GB1579002A

GB1579002A - Polymer surface treatment

Info

Publication number: GB1579002A
Application number: GB1504378A
Authority: GB
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1977-04-18
Filing date: 1978-04-17
Publication date: 1980-11-12
Also published as: JPS53129262A; JPS6016614B2; DE2816856C2; DE2816856A1

Description

(54) POLYMER SURFACE TREATMENT (71) We, FUJI PHOTO FILM CO., LTD., a Japanese Company, of No.

210, Nakanuma, Minami Ashigara-Shi, Kanagawa, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention is directed to a method for treating the surface of a shaped article made of a polymer, and more particularly to a method for an improved vacuum glow discharge treatment of polymers.

A variety of surface treatments such as a corona discharge treatment, a vacuum glow discharge treatment, a non-electrode plasma discharge treatment, an ultraviolet light irradiation treatment, and the like have been heretofore employed for the purposes of improving adhesion between synthetic resin films, metal plates, etc. and a synthetic resin layer or metal layer to be provided thereon. For instance, for the purposes of improving adhesion, hydrophilic properties, dyeing capability, and the like of polymers, it is known to subject the polymers to a vacuum glow discharge treatment, as disclosed in Japanese Patent Publications 7578/60, 10336/71, 22004/70, 22005/70, 24040/70 and 43480/71, U.S. Patents 3,057,792, 3,057,795, 3,179,482, 3,288,638, 3,309,299, 3,424,735, 3,462,335, 3,475,307 and 3,761,299 and British Patent 997,093. According to these methods, the hydrophilic properties of the polymers, the property of adhesion to the polymers and the dyeing property of the polymers are improved. However, these methods have the defect that if the glow discharge treatment of the polymer film is sufficient to cause photographic emulsion layers to strongly adhere to a polymer film, which is used as a support in photographic materials, the polymer film is colored yellow. This yellow coloration not only is a problem from the standpoint of the product image, but also results in prolonged printing time due to absorption of ultraviolet light upon exposure, especially in lith type photographic light sensitive materials. Thus this defect is extremely serious in practical use. Therefore, surface treatments where this coloration does not arise or occur to as low an extent as possible are required.

However, in conventional techniques, when the surface treatment is conducted to only a small extent in order to reduce coloration, very poor adhesion between the polymer support and photographic emulsions occurs and this is a serious defect in practical use. Therefore, a method by which good adhesion to the polymer can be obtained with slight coloration has been eagerly desired in the photographic field for photographic light-sensitive materials in which the color hue of and the transparency of the polymer support are very important.

An object of the present invention is to provide a method for surface treatment of a polymer by which undesired coloration is reduced and good adhesion to the surface of the polymer is obtained.

Another object of the present invention is to provide a method for surface treatment of a polymer in which the period of time for surface treatment is decreased and by which good adhesion to the polymer is obtained.

As a result of continuous investigations in order to achieve these objects, it has now been found that by heating the surface of the polymers while subjecting such to a vacuum glow discharge treatment, sufficiently high adhesion to the polymers can be obtained and at the same time coloration of the polymers can be reduced to one-fourth to one-fifth that of the coloration obtained using conventional methods.

According to the invention we provide a method of treating a surface of a shaped article made of a polymer, which method comprises subjecting said polymer to a glow discharge treatment in a vacuum of up to 20 Torr, and immediately before or during said glow discharge treatment heating the surface of the said article to a temperature of at least 500C and for a temperature and time such that improved adhesivity of the surface is obtained and without substantial adverse effect on the physical properties or color of said polymer.

By the method of the present invention, the adhesive property of polymers to materials to be adhered thereto is remarkably improved by treatment for an extremely short period of time with heating, and the degree of yellowing of polymers which occurs in a discharge treatment can be markedly reduced. It is unexpected that the yellowing of polymers, which could not be reduced even by variations of any of the various conditions used in a vacuum glow discharge treatment, can be markedly reduced by simply previously heating the polymers to be treated. In particular, it is quite surprising that yellowing can be reduced, when it would have been expected that a vacuum glow discharge treatment under heating of a polymer would rather accelerate the yellowing of the polymer treated.

The method of this invention provides the ability to improve adhesion of polymer surfaces to other materials and yet at the same time to prevent polymers from yellowing, which is undesired, which occurs when polymers are subjected to a vacuum glow discharge treatment which is generally used to improve adhesivity of polymers. It has been found in this invention that if during the vacuum glow discharge treatment of the polymer the surface of the polymer is heated, good adhesivity is obtained and the degree of undesired coloration or yellowing is extremely reduced. Of course, it is to be recognized that the heating temperature which is used to achieve the improved adhesion and yet to prevent polymers from yellowing will be dependent upon the nature of the polymer material being subjected to the vacuum glow discharge treatment and will also be related to the degree of undesired coloration which can be permitted depending upon the enduse of the polymer contemplated, and the degree of adhesivity which is required for the end-use of the polymer contemplated. More specifically, for polymers intended to be used in photographic materials, no coloration or at least a very low degree of coloration can be permitted, due to the necessity for high transparency and the need for control of the color hue formed. Therefore, this invention is particularly useful for treating polymers intended for photographic use.

According to this invention, however, since sufficient adhesion is obtained in a shorter time, this invention is effective in case of treating polymers for which prevention of undesired coloration is not required.

As discussed above, in general the temperature used for the heating during the vacuum glow discharge treatment should be determined by the nature of the polymer subjected to the vacuum glow discharge treatment, the degree of undesired coloration which can be permitted and the degree of adhesion which is required. Therefore, it is difficult to specify temperature conditions unequivocally, but in many cases, especially for photographic end-uses of polymers, it has been found that markedly improved adhesion can be obtained and yet yellowing can be markedly reduced where heating temperatures of about 50"C or higher are employed. Especially, the maximum temperature during the vacuum glow discharge treatment is not limited by effects achieved in the invention, i.e., yellowing prevention and improvement in adhesion, but rather is dependent upon physical factors of which deformation and softening of the polymer, are important examples. More specifically, at temperatures above which a yellowing prevention effect is achieved, an increase in the heating temperature used above that point during the vacuum glow discharge treatment results in an even further improved yellowing prevention effect. This increase in yellowing prevention effect continues until a certain point is reached and above that point, while the improved yellowing prevention effect achieved up to that point is maintained, little additional enhancement of the yellowing prevention effect is observed with further temperature increases. Therefore, in practising this invention, the maximum temperature is not nearly as important.

Thus, the maximum heating temperature which can be used in this invention is up to a temperature below which a physical deformation or change in the polymer occurs, such as a softening or melting of the polymer. In general, such a temperature is about 10 C below the melting temperature. For amorphous polymers, however, since polymers are softened at the glass transition point, the maximum temperature is below the glass transition point of the polymers, for example, for amorphous polymers such as polystyrene, the maximum heating temperature is about 5"C less than the glass transition point.

In summary, both the heating temperature which can be employed and the maximum heating temperature are dependent upon the nature of the polymer and the end use contemplated, since the end use contemplated will determine the degree of adhesion desired and the degree of yellowing which can be accepted. On considering these characteristics, it has been found that a suitable heating temperature range for a polyester such as polyethylene terephthalate is about 50 to about 1200C, for a polystyrene polymer such as polystyrene is about 50 to about 95"C, for a polyolefin such as polyethylene is about 50 to about 1 100C and for a cellulose derivative such as cellulose triacetate is about 50 to about 1200C, where such are to be used for photographic supports, i.e., where the degree of yellowing must be held below the permitted value or a marked yellowing prevention effect during vacuum glow discharge treatment due to heating must be obtained.

Accordingly, operation of the method of this invention within these temperatures hereinbefore described will give rise to markedly improved adhesion characteristics for the surface of the polymer and give sufficient yellowing prevention effect particularly advantageous for use of such polymers as photographic supports.

The yellowing preventing effect is, in general, increased as the treatment temperature is elevated. However, as described above yellowing prevention is not continually increased and generally after the temperature reaches a certain level, the yellowing preventing effect stops there. For instance, it has been found that where the polymer is a biaxially stretched polyethylene terephthalate film, an increase in the yellowing preventing effect is observed up to about 100"C., but the above effect stays approximately constant without any increase even if the temperature of the polyethylene terephthalate film surface is further elevated. In addition, where the polymer is a biaxially stretched polystyrene film, a marked effect begins to appear likewise from about 50"C, and with an elevation in the temperature, the effect increases but at temperatures above about 100"C., the glass transition point for the polystyrene is exceeded so that the film shrinks very seriously due to heat and hence higher temperatures are meaningless.

Specific methods for elevating the surface temperature of polymers in a vacuum include heating using an infrared heater, heating by contact with a heating roll, and the like. Since these are in a vacuum, there is no thermal loss in the film once heated due to thermal conduction into the ambient air and for this reason, heating can be very effectively facilitated. For instance, where one wants to heat the film surface at 1000C., it is sufficient to bring the film into contact with a heated roll at 100"C. only for 1 second.

The method in accordance with the present invention is particularly effective for polymers which form a color in the discharge treatment. For instance, the method of the present invention can be effectively applied to polyesters such as polyethylene terephthalate, polybutylene terephthalate; polyolefins such as polyethylene, polypropylene; polystyrene such as polystyrene, poly-amethylstyrene; acrylic esters such as polymethyl methacrylate; polycarbonates; cellulose derivatives such as cellulose triacetate, cellulose acetate butyrate, and the like.

In addition, the method of the present invention is applicable to a shaped article made of a polymer regardless of the shape of the article. That is, the article can be in the form of a film, fibres, or a molded shaped article.

The glow discharge treatment in the present invention can be performed using otherwise heretofore known methods, for example, by the methods as are described in Japanese Patent Publications 7578/60, 10336/71, 22004/70, 22005/70, 24040/70 and 43480/71, U.S. Patents 3,057,792, 3,057,795, 3,179,482, 3,288,638, 3,309,299, 3,424,735, 3,462,335, 3,475,307 and 3,761,299 and British Patent 997,093.

The method described in U.S. Patent 3,761,299 (Corresponding to Japanese Patent Application (OPI) 13672/78) can be particularly advantageously used.

Representative conditions which can be used in the glow discharge treatment are described below. A suitable pressure range in the apparatus is between 0.005 and 20 Torr, preferably 0.02 and 2 Torr. If the pressure is overly low, the surface treatment effect is decreased, and if the pressure is too high, an overcurrent flows and arcing easily occurs with ease, which is not only dangerous but also results in the danger of destroying the substance to be treated. A glow discharge is achieved by applying a high voltage between at least one metal plate or metal rod which is arranged and positioned at a predetermined interval in a vacuum tank. Suitable electrode materials which can be used are described in Japanese Patent Application (OPI) 13672/78. This voltage used can vary widely depending upon the composition of the ambient gases and pressure, but generally within the pressure range described above, a stable constant glow discharge can be achieved using a voltage between about 500 and about 5000 V. A particularly appropriate voltage range for improving adhesion is from 2000 to 4000 V. A discharge is induced by ionizing ambient gaseous molecules or atoms by the electric field, whereby ions, electrons, excited molecules, ultraviolet light, visible light and infrared light having a variety of energy levels are generated. Ambient gases which can be present during the vacuum glow discharge treatment, depending upon the degree of vacuum used, can be air, nitrogen, argon, oxygen, etc. for example, the glow discharge treatment described in British Patent 997,093, U.S. Patent 3,309,299, 3,424,735 and 3,475,307 can be used. By putting the material to be treated in this atmosphere, a change occurs at the surface of the material treated. The rate of treatment of the polymer surface will differ, of course, depending on the nature of the polymer, the end-use, the pressure and a voltage and the number and positioning of the electrodes, etc.

As a result a suitahle treatment rate cannot be set forth unequivocally and rather is determined by routine testing balancing the degree of adhesion obtained and the degree of yellowing of the polymer resulting. Generally, however, a suitable treating time has been found to range from about 0.2 to about 60 sec, preferably 0.5 to 5 sec, for a photographic support. At present, it is unclear as to what factors mainly contribute to the improvement of adhesion obtained and what gives rise to coloration (yellowing) of the material to be treated.

As described hereabove, adhesion to photographic emulsions is improved in conventional techniques because the surface treatment is quite vigorous, for instance, for a prolonged treating time, but on the other hand, undesired yellowing in the material treated is unavoidably increased. This is the situation which exists in conventional methods. Viewing this relationship from the standpoint of yellowing, the coloration, where a treatment just sufficient to provide a surface condition having a certain adhesion level was performed was always the same even if the gaseous composition was varied, the voltage was varied, or the pressure was varied.

However, by using the heating method in accordance with the present invention, this situation has been altered, and it has become possible to obtain adhesion to the same level as achieved in conventional methods while still reducing yellowing to one-fourth to one-fifth that produced in conventional methods. In addition, the method of the present invention provides an effect that adhesion to the same degree can be obtained with a treating time of one-fourth to one-fifth the time required in conventional methods. Furthermore, according to the present invention it has become possible that polymers treated with a vacuum glow discharge can be practically used as supports for photographic materials which have severe requirements, particularly as to transparency and color hue. As a result, a method for improved adhesion is provided which is extremely low in cost from the standpoints of procedural steps as well as starting materials, as compared to the use of a so-called subbing layer which heretofore must be employed in order to sufficiently strongly adhere photographic layers and a polymer support to each other. In addition, also from a consideration of the quality of photographic materials obtained, coating accidents accompanying the coating of subbing layers are not encountered and an improvement in resolving power is also achieved due to the absence of the unrequired subbing layer and thus the method of the present invention is extremely advantageous. Furthermore, the method of the present invention is extremely significant from a social and environmental standpoint because industrial waste materials are not formed, unlike the case which exists when subbing layers are used.

The present invention has been explained above with reference to photographic materials which require especially delicate control. However, the present invention is not limited to the photographic field and is applicable to all other surface treatment fields. For instance, the present invention is applicable to a very wide variety of fields, such as pre-treatments of plastics films for magnetic tapes, supports for metal evaporation and supports for adhesive tapes and pretreatments of plastic films for imparting dyeability thereto.

The present invention will be explained in more detail with reference to examples given hereinbelow.

EXAMPLE 1 Four electrode rods of a length of 40 cm having a semicircular cross-section with a diameter of 2 cm were fixed at 10 cm intervals on an electrically insulating plate. This electrode plate was placed in a vacuum tank. At a distance of 15 cm from the electrode surface, a biaxially stretched polyethylene terephthalate film having a thickness of 100 and a width of 30 cm was travelled so that it was parallel to and opposite the electrode surface. Immediately before the film passed over the electrodes, a heating roll, equipped with a temperature controller and having a diameter of 50 cm, was positioned such that the film contacted the heating roll to an extent of 3/4 of the circumference of the heating roll. Further the film surface between the heating roll and the electrode zone was brought into contact with a thermocouple by which temperatures on the film surface were controlled to the desired temperatures. Thus, by appropriately adjusting the travelling speed of the film and the temperature of the heating roll, the time period for the glow discharge treatment and the temperature on the film surface could be controlled over a wide range. The glow discharge was performed by applying a voltage of 3000 V to the above electrodes, while maintaining the inside of the vacuum tank at 0.05 Torr. The current for the electrodes was 0.4 A.

Seventy two different samples of film were obtained by this method, by varying the temperature at the film surface and the discharge treating time, each sample was coated with a gelatin-silver halide photographic emulsion for an ordinary lithographic sensitive material, and the adhesion levels thereof were examined.

The adhesion levels were evaluated as follows: notches were made with a razor (crosswise; six lines each at a 5 mm. distance) onto the emulsion surface of the thus prepared silver halide photographic film, and an adhesive tape (polyester tape made by Nitto Electric Industries, Co.) was adhered thereon. Then, the adhesive tape was rapidly stripped off manually at a 1800 direction. Adhesion was evaluated by evaluating the degree of emulsion layer stripped off into A, B and C grades in which A means no stripping-off at all, B partial stripping-off, and C stripping-off over the entire surface.

On the other hand, the coloration of the glow discharge treated-film was measured at a wavelength of 3660 A using a Macbeth densitometer and the coloration was evaluated by the difference in optical density between the treated film and the untreated film. That is, Coloration Degree=D 3660=(Optical density of Surface Treated Film at 3660 A) - (Optical Density of Untreated Film at 3660 A).

The results obtained are summarized in Table 1 below.

TABLE 1 Level of Adhesion Coloration Degree Occurring at Minimum Time for Discharge Treatment Treating Time to Temperature at (Second) Reach an Adhesion Film Surface 0.5 1.0 1.5 2.0 2.5 3.0 Level of A 25"C (no heating) C C C B A A 0.020 400C C C C B A A 0.020 50"C C C B A A A 0.016 60"C C C B A A A 0.016 70"C C B A A A A 0.012 80"C B A A A A A 0.008 90"C A A A A A A 0.004 100 C A A A A A A 0.004 1200C A A A A A A 0.004 As can be clearly seen from the results shown in Table 1, a high degree of coloration of 0.02 occurred when an adhesion of A with the glow discharge treatment without heating (conventional method) was obtained. However, when the heating in accordance with the method of the present invention was employed, the degree of coloration was reduced, in particular, an adhesion of A could be obtained when heated at 90 to 1200C with only one-fifth the coloration. In addition, the treating time for the glow discharge necessary for obtaining good adhesion could be shortened from 2.5 seconds to 0.5 second. This means that in using a discharge treating zone of 30 cm as in this Example, a web speed was 7.2 m/min. in conventional methods whereas in the method of the present invention, the treatment can be conducted at a high speed of 36 m/min. which is 5 times that of conventional methods.

EXAMPLE 2 A biaxially stretched polystyrene film was subjected to a glow discharge treatment in a manner similar to Example 1 except that heating was performed in a temperature range up to 950C since polystyrene is a non-crystalline polymer and shrinkage of polystyrene film is marked if the temperature exceeds the glass transition point (1000C) of polystyrene.

As a result, where no heating was employed, a treating time longer than 1.5 seconds was required in order to obtain. an adhesion of A and the degree of coloration was 0.015. However, on heating to 900C in accordance with the present invention, an adhesion of A was obtained with a treating time for 0.5 second and the degree of coloration was 0.004. The method of the present invention is effective for polystyrene films, in which the desired adhesion can be obtained while reducing the degree of coloration to 1/4 that obtained in conventional methods.

EXAMPLE 3 Using the same device as described in Example 1, a biaxially stretched polyethylene terephthalate film was subjected to a glow discharge treatment under conditions of no heating (25"C) and heating at 1000C by applying a voltage of 1500 V while maintaining the inside of the vacuum tank at 0.2 Torr. Onto the film treated was coated a gelatin-silver halide emulsion for ordinary light sensitive materials.

The adhesion and coloration degree thereof were evaluated in a manner similar to Example 1. The minimum treating time necessary for gaining an adhesion level of A and coloration degree thereof are shown in Table 2 below.

TABLE 2 Treating Time Coloration (secs) Degree No Heating 5 0.07 Heating at 1000C 1.5 0.02 As can be clearly seen from the results shown in Table 2 above, in order to gain an adhesion of A with the conventional glow discharge treatment without heating, the coloration degree was unavoidably high, or 0.07. However according to the present invention, the desired adhesion could be obtained with a coloration degree of approximately 1/4 that obtained in the conventional method.

WHAT WE CLAIM IS: 1. A method of treating a surface of a shaped article made of a polymer, which method comprises subjecting said polymer to a glow discharge treatment in a vacuum of up to 20 Torr, and immediately before or during said glow discharge treatment heating the surface of the said article to a temperature of at least 500C and for a temperature and time such that improved adhesivity of the surface is obtained and without substantial adverse effect on the physical properties or color of said polymer.

2. A method as claimed in Claim 1, wherein said surface is heated to a temperature of about 10 C lower than the melting point of said polymer.

3. A method as claimed in any preceding claim, wherein said vacuum glow discharge is performed at a pressure of 0.005 to 20 Torr.

4. A method as claimed in Claim 3, wherein said pressure is from 0.02 to 2 Torr.

5. A method as claimed in any preceding claim, wherein said discharge treatment is performed with a discharge voltage of from 500 to 5000 V.

6. A method as claimed in Claim 5, wherein said discharge voltage is from 2000 to 4000 V.

7. A method as claimed in any preceding claim, wherein said polymer is a support for a photographic film.

8. A method as claimed in Claim 7, wherein said polymer is a polyester and said surface is heated to a temperature of from 50 to 1200C.

9. A method as claimed in Claim 7, wherein said polymer is polystyrene and said surface is heated at a temperature of from 50 to 950C.

10. A method as claimed in Claim 7, wherein said polymer is a polyolefin and said surface is heated at a temperature of from 50 to 110"C.

11. A method as claimed in Claim 7, wherein said polymer is a cellulose derivative and said surface is heated at a temperature of from 50 to 1200C.

12. A method as claimed in any of Claims 1 to 6, wherein said polymer is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. EXAMPLE 2 A biaxially stretched polystyrene film was subjected to a glow discharge treatment in a manner similar to Example 1 except that heating was performed in a temperature range up to 950C since polystyrene is a non-crystalline polymer and shrinkage of polystyrene film is marked if the temperature exceeds the glass transition point (1000C) of polystyrene. As a result, where no heating was employed, a treating time longer than 1.5 seconds was required in order to obtain. an adhesion of A and the degree of coloration was 0.015. However, on heating to 900C in accordance with the present invention, an adhesion of A was obtained with a treating time for 0.5 second and the degree of coloration was 0.004. The method of the present invention is effective for polystyrene films, in which the desired adhesion can be obtained while reducing the degree of coloration to 1/4 that obtained in conventional methods. EXAMPLE 3 Using the same device as described in Example 1, a biaxially stretched polyethylene terephthalate film was subjected to a glow discharge treatment under conditions of no heating (25"C) and heating at 1000C by applying a voltage of 1500 V while maintaining the inside of the vacuum tank at 0.2 Torr. Onto the film treated was coated a gelatin-silver halide emulsion for ordinary light sensitive materials. The adhesion and coloration degree thereof were evaluated in a manner similar to Example 1. The minimum treating time necessary for gaining an adhesion level of A and coloration degree thereof are shown in Table 2 below. TABLE 2 Treating Time Coloration (secs) Degree No Heating 5 0.07 Heating at 1000C 1.5 0.02 As can be clearly seen from the results shown in Table 2 above, in order to gain an adhesion of A with the conventional glow discharge treatment without heating, the coloration degree was unavoidably high, or 0.07. However according to the present invention, the desired adhesion could be obtained with a coloration degree of approximately 1/4 that obtained in the conventional method. WHAT WE CLAIM IS:

1. A method of treating a surface of a shaped article made of a polymer, which method comprises subjecting said polymer to a glow discharge treatment in a vacuum of up to 20 Torr, and immediately before or during said glow discharge treatment heating the surface of the said article to a temperature of at least 500C and for a temperature and time such that improved adhesivity of the surface is obtained and without substantial adverse effect on the physical properties or color of said polymer.

12. A method as claimed in any of Claims 1 to 6, wherein said polymer is

selected from polyethylene terephthalates, polybutylene terephthalates, polyethylenes, polypropylenes, polystyrenes, poly-a-methylstyrenes, polymethyl methacrylates, cellulose triacetates, cellulose acetate butyrates and polycarbonates.

13. A method as claimed in Claim 1 and substantially as herein described.

14. A method as claimed in Claim 1 of treating a surface of a polymer, substantially as herein described with reference to any one of Examples I to 3.

15. Polymer having a surface treated by a method as claimed in any preceding claim.