Thermoplastic- and UP- or EP-based laminate plastics

The invention relates to laminate plastics, preferably in the form of tubes, having an inner layer of thermoplastic and an outer layer of typically fiber-reinforced reaction resins, and is characterized in that the curing of the reaction resins is effected by light curing at temperatures between approximately 20 and 60.degree. C.

FIELD OF THE INVENTION
 The invention relates to laminate or composite plastics, which are finding
 increasing use in many fields in industry. By combining two or more
 plastics, it is often possible to positively affect or eliminate
 disadvantageous characteristics of one plastic by combining it with
 another plastic. Composite plastics also include combinations in which,
 for example, an inner layer of a certain plastic is combined with an often
 fiber-reinforced outer layer of unsaturated polyester or epoxy resins.
 BACKGROUND OF THE INVENTION
 A disadvantage of unsaturated polyester resins, hereinafter called UP,
 which have many industrially desirable properties, is the considerable
 shrinkage of these plastics upon curing, however; it may amount to up to
 60 to 10% and may still be considerable even when fiber fillings, in
 particular glass fibers, are added. If shrinkage of the UP resins in
 cross-linking is to be avoided, it is necessary as a rule to use fillers,
 yet they are often undesirable for other reasons or can cause difficulties
 in industrial processing. Epoxy resins, hereinafter called EP, have the
 same disadvantages.
 Laminate plastics for tubes, for instance, have therefore so far required a
 relatively complicated production process, since as a rule the inner layer
 is embodied as a so-called liner, which must be mounted on a mandrel and
 then provided with the jacket layer wound on its outside. In cross-linking
 of the jacket layer, which was previously typically done thermally,
 shrinkage occurs, however, which can in turn lead to hairline cracks in
 the liner. The production of such tubes therefore requires not only a
 great deal of experience, but is also time-consuming and expensive, and
 this makes itself felt in the relatively high prices for the finished
 products. Instead of the usual thermal cross-linking of the outer layer,
 cold curing of such synthetic resins is already known, but that has the
 disadvantage in turn that the UP resin, provided with hardeners and
 accelerators, allows only very brief processing times of the starting
 mixture. EP resins can also be processed by cold curing; however, the
 curing time is longer than with UP resins.
 There is accordingly a need for practically shrinkage-free laminate
 plastics of thermal plastics for the inner and reaction resins for the
 outer layer that can be produced in a relatively economical process.
 SUMMARY OF THE INVENTION
 Surprisingly, it has now been found that composite plastics, preferably in
 the form of tubes, can be produced in it simple manner with an inner layer
 of thermal plastics and an outer layer of typically fiber-reinforced
 reaction resin, if the curing of the reaction resin is performed as light
 curing at approximately 20 to 60.degree..

DESCRIPTION OF THE INVENTION
 UP resins are obtained from multibasic unsaturated carboxylic acids, such
 as maleic acid, fumaric acid, itaconic acid or their anhydrides, phthalic
 acid and other unsaturated acids, by conversion with saturated divalent
 alcohols, such as ethylene glycol, propane and butane diols, cyclohexane
 dimethanol or neopentylglycol. In the conversion, resins are obtained that
 have a molecular weight of approximately 2000 to 5000, which immediately
 dissolve in monomers suitable for the cross linking. These solvents, which
 can have a bridging effect by addition at two double bonds, mainly are
 styrene, methyl styrene or various allyl or acrylic esters. The cross
 linking ensues upon heating and/or under the influence of peroxide
 catalysts, with the cooperation of accelerators, such as amine salts and
 heavy metal salts. Optionally, the curing may also be performed by the
 action of ionizing radiation or UV radiation in the presence of
 sensitizers, such as quinones.
 According to the invention, UP resins available on the market are used,
 having a high proportion of neopentylglycol in the alcoholic component, of
 the kind sold for instance by various firms, including Hoechst AG, Bayer
 AG, BASF AG, CW Huls AG, or Vieanova Kunstharz AG. Preferably, however, a
 mixture of approximately at least 30% neopentylglycol, 30% vinyl ester and
 the remainder being isophthalic acid is used, with styrene or optionally
 acrylic ester being usable as a solvent and stabilizer. The glass fiber
 component in these mixtures should amount to approximately 70 to 80% as a
 rule, all these figures being referred to the weight. Approximately 1.5%
 BPO, 2% of a quinone, and a very small quantity, in the range from
 approximately 0.0 to 0.1%, of a mixture of a cobalt soap and
 diethylaniline are added as the peroxide catalyst. Preferably, the mixture
 also includes a proportion on the order of approximately 10% of a
 thermoplastic, especially the particular thermoplastic that is
 simultaneously used as an inner layer or liner. It has in fact been found
 that by the addition of a slight quantity of a thermoplastic, the
 shrinkage resistance in tubes can be increased so much that virtually no
 further shrinkage occurs.
 Epoxy resins are created by the poly addition of compounds that contain one
 or more reactable terminal epoxy groups, with acids, acid anhydrides or
 amines. In these reactions, the resins cross-link and cure. The prototype
 of the EP resins is the conversion product of bisphenol A and
 epichlorohydrin, but other phenols may also be used instead of the
 aromatic bisphenyl A, and the epichlorohydrin can be replaced by
 cycloaliphatic oxides. In the reaction of the epoxidy resin with alcohols,
 acid, acid anhydrides or amines, which are present not as catalysts but
 rather as reaction partners, it is critical to adhere precisely to the
 quantity ratios, if plastics with particular properties are to be
 produced. Acid anhydrides or aromatic amines are predominantly used as
 curing agents which accordingly enter into the reactions; the curing time
 is several hours at temperatures above 100.degree. C. For EP resins as
 well, cold hardeners are known, namely polyamines, polyaminoamides and
 special acid anhydrides. As diluents and to adjust the viscosity,
 so-called reactive diluents are used, which themselves contain epoxy
 groups and are involved in the curing mechanism.
 Unmodified EP resins are typically relatively hard and brittle and tend to
 form hairline cracks. EP resins are therefore often processed with
 plasticizers, or a slight quantity of a thermoplastic may be dissolved in
 the reactive hardener, to improve the flexibility. EP resins may also be
 subjected to light curing.
 As an inner layer or liner, PVC and, depending on the application, super
 pure PVC or CPVC are preferably used. Rechlorinated polyvinylchloride,
 which may have chloride contents of up to 64% by weight and is
 distinguished over PVC homopolymers by a higher temperature resistance and
 better chemical stability, is called CPVC. Plasticizer-free rechlorinated
 polyvinylchloride is unobjectionable in foods and is allowed to be used to
 produce hoses, bar equipment and the like.
 Depending on the later use intended, the inner layer or liner may also be
 of other thermoplastics; for instance, the use of PPO is preferred in
 those cases in which increased resistance to chemicals is needed. PPO can
 also be used in foods and is distinguished by its chemical and mechanical
 resistance even at elevated temperatures. For certain purposes, the
 physiologically unobjectionable PVDF may also be used.
 The EP resins may also be subjected to cold curing, and again light is
 used, at a wavelength of from 300 to 350 nm. Photoinitiators in cold
 curing of EP resins include special substituted phosphine oxides, for
 instance, often used together with polyamines, which are likewise reaction
 partners in the polyaddition, or cyclopentadiene-benzene-iron sandwich
 complexes. In accordance with current knowledge, it must be presumed in
 these cases as well that a complete solid connection takes place between
 the liner and the reaction resin, because a partial dissolution of the
 liner also occurs in the cold curing, apparently from the reactive
 hardeners.
 Because of the production process, the wall thicknesses of the jacket layer
 can be reduced considerably in comparison with previous products, while
 having the same load capacity, which begins at operating pressures of up
 to 70 bar. Because of the resultant saving in material and the very much
 less time-consuming production process, the products can be produced
 extremely economically.
 The considerable pressure resistance of the plastics according to the
 invention, despite the relatively thin jacket layers, is especially
 surprising. While epoxy-based tubes of typical design, without liners,
 must have a wall thickness of up to 5 bar at operating pressures of 10
 bar, for instance, the jacket thickness of corresponding tubes according
 to the invention is barely 1 cm at operating pressures of up to 25 bar,
 with a safety factor of S6. The safety factor indicates the multiple of
 the operating pressure up to the bursting pressure, or in other words, the
 tubes briefly withstand loads of up to 300 bar. A special advantage is
 that the tubes, because of the liner, are media-tight even at this kind of
 operating pressures, in contrast to the tubes used previously, which upon
 continuous load tend to seep, because of hairline cracks. In a preferred
 embodiment, the invention therefore includes laminate plastics that are
 media-tight at operating pressures of 25 bar or above and a safety factor
 of 4 or 6 (as defined by ASTM X).
 It has also been found that by cold curing under the conditions given, a
 practically completely polymerization of the styrene or acrylic ester used
 as the solvent and stabilizer can be attained, so that the styrene residue
 contents in the final product are below 0.07% and preferably below 0.005%.
 The composite plastics according to the invention are preferably produced
 in the form of tubes and are used in this form in reverse osmosis or ultra
 filtration. However, they may also be used in the food industry, for
 instance in processing beer, dairy products, fruit juices, or the like.
 Another field of application is the production of super pure water, as
 needed for instance in the production of electronic components. The
 primary field of application, however, is seawater desalination, because
 in this form of practically employed reverse osmosis, the physiological
 unobjectionability of the liner is important, and a further consideration
 is that the pure PVC liners typically used have a very smooth surface, for
 the sake of a low-growth inner layer that prevents or greatly reduces the
 otherwise typical deposition of algae and other microorganisms from the
 seawater.
 The invention is described in further detail below in terms of an example:
 PVC tubes for reverse osmosis with a diameter of approximately 11 cm, are
 sheathed in a manner known per se with glass fibers, saturated in UP
 resin, in a winding process. A product is used as the UP resin that
 contains a reaction resin comprising approximately 30% neopentylglycol,
 30% vinyl ester, 30% isophthalic acid and 10% PVC in styrene as a solvent.
 Approximately 1.5% BPO, 1% photoinitiator, 3% of a quinone and 0.05% of a
 mixture of cobalt soap and diethylaniline are added as an
 accelerator/sensitizer system. Curing is done by exposure to UV light at a
 wavelength of 300 nm for a period of approximately 10 minutes.