DE10319235A1 - Molded plastic product with gas barrier properties, e.g. polyester bottle for beer or other drinks, contains polyvinyl alcohol in the gas barrier layer and also contains a thermal insulator, e.g. aerogel particles - Google Patents

Abstract

Molded plastic products with barrier layer(s) and optionally an outer layer, in which the barrier layer(s) contain(s) polyvinyl alcohol (PVAL) (I) and the product also contains thermal (hot or cold) insulating material(s) (II). An independent claim is also included for a method for coating plastic products by applying an aqueous solution containing (I) and (II) and then drying the solution.

Description

The Use of weight-reduced packaging, especially in the area the beverage packaging, takes constantly to. The substitution of glass by plastics, especially by PET containers, steadily progressing. However, about the properties To achieve glass in terms of gas barriers is enough for PET from when the bottles are thick-walled. In order to however, is a higher one Use of material necessary as would be necessary for structural reasons. This but affects alongside higher ones Material costs especially disadvantageous at the expense of the desired Weight loss.

Out for this reason the use of barrier layers is necessary. Next the known possibilities among other things, cost-intensive coextrusion processes in which in the simplest case, a multi-layer sequence such as Polyethylene terephthalate (PET) / barrier layer / polyethylene terephthalate (PET) is achieved, there are also procedures for applying a inner or outer barrier layer. These are in particular plasma-assisted vapor deposition processes, preferably with aluminum or its oxides, silicon or its Oxides or carbon as the primary Layer material. However, these techniques often require use of high vacuum and the generation of a plasma. In addition to the expensive purchase costs for such Equipment is the machine running time, due to highly sensitive devices Problem. Furthermore, outer plasma coatings the achievable mechanical resistance is a problem. The coated bottles are in the normal filling and packaging process already big exposed to mechanical loads that damage the surface can and thus dramatically reduce the barrier achieved. This results in the Practice that another protective layer is applied, the must protect the vaporization layer from mechanical influences.

Furthermore would it be desirable if these plastic moldings, especially PET bottles, which would also be heat or cold insulating, so that, for example, chilled drinks contained therein e.g. when traveling longer desired Maintain temperature and do not get warm or heated as quickly Beverages, longer stay warm.

task The present invention was therefore to provide molded plastic articles, that meet the high requirements for the gas barrier, mechanically are stable, with normal use sufficiently good performance properties have and also heat or cold insulating are. Furthermore, in the manufacture of these moldings, the Use of technically complex equipment to be avoided as far as possible on the one hand to maximize machine run times and on the other hand the necessary Investment and Minimize maintenance costs.

Surprisingly It has now been found that molded plastic bodies that have a heat insulating Contain material and have a barrier layer, the polyvinyl alcohol contains solve the above problem.

object the present invention are thus molded plastic articles that with at least one barrier layer and optionally a top layer are coated, which are characterized in that the at least contains a barrier layer of polyvinyl alcohol and it contains at least one heat or cold insulating Material included.

As Plastics for the moldings can do it all known, commercially available Plastics are used. However, preference is given to plastic Polyethylene terephthalate (PET). It can be both so-called preforms as well as those already (blow) extruded finished moldings act. The use of preforms in particular has the advantage that the coating according to the invention can already be applied during the production of the same and the subsequent use, for example with bottlers, no changes in the existing facilities.

As Polyvinyl alcohols can all known polyvinyl alcohols are used. However, are preferred Polyvinyl alcohols with a degree of hydrolysis of 60 to 99.9 mol%, particularly preferably 80 to 99.9 mol%, and a viscosity of the 4th wt .-% aqueous solution from 2 to 100 mPas, particularly preferably 8 to 80 mPas (measured according to DIN 53015).

In a special embodiment can also Polyvinyl alcohol copolymers are used. Preferred as copolymers are ethylene-vinyl alcohol copolymers (EVAL).

In another special embodiment polyvinyl alcohols are used which have a degree of hydrolysis of have more than 99.9 mol%.

in the In the case of the ethylene-vinyl alcohol copolymer and in the case of the polyvinyl alcohol with a degree of hydrolysis of more than 99.9 mol% to insoluble in water Materials so that the barrier layer doubles as a top layer suitable is. The entire coating of the molded plastic body can thus consist of only one layer.

in the Generally, however, the coating will have at least two layers have, namely at least a barrier layer and at least one top layer, preferably a barrier layer and a top layer, the barrier layer The task is to form a gas barrier, and the top layer The task is to protect the barrier layer, especially with regard to on humidity, water vapor and water.

As Top layer can all plastic compositions known to the person skilled in the art are used, that are compatible with the at least one barrier layer, and also water-insoluble and are film-forming.

The top layer preferably contains polyurethanes, acrylates, styrene acrylates, ethylene vinyl acetates, polyvinyl acetates and polyvinyl acetals. However, the cover layer particularly preferably contains polyvinyl acetals and here in particular polyvinyl butyrals. All polyvinyl butyrals known to the person skilled in the art can be used as polyvinyl butyrals. It is also possible to use polyvinyl acetals made from two or more different aldehydes, such as, for example, mixtures of butyraldehyde with acetaldehyde and / or formaldehyde. Mixtures of polyvinyl acetals (e.g. with different molecular weights, different residual acetate contents, different degrees of acetalization and / or different acetalization components (aldehydes)) can also be used. For example, polyvinyl acetals which have been prepared from other aldehydes as the starting material can be mixed and used. There are no limits to the possible combinations. It can be particularly advantageous to increase the resistance of the protective layer to mechanical influences through increased intrinsic hardness, for example by using C ₁ -C ₃ -aldehydes, preferably C ₁ - and C ₂ -aldehydes, such as, for example, formaldehyde, acetaldehyde and their tri- and / or tetramers. This can be done, for example, by selecting the aldehydes or mixtures of aldehydes used in such a way that the glass transition temperature T _{g of} the top layer is as high as possible. For example, while a product that is acetalized exclusively with butyraldehyde has a T _g of approximately 65 ° C., a product that is produced from a mixture of butyraldehyde and acetaldehyde (or paraldehyde) in a molar ratio of 40:60 , a T _g of> 90 ° C. This is reflected in the higher mechanical strength of the top layer.

Also can Polyvinyl acetals are used by the implementation of copolymers Polyvinyl alcohols are produced. These copolymeric polyvinyl acetals are by copolymerization of vinyl acetate with other, in particular vinylic, monomers representable. These monomers carry, for example groups containing silicon, sulfur and / or nitrogen. Further are also carboxyl-containing monomers (for example acrylates, substituted Acrylates, maleic acid or its anhydride, itaconic acid, crotonic and similar Connections) ideally suited. Even with copolymerization of these monomers with vinyl acetate can range from less than one (mole) percent of products are already received changed significantly Properties in the resulting copolyvinyl alcohol result.

As thermal insulating Material come all materials known to the person skilled in the art for this purpose in question. However, transparent and / or translucent are preferred Materials.

The heat-insulating materials are preferably materials in particle form, particularly preferably in powder form. According to the invention, particularly preferably highly disperse, pyrogenic silicas (so-called aerosils) or highly porous materials made of silicon or metal oxides (so-called aerogels), in particular SiO ₂ aerogels, are used as heat-insulating materials. The aerogels are transparent or translucent materials in particle form that can be produced in a wide variety of particle sizes. Due to their very low density (<0.6 g / cm ³ ) and their very high porosity of over 60%, they have an extremely low thermal conductivity and are therefore used as a heat insulation material. The production of the aerogels is described in a large number of patent applications. Both manufacturing processes with supercritical drying, such as in the EP-A-0 396 076 described, as well as with subcritical drying, such as in the DE-A-43 42 548 described. Depending on the process, aerogels with hydrophobic surface groups, such as trimethylsilyl groups, are obtained in the subcritical drying. These are particularly preferred.

The thermal insulation material can either in the material forming the plastic molded body, preferably the PET. However, it is preferred in the gas barrier and / or cover layer, particularly preferably in the gas barrier layer contain. The amount of thermal insulation Material can vary in a wide range.

If desired, the plastic molded body according to the invention, for example the plastic bottle made of PET, can also be colored. This can be done on the one hand by the fact that the dye is already contained in the PET molded body, on the other on the other hand, the dye can also be contained in the barrier and / or top layer. Depending on which layer is to be colored, water-soluble or water-insoluble colors or color or pigment pastes must be used. If the barrier layer is colored, a suitable water-soluble color can be added to the polyvinyl alcohol solution. For example, products made from ^® Vitasyn dyes are suitable (e.g. ^® Vitasyn - blue AE 90 and ^® Vitasyn-Tartrazine X 90; Clariant). Depending on the desired color intensity, the amount of color to be added can be in the single-digit percentage range.

If the top layer is to be colored, water-insoluble paints, pigments or color or pigment pastes are preferably used. Here, for example, the pigment preparations ^® Renol HW 30 (Clariant) can be used. ^® Savinyl dyes (Clariant) are also available. Depending on the desired depth of color, all the products used for coloring can be used in the single-digit percentage range with excellent results.

object the present invention is also a method of coating of plastic moldings, which is characterized in that an aqueous solution of at least one polyvinyl alcohol onto the plastic molded body and the solution subsequently dries. The plastic molded body is preferred in the watery solution of the at least one polyvinyl alcohol immersed or with the aqueous Solution (electrostatic) sprayed. The application of the polyvinyl alcohol-containing barrier layer can either in one step or in several steps respectively. Can too solutions are used, the mixtures of various copolymers Contain polyvinyl alcohols.

The Gas barrier layer is preferably made of polyvinyl alcohol directly on the plastic surface, especially PET surface, can be applied. The liability is sufficiently large, adhesion promoter are generally not required. If a special increase in adhesion is desired, the PET surface can be used known surface treatment processes, such as corona treatment or flame treatment, in the surface tension be raised, which further increases liability becomes.

Should the warmth or cold-insulating Material, preferably the airgel particles, in the gas barrier layer are contained, the airgel particles are preferably together applied to the plastic molded body with the polyvinyl alcohol.

As is known Polyvinyl alcohol has the best gas barrier properties of polymers, in particular a very high oxygen and carbon dioxide barrier. adversely is that these barrier properties are due to (air) moisture be reduced. Moreover polyvinyl alcohol is generally a water-soluble polymer. thats why this layer opposite protect against the adverse influence of moisture. This is in a preferred embodiment achieved by applying another layer. Especially The use of polyvinyl acetals has proven advantageous. The adhesion of such a coating on the polyvinyl alcohol layer is excellent and there are optically perfect coatings achieved. The coating system is mechanically stable (important for the Pass through a filling system as well when used as required), flexible (expansion / shrinkage of the PET container due to internal gas pressure, temperature, handling and the like), clear, transparent (unobstructed view of the Content) and smooth (no differences in gripping in comparison to an uncoated PET bottle).

at the production of the plastic molded body according to the invention on the use of special techniques such as coextrusion and plasma coating can be dispensed with. The coating can be carried out using known techniques, and because of the Simplicity of these devices or units a long machine runtime and - Utilization can be achieved. The layers are applied successively and it can all known coating processes, such as dipping, Spraying, pouring, spraying, as well as electrostatic spraying, are used.

First of all the polyvinyl alcohol-containing barrier layer of preferably aqueous Medium applied. Conventional polyvinyl alcohols are suitable, i.e. fully and partially saponified polyvinyl alcohols. However, since the barrier effect with increasing degree of hydrolysis are such polyvinyl alcohols preferred with a high degree of saponification. Commercially available highly hydrolyzed Polyvinyl alcohols have a degree of saponification of ≤ 99 mol%. such Products are water soluble, which is why the application from watery solution possible is. The molecular weight of the polyvinyl alcohols used is not limited. Products which have a molecular weight are particularly suitable which enables good film formation. These are preferred medium to high molecular weights. The mechanical ones are corresponding Film properties of these products are particularly favorable.

If the insulating material is to be contained in the gas barrier layer, it is preferably introduced beforehand into the aqueous polyvinyl alcohol solution and together with this onto the art Fabric molded body applied.

The from the watery Medium applied polyvinyl alcohol layer, if necessary contains the insulating material, will be in the next Step preferably dried. This is beneficial to the application to optimize the second layer, which may consist of a solvent other than Water is applied. With wet on wet orders there is namely Risk of intermixing of the layers, which on the one hand has a barrier effect adversely affects and on the other hand the visual appearance worsened (cloudiness). The Drying can be varied Sort of. It is important that the base material through the Drying not changed or even damaged will (thermal deformation). In addition to (hot) air dryers, drying can also be carried out Infrared or microwave radiation can be used. The best and cheapest System depends on the requirements for residence times, throughputs, thermal Loads and the like. The concentration of the used solution depends on the macroscopic properties of the same. ever more concentrated, the higher the viscosity. Depending on the system, there are optimal areas that are used in the Temperature represent an optimum. The concentrations are preferably in the range from 1 to 30% by weight, particularly preferably in the range from 3 to 20% by weight and in particular in the range from 5 to 15% by weight.

With the layer formation and drying of the polyvinyl alcohol layer it is particularly well able to absorb the top layer. The top layer is also by means of the coating technologies described above applied. The chosen one Technology can for each layer is different and need not be the same for both layers his. This also depends on the desired requirements already described in more detail above were. Contains the top layer particularly preferably a polyvinyl acetal which is in an organic solvent solved is applied. All polyvinylacetals are suitable for this, and it also good and mechanically stressable film formation is important here. A limitation does not insist on certain molecular weights, rather they are Processability of product solutions, such as viscosity and solvents, the criteria that primarily influence the selection of the polyvinyl acetal. Commercially significant and readily available polyvinyl acetals are Polyvinyl formal and polyvinyl butyral, the latter in particular are preferred. In addition to the molecular weight, the so-called Degree of acetalization plays an important role. Under degree of acetalization one understands the proportion of 1,3-dioxanes, which by conversion of a Aldehyde with two (adjacent) hydroxyl groups of polyvinyl alcohol be formed. Depending on the number of hydroxyl groups converted there remains a lot of unreacted hydroxyl groups in the polyvinyl alcohol. This proportion of hydroxyl groups still present is sometimes reduced referred to as residual polyvinyl alcohol. For use as a water repellent Layer on the polyvinyl alcohol layer are particularly such proven, which have a high degree of acetalization, i.e. a low percentage of Residual polyvinyl alcohol in the molecule exhibit. The higher the degree of acetalization, the more hydrophobic the outer layer, which in turn requires good water resistance. For example a difference in degrees of acetalization of about 10% that the lower acetalized film becomes cloudy when stored for a long time in water, during the higher acetalized Film completely remains clear.

The Thicknesses of the applied layers depend on the desired ones Characteristics. Already a layer thickness of 2 μm of each of the individual layers is sufficient for barrier values> 3 to achieve at the same time water resistance. This means at a 0.5 l bottle only gains about 0.2 g.

Become Coated preforms, it is advantageous to first apply the layer thickness accordingly higher too choose, because the components are stretched during stretch blow molding. Depending on the desired Final layer thickness, i.e. desired Layer thickness of the barrier and the top layer of the stretch-blown molded body are apply the barrier layer and the top layer correspondingly thicker. It can therefore be used in these cases a multiple (repeated) application of the individual components or the use of higher Concentrations can be an advantage. Because the preforms usually don't The speed is immediately processed in a stretch blow molding machine the application of the coatings regardless of the speed the filling system. Therefore can the preforms also using other techniques, such as by dipping.

The applied outer film is also dried, although here, as with Apply, make sure that it is used solvent an organic solvent can act and therefore the formation of explosive mixtures can come with air. As a result, work is carried out either under a protective gas atmosphere or other techniques that eliminate this source of danger. Since the containers to be manufactured are products, the primary The use of solvents is used in the food sector preferred from the area of by the respective legal Provisions approved to look for. Here are particularly suitable special alcohols, such as ethanol or butanol.

Should the insulating material will be contained in the cover layer, so it for example in the particularly preferred embodiment preferably introduced into the alcoholic polyvinyl acetal solution beforehand and applied together with this to the plastic molded body.

The effectiveness of the barrier achieved by means of the coating can be measured using suitable apparatus. These measurements result either in the measurement of an increase in pressure in a measuring cylinder or in the detection of the gas outside the bottle (also in a closed cylinder) by means of infrared spectroscopy. Measured against a standard, this results in a factor for the improvement of the barrier property, which in English is referred to as the barrier improvement factor (BIF). The BIF of an uncoated PET bottle is therefore approximately 1. A BIF of 3 then means that the protection of the filled product against CO ₂ loss and oxygen penetration is three times as high as with an uncoated PET bottle.

Next the blocking effect z. B. against carbon dioxide and oxygen to the outside, the other way round, there is also an external blocking effect. That means, that in particular the ingress of oxygen from the outside the vessel wall prevented becomes. This is particularly the case with goods important that are (easily) oxidizable or that are damaged by oxidation can. Vitamins, flavors and enzymes in particular can be damaged by oxidation, what the spoilage of the product means. In this respect, the barrier is not just one way limited, rather fulfilled they have two functions at the same time (for example: carbon dioxide remaining in the bottle (barrier to the outside) and protection against oxidation (Oxygen) from the outside (Barrier from the outside)). Logically, this barrier improvement means a longer shelf life the filling material, which is also called shelf life. With one BIF of 1 shelf life, for example 10 weeks, this doubles the time for a BIF from 2 to 20 weeks. at higher BIF values correspondingly longer. These examples apply to carbonated, soft drinks (such as colas and lemonades).

at Beer comes the oxygen barrier, next to the carbon dioxide barrier, play a significant role. Therefore, there are generally even higher minimum requirements to the BIF values. A minimum required BIF of 5 results in a shelf life of 4 to 6 months, for example. higher BIF values extend the shelf life time accordingly.

Claims (13)

Plastic moldings which are coated with at least one barrier layer and optionally a cover layer, characterized in that the at least one barrier layer contains polyvinyl alcohol and they contain at least one heat or cold insulating material. Plastic moldings according to claim 1, characterized in that it is the plastic moldings PET-shaped body is. Plastic moldings according to claim 1 or 2, characterized in that as a polyvinyl alcohol Ethylene vinyl alcohol copolymer is used. Plastic moldings according to claim 1 or 2, characterized in that as a polyvinyl alcohol Polyvinyl alcohol with a degree of hydrolysis of more than 99.9 mol% is used. Plastic moldings according to at least any of the preceding claims, characterized in that the top layer contains polyvinyl acetal. Plastic moldings according to claim 5, characterized in that as polyvinyl acetal polyvinyl butyral is used. Plastic moldings according to claim 5, characterized in that polyvinyl acetals are used, those with a mixture of butyraldehyde, acetaldehyde and / or formaldehyde getting produced. Plastic moldings according to at least any of the preceding claims, characterized in that the at least one heat or cold insulating Contain material in the material forming the plastic molded body is. Plastic moldings according to at least one of the claims 1 to 7, characterized in that the at least one heat or cold-insulating Material is contained in the barrier layer. Plastic moldings according to at least one of the claims 1 to 7, characterized in that the at least one heat or cold-insulating Material is contained in the top layer. Plastic moldings according to at least any of the preceding claims, characterized in that as a heat or cold insulating material airgel particles be used. Process for coating art Fabric moldings, characterized in that an aqueous solution of at least one polyvinyl alcohol which contains the at least one heat or cold insulating material is applied to the plastic moldings and the solution is then dried. Method according to claim 12, characterized in that the plastic molded body by Diving, spraying, pouring, spray and / or electrostatic spraying coated.