GB1568059A - Process for producing foamed products and synthetic leather comprising same - Google Patents

Description

(54) PROCESS FOR PRODUCING FOAMED PRODUCTS AND SYNTHETIC LEATHER COMPRISING SAME (71) We, TAKIRON CO., LTD., a Japanese Company of No. 30, 2-Chome, Azuchi-machi, Higashi-Ku, Osaka, 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:- This invention relates to a process for producing a U.V. ray cross-linked 1,2polybutadiene foamed product having a uniform structure and a comparatively high cross-linking degree and also to a synthetic leather formed of such a product.

Plastics are required to be durable when they are used as materials in, for example, industry, agriculture or engineering construction. Therefore, intensive research has been carried out to increase the durability of plastics.

In recent years, however, there has been an increasing demand to develop materials which exhibit controlled natural degradation after use in order to prevent environmental pollution due to plastic waste. In general, high molecular weight compounds gradually degrade when exposed to sunlight for several years, and, finally, they are degraded to such a degree that they no longer maintain their original form. This is attributable to the fact that sunlight comprises irradiation having the necessary wavelength and intensity to split high molecular weight chains. The quantum yield of the molecular bond split is generally as low as 10-3 to 10-5.However, one year S exposure to sunlight carries enough light energy to split ordinary high molecular weight chains, and hence high polymers are degraded, after accumulated degradation for several years, to such a degree that their original form is destroyed by a slight external force.

Ordinary plastics, such as polyethylene, polypropylene and polystyrene, are not easily degraded, when pure, by sunlight having a wavelength distribution of 290 and 400 mp since they do not absorb radiation having wavelengths longer then 300 my.

Therefore, in order to raise this quantum yield, it is necessary to add a photosensitizer absorbing radiation of wavelengths longer than 300 m,u thereby to increase the sensitization wavelength region.

Thus, research has been conducted on adjusting the degree of photodegradability using various photosensitizing agents. In the case where such agents are used, it still takes several hours to several months to make the plastics brittle.

In general, absorption of light by molecules is necessary for a photochemical reaction. For the effective absorption of light by molecules of a material to be irradiated, the irradiating light must be transmitted throughout the whole material, i.e., a totally uniform and sufficient degree of cross-linking cannot be attained unless the UV rays are transmitted through the material uniformly and sufficently. Taking the transmitting capability of UV rays into consideration, the degree of cross-linking unavoidably becomes non-uniform in the depthwise direction. The upper limit of the amount of UV irradiation is that which is necessary to cause photodegradation of the material to be irradiated.The efficiencies of transmission and absorption of UV rays and of cross-linking at this irradiation level mainly decide the maximum thickness of practically producable cross-linked materials, and, therefore, foamed products.

That is, when the efficiencies of transmission and absorption of UV irradiation or of cross-linking is low, the surface layer becomes over cross-linked, while the inner "core" is under cross-linked, resulting in inferior foamed products. 1,2polybutadiene transmits UV rays of longer than 240my well. The percent transmission thereof is at least double that of polyethylene.

In addition, since 1,2-polybutadiene is prone to photocross-linking because of the vinyl groups in its side chains, it has the merit that comparatively thick uniform cross-linked materials can be obtained.

However, in practice, various additives, such as fillers, colorants, antioxidants, lubricants and foaming agents are usually compounded therewith, and these materials generally scatter, obstruct or absorb UV rays thereby preventing transmission of the UV rays into inner portions of the plastics and reduce the efficiency of photosensitizers. Therefore, with opaque materials which contain various additives, it is difficult to attain a uniform and sufficient degree of cross-linking.

In order to obtain a comparatively highly expanded, cross-linked foamed product, it is necessary to compound a foaming agent with the plastics in a correspondingly high proportion. The foaming agent generally scatters, obstructs or absorbs UV rays and greatly reduces the efficiency of the transmission or the response of the material being irradiated thereto. Therefore, it is difficult to obtain a uniform cross-linked material having a comparatively high degree of cross-linking form foamable materials containing a large amount of a foaming agent so that comparatively thick, uniformly foamed products of a high expansion ratio are obtained only with difficulty. Thus, compounding ingredients which do not prevent the transmission of UV rays and a photo-sensitising action, rather which accelerate these effects would be especially valuable.

Cross-linking of rubbery plastics or rubber includes chemical cross-linking using an organic peroxide or a sulfur compound and physical cross-linking using ionizing radiation; the latter conveniently being utilized for the production of crosslinked foamed products.

Physical cross-linking enables the design of a process for continuously producing foamed products of good quality having uniform cells with a desired expansion ratio since it does not require heat and pressure to cause cross-linking as does chemical cross-linking.

On the other hand, chemical cross-linking attains cross-linking through the thermal decomposition of a cross-linking agent, and the process involves steps at various temperatures, i.e., softening point of the base resin S kneading temperature < temperature at which thermal decomposition of the cross-linking agent is initiated S temperature at which the thermal decomposition of a foaming agent is initiated S cross-linking and foaming temperature. In order to obtain foamed products having a uniform, fine cellular structure, it is generally necessary to conduct cross-linking prior to foaming, and thermal cross-linking takes a comparatively long period of time. This is the main factor which inhibits the practice of a simple, highly productive cross-linking process as compared with physical cross-linking.

However, cross-linking using ionizing radiation involves high equipment cost for related equipment to shield radiation harmful to humans as well as for the main equipment. In addition, such a process is not advantageous from the viewpoint of the step involved.

Japanese Patent Publication 10298/71 describes a process for cross-linking and foaming by irradiating polyethylene with ultraviolet rays of low energy. However, pure polyethylene does not absorb radiation having a wavelength of 150 m,u or longer, and has a molecular structure which is not influenced by ultraviolet rays of 290 to 400 mp in wavelength. Actually, the poor light resistance thereof is attributable to the absorption region in the longer wavelength region due to processing impurities which contaminate the resin and carbonyl groups formed by oxidation upon thermal hysteresis. Still, polyethylene per se is essentially non-responsive to light in the ultraviolet region.Therefore, even in the process of shifting the absorption wavelength region by the addition of a photosensitizer, ultraviolet rays travel through the materials to be irradiated only a short distance, resulting in non-uniform cross-linking. Also, cross-linking processes require a comparatively long period of time, so that the production of cross-linked foamed products has not extensively been put into practice.

Conventional processes for producing rubber foamed products are as follows.

Rubber foamed products can generally be classified into foam rubbers and sponge rubbers. Processes for producing the former are roughly classified into: (1) a sodium silicofluorde process; (2) a thermal coagulating process; and (3) a low temperature coagulating process, according to the process for coagulating the latex, while processes for producing the latter are roughly classified into (A) foaming by mechanical stirring; (B) decomposing a foaming agent; (C) injecting pressurized gas, followed by the removal of pressure: and (D) extracting soluble materials, according to the foaming type, or (a) press curing; (b) autoclave curing; and (c) air vulcanization, according to the type of curing rubber. (A), (B) and (C) are in many cases applied to (c), (a) and (b), respectively, with the application of pressure being a great factor.

In any case, a cross-linking process which is required in the production of rubber foamed products involves thermally crosslinking after mechanically compounding a cross-linking agent into the rubber, and requires a comparatively high temperature and a long time. Therefore, various compounding ingredients or modified production steps have been considered, but so far there has been no fundamental use of thermal cross-linking procedures.

1,2-polybutadiene has in every unit a hydrogen atom and a vinyl group both bonded to a tertiary carbon atom at the allyl position, and is therefore, liable to be activated by high energy source such as heat and light. For example, 1,2-polybutadiene comparatively easily undergoes crosslinking and cyclization by short wavelength irradiation (not longer than 350 m) and undergoes hardening type degradation.

Therefore, thin film 1,2-polybutadiene materials easily become brittle when exposed for several weeks to summer sunlight, and become destroyable by wind force. Due to this property, 1,2polybutadiene belongs to the class of photodegradable plastics.

It is known that, a 50y thick 1,2polybutadiene film (trade name: JSR RB820; made by Japan Synthetic Rubber Co., Ltd) the specific radiation amount necessary for the hardening degradation is 120 mw.hr/cm2 or less when the wavelength is 254 m,u, and 250 mw.hr/cm2 for 312 m and 600 mw.hr/cm2 for 352 mp.

The present invention is an industrially excellent process which enables the continuous production of wide, long rubber cross-linked foamed products of a high expansion ratio at ordinary pressure, which has so far been difficult, since it is not based on thermal cross-linking.

As a result of investigating the behavior of the physical properties of photodegradable 1,2-polybutadiene during UV irradiation to cause molecular cross-linking and, as the degree of cross-linking increases the movement of molecular chains becomes more inhibited with the main chain being split, to cause eventual molecular degradation, the inventors have found that the physical properties of the polymer in the cross-linking stage, (the initial stage of the photo chemical reaction) is suitable for the production of foamed products.

Further research has led the inventors to the present invention which enables the design of a simple process for producing rubber foamed products in a shorter time than is required in conventional processes for producing rubber foamed products, by adding various photosensitizers in a suitable amount to 1,2-polybutadiene and adjusting the strength of ultraviolet irradiation applied thereto.

According to the present invention, there is provided a process for producing a photodegradable foam rubber product which comprises the steps of (1) mixing (a) a 1,2-polybutadiene containing not less than 70% 1,2-bonds, a molecular weight of not less than 100,000, a degree of crystallinity (as defined herein) of 10% to 50 /O and not less than 200/, of a syndiotactic stereo specific structure, (b) 0.1 to 3 X" by weight, based on the weight of the 1,2polybutadiene, of a photosensitizer which sensitizes in the wavelength region of 240 to 400 m and (c) a thermally decomposable foaming agent, (2) irradiating the resultant mixture with ultraviolet readiation of a wavelength of 240 to 400 my for not more than 10 minutes to form a cross-linked material having a gel fraction (as defined herein) of 30 to 80%, and (3) heating the resulting cross-linked material to 150 to 2300C to form a photodegradable foam rubber product.

By this process a photodecomposable rubber foamed product with a high expansion ratio and excellent softness can be produced with high efficiency without the complicated equipment and procedures required by conventional processes.

Also, the present invention provides a synthetic leather comprising a substrate carrying a resin layer comprising a crosslinked, foamed 1,2-polybutadiene produced by the process as defined in the last preceding paragraph but one. Such a synthetic leather is soft to the touch and has other aesthetic properties extremely closely resembling high quality natural leathers.

In this specification, the degree of crystallinity was calculated using the following equation: l/d=x/d+( 1-x)/da where d=density of the sample density of 1,2-polybutadiene having a degree of crystallinity of 100% (ire do=0.963*) da=density of 1,2-polybutadiene having a degree of crystallinity of 0% (i.e. da=0.889) x=degree of crystallinity *(G. Natta J. Polymer Sci, vol 20 page 25, 1956) The density d was as measured by the density-gradient tube method in which the density-gradient tube is put into a constant termperature bath at 20"C and the sample of 1 ,2-polybutadiene is put into the tube and stored for at least 24 hours. Thereby, the density of the 1 ,2-polybutadiene sample was measured.

In this specification, "gel fraction" means the percent by weight determined by using a small piece of an ultraviolet ray irradiated molding as a sample, placing this sample in an extraction thimble whose retention particle size is 8 L with respect to liquid, refluxing boiling toluene for 7 hours using a Soxhlet extractor, drying for 48 hours under reduced pressure (not more than about 3 mmHg), and calculating the percent of the weight of the thus processed sample based on the weight of the sample before processing.

Preferably, the 1 ,2-polybutadiene used in the present invention is a reactive resin having pendant vinyl groups as side chains and it electrons present in the double bond of the vinyl groups are activated by a wavelength energy of 200 to 400 mp.

The 1 ,2-polybutadiene used in the process of the present invention has a good heat stability and the same moulding property as conventional thermoplastic resins and the same light responsiveness as photodegradable resins.

The 1 ,2-polybutadiene used in the process of the present invention is a solid having an adhesiveness insufficienf to form pellets at room temperature and having, at a temperature above its softening point, a melt viscosity sufficient to form using a conventional molding apparatus.

The 1 ,2-polybutadiene used in the process of the present invention can be obtained according to methods described in, for example, Japanese Patent Publications 32425/1969; 32426/1969; 38070/1970; 30699/1971 and 30700/1971. For example, a solvent, butadiene and catalyst [e.g., cobalt bisacetylacetonate (Co)., triphenylphosphine (p), triethyl aluminum (al)] are introduced into a glass tube in a proportion of Al/Co/p/butadiene= 430/1/2/100,000 (molar ratio) and allowed to react at 100C for about 18 hours, followed by adding an aging inhibitor and then stopping the reaction to thereby obtain the desired 1,2polybutadiene. From X-ray diffraction analysis, the vinyl units in the fine structure of the polymer are present in an amount of at least 90%,.

The 1,2-polybutadiene used in the process of the present invention shows a photoresponsiveness in the ultraviolet region based on the transition of it electrons present in the double bonds of the side chains thereof. This is increased by the addition of a photosensitizer to such a degree that the polymer can be degraded at the molecular level in a comparatively short time. However, deterioration of various physical properties due to this degradation of the molecular chains is not desirable from the viewpoint of working or use.

Therefore, photoresponsiveness must be adjusted so that the physical properties suitable for working or use of the crosslinked material can be maintained until the desired time for the degradation of the molecule. In addition, this must be conducted in a short time.

As mentioned above, the photosensitizer is one which sensitizes in the wavelength region of 240 to 400 m,u (corresponding to the wavelength region of a high pressure mercury lamp and the wavelength where UV irradiation is transmitted), and is preferably one which activates 1,2polybutadiene predominantly to cause cross-linking while preventing decomposition of the polymer. For the above purposes, triplet sensitizers, transient metal compounds, radical initiators and photooxidation weakening substances may be used. Of these, those which have toxicity or an offensive odor or which are colored are preferably not used in the process of the present invention. In addition, the photosensitizer is preferably one which can be mixed with the polymer to provide a homogeneous phase since uniform crosslinking is important in this invention.In this respect those photosensitizers having a relatively good oleophilicity can be employed with good results. For example, aromatic ketones such as benzophenone, p,p'-dimethoxybenzophenone, p,p' dichlorobenzophenone. p.p"- dimethylbenzophenone, acetophenone, acetonaphthone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, methyl-obenzoyl benzoate and benzil provide good results. In addition, there can be illustrated aromatic aldehydes such as terephthalaldehyde and quinone aromatic compounds such as methylanthraquinone and fluorenone. These photosensitizers are used in a concentration of 0.1 to 3.0%, preferably 0.3 to 1.00/, by weight based on the weight of 1,2-polybutadiene. If they are used in a lesser concentration physical properties suitable for the production of foamed products are difficult to obtain, while if they are used in greater concentration it is difficult to control the degree of cross-linking to a uniform level between the surface layer and the inner layer, resulting in a deterioration of the surface layer and the formation of a nonfoamable, thick surface layer.

1,2-polybutadiene having a threedimensional structure suitable for foaming can be obtained within 10 minutes by irradiating the polymer material containing the photosensitizer in such an amount with 365 melt light of a 10 to 150 w/m2 ultraviolet ray intensity for at least 15 seconds. The irradiation time cannot be specified as it varies depending upon the content of the photosensitizer, the composition involved and thickness of the article to be irradiated.

However, the radiation time is generally at least 15 seconds in order to obtain a uniform photochemical reaction of the article being subjected to irradiation. The thickness of the materials processed in accordance with this invention is usually from about 1 - to about 5 mm. When p,p'-oxybis(benzene sulfonyl hydrazide)[OBSH] is used as a foaming agent, materials 15 mm or more in thickness can be processed in accordance with this invention.

Since UV rays emitted from a UV lamp have a certain wavelength distribution, the total amount of energy of the UV rays having such a wavelength distribution irradiated on a spot varies depending upon the wavelength distribution and the distance of the spot form the light source (UV lamp).

The intensity of the UV rays irradiated on a certain spot of the article to be irradiated is not a function of light energy emitted from a certain point of the light source. Generally, the intensity of the UV rays is indicated by an intensity distribution curve where UV rays having a certain wavelength can be represented as an irradiation plane. Thus, in the present invention sufficient results are obtained by conducting irradiation such that the article to be irradiated receives such an amount of energy as provided by 365 m light of about 10 to about 150 w/m2 for about 15 seconds to about 10 minutes.

The gel fraction in boiling toluene of the thus irradiated material is 30 to 80 /n in 7 hours and about 10 to about 75% in 15 hours.

The irradiation time also varies depending upon the wavelength distribution of the light source: however, it is not preferrred to irradiate for above 10 minutes since side reactions occur due to the nature of 1,2-polybutadiene containing a photosensitizer. The temperature and pressure of UV irradiation are limited in no substantial way and usually irradiation is performed at room temperature and at atmospheric pressure. Of course, the usual care should be taken so as not to elevate the temperature of the resin above its softening point since manipulation becomes difficult and side reactions such as oxidation of the polymer occurs at such temperature.

If materials containing the photosensitizer in lesser concentrations than above are irradiated with stronger light or if materials containing the photosensitizer in a greater concentration are irradiated with weaker light, it is difficult to uniformly cross-link the materials.

In particular, it is necessary to adjust the viscosity by the ultraviolet ray cross-linking of the present invention since in the present invention as a photo-sensitizer responds to ultraviolet rays the photoresponsiveness of the 1,2-polybutadiene is raised, chemical cross-linking is predominantly conducted and splitting of the main chain proceeds less frequently. This is delicately influenced by the foaming agent and any antioxidant or other compounding ingredients employed.

Experiments have shown that the foaming agent is desirably added in an amount of up to 20 parts by weight based on 100 parts by weight of the 1,2-polybutadiene, and the anti-oxidant (when used) is employed in an amount of 0.05 to 1 part by weight, based on 100 parts by weight of the 1,2polybutadiene. As other compounding ingredients, there can be illustrated a filler.

Generally speaking, those ingredients which do not absorb UV rays are selected and there is no specific limitation on the amounts of other compounding ingredients to be added. The foaming temperature is 1500 to 230"C, at which temperature the cells are not destroyed by the blowing pressure. The UV cross-linked 1 ,2-polybutadiene used in the process of the present invention undergoes a reduction in viscosity with an increase in temperature as thermoplastic resins. Therefore, if the temperature is less than 1500C, the viscosity necessary for foaming cannot be obtained, while if it is higher than 230"C, gas leakage due to a reduction in viscosity becomes serious and oxidation proceeds, whereby good products with a high expansion ratio are difficult to obtain.

Although not to be construed as limitative, foaming is usually carried out at atmospheric pressure. It is preferred that foaming be performed at superatmospheric pressure when minute bubbles are desired.

The foaming time in which the foaming agent decomposes and expansion is completed varies depending upon the kind and amount of the foaming agent.

Foaming agents include, for example, azodicarbonamide, dinitrosopentamethylenetetramine, p-toluenesulfonylhydrazide and p,p'-oxybis(benzenesulfonylhydrazide), which may be used in combination. Foaming aids and foaming nuclei may also be added, if desired.

The amount of the foaming agent used varies depending upon aimed expansion ratio. The photosensitizer, the foaming agent and, any other desired additive eg an aging inhibitor, a softening agent and/or a colorant are added to 1,2-polybutadiene, and preferably fed to a kneader to be formed into a sheet or other form at a temperature higher than the resin softening point but lower than the decomposition point of the foaming agent used (generally, about 1500C), then irradiated with ultraviolet rays for a short time (e.g. 15 seconds to 10 minutes) to convert to a resin into a three dimensional structure, followed by heating to a temperature higher than the decomposition point of the foaming agent to foam and expand the resin. Thus, there can be continuously obtained photodegradable foamed products of excellent softness.

While not to be construed as limitative, usually employed expansion ratios are from about 1 to about 25 times the original volume.

The process of the present invention enables one to produce a cross-linked material capable of foaming to a depth of about 7 mm within 10 minutes using a high pressure mercury lamp emitting radiation of a wavelength of 240 to 400 m,u. Thus, a highly productive continuous process can be designed and can be put into practice.

As explained in detail above, UV ray cross-linked foamed products of 1,2polybutadiene can be obtained in accordance with the present invention by irradiating a material prepared by kneading a base resin with suitable amounts of a photosensitizer and a thermally decomposable foaming agent with UV rays to form a suitable cross-linked material, and then heating to a temperature higher than the decomposition point of the foaming agent. This cross-linking suitably adjusts and controls the photodegradable property of 1 ,2-polybutadiene from the viewpoint of mechanism and velocity, and hence the kind and amount of the photosensitizer, intensity and irradiation time of UV requires careful control to produce the desired results.Too much photosensitizer makes control difficult, resulting in over cross-linking, while insufficient photosensitizer fails to cause complete cross-linking at an economically advantageous velocity.

Compositions containing 1,2polybutadiene and a photosensitizer alone enable one to easily adjust the cross-linking degree, and obtain a comparatively high cross-linking degree. However, when a large amount of compounding ingredients are incorporated therein, the average crosslinking degree becomes low, and, taking this into consideration, the photosensitizer is usually added in excess as compared with the necessary amount. However, this is not favorable, since remaining photosensitizer causes post cross-linking, and hardening proceeds further to cause a degradation in product quality.

As earlier indicated, in practice various additives are utilized which generally scatter, obstruct or absorb UV rays to prevent full transmission to inter portion of the article being irradiated. Further, in the case that one desired to form cross-linked foamed products of a comparatively high expansion ratio, the foaming agent must be included in a relatively large amount, which typically also exhibits such a UV ray scattering, obstructing or absorbing effect.

In a highly preferred embodiment of the present invention, oxybis(benzenesulfonylhydrazide) [OBSH] is utilized, as this material does not prevent the transmission of UV rays, rather, accelerates the photosensitizing effect achieved.

OBSH is a powdery foaming agent having a decomposition point of about 165"C.

When this is used in a foaming agent the efficiency of the photosensitizer is scarcely reduced and, in addition, a uniform UV ray cross-linked material having a comparatively high cross-linking degree can be obtained since OBSH per se participates in the cross-linking. OBSH does not have a melting point and is slightly soluble in ordinary solvents. Therefore, it may appear to form a heterogeneous system with 1,2polybutadiene. It is, therefore, a surprising fact that OBSH transmits UV rays well and provides a uniform and relatively high crosslinking degree, and that OBSH per se participates in the cross-linking. This may be attributed to that OBSH is a strong absorbent of UV rays and has a sensitizing action, and that OBSH per se acts as a UV ray cross-linkable foaming agent on 1,2polybutadiene.The advantage of OBSH being a foamable cross-linking agent is that it does not possess, after its decomposition as a foaming agent, a sensitising action, that is, OBSH not having participated in the cross-linking is decomposed and consumed as a foaming agent.

The contribution of OBSH to the crosslinking becomes greater in proportion to the concentration thereof, and the effective compounding ratio is 0.5 part or more, desirably 1.0 part or more, by weight based on 100 parts by weight of 1,2polybutadiene.

If desired, in appropriate cases OBSH can be used in combination with other foaming agents such as azodicarbonamide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, etc. The other compounding ingredients earlier enumerated are, of course, compatible therewith.

Examples of the present invention are set forth below. Unless otherwise indicated all parts, percentages and ratio herein are by weight. The high pressure mercury lamps used in the Examples emit radiation having a wavelength of 240 to 400m,u.

EXAMPLE 1 Pellets prepared by mixing 100 parts of syndiotactic 1 ,2-polybutadiene having a density of 0.901 g/cm3, a 1,2-unit content of 90 /ns a molecular weight of not less than 100,000 a degree of crystallinity of 10% to 50 /", a syndiotactic structure content of 51%, a viscosity measured at 250C in toluene of 1.38 di/g, a vicat softening point of 75"C, a melting point of 39"C, and a glass transition point of-30 C. (trade name: JSR, RB--810; made by Japan Synthetic Rubber Co., Ltd.) with 10 parts of azodicarbonamide and 0.7 part of benzophenone were fed to an extruder and a sheet 30 cm in width and 0.3 cm in thickness continuously extruded at a velocity of 1 m/min.This sheet was then irradiated with ultraviolet rays for 3 minutes using 1 kw high pressure mercury lamps (H4000L/3; made by Tokyo Shibaura Electric Co., Ltd.) 30 cm from both sides.

The foaming agent was then decomposed by heating to 215 C to obtain a rubber foamed product of a 0.06 specific gravity having a uniform, fine cellular structure which was much softer than a polyethylene cross-linked foamed product of the same expansion ratio, and which showed no bending impression upon bending ascribable to the stretching property of the base resin. When this foamed material was exposed to outdoor sunlight, destruction of its original shape was quite easy within I month, whereas no change was observed when it was left for 6 months in a room. The production rate in this case was about 810 g/min., and, in terms of volume, about 13.5 Vmin, good productivity from the process thus being demonstrated. The gel fraction of this foamed product was about 35%.

EXAMPLE 2 100 parts of syndiotactic 1,2polybutadiene having a density of 0.906 g/cm3, a 1,unit content of 92%, a molecular weight of not less than 100,000 a degree of crystallinity of 10% to 50%, a syndiotactic structure content of 66%, a viscosity measured at 250C in toluene of 1.24, a vicat softening point of 52"C, a melting point of 80 C and a glass transition point of -25"C (trade name: JSR, RB-820: made by Japan Synthetic Rubber Co., Ltd.), 7.5 parts of an azodicarbonamide foaming agent (trade name:Spancel DW-25; made by Eiwakasei Kogyo Co., Ltd.) having a decomposition point of 170 to 1800C, 0.5 part of 2,6-di-tert-butyl-4-methylphenol, an ageing inhibitor, and 2.5 parts of benzophenone was kneaded at about 90 to about 100"C for 10 minutes using two heated rolls to obtain a crude sheet, which was pelletized to obtain a master batch. This master batch was diluted with pellets of JSR RB-820 to a dilution ratio of 1:5 by weight and the resulting mixture was extruded using a uniaxial extruder diameter of 90 mm under the conditions of a compression ratio of 3.1, a speed of 8 to 15 rpm and a temperature of 50 to 1100C to prepare various 1 mm thick sheets.These sheets were then irradiated with UV rays at a distance of 30 cm using 1 kw high pressure mercury lamp (from both sides), then the cross-linked sheet was foamed at a temperature of 170 to 230"C. As a result, sheets irradiated for 2 to 10 minutes showed a viscosity suitable for foaming. Under the specific conditions chosen in this Example, when irradiation time was shorter than 2 minutes, there resulted an insufficient viscosity which failed to foam an expanded material, while when longer than 10 minutes was used, oxidation of the surface layer proceeded so much that the surface skin layer became colored.The temperature suitable for foaming was found to be 180 to 230"C. Under the specific conditions chosen in this Example, lower temperatures led to insufficient expansion, while higher temperatures caused serious leakage of gas, resulting in a reduction in the expansion ratio and serious coloration due to oxidation. The gel fraction of sheets irradiated for 2 to 10 minutes was 30 to 600//n, and the expansion ratio (maximum) was 18 times.

EXAMPLE 3 Example 2 was repeated except for changing the amount of benzophenone to 0.1 to 3.0. As a result, a viscosity suitable for foaming was obtained by irradiating for 10 minutes or less. Comparatively good foamed products were obtained at a concentration of about 0.3 to 1.0% benzophenone. The gel fraction was 80 ,o (maximum) at a 1.0 weight 2n of benzophenone and an irradiation time of 10 minutes.

EXAMPLE 4 100 parts by weight of the same 1,2polybutadiene as was used in Example 1 was mixed with 10 parts by weight of p,p'oxybis(benzenesulfonylhydrazide) and 1.0 part by weight of terephthalaldehyde and the resulting mixture was kneaded using two heated rolls at about 80 to 90"C to prepare about a 5 mm thick crude sheet having a poor surface appearance, the she.et was then placed in a die 5 mm thick and then pressed at about 90 to about 100"C at a pressure of about 50 kg/cm2 for 5 to 10 minutes to prepare a 5mm thick sheet having a good surface appearance. The thus obtained sheet was withdrawn from the die after it was cooled, and then cross-linked in the same manner as in Example 1 and foamed at 165"C to obtain a foamed product of a 0.15 specific gravity.The gel fraction was 30%.

REFERENCE EXAMPLES 1 TO 9 AND EXAMPLE 5 100 parts of 1,2-polybutadiene rubber having properties falling within the scope of claim 1 was kneaded with predetermined amounts of a photosensitizer and a foaming agent as given in Table I using heated rolls at about 80 to about 90"C for about 10 minutes to prepare about a 1 mm thick crude sheet having a poor surface appearance. The sheet was placed in a die of 1 mm thickness and then pressed at about 90 to about 100"C and at a pressure of about 50 kg/cm2 for about 5 to about 10 minutes to prepare a i mm thick sheet having a good surface appearance. The thus obtained sheet was withdrawn from the die after it was cooled.The resulting sheet was then irradiated with UV rays for 5 minutes from both sides at a distance of 30 cm using I kw high pressure mercury lamp (H4000L/3: made by Tokyo Shibaura Electric Co., Ltd.). In general, gel fraction increases with increased cross-linking degrees because of solvent insolubility. Therefore, the gel fraction of irradiated sheets was measured by refluxing in boiling toluene for 7 hours using a Soxhlet extractor to compare the degree of cross-linking. The results are tabulated in Table 1.

TABLE 1 Comparison of Cross-linking Degree in Terms of Gel Fraction Reference Photosensitizer Foaming Agent Gel Example (parts by weight) . '(parts by weight) Fraction ( n) No. Benzophenone OBSH ADCA* Notes 0.5 0 0 67.5 transparent sheet containing the sensitizer and no foaming agent 2 0 5.0 0 25.0 OBSH alone 3 0 10.0 0 29.8 4 0 2.5 7.5 26.0 mixture of OBSH and ADCA alone 5 0.5 2.5 7.5 39.6 OBSHAl::)CA-sensitizer 6 0.5 0 10.0 30.5 ADCA-sensitizer 7 0 0 10.0 0 ADCA alone 8 0 0 0 0 blank test Example 5 0.5 10.0 0 74.5 OBSH-sensitizer * ADCA stands for azodicarbonamide The results in Table 1 show that an opaque sheet containing OBSH as shown in Example 5 provide a higher gel fraction than that of transparent sheet as set forth in Reference Example 1 containing a photosensitizer alone and not containing a foaming agent.

Judging from this fact and the values of Reference Example 3, it is seen that OBSH scarcely inhibits the. cross-linking effect of the photosensitizer. Reference Examples 2 and 3 show that OBSH per se functions as a foamable UV ray cross-linking agent. Also, another foaming agent, ADCA, provided a gel fraction of only about 10% as in Reference Example 6 where a sensitizer was used. Thus, ADCA reduces the crosslinking efficiency. Reference Examples 4 and 5 show that OBSH has the effect of improving the degree of cross-linking and Example 5 shows that a comparatively high degree of cross-linking can be obtained.

Reference Examples 7 and 8 correspond to blank tests. When irradiated sheets as in Example 5 and Reference Example 5 are foamed at a temperature higher than the decomposition point of the foaming agent, there can be obtained very soft foamed products having extremely uniform cells.

Thus, it can be seen that OBSH is an excellent UV ray cross-linkable foaming agent for 1,2-polybutadiene, capable of providing a uniform and comparatively high degree of cross-linking.

EXAMPLE 6 The same composition as was used in Example 5 was kneaded using two heated rolls in the same manner as in Example 4 to prepare sheets about 4 mm in thickness.

Three of the thus obtained sheets were placed in a die of 12 mm thickness one on the other followed by pressing using a heated press at about 90 to about 100"C and at a pressure of about 50 kg/cm2 to form a 12 mm thick sheet. The resulting sheet was then irradiated with UV rays for about 7 minutes from both sides at a distance of 30 cm using Ikw high pressure mercury lamp (H4000L/3; made by Tokyo Shibaura Electric Co., Ltd).The irradiated sheet was then heated at a temperature of 1900C for 10 minutes to obtain a 25 mm thick, white, elastic foamed product of a 0.08 g/cm3 specific gravity which was of good quality and had uniform bubbles throughout the thickness of the sheet.

EXAMPLE 7 100 parts of 1,2-polybutadiene (trade name: JSR, RB-810; made by Japan Synthetic Rubber Co., Ltd.), 0.5 parts of benzophenone, and 17 parts of a foaming agent consisting of ADCA and OBSH (ADCA:OBSH=I:I in part by weight) were kneaded in the same manner as in Example I to prepare a 1 mm thick sheet. The resulting sheet was irradiated with UV rays for 5 minutes from both sides at a distance of 30 cm using Ikw high pressure mercury lamp (H4()()OL/3; made by Tokyo Shibaura Electric Co. Ltd) followed by foaming at 205"C to obtain a uniformly foamed product of a 0.044 bulk density having minute bubbles. The gel fraction of this foamed product was about 40%.

A foamed product having a high expansion ratio such as those obtained in this example can be obtained with a considerably high gel fraction and in this regard the content of OBSH in the foaming agent used should be about 25%. The products of this invention are useful as shock absorbers, packing materials, wrapping materials, heat insulating materials, etc. In particular, the foamed products of the present invention are most suited for backing materials such as for carpets, mats and the like, since they have excellent flexibility, elasticity and buffering properties.

The foamed product obtained according to the process of this invention'is very soft, exhibits very little change in flexibility at temperatures of ordinary use, is particularly excellent in elasticity and smoothness, and easily absorbs such energy as tensile, bending and other deformation energy.

Accordingly, it follows the complicated shape of a coated substrate so accurately that it is particularly suitable as a synthetic leather for clothes. Also, it has a soft feel due to the vinyl groups in the side chains of the base resin, and has other aesthetic properties extremely closely resembling high quality natural leather. Further, it provides a warm agreeable touch since it is a foamed product. Thus, it has many advantages.

Most synthetic leathers have a multi layered structure comprising a base fabric layer, an adhesive boundary layer, a resin layer and a top layer. In the resin layer, synthetic leathers such as foamed or unfoamed polyvinyl chloride, polyamides polyurethanes or polyamino acids are conventionally used. Those which contain a base sheet comprising polyvinyl chloride are generally called vinyl leathers, and the foamed products thereof are called sponge leathers to differentiate them from ordinary synthetic leathers. Vinyl leathers have the practical advantages that they are comparatively inexpensive and can be produced with ease, and they enable one to obtain suitable physical properties for the artificial leather.Therefore, they are currently used in the largest amount in spite of various defects with respect to physical properties, i.e. since polyvinyl chloride is an essentially glassy and hard resin, a large amount of a plasticizer must be compounded therewith in order to convert it to a leather or like soft material. In particular, for high-grade synthetic leathers which require good softness through all seasons, plasticizers such as dioctyl phthalate, di-n-octyl phthalate or dioctyl sebacate are generally compounded therewith. These plasticizers are partly vaporized during production of the synthetic leather and cause the phenomenon of bleeding or migration, thus being unavoidably released from the base material to come into contact with the human body.Such a release of plasticizer can be the cause of a reduction in flexural fatigue resistance at low temperatures in winter and blocking at high temperatures in summer. Recently, many plasticizers have been suspected as having harmful effects.

From this viewpoint, there have been conducted various investigations of the use of foamed products of plasticizer-free high pressure process polyethylene or ethylenevinyl acetate copolymers containing vinyl acetate in high proportions. However, these are so poor in adhesive properties that adhesion to a base fabric layer or to a top layer is difficult. Further, they are inferior in softness. Thus, they have not yet replaced conventional vinyl leathers.

Cross-linked syndiotactic 1,2polybutadiene has none of the aforesaid difficulties of the prior art since it does not contain any plasticizer. In addition, it is very soft to the touch as well as having good flexibility, so that it has a feel closely resembling the feel of natural leather obtained by chrome tanning, and is completely different from conventional rubber sheets. Also, it has good adhesive properties and adhesion to a base fabric or top-coating can be conducted with ease using a suitable conventional adhesive or surface treating agent. In this case, cross linking imparts a suitable solvent resistance.

As an adhesive, natural rubber, chloroprene rubber, nitrile rubber, butyl rubber, urethane rubber or epoxy resin can be used.

The surface treating agents used in this invention should be such that they have substantially the same flexibility and elasticity as those of the cross-linked foamed syndiotactic 1 ,2-polybutadiene and and have adhesiveness, with urethanes, especially thermoplastic urethane, surface treating agent providing good results. The adhesive layer may be provided between the surface treating layer and a resin layer. The surface treating layer may also be coated in multi-layer form, if desired. For example, a surface treating agent belonging to polyamine acids, polyamides, polyvinyl chlorides or acrylic rubbers may be coated ob the surface layer of a polyurethane in one or more layers to thereby prepare a synthetic leather having desired properties, e.g., various lustres, feel and the like.

There can be also obtained a product with uniform and fine cells, which improve the abrasion resistance and scratch resistance of the surface.

The thickness of the foamed product suitable as a resin layer for sythetic leather is about 0.3 to about 2.0 mm, preferably 0.5 to 1.5 mm, (This thickness range applies only to the polybutadiene layer), and the expansion ratio ranges from about 3 to about 15 times (the bulk density being about 0.3 to about 0.05 g/cm3), preferably 5 to 10 times (the bulk density being 0.18 to 0.09 g/cm3), which renders it lighter than conventional sponge leathers.

Adhesion to woven fabrics, knitted fabrics, non-woven fabrics, paper, natural or synthetic resin products, various resin films or like base fabric can be effected according to general processes by properly selecting an adhesive agent and a solvent.

Examples of generally used substrates include staple fiber muslin, calico (unbleached muslin), cotton suede, various synthetic fabrics, tricot, polynosic, (rayon prepared by the viscose method and having a cotton-like feel) and single surface or both surface-raised-up cloths of these materials.

Although the thickness of adhesive is not limited, generally used thicknesses are from about 5 to 50 g/m2.

Further, a synthetic leather of better quality can be obtained by applying to a top coat (the top-coat thickness is usually from about 3 to about 50 g/m2, although such is not limitative) a conventional surface treating agent of excellent scratch resistance, abrasion resistance, solvent resistance, heat resistance, weatherability, and cold resistance, such as polyurethane, polyamide, or polyamino acid surface treating agents for synthetic leather; the surface treating agents are not limited to any particular kind.

The thus obtained synthetic leather can be used for various uses such as paper substitutes and linings for use in buildings and cars, book covers, chair covers, tablecloth substitutes, carpets, foot wear such as sandals and slippers, bands for wrist watches and as a belt for clothing, sacks and bags, and covers.

Additionally, in some cases, the crosslinked foamed product prepared by mixing the syndiotactic 1,2-polybutadiene of the present invention with low density polyethylene, an ethylene-vinyl acetate copolymer (desirably the vinyl acetate content is not more than about 40 mop%/) or another soft, i.e., flexible polyolefin copolymer having compatibility with the syndiotactic 1 ,2-polybutadiene, e.g., an ethylene-propylene copolymer, an ethyleneacrylic acid ester copolymer, an ethylenebutadiene copolymer and the like, may be used. The aesthetic properties, softness, weatherability, solvent resistance and like physical properties of the product can be adjusted according to the kind of soft polyolefin and the compounding ratio thereof.Generally such polyolefins are used in an amount of about 10 to about 50 iO by weight based on the total weight of the product in view of the flexibility, adhesive properties and feel, of the total weight of the 1,2-polybutadiene and the soft polyolefin.

EXAMPLE 8 Pellets, prepared by mixing 100 parts of syndiotactic 1,2-polybutadiene (trade name: JSR, RB--810; made by Japan Synthetic Rubber Co., Ltd.) having properties falling within the scope of claim 1 with 7.0 parts of azodicarbonamide, 1.0 part of p,p'oxybis(benzenesulfonylhydrazide) and 0.5 part of benzophenone, were fed to an extruder and continuously extruded into a 0.4 mm thick sheet. This sheet was then irradiated for 4 minutes with ultraviolet rays at a distance of 30 cm from both sides using I KW high pressure mercury lamp, and the foaming agent was decomposed at 210 C to obtain a foamed sheet, followed by passing the sheet between hot rolls (about 50 to about 60"C) to form a sheet having a smooth surface. There was thus obtained a foamed sheet of a specific gravity of 0.1 which was 1.2 mm in thickness having good surface properties and uniform, fine cells which was of extremely excellent flexibility and had aesthetic properties well resembling good natural leather. The gel fraction of the foamed sheet was 33.09/,.

When this foamed sheet was subjected to the physical tests specified for polyvinyl chloride leather [blocking test (JIS K6772); flexing resistance test (1 kgx5000 times Scott's process) measured by Scott's crumple tester as described in JIS K 6772; cold flexing test (20,000 times at -100C)], it withstood all the tests. (JIS=Japanese Industrial Standard).

On the other hand, a chloroprene adhesive was thinly coated (30g/m2) on knitted fabric or non-woven fabric, and the foamed sheet was laminated thereon.

Thereafter, an urethane surface treating agent (LU 1500, LU 3500 or LU 3560; made by Dainichi-seika Colour & Chemical Mfg.

Co., Ltd.) was coated thereon in a thickness of 15 to 30 g/m2 to form different samples, followed by drying. The thus obtained synthetic leather was extremely soft, and the flexibility thereof was hardly effected at temperatures of ordinary use (-20 to 45"C), the leather showing no adhesive properties.

When the base fabric was an elastic knitted fabric, the product was so elastic that it could be bent and stretched into complicated shapes.

Foamed sheets of 0.3 to 2.0 mm in thickness and a 3 to 5 times expansion ratio were prepared in the same manner, and the same synthetic leathers obtained by adhering these sheets to base fabric and subjecting them to a surface treatment.

EXAMPLE 9 90 to 50 parts by weight of syndiotactic 1,2-polybutadiene (the same as in Example 1) were respectively mixed with 10 to 50 parts by weight of ethylene-vinyl acetate copolymer (vinyl acetate content: not more than 40%) (trade name: Ultrathene; made by Toyo Soda Manufacturing Co., Ltd.) with 10 to 50 parts by weight of ethylenepropylene copolymer (melt index according to ASTM D1238: 0.25-90; density 0.88 g/cc) (trade name Tafmer; made by Mitsui Petrochemical Industries, Ltd.), and 100 parts by weight of each of the resultant mixtures were processed in the manner described in Example I to obtain foamed products, which were a little different in elasticity, softness and aesthetic properties. However, the same synthetic leathers as in Example 8 were obtained by properly selecting base fabric or a surfacetreating agent.

WHAT WE CLAIM IS: 1. A process for producing a photodegradable foam rubber product which comprises the steps of (1) mixing (a) a 1,2polybutadiene containing not less than 70% 1,2-bonds, a molecular weight of not less than 100,000, a degree of crystallinity (as defined herein) of 10% to 50% and not less than 20% of a syndiotactic stereo specific structure, (b) 0.1 to 3% by weight, based on the weight of the 1,2-polybutadiene, of a photosensitizer which sensitizes in the wavelength region of 240 to 400 my and (c) a thermally decomposable foaming agent, (2) irradiating the resultant mixture with ultraviolet radiation of a wavelength of 240 to 400 m,u for not more than 10 minutes to form a cross-linked material having a gel fraction (as defined herein) of 30 to 80%, and (3) heating the resulting cross-linked material to 150 to 2300C to form a photodegradable foam rubber product.

2. A process as claimed in claim 1 wherein said photosensitizer is an aromatic ketone, an aromatic aldehyde or a quinone aromatic compound.

3. A process as claimed in claim 2, wherein said photosensitizer is benzophenone, p,p'-dimethoxybenzophenone, p,p'-dichlorobenzophenone, p,p'-dimethylbenzophenone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, methyl-o-benzoyl benzoate, benzil, fluorenone, terephthalaldehyde or methyl anthraquinone.

4. A process as claimed in any preceding Claim, wherein said foaming agent is employed in an amount of up to 20parts by weight per 100 parts by weight of 1,2polybutadiene.

5. A process as claimed in claim 4, wherein said foaming agent is p,p' oxybis(benzenesulfonylhydrazide).

6. A process as claimed in Claim 4, wherein said foaming agent is azodicarbonamide, dinitrosopentamethylenetetramine or p-toluenesulfonylhydrazide.

7. A process as claimed in Claim 4, wherein the irradiating with ultraviolet rays is effected for at least 15 seconds.

8. A synthetic leather comprising a substrate carrying a resin layer comprising cross-linked, foamed, syndiotactic 1,2polybutadiene produced by the process as claimed in any preceding claim or in claim 13.

9. A synthetic leather as claimed in claim 8, in which said resin layer consists only of cross-linked, foamed syndiotactic 1,2polybutadiene.

10. A synthetic leather as claimed in claim 8, wherein said resin layer comprises 1,2polybutadiene and another synthetic resin.

11. A synthetic leather as claimed in Claim 10, wherein said another synthetic resin is low density polyethylene or an ethylenevinyl acetate copolymer having not more than about 40 mol % vinyl acetate.

12. A synthetic leather as claimed in Claim 11, wherein said another synthetic resin is used in an amount of about 10 to about 50 o, by weight based on the total weight of the synthetic leather.

13. A process as claimed in claim 1,

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

Claims (14)

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

   On the other hand, a chloroprene adhesive was thinly coated (30g/m2) on knitted fabric or non-woven fabric, and the foamed sheet was laminated thereon.

   Thereafter, an urethane surface treating agent (LU 1500, LU 3500 or LU 3560; made by Dainichi-seika Colour & Chemical Mfg.

   Co., Ltd.) was coated thereon in a thickness of 15 to 30 g/m2 to form different samples, followed by drying. The thus obtained synthetic leather was extremely soft, and the flexibility thereof was hardly effected at temperatures of ordinary use (-20 to 45"C), the leather showing no adhesive properties.

   When the base fabric was an elastic knitted fabric, the product was so elastic that it could be bent and stretched into complicated shapes.

   Foamed sheets of 0.3 to 2.0 mm in thickness and a 3 to 5 times expansion ratio were prepared in the same manner, and the same synthetic leathers obtained by adhering these sheets to base fabric and subjecting them to a surface treatment.

   EXAMPLE 9

   90 to 50 parts by weight of syndiotactic 1,2-polybutadiene (the same as in Example 1) were respectively mixed with 10 to 50 parts by weight of ethylene-vinyl acetate copolymer (vinyl acetate content: not more than 40%) (trade name: Ultrathene; made by Toyo Soda Manufacturing Co., Ltd.) with 10 to 50 parts by weight of ethylenepropylene copolymer (melt index according to ASTM D1238: 0.25-90; density 0.88 g/cc) (trade name Tafmer; made by Mitsui Petrochemical Industries, Ltd.), and 100 parts by weight of each of the resultant mixtures were processed in the manner described in Example I to obtain foamed products, which were a little different in elasticity, softness and aesthetic properties. However, the same synthetic leathers as in Example 8 were obtained by properly selecting base fabric or a surfacetreating agent.

   WHAT WE CLAIM IS: 1. A process for producing a photodegradable foam rubber product which comprises the steps of (1) mixing (a) a 1,2polybutadiene containing not less than 70% 1,2-bonds, a molecular weight of not less than 100,000, a degree of crystallinity (as defined herein) of 10% to 50% and not less than 20% of a syndiotactic stereo specific structure, (b) 0.1 to 3% by weight, based on the weight of the 1,2-polybutadiene, of a photosensitizer which sensitizes in the wavelength region of 240 to 400 my and (c) a thermally decomposable foaming agent, (2) irradiating the resultant mixture with ultraviolet radiation of a wavelength of 240 to 400 m,u for not more than 10 minutes to form a cross-linked material having a gel fraction (as defined herein) of 30 to 80%, and (3) heating the resulting cross-linked material to 150 to 2300C to form a photodegradable foam rubber product.
2. 2. A process as claimed in claim 1 wherein said photosensitizer is an aromatic ketone, an aromatic aldehyde or a quinone aromatic compound.
3. 3. A process as claimed in claim 2, wherein said photosensitizer is benzophenone, p,p'-dimethoxybenzophenone, p,p'-dichlorobenzophenone, p,p'-dimethylbenzophenone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, methyl-o-benzoyl benzoate, benzil, fluorenone, terephthalaldehyde or methyl anthraquinone.
4. 4. A process as claimed in any preceding Claim, wherein said foaming agent is employed in an amount of up to 20parts by weight per 100 parts by weight of 1,2polybutadiene.
5. 5. A process as claimed in claim 4, wherein said foaming agent is p,p' oxybis(benzenesulfonylhydrazide).
6. 6. A process as claimed in Claim 4, wherein said foaming agent is azodicarbonamide, dinitrosopentamethylenetetramine or p-toluenesulfonylhydrazide.
7. 7. A process as claimed in Claim 4, wherein the irradiating with ultraviolet rays is effected for at least 15 seconds.
8. 8. A synthetic leather comprising a substrate carrying a resin layer comprising cross-linked, foamed, syndiotactic 1,2polybutadiene produced by the process as claimed in any preceding claim or in claim 13.
9. 9. A synthetic leather as claimed in claim 8, in which said resin layer consists only of cross-linked, foamed syndiotactic 1,2polybutadiene.
10. 10. A synthetic leather as claimed in claim 8, wherein said resin layer comprises 1,2polybutadiene and another synthetic resin.
11. 11. A synthetic leather as claimed in Claim 10, wherein said another synthetic resin is low density polyethylene or an ethylenevinyl acetate copolymer having not more than about 40 mol % vinyl acetate.
12. 12. A synthetic leather as claimed in Claim 11, wherein said another synthetic resin is used in an amount of about 10 to about 50 o, by weight based on the total weight of the synthetic leather.
13. 13. A process as claimed in claim 1,

    substantially as hereinbefore described in any one of Examples 1 to 7.
14. 14. A synthetic leather as claimed in claim 8, substantially as hereinbefore described in Example 8 or 9.