JPH051068B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a masking film having heat resistance and air permeability for use in heat-drying or heat-curing coating.

(Prior Art) In the production process of automobiles, electrical appliances, etc., the length of time required for drying and solidifying the paint film during baking 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 for the shortest possible time.

Of course, it is important that the masking sheet used during painting be inexpensive, but in heat-drying and heat-curing type painting, it is particularly required that it be heat resistant and breathable. Ru. 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 tapes have been proposed that have air permeability (for example, Utility Model Application Publications No. 52-128661, No. 55-127745, No. 57-57).
150537, etc.).

(Problems to be Solved by the Invention) Masking tapes and films, which are inherently disposable, are required to have specific functions, be mass-producible, and be low-cost.This requirement is especially true for automobile painting, etc., where the masking surface is large. It is extremely important to respond to the following. In this sense, the above-mentioned method of imparting air permeability through biaxial stretching is an excellent method, and it is conceivable that the film obtained by this method could be used as a masking tape, but since the stretched film shrinks when heated. It is not suitable as a masking material for heat-drying or dry-curing 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 studies in view of the above-mentioned points, and its purpose is, for example, to withstand high-temperature heating and drying of about 80°C to 160°C, and to have a predetermined air permeability, The object of the present invention is to provide a method for producing a masking film for heat-drying or heat-curing coating, which is not only mass-producible but also can be supplied at low cost.

(Means for solving the problems) The method for manufacturing a masking film according to the present invention includes:
A method for producing a masking film for heat-drying or heat-curing coating, the method comprising: adding 10 to 10 parts by weight of an inorganic filler to 100 parts by weight of polypropylene as a base resin.
60 parts by weight of the inorganic filler-containing material is continuously molded into a film by an inflation method, a T-die method, etc., and the film is introduced into an adhesive coating device to coat at least one side of the film. This is a method of manufacturing a masking film in which an adhesive layer is continuously formed on both edges.

(Function) Inorganic filler per 100 parts by weight of polypropylene
10 to 60 parts by weight are mixed, and a film is continuously molded using this inorganic filler-containing material by an inflation method, a T-die method, etc., and the continuously molded film is introduced into an adhesive coating device to form a film. An adhesive layer is continuously formed on at least both edges of one side.
The molded film has heat resistance and air permeability, and an inexpensive masking film for heat-drying or heat-curing coating can be continuously produced.

As a result of various experiments, inorganic fillers such as calcium carbonate were added to 100 parts by weight of polypropylene.
It was found that when a film was formed by mixing 10 to 60 parts by weight, it withstood heating of about 140°C, and the inherent heat resistance of polypropylene did not deteriorate in any way. Furthermore, when a masking film was prepared using this method and heated, it was found that the masking film did not swell 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 method for manufacturing a masking film according to the present invention will be described with reference to the drawings. FIG. 1 is a layout diagram of a manufacturing device, FIG. 2 is an enlarged sectional view of the obtained masking film, FIG. 3 is a plan view of a masking sheet formed for a comparative experiment.

In the figure, 1 is a polypropylene made by using polypropylene 1a as a base resin and mixing it with an inorganic filler 1b, and forming a tape shape with this inorganic filler-containing material by rainflation method, T-die method, etc. It is a film, and 2 is an adhesive layer formed in a band shape on at least both edges of one side of the film 1.

In the present invention, the film 1 is made of a material in which 100 parts by weight of polypropylene is mixed with 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.

Polyethylene, which is inexpensive in terms of cost, can be used as a base resin for general masking films;
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 or heat-curing coatings, the degree of breathability of the masking film should be determined depending on the coating material, oven temperature, etc., but according to experiments, polypropylene 1a
It has been found that increasing the proportion of inorganic filler 1b to be mixed in 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 add 10 to 10 parts by weight of inorganic filler to 100 parts by weight of polypropylene.
60 parts by weight was found to be 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 Above 30 parts by weight of calcium carbonate was mixed with 100 parts by weight of polypropylene, and the mixture was kneaded to a thickness of 0.03 using an inflation method apparatus 3.
Film tape 1 with a width of 380 mm and a width of 380 mm was continuously molded.
This tape was introduced into an adhesive coating device 4, and an adhesive layer 2 was continuously formed on both edges of one side of the tape to obtain a masking film product 5. Note that 6 is a guide roll. In order to confirm the gas permeability, as shown in FIG. 3A, the film sheet 11
A masking sheet A was obtained by forming an adhesive layer 12 on each side of one side of the sheet (width: 380 mm, length: 380 mm).
In addition, as shown in Figure 3B for comparative experiments,
A sample B having the same thickness and size as the sheet A was obtained by providing an adhesive layer 22 on a film 21 made of polypropylene alone. The above sheet A and sample B were pasted on the pre-painted metal plate surface to form a mask, and then painted on top of the sheet and heated at 135℃ to 140℃ for 20 minutes using a "Ricoh Gas Hot Air Dryer" (manufactured by Riko Zoki Co., Ltd.). The coating was allowed to dry for a minute.

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, in 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 heating temperature is around 135 to 140°C, it is possible to set the blending amount of inorganic filler to about 60 parts by weight, but if the heating temperature is around 160°C
In order to withstand such high temperatures, the blending amount is preferably up to about 45 parts by weight. Moreover, if an inorganic filler is blended and then crosslinked using a well-known method, the heat resistance can be further improved. In addition to calcium carbonate, inorganic fillers include talc,
Calcium sulfite, aluminum hydroxide, clay, calcium silicate, etc. can be used, and the film forming method can also be a T-die method or the like. The adhesive layer 2 may be formed not only on both edges but also at a predetermined interval in the middle.

(Effects of the Invention) According to the method for producing a masking film according to the present invention, 10 to 60 parts by weight of an inorganic filler is mixed with 100 parts by weight of polypropylene, and this inorganic filler-containing material is used by an inflation method, a T-die method, etc. Since the adhesive layer is continuously formed on at least both edges of one side of the film by continuously molding the film and introducing the film into an adhesive coating device, the inherent heat resistance of polypropylene is not impaired. It is possible to continuously manufacture a masking film that has excellent heat resistance and can dry the coating film at high temperatures, shortening the drying and curing time of the coating film.Moreover, the masking film has a specified ventilation The film does not bulge due to the expansion of the air sealed inside, and the gas generated from the pre-painted film will not be sealed, and it will not damage the gloss of the pre-painted film. Therefore, it is most suitable as a masking film for heat-drying or heat-curing type coatings, and such masking films for heat-drying or heat-curing type coatings can be mass-produced at low cost.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining an embodiment of the masking film manufacturing method according to the present invention, in which FIG. 1 is a layout diagram of the apparatus, and FIG. 2 is an enlarged cross-section of the obtained masking film. It is a diagram. Fig. 3 shows a masking sheet prepared for a test for a comparative experiment, Fig. A is a back view of the masking sheet obtained by the present invention, and Fig. B is a back view of a sample made of a single polypropylene sheet. 1: polypropylene film, 1a: polypropylene, 1b: inorganic filler, 2: adhesive layer,
3: Film molding device, 4: Adhesive coating device,
5: Masking film product.

Claims (1)

[Claims] 1. A method for producing a masking film for heat-drying or heat-curing coatings, in which 10 to 60 parts by weight of an inorganic filler is mixed with 100 parts by weight of polypropylene, and this inorganic filler-containing material is used by an inflation method, A film having air permeability characterized in that an adhesive layer is continuously formed on at least both edges of one side of the film by continuously molding the film by a T-die method or the like and introducing the film into an adhesive coating device. Method of manufacturing masking film.