JPS5927782B2 - surface protection film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface protection film, and more particularly to a pressure-sensitive adhesive surface protection film for resin plates, painted resin plates, vinyl chloride plywood, vinyl chloride steel plates, copper plates, aluminum nameplates, etc.

Conventionally, a surface protection film coated with an adhesive mainly composed of polyisobutylene rubber has been used.

Since polyisobutylene rubber is non-polar and chemically inert, it is difficult to contaminate the surface of the board to be protected, but on the other hand, it has the disadvantage that it is difficult to adhere to the base plastic film. Conventionally, a blend of polyethylene and polypropylene has been used as this base film. For example, in JP-A-50-14667, the polyethylene/polypropylene ratio is 85-25/15-75;
0-52141 proposes 70-30/30-70, respectively. These protective films have the following drawbacks. 1. Poor cold resistance and easy to tear.

Therefore, especially in the winter, when the film is unrolled or peeled off from the surface of the board, slight defects on the film can cause it to tear, resulting in work being interrupted. 2. If you punch out a resin board or aluminum nameplate with the protective film still attached, the board will be completely punched out, but the film will not be completely punched out and will remain in the form of whiskers perpendicular to the cutting line, which is inconvenient for later processing. be.

Also, when cutting with a circular saw or drilling holes with a drill, the film near the cut surface lifts up, and chips enter the gap and stain the board. If the adhesive strength is made extremely strong, lifting can be prevented, but it becomes almost impossible to remove the protective film when it is not needed. 3. Unwinding resistance when unwinding from the wound state is large.

Furthermore, the surface of the film is highly uneven, and the adhesive digs into the recesses on the back surface over time when the film is stored in the wound state, further increasing the unwinding resistance. At the same time, since the unevenness is transferred to the adhesive surface, the adhesive force immediately after lamination (initial adhesive force) becomes lower than the set value. In order to compensate for this, the initial value must be set high in advance, which requires wasteful efforts such as making the adhesive thicker than necessary or setting a strong adhesive composition. This causes the disadvantage that the increase in adhesive strength over time is further accelerated. 4. Since the transparency is very poor, it is difficult to inspect the board while it is still bonded.

5. The adhesive strength between the adhesive, which is mainly composed of polyisobutylene rubber, and the base film is absolutely insufficient, and when it is removed from the board, the adhesive is relatively easily left on the board.

The advantage of polyisobutylene rubber, which is that it does not easily contaminate the board, is not fully utilized. Therefore, the present inventors have developed a film that is resistant to tearing in cold weather, has excellent punching properties, does not cause the cut end to float, has no unevenness on the back surface, is moderately transparent, and has a strong base material and adhesive. The present invention was arrived at as a result of various studies with the aim of providing a surface protection film that adheres closely to the surface at a low cost.

The surface protection film of the present invention is made of 60 to 95% polyethylene.
and 40 to 5% of polypropylene, and on the mixture layer of the coextruded film, the other layer is polyethylene. It is made by applying an adhesive mainly composed of polyisobutylene rubber via an undercoat.

To explain the present invention in more detail, first, the polyethylene used alone on the back side of the mixture layer is important because it directly affects the cold tearability, punchability, and floatability.

Melt index (which is commonly used for conventional films)
Below M. I. ) is less than 2, the punchability and floating properties are poor and M. I. is preferably 2 or more.
By using polyethylene alone on the back surface, the back surface is essentially flat and has no irregularities. Furthermore, it has a poorer affinity for polyisobutylene rubber than a polyethylene/polypropylene mixture surface, and its unwinding resistance is originally low. Also, when particularly required, a mold release agent is applied, and the corona treatment applied in advance at this time works more effectively than on a polyethylene/polypropylene blend surface, resulting in excellent adhesion of the mold release agent. Therefore, the unwinding resistance is even smaller, and there is less tendency for the release agent to fall off and transfer to the adhesive surface, so there is no decrease in the initial adhesive strength. As the mold release agent, a known mold release agent such as a modified acrylic mold release agent such as Nontak 501 (manufactured by Ipposha Yushi Kogyo Co., Ltd.) can be used. There is no particular limitation on the polyethylene used in the mixture layer containing polyethylene and polypropylene, which is then mixed with polypropylene.

The same or different grade of polyethylene for the back side can be used. Polypropylene is used, but homopolymers, copolymers, blends, etc. can be used. The mixing ratio of polyethylene and polypropylene in this mixture layer is important in two ways.

The first requirement is that the bonding strength between the two layers with the back polyethylene layer is sufficient, and the second requirement is that the adhesion with the adhesive is sufficient. As will be explained in detail in Examples, for the first one, 60% or more of polyethylene is required;
In particular, it is desirable that it be 70% or more. If the polyethylene content is below 60%, delamination may occur in some cases when the protective film is removed from the board, and the mixture layer may remain in spots on the board. This phenomenon exhibits a peculiar behavior in that it becomes most noticeable when the polyethylene content is around 50%, and once becomes less noticeable when the polyethylene content is around 25%. O%
In this case, the adhesive strength between the two layers cannot be determined at all. Regarding the second, the polypropylene content is required to be 5% or more, especially 1
It is desirable that it is 0% or more. Propylene content is 5%
If the adhesive is below this level, the adhesion of the adhesive mainly composed of polyisobutylene rubber applied via the primer becomes insufficient, and problems such as adhesive residue occur due to the slight increase in adhesive strength. From the above, in the mixture layer of the film of the present invention, polyethylene is 60 to 95%, preferably 70 to 90%,
The polypropylene content ranges from 40 to 5%, preferably from 30 to 10%. The appropriate thickness of the film is about 30 to 150 microns.

The ratio of the thickness of the polyethylene layer to the mixture layer is suitably about 5:1 to 1:5. A film having such a mixture layer and a polyethylene layer is produced by coextrusion.

The coextrusion film of the present invention is formed by a conventionally known coextrusion method such as a cast film method using a flat die or a tupular film method using a circular die. There are other methods called extrusion coating method and dry lamination method to form a composite film made by bonding two or more types of plastic films together. For example, if the structure of the present invention is to be obtained by an extrusion coating method, a laminate film can be obtained by melt-extruding a blend of polyethylene and polypropylene onto a pre-formed single polyethylene film from an extruder. However, the composite film obtained by such a method is difficult to obtain adhesion between two layers, and above all, it is disadvantageous in terms of cost, which is contrary to the purpose of the present invention. The same applies to the dry lamination method in which two films are bonded together using an adhesive. In the present invention, on the surface of the mixture layer of the film consisting of two layers,
Apply the primer before applying the adhesive.

The present inventors developed the undercoating agent (Japanese Patent Publication No. 59-9
(No. 589, Japanese Patent Application No. 54-125781) An undercoat consisting of a mixture mainly consisting of chlorinated polypropylene, polyisobutylene rubber and/or butyl rubber is used. The chlorine content of chlorinated polypropylene is 15-40%
The content of chlorinated propylene in the primer is preferably 5 to 80 parts, and the content of polyisobutylene rubber and/or butyl rubber is preferably 20 to 95 parts. This primer is usually used as a solution of such a mixture in an organic solvent such as benzene, toluene, xylene, n-hexane, or the like. The concentration is O. The content is preferably 1 to 15% from the viewpoint of processability, and a tackifier as described below may be added to this. As will be described in detail in the Examples, if the above-mentioned undercoat is used, the adhesion of the adhesive mainly composed of polyisobutylene rubber to the mixture layer of polyethylene and polypropylene is dramatically improved. In addition, it becomes possible to adhere closely to film compositions that could not be used conventionally. In other words, as stated in Japanese Patent Publication No. 50-14667, the conventional limit was a polypropylene content of 15 to 75%, but with this primer, the polypropylene content is 5%.
The above is now possible. Furthermore, as a result of the spread in the direction with less polypropylene, the spread in the direction with more polyethylene, which is advantageous for the adhesive strength between two layers. As described above, the adhesive used is one mainly composed of polyisobutylene non-polar rubber.

For example, it is used in various forms such as a polymer of isobutylene, a random copolymer of isoftylene and normal butylene, a copolymer of isobutylene and isoprene, or a vulcanizate. That is, polyisobutylene rubbers with a molecular weight of about 10,000 to 140,000 are known, such as those commercially available under the trade name "Vistanecs" manufactured by Etsuso Corporation and "Etsusobutyl" manufactured by Etsuso Corporation, and those with an unsaturation degree of 0.5 to 140,000. 3 (mol %), Mu-21 viscosity of 60 or less, and is resistant to aging and non-staining. These are dissolved in an organic solvent such as benzene, toluene, xylene, or n-hexane at a concentration of 3 to 30%, preferably 5 to 20%, to form an adhesive. Among these, toluene is economically the most suitable. This adhesive can adhere well to the above-mentioned primer without adding any other polar rubber or tackifier. However, the adhesive strength can also be adjusted by adding tackifiers such as polybutene, rosin, terpene resins, etc. Application of primer, adhesive, and, if necessary, release agent is performed in-line in one step, and the product is rolled up into a product.

The surface protection film obtained in this way is suitable for a surprisingly wide range of target plates such as resin plates, painted resin plates, vinyl chloride plywood, vinyl chloride steel plates, copper plates, and aluminum nameplates, and has excellent tear resistance, post-processability, transparency, and rewindability. This makes it an excellent product with a well-balanced combination of many advantages such as flexibility and adhesive adhesion.

Examples will be described in detail below, but the present invention is not limited by the examples.

Example 1 Density 0.9247/CC. M. I. 4 polyethylene from one extruder A at a temperature of 220°C, with a density of 0.924
y/CC. M. I. 4 and 90 parts of polyethylene with a density of 0.
901 Melt Flow Index (230℃, 7/10
Minutes or less M. F. I. )9. A mixture of O and 10 parts of polypropylene was melt-extruded separately from the other extruder B at a temperature of 220° C. with a discharge ratio of 4:1, combined in a molten state in one T die, and cooled on a cooling roll. A 60 micron coextruded film was formed while the polyethylene surface was subjected to corona treatment and wound up.

The obtained film has a tensile strength of 1.92 x 102 (vertical) and 1.22 x 102 (horizontal) k9/Cr! l1 elongation vertical 810,
It was 800% horizontal. This film was again coated with a toluene solution of Nontaku 501 (Ipposha Yushi Kogyo Co., Ltd.) as a mold release agent on the corona-treated surface using the coating machine, and dried. A toluene solution of the mixture was applied and dried, and then a toluene solution of a pressure-sensitive adhesive mainly composed of polyisobutylene rubber was applied and dried to a thickness of 0.01 mm after drying to form an adhesive layer. The state was set to 1.

The obtained protective film is 251/25m against the aluminum plate.
It has an initial adhesive strength (Note 1) of m width.

The wound film was brought into an atmosphere at -5°C and unwound at a speed of 10 m/min, and tearing was observed, but no tearing occurred at all. By the way, the initial value of the unwinding force (Note 2) is 125f7.
/501tm width and 115cm after being stored at 40℃ for 30 days in a rolled state. /50n width, 20℃ x 1107 after storage for 30 days
/50mm width and is stable. The adhesive strength (residual adhesive strength) after unwinding force measurement is 187/25mm width, 20f, respectively.
/2511 width, which is almost the same as the initial adhesive strength. Also, when the adhesive sides of the wound film were pasted together and the adhesion between the base film and the adhesive (Note 3) was checked, it was 820y/257!1m.
It is wide and very good. At the same time, we checked the adhesion between the two layers (Note 4) and found that there was no peeling between the two layers, and the adhesion was excellent. Adhesive strength changes over time, but after being pasted on an aluminum plate and stored for 3 months at 20℃, 110y/25mm width, 65℃
After 3 months, 450V/25m 1 width, Weatherometer -12
350y/25m after 0 hours! Width: 620t/25m7 after 3 months of outdoor exposure (from November in Shizuoka City, south facing 45m)!
It was L width, and in all cases there were no problems such as staining the aluminum plate or leaving glue residue.

Furthermore, when the aluminum plate to which this protective film was attached was punched, not only the plate but also the protective film was completely punched out, without leaving any whiskers. Further, the protective film was peeled off at once by placing it in an atmosphere of -5°C while attached to a 1 m x 2 m acrylic plate, but it did not tear.

Furthermore, when the film was cut with a circular saw while it was attached to both sides of the acrylic board, there was no lifting of the film at all at the cut end on both sides. Also, no lifting was observed when drilling holes. The haze (Note 5) of this protective film is 9.5%, and the wood grain pattern of the PVC sheet can be clearly observed when attached to the PVC plywood. (Note 1): Initial adhesive strength: The protective film is pasted on an aluminum plate by moving a 2 kg rubber roller back and forth twice, and the adhesive strength after 1 day is 3007! Measure the resistance value when turning 180 at a speed of Tll/min.

(Note 2): Unwinding force: 501n width winding film at 20℃
The resistance value is measured when pulled out at a speed of 10 m/min in a constant temperature room of X6O%RH.

(Note 3) Adhesive adhesion: Adhesive surfaces were pasted together using a 2kg roller twice and left for 65℃X10 minutes, then 20℃X6
90 at a speed of 3007 m1/min in a constant temperature room with O%RH
Measure the resistance value when R is peeled off. (Note 4): [ヱ
Adhesion between two layers: Peel the same sample as used for adhesive adhesion measurement at a speed of 10 m/min at 1800 m/min to see if there is separation between the two layers.

If even traces are separated, mark it as △.

(Note 5): Cloudiness, measured using a cloudiness meter manufactured by Nippon Denshoku Co., Ltd.

Large numbers mean less transparency. Example 2 A protective film was obtained by forming a film using the same polyethylene and polypropylene as in Example 1 and changing the mixing ratio of polyethylene (PE) and polypropylene (PP).

Table 1 shows the results of examining the adhesion between the two layers and the adhesion of the adhesive. From the results in Table 1, the polyethylene/polypropylene mixing ratio is 95/5 to 60/401, preferably 90/10.
It can be seen that ~70/30 is desirable.

Comparative Example 1 Density 0.924, M. I. O. 8 and 50 parts of polyethylene with a density of 0.90. M. F. I. 9.0 with 50 parts of polypropylene from the extruder.
A protective film was obtained in the same manner as in Example 1 by extruding at °C and forming a 50 micron film while subjecting one side to corona treatment.

The obtained protective film was 30y/'25 against the aluminum plate.
m71! It has an initial adhesion strength of

Take up the film. When the film was unwound at a speed of 10 m/min in an atmosphere at 5°C, tearing occurred starting from a slight defect in the film.The unwinding force was 1407/50mm width at initial value, 2507/5011tm width after 30 days at 40°C, 20℃
1607/50mm width after X3O days and change over time 1
is large. Residual adhesive strength is 77/25m1L width, 6y respectively
/25m1 width, which was an extremely low value. When the aluminum plate with this protective film pasted was punched out, it remained in the form of whiskers.

Also, when it was pasted on an acrylic board and cut with a circular saw or drilled with a drill, floating was noticeable. Also 1m x 2m
When the film was attached to an acrylic board and peeled off at once in an atmosphere of -5°C, the film tore. The haze of this protective film was 28%, and the underlying board could hardly be observed in the form of a pine tree. Comparative Example 2 Protective films Example 1-b and Comparative Example 1b were obtained in the same manner as in Example 1 and Comparative Example 1, except that only the primer was omitted.

These properties are shown in Table 2.

It can be seen from Table 2 that in the absence of a primer, the adhesion between the base film and the adhesive is poor, and even a slight increase in adhesive strength causes the adhesive to remain on the board and cause contamination.

As explained above, by applying an adhesive mainly composed of polyisobutylene rubber to the surface of the mixture layer of polyethylene and polypropylene via an undercoat, the following results can be compared with the case where a mixture film of polyethylene and polypropylene is used. The effect is remarkable. 1. It is clear from the unwinding and peelability tests that the tearability in cold weather is good.

2. It is clear from punching, cutting, and drilling tests that the workability is good.

3. The unwinding property is light and stable, and the residual adhesive strength is stable at the same level as the initial adhesive strength.

4. Good transparency.

5. It is clear from the adhesion test that the adhesive and the base film have good adhesion, and this is also supported by the change in adhesive strength over time, the weatherometer test, and the outdoor exposure test.

Therefore, the non-staining properties of the polyisobutylene rubber adhesive can be utilized to the fullest. 6. There is no concern about the adhesion between the two layers.

Claims (1)

[Claims] 1 60~95% polyethylene and 40~40% polypropylene
A primer consisting of a mixture mainly consisting of chlorinated polypropylene, polyisobutylene rubber, and/or butyl rubber is applied on the mixture layer of a coextruded film in which one layer is a mixture containing 5% and the other layer is polyethylene. A surface protection film coated with an adhesive mainly composed of polyisobutylene rubber.