JPH08257499A - Method for crosslinking rubber latex with low-energy electron beam - Google Patents

Abstract

PURPOSE: To continuously and economically crosslink a rubber latex by applying a rubber latex in uniform thickness with a coating machine for uniformly coating a material and irradiating the latex with an electron beam by means of a low-energy electron accelerator. CONSTITUTION: A rubber latex is crosslinked with an electron beam as follows. Namely, a coating material is uniformly applied to a substrate such as a rotating and circulating belt conveyor 4. For example, the rubber latex is applied in uniform thickness with a curtain-flow coater-type head 2, irradiated with an electron beam by means of a low-energy electron accelerator 1 and crosslinked. Meanwhile, although the head 2 used in this case is not specified, such systems as curtain-flow coating, knife coating, roll coating and grvure coating are appropriately used. Further, among the systems, the curtain-flow coating system is optimum because a relatively high-viscosity rubber latex is uniformly and easily applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electron beam crosslinking of rubber latex (hereinafter sometimes abbreviated as latex), and more specifically, a method for electron beam crosslinking rubber latex with a low energy electron accelerator in a coating machine. Is.

[0002]

2. Description of the Related Art As a radiation source for radiation crosslinking of rubber latex, radioactive isotope Cobalt-60 or medium
High energy electron beams are known.

These radiation sources have high energy, require a thick shield to ensure safety, and require a huge capital investment. In other words, this capital investment has been a barrier to the practical use of radiation crosslinking of rubber latex.

Further, the self-shielding electron accelerator is called a low energy electron accelerator and is economical in that it does not require thick shielding, but its penetration distance into rubber latex is extremely short at 1 mm or less. , It has been mainly used for radiation processing of thin materials such as surface coating and surface modification of plastics.

For this reason, radiation cross-linking of large quantities of rubber latex with low energy electron accelerators has not been dreamed of.

Therefore, the present inventors have filed Japanese Patent Application No. 6-2114.
In Japanese Patent No. 61, a batch-type irradiation method in which rubber latex is irradiated while being stirred in a container has already been proposed. This method is an epoch-making method because it enables radiation crosslinking of a large amount of rubber latex even with a low-energy electron accelerator having a poor penetrating power.

However, in the method of irradiating while stirring using a container, irradiation is stopped after a certain irradiation time, the irradiated rubber latex is taken out from the container, the inner surface of the container and the stirring blade are cleaned, and new rubber latex is filled. Operation was required. That is, it is difficult to continuously irradiate the rubber latex with an electron beam, and there is a problem that the utilization efficiency of the electron accelerator is low.

[0008]

That is, it is an object of the present inventors to provide a method for continuously and economically crosslinking a rubber latex with a low energy electron accelerator.

[0009]

According to the present invention, a low-energy electron accelerator is used after a rubber latex is applied to a substrate with a constant thickness by using an applicator for uniformly applying a coating material on the substrate. Is a method for electron beam crosslinking of a rubber latex by irradiating the rubber latex with an electron beam by using the above method, and such a method solves the conventional problems.

The present invention will be described in detail below by dividing it into constituent elements.

(Rubber Latex) The term “rubber latex” as used in the present invention means natural rubber latex, synthetic rubber latex and mixtures thereof.

Natural rubber latex is classified into high ammonia latex, low ammonia latex and the like depending on the type of preservative. In the present invention, any natural rubber latex can be applied regardless of the type of preservative.

Regarding synthetic latex, synthetic isoprene latex, polybutadiene latex, styrene / butadiene copolymer latex, acrylonitrile / butadiene copolymer latex, styrene / butadiene / vinylpyridine copolymer latex, carboxyl-modified styrene / butadiene latex. Copolymer latex, acrylate latex and the like are applicable, and according to the present invention, these synthetic latexes can be crosslinked.

Further, it may be a mixture of natural rubber latex and synthetic latex depending on the use, or natural rubber latex or synthetic latex previously cross-linked according to the present invention may be mixed with other non-crosslinked rubber latex. It is also possible to mix and apply.

Further, the viscosity of the latex may be such that it can be coated to 1 mm or less by a coating machine, but specifically, a range of 10 to 1000 cps (room temperature) is preferable. If it is less than 10 cps, it may be difficult to form a curtain at the time of coating, or the latex may be repelled on the base material. If it exceeds 1000 cps, fluidity may be insufficient and thickness control may be difficult. Because there is. In addition, from the viewpoint of better balance of the coating properties, the viscosity range of 30 to 450 cps (room temperature) is more preferable. The suitable viscosity range may be achieved by a viscosity modifier such as a solvent or a diluent, instead of the latex alone.

Furthermore, it is also suitable to add a predetermined amount of a so-called accelerator to the rubber latex of the present invention. This is because faster crosslinking is possible, the temperature rise is prevented, the required radiation dose is reduced, and as a result, the safety is improved. Examples of the accelerator suitable for the present invention include n-butyl acrylate as described in JP-B-3-36052. Further, the amount of the accelerator added is determined in consideration of the effect and the application,
The range of 1 to 20 parts by weight is suitable for 100 parts by weight of the latex. This is because if it is less than 1 part by weight, the effect of addition is poor, and if it exceeds 20 parts by weight, the latex may coagulate and precipitate.

In addition, in the latex of the present invention,
Depending on the application and purpose of use, phenol-based or phosphate-based antioxidants, ultraviolet absorbers, calcium carbonate, titanium oxide, fillers such as silica powder, conductive particles such as copper and nickel, heat-conductive particles such as alumina. It is also suitable to add a predetermined amount of a colorant, insulating particles, a masking agent, and the like.

(Low Energy Electron Accelerator) The low energy electron accelerator referred to in the present invention has an accelerating voltage of 15
A self-shielding device having a voltage of 0 to 500 kV is suitable, and the beam current does not need to be specified.

If the accelerating voltage is less than 150 kV, most of the radiation energy may be absorbed by the air, and the irradiation energy to the latex may be reduced, and if the accelerating voltage exceeds 500 kV, large-scale shielding may occur. This is because it is necessary and the device price will increase dramatically.

However, as will be described later, a "flow coating" device for rubber latex (hereinafter abbreviated as flow coater)
From the viewpoint of easy installation, a small-sized electron accelerator with a small size is preferable.

The electron beam irradiation of the rubber latex on the surface of the base material is preferably started after the rubber latex layer has passed through the head portion and the thickness of the rubber latex layer has become constant.

The irradiation dose to the rubber latex is the presence or absence of the accelerator, the rubber latex concentration, the irradiation temperature, the accelerating voltage, the beam current, the amount of the rubber latex, the distance from the beam window to the rubber latex, the material and thickness of the lid, Depending on the stirring efficiency, presence or absence of accelerator, type of rubber latex, etc.
It is 500 kGy.

If the irradiation dose is less than 20 kGy, the amount of uncrosslinked rubber latex may increase.
This is because if it exceeds 0 kGy, there is a possibility that crosslinking and an increase in ambient temperature become excessive, safety is lowered, or cost is increased.

Further, the temperature of the rubber latex during irradiation is not particularly limited as long as it is a temperature at which the latex can stably exist, but the higher the temperature is, the shorter the crosslinking time is. A temperature range is preferred.

Therefore, it is preferable to provide a temperature control mechanism to control the surroundings of the coating machine so as to attain such a temperature.

In addition, the irradiation atmosphere is not particularly limited, but in order to discharge the gas generated during irradiation to the outside of the irradiation container or prevent the oxidation of rubber by oxygen, it is not necessary to use nitrogen or the like. It is preferable to continuously introduce a trace amount of active gas.

(Coating machine) The coating machine used in the present invention is
Any material can be used as long as it can uniformly coat the rubber latex continuously on the substrate, for example, a coating head, a low energy electron beam accelerator, a substrate driving unit, a substrate winding unit, and a coating machine for fixing these. It is suitable to be composed of a main body or the like.

Further, the base material to be coated with the rubber latex used in the coating machine is also a rubber latex when the rubber latex such as polyester film, polypropylene film, polyethylene film, silicon film and fluorine film is coated. Any material that has a certain releasability so that it can be easily peeled off after crosslinking without being repelled, is acceptable.

Further, as another mode of the base material, a material such as a belt conveyor which can be rotated and circulated between drive shafts may be used. That is, the belt conveyor is a belt-shaped conveyor,
It is preferable that at least one drive shaft can be rotationally driven and is connected to at least two shafts including the drive shaft, and the drive speed thereof can be adjusted by a drive motor transmission unit or the like. Further, as the material of the belt conveyor and the like, in addition to the above-mentioned base material, stainless steel, silicon rubber, polyurethane, polyamide, etc. are preferable,
Any material can be used as long as it wets the rubber latex well and can easily peel off the rubber latex.

Next, the head portion of the coating machine in the method of the present invention will be described.

The head portion in the method of the present invention is not particularly limited, but flow coating type, knife coating type, roll coating type, gravure coating type and the like are preferable. Of these methods, the flow coating method is most suitable for the method of the present invention. This is because rubber latex having a relatively high viscosity can be applied uniformly and easily.

Here, the flow coat type head will be described in more detail. A thin curtain-shaped (film-shaped) rubber latex having a constant width is constantly made to flow down from above, and the rubber is provided on the surface of a conveyor or the like below it. A device for applying latex.

This is the same principle as a flow coater frequently used in the coating industry such as flat coating, and a commercially available flow coater can be modified and used. In the coating flow coater, the object to be coated is placed on the conveyor belt and the coating material is applied to the object to be coated, but in the method of the present invention, it is possible to directly apply the rubber latex to the substrate such as the conveyor belt. There is a clear difference from the coating flow coater.

That is, the flow coat type apparatus comprises, for example, a rubber latex transfer section, a flow coat head section and the like.

The rubber latex transfer section is for transferring the rubber latex to the flow coat head section, and means conventionally used in the rubber latex industry such as the use of a pump, a gravity falling method by gravity and a pressure feeding method are used. It is available.

When using a pump, it is necessary to select a pump suitable for rubber latex. Specifically, a diaphragm pump, a tube type pump, a centrifugal pump, a snake pump, etc. are suitable.

The flow coat type head is a device for applying rubber latex to the surface of the conveyor. The rubber latex is made into a thin curtain (film) having a constant width so that the rubber latex constantly flows down from above onto the conveyor belt. For example, it has a rectangular shape. Then, the head bottom has a slit composed of two edges and has a so-called die structure, from which rubber latex flows down with a predetermined width.

Further, the distance between the edges is variable, and the amount of rubber latex flowing down can be adjusted by adjusting this distance.

In addition, the head section is provided with a rubber latex storage section, in which a stirrer is used to uniformly stir,
Alternatively, it is also preferable to prevent the pulsating flow and the like from the rubber latex transfer section by natural convection so that the rubber latex can be applied more uniformly.

The thickness of the rubber latex layer applied in these head portions can be adjusted by the rubber latex transfer speed, the head slit width, the belt conveyor speed, and the like.

Since the flow rate of rubber latex transferred and the flow rate from the head slit depend on the viscosity of the rubber latex, a preliminary test should be carried out in advance to determine the viscosity conditions so that an appropriate thickness can be obtained. Is essential.

Next, other mechanical devices of the coating machine which can be used in the method of the present invention will be described.

That is, the coating machine in the method of the present invention is preferably provided with an edge for adjusting the thickness of the rubber latex layer and an edge for peeling off the rubber latex after crosslinking.

The peeling edge is for easily peeling off the rubber latex after irradiation cross-linking by contacting with a base material such as a drive shaft for a belt conveyor or a tension roller. Therefore, it must be at least behind the low energy accelerator in the coater.

The material of the peeling edge is preferably a material that easily peels off the rubber latex, has durability, is easy to mold, and is lightweight. For example, a metal such as stainless steel, aluminum, iron, or polyester. , Polyurethane, epoxy resin, phenol resin and the like are preferable. Further, the shape of the edge is not particularly limited, but a knife shape is preferable from the viewpoints of high peeling effect and easy workability.

In addition, it is preferable to provide a thickness controlling edge between the head portion of the coating machine and the low energy accelerator.

For example, for adjusting the thickness of the rubber latex that has flowed down from the flow coater head to the conveyor belt, it is possible to adjust the thickness of the rubber latex by adjusting the distance between the edge and the conveyor belt. This is because it is suitable. That is, the penetration distance into the rubber latex of a normal low energy electron accelerator is 1 mm.
The adjustment of the distance between this edge and the conveyor belt requires precision because it is below.

Therefore, in order to prevent or reduce uncrosslinked rubber latex as much as possible, such a thickness controlling edge allows at least one rubber latex to be obtained.
It is preferable that the thickness is less than or equal to mm.

The shape of the thickness controlling edge is not particularly limited as long as it has a thickness controlling function. For example, a roll shape such as a silicon roll may be used.
A knife-shaped blade made of aluminum or the like is also suitable. At that time, it is expected that the crosslinking efficiency will change due to the deterioration of the electron beam accelerator, etc., so that a micrometer, a pressure adjusting mechanism for adjusting the roll pressure, etc. should be provided so that the desired rubber latex thickness can be obtained accordingly. It is suitable.

Further, since the energy of the electron beam applied to the rubber latex may heat the base material such as the belt conveyor, a cooling device such as an aluminum block which is water-cooled is installed below the base material such as the belt conveyor. Is preferred.

Further, when a flat portion is provided at the contact portion of the belt conveyor or the like and a generally rectangular cooling device is used, the cooling function is exerted, and also the horizontal function of the belt conveyor is maintained, and rubber latex is It is also an effective and appropriate means for uniformly coating the substrate.

[0052]

EXAMPLE A rubber latex container was filled with 20 liters of high ammonia natural rubber latex (produced by Malaysia, rubber solid content 60.1%).

This rubber latex was transferred to the head portion of a pump equipped with a flow meter at a flow rate of 5.4 l / hour.

Next, tap water is passed through the cooling device,
The head slit width, the thickness controlling edge, and the belt conveyor speed were adjusted by a drive motor irregular unit so that the conveyor belt speed was 1 m / min and the rubber latex thickness was 0.6 mm.

The low energy electron accelerator used for irradiation is CB250 / 15/18 manufactured by Iwasaki Electric Co., Ltd.
The maximum acceleration voltage is 250 kV, the effective electron beam irradiation width is 15 cm, and the maximum beam current is 10 mA.

In this example, the acceleration voltage was 250 kV and the beam current was 5 mA. Then, the rubber latex after irradiation was peeled off at the edge of and was introduced into 10 irradiated rubber latex receiving containers. At that time, it took 3 hours and 45 minutes to irradiate 20 l of rubber latex.

Further, about 0.2 l of the irradiated rubber latex was sampled at intervals of 15 minutes during irradiation, and the appearance of the latex was observed. That is, a part of the irradiated rubber latex was cast on a horizontal glass plate, dried at room temperature until it became transparent, and then peeled off from the glass plate to obtain a film having a thickness of 0.45 mm. This was immersed in 1% ammonia water for a whole day and night to remove non-rubber components, and then dried at 80 ° C. for 1 hour. The physical properties of the rubber film were measured according to the method of JIS K-6301. The results are shown in the table below.

[0058]

[Table 1] As is clear from the results in the table, it was found that the present invention enables irradiation for a long time and provides a crosslinked rubber latex by radiation having sufficient physical properties.

[0059]

As described above, according to the present invention,
By a coating method such as a flow coater type, after being applied to a belt conveyor that circulates and circulates to a certain thickness, rubber latex is irradiated with an electron beam using a low energy electron accelerator,
It has become possible to obtain a crosslinked rubber latex continuously and economically.

Further, the rubber latex can be economically recovered, the low energy electron accelerator is effectively used, and the safety is improved.

Furthermore, the colloidal properties of the inexpensive crosslinked latex obtained by the present invention are the same as before irradiation,
Various compounding techniques that are commonly used in the technical field can be applied, various rubber products can be produced by dipping and other methods, and it is expected that the applications of the rubber products will dramatically expand.

[Brief description of drawings]

FIG. 1 is an outline of a rubber latex electron beam cross-linking apparatus using a flow coater method used in Examples of the present invention.

[Explanation of code] Low energy electron accelerator Flow coater type head Thickness control edge Belt conveyor Cooling device Crosslinked rubber latex stripping edge Belt conveyor drive motor Rubber latex container Pump with flow meter 10 Crosslinked rubber latex container 11 Cooling water inlet 12 Cooling water outlet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B29C 41/46 7310-4F B29C 41/46 // B29K 21:00 105: 24 B29L 9:00 ( 72) Inventor Shinji Oyama, 1-1 Irisatoyama-cho, Gyoda-shi, Saitama Iwasaki Electric Co., Ltd. Saitama Factory (72) Inventor Oizumi, 1-1, Iriyama-cho, Gyoda-shi, Saitama Prefecture Iwasaki Electric Co., Ltd. Saitama Factory

Claims (8)

[Claims] 1. A rubber latex is applied to a base material to a constant thickness by using an applicator for uniformly applying the applied material onto the base material, and then an electron beam is irradiated using a low energy electron accelerator. The rubber latex is crosslinked by the above-mentioned method. 2. The electron beam cross-linking of the rubber latex according to claim 1, wherein the rubber latex is at least one selected from the group consisting of natural rubber latex, synthetic rubber latex, and a mixture thereof. Method. 3. The accelerating voltage of the low energy electron accelerator is 150 to 500 kV.
Alternatively, the method of crosslinking the rubber latex according to item 2 with an electron beam. 4. The irradiation dose of the electron beam is 20 to 500 k.
Gy is any one of Claims 1-3 characterized by the above-mentioned.
The method for electron beam crosslinking of rubber latex according to item. 5. The coating machine is a system in which the rubber latex is dropped from a head portion and coated on a substrate, and the coating machine is used.
5. An electron beam crosslinking method for rubber latex according to any one of items 1 to 4. 6. The substrate of the coating machine is a belt conveyor that rotates and circulates, and the rubber latex is directly coated on the belt conveyor.
6. The electron beam crosslinking method for rubber latex according to any one of 5 above. 7. The stripping device for collecting the rubber latex after cross-linking is provided in the coating machine, and a step of collecting the rubber latex after cross-linking by the device is included. 7. An electron beam crosslinking method for rubber latex according to any one of 6 above. 8. The coating machine is provided with a cooling device for preventing heat generation of the coating machine by the electron beam, and a step of cooling the base material is included.
7. The electron beam crosslinking method for rubber latex according to any one of items 1 to 7.