper obtained by coating a substrate with a moisture-proof composition comprising waxes and a synthetic resin having flexibility and drying the coated paper at a temperature of 30 ° C. or higher By heating at a temperature below the melting point of the wax and aging treatment, the moisture resistance is significantly improved and at the same time it is excellent in the disaggregation property at the time of recycling, and it was processed by the conventionally used moisture resistance composition and dried. It has an unexpected and remarkable effect which cannot be obtained with the moisture-proof paper. Since the waxes and synthetic resins used here are relatively low molecular weight polymers, crystallization in the molecule is smooth and good results can be obtained for moisture resistance. It can be said that this is a great contribution to the industry because it is excellent in quality and productivity even when it is made of recycled paper, and the amount of wax used can be reduced.

Claims (2)

[Claims] 1. A moisture-proof composition prepared by mixing low molecular weight waxes and a synthetic resin having flexibility at a solid content of 90 to 50:10 to 50 on a substrate such as paper, paperboard and corrugated board. The coated paper obtained by working and drying is heated and aged at a temperature of 30 ° C. or higher and lower than the melting point of wax to produce a moisture-proof paper with excellent dissociation property and excellent moisture resistance. Method. 2. The method for producing a moisture-proof paper according to claim 1, wherein the moisture-proof composition is an aqueous emulsion.