JPH0128158B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for reinforcing corrugated board, and more specifically, the present invention relates to a method for reinforcing corrugated board, which is characterized by applying a modified polyisocyanate composition to the board. Conventionally, methods for strengthening corrugated cardboard have been known, such as applying wax, synthetic resin, or the like diluted in a solvent to the cardboard to increase its strength. However, these methods have drawbacks such as deterioration of the working environment due to solvent evaporation or the necessity of a solvent recovery step. As a method to improve these shortcomings,
-6557 publication discloses polyisocyanate monomers, dimers, and trimer oligomers, and
No. 57-95397 describes a method in which a polyisocyanate composition modified with a compound having at least two or more active hydrogen atoms in the molecule is applied to corrugated board and cured. These methods have been able to overcome the above-mentioned conventional drawbacks to some extent, and have achieved considerable results. However, when methylene crosslinked polyisocyanate (referred to as crude MDI) represented by the following general formula (1) is used as the polyisocyanate, The coated product became too brittle, causing problems such as cracking of the cardboard surface and poor impact resistance during packaging box processing. Particularly in the case of corrugated boxes, there is a serious drawback that creases occur during box manufacturing (cutting the corrugated board into a box shape) or during the assembly of the corrugated board, making it unusable as a corrugated box. Furthermore, these polyisocyanate monomers or modified polyisocyanates require a large amount of solvent for cleaning equipment after coating, and have many drawbacks from the viewpoint of working environment and economy. The present inventors have arrived at the present invention as a result of intensive studies aimed at improving these drawbacks. That is, the present invention relates to a modified polyisocyanate compound obtained by reacting a polyoxyalkylene monol obtained by addition polymerizing ethylene oxide (EO) or ethylene oxide (EO) and propylene oxide (PO) to a monofunctional alcohol. This is a method for reinforcing corrugated board, which comprises applying a polyisocyanate composition to corrugated board. The present invention makes it possible to obtain a coated product that is highly flexible and strong, which could not be obtained using conventional methods, and by using such a composition, it is no longer necessary to use a conventional solvent to clean the equipment after coating. Since cleaning can be done simply by washing with water, the working environment does not deteriorate, and the washing water emulsifies the polyisocyanate composition, making handling extremely easy. The polyisocyanates used in the present invention include diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), paraphenylene diisocyanate, and lysine isocyanate (LDI); crude tolylene diisocyanate,
Crude products of the above aliphatic, aromatic, and polyisocyanates such as crude diphenylmethane diisocyanate [polymethylene polyphenyl polyisocyanate], carbodiimide-modified MDI, trimethylolpropane adduct of TDI, water-modified biuret structure
These include modified products of the above aliphatic, aromatic, and alicyclic polyisocyanates such as HDI modified products, and two or more of these may be used as a mixture. Particularly preferred is crude diphenylmethane diisocyanate, which exhibits excellent performance in the processing of reinforced corrugated board according to the method of the present invention. The polyoxyalkylene monool used in the present invention uses a monofunctional alcohol as an initiator, and in the presence of a basic catalyst, ethylene oxide or ethylene oxide and propylene oxide are added thereto.
It is produced by a known method of adding EO/PO in a weight ratio of 100/0 to 40/60. The order of addition of ethylene oxide and propylene oxide or the form of their addition (random or block) may be any. If the amount of ethylene oxide is less than this range, when the modified polyisocyanate is applied to paper, the permeability will be lowered and sufficient effects will not be exhibited. Specific examples of monofunctional alcohols include methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, amyl alcohol,
Butyl carbinol, neopentyl alcohol,
Saturated monofunctional alcohols such as diethyl carbinol, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, propylene glycol monobutyl ether, allyl alcohol, crotyl alcohol, methyl vinyl carbinol, allyl carbinol, methyl propenyl carbinol unsaturated alcohols such as The preferred range of hydroxyl number of the polyoxyalkylene monol is 25-100. In the present invention, the blending ratio of polyisocyanate and polyoxyalkylene monol is preferably 0.5 to 10 parts, particularly preferably 1 to 5 parts, based on 100 parts by weight of the polyisocyanate compound (hereinafter, parts indicate parts by weight). It is. If the amount of polyoxyalkylene monol is less than 0.5 parts, the permeability of the chemical into the cardboard will be poor, and tack will remain, for example, when coated cardboard is stacked, uncured products will contaminate the uncoated surface and reduce the product value. After coating, the coated product becomes too brittle and does not have sufficient impact resistance, and if the amount exceeds 10 parts, the viscosity of the resulting modified polyisocyanate composition increases, making coating difficult and reducing the requirements for reinforced corrugated cardboard. Strength cannot be obtained. In the present invention, in order to react polyisocyanate and polyoxyalkylene monol, 70%
Heat at ~80°C for 1-2 hours. In this case, if necessary, tin octylate, lead octylate, dibutyltin dilaurate, etc. may be added as a catalyst.
The obtained modified isocyanate composition has a viscosity of 80−
It is a liquid with a temperature of 600 cps/25°C and an isocyanate content of 20-35% by weight. When applying the modified isocyanate composition to corrugated board according to the present invention, silicon-containing surfactants, pigments, fillers, organic acids such as adipic acid and salicylic acid, organic acid metal salts such as lead octylate and dibutyltin dilaurate, and Known curing accelerators for urethane such as tertiary amines such as ethylenediamine can also be added and used. Regarding the method and amount of application of the modified polyisocyanate composition according to the present invention, it is usually suitable to apply it on the surface of a corrugated board sheet using a roll coater, and the amount of application is 10 to 100 g/m ² and preferably 20 to 50 g/m ² for enhancement efficiency. It works well and there is no tack after coating. Further, the coating area can be applied to one side, both sides, or a part of the corrugated cardboard sheet. The modified polyisocyanate composition coated according to the present invention reacts with the hydroxyl groups of the cellulose constituting the paper fibers, the moisture present in the paper, and the moisture in the atmosphere, and exhibits maximum strength within 3 to 6 days. The present invention will be explained below with reference to Examples. Example 1 Diethylene glycol monomethyl ether
Polyoxyalkylene monool (hydroxy value 67) obtained by addition polymerizing 1052 parts of ethylene oxide and 211.4 parts of propylene oxide to 219 parts of potassium hydroxide in the presence of 4.45 parts of potassium hydroxide by a known method.
Add 2.5 parts of crude MDI (manufactured by Mitsui Nisso Urethane Co., Ltd., MDI
-CR200) mixed with 100 parts and heated at 80℃ in a nitrogen stream.
After heating for 2 hours, cool and reduce the isocyanate content to 29.
A modified polyisocyanate composition having a weight percent and a viscosity of 215 cps/25°C was obtained. Spread 30 to 40 g of this on one side of a rectangular liner paper (K-220, weight 220 g/m ² ) with a length of 250 mm and a width of 20 mm.
It was applied with a Meyer bar so that it was ² m2. 20 of this
After being left in an atmosphere at 65% relative humidity for 6 days, the physical properties of the paper were measured. The results were as shown in Table 1. Comparative Example 1 Table 1 also shows the case where coating was performed in the same manner as in Example 1 except that only crude MDI was used. Compared to Example 1, the permeability into paper was slow and the strength was low. Example 2 In place of the crude MDI of Example 1, a carbodiimide-modified product of pure MDI (MDI manufactured by Mitsui Nisso Urethane Co., Ltd.) was used.
A modified polyisocyanate composition (NCO % 27.2, viscosity 72 cps/25°C) was obtained in exactly the same manner as in Example 1 except that LK) was used. Example 3 Crude tolylene diisocyanate (TDI-manufactured by Mitsui Nisso Urethane Co., Ltd.) was used instead of crude MDI in Example 1.
A modified polyisocyanate composition (NCO% 39.1,
A viscosity of 62 cps/25°C was obtained. Example 4 A modified polyisocyanate composition (NCO% 12.1, Viscosity 315cps/25
°C) was obtained. Example 5 116 parts of allyl alcohol and 4.50 parts of potassium hydroxide
ethylene oxide in a known manner in the presence of
3.5 parts of polyoxyalkylene monool (hydroxyl value 74.8) obtained by addition polymerization of 1350 parts of
MDI (MDI-CR200 manufactured by Mitsui Nisso Urethane Co., Ltd.) 100
A modified polyisocyanate composition (NCO% 28.9, viscosity
195 cps/25°C). Example 6 Diethylene glycol monobutyl ether
Polyoxyalkylene monool (hydroxyl number 65) obtained by addition polymerizing 1012 parts of ethylene oxide and 204.1 parts of propylene oxide to 283.7 parts in the presence of 4.5 parts of potassium hydroxide by a known method.
25 parts of crude MDI (MDI manufactured by Mitsui Nisso Urethane Co., Ltd.)
A modified polyisocyanate composition (NCO% 29.0,
A viscosity of 230 cps/25°C was obtained. Example 7 Potassium hydroxide in 90 parts of 3-butyn-1-ol
MDI
A modified polyisocyanate composition (NCO % 29.0%, viscosity 180 cps/25°C) was obtained in exactly the same manner as in Example 1 by mixing with 1000 parts of -CR200 (described above). The modified polyisocyanate compositions obtained by the methods of Examples 2 to 7 were applied to rectangular liner paper (described above) in the same manner as in Example 1, and the physical properties of the paper were measured in the same manner as in Example 1. Example 8 Table 1 also shows the case in which the coating was applied in the same manner as in Example 1 except that 5.0 parts of polyoxyalkylene monool (hydroxyl number 67) was used. However, NCO% was 27.5. Compared to Example 1, the physical properties of the paper tended to be slightly lower. Example 9 A case in which 10.0 parts of polyoxyalkylene monool (hydroxyl number 67) was used and the coating was applied in the same manner as in Example 2 is also shown in Table 1, however, the NCO% was 24.6. . Compared to Example 2, the physical properties of the paper tended to be slightly lower. Examples 10 and 11 7.0 parts and 10.0 parts of polyoxyalkylene monool (hydroxyl value 74.8) were used, and the rest was as in Example 5.
Table 1 also shows the cases in which the coatings were applied in exactly the same manner as above. However, NCO% was 27.3 and 25.9. Compared to Example 5, the physical properties of the paper all showed a tendency to decrease slightly. The results were as shown in Table 1.

【table】

[Table] The water absorption rate shows the weight increase rate after immersion.

Claims (1)

[Claims] 1 Applying a modified polyisocyanate composition obtained by reacting a polyisocyanate with a polyoxyalkylene monool having a hydroxyl value of 25 to 100, which is obtained by addition polymerizing ethylene oxide or ethylene oxide and propylene oxide to a monofunctional alcohol. A distinctive method of strengthening cardboard.