JPH07165934A - Photo-crosslinking of polyethylene product by excimer laser - Google Patents

Abstract

PURPOSE:To perform the photo-crosslinking of a PE article useful as a heat- insulation material for roof, etc., in a short time and high efficiency at a low cost by irradiating a sheet or foamed PE article containing a benzophenone-type photo-initiator at a specific concentration with excimer laser beam. CONSTITUTION:This photo-crosslinking process is carried out by incorporating a PE raw material with preferably 0.01-1wt.% of a benzophenone-type compound such as benzophenone of formula I or 4-chlorobenzophenone of formula II as a photo-initiator, forming a sheet-formed or foamed PE article with an extruder and irradiating the PE article with excimer laser beam. The depth of the crosslinking reaction relative to the thickness of the PE article is arbitrarily adjustable by adjusting the concentration of the photo-initiator to enable the formation of PE article meeting the purpose.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to photocrosslinking of polyethylene products by an excimer laser, which makes it possible to inexpensively crosslink sheet-like or foam-like polyethylene products.

[0002]

2. Description of the Related Art Conventionally, electron beam irradiation has been known to improve the thermal and mechanical strength of sheet-shaped or foamed polyethylene products used for roof insulation of buildings, linings of automobiles and bath mats. However, in such means, electrons are accelerated in a high-vacuum accelerating tube at several hundred KV or more to irradiate a polyethylene product, and therefore, it is a small device with an output of about 800 KW. Is very expensive and requires a shield room in addition to the irradiation device, which has a drawback of high equipment cost.

Further, the cross-linking with a xenon lamp or a mercury lamp has a drawback that irradiation requires a long time because the light intensity is too weak.

[0004]

DISCLOSURE OF THE INVENTION The present invention efficiently causes a crosslinking reaction in a short time, reduces the manufacturing cost, and adjusts the concentration of the photoinitiator, and the depth of the crosslinking reaction with respect to the thickness of the polyethylene product. It is intended to provide photocrosslinking of a polyethylene product by an excimer laser, which can be arbitrarily adjusted to easily produce a polyethylene product according to various purposes of use.

[0005]

In view of the problems of equipment cost, irradiation time and the like based on the above conventional technique, the present invention uses a benzophenone photoinitiator such as benzophenone, 4-chlorobenzophenone and the like in a concentration of 0.01% by weight. Excimer laser that makes it possible to change the cross-linking ratio inside the polyethylene product by appropriately selecting the concentration while irradiating the polyethylene product manufactured by adding ~ 1 wt% with the excimer laser. The above-mentioned drawbacks are not solved by providing photo-crosslinking of polyethylene products according to.

[0006]

EXAMPLE An example of the present invention will be described below with reference to the drawings. A benzophenone system such as benzophenone or 4-chlorobenzophenone, which is a photoinitiator, is added to a polyethylene raw material at a predetermined concentration, and as shown in FIG. The sheet-shaped or foamed polyethylene product W is manufactured by the simple extruder 1.

The extruder 1 is provided with a screw 4 connected to a motor 3 in a cylindrical casing 2, a nozzle 5 having a rectangular cross section at the tip and a raw material inlet 6 at the base.

The chemical structural formulas of benzophenone and 4-chlorobenzophenone are shown in the following chemical formulas 1 and 2, respectively.

[0009]

[Chemical 1]

[0010]

[Chemical 2]

Then, the polyethylene product W is attached to the sample holder 8 mounted on the column 7 so as to be vertically movable, and the excimer laser oscillator 9 irradiates the polyethylene product W with an excimer laser to perform photocrosslinking.

The excimer laser has a wavelength of 249n.
KrF of m, XeF of wavelength 350, X of wavelength 308 nm
Excimer laser such as eCl and ArF with a wavelength of 193 nm is performed in the atmosphere at room temperature, usually around 20 ° C., and the pulse laser output is fixed at 300 mJ / pulse and the repetition frequency is 15 Hz, and the beam cross section at the laser irradiation port is fixed. The irradiation intensity on the surface of the polyethylene product W was 150 J / cm ^2, and the total irradiation amount on the front and back surfaces of the polyethylene product W was 450 J / g.

Further, the excimer laser emits a single pulse of ultraviolet light every about 50 nm by a combination of a rare gas and a halogen gas, and its output is, for example, Kr having a wavelength of 249 nm.
In F, the energy per pulse is 300 mJ / 10
ns, which is 30 megawatts when converted to energy per unit time.

Next, the amount of cross-linking of the polyethylene product W is measured by the Melt Flow Rete method (hereinafter abbreviated as "MFR method") specified in JIS, and the MFR method is as shown in FIG. The polyethylene product W contained in the cylindrical member 10 is applied with a constant pressure by the weight 11 and heated to a melting temperature of 190 degrees to be melted and dropped from the cylindrical member 10. A negative logarithmic ratio (hereinafter, abbreviated as "ΔMFR") of the dropping amount of the polyethylene product W irradiated with the excimer laser with respect to the dropping amount of the polyethylene product W not irradiated with is obtained as the crosslinking amount.

As shown in FIG. 4, the ΔMFR is linear with respect to other measuring methods such as the gel fraction method in the range of 1 ≦ −log (ΔMFR) ≦ 3 where the gel fraction is 35% or less. Have a relationship.

In the gel fraction method, as shown in FIG. 5, an excimer laser-irradiated polyethylene product W is finely cut and housed in a cylindrical filter 12 made of glass fiber and set in a Soxhlet extractor 13. Then, perform it in boiling xylene for about 20 hours in nitrogen gas so as not to oxidize it, and after extraction, wash the cylindrical filter 12 with acetone and vacuum dry at room temperature for about 7 hours. The precise amount of the network-like crosslinked polymer generated by the measurement is measured as the gel amount of the insoluble polymer.

The above two measuring methods can be appropriately selected.

Experimental Example 1 0.01% by weight of benzophenone was added to a polyethylene raw material as 0.01% by weight.
A plurality of sheet-shaped polyethylene products W having a thickness of 0.3 mm to 2.4 mm are manufactured by the extruder 1 after adding them so as to have a concentration of 1% by weight and 1% by weight. The excimer laser was irradiated at a total dose of 450 J / g for both sides of the polyethylene product W combined.

When the cross-linking was measured by the MFR method, the results shown in FIG. 6 were obtained. From these results, when the concentration of the benzophenone as the photoinitiator was 1% by weight, the cross-linking was carried out only near the surface of the polyethylene product W. It was confirmed that the crosslinking reaction occurred uniformly in the entire area of the polyethylene product W when it occurred or when the concentration was reduced to 0.01% by weight.

When the concentration is 0.1% by weight, the crosslinking reaction most effectively occurs up to a depth of about 1 mm from the surface,
At this concentration, the value of -log (ΔMFR) decreases proportionally with the thickness of polyethylene product W, that is, polyethylene product W
The light intensity within decays exponentially with thickness.

Experimental Example 2 Benzophenone and 4-chlorobenzophenone were added to a polyethylene raw material so as to have concentrations of 0.01% by weight, 0.1% by weight and 1% by weight, respectively. .2
mm to produce a plurality of sheet-shaped polyethylene products W,
The polyethylene product W was irradiated with a KrF excimer laser at a total irradiation amount of 450 J / g in total on both sides of the polyethylene product W.

When cross-linking was measured by the MFR method, the results shown in FIG. 7 were obtained. From these results, it was found that 0.1 wt% was more effective than any other photoinitiator than the other two. Was found to be

That is, when the photoinitiator is 0.1% by weight, the KrF excimer laser is effectively used for crosslinking within a depth of 0.6 mm from the surface, and when the concentration is low, the KrF excimer laser is less crosslinked. It reaches the deep region without being used for the reaction, but conversely, when the concentration becomes 1% by weight or more, most of the light is used for crosslinking only near the surface, and in both cases the average amount of crosslinking is 0. It becomes smaller than that of 0.1% by weight.

Experimental Example 3 Benzophenone was added to a polyethylene raw material so as to have a concentration of 0.1% by weight, and the thickness was 1.2 mm by an extruder 1.
A plurality of sheet-shaped polyethylene products W are manufactured, and the KrF excimer laser, Ar
F excimer laser, XeF excimer laser and X
The eCl excimer laser was irradiated at a total dose of 450 J / g for both sides of the polyethylene product W combined.

The cross-linking was measured by the MFR method, and the results shown in FIG. 8 were obtained.
The excimer laser was found to be the most effective,
Some effects were observed with other excimer lasers.

In order to cause the cross-linking reaction of polyethylene, it is necessary to first break the CH bond, as shown in Chemical formula 3 in the chemical reaction formula below, and then the bond dissociation of the CH bond molecule. Energy is about 100 kcal / mol, ie about
The photon energy of ArF excimer laser is about 6.4 eV, that of KrF excimer laser is about 5.0 eV, and that of XeCl excimer laser is about 4.0 eV.
That of 0eV and XeF excimer laser is about 3.4e
Since it is V, in principle, a KrF excimer laser and A
Only the rF excimer laser directly cuts the CH bond,
In other words, it can be used for crosslinking.

[0027]

[Chemical 3]

[0028]

[Chemical 4]

However, as shown in FIG. 9, benzophenone was added so as to have a concentration of 0.1% by weight and the spectrum of the polyethylene product W having a thickness of 0.3 mm was measured by the extruder 1. Has an absorption spectrum of 250n
Although a strong absorption band is shown in the vicinity of m, there is no strong absorption band in the vicinity of the wavelength of the ArF excimer laser, and the above result is obtained.

From this result and the following chemical reaction formulas (5), (6) and (7), it is understood that benzophenone excited by absorbing light starts a crosslinking reaction while acting as a photoinitiator.

[0031]

[Chemical 5]

[0032]

[Chemical 6]

[0033]

[Chemical 7]

Further, the chemical structure of 4-chlorobenzophenone is very similar to that of benzophenone and the ultraviolet absorption spectrum is almost the same, and 4-chlorobenzophenone acts similarly in photocrosslinking.

[0035]

In summary, the present invention adds a benzophenone-based photoinitiator such as benzophenone and 4-chlorobenzophenone to a polyethylene raw material at a predetermined concentration to form a polyethylene product in a sheet or foam form by an extruder. Since the polyethylene product was irradiated with an excimer laser, a gel fraction of 30% to 35% was obtained as the cross-linking rate, and it could be 50% in the layer 0.3 mm from the surface. If the deformation temperature is up to about 80 ° C, a sufficient cross-linking ratio required for it can be obtained, and by irradiating an excimer laser having a wavelength close to the absorption band of the photoinitiator in the atmosphere at room temperature, a conventional xenon lamp can be obtained. As compared with the cross-linking with a mercury lamp, the cross-linking reaction can occur efficiently in a short time,
The manufacturing cost can be reduced compared to the electron beam irradiation method,
Further, by adjusting the concentration of the photoinitiator, the depth of the crosslinking reaction with respect to the thickness of the polyethylene raw material can be arbitrarily adjusted.

When the concentration of the photoinitiator is 0.01% by weight, a substantially uniform crosslinking rate can be obtained regardless of the thickness of the polyethylene product, and when the concentration is 0.1% by weight, the polyethylene is It can be exponentially attenuated from the surface to the inside of the product, and when the concentration is 1% by weight, the crosslinking reaction can be obtained only in the layer within 0.3 mm from the surface of the polyethylene product, resulting in the use of the polyethylene product. The concentration of the photoinitiator can be appropriately selected according to the purpose, and if it is desired to obtain a high crosslinking rate only in the thin layer on the surface of the polyethylene product, 0.1 wt%
If you want to obtain a high concentration of 1% by weight and a uniform cross-linking rate in the entire area of a certain depth, select a low concentration of 0.01% by weight, and in the former case, for the lining of buildings and automobiles, The latter is the most suitable for bath mats, and its practical effects are enormous.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an extruder.

FIG. 2 is a diagram showing an irradiation device of an excimer laser.

FIG. 3 is a diagram showing a measuring instrument of the MFR method.

FIG. 4 is a graph showing the relationship between the MFR method and the gel fraction method.

FIG. 5 is a view showing a measuring instrument of the gel fraction method.

FIG. 6 is a graph showing the relationship between polyethylene product thickness and MFR ratio.

FIG. 7 is a graph showing the effect relationship of the concentration of benzophenone and 4-chlorobenzophenone on the MFR ratio.

FIG. 8: Excimer laser light wavelength and −log (ΔMF
It is a graph which shows the relationship with R).

FIG. 9: Benzophenone, 0.1% by weight of benzophenone
Added 0.3 mm thick polyethylene product and thickness of 0.3 mm.
It is an ultraviolet absorption spectrum of a 3 mm pure polyethylene product.

[Explanation of symbols]

 1 Extruder W Polyethylene products

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kiyoaki Sakai 3-17-14 Ninomiya, Fukui City, Fukui Prefecture

Claims (2)

[Claims] 1. A polyethylene raw material is benzophenone, 4
-A benzophenone-based photoinitiator such as chlorobenzophenone was added at a predetermined concentration to form a sheet-shaped or foamed polyethylene product by an extruder, and the polyethylene product was irradiated with an excimer laser. Photocrosslinking of polyethylene products. 2. The photo-crosslinking of a polyethylene product with an excimer laser according to claim 1, wherein the concentration of the photoinitiator is 0.01% by weight to 1% by weight.