JPH0428839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for strengthening corrugated board. More specifically, represented by the general formula (), [In formula (), n is an integer of 0 or 1 or more] methylene crosslinked polyphenylene polyisocyanate (hereinafter abbreviated as crude MDI) obtained as a distillation residue from the purification process of diphenylmethane diisocyanate is modified. The resulting self-emulsifying modified MDI composition is
This invention relates to a method for reinforcing cardboard used in a reinforcing coating agent. Regarding the conventional method of strengthening cardboard,
It is known to apply corrugated wax, synthetic resin, etc. diluted with a solvent to increase strength, for example. However, these methods have disadvantages in that the working environment deteriorates due to solvent evaporation and a solvent recovery step is required. As a method to improve these shortcomings,
-6557 publication discloses polyisocyanate monomers, doublets, and triplet oligomers, and
No. 57-95397 describes a method in which a crude MDI composition represented by the general formula () modified with a compound having at least two or more active hydrogen atoms in the molecule is applied to corrugated board and cured. Furthermore, JP-A No. 57-182436 has a general formula () as an improved method of JP-A-57-95397.
For 100 equivalents of -NCO group, the crude MDI shown by
A method using a crude MDI composition containing 1% by weight or more of a partial prepolymer modified with a polyol having 1 to 20 equivalents of two or more hydroxyl groups is described. However, when these polyisocyanates or modified polyisocyanate compositions are used, the physical properties such as strength of the corrugated board coating are not satisfactory, breakage occurs during handling, and the coating is difficult to coat as with conventional methods. A large amount of solvent was required to clean the equipment afterwards, and there were many drawbacks in terms of working environment and economy. For example, the crude oil described in JP-A No. 57-182436
If a reinforcing agent made by adding a prepolymer partially modified with a polyol having at least two hydroxyl groups to MDI is used for corrugated board coating, a certain degree of strength can be achieved, but spray coating is difficult due to the high viscosity. Due to certain reasons, it is limited to roll application.
In addition, due to poor permeability into the base paper, a resin film was formed near the surface of the base paper, making it impossible for the resin to exhibit its original strength. Therefore, like the conventional method, it is necessary to dilute with an inert organic solvent when coating.
Further, after coating, it was necessary to perform troublesome cleaning of the roll with an organic solvent. The present inventor has arrived at the present invention as a result of intensive studies to improve these drawbacks. That is, the present invention provides a crude compound represented by the above general formula ().
Modified crude MDI obtained by reacting MDI with a polyol having at least two hydroxyl groups and an average molecular weight of 1000 or more, and a polyoxyalkylene monool obtained by addition polymerizing ethylene oxide and propylene oxide with a monofunctional alcohol.
A method of reinforcing corrugated board, characterized by applying a composition. The reinforcing method used in the present invention is characterized by modifying crude MDI with a polyol having specific physical properties to impart strength and flexibility to the resulting corrugated board, and by modifying crude MDI with a polyol having specific physical properties. By modifying with alkylene monool,
It is made by appropriately emulsifying crude MDI and improving its permeability into base paper, and by using a crude MDI composition containing a prepolymer modified in this way as a reinforcing coating agent, strong corrugated board can be produced. Not only can it be obtained, but it can also be made into a low viscosity by emulsification, making it possible to arbitrarily control the amount of application and also to enable spray coating. Therefore, the method of the present invention does not necessarily require a coating method using a roll coater, and therefore cleaning the equipment after coating can be done simply by washing with water without using a solvent as in the conventional method, thereby reducing the deterioration of the working environment. This makes handling extremely easy. In the present invention, polyether polyols are preferable as polyols used for modifying crude MDI, and polyether polyols are polyether polyols in which propylene oxide, or propylene oxide and ethylene oxide are addition-polymerized to polyfunctional alcohols such as propylene glycol, glycerin, pentol, and sorbitol. Examples include polyoxyalkylene polyols, and so-called polymer polyols in which vinyl monomers such as acrylonitrile and styrene are graft-polymerized to these polyoxyalkylene polyols. The average molecular weight of the polyol is at least 1000 or more; if it is less than this, a certain degree of strength can be obtained, but flexibility is poor and desired physical properties are difficult to obtain. preferably has an average molecular weight of 1000 to 6000,
It is desirable to use polyols having a hydroxyl number in the range of 25 to 200. In addition, polyoxyalkylene monool is prepared by using a monofunctional alcohol such as methyl alcohol, ethyl alcohol, or propyl alcohol as an initiator, and preferably adding ethylene oxide (EO) and propylene oxide (PO) to this in the presence of a basic catalyst. It can be produced by a known method of adding EO/PO at a weight ratio of 90/10 to 40/60. The addition order of ethylene oxide and propylene oxide or their addition format (random or block) may be any, and the preferred range of the hydroxyl value of the polyoxyalkylene monol is 25
-200. The crude MDI used in the present invention is: It is a mixture of a benzene ring in the above formula () having a dinuclear form and a trinuclear form or more, and the benzene ring in the general formula ()
Although mixtures with n in a wide range can be used, it is usually a mixture containing n=0 to 4 as the main component obtained as a distillation residue liquid in the purification process of diphenylmethane diisocyanate. For example, it is used as a raw material for rigid polyurethane foam. It is easily available. The modification reaction with polyol and polyoxyalkylene monol carried out in the present invention is as follows:
A preferred method is to modify crude MDI with a polyol and then subsequently add polyoxyalkylene monool to the reaction system to complete the modification reaction. In the polyol modification reaction in the first stage of the crude MDI described above, the blending ratio of the crude MDI and polyol is 100 parts by weight of the modified crude MDI composition (hereinafter referred to as
5 to 50 parts, particularly preferably 15 to 25 parts, in the total amount (parts by weight). Therefore, the amount of polyol used is 5
Below 50%, the strength of the cardboard obtained is poor;
If it is more than 100%, the viscosity becomes high and the permeability when applied as an emulsion tends to be poor. The reaction temperature is 50-120℃, preferably 80-100℃.
C. for about 2 hours, and the end point of the modification reaction with the polyol is determined by measuring the --NCO group content in the reaction product. The -NCO group content of commercially available crude MDI is
It is about 30 to 32% by weight in 100 g of MDI, and in the present invention, -NCO
Generally, the group content is modified to 15 to 28% by weight, and the blending ratio of polyoxyalkylene monol is 1 to 5 parts per 100 parts of the crude MDI composition. − in the reactant
The NCO group content can now be set. Moreover, the amount of polyol charged is appropriately set according to the average molecular weight and hydroxyl value of the polyol. In the polyoxyalkylene monool modification reaction after the crude MDI of the present invention, the blending ratio of crude MDI and polyoxyalkylene monol is preferably 1 to 5 parts, particularly preferably 1 to 100 parts of crude MDI, as described above. It is in the range of 2 to 3 parts. If the amount of polyoxyalkylene monol is less than 1 part, when the resulting modified crude MDI composition is emulsified and applied, the emulsion will be insufficient, and if it exceeds 5 parts, the pot life of the emulsion will tend to be shortened. becomes. The modification reaction temperature using polyoxyalkylene monool is 70 to 80° C., and the modification reaction in the present invention is completed by heating for 1 to 2 hours. In the modification reactions before, after, and after, tin octylate, lead octylate, dibutyltin dilaurate, or the like may be added as a catalyst, if necessary. The resulting modified crude
Although the MDI composition is a highly viscous liquid with a viscosity of about 300-3000 cps/25°C and an isocyanate content of 15-28% by weight, it can be easily emulsified with water and coated at a low viscosity. When applying the modified crude MDI composition obtained according to the present invention to cardboard, it may be used as a stock solution, but it is better to add the same amount of water and emulsify it by stirring in a homogenizer. . Since the viscosity is thereby reduced, roll coating is of course possible, but spray coating is also possible. The amount of coating is 10 to 50 g/m ² , usually a small amount of 10 to 20 g/m ² is sufficient, the reinforcement efficiency is good, and there is no tack after coating. Furthermore, the coating area can be applied to one side or both sides of the corrugated cardboard sheet, or to the center core. When applied to the core, it has good compatibility with the glue used for adhesion and is reactive, so the adhesive force is strengthened. In addition, when applying silicone-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 tertiary amines such as triethylenediamine. It is also possible to add and use known curing accelerators for urethane such as. The modified crude MDI composition applied according to the present invention reacts with the hydroxyl groups of cellulose constituting the paper fibers or the moisture present in the paper and the moisture in the atmosphere,
Maximum strength is shown in 1 to 6 days. The present invention will be explained below with reference to Examples. Example 1 Polyoxypropylene polyol with an average molecular weight of 3000 and a hydroxyl value of 38.4 obtained by addition polymerization of propylene oxide to propylene glycol
180.6 parts of crude MDI (manufactured by Mitsui Nisso Urethane Co., Ltd., MDI-CR) with an NCO group content of 30.6 weight (%) was added in a nitrogen stream.
It was added dropwise into 82.26 parts of 300) at 100°C over 1 hour and kept at the same temperature for 2 hours to complete the reaction before and after. Next, 25.7 parts of polyoxyalkylene monool (hydroxylated 78.2) obtained by addition polymerization of ethylene oxide and propylene oxide to methanol (set to be contained at 2.5 (%) in the modified polyisocyanate composition) was added. The latter reaction was completed by heating at 100°C for 1 hour. After cooling, the resulting modified polyisocyanate composition had a viscosity of 800 cps/25°C and an isocyanate group content of 23.4% by weight. 100g of the modified crude MDI composition obtained as above was
The mixture was stirred and emulsified with 100 g of water at 10° C. in a homogenizer for 5 minutes (3000 rpm). The obtained emulsion has a low viscosity of 10 cps/25°C, and is sprayed with a spray gun at 20.0 x 25.0 cm.
Spray coat the liner paper with a weight of 200 g/m ² cut into corners and the center core with a weight of 125 g/m ² ,
When dried at 100°C for 60 seconds, the coated paper was evenly coated with no tack left. The pressure resistance strength according to the ring crush test after curing at 20°C/65(%) HR x 5 days was as shown in Table 1. Example 2 243.9 parts of a copolymer with a hydroxyl value of 41.4 obtained by graft polymerizing 192 parts of acrylonitrile and 52 parts of styrene to 770 parts of polyoxypropylene polyol with an average molecular weight of 3000 and an average functional group number of 3 in the presence of a radical generator. , NCO group content 30.6 weight (%)
Crude MDI (MDI-CR manufactured by Mitsui Nisso Urethane Co., Ltd.)
The mixture was added dropwise into 82.26 parts of 300) in a nitrogen stream at 100°C over 2 hours, and the reaction was further heated at the same temperature for 2 hours. Next, the same polyoxyalkylene monol as used in Example 1 (hydroxyl value 78.2 (%))
After adding 27.3 parts (set so that the content in the modified polyisocyanate composition is 2.5 (%)), 100 parts
The denaturation reaction was completed by heating at °C for 2 hours. After cooling, the resulting modified polyisocyanate composition had a viscosity of 1430 cps/25°C and an isocyanate group content of 21.7% by weight. Viscosity obtained after emulsification in exactly the same manner as in Example 1
Spray coat the emulsion at 20cps/25℃ in the same way and dry at 100℃/60 seconds. 20℃/65(%)
The compressive strength of the processed paper after curing for 5 days at RH was as shown in Table 1. Comparative Example A conventional product that was not modified with polyoxyalkylene monool was synthesized using the following procedure. That is, an average molecular weight of 2000 obtained by addition polymerizing propylene oxide to propylene glycol,
300 parts of polyoxypropylene polyol with a hydroxyl value of 56.1 was mixed with an NCO group content of 30.6 in a nitrogen stream.
The mixture was added dropwise to 324.4 parts by weight (%) of crude MDI at 80°C over 1 hour, and further heated at the same temperature for 2 hours to complete the reaction. The viscosity of the modified crude MDI composition obtained after cooling is
The temperature was 1370 cps/25°C, and the NCO group content was 21.2 (%). 100g of the modified crude MDI composition obtained in this way was
Emulsification was attempted using 100 g of water at 100 °C in the same manner as in Example 1, but no emulsification occurred, and when the mixture was allowed to stand for about 5 minutes, it was completely separated into an aqueous layer and an oil layer. Therefore, unlike the modified crude MDI compositions obtained in Examples 1 and 2, the modified crude MDI compositions obtained by modification as in Comparative Examples cannot be spray coated, so roll coating is not possible. did. That is, when liner paper and core paper were roll coated, tack remained due to the slow penetration of the resin into the base paper. Next, in order to make the coating conditions similar to those in Examples 1 and 2, after applying the same amount of water as the amount of resin applied using a spray gun,
After drying at 100°C for 60 seconds, it was cured at 20°C/65 (%) RH for 5 days. The compressive strength was as shown in Table-1. 【table】

Claims (1)

[Claims] 1 General formula () [In the formula (), n is an integer of 0 or 1 or more] Methylene-crosslinked polyphenylene polyisocyanate, a polyol having at least two or more hydroxyl groups and an average molecular weight of 1000 or more, and a monofunctional alcohol A method for reinforcing corrugated board, which comprises applying a modified methylene crosslinked polyphenylene polyisocyanate composition obtained by reacting ethylene oxide and polyoxyalkylene monool prepared by addition polymerization of propylene oxide to the substrate. 2. The method according to claim 1, wherein the polyol has an average molecular weight of 1,000 to 6,000. 3 5 parts by weight of polyol in 100 parts by weight of the modified methylene crosslinked polyphenylene polyisocyanate composition.
Claims using a methylene-crosslinked polyphenylene polyisocyanate composition modified to contain ~50 parts by weight, 1 to 5 parts by weight of polyoxyalkylene monool, and 15 to 28 parts by weight of -NCO groups. The method described in paragraph 1.