JPS6030265B2 - Method for producing biaxially oriented polypropylene film with mold releasability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a two-bag bag that has excellent template bendability for adhesives, that is, a large residual adhesive force of the adhesive after release from the mold, and is also excellent in transparency, stiffness, etc. The present invention relates to a method for producing a stretched polypropylene film.

In general, sheets made of paper, plastic sheets, or composites of these materials are coated with a silicone resin coating on the surface of the base material to give the base material release properties. A certain amount of a coating solution diluted to a certain concentration by adding a certain amount of curing agent or curing aid is applied to this, and then the solvent is evaporated by heating, and at the same time the heat of the curing agent or curing aid is applied. It is manufactured by a method in which the coating film is cured by catalytic action, and the coating film is brought into close contact with the surface of the substrate and has the desired release properties. However, when this manufacturing method is applied to a base material made of a biaxially oriented polypropylene film that has excellent mechanical strength and a high degree of transparency,
There are some difficulties in producing films with mold releasability using transparent base materials with excellent mechanical strength for reasons explained below. In other words, in general, if the heating temperature at the stage of applying a coating liquid containing silicone resin as a main component to a substrate and heating and curing it is low, the silicone resin will not be sufficiently cured, and the resulting mold releasability will be insufficient. Moreover, the adhesion between the coating film and Motomura is also poor, and when the coating film is rubbed with a finger, the area turns white and the coating film peels off, resulting in the so-called smear/rub-off phenomenon. . Furthermore, if the silicone resin is not sufficiently cured, a portion of the coated silicone resin may transfer to the non-coated surface of the base material, and adhesive processing may be applied to the non-coated surface in the subsequent process. , the problem of poor wetting of adhesives and printing inks during printing processing occurs, and in addition, the slippage between the coated film surface and the non-coated film surface is extremely poor, and after the coating process. In the winding process, problems such as blocking and stagnation occur. Therefore, the heat treatment after coating the silicone resin on the base material does not simply evaporate the solvent in the silicone resin coating;
It must be capable of completely curing the silicone resin coating by heating at high temperatures. As is clear from the above explanation, the silicone resin used as a mold release agent in sheets with mold release properties is thermosetting, and good chicks can only be obtained by applying sufficient heat treatment. It expresses type characteristics.

Sufficient heat treatment in this case naturally differs depending on conditions such as the type of silicone resin and the amount of coating applied, but considering the drying capacity of general coating machines actually used, it is recommended that the temperature be as high as possible. The heat treatment conditions required from the viewpoint of curing of the silicone resin are not so difficult to satisfy, for example, if Motomura is made of paper-like heat-resistant material. There are no particular problems with the curing properties of the silicone resin. However, when using a biaxially oriented polypropylene film as a base material, which has excellent various mechanical strengths and a high degree of transparency, since the biaxially oriented polypropylene film is basically weak against heat, If a biaxially oriented polypropylene film is subjected to heat conditions above a certain level, not only will the film lose various mechanical strengths, oil resistance, water vapor barrier properties, etc. that are characteristic of the film, but also the biaxially oriented polypropylene film itself will lose its properties. Due to heat shrinkage, there is also the problem of a decrease in the commercial value in terms of appearance, such as spots appearing during the subsequent winding stage. Therefore, since there are restrictions on the heat conditions that can be applied to the double-stretched polypropylene film that serves as the base material, it is desirable to perform gentle heat treatment at the lowest possible temperature and for the shortest time. As mentioned above, heat treatment at the highest possible temperature and for the longest time is desirable from the silicone resin side, which is the coating agent.Since it is necessary to satisfy two contradictory heat treatment conditions, two sea bream stretching with actual release plasticity is desirable. In the production of polypropylene film, compromise conditions are adopted to balance the demands of both to minimize the effect on the two-bag stretched polypropylene film and to advance the curing of the silicone resin to a level that is practically acceptable. has been done. Depending on the manufacturing method, if the thickness of the biaxially oriented polypropylene film serving as the base material is relatively thick, a biaxially oriented polypropylene film having a certain level of mold releasability, although not sufficient, may be produced. You can, but
The biaxially stretched polypropylene film serving as the base material is 15 to 2
When the thickness is as thin as 0 French or less, the influence of heat resistance is large, making it extremely difficult to produce a two-scale stretched polypropylene film with mold release properties. Naturally, various studies have been conducted on heat-resistant biaxially oriented polypropylene films as base materials, but the heat treatment conditions required to almost completely cure the silicone resins currently in use have not been met. It is difficult to produce durable biaxially oriented polypropylene films.

On the other hand, the development of low-temperature curing silicone resins is strongly desired, and as a result of various studies, it has become possible to obtain silicone resins with faster curing speeds than before, but the current biaxially oriented polypropylene film heat resistance,
In particular, a silicone resin that is sufficiently cured under heat treatment conditions that are permissible for biaxially oriented polypropylene films with small thicknesses has not yet been obtained. In addition, as mentioned above, 25 to 30
The production of biaxially stretched polypropylene films with mold releasability using a biaxially stretched polypropylene film with a wall thickness larger than 100% as a base material requires less favorable thermal conditions than when using a thinner wall thickness as a base material. However, since thermosetting silicone resin is coated, the heat treatment process not only evaporates the solvent from the silicone resin coating, but also requires curing the silicone resin with heat. This method has the disadvantage that the coating speed of silicone resin is greatly limited. As detailed above, we have developed a biaxially oriented polypropylene film, especially a polypropylene film with a small thickness, without changing the mechanical properties and excellent transparency of the biaxially oriented polypropylene film. It has been difficult to produce films with mold releasability for various reasons.

The present invention provides a method for producing a double-stretched polypropylene film having release plasticity in an extremely efficient manner without causing the above-mentioned drawbacks by having the structure described in the claims.

That is, the present invention involves applying a thermosetting silicone resin to the treated surface of a polypropylene film that has been subjected to a general adhesion improvement treatment such as corona discharge treatment or flame treatment, and then performing a stretching treatment. This process consists of turning a polypropylene film into a double-stretched polypropylene film, and at the same time curing the coated thermosetting silicone resin.

In the present invention, when a thermosetting silicone resin is coated on the surface of a wire-stretched polypropylene film, it is then subjected to a stretching treatment in two axes (longitudinal and horizontal directions), and stretched in advance in either the longitudinal or structural direction. When a thermosetting silicone resin is coated on the surface of the polypropylene film that has been treated, the polypropylene film as a material is then stretched in a direction perpendicular to the stretching direction described above. At the same time as forming a stretched polypropylene film, the thermosetting silicone resin coated on the surface is cured. At least one side of the axially stretched polypropylene film, which has been previously stretched in the longitudinal direction, is treated with adhesive properties. Then, a coating film of thermosetting silicone resin is formed on the treated surface, and then this is stretched in the transverse direction to turn the uniaxially oriented polypropylene film into a biaxially oriented polypropylene film, and at the same time, the coating is applied. A method of curing the thermosetting silicone resin is preferable from the viewpoint of controlling the amount of silicone resin coated.

In the present invention, a polypropylene film is used as a base material, and this is because polypropylene film has excellent transparency and various mechanical properties. Since the curing conditions for curing the polypropylene film and the stretching temperature of the polypropylene are in good agreement with each other, after forming a coating film of the thermosetting silicone resin on at least one side of the polypropylene film, the stretching heating when stretching the polypropylene film is performed. This is because the coating film made of thermosetting silicone resin can be completely cured. The polypropylene film used as the base material is made of a resin mainly composed of polypropylene, that is, a mixture of crystalline polypropylene, a monomer copolymerizable with propylene, a copolymer of propylene, or a mixture of polypropylene and the above copolymer. This is a film that is contained as a resin component in the components. Furthermore, in the present invention, a coating film of thermosetting silicone resin can be formed on either one or both sides of the polypropylene film that serves as the base material, but in either case, adhesion improvement treatment is applied in advance. It is necessary to form a coating film of thermosetting silicone resin on the exposed surface.

If this adhesion improvement treatment is not performed, the adhesion between the base material and the silicone resin coating will be poor, and in the next stretching process, the stretchability of the silicone resin coating will be lower than that of the base material. In most cases, it is not possible to obtain a biaxially oriented polypropylene film in which a uniform silicone resin coating is tightly adhered. Further, when an aqueous emulsion of thermosetting silicone resin is used as the coating liquid, the coating liquid itself is repelled by the surface of the substrate, making even the coating operation difficult. In the present invention, the thermosetting silicone resin applied to the base material includes silicone resins that are usually used as template-imparting agents, such as organic polysiloxanes having an OH group at the terminals and polyfunctional alkyl hydrogens. So-called condensation reaction type silicone resin, which is made of a mixture of polysiloxane and organic metal catalysts such as dibutyltin dilaurate and tin acylate;
A so-called addition polymerization type silicone resin consisting of a mixture of an organic polysiloxane having a pinyl group at the terminal or side chain or both, a polyfunctional methyl hydrogen polysiloxane, and an organometallic catalyst such as a silicone modified product of chloroplatinic acid. Either of these can be used, and a curing aid, release modifier, slip improver, etc. can also be added as appropriate to the mixture.

In addition, the form of the thermosetting silicone resin coating liquid applied to the substrate may be solvent-based, water-based, or solvent-free, and these coating liquids can be applied using normal coating methods. can do.

If the amount of thermosetting silicone resin applied in this process is too large, the silicone resin coating film will not be fully cured during the stretching process, resulting in incomplete adhesion between the silicone resin coating film and the base material. Because the silicone resin coating is stretched as it is, it not only becomes unevenly white, but also makes it impossible to obtain a homogeneous coating.
This also has the disadvantage that the base material cannot be stretched uniformly.
In addition, if the coating amount is too small, it will not be possible to obtain a film with sufficiently stable mold release properties, so generally the final product film after biaxial stretching is approximately 0.05 to 2.
It is preferable to apply the coating so that the coating amount is approximately 100 g. The present invention is constructed as described above, and is for producing a so-called on-machine biaxially oriented polypropylene film having scale-like properties, in which a coating film of thermosetting silicone resin is formed. When stretching a polypropylene film, the amount of stretching heat received by the polypropylene film is used as the amount of heat for curing the silicone resin coating formed on the surface of the polypropylene film.

The amount of heat that the polypropylene film receives during this stretching process is considerably greater than the amount of heat that the base material receives during the drying process of a general film coating machine. It is a feature of the present invention that the material is completely cured. That is, in the present invention, the amount of heat in the stretching process is used to completely cure the coating film of thermosetting silicone resin formed on the surface of the polypropylene film that is the base material. In this case, it is possible to eliminate the adverse effect that the amount of heat required to cure the silicone resin has on the polypropylene film. In other words, a homogeneous film having a thermosetting silicone resin coating film based on a biaxially stretched polypropylene film with an extremely small wall thickness has no properties inherent to the biaxially stretched polypropylene film. without making it
It has the effect of being able to be manufactured extremely efficiently. As already mentioned, this is not an on-machine coating that simply eliminates a process, which has been proposed many times in the past. It has technical value in the sense that it is possible. In general, silicone resin coatings can exhibit sufficient release properties even if they are quite thin as long as they are uniform. However, in reality, uniform coating is difficult due to coating technology, so the required coating amount is )) However, in the present invention, after the thermosetting silicone resin coating film is formed on the polypropylene film, it is stretched in at least one direction. As a result, the amount of thermosetting silicone resin applied during the coating operation is increased to the extent that the coating film of silicone resin becomes thinner due to the stretching process, and as a result, the amount of solvent used is reduced. Since a highly concentrated coating solution is used, the amount of solvent used can also be reduced. By using a solvent-free silicone resin, the present invention can exhibit further effects in terms of coating amount control and safety.

Furthermore, in the present invention, the coating of the thermosetting silicone resin is carried out before the single-touch or biaxial stretching process during the production of the Nito-stretched polypropylene film, and the thermosetting silicone resin is applied during the subsequent uniaxial or biaxial stretching process. The coating film of curable silicone resin is completely cured, and the silicone resin is applied using so-called on-machine coating, which reduces production compared to conventional off-machine coating. Of course, it has the characteristic of extremely high efficiency.

The present invention will be specifically explained below based on Examples, and the physical properties of the obtained biaxially oriented polypropylene film are shown in Table 1 together with the physical properties of the film having mold releasability obtained in the comparative example.

Example: A polypropylene sheet extruded from a T-die was stretched 5 times in the Ito direction, and one side of the resulting uniaxially stretched polypropylene film with a thickness of about 200 mm was subjected to a corona discharge treatment.
Next, on this corona discharge treated surface, the coating liquid shown in Table 1 below, prepared to a concentration of 10%, is applied at a ratio of solid secretion/filling, and then immediately and continuously passed through the width of the tenter. Stretching treatment was performed in the transverse direction so that the effective magnification was 9 times.

Table 1 shows the physical properties of the obtained biaxially stretched polypropylene film with about 20 peaks.

Comparative Example One side of a double-stretched polypropylene film with a thickness of 20mm was subjected to corona discharge treatment, and then the coating liquid shown in Table 1 below, adjusted to a concentration of 2%, was applied to the corona discharge treated side as a solid. Minutes approx. 0. Apply the coating to the desired amount,
This was subjected to sand heat treatment at 120° C. in a hot air dryer.

Table 1 shows the physical properties of the obtained film.

In addition, in the process of the comparative example, when the heat treatment temperature using the hot air dryer was set to 130°C or higher, the biaxially oriented polypropylene film used as the base material experienced shrinkage and deformation due to heating. Table 1 The physical properties in Table 1 above are the results of measurements made using the methods described below using samples that have been produced one day after the film was produced.

(1) Smear Rub The thermosetting silicone resin coated surface of the obtained film was rubbed with a finger, and judgment was made based on the degree of whitening of the surface and the presence or absence of detachment of the silicone resin.

Note that 0 in the table indicates neither whitening nor detachment.

△ shows slight whitening but no detachment × means whitening and detachment It shows that.

'2' Peeling force (g/5 ribs) Apply adhesive [manufactured by Toyo Ink ■: BPS-8170] to the coating surface of thermosetting silicone resin of the obtained film to a thickness of 70↓ with solvent. After drying for 70oo for 2 minutes,
50g/finish high-quality paper (Kobayashi Recording Paper) on this adhesive coated surface
was pasted.

This was left for one day at 20°C and 65% RH, and the peel resistance between the silicone resin coating surface and the adhesive was reduced to 0.3 h/
The value was measured at a tensile speed of 100 min.

'3} Residual adhesion rate (%) Laminate adhesive tape [Nitto Polyester Tape: 31B] on the surface of the Teflon sheet,
This was left at 70℃ for one day under a load of 20g/kg, then peeled off from the adhesive tape, and then the adhesive tape was pasted on a clean stainless steel plate (#280), and after being left for 2000℃ for 1 hour, the adhesive tape was removed. The adhesive strength between the
The value obtained by tensile measurement in minutes was set as [1], and the above-mentioned adhesive tape was laminated on the coating surface of the thermosetting silicone resin of the film obtained in each of the above-mentioned Examples and Comparative Examples, and the above-mentioned Teflon sheet was When the adhesive force between the adhesive tape and the stainless steel plate is measured in the same manner as in the case of [B],
It was expressed as residual adhesion rate (%)=[D]×100/[1].

(4) Sliding property The coated film surface of the thermosetting silicone resin and the uncoated film surface of the obtained film were overlapped and allowed to slide, and the slipping property was evaluated.

Furthermore, 0 in the table is slipping. △ is slightly slippery × does not slip Display each thing.

Wind value (%) Measured using a hazemeter ND-67 manufactured by Nippon Denshoku ■.

As is clear from Table 1, the film with mold releasability obtained by the present invention is superior in all physical respects to the template film obtained by the conventional method. I can see that it is excellent.

Furthermore, with the method for producing a biaxially oriented polypropylene film of the present invention, it is possible to easily obtain a biaxially oriented polypropylene film having a thin wall thickness and template-like properties, which has been difficult to produce in the past. In addition, in terms of cost, it is clear that O-Naka is advantageous compared to conventional off-machine coating in terms of so-called ortho-machine coating.

Claims (1)

[Claims] 1. Applying an adhesion improvement treatment to at least one side of an unstretched polypropylene film or a polypropylene film that has been subjected to a stretching treatment in either the vertical or horizontal direction, and then coating the treated surface with a thermosetting silicone resin, Thereafter, the polypropylene film is made into a biaxially stretched polypropylene film by stretching in two directions (vertical and horizontal) or in one of the horizontal and vertical directions, and at the same time, the thermosetting silicone resin coated is cured. 1. A method for producing a biaxially oriented polypropylene film having mold releasability.