JP3273548B2 - Corona discharge treatment method for olefin polymer sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for corona discharge treatment of an olefin polymer sheet, and more particularly, to an improved method for corona discharge treatment of an olefin polymer sheet for eliminating generation of offensive odor.

[0002]

2. Description of the Related Art Generally, in an olefin-based polymer sheet which lacks surface adhesion to an adherend, various means have been known for improving the surface adhesion, and are also in practical use. One of the means is a corona discharge treatment method. Regarding the surface treatment of the olefin-based polymer sheet by corona discharge, it is needless to say that it is extremely important to develop the maximum effect in a short time as possible.

[0003] Various methods have heretofore been taken as specific methods for achieving the maximum surface treatment effect in a short time by corona discharge and increasing the productivity. For example, it simply involves shortening the distance between the electrode of corona discharge and the object to be processed, changing the shape of the electrode, increasing the number of installations, and the like, and achieving the purpose accordingly. I have. On the other hand, the effective output (effective output is hereinafter abbreviated as We) applied to the electrode itself is sometimes made larger than in the past, and this is also used as a more effective method. For this output, in the corona discharge performed by AC,
It is obtained by the product of a peak current (hereinafter, abbreviated as Ap) and a peak voltage (hereinafter, abbreviated as Vp). Generally, a method for improving the surface treatment effect by corona discharge and further improving the productivity. as,
By increasing this Ap, a higher output is obtained,
This is applied to the electrode, and the surface of the olefin-based polymer sheet is treated by corona discharge.

[0004] For example, when a polypropylene film is subjected to a corona discharge treatment at a running speed of 70 m / min, generally A
In the case where the output is performed under the output of about 2.1 Ap and about 11 kVp, if the speed is increased by 1.5 times, a high current and high output by about 4.9 Ap of Ap and about 11.5 kVp of Vp A lower corona discharge was required. However, the higher the current and the higher the output, the more the odor begins to develop and the odor of the polypropylene film begins to increase, and even if it changes over time, it does not disappear at all and remains in a state where it adheres for a long time Problem. The stench is an important issue that must be avoided regardless of the type and extent of the stench.

[0005] Regarding the cause of the offensive odor due to the corona discharge treatment under high current and high output, various additives (for example, antistatic agent, nucleating agent, ultraviolet ray inhibitor, antioxidant, etc.) generally added to polypropylene are used. Since it was considered to be due to decomposition, the presence or absence of additives and the state of generation of offensive odors were checked, including other olefin-based polymer sheets. As a result, although there was a slight difference in the generation of offensive odor depending on the presence or absence of the additive, it was found that the odor was due to the olefin-based polymer sheet itself. This is thought to be due to the thermal decomposition of the resin precursor (a low molecular weight substance such as a monomer or an oligomer) in the olefin-based polymer sheet or other compounds by-produced during the polymerization, but it is not clear.

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to the odor which is the biggest problem in the corona discharge treatment of an olefin-based polymer sheet under the above-mentioned conventional conditions. Various investigations have been made on a means for producing a reforming effect and preventing generation of a bad smell.

[0007]

That is, the present invention provides a corona discharge by placing an olefin-based polymer sheet under an electrode applied with a smaller peak current and a smaller effective output due to a larger peak voltage. Is achieved by Specifically, a peak current of 0.1 to 3 Ap and 12
Effective output by peak voltage of ~ 30kVp is 0.6 ~ 4
This is achieved by performing corona discharge at a processing intensity of 5 kW and 5 to 40 W · min / m ² . Hereinafter, the present means will be described in more detail with examples.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an object to be processed is a thermoplastic resin continuous sheet molded article which is often used by winding a sheet into a roll. This is because, after the corona discharge treatment, the product is immediately wound into a roll and shipped, so that even if it is left for a long time, even a slight odor is not emitted and is kept forever. Therefore, this continuous sheet of the thermoplastic resin is a preferable object for the present invention.

Further, among the above continuous sheets of thermoplastic resin, a sheet made of an olefin polymer is more effective. This is because when the olefin polymer is used, the effect of preventing the generation of offensive odor is greater than that of other synthetic resin sheet materials, and the effect of surface treatment is also greater.

The sheet-like material is not limited to a single layer structure, but may be a laminate of the same type or different types.

The olefin-based polymer is specifically a polymer obtained by homopolymerization of α-olefins such as ethylene, propylene and butene-1 alone or by copolymerization of the monomers, and the olefin monomer and acetic acid. It is a polymer obtained by copolymerization with vinyl monomers such as vinyl and acrylic monomers.

Further, as is clear from the above, first, even if various additives are added to the olefin-based polymer sheet, the achievement of the means of the present invention is not hindered.
Conversely, depending on the type of the additive, an effect of suppressing the concurrent occurrence of offensive odor is also expected.

Since the olefin-based polymer sheet itself tends to be charged with static electricity, among the additives,
Generally added are antistatic agents (four types of nonionic, cationic, anionic and amphoteric).
Depending on the type of the synthetic resin, the type of the inhibitor to be added is determined. In the case of a molded article made of an olefin polymer, a nonionic type (eg, a hydroxy fatty acid ester, an aliphatic hydroxyamine compound, etc.) is added. Is done.

Next, when the olefin-based polymer sheet is subjected to corona discharge treatment, a smaller peak current (Ap) and a smaller effective voltage due to a larger peak voltage (Vp), which are conditions for application to the electrode. The application of the output (We) to the electrodes will be described.

First, in Ap, Vp and We, the meaning of smaller or larger means that the Ap value, Vp value, We, which are generally adopted and used in the corona discharge treatment of an olefin-based polymer sheet. It means smaller or larger than the value.

For example, Ap, Vp and We when a corona discharge treatment is continuously performed on a polypropylene film having a roll width of 4 to 5 m, which has been conventionally adopted and implemented, are as follows when the running speed is 70 m / min. As shown in FIG.
1 Ap, Vp about 11 kVp, We about 11.6 kW. This condition is about 38 (W · min /
m ² ), the surface of the film is constantly irradiated with corona discharge, so that a desired surface treatment effect (wetting property) is obtained, but a problematic odor is generated. Therefore, in the present invention, the value of Ap, Vp, and We is smaller than the value of Ap, and the value of Vp
In this case, the value of We is made larger and the We obtained by the product of the two is a value smaller than the conventional We.

The actually applied smaller effective output We is obtained by multiplying the effective current obtained by dividing the smaller peak current Ap by √2 and the effective voltage obtained by similarly dividing the larger peak voltage Vp by √2. It is obtained. This means that since the corona discharge process is performed by alternating current, the discharge is performed with a sinusoidal waveform, so that the output that is actually effectively applied is not 100%, but one half of the product of Ap and Vp. become.

The smaller We due to the smaller Ap and the larger Vp means that in the olefin-based polymer:
When the peak current Ap is 0.1 to 3 Ap and the peak voltage Vp is 1
2 to 30 kVp, so the effective output We is 0.6 to 45 k
W, and the processing strength received by the sheet at that time is 5 to 40 (W · min / m ² ), more preferably 1 to 40 (W · min / m ² ).
It is preferable to set it to 0 to 25 (W · min / m ² ).
Here, the treatment strength is also added under the condition that the continuous sheet-like material is subjected to continuous corona discharge treatment while running, and the surface treatment effect on the production speed (desired wetting and bad odor are not generated). This is because there is a desirable range from the relationship. That is, the processing intensity is equal to the effective output (W
e) is divided by the product of the surface treatment speed (running speed) and the corona discharge width (generally equal to the length of the electrode). Since the present invention is effectively implemented within the range of the limitation, there is a preferable range of the treatment intensity.

The means for obtaining a smaller Ap and a larger Vp for the smaller We setting is not particularly limited. For example, a plurality of high-voltage generating transformers are connected in series, and an AC voltage power supply is gradually increased to a predetermined voltage, or an AC voltage power supply is first input to a control panel having a wiring mechanism capable of varying a current voltage. Here, the current is decreased, the voltage is increased to some extent, the voltage is further sent to a high-voltage generating transformer, the voltage is increased to a predetermined voltage, and the voltage is applied to the electrodes.

The shape and size of the electrode to which the effective output We is applied may be determined according to the size of a portion requiring surface treatment. These are provided with an appropriate gap in opposition to the counter electrode, but it is desirable to adjust the tip of the opposing electrode to an appropriate thickness so that corona discharge can be effectively performed. In the case of an olefin-based polymer continuous sheet, use a plate-like electrode that is generally the same length as the sheet width and a slightly thinner tip, and use a rotating roll with a thin insulating layer provided on the surface of a metal roll as the counter electrode. It is desirable to use.

In the case of the above-mentioned sheet-like material, the plate-like electrode may have a single pole, but may have two or more poles depending on the sheet width, and may be provided with a plurality of branches (polarization). It is also a target. This is because, as the length of the electrode becomes longer, there is a limit in obtaining a lower current value set, and it becomes more difficult to achieve the current value. In addition, for obtaining the same surface treatment effect, it is possible to reduce the effective output applied to the electrode by polarizing the electrode when the polarization is performed. In other words, how to use in polarization
The effects of the present invention are more easily exhibited, and the power consumption is reduced.

In the above-mentioned polarization method, for example, in the case of a single plate-shaped electrode, the electrode may be divided into two or three, and wired and connected to an effective output source applied in parallel. . The atmosphere in which the corona discharge is performed is generally in the air, but is not limited to this.

Although it is not clear what mechanism the effect of the present invention exerts,
The present inventors speculate as follows. First, with regard to the offensive odor, since the peak current was suppressed to a low level, the heat generated during corona discharge was also small, and as a result, the odor-causing substances present on the surface of the continuous sheet of olefin-based polymer due to decomposition were not subjected to thermal decomposition Think of things. And, regarding the surface treatment effect, in general, in corona discharge in air, it is considered that it is mainly due to active oxygen atoms. It is considered that more is generated. This means that the amount of by-product ozone is expected to be smaller than before.

[0024]

EXAMPLES Hereafter, the present invention will be described in more detail with reference to examples together with comparative examples. In the text, the surface treatment effect is represented by a wetting index (dyne / cm) in this example, and the larger the effect is, the greater the effect is and the stronger the surface adhesive force is. And the measuring method was measured according to JIS K6768-1977.

In addition, the evaluation of the degree of offensive odor was made by two men and women,
A total of four judge members were designated, and the results of the evaluation were evaluated based on the following five-stage evaluations. In addition, the sensory check of each person,
The rolled film that has been subjected to corona discharge treatment and wound up is overlaid in the MD direction (longitudinal) in multiple layers, cut quickly, and the cut surface is sequentially smelled by four judges, and each is scored. Was repeated three times and averaged. (1): The odor is extremely strong and unbearable. (2): It has a strong odor and cannot be tolerated by some people. (3): Stinks are felt. (4): It smells faint, but does not feel bad. (5): No odor.

Example 1 Using a roll-shaped polypropylene film having a width of 4.5 m and a thickness of 40 μm, a corona discharge was carried out while running under the electrode under the following conditions, and the film was wound up by 2,000 m. A. (Effective output) Applied electrode: Two plate-like electrodes each having a thickness of 4 mm and a length of 2.2 m are provided side by side in parallel with each other, and this is used as a counter electrode (length of 4 provided with an insulating layer). 6 m metal rotating roll) with a gap of about 5 mm. In addition, the corona discharge length was set to 4.4 m of the entire length of the electrode. B. B. Corona discharge processing speed (running speed): 70 m / min and 100 m / min Conditions for application to the two electrodes: When running speed is 70 m / min: Ap = 0.6 Ap,
Vp = 14 kVp, We = 4.2 kW ・ In the case of a running speed of 100 m / min: Ap = 0.6 A
p, Vp = 17.5 kVp, We = 5.3 kW Processing strength: 7 obtained by the following equation 1
In the case of 0 m / min, it is 14 (W · min / m ² ), and in the case of 100 m / min, it is 12 (W · min / m ² ).

[0027]

(Equation 1)

With respect to the polypropylene film subjected to the corona discharge treatment, the wetting index and the offensive odor were evaluated and are summarized in Table 1. The wetting index was measured at each of the first, middle, and rear portions of the film, and measured to obtain an average value. The wettability index of the polypropylene film before this treatment was 2
8 dynes / cm, no odor, and the degree was 5.

(Comparative Example 1) A continuous corona discharge treatment was performed on a polypropylene film under the same conditions as in Example 1 except that the application conditions to the electrodes were changed as follows. The results are summarized in Table 1. -When the traveling speed is 70 m / min: Ap = 2.1 Ap,
Vp = 11 kVp, We = 11.6 kW-When the running speed is 100 m / min-Ap = 4.7 Ap,
Vp = 11 kVp, We = 25.9 kW The processing intensity is 38 (W · min / m ² ) at a running speed of 70 m / min, and 59 (W · min / m ² ) at a running speed of 100 m / min.
m ² ).

[0030]

[0031]

Since the present invention is configured as described above,
The following effects are obtained.

In the corona discharge treatment, which is performed as one method for the surface modification (adhesion) of the olefin-based polymer sheet, the electric conditions in the discharge are determined by the high current and high current conventionally performed. It can be performed under low current and low output conditions with respect to output conditions. This is also advantageous in terms of power consumption

Even when corona discharge is performed under low current and low output conditions, the surface modification effect is not only the same as that of the conventional one, but also the generation of offensive odor which is extremely problematic can be eliminated.

With respect to the processing strength, the effect according to the present invention can be exhibited in less than half of the conventional strength under the general conditions. Therefore, the same strength as the conventional one is set. When performing corona discharge treatment, 2
Since the surface treatment speed (running speed) can be doubled or more, it is advantageous in terms of productivity.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ikuyuki Sakumura 163 Morikawaramachi, Moriyama-shi, Shiga Gunze Co., Ltd. Examiner, Plastics Division, Satoshi Morikawa (56) References JP-A-7-204263 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08J 7/00 303

Claims (2)

(57) [Claims] A peak current of 0.1 to 3 Ap and 12 to 30 Ap
Effective output by peak voltage of kVp is 0.6 to 45 kW
And performing a corona discharge at a processing intensity of ⁵ to 40 W · min / m ² , wherein the corona discharge is applied to an olefin-based polymer sheet. 2. The method according to claim 1, wherein the electrode is polarized into a plurality of pieces.