JPS5916038B2 - Method for producing processed paper with enhanced wet compressive strength - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing paperboard for packaging having excellent wet and dry tensile strength and wet and dry compressive strength.

5. More specifically, the present invention is a reaction product of an unsaturated basic acid and a bisphenol A type diglycidyl ether or an epoxy compound, and in the same molecule, at least one α, β has one ethylenically unsaturated double bond and β for the 0 ester bond
Has at least one hydroxyl group at the position and has a molecular weight of 300 to 3
, 000, preferably in the range of 500 to 2,000 (hereinafter abbreviated as "prepolymer"), and methyl acrylate, ethylacrylate and butyl acrylate. At least one monomer in a weight ratio of 10
Processed paperboard with enhanced wet compressive strength characterized by impregnating and/or coating paperboard with a mixture in a ratio of 290 to 40:60 and polymerizing it by irradiating it with high-energy electron beams. Relating to a manufacturing method.

Although paperboard is useful as a packaging material, its use is limited by its poor water resistance.

With the development of cold chain and improvement of distribution process, i5
Packaging materials for vegetables, fruits, frozen fish, fresh fish, etc., are increasingly required to be water resistant, and their rigidity and compressive strength are particularly important in order to prevent them from collapsing during transportation or compressive destruction during stacking. It is strongly desired to improve the rigidity and compressive strength when wet with water. Conventional techniques for imparting water resistance to paperboard include impregnation or coating with a synthetic resin solution such as molten paraffin or vinyl polymer, or impregnation with an unsaturated compound and polymerization within the paper. However, impregnation with molten paraffin not only significantly discolors the paper surface and impairs its appearance, but also has the drawback of being slippery. Furthermore, in order to obtain sufficient wet compressive strength, it is necessary to deposit a considerable amount of wax, and it is also difficult to control the amount of wax deposited.
In order to obtain the desired strength by impregnating and coating a solution of a synthetic resin such as a vinyl polymer, it is necessary to deposit a considerable amount of the polymer, which poses problems in the selection of solution viscosity, solvent, etc.

Furthermore, a polymerizable unsaturated compound such as methyl methacrylate, styrene, acrylonitrile, or a mixture of these polymerizable unsaturated compounds and the polymer is impregnated and/or coated, and a suitable initiation means such as a ferrous salt is applied. Methods are known in which the unsaturated compound is polymerized inside the paper by means such as redox systems using hydrogen oxide, ultraviolet irradiation, and irradiation with high-energy ionizing radiation.

However, when producing processed paperboard using this method, the amount of resin required to sufficiently improve the wet tensile strength and wet compressive strength of the processed paperboard must be applied, and at the same time, the dry bending strength of the processed paperboard will decrease. However, there was also the tradeoff that it was easy to cause damage during Nicol gate processing during box manufacturing. The present inventors have conducted repeated research on a method for waterproofing paperboard using a polymerization treatment method by irradiating electron beams from an accelerator using the above-mentioned vinyl monomer or vinyl monomer/polymer mixture. By using a mixture of and at least one monomer selected from methyl acrylate, ethyl acrylate, and butyl acrylate, the drawbacks of the conventional method can be overcome, and while maintaining sufficient dry bending strength, it also has excellent wet resistance. The inventors have discovered that it is possible to obtain paperboard having high tensile strength and wet compressive strength, and have arrived at the present invention. Since the method of the present invention uses an electron beam from an accelerator, it is not only possible to process paperboard at high speed at room temperature, but also the processed paperboard obtained by the method of the present invention can be processed using conventional methods such as methyl methacrylate, styrene, Compared to processed paperboard obtained by polymerizing a polymerizable unsaturated compound such as acrylonitrile, it has considerably higher hygroscopicity and dry bending strength, as well as superior wet tensile strength and wet compressive strength.

In the conventional method of impregnating and coating paperboard with polymerizable unsaturated compounds such as methyl methacrylate, styrene, and acrylonitrile and polymerizing them, the glass transition temperature of the polymers produced from these monomers is higher than room temperature; Since polymers are hydrophobic, the wet tensile and compressive strengths of processed paperboards are usually due to these polymers. In particular, with regard to compressive strength, the higher the rigidity of the polymer at room temperature, the smaller the amount of adhesion to obtain a predetermined wet compressive strength. However, these polymers are generally brittle and therefore reduce the bending strength of paperboards to which they are applied. In order to maintain a sufficient bending strength, it is necessary to copolymerize monomers such as vinyl acetate, methyl acrylate, and ethyl acrylate, whose glass transition temperature is lower than room temperature, or to mix these polymers or polymers such as polybutadiene. It is conceivable to carry out a polymerization treatment. However, if the requirements for bending strength are satisfied by these means, the wet tensile strength and wet compressive strength become insufficient. It was extremely difficult to satisfy these demands. The present inventors have conducted various research studies on polymer compounds that can be rapidly polymerized and cured by electron beam irradiation, and that can increase the wet tensile strength and wet compressive strength of paperboard without impairing the bending strength. However, in the reaction product of an unsaturated basic acid and a bisphenol A type diglycidyl ether or epoxy compound, at least one α,β monoethylenically unsaturated substance is present at the end of the molecule directly via an ester bond. An unsaturated vinyl ester prepolymer having a double bond and at least one hydroxyl group at the β position relative to the ester bond and having a molecular weight in the range of 300 to 3,000, methyl acrylate, ethyl acrylate, and At least one monomer selected from the group consisting of butyl acrylate in a weight ratio of 10:90 to 40.
It was discovered that the desired object could be achieved by impregnating and/or coating a paperboard with a mixture in a ratio of 60:60 and irradiating it with an electron beam to polymerize it, thereby achieving the present invention.

In the conventional method, for example, a paperboard sample is impregnated with a methanol solution of methyl methacrylate, and a dose rate of 0.25 is applied using a Vandegraaf electrostatic accelerator at 1.5 MeV 1501 tA.
When methyl methacrylate is polymerized in paper by irradiation with 5 Mrad/Sec electron beam, a satisfactory wet ring luster strength (152.4 m7!L×12.
Measurement on a 7mm ring-shaped piece of paper, when wet 2
(Test result after 1 hour immersion in 0°C water) The amount of polymer adhesion required to reach 10 kg is 339/TI.

(The ring crush strength of untreated paper when wet is only 2 kg.) The number of folds required to cause a break when dry (hereinafter sometimes abbreviated as ゜5 dry fold strength 1f) is the same as for untreated paper. Compared to 850 times for paper, treated paper with the above polymer adhesion amount was only 30 times. When styrene is used instead of methyl methacrylate, the ring crush strength when wet is 1.
The amount of polystyrene attached to reach 0 kg is 189/
The dry bending strength was 100 times with this amount of polymer adhesion. Acrylonitrile also obtained almost the same results as styrene. Practically speaking, the performance of paperboard required for such processing is a wet ring crushing strength of 10 kg and a dry bending strength of 200 times or more.
In conventional methods, it has been difficult to satisfy such requirements. Although polystyrene is quite effective as a polymer for improving wet compressive strength, styrene has a very slow radiation polymerization rate and the above dose rate (0.
Even after irradiation with 10 Mrad of electron beam (25 Mrad/Sec), the polymerization rate was only 65%, and it was difficult to completely polymerize styrene. That is, styrene is not suitable as a monomer to be polymerized by electron beams. Acrylonitrile has a fairly high polymerization rate with electron beams, reaching a polymerization rate of 90% or more with irradiation of 5 Mrad, but the surface of paper to which acrylonitrile polymer is attached is uneven, which is inconvenient for obtaining a uniform and smooth surface. In contrast, the prepolymer used in the method of the present invention,
For example, a mixture of a prepolymer with a molecular weight of 2,000 obtained by reacting bisphenol A type diglycidyl ether (Ciel Corp., Epicote 1004) with acrylic acid and ethyl acrylate in a mixing ratio of 25:75 (weight ratio) is applied to paperboard. When the material was impregnated and polymerized and cured by 5 Mrad electron beam irradiation, the amount of polymer adhesion required to reach a wet ring crush strength of 10k9 was 99/I, and the dry bending strength was 360 times.

Further, the above prepolymer-ethyl acrylate mixture reaches a polymerization rate of 90% or more at 3 Mrad, and is convenient for polymerization treatment by electron beam irradiation. This is one of the major advantages of the method of the invention. Furthermore, paperboard obtained by polymer processing using a prepolymer-ethyl arylate mixture has greater water absorption than paperboard obtained by conventional polymerization of monomers such as methyl methacrylate, styrene, and acrylonitrile. There is a characteristic that there is

The water absorption rate obtained by soaking an untreated paperboard sample in water at 20°C for 10 minutes and measuring the weight increase after pulling it up was 64.
It was %. The water absorption of paperboard coated with styrene or methyl methacrylate polymers at 109/l each is 3
0% and 32%. On the other hand, the water absorption of paperboard to which the mixture of prepolymer ethyl acrylate (25:75) was polymerized was 46%, and despite its considerable water absorption, it had excellent ring crush strength when wet. The indication is clear. In the case of styrene polymer, the adhesion amount required to obtain a ring crush strength of 10k9 is 199/i, so the water absorption in this case is 11%.
It's nothing more than that. That is, when comparing the amount of polymer adhesion required to obtain a satisfactory compressive strength when wet, the paperboard obtained by the method of the present invention exhibits a characteristic of having a considerably high water absorbency. In conventional methods, the basic idea was that it was necessary to reduce water absorption in order to increase the compressive strength when wet, but the method of the present invention is completely different from the conventional concept. It is possible to produce processed paperboard that has excellent wet tensile strength and wet compressive strength while retaining the same properties. The amount of polymer coverage required to obtain satisfactory wet compressive strength in the process of the present invention is fairly small. In order to adjust the amount of polymer attached, it may be diluted with acetone, methanol or other organic solvent to an appropriate concentration. Since the prepolymer-ethyl acrylate mixture alone has a fairly high viscosity, diluting it with the above solvent is an effective means for uniformly impregnating and coating the paperboard.

In the method of the present invention, if the prepolymer or methyl acrylate, ethyl acrylate, or butyl acrylate is used alone, satisfactory performance of the processed paperboard cannot be expected.

a prepolymer and at least one selected from the group of methyl acrylate, ethyl acrylate, and butyl acrylate
The mixing ratio of seed monomers is 10:90 to 40:6 by weight.
0, preferably 20:80 to 30:70.
Due to this composition ratio, if the amount of one prepolymer component increases, the dry bending strength of the processed paperboard will be insufficient at the amount of polymer adhesion required to obtain a satisfactory wet compressive strength, and if the acrylate monomer component increases, the wet compressive strength will not be satisfactory. It becomes difficult to obtain processed paperboard with The prepolymer used in the method of the present invention has a molecular weight of 30
A range of 0 to 3,000, preferably 500 to 2,000 is suitable.

If the molecular weight is lower than 300, the amount of polymer attached to obtain a satisfactory wet compressive strength increases and the polymerization rate by electron beam irradiation decreases. In addition, if the molecular weight is too high, the viscosity will not only be high and difficult to handle during impregnation coating, but also
The amount of polymer coverage required to obtain satisfactory wet compressive strength increases. The prepolymer used in the present invention is a reaction product of an unsaturated basic acid and a bisphenol A type diglycidyl ether or an epoxy compound, and in the same molecule, at least one α, α,
An unsaturated vinyl ester prepolymer having a β-ethylenically unsaturated double bond, at least one hydroxyl group at the β position relative to the ester bond, and having a molecular weight in the range of 300 to 3,000. Yes, generally CH2=CH-0CC
It is a compound having at least one structure consisting of H2CHsM, for example, a compound having the structural formula shown below.

(n=0,1,2,--1) These prepolymers are compounds having one or more epoxy groups in one molecule, such as glycidyl ether synthesized by the reaction of epihalohydrin and polyhydroxyphenol or polyol. or glycidyl ester, or at least one epoxy compound selected from epoxy compounds having a double bond in the molecule and obtained by oxidation thereof, and an unsaturated monobase represented by acrylic acid or methacrylic acid. The prepolymers of the invention are obtained by reaction of polyhydroxyphenols or polycarboxylic acids with glycidyl acrylate or glycidyl methacrylate.

Furthermore, the prepolymers used in the present invention also include modified epoxy acrylates disclosed in Japanese Patent Publication No. 1465-1983. The electron beam that can be used in the method of the present invention is 100 KeV to 5 KeV, preferably 500 K, from an accelerator such as a Vandegraaf electrostatic accelerator or an insulated core transformer type accelerator.
An electron beam of eV to 3 KeV is used.

There is no particular limit to the irradiation dose, but 0.3 to 10 Mrad is most commonly used. As is well known, polymerization treatment using electron beams allows the reaction to be carried out in a short time and with irradiation, and the method of the present invention also allows paperboard with excellent wet and dry compressive strength to be produced at high speed and with good productivity. The method of the present invention will be explained in detail below with reference to Examples. Example 1 Corrugated paperboard (2209/M2, thickness 0.30m0 (hereinafter abbreviated as 5?paperboard sample 1°) was cut into strips of length 120m7!L width 70mm, and heated at 20°C and 65% relative humidity ( Adjust the weight in the air at RH until it reaches a certain weight.

The weight was 1.8439. Bisphenol A type diglycidyl ether (Ciel trade name Epicote 10)
01) and acrylic acid in the presence of a polymerization inhibitor and an esterification catalyst to produce a prepolymer (1) (with a reaction rate of 95%).
An average molecular weight of 1100) was obtained. This prepolymer (1)
and ethyl acrylate and acetone at a weight ratio of 5.
:15:80 mixture was prepared. The paperboard samples were immersed in the mixture for approximately 10 seconds and placed into pre-weighed polyethylene lined aluminum bags. Nitrogen gas was blown into the bag for about 20 seconds to expel the air, and then the bag was melt-sealed. The weight of each bag was measured and the weight of the aluminum bag was subtracted to find that the weight of the liquid mixture impregnated into the paperboard was 0.3279. A paperboard sample placed in an aluminum bag prepared in this way was
Place it on a conveyor belt that moves at the speed of an eclipse.
Vandegraaf electrostatic accelerator (1.5MeV150μAl
It was irradiated with an electron beam at a dose rate of 0.25 Mrad/Sec) to give an irradiation dose of 5 Mrad. After irradiation, the sample was removed from the aluminum bag and placed in a vacuum dryer at 70°C for 2 days.
The mixture was kept for 4 hours, and unreacted monomers and solvent were removed. Then, it was adjusted in air at 20° C. and 65% RH, and its weight was measured and found to be 1.9079. It was found that the polymerization rate of the impregnated ethyl acrylate was 99%, and that the polymer was attached to the paperboard at a rate of 7.29/I. The surface of the paperboard after such treatment was smooth. The dry tensile strength (Note 1) and dry ring crush (Note 2) of the paperboard sample treated in this manner were measured and were 34.
7kg, 35.0k9, and 31.9kg each of the original paperboard.
It was somewhat increased compared to 81<9, 32, and 1k9. Next, the wet tensile strength (Note 3) and wet ring crush (Note 4) of the treated paperboard were measured and found to be 10.3k9, respectively.
It was found that it was 8.0k9, which was significantly improved compared to the original paperboard's 3.2k9 and 2.5k9. The dry bending strength (Note 5) of the treated paperboard was 400 times, which was lower than the 850 times of the original paperboard, but it did not cause any practical problems. Treated paperboards with various amounts of polymer adhesion were prepared by changing the amount of impregnation of the mixed solution and the amount of irradiation using exactly the same procedure, and the wet tensile strength, wet ring crush, dry bending strength, and water absorption (Note 6) were tested. . The test results are shown in Table 1.
It's like this. For comparison, a mixed solution containing Prepolymer 1 (1) that does not contain ethyl acrylate and acetone in a ratio of 10:90 (weight ratio), and a mixture solution that does not contain Prepolymer 1 (1) and has a ratio of 60:40 (weight ratio) of ethyl acrylate and methanol ) in exactly the same manner using a mixture of
The results of testing its performance are listed in Table 2 for reference.

Looking at these results, it is clear that paperboard made from a mixture of prepolymer 1.(1) (average molecular weight 1100) and ethyl acrylate is superior to paperboard made using either material alone in terms of the required amount of polymer and dry bending strength. It can be seen that this has been improved.

Note 1 Dry tensile strength was measured using an Instron TM-M model under the following conditions.

The sample was adjusted in the atmosphere at 20°C and 65% RH.

Note 2 Measurement was carried out using a dry ring crush Instron TM-M model under the following conditions.

The sample was adjusted in the atmosphere at 20°C and 65% RH.

Note 3 Wet tensile strength Instron TM-M type was used.

The sample was immersed in water at 20° C. for 10 minutes and immediately measured.

Other conditions are that of dry tensile strength, load 1k920℃,
Prepared in air at 65% RH. Note 6 Water absorbency After immersing the sample in water at 20°C for 10 minutes, remove excess water with filter paper and check the water absorption by measuring the weight difference before and after immersion in water.

Example 2 A mixed solution of prepolymer 1 (1) (average molecular weight 1,100), ethyl acrylate and acetone in a weight ratio of 8:12:80 was prepared.

The paperboard treatment method and paperboard testing method were the same as in Example 1. The results of the tests on the treated paperboard are shown in Table 3. The results show that when the amount of prepolymer is increased and the amount of ethyl acrylate is decreased, the amount of polymer required in wet conditions becomes larger than the results of Example 1, and the dry bending strength also decreases. Example 3 Prepolymer 1 (1) (average molecular weight 1100), ethyl acrylate and acetone were mixed at a ratio of 5:35:60 (
A mixed solution (weight ratio) was prepared.

The paperboard treatment method and paperboard testing method were the same as in Example 1. The test results for the treated paperboard are shown in Table 4. The results show that when the amount of ethyl acrylate is increased, the required amount of polymer is larger than in Example 1, and the dry bending strength is slightly improved compared to Example 2.

Example 4 In Examples 1, 2, and 3, ethyl acrylate was used as a monomer, but in Example 4, it can be seen that the wet tensile strength and dry bending strength are extremely low when the monomer methyl arylate is used alone.

Example 5 Prepolymer 1 (1) (average molecular weight 1,100), methyl acrylate was used as the filler.

Prepolymer (1) (average molecular weight 1,100), methyl acrylate and acetone were mixed at a weight ratio of 5:15.
:80 mixture was prepared. The paperboard treatment method and paperboard testing method were the same as in Example 1. The results are shown in Table-5. For comparison, a mixed solution of methyl acrylate and methanol containing no prepolymer (1) was prepared at a ratio of 40:60 (by weight), and paperboard was treated in exactly the same manner as in Example 1. 6.

The results for the above mixed solution show values that are almost the same as in Example 1, but the dry bending strength is lower. For comparison, a mixture of butyl acrylate tote and methanol containing no prepolymer and methanol at a ratio of 40:60 (weight ratio) was prepared, and Example 1 was prepared.
Table 8 shows the results of processing paperboard in the same manner as above. Butyl acrylate alone, similar to methyl acrylate,
It can be seen that the wet tensile strength and dry bending strength are extremely low.

Example 6 The prepolymer (1) used in Examples 1 to 5 had a molecular weight of 1
, 100, but in Example 6, bisphenol A type diglycidyl ether (Ciba Geigy Araldite GY-250) and acrylic acid were reacted in the presence of a polymerization inhibitor and an esterification catalyst to produce a prepolymer with a reaction rate of 96%. 1 () (average molecular weight 530) was obtained.

A mixed solution of this prepolymer (H), ether acrylate and acetone was prepared in a weight ratio of 5:15:80. The paperboard treatment and testing methods were the same as in Example 1. The results are shown in Table-9. The difference from Examples 1 to 5 is that the amount of polymer deposited at a wet tensile strength of 10k9 from this result requires a larger amount of polymer than that of the wet ring crush. Example 7 Bisphenol A type diglycidyl ether (Ciel Epicote 1004) and acrylic acid: polymerization inhibitor,
The reaction was carried out in the presence of an esterification catalyst to obtain a prepolymer (average molecular weight 2,100) with a reaction rate of 93%.

A mixed solution was prepared in which the mixing ratio of prepolymer (m), ethyl acrylate, and acetone was 5:15:80 (weight ratio). The paperboard processing method and test method were performed in the same manner as in Example 1. The results are shown in the table. 10. Example 8 Aliphatic dicarboxylic acid type diglycidyl ester (Syodyne 550, manufactured by Showa Denko K.K.) and acrylic acid were reacted in the presence of a polymerization inhibitor and an esterification catalyst, and the reaction rate was 95.
% prepolymer (M (average molecular weight 475)) was obtained.

A mixed solution containing prepolymer, ethyl acrylate, and methanol in a weight ratio of 5:15:80 was prepared. The paperboard treatment and testing methods were the same as in Example 1. The results are shown in Table-11. For comparison, a mixed solution was prepared in which the mixing ratio of prepolymer M and methanol was 10:90 (weight ratio) without using ethyl acrylate, and a paperboard was treated in the same manner as in Example 1 for testing.

Table 12 shows the results. Example 9 Polyepichlorohydrin diglycidyl ether (Nitto Kasei Eponite 012) and acrylic acid were reacted in the presence of a polymerization inhibitor and an esterification catalyst to obtain prepolymer V (average molecular weight 400) with a reaction rate of 95%. Ta.

A mixture of prepolymer, ethyl acrylate, and methanol in a ratio of 7:21:72 (weight ratio) was prepared. The paperboard treatment and testing methods were the same as in Example 1.
The results are shown in Table-13. Example 10 Dimer acid-modified bisphenol A diglycidyl ether (Ciel Corporation, Epicote 872) represented by the general formula was reacted with acrylic acid in the presence of a polymerization inhibitor and an esterification catalyst to form a prepolymer with a reaction rate of 95%. (W) (average molecular weight 990)
I got it.

A mixed solution of prepolymer, ethyl acrylate, and methanol in a ratio of 7:21:72 (weight ratio) was prepared. The paperboard treatment and testing methods were the same as in Example 1.
The results are shown in Table-14. Example 11 Changes in the physical properties of paperboard 1 manufactured by repeating the same method as Example 1 except that the mixing ratio of prepolymer 1 (1) and ethyl acrylate were changed as shown in the table below were observed. Ta.

As above, mix the prepolymer and monomer in a ratio of 10:90 to 40.
: In the case of a system mixed in the range of 60, the folding strength required when paperboard is made into a corrugated box is more than 200 times, and the water absorption is about 40% or more when the prepolymer is 10% or more, and it can be used as a corrugated board. It can be seen that this method is effective in terms of adhesion compatibility and preservation of package contents.

Claims (1)

[Claims] 1 In a method for producing processed paperboard with excellent wet pressure strength by impregnating paperboard with a polymer or the like and polymerizing it inside the paperboard; At least one α, β-
having an ethylenically unsaturated double bond, at least one hydroxyl group at the β position relative to the ester bond, and a molecular weight of 3
00 to 3,000 and at least one monomer selected from the group consisting of methyl acrylate, ethyl acrylate and butyl acrylate in a weight ratio of 10:90 to 10:60. 1. A method for producing processed paperboard having enhanced wet compressive strength, which comprises impregnating and/or coating a mixed mixture onto paperboard and polymerizing it by irradiating it with an electron beam.