JPH0454855Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a masking film having heat resistance and air permeability.

(Prior Art) In the production process of automobiles, electrical appliances, etc., the length of time required for drying and solidifying the paint film after painting greatly affects the production volume and cost of the product per unit time. Therefore, when drying in an oven at a predetermined temperature, it is an important issue to dry at the most suitable high temperature in the shortest possible time.

It goes without saying that it is important that the masking sheet used during painting be inexpensive, but in heat-drying type painting, it is particularly required that it have heat resistance and air permeability. That is, if the masking sheet does not have air permeability, the masking sheet will swell due to thermal expansion of the internal air, and gas generated from the pre-painted film will not be discharged, resulting in uneven gloss on the pre-painted film.

Conventionally, heat-resistant masking sheets include those made of kraft paper laminated with polyethylene film, and are heat-resistant at relatively high temperatures.

However, this kraft paper laminated with polyethylene film has disadvantages such as not only insufficient breathability but also poor elongation, poor workability in pre- and post-processing, and increased costs. At present, the process is performed in a low-temperature oven using other masking sheets.

There have been various methods for imparting air permeability to plastic sheets and films, such as mechanical perforation and perforation through chemical treatment.
A method has been proposed in which two or more types of thermoplastic synthetic resins with poor compatibility are kneaded to form a sheet or film, and this is stretched biaxially in the longitudinal and transverse directions (for example, Japanese Patent Publication No. 48-28789). Public bulletin).

In addition, various types of masking tape with breathability have been proposed (for example,
Utility Model No. 52-128661, No. 55-127745, No. 57-
150537 (publications, etc.).

(Problems to be solved by the invention) Masking tapes and films, which are disposable in nature, are required to have specific functions, be mass-producible, and be low-cost.Especially in applications such as automobile painting, where the masking surface is large, this is necessary. It is extremely important to respond to requests. In this sense, the method of imparting air permeability by the biaxial stretching method described above is excellent, and it is possible to use the film obtained by this method as a masking tape, but the biaxially stretched film does not shrink when heated. Because of this, it is not suitable for masking in heat-drying type coatings.

Various data have been reported regarding the gas permeability of single plastic films made of various materials, and it is known that the gas permeability increases as the temperature rises. Additionally, in general, it has been conventional to mix inorganic fillers into plastics as bulking agents or incineration temperature lowering agents, and a large amount of data has been reported regarding the physical properties such as tensile strength in this case. It has not been reported that mixing an inorganic filler into plastic increases the gas permeability of the film produced thereby.

The present invention was completed as a result of various researches in view of the above points, and its purpose is, for example, to be able to withstand high temperature heating and drying of about 80°C to 160°C, and to have a specified air permeability. The object of the present invention is to provide a masking film for heat-drying or heat-curing coating that can be mass-produced and can be supplied at low cost.

(Means for solving the problem) The present invention provides a masking film for heat-drying or heat-curing coatings that uses polypropylene.
This masking film is characterized by comprising a film made of a material in which 10 to 60 parts by weight of an inorganic filler is mixed with 100 parts by weight, and an adhesive layer is provided at a predetermined interval on one side of the film.

In this case, in order to provide a predetermined air permeability and not to reduce the inherent heat resistance of polypropylene, it is optimal to use 10 to 60 parts by weight of the inorganic filler per 100 parts by weight of polypropylene.

(Function) As a result of various experiments, when a film is formed by mixing 10 to 60 parts by weight of an inorganic filler such as calcium carbonate or talc with 100 parts by weight of polypropylene, it can withstand heating to about 140°C, and the polypropylene It was found that the original heat resistance did not deteriorate in any way. Furthermore, when a masking film was constructed using this and heated, it was found that the masking film did not bulge and had appropriate gas permeability.

The reason why breathability occurs when inorganic fillers are mixed into polypropylene is currently unknown, but these inorganic fillers are generally fine particles of about 3 to 5 microns and have excellent hygroscopic properties. Since these fine particles exist continuously in polypropylene, it is thought that this property has some effect.

(Example) An example of the masking film according to the present invention will be described based on the drawings. In the figure, 1 is a tape-shaped polypropylene film,
Reference numeral 2 denotes an adhesive layer provided in the form of a band on both edges of one side of the film 1.

In the present invention, the film 1 is made of a material mixed with 100 parts by weight of polypropylene and 10 to 60 parts by weight of an inorganic filler, but in the drawings, it is virtually shown as polypropylene 1a and inorganic filler 1b. There is.

Low-cost polyethylene may be used as a base resin for general masking films, but it cannot be
It does not have front and rear heat resistance, and other heat-resistant base resins such as nylon and polyester are expensive, making it more expensive than conventional kraft paper/polyethylene laminate films.
Polypropylene is optimal as a masking film that has heat resistance and is advantageous in terms of cost.

In heat-drying painting, the degree of air permeability of the masking film should be determined depending on the paint material, oven temperature, etc.
Experiments have revealed that increasing the proportion of inorganic filler 1b mixed into polypropylene 1a increases air permeability. However, if the amount is too large, the heat resistance of polypropylene will decrease, so in order to provide the specified air permeability without impairing the heat resistance of polypropylene, it is necessary to
It has been found that 10 to 60 parts by weight of inorganic filler per 100 parts by weight is optimal.

Next, a specific example of implementation will be explained.

(1) Polypropylene used HomoPP (melting point 160-170℃) Melt index: 4-9g/10min. Density: 0.90-0.91g/cc (2) Inorganic filler Calcium carbonate (3) Film processing method Inflation method As described above 30 parts by weight of calcium carbonate were mixed and kneaded with 100 parts by weight of polypropylene, and a film sheet having a thickness of 0.03 mm and a width of 380 mm was produced by an inflation method.

In order to confirm the gas permeability, a film sheet 11 (width 380 mm, length 380 mm) was prepared as shown in Figure 2A.
A masking sheet A was obtained by forming an adhesive layer 12 on each side of one side of the sheet (mm). Further, for a comparative experiment, as shown in FIG. 2B, a sample B having the same size as the sheet A was obtained by providing an adhesive layer 22 on a film 21 made of polypropylene alone. Above sheet A
Sample B was pasted on the pre-painted metal plate surface to mask it, and then coated on top of it and heated to 135℃ using a "Ricoh Gas Hot Air Dryer" (manufactured by Riko Zoki Co., Ltd.).
The coating was dried at 140°C for 20 minutes.

As a result, for sample B, the internal air thermally expanded, causing the entire masking film 1 to swell, and the remaining gas, which was thought to have been generated from the pre-painted film, could not pass through the film, resulting in uneven gloss on the pre-painted surface. . On the other hand, sheet A of the present invention
No abnormality such as swelling was observed in the masking film, and the gloss of the pre-painted film was also good. As a result, it was found that the masking film had heat resistance and internal gas was properly discharged from the film. Furthermore, it is easy to understand that polypropylene film is most suitable as a masking film for high-temperature drying type coatings because its gas permeability generally increases as the temperature increases.

When the drying temperature was further increased to 160℃, no abnormality was observed when the inorganic filler was added in an amount of 30 to 45 parts by weight, but when the blend amount was increased beyond this level, the heat resistance of the film deteriorated slightly. Admitted. Therefore, if the drying temperature is around 135 to 140°C, it is possible to set the blend amount of inorganic filler to about 60 parts by weight, but if the drying temperature is around 160°C
In order to withstand such high temperatures, the blending amount is preferably up to about 45 parts by weight. In addition to calcium carbonate, inorganic fillers include talc,
Calcium sulfite, aluminum hydroxide, clay, calcium silicate, etc. can be used, and it goes without saying that the film can be formed by a T-die method or the like.

(Effect of the invention) According to the masking film according to the invention, 10 to 10 parts by weight of inorganic filler is added to 100 parts by weight of polypropylene.
The adhesive layer is placed at a predetermined interval on one side of the film formed from a mixture of 60 parts by weight, so it has excellent heat resistance without impairing the inherent heat resistance of polypropylene, and the coating film can be dried at high temperatures, shortening the drying and curing time of the coating film. In addition, the masking film has a predetermined air permeability, so the film does not bulge due to the expansion of the air sealed inside, and the gas generated from the pre-painted film is not sealed. Does not damage the gloss of the paint film, etc.
Ideal as a masking film for heat-drying or heat-curing coatings.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a masking film according to the present invention, and FIG. 2 is a masking film prepared for a test for a comparative experiment.
Figure A is a back view of the product according to the present invention, and Figure B is a back view of a sample made of a single polypropylene film. 1...Polypropylene film, 1a...Polypropylene, 1b...Inorganic filler, 2...Adhesive layer.

Claims (1)

[Scope of utility model registration request] A masking film for heat-drying or heat-curing coating includes a film made of a mixture of 100 parts by weight of polypropylene and 10 to 60 parts by weight of an inorganic filler, and an adhesive layer on one side of the film at predetermined intervals. A masking film characterized by: